publicationDate,title,abstract,id
2013-01-03,Coherent spin dynamics of nanomolecules and magnetic nanoclusters,"Spin dynamics of nanomolecules and nanoclusters are analyzed. The nanosizes
of these objects make it possible to consider them as single-domain magnets
with a large total spin, where the motion of the spins of all atoms, composing
a nanocluster, occurs in a coherent way. Another meaning of coherence in spin
dynamics is the coherent spin motion of several nanomolecules or nanoclusters.
Different approaches for treating spin dynamics are compared and the main
mechanisms influencing the spin motion are studied. Spin dynamics of separate
magnetic nanomolecules and nanoclusters are investigated, as well as the spin
dynamics of the ensembles of these nano-objects.",1301.0421v1
2005-07-07,Conservation of spin current,"The conventional definition of spin-current, namely spin density multiplied
by the group velocity, is not a conserved quantity due to possible spin
rotations caused by spin-orbit (SO) interaction. However, in a model with
spin-spin interactions, rotation of a spin causes a dynamic response of
surrounding spins that opposes the rotation. Such a many-body effect restores
the spin-current conservation. Here we prove that the non-conservation problem
of spin-current can be resolved if a self-consistent spin-spin interaction is
included in the analysis. We further derive a spin-conductance formula which
partitions spin-current into different leads of a multi-lead conductor.",0507159v2
2020-02-28,Dynamics of the relativistic electron spin in an electromagnetic field,"A relativistic spin operator cannot be uniquely defined within relativistic
quantum mechanics. Previously, different proper relativistic spin operators
have been proposed, such as spin operators of the Foldy-Wouthuysen and Pryce
type, that both commute with the free-particle Dirac Hamiltonian and represent
constants of motion. Here we consider the dynamics of a relativistic electron
spin in an external electromagnetic field. We use two different Hamiltonians to
derive the corresponding spin dynamics. These two are: (a) the Dirac
Hamiltonian in presence of an external field, (b) the semirelativistic
expansion of the same. Considering the Foldy-Wouthuysen and Pryce spin
operators we show that these lead to different spin dynamics in an external
electromagnetic field, which offers possibilities to distinguish their action.
We find that the dynamics of both spin operators involve spin-dependent and
spin-independent terms, however, the Foldy-Wouthuysen spin dynamics
additionally accounts for the relativistic particle-antiparticle coupling. We
conclude that the Pryce spin operator provides a suitable description of the
relativistic spin dynamics in a weak-to-intermediate external field, whereas
the Foldy-Wouthuysen spin operator is more suitable in the strong field regime.",2003.02226v1
2019-12-05,Spin pumping into a spin glass material,"Spin pumping is a recently established means for generating a pure spin
current, whereby spins are pumped from a magnet into the adjacent target
material under the ferromagnetic resonance condition. We theoretically
investigate the spin pumping from an insulating ferromagnet into spin glass
materials. Combining a dynamic theory of spin glasses with the linear-response
formulation of the spin pumping, we calculate temperature dependence of the
spin pumping near the spin glass transition. The analysis predicts that a
characteristic peak appears in the spin pumping signal, reflecting that the
spin fluctuations slow down upon the onset of spin freezing.",1912.02337v2
2011-03-16,Spin relaxation in Rashba rings,"Spin relaxation dynamics in rings with Rashba spin-orbit coupling is
investigated using spin kinetic equation. We find that the spin relaxation in
rings occurs toward a persistent spin configuration whose final shape depends
on the initial spin polarization profile. As an example, it is shown that a
homogeneous parallel to the ring axis spin polarization transforms into a
persistent crown-like spin structure. It is demonstrated that the ring geometry
introduces a geometrical contribution to the spin relaxation rate speeding up
the transient dynamics. Moreover, we identify several persistent spin
configurations as well as calculate the Green function of spin kinetic
equation.",1103.3231v1
2018-05-25,Generation of Spin Current from Lattice Distortion Dynamics: Spin-Orbit Routes,"Generation of spin current from lattice distortion dynamics in metals is
studied with special attention on the effect of spin-orbit coupling. Treating
the lattice distortion by local coordinate transformation, we calculate spin
current and spin accumulation with the linear response theory. It is found that
there are two routes to the spin-current generation, one via the spin Hall
effect and the other via the spin accumulation. The present effect due to
spin-orbit coupling can be comparable to, or even larger than, the one based on
the spin-vorticity coupling in systems with strong spin-orbit coupling.",1805.10328v2
2009-10-06,Diffusive and precessional spin dynamics in a two-dimensional electron gas with disorder: a gauge theory view,"We develop a gauge theory for diffusive and precessional spin dynamics in
two-dimensional electron gas with disorder. Our approach reveals a direct
connections between the absence of the equilibrium spin current and strong
anisotropy in the spin relaxation: both effects arise if the spin-orbit
coupling is reduced to a pure gauge SU(2) field. In this case, by a gauge
transformation in the form of a local SU(2) rotation in the spin subspace the
spin-orbit coupling can be removed. The resulting spin dynamics is exactly
described in terms of two kinetic coefficients: the spin diffusion and electron
mobility. After the inverse transformation, full diffusive and precessional
spin density dynamics, including the anisotropic spin relaxation, formation of
stable spin structures, and spin precession induced by a macroscopic current,
is restored. Explicit solutions of the spin evolution equations are found for
the initially uniform spin density and for stable nonuniform structures. Our
analysis demonstrates a universal relation between the spin relaxation rate and
spin diffusion coefficient.",0910.0951v2
2009-12-18,Diffusive versus local spin currents in dynamic spin pumping systems,"Using microscopic theory, we investigate the properties of a spin current
driven by magnetization dynamics. In the limit of smooth magnetization texture,
the dominant spin current induced by the spin pumping effect is shown to be the
diffusive spin current, i.e., the one arising from only a diffusion associated
with spin accumulation. That is to say, there is no effective field that
locally drives the spin current. We also investigate the conversion mechanism
of the pumped spin current into a charge current by spin-orbit interactions,
specifically the inverse spin Hall effect. We show that the spin-charge
conversion does not always occur and that it depends strongly on the type of
spin-orbit interaction. In a Rashba spin-orbit system, the local part of the
charge current is proportional to the spin relaxation torque, and the local
spin current, which does not arise from the spin accumulation, does not play
any role in the conversion. In contrast, the diffusive spin current contributes
to the diffusive charge current. Alternatively, for spin-orbit interactions
arising from random impurities, the local charge current is proportional to the
local spin current that constitutes only a small fraction of the total spin
current. Clearly, the dominant spin current (diffusive spin current) is not
converted into a charge current. Therefore, the nature of the spin current is
fundamentally different depending on its origin and thus the spin transport and
the spin-charge conversion behavior need to be discussed together along with
spin current generation.",0912.3607v2
2011-12-07,Spin Pumping Driven by Bistable Exchange Spin Waves,"Spin pumping driven by bistable exchange spin waves is demonstrated in a
Pt/Y$_3$Fe$_5$O$_{12}$ film under parametric excitation. In the
Pt/Y$_3$Fe$_5$O$_{12}$ film, the spin pumping driven by parametric excitation
selectively enhances the relaxation of short-wavelength exchange spin waves,
indicating strong coupling between the exchange spin waves and spin currents at
the interface through efficient spin transfer. The parametric spin pumping,
furthermore, allows direct access to nonlinear spin wave dynamics in
combination with the inverse spin Hall effect, revealing unconventional
bistability of the exchange spin waves.",1112.1596v2
2010-03-30,Disentangling phonons from spins in ion-trap-based quantum spin simulators,"We compute how phonon creation affects the fidelity of the quantum spin
dynamics in trapped ion simulators. A rigorous treatment of the quantum
dynamics is made by employing an exact operator factorization of the evolution
operator. Although it is often assumed that phonon creation modifies the
dynamics of the spin evolution, for an Ising spin-spin interaction in an
external magnetic field, phonons have \textit{no effect} on the probabilities
of spin product states measured in the direction of the Ising model axis.
Phonons play a much more important role in influencing the effective spin
dynamics for Heisenberg or XY model spin simulators or for other observables,
like witness operators in the Ising model.",1003.5901v1
2011-09-02,Spin-resolved bunching and noise characteristics in double quantum dots coupled to ferromagnetic electrodes,"We study spin-resolved noise in Coulomb blockaded double quantum dots coupled
to ferromagnetic electrodes. The modulation of the interdot coupling and spin
polarization in the electrodes gives rise to an intriguing dynamical spin
$\uparrow$-$\uparrow$ ($\downarrow$-$\downarrow$) blockade mechanism: Bunching
of up (down) spins due to dynamical blockade of an up (down) spin. In contrast
to the conventional dynamical spin $\uparrow$-$\downarrow$ bunching (bunching
of up spins entailed by dynamical blockade of a down spin), this new bunching
behavior is found to be intimately associated with the spin mutual-correlation,
i.e., the noise fluctuation between opposite spin currents. We further
demonstrate that the dynamical spin $\uparrow$-$\uparrow$ and
$\uparrow$-$\downarrow$ bunching of tunneling events may be coexistent in the
regime of weak interdot coupling and low spin polarization.",1109.0481v2
2006-01-25,Spin-Dynamical Analysis of Supercell Spin Configurations,"A model-independent approach capable of extracting spin-wave frequencies and
displacement vectors from ensembles of supercell spin configurations is
presented. The method is appropriate for those systems whose spin-dynamical
motion is well characterised by small-amplitude fluctuations that give harmonic
spin waves. First, the the spin-dynamical matrix is described and its
eigenvalues shown to correspond to the spin-wave mode frequencies. The
generalised spin coordinate matrix - a quantity that may be calculated from the
observed spin orientations in an ensemble of spin configurations - is then
introduced and its relationship to the spin-dynamical matrix established. Its
eigenvalues are subsequently shown to be related to the spin-wave mode
frequencies, allowing the extraction of spin-wave dispersion curves from
configurational ensembles. Finally, a quantum-mechanical derivation of the same
results is given, and the method applied as a case study to spin Monte-Carlo
configurations of a 3D Heisenberg ferromagnet.",0601559v2
2016-07-06,Quantum dynamics of nuclear spins and spin relaxation in organic semiconductors,"We investigate the role of the nuclear spin quantum dynamics in
hyperfine-induced spin relaxation of hopping carriers in organic
semiconductors. The fast hopping regime with a small carrier spin precession
during a waiting time between hops is typical for organic semiconductors
possessing long spin coherence times. We consider this regime and focus on a
carrier random walk diffusion in one dimension, where the effect of the nuclear
spin dynamics is expected to be the strongest. Exact numerical simulations of
spin systems with up to 25 nuclear spins are performed using the Suzuki-Trotter
decomposition of evolution operator. Larger nuclear spin systems are modeled
utilizing the spin-coherent state $P$-representation approach developed
earlier. We find that the nuclear spin dynamics strongly influences the carrier
spin relaxation at long times. If the random walk is restricted to a small
area, it leads to the quenching of carrier spin polarization at a non-zero
value at long times. If the random walk is unrestricted, the carrier spin
polarization acquires a long-time tail, decaying as $ 1/\sqrt{t}$. Based on the
numerical results, we devise a simple formula describing the effect
quantitatively.",1607.01640v1
2005-09-02,Dynamics of localized spins coupled to the conduction electrons with charge/spin currents,"The effects of the charge/spin currents of conduction electrons on the
dynamics of the localized spins are studied in terms of the perturbation in the
exchange coupling $J_{K}$ between them. The equations of motion for the
localized spins are derived exactly up to $O(J_{K}^2)$, and the equations for
the two-spin system is solved numerically. It is found that the dynamics
depends sensitively upon the relative magnitude of the charge and spin
currents, i.e., it shows steady state, periodic motion, and even chaotic
behavior. Extension to the multi-spin system and its implications including
possible ``spin current detector'' are also discussed.",0509058v1
2013-09-10,Spin rectification induced by dynamical Hanle effect,"Dynamic response of spin accumulation to a time-dependent magnetic field has
been investigated in a ferromagnetic/nonmagnetic bilayer under ferromagnetic
resonance. In this system, magnetization precession driven by a microwave
generates direct-current (dc) and alternate-current (ac) spin accumulation in
the nonmagnetic layer by the spin pumping. The ac spin accumulation is coupled
with the microwave magnetic field through a dynamical Hanle spin precession,
giving rise to rectified spin accumulation comparable with the dc spin
accumulation directly generated by the spin pumping.",1309.2365v1
2015-05-16,Dynamics of a macroscopic spin qubit in spin-orbit coupled Bose-Einstein condensates,"We consider a macroscopic spin qubit based on spin-orbit coupled
Bose-Einstein condensates, where, in addition to the spin-orbit coupling, spin
dynamics strongly depends on the interaction between particles. The evolution
of the spin for freely expanding, trapped, and externally driven condensates is
investigated. For condensates oscillating at the frequency corresponding to the
Zeeman splitting in the synthetic magnetic field, the spin Rabi frequency does
not depend on the interaction between the atoms since it produces only internal
forces and does not change the total momentum. However, interactions and
spin-orbit coupling bring the system into a mixed spin state, where the total
spin is inside rather than on the Bloch sphere. This greatly extends the
available spin space making it three-dimensional, but imposes limitations on
the reliable spin manipulation of such a macroscopic qubit. The spin dynamics
can be modified by introducing suitable spin-dependent initial phases,
determined by the spin-orbit coupling, in the spinor wave function.",1505.04301v1
2006-09-05,Single Electron Spin Decoherence by Nuclear Spin Bath: Linked Cluster Expansion Approach,"We develop a theoretical model for transverse dynamics of a single electron
spin interacting with a nuclear spin bath. The approach allows a simple
diagrammatic representation and analytical expressions of different nuclear
spin excitation processes contributing to electron spin decoherence and
dynamical phase fluctuations. It accounts for nuclear spin dynamics beyond
conventional pair correlation models. As an illustration of the theory, we
evaluated the coherence dynamics of a P donor electron spin in a Si crystal.",0609105v1
2003-09-18,Electron spin operation by electric fields: spin dynamics and spin injection,"Spin-orbit interaction couples electron spins to electric fields and allows
electrical monitoring of electron spins and electrical detection of spin
dynamics. Competing mechanisms of spin-orbit interaction are compared, and
optimal conditions for the electric operation of electrons spins in a quantum
well by a gate voltage are established. Electric spin injection into
semiconductors is discussed with a special emphasis on the injection into
ballistic microstructures. Dramatic effect of a long range Coulomb interaction
on transport phenomena in space-quantized low-dimensional conductors is
discussed in conclusion.",0309441v1
2008-12-13,Spin-Transfer Torque in Helical Spin-Density Waves,"The current driven magnetisation dynamics of a helical spin-density wave is
investigated. Expressions for calculating the spin-transfer torque of real
systems from first principles density functional theory are presented. These
expressions are used for calculating the spin-transfer torque for the spin
spirals of Er and fcc Fe at two different lattice volumes. It is shown that the
calculated torque induces a rigid rotation of the order parameter with respect
to the spin spiral axis. The torque is found to depend on the wave vector of
the spin spiral and the spin-polarisation of the Fermi surface states. The
resulting dynamics of the spin spiral is also discussed.",0812.2509v1
2008-07-23,Dynamics of coupled spins in quantum dots with strong spin-orbit interaction,"We investigated the time dependence of two-electron spin states in a double
quantum dot fabricated in an InAs nanowire. In this system, spin-orbit
interaction has substantial influence on the spin states of confined electrons.
Pumping single electrons through a Pauli spin-blockade configuration allowed to
probe the dynamics of the two coupled spins via their influence on the pumped
current. We observed spin-relaxation with a magnetic field dependence different
from GaAs dots, which can be explained by spin-orbit interaction. Oscillations
were detected for times shorter than the relaxation time, which we attribute to
coherent evolution of the spin states.",0807.3654v1
2021-09-30,Spin waves in doped graphene: a time-dependent spin-density-functional approach to collective excitations in paramagnetic two-dimensional Dirac fermion gases,"In spin-polarized itinerant electron systems, collective spin-wave modes
arise from dynamical exchange and correlation (xc) effects. We here consider
spin waves in doped paramagnetic graphene with adjustable Zeeman-type band
splitting. The spin waves are described using time-dependent
spin-density-functional response theory, treating dynamical xc effects within
the Slater and Singwi-Tosi-Land-Sjolander approximations. We obtain spin-wave
dispersions and spin stiffnesses as a function of doping and spin polarization,
and discuss prospects for their experimental observation.",2110.00045v1
2019-02-18,Spin-polarized currents driven by spin-dependent surface screening,"We have examined the spin polarization of the electron current in a
ferromagnetic metal induced by the spin-dependent surface screening at the
dielectric-ferromagnetic metal (D-FM) interface. In an applied ac voltage, the
dynamic band splitting driven by the changes in the screening charge at the
D-FM interface develops spin accumulation. The resultant spin accumulation
gradient produces a time-dependent spin current. We have derived the rate of
the spin accumulation on the rate of the screening charge density accumulation
within the Stoner band model. The spin-charge dynamics in the system is then
modeled by a set of diffusive equations with the contributions from
spin-dependent surface screening ands spin-dependent conductivity. We show for
MgO-Cu-Co-MgO system that the spin-dependent screening in thin Co film produces
spin accumulation 7 times higher than that obtained by the spin-dependent
conductivity in thick Co films. We propose an experimental approach to validate
our numerical predictions and to distinguish between spin accumulation induced
by the spin-dependent conductivity and by the spin-dependent surface screening.",1902.06481v2
1997-09-29,"Spin conductance, dynamic spin stiffness and spin diffusion in itinerant magnets","We discuss analogies between the charge- and spin response functions of
itinerant magnets. We show that the spin-analog of the charge stiffness is not
given by the usual spin stiffness rho_s, but by the dynamic spin stiffness D_s,
which is obtained from the dynamic spin conductance G_s (omega) in the limit of
vanishing frequency omega. The low-frequency behavior of G_s (omega) is used to
define ideal spin conductors, normal spin conductors, and spin insulators.
Assuming diffusive spin dynamics, we show that the spin diffusion coefficient
is proportional to lim_{omega rightarrow 0} {Re} {G}_s (omega). We exploit this
fact to develop a new extrapolation scheme for the spin diffusion coefficient
in the paramagnetic phase of the Hubbard model.",9709316v2
2018-02-28,Effect of exchange-correlation spin-torque on spin dynamics,"A recently proposed exchange-correlation functional (Dewhurst et al.
10.1021/acs.jctc.7b01049) with in density functional theory, which ensures that
the exchange-correlation magnetic field is source-free, is shown to give
non-zero internal spin-torque. This spin-torque is identically zero for all
conventional local and semi-local functionals. Extension of this source-free
functional to the time domain is used to study the effect of the internal
spin-torque on the laser induced spin-dynamics in bulk Co, Ni and interfaces of
these metals with Pt. It is shown that the internal spin-torque contribute
significantly to spin-dynamics only when the magneto crystalline anisotropy
energy is small, as in the case of cubic bulk materials. For surfaces or
interfaces, where the anisotropy energy is large, these torques are too small
to cause any significant precession of spins in early times ($<$ 100fs).
Further more it is shown that the spin-dynamics caused by the internal
spin-torque is slow compared to the inter-site spin transfer and spin-orbit
mediated spin-flips.",1802.10382v1
2018-10-17,Unified theory of magnetization dynamics with relativistic and nonrelativistic spin torques,"Spin torques play a crucial role in operative properties of modern spintronic
devices. To study current-driven magnetization dynamics, spin-torque terms
providing the action of spin-polarized currents have previously often been
added in a phenomenological way to the Landau-Lifshitz-Gilbert equation
describing the local spin dynamics, yet without derivation from fundamental
principles. Here, starting from the Dirac-Kohn-Sham theory and incorporating
nonlocal spin transport we rigorously derive the various spin-torque terms that
appear in current-driven magnetization dynamics. In particular we obtain an
extended magnetization dynamics equation that precisely contains the
nonrelativistic adiabatic and relativistic nonadiabatic spin-transfer torques
(STTs) of the Berger and Zhang-Li forms as well as relativistic spin-orbit
torques (SOTs). We derive in addition a previously unnoticed relativistic
spin-torque term and moreover show that the various obtained spin-torque terms
do not appear in the same mathematical form in both the Landau-Lifshitz and
Landau-Lifshitz-Gilbert equations of spin dynamics.",1810.07438v1
2013-11-05,Spin accumulation detection of FMR driven spin pumping in silicon-based metal-oxide-semiconductor heterostructures,"The use of the spin Hall effect and its inverse to electrically detect and
manipulate dynamic spin currents generated via ferromagnetic resonance (FMR)
driven spin pumping has enabled the investigation of these dynamically injected
currents across a wide variety of ferromagnetic materials. However, while this
approach has proven to be an invaluable diagnostic for exploring the spin
pumping process it requires strong spin-orbit coupling, thus substantially
limiting the materials basis available for the detector/channel material
(primarily Pt, W and Ta). Here, we report FMR driven spin pumping into a weak
spin-orbit channel through the measurement of a spin accumulation voltage in a
Si-based metal-oxide-semiconductor (MOS) heterostructure. This alternate
experimental approach enables the investigation of dynamic spin pumping in a
broad class of materials with weak spin-orbit coupling and long spin lifetime
while providing additional information regarding the phase evolution of the
injected spin ensemble via Hanle-based measurements of the effective spin
lifetime.",1311.0965v1
2024-02-07,Quantum Theory of Spin-Transfer and Spin-Pumping in Collinear Antiferromagnets and Ferrimagnets,"Antiferromagnets are promising candidates as active components in spintronic
applications. They share features with ferrimagnets in that opposing spin
orientations exist in two or more sublattices. Spin transfer torque and spin
pumping are essential ingredients in antiferromagnetic and ferrimagnet
spintronics. This paper develops an out-of-equilibrium quantum theory of the
spin dynamics of collinear magnets containing many spins coupled to normal
metal reservoirs. At equilibrium, the spins are parallel or antiparallel to the
easy axis. The theory, therefore, covers collinear antiferromagnets and
ferrimagnets. We focus on the resulting semi-classical spin dynamics. The
dissipation in the spin dynamics is enhanced due to spin-pumping. Spin
accumulations in the normal metals induce deterministic spin-transfer torques
on the magnet. Additionally, each electron's discrete spin angular momentum
causes stochastic fluctuating torques on the antiferromagnet or ferrimagnet. We
derive these fluctuating torques. The fluctuation-dissipation theorem holds at
high temperatures, including the effects of spin-pumping. At low temperatures,
we derive shot noise contributions to the fluctuations.",2402.04719v1
2005-01-03,Spin chains from dynamical quadratic algebras,"We present a construction of integrable quantum spin chains where local
spin-spin interactions are weighted by ``position''-dependent potential
containing abelian non-local spin dependance. This construction applies to the
previously defined three general quadratic reflection-type algebras:
respectively non-dynamical, semidynamical, fully dynamical.",0501029v2
2015-07-22,Spin-current emission governed by nonlinear spin dynamics,"Coupling between conduction electrons and localized magnetization is
responsible for a variety of phenomena in spintronic devices. This coupling
enables to generate spin currents from dynamical magnetization. Due to the
nonlinearity of magnetization dynamics, the spin-current emission through the
dynamical spin-exchange coupling offers a route for nonlinear generation of
spin currents. Here, we demonstrate spin-current emission governed by nonlinear
magnetization dynamics in a metal/magnetic insulator bilayer. The spin-current
emission from the magnetic insulator is probed by the inverse spin Hall effect,
which demonstrates nontrivial temperature and excitation power dependences of
the voltage generation. The experimental results reveal that nonlinear
magnetization dynamics and enhanced spin-current emission due to magnon
scatterings are triggered by decreasing temperature. This result illustrates
the crucial role of the nonlinear magnon interactions in the spin-current
emission driven by dynamical magnetization, or nonequilibrium magnons, from
magnetic insulators.",1507.06081v1
2006-11-06,Spin relaxation in a generic two-dimensional spin-orbit coupled system,"We study the relaxation of a spin density injected into a two-dimensional
electron system with generic spin-orbit interactions. Our model includes the
Rashba as well as linear and cubic Dresselhaus terms. We explicitly derive a
general spin-charge coupled diffusion equation. Spin diffusion is characterized
by just two independent dimensionless parameters which control the interplay
between different spin-orbit couplings. The real-time representation of the
diffuson matrix (Green's function of the diffusion equation) is evaluated
analytically. The diffuson describes space-time dynamics of the injected spin
distribution. We explicitly study two regimes: The first regime corresponds to
negligible spin-charge coupling and is characterized by standard charge
diffusion decoupled from the spin dynamics. It is shown that there exist
several qualitatively different dynamic behaviors of the spin density, which
correspond to various domains in the spin-orbit coupling parameter space. We
discuss in detail a few interesting phenomena such as an enhancement of the
spin relaxation times, real space oscillatory dynamics, and anisotropic
transport. In the second regime, we include the effects of spin-charge
coupling. It is shown that the spin-charge coupling leads to an enhancement of
the effective charge diffusion coefficient. We also find that in the case of
strong spin-charge coupling, the relaxation rates formally become complex and
the spin/charge dynamics is characterized by real time oscillations. These
effects are qualitatively similar to those observed in spin-grating experiments
[Weber et al., Nature 437, 1330 (2005)].",0611165v1
2002-12-24,Energy spectrum of the equal spin-spin interactions Hamiltonian,"The energy spectrum of eigenvalues of the equal spin-spin interactions (ESSI)
Hamiltonian has been found. The obtained spectrum is free from limitations
imposed on number of spins and parameters of the ESSI Hamiltonian. This model
can be used for consideration of spin dynamics of mesoscopic systems and
molecules with large number of nuclei spins.",0212138v1
2010-05-20,Cavity spin optodynamics,"The dynamics of a large quantum spin coupled parametrically to an optical
resonator is treated in analogy with the motion of a cantilever in cavity
optomechanics. New spin optodynamic phenonmena are predicted, such as
cavity-spin bistability, optodynamic spin-precession frequency shifts, coherent
amplification and damping of spin, and the spin optodynamic squeezing of light.",1005.3853v2
2016-04-20,Second post-Newtonian Lagrangian dynamics of spinning compact binaries,"The leading-order spin-orbit coupling is included in a post-Newtonian
Lagrangian formulation of spinning compact binaries, which consists of the
Newtonian term, first post-Newtonian (1PN) and 2PN non-spin terms and 2PN
spin-spin coupling. This makes a 3PN spin-spin coupling occur in the derived
Hamiltonian. The spin-spin couplings are mainly responsible for chaos in the
Hamiltonians. However, the 3PN spin-spin Hamiltonian is small and has different
signs, compared with the 2PN spin-spin Hamiltonian equivalent to the 2PN
spin-spin Lagrangian. As a result, the probability of the occurrence of chaos
in the Lagrangian formulation without the spin-orbit coupling is larger than
that in the Lagrangian formulation with the spin-orbit coupling. Numerical
evidences support the claim.",1604.05810v2
2007-05-02,Charge current driven by spin dynamics in disordered Rashba spin-orbit system,"Pumping of charge current by spin dynamics in the presence of the Rashba
spin-orbit interaction is theoretically studied. Considering disordered
electron, the exchange coupling and spin-orbit interactions are treated
perturbatively. It is found that dominant current induced by the spin dynamics
is interpreted as a consequence of the conversion from spin current via the
inverse spin Hall effect. We also found that the current has an additional
component from a fictitious conservative field. Results are applied to the case
of moving domain wall.",0705.0277v3
2010-04-08,Spin-charge and spin-orbital coupling effects on spin dynamics in ferromagnetic manganites,"Correlation-induced spin-charge and spin-orbital coupling effects on spin
dynamics in ferromagnetic manganites are calculated with realistic parameters
in order to provide a quantitative comparison with experimental results for
spin stiffness, magnon dispersion, magnon damping, anomalous zone-boundary
magnon softening, and Curie temperature. The role of orbital degeneracy,
orbital ordering, and orbital correlations on spin dynamics in different doping
regimes is highlighted.",1004.1352v2
2008-01-16,Charge and Spin Currents Generated by Dynamical Spins,"We demonstrate theoretically that a charge current and a spin current are
generated by spin dynamics in the presence of spin-orbit interaction in the
perturbative regime. We consider a general spin-orbit interaction including the
spatially inhomogeneous case. Spin current due to spin damping is identified as
one origin of generated charge current, but other contributions exist, such as
the one due to an induced conservative field and the one arising from the
inhomogeneity of spin-orbit interaction.",0801.2466v2
2014-09-28,Spin-electron acoustic waves: The Landau damping and ion contribution in the spectrum,"Separated spin-up and spin-down quantum kinetics is derived for more detailed
research of the spin-electron acoustic waves. Kinetic theory allows to obtain
spectrum of the spin-electron acoustic waves including effects of occupation of
quantum states more accurately than quantum hydrodynamics. We apply quantum
kinetic to calculate the Landau damping of the spin-electron acoustic waves. We
have considered contribution of ions dynamics in the spin-electron acoustic
wave spectrum. We obtain contribution of ions in the Landau damping in
temperature regime of classic ions. Kinetic analysis for ion-acoustic, zero
sound, and Langmuir waves at separated spin-up and spin-down electron dynamics
is presented as well.",1409.7885v1
2016-02-15,Effects of Dephasing on Spin Lifetime in Ballistic Spin-Orbit Materials,"We theoretically investigate spin dynamics in spin-orbit-coupled materials.
In the ballistic limit, the spin lifetime is dictated by dephasing that arises
from energy broadening plus a non-uniform spin precession. For the case of
clean graphene, we find a strong anisotropy with spin lifetimes that can be
short even for modest energy scales, on the order of a few ns. These results
offer deeper insight into the nature of spin dynamics in graphene, and are also
applicable to the investigation of other systems where spin-orbit coupling
plays an important role.",1602.04611v1
2017-01-08,Dynamical Generation of Spin Current and Phase Slip in Exciton-Polariton Condensates,"We show that how to generate propagation of spin degree in spin-symmetric
exciton-polariton condensates in a semiconductor microcavity. Due to the
stimulated spin-dependent scattering between hot excitons and condensates,
exciton polaritons form a circular polarized condensate with spontaneous
breaking of the spin rotation symmetry. The spin antiferromagnetic state is
developed evidently from the density and spin flow pumped by localized laser
source. The low energy spin current is identified where the steady state is
characterized by the oscillating spin pattern. Finally, we predict via
simulation how to dynamical generation of phase slip where ring-shape phase
jump shows the behavior of splitting and joining together.",1701.02006v2
2011-04-24,Controlling the quantum dynamics of a mesoscopic spin bath in diamond,"Understanding and mitigating decoherence is a key challenge for quantum
science and technology. The main source of decoherence for solid-state spin
systems is the uncontrolled spin bath environment. Here, we demonstrate quantum
control of a mesoscopic spin bath in diamond at room temperature that is
composed of electron spins of substitutional nitrogen impurities. The resulting
spin bath dynamics are probed using a single nitrogen-vacancy (NV) centre
electron spin as a magnetic field sensor. We exploit the spin bath control to
dynamically suppress dephasing of the NV spin by the spin bath. Furthermore, by
combining spin bath control with dynamical decoupling, we directly measure the
coherence and temporal correlations of different groups of bath spins. These
results uncover a new arena for fundamental studies on decoherence and enable
novel avenues for spin-based magnetometry and quantum information processing.",1104.4648v2
2007-07-17,Decoherence of coupled electron spins via nuclear spin dynamics in quantum dots,"In double quantum dots, the exchange interaction between two electron spins
renormalizes the excitation energy of pair-flips in the nuclear spin bath,
which in turn modifies the non-Markovian bath dynamics. As the energy
renormalization varies with the Overhauser field mismatch between the quantum
dots, the electron singlet-triplet decoherence resulting from the bath dynamics
depends on sampling of nuclear spin states from an ensemble, leading to the
transition from exponential decoherence in single-sample dynamics to power-law
decay under ensemble averaging. In contrast, the decoherence of a single
electron spin in one dot is essentially the same for different choices of the
nuclear spin configuration.",0707.2529v1
2010-01-07,Localization of spin mixing dynamics in a spin-1 Bose-Einstein condensate,"We propose to localize spin mixing dynamics in a spin-1 Bose-Einstein
condensate by a temporal modulation of spin exchange interaction, which is
tunable with optical Feshbach resonance. Adopting techniques from coherent
control, we demonstrate the localization/freezing of spin mixing dynamics, and
the suppression of the intrinsic dynamic instability and spontaneous spin
domain formation in a ferromagnetically interacting condensate of $^{87}$Rb
atoms. This work points to a promising scheme for investigating the weak
magnetic spin dipole interaction, which is usually masked by the more dominant
spin exchange interaction.",1001.1035v2
2023-01-06,Manipulation of nonequilibrium spin dynamics of an ultracold gas in a moving optical lattice,"The isolation and control of disparate degrees of freedom underpin quantum
simulators. We advance the programmability of cold atom quantum simulators with
a first realization of the dynamic interplay of spatial and spin degrees of
freedom. We experimentally demonstrate that violent spatial evolutions tune
long-lived coherent spin dynamics and develop a model of quantum spin-mixing
incorporating the spatial evolution via time-dependent spin-spin interactions.
Our results open new paths towards the simulation of quantum spin models with
tunable interactions via tailored spatial dynamics.",2301.02707v1
2022-08-03,Tunable itinerant spin dynamics with polar molecules,"Strongly interacting spins underlie many intriguing phenomena and
applications ranging from magnetism to quantum information processing.
Interacting spins combined with motion display exotic spin transport phenomena,
such as superfluidity arising from pairing of spins induced by spin attraction.
To understand these complex phenomena, an interacting spin system with high
controllability is desired. Quantum spin dynamics have been studied on
different platforms with varying capabilities. Here we demonstrate tunable
itinerant spin dynamics enabled by dipolar interactions using a gas of
potassium-rubidium molecules confined to two-dimensional planes, where a
spin-1/2 system is encoded into the molecular rotational levels. The dipolar
interaction gives rise to a shift of the rotational transition frequency and a
collision-limited Ramsey contrast decay that emerges from the coupled spin and
motion. Both the Ising and spin exchange interactions are precisely tuned by
varying the strength and orientation of an electric field, as well as the
internal molecular state. This full tunability enables both static and
dynamical control of the spin Hamiltonian, allowing reversal of the coherent
spin dynamics. Our work establishes an interacting spin platform that allows
for exploration of many-body spin dynamics and spin-motion physics utilizing
the strong, tunable dipolar interaction.",2208.02216v2
2024-03-19,Unraveling the dynamics of magnetization in topological insulator-ferromagnet heterostructures via spin-orbit torque,"Spin-orbit coupling stands as a pivotal determinant in the realm of condensed
matter physics. In recent, its profound influence on spin dynamics opens up a
captivating arena with promising applications. Notably, the topological
insulator-ferromagnet heterostructure has been recognized for inducing spin
dynamics through applied current, driven by spin-orbit torque. Building upon
recent observations revealing spin flip signals within this heterostructure,
our study elucidates the conditions governing spin flips by studying the
magnetization dynamics. We establish that the interplay between spin-anisotropy
and spin-orbit torque plays a crucial role in shaping the physics of
magnetization dynamics within the heterostructure. Furthermore, we categorize
various modes of magnetization dynamics, constructing a comprehensive phase
diagram across distinct energy scales, damping constants, and applied
frequencies. This research not only offers insights into controlling spin
direction but also charts a new pathway to the practical application of
spin-orbit coupled systems.",2403.12701v1
2024-01-30,A novel non-adiabatic spin relaxation mechanism in molecular qubits,"The interaction of electronic spin and molecular vibrations mediated by
spin-orbit coupling governs spin relaxation in molecular qubits. I derive an
extended molecular spin Hamiltonian that includes both adiabatic and
non-adiabatic spin-dependent interactions, and I implement the computation of
its matrix elements using state-of-the-art density functional theory. The new
molecular spin Hamiltonian contains a novel spin-vibrational orbit interaction
with non-adiabatic origin together with the traditional molecular Zeeman and
zero-field splitting interactions with adiabatic origin. The spin-vibrational
orbit interaction represents a non-Abelian Berry curvature on the ground-state
electronic manifold and corresponds to an effective magnetic field in the
electronic spin dynamics. I further develop a spin relaxation rate model that
estimates the spin relaxation time via the two-phonon Raman process. An
application of the extended molecular spin Hamiltonian together with the spin
relaxation rate model to Cu(II) porphyrin, a prototypical $S=1/2$ molecular
qubit, demonstrates that the spin relaxation time at elevated temperatures is
dominated by the non-adiabatic spin-vibrational orbit interaction. The computed
spin relaxation rate and its magnetic field orientation dependence are in
excellent agreement with experimental measurements.",2401.16738v1
2000-06-06,Effect of the additional second neighbor hopping on the spin dynamics in the t-J model,"The effect of the additional second neighbor hopping t' on the spin dynamics
in the t-J model is studied within the fermion-spin theory. Although the
additional second neighbor hopping t' is systematically accompanied with the
reduction of the dynamical spin structure factor and susceptibility, the
qualitative behaviors of the dynamical spin structure factor and susceptibility
are the same as in the case of t-J model. It is also shown that the integrated
dynamical spin structure factor is almost t' independent in the underdoped
regime.",0006081v1
2006-08-18,Electric Dipole Spin Resonance for Heavy Holes in Quantum Dots,"We propose and analyze a new method for manipulation of a heavy hole spin in
a quantum dot. Due to spin-orbit coupling between states with different orbital
momenta and opposite spin orientations, an applied rf electric field induces
transitions between spin-up and spin-down states. This scheme can be used for
detection of heavy-hole spin resonance signals, for the control of the spin
dynamics in two-dimensional systems, and for determining important parameters
of heavy-holes such as the effective $g$-factor, mass, spin-orbit coupling
constants, spin relaxation and decoherence times.",0608410v1
2013-12-29,Effect of anisotropic spin absorption on the Hanle effect in lateral spin valves,"We have succeeded in fully describing dynamic properties of spin current
including the different spin absorption mechanism for longitudinal and
transverse spins in lateral spin valves, which enables to elucidate intrinsic
spin transport and relaxation mechanism in the nonmagnet. The deduced spin
lifetimes are found independent of the contact type. From the transit-time
distribution of spin current extracted from the Fourier transform in Hanle
measurement data, the velocity of the spin current in Ag with Py/Ag Ohmic
contact turns out much faster than that expected from the widely used model.",1312.7481v1
2012-04-25,Spin freezing by Anderson localization in one-dimensional semiconductors,"One-dimensional quantum wires are considered as prospective elements for spin
transport and manipulation in spintronics. We study spin dynamics in
semiconductor GaAs-like nanowires with disorder and spin-orbit interaction by
using a rotation in the spin subspace gauging away the spin-orbit field. If the
disorder is sufficiently strong, the spin density after a relatively short
relaxation time reaches a plateau. This effect is a manifestation of the
Anderson localization and depends in a universal way on the disorder and the
spin-orbit coupling strength. As a result, at a given disorder, semiconductor
nanowires can permit a long-term spin polarization tunable with the spin-orbit
interactions.",1204.5597v1
2016-08-29,Spin pumping and measurement of spin currents in optical superlattices,"We report on the experimental implementation of a spin pump with ultracold
bosonic atoms in an optical superlattice. In the limit of isolated double wells
it represents a 1D dynamical version of the quantum spin Hall effect. Starting
from an antiferromagnetically ordered spin chain, we periodically vary the
underlying spin-dependent Hamiltonian and observe a spin current without charge
transport. We demonstrate a novel detection method to measure spin currents in
optical lattices via superexchange oscillations emerging after a projection
onto static double wells. Furthermore, we directly verify spin transport
through in-situ measurements of the spins' center of mass displacement.",1608.08153v1
2019-06-11,Spin imbalance of charge carriers induced by an electric current,"We analyze the contribution of the inhomogeneous magnetic field induced by an
electrical current to the spin Hall effect in metals. The Zeeman coupling
between the field and the electron spin leads to a spin dependent force, and to
spin accumulation at the edges. We compare the effect of this relativistic
correction to the electron dynamics to the features induced by the spin-orbit
interaction. The effect of current induced magnetic fields on the spin Hall
effect can be comparable to the extrinsic contribution from the spin-orbit
interaction, although it does not require the presence of heavy elements with a
strong spin-orbit interaction. The induced spins are oriented normal to the
metal slab.",1906.04851v1
2023-05-21,"Patterns, spin-spin correlations and competing instabilities in driven quasi-two-dimensional spin-1 Bose-Einstein condensates","We analyze the formation of transient patterns and spin-spin correlations in
quasi-two-dimensional spin-1 homogeneous Bose-Einstein condensates subjected to
parametric driving of $s$-wave scattering lengths. The dynamics for an initial
ferromagnetic phase is identical to that of a scalar condensate. In contrast,
intriguing dynamics emerges for an initial polar state. For instance, we show
that competition exists between density patterns and spin-mixing dynamics.
Dominant spin-mixing dynamics lead to a gas of polar core vortices and
anti-vortices of different spin textures. The density modes of the Bogoliubov
spectrum govern the wavenumber selection of Faraday patterns. The spin modes
determine the vortex density and the spatial dependence of spin-spin
correlation functions. When the density patterns outgrow the spin-mixing
dynamics, the spin-spin correlations decay exponentially with a correlation
length of the order a spin healing length; otherwise, they exhibit a Bessel
function dependence. Strikingly, competing instabilities within density and
spin modes emerge when both scattering lengths are modulated at different
frequencies and appropriate modulation amplitudes. The competing instability
leads to a superposition of density patterns or correlation functions of two
distinct wavelengths. Our studies reveal that fine control over the driven
dynamics can be attained by tuning interaction strengths, quadratic Zeeman
field, driving frequencies, and amplitudes.",2305.12385v2
2004-08-05,Spin Dynamics and Spin Transport,"Spin-orbit (SO) interaction critically influences electron spin dynamics and
spin transport in bulk semiconductors and semiconductor microstructures. This
interaction couples electron spin to dc and ac electric fields. Spin coupling
to ac electric fields allows efficient spin manipulating by the electric
component of electromagnetic field through the electric dipole spin resonance
(EDSR) mechanism. Usually, it is much more efficient than the magnetic
manipulation due to a larger coupling constant and the easier access to spins
at a nanometer scale. The dependence of the EDSR intensity on the magnetic
field direction allows measuring the relative strengths of the competing SO
coupling mechanisms in quantum wells. Spin coupling to an in-plane electric
field is much stronger than to a perpendicular field. Because electron bands in
microstructures are spin split by SO interaction, electron spin is not
conserved and spin transport in them is controlled by a number of competing
parameters, hence, it is rather nontrivial. The relation between spin
transport, spin currents, and spin populations is critically discussed.
Importance of transients and sharp gradients for generating spin magnetization
by electric fields and for ballistic spin transport is clarified.",0408119v1
2001-12-19,Novel aspects of spin-polarized transport and spin dynamics,"There is a renewed interest to study spin-polarized transport and spin
dynamics in various electronic materials. The motivation to examine the spin
degrees of freedom (mostly in electrons, but also in holes and nuclei) comes
from various sources: ranging from novel applications which are either not
feasible or ineffective with conventional electronics, to using spin-dependent
phenomena to explore the fundamental properties of solid state systems. Taken
in a broader context, term spintronics is addressing various aspects of these
efforts and stimulating new interactions between different subfields of
condensed matter physics. Recent advances in material fabrication made it
possible to introduce the nonequilibrium spin in novel class of systems,
including ferromagnetic semiconductors, high temperature superconductors and
carbon nanotubes--which leads to a question of how such a spin could be
utilized. For this purpose it is important to extend the understanding of
spin-polarized transport and spin dynamics to consider inhomogeneous systems,
various heterostructures, and the role of interfaces. This article presents
some views on novel aspects of spin-polarized transport and spin dynamics
(referring also to the topics which were addressed at the conference
Spintronics 2001) and suggests possible future research directions.",0112368v1
2003-11-10,Drift-diffusion model for spin-polarized transport in a non-degenerate 2DEG controlled by a spin-orbit interaction,"We apply the Wigner function formalism to derive drift-diffusion transport
equations for spin-polarized electrons in a III-V semiconductor single quantum
well. Electron spin dynamics is controlled by the linear in momentum spin-orbit
interaction. In a studied transport regime an electron momentum scattering rate
is appreciably faster than spin dynamics. A set of transport equations is
defined in terms of a particle density, spin density, and respective fluxes.
The developed model allows studying of coherent dynamics of a non-equilibrium
spin polarization. As an example, we consider a stationary transport regime for
a heterostructure grown along the (0, 0, 1) crystallographic direction. Due to
the interplay of the Rashba and Dresselhaus spin-orbit terms spin dynamics
strongly depends on a transport direction. The model is consistent with results
of pulse-probe measurement of spin coherence in strained semiconductor layers.
It can be useful for studying properties of spin-polarized transport and
modeling of spintronic devices operating in the diffusive transport regime.",0311221v3
2005-01-06,Electron Spin Dynamics and Hyperfine Interactions in Fe/Al_0.1Ga_0.9As/GaAs Spin Injection Heterostructures,"We have studied hyperfine interactions between spin-polarized electrons and
lattice nuclei in Al_0.1Ga_0.9As/GaAs quantum well (QW) heterostructures. The
spin-polarized electrons are electrically injected into the semiconductor
heterostructure from a metallic ferromagnet across a Schottky tunnel barrier.
The spin-polarized electron current dynamically polarizes the nuclei in the QW,
and the polarized nuclei in turn alter the electron spin dynamics. The
steady-state electron spin is detected via the circular polarization of the
emitted electroluminescence. The nuclear polarization and electron spin
dynamics are accurately modeled using the formalism of optical orientation in
GaAs. The nuclear spin polarization in the QW is found to depend strongly on
the electron spin polarization in the QW, but only weakly on the electron
density in the QW. We are able to observe nuclear magnetic resonance (NMR) at
low applied magnetic fields on the order of a few hundred Oe by electrically
modulating the spin injected into the QW. The electrically driven NMR
demonstrates explicitly the existence of a Knight field felt by the nuclei due
to the electron spin.",0501096v1
2014-08-28,Interplay of spin-orbit and hyperfine interactions in dynamical nuclear polarization in semiconductor quantum dots,"We theoretically study the interplay of spin-orbit and hyperfine interactions
in dynamical nuclear polarization in two-electron semiconductor double quantum
dots near the singlet $(S)$ - triplet $(T_+)$ anticrossing. The goal of the
scheme under study is to extend the singlet $(S)$ - triplet $(T_0)$ qubit
decoherence time $T_2^{*}$ by dynamically transferring the polarization from
the electron spins to the nuclear spins. This polarization transfer is achieved
by cycling the electron spins over the $S-T_+$ anticrossing. Here, we
investigate, both quantitatively and qualitatively, how this hyperfine mediated
dynamical polarization transfer is influenced by the Rashba and Dresselhaus
spin-orbit interaction. In addition to $T_2^*$, we determine the singlet return
probability $P_s$, a quantity that can be measured in experiments. Our results
suggest that the spin-orbit interaction establishes a mechanism that can
polarize the nuclear spins in the opposite direction compared to hyperfine
mediated nuclear spin polarization. In materials with relatively strong
spin-orbit coupling, this interplay of spin-orbit and hyperfine mediated
nuclear spin polarizations prevents any notable increase of the $S-T_0$ qubit
decoherence time $T_2^{*}$.",1408.6700v1
2020-12-14,Driven dynamics of a quantum dot electron spin coupled to bath of higher-spin nuclei,"The interplay of optical driving and hyperfine interaction between an
electron confined in a quantum dot and its surrounding nuclear spin environment
produces a range of interesting physics such as mode-locking. In this work, we
go beyond the ubiquitous spin 1/2 approximation for nuclear spins and present a
comprehensive theoretical framework for an optically driven electron spin in a
self-assembled quantum dot coupled to a nuclear spin bath of arbitrary spin.
Using a dynamical mean-field approach, we compute the nuclear spin polarization
distribution with and without the quadrupolar coupling. We find that while
hyperfine interactions drive dynamic nuclear polarization and mode-locking,
quadrupolar couplings counteract these effects. The tension between these
mechanisms is imprinted on the steady-state electron spin evolution, providing
a way to measure the importance of quadrupolar interactions in a quantum dot.
Our results show that higher-spin effects such as quadrupolar interactions can
have a significant impact on the generation of dynamic nuclear polarization and
how it influences the electron spin evolution.",2012.07227v2
2018-07-25,Nuclear spin dynamics influenced and detected by electron spin polarization in CdTe/CdMgTe quantum wells,"Nuclear spin coherence and relaxation dynamics of all constituent isotopes of
an n-doped CdTe/(Cd,Mg)Te quantum well structure are studied employing
optically detected nuclear magnetic resonance. Using time-resolved pump-probe
Faraday ellipticity, we generate and detect the coherent spin dynamics of the
resident electrons. The photogenerated electron spin polarization is
transferred into the nuclear spin system, which becomes polarized and acts back
on the electron spins as the Overhauser field. Under the influence of resonant
radio frequency pulses, we trace the coherent spin dynamics of the nuclear
isotopes $^{111}$Cd, $^{113}$Cd, and $^{125}$Te. We measure nuclear Rabi
oscillations, the inhomogeneous dephasing time $T_2^*$, the spin coherence time
$T_2$, and the longitudinal relaxation time $T_1$. Furthermore, we investigate
the influence of the laser excitation and the corresponding electron spin
polarization on the nuclear spin relaxation time and find a weak extension of
this time induced by interaction with the electron spins.",1807.09672v2
2021-06-21,Resonant Measurement of Non-Reorientable Spin-Orbit Torque from a Ferromagnetic Source Layer Accounting for Dynamic Spin Pumping,"Using a multilayer structure containing (cobalt detector layer)/(copper
spacer)/(Permalloy source layer), we show experimentally how the
non-reorientable spin-orbit torque generated by the Permalloy source layer (the
component of spin-orbit torque that does not change when the Permalloy
magnetization is rotated) can be measured using spin-torque ferromagnetic
resonance (ST-FMR) with lineshape analysis. We find that dynamic spin pumping
between the magnetic layers exerts torques on the magnetic layers as large or
larger than the spin-orbit torques, so that if dynamic spin pumping is
neglected the result would be a large overestimate of the spin-orbit torque.
Nevertheless, the two effects can be separated by performing ST-FMR as a
function of frequency. We measure a non-reorientable spin torque ratio
$\xi_{\text{Py}} = 0.04 \pm 0.01$ for spin current flow from Permalloy through
an 8 nm Cu spacer to the Co, and a strength of dynamic spin pumping that is
consistent with previous measurements by conventional ferromagnetic resonance.",2106.11127v1
2022-11-28,Superfluid-like spin transport in the dynamic states of easy-axis magnets,"The existing proposals for superfluid-like spin transport have been based on
easy-plane magnets where the U(1) spin-rotational symmetry is spontaneously
broken in equilibrium, and this has been limiting material choices for
realizing superfluid-like spin transport to restricted class of magnets. In
this work, we lift this limitation by showing that superfluid-like spin
transport can also be realized based on easy-axis magnets, where the U(1)
spin-rotational symmetry is intact in equilibrium but can be broken in
non-equilibrium. Specifically, we find the condition to engender a
non-equilibrium easy-cone state by applying a spin torque to easy-axis magnets,
which dynamically induces the spontaneous breaking of the U(1) spin-rotational
symmetry and thereby can support superfluid-like spin transport. By exploiting
this dynamic easy-cone state, we show theoretically that superfluid-like spin
transport can be achieved in easy-axis magnets under suitable conditions and
confirmed the prediction by micromagnetic simulations. We envision that our
work broadens material library for realizing superfluid-like spin transport,
showing the potential utility of dynamic states of magnets as venue to look for
spin-transport phenomena that do not occur in static magnetic backgrounds.",2211.15091v1
2011-04-23,Nuclear Dynamics During Landau-Zener Singlet-Triplet Transitions in Double Quantum Dots,"We consider nuclear spin dynamics in a two-electron double dot system near
the intersection of the electron spin singlet $S$ and the lower energy
component $T_{+}$ of the spin triplet. The electron spin interacts with nuclear
spins and is influenced by the spin-orbit coupling. Our approach is based on a
quantum description of the electron spin in combination with the coherent
semiclassical dynamics of nuclear spins. We consider single and double
Landau-Zener passages across the $S$-$T_{+}$ anticrossings. For linear sweeps,
the electron dynamics is expressed in terms of parabolic cylinder functions.
The dynamical nuclear polarization is described by two complex conjugate
functions $\Lambda ^{\pm}$ related to the integrals of the products of the
singlet and triplet amplitudes ${\tilde{c}}_{S}^{\ast}{\tilde{c}}_{T_{+}}$
along the sweep. The real part $P$ of $\Lambda ^{\pm}$ is related to the
$S$-$T_{+}$ spin-transition probability, accumulates in the vicinity of the
anticrossing, and for long linear passages coincides with the Landau-Zener
probability $P_{LZ}=1-e^{-2\pi \gamma}$, where $\gamma $ is the Landau-Zener
parameter. The imaginary part $Q$ of $\Lambda^{+}$ is specific for the nuclear
spin dynamics, accumulates during the whole sweep, and for $\gamma \gtrsim 1$
is typically an order of magnitude larger than $P$. $Q$ has a profound effect
on the nuclear spin dynamics, by (i) causing intensive shake-up processes among
the nuclear spins and (ii) producing a high nuclear spin generation rate when
the hyperfine and spin-orbit interactions are comparable in magnitude. We find
analytical expressions for the back-action of the nuclear reservoir represented
via the change in the Overhauser fields the electron subsystem experiences.",1104.4591v1
2011-01-20,Many-body singlets by dynamic spin polarization,"We show that dynamic spin polarization by collective raising and lowering
operators can drive a spin ensemble from arbitrary initial state to many-body
singlets, the zero-collective-spin states with large scale entanglement. For an
ensemble of $N$ arbitrary spins, both the variance of the collective spin and
the number of unentangled spins can be reduced to O(1) (versus the typical
value of O(N)), and many-body singlets can be occupied with a population of
$\sim 20 %$ independent of the ensemble size. We implement this approach in a
mesoscopic ensemble of nuclear spins through dynamic nuclear spin polarization
by an electron. The result is of two-fold significance for spin quantum
technology: (1) a resource of entanglement for nuclear spin based quantum
information processing; (2) a cleaner surrounding and less quantum noise for
the electron spin as the environmental spin moments are effectively
annihilated.",1101.3888v1
2017-04-25,Unified Treatment of Spin Torques using a Coupled Magnetisation Dynamics and Three-Dimensional Spin Current Solver,"A three-dimensional spin current solver based on a generalised spin
drift-diffusion description, including the spin Hall effect, is integrated with
a magnetisation dynamics solver. The resulting model is shown to simultaneously
reproduce the spin-orbit torques generated using the spin Hall effect, spin
pumping torques generated by magnetisation dynamics in multilayers, as well as
the spin transfer torques acting on magnetisation regions with spatial
gradients, whilst field-like and spin-like torques are reproduced in a spin
valve geometry. Two approaches to modelling interfaces are analysed, one based
on the spin mixing conductance and the other based on continuity of spin
currents where the spin dephasing length governs the absorption of transverse
spin components. In both cases analytical formulas are derived for the
spin-orbit torques in a heavy metal / ferromagnet bilayer geometry, showing in
general both field-like and damping-like torques are generated. The limitations
of the analytical approach are discussed, showing that even in a simple bilayer
geometry, due to the non-uniformity of the spin currents, a full
three-dimensional treatment is required. Finally the model is applied to the
quantitative analysis of the spin Hall angle in Pt by reproducing published
experimental data on the ferromagnetic resonance linewidth in the bilayer
geometry.",1704.07758v2
2002-08-23,Comment on: ``Semiclassical theory of spin-orbit interactions using spin coherent states'',"We point out that a certain kind of combined classical translational and spin
dynamics -- claimed in [M. Pletyukhov, et al. Phys. Rev. Lett. 89 (2002)
116601] to arise from the Pauli equation in the semiclassical limit $\hbar\to0$
for fixed spin -- only shows up if one simultaneously considers the high spin
limit $S\to\infty$.",0208031v1
2011-10-01,Spin-orbital phase synchronization in the magnetic field-driven electron dynamics in a double quantum dot,"We study the dynamics of an electron confined in a one-dimensional double
quantum dot in the presence of driving external magnetic fields. The orbital
motion of the electron is coupled to the spin dynamics by spin orbit
interaction of the Dresselhaus type. We derive an effective time-dependent
Hamiltonian model for the orbital motion of the electron and obtain a
synchronization condition between the orbital and the spin dynamics. From this
model we deduce an analytical expression for the Arnold tongue and propose an
experimental scheme for realizing the synchronization of the orbital and spin
dynamics.",1110.0114v1
2004-02-23,Spin and Current Variations in Josephson Junctions,"We study the dynamics of a single spin embedded in the tunneling barrier
between two superconductors. As a consequence of pair correlations in the
superconducting state, the spin displays rich and unusual dynamics. To properly
describe the time evolution of the spin we derive the effective Keldysh action
for the spin. The superconducting correlations lead to an effective spin
action, which is non-local in time, leading to unconventional precession. We
further illustrate how the current is modulated by this novel spin dynamics.",0402548v1
2005-07-07,Classical memory effects on spin dynamics in two-dimensional systems,"We discuss classical dynamics of electron spin in two-dimensional
semiconductors with a spin-split spectrum. We focus on a special case, when
spin-orbit induced random magnetic field is directed along a fixed axis. This
case is realized in III-V-based quantum wells grown in [110] direction and also
in [100]-grown quantum wells with equal strength of Dresselhaus and
Bychkov-Rashba spin-orbit couplings. We show that in such wells the long-time
spin dynamics is determined by non-Markovian memory effects. Due to these
effects the non-exponential tail $1/t^2$ appears in the spin polarization.",0507171v2
2007-09-28,Semi-Classical Dynamics in Quantum Spin Systems,"We consider two limiting regimes, the large-spin and the mean-field limit,
for the dynamical evolution of quantum spin systems. We prove that, in these
limits, the time evolution of a class of quantum spin systems is determined by
a corresponding Hamiltonian dynamics of classical spins. This result can be
viewed as a Egorov-type theorem. We extend our results to the thermodynamic
limit of lattice spin systems and continuum domains of infinite size, and we
study the time evolution of coherent spin states in these limiting regimes.",0709.4561v1
2013-02-08,Spin dynamics of cold fermions with synthetic spin-orbit coupling,"We consider spin relaxation dynamics in cold Fermi gases with a pure-gauge
spin-orbit coupling corresponding to recent experiments. We show that such
experiments can give a direct access to the collisional spin drag rate, and
establish conditions for the observation of spin drag effects. In the recent
experiments the dynamics is found to be mainly ballistic leading to new regimes
of reversible spin relaxation-like processes.",1302.2121v1
2016-07-08,Competition between Bose Einstein Condensation and spin dynamics,"We study the impact of spin-exchange collisions on the dynamics of
Bose-Einstein condensation, by rapidly cooling a chromium multi-component Bose
gas. Despite relatively strong spin-dependent interactions, the critical
temperature for Bose-Einstein condensation is reached before the spin-degrees
of freedom fully thermalize. The increase in density due to Bose-Einstein
condensation then triggers spin dynamics, hampering the formation of
condensates in spin excited states. Small metastable spinor condensates are
nevertheless produced, and manifest strong spin fluctuations.",1607.02406v1
2020-04-04,Energy and momentum conservation in spin transfer,"We utilize simulations of spin-polarized electron scattering by a chain of
localized quantum spins to show that energy and linear momentum conservation
laws impose strong constraints on the properties of magnetic excitations
induced by spin transfer. In turn, electron's orbital and spin dynamics depends
on the dynamical characteristics of the local spins. Our results suggest the
possibility to achieve precise control of spin transfer-driven magnetization
dynamics by tailoring the spectral characteristics of the magnetic systems and
the driving electrons.",2004.01957v1
2017-05-15,Spin and tunneling dynamics in an asymmetrical double quantum dot with spin - orbit coupling,"In this article we study the spin and tunneling dynamics as a function of
magnetic field in a one-dimensional GaAs double quantum dot with both the
Dresselhaus and Rashba spin-orbit coupling. In particular we consider different
spatial widths for the spin-up and spin-down electronic states. We find that
the spin dynamics is a superposition of slow as well as fast Rabi oscillations.
It is found that the Rashba interaction strength as well as the external
magnetic field strongly modifies the slow Rabi oscillations which is
particularly useful for single qubit manipulation for possible quantum computer
applications.",1705.05395v1
2019-02-26,Dynamic spin-charge coupling: spin Hall magnetoresistance in non-magnetic conductors,"The dynamic coupling between spin and charge currents in non-magnetic
conductors is considered. As a consequence of this coupling, the spin dynamics
is directly reflected in the electrical impedance of the sample, with a
relevant frequency scale defined by spin relaxation and spin diffusion. This
allows the observation of the electron spin resonance by purely electrical
measurements.",1902.09784v1
2020-09-22,From Chaotic Spin Dynamics to Non-collinear Spin Textures in YIG Nano-films by Spin Current Injection,"In this article I report about a numerical investigation of nonlinear spin
dynamics in a magnetic thin-film, made of Yttrium-Iron-Garnet (YIG). This film
is exposed to a small in-plane oriented magnetic field, and strong spin
currents. The rich variety of findings encompass dynamic regimes hosting
localized, non-propagating solitons, a turbulent chaotic regime, which
condenses into a quasi-static phase featuring a non-collinear spin texture.
Eventually, at largest spin current, a homogeneously switched state is
established.",2009.10628v1
2021-09-26,Monte Carlo simulation of ultrafast nonequilibrium spin and charge transport in iron,"Spin transport and spin dynamics after femtosecond laser pulse irradiation of
iron (Fe) are studied using a kinetic Monte Carlo model. This model simulates
spin dependent dynamics by taking into account two interaction processes during
nonequilibrium: Elastic electron - lattice scattering, where only the direction
of the excited electrons changes neglecting the energy loss, and inelastic
electron - electron interaction, where secondary electrons are generated. An
analysis of the particle kinetics inside the material shows that a smaller
elastic scattering time affects the spin dynamics by leading to a larger
spatial spread of electrons in the material, whereas generation of secondary
electrons affects the spin transport with a larger time of propagation of
homogeneous spin polarization.",2109.12578v1
2010-06-29,Spin dynamics of current driven single magnetic adatoms and molecules,"A scanning tunneling microscope can probe the inelastic spin excitations of a
single magnetic atom in a surface via spin-flip assisted tunneling in which
transport electrons exchange spin and energy with the atomic spin. If the
inelastic transport time, defined as the average time elapsed between two
inelastic spin flip events, is shorter than the atom spin relaxation time, the
STM current can drive the spin out of equilibrium. Here we model this process
using rate equations and a model Hamiltonian that describes successfully spin
flip assisted tunneling experiments, including a single Mn atom, a Mn dimer and
Fe Phthalocyanine molecules. When the STM current is not spin polarized, the
non-equilibrium spin dynamics of the magnetic atom results in non-monotonic
$dI/dV$ curves. In the case of spin polarized STM current, the spin orientation
of the magnetic atom can be controlled parallel or anti-parallel to the
magnetic moment of the tip. Thus, spin polarized STM tips can be used both to
probe and to control the magnetic moment of a single atom.",1006.5608v1
2022-06-01,Substrate Effects on Spin Relaxation in Two-Dimensional Dirac Materials with Strong Spin-Orbit Coupling,"Understanding substrate effects on spin dynamics and relaxation in
two-dimensional (2D) materials is of key importance for spintronics and quantum
information applications. However, the key factors that determine the substrate
effect on spin relaxation, in particular for materials with strong spin-orbit
coupling, have not been well understood. Here we performed first-principles
real-time density-matrix dynamics simulations with spin-orbit coupling (SOC)
and quantum descriptions of electron-phonon and electron-impurity scattering
for the spin lifetimes of supported/free-standing germanene, a prototypical
strong SOC 2D Dirac material. We show that the effects of different substrates
on spin lifetime can surprisingly differ by two orders of magnitude. We find
that substrate effects on $\tau_s$ are closely related to substrate-induced
modifications of the SOC-field anisotropy, which changes the spin-flip
scattering matrix elements. We propose a new electronic quantity, named
spin-flip angle $\theta^{\uparrow\downarrow}$, to characterize spin relaxation
caused by intervalley spin-flip scattering. We find that the spin relaxation
rate is approximately proportional to the averaged value of
$\mathrm{sin}^{2}\left(\theta^{\uparrow\downarrow}/2\right)$, which can be used
as a guiding parameter of controlling spin relaxation.",2206.00784v2
2004-10-20,Spin-Transfer Torque and Electron-Magnon Scattering,"According to the spin-torque model, current-driven magnetic dynamics in
ferromagnetic multilayers is determined by the transfer of electron spin
perpendicular to the layers' magnetizations. By separating the largest
contributions to the magnetic dynamics, we demonstrate that the dominant effect
of spin-torque is rather due to the electron spin parallel to the field. We
show that this effect can be equivalently described as stimulated
current-driven excitation of spin-waves, and discuss four specifically
quantum-mechanical aspects of spin-transfer, not described by the spin-torque.",0410520v1
2006-11-13,Quantum Dynamics of Electron-Nuclei Coupled System in Quantum Dots,"We have investigated the dynamics of the electron-nuclei coupled system in
quantum dots. The bunching of results of the electron spin measurements and the
revival in the conditional probabilities are salient features of the nuclear
spin memory. The underlying mechanism is the squeezing of the nuclear spin
state and the correlations between the successive electron spin measurements.
Further we make a proposal for the preparation and detection of superposition
states of nuclear spins merely relying on electron spin measurements. For
unpolarized, completely random nuclear spin state one can still trace the
quantum interference effects. We discuss the realization of these schemes for
electron spins on both single and double QDs.",0611314v1
2010-01-26,Spin-wave instabilities in spin-transfer-driven magnetization dynamics,"We study the stability of magnetization precessions induced in spin-transfer
devices by the injection of spin-polarized electric currents. Instability
conditions are derived by introducing a generalized, far-from-equilibrium
interpretation of spin-waves. It is shown that instabilities are generated by
distinct groups of magnetostatically coupled spin-waves. Stability diagrams are
constructed as a function of external magnetic field and injected
spin-polarized current. These diagrams show that applying larger fields and
currents has a stabilizing effect on magnetization precessions. Analytical
results are compared with numerical simulations of spin-transfer-driven
magnetization dynamics.",1001.4806v1
2010-12-16,Magnetic dynamics driven by the spin-current generated via spin-Seebeck effect,"We consider the spin-current driven dynamics of a magnetic nanostructure in a
conductive magnetic wire under a heat gradient in an open circuit, spin Seebeck
effect geometry. It is shown that the spin-current scattering results in a
spin-current torque acting on the nanostructure and leading to precession and
displacement. The scattering leads also to a redistribution of the spin
electrochemical potential along the wire resulting in a break of the
polarity-reversal symmetry of the inverse spin Hall effect voltage with respect
to the heat gradient inversion.",1012.3552v2
2014-03-03,Chaos in two black holes with next-to-leading order spin-spin interactions,"We take into account the dynamics of a complete third post-Newtonian
conservative Hamiltonian of two spinning black holes, where the orbital part
arrives at the third post-Newtonian precision level and the spin-spin part with
the spin-orbit part includes the leading-order and next-to-leading-order
contributions. It is shown through numerical simulations that the
next-to-leading order spin-spin couplings play an important role in chaos. A
dynamical sensitivity to the variation of single parameter is also
investigated. In particular, there are a number of \textit{observable} orbits
whose initial radii are large enough and which become chaotic before
coalescence.",1403.0378v1
2011-11-23,Rashba spin torque in an ultrathin ferromagnetic metal layer,"In a two-dimensional ferromagnetic metal layer lacking inversion symmetry,
the itinerant electrons mediate the interaction between the Rashba spin-orbit
interaction and the ferromagnetic order parameter, leading to a Rashba spin
torque exerted on the magnetization. Using Keldysh technique, in the presence
of both magnetism and a spin-orbit coupling, we derive a spin diffusion
equation that provides a coherent description to the diffusive spin dynamics.
The characteristics of the spin torque and its implication on magnetization
dynamics are discussed in the limits of large and weak spin-orbit coupling.",1111.5466v1
1997-11-25,Spin and energy correlations in the one dimensional spin 1/2 Heisenberg model,"In this paper, we study the spin and energy dynamic correlations of the one
dimensional spin 1/2 Heisenberg model, using mostly exact diagonalization
numerical techniques. In particular, observing that the uniform spin and energy
currents decay to finite values at long times, we argue for the absence of spin
and energy diffusion in the easy plane anisotropic Heisenberg model.",9711264v1
2013-01-11,A new type of nuclear collective motion - the spin scissors mode,"The coupled dynamics of low lying modes and various giant resonances are
studied with the help of the Wigner Function Moments method on the basis of
Time Dependent Hartree-Fock equations in the harmonic oscillator model
including spin-orbit potential plus quadrupole-quadrupole and spin-spin
residual interactions. New low lying spin dependent modes are analyzed. Special
attention is paid to the spin scissors mode.",1301.2513v1
2022-07-25,Spin Coulomb drag by non-equilibrium magnetic textures,"Interaction between local magnetization and conduction electrons is
responsible for a variety of phenomena in magnetic materials. We have shown
that the spin-dependent motive force induced by magnetization dynamics in a
conducting ferromagnet lead to the spin Coulomb drag effect. The spin Coulomb
drag an intrinsic friction mechanism which operates whenever the average
velocities of up-spin and down-spin electrons differ.",2207.11978v1
2010-12-16,Spin Relaxation in Quantum Wires,"The spin dynamics and spin relaxation of itinerant electrons in quantum wires
with spin-orbit coupling is reviewed. We give an introduction to spin dynamics,
and review spin-orbit coupling mechanisms in semiconductors. The spin diffusion
equation with spin-orbit coupling is derived, using only intuitive, classical
random walk arguments. We give an overview of all spin relaxation mechanisms,
with particular emphasis on the motional narrowing mechanism in disordered
conductors, the D'yakonov-Perel'-Spin relaxation. Here, we discuss in
particular, the existence of persistent spin helix solutions of the spin
diffusion equation, with vanishing spin relaxation rates. We then, derive
solutions of the spin diffusion equation in quantum wires, and show that there
is an effective alignment of the spin-orbit field in wires whose width is
smaller than the spin precession length $L_{\rm SO}$. We show that the
resulting reduction in the spin relaxation rate results in a change in the sign
of the quantum corrections to the conductivity. Finally, we present recent
experimental results which confirm the decrease of the spin relaxation rate in
wires whose width is smaller than $L_{\rm SO}$: the direct optical measurement
of the spin relaxation rate, as well as transport measurements, which show a
dimensional crossover from weak antilocalization to weak localization as the
wire width is reduced. Open problems remain, in particular in narrower,
ballistic wires, were optical and transport measurements seem to find opposite
behavior of the spin relaxation rate: enhancement, suppression, respectively.
We conclude with a review of these and other open problems which still
challenge the theoretical understanding and modeling of the experimental
results.",1012.3575v1
2013-09-12,Observation of Pure Spin Transport in a Diamond Spin Wire,"Spin transport electronics - spintronics - focuses on utilizing electron spin
as a state variable for quantum and classical information processing and
storage. Some insulating materials, such as diamond, offer defect centers whose
associated spins are well-isolated from their environment giving them long
coherence times; however, spin interactions are important for transport,
entanglement, and read-out. Here, we report direct measurement of pure spin
transport - free of any charge motion - within a nanoscale quasi 1D 'spin
wire', and find a spin diffusion length ~ 700 nm. We exploit the statistical
fluctuations of a small number of spins ($\sqrt{N}$ < 100 net spins) which are
in thermal equilibrium and have no imposed polarization gradient. The spin
transport proceeds by means of magnetic dipole interactions that induce
flip-flop transitions, a mechanism that can enable highly efficient, even
reversible, pure spin currents. To further study the dynamics within the spin
wire, we implement a magnetic resonance protocol that improves spatial
resolution and provides nanoscale spectroscopic information which confirms the
observed spin transport. This spectroscopic tool opens a potential route for
spatially encoding spin information in long-lived nuclear spin states. Our
measurements probe intrinsic spin dynamics at the nanometre scale, providing
detailed insight needed for practical devices which seek to control spin.",1309.3199v3
2000-03-28,Metallic Spin Glass in Infinite Dimensions,"We have combined the dynamical mean field theories of the Mott transition and
the spin glass in infinite dimensions and derived a metallic spin-glass state
from a random spin-fermion model.",0003449v1
2003-06-12,Mean field master equation for self-interacting baths: comparison with exact spin--spin-bath dynamics,"A mean field approximation is employed to derive a master equation suitable
for self-interacting baths and strong system-bath coupling. Solutions of the
master equation are compared with exact solutions for a central spin
interacting with a spin-bath.",0306087v1
2008-12-29,Theory of spin-polarized scanning tunneling microscopy applied to local spins,"We provide a theory for scanning tunneling microscopy and spectroscopy using
a spin-polarized tip. It it shown that the tunneling conductance can be
partitioned into three separate contributions, a background conductance which
is independent of the local spin, a dynamical conductance which is proportional
to the local spin moment, and a conductance which is proportional to the noise
spectrum of the local spin interactions. The presented theory is applicable to
setups with magnetic tip and substrate in non-collinear arrangement, as well as
for non-magnetic situations. The partitioning of the tunneling current suggests
a possibility to extract the total spin moment of the local spin from the
dynamical conductance. The dynamical conductance suggests a possibility to
generate very high frequency spin-dependent ac currents and/or voltages. We
also propose a measurement of the dynamical conductance that can be used to
determine the character of the effective exchange interaction between
individual spins in clusters. The third contribution to the tunneling current
is associated with the spin-spin correlations induced by the exchange
interaction between the local spin moment and the tunneling electrons. We
demonstrate how this term can be used in the analysis of spin excitations
recorded in conductance measurements. Finally, we propose to use spin-polarized
scanning tunneling microscopy for detailed studies of the spin excitation
spectrum.",0812.4956v3
2011-06-22,Effect of spin diffusion on current generated by spin motive force,"Spin motive force is a spin-dependent force on conduction electrons induced
by magnetization dynamics. In order to examine its effects on magnetization
dynamics, it is indispensable to take into account spin accumulation, spin
diffusion, and spin-flip scattering since the spin motive force is in general
nonuniform. We examine the effects of all these on the way the spin motive
force generates the charge and spin currents in conventional situations, where
the conduction electron spin relaxation dynamics is much faster than the
magnetization dynamics. When the spin-dependent electric field is spatially
localized, which is common in experimental situations, we find that the
conservative part of the spin motive force is unable to generate the charge
current due to the cancelation effect by the diffusion current. We also find
that the spin current is a nonlocal function of the spin motive force and can
be effectively expressed in terms of nonlocal Gilbert damping tensor. It turns
out that any spin independent potential such as Coulomb potential does not
affect our principal results. At the last part of this paper, we apply our
theory to current-induced domain wall motion.",1106.4389v2
2023-12-30,Ultrafast X-ray Diffraction Probe of Coherent Spin-state Dynamics in Molecules,"We propose an approach to probe coherent spin-state dynamics of molecules
using circularly polarized hard x-ray pulses. For the dynamically aligned
nitric oxide molecules in a coherent superposition spin-orbit coupled
electronic state that can be prepared through stimulated Raman scattering, we
demonstrate the capability of ultrafast x-ray diffraction to not only reveal
the quantum beating of the coherent spin-state wave packet, but also image the
spatial spin density of the molecule. With circularly polarized ultrafast x-ray
diffraction signal, we show that the electronic density matrix can be
retrieved. The spatio-temporal resolving power of ultrafast x-ray diffraction
paves the way for tracking transient spatial wave function in molecular
dynamics involving spin degree of freedom.",2401.00259v1
2013-10-17,Entanglement dynamics in a system attached to self-interacting spinbaths,"Dynamics of quantum entanglement shared between system spins which are
connected to thermal equilibrium baths is studied. Central spin system
comprises of the entangled spins, and is connected to baths and one of the bath
has strong intra-environmental coupling. The dynamics between the system and
baths are studied and inferred that that intra-envirnomental coupling guards
against the system from the effects of the spin baths.",1310.4811v1
1996-09-11,Charge and spin dynamics in the one-dimensional $t-J_z$ and $t-J$ models,"The impact of the spin-flip terms on the (static and dynamic) charge and spin
correlations in the Luttinger-liquid ground state of the 1D $t-J$ model is
assessed by comparison with the same quantities in the 1D $t-J_z$ model, where
spin-flip terms are absent. We employ the recursion method combined with a
weak-coupling or a strong-coupling continued-fraction analysis. At $J_z/t=0^+$
we use the Pfaffian representation of dynamic spin correlations. The changing
nature of the dynamically relevant charge and spin excitations on approach of
the transition to phase separation is investigated in detail. The $t-J_z$
charge excitations (but not the spin excitations) at the transition have a
single-mode nature, whereas charge and spin excitations have a complicated
structure in the $t-J$ model. In the $t-J_z$ model, phase separation is
accompanied by N\'eel long-range order, caused by the condensation of electron
clusters with an already existing alternating up-down spin configuration
(topological long-range order). In the $t-J$ model, by contrast, the spin-flip
processes in the exchange coupling are responsible for continued strong spin
fluctuations (dominated by 2-spinon excitations) in the phase-separated state.",9609101v1
2009-07-17,Current-induced dynamics in non-collinear dual spin-valves,"Spin-transfer torque and current induced spin dynamics in spin-valve
nanopillars with the free magnetic layer located between two magnetic films of
fixed magnetic moments is considered theoretically. The spin-transfer torque in
the limit of diffusive spin transport is calculated as a function of magnetic
configuration. It is shown that non-collinear magnetic configuration of the
outermost magnetic layers has a strong influence on the spin torque and spin
dynamics of the central free layer. Employing macrospin simulations we make
some predictions on the free layer spin dynamics in spin valves composed of
various magnetic layers. We also present a formula for critical current in
non-collinear magnetic configurations, which shows that the magnitude of
critical current can be several times smaller than that in typical single spin
valves.",0907.3094v2
2014-09-05,Room temperature spin thermoelectrics in metallic films,"Considering metallic films at room temperature, we present the first
theoretical study of the spin Nernst and thermal Edelstein effects which takes
into account dynamical spin-orbit coupling, i.e., direct spin-orbit coupling
with the vibrating lattice (phonons) and impurities. This gives rise to two
novel processes, namely a dynamical Elliott-Yafet spin relaxation and a
dynamical side-jump mechanism. Both are the high-temperature counterparts of
the well-known $T = 0$ Elliott-Yafet and side-jump, central to the current
understanding of the spin Hall, spin Nernst and Edelstein effects at low $T$.
We consider the experimentally relevant regime $T > T_D$, with $T_D$ the Debye
temperature, as the latter is lower than room temperature in transition metals
such as Pt, Au and Ta typically employed in spin injection/extraction
experiments. We show that the interplay between intrinsic (Bychkov-Rashba type)
and extrinsic (dynamical) spin-orbit coupling yields a nonlinear $T$-
dependence of the spin Nernst and spin Hall conductivities.",1409.1809v1
2016-12-30,Derivation of Spin Torques of the Magnetic System in Broken Inversion Symmetry,"We propose a new approach to derive spin torque in systems of broken
inversion symmetry. It uses the concepts of asymmetric and directional
spin-spin interactions to obtain their effective fields. We applied the
effective fields into the Landau-Lifshitz equation and obtained spin torques.
The model offers a new and general approach for spin dynamics, one that
effectively merges the Dzyaloshinskii-Moriya interaction, spin transfer
torques, and spin-orbit torque into the spin dynamics equation. We discussed
how our model is imposed on the spin dynamics and compared our approach with
the traditional discussions on spin dynamics.",1612.09405v3
2017-10-30,Probe of Spin Dynamics in Superconducting NbN Thin Films via Spin Pumping,"The emerging field of superconductor (SC) spintronics has attracted intensive
attentions recently. Many fantastic spin dependent properties in SC have been
discovered, including the observation of large magnetoresistance, long spin
lifetimes and the giant spin Hall effect in SC, as well as spin supercurrent in
Josephson junctions, etc. Regarding the spin dynamic in SC films, few studies
has been reported yet. Here, we report the investigation of the spin dynamics
in an s-wave superconducting NbN film via spin pumping from an adjacent
insulating ferromagnet GdN layer. A profound coherence peak of the Gilbert
damping is observed slightly below the superconducting critical temperature of
the NbN layer, which is consistent with recent theoretical studies. Our results
further indicate that spin pumping could be a powerful tool for investigating
the spin dynamics in 2D crystalline superconductors.",1710.10833v2
2021-03-15,Entanglement Dynamics between Ising Spins and a Central Ancilla,"We investigate competing entanglement dynamics in an open Ising-spin chain
coupled to an external central ancilla qudit. In studying the real-time
behavior following a quench from an unentangled spin-ancilla state, we find
that the ancilla entanglement entropy $S_{vN;\mathcal{A}}$ tracks the dynamical
phase transition in the underlying spin system. In this composite setting,
purely spin-spin entanglement metrics such as mutual information and quantum
Fisher information (QFI) decay as the ancilla entanglement entropy grows. We
define multipartite entanglement loss (MEL) as the difference between
collective magnetic fluctuations and QFI, which is zero in the pure spin chain
limit. MEL directly quantifies the ancilla's effect on the development of
spin-spin entanglement. One of our central results is that $MEL(t) \propto
e^{S_{vN;\mathcal{A}}(t)}$. Our results provide a platform for exploring
composite system entanglement dynamics and suggest that MEL serves as a
quantitative estimate of information entropy shared between collective spins
and the ancilla qudit. Our results present a new framework that connects
physical spin-fluctuations, QFI, and bipartite entanglement entropy between
collective quantum systems.",2103.08517v3
2023-11-15,Control of individual electron-spin pairs in an electron-spin bath,"The decoherence of a central electron spin due to the dynamics of a coupled
electron-spin bath is a core problem in solid-state spin physics. Ensemble
experiments have studied the central spin coherence in detail, but such
experiments average out the underlying quantum dynamics of the bath. Here, we
show the coherent back-action of an individual NV center on an electron-spin
bath and use it to detect, prepare and control the dynamics of a pair of bath
spins. We image the NV-pair system with sub-nanometer resolution and reveal a
long dephasing time ($T_2^* = 44(9)$ ms) for a qubit encoded in the
electron-spin pair. Our experiment reveals the microscopic quantum dynamics
that underlie the central spin decoherence and provides new opportunities for
controlling and sensing interacting spin systems.",2311.10110v2
2005-01-09,Electron Spin Dynamics in Impure Quantum Wells for Arbitrary Spin-Orbit Coupling,"Strong interest has arisen recently on low-dimensional systems with strong
spin-orbit interaction due to their peculiar properties of interest for some
spintronic applications. Here, the time evolution of the electron spin
polarization of a disordered two-dimensional electron gas is calculated exactly
within the Boltzmann formalism for arbitrary couplings to a Rashba spin-orbit
field. The classical Dyakonov-Perel mechanism of spin relaxation is shown to
fail for sufficiently strong Rashba fields, in which case new regimes of spin
decay are identified. These results suggest that spin manipulation can be
greatly improved in strong spin-orbit interaction materials.",0501174v3
2006-06-07,An Exact SU(2) Symmetry and Persistent Spin Helix in a Spin-Orbit Coupled System,"Spin-orbit coupled systems generally break the spin rotation symmetry.
However, for a model with equal Rashba and Dresselhauss coupling constant (the
ReD model), and for the $[110]$ Dresselhauss model, a new type of SU(2) spin
rotation symmetry is discovered. This symmetry is robust against
spin-independent disorder and interactions, and is generated by operators whose
wavevector depends on the coupling strength. It renders the spin lifetime
infinite at this wavevector, giving rise to a Persistent Spin Helix (PSH). We
obtain the spin fluctuation dynamics at, and away, from the symmetry point, and
suggest experiments to observe the PSH.",0606196v1
2015-11-24,New pathways towards efficient metallic spin Hall spintronics,"Spin Hall effects interconvert spin- and charge currents due to spin-orbit
interaction, which enables convenient electrical generation and detection of
diffusive spin currents and even collective spin excitations in magnetic
solids. Here, we review recent experimental efforts exploring efficient spin
Hall detector materials as well as new approaches to drive collective
magnetization dynamics and to manipulate spin textures by spin Hall effects.
These studies are also expected to impact practical spintronics applications
beyond their significance in fundamental research.",1511.07739v1
2017-02-17,Arbitrary Nuclear Spin Gates in Diamond Mediated by a NV-center Electron Spin,"We propose a protocol that achieves arbitrary N-qubit interactions between
nuclear spins and that can measure directly nuclear many-body correlators by
appropriately making the nuclear spins interact with a nitrogen vacancy (NV)
center electron spin. The method takes advantage of recently introduced
dynamical decoupling techniques and demonstrates that action on the electron
spin is sufficient to fully exploit nuclear spins as robust quantum registers.
Our protocol is general, being applicable to other nuclear spin based platforms
with electronic spin defects acting as mediators as the case of silicon
carbide.",1702.05330v2
2012-04-23,Spin Transfer Torque with Spin Diffusion in Magnetic Tunnel Junctions,"Spin transport in magnetic tunnel junctions in the presence of spin diffusion
is considered theoretically. Combining ballistic tunneling across the barrier
and diffusive transport in the electrodes, we solve the spin dynamics equation
in the metallic layers. We show that spin diffusion mixes the transverse spin
current components and dramatically modifies the bias dependence of the
effective spin transfer torque. This leads to a significant linear bias
dependence of the out-of-plane torque, as well as a non-conventional thickness
dependence of both spin torque components.",1204.5000v2
2014-02-11,Dynamical decoupling design for identifying weakly coupled nuclear spins in a bath,"Identifying weakly coupled nuclear spins around single electron spins is a
key step of implementing quantum information processing using coupled
electron-nuclei spin systems or sensing like single spin nuclear magnetic
resonance detection using diamond defect spins. Dynamical decoupling control of
the center electron spin with periodic pulse sequences [e.g., the
Carre-Purcell-Meiboom-Gill (CPMG) sequence] has been successfully used to
identify single nuclear spins and to resolve structure of nuclear spin
clusters. Here, we design a new type of pulse sequences by replacing the
repetition unit (a single $\pi$-pulse) of the CPMG sequence with a group of
nonuniformly-spaced $\pi$-pulses. Using nitrogen-vacancy center system in
diamond, we show that the designed pulse sequence improves the resolution of
nuclear spin noise spectroscopy, and more information about the surrounding
nuclear spins is extracted. The principle of dynamical decoupling design
proposed in this paper is useful in many systems (e.g., defect spin qubit in
solids, trapped ion and superconducting qubit) for high-resolution noise
spectroscopy.",1402.2345v1
2023-11-23,Spin dynamics in intermediate-energy heavy-ion collisions with rigorous angular momentum conservation,"We have revisited the spin dynamics in intermediate-energy heavy-ion
collisions based on the improved spin- and isospin-dependent
Boltzmann-Uehling-Uhlenbeck transport model, particularly with the constraint
of rigorous angular momentum conservation incorporated. We have studied the
spin polarization of free nucleons and tritons/$^3$He as well as the spin
alignment of deuterons, and predicted the flow splittings for their different
spin states. We have also demonstrated that the spin-dependent potential may
enhance dissipations and thus have a non-negligible effect on the spin-averaged
transverse flow at low collision energies. When rigorous angular momentum
conservation in each spin-dependent nucleon-nucleon collision is incorporated,
it affects the overall dynamics, the flow, and also the spin polarization,
while the effects of the spin-orbit potential on the spin-related observables
are still appreciable. The well-developed SIBUU model could be further extended
to include hyperons or vector mesons, or used as a hadronic afterburner for
spin-related studies in relativistic heavy-ion collisions, with more inelastic
channels incorporated in the future.",2311.13769v2
2005-11-03,High-Field Low-Frequency Spin Dynamics,"The theory of exchange symmetry of spin ordered states is extended to the
case of high magnetic field. Low frequency spin dynamics equation for
quasi-goldstone mode is derived for two cases of collinear and noncollinear
antiferromagnets.",0511090v1
2016-02-17,Fractional Spin Fluctuation as a Precursor of Quantum Spin Liquids: Majorana Dynamical Mean-Field Study for the Kitaev Model,"Experimental identification of quantum spin liquids remains a challenge, as
the pristine nature is to be seen in asymptotically low temperatures. We here
theoretically show that the precursor of quantum spin liquids appears in the
spin dynamics in the paramagnetic state over a wide temperature range. Using
the cluster dynamical mean-field theory and the continuous-time quantum Monte
Carlo method, which are newly developed in the Majorana fermion representation,
we calculate the dynamical spin structure factor, relaxation rate in nuclear
magnetic resonance, and magnetic susceptibility for the honeycomb Kitaev model
whose ground state is a canonical example of the quantum spin liquid. We find
that dynamical spin correlations show peculiar temperature and frequency
dependence even below the temperature where static correlations saturate. The
results provide the experimentally-accessible symptoms of the fluctuating
fractionalized spins evincing the quantum spin liquids.",1602.05253v2
2016-06-10,Nanoscale confinement of ultrafast spin transfer torque exciting non-uniform spin dynamics by femtosecond spin current pulses,"Spintronics had a widespread impact over the past decades due to transferring
information by spin rather than electric currents. Its further development
requires miniaturization and reduction of characteristic timescales of spin
dynamics combining the sub-nanometer spatial and femtosecond temporal ranges.
These demands shift the focus of interest towards the fundamental open question
of the interaction of femtosecond spin current (SC) pulses with a ferromagnet
(FM). The spatio-temporal properties of the impulsive spin transfer torque
exerted by ultrashort SC pulses on the FM open the time domain for probing
non-uniform magnetization dynamics. Here we employ laser-generated ultrashort
SC pulses for driving ultrafast spin dynamics in FM and analyzing its transient
local source. Transverse spins injected into FM excite inhomogeneous
high-frequency spin dynamics up to 0.6 THz, indicating that the perturbation of
the FM magnetization is confined to 2 nm.",1606.03403v1
2016-09-18,Inertia effects in the real-time dynamics of a quantum spin coupled to a Fermi sea,"Spin dynamics in the Kondo impurity model, initiated by suddenly switching
the direction of a local magnetic field, is studied by means of the
time-dependent density-matrix renormalization group. Quantum effects are
identified by systematic computations for different spin quantum numbers $S$
and by comparing with tight-binding spin-dynamics theory for the classical-spin
Kondo model. We demonstrate that, besides the conventional precessional motion
and relaxation, the quantum-spin dynamics shows nutation, similar to a spinning
top. Opposed to semiclassical theory, however, the nutation is efficiently
damped on an extremely short time scale. The effect is explained in the
large-$S$ limit as quantum dephasing of the eigenmodes in an emergent two-spin
model that is weakly entangled with the bulk of the system. We argue that,
apart from the Kondo effect, the damping of nutational motion is essentially
the only characteristics of the quantum nature of the spin. Qualitative
agreement between quantum and semiclassical spin dynamics is found down to
$S=1/2$.",1609.05526v1
2018-06-03,Quantum Spin Dynamics in a Normal Bose Gas with Spin-orbit Coupling,"In this Letter, we investigate spin dynamics of a two-component Bose gas with
spin-orbit coupling realised in cold atom experiments. We derive coupled
hydrodynamic equations for number and spin densities as well as their
associated currents. Specialising to quasi-one-dimensional situation, we obtain
analytic solutions of the spin helix structure and its dynamics in both
adiabatic and diabatic regimes. In the adiabatic regime, the transverse spin
decays parabolically in the short-time limit and exponentially in the long time
limit, depending on initial polarisation. In contrast, in the diabatic regime,
transverse spin density and current oscillate in a way similar to the
charge-current oscillation in an undamped LC circuit. The effects of Rabi
coupling on the short-time spin dynamics is also discussed. Finally, using
realistic experimental parameters for $^{87}$Rb, we show that the time scales
for spin dynamics is of order of milliseconds to a few seconds and can be
observed experimentally.",1806.00766v2
2024-03-02,Negative Temperature in Spin Dynamics Simulations,"A simple and computationally efficient algorithm enables implementing
negative temperature values in a spin dynamics simulation. The algorithm uses a
Langevin spin dynamics thermostat with a negative damping parameter, enabling
the thermalization of an arbitrary interacting spin system to the Gibbs energy
distribution with a given negative temperature value. Canonical spin dynamics
simulations at a negative temperature are as robust as conventional positive
spin temperature simulations, providing a tool for quantitative dynamic studies
of the physics of highly excited magnetic states. Two simulation case studies
describing spin systems with antiferromagnetic and ferromagnetic ground states
are explored. The phase transitions occurring in the negative temperature range
do not necessarily exhibit similarities with their positive temperature
counterparts. The transition temperatures and the character of spin alignment
vary depending on the spatial range and strength of spin-spin interactions.",2403.01307v1
1999-01-27,Femtosecond electron and spin dynamics probed by nonlinear optics,"A theoretical calculation is performed for the ultrafast spin dynamics in
nickel using an exact diagonalization method. The present theory mainly focuses
on a situation where the intrinsic charge and spin dynamics is probed by the
nonlinear (magneto-)optical responses on the femtosecond time scale, i.e.
optical second harmonic generation (SHG) and the nonlinear magneto-optical Kerr
effect (NOLIMOKE). It is found that the ultrafast charge and spin dynamics are
observable on the time scale of 10 fs. The charge dynamics proceeds ahead of
the spin dynamics, which indicates the existence of a spin memory time. The
fast decay results from the loss of coherence in the initial excited state.
Both the material specific and experimental parameters affect the dynamics. We
find that the increase of exchange interaction mainly accelerates the spin
dynamics rather than the charge dynamics. A reduction of the hopping integrals,
such as present at interfaces, slows down the spin dynamics significantly.
Besides, it is found that a spectrally broad excitation yields the intrinsic
speed limit of the charge (SHG) and spin dynamics (NOLIMOKE) while a narrower
width prolongs the dynamics. This magnetic interface dynamics then should
become accessible to state of art time resolved nonlinear-optical experiments.",9901303v1
2011-06-16,Synchronous Spatial Oscillation of Electron- and Mn-Spin Polarizations in Dilute-Magnetic-Semiconductor Quantum Wells under Spin-Orbit Effective Magnetic Fields,"In semiconductors, spin-orbit effective magnetic fields, i.e., the Rashba and
Dresselhaus fields, are used to control electron-spin polarization. This
operation, however, destroys the electron-spin coherence, and the spin
polarization is limited to the vicinity of a ferromagnetic source electrode. In
this paper, we propose the use of dilute magnetic semiconductors to improve the
coherence of spatially oscillating electron-spin polarization. In dilute
magnetic semiconductors, the electron-spin polarization near the source
electrode dynamically induces the local spin polarization of magnetic
impurities through s-d spin-flip scattering. This impurity-spin polarization
improves, in turn, the coherence of the electron-spin polarization, and this
improved electron-spin polarization induces impurity-spin polarization farther
in the adjacent region. Because of this positive feedback, the coherent and
synchronized spatial oscillations of electron- and impurity-spin polarizations
grow cooperatively. A numerical calculation for a CdMnTe quantum well
demonstrates the validity of this mechanism.",1106.3124v2
2012-12-18,Thermoelectric spin accumulation and long-time spin precession in a non-collinear quantum dot spin valve,"We explore thermoelectric spin transport and spin dependent phenomena in a
non-collinear quantum dot spin valve set up. Using this set up, we demonstrate
the possibility of a thermoelectric excitation of single spin dynamics inside
the quantum dot. Many-body exchange fields generated on the single spins in
this set up manifest as effective magnetic fields acting on the net spin
accumulation in the quantum dot. We first identify generic conditions by which
a zero bias spin accumulation in the dot may be created in the thermoelectric
regime. The resulting spin accumulation is then shown to be subject to a
field-like spin torque due to the effective magnetic field associated with
either contact. This spin torque that is generated may yield long-time
precession effects due to the prevailing blockade conditions. The implications
of these phenomena in connection with single spin manipulation and pure spin
current generation are then discussed.",1212.4353v2
2008-07-16,Spin currents and spin superfluidity,"The present review analyzes and compares various types of dissipationless
spin transport: (1) Superfluid transport, when the spin-current state is a
metastable state (a local but not the absolute minimum in the parameter space).
(2) Ballistic spin transport, when spin is transported without losses simply
because sources of dissipation are very weak. (3) Equilibrium spin currents,
i.e., genuine persistent currents. (4) Spin currents in the spin Hall effect.
Since superfluidity is frequently connected with Bose condensation, recent
debates about magnon Bose condensation are also reviewed. For any type of spin
currents simplest models were chosen for discussion in order to concentrate on
concepts rather than details of numerous models. The various hurdles on the way
of using the concept of spin current (absence of the spin-conservation law,
ambiguity of spin current definition, etc.) were analyzed. The final conclusion
is that the spin-current concept can be developed in a fully consistent manner,
and is a useful language for description of various phenomena in spin dynamics.",0807.2524v3
2022-12-09,Spin/momentum properties of the paraxial optical beams,"Spin angular momentum, an elementary dynamical property of classical
electromagnetic fields, plays an important role in spin-orbit and light-matter
interactions, especially in near-field optics. The research on optical spins
has led to the discovery of phenomena such as optical spin-momentum locking and
photonic topological quasiparticles, as well as applications in high-precision
detection and nanometrology. Here, we investigate spin-momentum relations in
paraxial optical systems and show that the optical spin angular momentum
contains transverse and longitudinal spin components simultaneously. The
transverse spin originates from inhomogeneities of field and governed by the
vorticity of the kinetic momentum density, whereas the longitudinal spin
parallel to the local canonical momentum is proportional to the polarization
ellipticity of light. Moreover, the skyrmionlike spin textures arise from the
optical transverse spin can be observed in paraxial beams, and their topologies
are maintained free from the influence of the Gouy phase during propagation.
Interestingly, the optical singularities, including both phase and polarization
singularities, can also affect the spin-momentum properties significantly. Our
findings describe the intrinsic spin-momentum properties in paraxial optical
systems and apply in the analysis of the properties of spin-momentum in optical
focusing, imaging, and scattering systems.",2212.04697v1
2018-12-30,Thermalization in Solid-State NMR Controlled by Quantum Chaos in Spin Bath,"We theoretically investigate thermalization and spin diffusion driven by a
quantum spin bath for a realistic solid-state NMR experiment. We consider
polycrystalline L-alanine, and investigate how the spin polarization spreads
among several $^{13}$C nuclear spins, which interact via dipole-dipole coupling
with the bath of strongly dipolar-coupled $^1$H nuclear (proton) spins. We do
this by using direct numerical simulation of the many-spin time-dependent
Schr\""odinger equation. We find that, although the proton spins located near
the carbon sites interact most strongly with the $^{13}$C spins, this
interaction alone is not enough to drive spin diffusion and thermalize the
$^{13}$C nuclear spins. We demonstrate that the thermalization within the
$^{13}$C subsystem is driven by the collective many-body dynamics of the proton
spin bath, and specifically, that the onset of thermalization among the
$^{13}$C spins is directly related to the onset of chaotic behavior in the
proton spin bath. Therefore, thermalization and spin diffusion within the
$^{13}$C subsystem is controlled by the proton spins located far from the C
sites. In spite of their weak coupling to the $^{13}$C spins, these far-away
protons help produce a network of strongly coupled proton spins with collective
dynamics, that drives thermalization.",1812.11638v2
2002-06-14,Intersubband spin-density excitations in quantum wells with Rashba spin splitting,"In inversion-asymmetric semiconductors, spin-orbit coupling induces a
k-dependent spin splitting of valence and conduction bands, which is a
well-known cause for spin decoherence in bulk and heterostructures.
Manipulating nonequilibrium spin coherence in device applications thus requires
understanding how valence and conduction band spin splitting affects carrier
spin dynamics. This paper studies the relevance of this decoherence mechanism
for collective intersubband spin-density excitations (SDEs) in quantum wells. A
density-functional formalism for the linear spin-density matrix response is
presented that describes SDEs in the conduction band of quantum wells with
subbands that may be non-parabolic and spin-split due to bulk or structural
inversion asymmetry (Rashba effect). As an example, we consider a 40 nm
GaAs/AlGaAs quantum well, including Rashba spin splitting of the conduction
subbands. We find a coupling and wavevector-dependent splitting of the
longitudinal and transverse SDEs. However, decoherence of the SDEs is not
determined by subband spin splitting, due to collective effects arising from
dynamical exchange and correlation.",0206251v1
2004-05-21,Spintronics: Fundamentals and applications,"Spintronics, or spin electronics, involves the study of active control and
manipulation of spin degrees of freedom in solid-state systems. This article
reviews the current status of this subject, including both recent advances and
well-established results. The primary focus is on the basic physical principles
underlying the generation of carrier spin polarization, spin dynamics, and
spin-polarized transport in semiconductors and metals. Spin transport differs
from charge transport in that spin is a nonconserved quantity in solids due to
spin-orbit and hyperfine coupling. The authors discuss in detail spin
decoherence mechanisms in metals and semiconductors. Various theories of spin
injection and spin-polarized transport are applied to hybrid structures
relevant to spin-based devices and fundamental studies of materials properties.
Experimental work is reviewed with the emphasis on projected applications, in
which external electric and magnetic fields and illumination by light will be
used to control spin and charge dynamics to create new functionalities not
feasible or ineffective with conventional electronics.",0405528v1
2019-03-04,Spin-Phonon Relaxation in Molecular Qubits from First Principles Spin Dynamics,"The coupling between electronic spins and lattice vibrations is fundamental
for driving relaxation in magnetic materials. The debate over the nature of
spin-phonon coupling dates back to the 40's, but the role of spin-spin,
spin-orbit and hyperfine interactions, has never been fully established. Here
we present a comprehensive study of the spin dynamics of a crystal of
Vanadyl-based molecular qubits by means of first-order perturbation theory and
first-principles calculations. We quantitatively determine the role of the
Zeeman, hyperfine and electronic spin dipolar interactions in the direct
mechanism of spin relaxation. We show that, in a high magnetic field regime,
the modulation of the Zeeman Hamiltonian by the intra-molecular components of
the acoustic phonons dominates the relaxation mechanism. In low fields,
hyperfine coupling takes over, with the role of spin-spin dipolar interaction
remaining the less important for the spin relaxation.",1903.01424v1
2021-04-16,PT-symmetry enabled spin circular photogalvanic effect in antiferromagnetic insulators,"The short timescale spin dynamics in antiferromagnets is an attractive
feature from the standpoint of ultrafast spintronics. Yet generating highly
polarized spin currents at room temperature remains a fundamental challenge for
antiferromagnets. We propose a spin circular photogalvanic effect (spin-CPGE),
in which circularly polarized light can produce a spin current without net
charge current at room temperature, through an ""injection-current-like""
mechanism in parity-time(PT)-symmetric antiferromagnetic (AFM) insulators. We
demonstrate this effect by first-principles simulations of bilayer CrI3 and
room-temperature AFM hematite. Our calculations show that the spin-CPGE is
significant, and the magnitude of spin photo-current is comparable with the
widely observed charge photocurrent in ferroelectric materials. Interestingly,
this spin photocurrent is not sensitive to spin-orbit interactions, which were
regarded as fundamental mechanisms for generating spin current. Given the fast
response of light-matter interactions, large energy scale, and insensitivity to
spin-orbit interactions, our work gives hope to realizing a fast-dynamic and
temperature-robust pure spin current in a wide range of PT-symmetric AFM
materials, including weak-relativistic magnetic insulators and topological
axion insulators.",2104.08341v1
2021-09-05,Electric field effect on electron gas spins in two-dimensional magnets with strong spin-orbit coupling,"The recent rise of material platforms combining magnetism and
two-dimensionality of mobile carriers reveals a diverse spectrum of spin-orbit
phenomena and stimulates its ongoing theoretical discussions. In this work we
use the density matrix approach to provide a unified description of subtle
microscopic effects governing the electron gas spin behavior in the clean limit
upon electric perturbations in two-dimensional magnets with strong spin-orbit
coupling. We discuss that an inhomogeneity of electrostatic potential generally
leads to the electron gas spin tilting with the subsequent formation of
equilibrium skyrmion-like spin textures and demonstrate that several
microscopic mechanisms of 2DEG spin response are equally important for this
effect. We analyze the dynamics of 2DEG spin upon an oscillating electric field
with a specific focus on the emergent electric dipole spin resonance. We
address the resonant enhancement of magneto-optical phenomena from the spin
precession equation perspective and discuss it in terms of the resonant spin
generation. We also clarify the connection of both static and dynamic spin
phenomena arising in response to a scalar perturbation with the electronic band
Berry curvature.",2109.02151v1
1997-09-24,Ultrafast Spin Dynamics in Nickel,"The spin dynamics in Ni is studied by an exact diagonalization method on the
ultrafast time scale. It is shown that the femtosecond relaxation of the
magneto-optical response results from exchange interaction and spin-orbit
coupling. Each of the two mechanisms affects the relaxation process
differently. We find that the intrinsic spin dynamics occurs during about 10 fs
while extrinsic effects such as laser-pulse duration and spectral width can
slow down the observed dynamics considerably. Thus, our theory indicates that
there is still room to accelerate the spin dynamics in experiments.",9709264v1
2006-06-02,Magnetically tuned spin dynamics resonance,"We present the experimental observation of a magnetically tuned resonance
phenomenon resulting from spin mixing dynamics of ultracold atomic gases. In
particular we study the magnetic field dependence of spin conversion in F=2
87Rb spinor condensates in the crossover from interaction dominated to
quadratic Zeeman dominated dynamics. We discuss the observed phenomenon in the
framework of spin dynamics as well as matter wave four wave mixing. Furthermore
we show that the validity range of the single mode approximation for spin
dynamics is significantly extended in the regime of high magnetic field.",0606046v1
2021-09-13,Revisiting the quantum open system dynamics of central spin model,"In this article we revisit the theory of open quantum systems from the
perspective of fermionic baths. Specifically, we concentrate on the dynamics of
a central spin half particle interacting with a spin bath. We have calculated
the exact reduced dynamics of the central spin and constructed the Kraus
operators in relation to that. Further, the exact Lindblad type cannonical
master equation corresponding to the reduced dynamics is constructed. We have
also briefly touch upon the aspect of non-Markovianity from the backdrop of the
reduced dynamics of the central spin.",2109.05775v1
2014-08-20,Coherent transport and manipulation of spins in indirect exciton nanostructures,"We report on the coherent control and transport of indirect exciton (IX)
spins in GaAs double quantum well (DQW) nanostructures. The spin dynamics was
investigated by optically generating spins using a focused, circularly
polarized light spot and by probing their spatial distribution using spatially
and polarization resolved photoluminescence spectroscopy. Optically injected
exciton spins precess while diffusing over distances exceeding 20 {\mu}m from
the excitation spot with a spatial precession frequency that depends on the
spin transport direction as well as on the bias applied across the DQW
structure. This behavior is attributed to the spin precession in the effective
magnetic field induced by the spin-orbit interaction. From the dependence of
the spin dynamics on the transport direction, bias and external magnetic fields
we directly determined the Dresselhaus and Rashba spin splitting coefficients
for the structure. The precession dynamics is essentially independent on the IX
density, thus indicating that the long spin lifetimes are not associated with
IX collective effects. The latter, together with the negligible contribution of
holes to the spin dynamics, are rather attributed to spatial separation of the
electron and hole wave functions by the electric field, which reduces the
electron-hole exchange interaction. Coherent spin precession over long
transport distances as well as the control of the spin vector using electric
and magnetic fields open the way for the application of IX spins in the quantum
information processing.",1408.4547v1
2013-08-24,Spin Dynamics in Graphene and Graphene like Nanocarbon Doped with Nitrogen the ESR Analysis,"Nano engineered spin degree of freedom in carbon system may offer desired
exchange coupling with optimum spin orbit interaction which is essential, to
construct solid state qubits, for fault tolerant quantum computation. The
purpose of this communication is to analyze spin dynamics of, basically, four
types of systems, (i) Graphene (system with inversion symmetry), (ii) Graphene
like nanocarbons (GNCs, broken inversion symmetry and heterostructure, sp2 and
sp3, environment), and (iii) their nitrogen doped derivatives. The spin
transport data was obtained using the electron spin resonance spectroscopy
(ESR) technique, carried out over 123 to 473K temperature range. Analysis of
shape, linewidths of dispersion derivatives,, and g factor anisotropy has been
carried out. Spin parameters such as, spin spin relaxation time, spin lattice
relaxation time, spin flip parameter,spin relaxation rate,spin, momentum
relaxation rate,pseudo chemical potential, density of states, effective
magnetic moment, spin concentration, defect concentration, and Pauli
susceptibility, has been estimated, and examined for their temperature as well
as interdependence. Details of the analysis are presented. The quantitative
study underlined the following facts: (i) by and large, spin dynamics in
Graphene and GNCs is significantly different, (ii) transport of spin behaves in
opposite fashion, after doping nitrogen, in both the systems, (iii) reduction
in the magnetization has been observed for both GNCs and Graphene, after doping
nitrogen, (iv) hyperfine interactions have been observed in all classes of
systems except in GNCs, (v) nitrogen doped GNCs seems to be appropriate for
qubit designing.",1308.5291v1
2021-01-21,Effects of the dynamical magnetization state on spin transfer,"We utilize simulations of electron scattering by a chain of dynamical quantum
spins, to analyze the interplay between the spin transfer effect and the
magnetization dynamics. We show that the complex interactions between the
spin-polarized electrons and the dynamical states of the local spins can be
decomposed into separate processes involving electron reflection and
transmission, as well as absorption and emission of magnons - the quanta of
magnetization dynamics. Analysis shows that these processes are substantially
constrained by the energy and momentum conversation laws, resulting in a
significant dependence of spin transfer on the electron's energy and the
dynamical state of the local spins. Our results suggest that exquisite control
of spin transfer efficiency and of the resulting dynamical magnetization states
may be achievable by tailoring the spectral characteristics of the conduction
electrons and of the magnetic systems.",2101.08868v1
2022-07-21,Probing dynamics of a two-dimensional dipolar spin ensemble using single qubit sensor,"Understanding the thermalization dynamics of quantum many-body systems at the
microscopic level is among the central challenges of modern statistical
physics. Here we experimentally investigate individual spin dynamics in a
two-dimensional ensemble of electron spins on the surface of a diamond crystal.
We use a near-surface NV center as a nanoscale magnetic sensor to probe
correlation dynamics of individual spins in a dipolar interacting surface spin
ensemble. We observe that the relaxation rate for each spin is significantly
slower than the naive expectation based on independently estimated dipolar
interaction strengths with nearest neighbors and is strongly correlated with
the timescale of the local magnetic field fluctuation. We show that this
anomalously slow relaxation rate is due to the presence of strong dynamical
disorder and present a quantitative explanation based on dynamic resonance
counting. Finally, we use resonant spin-lock driving to control the effective
strength of the local magnetic fields and reveal the role of the dynamical
disorder in different regimes. Our work paves the way towards microscopic study
and control of quantum thermalization in strongly interacting disordered spin
ensembles.",2207.10688v2
2016-05-02,Electrical Detection of Magnetization Dynamics via Spin Rectification Effects,"The purpose of this article is to review the current status of a frontier in
dynamic spintronics and contemporary magnetism, in which much progress has been
made in the past decade, based on the creation of a variety of micro- and
nano-structured devices that enable electrical detection of magnetization
dynamics. The primary focus is on the physics of spin rectification effects,
which are well suited for studying magnetization dynamics and spin transport in
a variety of magnetic materials and spintronic devices. Intended to be
intelligible to a broad audience, the paper begins with a pedagogical
introduction, comparing the methods of electrical detection of charge and spin
dynamics in semiconductors and magnetic materials respectively. After that it
provides a comprehensive account of the theoretical study of both the angular
dependence and line shape of electrically detected ferromagnetic resonance
(FMR), which is summarized in a handbook formate easy to be used for analyzing
experimental data. We then review and examine the similarity and differences of
various spin rectification effects found in ferromagnetic films, magnetic
bilayers and magnetic tunnel junctions, including a discussion of how to
properly distinguish spin rectification from the spin pumping/inverse spin Hall
effect generated voltage. After this we review the broad applications of
rectification effects for studying spin waves, nonlinear dynamics, domain wall
dynamics, spin current, and microwave imaging. We also discuss spin
rectification in ferromagnetic semiconductors. The paper concludes with both
historical and future perspectives, by summarizing and comparing three
generations of FMR spectroscopy which have been developed for studying
magnetization dynamics.",1605.00710v2
2020-09-14,Non-Hamiltonian dynamics of indirectly coupled classical impurity spins,"We discuss the emergence of an effective low-energy theory for the real-time
dynamics of two classical impurity spins within the framework of a prototypical
and purely classical model of indirect magnetic exchange: Two classical
impurity spins are embedded in a host system which consists of a finite number
of classical spins localized on the sites of a lattice and interacting via a
nearest-neighbor Heisenberg exchange. An effective low-energy theory for the
slow impurity-spin dynamics is derived for the regime, where the local exchange
coupling between impurity and host spins is weak. To this end we apply the
recently developed adiabatic spin dynamics (ASD) theory. Besides the
Hamiltonian-like classical spin torques, the ASD additionally accounts for a
novel topological spin torque that originates as a holonomy effect in the
close-to-adiabatic-dynamics regime. It is shown that the effective low-energy
precession dynamics cannot be derived from an effective Hamilton function and
is characterized by a non-vanishing precession frequency even if the initial
state deviates only slightly from a ground state. The effective theory is
compared to the fully numerical solution of the equations of motion for the
whole system of impurity and host spins to identify the parameter regime where
the adiabatic effective theory applies. Effective theories beyond the adiabatic
approximation must necessarily include dynamic host degrees of freedom and go
beyond the idea of a simple indirect magnetic exchange. We discuss an example
of a generalized constrained spin dynamics which does improve the description
but also fails for certain geometrical setups.",2009.06296v2
1997-01-15,Spin dynamics of the spin-Peierls compound CuGeO_3 under magnetic field,"The magnetic field--driven transition in the spin-Peierls system CuGeO_3
associated with the closing of the spin gap is investigated numerically. The
field dependence of the spin dynamical structure factor (seen by inelastic
neutron scattering) and of the momentum dependent static susceptibility are
calculated. In the dimerized phase (H<H_c), we suggest that the strong field
dependence of the transverse susceptibility could be experimentally seen from
the low temperature spin-echo relaxation rate 1/T_{2G} or the second moment of
the NMR spectrum. Above H_c low energy spin excitations appear at
incommensurate wave vectors where the longitudinal susceptibility chi_{zz}(q)
peaks.",9701107v1
2005-12-16,Spin dynamics in a compound semiconductor spintronic structure with a Schottky barrier,"We demonstrate theoretically that spin dynamics of electrons injected into a
GaAs semiconductor structure through a Schottky barrier possesses strong
non-equilibrium features. Electrons injected are redistributed quickly among
several valleys. Spin relaxation driven by the spin-orbital coupling in the
semiconductor is very rapid. At T = 4.2 K, injected spin polarization decays on
a distance of the order of 50 - 100 nm from the interface. This spin
penetration depth reduces approximately by half at room temperature. The spin
scattering length is different for different valleys.",0512414v1
2006-09-12,Nonlinear dynamics of quantum dot nuclear spins,"We report manifestly nonlinear dependence of quantum dot nuclear spin
polarization on applied magnetic fields. Resonant absorption and emission of
circularly polarized radiation pumps the resident quantum dot electron spin,
which in turn leads to nuclear spin polarization due to hyperfine interaction.
We observe that the resulting Overhauser field exhibits hysteresis as a
function of the external magnetic field. This hysteresis is a consequence of
the feedback of the Overhauser field on the nuclear spin cooling rate. A
semi-classical model describing the coupled nuclear and electron spin dynamics
successfully explains the observed hysteresis but leaves open questions for the
low field behaviour of the nuclear spin polarization.",0609291v1
2006-10-03,Non-diffusive spin dynamics in a two-dimensional electron gas,"We describe measurements of spin dynamics in the two-dimensional electron gas
in GaAs/GaAlAs quantum wells. Optical techniques, including transient
spin-grating spectroscopy, are used to probe the relaxation rates of spin
polarization waves in the wavevector range from zero to $6\times 10^4$
cm$^{-1}$. We find that the spin polarization lifetime is maximal at nonzero
wavevector, in contrast with expectation based on ordinary spin diffusion, but
in quantitative agreement with recent theories that treat diffusion in the
presence of spin-orbit coupling.",0610054v1
2007-06-11,Electron and hole spin dynamics and decoherence in quantum dots,"In this article we review our work on the dynamics and decoherence of
electron and hole spins in single and double quantum dots. The first part, on
electron spins, focuses on decoherence induced via the hyperfine interaction
while the second part covers decoherence and relaxation of heavy-hole spins due
to spin-orbit interaction as well as the manipulation of heavy-hole spin using
electric dipole spin resonance.",0706.1514v1
2008-03-29,Quantized spin waves and perpendicular standing spin waves stimulated by current in a single-layered ferromagnetic wire,"The rectifying effect of radio-frequency (RF) current is highly sensitive in
terms of the spatial spin distribution and dynamics. It emerged that an
additional spin wave mode was stimulated by the direct-current (DC) current and
that this spin wave was detectable via rectification of the RF current. A
phenomenological model to describe the time-dependent anisotropic
magnetoresistance or time-dependent planer Hall effect is proposed and found to
correlate well to the experimental results. The nonlinear spin dynamics
accompanying additional spin waves are studied as functions of the RF and DC
currents, the external magnetic field, and the applied field direction.",0803.4271v1
2008-08-09,Quantum frustration of dissipation by a spin bath,"We investigate the evolution of a central spin coupled to a spin bath without
internal dynamics. We compare the cases where the bath couples to one or two
components of the spin. It is found that the central spin dynamics is enhanced
in the latter case, which may be interpreted as a frustration of dissipation.
However, the quantum purity of the spin decays fast in both scenarios. We
conclude that symmetric coupling of the bath to two orthogonal components of
the spin inhibits dissipation but not decoherence.",0808.1377v1
2008-11-17,Dynamics in two-leg spin ladder with a four-spin cyclic interaction,"We study two-leg Heisenberg ladder with four-spin cyclic interaction using
the (dynamical) density-matrix renormalization group method. We demonstrate the
dependence of the low-lying excitations in the spin wave, staggered dimer
order, and scalar-chirality order structure factors on the four-spin cyclic
interaction. We find that the cyclic interaction enhances spin-spin
correlations with wave vector around momentum $(q_x,q_y)=(\frac{\pi}{2},0)$.
Also, the presence of long-range order in the staggered dimer and
scalar-chirality phases is confirmed by a $\delta$-function peak contribution
of the structure factors at energy $\omega=0$.",0811.2456v1
2009-06-16,Entanglement enhancement for two spins assisted by two phase kicks,"We study the entanglement dynamics in a two-spin system governed by a
bilinear Hamiltonian and assisted by phase kicks. It is found that the
application of instant kicks to both spins at some specific moments leads to
enhancement of entanglement. This procedure also improves the transient
character of entanglement leading, for large spins, to a formation of a plateau
for the I-concurrence. We have numerically investigated the spin-spin dynamics
for several values of spins and observed a substantial enhancement of
entanglement in comparison to the evolution without kicks.",0906.2986v1
2012-08-28,Non-Markovian Dynamics of Spin Squeezing,"We evaluate the spin squeezing dynamics of N independent spin-1/2 particles
with exchange symmetry. Each spin interacts with its own reservoir, and the
reservoirs are independently and identical. The spin squeezing parameter is
analytically calculated with different kinds of decoherence. The spin squeezing
property vanishes with evolution time under the Markovian decoherence. Whereas
coupled to the non-Markovian decoherence channels, the spin squeezing property
collapses and revives with time. As spin squeezing can be regarded as a witness
of multipartite entanglement, thus our scheme shows the collapse and revival of
multipartite entanglement under non-Markovian decoherence.",1208.5681v2
2012-12-13,Spin dynamics in tunneling decay of a metastable state,"We analyze spin dynamics in the tunneling decay of a metastable localized
state in the presence of spin-orbit coupling. We find that the spin
polarization at short time scales is affected by the initial state while at
long time scales both the probability- and the spin density exhibit
diffraction-in-time phenomenon. We find that in addition to the tunneling time
the tunneling in general can be characterized by a new parameter, the tunneling
length. Although the tunneling length is independent on the spin-orbit
coupling, it can be accessed by the spin rotation measurement.",1212.3325v1
2013-01-23,Decoherence of a single-ion qubit immersed in a spin-polarized atomic bath,"We report on the immersion of a spin-qubit encoded in a single trapped ion
into a spin-polarized neutral atom environment, which possesses both continuous
(motional) and discrete (spin) degrees of freedom. The environment offers the
possibility of a precise microscopic description, which allows us to understand
dynamics and decoherence from first principles. We observe the spin dynamics of
the qubit and measure the decoherence times (T1 and T2), which are determined
by the spin-exchange interaction as well as by an unexpectedly strong
spin-nonconserving coupling mechanism.",1301.5452v2
2012-01-20,Josephson dynamics of a spin-orbit coupled Bose-Einstein condensate in a double well potential,"We investigate the quantum dynamics of an experimentally realized spin-orbit
coupled Bose-Einstein condensate in a double well potential. The spin-orbit
coupling can significantly enhance the atomic inter-well tunneling. We find the
coexistence of internal and external Josephson effects in the system, which are
moreover inherently coupled in a complicated form even in the absence of
interatomic interactions. Moreover, we show that the spin-dependent tunneling
between two wells can induce a net atomic spin current referred as spin
Josephson effects. Such novel spin Josephson effects can be observable for
realistically experimental conditions.",1201.4306v1
2017-09-13,Ultrafast spin-lattice relaxation in ferromagnets including effective spin-orbit fields,"We investigate ultrafast demagnetization due to electron-phonon interaction
in a model band-ferromagnet. We show that the microscopic mechanism behind the
spin dynamics due to electron-phonon interaction is the interplay of scattering
and the precession around momentum-dependent effective internal spin-orbit
magnetic fields. The resulting magnetization dynamics can only be mimicked by
spin-flip transitions if the spin precession around the internal fields is
sufficiently fast (compared to the scattering time) so that it averages out the
transverse spin components.",1709.04253v1
2015-02-18,Quenching of dynamic nuclear polarization by spin-orbit coupling in GaAs quantum dots,"The central-spin problem, in which an electron spin interacts with a nuclear
spin bath, is a widely studied model of quantum decoherence. Dynamic nuclear
polarization (DNP) occurs in central spin systems when electronic angular
momentum is transferred to nuclear spins and is exploited in spin-based quantum
information processing for coherent electron and nuclear spin control. However,
the mechanisms limiting DNP remain only partially understood. Here, we show
that spin-orbit coupling quenches DNP in a GaAs double quantum dot, even though
spin-orbit coupling in GaAs is weak. Using Landau-Zener sweeps, we measure the
dependence of the electron spin-flip probability on the strength and direction
of in-plane magnetic field, allowing us to distinguish effects of the
spin-orbit and hyperfine interactions. To confirm our interpretation, we
measure high-bandwidth correlations in the electron spin-flip probability and
attain results consistent with a significant spin-orbit contribution. We
observe that DNP is quenched when the spin-orbit component exceeds the
hyperfine, in agreement with a theoretical model. Our results shed new light on
the surprising competition between the spin-orbit and hyperfine interactions in
central-spin systems.",1502.05400v1
2007-10-28,On the nature of steady states of spin distributions in the presence of spin-orbit interactions,"In the presence of spin-orbit interactions, the steady state established for
spin distributions in an electric field is qualitatively different from the
steady state for charge distributions. This is primarily because the steady
state established for spin distributions involves spin precession due to
spin-orbit coupling. We demonstrate in this work that the spin density matrix
in an external electric field acquires two corrections with different
dependencies on the characteristic momentum scattering time. One part is
associated with conserved spins, diverges in the clean limit and is responsible
for the establishment of a steady-state spin density in electric fields.
Another part is associated with precessing spins, is finite in the clean limit
and is responsible for the establishment of spin currents in electric fields.
Scattering between these distributions has important consequences for spin
dynamics and spin-related effects in general, and explains some recent puzzling
observations, which are captured by our unified theory.",0710.5260v1
2009-06-27,Steady-state spin densities and currents,"This article reviews steady-state spin densities and spin currents in
materials with strong spin-orbit interactions. These phenomena are intimately
related to spin precession due to spin-orbit coupling which has no equivalent
in the steady state of charge distributions. The focus will be initially on
effects originating from the band structure. In this case spin densities arise
in an electric field because a component of each spin is conserved during
precession. Spin currents arise because a component of each spin is continually
precessing. These two phenomena are due to independent contributions to the
steady-state density matrix, and scattering between the conserved and
precessing spin distributions has important consequences for spin dynamics and
spin-related effects in general. In the latter part of the article extrinsic
effects such as skew scattering and side jump will be discussed, and it will be
shown that these effects are also modified considerably by spin precession.
Theoretical and experimental progress in all areas will be reviewed.",0906.5111v1
2014-09-14,Generation and Detection of Spin Currents in Semiconductor Nanostructures with Strong Spin-Orbit Interaction,"Storing, transmitting, and manipulating information using the electron spin
resides at the heart of spintronics. Fundamental for future spintronics
applications is the ability to control spin currents in solid state systems.
Among the different platforms proposed so far, semiconductors with strong
spin-orbit interaction are especially attractive as they promise fast and
scalable spin control with all-electrical protocols. Here we demonstrate both
the generation and measurement of pure spin currents in semiconductor
nanostructures. Generation is purely electrical and mediated by the spin
dynamics in materials with a strong spin-orbit field. Measurement is
accomplished using a spin-to-charge conversion technique, based on the magnetic
field symmetry of easily measurable electrical quantities. Calibrating the
spin-to-charge conversion via the conductance of a quantum point contact, we
quantitatively measure the mesoscopic spin Hall effect in a multiterminal GaAs
dot. We report spin currents of 174 pA, corresponding to a spin Hall angle of
34%.",1409.4045v2
2018-02-19,Strong enhancement of the spin Hall effect by spin fluctuations near the Curie point of FexPt1-x alloys,"Robust spin Hall effects (SHE) have recently been observed in non-magnetic
heavy metal systems with strong spin-orbit interactions. These SHE are either
attributed to an intrinsic band-structure effect or to extrinsic spin-dependent
scattering from impurities, namely side-jump or skew scattering. Here we report
on an extraordinarily strong spin Hall effect, attributable to spin
fluctuations, in ferromagnetic FexPt1-x alloys near their Curie point, tunable
with x. This results in a damping-like spin-orbit torque being exerted on an
adjacent ferromagnetic layer that is strongly temperature dependent in this
transition region, with a peak value that indicates a lower bound 0.34 (+-)
0.02 for the peak spin Hall ratio within the FePt. We also observe a pronounced
peak in the effective spin-mixing conductance of the FM/FePt interface, and
determine the spin diffusion length in these FexPt1-x alloys. These results
establish new opportunities for fundamental studies of spin dynamics and
transport in ferromagnetic systems with strong spin fluctuations, and a new
pathway for efficiently generating strong spin currents for applications.",1802.06911v1
2018-04-23,Microscopic linear response theory of spin relaxation and relativistic transport phenomena in graphene,"We present a unified theoretical framework for the study of spin dynamics and
relativistic transport phenomena in disordered two-dimensional Dirac systems
with pseudospin-spin coupling. The formalism is applied to the paradigmatic
case of graphene with uniform Bychkov-Rashba interaction and shown to capture
spin relaxation processes and associated charge-to-spin interconversion
phenomena in response to generic external perturbations, including spin density
fluctuations and electric fields. A controlled diagrammatic evaluation of the
generalized spin susceptibility in the diffusive regime of weak spin-orbit
interaction allows us to show that the spin and momentum lifetimes satisfy the
standard Dyakonov-Perel relation for both weak (Gaussian) and resonant
(unitary) nonmagnetic disorder. Finally, we demonstrate that the spin
relaxation rate can be derived in the zero-frequency limit by exploiting the
SU(2) covariant conservation laws for the spin observables. Our results set the
stage for a fully quantum-mechanical description of spin relaxation in both
pristine graphene samples with weak spin-orbit fields and in graphene
heterostructures with enhanced spin-orbital effects currently attracting much
attention.",1804.08634v2
2020-11-06,Acoustic spin Hall effect in strong spin-orbit metals,"We report on the observation of the acoustic spin Hall effect that
facilitates lattice motion induced spin current via spin orbit interaction
(SOI). Under excitation of surface acoustic wave (SAW), we find a spin current
flows orthogonal to the propagation direction of a surface acoustic wave (SAW)
in non-magnetic metals. The acoustic spin Hall effect manifests itself in a
field-dependent acoustic voltage in non-magnetic metal (NM)/ferromagnetic metal
(FM) bilayers. The acoustic voltage takes a maximum when the NM layer thickness
is close to its spin diffusion length, vanishes for NM layers with weak SOI and
increases linearly with the SAW frequency. To account for these results, we
find the spin current must scale with the SOI and the time derivative of the
lattice displacement. Such form of spin current can be derived from a Berry
electric field associated with time varying Berry curvature and/or an
unconventional spin-lattice interaction mediated by SOI. These results, which
imply the strong coupling of electron spins with rotating lattices via the SOI,
show the potential of lattice dynamics to supply spin current in strong spin
orbit metals.",2011.03246v2
2004-04-02,Quantum Spin Dynamics in Single-Molecule Magnets,"This thesis contains a thorough investigation of the quantum spin dynamics in
Mn12-ac and Mn6 Single-molecule magnets. In particular, we have investigated
the interplay between quantum tunneling of magnetization and nuclear spin
dynamics in Mn12-ac by ultra-low temperature NMR experiments. We discuss the
effect of quantum tunneling on the nuclear spin-lattice relaxation, the nuclear
spin diffusion, the thermalization of the nuclear spins, the isotope effect,
the influence of strong perpendicular fields, and we propose a model to unify
all our observations. For the isotropic Mn6 molecule, we report the observation
of long-range ferromagentic ordering of the cluster spins, due to dipolar
interactions only. The nuclear spin dynamics provides an interesting comparison
with the case of Mn12-ac. Two large introductory chapters describe the design
of our ultra-low temperature setups, and the theoretical background necessary
to understand the interplay between nuclear spins and quantum tunneling, with
emphasis on the Prokof'ev-Stamp theory of the ""spin-bath"".",0404049v1
2015-04-15,Acoustic study for dynamical molecular-spin state without undergoing magnetic phase transition in spin-frustrated ZnFe$_2$O$_4$,"Ultrasound velocity measurements were performed on a single crystal of
spin-frustrated ferrite spinel ZnFe$_2$O$_4$ from 300 K down to 2 K. In this
cubic crystal, all the symmetrically-independent elastic moduli exhibit
softening with a characteristic minimum with decreasing temperature below
$\sim$100 K. This elastic anomaly suggests a coupling between dynamical lattice
deformations and molecular-spin excitations. In contrast, the elastic
anomalies, normally driven by the magnetostructural phase transition and its
precursor, are absent in ZnFe$_2$O$_4$, suggesting that the spin-lattice
coupling cannot play a role in relieving frustration within this compound. The
present study infers that, for ZnFe$_2$O$_4$, the dynamical molecular-spin
state evolves at low temperatures without undergoing precursor spin-lattice
fluctuations and spin-lattice ordering. It is expected that ZnFe$_2$O$_4$
provides the unique dynamical spin-lattice liquid-like system, where not only
the spin molecules but also the cubic lattice fluctuate spatially and
temporally.",1504.03792v3
2016-08-27,Tunneling induced spin dynamics in a quantum dot-lead hybrid system,"Semiconductor quantum dots (QDs) offer a platform to explore the physics of
quantum electronics including spins. Electron spins in QDs are considered good
candidates for quantum bits in quantum information processing, and spin control
and readout have been established down to a single electron level. We use these
techniques to explore spin dynamics in a hybrid system, namely a QD coupled to
a two dimensional electronic reservoir. The proximity of the lead results in
relaxation dynamics of both charge and spin, the mechanism of which is revealed
by comparing the charge and spin signal. For example, higher order charge
tunneling events can be monitored by observing the spin. We expect these
results to stimulate further exploration of spin dynamics in QD-lead hybrid
systems and expand the possibilities for controlled spin manipulations.",1608.07646v1
2009-09-01,Phase-Sensitive Probes of Nuclear Polarization in Spin-Blockaded Transport,"Spin-blockaded quantum dots provide a unique setting for studying
nuclear-spin dynamics in a nanoscale system. Despite recent experimental
progress, observing phase-sensitive phenomena in nuclear spin dynamics remains
challenging. Here we point out that such a possibility opens up in the regime
where hyperfine exchange directly competes with a purely electronic spin-flip
mechanism such as the spin-orbital interaction. Interference between the two
spin-flip processes, resulting from long-lived coherence of the nuclear-spin
bath, modulates the electron-spin-flip rate, making it sensitive to the
transverse component of nuclear polarization. In a system repeatedly swept
through a singlet-triplet avoided crossing, nuclear precession is manifested in
oscillations and sign reversal of the nuclear-spin pumping rate as a function
of the waiting time between sweeps. This constitutes a purely electrical method
for the detection of coherent nuclear-spin dynamics.",0909.0060v2
2011-01-27,Magnetic excitations in one-dimensional spin-orbital models,"We study the dynamics and thermodynamics of one-dimensional spin-orbital
models relevant for transition metal oxides. We show that collective spin,
orbital, and combined spin-orbital excitations with infinite lifetime can
exist, if the ground state of both sectors is ferromagnetic. Our main focus is
the case of effectively ferromagnetic (antiferromagnetic) exchange for the spin
(orbital) sector, respectively, and we investigate the renormalization of spin
excitations via spin-orbital fluctuations using a boson-fermion representation.
We contrast a mean-field decoupling approach with results obtained by treating
the spin-orbital coupling perturbatively. Within the latter self-consistent
approach we find a significant increase of the linewidth and additional
structures in the dynamical spin structure factor as well as Kohn anomalies in
the spin-wave dispersion caused by the scattering of spin excitations from
orbital fluctuations. Finally, we analyze the specific heat c(T) by comparing a
numerical solution of the model obtained by the density-matrix renormalization
group with perturbative results. At low temperatures T we find numerically c(T)
T pointing to a low-energy effective theory with dynamical critical exponent
z=1.",1101.5301v1
2011-12-03,Spectroscopy of composite solid-state spin environments for improved metrology with spin ensembles,"For precision coherent measurements with ensembles of quantum spins the
relevant Figure-of-Merit (FOM) is the product of polarized spin density and
coherence lifetime, which is generally limited by the dynamics of the spin
environment. Here, we apply a coherent spectroscopic technique to characterize
the dynamics of the composite solid-state spin environment of Nitrogen-Vacancy
(NV) centers in room temperature diamond. For samples of very different NV
densities and impurity spin concentrations, we show that NV FOM values can be
almost an order of magnitude larger than previously achieved in other
room-temperature solid-state spin systems, and within an order of magnitude of
the state-of-the-art atomic system. We also identify a new mechanism for
suppression of electronic spin bath dynamics in the presence of a nuclear spin
bath of sufficient concentration. This suppression could inform efforts to
further increase the FOM for solid-state spin ensemble metrology and collective
quantum information processing.",1112.0667v2
2012-09-25,Spin noise spectroscopy of donor bound electrons in ZnO,"We investigate the intrinsic spin dynamics of electrons bound to Al
impurities in bulk ZnO by optical spin noise spectroscopy. Spin noise
spectroscopy enables us to investigate the longitudinal and transverse spin
relaxation time with respect to nuclear and external magnetic fields in a
single spectrum. On one hand, the spin dynamic is dominated by the intrinsic
hyperfine interaction with the nuclear spins of the naturally occurring
$^{67}$Zn isotope. We measure a typical spin dephasing time of 23 ns in
agreement with the expected theoretical values. On the other hand, we measure a
third, very high spin dephasing rate which is attributed to a high defect
density of the investigated ZnO material. Measurements of the spin dynamics
under the influence of transverse as well as longitudinal external magnetic
fields unambiguously reveal the intriguing connections of the electron spin
with its nuclear and structural environment.",1209.5667v1
2013-04-17,Universal spin dynamics in two-dimensional Fermi gases,"Harnessing spins as carriers for information has emerged as an elegant
extension to the transport of electrical charges. The coherence of such spin
transport in spintronic circuits is determined by the lifetime of spin
excitations and by spin diffusion. Fermionic quantum gases are a unique system
to study the fundamentals of spin transport from first principles since
interactions can be precisely tailored and the dynamics is on time scales which
are directly observable. In particular at unitarity, spin transport is dictated
by diffusion and is expected to reach a universal, quantum-limited diffusivity
on the order of hbar/m. Here, we study the non-equilibrium dynamics of a
two-dimensional Fermi gas following a quench into a metastable, transversely
polarized spin state. Using the spin-echo technique, we measure the yet lowest
transverse spin diffusion constant of 0.25(3) hbar/m. For weak interactions, we
observe a coherent collective transverse spin-wave mode that exhibits mode
softening when approaching the hydrodynamic regime.",1304.4980v1
2014-01-18,Position and Spin Control by Dynamical Ultrastrong Spin-Orbit Coupling,"Focusing on the efficient probe and manipulation of single-particle spin
states, we investigate the coupled spin and orbital dynamics of a spin 1/2
particle in a harmonic potential subject to ultrastrong spin-orbit interaction
and external magnetic field. The advantage of these systems is the clear
visualization of the strong spin-orbit coupling in the orbital dynamics. We
also investigate the effect of a time-dependent coupling: Its nonadiabatic
change causes an interesting interplay of spin and orbital motion which is
related to the direction and magnitude of the applied magnetic field. This
result suggests that orbital state manipulation can be realized through
ultrastrong spin-orbit interactions, becoming a useful tool for handling
entangled spin and orbital degrees of freedom to produce, for example, spin
desirable polarizations in time interesting for spintronics implementations.",1401.4554v1
2014-01-29,Initial correlation in a system of a spin coupled to a spin bath through an intermediate spin,"The strong system-bath correlation is a typical initial condition in many
condensed matter and some quantum optical systems. Here, the dynamics of a spin
interacting with a spin bath through an intermediate spin are studied. Initial
correlations between the spin and the intermediate spin are taken into account.
The exact analytical expression for the evolution operator of the spin is
found. Furthermore, correlated projection superoperator techniques are applied
to the model and a time-convolutionless master equation to second order is
derived. It is shown that the time-convolutionless master equation to second
order reproduces the exact dynamics for time-scales of the order 1/{\gamma},
where {\gamma} is the coupling of the central spin to the intermediate spin. It
is found that there is a strong dependence on the initial system-bath
correlations in the dynamics of the reduced system, which cannot be neglected.",1401.7572v1
2016-09-08,Pumping dynamics of nuclear spins in GaAs quantum wells,"Irradiating a semiconductor with circularly polarized light creates
spin-polarized charge carriers. If the material contains atoms with non-zero
nuclear spin, they interact with the electron spins via the hyperfine coupling.
Here, we consider GaAs/AlGaAs quantum wells, where the conduction-band electron
spins interact with three different types of nuclear spins. The hyperfine
interaction drives a transfer of spin polarization to the nuclear spins, which
therefore acquire a polarization that is comparable to that of the electron
spins. In this paper, we analyze the dynamics of the optical pumping process in
the presence of an external magnetic field while irradiating a single quantum
well with a circularly polarized laser. We measure the time dependence of the
photoluminescence polarization to monitor the buildup of the nuclear spin
polarization and thus the average hyperfine interaction acting on the electron
spins. We present a simple model that adequately describes the dynamics of this
process and is in good agreement with the experimental data.",1609.02319v1
2018-05-15,Spin-orbit effects on the spin and pseudospin polarization in ac-driven silicene,"We study the pseudospin and spin dynamical effects in single-layer silicene
due to a perpendicular electric field periodically driven and its interplay
with the intrinsic and extrinsic (Rashba) spin-orbit interaction. We find that
the spin nonconserving processes of the real spin of the quasiparticles in
silicene, -- induced by the rather weak spin-orbit mechanisms --, manifest
themselves as shifts of the resonances of its quasienergy spectrum in the low
coupling regime to the driving field. We show that there is an interesting
cooperative effect among the, in principle, competing Rashba and intrinsic
spin-orbit contributions. This is explicitly illustrated by exact and
approximated analytical solutions of the dynamical equations. In addition, we
show that a finite Rashba spin-orbit interaction is indeed necessary in order
to achieve a nonvanishing spin polarization. As additional feature, trivial and
nontrivial topological phases might be distinguished from each other as fast or
slow dynamical fluctuations of the spin polarization. We mention the possible
experimental detection schemes of our theoretical results and their relevance
in new practical implementation of periodically driven interactions in silicene
physics and related two-dimensional systems.",1805.05833v1
2018-06-06,Control of magnetization dynamics by spin Nernst torque,"Control of magnetization dynamics is one of the primary goals in spintronics.
It has been demonstrated using spin Hall effect i.e charge current to spin
current conversion in non-magnetic metal which has large spin-orbit coupling
such as Pt, W etc. Recently different groups have shown generation of spin
current in Pt, W while thermal gradient is created by virtue of spin Nernst
effect. In this work we show the evidence of magnetization control by spin
Nernst torque in Pt/Py bi-layer. We compared relative strength of spin Nernst
Torque and spin Hall torque by measuring the systematic variation of magnetic
linewidth on application of constant heat or charge current. Spin-torque
ferromagnetic resonance (ST-FMR) technique is adopted to excite the magnet and
to measure line-width precisely from the symmetric and anti-symmetric voltage
component. Control of magnetization dynamics by spin Nernst torque will emerge
as an alternative way to manipulate nano-magnets.",1806.01978v1
2020-05-04,Spin-orbit-torque magnonics,"The field of magnonics, which utilizes propagating spin waves for nano-scale
transmission and processing of information, has been significantly advanced by
the advent of the spin-orbit torque. The latter phenomenon can allow one to
overcome two main drawbacks of magnonic devices - low energy efficiency of
conversion of electrical signals into spin wave signals, and fast spatial decay
of spin waves in thin-film waveguiding structures. At first glance, the
excitation and amplification of spin waves by spin-orbit torques can seem to be
straightforward. Recent research indicates, however, that the lack of the
mode-selectivity in the interaction of spin currents with dynamic magnetic
modes and the onset of dynamic nonlinear phenomena represent significant
obstacles. Here, we discuss the possible route to overcoming these limitations,
based on the suppression of nonlinear spin-wave interactions in magnetic
systems with perpendicular magnetic anisotropy. We show that this approach
enables efficient excitation of coherent magnetization dynamics and propagating
spin waves in extended spatial regions, and is expected to enable practical
implementation of complete compensation of spin-wave propagation losses.",2005.01391v1
2021-06-21,Spin structure factors of doped monolayer Germanene in the presence of spin-orbit coupling,"In this paper, we present a Kane-Mele model in the presence of magnetic field
and next nearest neighbors hopping amplitudes for investigations of the spin
susceptibilities of Germanene layer. Green's function approach has been
implemented to find the behavior of dynamical spin susceptibilities of
Germanene layer within linear response theoryand in the presence of magnetic
field and spin-orbit coupling at finite temperature. Our results show the
magnetic excitation mode for both longitudinal and transverse components of
spin tends to higher frequencies with spin-orbit coupling strength. Moreover
the frequency positions of sharp peaks in longitudinal dynamical spin
susceptibility are not affected by variation of magnetic field while the peaks
in transverse dynamical susceptibility moves to lower frequencies with magnetic
field. The effects of electron doping on frequency behaviors of spin
susceptibilities have been addressed in details. Finally the temperature
dependence of static spin structure factors due to the effects of spin-orbit
coupling, magnetic field and chemical potential has been studied.",2106.11377v1
2022-06-27,Unveiling the electron-nuclear spin dynamics in an n-doped InGaAs epilayer by spin noise spectroscopy,"We discuss the implications of a small indium content (3%) in a GaAs epilayer
on the electron- and nuclear-spin relaxation due to enhanced quadrupolar
effects induced by the strain. Using the weakly perturbative spin-noise
spectroscopy, we study the electron-spin relaxation dynamics without explicit
excitation. The observed temperature dependence indicates the presence of
localized states, which have an increased interaction with the surrounding
nuclear spins. Time-resolved spin-noise spectroscopy is then applied to study
the relaxation dynamics of the optically pumped nuclear-spin system. It shows a
multi-exponential decay with time components, ranging from several seconds to
hundreds of seconds. Further, we provide a measurement of the local magnetic
field acting between the nuclear spins and discover a strong contribution of
quadrupole effects. Finally, we apply the nuclear spin diffusion model, that
allows us to estimate the concentration of the localized carrier states and to
determine the nuclear spin diffusion constant characteristic for this system.",2206.13177v1
2022-08-20,Many-body theory of phonon-induced spin relaxation and decoherence,"First-principles calculations enable accurate predictions of electronic
interactions and dynamics. However, computing the electron spin dynamics
remains challenging. The spin-orbit interaction causes various dynamical
phenomena that couple with phonons, such as spin precession and spin-flip e-ph
scattering, which are difficult to describe with current first-principles
calculations. In this work, we show a rigorous framework to study
phonon-induced spin relaxation and decoherence, by computing the spin-spin
correlation function and its vertex corrections due to e-ph interactions. We
apply this approach to a model system and develop corresponding
first-principles calculations of spin relaxation in GaAs. Our vertex-correction
formalism is shown to capture the Elliott-Yafet, Dyakonov-Perel, and
strong-precession mechanisms - three independent spin decoherence regimes with
distinct physical origins - thereby unifying their theoretical treatment and
calculation. Our method is general and enables quantitative studies of spin
relaxation, decoherence, and transport in a wide range of materials and
devices.",2208.09575v1
2023-03-25,Muon spin relaxation and emergence of disorder-induced unconventional dynamic magnetic fluctuations in Dy$_{2}$Zr$_{2}$O$_{7}$,"The disordered pyrochlore oxide Dy$_{2}$Zr$_{2}$O$_{7}$ shows the signatures
of field-induced spin freezing with remnant zero-point spin-ice entropy at 5
kOe magnetic field. We have performed zero-field and longitudinal field Muon
spin relaxation ($\mu$SR) studies on Dy$_{2}$Zr$_{2}$O$_{7}$. Our zero field
studies reveal the absence of both long-range ordering and spin freezing down
to 62 mK. The $\mu$SR relaxation rate exhibits a temperature-independent
plateau below 4 K, indicating a dynamic ground state of fluctuating spins
similar to the well-known spin ice system Dy$_{2}$Ti$_{2}$O$_{7}$. The
low-temperature spin fluctuations persist in the longitudinal field of 20 kOe
as well and show unusual field dependence of the relaxation rate, which is
uncommon for a spin-liquid system. Our results, combined with the previous
studies do not show any evidence of spin ice or spin glass ground state, rather
point to a disorder-induced dynamic magnetic ground state in the
Dy$_{2}$Zr$_{2}$O$_{7}$ material.",2303.14426v1
2023-10-09,Bath-induced spin inertia,"Spin dynamics is usually described as massless or, more precisely, as free of
inertia. Recent experiments, however, found direct evidence for inertial spin
dynamics. In turn, it is necessary to rethink the basics of spin dynamics.
Focusing on a macrospin in an environment (bath), we show that the spin-to-bath
coupling gives rise to spin inertia. This bath-induced spin inertia appears
universally from all the high-frequency bath modes. We expect our results to
provide new insights into recent experiments on spin inertia. Moreover, they
indicate that any channel for spin dissipation should also be accompanied by a
term accounting for bath-induced spin inertia. As an illustrative example, we
consider phonon-bath-induced spin inertia in a YIG/GGG stack.",2310.05621v2
1998-05-11,Dynamical simulation of spin-glass and chiral-glass orderings in three-dimensional Heisenberg spin glasses,"Spin-glass and chiral-glass orderings in three-dimensional Heisenberg spin
glasses are studied with and without randaom magnetic anisotropy by dynamical
Monte Carlo simulations. In isotropic case, clear evidence of a
finite-temperature chiral-glass transition is presented. While the spin
autocorrelation exhibits only an interrupted aging, the chirality
autocorrelation persists to exhibit a pronounced aging effect reminisecnt of
the one observed in the mean-field model. In anisotropic case, asymptotic
mixing of the spin and the chirality is observed in the off-equilibrium
dynamics.",9805117v1
2004-08-18,Hole dynamics in spin and orbital ordered vanadium perovskites,"Hole dynamics in spin and orbital ordered vanadates with perovskite structure
is investigated. A mobile hole coupled to the spin excitation (magnon) in the
spin G-type and orbital C-type (SG/OC) ordered phase, and that to the orbital
excitation (orbiton) in the spin C-type and orbital G-type (SC/OG) one are
formulated on an equal footing. The observed fragile character of the (SG/OC)
order is attributed to the orbiton softening caused by a reduction of the
taggered magnetic order parameter. It is proposed that the qualitatively
different hole dynamics in the two spin-orbital ordered phases in vanadates can
be probed by the optical spectra.",0408395v1
2008-06-24,Spin dynamics in point contacts to single ferromagnetic films,"Excitation of magnons or spin-waves driven by nominally unpolarized transport
currents in point contacts of normal and ferromagnetic metals is probed by
irradiating the contacts with microwaves. Two characteristic dynamic effects
are observed: a rectification of off-resonance microwave current by spin-wave
nonlinearities in the point contact conductance, and a resonant stimulation of
spin-wave modes in the nano-contact core by the microwave field. These
observations provide a direct evidence that the magnetoconductance effects
observed are due to GHz spin dynamics at the ferromagnetic interface driven by
the spin transfer torque effect of the transport current.",0806.3805v1
2010-03-22,Dynamical central peak and spinon deconfinement in frustrated spin chains,"Studying the dynamical spin structure factor in frustrated spin chains with
spontaneously dimerized ground state we show that besides the gapped spin-wave
excitations there appears at finite temperatures also a sharp central peak. The
latter can be attributed to deconfined spinons, accounted well within the
variational approach. The central peak remains well pronounced within the local
spin dynamics and may be relevant for experiments on materials with 1D
frustrated spin chains.",1003.4232v1
2011-04-08,Zero temperature geometric spin dephasing on a ring in presence of an Ohmic environment,"We study zero temperature spin dynamics of a particle confined to a ring in
presence of spin orbit coupling and Ohmic electromagnetic fluctuations. We show
that the dynamics of the angular position $\theta(t)$ are decoupled from the
spin dynamics and that the latter is mapped to certain correlations of a
spinless particle. We find that the spin correlations in the $z$ direction
(perpendicular to the ring) are finite at long times, i.e. do not dephase. The
parallel (in plane) components for spin $\half$ do not dephase at weak
dissipation but they probably decay as a power law with time at strong
dissipation.",1104.1637v1
2012-03-29,Soliton Magnetization Dynamics in Spin-Orbit Coupled Bose-Einstein Condensates,"Ring-trapped Bose-Einstein condensates subject to spin-orbit coupling support
localized dark soliton excitations that show periodic density dynamics in real
space. In addition to the density feature, solitons also carry a localized
pseudo-spin magnetization that exhibits a rich and tunable dynamics. Analytic
results for Rashba-type spin-orbit coupling and spin-invariant interactions
predict a conserved magnitude and precessional motion for the soliton
magnetization that allows for the simulation of spin-related geometric phases
recently seen in electronic transport measurements.",1203.6684v1
2013-06-25,Dynamical spin-spin coupling of quantum dots,"We carried out a nested Schrieffer-Wolff transformation of an Anderson
two-impurity Hamiltonian to study the spin-spin coupling between two dynamical
quantum dots under the influence of rotating transverse magnetic field. As a
result of the rotating field, we predict a novel Ising type spin-spin coupling
mechanism between quantum dots, whose strength is tunable via the magnitude of
the rotating field. The strength of the new coupling could be comparable to the
strength of the RKKY coupling. The dynamical coupling with the intristic RKKY
coupling enables to construct a four level system of maximally entangled Bell
states in a controllable manner.",1306.5889v2
2014-12-15,Characterization of S-T$_+$ Transition Dynamics via Correlation Measurements,"Nuclear spins are an important source of dephasing for electron spin qubits
in GaAs quantum dots. Most studies of their dynamics have focused on the
relatively slow longitudinal polarization. We show, based on a semiclassical
model and experimentally, that the dynamics of the transverse hyperfine field
can be probed by correlating individual Landau-Zener sweeps across the S-T$_+$
transition of a two-electron spin qubit. The relative Larmor precession of
different nuclear spin species leads to oscillations in these correlations,
whose decay arises from dephasing of the nuclei. In the presence of spin orbit
coupling, oscillations with the absolute Larmor frequencies whose amplitude
reflects the spin orbit coupling strength are expected.",1412.4551v1
2017-04-11,Dynamics of Pure Spin Current in High-frequency Quantum Regime,"Pure spin current is a powerful tool for manipulating spintronic devices, and
its dynamical behavior is an important issue. By using mesoscopic transport
theory for electron tunneling induced by spin accumulation, we investigate the
dynamics of the spin current in the high-frequency quantum regime, where the
frequency is much larger than temperature and bias voltage. Besides the thermal
noise, frequency-dependent finite noise emerges, signaling the spin current
across the tunneling barrier. We also find that the autocorrelation of the spin
current exhibits sinusoidal oscillation in time as a consequence of the Pauli
exclusion principle even without any net charge current.",1704.03133v1
2009-12-09,Microscopic Theory of Current-Spin Interaction in Ferromagnets,"Interplay between magnetization dynamics and electric current in a conducting
ferromagnet is theoretically studied based on a microscopic model calculation.
First, the effects of the current on magnetization dynamics (spin torques) are
studied with special attention to the ""dissipative"" torques arising from
spin-relaxation processes of conduction electrons. Next, an analysis is given
of the ""spin motive force"", namely, a spin-dependent 'voltage' generation due
to magnetization dynamics, which is the reaction to spin torques. Finally, an
attempt is presented of a unified description of these effects.",0912.1676v1
2019-01-03,Observing zero-field spin dynamics with spin noise in a pi-pulse modulated field,"Spin noise spectroscopic study of spin dynamics in a zero magnetic field is
commonly frustrated by the dominating 1/f noise. We show that in a pi-pulse
modulated magnetic field, spin noise spectrum centered one-half of the field
modulation frequency reveals spin dynamics in zero-fields, free of any
low-frequency noises.",1901.00714v3
2021-04-16,Spin-ice dynamics of pyrochlore Dy2GaSbO7 with enhanced Pauling zero-point entropy,"We report the low-temperature magnetothermal properties and spin dynamics of
a mixed pyrochlore, Dy2GaSbO7 through the coordination of measurements of dc
magnetization, ac susceptibility, and heat capacity, and CF computation. In
Dy2GaSbO7, the spins freeze at temperature Tice = 3.1 K, corresponding to
dynamical spin-freezing into a disordered state in compliance with the spin-ice
rules, but with enhanced zero-point entropy, unlike cannonical dipolar spin-ice
materials, Dy2Ti2O7 and Ho2Ti2O7, due to random disorder and varied chemical
pressure of B-site (GaSb tetrahedra) ions.",2104.07890v1
2007-07-08,Universal dynamics of quantum spin decoherence in a spin bath,"We systematically investigate the universal spin decoherence dynamics of a
localized electron in an arbitrary nuclear spin bath, which can be even far
away from equilibrium due to the weak nuclear-lattice interaction. We show that
the electron spin relaxation dynamics (as well as spin pure dephasing and Hahn
echo decay) can {\it always} have a universal behavior as long as the initial
state is composed of a sufficiently large amount of spin eigenstates. For a
given system, the pattern of the universal dynamics depends on the complicated
initial condition only via a {\it single} parameter, which measures the amount
of phase coherence between different spin eigenstates in the initial state. Our
results apply even when the number of the involved nuclei is not large, and
therefore provide a solid foundation in the comparison of theoretical/numerical
results with the experimental measurement. As an example, we also show
numerical results for systems of noninteracting spin bath in zero magnetic
field regime, and discuss the features of universal decoherent dynamics.",0707.1131v2
2013-03-19,Reading charge transport from spin dynamics on the surface of topological insulator,"Resolving the conductance of the topological surface states (TSSs) from the
bulk contribution has been a great challenge for studying the transport
property of topological insulators. By developing a non-purturbative diffusion
equation that describes fully the spin-charge dynamics in the strong spin-orbit
coupling regime, we present a proposal to read the charge transport information
of TSSs from its spin dynamics which can be isolated from the bulk contribution
by time-resolved second harmonic generation pump-probe measurement. We
demonstrate the qualitatively different Dyaknov-Perel spin relaxation behavior
between the TSSs and the two-dimensional spin-orbit coupling electron gas. The
decay time of both in-plane and out-of-plane spin polarization is naturally
proved to be identical to the charge transport time. The out-of-plane spin
dynamics is shown to be in the experimentally reachable regime of the
femtosecond pump probe spectroscopy and thereby we suggest experiments to
detect the charge transport property of the TSSs from their unique spin
dynamics.",1303.4478v3
2013-12-27,Spin Transfer Torque and Electric Current in Helical Edge States in Quantum Spin Hall Devices,"We study the dynamics of a quantum spin Hall edge coupled to a magnet with
its own dynamics. Using spin transfer torque principles, we analyze the
interplay between spin currents in the edge state and dynamics of the axis of
the magnet, and draw parallels with circuit analogies. As a highlighting
feature, we show that while coupling to a magnet typically renders the edge
state insulating by opening a gap, in the presence of a small potential bias,
spin-transfer torque can restore perfect conductance by transferring angular
momentum to the magnet. In the presence of interactions within the edge state,
we employ a Luttinger liquid treatment to show that the edge, when subject to a
small voltage bias, tends to form a unique dynamic rotating spin wave state
that naturally couples into the dynamics of the magnet. We briefly discuss
realistic physical parameters and constraints for observing this interplay
between quantum spin Hall and spin-transfer torque physics.",1312.7303v1
2008-05-30,Time-resolved Dynamics of the Spin Hall Effect,"The generation and manipulation of carrier spin polarization in
semiconductors solely by electric fields has garnered significant attention as
both an interesting manifestation of spin-orbit physics as well as a valuable
capability for potential spintronics devices. One realization of these
spin-orbit phenomena, the spin Hall effect (SHE), has been studied as a means
of all-electrical spin current generation and spin separation in both
semiconductor and metallic systems. Previous measurements of the spin Hall
effect have focused on steady-state generation and time-averaged detection,
without directly addressing the accumulation dynamics on the timescale of the
spin coherence time. Here, we demonstrate time-resolved measurement of the
dynamics of spin accumulation generated by the extrinsic spin Hall effect in a
doped GaAs semiconductor channel. Using electrically-pumped time-resolved Kerr
rotation, we image the accumulation, precession, and decay dynamics near the
channel boundary with spatial and temporal resolution and identify multiple
evolution time constants. We model these processes using time-dependent
diffusion analysis utilizing both exact and numerical solution techniques and
find that the underlying physical spin coherence time differs from the
dynamical rates of spin accumulation and decay observed near the sample edges.",0806.0019v1
2009-05-04,Collective dynamics of interacting Ising spins: Exact results for the Bethe lattice,"We study the low temperature dynamics in films made of molecular magnets, i.
e. crystals composed of molecules having large electronic spin S in their
ground state. The electronic spin dynamics is mediated by coupling to a nuclear
spin bath; this coupling allows transitions for a small fraction of electronic
spins between their two energy minima, Sz=+- S, under resonant conditions when
the change of the Zeeman energy in magnetic dipolar field of other electronic
spins is compensated by interaction with nuclear spins. Transitions of resonant
spins can result in opening or closing resonances in their neighbors leading to
the collective dynamics at sufficiently large density P0 of resonant spins. We
formulate and solve the equivalent dynamic percolation problem for the Bethe
lattice (BL) of spins interacting with z neighbors and find that depending on
the density of resonant spins P0 and the number of neighbors z the system has
either one (2<z<6) or two (z > 5) kinetic transitions at P_{0}=Pc1 ~
exp(-1/3)/(3z) and P0=Pc2 ~ exp(-1)/z. The former transition is continuous and
associated with the formation of an infinite cluster of coupled resonant spins
similarly to the static percolation transition occurring at P0 ~ 1/z. The
latter transition, z>5, is discontinuous and associated with the instantaneous
increase in the density of resonant spins from the small value ~ 1/z to near
unity. Experimental implications of our results are discussed.",0905.0482v1
2019-12-16,Spin-current manipulation of photoinduced magnetization dynamics in heavy metal / ferromagnet double layer based nanostructures,"Spin currents offer a way to control static and dynamic magnetic properties,
and therefore they are crucial for next-generation MRAM devices or spin-torque
oscillators. Manipulating the dynamics is especially interesting within the
context of photo-magnonics. In typical $3d$ transition metal ferromagnets like
CoFeB, the lifetime of light-induced magnetization dynamics is restricted to
about 1 ns, which e.g. strongly limits the opportunities to exploit the wave
nature in a magnonic crystal filtering device. Here, we investigate the
potential of spin-currents to increase the spin wave lifetime in a functional
bilayer system, consisting of a heavy metal (8 nm of $\beta$-Tantalum
(Platinum)) and 5 nm CoFeB. Due to the spin Hall effect, the heavy metal layer
generates a transverse spin current when a lateral charge current passes
through the strip. Using time-resolved all-optical pump-probe spectroscopy, we
investigate how this spin current affects the magnetization dynamics in the
adjacent CoFeB layer. We observed a linear spin current manipulation of the
effective Gilbert damping parameter for the Kittel mode from which we were able
to determine the system's spin Hall angles. Furthermore, we measured a strong
influence of the spin current on a high-frequency mode. We interpret this mode
an an exchange dominated higher order spin-wave resonance. Thus we infer a
strong dependence of the exchange constant on the spin current.",1912.07728v1
2013-10-29,Self-Quenching of Nuclear Spin Dynamics in Central Spin Problem,"We consider, in the framework of the central spin $s=1/2$ model, driven
dynamics of two electrons in a double quantum dot subject to hyperfine
interaction with nuclear spins and spin-orbit coupling. The nuclear subsystem
dynamically evolves in response to Landau-Zener singlet-triplet transitions of
the electronic subsystem controlled by external gate voltages. Without noise
and spin-orbit coupling, subsequent Landau-Zener transitions die out after
about $10^4$ sweeps, the system self-quenches, and nuclear spins reach one of
the numerous glassy dark states. We present an analytical model that captures
this phenomenon. We also account for the multi-nuclear-specie content of the
dots and numerically determine the evolution of around $10^7$ nuclear spins in
up to $2\times10^5$ Landau-Zener transitions. Without spin-orbit coupling,
self-quenching is robust and sets in for arbitrary ratios of the nuclear spin
precession times and the waiting time between Landau-Zener sweeps as well as
under moderate noise. In presence of spin-orbit coupling of a moderate
magnitude, and when the waiting time is in resonance with the precession time
of one of the nuclear species, the dynamical evolution of nuclear polarization
results in stroboscopic screening of spin-orbit coupling. However, small
deviations from the resonance or strong spin-orbit coupling destroy this
screening. We suggest that the success of the feedback loop technique for
building nuclear gradients is based on the effect of spin-orbit coupling.",1310.7847v1
2004-06-03,Dynamics of Spin Relaxation near the Edge of Two-Dimensional Electron Gas,"We report calculations of spin relaxation dynamics of two-dimensional
electron gas with spin-orbit interaction at the edge region. It is found that
the relaxation of spin polarization near the edge is more slow than relaxation
in the bulk. That results finally in the spin accumulation at the edge. Time
dependence of spin polarization density is calculated analytically and
numerically. The mechanism of slower spin relaxation near the edge is related
to electrons reflections from the boundary and the lack of the translation
symmetry. These reflections partially compensate electron spin precession
generated by spin-orbit interaction, consequently making the spin polarization
near the edge long living. This effect is accompanied by spin polarization
oscillations and spin polarization transfer from the perpendicular to in-plane
component.",0406064v1
2005-09-23,Physical Limits of the ballistic and non-ballistic Spin-Field-Effect Transistor: Spin Dynamics in Remote Doped Structures,"We investigate the spin dynamics and relaxation in remotely-doped two
dimensional electron systems where the dopants lead to random fluctuations of
the Rashba spin-orbit coupling. Due to the resulting random spin precession,
the spin relaxation time is limited by the strength and spatial scale of the
random contribution to the spin-orbit coupling. We concentrate on the role of
the randomness for two systems where the direction of the spin-orbit field does
not depend on the electron momentum: the spin field-effect transistor with
balanced Rashba and Dresselhaus couplings and the (011) quantum well. Both of
these systems are considered as promising for the spintronics applications
because of the suppression of the Dyakonov-Perel' mechanism there makes the
realization of a spin field effect transistor in the diffusive regime possible.
We demonstrate that the spin relaxation through the randomness of spin-orbit
coupling imposes important physical limitations on the operational properties
of these devices.",0509611v1
2014-04-10,Uncovering many-body correlations in nanoscale nuclear spin baths by central spin decoherence,"Many-body correlations can yield key insights into the nature of interacting
systems; however, detecting them is often very challenging in many-particle
physics, especially in nanoscale systems. Here, taking a phosphorus donor
electron spin in a natural-abundance 29Si nuclear spin bath as our model
system, we discover both theoretically and experimentally that many-body
correlations in nanoscale nuclear spin baths produce identifiable signatures in
the decoherence of the central spin under multiple-pulse dynamical decoupling
control. We find that when the number of decoupling -pulses is odd, central
spin decoherence is primarily driven by second-order nuclear spin correlations
(pairwise flip-flop processes). In contrast, when the number of -pulses is
even, fourth-order nuclear spin correlations (diagonal interaction renormalized
pairwise flip-flop processes) are principally responsible for the central spin
decoherence. Many-body correlations of different orders can thus be selectively
detected by central spin decoherence under different dynamical decoupling
controls, providing a useful approach to probing many-body processes in
nanoscale nuclear spin baths.",1404.2717v1
2014-10-07,Y3Fe5O12 Spin Pumping for Quantitative Understanding of Pure Spin Transport and Spin Hall Effect in a Broad Range of Materials,"Using Y3Fe5O12 (YIG) thin films grown by our sputtering technique, we study
dynamic spin transport in nonmagnetic (NM), ferromagnetic (FM) and
antiferromagnetic (AF) materials by ferromagnetic resonance (FMR) spin pumping.
From both inverse spin Hall effect (ISHE) and damping enhancement, we determine
the spin mixing conductance and spin Hall angle in many metals. Surprisingly,
we observe robust spin conduction in AF insulators excited by an adjacent YIG
at resonance. This demonstrates that YIG spin pumping is a powerful and
versatile tool for understanding spin Hall physics, spin-orbit coupling (SOC),
and magnetization dynamics in a broad range of materials.",1410.1597v1
2016-03-11,Time-dependent spin and transport properties of a single-molecule magnet in a tunnel junction,"In single-molecule magnets, the exchange between a localized spin moment and
the electronic background provides a suitable laboratory for studies of
dynamical aspects of both local spin and transport properties. Here we address
the time evolution of a localized spin moment coupled to an electronic level in
a molecular quantum dot embedded in a tunnel junction between metallic leads.
The interactions between the localized spin moment and the electronic level
generate an effective interaction between the spin moment at different
instances in time. Therefore, we show that, despite being a single-spin system,
there are effective contributions of isotropic Heisenberg, and anisotropic
Ising and Dzyaloshinski-Moriya character acting on the spin moment. The
interactions can be controlled by gate voltage, voltage bias, the spin
polarization in the leads, in addition to external magnetic fields. Signatures
of the spin dynamics are found in the transport properties of the tunneling
system, and we demonstrate that measurements of the spin current may be used
for read-out of the local spin moment orientation.",1603.03628v2
2016-12-29,Theory of electron transport and magnetization dynamics in metallic ferromagnets,"Magnetic electric effects in ferromagnetic metals are discussed from the
viewpoint of effective spin electromagnetic field that couples to conduction
electron spin. The effective field in the adiabatic limit is the spin Berry's
phase in space and time, and it leads to spin motive force (voltage generated
by magnetization dynamics) and topological Hall effect due to spin chirality.
Its gauge coupling to spin current describes the spin transfer effect, where
magnetization structure is driven by an applied spin current. The idea of
effective gauge field can be extended to include spin relaxation and Rashba
spin-orbit interaction. Voltage generation by the inverse Edelstein effect in
junctions is interpreted as due to the electric component of Rashba-induced
spin gauge field. The spin gauge field arising from the Rashba interaction
turns out to coincides with troidal moment, and causes asymmetric light
propagation (directional dichroism) as a result of the Doppler shift. Rashba
conductor without magnetization is shown to be natural metamaterial exhibiting
negative refraction.",1612.09019v1
2021-09-12,"Spin excitation spectra in helimagnetic states: proper-screw, cycloid, vortex crystal, and hedgehog lattice","We investigate the spin excitation spectra in chiral and polar magnets by the
linear spin-wave theory for an effective spin model with symmetric and
antisymmetric long-range interactions. In one dimension, we obtain the analytic
form of the dynamical spin structure factor for proper-screw and cycloidal
helical spin states with uniform twists, which shows a gapless mode with strong
intensity at the helical wave number. When introducing spin anisotropy in the
symmetric interactions, we numerically show that the stable spin spirals become
elliptically anisotropic with nonuniform twists and the spin excitation is
gapped. In higher dimensions, we find that similar anisotropy stabilizes
multiple-$Q$ spin states, such as vortex crystals and hedgehog lattices. We
show that the anisotropy in these states manifests itself in the dynamical spin
structure factor: a strong intensity in the transverse components to the wave
number appears only when the helical wave vector and the corresponding easy
axis are perpendicular to each other. Our findings could be useful not only to
identify the spin structure but also to deduce the stabilization mechanism by
inelastic neutron scattering measurements.",2109.05628v2
2021-10-03,Giant Spin Lifetime Anisotropy and Spin-Valley Locking in Silicene and Germanene from First-Principles Density-Matrix Dynamics,"Through First-Principles real-time Density-Matrix (FPDM) dynamics
simulations, we investigate spin relaxation due to electron-phonon and
electron-impurity scatterings with spin-orbit coupling in two-dimensional Dirac
materials - silicene and germanene, at finite temperatures and under external
fields. We discussed the applicability of conventional descriptions of spin
relaxation mechanisms by Elliott-Yafet (EY) and D'yakonov-Perel' (DP) compared
to our FPDM method, which is determined by a complex interplay of intrinsic
spin-orbit coupling, external fields, and electron-phonon coupling strength,
beyond crystal symmetry. For example, the electric field dependence of spin
relaxation time is close to DP mechanism for silicene at room temperature, but
rather similar to EY mechanism for germanene. Due to its stronger spin-orbit
coupling strength and buckled structure in sharp contrast to graphene,
germanene has a giant spin lifetime anisotropy and spin valley locking effect
under nonzero Ez and relatively low temperature. More importantly, germanene
has extremely long spin lifetime (~100 ns at 50 K) and ultrahigh carrier
mobility, which makes it advantageous for spin-valleytronic applications.",2110.01128v1
2023-03-08,Spin selective charge recombination in chiral donor-bridge-acceptor triads,"In this paper we outline a physically motivated framework for describing
spin-selective recombination processes in chiral systems, from which we derive
spin-selective reaction operators for recombination reactions of
donor-bridge-acceptor molecules, where the electron transfer is mediated by
chirality and spin-orbit coupling. In general the recombination process is
selective only for spin-coherence between singlet and triplet states, and it is
not in general selective for spin polarisation. We find that spin polarisation
selectivity only arises in hopping mediated electron transfer. We describe how
this effective spin-polarisation selectivity is a consequence of
spin-polarisation generated transiently in the intermediate state. The
recombination process also augments the coherent spin dynamics of the charge
separated state, which is found to have a significant effect on recombination
dynamics and to destroy any long-lived spin polarisation. Although we only
consider a simple donor-bridge-acceptor system, the framework we present here
can be straightforwardly extended to describe spin-selective recombination
processes in more complex systems.",2303.04742v1
2020-12-16,Ab initio Ultrafast Spin Dynamics in Solids,"Spin relaxation and decoherence is at the heart of spintronics and spin-based
quantum information science. Currently, theoretical approaches that can
accurately predict spin relaxation of general solids including necessary
scattering pathways and capable for ns to ms simulation time are urgently
needed. We present a first-principles real-time density-matrix approach based
on Lindblad dynamics to simulate ultrafast spin dynamics for general
solid-state systems. Through the complete first-principles descriptions of
pump, probe and scattering processes including electron-phonon,
electron-impurity and electron-electron scatterings with self-consistent
electronic spin-orbit couplings, our method can directly simulate the ultrafast
pump-probe measurements for coupled spin and electron dynamics over ns at any
temperatures and doping levels. We first apply this method to a prototypical
system GaAs and obtain excellent agreement with experiments. We find that the
relative contributions of different scattering mechanisms and phonon modes
differ considerably between spin and carrier relaxation processes. In sharp
contrast to previous work based on model Hamiltonians, we point out that the
electron-electron scattering is negligible at room temperature but becomes
dominant at low temperatures for spin relaxation in n-type GaAs. We further
examine ultrafast dynamics in novel spin-valleytronic materials - monolayer and
bilayer WSe2 with realistic defects. We find that spin relaxation is highly
sensitive to local symmetry and chemical bonds around defects. Our work
provides a predictive computational platform for spin dynamics in solids, which
has unprecedented potentials for designing new materials ideal for spintronics
and quantum information technology.",2012.08711v3
2008-03-06,Effective one body approach to the dynamics of two spinning black holes with next-to-leading order spin-orbit coupling,"Using a recent, novel Hamiltonian formulation of the gravitational
interaction of spinning binaries, we extend the Effective One Body (EOB)
description of the dynamics of two spinning black holes to next-to-leading
order (NLO) in the spin-orbit interaction. The spin-dependent EOB Hamiltonian
is constructed from four main ingredients: (i) a transformation between the
``effective'' Hamiltonian and the ``real'' one, (ii) a generalized effective
Hamilton-Jacobi equation involving higher powers of the momenta, (iii) a
Kerr-type effective metric (with Pad\'e-resummed coefficients) which depends on
the choice of some basic ``effective spin vector'' $\bf{S}_{\rm eff}$, and
which is deformed by comparable-mass effects, and (iv) an additional effective
spin-orbit interaction term involving another spin vector $\bsigma$. As a first
application of the new, NLO spin-dependent EOB Hamiltonian, we compute the
binding energy of circular orbits (for parallel spins) as a function of the
orbital frequency, and of the spin parameters. We also study the
characteristics of the last stable circular orbit: binding energy, orbital
frequency, and the corresponding dimensionless spin parameter $\hat{a}_{\rm
LSO}\equiv c J_{\rm LSO}/\boldsymbol(G(H_{\rm LSO}/c^2)^2\boldsymbol)$. We find
that the inclusion of NLO spin-orbit terms has a significant ``moderating''
effect on the dynamical characteristics of the circular orbits for large and
parallel spins.",0803.0915v1
2001-09-13,Formation of energy gap in higher dimensional spin-orbital liquids,"A Schwinger boson mean field theory is developed for spin liquids in a
symmetric spin-orbital model in higher dimensions. Spin, orbital and coupled
spin-orbital operators are treated equally. We evaluate the dynamic correlation
functions and collective excitations spectra. As the collective excitations
have a finite energy gap, we conclude that the ground state is a spin-orbital
liquid with a two-fold degeneracy, which breaks the discrete spin-orbital
symmetry. Possible relevence of this spin liquid state to several realistic
systems, such as CaV$_4$V$_9$ and Na$_2$Sb$_2$Ti$_2$O, are discussed.",0109234v1
2002-03-18,Relaxation of Shallow Donor Electron Spin due to Interaction with Nuclear Spin Bath,"We study the low-temperature dynamics of a shallow donor, e.g., $^{31}$P,
impurity electron spin in silicon, interacting with the bath of nuclear spins
of the $^{29}$Si isotope. For small applied magnetic fields, the electron spin
relaxation is controlled by the steady state distribution of the nuclear spins.
We calculate the relaxation times $T_1$ and $T_2$ as functions of the external
magnetic field, and conclude that nuclear spins play an important role in the
donor electron spin decoherence in Si:P at low magnetic fields.",0203362v1
2003-08-20,Zero-dimensional spin accumulation and spin dynamics in a mesoscopic metal island,"We have measured electron spin accumulation at 4.2 K and at room temperature
in an aluminium island with all dimensions (400nm x 400nm x 30nm) smaller than
the spin relaxation length. For the first time, we obtain uniform spin
accumulation in a four-terminal lateral device with a magnitude exceeding the
ohmic resistance in the island. By controlling the magnetisation directions of
the four magnetic electrodes that contact the island, we have performed a
detailed study of the spin accumulation. Spin precession measurements confirm
the uniformity of our system and provide an accurate method to extract the spin
relaxation time.",0308395v1
2005-06-06,The spin-dependent semiconductor Bloch equations: a microscopic theory of Bir-Aronov-Pikus spin-relaxation,"Semiconductor Bloch equations, in their extension including the spin degree
of freedom of the carriers, are capable to describe spin dynamics on a
microscopic level. In the presence of free holes, electron spins can flip
simultaneously with hole spins due to electron-hole exchange interaction. This
mechanism named after Bir, Aronov and Pikus, is described here by using the
extended semiconductor Bloch equations and considering carrier-carrier
interaction beyond the Hartree-Fock truncation. As a result we derive
microscopic expressions for spin-relaxation and spin-dephasing rates.",0506135v1
2005-10-31,Intrinsic spin current for an arbitrary Hamiltonian and scattering potential,"We have described electron spin dynamics in the presence of the spin-orbit
interaction and disorder using the spin-density matrix method. Exact solution
is obtained for an arbitrary 2D spin-orbit Hamiltonian and arbitrary smoothness
of the disorder potential. Spin current depends explicitely on the disorder
properties, namely the smoothness of the disorder potential, even in the
ballistic limit when broadening by scattering is much smaller than the
spin-orbit related splitting of the energy spectrum. In this sense universal
intrinsic spin current does not exist.",0510815v2
2006-09-09,Quantum Dynamics of Electron-Nuclei Coupled System in a Double Quantum Dot,"Hyperfine interaction of electron spins with nuclear spins, in coupled double
quantum dots is studied. Results of successive electron spin measurements
exhibit bunching due to correlations induced via the nuclear spins. Further
nuclear spins can be purified via conditional electron spin measurements which
lead to electron spin revivals in the conditional probabilities. The electron
spin coherence time can be extended via conditional measurements. The results
are extended to a single electron on a single QD.",0609217v2
2002-09-11,Decoherence in a spin--spin-bath model with environmental self-interaction,"A low temperature model system consisting of a central spin coupled to a
spin-bath is studied to determine whether interaction among bath spins has an
effect on central spin dynamics. In the absence of intra-environmental
coupling, decoherence of the central spin is fast and irreversible. Strong
intra-environmental interaction results in an effective decoupling of the
central spin from the bath and suppression of decoherence. Weaker
intra-environmental coupling reduces but does not eliminate decoherence. We
believe that similar behaviour will be observed in any system with a
self-interacting environment.",0209079v1
2007-05-22,Spin dynamics in rolled-up two dimensional electron gases,"A curved two dimensional electron gas with spin-orbit interactions due to the
radial confinement asymmetry is considered. At certain relation between the
spin-orbit coupling strength and curvature radius the tangential component of
the electron spin becomes a conserved quantity for any spin-independent
scattering potential that leads to a number of interesting effects such as
persistent spin helix and strong anisotropy of spin relaxation times. The
effect proposed can be utilized in the non-ballistic spin-field-effect
transistors.",0705.3174v1
2007-07-17,Subnanosecond switching of local spin-exchange coupled to ferromagnets,"The dynamics of a single spin embedded in a the tunnel junction between
ferromagnetic contacts is strongly affected by the exchange coupling to the
tunneling electrons. Using time-dependent equation of motion for the spin under
influence of the spin-polarized tunneling current, it is shown that the
magnetic field induced by bias voltage pulses allows for sub-nanosecond
switching of the local spin and the possibility of spin reversal is
illustrated. Furthermore, it is shown that the time-evolution of the Larmor
frequency sharply peaks around the spin-flip event, and it is argued that this
feature can be used as an indicator for the spin-flip.",0707.2600v2
2007-09-13,Spin polarization in biased Rashba-Dresselhaus two-dimensional electron systems,"Based on spin-charge coupled drift-diffusion equations, which are derived
from kinetic equations for the spin-density matrix in a rigorous manner, the
electric-field-induced nonequilibrium spin polarization is treated for a
two-dimensional electron gas with both Rashba and Dresselhaus spin-orbit
coupling. Most emphasis is put on the consideration of the field-mediated spin
dynamics for a model with equal Rashba and Dresselhaus coupling constants, in
which the spin relaxation is strongly suppressed. Weakly damped
electric-field-induced spin excitations are identified, which remind of
space-charge waves in crystals.",0709.2054v1
2009-11-12,Theory of Electron Spin Relaxation in n-Doped Quantum Wells,"Recent experiments have demonstrated long spin lifetimes in uniformly n-doped
quantum wells. The spin dynamics of exciton, localized, and conduction spins
are important for understanding these systems. We explain experimental behavior
by invoking spin exchange between all spin species. By doing so we explain
quantitatively and qualitatively the striking and unusual temperature
dependence in (110)-GaAs quantum wells. We discuss possible future experiments
to resolve the pertinent localized spin relaxation mechanisms. In addition, our
analysis allows us to propose possible experimental scenarios that will
optimize spin relaxation times in GaAs and CdTe quantum wells.",0911.2452v2
2010-11-11,Spin Torque Ferromagnetic Resonance Induced by the Spin Hall Effect,"We demonstrate that the spin Hall effect in a thin film with strong
spin-orbit scattering can excite magnetic precession in an adjacent
ferromagnetic film. The flow of alternating current through a Pt/NiFe bilayer
generates an oscillating transverse spin current in the Pt, and the resultant
transfer of spin angular momentum to the NiFe induces ferromagnetic resonance
(FMR) dynamics. The Oersted field from the current also generates an FMR signal
but with a different symmetry. The ratio of these two signals allows a
quantitative determination of the spin current and the spin Hall angle.",1011.2788v1
2011-05-24,Scalable Spin Amplification with a Gain over a Hundred,"We propose a scalable and practical implementation of spin amplification
which does not require individual addressing nor a specially tailored spin
network. We have demonstrated a gain of 140 in a solid-state nuclear spin
system of which the spin polarization has been increased to 0.12 using dynamic
nuclear polarization with photoexcited triplet electron spins. Spin
amplification scalable to a higher gain opens the door to the single spin
measurement for a readout of quantum computers as well as practical
applications of nuclear magnetic resonance (NMR) spectroscopy to infinitesimal
samples which have been concealed by thermal noise.",1105.4740v1
2018-11-19,Correlation effects in spin models in the presence of a spin bath,"We analyze the effect of a bath of spins interacting with a spin system in
terms of the equation of motion technique. We show that this formalism can be
used with general spin systems and baths, and discuss the concrete case of a
Quantum Ising model longitudinally coupled to the bath. We show how the
uncorrelated solutions change when spin-spin correlations are included, the
properties of the quasiparticle excitations and the effect of internal dynamics
in the spin bath.",1811.07681v2
2019-05-17,Universal power law decay of spin polarization in double quantum dot,"We study the spin dynamics and spin noise in a double quantum dot taking into
account the interplay between hopping, exchange interaction and the hyperfine
interaction. At short time scales the spin relaxation is governed by the spin
dephasing in the random nuclear fields. At long time scales the spin
polarization obeys universal power law $1/t$ independent of the relation
between all the parameters of the system. This effect is related to the
competition between the spin blockade effect and the hyperfine interaction. The
spin noise spectrum of the system universally diverges as $\ln(1/\omega)$ at
low frequencies.",1905.07305v1
2012-01-18,Spin-selective Kondo insulator: Cooperation of ferromagnetism and Kondo effect,"We propose the notion of spin-selective Kondo insulator, which provides a
fundamental mechanism to describe the ferromagnetic phase of the Kondo lattice
model with antiferromagnetic coupling. This unveils a remarkable feature of the
ferromagnetic metallic phase: the majority-spin conduction electrons show
metallic- while the minority-spin electrons show insulating-behavior. The
resulting Kondo gap in the minority spin sector, which is due to the
cooperation of ferromagnetism and partial Kondo screening, evidences a
dynamically-induced commensurability for a combination of minority-spin
electrons and parts of localized spins. Furthermore, this mechanism predicts a
nontrivial relation between the macroscopic quantities such as electron
magnetization, spin polarization and electron filling.",1201.3680v1
2013-09-02,Temperature Dependence of Spin Hall Angle of Palladium,"In this study, the temperature dependence of the spin Hall angle of palladium
(Pd) was experimentally investigated by spin pumping. A Ni80Fe20/Pd bilayer
thin film was prepared, and a pure spin current was dynamically injected into
the Pd layer. This caused the conversion of the spin current to a charge
current owing to the inverse spin Hall effect. It was found that the spin Hall
angle varies as a function of temperature, whereby the value of the spin Hall
angle increases to ca. 0.02 at 123 K.",1309.0306v1
2016-08-07,Spin-orbit coupling in Fe-based superconductors,"We study the spin resonance peak in recently discovered iron-based
superconductors. The resonance peak observed in inelastic neutron scattering
experiments agrees well with predicted results for the extended $s$-wave
($s_\pm$) gap symmetry. Recent neutron scattering measurements show that there
is a disparity between longitudinal and transverse components of the dynamical
spin susceptibility. Such breaking of the spin-rotational invariance in the
spin-liquid phase can occur due to spin-orbit coupling. We study the role of
the spin-orbit interaction in the multiorbital model for Fe-pnictides and show
how it affects the spin resonance feature.",1608.02230v1
2019-03-28,Spin Seebeck and Spin Nernst Effects of Magnons in Noncollinear Antiferromagnetic Insulators,"Our joint theoretical and computer experimental study of heat-to-spin
conversion reveals that noncollinear antiferromagnetic insulators are promising
materials for generating magnon spin currents upon application of a temperature
gradient: they exhibit spin Seebeck and spin Nernst effects. Using Kubo theory
and spin dynamics simulations, we explicitly evaluate these effects in a single
kagome sheet of potassium iron jarosite, KFe$_3$(OH)$_6$(SO$_4$)$_2$, and
predict a spin Seebeck conversion factor of $0.2 \mu\mathrm{V}/\mathrm{K}$ at a
temperature of $20 \mathrm{K}$.",1903.11896v1
2022-05-19,Spin-spin coupling-based quantum and classical phase transitions in two-impurity spin-boson models,"The class of two-interacting-impurity spin-boson models with vanishing
transverse fields on the spin-pair is studied. The model can be exactly mapped
into two independent standard single-impurity spin-boson models where the role
of the tunnelling parameter is played by the spin-spin coupling. The dynamics
of the magnetization is analysed for different levels of (an)isotropy. Further,
the existence of a decoherence-free subspace as well as of both classical and
quantum (first-order and Kosterlitz-Thouless type) phase transitions, in the
Omhic regime, is brought to light.",2205.09367v1
2014-08-05,Dynamics of a Mn spin coupled to a single hole confined in a quantum dot,"Using the emission of the positively charged exciton as a probe, we analyze
the dynamics of the optical pumping and the dynamics of the relaxation of a Mn
spin exchange-coupled with a confined hole spin in a II-VI semiconductor
quantum dot. The hole-Mn spin can be efficiently initialized in a few tens of
$ns$ under optical injection of spin polarized carriers. We show that this
optical pumping process and its dynamics are controlled by electron-Mn
flip-flops within the positively charged exciton-Mn complex. The pumping
mechanism and its magnetic field dependence are theoretically described by a
model including the dynamics of the electron-Mn complex in the excited state
and the dynamics of the hole-Mn complex in the ground state of the positively
charged quantum dot. We measure at zero magnetic field a spin relaxation time
of the hole-Mn spin in the $\mu s$ range or shorter. This hole-Mn spin
relaxation is induced by the presence of valence band mixing in self-assembled
quantum dots.",1408.0930v2
2021-03-19,Domain wall dynamics of ferrimagnets induced by spin-current near the angular momentum compensation temperature,"We report on a theoretical study of the spin-current excited dynamics of
domain walls (DWs) in ferrimagnets in the vicinity of the angular momentum
compensation point. Effective Lagrangian and nonlinear dynamic equations are
derived for a two-sublattice ferrimagnet taking into account both spin-torques
and external magnetic field. The dynamics of the DW before and after the Walker
breakdown is calculated for any direction of the spin current polarization. It
is shown that for the in-plane polarization of the spin current, the DW
mobility reaches a maximum near the temperature of the angular momentum
compensation. For the out-of-plane spin polarization, in contrast, a spin
current with the densities below the Walker breakdown does not excite the
dynamics of the DW. After overcoming the Walker breakdown, the domain wall
velocity increases linearly with increasing the current density. In this
spin-current polarization configuration the possibility of a gigahertz
oscillation dynamics of the quasi-antiferromagnetic vector under the action of
a damping-like torque in the angular momentum compensation point is
demonstrated. Possible structures for experimental demonstration of the
considered effects are discussed.",2103.10711v1
1997-10-15,Evolution of the low-frequency spin dynamics in ferromagnetic manganites,"Elastic and inelastic neutron scattering was used to study two ferromagnetic
manganites A$_{1-x}$B$_{x}$MnO$_3$ (x $\approx$ 0.3) with $T_c$=197.9 K and
300.9 K. The spin dynamical behavior of these is similar at low temperatures,
but drastically different at temperatures around $T_c$. While the formation of
spin clusters of size ($\sim20$ \AA) dominates the spin dynamics of the 197.9 K
sample close to $T_c$, the paramagnetic to ferromagnetic transition for the
300.9 K sample is more conventional. These results, combined with seemingly
inconsistent earlier reports, reveal clear systematics in the spin dynamics of
the manganites.",9710160v1
1998-02-04,Dynamical effects of phonons on soliton binding in spin-Peierls systems,"The role of dynamical magneto-elastic coupling in spin-Peierls chains is
investigated by numerical and analytical techniques. We show that a Heisenberg
spin chain coupled to dynamical optical phonons exhibits a transition towards a
spontaneously dimerized state in a wide range of parameter space. The low
energy excitations are characterized as solitons. No binding between solitons
occurs in the isolated spin-phonon chain and the dynamical spin structure
factor shows a broad magnon dispersion. However, elastic interchain coupling
can lead to the formation of bound states.",9802053v2
1999-09-06,Low-Energy Spin Dynamics of CuO Chains in YBa(2)Cu(3)O(6+x),"We study the spin fluctuation dynamics of Cu-O chains in the oxygen deficient
planes of YBa(2)Cu(3)O(6+x). The chains are described by a model including
antiferromagnetic interactions between the spins and Kondo-like scattering of
the oxygen holes by the copper spins. There are incommensurate spin
fluctuations along the direction of the chains. The dynamic structure factor of
this system is qualitatively different from that of a quasi one-dimensional
localized antiferromagnet due to the presence of itinerant holes. We compute
the dynamic structure factor that could be measured in neutron scattering
experiments.",9909081v1
2003-04-04,Dynamic exchange coupling and Gilbert damping in magnetic multilayers,"We theoretically study dynamic properties of thin ferromagnetic films in
contact with normal metals. Moving magnetizations cause a flow of spins into
adjacent conductors, which relax by spin flip, scatter back into the
ferromagnet, or are absorbed by another ferromagnet. Relaxation of spins
outside the moving magnetization enhances the overall damping of the
magnetization dynamics in accordance with the Gilbert phenomenology. Transfer
of spins between different ferromagnets by these nonequilibrium spin currents
leads to a long-ranged dynamic exchange interaction and novel collective
excitation modes. Our predictions agree well with recent
ferromagnetic-resonance experiments on ultrathin magnetic films.",0304116v1
2005-05-18,Spin Dynamics in the Two-Dimensional Spin 1/2 Heisenberg Antiferromagnet,"We present low-temperature dynamic properties of the quantum two-dimensional
antiferromagnetic Heisenberg model with spin S=1/2. The calculation of the
dynamic correlation function is performed by combining a projection operator
formalism and the modified spin-wave theory (MSW), which gives a gap in the
dispersion relation for finite temperatures. The so calculated dynamic
correlation function shows a double peak structure.We also obtain the spin-wave
damping and compare our results to experimental data and to theoretical results
obtained by other authors using different approaches.",0505458v1
2008-06-06,Quantum-Fluctuation-Driven Coherent Spin Dynamics in Small Condensates,"We have studied quantum spin dynamics of small condensates of cold sodium
atoms. For a condensate initially prepared in a mean field ground state, we
show that coherent spin dynamics are {\em purely} driven by quantum
fluctuations of collective spin coordinates and can be tuned by quadratic
Zeeman coupling and magnetization. These dynamics in small condensates can be
probed in a high-finesse optical cavity where temporal behaviors of excitation
spectra of a coupled condensate-photon system reveal the time evolution of
populations of atoms at different hyperfine spin states.",0806.1220v1
2010-12-18,Ultrafast Hole-Spin Dynamics in Optically Excited Bulk GaA,"We present experimental and theoretical results on hole-spin dynamics in bulk
GaAs after ultrafast optical excitation. The experimental differential
transmission are compared with a dynamical calculation of the momentum-resolved
hole distributions, which includes the carrier-carrier, carrier-phonon and
carrier-impurity interaction at the level of Boltzmann scattering integrals. We
obtain good agreement with the experimentally determined hole-spin relaxation
times, but point out that depending on how the spin-polarization dynamics is
extracted, deviations from an exponential decay at short times occur. We also
study theoretically the behavior of the spin-relaxation for heavily p-doped
GaAs at low temperatures.",1012.4115v1
2013-10-18,Many-body effects on electron spin dynamics in semiconductors from a geometrical viewpoint,"Many body effects on spin dynamics in semiconductors have attracted a lot of
attentions in recent years. In this paper, we show why and how the many body
effects have to be considered by a simple Bloch sphere geometry approach. The
micro dynamics here are viewed as a time dependent sequence of unitary group
action on the spin density matrix. Based on this physical picture, we give the
explicit unitary group for conventional spin dynamics mechanism such as DP, EY,
and BAP using pure density matrix. And we also show the various scattering
processes how influence the spin system via mixed density matrix and Feynman
diagrams.",1310.4895v1
2008-07-10,Spin squeezing in a bimodal condensate: spatial dynamics and particle losses,"We propose an analytical method to study the entangled spatial and spin
dynamics of interacting bimodal Bose-Einstein condensates. We show that at
particular times during the evolution spatial and spin dynamics disentangle and
the spin squeezing can be predicted by a simple two-mode model. We calculate
the maximum spin squeezing achievable in experimentally relevant situations
with Sodium or Rubidium bimodal condensates, including the effect of the
dynamics and of one, two and three-body losses.",0807.1580v2
2018-06-19,Dynamical exchange and phase induced switching of a localized molecular spin,"The dynamics of a localized molecular spin under the influence of external
voltage pulses is addressed using a generalized spin equation of motion. The
approach incorporates anisotropic fields, non-equilibrium conditions, and
non-adiabatic dynamics. By application of a voltage pulse of temporal length
$\tau$, a recurring $4\pi$-periodic switching of the localized spin is
observed. The switching phenomena can be explained by dynamical exchange
interactions, internal transient fields, and self-interactions acting on the
localized spin moment.",1806.07092v2
2017-04-10,Majorana dynamical mean-field study of spin dynamics at finite temperatures in the honeycomb Kitaev model,"A prominent feature of quantum spin liquids is fractionalization of the spin
degree of freedom. Fractionalized excitations have their own dynamics in
different energy scales, and hence, affect finite-temperature ($T$) properties
in a peculiar manner even in the paramagnetic state harboring the quantum spin
liquid state. We here present a comprehensive theoretical study of the spin
dynamics in a wide $T$ range for the Kitaev model on a honeycomb lattice, whose
ground state is such a quantum spin liquid. In this model, the
fractionalization occurs to break up quantum spins into itinerant matter
fermions and localized gauge fluxes, which results in two crossovers at very
different $T$ scales. Extending the previous study for the isotropic coupling
case [J. Yoshitake, J. Nasu, and Y. Motome, Phys. Rev. Lett. ${\textbf 117}$,
157203 (2016)], we calculate the dynamical spin structure factor, the NMR
relaxation rate, and the magnetic susceptibility while changing the anisotropy
in the exchange coupling constants, by using the dynamical mean-field theory
and the continuous-time quantum Monte Carlo method based on a Majorana fermion
representation. We find that the system exhibits peculiar behaviors below the
high-$T$ crossover whose temperature is comparable to the average of the
exchange constants, reflecting the spin fractionalization in the paramagnetic
region. Among them, the dichotomy between the static and dynamical spin
correlations is unusual behavior hardly seen in conventional magnets. We
discuss the relation between the dichotomy and the spatial configuration of
gauge fluxes. Our results could stimulate further experimental and theoretical
analyses of candidate materials for the Kitaev quantum spin liquids.",1704.02707v1
2019-09-23,"Coherent spin dynamics of solitons in the organic spin chain compounds ($o$-DMTTF)$_2X$ ($X$ = Cl, Br)","We studied the magnetic properties, in particular dynamics, of the correlated
spins associated with natural defects in the organic spin chain compounds
($o$-DMTTF)$_2X$ ($X$ = Br, Cl) by means of electron spin resonance (ESR)
spectroscopy. Both materials exhibit spin-Peierls transitions at temperatures
around 50 K [P. Foury-Leylekian et al. Phys. Rev. B 84, 195134 (2011)], which
allow a separation of the properties of defects inside the chains from the
magnetic response of the spin chains. Indeed, continuous wave ESR measurements
performed over a wide temperature range evidence the evolution of the spin
dynamics from being governed by the spins in the chains at elevated
temperatures to a low-temperature regime which is dominated by defects within
the spin-dimerized chains. Such defects polarize the antiferromagnetically
coupled spins in their vicinity, thereby leading to a finite local alternating
magnetization around the defect site which can be described in terms of a
soliton, i.e. a spin 1/2 quasiparticle built of many correlated spins, pinned
to the defect. In addition, contributions of triplon excitations of the
spin-dimerized state to the ESR response below the transition temperature were
observed which provides a spectroscopic estimate for the spin-gap of the
studied systems. Moreover, details of spin dynamics deep in the spin-Peierls
phase were investigated by pulse ESR experiments which revealed
Rabi-oscillations as signatures of coherent spin dynamics. From a comparison of
the characteristic damping times of the Rabi oscillations with measurements of
the spin relaxation times by means of primary-echo decay and CPMG methods it
becomes evident that inhomogeneities in local magnetic fields strongly
contribute to the soliton decoherence.",1909.10301v2
1996-02-28,Static and Dynamic Spin Structure Factors of Frustrated Heisenberg Antiferromagnet,"Using the modified spin-wave theory we calculate static and dynamic spin
structure factors in spin-liquid state of the J1-J2 model. The spectrum of
excitations in the vector channel is discussed. The developed technique can
also be applied to the t-J model describing copper oxide superconductors.",9602150v1
1999-01-14,Spin dynamics in the generalized ferromagnetic Kondo model for manganites,"Dynamical spin susceptibility is calculated for the generalized ferromagnetic
Kondo model which describes itinerant $e_{g}$ electrons interacting with
localized $t_{2g}$ electrons with antiferromagnetic coupling. The calculations
done in the mean field approximation show that the spin-wave spectrum of the
system in ferromagnetic state has two branches, acoustic and optic ones.
Self-energy corrections to the spectrum are considered and the acoustic
spin-wave damping is evaluated.",9901141v1
2002-06-07,"Comment on ""Spin Dynamics of the 2D Spin 1/2 Quantum Antiferromagnet Copper Deuteroformate Tetradeuterate (CFTD)""","Comment on ""Spin Dynamics of the 2D Spin 1/2 Quantum Antiferromagnet Copper
Deuteroformate Tetradeuterate (CFTD)"", H. M. Ronnow et al., Phys. Rev. Lett.
87, 037202 (2001)",0206106v1
2005-08-29,Effect of nuclear spins on the electron spin dynamics in negatively charged InP quantum dots,"Kinetics of polarized photoluminescence of the negatively charged InP quantum
dots in weak magnetic field is studied experimentally. Effect of both the
nuclear spin fluctuations and the dynamical nuclear polarization on the
electron spin orientation is observed.",0508698v1
2022-04-29,Dynamics of a Pair of Overlapping Polar Bright Solitons in Spin-1 Bose-Einstein Condensates,"We analyze the dynamics of both population and spin densities, emerging from
the spatial overlap between two distinct polar bright solitons in Spin-1 Spinor
Condensates. The dynamics of overlapping solitons in scalar condensates
exhibits soliton fusion, atomic switching from one soliton to another and
repulsive dynamics depending on the extent of overlap and the relative phase
between the solitons. The scalar case also helps us understand the dynamics of
the vector solitons. In the spinor case, non-trivial dynamics emerge in spatial
and spin degrees of freedom. In the absence of spin changing collisions, we
observe Josephson-like oscillations in the population dynamics of each spin
component. In this case, the population dynamics is independent of the relative
phase, but the dynamics of the spin-density vector depends on it. The latter
also witnesses the appearance of oscillating domain walls. The pair of
overlapping polar solitons emerge as four ferromagnetic solitons irrespective
of the initial phase difference for identical spin-dependent and
spin-independent interaction strengths. But the dynamics of final solitons
depends explicitly on the relative phase. Depending on the ratio of
spin-dependent and spin-independent interaction strengths, a pair of
oscillatons can also emerge as the final state. Then, increasing the extent of
overlap may lead to the simultaneous formation of both a stationary
ferromagnetic soltion and a pair of oscillatons depending on the relative
phase.",2204.14087v1
1998-07-17,Quantum spins mixing in spinor Bose-Einstein condensates,"We examine the internal structure of the ground states of a trapped
Bose-Einstein condensate in which atoms have three internal hyperfine spins. We
determine a set of collective spin states which minimize the interaction energy
between condensate atoms. We also examine the internal dynamics of an initially
spin polarized condensate. The time scale of spin-mixing is predicted.",9807258v1
2002-10-31,Superradiant Operation of Spin Masers,"The theory of spin superradiance, developed earlier for nuclear magnets, is
generalized to a wider class of spin systems, such as granular magnets and
molecular magnets. The latter may possess strong single-site magnetocrystalline
anisotropy, whose role in nonlinear spin dynamics is analysed. Transient as
well as pulsing superradiant regimes are described. These coherent regimes may
be employed in the operation of spin masers.",0210698v1
1998-03-20,Spin Effects in Heavy Quark Processes,"In the infinite mass limit for a heavy quark its spin decouples from the QCD
dynamics, which leads to the heavy-quark spin symmetry. After a short
discussion of spin symmetry some applications are considered.",9803398v1
2014-09-07,Spin transport in non-degenerate Si with a spin MOSFET structure at room temperature,"Spin transport in non-degenerate semiconductors is expected to pave a way to
the creation of spin transistors, spin logic devices and reconfigurable logic
circuits, because room temperature (RT) spin transport in Si has already been
achieved. However, RT spin transport has been limited to degenerate Si, which
makes it difficult to produce spin-based signals because a gate electric field
cannot be used to manipulate such signals. Here, we report the experimental
demonstration of spin transport in non-degenerate Si with a spin
metal-oxide-semiconductor field-effect transistor (MOSFET) structure. We
successfully observed the modulation of the Hanle-type spin precession signals,
which is a characteristic spin dynamics in non-degenerate semiconductor. We
obtained long spin transport of more than 20 {\mu}m and spin rotation, greater
than 4{\pi} at RT. We also observed gate-induced modulation of spin transport
signals at RT. The modulation of spin diffusion length as a function of a gate
voltage was successfully observed, which we attributed to the Elliott-Yafet
spin relaxation mechanism. These achievements are expected to make avenues to
create of practical Si-based spin MOSFETs.",1409.2178v1
2021-10-21,The spin-spin problem in Celestial Mechanics,"We study the dynamics of two homogeneous rigid ellipsoids subject to their
mutual gravitational influence. We assume that the spin axis of each ellipsoid
coincides with its shortest physical axis and is perpendicular to the orbital
plane. Due to such assumptions, the problem is planar and depends on particular
parameters of the ellipsoids, most notably, the equatorial oblateness and the
flattening with respect to the shortest physical axes. We consider two models
for such configuration: while in the full model, there is a coupling between
the orbital and rotational motions, in the Keplerian model, the centers of mass
of the bodies are constrained to move on coplanar Keplerian ellipses. The
Keplerian case, in the approximation that includes the coupling between the
spins of the two ellipsoids, is what we call spin-spin problem, that is a
generalization of the classical spin-orbit problem. In this paper we continue
the investigations of [Mis21] on the spin-spin problem by comparing it with the
spin-orbit problem and also with the full model.
  Beside detailing the models associated to the spin-orbit and spin-spin
problems, we introduce the notions of standard and balanced resonances, which
lead us to investigate the existence of periodic and quasi-periodic solutions.
We also give a qualitative description of the phase space and provide results
on the linear stability of solutions for the spin-orbit and spin-spin problems.
We conclude by providing a comparison between the full and the Keplerian models
with particular reference to the interaction between the rotational and orbital
motions.",2110.11152v1
2023-07-30,"Ab-initio predictions of spin relaxation, dephasing and diffusion in solids","Spin relaxation, dephasing and diffusion are at the heart of spin-based
information technology. Accurate theoretical approaches to simulate spin
lifetimes ($\tau_s$), determining how fast the spin polarization and phase
information will be lost, are important to the understandings of underlying
mechanism of these spin processes, and invaluable to search for promising
candidates of spintronic materials. Recently, we develop a first-principles
real-time density-matrix (FPDM) approach to simulate spin dynamics for general
solid-state systems. Through the complete first-principles' descriptions of
light-matter interaction and scattering processes including electron-phonon,
electronimpurity and electron-electron scatterings with self-consistent
spin-orbit coupling, as well as ab initio Land'e g-factor, our method can
predict $\tau_s$ at various conditions as a function of carrier density and
temperature, under electric and magnetic fields. By employing this method, we
successfully reproduce experimental results of disparate materials and identify
the key factors affecting spin relaxation, dephasing, and diffusion in
different materials. Specifically, we predict that germanene has long $\tau_s$
(~100 ns at 50 K), a giant spin lifetime anisotropy and spin-valley locking
effect under electric fields, making it advantageous for spin-valleytronic
applications. Based on our theoretical derivations and ab initio simulations,
we propose a new useful electronic quantity, named spin-flip angle
$\theta^{\uparrow\downarrow}$, for the understanding of spin relaxation through
intervalley spin-flip scattering processes. Our method can be further applied
to other emerging materials and extended to simulate exciton spin dynamics and
steady-state photocurrents due to photogalvanic effect.",2307.16311v1
2009-09-21,Engineering ultralong spin coherence in two-dimensional hole systems at low temperatures,"For the realisation of scalable solid-state quantum-bit systems, spins in
semiconductor quantum dots are promising candidates. A key requirement for
quantum logic operations is a sufficiently long coherence time of the spin
system. Recently, hole spins in III-V-based quantum dots were discussed as
alternatives to electron spins, since the hole spin, in contrast to the
electron spin, is not affected by contact hyperfine interaction with the
nuclear spins. Here, we report a breakthrough in the spin coherence times of
hole ensembles, confined in so called natural quantum dots, in narrow
GaAs/AlGaAs quantum wells at temperatures below 500 mK. Consistently,
time-resolved Faraday rotation and resonant spin amplification techniques
deliver hole-spin coherence times, which approach in the low magnetic field
limit values above 70 ns. The optical initialisation of the hole spin
polarisation, as well as the interconnected electron and hole spin dynamics in
our samples are well reproduced using a rate equation model.",0909.3711v3
2010-07-06,Radial Spin Helix in Two-Dimensional Electron Systems with Rashba Spin-Orbit Coupling,"We suggest a long-lived spin polarization structure, a radial spin helix, and
study its relaxation dynamics. For this purpose, starting with a simple and
physically clear consideration of spin transport, we derive a system of
equations for spin polarization density and find its general solution in the
axially symmetric case. It is demonstrated that the radial spin helix of a
certain period relaxes slower than homogeneous spin polarization and plain spin
helix. Importantly, the spin polarization at the center of the radial spin
helix stays almost unchanged at short times. At longer times, when the initial
non-exponential relaxation region ends, the relaxation of the radial spin helix
occurs with the same time constant as that describing the relaxation of the
plain spin helix.",1007.0853v1
2011-07-21,Theory of a.c. spin current noise and spin conductance through a quantum dot in the Kondo regime I: The equilibrium case,"We analyze the equilibrium frequency-dependent spin current noise and spin
conductance through a quantum dot in the local moment regime. Spin current
correlations behave markedly differently from charge correlations. Equilibrium
spin correlations are characterized by two universal scaling functions in the
absence of an external field: one of them is related to charge correlations,
while the other one describes cross-spin correlations. We characterize these
functions using a combination of perturbative and non-perturbative methods. We
find that at low temperatures spin cross-correlations are suppressed at
frequencies below the Kondo scale, $T_K$, and a dynamical spin accumulation
resonance is found at the Kondo energy, $\omega \sim T_K$. At higher
temperatures, $T>T_K$, surprising low-frequency anomalies related to overall
spin conservation appear in the spin noise and spin conductance, and the
Korringa rate is shown to play a distinguished role. The transient spin current
response also displays universal and singular properties.",1107.4265v1
2013-12-19,Dynamics of a localized spin excitation close to the spin-helix regime,"The time evolution of a local spin excitation in a (001)-confined
two-dimensional electron gas subjected to Rashba and Dresselhaus spin-orbit
interactions of similar strength is investigated theoretically and compared
with experimental data. Specifically, the consequences of the finite spatial
extension of the initial spin polarization is studied for non-balanced Rashba
and Dresselhaus terms and for finite cubic Dresselhaus spin-orbit interaction.
We show that the initial out-of-plane spin polarization evolves into a helical
spin pattern with a wave number that gradually approaches the value $q_0$ of
the persistent spin helix mode. In addition to an exponential decay of the spin
polarization that is proportional to both the spin-orbit imbalance and the
cubic Dresselhaus term, the finite width $w$ of the spin excitation reduces the
spin polarization by a factor that approaches $\exp(-q_0^2 w^2/2)$ at longer
times.",1312.5529v1
2016-03-21,Rashba semiconductor as spin Hall material: Experimental demonstration of spin pumping in wurtzite $n$-GaN:Si,"Pure spin currents in semiconductors are essential for implementation in the
next generation of spintronic elements. Heterostructures of III- nitride
semiconductors are currently employed as central building-blocks for lighting
and high-power devices. Moreover, the long relaxation times and the spin-orbit
coupling (SOC) in these materials indicate them as privileged hosts for spin
currents and related phenomena. Spin pumping is an efficient mechanism for the
inception of spin current and its conversion into charge current in
non-magnetic metals and semiconductors with Rashba SOC $via$ spin Hall effects.
We report on the generation in $n$-GaN:Si\,--\,at room temperature and through
spin pumping\,--\,of pure spin current, fundamental for the understanding of
the spin dynamics in these non-centrosymmetric Rashba systems. We find for
$n$-GaN:Si a spin Hall angle $\theta_{\mathrm{SH}}$=$3.03\times10^{-3}$,
exceeding by one order of magnitude those reported for other semiconductors,
pointing at III-nitrides as particularly efficient spin current generators.",1603.06471v1
2016-09-12,Spin decoherence of magnetic atoms on surfaces,"We review the problem of spin decoherence of magnetic atoms deposited on a
surface. Recent breakthroughs in scanning tunnelling microscopy (STM) make it
possible to probe the spin dynamics of individual atoms, either isolated or
integrated in nanoengineered spin structures. Transport pump and probe
techniques with spin polarized tips permit measuring the spin relaxation time
$T_1$, while novel demonstration of electrically driven STM single spin
resonance has provided a direct measurement of the spin decoherence time $T_2$
of an individual magnetic adatom. Here we address the problem of spin
decoherence from the theoretical point of view. First we provide a short
general overview of decoherence in open quantum systems and we discuss with
some detail ambiguities that arise in the case of degenerate spectra, relevant
for magnetic atoms. Second, we address the physical mechanisms that allows
probing the spin coherence of magnetic atoms on surfaces. Third, we discuss the
main spin decoherence mechanisms at work on a surface, most notably, Kondo
interaction, but also spin-phonon coupling and dephasing by Johnson noise.
Finally, we propose some schemes to engineer spin decoherence.",1609.03389v2
2017-02-16,Microscopic theory of electrically induced spin torques in magnetic Weyl semimetals,"We theoretically study electrical responses of magnetization in Weyl
semimetals. The Weyl semimetal is a new class of topological semimetals,
possessing hedgehog type spin textures in momentum space. Because of this
peculiar spin texture, an interplay of electron transport and spin dynamics
might provide new method to electrical control of magnetization. In this paper,
we consider the magnetically doped Weyl semimetals, and systematically study
current- and charge-induced spin torque exerted on the local magnetization in
three-dimensional Dirac-Weyl metals. We determine all current-induced spin
torques including spin-orbit torque, spin-transfer torque, and the so-called
$\beta$-term, up to first order with respect to spatial and temporal derivation
and electrical currents. We find that spin-transfer torque and $\beta$-term are
absent while spin-orbit torque is proportional to the axial current density. We
also calculate the charge-induced spin torque microscopically. We find the
charge-induced spin torque originates from the chiral anomaly due to the
correspondence between spin operators and axial current operators in our model.",1702.04918v1
2018-02-05,Cooper-Pair Spin Current in a Strontium Ruthenate Heterostructure,"It has been recognized that the condensation of spin-triplet Cooper pairs
requires not only the broken gauge symmetry but also the spin ordering as well.
One consequence of this is the possibility of the Cooper-pair spin current
analogous to the magnon spin current in magnetic insulators, the analogy also
extending to the existence of the Gilbert damping of the collective
spin-triplet dynamics. The recently fabricated heterostructure of the thin film
of the itinerant ferromagnet SrRuO3 on the bulk Sr2RuO4, the best-known
candidate material for the spin-triplet superconductor, offers a promising
platform for generating such spin current. We will show how such
heterostructure allows us to not only realize the long-range spin valve but
also electrically drive the collective spin mode of the spin-triplet order
parameter. Our proposal represents both a new realization of the spin
superfluidity and a transport signature of the spin-triplet superconductivity.",1802.01599v1
2017-06-09,Spin-wave analysis for Kagome-triangular spin system and coupled spin tubes: low-energy excitation for the cuboc order,"The coupled spin tube system, which is equivalent to a stacked
Kagome-triangular spin system, exhibits the cuboc order -- a non-coplanar spin
order with a twelve-sublattice structure accompanying spontaneous breaking of
the translational symmetry -- in the Kagome-triangular plane. On the basis of
the spin-wave theory, we analyze spin-wave excitations of the planar
Kagome-triangular spin system, where the geometric phase characteristic to the
cuboc spin structure emerges. We further investigate spin-wave excitations and
dynamical spin structure factors for the coupled spin tubes, assuming the
staggered cuboc order.",1706.02879v2
2017-12-08,Spin Hall and spin swapping torques in diffusive ferromagnets,"A complete set of the generalized drift-diffusion equations for a coupled
charge and spin dynamics in ferromagnets in the presence of extrinsic
spin-orbit coupling is derived from the quantum kinetic approach, covering
major transport phenomena, such as the spin and anomalous Hall effects, spin
swapping, spin precession and relaxation processes. We argue that the spin
swapping effect in ferromagnets is enhanced due to spin polarization, while the
overall spin texture induced by the interplay of spin-orbital and spin
precessional effects displays a complex spatial dependence that can be
exploited to generate torques and nucleate/propagate domain walls in
centrosymmetric geometries without use of external polarizers, as opposed to
the conventional understanding of spin-orbit mediated torques.",1712.03009v1
2020-02-04,Isotropic All-electric Spin analyzer based on a quantum ring with spin-orbit coupling,"Here we propose an isotropic all electrical spin analyzer in a quantum ring
with spin-orbit coupling by analytically and numerically modeling how the
charge transmission rates depend on the polarization of the incident spin. The
formalism of spin transmission and polarization rates in an arbitrary direction
is also developed by analyzing the Aharonov-Bohm and the Aharonov-Casher
effects. The topological spin texture induced by the spin-orbit couplings
essentially contributes to the dynamic phase and plays an important role in
spin transport. The spin transport features derived analytically has been
confirmed numerically. This interesting two-dimensional electron system can be
designed as a spin filter, spin polarizer and general analyzer by simply tuning
the spin-orbit couplings, which paves the way for realizing the tunable and
integrable spintronics device.",2002.01151v1
2020-12-07,Continuous dynamical decoupling of spin chains: Inducing two-qubit interactions to generate perfect entanglement,"Efficient control over entanglement in spin chains is useful for quantum
information processing applications. In this paper, we propose the use of a
combination of two different configurations of strong static and oscillating
fields to control and generate near-perfect entanglement between any two spins
in a spin chain, even in the presence of noise. This is made possible by the
fact that our control fields not only decouple the spin chain from its
environment but also selectively modify the spin-spin interactions. By suitably
tuning these spin-spin interactions via the control fields, we show that the
quantum state of any two spins in the spin chain can be made to be a Bell
state. We illustrate our results for various spin chains, such as the XY model,
the XYZ model, and the Ising spin chain.",2012.03873v3
2020-06-15,Control of Spin Relaxation Anisotropy by Spin-Orbit-Coupled Diffusive Spin Motion,"Spatiotemporal spin dynamics under spin-orbit interaction is investigated in
a (001) GaAs two-dimensional electron gas using magneto-optical Kerr rotation
microscopy. Spin polarized electrons are diffused away from the excited
position, resulting in spin precession because of the diffusion-induced
spin-orbit field. Near the cancellation between spin-orbit field and external
magnetic field, the induced spin precession frequency depends nonlinearly on
the diffusion velocity, which is unexpected from the conventional linear
relation between the spin-orbit field and the electron velocity.This behavior
originates from an enhancement of the spin relaxation anisotropy by the
electron velocity perpendicular to the diffused direction. We demonstrate that
the spin relaxation anisotropy, which has been regarded as a material constant,
can be controlled via diffusive electron motion.",2006.08253v1
2023-11-19,Spin squeezing generated by the anisotropic central spin model,"Spin squeezing, as a crucial quantum resource, plays a pivotal role in
quantum metrology, enabling us to achieve high-precision parameter estimation
schemes. Here we investigate the spin squeezing and the quantum phase
transition in an anisotropic central spin system. We find that this kind of
central spin systems can be mapped to the anisotropic Lipkin-Meshkov-Glick
model in the limit where the ratio of transition frequencies between the
central spin and the spin bath tends towards infinity. This property can induce
a one-axis twisting interaction and provides a new possibility for generating
spin squeezing. We separately consider generating spin-squeezed states via the
ground state and the dynamic evolution of the central spin model. The results
show that the spin squeezing parameter improves as the anisotropy parameter
decreases, and its value scales with system size as $N^{-2/3}$. Furthermore, we
obtain the critical exponent of the quantum Fisher information around the
critical point by numerical simulation, and find its value tends to $4/3$ as
the frequency ratio and the system size approach infinity. This work offers a
promising scheme for generating spin-squeezed state and paves the way for
potential advancements in quantum sensing.",2311.11308v2
1999-10-26,Spin dynamics simulations of the magnetic dynamics of RbMnF$_3$ and direct comparison with experiment,"Spin-dynamics techniques have been used to perform large-scale simulations of
the dynamic behavior of the classical Heisenberg antiferromagnet in simple
cubic lattices with linear sizes $L\leq 60$. This system is widely recognized
as an appropriate model for the magnetic properties of RbMnF$_3$.
Time-evolutions of spin configurations were determined numerically from coupled
equations of motion for individual spins using a new algorithm implemented by
Krech {\it etal}, which is based on fourth-order Suzuki-Trotter decompositions
of exponential operators. The dynamic structure factor was calculated from the
space- and time-displaced spin-spin correlation function. The crossover from
hydrodynamic to critical behavior of the dispersion curve and spin-wave
half-width was studied as the temperature was increased towards the critical
temperature. The dynamic critical exponent was estimated to be $z=(1.43\pm
0.03)$, which is slightly lower than the dynamic scaling prediction, but in
good agreement with a recent experimental value. Direct, quantitative
comparisons of both the dispersion curve and the lineshapes obtained from our
simulations with very recent experimental results for RbMnF$_3$ are presented.",9910429v1
1999-12-20,Spin dynamics simulations of excitations and critical dynamics in RbMnF_3,"Spin-dynamics simulations have been used to investigate the dynamic behavior
of RbMnF_3, treating it as a classical Heisenberg antiferromagnet on a simple
cubic lattice. Time-evolutions of spin configurations were determined
numerically from coupled equations of motion for individual spins using a new
algorithm which is based on Suzuki-Trotter decompositions of exponential
operators. The dynamic structure factor was calculated from the space- and
time-displaced spin-spin correlation function. The crossover from hydrodynamic
to critical behavior of the dispersion curve and spin-wave half-width was
studied as the temperature was increased towards the critical value. The
dynamic critical exponent was estimated to be z=(1.43\pm 0.03), which is
slightly lower than the dynamic scaling prediction, but in good agreement with
a recent experimental value. Comparisons are made of both the dispersion curve
and the lineshapes obtained from our simulations with very recent experimental
results for RbMnF_3 are presented.",9912374v1
2007-03-27,Control of electron spin decoherence caused by electron-nuclear spin dynamics in a quantum dot,"Control of electron spin decoherence in contact with a mesoscopic bath of
many interacting nuclear spins in an InAs quantum dot is studied by solving the
coupled quantum dynamics. The nuclear spin bath, because of its bifurcated
evolution predicated on the electron spin up or down state, measures the
which-state information of the electron spin and hence diminishes its
coherence. The many-body dynamics of nuclear spin bath is solved with a
pair-correlation approximation. In the relevant timescale, nuclear pair-wise
flip-flops, as elementary excitations in the mesoscopic bath, can be mapped
into the precession of non-interacting pseudo-spins. Such mapping provides a
geometrical picture for understanding the decoherence and for devising control
schemes. A close examination of nuclear bath dynamics reveals a wealth of
phenomena and new possibilities of controlling the electron spin decoherence.
For example, when the electron spin is flipped by a $\pi$-pulse at $\tau$, its
coherence will partially recover at $\sqrt{2}\tau$ as a consequence of quantum
disentanglement from the mesoscopic bath. In contrast to the re-focusing of
inhomogeneously broadened phases by conventional spin-echoes, the
disentanglement is realized through shepherding quantum evolution of the bath
state via control of the quantum object. A concatenated construction of pulse
sequences can eliminate the decoherence with arbitrary accuracy, with the
nuclear-nuclear spin interaction strength acting as the controlling small
parameter.",0703690v1
2015-06-02,Long-lived nanosecond spin relaxation and spin coherence of electrons in monolayer MoS_2 and WS_2,"The recently-discovered monolayer transition metal dichalcogenides (TMDCs)
provide a fertile playground to explore new coupled spin-valley physics.
Although robust spin and valley degrees of freedom are inferred from polarized
photoluminescence (PL) experiments, PL timescales are necessarily constrained
by short-lived (3-100ps) electron-hole recombination. Direct probes of
spin/valley polarization dynamics of resident carriers in electron (or hole)
doped TMDCs, which may persist long after recombination ceases, are at an early
stage. Here we directly measure the coupled spin-valley dynamics in
electron-doped MoS_2 and WS_2 monolayers using optical Kerr spectroscopy, and
unambiguously reveal very long electron spin lifetimes exceeding 3ns at 5K (2-3
orders of magnitude longer than typical exciton recombination times). In
contrast with conventional III-V or II-VI semiconductors, spin relaxation
accelerates rapidly in small transverse magnetic fields. Supported by a model
of coupled spin-valley dynamics, these results indicate a novel mechanism of
itinerant electron spin dephasing in the rapidly-fluctuating internal
spin-orbit field in TMDCs, driven by fast intervalley scattering. Additionally,
a long-lived spin coherence is observed at lower energies, commensurate with
localized states. These studies provide crucial insight into the physics
underpinning spin and valley dynamics of resident electrons in atomically-thin
TMDCs.",1506.00996v1
2016-11-10,Spin-charge coupled dynamics driven by a time-dependent magnetization,"The spin-charge coupled dynamics in a thin, magnetized metallic system are
investigated. The effective driving force acting on the charge carriers is
generated by a dynamical magnetic texture, which can be induced, e.g., by a
magnetic material in contact with a normal-metal system. We consider a general
inversion-asymmetric substrate/normal-metal/magnet structure, which, by
specifying the precise nature of each layer, can mimick various experimentally
employed setups. Inversion symmetry breaking gives rise to an effective Rashba
spin-orbit interaction. We derive general spin-charge kinetic equations which
show that such spin-orbit interaction, together with anisotropic Elliott-Yafet
spin relaxation, yields significant corrections to the magnetization-induced
dynamics. In particular, we present a consistent treatment of the spin density
and spin current contributions to the equations of motion, inter alia
identifying a novel term in the effective force which appears due to a spin
current polarized parallel to the magnetization. This ""inverse spin filter""
contribution depends markedly on the parameter which describes the anisotropy
in spin relaxation. To further highlight the physical meaning of the different
contributions, the spin pumping configuration of typical experimental setups is
analyzed in detail. In the two-dimensional limit the build-up of a DC voltage
is dominated by the spin galvanic (inverse Edelstein) effect. A measuring
scheme that could isolate this contribution is discussed.",1611.03378v3
2021-12-31,Spin-injection-generated shock waves and solitons in a ferromagnetic thin film: the spin piston problem,"The unsteady, nonlinear magnetization dynamics induced by spin injection in
an easy-plane ferromagnetic channel subject to an external magnetic field are
studied analytically. Leveraging a dispersive hydrodynamic description, the
Landau-Lifshitz equation is recast in terms of hydrodynamic-like variables for
the magnetization's perpendicular component (spin density) and azimuthal phase
gradient (fluid velocity). Spin injection acts as a moving piston that
generates nonlinear, dynamical spin textures in the ferromagnetic channel with
downstream quiescent spin density set by the external field. In contrast to the
classical problem of a piston accelerating a compressible gas, here, variable
spin injection and field lead to a rich variety of nonlinear wave phenomena
from oscillatory spin shocks to solitons and rarefaction waves. A full
classification of solutions is provided using nonlinear wave modulation theory
by identifying two key aspects of the fluid-like dynamics: subsonic/supersonic
conditions and convex/nonconvex hydrodynamic flux. Familiar waveforms from the
classical piston problem such as rarefaction (expansion) waves and shocks
manifest in their spin-based counterparts as smooth and highly oscillatory
transitions, respectively. The spin shock is an example of a dispersive shock
wave, which arises in many physical systems. New features without a gas
dynamics counterpart include composite wave complexes with ""contact"" spin
shocks and rarefactions. Magnetic supersonic conditions lead to two pronounced
piston edge behaviors including a stationary soliton and an oscillatory
wavetrain. These coherent wave structures have physical implications for the
generation of high frequency spin waves from pulsed injection and persistent,
stable stationary and/or propagating solitons in the presence of magnetic
damping. The analytical results are favorably compared with numerical
simulations.",2112.15301v2
2006-11-24,Spin dynamics in the regime of hopping conductivity,"We consider spin dynamics in the impurity band of a semiconductor with
spin-split spectrum. Due to the splitting, phonon-assisted hops from one
impurity to another are accompanied by rotation of the electron spin, which
leads to spin relaxation. The system is strongly inhomogeneous because of
exponential variation of hopping times. However, at very small couplings an
electron diffuses over a distance exceeding the characteristic scale of the
inhomogeneity during the time of spin relaxation, so one can introduce an
averaged spin relaxation rate. At larger values of coupling the system is
effectively divided into two subsystems: the one where relaxation is very fast
and another one where relaxation is rather slow. In this case, spin decays due
to escape of the electrons from one subsystem to another. As a result, the spin
dynamics is non-exponential and hardly depends on spin-orbit coupling.",0611626v1
2007-03-19,Non-equilibrium spin dynamics in a trapped Fermi gas with effective spin-orbit interaction,"We consider a trapped atomic system in the presence of spatially varying
laser fields. The laser-atom interaction generates a pseudospin degree of
freedom (referred to simply as spin) and leads to an effective spin-orbit
coupling for the fermions in the trap. Reflections of the fermions from the
trap boundaries provide a physical mechanism for effective momentum relaxation
and non-trivial spin dynamics due to the emergent spin-orbit coupling. We
explicitly consider evolution of an initially spin-polarized Fermi gas in a
two-dimensional harmonic trap and derive non-equilibrium behavior of the spin
polarization. It shows periodic echoes with a frequency equal to the harmonic
trapping frequency. Perturbations, such as an asymmetry of the trap, lead to
the suppression of the spin echo amplitudes. We discuss a possible experimental
setup to observe spin dynamics and provide numerical estimates of relevant
parameters.",0703500v2
2007-11-07,Hamiltonian of two spinning compact bodies with next-to-leading order gravitational spin-orbit coupling,"A Hamiltonian formulation is given for the gravitational dynamics of two
spinning compact bodies to next-to-leading order ($G/c^4$ and $G^2/c^4$) in the
spin-orbit interaction. We use a novel approach (valid to linear order in the
spins), which starts from the second-post-Newtonian metric (in ADM coordinates)
generated by two spinless bodies, and computes the next-to-leading order
precession, in this metric, of suitably redefined ``constant-magnitude''
3-dimensional spin vectors ${\bf S}_1$, ${\bf S}_2$. We prove the Poincar\'e
invariance of our Hamiltonian by explicitly constructing ten phase-space
generators realizing the Poincar\'e algebra. A remarkable feature of our
approach is that it allows one to derive the {\it orbital} equations of motion
of spinning binaries to next-to-leading order in spin-orbit coupling without
having to solve Einstein's field equations with a spin-dependent stress tensor.
We show that our Hamiltonian (orbital and spin) dynamics is equivalent to the
dynamics recently obtained by Faye, Blanchet, and Buonanno, by solving
Einstein's equations in harmonic coordinates.",0711.1048v2
2009-08-03,Signatures of dynamically polarized nuclear spins in all-electrical lateral spin transport devices,"The effect of nuclear spins in Fe/GaAs all-electrical spin-injection devices
is investigated. At temperatures below 50 K, strong modifications of the
non-local spin signal are found that are characteristic for hyperfine coupling
between conduction electrons and dynamically polarized nuclear spins. The
perpendicular component of the nuclear Overhauser field depolarizes electron
spins near zero in-plane external magnetic field, and can suppress such
dephasing when antialigned with the external field, leading to satellite peaks
in a Hanle measurement. The features observed agree well with a Monte Carlo
simulation of the spin diffusion equation including hyperfine interaction, and
are used to study the nuclear spin dynamics and relate it to the spin
polarization of injected electrons.",0908.0273v1
2011-09-12,Spin Excitation Assisted by Non-Softening Phonon for Spin-Peierls Model,"We study spin dynamics of a spin-Peierls chain with nearest-neighbor and
next-nearest-neighbor Heisenberg spin exchange interactions together with a
gapped and dispersionless phonon. The dynamical spin correlation function and
phonon excitation spectrum are calculated at zero temperature by using
dynamical density-matrix renormalization-group method. We find a new spin
excitation assisted by non-softening phonon. The excitation is located above
phonon in energy and shows a dispersive feature with strong intensity near the
momentum $\pi$. The phonon excitation spectrum is also influenced by the
spin-phonon interaction. We discuss the possibility of observing the
spin-phonon coupled features in inorganic spin-Peierls compound CuGeO$_3$.",1109.2410v2
2012-02-07,Prediction of Giant Spin Motive Force due to Rashba Spin-Orbit Coupling,"Magnetization dynamics in a ferromagnet can induce a spin-dependent electric
field through spin motive force. Spin current generated by the spin-dependent
electric field can in turn modify the magnetization dynamics through
spin-transfer torque. While this feedback effect is usually weak and thus
ignored, we predict that in Rashba spin-orbit coupling systems with large
Rashba parameter $\alpha_{\rm R}$, the coupling generates the spin-dependent
electric field [$\pm(\alpha_{\rm R}m_e/e\hbar) (\vhat{z}\times \partial
\vec{m}/\partial t)]$, which can be large enough to modify the magnetization
dynamics significantly. This effect should be relevant for device applications
based on ultrathin magnetic layers with strong Rashba spin-orbit coupling.",1202.1406v2
2015-02-13,Spin Dynamics with Inertia in Metallic Ferromagnets,"Non-adiabatic contribution of environmental degrees of freedom yields
effective inertia of spin in effective spin dynamics. In this paper, we study
several aspects of the inertia of spin in metallic ferromagnets. (i) a concrete
expression of the spin inertia $m_s$: $m_s=\hbar S_c/(2g_{\rm sd})$, where
$S_c$ is the spin polarization of conduction electrons and $g_{\rm sd}$ is the
$sd$ coupling constant. (ii) dynamical behavior of spin with inertia, discussed
from viewpoints of a spinning top and of a particle on a sphere. (iii) behavior
of spin waves and domain walls in the presence of inertia, and behavior of spin
with inertia in the case of a time-dependent magnetic field.",1502.04107v2
2015-03-11,Spin-wave-induced spin torque in Rashba spin-orbit coupling system,"We study the effects of Rashba spin-orbit coupling on the spin torque induced
by spin waves, which are the plane wave dynamics of magnetization. The spin
torque is derived from linear response theory, and we calculate the dynamic
spin torque by considering the impurity-ladder-sum vertex corrections. This
dynamic spin torque is divided into three terms: a damping term, a $distortion$
term, and a correction term for the equation of motion. The $distorting$ torque
describes a phenomenon unique to the Rashba spin-orbit coupling system, where
the distorted motion of magnetization precession is subjected to the
anisotropic force from the Rashba coupling. The oscillation mode of the
precession exhibits an elliptical trajectory, and the ellipticity depends on
the strength of the nesting effects, which could be reduced by decreasing the
electron lifetime.",1503.03171v2
2015-09-26,Spin Dynamics and Relaxation in Graphene Dictated by Electron-hole Puddles,"The understanding of spin dynamics and relaxation mechanisms in clean
graphene and the upper time and length scales on which spin devices can operate
are prerequisites to realizing graphene spintronic technologies. Here we
theoretically reveal the nature of fundamental spin relaxation mechanisms in
clean graphene on different substrates with spin-orbit Rashba fields as low as
a few tens of micron eV. Spin lifetimes ranging from 50 picoseconds up to
several nanoseconds are found to be dictated by substrate-induced electron-hole
characteristics. A crossover in the spin relaxation mechanism from a
Dyakonov-Perel type for SiO2 substrates to a broadening-induced dephasing for
hBN substrates is described. The energy dependence of spin lifetimes, their
ratio for spins pointing out-of-plane and in-plane, and the scaling with
disorder provide a global picture about spin dynamics and relaxation in
ultraclean graphene in presence of electron-hole puddles.",1509.07949v1
2016-02-01,Equations of motion of test particles for solving the spin-dependent Boltzmann-Vlasov equation,"A consistent derivation of the equations of motion (EOMs) of test particles
for solving the spin-dependent Boltzmann-Vlasov equation is presented. The
resulting EOMs in phase space are similar to the canonical equations in
Hamiltonian dynamics, and the EOM of spin is the same as that in the Heisenburg
picture of quantum mechanics. Considering further the quantum nature of spin
and choosing the direction of total angular momentum in heavy-ion reactions as
a reference of measuring nucleon spin, the EOMs of spin-up and spin-down
nucleons are given separately. The key elements affecting the spin dynamics in
heavy-ion collisions are identified. The resulting EOMs provide a solid
foundation for using the test-particle approach in studying spin dynamics in
heavy-ion collisions at intermediate energies. Future comparisons of model
simulations with experimental data will help constrain the poorly known
in-medium nucleon spin-orbit coupling relevant for understanding properties of
rare isotopes and their astrophysical impacts.",1602.00404v2
2017-03-11,Generalized Boundary Conditions for Spin Transfer,"We develop a comprehensive description of static and dynamic spin-transfer
torque at interfaces between a normal metal and a magnetic material. Specific
examples of the latter include ferromagnets, collinear and noncollinear
antiferromagnets, general ferrimagnets, and spin glasses. We study the limit of
the exchange-dominated interactions, so that the full system is isotropic in
spin space, apart from a possible symmetry-breaking order. A general such
interface yields three coefficients (corresponding to three independent
generators of rotations) generalizing the well-established notion of the
spin-mixing conductance, which pertains to the collinear case. We develop a
nonequilibrium thermodynamic description of the emerging interfacial spin
transfer and its effect on the collective spin dynamics, while circumventing
the usual discussion of spin currents and net spin dynamics. Instead, our focus
is on the dissipation and work effectuated by the interface. Microscopic
scattering-matrix based expressions are derived for the generalized
spin-transfer coefficients.",1703.04020v2
2013-08-10,Spin Chaos Manifestation in a Driven Quantum Billiard with Spin-Orbit Coupling,"The coupling of orbital and spin degrees of freedom is the source of many
interesting phenomena. Here, we study the electron dynamics in a quantum
billiard --a mesoscopic rectangular quantum dot-- with spin-orbit coupling
driven by a periodic electric field. We find that both the spatial and temporal
profiles of the observables demonstrate the transition to chaotic dynamics with
qualitative modifications of the power spectra and patterns of probability and
spin density. The time dependence of the wavefunctions and spin density
distributions indicates spin-charge separation {seen in the decay of the
spin-charge density correlators}. This new spin chaos effect can be
experimentally verified leading to a better understanding of the interplay
between spin and spatial degrees of freedom, relevant to fundamental and
applied quantum physics.",1308.2333v2
2017-01-19,Spin separation and exchange for quantum dots in the Overhauser field,"We describe the spin and charge dynamics of the system of two electrons
confined within a double quantum dot defined in a quantum wire. The spin
dynamics is driven by the electron motion in presence of the spin-orbit
interaction and the randomly varying local Overhauser field due to the nuclear
spins. The Schroedinger equation is solved with the time-dependent
configuration interaction method that allows for an exact description of the
system dynamics. The procedures of the spin separation, exchange and read-out
by the spin to charge conversion all induced by the detuning variation are
simulated. The rates of the potential variation that are necessary for the spin
separation and spin to charge conversion in the context of the Landau-Zener
transitions are determined. The average over random configurations of the
hyperfine field produce spin exchange results which qualitatively agree with
the experimental data.",1701.05471v1
2018-06-28,Spin Inertia of Resident and Photoexcited Carriers in Singly-Charged Quantum Dots,"The spin dynamics in a broad range of systems can be studied using circularly
polarized optical excitation with alternating helicity. The dependence of spin
polarization on the frequency of helicity alternation, known as the spin
inertia effect, is used here to study the spin dynamics in singly-charged
(In,Ga)As/GaAs quantum dots (QDs) providing insight into spin generation and
accumulation processes. We demonstrate that the dependence of spin polarization
in $n$- and $p$-type QDs on the external magnetic field has a characteristic V-
and M-like shape, respectively. This difference is related to different
microscopic mechanisms of resident carriers spin orientation. It allows us to
determine the parameters of the spin dynamics both for the ground and excited
states of singly-charged QDs.",1806.11100v2
2021-12-02,Spin dynamics of the spin chain antiferromagnet RbFeS$_2$,"We report transport and inelastic neutron scattering studies on electronic
properties and spin dynamics of the quasi-one-dimensional spin chain
antiferromagnet RbFeS$_2$. An antiferromagnetic phase transition at
$T_N\approx195$ K and dispersive spin waves with a spin gap of 5 meV are
observed. By modeling the spin excitation spectra using linear spin wave
theory, intra and inter-chain exchange interactions are found to be
$SJ_1=100(5)$ meV and $SJ_3=0.9(3)$ meV, respectively, together with a small
single-ion anisotropy of $SD_{zz}=0.04(1)$ meV. Comparison with previous
results for other materials in the same class of Fe$^{3+}$ spin chain systems
reveals that although the magnetic order sizes show significant variation from
1.8 to 3.0$\mu_B$ within the family of materials, the exchange interactions
$SJ$ are nevertheless quite similar, analogous to the iron pnictide
superconductors where both localized and delocalized electrons contribute to
the spin dynamics.",2112.00951v3
2023-03-16,Ultrafast dynamics of electrons excited by femtosecond laser pulses: spin polarization and spin-polarized currents,"Laser radiation incident on a ferromagnetic sample produces excited electrons
and currents whose spin polarization must not be aligned with the magnetization
-- an effect due to spin-orbit coupling that is ubiquitous in spin- and
angle-resolved photoemission. In this Paper, we report on a systematic
investigation of the dynamics of spin polarization and spin-polarized currents
produced by femtosecond laser pulses, modeled within our theoretical framework
EVOLVE. The spin polarization depends strongly on the properties of the laser
pulse and on the sample composition, as is shown by comparing results for
Cu(100), Co(100), and a Co/Cu heterostructure. We find a transition from
coherence before the laser pulse's maximum to incoherence thereafter. Moreover,
the time dependence of the spin-polarization components induced by spin-orbit
coupling differ significantly in Cu and Co: in Cu, we find long-period
oscillations with tiny rapid modulations, whereas in Co prominent rapid
oscillations with long period ones are superimposed. The pronounced spatial
dependencies of the signals underline the importance of inhomogeneities, in
particular magnetic/non-magnetic interfaces `act as source' for ultrafast
spin-polarization effects. Our investigation provides detailed insight into
electron dynamics during and shortly after a femtosecond laser excitation.",2303.09291v1
2005-01-05,Post-Newtonian accurate parametric solution to the dynamics of spinning compact binaries in eccentric orbits: The leading order spin-orbit interaction,"We derive Keplerian-type parametrization for the solution of post-Newtonian
(PN) accurate conservative dynamics of spinning compact binaries moving in
eccentric orbits. The PN accurate dynamics that we consider consists of the
third post-Newtonian accurate conservative orbital dynamics influenced by the
leading order spin effects, namely the leading order spin-orbit interactions.
The orbital elements of the representation are explicitly given in terms of the
conserved orbital energy, angular momentum and a quantity that characterizes
the leading order spin-orbit interactions in Arnowitt, Deser, and Misner-type
coordinates. Our parametric solution is applicable in the following two
distinct cases: (i) the binary consists of equal mass compact objects, having
two arbitrary spins, and (ii) the binary consists of compact objects of
arbitrary mass, where only one of them is spinning with an arbitrary spin. As
an application of our parametrization, we present gravitational wave
polarizations, whose amplitudes are restricted to the leading quadrupolar
order, suitable to describe gravitational radiation from spinning compact
binaries moving in eccentric orbits. The present parametrization will be
required to construct `ready to use' reference templates for gravitational
waves from spinning compact binaries in inspiralling eccentric orbits. Our
parametric solution for the post-Newtonian accurate conservative dynamics of
spinning compact binaries clearly indicates, for the cases considered, the
absence of chaos in these systems. Finally, we note that our parametrization
provides the first step in deriving a fully second post-Newtonian accurate
`timing formula', that may be useful for the radio observations of relativistic
binary pulsars like J0737-3039.",0501011v1
2014-10-22,Spin dynamics of Mn impurities and their bound acceptors in GaAs,"We present results of tight-binding spin-dynamics simulations of individual
and pairs of substitutional Mn impurities in GaAs. Our approach is based on the
mixed quantum-classical scheme for spin dynamics, with coupled equations of
motions for the quantum subsystem, representing the host, and the localized
spins of magnetic dopants, which are treated classically. In the case of a
single Mn impurity, we calculate explicitly the time evolution of the Mn spin
and the spins of nearest-neighbors As atoms, where the acceptor (hole) state
introduced by the Mn dopant resides. We relate the characteristic frequencies
in the dynamical spectra to the two dominant energy scales of the system,
namely the spin-orbit interaction strength and the value of the p-d exchange
coupling between the impurity spin and the host carriers. For a pair of Mn
impurities, we find signatures of the indirect (carrier-mediated) exchange
interaction in the time evolution of the impurity spins. Finally, we examine
temporal correlations between the two Mn spins and their dependence on the
exchange coupling and spin-orbit interaction strength, as well as on the
initial spin-configuration and separation between the impurities. Our results
provide insight into the dynamic interaction between localized magnetic
impurities in a nano-scaled magnetic-semiconductor sample, in the extremely
dilute (solotronics) regime.",1410.5978v1
2023-09-07,Coherent spin dynamics between electron and nucleus within a single atom,"The nuclear spin, being much more isolated from the environment than its
electronic counterpart, enables quantum experiments with prolonged coherence
times and presents a gateway towards uncovering the intricate dynamics within
an atom. These qualities have been demonstrated in a variety of nuclear spin
qubit architectures, albeit with limited control over the direct environment of
the nuclei. As a contrasting approach, the combination of electron spin
resonance (ESR) and scanning tunnelling microscopy (STM) provides a bottom-up
platform to study the fundamental properties of nuclear spins of single atoms
on a surface. However, access to the time evolution of these nuclear spins, as
was recently demonstrated for electron spins, remained a challenge. Here, we
present an experiment resolving the nanosecond coherent dynamics of a
hyperfine-driven flip-flop interaction between the spin of an individual
nucleus and that of an orbiting electron. We use the unique local
controllability of the magnetic field emanating from the STM probe tip to bring
the electron and nuclear spins in tune, as evidenced by a set of avoided level
crossings in ESR-STM. Subsequently, we polarize both spins through scattering
of tunnelling electrons and measure the resulting free evolution of the coupled
spin system using a DC pump-probe scheme. The latter reveals a complex pattern
of multiple interfering coherent oscillations, providing unique insight into
the atom's hyperfine physics. The ability to trace the coherent hyperfine
dynamics with atomic-scale structural control adds a new dimension to the study
of on-surface spins, offering a pathway towards dynamic quantum simulation of
low-dimensional magnonics.",2309.03749v1
2011-06-18,Electrical control of spin dynamics in finite one-dimensional systems,"We investigate the possibility of the electrical control of spin transfer in
monoatomic chains incorporating spin-impurities. Our theoretical framework is
the mixed quantum-classical (Ehrenfest) description of the spin dynamics, in
the spirit of the s-d-model, where the itinerant electrons are described by a
tight-binding model while localized spins are treated classically. Our main
focus is on the dynamical exchange interaction between two well-separated
spins. This can be quantified by the transfer of excitations in the form of
transverse spin oscillations. We systematically study the effect of an
electrostatic gate bias V_g on the interconnecting channel and we map out the
long-range dynamical spin transfer as a function of V_g. We identify regions of
V_g giving rise to significant amplification of the spin transmission at low
frequencies and relate this to the electronic structure of the channel.",1106.3687v1
2016-11-23,Dynamical Time-Reversal Symmetry Breaking and Photo-Induced Chiral Spin Liquids in Frustrated Mott Insulators,"The search for quantum spin liquids in frustrated quantum magnets recently
has enjoyed a surge of interest, with various candidate materials under intense
scrutiny. However, an experimental confirmation of a gapped topological spin
liquid remains an open question. Here, we show that circularly-polarized light
can provide a novel knob to drive frustrated Mott insulators into a chiral spin
liquid (CSL), realizing an elusive quantum spin liquid with topological order.
We find that the dynamics of a driven Kagome Mott insulator is well-captured by
an effective Floquet spin model, with heating strongly suppressed, inducing a
scalar spin chirality $S_i \cdot (S_j \times S_k)$ term which dynamically
breaks time-reversal while preserving SU(2) spin symmetry. We fingerprint the
transient phase diagram and find a stable photo-induced CSL near the
equilibrium state. The results presented suggest employing dynamical symmetry
breaking to engineer quantum spin liquids and access elusive phase transitions
that are not readily accessible in equilibrium.",1611.07964v2
2012-04-20,Magnetic order and spin dynamics in the proximity of a ferromagnetic quantum critical point: A μSR study of YbNi4P2,"The local 4f-electronic spin dynamics and magnetic order in YbNi4P2 were
studied by means of muon-spin relaxation measurements. Zero-field muon-spin
relaxation proves static magnetic order with a strongly reduced ordered Yb3+
moment of (2.5-4.6) \times 10-2{\mu}B, below TC = 140 mK. Above TC, the
muon-spin polarization P(t,B) is dominated by quasihomogeneous spin
fluctuations and exhibits a time-field scaling relation P(t,B) =
P(t/B{\gamma}), indicating cooperative critical spin dynamics in the system. At
T = 190 mK, slightly above TC, {\gamma} = 0.81(5), suggesting time-scale
invariant power-law behavior for the dynamic electronic spin-spin
autocorrelation function.",1204.4632v1
2014-06-04,SU(3) semiclassical representation of quantum dynamics of interacting spins,"We present a formalism for simulating quantum dynamics of lattice spin-one
systems by first introducing local hidden variables and then doing
semiclassical (truncated Wigner) approximation in the extended phase space. In
this way we exactly take into account the local on-site Hamiltonian and
approximately treat spin-spin interactions. In particular, we represent each
spin with eight classical SU(3) variables. Three of them represent the usual
spin components and five others are hidden variables representing local
spin-spin correlations. We compare our formalism with exact quantum dynamics of
fully connected spin systems and find very good agreement. As an application we
discuss quench dynamics of a Bose-Hubbard model near the superfluid-insulator
transition for a 3D lattice system consisting of 1000 sites.",1406.1192v2
2017-10-26,Spin dynamics in helical molecules with non-linear interactions,"It is widely admitted that the helical conformation of certain chiral
molecules may induce a sizable spin selectivity observed in experiments. Spin
selectivity arises as a result of the interplay between a helicity-induced
spin-orbit coupling and electric dipole fields in the molecule. From the
theoretical point of view, different phenomena might affect the spin dynamics
in helical molecules, such as quantum dephasing, dissipation and the role of
metallic contacts. Previous studies neglected the local deformation of the
molecule about the carrier thus far, but this assumption seems unrealistic to
describe charge transport in molecular systems. We introduce an effective model
describing the electron spin dynamics in a deformable helical molecule with
weak spin-orbit coupling. We find that the electron-lattice interaction allows
the formation of stable solitons such as bright solitons with well defined spin
projection onto the molecule axis. We present a thorough study of these bright
solitons and analyze their possible impact on the spin dynamics in deformable
helical molecules.",1710.09582v1
2020-04-17,Spectroscopic signatures of next-nearest-neighbor hopping in the charge and spin dynamics of doped one-dimensional antiferromagnets,"We study the impact of next-nearest-neighbor (nnn) hopping on the low-energy
collective excitations of strongly correlated doped antiferromagnetic cuprate
spin chains. Specifically, we use exact diagonalization and the density matrix
renormalization group method to study the single-particle spectral function,
the dynamical spin and charge structure factors, and the Cu $L$-edge resonant
inelastic x-ray scattering (RIXS) intensity of the doped $t$-$t^\prime$-$J$
model for a set of $t^\prime$ values. We find evidence for the breakdown of
spin-charge separation as $|t^\prime|$ increases and identify its fingerprints
in the dynamical response functions. The inclusion of nnn hopping couples the
spinon and holon excitations, resulting in the formation of a spin-polaron,
where a ferromagnetic spin polarization cloud dresses the doped carrier. The
spin-polaron manifests itself as additional spectral weight in the dynamical
correlation functions, which appear simultaneously in the spin- and
charge-sensitive channels. We also demonstrate that RIXS can provide a unique
view of the spin-polaron, due to its sensitivity to both the spin and charge
degrees of freedom.",2004.08435v1
2022-03-26,Nonequilibrium dynamics in a spin valve with noncollinear magnetization,"We utilize a hybrid quantum-classical equation of motion approach to
investigate the spin dynamics and spin-transfer torque in a spin valve under
bias voltage. We show that the interplay between localized classical magnetic
moments and conduction electrons induces a complex effective exchange coupling
between the magnetic layers. This leads to a declination of magnetizations from
layers anisotropy axes even in equilibrium. Introducing a finite bias voltage
triggers spin currents and related spin-transfer torques which further tilt the
magnetizations and govern the relaxation processes of the spin dynamics.
Analyzing different scenarios of the applied bias voltage, we show that
symmetric and asymmetric voltage drops can lead to relaxation times of the spin
dynamics that differ by several orders of magnitude at comparable charge
currents. In both cases we observe resonant features, where the relaxation is
boosted whenever the chemical potential of the leads matches the maxima in the
density of the states of the spin-valve electrons.",2203.14068v2
2022-04-30,Dynamic quantum-enhanced sensing without entanglement in central spin systems,"We propose a dynamic quantum sensing scheme by using a quantum many-spin
system composed of a central spin interacting with many surrounding spins.
Starting from a generalized Ising ring model, we investigate the error
propagation formula of the central spin and it indicates that Heisenberg
scaling can be reached while the probe state only needs to be a product state.
Particularly, we derive an analytical form of the dynamic quantum Fisher
information in a limit case, which explicitly exhibits the Heisenberg scaling.
By comparing with numerical results, we demonstrate that the general case can
be well approximated by the analytical result when the coupling strength among
the surrounding spins is much weaker than the coupling strength between the
central and surrounding spins. This analytic result guides us to find the
appropriate probe state and the proper measurement time, to achieve the
Heisenberg scaling in realistic situations. Furthermore, we investigate various
effects which are important in practical quantum systems, including the central
spin Zeeman term, the anisotropy of the hyperfine interaction and the
inhomogeneity of the hyperfine coupling strength. Our result indicates that the
dynamic quantum-enhanced sensing scheme seems feasible in realistic quantum
central spin systems, like semiconductor quantum dots.",2205.00292v1
2022-11-04,Derivation of Interacting Two-Qubit Dynamics from Spin-Boson Model,"We derive damping equations of motion for interacting two-spin states from a
spin-boson model in order to examine qubit dynamics in quantum computers. On
the basis of the composite operator method, we develop the Caldeira-Leggett
approach for open quantum systems so that the entanglement dynamics originated
from the two-spin correlation can be taken. We demonstrate numerical results
for time dependence on the two-spin dynamics. We find that the relaxation of
the total spin is described by a quantum version of the Landau-Lifshitz-Gilbert
equation for magnetic materials. We also find that a two-spin composite mode
keeps oscillation even after the total spin has been fully relaxed. We thus
conclude that the two-spin correlation due to the presence of the composite
mode is stable against dissipation. We consider the mechanism of why the
correlation is maintained.",2211.02490v1
2023-06-27,Quantum spin fluctuations in dynamical quantum phase transitions,"Quantum phase transitions have long been studied in their relation to quantum
fluctuations. These fluctuations can be quantified as the degree of spin
squeezing in spin models, where one of the two non-commutative observables
breaks the standard quantum limit of measurement by minimizing its uncertainty.
However, the understanding of their role in dynamical quantum phase transitions
(DQPTs) is still incomplete. In this work, we combine the Loschmidt amplitude,
which detects DQPTs, and the spin-squeezing parameter (SSP), the quantification
of spin squeezing, to study the spin dynamics in a quenched interacting spin
model around DQPT. We show that the extremal, mostly maximal, of SSP occurs
near DQPTs when the system is quenched between different phases. These
phenomena further unveil the spin correlations during DQPTs, for which the
highest contribution aligns with the preferred direction of spin interactions
in the post-quenched phase. We also demonstrate the time evolution of SSP
differs for various quench scenarios. These findings provide us with physical
insights into the dynamics of quantum fluctuations around DQPTs and their
relation to the equilibrium phase diagrams.",2306.15227v1
2007-09-24,The Spin Density Matrix II: Application to a system of two quantum dots,"This work is a sequel to our work ""The Spin Density Matrix I: General Theory
and Exact Master Equations"" (eprint arXiv:0708.0644 [cond-mat]). Here we
compare pure- and pseudo-spin dynamics using as an example a system of two
quantum dots, a pair of localized conduction-band electrons in an n-doped GaAs
semiconductor. Pure-spin dynamics is obtained by tracing out the orbital
degrees of freedom, whereas pseudo-spin dynamics retains (as is conventional)
an implicit coordinate dependence. We show that magnetic field inhomogeneity
and spin-orbit interaction result in a non-unitary evolution in pure-spin
dynamics, whereas these interactions contribute to the effective pseudo-spin
Hamiltonian via terms that are asymmetric in spin permutations, in particular,
the Dzyaloshinskii-Moriya (DM) spin-orbit interaction. We numerically
investigate the non-unitary effects in the dynamics of the triplet states
population, purity, and Lamb energy shift, as a function of interdot distance
and magnetic field difference. The spin-orbit interaction is found to produce
effects of roughly four orders of magnitude smaller than those due to magnetic
field difference in the pure-spin model. We estimate the spin-orbit interaction
magnitude in the DM-interaction term. Our estimate gives a smaller value than
that recently obtained by Kavokin [Phys. Rev. B 64, 075305 (2001)], who did not
include double occupancy effects. We show that a necessary and sufficient
condition for obtaining a universal set of quantum logic gates, involving only
two spins, in both pure- and pseudo-spin models is that the magnetic field
inhomogeneity and the Heisenberg interaction are both non-vanishing. We also
briefly analyze pure-spin dynamics in the electron on liquid helium system
recently proposed by Lyon [Phys. Rev. A 74, 052338 (2006)].",0709.3685v1
2010-08-12,"Semiconductor Spin Noise Spectroscopy: Fundamentals, Accomplishments, and Challenges","Semiconductor spin noise spectroscopy (SNS) has emerged as a unique
experimental tool that utilizes spin fluctuations to provide profound insight
into undisturbed spin dynamics in doped semiconductors and semiconductor
nanostructures. The technique maps ever present stochastic spin polarization of
free and localized carriers at thermal equilibrium via the Faraday effect onto
the light polarization of an off-resonant probe laser and was transferred from
atom optics to semiconductor physics in 2005. The inimitable advantage of spin
noise spectroscopy to all other probes of semiconductor spin dynamics lies in
the fact that in principle no energy has to be dissipated in the sample, i.e.,
SNS exclusively yields the intrinsic, undisturbed spin dynamics and promises
optical non-demolition spin measurements for prospective solid state based
optical spin quantum information devices. SNS is especially suitable for small
electron ensembles as the relative noise increases with decreasing number of
electrons. In this review, we first introduce the basic principles of SNS and
the difference in spin noise of donor bound and of delocalized conduction band
electrons. We continue the introduction by discussing the spectral shape of
spin noise and prospects of spin noise as a quantum interface between light and
matter. In the main part, we give a short overview about spin relaxation in
semiconductors and summarize corresponding experiments employing SNS. Finally,
we give in-depth insight into the experimental aspects and discuss possible
applications of SNS.",1008.2191v2
2017-01-20,A Unified Stochastic Formulation of Dissipative Quantum Dynamics. II. Beyond Linear Response of Spin Baths,"We use the ""generalized hierarchical equation of motion"" proposed in Paper I
to study decoherence in a system coupled to a spin bath. The present
methodology allows a systematic incorporation of higher order anharmonic
effects of the bath in dynamical calculations. We investigate the leading order
corrections to the linear response approximations for spin bath models. Two
types of spin-based environments are considered: (1) a bath of spins
discretized from a continuous spectral density and (2) a bath of physical spins
such as nuclear or electron spins. The main difference resides with how the
bath frequency and the system-bath coupling parameters are chosen to represent
an environment. When discretized from a continuous spectral density, the
system-bath coupling typically scales as $\sim 1/\sqrt{N_B}$ where $N_B$ is the
number of bath spins. This scaling suppresses the non-Gaussian characteristics
of the spin bath and justify the linear response approximations in the
thermodynamic limit. For the physical spin bath models, system-bath couplings
are directly deduced from spin-spin interactions with no reason to obey the
$1/\sqrt{N_B}$ scaling. It is not always possible to justify the linear
response approximations. Furthermore, if the spin-spin Hamiltonian and/or the
bath parameters are highly symmetrical, these additional constraints generate
non-Markovian and persistent dynamics that is beyond the linear response
treatments.",1701.05713v1
2018-01-30,Controlled spatial separation of spins and coherent dynamics in spin-orbit-coupled nanostructures,"The spatial separation of electron spins followed by the control of their
individual spin dynamics has recently emerged as an essential ingredient in
many proposals for spin-based technologies because it would enable both of the
two spin species to be simultaneously utilized, distinct from most of the
current spintronic studies and technologies wherein only one spin species could
be handled at a time. Here we demonstrate that the spatial spin splitting of a
coherent beam of electrons can be achieved and controlled using the interplay
between an external magnetic field and Rashba spin-orbit interaction in
semiconductor nanostructures. The technique of transverse magnetic focusing is
used to detect this spin separation. More notably, our ability to engineer the
spin-orbit interactions enables us to simultaneously manipulate and probe the
coherent spin dynamics of both spin species and hence their correlation, which
could open a route towards spintronics and spin-based quantum information
processing.",1801.10148v1
2018-09-24,Quantum spin-transfer torque induced nonclassical magnetization dynamics and electron-magnetization entanglement,"The standard spin-transfer torque (STT)---where spin-polarized current drives
dynamics of magnetization viewed as a classical vector---requires
noncollinearity between electron spins carried by the current and magnetization
of a ferromagnetic layer. However, recent experiments [A. Zholud et al., Phys.
Rev. Lett. 119, 257201 (2017)] observing magnetization dynamics in spin valves
at cryogenic temperatures, even when electron spin is collinear to
magnetization, point at overlooked quantum effects in STT which can lead to
highly nonclassical magnetization states. Using fully quantum many-body
treatment, where an electron injected as spin-polarized wave packet interacts
with local spins comprising the anisotropic quantum Heisenberg ferromagnetic
chain, we define quantum STT as any time evolution of local spins due to
initial many-body state not being an eigenstate of electron+local-spins system.
For time evolution caused by injected spin-down electron scattering off local
up-spins, entanglement between electron subsystem and local spins subsystem
takes place leading to decoherence and, therefore, shrinking of the total
magnetization but without rotation from its initial orientation which explains
the experiments. Furthermore, the same processes---entanglement and thereby
induced decoherence---are present also in standard noncollinear geometry,
together with the usual magnetization rotation. This is because STT in quantum
many-body picture is caused only by electron spin-down factor state, and the
only difference between collinear and noncollinear geometries is in relative
size of the contribution of initial many-body state containing such factor
state to superpositions of separable many-body quantum states generated during
time evolution.",1809.09090v1
2020-12-04,Robust Spin Interconnect with Isotropic Spin Dynamics in Chemical Vapour Deposited Graphene Layers and Boundaries,"The utilization of large-area graphene grown by chemical vapour deposition
(CVD) is crucial for the development of scalable spin interconnects in
all-spin-based memory and logic circuits. However, the fundamental influence of
the presence of multilayer graphene patches and their boundaries on spin
dynamics has not been addressed yet, which is necessary for basic understanding
and application of robust spin interconnects. Here, we report universal spin
transport and dynamic properties in specially devised single layer, bi-layer,
and tri-layer graphene channels and their layer boundaries and folds that are
usually present in CVD graphene samples. We observe uniform spin lifetime with
isotropic spin relaxation for spins with different orientations in graphene
layers and their boundaries at room temperature. In all the inhomogeneous
graphene channels, the spin lifetime anisotropy ratios for spins polarized
out-of-plane and in-plane are measured to be close to unity. Our analysis shows
the importance of both Elliott-Yafet and Dyakonov-Perel mechanisms, with an
increasing role of the latter mechanism in multilayer channels. These results
of universal and isotropic spin transport on large-area inhomogeneous CVD
graphene with multilayer patches and their boundaries and folds at room
temperature prove its outstanding spin interconnect functionality, beneficial
for the development of scalable spintronic circuits.",2012.02674v1
2021-09-14,The implications of high BH spins on the origin of BH-BH mergers,"The LIGO/Virgo collaboration has reported 50 black hole-black hole (BH-BH)
mergers and 8 candidates recovered from digging deeper into the detectors
noise. The majority of these mergers have low effective spins pointing toward
low BH spins and efficient angular momentum transport in massive stars as
proposed by several models (e.g., the Tayler-Spruit dynamo). However, out of
these 58 mergers, 7 are consistent with having high effective spin parameter
(chi_eff>0.3). Additionally, 2 events seem to have high effective spins sourced
from the spin of the primary (more massive) BH. These particular observations
could be used to discriminate between the isolated binary and dynamical
formation channels. It might seem that high BH spins point to a dynamical
origin if angular momentum transport in stars is efficient and forms
low-spinning BHs. In such a case dynamical formation is required to produce
second and third generations of BH-BH mergers with typically high-spinning BHs.
Here we show, however, that isolated binary BH-BH formation also naturally
reproduces such highly spinning BHs. Our models start with efficient angular
momentum transport in massive stars that is needed to reproduce the majority of
BH-BH mergers with low effective spins. Later, some of the binaries are subject
to a tidal spin-up allowing the formation of a moderate fraction (~10%) of
BH-BH mergers with high effective spins (chi_eff>=0.4-0.5). In addition,
isolated binary evolution can produce a small fraction of BH-BH mergers with
almost maximally spinning primary BHs. Therefore, the formation scenario of
these atypical BH-BH mergers remains to be found.",2109.06872v2
2023-04-02,Interedge spin resonance in the Kitaev quantum spin liquid,"The Kitaev model offers a platform for quantum spin liquids (QSLs) with
fractional excitations, itinerant Majorana fermions and localized fluxes. Since
these fractional excitations could be utilized for quantum computing, how to
create, observe, and control them through the spin degree of freedom is a
central issue. Here, we study dynamical spin transport in a wide range of
frequency for the Kitaev-Heisenberg model, by applying an AC magnetic field to
an edge of the system. We find that, in the Kitaev QSL phase, spin
polarizations at the other edge are resonantly induced in a specific spin
component, even though the static spin correlations are vanishingly small. This
interedge spin resonance appears around the input frequency over the broad
frequency range. Comparing with the dynamical spin correlations, we clarify
that the resonance is governed by the itinerant Majorana fermions with a broad
continuum excitation spectrum, which can propagate over long distances,
although it vanishes for the pure Kitaev model because of accidental degeneracy
and requires weak Heisenberg interactions. We also find that the spin
polarizations in the other spin components are weakly induced at an almost
constant frequency close to the excitation gap of the localized fluxes,
irrespective of the input frequency. These results demonstrate that the
dynamical spin transport is a powerful probe of the fractional excitations in
the Kitaev QSL. Possible experimental realization of the interedge spin
resonance is discussed.",2304.00528v2
2022-05-16,Emergent tracer dynamics in constrained quantum systems,"We show how the tracer motion of tagged, distinguishable particles can
effectively describe transport in various homogeneous quantum many-body systems
with constraints. We consider systems of spinful particles on a one-dimensional
lattice subjected to constrained spin interactions, such that some or even all
multipole moments of the effective spin pattern formed by the particles are
conserved. On the one hand, when all moments - and thus the entire spin pattern
- are conserved, dynamical spin correlations reduce to tracer motion
identically, generically yielding a subdiffusive dynamical exponent $z=4$. This
provides a common framework to understand the dynamics of several constrained
lattice models, including models with XNOR or $tJ_z$ - constraints. We consider
random unitary circuit dynamics with such a conserved spin pattern and use the
tracer picture to obtain exact expressions for their late-time dynamical
correlations. Our results can also be extended to integrable quantum many-body
systems that feature a conserved spin pattern but whose dynamics is insensitive
to the pattern, which includes for example the folded XXZ spin chain. On the
other hand, when only a finite number of moments of the pattern are conserved,
the dynamics is described by a convolution of the internal hydrodynamics of the
spin pattern with a tracer distribution function. As a consequence, we find
that the tracer universality is robust in generic systems if at least the
quadrupole moment of the pattern remains conserved. In cases where only total
magnetization and dipole moment of the pattern are constant, we uncover an
intriguing coexistence of two processes with equal dynamical exponent but
different scaling functions, which we relate to phase coexistence at a first
order transition.",2205.07901v1
2008-12-27,Jordan-Wigner Fermionization and the Theory of Low-Dimensional Quantum Spin Models. Dynamic Properties,"The Jordan-Wigner transformation is known as a powerful tool in condensed
matter theory, especially in the theory of low-dimensional quantum spin
systems. The aim of this chapter is to review the application of the
Jordan-Wigner fermionization technique for calculating dynamic quantities of
low-dimensional quantum spin models. After a brief introduction of the
Jordan-Wigner transformation for one-dimensional spin one-half systems and some
of its extensions for higher dimensions and higher spin values we focus on the
dynamic properties of several low-dimensional quantum spin models. We start
from the famous s=1/2 XX chain. As a first step we recall well-known results
for dynamics of the z-spin-component fluctuation operator and then turn to the
dynamics of the dimer and trimer fluctuation operators. The dynamics of the
trimer fluctuations involves both the two-fermion (one particle and one hole)
and the four-fermion (two particles and two holes) excitations. We discuss some
properties of the two-fermion and four-fermion excitation continua. The
four-fermion dynamic quantities are of intermediate complexity between simple
two-fermion (like the zz dynamic structure factor) and enormously complex
multi-fermion (like the xx or xy dynamic structure factors) dynamic quantities.
Further we discuss the effects of dimerization, anisotropy of XY interaction,
and additional Dzyaloshinskii-Moriya interaction on various dynamic quantities.
Finally we consider the dynamic transverse spin structure factor
$S_{zz}({\bf{k}},\omega)$ for the s=1/2 XX model on a spatially anisotropic
square lattice which allows one to trace a one-to-two-dimensional crossover in
dynamic quantities.",0812.4750v1
2011-06-16,Spin-phonon coupling in single Mn doped CdTe quantum dot,"The spin dynamics of a single Mn atom in a laser driven CdTe quantum dot is
addressed theoretically. Recent experimental
results\cite{Le-Gall_PRL_2009,Goryca_PRL_2009,Le-Gall_PRB_2010}show that it is
possible to induce Mn spin polarization by means of circularly polarized
optical pumping. Pumping is made possible by the faster Mn spin relaxation in
the presence of the exciton. Here we discuss different Mn spin relaxation
mechanisms. First, Mn-phonon coupling, which is enhanced in the presence of the
exciton. Second, phonon-induced hole spin relaxation combined with carrier-Mn
spin flip coupling and photon emission results in Mn spin relaxation. We model
the Mn spin dynamics under the influence of a pumping laser that injects
excitons into the dot, taking into account exciton-Mn exchange and phonon
induced spin relaxation of both Mn and holes. Our simulations account for the
optically induced Mn spin pumping.",1106.3188v1
2011-12-29,Coherent spin dynamics of electrons and holes in semiconductor quantum wells and quantum dots under periodical optical excitation: resonant spin amplification versus spin mode-locking,"The coherent spin dynamics of resident carriers, electrons and holes, in
semiconductor quantum structures is studied by periodical optical excitation
using short laser pulses and in an external magnetic field. The generation and
dephasing of spin polarization in an ensemble of carrier spins, for which the
relaxation time of individual spins exceeds the repetition period of the laser
pulses, are analyzed theoretically. Spin polarization accumulation is
manifested either as resonant spin amplification or as mode-locking of carrier
spin coherences. It is shown that both regimes have the same origin, while
their appearance is determined by the optical pump power and the spread of spin
precession frequencies in the ensemble.",1112.6404v1
2012-11-01,Dynamically-generated pure spin current in single-layer graphene,"The conductance mismatch problem limits the spin-injection efficiency
significantly, and spin-injection into graphene has been usually requiring
high-quality tunnel barriers to circumvent the conductance mismatch. We
introduce a novel approach, which enables generation of a pure spin current
into single-layer graphene (SLG) free from electrical conductance mismatch by
using dynamical spin injection. Experimental demonstration of
spin-pumping-induced spin current generation and spin transport in SLG at room
temperature was successfully achieved and the spin coherence was estimated to
be 1.36 {\mu}m by using a conventional theoretical model based on
Landau-Lifshitz-Gilbert equation. The spin coherence is proportional to the
quality of SLG, which indicates that spin relaxation in SLG is governed by the
Elliot-Yafet mechanism as was reported.",1211.0124v1
2013-10-17,Electrical Detection of Direct and Alternating Spin Current Injected from a Ferromagnetic Insulator into a Ferromagnetic Metal,"We report room temperature electrical detection of spin injection from a
ferromagnetic insulator (YIG) into a ferromagnetic metal (Permalloy, Py).
Non-equilibrium spins with both static and precessional spin polarizations are
dynamically generated by the ferromagnetic resonance of YIG magnetization, and
electrically detected by Py as dc and ac spin currents, respectively. The dc
spin current is electrically detected via the inverse spin Hall effect of Py,
while the ac spin current is converted to a dc voltage via the spin
rectification effect of Py which is resonantly enhanced by dynamic exchange
interaction between the ac spin current and the Py magnetization. Our results
reveal a new path for developing insulator spintronics, which is distinct from
the prevalent but controversial approach of using Pt as the spin current
detector.",1310.4840v1
2016-06-23,Spin-Hall nano-oscillator with oblique magnetization and Dzyaloshinskii-Moriya interaction as generator of skyrmions and nonreciprocal spin-waves,"Spin-Hall oscillators are promising sources of spin-wave signals for
magnonics applications, and can serve as building blocks for magnonic logic in
ultralow power computation devices. Here, we analytically and micromagnetically
study magnetization dynamics excited in a Spin-Hall oscillator with oblique
magnetization when the spin-Hall effect and interfacial Dzyaloshinskii-Moriya
interaction act simultaneously. Our key results are (i) excitation of
nonreciprocal spin-waves propagating perpendicularly to the in-plane projection
of the static magnetization, (ii) skyrmions generation by pure spin-current,
(iii) excitation of a new spin-wave mode with a spiral spatial profile
originating from a gyrotropic rotation of a dynamical skyrmion. These results
demonstrate that Spin-Hall oscillators can be used as generators of magnetic
skyrmions and different types of propagating spin-waves for magnetic data
storage and signal processing applications.",1606.07280v1
2016-06-27,Supercurrent-Induced Spin-Orbit Torques,"We theoretically investigate the supercurrent-induced magnetization dynamics
of a two-dimensional lattice of ferromagnetically ordered spins placed on a
conventional superconductor with broken spatial inversion symmetry and strong
spin-orbit coupling. We develop a phenomenological description of the coupled
dynamics of the superconducting condensate and the spin system, and demonstrate
that supercurrents produce a reactive spin-orbit torque on the magnetization.
By performing a microscopic self-consistent calculation, we show that the
spin-orbit torque originates from a spin-polarization of the Cooper pairs due
to current-induced spin-triplet correlations. Interestingly, we find that there
exists an intrinsic limitation for the maximum achievable spin-orbit torque,
which is determined by the coupling strength between the condensate and the
spin system. In proximitized hole-doped semiconductors, the maximum achievable
spin-orbit torque field is estimated to be on the order of $0.16$ mT, which is
comparable to the critical field for current-induced magnetization switching in
ferromagnetic semiconductors.",1606.08470v1
2010-05-28,Spinning compact binary inspiral II: Conservative angular dynamics,"We establish the evolution equations of the set of independent variables
characterizing the 2PN rigorous conservative dynamics of a spinning compact
binary, with the inclusion of the leading order spin-orbit, spin-spin and mass
quadrupole - mass monopole effects, for generic (noncircular, nonspherical)
orbits. More specifically, we give a closed system of first order ordinary
differential equations for the orbital elements of the osculating ellipse and
for the angles characterizing the spin orientations with respect to the
osculating orbit. We also prove that (i) the relative angle of the spins stays
constant for equal mass black holes, irrespective of their orientation, and
(ii) the special configuration of equal mass black holes with equal, but
antialigned spins, both laying in the plane of motion (leading to the largest
recoil found in numerical simulations) is preserved at 2PN level of accuracy,
with leading order spin-orbit, spin-spin and mass quadrupolar contributions
included.",1005.5330v2
2017-04-13,Spin pumping into superconductors: A new probe of spin dynamics in a superconducting thin film,"Spin pumping refers to the microwave-driven spin current injection from a
ferromagnet into the adjacent target material. We theoretically investigate the
spin pumping into superconductors by fully taking account of impurity
spin-orbit scattering that is indispensable to describe diffusive spin
transport with finite spin diffusion length. We calculate temperature
dependence of the spin pumping signal and show that a pronounced coherence peak
appears immediately below the superconducting transition temperature Tc, which
survives even in the presence of the spin-orbit scattering. The phenomenon
provides us with a new way of studying the dynamic spin susceptibility in a
superconducting thin film. This is contrasted with the nuclear magnetic
resonance technique used to study a bulk superconductor.",1704.04303v2
2019-10-14,Nonlocal Spin Dynamics in the Crossover from Diffusive to Ballistic Transport,"Improved fabrication techniques have enabled the possibility of ballistic
transport and unprecedented spin manipulation in ultraclean graphene devices.
Spin transport in graphene is typically probed in a nonlocal spin valve and is
analyzed using spin diffusion theory, but this theory is not necessarily
applicable when charge transport becomes ballistic or when the spin diffusion
length is exceptionally long. Here, we study these regimes by performing
quantum simulations of graphene nonlocal spin valves. We find that conventional
spin diffusion theory fails to capture the crossover to the ballistic regime as
well as the limit of long spin diffusion length. We show that the latter can be
described by an extension of the current theoretical framework. Finally, by
covering the whole range of spin dynamics, our study opens a new perspective to
predict and scrutinize spin transport in graphene and other two-dimensional
material-based ultraclean devices.",1910.06194v3
2020-01-24,Optical Resonance Shift Spin Noise Spectroscopy,"Quantum spin fluctuations provide a unique way to study spin dynamics without
system perturbation. Here we put forward an optical resonance shift spin noise
spectroscopy as a powerful tool to measure the spin noise of various systems
from magnetic impurities in solids to free atoms and molecules. The quantum
spin fluctuations in these systems can shift the optical resonances by more
than the homogeneous linewidth and produce huge Faraday rotation noise. We
demonstrate, that the resonance shift spin noise spectroscopy gives access to
the high order spin correlators, which contain complete information about the
spin dynamics in contrast with the second order correlator measured by
conventional Pauli-blocking spin noise spectroscopy. The high order quantum
spin correlators manifest themselves as a comb of peaks in the Faraday rotation
noise spectra in transverse magnetic field. This effect is closely related with
the multispin flip Raman scattering observed in the Mn-doped nanostructures.",2001.09060v1
2019-03-26,Nuclear spin assisted quantum tunnelling of magnetic monopoles in spin ice,"Extensive work on single molecule magnets has identified a fundamental mode
of relaxation arising from the nuclear-spin assisted quantum tunnelling of
nearly independent and quasi-classical magnetic dipoles. Here we show that
nuclear-spin assisted quantum tunnelling can also control the dynamics of
purely emergent excitations: magnetic monopoles in spin ice. Our low
temperature experiments were conducted on canonical spin ice materials with a
broad range of nuclear spin values. By measuring the magnetic relaxation, or
monopole current, we demonstrate strong evidence that dynamical coupling with
the hyperfine fields bring the electronic spins associated with magnetic
monopoles to resonance, allowing the monopoles to hop and transport magnetic
charge. Our result shows how the coupling of electronic spins with nuclear
spins may be used to control the monopole current. It broadens the relevance of
the assisted quantum tunnelling mechanism from single molecular spins to
emergent excitations in a strongly correlated system.",1903.11122v1
2019-04-02,Electronic spin-spin decoherence contribution in molecular qubits by quantum unitary spin dynamics,"The realisation of quantum computers based on molecular electronic spins
requires the design of qubits with very long coherence times, T2. Dephasing can
proceed over several different microscopic pathways, active at the same time
and in different regimes. This makes the rationalisation of the dephasing
process not straightforward. Here we present a computational methodology able
to address spin decoherence processes for a general ensemble of spins. The
method consists in the propagation of the unitary quantum spin dynamics on a
reduced Hilbert space. Then we study the dependence of spin dephasing over the
magnetic dilution for a crystal of Vanadyl-based molecular qubits. Our results
show the importance of long-range electronic spin-spin interactions and their
effect on the shape of the spin-echo signal.",1904.01331v1
2019-12-19,Spin rotation by resonant electric field in few-level quantum dots: Floquet dynamics and tunneling,"We study electric dipole spin resonance caused by sub-terahertz (THz)
radiation in a multilevel finite-size quantum dot formed in a nanowire focusing
on the range of driving electric fields amplitudes where a strong interplay
between the Rabi spin oscillations and tunneling from the dot to continuum
states can occur. A strong effect of the tunneling on the spin evolution in
this regime occurs due to formation of mixed spin states. As a result, the
tunneling strongly limits possible spin manipulations time. We demonstrate a
backaction of the spin dynamics on the tunneling and position of the electron.
The analysis of the efficiency of the spin manipulation in terms of the system
energy shows that tunneling decreases this efficiency. Fourier spectra of the
time-dependent expectation value of the electron position show a strong effect
of the spin-orbit coupling on their low-frequency components. This results can
be applied to operational properties of spin-based nanodevices and extending
the range of possible spin resonance frequencies to the THz domain.",1912.09054v2
2021-03-22,Dynamics of one-dimensional spin models under the line-graph operator,"We investigate the application of the line-graph operator to one-dimensional
spin models with periodic boundary conditions. The spins (or interactions) in
the original spin structure become the interactions (or spins) in the resulting
spin structure. We identify conditions which ensure that each new spin
structure is stable, that is, its spin configuration minimises its internal
energy. Then, making a correspondence between spin configurations and binary
sequences, we propose a model of information growth and evolution based on the
line-graph operator. Since this operator can generate frustrations in newly
formed spin chains, in the proposed model such frustrations are immediately
removed. Also, in some cases, the previously frustrated chains are allowed to
recombine into new stable chains. As a result, we obtain a population of spin
chains whose dynamics is studied using Monte Carlo simulations. Lastly, we
discuss potential applications to areas of research such as combinatorics and
theoretical biology.",2103.12034v1
2022-03-19,Spin wave excitation and directional propagation in presence of magnetic charges in square artificial spin ice,"Artificial spin ice is a special class of engineered lattice of highly shape
anisotropic single domain magnetic nanostructures which is used as one of the
model systems to study the spin ice behavior observed in pyrochlore oxides. The
nanomagnets interact via dipolar interaction which results in correlated
magnetization dynamics exhibiting macroscopic spin configuration states. Here,
we exploit the interplay of underlying magnetic state and external bias field
orientation to study controlled spin wave propagation in square Artificial Spin
Ice (sASI) by performing detailed micromagnetic simulations. We report that
careful selection of vertices with local magnetic charges can effectively
direct the anisotropic spin wave in presence of an external field. Further, we
explore the influence of local charges due to the excited state in
even-coordinated vertices as well as uncompensated charges due to
odd-coordinated vertices on spin wave behavior. Our studies suggest that there
is no perceptible difference on spin wave dynamical behavior due to the origin
of local magnetic charge in sASI. Our results of controlled and directional
spin wave propagation in sASI system may be useful for low-power consumption
based all magnonic on-chip devices.",2203.10345v1
2004-11-28,Non-Markovian dynamics of a localized electron spin due to the hyperfine interaction,"We review our theoretical work on the dynamics of a localized electron spin
interacting with an environment of nuclear spins. Our perturbative calculation
is valid for arbitrary polarization p of the nuclear spin system and arbitrary
nuclear spin I in a sufficiently large magnetic field. In general, the electron
spin shows rich dynamics, described by a sum of contributions with exponential
decay, non-exponential decay, and undamped oscillations. We have found an
abrupt crossover in the long-time spin dynamics at a critical shape and
dimensionality of the electron envelope wave function. We conclude with a
discussion of our proposed scheme to measure the relevant dynamics using a
standard spin-echo technique.",0411690v1
2009-10-20,Bifurcation and chaos in spin-valve pillars in a periodic applied magnetic field,"We study the bifurcation and chaos scenario of the macro-magnetization vector
in a homogeneous nanoscale-ferromagnetic thin film of the type used in
spin-valve pillars. The underlying dynamics is described by a generalized
Landau-Lifshitz-Gilbert (LLG) equation. The LLG equation has an especially
appealing form under a complex stereographic projection, wherein the
qualitative equivalence of an applied field and a spin-current induced torque
is transparent. Recently chaotic behavior of such a spin vector has been
identified by Zhang and Li using a spin polarized current passing through the
pillar of constant polarization direction and periodically varying magnitude,
owing to the spin-transfer torque effect. In this paper we show that the same
dynamical behavior can be achieved using a periodically varying applied
magnetic field, in the presence of a constant DC magnetic field and constant
spin current, which is technically much more feasible, and demonstrate
numerically the chaotic dynamics in the system for an infinitely thin film.
Further, it is noted that in the presence of a nonzero crystal anisotropy field
chaotic dynamics occurs at much lower magnitudes of the spin-current and DC
applied field.",0910.3776v1
2010-02-13,Electronic Dynamics Due to Exchange Interaction with Holes in Bulk GaAs,"We present an investigation of electron-spin dynamics in p-doped bulk GaAs
due to the electron-hole exchange interaction, aka the Bir-Aronov-Pikus
mechanism. We discuss under which conditions a spin relaxation times for this
mechanism is, in principle, accessible to experimental techniques, in
particular to 2-photon photoemission, but also Faraday/Kerr effect
measurements. We give numerical results for the spin relaxation time for a
range of p-doping densities and temperatures. We then go beyond the relaxation
time approximation and calculate numerically the spin-dependent electron
dynamics by including the spin-flip electron-hole exchange scattering and
spin-conserving carrier Coulomb scattering at the level of Boltzmann scattering
integrals. We show that the electronic dynamics deviates from the simple
spin-relaxation dynamics for electrons excited at high energies where the
thermalization does not take place faster than the spin relaxation time. We
also present a derivation of the influence of screening on the electron-hole
exchange scattering and conclude that it can be neglected for the case of GaAs,
but may become important for narrow-gap semiconductors.",1002.2699v1
2016-03-10,Observation of low frequency spin dynamics in INVAR Fe$_{65}$Ni$_{35}$,"We present ferromagnetic neutron spin echo measurements and muon spin
relaxation ($\mu$SR) measurements of the spin dynamics in the ordered phase of
the metallic alloy INVAR Fe$_{65}$Ni$_{35}$. Both techniques display evidence
of slow spin dynamics in the ordered phase which could be associated with the
INVAR effect. Zero field (ZF) and longitudinal field $\mu$SR measurements
suggest the presence of two separate timescales of slow spin-dynamics in the
ordered phase; a fast component corresponding to that observed in our
neutron-spin-echo measurements and a second slow component which may be related
to the ""cluster"" spin-fluctuations or to the dynamics of disordered local
moments or both as suggested by previous neutron scattering measurements and
recent theoretical studies.",1603.03334v2
2017-10-26,Spin dynamics in MgO based magnetic tunnel junctions with dynamical exchange coupling,"We study the spin dynamics in Fe|MgO|Fe tunnel junction with the dynamical
exchange coupling by coupled Landau-Lifshitz-Gilbert equations. The effects of
spin pumping on the spin dynamics are investigated in detail. It is observed
that the spin pumping can stabilize a quasi-antiparallel state rather than a
quasi-parallel one. More interestingly, our work suggests that the spin pumping
torque can efficiently modulate the magnetization, similar to the
thermal-bias-driven and electricbias-driven spin torques.",1710.09666v2
2019-03-22,Exceptional points in classical spin dynamics,"Non-conservative physical systems admit a special kind of spectral
degeneracy, known as exceptional point (EP), at which eigenvalues and
eigenvectors of the corresponding non-Hermitian Hamiltonian coalesce. Dynamical
parametric encircling of the EP can lead to non-adiabatic evolution associated
with a state flip, a sharp transition between the resonant modes. Physical
consequences of the dynamical encircling of EPs in open dissipative systems
have been explored in optics and photonics. Building on the recent progress in
understanding the parity-time (PT)-symmetric dynamics in spin systems, we use
topological properties of EPs to implement chiral non-reciprocal transmission
of a spin through the material with non-uniform magnetization, like helical
magnet. We consider an exemplary system, spin-torque-driven single spin
described by the time-dependent non-Hermitian Hamiltonian. We show that
encircling individual EPs in parameter space results in non-reciprocal spin
dynamics and find the range of optimal protocol parameters for high-efficiency
asymmetric spin filter based on this effect. Our findings offer a platform for
non-reciprocal spin devices for spintronics and magnonics.",1903.09729v2
2020-06-08,Time-dependent spintronic anisotropy in magnetic molecules,"We theoretically study the quench dynamics of induced anisotropy of a
large-spin magnetic molecule coupled to spin-polarized ferromagnetic leads. The
real-time evolution is calculated by means of the time-dependent density-matrix
numerical renormalization group method implemented within the matrix product
states framework, which takes into account all correlations in very accurate
manner. We determine the system's response to a quench in the spin-dependent
coupling to ferromagnetic leads. In particular, we focus on the transient
dynamics associated with crossing from the weak to the strong coupling regime,
where the Kondo correlations become important. The dynamics is examined by
calculating the time-dependent expectation values of the spin-quadrupole moment
and the associated spin operators. We identify the relevant time scales
describing the quench dynamics and determine the influence of the molecule's
effective exchange coupling and leads spin-polarization on the dynamical
behavior of the system. Furthermore, the generalization of our predictions for
large values of molecule's spin is considered. Finally, we analyze the effect
of finite temperature and show that it gives rise to a reduction of magnetic
anisotropy by strong suppression of the time-dependent spin-quadrupole moment
due to thermal fluctuations.",2006.04431v1
2022-04-15,Geometric integration of classical spin dynamics via a mean-field Schrödinger equation,"The Landau-Lifshitz equation describes the time-evolution of magnetic
dipoles, and can be derived by taking the classical limit of a quantum
mechanical spin Hamiltonian. To take this limit, one constrains the many-body
quantum state to a tensor product of coherent states, thereby neglecting
entanglement between sites. Expectation values of the quantum spin operators
produce the usual classical spin dipoles. One may also consider expectation
values of polynomials of the spin operators, leading to quadrupole and
higher-order spin moments, which satisfy a dynamical equation of motion that
generalizes the Landau-Lifshitz dynamics [Zhang and Batista, Phys. Rev. B 104,
104409 (2021)]. Here, we reformulate the dynamics of these $N^2-1$ generalized
spin components as a mean-field Schr\""odinger equation on the $N$-dimensional
coherent state. This viewpoint suggests efficient integration methods that
respect the local symplectic structure of the classical spin dynamics.",2204.07563v2
2023-04-28,Competing signatures of intersite and interlayer spin transfer in the ultrafast magnetization dynamics,"Optically driven intersite and interlayer spin transfer are individually
known as the fastest processes for manipulating the spin order of magnetic
materials on the sub 100 fs time scale. However, their competing influence on
the ultrafast magnetization dynamics remains unexplored. In our work, we show
that optically induced intersite spin transfer (also known as OISTR) dominates
the ultrafast magnetization dynamics of ferromagnetic alloys such as Permalloy
(Ni80Fe20) only in the absence of interlayer spin transfer into a substrate.
Once interlayer spin transfer is possible, the influence of OISTR is
significantly reduced and interlayer spin transfer dominates the ultrafast
magnetization dynamics. This provides a new approach to control the
magnetization dynamics of alloys on extremely short time scales by fine-tuning
the interlayer spin transfer.",2304.14957v1
2024-03-15,Microscopic understanding of NMR signals by dynamic mean-field theory for spins,"A recently developed dynamic mean-field theory for disordered spins
(spinDMFT) is shown to capture the spin dynamics of nuclear spins very well.
The key quantities are the spin autocorrelations. In order to compute the free
induction decay (FID), pair correlations are needed in addition. They can be
computed on spin clusters of moderate size which are coupled to the dynamic
mean fields determined in a first step by spinDMFT. We dub this versatile
approach non-local spinDMFT (nl-spinDMFT). It is a particular asset of
nl-spinDMFT that one knows from where the contributions to the FID stem. We
illustrate the strengths of nl-spinDMFT in comparison to experimental data for
CaF$_2$. Furthermore, spinDMFT provides the dynamic mean-fields explaining the
FID of the nuclear spins in $^{13}$C in adamantane up to some static noise. The
spin Hahn echo in adamantane is free from effects of static noise and agrees
excellently with the spinDMFT results without further fitting.",2403.10465v1
2000-03-29,Ultrafast spin dynamics and critical behavior in half-metallic ferromagnet : Sr_2FeMoO_6,"Ultrafast spin dynamics in ferromagnetic half-metallic compound Sr_2FeMoO_6
is investigated by pump-probe measurements of magneto-optical Kerr effect.
Half-metallic nature of this material gives rise to anomalous thermal
insulation between spins and electrons, and allows us to pursue the spin
dynamics from a few to several hundred picoseconds after the optical
excitation. The optically detected magnetization dynamics clearly shows the
crossover from microscopic photoinduced demagnetization to macroscopic critical
behavior with universal power law divergence of relaxation time for wide
dynamical critical region.",0003467v3
2002-06-29,"Dynamical Decimation Renormalization-Group Technique: Kinetic Gaussian Model on Non-Branching, Braching and Multi-branching Koch Curve","A generalizing formulation of dynamical real-space renormalization that suits
for arbitrary spin systems is suggested. The new version replaces the
single-spin flipping Glauber dynamics with the single-spin transition dynamics.
As an application, in this paper we mainly investigate the critical slowing
down of the Gaussian spin model on three fractal lattices, including
nonbranching, branching and multibranching Koch Curve. The dynamical critical
exponent $z$ is calculated for these lattices using an exact decimation
renormalization transformation in the assumption of the magnetic-like
perturbation, and a universal result $z=1/\nu $ is found.",0207008v1
2001-06-15,"""Dynamical"" non-minimal higher-spin interaction and gyromagnetic ratio g=2","The field-dependent invariant representation (the ""dynamical"" representation)
of the Poincar\'e algebra is considered as a dynamical principle in order to
get the corresponding ""dynamical"" electromagnetic coupling for higher spins
($s\geq 1$). If in lower-spin ($s=0,1/2$) cases the ""dynamical"" coupling is
taken to coincide with the minimal electromagnetic coupling the higher-spin
coupling is inevitably non-minimal, containing a term linear in the field
strength tensor $F_{\mu\nu}$. This term leads to $g=2$.",0106137v1
2009-09-30,A quantum jump description for the non-Markovian dynamics of the spin-boson model,"We derive a time-convolutionless master equation for the spin-boson model in
the weak coupling limit. The temporarily negative decay rates in the master
equation indicate short time memory effects in the dynamics which is explicitly
revealed when the dynamics is studied using the non-Markovian jump description.
The approach gives new insight into the memory effects influencing the spin
dynamics and demonstrates, how for the spin-boson model the the co-operative
action of different channels complicates the detection of memory effects in the
dynamics.",0909.5565v1
2014-12-31,Seeing spin dynamics in atomic gases,"The dynamics of internal spin, electronic orbital, and nuclear motion states
of atoms and molecules have preoccupied the atomic and molecular physics
community for decades. Increasingly, such dynamics are being examined within
many-body systems composed of atomic and molecular gases. Our findings
sometimes bear close relation to phenomena observed in condensed-matter
systems, while on other occasions they represent truly new areas of
investigation. I discuss several examples of spin dynamics that occur within
spinor Bose-Einstein gases, highlighting the advantages of spin-sensitive
imaging for understanding and utilizing such dynamics.",1501.00057v1
2011-06-02,Kinetics of Spin Relaxation in Wires and Channels: Boundary Spin Echo and Tachyons,"In this paper we use a spin kinetic equation to study spin polarization
dynamics in 1D wires and 2D channels. This approach is valid in both diffusive
and ballistic spin transport regimes and, therefore, more general than the
usual spin drift-diffusion equations. In particular, we demonstrate that in
infinite 1D wires with Rashba spin-orbit interaction the exponential spin
relaxation decay can be modulated by an oscillating function. In the case of
spin relaxation in finite length 1D wires, it is shown that an initially
homogeneous spin polarization spontaneously transforms into a persistent spin
helix. An interesting sound waves echo-like behavior of initially localized
spin polarization packet is found in finite length wires. We show that a
propagating spin polarization profile reflects from a system boundary and
returns back to its initial position similarly to the reflectance of sound
waves from an obstacle. Green's function of spin kinetic equation is found for
both finite and infinite 1D systems. Moreover, we demonstrate explicitly that
the spin relaxation in 2D channels with Rashba and Dresselhaus spin-orbit
interactions of equal strength occurs similarly to that in 1D wires of finite
length. Finally, a simple transformation mapping 1D spin kinetic equation into
the Klein-Gordon equation with an imaginary mass is found thus establishing an
interesting connection between semiconductor spintronics and relativistic
quantum mechanics.",1106.0355v1
2015-12-17,Multi-$Q$ hexagonal spin density waves and dynamically generated spin-orbit coupling: time-reversal invariant analog of the chiral spin density wave,"We study hexagonal spin-channel (""triplet"") density waves with commensurate
$M$-point propagation vectors. We first show that the three $Q=M$ components of
the singlet charge density and charge-current density waves can be mapped to
multi-component $Q=0$ nonzero angular momentum order in three dimensions ($3D$)
with cubic crystal symmetry. This one-to-one correspondence is exploited to
define a symmetry classification for triplet $M$-point density waves using the
standard classification of spin-orbit coupled electronic liquid crystal phases
of a cubic crystal. Through this classification we naturally identify a set of
non-coplanar spin density and spin-current density waves: the chiral spin
density wave and its time-reversal invariant analog. These can be thought of as
$3D$ $L=2$ and $L=4$ spin-orbit coupled isotropic $\beta$-phase orders. In
contrast, uniaxial spin density waves are shown to correspond to
$\alpha$-phases. The non-coplanar triple-$M$ spin-current density wave realizes
a novel $2D$ semimetal state with three flavors of four-component spin-momentum
locked Dirac cones, protected by a crystal symmetry akin to non-symmorphic
symmetry, and sits at the boundary between a trivial and topological insulator.
In addition, we point out that a special class of classical spin states,
defined as classical spin states respecting all lattice symmetries up to global
spin rotation, are naturally obtained from the symmetry classification of
electronic triplet density waves. These symmetric classical spin states are the
classical long-range ordered limits of chiral spin liquids.",1512.05673v3
2013-05-21,Transport of spin-anisotropy without spin currents,"We revisit the transport of spin-degrees of freedom across an electrically
and thermally biased tunnel junction between two ferromagnets with
non-collinear magnetizations. Besides the well-known charge and spin currents
we show that a non-zero spin-quadrupole current flows between the ferromagnets.
This tensor-valued current describes the non-equilibrium transport of
spin-anisotropy relating to both local and non-local multi-particle spin
correlations of the circuit. This quadratic spin-anisotropy, quantified in
terms of the spin-quadrupole moment, is fundamentally a two-electron quantity.
In spin-valves with an embedded quantum dot such currents have been shown to
result in a quadrupole accumulation that affects the measurable quantum dot
spin and charge dynamics. The spin-valve model studied here allows fundamental
questions about spin-quadrupole storage and transport to be worked out in
detail, while ignoring the detection by a quantum dot. This physical
understanding of this particular device is of importance for more complex
devices where spin-quadrupole transport can be detected. We demonstrate that,
as far as storage and transport are concerned, the spin anisotropy is only
partly determined by the spin polarization. In fact, for a thermally biased
spin-valve the charge- and spin-current may vanish, while a pure exchange
spin-quadrupole current remains, which appears as a fundamental consequence of
Pauli's principle. We extend the real-time diagrammatic approach to efficiently
calculate the average of multi-particle spin-observables, in particular the
spin-quadrupole current. Although the paper addresses only leading order and
spin-conserving tunneling we formulate the technique for arbitrary order in an
arbitrary, spin-dependent tunnel coupling in a way that lends itself to
extension to quantum-dot spin-valve structures.",1305.4843v1
2010-08-24,Modeling of diffusion of injected electron spins in spin-orbit coupled microchannels,"We report on a theoretical study of spin dynamics of an ensemble of
spin-polarized electrons injected in a diffusive microchannel with linear
Rashba and Dresselhaus spin-orbit coupling. We explore the dependence of the
spin-precession and spin-diffusion lengths on the strengths of spin-orbit
interaction and external magnetic fields, microchannel width, and orientation.
Our results are based on numerical Monte Carlo simulations and on approximate
analytical formulas, both treating the spin dynamics quantum-mechanically. We
conclude that spin-diffusion lengths comparable or larger than the
precession-length occur i) in the vicinity of the persistent spin helix regime
for arbitrary channel width, and ii) in channels of similar or smaller width
than the precession length, independent of the ratio of Rashba and Dresselhaus
fields. For similar strengths of the Rashba and Dresselhaus fields, the
steady-state spin-density oscillates or remains constant along the channel for
channels parallel to the in-plane diagonal crystal directions. An oscillatory
spin-polarization pattern tilted by 45$^{\circ}$ with respect to the channel
axis is predicted for channels along the main cubic crystal directions. For
typical experimental system parameters, magnetic fields of the order of Tesla
are required to affect the spin-diffusion and spin-precession lengths.",1008.4030v2
2018-01-13,Tailoring multilayer quantum wells for spin devices,"The electron spin dynamics in multilayer GaAs/AlGaAs quantum wells,
containing high-mobility dense two-dimensional electron gases, have been
studied using time-resolved Kerr rotation and resonant spin amplification
techniques. The electron spin dynamics was regulated through the wave function
engineering and quantum confinement in multilayer quantum wells. We observed
the spin coherence with a remarkably long dephasing time T2* > 13 ns for the
structure doped beyond metal-insulator transition. Dyakonov-Perel spin
relaxation mechanism, as well as the inhomogeneity of electron g-factor, was
suggested as the major limiting factors for the spin coherence time. In the
metallic regime, we found that the electron-electron collisions become dominant
over microscopic scattering on the electron spin relaxation with the
Dyakonov-Perel mechanism. Furthermore, the data analysis indicated that in our
structure, due to the spin relaxation anisotropy, Dyakonov-Perel spin
relaxation mechanism is efficient for the spins oriented in-plane and
suppressed along the quantum well growth direction resulting in the enhancement
of T2*. Our findings, namely, long-lived spin coherence persisting up to about
room temperature, spin polarization decay time with and without a magnetic
field, the spin-orbit field, single electron relaxation time, transport
scattering time, and the electron-electron Coulomb scattering time highlight
the attractiveness of n-doped multilayer systems for spin devices.",1801.04426v1
2019-10-09,Transverse spin dynamics of light: the generalized spin-momentum locking for structured guided modes,"Quantum spin-Hall effect, a manifestation of topological properties that
govern the behavior of surface states, was studied intensively in condensed
matter physics resulting in the discovery of topological insulators. The
quantum spin-Hall effect of light was introduced for surface plane-waves which
intrinsically carry transverse optical spin, leading to many intriguing
phenomena and applications in unidirectional waveguiding, metrology and quantum
technologies. In addition to spin, optical waves can exhibit complex
topological properties of vectorial electromagnetic fields, associated with
orbital angular momentum or nonuniform intensity variations. Here, by
considering both spin and angular momentum, we demonstrate a generalized
spin-momentum relationship that governs vectorial properties of guided
electromagnetic waves, extending optical quantum spin-Hall effect to a
two-dimensional vector field of structured guided wave. The effect results in
the appearance of the out-of-plane transverse optical spins, which vary
progressively from the 'up' state to the 'down' state around the energy flow,
and their variation is uniquely locked to the energy propagation direction. The
related spin-momentum locking in a chiral spin swirl is demonstrated with four
kinds of surface structured waves and proven both theoretically and
experimentally. The results provide understanding of the spin dynamics in
electromagnetic guided waves and show great importance in spin optics,
topological photonics and optical spin-based devices and techniques.",1910.03904v2
2023-06-13,Nonequilibrium spin transport in integrable and non-integrable classical spin chains,"Anomalous transport in low dimensional spin chains is an intriguing topic
that can offer key insights into the interplay of integrability and symmetry in
many-body dynamics. Recent studies have shown that spin-spin correlations in
spin chains, where integrability is either perfectly preserved or broken by
symmetry-preserving interactions, fall in the Kardar-Parisi-Zhang (KPZ)
universality class. Similarly, energy transport can show ballistic or
diffusive-like behaviour. Although such behaviour has been studied under
equilibrium conditions, no results on nonequilibrium spin transport in
classical spin chains has been reported so far. In this work, we investigate
both spin and energy transport in classical spin chains (integrable and
non-integrable) when coupled to two reservoirs at two different
temperatures/magnetization. In both the integrable case and
broken-integrability (but spin-symmetry preserving), we report anomalous
scaling of spin current with system size ($\mathbb{J}^s \propto L^{-\mu}$) with
an exponent, $\mu \approx 2/3$, falling under the KPZ universality class. On
the other hand, it is noteworthy that energy current remains ballistic
($\mathbb{J}^e \propto L^{-\eta}$ with $\eta \approx 0$) in the purely
integrable case and there is departure from ballistic behaviour ($\eta > 0$)
when integrability is broken regardless of spin-symmetry. Under nonequilibrium
conditions, we have thoroughly investigated spatial profiles of local
magnetization and energy. We find interesting nonlinear spatial profiles which
are hallmarks of anomalous transport. We also unravel subtle striking
differences between the equilibrium and nonequilibrium steady state through the
lens of spatial spin-spin correlations.",2306.07864v1
1993-03-23,Relativistic Dynamics of Spin in Strong External Fields,"The dynamics of relativistic spinning particles in strong external
electromagnetic or gravitational fields is discussed. Spin-orbit coupling is
shown to affect such relativistic phenomena as time-dilation and perihelion
shift. Possible applications include muon decay in a magnetic field and the
dynamics of neutron stars in binary systems.",9303124v1
2000-08-13,Spin-Orbital Motion: Symmetry and Dynamics,"We present the applications of variational--wavelet approach to nonlinear
(rational) model for spin-orbital motion: orbital dynamics and Thomas-BMT
equations for classical spin vector. We represent the solution of this
dynamical system in framework of periodical wavelets via variational approach
and multiresolution.",0008047v1
2003-06-03,The Model of the Theory of the Quantum Brain Dynamics can be cast on the Heisenberg Spin Hamiltonian,"In this note, we show that the model of the quantum brain dynamics can be
cast on a kind of the Heisenberg spin Hamiltonian. Therefore, we would like to
emphasize that the quantum dynamics of brain should be understood by the
physics of quantum spin systems.",0306021v1
2015-11-24,Relaxation dynamics in an isolated long-range Ising chain,"We consider a chain of trapped ions to interact with each other via
long-range interactions. This system can be used to simulate the long-range
Ising model. We study the dynamics of quantum coherence of a single spin in the
chain, where the spins are initially prepared in their upper states. The
relaxation dynamics exhibits due to the genuine long-range interaction. The
degree of quantum coherence of a single spin rapidly decreases and vanishes in
the steady state. However, our numerical result suggests that the conventional
spin chain model, which truncates the interactions between the distant spins,
cannot show the relaxation dynamics. This implies that the usual truncation in
approximating the long-range interaction is not applicable to describing the
non-equilibrium dynamics. The effect of the interaction range on the relaxation
dynamics is studied. The higher relaxation rate will show if a system has a
longer range of interaction. However, it takes a longer relaxation time in the
vicinity of infinite interaction range. We also examine the dynamics of quantum
coherence of a block of spins. Our result may shed light on the relationship
between long-range interaction and the coherence dynamics of a quantum
many-body system.",1511.07582v1
2022-08-03,Ultrafast Demagnetization Dynamics Due to Electron-Electron Scattering and Its Relation to Momentum Relaxation in Ferromagnets,"We analyze theoretically the demagnetization dynamics in a ferromagnetic
model system due to the interplay of spin-orbit coupling and electron-electron
Coulomb scattering. We compute the $k$-resolved electronic reduced spin-density
matrix including precessional dynamics around internal spin-orbit and exchange
fields as well as the electron-electron Coulomb scattering for densities and
spin coherences. Based on a comparison with numerical solutions of the full
Boltzmann scattering integrals, we establish that the $k$-resolved reduced
spin-density matrix dynamics are well described using a simpler generalized
relaxation-time ansatz for the reduced spin-density matrix. This ansatz allows
one to relate the complicated scattering dynamics underlying the
demagnetization dynamics to a physically meaningful momentum relaxation time
$\tau$. Our approach reproduces the behaviors of the demagnetization time
$\tau_{m} \propto 1/\tau$ and $\tau_{m} \propto \tau$ for the limits of short
and long $\tau$, respectively, and is also valid for the intermediate regime.
The ansatz thus provides a tool to include the correct demagnetization behavior
in approaches that treat other contributions to the magnetization dynamics such
as transport or magnon/phonon dynamics.",2208.02356v1
1994-01-29,Strong-Coupling Behavior of Two $t-J$ Chains with Interchain Single Electron Hopping,"Using the fermion-spin transformation to implement spin-charge separation of
constrained electrons, a model of two $t-J$ chains with interchain
single-electron hopping is studied by abelian bosonization. After spin-charge
decoupling the charge dynamics can be trivially solved, while the spin dynamics
is determined by a strong-coupling fixed point where the correlation functions
can be calculated explicitly. This is a generalization of the Luther-Emery line
for two-coupled $t-J$ chains. The interchain single-electron hopping changes
the asymptotic behavior of the interchain spin-spin correlation functions and
the electron Green function, but their exponents are independent of the
coupling strength.",9401070v1
2000-07-27,Single-hole dynamics in dimerized and frustrated spin-chains,"We present a unified account for the coupled single-hole- and spin-dynamics
in the spin-gap phase of dimerized and frustrated spin-chains and two-leg spin
ladders. Based on the strong dimer-limit of a one-dimensional
$t_123$-$J_123$-model a diagrammatic approach is presented which employs a
mapping of the spin-Hamiltonian onto a pseudo-fermion bond-boson model. Results
for the single-hole spectrum are detailed. A finite quasi-particle weight is
observed and studied for a variety of system parameters. A comparison with
existing exact diagonalization data is performed and good agreement is found.",0007447v1
2001-08-11,Spin dynamics from time-dependent spin density-functional theory,"We derive the spin-wave dynamics of a magnetic material from the
time-dependent spin density functional theory in the linear response regime.
The equation of motion for the magnetization includes, besides the static spin
stiffness, a ""Berry curvature"" correction and a damping term. A gradient
expansion scheme based on the homogeneous spin-polarized electron gas is
proposed for the latter two quantities, and the first few coefficients of the
expansion are calculated to second order in the Coulomb interaction.",0108193v1
2003-01-09,Energy dependence of commensurate neutron scattering peak in doped two-leg ladder antiferromagnet Sr_{14-x}Ca_{x}Cu_{24}O_{41},"The dynamical spin response of doped two-leg ladder antiferromagnets is
investigated based on the fermion-spin approach. Our calculations clearly
demonstrate a crossover from the incommensurate antiferromagnetism in the weak
interchain coupling regime to commensurate spin fluctuation in the strong
interchain coupling regime. In particular, the nuclear spin-lattice relaxation
rate extracted from the commensurate spin fluctuation decreases exponentially
with decreasing temperatures. The behaviors of the spin dynamics in the strong
coupling regime are quantitatively close to the experimental results of
Sr_{14-x}Ca_{x}Cu_{24}O_{41}.",0301113v2
2003-06-23,Normal-superfluid interaction dynamics in a spinor Bose gas,"Coherent behavior of spinor Bose-Einstein condensates is studied in the
presence of a significant uncondensed (normal) component. Normal-superfluid
exchange scattering leads to a near-perfect local alignment between the spin
fields of the two components. Through this spin locking, spin-domain formation
in the condensate is vastly accelerated as the spin populations in the
condensate are entrained by large-amplitude spin waves in the normal component.
We present data evincing the normal-superfluid spin dynamics in this regime of
complicated interdependent behavior.",0306584v1
2003-11-17,Spin projection chromatography,"We formulate the many-body spin dynamics at high temperature within the
non-equilibrium Keldysh formalism. For the simplest XY interaction, analytical
expressions in terms of the one particle solutions are obtained for linear and
ring configurations. For small rings of even spin number, the group velocities
of excitations depend on the parity of the total spin projection. This should
enable a dynamical filtering of spin projections with a given parity i.e. a
Spin projection chromatography.",0311395v1
2004-02-16,Selective Dynamic Nuclear Spin Polarization in Spin-Blocked Double-Dot,"We study the mechanism of dynamical nuclear spin polarization by hyperfine
interaction in spin-blocked double quantum dot system. We calculate the
hyperfine transition rates and solve the master equations for the nuclear
spins. Specifically, we incorporate the effects of the nuclear quadrupole
coupling due to the doping-induced local lattice distortion and strain. Our
results show that nuclear quadrupole coupling induced by the 5% indium
substitution can be used to explain the recent experimental observation of
missing arsenic NMR signal in the spin-blocked double dots.",0402428v2
2005-10-20,Low-energy Effective Theory for Spin Dynamics of Fluctuating Stripes,"We derive an effective Hamiltonian for spin dynamics of fluctuating smectic
stripes from the t-J model in the weak coupling limit t >> J. Besides the
modulation of spin magnitude, the high energy hopping term would induce a
low-energy anti-ferromagnetic interaction between two neighboring ``blocks of
spins"". Based on the effective Hamiltonian, we applied the linear spin-wave
theory and found that the spin-wave velocity is almost isotropic for
La_{2-x}Sr_x CuO_4 unless the structural effect is considered. The intensity of
the second harmonic mode is found to be about 10% to that of the fundamental
mode.",0510529v1
2007-03-27,Gauge Field Formulation of Adiabatic Spin Torques,"Previous calculation of spin torques for small-amplitude magnetization
dynamics around a uniformly magnetized state [J. Phys. Soc. Jpn. {\bf 75}
(2006) 113706] is extended here to the case of finite-amplitude dynamics. This
is achieved by introducing an `` adiabatic'' spin frame for conduction
electrons, and the associated SU(2) gauge field. In particular, the Gilbert
damping is shown to arise from the time variation of the spin-relaxation source
terms in this new frame, giving a new physical picture of the damping. The
present method will allow a `` first-principle'' derivation of spin torques
without any assumptions such as rotational symmetry in spin space.",0703705v1
2001-10-15,The Spin,"It is shown that the spin is naturally introduced into classical mechanics if
the latter is formulated as dynamics of the phase space density. It is shown
that the uncertainty principle, as the amendment in this dynamics, restricts
possible spins, and in particular equation for the particle with the spin
$\hbar /2$ is derived. Also equation for the charge with this spin is derived
when electromagnetic field is included. In one example it is shown that the
modulus of the spin changes with the gradient of the magnetic field.",0110090v1
2008-01-11,Giant dynamical Zeeman split in inverse spin valves,"The inversion of a spin valve device is proposed. Opposite to a conventional
spin valve of a non-magnetic spacer sandwiched between two ferromagnetic
metals, an inverse spin valve is a ferromagnet sandwiched between two
non-magnetic metals. It is predicted that, under a bias, the chemical
potentials of spin-up and spin-down electrons in the metals split at
metal-ferromagnet interfaces, a dynamical Zeeman effect. This split is of the
order of an applied bias. Thus, there should be no problem of generating an
$eV$ split that is not possible to be realized on the earth by the usual Zeeman
effect.",0801.1775v1
2008-01-27,Spin dynamics of two-dimensional electrons with Rashba spin-orbit coupling and electron-electron interactions,"We study the spin dynamics of two dimensional electron gases (2DEGs) with
Rashba spin-orbit coupling by taking account of electron-electron interactions.
The diffusion equations for charge and spin densities are derived by making use
of the path-integral approach and the quasiclassical Green's function.
Analyzing the effect of the interactions, we show that the spin-relaxation time
can be enhanced by the electron-electron interaction in the ballistic regime.",0801.4132v2
2008-04-09,Time-dependent current-density-functional theory of spin-charge separation and spin drag in one-dimensional ultracold Fermi gases,"Motivated by the large interest in the non-equilibrium dynamics of
low-dimensional quantum many-body systems, we present a fully-microscopic
theoretical and numerical study of the ""charge"" and ""spin"" dynamics in a
one-dimensional ultracold Fermi gas following a quench. Our approach, which is
based on time-dependent current-density-functional theory, is applicable well
beyond the linear-response regime and produces both spin-charge separation and
spin-drag-induced broadening of the spin packets.",0804.1514v1
2008-05-09,"Spin dynamics in (III,Mn)V ferromagnetic semiconductors: the role of correlations","We address the role of correlations between spin and charge degrees of
freedom on the dynamical properties of ferromagnetic systems governed by the
magnetic exchange interaction between itinerant and localized spins. For this
we introduce a general theory that treats quantum fluctuations beyond the
Random Phase Approximation based on a correlation expansion of the Green's
function equations of motion. We calculate the spin susceptibility, spin--wave
excitation spectrum, and magnetization precession damping. We find that
correlations strongly affect the magnitude and carrier concentration dependence
of the spin stiffness and magnetization Gilbert damping.",0805.1320v2
2008-06-24,Signal propagation in time-dependent spin transport,"This paper analyzes theoretically the signal propagation in spin transport by
modulating the current passing through magnetic multilayers. Using a
macroscopic description of spin transport based on the dynamical Boltzmann
equation, we show that time-dependent spin transport possesses a wave-like
character that leads to modifications of pure spin-diffusion dynamics. In
particular, the wave-like characteristics allow one to extract a finite spin
signal-propagation velocity.",0806.3843v3
2008-12-22,Spin-signal propagation in time-dependent noncollinear spin transport,"Using a macroscopic analysis, we show that time-dependent noncollinear spin
transport possesses a wavelike character. This leads to modifications of pure
spin-diffusion dynamics and allows one to extract a finite spin-signal
propagation velocity. We numerically study the dynamics of a pure spin current
pumped into a nonmagnetic layer for precession frequencies ranging from GHz to
THz.",0812.4215v2
2011-07-23,"Spin, Isospin and Strong Interaction Dynamics","The structure of spin and isospin is analyzed. Although both spin and isospin
are related to the same SU(2) group, they represent different dynamical
effects. The Wigner-Racah algebra is used for providing a description of bound
states of several Dirac particles in general and of the proton state in
particular. Isospin states of the four $\Delta (1232)$ baryons are discussed.
The work explains the small contribution of quarks spin to the overall proton
spin (the proton spin crisis). It is also proved that the addition of QCD's
color is not required for a construction of an antisymmetric state of the
$\Delta ^{++} (1232)$ baryon.",1107.4688v1
2012-11-16,Dependence of the Switching Current Density on the Junction Sizes in Spin Transfer Torque,"We investigate the dependence of switching current density on the junction
sizes in the spin transfer torque nanopillar structures by using micromagnetic
simulations. While the macro spin model predicts weak dependence of switching
current density on the junction sizes, we find that the switching current
density is a sensitive function of the junction sizes. It can be explained with
the complicated spin configurations and dynamics during the switching process.
The detail spin configurations and dynamics are determined by spin wave
excitation with the finite wave vector, which is related with the exchange
coupling energy and junction shape.",1211.3785v1
2016-07-12,Thermal spin dynamics of yttrium iron garnet,"Yttrium Iron Garnet is the prototypical material used to study pure spin
currents. It is a complex material with 20 magnetic atoms in the unit cell.
Almost all theories and experimental analysis approximates this complicated
material to a simple ferromagnet with a single spin wave mode. We use the
method of atomistic spin dynamics to study the temperature evolution of the
full 20 mode exchange spin wave spectrum. Our results show a strong frequency
dependence of the modes in quantitative agreement with neutron scattering
experiments. We find this causes in a reduction in the net spin pumping due to
the thermal occupation of optical modes with the opposite chirality to the FMR
mode.",1607.03263v1
2014-05-16,Inferring hidden states in a random kinetic Ising model: replica analysis,"We consider the problem of predicting the spin states in a kinetic Ising
model when spin trajectories are observed for only a finite fraction of sites.
In a Bayesian setting, where the probabilistic model of the spin dynamics is
assumed to be known, the optimal prediction can be computed from the
conditional (posterior) distribution of unobserved spins given the observed
ones. Using the replica method, we compute the error of the Bayes optimal
predictor for parallel discrete time dynamics in a fully connected spin system
with non symmetric random couplings. The results, exact in the thermodynamic
limit, agree very well with simulations of finite spin systems.",1405.4164v1
2015-12-08,Spin-Directed Momentum Transfers in SIDIS Baryon Production,"The measurement of transverse single-spin asymmetries for baryon production
in the target fragmentation region of semi-inclusive deep-inelastic scattering
(SIDIS), can produce important insight into those nonperturbative aspects of
QCD directly associated with confinement and with the dynamical breaking of
chiral symmetry. We discuss here, interns of spin-directed momentum transfers,
the powerful quantum field-theoretical constraints on the spin-orbit dynamics
underlying these transverse spin observables. The spin-directed momentum
shifts, originating either in the target nucleon or in the QCD jets produced in
the deep inelastic scattering process, represent significant quantum
entanglement effects connecting information from current fragmentation with
observables in target fragmentation.",1512.02557v1
2020-12-15,Dynamically stabilized spin superfluidity in frustrated magnets,"We study the onset of spin superfluidity, namely coherent spin transport
mediated by a topological spin texture, in frustrated exchange-dominated
magnetic systems, engendered by an external magnetic field. We show that for
typical device geometries used in nonlocal magnetotransport experiments, the
magnetic field stabilizes a spin superflow against fluctuations, up to a
critical current. For a given current, the critical field depends on the
precessional frequency of the texture, which can be separately controlled. We
contrast such dynamic stabilization of a spin superfluid to the conventional
approaches based on topological stabilization.",2012.08340v1
2019-11-25,Spin liquids in geometrically perfect triangular antiferromagnets,"The cradle of quantum spin liquids, triangular antiferromagnets show strong
proclivity to magnetic order and require deliberate tuning to stabilize a
spin-liquid state. In this brief review, we juxtapose recent theoretical
developments that trace the parameter regime of the spin-liquid phase, with
experimental results for Co-based and Yb-based triangular antiferromagnets.
Unconventional spin dynamics arising from both ordered and disordered ground
states is discussed, and the notion of a geometrically perfect triangular
system is scrutinized to demonstrate non-trivial imperfections that may assist
magnetic frustration in stabilizing dynamic spin states with peculiar
excitations.",1911.11157v2
2022-06-29,Simulating spin dynamics with quantum computers,"IBM quantum computers are used to simulate the dynamics of small systems of
interacting quantum spins. For time-independent systems with $N\leq 2$ spins,
we construct circuits which compute the exact time evolution at arbitrary times
and allow measurement of spin expectation values. Larger systems with spins
require a the Lie-Trotter decomposition of the time evolution operator, and we
investigate the case of $N=3$ explicitly. Basic readout-error mitigation is
introduced to improve the quality of results run on these noisy devices. The
simulations provide an interesting experimental component to the standard
treatment of quantum spin in an undergraduate quantum mechanics course.",2207.10567v1
2023-06-13,Angle dependence of $^{15}$N nuclear spin dynamics in diamond NV centers,"We report on the dynamics of the Rabi oscillation and the Larmor precession
of $^{15}$N nuclear spin using nonselective short microwave pulses for
initialization of $^{15}$N nuclear spins. We observe the Larmor precession of
$^{15}$N nuclear spin depending on the angle between the applied magnetic field
and the axis of the nitrogen vacancy center. We propose to utilize the change
of the Larmor frequency of the nuclear spins to detect static magnetic fields
at high sensitivity. Our results may contribute to enhancing the sensitivity of
dc magnetic fields and devising novel protocols using $^{15}$N nuclear spin in
nitrogen vacancy centers in diamonds.",2306.07556v1
2024-02-07,SWAP algorithm for lattice spin models,"We adapted the SWAP molecular dynamics algorithm for use in lattice Ising
spin models. We dressed the spins with a randomly distributed length and we
alternated long-range spin exchanges with conventional single spin flip Monte
Carlo updates, both accepted with a stochastic rule which respects detailed
balance. We show that this algorithm, when applied to the bidimensional
Edwards-Anderson model, speeds up significantly the relaxation at low
temperatures and manages to find ground states with high efficiency and little
computational cost. The exploration of spin models should help in understanding
why SWAP accelerates the evolution of particle systems and shed light on
relations between dynamics and free-energy landscapes.",2402.04981v1
2003-09-26,Spin Glasses: Model systems for non-equilibrium dynamics,"Spin glasses are frustrated magnetic systems due to a random distribution of
ferro- and antiferromagnetic interactions. An experimental three dimensional
(3d) spin glass exhibits a second order phase transition to a low temperature
spin glass phase regardless of the spin dimensionality. In addition, the low
temperature phase of Ising and Heisenberg spin glasses exhibits similar
non-equilibrium dynamics and an infinitely slow approach towards a
thermodynamic equilibrium state. There are however significant differences in
the detailed character of the dynamics as to memory and rejuvenation phenomena
and the influence of critical dynamics on the behaviour. In this article, some
aspects of the non-equilibrium dynamics of an Ising and a Heisenberg spin glass
are briefly reviewed and some comparisons are made to other glassy systems that
exhibit magnetic non-equilibrium dynamics.",0309602v1
2004-07-13,Dynamical solutions of a quantum Heisenberg spin glass model,"We consider quantum-dynamical phenomena in the $\mathrm{SU}(2)$, $S=1/2$
infinite-range quantum Heisenberg spin glass. For a fermionic generalization of
the model we formulate generic dynamical self-consistency equations. Using the
Popov-Fedotov trick to eliminate contributions of the non-magnetic fermionic
states we study in particular the isotropic model variant on the spin space.
Two complementary approximation schemes are applied: one restricts the quantum
spin dynamics to a manageable number of Matsubara frequencies while the other
employs an expansion in terms of the dynamical local spin susceptibility. We
accurately determine the critical temperature $T_c$ of the spin glass to
paramagnet transition. We find that the dynamical correlations cause an
increase of $T_c$ by 2% compared to the result obtained in the spin-static
approximation. The specific heat $C(T)$ exhibits a pronounced cusp at $T_c$.
Contradictory to other reports we do not observe a maximum in the $C(T)$-curve
above $T_c$.",0407328v1
2010-04-12,Influence of the particle number on the spin dynamics of ultracold atoms,"We study the dependency of the quantum spin dynamics on the particle number
in a system of ultracold spin-1 atoms within the single-spatial-mode
approximation. We find, for all strengths of the spin-dependent interaction,
convergence towards the mean-field dynamics in the thermodynamic limit. The
convergence is, however, particularly slow when the spin-changing collisional
energy and the quadratic Zeeman energy are equal, i.e. deviations between
quantum and mean-field spin dynamics may be extremely large under these
conditions. Our estimates show, that quantum corrections to the mean-field
dynamics may play a relevant role in experiments with spinor Bose-Einstein
condensates. This is especially the case in the regime of few atoms, which may
be accessible in optical lattices. Here, spin dynamics is modulated by a beat
note at large magnetic fields due to the significant influence of correlated
many-body spin states.",1004.1966v2
2012-06-13,Observation of elastic anomalies driven by coexisting dynamical spin Jahn-Teller effect and dynamical molecular spin state in paramagnetic phase of the frustrated MgCr$_2$O$_4$$,"Ultrasound velocity measurements of magnesium chromite spinel MgCr$_2$O$_4$
reveal elastic anomalies in the paramagnetic phase that are characterized as
due to geometrical frustration. The temperature dependence of the tetragonal
shear modulus $(C_{11}-C_{12})/2$ exhibits huge Curie-type softening, which
should be the precursor to spin Jahn-Teller distortion in the antiferromagnetic
phase. The trigonal shear modulus $C_{44}$ exhibits nonmonotonic temperature
dependence with a characteristic minimum at $\sim$50 K, indicating a coupling
of the lattice to dynamical molecular spin state. These results strongly
suggest the coexistence of dynamical spin Jahn-Teller effect and dynamical
molecular spin state in the paramagnetic phase, which is compatible with the
coexistence of magnetostructural order and dynamical molecular spin state in
the antiferromagnetic phase.",1206.2755v2
2013-01-24,Soliton dynamics of an atomic spinor condensate on a Ring Lattice,"We study the dynamics of macroscopically-coherent matter waves of an
ultra-cold atomic spin-one or spinor condensate on a ring lattice of six sites
and demonstrate a novel type of spatio-temporal internal Josephson effect.
Using a discrete solitary mode of uncoupled spin components as an initial
condition, the time evolution of this many-body system is found to be
characterized by two dominant frequencies leading to quasiperiodic dynamics at
various sites. The dynamics of spatially-averaged and spin-averaged degrees of
freedom, however, is periodic enabling an unique identification of the two
frequencies. By increasing the spin-dependent atom-atom interaction strength we
observe a resonance state, where the ratio of the two frequencies is a
characteristic integer multiple and the spin-and-spatial degrees of freedom
oscillate in ""unison"". Crucially, this resonant state is found to signal the
onset to chaotic dynamics characterized by a broad band spectrum. In a
ferromagnetic spinor condensate with attractive spin-dependent interactions,
the resonance is accompanied by a transition from oscillatory- to
rotational-type dynamics as the time evolution of the relative phase of the
matter wave of the individual spin projections changes from bounded to
unbounded.",1301.5851v1
2013-05-10,Spin dynamics in a spin-orbit coupled Fermi gas,"We study the dynamics of a non-degenerate, harmonically trapped Fermi gas
following a sudden ramp of the spin-orbit coupling strength. In the
non-interacting limit, we solve the Boltzmann equation in the presence of spin
orbit coupling analytically, and derive expressions for the dynamics of an
arbitrary initial spin state. In particular we show that for a fully spin
polarized initial state, the total magnetization exhibits collapse and revival
dynamics in time with a period set by the trapping potential. In real space,
this corresponds to oscillations between a fully polarized state and a spin
helix. We numerically study the effect of interactions on the dynamics using a
collisionless Boltzmann equation.",1305.2443v3
2009-12-18,Stochastic resonance of a nanomagnet excited by spin transfer torque,"Spin transfer torque from spin-polarized electrical current can excite
large-amplitude magnetization dynamics in metallic ferromagnets of nanoscale
dimensions. Since magnetic anisotropy energies of nanomagnets are comparable to
the thermal energy scale, temperature can have a profound effect on the
dynamics of a nanomagnet driven by spin transfer torque. Here we report the
observation of unusual types of microwave-frequency nonlinear magnetization
dynamics co-excited by alternating spin transfer torque and thermal
fluctuations. In these dynamics, temperature amplifies the amplitude of
GHz-range precession of magnetization and enables excitation of highly
nonlinear dynamical states of magnetization by weak alternating spin transfer
torque. We explain these thermally activated dynamics in terms of non-adiabatic
stochastic resonance of magnetization driven by spin transfer torque. This type
of magnetic stochastic resonance may find use in sensitive nanometer-scale
microwave signal detectors.",0912.3842v1
2017-10-26,Dynamical spin accumulation in large-spin magnetic molecules,"The frequency-dependent transport through a nano-device containing a
large-spin magnetic molecule is studied theoretically in the Kondo regime.
Specifically, the effect of magnetic anisotropy on dynamical spin accumulation
is of primary interest. Such accumulation arises due to finite off-diagonal in
spin components of the dynamical conductance. Here, employing the Kubo
formalism and the numerical renormalization group (NRG) method, we demonstrate
that the dynamical transport properties strongly depend on magnetic
configuration of the device and intrinsic parameters of the molecule.
Specifically, the effect of dynamical spin accumulation is found to be greatly
affected by the type of magnetic anisotropy exhibited by the molecule, and it
develops for frequencies corresponding to the Kondo temperature. For the
parallel magnetic configuration of the device, the presence of dynamical spin
accumulation is conditioned by the interplay of ferromagnetic-lead-induced
exchange field and the Kondo correlations.",1710.09623v1
2022-01-04,Quantum dynamics of Gaudin magnets,"Quantum dynamics of many-body systems is a fascinating and significant
subject for both theory and experiment. The question of how an isolated
many-body system evolves to its steady state after a sudden perturbation or
quench still remains challenging. In this paper, using the Bethe ansatz wave
function, we study the quantum dynamics of an inhomogeneous Gaudin magnet. We
derive explicit analytical expressions for various local dynamic quantities
with an arbitrary number of flipped bath spins, such as: the spin distribution
function, the spin-spin correlation function, and the Loschmidt echo. We also
numerically study the relaxation behavior of these dynamic properties, gaining
considerable insight into coherence and entanglement between the central spin
and the bath. In particular, we find that the spin-spin correlations relax to
their steady value via a nearly logarithmic scaling, whereas the Loschmidt echo
shows an exponential relaxation to its steady value. Our results advance the
understanding of relaxation dynamics and quantum correlations of long-range
interacting models of Gaudin type.",2201.01025v1
2022-06-27,Bridging atomistic spin dynamics methods and phenomenological models of single pulse ultrafast switching in ferrimagnets,"We bridge an essential knowledge gap on the understanding of all-optical
ultrafast switching in ferrimagnets; namely, the connection between atomistic
spin dynamics methods and macroscopic phenomenological models. All-optical
switching of the magnetization occurs after the application of a single
femtosecond laser pulse to specific ferrimagnetic compounds. This strong
excitation puts the involved degrees of freedom, electrons, lattice and spins
out-of-equilibrium between each other. Atomistic spin models have
quantitatively described all-optical switching in a wide range of experimental
conditions, while having failed to provide a simple picture of the switching
process. Phenomenological models are able to qualitatively describe the
dynamics of the switching process. However, a unified theoretical framework is
missing that describes the element-specific spin dynamics as atomistic spin
models with the simplicity of phenomenology. Here, we bridge this gap and
present an element-specific macrospin dynamical model which fully agrees with
atomistic spin dynamics simulations and symmetry considerations of the
phenomenological models.",2206.13593v1
2022-11-07,Simulation of the Einstein-de Haas effect combining molecular and spin dynamics,"The spin and lattice dynamics of a ferromagnetic nanoparticle are studied via
molecular dynamics and with semi-classical spin dynamics simulations where spin
and lattice degrees of freedom are coupled via a dynamic uniaxial anisotropy
term. We show that this model conserves total angular momentum, whereas spin
and lattice angular momentum are not conserved. We carry out simulations of the
the Einstein-de Haas effect for a Fe nanocluster with more than 500 atoms that
is free to rotate, using a modified version of the open-source spinlattice
dynamics code (SPILADY). We show that the rate of angular momentum transfer
between spin and lattice is proportional to the strength of the magnetic
anisotropy interaction. The addition of the anisotropy allows full spin-lattice
relaxation to be achieved on previously reported timescales of \sim 100 ps and
for tight-binding magnetic anisotropy energies comparable to those of small Fe
nanoclusters.",2211.03706v1
2019-04-11,Spin dynamics of the antiferromagnetic Heisenberg model on a kagome bilayer,"We study the spin dynamics of classical Heisenberg antiferromagnet with
nearest neighbor interactions on a quasi-two-dimensional kagome bilayer. This
geometrically frustrated lattice consists of two kagome layers connected by a
triangular-lattice linking layer. By combining Monte Carlo with precessional
spin dynamics simulations, we compute the dynamical structure factor of the
classical spin liquid in kagome bilayer and investigate the thermal and
dilution effects. While the low frequency and long wavelength dynamics of the
cooperative paramagnetic phase is dominated by spin diffusion, weak magnon
excitations persist at higher energies, giving rise the half moon pattern in
the dynamical structure factor. In the presence of spin vacancies, the
dynamical properties of the diluted system can be understood within the two
population picture. The spin diffusion of the ""correlated"" spin clusters is
mainly driven by the zero-energy weather-van modes, giving rise to an
autocorrelation function that decays exponentially with time. On the other
hand, the diffusive dynamics of the quasi-free ""orphan"" spins leads to a
distinctive longer time power-law tail in the autocorrelation function. We
discuss the implications of our work for the glassy behaviors observed in the
archetypal frustrated magnet SrCr$_{9p}$Ga$_{12-9p}$O$_{19}$ (SCGO).",1904.05863v3
2020-11-04,Dynamical spin correlations of the kagome antiferromagnet,"Temperature-dependent dynamical spin correlations, which can be readily
accessed via a variety of experimental techniques, hold the potential of
offering a unique fingerprint of quantum spin liquids and other intriguing
dynamical states. In this work we present an in-depth study of the
temperature-dependent dynamical spin structure factor $S({\bf q}, \omega)$ of
the antiferromagnetic (AFM) Heisenberg spin-1/2 model on the kagome lattice
with additional Dzyaloshinskii--Moriya (DM) interactions. Using the
finite-temperature Lanczos method on lattices with up to $N = 30$ sites we find
that even without DM interactions, chiral low-energy spin fluctuations of the
$120^\circ$ AFM order parameter dominate the dynamical response. This leads to
a nontrivial frequency dependence of $S({\bf q}, \omega)$ and the appearance of
a pronounced low-frequency mode at the M point of the extended Brillouin zone.
Adding an out-of-plane DM interactions $D^z$ gives rise to an anisotropic
dynamical response, a softening of in-plane spin fluctuations, and, ultimately,
the onset of a coplanar AFM ground-state order at $D^z > 0.1 J$. Our results
are in very good agreement with existing inelastic neutron scattering and
temperature-dependent NMR spin-lattice relaxation rate ($1/T_1$) data on the
paradigmatic kagome AFM herbertsmithite, where the effect of its small $D^z$ on
the dynamical spin correlations is shown to be rather small, as well as with
$1/T_1$ data on the novel kagome AFM YCu$_3$(OH)$_6$Cl$_3$, where its
substantial $D^z \approx 0.25 J$ interaction is found to strongly affect the
spin dynamics.",2011.02369v2
2004-05-28,Hyperfine interaction in a quantum dot: Non-Markovian electron spin dynamics,"We have performed a systematic calculation for the non-Markovian dynamics of
a localized electron spin interacting with an environment of nuclear spins via
the Fermi contact hyperfine interaction. This work applies to an electron in
the s -type orbital ground state of a quantum dot or bound to a donor impurity,
and is valid for arbitrary polarization p of the nuclear spin system, and
arbitrary nuclear spin I in high magnetic fields. In the limit of p=1 and
I=1/2, the Born approximation of our perturbative theory recovers the exact
electron spin dynamics. We have found the form of the generalized master
equation (GME) for the longitudinal and transverse components of the electron
spin to all orders in the electron spin--nuclear spin flip-flop terms. Our
perturbative expansion is regular, unlike standard time-dependent perturbation
theory, and can be carried-out to higher orders. We show this explicitly with a
fourth-order calculation of the longitudinal spin dynamics. In zero magnetic
field, the fraction of the electron spin that decays is bounded by the
smallness parameter \delta=1/p^{2}N, where N is the number of nuclear spins
within the extent of the electron wave function. However, the form of the decay
can only be determined in a high magnetic field, much larger than the maximum
Overhauser field. In general the electron spin shows rich dynamics, described
by a sum of contributions with non-exponential decay, exponential decay, and
undamped oscillations. There is an abrupt crossover in the electron spin
asymptotics at a critical dimensionality and shape of the electron envelope
wave function. We propose a scheme that could be used to measure the
non-Markovian dynamics using a standard spin-echo technique, even when the
fraction that undergoes non-Markovian dynamics is small.",0405676v2
1998-04-03,Phase transitions in the Potts spin glass model,"We have studied the Potts spin glass with 2-state Ising spins and s-state
Potts variables using a cluster Monte Carlo dynamics. The model recovers the +-
J Ising spin glass (SG) for s=1 and exhibits for all s a SG transition at
T_{SG}(s) and a percolation transition at higher temperature T_p(s). We have
shown that for all values of $s\neq 1$ at T_p(s) there is a thermodynamical
transition in the universality class of a ferromagnetic s-state Potts model.
The efficiency of the cluster dynamics is compared with that of standard spin
flip dynamics.",9804037v1
1998-09-01,Non-equilibrium dynamics in a 3d spin-glass,"Non-equilibrium dynamics in a Ag(11%Mn) spin-glass has been studied by low
frequency ac-susceptibility and magnetic relaxation experiments. The results
unequivocally show that spin structures that memorize the cooling process are
imprinted in the system. These imprinted structures disclose themselves through
dramatic changes of the dynamics on re-heating the spin-glass through the
temperatures where intermittent stops or changes of the cooling rate have been
imposed. We can qualitatively interpret our results in terms of the droplet
spin-glass model developed by Fisher and Huse [Phys. Rev. B 38 (1988) 373;
386].",9809021v1
1999-09-01,Dynamic spin susceptibility in the t-J model,"Dynamic spin susceptibility is calculated for the t-J model in the
paramagnetic phase by applying the memory function method in terms of the
Hubbard operators. A self-consistent system of equations for the memory
function is obtained within the mode coupling approximation. Both itinerant
hole excitations and localized spin fluctuations give contributions to the
memory function. Spin dynamics have a diffusive character in the hydrodynamic
limit; spin-wave-like excitations are regained in the high-frequency region.",9909019v1
2000-04-27,Entropy-vanishing transition and glassy dynamics in frustrated spins,"In an effort to understand the glass transition, the dynamics of a
non-randomly frustrated spin model has been analyzed. The phenomenology of the
spin model is similar to that of a supercooled liquid undergoing the glass
transition. The slow dynamics can be associated with the presence of extended
string-like structures which demarcate regions of fast spin flips. An
entropy-vanishing transition, with the string density as the order parameter,
is related to the observed glass transition in the spin model.",0004483v2
2004-05-12,The role of orbital dynamics in spin relaxation and weak antilocalization in quantum dots,"We develop a semiclassical theory for spin-dependent quantum transport to
describe weak (anti)localization in quantum dots with spin-orbit coupling. This
allows us to distinguish different types of spin relaxation in systems with
chaotic, regular, and diffusive orbital classical dynamics. We find, in
particular, that for typical Rashba spin-orbit coupling strengths, integrable
ballistic systems can exhibit weak localization, while corresponding chaotic
systems show weak antilocalization. We further calculate the magnetoconductance
and analyze how the weak antilocalization is suppressed with decreasing quantum
dot size and increasing additional in-plane magnetic field.",0405266v2
2004-07-07,Roles of non-equilibrium conduction electrons on magnetization dynamics of ferromagnets,"The mutual dependence of spin-dependent conduction and magnetization dynamics
of ferromagnets provides the key mechanisms in various spin-dependent
phenomena. We compute the response of the conduction electron spins to a
spatial and time varying magnetization ${\bf M} ({\bf r},t)$ within the
time-dependent semiclassical transport theory. We show that the induced
non-equilibrium conduction spin density in turn generates four spin torques
acting on the magnetization--with each torque playing different roles in
magnetization dynamics. By comparing with recent theoretical models, we find
that one of these torques that has not been previously identified is crucial to
consistently interpret experimental data on domain wall motion.",0407174v2
2007-03-14,Nonequilibrium nuclear-electron spin dynamics in semiconductor quantum dots,"We study the spin dynamics in charged quantum dots in the situation where the
resident electron is coupled to only about 200 nuclear spins and where the
electron spin splitting induced by the Overhauser field does not exceed
markedly the spectral broadening. The formation of a dynamical nuclear
polarization as well as its subsequent decay by the dipole-dipole interaction
is directly resolved in time. Because not limited by intrinsic nonlinearities,
almost complete nuclear polarization is achieved, even at elevated
temperatures. The data suggest a nonequilibrium mode of nuclear polarization,
distinctly different from the spin temperature concept exploited on bulk
semiconductors",0703386v2
2002-07-02,Gravitational Waves from Spinning Compact Binaries,"Binary systems of rapidly spinning compact objects, such as black holes or
neutron stars, are prime targets for gravitational wave astronomers. The
dynamics of these systems can be very complicated due to spin-orbit and
spin-spin couplings. Contradictory results have been presented as to the nature
of the dynamics. Here we confirm that the dynamics - as described by the second
post-Newtonian approximation to general relativity - is chaotic, despite claims
to the contrary. When dissipation due to higher order radiation reaction terms
are included, the chaos is dampened. However, the inspiral-to-plunge transition
that occurs toward the end of the orbital evolution does retain an imprint of
the chaotic behaviour.",0207016v1
2005-07-28,Quantum entanglement dynamics and decoherence wave in spin chains at finite temperatures,"We analyze the quantum entanglement at the equilibrium in a class of exactly
solvable one-dimensional spin models at finite temperatures and identify a
region where the quantum fluctuations determine the behavior of the system. We
probe the response of the system in this region by studying the spin dynamics
after projective measurement of one local spin which leads to the appearance of
the ``decoherence wave''. We investigate time-dependent spin correlation
functions, the entanglement dynamics, and the fidelity of the quantum
information transfer after the measurement.",0507266v1
2008-11-05,Multiple Quantum NMR Dynamics in Pseudopure States,"We investigate numerically the Multiple Quantum (MQ) NMR dynamics in systems
of nuclear spins 1/2 coupled by the dipole-dipole interactions in the case of
the pseudopure initial state. Simulations of the MQ NMR with the real molecular
structures such as six dipolar-coupled proton spins of a benzene, hydroxyl
proton chains in calcium hydroxyapatite and fluorine chains in calcium
fluorapatite open the way to experimental NMR testing of the obtained results.
It was found that multiple-spin correlations are created faster in such
experiments than in the usual MQ NMR experiments and can be used for the
investigation of many-spin dynamics of nuclear spins in solids",0811.0716v1
2009-03-12,Simulation of a spin-wave instability from atomistic spin dynamics,"We study the spin dynamics of a Heisenberg model at finite temperature in the
presence of an external field or a uniaxial anisotropy. For the case of the
uniaxial anisotropy our simulations show that the macro moment picture breaks
down. An effect which we refer to as a spin-wave instability (SWI) results in a
non-dissipative Bloch-Bloembergen type relaxation of the macro moment where the
size of the macro moment changes, and can even be made to disappear. This
relaxation mechanism is studied in detail by means of atomistic spin dynamics
simulations.",0903.2186v1
2009-05-23,Multiple Quantum Coherence and Entanglement Dynamics in Spin Clusters,"With the purpose to reveal consistency between multiple quantum (MQ)
coherences and entanglement, we investigate numerically the dynamics of these
phenomena in one-dimensional linear chains and ring of nuclear spins 1/2
coupled by dipole dipole interactions. As opposed to the calculation of the MQ
coherence intensity based on the density matrix describing the spin system as a
whole, we consider the ""differentiated"" intensity related only to the chosen
spin pair based on the reduced density matrix. It is shown that the
entanglement and the MQ coherence have similar dynamics only for nearest
neighbors while we did not obtained any consistency for remote spins.",0905.3826v1
2009-10-19,Derivatives of spin dynamics simulations,"We report analytical equations for the derivatives of spin dynamics
simulations with respect to pulse sequence and spin system parameters. The
methods described are significantly faster, more accurate and more reliable
than the finite difference approximations typically employed. The resulting
derivatives may be used in fitting, optimization, performance evaluation and
stability analysis of spin dynamics simulations and experiments.
  Keywords: NMR, EPR, simulation, analytical derivatives, optimal control, spin
chemistry, radical pair.",0910.3593v1
2010-08-16,Transient entanglement in a spin chain stimulated by phase pulses,"Dynamics of the one-dimensional open Ising chain under influence of $\pi$
-pulses is studied. It is shown that the application of a specific sequence of
such instant kicks to selective spins stimulates arising of perfect dynamical
pairwise entanglement between ends of the spin chain. Analytic formulas for the
concurrence dynamics are derived. It is also shown that the time required to
perfectly entangle the ends of the chains grows linearly with the number of
spins in the chain. The final entangled state of the ending spins is always the
same and does not depend on length the chain.",1008.2784v1
2010-12-15,Enhanced Tensor-Force Contribution in Collision Dynamics,"The tensor and spin-orbit forces contribute essentially to the formation of
the spin mean field, and give rise to the same dynamical effect, namely spin
polarization. In this paper, based on time-dependent density functional
calculations, we show that the tensor force, which usually acts like a small
correction to the spin-orbit force, becomes more important in heavy-ion
reactions and the effect increases with the mass of the system.",1012.3363v2
2011-08-26,Direct observation of correlation time of dynamic nuclear polarization in single quantum dots,"The spin interaction between an electron and nuclei was investigated
optically in a single self-assembled InAlAs quantum dot (QD). In spin dynamics,
the correlation time of the coupled electron-nuclear spin system and the
electron spin relaxation time play a crucial role. We examined on a positively
charged exciton in a QD to evaluate these key time constants directly via the
temporal evolution measurements of the Overhauser shift and the degree of
circular polarization. In addition, the validity of our used spin dynamics
model was discussed in the context of the experimentally obtained key
parameters.",1108.5239v1
2012-09-20,Quench dynamics in spin crossover induced by high pressure,"In this paper we have studied analytically and numerically dynamics of spin
crossover induced by time-dependent pressure. We show that quasi static
pressure, with a slow dependence on time, yields a spin crossover leading to
transition from the state of quantum system with high spin (HS) to the low spin
(LS). However, a quench dynamics under shock-wave load is more complicated. The
final state of the system depends on the amplitude and pulse velocity,
resulting in the mixture of the HS and LS states.",1209.4567v1
2013-03-06,A Quantum Approach of Meso-Magnet Dynamics with Spin Transfer Torque,"We present a theory of magnetization dynamics driven by spin-polarized
current in terms of the quantum master equation. In the spin coherent state
representation, the master equation becomes a Fokker-Planck equation, which
naturally includes the spin transfer and quantum fluctuation. The current
electron scattering state is correlated to the magnet quantum states, giving
rise to quantum correction to the electron transport properties in the usual
semiclassical theory. In the large spin limit, the magnetization dynamics is
shown to obey the Hamilton-Jacobi equation or the Hamiltonian canonical
equations.",1303.1250v2
2008-07-02,Dynamics of nonequilibrium thermal entanglement,"The dynamics of a simple spin chain (2 spins) coupled to bosonic baths at
different temperatures is studied. The analytical solution for the reduced
density matrix of the system is found. The dynamics and temperature dependence
of spin-spin entanglement is analyzed. It is shown that the system converges to
a steady-state. If the energy levels of the two spins are different, the
steady-state concurrence assumes its maximum at unequal bath temperatures. It
is found that a difference in local energy levels can make the steady-state
entanglement more stable against high temperatures.",0807.0379v2
2012-03-27,Spin dynamics in the Kapitza-Dirac effect,"Electron spin dynamics in Kapitza-Dirac scattering from a standing laser wave
of high frequency and high intensity is studied. We develop a fully
relativistic quantum theory of the electron motion based on the time-dependent
Dirac equation. Distinct spin dynamics, with Rabi oscillations and complete
spin-flip transitions, is demonstrated for Kapitza-Dirac scattering involving
three photons in a parameter regime accessible to future high-power X-ray laser
sources. The Rabi frequency and, thus, the diffraction pattern is shown to
depend crucially on the spin degree of freedom.",1204.0239v2
2017-12-22,Spinning and tumbling of micron-sized triangles in a micro-channel shear flow,"We report on measurements of the angular dynamics of micron-sized
equilaterally triangular platelets suspended in a micro-channel shear flow. Our
measurements confirm that such particles spin and tumble like a spheroid in a
simple shear. Since the triangle has corners we can observe the spinning
directly. In general the spinning frequency is different from the tumbling
frequency, and the spinning is affected by tumbling. This gives rise to
doubly-periodic angular dynamics.",1712.08505v1
2018-10-07,Tri-spin dynamics in alkali metal-noble gas NMR gyroscope,"Alkali metal-noble gas NMR gyroscope is widely used for precision rotation
measurement in fundamental and applied physics. By numerically simulating the
alkali-nuclear-nuclear tri-spin dynamics, we investigate the dependence of
gyroscope response on alkali spin relaxation time and nuclear spin
magnetization. We found additional resonance peaks appear due to a new source
of instability, namely the inherent multistability of tri-spin dynamics. The
numerical simulation results agree well with the recent experiment, enabling a
better understanding and exploitation of the gyroscope signal.",1810.03185v4
2019-12-23,Dynamical spin polarization of excess quasi-particles in superconductors,"We show that the annihilation dynamics of excess quasi-particles in
superconductors may result in the spontaneous formation of large spin-polarized
clusters. This presents a novel scenario for spontaneous spin polarization. We
estimate the relevant scales for aluminum, finding the feasibility of clusters
with total spin $S \simeq 10^4 \hbar$ that could be spread over microns. The
fluctuation dynamics of such large spins may be detected by measuring the flux
noise in a loop hosting a cluster.",1912.10661v1
2021-07-26,Universal scaling of spin mixing dynamics in a strongly interacting one-dimensional Fermi gas,"We study the spin-mixing dynamics of a one-dimensional strongly repulsive
Fermi gas under harmonic confinement. By employing a mapping onto an
inhomogeneous isotropic Heisenberg model and the symmetries under particle
exchange, we follow the dynamics till very long times. Starting from an initial
spin-separated state, we observe superdiffusion, spin-dipolar large amplitude
oscillations and thermalization. We report a universal scaling of the
oscillations with particle number N^1/4, implying a slow-down of the motion and
the decrease of the zero-temperature spin drag coefficient as the particle
number grows.",2107.12075v2
2023-08-11,Dynamical Majorana Ising spin response in a topological superconductor-magnet hybrid by microwave irradiation,"We study a dynamical spin response of surface Majorana modes in a topological
superconductor-magnet hybrid under microwave irradiation. We find a method to
toggle between dissipative and non-dissipative Majorana Ising spin dynamics by
adjusting the external magnetic field angle and the microwave frequency. This
reflects the topological nature of the Majorana modes, enhancing the Gilbert
damping of the magnet, thereby, providing a detection method for the Majorana
Ising spins. Our findings illuminate a magnetic probe for Majorana modes,
paving the path to innovative spin devices.",2308.05955v2
2024-03-01,Chaos-assisted Turbulence in Spinor Bose-Einstein Condensates,"We present a turbulence-sustaining mechanism in a spinor Bose-Einstein
condensate, which is based on the chaotic nature of internal spin dynamics.
Magnetic driving induces a complete chaotic evolution of the local spin state,
thereby continuously randomizing the spin texture of the condensate to maintain
the turbulent state. We experimentally demonstrate the onset of turbulence in
the driven condensate as the driving frequency changes and show that it is
consistent with the regular-to-chaotic transition of the local spin dynamics.
This chaos-assisted turbulence establishes the spin-driven spinor condensate as
an intriguing platform for exploring quantum chaos and related superfluid
turbulence phenomena.",2403.00524v1
2002-09-13,"Reply to a Comment by J. Bolte, R. Glaser and S. Keppeler on: Semiclassical theory of spin-orbit interactions using spin coherent states","We reply to a Comment on our recently proposed semiclassical theory for
systems with spin-orbit interactions.",0209028v1
2017-04-21,Rattleback dynamics and its reversal time of rotation,"A rattleback is a rigid, semi-elliptic toy which exhibits unintuitive
behavior; when it is spun in one direction, it soon begins pitching and stops
spinning, then it starts to spin in the opposite direction, but in the other
direction, it seems to spin just steadily. This puzzling behavior results from
the slight misalignment between the principal axes for the inertia and those
for the curvature; the misalignment couples the spinning with the pitching and
the rolling oscillations. It has been shown that under the no-slip condition
and without dissipation the spin can reverse in both directions, and Garcia and
Hubbard obtained the formula for the time required for the spin reversal $t_r$
[Proc. R. Soc. Lond. A 418, 165-197 (1988) ]. In this work, we reformulate the
rattleback dynamics in a physically transparent way and reduce it to a
three-variable dynamics for spinning, pitching, and rolling. We obtain an
expression of the Garcia-Hubbard formula for $t_r$ by a simple product of four
factors: (1) the misalignment angle, (2) the difference in the inverses of
inertia moment for the two oscillations, (3) that in the radii for the two
principal curvatures, and (4) the squared frequency of the oscillation. We
perform extensive numerical simulations to examine validity and limitation of
the formula, and find that (1) the Garcia-Hubbard formula is good for both
spinning directions in the small spin and small oscillation regime, but (2) in
the fast spin regime especially for the steady direction, the rattleback may
not reverse and shows a rich variety of dynamics including steady spinning,
spin wobbling, and chaotic behavior reminiscent of chaos in a dissipative
system.",1704.06717v2
2019-04-01,Mechanism of Electron Spin Relaxation in Spiral Magnetic Structures,"Spin dynamics in spiral magnetic structures has been investigated. It has
been shown that the internal spatially dependent magnetic field in such
structures produces a new mechanism of spin relaxation.",1904.00564v1
2004-06-22,"Spin susceptibilities, spin densities and their connection to spin-currents","We calculate the frequency dependent spin susceptibilities for a
two-dimensional electron gas with both Rashba and Dresselhaus spin-orbit
interaction. The resonances of the susceptibilities depends on the relative
values of the Rashba and Dresselhaus spin-orbit constants, which could be
manipulated by gate voltages. We derive exact continuity equations, with source
terms, for the spin density and use those to connect the spin current to the
spin density. In the free electron model the susceptibilities play a central
role in the spin dynamics since both the spin density and the spin current are
proportional to them.",0406531v2
2008-11-28,Coherence of single spins coupled to a nuclear spin bath of varying density,"The dynamics of single electron and nuclear spins in a diamond lattice with
different 13C nuclear spin concentration is investigated. It is shown that
coherent control of up to three individual nuclei in a dense nuclear spin
cluster is feasible. The free induction decays of nuclear spin Bell states and
single nuclear coherences among 13C nuclear spins are compared and analyzed.
Reduction of a free induction decay time T2* and a coherence time T2 upon
increase of nuclear spin concentration has been found. For diamond material
with depleted concentration of nuclear spin, T2* as long as 30 microseconds and
T2 of up to 1.8 ms for the electron spin has been observed. The 13C
concentration dependence of T2* is explained by Fermi contact and dipolar
interactions with nuclei in the lattice. It has been found that T2 decreases
approximately as 1/n, where n is 13C concentration, as expected for an electron
spin interacting with a nuclear spin bath.",0811.4731v2
2011-01-30,Spin transport in magnetically ordered systems: effect of the lattice relaxation time,"Spin resistivity $R$ has been shown to result mainly from the scattering of
itinerant spins with magnetic impurities and lattice spins. $R$ is proportional
to the spin-spin correlation so that its behavior is very complicated near and
at the magnetic phase transition of the lattice spins. For the time being there
are many new experimental data on the spin resistivity going from
semiconductors to superconductors. Depending on materials, various behaviors
have been observed. There is however no theory so far which gives a unified
mechanism for spin resistivity in magnetic materials. Recently, we have showed
Monte Carlo results for different systems. We found that the spin resistivity
is very different from one material to another. In this paper, we show for the
first time how the dynamic relaxation time of the lattice spins affects the
resistivity of itinerant spins observed in Monte Carlo simulation.",1101.5789v1
2013-04-09,Spin-orbital liquids in non-Kramers magnet on Kagome lattice,"Localized magnetic moments with crystal-field doublet or pseudo-spin 1/2 may
arise in correlated insulators with even number of electrons and strong
spin-orbit coupling. Such a non-Kramers pseudo-spin 1/2 is the consequence of
crystalline symmetries as opposed to the Kramers doublet arising from
time-reversal invariance, and is necessarily a composite of spin and orbital
degrees of freedom. We investigate possible spin-orbital liquids with fermionic
spinons for such non-Kramers pseudo-spin 1/2 systems on the Kagome lattice.
Using the projective symmetry group analysis, we find {\it ten} new phases that
are not allowed in the corresponding Kramers systems. These new phases are
allowed due to unusual action of the time reversal operation on non-Kramers
pseudo-spins. We compute the spin-spin dynamic structure factor that shows
characteristic features of these non-Kramers spin-orbital liquids arising from
their unusual coupling to neutrons, which is therefore relevant for neutron
scattering experiments. We also point out possible anomalous broadening of
Raman scattering intensity that may serve as a signature experimental feature
for gapless non-Kramers spin-orbital liquids.",1304.2766v1
2013-11-08,Ultra long spin decoherence times in graphene quantum dots with a small number of nuclear spins,"We study the dynamics of an electron spin in a graphene quantum dot, which is
interacting with a bath of less than ten nuclear spins via the anisotropic
hyperfine interaction. Due to substantial progress in the fabrication of
graphene quantum dots, the consideration of such a small number of nuclear
spins is experimentally relevant. This choice allows us to use exact
diagonalization to calculate the longtime average of the electron spin as well
as its decoherence time. We investigate the dependence of spin observables on
the initial states of nuclear spins and on the position of nuclear spins in the
quantum dot. Moreover, we analyze the effects of the anisotropy of the
hyperfine interaction for different orientations of the spin quantization axis
with respect to the graphene plane. Interestingly, we then predict remarkable
long decoherence times of more than 10ms in the limit of few nuclear spins.",1311.1979v2
2015-02-04,Effective-one-body Hamiltonian with next-to-leading order spin-spin coupling,"We propose a way of including the next-to-leading (NLO) order spin-spin
coupling into an effective-one-body (EOB) Hamiltonian. This work extends [S.
Balmelli and P. Jetzer, Phys. Rev. D 87, 124036 (2013)], which is restricted to
the case of equatorial orbits and aligned spins, to general orbits with
arbitrary spin orientations. This is done applying appropriate canonical
phase-space transformations to the NLO spin-spin Hamiltonian in
Arnowitt-Deser-Misner (ADM) coordinates, and systematically adding ""effectiv""
quantities at NLO to all spin-squared terms appearing in the EOB Hamiltonian.
As required by consistency, the introduced quantities reduce to zero in the
test- mass limit. We expose the result both in a general gauge and in a
gauge-fixed form. The last is chosen such as to minimize the number of new
coefficients that have to be inserted into the effective spin squared. As a
result, the 25 parameters that describe the ADM NLO spin-spin dynamics get
condensed into only 12 EOB terms.",1502.01343v1
2017-03-24,Gate control of the spin mobility through the modification of the spin-orbit interaction in two-dimensional systems,"Spin drag measurements were performed in a two-dimensional electron system
set close to the crossed spin helix regime and coupled by strong intersubband
scattering. In a sample with uncommon combination of long spin lifetime and
high charge mobility, the drift transport allows us to determine the spin-orbit
field and the spin mobility anisotropies. We used a random walk model to
describe the system dynamics and found excellent agreement for the Rashba and
Dresselhaus couplings. The proposed two-subband system displays a large tuning
lever arm for the Rashba constant with gate voltage, which provides a new path
towards a spin transistor. Furthermore, the data shows large spin mobility
controlled by the spin-orbit constants setting the field along the direction
perpendicular to the drift velocity. This work directly reveals the resistance
experienced in the transport of a spin-polarized packet as a function of the
strength of anisotropic spin-orbit fields.",1703.08405v2
2017-04-28,Quantum Spin Lenses in Atomic Arrays,"We propose and discuss `quantum spin lenses', where quantum states of
delocalized spin excitations in an atomic medium are `focused' in space in a
coherent quantum process down to (essentially) single atoms. These can be
employed to create controlled interactions in a quantum light-matter interface,
where photonic qubits stored in an atomic ensemble are mapped to a quantum
register represented by single atoms. We propose Hamiltonians for quantum spin
lenses as inhomogeneous spin models on lattices, which can be realized with
Rydberg atoms in 1D, 2D and 3D, and with strings of trapped ions. We discuss
both linear and non-linear quantum spin lenses: in a non-linear lens, repulsive
spin-spin interactions lead to focusing dynamics conditional to the number of
spin excitations. This allows the mapping of quantum superpositions of
delocalized spin excitations to superpositions of spatial spin patterns, which
can be addressed by light fields and manipulated. Finally, we propose
multifocal quantum spin lenses as a way to generate and distribute entanglement
between distant atoms in an atomic lattice array.",1704.08837v1
2017-06-04,Simulating spin dynamics with spin-dependent cross sections in heavy-ion collisions,"We have incorporated the spin-dependent nucleon-nucleon cross sections into a
Boltzmann-Uehling-Uhlenbeck transport model for the first time, using the
spin-singlet and spin-triplet nucleon-nucleon elastic scattering cross sections
extracted from the phase-shift analyses of nucleon-nucleon scatterings in free
space. We found that the spin splitting of the collective flows is not affected
by the spin-dependent cross sections, justifying it as a good probe of the
in-medium nuclear spin-orbit interaction. With the in-medium nuclear spin-orbit
mean-field potential that leads to local spin polarization, we found that the
spin-averaged observables, such as elliptic flows of free nucleons and light
clusters, becomes smaller with the spin-dependent differential nucleon-nucleon
scattering cross sections.",1706.01013v2
2017-12-10,Effective gauge field theory of spintronics,"The aim of this paper is to present a comprehensive theory of spintronics
phenomena based on the concept of effective gauge field, the spin gauge field.
An effective gauge field generally arises when we change a basis to describe
system and describes low energy properties of the system. In the case of
ferromagnetic metals we consider, it arises from structures of localized spin
(magnetization) and couples to spin current of conduction electron. The first
half of the paper is devoted to quantum mechanical arguments and phenomenology.
We show that the spin gauge field has adiabatic and nonadiabatic (off-diagonal)
components, consisting an SU(2) gauge field. The adiabatic component gives rise
to spin Berry's phase, topological Hall effect and spin motive force, while
nonadiabatic components are essential for spin-transfer torque and spin pumping
effects by inducing nonequilibrium spin accumulation. In the latter part of the
paper, field theoretic approaches are described. Dynamics of localized spins in
the presence of applied spin-polarized current is studied in a microscopic
viewpoint, and current-driven domain wall motion is discussed. Recent
developments on interface spin-orbit interaction is also mentioned.",1712.03489v2
2018-01-25,Theory of high-resolution tunneling spin transport on a magnetic skyrmion,"Tunneling spin transport characteristics of a magnetic skyrmion are described
theoretically in magnetic scanning tunneling microscopy (STM). The
spin-polarized charge current in STM (SP-STM) and tunneling spin transport
vector quantities, the longitudinal spin current and the spin transfer torque,
are calculated in high spatial resolution within the same theoretical
framework. A connection between the conventional charge current SP-STM image
contrasts and the magnitudes of the spin transport vectors is demonstrated that
enables the estimation of tunneling spin transport properties based on
experimentally measured SP-STM images. A considerable tunability of the spin
transport vectors by the involved spin polarizations is also highlighted. These
possibilities and the combined theory of tunneling charge and vector spin
transport pave the way for gaining deep insight into electric-current-induced
tunneling spin transport properties in SP-STM and to the related dynamics of
complex magnetic textures at surfaces.",1801.08375v2
2020-01-14,Simulating fermions in spin-dependent potentials with spin models on an energy lattice,"We study spin-1/2 fermions in spin dependent potentials under the \emph{spin
model approximation}, in which interatomic collisions that change the total
occupation of single-particle modes are ignored. The spin model approximation
maps the interacting fermion problem to an ensemble of lattice spin models in
energy space, where spin-spin interactions are long-ranged and
spin-anisotropic. We show that the spin model approximation is accurate for
weak interactions compared to the harmonic oscillator frequency, and captures
the collective spin dynamics to timescales much longer than would be expected
from perturbation theory. We explore corrections to the spin model, and the
relative importance of corrections when realistic anharmonic potential
corrections are taken into account. Additionally, we present numerical
techniques that are useful for analysis of spin models on an energy lattice,
including enacting a change of single-particle basis on a many-body state as an
effective time evolution, and fitting of spatially inhomogeneous long-range
interactions with exponentials. This latter technique is useful for
constructing matrix product operators for use in DMRG analyses, and may have
broader applicability within the tensor network community.",2001.04615v1
2019-12-23,Majorana-mediated spin transport without spin polarization in Kitaev quantum spin liquids,"We study the spin transport through the quantum spin liquid (QSL) by
investigating the real-time and real-space dynamics of the Kitaev spin system
with a zigzag structure in terms of the time-dependent Majorana mean-field
theory. After the magnetic field pulse is introduced to one of the edges, the
spin moments are excited in the opposite edge region although no spin moments
are induced in the Kitaev QSL region. This unusual spin transport originates
from the fact that the $S=1/2$ spins are fractionalized into the itinerant and
localized Majorana fermions in the Kitaev system. Although both Majorana
fermions are excited by the magnetic pulse, only the itinerant Majorana
fermions flow through the bulk regime without the spin excitation, resulting in
the spin transport in the Kitaev system. We also demonstrate that this
phenomenon can be observed even in the system with the Heisenberg interactions
using the exact diagonalization.",1912.10599v1
2020-08-17,Terahertz spin dynamics driven by an optical spin-orbit torque,"Spin torques are at the heart of spin manipulations in spintronic devices.
Here, we examine the existence of an optical spin-orbit torque, a relativistic
spin torque originating from the spin-orbit coupling of an oscillating applied
field with the spins. We compare the effect of the nonrelativistic Zeeman
torque with the relativistic optical spin-orbit torque for ferromagnetic
systems excited by a circularly polarised laser pulse. The latter torque
depends on the helicity of the light and scales with the intensity, while being
inversely proportional to the frequency. Our results show that the optical
spin-orbit torque can provide a torque on the spins, which is quantitatively
equivalent to the Zeeman torque. Moreover, temperature dependent calculations
show that the effect of optical spin-orbit torque decreases with increasing
temperature. However, the effect does not vanish in a ferromagnetic system,
even above its Curie temperature.",2008.07308v2
2021-06-29,Spin pumping in noncollinear antiferromagnets,"The ac spin pumping of noncollinear antiferromagnets is theoretically
investigated. Starting from an effective action description of the spin system,
we derive the Onsager coefficients connecting the spin pumping and
spin-transfer torque associated with the dynamics of the SO(3)-valued
antiferromagnetic order parameter. Our theory is applied to a kagome
antiferromagnet resonantly driven by a uniform external magnetic field. We
demonstrate that the reactive (dissipative) spin-transfer torque parameter can
be extracted from the pumped ac spin current in-phase (in quadrature) with the
driving field. Furthermore, we find that the three spin-wave bands of the
kagome AF generate spin currents with mutually orthogonal polarization
directions. This offers a unique way of controlling the spin orientation of the
pumped spin current by exciting different spin-wave modes.",2106.15187v2
2021-08-25,Probing Kondo spin fluctuations with scanning tunneling microscopy and electron spin resonance,"We theoretically analyze a state-of-the-art experimental method based on a
combination of electron spin resonance and scanning tunneling microscopy
(ESR-STM), to directly probe the spin fluctuations in the Kondo effect. The
Kondo impurity is exchange coupled to the probe spin, and the ESR-STM setup
detects the small level shifts in the probe spin induced by the spin
fluctuations of the Kondo impurity. We use the open quantum system approach by
regarding the probe spin as the ""system"" and the Kondo impurity spin as the
fluctuating ""bath"" to evaluate the resonance line shifts in terms of the
dynamic spin susceptibility of the Kondo impurity. We consider various common
adatoms on surfaces as possible probe spins and estimate the corresponding
level shifts. It is found that the sensitivity is most pronounced for the probe
spins with transverse magnetic anisotropy.",2108.11243v2
2021-08-29,Spin accumulation and dissipation excited by an ultrafast laser pulse,"An ultrafast spin current can be induced by femtosecond laser excitation in a
ferromagnetic (FM) thin film in contact with a nonmagnetic (NM) metal. The
propagation of an ultrafast spin current into NM metal has recently been found
in experiments to generate transient spin accumulation. Unlike spin
accumulation in equilibrium NM metals that occurs due to spin transport at the
Fermi energy, transient spin accumulation involves highly nonequilibrium hot
electrons well above the Fermi level. To date, the diffusion and dissipation of
this transient spin accumulation has not been well studied. Using the
superdiffusive spin transport model, we demonstrate how spin accumulation is
generated in NM metals after laser excitation in an FM|NM bilayer. The spin
accumulation shows an exponential decay from the FM|NM interface, with the
decay length increasing to the maximum value and then decreasing until
saturation. By analyzing the ultrafast dynamics of laser-excited hot electrons,
the ""effective mean free path"", which can be characterized by the averaged
product of the group velocity and lifetime of hot electrons, is found to play a
key role. The interface reflectivity has little influence on the spin
accumulation in NM metals. Our calculated results are in qualitative agreement
with recent experiments.",2108.12769v1
2022-03-12,Predicting Phonon-Induced Spin Decoherence from First Principles: Colossal Spin Renormalization in Condensed Matter,"Developing a microscopic understanding of spin decoherence is essential to
advancing quantum technologies. Electron spin decoherence due to atomic
vibrations (phonons) plays a special role as it sets an intrinsic limit to the
performance of spin-based quantum devices. Two main sources of phonon-induced
spin decoherence - the Elliott-Yafet (EY) and Dyakonov-Perel (DP) mechanisms -
have distinct physical origins and theoretical treatments. Here we show
calculations that unify their modeling and enable accurate predictions of spin
relaxation and precession in semiconductors. We compute the phonon-dressed
vertex of the spin-spin correlation function, with a treatment analogous to the
calculation of the anomalous electron magnetic moment in QED. We find that the
vertex correction provides a giant renormalization of the electron spin
dynamics in solids, greater by many orders of magnitude than the corresponding
correction in vacuum. Our work demonstrates a general approach for quantitative
analysis of spin decoherence in materials, advancing the quest for spin-based
quantum technologies.",2203.06401v2
2024-01-02,Hyperfine-enhanced gyroscope based on solid-state spins,"Solid-state platforms based on electro-nuclear spin systems are attractive
candidates for rotation sensing due to their excellent sensitivity, stability,
and compact size, compatible with industrial applications. Conventional
spin-based gyroscopes measure the accumulated phase of a nuclear spin
superposition state to extract the rotation rate and thus suffer from spin
dephasing. Here, we propose a gyroscope protocol based on a two-spin system
that includes a spin intrinsically tied to the host material, while the other
spin is isolated. The rotation rate is then extracted by measuring the relative
rotation angle between the two spins starting from their population states,
robust against spin dephasing. In particular, the relative rotation rate
between the two spins can be enhanced by their hyperfine coupling by more than
an order of magnitude, further boosting the achievable sensitivity. The
ultimate sensitivity of the gyroscope is limited by the lifetime of the spin
system and compatible with a broad dynamic range, even in the presence of
magnetic noises or control errors due to initialization and qubit
manipulations. Our result enables precise measurement of slow rotations and
exploration of fundamental physics.",2401.01334v2
2024-03-13,Spin-resolved counting statistics as a sensitive probe of spin correlation in transport through a quantum dot spin valve,"We investigate the noise in spin transport through a single quantum dot (QD)
tunnel coupled to ferromagnetic electrodes with noncollinear magnetizations.
Based on a spin-resolved quantum master equation, auto- and cross-correlations
of spin-resolved currents are analyzed to reveal the underlying spin transport
dynamics and characteristics for various polarizations. We find the currents of
majority and minority spins could be strongly autocorrelated despite
uncorrelated charge transfer. The interplay between tunnel coupling and the
Coulomb interaction gives rise to an exchange magnetic field, leading to the
precession of the accumulated spin in the QD. It strongly suppresses the
bunching of spin tunneling events and results in a unique double-peak structure
in the noise of the net spin current. The spin autocorrelation is found to be
susceptible to magnetization alignments, which may serve as a sensitive tool to
measure the magnetization directions between the ferromagnetic electrodes.",2403.08621v1
2023-02-28,Magnetic field control of light-induced spin accumulation in monolayer MoSe$_2$,"Semiconductor transition metal dichalcogenides (TMDs) have equivalent
dynamics for their two spin/valley species. This arises from their
energy-degenerated spin states, connected via time-reversal symmetry. When an
out-of-plane magnetic field is applied, time-reversal symmetry is broken and
the energies of the spin-polarized bands shift, resulting in different bandgaps
and dynamics in the K$_+$ and K$_-$ valleys. Here, we use time-resolved Kerr
rotation to study the magnetic field dependence of the spin dynamics in
monolayer MoSe$_2$. We show that the magnetic field can control the
light-induced spin accumulation of the two valley states, with a small effect
on the recombination lifetimes. We unveil that the magnetic field-dependent
spin accumulation is in agreement with hole spin dynamics at the longer
timescales, indicating that the electron spins have faster relaxation rates. We
propose a rate equation model that suggests that lifting the energy-degeneracy
of the valleys induces an ultrafast spin-flip toward the stabilization of the
valley with the higher valence band energy. Our results provide an experimental
insight into the ultrafast charge and spin dynamics in TMDs and a way to
control it, which will be useful for the development of new spintronic and
valleytronic applications.",2302.14206v1
2012-02-24,Dynamical Magnetic and Nuclear Polarization in Complex Spin Systems: Semi-magnetic II-VI Quantum Dots,"Dynamical magnetic and nuclear polarization in complex spin systems is
discussed on the example of transfer of spin from exciton to the central spin
of magnetic impurity in a quantum dot in the presence of a finite number of
nuclear spins. The exciton is described in terms of the electron and heavy hole
spins interacting via exchange interaction with magnetic impurity, via
hypeprfine interaction with a finite number of nuclear spins and via dipole
interaction with photons. The time-evolution of the exciton, magnetic impurity
and nuclear spins is calculated exactly between quantum jumps corresponding to
exciton radiative recombination. The collapse of the wavefunction and the
refilling of the quantum dot with new spin polarized exciton is shown to lead
to build up of magnetization of the magnetic impurity as well as nuclear spin
polarization. The competition between electron spin transfer to magnetic
impurity and to nuclear spins simultaneous with the creation of dark excitons
is elucidated. The technique presented here opens up the possibility of
studying optically induced Dynamical Magnetic and Nuclear Polarization in
Complex Spin Systems.",1202.5352v3
2009-12-17,An improved effective-one-body Hamiltonian for spinning black-hole binaries,"Building on a recent paper in which we computed the canonical Hamiltonian of
a spinning test particle in curved spacetime, at linear order in the particle's
spin, we work out an improved effective-one-body (EOB) Hamiltonian for spinning
black-hole binaries. As in previous descriptions, we endow the effective
particle not only with a mass m, but also with a spin S*. Thus, the effective
particle interacts with the effective Kerr background (having spin S_Kerr)
through a geodesic-type interaction and an additional spin-dependent
interaction proportional to S*. When expanded in post-Newtonian (PN) orders,
the EOB Hamiltonian reproduces the leading order spin-spin coupling and the
spin-orbit coupling through 2.5PN order, for any mass-ratio. Also, it
reproduces all spin-orbit couplings in the test-particle limit. Similarly to
the test-particle limit case, when we restrict the EOB dynamics to spins
aligned or antialigned with the orbital angular momentum, for which circular
orbits exist, the EOB dynamics has several interesting features, such as the
existence of an innermost stable circular orbit, a photon circular orbit, and a
maximum in the orbital frequency during the plunge subsequent to the inspiral.
These properties are crucial for reproducing the dynamics and
gravitational-wave emission of spinning black-hole binaries, as calculated in
numerical relativity simulations.",0912.3517v2
2020-05-08,$s$-$d$ model for local and nonlocal spin dynamics in laser-excited magnetic heterostructures,"We discuss a joint microscopic theory for the laser-induced magnetization
dynamics and spin transport in magnetic heterostructures based on the $s$-$d$
interaction. Angular momentum transfer is mediated by scattering of itinerant
$s$ electrons with the localized ($d$ electron) spins. We use the corresponding
rate equations and focus on a spin one-half $d$ electron system, leading to a
simplified analytical expression for the dynamics of the local magnetization
that is coupled to an equation for the non-equilibrium spin accumulation of the
$s$ electrons. We show that this description converges to the microscopic
three-temperature model in the limit of a strong $s$-$d$ coupling. The equation
for the spin accumulation is used to introduce diffusive spin transport. The
presented numerical solutions show that during the laser-induced
demagnetization in a ferromagnetic metal a short-lived spin accumulation is
created that counteracts the demagnetization process. Moreover, the spin
accumulation leads to the generation of a spin current at the interface of a
ferromagnetic and non-magnetic metal. Depending on the specific magnetic
system, both local spin dissipation and interfacial spin transport are able to
enhance the demagnetization rate by providing relaxation channels for the spin
accumulation that is build up during demagnetization in the ferromagnetic
material.",2005.03905v2
2022-09-27,Spin Berry curvature of the Haldane model,"The feedback of the geometrical Berry phase, accumulated in an electron
system, on the slow dynamics of classical degrees of freedom is governed by the
Berry curvature. Here, we study local magnetic moments, modelled as classical
spins, which are locally exchange coupled to the (spinful) Haldane model for a
Chern insulator. In the emergent equations of motion for the slow
classical-spin dynamics there is a an additional anomalous geometrical spin
torque, which originates from the corresponding spin-Berry curvature. Due to
the explicitly broken time-reversal symmetry, this is nonzero but usually small
in a condensed-matter system. We develop the general theory and compute the
spin-Berry curvature, mainly in the limit of weak exchange coupling, in various
parameter regimes of the Haldane model, particularly close to a topological
phase transition and for spins coupled to sites at the zigzag edge of the model
in a ribbon geometry. The spatial structure of the spin-Berry curvature tensor,
its symmetry properties, the distance dependence of its nonlocal elements and
further properties are discussed in detail. For the case of two classical
spins, the effect of the geometrical spin torque leads to an anomalous
non-Hamiltonian spin dynamics. It is demonstrated that the magnitude of the
spin-Berry curvature is decisively controlled by the size of the insulating
gap, the system size and the strength of local exchange coupling.",2209.13629v2
1998-10-20,Unconventional ferromagnetic and spin-glass states of the reentrant spin glass Fe0.7Al0.3,"Spin excitations of single crystal Fe0.7Al0.3 were investigated over a wide
range in energy and reciprocal space with inelastic neutron scattering. In the
ferromagnetic phase, propagating spin wave modes become paramagnon-like
diffusive modes beyond a critical wave vector q0, indicating substantial
disorder in the long-range ordered state. In the spin glass phase, spin
dynamics is strongly q-dependent, suggesting remnant short-range spin
correlations. Quantitative model for S(energy,q) in the ``ferromagnetic'' phase
is determined.",9810265v2
1999-09-16,Mean-Field Theory of a Quantum Heisenberg Spin Glass,"A full mean field solution of a quantum Heisenberg spin glass model is
presented in a large-N limit. A spin glass transition is found for all values
of the spin S. The quantum critical regime associated with the quantum
transition at S=0, and the various regimes in the spin glass phase at high spin
are analyzed. The specific heat is shown to vanish linearly with temperature.
In the spin-glass phase, intriguing connections between the equilibrium
properties of the quantum problem and the out-of-equilibrium dynamics of
classical models are pointed out.",9909239v1
2001-09-21,Spin waves in a Bose-condensed atomic spin chain,"The spin dynamics of atomic Bose-Einstein condensates confined in a
one-dimensional optical lattice is studied. The condensates at each lattice
site behave like spin magnets that can interact with each other through both
the light-induced dipole-dipole interaction and the static magnetic
dipole-dipole interaction. We show how these site-to-site dipolar interactions
can distort the ground state spin orientations and lead to the excitation of
spin waves. The dispersion relation of the spin waves is studied and possible
detection schemes are proposed.",0109415v1
2002-01-16,Quantum Spin dynamics of the Bilayer Ferromagnet La(1.2)Sr(1.8)Mn2O7,"We construct a theory of spin wave excitations in the bilayer manganite
La(1.2)Sr(1.8)Mn2O7 based on the simplest possible double-exchange model, but
including leading quantum corrections to the spin wave dispersion and damping.
Comparison is made with recent inelastic neutron scattering experiments. We
find that quantum effects account for some part of the measured damping of spin
waves, but cannot by themselves explain the observed softening of spin waves at
the zone boundary. Furthermore a doping dependence of the total spin wave
dispersion and the optical spin wave gap is predicted.",0201269v1
2003-04-16,Electron spin precession in semiconductor quantum wires with Rashba spin-orbit coupling,"The influence of the Rashba spin-orbit coupling on the electron spin dynamics
is investigated for a ballistic semiconductor quantum wire with a finite width.
We monitor the spin evolution using the time-dependent Schr\""odinger equation.
The pure spin precession characteristic of the 1D limit is lost in a 2D wire
with a finite lateral width. In general, the time evolution in the latter case
is characterized by several frequencies and a nonrigid spin motion.",0304372v1
2004-06-21,Decoherence of Nuclear Spin Quantum Memory in Quantum Dot,"Recently an ensemble of nuclear spins in a quantum dot have been proposed as
a long-lived quantum memory. A quantum state of an electron spin in the dot can
be faithfully transfered into nuclear spins through controlled hyperfine
coupling. Here we study the decoherence of this memory due to nuclear spin
dipolar coupling and inhomogeneous hyperfine interaction during the {\it
storage} period. We calculated the maximum fidelity of writing, storing and
reading operations. Our results show that nuclear spin dynamics can severely
limits the performance of the proposed device for quantum information
processing and storage based on nuclear spins.",0406478v1
2004-08-06,Nonexistence of intrinsic spin currents,"We have described the electron spin dynamics in the presence of the
spin-orbit interaction and disorder using the spin-density matrix method. We
showed that in the Born approximation in the scattering amplitude the spin
current is zero for an arbitrary ratio of the spin-orbit splitting and the
scattering rate. Various types of the disorder potential are studied. We argue
that the bulk spin current has always an {\it extrinsic} nature and depends
explicitely on scattering by impurities since it appears only beyond the Born
approximation in the scattering amplitude.",0408136v1
2005-06-16,Design and control of spin gates in two quantum dots arrays,"We study the spin-spin interaction between quantum dots coupled through a two
dimensional electron gas with spin-orbit interaction. We show that the
interplay between transverse electron focusing and spin-orbit coupling allows
to dynamically change the symmetry of the effective spin-spin Hamiltonian. That
is, the interaction can be changed from Ising-like to Heisenberg-like and vice
versa. The sign and magnitude of the coupling constant can also be tuned.",0506414v1
2005-08-31,Quantum Spin Effect and Short-Range Order above the Curie Temperature,"Using quantum Heisenberg model calculations with Green's function technique
generalized for arbitrary spins, we found that for a system of small spins the
quantum spin effects significantly contribute to the magnetic short-range order
and strongly affect physical properties of magnets. The spin dynamics
investigation confirms that these quantum spin effects favor the persistence of
propagating spin-wave excitations above the Curie temperature. Our
investigation suggests a reconsideration of prevailing point of view on finite
temperature magnetism to include quantum effects and the magnetic short-range
order.",0508781v1
2005-12-13,Knight Field Enabled Nuclear Spin Polarization in Single Quantum Dots,"We demonstrate dynamical nuclear spin polarization in the absence of an
external magnetic field, by resonant circularly polarized optical excitation of
a single electron or hole charged quantum dot. Optical pumping of the electron
spin induces an effective inhomogeneous magnetic (Knight) field that determines
the direction along which nuclear spins could polarize and enables nuclear-spin
cooling by suppressing depolarization induced by nuclear dipole-dipole
interactions. Our observations suggest a new mechanism for spin-polarization
where spin exchange with an electron reservoir plays a crucial role. These
experiments constitute a first step towards quantum measurement of the
Overhauser field.",0512269v1
2006-12-30,Realization of a Room-Temperature Spin Dynamo: The Spin Rectification Effect,"We demonstrate a room temperature spin dynamo where the precession of
electron spins in ferromagnets driven by microwaves manifests itself in a
collective way by generating d.c. currents. The current/power ratio is at least
three orders of magnitude larger than that found previously for spin-driven
currents in semiconductors. The observed bipolar nature and intriguing symmetry
are fully explained by the spin rectification effect via which the nonlinear
combination of spin and charge dynamics creates d.c. currents.",0701013v1
2007-01-26,Zeno and anti-Zeno dynamics in spin-bath models,"We investigate the quantum Zeno and anti-Zeno effects in spin bath models:
the spin-boson model and a spin-fermion model. We show that the Zeno-anti-Zeno
transition is critically controlled by the system-bath coupling parameter, the
same parameter that determines spin decoherence rate. We also discuss the
crossover in a biased system, at high temperatures, and for a nonequilibrium
spin-fermion system, manifesting the counteracting roles of electrical bias,
temperature, and magnetic field on the spin decoherence rate.",0701655v1
2007-09-26,Spin-polarized Current-induced Instability in Spin-Valve with Antiferromagnetic Layer,"In the framework of phenomenological model we consider dynamics of a
compensated collinear antiferromagnet (AFM) in the presence of spin-polarised
current. The model is based on the assumption that AFM spins are localised and
spin torque is transferred to each magnetic sublattice independently. It is
shown that in AFM spin current i) can be a source of the ""negative friction"";
and ii) modifies spin-wave frequencies. Equilibrium state of AFM can be
destabilized by the current polarized in parallel to AFM vector. Threshold
current at which the loss of stability takes place depends upon the magnetic
anisotropy of AFM.",0709.4172v1
2007-09-29,Elliptic functions and efficient control of Ising spin chains with unequal couplings,"In this article, we study optimal control of dynamics in a linear chain of
three spin 1/2, weakly coupled with unequal Ising couplings. We address the
problem of time-optimal synthesis of multiple spin quantum coherences. We
derive time-optimal pulse sequence for creating a desired spin order by
computing geodesics on a sphere under a special metric. The solution to the
geodesic equation is related to the nonlinear oscillator equation and the
minimum time to create multiple spin order can be expressed in terms of an
elliptic integral. These techniques are used for efficient creation of multiple
spin coherences in Ising spin-chains with unequal couplings.",0710.0075v1
2008-01-22,W-like states of N uncoupled spins 1/2,"The exact dynamics of a disordered spin star system, describing a central
spin coupled to N distinguishable and non interacting spins 1/2, is reported.
Exploiting their interaction with the central single spin system, we present
possible conditional schemes for the generation of W-like states, as well as of
well-defined angular momentum states, of the N uncoupled spins. We provide in
addition a way to estimate the coupling intensity between each of the N spins
and the central one. Finally the feasibility of our procedure is briefly
discussed.",0801.3391v1
2009-07-02,Theory of frequency-dependent spin current noise through correlated quantum dots,"We analyze the equilibrium and non-equilibrium frequency-dependent spin
current noise and spin conductance through a quantum dot in the local moment
regime. Spin current correlations are shown to behave markedly differently from
charge correlations: Equilibrium spin cross-correlations are suppressed at
frequencies below the Kondo scale, and are characterized by a universal
function that we determine numerically for zero temperature. For asymmetrical
quantum dots dynamical spin accumulation resonance is found for frequencies of
the order of the Kondo energy. At higher temperatures surprising low-frequency
anomalies related to overall spin conservation appear.",0907.0475v2
2009-09-18,GHz Spin Noise Spectroscopy in n-Doped Bulk GaAs,"We advance spin noise spectroscopy to an ultrafast tool to resolve high
frequency spin dynamics in semiconductors. The optical non-demolition
experiment reveals the genuine origin of the inhomogeneous spin dephasing in
n-doped GaAs wafers at densities at the metal-to-insulator transition. The
measurements prove in conjunction with depth resolved spin noise measurements
that the broadening of the spin dephasing rate does not result from thermal
fluctuations or spin-phonon interaction, as previously suggested, but from
surface electron depletion.",0909.3406v3
2010-03-09,Laser-catalyzed spin-exchange process in a Bose-Einstein condensate,"We show theoretically that it is possible to optically control collective
spin-exchange processes in spinor Bose condensates through virtual
photoassociation. The interplay between optically induced spin exchange and
spin-dependent collisions provides a flexible tool for the control of atomic
spin dynamics, including enhanced or inhibited quantum spin oscillations, the
optically-induced ferromagnetic-to-antiferromagnetic transition, and coherent
matter-wave spin conversion.",1003.1812v1
2011-03-30,Theory of spin noise in nanowires,"We develop a theory of spin noise in semiconductor nanowires considered as
prospective elements for spintronics. In these structures spin-orbit coupling
can be realized as a random function of coordinate correlated on the spatial
scale of the order of 10 nm. By analyzing different regimes of electron
transport and spin dynamics, we demonstrate that the spin relaxation can be
very slow and the resulting noise power spectrum increases algebraically as
frequency goes to zero. This effect makes spin effects in nanowires best
suitable for studies by rapidly developing spin-noise spectroscopy.",1103.6040v2
2011-06-15,Dynamics of Spin Relaxation in Finite-Size 2D Systems: an Exact Solution,"We find an exact solution for the problem of electron spin relaxation in a 2D
circle with Rashba spin-orbit interaction. Our analysis shows that the spin
relaxation in finite-size regions involves three stages and is described by
multiple spin relaxation times. It is important that the longest spin
relaxation time increases with decrease in system radius but always remains
finite. Therefore, at long times, the spin polarization in small 2D systems
decays exponentially with a size-dependent rate. This prediction is supported
by results of Monte Carlo simulations.",1106.2989v1
2011-12-02,Initialization and Readout of Spin Chains for Quantum Information Transport,"Linear chains of spins acting as quantum wires are a promising approach to
achieve scalable quantum information processors. Nuclear spins in apatite
crystals provide an ideal test-bed for the experimental study of quantum
information transport, as they closely emulate a one-dimensional spin chain.
Nuclear Magnetic Resonance techniques can be used to drive the spin chain
dynamics and probe the accompanying transport mechanisms. Here we demonstrate
initialization and readout capabilities in these spin chains, even in the
absence of single-spin addressability. These control schemes enable preparing
desired states for quantum information transport and probing their evolution
under the transport Hamiltonian. We further optimize the control schemes by a
detailed analysis of $^{19}$F NMR lineshape.",1112.0459v1
2012-07-22,Manipulating the Voltage Dependence of Tunneling Spin Torques,"Voltage-driven spin transfer torques in magnetic tunnel junctions provide an
outstanding tool to design advanced spin-based devices for memory and
reprogrammable logic applications. The non-linear voltage dependence of the
torque has a direct impact on current-driven magnetization dynamics and on
devices performances. After a brief overview of the progress made to date in
the theoretical description of the spin torque in tunnel junctions, I present
different ways to alter and control the bias dependence of both components of
the spin torque. Engineering the junction (barrier and electrodes) structural
asymmetries or controlling the spin accumulation profile in the free layer
offer promising tools to design efficient spin devices.",1207.5231v1
2012-11-21,The quantum dynamics of two coupled large spins,"We calculate the time evolution of mean spin components and the squared
I-concurrence of two coupled large spins S. As the initial conditions we take
two cases: spin coherent states and uniform superposition states. For the spin
coherent states we have obtained the asymptotic for-mulas at S>>1 and t<<T (T
is period). We draw a conclusion that quantum computation on qudits,
represented by large spins, do not get the principal limitations on the spin
number S.",1211.4926v1
2013-06-04,Collective Spin-Hall Effect for Electron-Hole Gratings,"We show that an electric field parallel to the wavefronts of an electron-hole
grating in a GaAs quantum well generates, via the electronic spin Hall effect,
a spin grating of the same wave vector and with an amplitude that can exceed 1%
of the amplitude of the initial density grating. We refer to this phenomenon as
""collective spin Hall effect"". A detailed study of the coupled-spin charge
dynamics for quantum wells grown in different directions reveals rich features
in the time evolution of the induced spin density, including the possibility of
generating a helical spin grating.",1306.0889v1
2015-04-27,Helical Spin Order from Topological Dirac and Weyl Semimetals,"We study dynamical mass generation and the resultant helical spin orders in
topological Dirac and Weyl semimetals, including the edge states of quantum
spin Hall insulators, the surface states of weak topological insulators, and
the bulk materials of Weyl semimetals. In particular, the helical spin textures
of Weyl semimetals manifest the spin-momentum locking of Weyl fermions in a
visible manner. The spin-wave fluctuations of the helical order carry electric
charge density; therefore, the spin textures can be electrically controlled in
a simple and predictable manner.",1504.07178v2
2015-06-23,Magnetic Excitations of Spin Nematic State in Frustrated Ferromagnetic Chain,"By exploiting density-matrix renormalization group techniques, we investigate
the dynamical spin structure factor of a spin-1/2 Heisenberg chain with
ferromagnetic nearest-neighbor and antiferromagnetic next-nearest-neighbor
exchange interactions in an applied magnetic field. In a field-induced spin
nematic regime, we find gapless longitudinal and gapped transverse spin
excitation spectra, in accordance with quasi-long-ranged longitudinal and
short-ranged transverse spin correlations, respectively. The gapless point
coincides with the dominant longitudinal spin correlation, whereas the gap
position exhibits a characteristic field dependence contradicting the dominant
transverse spin correlation.",1506.06891v1
2015-11-23,Nonlocal spin torques in Rashba quantum wires with steep magnetic textures,"We provide a general procedure to calculate the current-induced spin-transfer
torque which acts on a general steep magnetic texture due to the exchange
interaction with an applied spin-polarized current. As an example, we consider
a one-dimensional ferromagnetic quantum wire and also include a Rashba
spin-orbit interaction. The spin-transfer torque becomes generally spatially
non-local. Likewise, the Rashba spin-orbit interaction induces a spatially
nonlocal field-like nonequilibrium spin-transfer torque. We also find a
spatially varying nonadiabaticity parameter and markedly different domain wall
dynamics for very steep textures as compared to wide domain walls.",1511.07264v1
2016-09-19,Effective indirect multi-site spin-spin interactions in the s-d(f) model,"Using the diagram technique for Matsubara Green's functions it is shown that
the dynamics of the localized spin subsystem in the s-d(f) model can be
described in terms of an effective spin model with multi-site spin-spin
interactions. An exact representation of the action for the effective purely
spin model is derived as an infinite series in powers of s-d(f) exchange
interaction $J$. The indirect interactions of the 2-nd, 3-rd and 4-th order are
discussed.",1609.05603v1
2016-09-19,Characterization of spin-orbit fields in InGaAs quantum wells,"Coherent electron spin dynamics in 10-nm-wide InGaAs/InAlAs quantum wells is
studied from 10 K to room temperature using time-resolved Kerr rotation. The
spin lifetime exceeds 1 ns at 10 K and decreases with temperature. By varying
the spatial overlap between pump and probe pulses, a diffusive velocity is
imprinted on the measured electron spins and a spin precession in the
spin-orbit field is measured. A Rashba symmetry of the SOI is determined. By
comparing the spatial precession frequency gradient with the spin decay rate,
an upper limit for the Rashba coefficients $\alpha$ of 2$\times$10$^{-12}$ eVm
is estimated.",1609.05725v1
2016-10-30,"Kinetic analysis of spin current contribution to spectrum of electromagnetic waves in spin-1/2 plasma, Part I: Dielectric permeability tensor for magnetized plasmas","The dielectric permeability tensor for spin polarized plasmas is derived in
terms of the spin-1/2 quantum kinetic model in six-dimensional phase space.
Expressions for the distribution function and spin distribution function are
derived in linear approximations on the path of dielectric permeability tensor
derivation. The dielectric permeability tensor is derived the spin-polarized
degenerate electron gas. It is also discussed at the finite temperature regime,
where the equilibrium distribution function is presented by the spin-polarized
Fermi-Dirac distribution. Consideration of the spin-polarized equilibrium
states opens possibilities for the kinetic modeling of the thermal spin current
contribution in the plasma dynamics.",1610.09689v1
2010-05-03,Dynamical exchange interaction between localized spins out of equilibrium,"The electron mediated exchange interaction between local spins adsorbed on
two-dimensional surface is studied under non-equilibrium conditions. The
effective spin-spin interaction is found to depend both on the
spin-polarization of the substrate and the excitation spectrum of the local
spins. For spatially anisotropic spin-polarization of the substrate, the
spatial dependence of the interaction comprise components decaying as
sin(2k_FR)/(2k_FR) and sin(2k_FR)/(2k_FR)^2.",1005.0259v3
2008-07-03,First-principles study of the spin-lattice coulpling in spin frustrated DyMn$_2$O$_5$,"The lattice dynamic properties and spin-phonon coupling in DyMn$_2$O$_5$ are
studied by using the density-functional theory. The calculated phonon
frequencies are in very good agreement with experiments. We then compare the
phonon modes calculated from different spin configurations. The results show
that the phonon frequencies change substantially in different spin
configurations, suggesting that the spin-phonon coupling in this material is
very strong. Especially, the short range spin ordering has drastic effects on
the highest Raman and IR phonon modes that might be responsible for the
observed phonon anomalies near and above the magnetic phase transitions.",0807.0470v2
2012-04-03,Spin Turbulence in a Trapped Spin-1 Spinor Bose--Einstein Condensate,"We numerically study spin turbulence in a two-dimensional trapped spin-1
spinor Bose--Einstein condensate, focusing on the energy spectrum. The spin
turbulence in the trapped system is generated by instability of the helical
structure of the spin density vector in the initial state. Our numerical
calculation finds that in the trapped system the spectrum of the spin-dependent
interaction energy in the ferromagnetic case exhibits a -7/3 power law, which
was confirmed in a uniform system by our previous study. The relation between
the -7/3 power law and the motion of the spin density vector is discussed by
investigating the orbits of dynamical variables in the spin space.",1204.0619v1
2017-11-20,Dynamical suppression of fluctuations in an interacting nuclear spin bath of a self-assembled quantum dot using multiple pulse nuclear magnetic resonance,"Electron spin qubit coherence in quantum dots is ultimately limited by random
nuclear spin bath fluctuations. Here we aim to eliminate this randomness by
making spin bath evolution deterministic. We introduce spin bath control
sequences, which systematically combine Hahn and solid echoes to suppress
inhomogeneous broadening and nuclear-nuclear interactions. Experiments on
self-assembled quantum dots show a five-fold increase in nuclear spin
coherence. Numerical simulations show that these sequences can be used to
suppress decoherence via qubit-qubit interaction in point defect and dopant
spin systems.",1711.07238v1
2022-08-06,Driving a pure spin current from nuclear-polarization gradients,"A pure spin current is predicted to occur when an external magnetic field and
a linearly inhomogeneous spin-only field are appropriately aligned. Under these
conditions (such as originate from nuclear contact hyperfine fields that do not
affect orbital motion) a linear, spin-dependent dispersion for free electrons
emerges from the Landau Hamiltonian. The result is that spins of opposite
orientation flow in opposite directions giving rise to a pure spin current. A
classical model of the spin and charge dynamics reveals intuitive aspects of
the full quantum mechanical solution. We propose optical orientation or
electrical polarization experiments to demonstrate this outcome.",2208.03414v1
2023-03-10,Chiral spin channels in curved graphene $pn$ junctions,"We show that the chiral modes in circular graphene $pn$ junctions provide an
advantage for spin manipulation via spin-orbit coupling compared to
semiconductor platforms. We derive the effective Hamiltonian for the spin
dynamics of the junction's zero modes and calculate their quantum phases. We
find a sweet spot in parameter space where the spin is fully in-plane and
radially polarized for a given junction polarity. This represents a shortcut to
singular spin configurations that would otherwise require spin-orbit coupling
strengths beyond experimental reach.",2303.05833v2
2023-12-30,Spin current generation due to differential rotation,"We study nonequilibrium spin dynamics in differentially rotating systems,
deriving an effective Hamiltonian for conduction electrons in the comoving
frame. In contrast to conventional spin current generation mechanisms that
require vorticity, our theory describes spins and spin currents arising from
differentially rotating systems regardless of vorticity. We demonstrate the
generation of spin currents in differentially rotating systems, such as liquid
metals with Taylor-Couette flow. Our alternative mechanism will be important in
the development of nanomechanical spin devices.",2401.00174v1
2024-02-29,Inertial spin waves in spin spirals,"Inertial effects in spin dynamics emerge on picosecond time scales, giving
rise to nutational excitations at THz frequencies. Here, we describe a general
framework for investigating the precessional and nutational excitations in any
type of spin structure within linear spin-wave theory. We consider the
particular cases of planar and conical spin spirals in detail. We observe a
change in the sign of the curvature of the high-frequency nutational spin-wave
band as the spiral period is decreased when passing from the ferromagnetic to
the antiferromagnetic limit. We identify conditions for the interaction
parameters where the curvature changes sign and asymptotical flat bands are
formed.",2402.19141v1
2014-11-11,Magnonic Charge Pumping via Spin-Orbit Coupling,"The interplay between spin, charge, and orbital degrees of freedom has led to
the development of spintronic devices like spin-torque oscillators, spin-logic
devices, and spin-transfer torque magnetic random-access memories. In this
development spin pumping, the process where pure spin-currents are generated
from magnetisation precession, has proved to be a powerful method for probing
spin physics and magnetisation dynamics. The effect originates from direct
conversion of low energy quantised spin-waves in the magnet, known as magnons,
into a flow of spins from the precessing magnet to adjacent normal metal leads.
The spin-pumping phenomenon represents a convenient way to electrically detect
magnetisation dynamics, however, precessing magnets have been limited so far to
pump pure spin currents, which require a secondary spin-charge conversion
element such as heavy metals with large spin Hall angle or multi-layer layouts
to be detectable. Here, we report the experimental observation of charge
pumping in which a precessing ferromagnet pumps a charge current, demonstrating
direct conversion of magnons into high-frequency currents via the relativistic
spin-orbit interaction. The generated electric current, differently from spin
currents generated by spin-pumping, can be directly detected without the need
of any additional spin to charge conversion mechanism and amplitude and phase
information about the relativistic current-driven magnetisation dynamics. The
charge-pumping phenomenon is generic and gives a deeper understanding of the
recently observed spin-orbit torques, of which it is the reciprocal effect and
which currently attract interest for their potential in manipulating magnetic
information. Furthermore, charge pumping provides a novel link between
magnetism and electricity and may find application in sourcing alternating
electric currents.",1411.2779v1
2019-01-31,Chaos-preserving reduction of the spin-flip model for VCSELs: failure of the adiabatic elimination of the spin-population difference,"When studying the dynamics of Vertical-Cavity Surface-Emitting Lasers, and
their polarization properties, the spin-flip model appears to be the simplest
model qualitatively reproducing all dynamical features that have been observed
experimentally. Nonetheless, because of the fast time-scale of the
spin-relaxation processes, the specific role and the importance of the
spin-population difference - which is one of the specific feature of the
spin-flip model - has been continuously questioned. In fact, the debate
regarding the possible adiabatic elimination of the spin-population remains
fully open.
  In this paper, our goal is to bring new light into this issue by
demonstrating that this variable is essential to preserve the most complex
dynamical features predicted by the spin-flip model, such as polarization
chaos, and, therefore, needs to be conserved. To do so, we first perform a
detailed analysis, focusing on the chaotic dynamics, to determine the minimal
embedding dimension for the spin-flip model. As the latter confirms that a
reduction of the model could be envisaged, we then consider the adiabatic
elimination of the spin-population difference to highlight and explain its
failure to reproduce essential dynamical features obtained in the original
model.",1902.00055v3
2003-06-27,Spin Singlet Mott States and Evidence For Spin Singlet Quantum Condensates of Spin-One Bosons in Lattices,"We have investigated spin singlet Mott states of spin-one bosons with
antiferromagnetic interactions. These spin singlet states do not break
rotational symmetry and exhibit remarkably different macroscopic properties
compared with nematic Mott states of spin-one bosons. We demonstrate that the
dynamics of spin singlet Mott states is fully characterized by even- and
odd-class quantum dimer models. The difference between spin singlet Mott states
for even and odd numbers of atoms per site can be attributed to a selection
rule in the low energy sectors of on-site Hilbert spaces; alternatively, it can
also be attributed to an effect of Berry's phases on bosonic Mott states.
  We also discuss evidence for spin singlet quantum condensate of spin-one
atoms. Our main finding is that in a projected spin singlet Hilbert space, the
low energy physics of spin-one bosons is fully characterized by a Bose-Hubbard
model of interacting spinless bosons carrying charges of Ising gauge fields;
the other major finding is spin-charge separation in some one-dimensional Mott
states. We propose charge-e spin singlet superfluid for an odd number of atoms
per lattice site and charge-2e spin singlet superfluid for an even number of
atoms per lattice site in one-dimensional lattices. All discussions in this
article are limited to integer numbers of bosons per site.",0306697v2
2007-06-17,Frequency dependence of induced spin polarization and spin current in quantum wells,"Dynamic response of two-dimensional electron systems with spin-orbit
interaction is studied theoretically on the basis of quantum kinetic equation,
taking into account elastic scattering of electrons. The spin polarization and
spin current induced by the applied electric field are calculated for the whole
class of electron systems described by p-linear spin-orbit Hamiltonians. The
absence of nonequilibrium intrinsic static spin currents is confirmed for these
systems with arbitrary (nonparabolic) electron energy spectrum. Relations
between the spin polarization, spin current, and electric current are
established. The general results are applied to the quantum wells grown in
[001] and [110] crystallographic directions, with both Rashba and Dresselhaus
types of spin-orbit coupling. It is shown that the existence of the fixed
(momentum-independent) precession axes in [001]-grown wells with equal Rashba
and Dresselhaus spin velocities or in symmetric [110]-grown wells leads to
vanishing spin polarizability at arbitrary frequency of the applied electric
field. This property is explained by the absence of Dyakonov-Perel-Kachorovskii
spin relaxation for the spins polarized along these precession axes. As a
result, a considerable frequency dispersion of spin polarization at very low
frequency in the vicinity of the fixed precession axes is predicted. Possible
effects of extrinsic spin-orbit coupling on the obtained results are discussed.",0706.2463v1
2014-11-12,Spin Hall effect,"Spin Hall effects are a collection of relativistic spin-orbit coupling
phenomena in which electrical currents can generate transverse spin currents
and vice versa. Although first observed only a decade ago, these effects are
already ubiquitous within spintronics as standard spin-current generators and
detectors. Here we review the experimental and theoretical results that have
established this sub-field of spintronics. We focus on the results that have
converged to give us a clear understanding of the phenomena and how they have
evolved from a qualitative to a more quantitative measurement of spin-currents
and their associated spin-accumulation. Within the experimental framework, we
review optical, transport, and magnetization-dynamics based measurements and
link them to both phenomenological and microscopic theories of the effect.
Within the theoretical framework, we review the basic mechanisms in both the
extrinsic and intrinsic regime which are linked to the mechanisms present in
their closely related phenomenon in ferromagnets, the anomalous Hall effect. We
also review the connection to the phenomenological treatment based on
spin-diffusion equations applicable to certain regimes, as well as the
spin-pumping theory of spin-generation which has proven important in the
measurements of the spin Hall angle. We further connect the spin-current
generating spin Hall effect to the inverse spin galvanic effect, which often
accompanies the SHE, in which an electrical current induces a non-equilibrium
spin polarization. These effects share common microscopic origins and can
exhibit similar symmetries when present in ferromagnetic/non-magnetic
structures through their induced current-driven spin torques. Although we give
a short chronological overview, the main body is structured from a pedagogical
point of view, focusing on well-established and accepted physics.",1411.3249v1
2018-12-20,Continuous dynamical decoupling of spin chains: modulating the spin-environment and spin-spin interactions,"For spins chains to be useful for quantum information processing tasks, the
interaction between the spin chain and its environment generally needs to be
suppressed. In this paper, we propose the use of strong static and oscillating
control fields in order to effectively remove the spin chain-environment
interaction. We find that our control fields can also effectively transform the
spin chain Hamiltonian. In particular, interaction terms which are absent in
the original spin chain Hamiltonian appear in the time-averaged effective
Hamiltonian once the control fields are applied, implying that spin-spin
interactions can be engineered via the application of static and oscillating
control fields. This transformation of the spin chain can then potentially be
used to improve the performance of the spin chain for quantum information
processing tasks. For example, our control fields can be used to achieve almost
perfect quantum state transfer across a spin chain even in the presence of
noise. As another example, we show how the use of particular static and
oscillating control fields not only suppresses the effect of the environment,
but can also improve the generation of two-spin entanglement in the spin chain.",1812.08403v3
2001-07-02,Thermodynamics and Spin Tunneling Dynamics in Ferric Wheels with Excess Spin,"We study theoretically the thermodynamic properties and spin dynamics of a
class of magnetic rings closely related to ferric wheels, antiferromagnetic
ring systems, in which one of the Fe (III) ions has been replaced by a dopant
ion to create an excess spin. Using a coherent-state spin path integral
formalism, we derive an effective action for the system in the presence of a
magnetic field. We calculate the functional dependence of the magnetization and
tunnel splitting on the magnetic field and show that the parameters of the spin
Hamiltonian can be inferred from the magnetization curve. We study the spin
dynamics in these systems and show that quantum tunneling of the Neel vector
also results in tunneling of the total magnetization. Hence, the spin
correlation function shows a signature of Neel vector tunneling, and electron
spin resonance (ESR) techniques or AC susceptibility measurements can be used
to measure both the tunneling and the decoherence rate. We compare our results
with exact diagonalization studies on small ring systems. Our results can be
easily generalized to a wide class of nanomagnets, such as ferritin.",0107025v1
2004-12-14,A microscopic approach to spin dynamics: about the meaning of spin relaxation times,"We present an approach to spin dynamics by extending the optical Bloch
equations for the driven two-level system to derive microscopic expressions for
the transverse and longitudinal spin relaxation times. This is done for the
6-level system of electron and hole subband states in a semiconductor or a
semiconductor quantum structure to account for the degrees-of-freedom of the
carrier spin and the polarization of the exciting light and includes the
scattering between carriers and lattice vibrations on a microscopic level. For
the subsystem of the spin-split electron subbands we treat the electron-phonon
interaction in second order and derive a set of equations of motion for the 2x2
spin-density matrix which describes the electron spin dynamics and contains
microscopic expressions for the longitudinal (T_1) and the transverse (T_2)
spin relaxation times. Their meaning will be discussed in relation to
experimental investigations of these quantities.",0412370v1
2005-03-19,"Correlations, spin dynamics, defects: the highly-frustrated Kagomé bilayer","The SrCr$\_{9p}$Ga$\_{12-9p}$O$\_{19}$ and
Ba$\_{2}$Sn$\_{2}$ZnGa$\_{10-7p}$Cr$\_{7p}$O$\_{22}$ compounds are two
highly-frustrated magnets possessing a quasi-two-dimensional Kagom\'{e} bilayer
of spin 3/2 chromium ions with antiferromagnetic interactions. Their magnetic
susceptibility was measured by local Nuclear Magnetic Resonance and non-local
(SQUID) techniques, and their low-temperature spin dynamics by Muon Spin
Resonance. Consistent with the theoretical picture drawn for geometrically
frustrated systems, the Kagom\'{e} bilayer is shown here to exhibit: (i) short
range spin-spin correlations down to a temperature much lower than the
Curie-Weiss temperature, no conventional long-range transition occurring; (ii)
a Curie contribution to the susceptibility from paramagnetic defects generated
by spin vacancies; (iii) low-temperature spin fluctuations, at least down to 30
mK, which are a trademark of a dynamical ground state. These properties point
to a spin-liquid ground state, possibly built on Resonating Valence Bonds with
unconfined spinons as the magnetic excitations.",0503496v1
2006-02-02,Spin Decoherence from Hamiltonian dynamics in Quantum Dots,"The dynamics of a spin-1/2 particle coupled to a nuclear spin bath through an
isotropic Heisenberg interaction is studied, as a model for the spin
decoherence in quantum dots. The time-dependent polarization of the central
spin is calculated as a function of the bath-spin distribution and the
polarizations of the initial bath state. For short times, the polarization of
the central spin shows a gaussian decay, and at later times it revives
displaying nonmonotonic time dependence. The decoherence time scale dep ends on
moments of the bath-spin distribuition, and also on the polarization strengths
in various bath-spin channels. The bath polarizations have a tendency to
increase the decoherence time scale. The effective dynamics of the central spin
polarization is shown to be describ ed by a master equation with non-markovian
features.",0602027v2
2007-10-26,Electron Transport Driven by Nonequilibrium Magnetic Textures,"Spin-polarized electron transport driven by inhomogeneous magnetic dynamics
is discussed in the limit of a large exchange coupling. Electron spins rigidly
following the time-dependent magnetic profile experience spin-dependent
fictitious electric and magnetic fields. We show that the electric field
acquires important corrections due to spin dephasing, when one relaxes the
spin-projection approximation. Furthermore, spin-flip scattering between the
spin bands needs to be taken into account in order to calculate voltages and
spin accumulations induced by the magnetic dynamics. A phenomenological
approach based on the Onsager reciprocity principle is developed, which allows
us to capture the effect of spin dephasing and make a connection to the well
studied problem of current-driven magnetic dynamics. A number of results that
recently appeared in the literature are related and generalized.",0710.5193v2
2009-03-27,Comment on recent papers regarding next-to-leading order spin-spin effects in gravitational interaction,"It is argued that the tetrad in a recent paper by Porto and Rothstein on
gravitational spin-spin coupling should not have the given form. The fixation
of that tetrad was suggested by Steinhoff, Hergt, and Schaefer as a possible
source for the disagreement found in the spin-squared dynamics. However, this
inconsistency will only show up in the next-to-leading order spin-orbit
dynamics and not in the spin-squared dynamics. Instead, the disagreement found
at the next-to-leading order spin-squared level is due to a sign typo in the
spin-squared paper by Porto and Rothstein.",0903.4772v2
2010-06-07,Duality of the spin and density dynamics for two-dimensional electrons with a spin-orbit coupling,"We study spin dynamics in a two-dimensional electron gas with a pure gauge
non-Abelian spin-orbit field, for which systems with balanced Rashba and
Dresselhaus spin-orbit couplings, and the (110)-axis grown GaAs quantum wells
are typical examples. We demonstrate the duality of the spin evolution and the
electron-density dynamics in a system without spin-orbit coupling, which
considerably simplifies and deepens the analysis of spin-dependent processes.
This duality opens a venue for the understanding of this class of systems,
highly interesting for their applications in spintronics, through known
properties of the systems without spin-orbit coupling.",1006.1202v3
2013-04-22,Giant enhancement of spin pumping efficiency using Fe3Si ferromagnet,"Spincurrentronics, which involves the generation, propagation and control of
spin currents, has attracted a great deal of attention because of the
possibility of realizing dissipation-free information propagation. Whereas
electrical generation of spin currents originally made the field of
spincurrentronics possible, and significant advances in spin-current devices
has been made, novel spin-current-generation approaches such as dynamical
methods have also been vigorously investigated. However, the low spin-current
generation efficiency associated with dynamical methods has impeded further
progress towards practical spin devices. Here we show that by introducing a
Heusler-type ferromagnetic material, Fe3Si, pure spin currents can be generated
about twenty times more efficiently using a dynamical method. This achievement
paves the way to the development of novel spin-based devices.",1304.5890v1
2013-06-11,Decay of spin coherences in one-dimensional spin systems,"Strategies to protect multi-qubit states against decoherence are difficult to
formulate because of their complex many-body dynamics. A better knowledge of
the decay dynamics would help in the construction of decoupling control
schemes. Here we use solid-state nuclear magnetic resonance techniques to
experimentally investigate the decay of coherent multi-spin states in linear
spin chains. Leveraging on the quasi-one-dimensional geometry of Fluorapatite
crystal spin systems, we can gain a deeper insight on the multi-spin states
created by the coherent evolution, and their subsequent decay, than it is
possible in 3D systems. We are then able to formulate an analytical model that
captures the key features of the decay. We can thus compare the decoherence
behavior for different initial states of the spin chain and link their decay
rate to the state characteristics, in particular their coherence and long-range
correlation among spins. Our experimental and theoretical study shows that the
spin chains undergo a rich dynamics, with a slower decay rate than for the 3D
case, and thus might be more amenable to decoupling techniques.",1306.2620v1
2014-11-19,Dynamical spin injection at a quasi-one-dimensional ferromagnet-graphene interface,"We present a study of dynamical spin injection from a three-dimensional
ferromagnet into two-dimensional single-layer graphene. Comparative
ferromagnetic resonance (FMR) studies of ferromagnet/graphene strips buried
underneath the central line of a coplanar waveguide show that the FMR linewidth
broadening is the largest when the graphene layer protrudes laterally away from
the ferromagnetic strip, indicating that the spin current is injected into the
graphene areas away from the area directly underneath the ferromagnet being
excited. Our results confirm that the observed damping is indeed a signature of
dynamical spin injection, wherein a pure spin current is pumped into the
single-layer graphene from the precessing magnetization of the ferromagnet. The
observed spin pumping efficiency is difficult to reconcile with the expected
backflow of spins according to the standard spin pumping theory and the
characteristics of graphene, and constitutes an enigma for spin pumping in
two-dimensional structures.",1411.5339v2
2015-05-01,Spin-charge transport driven by magnetization dynamics on disordered surface of doped topological insulators,"We theoretically study the spin and charge generation along with the electron
transport on a disordered surface of a doped three-dimensional topological
insulator/magnetic insulator junction by using Green's function techniques. We
find that the spin and charge current are induced by not only local but also
nonlocal magnetization dynamics through nonmagnetic impurity scattering on the
disordered surface of the doped topological insulator. We also clarify that the
spin current as well as charge density are induced by spatially inhomogeneous
magnetization dynamics, and the spin current diffusively propagates on the
disordered surface. Using these results, we discuss both local and nonlocal
spin torques before and after the spin and spin current generation on the
surface, and provide a procedure to detect the spin current.",1505.00106v1
2015-05-18,Spin dynamics and fluctuations in the streaming regime,"Spin dynamics of two-dimensional electrons in moderate in-plane electric
fields is studied theoretically. The streaming regime is considered, where each
electron accelerates until reaching the optical phonon energy, then it emits an
optical phonon, and a new period of acceleration starts. Spin-orbit interaction
and elastic scattering result in anisotropic relaxation of electron spin
polarization. The overall spin dynamics is described by a superposition of spin
modes in the system. The relaxation time of the most long-living mode depends
quasi-periodically on the inverse electric field. The spin modes can be
conveniently revealed by means of spin noise spectroscopy. It is demonstrated
that the spectrum of spin fluctuations consists of peaks with the low-frequency
peak much narrower than satellite ones, and the widths of the peaks are
determined by the decay times of the modes.",1505.04745v1
2016-01-05,Dynamics of interacting fermions in spin-dependent potentials,"Recent experiments with dilute trapped Fermi gases observed that weak
interactions can drastically modify spin transport dynamics and give rise to
robust collective effects including global demagnetization, macroscopic spin
waves, spin segregation, and spin self-rephasing. In this work we develop a
framework for studying the dynamics of weakly interacting fermionic gases
following a spin-dependent change of the trapping potential which illuminates
the interplay between spin, motion, Fermi statistics, and interactions. The key
idea is the projection of the state of the system onto a set of lattice spin
models defined on the single-particle mode space. Collective phenomena,
including the global spreading of quantum correlations in real space, arise as
a consequence of the long-ranged character of the spin model couplings. This
approach achieves good agreement with prior measurements and suggests a number
of directions for future experiments.",1601.01004v3
2016-03-25,Microscopic theory of spin-orbit torques and skyrmion dynamics,"We formulate a general microscopic approach to spin-orbit torques in thin
ferromagnet/heavy-metal bilayers in linear response to electric current or
electric field. The microscopic theory we develop avoids the notion of spin
currents and spin-Hall effect. Instead, the torques are directly related to a
local spin polarization of conduction electrons, which is computed from
generalized Kubo-St\v{r}eda formulas. A symmetry analysis provides a one-to-one
correspondence between polarization susceptibility tensor components and
different torque terms in the Landau-Lifshitz-Gilbert equation for
magnetization dynamics. The spin-orbit torques arising from Rashba or
Dresselhaus type of spin-orbit interaction are shown to have different
symmetries. We analyze these spin-orbit torques microscopically for a generic
electron model in the presence of an arbitrary smooth magnetic texture. For a
model with spin-independent disorder we find a major cancelation of the
torques. In this case the only remaining torque corresponds to the
magnetization-independent Edelstein effect. Furthermore, our results are
applied to analyze the dynamics of a Skyrmion under the action of electric
current.",1603.07994v2
2016-04-15,Low-energy Spin Dynamics of the Honeycomb Spin Liquid Beyond the Kitaev Limit,"We investigate the generic features of the low energy dynamical spin
structure factor of the Kitaev honeycomb quantum spin liquid perturbed away
from its exact soluble limit by generic symmetry-allowed exchange couplings. We
find that the spin gap persists in the Kitaev-Heisenberg model, but generally
vanishes provided more generic symmetry-allowed interactions exist. We
formulate the generic expansion of the spin operator in terms of fractionalized
Majorana fermion operators according to the symmetry enriched topological order
of the Kitaev spin liquid, described by its projective symmetry group. The
dynamical spin structure factor displays power-law scaling bounded by Dirac
cones in the vicinity of the $\Gamma$, $K$ and $K'$ points of the Brillouin
zone, rather than the spin gap found for the exactly soluble point.",1604.04365v2
2017-02-13,Spin Pumping and Inverse Spin Hall Voltages from Dynamical Antiferromagnets,"Dynamical antiferromagnets pump spins efficiently into adjacent conductors as
ferromagnets. The high antiferromagnetic resonance frequencies represent a
challenge for experimental detection, but magnetic fields can reduce these
resonance frequencies. We compute the inverse spin Hall voltages resulting from
dynamical spin excitations as a function of a magnetic field along the easy
axis and the polarization of the driving AC magnetic field perpendicular to the
easy axis. We consider the insulating antiferromagnets MnF$_2$, FeF$_2$, and
NiO. Near the spin-flop transition, there is a significant enhancement of the
DC spin pumping and inverse spin Hall voltage for the uniaxial antiferromagnets
MnF$_2$ and FeF$_2$. In the biaxial NiO, the voltages are much weaker, and
there is no spin-flop enhancement of the DC component.",1702.03779v1
2011-11-21,Wave-diffusion theory of spin transport in metals after ultrashort-pulse excitation,"Spin and charge-current dynamics after ultrafast spin-polarized excitation in
a normal metal are studied theoretically using a wave-diffusion theory. It is
shown analytically how this macroscopic approach correctly describes the
ballistic and diffusive properties of spin and charge transport, but also
applies to the intermediate regime between these two limits. Using the
wave-diffusion equations we numerically analyze spin and charge dynamics after
ultrafast excitation of spin polarized carriers in thin gold films. Assuming
slightly spin-dependent momentum relaxation times, we find that a unified
treatment of diffusive and ballistic transport yields robust signatures in the
spin and charge dynamics, which are in qualitative agreement with recent
experimental results [Phys. Rev. Lett 107, 076601 (2011)]. The influence of
boundary effects on the temporal signatures of spin transport is also studied.",1111.4780v1
2016-08-01,Extended pump-probe Faraday rotation spectroscopy of the submicrosecond electron spin dynamics in n-type GaAs,"We develop an extended pump-probe Faraday rotation technique to study the
submicrosecond electron spin dynamics with picosecond time resolution in a wide
range of magnetic fields. The electron spin dephasing time $T_2^*$ and the
longitudinal spin relaxation time $T_1$, both approaching $250$ ns in weak
fields, are measured thereby in $n$-type bulk GaAs. By tailoring the pump pulse
train through increasing the contained number of pulses, the buildup of
resonant spin amplification is demonstrated for the electron spin polarization.
The spin precession amplitude in high magnetic fields applied in the Voigt
geometry shows a non-monotonic dynamics deviating strongly from a
mono-exponential decay and revealing slow beatings. The beatings indicate a two
spin component behavior with a $g$-factor difference of $\Delta g \sim
4\times10^{-4}$, much smaller than the $\Delta g$ expected for free and
donor-bound electrons. This $g$-factor variation indicates efficient, but
incomplete spin exchange averaging.",1608.00314v4
2017-10-12,Quasiclassical theory of spin dynamics in superfluid $^3$He: kinetic equations in the bulk and spin response of surface Majorana states,"We develop a theory based on the formalism of quasiclassical Green's
functions to study the spin dynamics in superfluid $^3$He. First, we derive
kinetic equations for the spin-dependent distribution function in the bulk
superfluid reproducing the results obtained earlier without quasiclassical
approximation. Then we consider a spin dynamics near the surface of fully
gapped $^3$He-B phase taking into account spin relaxation due to the
transitions in the spectrum of localized fermionic states. The lifetime of
longitudinal and transverse spin waves is calculate taking into account the
Fermi-liquid corrections which lead to the crucial modification of fermionic
spectrum and spin responses.",1710.04468v2
2019-07-11,Image of dynamic local exchange interactions in the dc magnetoresistance of spin-polarized current through a dopant,"We predict strong, dynamical effects in the dc magnetoresistance of current
flowing from a spin-polarized electrical contact through a magnetic dopant in a
nonmagnetic host. Using the stochastic Liouville formalism we calculate
clearly-defined resonances in the dc magnetoresistance when the applied
magnetic field matches the exchange interaction with a nearby spin. At these
resonances spin precession in the applied magnetic field is canceled by spin
evolution in the exchange field, preserving a dynamic bottleneck for spin
transport through the dopant. Similar features emerge when the dopant spin is
coupled to nearby nuclei through the hyperfine interaction. These features
provide a precise means of measuring exchange or hyperfine couplings between
localized spins near a surface using spin-polarized scanning tunneling
microscopy, without any ac electric or magnetic fields, even when the exchange
or hyperfine energy is orders of magnitude smaller than the thermal energy.",1907.05509v1
2018-03-06,Combined Molecular and Spin Dynamics Simulation of BCC Iron with Vacancy Defects,"Utilizing an atomistic computational model which handles both translational
and spin degrees of freedom, combined molecular and spin dynamics simulations
have been performed to investigate the effect of vacancy defects on spin wave
excitations in ferromagnetic iron. Fourier transforms of space and
time-displaced correlation functions yield the dynamic structure factor,
providing characteristic frequencies and lifetimes of the spin wave modes.
Comparison of the system with a 5% vacancy concentration with pure lattice data
shows a decrease in frequency as well as a decrease in lifetime for all
transverse spin wave excitations observed. Additionally, a rugged spin wave
line shape for low-q spin waves indicates the presence of multiple localized
excitations near defect sites resulting in reduced excitation lifetimes due to
increased magnon-magnon scattering. We observe further evidence of increased
magnon-magnon scattering as the peaks in the longitudinal spin wave spectrum
become less distinct.",1803.02468v1
2020-06-20,Stratonovich-Ito integration scheme in ultrafast spin caloritronics,"The magnonic spin Seebeck effect is a key element of spin caloritronic, a
field that exploits thermal effects for spintronic applications. Early studies
were focused on investigating the steady-state nonequilibrium magnonic spin
Seebeck current, and the underlying physics of the magnonic spin Seebeck effect
is now relatively well established. However, the initial steps of the formation
of the spin Seebeck current are in the scope of recent interest. To address
this dynamical aspect theoretically we propose here a new approach to the
time-resolved spin Seebeck effect. Our method exploits the supersymmetric
theory of stochastics and Ito - Stratonovich integration scheme. We found that
in the early step the spin Seebeck current has both nonzero transversal and
longitudinal components. As the magnetization dynamics approaches the
steady-state, the transversal components decay through dephasing over the
dipole-dipole reservoir. The time scale for this process is typically in the
sub-nanoseconds pointing thus to the potential of an ultrafast control of the
dynamical spin Seebeck during its buildup.",2006.11471v1
2021-09-22,Hopfion Dynamics in Chiral Magnets,"Resonant spin dynamics of topological spin textures are correlated with their
topological nature, which can be employed to understand this nature. In this
study, we present resonant spin dynamics of three-dimensional topological spin
texture, i.e., Neel and Bloch hopfions. Using micromagnetic simulations, we
stabilize Bloch and Neel hopfions with bulk and interfacial
Dzyaloshinskii-Moriya interaction (DMI), respectively. We identify the ground
state spin configuration of both hopfions, effects of anisotropies, geometric
confinements, and demagnetizing fields. To confirm topological nature, Hopf
number is calculated for each spin texture. Then, we calculate the resonance
frequencies and spin-wave modes of spin precessions under multiple magnetic
fields. Unique resonance frequencies and specific magnetic field dependence can
help to guide experimental studies to identify the three-dimensional
topological spin texture of hopfions in functioning chiral magnets when imaging
is not possible.",2109.10758v1
2022-01-18,Spin dynamics of electrons and holes interacting with nuclei in MAPbI$_3$ perovskite single crystals,"Methylammonium lead triiodine (MAPbI$_3$) is a material representative of the
hybrid organic-inorganic lead halide perovskites which attract currently great
attention due to their photovoltaic efficiency and bright optoelectronic
properties. Here, the coherent spin dynamics of charge carriers and spin
dependent phenomena induced by the carrier interaction with nuclear spins are
studied in MAPbI$_3$ single crystals, using time-resolved Kerr rotation at
cryogenic temperatures in magnetic fields up to 3 T. Spin dephasing times up to
a few nanoseconds and a longitudinal spin relaxation time of 37 ns are
measured. The Larmor spin precession of both resident electrons and holes is
identified in the Kerr rotation signals. The Land\'e factors ($g$-factors) in
the orthorhombic crystal phase show a strong anisotropy, ranging for the holes
from $-0.28$ to $-0.71$ and for the electrons from $+2.46$ to $+2.98$, while
the $g$-factor dispersion of about 1% is rather small. An exciton $g$-factor of
$+2.3$ is measured by magneto-reflectivity. A dynamic nuclear polarization by
means of spin polarized electrons and holes is achieved in tilted magnetic
fields giving access to the carrier-nuclei exchange interaction and the nuclei
spin relaxation time exceeding 16 minutes.",2201.06867v1
2023-03-01,Numerical Simulations of a Spin Dynamics Model Based on a Path Integral Approach,"Inspired by path integral molecular dynamics, we build a spin model, in terms
of spin coherent states, from which we can compute the quantum expectation
values of a spin in a constant magnetic field, at finite temperature. This
formulation facilitates the description of a discrete quantum spin system in
terms of a continuous classical model and recasts the quantum spin effects
within the framework of path integrals in a double $1/s$ and $\hbar s$
expansion, where $s$ is the magnitude of the spin. In particular, it allows for
a much more direct path to the low- and high-temperature limits of the quantum
system and to the definition of effective classical Hamiltonians that describe
both thermal and quantum fluctuations. In this formalism, the quantum
properties of the spins emerge as an effective anisotropy. We use atomistic
spin dynamics to sample the path integral, calculate thermodynamic observables
and show that our effective classical models can reproduce the thermal
expectation values of the quantum system within temperature ranges relevant for
studying magnetic ordering.",2303.00602v3
2023-06-22,Dynamic-nuclear-polarization-weighted spectroscopy of multi-spin electronic-nuclear clusters,"Nuclear spins and paramagnetic centers in a solid randomly group to form
clusters featuring nearly-degenerate, hybrid states whose dynamics are central
to processes involving nuclear spin-lattice relaxation and diffusion. Their
characterization, however, has proven notoriously difficult mostly due to their
relative isolation and comparatively low concentration. Here, we combine
field-cycling experiments, optical spin pumping, and variable radio-frequency
(RF) excitation to probe transitions between hybrid multi-spin states formed by
strongly coupled electronic and nuclear spins in diamond. Leveraging bulk
nuclei as a collective time-integrating sensor, we probe the response of these
spin clusters as we simultaneously vary the applied magnetic field and RF
excitation to reconstruct multi-dimensional spectra. We uncover complex nuclear
polarization patterns of alternating sign that we qualitatively capture through
analytical and numerical modeling. Our results unambiguously expose the impact
that strongly-hyperfine-coupled nuclei can have on the spin dynamics of the
crystal, and inform future routes to spin cluster control and detection.",2306.13193v1
2016-07-13,Dynamics of Stellar Spin Driven by Planets Undergoing Lidov-Kozai Migration: Paths to Spin-Orbit Misalignment,"Many exoplanetary systems containing hot Jupiters (HJs) exhibit significant
misalignment between the spin axes of the host stars and the orbital angular
momentum axes of the planets (""spin-orbit misalignment""). High-eccentricity
migration involving Lidov-Kozai oscillations of the planet's orbit induced by a
distant perturber is a possible channel for producing such misaligned HJ
systems. Previous works have shown that the dynamical evolution of the stellar
spin axis during the high-$e$ migration plays a dominant role in generating the
observed spin-orbit misalignment. Numerical studies have also revealed various
patterns of the evolution of the stellar spin axis leading to the final
misalignment. Here we develop an analytic theory to elucidate the evolution of
spin-orbit misalignment during the Lidov-Kozai migration of planets in stellar
binaries. Secular spin-orbit resonances play a key role in the misalignment
evolution. We include the effects of short-range forces and tidal dissipation,
and categorize the different possible paths to spin-orbit misalignment as a
function of various physical parameters (e.g. planet mass and stellar rotation
period). We identify five distinct spin-orbit evolution paths and outcomes,
only two of which are capable of producing retrograde orbits. We show that
these paths to misalignment and the outcomes depend only on two dimensionless
parameters, which compare the stellar spin precession frequency with the rate
of change of the planet's orbital axis, and the Lidov-Kozai oscillation
frequency. Our analysis reveals a number of novel phenomena for the stellar
spin evolution, ranging from bifurcation, adiabatic advection, to fully chaotic
evolution of spin-orbit angles.",1607.03937v1
2018-11-23,All-Optical Generation and Tuning of Ultrafast Spin-Hall Current via Optical Vortices,"Spin Hall effect, one of the cornerstones in spintronics refers to the
emergence of an imbalance in the spin density transverse to a charge flow in a
sample under voltage bias. This study points to a novel way for an ultrafast
generation and tuning of a unidirectional nonlinear spin Hall current by means
of subpicosecond laser pulses of optical vortices. When interacting with
matter, the optical orbital angular momentum (OAM) carried by the vortex and
quantified by its topological charge is transferred to the charge carriers. The
residual spin-orbital coupling in the sample together with confinement effects
allow exploiting the absorbed optical OAM for spatio-temporally controlling the
spin channels. Both the non-linear spin Hall current and the dynamical spin
Hall angle increase for a higher optical topological charge. The reason is the
transfer of a higher amount of OAM and the enhancement of the effective
spin-orbit interaction strength. No bias voltage is needed. We demonstrate that
the spin Hall current can be all-optically generated in an open circuit
geometry for ring-structured samples. These results follow from a full-fledged
propagation of the spin-dependent quantum dynamics on a time-space grid coupled
to the phononic environment. The findings point to a versatile and controllable
tool for the ultrafast generation of spin accumulations with a variety of
applications such as a source for ultrafast spin transfer torque and charge and
spin current pulse emitter.",1811.09519v1
2019-07-01,Spin dynamics of moving bodies in rotating black hole spacetimes,"The dynamics of spinning test bodies, moving in rotating black hole (Kerr,
Bardeen-like and Hayward-like) spacetimes, are investigated. In Kerr spacetime,
all the spherical, zoom-whirl and unbound orbits are considered numerically.
Along spherical orbits and for high spin, an amplitude modulation is found in
the harmonic evolution of the spin precessional angular velocity, caused by the
spin-curvature coupling. Along the discussed zoom-whirl and unbound orbits, the
test body approaches the center so much that it passes through the ergosphere.
Near and inside the ergosphere, the variation of the spin direction can be very
rapid. The effects of the spin-curvature coupling is also investigated. The
initial values are chosen such a way, that the body and its spin move in the
equatorial plane of the coordinate space and of the comoving frame,
respectively. Hence, a clear effect of the spin-curvature coupling is observed
as the orbit and the spin vector leave the equatorial plane. Additional effects
in the spin precessional angular velocity and in the evolution of the
Boyer-Lindquist coordinate components of the spin vector is also considered.
Finally, in case of different regular black holes, the spin-curvature coupling
influences differently the orbit and the spin evolutions.",1907.00974v2
2018-06-28,"Signatures of long-range spin-spin interactions in an (In,Ga)As quantum dot ensemble","We present an investigation of the electron spin dynamics in an ensemble of
singly-charged quantum dots subject to an external magnetic field and laser
pumping with circularly polarized light. The spectral laser width is tailored
such that different groups of quantum dots are coherently pumped. Surprisingly,
the dephasing time $T^*$ of the electron spin polarization depends only weakly
on the laser spectral width. These findings can be consistently explained by a
cluster theory of coupled quantum dots with a long range electronic spin-spin
interaction. We present a numerical simulation of the spin dynamics based on
the central spin model that includes a quantum mechanical description of the
laser pulses as well as a time-independent Heisenberg interaction between each
pair of electron spins. We discuss the individual dephasing contributions
stemming from the Overhauser field, the distribution of the electron
$g$-factors and the electronic spin-spin interaction as well as the spectral
width of the laser pulse. This analysis reveals the counterbalancing effect of
the total dephasing time when increasing the spectral laser width. On one hand,
the deviations of the electron $g$-factors increase. On the other hand, an
increasing number of coherently pumped electron spins synchronize due to the
spin-spin interaction. We find an excellent agreement between the experimental
data and the dephasing time in the simulation using an exponential distribution
of Heisenberg couplings with a mean value $\overline{J}\approx
0.26\,\mathrm{\mu eV}$.",1806.11025v1
2021-03-23,The Onset of Chaos in Permanently Deformed Binaries from Spin-Orbit and Spin-Spin Coupling,"Permanently deformed objects in binary systems can experience complex
rotation evolution, arising from the extensively studied effect of spin-orbit
coupling as well as more nuanced dynamics arising from spin-spin interactions.
The ability of an object to sustain an aspheroidal shape largely determines
whether or not it will exhibit non-trivial rotational behavior. In this work,
we adopt a simplified model of a gravitationally interacting primary and
satellite pair, where each body's quadrupole moment is approximated by two
diametrically opposed point masses. After calculating the net gravitational
torque on the satellite from the primary, and the associated equations of
motion, we employ a Hamiltonian formalism which allows for a perturbative
treatment of the spin-orbit and retrograde and prograde spin-spin coupling
states. By analyzing the resonances individually and collectively, we determine
the criteria for resonance overlap and the onset of chaos, as a function of
orbital and geometric properties of the binary. We extend the 2D planar
geometry to calculate the obliquity evolution, and find that satellites in
spin-spin resonances undergo precession when inclined out of the plane, but do
not tumble. We apply our resonance overlap criteria to the contact binary
system (216) Kleopatra, and find that its satellites, Cleoselene and
Alexhelios, may plausibly be exhibiting chaotic rotational dynamics from the
overlap of the spin-orbit and retrograde spin-spin resonances. While this model
is by construction generalizable to any binary system, it will be particularly
useful to study small bodies in the solar system, whose irregular shapes make
them ideal candidates for exotic rotational states.",2103.12484v1
1998-04-07,Peierls Dimerization with Non-Adiabatic Spin-Phonon Coupling,"We study the magnetic properties of a frustrated Heisenberg spin chain with a
dynamic spin-phonon interaction. By Lanczos diagonalization, preserving the
full lattice dynamics, we explore the non-adiabatic regime with phonon
frequencies comparable to the exchange coupling energy which is e.g. the
relevant limit for the spin-Peierls compound $CuGeO_3$. When compared to the
static limit of an alternating spin chain the magnetic properties are strongly
renormalized due to the coupled dynamics of spin and lattice degrees of
freedom. The magnitude of the spin triplet excitation gap changes from a strong
to a weak dimerization dependence with increasing phonon frequencies implying
the necessity to include dynamic effects in an attempt for a quantitative
description of the spin-Peierls state.",9804085v2
2005-11-04,Lattice effects on the spin dynamics in antiferromagnetic molecular rings,"We investigate spin dynamics in antiferromagnetic (AF) molecular rings at
finite temperature in the presence of spin-phonon (s-p) interaction. We derive
a general expression for the spin susceptibility in the weak s-p coupling limit
and then we focus on the low-frequency behavior, in order to discuss a possible
microscopic mechanism for nuclear relaxation in this class of magnetic
materials. To lowest order in a perturbative expansion, we find that the
susceptibility takes a Lorentzian profile and all spin operators ($S^x$, $S^y,
S^z$) contribute to spin dynamics at wave vectors $q\ne 0$. Spin anisotropies
and local s-p coupling play a key role in the proposed mechanism. Our results
prove that small changes in the spatial symmetry of the ring induce qualitative
changes in the spin dynamics at the nuclear frequency, providing a novel
mechanism for nuclear relaxation. Possible experiments are proposed.",0511118v1
2006-09-18,General Form of Magnetization Damping: Magnetization dynamics of a spin system evolving nonadiabatically and out of equilibrium,"Using an effective Hamiltonian including the Zeeman and internal
interactions, we describe the quantum theory of magnetization dynamics when the
spin system evolves non-adiabatically and out of equilibrium. The
Lewis-Riesenfeld dynamical invariant method is employed along with the
Liouville-von Neumann equation for the density matrix. We derive a dynamical
equation for magnetization defined with respect to the density operator with a
general form of magnetization damping that involves the non-equilibrium
contribution in addition to the Landau-Lifshitz-Gilbert equation. Two special
cases of the radiation-spin interaction and the spin-spin exchange interaction
are considered. For the radiation-spin interaction, the damping term is shown
to be of the Gilbert type, while in the spin-spin exchange interaction case the
results depend on a coupled chain of correlation functions.",0609431v2
2006-12-27,Spin-dependent electron dynamics and recombination in GaAs(1-x)N(x) alloys at room temperature,"We report on both experimental and theoretical study of conduction-electron
spin polarization dynamics achieved by pulsed optical pumping at room
temperature in GaAs(1-x)N(x) alloys with a small nitrogen content (x = 2.1,
2.7, 3.4%). It is found that the photoluminescence circular polarization
determined by the mean spin of free electrons reaches 40-45% and this giant
value persists within 2 ns. Simultaneously, the total free-electron spin decays
rapidly with the characteristic time ~150 ps. The results are explained by
spin-dependent capture of free conduction electrons on deep paramagnetic
centers resulting in dynamical polarization of bound electrons. We have
developed a nonlinear theory of spin dynamics in the coupled system of
spin-polarized free and localized carriers which describes the experimental
dependencies, in particular, electron spin quantum beats observed in a
transverse magnetic field.",0612639v1
2007-12-04,Microwave excitations associated with a wavy angular dependence of the spin transfer torque : model and experiments,"The spin transfer torque (STT) can lead to steady precession of magnetization
without any external applied field in magnetic spin valve where the magnetic
layer have very different spin diffusion length. This effect is associated with
an unusual angular dependence of the STT, called ""wavy"" (WAD-STT), predicted in
the frame of diffusive models of spin transfer. In this article, we present a
complete experimental characterization of the magnetization dynamics in the
presence of a WAD-STT. The results are compared to the prediction of the
magnetization dynamics obtained by single domain magnetic simulations
(macrospin approximation). The macrospin simulations well reproduced the main
static and dynamical experimental features (phase diagram, R(I) curves,
dependence of frequency with current and field) and suggest that the dynamical
excitations observed experimentally are associated with a large angle
out-of-plane precession mode. The present work validates the diffusive models
of the spin transfer and underlines the role of the spin accumulation and the
spin relaxation effects on the STT.",0712.0548v1
2009-02-02,Ultrafast Spin Dynamics in Optically Excited Bulk GaAs at Low Temperatures,"This paper presents a study of electron spin dynamics in bulk GaAs at low
temperatures for elevated optical excitation conditions. Our time-resolved
Faraday rotation measurements yield sub-nanosecond electron spin
dephasing-times over a wide range of n-doping concentrations in quantitative
agreement with a microscopic treatment of electron spin dynamics. The
calculation shows the occurrence and breakdown of motional narrowing for spin
dephasing under elevated excitation conditions. We also find a peak of the spin
dephasing time around a doping density for which, under lower excitation
conditions, a metal-insulator transition occurs. However, the experimental
results for high excitation can be explained without a metal-insulator
transition. We therefore attribute the peak in spin-dephasing times to the
influence of screening and scattering on the spin-dynamics of the excited
electrons.",0902.0270v2
2012-03-29,Theory of spin dynamics of magnetic adatoms traced by time-resolved scanning tunneling spectroscopy,"The inelastic scanning tunneling microscopy (STM) has been shown recently
(Loth et al. Science 329, 1628 (2010)) to be extendable as to access the
nanosecond, spin-resolved dynamics of magnetic adatoms and molecules. Here we
analyze theoretically this novel tool by considering the time-resolved spin
dynamics of a single adsorbed Fe atom excited by a tunneling current pulse from
a spin-polarized STM tip. The adatom spin-configuration can be controlled and
probed by applying voltage pulses between the substrate and the spin-polarized
STM tip. We demonstrate how, in a pump-probe manner, the relaxation dynamics of
the sample spin is manifested in the spin-dependent tunneling current. Our
model calculations are based on the scattering theory in a wave-packet
formulation. The scheme is nonpertubative and hence, is valid for all voltages.
The numerical results for the tunneling probability and the conductance are
contrasted with the prediction of simple analytical models and compared with
experiments.",1203.6476v1
2013-02-22,Landau-Zener dynamics of a nanoresonator containing a tunneling spin,"We study the Landau-Zener dynamics of a tunneling spin coupled to a torsional
resonator. For strong spin-phonon coupling, when the oscillator frequency is
large compared to the tunnel splitting, the system exhibits multiple
Landau-Zener transitions. Entanglement of spin and mechanical angular momentum
results in abrupt changes of oscillator dynamics which coincide in time with
spin transitions. We show that a large number of spins on a single oscillator
coupled only through the in-phase phonon field behaves as a single large spin,
greatly enhancing the spin-phonon coupling. We compare purely quantum and
semiclassical dynamics of the system and discuss their experimental
realizations. An experiment is proposed in which the field sweep is used to
read out the exact quantum state of the mechanical resonator.",1302.5726v1
2013-06-18,Dynamical Exchange Interaction From Time-Dependent Spin Density Functional Theory,"We report on {\it ab initio} time-dependent spin dynamics simulations for a
two-center magnetic molecular complex based on time-dependent non-collinear
spin density functional theory. In particular, we discuss how the dynamical
behavior of the {\it ab initio} spin-density in the time-domain can be mapped
onto a model Hamiltonian based on the classical Heisenberg spin-spin
interaction $J\vcr{S}_1\cdot \vcr{S}_2$. By analyzing individual localized-spin
trajectories, extracted from the spin-density evolution, we demonstrate a novel
method for evaluating the effective Heisenberg exchange coupling constant, $J$,
from first principles simulations. We find that $J$, extracted in such a new
dynamical way, agrees quantitatively to that calculated by the standard density
functional theory broken-symmetry scheme.",1306.4187v1
2017-02-20,Spin-resolved dynamical conductance of correlated large-spin magnetic molecules,"The finite-frequency transport properties of a large-spin molecule attached
to ferromagnetic contacts are studied theoretically in the Kondo regime. The
focus is on the behavior of the dynamical conductance in the linear response
regime, which is determined by using the numerical renormalization group
method. It is shown that the dynamical conductance depends greatly on the
magnetic configuration of the device and intrinsic parameters of the molecule.
In particular, conductance exhibits characteristic features for frequencies
corresponding to the dipolar and quadrupolar exchange fields resulting from the
presence of spin-dependent tunneling. Moreover, a dynamical spin accumulation
in the molecule, associated with the off-diagonal-in-spin component of the
conductance, is predicted. This spin accumulation becomes enhanced with
increasing the spin polarization of the leads, and it results in a nonmonotonic
dependence of the conductance on frequency, with local maxima occurring for
characteristic energy scales.",1702.05935v1
2018-07-18,Spin-dependent heat signatures of single-molecule spin dynamics,"We investigate transient spin-dependent thermoelectric signatures in a
single-molecule magnet under the effect of a time-dependent voltage pulse. We
model the system using nonequilibrium Green's functions and a generalized spin
equation of motion incorporating the dynamic electronic structure of the
molecule. We show that the generated heat current in the system is due to both
charge and spin contributions, related to the Peltier and the spin-dependent
Peltier effect. There is also a clear signature in the heat current due to the
spin dynamics of the single-molecule and a possibility to control the
spin-dependent heat currents by bias, tunneling coupling and exchange
interaction. A reversal of the net heat transfer in the molecule is found for
increasing bias voltage due to the local Zeeman split and we can correlate the
net heat transfer with the local anisotropies and dynamic exchange fields in
the system.",1807.07019v2
2020-03-28,Spin transport and dynamic properties of two-dimensional spin-momentum locked states,"Materials with spin-momentum locked surface or interface states provide an
interesting playground for studying physics and application of charge-spin
current conversion. To characterize their non-equilibrium magnetic and
transport properties in the presence of a time-dependent external magnetic
field and a spin injection from a contact, we introduce three macroscopic
variables: a vectorial helical magnetization, a scaler helical magnetization,
and the conventional magnetization. We derive a set of closed dynamic equations
for these variables by using the spinor Boltzmann approach with the collision
terms consistent with the symmetry of spin-momentum locked states. By solving
the dynamic equations, we predict several intriguing magnetic and transport
phenomena which are experimentally accessible, including magnetic resonant
response to an AC applied magnetic field, charge-spin conversion, and spin
current induced by the dynamics of helical magnetization.",2003.12700v1
2021-07-21,Dynamics of two ferromagnetic insulators coupled by superconducting spin current,"A conventional superconductor sandwiched between two ferromagnets can
maintain coherent equilibrium spin current. This spin supercurrent results from
the rotation of odd-frequency spin correlations induced in the superconductor
by the magnetic proximity effect. In the absence of intrinsic magnetization,
the superconductor cannot maintain multiple rotations of the triplet component
but instead provides a Josephson type weak link for the spin supercurrent. We
determine the analogue of the current-phase relation in various circumstances
and show how it can be accessed in experiments on dynamic magnetization. In
particular, concentrating on the magnetic hysteresis and the ferromagnetic
resonance response, we show how the spin supercurrent affects the
nonequilibrium dynamics of magnetization which depends on a competition between
spin supercurrent mediated static exchange contribution and a dynamic spin
pumping contribution. Depending on the outcome of this competition, a mode
crossing in the system can either be an avoided crossing or mode locking.",2107.09959v2
2022-06-22,Direct optical probing of ultrafast spin dynamics in a magnetic semiconductor,"We uncovered for the first time the spin dynamics involved in the birth and
growth of giant spin polarons in a magnetic semiconductor. For this purpose, we
developed a new measurement technique, which for the first time provides direct
access to the spin dynamics, irrespective of phonons and carriers involved in
the process. Moreover, we solved for the first time the Landau-Liftshitz
equation in the specific scenario of spin polarons, which fits our data
excellently, and demonstrates for the first time that the spin polaron growth
slows down dramatically when the sample is cooled in the paramagnetic phase.
Finally, temperature dependent Monte Carlo simulations were performed, which
are in excellent agreement with the observed slowdown, which demonstrates for
the first time that fluctuations in the Weiss field play a decisive role in
spin coherence generation induced by light in magnetic materials. These results
offer a new tool and new insight for spin dynamics investigations.",2206.10933v1
2022-09-02,Langevin dynamics of generalized spins as SU($N$) coherent states,"Classical models of spin systems traditionally retain only the dipole
moments, but a quantum spin state will frequently have additional structure.
Spins of magnitude $S$ have $N=2S+1$ levels. Alternatively, the spin state is
fully characterized by a set of $N^{2}-1$ local physical observables, which we
interpret as generalized spin components. For example, a spin with $S=1$ has
three dipole components and five quadrupole components. These components evolve
under a generalization of the classical Landau-Lifshitz dynamics, which can be
extended with noise and damping terms. In this paper, we reformulate the
dynamical equations of motion as a Langevin dynamics of SU($N$) coherent states
in the Schr\""odinger picture. This viewpoint is especially useful as the basis
for an efficient numerical method to sample spin configurations in thermal
equilibrium and to simulate the relaxation and driven motion of topological
solitons. To illustrate the approach, we simulate a non-equilibrium relaxation
process that creates CP$^{2}$ Skyrmions, which are topological defects with
both dipole and quadrupole character.",2209.01265v2
2022-09-21,Manipulating THz Spin Current Dynamics by the Dzyaloshinskii-Moriya Interaction in Antiferromagnetic Hematite,"An important vision of modern magnetic research is to use antiferromagnets as
controllable and active ultrafast components in spintronic devices. Hematite is
a promising model material in this respect because its pronounced
Dzyaloshinskii-Moriya interaction leads to the coexistence of
antiferromagnetism and weak ferromagnetism. Here, we use femtosecond laser
pulses to drive terahertz spin currents from hematite into an adjacent Pt
layer. We find two contributions to the generation of the spin current with
distinctly different dynamics: the impulsive stimulated Raman scatting that
relies on the antiferromagnetic order and the ultrafast spin Seebeck effect
that relies on the net magnetization. The total THz spin current dynamics can
thus be manipulated by a medium-strength magnetic field. The controllability of
the THz spin current achieved in hematite opens the pathway toward controlling
the exact spin current dynamics from ultrafast antiferromagnetic spin sources.",2209.10175v1
2023-05-10,Collisionless dynamics of superconducting gap excited by spin-splitting field,"We study the coherent dynamic interaction of a time-dependent spin-splitting
field with the homogeneous superconducting order parameter $\Delta(t)$ mediated
by spin-orbit coupling using the time-dependent Bogoliubov-de Gennes theory. In
the first part of the work we show that linear response of the superconductor
is strongly affected by the Zeeman field and spin-flip processes, giving rise
to multiple resonant frequencies of the superconducting Higgs modes. These
modes can be excited either by a quench, or by an additional non-stationary
component of the spin-splitting field, which couples linearly to the Higgs
modes. In the second part, we analyze the nonadiabatic dynamics of
quasiparticle states arising from the intersection of spectral branches from
different spin subbands, which can be provoked by a linearly growing Zeeman
field. We provide insights into the dependence of the order parameter
$\Delta(t)$ on this field and interference effects caused by tunneling of
states at the avoided crossing points. We also show that since the nonadiabatic
tunneling is related to spin-flip processes, the quasiparticle gas experiences
a dynamic magnetization that contributes to its spin susceptibility.",2305.06201v1
2023-08-14,Kernel Fusion in Atomistic Spin Dynamics Simulations on Nvidia GPUs using Tensor Core,"In atomistic spin dynamics simulations, the time cost of constructing the
space- and time-displaced pair correlation function in real space increases
quadratically as the number of spins $N$, leading to significant computational
effort. The GEMM subroutine can be adopted to accelerate the calculation of the
dynamical spin-spin correlation function, but the computational cost of
simulating large spin systems ($>40000$ spins) on CPUs remains expensive. In
this work, we perform the simulation on the graphics processing unit (GPU), a
hardware solution widely used as an accelerator for scientific computing and
deep learning. We show that GPUs can accelerate the simulation up to 25-fold
compared to multi-core CPUs when using the GEMM subroutine on both. To hide
memory latency, we fuse the element-wise operation into the GEMM kernel using
$\mathtt{CUTLASS}$ that can improve the performance by 26% $\sim$ 33% compared
to implementation based on $\mathtt{cuBLAS}$. Furthermore, we perform the
on-the-fly calculation in the epilogue of the GEMM subroutine to avoid saving
intermediate results on global memory, which makes the large-scale atomistic
spin dynamics simulation feasible and affordable.",2308.07487v1
2018-09-27,Evolution of two-time correlations in dissipative quantum spin systems: aging and hierarchical dynamics,"We consider the evolution of two-time correlations in the quantum XXZ
spin-chain in contact with an environment causing dephasing. Extending
quasi-exact time-dependent matrix product state techniques to consider the
dynamics of two-time correlations within dissipative systems, we uncover the
full quantum behavior for these correlations along all spin directions.
Together with insights from adiabatic elimination and kinetic Monte Carlo, we
identify three dynamical regimes. For initial times, their evolution is
dominated by the system unitary dynamics and depends on the initial state and
the Hamiltonian parameters. For weak spin-spin interaction anisotropy, after
this initial dynamical regime, two-time correlations enter an algebraic scaling
regime signaling the breakdown of time-translation invariance and the emergence
of aging. For stronger interaction anisotropy, these correlations first go
through a stretched exponential regime before entering the algebraic one. Such
complex relaxation arises due to the competition between the proliferation
dynamics of energetically costly excitations and their motion. As a result,
dissipative heating dynamics of spin systems can be used to probe the entire
spectrum of the underlying Hamiltonian.",1809.10464v1
1995-05-29,Hole dynamics in generalized spin backgrounds in infinite dimensions,"We calculate the dynamical behaviour of a hole in various spin backgrounds in
infinite dimensions, where it can be determined exactly. We consider hypercubic
lattices with two different types of spin backgrounds. On one hand we study an
ensemble of spin configurations with an arbitrary spin probability on each
sublattice. This model corresponds to a thermal average over all spin
configurations in the presence of staggered or uniform magnetic fields. On the
other hand we consider a definite spin state characterized by the angle between
the spins on different sublattices, i.e a classical spin system in an external
magnetic field. When spin fluctuations are considered, this model describes the
physics of unpaired particles in strong coupling superconductors.",9505145v1
2004-05-11,Spin relaxation dynamics of quasiclassical electrons in ballistic quantum dots with strong spin-orbit coupling,"We performed path integral simulations of spin evolution controlled by the
Rashba spin-orbit interaction in the semiclassical regime for chaotic and
regular quantum dots. The spin polarization dynamics have been found to be
strikingly different from the D'yakonov-Perel' (DP) spin relaxation in bulk
systems. Also an important distinction have been found between long time spin
evolutions in classically chaotic and regular systems. In the former case the
spin polarization relaxes to zero within relaxation time much larger than the
DP relaxation, while in the latter case it evolves to a time independent
residual value. The quantum mechanical analysis of the spin evolution based on
the exact solution of the Schroedinger equation with Rashba SOI has confirmed
the results of the classical simulations for the circular dot, which is
expected to be valid in general regular systems. In contrast, the spin
relaxation down to zero in chaotic dots contradicts to what have to be expected
from quantum mechanics. This signals on importance at long time of the
mesoscopic echo effect missed in the semiclassical simulations.",0405212v1
2005-11-11,The time dependence of muon spin relaxation spectra and spin correlation functions,"The existing theory of the microscopic interpretation of the dynamical
contribution to zero-field muon depolarization spectra in a longitudinal
geometry is developed. The predicted relaxation of the muon depolarization is
calculated from two forms of the spin correlation function. First, when the
spin correlation function has an exponential form with a single wave vector
dependent relaxation rate is considered, it is shown that this form of the spin
correlation function reproduces the slow and fast fluctuation limits of
stochastic spin theory regardless of the choice of microscopic spin model.
Second, if the spin correlation function is a homogeneous scaling function
(such as a power-law decay with time), as suggested by the mode-coupling theory
of spin dynamics, this results in a stretched exponential relaxation of the
muon spectra. For simple spin diffusion, the muon spectra are shown to be relax
with a root-exponential form.",0511288v1
2006-10-31,Spin- and entanglement-dynamics in the central spin model with homogeneous couplings,"We calculate exactly the time-dependent reduced density matrix for the
central spin in the central-spin model with homogeneous Heisenberg couplings.
Therefrom, the dynamics and the entanglement entropy of the central spin are
obtained. A rich variety of behaviors is found, depending on the initial state
of the bath spins. For an initially unpolarized unentangled bath, the
polarization of the central spin decays to zero in the thermodynamic limit,
while its entanglement entropy becomes maximal. On the other hand, if the
unpolarized environment is initially in an eigenstate of the total bath spin,
the central spin and the entanglement entropy exhibit persistent monochromatic
large-amplitude oscillations. This raises the question to what extent
entanglement of the bath spins prevents decoherence of the central spin.",0610856v3
2006-11-30,Equilibrium conditions of spinning test particles in Kerr-de Sitter spacetimes,"Equilibrium conditions and spin dynamics of spinning test particles are
discussed in the stationary and axially symmetric Kerr-de Sitter black-hole or
naked-singularity spacetimes. The general equilibrium conditions are
established, but due to their great complexity, the detailed discussion of the
equilibrium conditions and spin dynamics is presented only in the simple and
most relevant cases of equilibrium positions in the equatorial plane and on the
symmetry axis of the spacetimes. It is shown that due to the combined effect of
the rotation of the source and the cosmic repulsion the equilibrium is spin
dependent in contrast to the spherically symmetric spacetimes. In the
equatorial plane, it is possible at the so-called static radius, where the
gravitational attraction is balanced by the cosmic repulsion, for the spinless
particles as well as for spinning particles with arbitrarily large
azimuthal-oriented spin or at any radius outside the ergosphere with a
specifically given spin orthogonal to the equatorial plane. On the symmetry
axis, the equilibrium is possible at any radius in the stationary region and is
given by an appropriately tuned spin directed along the axis. At the static
radii on the axis the spin of particles in equilibrium must vanish.",0611153v1
2008-01-11,"Quantum dynamics in electron-nuclei coupled spin system in quantum dots: Bunching, revival, and quantum correlation in electron-spin measurements","We investigate quantum dynamics in the electron-nuclei coupled spin system in
quantum dots and clarify the fundamental features of quantum correlation
induced via successive electron spin measurements. This quantum correlation
leads to interesting phenomena such as the bunching of outcomes in the electron
spin measurements and the revival of an arbitrary initial electron spin state.
The nuclear spin system is also affected by the quantum correlation and is in
fact squeezed via conditional measurements or postselection. This squeezing is
confirmed by calculating the increase in the purity of the nuclear spin system.
Thus the successive electron spin measurements provide a probabilistic method
to squeeze the nuclear spin system. These new features are predicted not only
for the case of a double quantum dots occupied by a pair of electrons but also
for the case of a single quantum dot occupied by a single electron or a pair of
electrons.",0801.1723v1
2008-06-05,Magnetization Relaxation and Collective Spin Excitations in Correlated Double--Exchange Ferromagnets,"We study spin relaxation and dynamics of collective spin excitations in
correlated double--exchange ferromagnets. For this, we introduce an expansion
of the Green's functions equations of motion that treats non--perturbativerly
all correlations between a given number of spin and charge excitations and
becomes exact within a sub--space of states. Our method treats relaxation
beyond Fermi's Golden Rule while recovering previous variational results for
the spin--wave dispersion. We find that the momentum dependence of the
spin--wave dephasing rate changes qualitatively due to the on--site Coulomb
interaction, in a way that resembles experiment, and depends on its interplay
with the magnetic exchange interaction and itinerant spin lifetime. We show
that the collective spin relaxation and its dependence on the carrier
concentration depends sensitively on three--body correlations between a spin
excitation and a Fermi sea electron and hole. The above spin dynamics can be
controlled via the itinerant carrier population.",0806.0938v2
2011-08-01,Spin Pumping and Spin Transfer,"Spin pumping is the emission of a spin current by a magnetization dynamics
while spin transfer stands for the excitation of magnetization by spin
currents. Using Onsager's reciprocity relations we prove that spin pumping and
spin-transfer torques are two fundamentally equivalent dynamic processes in
magnetic structures with itinerant electrons. We review the theory of the
coupled motion of the magnetization order parameter and electron for textured
bulk ferromagnets (e.g. containing domain walls) and heterostructures (such as
spin valves). We present first-principles calculations for the
material-dependent damping parameters of magnetic alloys. Theoretical and
experimental results agree in general well.",1108.0385v3
2011-08-11,Decoherence and dynamical decoupling control of nitrogen-vacancy center electron spins in nuclear spin baths,"We theoretically study the decoherence and the dynamical decoupling control
of nitrogen-vacancy center electron spins in high-purity diamond, where the
hyperfine interaction with $^{13}$C nuclear spins is the dominating decoherence
mechanism. The decoherence is formulated as the entanglement between the
electron spin and the nuclear spins, which is induced by nuclear spin bath
evolution conditioned on the electron spin state. The nuclear spin bath
evolution is driven by elementary processes such as single spin precession and
pairwise flip-flops. The importance of different elementary processes in the
decoherence depends on the strength of the external magnetic field.",1108.2343v1
2012-06-28,Spin-orbit coupled transport and spin torque in a ferromagnetic heterostructure,"Ferromagnetic heterostructures provide an ideal platform to explore the
nature of spin-orbit torques arising from the interplay mediated by itinerant
electrons between a Rashba-type spin-orbit coupling and a ferromagnetic
exchange interaction. For such a prototypic system, we develop a set of coupled
diffusion equations to describe the diffusive spin dynamics and spin-orbit
torques. We characterize the spin torque and its two prominent--out-of-plane
and in-plane--components for a wide range of relative strength between the
Rashba coupling and ferromagnetic exchange. The symmetry and angular dependence
of the spin torque emerging from our simple Rashba model is in an agreement
with experiments. The spin diffusion equation can be generalized to incorporate
dynamic effect such as spin pumping and magnetic damping.",1206.6726v2
2014-10-01,"Internal Spin Control, Squeezing and Decoherence in Ensembles of Alkali Atomic Spins","This dissertation studies spin squeezing, entanglement and decoherence in
large ensembles of cold, trapped alkali atoms with hyperfine spin f interacting
with optical fields. Restricting the state of each atom to a qutrit embedded in
the 2f+1 dimensional hyperfine spin enables us to efficiently model the
coherent and dissipative dynamics of the ensemble. This formalism also allows
us to explore the effects of local control on the internal hyperfine spins of
the atoms. State preparation using such control increases the entangling power
of the atom-light interface for f>1/2. Subsequent control of the internal spins
converts entanglement into metrologically relevant spin squeezing. In the case
of squeezing by quantum nondemolition measurement, we employ a numerical search
to find state preparations that maximize spin squeezing in the presence of
decoherence. Dissipative dynamics on our system include optical pumping due to
spontaneous emission. While most works ignore optical pumping or treat it
phenomenologically, we employ a master equation derived from first principles.
This work is extended to the case of an atomic ensemble interacting with a
non-homogeneous paraxial probe. The geometries of the ensemble and the probe
are optimized to maximize both spatial mode matching and spin squeezing.",1410.0089v1
2015-05-06,Reexamination of the Elliott-Yafet spin-relaxation mechanism,"We analyze spin-dependent carrier dynamics due to incoherent electron-phonon
scattering, which is commonly referred to as Elliott-Yafet (EY) spin-relaxation
mechanism. For this mechanism one usually distinguishes two contributions: (1)
from the electrostatic interaction together with spin-mixing in the wave
functions, which is often called the Elliott contribution, and (2) the
phonon-modulated spin-orbit interaction, which is often called the Yafet or
Overhauser contribution. By computing the reduced electronic density matrix, we
improve Yafet's original calculation, which is not valid for pronounced spin
mixing as it equates the pseudo-spin polarization with the spin polarization.
The important novel quantity in our calculation is a torque operator that
determines the spin dynamics. The contribution (1) to this torque vanishes
exactly. From this general result, we derive a modified expression for the
Elliott-Yafet spin relaxation time.",1505.01432v2
2015-10-16,Dicke Model for Quantum Hall Systems,"Quantum Hall (QH) systems consist of many-body electron and nuclear spins.
They are coupled so weakly through the hyperfine interaction that normally
electron spin dynamics are scarcely affected by the nuclear spins. The dynamics
of the QH systems, however, may drastically change when the nuclear spins
interact with low-energy collective excitation modes of the electron spins. We
theoretically investigate the nuclear-electron spin interaction in the QH
systems as hybrid quantum systems driven by the hyperfine interaction. In
particular, we study the interaction between the nuclear spins and the
Nambu-Goldstone (NG) mode with the linear dispersion relation associated with
the U(1) spin rotational symmetry breaking. We show that such an interaction is
described as nuclear spins collectively coupled to the NG mode, and can be
effectively described by the Dicke model. Based on the model we suggest that
various collective spin phenomena realized in quantum optical systems also
emerge in the QH systems.",1510.04792v1
2016-11-04,Hybrid continuous dynamical decoupling: a photon-phonon doubly dressed spin,"We study the parametric interaction between a single Nitrogen-Vacancy
electronic spin and a diamond mechanical resonator in which the spin is
embedded. Coupling between spin and oscillator is achieved by crystal strain,
which is generated upon actuation of the oscillator and which parametrically
modulates the spins' energy splitting. Under coherent microwave driving of the
spin, this parametric drive leads to a locking of the spin Rabi frequency to
the oscillator mode in the megahertz range. Both the Rabi oscillation decay
time and the inhomogeneous spin dephasing time increase by two orders of
magnitude under this spin-locking condition. We present routes to prolong the
dephasing times even further, potentially to the relaxation time limit. The
remarkable coherence protection that our hybrid spin-oscillator system offers
is reminiscent of recently proposed concatenated continuous dynamical
decoupling schemes and results from our robust, drift-free strain-coupling
mechanism and the narrow linewidth of the high-quality diamond mechanical
oscillator employed. Our findings suggest feasible applications in quantum
information processing and sensing.",1611.01515v1
2017-04-04,Phonon-derived ultrafast relaxation of spin-valley polarized states in MoS_{2},"The valley degree of freedom and the possibility of spin-valley coupling of
solid materials have attracted growing interest, and the relaxation dynamics of
spin- and valley-polarized states has become an important focus of recent
studies. In spin-orbit-coupled inversion-asymmetric two-dimensional materials,
such as MoS_{2} it has been found that the spin randomization is
characteristically faster than the time scales for inter- and intra-valley
scatterings. In this study, we examined the ultrafast non-collinear spin
dynamics of an electron valley in monolayer MoS_{2} by using real-time
propagation time-dependent density functional theory. We found that the spin
precession of an electron in the valley is sharply coupled with the
lowest-lying optical phonon that release the in-plane mirror symmetry. This
indicates that the spin randomization of MoS_{2} is mainly caused by
spin-phonon interaction. We further suggest that flipping of spins in a
spin-orbit-coupled system can be achieved by the control over phonons.",1704.00921v1
2017-07-24,Universal Spin Dynamics in Quantum Wires,"We discuss the universal spin dynamics in quasi one-dimensional systems
including the real spin in narrow-gap semiconductors like InAs and InSb, the
valley pseudospin in staggered single-layer graphene, and the combination of
real spin and valley pseudospin characterizing single-layer transition metal
dichalcogenides (TMDCs) such as MoS$_2$, WS$_2$, MoSe$_2$, and WSe$_2$. All
these systems can be described by the same Dirac-like Hamiltonian.
Spin-dependent observable effects in one of these systems thus have
counterparts in each of the other systems. Effects discussed in more detail
include equilibrium spin currents, current-induced spin polarization (Edelstein
effect), and spin currents generated via adiabatic spin pumping. Our work also
suggests that a long-debated spin-dependent correction to the position operator
in single-band models should be absent.",1707.07408v2
2017-12-21,Dynamics of a single ion spin impurity in a spin-polarized atomic bath,"We report on observations of spin dynamics in single Yb$^+$ ions immersed in
a cold cloud of spin-polarized $^6$Li atoms. This species combination has been
proposed to be the most suitable system to reach the quantum regime in atom-ion
experiments. For $^{174}$Yb$^+$, we find that the atomic bath polarizes the
spin of the ion by 93(4)\,\% after a few Langevin collisions, pointing to
strong spin-exchange rates. For the hyperfine ground states of $^{171}$Yb$^+$,
we also find strong rates towards spin polarization. However, relaxation
towards the $F=0$ ground state occurs after 7.7(1.5) Langevin collisions. We
investigate spin impurity atoms as possible source of apparent spin-relaxation
leading us to interpret the observed spin-relaxation rates as an upper limit.
Using ab initio electronic structure and quantum scattering calculations, we
explain the observed rates and analyze their implications for the possible
observation of Feshbach resonances between atoms and ions once the quantum
regime is reached.",1712.07873v2
2020-09-03,Coincidence inelastic neutron scattering for detection of two-spin magnetic correlations,"Inelastic neutron scattering (INS) is one powerful technique to study the
low-energy single-spin dynamics of magnetic materials. A variety of quantum
magnets show novel magnetic correlations such as quantum spin liquids. These
novel magnetic correlations are beyond the direct detection of INS. In this
paper we propose a coincidence technique, coincidence inelastic neutron
scattering (cINS), which can detect the two-spin magnetic correlations of the
magnetic materials. In cINS there are two neutron sources and two neutron
detectors with an additional coincidence detector. Two neutrons from the two
neutron sources are incident on the target magnetic material, and they are
scattered by the electron spins of the magnetic material. The two scattered
neutrons are detected by the two neutron detectors in coincidence with the
coincidence probability described by a two-spin Bethe-Salpeter wave function.
Since the two-spin Bethe-Salpeter wave function defines the momentum-resolved
dynamical wave function with two spins excited, cINS can explicitly detect the
two-spin magnetic correlations of the magnetic material. Thus, it can be
introduced to study the various spin valence bond states of the quantum
magnets.",2009.01680v2
2021-01-30,Spin-spin interactions in solids from mixed all-electron and pseudopotential calculations $-$ a path to screening materials for spin qubits,"Understanding the quantum dynamics of spin defects and their coherence
properties requires accurate modeling of spin-spin interaction in solids and
molecules, for example by using spin Hamiltonians with parameters obtained from
first-principles calculations. We present a real-space approach based on
density functional theory for the calculation of spin-Hamiltonian parameters,
where only selected atoms are treated at the all-electron level, while the rest
of the system is described with the pseudopotential approximation. Our approach
permits calculations for systems containing more than 1000 atoms, as
demonstrated for defects in diamond and silicon carbide. We show that only a
small number of atoms surrounding the defect needs to be treated at the
all-electron level, in order to obtain an overall all-electron accuracy for
hyperfine and zero-field splitting tensors. We also present results for
coherence times, computed with the cluster correlation expansion method,
highlighting the importance of accurate spin-Hamiltonian parameters for
quantitative predictions of spin dynamics.",2102.00162v1
2021-09-08,All-optical noise spectroscopy of a solid-state spin,"Noise spectroscopy elucidates the fundamental noise sources in spin systems,
thereby serving as an essential tool toward developing spin qubits with long
coherence times for quantum information processing, communication, and sensing.
But existing techniques for noise spectroscopy that rely on microwave fields
become infeasible when the microwave power is too weak to generate Rabi
rotations of the spin. Here, we demonstrate an alternative all-optical approach
to performing noise spectroscopy. Our approach utilizes coherent Raman
rotations of the spin state with controlled timing and phase to implement
Carr-Purcell-Meiboom-Gill pulse sequences. Analyzing the spin dynamics under
these sequences enables us to extract the noise spectrum of a dense ensemble of
nuclear spins interacting with a single spin in a quantum dot, which has thus
far only been modeled theoretically. By providing spectral bandwidths of over
100 MHz, our approach enables the studies of spin dynamics and decoherence for
a broad range of solid-state spin qubits.",2109.03405v4
2022-10-12,"Linear Response, Hamiltonian and Radiative Spinning Two-Body Dynamics","Using the spinning, supersymmetric Worldline Quantum Field Theory formalism
we compute the momentum impulse and spin kick from a scattering of two spinning
black holes or neutron stars up to quadratic order in spin at third
post-Minkowskian (PM) order, including radiation-reaction effects and with
arbitrarily mis-aligned spin directions. Parts of these observables, both
conservative and radiative, are also inferred from lower-PM scattering data by
extending Bini and Damour's linear response formula to include mis-aligned
spins. By solving Hamilton's equations of motion we also use a conservative
scattering angle to infer a complete 3PM two-body Hamiltonian including
finite-size corrections and mis-aligned spin-spin interactions. Finally, we
describe mappings to the bound two-body dynamics for aligned spin vectors:
including a numerical plot of the binding energy for circular orbits compared
with numerical relativity, analytic confirmation of the NNLO PN binding energy
and the energy loss over successive orbits.",2210.06451v3
2022-12-07,Non-linear fluctuating hydrodynamics for KPZ scaling in isotropic spin chains,"Finite temperature spin transport in integrable isotropic spin chains is
known to be superdiffusive, with dynamical spin correlations that are
conjectured to fall into the Kardar-Parisi-Zhang (KPZ) universality class.
However, integrable spin chains have time-reversal and parity symmetries that
are absent from the KPZ/stochastic Burgers equation, which force higher-order
spin fluctuations to deviate from standard KPZ predictions. We put forward a
non-linear fluctuating hydrodynamic theory consisting of two coupled stochastic
modes: the local spin magnetization and its effective velocity. Our theory
fully explains the emergence of anomalous spin dynamics in isotropic chains: it
predicts KPZ scaling for the spin structure factor but with a symmetric,
quasi-Gaussian, distribution of spin fluctuations. We substantiate our results
using matrix-product states calculations.",2212.03696v5
2006-03-03,Nonequilibrium dynamic exponent and spin-glass transitions,"Nonequilibrium dynamics of the $\pm J$ Ising, the {\it XY}, and the
Heisenberg spin-glass models are investigated in three dimensions. A
nonequilibrium dynamic exponent is calculated from the dynamic correlation
length. The spin-glass dynamic exponent continuously depends on the
temperature. There is no anomaly at the critical temperature as is recently
reported by Katzgraber and Campbell. On the other hand, the chiral-glass
dynamic exponent takes a constant value above the spin-glass transition
temperature ($T_\mathrm{sg}$), and becomes temperature-dependent below
$T_\mathrm{sg}$.The finite-time scaling analyses on the spin- and the
chiral-glass susceptibility are performed using the temperature dependence of
the dynamic exponent. A difference of the spin- and the chiral-glass transition
temperatures is resolved in the Heisenberg model. The dynamic critical exponent
takes almost the same value for all transitions. It suggests that the
spin-glass and the chiral-glass transitions in three dimensions are dynamically
universal.",0603062v2
2020-08-19,Hybrid quantum-classical chaotic NEMS,"We present an exactly solvable model of a hybrid quantum-classical system of
a Nitrogen-Vacancy (NV) center spin (quantum spin) coupled to a nanocantilever
(classical) and analyze the enforcement of the regular or chaotic classical
dynamics onto the quantum spin dynamics. The main problem we focus in this
paper is whether the classical dynamical chaos may induce chaotic effects in
the quantum spin dynamics or not. We explore several characteristic criteria of
the quantum chaos, such as quantum Poincar\'{e} recurrences, generation of
coherence and energy level distribution and observe interesting chaotic effects
in the spin dynamics. Dynamical chaos imposed in the cantilever dynamics
through the kicking pulses induces the stochastic dynamics on the quantum
subsystem. We consider a quantum system of two and three levels and show that
in a two-level case, type of stochasticity is not conforming all the
characteristic features of the quantum chaos and is distinct from it. We also
explore the effect of quantum feedback on dynamics of the cantilever and the
entire system.",2008.08515v2
2020-02-11,Spintronics meets density matrix renormalization group: Quantum spin torque driven nonclassical magnetization reversal and dynamical buildup of long-range entanglement,"We introduce time-dependent density matrix renormalization group (tDMRG) as a
solution to long standing problem in spintronics -- how to describe
spin-transfer torque (STT) between flowing spins of conduction electrons and
localized spins within a magnetic material by treating the dynamics of both
spin species fully quantum-mechanically. In contrast to conventional
Slonczewski-Berger STT, where the localized spins are viewed as classical
vectors obeying the Landau-Lifshitz-Gilbert equation and where their STT-driven
dynamics is initiated only when the spin-polarization of flowing electrons and
localized spins are noncollinear, quantum STT can occur when these vectors are
collinear but antiparallel. Using tDMRG, we simulate the time evolution of a
many-body quantum state of electrons and localized spins, where the former are
injected as a spin-polarized current pulse while the latter comprise a quantum
Heisenberg ferromagnetic metallic (FM) spin-$\frac{1}{2}$ XXZ chain initially
in the ground state with spin-polarization antiparallel to that of injected
electrons. The quantum STT reverses the direction of localized spins, but
without rotation from the initial orientation, when the number of injected
electrons exceeds the number of localized spins. Such nonclassical reversal,
which is absent from LLG dynamics, is strikingly inhomogeneous across the FM
chain and it can be accompanied by reduction of the magnetization associated
with localized spins, even to zero at specific locations. This is because
quantum STT generates a highly entangled nonequilibrium many-body state of all
flowing and localized spins, despite starting from the initially unentangled
ground state of a mundane FM. Furthermore, the mutual information between
localized spins at the FM edges remains nonzero even at infinite separation as
the signature of dynamical buildup of long-range entanglement.",2002.04655v4
2023-08-24,Dynamics of quantum spin-nematics: Comparisons with canted antiferromagnets,"The identification of spin-nematic states is challenging due to the absence
of Bragg peaks. However, the study of dynamical physical quantities provides a
promising avenue for characterizing these states. In this study, we investigate
the dynamical properties of spin-nematic states in three-dimensional quantum
spin systems in a magnetic field, using a two-component boson theory that
incorporates magnons and bi-magnons. Our particular focus lies on the dynamical
spin structure factor at zero temperature and the nuclear magnetic resonance
(NMR) relaxation rate at finite temperatures. Our findings reveal that the
dynamical structure factor does not exhibit any diverging singularity across
momentum and frequency while providing valuable information about the form
factor of bi-magnon states and the underlying structure of spin-nematic order.
Furthermore, we find a temperature dependence in the NMR relaxation rate
proportional to $T^3$ at low temperatures, similar to canted antiferromagnets.
A clear distinction arises as there is no critical divergence of the NMR
relaxation rate at the spin-nematic transition temperature. Our theoretical
framework provides a comprehensive understanding of the excitation spectrum and
the dynamical properties of spin-nematic states, covering arbitrary spin values
$S$ and encompassing site and bond nematic orders. Additionally, we apply the
same methodology to analyze these dynamical quantities in a canted
antiferromagnetic state and compare the results with those in the spin-nematic
states.",2308.12569v2
1993-07-29,Spin Dynamics in the Normal State of High T_c Superconductors,"We summarize our recent theoretical studies on the spin dynamics in the
normal state of the metallic cuprates. The contrasting wave vector dependence
of the dynamical spin structure factor $S({\bf q}, \omega )$ in LaSrCuO and
YBaCuO systems are attributed to the differences in the fermiology, in
conjunction with strong Coulomb correlations. These effects are found to
account also for the anomalous temperature and frequency dependence of $S({\bf
q}, \omega )$. We conclude that the low energy spin dynamics of the metallic
cuprates are described in terms of correlated quasiparticles with a Luttinger
Fermi surface and a non-zero antiferromagnetic exchange interaction.",9307062v1
1998-05-24,Spin Dynamics for the t-J Model,"The spin dynamics at the finite temperature for the t-J model in the
underdoped and optimal doped regimes is studied within the fermion-spin theory.
It is shown that the dynamical spin structure factor spectrum at the
antiferromagnetic wave vector $Q=(\pi,\pi)$ are separated as low- and
high-frequency parts, respectively, but the high-frequency part is suppressed
in the dynamical susceptibility spectrum $\chi^{''}(Q,\omega)$, while the
low-frequency part is the temperature dependent, which are in qualitative
agreement with the experiments and numerical simulations.",9805308v2
2003-06-04,Nuclear Spin Dynamics in Parabolic Quantum Wells,"We present a detailed analytical and numerical analysis of the nuclear spin
dynamics in parabolic quantum wells. The shallow potential of parabolic quantum
wells permits substantial modification of the electronic wave function in small
electric fields. The nuclear spin relaxation via the hyperfine interaction
depends on the electronic local density of states, therefore the local nuclear
relaxation time depends sensitively on the electric field. For an inhomogeneous
nuclear magnetization, such as generated by dynamic nuclear polarization, the
total nuclear magnetization dynamics can similarly be altered. We examine this
effect quantitatively and the effect of temperature, field, well thickness, and
nuclear spin diffusion.",0306098v2
1995-09-15,Nodal trajectories of spin observables and kaon photoproduction dynamics,"Spin observables for the reaction $\gamma p \rightarrow K^+ \Lambda$ are
examined using three recent dynamical models and are compared to the general
features of such observables deduced earlier by Fasano, Tabakin and Saghai.
These general features, such as the energy dependence of spin observables and
the location of nodes in their angle dependence, are realized. Several
instructive surprises, which occur in this comparison to the conjectures of
Fasano et al., are then discussed. The sensitivity of spin observables to
isobar and {\it t-}channel dynamics is analyzed and suggestions for selecting
experiments which provide important dynamical information are presented.",9509027v1
2011-05-30,Dynamical spin-flip susceptibility for a strongly interacting ultracold Fermi gas,"The Stoner model predicts that a two-component Fermi gas at increasing
repulsive interactions undergoes a ferromagnetic transition. Using the
random-phase approximation we study the dynamical properties of the interacting
Fermi gas. For an atomic Fermi gas under harmonic confinement we show that the
transverse (spin-flip) dynamical susceptibility displays a clear signature of
the ferromagnetic phase in a magnon peak emerging from the Stoner particle-hole
continuum. The dynamical spin susceptibilities could be experimentally explored
via spin-dependent Bragg spectroscopy.",1105.5997v1
2023-02-15,Non-linear dynamics near exceptional points of synthetic antiferromagnetic spin-torque oscillators,"We consider a synthetic antiferromagnetic spin-torque oscillator with
anisotropic interlayer exchange coupling. This system exhibits exceptional
points in its linearized dynamics. We find the non-linear dynamics and the
dynamical phase diagram of the system both analytically and numerically.
Moreover, we show that, near one of the exceptional points, the power of the
oscillator depends extremely sensitively on the injected spin current. Our
findings may be useful for designing sensitive magnetometers and for other
applications of spin-torque oscillators.",2302.07607v1
2013-10-24,Dynamics in spinor condensates controlled by a microwave dressing field,"We experimentally study spin dynamics in a sodium antiferromagnetic spinor
condensate with off-resonant microwave pulses. In contrast to a magnetic field,
a microwave dressing field enables us to explore rich spin dynamics under the
influence of a negative net quadratic Zeeman shift $q_{\rm net}$. We find an
experimental signature to determine the sign of $q_{\rm net}$, and observe
harmonic spin population oscillations at every $q_{\rm net}$ except near each
separatrix in phase space where spin oscillation period diverges. In the
negative and positive $q_{\rm net}$ regions, we also observe a remarkably
different relationship between each separatrix and the magnetization. Our data
confirms an important prediction derived from the mean-field theory:
spin-mixing dynamics in spin-1 condensates substantially depends on the sign of
the ratio of $q_{\rm net}$ and the spin-dependent interaction energy. This work
may thus be the first to use only one atomic species to reveal mean-field spin
dynamics, especially the separatrix, which are predicted to appear differently
in spin-1 antiferromagnetic and ferromagnetic spinor condensates.",1310.6785v1
2014-08-19,Many-Body Quantum Spin Dynamics with Monte Carlo Trajectories on a Discrete Phase Space,"Interacting spin systems are of fundamental relevance in different areas of
physics, as well as in quantum information science, and biology. These spin
models represent the simplest, yet not fully understood, manifestation of
quantum many-body systems. An important outstanding problem is the efficient
numerical computation of dynamics in large spin systems. Here we propose a new
semiclassical method to study many-body spin dynamics in generic spin lattice
models. The method is based on a discrete Monte Carlo sampling in phase-space
in the framework of the so-called truncated Wigner approximation. Comparisons
with analytical and numerically exact calculations demonstrate the power of the
technique. They show that it correctly reproduces the dynamics of one- and
two-point correlations and spin squeezing at short times, thus capturing
entanglement. Our results open the possibility to study the quantum dynamics
accessible to recent experiments in regimes where other numerical methods are
inapplicable.",1408.4441v2
2014-10-07,Spin dynamics of a confined electron interacting with magnetic or nuclear spins: A semiclassical approach,"A physically transparent and mathematically simple semiclassical model is
employed to examine dynamics in the central-spin problem. The results reproduce
a number of previous findings obtained by various quantum approaches and, at
the same time, provide information on the electron spin dynamics and Berry's
phase effects over a wider range of experimentally relevant parameters than
available previously. This development is relevant to dynamics of bound
magnetic polarons and spin dephasing of an electron trapped by an impurity or a
quantum dot, and coupled by a contact interaction to neighboring localized
magnetic impurities or nuclear spins. Furthermore, it substantiates the
applicability of semiclassical models to simulate dynamic properties of
spintronic nanostructures with a mesoscopic number of spins.",1410.1717v1
2017-07-01,Dynamics of Topological Excitations in a Model Quantum Spin Ice,"We study the quantum spin dynamics of a frustrated XXZ model on a pyrochlore
lattice by using large-scale quantum Monte Carlo simulation and stochastic
analytic continuation. In the low-temperature quantum spin ice regime, we
observe signatures of coherent photon and spinon excitations in the dynamic
spin structure factor. As the temperature rises to the classical spin ice
regime, the photon disappears from the dynamic spin structure factor, whereas
the dynamics of the spinon remain coherent in a broad temperature window. Our
results provide experimentally relevant, quantitative information for the
ongoing pursuit of quantum spin ice materials.",1707.00099v2
2018-01-30,Massively parallel symplectic algorithm for coupled magnetic spin dynamics and molecular dynamics,"A parallel implementation of coupled spin-lattice dynamics in the LAMMPS
molecular dynamics package is presented. The equations of motion for both spin
only and coupled spin-lattice dynamics are first reviewed, including a detailed
account of how magneto-mechanical potentials can be used to perform a proper
coupling between spin and lattice degrees of freedom. A symplectic numerical
integration algorithm is then presented which combines the Suzuki-Trotter
decomposition for non-commuting variables and conserves the geometric
properties of the equations of motion. The numerical accuracy of the serial
implementation was assessed by verifying that it conserves the total energy and
the norm of the total magnetization up to second order in the timestep size.
Finally, a very general parallel algorithm is proposed that allows large
spin-lattice systems to be efficiently simulated on large numbers of processors
without degrading its mathematical accuracy. Its correctness as well as scaling
efficiency were tested for realistic coupled spin-lattice systems, confirming
that the new parallel algorithm is both accurate and efficient.",1801.10233v1
2020-04-09,Probing topological states through the exact non-Markovian decoherence dynamics of a spin coupled to a spin bath in real-time domain,"In this paper, we explore the decoherence dynamics of a probing spin coupled
to a spin bath, where the spin bath is given by a controllable 1D
transverse-field Ising chain. The 1D transverse-field Ising chain with
free-ends boundary condition is equivalent to a modified Kitaev model with
non-local Majorana bound states in its topological phase. We find that the
probing spin non-Markovian decoherence dynamics can manifest the topological
structure of the spin chain. By controlling the external magnetic field on the
Ising chain, we find the close relationships between the quantum phase
transitions, the topological edge states, and the non-Markovian dynamics in
real-time domain. We also investigate the corresponding quantum entanglement
dynamics in this topological system.",2004.04380v2
2021-10-26,Charge and Spin Dynamics and Enantioselectivity in Chiral Molecules,"Charge and spin dynamics is addressed in chiral molecules immediately after
the instantaneous coupling to an external metallic reservoir. It is shown how a
spin-polarization is induced in the chiral structure as a response to the
charge dynamics. The dynamics indicate that chiral induced spin selectivity is
an excited states phenomenon which, in the transient regime partly can be
captured using a simplistic single particle description, however, in the
stationary limit definitively shows that electron correlations, e.g.,
electron-vibration interactions, crucially contribute to sustain an intrinsic
spin anisotropy that can lead to a non-vanishing spin selectivity. The
dynamics, moreover, provide insight to enantiomer separation, due to different
acquired spin-polarizations.",2110.13462v2
2022-05-09,Dynamics of two central spins immersed in spin baths,"In this article we derive the exact dynamics of a two qubit (spin 1/2) system
interacting centrally with separate fermionic baths composed of qubits in
thermal state. Further, each spin of a bath is coupled to every other spin of
the same bath. The corresponding dynamical map is constructed. It is used to
analyse the non-Markovian nature of the two qubit central spin dynamics. We
further observe the evolution of quantum correlations like entanglement and
discord under the influence of the environmental interaction. Moreover, we
demonstrate the comparison between this exact two qubit dynamics and the
locally acting fermionic central spin model. This work is a stepping stone
towards the realization of non-Markovian heat engines and other quantum thermal
devices.",2205.04135v2
2022-12-22,Magnetoelasticity-driven phase inversion of ultrafast spin precession in NixFe100-x thin films,"We present strong evidences for the deterministic role of magnetoelasticity
in ultrafast spin dynamics of ferromagnetic NixFe100-x alloy films. Without a
change in the crystal structure, we observed sudden Pi-phase inversion of the
spin precession in the range of x = 87.0 - 97.5. In addition, it was found that
the phase was continuously changed and reversed its sign by varying the pump
fluence. These cannot be explained simply by temperature dependence of
magnetocrystalline, demagnetizing, and Zeeman fields which have been
conventionally considered so far in describing the spin dynamics. Through the
temperature- and composition-dependent simulations adding the magnetoelastic
field generated from the lattice thermal strain, we revealed that the
conventional and magnetoelastic fields were competing around x = 95.3, where
the spin dynamics showed the largest phase shift. For analytic understanding,
we further show that the temperature-dependent interplay of the Curie
temperature, saturation magnetization, and magnetostriction, which are
demonstrated to be the most important macroscopic parameters, determines the
ultrafast spin dynamics. Our extensive study emphasizes that magnetoelasticity
is the key ingredient for fully understanding the driving mechanism of
ultrafast spin dynamics.",2212.11852v1
2023-10-24,Singlet fission spin dynamics from molecular structure: a modular computational pipeline,"Singlet fission, which has applications in areas ranging form solar energy to
quantum information, relies critically on transitions within a multi-spin
manifold. These transitions are driven by fluctuations in the spin-spin
exchange interaction, which have been linked to changes in nuclear geometry or
exciton migration. Whilst simple calculations have supported this mechanism, to
date little effort has been made to model realistic fluctuations which are
informed by the actual structure and properties of physical materials. In this
paper, we develop a modular computational pipeline for calculating singlet
fission spin dynamics by way of electronic structural calculations, molecular
dynamics, and numerical models of spin dynamics. The outputs of this pipeline
aid in the interpretation of measured spin dynamics and allow us to place
constraints on geometric fluctuations which are consistent with these
observations.",2310.15678v1
2024-03-22,Coherent Phonon Control of Ultrafast Magnetization Dynamics in Fe$_\text{3}$GeTe$_\text{2}$ from Time-Dependent Ab Initio Theory,"Exploring ultrafast magnetization control in two-dimensional (2D) magnets
through optically driven coherent phonons has been well-established. Yet, the
microscopic interplay between spin dynamics and lattice degrees of freedom
remains less explored. Employing real-time time-dependent density functional
theory (rt-TDDFT) coupled with Ehrenfest dynamics, we systematically
investigate laser-induced spin-nuclei dynamics with coherent phonon excitation
in the 2D ferromagnet Fe3GeTe2. We found that selectively pre-exciting three
typical coherent phonon modes results in up to a 53% additional spin moment
loss in an out-of-plane A2 1g mode within ~50 fs. Coherent phonon control of
spin dynamics is closely linked to laser pulse parameters. The underlying
microscopic mechanism of this phenomenon is primarily governed by coherent
phonon-induced asymmetric spin-resolved charge transfer following the
disappearance of the laser pulse, thereby enabling effective control of the
spin moment loss. Our findings offer a novel insight into the coupling of
coherent phonons with spin systems in 2D limits on femtosecond timescales.",2403.15204v1
2022-12-15,Hamiltonian inference from dynamical excitations in confined quantum magnets,"Quantum-disordered models provide a versatile platform to explore the
emergence of quantum excitations in many-body systems. The engineering of spin
models at the atomic scale with scanning tunneling microscopy and the local
imaging of excitations with electrically driven spin resonance has risen as a
powerful strategy to image spin excitations in finite quantum spin systems.
Here, focusing on $S=1/2$ lattices as realized by Ti in MgO, we show that
dynamical spin excitations provide a robust strategy to infer the nature of the
underlying Hamiltonian. We show that finite-size interference of the dynamical
many-body spin excitations of a generalized long-range Heisenberg model allows
the underlying spin couplings to be inferred. We show that the spatial
distribution of local spin excitations in Ti islands and ladders directly
correlates with the underlying ground state in the thermodynamic limit. Using a
supervised learning algorithm, we demonstrate that the different parameters of
the Hamiltonian can be extracted by providing the spatially and
frequency-dependent local excitations that can be directly measured by
electrically driven spin resonance with scanning tunneling microscopy. Our
results put forward local dynamical excitations in confined quantum spin models
as versatile witnesses of the underlying ground state, providing an
experimentally robust strategy for Hamiltonian inference in complex real spin
models.",2212.07893v3
2023-09-26,Single-hole spectra of Kitaev spin liquids: from dynamical Nagaoka ferromagnetism to spin-hole fractionalization,"The dynamical response of a quantum spin liquid upon injecting a hole is a
pertinent open question. In experiments, the hole spectral function, measured
momentum-resolved in angle-resolved photoemission spectroscopy (ARPES) or
locally in scanning tunneling microscopy (STM), can be used to identify spin
liquid materials. In this study, we employ tensor network methods to simulate
the time evolution of a single hole doped into the Kitaev spin-liquid ground
state. Focusing on the gapped spin liquid phase, we reveal two fundamentally
different scenarios. For ferromagnetic spin couplings, the spin liquid is
highly susceptible to hole doping: a Nagaoka ferromagnet forms dynamically
around the doped hole, even at weak coupling. By contrast, in the case of
antiferromagnetic spin couplings, the hole spectrum demonstrates an intricate
interplay between charge, spin, and flux degrees of freedom, best described by
a parton mean-field ansatz of fractionalized holons and spinons. Moreover, we
find a good agreement of our numerical results to the analytically solvable
case of slow holes. Our results demonstrate that dynamical hole spectral
functions provide rich information on the structure of fractionalized quantum
spin liquids.",2309.15157v2
2024-02-23,Spin Doctors: How to diagnose a hierarchical merger origin,"Gravitational-wave observations provide the unique opportunity of studying
black hole formation channels and histories -- but only if we can identify
their origin. One such formation mechanism is the dynamical synthesis of black
hole binaries in dense stellar systems. Given the expected isotropic
distribution of component spins of binary black hole in gas-free dynamical
environments, the presence of anti-aligned or in-plane spins with respect to
the orbital angular momentum is considered a tell-tale sign of a merger's
dynamical origin. Even in the scenario where birth spins of black holes are
low, hierarchical mergers attain large component spins due to the orbital
angular momentum of the prior merger. However, measuring such spin
configurations is difficult. Here, we quantify the efficacy of the spin
parameters encoding aligned-spin ($\chieff$) and in-plane spin ($\chip$) at
classifying such hierarchical systems. Using Monte Carlo cluster simulations to
generate a realistic distribution of hierarchical merger parameters from
globular clusters, we can infer mergers' $\chieff$ and $\chip$. The cluster
populations are simulated using Advanced LIGO-Virgo sensitivity during the
detector network's third observing period and projections for design
sensitivity. Using a ""likelihood-ratio""-based statistic, we find that $\sim2\%$
of the recovered population by the current gravitational-wave detector network
has a statistically significant $\chip$ measurement, whereas no $\chieff$
measurement was capable of confidently determining a system to be anti-aligned
with the orbital angular momentum at current detector sensitivities. These
results indicate that measuring spin-precession through $\chip$ is a more
detectable signature of a hierarchical mergers and dynamical formation than
anti-aligned spins.",2402.15066v1
2007-05-24,Optical investigations of quantum-dot spin dynamics,"We have performed all-optical measurements of spin relaxation in single
self-assembled InAs/GaAs quantum dots (QD) as a function of static external
electric and magnetic fields. To study QD spin dynamics we measure the degree
of resonant absorption which results from a competition between optical spin
pumping induced by the resonant laser field and spin relaxation induced by
reservoirs. Fundamental interactions that determine spin dynamics in QDs are
hyperfine coupling to QD nuclear spin ensembles, spin-phonon coupling and
exchange-type interactions with a nearby Fermi sea of electrons. We show that
the strength of spin relaxation generated by the three fundamental interactions
can be changed by up to five orders of magnitude upon varying the applied
electric and magnetic fields. We find that the strength of optical spin pumping
that we use to study the spin relaxation is determined predominantly by
hyperfine-induced mixing of single-electron spin states at low magnetic fields
and heavy-light hole mixing at high magnetic fields. Our measurements allow us
to determine the rms value of the hyperfine (Overhauser) field to be ~15 mTesla
with an electron g-factor of g_e=0.6 and a hole mixing strength of |epsilon|^2
= 0.0005.",0705.3557v1
2014-01-23,Electron-spin dynamics induced by photon spins,"Strong rotating magnetic fields may cause a precession of the electron's spin
around the rotation axis of the magnetic field. The superposition of two
counterpropagating laser beams with circular polarization and opposite helicity
features such a rotating magnetic field component but also carries spin. The
laser's spin density, that can be expressed in terms of the lase's
electromagnetic fields and potentials, couples to the electron's spin via a
relativistic correction to the Pauli equation. We show that the quantum
mechanical interaction of the electron's spin with the laser's rotating
magnetic field and with the laser's spin density counteract each other in such
a way that a net spin rotation remains with a precession frequency that is much
smaller than the frequency one would expect from the rotating magnetic field
alone. In particular, the frequency scales differently with the laser's
electric field strength depending on if relativistic corrections are taken into
account or not. Thus, the relativistic coupling of the electron's spin to the
laser's spin density changes the dynamics not only quantitatively but also
qualitatively as compared to the nonrelativistic theory. The electron's spin
dynamics is a genuine quantum mechanical relativistic effect.",1401.5976v2
2015-12-15,Dynamics of nuclear spin polarization induced and detected by coherently precessing electron spins in fluorine-doped ZnSe,"We study the dynamics of optically-induced nuclear spin polarization in a
fluorine-doped ZnSe epilayer via time-resolved Kerr rotation. The nuclear
polarization in the vicinity of a fluorine donor is induced by interaction with
coherently precessing electron spins in a magnetic field applied in the Voigt
geometry. It is detected by nuclei-induced changes in the electron spin
coherence signal. This all-optical technique allows us to measure the
longitudinal spin relaxation time $T_{1}$ of the $^{77}\text{Se}$ isotope in a
magnetic field range from 10 to 130~mT under illumination. We combine the
optical technique with radio frequency methods to address the coherent spin
dynamics of the nuclei and measure Rabi oscillations, Ramsey fringes and the
nuclear spin echo. The inhomogeneous spin dephasing time $T_{2}^{*}$ and the
spin coherence time $T_{2}$ of the $^{77}\text{Se}$ isotope are measured. While
the $T_{1}$ time is on the order of several milliseconds, the $T_{2}$ time is
several hundred microseconds. The experimentally determined condition $T_{1}\gg
T_{2}$ verifies the validity of the classical model of nuclear spin cooling for
describing the optically-induced nuclear spin polarization.",1512.04876v3
2019-01-25,Fourth-order spin correlation function in the extended central spin model,"Spin noise spectroscopy has developed into a very powerful tool to access the
electron spin dynamics. While the spin-noise power spectrum in an ensemble of
quantum dots in a magnetic field is essentially understood, we argue that the
investigation of the higher order cumulants promises to provide additional
information not accessible by the conventional power noise spectrum. We present
a quantum mechanical approach to the correlation function of the spin-noise
power operators at two different frequencies for small spin bath sizes and
compare the results with a simulation obtained from the classical spin dynamics
for large number of nuclear spins. This bispectrum is defined as a
two-dimensional frequency cut in the parameter space of the fourth-order spin
correlation function. It reveals information on the influence of the
nuclear-electric quadrupolar interactions on the long-time electron spin
dynamics dominated by a magnetic field. For large bath sizes and spin lengths
the quantum mechanical spectra converge to those of the classical simulations.
The broadening of the bispectrum across the diagonal in the frequency space is
a direct measure of the quadrupolar interaction strength. A narrowing is found
with increasing magnetic field indicating a suppression of the influence of
quadrupolar interactions in favor of the nuclear Zeeman effect.",1901.08923v1
1993-08-22,Rotation Axis Variation Due To Spin Orbit Resonance,"Rotation axis variation due to spin orbit resonance: conference report;
keywords: planetary precession, rigid body, chaos, KAM, Arnold diffusion,
averaging, celestial mechanics, classical mechanics, large deviations",9308006v1
2002-05-10,Spin-dynamics simulations of the triangular antiferromagnetic XY model,"Using Monte Carlo and spin-dynamics methods, we have investigated the dynamic
behavior of the classical, antiferromagnetic XY model on a triangular lattice
with linear sizes $L \leq 300$. The temporal evolutions of spin configurations
were obtained by solving numerically the coupled equations of motion for each
spin using fourth-order Suzuki-Trotter decompositions of exponential operators.
  From space- and time-displaced spin-spin correlation functions and their
space-time Fourier transforms we obtained the dynamic structure factor $S({\bf
q},w)$ for momentum ${\bf q}$ and frequency $\omega$. Below
$T_{KT}$(Kosterlitz-Thouless transition), both the in-plane ($S^{xx}$) and the
out-of-plane ($S^{zz}$) components of $S({\bf q},\omega)$ exhibit very strong
and sharp spin-wave peaks. Well above $T_{KT}$, $S^{xx}$ and $S^{zz}$
apparently display a central peak, and spin-wave signatures are still seen in
$S^{zz}$. In addition, we also observed an almost dispersionless domain-wall
peak at high $\omega$ below $T_{c}$(Ising transition), where long-range order
appears in the staggered chirality. Above $T_{c}$, the domain-wall peak
disappears for all $q$. The lineshape of these peaks is captured reasonably
well by a Lorentzian form. Using a dynamic finite-size scaling theory, we
determined the dynamic critical exponent $z$ = 1.002(3). We found that our
results demonstrate the consistency of the dynamic finite-size scaling theory
for the characteristic frequeny $\omega_{m}$ and the dynamic structure factor
$S({\bf q},\omega)$ itself.",0205227v1
2014-10-02,Spin and dynamics in relativistic quantum theories,"The role of relativity and dynamics in defining the spin and orbital angular
momentum content of hadronic systems is discussed.",1410.0593v1
2015-09-23,Anomalously slow spin dynamics and short-range correlations in the quantum spin ice systems Yb2Ti2O7 and Yb2Sn2O7,"We report a positive muon spin relaxation and rotation (\muSR) study of the
quantum spin ice materials Yb2Ti2O7 and Yb2Sn2O7 focusing on the low field
response. In agreement with earlier reports, data recorded in small
longitudinal fields evidence anomalously slow spin dynamics in the microsecond
range below the temperature T_c at which the specific heat displays an intense
peak, namely T_c = 0.24 K and 0.15 K, respectively, for the two systems. We
found that slow dynamics extends above T_c up to at least 0.7 K for both
compounds. The conventional dynamical Gaussian Kubo-Toyabe model describes the
\muSR spectra recorded above T_c. At lower temperatures a published analytical
extension of the Gaussian Kubo-Toyabe model provides a good description,
consistent with the existence of short-range magnetic correlations. While the
physical response of the two systems is qualitatively the same, Yb2Ti2O7
exhibits a much larger local magnetic susceptibility than Yb2Sn2O7 below T_c.
Considering previously reported ac susceptibility, neutron scattering and \muSR
results, we suggest the existence of anomalously slow spin dynamics to be a
common physical property of pyrochlore magnetic materials. The possibility of
molecular spin substructures to be associated to the slow dynamics and
therefore the short-range correlations is mentioned. The slow spin dynamics
observed under field does not exclude the presence of much faster dynamics
detected in extremely low or zero field.",1509.06908v1
2022-05-26,Precession-induced nonclassicality of the free induction decay of NV centers by a dynamical polarized nuclear spin bath,"The ongoing exploration of the ambiguous boundary between the quantum and the
classical worlds has spurred substantial developments in quantum science and
technology. Recently, the nonclassicality of dynamical processes has been
proposed from a quantum-information-theoretic perspective, in terms of
witnessing nonclassical correlations with Hamiltonian ensemble simulations. To
acquire insights into the quantum-dynamical mechanism of the process
nonclassicality, here we propose to investigate the nonclassicality of the
electron spin free-induction-decay process associated with an NV$^-$ center. By
controlling the nuclear spin precession dynamics via an external magnetic field
and nuclear spin polarization, it is possible to manipulate the dynamical
behavior of the electron spin, showing a transition between classicality and
nonclassicality. We propose an explanation of the classicality-nonclassicality
transition in terms of the nuclear spin precession axis orientation and
dynamics. We have also performed a series of numerical simulations supporting
our findings. Consequently, we can attribute the nonclassical trait of the
electron spin dynamics to the behavior of nuclear spin precession dynamics.",2205.13512v3
2015-06-23,Dynamical effects of spin-dependent interactions in low- and intermediate-energy heavy-ion reactions,"It is well known that non-central nuclear forces, such as the spin-orbital
coupling and the tensor force, play important roles in understanding many
interesting features of nuclear structures. However, their dynamical effects in
nuclear reactions are poorly known since only the spin-averaged observables are
normally studied both experimentally and theoretically. Realizing that
spin-sensitive observables in nuclear reactions may carry useful information
about the in-medium properties of non-central nuclear interactions, besides
earlier studies using the time-dependent Hartree-Fock approach to understand
effects of spin-orbital coupling on the threshold energy and spin polarization
in fusion reactions, some efforts have been made recently to explore dynamical
effects of non-central nuclear forces in intermediate-energy heavy-ion
collisions using transport models. The focuses of these studies have been on
investigating signatures of the density and isospin dependence of the form
factor in the spin-dependent single-nucleon potential. Interestingly, some
useful probes were identified in the model studies while so far there is still
no data to compare with. In this brief review, we summarize the main physics
motivations as well as the recent progress in understanding the spin dynamics
and identifying spin-sensitive observables in heavy-ion reactions at
intermediate energies. We hope the interesting, important, and new physics
potentials identified in the spin dynamics of heavy-ion collisions will
stimulate more experimental work in this direction.",1506.06860v2
2006-01-23,Quasiclassical approach to the spin-Hall effect in the two-dimensional electron gas,"We study the spin-charge coupled transport in a two-dimensional electron
system using the method of quasiclassical ($\xi$-integrated) Green's functions.
In particular we derive the Eilenberger equation in the presence of a generic
spin-orbit field. The method allows us to study spin and charge transport from
ballistic to diffusive regimes and continuity equations for spin and charge are
automatically incorporated. In the clean limit we establish the connection
between the spin-Hall conductivity and the Berry phase in momentum space. For
finite systems we solve the Eilenberger equation numerically for the special
case of the Rashba spin-orbit coupling and a two-terminal geometry. In
particular, we calculate explicitly the spin-Hall induced spin polarization in
the corners, predicted by Mishchenko et al. [13]. Furthermore we find universal
spin currents in the short-time dynamics after switching on the voltage across
the sample, and calculate the corresponding spin-Hall polarization at the
edges. Where available, we find perfect agreement with analytical results.",0601525v1
2006-03-23,Dynamics of spin transport in voltage-biased Josephson junctions,"We investigate spin transport in voltage-biased spin-active Josephson
junctions. The interplay of spin filtering, spin mixing, and multiple Andreev
reflection leads to nonlinear voltage dependence of the dc and ac spin current.
We compute the voltage characteristics of the spin current (I_S) for
superconductor-ferromagnet-superconductor (SFS) Josephson junctions. The
sub-harmonic gap structure of I_S(V) is shown to be sensitive to the degree of
spin mixing generated by the ferromagnetic interface, and exhibits a pronounced
even-odd effect associated with spin transport during multiple Andreev
reflection processes. For strong spin mixing both the magnitude and the
direction of the dc spin current can be sensitively controlled by the bias
voltage.",0603610v2
2007-03-01,Spin dynamics across the superfluid-insulator transition of spinful bosons,"Bosons with non-zero spin exhibit a rich variety of superfluid and insulating
phases. Most phases support coherent spin oscillations, which have been the
focus of numerous recent experiments. These spin oscillations are Rabi
oscillations between discrete levels deep in the insulator, while deep in the
superfluid they can be oscillations in the orientation of a spinful condensate.
We describe the evolution of spin oscillations across the superfluid-insulator
quantum phase transition. For transitions with an order parameter carrying
spin, the damping of such oscillations is determined by the scaling dimension
of the composite spin operator. For transitions with a spinless order parameter
and gapped spin excitations, we demonstrate that the damping is determined by
an associated quantum impurity problem of a localized spin excitation
interacting with the bulk critical modes. We present a renormalization group
analysis of the quantum impurity problem, and discuss the relationship of our
results to experiments on ultracold atoms in optical lattices.",0703011v2
2007-07-11,Switched Control of Electron Nuclear Spin Systems,"In this article, we study control of electron-nuclear spin dynamics at
magnetic field strengths where the Larmor frequency of the nucleus is
comparable to the hyperfine coupling strength. The quantization axis for the
nuclear spin differs from the static B_0 field direction and depends on the
state of the electron spin. The quantization axis can be switched by flipping
the state of electron spin, allowing for universal control on nuclear spin
states. We show that by performing a sequence of flips (each followed by a
suitable delay), we can perform any desired rotation on the nuclear spins,
which can also be conditioned on the state of the electron spin. These
operations, combined with electron spin rotations can be used to synthesize any
unitary transformation on the coupled electron-nuclear spin system. We discuss
how these methods can be used for design of experiments for transfer of
polarization from the electron to the nuclear spins.",0707.1572v1
2007-07-31,Photon-assisted spin transport in a two-dimensional electron gas,"We study spin-dependent transport in a two-dimensional electron gas subject
to an external step-like potential $V(x)$ and irradiated by an electromagnetic
field (EF). In the absence of EF the electronic spectrum splits into spin
sub-bands originating from the ""Rashba"" spin-orbit coupling. We show that the
resonant interaction of propagating electrons with the component EF parallel to
the barrier induces a \textit{% non-equilibrium dynamic gap} $(2\Delta_{R})$
between the spin sub-bands. Existence of this gap results in coherent spin-flip
processes that lead to a spin-polarized current and a large magnetoresistance,
i.e the spin valve effect. These effects may be used for controlling spin
transport in semiconducting nanostructures, e.g. spin transistors,
spin-blockade devices etc., by variation of the intensity S and frequency
$\omega $ of the external radiation.",0707.4571v2
2007-08-14,Spin torque contribution to the a.c. spin Hall conductivity,"Using the recently proposed definition of a conserved spin-current operator
[J. Shi et al., Phys. Rev. Lett. 96, 076604 (2006)] we explore the frequency
dependent spin Hall conductivity for a two-dimensional electron gas with Rashba
and Dresselhaus spin-orbit interaction in response to an oscillating electric
field. We show that the optical spectrum of the spin Hall conductivity exhibit
remarkable changes when the new definition of spin current is applied. Such
behavior is mainly due to a significant contribution of the spin torque term
which is absent in the conventional form of the spin current. In addition, it
is observed that the magnitude and direction of the dynamic spin Hall current
strongly depends on the electric field frequency as with the interplay of the
spin-orbit coupling strengths.",0708.1957v2
2008-08-11,Pure spin current generation in a Rashba-Dresselhaus quantum channel,"We demonstrate a spin pump to generate pure spin current of tunable intensity
and polarization in the absence of charge current. The pumping functionality is
achieved by means of an ac gate voltage that modulates the Rashba constant
dynamically in a local region of a quantum channel with both static Rashba and
Dresselhaus spin-orbit interactions. Spin-resolved Floquet scattering matrix is
calculated to analyze the whole scattering process. Pumped spin current can be
divided into spin-preserved transmission and spin-flip reflection parts. These
two terms have opposite polarization of spin current and are competing with
each other. Our proposed spin-based device can be utilized for non-magnetic
control of spin flow by tuning the ac gate voltage and the driving frequency.",0808.1449v1
2008-12-18,Mesoscopic Spin-Hall Effect in 2D electron systems with smooth boundaries,"Spin-Hall effect in ballistic 2D electron gas with Rashba-type spin-orbit
coupling and smooth edge confinement is studied. We predict that the interplay
of semiclassical electron motion and quantum dynamics of spins leads to several
distinct features in spin density along the edge that originate from
accumulation of turning points from many classical trajectories. Strong peak is
found near a point of the vanishing of electron Fermi velocity in the lower
spin-split subband. It is followed by a strip of negative spin density that
extends until the crossing of the local Fermi energy with the degeneracy point
where the two spin subbands intersect. Beyond this crossing there is a wide
region of a smooth positive spin density. The total amount of spin accumulated
in each of these features exceeds greatly the net spin across the entire edge.
The features become more pronounced for shallower boundary potentials,
controlled by gating in typical experimental setups.",0812.3609v2
2009-03-05,Entanglement evolution of a spin chain bath in driving the decoherence of a coupled quantum spin,"For an electron spin in coupling with an interacting spin chain via
hyperfine-type interaction, we investigate the dynamical evolutions of the
pairwise entanglement of the spin chain and a correlation function joined the
electron spin with a pair of chain spins in correspondence to the electron spin
coherence evolution. Both quantities manifest a periodic and a decaying
evolution. The entanglement of the spin bath is significant in distinguishing
the zero-coherence status exhibited in periodic and decoherence evolutions of
the electron spin. The periodical concurrence evolution of the spin bath
characterizes the whole system in a coherence-preserving phase, particularly
for the case that the associated periodic coherence evolution is predominated
by zero-value in the infinite chain-length limit, which was often regarded as
the realization of decoherence.",0903.0944v1
2011-06-21,Effective one body Hamiltonian of two spinning black-holes with next-to-next-to-leading order spin-orbit coupling,"Building on the recently computed next-to-next-to-leading order (NNLO)
post-Newtonian (PN) spin-orbit Hamiltonian for spinning binaries
\cite{Hartung:2011te} we extend the effective-one-body (EOB) description of the
dynamics of two spinning black-holes to NNLO in the spin-orbit interaction. The
calculation that is presented extends to NNLO the next-to-leading order (NLO)
spin-orbit Hamiltonian computed in Ref. \cite{Damour:2008qf}. The present EOB
Hamiltonian reproduces the spin-orbit coupling through NNLO in the
test-particle limit case. In addition, in the case of spins parallel or
antiparallel to the orbital angular momentum, when circular orbits exist, we
find that the inclusion of NNLO spin-orbit terms moderates the effect of the
NLO spin-orbit coupling.",1106.4349v3
2011-07-02,Spin-pumping-induced spin transport in p-type Si at room temperature,"A spin battery concept is applied for the dynamical generation of pure spin
current and spin transport in p-type silicon (p-Si). Ferromagnetic resonance
and effective s-d coupling in Ni80Fe20 results in spin accumulation at the
Ni80Fe20/p-Si interface, inducing spin injection and the generation of spin
current in the p-Si. The pure spin current is converted to a charge current by
the inverse spin Hall effect of Pd evaporated onto the p-Si. This approach
demonstrates the generation and transport of pure spin current in p-Si at room
temperature.",1107.0376v4
2011-10-28,Spin Lifetime in Small Electron Spin Ensembles Measured by Magnetic Resonance Force Microscopy,"Magnetic Resonance Force Microscopy can enable nanoscale imaging of spin
lifetime. We report temperature dependent measurements of the spin correlation
time $\tau_m$ of the statistical fluctuations of the spin polarization---the
spin noise---of ensembles containing $\sim 100$ electron spins by this
technique. Magneto-mechanical relaxation due to spin-cantilever coupling was
controlled and spurious mechanisms that can affect the spin correlation time of
the microscopic signal were characterized. These measurements have
ramifications for optimizing spin sensitivity, understanding local spin
dynamics and for nanoscale imaging.",1110.6410v1
2013-11-07,Quantum Spin Ice: A Search for Gapless Quantum Spin Liquids in Pyrochlore Magnets,"The spin ice materials, including Ho2Ti2O7 and Dy2Ti2O7, are rare earth
pyrochlore magnets which, at low temperatures, enter a constrained paramagnetic
state with an emergent gauge freedom. Remarkably, the spin ices provide one of
very few experimentally realised examples of fractionalization because their
elementary excitations can be regarded as magnetic monopoles and, over some
temperature range, the spin ice materials are best described as liquids of
these emergent charges. In the presence of quantum fluctuations, one can
obtain, in principle, a quantum spin liquid descended from the classical spin
ice state characterised by emergent photon-like excitations. Whereas in
classical spin ices the excitations are akin to electrostatic charges, in the
quantum spin liquid these charges interact through a dynamic and emergent
electromagnetic field. In this review, we describe the latest developments in
the study of such a quantum spin ice, focussing on the spin liquid
phenomenology and the kinds of materials where such a phase might be found.",1311.1817v1
2015-05-15,Spin-current probe for phase transition in an insulator,"Spin fluctuation and transition have always been one of central topics of
magnetism and condensed matter science. Experimentally, the spin fluctuation is
found transcribed onto scattering intensity in the neutron scattering process,
which is represented by dynamical magnetic susceptibility and maximized at
phase transitions. Importantly, a neutron carries spin without electric charge,
and it can bring spin into a sample without being disturbed by electric energy,
although large facilities such as a nuclear reactor is necessary. Here we show
that spin pumping, frequently used in nanoscale spintronic devices, provides a
desktop micro probe for spin transition; spin current is a flux of spin without
an electric charge and its transport reflects spin excitation. We demonstrate
detection of antiferromagnetic transition in ultra-thin CoO films via frequency
dependent spin-current transmission measurements, which provides a versatile
probe for phase transition in an electric manner in minute devices.",1505.03926v3
2015-05-22,Local probing of nuclear bath polarization with a single electronic spin,"We demonstrate experimentally that a polarized nuclear spin modifies the
dynamic behavior of a neighboring electronic spin. Specifically, an
out-of-phase component appears in the electronic spin-echo signal. This
component is proportional to the nuclear spin degree of polarization and
strongly depends on the nuclear polarization direction. When the electronic
spin is surrounded by a polarized nuclear spin bath, the spin-echo quadrature
manifests a characteristic frequency related only to the nuclear spins
abundance and their collective polarization. We use this analysis to propose a
novel measurement method for the local nuclear spin bath of a single electronic
spin. We quantify the realistic experimental regimes at which the scheme is
efficient. Our proposal has potential applications for quantum sensing schemes,
and opens a route for a systematic study of polarized mesoscopical-systems.",1505.05944v1
2015-06-02,Nonlocal Magnetoresistance Mediated by Spin Superfluidity,"The electrical response of two diffusive metals is studied when they are
linked by a magnetic insulator hosting a topologically stable (superfluid) spin
current. We discuss how charge currents in the metals induce a spin
supercurrent state, which in turn generates a magnetoresistance that depends on
the topology of the electrical circuit. This magnetoresistance relies on phase
coherence over the entire magnet and gives direct evidence for spin
superfluidity. We show that driving the magnet with an ac current allows
coherent spin transport even in the presence of U(1)-breaking magnetic
anisotropy that can preclude dc superfluid transport. Spin transmission in the
ac regime shows a series of resonance peaks as a function of frequency. The
peak locations, heights, and widths can be used to extract static interfacial
properties, e.g., the spin-mixing conductance and effective spin Hall angle,
and to probe dynamic properties such as the spin-wave dispersion. Thus, ac
transport may provide a simpler route to realizing nonequilbrium coherent spin
transport and a useful way to characterize the magnetic system, serving as a
precursor to the realization of dc superfluid spin transport.",1506.01059v2
2015-07-10,Fractionalized spin-wave continuum in spin liquid states on the kagome lattice,"Motivated by spin-wave continuum (SWC) observed in recent neutron scattering
experiments in Herbertsmithite, we use Gutzwiller-projected wave functions to
study dynamic spin structure factor $S(\mathbf{q},\omega)$ of spin liquid
states on the kagome lattice. Spin-1 excited states in spin liquids are
represented by Gutzwiller-projected two-spinon excited wave functions. We
investigate three different spin liquid candidates, spinon Fermi-surface spin
liquid (FSL), Dirac spin liquid (DSL) and random-flux spin liquid (RSL). FSL
and RSL have low energy peaks in $S(\mathbf{q},\omega)$ at $K$ points in the
extended magnetic Brillouin zone, in contrast to experiments where low energy
peaks are found at $M$ points. There is no obviuos contradiction between DSL
and neutron scattering measurements. Besides a fractionalized spin (i.e.
spin-1/2), spinons in DSL carry a fractionalized crystal momentum which is
potentially detectable in SWC in the neutron scattering measurements.",1507.03007v1
2017-08-14,Large Proximity-Induced Spin Lifetime Anisotropy in Transition Metal Dichalcogenide/Graphene Heterostructures,"Van-der-Waals heterostructures have become a paradigm for designing new
materials and devices, in which specific functionalities can be tailored by
combining the properties of the individual 2D layers. A single layer of
transition metal dichalcogenide (TMD) is an excellent complement to graphene
(Gr), since the high quality of charge and spin transport in Gr is enriched
with the large spin-orbit coupling of the TMD via proximity effect. The
controllable spin-valley coupling makes these heterostructures particularly
attractive for spintronic and opto-valleytronic applications. In this work, we
study spin precession in a monolayer MoSe2/Gr heterostructure and observe an
unconventional, dramatic modulation of the spin signal, showing one order of
magnitude longer lifetime of out-of-plane spins (40 ps) compared with that of
in-plane spins (3.5 ps). This demonstration of a large spin lifetime anisotropy
in TMD/Gr heterostructures, is a direct evidence of induced spin-valley
coupling in Gr and provides an accessible route for manipulation of spin
dynamics in Gr, interfaced with TMDs.",1708.04067v1
2014-03-11,Spin Dependent Lifetimes and Spin-orbit Hybridization Points in Heusler Compounds,"We present an ab initio calculation of the k and spin-resolved electronic
lifetimes in the half-metallic Heusler compounds Co(2)MnSi and Co(2)FeSi. We
determine the spin-flip and spin-conserving contributions to the lifetimes and
study in detail the behavior of the lifetimes around states that are strongly
spin-mixed by spin-orbit coupling. We find that, for non-degenerate bands, the
spin mixing alone does not determine the energy dependence of the (spin-flip)
lifetimes. Qualitatively, the lifetimes reflect the lineup of electron and hole
bands. We predict that different excitation conditions lead to drastically
different spin-flip dynamics of excited electrons and may even give rise to an
enhancement of the non-equilibrium spin polarization.",1403.2590v2
2019-09-16,Spin current pumped by resonant skyrmion,"Spin pumping is a widely recognized method to generate the spin current in
the spintronics, which is acknowledged as a fundamentally dynamic process
equivalent to the spin-transfer torque. In this work, we theoretically verify
that the oscillating spin current can be pumped from the microwave-motivated
breathing skyrmion. The skyrmion spin pumping can be excited by a relatively
low frequency compared with the ferromagnetic resonance (FMR) and the current
density is larger than the ordinary FMR spin pumping. Based on the skyrmion
spin pumping, we build a high reading-speed racetrack memory model whose
reading speed is an order of magnitude higher than the SOT (spin-orbit torque)
/STT (spin-transfer torque) skyrmion racetrack. Our work explored the spin
pumping phenomenon in the skyrmion, and it may contribute to the applications
of the skyrmion-based device.",1909.07077v1
2017-09-25,Cubic interaction vertices for continuous-spin fields and arbitrary spin massive fields,"Light-cone gauge formulation of relativistic dynamics of a continuous-spin
field propagating in the flat space is developed. Cubic interaction vertices of
continuous-spin massless fields and totally symmetric arbitrary spin massive
fields are studied. We consider parity invariant cubic vertices that involve
one continuous-spin massless field and two arbitrary spin massive fields and
parity invariant cubic vertices that involve two continuous-spin massless
fields and one arbitrary spin massive field. We construct the complete list of
such vertices explicitly. Also we demonstrate that there are no cubic vertices
describing consistent interaction of continuous-spin massless fields with
arbitrary spin massless fields.",1709.08596v2
2018-03-09,Spin transport across antiferromagnets induced by the spin Seebeck effect,"For prospective spintronics devices based on the propagation of pure spin
currents, antiferromagnets are an interesting class of materials that
potentially entail a number of advantages as compared to ferromagnets. Here, we
present a detailed theoretical study of magnonic spin current transport in
ferromagnetic-antiferromagnetic multilayers by using atomistic spin dynamics
simulations. The relevant length scales of magnonic spin transport in
antiferromagnets are determined. We demonstrate the transfer of angular
momentum from a ferromagnet into an antiferromagnet due to the excitation of
only one magnon branch in the antiferromagnet. As an experimental system, we
ascertain the transport across an antiferromagnet in
YIG$|$Ir$_{20}$Mn$_{80}|$Pt heterostructures. We determine the spin transport
signals for spin currents generated in the YIG by the spin Seebeck effect and
compare to measurements of the spin Hall magnetoresistance in the
heterostructure stack. By means of temperature-dependent and
thickness-dependent measurements, we deduce conclusions on the spin transport
mechanism across IrMn and furthermore correlate it to its
paramagnetic-antiferromagnetic phase transition.",1803.03416v1
2018-03-16,Intrinsic spin-orbit torque in an antiferromagnet with a weakly noncollinear spin configuration,"An antiferromagnet is a promising material for spin-orbit torque generation.
Earlier studies of the spin-orbit torque in an antiferromagnet are limited to
collinear spin configurations. We calculate the spin-orbit torque in an
antiferromagnet whose spin ordering is weakly noncollinear. Such
noncollinearity may be induced spontaneously during the magnetization dynamics
even when the equilibrium spin configuration is perfectly collinear. It is
shown that deviation from perfect collinearity can modify properties of the
spin-orbit torque since noncollinearity generates extra Berry phase
contributions to the spin-orbit torque, which are forbidden for collinear spin
configurations. In sufficiently clean antiferromagnets, this modification can
be significant. We estimate this effect to be of relevance for fast
antiferromagnetic domain wall motion.",1803.06428v2
2020-09-13,Long-Distance Superexchange between Semiconductor Quantum-Dot Electron Spins,"Because of their long coherence times and potential for scalability,
semiconductor quantum-dot spin qubits hold great promise for quantum
information processing. However, maintaining high connectivity between
quantum-dot spin qubits, which favor linear arrays with nearest neighbor
coupling, presents a challenge for large-scale quantum computing. In this work,
we present evidence for long-distance spin-chain-mediated superexchange
coupling between electron spin qubits in semiconductor quantum dots. We weakly
couple two electron spins to the ends of a two-site spin chain. Depending on
the spin state of the chain, we observe oscillations between the distant end
spins. We resolve the dynamics of both the end spins and the chain itself, and
our measurements agree with simulations. Superexchange is a promising technique
to create long-distance coupling between quantum-dot spin qubits.",2009.06071v2
2020-09-16,Plasmon to exciton spin conversion in semiconductor-metal hybrid structures,"Optical control of electronic spins is the basis for ultrafast spintronics:
circularly polarized light in combination with spin-orbit coupling of the
electronic states allows for spin manipulation in condensed matter. However,
the conventional approach is limited to spin orientation along one particular
orientation that is dictated by the direction of photon propagation. Plasmonics
opens new capabilities, allowing one to tailor the light polarization at the
nanoscale. Here, we demonstrate ultrafast optical excitation of electron spin
on femtosecond time scales via plasmon to exciton spin conversion. By
time-resolving the THz spin dynamics in a hybrid (Cd,Mn)Te quantum well
structure covered with a metallic grating, we unambiguously determine the
orientation of the photoexcited electron spins which is locked to the
propagation direction of surface plasmon-polaritons. Using the spin of the
incident photons as additional degree of freedom, one can orient the
photoexcited electron spin at will in a two-dimensional plane.",2009.07658v1
2021-10-10,Spin-valley-coupled quantum spin Hall insulator with topological Rashba-splitting edge states in Janus monolayer $\mathrm{CSb_{1.5}Bi_{1.5}}$,"Achieving combination of spin and valley polarized states with topological
insulating phase is pregnant to promote the fantastic integration of
topological physics, spintronics and valleytronics. In this work, a
spin-valley-coupled quantum spin Hall insulator (svc-QSHI) is predicted in
Janus monolayer $\mathrm{CSb_{1.5}Bi_{1.5}}$ with dynamic, mechanical and
thermal stabilities. The inequivalent valleys have opposite Berry curvature and
spin moment, which can produce a spin-valley Hall effect. In the center of
Brillouin zone, a Rashba-type spin splitting can be observed due to missing
horizontal mirror symmetry. Moreover, monolayer $\mathrm{CSb_{1.5}Bi_{1.5}}$
shows unique Rashba-splitting edge states. Both energy band gap and
spin-splitting at the valley point are larger than the thermal energy of room
temperature (25 meV) with generalized gradient approximation (GGA) level, which
is very important at room temperature for device applications. It is proved
that the spin-valley-coupling and nontrivial quantum spin Hall (QSH) state are
robust again biaxial strain. Our work may provide a new platform to achieve
integration of topological physics, spintronics and valleytronics.",2110.04739v1
2021-11-23,Modeling ultrafast demagnetization and spin transport: the interplay of spin-polarized electrons and thermal magnons,"We theoretically investigate laser-induced spin transport in metallic
magnetic heterostructures using an effective spin transport description that
treats itinerant electrons and thermal magnons on an equal footing.
Electron-magnon scattering is included and taken as the driving force for
ultrafast demagnetization. We assume that in the low-fluence limit the magnon
system remains in a quasi-equilibrium, allowing a transient nonzero magnon
chemical potential. In combination with the diffusive transport equations for
the itinerant electrons, the description is used to chart the full spin
dynamics within the heterostructure. In agreement with recent experiments, we
find that in case the spin-current-receiving material includes an efficient
spin dissipation channel, the interfacial spin current becomes directly
proportional to the temporal derivative of the magnetization. Based on an
analytical calculation, we discuss that other relations between the spin
current and magnetization may arise in case the spin-current-receiving material
displays inefficient spin-flip scattering. Finally, we discuss the role of
(interfacial) magnon transport and show that, a priori, it cannot be neglected.
However, its significance strongly depends on the system parameters.",2111.11961v1
2021-12-02,Antiferromagnetic spin pumping via hyperfine interaction,"Spin pumping is an interfacial spin current generation from the ferromagnetic
layer to the non-magnetic metal at its interface. The polarization of the
pumped spin current $\textbf{J}_s \propto \textbf{m}\times \dot{\textbf{m}}$
depends on the dynamics of the magnetic moment $\textbf{m}$. When the materials
are based on light transition metals, mechanism behind the spin current
transfer is dominated by the exchange interaction between spin of localized
d-electrons and itinerant conduction electrons. In heavier transition metals,
however, the interaction is not limited to the exchange interaction. The spin
of the conduction electron can interact to its nuclear spin by means of
hyperfine interaction, as observed in the shift of NMR frequency. By studying
the spin polarization of conduction electron of the non-magnetic metallic layer
due to a nuclear magnetic moment $\textbf{I}$ of the ferromagnetic layer, we
show that the hyperfine interaction can mediate the spin pumping. The
polarization of the spin current generation is shown to have a similar form
$J_s\propto \textbf{I}\times\dot{\textbf{I}}$.",2112.01111v1
2022-01-27,Non-Collinear Spin Current for Switching of Chiral Magnetic Textures,"We propose a concept of non-collinear spin current, whose spin polarization
varies in space even in non-magnetic crystals. While it is commonly assumed
that the spin polarization of the spin Hall current is uniform, asymmetric
local crystal potential generally allows the spin polarization to be
non-collinear in space. Based on microscopic considerations we demonstrate that
such non-collinear spin Hall currents can be observed for example in layered
Kagome Mn$_3$X (X = Ge, Sn) compounds. Moreover, by referring to atomistic spin
dynamics simulations we show that non-collinear spin currents can be used to
switch the chiral spin texture of Mn$_3$X in a deterministic way even in the
absence of an external magnetic field. Our theoretical prediction can be
readily tested in experiments, which will open a novel route toward electric
control of complex spin structures in non-collinear antiferromagnets.",2201.11476v2
2022-01-29,Thermally enhanced Majorana-mediated spin transport in the Kitaev model,"We study how stable the Majorana-mediated spin transport in a quantum spin
Kitaev model is against thermal fluctuations. Using the time-dependent thermal
pure quantum state method, we examine finite-temperature spin dynamics in the
Kitaev model. The model exhibits two characteristic temperatures $T_L$ and
$T_H$, which correspond to energy scales of the local flux and the itinerant
Majorana fermion, respectively. At low temperatures $(T\ll T_L)$, an almost
flux-free state is realized and the spin excitation propagates in a similar way
to that for the ground state. Namely, after the magnetic pulse is introduced at
one of the edges, the itinerant Majorana fermions propagate the spin
excitations even through the quantum spin liquid state region, and oscillations
in the spin moment appear in the other edge with a tiny magnetic field. When
$T\sim T_L$, larger oscillations in the spin moments are induced in the other
edge, compared to the results at the ground state. At higher temperatures,
excited $Z_2$ fluxes disturb the coherent motion of the itinerant Majorana
fermions, which suppresses the spin propagation. Our results demonstrate a
crucial role of thermal fluctuations in the Majorana-mediated spin transport.",2201.12517v1
2022-05-05,Spin Manipulation by Giant Valley-Zeeman Spin-Orbit Field in Atom-Thick WSe2,"The phenomenon originating from spin-orbit coupling (SOC) provides
energy-efficient strategies for spin manipulation and device applications. The
broken inversion symmetry interface and resulting electric field induce a
Rashba-type spin-orbit field (SOF), which has been demonstrated to generate
spin-orbit torque for data storage applications. In this study, we found that
spin flipping can be achieved by the valley-Zeeman SOF in monolayer WSe2 at
room temperature, which manifests as a negative magnetoresistance in the
vertical spin valve. Quantum transmission calculations based on an effective
model near the K valley of WSe2 confirm the precessional spin transport of
carriers under the giant SOF, which is estimated to be 650 T. In particular,
the valley-Zeeman SOF-induced spin dynamics was demonstrated to be tunable with
the layer number and stacking phase of WSe2 as well as the gate voltage, which
provides a novel strategy for spin manipulation and can benefit the development
of ultralow-power spintronic devices.",2205.02876v1
2022-05-13,Migdal-Eliashberg theory as a classical spin chain,"We formulate the Migdal-Eliashberg theory of electron-phonon interactions in
terms of classical spins by mapping the free energy to a Heisenberg spin chain
in a Zeeman magnetic field. Spin components are energy-integrated normal and
anomalous Green's functions and sites of the chain are fermionic Matsubara
frequencies. The Zeeman field grows linearly with the spin coordinate and
competes with ferromagnetic spin-spin interaction that falls off as the square
of the inverse distance. The spin-chain representation makes a range of
previously unknown properties plain to see. In particular, infinitely many new
solutions of the Eliashberg equations both in the normal and superconducting
states emerge at strong coupling. These saddle points of the free-energy
functional correspond to spin flips. We argue that they are also fixed points
of kinetic equations and play an essential role in far from equilibrium
dynamics of strongly coupled superconductors. Up to an overall phase, the
frequency-dependent gap function that minimizes the free energy must be
non-negative. There are strong parallels between our Eliashberg spins and
Anderson pseudospins, though the two sets of spins never coincide.",2205.06442v2
2023-02-23,Photo-assisted spin transport in double quantum dots with spin-orbit interaction,"We investigate the effect of spin-orbit interaction on the intra- and
interdot particle dynamics of a double quantum dot under ac electric fields.
The former is modeled as an effective ac magnetic field that produces
electric-dipole spin resonance transitions, while the latter is introduced via
spin-flip tunneling amplitudes. We observe the appearance of non-trivial
spin-polarized dark states, arising from an ac-induced interference between
photo-assisted spin-conserving and spin-flip tunneling processes. These dark
states can be employed to precisely measure the spin-orbit coupling in quantum
dot systems. Furthermore, we show that the interplay between photo-assisted
transitions and spin-flip tunneling allows the system to operate as a highly
tunable spin filter. Finally, we investigate the operation of the system as a
resonant flopping-mode qubit for arbitrary ac voltage amplitudes, allowing for
high tunability and enhanced qubit control possibilities.",2302.12272v2
2024-01-17,Spin Orbit Torque on a Curved Surface,"We provide a general formulation of the spin-orbit coupling on a 2D curved
surface. Considering the wide applicability of spin-orbit effect in
spinor-based condensed matter physics, a general spin-orbit formulation could
aid the study of spintronics, Dirac graphene, topological systems, and quantum
information on curved surfaces. Particular attention is then devoted to the
development of an important spin-orbit quantity known as the spin-orbit torque.
As devices trend smaller in dimension, the physics of local geometries on
spin-orbit torque, hence spin and magnetic dynamics shall not be neglected. We
derived the general expression of a spin-orbit anisotropy field for the curved
surfaces and provided explicit solutions in the special contexts of the
spherical, cylindrical and flat coordinates. Our expressions allow spin-orbit
anisotropy fields and hence spin-orbit torque to be computed over the entire
surfaces of devices of any geometry.",2401.08966v1
1997-09-21,Spin Foam Models,"While the use of spin networks has greatly improved our understanding of the
kinematical aspects of quantum gravity, the dynamical aspects remain obscure.
To address this problem, we define the concept of a `spin foam' going from one
spin network to another. Just as a spin network is a graph with edges labeled
by representations and vertices labeled by intertwining operators, a spin foam
is a 2-dimensional complex with faces labeled by representations and edges
labeled by intertwining operators. Spin foams arise naturally as
higher-dimensional analogs of Feynman diagrams in quantum gravity and other
gauge theories in the continuum, as well as in lattice gauge theory. When
formulated as a `spin foam model', such a theory consists of a rule for
computing amplitudes from spin foam vertices, faces, and edges. The product of
these amplitudes gives the amplitude for the spin foam, and the transition
amplitude between spin networks is given as a sum over spin foams. After
reviewing how spin networks describe `quantum 3-geometries', we describe how
spin foams describe `quantum 4-geometries'. We conclude by presenting a spin
foam model of 4-dimensional Euclidean quantum gravity, closely related to the
state sum model of Barrett and Crane, but not assuming the presence of an
underlying spacetime manifold.",9709052v3
2008-10-27,"Spin polarized two-dimensional electron gas embedded in semimagnetic quantum well : ground state, spin responses, spin excitations, Raman spectrum","We present theoretical aspects of spin polarized two dimensional electron gas
(SP2DEG) which can be achieved in doped semimagnetic quantum wells. This
original model system has been recently studied by magneto Raman scattering
experiments has given a new access to spin resolved excitations and spectrum of
the SP2DEG. Starting from the Diluted Magnetic Semiconductor (DMS) Hamiltonian
in presence of the Coulomb interaction between conduction electrons, we define
the conditions to reach such a SP2DEG. The equilibrium state is studied at low
temperature; in particular a theory for the degree of spin polarization is
derived. Dynamical spin susceptibilities are further calculated in the
framework of a spin density functional formalism already developed in the past.
We then derive spin conserving and spin flip excitations dispersions using a
recent determination of the SP2DEG correlation energy corrected from the
thickness of the well. The SP2DEG presents two key features: the spin flip
wave, which existence is a direct consequence of the Coulomb interaction
between the spin polarized electrons, with a dispersion and energy range
typical to the SP2DEG obtained in DMS, the spin density fluctuations exhibiting
a specific collective behaviour when the spin polarization is increased. The
dissipation spectrum through these excitations is studied in detail. Particular
attention is given to the spectrum determined by resonant Raman scattering. We
show, indeed, that the latter gives unique access to the spin-fluctuations
spectrum of the SP2DEG.",0810.4872v1
2009-09-22,Spin Hall and longitudinal conductivity of a conserved spin current in two dimensional heavy-hole gases,"The spin Hall and longitudinal conductivity of a 2D heavy-hole gas with {\it
k}-cubic Rashba and Dresselhaus spin-orbit interaction is studied in the ac
frequency domain. Using Kubo linear-response theory and a recently proposed
definition for the (conserved) spin current operator suitable for spin-3/2
holes, it is shown that the spin conductivity tensor exhibit very
distinguishable features from those obtained with the standard definition of
the spin current. This is due to a significant contribution of the spin-torque
term arisen from the alternative definition of spin current which strongly
affects the magnitude and the sign of the dynamic spin current. In the dc (free
of disorder) limit, the spin Hall conductivity for only (or dominant) {\it
k}-cubic Rashba coupling is $\sigma^{s,z}_{xy}(0)=-9e/8\pi$, whereas
$\sigma^{s,z}_{xy}(0)=-3e/8\pi$ for only (or dominant) {\it k}-cubic
Dresselhaus coupling. Such anisotropic response is understood in terms of the
absence of mapping the {\it k}-cubic Rashba $\leftrightarrow$ Dresselhaus
Hamiltonians. This asymmetry is also responsible for the non-vanishing dc spin
Hall conductivity ($\sigma^{s,z}_{xy}(0)=-6e/8\pi$) when the Rashba and
Dresselhaus parameters have the same strength, in contrast with its
corresponding case for electrons. These results are of relevance to validate
the alternative definition of spin-current through measurements in the
frequency domain of the spin accumulation and/or spin currents in 2D hole
gases.",0909.4045v3
2010-11-08,Spin liquids in graphene,"We reveal that local interactions in graphene allow novel spin liquids
between the semi-metal and antiferromagnetic Mott insulating phases, identified
with algebraic spin liquid and Z$_{2}$ spin liquid, respectively. We argue that
the algebraic spin liquid can be regarded as the two dimensional realization of
one dimensional spin dynamics, where antiferromagnetic correlations show
exactly the same power-law dependence as valence bond correlations. Nature of
the Z$_{2}$ spin liquid turns out to be $d + i d'$ singlet pairing, but time
reversal symmetry is preserved, taking $d + i d'$ in one valley and $d - i d'$
in the other valley. We propose the quantized thermal valley Hall effect as an
essential feature of this gapped spin liquid state. Quantum phase transitions
among the semi-metal, algebraic spin liquid, and Z$_{2}$ spin liquid are shown
to be continuous while the transition from the Z$_{2}$ spin liquid to the
antiferromagnetic Mott insulator turns out to be the first order. We emphasize
that both algebraic spin liquid and $d \pm id'$ Z$_{2}$ spin liquid can be
verified by the quantum Monte Carlo simulation, showing the enhanced symmetry
in the algebraic spin liquid and the quantized thermal valley Hall effect in
the Z$_{2}$ spin liquid.",1011.1700v2
2012-08-02,Spin Imbalance and Spin-Charge Separation in a Mesoscopic Superconductor,"What happens to spin-polarised electrons when they enter a superconductor?
Superconductors at equilibrium and at finite temperature contain both paired
particles (of opposite spin) in the condensate phase as well as unpaired,
spin-randomised quasiparticles. Injecting spin-polarised electrons into a
superconductor thus creates both spin and charge imbalances [1, 2, 3, 4, 5, 6,
7] (respectively Q* and S*, cf. Ref. [4]). These must relax when the injection
stops, but not necessarily over the same time (or length) scale as spin
relaxation requires spin-dependent interactions while charge relaxation does
not. These different relaxation times can be probed by creating a dynamic
equilibrium between continuous injection and relaxation, which leads to
constant-in-time spin and charge imbalances. These scale with their respective
relaxation times and with the injection current. While charge imbalances in
superconductors have been studied in great detail both theoretically [8] and
experimentally [9], spin imbalances have not received much experimental
attention [6, 10] despite intriguing theoretical predictions of spin-charge
separation effects [11, 12]. These could occur e.g. if the spin relaxation time
is longer than the charge relaxation time, i.e. Q* relaxes faster than S*.
Fundamentally, spin-charge decoupling in superconductors is possible because
quasiparticles can have any charge between e and -e, and also because the
condensate acts as a particle reservoir [13, 11, 12]. Here we present evidence
for an almost-chargeless spin imbalance in a mesoscopic superconductor.",1208.0500v1
2015-06-30,Experimental Demonstration of Efficient Spin-Orbit Torque Switching of an MTJ with sub-100 ns Pulses,"Efficient generation of spin currents from charge currents is of high
importance for memory and logic applications of spintronics. In particular,
generation of spin currents from charge currents in high spin-orbit coupling
metals has the potential to provide a scalable solution for embedded memory. We
demonstrate a net reduction in critical charge current for spin torque driven
magnetization reversal via using spin-orbit mediated spin current generation.
We scaled the dimensions of the spin-orbit electrode to 400 nm and the
nanomagnet to 270 nm x 68 nm in a three terminal spin-orbit torque, magnetic
tunnel junction (SOT-MTJ) geometry. Our estimated effective spin Hall angle is
0.15-0.20 using the ratio of zero temperature critical current from spin Hall
switching and estimated spin current density for switching the magnet. We show
bidirectional transient switching using spin-orbit generated spin torque at 100
ns switching pulses reliably followed by transient read operations. We finally
compare the static and dynamic response of the SOT-MTJ with transient spin
circuit modeling showing the performance of scaled SOT-MTJs to enable
nanosecond class non-volatile MTJs.",1506.09177v4
2015-12-05,Kinetic theory of spin-polarized systems in electric and magnetic fields with spin-orbit coupling: II. RPA response functions and collective modes,"The spin and density response functions in the random phase approximation
(RPA) are derived by linearizing the kinetic equation including a magnetic
field, the spin-orbit coupling, and mean fields with respect to an external
electric field. Different polarization functions appear describing various
precession motions showing Rabi satellites due to an effective Zeeman field.
The latter turns out to consist of the mean-field magnetization, the magnetic
field, and the spin-orbit vector. The collective modes for charged and neutral
systems are derived and a threefold splitting of the spin waves dependent on
the polarization and spin-orbit coupling is shown. The dielectric function
including spin-orbit coupling, polarization and magnetic fields is presented
analytically for long wave lengths and in the static limit. The dynamical
screening length as well as the long-wavelength dielectric function shows an
instability in charge modes, which are interpreted as spin segregation and
domain formation. The spin response describes a crossover from damped
oscillatory behavior to exponentially damped behavior dependent on the
polarization and collision frequency. The magnetic field causes ellipsoidal
trajectories of the spin response to an external electric field and the
spin-orbit coupling causes a rotation of the spin axes. The spin-dephasing
times are extracted and discussed in dependence on the polarization, magnetic
field, spin-orbit coupling and single-particle relaxation times.",1512.01661v1
2017-10-31,Strongly anisotropic spin relaxation in graphene/transition metal dichalcogenide heterostructures at room temperature,"Graphene has emerged as the foremost material for future two-dimensional
spintronics due to its tuneable electronic properties. In graphene, spin
information can be transported over long distances and, in principle, be
manipulated by using magnetic correlations or large spin-orbit coupling (SOC)
induced by proximity effects. In particular, a dramatic SOC enhancement has
been predicted when interfacing graphene with a semiconducting transition metal
dechalcogenide, such as tungsten disulphide (WS$_2$). Signatures of such an
enhancement have recently been reported but the nature of the spin relaxation
in these systems remains unknown. Here, we unambiguously demonstrate
anisotropic spin dynamics in bilayer heterostructures comprising graphene and
WS$_2$. By using out-of-plane spin precession, we show that the spin lifetime
is largest when the spins point out of the graphene plane. Moreover, we observe
that the spin lifetime varies over one order of magnitude depending on the spin
orientation, indicating that the strong spin-valley coupling in WS$_2$ is
imprinted in the bilayer and felt by the propagating spins. These findings
provide a rich platform to explore coupled spin-valley phenomena and offer
novel spin manipulation strategies based on spin relaxation anisotropy in
two-dimensional materials.",1710.11568v3
2019-08-05,Spin inertia and polarization recovery in quantum dots: Role of pumping strength and resonant spin amplification,"Spin inertia measurements are a novel experimental tool to study long-time
spin relaxation processes in semiconductor nanostructures. We develop a theory
of the spin inertia effect for resident electrons and holes localized in
quantum dots. We consider the spin orientation by short optical pulses with
arbitrary pulse area and detuning from the trion resonance. The interaction
with an external longitudinal magnetic field and the hyperfine interaction with
the nuclear spin bath is considered in both the ground and excited (trion)
states of the quantum dots. We analyze how the spin inertia signal depends on
the magnetic field (polarization recovery) and on the modulation frequency of
the helicity of the pump pulses as well as on their power and detuning. In
particular, we elaborate how approaching the saturation limit of the spin
polarization influences the measurements. The quantitative description of spin
inertia measurements will enable the determination of the parameters of spin
dynamics such as the spin relaxation times in the ground and excited states and
the parameters of the hyperfine interaction. Finally, we predict the emergence
of resonant spin amplification due to the transverse components of the nuclear
spin fluctuations, which manifests itself as oscillations of the spin
polarization as a function of the longitudinal magnetic field.",1908.01531v3
2022-05-29,"Quantum Scattering Theory of Spin Transfer Torque, Spin Pumping and Fluctuations","Spin transfer torque and spin pumping are central reciprocal phenomena in
spintronics. These phenomena occur in hybrid systems of normal metals and
magnets. Spin transfer is the conversion of spin currents in metals to a torque
on the magnetization of magnets. Spin pumping is the emission of spin currents
from precessing magnets. Here, we demonstrate a general way to understand these
effects within a quantum out-of-equilibrium path-integral model. Our results
agree with known expressions for spin transfer and spin pumping in terms of
transverse (mixing) conductances when there are no fluctuations. However, at a
finite temperature, frequency or spin accumulation, the magnet also experiences
fluctuating torques. In the classical regime, when the thermal energy is larger
than the bias voltage and precession frequency, we reproduce the classical
Brownian-Langevin forces associated with spin transfer and spin pumping. At low
temperatures, in the quantum regime, we demonstrate that magnetization
fluctuations differ in the elastic and inelastic electron transport regimes.
Furthermore, we show how additional transport coefficients beyond the mixing
conductance govern the fluctuations. Some of these coefficients are related to
electron shot noise because of the discrete spin angular momentum of electrons.
We estimate the fluctuation coefficients of clean, tunnel, and disordered
junctions and in the case of an insulating magnet. Our results open a path for
exploring low-temperature magnetization dynamics and spin caloritronics.",2205.14672v2
2022-07-13,Jahn-Teller states mixed by spin-orbit coupling in an electromagnetic field,"Spin-orbit coupling plays a pivotal role in condensed matter physics. For
instance, spin-orbit interactions affect the magnetization and transport
dynamics in solids, while spins and momenta are locked in topological matter.
Alternatively, spin-orbit entanglement may play an important role in exotic
phenomena, like quantum spin liquids in 4d and 5d systems. An interesting
question is how electronic states mixed by spin orbit coupling interact with
electromagnetic fields, which may hold potential to tune their properties and
reveal interesting physics. Motivated by our recent discovery of large
gyrotropic signals in some Jahn-Teller manganites, here we explore the
interaction of light with spin-mixed states in a d4 transition metal. We show
that spin-orbit mixing enables electronic transitions that are sensitive to
circularly polarized light, giving rise to a gyrotropic response that increases
with spin-orbit coupling. Interestingly, photoexcited transitions that involve
spin reversal are behind such gyrotropic resonances. Additionally, we find that
the interaction with the electromagnetic field depends strongly on the relative
orientation of the propagation of light with respect to Jahn-Teller distortions
and spin quantization. We suggest that such interactions offer the opportunity
to use electromagnetic waves at optical wavelengths to entangle orbital and
spin degrees of freedom. Our approach, which includes a group-theoretical
treatment of spin-orbit coupling, has wide applicability and provides a
versatile tool to explore the interaction of electromagnetic fields with
electronic states in transition metals with arbitrary spin-orbit coupling
strength and pointgroup symmetries.",2207.06501v1
2022-10-07,Active spin lattice hyperpolarization: Application to hexagonal boron nitride color centers,"The active driving of the electron spin of a color center is known as a
method for the hyperpolarization of the surrounding nuclear spin bath and to
initialize a system with large number of spins. Here, we investigate the
efficiency of this approach for various spin coupling schemes in a
one-dimensional Heisenberg chain coupled to a central spin. To extend our study
to the realistic systems with a large number of interacting spins, we employ an
approximate method based on Holstein-Primakoff transformation. The validity of
the method for describing spin polarization dynamics is benchmarked by the
exact numerics for a small lattice, where the accuracy of the bosonic
Holstein-Primakoff approximation approach is confirmed. We, thus, extend our
analysis to larger spin systems where the exact numerics are out of reach. The
results prove the efficiency of the active driving method when the central spin
interaction with the spin bath is long range and the inter-spin interactions in
the bath spins is large enough. The method is then applied to the realistic
case of optically active negatively charged boron vacancy centers ($V_B$) in
hexagonal boron nitride. Our results suggest that a high degree of
hyperpolarization in the boron and nitrogen nuclear spin lattices is achievable
even starting from a fully thermal bath. As an initialization, our work
provides the first step toward the realization of a two-dimensional quantum
simulator based on natural nuclear spins and it can prove useful for extending
the coherence time of the $V_B$ centers.",2210.03334v1
2023-02-28,Quantum simulation of the central spin model with a Rydberg atom and polar molecules in optical tweezers,"Central spin models, where a single spinful particle interacts with a spin
environment, find wide application in quantum information technology and can be
used to describe, e.g., the decoherence of a qubit over time. We propose a
method of realizing an ultracold quantum simulator of a central spin model with
XX (spin-exchanging) interactions. The proposed system consists of a single
Rydberg atom (""central spin"") and surrounding polar molecules (""bath spins""),
coupled to each other via dipole-dipole interactions. By mapping internal
particle states to spin states, spin-exchanging interactions can be simulated.
As an example system geometry, we consider a ring-shaped arrangement of bath
spins, and show how it allows us to exact precise control over the interaction
strengths. We numerically analyze two example dynamical scenarios which can be
simulated in this setup: a decay of central spin polarization, which can
represent qubit decoherence in a disordered environment, and a transfer of an
input spin state to a specific output spin, which can represent the
transmission of a single bit across a quantum network. We demonstrate that this
setup allows us to realize a central spin model with highly tunable parameters
and geometry, for applications in quantum science and technology.",2302.14774v2
2020-12-12,Ultrafast spin-currents and charge conversion at 3d-5d interfaces probed by time-domain terahertz spectroscopy,"Spintronic structures are extensively investigated for their spin orbit
torque properties, required for magnetic commutation functionalities. Current
progress in these materials is dependent on the interface engineering for the
optimization of spin transmission. Here, we advance the analysis of ultrafast
spin-charge conversion phenomena at ferromagnetic-transition metal interfaces
due to their inverse spin-Hall effect properties. In particular the intrinsic
inverse spin Hall effect of Pt-based systems and extrinsic inverse spin-Hall
effect of Au:W and Au:Ta in NiFe/Au:(W,Ta) bilayers are investigated. The
spin-charge conversion is probed by complementary techniques -- ultrafast THz
time domain spectroscopy in the dynamic regime for THz pulse emission and
ferromagnetic resonance spin-pumping measurements in the GHz regime in the
steady state -- to determine the role played by the material properties,
resistivities, spin transmission at metallic interfaces and spin-flip rates.
These measurements show the correspondence between the THz time domain
spectroscopy and ferromagnetic spin-pumping for the different set of samples in
term of the spin mixing conductance. The latter quantity is a critical
parameter, determining the strength of the THz emission from spintronic
interfaces. This is further supported by ab-initio calculations, simulations
and analysis of the spin-diffusion and spin relaxation of carriers within the
multilayers in the time domain, permitting to determine the main trends and the
role of spin transmission at interfaces. This work illustrates that time domain
spectroscopy for spin-based THz emission is a powerful technique to probe
spin-dynamics at active spintronic interfaces and to extract key material
properties for spin-charge conversion.",2012.06900v1
2019-12-29,Synchronized excitation of magnetization dynamics via spin waves in Bi-YIG thin film by slot line waveguide,"We have studied magnetization dynamics of a single Bi-YIG thin film by means
of the high frequency power response induced by a slot line waveguide. Multiple
absorption peaks that correspond to excitement states in magnetization dynamics
appeared without the ferromagnetic resonance (FMR) condition. The peaks were
strongly influenced by a waveguide line width and a distance between the lines.
Micromagnetics simulation reveals that each line induces a local magnetization
dynamics oscillation and generates spin waves. The spin wave that propagates
from one of the lines interferences with the other side of local magnetization
dynamics oscillation around the other line, resulting in an amplification of
the oscillation when they are in synchronization with each other. This
amplification occurs at both sides of the lines by the interference. Thus, the
possible mechanism of the excitation in the magnetization dynamics oscillation
is the synchronization of mutual magnetization dynamics oscillation via spin
waves. This technique resonantly excites the local magnetization dynamics
without the FMR condition, which is applicable as a highly coherent spin waves
source.",1912.12663v1
2011-07-11,Spin and charge transport induced by gauge fields in a ferromagnet,"We present a microscopic theory of spin-dependent motive force (""spin motive
force"") induced by magnetization dynamics in a conducting ferromagnet, by
taking account of spin relaxation of conduction electrons. The theory is
developed by calculating spin and charge transport driven by two kinds of gauge
fields; one is the ordinary electromagnetic field $A^{\rm em}_{\mu}$, and the
other is the effective gauge field $A^{z}_{\mu}$ induced by dynamical magnetic
texture. The latter acts in the spin channel and gives rise to a spin motive
force. It is found that the current induced as a linear response to
$A^{z}_{\mu}$ is not gauge-invariant in the presence of spin-flip processes.
This fact is intimately related to the non-conservation of spin via Onsager
reciprocity, so is robust, but indicates a theoretical inconsistency. This
problem is resolved by considering the time dependence of spin-relaxation
source terms in the ""rotated frame"", as in the previous study on Gilbert
damping [J. Phys. Soc. Jpn. {\bf 76}, 063710 (2007)]. This effect restores the
gauge invariance while keeping spin non-conservation. It also gives a
dissipative spin motive force expected as a reciprocal to the dissipative spin
torque (""$\beta$-term"").",1107.2165v3
2017-04-21,A new high-temperature quantum spin liquid with polaron spins,"The existence of a quantum spin liquid (QSL) in which quantum fluctuations of
spins are sufficiently strong to preclude spin ordering down to zero
temperature was originally proposed theoretically more than 40 years ago, but
its experimental realisation turned out to be very elusive. Here we report on
an almost ideal spin liquid state that appears to be realized by atomic-cluster
spins on the triangular lattice of a charge-density wave (CDW) state of
1T-TaS$_2$. In this system, the charge excitations have a well-defined gap of
$\sim 0.3$ eV, while nuclear magnetic quadrupole resonance and muon spin
relaxation experiments reveal that the spins show gapless quantum spin liquid
dynamics and no long range magnetic order down to 70~mK. Canonical $T^{2}$
power-law temperature dependence of the spin relaxation dynamics characteristic
of a QSL is observed from 200~K to $T_f= 55$ K. Below this temperature we
observe a new gapless state with reduced density of spin excitations and high
degree of local disorder signifying new quantum spin order emerging from the
QSL.",1704.06450v1
2023-09-11,Scalable spin squeezing in two-dimensional arrays of dipolar large-$S$ spins,"Controlling the quantum many-body state of arrays of qudits, possessing a
large local Hilbert space, opens the path to a broad range of possibilities for
many-particle entanglement, interesting both for fundamental quantum science,
as well as for potential metrological applications. In this work we
theoretically show that the spin-spin interactions realized in two-dimensional
Mott insulators of large-spin magnetic atoms (such as Cr, Er or Dy) lead to
scalable spin squeezing along the non-equilibrium unitary evolution initialized
in a coherent spin state. An experimentally relevant perturbation to the
collective squeezing dynamics is offered by a quadratic Zeeman shift, which
leads instead to squeezing of individual spins. Making use of a truncated
cumulant expansion for the quantum fluctuations of the spin array, we show
that, for sufficiently small quadratic shifts, the spin squeezing dynamics is
akin to that produced by the paradigmatic one-axis-twisting (OAT) model -- as
expected from an effective separation between collective spin and spin-wave
variables. Spin squeezing with OAT-like scaling is shown to be protected by the
robustness of long-range ferromagnetic order to quadratic shifts in the
equilibrium phase diagram of the system, that we reconstruct via quantum Monte
Carlo and mean-field theory.",2309.05368v1
1999-05-10,Topological spin excitations of Heisenberg antiferromagnets in two dimensions,"In this paper we discuss the construction and the dynamics of vortex-like
topological spin excitations in the Schwinger-boson description of Heisenberg
antiferromagnets in two dimensions. The topological spin excitations are Dirac
fermions (with gap) when spin value $S$ is a half-integer. Experimental and
theoretical implications of these excitations are being investigated.",9905115v1
2001-10-17,Anomalous magneto-oscillations and spin precession,"A semiclassical analysis based on concepts developed in quantum chaos reveals
that anomalous magneto-oscillations in quasi two-dimensional systems with
spin-orbit interaction reflect the non-adiabatic spin precession of a classical
spin vector along the cyclotron orbits.",0110353v1
2003-12-10,Spin Gain Transistor in Ferromagnetic Semiconductors: the Semiconductor Bloch Equations Approach,"Scheme and principle of operation of a spin gain transistor are proposed: a
large unmagnetized current creates density sufficient for the ferromagnetic
transition; a small magnetized current initiates spontaneous magnetization;
large magnetized current is extracted. Therefore spin gain of more than 1000 is
predicted. Collective dynamics of spins under Coulomb exchange interaction is
described via Semiconductor Bloch Equations.",0312243v1
2004-05-18,Multichannel field-effect spin barrier selector,"We have studied spin carrier dynamics under full spin-orbit coupling. The
anisotropy of dispersions for independent circular spinor polarizations is
explored as a possible vertical multichannel voltage controlled spin-filter.
Small voltage variations are found to select the current polarizations in a
resonant tunneling geometry.",0405418v1
1997-12-04,Spin asymmetries at RHIC and nonperturbative aspects of hadron dynamics,"Some nonperturbative aspects of spin studies at RHIC are discussed and the
predictions for single- and two-spin asymmetries are given. Among them are
those which emphasize the role of angular orbital momentum in the spin
structure of the constituent quarks.",9712262v1
1999-04-20,Proton Spin Based On Chiral Dynamics,"Chiral spin fraction models agree with the proton spin data only when the
chiral quark-Goldstone boson couplings are pure spinflip. For axial-vector
coupling from soft-pion physics this is true for massless quarks but not for
constituent quarks. Axial-vector quark-Goldstone boson couplings with {\bf
constituent} quarks are found to be inconsistent with the proton spin data.",9904405v1
1998-10-31,Massive spinning particle in any dimension. II. (Half-)integer spins,"The general model of an arbitrary spin massive particle in any dimensional
space-time is derived on the basis of Kirillov - Kostant - Souriau approach.
  Keywords: spinning particles, Poincar\'e group, orbit method, constrained
dynamics, geometric quantization.",9811003v1
2002-08-29,Semiclassical spin coherent state method in the weak spin-orbit coupling limit,"We apply the semiclassical spin coherent state method for the density of
states by Pletyukhov et al. (2002) in the weak spin-orbit coupling limit and
recover the modulation factor in the semiclassical trace formula found by Bolte
and Keppeler (1998, 1999).",0208047v1
2007-06-03,Quantum superintegrable system for arbitrary spin,"In [1] was considered the superintegrable system which describes the magnetic
dipole with spin 1/2 (neutron) in the field of linear current. Here we present
its generalization for any spin which preserves superintegrability. The
dynamical symmetry stays the same as it is for spin 1/2.",0706.0310v2
2007-09-28,Motion of Spin 1/2 Massive Particle in a Curved Spacetime,"Quasi-classical picture of motion of spin 1/2 massive particle in a curved
spacetime is built on base of simple Lagrangian model. The one is constructed
due to analogy with Lagrangian of massive vector particle. Equations of motion
and spin propagation coincide with Papapetrou equations describing dynamic of
classical spinning particle in a curved spacetime.",0709.4607v1
2008-02-18,Motion of Spin 1/2 Massless Particle in a Curved Spacetime. I. Lagrangian Approach,"Quasi-classical picture of motion of spin 1/2 massless particle in a curved
spacetime is built on base of simple Lagrangian model. The one is constructed
due to analogy with Lagrangian of massive spin 1/2 particle. Equations of
motion and spin propagation coincide with Papapetrou equations describing
dynamic of photon in a curved spacetime.",0802.2450v1
2010-12-10,Spin relaxation and spin dynamics in semiconductors,"A chapter contribution to book: ""Handbook of Spin Transport and Magnetism"",
ed. by Evegeny Y. Tsymbal and Igor Zutic (Chapman & Hall/CRC, 2011)
http://www.crcpress.com/product/isbn/9781439803776 .",1012.2205v1
2013-02-26,Spin Mixing in Spinor Fermi Gases,"We study a spinor fermionic system under the effect of spin-exchange
interaction. We focus on the interplay between the spin-exchange interaction
and the effective quadratic Zeeman shift. We examine the static and the dynamic
properties of both two- and many-body system. We find that the spin-exchange
interaction induces coherent Rabi oscillation in the two-body system, but the
oscillation is quickly damped when the system is extended to the many-body
case.",1302.6549v1
2014-01-28,Phase space monitoring of exciton-polariton multistability,"Dynamics of exciton-polariton multistability is theoretically investigated.
Phase portraits are used as a tool to enlighten the microscopic phenomena which
influence spin multistability of a confined polariton field as well as
ultrafast reversible spin switching. The formation of a non-radiative
reservoir, due to polariton pairing into biexcitons is found to play the lead
role in the previously reported spin switching experiments. Ways to tailor this
reservoir formation are discussed in order to obtain optimal spin switching
reliability.",1401.7120v1
2017-12-13,Spin and maximal acceleration,"We study the spin current tensor of a Dirac particle at accelerations close
to the upper limit introduced by Caianiello. Continual interchange between
particle spin and angular momentum is possible only when the acceleration is
time-dependent. This represents a stringent limit on the effect that maximal
acceleration may have on spin physics in astrophysical applications. We also
investigate some dynamical consequences of maximal acceleration.",1712.04834v1
2016-06-24,Remotely detecting the signal of a local decohering process in spin chains,"We study the dynamics of a one dimensional quantum spin chain evolving from
unentangled or entangled initial state. At a given instant of time a quantum
dynamical process (ex. measurement) is performed on a single spin at one end of
the chain, decohering the system. Through the further unitary evolution, a
signal propagates in the spin chain, which can be detected from a measurement
on a different spin at later times. From the dynamical unitary evolution of the
decohered state from the epoch time, it is possible to detect the occurrence of
the dynamical process. The propagation of the signal for the dynamical process,
and the speed of the signal are investigated for various spin models, viz.
using the Ising, Heisenberg, and the transverse-XY dynamics.",1606.07563v2
2016-07-26,Neutron spin-echo study of the critical dynamics of spin-5/2 antiferromagnets in two and three dimensions,"We report a neutron spin-echo study of the critical dynamics in the $S=5/2$
antiferromagnets MnF$_2$ and Rb$_2$MnF$_4$ with three-dimensional (3D) and
two-dimensional (2D) spin systems, respectively, in zero external field. Both
compounds are Heisenberg antiferromagnets with a small uniaxial anisotropy
resulting from dipolar spin-spin interactions, which leads to a crossover in
the critical dynamics close to the N\'eel temperature, $T_N$. By taking
advantage of the $\mu\text{eV}$ energy resolution of the spin-echo
spectrometer, we have determined the dynamical critical exponents $z$ for both
longitudinal and transverse fluctuations. In MnF$_2$, both the characteristic
temperature for crossover from 3D Heisenberg to 3D Ising behavior and the
exponents $z$ in both regimes are consistent with predictions from the
dynamical scaling theory. The amplitude ratio of longitudinal and transverse
fluctuations also agrees with predictions. In Rb$_2$MnF$_4$, the critical
dynamics crosses over from the expected 2D Heisenberg behavior for $T\gg T_N$
to a scaling regime with exponent $z = 1.387(4)$, which has not been predicted
by theory and may indicate the influence of long-range dipolar interactions.",1607.07677v1
2020-05-13,Manipulation of heteronuclear spin dynamics with microwave and vector light shift,"We report the observation and manipulation of heteronuclear spin dynamics in
a spin-1 mixture of ultracold $^{87}$Rb and $^{23}$Na atoms. The dynamics is
driven by the interspecies spin-dependent interaction and shows a pronounced
dependence on magnetic fields with influences from both linear and quadratic
Zeeman shifts. Similar to the well-studied homonuclear cases, the interspecies
spin dynamics can be controlled by tuning the quadratic Zeeman shift with
far-detuned microwave fields. In addition, we successfully realize spin
dynamics control with vector light shifts which act as a species-selective
effective magnetic field on $^{87}$Rb atoms. Both methods show negligible loss
of atoms thus will be powerful techniques for investigating spin dynamics with
fast temporal and high spatial resolutions.",2005.06098v1
1996-07-08,Critical dynamics in the 2d classical XY-model: a spin dynamics study,"Using spin-dynamics techniques we have performed large-scale computer
simulations of the dynamic behavior of the classical three component XY-model
(i.e. the anisotropic limit of an easy-plane Heisenberg ferromagnet), on square
lattices of size up to 192^2, for several temperatures below, at, and above
T_KT. The temporal evolution of spin configurations was determined numerically
from coupled equations of motion for individual spins by a fourth order
predictor-corrector method, with initial spin configurations generated by a
hybrid Monte Carlo algorithm. The neutron scattering function S(q,omega) was
calculated from the resultant space-time displaced spin-spin correlation
function. Pronounced spin-wave peaks were found both in the in-plane and the
out-of-plane scattering function over a wide range of temperatures. The
in-plane scattering function S^xx also has a large number of clear but weak
additional peaks, which we interpret to come from two-spin-wave scattering. In
addition, we observed a small central peak in S^xx, even at temperatures well
below the phase transition. We used dynamic finite size scaling theory to
extract the dynamic critical exponent z. We find z=1.00(4) for all T <= T_KT,
in excellent agreement with theoretical predictions, although the shape of
S(q,omega) is not well described by current theory.",9607063v1
2014-09-25,Bloch-Landau-Zener dynamics in single-particle Wannier-Zeeman systems,"Stimulated by the experimental realization of spin-dependent tunneling via
gradient magnetic field [Phys. Rev. Lett. 111, 225301 (2013); Phys. Rev. Lett.
111, 185301 (2013)], we investigate dynamics of Bloch oscillations and
Landau-Zener tunneling of single spin-half particles in a periodic potential
under the influence of a spin-dependent constant force. In analogy to the
Wannier-Stark system, we call our system as the Wannier-Zeeman system. If there
is no coupling between the two spin states, the system can be described by two
crossing Wannier-Stark ladders with opposite tilts. The spatial crossing
between two Wannier-Stark ladders becomes a spatial anti-crossing if the two
spin states are coupled by external fields. For a wave-packet away from the
spatial anti-crossing, due to the spin-dependent constant force, it will
undergo spatial Landau-Zener transitions assisted by the intrinsic intra-band
Bloch oscillations, which we call the Bloch-Landau-Zener dynamics. If the
inter-spin coupling is sufficiently strong, the system undergoes adiabatic
Bloch-Landau-Zener dynamics, in which the spin dynamics follows the local
dressed states. Otherwise, for non-strong inter-spin couplings, the system
undergoes non-adiabatic Bloch-Landau-Zener dynamics.",1409.7262v3
2021-01-15,Bethe strings in the spin dynamical structure factor of the Mott-Hubbard phase in one-dimensional fermionic Hubbard model,"The spectra and role in the spin dynamical properties of bound states of
elementary magnetic excitations named Bethe strings that occur in some
integrable spin and electronic one-dimensional models have recently been
identified and realized in several materials by experiments. Corresponding
theoretical studies have usually relied on the one-dimensional spin-1/2
Heisenberg antiferromagnet in a magnetic field. At the isotropic point, it
describes the large onsite repulsion U limit of the spin degrees of freedom of
the one-dimensional fermionic Hubbard model with one electron per site in a
magnetic field h. In this paper we consider the thermodynamic limit and study
the effects of lowering the latter quantum problem ratio u=U/4t, where t is the
first-neighbor transfer integral, on the line-shape singularities in regions at
and just above the lower thresholds of the transverse and longitudinal spin
dynamical structure factors. The most significant spectral weight contribution
from Bethe strings leads to a gapped continuum in the spectrum of the spin
dynamical structure factor +-. Our study focuses on the line shape
singularities at and just above the gapped lower threshold of that continuum,
which have been identified in experiments. Our results are consistent with the
contribution of Bethe strings to the spin dynamical structure factor zz being
small at low spin densities and becoming negligible upon increasing that
density. Our results provide physically important information about how
electron itinerancy affects the spin dynamics.",2101.06198v1
2021-01-27,Coherent dynamics of multi-spin $\rm V_B^-$ centers in hexagonal boron nitride,"Hexagonal boron nitride (hBN) has recently been demonstrated to contain
optically polarized and detected electron spins that can be utilized for
implementing qubits and quantum sensors in nanolayered-devices. Understanding
the coherent dynamics of microwave driven spins in hBN is of crucial importance
for advancing these emerging new technologies. Here, we demonstrate and study
the Rabi oscillation and related dynamical phenomena of the negatively charged
boron vacancy ($\rm V_B^-$) spins in hBN. We report on different dynamics of
the $\rm V_B^-$ spins at weak and strong magnetic fields. In the former case
the defect behaves like a single electron spin system, while in the latter case
it behaves like a multi-spin system exhibiting the multiple-frequency dynamical
oscillation like clear beat in Ramsey fringes. We also carry out theoretical
simulations for the spin dynamics of $\rm V_B^-$ and reveal that the nuclear
spins can be driven via the strong electric-nuclear coupling existing in $\rm
V_B^-$ center, which can be modulated by the magnetic field and microwave
field.",2101.11220v3
2023-04-28,Interplay of electron-magnon scattering and spin-orbit induced electronic spin-flip fcattering in a two-band Stoner model,"Magnons are one of the carriers of angular momentum that are involved in the
ultrafast magnetization dynamics in ferromagnets, but their contribution to the
electronic dynamics and their interplay with other scattering process that
occur during ultrafast demagnetization has not yet been studied in the
framework of a microscopic dynamical model. The present paper presents such an
investigation of electronic scattering dynamics in itinerant ferromagnets at
the level of Boltzmann scattering integrals for the magnon distributions and
spin-dependent electron distributions. In addition to electron-magnon
scattering, we include spin-conserving and effective Elliott-Yafet like
spin-flip electron-electron scattering processes and the influence of phonons.
In our model system, the creation or annihilation of magnons leads to
transitions between two spin-split electronic bands with energy and momentum
conservation. Due to the presence of spin-orbit coupling, Coulomb scattering
transitions between these bands are also possible, and we describe them on an
equal footing in terms of Boltzmann scattering integrals. For an instantaneous
carrier excitation process we analyze the influence of both interaction
processes on the magnon and spin-dependent electron dynamics, and show that
their interplay gives rise to an efficient creation of magnons at higher
energies and wave vectors accompanied by only a small increase of the
electronic spin polarization. These results present a microscopic dynamical
scenario that shows how non-equilibrium magnons may dominate the magnetic
response of a ferromagnet on ultrafast timescales.",2304.14978v1
2015-05-29,Microscopic Theory for Coupled Atomistic Magnetization and Lattice Dynamics,"A coupled atomistic spin and lattice dynamics approach is developed which
merges the dynamics of these two degrees of freedom into a single set of
coupled equations of motion. The underlying microscopic model comprises local
exchange interactions between the electron spin and magnetic moment and the
local couplings between the electronic charge and lattice displacements. An
effective action for the spin and lattice variables is constructed in which the
interactions among the spin and lattice components are determined by the
underlying electronic structure. In this way, expressions are obtained for the
electronically mediated couplings between the spin and lattice degrees of
freedom, besides the well known inter-atomic force constants and spin-spin
interactions. These former susceptibilities provide an atomistic ab initio
description for the coupled spin and lattice dynamics. It is important to
notice that this theory is strictly bilinear in the spin and lattice variables
and provides a minimal model for the coupled dynamics of these subsystems and
that the two subsystems are treated on the same footing. Questions concerning
time-reversal and inversion symmetry are rigorously addressed and it is shown
how these aspects are absorbed in the tensor structure of the interaction
fields. By means of these results regarding the spin-lattice coupling, simple
explanations of ionic dimerization in double anti-ferromagnetic materials, as
well as, charge density waves induced by a non-uniform spin structure are
given. In the final parts, a set of coupled equations of motion for the
combined spin and lattice dynamics are constructed, which subsequently can be
reduced to a form which is analogous to the Landau-Lifshitz-Gilbert equations
for spin dynamics and damped driven mechanical oscillator for the ...",1505.08005v3
2017-02-07,One-dimensional Quantum Spin Dynamics of Bethe String States,"Quantum dynamics of strongly correlated systems is a challenging problem.
Although the low energy fractional excitations of one dimensional integrable
models are often well-understood, exploring quantum dynamics in these systems
remains challenging in the gapless regime, especially at intermediate and high
energies. Based on the algebraic Bethe ansatz formalism, we study spin dynamics
in a representative one dimensional strongly correlated model, {\it i.e. }, the
antiferromagnetic spin-$\frac{1}{2}$ XXZ chain with the Ising anisotropy, via
the form-factor formulae. Various excitations at different energy scales are
identified crucial to the dynamic spin structure factors under the guidance of
sum rules. At small magnetic polarizations, gapless excitations dominate the
low energy spin dynamics arising from the magnetic-field-induced
incommensurability. In contrast, spin dynamics at intermediate and high
energies is characterized by the two- and three-string states, which are
multi-particle excitations based on the commensurate N\'eel ordered background.
Our work is helpful for experimental studies on spin dynamics in both condensed
matter and cold atom systems beyond the low energy effective Luttinger liquid
theory. Based on an intuitive physical picture, we speculate that the dynamic
feature at high energies due to the multi-particle anti-bound state excitations
can be generalized to non-integrable spin systems.",1702.01854v2
2018-03-01,Classical and quantum spin dynamics of the honeycomb $Γ$ model,"Quantum to classical crossover is a fundamental question in dynamics of
quantum many-body systems. In frustrated magnets, for example, it is highly
non-trivial to describe the crossover from the classical spin liquid with a
macroscopically-degenerate ground-state manifold, to the quantum spin liquid
phase with fractionalized excitations. This is an important issue as we often
encounter the demand for a sharp distinction between the classical and quantum
spin liquid behaviors in real materials. Here we take the example of the
classical spin liquid in a frustrated magnet with novel bond-dependent
interactions to investigate the classical dynamics, and critically compare it
with quantum dynamics in the same system. In particular, we focus on signatures
in the dynamical spin structure factor. Combining Landau-Lifshitz dynamics
simulations and the analytical Martin-Siggia-Rose (MSR) approach, we show that
the low energy spectra are described by relaxational dynamics and highly
constrained by the zero mode structure of the underlying degenerate classical
manifold. Further, the higher energy spectra can be explained by precessional
dynamics. Surprisingly, many of these features can also be seen in the
dynamical structure factor in the quantum model studied by finite-temperature
exact diagonalization. We discuss the implications of these results, and their
connection to recent experiments on frustrated magnets with strong spin-orbit
coupling.",1803.00601v2
2000-05-30,Dynamical Properties of Spin-Orbital Chains in a Magnetic Field,"The excitation spectrum of the one-dimensional spin-orbital model in a
magnetic field is studied, using a recently developed dynamical density matrix
renormalization group technique. The method is employed on chains with up to 80
sites, and examined for test cases such as the spin-1/2 antiferromagnetic
Heisenberg chain, where the excitation spectrum is known exactly from the Bethe
Ansatz. In the spin-orbital chain, the characteristic dynamical response
depends strongly on the model parameters and the applied magnetic field. The
coupling between the spin and orbital degrees of freedom is found to influence
the incommensuration at finite magnetizations. In the regions of the phase
diagram with only massive spin and orbital excitations, a finite field is
required to overcome the spin gap. An incommensurate orbital mode is found to
become massless in this partially spin-polarized regime, indicating a strong
coupling between the two degrees of freedom. In the critical region with three
elementary gapless excitations, a prominent particle-hole excitation is
observed at higher energies, promoted by the biquadratic term in the model
Hamiltonian of the spin-orbital chain.",0005526v2
2001-04-28,Origin of enhanced dynamic nuclear polarization and all-optical nuclear magnetic resonance in GaAs quantum wells,"Time-resolved optical measurements of electron-spin dynamics in a (110) GaAs
quantum well are used to study the consequences of a strongly anisotropic
electron g-tensor, and the origin of previously discovered all-optical nuclear
magnetic resonance. All components of the g-tensor are measured, and a strong
anisotropy even along the in-plane directions is found. The amplitudes of the
spin signal allow the study of the spatial directions of the injected spin and
its precession axis. Surprisingly efficient dynamic nuclear polarization in a
geometry where the electron spins are injected almost transverse to the applied
magnetic field is attributed to an enhanced non-precessing electron spin
component. The small absolute value of the electron g-factor combined with
efficient nuclear spin polarization leads to large nuclear fields that dominate
electron spin precession at low temperatures. These effects allow for sensitive
detection of all-optical nuclear magnetic resonance induced by periodically
excited quantum-well electrons. The mechanism of previously observed Delta m =
2 transitions is investigated and found to be attributable to electric
quadrupole coupling, whereas Delta m = 1 transitions show signatures of both
quadrupole and electron-spin induced magnetic dipole coupling.",0104564v1
2001-09-21,"Dynamic spin-glass behavior in a disorder-free, two-component model of quantum frustrated magnets","Motivated by the observation of a spin-glass transition in almost
disorder-free Kagome antiferromagnets, and by the specific form of the
effective low-energy model of the S=1/2, trimerized Kagome antiferromagnet, we
investigate the possibility to obtain a spin-glass behavior in two-component,
disorder-free models. We concentrate on a toy-model, a modified Ashkin-Teller
model in a magnetic field that couples only to one species of spins, for which
we prove that a dynamic spin-glass behavior occurs. The dynamics of the
magnetization is closely related to that of the underlying Ising model in zero
field in which spins and pseudo-spins are intimately coupled. The spin-glass
like history dependence of the magnetization is a consequence of the ageing of
the underlying Ising model.",0109406v2
2003-02-21,Statistics of spinons in the spin-liquid phase of Cs2CuCl4,"Motivated by a recent experiment on Cs2CuCl4, we study the spin dynamics of
the spin-liquid phase of the spin-1/2 frustrated Heisenberg antiferromagnet on
the anisotropic triangular lattice. There have been two different proposals for
the spin-liquid phase of Cs2CuCl4. These spin-liquid states support different
statistics of spinons; the bosonic Sp(N) large-N mean field theory predicts
bosonic spinons while the SU(2) slave-boson mean field theory leads to
fermionic spinons. We compute the dynamical spin structure factor for both
types of spin-liquid state at zero and finite temperatures. While at zero
temperature both theories agree with experiment on a qualitative level, they
show substantial differences in the temperature dependence of the dynamical
spin structure factor.",0302452v2
2006-05-22,Geometrical phase effects on the Wigner distribution of Bloch electrons,"We investigate the dynamics of Bloch electrons using a density operator
method and connect this approach with previous theories based on wave packets.
We study non-interacting systems with negligible disorder and strong spin-orbit
interactions, which have been at the forefront of recent research on
spin-related phenomena. We demonstrate that the requirement of gauge invariance
results in a shift in the position at which the Wigner function of Bloch
electrons is evaluated. The present formalism also yields the correction to the
carrier velocity arising from the Berry phase. The gauge-dependent shift in
carrier position and the Berry phase correction to the carrier velocity
naturally appear in the charge and current density distributions. In the
context of spin transport we show that the spin velocity may be defined in such
a way as to enable spin dynamics to be treated on the same footing as charge
dynamics. Aside from the gauge-dependent position shift we find additional,
gauge-covariant multipole terms in the density distributions of spin, spin
current and spin torque.",0605528v1
2007-03-01,Driven dissipative dynamics of spins in quantum dots,"We have studied the dissipative dynamics of a driven electronic spin trapped
in a quantum dot. We consider the dissipative mechanism as due to the indirect
coupling of the electronic spin to acoustic phonons via the
spin-orbit/electron-phonon couplings. Using an effective spectral function of
the dissipative phonon bath, we evaluated the expectation values of the spin
components through the Bloch-Redfield theory. We show that due to a sharp bath
resonance present in the effective spectral function, with typical energy much
smaller than the electronic confinement energy, the dissipative spin has a rich
dynamical behavior that helps us to determine some features of the spin-bath
coupling. We also quantify the effects produced by the sharp bath resonance,
and thus indicate the best regimes of operation in order to achieve the longest
relaxation times for the spin.",0703009v1
2007-07-27,Oscillatory D'yakonov-Perel' spin dynamics in two dimensional electron gases,"Optical pump-probe measurements of spin-dynamics at temperatures down to 1.5K
are described for a series of (001)-oriented GaAs/AlGaAs quantum well samples
containing high mobility two-dimensional electron gases (2DEGs). For well
widths ranging from 5 nm to 20 nm and 2DEG sheet densities from 1.75x1011cm-2
to 3.5x1011cm-2 the evolution of a small injected spin population is found to
be a damped oscillation rather than exponential relaxation, consistent with the
quasi-collision-free regime of D'yakonov-Perel spin dynamics. A Monte Carlo
simulation method is used to extract the spin-orbit-induced electron spin
precession frequency |W(kF)| and electron momentum scattering time tp* at the
Fermi wavevector. The spin decay time passes through a minimum at a temperature
corresponding to the transition from collision-free to collision-dominated
regimes and tp* is found to be close to the ensemble momentum scattering time
tp obtained from Hall measurements of electron mobility. The values of |W(kF)|
give the Dresselhaus (BIA) coefficient of spin-orbit interaction as a function
of electron confinement energy in the quantum show, qualitatively, the
behaviour expected from k.p theory.",0707.4180v1
2008-11-03,Collective spin dynamics in magnetic nanomaterials,"Magnetic nanomaterials are considered, formed by magnetic nanomolecules with
high spins. The problem of spin reversal in these materials is analyzed, which
is of interest for the possible use of such materials for quantum information
processing and quantum computing. The fastest spin reversal can be achieved by
coupling the spin sample to a resonant electric circuit and by an appropriate
choice of the system parameters. A principal point is to choose these
parameters so that to organize coherent spin motion. Dynamics of collective
motion is modelled by computer simulations, which confirm the high level of
dynamical coherence of molecular spins in the process of spin reversal.",0811.0267v1
2009-04-23,Spin dynamics in rare earth single molecule magnets from muSR and NMR in [TbPc$_{2}$]$^{0}$ and [DyPc$_{2}$]$^{0}$,"The spin dynamics in [TbPc$_{2}$]$^{0}$ and [DyPc$_{2}$]$^{0}$ single
molecule magnets have been investigated by means of muon and nuclear
spin-lattice relaxation rate measurements. The correlation time for the spin
fluctuations was found to be close to 0.1 ms already at 50 K, about two orders
of magnitude larger than the one previously found in other lanthanide based
single molecule magnets. In [TbPc$_{2}$]$^{0}$ two different regimes for the
spin fluctuations have been evidenced: a high temperature activated one
involving spin fluctuations across a barrier $\Delta\simeq 880 K$ separating
the ground and first excited states and a low temperature regime involving
quantum fluctuations within the twofold degenerate ground-state. In
[DyPc$_{2}$]$^{0}$ a high temperature activated spin dynamics is also evidenced
which, however, cannot be explained in terms of a single spin-phonon coupling
constant.",0904.3619v1
2009-06-26,Nonlinear Spin-Charge Dynamics in a Driven Double Quantum Dot,"The coupled nonlinear coordinate and spin dynamics of an electron in a double
quantum dot with spin-orbit interaction is studied semiclassically. The system
is driven by an electric field with the frequency matching the orbital or the
Zeeman resonance in magnetic field. Calculated evolution of the spin state is
crucially sensitive to the irregularities in the spatial motion and the
geometry of the host nanostructure. The resulting spin-flip Rabi frequency has
an unusual dependence on the field amplitude, demonstrating approach to the
chaotic spin motion. In turn, the orbital dynamics depends strongly on the spin
evolution due to the spin-dependent term in the electron velocity.",0906.4854v1
2010-03-23,Protection of center-spin coherence by a dynamically polarized nuclear spin core,"Understanding fully the dynamics of coupled electron-nuclear spin systems,
which are important for the development of long-lived qubits based on
solid-state systems, remains a challenge. We show that in a singly charged
semiconductor quantum dot with inhomogeneous hyperfine coupling, the nuclear
spins relatively strongly coupled to the electron spin form a polarized core
during the dynamical polarization process. The polarized core provides a
protection effect against the electron spin relaxation, reducing the decay rate
by a factor of $N_1$, the number of the nuclear spins in the polarized core, at
a relatively small total polarization. This protection effect may occur in
quantum dots and solid-state spin systems defect centers, such as NV centers in
diamonds, and could be harnessed to fabricate in a relatively simple way
long-lived qubits and quantum memories.",1003.4321v1
2012-11-05,Spin Dynamics and Resonant Inelastic X-ray Scattering in Chromium with Commensurate Spin-Density Wave Order,"We theoretically investigate spin dynamics and $L_3$-edge resonant inelastic
X-ray scattering (RIXS) of Chromium with commensurate spin-density wave (SDW)
order, based on a multi-band Hubbard model composed of 3$d$ and 4$s$ orbitals.
Obtaining the ground state with the SDW mean-field approximation, we calculate
the dynamical transverse and longitudinal spin susceptibility by using
random-phase approximation. We find that a collective spin-wave excitation seen
in inelastic neutron scattering hardly damps up to $\sim$0.6 eV. Above the
energy, the excitation overlaps individual particle-hole excitations as
expected, leading to broad spectral weight. On the other hand, the collective
spin-wave excitation in RIXS spectra has a tendency to be masked by large
spectral weight coming from particle-hole excitations with various orbital
channels. This is in contrast with inelastic neutron scattering, where only
selected diagonal orbital channels contribute to the spectral weight. However,
it may be possible to detect the spin-wave excitation in RIXS experiments in
the future if resolution is high enough.",1211.1598v2
2013-07-03,General theory of feedback control of a nuclear spin ensemble in quantum dots,"We present a microscopic theory of the nonequilibrium nuclear spin dynamics
driven by the electron and/or hole under continuous wave pumping in a quantum
dot. We show the correlated dynamics of the nuclear spin ensemble and the
electron and/or hole under optical excitation as a quantum feedback loop and
investigate the dynamics of the many nuclear spins as a nonlinear collective
motion. This gives rise to three observable effects: (i) hysteresis, (ii)
locking (avoidance) of the pump absorption strength to (from) the natural
resonance, and (iii) suppression (amplification) of the fluctuation of weakly
polarized nuclear spins, leading to prolonged (shortened) electron spin
coherence time. A single nonlinear feedback function as a ""measurement"" of the
nuclear field operator in the quantum feedback loop is constructed which
determines the different outcomes of the three effects listed above depending
on the feedback being negative or positive. The general theory also helps to
put in perspective the wide range of existing theories on the problem of a
single electron spin in a nuclear spin bath.",1307.0897v1
2014-07-15,Generation of spin-polarized currents via cross-relaxation with dynamically pumped paramagnetic impurities,"Key to future spintronics and spin-based information processing technologies
is the generation, manipulation, and detection of spin polarization in a solid
state platform. Here, we theoretically explore an alternative route to spin
injection via the use of dynamically polarized nitrogen-vacancy (NV) centers in
diamond. We focus on the geometry where carriers and NV centers are confined to
proximate, parallel layers and use a 'trap-and-release' model to calculate the
spin cross-relaxation probabilities between the charge carriers and neighboring
NV centers. We identify near-unity regimes of carrier polarization depending on
the NV spin state, applied magnetic field, and carrier g-factor. In particular,
we find that unlike holes, electron spins are distinctively robust against
spin-lattice relaxation by other, unpolarized paramagnetic centers. Further,
the polarization process is only weakly dependent on the carrier hopping
dynamics, which makes this approach potentially applicable over a broad range
of temperatures.",1407.7438v1
2015-06-17,Interplay of Electron and Nuclear Spin Noise in GaAs,"We present spin noise (SN) measurements on an ensemble of donor-bound
electrons in ultrapure GaAs:Si covering temporal dynamics over six orders of
magnitude from milliseconds to nanoseconds. The SN spectra detected at the
donor-bound exciton transition show the multifaceted dynamical regime of the
ubiquitous mutual electron and nuclear spin interaction typical for III-V based
semiconductor systems. The experiment distinctly reveals the finite
Overhauser-shift of an electron spin precession at zero external magnetic field
and a second contribution around zero frequency stemming from the electron spin
components parallel to the nuclear spin fluctuations. Moreover, at very low
frequencies features related with time-dependent nuclear spin fluctuations are
clearly resolved making it possible to study the intricate nuclear spin
dynamics at zero and low magnetic fields. The findings are in agreement with
the developed model of electron and nuclear SN.",1506.05370v1
2015-09-20,Borghini's Mechanism for Dynamic Polarization in Polarized Targets,"This paper is a contribution to the memorial session for Michel Borghini at
the Spin 2014 conference in Bejing, honoring his pivotal role for the
development of polarized targets in high energy physics. Borghini proposed for
the first time the correct mechanism for dynamic polarization in polarized
targets using organic materials doped with free radicals. In these amorphous
materials the spin levels are broadened by spin-spin interactions and g-factor
anisotropy, which allows a high dynamic polarization of nuclei by cooling of
the spin-spin interaction reservoir. In this contribution I summarize the
experimental evidence for this mechanism. These pertinent experiments were done
at CERN in the years 1971 - 1974, when I was a graduate student under the
guidance of Michel Borghini. I finish by shortly describing how Borghini's spin
temperature theory is now applied in cancer therapy.",1509.06052v1
2015-11-14,Dynamics of spin-orbit coupled Bose-Einstein condensates in a random potential,"Disorder plays a crucial role in spin dynamics in solids and condensed matter
systems. We demonstrate that for a spin-orbit coupled Bose-Einstein condensate
in a random potential two mechanisms of spin evolution, that can be
characterized as ""precessional"" and ""anomalous"", are at work simultaneously.
The precessional mechanism, typical for solids, is due to the condensate
displacement. The unconventional ""anomalous"" mechanism is due to the
spin-dependent velocity producing the distribution of the condensate spin
polarization. The condensate expansion is accompanied by a random displacement
and fragmentation, where it becomes sparse, as clearly revealed in the spin
dynamics. Thus, different stages of the evolution can be characterized by
looking at the condensate spin.",1511.04588v1
2016-01-07,Dynamic Feedback in Ferromagnet/Spin Hall Metal Heterostructures,"In ferromagnet/normal metal heterostructures, spin pumping and spin-transfer
torques are two reciprocal processes that occur concomitantly. Their interplay
introduces a dynamic feedback effect interconnecting energy dissipation
channels of both magnetization and current. By solving the spin diffusion
process in the presence of the spin Hall effect in the normal metal, we show
that the dynamic feedback gives rise to: (i) a nonlinear magnetic damping that
is crucial to sustain uniform steady-state oscillations of a spin Hall
oscillator at large angles. (ii) a frequency dependent spin Hall
magnetoimpedance that reduces to the spin Hall magnetoresistance in the dc
limit.",1601.01618v3
2016-01-14,P-shell carriers assisted dynamic nuclear spin polarization in single quantum dots at zero external magnetic field,"Repeated injection of spin polarized carriers in a quantum dot leads to the
polarization of nuclear spins, a process known as dynamic nuclear spin
polarization (DNP). Here, we report the first observation of p-shell carrier
assisted DNP in single QDs at zero external magnetic field. The nuclear field -
measured by using the Overhauser shift of the singly charged exciton state of
the QDs - continues to increase, even after the carrier population in the
s-shell saturates. This is also accompanied by an abrupt increase in nuclear
spin buildup time as p-shell emission overtakes that of the s-shell. We
attribute the observation to p-shell electrons strongly altering the nuclear
spin dynamics in the QD, supported by numerical simulation results based on a
rate equation model of coupling between electron and nuclear spin system. DNP
with p-shell carriers could open up avenues for further control to increase the
degree of nuclear spin polarization in QDs.",1601.03480v2
2016-02-11,Probing ultrafast spin dynamics in the antiferromagnetic multiferroic HoMnO$_3$ through a magnon resonance,"We demonstrate a new approach for directly measuring the ultrafast energy
transfer between elec- trons and magnons, enabling us to track spin dynamics in
an antiferromagnet (AFM). In multiferroic HoMnO3, optical photoexcitation
creates hot electrons, after which changes in the spin order are probed with a
THz pulse tuned to a magnon resonance. This reveals a photoinduced
transparency, which builds up over several picoseconds as the spins heat up due
to energy transfer from hot elec- trons via phonons. This spin-lattice
thermalization time is ?10 times faster than that of typical ferromagnetic (FM)
manganites. We qualitatively explain the fundamental differences in
spin-lattice thermalization between FM and AFM systems and apply a Boltzmann
equation model for treating AFMs. Our work gives new insight into spin-lattice
thermalization in AFMs and demonstrates a new approach for directly monitoring
the ultrafast dynamics of spin order in these systems.",1602.03872v2
2016-06-17,Spin dynamics of an individual Cr atom in a semiconductor quantum dot under optical excitation,"We studied the spin dynamics of a Cr atom incorporated in a II-VI
semiconductor quantum dot using photon correlation techniques. We used recently
developed singly Cr-doped CdTe/ZnTe quantum dots (A. Lafuente-Sampietro {\it et
al.}, [1]) to access the spin of an individual magnetic atom. Auto-correlation
of the photons emitted by the quantum dot under continuous wave optical
excitation reveals fluctuations of the localized spin with a timescale in the
10 ns range. Cross-correlation gives quantitative transfer time between Cr spin
states. A calculation of the time dependence of the spin levels population in
Cr-doped quantum dots shows that the observed spin dynamics is controlled by
the exciton-Cr interaction. These measurements also provide a lower bound in
the 20 ns range for the intrinsic Cr spin relaxation time.",1606.05476v1
2017-03-10,Spin-orbit dynamics of single acceptor atoms in silicon,"Two-level quantum systems with strong spin-orbit coupling allow for
all-electrical qubit control and long-distance qubit coupling via microwave and
phonon cavities, making them of particular interest for scalable quantum
information technologies. In silicon, a strong spin-orbit coupling exists
within the spin-3/2 system of acceptor atoms and their energy levels and
properties are expected to be highly tunable. Here we show the influence of
local symmetry tuning on the acceptor spin-dynamics, measured in the
single-atom regime. Spin-selective tunneling between two coupled boron atoms in
a commercial CMOS transistor is utilised for spin-readout, which allows for the
probing of the two-hole spin relaxation mechanisms. A relaxation-hotspot is
measured and explained by the mixing of acceptor heavy and light hole states.
Furthermore, excited state spectroscopy indicates a magnetic field controlled
rotation of the quantization axes of the atoms. These observations demonstrate
the tunability of the spin-orbit states and dynamics of this spin-3/2 system.",1703.03538v1
2017-03-27,Micromagnetic simulations of spin-torque driven magnetisation dynamics with spatially resolved spin transport and magnetisation texture,"We present a simple and fast method to simulate spin-torque driven
magnetisation dynamics in nano-pillar spin-valve structures. The approach is
based on the coupling between a spin transport code based on random matrix
theory and a micromagnetics finite-elements software. In this way the spatial
dependence of both spin transport and magnetisation dynamics is properly taken
into account. Our results are compared with experiments. The excitation of the
spin-wave modes, in- cluding the threshold current for steady state
magnetisation precession and the nonlinear frequency shift of the modes are
reproduced correctly. The giant magneto resistance effect and the magnetisa-
tion switching also agree with experiment. The similarities with recently
described spin-caloritronics devices are also discussed.",1703.08959v2
2017-03-28,Resonant photoluminescence and dynamics of a hybrid Mn-hole spin in a positively charged magnetic quantum dot,"We analyze, through resonant photoluminescence, the spin dynamics of an
individual magnetic atom (Mn) coupled to a hole in a semiconductor quantum dot.
The hybrid Mn-hole spin and the positively charged exciton in a CdTe/ZnTe
quantum dot forms an ensemble of $\Lambda$ systems which can be addressed
optically. Auto-correlation of the resonant photoluminescence and resonant
optical pumping experiments are used to study the spin relaxation channels in
this multilevel spin system. We identified for the hybrid Mn-hole spin an
efficient relaxation channel driven by the interplay of the Mn-hole exchange
interaction and the coupling to acoustic phonons. We also show that the optical
$\Lambda$ systems are connected through inefficient spin-flips than can be
enhanced under weak transverse magnetic field. The dynamics of the resonant
photoluminescence in a p-doped magnetic quantum dot is well described by a
complete rate equation model. Our results suggest that long lived hybrid
Mn-hole spin could be obtained in quantum dot systems with large
heavy-hole/light-hole splitting.",1703.09441v2
2018-02-18,Dynamic spin injection into a quantum well coupled to a spin-split bound state,"We present a theoretical analysis of dynamic spin injection due to
spin-dependent tunneling between a quantum well (QW) and a bound state split in
spin projection due to an exchange interaction or external magnetic field. We
focus on the impact of Coulomb correlations at the bound state on spin
polarization and sheet density kinetics of the charge carriers in the QW. The
theoretical approach is based on kinetic equations for the electron occupation
numbers taking into account high order correlation functions for the bound
state electrons. It is shown that the on-site Coulomb repulsion leads to an
enhanced dynamic spin polarization of the electrons in the QW and a delay in
the carriers tunneling into the bound state. The interplay of these two effects
leads to non-trivial dependence of the spin polarization degree, which can be
probed experimentally using time-resolved photoluminescence experiments. It is
demonstrated that the influence of the Coulomb interactions can be controlled
by adjusting the relaxation rates. These findings open a new way of studying
the Hubbard-like electron interactions experimentally.",1802.06352v1
2018-11-05,Nonadiabatic dynamics and geometric phase of an ultrafast rotating electron spin,"The spin in a rotating frame has attracted a lot of attentions recently, as
it deeply relates to both fundamental physics such as pseudo-magnetic field and
geometric phase, and applications such as gyroscopic sensors. However, previous
studies only focused on adiabatic limit, where the rotating frequency is much
smaller than the spin frequency. Here we propose to use a levitated
nano-diamond with a built-in nitrogen-vacancy (NV) center to study the dynamics
and the geometric phase of a rotating electron spin without adiabatic
approximation. We find that the transition between the spin levels appears when
the rotating frequency is comparable to the spin frequency at zero magnetic
field. Then we use Floquet theory to numerically solve the spin energy
spectrum, study the spin dynamics and calculate the geometric phase under a
finite magnetic field, where the rotating frequency to fulfill the resonant
transition condition could be greatly reduced.",1811.01641v1
2019-05-20,Spin dynamics of hot excitons in diluted magnetic semiconductors with spin-orbit interaction,"We explore the impact of a Rashba-type spin-orbit interaction in the
conduction band on the spin dynamics of hot excitons in diluted magnetic
semiconductor quantum wells. In materials with strong spin-orbit coupling, we
identify parameter regimes where spin-orbit effects greatly accelerate the spin
decay and even change the dynamics qualitatively in the form of damped
oscillations. Furthermore, we show that the application of a small external
magnetic field can be used to either mitigate the influence of spin-orbit
coupling or entirely remove its effects for fields above a material-dependent
threshold.",1905.07947v3
2012-01-24,Hyperfine induced electron spin and entanglement dynamics in double quantum dots: The case of separate baths,"We consider a system of two strongly coupled electron spins in zero magnetic
field, each of which is interacting with an individual bath of nuclear spins
via the hyperfine interaction. Applying the long spin approximation (LSA)
introduced in Europhys. Lett. 95, 47009 (here each bath is replaced by a single
long spin), we numerically study the electron spin and entanglement dynamics.
We demonstrate that the decoherence time is scaling with the bath size
according to a power law. As expected, the decaying part of the dynamics
decreases with increasing bath polarization. However, surprisingly it turns out
that, under certain circumstances, combining quantum dots of different geometry
to the double dot setup has a very similar effect on the magnitude of the spin
decay. Finally, we show that even for a comparatively weak exchange coupling
the electron spins can be fully entangled.",1201.5036v2
2012-01-31,"Intrinsic spin fluctuations reveal the dynamical response function of holes coupled to nuclear spin baths in (In,Ga)As quantum dots","The problem of how single ""central"" spins interact with a nuclear spin bath
is essential for understanding decoherence and relaxation in many quantum
systems, yet is highly nontrivial owing to the many-body couplings involved.
Different models yield widely varying timescales and dynamical responses
(exponential, power-law, Gaussian, etc). Here we detect the small random
fluctuations of central spins in thermal equilibrium (holes in singly-charged
(In,Ga)As quantum dots) to reveal the timescales and functional form of
bath-induced spin relaxation. This spin noise indicates long (400 ns) spin
correlation times at zero magnetic field, that increase to $\sim$5 $\mu$s as
hole-nuclear coupling is suppressed with small (100 G) applied fields.
Concomitantly, the noise lineshape evolves from Lorentzian to power-law,
indicating a crossover from exponential to inverse-log dynamics.",1201.6619v1
2017-06-04,Slow Spin Dynamics and Self-Sustained Clusters in Sparsely Connected Systems,"To identify emerging microscopic structures in low temperature spin glasses,
we study self-sustained clusters (SSC) in spin models defined on sparse random
graphs. A message-passing algorithm is developed to determine the probability
of individual spins to belong to SSC. Results for specific instances, which
compare the predicted SSC associations with the dynamical properties of spins
obtained from numerical simulations, show that SSC association identifies
individual slow-evolving spins. This insight gives rise to a powerful approach
for predicting individual spin dynamics from a single snapshot of an
equilibrium spin configuration, namely from limited static information, which
can be used to devise generic prediction tools applicable to a wide range of
areas.",1706.01047v1
2018-10-01,Determination of spin Hall angle in heavy metal/CoFeB-based heterostructures with interfacial spin-orbit fields,"Magnetization dynamics in W/CoFeB, CoFeB/Pt and W/CoFeB/Pt multilayers was
investigated using spin-orbit-torque ferromagnetic resonance (SOT-FMR)
technique. An analytical model based on magnetization dynamics due to SOT was
used to fit heavy metal (HM) thickness dependence of symmetric and
antisymmetric components of the SOT-FMR signal. The analysis resulted in a
determination of the properties of HM layers, such as spin Hall angle and spin
diffusion length. The spin Hall angle of -0.36 and 0.09 has been found in the
W/CoFeB and CoFeB/Pt bilayers, respectively, which add up in the case of
W/CoFeB/Pt trilayer. More importantly, we have determined effective interfacial
spin-orbit fields at both W/CoFeB and CoFeB/Pt interfaces, which are shown to
cancel Oersted field for particular thicknesses of the heavy metal layers,
leading to pure spin-current-induced dynamics and indicating the possibility
for a more efficient magnetization switching.",1810.00641v1
2019-02-08,Spin dynamics of a millisecond pulsar orbiting closely around a massive black hole,"We investigate the spin dynamics of a millisecond pulsar (MSP) in a tightly
bounded orbit around a massive black hole. These binaries are progenitors of
the extreme-mass-ratio-inspirals (EMRIs) and intermediate-mass-ratio-inspirals
(IMRIs) gravitational wave events. The Mathisson-Papapetrou-Dixon (MPD)
formulation is used to determine the orbital motion and spin modulation and
evolution. We show that the MSP will not be confined in a planar Keplerian
orbit and its spin will exhibit precession and nutation induced by spin-orbit
coupling and spin-curvature interaction. These spin and orbital behaviours will
manifest observationally in the temporal variations in the MSP's pulsed
emission and, with certain geometries, in the self-occultation of the pulsar's
emitting poles. Radio pulsar timing observations will be able to detect such
signatures. These extreme-mass-ratio binaries (EMRBs) and
intermediate-mass-ratio binaries (IMRBs) are also strong gravitational wave
sources. Combining radio pulsar timing and gravitational wave observations will
allow us to determine the dynamics of these systems in high precision and hence
the subtle behaviours of spinning masses in strong gravity.",1902.03146v1
2019-04-02,Scale-invariant spin dynamics and the quantum limits of field sensing,"We describe quantum limits to field sensing that relate noise, geometry and
measurement duration to fundamental constants, with no reference to particle
number. We cast the Tesche and Clarke (TC) bound on dc-SQUID sensitivity as
such a limit, and find analogous limits for volumetric spin-precession
magnetometers. We describe how randomly-arrayed spins, coupled to an external
magnetic field of interest and to each other by the magnetic dipole-dipole
interaction, execute a spin dynamics that depolarizes the spin ensemble even in
the absence of coupling to an external reservoir. We show the resulting spin
dynamics are scale invariant, with a depolarization rate proportional to spin
number density and thus a number-independent quantum limit on the energy
resolution per bandwidth $E_R$. Numerically, we find $E_R \ge \alpha \hbar$,
$\alpha \sim 1$, in agreement with the TC limit, for paradigmatic spin-based
measurements of static and oscillating magnetic fields.",1904.01528v2
2020-08-06,Near Total Electronic Spin Separation as Caused by Nuclear Dynamics: Perturbing a Real-Valued Conical Intersection with Complex-Valued Spin-Orbit Coupling,"We investigate the nuclear dynamics near a real-valued conical intersection
that is perturbed by a complex-valued spin-orbit coupling. For a model
Hamiltonian with two outgoing channels, we find that even a small spin-orbit
coupling can dramatically affect the pathway selection on account of Berry
force, leading to extremely large spin selectivity (sometime as large as 100%).
Thus, this Letter opens the door for organic chemists to start designing
spintronic devices that use nuclear motion and conical intersections (combined
with standard spin-orbit coupling) in order to achieve spin selection. Vice
versa, for physical chemists, this Letter also emphasizes that future
semiclassical simulations of intersystem crossing (which have heretofore
ignored Berry force) should be corrected to account for the spin polarization
that inevitably arises when dynamics pass near conical intersections.",2008.02443v1
2020-10-01,Modeling coupled spin and lattice dynamics,"A unified model of molecular and atomistic spin dynamics is presented
enabling simulations both in microcanonical and canonical ensembles without the
necessity of additional phenomenological spin damping. Transfer of energy and
angular momentum between the lattice and the spin systems is achieved by a
coupling term based upon the spin-orbit interaction. The characteristic spectra
of the spin and phonon systems are analyzed for different coupling strength and
temperatures. The spin spectral density shows magnon modes together with the
uncorrelated noise induced by the coupling to the lattice. The effective
damping parameter is investigated showing an increase with both coupling
strength and temperature. The model paves the way to understanding magnetic
relaxation processes beyond the phenomenological approach of the Gilbert
damping and the dynamics of the energy transfer between lattice and spins.",2010.00642v1
2021-02-20,Observation of Coherent Spin Waves in a Three-Dimensional Artificial Spin Ice Structure,"Harnessing high-frequency spin dynamics in three-dimensional (3D)
nanostructures may lead to paradigm-shifting, next generation devices including
high density spintronics and neuromorphic systems. Despite remarkable progress
in fabrication, the measurement and interpretation of spin dynamics in complex
3D structures remain exceptionally challenging. Here we take a first step and
measure coherent spin waves within a 3D artificial spin ice (ASI) structure
using Brillouin light scattering. The 3D-ASI was fabricated by using a
combination of two-photon lithography and thermal evaporation. Two spin-wave
modes were observed in the experiment whose frequencies showed a monotonic
variation with the applied field strength. Numerical simulations qualitatively
reproduced the observed modes. The simulated mode profiles revealed the
collective nature of the modes extending throughout the complex network of
nanowires while showing spatial quantization with varying mode quantization
numbers. The study shows a well-defined means to explore high-frequency spin
dynamics in complex 3D spintronic and magnonic structures.",2102.10270v1
2021-04-30,Realistic simulations of spin squeezing and cooperative coupling effects in large ensembles of interacting two-level systems,"We describe an efficient numerical method for simulating the dynamics of
interacting spin ensembles in the presence of dephasing and decay. The method
builds on the discrete truncated Wigner approximation for isolated systems,
which combines the mean-field dynamics of a spin ensemble with a Monte Carlo
sampling of discrete initial spin values to account for quantum correlations.
Here we show how this approach can be generalized for dissipative spin systems
by replacing the deterministic mean-field evolution by a stochastic process,
which describes the decay of coherences and populations while preserving the
length of each spin. We demonstrate the application of this technique for
simulating nonclassical spin-squeezing effects or the dynamics and steady
states of cavity QED models with hundred thousand interacting two-level systems
and without relying on any symmetries. This opens up the possibility to perform
accurate real-scale simulations of a diverse range of experiments in quantum
optics or with solid-state spin ensembles under realistic laboratory
conditions.",2105.00004v3
2021-06-08,One-directional polarization transport in electron/nuclear spin chains with loss and gain,"Understanding the joint dynamics of electron and nuclear spins is central to
core concepts in solid-state magnetic resonance - such as spin-lattice
relaxation and dynamic nuclear polarization - but a generalization that
capitalizes on competing polarization loss and gain channels is still lacking.
Here, we theoretically study the non-Hermitian dynamics of hybrid
electron/nuclear spin systems in the simultaneous presence of electron spin
pumping and spin-lattice relaxation. Focusing on periodic, one-dimensional
chains, we find that by adjusting the electron spin pumping to a critical
level, it is possible to steer the flow of nuclear polarization to create
site-dependent distributions where either end of the array polarizes in
opposite ways, irrespective of the initial state. By contrast, we show that
ring-like patterns - where the limit nuclear polarization is uniform - exhibit
a non-decaying, externally-driven nuclear spin current. Interestingly, cyclic
magnetic field modulation can render these processes largely robust to defects
in the chain, a response featuring some interesting similarities - and
differences - with recent findings in other non-Hermitian physical platforms.",2106.04326v1
2022-03-27,Making a case for femto- phono- magnetism with FePt,"In the field of femtomagnetism magnetic matter is controlled by ultrafast
laser pulses; here we show that coupling phonon excitations of the nuclei to
spin and charge leads to femto-phono-magnetism, a powerful route to control
magnetic order at ultrafast times. With state-of-the-art theoretical
simulations of coupled spin-, charge-, and lattice-dynamics we identify strong
non-adiabatic spin-phonon coupled modes that dominate early time spin dynamics.
Activating these phonon modes we show leads to an additional (up to 40\% extra)
loss of moment in FePt occurring within 40 femtoseconds of the pump laser
pulse. Underpinning this enhanced ultrafast loss of spin moment we identify a
physical mechanism in which minority spin-current drives an enhanced inter-site
minority charge transfer, in turn promoting increased on-site spin flips. Our
finding demonstrates that the nuclear system, often assumed to play only the
role of an energy sink aiding long time re-magnetisation of the spin system,
can play a profound role in controlling femtosecond spin-dynamics in materials.",2203.14234v1
2022-12-06,Coherent Spin Dynamics of Electrons in Two-Dimensional (PEA)$_2$PbI$_4$ Perovskites,"The versatile potential of lead halide perovskites and two-dimensional
materials is merged in the Ruddlesen-Popper perovskites having outstanding
optical properties. Here, the coherent spin dynamics in Ruddlesen-Popper
(PEA)$_2$PbI$_4$ perovskites are investigated by picosecond pump-probe Kerr
rotation in an external magnetic field. The Larmor spin precession of resident
electrons with a spin dephasing time of 190~ps is identified. The longitudinal
spin relaxation time in weak magnetic fields measured by the spin inertia
method is as long as 25~$\mu$s. A significant anisotropy of the electron
$g$-factor with the in-plane value of $+2.45$ and out-of-plane value of $+2.05$
is found. The exciton out-of-plane $g$-factor is measured to be of $+1.6$ by
magneto-reflectivity. This work contributes to the understanding of the
spin-dependent properties of two-dimensional perovskites and their spin
dynamics.",2212.02878v1
2023-03-13,Coherent THz Spin Dynamics in Antiferromagnets Beyond the Approximation of the Néel vector,"Controlled generation of coherent spin waves with highest possible
frequencies and the shortest possible wavelengths is a cornerstone of
spintronics and magnonics. Here, using the Heisenberg antiferromagnet RbMF$_3$,
we demonstrate that laser-induced THz spin dynamics corresponding to pairs of
mutually coherent counter propagating spin waves with the wavevectors up to the
edge of the Brillouin zone cannot be understood in terms of magnetization and
antiferromagnetic (N\'eel) vectors, conventionally used to describe spin waves.
Instead, we propose to model such spin dynamics using the spin correlation
function. We derive a quantum-mechanical equation of motion for the latter and
emphasize that, unlike the magnetization and antiferromagnetic vectors the spin
correlations in antiferromagnets do not exhibit inertia.",2303.06996v4
2023-05-07,Lectures on spintronics and magnonincs,"In this series of lectures, we discuss the basic theoretical concepts of
magnonics and spintronics. We first briefly recall the relevant topics from
quantum mechanics, electrodynamics of continuous media, and basic theory of
magnetism. We then discuss the classical theory of magnetic dynamics:
ferromagnetic and antiferromagnetic resonance, dynamic susceptibilities, and
spin waves. We open the main discussion with phenomena of spin and exchange
spin currents, spin torques, the spin Hall effect, and the spin Hall and Hanle
magnetoresistance. Special emphasis is given to the effects of spin transfer
torque and spin pumping, where we follow the celebrated derivation utilizing
Landauer quantum multi-channel scattering matrix approach. Finally, we outline
the most important features distinguishing antiferromagnetic dynamics from
ferromagnetic one, which make antiferromagnets particularly promising material
candidates for spintronics and magnonics.",2305.04385v1
2023-05-16,Mixed-State Quantum Spin Liquids and Dynamical Anyon Condensations in Kitaev Lindbladians,"Quantum spin liquids and anyons, used to be subjects of condensed matter
physics, now are realized in various platforms of qubits, offering
unprecedented opportunities to investigate fundamental physics of many-body
quantum entangled states. Qubits are inevitably exposed to environment effects
such as decoherence and dissipation, which are believed to be detrimental to
many-body entanglement. Here, we argue that unlike the common belief
decoherence and dissipation can give rise to novel topological phenomena in
quantum spin liquids. We study open quantum systems of the Kitaev spin liquid
and the toric code via the Lindblad master equation approach. By using exact
solutions and numerical approaches, we show the dynamical occurrence of anyon
condensation by decoherence and dissipation, which results in a topological
transition from the initial state spin liquid to the steady state spin liquid.
The mechanism of the anyon condensation transition by the Lindblad dynamics is
elucidated. We also provide an insight into the relationship between the Kitaev
spin liquid and the toric code in the picture of anyon condensation. Our work
suggests open quantum systems to be a new venue for topological phenomena of
quantum spin liquids and anyons.",2305.09197v3
2023-07-24,Super narrow peaks in excitation spectrum of alkali spin polarization: non-adiabatic case of spin dynamics,"We theoretically describe the phenomenon of non-adiabatic spin dynamics,
which occurs in a gas cell filled by alkali vapor in presence of a strong
alternating magnetic field and pump light. Steep increase of the spin
polarization occurs if frequency of the magnetic field is equal to the certain
value. Although, the observable effect relies on the periodic field that
consists of two perpendicular components defined by harmonics with the same
amplitudes and different frequencies. Considered spin effect cannot be
explained by a resonance, because the own Larmor frequency of spin precession
is absent without a constant component of magnetic field. Moreover, there are
some clearly visible peaks in the excitation spectrum of spin polarization, and
they are super narrow in comparison to relaxation rate. Detailed analysis
according to proposed quantum model results in the reasoning of the effect via
qualitative properties of non-adiabatic dynamics of atomic spin.",2307.12647v2
2023-07-26,Understanding the dynamics of randomly positioned dipolar spin ensembles,"Dipolar spin ensembles with random spin positions attract much attention
currently because they help to understand decoherence as it occurs in solid
state quantum bits in contact with spin baths. Also, these ensembles are
systems which may show many-body localization, at least in the sense of very
slow spin dynamics. We present measurements of the autocorrelations of spins on
diamond surfaces in a doubly-rotating frame which eliminates local disorder.
Strikingly, the time scales in the longitudinal and the transversal channel
differ by more than one order of magnitude which is a factor much greater than
one would have expected from simulations of spins on lattices. A previously
developed dynamic mean-field theory for spins (spinDMFT) fails to explain this
phenomenon. Thus, we improve it by extending it to clusters (CspinDMFT). This
theory does capture the striking mismatch up to two orders of magnitude for
random ensembles. Without positional disorder, however, the mismatch is only
moderate with a factor below 4. The pivotal role of positional disorder
suggests that the strong mismatch is linked to precursors of many-body
localization.",2307.14188v2
2023-09-05,Dynamics of anisotropic frustrated antiferromagnet Cs2CoBr4 in a spin-liquid regime,"Cs2CoBr4 is a triangular-lattice antiferromagnet which can be viewed as
weakly interacting spin chains due to spatially anisotropic frustrating
exchange couplings. The spin-orbit interaction in Co(2+) spin-3/2 ions leads to
a strong easy-plane single-ion anisotropy which allows to consider the
low-energy spin dynamics of this system using an anisotropic pseudospin-1/2
model. By means of the electron spin resonance (ESR) technique, we study the
spin dynamics of Cs2CoBr4 in magnetic field in a spin-liquid regime, i.e.,
above the N'eel temperature of 1.3 K but below the temperature of the crossover
to in-chain correlations of pseudospins (6 K). Our experiments reveal two
bright branches of excitations which strongly differ both from excitations in
the low-temperature ordered phases and from high-temperature paramagnetic
resonance of uncorrelated pseudospins and spins. These two branches are
interpreted as excitations with zero momentum of an anisotropic spin-1/2 chain.
Besides, we observe several weak modes of unknown origin which arise mostly as
satellites of one of the bright modes.",2309.02266v1
2007-01-17,Projected single-spin flip dynamics in the Ising Model,"We study transition matrices for projected dynamics in the
energy-magnetization space, magnetization space and energy space. Several
single spin flip dynamics are considered such as the Glauber and Metropolis
canonical ensemble dynamics and the Metropolis dynamics for three
multicanonical ensembles: the flat energy-magnetization histogram, the flat
energy histogram and the flat magnetization histogram. From the numerical
diagonalization of the matrices for the projected dynamics we obtain the
sub-dominant eigenvalue and the largest relaxation times for systems of varying
size. Although, the projected dynamics is an approximation to the full state
space dynamics comparison with some available results, obtained by other
authors, shows that projection in the magnetization space is a reasonably
accurate method to study the scaling of relaxation times with system size. The
transition matrices for arbitrary single-spin flip dynamics are obtained from a
single Monte-Carlo estimate of the infinite temperature transition-matrix, for
each system size, which makes the method an efficient tool to evaluate the
relative performance of any arbitrary local spin-flip dynamics. We also present
new results for appropriately defined average tunnelling times of magnetization
and compute their finite-size scaling exponents that we compare with results of
energy tunnelling exponents available for the flat energy histogram
multicanonical ensemble.",0701408v1
1997-02-06,Dynamical stripe correlations and the spin fluctuations in cuprate superconductors,"It is conjectured that the anomalous spin dynamics observed in the normal
state of cuprate superconductors might find its origin in a nearly ordered spin
system which is kept in motion by thermally meandering charged domain walls.
`Temperature sets the scale' finds a natural explanation, while a crossover to
a low temperature quantum domain wall fluid is implied.",9702060v1
1998-08-03,Formfactors in the half-filled Hubbard model,"We consider dynamical spin-spin correlation functions in the one dimensional
repulsive half-filled Hubbard model. We propose an exact expression for the two
spinon formfactor of spin operators. We use this to derive the two spinon
contribution to the dynamical structure factor.",9808018v1
2003-10-30,Time and length scales in spin glasses,"We discuss the slow, nonequilibrium, dynamics of spin glasses in their glassy
phase. We briefly review the present theoretical understanding of the
spectacular phenomena observed in experiments and describe new numerical
results obtained in the first large-scale simulation of the nonequilibrium
dynamics of the three dimensional Heisenberg spin glass.",0310721v1
2007-11-13,Exciton Spin Dynamics in Semiconductor Quantum Wells,"In this paper we will review Exciton Spin Dynamics in Semiconductor Quantum
Wells. The spin properties of excitons in nanostructures are determined by
their fine structure. We will mainly focus in this review on GaAs and InGaAs
quantum wells which are model systems.",0711.2030v1
2009-05-04,Self-organized quantum transitions in a spin-electron coupled system,"We investigate quantum dynamics of the excited electronic states in the
double-exchange model at half-filling by solving coupled equations for the
quantum evolution of electrons and Landau-Lifshits-Gilbert equation for
classical spins. The non-adiabatic quantum transitions driving the relaxation
are coordinated through the self-organized space-time structure of the
electron/spin dynamics leading to a resonant precession analogous to the ESR
process.",0905.0311v1
2013-04-22,Exact dynamics of one-qubit system in layered environment,"We investigate the exact evolution of the reduced dynamics of a one qubit
system as central spin coupled to a femionic layered environment with unlimited
number of layers. Also, we study the decoherence induced on central spin by
analysis solution is obtained in the limit $N\rightarrow\infty$ of an infinite
number of bath spins. Finally, the Nakajima-Zwanzig (NZ) and the
time-convolutionless (TCL) projection operator techniques to second order are
derived.",1304.5917v1
1998-07-06,The XY Spin-Glass with Slow Dynamic Couplings,"We investigate an XY spin-glass model in which both spins and couplings
evolve in time: the spins change rapidly according to Glauber-type rules,
whereas the couplings evolve slowly with a dynamics involving spin correlations
and Gaussian disorder. For large times the model can be solved using replica
theory. In contrast to the XY-model with static disordered couplings, solving
the present model requires two levels of replicas, one for the spins and one
for the couplings. Relevant order parameters are defined and a phase diagram is
obtained upon making the replica-symmetric Ansatz. The system exhibits two
different spin-glass phases, with distinct de Almeida-Thouless lines, marking
continuous replica-symmetry breaking: one describing freezing of the spins
only, and one describing freezing of both spins and couplings.",9807082v1
2003-05-05,Spin Anisotropy and Slow Dynamics in Spin Glasses,"We report on an extensive study of the influence of spin anisotropy on spin
glass aging dynamics. New temperature cycle experiments allow us to compare
quantitatively the memory effect in four Heisenberg spin glasses with various
degrees of random anisotropy and one Ising spin glass. The sharpness of the
memory effect appears to decrease continuously with the spin anisotropy.
Besides, the spin glass coherence length is determined by magnetic field change
experiments for the first time in the Ising sample. For three representative
samples, from Heisenberg to Ising spin glasses, we can consistently account for
both sets of experiments (temperature cycle and magnetic field change) using a
single expression for the growth of the coherence length with time.",0305088v2
2003-09-04,Monte Carlo Modeling of Spin FETs Controlled by Spin-Orbit Interaction,"A method for Monte Carlo simulation of 2D spin-polarized electron transport
in III-V semiconductor heterojunction FETs is presented. In the simulation, the
dynamics of the electrons in coordinate and momentum space is treated
semiclassically. The density matrix description of the spin is incorporated in
the Monte Carlo method to account for the spin polarization dynamics. The
spin-orbit interaction in the spin FET leads to both coherent evolution and
dephasing of the electron spin polarization. Spin-independent scattering
mechanisms, including optical phonons, acoustic phonons and ionized impurities,
are implemented in the simulation. The electric field is determined
self-consistently from the charge distribution resulting from the electron
motion. Description of the Monte Carlo scheme is given and simulation results
are reported for temperatures in the range 77-300 K.",0309118v1
2004-07-16,Modulation of spin dynamics in a channel of a non-ballistic spin field effect transistor,"We have investigated the effect of the gate voltage on spin relaxation in an
Al0.3Ga0.7As/GaAs/Al0.3Ga0.7As heterostructure. The study is motivated by a
recent proposal for a non-ballistic spin field effect transistor that utilizes
the interplay between the Rashba and the Dresselhaus spin-orbit interaction in
the device channel. The model, which utilizes real material parameters, in
order to calculate spin dynamics as a function of the gate voltage has been
developed. From the obtained results we define the efficiency of the spin
polarization and spin density modulation. The estimated modulation of the spin
polarization at room temperature is of the order of 15-20%. The results show
that the effect is not sufficient for device applications. However, it can be
observed experimentally by optical pulse-probe techniques.",0407416v1
2004-11-01,Multiple quantum dynamics in a system of dipole-coupling spins in solid,"A perturbation method deals with dipolar coupling spins in solids is
presented. As examples of the application the method, the multile-quantum
coherence dynamics in clusters of a linear chain of four nuclear spins and a
ring of six spins coupled by dipole-dipole interaction are considered. The
calculated 0Q- and 2Q intensities in a linear chain of four nuclear spins and
6Q intensity in a ring of six spins vs the duration of the preparation period
agree well with the exact solutions (for linear chain of four nuclear spins)
and simulation data (for linear chain of four nuclear spins and a ring of six
spin).",0411016v4
2005-01-24,Multi-spin dynamics of the solid-state NMR Free Induction Decay,"We present a new experimental investigation of the NMR free induction decay
(FID) in a lattice of spin-1/2 nuclei in a strong Zeeman field. Following a
pi/2 pulse, evolution under the secular dipolar Hamiltonian preserves coherence
number in the Zeeman eigenbasis, but changes the number of correlated spins in
the state. The observed signal is seen to decay as single-spin, single-quantum
coherences evolve into multiple-spin coherences under the action of the dipolar
Hamiltonian. In order to probe the multiple-spin dynamics during the FID, we
measured the growth of coherence orders in a basis other than the usual Zeeman
eigenbasis. This measurement provides the first direct experimental observation
of the growth of coherent multiple-spin correlations during the FID.
Experiments were performed with a cubic lattice of spins (19F in calcium
fluoride) and a linear spin chain (19F in fluorapatite). It is seen that the
geometrical arrangement of the spins plays a significant role in the
development of higher order correlations. The results are discussed in light of
existing theoretical models.",0501578v1
2007-01-25,Polynomially scaling spin dynamics simulation algorithm based on adaptive state space restriction,"The conventional spin dynamics simulations are performed in direct products
of state spaces of individual spins. In a general system of n spins, the total
number of elements in the state basis is >4^n. A system propagation step
requires an action by an operator on the state vector and thus requires >4^2n
multiplications. It is obvious that with current computers there is no way
beyond about ten spins, and the calculation complexity scales exponentially
with the spin system size.
  We demonstrate that a polynomially scaling algorithm can be obtained if the
state space is reduced by neglecting unimportant or unpopulated spin states.
The class of such states is surprisingly wide. In particular, there are
indications that very high multi-spin orders can be dropped completely, as can
all the orders linking the spins that are remote on the interaction graph.
  The computational cost of the propagation step for a ktuples-restricted
densely connected n-spin system with k<<n is O(n^2k). In cases of favourable
interaction topologies (narrow graphs, e.g. in protein NMR) the asymptotic
scaling is linear.",0701294v1
2005-11-08,Maps for Lorentz transformations of spin,"Lorentz transformations of spin density matrices for a particle with positive
mass and spin 1/2 are described by maps of the kind used in open quantum
dynamics. They show how the Lorentz transformations of the spin depend on the
momentum. Since the spin and momentum generally are entangled, the maps
generally are not completely positive and act in limited domains. States with
two momentum values are considered, so the maps are for the spin qubit
entangled with the qubit made from the two momentum values, and results from
the open quantum dynamics of two coupled qubits can be applied. Inverse maps
are used to show that every Lorentz transformation completely removes the spin
polarization, and so completely removes the information, from a number of spin
density matrices. The size of the spin polarization that is removed is
calculated for particular cases.",0511067v1
2007-07-22,Quasi-equilibrium optical nonlinearities in spin-polarized GaAs,"Semiconductor Bloch equations, which microscopically describe the dynamics of
a Coulomb interacting, spin-unpolarized electron-hole plasma, can be solved in
two limits: the coherent and the quasi-equilibrium regime. These equations have
been recently extended to include the spin degree of freedom, and used to
explain spin dynamics in the coherent regime. In the quasi-equilibrium limit,
one solves the Bethe-Salpeter equation in a two-band model to describe how
optical absorption is affected by Coulomb interactions within a
spin-unpolarized plasma of arbitrary density. In this work, we modified the
solution of the Bethe-Salpeter equation to include spin-polarization and light
holes in a three-band model, which allowed us to account for spin-polarized
versions of many-body effects in absorption. The calculated absorption
reproduced the spin-dependent, density-dependent and spectral trends observed
in bulk GaAs at room temperature, in a recent pump-probe experiment with
circularly polarized light. Hence our results may be useful in the microscopic
modelling of density-dependent optical nonlinearities in spin-polarized
semiconductors.",0707.3262v1
2007-11-04,Electrical Control of Dynamic Spin Splitting Induced by Exchange Interaction as Revealed by Time Resolved Kerr Rotation in a Degenerate Spin-Polarized Electron Gas,"The manipulation of spin degree of freedom have been demonstrated in spin
polarized electron plasma in a heterostructure by using exchange-interaction
induced dynamic spin splitting rather than the Rashba and Dresselhaus types, as
revealed by time resolved Kerr rotation. The measured spin splitting increases
from 0.256meV to 0.559meV as the bias varies from -0.3V to -0.6V. Both the sign
switch of Kerr signal and the phase reversal of Larmor precessions have been
observed with biases, which all fit into the framework of
exchange-interaction-induced spin splitting. The electrical control of it may
provide a new effective scheme for manipulating spin-selected transport in spin
FET-like devices.",0711.0519v2
2008-06-02,"Photo-induced, non-equilibrium spin and charge polarization in quantum rings","We investigate the spin-dependent dynamical response of a quantum ring with a
spin-orbit interaction upon the application of linearly polarized, picosecond,
asymmetric electromagnetic pulses. The oscillations of the generated dipole
moment are sensitive to the parity of the occupation number in the ring and to
the strength of the spin-orbit coupling. It is shown how the associated
emission spectrum can be controlled via the pulse strength or a gate voltage.
In addition, we inspect how a static magnetic flux can modify the
non-equilibrium dynamics. In presence of the spin-orbit interaction and for a
paramagnetic ring, the applied pulse results in a spin-split, non-equilibrium
local charge density. The resulting temporal spin polarization is directed
perpendicular to the light-pulse polarization axis and oscillates periodically
with the frequency of the spin-split charge density. The spin-averaged
non-equilibrium charge density possesses a left-right symmetry with respect to
the pulse polarization axis. The calculations presented here are applicable to
nano-meter rings fabricated in heterojuctions of III-V and II-VI semiconductors
containing several hundreds electrons.",0806.0317v1
2008-06-30,Ultrafast manipulation of electron spins in a double quantum dot device: A real-time view,"We consider a double quantum dot system with two embedded and non-aligned
spin impurities to manipulate the magnitude and polarization of the electron
spin density. The device is attached to semi-infinite one-dimensional leads
which are treated exactly. We provide a real-time description of the electron
spin dynamics when a sequence of ultrafast voltage pulses acts on the device.
The numerical simulations are carried out using a spin generalized and modified
version of a recently proposed algorithm for the time propagation of open
systems [Phys. Rev. B {\bf 72}, 035308 (2005)]. Time-dependent spin
accumulations and spin currents are calculated during the entire operating
regime which includes spin injection and read-out processes. The full knowledge
of the electron dynamics allows us to engineer the transient responses and
improve the device performance. An approximate rate equation for the electron
spin is also derived and used to discuss the numerical results.",0806.4925v1
2010-01-18,Dynamical nuclear spin polarization induced by electronic current through double quantum dots,"We analyze electron spin relaxation in electronic transport through
coherently coupled double quantum dots in the spin blockade regime. In
particular, we focus on hyperfine interaction as the spin relaxation mechanism.
We pay special attention to the effect of the dynamical nuclear spin
polarization induced by the electronic current on the nuclear environment. We
discuss the behaviour of the electronic current and the induced nuclear spin
polarization versus an external magnetic field for different hyperfine coupling
intensities and interdot tunnelling strengths. We take into account, for each
magnetic field, all hyperfine mediated spin relaxation processes coming from
the different opposite spin levels approaches. We find that the current as a
function of the external magnetic field shows a peak or a dip, and that the
transition from a current dip to a current peak behaviour is obtained by
decreasing the hyperfine coupling or by increasing the interdot tunnelling
strength. We give a physical picture in terms of the interplay between the
electrons tunnelling out of the double quantum dot and the spin flip processes
due to the nuclear environment.",1001.3104v2
2010-08-21,Dynamical Corrections to Spin Wave Excitations in Quantum Wells due to Coulomb Interactions and Magnetic Ions,"We have measured dispersions of spin-flip waves and spin-flip single-particle
excitations of a spin polarized two-dimensional electron gas in a CdMnTe
quantum well using resonant Raman scattering. We find the energy of the
spin-flip wave to be below the spin-flip single particle excitation continuum,
a contradiction to the theory of spin waves in diluted magnetic semiconductors
put forth in [Phys. Rev. B 70, 045205 (2004)]. We show that the inclusion of
terms accounting for the Coulomb interaction between carriers in the spin wave
propagator leads to an agreement with our experimental results. The dominant
Coulomb contribution leads to an overall red shift of the mixed electron-Mn
spin modes while the dynamical coupling between Mn ions results in a small blue
shift. We provide a simulated model system which shows the reverse situation
but at an extremely large magnetic field.",1008.3663v1
2012-03-21,Persistent narrowing of nuclear-spin fluctuations in InAs quantum dots using laser excitation,"We demonstrate the suppression of nuclear spin fluctuations in an InAs
quantum dot and measure the timescales of the spin narrowing effect. By
initializing for tens of milliseconds with two continuous wave diode lasers,
fluctuations of the nuclear spins are suppressed via the hole assisted dynamic
nuclear polarization feedback mechanism. The fluctuation narrowed state
persists in the dark (absent light illumination) for well over one second even
in the presence of a varying electron charge and spin polarization. Enhancement
of the electron spin coherence time (T2*) is directly measured using coherent
dark state spectroscopy. By separating the calming of the nuclear spins in time
from the spin qubit operations, this method is much simpler than the spin echo
coherence recovery or dynamic decoupling schemes.",1203.4742v1
2013-04-04,Dynamics of Antiferromagnets Driven by Spin Current,"When a spin-polarized current flows through a ferromagnetic (FM) metal,
angular momentum is transferred to the background magnetization via
spin-transfer torques. In antiferromagnetic (AFM) materials, however, the
corresponding problem is unsolved. We derive microscopically the dynamics of an
AFM system driven by spin current generated by an attached FM polarizer, and
find that the spin current exerts a driving force on the local staggered order
parameter. The mechanism does not rely on the conservation of spin angular
momentum, nor does it depend on the induced FM moments on top the AFM
background. Two examples are studied: (i) A domain wall is accelerated to a
terminal velocity by purely adiabatic effect where the Walker's break-down is
avoided; and (ii) Spin injection modifies the AFM resonance frequency, and spin
current injection triggers spin wave instability of local moments above a
threshold.",1304.1284v5
2014-01-18,Von Neumann spin measurements with Rashba fields,"We show that dynamics in spin-orbit coupling field simulates the von Neumann
measurement of a particle spin. We demonstrate how the measurement influences
the spin and coordinate evolution of a particle by comparing two examples of
such a procedure. First example is a simultaneous measurement of spin
components, $\sigma _{x}$ and $\sigma _{y}$, corresponding to non-commuting
operators, which cannot be accurately obtained together at a given time instant
due to the Heisenberg uncertainty ratio. By mapping spin dynamics onto a
spatial walk such a procedure determines measurement-time averages of $\sigma
_{x}$ and $\sigma _{y}$, which already can be precisely evaluated in a single
short-time measurement. The other, qualitatively different, example is the spin
of a one-dimensional particle in a magnetic field. Here the outcome depends on
the angle between the spin-orbit coupling and magnetic fields. These results
can be applied to studies of spin-orbit coupled cold atoms and electrons in
solids.",1401.4551v1
2014-04-23,Semiclassical spin-spin dynamics and feedback control in transport through a quantum dot,"We present a theory of magnetotransport through an electronic orbital, where
the electron spin interacts with a (sufficiently) large external spin via an
exchange interaction. Using a semiclassical approximation, we derive a set of
equations of motions for the electron density matrix and the mean value of the
external spin that turns out to be highly nonlinear. The dissipation via the
electronic leads is implemented in terms of a quantum master equation that is
combined with the nonlinear terms of the spin-spin interaction. With an
anisotropic exchange coupling a variety of dynamics is generated, such as
self-sustained oscillations with parametric resonances or even chaotic
behavior. Within our theory we can integrate a Maxwell-demon-like closed-loop
feedback scheme that is capable of transporting particles against an applied
bias voltage and that can be used to implement a spin filter to generate
spin-dependent oscillating currents of opposite directions.",1404.5831v3
2014-09-09,Electron-spin dynamics in elliptically polarized light waves,"We investigate the coupling of the spin angular momentum of light beams with
elliptical polarization to the spin degree of freedom of free electrons. It is
shown that this coupling, which is of similar origin as the well-known
spin-orbit coupling, can lead to spin precession. The spin-precession frequency
is proportional to the product of the laser-field's intensity and its spin
density. The electron-spin dynamics is analyzed by employing exact numerical
methods as well as time-dependent perturbation theory based on the fully
relativistic Dirac equation and on the nonrelativistic Pauli equation that is
amended by a relativistic correction that accounts for the light's spin
density.",1409.2647v2
2014-11-25,Ultrafast Probes of Nonequilibrium Hole Spin Relaxation in Ferromagnetic Semiconductor GaMnAs,"We directly measure the hole spin lifetime in ferromagnetic GaMnAs via time-
and polarization-resolved spectroscopy. Below the Curie temperature Tc, an
ultrafast photoexcitation with linearly-polarized light is shown to create a
non-equilibrium hole spin population via the dynamical polarization of holes
through p-d exchange scattering with ferromagnetically-ordered Mn spins, and we
characterize their relaxation dynamics. The observed relaxation consists of a
distinct three-step recovery : (i) femtosecond (fs) hole spin relaxation ~
$160-200 fs, (ii) picosecond (ps) hole energy relaxation ~ 1-2 ps, and (iii) a
coherent, damped Mn spin precession with a period of ~ 250 ps. The transient
amplitude of the hole spin component diminishes with increasing temperature,
directly following the ferromagnetic order, while the hole energy amplitude
shows negligible temperature change, consistent with our interpretation. Our
results thus establish the hole spin lifetimes in ferromagnetic semiconductors
and demonstrate a novel spectroscopy method for studying non-equilibrium hole
spins in the presence of correlation and magnetic order.",1411.6979v1
2015-01-16,Longitudinal spin diffusion in a nondegenerate trapped $^{87}$Rb gas,"Longitudinal spin diffusion of two pseudo-spin domains is studied in a
trapped $^{87}$Rb sample above quantum degeneracy, and the effect of coherence
in the domain wall on the dynamics of the system is investigated. Coherence in
a domain wall leads to transverse-spin-mediated longitudinal spin diffusion
that is slower than classical predictions, as well as altering the domains'
oscillation frequency. The system also shows an instability in the longitudinal
spin dynamics as longitudinal and transverse spin components couple, and a
conversion of longitudinal spin to transverse spin is observed, resulting in an
increase in the total amount of coherence in the system.",1501.03866v2
2015-03-26,Longitudinal and transversal spin dynamics of donor-bound electrons in fluorine-doped ZnSe: spin inertia versus Hanle effect,"The spin dynamics of the strongly localized, donor-bound electrons in
fluorine-doped ZnSe epilayers is studied by pump-probe Kerr rotation
techniques. A method exploiting the spin inertia is developed and used to
measure the longitudinal spin relaxation time, $T_1$, in a wide range of
magnetic fields, temperatures, and pump densities. The $T_1$ time of the
donor-bound electron spin of about 1.6 $\mu$s remains nearly constant for
external magnetic fields varied from zero up to 2.5 T (Faraday geometry) and in
a temperature range $1.8-45$ K. The inhomogeneous spin dephasing time,
$T_2^*=8-33$ ns, is measured using the resonant spin amplification and Hanle
effects under pulsed and steady-state pumping, respectively. These findings
impose severe restrictions on possible spin relaxation mechanisms.",1503.07684v1
2016-03-01,Geometric spin echo under zero field,"Spin echo is a fundamental tool for quantum registers and biomedical imaging.
It is believed that a strong magnetic field is needed for the spin echo to
provide long memory and high resolution since a degenerate spin cannot be
controlled or addressed under a zero magnetic field. While a degenerate spin is
never subject to dynamic control, it is still subject to geometric control.
Here we show the spin echo of a degenerate spin subsystem, which is
geometrically controlled via a mediating state split by the crystal field, in a
nitrogen vacancy center in diamond. The demonstration reveals that the
degenerate spin is protected by inherent symmetry breaking called zero-field
splitting. The geometric spin echo under zero field provides an ideal way to
maintain the coherence without any dynamics, thus opening the way to
pseudo-static quantum random access memory and non-invasive biosensors.",1603.00144v2
2016-09-26,Relativistic theory of spin relaxation mechanisms in the Landau-Lifshitz-Gilbert equation of spin dynamics,"Starting from the Dirac-Kohn-Sham equation we derive the relativistic
equation of motion of spin angular momentum in a magnetic solid under an
external electromagnetic field. This equation of motion can be written in the
form of the well-known Landau-Lifshitz-Gilbert equation for a harmonic external
magnetic field, and leads to a more general magnetization dynamics equation for
a general time-dependent magnetic field. In both cases with an electronic
spin-relaxation term which stems from the spin-orbit interaction. We thus
rigorously derive, from fundamental principles, a general expression for the
anisotropic damping tensor which is shown to contain an isotropic Gilbert
contribution as well as an anisotropic Ising-like and a chiral,
Dzyaloshinskii-Moriya-like contribution. The expression for the spin relaxation
tensor comprises furthermore both electronic interband and intraband
transitions. We also show that when the externally applied electromagnetic
field possesses spin angular momentum, this will lead to an optical spin torque
exerted on the spin moment.",1609.07901v1
2016-10-21,Spin transport and dynamics in all-oxide perovskite La$_{2/3}$Sr$_{1/3}$MnO$_3$/SrRuO$_3$ bilayers probed by ferromagnetic resonance,"Thin films of perovskite oxides offer the possibility of combining emerging
concepts of strongly correlated electron phenomena and spin current in magnetic
devices. However, spin transport and magnetization dynamics in these complex
oxide materials are not well understood. Here, we experimentally quantify spin
transport parameters and magnetization damping in epitaxial perovskite
ferromagnet/paramagnet bilayers of La$_{2/3}$Sr$_{1/3}$MnO$_3$/SrRuO$_3$
(LSMO/SRO) by broadband ferromagnetic resonance spectroscopy. From the SRO
thickness dependence of Gilbert damping, we estimate a short spin diffusion
length of $\lesssim$1 nm in SRO and an interfacial spin-mixing conductance
comparable to other ferromagnet/paramagnetic-metal bilayers. Moreover, we find
that anisotropic non-Gilbert damping due to two-magnon scattering also
increases with the addition of SRO. Our results demonstrate LSMO/SRO as a
spin-source/spin-sink system that may be a foundation for examining
spin-current transport in various perovskite heterostructures.",1610.06661v1
2016-10-28,Density matrix based time-dependent configuration interaction approach to ultrafast spin-flip dynamics,"Recent developments in attosecond spectroscopy yield access to the correlated
motion of electrons on their intrinsic time scales. Spin-flip dynamics is
usually considered in the context of valence electronic states, where
spin-orbit coupling is weak and processes related to the electron spin are
usually driven by nuclear motion. However, for core-excited states, where the
core hole has a nonzero angular momentum, spin-orbit coupling is strong enough
to drive spin-flips on a much shorter time scale. Using density matrix based
time-dependent restricted active space configuration interaction including
spin-orbit coupling, we address an unprecedentedly short spin-crossover for the
example of L-edge (2p$\rightarrow$3d) excited states of a prototypical Fe(II)
complex. This process occurs on a time scale, which is faster than that of
Auger decay ($\sim$4\,fs) treated here explicitly. Modest variations of carrier
frequency and pulse duration can lead to substantial changes in the spin-state
yield, suggesting its control by soft X-ray light.",1610.09264v2
2018-04-26,Negative-Temperature State Relaxation and Reservoir-Assisted Quantum Entanglement in Double Spin Domain Systems,"Spin collective phenomena including superradiance are even today being
intensively investigated with experimental tests performed based on
state-of-the-art quantum technologies. Such attempts are not only for the
simple experimental verification of predictions from the last century but also
as a motivation to explore new applications of spin collective phenomena and
the coherent control of the coupling between spin ensembles and reservoirs. In
this paper, we investigate the open quantum dynamics of two spin ensembles
(double spin domains) coupled to a common bosonic reservoir. We analyze in
detail the dynamics of our collective state and its structure by focusing on
both the symmetry and asymmetry of this coupled spin system. We find that when
the spin size of one of the double domains is larger than that of the other
domain, at the steady state this system exhibits two novel collective
behaviors: the negative-temperature state relaxation in the smaller spin domain
and the reservoir-assisted quantum entanglement between the two domains. These
results are the consequence of the asymmetry of this system and the decoherence
driven by the common reservoir.",1804.09926v1
2014-03-04,Two-level system in spin baths: Non-adiabatic dynamics and heat transport,"We study the non-adiabatic dynamics of a two-state subsystem in a bath of
independent spins using the non-interacting blip approximation, and derive an
exact analytic expression for the relevant memory kernel. We show that in the
thermodynamic limit, when the subsystem-bath coupling is diluted (uniformly)
over many (infinite) degrees of freedom, our expression reduces to known
results, corresponding to the harmonic bath with an effective,
temperature-dependent, spectral density function. We then proceed and study the
heat current characteristics in the out-of-equilibrium spin-spin-bath model,
with a two-state subsystem bridging two thermal spin-baths of different
temperatures. We compare the behavior of this model to the case of a spin
connecting boson baths, and demonstrate pronounced qualitative differences
between the two models. Specifically, we focus on the development of the
thermal diode effect, and show that the spin-spin-bath model cannot support it
at weak (subsystem-bath) coupling, while in the intermediate-strong coupling
regime its rectifying performance outplays the spin-boson model.",1403.0897v1
2014-03-17,Dynamic strain-mediated coupling of a single diamond spin to a mechanical resonator,"The development of hybrid quantum systems is central to the advancement of
emerging quantum technologies, including quantum information science and
quantum-assisted sensing. The recent demonstration of high quality
single-crystal diamond resonators has led to significant interest in a hybrid
system consisting of nitrogen-vacancy center spins that interact with the
resonant phonon modes of a macroscopic mechanical resonator through crystal
strain. However, the nitrogen-vacancy spin-strain interaction has not been well
characterized. Here, we demonstrate dynamic, strain-mediated coupling of the
mechanical motion of a diamond cantilever to the spin of an embedded
nitrogen-vacancy center. Via quantum control of the spin, we quantitatively
characterize the axial and transverse strain sensitivities of the
nitrogen-vacancy ground state spin. The nitrogen-vacancy center is an atomic
scale sensor and we demonstrate spin-based strain imaging with a strain
sensitivity of 3 10^(-6) strain Hz^(-1/2). Finally, we show how this
spin-resonator system could enable coherent spin-phonon interactions in the
quantum regime.",1403.4173v3
2016-11-04,Limits on dynamically generated spin-orbit coupling: Absence of $l=1$ Pomeranchuk instabilities in metals,"An ordered state in the spin sector that breaks parity without breaking
time-reversal symmetry, i.e., that can be considered as dynamically generated
spin-orbit coupling, was proposed to explain puzzling observations in a range
of different systems. Here we derive severe restrictions for such a state that
follow from a Ward identity related to spin conservation. It is shown that
$l=1$ spin-Pomeranchuk instabilities are not possible in non-relativistic
systems since the response of spin-current fluctuations is entirely incoherent
and non-singular. This rules out relativistic spin-orbit coupling as an
emergent low-energy phenomenon. We illustrate the exotic physical properties of
the remaining higher angular momentum analogues of spin-orbit coupling and
derive a geometric constraint for spin-orbit vectors in lattice systems.",1611.01442v2
2018-05-06,"Spin-polaronics, an emerging technology","The static and dynamic properties of spin-polarons in La-doped $CaMnO_3$ are
explored theoretically, by means of an effective low energy Hamiltonian. All
parameters from the Hamiltoniain are evaluated from first principles theory,
without adjustable parameters. %We compare different geometries, like
spin-polarons in bulk, surface and as single two-dimensional layers. The
Hamiltonian is used to investigate the temperature stability as well as the
response to an external applied electric field, for spin-polarons in bulk,
surface and as single two-dimensional layers. Technically this involves
atomistic spin-dynamics simulations in combination with kinetic Monte Carlo
simulations. Where a comparison can be made, our simulations exhibit an
excellent agreement with available experimental data and previous theory.
Remarkably, we find that excellent control of the mobility of spin-polarons in
this material can be achieved, and that the critical parameters deciding this
is the temperature and strength of the applied electrical field. We outline
different technological implications of spin-polarons, and point to
spin-polaronics as an emerging sub-field of nano-technology. In particular, we
demonstrate that it is feasible to write and erase information on atomic scale,
by use of spin-polarons in $CaMnO_3$.",1805.02284v1
2009-12-02,Spinning compact binary inspiral: Independent variables and dynamically preserved spin configurations,"We establish the set of independent variables suitable to monitor the
complicated evolution of the spinning compact binary during the inspiral. Our
approach is valid up to the second post-Newtonian order, including leading
order spin-orbit, spin-spin and mass quadrupol-mass monopole effects, for
generic (noncircular, nonspherical) orbits. Then we analyze the conservative
spin dynamics in terms of these variables. We prove that the only binary black
hole configuration allowing for spin precessions with equal angular velocities
about a common intantaneous axis roughly aligned to the normal of the
osculating orbit, is the equal mass and parallel (aligned or antialigned) spin
configuration. This analytic result puts limitations on what particular
configurations can be selected in numerical investigations of compact binary
evolutions, even in those including only the last orbits of the inspiral.",0912.0459v3
2009-12-22,Dynamics of Overhauser Field under nuclear spin diffusion in a quantum dot,"The coherence of electron spin can be significantly enhanced by locking the
Overhauser field from nuclear spins using the nuclear spin preparation. We
propose a theoretical model to calculate the long time dynamics of the
Overhauser field under intrinsic nuclear spin diffusion in a quantum dot. We
obtain a simplified diffusion equation that can be numerically solved and show
quantitatively how the Knight shift and the electron-mediated nuclear spin
flip-flop affect the nuclear spin diffusion. The results explain several recent
experimental observations, where the decay time of Overhauser field is measured
under different configurations, including variation of the external magnetic
field, the electron spin configuration in a double dot, and the initial nuclear
spin polarization rate.",0912.4322v1
2017-12-08,Electron charge and spin delocalization revealed in the optically probed longitudinal and transverse spin dynamics in $n$-GaAs,"The evolution of the electron spin dynamics as consequence of carrier
delocalization in $n$-type GaAs is investigated by the recently developed
extended pump-probe Kerr/Faraday rotation spectroscopy. We find that isolated
electrons localized on donors demonstrate a prominent difference between the
longitudinal and transverse spin relaxation rates in magnetic field, which is
almost absent in the metallic phase. The inhomogeneous transverse dephasing
time $T_2^*$ of the spin ensemble strongly increases upon electron
delocalization as a result of motional narrowing that can be induced by
increasing either the donor concentration or the temperature. An unexpected
relation between $T_2^*$ and the longitudinal spin relaxation time $T_1$ is
found, namely that their product is about constant, as explained by the
magnetic field effect on the spin diffusion. We observe a two-stage
longitudinal spin relaxation which suggests the establishment of spin
temperature in the system of exchange-coupled donor-bound electrons.",1712.02998v1
2017-12-18,Assessing the Energetics of Spinning Binary Black Hole Systems,"In this work we study the dynamics of spinning binary black hole systems in
the strong field regime. For this purpose we extract from numerical relativity
simulations the binding energy, specific orbital angular momentum, and
gauge-invariant orbital frequency. The goal of our work is threefold: First, we
extract the individual spin contributions to the binding energy, in particular
the spin-orbit, spin-spin, and cubic-in-spin terms. Second, we compare our
results with predictions from waveform models and find that while
post-Newtonian approximants are not capable of representing the dynamics during
the last few orbits before merger, there is good agreement between our data and
effective-one-body approximants as well as the numerical relativity surrogate
models. Finally, we present phenomenological representations for the binding
energy for non-spinning systems with mass ratios up to $q = 10$ and for the
spin-orbit interaction for mass ratios up to $q = 8$ obtaining accuracies of
$\lesssim 0.1\%$ and $\lesssim 6\%$, respectively.",1712.06533v1
2018-09-20,Entangling Distant Spin qubits via a Magnetic Domain Wall,"The scalability of quantum networks based on solid-state spin qubits is
hampered by the short range of natural spin-spin interactions. Here, we propose
a scheme to entangle distant spin qubits via the soft modes of an
antiferromagnetic domain wall (DW). As spin qubits, we focus on quantum
impurities (QI's) placed in the vicinity of an insulating antiferromagnetic
thin film. The low-energy modes harbored by the DW are embedded in the
antiferromagnetic bulk, whose intrinsic spin-wave dynamics have a gap that can
exceed the THz range. By setting the QI frequency and the temperature well
within the bulk gap, we focus on the dipolar interaction between the QI and two
soft modes localized at the DW. One is a string-like mode associated with
transverse displacements of the DW position, while the dynamics of the other,
corresponding to planar rotations of the Neel order parameter, constitute a
spin superfluid. By choosing the geometry in which the QI does not couple to
the string mode, we use an external magnetic field to control the gap of the
spin superfluid and the qubit-qubit coupling it engenders. We suggest that a
tunable micron-range coherent coupling between qubits can be established using
common antiferromagnetic materials.",1809.07785v1
2019-10-18,Focusing on the dynamics of the entanglement in spin junction,"We study the dynamics of entanglement in the one-dimensional spin-1/2 XY
model in the presence of a transverse magnetic field. A pair of spins are
considered as an open quantum system, while the rest of the chain plays the
role of the environment. Our study focuses on the pair of spins in the system,
the edge spins, and the environment. It is observed that the entanglement
between the pair of spins in the system decreases and it can transfer to the
rest of the spins. For a value of anisotropy leading to the Ising model, the
entanglement is completely back to the system by passing time. On the other
hand, the entanglement can only be seen under certain conditions between edge
spins of the system and the environment. The pair of spins on the edge will be
entangled very quickly and it will disappear after a very short time. A pair of
spins far from the system was chosen to examine the behavior of entanglement in
the environment. As expected, the transmission of entanglement from the system
to the environment takes notable time.",1910.08633v1
2020-01-21,Nonresonant amplification of coherent spin waves through voltage-induced interface magnetoelectric effect and spin-transfer torque,"We present new mechanism for manipulation of the spin-wave amplitude through
the use of the dynamic charge-mediated magnetoelectric effect in ultrathin
multilayers composed of dielectric thin-film capacitors separated by a
ferromagnetic bilayer. Propagating spin waves can be amplified and attenuated
with rising and decreasing slopes of the oscillating voltage, respectively,
locally applied to the sample. The way the spin accumulation is generated makes
the interaction of the spin-transfer torque with the magnetization dynamics
mode-selective and restricted to some range of spin-wave frequencies, which is
in contrary to known types of the spin-transfer torque effects. The interfacial
nature of spin-dependent screening allows to reduce the thickness of the fixed
magnetization layer to a few nanometers, thus the proposed effect significantly
contributes toward realization of the magnonic devices and also miniaturization
of the spintronic devices.",2001.07474v1
2020-02-13,Dynamical spin susceptibility of spin-valley half-metal,"A few years ago we predicted theoretically that in systems with nesting of
the Fermi surface the spin-valley half-metal has lower energy than the spin
density wave state. In this paper we suggest a possible way to distinguish
these phases experimentally. We calculate dynamical spin susceptibility tensor
for both states in the framework of the Kubo formalism. Discussed phases have
different numbers of the bands: four bands in the spin-valley half-metal and
only two bands in the spin density wave. Therefore, their susceptibilities, as
functions of frequency, have different number of peaks. Besides, the
spin-valley half-metal does not have rotational symmetry, thus, in general the
off-diagonal components of susceptibility tensor are non-zero. The spin density
wave obeys robust rotational symmetry and off-diagonal components of the
susceptibility tensor are zero. These characteristic features can be observed
in experiments with inelastic neutron scattering.",2002.05504v1
2020-12-07,"Nuclear spin dynamics, noise, squeezing and entanglement in box model","We obtain a compact analytical solution for the nonlinear equation for the
nuclear spin dynamics in the central spin box model in the limit of many
nuclear spins. The total nuclear spin component along the external magnetic
field is conserved and the two perpendicular components precess or oscillate
depending on the electron spin polarization, with the frequency, determined by
the nuclear spin polarization. As applications of our solution, we calculate
the nuclear spin noise spectrum and describe the effects of nuclear spin
squeezing and many body entanglement in the absence of a system excitation.",2012.03872v2
2017-11-20,Precessional dynamics of black hole triples: binary mergers with near-zero effective spin,"The binary black hole mergers detected by Advanced LIGO/Virgo have shown no
evidence of large black hole spins. However, because LIGO/Virgo best measures
the effective combination of the two spins along the orbital angular momentum
($\chi_{\rm eff}$), it is difficult to distinguish between binaries with
slowly-spinning black holes and binaries with spins lying in the orbital plane.
Here, we study the spin dynamics for binaries with a distant black hole
companion. For spins initially aligned with the orbital angular momentum of the
binary, we find that $\chi_{\rm eff}$ ""freezes"" near zero as the orbit decays
through the emission of gravitational waves. Through a population study, we
show that this process predominantly leads to merging black hole binaries with
near-zero $\chi_{\rm eff}$. We conclude that if the detected black hole
binaries were formed in triples, then this would explain their low $\chi_{\rm
eff}$ without the need to invoke near-zero spins or initially large spin-orbit
angles.",1711.07142v2
2018-06-28,Theory of spin inertia in singly-charged quantum dots,"The spin inertia measurement is a recently emerged tool to study slow spin
dynamics, which is based on the excitation of the system by a train of
circularly polarized pulses with alternating helicity. Motivated by the
experimental results reported in E. A. Zhukov et al., arXiv:1806.11100 we
develop the general theory of spin inertia of localized charge carriers. We
demonstrate that the spin inertia measurement in longitudinal magnetic field
allows one to determine the parameters of the spin dynamics of resident charge
carriers and of photoexcited trions, such as the spin relaxation times,
longitudinal g-factors, parameters of hyperfine interaction and nuclear spin
correlation times.",1806.11098v2
2019-11-11,Theory and phase-field simulations on electrical control of spin cycloids in a multiferroic,"Cycloidal spin orders are common in multiferroics. One of the prototypical
examples is BiFeO3 (BFO) which shows a large polarization and a cycloidal
antiferromagnetic order at room temperature. Here we employ Landau theory and
phase-field simulations to analyze the coupled switching dynamics of
polarization and cycloidal antiferromagnetic orders in BFO. We are able to
identify 14 types of transitional spin structures between two cycloids and 9
electric-field-induced spin switching paths. We demonstrate the
electric-field-induced rotation of wave vectors of the cycloidal spins and
discover 2 types of cycloidal spin switching dynamics: fast local spin flips
and slow rotation of wave vectors. Also, we construct road maps to achieve the
switching between any two spin cycloids through multi-step applications of
electric fields. The work provides a theoretical framework for the
phenomenological description of spin cycloids and a fundamental understanding
of the switching mechanisms to achieve electrical control of magnetic orders.",1911.04023v2
2019-11-30,Spin Solitons in Spin-1 Bose-Einstein Condensates,"Solitons in multi-component Bose-Einstein condensates have been paid much
attention, due to the stability and wide applications of them. The exact
soliton solutions are usually obtained for integrable models. In this paper, we
present four families of exact spin soliton solutions for non-integrable cases
in spin-1 Bose-Einstein Condensates. The whole particle density is uniform for
the spin solitons, which is in sharp contrast to the previously reported
solitons of integrable models. The spectrum stability analysis and numerical
simulation indicate the spin solitons can exist stably. The spin density
redistribution happens during the collision process, which depends on the
relative phase and relative velocity between spin solitons. The non-integrable
properties of the systems can bring spin solitons experience weak amplitude and
location oscillations after collision. These stable spin soliton excitations
could be used to study the negative inertial mass of solitons, the dynamics of
soliton-impurity systems, and the spin dynamics in Bose-Einstein condensates.",1912.00182v1
2020-05-27,Relaxation of the collective magnetization of a dense 3D array of interacting dipolar S=3 atoms,"We report on measurements of the dynamics of the collective spin length
(total magnetization) and spin populations in an almost unit filled lattice
system comprising about 10^4 spin S=3 chromium atoms, under the effect of
dipolar interactions. The observed spin population dynamics is unaffected by
the use of a spin echo, and fully consistent with numerical simulations of the
S=3 XXZ spin model. On the contrary, the observed spin length decays slower
than in simulations, and surprisingly reaches a small but nonzero asymptotic
value within the longest timescale. Our findings show that spin coherences are
sensitive probes to systematic effects affecting quantum many-body behavior
that cannot be diagnosed by merely measuring spin populations.",2005.13487v1
2021-03-17,Spin/valley coupled dynamics of electrons and holes at the ${\text{MoS}_{2}-\text{MoSe}_{2}}$ interface,"The coupled spin and valley degrees of freedom in transition metal
dichalcogenides (TMDs) are considered a promising platform for information
processing. Here, we use a TMD heterostructure
${\text{MoS}_{2}-\text{MoSe}_{2}}$ to study optical pumping of spin/valley
polarized carriers across the interface and to elucidate the mechanisms
governing their subsequent relaxation. By applying time-resolved Kerr and
reflectivity spectroscopies, we find that the photoexcited carriers conserve
their spin for both tunneling directions across the interface. Following this,
we measure dramatically different spin/valley depolarization rates for
electrons and holes, $\sim 30\,{\text{ns}}^{-1}$ and $< 1\,{\text{ns}}^{-1}$,
respectively and show that this difference relates to the disparity in the
spin-orbit splitting in conduction and valence bands of TMDs. Our work provides
insights into the spin/valley dynamics of free carriers unaffected by complex
excitonic processes and establishes TMD heterostructures as generators of spin
currents in spin/valleytronic devices.",2103.09934v2
2021-08-12,Theory of spin-charge-coupled transport in proximitized graphene: An SO(5) algebraic approach,"Establishing the conditions under which orbital, spin and lattice-pseudospin
degrees of freedom are mutually coupled in realistic nonequilibrium conditions
is a major goal in the emergent field of graphene spintronics. Here, we use
linear-response theory to obtain a unified microscopic description of spin
dynamics and coupled spin-charge transport in graphene with an
interface-induced Bychkov-Rashba effect. Our method makes use of an SO(5)
extension of the familiar inverse-diffuson approach to obtain a quantum kinetic
equation for the single-particle density matrix that treats spin and pseudospin
on equal footing and is valid for arbitrary external perturbations. As an
application of the formalism, we derive a complete set of drift-diffusion
equations for proximitized graphene with scalar impurities in the presence of
electric and spin-injection fields which vary slowly in space and time. Our
approach is amenable to a wide variety of generalizations, including the study
of coupled spin-charge dynamics in layered materials with strong spin-valley
coupling and spin-orbit torques in van der Waals heterostructures.",2108.05559v2
2022-02-08,Precession of entangled spin and pseudospin in double quantum dots,"Quantum dot spin valves are characterized by exchange fields which induce
spin precession and generate current spin resonances even in absence of spin
splitting. Analogous effects have been studied in double quantum dots, in which
the orbital degree of freedom, the pseudospin, replaces the spin in the valve
configuration. We generalize, now, this setup to allow for arbitrary spin and
orbital polarization of the leads, thus obtaining an even richer variety of
current resonances, stemming from the precession dynamics of entangled spin and
pseudospin. We observe for both vectors a delicate interplay of decoherence,
pumping and precession which can only be understood by also considering the
dynamics of the spin-pseudospin correlators. The numerical results are obtained
in the framework of a generalized master equation within the cotunneling
approximation and are complemented by the analytics of a coherent sequential
tunneling model.",2202.04186v1
2022-03-26,Spin and Contextuality in Extended de Broglie-Bohm-Bell Quantum Mechanics,"This paper introduces an extension of the de Broglie-Bohm-Bell formulation of
quantum mechanics, which includes intrinsic particle degrees of freedom, such
as spin, as elements of reality. To evade constraints from the Kochen-Specker
theorem the discrete spin values refer to a specific basis -- i.e., a single
spin vector orientation for each particle; these spin orientations are,
however, not predetermined, but dynamic and guided by the (reduced, spin-only)
wave function of the system, which is conditional on the realized location
values of the particles. In this way, the unavoidable contextuality of spin is
provided by the wave function and its realized particle configuration, whereas
spin is still expressed as a local property of the individual particles. This
formulation, which furthermore features a rigorous discrete-time stochastic
dynamics, allows for numerical simulations of particle systems with entangled
spin, such as Bohm's version of the EPR experiment.",2203.14034v1
2022-06-14,Broadband microwave detection using electron spins in a hybrid diamond-magnet sensor chip,"Quantum sensing has developed into a main branch of quantum science and
technology. It aims at measuring physical quantities with high resolution,
sensitivity, and dynamic range. Electron spins in diamond are powerful magnetic
field sensors, but their sensitivity in the microwave regime is limited to a
narrow band around their resonance frequency. Here, we realize broadband
microwave detection using spins in diamond interfaced with a thin-film magnet.
A pump field locally converts target microwave signals to the sensor-spin
frequency via the non-linear spin-wave dynamics of the magnet. Two
complementary conversion protocols enable sensing and high-fidelity spin
control over a gigahertz bandwidth, allowing characterization of the spin-wave
band at multiple gigahertz above the sensor-spin frequency. The pump-tunable,
hybrid diamond-magnet sensor chip opens the way for spin-based sensing in the
100-gigahertz regime at small magnetic bias fields.",2206.07013v1
2022-10-30,Spin hydrodynamic generation in unsteady flows,"We theoretically investigate a spin-mediated conversion from fluid dynamics
to voltage, known as spin hydrodynamic generation (SHDG), in oscillatory and
transient unsteady flows. We consider unsteady flows of liquid metal between
two parallel infinite planes and then calculate its vorticity fields based on
the Navier--Stokes equation for an incompressible viscous fluid. The spin
accumulation and spin current generated by unsteady flows are derived using a
spin-diffusion equation, including spin-vorticity coupling, which is a couple
of angular momentum between electron spin and vorticity field in unsteady
flows. The estimation of SHDG in liquid mercury flow suggests that an
observable magnitude of voltage can be induced in unsteady flows. Our results
are expected to enable the realization of high-speed spin devices with unsteady
flows and broaden the range of fluid spintronics applicability.",2210.16762v2
2023-06-14,Coherent scattering from coupled two level systems,"We study the resonance fluorescence properties of an optically active spin
1/2 system, elucidating the effects of a magnetic field on the coherence of the
scattered light. We derive a master equation model for this system that
reproduces the results of a two level system (TLS) while also being applicable
to a spin system with ground state coupling. This model is then solved
analytically in the weak excitation regime. The inclusion of spin dynamics in
our model alters the properties of the coherently scattered light at a
fundamental level. For a TLS the coherence properties are known to be
determined by the input laser. We show that spin scattered light inherits the
coherence properties of the spin. This mapping allows us to measure spin
dynamics and coherence time through direct measurement of the scattered fields.
Furthermore, we show the ability to resolve sub-natural linewidth zeeman
splittings. Along with representing an invaluable tool for spin spectroscopy
understanding the coherence properties of the spin-scattered field will be
vital for spin-photon based quantum technologies.",2306.08439v1
2024-01-12,Spin Resonance Spectroscopy with an Electron Microscope,"Coherent spin resonance methods, such as nuclear magnetic resonance and
electron spin resonance spectroscopy, have led to spectrally highly sensitive,
non-invasive quantum imaging techniques. Here, we propose a pump-probe spin
resonance spectroscopy approach, designed for electron microscopy, based on
microwave pump fields and electron probes. We investigate how quantum spin
systems couple to electron matter waves through their magnetic moments and how
the resulting phase shifts can be utilized to gain information about the states
and dynamics of these systems. Notably, state-of-the-art transmission electron
microscopy provides the means to detect phase shifts almost as small as that
due to a single electron spin. This could enable state-selective observation of
spin dynamics on the nanoscale and indirect measurement of the environment of
the examined spin systems, providing information, for example, on the atomic
structure, local chemical composition and neighboring spins.",2401.06496v1
2024-02-16,Spin projection noise and the magnetic sensitivity of optically pumped magnetometers,"Present protocols for obtaining the ultimate magnetic sensitivity of
optically pumped magnetometers (OPMs) utilizing alkali-metal ensembles rely on
uncorrelated atoms in stretched states. A new approach for calculating the spin
projection noise (SPN)-limited signal to noise ratio (SNR) and the magnetic
sensitivity of OPMs is proposed. Our model is based solely on the mean-field
density matrix dynamics and in contrast to previous models, it applies to both
low and high field regimes, it takes into account the degree of spin
polarization, the intra- and interhyperfine correlations, the decoherence
processes, the atom-light coupling and the effects of the spin dynamics on the
spin-noise spectra. Fine tuning of the probe frequency allow us to explore
different hyperfine states and ground-state correlations. Especially in the
spin-exchange-relaxation-free (SERF) regime, alongside the magnetic resonance
narrowing and the increased number density, hallmarks of SERF magnetometers, we
report on a new SERF feature; the reduction of spin-projection noise at the
spin precession frequency as a consequence of strongly-correlated hyperfine
spins that attenuate and redistribute SPN when properly probed.",2402.10746v2
1995-11-03,A pair of interacting spins coupled to an environmental sea: dissipation and mutual decoherence,"We consider the quantum dynamics of two spin-1/2 systems, each coupled to a
bath of oscillators, so that a bath-mediated coupling is generated between the
spins. We find that the interactions destroys any coherent motion of the 2
spins, even if the coupling of each spin to the bath is quite weak, unless the
interaction is extremely small. This is because the dynamic mutual bias between
the spins blocks any coherent transitions between nearly degenerate states. In
many quantum measurement operations this means that decoherence effects will be
much stonger during the actual measurement",9511020v1
1998-03-02,Evolution of Hole and Spin Dynamics in High Temperature Superconductors within the Small Hole Density Limit of the t-J Model,"The evolution of hole and spin dynamics in high temperature superconductors
is studied within the self-consistent noncrossing approximation of the t-J
model in the small hole density limit. As the doping concentration is
increased, long-range electron correlations disappear rapidly and the
quasiparticle energy band becomes considerably narrow. At a small hole density
long-range antiferromagnetic order is destroyed leading to the inadequacy of
spin wave basis approximation near small wave vectors. Spin excitations near
the antiferromagnetic zone boundary are strongly renormalized and damped but
they are still well described within spin wave basis approximation.",9803016v1
1998-04-02,Quantum magnetism in the stripe phase: bond- versus site order,"It is argued that the spin dynamics in the charge-ordered stripe phase might
be revealing with regards to the nature of the anomalous spin dynamics in
cuprate superconductors. Specifically, if the stripes are bond ordered much of
the spin fluctuation will originate in the spin sector itself, while site
ordered stripes require the charge sector as the driving force for the strong
quantum spin fluctuations.",9804012v1
1999-03-18,Coherent dynamics of localized spins coupled with a two-dimensional hole gas in diluted-magnetic quantum wells,"Spin dynamics in a quantum well made of diluted-magnetic semiconductor is
studied theoretically. The exchange interaction of the ensemble of localized
spins with two-dimensional heavy-hole gas is shown to affect time evolution of
the spin system in an in-plane magnetic field. The Larmor frequency of
localized spins is reduced under influence of an oscillating effective field of
holes.",9903280v1
2001-02-12,Nonlinear Dynamics of Quasiclassical Spin Moment in a Swept Field,"Quantum dynamics of anisotropic spin system with large spin moment in a swept
magnetic field is theoretically investigated. Magnetic field of this type
induces vortex static electrical field, that breaks down the axial symmetry and
induces new coherent quantum phenomena: the occurrence of band energy spectrum
with continuous spin states, Bloch-type oscillations and interband Zener
tunnelling effect. These quantum phenomena display themselves, in particular,
in magnetization jumps and susceptibility peaks in the investigated spin
system.",0102198v2
2001-04-09,Spin transport in inhomogeneous magnetic fields: a proposal for Stern-Gerlach-like experiments with conduction electrons,"Spin dynamics in spatially inhomogeneous magnetic fields is studied within
the framework of Boltzmann theory. Stern-Gerlach-like separation of spin up and
spin down electrons occurs in ballistic and diffusive regimes, before spin
relaxation sets in. Transient dynamics and spectral response to time-dependent
inhomogeneous magnetic fields are investigated, and possible experimental
observations of our findings are discussed.",0104146v2
2002-12-05,Dynamic stiffness of spin valves,"The dynamics of the magnetic order parameters of
ferromagnet/normal-metal/ferromagnet spin valves and isolated ferromagnets may
be very different. We investigate the role of the nonequilibrium spin-current
exchange between the ferromagnets in the magnetization precession and
switching. We find a (low-temperature) critical current bias for a coherent
current-induced magnetization excitation in spin valves, which unifies and
generalizes previous ideas of Slonczewski and Berger. In the absence of an
applied bias, the effect of the spin transfer can be expressed as
magnetic--configuration-dependent Gilbert damping.",0212130v2
2002-12-06,Dynamics of entanglement between quantum dot spin-qubits,"We briefly review the physics of gate operations between quantum dot
spin-qubits and analyze the dynamics of quantum entanglement in such processes.
The indistinguishable character of the electrons whose spins realize the qubits
gives rise to further entanglement-like quantum correlations that go beyond
simple antisymmetrization effects. We also summarize further recent results
concerning this type of quantum correlations of indistinguishable particles.
Finally we discuss decoherence properties of spin-qubits when coupled to
surrounding nuclear spins in a semiconductor nanostructure",0212141v1
2003-08-29,Magnetic Order and Dynamics in Stripe-Ordered La2-xSrxNiO4,"We have studied magnetic correlations in several compositions of
stripe-ordered La2-xSrxNiO4. In this paper we show how polarized-neutron
scattering has helped uncover important features of the magnetic ordering and
spin dynamics. In particular, polarization analysis has enabled us (1) to
characterize a spin reorientation transition, (2) to identify anisotropy gaps
in the spin excitation spectrum, and (3) to investigate an anomalous dip in the
spin-wave intensity suggestive of coupling between collective spin and charge
excitations.",0308631v1
2004-02-12,Spin Dynamics of Double-Exchange Manganites with Magnetic Frustration,"This work examines the effects of magnetic frustration due to competing
ferromagnetic and antiferromagnetic Heisenberg interactions on the spin
dynamics of the double-exchange model. When the local moments are non-colinear,
a charge-density wave forms because the electrons prefer to sit on lines of
sites that are coupled ferromagnetically. With increasing hopping energy, the
local spins become aligned and the average spin-wave stiffness increases. Phase
separation is found only within a narrow range of hopping energies. Results of
this work are applied to the field-induced jump in the spin-wave stiffness
observed in the manganite Pr$_{1-x}$Ca$_x$MnO$_3$ with $0.3 \le x \le 0.4$.",0402344v1
2004-03-15,Dynamically generated dimension reduction and crossover in a spin orbital model,"We study a spin orbital model in which the spin-spin interaction couples
linearly to the orbital isospin. Fluctuations drive the transition from
paramagnetic state to C type ordered state into a strongly first order one, as
observed in $V_2O_3$. At T=0, there is a FOCS to FOGS transition. Close to the
transition point, the system shows dynamically generated dimension reduction
and crossover, resulting in one or more spin reentrant transitions.",0403370v1
2004-07-06,Dynamic properties of a diluted pyrochlore cooperative paramagnet (Tb_pY_{1-p})_2Ti_2O_7,"Investigations of the spin dynamics of the geometrically frustrated
pyrochlore (Tb_pY_{1-p})_2Ti_2O_7, using muon spin relaxation and neutron spin
echo, as a function of magnetic coverage p, have been carried out. Our major
finding is that paramagnetic fluctuations prevail as T->0 for all values of p,
and that they are sensitive to dilution, indicating a cooperative spin motion.
However, the percolation threshold p_c is not a critical point for the
fluctuations. We also find that the low temperatures spectral density has a 1/f
behavior, and that dilution slows down the spin fluctuations.",0407131v1
2005-09-28,Spin polarized photocurrent from quantum dots,"In this paper we show that it is possible to switch the spin polarization of
the photocurrent signal obtained from a single self-assembled quantum dot
photodiode under the effect of elliptically polarized light by just increasing
the light intensity. In the nonlinear mechanism treated here, intense
elliptically polarized light creates an effective exchange interaction between
the exciton spin states through the biexciton state. This effect can be used as
a dynamical switch to invert the spin-polarization of the extracted
photocurrent. We further show that the effect persists in realistic ensembles
of dots, making this a powerful technique to dynamically generate
spin-polarized electrons.",0509731v1
2005-10-10,Role of the spin-orbit splitting and the dynamical fluctuations in the Si(557)-Au surface,"Our it ab initio calculations show that spin-orbit coupling is crucial to
understand the electronic structure of the Si(557)-Au surface. The spin-orbit
splitting produces the two one-dimensional bands observed in photoemission,
which were previously attributed to spin-charge separation in a Luttinger
liquid. This spin splitting might have relevance for future device
applications. We also show that the apparent Peierls-like transition observed
in this surface by scanning tunneling microscopy is a result of the dynamical
fluctuations of the step-edge structure, which are quenched as the temperature
is decreased.",0510239v1
2001-07-11,On the Dynamical Invariants and the Geometric Phases for a General Spin System in a Changing Magnetic Field,"We consider a class of general spin Hamiltonians of the form
$H_s(t)=H_0(t)+H'(t)$ where $H_0(t)$ and $H'(t)$ describe the dipole
interaction of the spins with an arbitrary time-dependent magnetic field and
the internal interaction of the spins, respectively. We show that if $H'(t)$ is
rotationally invariant, then $H_s(t)$ admits the same dynamical invariant as
$H_0(t)$. A direct application of this observation is a straightforward
rederivation of the results of Yan et al [Phys. Lett. A, Vol: 251 (1999) 289
and Vol: 259 (1999) 207] on the Heisenberg spin system in a changing magnetic
field.",0107063v1
2006-06-20,Interpreting concurrence in terms of covariances in a generalized spin star system,"The quantum dynamics of M pairwise coupled spin 1/2 is analyzed and the time
evolution of the entanglement get established within a prefixed couple of spins
is studied. A conceptual and quantitative link between the concurrence function
and measurable quantities is brought to light providing a physical
interpretation for the concurrence itself as well as a way to measure it. A
generalized spin star system is exactly investigated showing that the
entanglement accompanying its rich dynamics is traceable back to the covariance
of appropriate commuting observables of the two spins.",0606163v1
2007-04-03,Exactly solvable spin dynamics of an electron coupled to large number of nuclei and the electron-nuclear spin echo in a quantum dot,"The model considered in the paper is used nowadays to describe spin dynamics
of quantum dots after optical excitation. Based on the exact diagonalization of
a model Hamiltonian, we solve the problems of the electron spin polarization
decay and magnetic field dependence of the steady state polarization. The
important role of the nuclear state is shown and methods of its calculation for
different regimes of optical excitation are proposed. The effect of spin echo
observed after application of the magnetic field $\pi$-pulse is predicted.",0704.0391v3
2007-07-19,Disentanglement of two qubits coupled to an XY spin chain: Role of quantum phase transition,"We study the disentanglement of two spin qubits which interact with a general
XY spin-chain environment. The dynamical process of the disentanglement is
numerically and analytically investigated in the vicinity of quantum phase
transition (QPT) of the spin chain in both weak and strong coupling cases. We
find that the disentanglement of the two qubits is in general enhanced greatly
when the environmental spin chain is exposed to QPT. We give a detailed
analysis to facilitate the understanding of the QPT-enhanced decaying behavior
of the disentanglement factor. Furthermore, the scaling behavior in the
disentanglement dynamics is also revealed and analyzed.",0707.2846v1
2008-05-09,Non-Markovian dynamics of a single electron spin coupled to a nuclear spin bath,"We apply the time-convolutionless (TCL) projection operator technique to the
model of a central spin which is coupled to a spin bath via nonuniform
Heisenberg interaction. The second-order results of the TCL method for the
coherences and populations of the central spin are determined analytically and
compared with numerical simulations of the full von Neumann equation of the
total system. The TCL approach is found to yield an excellent approximation in
the strong field regime for the description of both the short-time dynamics and
the long time behavior.",0805.1314v2
2008-06-11,Critical current of spin transfer torque-driven magnetization dynamics in magnetic multilayers,"The critical current of the spin transfer torque-driven magnetization
dynamics was studied by taking into account both spin pumping and the finite
penetration depth of the transverse spin current. We successfully reproduced
the recent experimental results obtained by Chen et al. [Phys. Rev. B {\bf 74},
144408 (2006)] and found that the critical current remains finite even in the
zero-thickness limit of the free layer. We showed that the remaining value of
the critical current is determined mainly by spin pumping.",0806.1822v2
2008-11-28,Effect of Nonlocal Spin-Transfer Torque on Current-Induced Magnetization Dynamics,"Using the self-consistent model, we present nonlocal spin-transfer effects
caused by the feedback between inhomogeneous magnetization and spin-transfer
torque on the current-induced magnetization dynamics in nanomagnets. The
nonlocal effects can substantially improve the coherence time of precession in
nanomagnets and thus reduce the linewidth of power spectrum. This narrow
linewidth results from the nonlinear damping of spin-waves due to the nonlocal
spin torque which is inherent and thus should be considered in future
experiments.",0811.4649v1
2009-01-18,Generation of pulse trains by current-controlled magnetic mirrors,"The evolution of a spin-wave packet trapped between two direct
current-carrying wires placed on the surface of a ferrite film is observed by
Brillouin light scattering. The wires act as semi-transparent mirrors confining
the packet. Because the spin-wave energy partially passes through these
mirrors, trains of spin-wave packets are generated outside the trap. A
numerical model of this process is presented and applied to the case when the
current in the wires is dynamically controlled. This dynamical control of the
mirror reflectivity provides new functionalities interesting for the field of
spin-wave logic like that of a spin-wave memory cell.",0901.2704v1
2009-02-24,Effect of Ka-band Microwave on the spin dynamics of electrons in a GaAs/Al0.35Ga0.65As heterostructure,"We report experimental results of the effect of Ka-band microwave on the spin
dynamics of electrons in a 2D electron system in a GaAs/Al0.35Ga0.65As
heterostructure, via time-resolved Kerr rotation measurements. While the
microwave reduces the transverse spin lifetime of the bulk GaAs when its
frequency is close to the Zeeman splitting of the electrons in the magnetic
field, it significantly increases that of electrons in the 2D electron system,
from 745 ps to 1213 ps. Such a microwave-enhanced spin lifetime is ascribed to
the microwave-induced electron scattering which leads to a motional narrowing
of spins via DP mechanism.",0902.4087v1
2009-04-04,Exact dynamics of XX central spin models,"The dynamical behavior of a star network of spins, wherein each of N
decoupled spins interact with a central spin through non uniform Heisenberg XX
interaction is exactly studied. The time-dependent Schrodinger equation of the
spin system model is solved starting from an arbitrary initial state. The
resulting solution is analyzed and briefly discussed.",0904.0695v1
2009-04-22,Magnetic field-induced soft mode in spin-gapped high-Tc superconductors,"We present an explanation of the dynamical in-gap spin mode in LSCO induced
by an applied magnetic field H as recently observed by J. Chang et al. Our
model consists of a phenomenological spin-only Hamiltonian, and the softening
of the spin mode is caused by vortex pinning of dynamical stripe fluctuations
which we model by a local ordering of the exchange interactions. The spin gap
vanishes experimentally around H=7T which in our scenario corresponds to the
field required for overlapping vortex regions.",0904.3404v1
2010-08-26,Localized collapse and revival of coherence in an ultracold Bose gas,"We study the collapse and revival of coherence induced by dipolar spin waves
in a trapped gas of Rb-87 atoms. In particular we observe spatially localized
collapse and revival of Ramsey fringe contrast and show how the pattern of
coherence depends on strength of the spin wave excitation. We find that the
spatial character of the coherence dynamics is incompatible with a simple model
based only on position-space overlap of wave functions. This phenomenon
requires a full phase-space description of the atomic spin using a quantum
Boltzmann transport equation, which highlights spin wave-induced coherent spin
currents and the ensuing dynamics they drive.",1008.4428v1
2010-11-15,Nuclear spin pumping and electron spin susceptibilities,"In this work we present a new formalism to evaluate the nuclear spin dynamics
driven by hyperfine interaction with non-equilibrium electron spins. To
describe the dynamics up to second order in the hyperfine coupling, it suffices
to evaluate the susceptibility and fluctuations of the electron spin. Our
approach does not rely on a separation of electronic energy scales or the
specific choice of electronic basis states, thereby overcoming practical
problems which may arise in certain limits when using a more traditional
formalism based on rate equations.",1011.3378v2
2011-01-12,The Spin-Exchange Dynamical Structure Factor of the S=1/2 Heisenberg Chain,"We determine the spin-exchange dynamical structure factor of the Heisenberg
spin chain, as is measured by indirect Resonant Inelastic X-ray Scattering
(RIXS). We find that two-spin RIXS excitations nearly entirely fractionalize
into *two spinon* states. These share the same continuum lower bound as
single-spin neutron scattering excitations, even if the relevant final states
belong to orthogonal symmetry sectors. The RIXS spectral weight is mainly
carried by higher-energy excitations, and is beyond the reach of the low-energy
effective theories of Luttinger liquid type.",1101.2356v1
2012-10-30,NMR relaxation in spin ice due to diffusing emergent monopoles,"At low temperatures, spin dynamics in ideal spin ice is due mainly to dilute,
thermally excited magnetic monopole excitations. I consider how these will
affect the dynamics of a nuclear spin (the same theory applies to muon spin
resonance if implanted muons do not diffuse). Up to the time scale for nearby
monopoles to be rearranged, a stretched-exponential form of the relaxation
functions is expected. I work out the expected exponent in that exponential and
the formulas for the $T_1$ (longitudinal) and $T_2$ (dephasing) relaxations, as
a function of the monopole density. Experimental NMR is incompatible with the
predictions and I suggest is due to magnetic impurities.",1210.8137v1
2015-02-06,Microscopic theory of Gilbert damping in metallic ferromagnets,"We present a microscopic theory for magnetization relaxation in metallic
ferromagnets of nanoscopic dimensions that is based on the dynamic spin
response matrix in the presence of spin-orbit coupling. Our approach allows the
calculation of the spin excitation damping rate even for perfectly crystalline
systems, where existing microscopic approaches fail. We demonstrate that the
relaxation properties are not completely determined by the transverse
susceptibility alone, and that the damping rate has a non-negligible frequency
dependence in experimentally relevant situations. Our results indicate that the
standard Landau-Lifshitz-Gilbert phenomenology is not always appropriate to
describe spin dynamics of metallic nanostructure in the presence of strong
spin-orbit coupling.",1502.02068v1
2015-03-01,Engineering nuclear spin dynamics with optically pumped nitrogen-vacancy center,"We present a general theory for using an optically pumped diamond
nitrogen-vacancy center as a tunable, non-equilibrium bath to control a variety
of nuclear spin dynamics (such as dephasing, relaxation, squeezing,
polarization, etc.) and the nuclear spin noise. It opens a new avenue towards
engineering the dissipative and collective nuclear spin evolution and solves an
open problem brought up by the $^{13}$C nuclear spin noise suppression
experiment [E. Togan \textit{et al}., Nature 478, 497 (2011)].",1503.00243v1
2015-03-27,Spin superradiance by magnetic nanomolecules and nanoclusters,"Spin dynamics of assemblies of magnetic nanomolecules and nanoclusters can be
made coherent by inserting the sample into a coil of a resonant electric
circuit. Coherence is organized through the arising feedback magnetic field of
the coil. The coupling of a magnetic sample with a resonant circuit induces
fast spin relaxation and coherent spin radiation, that is, superradiance. We
consider spin dynamics described by a realistic Hamiltonian, typical of
magnetic nanomolecules and nanoclusters. The role of magnetic anisotropy is
studied. A special attention is paid to geometric effects related to the mutual
orientation of the magnetic sample and resonator coil.",1503.08036v1
2015-06-23,Effects of magnetic anisotropy on spin dynamics of ferromagnetic frustrated chain,"By exploiting density-matrix renormalization group techniques, we investigate
the spin dynamics of a spin-1/2 one-dimensional J1-J2 XXZ model with competing
ferromagnetic J1 and antiferromagnetic J2 exchange couplings under applied
magnetic fields. Numerical results of spin excitation spectra show that in the
field-induced spin quadrupole regime, the longitudinal component has a gapless
mode and the transverse component has a gapped mode irrespective of the
exchange anisotropy. The excitation gap of the transverse spin excitation
increases as the exchange anisotropy increases over the XY-like and Ising-like
regions, demonstrating that two-magnon bound states are stabilized due to the
easy-axis anisotropy.",1506.06883v1
2018-11-06,Nonlinear dynamic interpretation of quantum spin,"In an effort to provide an alternative method to represent a quantum spin, a
precise nonlinear dynamics semi-classical model is used to show that standard
quantum spin analysis can be obtained. The model includes a multi-body,
anti-ferromagnetic ordering, highly coupled quantum spin and a semi-classical
interpretation of the torque on a spin magnetic moment in the presence of a
magnetic field. The deterministic nonlinear differential coupling equation is
used to introduce chaos, which is necessary to reproduce the correct
statistical quantum results.",1811.02624v1
2016-11-22,Electron spin dynamics of two-dimensional layered materials,"The growing library of two-dimensional layered materials is providing
researchers with a wealth of opportunity to explore and tune physical phenomena
at the nanoscale. Here, we review the experimental and theoretical state-of-art
concerning the electron spin dynamics in graphene, silicene, phosphorene,
transition metal dichalcogenides, covalent heterostructures of organic
molecules and topological materials. The spin transport, chemical and defect
induced magnetic moments, and the effect of spin-orbit coupling and spin
relaxation, are also discussed in relation to the field of spintronics.",1611.07208v1
2017-04-05,Spectroscopy and spin dynamics for strongly interacting few spinor bosons in one-dimensional traps,"We consider a one-dimensional trapped gas of strongly interacting few spin-1
atoms which can be described by an effective spin chain Hamiltonian. Away from
the SU(3) integrable point, where the energy spectrum is highly degenerate, the
rules of ordering and crossing of the energy levels and the symmetry of the
eigenstates in the regime of large but finite repulsion have been elucidated.
We study the spin-mixing dynamics which is shown to be very sensitive to the
ratio between the two channel interactions g0/g2 and the effective spin chain
transfers the quantum states more perfectly than the Heisenberg
bilinear-biquadratic spin chain.",1704.01245v1
2015-12-20,Shapiro like steps reveals molecular nanomagnets' spin dynamics,"We present an accurate way to detect spin dynamics of a nutating molecular
nanomagnet by inserting it in a tunnel Josephson junction and studying the
current voltage (I-V) characteristic. The spin nutation of the molecular
nanomagnet is generated by applying two circularly polarized magnetic fields.
We demonstrate that modulation of the Josephson current by the nutation of the
molecular nanomagnet's spin appears as a stepwise structure like Shapiro steps
in the I-V characteristic of the junction. Width and heights of these
Shapiro-like steps are determined by two parameters of the spin nutation,
frequency and amplitude of the nutation, which are simply tuned by the applied
magnetic fields.",1512.06406v1
2017-05-03,Anomalous spin precession under a geometrical torque,"Precession and relaxation predominantly characterize the real-time dynamics
of a spin driven by a magnetic field and coupled to a large Fermi sea of
conduction electrons. We demonstrate an anomalous precession with frequency
higher than the Larmor frequency or with inverted orientation in the limit
where the electronic motion adiabatically follows the spin dynamics. For a
classical spin, the effect is traced back to a geometrical torque resulting
from a finite spin Berry curvature.",1705.01313v2
2018-07-05,Analysis of continuous and discrete Wigner approximations for spin dynamics,"We compare the continuous and discrete truncated Wigner approximations of
various spin models' dynamics to exact analytical and numerical solutions. We
account for all components of spin-spin correlations on equal footing,
facilitated by a recently introduced geometric correlation matrix visualization
technique [R. Mukherjee {\em et al.}, Phys. Rev. A {\bf 97}, 043606 (2018)]. We
find that at modestly short times, the dominant error in both approximations is
to substantially suppress spin correlations along one direction.",1807.02171v2
2020-08-17,Supersymmetry of Relativistic Hamiltonians for Arbitrary Spin,"Hamiltonians describing the relativistic quantum dynamics of a particle with
an arbitrary spin are shown to exhibit a supersymmetric structure when the even
and odd elements of the Hamiltonian commute. For such supersymmetric
Hamiltonians an exact Foldy-Wouthuysen transformation exits which brings it
into a block-diagonal form separating the positive and negative energy
subspaces. Here the supercharges transform between energy eigenstates of
positive and negative energy. The relativistic dynamics of a charged particle
in a magnetic field is considered for the case of a scalar (spin-zero) boson
obeying the Klein-Gordan equation, a Dirac (spin one-half) fermion and a vector
(spin-one) boson characterised by the Proca equation.",2009.02153v1
2021-05-07,Non-linear extension of the dynamical linear response of spins; extended Heisenberg model,"We introduce a new extended Heisenberg model. The model contains the
orbital-dependent spins together with the retarded effects of spin torque. The
model is directly derived from the dynamical linear response functions on the
transversal spin fluctuation. Our model allows us to address effects which are
not accessible via the usual Heisenberg model. With the model, we can describe
not only the relaxation effects due to the Landau damping caused by the Stoner
excitations, but also the nesting effects of the Fermi surface. We discuss
possibilities of the extended Heisenberg model based on the high-resolution
plots of the spin susceptibility for Fe.",2105.03035v2
2022-04-08,Floquet theory of spin dynamics under circularly polarized light pulses,"Within the Floquet theory of periodically driven quantum systems, the
nonlinear single-spin dynamics under pulse of a circularly polarized
electromagnetic field is analyzed. It is demonstrated that the field, first,
lifts the spin degeneracy and, second, the field-induced spin splitting is
accompanied by the photon emission at the spitting frequency. This two-stage
process leads, particularly, to the polarization of spins along angular
momentum of the circularly polarized field. As a result, the pulse-induced
magnetization appears, what can be observed in state-of the-art measurements.",2204.04130v1
2022-08-29,The Effect of Duschinskii Rotations on Spin-Dependent Electron Transfer Dynamics,"We investigate spin-dependent electron transfer in the presence of a
Duschinskii rotation. In particular, we propagate dynamics for a two-level
model system for which spin-orbit coupling introduces an interstate coupling of
the form $e^{iWx}$, which is both position(x)-dependent and complex-valued. We
demonstrate that two-level systems coupled to Brownian oscillators with
Duschinskii rotations (and thus entangled normal modes) can produce marked
increases in transient spin polarization relative to two-level systems coupled
to simple shifted harmonic oscillators. These conclusions should have
significant relevance for modeling the effect of nuclear motion on chiral
induced spin selectivity.",2208.13378v1
2023-09-13,Energy-resolved spin correlation measurements: Decoding transverse spin dynamics in weakly interacting Fermi gases,"We study transverse spin dynamics on a microscopic level by measuring
energy-resolved spin correlations in weakly interacting Fermi gases (WIFGs).
The trapped cloud behaves as a many-body spin-lattice in energy space with
effective long-range interactions, simulating a collective Heisenberg model. We
observe the flow of correlations in energy space in this quasi-continuous
system, revealing the connection between the evolution of the magnetization and
the localization or spread of correlations. This work highlights energy-space
correlation as a new observable in quantum phase transition studies of WIFGs,
decoding system features that are hidden in macroscopic measurements.",2309.07226v2
2018-11-30,Dynamical precession of spin in the two-dimensional spin-orbit coupled systems,"We investigate the spin dynamics in the two-dimensional spin-orbit coupled
system subject to an in-plane ($x$-$y$ plane) constant electric field, which is
assumed to be turned on at the moment $t=0$. The equation of spin precession in
linear response to the switch-on of the electric field is derived in terms of
Heisenberg's equation by the perturbation method up to the first order of the
electric field. The dissipative effect, which is responsible for bringing the
dynamical response to an asymptotic result, is phenomenologically implemented
\`{a} la the Landau-Lifshitz-Gilbert equation by introducing damping terms upon
the equation of spin dynamics. Mediated by the dissipative effect, the
resulting spin dynamics asymptotes to a stationary state, where the spin and
the momentum-dependent effective magnetic field are aligned again and have
nonzero components in the out-of-plane ($z$) direction. In the linear response
regime, the asymptotic response obtained by the dynamical treatment is in full
agreement with the stationary response as calculated in the Kubo formula, which
is a time-independent approach treating the applied electric field as
completely time-independent. Our method provides a new perspective on the
connection between the dynamical and stationary responses.",1811.12626v2
2015-12-30,Magnetization dynamics and spin pumping induced by standing elastic waves,"The magnetization dynamics induced by standing elastic waves excited in a
thin ferromagnetic film is described with the aid of micromagnetic simulations
taking into account the magnetoelastic coupling between spins and lattice
strains. The simulations have been performed for the 2 nm thick Fe81Ga19 film
dynamically strained by longitudinal and transverse standing waves with various
frequencies, which span a wide range around the resonance frequency nu_res of
coherent magnetization precession in unstrained Fe81Ga19 film. It is found that
standing elastic waves give rise to complex local magnetization dynamics and
spatially inhomogeneous dynamic magnetic patterns. The spatio-temporal
distributions of the magnetization oscillations in standing elastic waves have
the form of standing spin waves with the same wavelength. Remarkably, the
amplitude of magnetization precession does not go to zero at the nodes of these
spin waves, which cannot be precisely described by simple analytical formulae.
In the steady-state regime, the magnetization oscillates with the frequency of
elastic wave, except for the case of longitudinal waves with frequencies well
below nu_res, where the magnetization precesses with a variable frequency
strongly exceeding the wave frequency. The precession amplitude at the
antinodes of standing spin waves strongly increases when the frequency of
elastic wave becomes close to nu_res. The results obtained for the
magnetization dynamics driven by elastic waves are used to calculate the spin
current pumped from the dynamically strained ferromagnet into adjacent
paramagnetic metal. Importantly, the transverse charge current created by the
spin current via the inverse spin Hall effect is high enough to be measured
experimentally.",1512.09051v1
2016-08-22,Spin dynamics of the ordered dipolar-octupolar pseudospin-$^1/_2$ pyrochlore Nd$_2$Zr$_2$O$_7$ probed by muon spin relaxation,"We present a muon spin relaxation study on the Ising pyrochlore
Nd$_2$Zr$_2$O$_7$ which develops an ""all-in-all-out"" magnetic order below
0.4~K. At 20~mK far below the ordering transition temperature, the zero-field
muon spin relaxation spectra show no static features and can be well described
by a dynamical Gaussian-broadened Gaussian Kubo-Toyabe function indicating
strong fluctuations of the ordered state. The spectra of the paramagnetic state
(below 4.2~K) reveal anomalously slow paramagnetic spin dynamics and show only
small difference with the spectra of the ordered state. We find that the
fluctuation rate decreases with decreasing temperature and becomes nearly
temperature independent below the transition temperature indicating persistent
slow spin dynamics in the ground state. The field distribution width shows a
small but sudden increase at the transition temperature and then becomes almost
constant. The spectra in applied longitudinal fields are well fitted by the
conventional dynamical Gaussian Kubo-Toyabe function, which further supports
the dynamical nature of the ground state. The fluctuation rate shows a peak as
a function of external field which is associated with a field-induced spin-flip
transition. The strong dynamics in the ordered state are attributed to the
transverse coupling of the Ising spins introduced by the multipole
interactions.",1608.06100v1
2019-11-22,Decay of spin-spin correlations in disordered quantum and classical spin chains,"The real-time dynamics of equal-site correlation functions is studied for
one-dimensional spin models with quenched disorder. Focusing on infinite
temperature, we present a comparison between the dynamics of models with
different quantum numbers $S = 1/2, 1, 3/2$, as well as of chains consisting of
classical spins. Based on this comparison as well as by analyzing the
statistics of energy-level spacings, we show that the putative many-body
localization transition is shifted to considerably stronger values of disorder
for increasing $S$. In this context, we introduce an effective disorder
strength $W_\text{eff}$, which provides a mapping between the dynamics for
different spin quantum numbers. For small $W_\text{eff}$, we show that the
real-time correlations become essentially independent of $S$, and are moreover
very well captured by the dynamics of classical spins. Especially for $S =
3/2$, the agreement between quantum and classical dynamics is remarkably
observed even for very strong values of disorder. This behavior also reflects
itself in the corresponding spectral functions, which are obtained via a
Fourier transform from the time to the frequency domain. As an aside, we also
comment on the self-averaging properties of the correlation function at weak
and strong disorder. Our work sheds light on the correspondence between quantum
and classical dynamics at high temperatures and extends our understanding of
the dynamics in disordered spin chains beyond the well-studied case of $S=1/2$.",1911.09917v2
2014-07-04,Mixed spin (1/2-1) hexagonal Ising nanowire: some dynamic behaviors,"The dynamic behaviors of a mixed spin (1/2-1) hexagonal Ising nanowire (HIN)
with core-shell structure in the presence of a time dependent magnetic field
are investigated by using the effective-field theory with correlations based on
the Glauber-type stochastic dynamics (DEFT). According to the values of
interaction parameters, temperature dependence of the dynamic magnetizations,
the hysteresis loop areas and the dynamic correlations are investigated to
characterize the nature (first- or second-order) of the dynamic phase
transitions (DPTs). Dynamic phase diagrams, including compensation points, are
also obtained. Moreover, from the thermal variations of the dynamic total
magnetization, the five compensation types can be found under certain
conditions, namely the Q-, R-, S-, P-, and N-types.",1407.1092v1
1999-08-06,Spin Dynamics of a Fermi Liquid in an Electric Field,"The influence of an external electric field on the spin dynamics of an
electrically neutral Fermi liquid is considered, the mechanism of such an
influence being the relativistic spin-orbital interaction. As a result,
Leggett's equations for the spin dynamics of weakly polarized Fermi liquids are
generalized to the case of non-zero external electric field. In addition, we
obtained the transverse spin dynamics equation for strongly spin-polarized
liquids in an electric field at zero temperature. In both situations covariant
derivatives depending on the electric field are shown to be substituted for
spatial gradients in line with the SU(2) gauge invariance of the microscopic
Hamiltonian. The new equations are applied to the study of spin flow along a
channel, where an electric field is found to bring about an additional phase
shift of the order of magnitude of the phase shift in superfluid $^3$He-$B$ but
growing with time.",9908091v2
2000-04-18,Influence of the additional second neighbor hopping on the spin response in the t-J model,"The influence of the additional second neighbor hopping t' on the spin
response of the t-J model in the underdoped and optimally doped regimes is
studied within the fermion-spin theory. Although the additional second neighbor
hopping t' is systematically accompanied with the reduction of the dynamical
spin structure factor and susceptibility, the qualitative behavior of the
dynamical spin structure factor and susceptibility of the t-t'-J model is the
same as in the case of t-J model. The integrated dynamical spin structure
factor spectrum is almost t' independent, and the integrated dynamical spin
susceptibility still shows the particularly universal behavior as
$I(\omega,T)\propto {\rm arctan}[a_{1}\omega/T+a_{3}(\omega/T)^{3}]$.",0004298v2
2004-01-28,Muon-spin-relaxation and magnetic-susceptibility studies of effects of the magnetic impurity Ni on the Cu-spin dynamics and superconductivity in La_2-x_Sr_x_Cu_1-y_Ni_y_O_4_ with x = 0.13,"Effects of the magnetic impurity Ni on the Cu-spin dynamics and
superconductivity have been studied in La_2-x_Sr_x_Cu_1-y_Ni_y_O_4_ with x =
0.13 changing y finely up to 0.10. Compared with the case of the nonmagnetic
impurity Zn, it has been found from the muon-spin-relaxation measurements that
a large amount of Ni is required to stabilize a magnetic order of Cu spins.
However, the evolution toward the stabilization of the magnetic order with
increasing impurity concentration is qualitatively similar to each other. The
area of the non-superconducting and slowly fluctuating or static region of Cu
spins around Ni has been found to be smaller than that around Zn, suggesting
that the pinning of rather long-ranged dynamical spin correlation such as the
so-called dynamical stripe by Ni is weaker than that by Zn. This may be the
reason why Zn destroys the superconductivity in the hole-doped high-T_c_
cuprates more markedly than Ni.",0401566v2
2005-11-02,The deterministic nature of conservative post-Newtonian accurate dynamics of compact binaries with leading order spin-orbit interaction,"We formally show that the conservative second post-Newtonian (PN) accurate
dynamics of spinning compact binaries moving in eccentric orbits, when spin
effects are restricted to the leading order spin-orbit interaction cannot be
chaotic for the following two distinct cases: (i) the binary consists of
compact objects of arbitrary mass, where only one of them is spinning with an
arbitrary spin and (ii) the binary consists of equal mass compact objects,
having two arbitrary spins. We rest our arguments on the recent determination
of PN accurate Keplerian-type parametric solutions to the above cases,
indicating that the PN accurate dynamics is integrable in these two situations.
We compare predictions of our case (i) with those from a numerical
investigation of an equivalent scenario that observed chaos in the associated
dynamics. We also present possible reasons for the discrepancies.",0511009v1
2007-11-27,Non-linear dynamics and two-dimensional solitons for spin $ S=1$ ferromagnets with biquadratic exchange,"We develop a consistent semiclassical theory of spin dynamics for an
isotropic ferromagnet with a spin $ S=1$ taking into consideration both
bilinear and biquadratic over spin operators exchange interaction. For such
non-Heisenberg magnets, a peculiar class of spin oscillations and waves, for
which the quantum spin expectation value $ {\rm {\bf m}}=<{\rm {\bf S}}>$ does
not change it direction, but changes in length, is presented. Such
``longitudinal'' excitations do not exist in regular magnets, dynamics of which
are described in terms of the Landau-Lifshitz equation or by means of the spin
Heisenberg Hamiltonian. We demonstrate the presence of non-linear uniform
oscillations and waves, as well as self-localized dynamical excitations
(solitons) with finite energy. A possibility of excitation of such oscillations
by ultrafast laser pulse is discussed.",0711.4285v1
2008-11-03,Electronic transport driven spin-dynamics,"We propose a model to explore the dynamics of spin-systems coupled by
exchange interaction to the conduction band electrons of a semiconductor
material that forms the channel in a ferromagnet/semiconductor/ferromagnet
spin-valve structure. We show that recent observation of the novel transient
transport signature in a MnAs/GaAs/MnAs spin-valve structure with paramagnetic
Mn impurities [D. Saha et al., Phys. Rev. Lett., 100, 196603 (2008)] can be
quantitatively understood in terms of current driven dynamical polarization of
Mn spins. Using our model of spin polarized transport through Schottky barriers
at the two ferromagnet/semiconductor junctions in a spin-valve structure and a
dynamical equation describing the paramagnetic impurities coupled to conduction
band electrons we explain the scaling behaviour of observed transient features
such as the magnitude and time-scale with temperature.",0811.0204v1
2009-02-11,Electromagnetic Pulse Driven Spin-dependent Currents in Semiconductor Quantum Rings,"We investigate the non-equilibrium charge and spin-dependent currents in a
quantum ring with a Rashba spin orbit interaction (SOI) driven by two
asymmetric picosecond electromagnetic pulses. The equilibrium persistent charge
and persistent spin-dependent currents are investigated as well. It is shown
that the dynamical charge and the dynamical spin-dependent currents vary
smoothly with a static external magnetic flux and the SOI provides a SU(2)
effective flux that changes the phases of the dynamic charge and the dynamic
spin-dependent currents. The period of the oscillation of the total charge
current with the delay time between the pulses is larger in a quantum ring with
a larger radius. The parameters of the pulse fields control to a certain extent
the total charge and the total spin-dependent currents. The calculations are
applicable to nano-meter rings fabricated in heterojuctions of III-V and II-VI
semiconductors containing several hundreds electrons.",0902.1845v1
2009-03-27,Dynamical magnetoelectric effects induced by the Dzyaloshinskii-Moriya interaction in multiferroics,"We study the dynamical interplay between ferroelectricity and magnetism in a
multiferroic with a helical magnetic order. We show that the dynamical
exchange-striction induces a biquadratic interaction between the spins and
transverse phonons resulting in quantum fluctuations of the spontaneous
ferroelectric polarization $\mathbf{P}$ in the ferroelectric phase. The
hybridization between the spin wave and the fluctuation of the electric
polarization leads to low-lying transverse phonon modes. Those are
perpendicular to $\mathbf{P}$ and to the helical spins at small wave vector but
then turn parallel to $\mathbf{P}$ at a wave vector close to the magnetic
modulation vector. For helical magnetic structure, the spin chirality which
determines the direction of $\mathbf{P}$, also possesses a long-range order.
Due to the dynamical Dzyaloshiskii-Moriya interaction, the spin-chirality is
strongly coupled to the spin fluctuation which implies an on-site inversion of
the spin-chirality in the ordered spin-1/2 system and results in a finite
scattering intensity of polarized neutrons from a cycloidal helimagnet.",0903.4751v1
2009-07-13,Spin freezing and dynamics in Ca_{3}Co_{2-x}Mn_{x}O_{6} (x ~ 0.95) investigated with implanted muons: disorder in the anisotropic next-nearest neighbor Ising model,"We present a muon-spin relaxation investigation of the Ising chain magnet
Ca_{3}Co_{2-x}Mn_{x}O_{6} (x~0.95). We find dynamic spin fluctuations
persisting down to the lowest measured temperature of 1.6 K. The previously
observed transition at around T ~18 K is interpreted as a subtle change in
dynamics for a minority of the spins coupling to the muon that we interpret as
spins locking into clusters. The dynamics of this fraction of spins freeze
below a temperature T_{SF}~8 K, while a majority of spins continue to
fluctuate. An explanation of the low temperature behavior is suggested in terms
of the predictions of the anisotropic next-nearest-neighbor Ising model.",0907.2152v1
2009-08-18,Dynamic spin susceptibility in the t-J model,"A relaxation-function theory for the dynamic spin susceptibility in the
$t$--$J$ model is presented. By a sum-rule-conserving generalized mean-field
approximation (GMFA), the two-spin correlation functions of arbitrary range,
the staggered magnetization, the uniform static susceptibility, and the
antiferromagnetic correlation length are calculated in a wide region of hole
doping and temperaturs. A good agreement with available exact diagonalization
(ED) data is found. The correlation length is in reasonable agreement with
neutron-scattering experiments on La_{2-\delta}Sr_\delta)CuO_4. Going beyond
the GMFA, the self-energy is calculated in the mode-coupling approximation. The
spin dynamics at arbitrary frequencies and wave vectors is studied for various
temperatures and hole doping. At low doping a spin-wave-type behavior is found
as in the Heisenberg model, while at higher doping a strong damping caused by
hole hopping occurs, and a relaxation-type spin dynamics is observed in
agreement with the ED results. The local spin susceptibility and its (\omega/T)
scaling behavior are calculated in a reasonable agreement with experimental and
ED data.",0908.2557v2
2010-11-07,Understanding spin glass transition as a dynamic phenomenon,"Existing theories explain spin glass transition in terms of a phase
transition and order parameters, and assume the existence of a distinct spin
glass phase. In addition to problems related to clarifying the nature of this
phase, the common challenge is to explain profound dynamic effects. Here, we
propose that the main experimental results of spin glass transition can be
understood in an entirely dynamic picture, without a reference to a distinct
spin glass phase, phase transition and order parameters. In this theory, the
susceptibility cusp at the glass transition temperature is due to the dynamic
crossover between the high-temperature relaxational and low-temperature spin
wave, or elastic, regime. The crossover takes place when $t=\tau$, where $t$ is
observation time and $\tau$ is relaxation time. Time-dependent effects,
inconsistent with the phase transition approach, and the logarithmic increase
of $T_g$ with field frequency in particular, originate as the immediate
consequence of the proposed picture. We comment on the behavior of non-linear
susceptibility. In our discussion, we explore similarities between the spin and
structural glass transitions.",1011.1676v3
2012-03-05,Coherent multi-flavour spin dynamics in a fermionic quantum gas,"Microscopic spin interaction processes are fundamental for global static and
dynamical magnetic properties of many-body systems. Quantum gases as pure and
well isolated systems offer intriguing possibilities to study basic magnetic
processes including non-equilibrium dynamics. Here, we report on the
realization of a well-controlled fermionic spinor gas in an optical lattice
with tunable effective spin ranging from 1/2 to 9/2. We observe long-lived
intrinsic spin oscillations and investigate the transition from two-body to
many-body dynamics. The latter results in a spin-interaction driven melting of
a band insulator. Via an external magnetic field we control the system's
dimensionality and tune the spin oscillations in and out of resonance. Our
results open new routes to study quantum magnetism of fermionic particles
beyond conventional spin 1/2 systems.",1203.0948v1
2012-03-21,Dynamic spin response of a strongly interacting Fermi gas,"We present an experimental investigation of the dynamic spin response of a
strongly interacting Fermi gas using Bragg spectroscopy. By varying the
detuning of the Bragg lasers, we show that it is possible to measure the
response in the spin and density channels separately. At low Bragg energies,
the spin response is suppressed due to pairing, whereas the density response is
enhanced. These experiments provide the first independent measurements of the
spin-parallel and spin-antiparallel dynamic and static structure factors and
open the way to a complete study of the structure factors at any momentum. At
high momentum the spin-antiparallel dynamic structure factor displays a
universal high frequency tail, proportional to $\omega^{-5/2}$, where $\hbar
\omega$ is the probe energy.",1203.4657v2
2014-07-16,Spin dynamics and magneto-optical response in charge-neutral tunnel-coupled quantum dots,"We model the electron and hole spin dynamics in an undoped double quantum dot
structure, considering the carrier tunneling between quantum dots. Taking into
account also the presence of an in-plane or tilted magnetic field, we provide
the simulation of magneto-optical experiments, like the time resolved Kerr
rotation measurement, which are performed currently on such structures to probe
the temporal spin dynamics. With our model, we reproduce the experimentally
observed effect of the extension of the spin polarization life time caused by
the spatial charge separation, which may occur in structures of this type.
Moreover, we provide a number of qualitative predictions concerning the
necessary conditions for observation of this effect as well as about possible
channels of its suppression, including the spin-orbit coupling, which leads to
tunneling of carriers accompanied by a spin-flip. We consider also the impact
of the magnetic field tilting, which results in an interesting spin
polarization dynamics.",1407.4529v4
2014-08-28,Quench dynamics and statistics of measurements for a line of quantum spins in two dimensions,"Motivated by recent experiments, we investigate the dynamics of a line of
spin-down spins embedded in the ferromagnetic spin-up ground state of a
two-dimensional xxz model close to the Ising limit. In a situation where the
couplings in x and y direction are different, the quench dynamics of this
system is governed by the interplay of one-dimensional excitations (kinks and
holes) moving along the line and single-spin excitations evaporating into the
two-dimensional background. A semiclassical approximation can be used to
calculate the dynamics of this complex quantum system. Recently, it became
possible to perform projective quantum measurements on such spin systems,
allowing to determine, e.g., the z-component of each individual spin. We
predict the statistical properties of such measurements which contain much more
information than correlation functions.",1408.6743v1
2015-01-06,Berry-phase effects and electronic dynamics in noncollinear antiferromagnetic texture,"Antiferromagnets (AFMs), in contrast to ferromagnets, show a nontrivial
magnetic structure with zero net magnetization. However, they share a number of
spintronic effects with ferromagnets, including spin-pumping and spin transfer
torques. Both phenomena stem from the coupled dynamics of free carriers and
localized magnetic moments. In the present paper I study the adiabatic dynamics
of a spin-polarized electrons in a metallic AFM exhibiting a noncollinear
120$^\circ$ magnetic structure. I show that the slowly varying AFM spin texture
produces a non-Abelian gauge potential related to the time/space gradients of
the N\'{e}el vectors. Corresponding emergent electric and magnetic fields
induce rotation of spin and influence the orbital dynamics of free electrons. I
discuss both the possibility of a topological spin Hall effect in the vicinity
of topological AFM solitons with nonzero curvature and rotation of the electron
spin traveling through the AFM domain wall.",1501.01189v2
2015-02-02,An Informal Summary of a New Formalism for Classifying Spin-Orbit Systems Using Tools Distilled from the Theory of Bundles,"We give an informal summary of ongoing work which uses tools distilled from
the theory of fibre bundles to classify and connect invariant fields associated
with spin motion in storage rings. We mention four major theorems. One ties
invariant fields with the notion of normal form, the second allows comparison
of different invariant fields and the two others tie the existence of invariant
fields to the existence of certain invariant sets. We explain how the theorems
apply to the spin dynamics of spin-$1/2$ and spin-$1$ particles. Our approach
elegantly unifies the spin-vector dynamics from the T-BMT equation with the
spin-tensor dynamics and other dynamics and suggests an avenue for addressing
the question of the existence of the invariant spin field.",1502.00538v1
2015-08-07,Spin Dynamics in Driven Composite Multiferroics,"A spin dynamics approach has been used to study the behavior of the magnetic
spins and the electric pseudo-spins in a 1-D composite multiferroic chain with
a linear magneto-electric coupling at the interface. The response is
investigated with either external magnetic or electric fields driving the
system. The spin dynamics is based on the Landau-Lifshitz-Gilbert equation. A
Gaussian white noise is later added into the dynamic process to include the
thermal effects. The interface requires a closer inspection of the
magneto-electric effects. Thus, we construct a 2-D ladder model to describe the
behavior of the magnetic spins and the electric pseudo-spins with different
magneto-electric couplings.",1508.01584v2
2015-10-07,Spin dynamics in paramagnetic diluted magnetic semiconductors,"Microscopic properties of low-energy spin dynamics in diluted magnetic
semiconductor are addressed in a framework of the Kondo lattice model including
random distribution of magnetic dopants. Based on the fluctuation-dissipation
theorem, we derive an explicit dependence of the spin diffusion coefficient on
the single-particle Green function which is directly evaluated by dynamical
mean-field theory. In the paramagnetic state, the magnetic scattering has been
manifested to suppress spin diffusion. In agreement with other ferromagnet
systems, we also point out that the spin diffusion in diluted magnetic
semiconductors at small carrier concentration displays a monotonic $1/T$-like
temperature dependence. By investigating the spin diffusion coefficient on a
wide range of the model parameters, the obtained results have provided a
significant scenario to understand the spin dynamics in the paramagnetic
diluted magnetic semiconductors.",1510.01807v1
2016-04-19,Spin-1 Quantum Walks,"We study the quantum walks of two interacting spin-1 bosons. We derive an
exact solution for the time-dependent wave function that describes the
two-particle dynamics governed by the one-dimensional spin-1 Bose-Hubbard
model. We show that propagation dynamics in real space and mixing dynamics in
spin space are correlated via the spin-dependent interaction in this system.
The spin-mixing dynamics has two characteristic frequencies in the limit of
large spin-dependent interactions. One of the characteristic frequencies is
determined by the energy difference between two bound states, and the other
frequency relates to the cotunneling process of a pair of spin-1 bosons.
Furthermore, we numerically analyze the growth of the spin correlations in
quantum walks. We find that long-range spin correlations emerge showing a clear
dependence on the sign of the spin-dependent interaction and the initial state.",1604.05407v1
2018-04-17,Probing Ferromagnetic Order in Few-Fermion Correlated Spin-Flip Dynamics,"We unravel the dynamical stability of a fully polarized one-dimensional
ultracold few-fermion spin-1/2 gas subjected to inhomogeneous driving of the
itinerant spins. Despite the unstable character of the total spin-polarization
the existence of an interaction regime is demonstrated where the
spin-correlations lead to almost maximally aligned spins throughout the
dynamics. The resulting ferromagnetic order emerges from the build up of
superpositions of states of maximal total spin. They comprise a decaying
spin-polarization and a dynamical evolution towards an almost completely
unpolarized NOON-like state. Via single-shot simulations we demonstrate that
our theoretical predictions can be detected in state-of-the-art ultracold
experiments.",1804.07199v2
2020-07-09,A partially linearized spin-mapping approach for nonadiabatic dynamics. I. Derivation of the theory,"We present a new partially linearized mapping-based approach for
approximating real-time quantum correlation functions in condensed-phase
nonadiabatic systems, called spin-PLDM. Within a classical trajectory picture,
partially linearized methods treat the electronic dynamics along forward and
backward paths separately by explicitly evolving two sets of mapping variables.
Unlike previously derived partially linearized methods based on the
Meyer-Miller-Stock-Thoss mapping, spin-PLDM uses the Stratonovich-Weyl
transform to describe the electronic dynamics for each path within the
spin-mapping space; this automatically restricts the Cartesian mapping
variables to lie on a hypersphere and means that the classical equations of
motion can no longer propagate the mapping variables out of the physical
subspace. The presence of a rigorously derived zero-point energy parameter also
distinguishes spin-PLDM from other partially linearized approaches. These new
features appear to give the method superior accuracy for computing dynamical
observables of interest, when compared with other methods within the same
class. The superior accuracy of spin-PLDM is demonstrated within this paper
through application of the method to a wide range of spin-boson models, as well
as to the Fenna-Matthews-Olsen complex.",2007.05047v2
2014-03-19,"Rabi oscillations, decoherence, and disentanglement in a qubit-spin-bath system: exact dynamics","We examine the influence of environmental interactions on simple quantum
systems by obtaining the exact reduced dynamics of a qubit coupled to a
one-dimensional spin bath. In contrast to previous studies, both the qubit-bath
coupling and the nearest neighbor intrabath couplings are taken as the
spin-flip XX-type. We first study the Rabi oscillations of a single qubit with
the spin bath prepared in a spin coherent state, finding that nonresonance and
finite intrabath interactions have significant effects on the qubit dynamics.
Next, we discuss the bath-induced decoherence of the qubit when the bath is
initially in the ground state, and show that the decoherence properties depend
on the internal phases of the spin bath. By considering two independent copies
of the qubit-bath system, we finally probe the disentanglement dynamics of two
noninteracting entangled qubits. We find that entanglement sudden death appears
when the spin bath is in its critical phase. We show that the single-qubit
decoherence factor is an upper bound for the two-qubit concurrence.",1403.4900v2
2012-04-02,"Spin dynamics of S-state ions in the filled skutterudites La1-xRx$Pt4Ge12 (R= Gd, Eu)","A detailed study of the spin dynamics of the S-state ions Gd3+ and Eu2+ in
the filled skutterudites La1-xRxPt4Ge12 (R= Gd, Eu) is reported. The spin
dynamics is investigated directly by means of Gd3+ and Eu2+ electron spin
resonance (ESR), performed at X-band (~ 9.4 GHz) and Q-band (~ 34 GHz)
frequencies in the temperature intervals 8<T<300 K and 1.5<T<300 K
respectively. The ESR parameters provide direct evidence for the vibrational
behavior of the Gd3+ ions but not for the Eu2+ ions. These results are
interpreted in the light of recent discussions about the spin relaxation in
cage systems. In particular, the Gd3+ spin relaxation in La0.9Gd0.1Pt4Ge12
provide evidence for the existence of an extra phonon mode with an Einstein
temperature (thetaE) ~ 24 K in this system. The work suggests that the
so-called ""rattling"" modes have a general and important role that should be
taken into account in the study of spin dynamics in cage systems.",1204.0481v1
2014-06-13,Dynamical spin effects in ultra-relativistic laser pulses,"The dynamics of single laser-driven electrons and many particle systems with
spin are investigated on the basis of a classical theory. We demonstrate that
the spin forces can alter the electron dynamics in an ultra-relativistic laser
field due to the coupling of the electron's spin degree of freedom to its
kinematic momentum. High-energy electrons can acquire significant
spin-dependent transverse momenta while passing through a counterpropagating
ultra-relativistic infrared laser pulse. Numerical calculations show that the
deflection of the electrons by the laser pulse is determined by the laser
intensity, the pulse duration, and the initial spin orientation of the
electron. We complement our investigation of these dynamical spin effects by
performing particle-in-cell simulations and point out possibilities of an
experimental realization of the predicted effect with available laser
parameters.",1406.3659v1
2019-09-13,Information scrambling and redistribution of quantum correlations through dynamical evolution in spin chains,"We investigate the propagation of local bipartite quantum correlations, along
with the tripartite mutual information to characterize the information
scrambling through dynamical evolution of spin chains. Starting from an initial
state with the first pair of spins in a Bell state, we study how quantum
correlations spread to other parts of the system, using different
representative spin Hamiltonians, viz. the Heisenberg Model, a spin-conserving
model, the transverse-field XY model, a non-conserving but integrable model,
and the kicked Harper model, a spin conserving but nonintegrable model. We show
that the local correlations spread consistently in the case of spin-conserving
dynamics in both integrable and nonintegrable cases, with a strictly
nonnegative tripartite mutual information. In contrast, in the case of
non-conserving dynamics, tripartite mutual information is negative and local
pair correlations do not propagate.",1909.06056v3
2020-12-24,Simulating non-Hermitian dynamics of a multi-spin quantum system and an emergent central spin model,"It is possible to simulate the dynamics of a single spin-$1/2$
($\mathsf{PT~}$ symmetric) system by conveniently embedding it into a subspace
of a larger Hilbert space with unitary dynamics. Our goal is to formulate a
many body generalization of this idea i.e., embedding many body non-Hermitian
dynamics. As a first step in this direction, we investigate embedding of ""$N$""
non-interacting spin-$1/2$ ($\mathsf{PT~}$ symmetric) degrees of freedom,
thereby unfolding the complex nature of such an embedding procedure. It turns
out that the resulting Hermitian Hamiltonian represents a cluster of $N+1$ spin
halves with ""all to all"", $q$-body interaction terms ($q=1,...,N+1$) in which
the additional spin-$1/2$ is a part of the larger embedding space. We can
visualize it as a strongly correlated central spin model with the additional
spin-$1/2$ playing the role of central spin. We find that due to the
orthogonality catastrophe, even a vanishing small exchange field applied along
the anisotropy axis of the central spin leads to a strong suppression of its
decoherence arising from spin-flipping perturbations.",2012.13415v1
2017-05-09,Topological spin dynamics in cubic FeGe near room temperature,"Understanding spin-wave dynamics in chiral magnets is a key step for the
development of high-speed, spin-wave based spintronic devices that take
advantage of chiral and topological spin textures for their operation. Here we
present an experimental and theoretical study of spin-wave dynamics in a cubic
B20 FeGe single crystal. Using the combination of waveguide microwave
absorption spectroscopy (MAS), micromagnetic simulations, and analytical
theory, we identify the resonance dynamics in all magnetic phases (field
polarized, conical, helical, and skyrmion phases). Because the resonance
frequencies of specific chiral spin textures are unique, quantitative agreement
between our theoretical predictions and experimental findings for all resonance
frequencies and spin wave modes enables us to unambiguously identify chiral
magnetic phases and to demonstrate that MAS is a powerful tool to efficiently
extract a magnetic phase diagram. These results provide a new tool to
accelerate the integration of chiral magnetic materials into spintronic
devices.",1705.03397v1
2017-05-10,Interplay of valley polarization and dynamic nuclear polarization in 2D transition metal dichalcogenides,"The interplay of Ising spin-orbit coupling and non-trivial band topology in
transition metal dichalcogenides (TMDs) produces anomalous transport and
optical properties that are very different from a regular 2D electron gas. The
spin-momentum locking of optically excited carriers near a valley point can
give rise to an anomalous spin-valley Hall current under the application of an
in-plane electric field. TMDs also exhibit strong electron-nuclear hyperfine
interactions, but their effect on spin-valley-locked currents remains unknown.
Here, we show that hyperfine interactions can create a feedback mechanism in
which spin-valley currents generate significant dynamical nuclear polarization
which in turn Zeeman shifts excitonic transitions out of resonance with an
optical driving field, saturating the production of spin-valley polarization.
We propose an experimental signature of dynamic nuclear polarization which can
be detected via measurements of the anomalous Hall current. Our results help to
elucidate the interplay of valley polarization and nuclear spin dynamics in
TMDs.",1705.03909v2
2018-08-09,Sub-picosecond molecular dynamics modulate the energies of spin states for hundreds of nanoseconds,"Molecular vibrations are increasingly seen as a key factor for spin dynamics
in single-ion magnets and molecular spin qubits. Herein we show how an
inexpensive combination of molecular dynamics calculations and a crystal field
analysis can be employed to obtain a dynamical picture of the crystal field
splitting. We present the time evolution during 500ns of the spin energy levels
in a terbium complex. Our calculations evidence an amplitude of up to tens of
cm-1 for the oscillations of the spin energy levels in the fs time scale.
Crucially, we also see that the oscillations average out and practically
disappear at longer time scales, thus ruling out the modulation of spin energy
levels by phonons of long wavelength $\lambda$ (up to $\lambda$ = 40 $\AA$).
Our results are compatible with the common approximation of focusing on local
vibrations, but at the same time highlight the risks of assuming that the spin
energy levels are time- and temperature-independent.",1808.03234v1
2019-04-30,Dynamics of strongly coupled disordered dissipative spin-boson systems,"Spin-boson Hamiltonians are an effective description for numerous quantum
many-body systems such as atoms coupled to cavity modes, quantum
electrodynamics in circuits and trapped ion systems. While reaching the limit
of strong coupling is possible in current experiments, the understanding of the
physics in this parameter regime remains a challenge, especially when disorder
and dissipation are taken into account. Here we investigate a regime where the
many-body spin dynamics can be related to a Ising energy function defined in
terms of the spin-boson couplings. While in the coherent weak coupling regime
it is known that an effective description in terms of spin Hamiltonian is
possible, we show that a similar viewpoint can be adopted in the presence of
dissipation and strong couplings. The resulting many-body dynamics features
approximately thermal regimes, separated by out-of-equilibrium ones in which
detailed balance is broken. Moreover, we show that under appropriately chosen
conditions one can even achieve cooling of the spin degrees of freedom. This
points towards the possibility of using strongly coupled dissipative spin-boson
systems for engineering complex energy landscapes together with an appropriate
cooling dynamics.",1904.13181v1
2019-08-13,Ultrafast spin dynamics in the proximate quantum spin liquid α-RuCl3,"{\alpha}-RuCl3 is a Kitaev material suggested to be a proximate quantum spin
liquid in a certain temperature and magnetic field range. Nonequilibrium
measurements of transient dynamics have been proposed to detect fractionalized
particles that emerge in the spin liquid and to possibly drive the system into
novel photoinduced magnetic states that cannot be accessed by conventional
equilibrium probes. Here we study ultrafast spin dynamics of photoinduced
excitations in {\alpha}-RuCl3 using pump-probe transient grating spectroscopy.
In the real part of the complex transient reflectance change {\Delta}R/R, we
observe the long-range antiferromagnetic correlation near the N\'eel
temperature. Most intriguingly, above the N\'eel temperature in the Kitaev
paramagnetic phase, we reveal a photoexcitation component sensitive to the
in-plane magnetic field in the imaginary part of {\Delta}R/R. This component
exhibits two distinct lifetimes of about tens of picoseconds. This
photoexcitation component may be connected to novel photoexcited states in the
Kitaev quantum spin liquid, and its lifetimes likely reflect the dynamics of
unconventional spin excitations in the Kitaev model.",1908.04807v2
2021-03-04,X-Ray Scattering from Light-Driven Spin Fluctuations in a Doped Mott Insulator,"Manipulating spin fluctuations with ultrafast laser pulses is a promising
route to dynamically control collective phenomena in strongly correlated
materials. However, understanding how photoexcited spin degrees of freedom
evolve at a microscopic level requires a momentum- and energy-resolved
characterization of their nonequilibrium dynamics. Here, we study the
photoinduced dynamics of finite-momentum spin excitations in two-dimensional
Mott insulators on a square lattice. By calculating the time-resolved resonant
inelastic x-ray scattering cross-section, we show that an ultrafast pump above
the Mott gap induces a prompt softening of the spin excitation energy,
compatible with a transient renormalization of the exchange interaction. While
spin fluctuations in a hole-doped system (paramagnons) are well described by
Floquet theory, magnons at half filling are found to deviate from this picture.
Furthermore, we show that the paramagnon softening is accompanied by an
ultrafast suppression of $d$-wave pairing correlations, indicating a link
between the transient spin excitation dynamics and superconducting pairing far
from equilibrium.",2103.03369v2
2021-10-12,Dynamics of Spin Helices in the One-Dimensional $XX$ Model,"Motivated by cold-atom experiments and a desire to understand
far-from-equilibrium quantum transport, we analytically study the dynamics of
spin helices in the one-dimensional $XX$ model. We use a Jordan-Wigner
transformation to map the spin chain onto a non-interacting Fermi gas with
simple equations of motion. The resulting dynamics are nontrivial, however, as
the spin-helix initial condition corresponds to a highly nonequilibrium
distribution of the fermions. We find a separation of timescales between the
in-plane and out-of-plane spin dynamics. We gain insights from analyzing the
case of a uniform spin chain and from a semiclassical model. One of our key
findings is that the spin correlation functions decay as $t^{-1/2}$ at long
time, in contrast to the experimentally observed exponential decay.",2110.05972v3
2022-10-28,Digital Quantum Simulation of the Spin-Boson Model under Open System Dynamics,"Digital quantum computers have the potential to simulate complex quantum
systems. The spin-boson model is one of such systems, used in disparate
physical domains. Importantly, in a number of setups, the spin-boson model is
open, i.e. the system is in contact with an external environment which can, for
instance, cause the decay of the spin state. Here we study how to simulate such
open quantum dynamics in a digital quantum computer, for which we use one of
IBM's hardware. We consider in particular how accurate different
implementations of the evolution result as a function of the level of noise in
the hardware and of the parameters of the open dynamics. For the regimes
studied, we show that the key aspect is to simulate the unitary portion of the
dynamics, while the dissipative part can lead to a more noise-resistant
simulation. We consider both a single spin coupled to a harmonic oscillator,
and also two spins coupled to the oscillator. In the latter case, we show that
it is possible to simulate the emergence of correlations between the spins via
the oscillator.",2210.15922v2
2023-01-26,"Optical orientation of excitons in a longitudinal magnetic field in indirect band gap (In,Al)As/AlAs quantum dots with type-I band alignment","The exciton recombination and spin dynamics in (In,Al)As/AlAs quantum dots
(QDs) with indirect band gap and type-I band alignment are studied. The
negligible (less than $0.2~\mu$eV) value of the anisotropic exchange
interaction in these QDs prevents a mixing of the excitonic basis states with
pure spin and allows for the formation of spin polarized bright excitons for
quasi-resonant circularly polarized excitation. In a longitudinal magnetic
field, the recombination and spin dynamics of the excitons are controlled by
the hyperfine interaction between the electron and nuclear spins. A QD blockade
by dark excitons is observed in magnetic field eliminating the impact of the
nuclear spin fluctuations. A kinetic equation model, which accounts for the
population dynamics of the bright and dark exciton states as well as for the
spin dynamics, has been developed, which allows for a quantitative description
of the experimental data.",2301.11138v1
2023-05-25,Dynamics of the antiferromagnetic spin ice phase in pyrochlore spinels,"Motivated by the classical spin-nematic state observed in the breathing
pyrochlore spinel LiGa$_{0.95}$In$_{0.05}$Cr$_4$O$_8$, we theoretically discuss
spin dynamics in models of spin-lattice coupling in these materials.
Semiclassical dynamical simulations successfully recover the key features of
inelastic neutron-scattering experiments on
LiGa$_{0.95}$In$_{0.05}$Cr$_4$O$_8$: a broad finite-energy peak alongside a
continuum of scattering near the (200) wave vector that extends from the
elastic line to high energies. To interpret this result, we develop a
small-fluctuation theory for the spin-ice-like nematic ground states, analogous
to linear spin-wave theory for conventionally ordered magnets, which reproduces
the numerical simulation results quantitatively. In particular, we find that
the inelastic peak is well explained by collective modes confined to
ferromagnetic loops of the underlying nematic order. In addition, we find a
sharp, linearly dispersing mode in the dynamical structure factor, which
originates in long-wavelength fluctuations of the nematic director: We believe
identifying this mode will be an interesting target for future experiments on
these materials. We also outline potential future applications of our methods
to both pyrochlore spinels and other spin-nematic systems.",2305.16386v1
2023-10-02,Breakdown of Linear Spin-Wave Theory in a Non-Hermitian Quantum Spin Chain,"We present the spin-wave theory of the excitation spectrum and quench
dynamics of the non-Hermitian transverse-field Ising model. The complex
excitation spectrum is obtained for a generic hypercubic lattice using the
linear approximation of the Holstein-Primakoff transformation together with the
complex bosonic Bogolyubov transformation. In the one-dimensional case, our
result compares very well with the exact quasiparticle dispersion relation
obtained via a fermionic representation of the problem, at least in the regime
of large dissipation and transverse field. When applied to the quench dynamics
we show however that the linear spin-wave approximation breaks down and the
bosonic theory is plagued by a divergence at finite times. We understand the
origin of this instability using a single mode approximation. While limited to
short times, we show that this approach allows us to characterize the dynamics
arising from the quench of the dissipative term and the structure of the
Lieb-Robinson light-cone of the propagation quantum correlations. Furthermore,
for the one-dimensional case, the linear spin-wave dynamics shows good
agreement with the exact fermionic solution, both for the local magnetization
and the spin-spin correlations.",2310.00985v1
2005-12-14,Quantum theory for electron spin decoherence induced by nuclear spin dynamics in semiconductor quantum computer architectures: Spectral diffusion of localized electron spins in the nuclear solid-state environment,"We consider the decoherence of a single localized electron spin due to its
coupling to the lattice nuclear spin bath in a semiconductor quantum computer
architecture. In the presence of an external magnetic field and at low
temperatures, the dominant decoherence mechanism is the spectral diffusion of
the electron spin resonance frequency due to the temporally fluctuating random
magnetic field associated with the dipolar interaction induced flip-flops of
nuclear spin pairs. The electron spin dephasing due to this random magnetic
field depends intricately on the quantum dynamics of the nuclear spin bath,
making the coupled decoherence problem difficult to solve. We provide a
formally exact solution of this non-Markovian quantum decoherence problem which
numerically calculates accurate spin decoherence at short times, which is of
particular relevance in solid-state spin quantum computer architectures. A
quantum cluster expansion method is developed, motivated, and tested for the
problem of localized electron spin decoherence due to dipolar fluctuations of
lattice nuclear spins. The method is presented with enough generality for
possible application to other types of spin decoherence problems. We present
numerical results which are in quantitative agreement with electron spin echo
measurements in phosphorus doped silicon. We also present spin echo decay
results for quantum dots in GaAs which differ qualitatively from that of the
phosphorus doped silicon system. Our theoretical results provide the ultimate
limit on the spin coherence (at least, as characterized by Hahn spin echo
measurements) of localized electrons in semiconductors in the low temperature
and the moderate to high magnetic field regime of interest in scalable
semiconductor quantum computer architectures.",0512323v3
2022-10-31,How Spin Relaxes and Dephases in Bulk Halide Perovskites,"Spintronics in halide perovskites has drawn significant attention in recent
years, due to highly tunable spin-orbit fields and intriguing interplay with
lattice symmetry. Spin lifetime -- a key parameter that determines the
applicability of materials for spintronics and spin-based quantum information
applications -- has been extensively measured in halide perovskites, but not
yet assessed from first-principles calculations. Here, we leverage our
recently-developed \emph{ab initio} density-matrix dynamics framework to
compute the spin relaxation time ($T_{1}$) and ensemble spin dephasing time
($T_{2}^{*}$) in a prototype halide perovskite, namely CsPbBr$_{3}$ with
self-consistent spin-orbit coupling (SOC) and quantum descriptions of the
electron scattering processes. We also implement the Land\'e $g$-factor for
solids from first principles and take it into account in our dynamics, which is
required to accurately capture spin dephasing at external magnetic fields. We
thereby predict intrinsic spin lifetimes as an upper bound for experiments,
identify the dominant spin relaxation pathways, and evaluate the dependence on
temperature, external fields, carrier density,and impurities. Importantly, we
find that the Fr{\""o}hlich interaction that dominates carrier relaxation
contributes negligibly to spin relaxation, consistent with the spin-conserving
nature of this interaction. We investigated the effect of spin-orbit field with
inversion asymmetry on spin lifetime, and we demonstrated from our calculation,
persistent spin helix can enhance spin lifetime when the spin-split is large,
but it can not be realized by Rashba SOC. Our theoretical approach may lead to
new strategies to optimize spin and carrier transport properties in spintronics
and quantum information applications.",2210.17074v3
2020-03-14,Enhanced longevity of the spin helix in low-symmetry quantum wells,"In a semiconductor, collective excitations of spin textures usually decay
rather fast due to D'yakonov-Perel' spin relaxation. The latter arises from
spin-orbit coupling, which induces wave-vector-dependent spin rotations that,
in conjunction with random disorder scattering, generate spin decoherence.
However, symmetries occurring under certain conditions can prevent the
relaxation of particular homogeneous and inhomogeneous spin textures. The
inhomogeneous spin texture, termed as persistent spin helix, is especially
appealing as it enables us to manipulate the spin orientation while retaining a
long spin lifetime. Recently, it was predicted that such symmetries can be
realized in zinc-blende two-dimensional electron gases if at least two
growth-direction Miller indices agree in modulus and the coefficients of the
Rashba and linear Dresselhaus spin-orbit couplings are suitably matched [PRL
117, 236801 (2016)]. In the present paper, we systematically analyze the impact
of the symmetry-breaking cubic Dresselhaus spin-orbit coupling, which
generically coexists in these systems, on the stability of the emerging spin
helices with respect to the growth direction. We find that, as an interplay
between orientation and strength of the effective magnetic field induced by the
cubic Dresselhaus terms, the spin relaxation is weakest for a low-symmetry
growth direction that can be well approximated by a [225] lattice vector. These
quantum wells yield a 30\% spin-helix lifetime enhancement compared to
[001]-oriented electron gases and, remarkably, require a negligible Rashba
coefficient. The rotation axis of the corresponding spin helix is only slightly
tilted out of the quantum-well plane. This makes the experimental study of the
spin-helix dynamics readily accessible for conventional optical spin
orientation measurements where spins are excited and detected along the
quantum-well growth direction.",2003.06544v2
1994-08-19,Spin dynamics of the doped t-J model,"We present a new method for studying the low energy excitations in finite
cluster systems and apply it to clarify the nature of the low energy spin
excitations in the moderately doped t-J model.
  We find that the character of the low energy spin excitations changes within
the Brillouin zone, with the dominant excitation for momentum transfer (pi,pi)
being a spin wave-like collective mode.
  Spin excitations with momentum transfer different from (pi,pi) have
particle-hole character. We give an explicit construction of a low energy
collective spin mode in a system with `almost broken symmetry' and demonstrate
its validity by explicit numerical check.",9408057v1
2000-12-18,The effects of electron-electron interactions on the spin transport dynamics of a two-dimensional electron gas,"Spin transport properties of a spin-polarized two-dimensional electron gas
are studied in the presence of electron-electron interactions. Longitudinal and
transverse spin diffusion coefficients are calculated with the quantum
transport equation which includes many-particle effects in the random phase
approximation. We find that the $e$-$e$ scattering, which does not contribute
to charge drift mobility, has a significant contribution to the spin diffusion.
Thus, $e$-$e$ interaction causes non-negligible effects on the operations of
proposed devices dependent on spin transport in semiconductor heterostructures.",0012318v2
2001-02-16,Quantum computing with spin qubits in semiconductor structures,"We survey recent work on designing and evaluating quantum computing
implementations based on nuclear or bound-electron spins in semiconductor
heterostructures at low temperatures and in high magnetic fields. General
overview is followed by a summary of results of our theoretical calculations of
decoherence time scales and spin-spin interactions. The latter were carried out
for systems for which the two-dimensional electron gas provides the dominant
carrier for spin dynamics via exchange of spin-excitons in the integer quantum
Hall regime.",0102308v1
2002-04-08,Effective Heisenberg-Model Description of the Coupled Spin-Pseudospin Model for Quarter-Filled Ladders,"Quantum Monte Carlo method is used to study the coupled spin-pseudospin
Hamiltonian in one-dimension (1D) that models the charge-ordering instability
of the anisotropic Hubbard ladder at quarter filling. We calculate the
temperature dependence of the uniform spin susceptibility and the spin and
charge excitation spectra of the system to show that there is a parameter and
temperature region where the spin degrees of freedom behave like a 1D
antiferromagnetic Heisenberg model. Anomalous spin dynamics in the disorder
phase of a typical charge-ordered material $\alpha'$-NaV$_2$O$_5$ is thereby
considered.",0204165v1
2002-09-21,Dynamical spin-electric coupling in a quantum dot,"Due to the spin-orbital coupling in a semiconductor quantum dot, a freely
precessing electron spin produces a time-dependent charge density. This creates
a sizeable electric field outside the dot, leading to promising applications in
spintronics. The spin-electric coupling can be employed for non-invasive single
spin detection by electrical methods. We also consider a spin relaxation
mechanism due to long-range coupling to electrons in gates and elsewhere in the
system, and find a contribution comparable to, and in some cases dominant over
previously discussed mechanisms.",0209507v1
2003-02-17,Finite temperature structure factor in the Haldane-Shastry spin chain,"The Haldane-Shastry spin chain can be mapped to the infinite coupling limit
of the SU(2) spin Calogero-Sutherland model. We use the $\mathfrak{gl}_2$ Jack
polynomials' technology to compute the form factors of the spin operator on the
multi-spinon spectrum. The spin structure factor is obtained through a form
factor expansion. The expansion is proven to converge in the small momentum
limit. Numerics based on two- and four-spinons contributions give an
approximate result for the infinite temperature static and dynamic spin
structure factor.",0302333v2
2003-05-04,Spin-spin correlators in Majorana representation,"In the Majorana representation of a spin 1/2 we find an identity which
relates spin-spin correlators to one-particle fermionic correlators. This
should be contrasted with the straightforward approach in which two-particle
(four-fermion) correlators need to be calculated. We discuss applications to
the analysis of the dynamics of a spin coupled to a dissipative environment and
of a quantum detector performing a continuous measurement of a qubit's state.",0305064v1
2003-10-20,Spin wave spectrum of a disordered double exchange model,"A double exchange model with quenched disorder for conduction electrons is
studied by field theoretical methods. By using a path integral formalism and
replica techniques based on it, an ensemble-averaged spin wave dispersion of
the localized spins is derived. It is shown that the spectrum of the spin wave
has gaps at the multiple of the Fermi wavenumber of the conduction electrons in
the presence of disorder, and hence, quenched disorder for electrons adds a
striking effect to the dynamics of the localized spins. In the strong disorder
limit, the present results suggest spin-glass like behavior due to the
frustration of the exchange coupling.",0310446v1
2004-01-12,Spin accumulation in forward-biased MnAs/GaAs Schottky diodes,"We describe a new means for electrically creating spin polarization in
semiconductors. In contrast to spin injection of electrons by tunneling through
a reverse-biased Schottky barrier, we observe spin accumulation at the
metal/semiconductor interface of forward-biased ferromagnetic Schottky diodes,
which is consistent with a theory of spin-dependent reflection off the
interface. Spatiotemporal Kerr microscopy is used to image the electron spin
and the resulting dynamic nuclear polarization that arises from the non
equilibrium carrier polarization.",0401197v1
2004-04-14,Long wavelength behavior of the dynamical spin-resolved local-field factor in a two-dimensional electron liquid,"The high frequency limits of the singular component $A(\omega)$ of the small
wavevector expansion of the longitudinal (L) and transverse (T) components of
the spin-resolved exchange-correlation kernel tensor $f_{xc,\sigma
\sigma'}^{L,T}(q,\omega)=-v(q)G_{\sigma \sigma'}^{L,T}(q,\omega)$ in a
two-dimensional isotropic electron liquid with arbitrary spin polarization are
studied. Here $G_{\sigma \sigma'}^{L,T}(q,\omega)$ is the spin-resolved local
field factor, $v(q)$ is the Coulomb interaction in momentum space, and $\sigma$
denotes spin. Particularly, the real part of $A(\omega)$ is found to be
logarithmically divergent at large $\omega$. the large wavevetor structure of
the corresponding spin-resolved static structure factor is also established.",0404325v1
2004-06-04,Competition between Spin-Orbit Interaction and Zeeman Coupling in Rashba 2DEGs,"We investigate systematically how the interplay between Rashba spin-orbit
interaction and Zeeman coupling affects the electron transport and the spin
dynamics in InGaAs-based 2D electron gases. From the quantitative analysis of
the magnetoconductance, measured in the presence of an in-plane magnetic field,
we conclude that this interplay results in a spin-induced breaking of time
reversal symmetry and in an enhancement of the spin relaxation time. Both
effects, due to a partial alignment of the electron spin along the applied
magnetic field, are found to be in excellent agreement with recent theoretical
predictions.",0406106v1
2004-06-27,Spin transfer and coherence in coupled quantum wells,"Spin dynamics of optically excited electrons confined in asymmetric coupled
quantum wells are investigated through time resolved Faraday rotation
experiments. The inter-well coupling is shown to depend on applied electric
field and barrier thickness. We observe three coupling regimes: independent
spin precession in isolated quantum wells, incoherent spin transfer between
single-well states, and coherent spin transfer in a highly coupled system.
Relative values of the inter-well tunneling time, the electron spin lifetime,
and the Larmor precession period appear to govern this behavior.",0406668v1
2004-07-21,Spin Gunn Effect,"We predict that the flow of unpolarized current in electron-doped GaAs and
InP at room temperature is unstable at high electric fields to the dynamic
formation of spin-polarized current pulses. Spin-polarized current is
spontaneously generated because the conductivity of a spin-polarized electron
gas differs from that of an unpolarized electron gas, even in the absence of
spin-orbit interaction. Magnetic fields are not required for the generation of
these spin-polarized current pulses, although they can help align the
polarization of sequential pulses along the same axis.",0407547v1
2004-10-29,How many electrons are needed to flip a local spin?,"Considering the spin of a local magnetic atom as a quantum mechanical
operator, we illustrate the dynamics of a local spin interacting with a
ballistic electron represented by a wave packet. This approach improves the
semi-classical approximation and provides a complete quantum mechanical
understanding for spin transfer phenomena. Sending spin-polarized electrons
towards a local magnetic atom one after another, we estimate the minimum number
of electrons needed to flip a local spin.",0410775v1
2005-01-13,Electron spin interferometry using a semiconductor ring structure,"A ring structure fabricated from GaAs is used to achieve interference of the
net spin polarization of conduction band electrons. Optically polarized spins
are split into two packets by passing through two arms of the ring in the
diffusive transport regime. Optical pumping with circularly polarized light on
one arm establishes dynamic nuclear polarization which acts as a local
effective magnetic field on electron spins due to the hyperfine interaction.
This local field causes one spin packet to precess faster than the other,
thereby controlling the spin interference when the two packets are combined.",0501306v1
2005-08-25,Current-induced Vortex Motion by Spin-Transfer Torque,"We investigate the dynamics of a magnetic vortex driven by spin-transfer
torque due to spin current in the adiabatic case. The vortex core represented
by collective coordinate experiences a transverse force proportional to the
product of spin current and gyrovector, which can be interpreted as the
geometric force determined by topological charges. We show that this force is
just a reaction force of Lorentz-type force from the spin current of conduction
electrons. Based on our analyses, we propose analytically and numerically a
possible experiment to check the vortex displacement by spin current in the
case of single magnetic nanodot.",0508599v1
2005-08-30,Effects of spin current on ferromagnets,"When a spin-polarized current flows through a ferromagnet, the local
magnetization receives a spin torque. Two consequences of this spin torque are
studied. First, the uniformly magnetized ferromagnet becomes unstable if a
sufficiently large current is applied. The characteristics of the instability
include spin wave generation and magnetization chaos. Second, the spin torque
has profound effects on the structure and dynamics of the magnetic domain wall.
A detail analysis on the domain wall mass, kinetic energy and wall depinning
threshold is given.",0508735v1
2005-09-14,Dissipation through spin Coulomb drag in electronic spin dynamics,"Spin Coulomb drag (SCD) constitutes an intrinsic source of dissipation for
spin currents in metals and semiconductors. We discuss the power loss due to
SCD in potential spintronics devices and analyze in detail the associated
damping of collective spin-density excitations. It is found that SCD
contributes substantially to the linewidth of intersubband spin plasmons in
parabolic quantum wells, which suggests the possibility of a purely optical
quantitative measurement of the SCD effect by means of inelastic light
scattering.",0509362v1
2005-12-19,Intrinsic vs. Extrinsic Spin Currents. Old Ideas in a New Light,"We have described the electron spin dynamics in the presence of Rashba spin-
orbit interaction and disorder using the spin-density matrix method. We showed
that in the Born approximation in the scattering amplitude the spin current is
zero for an arbitrary ratio of the spin-orbit splitting and the scattering rate
and for an arbitrary disorder potential. We also describe some magnetotransport
phenomena such as negative magnetoresistance and a negative charge Hall effect
which occur in the presence of spin-orbit coupling.",0512458v1
2006-01-24,MnO Spin-Wave Dispersion Curves from Powder Diffraction Data,"We describe a model-independent approach for the extraction of spin-wave
dispersion curves from neutron total scattering data. The method utilises a
statistical analysis of real-space spin configurations to calculate
spin-dynamical quantities. The RMCProfile implementation of the reverse Monte
Carlo refinement process is used to generate a large ensemble of supercell spin
configurations from powder diffraction data. Our analysis of these
configurations gives spin-wave dispersion curves that agree well with those
determined independently using neutron triple-axis spectroscopic techniques.",0601558v2
2006-11-28,Generation of dc spin current in a narrow channel with Rashba and Dresselhaus spin-orbit interaction,"We consider a finite range ac-biased front gate acting upon a quantum channel
with Rashba and Dresselhaus spin-orbit interaction effects. The ac-biased gate,
giving rise to a dynamical Rashba coupling, causes spin-resolved coherent
resonant inelastic scattering. A pure dc spin current is subsequently generated
without accompanying charge current. In the presence of Dresselhaus effect, the
dc spin current is suppressed in the low kinetic energy regime but is assisted
in the high kinetic energy regime.",0611703v1
2007-01-25,Current-induced spin polarization and the spin Hall effect: a quasiclassical approach,"The quasiclassical Green function formalism is used to describe charge and
spin dynamics in the presence of spin-orbit coupling. We review the results
obtained for the spin Hall effect on restricted geometries. The role of
boundaries is discussed in the framework of spin diffusion equations.",0701629v1
1996-11-06,Spin asymmetries of the proton-proton elastic scattering at HERA-N,"The spin correlation parameters, polarization - $A_{N}$ and double spin
correlation parameters - $A_{NN}$, are calculated in the framework of dynamical
model (GKS) of the hadron-hadron interection in the whole region of small
angles and for energy HERA-N $\sqrt{s}=40 GeV$. It is shown that the
measurements of such spin effects at small trunsfer momenta, in the region of
the dip structure and at $t=-4 GeV^{2}$ have to give significant values of such
spin correlation parameters.",9611252v1
2004-11-17,Spin Oscillations in Storage Rings,"The dependence of the particle rotation frequency on the particle orbit
perturbations is found. The exact equation of spin motion in the cylindrical
coordinate system is derived. The calculated formula for the frequency of g-2
precession is in the best agreement with previous results. Nevertheless, this
formula contains the additional oscillatory term that can be used for fitting.
The influence of spin oscillations on the spin dynamics in the EDM experiment
is negligible.",0411225v1
2000-07-06,Spin Structure of Many-Body Systems with Two-Body Random Interactions,"We investigate the spin structure of many-fermion systems with a
spin-conserving two-body random interaction. We find a strong dominance of
spin-0 ground states and considerable correlations between energies and wave
functions of low-lying states with different spin, but no indication of
pairing. The spectral densities exhibit spin-dependent shapes and widths, and
depend on the relative strengths of the spin-0 and spin-1 couplings in the
two-body random matrix. The spin structure of low-lying states can largely be
explained analytically.",0007013v1
2001-02-21,Spin-orbital motion and Thomas precession in the classical and quantum theories,"The motion of a magnetic spin particle in electromagnetic fields is
considered on the basis of general principles of the classical relativistic
theory. Alternative approaches in derivation of the equations of charge motion
and spin precession, the problem of noncollinearity of the momentum and
velocity of a particle with spin, the origin and the meaning of Thomas
precession in dynamics of the spin particle are also considered. The
correspondence principle in the spin theory is discussed.",0102107v1
2007-05-29,Parametric spin excitations in lateral quantum dots,"In this work, the spin dynamics of a single electron under parametric
modulation of a lateral quantum dot's electrostatic potential in the presence
of spin-orbit coupling is investigated. Numerical and theoretical calculations
demonstrate that, by squeezing and/or moving the electron's wave function, spin
rotations with Rabi frequencies on the order of tens of megahertz can be
achieved with experimentally accessible parameters in both parabolic and square
lateral quantum dots. Applications of parametric excitations for determining
spin-orbit coupling parameters and for increasing the spin polarization in the
electronic ground are demonstrated.",0705.4231v2
2007-11-21,Dynamic nuclear polarization and Knight shift measurements in a breakdown regime of integer quantum Hall effect,"Nuclear spins are polarized electrically in a breakdown regime of an
odd-integer quantum Hall effect (QHE). Electron excitation to the upper Landau
subband with the opposite spin polarity flips nuclear spins through the
hyperfine interaction. The polarized nuclear spins reduce the spin-splitting
energy and accelerate the QHE breakdown. The Knight shift of the nuclear spins
is also measured by tuning electron density during the irradiation of
radio-frequency magnetic fields.",0711.3259v1
2007-12-12,Comment on `On the next-to-leading order gravitational spin(1)-spin(2) dynamics' by J. Steinhoff et al,"In this comment we explain the discrepancy found between the results in
arXiv:0712.1716v1 for the 3PN spin-spin potential and those previously derived
in gr-qc/0604099. We point out that to compare one must include sub-leading
lower order spin-orbit effects which contribute to the spin-spin potential once
one transforms to the PN frame. When these effects are included the results in
arXiv:0712.1716v1 do indeed reproduce those found in gr-qc/0604099.",0712.2032v1
2008-04-09,Electric field control of spin-orbit splittings in GaAs/AlGaAs coupled quantum wells,"Electron spin dynamics is investigated in n-i-n GaAs/AlGaAs coupled quantum
wells. The electron spin dephasing time is measured as a function of an
external electrical bias under resonant excitation of the 1sHH intrawell
exciton using a time-resolved Kerr rotation technique. It is found a strong
electron spin dephasing time anisotropy caused by an interference of the
structure inversion asymmetry and the bulk inversion asymmetry. This anisotropy
is shown to be controlled by an electrical bias. A theoretical analysis of
electron spin dephasing time anisotropy is developed. The ratio of Rashba and
Dresselhaus spin splittings is studied as a function of applied bias.",0804.1483v1
2008-05-15,Spin polarizations and spin Hall currents in a two-dimensional electron gas with magnetic impurities,"We consider a two-dimensional electron gas in the presence of Rashba
spin-orbit coupling, and study the effects of magnetic s-wave impurities and
long-range non-magnetic disorder on the spin-charge dynamics of the system. We
focus on voltage induced spin polarizations and their relation to spin Hall
currents. Our results are obtained using the quasiclassical Green function
technique, and hold in the full range of the disorder parameter $\alpha
p_F\tau$.",0805.2346v2
2008-09-05,Multiple Quantum NMR and Entanglement Dynamics in Dipolar Coupling Spin,"We investigate numerically the time dependence of the multiple quantum
coherences and entanglement in linear chains up to nine nuclear spins of 1/2
coupled by the dipole-dipole interactions. Two models are considered: (1) a
spin chain with nearest-neighbor dipole -dipole interactions; (2) a more
realistic model with interactions between all spins. It is shown that the
entangled states appear between remote particles which do not interact directly
(model 1), while the interaction between all spins (model 2) not always results
in entanglement between remote spins.",0809.1049v1
2009-01-01,Generation of GHZ and W states for stationary qubits in spin network via resonance scattering,"We propose a simple scheme to establish entanglement among stationary qubits
based on the mechanism of resonance scattering between them and a
single-spin-flip wave packet in designed spin network. It is found that through
the natural dynamical evolution of an incident single-spin-flip wave packet in
a spin network and the subsequent measurement of the output single-spin-flip
wave packet,multipartite entangled states among n stationary qubits,
Greenberger-Horne-Zeilinger (GHZ) and W states can be generated.",0901.0161v2
2009-01-20,Role of Bound Magnon in Magnetic Domain Wall Motion,"We report on a quantum description of the domain wall (DW) motion under a
spin current. A bound magnon, which is the zero mode of DW, is found to play a
dominant role in DW dynamics. The bound magnon acquires its inertia by the hard
axis anisotropy and is a free particle even under the spin current. The full
transfer of spin angular momentum from the spin current to DW via the bound
magnon leads to the DW motion with the adiabatic velocity, decoupling of spin
waves from DW, and no Doppler shift in spin waves.",0901.3066v1
2009-08-20,Theory of anisotropic exchange in laterally coupled quantum dots,"The effects of spin-orbit coupling on the two-electron spectra in lateral
coupled quantum dots are investigated analytically and numerically. It is
demonstrated that in the absence of magnetic field the exchange interaction is
practically unaffected by spin-orbit coupling, for any interdot coupling,
boosting prospects for spin-based quantum computing. The anisotropic exchange
appears at finite magnetic fields. A numerically accurate effective spin
Hamiltonian for modeling spin-orbit-induced two-electron spin dynamics in the
presence of magnetic field is proposed.",0908.2961v2
2010-02-17,Isothermal remanent magnetization and the spin dimensionality of spin glasses,"The isothermal remanent magnetization is used to investigate dynamical
magnetic properties of spatially three dimensional spin glasses with different
spin dimensionality (Ising, XY, Heisenberg). The isothermal remanent
magnetization is recorded vs. temperature after intermittent application of a
weak magnetic field at a constant temperature $T_h$. We observe that in the
case of the Heisenberg spin glasses, the equilibrated spin structure and the
direction of the excess moment are recovered at $T_h$. The isothermal remanent
magnetization thus reflects the directional character of the
Dzyaloshinsky-Moriya interaction present in Heisenberg systems.",1002.3209v1
2010-04-05,Spin Modulation in Semiconductor Lasers,"We provide an analytic study of the dynamics of semiconductor lasers with
injection (pump) of spin-polarized electrons, previously considered in the
steady-state regime. Using complementary approaches of quasi-static and small
signal analyses, we elucidate how the spin modulation in semiconductor lasers
can improve performance, as compared to the conventional (spin-unpolarized)
counterparts. We reveal that the spin-polarized injection can lead to an
enhanced bandwidth and desirable switching properties of spin-lasers.",1004.0719v1
2011-01-18,Effects of interaction and polarization on spin-charge separation: A time-dependent spin-density-functional theory study,"We calculate the nonequilibrium dynamic evolution of a one-dimensional system
of two-component fermionic atoms after a strong local quench by using a
time-dependent spin-density-functional theory. The interaction quench is also
considered to see its influence on the spin-charge separation. It is shown that
the charge velocity is larger than the spin velocity for the system of on-site
repulsive interaction (Luttinger liquid), and vise versa for the system of
on-site attractive interaction (Luther-Emery liquid). We find that both the
interaction quench and polarization suppress the spin-charge separation.",1101.3373v1
2011-03-30,Photo-induced spin filtering in a double quantum dot,"We investigate the spin-resolved electron dynamics in a double quantum dot
driven by ultrafast asymmetric electromagnetic pulses. Using a analytical model
we show that applying an appropriate pulse sequence allows to control
coherently the spin degree of freedom on the femtosecond time scale. It can be
achieved that the spin-up state is localized in a selected quantum dot while
the spin-down state remains in the other dot. We show that this photo-induced
spin-dependent separation can be maintained for a desired period of time.",1103.5866v3
2011-05-26,Measurement of non-commuting spin components using spin-orbit interaction,"We analyze the physical meaning of a possible experiment aimed at the
simultaneous measurement of two non-commuting spin components. We demonstrate
that switching of a strong spin-orbit interaction, e.g., in a solid state or a
cold-atom system, for a short period of time simulates a simultaneous von
Neumann measurement of spin components, $\sigma_x$ and $\sigma_y$. By mapping
spin dynamics onto coordinate-space motion, such a measurement determines time
averages of $\sigma_x$ and $\sigma_y$ which, unlike their instantaneous values,
may be evaluated simultaneously to an arbitrary accuracy.",1105.5359v2
2011-06-15,Spin Scissors Mode and the Fine Structure of M1 States in Nuclei,"The coupled dynamics of low lying modes, including the scissors mode, and
various giant quadrupole resonances are studied with the help of the Wigner
Function Moments method generalized to take into account spin degrees of
freedom. Equations of motion for collective variables are derived on the basis
of Time Dependent Hartree-Fock equations in the model of harmonic oscillator
with spin orbital mean field potential plus quadrupole-quadrupole residual
interaction. Introducing spin allows one to consider new types of nuclear
collective motion where the nucleons with spin 'up' oscillate against nucleons
with spin 'down'.",1106.2963v1
2012-07-29,Squeezing of Collective Excitations in Spin Ensembles,"We analyse the possibility to create two-mode spin squeezed states of two
separate spin ensembles by inverting the spins in one ensemble and allowing
spin exchange between the ensembles via a near resonant cavity field. We
investigate the dynamics of the system using a combination of numerical and
analytic calculations, and we obtain squeezing for a wide range of parameters.
We also investigate the transfer of the squeezing properties to the cavity
field and to an output mode from the cavity. Finally, we investigate how the
squeezing is affected by effects of inhomogeneities which would be present in
solid state implementations of the spin ensembles.",1207.6772v1
2012-10-04,All Spin Nano-magnetic State Elements,"We propose an all spin state element to enable all spin state machines using
spin currents and nanomagnets. We demonstrate via numerical simulations the
operation of a state element a critical building block for synchronous,
sequential logic computation. The numerical models encompass
Landau-Lifshitz-Gilbert (LLG) nanomagnet dynamics with stochastic models and
vector spin-transport in metallic magnetic and non-magnetic channels. Combined
with all spin combinatorial logic, the state elements can enable synchronous
and asynchronous computing elements.",1210.1613v1
2013-05-04,Role of the Non-Collinear Polarizer Layer in Spin Transfer Torque Switching Processes,"We have recently reported that the spin transfer torque switching current
density is very sensitive to not only the junction sizes but also the exchange
stiffness constants of the free layer according to the micromagnetic
simulations. The results are very complicate and far from the macro-spin model
because of the non-coherent spin switching processes. The dependence of the
switching current density on the junction sizes and the exchange stiffness
constants becomes systematic when we employ the non-collinear polarizer layer.
It is found that the non-collinear polarizer layer enhances the coherency of
the spin dynamics by breaking symmetric spin configurations.",1305.0869v1
2013-12-04,Excitations and quasi-one-dimensionality in field-induced nematic and spin density wave states,"We study the excitation spectrum and dynamical response functions for several
quasi-one-dimensional spin systems in magnetic fields without dipolar spin
order transverse to the field. This includes both nematic phases, which harbor
""hidden"" breaking of spin-rotation symmetry about the field and have been
argued to occur in high fields in certain frustrated chain systems with
competing ferromagnetic and antiferromagnetic interactions, and spin density
wave states, in which spin-rotation symmetry is truly unbroken. Using
bosonization, field theory, and exact results on the integrable sine-Gordon
model, we establish the collective mode structure of these states, and show how
they can be distinguished experimentally.",1312.0992v1
2014-02-26,Spin nematic interaction in multiferroic compound Ba$_{2}$CoGe$_{2}$O$_{7}$,"We demonstrate the existence of the spin nematic interactions in an
easy-plane type antiferromagnet Ba$_{2}$CoGe$_{2}$O$_{7}$ by exploring the
magnetic anisotropy and spin dynamics. Combination of neutron scattering and
magnetic susceptibility measurements reveals that the origin of the in-plane
anisotropy is an antiferro-type interaction of the spin nematic operator. The
relation between the nematic operator and the electric polarization in the
ligand symmetry of this compound is presented. The introduction of the spin
nematic interaction is useful to understand the physics of spin and electric
dipole in multiferroic compounds.",1402.6436v1
2014-07-29,Quantum Model Of Spin Noise,"Any ensemble of quantum particles exhibits statistical fluctuations known as
spin noise. Here, we provide a description of spin noise in the language of
open quantum systems. The description unifies the signatures of spin noise
under both strong and weak measurements. Further, the model accounts for
arbitrary spin dynamics from an arbitrary initial state. In all cases we can
find both the spin noise and its time correlation function.",1407.7620v2
2014-07-29,Spin-Hall Nano-oscillator: a micromagnetic study,"This letter studies the dynamical behavior of spin-Hall nanoscillators from a
micromagnetic point of view. The model parameters have been identified by
reproducing recent experimental data quantitatively. Our results indicate that
a strongly localized mode is observed for in-plane bias fields such as in the
experiments, while predict the excitation of an asymmetric propagating mode for
large enough out-of plane bias field similarly to what observed in spin-torque
nanocontact oscillators. Our findings show that spin-Hall nanoscillators can
find application as spin-wave emitters for magnonic applications where spin
waves are used for transmission and processing information on nanoscale.",1407.7655v1
2014-10-06,Suppressed decay of a laterally confined persistent spin helix,"We experimentally investigate the dynamics of a persistent spin helix in
etched GaAs wire structures of 2 to 80 um width. Using magneto-optical Kerr
rotation with high spatial resolution, we determine the lifetime of the spin
helix. A few nanoseconds after locally injecting spin polarization into the
wire, the polarization is strongly enhanced as compared to the two-dimensional
case. This is mostly attributed to a transition to one-dimensional diffusion,
strongly suppressing diffusive dilution of spin polarization. The intrinsic
lifetime of the helical mode is only weakly increased, which indicates that the
channel confinement can only partially suppress the cubic Dresselhaus
spin-orbit interaction.",1410.1470v1
2015-03-23,Spin-Orbit Torques in Two-Dimensional Rashba Ferromagnets,"Magnetization dynamics in single-domain ferromagnets can be triggered by
charge current if spin-orbit coupling is sufficiently strong. We apply
functional Keldysh theory to investigate Rashba spin-orbit torques in metallic
two-dimensional ferromagnets. A reactive, anti-damping-like spin-orbit torque
as well as a dissipative, field-like torque are calculated microscopically, to
the leading order in the spin-orbit interaction strength. By calculating the
first vertex correction we show that the intrinsic anti-damping-like torque
vanishes unless the scattering rates are spin-dependent.",1503.06872v2
2015-07-22,Spin currents of exciton polaritons in a microcavity with (110)-oriented quantum well,"We study the polarization optical properties of microcavities with embedded
(110)-oriented quantum wells. The spin dynamics of exciton polaritons in such
structures is governed by the interplay of the spin-orbit splitting of exciton
states, which is odd in the in-plane momentum, and the longitudinal-transverse
splitting of cavity modes, which is even in the momentum. We demonstrate the
generation of polariton spin currents by linearly polarized optical pump and
analyze the arising polariton spin textures in the cavity plane. Tuning the
excitation spot size, which controls the polariton distribution in the momentum
space, one obtains symmetric or asymmetric spin textures.",1507.06205v1
2015-09-14,Spin Transport in Antiferromagnetic Insulators Mediated by Magnetic Correlations,"We report a systematic study of spin transport in antiferromagnetic (AF)
insulators having a wide range of ordering temperatures. Spin current is
dynamically injected from Y3Fe5O12 (YIG) into various AF insulators in
Pt/insulator/YIG trilayers. Robust, long-distance spin transport in the AF
insulators is observed, which shows strong correlation with the AF ordering
temperatures. We find a striking linear relationship between the spin decay
length in the AFs and the damping enhancement in YIG, suggesting the critical
role of magnetic correlations in the AF insulators as well as at the AF/YIG
interfaces for spin transport in magnetic insulators.",1509.04336v1
2016-03-24,Semiclassical Landau quantization of spin-orbit coupled systems,"A semiclassical quantization condition is derived for Landau levels in
general spin-orbit coupled systems. This generalizes the Onsager quantization
condition via a matrix-valued phase which describes spin dynamics along the
classical cyclotron trajectory. We discuss measurement of the matrix phase via
magnetic oscillations and electron spin resonance, which may be used to probe
the spin structure of the precessing wavefunction. We compare the resulting
semiclassical spectrum with exact results which are obtained for a variety of
spin-orbit interactions in 2D systems.",1603.07450v1
2018-04-10,Conversion of Heat into Charge Current by the Spin Wave Anomalous Nernst Effect,"A novel process of spin conversion from a temperature gradient to a
transverse voltage is addressed in this paper, viz. the anomalous Nernst effect
(ANE) in a ferromagnetic metal. We report that an additional voltage is
superposed on the conventional anomalous Nernst voltage in FePt crystalline
thin films. The dynamics of the local magnetization is modulated by the heat
current and excites spin waves. These generate a conduction electron spin
current via s-d coupling, which flows along the temperature gradient, and the
spin current is converted to a Nernst voltage by the inverse spin Hall effect.",1804.03751v1
2018-10-09,The spin-s homogeneous central spin model: exact spectrum and dynamics,"We consider the problem of a central spin with arbitrary spin s that
interacts pairwise and uniformly with a bath of N spins with s=1/2. We present
two approaches for determining the exact spectrum of this model, one based on
properties of SU(2), and the other based on integrability. We also analyze the
exact time evolution of a spin coherent state, and compute the time evolution
of various quantities of physical interest, including the entanglement entropy,
spin polarization and Loschmidt echo.",1810.03937v1
2018-10-17,Out-of-plane auto-oscillation in spin Hall oscillator with additional polarizer,"The theoretical investigation on magnetization dynamics excited by the spin
Hall effect in metallic multilayers having two ferromagnets is discussed. The
relaxation of the transverse spin in one ferromagnet enables us to manipulate
the direction of the spin-transfer torque excited in another ferromagnet,
although the spin-polarization originally generated by the spin Hall effect is
geometrically fixed. Solving the Landau-Lifshitz-Gilbert-Slonczewski equation,
the possibility to excite an out-of-plane auto-oscillation of an in-plane
magnetized ferromagnet is presented. An application to magnetic recording using
microwave-assisted magnetization reversal is also discussed.",1810.07831v1
2020-01-23,Bright solitons in a spin-tensor-momentum-coupled Bose-Einstein condensate,"Synthetic spin-tensor-momentum coupling has recently been proposed to realize
in atomic Bose-Einstein condensates. Here we study bright solitons in
Bose-Einstein condensates with spin-tensor-momentum coupling and spin-orbit
coupling. The properties and dynamics of spin-tensor-momentum-coupled and
spin-orbit-coupled bright solitons are identified to be different. We
contribute the difference to the different symmetries.",2001.08794v1
2021-01-28,New Developments in Relativistic Fluid Dynamics with spin,"In this work, we briefly review the progress made in the formulation of
hydrodynamics with spin with emphasis on the application to the relativistic
heavy-ion collisions. In particular, we discuss the formulation of
hydrodynamics with spin for perfect-fluid and the first order viscous
corrections with some discussion on the calculation of spin kinetic
coefficients. Finally, we apply relativistic hydrodynamics with spin to the
relativistic heavy-ion collisions to calculate the spin polarization of
$\Lambda$-particles.",2101.11964v2
2017-05-11,Stimulated Raman Adiabatic control of a nuclear spin in diamond,"Coherent manipulation of nuclear spins is a highly desirable tool for both
quantum metrology and quantum computation. However, most of the current
techniques to control nuclear spins lack of being fast impairing their
robustness against decoherence. Here, based on Stimulated Raman Adiabatic
Passage, and its modification including shortcuts to adiabaticity, we present a
fast protocol for the coherent manipulation of nuclear spins. Moreover, we show
how to initialise a nuclear spin starting from a thermal state, and how to
implement Raman control for performing Ramsey spectroscopy to measure the
dynamical and geometric phases acquired by nuclear spins.",1705.04229v1
2017-05-15,Reverse engineering protocols for controlling spin dynamics,"We put forward reverse engineering protocols to shape in time the components
of the magnetic field to manipulate a single spin, two independent spins with
different gyromagnetic factors, and two interacting spins in short amount of
times. We also use these techniques to setup protocols robust against the exact
knowledge of the gyromagnetic factors for the one spin problem, or to generate
entangled states for two or more spins coupled by dipole-dipole interactions.",1705.05164v1
2019-03-04,Subspace controllability of bipartite symmetric spin networks under global control,"We consider a class of spin networks where each spin in a certain set
interacts, via Ising coupling, with a set of central spins, and the control
acts simultaneously on all the spins. This is a common situation for instance
in NV centers in diamonds, and we focus on the physical case of up to two
central spins. Due to the permutation symmetries of the network, the system is
not globally controllable but it displays invariant subspaces of the underlying
Hilbert space. The system is said to be subspace controllable if it is
controllable on each of these subspaces. We characterize the given invariant
subspaces and the dynamical Lie algebra of this class of systems and prove
subspace controllability in every case.",1903.01429v1
2021-04-05,Thermal Hall Effect of Chiral Spin Fluctuations,"Using a two-dimensional square lattice Heisenberg model with a Rashba-type
Dzyaloshinskii-Moriya interaction, we demonstrate that chiral spin fluctuations
can give rise to a thermal Hall effect in the absence of any static spin
texture or momentum space topology. It is shown by means of Monte Carlo and
stochastic spin dynamics simulations that the thermal Hall response is finite
at elevated temperature outside of the linear spin wave regime and consistent
with the presence of thermal fluctuation-induced nontrivial topology. Our
result suggests that the high-fluctuation phases outside of the conventional
regime of magnonics may yet be a promising area of exploration for spin-based
electronics.",2104.02168v1
2021-07-14,Transitionless quantum driving in spin echo,"Spin echo can be used to refocus random dynamical phases caused by
inhomogeneities in control fields and thereby retain the purity of a spatial
distribution of quantum spins. This technique for accurate spin control is an
essential ingredient in many applications, such as nuclear magnetic resonance,
magnetic resonance imaging, and quantum information processing. Here, we show
how all the elements of a spin echo sequence can be performed at high speed by
means of transitionsless quantum driving. This technique promises accurate
control of rapid quantum spin evolution. We apply the scheme to universal
nonadiabatic geometric single- and two-qubit gates in a nuclear magnetic
resonance setting.",2107.06598v2
2022-03-03,Low-Energy Excitations of Skyrmion Crystals in a Centrosymmetric Kondo-Lattice Magnet: Decoupled Spin-Charge Excitations and Nonreciprocity,"We theoretically study spin and charge excitations of skyrmion crystals
stabilized by conduction-electron-mediated magnetic interactions via
spin-charge coupling in a centrosymmetric Kondo-lattice model by large-scale
spin-dynamics simulations combined with the kernel polynomial method. We reveal
clear segregation of spin and charge excitation channels and nonreciprocal
nature of the spin excitations governed by the Fermi-surface geometry, which
are unique to the skyrmion crystals in centrosymmetric itinerant hosts and can
be a source of novel physical phenomena.",2203.01496v2
2022-03-13,Spin-chain-star systems: entangling multiple chains of spin qubits,"We consider spin-chain-star systems characterized by N-wise many-body
interactions between the spins in each chain and the central one. We show that
such systems can be exactly mapped into standard spin-star systems through
unitary transformations. Such an approach allows the solution of the dynamic
problem of an XX spin-chain-star model and transparently shows the emergence of
quantum correlations in the system, based on the idea of entanglement between
chains.",2203.06711v1
2023-06-30,Phase transition in fluctuations of interacting spins at infinite temperature,"The high temperature limit of interacting spins is usually not associated
with ordering or critical phenomena. Nevertheless, spontaneous fluctuations of
a local spin polarization at equilibrium have nontrivial dynamics even in this
limit. Here, we demonstrate that the spin noise power spectrum of these
fluctuations can undergo discontinuous changes as a function of an external
magnetic field. As a simple illustration, we consider a model of Ising-like
long range spin-spin interactions with a transverse magnetic field as a control
parameter. This system undergoes a phase transition associated with
disappearance of the noise power peak responsible for the most detrimental
decoherence effect of the interactions. \end{abstract}",2306.17398v1
2023-10-17,Optical Regulation of Chiral-Induced Spin Selectivity,"We present a non-perturbative theory that describes how light regulates
chiral-induced spin selectivity (CISS) from the perspective of strong
light-matter interactions. The research results indicate that 1) light can have
opposite effects on the CISS, 2) the difference in CISS is caused by the steady
states of nuclei coupled to spin electrons and 3) this steady state differences
are caused by the different light-induced Lorentz forces felt by spin-up and
spin-down electrons. The fundamental reason for these results is the impact of
light on spin-orbital coupling (SOC), which is a complex process. This
theoretical framework is verified by the calculations of Floquet SOC
non-adiabatic nuclear dynamics.",2310.10929v1
2023-10-26,Gravitational Spin Hall Effect of Dirac Particle and the Weak Equivalence Principle,"We present a spin-induced none-geodesic effect of Dirac wave packets in a
static uniform gravitational field. Our approach is based on the
Foldy-Wouthuysen transformation of Dirac equation in a curved spacetime, which
predicts the gravitational spin-orbit coupling. Due to this coupling, we find
that the dynamics of the free-fall Dirac wave packets with opposite spin
polarization will yield the transverse splitting in the direction perpendicular
to spin orientation and gravity, which is known as the gravitational spin Hall
effect. Even in a static uniform gravitational field, such effect suggests that
the weak equivalence principle is violated for quantum particles.",2310.17581v1
2023-11-12,Sine-Gordon dynamics in spin transport,"We study spin transport in a one-dimensional finite-length wire connected to
fermionic leads. The interacting wire is described by the sine-Gordon model
while the leads are either noninteracting or interacting Luttinger liquids. We
calculate the spin current driven by a spin bias by solving numerically the
classical equation of motion, and find that the cosine term in the sine-Gordon
model gives rise to an oscillating spin current when the spin bias exceeds its
critical value. We discuss the results in connection with transport experiments
with ultracold atoms.",2311.06862v1
2024-04-08,"Spin Radiation of Electrons, Excitons, and Phonons","In the celebrated Stern-Gerlach experiment an inhomogeneous static magnetic
field separates a beam of charge-neutral atoms with opposite spins, thereby
driving a ``spin current"" normal to the propagation direction. Here we
generalize it to the dynamic scenario by demonstrating a spin transfer between
an AC inhomogeneous magnetic field and intraband electrons or charge-neutral
excitons and phonons. We predict that parametric pumping can efficiently
radiate their DC spin currents from local AC magnetic sources with van der
Waals semiconductors as prototypes. This mechanism brings a unified and
efficient paradigm in the spin transport of distinct mobile carriers.",2404.05593v1
1995-03-01,Geometrization of spin systems using cycle expansions,"It is shown that a spin system with long range interactions can be converted
into a chaotic dynamical system that is differentiable and low-dimensional. The
thermodynamic limit of the spin system is then equivalent to studying the long
term behavior of the dynamical system. Cycle expansions of chaotic systems
(expansion of the Fredholm determinant) are then used to study the
thermodynamic limit. By considering the smooth dynamical system, it is possible
to converge to the thermodynamic limit faster than with transfer matrices.",9502023v1
1998-11-03,Time scale separation and heterogeneous off-equilibrium dynamics in spin models over random graphs,"We study analytically and numerically the statics and the off-equilibrium
dynamics of spin models over finitely connected random graphs. We identify a
threshold value for the connectivity beyond which the loop structure of the
graph becomes thermodynamically relevant. Glauber dynamics simulations show
that this loop structure is responsible for the onset of dynamical features of
a local character (dynamical heterogeneities and spontaneous time scale
separation), consistently with previous (experimental and numerical) studies of
glasses and spin glasses in their approach to the low temperature phase.",9811033v1
2015-03-05,Single-spin-flip dynamics of the Ising chain,"We consider the most general single-spin-flip dynamics for the ferromagnetic
Ising chain with nearest-neighbour influence and spin reversal symmetry. This
dynamics is a two-parameter extension of Glauber dynamics corresponding
respectively to non-linearity and irreversibility. The associated stationary
state measure is given by the usual Boltzmann-Gibbs distribution for the
ferromagnetic Hamiltonian of the chain. We study the properties of this
dynamics both at infinite and at finite temperature, all over its parameter
space, with particular emphasis on special lines and points.",1503.01661v3
2018-02-08,Anomalous phonon lifetime shortening in paramagnetic CrN caused by magneto-lattice coupling: A combined spin and ab initio molecular dynamics study,"We study the mutual coupling of spin fluctuations and lattice vibrations in
paramagnetic CrN by combining atomistic spin dynamics and ab initio molecular
dynamics. The two degrees of freedom are dynamically coupled leading to
non-adiabatic effects. Those effects suppress the phonon life times at low
temperature compared to an adiabatic approach. The here identified dynamic
coupling provides an explanation for the experimentally observed unexpected
temperature dependence of the thermal conductivity of magnetic semiconductors
above the magnetic ordering temperature.",1802.02934v1
2022-09-20,Stochastic equations and dynamics beyond mean-field theory,"The dynamical transition occurring in spin-glass models with one step of
Replica-Symmetry-Breaking is a mean-field artifact that disappears in finite
systems and/or in finite dimensions. The critical fluctuations that smooth the
transition are described in the $\beta$ regime by dynamical stochastic
equations. The quantitative parameters of the dynamical stochastic equations
have been computed analytically on the 3-spin Bethe lattice Spin-Glass by means
of the (static) cavity method and the equations have been solved numerically.
The resulting parameter-free dynamical predictions are shown here to be in
excellent agreement with numerical simulation data for the correlation and its
fluctuations.",2209.09689v1
2004-02-03,Semiclassical kinetic theory of electron spin relaxation in semiconductors,"We develop a semiclassical kinetic theory for electron spin relaxation in
semiconductors. Our approach accounts for elastic as well as inelastic
scattering and treats Elliott-Yafet and motional-narrowing processes, such as
D'yakonov-Perel' and variable g-factor processes, on an equal footing. Focusing
on small spin polarizations and small momentum transfer scattering, we derive,
starting from the full quantum kinetic equations, a Fokker-Planck equation for
the electron spin polarization. We then construct, using a rigorous multiple
time scale approach, a Bloch equation for the macroscopic ($\vec{k}$-averaged)
spin polarization on the long time scale, where the spin polarization decays.
Spin-conserving energy relaxation and diffusion, which occur on a fast time
scale, after the initial spin polarization has been injected, are incorporated
and shown to give rise to a weight function which defines the energy averages
required for the calculation of the spin relaxation tensor in the Bloch
equation. Our approach provides an intuitive way to conceptualize the dynamics
of the spin polarization in terms of a ``test'' spin polarization which
scatters off ``field'' particles (electrons, impurities, phonons). To
illustrate our approach, we calculate for a quantum well the spin lifetime at
temperatures and densities where electron-electron and electron-impurity
scattering dominate. The spin lifetimes are non-monotonic functions of
temperature and density. Our results show that at electron densities and
temperatures, where the cross-over from the non-degenerate to the degenerate
regime occurs, spin lifetimes are particularly long.",0402085v4
2005-11-01,"Spin relaxation of ""upstream"" electrons: beyond the drift diffusion model","The classical drift diffusion (DD) model of spin transport treats spin
relaxation via an empirical parameter known as the ``spin diffusion length''.
According to this model, the ensemble averaged spin of electrons drifting and
diffusing in a solid decays exponentially with distance due to spin dephasing
interactions. The characteristic length scale associated with this decay is the
spin diffusion length. The DD model also predicts that this length is different
for ``upstream'' electrons traveling in a decelerating electric field than for
``downstream'' electrons traveling in an accelerating field. However this
picture ignores energy quantization in confined systems (e.g. quantum wires)
and therefore fails to capture the non-trivial influence of subband structure
on spin relaxation. Here we highlight this influence by simulating upstream
spin transport in a multi-subband quantum wire, in the presence of
D'yakonov-Perel' spin relaxation, using a semi-classical model that accounts
for the subband structure rigorously. We find that upstream spin transport has
a complex dynamics that defies the simplistic definition of a ``spin diffusion
length''. In fact, spin does not decay exponentially or even monotonically with
distance, and the drift diffusion picture fails to explain the qualitative
behavior, let alone predict quantitative features accurately. Unrelated to spin
transport, we also find that upstream electrons undergo a ``population
inversion'' as a consequence of the energy dependence of the density of states
in a quasi one-dimensional structure.",0511027v1
2006-02-09,"Spin relaxation of ""upstream"" electrons in quantum wires: Failure of the drift diffusion model","The classical drift diffusion (DD) model of spin transport treats spin
relaxation via an empirical parameter known as the ``spin diffusion length''.
According to this model, the ensemble averaged spin of electrons drifting and
diffusing in a solid decays exponentially with distance due to spin dephasing
interactions. The characteristic length scale associated with this decay is the
spin diffusion length. The DD model also predicts that this length is different
for ``upstream'' electrons traveling in a decelerating electric field than for
``downstream'' electrons traveling in an accelerating field. However this
picture ignores energy quantization in confined systems (e.g. quantum wires)
and therefore fails to capture the non-trivial influence of subband structure
on spin relaxation. Here we highlight this influence by simulating upstream
spin transport in a multi-subband quantum wire, in the presence of
D'yakonov-Perel' spin relaxation, using a semi-classical model that accounts
for the subband structure rigorously.
  We find that upstream spin transport has a complex dynamics that defies the
simplistic definition of a ``spin diffusion length''.
  In fact, spin does not decay exponentially or even monotonically with
distance, and the drift diffusion picture fails to explain the qualitative
behavior, let alone predict quantitative features accurately. Unrelated to spin
transport, we also find that upstream electrons undergo a ``population
inversion'' as a consequence of the energy dependence of the density of states
in a quasi one-dimensional structure.",0602241v1
2017-02-14,Spin-relaxation time in materials with broken inversion symmetry and large spin-orbit coupling,"We study the spin-relaxation time in materials where a large spin-orbit
coupling (SOC) is present which breaks the spatial inversion symmetry. Such a
spin-orbit coupling is realized in zincblende structures and heterostructures
with a transversal electric field and the spin relaxation is usually described
by the so-called D'yakonov-Perel' (DP) mechanism. We combine a Monte Carlo
method and diagrammatic calculation based approaches in our study; the former
tracks the time evolution of electron spins in a quasiparticle dynamics
simulation in the presence of the built-in spin-orbit magnetic fields and the
latter builds on the spin-diffusion propagator by Burkov and Balents [Burkov
and Balents Phys. Rev. B. 69, 245312 (2004).]. Remarkably, we find a parameter
free quantitative agreement between the two approaches and it also returns the
conventional result of the DP mechanism in the appropriate limit. We discuss
the full phase space of spin relaxation as a function of SOC strength, its
distribution, and the magnitude of the momentum relaxation rate. This allows us
to identify two novel spin-relaxation regimes; where spin relaxation is
strongly non-exponential and the spin relaxation equals the momentum
relaxation. A compelling analogy between the spin-relaxation theory and the NMR
motional narrowing is highlighted.",1702.04162v1
2019-05-27,Spin-Cooling of the Motion of a Trapped Diamond,"Observing and controlling macroscopic quantum systems has long been a driving
force in research on quantum physics. In this endeavor, strong coupling between
individual quantum systems and mechanical oscillators is being actively
pursued. While both read-out of mechanical motion using coherent control of
spin systems and single spin read-out using pristine oscillators have been
demonstrated, temperature control of the motion of a macroscopic object using
long-lived electronic spins has not been reported. Here, we observe both a
spin-dependent torque and spin-cooling of the motion of a trapped microdiamond.
Using a combination of microwave and laser excitation enables the spin of
nitrogen-vacancy centers to act on the diamond orientation and to cool the
diamond libration via a dynamical back-action. Further, driving the system in
the non-linear regime, we demonstrate bistability and self-sustained coherent
oscillations stimulated by the spin-mechanical coupling, which offers prospects
for spin-driven generation of non-classical states of motion. Such a levitating
diamond operated as a compass with controlled dissipation has implications in
high-precision torque sensing, emulation of the spin-boson problem and probing
of quantum phase transitions. In the single spin limit and employing ultra-pure
nano-diamonds, it will allow quantum non-demolition read-out of the spin of
nitrogen-vacancy centers under ambient conditions, deterministic entanglement
between distant individual spins and matter-wave interferometry.",1905.11509v2
2016-11-17,Inductive detection of field-like and damping-like AC inverse spin-orbit torques in ferromagnet/normal metal bilayers,"Functional spintronic devices rely on spin-charge interconversion effects,
such as the reciprocal processes of electric field-driven spin torque and
magnetization dynamics-driven spin and charge flow. Both damping-like and
field-like spin-orbit torques have been observed in the forward process of
current-driven spin torque and damping-like inverse spin-orbit torque has been
well-studied via spin pumping into heavy metal layers. Here we demonstrate that
established microwave transmission spectroscopy of ferromagnet/normal metal
bilayers under ferromagnetic resonance can be used to inductively detect the AC
charge currents driven by the inverse spin-charge conversion processes. This
technique relies on vector network analyzer ferromagnetic resonance (VNA-FMR)
measurements. We show that in addition to the commonly-extracted spectroscopic
information, VNA-FMR measurements can be used to quantify the magnitude and
phase of all AC charge currents in the sample, including those due to spin
pumping and spin-charge conversion. Our findings reveal that
Ni$_{80}$Fe$_{20}$/Pt bilayers exhibit both damping-like and field-like inverse
spin-orbit torques. While the magnitudes of both the damping-like and
field-like inverse spin-orbit torque are of comparable scale to prior reported
values for similar material systems, we observed a significant dependence of
the damping-like magnitude on the order of deposition. This suggests interface
quality plays an important role in the overall strength of the damping-like
spin-to-charge conversion.",1611.05798v2
2018-01-08,Spin-resolved inelastic electron scattering by spin waves in noncollinear magnets,"Topological non-collinear magnetic phases of matter are at the heart of many
proposals for future information nanotechnology, with novel device concepts
based on ultra-thin films and nanowires. Their operation requires understanding
and control of the underlying dynamics, including excitations such as
spin-waves. So far, no experimental technique has attempted to probe large
wave-vector spin-waves in non-collinear low-dimensional systems. In this work,
we explain how inelastic electron scattering, being suitable for investigations
of surfaces and thin films, can detect the collective spin-excitation spectra
of non-collinear magnets. To reveal the particularities of spin-waves in such
non-collinear samples, we propose the usage of spin-polarized
electron-energy-loss spectroscopy augmented with a spin-analyzer. With the
spin-analyzer detecting the polarization of the scattered electrons, four
spin-dependent scattering channels are defined, which allow to filter and
select specific spin-wave modes. We take as examples a topological non-trivial
skyrmion lattice, a spin-spiral phase and the conventional ferromagnet. Then we
demonstrate that, counter-intuitively and in contrast to the ferromagnetic
case, even non spin-flip processes can generate spin-waves in non-collinear
substrates. The measured dispersion and lifetime of the excitation modes permit
to fingerprint the magnetic nature of the substrate.",1801.02542v2
2018-08-06,Atomtronics with a spin: statistics of spin transport and non-equilibrium orthogonality catastrophe in cold quantum gases,"We propose to investigate the full counting statistics of nonequilibrium spin
transport with an ultracold atomic quantum gas. The setup makes use of the spin
control available in atomic systems to generate spin transport induced by an
impurity atom immersed in a spin-imbalanced two-component Fermi gas. In
contrast to solid-state realizations, in ultracold atoms spin relaxation and
the decoherence from external sources is largely suppressed. As a consequence,
once the spin current is turned off by manipulating the internal spin degrees
of freedom of the Fermi system, the nonequilibrium spin population remains
constant. Thus one can directly count the number of spins in each reservoir to
investigate the full counting statistics of spin flips, which is notoriously
challenging in solid state devices. Moreover, using Ramsey interferometry, the
dynamical impurity response can be measured. Since the impurity interacts with
a many-body environment that is out of equilibrium, our setup provides a way to
realize the non-equilibrium orthogonality catastrophe. Here, even for spin
reservoirs initially prepared in a zero-temperature state, the Ramsey response
exhibits an exponential decay, which is in contrast to the conventional
power-law decay of Anderson's orthogonality catastrophe. By mapping our system
to a multi-step Fermi sea, we are able to derive analytical expressions for the
impurity response at late times. This allows us to reveal an intimate
connection of the decay rate of the Ramsey contrast and the full counting
statistics of spin flips.",1808.02062v1
2020-08-03,Interfacial spin-orbit torques,"Spin-orbit torques offer a promising mechanism for electrically controlling
magnetization dynamics in nanoscale heterostructures. While spin-orbit torques
occur predominately at interfaces, the physical mechanisms underlying these
torques can originate in both the bulk layers and at interfaces. Classifying
spin-orbit torques based on the region that they originate in provides clues as
to how to optimize the effect. While most bulk spin-orbit torque contributions
are well studied, many of the interfacial contributions allowed by symmetry
have yet to be fully explored theoretically and experimentally. To facilitate
progress, we review interfacial spin-orbit torques from a semiclassical
viewpoint and relate these contributions to recent experimental results. Within
the same model, we show the relationship between different interface transport
parameters. For charges and spins flowing perpendicular to the interface,
interfacial spin-orbit coupling both modifies the mixing conductance of
magnetoelectronic circuit theory and gives rise to spin memory loss. For
in-plane electric fields, interfacial spin-orbit coupling gives rise to torques
described by spin-orbit filtering, spin swapping and precession. In addition,
these same interfacial processes generate spin currents that flow into the
non-magnetic layer. For in-plane electric fields in trilayer structures, the
spin currents generated at the interface between one ferromagnetic layer and
the non-magnetic spacer layer can propagate through the non-magnetic layer to
produce novel torques on the other ferromagnetic layer.",2008.01182v1
2021-02-06,Spin pumping and inverse spin Hall effect in CoFeB/IrMn heterostructures,"High spin to charge conversion efficiency is the requirement for the
spintronics devices which is governed by spin pumping and inverse spin Hall
effect (ISHE). In last one decade, ISHE and spin pumping are heavily
investigated in ferromagnet/ heavy metal (HM) heterostructures. Recently
antiferromagnetic (AFM) materials are found to be good replacement of HMs
because AFMs exhibit terahertz spin dynamics, high spin-orbit coupling, and
absence of stray field. In this context we have performed the ISHE in CoFeB/
IrMn heterostructures. Spin pumping study is carried out for
$Co_{40}Fe_{40}B_{20} (12\ nm)/ Cu (3\ nm)/ Ir_{50}Mn_{50} (t\ nm)/ AlO_{x} (3\
nm)$ samples where \textit{t} value varies from 0 to 10 nm. Damping of all the
samples are higher than the single layer CoFeB which indicates that spin
pumping due to IrMn is the underneath mechanism. Further the spin pumping in
the samples are confirmed by angle dependent ISHE measurements. We have also
disentangled other spin rectifications effects and found that the spin pumping
is dominant in all the samples. From the ISHE analysis the real part of spin
mixing conductance (\textit{$g_{r}^{\uparrow \downarrow}$}) is found to be
0.704 $\pm$ 0.003 $\times$ $10^{18}$ $m^{-2}$.",2102.03624v2
2022-01-03,Handedness-filter and Doppler shift of spin waves in ferrimagnetic domain walls,"Excitation and propagation of spin waves inside magnetic domain walls has
received attention because of their potentials in spintronic and communication
applications. Besides wave amplitude and frequency, spin-wave has its third
character: handedness, whose manipulation is certainly of interest. We propose
in this Letter that the handedness of low energy spin-wave excitations can be
controlled by tuning the net angular momentum {\delta}s in a ferrimagnetic
(FiM) domain wall, attributing to the inequivalent magnetic sublattices. The
results indicate that the spin-wave dispersion depends on both {\delta}s and
wave handedness. For a positive (negative) {\delta}s, a gapless dispersion is
observed for the left-handed (righ-handed) spin waves, while a frequency gap
appears for the right-handed (left-handed) spin waves. Thus a FiM wall could
serve as a multifold filter of low energy spin-wave in which only spin waves
with particular handedness can propagate. Furthermore, the energy consumption
loss for spin-wave excitation in the wall is much lower than that inside the
domain, while the group velocity is much faster too, demonstrating the
advantages of domain walls serving as spin waveguides. Moreover, the
current-induced spin-wave Doppler shift in the FiM wall is also revealed, and
can be controlled by {\delta}s. This work unveils for the first time the
interesting spin-wave dynamics in FiM domain walls, benefiting future spin-wave
applications.",2201.00623v2
2022-07-25,Spin-transfer and spin-orbit torques in the Landau-Lifshitz-Gilbert equation,"Dynamic simulations of spin-transfer and spin-orbit torques are increasingly
important for a wide range of spintronic devices including magnetic random
access memory, spin-torque nano-oscillators and electrical switching of
antiferromagnets. Here we present a computationally efficient method for the
implementation of spin-transfer and spin-orbit torques within the
Landau-Lifshitz-Gilbert equation used in micromagnetic and atomistic
simulations. We consolidate and simplify the varying terminology of different
kinds of torques into a physical action and physical origin that clearly shows
the common action of spin torques while separating their different physical
origins. Our formalism introduces the spin torque as an effective magnetic
field, greatly simplifying the numerical implementation and aiding the
interpretation of results. The strength of the effective spin torque field
unifies the action of the spin torque and subsumes the details of experimental
effects such as interface resistance and spin Hall angle into a simple
transferable number between numerical simulations. We present a series of
numerical tests demonstrating the mechanics of generalised spin torques in a
range of spintronic devices. This revised approach to modelling spin-torque
effects in numerical simulations enables faster simulations and a more direct
way of interpreting the results, and thus it is also suitable to be used in
direct comparisons with experimental measurements or in a modelling tool that
takes experimental values as input.",2207.12071v2
2023-10-23,Microscopic theory of spin Seebeck effect in antiferromagnets,"We develop a microscopic theory for the spin Seebeck effect (SSE) in N\'eel
and canted phases of antiferromagnetic insulators. We calculate the DC spin
current tunneling from the antiferromagnet to an attached metal, incorporating
the spin-wave theory and the non-equilibrium Green's function approach. Our
result shows a sign change of the spin current at the spin-flop phase
transition between N\'eel and canted phases, which is in agreement with a
recent experiment for the SSE of $\rm Cr_2O_3$ in a semi-quantitative level.
The sign change can be interpreted from the argument based on the density of
states of up- and down-spin magnons, which is related to the polarized-neutron
scattering spectra. The theory also demonstrates that the spin current in the
N\'eel phase is governed by the magnon correlation, while that in the canted
phase consists of two parts: Contributions from not only the magnon dynamics
but also the static transverse magnetization. This result leads to a prediction
that at sufficiently low temperatures, the spin current non-monotonically
changes as a function of magnetic field in the canted phase. Towards a more
unified understanding of the SSE in antiferromagnets, we further discuss some
missing links of theories of SSE: Interface properties, effects of the
transverse spin moment in the canted phase, the spin-orbit coupling in the
metal, etc. Finally, we compare the SSE of antiferromagnets with those of
different magnetic phases such as ferromagnets, ferrimagnets, an
one-dimensional spin liquid, a spin-nematic liquid, and a spin-Peierls
(dimerized) phase.",2310.15292v2
2020-07-09,A partially linearized spin-mapping approach for nonadiabatic dynamics. II. Analysis and comparison with related approaches,"In the previous paper [J. R. Mannouch and J. O. Richardson,
J.~Chem.~Phys.~xxx, xxxxx (xxxx)] we derived a new partially linearized
mapping-based classical-trajectory technique, called spin-PLDM. This method
describes the dynamics associated with the forward and backward electronic path
integrals, using a Stratonovich-Weyl approach within the spin-mapping space.
While this is the first example of a partially linearized spin mapping method,
fully linearized spin mapping is already known to be capable of reproducing
dynamical observables for a range of nonadiabatic model systems reasonably
accurately. Here we present a thorough comparison of the terms in the
underlying expressions for the real-time quantum correlation functions for
spin-PLDM and fully linearized spin mapping in order to ascertain the relative
accuracy of the two methods. In particular, we show that spin-PLDM contains an
additional term within the definition of its real-time correlation function,
which diminishes many of the known errors that are ubiquitous for fully
linearized approaches. One advantage of partially linearized methods over their
fully linearized counterparts is that the results can be systematically
improved by re-sampling the mapping variables at intermediate times. We derive
such a scheme for spin-PLDM and show that for systems for which the
approximation of classical nuclei is valid, numerically exact results can be
obtained using only a few `jumps'. Additionally, we implement focused initial
conditions for the spin-PLDM method, which reduces the number of classical
trajectories that are needed in order to reach convergence of dynamical
quantities, with seemingly little difference to the accuracy of the result.",2007.05048v2
2021-02-09,Spin drift-diffusion for two-subband quantum wells,"Controlling the spin dynamics and spin lifetimes is one of the main
challenges in spintronics. To this end, the study of the spin diffusion in
two-dimensional electron gases (2DEGs) shows that when the Rashba and
Dresselhaus spin-orbit couplings (SOC) are balanced, a persistent spin helix
regime arises. There, a striped spin pattern shows a long lifetime, limited
only by the cubic Dresselhaus SOC, and its dynamics can be controlled by
in-plane drift fields. Here, we derive a spin diffusion equation for
non-degenerate two-subbands 2DEGs. We show that the intersubband scattering
rate, which is defined by the overlap of the subband densities, enters as a new
nob to control the spin dynamics, and can be controlled by electric fields,
being maximum for symmetric quantum wells. We find that for large intersubband
couplings the dynamics follow an effective diffusion matrix given by
approximately half of the subband-averaged matrices. This extra 1/2 factor
arises from Matthiessen's rule summing over the intra- and intersubband
scattering rates, and leads to a reduced diffusion constant and larger spin
lifetimes. We illustrate our findings with numerical solutions of the diffusion
equation with parameters extracted from realistic Schr\""odinger-Poisson
calculations.",2102.04831v2
2022-02-04,Direct observation of a dynamical glass transition in a nanomagnetic artificial Hopfield network,"Spin glasses, generally defined as disordered systems with randomized
competing interactions, are a widely investigated complex system. Theoretical
models describing spin glasses are broadly used in other complex systems, such
as those describing brain function, error-correcting codes, or stock-market
dynamics. This wide interest in spin glasses provides strong motivation to
generate an artificial spin glass within the framework of artificial spin ice
systems. Here, we present the experimental realization of an artificial spin
glass consisting of dipolar coupled single-domain Ising-type nanomagnets
arranged onto an interaction network that replicates the aspects of a Hopfield
neural network. Using cryogenic x-ray photoemission electron microscopy
(XPEEM), we performed temperature-dependent imaging of thermally driven moment
fluctuations within these networks and observed characteristic features of a
two-dimensional Ising spin glass. Specifically, the temperature dependence of
the spin glass correlation function follows a power law trend predicted from
theoretical models on two-dimensional spin glasses. Furthermore, we observe
clear signatures of the hard to observe rugged spin glass free energy in the
form of sub-aging, out of equilibrium autocorrelations and a transition from
stable to unstable dynamics.",2202.02372v1
2023-07-27,The dynamical magnetic-induced quark spin polarization at the early stage in heavy-ion collisions,"There has been significant interest in recent years in studying the spin
polarization of hyperons in heavy-ion collisions. However, describing the
dynamic spin polarization of quarks in quark-gluon plasma fireballs in detail
presents a significant challenge. In this study, we conducted a
phenomenological investigation of the dynamical spin polarization of quarks
induced by the magnetic field at the pre-thermal stage in heavy-ion collisions
using the recently developed theoretical tool of chiral kinetic theory. This
study presents a comprehensive analysis of the dynamic process of quark spin
polarization induced by magnetic fields. Our findings demonstrate that the spin
polarization of quarks is highly sensitive to the interactions between quarks.
These interactions can delay the decay of the early spin polarization vector
while accelerating the decay of the later spin polarization vector.
Specifically, our simulations model the detailed process of how magnetic fields
polarize quarks within the fireball by the average spin vector and reveal that
quark interactions lead to an acceleration effect on the average spin, causing
it to rapidly increase from zero before being rapidly destroyed. Notably, the
induced magnetic field in the fireball has an incomplete electromagnetic
response effect, and its increase in the opposite direction of the external
magnetic field decaying has a delay effect.",2308.00075v1
2007-05-28,"Muon spin relaxation and hyperfine-enhanced 141Pr nuclear spin dynamic in Pr(Os,Ru)4Sb12 and (Pr,La)Os4Sb12","Zero- and longitudinal-field muon spin relaxation (MuSR) experiments have
been carried out in the alloy series Pr(Os1-xRux)4Sb12 and Pr1-yLayOs4Sb12 to
elucidate the anomalous dynamic muon spin relaxation observed in these
materials. The damping rate associated with this relaxation varies with
temperature, applied magnetic field, and dopant concentrations x and y in a
manner consistent with the ``hyperfine enhancement'' of 141Pr nuclear spins
first discussed by Bleaney in 1973. This mechanism arises from Van Vleck-like
admixture of magnetic Pr3+ crystalline-electric-field-split excited states into
the nonmagnetic singlet ground state by the nuclear hyperfine coupling, thereby
increasing the strengths of spin-spin interactions between 141Pr and muon spins
and within the 141Pr spin system. We find qualitative agreement with this
scenario, and conclude that electronic spin fluctuations are not directly
involved in the dynamic muon spin relaxation.",0705.4087v1
2007-06-18,Binary Black Holes: Spin Dynamics and Gravitational Recoil,"We present a study of spinning black hole binaries focusing on the spin
dynamics of the individual black holes as well as on the gravitational recoil
acquired by the black hole produced by the merger. We consider two series of
initial spin orientations away from the binary orbital plane. In one of the
series, the spins are anti-aligned; for the second series, one of the spins
points away from the binary along the line separating the black holes. We find
a remarkable agreement between the spin dynamics predicted at 2nd
post-Newtonian order and those from numerical relativity. For each
configuration, we compute the kick of the final black hole. We use the kick
estimates from the series with anti-aligned spins to fit the parameters in the
\KKF{,} and verify that the recoil along the direction of the orbital angular
momentum is $\propto \sin\theta$ and on the orbital plane $\propto \cos\theta$,
with $\theta$ the angle between the spin directions and the orbital angular
momentum. We also find that the black hole spins can be well estimated by
evaluating the isolated horizon spin on spheres of constant coordinate radius.",0706.2541v2
2011-07-14,Extending the effective-one-body Hamiltonian of black-hole binaries to include next-to-next-to-leading spin-orbit couplings,"In the effective-one-body (EOB) approach the dynamics of two compact objects
of masses m1 and m2 and spins S1 and S2 is mapped into the dynamics of one test
particle of mass mu = m1 m2/(m1+m2) and spin S* moving in a deformed Kerr
metric with mass M = m1+m2 and spin Skerr. In a previous paper we computed an
EOB Hamiltonian for spinning black-hole binaries that (i) when expanded in
post-Newtonian orders, reproduces the leading order spin-spin coupling and the
leading and next-to-leading order spin-orbit couplings for any mass ratio, and
(iii) reproduces all spin-orbit couplings in the test-particle limit. Here we
extend this EOB Hamiltonian to include next-to-next-to-leading spin-orbit
couplings for any mass ratio. We discuss two classes of EOB Hamiltonians that
differ by the way the spin variables are mapped between the effective and real
descriptions. We also investigate the main features of the dynamics when the
motion is equatorial, such as the existence of the innermost stable circular
orbit and of a peak in the orbital frequency during the plunge subsequent to
the inspiral.",1107.2904v2
2012-06-26,Transport and semiclassical dynamics of coupled quantum dots interacting with a local magnetic moment,"We present a theory of magnetotransport through a system of two coupled
electronic orbitals, where the electron spin interacts with a (large) local
magnetic moment via an exchange interaction. For the physical realization of
such a set-up we have in mind, for example, semiconductor quantum dots coupled
to an ensemble of nuclear spins in the host material or molecular orbitals
coupled to a local magnetic moment. Using a semiclassical approximation, we
derive a set of Ehrenfest equations of motion for the electron density matrix
and the mean value of the external spin (Landau equations): Due to the spin
coupling they turn out to be nonlinear and, importantly, also coherences
between electron states with different spin directions need to be considered.
The electronic spin-polarized leads are implemented in form of a Lindblad-type
dissipator in the infinite bias limit. We have solved this involved dynamical
system numerically for various isotropic and anisotropic coupling schemes. For
isotropic spin coupling and spin-polarized leads we study the effect of
current-induced magnetization of the attached spin and compare this with a
single quantum dot set-up. We further demonstrate that an anisotropic coupling
can lead to a rich variety of parametric oscillations in the average current
reflecting the complicated interplay between the Larmor precession of the
external spin and the dissipative coherent dynamics of the electron spin.",1206.5994v2
2013-05-28,Protection of center-spin coherence by dynamically polarizing nuclear spin core in diamond,"We experimentally investigate the protection of electron spin coherence of
nitrogen vacancy (NV) center in diamond by dynamical nuclear polarization. The
electron spin decoherence of an NV center is caused by the magnetic ield
fluctuation of the $^{13}$C nuclear spin bath, which contributes large thermal
fluctuation to the center electron spin when it is in equilibrium state at room
temperature. To address this issue, we continuously transfer the angular
momentum from electron spin to nuclear spins, and pump the nuclear spin bath to
a polarized state under Hartman-Hahn condition. The bath polarization effect is
verified by the observation of prolongation of the electron spin coherence time
($T_2^*$). Optimal conditions for the dynamical nuclear polarization (DNP)
process, including the pumping pulse duration and depolarization effect of
laser pulses, are studied. Our experimental results provide strong support for
quantum information processing and quantum simulation using polarized nuclear
spin bath in solid state systems.",1305.6424v1
2016-06-28,Simulating generic spin-boson models with matrix product states,"The global coupling of few-level quantum systems (""spins"") to a discrete set
of bosonic modes is a key ingredient for many applications in quantum science,
including large-scale entanglement generation, quantum simulation of the
dynamics of long-range interacting spin models, and hybrid platforms for force
and spin sensing. We present a general numerical framework for treating the
out-of-equilibrium dynamics of such models based on matrix product states. Our
approach applies for generic spin-boson systems: it treats any spatial and
operator dependence of the two-body spin-boson coupling and places no
restrictions on relative energy scales. We show that the full counting
statistics of collective spin measurements and infidelity of quantum simulation
due to spin-boson entanglement, both of which are difficult to obtain by other
techniques, are readily calculable in our approach. We benchmark our method
using a recently developed exact solution for a particular spin-boson coupling
relevant to trapped ion quantum simulators. Finally, we show how decoherence
can be incorporated within our framework using the method of quantum
trajectories, and study the dynamics of an open-system spin-boson model with
spatially non-uniform spin-boson coupling relevant for trapped atomic ion
crystals in the presence of molecular ion impurities.",1606.08781v1
2017-02-09,Nonexponential spin decay in a quantum kinetic description of the D'yakonov-Perel' mechanism mediated by impurity scattering,"The electron spin dynamics in an optically excited narrow quantum well is
studied, where the electron spins precess in a k-dependent magnetic field while
the electrons scatter at localized impurities. For the resulting spin decay,
which is commonly known as the D'yakonov-Perel' mechansim, analytical
expressions in the strong- and weak-scattering limits are available. It is
found by the numerical solution of quantum kinetic equations in a broad range
of parameters that, in situations that are typically relevant for ultrafast
optical experiments, the dynamics of the total spin polarization significantly
deviates from the pertinent analytical results. This is attributed to the broad
spectral width of the optically excited spin-polarized electron distribution,
which gives rise to a spin dephasing due to inhomogeneous broadening.
Furthermore, it is found that the decay of the spin polarization need not be
exponential. The notion of a spin decay time becomes ambiguous and different
definitions of spin decay times can lead to different outcomes. The long-term
dynamics of the decay of the spin polarization is even dominated by an
algebraically decaying component. These findings highlight the importance of
the effects of the broad spectral distribution of optically excited carriers in
ultrashort magneto-optical experiments.",1702.02757v2
2021-07-13,Investigation of spin-phonon coupling and local magnetic properties in magnetoelectric Fe2TeO6,"Spin-phonon coupling originated from spin-lattice correlation depends upon
different exchange interactions in transition metal oxides containing 3d
magnetic ions. Spin-lattice coupling can influence the coupling mechanism in
magnetoelectric material. To understand the spin-lattice correlation in inverse
trirutile Fe2TeO6 (FTO), magnetic properties and phonon spectra are studied.
Signature of short-range magnetic correlation induced by 5/2-5/2 dimeric
interaction and magnetic anomaly at 150 K is perceived apart from the familiar
sharp transition (TN~210K) corresponding to long-range order by magnetization
and heat capacity measurement. The magnetic transitions and the spin dynamics
are further locally probed by muon spin resonance ({\mu}SR) measurement in both
zero fields (ZF) and longitudinal field (LF) mode. Three dynamically distinct
temperature regimes; (i) T >TN, (ii) TN>T>150 K, and (iii) T<150 K, are
observed. A swift change in spin dynamics is realized at 150K by {\mu}SR,
though previous studies suggest long-range antiferromagnetic order. The
observation of renormalization of different Raman modes below 210K suggests the
existence of spin-phonon coupling in the material. The coupling strength is
quantified as in the range 0.1-1.2 cm-1 following the two-spin cluster
approximation. We propose that the spin-phonon coupling is mediated by the
Fe-O2-Fe interbilayer exchange play a significant role in ME coupling observed
in the material.",2107.06269v2
2021-10-05,Bound state dynamics in the long-range spin-$\frac{1}{2}$ XXZ model,"Experimental platforms based on trapped ions, cold molecules, and Rydberg
atoms have made possible the investigation of highly-nonlocal spin-${1/2}$
Hamiltonians with long-range couplings. Here, we study the effects of such
non-local couplings in the long-range spin-${1/2}$ XXZ Heisenberg Hamiltonian.
We calculate explicitly the two-spin energy spectrum, which describes all
possible energetic configurations of two spins pointing in a specific direction
embedded in a background of spins with opposite orientation. For fast decay of
the spin-spin couplings, we find that the two-spin energy spectrum is
characterized by well-defined discrete values, corresponding to bound states,
separated by a set of continuum states describing the scattering region. In the
deep long-range regime instead, the bound states disappear as they get
incorporated by the scattering region. The presence of two-spin bound states
results to be crucial to determine both two- and many-spin dynamics. On one
hand, radically different two-spin spreadings can be observed by tuning the
decay of the spin couplings. On the other hand, two-spin bound states enable
the dynamical stabilization of effective antiferromagnetic states in the
presence of ferromagnetic couplings. Finally, we propose a novel scheme based
on a trapped-ion quantum simulator to experimentally realize the long-range XXZ
model and to study its out-of-equilibrium properties.",2110.01760v1
2021-12-14,Low-energy Spin Dynamics of Quantum Spin Liquid Candidate $NaYbSe_{2}$,"The family of rare earth chalcogenides $ARECh_{2}$ (A = alkali or monovalent
ions, RE = rare earth, and Ch = O, S, Se, and Te) appears as an inspiring
playground for studying quantum spin liquids (QSL). The crucial low-energy spin
dynamics remain to be uncovered. By employing muon spin relaxation ($\mu$SR)
and zero-field (ZF) AC susceptibility down to 50 mK, we are able to identify
the gapless QSL in $NaYbSe_{2}$, a representative member with an effective
spin-1/2, and explore its unusual spin dynamics. The ZF $\mu$SR experiments
unambiguously rule out spin ordering or freezing in $NaYbSe_{2}$ down to 50 mK,
two orders of magnitude smaller than the exchange coupling energies. The spin
relaxation rate, $\lambda$, approaches a constant below 0.3 K, indicating
finite spin excitations featured by a gapless QSL ground state. This is
consistently supported by our AC susceptibility measurements. The careful
analysis of the longitudinal field (LF) $\mu$SR spectra reveals a strong
spatial correlation and a temporal correlation in the spin-disordered ground
state, highlighting the unique feature of spin entanglement in the QSL state.
The observations allow us to establish an experimental H-T phase diagram. The
study offers insight into the rich and exotic magnetism of the rare earth
family.",2112.07199v2
2022-10-28,Field-free-switching state diagram of perpendicular magnetization subjected to conventional and unconventional spin-orbit torques,"The lack of certain crystalline symmetries in strong spin-orbit-coupled
non-magnetic materials allows for the existence of uncoventional spin Hall
responses, with electrically generated transverse spin currents possessing
collinear flow and spin directions. The injection of such spin currents into an
adjacent ferromagnetic layer can excite magnetization dynamics via
unconventional spin-orbit torques, leading to deterministic switching in
ferromagnets with perpendicular magnetic anisotropy. We study the interplay
between conventional and unconventional spin-orbit torques on the magnetization
dynamics of a perpendicular ferromagnet in the small intrinsic damping limit,
and identify a rich set of dynamical regimes that includes deterministic and
probabilistic switching, precessional and pinning states. Contrary to common
belief, we found that there exists a critical conventional spin Hall angle,
beyond which deterministic magnetization switching transitions to a
precessional or pinned state. Conversely, we showed that larger unconventional
spin Hall angle is generally beneficial for deterministic switching. We derive
an approximate expression that qualitatively describes the state diagram
boundary between the full deterministic switching and precessional states and
discuss a criterion for searching symmetry-broken spin Hall materials in order
to maximize switching efficiency. Our work offers a roadmap towards energy
efficient spintronic devices, which might opens doors for applications in
advanced in-memory computing technologies.",2210.16344v1
2022-12-23,Dropping Anchor: Understanding the Populations of Binary Black Holes with Random and Aligned Spin Orientations,"The relative spin orientations of black holes (BHs) in binaries encode their
evolutionary history: BHs assembled dynamically should have isotropically
distributed spins, while spins of the BHs originating in the field should be
aligned with the orbital angular momentum. In this article, we introduce a
simple population model for these dynamical and field binaries that uses spin
orientations as an anchor to disentangle these two evolutionary channels. We
then analyze binary BH mergers in the Third Gravitational-Wave Transient
Catalog (GWTC-3) and ask whether BHs from the isotropic-spin population possess
different distributions of mass ratio, spin magnitudes, or redshifts from the
preferentially-aligned-spin population. We find no compelling evidence that
binary BHs in GWTC-3 have different source-property distributions depending on
their spin alignment, but we do find that the dynamical and field channels
cannot both have mass-ratio distributions that strongly favor equal masses. We
give an example of how this can be used to provide insights into the various
processes that drive these BHs to merge. We also find that the current
detections are insufficient in extracting differences in spin magnitude or
redshift distributions of isotropic and aligned spin populations.",2212.12113v2
1999-02-10,Low Temperature Static and Dynamic Behavior of the Two-Dimensional Easy-Axis Heisenberg Model,"We apply the self-consistent harmonic approximation (SCHA) to study static
and dynamic properties of the two-dimensional classical Heisenberg model with
easy-axis anisotropy. The static properties obtained are magnetization and spin
wave energy as functions of temperature, and the critical temperature as a
function of the easy-axis anisotropy. We also calculate the dynamic correlation
functions using the SCHA renormalized spin wave energy. Our analytical results,
for both static properties and dynamic correlation functions, are compared to
numerical simulation data combining cluster-Monte Carlo algorithms and Spin
Dynamics. The comparison allows us to conclude that far below the transition
temperature, where the SCHA is valid, spin waves are responsible for all
relevant features observed in the numerical simulation data; topological
excitations do not seem to contribute appreciably. For temperatures closer to
the transition temperature, there are differences between the dynamic
correlation functions from SCHA theory and Spin Dynamics; these may be due to
the presence of domain walls and solitons.",9902149v1
2016-09-01,Spinning test-body orbiting around Schwarzschild black hole: circular dynamics and gravitational-wave fluxes,"We consider a spinning test-body in circular motion around a nonrotating
black hole and analyze different prescriptions for the body's dynamics. We
compare, for the first time, the Mathisson-Papapetrou formalism under the
Tulczyjew spin-supplementary-condition (SSC), the Pirani SSC and the
Ohashi-Kyrian-Semerak SSC, and the spinning particle limit of the
effective-one-body Hamiltonian of [Phys.~Rev.~D.90,~044018(2014)]. We analyze
the four different dynamics in terms of the ISCO shifts and in terms of the
coordinate invariant binding energies, separating higher-order spin
contributions from spin-orbit contributions. The asymptotic gravitational wave
fluxes produced by the spinning body are computed by solving the inhomogeneous
$(2+1)D$ Teukolsky equation and contrasted for the different cases. For small
orbital frequencies $\Omega$, all the prescriptions reduce to the same dynamics
and the same radiation fluxes. For large frequencies, ${x \equiv (M
\Omega)^{2/3} >0.1 }$, where $M$ is the black hole mass, and especially for
positive spins (aligned with orbital angular momentum) a significant
disagreement between the different dynamics is observed. The ISCO shifts can
differ up to a factor two for large positive spins; for the
Ohashi-Kyrian-Semerak and the Pirani SSC the ISCO diverges around dimensionless
spins $\sim0.52$ and $\sim0.94$ respectively. In the spin-orbit part of the
energetics the deviation from the Hamiltonian dynamics is largest for the
Ohashi-Kyrian-Semerak SSC; it exceeds $10\%$ for $x>0.17$. The Tulczyjew and
the Pirani SSCs behave compatible across almost the whole spin and frequency
range. Our results will have direct application in including spin effects to
effective-one-body waveform models for circularized binaries in the
extreme-mass-ratio limit.",1609.00356v2
2007-03-06,Signatures of a quantum dynamical phase transition in a three-spin system in presence of a spin environment,"We have observed an environmentally induced quantum dynamical phase
transition in the dynamics of a two spin experimental swapping gate [J. Chem.
Phys. 124, 194507 (2006)]. There, the exchange of the coupled states |+,-> and
,+> gives an oscillation with a Rabi frecuency b/$\hbar$ (the spins coupling).
The interaction, $\hbar$/tSE with a spin-bath degrades the oscillation with a
characteristic decoherence time. We showed that the swapping regime is
restricted only to b\tSE>$hbar$. However, beyond a critical interaction with
the environment the swapping freezes and the system enters to a Quantum Zeno
dynamical phase where relaxation decreases as coupling with the environment
increases. Here, we solve the quantum dynamics of a two spin system coupled to
a spin-bath within a Liouville-von Neumann quantum master equation and we
compare the results with our previous work within the Keldysh formalism. Then,
we extend the model to a three interacting spin system where only one is
coupled to the environment. Beyond a critical interaction the two spins not
coupled to the environment oscillate with the bare Rabi frequency and relax
more slowly. This effect is more pronounced when the anisotropy of the
system-environment interaction goes from a purely XY to an Ising interaction
form.",0703158v1
2015-07-29,Spin dynamics and relaxation in the classical-spin Kondo-impurity model beyond the Landau-Lifschitz-Gilbert equation,"The real-time dynamics of a classical spin in an external magnetic field and
locally exchange coupled to an extended one-dimensional system of
non-interacting conduction electrons is studied numerically. Retardation
effects in the coupled electron-spin dynamics are shown to be the source for
the relaxation of the spin in the magnetic field. Total energy and spin is
conserved in the non-adiabatic process. Approaching the new local ground state
is therefore accompanied by the emission of dispersive wave packets of
excitations carrying energy and spin and propagating through the lattice with
Fermi velocity. While the spin dynamics in the regime of strong exchange
coupling J is rather complex and governed by an emergent new time scale, the
motion of the spin for weak J is regular and qualitatively well described by
the Landau-Lifschitz-Gilbert (LLG) equation. Quantitatively, however, the full
quantum-classical hybrid dynamics differs from the LLG approach. This is
understood as a breakdown of weak-coupling perturbation theory in J in the
course of time. Furthermore, it is shown that the concept of the Gilbert
damping parameter is ill-defined for the case of a one-dimensional system.",1507.08227v2
2021-09-08,Dynamics of spin relaxation in nonequilibrium magnetic nanojunctions,"We investigate nonequilibrium phenomena in magnetic nano-junctions using a
numerical approach that combines classical spin dynamics with the hierarchical
equations of motion technique for quantum dynamics of conduction electrons. Our
focus lies on the spin dynamics, where we observe non-monotonic behavior in the
spin relaxation rates as a function of the coupling strength between the
localized spin and conduction electrons. Notably, we identify a distinct
maximum at intermediate coupling strength, which we attribute to a competition
that involves the increasing influence of the coupling between the classical
spin and electrons, as well as the influence of decreasing local density of
states at the Fermi level. Furthermore, we demonstrate that the spin dynamics
of a large open system can be accurately simulated by a short chain coupled to
semi-infinite metallic leads. In the case of a magnetic junction subjected to
an external DC voltage, we observe resonant features in the spin relaxation,
reflecting the electronic spectrum of the system. The precession of classical
spin gives rise to additional side energies in the electronic spectrum, which
in turn leads to a broadened range of enhanced damping in the voltage.",2109.03476v3
2023-07-30,Spin dynamics in ordered phases of anisotropic triangular-lattice antiferromagnet Cs2CoBr4,"We study spin dynamics of ordered phases of Cs2CoBr4 in a magnetic field
using electron spin resonance (ESR) technique and theoretical analysis. This
material hosts weakly interacting distorted-triangular-lattice planes of
spin-3/2 Co(2+) ions which can be viewed as spin chains coupled by frustrating
interactions. Strong single-ion anisotropy allows to describe the low-energy
spin dynamics of this system by an effective strongly anisotropic
pseudospin-1/2 model. Our ESR data show up to seven branches of magnetic
resonance in four magnetic phases arising due to subtle interplay of
frustration, low dimensionality and strong anisotropy. In particular, in the
low-field collinear stripe phase, the field evolution of modes lying below 200
GHz is described reasonably good by spectra of spin-1 and spin-0 quasiparticles
which we obtain using the bond-operator technique. These well-defined
excitations can be treated as conventional magnons and bound states of two
magnons, respectively. In contrast, numerous excitations lying above 200 GHz
are not captured by our theory due to pronounced one-dimensional correlations
inside spin chains which govern the spin dynamics at high enough energies. As
it was shown before, these modes can be most naturally interpreted as bound
states of domain walls in individual chains and their sequence resembles the
so-called ""Zeeman ladder"" in anisotropic Ising-like spin chains. Thus, Cs2CoBr4
is a system showing spin-dynamics in ordered state characteristic of both
two-dimensional and one-dimensional magnets.",2307.16251v1
2024-02-08,Assessing the atomic moment picture of spin dynamics: the perspective of \textit{ab initio} magnon wavefunction,"Our understanding of collective spin fluctuation in materials relies largely
on Heisenberg-type spin Hamiltonians. Implicit in these spin models is the
atomic moment picture that in transverse spin dynamics the magnetization around
an atom undergoes precessional motion as a rigid moment, which has been
challenged by emerging theoretical and experimental advances. To assess the
validity of the atomic moment picture in spin dynamics, however, necessitates
magnon wavefunctions from \textit{ab initio} methods without \textit{a priori}
spin models. To this end, we develop an efficient model-free {\it ab initio}
method for computing magnon spectrum and wavefunctions. Niu-Kleinman's
adiabatic spin-wave dynamics is reformulated using linear perturbation theory
into a generalized eigenvalue problem, which can be solved to produce magnon
spectrum and wavefunctions without assuming atomic moments. We have implemented
this method in the framework of density functional perturbation theory (DFPT).
A dynamical extension of Niu-Kleinman equation of motion is proposed to improve
inaccurate predicted magnon energies due to imperfect adiabaticity at higher
energies. Based on so-obtained {\it ab initio} magnon wavefunctions, we find
the atomic moment picture to be valid in typical ferromagnets and
antiferromagnets, but fails in the molecular orbital crystal Na$_2$IrO$_3$. Our
results suggest that the usual spin Hamiltonian approach should be taken with a
grain of salt, and possible experimental ramification on the issue is
discussed.",2402.05473v2
1994-10-24,Anomalous Spin Dynamics in Doped Quantum Antiferromagnets,"Finite-temperature spin dynamics in planar t-J model is studied using the
method based on the Lanczos diagonalization of small systems. Dynamical spin
structure factor at moderate dopings shows the coexistence of free-fermion-like
and spin-fluctuation timescales. At T<J, the low-frequency and static
susceptibility show pronounced T dependence, supporting a scenario, related to
the marginal Fermi-liquid one, for the explanation of neutron-scattering and
NMR-relaxation experiments in cuprates. Calculated NMR relaxation rates
reasonably reproduce experimental ones.",9410085v1
1995-07-24,Dynamical Replica Theory for Disordered Spin Systems,"We present a new method to solve the dynamics of disordered spin systems on
finite time-scales. It involves a closed driven diffusion equation for the
joint spin-field distribution, with time-dependent coefficients described by a
dynamical replica theory which, in the case of detailed balance, incorporates
equilibrium replica theory as a stationary state. The theory is exact in
various limits. We apply our theory to both the symmetric- and the
non-symmetric Sherrington-Kirkpatrick spin-glass, and show that it describes
the (numerical) experiments very well.",9507101v1
1997-06-18,Kinetic Theory Approach to the SK Spin Glass Model with Glauber Dynamics,"I present a new method to analyze Glauber dynamics of the
Sherrington-Kirkpatrick (SK) spin glass model. The method is based on ideas
used in the classical kinetic theory of fluids. I apply it to study spin
correlations in the high temperature phase ($T\ge T_c$) of the SK model at zero
external field. The zeroth order theory is equivalent to a disorder dependent
local equilibrium approximation. Its predictions agree well with computer
simulation results. The first order theory involves coupled evolution equations
for the spin correlations and the dynamic (excess) parts of the local field
distributions. It accounts qualitatively for the error made in the zeroth
approximation.",9706185v1
2001-02-27,Control of Spin Dynamics of Excitons in Nanodots for Quantum Operations,"This work presents a step furthering a new perspective of proactive control
of the spin-exciton dynamics in the quantum limit. Laser manipulation of
spin-polarized optical excitations in a semiconductor nanodot is used to
control the spin dynamics of two interacting excitons. Shaping of femtosecond
laser pulses keeps the quantum operation within the decoherence time.
Computation of the fidelity of the operations and application to the complete
solution of a basic quantum computing algorithm demonstrate in theory the
feasibility of quantum control.",0102482v1
2002-01-09,Complex and Non-Complex Phase Structures in Models of Spin Glasses and Information Processing,"The gauge theory of spin glasses and statistical-mechanical formulation of
error-correcting codes are reviewed with an emphasis on their similarities. For
the gauge theory, we explain the functional identities on dynamical
autocorrelation functions and on the distribution functions of order
parameters. These functional identities restrict the possibilities of slow
dynamics and complex structure of the phase space. An inequality for
error-correcting codes is shown to be interpreted to indicate non-monotonicity
of spin orientation as a function of the temperature in spin glasses.",0201121v1
2002-07-18,Spin dynamics in a structurally ordered non-Fermi liquid compound: YbRh_2Si_2,"Muon spin relaxation (muSR) experiments have been carried out at low
temperatures in the non-Fermi-liquid heavy-fermion compound YbRh_2Si_2. The
longitudinal-field muSR relaxation function is exponential, indicative that the
dynamic spin fluctuations are homogeneous. The relaxation rate 1/T_1 varies
with applied field as H^{-y}, y = 1.0 \pm 0.1, which implies a scaling law of
the form \chi''(\omega) \propto \omega^{-y} f(\omega/T), \lim_{x\to0} f(x) = x
for the dynamic spin susceptibility.",0207464v1
2004-07-01,Perturbation approach to dipolar coupling spin dynamics,"A perturbation method is presented which can be applied to the description of
a wide range of physical problems that deal with dynamics of dipolar coupled
spins in solids. The method is based on expansion of the operator exponent in a
perturbation series. As example of application the method, the multile-quantum
coherence dynamics in three and four spin cluster are considered. The
calculated 0Q- and 2Q intensities vs the duration of the preparation period
give closed agreement with exact results and simulations data. The exact
solutions for J0Q and J2Q coherences in four spin system are obtained.",0407024v2
2005-09-22,Intrinsic spin dynamics in semiconductor quantum dots,"We investigate the characteristic spin dynamics corresponding to
semiconductor quantum dots within the multiband envelope function approximation
(EFA). By numerically solving an $8\times8$ $k\cdot p$ Hamiltonian we treat
systems based on different III-V semiconductor materials.It is shown that, even
in the absence of an applied magnetic field, these systems show intrinsic spin
dynamics governed by intraband and interband transitions leading to
characteristic spin frequencies ranging from the THz to optical frequencies.",0509587v1
2008-04-15,Exciton and hole spin dynamics in ZnO,"The carrier spin dynamics in ZnO is investigated by time-resolved optical
orientation experiments. We evidence a clear circular polarization of the
donor-bound exciton luminescence in both ZnO epilayer and non-intentionally
doped bulk ZnO. This allows us to measure the localized hole spin relaxation
time. We find $\tau^{s}_h$$\sim$350 ps at T=1.7 K in the ZnO epilayer. The
strong energy and temperature dependences of the photoluminescence polarization
dynamics are well explained by the fast free exciton spin relaxation time and
the ionization of bound excitons.",0804.2369v1
2008-10-05,Current-Induced Dynamics in Almost Symmetric Magnetic Nanopillars,"Magnetic nanodevices usually include a free layer whose configuration can be
changed by spin-polarized current via the spin transfer effect, and a fixed
reference layer. Here, we demonstrate that the roles of the free and the
reference layers interchange over a small range of their relative thicknesses.
Precession of both layers can be induced by spin transfer in symmetric devices,
but the dynamics of one of the layers is rapidly suppressed in asymmetric
devices. We interpret our results in terms of the dynamical coupling between
magnetic layers due to spin transfer.",0810.0863v1
2009-02-20,Perturbation theory of the dynamic inverse spin Hall effect with charge conservation,"We present gauge-invariant theory of the dynamic inverse spin Hall effect
driven by the spin--orbit interaction in metallic systems. Charge conservation
is imposed diagrammatically by including vertex corrections. We show the charge
current is induced by an effective electric field that is proportional to the
spin current pumped by the magnetization dynamics. The result is consistent
with recent experiments.",0902.3507v2
2009-03-10,Dynamics of coupled spins in the white- and quantum-noise regime,"We study the dynamics of dissipative spins for general spin-spin coupling. We
investigate the population dynamics and relaxation of the purity in the white
noise regime, in which exact results are available. Inter alia, we find
distinct reduction of decoherence and slowdown of purity decay around
degeneracy points. We also determine in analytic form the one-phonon exchange
contribution to decoherence and relaxation in the ohmic quantum noise regime
valid down to zero temperature.",0903.1809v1
2010-07-25,On the dynamics of classical particle with spin,"The complete explicitly covariant 4-dimensional description of the dynamics
of a free classical particle with spin within the framework of the special
relativity theory is presented. The key point of our approach is the the
introduction of the new vector field which enables to define the analogues of
the mean spin and position variables. The supplementary conditions are
discussed and it is demonstrated that the Frenkel condition unambiguously
determines the dynamics of a spinning particle.",1007.4337v1
2011-10-07,Dynamical Decoupling of Spin-Clusters using Solid State NMR,"In this work we experimentally study the efficiency of various dynamical
decoupling sequences for suppressing decoherence of single as well as multiple
quantum coherences on large spin-clusters. The system involves crystallites of
a powdered sample containing a large number of molecular protons interacting
via long-range dipole-dipole interaction. The multiple quantum coherences are
prepared by progressively creating correlations in the spin lattice using
standard pulse sequences implementing two-quantum average Hamiltonian. The spin
system is then subjected to various dynamical decoupling sequences, followed by
conversion into observable single quantum coherence by using time-reversal
sequence. The experiments reveal superior performance of the recently
introduced RUDD sequences in suppressing the decoherence.",1110.1473v1
2012-10-16,Spinning motion of a deformable self-propelled particle in two dimensions,"We investigate the dynamics of a single deformable self-propelled particle
which undergoes a spinning motion in a two-dimensional space. Equations of
motion are derived from the symmetry argument for three kinds of variables. One
is a vector which represents the velocity of the centre of mass. The second is
a traceless symmetric tensor representing deformation. The third is an
antisymmetric tensor for spinning degree of freedom. By numerical simulations,
we have obtained variety of dynamical states due to interplay between the
spinning motion and the deformation. The bifurcations of these dynamical states
are analyzed by the simplified equations of motion.",1210.4424v1
2012-12-21,Dynamical spin response of electron doped Mott insulators on a triangular lattice,"The spin dynamics of electron doped Mott insulators on a triangular lattice
is studied based on the $t-J$ model. It is found that the particularly
universal behaviors of integrated dynamical spin structure factor seen in the
doped Mott insulators on a square lattice, are absent in the doped Mott
insulators on a triangular lattice, indicating the presence of the normal state
gap. As a result, the spin-lattice relaxation rate 1/$T_{1}$ divided by $T$
reduces with decreasing temperatures in the temperature region above
0.2$J$$\approx$50K, then follows a Curie-Weiss-like behavior at the temperature
less than 50K, in qualitative agreement with experimental observations.",1212.5371v1
2013-06-05,Inertial longitudinal magnetization reversal for non-Heisenberg ferromagnets,"We analyze theoretically the novel pathway of ultrafast spin dynamics for
ferromagnets with high enough single-ion anisotropy (non-Heisenberg
ferromagnets). This longitudinal spin dynamics includes the coupled
oscillations of the modulus of the magnetization together with the quadrupolar
spin variables, which are expressed through quantum expectation values of
operators bilinear on the spin components. Even for a simple single-element
ferromagnet, such a dynamics can lead to an inertial magnetization reversal
under the action of an ultrashort laser pulse.",1306.1108v2
2014-10-15,Micromagnetic Study of Spin Transfer driven Vortex Dipole and Vortex Quadrupole Dynamics,"Vortices and antivortices are typical non uniform magnetization
configurations that can be achieved in spin-torque oscillators with in-plane
materials. Dynamics of a vortex-antivortex pair, namely vortex dipole, were
predicted and already observed. In this paper, we present a systematic
micromagnetic study on that kind of dynamics in different spin-valves where the
current is injected through a nano-aperture. Rotation and translation of vortex
dipoles and rotation of vortex quadrupoles are shown depending on the shape and
the size of the spin-valve. The origin of the different behaviors is explained
within a micromagnetic framework.",1410.3957v1
2015-06-29,Pseudo-Spin Based Dynamical Model for Polarisation Switching in Ferroelectrics,"A microscopic view of the response of the electric dipoles to a dynamic
external field in a ferroelectric (FE) chain has been studied by two spin
dynamics methods. One is the prominent micromagnetic approach, and the other is
the micromagnetic approach with a variable size of the pseudo-spin. The energy
stored in the ferroelectric chain is described by the transverse Ising model
(TIM) with electric pseudo-spins. The simulations are based on a modified
Landau-Lifshitz-Gilbert (LLG) equation which is precession free. The results
obtained are shown and compared with the result supplemented by
Landau-Devonshire (L-D) theory in the Appendix.",1506.08500v2
2017-02-09,Transient spin dynamics in a single-molecule magnet,"We explore the limitations and validity of semi-classically formulated spin
equations of motion. Using a single-molecule magnet as a test model, we employ
three qualitatively different approximation schemes. From a microscopic model,
we derive a generalized spin equation of motion in which the parameters have a
non-local time-dependence. This dynamical equation is simplified to the
Landau-Lifshitz-Gilbert equation with i) time-dependent, and ii)
time-independent parameters. We show that transient dynamics is essentially
non-existing in the latter approximation, while the former breaks down in the
regime of strong coupling between the spin and the itinerant electrons.",1702.02820v2
2010-05-17,QND Measurement of Large-Spin Ensembles by Dynamical Decoupling,"Quantum non-demolition (QND) measurement of collective variables by
off-resonant optical probing has the ability to create entanglement and
squeezing in atomic ensembles. Until now, this technique has been applied to
real or effective spin one-half systems. We show theoretically that the
build-up of Raman coherence prevents the naive application of this technique to
larger spin atoms, but that dynamical decoupling can be used to recover the
ideal QND behavior. We experimentally demonstrate dynamical decoupling by using
a two-polarization probing technique. The decoupled QND measurement achieves a
sensitivity 5.7(6) dB better than the spin projection noise.",1005.2807v1
2014-05-02,Dynamic nuclear polarization from current-induced electron spin polarization,"Current-induced electron spin polarization is shown to produce nuclear
hyperpolarization through dynamic nuclear polarization. Saturated fields of
several millitesla are generated upon the application of electric field over a
timescale of a hundred seconds in InGaAs epilayers and measured using optical
Larmor magnetometry. The dependence on temperature, external magnetic field,
and applied voltage is investigated. We find an asymmetry in which the
saturation nuclear field depends on the relative alignment of the electrically
generated spin polarization and the external magnetic field, which we attribute
to an interplay between various electron spin dynamical processes.",1405.0342v1
2016-05-08,Heisenberg Operator Approach for Spin Squeezing Dynamics,"We reconsider the one-axis twisting Hamiltonian, which is commonly used for
generating spin squeezing, and treat its dynamics within the Heisenberg
operator approach. To this end we solve the underlying Heisenberg equations of
motion perturbatively and evaluate the expectation values of the resulting
time-dependent Heisenberg operators in order to determine approximately the
dynamics of spin squeezing. Comparing our results with those originating from
exact numerics reveals that they are more accurate than the commonly used
frozen spin approximation.",1605.02274v3
2018-03-27,The fate of atomic spin in atomic scattering off surfaces,"We explore model electron dynamics of an atom scattering off a surface within
the time-dependent complete active space self consistent field (TD-CASSCF)
approximation. We focus especially on the scattering of a hydrogen atom and its
resulting spin-dynamics starting from an initially spin-polarized state. Our
results reveal competing electronic time-scales that are governed by the
electronic structure of the surface as well as the character of the atom. The
timescales and nonadiabaticity of the dynamics are reported on by the final
spin-polarization of the scattered atom, which may be probed in future
experiments.",1803.09895v1
2022-08-26,"Cooperative dynamics in two-component out-of-equilibrium systems: Molecular ""spinning tops""","We study the two-dimensional Langevin dynamics of a two-component system,
whose components are in contact with heat baths kept at different temperatures.
Dynamics is constrained by an optical trap and
  the \text{dissimilar} species interact via a quadratic potential. We realize
that the system evolves towards a peculiar non-equilibrium steady-state with a
non-zero probability current possessing a non-zero curl, such that the randomly
moving particles are spinning around themselves, like ""spinning top"" toys. Our
analysis shows that the spinning motion is correlated and also reveals an
emerging cooperative behavior of the spatial components of the probability
currents of dissimilar species.",2208.12768v1
2023-02-10,Patterning by dynamically unstable spin-orbit-coupled Bose-Einstein condensates,"In a two-dimensional atomic Bose-Einstein condensate, we demonstrate Rashba
spin-orbit coupling can always introduce dynamical instability into specific
zero-quasimomentum states in all parameter regimes. During the evolution of the
zero-quasimomentum states, such spin-orbit-coupling-induced instability can
fragment the states and lead to a dynamically patterning process.
  The features of formed patterns are identified from the symmetries of the
Bogoliubov-de Gennes Hamiltonian. We show that spin-orbit-coupled Bose-Einstein
condensates provide an interesting platform for the investigation of pattern
formations.",2302.05101v2
2023-11-17,Enhancing Electron-Nuclear Resonances by Dynamical Control Switching,"We present a general method to realize resonant coupling between spins even
though their energies are of different scales. Applying the method to the
electron and nuclear spin systems such as a nitrogen-vacancy (NV) center with
its nearby nuclei, we show that a specific dynamical switching of the electron
spin Rabi frequency achieves efficient electron-nuclear coupling, providing a
much stronger quantum sensing signal and dynamic nuclear polarization than
previous methods. This protocol has applications in high-field nanoscale
nuclear magnetic resonances as well as low-power quantum control of nuclear
spins.",2311.10650v1
2024-01-30,One-excitation spin dynamics in homogeneous closed chain governed by XX-Hamiltonian,"We analytically investigate the one-excitation spin dynamics in a homogeneous
closed spin-1/2 chain via diagonalization of the one-excitation block of the
XX-Hamiltonian, which allows to derive the analytical expressions for
probability amplitudes describing state transfers between any two spins of a
chain. We analytically investigate the $M$-neighbor approximation ($M\ge 1$) of
spin dynamics with arbitrary initial state and analyze its accuracy using
special integral characteristics defined in terms of the above probability
amplitudes. We find $M$ providing the required accuracy of evolution
approximation for chains of different lengths.",2401.16902v1
2013-04-02,Modeling Multi-Magnet Networks Interacting Via Spin Currents,"The significant experimental advances of the last few decades in dealing with
the interaction of spin currents and nanomagnets, at the device level, has
allowed envisioning a broad class of devices that propose to implement
information processing using spin currents and nanomagnets. To analyze such
spin-magnet logic circuits, in general, we have developed a coupled
spin-transport/ magnetization-dynamics simulation framework that could be
broadly applicable to various classes of spin-valve/ spin-torque devices.
Indeed, the primary purpose of this chapter is to describe in detail, the
overall approach we have developed to include a description of spin transport
coupled with magnetization dynamics and to show how it was benchmarked against
available data on experiments.
  We address non-collinear spin-transport in Section-2 using a lumped
""4-component spin-circuit formalism"" that describes the interaction of
non-collinear magnets (required for modeling spin torque), by computing
4-component currents and voltages at every node of a ""circuit"". For modeling
the magnetization dynamics, we use the standard Landau-Lifshitz-Gilbert (LLG)
equation with the Slonczewski and the field-like terms included for spin
torque. Section-3 describes how this LLG model is coupled with the spin
transport model to analyze spin-torque experiments and spin-magnet circuits in
general.
  We include MATLAB codes in the Appendix to facilitate a ""hands-on""
understanding of our model and hope it will enable interested readers to
conveniently analyze their own experiments, develop a deeper insight into
spin-magnet circuits or come up with their own creative designs.",1304.0742v3
2017-03-22,Fast domain wall motion induced by antiferromagnetic spin dynamics at the angular momentum compensation temperature of ferrimagnets,"Antiferromagnetic spintronics is an emerging research field which aims to
utilize antiferromagnets as core elements in spintronic devices. A central
motivation toward this direction is that antiferromagnetic spin dynamics is
expected to be much faster than ferromagnetic counterpart because
antiferromagnets have higher resonance frequencies than ferromagnets. Recent
theories indeed predicted faster dynamics of antiferromagnetic domain walls
(DWs) than ferromagnetic DWs. However, experimental investigations of
antiferromagnetic spin dynamics have remained unexplored mainly because of the
immunity of antiferromagnets to magnetic fields. Furthermore, this immunity
makes field-driven antiferromagnetic DW motion impossible despite rich physics
of field-driven DW dynamics as proven in ferromagnetic DW studies. Here we show
that fast field-driven antiferromagnetic spin dynamics is realized in
ferrimagnets at the angular momentum compensation point TA. Using rare-earth
3d-transition metal ferrimagnetic compounds where net magnetic moment is
nonzero at TA, the field-driven DW mobility remarkably enhances up to 20 km/sT.
The collective coordinate approach generalized for ferrimagnets and atomistic
spin model simulations show that this remarkable enhancement is a consequence
of antiferromagnetic spin dynamics at TA. Our finding allows us to investigate
the physics of antiferromagnetic spin dynamics and highlights the importance of
tuning of the angular momentum compensation point of ferrimagnets, which could
be a key towards ferrimagnetic spintronics.",1703.07515v1
2013-11-07,Spin-Orbit Torques and Anisotropic Magnetization Damping in Skyrmion Crystals,"The length scale of the magnetization gradients in chiral magnets is
determined by the relativistic Dzyaloshinskii-Moriya interaction. Thus, even
conventional spin-transfer torques are controlled by the relativistic
spin-orbit coupling in these systems, and additional relativistic corrections
to the current-induced torques and magnetization damping become important for a
complete understanding of the current-driven magnetization dynamics. We
theoretically study the effects of reactive and dissipative homogeneous
spin-orbit torques and anisotropic damping on the current-driven skyrmion
dynamics in cubic chiral magnets. Our results demonstrate that spin-orbit
torques play a significant role in the current-induced skyrmion velocity. The
dissipative spin-orbit torque generates a relativistic Magnus force on the
skyrmions, whereas the reactive spin-orbit torque yields a correction to both
the drift velocity along the current direction and the transverse velocity
associated with the Magnus force. The spin-orbit torque corrections to the
velocity scale linearly with the skyrmion size, which is inversely proportional
to the spin-orbit coupling. Consequently, the reactive spin-orbit torque
correction can be the same order of magnitude as the non-relativistic
contribution. More importantly, the dissipative spin-orbit torque can be the
dominant force that causes a deflected motion of the skyrmions if the torque
exhibits a linear or quadratic relationship with the spin-orbit coupling. In
addition, we demonstrate that the skyrmion velocity is determined by
anisotropic magnetization damping parameters governed by the skyrmion size.",1311.1778v1
2013-11-08,Spin-noise in the anisotropic central spin model,"Spin-noise measurements can serve as direct probe for the microscopic
decoherence mechanism of an electronic spin in semiconductor quantum dots
(QD).We have calculated the spin-noise spectrum in the anisotropic central spin
model using a Chebyshev expansion technique which exactly accounts for the
dynamics up to an arbitrary long but fixed time in a finite size system. In the
isotropic case, describing QD charged with a single electron, the short-time
dynamics is in good agreement with a quasi-static approximation for the
thermodynamic limit. The spin-noise spectrum, however, shows strong deviations
at low frequencies with a power-law behavior. In the Ising limit, applicable to
QDs with heavy-hole spins, the spin-noise spectrum exhibits a threshold
behavior above the Larmor frequency. In the generic anisotropic central spin
model we have found a crossover from a Gaussian type of spin-noise spectrum to
a more Ising-type spectrum with increasing anisotropy in a finite magnetic
field. In order to make contact with experiments, we present ensemble averaged
spin-noise spectra for QD ensembles charged with single electrons or holes. The
Gaussian-type noise spectrum evolves to a more Lorentzian shape spectrum with
increasing spread of characteristic time-scales and g-factors of the individual
QDs.",1311.2030v1
2014-06-24,Real-time dynamics of spin-dependent transport through a double-quantum-dot Aharonov-Bohm interferometer with spin-orbit interaction,"The spin-resolved non-equilibrium real-time electron transport through a
double-quantum-dot (DQD) Aharonov-Bohm (AB) interferometer with spin-orbit
interaction (SOI) is explored. The SOI and AB interference in the real-time
dynamics of spin transport is expressed by effective magnetic fluxes.
Analytical formulae for the time-dependent currents, for initially unpolarized
spins, are presented. In many cases, there appear spin currents in the
electrodes, for which the spins in each electrode are polarized along
characteristic directions, pre-determined by the SOI parameters and by the
geometry of the system. Special choices of the system parameters yield
steady-state currents in which the spins are fully polarized along these
characteristic directions. The time required to reach this steady state depends
on the couplings of the DQD to the leads. The magnitudes of the currents depend
strongly on the SOI-induced effective fluxes. Without the magnetic flux, the
spin-polarized current cannot be sustained to the steady states, due to the
phase rigidity for this system. For a non-degenerate DQD, transient spin
transport can be produced by the sole effects of SOI. We also show that one can
extract the spin-resolved currents from measurements of the total charge
current.",1406.6258v2
2019-06-12,Binary neutron star mergers: Effects of spin and post-merger dynamics,"Spin can have significant effects on the electromagnetic transients
accompanying binary neutron star mergers. The measurement of spin can provide
important information about binary formation channels. In the absence of a
strong neutron star spin prior, the degeneracy of spin with other parameters
leads to significant uncertainties in their estimation, in particular limiting
the power of gravitational waves to place tight constraints on the nuclear
equation of state. Thus detailed studies of highly spinning neutron star
mergers are essential to understand all aspects of multimessenger observation
of such events. We perform a systematic investigation of the impact of neutron
star spin---considering dimensionless spin values up to $a_{\rm NS}=0.33$---on
the merger of equal mass, quasicircular binary neutron stars using fully
general-relativistic simulations. We find that the peak frequency of the
post-merger gravitational wave signal is only weakly influenced by the neutron
star spin, with cases where the spin is aligned (antialigned) with the orbital
angular momentum giving slightly lower (higher) values compared to the
irrotational case. We find that the one-arm instability arises in a number of
cases, with some dependence on spin. Spin has a pronounced impact on the mass,
velocity, and angular distribution of the dynamical ejecta, and the mass of the
disk that remains outside the merger remnant. We discuss the implications of
these findings on anticipated electromagnetic signals, and on constraints that
have been placed on the equation of state based on multimessenger observations
of GW170817.",1906.05288v2
2018-07-24,Microscopic Theory of Spin Relaxation Anisotropy in Graphene with Proximity-Induced Spin-Orbit Coupling,"Inducing sizable spin--orbit interactions in graphene by proximity effect is
establishing as a successful route to harnessing two-dimensional Dirac fermions
for spintronics. Semiconducting transition metal dichalcogenides (TMDs) are an
ideal complement to graphene because of their strong intrinsic spin--orbit
coupling (SOC) and spin/valley-selective light absorption, which allows
all-optical spin injection into graphene. In this study, we present a
microscopic theory of spin dynamics in weakly disordered graphene samples
subject to uniform proximity-induced SOC as realized in graphene/TMD bilayers.
A time-dependent perturbative treatment is employed to derive spin Bloch
equations governing the spin dynamics at high electronic density. Various
scenarios are predicted, depending on a delicate competition between
interface-induced Bychkov-Rashba and spin--valley (Zeeman-type) interactions
and the ratio of intra- to inter-valley scattering rates. For weak SOC compared
to the disorder-induced quasiparticle broadening, the anisotropy ratio of
out-of-plane to in-plane spin lifetimes
$\zeta=\tau_{s}^{\perp}/\tau_{s}^{\parallel}$ agrees qualitatively with a toy
model of spins in a weak fluctuating SOC field recently proposed by Cummings
and co-workers [PRL 119, 206601 (2017)]. In the opposite regime of
well-resolved SOC, qualitatively different formulae are obtained, which can be
tested in ultra-clean heterostructures characterized by uniform
proximity-induced SOC in the graphene layer.",1807.09275v1
2020-05-20,Controlling the propagation of dipole-exchange spin waves using local inhomogeneity of the anisotropy,"Spin waves are promising candidates to carry, transport, and process
information. Controlling the propagation characteristics of spin waves in
magnetic materials is an essential ingredient for designing spin-wave based
computing architectures. Here, we study the influence of surface
inhomogeneities on the spin-wave signals transmitted through thin films. We use
micromagnetic simulations to study the spin-wave dynamics in an in-plane
magnetized yttrium iron garnet thin film with a thickness in the nanometre
range in the presence of surface defects in the form of locally introduced
uniaxial anisotropies. These defects are used to demonstrate that the Backward
Volume Magnetostatic Spin Waves (BVMSW) are more responsive to backscattering
in comparison to Magnetostatic Surface Spin Waves (MSSWs). For this particular
defect type, the reason for this behavior can be quantitatively related to the
difference in the magnon band structures for the two types of spin waves. To
demonstrate this, we develop a quasi-analytical theory for the scattering
process. It shows an excellent agreement with the micromagnetic simulations,
sheds light on the backscattering processes and provides a new way to analyze
the spin-wave transmission rates in the presence of surface inhomogeneities in
sufficiently thin films, for which the role of exchange energy in the spin-wave
dynamics is significant. Our study paves the way to designing magnonic logic
devices for data processing which rely on a designed control of the spin-wave
transmission.",2005.09965v2
2021-03-30,"Theoretical study of quantum spin liquids in $S=1/2$ hyper-hyperkagome magnets: classification, heat capacity, and dynamical spin structure factor","Recent experiments suggest a quantum spin liquid ground state in the material
PbCuTe$_2$O$_6$, where $S=1/2$ moments are coupled by antiferromagnetic
Heisenberg interactions into a three dimensional structure of corner sharing
triangles dubbed the hyper-hyperkagome lattice. It exhibits a richer
connectivity, and thus likely a stronger geometric frustration, than the
relatively well studied hyperkagome lattice. Here, we investigate the possible
quantum spin liquids in the $S=1/2$ hyper-hyperkagome magnet using the complex
fermion mean field theory. Extending the results of a previous projective
symmetry group analysis, we identify only two $\mathbb{Z}_2$ spin liquids and a
$U(1)$ spin liquid that are compatible with the hyper-hyperkagome structure.
The $U(1)$ spin liquid has a spinon Fermi surface. For the $\mathbb{Z}_2$ spin
liquids, one has a small excitation gap, while the other is gapless and
proximate to the $U(1)$ spin liquid. We show that the gapped and gapless spin
liquids can in principle be distinguished by heat capacity measurements.
Moreover, we calculate the dynamical spin structure factors of all three spin
liquids and find that they highly resemble the inelastic neutron scattering
spectra of PbCuTe$_2$O$_6$. Implications of our work to the experiments, as
well as its relations to the existing theoretical studies, are discussed.",2103.16570v1
2021-09-22,Dynamical Spin-Orbit-Based Spin Transistor,"Spin-orbit interaction (SOI) has been a key tool to steer and manipulate
spin-dependent transport properties in two-dimensional electron gases. Here we
demonstrate how spin currents can be created and efficiently read out in nano-
or mesoscale conductors with time-dependent and spatially inhomogeneous Rashba
SOI. Invoking an underlying non-Abelian SU(2) gauge structure we show how
time-periodic spin-orbit fields give rise to spin electric forces and enable
the generation of pure spin currents of the order of several hundred
nano-Amperes. In a complementary way, by combining gauge transformations with
""hidden"" Onsager relations, we exploit spatially inhomogeneous Rashba SOI to
convert spin currents (back) into charge currents. In combining both concepts,
we devise a spin transistor that integrates efficient spin current generation,
by employing dynamical SOI, with its experimentally feasible detection via
conversion into charge signals. We derive general expressions for the
respective spin- and charge conductance, covering large parameter regimes of
SOI strength and driving frequencies, far beyond usual adiabatic approaches
such as the frozen scattering matrix approximation. We check our analytical
expressions and approximations with full numerical spin-dependent transport
simulations and demonstrate that the predictions hold true in a wide range from
low to high driving frequencies.",2109.10991v4
2022-07-06,Robust millisecond coherence times of erbium electron spins,"Erbium-doped solids are prime candidates for optical quantum communication
networks due to erbium's telecom C-band emission. A long-lived electron spin of
erbium with millisecond coherence time is highly desirable for establishing
entanglement between adjacent quantum repeater nodes while long-term storage of
the entanglement could rely on transferring to erbium's second-long coherence
nuclear spins. Here we report GHz-range electron spin transitions of
$^{167}\mathrm{Er}^{3+}$ in yttrium oxide ($\mathrm{Y_2O_3}$) matrix with
coherence times that are consistently longer than a millisecond. Instead of
addressing field-specific Zero First-Order Zeeman transitions, we probe weakly
mixed electron spins with the field orientation along the lower g-factors.
Using pulsed electron spin resonance spectroscopy, we find paramagnetic
impurities are the dominant source of decoherence, and by polarizing them we
achieve a Hahn echo spin $\mathrm{T_2}$ up to 1.46 ms, and a coherence time up
to 7.1 ms after dynamical decoupling. These coherence lifetimes are among the
longest found in crystalline hosts especially those with nuclear spins. We
further enhance the coherence time beyond conventional dynamical decoupling,
using customized sequences to simultaneously mitigate spectral diffusion and
Er-Er dipolar interactions. Despite nuclear and impurity spins in the host,
this work shows that long-lived erbium spins comparable to non-nuclear spin
hosts can be achieved. Our study not only establishes $^{167}\mathrm{Er}^{3+}$:
$\mathrm{Y_2 O_3}$ as a significantly promising quantum memory platform but
also provides a general guideline for engineering long-lived erbium spins in a
variety of host materials for quantum technologies.",2207.02708v1
2022-02-28,"Density Functional description of spin, lattice, and spin-lattice dynamics in antiferromagnetic and paramagnetic phases at finite temperatures","Describing the (a) electronic and magnetic properties (EMP) of
antiferromagnetic or paramagnetic phases of compounds generally requires the
knowledge of (b) the spin configurations and lattice structure (SCLS) of such
phases at a given temperature. Indeed, studying the coupling between (a) and
(b) has been an outstanding challenge in the theory of magnetism. The
traditional approach to electronic phases of matter has generally focused on
solving the problem of EMP regarding the SCLS as a spectator degree of freedom
(DOF). Yet, it has been recognized that EMP of a compound generally respond
self-consistently to changes in SCLS and vice versa. We construct here a
practical, density functional theory (DFT)-based approach that provides the
SCLS as a function of temperature, involving the description of spin, lattice,
and spin-lattice dynamics of different magnetic phases. We distinguish three
Levels of dynamics: (I) dynamics of the spin DOF treated via noncollinear
Heisenberg Monte-Carlo with exchange energies from DFT, (II) dynamics of the
lattice DOF treated by ab initio molecular dynamics (AIMD) employing a fixed
spin configuration from Level I at the simulated temperature, and (III)
coupling of spin and lattice dynamics via Landau-Lifshitz-Gilbert spin dynamics
combined with AIMD. Such SCLS at each of the three levels are used as inputs to
DFT supercell calculations, providing the EMP at each temperature. The results
of this sequence include electronic band structures, band gaps, density of
states, as well as the statistical distribution of local moments and the
short-range order parameters, each as a function of temperature. Using NiO as a
test case, we address the separability of the DOF in magnetic insulators for a
minimal description of electronic and magnetic properties, demonstrating that
inclusion of spin dynamics and, to some level, lattice dynamics is enough to
explain the EMP.",2202.13723v2
1995-09-22,Critical Dynamics of Magnets,"We review our current understanding of the critical dynamics of magnets above
and below the transition temperature with focus on the effects due to the
dipole--dipole interaction present in all real magnets. Significant progress in
our understanding of real ferromagnets in the vicinity of the critical point
has been made in the last decade through improved experimental techniques and
theoretical advances in taking into account realistic spin-spin interactions.
We start our review with a discussion of the theoretical results for the
critical dynamics based on recent renormalization group, mode coupling and spin
wave theories. A detailed comparison is made of the theory with experimental
results obtained by different measuring techniques, such as neutron scattering,
hyperfine interaction, muon--spin--resonance, electron--spin--resonance, and
magnetic relaxation, in various materials. Furthermore we discuss the effects
of dipolar interaction on the critical dynamics of three--dimensional isotropic
antiferromagnets and uniaxial ferromagnets. Special attention is also paid to a
discussion of the consequences of dipolar anisotropies on the existence of
magnetic order and the spin--wave spectrum in two--dimensional ferromagnets and
antiferromagnets. We close our review with a formulation of critical dynamics
in terms of nonlinear Langevin equations.",9509141v1
2000-09-06,Dynamical Properties of the 1/r^2-Type Supersymmetric t-J Model in a Magnetic Field: Manifestation of Spin-Charge Separation,"Quasi-particle picture in a magnetic field is pursued for dynamical spin and
charge correlation functions of the one-dimensional supersymmetric t-J model
with inverse-square interaction. With use of exact diagonalization and the
asymptotic Bethe-ansatz equations for finite systems, excitation contents of
relevant excited states are identified which are valid in the thermodynamic
limit. The excitation contents are composed of spinons, antispinons, holons and
antiholons obeying fractional statistics. Both longitudinal and transverse
components of the dynamical spin structure factor are independent of the
electron density in the region where only quasi-particles with spin degrees of
freedom (spinons and antispinons) contribute. The dynamical charge structure
factor does not depend on the spin-polarization density in the region where
only quasi-particles with charge (holons and antiholons) are excited. These
features indicate the strong spin-charge separation in dynamics, reflecting the
high symmetry of the model.",0009075v1
2004-07-20,Solution for the dynamics of the BCS and central spin problems,"We develop an explicit description of a time-dependent response of fermionic
condensates to perturbations. The dynamics of Cooper pairs at times shorter
than the energy relaxation time can be described by the BCS model. We obtain a
general explicit solution for the dynamics of the BCS model. We also solve a
closely related dynamical problem - the central spin model, which describes a
localized spin coupled to a ""spin bath"". Here, we focus on presenting the
solution and describing its general properties, but also mention some
applications, e.g. to nonstationary pairing in cold Fermi gases and to the
issue of electron spin decoherence in quantum dots. A typical dynamics of the
BCS and central spin models is quasi-periodic with a large number of
frequencies and stable under small perturbations. We show that for certain
special initial conditions the number of frequencies decreases and the solution
simplifies. In particular, periodic solutions correspond to the ground state
and excitations of the BCS model.",0407501v2
2006-09-07,Spin dynamics in copper metaborate $CuB_2 O_4$ studied by muon spin relaxation,"Copper metaborate CuB$_2$O$_{4}$ was studied by muon spin relaxation
measurements in order to clarify its static and dynamic magnetic properties.
The time spectra of muon spin depolarization suggest that the local fields at
the muon site contain both static and fluctuating components in all ordered
phases down to 0.3 K. In the weak ferromagnetic phase (20 K~$>T>$~9.3 K), the
static component is dominant. On the other hand, upon cooling the fluctuating
component becomes dominant in the incommensurate helix phase (9.3K > T > 1.4K).
The dynamical fluctuations of the local fields persist down to 0.3K, where a
new incommensurate phase (T < 1.4K) is expected to appear. This result suggests
that spins fluctuate even at T \to 0. We propose two possible origins of the
remnant dynamical spin fluctuations: frustration of the exchange interactions
and the dynamic behavior of the soliton lattice.",0609152v1
2006-11-21,Exact results for spin dynamics and fractionization in the Kitaev Model,"We present certain exact analytical results for dynamical spin correlation
functions in the Kitaev Model. It is the first result of its kind in
non-trivial quantum spin models. The result is also novel: in spite of presence
of gapless propagating Majorana fermion excitations, dynamical two spin
correlation functions are identically zero beyond nearest neighbor separation,
showing existence of a gapless but short range spin liquid. An unusual,
\emph{all energy scale fractionization}of a spin -flip quanta, into two
infinitely massive $\pi$-fluxes and a dynamical Majorana fermion, is shown to
occur. As the Kitaev Model exemplifies topological quantum computation, our
result presents new insights into qubit dynamics and generation of topological
excitations.",0611547v2
2009-05-28,Hydrodynamic theory of coupled current and magnetization dynamics in spin-textured ferromagnets,"We develop the hydrodynamical theory of collinear spin currents coupled to
magnetization dynamics in metallic ferromagnets. The collective spin density
couples to the spin current through a U(1) Berry-phase gauge field determined
by the local texture and dynamics of the magnetization. We determine
phenomenologically the dissipative corrections to the equation of motion for
the electronic current, which consist of a dissipative spin-motive force
generated by magnetization dynamics and a magnetic texture-dependent
resistivity tensor. The reciprocal dissipative, adiabatic spin torque on the
magnetic texture follows from the Onsager principle. We investigate the effects
of thermal fluctuations and find that electronic dynamics contribute to a
nonlocal Gilbert damping tensor in the Landau-Lifshitz-Gilbert equation for the
magnetization. Several simple examples, including magnetic vortices, helices,
and spirals, are analyzed in detail to demonstrate general principles.",0905.4544v2
2011-07-06,"Eu2+ spin dynamics in the filled skutterudites EuM4Sb12 (M = Fe, Ru, Os)","We report evidence for a close relation between the thermal activation of the
rattling motion of the filler guest atoms, and inhomogeneous spin dynamics of
the Eu2+ spins. The spin dynamics is probed directly by means of Eu2+ electron
spin resonance (ESR), performed in both X-band (9.4 GHz) and Q-band (34 GHz)
frequencies in the temperature interval 4.2 < T < 300 K. A comparative study
with ESR measurements on the Beta-Eu8Ga16Ge30 clathrate compound is presented.
Our results point to a correlation between the rattling motion and the spin
dynamics which may be relevant for the general understanding of the dynamics of
cage systems.",1107.1165v1
2015-03-30,Nonequilibrium dynamics of spin-orbit coupled lattice bosons,"We study the non-equilibrium dynamics of two component bosonic atoms in a
one-dimensional optical lattice in the presence of spin-orbit coupling. In the
Mott insulating regime, the two-component bosonic system at unity filling can
be described by the quantum spin XXZ model. The atoms are initially prepared in
their lower spin states. The system becomes out of equilibrium by suddenly
introducing spin-orbit coupling to the atoms. The system shows the relaxation
and non-stationary dynamics, respectively, in the different interaction
regimes. We find that the time average of magnetization is useful to
characterize the many-body dynamics. The effects of even and odd numbers of
sites are discussed. Our result sheds light on non-equilibrium dynamics due to
the interplay between spin-orbit coupling and atomic interactions.",1503.08605v2
2018-02-02,Controllable Non-Markovianity for a Spin Qubit in Diamond,"We present a flexible scheme to realize non-artificial non-Markovian dynamics
of an electronic spin qubit, using a nitrogen-vacancy center in diamond where
the inherent nitrogen spin serves as a regulator of the dynamics. By changing
the population of the nitrogen spin, we show that we can smoothly tune the
non-Markovianity of the electron spin's dynamic. Furthermore, we examine the
decoherence dynamics induced by the spin bath to exclude other sources of
non-Markovianity. The amount of collected measurement data is kept at a minimum
by employing Bayesian data analysis. This allows for a precise quantification
of the parameters involved in the description of the dynamics and a prediction
of so far unobserved data points.",1802.00819v2
2020-07-13,Quenching dynamics of the bright solitons and other localized states in spin-orbit coupled Bose-Einstein condensates,"We study the dynamics of binary Bose-Einstein condensates made of ultracold
and dilute alkali-metal atoms in a quasi-one-dimensional setting. Numerically
solving the two coupled Gross-Pitaevskii equations which accurately describe
the system dynamics, we demonstrate that the spin transport can be controlled
by suitably quenching spin-orbit (SO) and Rabi coupling strengths. Moreover, we
predict a variety of dynamical features induced by quenching: broken
oscillations, breathers-like oscillating patterns, spin-mixing-demixing,
miscible-immiscible transition, emerging dark-bright states, dark solitons, and
spin-trapping dynamics. We also outline the experimental relevance of the
present study in manipulating the spin states in $^{39}$K condensates.",2007.06171v1
2010-05-04,Hamiltonian dynamics and spectral theory for spin-oscillators,"We study the Hamiltonian dynamics and spectral theory of spin-oscillators.
Because of their rich structure, spin-oscillators display fairly general
properties of integrable systems with two degrees of freedom. Spin-oscillators
have infinitely many transversally elliptic singularities, exactly one
elliptic-elliptic singularity and one focus-focus singularity. The most
interesting dynamical features of integrable systems, and in particular of
spin-oscillators, are encoded in their singularities. In the first part of the
paper we study the symplectic dynamics around the focus-focus singularity. In
the second part of the paper we quantize the coupled spin-oscillators systems
and study their spectral theory. The paper combines techniques from
semiclassical analysis with differential geometric methods.",1005.0439v1
2014-03-21,Interface boundary conditions for dynamic magnetization and spin wave dynamics in a ferromagnetic layer with the interface Dzyaloshinskii-Moriya interaction,"In this work we derive the interface exchange boundary conditions for the
classical linear dynamics of magnetization in ferromagnetic layers with the
interface Dzyaloshinskii-Moriya interaction (IDMI). We show that IDMI leads to
pinning of dynamic magnetization at the interface. An unusual peculiarity of
the IDMI-based pinning is that its scales as the spin-wave wave number. We
incorporate these boundary conditions into an existing numerical model for the
dynamics of the Damon-Eshbach spin wave in ferromagnetic films. IDMI affects
the dispersion and the frequency non-reciprocity of the traveling Damon-Eshbach
spin wave. For a broad range of film thicknesses L and wave numbers the results
of the numerical simulations of the spin wave dispersion are in a good
agreement with a simple analytical expression which shows that the contribution
of IDMI to the dispersion scales as 1/L, similarly to the effect of other types
of interfacial anisotropy. Suggestions to experimentalists how to detect the
presence of IDMI in a spin wave experiment are given.",1403.5385v4
2008-07-23,Dynamical Dzyaloshinsky-Moriya Interaction in KCuF3,"The spin dynamics of the prototypical quasi one-dimensional antiferromagnetic
Heisenberg spin S=1/2 chain KCuF3 is investigated by electron spin resonance
spectroscopy. Our analysis shows that the peculiarities of the spin dynamics
require a new dynamical form of the antisymmetric anisotropic spin-spin
interaction. This dynamical Dzyaloshinsky-Moriya interaction is related to
strong oscillations of the bridging fuorine ions perpendicular to the
crystallographic c axis. This new mechanism allows to resolve consistently the
controversies in observation of the magnetic and structural properties of this
orbitally ordered perovskite compound.",0807.3641v1
2021-01-03,Spin Polarization Induced by Inhomogeneous Dynamical Condensate,"The role of dynamical chiral condensate in spin polarization is investigated
in a kinetic theory framework. Transport equations for quark matter are derived
in the mean-field approximation for the Nambu--Jona-Lasinio model. The
dynamical condensate carries part of the energy momentum tensor (EMT) and the
angular momentum tensor (AMT), the conservation of EMT and AMT can be proved
from the kinetic equations as required by the symmetry. The transport equations
of vector and axial-vector components are derived taking the spin decomposition
as well as semi-classical expansion. Inhomogeneous mass introduces novel effect
at $\mathcal{O}(\hbar)$, for an initially unpolarized system, spin polarization
can be generated from the dynamical chiral condensate, even without the
collision term. The stable spin distribution function is found to be robust,
namely in the case with non-trivial dynamical mass, the spin polarization is
still enslaved by the thermal vorticity, while the Killing condition can be
loosened.",2101.00586v2
2019-02-14,Coupled dynamics of long-range and internal spin cluster order in Cu$_{2}$OSeO$_{3}$,"Cu$_4$ triplet clusters form the relevant spin entity for the formation of
long-range magnetic order in the cluster magnet Cu$_2$OSeO$_3$. Using
time-resolved Raman spectroscopy, we probed photoinduced spin and lattice
dynamics in this Mott insulator. Multiple ps-decade spin-lattice relaxation
dynamics is observed, evidencing a separation of the order parameter dynamics
into disordering of long-range and internal spin cluster order. Our study
exemplifies the double order parameter dynamics of generalized molecular
crystals of charge, spin, and orbital nature.",1902.05329v1
2020-10-19,Ultrafast dynamics in relativistic Mott insulators,"We study the photoinduced ultrafast dynamics in relativistic Mott insulators,
i.e., Mott insulators with strong spin-orbit coupling. For this purpose, we
consider a minimal one-band Hubbard model on lattices with square and
triangular symmetries, as relevant for layered transition metal compounds such
as Sr$_2$IrO$_4$. Depending on the lattice and the spin-orbit coupling, the
systems have canted antiferromagnetic or $120^\circ$ order. They are excited by
simulating a short laser pulse, and the dynamics is solved using nonequilibrium
dynamical mean-field theory. The pulse generates hot carriers, which
subsequently perturb the magnetic order due to the coupling between the
collective order and photocarriers. We find that this dynamics, which is known
form regular antiferromagnets, depends sensitively on the spatial structure of
the spin-orbit coupling. On the triangular lattice, in particular, relaxation
times are influenced by the spin-orbit coupling for the chiral $120^\circ$
order, while on the square lattice with canted antiferromagnetic order the
spin-orbit induced canting angle remains unchanged after the excitation. Our
study opens up new possibilities of controlling magnetism and exotic spin
states on the ultrafast timescales.",2010.09253v1
2021-06-27,Classical spin dynamics based on SU($N$) coherent states,"We introduce a classical limit of the dynamics of quantum spin systems based
on coherent states of SU($N$), where $N$ is the dimension of the local Hilbert
space. This approach, that generalizes the well-known Landau-Lifshitz dynamics
from SU(2) to SU($N$), provides a better approximation to the exact quantum
dynamics for a large class of realistic spin Hamiltonians, including $S \geq 1$
systems with large single-ion anisotropy and weakly-coupled multi-spin units,
such as dimers or trimers. We illustrate this idea by comparing the spin
structure factors of a single-ion $S=1$ model that are obtained with the SU(2)
and SU(3) classical spin dynamics against the exact solution.",2106.14125v2
2021-10-20,Prediction of $^1$H singlet relaxation via intermolecular dipolar couplings using the molecular dynamics method,"Dissolution dynamical nuclear polarization has been applied in various
fields, including chemistry, biology, and medical science. To expand the scope
of these applications, the nuclear singlet state, which is decoherence-free
against dipolar relaxation between spin pairs, has been studied experimentally,
theoretically, and numerically. The singlet state composed of proton spins is
used in several applications, such as enhanced polarization preservation,
molecular tag to probe slow dynamic processes, and detection of ligand--protein
complexes. In this study, we predict the lifetimes of the nuclear spin states
composed of proton spin pairs using the molecular dynamics method and quantum
chemistry simulations. We consider intramolecular and intermolecular dipolar,
chemical shift anisotropy, and spin--rotation interactions. In particular, the
relaxation rate of intermolecular dipolar interactions is calculated using the
molecular dynamics method for various solvents. The calculated values and the
experimental values are of the same order of magnitude. Our program would
provide insight into the molecular design of several NMR applications and would
be helpful in predicting the nuclear spin relaxation time of synthetic
molecules in advance.",2110.10488v2
2022-12-19,Discrete Laplacian Thermostat for Spin Systems with Conserved Dynamics,"A well-established numerical technique to study the dynamics of spin systems
in which symmetries and conservation laws play an important role is to
microcanonically integrate their reversible equations of motion, obtaining
thermalization through initial conditions drawn with the canonical
distribution. In order to achieve a more realistic relaxation of the magnetic
energy, numerically expensive methods that explicitly couple the spins to the
underlying lattice are normally employed. Here we introduce a stochastic
conservative thermostat that relaxes the magnetic energy while preserving the
constant of motions, thus turning microcanonical spin dynamics into a
conservative canonical dynamics, without actually simulating the lattice. We
test the thermostat on the Heisenberg antiferromagnet in d=3 and show that the
method reproduces the exact values of the static and dynamic critical
exponents, while in the low-temperature phase it yields the correct spin wave
phenomenology. Finally, we demonstrate that the relaxation coefficient of the
new thermostat is quantitatively connected to the microscopic parameters of the
spin-lattice coupling.",2212.09647v2
2023-08-18,Suppression of Pulsed Dynamic Nuclear Polarization by Many-Body Spin Dynamics,"We study a mechanism by which nuclear hyperpolarization due to the
polarization transfer from a microwave-pulse-controlled electron spin is
suppressed. From analytical and numerical calculations of the unitary dynamics
of multiple nuclear spins, we uncover that, combined with the formation of the
dark state within a cluster of nuclei, coherent higher-order nuclear spin
dynamics impose limits on the efficiency of the polarization transfer even in
the absence of mundane depolarization processes such as nuclear spin diffusion
and relaxation. Furthermore, we show that the influence of the dark state can
be partly mitigated by introducing a disentangling operation. Our analysis is
applied to the nuclear polarizations observed in $^{13}$C nuclei coupled with a
single nitrogen-vacancy center in diamond [Science 374, 1474 (2021) by J.
Randall et al.]. Our work sheds light on collective engineering of nuclear
spins as well as future designs of pulsed dynamic nuclear polarization
protocols.",2308.09272v1
2002-11-25,Spin-polarized current oscillations in diluted magnetic semiconductor multiple quantum wells,"We study the spin and charge dynamics of electrons in n-doped II--VI
semiconductor multiple quantum wells when one or more quantum wells are doped
with Mn. The interplay between strongly nonlinear inter-well charge transport
and the large tunable spin-splitting induced by exchange interactions with
spin-polarized Mn ions produces interesting new spin dependent features. The
tunneling current between quantum wells can be strongly spin polarized and,
under certain conditions, can develop self sustained oscillations under a
finite dc voltage. The spin polarization oscillates in both magnetic and
nonmagnetic quantum wells and the time average in magnetic wells can differ
from its zero-voltage value. Our numerical simulations demonstrate that the
amplitude of the spin polarization oscillations depends on the distribution of
magnetic wells within the sample. We discuss how the spin polarized current and
the spin polarization of the quantum wells can be tailored experimentally.",0211557v1
2002-12-03,Tunneling measurement of quantum spin oscillations,"We consider the problem of tunneling between two leads via a localized spin
1/2 or any other microscopic system which can be modeled by a two-level
Hamiltonian. We assume that a constant magnetic field ${\bf B}_0$ acts on the
spin, that electrons in the leads are in the thermal equilibrium and that the
tunneling electrons are coupled to the spin through exchange and spin-orbit
interactions. Using the non-equilibrium Keldysh formalism we find the
dependence of the spin-spin and current-current correlation functions on the
applied voltage between leads $V$, temperature $T$, ${\bf B}_0$, and on the
degree and orientation ${\bf m}_{\alpha}$ of spin polarization of the electrons
in the right ($\alpha=$R) and left ($\alpha=$L) leads. We compare our results
of a full quantum-mechanical treatment of the tunneling-via-spin model with
those previously obtained in the quasi-classical approach, and discuss the
experimental results observed using STM dynamic probes of the localized spin.",0212049v3
2005-12-20,Manipulating Single Spins in Quantum Dots Coupled to Ferromagnetic Leads,"We discuss the possibility to generate, manipulate, and probe single spins in
single-level quantum dots coupled to ferromagnetic leads. The spin-polarized
currents flowing between dot and leads lead to a non-equilibrium spin
accumulation, i.e., a finite polarization of the dot spin. Both the magnitude
and the direction of the dot's spin polarization depends on the magnetic
properties of leads and their coupling to the dot. They can be, furthermore,
manipulated by either an externally applied magnetic field or an intrinsically
present exchange field that arises due to the tunnel coupling of the
strongly-interacting quantum-dot states to spin-polarized leads. The exchange
field can be tuned by both the gate and bias voltage, which, therefore, provide
convenient handles to manipulate the quantum-dot spin. Since the transmission
through the quantum-dot spin valve sensitively depends on the state of the
quantum-dot spin, all the dynamics of the latter is reflected in the transport
properties of the device.",0512519v1
2006-12-27,Gravitational and higher-derivative interactions of massive spin 5/2 field in (A)dS space,"Using on-shell gauge invariant formulation of relativistic dynamics we study
interaction vertices for a massive spin 5/2 Dirac field propagating in (A)dS
space of dimension greater than or equal to four. Gravitational interaction
vertex for the massive spin 5/2 field and all cubic vertices for the massive
spin 5/2 field and massless spin 2 field with two and three derivatives are
obtained. In dimension greater that four, we demonstrate that the gravitational
vertex of the massive spin 5/2 field involves, in addition to the standard
minimal gravitational vertex, contributions with two and three derivatives. We
find that for the massive spin 5/2 and massless spin 2 fields one can build two
higher-derivative vertices with two and three derivatives. Limits of massless
and partial massless spin 5/2 fields in (A)dS space and limits of massive and
massless spin 5/2 fields in flat space are discussed.",0612279v3
2000-02-12,A model for ensemble NMR quantum computer using antiferromagnetic structure,"The one-dimensional homonuclear periodic array of nuclear spins I = 1/2,
owing to hyperfine interaction of nuclear spins with electronic magnetic
moments in antiferromagnetic structure, is considered. The neighbor nuclear
spins in such array are opposite oriented and have resonant frequencies
determined by hyperfine interaction constant, applied magnetic field value and
interaction with the left and right nuclear neighbor spins. The resonant
frequencies difference of nuclear spins, when the neighbor spins have different
and the same states, is used to control the spin dynamics by means of selective
resonant RF-pulses both for single nuclear spins and for ensemble of nuclear
spins with the same resonant frequency.
  A model for the NMR quantum computer of cellular-automata type based on an
one-dimensional homonuclear periodic array of spins is proposed. This model may
be generalized to a large ensemble of parallel working one-dimensional arrays
and to two-dimensional and three-dimensional structures.",0002034v1
2009-05-28,Emerging nonequilibrium bound state in spin-current-local-spin scattering,"Magnetization reversal is a well-studied problem with obvious applicability
in computer hard-drives. One can accomplish a magnetization reversal in at
least one of two ways: application of a magnetic field, or through a spin
current. The latter is more amenable to a fully quantum mechanical analysis. We
formulate and solve the problem whereby a spin current interacts with a
ferromagnetic Heisenberg spin chain, to eventually reverse the magnetization of
the chain. Spin-flips are accomplished through both elastic and inelastic
scattering. A consequence of the inelastic scattering channel, when it is no
longer energetically possible, is the occurrence of a new entity: a
non-equilibrium bound state (NEBS), which is an emergent property of the
coupled local plus itinerant spin system. For certain definite parameter values
the itinerant spin lingers near the local spins for some time, before
eventually leaking out as an outwardly diffusing state. This phenomenon results
in novel spin-flip dynamics and filtering properties for this type of system.",0905.4708v2
2010-03-26,Quantum-dot-spin single-photon interface,"Using background-free detection of spin-state-dependent resonance
fluorescence from a single-electron charged quantum dot with an efficiency of
0:1%, we realize a single spin-photon interface where the detection of a
scattered photon with 300 picosecond time resolution projects the quantum dot
spin to a definite spin eigenstate with fidelity exceeding 99%. The bunching of
resonantly scattered photons reveals information about electron spin dynamics.
High-fidelity fast spin-state initialization heralded by a single photon
enables the realization of quantum information processing tasks such as
non-deterministic distant spin entanglement. Given that we could suppress the
measurement back-action to well below the natural spin-flip rate, realization
of a quantum non-demolition measurement of a single spin could be achieved by
increasing the fluorescence collection efficiency by a factor exceeding 20
using a photonic nanostructure.",1003.5195v3
2010-06-21,Spin transfer torque enhancement in dual spin valve in the ballistic regime,"The spin transfer torque in all-metal dual spin valve, in which two
antiparallelly aligned pinned ferromagnetic layers are on the two sides of a
free ferromagnetic layer with two thin nonmagnetic spacers in between, is
studied in the ballistic regime. It is argued that, similar to the results in
the diffusion regime, the spin transfer torque is dramatically enhanced in
comparison to that in a conventional spin valve although no spin accumulation
exists at the magnetic-nonmagnetic interfaces. Within the Slonczewski's
approach, an analytical expression of the torque on the free magnetic layer is
obtained, which may serve as a theoretical model for the micromagnetic
simulation of the spin dynamics in dual spin valve. Depending on the
orientation of free layer and the degree of electron polarization, the spin
transfer torque enhancement could be tens times. The general cases when
transmission and reflection probabilities of free layer are different from zero
or one are also numerically calculated.",1006.4003v3
2011-07-30,Electron spin dephasing in two-dimensional systems with anisotropic scattering,"We develop a microscopic theory of spin relaxation of a two-dimensional
electron gas in quantum wells with anisotropic electron scattering. Both
precessional and collision-dominated regimes of spin dynamics are studied. It
is shown that, in quantum wells with noncentrosymmetric scatterers, the
in-plane and out-of-plane spin components are coupled: spin dephasing of
carriers initially polarized along the quantum well normal leads to the
emergence of an in-plane spin component even in the case of isotropic
spin-orbit splitting. In the collision-dominated regime, the
spin-relaxation-rate tensor is expressed in terms of the electric conductivity
tensor. We also study the effect of an in-plane and out-of-plane external
magnetic field on spin dephasing and show that the field dependence of electron
spin can be very intricate.",1108.0107v1
2011-12-03,Spin Currents in Metallic Nanostructures; Explicit Calculations,"In ultrathin ferromagnets deposited on metallic substrates, excitation of
precessional motion of the spins produces a spin current in the substrate that
transports angular momentum out of the film. This phenomenon is referred to as
spin pumping, and is a source of damping of the spin motion. Spin pumping
enters importantly in the description of spin dynamics in other nanoscale and
subnanoscale systems as well. In this paper, we present an approach based on
the Kubo formalism that allows the explicit calculation of this spin current
and its spatial variation. We use the formalism to explore features of the spin
current generated by spin motions in a simple model system.",1112.0615v1
2012-06-19,Optical measurements of spin noise as a high resolution spectroscopic tool,"The intrinsic fluctuations of electron spins in semiconductors and atomic
vapors generate a small, randomly-varying ""spin noise"" that can be detected by
sensitive optical methods such as Faraday rotation. Recent studies have
demonstrated that the frequency, linewidth, and lineshape of this spin noise
directly reveals dynamical spin properties such as dephasing times, relaxation
mechanisms and g-factors without perturbing the spins away from equilibrium.
Here we demonstrate that spin noise measurements using wavelength-tunable probe
light forms the basis of a powerful and novel spectroscopic tool to provide
unique information that is fundamentally inaccessible via conventional linear
optics. In particular, the wavelength dependence of the detected spin noise
power can reveal homogeneous linewidths buried within inhomogeneously-broadened
optical spectra, and can resolve overlapping optical transitions belonging to
different spin systems. These new possibilities are explored both theoretically
and via experiments on spin systems in opposite limits of inhomogeneous
broadening (alkali atom vapors and semiconductor quantum dots).",1206.4168v1
2013-05-24,Effective-one-body Hamiltonian with next-to-leading order spin-spin coupling for two nonprecessing black holes with aligned spins,"The canonical Arnowitt-Deser-Misner (ADM) Hamiltonian with next-to-leading
order spin-spin coupling [J. Steinhoff, S. Hergt, and G. Sch\""afer] is
converted into the EOB formalism of T. Damour, P. Jaranowski, and G. Sch\""afer
for the special case of spinning black hole binaries whose spins are aligned
with the angular momentum. In particular, we propose to include the new terms
by adding a dynamical term of next-to-leading order to the Kerr parameter
squared entering the effective metric. The modified EOB Hamiltonian
consistently reduces to the Kerr Hamiltonian as the mass ratio tends to zero;
moreover, it predicts the existence of an Innermost Stable Circular Orbit. We
also derive, for the general case of arbitrarily oriented spins but in the
vanishing mass-ratio limit, a coordinate transformation that maps the
next-to-leading order spin-spin contribution of the ADM Hamiltonian to the EOB
Hamiltonian.",1305.5674v3
2013-10-28,"Spin polarization, dephasing and photoinduced spin diffusion in (110)-grown two-dimensional electron systems","We study the optically induced spin polarization, spin dephasing and
diffusion in several high-mobility two-dimensional electron systems, which are
embedded in GaAs quantum wells grown on (110)-oriented substrates. The
experimental techniques comprise a two-beam magneto-optical spectroscopy system
and polarization-resolved photoluminescence. Under weak excitation conditions
at liquid-helium temperatures, we observe spin lifetimes above 100 ns in one of
our samples, which are reduced with increasing excitation density due to
additional, hole-mediated, spin dephasing. The spin dynamic is strongly
influenced by the carrier density and the ionization of remote donors, which
can be controlled by temperature and above-barrier illumination. The absolute
value of the average electron spin polarization in the samples is directly
observable in the circular polarization of photoluminescence collected under
circularly polarized excitation and reaches values of about 5 percent. Spin
diffusion is studied by varying the distance between pump and probe beams in
micro-spectroscopy experiments. We observe diffusion lengths above 100 $\mu$m
and, at high excitation intensity, a nonmonotonic dependence of the spin
polarization on the pump-probe distance.",1310.7345v1
2014-07-30,Room Temperature Spin Pumping in Topological Insulator Bi2Se3,"Three-dimensional (3D) topological insulators are known for their strong
spin-orbit coupling and the existence of spin-textured topological surface
states which could be potentially exploited for spintronics. Here, we
investigate spin pumping from a metallic ferromagnet (CoFeB) into a 3D
topological insulator (Bi2Se3) and demonstrate successful spin injection from
CoFeB into Bi2Se3 and the direct detection of the electromotive force generated
by the inverse spin Hal effect (ISHE) at room temperature. The spin pumping,
driven by the magnetization dynamics of the metallic ferromagnet, introduces a
spin current into the topological insulator layer, resulting in a broadening of
the ferromagnetic resonance (FMR) linewidth. We find that the FMR linewidth
more than quintuples, the spin mixing conductance can be as large as
3.4*10^20m^-2 and the spin Hall angle can be as large as 0.23 in the Bi2Se3
layer.",1407.7940v1
2014-09-12,Protecting a solid-state spin from decoherence using dressed spin states,"Dressed spin states, a spin coupling to continuous radiation fields, can
fundamentally change how a spin responds to magnetic fluctuations. Using
dressed spin states, we were able to protect an electron spin in diamond from
decoherence. Dressing a spin with resonant microwaves at a coupling rate near 1
MHz leads to a 50 times reduction in the linewidth of the spin transition,
limited by transit-time broadening. The spin decoherence and the energy level
structure of the dressed states were probed with optical
coherent-population-trapping processes. Compared with dynamical decoupling,
where effects of the bath are averaged out at specific times, the dressed state
provides a continuous protection from decoherence.",1409.3786v1
2014-09-19,Angular dependence of spin-orbit spin transfer torques,"In ferromagnet/heavy metal bilayers, an in-plane current gives rise to
spin-orbit spin transfer torque which is usually decomposed into field-like and
damping-like torques. For two-dimensional free-electron and tight-binding
models with Rashba spin-orbit coupling, the field-like torque acquires
nontrivial dependence on the magnetization direction when the Rashba spin-orbit
coupling becomes comparable to the exchange interaction. This nontrivial
angular dependence of the field-like torque is related to the Fermi surface
distortion, determined by the ratio of the Rashba spin-orbit coupling to the
exchange interaction. On the other hand, the damping-like torque acquires
nontrivial angular dependence when the Rashba spin-orbit coupling is comparable
to or stronger than the exchange interaction. It is related to the combined
effects of the Fermi surface distortion and the Fermi sea contribution. The
angular dependence is consistent with experimental observations and can be
important to understand magnetization dynamics induced by spin-orbit spin
transfer torques",1409.5600v1
2014-10-20,Spin-heat relaxation and thermo-spin diffusion in atomic Bose and Fermi gases,"We study spin-dependent heat transport in quantum gases, focusing on
transport phenomena related to pure spin currents and spin-dependent
temperatures. Using the Boltzmann equation, we compute the coupled spin and
heat transport coefficients as a function of temperature and interaction
strength for energy dependent $s$-wave scattering. We address the issue of
whether spin-dependent temperatures can be sustained on a time and length scale
relevant for experiments by computing the spin-heat relaxation time and
diffusion length. We find that the time scale for spin-heat relaxation time
diverges at low temperatures for both bosons and fermions, indicating that the
concept of spin-heat accumulation is well defined for degenerate gases. For
bosons, we find power-law behavior on approach to Bose condensation above the
critical temperature, as expected from the theory of dynamical critical
phenomena.",1410.5378v3
2014-11-12,Spin transport in intermediate-energy heavy-ion collisions as a probe of in-medium spin-orbit interactions,"The spin up-down splitting of collective flows in intermediate-energy
heavy-ion collisions as a result of the nuclear spin-orbit interaction is
investigated within a spin- and isospin-dependent Boltzmann-Uehing-Uhlenbeck
transport model SIBUU12. Using a Skyrme-type spin-orbit coupling quadratic in
momentum, we found that the spin splittings of the directed flow and elliptic
flow are largest in peripheral Au+Au collisions at beam energies of about
100-200 MeV/nucleon, and the effect is considerable even in smaller systems
especially for nucleons with high transverse momenta. The collective flows of
light clusters of different spin states are also investigated using an improved
dynamical coalescence model with spin. Our study can be important in
understanding the properties of in-medium nuclear spin-orbit interactions once
the spin-dependent observables proposed in this work can be measured.",1411.3057v2
2015-04-14,Spin dynamics in relativistic light-matter interaction,"Various spin effects are expected to become observable in light-matter
interaction at relativistic intensities. Relativistic quantum mechanics
equipped with a suitable relativistic spin operator forms the theoretical
foundation for describing these effects. Various proposals for relativistic
spin operators have been offered by different authors, which are presented in a
unified way. As a result of the operators' mathematical properties only the
Foldy-Wouthuysen operator and the Pryce operator qualify as possible proper
relativistic spin operators. The ground states of highly charged hydrogen-like
ions can be utilized to identify a legitimate relativistic spin operator
experimentally. Subsequently, the Foldy-Wothuysen spin operator is employed to
study electron-spin precession in high-intensity standing light waves with
elliptical polarization. For a correct theoretical description of the predicted
electron-spin precession relativistic effects due to the spin angular momentum
of the electromagnetic wave has to be taken into account even in the limit of
low intensities.",1504.03489v1
2015-08-04,Spin structure of harmonically trapped one-dimensional atoms with spin-orbit coupling,"We introduce a theoretical approach to determine the spin structure of
harmonically trapped atoms with two-body zero-range interactions subject to an
equal mixture of Rashba and Dresselhaus spin-orbit coupling created through
Raman coupling of atomic hyperfine states. The spin structure of bosonic and
fermionic two-particle systems with finite and infinite two-body interaction
strength $g$ is calculated. Taking advantage of the fact that the $N$-boson and
$N$-fermion systems with infinitely large coupling strength $g$ are
analytically solvable for vanishing spin-orbit coupling strength $k_{so}$ and
vanishing Raman coupling strength $\Omega$, we develop an effective spin model
that is accurate to second-order in $\Omega$ for any $k_{so}$ and infinite $g$.
The three- and four-particle systems are considered explicitly. It is shown
that the effective spin Hamiltonian, which contains a Heisenberg exchange term
and an anisotropic Dzyaloshinskii-Moriya exchange term, describes the
transitions that these systems undergo with the change of $k_{so}$ as a
competition between independent spin dynamics and nearest-neighbor spin
interactions.",1508.00932v1
2015-08-20,Quadrupolar and anisotropy effects on dephasing in two-electron spin qubits in GaAs,"Understanding the decoherence of electron spins in semiconductors due to
their interaction with nuclear spins is of fundamental interest as they realize
the central spin model and of practical importance for using electron spins as
qubits. Interesting effects arise from the quadrupolar interaction of nuclear
spins with electric field gradients, which have been shown to suppress
diffusive nuclear spin dynamics. One might thus expect them to enhance electron
spin coherence. Here we show experimentally that for gate-defined GaAs quantum
dots, quadrupolar broadening of the nuclear Larmor precession can also reduce
electron spin coherence due to faster decorrelation of transverse nuclear
fields. However, this effect can be eliminated for appropriate field
directions. Furthermore, we observe an additional modulation of spin coherence
that can be attributed to an anisotropic electronic $g$-tensor. These results
complete our understanding of dephasing in gated quantum dots and point to
mitigation strategies. They may also help to unravel unexplained behaviour in
related systems such as self-assembled quantum dots and III-V nanowires.",1508.05136v1
2015-08-31,All electrical manipulation of magnetization dynamics in a ferromagnet by antiferromagnets with anisotropic spin Hall effects,"We investigate spin-orbit torques of metallic CuAu-I-type antiferromagnets
using spin-torque ferromagnetic resonance tuned by a dc-bias current. The
observed spin torques predominantly arise from diffusive transport of spin
current generated by the spin Hall effect. We find a growth-orientation
dependence of the spin torques by studying epitaxial samples, which may be
correlated to the anisotropy of the spin Hall effect. The observed anisotropy
is consistent with first-principles calculations on the intrinsic spin Hall
effect. Our work demonstrates large tunable spin-orbit effects in
magnetically-ordered materials.",1508.07906v2
2015-09-09,Quantum spin transport and dynamics through a novel F/N junction,"We study the spin transport in the low temperature regime (often referred to
as the precession-dominated regime) between a ferromagnetic Fermi liquid (FFL)
and a normal metal metallic Fermi liquid (NFL), also known as the F/N junction,
which is considered as one of the most basic spintronic devices. In particular,
we explore the propagation of spin waves and transport of magnetization through
the interface of the F/N junction where nonequilibrium spin polarization is
created on the normal metal side of the junction by electrical spin injection.
We calculate the probable spin wave modes in the precession-dominated regime on
both sides of the junction especially on the NFL side where the system is out
of equilibrium. Proper boundary conditions at the interface are introduced to
establish the transport of the spin properties through the F/N junction. A
possible transmission conduction electron spin resonance (CESR) experiment is
suggested on the F/N junction to see if the predicted spin wave modes could
indeed propagate through the junction. Potential applications based on this
novel spin transport feature of the F/N junction are proposed in the end.",1509.02582v1
2016-04-21,Electron spin filter and polarizer in a standing light wave,"We demonstrate the theoretical feasibility of spin-dependent diffraction and
spin-polarization of an electron in two counter-propagating, circularly
polarized laser beams. The spin-dynamics appears in a two-photon process of the
Kapitza-Dirac effect in the Bragg regime. We show the spin-dependence of the
diffraction process by comparison of the time-evolution of a spin-up and
spin-down electron in a relativistic quantum simulation. We further discuss the
spin properties of the scattering by studying an analytically approximated
solution of the time-evolution matrix. A classification scheme in terms of
unitary or non-unitary propagation matrices is used for establishing a
generalized and spin-independent description of the spin properties in the
diffraction process.",1604.06201v5
2016-09-28,Resonant optical control of the spin of a single Cr atom in a quantum dot,"A Cr atom in a semiconductor host carries a localized spin with an intrinsic
large spin to strain coupling particularly promising for the development of
hybrid spin-mechanical systems and coherent mechanical spin driving. We
demonstrate here that the spin of an individual Cr atom inserted in a
semiconductor quantum dot can be controlled optically. We first show that a Cr
spin can be prepared by resonant optical pumping. Monitoring the time
dependence of the intensity of the resonant fluorescence of the quantum dot
during this process permits to probe the dynamics of the optical initialization
of the Cr spin. Using this initialization and read-out technique we measured a
Cr spin relaxation time at T=5 K of about 2 microseconds. We finally
demonstrate that, under a resonant single mode laser field, the energy of any
spin state of an individual Cr atom can be independently tuned by using the
optical Stark effect.",1609.08829v1
2017-03-27,Spin transfer due to quantum fluctuations of magnetization,"Spin transfer - the transfer of angular momentum from spin-polarized
electrical current to magnetic materials - has been extensively researched as
an efficient mechanism for the electronic manipulation of the static and
dynamic states in nanomagnetic systems, advancing our understanding of
nanomagnetism and electronic transport, and enabling the development of
energy-efficient magnetic nanodevices. Our present understanding of spin
transfer is based on the classical approximation for the magnetization, even
though the spin-polarized electrons mediating spin transfer are treated
quantum-mechanically. Here, we utilize a nanoscale magnetic spin-valve
structure to demonstrate that quantum zero-point fluctuations of magnetization,
neglected in the existing theories of spin transfer, provide the dominant
contribution to this effect at cryogenic temperatures, and remain
non-negligible even at room temperature. The demonstrated quantum spin transfer
(QST) is distinguished by a non-smooth piecewise-linear dependence of the
fluctuation intensity on current, and can be driven not only by the directional
flows of electrons, but also by their thermal motion. This effect can enhance
current-induced phenomena, overcoming the efficiency limitations that are
presently perceived as fundamental to the spin transfer mechanism.",1703.09335v2
2018-02-03,Randomness induced spin-liquid-like phase in the spin-$1/2$ $J_1 - J_2$ triangular Heisenberg model,"We study the effects of bond randomness in the spin-$1/2$ $J_1-J_2$
triangular Heisenberg model using exact diagonalization and density matrix
renormalization group. With increasing bond randomness, we identify a
randomness induced spin-liquid-like phase without any magnetic order, dimer
order, spin glass order, or valence-bond glass order. The finite-size scaling
of gaps suggests the gapless nature of both spin triplet and singlet
excitations, which is further supported by the broad continuum of dynamical
spin structure factor. By studying the bipartite entanglement spectrum of the
system on cylinder geometry, we identify the features of the low-lying
entanglement spectrum in the spin-liquid-like phase, which may distinguish this
randomness induced spin-liquid-like phase and the intrinsic spin liquid phase
in the clean $J_1 - J_2$ triangular Heisenberg model. We further discuss the
nature of this spin-liquid-like phase and the indication of our results for
understanding spin-liquid-like materials with triangular-lattice structure.",1802.00935v4
2018-04-16,Spin manipulation and spin dephasing in quantum dot integrated with a slanting magnetic field,"A slanting magnetic field is usually used to realize a slight hybridization
between the spin and orbital degrees of freedom in a semiconductor quantum dot,
such that the spin is manipulable by an external oscillating electric field.
Here we show that, the longitudinal slanting field mediates a longitudinal
driving term in the electric-dipole spin resonance, such that the spin
population inversion exhibits a modulated Rabi oscillation. Fortunately, we can
reduce this modulation by increasing the static magnetic field. The
longitudinal slanting field also mediates a spin-1/f-charge noise interaction,
which causes the pure dephasing of the spin qubit. Choosing proper spectrum
function strength, we find the spin dephasing time is about $T^{*}_{2}=20$
$\mu$s and the spin echo time is about $T^{\rm echo}_{2}=100$ $\mu$s in a Si
quantum dot. We also propose several strategies to alleviate the spin
dephasing, such as lowering the experimental temperature, reducing the quantum
dot size, engineering the slanting field, or using the dynamical decoupling
scheme.",1804.05476v3
2018-05-10,Spin-related phenomena in two-dimensional hopping regime in magnetic field,"The spin relaxation time of localized charge carriers is few orders of
magnitude larger than that of free electrons and holes. Therefore mutual
conversion of spin polarization, charge current and spin current turns out to
be underlined in the hopping conductivity regime. We reveal different regimes
of the coupled spin and charge dynamics depending on the relation between spin
relaxation time and the characteristic hopping time. We derive kinetic
equations to describe electrical spin orientation, dc spin-Hall effect, and
spin galvanic effect in the transverse magnetic field. The generalized
macroscopic conductivities describing these effects are calculated using
percolation theory supported by numerical simulation. The conductivities change
the sign at least once as functions of magnetic field for all values of the
spin relaxation time.",1805.04061v1
2012-04-24,Sensing distant nuclear spins with a single electron spin,"We experimentally demonstrate the use of a single electronic spin to measure
the quantum dynamics of distant individual nuclear spins from within a
surrounding spin bath. Our technique exploits coherent control of the electron
spin, allowing us to isolate and monitor nuclear spins weakly coupled to the
electron spin. Specifically, we detect the evolution of distant individual
carbon-13 nuclear spins coupled to single nitrogen vacancy centers in a diamond
lattice with hyperfine couplings down to a factor of 8 below the electronic
spin bare dephasing rate. Potential applications to nanoscale magnetic
resonance imaging and quantum information processing are discussed.",1204.5483v2
2016-05-27,Role of Entropy and Structural Parameters in the Spin State Transition of LaCoO$_3$,"The spin state transition in LaCoO$_3$ has eluded description for decades
despite concerted theoretical and experimental effort. In this study, we
approach this problem using fully charge self-consistent Density Functional
Theory + Embedded Dynamical Mean Field Theory (DFT+DMFT). We show from first
principles that LaCoO$_3$ cannot be described by a single, pure spin state at
any temperature. Instead, we observe a gradual change in the population of
higher spin multiplets with increasing temperature, with the high spin
multiplets being excited at the onset of the spin state transition followed by
the intermediate spin multiplets being excited at the metal insulator
transition temperature. We explicitly elucidate the critical role of lattice
expansion and oxygen octahedral rotations in the spin state transition. We also
reproduce, from first principles, that the spin state transition and the
metal-insulator transition in LaCoO$_3$ occur at different temperature scales.
In addition, our results shed light on the importance of electronic entropy in
driving the spin state transition, which has so far been ignored in all first
principles studies of this material.",1605.08611v3
2018-09-28,Observation of magnetic-field-sweep-direction-dependent dynamic nuclear polarization under periodic optical electron spin pumping,"Optical pump-probe techniques are used to generate and measure electron spin
polarization in a gallium arsenide epilayer in which the electron spin
coherence time exceeds the mode-locked laser repetition period. Resonant spin
amplification occurs at magnetic fields at which the electron spin polarization
excited by successive laser pulses add constructively. Measurements of Kerr
rotation as a function of applied magnetic field reveal nuclear spin
polarization that aligns either with or against the external magnetic field
depending on whether the applied magnetic field is being decreased or
increased. Furthermore, the nuclear spin polarization magnitude varies in
proportion to the perpendicular net electron spin polarization as the latter
changes due to resonant spin amplification and other causes. We also report an
experimental technique that reveals a minutes-long memory of precise field
history in the electron-nuclear spin system.",1810.00055v2
2019-07-25,Quantum correlations protection through spin self-rephasing in 1-D Bose gas,"System consisting of a number of trapped atoms evolving under the influence
of external inhomogenous magnetic field undergoes spin dephasing: classically,
since each atom feels different field along its trajectory, the spin rotation
rates differ; as a result the average spin decays. In a quantum mechanical
context this corresponds to entanglement of spin and spatial degrees of freedom
and nontrivial internal spin dynamics. The spin dephasing can be prevented by
tuning the interaction between the atoms. This phenomenon, called spin
self-rephasing, has been observed experimentally and can increase the coherence
time by a large factor. While such systems have been studied from a
semiclassical point of view, a quantum mechanical description is limited,
especially in the case of entangled states.
  In this work we provide a numerical simulation of an ab initio model and
provide realistic examples of spin self-rephasing used to counteract the effect
of inhomogenous magnetic field. We analyze in particular the joint effect of
magnetic field inhomogeneity and interactions on the coherent and spin squeezed
states evolution.",1907.11282v1
2019-10-24,Spin waves in ferromagnetic thin films,"A spin wave is the disturbance of intrinsic spin order in magnetic materials.
In this paper, a spin wave in the Landau-Lifshitz-Gilbert equation is obtained
based on the assumption that the spin wave maintains its shape while it
propagates at a constant velocity. Our main findings include: (1) in the
absence of Gilbert damping, the spin wave propagates at a constant velocity
with the increment proportional to the strength of the magnetic field; (2) in
the absence of magnetic field, at a given time the spin wave converges
exponentially fast to its initial profile as the damping parameter goes to zero
and in the long time the relaxation dynamics of the spin wave converges
exponentially fast to the easy-axis direction with the exponent proportional to
the damping parameter; (3) in the presence of both Gilbert damping and magnetic
field, the spin wave converges to the easy-axis direction exponentially fast at
a small timescale while propagates at a constant velocity beyond that. These
provides a comprehensive understanding of spin waves in ferromagnetic
materials.",1910.11200v1
2020-02-28,Spin-orbit torques driven by the interface-generated spin currents,"The spin currents generated by spin-orbit coupling (SOC) in the nonmagnetic
metal layer or at the interface with broken inversion symmetry are of
particular interest and importance. Here, we have explored the spin current
generation mechanisms through the spin-orbit torques (SOTs) measurements in the
Ru/Fe heterostructures with weak perpendicular magnetic anisotropy (PMA).
Although the spin Hall angle (SHA) of Ru is smaller than that in Pt, Ta or W,
reversible SOT in Ru/Fe heterostructures can still be realized. Through
non-adiabatic harmonic Hall voltage measurements and macrospin simulation, the
effective SHA in Ru/Fe heterostructures is compared with Pt. Moreover, we also
explore that the spin current driven by interface strongly depends on the
electrical conductivities. Our results suggest a new method for efficiently
generating finite spin currents in ferromagnet/nonmagnetic metal bilayers,
which establishes new opportunities for fundamental study of spin dynamics and
transport in ferromagnetic systems.",2002.12545v1
2021-01-09,Many-particle Quantum Hydrodynamics of Spin-1 Bose-Einstein Condensates,"We develop a novel model of the magnetized spin-1 Bose-Einstein condensate
(BEC) of neutral atoms, using the method of many-particle quantum hydrodynamic
(QHD) and propose an original derivation of the system of continual equations.
We consider bosons with a spin-spin interaction and a short range interaction
in the first order in the interaction radius, on the of basis of the
self-consistent field approximation of the QHD equations. We demonstrate that
the dynamics of the fluid velocity and magnetization is determined by a
nontrivial modification of the Euler and Landau-Lifshitz equation, and show
that a nontrivial modification of the spin density evolution equation contains
the spin torque effect that arises from the self-interactions between spins of
the bosons. The properties of the dispersion spectrum of collective excitations
are described. We obtain the new contribution of the self-interaction of spins
in the spin wave spectrum together with the influence of an external magnetic
field and spin-spin interactions between polarized particles. The anisotropic
spin wave instability is predicted.",2101.03422v1
2012-05-18,Detection and control of individual nuclear spins using a weakly coupled electron spin,"We experimentally isolate, characterize and coherently control up to six
individual nuclear spins that are weakly coupled to an electron spin in
diamond. Our method employs multi-pulse sequences on the electron spin that
resonantly amplify the interaction with a selected nuclear spin and at the same
time dynamically suppress decoherence caused by the rest of the spin bath. We
are able to address nuclear spins with interaction strengths that are an order
of magnitude smaller than the electron spin dephasing rate. Our results provide
a route towards tomography with single-nuclear-spin sensitivity and greatly
extend the number of available quantum bits for quantum information processing
in diamond.",1205.4128v1
2017-09-21,Spin noise spectroscopy of randomly moving spins in the model of light scattering: Two-beam arrangement,"A strict analytical solution of the problem of spin-noise signal formation in
a volume medium with randomly moving spin carriers is presented. The treatment
is performed in the model of light scattering in a medium with fluctuating
inhomogeneity. Along with conventional single-beam, geometry, we consider the
two-beam arrangement, with the scattering field of the auxiliary (""tilted"")
beam heterodyned on the photodetector illuminated by the main beam. It is shown
that the spin noise signal detected in the two-beam arrangement is highly
sensitive to motion (diffusion) of the spin carriers within the illuminated
volume and thus can provide additional information about spin dynamics and
spatial correlations of spin polarization in volume media. Our quantitative
estimates show that, under real experimental conditions, spin diffusion may
strongly suppress the spin-noise signal in the two-beam geometry. Mechanism of
this suppression is similar to that of the time-of-flight broadening with the
critical distance determined by the period of spatial interference of the two
beams rather than by the beam diameter.",1709.07360v1
2018-03-28,Dissipative cooling of spin chains by a bath of dipolar particles,"We consider a spin chain of fermionic atoms in an optical lattice,
interacting with each other by super-exchange interactions. We theoretically
investigate the dissipative evolution of the spin chain when it is coupled by
magnetic dipole-dipole interaction to a bath consisting of atoms with a strong
magnetic moment. Dipolar interactions with the bath allow for a dynamical
evolution of the collective spin of the spin chain. Starting from an
uncorrelated thermal sample, we demonstrate that the dissipative cooling
produces highly entangled low energy spin states of the chain in a timescale of
a few seconds. In practice, the lowest energy singlet state driven by
super-exchange interactions is efficiently produced. This dissipative approach
is a promising alternative to cool spin-full atoms in spin-independent
lattices. It provides direct thermalization of the spin degrees of freedom,
while traditional approaches are plagued by the inherently long timescale
associated to the necessary spatial redistribution of spins under the effect of
super-exchange interactions.",1803.10663v2
2018-03-29,Detecting End-States of Topological Quantum Paramagnets via Spin Hall Noise Spectroscopy,"We theoretically study the equilibrium spin current fluctuations and the
corresponding charge noise generated by inverse spin Hall effect (ISHE) in a
metal with strong spin-orbit coupling deposited on top of a quantum paramagnet.
It is shown that the charge noise power spectra measured along different
spatial axes can directly probe the different spin components of the boundary
dynamic spin correlations of the quantum paramagnet. We report the utility of
this ISHE-facilitated spin noise probe as a tool to unambiguously detect
topological phase transitions in an S=1/2 quantum spin ladder that hosts a
trivial ground state of singlet product states, but topologically-protected
fractional spin excitations localized at its ends. Our work demonstrates the
general usefulness of the ISHE-mediated spin noise spectroscopy for the
detection of topological phases in quantum paramagnets.",1803.11239v1
2018-06-25,Wideband and on-chip excitation for dynamical spin injection into graphene,"Graphene is an ideal material for spin transport as very long spin relaxation
times and lengths can be achieved even at room temperature. However, electrical
spin injection is challenging due to the conductivity mismatch problem. Spin
pumping driven by ferromagnetic resonance is a neat way to circumvent this
problem as it produces a pure spin current in the absence of a charge current.
Here, we show spin pumping into single layer graphene in micron scale devices.
A broadband on-chip RF current line is used to bring micron scale permalloy
(Ni$_{80}$Fe$_{20}$) pads to ferromagnetic resonance with a magnetic field
tunable resonance condition. At resonance, a spin current is emitted into
graphene, which is detected by the inverse spin hall voltage in a close-by
platinum electrode. Clear spin current signals are detected down to a power of
a few milliwatts over a frequency range of 2 GHz to 8 GHz. This compact device
scheme paves the way for more complex device structures and allows the
investigation of novel materials.",1806.09356v1
2018-12-09,Manipulating Quantum Spins by a Spin-Polarized Current: An Approach Based Upon PT-Symmetric Quantum Mechanics,"We propose a quantum processor based upon single-molecule magnets and spin
transfer torque described by PT-symmetric quantum mechanics. In recent years
PT-symmetric Hamiltonians have been used to obtain stability thresholds of
various systems out of equilibrium. One such problem is the magnetization
reversal due to the spin transfer torque generated by a spin-polarized current.
So far the studies of this problem have mostly focused on a classical limit of
a large spin. In this work we are discussing spin tunneling and quantum
dynamics of a small spin induced by a spin polarized current within a
PT-symmetric theory. This description can be used for manipulating spin qubits
by electric currents.",1812.03481v1
2019-01-07,Simultaneous Optical and Electrical Spin-Torque Magnetometry with Stroboscopic Detection of Spin-Precession Phase,"Spin-based coherent information processing and encoding utilize the
precession phase of spins in magnetic materials. However, the detection and
manipulation of spin precession phases remain a major challenge for advanced
spintronic functionalities. By using simultaneous electrical and optical
detection, we demonstrate the direct measurement of the precession phase of
Permalloy ferromagnetic resonance driven by the spin-orbit torques from
adjacent heavy metals. The spin Hall angle of the heavy metals can be
independently determined from concurrent electrical and optical signals. The
stroboscopic optical detection also allows spatially measuring local
spin-torque parameters and the induced ferromagnetic resonance with
comprehensive amplitude and phase information. Our study offers a route towards
future advanced characterizations of spin-torque oscillators, magnonic
circuits, and tunnelling junctions, where measuring the current-induced spin
dynamics of individual nanomagnets are required.",1901.01923v1
2019-11-04,The generic phase diagram of spin relaxation in solids and the Loschmidt echo,"The spin relaxation time in solids is determined by several competing energy
scales and processes and distinct methods are called for to analyze the various
regimes. We present a stochastic model for the spin dynamics in solids which is
equivalent to solving the spin Boltzmann equation and takes the relevant
processes into account on equal footing. The calculations reveal yet unknown
parts of the spin-relaxation phase diagram, where strong spin-dephasing occurs
in addition to spin-relaxation. Spin-relaxation times are obtained for this
regime by introducing the numerical Loschmidt echo. This allows us to construct
a generic approximate formula for the spin-relaxation time, $\tau_{\text{s}}$,
for the entire phase diagram, involving the quasiparticle scattering rate,
$\Gamma$, spin-orbit coupling strength, $\mathcal{L}$, and a magnetic term,
$\Delta_{\text{Z}}$ due to the Zeeman effect. The generic expression reads as
$\hbar/\tau_{\text{s}}\approx \Gamma\cdot \mathcal{L}^2
/(\Gamma^2+\mathcal{L}^2+\Delta_{\text{Z}}^2)$.",1911.01482v1
2020-09-10,Spin polarization recovery and Hanle effect for charge carriers interacting with nuclear spins in semiconductors,"We report on theoretical and experimental study of the spin polarization
recovery and Hanle effect for the charge carriers interacting with the
fluctuating nuclear spins in the semiconductor structures. We start the
theoretical description from the simplest model of static and isotropic nuclear
spin fluctuations. Then we describe the modification of the polarization
recovery and Hanle curves due to the anisotropy of the hyperfine interaction,
finite nuclear spin correlation time, and the strong pulsed spin excitation.
For the latter case, we describe the resonance spin amplification effect in the
Faraday geometry and discuss the manifestations of the quantum Zeno effect. The
set of the experimental results for various structures and experimental
conditions is chosen to highlight the specific effects predicted theoretically.
We show that the spin polarization recovery is a very valuable tool for
addressing carrier spin dynamics in semiconductors and their nanostructures.",2009.04805v1
2021-09-22,Spin precession of binary neutron stars with magnetic dipole moments,"Spin precession equations including the spin-orbit (SO), spin-spin (SS),
quadrupole-monopole (QM) and magnetic dipole-magnetic dipole (DD) leading-order
interactions are derived for compact binary systems in order to investigate the
DD contribution in the orbit-averaged spin precession equations for binary
neutron star systems neglecting the gravitational radiation-reaction effect. It
is known that the magnitudes of spins are not conserved quantities due to the
DD interaction. We give a simple analytical description for the pure DD
interaction making the magnitudes of spins almost constant by neglecting the
SO, SS and QM contributions. We also demonstrate the evolutions of the relative
angles of spins and magnetic dipoles with the help of numeric simulations
including all contributions (SO, SS, QM and DD) and introduce a dimensionless
magnetic dipole parameter to characterize the strength of magnetic fields for
some realistic neutron star binaries. We find that for realistic configurations
the strong magnetic fields of neutron stars can modify the spin dynamics over
long periods of time.",2109.10722v1
2022-01-05,Selective nuclear-spin interaction based on a dissipatively stabilized nitrogen-vacancy center,"Current typical methods to realize nuclear-nuclear quantum gates require a
sequence of electronnuclear quantum gates by using dynamical decoupling
techniques, which are implemented at low temperature because of short
decoherence and relaxation time of the NV spin at room temperature. This
limitation could be overcome by using periodical resets of an NV spin as a
mediator of interaction between two nuclear spins [Chen, Schwarz, and Plenio,
119, 010801 (2017)]. However, this method works under stringent coupling
strengths condition, which makes it not applicable to heteronuclear quantum
gate operations. Here we develop this scheme by using radio-frequency (RF)
fields to control different nuclear spin species. Periodical resets of the NV
center protect the nuclear spins from decoherence and relaxation of the NV
spin. RF control provides probability to have highly selective and high
fidelity quantum gates between heteronuclear spins as well as detecting nuclear
spins by using a nuclear spin sensor under ambient conditions.",2201.01567v1
2022-12-22,Spin-phonon decoherence in solid-state paramagnetic defects from first principles,"Paramagnetic defects in diamond and hexagonal boron nitride possess a unique
combination of spin and optical properties that make them prototypical
solid-state qubits. Despite the coherence of these spin qubits being critically
limited by spin-phonon relaxation, a full understanding of this process is not
yet available. Here we apply ab initio spin dynamics simulations to this
problem and quantitatively reproduce the experimental temperature dependence of
spin relaxation time and spin coherence time. We demonstrate that low-frequency
two-phonon modulations of the zero-field splitting are responsible for spin
relaxation and decoherence, and point to the nature of vibrations in
2-dimensional materials as the culprit for their shorter coherence time. These
results provide a novel interpretation to spin-phonon decoherence in
solid-state paramagnetic defects, offer a new strategy to correctly interpret
experimental results, and pave the way for the accelerated design of new spin
qubits.",2212.11705v2
2023-03-10,Phonon-mediated spin dynamics in a two-electron double quantum dot under a phonon temperature gradient,"We have theoretically studied phonon-mediated spin-flip processes of
electrons in a GaAs double quantum dot (DQD) holding two spins, under a phonon
temperature gradient over the DQD. Transition rates of inter-dot
phonon-assisted tunnel processes and intra-dot spin-flip processes involving
spin triplet states are formalized by the electron-phonon interaction
accompanied with the spin-orbit interaction. The calculations of the spin-flip
rates and the occupation probabilities of the spin-states in the two-electron
DQD with respect to the phonon temperature difference between the dots are
quantitatively consistent with our previous experiment. This theoretical study
on the temperature gradient effect onto spins in coupled QDs would be essential
for understanding spin-related thermodynamic physics.",2303.05700v1
2023-09-06,Vector spin Seebeck effect and spin swapping effect in antiferromagnetic insulators with non-collinear spin structure,"Antiferromagnets (AFs) are prospective for next-generation high-density and
high-speed spintronic applications due to their negligible stray field and
ultrafast spin dynamics, notwithstanding the challenges in detecting and
manipulating AF order with no magnetization (M = 0). Among the AFs,
non-collinear AFs are of particular interest because of their unique properties
arising from the non-collinear spin structure and the small magnetization M. In
this work, we describe the recently observed vector spin Seebeck effect in
non-collinear LuFeO$_3$, where the magneto-thermovoltage under an in-plane
temperature gradient, not previously observed, is consistent with the predicted
spin swapping effect. Our results shed light on the importance of the
non-collinear spin structure in the emerging spin phenomena in non-collinear
AFs and offer a new class of materials for AF spintronics and spin
caloritronics.",2309.03382v1
2023-09-10,Non-zero Integral Spin of Acoustic Vortices and Spin-orbit Interaction in Longitudinal Acoustics,"Spin and orbital angular momenta (AM) are of fundamental interest in wave
physics. Acoustic wave, as a typical longitudinal wave, has been well studied
in terms of orbital AM, but still considered unable to carry non-zero integral
spin AM or spin-orbital interaction in homogeneous media due to its spin-0
nature. Here we give the first self-consistent analytical calculations of spin,
orbital and total AM of guided vortices under different boundary conditions,
revealing that vortex field can carry non-zero integral spin AM. We also
introduce for acoustic waves the canonical-Minkowski and kinetic-Abraham AM,
which has aroused long-lasting debate in optics, and prove that only the former
is conserved with the corresponding symmetries. Furthermore, we present the
theoretical and experimental observation of the spin-orbit interaction of
vortices in longitudinal acoustics, which is thought beyond attainable in
longitudinal waves in the absence of spin degree of freedom. Our work provides
a solid platform for future studies of the spin and orbital AM of guided
acoustic waves and may open up a new dimension for acoustic vortex-based
applications such as underwater communications and object manipulations.",2309.04989v1
2023-11-27,High-fidelity spin qubit shuttling via large spin-orbit interaction,"Shuttling spins with high fidelity is a key requirement to scale up
semiconducting quantum computers, enabling qubit entanglement over large
distances and favoring the integration of control electronics on-chip. To
decouple the spin from the unavoidable charge noise, state-of-the-art spin
shuttlers try to minimize the inhomogeneity of the Zeeman field. However, this
decoupling is challenging in otherwise promising quantum computing platforms
such as hole spin qubits in silicon and germanium, characterized by a large
spin-orbit interaction and electrically-tunable qubit frequency. In this work,
we show that, surprisingly, the large inhomogeneity of the Zeeman field
stabilizes the coherence of a moving spin state, thus enabling high-fidelity
shuttling also in these systems. We relate this enhancement in fidelity to the
deterministic dynamics of the spin which filters out the dominant low-frequency
contributions of the charge noise. By simulating several different scenarios
and noise sources, we show that this is a robust phenomenon generally occurring
at large field inhomogeneity. By appropriately adjusting the motion of the
quantum dot, we also design realistic protocols enabling faster and more
coherent spin shuttling. Our findings are generally applicable to a wide range
of setups and could pave the way toward large-scale quantum processors.",2311.15970v1
2023-11-30,Observing coherence in an incoherent paramagnetic nitrogen spin bath,"The unpolarized spin environment surrounding a central spin qubit is
typically considered as an incoherent source of dephasing, however, precise
characterization and control of the spin bath can yield a resource for storing
and sensing with quantum states. In this work, we use nitrogen-vacancy (NV)
centers in diamond to measure the coherence of optically-dark paramagnetic
nitrogen defects (P1 centers) and detect coherent interactions between the P1
centers and a local bath of $^{13}$C nuclear spins. The dipolar coupling
between the P1 centers and $^{13}$C nuclear spins is identified by signature
periodic collapses and revivals in the P1 spin coherence signal. We then
demonstrate, using a range of dynamical decoupling protocols, that the probing
NV centers and the P1 spins are coupled to independent ensembles of $^{13}$C
nuclear spins. Our work illustrates how the optically-dark P1 spins, despite
being unpolarized, can be used to extract information from their local
environment and offers new insight into the interactions within a many-body
system.",2311.18181v1
2024-03-10,Spin Waves and Spin Currents in Magnon-Phonon Composite Resonator Induced by Acoustic Waves of Various Polarizations,"In this work, we present the results of a systematic experimental study of
linear and parametric spin wave resonant excitation accompanied by spin
currents (spin pumping) in a multifrequency composite bulk acoustic wave
resonator with a ZnO-YIG-GGG-YIG/Pt structure. The features of magnetic
dynamics excitation in YIG films due to magnetoelastic coupling with acoustic
thickness modes of various polarizations are studied. Acoustic spin waves and
spin pumping are detected by simultaneous frequency-field mapping of the
inverse spin Hall effect voltage and the resonant frequencies of thickness
extensional modes. In the parametric range of frequencies and fields, acoustic
spin pumping induced by both shear and longitudinal polarization modes was
observed. Linear acoustic spin waves are excited only by shear thickness
extensional modes because longitudinal acoustic waves do not couple with the
magnetic subsystem in linear regime.",2403.06274v1
2012-08-23,Spin dynamics of molecular nanomagnets fully unraveled by four-dimensional inelastic neutron scattering,"Molecular nanomagnets are among the first examples of spin systems of finite
size and have been test-beds for addressing a range of elusive but important
phenomena in quantum dynamics. In fact, for short-enough timescales the spin
wavefunctions evolve coherently according to the an appropriate cluster
spin-Hamiltonian, whose structure can be tailored at the synthetic level to
meet specific requirements. Unfortunately, to this point it has been impossible
to determine the spin dynamics directly. If the molecule is sufficiently
simple, the spin motion can be indirectly assessed by an approximate model
Hamiltonian fitted to experimental measurements of various types. Here we show
that recently-developed instrumentation yields the four-dimensional
inelastic-neutron scattering function S(Q,E) in vast portions of reciprocal
space and enables the spin dynamics to be determined with no need of any model
Hamiltonian. We exploit the Cr8 antiferromagnetic ring as a benchmark to
demonstrate the potential of this new approach. For the first time we extract a
model-free picture of the quantum dynamics of a molecular nanomagnet. This
allows us, for example, to examine how a quantum fluctuation propagates along
the ring and to directly test the degree of validity of the
N\'{e}el-vector-tunneling description of the spin dynamics.",1208.4785v1
2014-04-24,Computer Simulation of Quantum Dynamics in a Classical Spin Environment,"In this paper a formalism for studying the dynamics of quantum systems
coupled to classical spin environments is reviewed. The theory is based on
generalized antisymmetric brackets and naturally predicts open-path
off-diagonal geometric phases in the evolution of the density matrix. It is
shown that such geometric phases must also be considered in the
quantum-classical Liouville equation for a classical bath with canonical phase
space coordinates; this occurs whenever the adiabatics basis is complex (as in
the case of a magnetic field coupled to the quantum subsystem). When the
quantum subsystem is weakly coupled to the spin environment, non-adiabatic
transitions can be neglected and one can construct an effective non-Markovian
computer simulation scheme for open quantum system dynamics in classical spin
environments. In order to tackle this case, integration algorithms based on the
symmetric Trotter factorization of the classical-like spin propagator are
derived. Such algorithms are applied to a model comprising a quantum two-level
system coupled to a single classical spin in an external magnetic field.
Starting from an excited state, the population difference and the coherences of
this two-state model are simulated in time while the dynamics of the classical
spin is monitored in detail. It is the author's opinion that the numerical
evidence provided in this paper is a first step toward developing the
simulation of quantum dynamics in classical spin environments into an effective
tool. In turn, the ability to simulate such a dynamics can have a positive
impact on various fields, among which, for example, nano-science.",1404.6143v1
2018-05-23,Dynamical spin effects in the holographic light-front wavefunctions of light pseudoscalar mesons,"We quantify the importance of dynamical spin effects in the holographic
light-front wavefunctions of the pion, kaon, $\eta$ and $\eta^\prime$. Using a
universal AdS/QCD scale and constituent quark masses, we find that such effects
are maximal in the pion where they lead to an excellent simultaneous
description of a wide range of data: the decay constant, charge radius,
spacelike EM and transition form factors, as well as, after QCD evolution, both
the parton distribution function and the parton distribution amplitude data
from Fermilab. These dynamical spin effects lead up to a $30\%$ chance of
finding the valence quark and antiquark with aligned spins in the pion. The
situation is very different for the kaon, where a simultaneous description of
the available data (decay constant, radius and spacelike EM form factor) prefer
no dynamical spin effects at all. The situation is less clear for the $\eta$
and $\eta^\prime$: while their radiative decay widths data are consistent with
dynamical spin effects only in $\eta^\prime$, the data on their spacelike
transition form factors clearly favor maximal dynamical spin effects in both
mesons.",1805.08911v2
2017-05-22,Temperature evolution of spin dynamics in two- and three-dimensional Kitaev models: Influence of fluctuating gauge fluxes,"The long-sought quantum spin liquid is a quantum-entangled magnetic state
leading to the fractionalization of spin degrees of freedom. Quasiparticles
emergent from the fractionalization affect not only the ground state properties
but also thermodynamic behavior in a peculiar manner. We here investigate how
the spin dynamics evolves from the high-temperature paramagnet to the quantum
spin liquid ground state, for the Kitaev spin model describing the
fractionalization into itinerant matter fermions and localized $Z_2$ gauge
fluxes. Beyond the previous study [J. Yoshitake, J. Nasu, and Y. Motome, Phys.
Rev. Lett. $\textbf{117}$, 157203 (2016)], in which the mean-field nature of
the cluster dynamical mean-field theory prevented us from studying
low-temperature properties, we develop a numerical technique by applying the
continuous-time quantum Monte Carlo (CTQMC) method to statistical samples
generated by the quantum Monte Carlo (QMC) method in a Majorana fermion
representation. This QMC+CTQMC method is fully unbiased and enables us to
investigate the low-temperature spin dynamics dominated by thermally excited
gauge fluxes, including the unconventional phase transition caused by gauge
flux loops in three dimensions, which was unreachable by the previous methods.
We apply this technique to the Kitaev model in both two and three dimensions.
Our results clearly distinguish two cases: while the dynamics changes smoothly
through the crossover in the two-dimensional honeycomb case, it exhibits
singular behaviors at the phase transition in the three-dimensional
hyperhoneycomb case. We show that the low-temperature spin dynamics is a
sensitive probe for thermally fluctuating gauge fluxes that behave very
differently between two and three dimensions.",1705.07760v1
2021-11-30,The AiiDA-Spirit plugin for automated spin-dynamics simulations and multi-scale modelling based on first-principles calculations,"Landau-Lifshitz-Gilbert (LLG) spin-dynamics calculations based on the
extended Heisenberg Hamiltonian is an important tool in computational materials
science involving magnetic materials. LLG simulations allow to bridge the gap
from expensive quantum mechanical calculations with small unit cells to large
supercells where the collective behavior of millions of spins can be studied.
In this work we present the AiiDA-Spirit plugin that connects the spin-dynamics
code Spirit to the AiiDA framework. AiiDA provides a Python interface that
facilitates performing high-throughput calculations while automatically
augmenting the calculations with metadata describing the data provenance
between calculations in a directed acyclic graph. The AiiDA-Spirit interface
thus provides an easy way for high-throughput spin-dynamics calculations. The
interface to the AiiDA infrastructure furthermore has the advantage that input
parameters for the extended Heisenberg model can be extracted from
high-throughput first-principles calculations including a proper treatment of
the data provenance that ensures reproducibility of the calculation results in
accordance to the FAIR principles. We describe the layout of the AiiDA-Spirit
plugin and demonstrate its capabilities using selected examples for LLG
spin-dynamics and Monte Carlo calculations. Furthermore, the integration with
first-principles calculations through AiiDA is demonstrated at the example of
$\gamma$-Fe, where the complex spin-spiral ground state is investigated.",2111.15229v1
2022-03-15,Spin-optical dynamics and quantum efficiency of single V1 center in silicon carbide,"Color centers in silicon carbide are emerging candidates for distributed
spin-based quantum applications due to the scalability of host materials and
the demonstration of integration into nanophotonic resonators. Recently,
silicon vacancy centers in silicon carbide have been identified as a promising
system with excellent spin and optical properties. Here, we in-depth study the
spin-optical dynamics of single silicon vacancy center at hexagonal lattice
sites, namely V1, in 4H-polytype silicon carbide. By utilizing resonant and
above-resonant sub-lifetime pulsed excitation, we determine spin-dependent
excited-state lifetimes and intersystem-crossing rates. Our approach to
inferring the intersystem-crossing rates is based on all-optical pulsed
initialization and readout scheme, and is applicable to spin-active color
centers with similar dynamics models. In addition, the optical transition
dipole strength and the quantum efficiency of V1 defect are evaluated based on
coherent optical Rabi measurement and local-field calibration employing
electric-field simulation. The measured rates well explain the results of
spin-state polarization dynamics, and we further discuss the altered
photoemission dynamics in resonant enhancement structures such as radiative
lifetime shortening and Purcell enhancement. By providing a thorough
description of V1 center's spin-optical dynamics, our work provides deep
understanding of the system which guides implementations of scalable quantum
applications based on silicon vacancy centers in silicon carbide.",2203.08177v2
2022-12-30,Selection rules for ultrafast laser excitation and detection of spin correlations dynamics in a cubic antiferromagnet,"Exchange interactions determine the correlations between microscopic spins in
magnetic materials. Probing the dynamics of these spin correlations on
ultrashort length and time scales is, however rather challenging, since it
requires simultaneously high spatial and high temporal resolution. Recent
experimental demonstrations of laser-driven two-magnon modes - zone-edge
excitations in antiferromagnets governed by exchange coupling - posed questions
about the microscopic nature of the observed spin dynamics, the mechanism
underlying its excitation, and their macroscopic manifestation enabling
detection. Here, on the basis of a simple microscopic model, we derive the
selection rules for cubic systems that describe the polarization of pump and
probe pulses required to excite and detect dynamics of nearest-neighbor spin
correlations, and can be employed to isolate such dynamics from other magnetic
excitations and magneto-optical effects. We show that laser-driven spin
correlations contribute to optical anisotropy of the antiferromagnet even in
the absence of spin-orbit coupling. In addition, we highlight the role of
subleading anisotropy in the spin system and demonstrate that the dynamics of
the antiferromagnetic order parameter occurs only in next-to-leading order,
determined by the smallness of the magnetic anisotropy as compared to the
isotropic exchange interactions in the system. We expect that our results will
stimulate and support further studies of magnetic correlations on the shortest
length and time scale.",2212.14698v2
2023-11-09,Skyrmion-Excited Spin Wave Fractal Network,"Magnetic skyrmions exhibit unique, technologically relevant pseudo-particle
behaviors which arise from their topological protection, including
well-defined, three-dimensional dynamic modes that occur at microwave
frequencies. During dynamic excitation, spin waves are ejected into the
interstitial regions between skyrmions, creating the magnetic equivalent of a
turbulent sea. However, since the spin waves in these systems have a
well-defined length scale, and the skyrmions are on an ordered lattice, ordered
structures from spin wave interference can precipitate from the chaos. This
work uses small angle neutron scattering (SANS) to capture the dynamics in
hybrid skyrmions and investigate the spin wave structure. Performing
simultaneous ferromagnetic resonance and SANS, the diffraction pattern shows a
large increase in low-angle scattering intensity which is present only in the
resonance condition. This scattering pattern is best fit using a mass fractal
model, which suggests the spin waves form a long-range fractal network. The
fractal structure is constructed of fundamental units with a size that encodes
the spin wave emissions and are constrained by the skyrmion lattice. These
results offer critical insights into the nanoscale dynamics of skyrmions,
identify a new dynamic spin wave fractal structure, and demonstrates SANS as a
unique tool to probe high-speed dynamics.",2311.05469v1
2009-05-29,Second-order dynamic transition in a p=2 spin-glass model,"We consider the dynamics of a disordered p-spin model with p=2, analyzing the
dynamics within Ruelle's thermodynamic formalism, We use an indicator of the
dynamical activity to construct the relevant dynamical Gibbs ensemble. We prove
that the dynamics in the low-temperature (spin glass) phase of the model take
place at a second-order phase transition between dynamically active and
inactive trajectories. We also show that the same behaviour is found in a
related model of a three-dimensional ferromagnet.",0905.4878v1
2022-12-10,Collective dynamics of polarized spin-half fermions in relativistic heavy-ion collisions,"Relativistic hydrodynamics has been quite successful in describing the
properties of strongly-interacting matter produced in heavy-ion collision
experiments. Recently, there has been a significant advancement in this field
to explain the spin polarization of hadrons emitted in these processes.
Although current models have successfully explained some of the experimental
data based on spin-vorticity coupling, they still lack a clear understanding of
differential measurements. This is an indication that the spin needs to be
treated as an independent degree of freedom whose dynamics is not entirely
bound to flow circulation. In particular, if the spin is a macroscopic property
of the system, in equilibrium its dynamics should follow hydrodynamic laws. In
this thesis, we develop a framework of relativistic perfect-fluid hydrodynamics
which includes spin degrees of freedom from kinetic theory, and use it for
modeling the dynamics of matter produced in relativistic heavy-ion collisions.
Following experimental observations, we assume that the polarization effects
are small and derive conservation laws for net-baryon current, energy-momentum
tensor, and spin tensor based on the de Groot-van Leeuwen-van Weert
pseudogauge. Subsequently, we present various properties of the spin
polarization tensor and its components, analyze the propagation properties of
the spin polarization components, and derive the spin-wave velocity for
arbitrary statistics. We find that only the transverse spin components
propagate, analogously to the EM waves. Finally, we study the spacetime
evolution of spin polarization for the systems respecting certain spacetime
symmetries and calculate the mean spin polarization per particle, which can be
compared to the experimental data. We find that, for some observables, our spin
polarization results agree qualitatively with the experimental findings and
other model calculations.",2212.06569v2
2011-02-09,Observation of second-harmonic generation induced by pure spin currents,"Extensive efforts are currently being devoted to developing a new electronic
technology, called spintronics, where the spin of electrons is explored to
carry information. [1,2] Several techniques have been developed to generate
pure spin currents in many materials and structures. [3-10] However, there is
still no method available that can be used to directly detect pure spin
currents, which carry no net charge current and no net magnetization.
Currently, studies of pure spin currents rely on measuring the induced spin
accumulation with optical techniques [5, 11-13] or spin-valve configurations.
[14-17] However, the spin accumulation does not directly reflect the spatial
distribution or temporal dynamics of the pure spin current, and therefore
cannot monitor the pure spin current in a real-time and real-space fashion.
This imposes severe constraints on research in this field. Here we demonstrate
a second-order nonlinear optical effect of the pure spin current. We show that
such a nonlinear optical effect, which has never been explored before, can be
used for the non-invasive, non-destructive, and real-time imaging of pure spin
currents. Since this detection scheme does not rely on optical resonances, it
can be generally applied in a wide range of materials with different electronic
bandstructures. Furthermore, the control of nonlinear optical properties of
materials with pure spin currents may have potential applications in photonics
integrated with spintronics.",1102.1784v1
2013-05-24,"On Ultrafast Spin Dynamics: Spin Dependent Fast Response of Hot Electrons, of Band--Structure","Different energy shifts for majority and minority electrons occur. Thus, for
example in case of (laser) excited ferromagnetic metals majority and minority
electrons may respond differently in time during closing the exchange
splitting. Spin flip transitions of the hot electrons due to electron
interactions cause quasi hybridization of the spin split states. This is also
the case in itinerant ferromagnetic metals due to hopping between sites having
magnetic moments pointing in direction of the magnetization (+) and opposite
direction (-) and with energy levels $\varepsilon^+_{i\sigma}$ and
$\varepsilon^-_{i\sigma}$. For energetic reasons the molecular field acts
asymmetrically on the spins of the electrons and on spin flip transitions and
thus causes different lifetimes of minority and majority electrons and spin
dependent electron energy shifts. Quite general minority hot electrons in spin
split states may respond faster than majority electrons at non--equilibrium.
The molecular field acting on the spins delays spin flip transitions $\uparrow
\rightarrow \downarrow$ and thus a response of the hot majority electrons and
their energy levels. The closing of the exchange splitting in the electron
spectrum of ferromagnetic transition and rare--earth metals, ferromagnetic
semiconductors, spin split quantum well states in thin ferromagnetic films,
etc. will reflect this. The time and spin dependent energy shifts of electrons
at non--equilibrium may cause interesting behavior, in particular of magnetic
tunnel junctions, spin currents etc.. In ferromagnets the moment reversal
lifetime of (local) magnetic moments parallel to the global magnetization is
larger than of moments pointing in opposite direction.",1305.5698v1
2014-11-05,Hybrid optical-electrical detection of donor electron spins with bound excitons in silicon,"Electrical detection of spins is an essential tool in understanding the
dynamics of spins in semiconductor devices, providing valuable insights for
applications ranging from optoelectronics and spintronics to quantum
information processing. For electron spins bound to shallow donors in silicon,
bulk electrically-detected magnetic resonance has relied on coupling to spin
readout partners such as paramagnetic defects or conduction electrons which
fundamentally limits spin coherence times. Here we demonstrate electrical
detection of phosphorus donor electron spin resonance by transport through a
silicon device, using optically-driven donor-bound exciton transitions. We use
this method to measure electron spin Rabi oscillations, and, by avoiding use of
an ancillary spin for readout, we are able to obtain long intrinsic electron
spin coherence times, limited only by the donor concentration. We go on to
experimentally address critical issues for adopting this scheme for single spin
measurement in silicon nanodevices, including the effects of strain, electric
fields, and non-resonant excitation. This lays the foundations for realising a
versatile readout method for single spin readout with relaxed magnetic field
and temperature requirements compared with spin-dependent tunneling.",1411.1324v1
2014-12-04,Spin-dependent recombination and hyperfine interaction at the deep defects,"We present a theoretical study of optical electron-spin orientation and
spin-dependent Shockley-Read-Hall recombination taking into account the
hyperfine coupling between the bound-electron spin and the nuclear spin of a
deep paramagnetic center. We show that the number of master rate equations for
the components of the electron-nuclear spin-density matrix is considerably
reduced due to the restrictions imposed by the axial symmetry of the system
under consideration. The rate equations describe the Zeeman splitting of the
electron spin sublevels in the longitudinal magnetic field, the spin relaxation
of free and bound electrons, and the nuclear spin relaxation in the two defect
states, with one and two (singlet) bound electrons. The general theory is
developed for an arbitrary value of the nuclear spin I, the magnetic-field and
excitation-power dependencies of the electron and nuclear spin polarizations
are calculated for the particular value of I = 1/2. The role of the nuclear
spin relaxation in each of the both defect states is analyzed. The circular
polarization and intensity of the edge photoluminescence as well as the dynamic
nuclear spin polarization as functions of the excitation power are shown to
have bell-shaped forms",1412.1664v2
2015-07-31,Electron spin resonance spectroscopy of small ensemble paramagnetic spins using a single nitrogen-vacancy center in diamond,"A nitrogen-vacancy (NV) center in diamond is a promising sensor for nanoscale
magnetic sensing. Here we report electron spin resonance (ESR) spectroscopy
using a single NV center in diamond. First, using a 230 GHz ESR spectrometer,
we performed ensemble ESR of a type-Ib sample crystal and identified a
substitutional single nitrogen impurity as a major paramagnetic center in the
sample crystal. Then, we carried out free-induction decay and spin echo
measurements of the single NV center to study static and dynamic properties of
nanoscale bath spins surrounding the NV center. We also measured ESR spectrum
of the bath spins using double electron-electron resonance spectroscopy with
the single NV center. The spectrum analysis of the NV-based ESR measurement
identified that the detected spins are the nitrogen impurity spins. The
experiment was also performed with several other single NV centers in the
diamond sample and demonstrated that the properties of the bath spins are
unique to the NV centers indicating the probe of spins in the microscopic
volume using NV-based ESR. Finally, we discussed the number of spins detected
by the NV-based ESR spectroscopy. By comparing the experimental result with
simulation, we estimated the number of the detected spins to be $\leq$ 50
spins.",1507.08744v2
2017-10-04,Possible evidence for spin-transfer torque induced by spin-triplet supercurrent,"Cooper pairs in superconductors are normally spin singlet. Nevertheless,
recent studies suggest that spin-triplet Cooper pairs can be created at
carefully engineered superconductor-ferromagnet interfaces. If Cooper pairs are
spin-polarized they would transport not only charge but also a net spin
component, but without dissipation, and therefore minimize the heating effects
associated with spintronic devices. Although it is now established that triplet
supercurrents exist, their most interesting property - spin - is only inferred
indirectly from transport measurements. In conventional spintronics, it is well
known that spin currents generate spin-transfer torques that alter
magnetization dynamics and switch magnetic moments. The observation of similar
effects due to spin-triplet supercurrents would not only confirm the net spin
of triplet pairs but also pave the way for applications of superconducting
spintronics. Here, we present a possible evidence for spin-transfer torques
induced by triplet supercurrents in superconductor/ferromagnet/superconductor
(S/F/S) Josephson junctions. Below the superconducting transition temperature
T_c, the ferromagnetic resonance (FMR) field at X-band (~ 9.0 GHz) shifts
rapidly to a lower field with decreasing temperature due to the spin-transfer
torques induced by triplet supercurrents. In contrast, this phenomenon is
absent in ferromagnet/superconductor (F/S) bilayers and
superconductor/insulator/ferromagnet/superconductor (S/I/F/S) multilayers where
no supercurrents pass through the ferromagnetic layer. These experimental
observations are discussed with theoretical predictions for ferromagnetic
Josephson junctions with precessing magnetization.",1710.01534v1
2020-05-27,AGN anisotropic radiative feedback set by black hole spin,"We consider the impact of anisotropic radiation on the active galactic
nucleus (AGN) radiative dusty feedback. The radiation pattern originating from
the accretion disc is determined by the central black hole (BH) spin. Here we
analyse how such BH spin-induced angular dependence affects the dynamics and
energetics of the radiation pressure-driven outflows, as well as AGN
obscuration and BH accretion. In addition, we explore the effect of a spatially
varying dust-to-gas ratio on the outflow propagation. We obtain two distinct
trends for high-spin and low-spin objects, providing a direct connection
between anisotropic feedback and BH spin. In the case of maximum spin, powerful
quasi-spherical outflows can propagate on large scales, at all inclination
angles with fairly uniform energetics. In contrast, in the case of zero spin,
only weaker bipolar outflows can be driven in the polar directions. As a
result, high BH spins can efficiently clear out the obscuring gas from most
directions, whereas low BH spins can only remove dusty gas from the polar
regions, hence also determining the overall AGN obscuration geometry. Due to
such anisotropic feedback, high BH spins can prevent accretion of gas from most
directions (except in the equatorial plane), while low BH spins allow inflows
to proceed from a wider range of directions. This may have important
implications for the BH growth in the early Universe. Anisotropic radiative
dusty feedback, ruled by the BH spin, may thus play a major role in shaping AGN
evolution over cosmic time.",2005.13633v1
2020-09-06,Adiabatic and Nonadiabatic Spin-transfer Torques in Antiferromagnets,"Electron transport in magnetic orders and the magnetic orders dynamics have a
mutual dependence, which provides the key mechanisms in spin-dependent
phenomena. Recently, antiferromagnetic orders are focused on as the magnetic
order, where current-induced spin-transfer torques, a typical effect of
electron transport on the magnetic order, have been debatable mainly because of
the lack of an analytic derivation based on quantum field theory. Here, we
construct the microscopic theory of spin-transfer torques on the slowly-varying
staggered magnetization in antiferromagnets with weak canting. In our theory,
the electron is captured by bonding/antibonding states, each of which is the
eigenstate of the system, doubly degenerates, and spatially spreads to
sublattices because of electron hopping. The spin of the eigenstates depends on
the momentum in general, and a nontrivial spin-momentum locking arises for the
case with no site inversion symmetry, without considering any spin-orbit
couplings. The spin current of the eigenstates includes an anomalous component
proportional to a kind of gauge field defined by derivatives in momentum space
and induces the adiabatic spin-transfer torques on the magnetization.
Unexpectedly, we find that one of the nonadiabatic torques has the same form as
the adiabatic spin-transfer torque, while the obtained forms for the adiabatic
and nonadiabatic spin-transfer torques agree with the phenomenological
derivation based on the symmetry consideration. This finding suggests that the
conventional explanation for the spin-transfer torques in antiferromagnets
should be changed. Our microscopic theory provides a fundamental understanding
of spin-related physics in antiferromagnets.",2009.02686v1
2020-10-26,Spin Insulatronics,"Spin insulatronics covers efforts to generate, detect, control, and utilize
high-fidelity pure spin currents and excitations inside magnetic insulators.
Ultimately, the new findings may open doors for pure spin-based information and
communication technologies. The aim is to replace moving charges with dynamical
entities that utilize low-dissipation coherent and incoherent spin excitations
in antiferromagnetic and ferromagnetic insulators. The ambition is that the new
pure spin-based system will suffer reduced energy losses and operate at high
frequencies. In magnetic insulators, there are no mobile charge carriers that
can dissipate energy. Integration with conventional electronics is possible via
interface exchange interactions and spin-orbit couplings. In this way, the free
electrons in the metals couple to the localized spins in the magnetic
insulators. In turn, these links facilitate spin-transfer torques and
spin-orbit torques across metal-insulator interfaces and the associated
phenomena of spin-pumping and charge-pumping. The interface couplings also
connect the electron motion inside the metals with the spin fluctuations inside
the magnetic insulators. These features imply that the system can enable
unprecedented control of correlations resulting from the electron-magnon
interactions. We review recent developments to realize electric and thermal
generation, manipulation, detection, and control of pure spin information in
insulators.",2010.13512v1
2021-08-29,Nuclear spin-wave quantum register for a solid state qubit,"Solid-state nuclear spins surrounding individual, optically addressable
qubits provide a crucial resource for quantum networks, computation and
simulation. While hosts with sparse nuclear spin baths are typically chosen to
mitigate qubit decoherence, developing coherent quantum systems in nuclear
spin-rich hosts enables exploration of a much broader range of materials for
quantum information applications. The collective modes of these dense nuclear
spin ensembles provide a natural basis for quantum storage, however, utilizing
them as a resource for single spin qubits has thus far remained elusive. Here,
by using a highly coherent, optically addressed 171Yb3+ qubit doped into a
nuclear spin-rich yttrium orthovanadate crystal, we develop a robust quantum
control protocol to manipulate the multi-level nuclear spin states of
neighbouring 51V5+ lattice ions. Via a dynamically-engineered spin exchange
interaction, we polarise this nuclear spin ensemble, generate collective spin
excitations, and subsequently use them to implement a long-lived quantum
memory. We additionally demonstrate preparation and measurement of maximally
entangled 171Yb--51V Bell states. Unlike conventional, disordered nuclear spin
based quantum memories, our platform is deterministic and reproducible,
ensuring identical quantum registers for all 171Yb qubits. Our approach
provides a framework for utilising the complex structure of dense nuclear spin
baths, paving the way for building large-scale quantum networks using single
rare-earth ion qubits.",2108.12723v1
2023-10-25,Competing Gauge Fields and Entropically-Driven Spin Liquid to Spin Liquid Transition in non-Kramers Pyrochlores,"Gauge theories are powerful tools in theoretical physics, allowing complex
phenomena to be reduced to simple principles, and are used in both high-energy
and condensed matter physics. In the latter context, gauge theories are
becoming increasingly popular for capturing the intricate spin correlations in
spin liquids, exotic states of matter in which the dynamics of quantum spins
never ceases, even at absolute zero temperature. We consider a spin system on a
three-dimensional pyrochlore lattice where emergent gauge fields not only
describe the spin liquid behaviour at zero temperature but crucially determine
the system's temperature evolution, with distinct gauge fields giving rise to
different spin liquid phases in separate temperature regimes. Focusing first on
classical spins, in an intermediate temperature regime, the system shows an
unusual coexistence of emergent vector and matrix gauge fields where the former
is known from classical spin ice systems while the latter has been associated
with fractonic quasiparticles, a peculiar type of excitation with restricted
mobility. Upon cooling, the system transitions into a low-temperature phase
where an entropic selection mechanism depopulates the degrees of freedom
associated with the matrix gauge field, rendering the system spin ice like. We
further provide numerical evidence that in the corresponding quantum model, a
spin liquid with coexisting vector and matrix gauge fields has a finite window
of stability in the parameter space of spin interactions down to zero
temperature. Finally, we discuss the relevance of our findings for non-Kramers
pyrochlore materials.",2310.16682v1
2021-03-19,Spin-Injection-Generated Shock Waves and Solitons in a Ferromagnetic Thin Film,"Unsteady nonlinear magnetization dynamics are studied in an easy-plane
ferromagnetic channel subject to spin injection at one edge. The model
Landau-Lifshitz equation is known to support steady-state solutions, termed
dissipative exchange flows (DEFs) or spin superfluids. In this work, by means
of numerical simulations and theoretical analysis, we provide a full
description of the injection-induced, large-amplitude, nonlinear magnetization
dynamics up to the steady state. The dynamics prior to reaching steady state
are driven by spin injection, the perpendicular applied magnetic field, the
exchange interaction, and local demagnetizing fields. We show that the dynamics
take well-defined profiles in the form of rarefaction waves (RW), dispersive
shock waves (DSW), and solitons. The combination of these building blocks
depends on the interplay between the spin injection strength and the applied
magnetic field. A solitonic feature at the injection boundary, signaling the
onset of the magnetic ""supersonic"" condition at the injection edge, rapidly
develops and persists in the steady-state configuration of a contact soliton
DEF. We also demonstrate the existence of sustained soliton-train dynamics in
long time that can only arise in a nonzero applied magnetic field scenario. The
dynamical evolution of spin-injection-induced magnetization dynamics presented
here may help guide observations in long-distance spin transport experiments.",2103.10616v1
2001-04-17,Relaxational dynamics study of the classical Heisenberg spin XY model in spherical coordinate representation,"The two- and three-dimensional classical Heisenberg spin XY (CHSXY) models,
with the spherical coordinates of spins taken as dynamic variables, are
numerically investigated. We allow the polar $\theta$ and azimuthal $\phi$
angles to have uniform values in $[0,\pi)$ and $[-\pi, \pi)$, respectively, and
the static universality class is shown to be identical to the classical XY
model with two-component spins, as well as the CHSXY model with a different
choice of dynamic variables, conventionally used in the literature. The
relaxational dynamic simulation reveals that the dynamic critical exponent $z$
is found to have the value $z \approx 2.0$ for both two and three dimensions,
in contrast to $z \approx d/2$ ($d=$ spatial dimension) found previously with
spin dynamics simulation of the conventional CHSXY model. Comparisons with the
usual two-component classical XY model are also made.",0104288v2
2007-09-04,Chaotic dynamics of two 1/2 spin-qubit system in the optical cavity,"Spin systems are one of the most promising candidates for quantum
computation. At the same time control of a system's quantum state during time
evolution is one of the actual problems. It is usually considered that to hold
well-known resonance condition in magnetic resonance is sufficient to control
spin system. But because of nonlinearity of the system, obstructions of control
of system's quantum state may emerge.
  In particular quantum dynamics of two 1/2 spin-qubit system in the optical
cavity is studied in this work. The problem under study is a generalization of
paradigmatic model for Cavity Quantum Electrodynamics of James-Cummings model
in case of interacting spins. In this work it is shown that dynamics is chaotic
when taking into account center-of-mass motion of the qubit and recoil effect.
And besides even in case of zero detuning chaotic dynamics emerges in the
system. It is also shown in this work that because of the chaotic dynamics the
system execute irreversible transition from pure quantum-mechanical state to
mixed one. Irreversibility in its turn is an obstacle for controlling state of
quantum-mechanical system.",0709.0496v1
2010-01-11,"Nuclear Spin Dynamics in Double Quantum Dots: Fixed Points, Transients, and Intermittency","Transport through spin-blockaded quantum dots provides a means for electrical
control and detection of nuclear spin dynamics in the host material. Although
such experiments have become increasingly popular in recent years,
interpretation of their results in terms of the underlying nuclear spin
dynamics remains challenging. Here we point out a fundamental process in which
nuclear spin dynamics can be driven by electron shot noise; fast electric
current fluctuations generate much slower nuclear polarization dynamics, which
in turn affect electron dynamics via the Overhauser field. The resulting
extremely slow intermittent current fluctuations account for a variety of
observed phenomena that were not previously understood.",1001.1735v3
2016-10-07,Local thermomagnonic torques in two-fluid spin dynamics,"We develop a general phenomenology describing the interplay between coherent
and incoherent dynamics in ferromagnetic insulators. Using the Onsager
reciprocity and Neumann's principle, we derive expressions for the local
thermomagnonic torques exerted by thermal magnons on the order-parameter
dynamics and the reciprocal pumping processes, which are in close analogy to
the spin-transfer torque and spin pumping at metallic interfaces. Our formalism
is applicable to general long-wavelength dynamics and, although here we
explicitly focus on ferromagnetic insulators possessing U(1) symmetry, our
approach can be easily extended to other classes of magnetic materials. As an
illustrative example, we apply our theory to investigate a domain wall floating
over a spin superfluid, whose dynamics is triggered thermally at the system's
edge. Our results demonstrate that the local pumping of coherent spin dynamics
by a thermal magnon gas offers an alternative route - with no need for
conducting components and thus devoid of Ohmic losses - for the control and
manipulation of topological solitons.",1610.02224v1
2019-07-17,Dynamics of quasiperiodically driven spin systems,"We study the stroboscopic dynamics of a spin-$S$ object subjected to
$\delta$-function kicking in the transverse magnetic field which is generated
following the Fibonacci sequence. The corresponding classical Hamiltonian map
is constructed in the large spin limit, $S \rightarrow \infty$. Upon evolving
such a map for large kicking strength and time period, the phase space appears
to be chaotic; interestingly, however, the geodesic distance increases linearly
with the stroboscopic time implying that the Lyapunov exponent is zero. We
derive the Sutherland invariant for the underlying $SO(3)$ matrix governing the
dynamics of classical spin variables and study the orbits for weak kicking
strength. For the quantum dynamics, we observe that although the phase
coherence of a state is retained throughout the time evolution, the
fluctuations in the mean values of the spin operators exhibit fractality which
is also present in the Floquet eigenstates. Interestingly, the presence of an
interaction with another spin results in an ergodic dynamics leading to
infinite temperature thermalization.",1907.07492v1
2019-09-09,Kardar-Parisi-Zhang physics in integrable rotationally symmetric dynamics on discrete space-time lattice,"We introduce a deterministic SO(3) invariant dynamics of classical spins on a
discrete space-time lattice and prove its complete integrability by explicitly
finding a related non-constant (baxterized) solution of the set-theoretic
quantum Yang-Baxter equation over the 2-sphere. Equipping the algebraic
structure with the corresponding Lax operator we derive an infinite sequence of
conserved quantities with local densities. The dynamics depend on a single
continuous spectral parameter and reduce to a (lattice) Landau-Lifshitz model
in the limit of a small parameter which corresponds to the continuous time
limit. Using quasi-exact numerical simulations of deterministic dynamics and
Monte Carlo sampling of initial conditions corresponding to a maximum entropy
equilibrium state we determine spin-spin spatio-temporal (dynamical)
correlation functions with relative accuracy of three orders of magnitude. We
demonstrate that in the equilibrium state with a vanishing total magnetization
the correlation function precisely follow Kardar-Parisi-Zhang scaling hence the
spin transport belongs to the universality class with dynamical exponent z=3/2,
in accordance to recent related simulations in discrete and continuous time
quantum Heisenberg spin 1/2 chains.",1909.03799v1
2023-04-28,Spin-boson model under dephasing: Markovian vs Non-Markovian dynamics,"The spin-boson model, describing a two-level system strongly coupled to a
bosonic bath, is extensively studied as a paradigmatic dissipative quantum
system, exhibiting rich dynamical behavior and even a localization transition
in the strong coupling regime. Here, we additionally consider dephasing as a
source of Markovian dissipation on top of the non-Markovian dynamics due to an
Ohmic bath, and investigate the dynamics of the spin. We show that the
characteristic frequency of the spin dynamics, while strongly renormalized by
the bosonic bath, changes in a simple fashion (or doesn't change at all) with
dephasing. To obtain these results, we develop an exact non-perturbative method
known as the stochastic Schr\""{o}dinger equation, mimicking the Ohmic bath via
a stochastic magnetic field combined with the Lindblad quantum master equation
due to dephasing, which allows us to numerically compute the dynamics.
Furthermore, we derive weak-coupling analytic results utilizing the well-known
non-interacting blip approximation. Our findings are relevant to quantum
simulation of the spin-boson model in the regime of strong coupling in trapped
ions and circuit QED architectures among others.",2305.00110v1
2001-01-06,Electron and Nuclear Spin Dynamics in Antiferromagnetic Molecular Rings,"We study theoretically the spin dynamics of the ferric wheel, an
antiferromagnetic molecular ring. For a single nuclear or impurity spin coupled
to one of the electron spins of the ring, we calculate nuclear and electronic
spin correlation functions and show that nuclear magnetic resonance (NMR) and
electron spin resonance (ESR) techniques can be used to detect coherent
tunneling of the Neel vector in these rings. The location of the NMR/ESR
resonances gives the tunnel splitting and its linewidth an upper bound on the
decoherence rate of the electron spin dynamics. We illustrate the experimental
feasibility of our proposal with estimates for Fe_10 molecules.",0101073v2
2001-01-24,Effects of dipolar field in the spin dynamics of a Fermi liquid,"We study spin dynamics of a normal Fermi liquid taking into account the
demagnetizing field produced by the spin system itself. Linear solutions of the
spin dynamics equations in the form of standing spin waves in a finite volume
of liquid are found. At almost all known experimental conditions the influence
of demagnetizing field can be satisfactorily described by the first order of
perturbation theory. We carried out perturbational calculations for two
geometries of experimental cell -- spherical and finite-cylindrical. We
performed also exact numerical simulations of the spin wave spectra in a
spherical cell at an arbitrary strength of the demagnetizing field.
  The obtained results are applied in particular to conditions of recent
experiment (G.Vermeulen and A.Roni, Phys. Rev. Lett. 86, 248 (2001)) related to
the problem of zero temperature transverse relaxation in a polarized Fermi
liquid. We found that not taking into account demagnetizing field leads to
negligible errors in the measured relaxation time, thus supporting the
conclusion of the absence of zero temperature spin wave damping.",0101368v3
2001-07-13,Probing exotic spin correlations by Muon Spin depolarization measurements with applications to spin glass dynamics,"We develop a new method to probe the local spin dynamic autocorrelation
function, using magnetic field dependent muon depolarization measurements. We
apply this method to muSR experiments in the dilute Heisenberg spin glass
AgMn(p at. %) at T>T_g where the correlations of the Mn local magnetic moment
are strongly non-exponential. Our results clearly indicate that the dynamics of
this spin glass cannot be described by a distribution of correlation times.
Therefore, we analyze the data assuming a local spin correlation function which
is the product of a power law times a cutoff function. The concentration and
temperature dependence of the parameters of this function are determined. Our
major conclusion is that in the temperature region close to Tg the correlation
function is dominated by an algebraic relaxation term.",0107301v1
2002-08-06,Spin pumping and magnetization dynamics in metallic multilayers,"We study the magnetization dynamics in thin ferromagnetic films and small
ferromagnetic particles in contact with paramagnetic conductors. A moving
magnetization vector causes \textquotedblleft pumping\textquotedblright of
spins into adjacent nonmagnetic layers. This spin transfer affects the
magnetization dynamics similar to the Landau-Lifshitz-Gilbert phenomenology.
The additional Gilbert damping is significant for small ferromagnets, when the
nonmagnetic layers efficiently relax the injected spins, but the effect is
reduced when a spin accumulation build-up in the normal metal opposes the spin
pumping. The damping enhancement is governed by (and, in turn, can be used to
measure) the mixing conductance or spin-torque parameter of the
ferromagnet--normal-metal interface. Our theoretical findings are confirmed by
agreement with recent experiments in a variety of multilayer systems.",0208091v2
2002-11-26,Spin dynamics of stripes,"The spin dynamics of stripes in high-temperature superconductors and related
compounds is studied in the framework of a spin-wave theory for a simple
spin-only model. The magnon dispersion relation and the magnetic structure
factor are calculated for diagonal and vertical stripes. Acoustical as well as
optical bands are included in the analysis. The incommensurability and the
$\pi$ resonance appear as complementary features of the band structure at
different energy scales. The dependence of spin-wave velocities and resonance
frequencies on the stripe spacing and coupling is calculated. At low doping,
the resonance frequency is found to scale roughly inversely proportional to the
stripe spacing. The favorable comparison of the results with experimental data
suggests that the spin-only model provides a suitable and simple basis for
calculating and understanding the spin dynamics of stripes.",0211593v1
2003-04-02,A gauge invariant dressed holon and spinon description of the normal-state of underdoped cuprates,"A partial charge-spin separation fermion-spin theory is developed to study
the normal-state properties of the underdoped cuprates. In this approach, the
physical electron is decoupled as a gauge invariant dressed holon and spinon,
with the dressed holon behaving like a spinful fermion, and represents the
charge degree of freedom together with the phase part of the spin degree of
freedom, while the dressed spinon is a hard-core boson, and representing the
amplitude part of the spin degree of freedom. The electron local constraint for
single occupancy is satisfied. Within this approach, the charge and spin
dynamics of the underdoped cuprates are studied based on the t-t'-J model. It
is shown that the charge dynamics is mainly governed by the scattering from the
dressed holons due to the dressed spinon fluctuation, while the scattering from
the dressed spinons due to the dressed holon fluctuation dominates the spin
dynamics.",0304042v4
2003-06-30,Novel Spin Dynamics in a Josephson Junction,"We address the dynamics of a single spin embedded in the tunneling barrier
between two superconductors. As a consequence of pair correlations in the
superconducting state, the spin displays a rich and unusual dynamics. To
properly describe the time evolution of the spin we find the generalized
Wess-Zumino-Witten-Novikov term in the effective action for the spin on the
Keldysh contour. The superconducting correlations lead to an effective spin
action which is non-local in time leading to unconventional precessions. Our
predictions might be directly tested for macroscopic spin clusters.",0306710v4
2003-11-07,Electron spin dynamics in quantum dots and related nanostructures due to hyperfine interaction with nuclei,"We review and summarize recent theoretical and experimental work on electron
spin dynamics in quantum dots and related nanostructures due to hyperfine
interaction with surrounding nuclear spins. This topic is of particular
interest with respect to several proposals for quantum information processing
in solid state systems. Specifically, we investigate the hyperfine interaction
of an electron spin confined in a quantum dot in an s-type conduction band with
the nuclear spins in the dot. This interaction is proportional to the square
modulus of the electron wave function at the location of each nucleus leading
to an inhomogeneous coupling, i.e. nuclei in different locations are coupled
with different strength. In the case of an initially fully polarized nuclear
spin system an exact analytical solution for the spin dynamics can be found.
For not completely polarized nuclei, approximation-free results can only be
obtained numerically in sufficiently small systems. We compare these exact
results with findings from several approximation strategies.",0311159v1
2003-12-12,Aging Dynamics of the Heisenberg Spin Glass,"We numerically study the non-equilibrium dynamics of the three dimensional
Heisenberg Edwards-Anderson spin glass following a sudden quench to its low
temperature phase. The subsequent aging behavior of the system is analyzed in
detail, and the scaling behavior of various space-time correlation functions is
investigated for both spin and chiral degrees of freedom. We carefully compare
our results with those obtained from simulations of the more studied Ising
version of the model, and with experiments on real spin glasses in which the
spins have vectorial character. Finally, the present dynamical study offers new
perspectives into the possibility of spin-chirality decoupling at low
temperature in vectorial spin glasses.",0312327v1
2005-01-28,Spin waves in paramagnetic BCC iron: spin dynamics simulations,"Large scale computer simulations are used to elucidate a longstanding
controversy regarding the existence, or otherwise, of spin waves in
paramagnetic BCC iron. Spin dynamics simulations of the dynamic structure
factor of a Heisenberg model of Fe with first principles interactions reveal
that well defined peaks persist far above Curie temperature T_c. At large wave
vectors these peaks can be ascribed to propagating spin waves, at small wave
vectors the peaks correspond to over-damped spin waves. Paradoxically, spin
wave excitations exist despite only limited magnetic short-range order at and
above T_c.",0501713v1
2005-02-04,Universal Scaling of Hyperfine-Induced Electron Spin Echo Decay,"The decoherence of a localized electron spin in a lattice of nuclear spins is
an important problem for potential solid-state implementations of a quantum
computer. We demonstrate that even at high fields, virtual electron spin-flip
processes due solely to the hyperfine interaction can lead to complex nuclear
spin dynamics. These dynamics, in turn, can lead to single electron spin phase
fluctuation and decoherence. We show here that remarkably, a spin echo pulse
sequence can almost completely reverse these nuclear dynamics except for a
small visibility loss, thereby suppressing contribution of the hyperfine
interaction to T_2 processes. For small systems, we present numerical evidence
which demonstrates a universal scaling of the magnitude of visibility loss that
depends only on the inhomogeneous line width of the system and the magnetic
field.",0502143v2
2005-12-29,Current-induced magnetization dynamics in disordered itinerant ferromagnets,"Current-driven magnetization dynamics in ferromagnetic metals are studied in
a self-consistent adiabatic local-density approximation in the presence of
spin-conserving and spin-dephasing impurity scattering. Based on a quantum
kinetic equation, we derive Gilbert damping and spin-transfer torques entering
the Landau-Lifshitz equation to linear order in frequency and wave vector.
Gilbert damping and a current-driven dissipative torque scale identically and
compete, with the result that a steady current-driven domain-wall motion is
insensitive to spin dephasing in the limit of weak ferromagnetism. A uniform
magnetization is found to be much more stable against spin torques in the
itinerant than in the \textit{s}-\textit{d} model for ferromagnetism. A dynamic
spin-transfer torque reminiscent of the spin pumping in multilayers is
identified and shown to govern the current-induced domain-wall distortion.",0512715v4
2006-09-18,Critical spin liquid at 1/3 magnetization in a spin-1/2 triangular antiferromagnet,"Although magnetically ordered at low temperatures, the spin-1/2 triangular
antiferromagnet Cs_2CuCl_4 exhibits remarkable spin dynamics that strongly
suggest proximity to a spin liquid phase. Here we address the question of
whether a proximate spin liquid may also occur in an applied magnetic field,
leaving a similar imprint on the dynamical spin correlations of this material.
Specifically, we explore a spatially anisotropic Heisenberg spin-1/2 triangular
antiferromagnet at 1/3 magnetization from a dual vortex perspective, and indeed
find a new ``critical'' spin liquid phase described by QED3 with an emergent
SU(6) symmetry. A number of nontrivial predictions are given for the dynamical
spin structure factor in this ``algebraic vortex liquid'' phase, which can be
tested experimentally via inelastic neutron scattering. We also discuss how the
well-studied ``up-up-down'' magnetization plateaus can be captured within our
approach, and further predict the existence of a stable gapless solid phase in
a weakly ordered up-up-down state. Finally, we predict several anomalous
``roton'' minima in the excitation spectrum in the regime of lattice anisotropy
where the canted Neel state appears.",0609439v2
2006-09-26,Spin Dynamics in a Tunnel Junction between Ferromagnets,"The dynamics of a single spin embedded in the tunnel junction (quantum point
contact) between ferromagnets is addressed. Using the Keldysh technique, we
derive a quantum Langevin equation. As a consequence of the spin-polarization
in the leads, the spin displays a rich and unusual dynamics. Parallel
configured and equally strong magnetic moments in the leads yield an ordinary
spin precession with a Larmor frequency given by the effective magnetic field.
Unequal and/or non-parallel configured magnetization, however, causes nutation
of the spin in addition to the precession. Our predictions may be directly
tested for macroscopic spin clusters.",0609673v3
2002-02-01,Spin Solitons and Quantum Control of Spin Chain Dynamics,"Experiments in coherent spectroscopy correspond to control of quantum
mechanical ensembles guiding them from initial to final target states by
unitary transformations. The control inputs (pulse sequences) that accomplish
these unitary transformations should take as little time as possible so as to
minimize the effects of relaxation and to optimize the sensitivity of the
experiments. Here, we present a radically different and generally applicable
approach to efficient control of dynamics in spin chains of arbitrary length.
The approach relies on the creation of localized spin waves, ``spin solitons'',
and efficient propagation of these soliton states through the spin chain. The
methods presented are expected to find immediate applications in control of
spin dynamics in coherent spectroscopy and quantum information processing.",0202013v2
2007-05-21,Depth dependent spin dynamics of canonical spin glass films: A low-energy muon spin rotation study,"We have performed depth dependent muon spin rotation/relaxation studies of
the dynamics of single layer films of {\it Au}Fe and {\it Cu}Mn spin glasses as
a function of thickness and of its behavior as a function of distance from the
vacuum interface (5-70 nm). A significant reduction in the muon spin relaxation
rate as a function of temperature with respect to the bulk material is observed
when the muons are stopped near (5-10 nm) the surface of the sample. A similar
reduction is observed for the whole sample if the thickness is reduced to e.g.
20 nm and less. This reflects an increased impurity spin dynamics (incomplete
freezing) close to the surface although the freezing temperature is only
modestly affected by the dimensional reduction.",0705.2986v2
2007-07-12,Stimulated Raman spin coherence and spin-flip induced hole burning in charged GaAs quantum dots,"High-resolution spectral hole burning (SHB) in coherent nondegenerate
differential transmission spectroscopy discloses spin-trion dynamics in an
ensemble of negatively charged quantum dots. In the Voigt geometry, stimulated
Raman spin coherence gives rise to Stokes and anti-Stokes sidebands on top of
the trion spectral hole. The prominent feature of an extremely narrow spike at
zero detuning arises from spin population pulsation dynamics. These SHB
features confirm coherent electron spin dynamics in charged dots, and the
linewidths reveal spin spectral diffusion processes.",0707.1726v2
2008-02-26,Dynamical Structure Factor and Spin-Density Separation for a Weakly-Interacting Two-Component Bose Gas,"We show that spin-density separation in a Bose gas is not restricted to 1D
but also occurs in higher dimension. The ratio ($\alpha$) of the intra-species
atom-atom interaction strength to the inter-species interaction strength,
strongly influences the dynamics of spin-density separation and the elementary
excitations. The density wave is phonon-like for all values of $\alpha$. For
$\alpha<1$, spin wave is also phonon-like. The spin waves have a quadratic
dispersion in the $\alpha=1$ coupling regime, while in the phase separated
regime ($\alpha>1$) the spin waves are found to be damped. The dynamical
structure factor (DSF) reveals two distinct peaks corresponding to the density
and spin waves for $\alpha \le 1$. For $\alpha > 1$ there is only one DSF peak
corresponding to the density wave.",0802.3818v5
2008-05-14,Persistent Spin Dynamics in the $S=1/2$ V$_{15}$ Molecular Nano-Magnet,"We present muon spin lattice relaxation measurements in the V15 spin 1/2
molecular nano-magnet. We find that the relaxation rate in low magnetic fields
(<5 kG) is temperature independent below ~10 K, implying that the molecular
spin is dynamically fluctuating down to 12 mK. These measurements show that the
fluctuation time increases as the temperature is decreased and saturates at a
value of ~6 nsec at low temperatures. The fluctuations are attributed to V15
molecular spin dynamics perpendicular to the applied magnetic field direction,
induced by coupling between the molecular spin and nuclear spin bath in the
system.",0805.2164v1
2009-01-15,Spin Rotation Technique for Non-Collinear Magnetic Systems: Application to the Generalized Villain Model,"This work develops a new generalized technique for determining the static and
dynamic properties of any non-collinear magnetic system. By rotating the spin
operators into the local spin reference frame, we evaluate the zeroth, first,
and second order terms in a Holstein-Primakoff expansion, and through a Green's
functions approach, we determine the structure factor intensities for the
spin-wave frequencies. To demonstrate this technique, we examine the spin-wave
dynamics of the generalized Villain model with a varying interchain
interaction. The new interchain coupling expands the overall phase diagram with
the realization of two non-equivalent canted spin configurations. The
rotational Holstein-Primakoff expansion provides both analytical and numerical
results for the spin dynamics and intensities of these phases.",0901.2332v2
2009-04-24,Nonlinear dynamics of spin and charge in spin-Calogero model,"The fully nonlinear dynamics of spin and charge in spin-Calogero model is
studied. The latter is an integrable one-dimensional model of quantum spin-1/2
particles interacting through inverse-square interaction and exchange.
Classical hydrodynamic equations of motion are written for this model in the
regime where gradient corrections to the exact hydrodynamic formulation of the
theory may be neglected. In this approximation variables separate in terms of
dressed Fermi momenta of the model. Hydrodynamic equations reduce to a set of
decoupled Riemann-Hopf (or inviscid Burgers') equations for the dressed Fermi
momenta. We study the dynamics of some non-equilibrium spin-charge
configurations for times smaller than the time-scale of the gradient
catastrophe. We find an interesting interplay between spin and charge degrees
of freedom. In the limit of large coupling constant the hydrodynamics reduces
to the spin hydrodynamics of the Haldane-Shastry model.",0904.3762v2
2009-09-28,Is there a dynamical cause of the spin-statistics connection?,"Extant proofs of the spin-statistics connection (SSC) are kinematical. C S
Unnikrishnan has suggested that a dynamical interaction leading to the SSC
would involve spin and perforce gravity, the only known universal force. For
the scattering of two identical particles, he considers [arXiv: gr-qc/0406043]
the interaction of their spins with the gravito-magnetic field generated by
their scattering motion through cosmic matter-energy. There the direct and
particles-exchanged scattering amplitudes accumulate different quantum phases
which provide the relevant bosonic/fermionic sign between them without applying
the ad hoc SSC rule. Here it is shown that the scattering probabilities given
by the standard implementation of SSC in quantum mechanics are actually not
obtained from the above interaction for most initial spin states of the
scattering particles. Instead, an unrealized peculiar dynamical interaction is
required. Further, a spin-gravito-magnetic interaction as above (with caveats)
would result in a large unmeasured spin-orbit coupling type effect on atomic
energy levels. A comparison with a typical rotation based proof is also
provided.",0909.5159v1
2010-01-05,Spin dynamics in semiconductors,"This article reviews the current status of spin dynamics in semiconductors
which has achieved a lot of progress in the past years due to the fast growing
field of semiconductor spintronics. The primary focus is the theoretical and
experimental developments of spin relaxation and dephasing in both spin
precession in time domain and spin diffusion and transport in spacial domain. A
fully microscopic many-body investigation on spin dynamics based on the kinetic
spin Bloch equation approach is reviewed comprehensively.",1001.0606v3
2010-08-31,Dynamics of the collective modes of an inhomogeneous spin ensemble in a cavity,"We study the excitation dynamics of an inhomogeneously broadened spin
ensemble coupled to a single cavity mode. The collective excitations of the
spin ensemble can be described in terms of generalized spin waves and, in the
absence of the cavity, the free evolution of the spin ensemble can be described
as a drift in the wave number without dispersion. In this article we show that
the dynamics in the presence of coupling to the cavity mode can be described
solely by a modified time evolution of the wave numbers. In particular, we show
that collective excitations with a well- defined wave number pass without
dispersion from negative to positive valued wave numbers without populating the
zero wave number spin wave mode. The results are relevant for multi-mode
collective quantum memories where qubits are encoded in different spin waves.",1008.5197v2
2010-09-22,Optimal control of magnetization dynamics in ferromagnetic heterostructures by spin--polarized currents,"We study the switching-process of the magnetization in a
ferromagnetic-normal-metal multilayer system by a spin polarized electrical
current via the spin transfer torque. We use a spin drift-diffusion equation
(SDDE) and the Landau-Lifshitz-Gilbert equation (LLGE) to capture the coupled
dynamics of the spin density and the magnetization dynamic of the
heterostructure. Deriving a fully analytic solution of the stationary SDDE we
obtain an accurate, robust, and fast self-consistent model for the
spin-distribution and spin transfer torque inside general ferromagnetic/normal
metal heterostructures. Using optimal control theory we explore the switching
and back-switching process of the analyzer magnetization in a seven-layer
system. Starting from a Gaussian, we identify a unified current pulse profile
which accomplishes both processes within a specified switching time.",1009.4296v2
2011-02-15,Spin dynamics in the strong spin-orbit coupling regime,"We study the spin dynamics in a high-mobility two dimensional electron gas
(2DEG) with generic spin-orbit interactions (SOIs). We derive a set of spin
dynamic equations which capture the purely exponential to the damped
oscillatory spin evolution modes observed in different regimes of SOI strength.
Hence we provide a full treatment of the D'yakonov-Perel's mechanism by using
the microscopic linear response theory from the weak to the strong SOI limit.
We show that the damped oscillatory modes appear when the electron scattering
time is larger than half of the spin precession time due to the SOI, in
agreement with recent observations. We propose a new way to measure the
scattering time and the relative strength of Rashba and linear Dresselhaus SOIs
based on these modes and optical grating experiments. We discuss the physical
interpretation of each of these modes in the context of Rabi oscillation.",1102.3170v1
2012-02-28,Spin-precession-assisted supercurrent in a superconducting quantum point contact coupled to a single-molecule magnet,"The supercurrent of a quantum point contact coupled to a nanomagnet strongly
depends on the dynamics of the nanomagnet's spin. We employ a fully microscopic
model to calculate the transport properties of a junction coupled to a spin
whose dynamics is modeled as Larmor precession brought about by an external
magnetic field and find that the dynamics affects the charge and spin currents
by inducing transitions between the continuum states below the superconducting
gap edge and the Andreev levels. This redistribution of the quasiparticles
leads to a non-equilibrium population of the Andreev levels and an enhancement
of the supercurrent which is visible as a modified current-phase relation as
well as a non-monotonous critical current as function of temperature. The
non-monotonous behavior is accompanied by a corresponding change in
spin-transfer torques acting on the precessing spin and leads to the
possibility of using temperature as a means to tune the back-action on the
spin.",1202.6197v1
2012-03-23,Spin dynamics in a strongly driven system: very slow Rabi oscillations,"We consider joint effects of tunneling and spin-orbit coupling on driven by
electric field spin dynamics in a double quantum dot with a multi-level
resonance scenario. We demonstrate that tunneling plays the crucial role in the
formation of the Rabi-like spin-flip transitions. In contrast to the linear
behavior for weak electric fields, the spin flip rate becomes much smaller than
expected for the two-level model and shows oscillating dependence on the
driving field amplitude in stronger fields. In addition, the full spin flip is
very difficult to achieve in a multi-level resonant system. These two effects
have a similarity with the Zeno effect of slowing down the dynamics of an
observable by its measurement. As a result, spin manipulation by electric field
becomes much less efficient than expected.",1203.5287v1
2012-07-09,Non-Markovian dynamics in a spin star system: The failure of thermalization,"In most cases, a small system weakly interacting with a thermal bath will
finally reach the thermal state with the temperature of the bath. We show that
this intuitive picture is not always true by a spin star model where non-Markov
effect predominates in the whole dynamical process. The spin star system
consists a central spin homogeneously interacting with an ensemble of identical
noninteracting spins. We find that the correlation time of the bath is
infinite, which implies that the bath has a perfect memory, and that the
dynamical evolution of the central spin must be non- Markovian. A direct
consequence is that the final state of the central spin is not the thermal
state equilibrium with the bath, but a steady state which depends on its
initial state.",1207.2036v4
2013-02-15,Spin dynamics of a Mn atom in a semiconductor quantum dot under resonant optical excitation,"We analyze the spin dynamics of an individual magnetic atom (Mn) inserted in
a II-VI semiconductor quantum dot under resonant optical excitation. In
addition to standard optical pumping expected for a resonant excitation, we
show that for particular conditions of laser detuning and excitation intensity,
the spin population can be trapped in the state which is resonantly excited.
This effect is modeled considering the coherent spin dynamics of the coupled
electronic and nuclear spin of the Mn atom optically dressed by a resonant
laser field. This spin population trapping mechanism is controlled by the
combined effect of the coupling with the laser field and the coherent
interaction between the different Mn spin states induced by an anisotropy of
the strain in the plane of the quantum dot.",1302.3769v1
2014-01-29,Arbitrary spin in a spin bath: Exact dynamics and approximation techniques,"A model of an arbitrary spin coupled to a bath of spins 1/2 in a star
configuration is considered. The exact reduced dynamics of the central spin is
found for the case of non-correlated initial conditions of the system and the
bath. The exact solution is used to test two approximation techniques, namely,
the Nakajima-Zwanzig projection operator technique and the time-convolutionless
projection operator technique corresponding to the second order of the coupling
constant. Two types of projection operators are used for deriving the master
equations and the results are compared with the exact solution for a central
spin equal to one. It is shown that the approximate master equations reproduce
the exact dynamics on time-scales $1/(A\sqrt{N})$, where A is the coupling
constant and N is the number of spins in the bath.",1401.7575v2
2014-08-11,Hole spin dynamics and hole $g$ factor anisotropy in coupled quantum well systems,"Due to its p-like character, the valence band in GaAs-based heterostructures
offers rich and complex spin-dependent phenomena. One manifestation is the
large anisotropy of Zeeman spin splitting. Using undoped, coupled quantum wells
(QWs), we examine this anisotropy by comparing the hole spin dynamics for high-
and low-symmetry crystallographic orientations of the QWs. We directly measure
the hole $g$ factor via time-resolved Kerr rotation, and for the low-symmetry
crystallographic orientations (110) and (113a), we observe a large in-plane
anisotropy of the hole $g$ factor, in good agreement with our theoretical
calculations. Using resonant spin amplification, we also observe an anisotropy
of the hole spin dephasing in the (110)-grown structure, indicating that
crystal symmetry may be used to control hole spin dynamics.",1408.2360v1
2014-10-02,Non-Markovian dynamics of a single-mode cavity strongly coupled to an inhomogeneously broadened spin ensemble,"We study the dynamics of a spin ensemble strongly coupled to a single-mode
resonator driven by external pulses. When the mean frequency of the spin
ensemble is in resonance with the cavity mode, damped Rabi oscillations are
found between the spin ensemble and the cavity mode which we describe very
accurately, including the dephasing effect of the inhomogeneous spin
broadening. We demonstrate that a precise knowledge of this broadening is
crucial both for a qualitative and a quantitative understanding of the temporal
spin-cavity dynamics. On this basis we show that coherent oscillations between
the spin ensemble and the cavity can be enhanced by a few orders of magnitude,
when driving the system with pulses that match special resonance conditions.
Our theoretical approach is tested successfully with an experiment based on an
ensemble of negatively charged nitrogen-vacancy (NV) centers in diamond
strongly coupled to a superconducting coplanar single-mode waveguide resonator.",1410.0728v1
2014-10-03,Neutron Scattering Studies of the Ferroelectric Distortion and Spin Dynamics in the Type-1 Multiferroic Perovskite Sr0.56Ba0.44MnO3,"The magnetic order, spin dynamics, and crystal structure of the multiferroic
Sr0.56Ba0.44MnO3 have been investigated using neutron and x-ray scattering.
Ferroelectricity develops at TC=305 K with a polarization of 4.2 microC/cm2
associated with the displacements of the Mn ions, while the Mn4+ spins order
below TN = 200 K into a simple G-type commensurate magnetic structure. Below TN
the ferroelectric order decreases dramatically demonstrating that the two order
parameters are strongly coupled. The ground state spin dynamics are
characterized by a spin gap of 4.6(5) meV and the magnon density of states
peaking at 43 meV. Detailed spin wave simulations with a gap and isotropic
exchange of J=4.8(2) meV describe the excitation spectrum well. Above TN strong
spin correlations coexist with robust ferroelectric order.",1410.0922v1
2015-02-13,Coherent heteronuclear spin dynamics in an ultracold spin-1 mixture,"We report the observation of coherent heteronuclear spin dynamics driven by
inter-species spin-spin interaction in an ultracold spinor mixture, which
manifests as periodical and well correlated spin oscillations between two
atomic species. In particular, we investigate the magnetic field dependence of
the oscillations and find a resonance behavior which depends on {\em both} the
linear and quadratic Zeeman effects and the spin-dependent interaction. We also
demonstrate a unique knob for controlling the spin dynamics in the spinor
mixture with species-dependent vector light shifts. Our finds are in agreement
with theoretical simulations without any fitting parameters.",1502.03867v1
2015-04-03,Single-shot measurement of transient nuclear magnetization with spin-noise spectroscopy in n-GaAs microcavities,"We exploit spin noise spectroscopy (SNS) to directly observe build-up of
dynamic nuclear polarization and relaxation of a perturbed nuclear spin-system
to its equilibrium state in a single-shot experiment. The SNS experiments were
performed on a layer of bulk $n$-type GaAs embedded into a high-finesse
microcavity with negative detuning. The dynamic nuclear spin polarization is
observed as a shift of the peak in the electron spin noise spectrum due to the
build-up of the Overhauser field acting on the electron spin. The relaxation
dynamics of nuclear spin system was revealed in the time-resolved SNS
experiments where the exponential decay of the Overhauser field with
characteristic timescale of hundreds of seconds was detected. We show that
elliptically polarized laser beam tuned in resonance with the cavity mode,
whose energy corresponds to nominal transparency of the semiconductor, can
nevertheless produce a sizable nuclear polarization.",1504.00799v1
2015-06-12,Control of spin dynamics in a two-dimensional electron gas by electromagnetic dressing,"We solved the Schr\""odinger problem for a two-dimensional electron gas (2DEG)
with the Rashba spin-orbit interaction in the presence of a strong
high-frequency electromagnetic field (dressing field). The found eigenfunctions
and eigenenergies of the problem are used to describe the spin dynamics of the
dressed 2DEG within the formalism of the density matrix response function.
Solving the equations of spin dynamics, we show that the dressing field can
switch the spin relaxation in the 2DEG between the cases corresponding to the
known Elliott-Yafet and D'yakonov-Perel' regimes. As a result, the spin
properties of the 2DEG can be tuned by a high-frequency electromagnetic field.
The present effect opens an unexplored way for controlling the spin with light
and, therefore, forms the physical prerequisites for creating light-tuned
spintronics devices.",1506.03992v3
2015-08-26,Multistability and spin diffusion enhanced lifetimes in dynamic nuclear polarization in a double quantum dot,"The control of nuclear spins in quantum dots is essential to explore their
many-body dynamics and exploit their prospects for quantum information
processing. We present a unique combination of dynamic nuclear spin
polarization and electric-dipole-induced spin resonance in an electrostatically
defined double quantum dot (DQD) exposed to the strongly inhomogeneous field of
two on-chip nanomagnets. Our experiments provide direct and unrivaled access to
the nuclear spin polarization distribution and allow us to establish and
characterize multiple fixed points. Further, we demonstrate polarization of the
DQD environment by nuclear spin diffusion which significantly stabilizes the
nuclear spins inside the DQD.",1508.06522v2
2015-09-15,Relaxation and coherent oscillations in the spin dynamics of II-VI diluted magnetic quantum wells,"We study theoretically the ultrafast spin dynamics of II-VI diluted magnetic
quantum wells in the presence of spin-orbit interaction. We extend a recent
study where it was shown that the spin-orbit interaction and the exchange sd
coupling in bulk and quantum wells can compete resulting in qualitatively new
dynamics when they act simultaneously. We concentrate on
Hg$_{1-x-y}$Mn$_x$Cd$_y$Te quantum wells, which have a highly tunable Rashba
spin-orbit coupling. Our calculations use a recently developed formalism which
incorporates electronic correlations originating from the exchange
$sd$-coupling. We find that the dependence of electronic spin oscillations on
the excess energy changes qualitatively depending on whether or not the
spin-orbit interaction dominates or is of comparable strength with the sd
interaction.",1509.04588v1
2015-09-28,Perturbation on Hyperfine-enhanced $^{141}$Pr Nuclear Spin Dynamics Associated with Antiferroquadrupolar Order in PrV$_2$Al$_{20}$,"The nature of multipolar order and hyperfine-enhanced (HE) $^{141}$Pr nuclear
spin dynamics in PrV$_2$Al$_{20}$ was investigated using the muon spin
relaxation technique. No explicit sign of time-reversal symmetry breaking was
found below the multipolar order temperature $T_Q\sim 0.6$ K in a zero applied
field as anticipated on the basis of the antiferroquadrupolar (AFQ) order
picture proposed by Sakai and Nakatsuji [J. Phys. Soc. Jpn. 80, 063701 (2011)].
Further evidence of the nonmagnetic ground state was obtained from the
observation of HE $^{141}$Pr nuclear spin fluctuations in the MHz scale. A
marked increase in the muon spin-lattice relaxation rate (1/$T_{\rm 1,\mu}$)
was observed below 1 K with decreasing temperature, which was attributed to the
perturbation on the HE $^{141}$Pr nuclear spin dynamics associated with the
development of AFQ correlations. The longitudinal field dependence of 1/$T_{\rm
  1,\mu}$ revealed that the enhanced $^{141}$Pr nuclear spin accidentally has
an effective gyromagnetic ratio close to that of the muon.",1509.08207v1
2018-04-26,Orbital quantum magnetism in spin dynamics of strongly interacting magnetic lanthanide atoms,"Laser cooled lanthanide atoms are ideal candidates with which to study strong
and unconventional quantum magnetism with exotic phases. Here, we use
state-of-the-art closed-coupling simulations to model quantum magnetism for
pairs of ultracold spin-6 erbium lanthanide atoms placed in a deep optical
lattice. In contrast to the widely used single-channel Hubbard model
description of atoms and molecules in an optical lattice, we focus on the
single-site multi-channel spin evolution due to spin-dependent contact,
anisotropic van der Waals, and dipolar forces. This has allowed us to identify
the leading mechanism, orbital anisotropy, that governs molecular spin dynamics
among erbium atoms. The large magnetic moment and combined orbital angular
momentum of the 4f-shell electrons are responsible for these strong anisotropic
interactions and unconventional quantum magnetism. Multi-channel simulations of
magnetic Cr atoms under similar trapping conditions show that their
spin-evolution is controlled by spin-dependent contact interactions that are
distinct in nature from the orbital anisotropy in Er. The role of an external
magnetic field and the aspect ratio of the lattice site on spin dynamics is
also investigated.",1804.10102v1
2018-11-06,Perspective: (Beyond) spin transport in insulators,"Insulating materials with dynamical spin degrees of freedom have recently
emerged as viable conduits for spin flows. Transport phenomena harbored therein
are, however, turning out to be much richer than initially envisioned. In
particular, the topological properties of the collective order-parameter
textures can give rise to conservation laws that are not based on any specific
symmetries. The emergent continuity relations are thus robust against
structural imperfections and anisotropies, which would be detrimental to the
conventional spin currents (that rely on approximate spin-rotational
symmetries). The underlying fluxes thus supersede the notion of spin flow in
insulators, setting the stage for nonequilibrium phenomena termed topological
hydrodynamics. Here, we outline our current understanding of the essential
ingredients, based on the energetics of the electrically-controlled injection
of topological flows through interfaces, along with a reciprocal signal
generation by the outflow of the conserved quantity. We will focus on two
examples for the latter: winding dynamics in one-dimensional systems, which
supplants spin superfluidity of axially-symmetric easy-plane magnets, and
skyrmion dynamics in two-dimensional Heisenberg-type magnets. These examples
will illustrate the essential common aspects of topological flows and hint on
generic strategies for their generation and detection in spintronic systems.
Generalizations to other dimensions and types of order-parameter spaces will
also be briefly discussed.",1811.02621v1
2013-08-15,Detection of the microwave spin pumping using the inverse spin Hall effect,"We report electrical detection of the dynamical part of the spin pumping
current emitted during ferromagnetic resonance (FMR) using the inverse Spin
Hall Effect (ISHE). The experiment is performed on a YIG$|$Pt bilayer. The
choice of YIG, a magnetic insulator, ensures that no charge current flows
between the two layers and only pure spin current produced by the magnetization
dynamics are transferred into the adjacent strong spin-orbit Pt layer via spin
pumping. To avoid measuring the parasitic eddy currents induced at the
frequency of the microwave source, a resonance at half the frequency is induced
using parametric excitation in the parallel geometry. Triggering this nonlinear
effect allows to directly detect on a spectrum analyzer the microwave component
of the ISHE voltage. Signals as large as 30 $\mu$V are measured for precession
angles of a couple of degrees. This direct detection provides a novel efficient
means to study magnetization dynamics on a very wide frequency range with great
sensitivity.",1308.3433v2
2017-04-03,Simulating spin-boson models with trapped ions,"We propose a method to simulate the dynamics of spin-boson models with small
crystals of trapped ions where the electronic degree of freedom of one ion is
used to encode the spin while the collective vibrational degrees of freedom are
employed to form an effective harmonic environment. The key idea of our
approach is that a single damped mode can be used to provide a harmonic
environment with Lorentzian spectral density. More complex spectral functions
can be tailored by combining several individually damped modes. We propose to
work with mixed-species crystals such that one species serves to encode the
spin while the other species is used to cool the vibrational degrees of freedom
to engineer the environment. The strength of the dissipation on the spin can be
controlled by tuning the coupling between spin and vibrational degrees of
freedom. In this way the dynamics of spin-boson models with macroscopic and
non-Markovian environments can be simulated using only a few ions. We
illustrate the approach by simulating an experiment with realistic parameters
and show by computing quantitative measures that the dynamics is genuinely
non-Markovian.",1704.00629v1
2013-09-22,Low temperature MQ NMR dynamics in dipolar ordered state,"We investigate analytically and numerically the Multiple Quantum (MQ) NMR
dynamics in dipolar ordered spin systems of nuclear spins 1/2 at a low
temperatures. We suggest two different methods of MQ NMR. One of them is based
on the measurement of the dipolar energy. The other method uses an additional
resonance ({\pi}/4)_{y}-pulse after the preparation period of the standard MQ
NMR experiment in solids and allows one to measure the Zeeman energy. The both
considered methods are sensitive to the contribution of remote spins in the
interaction and to the spin system structure. The QS method is sensitive to the
spin number in the molecule while the PS method gives very similar time
dependencies of the intensities of MQ coherences for different spin numbers. It
is shown that the use of the dipolar ordered initial state has the advantage of
exciting the highest order MQ coherences in clusters of 4m identical spins,
where m=1,2,3..., that is impossible to do with the standard MQ method. MQ NMR
methods based on the dipolar ordered initial states at low temperatures
complement the standard NMR spectroscopy for better studying structures and
dynamic processes in solids.",1309.5591v1
2016-12-15,On the equal-mass limit of precessing black-hole binaries,"We analyze the inspiral dynamics of equal-mass precessing black-hole binaries
using multi-timescale techniques. The orbit-averaged post-Newtonian
evolutionary equations admit two constants of motion in the equal-mass limit,
namely the magnitude of the total spin $S$ and the effective spin $\xi$. This
feature makes the entire dynamics qualitatively different compared to the
generic unequal-mass case, where only $\xi$ is constant while the variable $S$
parametrizes the precession dynamics. For fixed individual masses and spin
magnitudes, an equal-mass black-hole inspiral is uniquely characterized by the
two parameters $(S,\xi)$: these two numbers completely determine the entire
evolution under the effect of radiation reaction. In particular, for equal-mass
binaries we find that (i) the black-hole binary spin morphology is constant
throughout the inspiral, and that (ii) the precessional motion of the two
black-hole spins about the total spin takes place on a longer timescale than
the precession of the total spin and the orbital plane about the total angular
momentum.",1612.05263v2
2017-07-07,Nonequilibrium-induced enhancement of dynamical quantum coherence and entanglement of spin arrays,"The random magnetic field produced by nuclear spins has long been viewed as
the dominating source of decoherence in the quantum-dot based spins. Here we
obtain in both exact and analytical manner the dynamics of spin qubits coupled
to nuclear spin environments via the hyperfine interaction, going beyond the
weak system-bath interaction and Markovian approximation. We predict that the
detailed-balance breaking produced by chemical potential gradient in nuclear
baths leads to the rapid oscillations of populations, quantum coherence and
entanglement, which are absent in the conventional case (i.e., Overhauser
noise). This is attributed to the nonequilibrium feature of the system as shown
in the relation between the oscillation period and the chemical potential
imbalance. Our results reveal the essentiality of nonequilibriumness with
detailed-balance breaking for enhancing the dynamical coherence and
entanglement of spin qubits. Moreover, our exact solution explicitly
demonstrates that the non-Markovian bath comprised by nuclear spins can
preserve the collective quantum state, due to the recovery of coherence.
Finally, we propose an experiment using ultracold trapped ions to observe these
nonequilibrium and memory effects.",1707.02001v1
2017-10-02,Multi-scale modelling of current-induced switching in magnetic tunnel junctions using ab initio spin transfer torques,"There exists a significant challenge in developing efficient magnetic tunnel
junctions with low write currents for non-volatile memory devices. With the aim
of analysing potential materials for efficient current-operated magnetic
junctions we have developed a multi-scale methodology combining the ab initio
calculations of spin-transfer torque with large-scale time-dependent
simulations using atomistic spin dynamics. In this work we introduce our
multi-scale approach including a discussion on a number of possible mapping
schemes the ab initio spin torques into the spin dynamics. We demonstrate this
methodology on a prototype Co/MgO/Co/Cu tunnel junction showing that the spin
torques are primarily acting at the interface between the Co free layer and
MgO. Using spin dynamics we then calculate the reversal switching times for the
free layer and the critical voltages and currents required for such switching.
Our work provides an efficient, accurate and versatile framework for designing
novel current-operated magnetic devices, where all the materials details are
take into account.",1710.00574v1
2017-12-01,Coherent spin dynamics of ytterbium ions in yttrium orthosilicate,"We investigate the electron and nuclear spin coherence properties of
ytterbium ($\mathrm{Yb}^{3+}$) ions with non-zero nuclear spin, within an
yttrium orthosilicate (Y$_2$SiO$_5$) crystal, with a view to their potential
application in quantum memories or repeaters. We find electron spin-lattice
relaxation times are maximised at low magnetic field ($<100$ mT) where
$g~\sim6$, reaching 5 s at 2.5 K, while coherence times are maximised when
addressing ESR transitions at higher fields where $g\sim0.7$ where a Hahn echo
measurement yields $T_2$ up to 73 $\mu$s. Dynamical decoupling (XY16) can be
used to suppress spectral diffusion and extend the coherence lifetime to over
0.5 ms, close to the limit of instantaneous diffusion. Using Davies
electron-nuclear-double-resonance (ENDOR), we performed coherent control of the
$^{173}\mathrm{Yb}^{3+}$ nuclear spin and studied its relaxation dynamics. At
around 4.5 K we measure a nuclear spin $T_1$ and $T_2$ of 4 and 0.35 ms,
respectively, about 4 and 14 times longer than the corresponding times for the
electron spin.",1712.00435v1
2017-12-30,Sensing coherent dynamics of electronic spin clusters in solids,"We present experimental observations and a study of quantum dynamics of
strongly interacting electronic spins, at room temperature in the solid state.
In a diamond substrate, a single nitrogen vacancy (NV) center coherently
interacts with two adjacent S = 1/2 dark electron spins. We quantify
NV-electron and electron-electron couplings via detailed spectroscopy, with
good agreement to a model of strongly interacting spins. The electron-electron
coupling enables an observation of coherent flip-flop dynamics between
electronic spins in the solid state, which occur conditionally on the state of
the NV. Finally, as a demonstration of coherent control, we selectively couple
and transfer polarization between the NV and the pair of electron spins. These
results demonstrate a key step towards full quantum control of electronic spin
registers in room temperature solids.",1801.00198v2
2019-10-11,Coupled density-spin Bose-Einstein condensates dynamics and collapse in systems with quintic nonlinearity,"We investigate the effects of spin-orbit coupling and Zeeman splitting on the
coupled density-spin dynamics and collapse of the Bose-Einstein condensate
driven by the quintic self-attraction in the same- and cross-spin channels. The
characteristic feature of the collapse is the decrease in the width as given by
the participation ratio of the density rather than by the expectation values of
the coordinate. Qualitative arguments and numerical simulations reveal the
existence of a critical spin-orbit coupling strength which either prohibits or
leads to the collapse, and its dependence on other parameters, such as the
condensates norm, spin-dependent nonlinear coupling, and the Zeeman splitting.
The entire nonlinear dynamics critically depend on the initial spin sate.",1910.05023v1
2021-01-15,The dynamics of local magnetic moments induced by itinerant Weyl electrons,"We derive the effective interactions between local magnetic moments which are
mediated by Weyl electrons in magnetic topological semimetals. The resulting
spin dynamics is governed by the induced Heisenberg, Kitaev and
Dzyaloshinskii-Moriya (DM) interactions with extended range and oscillatory
dependence on the distance between the spins. These interactions are realized
in multiple competing channels shaped by the multitude of Weyl nodes in the
electron spectrum. Microscopic spins need to be spatially modulated with a
channel-dependent wavevector in order to take advantage of the interactions.
The DM vector is parallel to the displacement between the two interacting
spins, and requires the presence of Weyl electron Fermi surfaces. We also
derive the Weyl-induced chiral three-spin interaction in the presence of an
external magnetic field. This interaction has an extended range as well, and
acts upon the spatially modulated spins in various channels. Its tendency is to
produce a skyrmion lattice or a chiral spin liquid which exhibits topological
Hall effect. Ultimately, the theory developed here addresses magnetic dynamics
in relativistic metals even when chiral magnetism is microscopically precluded.
We discuss insights into the ordered state of the magnetic Weyl semimetal
NdAlSi.",2101.06274v1
2018-03-29,Diagnosing Fractionalization from the Spin Dynamics of $Z_2$ Spin Liquids on the Kagome Lattice by Quantum Monte Carlo Simulations,"Based on large-scale quantum Monte Carlo simulations, we examine the
dynamical spin structure factor of the Balents-Fisher-Girvin kagome lattice
quantum spin-$1/2$ model, which is known to harbor an extended $Z_2$ quantum
spin liquid phase. We use a correlation-matrix sampling scheme combined with a
stochastic analytic continuation method to resolve the spectral functions of
this anisotropic quantum spin model with a three-site unit-cell. Based on this
approach, we monitor the spin dynamics throughout the phase diagram of this
model, from the XY-ferromagnetic region to the $Z_2$ quantum spin liquid
regime. In the latter phase, we identify a gapped two-spinon continuum in the
transverse scattering channel, which is faithfully modeled by an effective
spinon tight-binding model. Within the longitudinal channel, we identify gapped
vison excitations and exhibit indications for the translational symmetry
fractionalization of the visons via an enhanced spectral periodicity.",1803.10970v2
2019-02-06,Accelerating spin-space sampling by auxiliary spin-dynamics and temperature-dependent spin-cluster expansion,"Atomistic simulations of thermodynamic properties of magnetic materials rely
on an accurate modelling of magnetic interactions and an efficient sampling of
the high-dimensional spin space. Recent years have seen significant progress
with a clear trend from model systems to material specific simulations that are
usually based on electronic-structure methods. Here we develop a Hamiltonian
Monte Carlo framework that makes use of auxiliary spin-dynamics and an
auxiliary effective model, the temperature-dependent spin-cluster expansion, in
order to efficiently sample the spin space. Our method does not require a
specific form of the model and is suitable for simulations based on
electronic-structure methods. We demonstrate fast warm-up and a reasonably
small dynamical critical exponent of our sampler for the classical Heisenberg
model. We further present an application of our method to the magnetic phase
transition in bcc iron using magnetic bond-order potentials.",1902.02116v1
2019-08-15,Natural orbital functional for multiplets,"A natural orbital functional for electronic systems with any value of the
spin is proposed. This energy functional is based on a new reconstruction for
the two-particle reduced density matrix (2RDM) of the multiplet, that is, of
the mixed quantum state that allows all possible spin projections. The mixed
states of maximum spin multiplicity are considered. This approach differs from
the methods routinely used in electronic structure calculations that focus on
the high-spin component or break the spin symmetry. In the ensemble, there are
no interactions between electrons with opposite spins in singly occupied
orbitals, as well as new inter-pair alpha-beta-contributions are proposed in
the 2RDM. The proposed 2RDM fulfills (2,2)-positivity necessary
N-representability conditions and guarantees the conservation of the total
spin. The NOF for multiplets is able to recover the non-dynamic and the
intrapair dynamic electron correlation. The missing dynamic correlation is
recovered by the NOF-MP2 method. Calculation of ionization potentials of the
first-row transition-metal atoms is presented as test case. The values obtained
agree with those reported at the coupled cluster singles and doubles level of
theory with perturbative triples and experimental data.",1908.05501v1
2020-03-10,Dynamics of a two-dimensional quantum spin-orbital liquid: spectroscopic signatures of fermionic magnons,"We provide an exact study of dynamical correlations for the quantum
spin-orbital liquid phases of an SU(2)-symmetric Kitaev honeycomb lattice
model. We show that the spin dynamics in this Kugel-Khomskii type model is
exactly the density-density correlation function of S=1 fermionic magnons,
which could be probed in resonant inelastic x-ray scattering experiments. We
predict the characteristic signatures of spin-orbital fractionalization in
inelastic scattering experiments and compare them to the ones of the
spin-anisotropic Kitaev honeycomb spin liquid. In particular, the resonant
inelastic x-ray scattering response shows a characteristic momentum dependence
directly related to the dispersion of fermionic excitations. The neutron
scattering cross section displays a mixed response of fermionic magnons as well
as spin-orbital excitations. The latter has a bandwidth of broad excitations
and a vison gap that is three times larger than that of the spin-1/2 Kitaev
model.",2003.04835v3
2020-08-20,Anisotropic ultrafast spin/valley dynamics in WTe2 films,"WTe2 Weyl semimetal hosts the natural broken inversion symmetry and strong
spin orbit coupling, making it promising for exotic spin/valley dynamics within
a picosecond timescale. Here, we unveil an anisotropic ultrafast spin/valley
dynamics in centimeter-scale, single-crystalline Td-WTe2 films using a
femtosecond pump-probe technique at room temperature. We observe a transient
(~0.8 ps) intra-valley transition and a subsequent polarization duration (~5
ps) during the whole spin/valley relaxation process. Furthermore, the
relaxation exhibits the remarkable anisotropy of approximately six-fold and
two-fold symmetries due to the intrinsic anisotropy along the crystalline
orientation and the extrinsic matrix element effect, respectively. Our results
offer a prospect for the ultrafast manipulation of spin/valleytronics in
topological quantum materials for dissipationless high-speed spin/valleytronic
devices.",2008.08785v2
2020-10-02,Gravitational spin-orbit and aligned spin$_1$-spin$_2$ couplings through third-subleading post-Newtonian orders,"The study of scattering encounters continues to provide new insights into the
general relativistic two-body problem. The local-in-time conservative dynamics
of an aligned-spin binary, for both unbound and bound orbits, is fully encoded
in the gauge-invariant scattering-angle function, which is most naturally
expressed in a post-Minkowskian (PM) expansion, and which exhibits a remarkably
simple dependence on the masses of the two bodies (in terms of appropriate
geometric variables). This dependence links the PM and small-mass-ratio
approximations, allowing gravitational self-force results to determine new
post-Newtonian (PN) information to all orders in the mass ratio. In this paper,
we exploit this interplay between relativistic scattering and self-force theory
to obtain the third-subleading (4.5PN) spin-orbit dynamics for generic spins,
and the third-subleading (5PN) spin$_1$-spin$_2$ dynamics for aligned spins. We
further implement these novel PN results in an effective-one-body framework,
and demonstrate the improvement in accuracy by comparing against
numerical-relativity simulations.",2010.02018v2
2020-11-01,Long-time relaxation dynamics of a spin coupled to a Chern insulator,"The relaxation of a classical spin, exchange coupled to the local magnetic
moment at an edge site of the one-dimensional spinful Su-Schrieffer-Heeger
model is studied numerically by solving the full set of equations of motion. A
Lindblad coupling of a few sites at the opposite edge to an absorbing bath
ensures that convergence with respect to the system size is achieved with only
a moderate number of core sites. This allows us to numerically exactly study
the long-time limit and to determine the parameter regimes where spin
relaxation takes place. Corresponding dynamical phase diagrams for the
topologically trivial and the nontrivial cases are constructed. The dynamical
phase boundaries, the role of the topological edge state and its internal
Zeeman splitting for the spin-relaxation process, as well as incomplete spin
relaxation on long time scales can be explained within the framework of a
renormalized linear-response approach when explicitly taking retardation
effects and nonequilibrium spin-exchange processes into account.",2011.00581v2
2020-11-09,Spin-wave dynamics and symmetry breaking in an artificial spin ice,"Artificial spin ices are periodic arrangements of interacting nanomagnets
successfully used to investigate emergent phenomena in the presence of
geometric frustration. Recently, it has been shown that artificial spin ices
can be used as building blocks for creating functional materials, such as
magnonic crystals, and support a large number of programmable magnetic states.
We investigate the magnetization dynamics in a system exhibiting anisotropic
magnetostatic interactions owing to locally broken structural inversion
symmetry. We find a rich spin-wave spectrum and investigate its evolution in an
external magnetic field. We determine the evolution of individual modes, from
building blocks up to larger arrays, highlighting the role of symmetry breaking
in defining the mode profiles. Moreover, we demonstrate that the mode spectra
exhibit signatures of long-range interactions in the system. These results
contribute to the understanding of magnetization dynamics in spin ices beyond
the kagome and square ice geometries and are relevant for the realization of
reconfigurable magnonic crystals based on spin ices.",2011.04505v2
2022-02-28,Observation of long-range orbital transport and giant orbital torque,"Modern spintronics relies on the generation of spin currents through
spin-orbit coupling. The spin-current generation has been believed to be
triggered by current-induced orbital dynamics, which governs the angular
momentum transfer from the lattice to the electrons in solids. The fundamental
role of the orbital response in the angular momentum dynamics suggests the
importance of the orbital counterpart of spin currents: orbital currents.
However, evidence for its existence has been elusive. Here, we demonstrate the
generation of giant orbital currents and uncover fundamental features of the
orbital response. We experimentally and theoretically show that orbital
currents propagate over longer distances than spin currents by more than an
order of magnitude in a ferromagnet and nonmagnets. Furthermore, we find that
the orbital current enables electric manipulation of magnetization with
efficiencies significantly higher than the spin counterpart. These findings
open the door to orbitronics that exploits orbital transport and spin-orbital
coupled dynamics in solid-state devices.",2202.13896v2
2022-05-26,Quantum correlations and speed limit of central spin system,"In this article, we consider single, and two-qubit central spin systems
interacting with spin baths and discuss their dynamical properties. We consider
the cases of interacting and non-interacting spin baths and investigate the
quantum speed limit (QSL) time of evolution. The impact of the size of the spin
bath on the quantum speed limit for a single qubit central spin model is
analyzed. We estimate the quantum correlations for (non-)interacting two
central spin qubits and compare their dynamical behaviour with that of QSL time
under various conditions. We show how QSL time could be availed to analyze the
dynamics of quantum correlations.",2205.13195v2
2022-07-22,Ferroelectricity driven by magnetism in quasi-one-dimensional Ba9Fe3Se15,"The spin-induced ferroelectricity in quasi-1D spin chain system is little
known, which could be fundamentally different from those in three-dimensional
(3D) system. Here, we report the ferroelectricity driven by a tilted screw spin
order and its exotic dynamic in the spin-chain compound Ba9Fe3Se15. It is found
that the spin-induced polarization has already occurred and exhibits
magnetoelectric coupling behavior far above the long-range spin order (LRSO) at
TN = 14 K. The polarized entities grow and their dynamic responses slow down
gradually with decreasing temperature and permeate the whole lattice to form 3D
ferroelectricity at TN. Our results reveal that the short-range spin orders
(SRSOs) in the decoupled chains play a key role for the exotic dynamic in this
dimension reduced system. Ba9Fe3Se15 is the only example so far which exhibits
electric polarization above LRSO temperature because of the formation of SRSOs.",2207.10834v1
2022-09-04,Non-Hermitian dynamics of a two-spin system with PT symmetry,"A system of interacting spins that are under the influence of spin-polarized
currents can be described using a complex functional, or a non-Hermitian (NH)
Hamiltonian. We study the dynamics of two exchange-coupled spins on the Bloch
sphere. In the case of currents leading to PT symmetry, an exceptional point
that survives also in the nonlinear system is identified. The nonlinear system
is bistable for small currents and it exhibits stable oscillating motion or it
can relax to a fixed point. The oscillating motion of the two spins is akin to
synchronized spin-torque oscillators. For the full nonlinear system, we derive
two conserved quantities that furnish a geometric description of the spin
trajectories in phase space and indicate stability of the oscillating motion.
Our analytical results provide tools for the description of the dynamics of NH
systems that are defined on the Bloch sphere.",2209.01572v2
2023-01-01,Spin Hall Induced Magnetization Dynamics in Multiferroic Tunnel Junction,"The combination of spin-orbit coupling driven effects and multiferroic
tunneling properties was explored experimentally in thin Pt/Co/BTO/LSMO
multilayers. The presence of a Pt heavy metal allows for the spin
current-induced magnetization precession of Co upon radio-frequency charge
current injection. The utilization of a BTO ferroelectric tunnel barrier
separating the Co and LSMO ferromagnetic electrodes gives rise to both
tunneling-magnetoresistance and electroresistance. Using the spin-orbit torque
ferromagnetic resonance, the maganetization dynamics of the Co/Pt bilayers was
studied at room temperature. Unexpectedly the magnetization dynamics study in
the same geometry performed at low temperature reveals the existence of both Co
and LSMO resonance peaks indicating efficient spin current generation both
using the spin Hall effect in Pt and spin pumping in LSMO that tunnel via the
BTO barrier.",2301.00459v1
2023-03-10,Ultrafast magnetization reversal in ferromagnetic spin-valves: an s-d model perspective,"We present an extension to simple s-d models, aiming at simulating ultrafast
magnetization dynamics and spin transport in metallic heterostructures. In
particular, we consider an alternative spin dissipation channel due to a finite
exchange splitting of the s band. From this theory, we show three different
mechanisms governing the dynamics of spin accumulation. On top of the already
widely discussed ""-dM/dt"" electron-magnon mechanism, we study the role of a
dynamic change of exchange splitting (of conduction electrons) as well as the
rotation of spins reflected at an interface with a ferromagnet. Finally, we use
the presented theory to explain the recent observation of subpicosecond
reversal of a ferromagnet in rare-earth free spin-valves. Our conclusion agrees
with the one of reference [1] favoring magnetization reversal due to the
rotation of the spin polarization of a reflected spin current.",2303.05907v1
2023-05-25,Polarization response of spin-lasers under amplitude modulation,"Lasers with injected spin-polarized carriers show an outstanding performance
in both static and dynamic operation. In addition to the intensity response of
conventional lasers, without spin-polarized carriers, both intensity and
polarization of light can be exploited for optical communication in
spin-lasers. However, the polarization dynamics of spin-lasers under amplitude
modulation has been largely overlooked. Here we reveal, analytically and
numerically, a nontrivial polarization response that accompanies the well-known
intensity dynamics of a spin-laser under amplitude modulation. We evaluate the
polarization and intensity response under the same amplitude modulation, and
further assess the capability of such a polarization response in digital data
transfer with eye diagram simulations. Our results provide a more complete
understanding of the modulation response in spin-lasers and open up unexplored
opportunities in optical communication and spintronics.",2305.15819v1
2023-09-22,Laser-induced real-space topology control of spin wave resonances,"Femtosecond laser excitation of materials that exhibit magnetic spin textures
promises advanced magnetic control via the generation of ultrafast and
non-equilibrium spin dynamics. We explore such possibilities in ferrimagnetic
[Fe(0.35 nm)/Gd(0.40 nm)]$_{160}$ multilayers, which host a rich diversity of
magnetic textures from stripe domains at low magnetic fields, a dense
bubble/skyrmion lattice at intermediate fields, and a single domain state for
high magnetic fields. Using femtosecond magneto-optics, we observe distinct
coherent spin wave dynamics in response to a weak laser excitation allowing us
to unambiguously identify the different magnetic spin textures. Moreover,
employing strong laser excitation we show that we achieve versatile control of
the coherent spin dynamics via non-equilibrium and ultrafast transformation of
magnetic spin textures by both creating and annihilating bubbles/skyrmions. We
corroborate our findings by micromagnetic simulations and by Lorentz
transmission electron microscopy before and after laser exposure.",2309.12956v1
2024-03-02,Spin-Dependent Stereochemistry: A Non-adiabatic Quantum Dynamics Case Study of S + H2 -> SH + H Reaction,"We study the spin-dependent stereodynamics of the S + H2 -> SH + H reaction
using full-dimensional quantum dynamics calculations with zero total nuclear
angular momentum along the triplet 3A"" states and singlet 1A' states. We find
that the interplay between the electronic spin direction and the molecular
geometry has a measurable influence on the singlet-triplet intersystem crossing
reaction probabilities. Our results show that for some incident scattering
angles in the body-fixed frame, the relative difference in intersystem crossing
reaction probabilities (as determined between spin up and spin down initial
states) can be as large as 15%. Our findings are an ab initio demonstration of
spin-dependent nonadiabatic dynamics which we hope will shine light as far as
understanding the chiral-induced spin selectivity effect.",2403.01288v1
2024-03-16,Machine Learning Exchange Fields for Ab-initio Spin Dynamics,"We add the magnetic degrees of freedom to the widely used Gaussian
Approximation Potential of machine learning (ML) and present a model that
describes the potential energy surface of a crystal based on the atomic
coordinates as well as their noncollinear magnetic moments. Assuming an
adiabatic approximation for the spin directions and magnitudes, the ML model
depends solely on spin coordinates and orientation, resulting in computational
efffciency and enabling ab initio spin dynamics. Leveraging rotational
symmetries of magnetic interactions, the ML model can incorporate various
magnetic interactions, expanding into two-body, three-body terms, etc.,
following the spirit of cluster expansion. For simplicity, we implement the ML
model with a two-body form for the exchange interaction. Comparing total
energies and local fields predicted by the model for noncollinear spin
arrangements with explicit results of constrained noncollinear density
functional calculations for bcc Fe yields excellent results, within 1 meV/spin
for the total energy. Further optimization, including three-body and other
terms, is expected to encompass diverse magnetic interactions and enhance the
model's accuracy. This will extend the model's applicability to a wide range of
materials and facilitate the machine learning ab initio spin dynamics.",2403.10769v1
1996-11-27,Muon Spin Relaxation Investigation of the Spin Dynamics of Geometrically Frustrated Antiferromagnets Y2Mo2O7 and Tb2Mo2O7 Static Critical Behavior of the Spin-Freezing,"The spin dynamics of geometrically frustrated pyrochlore antiferromagnets
Y2Mo2O7 and Tb2Mo2O7 have been investigated using muon spin relaxation. A
dramatic slowing down of the moment fluctuations occurs as one approaches the
spin freezing temperatures (TF=22 K and 25 K respectively) from above. Below TF
there is a disordered magnetic state similar to that found in a spin glass but
with a residual muon spin relaxation rate at low temperatures. These results
show that there is a large density of states for magnetic excitations in these
systems near zero energy.",9611222v2
2001-06-01,Spin currents and spin dynamics in time-dependent density-functional theory,"We derive and analyse the equation of motion for the spin degrees of freedom
within time-dependent spin-density-functional theory (TD-SDFT). Results are (i)
a prescription for obtaining many-body corrections to the single-particle spin
currents from the Kohn-Sham equation of TD-SDFT, (ii) the existence of an
exchange-correlation (xc) torque within TD-SDFT, (iii) a prescription for
calculating, from TD-SDFT, the torque exerted by spin currents on the spin
magnetization, (iv) a novel exact constraint on approximate xc functionals, and
(v) the discovery of serious deficiencies of popular approximations to TD-SDFT
when applied to spin dynamics.",0106021v3
2003-02-17,Magnetization dynamics with a spin-transfer torque,"The magnetization reversal and dynamics of a spin valve pillar, whose lateral
size is 64$\times$64 nm$^2$, are studied by using micromagnetic simulation in
the presence of spin transfer torque. Spin torques display both characteristics
of magnetic damping (or anti-damping) and of an effective magnetic field. For a
steady-state current, both M-I and M-H hysteresis loops show unique features,
including multiple jumps, unusual plateaus and precessional states. These
states originate from the competition between the energy dissipation due to
Gilbert damping and the energy accumulation due to the spin torque supplied by
the spin current. The magnetic energy oscillates as a function of time even for
a steady-state current. For a pulsed current, the minimum width and amplitude
of the spin torque for achieving current-driven magnetization reversal are
quantitatively determined. The spin torque also shows very interesting thermal
activation that is fundamentally different from an ordinary damping effect.",0302337v1
2003-07-05,Anisotropic splitting of intersubband spin plasmons in quantum wells with bulk and structural inversion asymmetry,"In semiconductor heterostructures, bulk and structural inversion asymmetry
and spin-orbit coupling induce a k-dependent spin splitting of valence and
conduction subbands, which can be viewed as being caused by momentum-dependent
crystal magnetic fields. This paper studies the influence of these effective
magnetic fields on the intersubband spin dynamics in an asymmetric n-type
GaAs/AlGaAs quantum well. We calculate the dispersions of intersubband spin
plasmons using linear response theory. The so-called D'yakonov-Perel'
decoherence mechanism is inactive for collective intersubband excitations,
i.e., crystal magnetic fields do not lead to decoherence of spin plasmons.
Instead, we predict that the main signature of bulk and structural inversion
asymmetry in intersubband spin dynamics is a three-fold, anisotropic splitting
of the spin plasmon dispersion. The importance of many-body effects is pointed
out, and conditions for experimental observation with inelastic light
scattering are discussed.",0307124v1
2003-07-11,"Photo-induced spin dynamics in ferromagnetic semiconductor $p$-(Ga,Mn)As","Spin dynamics in ferromagnetic $p$-(Ga,Mn)As ($x$ = 0.011, $T_{C}$ = 30 K)
has been studied by carefully comparing the decay time of the photo-induced
reflectivity change with the transient behavior of polar Kerr rotation induced
by photo-generated carrier spins with a femtosecond light pulse of various
polarizations. As to the rising process, the rate of Kerr rotation is found
comparable to the generation rate of spin-polarized carriers. For the decay
process, the Kerr rotation and reflectivity signal both show the same decay
rate at above the $T_{C}$, whereas, below the $T_{C}$, the former becomes
slower than the latter. The magnitude of Kerr rotation suggests that 10$^{2}$
Mn spins are revolved by injecting one hole spin. On the basis of these
observations, collective rotation of ferromagnetically coupled Mn spins is
discussed in terms of $p$-$d$ exchange interaction and successive transverse
spin relaxation. Development of another long-lived behavior under external
perpendicular magnetic fields is also disclosed.",0307268v1
2003-09-24,Magnetic susceptibilities of diluted magnetic semiconductors and anomalous Hall-voltage noise,"The carrier spin and impurity spin densities in diluted magnetic
semiconductors are considered using a semiclassical approach. Equations of
motions for the spin densities and the carrier spin current density in the
paramagnetic phase are derived, exhibiting their coupled diffusive dynamics.
The dynamical spin susceptibilities are obtained from these equations. The
theory holds for p-type and n-type semiconductors doped with magnetic ions of
arbitrary spin quantum number. Spin-orbit coupling in the valence band is shown
to lead to anisotropic spin diffusion and to a suppression of the Curie
temperature in p-type materials. As an application we derive the Hall-voltage
noise in the paramagnetic phase. This quantity is critically enhanced close to
the Curie temperature due to the contribution from the anomalous Hall effect.",0309547v1
2004-05-12,Monte Carlo modeling of spin injection through a Schottky barrier and spin transport in a semiconductor quantum well,"We develop a Monte Carlo model to study injection of spin-polarized electrons
through a Schottky barrier from a ferromagnetic metal contact into a
non-magnetic low-dimensional semiconductor structure. Both mechanisms of
thermionic emission and tunneling injection are included in the model. Due to
the barrier shape, the injected electrons are non-thermalized. Spin dynamics in
the semiconductor heterostructure is controlled by the Rashba and Dresselhaus
spin-orbit interactions and described by a single electron spin density matrix
formalism. In addition to the linear term, the third order term in momentum for
the Dresselhaus interaction is included. Effect of the Schottky potential on
the spin dynamics in a 2 dimensional semiconductor device channel is studied.
It is found that the injected current can maintain substantial spin
polarization to a length scale in the order of 1 micrometer at room temperature
without external magnetic fields.",0405270v2
2004-10-21,Spin Transport in Disordered Two-Dimensional Hopping Systems with Rashba Spin-Orbit Interaction,"The influence of Rashba spin-orbit interaction on the spin dynamics of a
topologically disordered hopping system is studied in this paper. This is a
significant generalization of a previous investigation, where an ordered
(polaronic) hopping system has been considered instead. It is found, that in
the limit, where the Rashba length is large compared to the typical hopping
length, the spin dynamics of a disordered system can still be described by the
expressions derived for an ordered system, under the provision that one takes
into account the frequency dependence of the diffusion constant and the
mobility (which are determined by charge transport and are independent of
spin). With these results we are able to make explicit the influence of
disorder on spin related quantities as, e.g., the spin life-time in hopping
systems.",0410531v2
2005-06-15,Global and local relaxation of a spin-chain under exact Schroedinger and master-equation dynamics,"We solve the Schroedinger equation for an interacting spin-chain locally
coupled to a quantum environment with a specific degeneracy structure. The
reduced dynamics of the whole spin-chain as well as of single spins is
analyzed. We show, that the total spin-chain relaxes to a thermal equilibrium
state independently of the internal interaction strength. In contrast, the
asymptotic states of each individual spin are thermal for weak but non-thermal
for stronger spin-spin coupling. The transition between both scenarios is found
for couplings of the order of $0.1 \times \Delta E$, with $\Delta E$ denoting
the Zeeman-splitting. We compare these results with a master equation
treatment; when time averaged, both approaches lead to the same asymptotic
state and finally with analytical results.",0506355v2
2006-02-05,Nuclear Spin Noise and STM Noise Spectroscopy,"We consider fluctuations of the electronic spin due to coupling to nuclear
spin. Noise spectroscopy of an electronic spin can be revealed in the Scanning
Tunnelling Microscope (STM). We argue that the noise spectroscopy of electronic
spin can reveal the nuclear spin dynamics due to hyperfine coupling. Tunnelling
current develops satellites of the main lines at Larmor frequency and at zero
frequency due to hyperfine coupling. We also address the role of the rf field
that is at or near the resonance with the nuclear hyperfine field. This
approach is similar to Electron Nuclear Double Resonance (ENDOR), in that is
allows one to detect nuclear spin dynamics indirectly through its effect on
electronic spin.",0602113v1
2007-03-02,Ultrafast demagnetization in the sp-d model: a theoretical study,"We propose and analyze a theoretical model of ultrafast light-induced
magnetization dynamics in systems of localized spins that are coupled to
carriers' spins by sp-d exchange interaction. A prominent example of a class of
materials falling into this category are ferromagnetic (III,Mn)V
semiconductors, in which ultrafast demagnetization has been recently observed.
In the proposed model light excitation heats up the population of carriers,
taking it out of equilibrium with the localized spins. This triggers the
process of energy and angular momentum exchange between the two spin systems,
which lasts for the duration of the energy relaxation of the carriers. We
derive the Master equation for the density matrix of a localized spin
interacting with the hot carriers and couple it with a phenomenological
treatment of the carrier dynamics. We develop a general theory within the sp-d
model and we apply it to the ferromagnetic semiconductors, taking into account
the valence band structure of these materials. We show that the fast spin
relaxation of the carriers can sustain the flow of polarization between the
localized and itinerant spins leading to significant demagnetization of the
localized spin system, observed in (III,Mn)V materials.",0703049v2
2001-08-06,Quantum Measurement of a Single Spin using Magnetic Resonance Force Microscopy,"Single-spin detection is one of the important challenges facing the
development of several new technologies, e.g. single-spin transistors and
solid-state quantum computation. Magnetic resonance force microscopy with a
cyclic adiabatic inversion, which utilizes a cantilever oscillations driven by
a single spin, is a promising technique to solve this problem. We have studied
the quantum dynamics of a single spin interacting with a quasiclassical
cantilever. It was found that in a similar fashion to the Stern-Gerlach
interferometer the quantum dynamics generates a quantum superposition of two
quasiclassical trajectories of the cantilever which are related to the two spin
projections on the direction of the effective magnetic field in the rotating
reference frame. Our results show that quantum jumps will not prevent a
single-spin measurement if the coupling between the cantilever vibrations and
the spin is small in comparison with the amplitude of the radio-frequency
external field.",0108025v1
2003-12-16,Dynamics of a large spin with weak dissipation,"We investigate the generalization of the spin-boson model to arbitrary spin
size. The Born-Markov approximation is employed to derive a master equation in
the regime of small coupling strengths to the environment. For spin one half,
the master equation transforms into a set of Bloch equations, the solution of
which is in good agreement with results of the spin-boson model for weak ohmic
dissipation. For larger spins, we find a superradiance-like behavior known from
the Dicke model. The influence of the nonresonant bosons of the dissipative
environment can lead to the formation of a beat pattern in the dynamics of the
$z$-component of the spin. The beat frequency is approximately proportional to
the cutoff $\omega_c$ of the spectral function.",0312140v1
2007-08-29,Spin-charge separation in a strongly correlated spin-polarized chain,"We combine the first-quantized path-integral formalism and bosonization to
develop a phenomenological theory for spin-charge coupled dynamics in
one-dimensional (1D) ferromagnetic systems with strong interparticle repulsion,
at low temperatures. We assume an effective spin-charge separation and retain
the standard Luttinger-liquid plasmon branch, which is explicitly coupled to a
ferromagnetic spin-wave texture with a quadratic dispersion. The dynamic spin
structure severely suppresses the plasmon peak in the single-particle
propagator, in both fermionic and bosonic systems. Our analysis provides an
effective theory for the new universality class of 1D ferromagnetic systems,
capturing both the trapped spin and propagating spin-wave regimes of the
long-time behavior.",0708.4012v4
2007-12-19,Wavefunction considerations for the central spin decoherence problem in a nuclear spin bath,"Decoherence of a localized electron spin in a solid state material (the
``central spin'' problem) at low temperature is believed to be dominated by
interactions with nuclear spins in the lattice. This decoherence is partially
suppressed through the application of a large magnetic field that splits the
energy levels of the electron spin and prevents depolarization. However,
dephasing decoherence resulting from a dynamical nuclear spin bath cannot be
removed in this way. Fluctuations of the nuclear field lead to uncertainty of
the electron's precessional frequency in a process known as spectral diffusion.
This article considers the effect of the electron's wavefunction shape upon
spectral diffusion and provides wavefunction dependent decoherence time
formulas for free induction decay as well as spin echoes and concatenated
dynamical decoupling schemes for enhancing coherence. We also discuss dephasing
of a qubit encoded in singlet-triplet states of a double quantum dot. A central
theoretical result of this work is the development of a continuum approximation
for the spectral diffusion problem which we have applied to GaAs and InAs
materials specifically.",0712.3065v2
2008-03-04,Induced decoherence and entanglement by interacting quantum spin baths,"The reduced dynamics of a single or two qubits coupled to an interacting
quantum spin bath modeled by a XXZ spin chain is investigated. By using the
method of time-dependent density matrix renormalization group (t-DMRG), we go
beyond the uniform coupling central spin model and evaluate nonperturbatively
the induced decoherence and entanglement. It is shown that both decoherence and
entanglement strongly depend on the phase of the underlying spin bath. We show
that in general, spin baths can induce entanglement for an initially
disentangled pair of qubits. Furthermore, when the spin bath is in the
ferromagnetic phase, because qubits directly couple to the order parameter, the
reduced dynamics shows oscillatory type behavior. On the other hand, only for
paramagnetic and antiferromagnetic phases, initially entangled states suffer
from the entanglement sudden death. By calculating concurrence, the finite
disentanglement time is mapped out for all phases in the phase diagram of the
spin bath.",0803.0364v1
2008-08-22,Perturbation Method for Classical Spinning Particle Motion: I. Kerr Space-Time,"This paper presents an analytic perturbation approach to the dynamics of a
classical spinning particle, according to the Mathisson-Papapetrou-Dixon (MPD)
equations of motion, with a direct application to circular motion around a Kerr
black hole. The formalism is established in terms of a power series expansion
with respect to the particle's spin magnitude, where the particle's kinematic
and dynamical degrees are expressed in a completely general form that can be
constructed to infinite order in the expansion parameter. It is further shown
that the particle's squared mass and spin magnitude can shift due to a
classical analogue of radiative corrections that arise from spin-curvature
coupling. Explicit expressions are determined for the case of circular motion
near the event horizon a Kerr black hole, where the mass and spin shift
contributions are dependent on the initial conditions of the particle's spin
orientation. A preliminary analysis of the stability properties of the orbital
motion in the Kerr background due to spin-curvature interactions is explored
and briefly discussed.",0808.3005v2
2008-09-19,Spin noise spectroscopy in GaAs (110) quantum wells: Access to intrinsic spin lifetimes and equilibrium electron dynamics,"In this letter, the first spin noise spectroscopy measurements in
semiconductor systems of reduced effective dimensionality are reported. The
non-demolition measurement technique gives access to the otherwise concealed
intrinsic, low temperature electron spin relaxation time of n-doped GaAs (110)
quantum wells and to the corresponding low temperature anisotropic spin
relaxation. The Brownian motion of the electrons within the spin noise probe
laser spot becomes manifest in a modification of the spin noise line width.
Thereby, the spatially resolved observation of the stochastic spin polarization
uniquely allows to study electron dynamics at equilibrium conditions with a
vanishing total momentum of the electron system.",0809.3338v1
2009-05-13,Spin-dependent dipole excitation in alkali-metal nanoparticles,"We study the spin-dependent electronic excitations in alkali-metal
nanoparticles. Using numerical and analytical approaches, we focus on the
resonances in the response to spin-dependent dipole fields. In the spin-dipole
absorption spectrum for closed-shell systems, we investigate in detail the
lowest-energy excitation, the ""surface paramagnon"" predicted by L. Serra et al.
[Phys. Rev. A 47, R1601 (1993)]. We estimate its frequency from simple
assumptions for the dynamical magnetization density. In addition, we
numerically determine the dynamical magnetization density for all low-energy
spin-dipole modes in the spectrum. Those many-body excitations can be traced
back to particle-hole excitations of the noninteracting system. Thus, we argue
that the spin-dipole modes are not of collective nature. In open-shell systems,
the spin-dipole response to an electrical dipole field is found to increase
proportionally with the ground-state spin polarization.",0905.2076v1
2009-08-31,Hyperfine Interactions and Spin Transport in Ferromagnet-Semiconductor Heterostructures,"Measurements and modeling of electron spin transport and dynamics are used to
characterize hyperfine interactions in Fe/GaAs devices with $n$-GaAs channels.
Ga and As nuclei are polarized by electrically injected electron spins, and the
nuclear polarization is detected indirectly through the depolarization of
electron spins in the hyperfine field. The dependence of the electron spin
signal on injector bias and applied field direction is modeled by a coupled
drift-diffusion equation, including effective fields from both the electronic
and nuclear polarizations. This approach is used to determine the electron spin
polarization independently of the assumptions made in standard transport
measurements. The extreme sensitivity of the electron spin dynamics to the
nuclear spin polarization also facilitates the electrical detection of nuclear
magnetic resonance.",0909.0048v1
2010-07-31,Random walk approach to spin dynamics in a two-dimensional electron gas with spin-orbit coupling,"We introduce and solve a semi-classical random walk (RW) model that describes
the dynamics of spin polarization waves in zinc-blende semiconductor quantum
wells. We derive the dispersion relations for these waves, including the
Rashba, linear and cubic Dresselhaus spin-orbit interactions, as well as the
effects of an electric field applied parallel to the spin polarization
wavevector. In agreement with fully quantum mechanical calculations [Kleinert
and Bryksin, Phys. Rev. B \textbf{76}, 205326 (2007)], the RW approach predicts
that spin waves acquire a phase velocity in the presence of the field that
crosses zero at a nonzero wavevector, $q_0$. In addition, we show that the
spin-wave decay rate is independent of field at $q_0$ but increases as
$(q-q_0)^2$ for $q\neq q_0$. These predictions can be tested experimentally by
suitable transient spin grating experiments.",1008.0132v2
2010-08-24,Low temperature electron-spin relaxation in the crystalline and glassy states of solid ethanol,"X-band electron paramagnetic resonance (EPR) spectroscopy was used to study
the spectral properties of a nitroxide spin probe in ethanol glass and
crystalline ethanol, at 5 - 11.5 K. The different anisotropy of molecular
packing in the two host matrices was evidenced by different rigid limit values
for maximal hyperfine splitting in the signal of the spin probe. The
significantly shorter phase memory time, , for the spin probe dissolved in
crystalline ethanol, as compared to ethanol glass, was discussed in terms of
contribution from spectral diffusion. The effect of low-frequency dynamics was
manifested in the temperature dependence of and in the difference between the
data measured at different spectral positions. This phenomenon was addressed
within the framework of the slow-motional isotropic diffusion model [S. Lee,
and S. Z. Tang, Phys. Rev. B 31, 1308 (1985)] predicting the spin probe
dynamics within the millisecond range, at very low temperatures. The shorter
spin-lattice relaxation time of the spin probe in ethanol glass was interpreted
in terms of enhanced energy exchange between the spin system and the lattice in
the glass matrix due to boson peak excitations.",1008.4032v1
2010-08-27,Geometric Correlations and Breakdown of Mesoscopic Universality in Spin Transport,"We construct a unified semiclassical theory of charge and spin transport in
chaotic ballistic and disordered diffusive mesoscopic systems with spin-orbit
interaction. Neglecting dynamic effects of spin-orbit interaction, we reproduce
the random matrix theory results that the spin conductance fluctuates
universally around zero average. Incorporating these effects in the theory, we
show that geometric correlations generate finite average spin conductances, but
that they do not affect the charge conductance to leading order. The theory,
which is confirmed by numerical transport calculations, allows us to
investigate the entire range from the weak to the previously unexplored strong
spin-orbit regime, where the spin rotation time is shorter than the momentum
relaxation time.",1008.4656v1
2010-09-25,Pulse-pumped double quantum dot with spin-orbit coupling,"We consider the full driven quantum dynamics of a qubit realized as spin of
electron in a one-dimensional double quantum dot with spin-orbit coupling. The
driving perturbation is taken in the form of a single half-period pulse of
electric field. Spin-orbit coupling leads to a nontrivial evolution in the spin
and charge densities making the dynamics in both quantities irregular. As a
result, the charge density distribution becomes strongly spin-dependent. The
transition from the field-induced tunneling to the strong coupling regime is
clearly seen in the charge and spin channels. These results can be important
for the understanding of the techniques for the spin manipulation in
nanostructures.",1009.5013v1
2010-10-06,Spin dynamics in the optical cycle of single nitrogen-vacancy centres in diamond,"We investigate spin-dependent decay and intersystem crossing in the optical
cycle of single negatively-charged nitrogen-vacancy (NV) centres in diamond. We
use spin control and pulsed optical excitation to extract both the
spin-resolved lifetimes of the excited states and the degree of
optically-induced spin polarization. By optically exciting the centre with a
series of picosecond pulses, we determine the spin-flip probabilities per
optical cycle, as well as the spin-dependent probability for intersystem
crossing. This information, together with the indepedently measured decay rate
of singlet population provides a full description of spin dynamics in the
optical cycle of NV centres. The temperature dependence of the singlet
population decay rate provides information on the number of singlet states
involved in the optical cycle.",1010.1192v1
2010-10-27,Coupling molecular spin states by photon-assisted tunneling,"Artificial molecules containing just one or two electrons provide a powerful
platform for studies of orbital and spin quantum dynamics in nanoscale devices.
A well-known example of these dynamics is tunneling of electrons between two
coupled quantum dots triggered by microwave irradiation. So far, these
tunneling processes have been treated as electric dipole-allowed
spin-conserving events. Here we report that microwaves can also excite
tunneling transitions between states with different spin. In this work, the
dominant mechanism responsible for violation of spin conservation is the
spin-orbit interaction. These transitions make it possible to perform detailed
microwave spectroscopy of the molecular spin states of an artificial hydrogen
molecule and open up the possibility of realizing full quantum control of a two
spin system via microwave excitation.",1010.5682v1
2011-08-09,Selective probing of photo-induced charge and spin dynamics in the bulk and surface of a topological insulator,"Topological insulators possess completely different spin-orbit coupled bulk
and surface electronic spectra that are each predicted to exhibit exotic
responses to light. Here we report time-resolved fundamental and second
harmonic optical pump-probe measurements on the topological insulator Bi2Se3 to
independently measure its photo-induced charge and spin dynamics with bulk and
surface selectivity. Our results show that a transient net spin density can be
optically induced in both the bulk and surface, which may drive spin transport
in topological insulators. By utilizing a novel rotational anisotropy analysis
we are able to separately resolve the spin de-polarization, intraband cooling
and interband recombination processes following photo-excitation, which reveal
that spin and charge degrees of freedom relax on very different time scales
owing to strong spin-orbit coupling.",1108.1848v1
2012-03-05,Inducing spin-dependent tunneling to probe magnetic correlations in optical lattices,"We suggest a simple experimental method for probing antiferromagnetic spin
correlations of two-component Fermi gases in optical lattices. The method
relies on a spin selective Raman transition to excite atoms of one spin species
to their first excited vibrational mode where the tunneling is large. The
resulting difference in the tunneling dynamics of the two spin species can then
be exploited, to reveal the spin correlations by measuring the number of doubly
occupied lattice sites at a later time. We perform quantum Monte Carlo
simulations of the spin system and solve the optical lattice dynamics
numerically to show how the timed probe can be used to identify
antiferromagnetic spin correlations in optical lattices.",1203.0925v1
2013-05-07,High-Resolution Correlation Spectroscopy of 13C Spins Near a Nitrogen-Vacancy Center in Diamond,"Spin complexes comprising the nitrogen-vacancy (NV) center and neighboring
spins are being considered as a building block for a new generation of
spintronic and quantum information processing devices. Because assembling
identical spin clusters is difficult, new strategies are in order to determine
individual node structures with the highest precision. Here we use a pulse
protocol to monitor the time evolution of the 13C ensemble in the vicinity of a
NV center. We observe long-lived time correlations in the nuclear spin
dynamics, limited by NV spin-lattice relaxation. We use the host 14N spin as a
quantum register, and demonstrate that hyperfine-shifted resonances can be
separated upon proper NV initialization. Intriguingly, we find that the
amplitude of the correlation signal exhibits a sharp dependence on the applied
magnetic field. We discuss this observation in the context of the
quantum-to-classical transition proposed recently to explain the field
dependence of the spin cluster dynamics.",1305.1536v1
2013-05-28,Spin fluctuations with two-dimensional XY behavior in a frustrated S = 1/2 square-lattice ferromagnet,"The spin dynamics of the layered square-lattice vanadate Pb2VO(PO4)2 is
investigated by electron spin resonance at various magnetic fields and at
temperatures above magnetic ordering. The linewidth divergence towards low
temperatures seems to agree with isotropic Heisenberg-type spin exchange
suggesting that the spin relaxation in this quasi-two dimensional compound is
governed by low-dimensional quantum fluctuations. However, a weak easy- plane
anisotropy of the g factor points to the presence of a planar XY type of
exchange. Indeed, we found that the linewidth divergence is described best by
XY-like spin fluctuations which requires a single parameter only. Therefore,
ESR-probed spin dynamics could establish Pb2VO(PO4)2 as the first frustrated
square lattice system with XY-inherent spin topological fluctuations.",1305.6518v1
2013-06-12,Non-equilibrium quantum magnetism in a dipolar lattice gas,"Research on quantum magnetism with ultra-cold gases in optical lattices is
expected to open fascinating perspectives for the understanding of fundamental
problems in condensed-matter physics. Here we report on the first realization
of quantum magnetism using a degenerate dipolar gas in an optical lattice. In
contrast to their non-dipolar counterparts, dipolar lattice gases allow for
inter-site spin-spin interactions without relying on super-exchange energies,
which constitutes a great advantage for the study of spin lattice models. In
this paper we show that a chromium gas in a 3D lattice realizes a lattice model
resembling the celebrated t-J model, which is characterized by a
non-equilibrium spinor dynamics resulting from inter-site Heisenberg-like
spin-spin interactions provided by non-local dipole-dipole interactions.
Moreover, due to its large spin, chromium lattice gases constitute an excellent
environment for the study of quantum magnetism of high-spin systems, as
illustrated by the complex spin dynamics observed for doubly-occupied sites.",1306.2754v2
2014-07-25,A critique of recent semi-classical spin-half quantum plasma theories,"Certain recent semi-classical theories of spin-half quantum plasmas are
examined with regard to their internal consistency, physical applicability and
relevance to fusion, astrophysical and condensed matter plasmas. It is shown
that the derivations and some of the results obtained in these theories are
internally inconsistent and contradict well-established principles of quantum
and statistical mechanics, especially in their treatment of fermions and spin.
Claims of large semi-classical effects of spin magnetic moments that could
dominate the plasma dynamics are found to be invalid both for single-particles
and collectively. Larmor moments dominate at high temperature while spin
moments cancel due to Pauli blocking at low temperatures. Explicit numerical
estimates from a variety of plasmas are provided to demonstrate that spin
effects are indeed much smaller than many neglected classical effects. The
analysis presented suggests that the aforementioned `Spin Quantum Hydrodynamic'
theories are not relevant to conventional laboratory or astrophysical plasmas.",1407.6865v2
2014-09-08,Dynamic control of spin wave spectra using spin-polarized currents,"We describe a method of controlling the spin wave spectra dynamically in a
uniform nanostripe waveguide through spin-polarized currents. A stable periodic
magnetization structure is observed when the current flows vertically through
the center of nanostripe waveguide. After being excited, the spin wave is
transmitted at the sides of the waveguide. Numerical simulations of spin-wave
transmission and dispersion curves reveal a single, pronounced band gap.
Moreover, the periodic magnetization structure can be turned on and off by the
spin-polarized current. The switching process from full rejection to full
transmission takes place within less than 3ns. Thus, this type magnonic
waveguide can be utilized for low-dissipation spin wave based filters.",1409.2421v2
2014-09-17,Momentum resolved spin dynamics of bulk and surface excited states in the topological insulator $\mathrm{Bi_{2}Se_{3}}$,"The prospective of optically inducing a spin polarized current for spintronic
devices has generated a vast interest in the out-of-equilibrium electronic and
spin structure of topological insulators (TIs). In this Letter we prove that
only by measuring the spin intensity signal over several order of magnitude in
spin, time and angle resolved photoemission spectroscopy (STAR-PES) experiments
is it possible to comprehensively describe the optically excited electronic
states in TIs materials. The experiments performed on $\mathrm{Bi_{2}Se_{3}}$
reveal the existence of a Surface-Resonance-State in the 2nd bulk band gap
interpreted on the basis of fully relativistic ab-initio spin resolved
photoemission calculations. Remarkably, the spin dependent relaxation of the
hot carriers is well reproduced by a spin dynamics model considering two
non-interacting electronic systems, derived from the excited surface and bulk
states, with different electronic temperatures.",1409.5018v1
2015-01-07,Quadratic-in-spin effects in the orbital dynamics and gravitational-wave energy flux of compact binaries at the 3PN order,"We investigate the dynamics of spinning binaries of compact objects at the
next-to-leading order in the quadratic-in-spin effects, which corresponds to
the third post-Newtonian order (3PN). Using a Dixon-type multipolar formalism
for spinning point particles endowed with spin-induced quadrupoles and
computing iteratively in harmonic coordinates the relevant pieces of the PN
metric within the near zone, we derive the post-Newtonian equations of motion
as well as the equations of spin precession. We find full equivalence with
available results. We then focus on the far-zone field produced by those
systems and obtain the previously unknown 3PN spin contributions to the
gravitational-wave energy flux by means of the multipolar post-Minkowskian
(MPM) wave generation formalism. Our results are presented in the
center-of-mass frame for generic orbits, before being further specialized to
the case of spin-aligned, circular orbits. We derive the orbital phase of the
binary based on the energy balance equation and briefly discuss the relevance
of the new terms.",1501.01529v1
2015-06-08,Demagnetization dynamics of non-interacting trapped fermions,"Motivated by several experimental efforts to understand spin diffusion and
transport in ultracold fermionic gases, we study the spin dynamics of initially
spin-polarized ensembles of harmonically trapped non-interacting spin-1/2
fermionic atoms, subjected to a magnetic field gradient. We obtain simple
analytic expressions for spin observables in the presence of both constant and
linear magnetic field gradients, with and without a spin-echo pulse, and at
zero and finite temperatures. The analysis shows the relevance of spin-motional
coupling in the non-interacting regime where the demagnetization decay rate at
short times can be faster than the experimentally measured rates in the
strongly interacting regime under similar trapping conditions. Our calculations
also show that particle motion limits the ability of a spin-echo pulse to
remove the effect of magnetic field inhomogeneity, and that a spin-echo pulse
can instead lead to an increased decay of magnetization at times comparable to
the trapping period.",1506.02353v1
2015-08-06,Large spin-wave bullet in a ferrimagnetic insulator driven by spin Hall effect,"Due to its transverse nature, spin Hall effects (SHE) provide the possibility
to excite and detect spin currents and magnetization dynamics even in magnetic
insulators. Magnetic insulators are outstanding materials for the investigation
of nonlinear phenomena and for novel low power spintronics applications because
of their extremely low Gilbert damping. Here, we report on the direct imaging
of electrically driven spin-torque ferromagnetic resonance (ST-FMR) in the
ferrimagnetic insulator Y$_3$Fe$_5$O$_{12}$ based on the excitation and
detection by SHEs. The driven spin dynamics in Y$_3$Fe$_5$O$_{12}$ is directly
imaged by spatially-resolved microfocused Brillouin light scattering (BLS)
spectroscopy. Previously, ST-FMR experiments assumed a uniform precession
across the sample, which is not valid in our measurements. A strong spin-wave
localization in the center of the sample is observed indicating the formation
of a nonlinear, self-localized spin-wave `bullet'.",1508.01427v1
2015-08-10,Anisotropic spin relaxation in $n$-GaAs from strong inhomogeneous hyperfine fields produced by the dynamical polarization of nuclei,"The hyperfine field from dynamically polarized nuclei in n-GaAs is very
spatially inhomogeneous, as the nu- clear polarization process is most
efficient near the randomly-distributed donors. Electrons with polarized spins
traversing the bulk semiconductor will experience this inhomogeneous hyperfine
field as an effective fluctuating spin precession rate, and thus the spin
polarization of an electron ensemble will relax. A theory of spin relaxation
based on the theory of random walks is applied to such an ensemble precessing
in an oblique magnetic field, and the precise form of the (unequal)
longitudinal and transverse spin relaxation analytically derived. To
investigate this mechanism, electrical three-terminal Hanle measurements were
performed on epitaxially grown Co$_2$MnSi/$n$-GaAs heterostructures fabricated
into electrical spin injection devices. The proposed anisotropic spin
relaxation mechanism is required to satisfactorily describe the Hanle
lineshapes when the applied field is oriented at large oblique angles.",1508.02423v1
2015-08-14,Extraordinary Spin specific beam shift of Light in an Inhomogeneous Anisotropic medium,"Spin orbit interaction and the resulting Spin Hall effect of light are under
recent intensive investigations because of their fundamental nature and
potential applications. Here, we report an extraordinary spin specific beam
shift of light and demonstrate its tunability in an inhomogeneous anisotropic
medium exhibiting spatially varying retardance level. The spin specificity
(shift occurs only for one circular polarization mode, keeping the other
orthogonal mode unaffected) is shown to arise due to the combined spatial
gradients of the geometric phase and the dynamical phase of light. The
constituent two orthogonal circular polarization modes of an input linearly
polarized light evolve in different trajectories, eventually manifesting as a
large and tunable spin separation. The spin specificity of the beam shift and
the demonstrated principle of simultaneously tailoring space-varying geometric
and dynamical phase of light for achieving its tunability (of both magnitude
and direction), may provide an attractive route towards development of
spin-optical devices.",1508.03469v1
2015-09-14,Antiferromagnonic Spin Transport from Y$_3$Fe$_5$O$_{12}$ into NiO,"We observe highly efficient dynamic spin injection from Y$_3$Fe$_5$O$_{12}$
(YIG) into NiO, an antiferromagnetic (AF) insulator, via strong coupling, and
robust spin propagation in NiO up to 100-nm thickness mediated by its AF spin
correlations. Strikingly, the insertion of a thin NiO layer between YIG and Pt
significantly enhances the spin currents driven into Pt, suggesting
exceptionally high spin transfer efficiency at both YIG/NiO and NiO/Pt
interfaces. This offers a powerful platform for studying AF spin pumping and AF
dynamics as well as for exploration of spin manipulation in tailored structures
comprising metallic and insulating ferromagnets, antiferromagnets and
nonmagnetic materials.",1509.04337v1
2015-11-05,Cassini states for black hole binaries,"Cassini states correspond to the equilibria of the spin axis of a body when
its orbit is perturbed. They were initially described for planetary satellites,
but the spin axes of black hole binaries also present this kind of equilibria.
In previous works, Cassini states were reported as spin-orbit resonances, but
actually the spin of black hole binaries is in circulation and there is no
resonant motion. Here we provide a general description of the spin dynamics of
black hole binary systems based on a Hamiltonian formalism. In absence of
dissipation the problem is integrable and it is easy to identify all possible
trajectories for the spin for a given value of the total angular momentum. As
the system collapses due to radiation reaction, the Cassini states are shifted
to different positions, which modifies the dynamics around them. This is why
the final spin distribution may differ from the initial one. Our method
provides a simple way of predicting the distribution of the spin of black hole
binaries at the end of the inspiral phase.",1511.01890v2
2015-11-11,Quantum Fingerprints in Higher Order Correlators of a Spin Qubit,"The spin of an electron in a semiconductor quantum dot represents a natural
nanoscale solid state qubit. Coupling to nuclear spins leads to decoherence
that limits the number of allowed quantum logic operations for this qubit.
Traditional approach to characterize decoherence is to explore spin Relaxation
and the spin echo, which are equivalent to the studies of the spins 2nd order
time-correlator at various external conditions. Here we develop an alternative
technique by showing that considerable information about dynamics can be
obtained from direct measurements of higher than the 2nd order correlators,
which to date have been hindered in semiconductor quantum dots. We show that
such correlators are sensitive to pure quantum effects that cannot be explained
within the classical framework, and which allow direct determination of
ensemble and quantum dephasing times with only repeated projective measurements
without the need for coherent spin control. Our method enables studies of pure
quantum effects, including tests of the Leggett-Garg type inequalities that
rule out local hidden variable interpretation of the spin qubit dynamics.",1511.03684v1
2016-02-11,Spinon dynamics in quantum integrable antiferromagnets,"The excitations of the Heisenberg antiferromagnetic spin chain in zero field
are known as spinons. As pairwise-created fractionalized excitations, spinons
are important in the understanding of inelastic neutron scattering experiments
in (quasi) one-dimensional materials. In the present work, we consider the real
space-time dynamics of spinons originating from a local spin flip on the
antiferromagnetic ground state of the (an)isotropic Heisenberg spin-1/2 model
and the Babujan-Takhtajan spin-1 model. By utilizing algebraic Bethe ansatz
methods at finite system size to compute the expectation value of the local
magnetization and spin-spin correlations, spinons are visualized as propagating
domain walls in the antiferromagnetic spin ordering with anisotropy dependent
behavior. The spin-spin correlation after the spin flip displays a light cone,
satisfying the Lieb-Robinson bound for the propagation of correlations at the
spinon velocity.",1602.03745v1
2016-06-28,Spin-multipole effects in binary black holes and the test-body limit,"We discuss the effects of the black holes' spin-multipole structure in the
orbital dynamics of binary black holes according to general relativity,
focusing on the leading-post-Newtonian-order couplings at each order in an
expansion in the black holes' spins. We first review previous widely confirmed
results up through fourth order in spin, observe suggestive patterns therein,
and discuss how the results can be extrapolated to all orders in spin with
minimal information from the test-body limit. We then justify this
extrapolation by providing a complete derivation within the post-Newtonian
framework of a canonical Hamiltonian for a binary black hole, for generic
orbits and spin orientations, which encompasses the leading post-Newtonian
orders at all orders in spin. At the considered orders, the results reveal a
precise equivalence between arbitrary-mass-ratio two-spinning-black-hole
dynamics and the motion of a test black hole in a Kerr spacetime, as well as an
intriguing relationship to geodesic motion in a Kerr spacetime.",1606.08832v3
2016-07-28,Single spin probe of Many-Body Localization,"We use an external spin as a dynamical probe of many body localization. The
probe spin is coupled to an interacting and disordered environment described by
a Heisenberg spin chain in a random field. The spin-chain environment can be
tuned between a thermalizing delocalized phase and non-thermalizing localized
phase, both in its ground- and high-energy states. We study the decoherence of
the probe spin when it couples to the environment prepared in three states: the
ground state, the infinite temperature state and a high energy N\'eel state. In
the non-thermalizing many body localized regime, the coherence shows scaling
behaviour in the disorder strength. The long-time dynamics of the probe spin
shows a logarithmic dephasing in analogy with the logarithmic growth of
entanglement entropy for a bi-partition of a many-body localized system. In
summary, we show that decoherence of the probe spin provides clear signatures
of many-body localization.",1607.08617v2
2016-09-07,Cu nuclear magnetic resonance study of charge and spin stripe order in La$_{1.875}$Ba$_{0.125}$CuO$_4$,"We present a Cu nuclear magnetic/quadrupole resonance study of the charge
stripe ordered phase of LBCO, with detection of previously unobserved
('wiped-out') signal. We show that spin-spin and spin-lattice relaxation rates
are strongly enhanced in the charge ordered phase, explaining the apparent
signal decrease in earlier investigations. The enhancement is caused by
magnetic, rather than charge fluctuations, conclusively confirming the
long-suspected assumption that spin fluctuations are responsible for the
wipeout effect. Observation of the full Cu signal enables insight into the spin
and charge dynamics of the stripe-ordered phase, and measurements in external
magnetic fields provide information on the nature and suppression of spin
fluctuations associated with charge order. We find glassy spin dynamics, in
agreement with previous work, and incommensurate static charge order with
charge modulation amplitude similar to other cuprate compounds, suggesting that
the amplitude of charge stripes is universal in the cuprates.",1609.02162v1
2018-04-02,Spin torques and magnetic texture dynamics driven by the supercurrent in superconductor/ferromagnet structures,"We introduce the general formalism to describe spin torques induced by the
supercurrents injected from the adjacent superconducting electrodes into the
spin-textured ferromagnets. By considering the adiabatic limit for the
equal-spin superconducting correlations in the ferromagnet we show that the
supercurrent can generate both the field-like spin transfer torque and the
spin-orbital torque. These dissipationless spin torques are expressed through
the current-induced corrections to the effective field derived from the system
energy. The general formalism is applied to show that the supercurrent can
either shift or move the magnetic domain walls depending on their structure and
the type of spin-orbital interaction in the system. These results can be used
for the prediction and interpretation of the experiments studying magnetic
texture dynamics in superconductor/ferromagnet/superconductor Josephson
junctions and other hybrid structures.",1804.00718v2
2018-04-05,Dynamics of macrospin under periodic field and spin transfer torque,"The dynamics of a macrospin model for a single magnetic domain is
investigated in two cases: (i) under the action of a periodic magnetic field
and (ii) under the external field plus a spin transfer torque from
spin-polarized current or spin current. It has been proved that (i) without
spin transfer torque, the trajectory of magnetization (hysteresis) is always a
closed curve oscillating between two stable points and following the same path
each time; (ii) under the action of a constant field (or with small periodic
perturbation) and a constant spin transfer torque, the spin would always turn
to the stable solution finally, which is independent of the parameters or
initial conditions; (iii) considering a periodic oscillating field plus a spin
transfer torque, the system can also have a stable solution around a limit
circle, but on some special points on the attractor, the system may be
sensitive to the initial conditions and have no limit circle.",1804.01667v1
2019-05-31,Origin of Two Larmor Frequencies in the Coherent Spin Dynamics of Colloidal CdSe Quantum Dots Revealed by Controlled Charging,"Coherent spin dynamics in colloidal CdSe quantum dots (QDs) typically show
two spin components with different Larmor frequencies, whose origin is an open
question. We exploit the photocharging approach to identify their origin and
find that surface states play a key role in the appearance of the spin signals.
By controlling the photocharging with electron or hole acceptors, we show that
the specific spin component can be enhanced by the choice of acceptor type. In
core/shell CdSe/ZnS QDs, the spin signals are significantly weaker. Our results
exclude the neutral exciton as the spin origin and suggest that both Larmor
frequencies are related to the coherent spin precession of electrons in
photocharged QDs. The lower frequency is due to the electron confined in the
middle of the QD, and the higher frequency to the electron additionally
localized in the vicinity of the surface.",1905.13385v2
2016-11-15,Metastability on the hierarchical lattice,"We study metastability for Glauber spin-flip dynamics on the $N$-dimensional
hierarchical lattice with $n$ hierarchical levels. Each vertex carries an Ising
spin that can take the values $-1$ or $+1$. Spins interact with an external
magnetic field $h>0$. Pairs of spins interact with each other according to a
ferromagnetic pair potential $\vec{J}=\{J_i\}_{i=1}^n$, where $J_i>0$ is the
strength of the interaction between spins at hierarchical distance $i$. Spins
flip according to a Metropolis dynamics at inverse temperature $\beta$. In the
limit as $\beta\to\infty$, we analyse the crossover time from the metastable
state $\boxminus$ (all spins $-1$) to the stable state $\boxplus$ (all spins
$+1$). Under the assumption that $\vec{J}$ is non-increasing, we identify the
mean transition time up to a multiplicative factor $1+o_\beta(1)$. On the scale
of its mean, the transition time is exponentially distributed. We also identify
the set of configurations representing the gate for the transition. For the
special case where $J_i = \tilde{J}/N^i$, $1 \leq i \leq n$, with $\tilde{J}>0$
the relevant formulas simplify considerably. Also the hierarchical mean-field
limit $N\to\infty$ can be analysed in detail.",1611.04912v1
2017-04-10,The Spectral Periodicity of Spinon Continuum in Quantum Spin Ice,"Motivated by the rapid experimental progress of quantum spin ice materials,
we study the dynamical properties of pyrochlore spin ice in the U(1) spin
liquid phases. In particular, we focus on the spinon excitations that appear at
high energies and show up as an excitation continuum in the dynamic spin
structure factor. The keen connection between the crystal symmetry
fractionalization of the spinons and the spectral periodicity of the spinon
continuum is emphasized and explicitly demonstrated. When the spinon
experiences a background $\pi$ flux and the spinon continuum exhibits an
enhanced spectral periodicity with a folded Brillouin zone, this spectral
property can then be used to detect the spin quantum number fractionalization
and U(1) spin liquid. Our prediction can be immediately examined by inelastic
neutron scattering experiments among quantum spin ice materials with Kramers'
doublets. Further application to the non-Kramers' doublets is discussed.",1704.02734v3
2017-04-20,Dynamics of a j=3/2 quantum spin liquid,"We study a spin-orbital model for 4$d^{1}$ or 5$d^{1}$ Mott insulators in
ordered double perovskites with strong spin-orbit coupling. This model is
conveniently written in terms of pseudospin and pseudo-orbital operators
representing multipoles of the effective $j=3/2$ angular momentum. Similarities
between this model and the effective theories of Kitaev materials motivate the
proposal of a chiral spin-orbital liquid with Majorana fermion excitations. The
thermodynamic and spectroscopic properties of this quantum spin liquid are
characterized using parton mean-field theory. The heat capacity, spin-lattice
relaxation rate, and dynamic structure factor for inelastic neutron scattering
are calculated and compared with the experimental data for the spin liquid
candidate Ba$_{2}$YMoO$_{6}$. Moreover, based on a symmetry analysis, we
discuss the operators involved in resonant inelastic X-ray scattering (RIXS)
amplitudes for double perovskite compounds. In general, the RIXS cross sections
allow one to selectively probe pseudospin and pseudo-orbital degrees of
freedom. For the chiral spin-orbital liquid in particular, these cross sections
provide information about the spectrum for different flavors of Majorana
fermions.",1704.06134v3
2008-07-31,Optical probing of spin fluctuations of a single magnetic atom,"We analyzed the photoluminescence intermittency generated by a single
paramagnetic spin localized in an individual semiconductor quantum dot. The
statistics of the photons emitted by the quantum dot reflect the quantum
fluctuations of the localized spin interacting with the injected carriers.
Photon correlation measurements which are reported here reveal unique
signatures of these fluctuations. A phenomenological model is proposed to
quantitatively describe these observations, allowing a measurement of the spin
dynamics of an individual magnetic atom at zero magnetic field. These results
demonstrate the existence of an efficient spin relaxation channel arising from
a spin-exchange with individual carriers surrounding the quantum dot. A
theoretical description of a spin-flip mechanism involving spin exchange with
surrounding carriers gives relaxation times in good agreement with the measured
dynamics.",0807.5002v1
2009-12-17,Solid-State Spin-Photon Quantum Interface without Spin-Orbit Coupling,"We show that coherent optical manipulation of a single confined spin is
possible even in the absence of spin-orbit coupling. To this end, we consider
the non-Markovian dynamics of a single valence orbital hole spin that has
optically induced spin exchange coupling to a low temperature partially
polarized electron gas. We show that the fermionic nature of the reservoir
induces a coherent component to the hole spin dynamics that does not generate
entanglement with the reservoir modes. We analyze in detail the competition of
this reservoir-assisted coherent contribution with dissipative components
displaying markedly different behavior at different time scales and determine
the fidelity of optically controlled spin rotations.",0912.3378v1
2011-11-22,Spatial Analogue of Quantum Spin Dynamics via Spin-Orbit Interaction,"We map electron spin dynamics from time to space in quantum wires with
spatially uniform and oscillating Rashba spin-orbit coupling. The presence of
the spin-orbit interaction introduces pseudo-Zeeman couplings of the electron
spins to effective magnetic fields. We show that by periodically modulating the
spin-orbit coupling along the quantum wire axis, it is possible to create the
spatial analogue of spin resonance, without the need for any real magnetic
fields. The mapping of time-dependent operations onto a spatial axis suggests a
new mode for quantum information processing in which gate operations are
encoded into the band structure of the material. We describe a realization of
such materials within nanowires at the interface of LaAlO3/SrTiO3
heterostructures.",1111.5311v1
2016-08-30,Quantum speed limit time in a magnetic resonance,"A visualization for dynamics of a qudit spin vector in a time-dependent
magnetic field is realized by means of mapping a solution for a spin vector on
the three-dimensional spherical curve (vector hodograph). The obtained results
obviously display the quantum interference of precessional and nutational
effects on the spin vector in the magnetic resonance. For any spin the bottom
bounds of the quantum speed limit time (QSL) are found. It is shown that the
bottom bound goes down when using multilevel spin systems. Under certain
conditions the non-nil minimal time, which is necessary to achieve the
orthogonal state from the initial one, is attained at spin S=2. An estimation
of the product of two and three standard deviations of the spin components are
presented. We discuss the dynamics of the mutual uncertainty, conditional
uncertainty and conditional variance in terms of spin standard deviations. The
study can find practical applications in the magnetic resonance, 3D
visualization of computational data and in designing of optimized information
processing devices for quantum computation and communication.",1608.08537v3
2017-07-10,Critical spin superflow in a spinor Bose-Einstein condensate,"We investigate the critical dynamics of spin superflow in an easy-plane
antiferromagnetic spinor Bose-Einstein condensate. Spin-dipole oscillations are
induced in a trapped condensate by applying a linear magnetic field gradient
and we observe that the damping rate increases rapidly as the field gradient
increases above a certain critical value. The onset of dissipation is found to
be associated with the generation of dark-bright solitons due to the modulation
instability of the counterflow of two spin components. Spin turbulence emerges
as the solitons decay because of their snake instability. We identify another
critical point for spin superflow, in which transverse magnon excitations are
dynamically generated via spin-exchanging collisions, which leads to the
transient formation of axial polar spin domains.",1707.03054v1
2017-12-04,Phase-resolved Spin-Wave Tomography,"The propagation dynamics of spin waves are represented by their dispersion
relations. Recently, we have developed a method, called spin-wave tomography
(SWaT), to obtain dispersion relation of spin waves in the long wavelength
regime, so-called pure magnetostatic waves. In our previous studies on SWaT,
phase information of spin waves was disregarded. In this report, we demonstrate
an advanced SWaT analysis, called phase-resolved spin-wave tomography (PSWaT),
to realize the direct observation of the amplitude and the phase of spin waves.
The PSWaT spectra are obtained by separating the real and the imaginary
components of the complex Fourier transform in the SWaT analysis. We
demonstrate the PSWaT spectra of spin waves excited by the photo-induced
demagnetization in a Bi-doped garnet film, reflecting the characteristic
features of the complex dynamical susceptibility affected by magnetostatic
coupling in the film.",1712.00927v2
2019-10-17,Optical storage for 0.53 seconds in a solid-state atomic frequency comb memory using dynamical decoupling,"Quantum memories with long storage times are key elements in long-distance
quantum networks. The atomic frequency comb (AFC) memory in particular has
shown great promise to fulfill this role, having demonstrated multimode
capacity and spin-photon quantum correlations. However, the memory storage
times have so-far been limited to about one millisecond, realized in a
Eu${}^{3+}$ doped Y${}_2$SiO${}_5$ crystal at zero applied magnetic field.
Motivated by studies showing increased spin coherence times under applied
magnetic field, we developed a AFC spin-wave memory utilizing a weak 15 mT
magnetic field in a specific direction that allows efficient optical and spin
manipulation for AFC memory operations. With this field configuration the AFC
spin-wave storage time increased to 40 ms using a simple spin-echo sequence.
Furthermore, by applying dynamical decoupling techniques the spin-wave
coherence time reaches 530 ms, a 300-fold increase with respect to previous AFC
spin-wave storage experiments. This result paves the way towards long duration
storage of quantum information in solid-state ensemble memories.",1910.08009v2
2020-01-15,Low-lying level structure of $Λ$ hypernuclei and spin dependence of $ΛN$ interaction with antisymmetrized molecular dynamics,"$\Lambda N$ spin-spin and spin-orbit splittings in low-lying excitation
spectra are investigated for $p$-shell $\Lambda$ hypernuclei on the basis of
the microscopic structure calculation within the antisymmetrized molecular
dynamics, where the $\Lambda N$ $G$-matrix interaction derived from the
baryon-baryon interaction model ESC (extended soft core) is used. It is found
that the ground-state spin-parity is systematically reproduced in the $p$-shell
$\Lambda$ hypernuclei by tuning the $\Lambda N$ spin-spin and spin-orbit
interactions so as to reproduce the experimental data of $^{4}_\Lambda$H,
$^{7}_\Lambda$Li and $^9_\Lambda$Be. Furthermore, we also focus on the
excitation energies of the excited doublets as well as the energy shifts of
them by the addition of a $\Lambda$ particle.",2001.05145v1
2020-02-05,Topological spin torque emerging in classical-spin systems with different time scales,"In classical spin systems with two largely different inherent time scales,
the configuration of the fast spins almost instantaneously follows the
slow-spin dynamics. We develop the emergent effective theory for the slow-spin
degrees of freedom and demonstrate that this generally includes a topological
spin torque. This torque gives rise to anomalous real-time dynamics. It derives
from the holonomic constraints defining the fast-spin configuration space and
is given in terms of a topological charge density which becomes a quantized
homotopy invariant when integrated.",2002.01914v2
2021-01-06,Generation of spin currents by a temperature gradient in a two-terminal device,"Theoretical and experimental studies of the interaction between spins and
temperature are vital for the development of spin caloritronics, as they
dictate the design of future devices. In this work, we propose a two-terminal
cold-atom simulator to study that interaction. The proposed quantum simulator
consists of strongly interacting atoms that occupy two temperature reservoirs
connected by a one-dimensional link. First, we argue that the dynamics in the
link can be described using an inhomogeneous Heisenberg spin chain whose
couplings are defined by the local temperature. Second, we show the existence
of a spin current in a system with a temperature difference by studying the
dynamics that follows the spin-flip of an atom in the link. A temperature
gradient accelerates the impurity in one direction more than in the other,
leading to an overall spin current similar to the spin Seebeck effect.",2101.02020v2
2018-06-07,Spin accumulation and dynamics in inversion-symmetric van der Waals crystals,"Inversion symmetric materials are forbidden to show an overall spin texture
in their band structure in the presence of time-reversal symmetry. However, in
van der Waals materials which lack inversion symmetry within a single layer, it
has been proposed that a layer-dependent spin texture can arise leading to a
coupled spin-layer degree of freedom. Here we use time-resolved Kerr rotation
in inversion symmetric WSe$_{2}$ and MoSe$_{2}$ bulk crystals to study this
spin-layer polarization and unveil its dynamics. Our measurements show that the
spin-layer relaxation time in WSe$_2$ is limited by phonon-scattering at high
temperatures and that the inter-layer hopping can be tunned by a small in-plane
magnetic field at low temperatures, enhancing the relaxation rates. We find a
significantly lower lifetime for MoSe$_{2}$ which agrees with theoretical
expectations of a spin-layer polarization stabilized by the larger spin-orbit
coupling in WSe$_2$.",1806.02558v1
2018-06-28,$μ$SR study of spin freezing and persistent spin dynamics in NaCaNi$_2$F$_7$,"A new pyrochlore compound, NaCaNi$_2$F$_7$, was recently synthesized and has
a single magnetic site with spin-1 Ni$^{2+}$. We present zero field (ZF) and
longitudinal field (LF) muon spin rotation ($\mu$SR) measurements on this
pyrochlore. Density functional theory (DFT) calculations show that the most
likely muon site is located between two fluorine ions, but off-centre. A
characteristic F-$\mu$-F muon spin polarization function is observed at high
temperatures where Ni spin fluctuations are sufficiently rapid. The Ni$^{2+}$
spins undergo spin freezing into a disordered ground state below 4~K, with a
characteristic internal field strength of 140~G. Persistent Ni spin dynamics
are present to our lowest temperatures (75~mK), a feature characteristic of
many geometrically frustrated magnetic systems.",1806.10970v1
2018-07-17,Posner qubits: spin dynamics of entangled Ca$_9$(PO$_4$)$_6$ molecules and their role in neural processing,"It has been suggested that 31P nuclear spins in Ca9(PO4)6 molecules could
form the basis of a quantum mechanism for neural processing in the brain. A
fundamental requirement of this proposal is that spins in different Ca9(PO4)6
molecules can become entangled and remain so for periods (estimated at many
hours) that hugely exceed typical 31P spin relaxation times. Here, we consider
the coherent and incoherent spin dynamics of Ca9(PO4)6 arising from dipolar and
scalar spin-spin interactions and derive an upper bound of 37 min on the
entanglement lifetime under idealized physiological conditions. We argue that
the spin relaxation in Ca9(PO4)6 is likely to be much faster than this
estimate.",1807.06339v1
2019-08-26,Enhanced Superexchange in a Tilted Mott Insulator,"In an optical lattice entropy and mass transport by first-order tunneling is
much faster than spin transport via superexchange. Here we show that adding a
constant force (tilt) suppresses first-order tunneling, but not spin transport,
realizing new features for spin Hamiltonians. Suppression of the superfluid
transition can stabilize larger systems with faster spin dynamics. For the
first time in a many-body spin system, we vary superexchange rates by over a
factor of 100 and tune spin-spin interactions via the tilt. In a tilted
lattice, defects are immobile and pure spin dynamics can be studied.",1908.09870v2
2020-03-11,Excitation and relaxation dynamics of spin-waves triggered by ultrafast photo-induced demagnetization in a ferrimagnetic insulator,"Excitation and propagation dynamics of spin waves in an iron-based garnet
film under out-of-plane magnetic field were investigated by time-resolved
magneto-optical imaging. The experimental results and the following data
analysis by phase-resolved spin-wave tomography reveal the excitation of spin
waves triggered by photo-induced demagnetization (PID) along the sample depth
direction. Moreover, the fast relaxation of PID accompanied by the spin
transfer due to spin-wave emission was observed. Possible scenarios of PID in
the garnet film are discussed. Finally, we develop a model for the spin-wave
excitation triggered by PID and explain the magnetic-field dependence in the
amplitude of the observed spin waves.",2003.05159v1
2020-05-22,Signatures of a liquid-crystal transition in spin-wave excitations of skyrmions,"Understanding the spin-wave excitations of chiral magnetic order, such as the
skyrmion crystal (SkX), is of fundamental interest to confirm such exotic
magnetic order. The SkX is realized by competing Dzyaloshinskii-Moriya and
ferromagnetic-exchange interactions with a magnetic field or anisotropy. Here
we compute the dynamical spin structure factor, using Monte Carlo and spin
dynamics simulations, extracting the spin-wave spectrum in the SkX, in the
vicinity of the paramagnet to SkX transition. Inside the SkX, we find six
spin-wave modes, which are supplemented by another mode originating from the
ferromagnetic background. Above the critical temperature $T_s$ for the skyrmion
crystallization, we find a diffusive regime, reminiscent of the
liquid-to-crystal transition, revealing that topological spin texture of
skyrmionic character starts to develop above $T_s$ as the precursor of the SkX.
We discuss the opportunities for the detection of the spin waves of the SkX
using inelastic-neutron-scattering experiments in manganite-iridate
heterostructures.",2005.11399v2
2020-05-29,Microscopic Theory of the Spin Hall Magnetoresistance,"We consider a microscopic theory for the spin Hall magnetoresistance (SMR).
We generally formulate a spin conductance at an interface between a normal
metal and a magnetic insulator in terms of spin susceptibilities. We reveal
that SMR is composed of static and dynamic parts. The static part, which is
almost independent of the temperature, originates from spin flip caused by an
interfacial exchange coupling. However, the dynamic part, which is induced by
the creation or annihilation of magnons, has an opposite sign from the static
part. By the spin-wave approximation, we predict that the latter results in a
nontrivial sign change of the SMR signal at a finite temperature. In addition,
we derive the Onsager relation between spin conductance and thermal
spin-current noise.",2005.14494v3
2020-06-13,Magnetic-field-induced delocalization in hybrid electron-nuclear spin ensembles,"We use field-cycling-assisted dynamic nuclear polarization and continuous
radio-frequency (RF) driving over a broad spectral range to demonstrate
magnetic-field-dependent activation of nuclear spin transport from
strongly-hyperfine-coupled 13C sites in diamond. We interpret our observations
with the help of a theoretical framework where nuclear spin interactions are
mediated by electron spins. In particular, we build on the results from a
4-spin toy model to show how otherwise localized nuclear spins must thermalize
as they are brought in contact with a larger ancilla spin network. Further, by
probing the system response to a variable driving field amplitude, we witness
stark changes in the RF-absorption spectrum, which we interpret as partly due
to contributions from heterogeneous multi-spin sets, whose 'zero-quantum'
transitions become RF active thanks to the hybrid electron-nuclear nature of
the system. These findings could prove relevant in applications to dynamic
nuclear polarization, spin-based quantum information processing, and nanoscale
sensing.",2006.07736v2
2020-06-19,Subspace controllability of multi-partite spin networks,"In a network of spin 1/2 particles, controlled through an external
electro-magnetic field, the gyromagnetic ratio of each spin is a parameter that
characterizes the interaction of the spin with the external control field.
Multipartite networks are such that the spins are divided into subsets
according to their gyromagnetic ratio and spins in one set interact in the same
way with all spins in another set. Due to the presence of symmetries in this
type of systems, the underlying Hilbert state space splits into invariant
subspaces for the dynamics. Subspace controllability is verified if every
unitary evolution can be generated by the dynamics on these subspaces. We give
an exact characterization, in term of graph theoretic conditions, of subspace
controllability for multipartite quantum spin networks. This extends and
unifies previous results.",2006.11402v1
2021-06-03,Real-time observation of charge-spin cooperative dynamics driven by a nonequilibrium phonon environment,"Quantum dots are recognized as a suitable platform for studying thermodynamic
phenomena involving single electronic charges and spins in nano-scale devices.
However, such a thermodynamic system is usually driven by electron reservoirs
at different temperatures, not by a lattice temperature gradient. We report on
experimental observations of charge-spin cooperative dynamics in transitions of
two-electron spin states in a GaAs double quantum dot located in a
non-equilibrium phonon environment. Enhancements in the spin-flip processes are
observed, originating from phonon excitation combined with the spin-orbit
interaction. In addition, due to the spatial gradient of phonon density between
the dots, the spin-flip rate during an inter-dot electron tunnel from a hot to
a cold dot is more enhanced than in the other direction, resulting in
accumulation of parallel spin states in the double dot.",2106.01576v1
2021-07-07,Acoustic Rashba-Edelstein effect,"We theoretically study the mechanical induction of the spin density via the
Rashba spin--orbit interaction (SOI). The spin density in the linear response
to lattice distortion dynamics is calculated based on the microscopic theory.
We reveal that there are two mechanisms of spin induction: one is the acoustic
Edelstein effect (AEE) from the acceleration of the lattice dynamics and the
other is caused by the Rashba spin--vorticity coupling (RSVC). We find that the
AEE induces a more efficient spin-to-charge conversion in comparison with the
conventional electric Edelstein effect. The induced spin density due to the
RSVC is expressed as a Berry curvature-like quantity; therefore, it can be
attributed to the spatial symmetry breaking due to the Rashba SOI. Our work
demonstrates high-efficiency spin generation in Rashba systems.",2107.03115v1
2021-11-08,Nuclear spin dynamics and noise in anisotropic large box model,"We consider the central spin model in the box approximation taking into
account external magnetic field and anisotropy of the hyperfine interaction.
From the exact Hamiltonian diagonalization we obtain analytical expressions for
the nuclear spin dynamics in the limit of many nuclear spins. We predict the
nuclear spin precession in zero magnetic field for the case of anisotropic
interaction between electron and nuclear spins. We calculate and describe the
nuclear spin noise spectra in the thermodynamic equilibrium. The obtained
results can be used for the analysis of the nuclear spin induced current
fluctuations in organic semiconductors.",2111.04603v1
2021-12-19,Off-shell Supersymmetric Continuous Spin Gauge Theory,"We construct, for the first time, an off-shell supersymmetric continuous spin
gauge theory in 4-dimensional Minkowski spacetime, in both constrained and
unconstrained Lagrangian formulations. As an extension to the on-shell
description [1], we employ an auxiliary field to close the algebra of
supersymmetry transformations off-shell. The 4d $\mathcal{N}=1$ massless
continuous spin supermultiplet is then denoted by $(\mathrm{\Phi}, \mathrm{H}
\,; \mathrm{\Psi})$, comprised of a dynamical and a non-dynamical complex
scalar continuous spin gauge fields $\mathrm{\Phi}$ and $\mathrm{H}$, as well
as a Dirac continuous spin gauge field $\mathrm{\Psi}$. In particular, we
demonstrate that the off-shell continuous spin supermultiplet, in a limit,
reproduces off-shell supersymmetry transformations of the known scalar
supermultiplet $(\,{\scriptstyle 0}\,,\, {\scriptstyle 1/2}\,)$, all
integer-spin supermultiplets $(\,s\,,\, s\, {\scriptstyle +\, 1/2}\,),\,
s\geqslant1$, and all half-integer spin supermultiplets $(\, s\, {\scriptstyle
-\, 1/2}\,,\, s \,\,),\, s\geqslant1$.",2112.10178v2
2021-12-22,Surface Cooper pair spin waves in triplet superconductors,"We study the electrodynamics of spin triplet superconductors including
dipolar interactions, which give rise to an interplay between the collective
spin dynamics of the condensate and orbital Meissner screening currents. Within
this theory, we identify a class of spin waves that originate from the coupled
dynamics of the spin-symmetry breaking triplet order parameter and the
electromagnetic field. In particular, we study magnetostatic spin wave modes
that are localized to the sample surface. We show that these surface modes can
be excited and detected using experimental techniques such as microwave spin
wave resonance spectroscopy or nitrogen-vacancy magnetometry, and propose that
the detection of these modes offers a means for the identification of spin
triplet superconductivity.",2112.12146v2
2021-12-23,Nutation spin waves in ferromagnets,"Magnetization dynamics and spin waves in ferromagnets are investigated using
the inertial Landau-Lifshitz-Gilbert equation. Taking inertial magnetization
dynamics into account, dispersion relations describing the propagation of
nutation spin waves in an arbitrary direction relative to the applied magnetic
field are derived via Maxwell's equations. It is found that the inertia of
magnetization causes the hybridization of electromagnetic waves and nutation
spin waves in ferromagnets, hybrid nutation spin waves emerge, and the redshift
of frequencies of precession spin waves is initiated, which transforms to
precession-nutation spin waves. These effects depend sharply on the direction
of wave propagation relative to the applied magnetic field. Moreover, the waves
propagating parallel to the applied field are circularly polarized, while the
waves propagating perpendicular to that field are elliptically polarized. The
characteristics of these spin nutation waves are also analyzed.",2112.12503v3
2022-08-20,Unravelling the contributions to spin-lattice relaxation in Kramers single-molecule magnets,"The study of how spin interacts with lattice vibrations and relaxes to
equilibrium provides unique insights on its chemical environment and the
relation between electronic structure and molecular composition. Despite its
importance for several disciplines, ranging from magnetic resonance to quantum
technologies, a convincing interpretation of spin dynamics in crystals of
magnetic molecules is still lacking due to the challenging experimental
determination of the correct spin relaxation mechanism. We apply ab initio spin
dynamics to a series of twelve coordination complexes of Co(II) and Dy(III)
ions selected among $\sim$240 compounds that largely cover the literature on
single-molecule magnets and well represent different regimes of spin
relaxation. Simulations reveal that the Orbach spin relaxation rate of known
compounds mostly depends on the ions' zero-field splitting and little on the
details of molecular vibrations. Raman relaxation is instead found to be also
significantly affected by the features of low-energy phonons. These results
provide a complete understanding of the factors limiting spin lifetime in
single-molecule magnets and revisit years of experimental investigations by
making it possible to transparently distinguish Orbach and Raman relaxation
mechanisms.",2208.09674v1
2023-02-16,Higher Spin Gravity in $AdS_3$ and Folds on Fermi Surface,"In this paper, we introduce new sets of boundary conditions for higher spin
gravity in $AdS_3$ where the boundary dynamics of spin two and other higher
spin fields are governed by the interacting collective field theory Hamiltonian
of Avan and Jevicki. We show that the time evolution of spin two and higher
spin fields can be captured by the classical dynamics of folded fermi surfaces
in the similar spirit of Lin, Lunin and Maldacena. We also construct infinite
sequences of conserved charges showing the integrable structure of higher spin
gravity (for spin 3) under the boundary conditions we considered. Further, we
observe that there are two possible sequences of conserved charges depending on
whether the underlying boundary fermions are non-relativistic or relativistic.",2302.08471v3
2023-09-25,Fast coherent control of nitrogen-14 spins associated with nitrogen-vacancy centers in diamonds using dynamical decoupling,"A nitrogen-vacancy (NV) center in a diamond enables the access to an electron
spin, which is expected to present highly sensitive quantum sensors. Although
exploiting a nitrogen nuclear spin improves the sensitivity, manipulating it
using a resonant pulse requires a long gate time owing to its small
gyromagnetic ratio. Another technique to control nuclear spins is a conditional
rotation gate based on dynamical decoupling, which is faster but unavailable
for nitrogen spins owing to the lack of transverse hyperfine coupling with the
electron spin. In this study, we generated effective transverse coupling by
applying a weak off-axis magnetic field. An effective coupling depends on the
off-axis field; the conditional rotation gate on the nitrogen-14 spins of an NV
center was demonstrated within 4.2 {\mu}s under an 1.8% off-axis field and a
longitudinal field of approximately 280 mT. We estimated that a population
transfer from the electron to nitrogen spins can be implemented with 8.7
{\mu}s. Our method is applicable to an ensemble of NV centers, in addition to a
single NV center.",2309.14278v1
2023-09-27,Direct Sensing of Remote Nuclei: Expanding the Reach of Cross-Effect Dynamic Nuclear Polarization,"Dynamic Nuclear Polarization (DNP) has revolutionized the field of
solid-state NMR spectroscopy by significantly enhancing the sensitivity of
nuclear magnetic resonance experiments. Conventionally, cross effect DNP relies
on biradicals to transfer polarization from coupled electron spins to nearby
nuclear spins and subsequent relay to target nuclei via spin diffusion
mechanism. However, the direct transfer of polarization to distant nuclei
remains a significant challenge, limiting its applicability in various
contexts. In this work, we propose a novel biradical design concept that
involves a very strong electron-electron coupling, with a magnitude of hundreds
of MHz, which enables efficient direct polarization transfer from electron
spins to nuclear spins over much longer distances, exceeding 2.0 nm. We discuss
the potential of this tailored biradicals in scenarios where conventional spin
diffusion mechanisms are inefficient or when direct nuclear spin sensing
through electron spin interactions is desired. Our study presents a promising
avenue for expanding the scope of cross effect DNP in solid-state NMR
spectroscopy and opens new opportunities for investigating a wide range of
biological and material systems. Our research also provides insight into the
DNP buildup time of commercially available biradicals.",2309.15653v1
2023-10-18,Chiral spin textures creation and dynamics in a rectangular nanostructure,"Controlled creation of stable chiral spin textures is required to use them as
an energy-efficient information carrier in spintronics. Here we have studied
the stable creation of isolated chiral spin texture (skyrmion and antiskyrmion)
and its pair through the magnetization reversal of a rectangular nanostructure
using spin-polarized currents. An isolated spin texture is created through a
negative current pulse. Dynamics of the stable spin texture are explored under
external magnetic fields, and the resonant frequencies are calculated. A stable
skyrmion pair is created using an asymmetric current pulse, and their
interaction is studied using the Thiele equation. The stability of isolated or
paired spin texture depends on the DMI strength, spin-polarized current
density, and pulse duration. In addition, the stability of the skyrmion pair
depends on their initial separation, and a threshold for the separation between
skyrmions of 78 nm is observed.",2310.12129v1
2023-12-21,Generation of femtosecond spin-polarized current pulses at Fe/MgO interface by quasi-static voltage,"The generation of short spin-current pulses is essential for fast spintronic
devices. So far, spin current pulses are generated by femtosecond laser pulses
which drive spins from a ferromagnetic metal layer. However, the need for
miniaturization, simplicity and energy efficiency favour electric-field control
of spintronic devices over optic or thermal control. Here, we combine ab initio
calculations of electronic density of states at MgO/Fe interface with
continuous model for charge transport to investigate the dynamics of the
spin-dependent potential. We demonstrate that the voltage-driven instability of
the electronic band structure due to the electronic resonant states at the
Fe/MgO interface results in the generation of the femtosecond spin-polarized
current pulse with the spin polarization up to P=700% that propagates from the
interface to the bulk. The dynamics of the current pulses driven by the Stoner
instability depends neither on the dielectric relaxation time nor on the
details of how the instability is achieved by changing the voltage, i.e. as
long as the voltage changes are slow (quasi-static) with respect to the time
determined by the spin diffusion constant, being of the order of fs.The
presence of the instability may be detected by transport or magnetic
measurements.",2312.13698v1
2024-01-10,Narrowly avoided spin-nematic phase in BaCdVO(PO$_4$)$_2$: NMR evidence,"We present a $^{31}$P nuclear magnetic resonance (NMR) investigation of
BaCdVO(PO$_4$)$_2$ focusing on the nearly saturated regime between
$\mu_0H_{c1}$ = 4.05 T and $\mu_0H_{c2}$ = 6.5 T, used to be considered as a
promising candidate for a spin-nematic phase. NMR spectra establish the absence
of any dipolar order there, whereas the weak field dependence of the
magnetization above $H_{c1}$ is accounted for by Dzyaloshinskii-Moriya
interaction terms. The low-energy spin dynamics (fluctuations), measured by
nuclear spin-lattice relaxation rate ($T_1^{-1}$), confirms the continuity of
this phase and the absence of any low-temperature phase transition.
Unexpectedly, the spin dynamics above $H_{c1}$ is largely dominated by
two-magnon processes, which is expected above the saturation field of a
spin-nematic phase, but not inside. This shows that BaCdVO(PO$_4$)$_2$ is
indeed close to a spin-nematic instability, however, this phase is not
stabilized. We thus confirm recent theoretical predictions that the
spin-nematic phase can be stabilized, at most, in an extremely narrow field
range close to saturation or is rather narrowly avoided [Jiang et al., Phys.
Rev. Lett. 130, 116701 (2023)].",2401.05269v1
2024-03-25,Remote Cooling of Spin-ensembles Coupled to a Spin-mechanical Hybrid Interface,"We present here a protocol for the ground-state cooling of a hybrid quantum
system consisting of a spin ensemble, an oscillator, and a single probe spin.
In the weak dispersive coupling limit between the spins and the oscillator, a
back-action effect from frequent measurements of the probe spin allows
exponential cooling of the hybrid system. We identify the parameter regimes
necessary to cool the ensemble, the oscillator, or both to their thermal ground
states. Our results contribute to the development of a practical solution for
cooling/polarizing large spin ensembles. More importantly, we show that even
with weak coupling, significant changes in the dynamics of such
ensemble-oscillator hybrid systems can be achieved by manipulating a single
spin. This result provides a relatively simple means of tuning the dynamics of
a hybrid system, which might facilitate advances in many quantum technology
applications such as preparing entangled states in macroscopic objects.",2403.16839v1
2002-01-17,Hadron Spin Dynamics,"Spin effects in exclusive and inclusive reactions provide an essential new
dimension for testing QCD and unraveling hadron structure. Remarkable new
experiments from SLAC, HERMES (DESY), and the Jefferson Laboratory present many
challenges to theory, including measurements at HERMES and SMC of the single
spin asymmetries in pion electroproduction, where the proton is polarized
normal to the scattering plane. This type of single spin asymmetry may be due
to the effects of rescattering of the outgoing quark on the spectators of the
target proton, an effect usually neglected in conventional QCD analyses. Many
aspects of spin, such as single-spin asymmetries and baryon magnetic moments
are sensitive to the dynamics of hadrons at the amplitude level, rather than
probability distributions. I illustrate the novel features of spin dynamics for
relativistic systems by examining the explicit form of the light-front
wavefunctions for the two-particle Fock state of the electron in QED, thus
connecting the Schwinger anomalous magnetic moment to the spin and orbital
momentum carried by its Fock state constituents and providing a transparent
basis for understanding the structure of relativistic composite systems and
their matrix elements in hadronic physics. I also present a survey of
outstanding spin puzzles in QCD, particularly the double transverse spin
asymmetry A_{NN} in elastic proton-proton scattering, the J/psi to rho-pi
puzzle, and J/psi polarization at the Tevatron.",0201165v1
2015-02-24,Valley and spin dynamics in monolayer MoS$_{2}$,"Valleytronics targets the exploitation of the additional degrees of freedom
in materials where the energy of the carriers may assume several equal minimum
values (valleys) at non-equivalent points of the reciprocal space. In single
layers of transition metal dichalcogenides (TMDs) the lack of inversion
symmetry, combined with a large spin-orbit interaction, leads to a conduction
(valence) band with different spin-polarized minima (maxima) having equal
energies. This offers the opportunity to manipulate information at the level of
the charge (electrons or holes), spin (up or down) and crystal momentum
(valley). Any implementation of these concepts, however, needs to consider the
robustness of such degrees of freedom, which are deeply intertwined. Here we
address the spin and valley relaxation dynamics of both electrons and holes
with a combination of ultrafast optical spectroscopy techniques, and determine
the individual characteristic relaxation times of charge, spin and valley in a
MoS$_{2}$ monolayer. These results lay the foundations for understanding the
mechanisms of spin and valley polarization loss in two-dimensional TMDs:
spin/valley polarizations survive almost two-orders of magnitude longer for
holes, where spin and valley dynamics are interlocked, than for electrons,
where these degrees of freedom are decoupled. This may lead to novel approaches
for the integration of materials with large spin-orbit in robust
spintronic/valleytronic platforms.",1502.06817v1
2015-07-16,Decoherence of a single spin coupled to an interacting spin bath,"Decoherence of a central spin coupled to an interacting spin bath via
inhomogeneous Heisenberg coupling is studied by two different approaches,
namely an exact equations of motion (EOMs) method and a Chebyshev expansion
technique (CET). By assuming a wheel topology of the bath spins with uniform
nearest-neighbor $XX$-type intrabath coupling, we examine the central spin
dynamics with the bath prepared in two different types of bath initial
conditions. For fully polarized baths in strong magnetic fields, the
polarization dynamics of the central spin exhibits a collapse-revival behavior
in the intermediate-time regime. Under an antiferromagnetic bath initial
condition, the two methods give excellently consistent central spin decoherence
dynamics for finite-size baths of $N\leq14$ bath spins. The decoherence factor
is found to drop off abruptly on a short time scale and approach a finite
plateau value which depends on the intrabath coupling strength
non-monotonically. In the ultrastrong intrabath coupling regime, the plateau
values show an oscillatory behavior depending on whether $N/2$ is even or odd.
The observed results are interpreted qualitatively within the framework of the
EOM and perturbation analysis. The effects of anisotropic spin-bath coupling
and inhomogeneous intrabath bath couplings are briefly discussed. Possible
experimental realization of the model in a modified quantum corral setup is
suggested.",1507.04514v2
2016-11-22,Gravitational waves and mass ejecta from binary neutron star mergers: Effect of the stars' rotation,"We present new (3+1) dimensional numerical relativity simulations of the
binary neutron star (BNS) mergers that take into account the NS spins. We
consider different spin configurations, aligned or antialigned to the orbital
angular momentum, for equal and unequal mass BNS and for two equations of
state. All the simulations employ quasiequilibrium circular initial data in the
constant rotational velocity approach, i.e. they are consistent with Einstein
equations and in hydrodynamical equilibrium. We study the NS rotation effect on
the energetics, the gravitational waves (GWs) and on the possible
electromagnetic (EM) emission associated to dynamical mass ejecta. For
dimensionless spin magnitudes of $\chi\sim0.1$ we find that spin-orbit
interactions and also spin-induced-quadrupole deformations affect the
late-inspiral-merger dynamics. The latter is, however, dominated by finite-size
effects. Spin (tidal) effects contribute to GW phase differences up to 5 (20)
radians accumulated during the last eight orbits to merger. Similarly, after
merger the collapse time of the remnant and the GW spectrogram are affected by
the NSs rotation. Spin effects in dynamical ejecta are clearly observed in
unequal mass systems in which mass ejection originates from the tidal tail of
the companion. Consequently kilonovae and other EM counterparts are affected by
spins. We find that spin aligned to the orbital angular momentum leads to
brighter EM counterparts than antialigned spin with luminosities up to a factor
of two higher.",1611.07367v1
2014-05-29,Dynamical spin response in cuprate superconductors from low-energy to high-energy,"Within the framework of the kinetic energy driven superconducting mechanism,
the dynamical spin response of cuprate superconductors is studied from
low-energy to high-energy. The spin self-energy is evaluated explicitly in
terms of the collective charge carrier modes in the particle-hole and
particle-particle channels, and employed to calculate the dynamical spin
structure factor. Our results show the existence of damped but well-defined
dispersive spin excitations in the whole doping phase diagram. In particular,
the low-energy spin excitations in the superconducting-state have an
hour-glass-shaped dispersion, with commensurate resonance that appears in the
superconducting-state only, while the low-energy incommensurate spin
fluctuations can persist into the normal-state. The high-energy spin
excitations in the superconducting-state on the other hand retain roughly
constant energy as a function of doping, with spectral weights and dispersion
relations comparable to those in the corresponding normal-state. The theory
also shows that the unusual magnetic correlations in cuprate superconductors
can be ascribed purely to the spin self-energy effects which arise directly
from the charge carrier-spin interaction in the kinetic energy of the system.",1405.7448v2
2019-03-18,Anomalous spin diffusion in one-dimensional antiferromagnets,"The problem of characterizing low-temperature spin dynamics in
antiferromagnetic spin chains has so far remained elusive. We reinvestigate it
by focusing on isotropic antiferromagnetic chains whose low-energy effective
field theory is governed by the quantum non-linear sigma model. We outline an
exact non-perturbative theoretical approach to analyse the low-temperature
behaviour in the vicinity of non-magnetized states, and obtain explicit
expressions for the spin diffusion constant and the NMR relaxation rate, which
we compare with previous theoretical results in the literature. Surprisingly,
in SU(2)-invariant spin chains in the vicinity of half-filling we find a
crossover from the semi-classical regime to a strongly interacting quantum
regime characterized by zero spin Drude weight and diverging spin conductivity,
indicating super-diffusive spin dynamics. The dynamical exponent of spin
fluctuations is argued to belong to the Kardar-Parisi-Zhang universality class.
Furthermore, by employing numerical tDMRG simulations, we find robust evidence
that the anomalous spin transport persists also at high temperatures,
irrespectively of the spectral gap and integrability of the model.",1903.07598v3
2021-06-18,Inelastic spin-wave beam scattering by edge-localized spin waves in ferromagnetic thin film,"Spin waves are promising chargeless information carriers for the future,
energetically efficient beyond-CMOS systems. Among many advantages there are
the ease of achieving nonlinearity, the variety of possible interactions, and
excitation types. Although the rapidly developing magnonic research has already
yielded impressive realizations, multi-mode nonlinear effects, particularly
with the propagating waves and their nanoscale realizations, are still an open
research problem. We study theoretically the dynamic interactions of the spin
waves confined to the edge of a thin ferromagnetic film with the spin-wave beam
incident at this edge. We found the inelastically scattered spin-wave beams at
frequencies increased and decreased by the frequency of the edge spin-wave
relative to the specularly reflected beam. We observed a strong dependence of
the angular shift of the inelastic scattered spin-wave beam on the edge-mode
frequency, which allowed us to propose a magnonic demultiplexing of the signal
encoded in spin waves propagating along the edge. Since dynamic magnetostatic
interactions, which are ubiquitous in the spin-wave dynamics, are decisive in
this process, this indicates the possibility of implementing the presented
effects, also in other configurations and their use in magnonic systems.",2106.09954v3
2022-12-08,Integrability and quench dynamics in the spin-1 central spin XX model,"Central spin models provide an idealized description of interactions between
a central degree of freedom and a mesoscopic environment of surrounding spins.
We show that the family of models with a spin-1 at the center and XX
interactions of arbitrary strength with surrounding spins is integrable.
Specifically, we derive an extensive set of conserved quantities and obtain the
exact eigenstates using the Bethe ansatz. As in the homogenous limit, the
states divide into two exponentially large classes: bright states, in which the
spin-1 is entangled with its surroundings, and dark states, in which it is not.
On resonance, the bright states further break up into two classes depending on
their weight on states with central spin polarization zero. These classes are
probed in quench dynamics wherein they prevent the central spin from reaching
thermal equilibrium. In the single spin-flip sector we explicitly construct the
bright states and show that the central spin exhibits oscillatory dynamics as a
consequence of the semilocalization of these eigenstates. We relate the
integrability to the closely related class of integrable Richardson-Gaudin
models, and conjecture that the spin-$s$ central spin XX model is integrable
for any $s$.",2212.04477v4
2003-06-10,Muon-spin-relaxation and magnetic-susceptibility studies of the effects of nonmagnetic impurities on the Cu-spin dynamics and superconductivity in La_2-x_Sr_x_Cu_1-y_Zn_y_O_4_ around x = 0.115,"Zero-field muon-spin-relaxation (muSR) and magnetic-susceptibility
measurements have been carried out in La_2-x_Sr_x_Cu_1-y_Zn_y_O_4_ with x =
0.10, 0.115 and 0.13 changing the Zn-concentration y finely up to 0.10, with
the aim to clarify effects of the nonmagnetic impurity Zn on the Cu-spin
dynamics and superconductivity. The muSR measurements have revealed that, in
each x, a magnetic order of Cu spins is observed at y ~ 0.0075, while it
disappears and Cu spins turn into a fast fluctuating state for y > 0.03. From
the magnetic-susceptibility measurements, on the other hand, it has been found
that the volume fraction of the superconducting state rapidly decreases through
the slight doping of Zn and that its y dependence corresponds to the y
dependence of the volume fraction of the fast fluctuating region of Cu spins
estimated from the muSR results. Both the rapid decrease of the volume fraction
of the superconducting state and the formation of the magnetic order through
the slight doping of Zn can be interpreted in terms of the development of the
so-called ""Swiss cheese"" model. That is, it is concluded that Cu spins in a
non-superconducting region around Zn exhibit slowing-down of the fluctuations
or form an incoherent or coherent static magnetic order. Moreover, the
formation of a non-superconducting region around Zn is considered to be due to
the pinning of the dynamical spin correlation or dynamical stripe correlations.",0306233v2
2012-09-27,"Magnetic order, magnetic correlations and spin dynamics in the pyrochlore antiferromagnet Er2Ti2O7","Er2Ti2O7 is believed to be a realization of an XY antiferromagnet on a
frustrated lattice of corner-sharing regular tetrahedra. It is presented as an
example of the order-by-disorder mechanism in which fluctuations lift the
degeneracy of the ground state, leading to an ordered state. Here we report
detailed measurements of the low temperature magnetic properties of Er2Ti2O7,
which displays a second-order phase transition at T_N \simeq 1.2 K with
coexisting short- and long-range orders. Magnetic-susceptibility studies show
that there is no spin-glass-like irreversible effect. Heat-capacity
measurements reveal that the paramagnetic critical exponent is typical of a
3-dimensional XY magnet while the low-temperature specific heat sets an upper
limit on the possible spin-gap value and provides an estimate for the spin-wave
velocity. Muon spin relaxation measurements show the presence of spin dynamics
in the nanosecond time scale down to 21 mK. This time range is intermediate
between the shorter time characterizing the spin dynamics in Tb2Sn2O7, which
also displays long- and short-range magnetic order, and the time scale typical
of conventional magnets. Hence the ground state is characterized by exotic spin
dynamics. We determine the parameters of a symmetry-dictated Hamiltonian
restricted to the spins in a tetrahedron, by fitting the paramagnetic diffuse
neutron scattering intensity for two reciprocal lattice planes. These data are
recorded in a temperature region where the assumption that the correlations are
limited to nearest neighbors is fair.",1209.6153v1
2014-07-02,Spin Waves in Ferromagnetic Insulators Coupled via a Normal Metal,"Herein, we study the spin-wave dispersion and dissipation in a ferromagnetic
insulator--normal metal--ferromagnetic insulator system. Long-range dynamic
coupling because of spin pumping and spin transfer lead to collective magnetic
excitations in the two thin-film ferromagnets. In addition, the dynamic dipolar
field contributes to the interlayer coupling. By solving the
Landau-Lifshitz-Gilbert-Slonczewski equation for macrospin excitations and the
exchange-dipole volume as well as surface spin waves, we compute the effect of
the dynamic coupling on the resonance frequencies and linewidths of the various
modes. The long-wavelength modes may couple acoustically or optically. In the
absence of spin-memory loss in the normal metal, the spin-pumping-induced
Gilbert damping enhancement of the acoustic mode vanishes, whereas the optical
mode acquires a significant Gilbert damping enhancement, comparable to that of
a system attached to a perfect spin sink. The dynamic coupling is reduced for
short-wavelength spin waves, and there is no synchronization. For intermediate
wavelengths, the coupling can be increased by the dipolar field such that the
modes in the two ferromagnetic insulators can couple despite possible small
frequency asymmetries. The surface waves induced by an easy-axis surface
anisotropy exhibit much greater Gilbert damping enhancement. These modes also
may acoustically or optically couple, but they are unaffected by thickness
asymmetries.",1407.0635v1
2018-08-01,Spin fluctuations in the light-induced high spin state of Cobalt valence tautomers,"We present a study of the static magnetic properties and spin dynamics in
Cobalt valence tautomers (VT), molecules where a low-spin (LS) to high-spin
(HS) crossover driven by an intramolecular electron transfer can be controlled
by the temperature, by the external pressure or by light irradiation. In the
investigated complex, a LS-Co(III) ion bound to a dinegative organic ligand can
be reversibly converted into the HS-Co(II) bound to a mononegative one. By
combining magnetization measurements with Nuclear Magnetic Resonance (NMR) and
Muon Spin Relaxation ({\mu}SR), we have investigated the static magnetic
properties and the spin dynamics as a function of the temperature. Moreover,
the effect of the external pressure as well as of the infrared light
irradiation have been explored through magnetometry and NMR measurements to
determine the spin dynamics of the HS state. The photoinduced HS state, which
can have a lifetime of several hours below 30 K, is characterized by spin
dynamics in the MHz range, which persist at least down to 10 K. The application
of an external pressure causes a progressive increase of the LS-HS crossover,
which reaches room temperature for pressures around 10 kbar.",1808.04229v1
2018-12-26,Discretized dynamics of exchange spin wave bulk and edge modes in honeycomb nanoribbons with armchair edge boundaries,"We develop a field theory to study the dynamics of long wavelength exchange
spin wave excitations on honeycomb nanoribbons characterized by armchair edge
boundaries and the N\'eel antiferromagnetic ordering state. Appropriate
boundary conditions are established by requiring that the bulk and edge spins
precess with the same frequency for any given spin wave eigenmode in these
systems. A set of characteristic boundary equations, common for bulk and edge
spin wave modes, are hence derived. The equations of motion for the spin
dynamics are then solved to determine the propagating and evanescent exchange
spin wave modes. We prove in general that the bulk spin wave dynamics is
discretized due to the finite width of the nanoribbon. For an isotropic
magnetic nanoribbon, the Dirac cone is reduced to a single linear dispersion
curve due to this discretization. The number and wavelengths of allowed bulk
modes for isotropic and anisotropic nanoribbons are determined from the derived
characteristic boundary equations. As witnessed by our numerical results for
different examples it is shown that the characteristics of these modes depend
on the width of the nanoribbon and its antiferromagnetic anisotropy. Further,
anisotropic nanoribbons, even those with the slightest anisotropy, present
evanescent modes with non-linear dispersion relations. The spatial variation of
the amplitudes of the evanescent exchange spin waves across the finite widths
of the nanoribbons, is found to be strongly dependent on the system magnetic
anisotropy and its width. The developed theoretical approach is general and can
be applied for nanoribbons with all types of boundary edges.",1812.10204v2
2022-05-06,Mapping the energy-time landscape of spins with helical X-rays,"Unveiling the key mechanisms that determine optically driven spin dynamics is
essential both to probe the fundamental nature of ultrafast light-matter
interactions, but also to drive future technologies of smaller, faster, and
more energy efficient devices. Essential to this task is the ability to use
experimental spectroscopic tools to evidence the underlying energy- and
spin-resolved dynamics of non-equilibrium electron occupations. In this joint
theory and experimental work, we demonstrate that ultrafast helicity-dependent
soft X-ray absorption spectroscopy (HXAS) allows access to spin-, time- and
energy specific state occupation after optical excitation. We apply this method
to the prototype transition metal ferromagnet cobalt and find convincing
agreement between theory and experiment. The richly structured energy-resolved
spin dynamics unveil the subtle interplay and characteristic time scales of
optical excitation and spin-orbit induced spin-flip transitions in this
material: the spin moment integrated in an energy window below the Fermi level
first exhibits an ultrafast increase as minority carriers are excited by the
laser pulse, before it is reduced as spin-flip process in highly localized, low
energy states start to dominate. The results of this study demonstrate the
power of element specific transient HXAS, placing it as a potential new tool
for identifying and determining the role of fundamental processes in optically
driven spin dynamics in magnetic materials.",2205.03172v1
2003-06-30,Multiple-Quantum Spin Dynamics of Entanglement,"Dynamics of entanglement is investigated on the basis of exactly solvable
models of multiple-quantum (MQ) NMR spin dynamics. It is shown that the time
evolution of MQ coherences of systems of coupled nuclear spins in solids is
directly connected with dynamics of the quantum entanglement. We studied
analytically dynamics of entangled states for two- and three-spin systems
coupled by the dipole-dipole interaction. In this case dynamics of the quantum
entanglement is uniquely determined by the time evolution of MQ coherences of
the second order. The real part of the density matrix describing MQ dynamics in
solids is responsible for MQ coherences of the zeroth order while its imaginary
part is responsible for the second order. Thus, one can conclude that dynamics
of the entanglement is connected with transitions from the real part of the
density matrix to the imaginary one and vice versa. A pure state which
generalizes the GHZ and W states is found. Different measures of the
entanglement of this state are analyzed for three-partite systems.",0306204v1
2012-08-02,Unified theory of spin-dynamics in a two dimensional electron gases with arbitrary spin-orbit coping strength at finite temperature,"We study the spin dynamics in the presence of impurity and electron-electron
(e-e) scattering in a III-V semiconductor quantum well with arbitrary
spin-orbit coupling (SOC) strength and symmetry at finite temperature. We
derive the coupled spin-charge dynamic equations in the presence of inelastic
scattering and provide a new formalism that describes the spin relaxation and
dynamics in both the weak and the strong SOC regime in a unified way. In the
weak SOC regime, as expected, our theory reproduces all previous
zero-temperature results, most of which have focused on impurity-scattering
induced spin-charge dynamics. In the regime where the strength of the Rashba
and linear Dresselhaus SOC match, known as the SU(2) symmetry point,
experiments have observed the spin-helix mode with a large spin-lifetime whose
unexplained non-monotonic temperature dependence peaks at around 75 K. As a key
test of our theory, we are able to naturally explain quantitatively this
non-monotonic dependence and show that it arises as a competition between the
Dyakonov-Perel mechanism, suppressed at the SU(2) point, and the Elliott-Yafet
mechanism. In the strong SOC regime, we show that our theory directly
reproduces the only previous known analytical result at the SU(2) symmetry
point in the ballistic regime. It also explains, as we have shown previously,
the rise of damped oscillating dynamics when the electron scattering time is
larger than half of the spin precession time due to the SOC. Hence, we provide
a unified theory of the spin-dynamics in two dimensional electron gases in the
full phase diagram experimentally accessible.",1208.0379v2
2003-11-29,Quantum Dynamical Entropy of Spin Systems,"We investigate a quantum dynamical entropy of one-dimesional quantum spin
systems. We show that the dynamical entropy is bounded from above by a quantity
which is related with group velocity determined by the interaction and mean
entropy of the state.",0312002v2
2009-09-10,Hydrodynamic Limit for the Spin Dynamics of the Heisenberg Chain,"We show that Quantum-Monte-Carlo calculations of the dynamic structure factor
of the isotropic spin-1/2 antiferromagnetic chain at intermediate temperatures
corroborate a picture of diffusive spin dynamics at finite frequencies in the
low-energy long wave-length limit and are in good agreement with recent
predictions for this by J. Sirker, R. G. Pereira, and I. Affleck
[arXiv:0906.1978v1].",0909.1972v1
2009-09-30,Low energy dynamics of spinor condensates,"We present a derivation of the low energy Lagrangian governing the dynamics
of the spin degrees of freedom in a spinor Bose condensate, for any phase in
which the average magnetization vanishes. This includes all phases found within
mean-field treatments except for the ferromagnet, for which the low energy
dynamics has been discussed previously. The Lagrangian takes the form of a
sigma model for the rotation matrix describing the local orientation of the
spin state of the gas.",0909.5620v1
2014-07-31,On gliding Lagrange top equations and their asymptotic behaviour,"The dynamical equations for a gliding Lagrange top are not integrable. They
have 5 dynamical variables and admit one integral of motion. We show that all
solutions go to one of the two vertical spinning solutions and determine
conditions of their stability. This means that solutions starting close to
either of the spinning solutions go asymptotically to this solution.",1407.8514v1
2014-08-27,On the Dynamics of XY Spin Chains with Impurities,"We provide a theoretical set up for studying the dynamics in quantum spin
chain models with inhomogeneous two-body interaction. We frame in our formalism
models that can be mapped into a fermion system with a quadratic Hamiltonian.
Local and global existence results of the dynamics are discussed.",1408.6338v2
1999-01-07,^{139}La Spectrum and Spin-Lattice Relaxation Measurements of La_{2/3}Ca_{1/3}MnO_3 in the Paramagnetic State,"^{139}La NMR measurements of La_{2/3}Ca_{1/3}MnO_3 performed in the
paramagnetic state and high magnetic fields are reported. Analysis of the high
temperature spectrum measured establishes that the spectrum it is a standard
powder pattern broadened by a variation in lattice distortions. At lower
temperatures, the spectrum shifts and broadens. Both the shift and broadening
exhibit Curie-Weiss behavior, indicating that the shift measures the
polarization of the electron spin system, and the broadening reflects a
distribution of magnetic susceptibilities. This distribution may result from
variations of local susceptibility in the bulk of the sample or from
differences in demagnetizing factors among powder grains. The spectrum also
indicates that the lattice distortions do not change as the temperature lowers.
Spectral diffusion measurements suggest that the temperature dependence of the
spectrum shape does not result from freezing out of motion of magnetic
polarons. Variation of the nuclear spin-lattice relaxation across the spectrum
indicate that magnetic fluctuations, not lattice vibrations, dominate nuclear
relaxation. Nuclear spin-lattice relaxation therefore measures electron spin
dynamics in this system. The magnetic field dependence of the spin-lattice
relaxation indicates that the electron spin-spin correlation function adopts
simple single exponential behavior with a slow field-independent correlation
time of 10^{-8} seconds near Tc. The spin-spin correlation function changes
form at higher temperatures, but remains slow. The spin-lattice relaxation
therefore indicates the presence of extremely slow dynamics above Tc.",9901048v1
2000-02-16,Theoretical Perspectives on Spintronics and Spin-Polarized Transport,"Selected problems of fundamental importance for spintronics and
spin-polarized transport are reviewed, some of them with a special emphasis on
their applications in quantum computing and coherent control of quantum
dynamics. The role of the solid-state environment in the decoherence of
electron spins is discussed. In particular, the limiting effect of the
spin-orbit interaction on spin relaxation of conduction electrons is carefully
examined in the light of recent theoretical and experimental progress. Most of
the proposed spintronic devices involve spin-polarized transport across
interfaces in various hybrid structures. The specific example discussed here,
of a magnetic semiconductor/superconductor interface, displays many intricacies
which a complex spin-dependent interface introduces in the spin-polarized
transport. It is proposed that pairs of entangled electrons in a superconductor
(Cooper pairs) can be transfered to a non-superconducting region, and
consequently separated for a transport study of the spin entanglement. Several
important theoretical proposals for quantum computing are based on electronic
and nuclear spin entanglement in a solid. Physical requirements for these
proposals to be useful are discussed and some alternative views are presented.
Finally, a recent discovery of optical control of nuclear spins in
semiconductors is reviewed and placed in the context of a long-standing search
for electronic control of nuclear dynamics.",0002256v1
2005-04-08,"CP^1+U(1) Lattice Gauge Theory in Three Dimensions: Phase Structure, Spins, Gauge Bosons, and Instantons","In this paper we study a 3D lattice spin model of CP$^1$ Schwinger-bosons
coupled with dynamical compact U(1) gauge bosons. The model contains two
parameters; the gauge coupling and the hopping parameter of CP$^1$ bosons. At
large (weak) gauge couplings, the model reduces to the classical O(3) (O(4))
spin model with long-range and/or multi-spin interactions. It is also closely
related to the recently proposed ""Ginzburg-Landau"" theory for quantum phase
transitions of $s=1/2$ quantum spin systems on a 2D square lattice at zero
temperature. We numerically study the phase structure of the model by
calculating specific heat, spin correlations, instanton density, and
gauge-boson mass. The model has two phases separated by a critical line of
second-order phase transition; O(3) spin-ordered phase and spin-disordered
phase. The spin-ordered phase is the Higgs phase of U(1) gauge dynamics,
whereas the disordered phase is the confinement phase. We find a crossover in
the confinement phase which separates dense and dilute regions of instantons.
On the critical line, spin excitations are gapless, but the gauge-boson mass is
{\it nonvanishing}. This indicates that a confinement phase is realized on the
critical line. To confirm this point, we also study the noncompact version of
the model. A possible realization of a deconfinement phase on the criticality
is discussed for the CP$^N$+U(1) model with larger $N$.",0504193v3
2001-05-17,Universal Lax pairs for Spin Calogero-Moser Models and Spin Exchange Models,"For any root system $\Delta$ and an irreducible representation ${\cal R}$ of
the reflection (Weyl) group $G_\Delta$ generated by $\Delta$, a {\em spin
Calogero-Moser model} can be defined for each of the potentials: rational,
hyperbolic, trigonometric and elliptic. For each member $\mu$ of ${\cal R}$, to
be called a ""site"", we associate a vector space ${\bf V}_{\mu}$ whose element
is called a ""spin"". Its dynamical variables are the canonical coordinates
$\{q_j,p_j\}$ of a particle in ${\bf R}^r$, ($r=$ rank of $\Delta$), and spin
exchange operators $\{\hat{\cal P}_\rho\}$ ($\rho\in\Delta$) which exchange the
spins at the sites $\mu$ and $s_{\rho}(\mu)$. Here $s_\rho$ is the reflection
generated by $\rho$. For each $\Delta$ and ${\cal R}$ a {\em spin exchange
model} can be defined. The Hamiltonian of a spin exchange model is a linear
combination of the spin exchange operators only. It is obtained by ""freezing""
the canonical variables at the equilibrium point of the corresponding classical
Calogero-Moser model. For $\Delta=A_r$ and ${\cal R}=$ vector representation it
reduces to the well-known Haldane-Shastry model. Universal Lax pair operators
for both spin Calogero-Moser models and spin exchange models are presented
which enable us to construct as many conserved quantities as the number of
sites for {\em degenerate} potentials.",0105164v1
2008-02-09,Spin dynamics near the critical doping in weakly-superconducting underdoped YBa2Cu3O6.35 (Tc=18K),"Using neutron scattering we have determined the magnetic structure and
fluctuations in the YBa2Cu3O6.35 superconductor (Tc=18 K). The long-range
ordered collinear spins of the insulating antiferromagnet are replaced by a
commensurate central mode arising from slow, isotropically polarized,
short-range spin correlations. The inelastic spectrum up to 30 meV is broad in
wave vector and commensurate. In contrast to the the resonance peak of higher
Tc superconductors, the spins exhibit a single overdamped spectrum whose rate
of relaxation decreases on cooling and saturates at 5 meV below 50 K. As the
relaxation rate saturates the quasi-static spin correlations grow and become
resolution limited in energy. The spin susceptibility at high temperatures
illustrates that the dominant energy scale is set by the temperature. At low
temperatures, the scale length is geometric and not linked by velocity to
dynamic widths. There is no observable suppression of the spin fluctuations or
central mode upon the onset of superconductivity. The spins respond not to
coherent charge pairs but to hole doping allowing coexistence of glassy short
range spin order with superconductivity. Since the physics of the weakly
superconducting system YBCO6.35 must connect continuously with that in more
strongly superconducting YBCO6.5, we find that neither incommensurate
stripe-like spin modulations nor a well-defined neutron spin resonance are
essential for the onset with doping of pairing in a high temperature cuprate
superconductor.",0802.1252v1
2008-10-10,Junctions of Spin-Incoherent Luttinger Liquids with Ferromagnets and Superconductors,"We discuss the properties of a strongly interacting spin-charge separated one
dimensional system coupled to ferromagnets and/or superconductors. Our results
are valid for arbitrary temperatures with respect to the spin energy, but
require temperature be small compared to the charge energy. We focus mainly on
the spin-incoherent regime where temperature is large compared to the spin
energy, but small compared to the charge energy. In the case of a ferromagnet
we study spin pumping and the renormalized dynamics of a precessing magnetic
order parameter. We find the interaction-dependent temperature dependence of
the spin pumping can be qualitatively different in the spin-incoherent regime
from the Luttinger liquid regime, allowing an identification of the former.
Likewise, the temperature dependence of the renormlized magnetization dynamics
can be used to identify spin-incoherent physics. For the case of a
spin-incoherent Luttinger liquid coupled to two superconductors, we compute the
ac and dc Josephson current for a wire geometry in the limit of tunnel coupled
superconductors. Both the ac and dc response contain ""smoking gun"" signatures
that can be used to identify spin-incoherent behavior. Experimental
requirements for the observation of these effects are laid out.",0810.1788v1
2008-11-05,Spin dynamics in high-mobility two-dimensional electron systems,"Understanding the spin dynamics in semiconductor heterostructures is highly
important for future semiconductor spintronic devices. In high-mobility
two-dimensional electron systems (2DES), the spin lifetime strongly depends on
the initial degree of spin polarization due to the electron-electron
interaction. The Hartree-Fock (HF) term of the Coulomb interaction acts like an
effective out-of-plane magnetic field and thus reduces the spin-flip rate. By
time-resolved Faraday rotation (TRFR) techniques, we demonstrate that the spin
lifetime is increased by an order of magnitude as the initial spin polarization
degree is raised from the low-polarization limit to several percent. We perform
control experiments to decouple the excitation density in the sample from the
spin polarization degree and investigate the interplay of the internal HF field
and an external perpendicular magnetic field. The lifetime of spins oriented in
the plane of a [001]-grown 2DES is strongly anisotropic if the Rashba and
Dresselhaus spin-orbit fields are of the same order of magnitude. This
anisotropy, which stems from the interference of the Rashba and the Dresselhaus
spin-orbit fields, is highly density-dependent: as the electron density is
increased, the kubic Dresselhaus term becomes dominant and reduces the
anisotropy.",0811.0720v1
2010-04-28,Bar-mode instability of rapidly spinning black hole in higher dimensions: Numerical simulation in general relativity,"Numerical-relativity simulation is performed for rapidly spinning black holes
(BHs) in a higher-dimensional spacetime of special symmetries for the
dimensionality $6 \leq d \leq 8$. We find that higher-dimensional BHs, spinning
rapidly enough, are dynamically unstable against nonaxisymmetric bar-mode
deformation and spontaneously emit gravitational waves, irrespective of $d$ as
in the case $d=5$ \cite{SY09}. The critical values of a nondimensional spin
parameter for the onset of the instability are $q:=a/\mu^{1/(d-3)} \approx
0.74$ for $d=6$, $\approx 0.73$ for $d=7$, and $\approx 0.77$ for $d=8$ where
$\mu$ and $a$ are mass and spin parameters. Black holes with a spin smaller
than these critical values ($q_{\rm crit}$) appear to be dynamically stable for
any perturbation. Longterm simulations for the unstable BHs are also performed
for $d=6$ and 7. We find that they spin down as a result of gravitational-wave
emission and subsequently settle to a stable stationary BH of a spin smaller
than $q_{\rm crit}$. For more rapidly spinning unstable BHs, the timescale, for
which the new state is reached, is shorter and fraction of the spin-down is
larger. Our findings imply that a highly rapidly spinning BH with $q > q_{\rm
crit}$ cannot be a stationary product in the particle accelerators, even if it
would be formed as a consequence of a TeV-gravity hypothesis. Its implications
for the phenomenology of a mini BH are discussed.",1004.4970v1
2011-05-06,Decoherence-assisted initialization of a resident hole spin polarization in a two-dimensional hole gas,"We investigate spin dynamics of resident holes in a p-modulation-doped
GaAs/Al$_{0.3}$Ga$_{0.7}$As single quantum well. Time-resolved Faraday and Kerr
rotation, as well as resonant spin amplification, are utilized in our study. We
observe that nonresonant or high power optical pumping leads to a resident hole
spin polarization with opposite sign with respect to the optically oriented
carriers, while low power resonant optical pumping only leads to a resident
hole spin polarization if a sufficient in-plane magnetic field is applied. The
competition between two different processes of spin orientation strongly
modifies the shape of resonant spin amplification traces. Calculations of the
spin dynamics in the electron--hole system are in good agreement with the
experimental Kerr rotation and resonant spin amplification traces and allow us
to determine the hole spin polarization within the sample after optical
orientation, as well as to extract quantitative information about spin
dephasing processes at various stages of the evolution.",1105.1338v2
2021-01-29,Comparison of Spin-Wave Modes in Connected and Disconnected Artificial Spin Ice Nanostructures Using Brillouin Light Scattering Spectroscopy,"Artificial spin ice systems have seen burgeoning interest due to their
intriguing physics and potential applications in reprogrammable memory, logic
and magnonics. Integration of artificial spin ice with functional magnonics is
a relatively recent research direction, with a host of promising results. As
the field progresses, direct in-depth comparisons of distinct artificial spin
systems are crucial to advancing the field. While studies have investigated the
effects of different lattice geometries, little comparison exists between
systems comprising continuously connected nanostructures, where spin-waves
propagate via dipole-exchange interaction, and systems with nanobars
disconnected at vertices where spin-wave propagation occurs via stray
dipolar-field. Gaining understanding of how these very different coupling
methods affect both spin-wave dynamics and magnetic reversal is key for the
field to progress and provides crucial system-design information including for
future systems containing combinations of connected and disconnected elements.
Here, we study the magnonic response of two kagome spin ices via Brillouin
light scattering, a continuously connected system and a disconnected system
with vertex gaps. We observe distinct high-frequency dynamics and magnetization
reversal regimes between the systems, with key distinctions in spin-wave
localization and mode quantization, microstate-trajectory during reversal and
internal field-profiles. These observations are pertinent for the fundamental
understanding of artificial spin systems and broader design and engineering of
reconfigurable functional magnonic crystals.",2101.12619v2
2018-06-19,Spin-Precessing Black Hole Binaries in Dynamical Chern-Simons Gravity,"Gravitational waves from spin-precessing binaries exhibit amplitude
oscillations that provide an invaluable method to extract the spins of the
inspiraling compact objects. The spin-spin and spin-orbit interactions that
cause this effect are sensitive to the fundamental nature of gravity, which
will allow us to constrain modified theories of gravity using gravitational
wave observations of precessing binaries. We here consider precessing black
hole binaries in dynamical Chern-Simons gravity, an effective theory of gravity
that enhances parity violating interactions. We model the black holes as
modified point particles using effective field theory, and derive the
spin-precession equations for a binary system by working within the
post-Newtonian formalism. We find that the spin-spin and quadrupole-monopole
interactions of General Relativity are modified due to an interaction between
the scalar dipoles of the two black holes and the modified black hole
quadrupole as a result of the violation of the no hair theorems. These
modifications enter the precession equations at leading post-Newtonian order.
We further show that these precession equations admit seven constants of motion
when neglecting radiation reaction, with only the mass-weighted effective spin
being modified from General Relativity. We discuss how these may be used to
reduce the precession equations to quadrature and the possibility of
constructing analytic Fourier domain waveforms for generic spin-precessing
binaries in dCS gravity.",1806.07431v2
2019-01-15,Spin backflow: a non-Markovian effect on spin pumping,"The miniaturization of spintronic devices, specifically, nanoscale devices
employing spintronics, has attracted intensive attention from a scientific as
well as engineering perspective. In this paper, we study non-Markovian effect
on spin pumping to describe spin current generation driven by arbitrary
precession frequency of magnetization in a quantum dot attached to an electron
lead. Although the Markovian approximation can be used when driving is
sufficiently slow compared with relaxation times in electron tunneling, recent
developments in nano-spintronic devices show that we need to include
non-Markovian effects. In contrast to the one-way-only nature of the spin
current generation under the Markovian dynamics, we find that the non-Markovian
dynamics exhibits a temporal backflow of spin, call spin backflow for brevity.
We capture the phenomenon by introducing its quantifier, and show that the
backflow significantly reduces the amount of spin current when the frequency
exceeds the relaxation rate. This prevents unphysical divergence of the spin
current in the high frequency limit that occurs under the Markovian
approximation. We believe our analysis provides an understanding of the spin
pumping particularly in regard to producing a more efficient spin current
generation over shorter time scales by going beyond the conventional Markovian
approximation.",1901.04965v2
2019-12-16,Dynamics of reconfigurable artificial spin ice: towards magnonic functional materials,"Over the past few years, the study of magnetization dynamics in artificial
spin ices has become a vibrant field of study. Artificial spin ices are
ensembles of geometrically arranged, interacting magnetic nanoislands, which
display frustration by design. These were initially created to mimic the
behavior in rare earth pyrochlore materials and to study emergent behavior and
frustration using two-dimensional magnetic measurement techniques. Recently, it
has become clear that it is possible to create artificial spin ices, which can
potentially be used as functional materials. In this Perspective, we review the
resonant behavior of spin ices (which is in the GHz frequency range), focusing
on their potential application as magnonic crystals. In magnonic crystals, spin
waves are functionalized for logic applications by means of band structure
engineering. While it has been established that artificial spin ices can
possess rich mode spectra, the applicability of spin ices to create magnonic
crystals hinges upon their reconfigurability. Consequently, we describe recent
work aiming to develop techniques and create geometries allowing full
reconfigurability of the spin ice magnetic state. We also discuss experimental,
theoretical, and numerical methods for determining the spectral response of
artificial spin ices, and give an outlook on new directions for reconfigurable
spin ices.",1912.07280v2
2021-09-21,Controlling the real-time dynamics of a spin coupled to the helical edge states of the Kane-Mele model,"The time-dependent state of a classical spin locally exchange coupled to an
edge site of a Kane-Mele model in the topologically non-trivial phase is
studied numerically by solving the full set of coupled microscopic equations of
motion for the spin and the electron system. Dynamics in the long-time limit is
accessible thanks to dissipative boundary conditions, applied to all but the
zigzag edge of interest. We study means to control the state of the spin via
transport of a spin-polarization cloud through the helical edge states. The
cloud is formed at a distant edge site using a local magnetic field to inject
an electron spin density and released by suddenly switching off the injection
field. This basic process, consisting of spin injection, propagation of the
spin-polarization cloud, and scattering of the cloud from the classical spin,
can be used to steer the spin state in a controlled way. We find that the
effect of a single basic process can be reverted to a high degree with a
subsequent process. Furthermore, we show that by concatenating several basic
injection-propagation-scattering processes, the spin state can be switched
completely and that a full reversal can be achieved.",2109.10089v2
2022-10-18,Coherent spin dynamics of hyperfine-coupled vanadium impurities in silicon carbide,"Progress with quantum technology has for a large part been realized with the
nitrogen-vacancy centre in diamond. Part of its properties, however, are
nonideal and this drives research into other spin-active crystal defects.
Several of these come with much stronger energy scales for spin-orbit and
hyperfine coupling, but how this affects their spin coherence is little
explored. Vanadium in silicon carbide is such a system, with technological
interest for its optical emission at a telecom wavelength and compatibility
with semiconductor industry. Here we show coherent spin dynamics of an ensemble
of vanadium defects around a clock-transition, studied while isolated from, or
coupled to neighbouring nuclear spins. We find spin dephasing times up to 7.2
$\mu$s, and via spin-echo studies coherence lifetimes that go well beyond tens
of microseconds. We demonstrate operation points where strong coupling to
neighbouring nuclear spins does not compromise the coherence of the central
vanadium spin, which identifies how these can be applied as a coherent spin
register. Our findings are relevant for understanding a wide class of defects
with similar energy scales and crystal symmetries, that are currently explored
in diamond, silicon carbide, and hexagonal boron nitride.",2210.09942v1
2023-03-13,Experimental investigation of the effect of topological insulator on the magnetization dynamics of ferromagnetic metal: $BiSbTe_{1.5}Se_{1.5}$ and $Ni_{80}Fe_{20}$ heterostructure,"We have studied ferromagnetic metal/topological insulator bilayer system to
understand magnetization dynamics of ferromagnetic metal (FM) in contact with a
topological insulator (TI). At magnetic resonance condition, the precessing
magnetization in the metallic ferromagnet ($Ni_{80}Fe_{20}$) injects spin
current into the topological insulator ($BiSbTe_{1.5}Se_{1.5}$), a phenomenon
known as spin-pumping. Due to the spin pumping effect, fast relaxation in the
ferromagnet results in the broadening of ferromagnetic resonance linewidth
($\Delta H$). We evaluated the parameters like effective Gilbert damping
coefficient ($\alpha_{eff}$), spin-mixing conductance ($g_{eff}^{\uparrow
\downarrow}$) and spin current density ($j_S^0$) to confirm a successful spin
injection due to spin-pumping into the $BiSbTe_{1.5}Se_{1.5}$ layer. TIs embody
a spin-momentum locked surface state that span the bulk band-gap. It can act
differently to the FM magnetization than the other normal metals. To probe the
effect of topological surface state, a systematic low temperature study is
crucial as surface state of TI dominates at lower temperatures. The exponential
growth of $\Delta H$ for all different thickness combination of FM/TI bilayers
and effective Gilbert damping coefficient ($\alpha_{eff}$) with lowering
temperature confirms the prediction that spin chemical bias generated from
spin-pumping induces surface current in TI due to spin-momentum locking. The
hump-like feature of magnetic anisotropy field ($H_K$)of the bilayer around 60K
suggests that the decrease of interfacial in-plane magnetic anisotropy can
result from exchange coupling between the TI surface state and the local
moments of FM layer.",2303.07025v2
2015-12-05,Kinetic theory of spin-polarized systems in electric and magnetic fields with spin-orbit coupling: I. Kinetic equation and anomalous Hall and spin-Hall effects,"The coupled kinetic equation for density and spin Wigner functions are
derived including spin-orbit coupling, electric and magnetic field as well as
selfconsistent Hartree meanfields suited for SU(2) transport. The interactions
are assumed to be with scalar and magnetic impurities as well as scalar and
spin-flip potentials among the particles. The spin-orbit interaction is used in
a form suitable to solid state physics with Rashba or Dresselhaus coupling,
graphene, extrinsic spin-orbit coupling as well as effective nuclear matter
coupling. The deficiencies of the two-fluid model are worked out consisting in
the appearance of an effective in-medium spin-precession. The stationary
solution of all these systems shows a band splitting controlled by an effective
medium-dependent Zeeman field. The selfconsistent precession direction is
discussed and a cancellation of linear spin-orbit coupling at zero temperature
is reported. The precession of spin around this effective direction caused by
spin-orbit coupling leads to anomalous charge and spin currents in an electric
field. Anomalous Hall conductivity is shown to consists of the known results
obtained from Kubo formula or Berry phases and a new symmetric part interpreted
as inverse Hall effect. Analogously the spin-Hall and inverse spin-Hall effect
of spin currents are discussed which are present even without magnetic fields
showing a spin accumulation triggered by currents. The analytical dynamical
expressions for zero temperature are derived and discussed in dependence on the
magnetic field and effective magnetizations. The anomalous Hall and spin-Hall
effect changes sign at higher than a critical frequency dependent on the
relaxation time.",1512.01660v1
2020-05-27,High-resolution tunneling spin transport characteristics of topologically distinct magnetic skyrmionic textures from theoretical calculations,"High-resolution tunneling electron spin transport properties (longitudinal
spin current (LSC) and spin transfer torque (STT) maps) of topologically
distinct real-space magnetic skyrmionic textures are reported by employing a
3D-WKB combined scalar charge and vector spin transport theory in the framework
of spin-polarized scanning tunneling microscopy (SP-STM). For our theoretical
investigation metastable skyrmionic spin structures with various topological
charges ($Q=-3,-2,-1,0,1,2$) in the (Pt$_{0.95}$Ir$_{0.05}$)/Fe/Pd(111)
ultrathin magnetic film are considered. Using an out-of-plane magnetized SP-STM
tip it is found that the maps of the LSC vectors acting on the spins of the
magnetic textures and all STT vector components exhibit the same topology as
the skyrmionic objects. In contrast, an in-plane magnetized tip generally does
not result in spin transport vector maps that are topologically equivalent to
the underlying spin structure, except for the LSC vectors acting on the spins
of the skyrmionic textures at a specific relation between the spin
polarizations of the sample and the tip. The magnitudes of the spin transport
vector quantities exhibit close relations to charge current SP-STM images
irrespectively of the skyrmionic topologies. Moreover, we find that the STT
efficiency (torque/current ratio) acting on the spins of the skyrmions can
reach large values up to $\sim$25 meV/$\mu$A ($\sim$0.97 $h/e$) above the rim
of the magnetic objects, but it considerably varies between large and small
values depending on the lateral position of the SP-STM tip above the
topological spin textures. A simple expression for the STT efficiency is
introduced to explain its variation. Our calculated spin transport vectors can
be used for the investigation of spin-polarized tunneling-current-induced spin
dynamics of topologically distinct surface magnetic skyrmionic textures.",2005.13266v2
2024-01-24,Spin Seebeck Effect as a Probe for Majorana Fermions in Kitaev Spin Liquids,"Quantum entanglement in strongly correlated electron systems often leads to
exotic elementary excitations. Quantum spin liquids (QSLs) provide a
paradigmatic example, where the elementary excitations are described by
fractional quasiparticles such as spinons. However, such fractional
quasiparticles behave differently from electrons, making their experimental
identification challenging. Here, we theoretically investigate the spin Seebeck
effect, which is a thermoelectric response via a spin current, as an efficient
probe of the fractional quasiparticles in QSLs, focusing on the Kitaev
honeycomb model. By comprehensive studies using the real-time dynamics, the
perturbation theory, and the linear spin-wave theory based on the tunnel
spin-current theory, we find that the spin current is induced by thermal
gradient in the Kitaev spin liquid, via the low-energy fractional Majorana
excitations. This underscores the ability of Majorana fermions to carry spin
current, despite lacking spin angular momentum. Furthermore, we find that the
induced spin current changes its sign depending on the sign of the Kitaev
interaction, indicating that the Majorana fermions contribute to the spin
current with (up-)down-spin like nature when the exchange coupling is
(anti)ferromagnetic. Thus, in contrast to the negative spin current already
found in a one-dimensional QSL, our finding reveals that the spin Seebeck
effect can exhibit either positive or negative signals, contingent upon the
nature of fractional excitations in the QSLs. We also clarify contrasting
field-angle dependence between the Kitaev spin liquid in the low-field limit
and the high-field ferromagnetic state, which is useful for the experimental
identification. Our finding suggests that the spin Seebeck effect could be used
not only to detect fractional quasiparticles emerging in QSLs but also to
generate and control them.",2401.13175v1
2001-09-25,Single Spin Dynamics and Decoherence in a Quantum Dot via Charge Transport,"We investigate the spin dynamics of a quantum dot with a spin-1/2 ground
state in the Coulomb blockade regime and in the presence of a magnetic rf field
leading to electron spin resonances (ESR). We show that by coupling the dot to
leads, spin properties on the dot can be accessed via the charge current in the
stationary and non-stationary limit. We present a microscopic derivation of the
current and the master equation of the dot using superoperators, including
contributions to decoherence and energy shifts due to the tunnel coupling. We
give a detailed analysis of sequential and co-tunneling currents, for linearly
and circularly oscillating ESR fields, applied in cw and pulsed mode. We show
that the sequential tunneling current exhibits a spin satellite peak whose
linewidth gives a lower bound on the decoherence time T_2 of the dot-spin.
Similarly, the spin decoherence can be accessed also in the cotunneling regime
via ESR induced spin flips. We show that the conductance ratio of the spin
satellite peak and the conventional peak due to sequential tunneling saturates
at the universal conductance ratio of 0.71 for strong ESR fields. We describe a
double-dot setup which generates spin dependent tunneling and acts as a current
pump (at zero bias), and as a spin inverter which inverts the spin-polarization
of the current. We show that Rabi oscillations of the dot-spin induce coherent
oscillations in the time-dependent current. These oscillations are observable
in the time-averaged current as function of ESR pulse-duration, and they allow
one to access the spin coherence directly in the time domain. We analyze the
measurement and read-out process of the dot-spin via currents in spin-polarized
leads and identify measurement time and efficiency by calculating the counting
statistics, noise, and the Fano factor.",0109470v1
2024-01-30,Partial tidal disruptions of spinning eccentric white dwarfs by spinning intermediate mass black holes,"Intermediate mass black holes (IMBHs, $\sim 10^2-10^5M_{\odot}$) are often
dubbed as the missing link between stellar mass ($\lesssim 10^2M_{\odot}$) and
super-massive ($\gtrsim 10^{5-6} M_{\odot}$) black holes. Observational
signatures of these can result from tidal disruption of white dwarfs (WDs),
which would otherwise be captured as a whole by super-massive black holes.
Recent observations indicate that IMBHs might be rapidly spinning, while it is
also known that isolated white dwarfs might have large spins, with spin periods
of the order of minutes. Here, we aim to understand the effects of ``coupling''
between black hole and stellar spin, focussing on the tidal disruption of
spinning WDs in the background of spinning IMBHs. Using smoothed particle
hydrodynamics, we perform a suite of numerical simulations of partial tidal
disruptions, where spinning WDs are in eccentric orbits about spinning IMBHs.
We take a hybrid approach, where we integrate the Kerr geodesic equations while
being in a regime where we can treat the internal stellar fluid dynamics in the
Newtonian limit. We find substantial effects of the ``coupling'' between the
black hole spin and the spin of the white dwarf, although the pericenter
distance of the white dwarf is taken to be large enough so that the Newtonian
limit of its fluid dynamics is a robust approximation. In particular, the core
mass, the bound tail mass, and the mass difference between the two tidal tails
strongly depend on such ``coupled'' spin effects. However, the late time
fallback rate of the debris behaves similar to the non-spinning cases. We also
compute gravitational wave amplitudes and find that while the black hole spin
influences the same, there is no evidence of influence of stellar spin on such
amplitudes in our regime of interest.",2401.17031v1
1994-03-01,On Mean Field Glassy Dynamics out of Equilibrium,"We study the off equilibrium dynamics of a mean field disordered systems
which can be interpreted both as a long range interaction spin glass and as a
particle in a random potential. The statics of this problem is well known and
exhibits a low temperature spin glass phase with continuous replica symmetry
breaking. We study the equations of off equilibrium dynamics with analytical
and numerical methods. In the spin glass phase, we find that the usual
equilibrium dynamics (observed when the observation time is much smaller than
the waiting time) coexists with an aging regime. In this aging regime, we
propose a solution implying a hierarchy of crossovers between the observation
time and the waiting time.",9403004v1
2001-11-26,Testing the Edwards hypothesis in spin systems under tapping dynamics,"The Edwards hypothesis of ergodicity of blocked configurations for gently
tapped granular materials is tested for abstract models of spin systems on
random graphs and spin chains with kinetic constraints. The tapping dynamics is
modeled by considering two distinct mechanisms of energy injection: thermal and
random tapping. We find that ergodicity depends upon the tapping procedure
(i.e. the way the blocked configurations are dynamically accessed): for thermal
tapping ergodicity is a good approximation, while it fails to describe the
asymptotic stationary state reached by the random tapping dynamics.",0111485v2
2002-03-14,Spin dynamics in a hole-doped S=1/2 Heisenberg antiferromagnet with a disordered ground state,"Only 3% hole doping by Li is sufficient to suppress the long-range
antiferromagnetic order in La2CuO4. Spin dynamics in such a disordered state
was investigated with measurements of the dynamic magnetic structure factor
S(omega,q), using cold neutron spectroscopy, for La2(Cu0.94Li0.06)O4. The
S(omega,q) is found to sharply peak at (pi,pi), and its dynamics to be
relaxational. Confirming theoretical expectation for the quantum disordered 2D
S=1/2 Heisenberg antiferromagnet, the energy scale saturates at a finite value
at low temperatures. Possible connection to the ``pseudo spin gap'' phenomenon
observed in the NMR/NQR studies on underdoped cuprates is discussed.",0203318v1
2002-06-29,Glauber Critical Dynamics: Exact Solution of the Kinetic Gaussian Model,"In this paper, we have exactly solved Glauber critical dynamics of the
Gaussian model on three dimensions. Of course, it is much easy to apply to low
dimensional case. The key steps are that we generalize the spin change
mechanism from Glauber's single-spin flipping to single-spin transition and
give a normalized version of the transition probability . We have also
investigated the dynamical critical exponent and found surprisingly that the
dynamical critical exponent is highly universal which refer to that for one-
two- and three-dimensions they have same value independent of spatial
dimensionality in contrast to static (equilibrium) critical exponents.",0207006v1
1999-04-21,Nonlinear Accelerator Problems via Wavelets: 4. Spin-Orbital Motion,"In this series of eight papers we present the applications of methods from
wavelet analysis to polynomial approximations for a number of accelerator
physics problems. In this part we consider a model for spin-orbital motion:
orbital dynamics and Thomas-BMT equations for classical spin vector. We
represent the solution of this dynamical system in framework of biorthogonal
wavelets via variational approach. We consider a different variational
approach, which is applied to each scale.",9904042v1
2008-02-04,Dynamic properties of quantum spin chains: Simple route to complex behavior,"We examine dynamic structure factors of spin-1/2 chains with nearest-neighbor
interactions of XX and Dzyaloshinskii-Moriya type, and with periodic and random
changes in the sign of these interactions. This special kind of inhomogeneity
can be eliminated from the Hamiltonian by suitable transformation of the spin
variables. As a result, the dynamic structure factors of periodic or random
chains can be computed from those of the uniform chains. Using the exact
analytical and precise numerical results available for the uniform systems we
illustrate the effects of regular alternation or random disorder on dynamic
structure factors of quantum spin chains.",0802.0389v1
2010-09-09,Hydrodynamic equation of a spinor dipolar Bose-Einstein condensate,"We introduce equations of motion for spin dynamics in a ferromagnetic
Bose-Einstein condensate with magnetic dipole-dipole interaction, written using
a vector expressing the superfluid velocity and a complex scalar describing the
magnetization. This simple hydrodynamical description extracts the dynamics of
spin wave and affords a straightforward approach by which to investigate the
spin dynamics of the condensate. To demonstrate the advantages of the
description, we illustrate dynamical instability and magnetic fluctuation
preference, which are expressed in analytical forms.",1009.1671v3
2013-02-21,Rates for irreversible Gibbsian Ising models,"Dynamics under which a system of Ising spins relaxes to a stationary state
with Bolzmann-Gibbs measure and which do not fulfil the condition of detailed
balance are irreversible and asymmetric. We revisit the problem of the
determination of rates yielding such a stationary state for models with
single-spin flip dynamics. We add some supplementary material to this study and
confirm that Gibbsian irreversible Ising models exist for one and
two-dimensional lattices but not for the three-dimensional cubic lattice. We
also analyze asymmetric Gibbsian dynamics in the limit of infinite temperature.
We finally revisit the case of a linear chain of spins under asymmetric
conserved dynamics.",1302.5279v2
2015-10-01,Dynamics of quantized vortices in Bose-Einstein condensates with laser-induced spin-orbit coupling,"We study vortex dynamics in trapped two-component Bose-Einstein condensates
with a laser- induced spin-orbit coupling using the numerical analysis of the
Gross-Pitaevskii equation. The spin-orbit coupling leads to three distinct
ground state phases, which depend on some experimentally controllable
parameters. When a vortex is put in one or both of the two-component
condensates, the vortex dynamics exhibits very different behaviors in each
phase, which can be observed in experiments. These dynamical behaviors can be
understood by clarifying the stable vortex structure realized in each phase.",1510.00142v1
2015-11-10,Static and dynamic properties of vortex pairs in asymmetric nanomagnets,"Stacked spin-vortex pairs in magnetic multilayered nanopillars, with vertical
separation between the vortices small compared to the vortex core size, exhibit
spin dynamics absent in individual vortices. This dynamics is nonlinear and is
due to the strong direct core-core coupling in the system, dominating
energetically for small- signal excitation. We observe and explain the
appearance of spin resonance modes, forbidden within linear dynamics, and
discuss how they depend on the magnetic and morphological asymmetries in the
samples.",1511.03092v1
2016-01-26,Dynamics and control of a qubit in spin environment: an exact master equation study,"We present an exact master equation for a central spin-$1/2$ system coupled
to a spin-$1/2$ bath in terms of hyperfine interaction, which provides a
unified formalism for both free evolution and controlled dynamics of the
central spin. The equation enables us to study controllability of dynamics
processes with various degrees of non-Markovianity. We investigate the
Overhauser's effect on decoherence dynamics of the central spin under different
bath spectra and the system-bath coupling strengths. Nonperturbative leakage
elimination approach is applied to the system to suppress decoherence in
solid-state quantum information processing.",1601.07197v1
2018-06-27,Thermal Marangoni-driven Dynamics of Spinning Liquid Films,"Spin coating of thin films of viscous liquids on a rotating substrate is a
core technological component of semiconductor microchip fabrication. The
thinning dynamics is influenced by many physical processes. Specifically
temperature gradients affect thin liquid films through their influence on the
local fluid surface tension. We show here experimentally and numerically that
adding a static temperature gradient has a significant effect on the
equilibrium film thickness and height profile reached in spin coating. Our
results suggest that thermal gradients can be used to control film height
profile dynamics.",1806.10595v1
2020-05-12,Analysis in k-space of Magnetization Dynamics Driven by Strong Terahertz Fields,"Demagnetization in a thin film due to a terahertz pulse of magnetic field is
investigated. Linearized LLG equation in the Fourier space to describe the
magnetization dynamics is derived, and spin waves time evolution is studied.
Finally, the demagnetization due to spin waves dynamics and recent experimental
observations on similar magnetic system are compared. As a result of it, the
marginal role of spin waves dynamics in loss of magnetization is established.",2005.05742v1
2022-08-05,"Beyond DMFT: Spin Fluctuations, Pseudogaps and Superconductivity","This Chapter of the J\""ulich Summer School 2022 provides for a first reading
on diagrammatic extensions of dynamical-mean-field theory and their application
to spin fluctuations, pseudogap physics and supercondcutivtiy. The contents is
as follows:
  1 Introduction
  2 Dynamical vertex approximation
  3 Ladder dynamical vertex approximation
  4 Hubbard model, cuprates and nickelates
  5 Spin fluctuations
  6 Pseudogap
  7 Superconductivity
  8 Conclusion and outlook",2208.03174v1
2023-02-10,Feedback Assisted Spin Dynamics in an Inhomogeneous Bias Magnetic Field,"We study dynamics of spins in the presence of a feedback magnetic field. The
inhomogeneity of the bias magnetic field results in that of the Larmor
frequencies of the spins. We find that the system exhibits rich nonlinear
dynamics: beyond limit cycles which have been the focus of previous studies,
quasi-periodic orbits and chaos emerge in a wide parameter space. The stable
regions of each phases are determined analytically or numerically. We establish
the relation between the synchronization frequency of limit cycles and the
field inhomogeneity. Our results have important implications to precision
measurement.",2302.05264v1
2015-04-22,Far-from-equilibrium field theory of many-body quantum spin systems: Prethermalization and relaxation of spin spiral states in three dimensions,"We study theoretically the far-from-equilibrium relaxation dynamics of spin
spiral states in the three dimensional isotropic Heisenberg model. The
investigated problem serves as an archetype for understanding quantum dynamics
of isolated many-body systems in the vicinity of a spontaneously broken
continuous symmetry. We present a field-theoretical formalism that
systematically improves on mean-field for describing the real-time quantum
dynamics of generic spin-1/2 systems. This is achieved by mapping spins to
Majorana fermions followed by a 1/N expansion of the resulting two-particle
irreducible (2PI) effective action. Our analysis reveals rich
fluctuation-induced relaxation dynamics in the unitary evolution of spin spiral
states. In particular, we find the sudden appearance of long-lived
prethermalized plateaus with diverging lifetimes as the spiral winding is tuned
toward the thermodynamically stable ferro- or antiferromagnetic phases. The
emerging prethermalized states are characterized by different bosonic modes
being thermally populated at different effective temperatures, and by a
hierarchical relaxation process reminiscent of glassy systems. Spin-spin
correlators found by solving the non-equilibrium Bethe-Salpeter equation
provide further insight into the dynamic formation of correlations, the fate of
unstable collective modes, and the emergence of fluctuation-dissipation
relations. Our predictions can be verified experimentally using recent
realizations of spin spiral states with ultracold atoms in a quantum gas
microscope [S. Hild, et al. Phys. Rev. Lett. 113, 147205 (2014)].",1504.05956v2
2018-10-06,Exact quantum dynamics of XXZ central spin problems,"We obtain analytically close forms of benchmark quantum dynamics of the
collapse and revival (CR), reduced density matrix, Von Neumann entropy, and
fidelity for the XXZ central spin problem. These quantities characterize the
quantum decoherence and entanglement of the system with few to many bath spins,
and for a short to infinitely long time evolution. For the homogeneous central
spin problem, the effective magnetic field $B$, coupling constant $A$ and
longitudinal interaction $\Delta$ significantly influence the time scales of
the quantum dynamics of the central spin and the bath, providing a tunable
resource for quantum metrology. Under the resonance condition $B=\Delta=A$, the
location of the $m$-th revival peak in time reaches a simple relation $t_{r}
\simeq\frac{\pi N}{A} m$ for a large $N$. For $\Delta =0$, $N\to \infty$ and a
small polarization in the initial spin coherent state, our analytical result
for the CR recovers the known expression found in the Jaynes-Cummings model,
thus building up an exact dynamical connection between the central spin
problems and the light-matter interacting systems in quantum nonlinear optics.
In addition, the CR dynamics is robust to a moderate inhomogeneity of the
coupling amplitudes, while disappearing at strong inhomogeneity.",1810.03012v4
2021-07-13,Dynamical and static spin structure factors of Heisenberg antiferromagnet on honeycomb lattice in the presence of Dzyaloshinskii-Moriya interaction,"We have theoretically studied the spin structure factors of Heisenberg model
on honeycomb lattice in the presence of longitudinal magnetic field, i.e.
magnetic field perpendicular to the honeycomb plane, and Dzyaloshinskii-Moriya
interaction. The possible effects of next nearest neighbor exchange constant
are investigated in terms of anisotropy in the Heisenberg interactions. This
spatial anisotropy is due to the difference between nearest neighbor exchange
coupling constant and next nearest neighbor exchange coupling constant. The
original spin model hamiltonian is mapped to a bosonic model via a hard core
bosonic transformation where an infinite hard core repulsion is imposed to
constrain one boson occupation per site. Using Green's function approach, the
energy spectrum of quasiparticle excitation has been obtained. The spectrum of
the bosonic gas has been implemented in order to obtain two particle propagator
which corresponds to spin structure factor of original Heisenberg chain model
Hamiltonian. The results show the position of peak in the dynamical transverse
spin structure factor at fixed value for Dzyaloshinskii Moriya interaction
moves to higher frequency with magnetic field. Also the intensity of dynamical
transverse spin structure factor is not affected by magnetic field. However the
Dzyaloshinskii Moriya interaction strength causes to decrease the intensity of
dynamical transverse spin structure factor. The increase of magnetic field does
not varied the frequency position of peaks in dynamical longitudinal spin
susceptibility however the intensity reduces with magnetic field. Our results
show static transverse structure factor is found to be monotonically decreasing
with magnetic field and temperature for different vlaues of next nearest
neighbor coupling exchange constant.",2107.05862v1
2022-09-06,Temperature- and field angular-dependent helical spin period characterized by magnetic dynamics in a chiral helimagnet $MnNb_3S_6$,"The chiral magnets with topological spin textures provide a rare platform to
explore topology and magnetism for potential application implementation. Here,
we study the magnetic dynamics of several spin configurations on the monoaxial
chiral magnetic crystal $MnNb_3S_6$ via broadband ferromagnetic resonance (FMR)
technique at cryogenic temperature. In the high-field forced ferromagnetic
state (FFM) regime, the obtained frequency f vs. resonance field Hres
dispersion curve follows the well-known Kittel formula for a single FFM, while
in the low-field chiral magnetic soliton lattice (CSL) regime, the dependence
of Hres on magnetic field angle can be well-described by our modified Kittel
formula including the mixture of a helical spin segment and the FFM phase.
Furthermore, compared to the sophisticated Lorentz micrograph technique, the
observed magnetic dynamics corresponding to different spin configurations allow
us to obtain temperature- and field-dependent proportion of helical spin
texture and helical spin period ratio L(H)/L(0) via our modified Kittel
formula. Our results demonstrated that field- and temperature-dependent
nontrivial magnetic structures and corresponding distinct spin dynamics in
chiral magnets can be an alternative and efficient approach to uncovering and
controlling nontrivial topological magnetic dynamics.",2209.02266v1
2023-12-24,Improving the understanding of the dynamics of open quantum systems,"This thesis presents studies performed on open quantum systems, that is,
quantum systems interacting with their surrounding environment. Such systems
are important not only in understanding the quantum-to-classical transition but
also for the practical implementation of modern quantum technologies. In
studies of open quantum systems performed to date, a very common assumption is
that the system and the environment are in separated initial states to begin
with. One primary objective of this thesis is to critically analyse this
assumption. We follow two different approaches to investigate the dynamics.
First, we solve an exactly solvable spin-spin model where a central spin system
interacts with a collection of quantum spins. We analyse exactly the central
spin dynamics, starting from both initially correlated and uncorrelated SE
states, and look at the dynamical differences due to the different starting
states. Second, we consider an arbitrary system interacting with an arbitrary
environment and derive a master equation that describes the system dynamics and
incorporates the effect of the initial SE correlations. This effect of initial
correlations is captured by an extra term appearing in the master equation. The
master equation is subsequently applied to the paradigmatic SE models such as
the spin-boson model and the spin-spin model. We demonstrate that the role
played by initial correlations can be noticeable even if the SE coupling
strength is kept smaller. The next part of the thesis deals with estimating the
parameters characterizing the environment of a quantum system where we show
that the use of two two-level systems can greatly enhance the estimation of the
environment parameters.",2402.10901v1
2001-01-11,Tapping Spin Glasses,"We consider a tapping dynamics, analogous to that in experiments on granular
media, on spin glasses and ferromagnets on random thin graphs. Between taps,
zero temperature single spin flip dynamics takes the system to a metastable
state. Tapping, corresponds to flipping simultaneously any spin with
probability $p$. This dynamics leads to a stationary regime with a steady state
energy $E(p)$. We analytically solve this dynamics for the one dimensional
ferromagnet and $\pm J$ spin glass. Numerical simulations for spin glasses and
ferromagnets of higher connectivity are carried out, in particular we find a
novel first order transition for the ferromagnetic systems.",0101166v1
2002-03-08,Pinning of dynamic spin density wave fluctuations in the cuprate superconductors,"We present a theory of the pinning of dynamic spin density wave (SDW)
fluctuations in a d-wave superconductor by local imperfections which preserve
spin-rotation invariance, such as impurities or vortex cores. The pinning leads
to static spatial modulations in spin-singlet observables, while the SDW
correlations remain dynamic: these are the `Friedel oscillations' of a spin-gap
antiferromagnet. We connect the spectrum of these modulations as observed by
scanning tunnelling microscopy to the dynamic spin structure factor measured by
inelastic neutron scattering.",0203176v2
2003-05-02,Aging dynamics of heterogeneous spin models,"We investigate numerically the dynamics of three different spin models in the
aging regime. Each of these models is meant to be representative of a distinct
class of aging behavior: coarsening systems, discontinuous spin glasses, and
continuous spin glasses. In order to study dynamic heterogeneities induced by
quenched disorder, we consider single-spin observables for a given disorder
realization. In some simple cases we are able to provide analytical predictions
for single-spin response and correlation functions.
  The results strongly depend upon the model considered. It turns out that, by
comparing the slow evolution of a few different degrees of freedom, one can
distinguish between different dynamic classes. As a conclusion we present the
general properties which can be induced from our results, and discuss their
relation with thermometric arguments.",0305044v1
2005-05-29,Dynamical Aspects of Photoinduced Magnetism and Spin-Crossover phenomena in Prussian Blue Analogs,"We present dynamical properties of spin crossover compounds with
photomagnetization, proposing a new model in which the spin-crossover phenomena
and magnetic ordering are incorporated in a unified way. By using this model,
the novel characteristics observed in Prussian blue analogs are qualitatively
well reproduced. We investigate the time evolution of the magnetization and
high spin fraction taking into account multi-time scales in a master equation
approach for the magnetic relaxation, the lattice (electronic) relaxation, and
the photoexcitation process. In particular, processes with different
temperature cycles starting from the photoinduced saturated magnetic state are
studied including the effect of photoirradiation. In the temperature cycle in
the low temperature region where the high spin state has a strong
metastability, the magnetization almost exactly follows the quasi-static
process. On the other hand, when the temperature is raised above the region,
the dynamics of the spin state and the magnetization couple and exhibit various
types of dynamical cooperative phenomena under time-dependent control of
temperature and photoirradiation.",0505702v1
2007-02-21,Effect of initial conditions on Glauber dynamics in complex networks,"The effect of initial spin configurations on zero-temperature Glauber spin
dynamics in complex networks is investigated. In a system in which the initial
spins are defined by centrality measures at the vertices of a network, a
variety of non-trivial diffusive behaviors arise, particularly in relation to
functional relationships between the initial and final fractions of positive
spins, some of which exhibit a critical point. Notably, the majority spin in
the initial state is not always dominant in the final state, and the phenomena
that occur as a result of the dynamics differ according on the initial
condition, even for the same network. It is thus concluded that the initial
condition of a complex network exerts an influence on spin dynamics that is
equally as strong as that exerted by the network structure.",0702482v1
2007-08-10,Diffusive spin transport,"Information to be stored and transported requires physical carriers. The
quantum bit of information (qubit) can for instance be realised as the spin 1/2
degree of freedom of a massive particle like an electron or as the spin 1
polarisation of a massless photon. In this lecture, I first use irreducible
representations of the rotation group to characterise the spin dynamics in a
least redundant manner. Specifically, I describe the decoherence dynamics of an
arbitrary spin S coupled to a randomly fluctuating magnetic field in the
Liouville space formalism. Secondly, I discuss the diffusive dynamics of the
particle's position in space due to the presence of randomly placed impurities.
Combining these two dynamics yields a coherent, unified picture of diffusive
spin transport, as applicable to mesoscopic electronic devices or photons
propagating in cold atomic clouds.",0708.1409v2
2010-07-05,Laser-induced Spin Dynamics in Metallic Multilayers,"Electronic excitations in a ferromagnet can trigger ultrafast spin dynamics
with potential applications in a speed increase in magnetic recording. The
project investigates ultrafast magnetization dynamics, which is driven in
metallic layers by ballistic hot electrons. In a ferromagnet these electrons
induce a change in the absolute value of the magnetization M through
spin-dependent scattering. If the electrons are spin-polarized, scattering at
the interface of a noble metal and a ferromagnet results in spin-transfer
torque and hence modifies the direction of M. To reveal the underlying
mechanisms, we study model systems, which are realized by layers of Au with its
large ballistic mean free path and Fe as an itinerant ferromagnet. We aim at
understanding ultrafast demagnetization and femtosecond all-optical generation
of spin transfer torque effects (excitation of hot electrons with a femtosecond
laser). The launched dynamics are probed by magneto-optics in a time-resolved
experiment.",1007.0726v1
2011-03-16,Enhancement of spin coherence in a spin-1 Bose condensate by dynamical decoupling approaches,"We present a theoretical investigation on the enhancement of the spin
coherence with periodic, concatenated, or Uhrig dynamical decoupling $N$-pulse
sequences in a $^{87}$Rb spin-1 Bose condensate, where the intrinsic dynamical
instability in such a ferromagnetically interacting condensate causes spin
decoherence and eventually leads to a multiple spatial-domain structure or a
spin texture. Our results show that all the three sequences successfully
enhance the spin coherence by pushing the wave vector of the most unstable mode
in the condensate to a larger value. Among the three sequences with the same
number of pulses, the concatenated one shows the best performance in preserving
the spin coherence. Interestingly, we find that all the three sequences exactly
follow the same enhancement law, $k_- T^{1/2} = c$, with $k_-$ the wave vector
of the most unstable mode, $T$ the sequence period, and $c$ a
sequence-dependent constant. Such a law between $k_-$ and $T$ is also derived
analytically for an attractive scalar Bose condensate subjecting to a periodic
dynamical decoupling sequence.",1103.3087v2
2011-10-29,Mechanism of half-frequency electric dipole spin resonance in double quantum dots: Effect of nonlinear charge dynamics inside the singlet manifold,"Electron dynamics in quantum dots manifests itself in spin-flip spectra
through electric dipole spin resonance (EDSR). Near a neutrality point
separating two different singlet charged states of a double quantum dot, charge
dynamics inside a $2\times2$ singlet manifold can be described by a
1/2-pseudospin. In this region, charge dynamics is highly nonlinear and
strongly influenced by flopping its soft pseudospin mode. As a result, the
responses to external driving include first and second harmonics of the driving
frequency and their Raman satellites shifted by the pseudospin frequency. In
EDSR spectra of a spin-orbit couplet doublet dot, they manifest themselves as
charge satellites of spin-flip transitions. The theory describes gross features
of the anomalous half-frequency EDSR in spin blockade spectra [Laird et al.,
Semicond. Sci. Techol. {\bf 24}, 064004 (2009)].",1110.6569v2
2013-03-12,Optical signals of spin switching using the optical Stark effect in a Mn doped quantum dot,"The optically induced spin dynamics of a single Mn atom embedded into a
single semiconductor quantum dot can be strongly influenced by using the
optical Stark effect. The exchange interaction gives rise to simultaneous spin
flips between the quantum dot electron and Mn. In the time domain these flips
correspond to exchange induced Rabi oscillations, which are typically
off-resonant. By applying a detuned laser pulse, the states involved in the
flipping can be brought into resonance by means of the optical Stark effect
increasing the amplitude of the Rabi oscillations to one. In this paper we
study theoretically how this spin dynamics can be monitored in time-resolved
spectroscopy. In the spectrum the exchange interaction leads to a splitting of
the exciton line into six lines, each corresponding to one of the six Mn spin
states. The dynamical behavior of the Mn spin is reflected by the strength of
the individual lines as a function of time. When an off-resonant optical pulse
is applied the spectral positions of the lines shift, but still the flipping
dynamics is visible.",1303.2909v1
2015-03-08,Antiferromagnetic order and spin dynamics in iron-based superconductors,"High-transition temperature (high-$T_c$) superconductivity in the iron
pnictides/chalcogenides emerges from the suppression of the static
antiferromagnetic order in their parent compounds, similar to copper oxides
superconductors. This raises a fundamental question concerning the role of
magnetism in the superconductivity of these materials. Neutron scattering, a
powerful probe to study the magnetic order and spin dynamics, plays an
essential role in determining the relationship between magnetism and
superconductivity in high-$T_c$ superconductors. The rapid development of
modern neutron time-of-flight spectrometers allows a direct determination of
the spin dynamical properties of iron-based superconductors throughout the
entire Brillouin zone. In this review, we present an overview of the neutron
scattering results on iron-based superconductors, focusing on the evolution of
spin excitation spectra as a function of electron/hole-doping and isoelectronic
substitution. We compare spin dynamical properties of iron-based
superconductors with those of copper oxide and heavy fermion superconductors,
and discuss the common features of spin excitations in these three families of
unconventional superconductors and their relationship with superconductivity.",1503.02340v2
2018-11-10,Spin dynamics in lattices of spinor atoms with quadratic Zeeman effect,"A lattice system of spinor atoms or molecules experiencing quadratic Zeeman
effect is considered. This can be an optical lattice with sufficiently deep
wells at lattice sites, so that the system is in an isolating state, where
atoms are well localized. But their effective spins can move in the presence of
external magnetic fields. The dynamics of spins, starting from an initial
nonequilibrium state, is investigated. The system is immersed into a magnetic
coil of an electric circuit, creating a magnetic feedback field. Two types of
quadratic Zeeman effect are treated, a nonresonant, so-called static-current
quadratic Zeeman effect and a quasi-resonant alternating-current quadratic
Zeeman effect. Spin dynamics in these conditions is highly nonlinear. Different
regimes of spin dynamics, starting from a strongly nonequilibrium state, are
studied. Conditions for realizing fast spin reversal are found, which can be
used in quantum information processing and spintronics.",1811.04271v1
2020-07-10,Orbital spin dynamics of a millisecond pulsar around a massive black hole with an general mass quadrupole,"We investigate the spin dynamics of a millisecond pulsar (MSP) in compact
orbit around a Kerr-like massive black hole with an general mass quadrupole. We
use the Mathisson-Papetrou-Dixon formulation to compute the orbital and spin
evolution of the MSP, accounting for the non-linear interaction of the pulsar's
energy-momentum tensor on the background spacetime metric. We investigate how
the MSP spin and BH quadrupole moment manifest in the pulsar spin-orbital
dynamics. We discuss the astrophysical observational implications of these spin
and orbital dynamics on the timing of a radio pulsar in an Extreme Mass Ratio
Binary, e.g. a Galactic Centre pulsar. In particular, notable timing variations
in the Einstein delay and Roemer delay are observed, along with modifications
to the pulsar pulse profile.",2007.05219v1
2010-05-26,Spin diffusion in the Mn2+ ion system of II-VI diluted magnetic semiconductor heterostructures,"The magnetization dynamics in diluted magnetic semiconductor heterostructures
based on (Zn,Mn)Se and (Cd,Mn)Te has been studied experimentally by optical
methods and simulated numerically. In the samples with nonhomogeneous magnetic
ion distribution this dynamics is contributed by spin-lattice relaxation and
spin diffusion in the Mn spin system. The spin diffusion coefficient of
7x10^(-8) cm^2/s has been evaluated for Zn(0.99)Mn(0.01)Se from comparison of
experimental and numerical results. Calculations of the giant Zeeman splitting
of the exciton states and the magnetization dynamics in the ordered alloys and
parabolic quantum wells fabricated by the digital growth technique show perfect
agreement with the experimental data. In both structure types the spin
diffusion has an essential contribution to the magnetization dynamics.",1005.4862v1
2016-11-18,Propagating spin-wave normal modes: A dynamic matrix approach using plane-wave demagnetizating tensors,"We present a finite-difference micromagnetic approach for determining the
normal modes of spin-waves propagating in extended magnetic films and strips,
which is based on the linearized Landau-Lifshitz equation and uses the dynamic
matrix method. The model takes into account both short range exchange
interactions and long range dipole-dipole interactions. The latter are
accounted for through plane-wave dynamic demagnetization factors, which depend
not only on the geometry and relative positions of the magnetic cells, as usual
demagnetization factors do, but also on the wave vector of the propagating
waves. Such a numerical model is most relevant when the spin-wave medium is
spatially inhomogeneous perpendicular to the direction of propagation, either
in its magnetic properties or in its equilibrium magnetic configuration. We
illustrate this point by studying surface spin-waves in magnetic bilayer films
and spin-waves channelized along magnetic domain walls in perpendicularly
magnetized strips. In both cases, dynamic dipolar interactions produce
non-reciprocity effects, where counter-propagative spin-waves have different
frequencies.",1611.06153v1
2017-01-06,Emergence and scaling of spin turbulence in quenched antiferromagnetic spinor Bose-Einstein condensates,"We investigate the phase transition dynamics of a quasi-2D antiferromagnetic
spin-1 Bose-Einstein condensate from the easy-axis polar phase to the
easy-plane polar phase, which is initiated by suddenly changing the sign of the
quadratic Zeeman energy $q$. We observe the emergence and decay of spin
turbulence and the formation of half-quantum vortices (HQVs) in the quenched
condensate. The characteristic time and length scales of the turbulence
generation dynamics are proportional to $|q|^{-1/2}$ as inherited from the
dynamic instability of the initial state. In the evolution of the spin
turbulence, spin wave excitations develop from large to small length scales,
suggesting a direct energy cascade, and the spin population for the axial polar
domains exhibit a nonexponential decay. The final equilibrated condensate
contains HQVs, and the number is found to increase and saturate with increasing
$|q|$. Our results demonstrate the time-space scaling properties of the phase
transition dynamics near the critical point and the peculiarities of the spin
turbulence state of the antiferromagnetic spinor condensate.",1701.01559v2
2013-09-03,Detection and measurement of spin-dependent dynamics in random telegraph signals,"A quantum point contact was used to observe single-electron fluctuations of a
quantum dot in a GaAs heterostructure. The resulting random telegraph signals
(RTS) contain statistical information about the electron spin state if the
tunneling dynamics are spin-dependent. We develop a statistical method to
extract information about spin-dependent dynamics from RTS and use it to
demonstrate that these dynamics can be studied in the thermal energy regime.
The tunneling rates of each spin state are independently measured in a finite
external magnetic field. We confirm previous findings of a decrease in overall
tunneling rates for the spin excited state compared to the ground state as an
external magnetic field is increased.",1309.0567v2
2013-09-10,Ultrafast spin-resolved spectroscopy reveals dominant exciton dynamics in conducting polymer polyaniline,"The conducting polymer polyaniline (PANI) has a wide range of optoelectronic
applications due to its unique electronic and optical characteristics. Although
extensive works have been performed to understand the equilibrium properties,
the nature of the charge type that governs its non-equilibrium optical response
has been barely understood; a number of studies have debated the nature of
photo-generated charge type in PANI, specifically whether it is polaron or
exciton based. Here, we report experimental evidence that the charge relaxation
dynamics of PANI are dominated by excitons. Utilizing ultrafast spin-resolved
pump-probe spectroscopy, we observed that PANI charge dynamics are strongly
spin-polarized, exhibiting a spin Pauli-blocking effect. Investigations
including both spin-independent and spindependent dynamics reveal that there is
no spin-flip process involved in charge relaxation. This provides compelling
evidence of an exciton-dominated photo-response in PANI.",1309.2400v1
2018-10-02,Dynamical structure factor in the non-Abelian phase of the Kitaev honeycomb model in the presence of quenched disorder,"Kitaev's model of spins interacting on a honeycomb lattice describes a
quantum spin-liquid, where an emergent static $\mathbb{Z}_2$ gauge field is
coupled to Majorana fermions. In the presence of an external magnetic field and
for a range of interaction strengths, the system behaves as a gapped,
non-Abelian quantum spin-liquid. In this phase, the vortex excitations of the
emergent $\mathbb{Z}_2$ gauge field have Majorana zero modes bound to them.
Motivated by recent experimental progress in measuring and characterizing real
materials that could exhibit spin-liquid behavior, we analytically calculate
the dynamical spin structure factor in the non-Abelian phase of the Kitaev's
honeycomb model. In particular, we treat the case of quenched disorder in the
vortex configurations. Our calculations reveal a peak in the low-energy
dynamical structure factor that is a signature of the spin-liquid behavior. We
map the effective Hamiltonian to that of a chiral p-wave superconductor by
using the Jordan-Wigner transformation. Subsequently, we analytically calculate
the wave functions of the Majorana zero modes, the energy splitting for finite
separation of the vortices and finally, the dynamical structure factor in
presence of quenched disorder.",1810.01426v1
2017-05-04,Density and spin modes in imbalanced normal Fermi gases from collisionless to hydrodynamic regime,"We study mass and population imbalance effect on density (in-phase) and spin
(out-of-phase) collective modes in a two-component normal Fermi gas. By
calculating eigenmodes of the linearized Boltzmann equation as well as the
density/spin dynamic structure factor, we show that mass and population
imbalance effects offer a variety of collective mode crossover behaviors from
collisionless to hydrodynamic regimes. The mass imbalance effect shifts the
crossover regime to the higher-temperature, and a significant peak of the spin
dynamic structure factor emerges only in the collisionless regime. This is in
contrast to the case of mass and population balanced normal Fermi gases, where
the spin dynamic response is always absent. Although the population imbalance
effect does not shift the crossover regime, the spin dynamic structure factor
survives both in the collisionless and hydrodynamic regimes.",1705.01863v2
2018-08-06,Temperature dependence of butterfly effect in a classical many-body system,"We study the chaotic dynamics in a classical many-body system of interacting
spins on the kagome lattice. We characterise many-body chaos via the butterfly
effect as captured by an appropriate out-of-time-ordered correlator. Due to the
emergence of a spin liquid phase, the chaotic dynamics extends all the way to
zero temperature. We thus determine the full temperature dependence of two
complementary aspects of the butterfly effect: the Lyapunov exponent, $\mu$,
and the butterfly speed, $v_b$, and study their interrelations with usual
measures of spin dynamics such as the spin-diffusion constant, $D$ and
spin-autocorrelation time, $\tau$. We find that they all exhibit power law
behaviour at low temperature, consistent with scaling of the form $D\sim
v_b^2/\mu$ and $\tau^{-1}\sim T$. The vanishing of $\mu\sim T^{0.48}$ is
parametrically slower than that of the corresponding quantum bound, $\mu\sim
T$, raising interesting questions regarding the semi-classical limit of such
spin systems.",1808.02054v2
2020-10-06,Emergent spin dynamics enabled by lattice interactions in a bicomponent artificial spin ice,"Artificial spin ice (ASI) are arrays on nanoscaled magnets that can serve
both as models for frustration in atomic spin ice as well as for exploring new
spin-wave-based strategies to transmit, process, and store information. Here,
we exploit the intricate interplay of the magnetization dynamics of two
dissimilar ferromagnetic metals arranged on complimentary lattice sites in a
square ASI to effectively modulate the spin-wave properties. We show that the
interaction between the two sublattices results in unique spectra attributed to
each sublattice and we observe inter- and intra-lattice dynamics facilitated by
the distinct magnetization properties of the two materials. The dynamic
properties are systematically studied by angular-dependent broadband
ferromagnetic resonance and confirmed by micromagnetic simulations. We show
that the combination of materials with dissimilar magnetic properties enables
the realization of a wide range of two-dimensional structures potentially
opening the door to new concepts in nanomagnonics.",2010.03008v1
2021-03-25,Non-Adiabatic Ring Polymer Molecular Dynamics with Spin Mapping Variables,"We present a new non-adiabatic ring polymer molecular dynamics (NRPMD) method
based on the spin mapping formalism, which we refer to as the spin-mapping
NRPMD (SM-NRPMD) approach. We derive the path-integral partition function
expression using the spin coherent state basis for the electronic states and
the ring polymer formalism for the nuclear degrees of freedom (DOFs). This
partition function provides an efficient sampling of the quantum statistics.
Using the basic property of the Stratonovich-Weyl transformation, we derive a
Hamiltonian which we propose for the dynamical propagation of the coupled spin
mapping variables and the nuclear ring polymer. The accuracy of the SM-NRPMD
method is numerically demonstrated by computing nuclear position and population
auto-correlation functions of non-adiabatic model systems. The results from
SM-NRPMD agree very well with the numerically exact results. The main advantage
of using the spin mapping variables over the harmonic oscillator mapping
variables is numerically demonstrated, where the former provides nearly
time-independent expectation values of physical observables for systems under
thermal equilibrium, the latter can not preserve the initial quantum Boltzmann
distribution. We also explicitly demonstrate that SM-NRPMD provides invariant
dynamics upon various ways of partitioning the state-dependent and
state-independent potentials.",2103.14119v1
2023-03-27,Temperature dependent study of the spin dynamics of coupled Y$_3$Fe$_5$O$_{12}$/Gd$_3$Fe$_5$O$_{12}$/Pt trilayers,"In this study, we investigate the dynamic response of a Y$_3$Fe$_5$O$_{12}$
(YIG)/ Gd$_3$Fe$_5$O$_{12}$ (GdIG)/ Pt trilayer system by measurements of the
ferromagnetic resonance (FMR) and the pumped spin current detected by the
inverse spin Hall effect. This trilayer system offers the unique opportunity to
investigate the spin dynamics of the ferrimagnetic GdIG, close to its
compensation temperature. We show that our trilayer acts as a highly tunable
spin current source. Our experimental results are supported by micro-magnetic
simulations. As the detected spin current in the top Pt layer is distinctly
dominated by the GdIG layer, this gives the unique opportunity to investigate
the excitation and dynamic properties of GdIG while comparing it to the
broadband FMR absorption spectrum of the heterostructure.",2303.15085v1
2023-04-21,A High-Performance Implementation of Atomistic Spin Dynamics Simulations on x86 CPUs,"Atomistic spin dynamics simulations provide valuable information about the
energy spectrum of magnetic materials in different phases, allowing one to
identify instabilities and the nature of their excitations. However, the time
cost of evaluating the dynamical correlation function $S(\mathbf{q}, t)$
increases quadratically as the number of spins $N$, leading to significant
computational effort, making the simulation of large spin systems very
challenging. In this work, we propose to use a highly optimized general matrix
multiply (GEMM) subroutine to calculate the dynamical spin-spin correlation
function that can achieve near-optimal hardware utilization. Furthermore, we
fuse the element-wise operations in the calculation of $S(\mathbf{q}, t)$ into
the in-house GEMM kernel, which results in further performance improvements of
44\% - 71\% on several relatively large lattice sizes when compared to the
implementation that uses the GEMM subroutine in OpenBLAS, which is the
state-of-the-art open source library for Basic Linear Algebra Subroutine
(BLAS).",2304.10966v1
2023-05-01,Ultrafast electron-phonon scattering in antiferromagnetic Dirac semimetals,"Topological antiferromagnetic systems, which exhibit anisotropic band
structures combined with complex relativistic spin structures in momentum
space, have shown strong magnetoresistance effects driven by Dirac fermion
characteristics. While these new antiferromagnets have been studied in
transport experiments, very little is known about their spin-dependent
electronic dynamics on ultrafast timescales and far-from-equilibrium behavior.
This paper investigates theoretically the spin-dependent electronic dynamics
due to electron-phonon scattering in a model electronic band structure that
corresponds to a Dirac semimetal antiferromagnet. Following a spin conserving
instantaneous excitation we obtain a change of the antiferromagnetic spin
polarization due to the scattering dynamics for the site-resolved spin
expectation values. This allows us to identify fingerprints of the anisotropic
band structure in the carrier dynamics on ultrashort timescales which should be
observable in present experimental set-ups.",2305.00775v2
2023-07-25,Unconventional spin transport in strongly correlated kagome systems,"Recent progress in material design enables the study of correlated,
low-temperature phases and associated anomalous transport in two-dimensional
kagome systems. Here, we show that unconventional spin transport can arise in
such systems even at elevated temperatures due to emergent dynamical
constraints. To demonstrate this effect, we consider a strong-coupling limit of
an extended Hubbard model on the kagome lattice with density of $2/3$. We
numerically investigate the charge and spin transport by a cellular automaton
circuit, allowing us to perform simulations on large systems to long times
while preserving the essential conservation laws. The charge dynamics reflects
the constraints and can be understood by a Gaussian field theory of a scalar
height field. Moreover, the system exhibits a hidden spin conservation law with
a dynamic sublattice structure, which enables additional slow relaxation
pathways for spin excitations. These features can be directly tested by
measuring the dynamic spin structure factor with neutron scattering.",2307.13725v2
2024-01-08,Optically Helicity-Dependent Orbital and Spin Dynamics in Two-Dimensional Ferromagnets,"Disentangling orbital (OAM) and spin (SAM) angular momenta in the ultrafast
spin dynamics of two-dimensional (2D) ferromagnets on subfemtoseconds is a
challenge in the field of ultrafast magnetism. Herein, we employed
non-collinear spin version of real-time time-dependent density functional
theory to investigate the orbital and spin dynamics of 2D ferromagnets Fe3GeTe2
(FGT) induced by circularly polarized light. Our results show the
demagnetization of Fe sublattice in FGT is accompanied by helicity-dependent
precession of OAM and SAM excited by circularly polarized lasers. We further
identify that precession of OAM and SAM in FGT is faster than the
demagnetization within a few femtoseconds. Remarkably, circularly polarized
lasers can significantly induce a periodically transverse response of OAM and
SAM on very ultrafast timescales of ~250 attoseconds. Our finding suggests a
powerful new route for attosecond regimes of the angular momentum manipulation
to coherently control helicity-dependent orbital and spin dynamics in 2D
limits.",2401.04038v1
2020-06-22,The dynamics of a driven harmonic oscillator coupled to pairwise interacting Ising spins in random fields,"In general we are interested in dynamical systems coupled to complex
hysteresis. Therefore as a first step we investigated recently the dynamics of
a periodically driven damped harmonic oscillator coupled to independent Ising
spins in a random field. Although such a system does not produce hysteresis, we
showed how to characterize the dynamics of such a piecewise-smooth system,
especially in the case of a large number of spins [P. Zech, A. Otto, and G.
Radons, Phys. Rev. E 101, 042217 (2020)]. In this paper we extend our model to
spin dimers, thus pairwise interacting spins. We show in which cases two
interacting spins can show elementary hysteresis and we give a connection to
the Preisach model, which allows us to consider an infinite number of
spin-pairs. This thermodynamic limit leads us to a dynamical system with an
additional hysteretic force in the form of a generalized play operator. By
using methods from general chaos theory, piecewise-smooth system theory and
statistics we investigate the chaotic behavior of the dynamical system for a
few spins and also in case of a larger number of spins by calculating
bifurcation diagrams, Lyapunov exponents, fractal dimensions and self-averaging
properties. We find that the fractal dimensions and the magnetization are in
general not self-averaging quantities. We show, how the dynamical properties of
the piecewise-smooth system for a large number of spins differs from the system
in its thermodynamic limit.",2006.12429v10
2003-08-07,Crossovers in spin-boson and central spin models,"We discuss how the crossovers in models like spin-boson model are changed by
adding the coupling of the central spin to localised modes- the latter modelled
as a 'spin bath'. These modes contain most of the environmental entropy and
energy at low T in solid-state systems. We find that the low T crossover
between oscillator bath and spin bath dominated decoherence, occurring as one
reduces the energy scale of the central spin, is characterised by very low
decoherence- we show how this works out in practise in magnetic insulators. We
then reconsider the standard quantum-classical crossover in the dynamics of a
tunneling system, including both spin and oscillator baths. It is found that
the general effect of the spin bath is to broaden the crossover in temperature
between the quantum and classical activated regimes. The example of tunneling
nanomagnets is used to illustrate this.",0308139v2
2003-09-18,Separated Spin and Charge Excitations and their Coupling in the Spin-Pseudospin Model for Quarter-Filled Ladders,"Quantum Monte Carlo (QMC) and density-matrix renormalization group (DMRG)
methods are used to study the coupled spin-pseudospin Hamiltonian in
one-dimension (1D) that models the charge-ordering instability of the
anisotropic Hubbard ladder at quarter filling. We calculate the temperature
dependence of the uniform spin susceptibility and specific heat as well as the
spin and charge excitation spectra of the system. We show that there is a
parameter and temperature region where the spin degrees of freedom are
separated from the charge degrees of freedom and behave like a 1D
antiferromagnetic Heisenberg model, and that, outside this parameter region and
above a crossover temperature, the spin excitations are largely affected by the
charge fluctuation. We argue that observed anomalous spin dynamics in the
disorder phase of a typical charge-ordered material $\alpha'$-NaV$_2$O$_5$ may
possibly be a consequence of this type of spin-charge coupling.",0309433v1
2005-02-08,Monte Carlo Simulations of Spin-Diffusion in a 2-D Heisenberg Paramagnet,"We study spin diffusion and spin waves in paramagnetic quantum crystals
(solid He-3, for example) by direct simulation of a square lattice of atoms
interacting via a nearest-neighbor Heisenberg exchange Hamiltonian. Recently,
Cowan and Mullin have used a moments method to study spin transport at
arbitrary polarizations. We test their analytic results by calculating the
statistical spin correlation function from molecular dynamics simulations using
a Monte Carlo algorithm to average over initial spin configurations. Since it
is not practical to diagonalize the S=1/2 exchange Hamiltonian for a lattice
which is of sufficient size to study long-wavelength (hydrodynamic)
fluctuations, we instead study the S -> infinity limit and treat each spin as a
vector with a classical equation of motion. We compare our simulations with the
assumptions of the moments method regarding the short-time behavior and the
long exponential tail of the correlation function. We also present our
numerical results for the polarization dependence of the longitudinal spin
diffusion coefficient and the complex transverse spin diffusion coefficient.",0502214v1
2005-08-18,Theory of electron spin decoherence by interacting nuclear spins in a quantum dot,"We present a quantum solution to the electron spin decoherence by a nuclear
pair-correlation method for the electron-nuclear spin dynamics under a strong
magnetic field and a temperature high for the nuclear spins but low for the
electron. The theory incorporates the hyperfine interaction, the intrinsic
(both direct and indirect) nuclear interactions, and the extrinsic nuclear
coupling mediated by the hyperfine interaction with the single electron in
question. The last is shown to be important in free-induction decay (FID) of
the single electron spin coherence. The spin echo eliminates the
hyperfine-mediated decoherence but only reduces the decoherence by the
intrinsic nuclear interactions. Thus, the decoherence times for single spin FID
and ensemble spin echo are significantly different. The decoherence is
explained in terms of quantum entanglement, which involves more than the
spectral diffusion.",0508441v3
2005-09-05,Spin dynamics in HTSC cuprates: The singlet--correlated band (or t-J-V) model and its applications,"So far calculations of the spin susceptibility in the superconducting state
of cuprates have been performed in the framework of weak-coupling
approximations. However, it is known that cuprates belong to Mott-Hubbard doped
materials where electron correlations are important. In this paper an
analytical expression for the spin susceptibility in the superconducting state
of cuprates is derived within the singlet-correlated band model, which takes
into account strong correlations. The expression of the spin susceptibility is
evaluated using values for the hopping parameters adapted to measurements of
the Fermi surface of the materials YBa2Cu3O7 and Bi2Sr2CaCu2O8. We show that
the available experimental data which are directly related to the spin
susceptibility can be explained consistently within one set of model parameters
for each material. These experiments include the magnetic resonance peak
observed by inelastic neutron scattering and the temperature dependence of the
NMR spin shift, spin-spin and spin-lattice relaxation rates in the
superconducting state.",0509110v1
2006-04-25,Multiple-pulse coherence enhancement of solid state spin qubits,"We describe how the spin coherence time of a localized electron spin in
solids, i.e. a solid state spin qubit, can be prolonged by applying designed
electron spin resonance pulse sequences. In particular, the spin echo decay due
to the spectral diffusion of the electron spin resonance frequency induced by
the non-Markovian temporal fluctuations of the nuclear spin flip-flop dynamics
can be strongly suppressed using multiple-pulse sequences akin to the
Carr-Purcell-Meiboom-Gill pulse sequence in nuclear magnetic resonance. Spin
coherence time can be enhanced by factors of 4-10 in GaAs quantum dot and Si:P
quantum computer architectures using composite sequences with an even number of
pulses.",0604577v2
2006-07-05,Hole Doping Effects on Spin-gapped Na2Cu2TeO6 via Topochemical Na Deficiency,"We report the magnetic susceptibility and NMR studies of a spin-gapped
layered compound
  Na2Cu2TeO6 (the spin gap $\Delta\sim$ 250 K), the hole doping effect on the
Cu2TeO6 plane via a topochemical Na deficiency by soft chemical treatment, and
the static spin vacancy effect by nonmagnetic impurity Zn substitution for Cu.
  A finite Knight shift at the $^{125}$Te site was observed for pure
Na2Cu2TeO6.
  The negative hyperfine coupling constant $^{125}A_{tr}$ is an evidence for
the existence of a superexchange pathway of the Cu-O-Te-O-Cu bond. It turned
out that both the Na deficiency and Zn impurities induce a Curie-type magnetism
in the uniform spin susceptibility in an external magnetic field of 1 T, but
only the Zn impurities enhance the low-temperature $^{23}$Na nuclear
spin-lattice relaxation rate whereas the Na deficiency suppresses it. A spin
glass behavior was observed for the Na-deficient samples but not for the
Zn-substituted samples. The dynamics of the unpaired moments of the doped holes
are different from that of the spin vacancy in the spin-gapped Cu2TeO6 planes.",0607141v1
2006-11-28,Optical and electrical spin injection and spin transport in hybrid Fe/GaAs devices,"We discuss methods for imaging the nonequilibrium spin polarization of
electrons in Fe/GaAs spin transport devices. Both optically- and
electrically-injected spin distributions are studied by scanning
magneto-optical Kerr rotation microscopy. Related methods are used to
demonstrate electrical spin detection of optically-injected spin polarized
currents. Dynamical properties of spin transport are inferred from studies
based on the Hanle effect, and the influence of strain on spin transport data
in these devices is discussed.",0611729v1
1998-07-08,Spinning Particles on Spacelike Hypersurfaces and their Rest-Frame Description,"A new spinning particle with a definite sign of the energy is defined on
spacelike hypersurfaces after a critical discussion of the standard spinning
particles. They are the pseudoclassical basis of the positive energy $({1\over
2},0)$ [or negative energy $(0,{1\over 2})$] parts of the $({1\over 2},{1\over
2})$ solutions of the Dirac equation. The study of the isolated system of N
such spinning charged particles plus the electromagnetic field leads to their
description in the rest-frame Wigner-covariant instant form of dynamics on the
Wigner hyperplanes orthogonal to the total 4-momentum of the isolated system
(when it is timelike). We find that on such hyperplanes these spinning
particles have a nonminimal coupling only of the type ""spin-magnetic field""
like the nonrelativistic Pauli particles to which they tend in the
nonrelativistic limit. The Lienard-Wiechert potentials associated with these
charged spinning particles are found. Then, a comment on how to quantize the
spinning particles respecting their fibered structure describing the spin
structure is done.",9807052v1
2000-04-27,Transverse Spin in QCD: Radiative Corrections,"In this paper we address various issues connected with transverse spin in
light front QCD. The transverse spin operators, in $A^+ = 0$ gauge, expressed
in terms of the dynamical variables are explicitly interaction dependent unlike
the helicity operator which is interaction independent in the topologically
trivial sector of light-front QCD. Although it cannot be separated into an
orbital and a spin part, we have shown that there exists an interesting
decomposition of the transverse spin operator. We discuss the physical
relevance of such a decomposition. We perform a one loop renormalization of the
full transverse spin operator in light-front Hamiltonian perturbation theory
for a dressed quark state. We explicitly show that all the terms dependent on
the center of mass momenta get canceled in the matrix element. The entire
non-vanishing contribution comes from the fermion intrinsic -like part of the
transverse spin operator as a result of cancellation between the gluonic
intrinsic-like and the orbital-like part of the transverse spin operator. We
compare and contrast the calculations of transverse spin and helicity of a
dressed quark in perturbation theory.",0004193v2
2006-10-26,Loschmidt Echo and Berry phase of the quantum system coupled to the XY spin chain: Proximity to quantum phase transition,"We study the Loschmidt echo (LE) of a coupled system consisting of a central
spin and its surrounding environment described by a general XY spin-chain
model. The quantum dynamics of the LE is shown to be remarkably influenced by
the quantum criticality of the spin chain. In particular, the decaying behavior
of the LE is found to be controlled by the anisotropy parameter of the spin
chain. Furthermore, we show that due to the coupling to the spin chain, the
ground-state Berry phase for the central spin becomes nonanalytical and its
derivative with respect to the magnetic parameter $\lambda$ in spin chain
diverges along the critical line $\lambda=1$, which suggests an alternative
measurement of the quantum criticality of the spin chain.",0610218v1
2007-08-15,Spin dynamics in InAs-nanowire quantum-dots coupled to a transmission line,"We study theoretically electron spins in nanowire quantum dots placed inside
a transmission line resonator. Because of the spin-orbit interaction, the spins
couple to the electric component of the resonator electromagnetic field and
enable coherent manipulation, storage, and read-out of quantum information in
an all-electrical fashion. Coupling between distant quantum-dot spins, in one
and the same or different nanowires, can be efficiently performed via the
resonator mode either in real time or through virtual processes. For the latter
case we derive an effective spin-entangling interaction and suggest means to
turn it on and off. We consider both transverse and longitudinal types of
nanowire quantum-dots and compare their manipulation timescales against the
spin relaxation times. For this, we evaluate the rates for spin relaxation
induced by the nanowire vibrations (phonons) and show that, as a result of
phonon confinement in the nanowire, this rate is a strongly varying function of
the spin operation frequency and thus can be drastically reduced compared to
lateral quantum dots in GaAs. Our scheme is a step forward to the formation of
hybrid structures where qubits of different nature can be integrated in a
single device.",0708.2091v1
2007-11-03,Spin-echo of a single electron spin in a quantum dot,"We report a measurement of the spin-echo decay of a single electron spin
confined in a semiconductor quantum dot. When we tip the spin in the transverse
plane via a magnetic field burst, it dephases in 37 ns due to the Larmor
precession around a random effective field from the nuclear spins in the host
material. We reverse this dephasing to a large extent via a spin-echo pulse,
and find a spin-echo decay time of about 0.5 microseconds at 70 mT. These
results are in the range of theoretical predictions of the electron spin
coherence time governed by the dynamics of the electron-nuclear system.",0711.0479v1
2007-11-14,Non-Abelian gauge field effects and its relevance to spinning particle dynamics in the technology of spintronics,"We describe formally the precession of spin vector about the k-space
effective magnetic field in condensed matter system with spin orbital effects
as constituting a local transformation of the electron wavefunction which
necessarily invokes the SU(2) transformation rule to ensure covariance. We
showed a ""no-precession"" condition as pre-requisite for the spin gauge field to
exert its influence on spin particle motion. The effects of the spin gauge
field on spin particle motion were shown to be consistent in both classical and
quantum pictures, which hence should underpin theoretical explanations for
important effects in anomalous Hall, spin Hall, spin torque, optical Magnus,
geometric quantum computation.",0711.2120v1
2008-01-07,Magnetization reversal driven by spin-injection : a mesoscopic spin-transfer effect,"A mesoscopic description of spin-transfer effect is proposed, based on the
spin-injection mechanism occurring at the junction with a ferromagnet. The
effect of spin-injection is to modify locally, in the ferromagnetic
configuration space, the density of magnetic moments. The corresponding
gradient leads to a current-dependent diffusion process of the magnetization.
In order to describe this effect, the dynamics of the magnetization of a
ferromagnetic single domain is reconsidered in the framework of the
thermokinetic theory of mesoscopic systems. Assuming an Onsager
cross-coefficient that couples the currents, it is shown that spin-dependent
electric transport leads to a correction of the Landau-Lifshitz-Gilbert
equation of the ferromagnetic order parameter with supplementary diffusion
terms. The consequence of spin-injection in terms of activation process of the
ferromagnet is deduced, and the expressions of the effective energy barrier and
of the critical current are derived. Magnetic fluctuations are calculated: the
correction to the fluctuations is similar to that predicted for the activation.
These predictions are consistent with the measurements of spin-transfer
obtained in the activation regime and for ferromagnetic resonance under
spin-injection.",0801.1019v1
2008-03-25,Quantum dissipative Rashba spin ratchets,"We predict the possibility to generate a finite stationary spin current by
applying an unbiased ac driving to a quasi-one-dimensional asymmetric periodic
structure with Rashba spin-orbit interaction and strong dissipation. We show
that under a finite coupling strength between the orbital degrees of freedom
the electron dynamics at low temperatures exhibits a pure spin ratchet
behavior, {\it i.e.} a finite spin current and the absence of charge transport
in spatially asymmetric structures. It is also found that the equilibrium spin
currents are not destroyed by the presence of strong dissipation.",0803.3526v2
2009-04-03,Ultrafast optical spin echo for electron spins in semiconductors,"Spin-based quantum computing and magnetic resonance techniques rely on the
ability to measure the coherence time, T2, of a spin system. We report on the
experimental implementation of all-optical spin echo to determine the T2 time
of a semiconductor electron-spin system. We use three ultrafast optical pulses
to rotate spins an arbitrary angle and measure an echo signal as the time
between pulses is lengthened. Unlike previous spin-echo techniques using
microwaves, ultrafast optical pulses allow clean T2 measurements of systems
with dephasing times T2* fast in comparison to the timescale for microwave
control. This demonstration provides a step toward ultrafast optical dynamic
decoupling of spin-based qubits.",0904.0632v1
2010-03-31,Inverse Spin Hall Effect and Anomalous Hall Effect in a Two-Dimensional Electron Gas,"We study the coupled dynamics of spin and charge currents in a
two-dimensional electron gas in the transport diffusive regime. For systems
with inversion symmetry there are established relations between the spin Hall
effect, the anomalous Hall effect and the inverse spin Hall effect. However, in
two-dimensional electron gases of semiconductors like GaAs, inversion symmetry
is broken so that the standard arguments do not apply. We demonstrate that in
the presence of a Rashba type of spin-orbit coupling (broken structural
inversion symmetry) the anomalous Hall effect, the spin Hall and inverse spin
Hall effect are substantially different effects. Furthermore we discuss the
inverse spin Hall effect for a two-dimensional electron gas with Rashba and
Dresselhaus spin-orbit coupling; our results agree with a recent experiment.",1003.6018v1
2010-04-01,Electron spin dynamics and electron spin resonance in graphene,"A theory of spin relaxation in graphene including intrinsic, Bychkov-Rashba,
and ripple spin-orbit coupling is presented. We find from spin relaxation data
by Tombros et al. [Nature 448, 571 (2007).] that intrinsic spin-orbit coupling
dominates over other contributions with a coupling constant of 3.7 meV.
Although it is 1-3 orders of magnitude larger than those obtained from first
principles, we show that comparable values are found for other honeycomb
systems, MgB2 and LiC6; the latter is studied herein by electron spin resonance
(ESR). We predict that spin coherence is longer preserved for spins
perpendicular to the graphene plane, which is beneficial for spintronics. We
identify experimental conditions when bulk ESR is realizable on graphene.",1004.0210v1
2010-09-15,Spin-wave interference patterns created by spin-torque nano-oscillators for memory and computation,"Magnetization dynamics in nanomagnets has attracted broad interest since it
was predicted that a dc-current flowing through a thin magnetic layer can
create spin-wave excitations. These excitations are due to spin-momentum
transfer, a transfer of spin angular momentum between conduction electrons and
the background magnetization, that enables new types of information processing.
Here we show how arrays of spin-torque nano-oscillators (STNO) can create
propagating spin-wave interference patterns of use for memory and computation.
Memristic transponders distributed on the thin film respond to threshold tunnel
magnetoresistance (TMR) values thereby detecting the spin-waves and creating
new excitation patterns. We show how groups of transponders create resonant
(reverberating) spin-wave interference patterns that may be used for
polychronous wave computation of arithmetic and boolean functions and
information storage.",1009.4116v1
2010-09-29,Transport through quantum-dot spin valves containing magnetic impurities,"We investigate transport through a single-level quantum dot coupled to
noncollinearly magnetized ferromagnets in the presence of localized spins in
either the tunnel barrier or on the quantum dot. For a spin embedded in the
tunnel barrier, we find an interplay between current-induced switching of the
spin, spin-dependent tunneling through the barrier and spin accumulation on the
dot resulting in characteristic signals in the current. We, furthermore, find
huge Fano factors due to random telegraph noise. For noncollinear geometries,
an exchange field that depends on the impurity spin state leads to
characteristic fingerprints in the transport properties. In the case of a spin
on the quantum dot, we find that the frequency-dependent Fano factor can be
used to study the nontrivial dynamics of the spins on the dot due to the
interplay between exchange interaction and coupling to external and exchange
magnetic fields.",1009.5901v2
2010-10-08,Time-resolved detection of spin-transfer-driven ferromagnetic resonance and spin torque measurement in magnetic tunnel junctions,"Several experimental techniques have been introduced in recent years in
attempts to measure spin transfer torque in magnetic tunnel junctions (MTJs).
The dependence of spin torque on bias is important for understanding
fundamental spin physics in magnetic devices and for applications. However,
previous techniques have provided only indirect measures of the torque and
their results to date for the bias dependence are qualitatively and
quantitatively inconsistent. Here we demonstrate that spin torque in MTJs can
be measured directly by using time-domain techniques to detect resonant
magnetic precession in response to an oscillating spin torque. The technique is
accurate in the high-bias regime relevant for applications, and because it
detects directly small-angle linear-response magnetic dynamics caused by spin
torque it is relatively immune to artifacts affecting competing techniques. At
high bias we find that the spin torque vector differs markedly from the simple
lowest-order Taylor series approximations commonly assumed.",1010.1777v1
2010-10-29,Temperature and Electron Density Dependence of Spin Relaxation in GaAs/AlGaAs Quantum Well,"Temperature and carrier density dependent spin dynamics for GaAs/AlGaAs
quantum wells (QWs) with different structural symmetry has been studied by
using time-resolved Kerr rotation technique. The spin relaxation time is
measured to be much longer for the symmetrically-designed GaAs quantum well
comparing with the asymmetrical one, indicating the strong influence of Rashba
spin-orbit coupling on spin relaxation. D'yakonov-Perel' (DP) mechanism has
been revealed to be the dominant contribution for spin relaxation in
GaAs/AlGaAs QWs. The spin relaxation time exhibits non-monotonic dependent
behavior on both temperature and photo-excited carrier density, revealing the
important role of non-monotonic temperature and density dependence of
electron-electron Coulomb scattering. Our experimental observations demonstrate
good agreement with recently developed spin relaxation theory based on
microscopic kinetic spin Bloch equation approach.",1010.6144v1
2010-12-09,Spin-Currents and Spin-Pumping Forces for Spintronics,"A general definition of the Spintronics concept of spin-pumping is proposed
as generalized forces conjugated to the spin degrees of freedom in the
framework of the theory of mesoscopic non-equilibrium thermodynamics. It is
shown that at least three different kinds of spin-pumping forces and associated
spin-currents can be defined in the most simple spintronics system (the
Ferromagnetic/Non-Ferromagnetic metal interface). Furthermore, the generalized
force associated to the ferromagnetic collective variable is also introduced in
an equal footing, in order to describe the coexistence of the spin of the
conduction electrons (paramagnetic spins attached to $s$-band electrons) and
the ferromagnetic-order parameter. The dynamical coupling between these two
kinds of magnetic degrees of freedom is presented, and interpreted in terms of
spin-transfer effects.",1012.2083v1
2011-01-18,Generating Entanglement and Squeezed States of Nuclear Spins in Quantum Dots,"Entanglement generation and detection are two of the most sought-after goals
in the field of quantum control. Besides offering a means to probe some of the
most peculiar and fundamental aspects of quantum mechanics, entanglement in
many-body systems can be used as a tool to reduce fluctuations below the
standard quantum limit. For spins, or spin-like systems, such a reduction of
fluctuations can be realized with so-called squeezed states. Here we present a
scheme for achieving coherent spin squeezing of nuclear spin states in
few-electron quantum dots. This work represents a major shift from earlier
studies in quantum dots, which have explored classical ""narrowing"" of the
nuclear polarization distribution through feedback involving stochastic spin
flips. In contrast, we use the nuclear-polarization-dependence of the electron
spin resonance (ESR) to provide a non-linearity which generates a non-trivial,
area-preserving, ""twisting"" dynamics that squeezes and stretches the nuclear
spin Wigner distribution without the need for nuclear spin flips.",1101.3370v2
2011-07-07,Reduced effective spin-orbital degeneracy and spin-orbital ordering in paramagnetic transition metal oxides: Sr2IrO4 vs. Sr2RhO4,"We discuss the notions of spin-orbital polarization and ordering in
paramagnetic materials, and address their consequences in transition metal
oxides. Extending the combined density functional and dynamical mean field
theory scheme to the case of materials with large spin-orbit interactions, we
investigate the electronic excitations of the paramagnetic phases of Sr2IrO4
and Sr2RhO4. We show that the interplay of spin-orbit interactions, structural
distortions and Coulomb interactions suppresses spin-orbital fluctuations. As a
result, the room temperature phase of Sr2IrO4 is a paramagnetic spin-orbitally
ordered Mott insulator. In Sr2RhO4, the effective spin-orbital degeneracy is
reduced, but the material remains metallic, due to both, smaller spin-orbit and
smaller Coulomb interactions. We find excellent agreement of our ab-initio
calculations for Sr2RhO4 with angle-resolved photoemission, and make
predictions for spectra of the paramagnetic phase of Sr2IrO4.",1107.1371v1
2011-09-18,Nuclear Spin Dynamics of Ionized Phosphorus Donors in Silicon,"We demonstrate the coherent control and electrical readout of the nuclear
spins of ionized phosphorus donors in natural silicon. By combining pulsed
illumination with coherent electron spin manipulation, we selectively ionize
the donor depending on its nuclear spin state, exploiting a spin-dependent
recombination process via a spin pair at the Si/SiO2 interface. The
nuclear-spin coherence time of the ionized donor is 18 ms, two orders of
magnitude longer than in the neutral donor state, rendering the ionized donor a
potential resource as a quantum memory. The presented experimental techniques
allow for spectroscopy of ionized-donor nuclear spins, increase the sensitivity
of electrically detected electron nuclear double resonance by more than two
orders of magnitude, and give experimental access to the lifetime of parallel
electron spin pairs.",1109.3864v2
2012-06-04,Von Neumann Entropy Spectra and Entangled Excitations in Spin-Orbital Models,"We consider the low-energy excitations of one-dimensional spin-orbital models
which consist of spin waves, orbital waves, and joint spin-orbital excitations.
Among the latter we identify strongly entangled spin-orbital bound states which
appear as peaks in the von Neumann entropy (vNE) spectral function introduced
in this work. The strong entanglement of bound states is manifested by a
universal logarithmic scaling of the vNE with system size, while the vNE of
other spin-orbital excitations saturates. We suggest that spin-orbital
entanglement can be experimentally explored by the measurement of the dynamical
spin-orbital correlations using resonant inelastic x-ray scattering, where
strong spin-orbit coupling associated with the core hole plays a role.",1206.1062v1
2012-11-15,Spin transport and tunable Gilbert damping in a single-molecule magnet junction,"We study time-dependent electronic and spin transport through an electronic
level connected to two leads and coupled with a single-molecule magnet via
exchange interaction. The molecular spin is treated as a classical variable and
precesses around an external magnetic field. We derive expressions for charge
and spin currents by means of the Keldysh non-equilibrium Green's functions
technique in linear order with respect to the time-dependent magnetic field
created by this precession. The coupling between the electronic spins and the
magnetization dynamics of the molecule creates inelastic tunneling processes
which contribute to the spin currents. The inelastic spin currents, in turn,
generate a spin-transfer torque acting on the molecular spin. This back-action
includes a contribution to the Gilbert damping and a modification of the
precession frequency. The Gilbert damping coefficient can be controlled by the
bias and gate voltages or via the external magnetic field and has a
non-monotonic dependence on the tunneling rates.",1211.3611v2
2013-03-15,Nuclear spin polarization in a single quantum dot pumped by two laser beams,"We theoretically investigate dynamic nuclear spin polarization in a
self-assembled quantum dot pumped optically by two laser beams. With the
assumption that a noncollinear interaction between the hole spin and nuclear
spins leads to nuclear spin polarization, we find that both weak and strong
nuclear spin polarizations can arise, depending on the intensities and central
frequencies of the lasers. For weak nuclear spin polarization, we use a
perturbation method to show that the distribution of the nuclear spin
Overhauser field may become significantly narrower. Using Monte Carlo
simulations to study a single quantum dot, we find that strong nuclear spin
polarization can also be generated via appropriate optical pumping.",1303.3859v3
2013-06-13,Optical Spin Noise of a Single Hole Spin Localized in an (InGa)As Quantum Dot,"We advance spin noise spectroscopy to the ultimate limit of single spin
detection. This technique enables the measurement of the spin dynamic of a
single heavy hole localized in a flat (InGa)As quantum dot. Magnetic field and
light intensity dependent studies reveal even at low magnetic fields a strong
magnetic field dependence of the longitudinal heavy hole spin relaxation time
with an extremely long $T_1$ of $\ge$ 180 $\mu$s at 31 mT and 5 K. The
wavelength dependence of the spin noise power discloses for finite light
intensities an inhomogeneous single quantum dot spin noise spectrum which is
explained by charge fluctuations in the direct neighborhood of the quantum dot.
The charge fluctuations are corroborated by the distinct intensity dependence
of the effective spin relaxation rate.",1306.3183v3
2014-04-29,Nanowire Spin Torque Oscillator Driven by Spin Orbit Torques,"Spin torque from spin current applied to a nanoscale region of a ferromagnet
can act as negative magnetic damping and thereby excite self-oscillations of
its magnetization. In contrast, spin torque uniformly applied to the
magnetization of an extended ferromagnetic film does not generate
self-oscillatory magnetic dynamics but leads to reduction of the saturation
magnetization. Here we report studies of the effect of spin torque on a system
of intermediate dimensionality - a ferromagnetic nanowire. We observe coherent
self-oscillations of magnetization in a ferromagnetic nanowire serving as the
active region of a spin torque oscillator driven by spin orbit torques. Our
work demonstrates that magnetization self-oscillations can be excited in a
one-dimensional magnetic system and that dimensions of the active region of
spin torque oscillators can be extended beyond the nanometer length scale.",1404.7262v2
2014-07-01,Gapless spin-liquid phase in an extended spin 1/2 triangular Heisenberg model,"We numerically study the Heisenberg models on triangular lattices by
extending it from the simplest equilateral lattice with only the
nearest-neighbor exchange interaction. We show that, by including an additional
weak next-nearest-neighbor interaction, a quantum spin-liquid phase is
stabilized against the antiferromagnetic order. The spin gap (triplet
excitation gap) and spin correlation at long distances decay algebraically with
increasing system size at the critical point between the antiferromagnetic
phase and the spin-liquid phase. This algebraic behavior continues in the
spin-liquid phase as well, indicating the presence of an unconventional
critical (algebraic spin-liquid) phase characterized by the dynamical and
anomalous critical exponents $z+\eta\sim1$. Unusually small triplet and singlet
excitation energies found in extended points of the Brillouin zone impose
constraints on this algebraic spin liquid.",1407.0318v2
2014-11-17,Spin-orbital exchange of strongly interacting fermions on the $p$-band of a two-dimensional optical lattice,"Mott insulators with both spin and orbital degeneracy are pertinent to a
large number of transition metal oxides. The intertwined spin and orbital
fluctuations can lead to rather exotic phases such as quantum spin-orbital
liquids. Here we consider two-component (spin 1/2) fermionic atoms with strong
repulsive interactions on the $p$-band of the optical square lattice. We derive
the spin-orbital exchange for quarter filling of the $p$-band when the density
fluctuations are suppressed, and show it frustrates the development of long
range spin order. Exact diagonalization indicates a spin-disordered ground
state with ferro-orbital order. The system dynamically decouples into
individual Heisenberg spin chains, each realizing a Luttinger liquid accessible
at higher temperatures compared to atoms confined to the $s$-band.",1411.4496v2
2015-03-19,Above-threshold ionization with highly charged ions in super-strong laser fields: III. Spin effects and its dependence on laser polarization,"Spin effects in the tunneling regime of strong field ionization of
hydrogenlike highly charged ions in linearly as well as circularly polarized
laser fields are investigated. The impact of the polarization of a laser field
on the spin effects are analyzed. Spin-resolved differential ionization rates
are calculated employing the relativistic Coulomb-corrected strong-field
approximation (SFA) developed in the previous paper of the series. Analytical
expressions for spin asymmetries and spin flip probability, depending on the
laser's polarization, are obtained for the photoelectron momentum corresponding
to the maximum of tunneling probability. A simpleman model is developed for the
description of spin dynamics in tunnel-ionization, which provides an intuitive
explanation for the spin effects. The spin flip is shown to be experimentally
observable by using moderate highly charged ions with a charge of the order of
20 and a laser field with an intensity of $I\sim 10^{22}$ W/cm$^2$.",1503.05817v2
2015-05-07,Irreversible decoherence of dipole interacting nuclear spins coupled with a phonon bath,"We report a first-principle theoretical study of the adiabatic decoherence
undergone by a nuclear spin system in a solid, coupled to the phonon field
through the dipolar interaction. The calculations are performed for a chain of
weakly interacting 1/2-spin pairs, considered as an open quantum system in
contact with a bosonic heat bath. By incorporating to the whole system
Hamiltonian the fluctuations of the local dipolar energy produced by low
frequency phonons, and assuming that this low energy fluctuations are
adiabatic, we find that the spin dynamics can be described in closed form
through a spin-boson model. The obtained results show that the coupling with
the phonons destroy the spin coherence, and the efficiency of the process
significantly depends on the complexity of the involved spin states. By using
realistic values for the various parameters of the model, we conclude that this
mechanism can be particularly efficient to degrade multi-spin coherences, when
the number of `active' spins involved in a given coherence is high. In this
way, we show that the spin coherence in the adiabatic regime can be noticeably
affected by this mechanism.",1505.01559v1
2015-05-12,Spin-orbit interactions of light,"Light carries spin and orbital angular momentum. These dynamical properties
are determined by the polarization and spatial degrees of freedom of light.
Modern nano-optics, photonics, and plasmonics, tend to explore subwavelength
scales and additional degrees of freedom of structured, i.e.,
spatially-inhomogeneous, optical fields. In such fields, spin and orbital
properties become strongly coupled with each other. We overview the fundamental
origins and important applications of the main spin-orbit interaction phenomena
in optics. These include: spin-Hall effects in inhomogeneous media and at
optical interfaces, spin-dependent effects in nonparaxial (focused or
scattered) fields, spin-controlled shaping of light using anisotropic
structured interfaces (metasurfaces), as well as robust spin-directional
coupling via evanescent near fields. We show that spin-orbit interactions are
inherent in all basic optical processes, and they play a crucial role at
subwavelength scales and structures in modern optics.",1505.02864v2
2015-06-08,Coherent ultrafast spin-dynamics probed in three dimensional topological insulators,"Topological insulators are candidates to open up a novel route in spin based
electronics. Different to traditional ferromagnetic materials, where the
carrier spin-polarization and magnetization are based on the exchange
interaction, the spin properties in topological insulators are based on the
coupling of spin- and orbit interaction connected to its momentum. Specific
ways to control the spin-polarization with light have been demonstrated: the
energy momentum landscape of the Dirac cone provides spin-momentum locking of
the charge current and its spin. The directionality of spin and momentum, as
well as control with light has been demonstrated. Here we demonstrate a
coherent femtosecond control of spin-polarization for states in the valence
band at around the Dirac cone.",1506.02692v1
2015-06-25,Equilibration in closed quantum systems: Application to spin qubits,"We study an observable-based notion of equilibration and its application to
realistic systems like spin qubits in quantum dots. On the basis of the
so-called distinguishability, we analytically derive general equilibration
bounds, which we relate to the standard deviation of the fluctuations of the
corresponding observable. Subsequently, we apply these ideas to the central
spin model describing the spin physics in quantum dots. We probe our bounds by
analyzing the spin dynamics induced by the hyperfine interaction between the
electron spin and the nuclear spins using exact diagonalization. Interestingly,
even small numbers of nuclear spins as found in carbon or silicon based quantum
dots are sufficient to significantly equilibrate the electron spin.",1506.07697v2
2015-06-18,Ultra-low-energy computing paradigm using giant spin Hall devices,"Spin Hall effect converts charge current to spin current, which can exert
spin-torque to switch the magnetization of a nanomagnet. Recently, it is shown
that the ratio of spin current to charge current using spin Hall effect can be
made more than unity by using the areal geometry judiciously, unlike the case
of conventional spin-transfer-torque switching of nanomagnets. This can enable
energy-efficient means to write a bit of information in nanomagnets. Here, we
study the energy dissipation in such spin Hall devices. By solving stochastic
Landau-Lifshitz-Gilbert equation of magnetization dynamics in the presence of
room temperature thermal fluctuations, we show a methodology to simultaneously
reduce switching delay, its variance and energy dissipation, while lateral
dimensions of the spin Hall devices are scaled down.",1506.07863v1
2015-07-07,"Magnetic order, spin waves and fluctuations in the triangular antiferromagnet La2Ca2MnO7","We report magnetic susceptibility, specific heat and muon spin relaxation
(muSR) experiments on the triangular antiferromagnet La2Ca2MnO7 which develops
a genuine two-dimensional, three-sublattice \sqrt{3} \times \sqrt{3} magnetic
order below T_N = 2.8 K. From the susceptibility and specific heat data an
estimate of the exchange interaction is derived. A value for the spin-wave gap
is obtained from the latter data. The analysis of a previously reported
inelastic neutron scattering study yields values for the exchange and spin-wave
gap compatible with the results obtained from macroscopic measurements. An
appreciable entropy is still missing at 10 K that may be ascribed to intense
short-range correlations. The critical paramagnetic fluctuations extend far
above T_N, and can be partly understood in terms of two-dimensional spin-wave
excitations. While no spontaneous muSR field is observed below T_N, persistent
spin dynamics is found. Short-range correlations are detected in this
temperature range. Their relation to a possible molecular spin substructure and
the observed exotic spin fluctuations is discussed.",1507.01740v1
2015-09-28,Analytical solvability of the two-axis countertwisting spin squeezing Hamiltonian,"There is currently much interest in the two-axis countertwisting spin
squeezing Hamiltonian suggested originally by Kitagawa and Ueda, since it is
useful for interferometry and metrology. No analytical solution valid for
arbitrary spin values seems to be available. In this article we systematically
consider the issue of the analytical solvability of this Hamiltonian for
various specific spin values. We show that the spin squeezing dynamics can be
considered to be analytically solved for angular momentum values upto $21/2$,
i.e. for $21$ spin half particles. We also identify the properties of the
system responsible for yielding analytic solutions for much higher spin values
than based on naive expectations. Our work is relevant for analytic
characterization of squeezing experiments with low spin values, and
semi-analytic modeling of higher values of spins.",1509.08530v1
2015-10-03,Strong Suppression of the Spin Hall Effect in the Spin Glass State,"We have measured spin Hall effects in spin glass metals, CuMnBi alloys, with
the spin absorption method in the lateral spin valve structure. Far above the
spin glass temperature Tg where the magnetic moments of Mn impurities are
randomly frozen, the spin Hall angle of CuMnBi ternary alloy is as large as
that of CuBi binary alloy. Surprisingly, however, it starts to decrease at
about 4Tg and becomes as little as 7 times smaller at 0.5Tg. A similar tendency
was also observed in anomalous Hall effects in the ternary alloys. We propose
an explanation in terms of a simple model considering the relative dynamics
between the localized moment and the conduction electron spin.",1510.00808v2
2015-10-23,Goldstone mode stochastization in quantum Hall ferromagnet,"Experimental and theoretical studies of the coherent spin dynamics of
two-dimensional GaAs/AlGaAs electron gas were performed. The system in the
quantum Hall ferromagnet state exhibits a spin relaxation mechanism that is
determined by many-particle Coulomb interactions. In addition to the spin
exciton with changes in the spin quantum numbers of $\delta S\!=\!\delta S_z
\!=\!-1$, the quantum Hall ferromagnet supports a Goldstone spin exciton that
changes the spin quantum numbers to $\delta S\!=\!0$ and $\delta S_z\!=\!-1$,
which corresponds to a coherent spin rotation of the entire electron system to
a certain angle. The Goldstone spin exciton decays through a specific
relaxation mechanism that is unlike any other collective spin state.",1510.06900v1
2016-03-02,Spin Manipulation in Graphene by Chemically-Induced Sublattice Pseudospin Polarization,"Spin manipulation is one of the most critical challenges to realize
spin-based logic devices and spintronic circuits. Graphene has been heralded as
an ideal material to achieve spin manipulation but so far new paradigms and
demonstrators are limited. Here we show that certain impurities such as
fluorine ad-atoms, which locally break sublattice symmetry without the
formation of strong magnetic moment, could result in a remarkable variability
of spin transport characteristics. The impurity resonance level is found to be
associated with a long range sublattice pseudospin polarization, which by
locally decoupling spin and pseudospin dynamics, provokes a huge spin lifetime
electron-hole asymmetry. In the dilute impurity limit, spin lifetimes could be
tuned electrostatically from hundred picoseconds to several nanoseconds,
providing a protocol to chemically engineer an unprecedented spin device
functionality.",1603.00834v1
2016-03-18,"Quantum Spin Dynamics with Pairwise-Tunable, Long-Range Interactions","We present a platform for the simulation of quantum magnetism with full
control of interactions between pairs of spins at arbitrary distances in one-
and two-dimensional lattices. In our scheme, two internal atomic states
represent a pseudo-spin for atoms trapped within a photonic crystal waveguide
(PCW). With the atomic transition frequency aligned inside a band gap of the
PCW, virtual photons mediate coherent spin-spin interactions between lattice
sites. To obtain full control of interaction coefficients at arbitrary
atom-atom separations, ground-state energy shifts are introduced as a function
of distance across the PCW. In conjunction with auxiliary pump fields,
spin-exchange versus atom-atom separation can be engineered with arbitrary
magnitude and phase, and arranged to introduce non-trivial Berry phases in the
spin lattice, thus opening new avenues for realizing novel topological spin
models. We illustrate the broad applicability of our scheme by explicit
construction for several well known spin models.",1603.05860v1
2016-06-05,Spin current contribution in the spectrum of collective excitations of degenerate partially polarized spin-1/2 fermions at separate dynamics of spin-up and spin-down fermions,"The spectrum of collective excitations of degenerate partially polarized
spin-1/2 fermions is considered. The spin-up fermions and the spin-down
fermions are considered as different fluids. Corresponding two-fluid
hydrodynamics consistent with a non-linear Pauli equation is suggested. An
equation of state for the spin current caused by the distribution of particles
on different energy levels is suggested for the degenerate regime, where the
spin current is caused by the Pauli blocking. Spectrum of three waves is found
as a solution of the hydrodynamic equations: two sound waves and one spin wave.
Their spectrums are calculated for two regimes: propagation parallel and
perpendicular to the direction of the equilibrium spin polarization.",1606.01562v2
2017-08-28,Observation of quantum spin noise in a 1D light-atoms quantum interface,"We observe collective quantum spin states of an ensemble of atoms in a
one-dimensional light-atom interface. Strings of hundreds of cesium atoms
trapped in the evanescent fiel of a tapered nanofiber are prepared in a
coherent spin state, a superposition of the two clock states. A weak quantum
nondemolition measurement of one projection of the collective spin is performed
using a detuned probe dispersively coupled to the collective atomic observable,
followed by a strong destructive measurement of the same spin projection. For
the coherent spin state we achieve the value of the quantum projection noise 40
dB above the detection noise, well above the 3 dB required for reconstruction
of the negative Wigner function of nonclassical states. We analyze the effects
of strong spatial inhomogeneity inherent to atoms trapped and probed by the
evanescent waves. We furthermore study temporal dynamics of quantum
fluctuations relevant for measurement-induced spin squeezing and assess the
impact of thermal atomic motion. This work paves the road towards observation
of spin squeezed and entangled states and many-body interactions in 1D spin
ensembles.",1708.08387v2
2019-05-09,Bidirectional spin-wave-driven domain wall motion in antiferromagnetically coupled ferrimagnets,"We investigate ferrimagnetic domain wall dynamics induced by circularly
polarized spin waves theoretically and numerically. We find that the direction
of domain wall motion depends on both the circular polarization of spin waves
and the sign of net spin density of ferrimagnet. Below the angular momentum
compensation point, left- (right-) circularly polarized spin waves push a
domain wall towards (away from) the spin-wave source. Above the angular
momentum compensation point, on the other hand, the direction of domain wall
motion is reversed. This bidirectional motion originates from the fact that the
sign of spin-wave-induced magnonic torque depends on the circular polarization
and the subsequent response of the domain wall to the magnonic torque is
governed by the net spin density. Our finding provides a way to utilize a spin
wave as a versatile driving force for bidirectional domain wall motion.",1905.03521v1
2010-05-04,"Spin squeezing of high-spin, spatially extended quantum fields","Investigations of spin squeezing in ensembles of quantum particles have been
limited primarily to a subspace of spin fluctuations and a single spatial mode
in high-spin and spatially extended ensembles. Here, we show that a wider range
of spin-squeezing is attainable in ensembles of high-spin atoms, characterized
by sub-quantum-limited fluctuations in several independent planes of
spin-fluctuation observables. Further, considering the quantum dynamics of an
$f=1$ ferromagnetic spinor Bose-Einstein condensate, we demonstrate
theoretically that a high degree of spin squeezing is attained in multiple
spatial modes of a spatially extended quantum field, and that such squeezing
can be extracted from spatially resolved measurements of magnetization and
nematicity, i.e.\ the vector and quadrupole magnetic moments, of the quantum
gas. Taking into account several experimental limitations, we predict that the
variance of the atomic magnetization and nematicity may be reduced as far as 20
dB below the standard quantum limits.",1005.0603v1
2014-03-03,Faraday rotation echo spectroscopy and detection of quantum fluctuations,"Central spin decoherence is useful for detecting many-body physics in
environments and moreover, the spin echo control can remove the effects of
static thermal fluctuations so that the quantum fluctuations are revealed. The
central spin decoherence approach, however, is feasible only in some special
configurations and often requires uniform coupling between the central spin and
individual spins in the baths, which are very challenging in experiments. Here,
by making analogue between central spin decoherence and depolarization of
photons, we propose a scheme of Faraday rotation echo spectroscopy (FRES) for
studying quantum fluctuations in interacting spin systems. The echo control of
the photon polarization is realized by flipping the polarization with a
birefringence crystal. The FRES, similar to spin echo in magnetic resonance
spectroscopy, can suppress the effects of the static magnetic fluctuations and
therefore reveal dynamical magnetic fluctuations. We apply the scheme to a
rare-earth compound LiHoF4 and calculate the echo signal, which is related to
the quantum fluctuations of the system. We observe enhanced signals at the
phase boundary. The FRES should be useful for studying quantum fluctuations in
a broad range of spin systems, including cold atoms, quantum dots, solid-state
impurities, and transparent magnetic materials.",1403.0420v1
2008-07-16,Theory of electric dipole spin resonance in quantum dots: Mean field theory with Gaussian fluctuations and beyond,"Very recently, the electric dipole spin resonance (EDSR) of single electrons
in quantum dots was discovered by three independent experimental groups.
Remarkably, these observations revealed three different mechanisms of EDSR:
coupling of electron spin to its momentum (spin-orbit), to the operator of its
position (inhomogeneous Zeeman coupling), and to the hyperfine Overhauser field
of nuclear spins. In this paper, I present a unified microscopic theory of
these resonances in quantum dots. A mean field theory, derived for all three
mechanisms and based on retaining only two-spin correlators, justifies applying
macroscopic description of nuclear polarization to the EDSR theory. In the
framework of the mean field theory, a fundamental difference in the time
dependence of EDSR inherent of these mechanisms is revealed; it changes from
the Rabi-type oscillations to a nearly monotonic growth. The theory provides a
regular procedure to account for the higher nuclear-spin correlators that
become of importance for a wider time span and can change the asymptotic
behavior of EDSR. It also allows revealing the effect of electron spin dynamics
on the effective coupling between nuclear spins.",0807.2624v1
2011-11-10,Electronic Pumping of Quasiequilibrium Bose-Einstein Condensed Magnons,"We theoretically investigate spin transfer between a system of
quasiequilibrated Bose-Einstein condensed magnons in an insulator in direct
contact with a conductor. While charge transfer is prohibited across the
interface, spin transport arises from the exchange coupling between insulator
and conductor spins. In normal insulator phase, spin transport is governed
solely by the presence of thermal and spin-diffusive gradients; the presence of
Bose-Einstein condensation (BEC), meanwhile, gives rise to a
temperature-independent condensate spin current. Depending on the thermodynamic
bias of the system, spin may flow in either direction across the interface,
engendering the possibility of a dynamical phase transition of magnons. We
discuss experimental feasibility of observing a BEC steady state (fomented by a
spin Seebeck effect), which is contrasted to the more familiar spin-transfer
induced classical instabilities.",1111.2382v2
2011-11-22,Optical spin injection and spin lifetime in Ge heterostructures,"We demonstrate optical orientation in Ge/SiGe quantum wells and study their
spin properties. The ultrafast electron transfer from the center of the
Brillouin zone to its edge allows us to achieve high spin-polarization
efficiencies and to resolve the spin dynamics of holes and electrons. The
circular polarization degree of the direct-gap photoluminescence exceeds the
theoretical bulk limit, yielding ~37% and ~85% for transitions with heavy and
light holes states, respectively. The spin lifetime of holes at the top of the
valence band is found to be ~0.5 ps and it is governed by transitions between
heavy and light hole states. Electrons at the bottom of the conduction band, on
the other hand, have a spin lifetime that exceeds 5 ns below 150 K. Theoretical
analysis of the electrons spin relaxation indicates that phonon-induced
intervalley scattering dictates the spin lifetime.",1111.5209v1
2012-04-29,Sensing remote nuclear spins,"Sensing single nuclear spins is a central challenge in magnetic resonance
based imaging techniques. Although different methods and especially diamond
defect based sensing and imaging techniques in principle have shown sufficient
sensitivity, signals from single nuclear spins are usually too weak to be
distinguished from background noise. Here, we present the detection and
identification of remote single C-13 nuclear spins embedded in nuclear spin
baths surrounding a single electron spins of a nitrogen-vacancy centre in
diamond. With dynamical decoupling control of the centre electron spin, the
weak magnetic field ~10 nT from a single nuclear spin located ~3 nm from the
centre with hyperfine coupling as weak as ~500 Hz is amplified and detected.
The quantum nature of the coupling is confirmed and precise position and the
vector components of the nuclear field are determined. Given the distance over
which nuclear magnetic fields can be detected the technique marks a firm step
towards imaging, detecting and controlling nuclear spin species external to the
diamond sensor.",1204.6513v1
2013-09-12,Charge and spin Hall effect in spin chiral ferromagnetic graphene,"We predict a specific type of charge Hall effect in undoped ferromagnetic
graphene that is generated by the spin Hall mechanism in the absence of an
external magnetic field. The essential feature is the so-called spin chiral
configuration of the spin subbands in such a magnetic material where carriers
with opposite spin direction are of different type of electron-like or
hole-like. Within the semiclassical theory of spin-orbital dynamics of
electrons, we obtain that a longitudinal electric field can produce a
spin-orbit transverse current of pure charge with no polarization of the spin
and the valley.",1309.3080v1
2014-05-20,Coherent properties of single rare-earth spin qubits,"Rare-earth-doped crystals are excellent hardware for quantum storage of
optical information. Additional functionality of these materials is added by
their waveguiding properties allowing for on-chip photonic networks. However,
detection and coherent properties of rare-earth single-spin qubits have not
been demonstrated so far. Here, we present experimental results on
high-fidelity optical initialization, effcient coherent manipulation, and
optical readout of a single electron spin of Ce$^{3+}$ ion in a YAG crystal.
Under dynamic decoupling, spin coherence lifetime reaches $T_2$=2 ms and is
almost limited by the measured spin-lattice relaxation time $T_1$=3.8 ms.
Strong hyperfine coupling to aluminium nuclear spins suggests that cerium
electron spins can be exploited as an interface between photons and long-lived
nuclear spin memory. Combined with high brightness of Ce$^{3+}$ emission and a
possibility of creating photonic circuits out of the host material, this makes
cerium spins an interesting option for integrated quantum photonics.",1405.5258v1
2016-08-17,A generalized Theory of Diffusion based on Kinetic Theory,"We propose to use spin hydrodynamics, a two-fluid model of spin propagation,
as a generalization of the diffusion equation. We show that in the dense limit
spin hydrodynamics reduces to Fick's law and the diffusion equation. In the
opposite limit spin hydrodynamics is equivalent to a collisionless Boltzmann
treatment of spin propagation. Spin hydrodynamics avoids unphysical effects
that arise when the diffusion equation is used to describe to a strongly
interacting gas with a dilute corona. We apply spin hydrodynamics to the
problem of spin diffusion in a trapped atomic gas. We find that the observed
spin relaxation rate in the high temperature limit [Sommer et al., Nature 472,
201 (2011)] is consistent with the diffusion constant predicted by kinetic
theory.",1608.05083v2
2017-07-09,Nuclear spin cooling by helicity-alternated optical pumping at weak magnetic fields in $n$-GaAs,"The spin dynamics of localized donor-bound electrons interacting with the
nuclear spin ensemble in $n$-doped GaAs epilayers is studied using nuclear spin
polarization by light with modulated circular polarization. We show that the
observed build-up of the nuclear spin polarization is a result of competition
between nuclear spin cooling and nuclear spin warm-up in the oscillating Knight
field. The developed model allows us to explain the dependence of nuclear spin
polarization on the modulation frequency and to estimate the equilibration time
of the nuclear spin system that appears to be shorter than the transverse
relaxation time $T_2$ determined from nuclear magnetic resonance.",1707.02658v2
2018-01-09,Inverse engineering for fast transport and spin control of spin-orbit-coupled Bose-Einstein condensates in moving harmonic traps,"We investigate fast transport and spin manipulation of tunable
spin-orbit-coupled Bose-Einstein condensates in a moving harmonic trap.
Motivated by the concept of ""shortcuts to adiabaticity"", we design inversely
the time-dependent trap position and spin-orbit coupling strength. By choosing
appropriate boundary conditions we obtain fast transport and spin flip
simultaneously. The non-adiabatic transport and relevant spin dynamics are
illustrated with numerical examples, and compared with the adiabatic transport
with constant spin-orbit-coupling strength and velocity. Moreover, the
influence of nonlinearity induced by interatomic interaction is discussed in
terms of the Gross-Pitaevskii approach, showing the robustness of the proposed
protocols. With the state-of-the-art experiments, such inverse engineering
technique paves the way for coherent control of spin-orbit-coupled
Bose-Einstein condensates in harmonic traps.",1801.02887v1
2018-01-29,Current-induced spin-orbit torques in ferromagnetic and antiferromagnetic systems,"Spin-orbit coupling in inversion-asymmetric magnetic crystals and structures
has emerged as a powerful tool to generate complex magnetic textures,
interconvert charge and spin under applied current, and control magnetization
dynamics. Current-induced spin-orbit torques mediate the transfer of angular
momentum from the lattice to the spin system, leading to sustained magnetic
oscillations or switching of ferromagnetic as well as antiferromagnetic
structures. The manipulation of magnetic order, domain walls and skyrmions by
spin-orbit torques provides evidence of the microscopic interactions between
charge and spin in a variety of materials and opens novel strategies to design
spintronic devices with potentially high impact in data storage, nonvolatile
logic, and magnonic applications. This paper reviews recent progress in the
field of spin-orbitronics, focusing on theoretical models, material properties,
and experimental results obtained on bulk noncentrosymmetric conductors and
multilayer heterostructures, including metals, semiconductors, and topological
insulator systems. Relevant aspects for improving the understanding and
optimizing the efficiency of nonequilibrium spin-orbit phenomena in future
nanoscale devices are also discussed.",1801.09636v2
2018-09-09,Spin transfer torques and spin-dependent transport in a metallic F/AF/N tunneling junction,"We study spin-dependent electron transport through a
ferromagnetic-antiferromagnetic-normal metal tunneling junction subject to a
voltage or temperature bias, in the absence of spin-orbit coupling. We derive
microscopic formulas for various types of spin torque acting on the
antiferromagnet as well as for charge and spin currents flowing through the
junction. The obtained results are applicable in the limit of slow
magnetization dynamics. We identify a parameter regime in which an
unconventional damping-like torque can become comparable in magnitude to the
equivalent of the conventional Slonczewski's torque generalized to
antiferromagnets. Moreover, we show that the antiferromagnetic sublattice
structure opens up a channel of electron transport which does not have a
ferromagnetic analogue and that this mechanism leads to a pronounced field-like
torque. Both charge conductance and spin current transmission through the
junction depend on the relative orientation of the ferromagnetic and the
antiferromagnetic vectors (order parameters). The obtained formulas for charge
and spin currents allow us to identify the microscopic mechanisms responsible
for this angular dependence and to assess the efficiency of an
antiferromagnetic metal acting as a spin current polarizer.",1809.02950v1
2018-10-08,Scalable nuclear-spin entanglement mediated by a mechanical oscillator,"We propose a solid-state hybrid platform based on an array of implanted
nitrogen-vacancy (NV) centers in diamond magnetically coupled to a mechanical
oscillator. The mechanical oscillator and the NV electronic spins both act as a
quantum bus and allow us to induce an effective long-range interaction between
distant nuclear spins, relaxing the requirements on their spatial distance. The
coherent nuclear spin-spin interaction, having the form of an Ising model, can
be maintained in the presence of mechanical damping and spin dephasing via a
pulsed dynamical decoupling of the nuclear spins in addition to the microwave
driving field of the electronic spins. The present hybrid platform provides a
scalable way to prepare multipartite entanglement among nuclear spins with long
coherence times and can be applied to generate graph states that may be used
for universal quantum computing.",1810.03253v1
2019-09-09,Strong polarization of individual nuclear spins weakly coupled to nitrogen-vacancy color centers in diamond,"We experimentally demonstrate high degree of polarization of 13C nuclear
spins weakly interacting with nitrogen-vacancy (NV) centers in diamond. We
combine coherent microwave excitation pulses with optical illumination to
provide controlled relaxation and achieve a polarity-tunable, fast nuclear
polarization of degree higher than 85% at room temperature for remote 13C
nuclear spins exhibiting hyperfine interaction strength with NV centers of the
order of 600 kHz. We show with the aid of numerical simulation that the
anisotropic hyperfine tensor components naturally provide a route to control
spin mixing parameter so that highly efficient nuclear polarization is enabled
through careful tuning of nuclear quantization axis by external magnetic field.
We further discuss spin dynamics and wide applicability of this method to
various target 13C nuclear spins around the NV center electron spin. The
proposed control method demonstrates an efficient and versatile route to
realize, for example, high-fidelity spin register initialization and quantum
metrology using nuclear spin resources in solids.",1909.03614v1
2019-09-26,Full Counting Statistics of Spin-Flip/Conserving Charge Transitions in Pauli-Spin Blockade,"We investigate the full counting statistics (FCS) of spin-conserving and
spin-flip charge transitions in Pauli-spin blockade regime of a GaAs double
quantum dot. A theoretical model is proposed to evaluate all spin-conserving
and spin-flip tunnel rates, and to demonstrate the fundamental relation between
FCS and waiting time distribution. We observe the remarkable features of parity
effect and a tail structure in the constructed FCS, which do not appear in the
Poisson distribution, and are originated from spin degeneracy and coexistence
of slow and fast transitions, respectively. This study is potentially useful
for elucidating the spin-related and other complex transition dynamics in
quantum systems.",1909.12027v1
2019-10-29,Spin noise at electron paramagnetic resonance,"We develop a microscopic theory of spin noise in solid-state systems at
electron paramagnetic resonance, when the spin dynamics is driven by static and
radio-frequency (RF) magnetic fields and the stochastic effective magnetic
field stemming from the interaction with environment. The RF field splits the
peaks in the power spectrum of spin noise into the Mollow-like triplets and
also gives rise to additional spin-spin correlations which oscillate in the
absolute time at the RF frequency and the double frequeqncy. Even in systems
with strong inhomogeneous broadening, the spin noise spectrum contains narrow
lines insensitive to the dispersion of the effective $g$-factors. Thus, the
measurements of spin noise at electron paramagnetic resonance provides an
access to the intrinsic spin lifetime of electrons.",1910.13167v1
2019-10-31,Spin-phonon relaxation from a universal \emph{ab initio} density-matrix approach,"Designing new quantum materials with long-lived electron spin states urgently
requires a general theoretical formalism and computational technique to
reliably predict intrinsic spin relaxation times. We present a new, accurate
and universal first-principles methodology based on Lindbladian dynamics of
density matrices to calculate spin-phonon relaxation time ($\tau_s$) of solids
with arbitrary spin mixing and crystal symmetry. This method describes
contributions of Elliott-Yafet (EY) and D'yakonov-Perel' (DP) mechanisms to
spin relaxation for systems with and without inversion symmetry on an equal
footing. We show that intrinsic spin and momentum relaxation times both
decrease with increasing temperature; however, for the DP mechanism, spin
relaxation time varies inversely with extrinsic scattering time. We predict
large anisotropy of spin lifetime in transition metal dichalcogenides. The
excellent agreement with experiments for a broad range of materials underscores
the predictive capability of our method for properties critical to quantum
information science.",1910.14198v2
2020-04-03,Modulation of field-like spin orbit torque in heavy metal / ferromagnet heterostructure,"Recent studies rediscovered the crucial role of field-like spin orbit torque
(SOT) in nanosecond-timescale SOT dynamics. However, there is not yet an
effective way to control its relative amplitude. Here, we experimentally
modulate the field-like SOT in W/CoFeB/MgO trilayers through tuning the
interfacial spin accumulation. By performing spin Hall magnetoresistance
measurement, we find that the CoFeB with enhanced spin dephasing, either
generated from larger layer thickness or from proper annealing, can distinctly
boost the spin absorption and enhance the interfacial spin mixing conductance
G_r. While the damping-like torque efficiency increases with G_r, the
field-like torque efficiency turns out to decrease with it. The results suggest
that the interfacial spin accumulation, which largely contributes to a
field-like torque, is reduced by higher interfacial spin transparency. Our work
shows a new path to further improve the performance of SOT-based magnetic
devices.",2004.01357v1
2020-04-10,Holographic spin liquids and Lovelock Chern-Simons gravity,"We explore the role of torsion as source of spin current in strongly
interacting conformal fluids using holography. We establish the constitutive
relations of the basic hydrodynamic variables, the energy-momentum tensor and
the spin current based on the classification of the spin sources in irreducible
Lorentz representations. The fluids we consider are assumed to be described by
the five dimensional Lovelock-Chern-Simons gravity with independent vielbein
and spin connection. We construct a hydrodynamic expansion that involves the
stress tensor and the spin current and compute the corresponding one-point
functions holographically. As a byproduct we find a class of interesting
analytic solutions to the Lovelock-Chern-Simons gravity, including blackholes,
by mapping the equations of motion into non-linear algebraic constraints for
the sources. We also derive a Lee-Wald entropy formula for these blackholes in
Chern-Simons theories with torsion. The blackhole solutions determine the
thermodynamic potentials and the hydrodynamic constitutive relations in the
corresponding fluid on the boundary. We observe novel spin induced transport in
these holographic models: a dynamical version of the Barnett effect where
vorticity generates a spin current and anomalous vortical transport transverse
to a vector-like spin source.",2004.05148v1
2020-04-20,"Optical detection of electron spin dynamics driven by fast variations of a magnetic field: a simple method to measure $T_1$, $T_2$, and $T_2^*$ in semiconductors","We develop a simple method for measuring the electron spin relaxation times
$T_1$, $T_2$ and $T_2^*$ in semiconductors and demonstrate its exemplary
application to $n$-type GaAs. Using an abrupt variation of the magnetic field
acting on electron spins, we detect the spin evolution by measuring the Faraday
rotation of a short laser pulse. Depending on the magnetic field orientation,
this allows us to measure either the longitudinal spin relaxation time $T_1$ or
the inhomogeneous transverse spin dephasing time $T_2^*$. In order to determine
the homogeneous spin coherence time $T_2$, we apply a pulse of an oscillating
radiofrequency (rf) field resonant with the Larmor frequency and detect the
subsequent decay of the spin precession. The amplitude of the rf-driven spin
precession is significantly enhanced upon additional optical pumping along the
magnetic field.",2004.09408v1
2017-05-30,Efficient algorithms for the dynamics of large and infinite classical central spin models,"We investigate the time dependence of correlation functions in the central
spin model, which describes the electron or hole spin confined in a quantum
dot, interacting with a bath of nuclear spins forming the Overhauser field. For
large baths, a classical description of the model yields quantitatively correct
results. We develop and apply various algorithms in order to capture the
long-time limit of the central spin for bath sizes from 1000 to infinitely many
bath spins. Representing the Overhauser field in terms of orthogonal
polynomials, we show that a carefully reduced set of differential equations is
sufficient to compute the spin correlations of the full problem up to very long
times, for instance up to $10^5\hbar/J_\mathrm{Q}$ where $J_\mathrm{Q}$ is the
natural energy unit of the system. This technical progress renders an analysis
of the model with experimentally relevant parameters possible. We benchmark the
results of the algorithms with exact data for a small number of bath spins and
we predict how the long-time correlations behave for different effective
numbers of bath spins.",1705.10511v2
2018-06-08,Optically-detected long-lived spin coherence in multilayer systems: Double and triple quantum wells,"In this contribution, we investigated the spin coherence of high-mobility
dense two-dimensional electron gases confined in multilayer systems. The
dynamics of optically-induced spin polarization was experimentally studied
employing the time-resolved Kerr rotation and resonant spin amplification
techniques. For both the double and triple quantum wells doped beyond the
metal-insulator transition, where the spin coherence is greatly suppressed, we
found remarkably long spin lifetimes limited by the Dyakonov-Perel mechanism
and spin hopping process between the donor sites as well as the spread of
ensemble g-factor. The double quantum well structure yields a spin lifetime of
6.25 ns at T = 5 K while the triple quantum well shows a spin lifetime
exceeding 25 ns at T = 8 K.",1806.03092v1
2018-07-09,Spin wave dynamics in artificial anti spin-ice systems: experimental and theoretical investigations,"Reversed structures of artificial spin-ice systems, where elongated holes
with elliptical shape (antidots) are arranged into a square array with two
orthogonal sublattices, are referred to as anti-squared spin-ice. Using
Brillouin light scattering spectroscopy and plane wave method calculations, we
investigate the spin wave propagation perpendicular to the applied field
direction for two 20 nm thick Permalloy nanostructures which differ by the
presence of single and double elliptical antidots. For the spin waves
propagation along the principal antidot lattice axis, the spectrum consists of
flat bands separated by several frequency gaps which are the effect of spin
wave amplitude confinement in the regions between antidots. Contrarily, for
propagation direction at 45 degrees with respect to the antidot symmetry axis,
straight and narrow channels of propagation are formed, leading to broadening
of bands and closing of the magnonics gaps. Interestingly, in this case, extra
magnonic band gaps occur due to the additional periodicity along this
direction. The width and the position of these gaps depend on the presence of
single or double antidots. In this context, we discuss possibilities for the
tuning of spin wave spectra in anti-squared spin ice structures.",1807.03016v1
2018-12-25,Thermodynamics and spin mapping of quantum excitations in a Heisenberg spin heptamer,"In this study, we examine the thermodynamics and spin dynamics of spin-1/2
and spin-3/2 heptamers. Through an exact diagonalization of the isotropic
Heisenberg Hamiltonian, we find the closed-form, analytical representations for
thermodynamic properties, spin excitations, and neutron scattering structure
factors. Furthermore, we investigate the {cluster-like excitations of quantum
spin heptamer} in the three-dimensional pyrochlore lattice material
MgCr$_2$O$_4$. Using a spin mapping of the spin-1/2 heptamer excitations, the
calculated structure factors of the spin-3/2 heptamer are be determined, which
provides clarification for the spin excitations in MgCr$_2$O$_4$. Overall, this
study demonstrates the ability to use the spin mapping of structure factors for
small spin systems to analyze more complex structures.",1812.10155v1
2019-03-08,Intra- and inter-orbital correlated electron spin dynamics in $\rm Sr_2 Ir O_4$: spin-wave gap and spin-orbit exciton,"Transformation of Coulomb interaction terms to the pseudo-orbital basis
constituted by $J=1/2$ and $3/2$ states arising from spin-orbit coupling
provides a versatile tool. This formalism is applied to investigate magnetic
anisotropy effects on low-energy spin-wave excitations as well as high-energy
spin-orbit exciton modes in $\rm Sr_2 Ir O_4$. The Hund's coupling term
explictly yields easy-plane anisotropy, resulting in gapless (in-plane) and
gapped (out-of-plane) modes, in agreement with recent resonant inelastic x-ray
scattering (RIXS) measurements. The collective mode of inter-orbital,
spin-flip, particle-hole excitations with appropriate interaction strengths and
renormalized spin-orbit gap yields two well-defined propagating spin-orbit
exciton modes, with energy scale and dispersion in good agreement with RIXS
studies.",1903.03360v1
2019-03-09,Instability of subdiffusive spin dynamics in strongly disordered Hubbard chain,"We study spin transport in a Hubbard chain with strong, random, on--site
potential and with spin--dependent hopping integrals, $t_{\sigma}$. For the the
SU(2) symmetric case, $t_{\uparrow} =t_{\downarrow}$, such model exhibits only
partial many-body localization with localized charge and (delocalized)
subdiffusive spin excitations. Here, we demonstrate that breaking the SU(2)
symmetry by even weak spin--asymmetry, $t_{\uparrow} \ne t_{\downarrow}$,
localizes spins and restores full many-body localization. To this end we derive
an effective spin model, where the spin subdiffusion is shown to be destroyed
by arbitrarily weak $t_{\uparrow} \ne t_{\downarrow}$. Instability of the spin
subdiffusion originates from an interplay between random effective fields and
singularly distributed random exchange interactions.",1903.03770v1
2019-03-19,Nonlinear Inverse Spin Galvanic Effect in Anisotropic Disorder-free Systems,"Spin transport phenomena in solid materials suffer limitations from spin
relaxation associated to disorder or lack of translational invariance.
Ultracold atoms, free of that disorder, can provide a platform to observe
phenomena beyond the usual two-dimensional electron gas. By generalizing the
approach used for isotropic two-dimensional electron gases, we theoretically
investigate the inverse spin galvanic effect in the two-level atomic system in
the presence of anisotropic Rashba-Dresselhaus spin-orbit couplings (SOC) and
external magnetic field. We show that the combination of the SOC results in an
asymmetric case: the total spin polarization considered for a small momentum
has a longer spin state than in a two-dimensional electron gas when the SOC
field prevails over the external electric field. Our results can be relevant
for advancing experimental and theoretical investigations in spin dynamics as a
basic approach for studying spin state control.",1903.08269v1
2019-08-21,Lyapunov growth in quantum spin chains,"The Ising spin chain with longitudinal and transverse magnetic fields is
often used in studies of quantum chaos, displaying both chaotic and integrable
regions in its parameter space. However, even at a strongly chaotic point this
model does not exhibit Lyapunov growth of the commutator squared of spin
operators, as this observable saturates before exponential growth can manifest
itself (even in situations where a spatial suppression factor makes the initial
commutator small). We extend this model from the spin 1/2 Ising model to higher
spins, demonstrate numerically that a window of exponential growth opens up for
sufficiently large spin, and extract a quantity which corresponds to a notion
of a Lyapunov exponent. In the classical infinite-spin limit, we identify and
compute the appropriate classical analogue of the commutator squared, and show
that the corresponding exponent agrees with the infinite-spin limit extracted
from the quantum spin chain.",1908.08059v3
2019-11-13,Tailoring spin wave channels in a reconfigurable artificial spin ice,"Artificial spin ices are ensembles of geometrically-arranged, interacting
nanomagnets which have shown promising potential for the realization of
reconfigurable magnonic crystals. Such systems allow for the manipulation of
spin waves on the nanoscale and their potential use as information carriers.
However, there are presently two general obstacles to the realization of
artificial spin ice-based magnonic crystals: the magnetic state of artificial
spin ices is difficult to reconfigure and the magnetostatic interactions
between the nanoislands are often weak, preventing mode coupling. We
demonstrate, using micromagnetic modeling, that coupling a reconfigurable
artificial spin ice geometry made of weakly interacting nanomagnets to a soft
magnetic underlayer creates a complex system exhibiting dynamically coupled
modes. These give rise to spin wave channels in the underlayer at well-defined
frequencies, based on the artificial spin ice magnetic state, which can be
reconfigured. These findings open the door to the realization of reconfigurable
magnonic crystals with potential applications for data transport and processing
in magnonic-based logic architectures.",1911.05354v4
2020-03-05,Observation of plaquette fluctuations in the spin-1/2 honeycomb lattice,"Quantum spin liquids are materials that feature quantum entangled spin
correlations and avoid magnetic long-range order at T = 0 K. Particularly
interesting are two-dimensional honeycomb spin lattices where a plethora of
exotic quantum spin liquids have been predicted. Here, we experimentally study
an effective S=1/2 Heisenberg honeycomb lattice with competing nearest and
next-nearest neighbor interactions. We demonstrate that YbBr$_3$ avoids order
down to at least T=100 mK and features a dynamic spin-spin correlation function
with broad continuum scattering typical of quantum spin liquids near a quantum
critical point. The continuum in the spin spectrum is consistent with plaquette
type fluctuations predicted by theory. Our study is the experimental
demonstration that strong quantum fluctuations can exist on the honeycomb
lattice even in the absence of Kitaev-type interactions, and opens a new
perspective on quantum spin liquids.",2003.02529v2
2020-03-13,Protecting Spin Coherence in a Tunable Heisenberg Model,"Using an ensemble of atoms in an optical cavity, we engineer a family of
nonlocal Heisenberg Hamiltonians with continuously tunable anisotropy of the
spin-spin couplings. We thus gain access to a rich phase diagram, including a
paramagnetic-to-ferromagnetic Ising phase transition that manifests as a
diverging magnetic susceptibility at the critical point. The susceptibility
displays a symmetry between Ising interactions and XY (spin-exchange)
interactions of the opposite sign, which is indicative of the spatially
extended atomic system behaving as a single collective spin. Images of the
magnetization dynamics show that spin-exchange interactions protect the
coherence of the collective spin, even against inhomogeneous fields that
completely dephase the non-interacting and Ising systems. Our results
underscore prospects for harnessing spin-exchange interactions to enhance the
robustness of spin squeezing protocols.",2003.06087v2
2020-03-24,Third Stable Branch and Tristability of Nuclear Spin Polarization in Single Quantum Dot System,"Semiconductor quantum dots provide a spin-coupled system of an electron and
nuclei via enhanced hyperfine interaction. We showed that the nuclear spin
polarization in single quantum dots can have three stable branches under a
longitudinal magnetic field. The states were accompanied by hysteresis loops
around the boundaries of each branch with a change in the excitation condition.
To explain these findings, we incorporated the electron spin relaxation caused
by the nuclear spin fluctuation into the previously-studied dynamic nuclear
spin polarization mechanism. The model reproduces the new features of nuclear
spin polarization and the associated strong reduction in the observed electron
spin polarization, and can refer to the tristability of nuclear spin
polarization.",2003.10587v1
2020-11-03,Intensity equations for birefringent spin lasers,"Semiconductor spin lasers are distinguished from their conventional
counterparts by the presence of spin-polarized carriers. The transfer of
angular momentum of the spin-polarized carriers to photons provides important
opportunities for the operation of lasers. With the injection of spin-polarized
carriers, which lead to the circularly polarized light, the polarization of the
emitted light can be changed an order of magnitude faster than its intensity.
This ultrafast operation of spin lasers relies on a large birefringence,
usually viewed as detrimental in spin and conventional lasers. We introduce a
transparent description of spin lasers using intensity equations, which
elucidate the influence of birefringence on the intensity and polarization
modulation of lasers. While intensity modulation is independent of
birefringence, for polarization modulation an increase in birefringence
directly increases the resonant frequency. Our results for dynamical operation
of lasers provide a guide for their spin-dependent response and spintronic
applications beyond magnetoresistance.",2011.01486v1
2021-03-14,Dispersion relation of nutation surface spin waves in ferromagnets,"Inertia effects in magnetization dynamics are theoretically shown to result
in a different type of spin waves, i.e. nutation surface spin waves, which
propagate at terahertz frequencies in in-plane magnetized ferromagnetic thin
films. Considering the magnetostatic limit, i.e. neglecting exchange coupling,
we calculate dispersion relation and group velocity, which we find to be slower
than the velocity of conventional (precession) spin waves. In addition, we find
that the nutation surface spin waves are backward spin waves. Furthermore, we
show that inertia causes a decrease of the frequency of the precession spin
waves, namely magnetostatic surface spin waves and backward volume
magnetostatic spin waves. The magnitude of the decrease depends on the magnetic
properties of the film and its geometry.",2103.07864v2
2021-04-01,Multifunctional Antiferromagnetic Materials with Giant Piezomagnetism and Noncollinear Spin Current,"We propose a new type of spin-valley locking (SVL), named $\textit{C}$-paired
SVL, in antiferromagnetic systems, which directly connects the spin/valley
space with the real space, and hence enables both static and dynamical controls
of spin and valley to realize a multifunctional antiferromagnetic material. The
new emergent quantum degree of freedom in the $\textit{C}$-paired SVL is
comprised of spin-polarized valleys related by a crystal symmetry instead of
the time-reversal symmetry. Thus, both spin and valley can be accessed by
simply breaking the corresponding crystal symmetry. Typically, one can use a
strain field to induce a large net valley polarization/magnetization and use a
charge current to generate a large noncollinear spin current. We predict the
realization of the $\textit{C}$-paired SVL in monolayer V$_2$Se$_2$O, which
indeed exhibits giant piezomagnetism and can generate a large transverse spin
current. Our findings provide unprecedented opportunities to integrate various
controls of spin and valley with nonvolatile information storage in a single
material, which is highly desirable for versatile fundamental research and
device applications.",2104.00561v1
2021-06-04,Insights on the coupling between vibronically active molecular vibrations and lattice phonons in molecular nanomagnets,"Spin-lattice relaxation is a key open problem to understand the spin dynamics
of single-molecule magnets and molecular spin qubits. While modelling the
coupling between spin states and local vibrations allows to determine the more
relevant molecular vibrations for spin relaxation, this is not sufficient to
explain how energy is dissipated towards the thermal bath. Herein, we employ a
simple and efficient model to examine the coupling of local vibrational modes
with long-wavelength longitudinal and transverse phonons in the clock-like spin
qubit [Ho(W$_5$O$_{18}$)$_2$]$^{9-}$. We find that in crystals of this
polyoxometalate the vibrational mode previously found to be vibronically active
at low temperature does not couple significantly to lattice phonons. This means
that further intramolecular energy transfer via anharmonic vibrations is
necessary for spin relaxation in this system. Finally, we discuss implications
for the spin-phonon coupling of [Ho(W$_5$O$_{18}$)$_2$]$^{9-}$ deposited on a
MgO (001) substrate, offering a simple methodology that can be extrapolated to
estimate the effects on spin relaxation of different surfaces, including 2D
materials.",2106.02611v1
2021-06-09,Chiral control of quantum states in non-Hermitian spin-orbit-coupled fermions,"Spin-orbit coupling is an essential mechanism underlying quantum phenomena
such as the spin Hall effect and topological insulators. It has been widely
studied in well-isolated Hermitian systems, but much less is known about the
role dissipation plays in spin-orbit-coupled systems. Here, we implement
dissipative spin-orbit-coupled bands filled with ultracold fermions, and
observe parity-time symmetry breaking as a result of the competition between
the spin-orbit coupling and dissipation. Tunable dissipation, introduced by
state-selective atom loss, enables us to tune the energy gap and close it at
the critical dissipation value, the so-called exceptional point. In the
vicinity of the critical point, the state evolution exhibits a chiral response,
which enables us to tune the spin-orbit coupling and dissipation dynamically,
revealing topologically robust chiral spin transfer when the quantum state
encircles the exceptional point. This demonstrates that we can explore
non-Hermitian topological states with spin-orbit coupling.",2106.04874v2
2021-07-15,Local evidence for collective spin excitations in the distorted kagome antiferromagnet Pr$_3$BWO$_9$,"We report the local probe investigation of a frustrated antiferromagnet
Pr$_3$BWO$_9$ with the distorted kagome lattice. Absence of magnetic order or
spin freezing is indicated by the spectral analysis down to 0.3 K and specific
heat measurements down to 0.09 K. The Knight shifts show an upturn behavior
with the sample cooling down, which is further suppressed by external field.
For the spin dynamics, gapped spin excitation is observed from the temperature
dependence of spin-lattice relaxation rates, with the gap size proportional to
the applied magnetic field intensity. Comparatively, an unexpected sharp peak
is observed in the nuclear spin-spin relaxation rate data at $T^*\sim 4-5$ K.
These results indicate an unconventional persistent fluctuating paramagnetic
ground state with antiferromagnetic collective spin excitations in the strongly
frustrated spin system.",2107.07227v2
2021-07-25,Analytic solutions of relativistic dissipative spin hydrodynamics with Bjorken expansion,"We have studied analytically the longitudinally boost-invariant motion of a
relativistic dissipative fluid with spin. We have derived the analytic
solutions of spin density and spin chemical potential as a function of proper
time $\tau$ in the presence of viscous tensor and the second order relaxation
time corrections for spin. Interestingly, analogous to the ordinary particle
number density and chemical potential, we find that the spin density and spin
chemical potential decay as $\sim\tau^{-1}$ and $\sim\tau^{-1/3}$,
respectively. It implies that the initial spin density may not survive at the
freezeout hyper-surface. These solutions can serve both to gain insight on the
dynamics of spin polarization in relativistic heavy-ion collisions and as
testbeds for further numerical codes.",2107.11726v1
2021-10-14,Thermalization in a Spin-Orbit coupled Bose gas by enhanced spin Coulomb drag,"An important component of the structure of the atom, the effects of
spin-orbit coupling are present in many sub-fields of physics. Most of these
effects are present continuously. We present a detailed study of the dynamics
of changing the spin-orbit coupling in an ultra-cold Bose gas, coupling the
motion of the atoms to their spin. We find that the spin-orbit coupling greatly
increases the damping towards equilibrium. We interpret this damping as spin
drag, which is enhanced by spin-orbit coupling rate, scaled by a remarkable
factor of $8.9(6)$~s. We also find that spin-orbit coupling lowers the final
temperature of the Bose gas after thermalization.",2110.07094v3
2021-11-23,Hyperfine Interaction in a MoS$_2$ Quantum Dot: Decoherence of a Spin-Valley Qubit,"A successful and promising device for the physical implementation of electron
spin-valley based qubits is the Transition Metal Dichalcogenide monolayer
(TMD-ML) semiconductor quantum dot. The electron spin in TMD-ML semiconductor
quantum dots can be isolated and controlled with high accuracy, but it still
suffers from decoherence due to the unavoidable coupling with the surrounding
environment, such as nuclear spin environments. A common tool to investigate
systems like the one considered in this work is the density matrix formalism by
presenting an exact master equation for a central spin (spin-qubit) system in a
time-dependent and coupled to a nuclear spin bath in terms of hyperfine
interaction. The master equation provides a unified description of the dynamics
of the central spin. Analyzing this in more detail, we calculate fidelity loss
due to the Overhauser field from hyperfine interaction in a wide range number
of nuclear spins $\mathcal{N}$.",2111.11621v1
2021-12-02,Observing Magnetic Monopoles in Spin Ice using Electron Holography,"While there is compelling evidence for the existence of magnetic monopoles in
spin ice, the direct observation of a point-like source of magnetic field in
these systems remains an open challenge. One promising approach is electron
holography, which combines atomic-scale resolution with extreme sensitivity to
magnetic vector potentials, through the Aharonov-Bohm effect. Here we explore
what holography can teach us about magnetic monopoles in spin ice, through
experiments on artificial spin ice, and numerical simulations of pyrochlore
spin ice. In the case of artificial spin ice, we show that holograms can be
used to measure local magnetic charge. For pyrochlore spin ice, we demonstrate
that holographic experiments are capable of resolving both magnetic monopoles
and their dynamics, including the emergence of electric fields associated with
fluctuations of closed loops of spins. These results establish that the
observation of both magnetic monopoles and emergent electric fields in
pyrochlore spin ice is a realistic possibility in an electron microscope with
sufficiently--high phase resolution.",2112.01362v2
2021-12-16,Towards exact predictions of spin-phonon relaxation times: an ab initio implementation of open quantum systems theory,"Spin-phonon coupling is the main drive of spin relaxation and decoherence in
solid-state semiconductors at finite temperature. Controlling this interaction
is a central problem for many disciplines, ranging from magnetic resonance to
quantum technologies. Spin relaxation theories have been developed for almost a
century but often employ a phenomenological description of phonons and their
coupling to spin, resulting in a non-predictive tool and hindering our detailed
understanding of spin dynamics. Here we combine fourth-order time-local quantum
master equations with advanced electronic structure methods and perform
predictions of spin-phonon relaxation time for a series of solid-state
coordination compounds based on both transition metals and lanthanide Kramers
ions. The agreement between experiments and simulations demonstrates that an
accurate, universal and fully ab initio implementation of spin relaxation
theory is possible, thus paving the way to a systematic study of spin-phonon
relaxation in solid-state materials.",2112.09236v1
2022-01-18,Spin generalizations of the Benjamin-Ono equation,"We present new soliton equations related to the $A$-type spin Calogero-Moser
(CM) systems introduced by Gibbons and Hermsen. These equations are spin
generalizations of the Benjamin-Ono (BO) equation and the recently introduced
non-chiral intermediate long-wave (ncILW) equation. We obtain multi-soliton
solutions of these spin generalizations of the BO equation and the ncILW
equation via a spin-pole ansatz where the spin-pole dynamics is governed by the
spin CM system in the rational and hyperbolic cases, respectively. We also
propose physics applications of the new equations, and we introduce a spin
generalization of the standard intermediate long-wave equation which
interpolates between the matrix Korteweg-de Vries equation, the Heisenberg
ferromagnet equation, and the spin BO equation.",2201.07269v1
2022-02-18,Intrinsic spin-momentum dynamics of surface electromagnetic waves in complex dispersive system,"Spin-momentum locking is an intrinsic property of surface electromagnetic
fields and its study has led to the discovery of photonic spin lattices and
diverse applications. Previously, dispersion was ignored in the spin-momentum
locking, giving rise to abnormal phenomena contradictory to the physical
realities. Here, we formulate four dispersive spin-momentum equations for
surface waves, revealing universally that the transverse spin vector is locked
with the momentum. The locking property obeys the right-hand rule in the
dielectric but the left-hand rule in the dispersive metal/magnetic materials.
In addition to the dispersion, the structural features can affect the
spin-momentum locking significantly. Remarkably, an extraordinary longitudinal
spin originating from the coupling polarization ellipticity is uncovered even
for the purely polarized state. We further demonstrate the spin-momentum
locking properties with diverse photonic topological lattices by engineering
the rotating symmetry. The findings open up opportunities for designing robust
nanodevices with practical importance in chiral quantum optics.",2202.09007v1
2022-06-19,Enhancement of spin mixing conductance by $s$-$d$ orbital hybridization in heavy metals,"In a magnetic multilayer, the spin transfer between localized magnetization
dynamics and itinerant conduction spin arises from the interaction between a
normal metal and an adjacent ferromagnetic layer. The spin-mixing conductance
then governs the spin-transfer torques and spin pumping at the magnetic
interface. Theoretical description of spin-mixing conductance at the magnetic
interface often employs a single conduction-band model. However, there is
orbital hybridization between conduction $s$ electron and localized $d$
electron of the heavy transition metal, in which the single conduction-band
model is insufficient to describe the $s$-$d$ orbital hybridization. In this
work, using the generalized Anderson model, we estimate the spin-mixing
conductance that arises from the $s$-$d$ orbital hybridization. We find that
the orbital hybridization increases the magnitude of the spin-mixing
conductance.",2206.09347v2
2022-07-05,"Observation of enhanced spin-spin correlations at triple point in 2D ferromagnetic Cr2X2Te6 (X=Si, Ge)","The domain dynamics and spin-spin correlation of 2D ferromagnets Cr2X2Te6
(X=Si, Ge) are investigated by a composite magnetoelectric method. The magnetic
field-temperature phase diagrams for both in-plane and out-of-plane magnetic
fields disclose a triple point around TC and 1 kOe, where ferromagnetic,
paramagnetic, and spin-polarized phases coexist. The magnetoelectric signal
shows peak features at the phase boundaries and reaches the maximum at the
triple point, suggesting significant enhancement of spin-spin correlations at
this point. A comparison between two systems reveals that the spin-spin
correlations in Cr2Si2Te6 are stronger than that in Cr2Ge2Te6.",2207.01846v1
2022-10-12,"Spin Diffusion in Spin Glasses Require Two Magnetic Variables, $\vec{M}$ and $\vec{m}$","Experiment has established that spin-glasses can support a steady-state spin
current $\vec{j}_{i}$. However, the accepted theory of spin glass dynamics
permits oscillations but no steady-state spin current. Onsager's irreversible
thermodynamics implies that the spin current is proportional to the gradient of
a magnetization. We argue, however, that the magnon distribution function
associated with the local equilibrium magnetization $\vec{M}$ cannot diffuse
because it represents $10^{23}$ variables. We therefore invoke the
non-equilibrium magnetization $\vec{m}$, which in spintronics is called the
{\it spin accumulation}. Applying the theory of irreversible thermodynamics we
indeed find that it predicts spin diffusion, and we consider other experimental
consequences of the theory, including a wavelength-dependent coupling between
the reactive and the diffusive degrees of freedom.",2210.05865v2
2022-12-19,Polarization Modulation in Quantum-Dot Spin-VCSELs for Ultrafast Data Transmission,"Spin-Vertical Cavity Surface Emitting Lasers (spin-VCSELs) are undergoing
increasing research effort for new paradigms in high-speed optical
communications and photon-enabled computing. To date research in spin-VCSELs
has mostly focused on Quantum-Well (QW) devices. However, novel Quantum-Dot
(QD) spin-VCSELs, offer enhanced parameter controls permitting the effective,
dynamical and ultrafast manipulation of their light emissions polarization. In
the present contribution we investigate in detail the operation of QD
spin-VCSELs subject to polarization modulation for their use as ultrafast light
sources in optical communication systems. We reveal that QD spin-VCSELs
outperform their QW counterparts in terms of modulation efficiency, yielding a
nearly two-fold improvement. We also analyse the impact of key device
parameters in QD spin-VCSELs (e.g. photon decay rate and intra-dot relaxation
rate) on the large signal modulation performance with regard to optical
modulation amplitude and eye-diagram opening penalty. We show that in addition
to exhibiting enhanced polarization modulation performance for data rates up to
250Gbps, QD spin-VCSELs enable operation in dual (ground and excited state)
emission thus allowing future exciting routes for multiplexing of information
in optical communication links.",2212.09351v1
2022-12-21,Chirality-dependent spin current generation in a helimagnet: zero-field probe of chirality,"In a magnetic texture, the spin of a conduction electron is forced to be
aligned to the localized moment. As a result, the topology of the magnetic
texture affects the electron dynamics in nontrivial ways. A representative
example is the topological Hall effect in noncoplanar spin textures with finite
spin chirality. While propagating in the noncoplanar spin texture, electrons
acquire Berry phase, and their motion is deflected as if they were in a
magnetic field. Here, we report a distinct Berry phase effect in a coplanar
helimagnet: the spin moment of the conduction electron is polarized under
electric currents depending on the chirality of the helimagnet. The accumulated
spin polarization works as a source of spin current, and the chirality can be
detected by the inverse spin Hall mechanism. The functionality allows us to
read out the chirality without magnetic fields, and therefore paves the way to
future helimagnet-based spintronics.",2212.10980v1
2023-02-02,Spin-driven stationary turbulence in spinor Bose-Einstein condensates,"We report the observation of stationary turbulence in antiferromagnetic
spin-1 Bose-Einstein condensates driven by a radio-frequency magnetic field.
The magnetic driving injects energy into the system by spin rotation and the
energy is dissipated via dynamic instability, resulting in the emergence of an
irregular spin texture in the condensate. Under continuous driving, the spinor
condensate evolves into a nonequilibrium steady state with characteristic spin
turbulence, while the low energy scale of spin excitations ensures that the
sample's lifetime is minimally affected. When the driving strength is on par
with the system's spin interaction energy and the quadratic Zeeman energy,
remarkably, the stationary turbulent state exhibits spin-isotropic features in
spin composition and spatial spin texture. We numerically show that ambient
field fluctuations play a crucial role in sustaining the turbulent state within
the system. These results open up new avenues for exploring quantum turbulence
in spinor superfluid systems.",2302.00895v2
2023-02-20,Néel-Vector Switching and THz Spin-Wave Excitation in Mn$_2$Au due to Femtosecond Spin-Transfer Torques,"Efficient and fast manipulation of antiferromagnets has to date remained a
challenging task, hindering their application in spintronic devices. For
ultrafast operation of such devices, it is highly desirable to be able to
control the antiferromagnetic order within picoseconds - a timescale that is
difficult to achieve with electrical circuits. Here, we demonstrate that bursts
of spin-polarized hot-electron currents emerging due to laser-induced ultrafast
demagnetization are able to efficiently excite spin dynamics in
antiferromagnetic Mn$_2$Au by exerting a spin-transfer torque on femtosecond
timescales. We combine quantitative superdiffusive transport and atomistic
spin-model calculations to describe a spin-valve-type trilayer consisting of
Fe$|$Cu$|$Mn$_2$Au. Our results demonstrate that femtosecond spin-transfer
torques can switch the Mn$_2$Au layer within a few picoseconds. In addition, we
find that spin waves with high frequencies up to several THz can be excited in
Mn$_2$Au.",2302.09822v1
2023-08-24,Inter-species spin-noise correlations in hot atomic vapors,"We report an experimental and theoretical study of spin noise correlations in
a $^{87}$Rb-$^{133}$Cs unpolarized alkali-metal vapor dominated by
spin-exchange collisions. We observe strong unequal-time inter-species
correlations and account for these with a first-principles theoretical model.
Since the two atomic species have different spin precession frequencies, the
dual-species vapor enables the use of an additional experimental handle, the
applied magnetic field, for untangling various sub-types of spin correlations.
In particular, the measured cross-correlation and auto-correlation spectra shed
light on a number of spin-dynamic effects involving intra-atom, inter-atom,
intra-species and inter-species correlations. Cross-correlation coefficients
exceeding $60\%$ have been observed at low-magnetic fields, where the two spin
species couple strongly via spin-exchange collisions. The understanding of such
spontaneously generated correlations can motivate the design of
quantum-enhanced measurements with single or multi-species spin-polarized
alkali-metal vapors used in quantum sensing applications.",2308.13090v2
2023-08-30,Spin Rotations in a Bose-Einstein Condensate Driven by Counterflow and Spin-independent Interactions,"We observe spin rotations caused by atomic collisions in a non-equilibrium
Bose-condensed gas of $^{87}$Rb. Reflection from a pseudomagnetic barrier
creates counterflow in which forward- and backward-propagating matter waves
have partly transverse spin directions. Even though inter-atomic interaction
strengths are state-independent, the indistinguishability of parallel spins
leads to spin dynamics. A local magnetodynamic model, which captures the
salient features of the observed spin textures, highlights an essential
connection between four-wave mixing and collisional spin rotation. The observed
phenomenon has previously been thought to exist only in nondegenerate gases;
our observations and model clarify the nature of these effective-magnetic spin
rotations.",2308.16069v1
2023-11-15,Broad-Wavevector Spin Pumping of Flat-Band Magnons,"We report the experimental observation of large spin pumping signals in
YIG/Pt system driven by broad-wavevector spin-wave spin current. 280 nm-wide
microwave inductive antennas offer broad-wavevector excitation which, in
combination with quasi-flatband of YIG, allows a large number of magnons to
participate in spin pumping at a given frequency. Through comparison with
ferromagnetic resonance spin pumping, we attribute the enhancement of the spin
current to the multichromatic magnons. The high efficiency of spin current
generation enables us to uncover nontrivial propagating properties in ultra-low
power regions. Additionally, our study achieves the spatially separated
detection of magnons, allowing the direct extraction of the decay length. The
synergistic combination of the capability of broad-wavevector excitation,
enhanced voltage signals, and nonlocal detection provides a new avenue for the
electrical exploration of spin waves dynamics.",2311.09098v1
2023-11-24,From higher-spin gauge interactions to Compton amplitudes for root-Kerr,"We develop massive higher-spin theory as a framework for describing dynamics
of rotating compact objects, such as Kerr black holes. In this paper, we
explore gauge interactions up to quartic order and corresponding Compton
amplitudes of higher-spin massive objects coupled to electromagnetism and
Yang-Mills theory. Their classical counterparts are known as root-Kerr
gauge-theory solutions, whose amplitudes are closely related to those of Kerr
black holes. We use three distinct approaches: (i) massive higher-spin gauge
symmetry to introduce cubic interactions for all spins and the quartic
interactions up to spin 3, which is implemented both off shell and via Ward
identities; (ii) a chiral higher-spin approach to construct quartic Lagrangians
with correct degrees of freedom to all spins; (iii) on-shell functional
patterns before and after taking the classical limit to constrain the Compton
amplitudes. As final results, we arrive at simple local formulae for the
candidate root-Kerr Compton amplitudes both in the quantum regime and classical
limit, to all orders in spin. This is a precursor to the gravitational Kerr
case, which is presented in a follow-up paper.",2311.14668v1
2024-01-26,Spin Noise Spectroscopy of a Single Spin using Single Detected Photons,"Spin noise spectroscopy has become a widespread technique to extract
information on spin dynamics in atomic and solid-state systems, in a
potentially non-invasive way, through the optical probing of spin fluctuations.
Here we experimentally demonstrate a new approach in spin noise spectroscopy,
based on the detection of single photons. Due to the large spin-dependent
polarization rotations provided by a deterministically-coupled quantum
dot-micropillar device, giant spin noise signals induced by a single-hole spin
are extracted in the form of photon-photon cross-correlations. Ultimately, such
a technique can be extended to an ultrafast regime probing mechanisms down to
few tens of picoseconds.",2401.14976v1
2020-06-25,Temperature-Dependent Anisotropic Magnetoresistance and Spin-Torque-Driven Vortex Dynamics in a Single Microdisk,"Spin-orbit-torque-driven dynamics have recently gained interest in the field
of magnetism due to the reduced requirement of current densities and an
increase in efficiency, as well as the ease of implementation of different
devices and materials. From a practical point of view, the low-frequency
dynamics below 1 GHz is particularly interesting since dynamics associated with
magnetic domains lie in this frequency range. While spin-torque excitation of
high-frequency modes has been extensively studied, the intermediate
low-frequency dynamics have received less attention, although spin torques
could potentially be used for both manipulation of the spin texture, as well as
the excitation of dynamics. In this work, we demonstrate that it is possible to
drive magnetic vortex dynamics in a single microdisk by spin-Hall torque at
varying temperatures, and relate the results to transport properties. We find
that the gyrotropic mode of the core couples to the low-frequency microwave
signal and produces a measurable voltage. The dynamic measurements are in
agreement with magnetic transport measurements and are supported by
micromagnetic simulations. Our results open the door for integrating magnetic
vortex devices in spintronic applications.",2006.14454v1
2012-08-14,Spin dynamics and spin freezing in the triangular lattice antiferromagnets FeGa2S4 and NiGa2S4,"Magnetic susceptibility and muon spin relaxation (muSR) experiments have been
carried out on the quasi-2D triangular-lattice spin S = 2 antiferromagnet
FeGa2S4. The muSR data indicate a sharp onset of a frozen or nearly-frozen spin
state at T* = 31(2) K, twice the spin-glass-like freezing temperature T_f =
16(1) K. The susceptibility becomes field dependent below T*, but no sharp
anomaly is observed in any bulk property. A similar transition is observed in
muSR data from the spin-1 isomorph NiGa2S4. In both compounds the dynamic muon
spin relaxation rate lambda_d(T) above T* agrees well with a calculation of
spin-lattice relaxation by Chubukov, Sachdev, and Senthil in the renormalized
classical regime of a 2D frustrated quantum antiferromagnet. There is no firm
evidence for other mechanisms. At low temperatures lambda_d(T) becomes
temperature independent in both compounds, indicating persistence of spin
dynamics. Scaling of lambda_d(T) between the two compounds is observed from
~T_f to ~1.5T*. Although the muSR data by themselves cannot exclude a truly
static spin component below T*, together with the susceptibility data they are
consistent with a slowly-fluctuating ""spin gel"" regime between T_f and T*. Such
a regime and the absence of a divergence in lambda_d(T) at T* are features of
two unconventional mechanisms: (1) binding/unbinding of Z_2 vortex excitations,
and (2) impurity spins in a nonmagnetic spin-nematic ground state. The absence
of a sharp anomaly or history dependence at T* in the susceptibility of
FeGa2S4, and the weakness of such phenomena in NiGa2S4, strongly suggest
transitions to low-temperature phases with unconventional dynamics.",1208.2914v1
2011-03-08,Effect of dimerization on dynamics of spin-charge separation in Pariser-Parr-Pople model: A time-dependent density matrix renormalization group study,"We investigate the effect of static electron-phonon coupling, on real-time
dynamics of spin and charge transport in $\pi$-conjugated polyene chains. The
polyene chain is modeled by the Pariser-Parr-Pople Hamiltonian with dimerized
nearest-neighbor parameter $t_{0}(1+\delta)$ for short bonds and
$t_{0}(1-\delta)$ for long bonds, and long-range electron-electron
interactions. We follow the time evolution of the spin and charge using
time-dependent density matrix renormalization group technique, when a hole is
injected at one end of the chain in its ground state. We find that spin and
charge dynamics followed through spin and charge velocities, depend both on
chain length and extent of dimerization, $\delta$. Analysis of the results
requires focusing on physical quantities such as average spin and charge
polarizations, particularly in the large dimerization limit. In the
dimerization range 0.0 $\le$ $\delta$ $\le$ 0.15, spin-charge dynamics is found
to have a well defined behavior, with spin-charge separation (measured as the
ratio of charge velocity to spin velocity) as well as, the total amount of
charge and spin transported in a given time, along the chain, decreasing as
dimerization increases. However, in the range 0.3 $\le$ $\delta$ $\le$ 0.5, it
is observed that the dynamics of spin and charge transport becomes complicated.
It is observed that for large $\delta$ values, spin-charge separation is
suppressed and the injected hole fails to travel the entire length of the
chain.",1103.1478v3
2016-04-20,Dynamics of two coupled semiconductor spin qubits in a noisy environment,"We theoretically consider the temporal dynamics of two coupled spin qubits
(e.g., semiconductor quantum dots) driven by the inter-qubit spin-spin
coupling. The presence of environmental noise (e.g., charge traps, nuclear
spins, random magnetic impurities) is accounted for by including random
magnetic field and random inter-qubit coupling terms in the Hamiltonian. Both
Heisenberg coupling and Ising coupling between the spin qubits are considered,
corresponding respectively to exchange and capacitive gates as appropriate for
single spin and singlet-triplet semiconductor qubit systems, respectively. Both
exchange (Heisenberg) and capacitive (Ising) coupling situations can be solved
numerically exactly even in the presence of noise, leading to the key findings
that (i) the steady-state return probability to the initial state remains close
to unity in the presence of strong noise for many, but not all, starting spin
configurations, and (ii) the return probability as a function of time is
oscillatory with a characteristic noise-controlled decay toward the
steady-state value. We also provide results for the magnetization dynamics of
the coupled two-qubit system. Our predicted dynamics can be directly tested in
the already existing semiconductor spin qubit setups providing insight into
their coherent interaction dynamics. Retention of the initial state spin memory
even in the presence of strong environmental noise has important implications
for quantum computation using spin qubits.",1604.06110v2
2021-08-16,Relaxation of antiferromagnetic order and growth of Rényi entropy in a generalized Heisenberg star,"Interacting central spin systems, in which a central spin is coupled to a
strongly correlated spin bath with intrabath interaction, consist of an
important class of spin systems beyond the usual Gaudin magnet. These systems
are relevant to several realistic setups and serve as an interesting platform
to study interaction controlled decoherence and frustration induced instability
of magnetic order. Using an equations-of-motion method based on analytical
representations of spin-operator matrix elements in the XX chain, we obtain
exact long-time dynamics of a generalized Heisenberg star consisting of a
spin-$S$ central spin and an inhomogeneously coupled XXZ chain of $N\leq 16$
bath spins. In contrast to previous studies where the central spin dynamics is
mainly concerned, we focus on the influence of the central spin on the dynamics
of magnetic orders within the spin bath. By preparing the XXZ bath in a N\'eel
state, we find that in the gapless phase of the bath even weak system-bath
coupling could lead to nearly perfect relaxation of the antiferromagnetic
order. In the gapped phase, the staggered magnetization decays rapidly and
approaches a steady value that increases with increasing anisotropy parameter.
These findings suggest the possibility of controlling internal dynamics of
strongly correlated many-spin systems by certain coupled auxiliary systems of
even few degrees of freedom. We also study the dynamics of the R\'enyi
entanglement entropy of the central spin when the bath is prepared in the
ground state. Both the overall profile and initial growth rate of the R\'enyi
entropy are found to exhibit minima at the critical point of the XXZ bath.",2108.07055v3
2020-04-13,Theory of Current-Induced Angular Momentum Transfer Dynamics in Spin-Orbit Coupled Systems,"Motivated by the importance of understanding competing mechanisms to
current-induced spin-orbit torque in complex magnets, we develop a unified
theory of current-induced spin-orbital coupled dynamics. The theory describes
angular momentum transfer between different degrees of freedom in solids, e.g.,
the electron orbital and spin, the crystal lattice, and the magnetic order
parameter. Based on the continuity equations for the spin and orbital angular
momenta, we derive equations of motion that relate spin and orbital current
fluxes and torques describing the transfer of angular momentum between
different degrees of freedom. We then propose a classification scheme for the
mechanisms of the current-induced torque in magnetic bilayers. Based on our
first-principles implementation, we apply our formalism to two different
magnetic bilayers, Fe/W(110) and Ni/W(110), which are chosen such that the
orbital and spin Hall effects in W have opposite sign and the resulting spin-
and orbital-mediated torques can compete with each other. We find that while
the spin torque arising from the spin Hall effect of W is the dominant
mechanism of the current-induced torque in Fe/W(110), the dominant mechanism in
Ni/W(110) is the orbital torque originating in the orbital Hall effect of W. It
leads to negative and positive effective spin Hall angles, respectively, which
can be directly identified in experiments. This clearly demonstrates that our
formalism is ideal for studying the angular momentum transfer dynamics in
spin-orbit coupled systems as it goes beyond the ""spin current picture"" by
naturally incorporating the spin and orbital degrees of freedom on an equal
footing. Our calculations reveal that, in addition to the spin and orbital
torque, other contributions such as the interfacial torque and self-induced
anomalous torque within the ferromagnet are not negligible in both material
systems.",2004.05945v2
2018-03-08,Probing the collective dynamics of nuclear spin bath in a rare-earth ion doped crystal,"Probing collective spin dynamics is a current challenge in the field of
magnetic resonance spectroscopy and has important applications in material
analysis and quantum information protocols. Recently, the rare-earth ion doped
crystals are an attractive candidate for making long-lived quantum memory.
Further enhancement of its performance would benefit from the direct knowledge
on the dynamics of nuclear-spin bath in the crystal. Here we detect the
collective dynamics of nuclear-spin bath located around the rare-earth ions in
a crystal using dynamical decoupling spectroscopy method. From the measured
spectrum, we analyze the configuration of the spin bath and characterize the
flip-flop time between two correlated nuclear spins in a long time scale ($\sim
$1s). Furthermore, we experimentally demonstrate that the rare-earth ions can
serve as a magnetic quantum sensor for external magnetic field. These results
suggest that the rare-earth ion is a useful probe for complex spin dynamics in
solids and enable quantum sensing in the low-frequency regime, revealing
promising possibilities for applications in diverse fields.",1803.03075v2
2022-03-22,Adiabatic spin dynamics and effective exchange interactions from constrained tight-binding electronic structure theory: Beyond the Heisenberg regime,"We consider an implementation of the adiabatic spin dynamics approach in a
tight-binding description of the electronic structure. The adiabatic
approximation for spin-degrees of freedom assumes that the faster electronic
degrees of freedom are always in a quasi-equilibrium state, which significantly
reduces the numerical complexity in comparison to the full electron dynamics.
Non-collinear magnetic configurations are stabilized by a constraining field,
which allows to directly obtain the effective magnetic field from the negative
of the constraining field. While the dynamics are shown to conserve energy, we
demonstrate that adiabatic spin dynamics does not conserve the total spin
angular momentum when the lengths of the magnetic moments are allowed to
change, which is confirmed by numerical simulations. Furthermore, we develop a
method to extract an effective two-spin exchange interaction from the energy
curvature tensor of non-collinear states, which we calculate at each time step
of the numerical simulations. We demonstrate the effect of non-collinearity on
this effective exchange and limitations due to multi-spin interactions in
strongly non-collinear configurations beyond the regime where the Heisenberg
model is valid. The relevance of the results are discussed with respect to
experimental pump-probe experiments that follow the ultra-fast dynamics of
magnetism.",2203.11759v3
2022-09-20,Terahertz spin dynamics in rare-earth orthoferrites,"Recent interest in developing fast spintronic devices and laser-controllable
magnetic solids has sparked tremendous experimental and theoretical efforts to
understand and manipulate ultrafast dynamics in materials. Studies of spin
dynamics in the terahertz (THz) frequency range are particularly important for
elucidating microscopic pathways toward novel device functionalities. Here, we
review THz phenomena related to spin dynamics in rare-earth orthoferrites, a
class of materials promising for antiferromagnetic spintronics. We expand this
topic into a description of four key elements. (1) We start by describing THz
spectroscopy of spin excitations for probing magnetic phase transitions in
thermal equilibrium. While acoustic magnons are useful indicators of spin
reorientation transitions, electromagnons that arise from dynamic
magnetoelectric couplings serve as a signature of inversion-symmetry-breaking
phases at low temperatures. (2) We then review the strong laser driving
scenario, where the system is excited far from equilibrium and thereby subject
to modifications to the free energy landscape. Microscopic pathways for
ultrafast laser manipulation of magnetic order are discussed. (3) Furthermore,
we review a variety of protocols to manipulate coherent THz magnons in time and
space, which are useful capabilities for antiferromagnetic spintronic
applications. (4) Finally, new insights on the connection between dynamic
magnetic coupling in condensed matter and the Dicke superradiant phase
transition in quantum optics are provided. By presenting a review on an array
of THz spin phenomena occurring in a single class of materials, we hope to
trigger interdisciplinary efforts that actively seek connections between
subfields of spintronics, which will facilitate the invention of new protocols
of active spin control and quantum phase engineering.",2209.09468v1
2012-11-06,Non-perturbative stochastic method for driven spin-boson model,"We introduce and apply a numerically exact method for investigating the
real-time dissipative dynamics of quantum impurities embedded in a macroscopic
environment beyond the weak-coupling limit. We focus on the spin-boson
Hamiltonian that describes a two-level system interacting with a bosonic bath
of harmonic oscillators. This model is archetypal for investigating dissipation
in quantum systems and tunable experimental realizations exist in mesoscopic
and cold-atom systems. It finds abundant applications in physics ranging from
the study of decoherence in quantum computing and quantum optics to extended
dynamical mean-field theory. Starting from the real-time Feynman-Vernon path
integral, we derive an exact stochastic Schr\""odinger equation that allows to
compute the full spin density matrix and spin-spin correlation functions beyond
weak coupling. We greatly extend our earlier work (P. P. Orth, A. Imambekov,
and K. Le Hur, Phys. Rev. A {\bf 82}, 032118 (2010)) by fleshing out the core
concepts of the method and by presenting a number of interesting applications.
Methodologically, we present an analogy between the dissipative dynamics of a
quantum spin and that of a classical spin in a random magnetic field. This
analogy is used to recover the well-known non-interacting-blip-approximation in
the weak-coupling limit. We explain in detail how to compute spin-spin
autocorrelation functions. As interesting applications of our method, we
explore the non-Markovian effects of the initial spin-bath preparation on the
dynamics of the coherence $\sigma^x(t)$ and of $\sigma^z(t)$ under a
Landau-Zener sweep of the bias field. We also compute to a high precision the
asymptotic long-time dynamics of $\sigma^z(t)$ without bias and demonstrate the
wide applicability of our approach by calculating the spin dynamics at non-zero
bias and different temperatures.",1211.1201v2
2002-06-29,Solvable Kinetic Gaussian Model in External Field,"In this paper, the single-spin transition dynamics is used to investigate the
kinetic Gaussian model in a periodic external field. We first derive the
fundamental dynamic equations, and then treat an isotropic d-dimensional
hypercubic lattice Gaussian spin system with Fourier's transformation method.
We obtain exactly the local magnetization and the equal-time pair correlation
function. The critical characteristics of the dynamical, the complex
susceptibility, and the dynamical response are discussed. The results show that
the time evolution of the dynamical quantities and the dynamical responses of
the system strongly depend on the frequency and the wave vector of the external
field.",0207007v1
2006-03-25,Inflow versus outflow zero-temperature dynamics in one dimension,"It has been suggested that Glauber (inflow) and Sznajd (outflow)
zero-temperature dynamics for the one dimensional Ising ferromagnet with the
nearest neighbors interactions are equivalent. Here we compare both dynamics
from analytical and computational points of view. We use the method of mapping
an Ising spin system onto the dimer RSA model and show that already this simple
mapping allows to see the differences between inflow and outflow
zero-temperature dynamics. Then we investigate both dynamics with synchronous,
partially synchronous and random sequential updating using the Monte Carlo
technique and compare both dynamics in terms of the number of persistent spins,
clusters, mean relaxation time and relaxation time distribution.",0603680v1
2004-06-30,A Description of Quantum Chaos,"A measure describing the chaos of a dynamics was introduced by two
complexities in information dynamics, and it is called the chaos degree. In
particular, the entropic chaos degree has been used to characterized several
dynamical maps such that logistis, Baker's, Tinckerbel's in classical or
quantum systems. In this paper, we give a new treatment of quantum chaos by
defining the entropic chaos degree for quantum transition dynamics, and we
prove that every non-chaotic quantum dynamics, e.g., dissipative dynamics, has
zero chaos degree. A quantum spin 1/2 system is studied by our chaos degree,
and it is shown that this degree well describes the chaotic behavior of the
spin system.",0406227v1
2016-06-07,Non-markovian mesoscopic dissipative dynamics of open quantum spin chains,"We study the dissipative dynamics of $N$ quantum spins with Lindblad
generator consisting of operators scaling as fluctuations, namely with the
inverse square-root of $N$. In the large $N$ limit, the microscopic dissipative
time-evolution converges to a non-Markovian unitary dynamics on strictly local
operators, while at the mesoscopic level of fluctuations it gives rise to a
dissipative non-Markovian dynamics. The mesoscopic time-evolution is Gaussian
and exhibits either a stable or an unstable asymptotic character; furthermore,
the mesoscopic dynamics builds correlations among fluctuations that survive in
time even when the original microscopic dynamics is unable to correlate local
observables.",1606.02173v1
2004-02-23,$p$-adic discrete dynamical systems and their applications in physics and cognitive sciences,"This review is devoted to dynamical systems in fields of $p$-adic numbers:
origin of $p$-adic dynamics in $p$-adic theoretical physics (string theory,
quantum mechanics and field theory, spin glasses), continuous dynamical systems
and discrete dynamical systems. The main attention is paid to discrete
dynamical systems - iterations of maps in the field of $p$-adic numbers (or
their algebraic extensions): conjugate maps, ergodicity, random dynamical
systems, behaviour of cycles, holomorphic dynamics. dynamical systems in finite
fields. We also discuss applications of $p$-adic discrete dynamical systems to
cognitive sciences and psychology.",0402042v1
1995-11-02,"Decoherence in the Quantum Dynamics of a ""Central Spin"" Coupled to a Spin Environment","We consider here the problem of a ""central spin"", with spin quantum number $S
\gg 1$, interacting with a set of microscopic spins. Interactions between the
microscopic spins are ignored. This model describes magnetic grains or magnetic
macromolecules (ferromagnetically or antiferromagnetically ordered) interacting
with nuclear spins and with any surrounding paramagnetic electronic spins. It
has also been used to describe $Si:P$ near the metal-insulator transition, and
quantum spin glasses.
  In this paper we consider the possible coherent motion of the central spin.
We reduce the model to an effective low-energy Hamiltonian, and then calculate
the correlation function <S(t)S(0)> using instanton methods. The general
solution is given for the unbiased case, for all relevant values of the
couplings. Under certain conditions, nuclear spin diffusion also plays a role.
The results are then used to calculate the spectral absorption for 2
experimental systems, viz., $TbFe_3$ grains, and ferritin molecules. Our
results have general implications for the observation of mesoscopic and
macroscopic quantum coherence, and for the foundations of quantum mechanics.
They show that a spin environment usually has a very destructive effect on
coherence, which cannot be understood using the conventional ""oscillator bath""
models of quantum environments.",9511011v2
1998-03-20,Studies of the phase diagram of randomly interacting fermionic systems,"We present details of the phase diagrams of fermionic systems with random and
frustrated interactions, emphasizing the important role of the chemical
potential. The insulating fermionic Ising spin glass model is shown to reveal
different entangled magnetic instabilities and phase transitions. We review
tricritical phenomena related to the strong correspondence between charge and
spin fluctuations, being controlled by quantum statistics. We compare the spin
density diluted Sherrington-Kirkpatrick spin glass with classical spin 1 models
such as the BEG model. We analyse in detail the infinite range model and show
that spin glass order must decay discontinuously as the chemical potential
exceeds a critical value, provided the temperature is below the tricritical
one, and that the T=0 transition is of classical type. Parisi replica
permutation symmetry breaking (RPSB) governs the thermal spin glass transitions
and fermionic modifications of the SK-models AT-line emerge. RPSB takes place
everywhere within the fermionic spin glass phase. Although the critical field
theory of the quantum paramagnet to spin glass transition in metallic systems
remains replica--symmetric at T=0, with only small corrections at low T from
RPSB, the phase diagram is affected at O(T^0) by RPSB. Generalizing our results
for the fermionic Ising spin glass we consider aspects of models with
additional spin and charge quantum--dynamics such as metallic spin glasses.",9803249v1
2005-12-19,"Voltage probe model of spin decay in a chaotic quantum dot, with applications to spin-flip noise and entanglement production","The voltage probe model is a model of incoherent scattering in quantum
transport. Here we use this model to study the effect of spin-flip scattering
on electrical conduction through a quantum dot with chaotic dynamics. The spin
decay rate gamma is quantified by the correlation of spin-up and spin-down
current fluctuations (spin-flip noise). The resulting decoherence reduces the
ability of the quantum dot to produce spin-entangled electron-hole pairs. For
gamma greater than a critical value gamma_c, the entanglement production rate
vanishes identically. The statistical distribution P(gamma_c) of the critical
decay rate in an ensemble of chaotic quantum dots is calculated using the
methods of random-matrix theory. For small gamma_c this distribution is
proportional to gamma_c^(-1+beta/2), depending on the presence (beta=1) or
absence (beta=2) of time-reversal symmetry. To make contact with experimental
observables, we derive a one-to-one relationship between the entanglement
production rate and the spin-resolved shot noise, under the assumption that the
density matrix is isotropic in the spin degrees of freedom. Unlike the Bell
inequality, this relationship holds for both pure and mixed states. In the
tunneling regime, the electron-hole pairs are entangled if and only if the
correlator of parallel spin currents is at least twice larger than the
correlator of antiparallel spin currents.",0512465v3
2007-07-27,Dependence of spin dephasing on initial spin polarization in a high-mobility two-dimensional electron system,"We have studied the spin dynamics of a high-mobility two-dimensional electron
system in a GaAs/Al_{0.3}Ga_{0.7}As single quantum well by time-resolved
Faraday rotation and time-resolved Kerr rotation in dependence on the initial
degree of spin polarization, P, of the electrons. By increasing the initial
spin polarization from the low-P regime to a significant P of several percent,
we find that the spin dephasing time, $T_2^\ast$, increases from about 20 ps to
200 ps; Moreover, $T_2^\ast$ increases with temperature at small spin
polarization but decreases with temperature at large spin polarization. All
these features are in good agreement with theoretical predictions by Weng and
Wu [Phys. Rev. B {\bf 68}, 075312 (2003)]. Measurements as a function of spin
polarization at fixed electron density are performed to further confirm the
theory. A fully microscopic calculation is performed by setting up and
numerically solving the kinetic spin Bloch equations, including the
D'yakonov-Perel' and the Bir-Aronov-Pikus mechanisms, with {\em all} the
scattering explicitly included. We reproduce all principal features of the
experiments, i.e., a dramatic decrease of spin dephasing with increasing $P$
and the temperature dependences at different spin polarizations.",0707.4111v3
2007-08-07,Spin Pumping of Current in Non-Uniform Conducting Magnets,"Using irreversible thermodynamics we show that current-induced spin transfer
torque within a magnetic domain implies spin pumping of current within that
domain. This has experimental implications for samples both with conducting
leads and that are electrically isolated. These results are obtained by
deriving the dynamical equations for two models of non-uniform conducting
magnets: (1) a generic conducting magnet, with net conduction electron density
n and net magnetization $\vec{M}$; and (2) a two-band magnet, with up and down
spins each providing conduction and magnetism. For both models, in regions
where the equilibrium magnetization is non-uniform, voltage gradients can drive
adiabatic and non-adiabatic bulk spin torques. Onsager relations then ensure
that magnetic torques likewise drive adiabatic and non-adiabatic currents --
what we call bulk spin pumping. For a given amount of adiabatic and
non-adiabatic spin torque, the two models yield similar but distinct results
for the bulk spin pumping, thus distinguishing the two models. As in the recent
spin-Berry phase study by Barnes and Maekawa, we find that within a domain wall
the ratio of the effective emf to the magnetic field is approximately given by
$P(2\mu_{B}/e)$, where P is the spin polarization. The adiabatic spin torque
and spin pumping terms are shown to be dissipative in nature.",0708.0997v1
2007-11-09,Semiconductor Spintronics,"Spintronics refers commonly to phenomena in which the spin of electrons in a
solid state environment plays the determining role. In a more narrow sense
spintronics is an emerging research field of electronics: spintronics devices
are based on a spin control of electronics, or on an electrical and optical
control of spin or magnetism. This review presents selected themes of
semiconductor spintronics, introducing important concepts in spin transport,
spin injection, Silsbee-Johnson spin-charge coupling, and spindependent
tunneling, as well as spin relaxation and spin dynamics. The most fundamental
spin-dependent nteraction in nonmagnetic semiconductors is spin-orbit coupling.
Depending on the crystal symmetries of the material, as well as on the
structural properties of semiconductor based heterostructures, the spin-orbit
coupling takes on different functional forms, giving a nice playground of
effective spin-orbit Hamiltonians. The effective Hamiltonians for the most
relevant classes of materials and heterostructures are derived here from
realistic electronic band structure descriptions. Most semiconductor device
systems are still theoretical concepts, waiting for experimental
demonstrations. A review of selected proposed, and a few demonstrated devices
is presented, with detailed description of two important classes: magnetic
resonant tunnel structures and bipolar magnetic diodes and transistors. In most
cases the presentation is of tutorial style, introducing the essential
theoretical formalism at an accessible level, with case-study-like
illustrations of actual experimental results, as well as with brief reviews of
relevant recent achievements in the field.",0711.1461v1
2009-09-10,Dynamic spin-Hall effect and driven spin helix for linear spin-orbit interactions,"We derive boundary conditions for the electrically induced spin accumulation
in a finite, disordered 2D semiconductor channel. While for DC electric fields
these boundary conditions select spatially constant spin profiles equivalent to
a vanishing spin-Hall effect, we show that an in-plane ac electric field
results in a non-zero ac spin-Hall effect, i.e., it generates a spatially
non-uniform out-of-plane polarization even for linear intrinsic spin-orbit
interactions. Analyzing different geometries in [001] and [110]-grown quantum
wells, we find that although this out-of-plane polarization is typically
confined to within a few spin-orbit lengths from the channel edges, it is also
possible to generate spatially oscillating spin profiles which extend over the
whole channel. The latter is due to the excitation of a driven spin-helix mode
in the transverse direction of the channel. We show that while finite
frequencies suppress this mode, it can be amplified by a magnetic field tuned
to resonance with the frequency of the electric field. In this case, finite
size effects at equal strengths of Rashba- and Dresselhaus SOI lead to an
enhancement of the magnitude of this helix mode. We comment on the relation
between spin currents and boundary conditions.",0909.1892v2
2010-03-08,A theoretical study of spin filtering and its application to polarizing antiprotons,"There has been much recent research into possible methods of polarizing an
antiproton beam, the most promising being spin filtering, the theoretical
understanding of which is currently incomplete. The method of polarization
buildup by spin filtering requires many of the beam particles to remain within
the beam after repeated interaction with an internal target in a storage ring.
Hence small scattering angles, where we show that electromagnetic effects
dominate hadronic effects, are important. All spin-averaged and spin-dependent
electromagnetic cross-sections and spin observables for elastic spin 1/2 - spin
1/2 scattering, for both point-like particles and non-point-like particles with
internal structure defined by electromagnetic form factors, are derived to
first order in QED. Particular attention is paid to spin transfer and
depolarization cross-sections in antiproton-proton, antiproton-electron and
positron-electron scattering, in the low | t | region of momentum transfer. A
thorough mathematical treatment of spin filtering is then presented,
identifying the key physical processes involved and highlighting the dynamical
properties of the physical system. We present and solve sets of differential
equations which describe the buildup of polarization by spin filtering in many
different scenarios of interest. The advantages of using a lepton target are
outlined, and finally a proposal to polarize antiprotons by spin filtering off
an opposing polarized electron beam is investigated.",1003.1604v1
2011-12-12,Intrinsic phonon effects on analog quantum simulators with ultracold trapped ions,"Linear Paul traps have been used recently to simulate the transverse field
Ising model with long-range spin-spin couplings. We study the intrinsic effects
of phonon creation (from the initial phonon ground state) on the spin-state
probability and spin entanglement for such quantum spin simulators. While it
has often been assumed that phonon effects are benign because they play no role
in the pure Ising model, they can play a significant role when a transverse
field is added to the model. We use a many-body factorization of the quantum
time-evolution operator of the system, adiabatic perturbation theory and exact
numerical integration of the Schr\""odinger equation in a truncated spin-phonon
Hilbert space followed by a tracing out of the phonon degrees of freedom to
study this problem. We find that moderate phonon creation often makes the
probabilities of different spin states behave differently from the static spin
Hamiltonian. In circumstances in which phonon creation is minor, the spin
dynamics state probabilities converge to the static spin Hamiltonian prediction
at the cost of reducing the spin entanglement. We show how phonon creation can
severely impede the observation of kink transitions in frustrated spin systems
when the number of ions increases. Many of our results also have implications
for quantum simulation in a Penning trap.",1112.2715v3
2013-01-23,Spin Liquid Regimes at Nonzero Temperature in Quantum Spin Ice,"Quantum spin liquids are highly entangled ground states of quantum systems
with emergent gauge structure, fractionalized spinon excitations, and other
unusual properties. While these features clearly distinguish quantum spin
liquids from conventional, mean-field-like states at zero temperature (T),
their status at T>0 is less clear. Strictly speaking, it is known that most
quantum spin liquids lose their identity at non-zero temperature, being in that
case adiabatically transformable into a trivial paramagnet. This is the case
for the U(1) quantum spin liquid states recently proposed to occur in the
quantum spin ice pyrochlores. Here we propose, however, that in practical
terms, the latter quantum spin liquids can be regarded as distinct phases from
the high temperature paramagnet. Through a combination of gauge mean field
theory calculations and physical reasoning, we argue that these systems sustain
both quantum spin liquid and thermal spin liquid phases, dominated by quantum
fluctuations and entropy, respectively. These phases are separated by a first
order ""thermal confinement"" transition, such that for temperatures below the
transition, spinons and emergent photons are coherently propagating
excitations, and above it the dynamics is classical. Even for parameters for
which the ground state is magnetically ordered and not a quantum spin liquid,
this strong first order transition occurs, pre-empting conventional Landau-type
criticality. We argue that this picture explains the anomalously low
temperature phase transition observed in the quantum spin ice material
Yb2Ti2O7.",1301.5643v1
2014-08-08,Superconductor spintronics: Modeling spin and charge accumulation in out-of-equilibrium NS junctions subjected to Zeeman magnetic fields,"We study the spin and charge accumulation in junctions between a
superconductor and a ferromagnet or a normal metal in the presence of a Zeeman
magnetic field, when the junction is taken out of equilibrium by applying a
voltage bias. We write down the most general form for the spin and charge
current in such junctions, taking into account all spin-resolved possible
tunneling processes. We make use of these forms to calculate the spin
accumulation in NS junctions subjected to a DC bias, and to an AC bias,
sinusoidal or rectangular. We observe that in the limit of negligeable changes
on the superconducting gap, the NS dynamical conductance is insensitive to spin
imbalance. Therefore to probe the spin accumulation in the superconductor, one
needs to separate the injection and detection point, i. e. the electrical spin
detection must be non-local. We address also the effect of the spin
accumulation induced in the normal leads by driving a spin current and its
effects on the detection of the spin accumulation in the superconductor.
Finally, we investigate the out-of-equilibrium spin susceptibility of the SC,
and we show that it deviates drastically from it's equilibrium value.",1408.1833v3
2014-09-30,"Decoherence of nuclear spins in the ""frozen core"" of an electron spin","Hybrid qubit systems combining electronic spins with nearby (""proximate"")
nuclear spin registers offer a promising avenue towards quantum information
processing, with even multi-spin error correction protocols recently
demonstrated in diamond. However, for the important platform offered by spins
of donor atoms in cryogenically-cooled silicon,decoherence mechanisms of
$^{29}$Si proximate nuclear spins are not yet well understood.The reason is
partly because proximate spins lie within a so-called ""frozen core"" region
where the donor electronic hyperfine interaction strongly suppresses nuclear
dynamics. We investigate the decoherence of a central proximate nuclear qubit
arising from quantum spin baths outside, as well as inside, the frozen core
around the donor electron. We consider the effect of a very large nuclear spin
bath comprising many ($\gtrsim 10^8$) weakly contributing pairs outside the
frozen core. We also propose that there may be an important contribution from a
few (of order $100$) symmetrically sited nuclear spin pairs (""equivalent
pairs""), which were not previously considered as their effect is negligible
outside the frozen core. If equivalent pairs represent a measurable source of
decoherence, nuclear coherence decays could provide sensitive probes of the
symmetries of electronic wavefunctions. For the phosphorus donor system, we
obtain $T_{2n}$ values of order 1 second for both the ""far bath"" and
""equivalent pair"" models, confirming the suitability of proximate nuclei in
silicon as very long-lived spin qubits.",1409.8655v4
2015-06-24,Ultrafast quantum spin-state switching in the Co-octaethylporphyrin molecular magnet with a terahertz pulsed magnetic field,"Molecular spin crossover switches are the objects of intense theoretical and
experimental studies in recent years. This interest is due to the fact that
these systems allow one to control their spin state by applying an external
photo-, thermo-, piezo-, or magnetic stimuli. The greatest amount of research
is currently devoted to the study the effect of the photoexcitation on the
bi-stable states of spin crossover single molecular magnets (SMMs). The main
limitation of photo-induced bi-stable states is their short lifetime. In this
paper we present the results of a study of the spin dynamics of the CoOEP
molecule in the Low Spin (LS) state and the High Spin (HS) state induced by
applying the magnetic pulse of 36.8 T. We show that the spin switching in case
of the HS state of the CoOEP molecule is characterized by a long lifetime and
is dependent on the magnitude and duration of the applied field. Thus, after
applying an external stimuli the system in the LS state after the spin
switching reverts to its ground state, whereas the system in the HS state
remains in the excited state for a long time. We found that the temperature
dependency of magnetic susceptibility shows an abrupt thermal spin transition
between two spin states at 40K. The proposed here theoretical approach opens
the way to create modern devices for spintronics with the controllable spin
switching process.",1506.07315v1
2016-02-25,Phase diagram and collective excitation in excitonic insulator: from the orbital physics viewpoint,"Excitonic insulating system is studied from the viewpoints of the orbital
physics in strongly correlated electron systems. An effective model Hamiltonian
for low-energy electronic states is derived from the two-orbital Hubbard model
with a finite energy difference corresponding to the crystalline field
splitting. The effective model is represented by the spin operators and the
pseudo-spin operators for the spin-state degrees of freedom. The ground state
phase diagram is analyzed by the mean-field approximation. In addition to the
low-spin state and high-spin state phases, two kinds of the excitonic
insulating phases emerge as a consequence of the competition between the
crystalline field effect and the Hund coupling. The excitonic transition is
classified to be an Ising-like transition reflecting a spontaneous breaking of
the $Z_2$ symmetry. Magnetic structures in the two excitonic insulating phases
are different from each other; an antiferromagnetic order and a spin nematic
order. Collective excitations in each phase are examined by using the
generalized spin-wave method. The Goldstone modes in the excitonic insulating
phases appear in the dynamical correlation functions for the spins and
pseudo-spin operators. Both the transverse and longitudinal spin excitation
modes are active in the two excitonic insulating phases in contrast to the
low-spin state and high-spin state phases. Connections of the present results
to the perovskite cobalt oxides are discussed.",1602.07831v2
2016-06-17,Discrimination between spin-dependent charge transport and spin dependent recombination in π-conjugated polymers by correlated current and electroluminescence-detected magnetic resonance,"Spin-dependent processes play a crucial role in organic electronic devices.
Spin coherence can give rise to spin mixing due to a number of processes such
as hyperfine coupling, and leads to a range of magnetic field effects. However,
it is not straightforward to differentiate between pure single-carrier
spin-dependent transport processes which control the current and therefore the
electroluminescence, and spin-dependent electron-hole recombination which
determines the electroluminescence yield and in turn modulates the current. We
therefore investigate the correlation between the dynamics of spin-dependent
electric current and spin-dependent electroluminescence in two derivatives of
the conjugated polymer poly(phenylene-vinylene) using simultaneously measured
pulsed electrically detected (pEDMR) and optically detected (pODMR) magnetic
resonance spectroscopy. This experimental approach requires careful analysis of
the transient response functions under optical and electrical detection. At
room temperature and under bipolar charge-carrier injection conditions, a
correlation of the pEDMR and the pODMR signals is observed, consistent with the
hypothesis that the recombination currents involve spin-dependent electronic
transitions. This observation is inconsistent with the hypothesis that these
signals are caused by spin-dependent charge carrier transport. These results
therefore provide no evidence that supports earlier claims that spindependent
transport plays a role for room temperature magnetoresistance effects. At low
temperatures, however, the correlation between pEDMR and pODMR is weakened,
demonstrating that more than one spin-dependent process influences the
optoelectronic materials properties.",1606.05680v1
2016-10-20,The relation of the Dzyaloshinskii-Moriya interaction to spin currents and to the spin-orbit field,"Starting from the general Berry phase theory of the Dzyaloshinskii-Moriya
interaction (DMI) we derive an expression for the linear contribution of the
spin-orbit interaction (SOI). Thereby, we show analytically that at the first
order in SOI DMI is given by the ground-state spin current. We verify this
finding numerically by ab-initio calculations in Mn/W(001) and Co/Pt(111)
magnetic bilayers. We show that despite the strong SOI from the 5$d$ heavy
metals DMI is well-approximated by the first order in SOI, while the
ground-state spin current is not. We decompose the SOI-linear contribution to
DMI into two parts. One part has a simple interpretation in terms of the Zeeman
interaction between the spin-orbit field and the spin misalignment that
electrons acquire in magnetically noncollinear textures. This interpretation
provides also an intuitive understanding of the symmetry of DMI on the basis of
the spin-orbit field and it explains in a simple way why DMI and ground-state
spin currents are related. Moreover, we show that energy currents driven by
magnetization dynamics and associated to DMI can be explained by
counter-propagating spin currents that carry energy due to their Zeeman
interaction with the spin-orbit field. Finally, we discuss options to modify
DMI by nonequilibrium spin currents excited by electric fields or light.",1610.06541v4
2018-04-24,High-resolution combined tunneling electron charge and spin transport theory of Néel and Bloch skyrmions,"Based on a combined charge and vector spin transport theory capable of
imaging noncollinear magnetic textures on surfaces with spin-polarized scanning
tunneling microscopy (SP-STM), the high-resolution tunneling electron charge
and coupled spin transport properties of a variety of N\'eel- and Bloch-type
skyrmions are investigated. Axially symmetric skyrmions are considered within
the same topology class characterized by a vorticity value of $m=1$, and their
helicities are varied by taking $\gamma=0$ and $\pi$ values for the N\'eel
skyrmions and $\gamma=-\pi/2$ and $\pi/2$ values for the Bloch skyrmions.
Depending on the orientation of the magnetization of the STM tip as well as on
the helicity and the time-reversal of the skyrmionic spin structures, several
relationships between their spin transport vector components, the in-plane and
out-of-plane spin transfer torque and the longitudinal spin current, are
identified. The magnitudes of the spin transport vector quantities show close
relation to standard charge current SP-STM images. It is also demonstrated that
the SP-STM images can be used to determine the helicity of the skyrmions.
Moreover, the modified spin polarization vectors of the conduction electrons
due to the local chirality of the complex spin texture are incorporated into
the tunneling model. It is found that this effect modifies the apparent size of
the skyrmions. These results contribute to the proper identification of
topological surface magnetic objects imaged by SP-STM, and deliver important
parameters for current-induced spin dynamics.",1804.09096v2
2014-06-22,Spins of large asteroids: Hint on a primordial distribution of their spin rates,"The Asteroid Belt and the Kuiper Belt are relics from the formation of our
solar system. Understanding the size and spin distribution of the two belts is
crucial for a deeper understanding of the formation of our solar system and the
dynamical process that govern it. In this paper, we investigate the effect of
collisions on the evolution of the spin distribution of asteroids and KBO's.
  We find that the power law nature of the impactors' size distribution leads
to a L\'evy distribution of the spin rates. This results in a power law tail of
the spin distribution, in stark contrast to the usually quoted Maxwellian
distribution. We show that for bodies larger than 10 km, collisions alone lead
to spin rates peaking at 0.15-0.5 revolutions per day. Comparing that to the
observed spin rates of large asteroids ($R>50$ km), we find that the spins of
large asteroids, peaking at $\sim1-2$ revolutions per day, are dominated by a
primordial component that reflects the formation mechanism of the asteroids.
Similarly, the Kuiper Belt has undergone virtually no collisional spin
evolution, assuming current day density. Collisions contribute a spin rate of
$\sim0.01$ revolutions per day, thus the observed fast spin rates of KBOs are
also primordial in nature.",1406.5730v2
2019-10-21,High-frequency magnon excitation due to femtosecond spin-transfer torques,"Femtosecond laser pulses can induce ultrafast demagnetization as well as
generate bursts of hot electron spin currents. In trilayer spin valves
consisting of two metallic ferromagnetic layers separated by a nonmagnetic one,
hot electron spin currents excited by an ultrashort laser pulse propagate from
the first ferromagnetic layer through the spacer reaching the second magnetic
layer. When the magnetizations of the two magnetic layers are noncollinear,
this spin current exerts a torque on magnetic moments in the second
ferromagnet. Since this torque is acting only within the sub-ps timescale, it
excites coherent high-frequency magnons as recently demonstrated in
experiments. Here, we calculate the temporal shape of the hot electron spin
currents using the superdiffusive transport model and simulate the response of
the magnetic system to the resulting ultrashort spin-transfer torque pulse by
means of atomistic spin-dynamics simulations. Our results confirm that the
acting spin-current pulse is short enough to excite magnons with frequencies
beyond 1 THz, a frequency range out of reach for current induced spin-transfer
torques. We demonstrate the formation of thickness dependent standing spin
waves during the first picoseconds after laser excitation. In addition, we vary
the penetration depth of the spin-transfer torque to reveal its influence on
the excited magnons. Our simulations clearly show a suppression effect of
magnons with short wavelengths already for penetration depths in the range of 1
nm confirming experimental findings reporting penetration depths below $2\,
{\rm nm}$.",1910.09412v1
2019-10-24,Radiative cooling of a spin ensemble,"Physical systems reach thermal equilibrium through energy exchange with their
environment, and for spins in solids the relevant environment is almost always
the host lattice in which they sit. However, recent studies motivated by
observations from Purcell showed how coupling to a cavity can become the
dominant form of relaxation for spins, given suitably strong spin-cavity
coupling. In this regime, the cavity electromagnetic field takes over from the
lattice as the dominant environment, inviting the prospect of controlling the
spin temperature independently from that of the lattice, by engineering a
suitable cavity field. Here, we report on precisely such control over spin
temperature, illustrating a novel and universal method of electron spin
hyperpolarisation. By switching the cavity input between loads at different
temperatures we can control the electron spin polarisation, cooling it below
the lattice temperature. Our demonstration uses donor spins in silicon coupled
to a superconducting micro-resonator and we observe an increase of spin
polarisation of over a factor of two. This approach provides general route to
signal enhancement in electron spin resonance, or indeed nuclear magnetic
resonance through dynamical nuclear spin polarisation (DNP).",1910.11092v1
2020-04-22,Bath assisted transport in a three-site spin chain: global {\sl vs} local approach,"Within the standard weak-coupling limit, the reduced dynamics of open quantum
spin chains with their two end spins coupled to two distinct heat baths at
different temperatures are mainly derived using the so-called \textit{global}
and \textit{local} approaches, in which, respectively, the spin
self-interaction is and is not taken into account. In order to compare the
differences between the two regimes, we concentrate on an open three-site $XX$
spin-chain, provide systematic techniques to addressing the global and local
asymptotic states and then compare the asymptotic spin-transport features by
studying the spin flux through the middle site. %we examine the transport
properties of an open three-site $XX$ spin-chain. %We analytically derive the
exact steady state of the open chain in the global approach and its first order
expansion with respect to the self-interaction in the local one. %The steady
state transport properties through the middle spin is then studied %in order to
compare the physical scenarios associated with the two regimes. %By analytical
and numerical means, Basing on the analytical expressions of the stationary
states in the two regimes, we find that the local approach misses important
global effects emerging as spin sink and source terms that can only be due to
non negligible inter-spin interactions. Moreover, we show that the local
asympotic transport features cannot be recovered from the global ones by
letting the inter-spin coupling vanish thus pointing to the existence of
different coupling ranges where only one approach is physically tenable and
possibly a region where the two descriptions may coexist.",2004.10433v3
2017-11-20,Multi-spin-assisted optical pumping of bulk 13C nuclear spin polarization in diamond,"One of the most remarkable properties of the nitrogen-vacancy (NV) center in
diamond is that optical illumination initializes its electronic spin almost
completely, a feature that can be exploited to polarize other spin species in
their proximity. Here we use field-cycled nuclear magnetic resonance (NMR) to
investigate the mechanisms of spin polarization transfer from NVs to 13C spins
in diamond at room temperature. We focus on the dynamics near 51 mT, where a
fortuitous combination of energy matching conditions between electron and
nuclear spin levels gives rise to alternative polarization transfer channels.
By monitoring the 13C spin polarization as a function of the applied magnetic
field, we show 13C spin pumping takes place via a multi-spin cross relaxation
process involving the NV- spin and the electronic and nuclear spins of
neighboring P1 centers. Further, we find that this mechanism is insensitive to
the crystal orientation relative to the magnetic field, although the absolute
level of 13C polarization - reaching up to ~3% under optimal conditions - can
vary substantially depending on the interplay between optical pumping
efficiency, photo-generated carriers, and laser-induced heating.",1711.07576v1
2023-02-14,Collapsar Gamma-ray Bursts Grind their Black Hole Spins to a Halt,"The spin of a newly formed black hole (BH) at the center of a massive star
evolves from its natal value due to two competing processes: accretion of gas
angular momentum that increases the spin, and extraction of BH angular momentum
by outflows that decreases the spin. Ultimately, the final, equilibrium spin is
set by the balance between both processes. In order for the BH to launch
relativistic jets and power a $ \gamma $-ray burst (GRB), the BH magnetic field
needs to be dynamically important. Thus, we consider the case of a magnetically
arrested disk (MAD) driving the spin evolution of the BH. By applying the
semi-analytic MAD BH spin evolution model of Lowell et al. (2023) to
collapsars, we show that if the BH accretes $ \sim 20\% $ of its initial mass,
its dimensionless spin inevitably reaches small values, $ a \lesssim 0.2 $. For
such spins, and for mass accretion rates inferred from collapsar simulations,
we show that our semi-analytic model reproduces the energetics of typical GRB
jets, $L_{\rm jet}\sim10^{50}\,\,{\rm erg\,s^{-1}}$. We show that our
semi-analytic model reproduces the nearly constant power of typical GRB jets.
If the MAD onset is delayed, this allows powerful jets at the high end of the
GRB luminosity distribution, $L_{\rm jet}\sim10^{52}\,\,{\rm erg\,s^{-1}}$, but
the final spin remains low, $ a \lesssim 0.3 $. These results are consistent
with the low spins inferred from gravitational wave detections of binary BH
mergers. In a companion paper, Gottlieb et al. (2023), we use GRB observations
to constrain the natal BH spin to be $ a \simeq 0.2 $.",2302.07281v1
2007-05-03,"On the Dynamical Ferromagnetic, Quantum Hall, and Relativistic Effects on the Carbon Nanotubes Nucleation and Growth Mechanism","The mechanism of carbon nanotube (CNT) nucleation and growth has been a
mystery for over 15 years. Prior models have attempted the extension of older
classical transport mechanisms. In July 2000, a more detailed and accurate
nonclassical, relativistic mechanism was formulated considering the detailed
dynamics of the electronics of spin and orbital rehybridization between the
carbon and catalyst via novel mesoscopic phenomena and quantum dynamics.
Ferromagnetic carbon was demonstrated. Here, quantum (Hall) effects and
relativistic effects of intense many body spin-orbital interactions for novel
orbital rehybridization dynamics (Little Effect) are proposed in this new
dynamical magnetic mechanism. This dynamic ferromagnetic mechanism is proven by
imposing dynamic and static magnetic fields during CNT syntheses and observing
the different influence of these external magnetic environments on the
catalyzing spin currents and spin waves and the resulting CNT formation.",0705.0407v1
2019-05-21,Quantum quench and non-equilibrium dynamics in lattice-confined spinor condensates,"We present an experimental study on non-equilibrium dynamics of a spinor
condensate after it is quenched across a superfluid to Mott insulator (MI)
phase transition in cubic lattices. Intricate dynamics consisting of
spin-mixing oscillations at multiple frequencies are observed in time
evolutions of the spinor condensate localized in deep lattices after the
quantum quench. Similar spin dynamics also appear after spinor gases in the MI
phase are suddenly moved away from their ground states via quenching magnetic
fields. We confirm these observed spectra of spin-mixing dynamics can be
utilized to reveal atom number distributions of an inhomogeneous system, and to
study transitions from two-body to many-body dynamics. Our data also imply the
non-equilibrium dynamics depend weakly on the quench speed but strongly on the
lattice potential. This enables precise measurements of the spin-dependent
interaction, a key parameter determining the spinor physics.",1905.08738v1
2018-07-09,Hybrid-State Free Precession in Nuclear Magnetic Resonance,"The dynamics of large spin-1/2 ensembles in the presence of a varying
magnetic field are commonly described by the Bloch equation. Most magnetic
field variations result in unintuitive spin dynamics, which are sensitive to
small deviations in the driving field. Although simplistic field variations can
produce robust dynamics, the captured information content is impoverished.
Here, we identify adiabaticity conditions that span a rich experiment design
space with tractable dynamics. These adiabaticity conditions trap the spin
dynamics in a one-dimensional subspace. Namely, the dynamics is captured by the
absolute value of the magnetization, which is in a transient state, while its
direction adiabatically follows the steady state. We define the hybrid state as
the co-existence of these two states and identify the polar angle as the
effective driving force of the spin dynamics. As an example, we optimize this
drive for robust and efficient quantification of spin relaxation times and
utilize it for magnetic resonance imaging of the human brain.",1807.03424v1
2021-12-09,Orbital Dynamics in Centrosymmetric Systems,"Orbital dynamics in time-reversal-symmetric centrosymmetric systems is
examined theoretically. Contrary to common belief, we demonstrate that many
aspects of orbital dynamics are qualitatively different from spin dynamics
because the algebraic properties of the orbital and spin angular momentum
operators are different. This difference generates interesting orbital
responses, which do not have spin counterparts. For instance, the orbital
angular momentum expectation values may oscillate even without breaking neither
the time-reversal nor the inversion symmetry. Our quantum Boltzmann approach
reproduces the previous result on the orbital Hall effect and reveals
additional orbital dynamics phenomena, whose detection schemes are discussed
briefly. Our work will be useful for the experimental differentiation of the
orbital dynamics from the spin dynamics.",2112.04659v2
1999-04-26,Low-Temperature Spin Dynamics of Doped Manganites: roles of Mn-t2g and eg and O-2p states,"The low-temperature spin dynamics of doped manganites have been analyzed
within a tight-binding model, the parameters of which are estimated by mapping
the results of ab initio density functional calculations onto the model. This
approach is found to provide a good description of the spin dynamics of the
doped manganites, observed earlier within the ab initio calculations. Our
analysis not only provides some insight into the roles of the eg and the t2g
states but also indicates that the oxygen p states play an important role in
the spin dynamics. This may cast doubt on the adaptability of the conventional
model Hamiltonian approaches to the analysis of spin dynamics of doped
manganites.",9904369v1
2005-09-12,Spin and Charge Dynamics in a Renormalised Perturbation Theory,"We calculate the spin and charge dynamical susceptibilities of a strongly
correlated impurity model in a renormalised perturbation theory.
  The irreducible for vertices for the quasiparticle scattering are deduced
from the renormalised parameters, which have been calculated by fitting of the
low-lying levels of a numerical renormalisation group (NRG) calculation to
those of an effective Anderson model. The susceptibilities are asymptotically
exact in the low frequency limit and satisfy the Korringa-Shiba relation. By
comparing the results with those calculated from a direct NRG calculation, we
show that the renormalised perturbation theory (RPT) description gives a very
good description of spin dynamics for all values of the local interaction U,
not only at low frequencies but over the whole relevant frequency range.
  In the presence of a magnetic field the approach can be generalised using
field dependent renormalised parameters to calculate the transverse and
parallel spin dynamic susceptibilities. The RPT results give accurate results
for the spin dynamics over the whole frequency range and for all values of the
magnetic field.",0509296v1
2007-07-09,Tunable Quantum Fluctuation-Controlled Coherent Spin Dynamics,"Temporal evolution of a macroscopic condensate of ultra cold atoms is usually
driven by mean field potentials, either due to scattering between atoms or due
to coupling to external fields; and coherent quantum dynamics have been
observed in various cold-atom experiments. In this article, we report results
of studies of a class of quantum spin dynamics which are purely driven by zero
point quantum fluctuations of spin collective coordinates. Unlike the usual
mean-field coherent dynamics, quantum fluctuation-controlled spin dynamics or
QFCSD studied here are very sensitive to variation of quantum fluctuations and
can be tuned by four to five order of magnitude using optical lattices. They
have unique dependence on optical lattice potential depths and quadratic Zeeman
fields. QFCSD can be potentially used to calibrate quantum fluctuations and
investigate correlated fluctuations and various universal scaling properties
near quantum critical points.",0707.1036v3
2007-11-20,Chiral Dynamics and Single-Spin Asymmetries,"Parity-conserving single-spin asymmetries provide a specific measure of
coherent spin-orbit dynamics in quantum chromodynamics. The origin of these
effects can be traced to the interplay of chiral dynamics and confinement in
the theory. The most elegant display of the relevant mechanisms occurs in the
Collins functions and the polarizing fragmentation functions and fracture
functions for particles with spin. In the nucleon, these same dynamical
mechanisms generate virtual quantum structures leading to the Boer-Mulders
functions and orbital distributions. Two complementary formalisms for these
distributions appear. The familiar gauge-link formalism incorporates oll
nonperturbative dynamics into nonlocal correlators. The constructive formalism
introduced by the author describes distributions normalized to an intrinsic
property of the nucleon, namely, the currents specified in the
Bakker-Leader-Trueman sum rule. The connection between these two approaches can
be explored in the process dependence of single-spin asymmetries in various
hard-scattering processes. The study of the SU(2) Weyl-Dirac equation in
spherical coordinates allows typical Wilson operators that determine this
process dependence to be evaluated in the coordinate gauge.",0711.3185v1
2014-09-16,Experimental observation of a phase transition in the evolution of many-body systems with dipolar interactions,"Non-equilibrium dynamics of many-body systems is important in many branches
of science, such as condensed matter, quantum chemistry, and ultracold atoms.
Here we report the experimental observation of a phase transition of the
quantum coherent dynamics of a 3D many-spin system with dipolar interactions,
and determine its critical exponents. Using nuclear magnetic resonance (NMR) on
a solid-state system of spins at room-temperature, we quench the interaction
Hamiltonian to drive the evolution of the system. The resulting dynamics of the
system coherence can be localized or extended, depending on the quench
strength. Applying a finite-time scaling analysis to the observed
time-evolution of the number of correlated spins, we extract the critical
exponents v = s = 0.42 around the phase transition separating a localized from
a delocalized dynamical regime. These results show clearly that such
nuclear-spin based quantum simulations can effectively model the
non-equilibrium dynamics of complex many-body systems, such as 3D spin-networks
with dipolar interactions.",1409.4562v1
2015-03-23,Local dynamics of topological magnetic defects in the itinerant helimagnet FeGe,"Chiral magnetic interactions induce complex spin textures including helical
and conical spin waves, as well as particle-like objects such as magnetic
skyrmions and merons. These spin textures are the basis for innovative device
paradigms and give rise to exotic topological phenomena, thus being of interest
for both applied and fundamental sciences. Present key questions address the
dynamics of the spin system and emergent topological defects. Here we analyze
the micromagnetic dynamics in the helimagnetic phase of FeGe. By combining
magnetic force microscopy, single-spin magnetometry, and
Landau-Lifschitz-Gilbert simulations we show that the nanoscale dynamics are
governed by the depinning and subsequent motion of magnetic edge dislocations.
The motion of these topologically stable objects triggers perturbations that
can propagate over mesoscopic length scales. The observation of stochastic
instabilities in the micromagnetic structure provides new insight to the
spatio-temporal dynamics of itinerant helimagnets and topological defects, and
discloses novel challenges regarding their technological usage.",1503.06622v2
2017-03-27,Quantum correlations at infinite temperature: the dynamical Nagaoka effect,"Do quantum correlations play a role in high temperature dynamics of many-body
systems? A common expectation is that thermal fluctuations lead to fast
decoherence and make dynamics classical. In this paper, we provide a striking
example of a single particle created in a featureless, infinite temperature
spin bath which not only exhibits non-classical dynamics but also induces
strong long-lived correlations between the surrounding spins. We study the
non-equilibrium dynamics of a hole created in a fermionic or bosonic Mott
insulator in the atomic limit, which corresponds to a degenerate spin system.
In the absence of interactions, the spin correlations arise purely from quantum
interference, and the correlations are both antiferromagnetic and
ferromagnetic, in striking contrast to the equilibrium Nagaoka effect. These
results are relevant for several condensed matter spin systems, and should be
observable using state of the art bosonic or fermionic quantum gas microscopes.",1703.09231v1
2015-12-16,Parity-time symmetry breaking in magnetic systems,"The understanding of out-of-equilibrium physics, especially dynamic
instabilities and dynamic phase transitions, is one of the major challenges of
contemporary science, spanning the broadest wealth of research areas that range
from quantum optics to living organisms. Focusing on nonequilibrium dynamics of
an open dissipative spin system, we introduce a non-Hermitian Hamiltonian
approach, in which non-Hermiticity reflects dissipation and deviation from
equilibrium. The imaginary part of the proposed spin Hamiltonian describes the
effects of Gilbert damping and applied Slonczewski spin-transfer torque. In the
classical limit, our approach reproduces Landau-Lifshitz-Gilbert-Slonczewski
dynamics of a large macrospin. We reveal the spin-transfer torque-driven
parity-time symmetry-breaking phase transition corresponding to a transition
from precessional to exponentially damped spin dynamics. Micromagnetic
simulations for nanoscale ferromagnetic disks demonstrate the predicted effect.
Our findings can pave the way to a general quantitative description of
out-of-equilibrium phase transitions driven by spontaneous parity-time symmetry
breaking.",1512.05408v2
2015-12-31,Dynamical sensitivity control of a single-spin quantum sensor,"The Nitrogen-Vacancy (NV) defect in diamond is a unique quantum system that
offers precision sensing of nanoscale physical quantities beyond the current
state-of-the-art. Here we present a method to controllably encode the
interactions in the population of the spin states, thereby introducing a way to
control the sensitivity of a single spin as a continuum in contrast to
free-evolution based methods. By adopting this feature we demonstrate
high-accuracy NV magnetometry without 2pi ambiguities, enhance the dynamic
range by a factor of 4*10^3 achieve interaction times exceeding 2 ms in
off-the-shelf diamond. We perform nuclear spin-noise spectroscopy in the
frequency domain by dynamically controlling the NV spin's sensitivity piecewise
and in a smooth manner thereby precluding harmonic artefacts and undesired
interactions. On a broader perspective dynamical sensitivity control provides
an elegant handle on the inherent dynamics of quantum systems, while offering
decisive advantages for NV centre applications notably in quantum controls and
single molecule NMR/MRI.",1512.09256v1
2018-12-20,Tunable Angle Dependent Magnetization Dynamics in Ni80Fe20 Nano-cross Structures of Varying Size,"We demonstrate a large angular dependence of magnetization dynamics in
Ni80Fe20 nano-cross arrays of varying sizes. By subtle variation of the
azimuthal angle of an in-plane bias magnetic field, the spin configuration and
the ensuing spin-wave dynamics, including mode softening, mode splitting, mode
crossover and mode merging, can be drastically varied to the extent that a
frequency minimum corresponding to mode softening converts to a mode crossover,
various mode splitting and mode crossover disappear and additional mode
splitting appears. Numerically simulated spin-wave spectra and phase profiles
revealed the nature of various spin-wave modes and the origin of above
variation of the dynamics with bias-field angle. All of these above
observations are further modified with the variation of dimensions of the
nano-cross. The numerically calculated magnetostatic field distributions
further supports the variation of dynamics with bias-field angle. These results
open a new avenue for engineering the nano-cross based magnetic devices such as
magnetic storage, spin-wave logic and on-chip data communication devices.",1812.08393v1
2019-04-17,Dynamical spin-orbit coupling of a quantum gas,"We realize the dynamical 1D spin-orbit-coupling (SOC) of a Bose-Einstein
condensate confined within an optical cavity. The SOC emerges through
spin-correlated momentum impulses delivered to the atoms via Raman transitions.
These are effected by classical pump fields acting in concert with the quantum
dynamical cavity field. Above a critical pump power, the Raman coupling emerges
as the atoms superradiantly populate the cavity mode with photons.
Concomitantly, these photons cause a back-action onto the atoms, forcing them
to order their spin-spatial state. This SOC-inducing superradiant Dicke phase
transition results in a spinor-helix polariton condensate. We observe emergent
SOC through spin-resolved atomic momentum imaging. Dynamical SOC in quantum gas
cavity QED, and the extension to dynamical gauge fields, may enable the
creation of Meissner-like effects, topological superfluids, and exotic quantum
Hall states in coupled light-matter systems.",1904.08388v1
2020-11-29,Discrete gravity dynamics from effective spin foams,"The first computation of a spin foam dynamics that provides a test of the
quantum equations of motions of gravity is presented. Specifically, a
triangulation that includes an inner edge is treated. The computation leverages
the recently introduced effective spin foam models, which are particularly
numerically efficient. Previous work has raised the concern of a flatness
problem in spin foam dynamics, identifying the potential for the dynamics to
lead to flat geometries in the small $\hbar$ semiclassical limit. The numerical
results presented here expose a rich semiclassical regime, but one that must be
understood as an interplay between the various parameters of the spin foam
model. In particular, the scale of the triangulation, fixed by the areas of its
boundary triangles, the discreteness of the area spectrum, input from Loop
Quantum Gravity, and the curvature scales around the bulk triangles, all enter
the characterization of the semiclassical regime identified here. In addition
to these results on the dynamics, we show that the subtle nature of the
semiclassical regime is a generic feature of the path integral quantization of
systems with second class constraints.",2011.14468v2
2022-06-30,Modeling Spin-Dependent Nonadiabatic Dynamics with Electronic Degeneracy: A Phase-Space Surface-Hopping Method,"Nuclear Berry curvature effects emerge from electronic spin degeneracy and
canlead to non-trivial spin-dependent (nonadiabatic) nuclear dynamics. However,
such effects are completely neglected in all current mixed quantum-classical
methods such as fewest switches surface-hopping. In this work, we present a
phase-space surface-hopping (PSSH) approach to simulate singlet-triplet
intersystem crossing dynamics. We show that with a simple pseudo-diabatic
ansatz, a PSSH algorithm can capture the relevant Berry curvature effects and
make predictions in agreement with exact quantum dynamics for a simple
singlet-triplet model Hamiltonian. Thus, this approach represents an important
step towards simulating photochemical and spin processes concomitantly, as
relevant to intersystem crossing and spin-lattice relaxation dynamics.",2206.15406v2
2023-05-26,Accounting for Quantum Effects in Atomistic Spin Dynamics,"Atomistic spin dynamics (ASD) is a standard tool to model the magnetization
dynamics of a variety of materials. The fundamental dynamical model underlying
ASD is entirely classical. In this letter, we present two approaches to
effectively incorporate quantum effects into ASD simulations, thus enhancing
their low temperature predictions. The first allows to simulate the magnetic
behavior of a quantum spin system by solving the equations of motions of a
classical spin system at an effective temperature. This effective temperature
is determined a priori from the microscopic properties of the system. The
second approach is based on a semi-classical model where classical spins
interact with an environment with a quantum-like power spectrum. The parameters
that characterize this model can be calculated ab initio or extracted from
experiments. This semi-classical model quantitatively reproduces the
low-temperature behavior of a magnetic system, thus accounting for the quantum
mechanical aspects of its dynamics. The methods presented here can be readily
implemented in current ASD simulations with no additional complexity cost.",2305.17082v1
2023-11-28,Machine learning force-field models for metallic spin glass,"Metallic spin glass systems, such as dilute magnetic alloys, are
characterized by randomly distributed local moments coupled to each other
through a long-range electron-mediated effective interaction. We present a
scalable machine learning (ML) framework for dynamical simulations of metallic
spin glasses. A Behler-Parrinello type neural-network model, based on the
principle of locality, is developed to accurately and efficiently predict
electron-induced local magnetic fields that drive the spin dynamics. A crucial
component of the ML model is a proper symmetry-invariant representation of
local magnetic environment which is direct input to the neural net. We develop
such a magnetic descriptor by incorporating the spin degrees of freedom into
the atom-centered symmetry function methods which are widely used in ML
force-field models for quantum molecular dynamics. We apply our approach to
study the relaxation dynamics of an amorphous generalization of the s-d model.
Our work highlights the promising potential of ML models for large-scale
dynamical modeling of itinerant magnets with quenched disorder.",2311.16964v1
2009-01-27,What can we learn about the dynamics of transported spins by measuring shot noise in spin-orbit-coupled nanostructures?,"We review recent studies of the shot noise of spin-polarized charge currents
and pure spin currents in multiterminal semiconductor nanostructures, while
focusing on the effects brought by the intrinsic Rashba spin-orbit (SO)
coupling and/or extrinsic SO scattering off impurities in two-dimensional
electron gas (2DEG) based devices. By generalizing the scattering theory of
quantum shot noise to include the full spin-density matrix of electrons
injected from a spin-filtering electrode, we show how decoherence and dephasing
in the course of spin precession can lead to substantial enhancement of the
Fano factor (noise-to-current ratio) of spin-polarized charge currents. In
four-terminal SO-coupled nanostructures, injection of unpolarized charge
current through the longitudinal leads is responsible not only for the pure
spin Hall current in the transverse leads, but also for nonequilibrium random
time-dependent current fluctuations. The analysis of the shot noise of
transverse pure spin Hall current and zero charge current, or transverse spin
current and non-zero charge Hall current, driven by unpolarized or
spin-polarized injected longitudinal charge current, respectively, reveals a
unique experimental tool to differentiate between the intrinsic Rashba and
extrinsic SO mechanisms underlying the spin Hall effect in 2DEG devices.
Finally, we discuss the shot noise of transverse spin and zero charge currents
in the quantum-interference-driven spin Hall effect in ballistic four-terminal
Aharonov-Casher rings realized using high-mobility 2DEG with the Rashba SO
coupling.",0901.4182v2
2020-07-25,Spin and Eccentricity Evolution in Triple Systems: from the Lidov-Kozai Interaction to the Final Merger of the Inner Binary,"We study the spin and eccentricity evolution of black-hole (BH) binaries that
are perturbed by tertiary masses and experience the Lidov-Kozai (LK)
excitation. We focus on three aspects. Firstly, we study the spin-orbit
alignment of the inner binary following the approach outlined by Antonini et
al. [MNRAS 480, L58 (2018)] and Liu and Lai [ApJ 863, 68 (2018)], yet allowing
the spins to have random initial orientations. We confirm the existence of a
dynamical attractor that drives the spin-orbit angle at the end of the LK
evolution to a value given by the initial angle between the spin and the outer
orbital angular momentum (instead of to a specific value of the effective
spin). Secondly, we follow the (inner) binary's evolution further to the merger
to study the final spin-spin alignment. We generalize the effective potential
theory to include orbital eccentricity, which allows us to efficiently evolve
the system in the early inspiral stages. We further find that the spin-spin and
spin-orbit alignments are correlated and the correlation is determined by the
initial spin-orbit angle. For systems with the spin vectors initially in the
orbital plane, the final spins strongly disfavor an aligned configuration and
could thus lead to a greater value of the GW recoil than a uniform spin-spin
alignment would predict. Lastly, we study the maximum eccentricity excitation
that can be achieved during the LK process, including the effects of
gravitational-wave radiation. We find that when the tertiary mass is a
super-massive BH and the inner binary is massive, then even with the maximum LK
excitation, the residual eccentricity is typically less than 0.1 when the
binary's orbital frequency reaches 10 Hz, and a decihertz detector would be
necessary to follow such a system's orbital evolution.",2007.12978v2
2016-12-29,The magnetic Hamiltonian and phase diagram of the quantum spin liquid Ca10Cr7O28,"A spin liquid is a new state of matter with topological order where the spin
moments continue to fluctuate coherently down to the lowest temperatures rather
than develop static long-range magnetic order as found in conventional magnets.
For spin liquid behavior to arise in a material the magnetic Hamiltonian must
be ""frustrated"" where the combination of lattice geometry, interactions and
anisotropies gives rise to competing spin arrangements in the ground state.
Theoretical Hamiltonians which produce spin liquids are spin ice, the Kitaev
honeycomb model and the Heisenberg kagome antiferromagnet. Spin liquid behavior
however in real materials is rare because they can only approximate these
Hamiltonians and often have weak higher order terms that destroy the spin
liquid state. Ca10Cr7O28 is a new quantum spin liquid with magnetic Cr5+ ions
that possess quantum spin number S=1/2. The spins are entirely dynamic in the
ground state and the excitation spectrum is broad and diffuse as is typical of
spinons which are the excitations of a spin liquid. In this paper we determine
the Hamiltonian of Ca10Cr7O28 using inelastic neutron scattering under high
magnetic field to induce a ferromagnetic ground state and spin-wave excitations
that can be fitted to extract the interactions. We further explore the phase
diagram by using inelastic neutron scattering and heat capacity measurements
and establish the boundaries of the spin liquid phase as a function of magnetic
field and temperature. Our results show that Ca10Cr7O28 consists of distorted
kagome bilayers with several isotropic ferromagnetic and antiferromagnetic
interactions where unexpectedly the ferromagnetic interactions are stronger
than the antiferromagnetic ones. This complex Hamiltonian does not correspond
to any known spin liquid model and points to new directions in the search for
quantum spin liquid behavior.",1612.09149v1
1996-02-08,Generalized Coherent States and Spin $S\geq 1$ Systems,"Generalized Coherent States (GCS) are constructed (and discussed) in order to
study quasiclassical behaviour of quantum spin models of the Heisenberg type.
Several such models are taken to their semiclassical limits, whose form depends
on the spin value as well as the Hamiltonian symmetry. In the continuum
approximation, SU(2)/U(1) GCS when applied give rise to the well-known
Landau-Lifshitz classical phenomenology. For arbitrary spin values one obtains
a lattice of coupled nonlinear oscillators. Corresponding classical continuum
models are described as well.",9602009v1
1996-04-23,Dynamics of coupled quantum spin chains,"Static and dynamical properties of weakly coupled antiferromagnetic spin
chains are treated using a mean--field approximation for the interchain
coupling and exact results for the resulting effective one--dimensional
problem. Results for staggered magnetization, N\'eel temperature and spin wave
excitations are in agreement with experiments on $\rm KCuF_3$. The existence of
a narrow longitudinal mode is predicted. The results are in agreement with
general scaling arguments, contrary to spin wave theory.",9604144v2
1997-01-30,Quasi One-Dimensional Spin Fluctuations in YBa(2)Cu(3)O(6+x),"We study the spin fluctuation of the oxygen deficient planes of
YBa(2)Cu(3)O(6+x). The Cu-O chains that constitute these planes are described
by a model that includes antiferromagnetic interactions between spins and
Kondo-like scattering of oxygen holes. The spectrum of magnetic excitations
shows the presence of incommensurate dynamic fluctuations along the direction
of the chains. The presence of itinerant holes is responsible for the existence
of important differences between the spin dynamics of this system and that of a
quasi-one-dimensional localized antiferromagnet. We comment on the possibility
of experimental observation of these fluctuations.",9701216v1
1997-07-08,Dynamical Effective Medium Theory for Quantum Spins and Multipoles,"A dynamical effective medium theory is presented for quantum spins and higher
multipoles such as quadrupole moments. The theory is a generalization of the
spherical model approximation for the Ising model, and is accurate up to
O(1/z_n) where z_n is the number of interacting neighbors. The polarization
function is optimized under the condition that it be diagonal in site indices.
With use of auxiliary fields and path integrals, the theory is flexibly applied
to quantum spins and higher multipoles with many interacting neighbors. A
Kondo-type screening of each spin is proposed for systems with extreme quantum
fluctuations but without conduction electrons.",9707075v1
1998-04-22,The Spin Glass Transition : Exponents and Dynamics,"Numerical simulations on Ising Spin Glasses show that spin glass transitions
do not obey the usual universality rules which hold at canonical second order
transitions. On the other hand the dynamics at the approach to the transition
appear to take up a universal form for all spin glasses. The implications for
the fundamental physics of transitions in complex systems are addressed.",9804244v1
1998-11-26,Competition between glassiness and order in a multi-spin glass,"A mean-field multi-spin interaction spin glass model is analyzed in the
presence of a ferromagnetic coupling. The static and dynamical phase diagrams
contain four phases (paramagnet, spin glass, ordinary ferromagnet and glassy
ferromagnet) and exhibit reentrant behavior. The glassy ferromagnet phase has
anomalous dynamical properties. The results are consistent with a
nonequilibrium thermodynamics that has been proposed for glasses.",9811373v2
1999-05-13,Dynamics of the Measurement of Nuclear Spins in a Solid-State Quantum Computer,"We study numerically the process of nuclear spin measurement in a solid-state
quantum computer of the type proposed by Kane by modeling the quantum dynamics
of two coupled nuclear spins on $^{31}$P donors implanted in silicon. We
estimate the minimum measurement time necessary for the reliable transfer of
quantum information from the nuclear spin subsystem to the electronic
subsystem. We also calculate the probability of error for typical values of the
external noise.",9905200v1
1999-07-12,"Dynamics of the Compact, Ferromagnetic ν=1 Edge","We consider the edge dynamics of a compact, fully spin polarized state at
filling factor $\nu=1$. We show that there are two sets of collective
excitations localized near the edge: the much studied, gapless, edge
magnetoplasmon but also an additional edge spin wave that splits off below the
bulk spin wave continuum. We show that both of these excitations can soften at
finite wave-vectors as the potential confining the system is softened, thereby
leading to edge reconstruction by spin texture or charge density wave
formation. We note that a commonly employed model of the edge confining
potential is non-generic in that it systematically underestimates the texturing
instability.",9907175v1
1999-07-27,Kinetic induced phase transition,"An Ising model with local Glauber dynamics is studied under the influence of
additional kinetic restrictions for the spin-flip rates depending on the
orientation of neighboring spins. Even when the static interaction between the
spins is completely eliminated and only an external field is taken into account
the system offers a phase transition at a finite value of the applied field.
The transition is realized due to a competition between the activation
processes driven by the field and the dynamical rules for the spin-flips. The
result is based on a master equation approach in a quantum formulation.",9907414v1
1999-12-20,Improved Spin Dynamics Simulations of Magnetic Excitations,"Using Suzuki-Trotter decompositions of exponential operators we describe new
algorithms for the numerical integration of the equations of motion for
classical spin systems. These techniques conserve spin length exactly and, in
special cases, also conserve the energy and maintain time reversibility. We
investigate integration schemes of up to eighth order and show that these new
algorithms can be used with much larger time steps than a well established
predictor-corrector method. These methods may lead to a substantial speedup of
spin dynamics simulations, however, the choice of which order method to use is
not always straightforward.",9912373v1
2000-02-09,Spin-fermion model near the quantum critical point: one-loop renormalization group results,"We consider spin and electronic properties of itinerant electron systems,
described by the spin-fermion model, near the antiferromagnetic critical point.
We expand in the inverse number of hot spots in the Brillouin zone, N and
present the results beyond previously studied $N = \infty $ limit. We found two
new effects: (i) Fermi surface becomes nested at hot spots, and (ii) vertex
corrections give rise to anomalous spin dynamics and change the dynamical
critical exponent from z=2 to z>2.
  To first order in 1/N we found $z = 2N/(N-2)$ which for a physical N=8 yields
$z\approx 2.67$.",0002122v1
2000-09-21,Dynamics of spin correlations in the spin-1/2 isotropic XY chain in a transverse field,"Dynamic xx spin pair correlation functions for the isotropic spin-1/2 XY
chain are calculated numerically for long open chains in the presence of a
transverse magnetic field at finite temperature. As an application we discuss
the temperature dependence of the spin-spin relaxation time in PrCl_3.",0009334v1
2000-12-21,On random graphs and the statistical mechanics of granular matter,"The dynamics of spins on a random graph with ferromagnetic three-spin
interactions is used to model the compaction of granular matter under a series
of taps. Taps are modelled as the random flipping of a small fraction of the
spins followed by a quench at zero temperature. We find that the density
approached during a logarithmically slow compaction
  - the random-close-packing density - corresponds to a dynamical phase
transition. We discuss the the role of cascades of successive spin-flips in
this model and link them with density-noise power fluctuations observed in
recent experiments.",0012416v2
2001-07-10,Spin Dynamics near the Superconductor-to-Insulator Transition in Impurity-Doped YBa2Cu4O8,"We studied low-frequency spin dynamics near the impurity-induced
superconductor-to-insulator transition for underdoped high-Tc superconductor
YBa2(Cu1-xMx)4O8 (M=Ni, Zn) using the Cu nuclear quadrupole resonance (NQR)
spin-echo technique. We observed remarkable suppression of the normal-state
pseudo spin-gap and a loss of Cu NQR spectrum intensity at low temperatures
around the critical impurity concentration.",0107187v1
2002-03-08,High-Energy Spin Dynamics in La$_{1.69}$Sr$_{0.31}$NiO$_4$,"We have mapped out the spin dynamics in a stripe-ordered nickelate,
La$_{2-x}$Sr$_{x}$NiO$_{4}$ with $x \simeq 0.31$, using inelastic neutron
scattering. We observe spin-wave excitations up to 80 meV emerging from the
incommensurate magnetic peaks with an almost isotropic spin-velocity: $\hbar
c_s\sim 0.32$ eV \AA, very similar to the velocity in the undoped, insulating
parent compound, La$_{2}$NiO$_{4}$. We also discuss the similarities and
differences of the inferred spin-excitation spectrum with those reported in
superconducting high-$T_c$ cuprates.",0203187v1
2002-12-16,Entropy Driven Dimerization in a One-Dimensional Spin-Orbital Model,"We study a new version of the one-dimensional spin-orbital model with spins
S=1 relevant to cubic vanadates. At small Hund's coupling J_H we discover
dimerization in a pure electronic system solely due to a dynamical spin-orbital
coupling. Above a critical value J_H, a uniform ferromagnetic state is
stabilized at zero temperature. More surprisingly, we observe a temperature
driven dimerization of the ferrochain, which occurs due to a large entropy
released by dimer states. This dynamical dimerization seems to be the mechanism
driving the peculiar intermediate phase of YVO_3.",0212368v1
2003-06-30,Freezing and large time scales induced by geometrical frustration,"We investigate the properties of an effective Hamiltonian with competing
interactions involving spin and chirality variables, relevant for the
description of the {\it trimerized} version of the spin-1/2 {\it kagome}
antiferromagnet. Using classical Monte Carlo simulations, we show that
remarkable behaviors develop at very low temperatures. Through an {\it order by
disorder} mechanism, the low-energy states are characterized by a dynamical
freezing of the chiralities, which decouples the lattice into ``dimers'' and
``triangles'' of antiferromagnetically coupled spins. Under the presence of an
external magnetic field, the particular topology of the chiralities induces a
very slow spin dynamics, reminiscent of what happens in ordinary spin glasses.",0306744v1
2003-11-27,Dissipative dynamics of spins in quantum dots,"We present a theory for the dissipation of electronic spins trapped in
quantum dots due to their coupling to the host lattice acoustic phonon modes.
Based on the theory of dissipative two level systems for the spin dynamics, we
derive a relation between the spin dissipative bath, the electron confinement,
and the electron-phonon interaction. We find that there is an energy scale,
typically smaller than the electronic lateral confinement energy, which sets
the boundary between different dissipative regimes .",0311632v2
2004-02-25,Spin Dynamics of a Canted Antiferromagnet in a Magnetic Field,"The spin dynamics of a canted antiferromagnet with a quadratic spin-wave
dispersion near $\vq =0$ is shown to possess a unique signature. When the
anisotropy gap is negligible, the spin-wave stiffness $\dsw (\vq, B) =
(\omega_{\vq}-B)/q^2$ depends on whether the limit of zero field or zero
wavevector is taken first. Consequently, $\dsw $ is a strong function of
magnetic field at a fixed wavevector. Even in the presence of a sizeable
anisotropy gap, the field dependence of both $\dsw $ and the gap energy
distinguishes a canted antiferromagnet from a phase-separated mixture
containing both ferromagnetic and antiferromagnetic regions.",0402633v2
2004-11-02,Spin dynamics in the stripe phase of the cuprates,"Within a model that supports stripe spin and charge order coexisting with a
d$_{x^2-y^2}$-wave superconducting phase, we study the self-consistently
obtained electronic structure and the associated transverse dynamical spin
susceptibility. In the coexisting phase of superconducting and static stripe
order, the resulting particle-hole continuum can strongly damp parts of the
low-energy spin wave branches. This provides insight into recent inelastic
neutron scattering data revealing the dispersion of the low-energy collective
magnetic modes of lanthanum based cuprate superconductors.",0411065v1
2005-02-22,Dynamics of weakly coupled random antiferromagnetic quantum spin chains,"We study the low-energy collective excitations and dynamical response
functions of weakly coupled random antiferromagnetic spin-1/2 chains. The
interchain coupling leads to Neel order at low temperatures. We use the
real-space renormalization group technique to tackle the intrachain couplings
and treat the interchain couplings within the Random Phase Approximation (RPA).
We show that the system supports collective spin wave excitations, and
calculate the spin wave velocity and spectra weight within RPA. Comparisons
will be made with inelastic neutron scattering experiments
quasi-one-dimensional disordered spin systems such as doped CuGeO$_3$",0502530v2
2006-03-27,Visualizing high-temperature spin dynamics in La1-xCaxMnO3 from a mapping of EPR linewidth and g factor,"This paper presents an analysis of electron paramagnetic resonance
parameters, i.e., g factor, linewidth, and intensity on powder samples of
La1-xCaxMnO3 at the commensurate carrier concentrations of x = N/8 (N = 1, 2,
3, 4, 5, 6, and 7). We demonstrate that the mapping of EPR parameters offers a
powerful tool to investigate high-temperature spin dynamics in the phase
diagram of colossal magnetoresistance (CMR) manganites. Our results convince
that the spin-spin relaxation mechanism should dominate the high-temperature
paramagnetic regime in CMR manganites.",0603705v2
2006-08-09,Origin of the second coherent peak in the dynamical structure factor of an asymmetric spin-ladder,"Appearance of the second coherent peak in the dynamical structure factor of
an asymmetric spin ladder is suggested. The general arguments are confirmed by
the first order (with respect to the asymmetry) calculation for a spin ladder
with singlet-rung ground state. Basing on this result a new interpretation is
proposed for the inelastic neutron scattering data in the spin gap compound
CuHpCl.",0608231v2
2006-08-31,A Theory for Spin Glass Phenomena in Interacting Nanoparticle Systems,"Dilute magnetic nanoparticle systems exhibit slow dynamics [1] due to a broad
distribution of relaxation times that can be traced to a correspondingly broad
distribution of particle sizes [1]. However, at higher concentrations
interparticle interactions lead to a slow dynamics that is qualitatively
indistinguishable from that dislayed by atomic spin glasses. A theory is
derived below that accounts quantitatively for the spin-glass behaviour. The
theory predicts that if the interactions become too strong the spin glass
behaviour disappears. This conclusion is in agreement with preliminary
experimental results.",0608696v1
2006-09-19,Dipolar effect in coherent spin mixing of two atoms in a single optical lattice site,"We show that atomic dipolar effects are detectable in the system that
recently demonstrated two-atom coherent spin dynamics within individual lattice
sites of a Mott state. Based on a two-state approximation for the two-atom
internal states and relying on a variational approach, we have estimated the
spin dipolar effect. Despite the absolute weakness of the dipole-dipole
interaction, it is shown that it leads to experimentally observable effects in
the spin mixing dynamics.",0609474v1
2006-09-20,Non-Markovian spin relaxation in two-dimensional electron gas,"We analyze by Monte-Carlo simulations and analytically spin dynamics of
two-dimensional electron gas (2DEG) interacting with short-range scatterers in
nonquantizing magnetic fields. It is shown that the spin dynamics is
non-Markovian with the exponential spin relaxation followed by the oscillating
tail due to the electrons residing on the closed trajectories. The tail relaxes
on a long time scale due to an additional smooth random potential and inelastic
processes. The developed analytical theory and Monte-Carlo simulations are in
the quantitative agreement with each other.",0609528v1
2007-03-17,Dynamic spin susceptibility of paramagnetic spinel LiV2O4,"In an attempt to explain inelastic neutron scattering data for LiV2O4 the
dynamical spin susceptibility \chi(Q,w) at zero temperature is calculated.
Starting point is a weak coupling approach based on the LDA bandstructure for
that material. It is supplemented by a RPA treatment of local on-site
interactions and contains an adjustable parameter. Due to the geometrically
frustrated lattice structure the magnetic response is strongly enhanced in the
vicinity of a nearly spherical surface in Q-space. We compare these results
with recent low-temperature neutron scattering data. The measured spin
relaxation rate \Gamma is used to estimate the spin fluctuation contribution to
the specific heat.",0703456v1
2002-03-06,SPINning Parallel Systems Software,"We describe our experiences in using SPIN to verify parts of the Multi
Purpose Daemon (MPD) parallel process management system. MPD is a distributed
collection of processes connected by Unix network sockets. MPD is dynamic:
processes and connections among them are created and destroyed as MPD is
initialized, runs user processes, recovers from faults, and terminates. This
dynamic nature is easily expressible in the SPIN/PROMELA framework but poses
performance and scalability challenges. We present here the results of
expressing some of the parallel algorithms of MPD and executing both simulation
and verification runs with SPIN.",0203009v1
1999-03-02,Spin Physics at e^+e^- Colliders,"A large number of measurements with polarized beams and/or spin analysis of
final state particles has been performed at the e^+e^- colliders LEP and SLC,
providing important information on the dynamics of high energy interactions. In
this paper three subjects, for which the role of spin studies was particularly
relevant, will be covered: the measurements of the electroweak couplings, the
study of fragmentation dynamics and the search for physics beyond the Standard
Model.",9903001v1
1997-12-17,Vortex Dynamics in Classical Non--Abelian Spin Models,"We discuss the abelian vortex dynamics in the abelian projection approach to
non-abelian spin models. We show numerically that in the three-dimensional
SU(2) spin model in the Maximal Abelian projection the abelian off-diagonal
vortices are not responsible for the phase transition contrary to the diagonal
vortices. A generalization of the abelian projection approach to SU(N) spin
models is briefly discussed.",9712018v2
2007-03-19,Neutrinos from spin dynamics,"We conjecture that neutrino physics might correspond to the spontaneous
magnetisation phase of an Ising-like spin model interaction coupled to neutrino
chirality which operates at scales close to the Planck mass. We argue that this
scenario leads to a simple extension of the Standard Model with no additional
parameters that dynamically generates parity violation and spontaneous symmetry
breaking for the gauge bosons which couple to the neutrino. The neutrino mass
in the model ~ (the electroweak scale)^2 / 2M where M is the scale of the
``spin-spin'' interaction. For the ground state of the model the free energy
density corresponding to the cosmological constant is ~ the neutrino mass,
consistent with observation.",0703206v1
2004-01-27,An efficient geometric integrator for thermostatted anti-/ferromagnetic models,"(Anti)-/ferromagnetic Heisenberg spin models arise from discretization of
Landau-Lifshitz models in micromagnetic modelling. In many applications it is
essential to study the behavior of the system at a fixed temperature. A
formulation for thermostatted spin dynamics was given by Bulgac and Kusnetsov
which incorporates a complicated nonlinear dissipation/driving term while
preserving spin length. It is essential to properly model this term in
simulation, and simplified schemes give poor numerical performance, e.g.
requiring an excessively small timestep for stable integration. In this paper
we present an efficient, structure-preserving method for thermostatted spin
dynamics.",0401369v1
2006-12-06,Dynamics of spin 1/2 quantum plasmas,"The fully nonlinear governing equations for spin 1/2 quantum plasmas are
presented. Starting from the Pauli equation, the relevant plasma equations are
derived, and it is shown that nontrivial quantum spin couplings arise, enabling
studies of the combined collective and spin dynamics. The linear response of
the quantum plasma in an electron--ion system is obtained and analyzed.
Applications of the theory to solid state and astrophysical systems as well as
dusty plasmas are pointed out.",0612062v1
2002-02-06,Cluster of Dipolar Coupled Spins as a Quantum Memory Storage,"Spin dynamics of a cluster of coupled spins 1/2 can be manipulated to store
and process a large amount of information. A new type of dynamic response makes
it possible to excite coherent long-living signals, which can be used for
exchanging information with a mesoscopic quantum system. An experimental
demonstration is given for a system of 19 proton spins of a liquid crystal
molecule.",0202035v1
2007-04-20,Semiclassical theory of ballistic transport through chaotic cavities with spin-orbit interaction,"We investigate the influence of spin-orbit interaction on ballistic transport
through chaotic cavities by using semiclassical methods. Our approach is based
on the Landauer formalism and the Fisher-Lee relations, appropriately
generalized to spin-orbit interaction, and a semiclassical representation of
Green functions. We calculate conductance coefficients by exploiting ergodicity
and mixing of suitably combined classical spin-orbit dynamics, and making use
of the Sieber-Richter method and its most recent extensions. That way we obtain
weak anti-localization and confirm previous results obtained in the symplectic
ensemble of Random Matrix Theory.",0704.2702v1
2007-07-13,Multiphoton antiresonance in large-spin systems,"We study nonlinear response of a spin $S>1/2$ with easy-axis anisotropy. The
response displays sharp dips or peaks when the modulation frequency is
adiabatically swept through multiphoton resonance. The effect is a consequence
of a special symmetry of the spin dynamics in a magnetic field for the
anisotropy energy $\propto S_z^2$. The occurrence of the dips or peaks is
determined by the spin state. Their shape strongly depends on the modulation
amplitude. Higher-order anisotropy breaks the symmetry, leading to sharp steps
in the response as function of frequency. The results bear on the dynamics of
molecular magnets in a static magnetic field.",0707.2107v1
2008-01-14,Dynamic nuclear polarization and spin-diffusion in non-conducting solids,"There has been much renewed interest in dynamic nuclear polarization (DNP),
particularly in the context of solid state biomolecular NMR and more recently
dissolution DNP techniques for liquids. This paper reviews the role of spin
diffusion in polarizing nuclear spins and discusses the role of the spin
diffusion barrier, before going on to discuss some recent results.",0801.2170v1
2008-02-04,Detection of spin reversal and nutations through current measurements,"The dynamics of a single spin embedded in a the tunnel junction between
ferromagnetic contacts is strongly affected by the exchange coupling to the
tunneling electrons. Moment reversal of the local spin induced by the bias
voltage across the junction is shown to have a measurable effect on the
tunneling current. Furthermore, the frequency of a harmonic bias voltage is
picked up by the local spin dynamics and transferred back to the current
generating a double frequency component.",0802.0473v2
2008-08-02,Electric-field control of a hydrogenic donor's spin in a semiconductor,"An AC electric field applied to a donor-bound electron in a semiconductor
modulates the orbital character of its wave function, which affects the
electron's spin dynamics via the spin-orbit interaction. Numerical calculations
of the spin dynamics of a hydrogenic donor (Si) embedded in GaAs, using a
real-space multi-band k.p formalism, show the high symmetry of the hydrogenic
donor state results in strongly nonlinear dependences of the electronic g
tensor on applied fields. A nontrivial consequence is that the most rapid Rabi
oscillations occur for electric fields modulated at a subharmonic of the Larmor
frequency.",0808.0208v1
2008-08-09,Observation of Spin Glass Dynamics in Dilute LiHo$_x$Y$_{1-x}$F$_4$,"AC susceptibility measurements are presented on the dilute, dipolar coupled,
Ising magnet LiHo$_x$Y$_{1-x}$F$_4$ for a concentration $x = 0.045$. The
frequency and temperature dependences of the susceptibility show characteristic
glassy relaxation. The absorption spectrum is found to broaden with decreasing
temperature suggesting that the material is behaving as a spin glass and not as
an exotic spin liquid as was previously observed. A dynamical scaling analysis
suggests a spin glass transition temperature of 42.6 mK $\pm 2$ mK with an
exponent $z\nu = 7.8 \pm 0.23$.",0808.1370v1
2009-02-03,Dependence of critical current of spin transfer torque-driven magnetization dynamics on free layer thickness,"The dependence of the critical current of spin transfer torque-driven
magnetization dynamics on the free-layer thickness was studied by taking into
account both the finite penetration depth of the transverse spin current and
spin pumping. We showed that the critical current remains finite in the
zero-thickness limit of the free layer for both parallel and anti-parallel
alignments. We also showed that the remaining value of the critical current of
parallel to anti-parallel switching is larger than that of anti-parallel to
parallel switching.",0902.0420v1
2009-02-24,Generalized Spin Glass Relaxation,"Spin relaxation close to the glass temperature of CuMn and AuFe spin glasses
is shown, by neutron spin echo, to follow a generalised exponential function
which explicitly introduces hierarchically constrained dynamics and macroscopic
interactions. The interaction parameter is directly related to the normalised
Tsallis non-extensive entropy parameter, q, and exhibits universal scaling with
reduced temperature. At the glass temperature q=5/3 corresponding, within
Tsallis' q-statistics, to a mathematically defined critical value for the onset
of strong disorder and non-linear dynamics.",0902.4183v1
2009-03-30,Numerical and Analytical Approach to the Quantum Dynamics of Two Coupled Spins in Bosonic Baths,"The quantum dynamics of a spin chain interacting with multiple bosonic baths
is described in a mixed Wigner-Heisenberg representation. The formalism is
illustrated by simulating the time evolution of the reduced density matrix of
two coupled spins, where each spin is also coupled to its own bath of harmonic
oscillators. In order to prove the validity of the approach, an analytical
solution in the Born-Markov approximation is found. The agreement between the
two methods is shown.",0903.5181v1
2009-04-01,Decay of Rabi oscillations by dipolar-coupled dynamical spin environments,"We investigate the Rabi oscillations decay of a spin decohered by a spin bath
whose internal dynamics is caused by dipolar coupling between the bath spins.
The decay form and rate as a function of the intra-bath coupling is studied
analytically, and confirmed numerically. The decay in general has neither
exponential/Gaussian or power-law form, and changes non-monotonically with the
intra-bath coupling, decelerating for both slow and fast baths. The form and
rate of Rabi oscillations decay can be used to experimentally determine the
intra-bath coupling strength for a broad class of solid-state systems.",0904.0263v1
2010-02-13,Spin and Charge Dynamics Ruled by Antiferromagnetic Order in Iron Pnictides,"We examine the spin and charge excitations in antiferromagnetic iron
pnictides by mean-field calculations with a random phase approximation in a
five-band itinerant model. The calculated excitation spectra reproduce well
spin-wave dispersions observed in inelastic neutron scattering, with a
realistic magnetic moment for CaFe$_2$As$_2$. A particle-hole gap is found to
be crucial to obtain consistent results; we predict the spin wave in LaFeAsO
disappears at a lower energy than in CaFe$_2$As$_2$. We analyze that the charge
dynamics to make predictions for resonant inelastic x-ray scattering spectra.",1002.2701v2
2010-10-07,Dynamics of test bodies with spin in de Sitter spacetime,"We study the motion of spinning test bodies in the de Sitter spacetime of
constant positive curvature. With the help of the 10 Killing vectors, we derive
the 4-momentum and the tensor of spin explicitly in terms of the spacetime
coordinates. However, in order to find the actual trajectories, one needs to
impose the so-called supplementary condition. We discuss the dynamics of
spinning test bodies for the cases of the Frenkel and Tulczyjew conditions.",1010.1451v2
2010-10-07,Optical orientation of Mn^2+ ions in GaAs,"We report on optical orientation of Mn^2+ in bulk GaAs under application of
weak longitudinal magnetic field (B <= 100 mT). The manganese spin polarization
of 25% is directly evaluated using spin flip Raman scattering spectroscopy. The
dynamical polarization of Mn^2+ occurs due to s-d exchange interaction with
optically oriented conduction band electrons. Time-resolved photoluminescence
uncovers nontrivial electron spin dynamics where the oriented Mn^2+ ions tend
to stabilize the electron spin.",1010.1463v1
2011-04-21,Spin Damping Monopole,"We present theoretical evidence that a magnetic monopole emerges in dynamic
magnetic systems in the presence of the spin-orbit interaction. The monopole
field is expressed in terms of spin damping associated with magnetization
dynamics. We demonstrate that the observation of this spin damping monopole is
accomplished electrically using Ampere's law for monopole current. Our
discovery suggests the integration of monopoles into electronics, namely,
monopolotronics.",1104.4215v2
2011-06-13,Quantum Dynamics of a Nanomagnet driven by Spin-Polarized Current,"A quantum theory of magnetization dynamics of a nanomagnet as a sequence of
scatterings of each electron spin with the macrospin state of the magnetization
results in each encounter a probability distribution of the magnetization
recoil state associated with each outgoing state of the electron. The quantum
trajectory of the magnetization contains the average motion tending in the
large spin limit to the semi-classical results of spin transfer torque and the
fluctuations giving rise to a quantum magnetization noise and an additional
noise traceable to the current noise.",1106.2359v1
2011-08-25,Real-Time Dynamics of a Spin Chain with Dzyaloshinskii-Moriya Interactions: Spiral Formation and Quantum Spin Oscillations,"We studied the non-equilibrium short-time dynamics of a spin-1/2 chain with
Dzyaloshinskii-Moriya interactions after a sudden quench by a transverse field.
We found that inhomogeneous spin-spirals with opposite chiralities propagate
from the edges towards the center of the chain. This propagation is accompanied
by quantum spin oscillations which decay asymptotically with time. A
theoretical description of this phenomenon is given to a good accuracy with the
help of numerical calculations with the adaptive time-dependent density matrix
renormalization group algorithm.",1108.5156v1
2012-03-05,String Amplitudes and Frame-like Formalism for Higher Spins,"We analyze open string vertex operators describing connection gauge fields
for spin 3 in Vasiliev's frame-like formalism and perform their extended BRST
analysis. Gauge symmetry transformations, generalized zero torsion constraints
relating extra fields to the dynamical frame-like field and relation between
dynamical frame-like field and fully symmetric Fronsdal's field for spin 3 are
all realized in terms of BRST constraints on these vertex operators in string
theory. Using the construction, we analyze the 3-point correlator for spin 3
field and calculate Chern-Simons type cubic interactions described by
3-derivative Berends-Burgers-van Dam (BBD) type vertex in the frame-like
formalism.",1203.0909v1
2012-06-11,Preparation of two-particle total hyperfine spin singlet states via spin-changing dynamics,"We present our proposals for generating total hyperfine spin zero state for
two f=1 or two f=2 particles, starting from initial unentangled states. We show
that our goal can be achieved by exploiting spin changing dynamics and
quadratic Zeeman shifts with realistic choices of external magnetic fields and
evolution time intervals.",1206.2196v1
2012-12-18,Spin system trajectory analysis under optimal control pulses,"Several methods are proposed for the analysis, visualization and
interpretation of high-dimensional spin system trajectories produced by quantum
mechanical simulations. It is noted that expectation values of specific
observables in large spin systems often feature fast, complicated and
hard-to-interpret time dynamics and suggested that populations of carefully
selected subspaces of states are much easier to analyze and interpret. As an
illustration of the utility of the proposed methods, it is demonstrated that
the apparent ""noisy"" appearance of many optimal control pulses in NMR and EPR
spectroscopy is an illusion - the underlying spin dynamics is shown to be
smooth, orderly and very tightly controlled.",1212.4454v1
2013-02-20,Doping Induced Spin State Transition in LaCoO3: Dynamical Mean-Field Study,"Hole and electron doped LaCoO3 is studied using dynamical mean-field theory.
The one-particle spectra are analyzed and compared to the available
experimental data, in particular the x-ray absorption spectra. Analyzing the
temporal spin-spin correlation functions we find the atomic intermediate spin
state is not important for the observed Curie-Weiss susceptibility. Contrary to
the commonly held view about the roles played by the t2g and eg electrons we
find narrow quasiparticle bands of t2g character crossing the Fermi level
accompanied by strongly damped eg excitations.",1302.4925v2
2013-06-12,A variational surface hopping algorithm for the sub-Ohmic spin-boson model,"The Davydov D1 ansatz, which assigns an individual bosonic trajectory to each
spin state, is an efficient, yet extremely accurate trial state for
time-dependent variation of the sub-Ohmic spin-boson model [J. Chem. Phys. 138,
084111 (2013)]. A surface hopping algorithm is developed employing the Davydov
D1 ansatz to study the spin dynamics with a sub-Ohmic bosonic bath. The
algorithm takes into account both coherent and incoherent dynamics of the
population evolution in a unified manner, and compared with semiclassical
surface hopping algorithms, hopping rates calculated in this work follow more
closely the Marcus formula.",1306.2865v2
2013-12-27,Spin echo dynamics under an applied drift field in graphene nanoribbon superlattices,"We investigate the evolution of spin dynamics in graphene nanoribbon
superlattices (GNSLs) with armchair and zigzag edges in the presence of a drift
field. We determine the exact evolution operator and show that it exhibits spin
echo phenomena due to rapid oscillations of the quantum states along the
ribbon. The evolution of the spin polarization is accompanied by strong beating
patterns. We also provide detailed analysis of the band structure of GNSLs with
armchair and zigzag edges.",1312.7317v1
2014-09-04,Quantum theory of nuclear spin dynamics in diamond nitrogen-vacancy center,"We develop a quantum theory for a variety of nuclear spin dynamics such as
dephasing, relaxation, squeezing, and narrowing due to the hyperfine
interaction with a generic, dissipative electronic system. The first-order
result of our theory reproduces and generalizes the nonlinear Hamiltonian for
nuclear spin squeezing [M. S. Rudner, Phys. Rev. Lett. 107, 206806 (2011)]. The
second-order result of our theory provides a good explanation to the
experimentally observed $^{13}$C nuclear spin bath narrowing in diamond
nitrogen-vacancy center [E. Togan, Nature 478, 497 (2011)",1409.1482v1
2014-11-20,Pressure-induced spin transition of Fe$^{2+}$ ion in ferropericlase from Dynamical Mean-Field Theory,"The results of magnetic and spectral properties calculation for paramagnetic
phase of ferropericlase (Fe$_{1/4}$Mg$_{3/4}$)O at ambient and high pressures
are reported. Calculations were performed by combined Local Density
Approximation + Dynamical Mean-Field Theory method (LDA+DMFT). At ambient
pressure calculation gave (Fe$_{1/4}$Mg$_{3/4}$)O as insulator with Fe
3$d$-shell in high-spin state. Experimentally observed high-spin to low-spin
transition of Fe$^{2+}$ ion at high pressure is successfully reproduced in
calculations. Our results indicate the absence of metal-insulator transition up
to the pressure 107~GPa.",1411.5520v1
2015-03-06,Localizing spin dynamics in a spin-1 Bose-Einstein condensate via magnetic pulses,"Spin exchange interaction between atoms in a spin-1 Bose-Einstein condensate
causes atomic spin evolving periodically under the single spatial mode
approximation in the mean field theory. By applying fast magnetic pulses
according to a two-step or a four-step control protocol, we find analytically
that the spin dynamics is significantly suppressed for an arbitrary initial
state. Numerical calculations under single mode approximation are carried out
to confirm the validity and robustness of these protocols. This localization
method can be readily utilized to improve the sensitivity of a magnetometer
based on spin-1 Bose-Einstein condensates.",1503.01828v1
2015-06-11,Robust Dynamical Decoupling Sequences for Individual Nuclear Spin Addressing,"We propose the use of non-equally spaced decoupling pulses for
high-resolution selective addressing of nuclear spins by a quantum sensor. The
analytical model of the basic operating principle is supplemented by detailed
numerical studies that demonstrate the high degree of selectivity and the
robustness against static and dynamic control field errors of this scheme. We
exemplify our protocol with an NV center-based sensor to demonstrate that it
enables the identification of individual nuclear spins that form part of a
large spin ensemble.",1506.03766v2
2015-08-24,Spin Dynamics Simulation of the Magneto-Electric Effect in a Composite Multiferroic Chain,"A composite multiferroic chain with an interfacial linear magneto-electric
coupling is used to study the magnetic and electric responses to an external
magnetic or electric field. The simulation uses continuous spin dynamics
through the Landau-Lifshitz-Gilbert equations of the magnetic spin and the
electric pseudo-spin. The results demonstrate an accurate description of the
distribution of the magnetisation and polarisation are induced by applied
electric and magnetic field, respectively.",1508.05693v1
2016-02-23,Particle-Time Duality in the Kicked Ising Chain I: The Dual Operator,"We demonstrate that the dynamics of kicked spin chains possess a remarkable
duality property. The trace of the unitary evolution operator for $N$ spins at
time $T$ is related to one of a non-unitary evolution operator for $T$ spins at
time $N$. We investigate the spectrum of this dual operator with a focus on the
different parameter regimes (chaotic, regular) of the spin chain. We present
applications of this duality relation to spectral statistics in an accompanying
paper.",1602.07130v1
2016-02-24,Particle-Time Duality in the Kicked Ising Chain II: Applications to the Spectrum,"Previously, we demonstrated that the dynamics of kicked spin chains possess a
remarkable duality property. The trace of the unitary evolution operator for
$N$ spins at time $T$ is related to one of a non-unitary evolution operator for
$T$ spins at time $N$. Using this duality relation we obtain the oscillating
part of the density of states for a large number of spins. Furthermore, the
duality relation explains the anomalous short-time behavior of the spectral
form factor previously observed in the literature.",1602.07479v1
2016-06-30,Skyrmion dynamics in a chiral magnet driven by periodically varying spin currents,"In this work, we investigated the spin dynamics in a slab of chiral magnets
induced by an alternating (ac) spin current. Periodic trajectories of the
skyrmion in real space are discovered under the ac current as a result of the
Magnus and viscous forces, which originate from the Gilbert damping, the spin
transfer torque, and the $ \beta $-nonadiabatic torque effects. The results are
obtained by numerically solving the Landau-Lifshitz-Gilbert equation and can be
explained by the Thiele equation characterizing the skyrmion core motion.",1606.09326v2
2017-03-10,A microscopic formulation of dynamical spin injection in ferromagnetic-nonmagnetic heterostructures,"We develop a microscopic formulation of dynamical spin injection in
heterostructure comprising nonmagnetic metals in contact with ferromagnets. The
spin pumping current is expressed in terms of Green's function of the
nonmagnetic metal attached to the ferromagnet where a precessing magnetization
is induced. The formulation allows for the inclusion of spin-orbit coupling and
disorder. The Green's functions involved in the expression for the current are
expressed in real-space lattice coordinates and can thus be efficiently
computed using recursive methods.",1703.03775v2
2018-02-23,Exact results in 3d $\mathcal{N}=2$ $Spin(7)$ gauge theories with vector and spinor matters,"We study three-dimensional $\mathcal{N}=2$ $Spin(7)$ gauge theories with
$N_S$ spinorial matters and with $N_f$ vectorial matters. The quantum Coulomb
branch on the moduli space of vacua is one- or two-dimensional depending on the
matter contents. For particular values of $(N_f,N_S)$, we find s-confinement
phases and derive exact superpotentials. The 3d dynamics of $Spin(7)$ is
connected to the 4d dynamics via KK-monopoles. Along the Higgs branch of the
$Spin(7)$ theories, we obtain 3d $\mathcal{N}=2$ $G_2$ or $SU(4)$ theories and
some of them lead to new s-confinement phases. As a check of our analysis we
compute superconformal indices for these theories.",1802.08716v1
2018-11-06,Nonlinear Dynamics Semi-classical Model of Quantum Spin,"A nonlinear dynamics semi-classical model is used to show that standard
quantum spin analysis can be obtained. The model includes a classically driven
nonlinear differential equation with dissipation and a semi-classical
interpretation of the torque on a spin magnetic moment in the presence of a
realistic magnetic field, which will represent two equilibrium positions. The
highly complicated driven nonlinear dissipative semi-classical model is used to
introduce chaos, which is necessary to produce the correct statistical quantum
results. The resemblance between this semi-classical spin model and the
thoroughly studied classical driven-damped nonlinear pendulum are shown and
discussed.",1811.02645v1
2016-11-01,Spin-Mechanical Inertia in Antiferromagnet,"Angular momentum conservation has served as a guiding principle in the
interplay between spin dynamics and mechanical rotations. However, in an
antiferromagnet with vanishing magnetization, new fundamental rules are
required to properly describe spin-mechanical phenomena. Here we show that the
N\'eel order dynamics affects the mechanical motion of a rigid body by
modifying its inertia tensor in the presence of strong magnetocrystalline
anisotropy. This effect depends on temperature when magnon excitations are
considered. Such a spin-mechanical inertia can produce measurable consequences
at small scales.",1611.00100v3
2017-01-17,Vortex pairs in a spin-orbit coupled Bose-Einstein condensate,"Static and dynamic properties of vortices in a two-component Bose-Einstein
condensate with Rashba spin-orbit coupling are investigated. The mass current
around a vortex core in the plane-wave phase is found to be deformed by the
spin-orbit coupling, and this makes the dynamics of the vortex pairs quite
different from those in a scalar Bose-Einstein condensate. The velocity of a
vortex-antivortex pair is much smaller than that without spin-orbit coupling,
and there exist stationary states. Two vortices with the same circulation move
away from each other or unite to form a stationary state.",1701.04591v1
2018-05-02,The hydrodynamic limit for local mean-field dynamics with unbounded spins,"We consider the dynamics of a class of spin systems with unbounded spins
interacting with local mean field interactions. We proof convergence of the
empirical measure to the solution of a McKean-Vlasov equation in the
hydrodynamic limit and propagation of chaos. This extends earlier results of
G\""artner, Comets and others for bounded spins or strict mean field
interactions.",1805.00641v2
2008-07-15,Dynamics of dissipative coupled spins: decoherence and relaxation,"We study the reduced dynamics of interacting spins, each coupled to its own
bath of bosons. We derive the solution in analytic form in the white-noise
limit and analyze the rich behaviors in diverse limits ranging from weak
coupling and/or low temperature to strong coupling and/or high temperature. We
also view the one spin as being coupled to a spin-boson environment and
consider the regimes in which it is effectively nonlinear, and in which it can
be regarded as a resonant bosonic environment.",0807.2342v1
2011-11-17,Comment on 'Spin Ice: Magnetic Excitations without Monopole Signature Using $μ$SR' (arXiv:1110.0877),"Dunsiger and co-workers have criticised our paper on magnetic monopole
dynamics spin ice [S. T. Bramwell et al., Nature, 461 956 (2009)]. We consider
their criticisms and results but show that these do not warrant any revision of
our earlier conclusions. In contrast, we point out that their conclusion of a
`new' type of spin dynamics in spin ice is inconsistent with established facts.",1111.4168v1
2000-06-09,Dynamical dimer-dimer correlation functions from exact diagonalization,"A regularization method is presented to deduce dynamic correlation functions
from exact diagonalization calculations. It is applied to dimer-dimer
correlation functions in quantum spin chains relevant for the description of
spin-Peierls systems. Exact results for the XY model are presented. The
analysis draws into doubt that the dimer-dimer correlation functions show the
same scale invariance as spin-spin correlation functions. The results are
applied to describe the quasi-elastic scattering in CuGeO$_3$.",0006168v1
2017-08-10,A Quantum Kinetic Monte Carlo Method for Quantum Many-body Spin Dynamics,"We propose a general framework of quantum kinetic Monte Carlo algorithm,
based on a stochastic representation of a series expansion of the quantum
evolution. Two approaches have been developed in the context of quantum
many-body spin dynamics, using different decomposition of the Hamiltonian. The
effectiveness of the methods is tested for many-body spin systems up to 40
spins.",1709.00386v2
2020-05-19,Properties of a nematic spin vortex in an antiferromagnetic spin-1 Bose-Einstein condensate,"A spin-1 condensate with antiferromagnetic interactions supports nematic spin
vortices in the easy-plane polar phase. These vortices have a $2\pi$ winding of
the nematic director, with a core structure that depends on the quadratic
Zeeman energy. We characterize the properties of the nematic spin vortex in a
uniform quasi-two-dimensional system. We also obtain the vortex excitation
spectrum and use it to quantify its stability against dissociating into two
half-quantum vortices, finding a parameter regime where the nematic spin vortex
is dynamically stable. These results are supported by full dynamical
simulations.",2005.09203v1
2020-08-25,Dissipative Spin Dynamics in Relativistic Matter,"Using classical description of spin degrees of freedom, we extend recent
formulation of the perfect-fluid hydrodynamics for spin-polarized fluids to the
case including dissipation. Our work is based on the analysis of classical
kinetic equations for massive particles with spin-1/2, with the collision terms
treated in the relaxation time approximation. The kinetic-theory framework
determines the structure of viscous and diffusive terms and allows to
explicitly calculate a complete set of new kinetic coefficients that
characterize dissipative spin dynamics.",2008.10976v2
2021-12-10,Dynamic spin polarization in organic semiconductors with intermolecular exchange interaction,"It is shown that in organic semiconductors where organic magnetoresistance
(OMAR) is observed, the exchange interaction between electrons and holes
localized at different molecules leads to dynamic spin polarization in the
direction of the applied magnetic field. The polarization appears even at room
temperature due to the non-equilibrium conditions. The strong spin polarization
requires exchange energy to be comparable with Zeeman energy in the external
field and be larger or comparable with the energy of hyperfine interaction of
electron and nuclear spins. The exchange interaction also modifies the
lineshape of OMAR.",2112.05656v1
2022-07-30,Inertial spin waves in ferromagnets and antiferromagnets,"Inertial effects in spin dynamics are theoretically predicted to emerge at
ultrashort time scales, but their experimental signatures are often ambiguous.
Here, we calculate the spin-wave spectrum in ferromagnets and two-sublattice
antiferromagnets in the presence of inertial effects. It is shown how
precession and nutation spin waves hybridize with each other, leading to the
renormalization of the frequencies, the group velocities, the effective
gyromagnetic ratios and the effective damping parameters. Possible ways of
distinguishing between the signatures of inertial dynamics and similar effects
explainable within conventional models are discussed.",2208.00131v1
2022-09-28,Unidirectional magnetic coupling,"We show that interlayer Dzyaloshinskii-Moriya interaction in combination with
non-local Gilbert damping gives rise to unidirectional magnetic coupling. That
is, the coupling between two magnetic layers -- say the left and right layer --
is such that dynamics of the left layer leads to dynamics of the right layer,
but not vice versa. We discuss the implications of this result for the magnetic
susceptibility of a magnetic bilayer, electrically-actuated spin-current
transmission, and unidirectional spin-wave packet generation and propagation.
Our results may enable a route towards spin-current and spin-wave diodes and
further pave the way to design spintronic devices via reservoir engineering.",2209.14179v1
2022-10-19,Qubit-environment entanglement outside of pure decoherence: hyperfine interaction,"In spin-based architectures of quantum devices, the hyperfine interaction
between the electron spin qubit and the nuclear spin environment remains one of
the main sources of decoherence. This paper provides a short review of the
current advances in the theoretical description of the qubit decoherence
dynamics. Next, we study the qubit-environment entanglement using negativity as
its measure. For an initial maximally mixed state of the environment, we study
negativity dynamics as a function of environment size, changing the numbers of
environmental nuclei and the total spin of the nuclei. Furthermore, we study
the effect of the magnetic field on qubit-environment disentangling time
scales.",2210.10553v1
2023-01-10,Majorana Spin Current Generation by Dynamic Strain,"Majorana fermions that emerge on the surface of topological superconductors
are charge neutral but can have higher-rank electric multipoles by allowing for
account time-reversal and crystalline symmetries. Applying the general
classification of these multipoles, we show that the spin current of Majorana
fermions is driven by spatially nonuniform dynamic strains on the (001) surface
of superconducting antiperovskite Sr3SnO. We also find that the frequency
dependence of the Majorana spin current reflects the energy dispersion of
Majorana fermions. Our results suggest that the spin current can be a probe for
Majorana fermions.",2301.03937v2
2023-10-27,Resilient Intraparticle Entanglement and its Manifestation in Spin Dynamics of Disordered Dirac Matter,"Topological quantum matter exhibits novel transport phenomena driven by
entanglement between internal degrees of freedom, as for instance generated by
spin-orbit coupling effects. Here we report on a direct connection between the
mechanism driving spin relaxation and the intertwined dynamics between spin and
sublattice degrees of freedom in disordered graphene. Beyond having a direct
observable consequence, such intraparticle entanglement is shown to be
resilient to disorder, pointing towards a novel resource for quantum
information processing.",2310.17950v1
2001-09-20,Pulsar Spin-Down Induced Phenomena: Heating; Magnetic Field Evolution; Glitches; Pulse-Period Modulations,"Modeling the dynamics of the quantum fluids within a spinning-down neutron
star gives a description consistent with observed pulsar magnetic field
evolution and spin-period ""glitches."" The long-standing problem of large
predicted excesses in spin-down sustained pulsar heating from such models now
see ms resolvable. However, the origin of some pulsar spin-period and
pulse-shape modulations which have been interpreted as manifestations of very
long period (~year) stellar precession is a crucial challenge to canonical
neutron star models.",0109353v1
1995-08-25,Simple theory for spin-lattice relaxation in metallic rare earth ferromagnets,"The spin-lattice relaxation time $\tau_{SL}$ is a key quantity both for the
dynamical response of ferromagnets excited by laser pulses and as the speed
limit of magneto-optical recording. Extending the theory for the electron
paramagnetic resonance of magnetic impurities to spin-lattice relaxation in
ferromagnetic rare earths we calculate $\tau_{SL}$ for Gd and find a value of
48 ps in very good agreement with time-resolved spin-polarized photoemission
experiments. We argue that the time scale for $\tau_{SL}$ in metals is
essentially given by the spin-orbit induced magnetocrystalline anisotropy
energy.",9508120v1
1997-05-20,Magnetic Excitations in quasi two-dimensional Spin-Peierls Systems,"A study is presented of a two-dimensional frustrated and dimerized quantum
spin-system which models the effect of inter-chain coupling in a spin-Peierls
compound. Employing a bond-boson method to account for quantum disorder in the
ground state the elementary excitations are evaluated in terms of gapful
triplet modes. Results for the ground state energy and the spin gap are
discussed. The triplet dispersion is found to be in excellent agreement with
inelastic neutron scattering data in the dimerized phase of the spin-Peierls
compound CuGeO_3. Moreover, consistent with these neutron scattering
experiments, the low-temperature dynamic structure factor exhibits a
high-energy continuum split off from the elementary triplet mode.",9705193v1
1998-02-23,Magnetic Structure and NMR signal of Spin Peierls Solitons,"We compute the magnetic profile of spin Peierls solitons in a simple
Heisenberg model with magneto elastic couplings, using independently the DMRG
method and the Hartree Fock approximation. Our results agree qualitatively with
published NMR data provided we average over the spin profiles. We conclude that
he dynamics of the spin plus lattice system must be included in a more detailed
theory of the spin Peierls transition in CuGeO.",9802245v1
1998-03-20,Universal Spin Response in Copper Oxide Materials,"The spin response in the copper oxide materials at finite temperatures in the
underdoped and optimal doped regimes is studied within the framework of the
fermion-spin theory. The integrated dynamical spin structure factor is almost
temperature independent, the integrated susceptibility shows the particularly
universal behavior as $I(\omega, T) \propto arctan [ a_{1}\omega/T +
a_{3}(\omega/T)^{3}]$, and the spin-lattice relaxation time is weakly
temperature dependent, which are consistent with experiments and numerical
simulations.",9803246v2
1998-06-02,Lattice Dimerization in the Spin-Peierls Compound CuGeO$_3$,"The uniaxial pressure dependences of the exchange coupling and the structural
distortion in the dimerized phase of CuGeO$_3$ are analyzed. A minimum magnetic
dimerization of 3 % is obtained, incompatible with an adiabatic approach to the
spin-Peierls transition. Exploring the properties of an Heisenberg spin chain
with dynamical spin-phonon coupling, the dimerization dependence of the spin
excitation gap is found to be in qualitative agreement with experiment.",9806022v1
1998-06-25,SU(2)-spin Invariant Auxiliary Field Quantum Monte Carlo Algorithm for Hubbard models,"Auxiliary field quantum Monte Carlo methods for Hubbard models are generally
based on a Hubbard-Stratonovitch transformation where the field couples to the
z-component of the spin. This transformation breaks SU(2) spin invariance. The
symmetry is restored only after summation over the auxiliary fields. Here, we
analyze an alternative decomposition, which conserves SU(2) spin invariance,
but requires the use of complex numbers. We show that this algorithm gets rid
of the very large fluctuations observed in imaginary time displaced correlation
functions of quantities which do not commute with the z-component of the total
spin. The algorithm prooves to be efficient for the study of spin dynamics.",9806307v1
1998-10-05,Quantum critical point with competing propagating and diffusive spin excitations,"Feedback effects due to spin fluctuation induced precursors in the fermionic
quasiparticle spectrum are taken into account in the description of a quantum
critical point of itinerant spin systems. A correlation length dependent spin
damping occurs, leading to a dynamical scaling with z\approx 1 which
non-trivially competes with the conventional spin wave behavior. We obtain,
within a one loop renormalization group approach, a quantitative explanation
for the scaling behavior seen in underdoped cuprate superconductors.",9810041v1
1999-07-27,Charge and spin dynamics of the Hubbard chains,"We calculate the local correlation functions of charge and spin for the
one-chain and two-chain Hubbard model using the density matrix renormalization
group method and the recursion technique. Keeping only finite number of states
we get good accuracy for the low energy excitations. We study the charge and
spin gaps, bandwidths and weights of the spectra for various values of the
on-site Coulomb interaction U and the electron filling. In the low energy part,
the local correlation functions are different for the charge and spin. The
bandwidths are proportional to t for the charge and J for the spin,
respectively.",9907420v1
1999-08-26,Magnons in real materials from density-functional theory,"We present an implementation of the adiabatic spin-wave dynamics of Niu and
Kleinman. This technique allows to decouple the spin and charge excitations of
a many-electron system using a generalization of the adiabatic approximation.
The only input for the spin-wave equations of motion are the energies and Berry
curvatures of many-electron states describing frozen spin spirals. The latter
are computed using a newly developed technique based on constrained
density-functional theory, within the local spin density approximation and the
pseudo-potential plane-wave method. Calculations for iron show an excellent
agreement with experiments.",9908386v1
2000-12-10,Theory of spin wave excitations of metallic A-type antiferromagnetic manganites,"The spin dynamic of the metallic A-type antiferromagnetic manganites is
studied. An effective nearest-neighbour Heisenberg spin wave dispersion is
derived from the double exchange model taking into account the superexchange
interaction between the core spins. The result of inelastic neutron scattering
experiment on ${Nd}_{0.45}{Sr}_{0.55}{Mn} {O}_{3}$ is qualitatively reproduced.
Comparing theory with experimental data two main parameters of the model:
nearest-neighbour electron transfer amplitude and superexchange coupling
between the core spins are estimated.",0012166v2
2001-07-24,Control of spin in quantum dots with non-Fermi liquid correlations,"Spin effects in the transport properties of a quantum dot with spin-charge
separation are investigated. It is found that the non-linear transport spectra
are dominated by spin dynamics. Strong spin polarization effects are observed
in a magnetic field. They can be controlled by varying gate and bias voltages.
Complete polarization is stable against interactions. When polarization is not
complete, it is power-law enhanced by non-Fermi liquid effects.",0107505v1
2002-03-12,T-shaped spin filter with a ring resonator,"A planar ballistic structure is predicted to be highly effective in filtering
electron spin from an unpolarized source into two output fluxes with the
opposite and practically pure spin polarizations. The operability of the
proposed device relies on the peculiar spin-dependent transmission properties
of the T-shaped connector in the presence of the Rashba spin-orbit interaction
as well as the difference in the dynamic phase gains of the two alternative
paths around the ring resonator through upper and lower branches for even and
odd eigenmodes.",0203261v1
2002-08-16,Electric field tunability of nuclear and electronic spin dynamics due to the hyperfine interaction in semiconductor nanostructures,"We present formulas for the nuclear and electronic spin relaxation times due
to the hyperfine interaction for nanostructed systems and show that the times
depend on the square of the local density of electronic states at the nuclear
position. A drastic sensitivity (orders of magnitude) of the electronic and
nuclear spin coherence times to small electric fields is predicted for both
uniformly distributed nuclear spins and for $\d$-doped layers of specific
nuclei. This sensitivity is robust to nuclear spin diffusion.",0208336v2
2002-09-24,Metastable spin-polarized carbon clusters C_8 and their ensembles,"Results of tight-binding calculations on metastable spin-polarized carbon
clusters C_8 (prismanes) are presented. It is shown that those clusters can
form ensembles due to intercluster bonding. The binding energy of a given
metastable configuration decreases monotonously with the total spin S, while
the activation energy for the decay of a metastable state has distinct maxima
as a function of S. For specific values of S, the dynamical stability of
spin-polarized ensembles of prismanes appears to be higher than that of an
isolated prismane, pointing to a possibility of existence of ""cluster matter""
composed of spin-polarized clusters C_8",0209556v1
2003-01-13,Spin freezing and magnetic inhomogeneities in bilayer manganites,"We have performed a muon spin rotation study on polycrystalline samples of
electron-doped layered manganites, La$_{2-2x}$Sr$_{1+2x}$Mn$_2$O$_7$ (0.4<
x<1), in order to investigate the local magnetic structure and spin dynamics.
Our results provide evidence for phase separation into A-type antiferromagnetic
and charge-ordered phases for x=0.52 and spin freezing at low temperatures
(T<100K) for 0.52<x<0.75. A new phase diagram which includes this spin freezing
region is proposed.",0301177v1
2003-02-18,Flow equation renormalization of a spin-boson model with a structured bath,"We discuss the dynamics of a spin coupled to a damped harmonic oscillator.
This system can be mapped to a spin-boson model with a structured bath, i.e.
the spectral function of the bath has a resonance peak. We diagonalize the
model by means of infinitesimal unitary transformations (flow equations),
thereby decoupling the small quantum system from its environment, and calculate
spin-spin correlation functions.",0302357v1
2003-05-20,Spin-dependent Rabi oscillations in single quantum=0D dot,"Ultrafast optical pump of exciton resonance in single quantum dot by an
elliptically polarized laser pulse is described by the non-Markov balance
equations. Population and spin dynamics are investigated and spin-dependent
Rabi oscillations are considered for the case of a flat quantum dot, with the
lateral size greater than the height. The following peculiarities of temporal
evolution have been found: a) a beating of Rabi oscillations under an
elliptically polarized pump and b) quenching of spin orientation due to a
spin-orbit splitting effect.",0305473v1
2004-01-22,Spin fluctuations in the quasi-two dimensional Heisenberg ferromagnet GdI_2 studied by Electron Spin Resonance,"The spin dynamics of GdI_2 have been investigated by ESR spectroscopy. The
temperature dependences of the resonance field and ESR intensity are well
described by the model for the spin susceptibility proposed by Eremin et al.
[Phys. Rev. B 64, 064425 (2001)]. The temperature dependence of the resonance
linewidth shows a maximum similar to the electrical resistance and is discussed
in terms of scattering processes between conduction electrons and localized
spins.",0401415v1
2004-02-11,Spin-precession in an adiabatically rotating electric field,"Due to spin-orbit coupling, the adiabatic perturbation of an electron's
orbital motion induced by a revolving external electric field lead to the
electron spin-precession. The obtained results describe both transverse and
longitudinal dynamics of an effective spin, for conical and figure-8
trajectories of a driving electric field, and elucidate the link between the
quantum-mechanical, geometrical, and classical pictures of spin rotation.
Within the limit of adiabatic approximation the derived formulas are valid
regardless of whether eigenvectors of the total Hamiltonian of the problem are
explicitly available or not, and are convenient for approximate calculations.
The main expression for the time evolution of the Bloch vector has pure
geometric character and is independent of the physical context.",0402319v1
2004-02-21,NMR characterization of spin-1/2 alternating antiferromagnetic chains in the high-pressure phase of (VO)2P2O7,"Local-susceptibility measurements via the NMR shifts of $^{31}$P and $^{51}$V
nuclei in the high-pressure phase of (VO)$_{2}$P$_{2}$O$_{7}$ confirmed the
existence of a unique alternating antiferromagnetic chain with a zero-field
spin gap of 34 K. The $^{31}$P nuclear spin-lattice relaxation rate scales with
the uniform spin susceptibility below about 15 K which shows that the
temperature dependence of both the static and dynamical spin susceptibilities
becomes identical at temperatures not far below the spin-gap energy.",0402540v1
2004-03-16,Current induced electron spin polarization in strained semiconductors,"The polarization of conduction electron spins due to an electrical current is
observed in strained nonmagnetic semiconductors using static and time-resolved
Faraday rotation. The density, lifetime, and orientation rate of the
electrically-polarized spins are characterized by a combination of optical and
electrical methods. In addition, the dynamics of the current-induced spins are
investigated by utilizing electrical pulses generated from a photoconductive
switch. These results demonstrate the possibility of a spin source for
semiconductor spintronic devices without the use of magnetic materials.",0403407v1
2005-04-28,The Interplay of Spin and Charge Channels in Zero Dimensional Systems,"We present a full fledged quantum mechanical treatment of the interplay
between the charge and the spin zero-mode interactions in quantum dots. Quantum
fluctuations of the spin-mode suppress the Coulomb blockade and give rise to
non-monotonic behavior near this point. They also greatly enhance the dynamic
spin susceptibility. Transverse fluctuations become important as one approaches
the Stoner instability. The non-perturbative effects of zero-mode interaction
are described in terms of charge (U(1)) and spin (SU(2)) gauge bosons.",0504751v1
2005-07-20,Spin-lattice relaxation phenomena in manganite La0.7Sr0.3MnO3 thin films,"Time-resolved magneto-optics was used to study spin-lattice relaxation
dynamics in thin epitaxial La0.7Sr0.3MnO3 films. Two distinct recovery regimes
of the ferromagnetic order can be resolved upon photoexcitation, which manifest
themselves by two different relaxation times. A pump pulse energy independent
spin-lattice relaxation time can be deduced. Due to a weak spin-orbit coupling
in manganites this spin-lattice relaxation time is much longer than in
ferromagnetic metals. Heat flow into the substrate sets the ultimate recovery
speed of the ferromagnetic order and allows for a determination of heat
diffusion properties of manganite films.",0507481v1
2006-03-10,Stray-field-induced modification of coherent spin dynamics,"Electron spins in an InGaAs semiconductor quantum well are used as a
magnetometer of magnetic stray-fields from patterned Fe stripes. Using
time-resolved Faraday rotation, the coherent precession of quantum-well spins
in the inhomogeneous field below the Fe stripes is measured for varying
magnetic fields. Comparing with reference stripes made of Au, we find an
enhancement of the spin precession frequency proportional to the Fe
magnetization, in line with a decrease of the spin decay time, which is
attributed to the inhomogeneous magnetic stray-field in the quantum well layer.",0603296v1
2006-06-21,Quantum Dynamics of Spin Wave Propagation Through Domain Walls,"Through numerical solution of the time-dependent Schrodinger equation, we
demonstrate that magnetic chains with uniaxial anisotropy support stable
structures, separating ferromagnetic domains of opposite magnetization. These
structures, domain walls in a quantum system, are shown to remain stable if
they interact with a spin wave. We find that a domain wall transmits the
longitudinal component of the spin excitations only. Our results suggests that
continuous, classical spin models described by LLG equation cannot be used to
describe spin wave-domain wall interaction in microscopic magnetic systems.",0606549v1
2006-09-20,Coherent spin dynamics in quantum wells in quantizing magnetic field,"We investigate theoretically the coherent longitudinal and transversal spin
relaxation of photoexcited electrons in quantum wells in quantized magnetic
fields. We find the relaxation time for typical quantum well parameters between
100 and 1000 ps. For a realistic random potential the relaxation process
depends on the electron energy and g-factor, demonstrating oscillations in the
spin polarization accompanying the spin relaxation. The dependence of spin
relaxation on applied field, and thus on the corresponding ""magnetic"" length,
can be used to characterize the spatial scale of disorder in quantum wells.",0609522v1
2006-10-16,Mixing of two-electron spin states in a semiconductor quantum dot,"We show that the low lying spin states of two electrons in a semiconductor
quantum dot can be strongly mixed by electron-electron asymmetric exchange.
This mixing is generated by the coupling of electron spin to its orbital motion
and to the relative orbital motion of the two electrons. The asymmetric
exchange can be as large as 50% of the isotropic exchange, even for cylindrical
quantum dots. The resulting spin mixing contributes to understanding spin
dynamics in quantum dots, including light polarization reversal.",0610405v1
2006-11-16,Electrical polarization of nuclear spins in a breakdown regime of quantum Hall effect,"We have developed a method for electrical polarization of nuclear spins in
quantum Hall systems. In a breakdown regime of odd-integer quantum Hall effect
(QHE), excitation of electrons to the upper Landau subband with opposite spin
polarity dynamically polarizes nuclear spins through the hyperfine interaction.
The polarized nuclear spins in turn accelerate the QHE breakdown, leading to
hysteretic voltage-current characteristics of the quantum Hall conductor.",0611420v1
2006-11-26,Spin dynamics in semiconductor nanostructures,"We review our theoretical investigation on the spin relaxation/dephasing in
spin precession and spin diffusion/transport in semiconductor nanostructures
based on the kinetic spin Bloch equation approach.",0611649v1
2007-02-07,Damping of antiferromagnetic spin waves by valence fluctuations in the double layer perovskite YBaFe2O5,"Inelastic neutron scattering experiments show that spin dynamics in the
charge ordered insulating ground state of the double-layer perovskite YBaFe2O5
is well described in terms of eg superexchange interactions. Above the Verwey
transition at TV = 308 K, t2g double exchange-type conduction within
antiferromagnetic FeO2--BaO--FeO2 double layers proceeds by an electron hopping
process that requires a spin flip of the five-fold coordinated Fe ions, costing
an energy 5<J>S^2 of approximately 0.1 eV. The hopping process disrupts
near-neighbor spin correlations, leading to massive damping of zone-boundary
spin waves.",0702181v1
1992-06-30,Numerical Analysis of the Quark Fraction of the Proton Spin,"We report on a lattice QCD estimate of the quark spin fraction of the proton
spin. The estimate is arrived at by means of a lattice QCD simulation of the
polarized proton matrix element of the Adler-Bell-Jackiw anomaly. The
preliminary result of the simulation is that this fraction is rather small.
This is in accord with the interpretation of the EMC experiment that the quark
spins are responsible for very little, if any, of the proton spin. (Talk given
at the Adriatico Research Conference on Polarization Dynamics in Nuclear and
Particle Physics, Trieste, January, 1992) NOTE: This paper is available only in
postscript form.",9206027v1
1996-08-06,Spin-spin correlation functions of spin systems coupled to 2-d quantum gravity for $0 < c < 1$,"We perform Monte Carlo simulations of 2-d dynamically triangulated surfaces
coupled to Ising and three--states Potts model matter. By measuring spin-spin
correlation functions as a function of the geodesic distance we provide
substantial evidence for a diverging correlation length at $\beta_c$. The
corresponding scaling exponents are directly related to the KPZ exponents of
the matter fields as conjectured in [4] (NPB454(1995)313).",9608022v1
2002-01-16,Single spin asymmetries in QCD,"Measurements of single transverse spin asymmetries in high energy inclusive
processes have always shown unexpected and challenging results. Several cases
are considered and discussed within a QCD approach which couples perturbative
dynamics to new non perturbative partonic information; the aim is that of
developing a consistent phenomenological description of these unusual single
spin phenomena, based on a generalized QCD factorization scheme.",0201150v1
2002-03-02,Spin waves in the magnetized plasma of a supernova and its excitation by neutrino fluxes,"The spin effects on electromagnetic waves in a strongly magnetized plasma
with rare collisions is considered with the help of relativistic kinetic
equations, which takes into account the electron spin dynamics in the
selfconsistent electric and magnetic fields. It is shown that for
electromagnetic waves propagating almost perpendicular to ambient magnetic
field the spin effects become essential in the vicinity of electron
gyrofrequency and the corresponding wave dispersion and growth rate of the
electromagnetic spin waves in the presence of intense quasi monoenergetic
fluxes of neutrino is determined.",0203020v1
2004-01-22,Equation of spin motion in storage rings in a cylindrical coordinate system,"The exact equation of spin motion in a cylindrical coordinate system with
allowance for electric dipole moments of particles has been derived. This
equation is convenient for analytical calculations of spin dynamics in circular
storage rings when the configuration of main fields is simple enough. The
generalized formula for the influence of a vertical betatron oscillation on the
angular velocity of spin rotation has been found. This formula agrees with the
previously obtained result and contains an additional oscillatory term that can
be used for fitting. The relative importance of terms in the equation of spin
motion is discussed.",0401166v2
1993-11-17,Dynamical Equations of Spinning Particles: Feynman's Proof,"In this letter, we discuss the extension of Feynman's derivation of the
equation of motion to the case of spinning particles. We show that a spinning
particle interacts only with the electromagnetic and gravitational fields. In
the absence of the electromagnetic interactions, we rederive Papapetrou's
equations for spinning particles in the background of the conformal gravity. We
also find that the effect of spin coupled to non-constant electromagnetic
fields leads to further corrections to the Lorentz force equations. Some
discussions of these results are given at the end.",9311091v1
2004-10-28,Higher spin fields from indefinite Kac-Moody algebras,"The emergence of higher spin fields in the Kac-Moody theoretic approach to
M-theory is studied. This is based on work done by Schnakenburg, West and the
second author. We then study the relation of higher spin fields in this
approach to other results in different constructions of higher spin field
dynamics. Of particular interest is the construction of space-time in the
present set-up and we comment on the various existing proposals.",0410274v1
2001-03-14,Threshold suppression of Lambda spin-orbit splitting,"New experimental data on medium to heavy single Lambda hypernuclei revealed a
much larger spin-orbit splitting than observed in older measurements of light
hypernuclei. Taking into account particle threshold effects and the
density-dependence of in-medium coupling constants the apparent suppression of
spin-orbit strength in light hypernuclei as well as the spin-orbit structure
observed in medium to heavy nuclei are explained in a unified manner within the
density dependent relativistic hadron field theory. It is concluded that the
most valuable information on the Lambda spin-orbit dynamics in finite nuclei
has to be extracted from medium to heavy mass nuclei.",0103035v1
2004-02-18,"Preparation of pseudopure state in a cluster of dipolar-coupled spins with ""unresolved"" spectrum","A method of creating pseudopure spin states in large clusters of coupled
spins is described. It is based on filtering multiple-quantum coherence of the
highest order followed by a time-reversal period and partial saturation.
Experimental demonstration is presented for a cluster of six dipolar-coupled
proton spins of a benzene molecule in liquid crystalline matrix, and the
details of spin dynamics are studied numerically.",0402132v1
2005-02-27,Collective Decoherence of Nuclear Spin Clusters,"The problem of dipole-dipole decoherence of nuclear spins is considered for
strongly entangled spin cluster. Our results show that its dynamics can be
described as the decoherence due to interaction with a composite bath
consisting of fully correlated and uncorrelated parts. The correlated term
causes the slower decay of coherence at larger times. The decoherence rate
scales up as a square root of the number of spins giving the linear scaling of
the resulting error. Our theory is consistent with recent experiment reported
in decoherence of correlated spin clusters.",0502178v2
2007-05-14,Cooling Torsional Nanomechanical Vibration by Spin-Orbit Interactions,"We propose and study a spin-orbit interaction based mechanism to actively
cool down the torsional vibration of a nanomechanical resonator made by
semiconductor materials. We show that the spin-orbit interactions of electrons
can induce a coherent coupling between the electron spins and the torsional
modes of nanomechanical vibration. This coherent coupling leads to an active
cooling for the torsional modes via the dynamical thermalization of the
resonator and the spin ensemble.",0705.1964v1
2007-07-30,Temperature Dependence of Rashba Spin-orbit Coupling in Quantum Wells,"We perform an all-optical spin-dynamic measurement of the Rashba spin-orbit
interaction in (110)-oriented GaAs/AlGaAs quantum wells. The crystallographic
direction of quantum confinement allows us to disentangle the contributions to
spin-orbit coupling from the structural inversion asymmetry (Rashba term) and
the bulk inversion asymmetry. We observe an unexpected temperature dependence
of the Rashba spin-orbit interaction strength that signifies the importance of
the usually neglected higher-order terms of the Rashba coupling.",0707.4493v1
2007-10-03,Nuclear Tuning and Detuning of the Electron Spin Resonance in a Quantum Dot,"We study nuclear spin dynamics in a quantum dot close to the conditions of
electron spin resonance. We show that at small frequency mismatch the nuclear
field detunes the resonance. Remarkably, at larger frequency mismatch its
effect is opposite: The nuclear system is bistable, and in one of the stable
states the field accurately tunes the electron spin splitting to resonance. In
this state the nuclear field fluctuations are strongly suppressed and nuclear
spin relaxation is accelerated.",0710.0750v2
2007-10-30,Progress in Gauge Invariant Lagrangian Construction for Massive Higher Spin Fields,"We review the recently developed general gauge invariant approach to
Lagrangian construction for massive higher spin fields in Minkowski and AdS
spaces of arbitrary dimension. Higher spin Lagrangian, describing the dynamics
of the fields with any spin, is formulated with help of BRST-BFV operator in
auxiliary Fock space. No off-shell constraints on the fields and gauge
parameters are imposed. The construction is also applied to tensor higher spin
fields with index symmetry corresponding to a multirow Young tableau.",0710.5715v2
2007-12-23,Spin-orbit coupling in bulk GaAs,"We study the spin-orbit coupling in the whole Brillouin zone for GaAs using
both the $sp^3s^{\ast}d^5$ and $sp^3s^{\ast}$ nearest-neighbor tight-binding
models. In the $\Gamma$-valley, the spin splitting obtained is in good
agreement with experimental data. We then further explicitly present the
coefficients of the spin splitting in GaAs $L$ and $X$ valleys. These results
are important to the realization of spintronic device and the investigation of
spin dynamics far away from equilibrium.",0712.3890v3
2008-02-19,Entanglement purification without controlled-NOT gates by using the natural dynamics of spin chains,"We present a simple protocol to purify bipartite entanglement in spin-1/2
particles by utilizing only natural spin-spin interactions, i.e. those that can
commonly be realized in realistic physical systems, and S_z-measurements on
single spins. Even the standard isotropic Heisenberg interaction is shown to be
sufficient to purify mixed state entanglement if there are at least three pairs
of spins. This approach could be useful for quantum information processing in
solid-state-based systems.",0802.2588v2
2008-03-12,Spin-lattice model of Magneto-electric Transitions in RbCoBr$_3$,"Extensive Monte Carlo simulations are performed to analyze a recent neutron
diffraction experiment on a distorted triangular lattice compound RbCoBr$_3$.
We consider a spin-lattice model, where both spin and lattice are Ising
variables. This model explains well successive magnetic and dielectric
transitions observed in the experiment. The exchange interaction parameters and
the spin-lattice coupling are estimated. It is found that the spin-lattice
coupling is important to explain the slow growth of a ferrimagnetic order. The
present simulations were made possible by developing a new Monte Carlo
algorithm, which accelerates slow Monte Carlo dynamics of quasi-one-dimensional
frustrated systems.",0803.1710v2
2008-08-29,Coherent manipulation of nuclear spins in the breakdown regime of integer quantum Hall states,"We demonstrate a new method for electrical manipulation of nuclear spins
utilizing dynamic nuclear polarization induced by quantum Hall effect
breakdown. Nuclear spins are polarized and detected through the hyperfine
interaction between a nuclear spin system and a two-dimensional electron system
located at an interface of GaAs/AlGaAs single heterostructure. Coherent
oscillations between the nuclear-spin quantum states are observed by measuring
the longitudinal voltage of the conductor.",0808.4021v1
2008-11-13,Optical spin orientation of a single manganese atom in a quantum dot,"A hight degree of spin polarization is achieved for a Mn atom localized in a
semiconductor quantum dot using quasi-resonant optical excitation at zero
magnetic field. Optically created spin polarized carriers generate an energy
splitting of the Mn spin and enable magnetic moment orientation controlled by
the photon helicity and energy. The dynamics and the magnetic field dependence
of the optical pumping mechanism shows that the spin lifetime of an isolated Mn
atom at zero magnetic field is controlled by a magnetic anisotropy induced by
the built-in strain in the quantum dots.",0811.2165v1
2009-02-23,Spin dynamics of electrons in the first excited subband of a high-mobility low-density 2D electron system,"We report on time-resolved Kerr rotation measurements of spin coherence of
electrons in the first excited subband of a high-mobility low-density
two-dimensional electron system in a GaAs/Al0.35Ga0.65As heterostructure. While
the transverse spin lifetime (T2*) of electrons decreases monotonically with
increasing magnetic field, it has a non-monotonic dependence on the
temperature, with a peak value of 596 ps at 36 K, indicating the effect of
inter-subband electron-electron scattering on the electron spin relaxation. The
spin lifetime may be long enough for potential device application with
electrons in excited subbands.",0902.3875v1
2009-07-05,Magnetic quantum tunnelling in Fe8 with excited nuclei,"We investigate the effect of dynamic nuclear spin fluctuation on quantum
tunneling of the magnetization (QTM) in the molecular magnet Fe8 by increasing
the nuclei temperature using radio frequency (RF) pulses before the hysteresis
loop measurements. The RF pulses do not change the electrons spin temperature.
Independently we show that the nuclear spin-spin relaxation time T2 has strong
temperature dependence. Nevertheless, we found no effect of the nuclear spin
temperature on the tunneling probability. This suggests that in our
experimental conditions only the hyperfine field strength is relevant for QTM.
We demonstrate theoretically how this can occur.",0907.0844v1
2009-07-16,Long-lived spin memory in Mn-doped GaAs: Time resolved study,"We study the electron spin dynamics in p-type GaAs doped with magnetic Mn
acceptors by means of time-resolved pump-probe and photoluminescence
techniques. Measurements in transverse magnetic fields show a long spin
relaxation time of 20 ns that can be uniquely related to electrons. Application
of weak longitudinal magnetic fields above 100 mT extends the spin relaxation
times up to microseconds which is explained by suppression of the
Bir-Aronov-Pikus spin relaxation for the electron on the Mn acceptor.",0907.2851v1
2010-07-01,Spin dynamics at the singlet-triplet crossings in double quantum dot,"We simulate the control of the spin states in a two-electron double quantum
dot when an external detuning potential is used for passing the system through
an anticrossing. The hyperfine coupling of the electron spins with the
surrounding nuclei causes the anticrossing of the spin states but also the
decoherence of the spin states. We calculate numerically the singlet-triplet
decoherence for different detuning values and find a good agreement with
experimental measurement results of the same setup. We predict an interference
effect due to the coupling of T0 and T+ states.",1007.0080v2
2010-08-06,Ferromagnetic phases in spin-Fermion systems,"Spin-Fermion systems which obtain their magnetic properties from a system of
localized magnetic moments being coupled to conducting electrons are
considered. The dynamical degrees of freedom are spin-$s$ operators of
localized spins and spin-1/2 Fermi operators of itinerant electrons.
Renormalized spin-wave theory, which accounts for the magnon-magnon
interaction, and its extension are developed to describe the two ferrimagnetic
phases in the system: low temperature phase $0<T<T^{*}$, where all electrons
contribute the ordered ferromagnetic moment, and high temperature phase
$T^{*}<T<T_C$, where only localized spins form magnetic moment. The
magnetization as a function of temperature is calculated. The theoretical
predictions are utilize to interpret the experimentally measured
magnetization-temperature curves of $UGe_2$..",1008.1148v1
2010-09-26,Spin dependent electron-phonon interaction in SmFeAsO by low-temperature Raman spectroscopy,"The interplay between spin dynamics and lattice vibration has been suggested
as an important part of the puzzle of high-temperature superconductivity. Here
we report the strong interaction between spin fluctuation and phonon in
SmFeAsO, a parent compound of the iron arsenide family of superconductors,
revealed by low-temperature Raman spectroscopy. Anomalous zone-boundary-phonon
Raman scattering from spin superstructure was observed at temperatures below
the antiferromagnetic ordering point, which offers compelling evidence on spin
dependent electron-phonon coupling in pnictides.",1009.5050v2
2010-10-28,Theoretically predicted picosecond optical switching of spin chirality in multiferroics,"We show theoretically with an accurate spin Hamiltonian describing the
multiferroic Mn perovskites that the application of the picosecond optical
pulse with a terahertz frequency can switch the spin chirality through
intensely exciting the electromagnons. There are four states with different
spin chiralities, i.e. clockwise and counterclockwise ab/bc-plane spin spirals,
and by tuning the strength, shape and length of the pulse, the switching among
these states can be controlled at will. Dynamical pattern formation during the
switching is also discussed.",1010.6006v1
2010-11-17,Magnetotransport and spin dynamics in an electron gas formed at oxide interfaces,"We investigate the spin-dependent transport properties of a two-dimensional
electron gas formed at oxides' interface in the presence of a magnetic field.
We consider several scenarios for the oxides' properties, including oxides with
co-linear or spiral magnetic and ferroelectric order. For spiral multiferroic
oxides, the magnetoelectric coupling and the topology of the localized magnetic
moments introduce additional, electric field controlled spin-orbit coupling
that affects the magneto-oscillation of the current. An interplay of this
spin-orbit coupling, the exchange field, and of the applied magnetic field
results in a quantum, gate-controlled spin and charge Hall conductance.",1011.3924v1
2011-03-10,Spin-orbit interactions mediated negative differential resistance in a quasi-two-dimensional electron gas with finite thickness,"Effects of the spin-orbit interactions on the energy spectrum, Fermi surface
and spin dynamics are studied in structural- and bulk-inversion asymmetric
quasi-two-dimensional structures with a finite thickness in the presence of a
parabolic transverse confining potential. One-particle quantum mechanical
problem in the presence of an in-plane magnetic field is solved numerically
exact. Interplay of the spin-orbit interactions, orbital- and Zeeman-effects of
the in-plane magnetic field yields a multi-valley subband structure, typical
for realization of the Gunn effect. A possible Gunn-effect-mediated spin
accumulation is discussed.",1103.2036v1
2011-03-11,Disproportionation and Metallization at Low-Spin to High-Spin Transition in Multiorbital Mott Systems,"We study the thermally driven spin state transition in a two-orbital Hubbard
model with crystal field splitting, which provides a minimal description of the
physics of LaCoO3. We employ the dynamical mean-field theory with quantum
Monte-Carlo impurity solver. At intermediate temperatures we find a spin
disproportionated phase characterized by checkerboard order of sites with small
and large spin moments. The high temperature transition from the
disproportionated to a homogeneous phase is accompanied by vanishing of the
charge gap. With the increasing crystal-field splitting the temperature range
of the disproportionated phase shrinks and eventually disappears completely.",1103.2249v1
2011-04-06,Optical polarization of localized hole spins in p-doped quantum wells,"The initialization of spin polarization in localized hole states is
investigated using time-resolved Kerr rotation. We find that the sign of the
polarization depends on the magnetic field, and the power and the wavelength of
the circularly polarized pump pulse. An analysis of the spin dynamics and the
spin-initialization process shows that two mechanisms are responsible for spin
polarization with opposite sign: The difference of the g factor between the
localized holes and the trions, as well as the capturing process of dark
excitons by the localized hole states.",1104.1092v1
2011-09-17,Impact of geometrical frustration on charge transport near the Mott transition in pyrochlore (Y$_{1-x}$Cd$_{x}$)$_{2}$Mo$_{2}$O$_{7}$,"To search for novel spin-charge coupled phenomena in the strongly correlated
electron system on a frustration lattice, charge transport and dynamics have
been investigated for the hole-doped spin-glass (Mott) insulator
(Y$_{1-x}$Cd$_{x}$)$_{2}$Mo$_{2}$O$_{7}$ with pyrochlore structure. Coincident
with the disappearance of spin-glass state by hole doping, a diffusive metallic
transport with strongly renormalized electron mass shows up with no long range
spin order, which is caused by strong antiferromagnetic spin fluctuation due to
the geometrical frustration.",1109.3744v1
2011-09-30,Ripples in a string coupled to Glauber spins,"Each oscillator in a linear chain (a string) interacts with a local Ising
spin in contact with a thermal bath. These spins evolve according to Glauber
dynamics. Below a critical temperature, a rippled state in the string is
accompanied by a nonzero spin polarization. The system is shown to form ripples
in the string which, for slow spin relaxation, vibrates rapidly about
quasi-stationary states described as snapshots of a coarse-grained stroboscopic
map. For moderate observation times, ripples are observed irrespective of the
final thermodynamically stable state (rippled or not).",1109.6766v1
2011-12-12,Circuit Theory for SPICE of Spintronic Integrated Circuits,"We present a theoretical and a numerical formalism for analysis and design of
spintronic integrated circuits (SPINICs). The formalism encompasses a
generalized circuit theory for spintronic integrated circuits based on
nanomagnetic dynamics and spin transport. We propose an extension to the
Modified Nodal Analysis technique for the analysis of spin circuits based on
the recently developed spin conduction matrices. We demonstrate the
applicability of the framework using an example spin logic circuit described
using spin Netlists.",1112.2746v2
2012-08-24,Fast and robust spin manipulation in a quantum dot by electric fields,"We apply an invariant-based inverse engineering method to control by
time-dependent electric fields electron spin dynamics in a quantum dot with
spin-orbit coupling in a weak magnetic field. The designed electric fields
provide a shortcut to adiabatic processes that flips the spin rapidly, thus
avoiding decoherence effects. This approach, being robust with respect to the
device-dependent noise, can open new possibilities for the spin-based quantum
information processing.",1208.4890v2
2012-09-07,Self-sustained current oscillations in spin-blockaded quantum dots,"Self-sustained current oscillation observed in spin-blockaded double quantum
dots is explained as a consequence of periodic motion of dynamically polarized
nuclear spins (along a limit cycle) in the spin-blockaded regime under an
external magnetic field and a spin-transfer torque. It is shown, based on the
Landau-Lifshtz-Gilbert equation, that a sequence of semistable limit cycle,
Hopf and homoclinic bifurcations occurs as the external field is tuned. The
divergent period near the homoclinic bifurcation explains well why the period
in the experiment is so long and varies by many orders of magnitudes.",1209.1548v1
2012-12-12,Anisotropic rare-earth spin ensemble strongly coupled to a superconducting resonator,"Interfacing photonic and solid-state qubits within a hybrid quantum
architecture offers a promising route towards large scale distributed quantum
computing. Ideal candidates for coherent qubit interconversion are optically
active spins magnetically coupled to a superconducting resonator. We report on
a cavity QED experiment with magnetically anisotropic Er3+:Y2SiO5 crystals and
demonstrate strong coupling of rare-earth spins to a lumped element resonator.
In addition, the electron spin resonance and relaxation dynamics of the erbium
spins are detected via direct microwave absorption, without aid of a cavity.",1212.2856v1
2013-01-09,Devices with electrically tunable topological insulating phases,"Solid-state topological insulating phases, characterized by spin-momentum
locked edge modes, provide a powerful route for spin and charge manipulation in
electronic devices. We propose to control charge and spin transport in the
helical edge modes by electrically switching the topological insulating phase
in a HgTe/CdTe double quantum well device. We introduce the concept of a
topological field-effect-transistor and analyze possible applications to a spin
battery, which also realize a set up for an all-electrical investigation of the
spin-polarization dynamics in metallic islands.",1301.1823v2
2013-01-29,Model of coherent optical spin manipulation through hot trion states in p-doped InAs/GaAs quantum dots,"A new generalised group-theoretical approach, based on master
Maxwell-pseudospin equations, is proposed to explain recently observed enhanced
circular dichroism in the excited state emission from p-doped quantum dot
ensembles under resonant circularly polarised excitation into hot trion states,
herein referred to as ""spin-filtering effect"". The theory agrees remarkably
well with polarised time-resolved photoluminescence experiments, yielding
largely unknown inter- and intra-shell spin relaxation time scales. This
approach allows to predict optimum pulse parameters for control of spin
dynamics, which will enable exploitation of the effect in all-optical
spin-based quantum technologies.",1301.7018v1
2013-06-14,Suspended Long-Lived NMR Echo in Solids,"We report an observation of extremely long-lived spin states in systems of
dipolar-coupled nuclear spins in solids. The 'suspended echo' experiment uses a
simple stimulated echo pulse sequence and creates non-equilibrium states which
live many orders of magnitude longer than the characteristic time of spin-spin
dynamics T2. Large amounts of information can be encoded in such long-lived
states, stored in a form of multi-spin correlations, and subsequently retrieved
by an application of a single 'reading' pulse.",1306.3485v1
2013-06-18,Spectrum of a magnetized strong-leg quantum spin ladder,"Inelastic neutron scattering is used to measure the spin excitation spectrum
of the Heisenberg $S=1/2$ ladder material (C$_7$H$_10$N)$_2$CuBr$_4$ in its
entirety, both in the gapped spin-liquid and the magnetic field induced
Tomonaga-Luttinger spin liquid regimes. A fundamental change of the spin
dynamics is observed between these two regimes. DMRG calculations
quantitatively reproduce and help understand the observed commensurate and
incommensurate excitations. The results validate long-standing quantum field
theoretical predictions, but also test the limits of that approach.",1306.4216v1
2013-06-25,Designing a Spin-Seebeck Diode,"Using micromagnetic simulations, we have investigated spin dynamics in a
spin-valve bi-layer in the presence of a thermal gradient. The direction and
the intensity of the gradient allow to excite the spin wave modes of each layer
selectively. This permits to synchronize the magnetization precession of the
two layers and to rectify the flows of energy and magnetization through the
system. Our study yields promising opportunities for applications in spin
caloritronics and nanophononics devices.",1306.5924v2
2013-07-27,NMR Investigation of the Diluted Magnetic Semiconductor Li(Zn1-xMnx)P (x = 0.1),"We employ NMR techniques to investigate the nature of Mn spins in the I-II-V
diluted magnetic semiconductor Li(Zn1-xMnx)P (x = 0.1, Curie temperature Tc =
25 K). We successfully identify the 7Li NMR signals arising from the Li sites
adjacent to Mn2+, and probe the static and dynamic properties of Mn spins. From
the NMR spin-lattice relaxation data, we show that the Mn spin-spin
interactions extend over many unit cells.",1307.7230v1
2013-10-02,Excitonic Instability at the Spin-State Transition in the Two-Band Hubbard Model,"Using linear response theory with the dynamical mean-field approximation we
investigate the particle-hole instabilities of the two-band Hubbard model in
the vicinity of the spin-state transition. Besides the previously reported
high-spin--low-spin order we find an instability towards triplet excitonic
condensate. We discuss the strong and weak coupling limits of the model, in
particular, a connection to the spinful hard-core bosons with a
nearest-neighbor interaction. Possible realization in LaCoO3 at intermediate
temperatures is briefly discussed.",1310.0669v2
2013-11-22,A standard format and a graphical user interface for spin system specification,"We introduce a simple and general XML format for spin system description that
is the result of extensive consultations within Magnetic Resonance community
and unifies under one roof all major existing spin interaction specification
conventions. The format is human-readable, easy to edit and easy to parse using
standard XML libraries. We also describe a graphical user interface that was
designed to facilitate construction and visualization of complicated spin
systems. The interface is capable of generating input files for several popular
spin dynamics simulation packages.",1311.5770v1
2013-12-23,Acoustic parametric pumping of spin waves,"Recent experiments demonstrated generation of spin currents by ultrasound. We
can understand this acoustically induced spin pumping in terms of the coupling
between magnetization and lattice waves. Here we study the parametric
excitation of magnetization by longitudinal acoustic waves and calculate the
acoustic threshold power. The induced magnetization dynamics can be detected by
the spin pumping into an adjacent normal metal that displays the inverse spin
Hall effect.",1312.6499v1
2014-01-16,Spin and Valley Noise in Two-Dimensional Dirac Materials,"We develop a theory for optical Faraday rotation noise in two-dimensional
Dirac materials. In contrast to spin noise in conventional semiconductors, we
find that the Faraday rotation fluctuations are influenced not only by spins
but also the valley degrees of freedom attributed to intervalley scattering
processes. We illustrate our theory with two-dimensional transition metal
dichalcogenides and discuss signatures of spin and valley noise in the Faraday
noise power spectrum. We propose optical Faraday noise spectroscopy as a
technique for probing both spin and valley relaxation dynamics in
two-dimensional Dirac materials.",1401.4162v1
2014-02-10,Damping of a nanocantilever by paramagnetic spins,"We compute damping of mechanical oscillations of a cantilever that contains
flipping paramagnetic spins. This kind of damping is mandated by the dynamics
of the total angular momentum, spin + mechanical. Rigorous expression for the
damping rate is derived in terms of measurable parameters. The effect of spins
on the quality factor of the cantilever can be significant in cantilevers of
small length that have large concentration of paramagnetic spins of atomic
and/or nuclear origin.",1402.2326v1
2014-04-09,Current-induced spin torque resonance of magnetic insulators,"We formulate a theory of the AC spin Hall magnetoresistance (SMR) in a
bilayer system consisting of a magnetic insulator such as yttrium iron garnet
(YIG) and a heavy metal such as platinum (Pt). We derive expressions for the DC
voltage generation based on the drift-diffusion spin model and quantum
mechanical boundary condition at the interface that reveal a spin torque
ferromagnetic resonance (ST-FMR). We predict that ST-FMR experiments will
reveal valuable information on the current-induced magnetization dynamics of
magnetic insulators and AC spin Hall effect.",1404.2360v2
2014-07-18,Microwave-induced spin currents in ferromagnetic-insulator|normal-metal bilayer system,"A microwave technique is employed to simultaneously examine the spin pumping
and the spin Seebeck effect processes in a YIG|Pt bilayer system. The
experimental results show that for these two processes, the spin current flows
in opposite directions. The temporal dynamics of the longitudinal spin Seebeck
effect exhibits that the effect depends on the diffusion of bulk
thermal-magnons in the thermal gradient in the
ferromagnetic-insulator|normal-metal system.",1407.4957v2
2015-01-28,Phase effects due to previous pulses in time-resolved Faraday rotation measurements,"Time-resolved Faraday rotation measurements have proved transformative in the
investigation of spin dynamics in semiconductors. In materials with spin
lifetimes which are on the order of, or greater than, the laser repetition
time, the collective effect of spin polarization due to the whole pump pulse
train becomes important. Here, we discuss a relative phase shift which results
from these spins. We derive and experimentally validate a closed-form
expression which describes this phase shift, and characterize it throughout
parameter space. A spin lifetime measurement based on this phase shift is
described, and we discuss situations in which the model used must be augmented
to be applicable",1501.06963v1
2015-02-03,Generation of Spin Currents in the Skyrmion Phase of a Helimagnetic Insulator $\mathrm{Cu_2OSeO_3}$,"We report spin-current generation related with skyrmion dynamics resonantly
excited by a microwave in a helimagnetic insulator $\mathrm{Cu_2OSeO_3}$. A Pt
layer was fabricated on $\mathrm{Cu_2OSeO_3}$ and voltage in the Pt layer was
measured upon magnetic resonance of $\mathrm{Cu_2OSeO_3}$ to electrically
detect injected spin currents via the inverse spin Hall effect (ISHE) in Pt. We
found that ISHE-induced electromotive forces appear in the skyrmion phase of
$\mathrm{Cu_2OSeO_3}$ as well as in the ferrimagnetic phase, which shows that
magnetic skyrmions can contribute to the spin pumping effect.",1502.00742v1
2015-07-31,Spin-selective localization of correlated lattice fermions,"The interplay between local, repulsive interactions and disorder acting only
on one spin orientation of lattice fermions (""spin-dependent disorder"") is
investigated. The nonmagnetic disorder vs. interaction phase diagram is
computed using Dynamical Mean-Field Theory in combination with the geometric
average over disorder. The latter determines the typical local density of
states and is therefore sensitive to Anderson localization. The effect of
spin-dependent disorder is found to be very different from that of conventional
disorder. In particular, it destabilizes the metallic solution and leads to a
novel spin-selective, localized phase at weak interactions and strong disorder.",1507.08944v1
2015-09-07,Time-optimal polarization transfer from an electron spin to a nuclear spin,"Polarization transfers from an electron spin to a nuclear spin are essential
for various physical tasks, such as dynamic nuclear polarization in nuclear
magnetic resonance and quantum state transformations on hybrid electron-nuclear
spin systems. We present time-optimal schemes for electron-nuclear polarization
transfers which improve on conventional approaches and will have wide
applications.",1509.02072v1
2015-09-08,Anomalous Hall effect driven by dipolar spin waves in uniform ferromagnets,"A new type of anomalous Hall effect is shown to arise from the interaction of
conduction electrons with dipolar spin waves in ferromagnets. This effect
exists even in homogeneous ferromagnets without relativistic spin-orbit
coupling. The leading contribution to the Hall conductivity is proportional to
the chiral spin correlation of dynamical spin textures and is physically
understood in terms of the skew scattering by dipolar magnons.",1509.02284v1
2016-02-02,Magnetization Dynamics of Topological Defects and the Spin Solid in Kagome Artificial Spin Ice,"We report broadband spin-wave spectroscopy on kagome artificial spin ice
(ASI) made of large arrays of interconnected Ni$_{80}$Fe$_{20}$ nanobars.
Spectra taken in saturated and disordered states exhibit a series of resonances
with characteristic magnetic field dependencies. Making use of micromagnetic
simulations, we identify resonances that reflect the spin-solid-state and
monopole-antimonopole pairs on Dirac strings. The latter resonances allow for
the generation of highly-charged vertices in ASIs via microwave assisted
switching. Our findings open further perspectives for fundamental studies on
ASIs and their usage in reprogrammable magnonics.",1602.00918v1
2016-02-23,Spontaneous Spin Textures in Multiorbital Mott Systems,"Spin textures in k-space arising from spin-orbit coupling in
non-centrosymmetric crystals find numerous applications in spintronics. We
present a mechanism that leads to appearance of k-space spin texture due to
spontaneous symmetry breaking driven by electronic correlations. Using
dynamical mean-field theory we show that doping a spin-triplet excitonic
insulator provides a means of creating new thermodynamic phases with unique
properties. The numerical results are interpreted using analytic calculations
within a generalized double-exchange framework.",1602.07122v3
2017-03-05,Protecting a nuclear spin from a noisy electron spin in diamond,"Although a nuclear spin is weakly coupled to its environment, due to its
small gyromagnetic ratio, its coherence time is limited by the hyperfine
coupling to a nearby noisy electron. Here, we propose to utilize continuous
dynamical decoupling to refocus the coupling to the electron. If the random
phase accumulated by the nuclear spin through the reduced coupling terms is
sufficient small, we can increase the nuclear coherence time. Initially, we
demonstrate this on a simple case with a two-level electron spin, while taking
all relevant hyperfine coupling terms and noise terms into account. We then
extend the analysis to a nitrogen-vacancy center in diamond having a three
level structure.",1703.01596v1
2017-08-24,Spin-dependent Optical Superlattice,"We propose and implement a lattice scheme for coherently manipulating atomic
spins. Using the vector light shift and a superlattice structure, we
demonstrate experimentally the capability on parallel spin addressing in
double-wells and square plaquettes with subwavelength resolution. Quantum
coherence of spin manipulations is verified through measuring atom tunneling
and spin exchange dynamics. Our experiment presents a building block for
engineering many-body quantum states in optical lattices for realizing quantum
simulation and computation tasks.",1708.07406v1
2018-02-21,Spin-fluctuations drive the inverse magnetocaloric effect in Mn5Si3,"Inelastic neutron scattering measurements were performed on single crystals
of the antiferromagnetic compound Mn5Si3 in order to investigate the relation
between the spin dynamics and the magneto-thermodynamic properties. It is shown
that among the two stable antiferromagnetic phases of this compound, the high
temperature one has an unusual magnetic excitation spectrum where propagative
spin-waves and diffuse spin-fluctuations coexist. Moreover, it is evidenced
that the inverse magnetocaloric effect of Mn5Si3, the cooling by adiabatic
magnetization, is associated with field induced spin-fluctuations.",1802.07511v1
2019-05-29,Spin wave propagation in ferrimagnetic $Gd_{x}Co_{1-x}$,"Recent advances in antiferromagnetic spin dynamics using rare-earth (RE) and
transition-metal (TM) ferrimagnets have attracted much interest for spintronic
devices with a high speed and density. In this study, the spin wave properties
in the magnetostatic backward volume mode and surface mode in RE-TM
ferrimagnetic $Gd_{x}Co_{1-x}$ films with various composition x are
investigated using spin wave spectroscopy. The obtained group velocity and
attenuation length are well explained by the ferromagnet-based spin wave theory
when the composition of $Gd_{x}Co_{1-x}$ is far from the compensation point.",1905.12771v1
2017-01-30,Quantum Monte Carlo Annealing with Multi-Spin Dynamics,"We introduce a novel Simulated Quantum Annealing (SQA) algorithm which
employs a multispin quantum fluctuation operator. At variance with the usual
transverse field, short-range two-spin flip interactions are included in the
driver Hamiltonian. A Quantum Monte Carlo algorithm, capable of efficiently
simulating large disordered systems, is described and tested. A first
application to SQA, on a random square lattice Ising spin glass reveals that
the multi-spin driver Hamiltonian improves upon the usual transverse field.
This work paves the way for more systematic investigations using multi-spin
quantum fluctuations on a broader range of problems.",1701.08775v1
2011-11-07,Spinor particle. An indeterminacy in the motion of relativistic dynamical systems with separately fixed mass and spin,"We give an argument that a broad class of geometric models of spinning
relativistic particles with Casimir mass and spin being separately fixed
parameters, have indeterminate worldline (while other spinning particles have
definite worldline). This paradox suggests that for a consistent description of
spinning particles something more general than a worldline concept should be
used. As a particular case, we study at the Lagrangian level the Cauchy problem
for a spinor particle and then, at the constrained Hamiltonian level, we
generalize our result to other particles.",1111.1583v1
2011-11-15,"Monopoles, magnetricity and the stray field from spin ice","An analysis is presented of the behaviour of muons in the low-temperature
state in spin ice. It is shown in detail how the behavior observed in some
previous muon experiments on spin ice in a weak transverse field may result
from the macroscopic stray field of magnetized spin ice. A model is presented
which allows these macroscopic field effects to be simulated and the results
agree with experiment. The persistent spin dynamics at low temperature
originate from the sample and could be a muon-induced implantation effect that
is operative in out-of-equilibrium systems with long relaxation times.",1111.3657v3
2012-01-10,Spinning particles in de Sitter spacetime,"We report on the multipolar equations of motion for spinning test bodies in
the de Sitter spacetime of constant positive curvature. The dynamics of
spinning particles is discussed for the two supplementary conditions of Frenkel
and Tulczyjew. Furthermore, the 4-momentum and the spin are explicitly
expressed in terms of the spacetime coordinates with the help of the 10 Killing
vectors available in de Sitter spacetime.",1201.2053v1
2012-01-17,Spin wave excitation in magnetic insulators by spin-transfer torque,"We study the excitation of spin waves in magnetic insulators by the
current-induced spin-transfer torque. We predict preferential excitation of
surface spin waves induced by an easy-axis surface anisotropy with critical
current inversely proportional to the penetration depth and surface anisotropy.
The surface modes strongly reduce the critical current and enhance the
excitation power of the current-induced magnetization dynamics.",1201.3442v1
2013-09-12,Description of 158Er at ultrahigh spin in nuclear density functional theory,"Rotational bands in $^{158}$Er at ultra-high spin have been studied in the
framework of relativistic and non-relativistic nuclear density functional
theories. Consistent results are obtained across the theoretical models used
but some puzzles remain when confronted with experiment. Namely, the many-body
configurations which provide good description of experimental transition
quadrupole moments and dynamic moments of inertia require substantial increase
of the spins of observed bands as compared with experimental estimates, which
are still subject to large uncertainties. If, however, the theoretical spins
assignments turned out to be correct, the experimental band 1 in $^{158}$Er
would be the highest-spin structure ever observed.",1309.3311v1
2015-12-07,Spin squeezing in dipolar spinor condensates,"We study the effect of dipolar interactions on the level of squeezing in
spin-1 Bose-Einstein condensates by using the single mode approximation. We
limit our consideration to the $\mathfrak{su}(2)$ Lie subalgebra spanned by
spin operators. The biaxial nature of dipolar interactions allows for dynamical
generation of spin-squeezed states in the system. We analyze the phase
portraits in the reduced mean-filed space in order to determine positions of
unstable fixed points. We calculate numerically spin squeezing parameter
showing that it is possible to reach the strongest squeezing set by the
two-axis countertwisting model. We partially explain scaling with the system
size by using the Gaussian approach and the frozen spin approximation.",1512.01965v1
2016-05-30,Thermal Transport in a one-dimensional Z$_{2}$ Spin Liquid,"We study the dynamical thermal conductivity of the Kitaev spin model on a
two-leg ladder. In contrast to conventional integrable one-dimensional spin
systems, we show that heat transport is completely dissipative. This is a
direct consequence of fractionalization of spins into mobile Majorana matter
and a static $Z_{2}$ gauge field, which acts as an emergent thermally activated
disorder. Our finding rests on three complementary calculations of the current
correlation function, comprising a phenomenological mean-field treatment of
thermal gauge fluctuations, a complete summation over all gauge sectors, as
well as exact diagonalization of the original spin model. The results will also
be contrasted against the conductivity discarding gauge fluctuations.",1605.09390v1
2016-12-27,Reinventing atomistic magnetic simulations with spin-orbit coupling,"We propose a powerful extension to combined molecular and spin dynamics that
fully captures the coupling between the atomic and spin subsystems via
spin-orbit interactions. Its foundation is the inclusion of the local magnetic
anisotropies that arise as a consequence of the lattice symmetry breaking due
to phonons or defects. We demonstrate that our extension enables the exchange
of angular momentum between the atomic and spin subsystems, which is critical
to the challenges arising in the study of fluctuations and non-equilibrium
processes in complex, natural, and engineered magnetic materials.",1612.08503v1
2019-06-17,Electronic structure and Magneto-transport in MoS$_2$/Phosphorene van der Waals heterostructure,"The time-dependent spin current mediated spin transfer torque behaviour has
been investigated via scattering formalism within density functional theory
framework supported by Green's function. Quantum magnetotransport
characteristics have been revealed in a model semiconducting
MoS$_2$/phosphorene van der Waals heterostructure. The dynamics of spin current
channelized heterolayer transport has been studied with rotational variation in
magnetization angle. It is observed that the time-dependent spin transport
torque remains invariant irrespective of magnetization angle direction. The
polarized spin-current is persistent with the external magnetic field for
potential applicability towards spintronics.",1906.09187v1
2020-04-17,Collective coordinate study of spin wave emission from dynamic domain wall,"We study theoretically the spin wave emission from a moving domain wall in a
ferromagnet. Introducing a deformation mode describing a modulation of the wall
thickness in the collective coordinate description, we show that thickness
variation couples to the spin wave linearly and induces spin wave emission. The
dominant emitted spin wave turns out to be polarized in the out-of wall plane
($\phi$)-direction. The emission contributes to the Gilbert damping parameter
proportional to $\hbar\omega_\phi/K$, the ratio of the angular frequency
$\omega_\phi$ of $\phi$ and the easy-axis anisotropy energy $K$.",2004.08082v1
2021-01-03,Conservation of Angular Momentum in the Elastic Medium with Spins,"Exact conservation of the angular momentum is worked out for an elastic
medium with spins. The intrinsic anharmonicity of the elastic theory is shown
to be crucial for conserving the total momentum. As a result, any spin-lattice
dynamics inevitably involves multiphonon processes and interaction between
phonons. This makes transitions between spin states in a solid fundamentally
different from transitions between atomic states in vacuum governed by linear
electrodynamics. Consequences for using solid-state spins as qubits are
discussed.",2101.00620v1
2021-01-11,Bose Einstein condensation and ferromagnetism of low density Bose gas of particles with arbitrary spin,"Properties of the ground state and the spectrum of elementary excitations are
investigated for the low density ultracold spinor 3D Bose gas of particles with
arbitrary nonzero spin. Gross-Pitaevskii equations are derived. Within the
framework of the considering interaction Hamiltonian it is shown that the
ground state spin structure and spin part of the chemical potential is
determined by the renormalized interaction, being defined by the contribution
of the virtual large momenta. The ferromagnetic structure of the ground state,
and the equation of the phase, density, and spin dynamics are obtained from
Gross-Pitaevskii equations.",2101.03744v2
2017-11-07,Rebuilding of destroyed spin squeezing in noisy environments,"We investigate the process of spin squeezing in a ferromagnetic dipolar
spin-1 Bose-Einstein condensate under the driven oneaxis twisting scheme, with
emphasis on the detrimental effect of noisy environments (stray magnetic
fields) which completely destroy the spin squeezing. By applying concatenated
dynamical decoupling pulse sequences with a moderate bias magnetic field to
suppress the effect of the noisy environments, we faithfully reconstruct the
spin squeezing process under realistic experimental conditions. Our
noise-resistant method is ready to be employed to generate the spin squeezed
state in a dipolar spin-1 Bose-Einstein condensate and paves a feasible way to
the Heisenberg-limit quantum metrology",1711.02299v1
2018-03-26,Spin subdiffusion in disordered Hubbard chain,"We derive and study the effective spin model that explains the anomalous spin
dynamics in the one-dimensional Hubbard model with strong potential disorder.
Assuming that charges are localized, we show that spins are delocalized and
their subdiffusive transport originates from a singular random distribution of
spin exchange interactions. The exponent relevant for the subdiffusion is
determined by the Anderson localization length and the density of electrons.
While the analytical derivations are valid for low particle density, numerical
results for the full model reveal a qualitative agreement up to half-filling.",1803.09667v1
2018-08-17,Emergent units of itinerant spin-state excitations in LaCoO$_3$,"Spin crossover is expected to enrich unusual physical states in various types
of condensed matter. Through inelastic neutron scattering, we study the
spin-state excitations in the canonical and advanced platform, LaCoO$_3$, and
reveal that the spatial correlation robustly maintains the seven-Co-site size
below 300 K and the internal Co-$d$ electrons are spatially delocalized. By
combining theoretical calculations, this dynamical short-range order is
identified as a new collective unit for describing spin-state with dual
spin-state nature beyond the conventional one-Co-site classification.",1808.05888v1
2018-12-05,Classical spin simulations with a quantum two-spin correction,"Classical simulations of high-temperature nuclear spin dynamics in solids are
known to accurately predict relaxation for spin 1/2 lattices with a large
number of interacting neighbors. Once the number of interacting neighbors
becomes four or smaller, classical simulations lead to noticeable
discrepancies. Here we attempt to improve the performance of the classical
simulations by adding a term representing two-spin quantum correlations. The
method is tested for a spin-1/2 chain. It exhibits good performance at shorter
times, but, at longer times, it is hampered by a singular behavior of the
resulting equations of motion.",1812.02155v1
2019-01-23,Coupled dynamics of magnetizations in spin-Hall oscillators via spin current injection,"An array of spin torque oscillators (STOs) for practical applications such as
pattern recognition was recently proposed, where several STOs are connected by
a common nonmagnet. In this structure, in addition to the electric and/or
magnetic interactions proposed in previous works, the STOs are spontaneously
coupled to each other through the nonmagnetic connector, due to the injection
of spin current. Solving the Landau-Lifshitz-Gilbert equation numerically for
such system consisting of three STOs driven by the spin Hall effect, it is
found that both in-phase and antiphase synchronization of the STOs can be
achieved by adjusting the current density and appropriate distance between the
oscillators.",1901.07669v1
2019-03-17,Sensing Kondo correlations in a suspended carbon nanotube mechanical resonator with spin-orbit coupling,"We study electron mechanical coupling in a suspended carbon nanotube (CNT)
quantum dot device. Electron spin couples to the flexural vibration mode due to
spin-orbit coupling in the electron tunneling processes. In the weak coupling
limit, i.e. electron-vibration coupling is much smaller than the electron
energy scale, the damping and resonant frequency shift of the CNT resonator can
be obtained by calculating the dynamical spin susceptibility. We find that
strong spin-flip scattering processes in Kondo regime significantly affect the
mechanical motion of the carbon nanotube: Kondo effect induces strong damping
and frequency shift of the CNT resonator.",1903.07049v1
2019-03-30,Background noise pushes azimuthal instabilities away from spinning states,"Azimuthal instabilities occur in rotationally symmetric systems, either as
spinning (rotating) waves or standing waves. We make use of a novel ansatz to
derive a differential equation characterizing the state of these instabilities
in terms of their amplitude, orientation, nature (standing/spinning) and
temporal phase. For the first time we show how source terms determine
quantitatively the system preference for spinning and/or standing states. In
particular we find that, when present, background noise pushes the system away
from spinning states and towards standing states, consistently with
experiments.",1904.00213v1
2019-08-21,Artificial Spin Ice Phase-Change Memory Resistors,"We study the implications of the anisotropic magnetic resistance on permalloy
nanowires, and in particular on the property of the resistance depending on the
type of lattice. We discuss how the internal spin configuration of artificial
spin ice nanowires can affect their effective resistive state, and which
mechanisms can introduce a current-dependent effect dynamic resistive state. We
discuss a spin-induced thermal phase-change mechanism, and an athermal
domain-wall spin inversion. In both cases we observe memory behavior
reminiscent of a memristor, with an I-V hysteretic pinched behavior.",1908.08073v1
2020-05-11,Effect of the spin-orbit interaction on thermodynamic properties of liquid uranium,"We present the first quantum molecular dynamics calculation of zero-pressure
isobar of solid and liquid uranium that account for spin-orbit coupling. We
demonstrate that inclusion of spin-orbit interaction leads to higher degree of
the thermal expansion of uranium, especially in the liquid phase. Full
accounting of relativistic effects for valence electrons, particularly
spin-orbital splitting of the 5f band, is substantial for the reproduction of
the experimental density of molten uranium at the melting temperature.
Influence of the spin-orbit interaction on the thermodynamic properties at high
temperatures and pressures is also analyzed.",2005.05468v1
2020-05-25,Multiple Spin-Phonon Relaxation Pathways in a Kramer Single-Ion Magnet,"We present a first-principles investigation of spin-phonon relaxation in a
molecular crystal of Co(II) single-ion magnets. Our study combines electronic
structure calculations with machine-learning force fields and unravels the
nature of both the Orbach and the Raman relaxation channels in terms of
atomistic processes. We find that although both mechanisms are mediated by the
excited spin states, the low temperature spin dynamics is dominated by phonons
in the THz energy range, which partially suppress the benefit of having a large
magnetic anisotropy. This study also determines the importance of
intra-molecular motions for both the relaxation mechanisms and paves the way to
the rational design of a new generation of single-ion magnets with tailored
spin-phonon coupling.",2005.12429v1
2020-06-26,Quantum walk on a graph of spins: magnetism and entanglement,"We introduce a model of a quantum walk on a graph in which a particle jumps
between neighboring nodes and interacts with independent spins sitting on the
edges. Entanglement propagates with the walker. We apply this model to the case
of a one dimensional lattice, to investigate its magnetic and entanglement
properties. In the continuum limit, we recover a Landau-Lifshitz equation that
describes the precession of spins. A rich dynamics is observed, with regimes of
particle propagation and localization, together with spin oscillations and
relaxation. Entanglement of the asymptotic states follows a volume law for most
parameters (the coin rotation angle and the particle-spin coupling).",2006.14883v1
2020-08-19,Loop spin effects in intense background fields,"Radiative and non-radiative electron spin flip probabilities are analysed in
both plane wave and focussed laser backgrounds. We provide a simple and
physically transparent description of spin dynamics in plane waves, and
demonstrate that there exists a kinematic regime in which the usual leading
order perturbative hierarchy of QED is reversed, and non-radiative loop effects
dominate over radiative tree-level spin-flips. We show that while this
loop-dominance becomes suppressed in focussed laser pulses due to a high
sensitivity to field geometry, there is nevertheless a regime in which, in
principle, loop effects on spin transitions can be discerned.",2008.08578v1
2021-02-24,Spin texture in a bilayer high-temperature cuprate superconductor,"We investigate the possibility of spin texture in the bilayer cuprate
superconductor $\rm Bi_2Sr_2CaCu_2O_{8+\delta}$ using cluster dynamical mean
field theory (CDMFT). The one-band Hubbard model with a small interlayer
hopping and a Rashba spin-orbit coupling is used to describe the material. The
$d$-wave order parameter is not much affected by the presence of the Rashba
coupling, but a small triplet component appears. We find a spin texture
circulating in the same direction around $\mathbf{k}=(0,0)$ and
$\mathbf{k}=(\pi,\pi)$ and stable against the superconducting phase. The
amplitude of the spin structure, however, is strongly affected by the pseudogap
phenomenon, more so than the spectral function itself.",2102.12015v1
2021-04-01,Speedup of nuclear-spin diffusion in hyperpolarized solids,"We propose a correction to the coefficient of nuclear-spin diffusion by a
factor $1/\sqrt{1-\overline{p}^{2}}$, where $\overline{p}$ is the average
nuclear-spin polarization. The correction, derived by extending the Lowe-Gade
theory to low-temperature cases, implies that transportation of nuclear
magnetization through nuclear-spin diffusion accelerates when the system is
hyperpolarized, whereas for low-polarization the correction factor approaches
unity and the diffusion coefficient coincides with the conventional diffusion
coefficient valid in the high-temperature limit. The proposed scaling of the
nuclear-spin diffusion coefficient can lead to observable effects in the
buildup of nuclear polarization by dynamic nuclear polarization.",2104.00256v1
2021-04-27,Vector resonances spin alignement as a probe of spin hydrodynamics and freeze-out,"We argue that a detailed analysis of the spin alignement of vector mesons can
serve as a probe of two little-understood aspects of spin dynamics in the
vortical fluid: The degree of relaxation between vorticity and parton spin
polarization, and the degree of coherence of the hadron wavefunction at
freeze-out.
  We illustrate these with a coalescence model.",2104.12941v4
2021-06-03,Magnon spin transport around the compensation magnetic field in easy-plane antiferromagnetic insulators,"In this work, we theoretically study the magnon spin transport in easy-plane
antiferromagnetic insulators in the presence of an in-plane magnetic field. By
exactly calculating the magnon spectrum, we find the band splitting due to the
magnetic anisotropy can be fully compensated by the external field at a
particular strength, which makes its dynamics nearly equivalent to an easy-axis
antiferromagnet. As a result, the intrinsic magnon spin Hall effect due to the
dipole-dipole interaction, previously predicted in easy-axis antiferromagnets
is activated in easy-plane antiferromagnets. The compensation feature also
allows the field control of magnon spin lifetime and hence the spin diffusion
length. The compensation feature is robust against the biaxial anisotropy.",2106.02178v1
2021-07-25,Ancilla assisted Discrete Time Crystals in Non-interacting Spin Systems,"We show here through experiments and exact analytical models the emergence of
discrete time translation symmetry breaking in non-interacting systems. These
time-periodic structures become stable against perturbations only in the
presence of their interaction with the ancillary quantum system and display
subharmonic response over a range of rotation angle errors. We demonstrate this
effect for central spin and spin-mechanical systems, where the ancillary
induced interaction among the spins stabilizes the spin dynamics against finite
errors. Further, we extend these studies and show the possibility to even
achieve non-local (remote) synchronization of such Floquet crystals.",2107.11748v1
2022-07-05,An Algebraic Theory of Non-Relativistic Spin,"In this paper we present a new, elementary derivation of non-relativistic
spin using exclusively real algebraic methods. To do this, we formulate a novel
method to decompose the domain of a real endomorphism according to its
algebraic properties. We reveal non-commutative multipole tensors as the
primary physically meaningful observables of spin, and indicate that spin is
fundamentally geometric in nature. In so doing, we demonstrate that neither
dynamics nor complex numbers are essential to the fundamental description of
spin.",2207.02351v2
2023-06-07,Tunable superdiffusion in integrable spin chains using correlated initial states,"Although integrable spin chains only host ballistically propagating particles
they can still feature diffusive spin transport. This diffusive spin transport
originates from quasiparticle charge fluctuations inherited from the initial
state's magnetization Gaussian fluctuations. We show that ensembles of initial
states with quasi-long range correlations lead to superdiffusive spin transport
with a tunable dynamical exponent. We substantiate our prediction with
numerical simulations and explain how deviations arise from finite time and
finite size effects.",2306.04682v1
2023-12-15,Observables from the Spinning Eikonal,"We study the classical dynamics of spinning particles using scattering
amplitudes and eikonal exponentiation. We show that observables are determined
by a simple algorithm. A wealth of complexity arises in perturbation theory as
positions, momenta and spins must be iteratively corrected at each order. Even
though we restrict ourselves to one-loop computations at quadratic order in
spin, nevertheless we encounter and resolve a number of subtle effects.
Finally, we clarify the links between our work and various other eikonal
approaches to spinning observables.",2312.09960v1
2024-01-16,Classical 'spin' filtering with two degrees of freedom and dissipation,"Coupling of angular motion to a spin degree of freedom gives rise to various
transport phenomena in quantum systems that are beyond the standard paradigms
of classical physics. Here, we discuss features of spin-orbit dynamics that can
be visualized using a classical model with two coupled angular degrees of
freedom. Specifically, we demonstrate classical 'spin' filtering through our
model and show that the interplay between angular degrees of freedom and
dissipation can lead to asymmetric 'spin' transport.",2401.08454v1
2024-01-18,"Editorial note to Jean-Marie Souriau's "" On the motion of spinning particles in general relativity""","The gravitational interaction of (classical and quantum) spinning bodies is
currently the focus of many works using a variety of approaches. This note is a
comment on a short paper by Jean-Marie Souriau, now reprinted in the GRG Golden
Oldies collection. Souriau's short 1970 note was a pioneering contribution to a
symplectic description of the dynamics of spinning particles in general
relativity which remained somewhat unnoticed. We explain the specificity of
Souriau's approach and emphasize its potential interest within the current
flurry of activity on the gravitational interaction of spinning particles.",2401.10013v1
2024-02-26,Onsager Relations between Spin Currents and Charge Currents,"We consider the macroscopic dynamics of systems with charge and spin
currents, using the methods of Onsager's irreversible thermodynamics. Applied
to systems with spin-orbit interaction (SOI), we derive Onsager relations
showing that, if electrical disequilibrium leads to spin currents, then
magnetic disequilibrium leads to charge currents. We consider three examples of
such SOI. Two of these predicted charge currents have not previously appeared.
By measuring these charge currents one can infer the corresponding spin
currents.",2402.16233v1
2012-02-21,Nuclear spin physics in quantum dots: an optical investigation,"The mesoscopic spin system formed by the 10E4-10E6 nuclear spins in a
semiconductor quantum dot offers a unique setting for the study of many-body
spin physics in the condensed matter. The dynamics of this system and its
coupling to electron spins is fundamentally different from its bulk
counter-part as well as that of atoms due to increased fluctuations that result
from reduced dimensions. In recent years, the interest in studying quantum dot
nuclear spin systems and their coupling to confined electron spins has been
fueled by its direct implication for possible applications of such systems in
quantum information processing as well as by the fascinating nonlinear
(quantum-)dynamics of the coupled electron-nuclear spin system. In this
article, we review experimental work performed over the last decades in
studying this mesoscopic,coupled electron-nuclear spin system and discuss how
optical addressing of electron spins can be exploited to manipulate and
read-out quantum dot nuclei. We discuss how such techniques have been applied
in quantum dots to efficiently establish a non-zero mean nuclear spin
polarization and, most recently, were used to reduce fluctuations of the
average quantum dot nuclear spin orientation. Both results in turn have
important implications for the preservation of electron spin coherence in
quantum dots, which we discuss. We conclude by speculating how this recently
gained understanding of the quantum dot nuclear spin system could in the future
enable experimental observation of quantum-mechanical signatures or possible
collective behavior of mesoscopic nuclear spin ensembles.",1202.4637v2
1999-07-06,Model glasses coupled to two different heat baths,"In a $p$-spin interaction spherical spin-glass model both the spins and the
couplings are allowed to change in the course of time. The spins are coupled to
a heat bath with temperature $T$, while the coupling constants are coupled to a
bath having temperature $T_{J}$. In an adiabatic limit (where relaxation time
of the couplings is much larger that of the spins) we construct a generalized
two-temperature thermodynamics. It involves entropies of the spins and the
coupling constants. The application for spin-glass systems leads to a standard
replica theory with a non-vanishing number of replicas, $n=T/T_J$. For $p>2$
there occur at low temperatures two different glassy phases, depending on the
value of $n$. The obtained first-order transitions have positive latent heat,
and positive discontinuity of the total entropy. This is the essentially
non-equilibrium effect. The predictions of longtime dynamics and infinite-time
statics differ only for $n<1$ and $p>2$. For $p=2$ correlation of the disorder
(leading to a non-zero $n$) removes the known marginal stability of the spin
glass phase. If the observation time is very large there occurs no
finite-temperature spin glass phase. In this case there are analogies with the
broken-ergodicity dynamics in the usual spin-glass models and non-equilibrium
(aging) dynamics. A generalized fluctuation-dissipation relation is derived.",9907090v1
2000-01-07,Theory of the spin bath,"The quantum dynamics of mesoscopic or macroscopic systems is always
complicated by their coupling to many ""environmental"" modes.At low T these
environmental effects are dominated by localised modes, such as nuclear and
paramagnetic spins, and defects (which also dominate the entropy and specific
heat). This environment, at low energies, maps onto a ""spin bath"" model. This
contrasts with ""oscillator bath"" models (originated by Feynman and Vernon)
which describe {\it delocalised} environmental modes such as electrons,
phonons, photons, magnons, etc. One cannot in general map a spin bath to an
oscillator bath (or vice-versa); they constitute distinct ""universality
classes"" of quantum environment. We show how the mapping to spin bath models is
made, and then discuss several examples in detail, including moving particles,
magnetic solitons, nanomagnets, and SQUIDs, coupled to nuclear and paramagnetic
spin environments. We show how to average over spin bath modes, using an
operator instanton technique, to find the system dynamics, and give analytic
results for the correlation functions, under various conditions. We then
describe the application of this theory to magnetic and superconducting
systems.Particular attention is given to recent work on tunneling magnetic
macromolecules, where the role of the nuclear spin bath in controlling the
tunneling is very clear; we also discuss other magnetic systems in the quantum
regime, and the influence of nuclear and paramagnetic spins on flux dynamics in
SQUIDs.",0001080v2
2006-10-18,Frustrated impurity spins in ordered two-dimensional quantum antiferromagnets,"Dynamical properties of an impurity spin coupled symmetrically to sublattices
of ordered 2D Heisenberg quantum antiferromagnet (i.e., frustrated impurity
spin) are discussed at $T\ge0$ (existence of a small interaction stabilizing
the long range order at $T\ne0$ is implied). We continue our study on this
subject started in Phys.Rev.B 72, 174419 (2005), where spin-1/2 defect is
discussed and the host spins fluctuations are considered within the spin-wave
approximation (SWA). In the present paper we i) go beyond SWA and ii) study
impurities with spins $S\ge1/2$. It is demonstrated that in contrast to defects
coupled to sublattices asymmetrically longitudinal host spins fluctuations play
important role in the frustrated impurity dynamics. The spectral function, that
is proportional to $\omega^2$ within SWA, acquires new terms proportional to
$\omega^2$ and $\omega T^2$. It is observed that the spin-1/2 impurity
susceptibility has the same structure as that obtained within SWA: the Lorenz
peak and the non-resonant term. The difference is that the width of the peak
becomes larger being proportional to $f^2(T/J)^3$ rather than $f^4(T/J)^3$,
where $f$ is the dimensionless coupling parameter. We show that transverse
static susceptibility acquires a new negative logarithmic contribution. In
accordance with previous works we find that host spins fluctuations lead to an
effective one-ion anisotropy on the impurity site. Then defects with $S>1/2$
appears to be split. We observe strong reduction of the value of the splitting
due to longitudinal host spins fluctuations. We demonstrate that the dynamical
impurity susceptibility contains $2S$ Lorenz peaks corresponding to transitions
between the levels, and the non-resonant term.",0610506v1
2006-12-04,Non-Markovian reduced dynamics and entanglement evolution of two coupled spins in a quantum spin environment,"The exact quantum dynamics of the reduced density matrix of two coupled spin
qubits in a quantum Heisenberg XY spin star environment in the thermodynamic
limit at arbitrarily finite temperatures is obtained using a novel operator
technique. In this approach, the transformed Hamiltonian becomes effectively
Jaynes-Cumming like and thus the analysis is also relevant to cavity quantum
electrodynamics. This special operator technique is mathematically simple and
physically clear, and allows us to treat systems and environments that could
all be strongly coupled mutually and internally. To study their entanglement
evolution, the concurrence of the reduced density matrix of the two coupled
central spins is also obtained exactly. It is shown that the dynamics of the
entanglement depends on the initial state of the system and the coupling
strength between the two coupled central spins, the thermal temperature of the
spin environment and the interaction between the constituents of the spin
environment. We also investigate the effect of detuning which in our model can
be controlled by the strength of a locally applied external magnetic field. It
is found that the detuning has a significant effect on the entanglement
generation between the two spin qubits.",0612049v1
2007-03-23,Semiclassical dynamics and long time asymptotics of the central-spin problem in a quantum dot,"The spin of an electron trapped in a quantum dot is a promising candidate
implementation of a qubit for quantum information processing. We study the
central spin problem of the effect of the hyperfine interaction between such an
electron and a large number of nuclear moments. Using a spin coherent path
integral, we show that in this limit the electron spin evolution is well
described by classical dynamics of both the nuclear and electron spins. We then
introduce approximate yet systematic methods to analyze aspects of the
classical dynamics, and discuss the importance of the exact integrability of
the central spin Hamiltonian. This is compared with numerical simulation.
Finally, we obtain the asymptotic long time decay of the electron spin
polarization. We show that this is insensitive to integrability, and determined
instead by the transfer of angular momentum to very weakly coupled spins far
from the center of the quantum dot. The specific form of the decay is shown to
depend sensitively on the form of the electronic wavefunction.",0703631v5
2005-08-16,Transition from inspiral to plunge in precessing binaries of spinning black holes,"We investigate the non-adiabatic dynamics of spinning black hole binaries by
using an analytical Hamiltonian completed with a radiation-reaction force,
containing spin couplings, which matches the known rates of energy and angular
momentum losses on quasi-circular orbits. We consider both a straightforward
post-Newtonian-expanded Hamiltonian (including spin-dependent terms), and a
version of the resummed post-Newtonian Hamiltonian defined by the Effective
One-Body approach. We focus on the influence of spin terms onto the dynamics
and waveforms. We evaluate the energy and angular momentum released during the
final stage of inspiral and plunge. For an equal-mass binary the energy
released between 40Hz and the frequency beyond which our analytical treatment
becomes unreliable is found to be, when using the more reliable Effective
One-Body dynamics: 0.6% M for anti-aligned maximally spinning black holes, 5% M
for aligned maximally spinning black hole, and 1.8% M for non-spinning
configurations. In confirmation of previous results, we find that, for all
binaries considered, the dimensionless rotation parameter J/E^2 is always
smaller than unity at the end of the inspiral, so that a Kerr black hole can
form right after the inspiral phase. By matching a quasi-normal mode ringdown
to the last reliable stages of the plunge, we construct complete waveforms
approximately describing the gravitational wave signal emitted by the entire
process of coalescence of precessing binaries of spinning black holes.",0508067v1
2010-03-01,"Optical initialization, readout and dynamics of a Mn spin in a quantum dot","We have investigated the spin preparation efficiency by optical pumping of
individual Mn atoms embedded in CdTe/ZnTe quantum dots. Monitoring the time
dependence of the intensity of the fluorescence during the resonant optical
pumping process in individual quantum dots allows to directly probe the
dynamics of the initialization of the Mn spin. This technique presents the
convenience of including preparation and read-out of the Mn spin in the same
step. Our measurements demonstrate that Mn spin initialization, at zero
magnetic field, can reach an efficiency of 75% and occurs in the tens of
\emph{ns} range when a laser resonantly drives at saturation one of the quantum
dot transition. We observe that the efficiency of optical pumping changes from
dot to dot and is affected by a magnetic field of a few tens of mT applied in
Voigt or Faraday configuration. This is attributed to the local strain
distribution at the Mn location which predominantly determines the dynamics of
the Mn spin under weak magnetic field. The spectral distribution of the
spin-flip scattered photons from quantum dots presenting a weak optical pumping
efficiency reveals a significant spin relaxation for the exciton split in the
exchange field of the Mn spin.",1003.0370v2
2011-09-29,Dynamical spin structure factors of quantum spin nematic states,"Dynamical spin structure factors of quantum spin nematic states are
calculated in a spin-1/2 square-lattice J1-J2 model with ferromagnetic J1 and
competing antiferromagnetic J2 interactions. To this end, we use a fermion
representation, generalizing it to N flavors. We begin with a spin-triplet
pairing state of fermion fields, called Z2 planar state, which is a stable
saddle-point solution in the large-N limit in a finite parameter range where
the couplings J1 and J2 compete strongly [R. Shindou and T. Momoi, Phys. Rev. B
80, 064410 (2009)]. Using a large-N expansion, we take into account
fluctuations around this saddle point up to corrections of order 1/N. The
dynamical spin structure factors thus obtained signify the existence of gapless
q-linear director-wave (spin-wave) modes at q=(0,0) and gapped `gauge-field'
like collective modes at q=(pi,pi), whose spectral weight vanishes as a linear
and quadratic function of the momentum respectively. The low-energy collective
modes contain fluctuations of nematic-director, spin, and gauge degrees of
freedom. Associated with the gapless q-linear modes, we evaluate the
temperature dependence of the nuclear spin relaxation rate 1/T1 in the
low-temperature regime as 1/T1 \propto T^{2d-1}, where d is the effective
spatial dimension.",1109.6464v3
2013-12-11,"Magnonic Band Structure, Complete Bandgap and Collective Spin Wave Excitation in Nanoscale Two--Dimensional Magnonic Crystals","We present the observation of a complete bandgap and collective spin wave
excitation in two-dimensional magnonic crystals comprised of arrays of
nanoscale antidots and nanodots, respectively. Considering that the frequencies
dealt with here fall in the microwave band, these findings can be used for the
development of suitable magnonic metamaterials and spin wave based signal
processing. We also present the application of a numerical procedure, to
compute the dispersion relations of spin waves for any high symmetry direction
in the first Brillouin zone. The results obtained from this procedure has been
reproduced and verified by the well established plane wave method for an
antidot lattice, when magnetization dynamics at antidot boundaries is pinned.
The micromagnetic simulation based method can also be used to obtain
iso--frequency countours of spin waves. Iso--frequency contours are analougous
of the Fermi surfaces and hence, they have the potential to radicalize our
understanding of spin wave dynamics. The physical origin of bands, partial and
full magnonic bandgaps has been explained by plotting the spatial distribution
of spin wave energy spectral density. Although, unfettered by rigid assumptions
and approximations, which afflict most analytical methods used in the study of
spin wave dynamics, micromagnetic simulations tend to be computationally
demanding. Thus, the observation of collective spin wave excitation in the case
of nanodot arrays, which can obviate the need to perform simulations may also
prove to be valuable.",1312.3044v1
2014-11-06,Ising-nematic order in the bilinear-biquadratic model for the iron pnictides,"Motivated by the recent inelastic neutron scattering (INS) measurements in
the iron pnictides which show a strong anisotropy of spin excitations in
directions perpendicular and parallel to the ordering wave-vector even above
the magnetic transition temperature $T_N$, we study the frustrated Heisenberg
model with a biquadratic spin-spin exchange interaction. Using the Dyson-Maleev
(DM) representation, which proves appropriate for all temperature regimes, we
find that the spin-spin dynamical structure factors are in excellent agreement
with experiment, exhibiting breaking of the $C_4$ symmetry even into the
paramagnetic region $T_N<T<T_{\sigma}$ which we refer to as the Ising-nematic
phase. In addition to the Heisenberg spin interaction, we include the
biquadratic coupling $K (\mathbf{S}_i\cdot \mathbf{S}_j)^2$ and study its
effect on the dynamical temperature range $T_{\sigma}-T_N$ of the Ising-nematic
phase. We find that this range reduces dramatically when even small values of
the interlayer exchange $J_c$ and biquadratic coupling $K$ are included. To
supplement our analysis, we benchmark the results obtained using the DM method
against those from different non-linear spin-wave theories, including the
recently developed generalized spin-wave theory (GSWT), and find good
qualitative agreement among the different theoretical approaches as well as
experiment for both the spin-wave dispersions and the dynamical structure
factors.",1411.1462v2
2015-03-02,Spin-glass-like freezing of inner and outer surface layers in hollow γFe$_2$O$_3$ nanoparticles,"Disorder among surface spins largely dominates the magnetic response of
ultrafine magnetic particle systems. In this work, we examine time-dependent
magnetization in high-quality, monodisperse hollow maghemite nanoparticles with
a 14.8 $\pm$ 0.5 nm outer diameter and enhanced surface-to-volume ratio. The
nanoparticle ensemble exhibits spin-glass-like signatures in dc magnetic aging
and memory protocols and ac magnetic susceptibility. The dynamics of the system
slows near 50 K, and becomes frozen on experimental time scales below 20 K.
Remanence curves indicate the development of magnetic irreversibility
concurrent with the freezing of the spin dynamics. A strong exchange-bias
effect and its training behavior point to highly frustrated surface spins that
rearrange much more slowly than interior spins with bulk coordination. Monte
Carlo simulations of a hollow particle reproducing the experimental morphology
corroborated strongly disordered surface layers with complex energy landscapes
that underlie both glass-like dynamics and magnetic irreversibility. Calculated
hysteresis loops reveal that magnetic behavior is not identical at the inner
and outer surfaces, with spins at the outer surface layer of the 15 nm hollow
particles exhibiting a higher degree of frustration. Our study sheds light on
the origin of spin-glass-like phenomena and the role of surface spins in
magnetic hollow nanostructures.",1503.00602v2
2019-05-13,Dynamic spin localization and gamma-magnets,"We explore an unusual type of quantum matter that can be realized by qubits
having different physical origin. Interactions in this matter are described by
essentially different coupling operators for all qubits. We show that at least
the simplest such models, which can be realized with localized states in Dirac
materials, satisfy integrability conditions that we use to describe pseudospin
dynamics in a linearly time-dependent magnetic field. Generalizing to an
arbitrary number of qubits, we construct a spin Hamiltonian, which we call the
gamma-magnet. This system does not conserve polarization of any spin and the
net spin polarization. Nevertheless, for arbitrarily strong interactions,
nonadiabatic dynamics, and any initial eigenstate, we find that quantum
interference suppresses spin-flips. This behavior resembles many-body
localization but occurs in phase space of many spins rather than real space.
This effect may not have a counterpart in classical physics and can be a
signature of a new type of spin ordering, which is different from both
disordered spin glasses and ordered phases of spin lattices.",1905.05287v4
2019-04-18,Two-electron-spin ratchets as a platform for microwave-free dynamic nuclear polarization of arbitrary material targets,"Optically-pumped color centers in semiconductor powders can potentially
induce high levels of nuclear spin polarization in surrounding solids or fluids
at or near ambient conditions, but complications stemming from the random
orientation of the particles and the presence of unpolarized paramagnetic
defects hinder the flow of polarization beyond the defect's host material.
Here, we theoretically study the spin dynamics of interacting nitrogen-vacancy
(NV) and substitutional nitrogen (P1) centers in diamond to show that outside
protons spin-polarize efficiently upon a magnetic field sweep across the NV-P1
level anti-crossing. The process can be interpreted in terms of an NV-P1 spin
ratchet, whose handedness - and hence the sign of the resulting nuclear
polarization - depends on the relative timing of the optical excitation pulse.
Further, we find that the polarization transfer mechanism is robust to NV
misalignment relative to the external magnetic field, and efficient over a
broad range of electron-electron and electron-nuclear spin couplings, even if
proxy spins feature short coherence or spin-lattice relaxation times.
Therefore, these results pave the route towards the dynamic nuclear
polarization of arbitrary spin targets brought in proximity with a diamond
powder under ambient conditions.",1904.08563v1
2020-10-19,The spin-spin model and the capture into the double synchronous resonance,"The aim of this article is to propose a model, that is a planar version of
the Full Two-Body Problem, and discuss the existence and stability of a
relevant periodic solution. Consider two homogeneous ellipsoids orbiting around
each other in fixed coplanar Keplerian orbits. Moreover, their respective spin
axes are assumed to be perpendicular to the orbital plane, that is also a
common equatorial plane. The spin-spin model deals with the coupled rotational
dynamics of both ellipsoids. For a non-zero orbital eccentricity, it has the
structure of a non-autonomous system of coupled pendula. This model is a
natural extension of the classical spin-orbit problem for two extended bodies.
In addition, we consider dissipative tidal torques, that can trigger the
capture of the system into spin-orbit and spin-spin resonances. In this paper
we give some theoretical results for both the conservative model and the
dissipative one. The conservative model has a Hamiltonian structure. We use
properties of Hamiltonian systems to give some sufficient conditions in the
space of parameters of the model, that guarantee existence, uniqueness and
linear stability of an odd periodic solution. This solution represents a double
synchronous resonance in the conservative regime. Such solution can be
continued to the dissipative regime, where it becomes asymptotically stable. We
see asymptotic stability as a dynamical mechanism for the capture into the
double synchronous resonance. Finally we apply our results to several cases
including the Pluto-Charon binary system and the Trojan binary asteroid 617
Patroclus, target of the LUCY mission.",2010.09354v1
2023-01-18,Emergence of field-induced memory effect in spin ices,"Out-of-equilibrium investigation of strongly correlated materials deciphers
the hidden equilibrium properties. Herein, we have investigated the
out-of-equilibrium magnetic properties of polycrystalline Dy2Ti2O7 and Ho2Ti2O7
spin ices. The experimental results show the emergence of magnetic
field-induced anomalous hysteresis observed only in temperature/magnetic
field-dependent ac susceptibility measurements. The observed memory effect
(anomalous thermomagnetic hysteresis) strongly depends on the driving thermal
and non-thermal variables. Contrary, in the absence of the magnetic field,
dipolar interaction induced Ising paramagnetic to spin ice crossover develops a
liquid-gas transition type hysteresis below 4 K. Unlike field-induced
hysteresis, it shows weak dependency on thermal and non-thermal variables. Due
to the non-colinear spin structure, the applied dc bias magnetic field produces
quench disorder sites in the cooperative Ising spin matrix and suppresses the
spin-phonon coupling. These quench disorders create dynamic spin correlations
governed by quantum fluctuations, having slow spin relaxation and quick decay
times, which additionally contribute to ac susceptibility. The initial
conditions and measurement protocol decide the magnitude and sign of this
dynamical term contributing to ac susceptibility. It has been suggested that
such kind of out-of-equilibrium properties emerge by the cumulative effect of
geometric frustration, disorder, quantum fluctuations, and the cooperative
nature of spin dynamics of these materials.",2301.07741v1
2023-11-09,Lagrangian dynamics and regularity of the spin Euler equation,"We derive the spin Euler equation for ideal flows by applying the spherical
Clebsch mapping. This equation is based on the spin vector rather than the
velocity. It enables a feasible Lagrangian study of fluid dynamics, as the
isosurface of a spin-vector component is a vortex surface and material surface
in ideal flows. The spin Euler equation is also equivalent to a special case of
the Landau-Lifshitz equation with a specific effective magnetic field,
revealing a possible connection between ideal flow and magnetic crystal. We
conduct direct numerical simulations of three ideal flows of the vortex knot,
vortex link and modified Taylor-Green flow by solving the spin Euler equation.
The evolution of the Lagrangian vortex surface illustrates that the regions
with large vorticity are rapidly stretched into spiral sheets. We establish a
non-blowup criterion for the spin Euler equation, suggesting that the Laplacian
of the spin vector must diverge if the solution forms a singularity at some
finite time. The DNS result exhibits a pronounced double-exponential growth of
the maximum norm of Laplacian of the spin vector, showing no evidence of the
finite-time singularity formation if the double-exponential growth holds at
later times. Moreover, the present criterion with Lagrangian nature appears to
be more sensitive than the Beale-Kato-Majda criterion in detecting the flows
that are incapable of producing finite-time singularities.",2311.05149v1
2001-07-24,The Potts frustrated model: relations with glasses,"Similarities between fragile glasses and spin glasses (SG) suggest the study
of frustrated spin model to understand the complex dynamics of glasses above
the glass transition. We consider a frustrated spin model with Ising spins and
s-state Potts spins both with and without disorder. We study the two models by
Monte Carlo simulations in two dimensions. The Potts spins mimic orientational
degrees of freedom and the coupled frustrated Ising spins take into account for
frustrating effects like the geometrical hindrance. We show that in this model
dynamical transitions and crossovers are related to static transitions. In
particular, when disorder is present, as predicted and verified in SG, a
dynamical transition between high-temperatures exponential to low-temperatures
non-exponential correlation functions numerically coincides with the ordering
temperature of the ferromagnetic regions, i.e. the Griffiths temperature
$T_c(s)$, while a crossover between power law growth of correlation times to
Arrhenius law occurs near a Potts transition at $T_p(s)<T_c(s)$. In the model
without disorder, where $T_c(s)$ is not defined, both dynamical transition and
crossover occur at $T_p(s)$. Furthermore the static susceptibility and the
autocorrelation times of quantities depending on Potts spins diverge at
$T_p(s)$. This is reminescent of recent experimental results on glass-forming
liquids.",0107490v1
2001-03-07,Coalescence of Two Spinning Black Holes: An Effective One-Body Approach,"We generalize to the case of spinning black holes a recently introduced
``effective one-body'' approach to the general relativistic dynamics of binary
systems. The combination of the effective one-body approach, and of a Pad\'e
definition of some crucial effective radial functions, is shown to define a
dynamics with much improved post-Newtonian convergence properties, even for
black hole separations of the order of $6 GM / c^2$. We discuss the approximate
existence of a two-parameter family of ``spherical orbits'' (with constant
radius), and, of a corresponding one-parameter family of ``last stable
spherical orbits'' (LSSO). These orbits are of special interest for forthcoming
LIGO/VIRGO/GEO gravitational wave observations. It is argued that for most (but
not all) of the parameter space of two spinning holes the effective one-body
approach gives a reliable analytical tool for describing the dynamics of the
last orbits before coalescence. This tool predicts, in a quantitative way, how
certain spin orientations increase the binding energy of the LSSO. This leads
to a detection bias, in LIGO/VIRGO/GEO observations, favouring spinning black
hole systems, and makes it urgent to complete the conservative effective
one-body dynamics given here by adding (resummed) radiation reaction effects,
and by constructing gravitational waveform templates that include spin effects.
Finally, our approach predicts that the spin of the final hole formed by the
coalescence of two arbitrarily spinning holes never approaches extremality.",0103018v2
2001-09-06,Dynamics of the spinning particle in one dimension,"The most general N=1 Lagrangian for the spinning particle with local
supersymmetry is found and the constraints of the system are analysed. The
Dirac quantisation of the model is also investigated.",0109052v2
2002-05-08,Spin Processor,"It is experimentally demonstrated that with multi-frequency excitation of
weak amplitude the dynamics of a cluster of dipolar-coupled spins can be
manipulated to perform parallel logic operations with long bit arrays.",0205040v1
2009-02-18,Quantum many-body theory of qubit decoherence in a finite-size spin bath. II. Ensemble dynamics,"Decoherence of a center spin or qubit in a spin bath is essentially
determined by the many-body bath evolution. The bath dynamics can start either
from a pure state or, more generally, from a statistical ensemble. In the
preceding article [W. Yang and R. B. Liu, Phys. Rev. B \textbf{78}, 085315
(2008)], we have developed the cluster-correlation expansion (CCE) theory for
the so-called single-sample bath dynamics initiated from a factorizable pure
state. Here we present the ensemble CCE theory, which is based on similar ideas
of the single-sample CCE: The bath evolution is factorized into the product of
all possible cluster correlations, each of which accounts for the authentic
(non-factorizable) collective excitation of a group of bath spins, and for the
finite-time evolution in the qubit decoherence problem, convergent results can
be obtained by truncating the ensemble CCE by keeping cluster correlations up
to a certain size. A difference between the ensemble CCE and single-sample CCE
is that the mean-field treatment in the latter formalism of the diagonal part
of the spin-spin interaction in the bath is not possible in the former case.
The ensemble CCE can be applied to non-factorizable initial states. The
ensemble CCE is checked against the exact solution of an XY spin bath model.
For small spin baths, it is shown that single-sample dynamics is sensitive to
the sampling of the initial state from a thermal ensemble and hence very
different from the ensemble average.",0902.3055v1
2010-03-21,Conserving optical currents: angular momentum and spin,"Within the first quantisation of Maxwell's equations, we introduce the
dynamic energy, linear momentum, angular momentum and optical spin of the
electromagnetic fields. We show that these different quantities are conserved
during the propagation of light in vacuum and are additive only for eigenmodes
of the electromagnetic field.",1003.4019v1
2015-07-06,NMR spin-lattice relaxation in molecular rotor systems,"A general expression is derived for the dipolar NMR spin-lattice relaxation
rate $1/T_1$ of a system exhibiting Brownian dynamics in a discrete and finite
configuration space. It is shown that this approach can be particularly useful
to model the proton relaxation rate in molecular rotors.",1507.01419v1
2015-09-21,Isotropic and Anisotropic Regimes of the Field-Dependent Spin Dynamics in Sr2IrO4: Raman Scattering Studies,"A major focus of experimental interest in Sr2IrO4 has been to clarify how the
magnetic excitations of this strongly spin-orbit coupled system differ from the
predictions of anisotropic 2D spin-1/2 Heisenberg model and to explore the
extent to which strong spin-orbit coupling affects the magnetic properties of
iridates. Here, we present a high-resolution inelastic light (Raman) scattering
study of the low energy magnetic excitation spectrum of Sr2IrO4 and doped
Eu-doped Sr2IrO4 as functions of both temperature and applied magnetic field.
We show that the high-field (H>1.5 T) in-plane spin dynamics of Sr2IrO4 are
isotropic and governed by the interplay between the applied field and the small
in-plane ferromagnetic spin components induced by the Dzyaloshinskii-Moriya
interaction. However, the spin dynamics of Sr2IrO4 at lower fields (H<1.5 T)
exhibit important effects associated with interlayer coupling and in-plane
anisotropy, including a spin-flop transition at Hc in Sr2IrO4 that occurs
either discontinuously or via a continuous rotation of the spins, depending
upon the in-plane orientation of the applied field. These results show that
in-plane anisotropy and interlayer coupling effects play important roles in the
low-field magnetic and dynamical properties of Sr2IrO4.",1509.06409v1
2019-09-26,Dependence of persistence exponent on initial state,"We examine persistence in one dimensional Ising model under zero temperature
Glauber dynamics for random initial states with unequal fraction of up and down
spins. We find the persistence exponent varies continuously with the fraction
of up spins in the initial state. Apparently this feature has been overlooked
in the studies so far.",1909.13677v1
2017-05-02,Slow spin tunneling in the paramagnetic phase of the pyrochlore Nd2Sn2O7,"The insulating pyrochlore compound Nd2Sn2O7 has been shown to undergo a
second order magnetic phase transition at Tc ~ 0.91 K to a noncoplanar
all-in--all-out magnetic structure of the Nd3+ magnetic moments. An anomalously
slow paramagnetic spin dynamics has been evidenced from neutron backscattering
and muon spin relaxation (muSR). In the case of muSR this has been revealed
through the strong effect of a 50 mT longitudinal field on the spin-lattice
relaxation rate. Here, motivated by a recent successful work performed for
Yb2Ti2O7 and Yb2Sn2O7, analyzing the shape of the muSR longitudinal
polarization function, we substantiate the existence of extremely slow
paramagnetic spin dynamics in the microsecond time range for Nd2Sn2O7. Between
1.7 and 7 K, this time scale is temperature independent. This suggests a double
spin-flip tunneling relaxation mechanism to be at play, probably involving spin
substructures such as tetrahedra. Unexpectedly, the standard deviation of the
field distribution at the muon site increases as the system is cooled. This
exotic spin dynamics is in sharp contrast with the dynamics above 100 K which
is driven by the Orbach relaxation mechanism involving single Nd3+ magnetic
moments.",1705.01004v1
2017-09-11,Identifying and decoupling many-body interactions in spin ensembles in diamond,"We simulate the dynamics of varying density quasi-two-dimensional spin
ensembles in solid-state systems, focusing on the nitrogen-vacancy centers in
diamond. We consider the effects of various control sequences on the averaged
dynamics of large ensembles of spins, under a realistic ""spin-bath""
environment. We reveal that spin locking is efficient for decoupling spins
initialized along the driving axis, both from coherent dipolar interactions and
from the external spin-bath environment, when the driving is two orders of
magnitude stronger than the relevant coupling energies. Since the application
of standard pulsed dynamical decoupling sequences leads to strong decoupling
from the environment, while other specialized pulse sequences can decouple
coherent dipolar interactions, such sequences can be used to identify the
dominant interaction type. Moreover, a proper combination of pulsed decoupling
sequences could lead to the suppression of both interaction types, allowing
additional spin manipulations. Finally, we consider the effect of finite-width
pulses on these control protocols and identify improved decoupling efficiency
with increased pulse duration, resulting from the interplay of dephasing and
coherent dynamics.",1709.03370v5
2019-12-19,Dynamics of rotated spin states and magnetic ordering with two-component bosonic atoms in optical lattices,"The microscopic control available over cold atoms in optical lattices has
opened new opportunities to study the properties of quantum spin models. While
a lot of attention is focussed on experimentally realizing ground or thermal
states via adiabatic loading, it would often be more straightforward to prepare
specific simple product states and to probe the properties of interacting spins
by observing their dynamics. We explore this possibility for spin-1/2 and
spin-1 models that can be realized with bosons in optical lattices, and which
exhibit \textit{XY}-ferromagnetic (or counterflow spin superfluid) phases. We
consider the dynamics of initial spin-rotated states corresponding to a
mean-field version of the phases of interest. Using matrix product state
methods in one dimension, we compute both non-equilibrium dynamics and
ground/thermal states for these systems. We compare and contrast their
behaviour in terms of correlation functions and induced spin currents, which
should be directly observable with current experimental techniques. We find
that although spin correlations decay substantially at large distances and on
long timescales, for induction of spin currents, the rotated states behave
similarly to the ground states on experimentally observable timescales.",1912.10028v2
2021-09-25,Spin Multipole Expansion of the Memory Effect,"Using two-dimensional duals of soft dynamics in QED and gravity, we perform
an expansion of the respective memory effects in spin multipoles.",2109.12368v1
2022-06-08,Coherent spin dynamics of rare-earth doped crystals in the high-cooperativity regime,"Rare-earth doped crystals have long coherence times and the potential to
provide quantum interfaces between microwave and optical photons. Such
applications benefit from a high cooperativity between the spin ensemble and a
microwave cavity -- this motivates an increase in the rare earth ion
concentration which in turn impacts the spin coherence lifetime. We measure
spin dynamics of two rare-earth spin species, $^{145}$Nd and Yb doped into
Y$_{2}$SiO$_{5}$, coupled to a planar microwave resonator in the high
cooperativity regime, in the temperature range 1.2 K to 14 mK. We identify
relevant decoherence mechanisms including instantaneous diffusion arising from
resonant spins and temperature-dependent spectral diffusion from impurity
electron and nuclear spins in the environment. We explore two methods to
mitigate the effects of spectral diffusion in the Yb system in the
low-temperature limit, first, using magnetic fields of up to 1 T to suppress
impurity spin dynamics and, second, using transitions with low effective
g-factors to reduce sensitivity to such dynamics. Finally, we demonstrate how
the `clock transition' present in the $^{171}$Yb system at zero field can be
used to increase coherence times up to $T_{2} = 6(1)$ ms.",2206.04027v2
2023-12-19,Microscopic theory of current-induced skyrmion transport and its application in disordered spin textures,"Magnetic skyrmions hold great promise for realizing compact and stable memory
devices that can be manipulated at very low energy costs via electronic current
densities. In this work, we extend a recently introduced method to describe
classical skyrmion textures coupled to dynamical itinerant electrons. In this
scheme, the electron dynamics is described via nonequilibrium Green's functions
(NEGF) within the generalized Kadanoff-Baym ansatz, and the classical spins are
treated via the Landau-Lifshitz-Gilbert equation. The framework is here
extended to open systems, by the introduction of a non-interacting
approximation to the collision integral of NEGF. This, in turn, allows us to
perform computations of the real-time response of skyrmions to electronic
currents in large quantum systems coupled to electronic reservoirs, which
exhibit a linear scaling in the number of time steps. We use this approach to
investigate how electronic spin currents and dilute spin disorder affects
skyrmion transport and the skyrmion Hall drift. Our results show that the
skyrmion dynamics is sensitive to the specific form of spin disorder, such that
different disorder configurations leads to qualitatively different skyrmion
trajectories for the same applied bias. This sensitivity arises from the local
spin dynamics around the magnetic impurities, a feature that is expected not to
be well captured by phenomenological or spin-only descriptions. At the same
time, our findings illustrate the potential of engineering microscopic impurity
patterns to steer skyrmion trajectories.",2312.12201v1
2024-04-08,"The spin, expansion and contraction of open star clusters","Empirical constraints on the internal dynamics of open clusters are important
for understanding their evolution and evaporation. High precision astrometry
from Gaia DR3 are thus useful to observe aspects of the cluster dynamics. This
work aims to identify dynamically peculiar clusters such as spinning and
expanding clusters. We also quantify the spin frequency and expansion rate and
compare them with $N$-body models to identify the origins of the peculiarities.
We used the latest Gaia DR3 and archival spectroscopic surveys to analyse the
radial velocities and proper motions of the cluster members in 1379 open
clusters. A systematic analysis of synthetic clusters is performed to
demonstrate the observability of the cluster spin along with effects of
observational uncertainties. $N$-body simulations were used to understand the
evolution of cluster spin and expansion for initially non-rotating clusters. We
identified spin signatures in 10 clusters (and 16 candidates). Additionally, we
detected expansion in 18 clusters and contraction in 3 clusters. The expansion
rate is compatible with previous theoretical estimates based on expulsion of
residual gas. The orientation of the spin axis is independent of the orbital
angular momentum. The spin frequencies are much larger than what is expected
from simulated initially non-rotating clusters. This indicates that >1% of the
clusters are born rotating and/or they have undergone strong interactions.
Higher precision observations are required to increase the sample of such
dynamically peculiar clusters and to characterise them.",2404.05327v1
2003-02-20,A prime factorization based on quantum dynamics on a spin ensemble (I),"In this paper it has been described how to use the unitary dynamics of
quantum mechanics to solve the prime factorization problem on a spin ensemble
without any quantum entanglement. The ensemble quantum computation for the
prime factorization is based on the basic principle that both a closed quantum
system and its ensemble obey the same unitary dynamics of quantum mechanics if
there is not any decoherence effect in both the quantum system and its
ensemble. It uses the NMR multiple-quantum measurement techniques to output the
quantum computational results that are the inphase multiple-quantum spectra of
the spin ensemble. It has been shown that the inphase NMR multiple-quantum
spectral intensities used to search for the period of the modular exponential
function may reduce merely in a polynomial form as the qubit number of the spin
ensemble. The time evolution process of the modular exponential operation on
the quantum computer obeys the unitary dynamics of quantum mechanics and hence
the computational output is governed by the quantum dynamics. This essential
difference between the quantum computer and the classical one could be the key
point for the quantum computation outperforming the classical one in the prime
factorization on a spin ensemble without any quantum entanglement. It has been
shown that the prime factorization based on the quantum dynamics on a spin
ensemble is locally efficient at least. This supports the conjecture that the
quantum dynamics could play an important role for the origin of power of
quantum computation and quantum entanglement could not be a unique resource to
achieve power of quantum computation in the prime factorization.",0302153v1
2020-08-13,Magnetization Dynamics of Nanoscale Magnetic Materials: A Perspective,"Nanomagnets form the building blocks for a gamut of miniaturized
energy-efficient devices including data storage, memory, wave-based computing,
sensors and biomedical devices. They also offer a span of exotic phenomena and
stern challenges. The progress in the magnetization dynamics of single
nanomagnets and one- and two-dimensional arrays of nanostructures in the form
of dots, antidots, nanoparticles, binary and bicomponent structures and
patterned multilayers have been presented. Progress in unconventional and new
structures like artificial spin ice and three-dimensional nanomagnets and spin
textures like domain walls, vortex and skyrmions have been presented.
Furthermore, a huge variety of new topics in the magnetization dynamics of
magnetic nanostructures are rapidly emerging. An overview of the steadily
evolving topics like spatio-temporal imaging of fast dynamics of
nanostructures, dynamics of spin textures, artificial spin ice have been
discussed. In addition, dynamics of contemporary and newly transpired magnetic
architectures such as nanomagnet arrays with complex basis and symmetry,
magnonic quasicrystals, fractals, defect structures, novel three-dimensional
structures have been introduced. Effects of various spin-orbit coupling and
ensuing spin textures as well as quantum hybrid systems comprising of
magnon-photon, magnon-phonon and magnon-magnon coupling, antiferromagnetic
nanostructures are rapidly growing and are expected to dominate this research
field in the coming years. Finally, associated topics like nutation dynamics
and nanomagnet antenna are briefly discussed. Despite showing a great progress,
only a small fraction of nanomagnetism and its ancillary topics have been
explored so far and huge efforts are envisaged in this evergrowing research
area in the generations to come.",2008.05819v1
2022-01-26,Directly Revealing Entanglement Dynamics through Quantum Correlation Transfer Functions with Resultant Demonstration of the Mechanism of Many-Body Localization,"The fundamental link between entanglement dynamics and non-equilibrium
statistics in isolated quantum systems has been established in theory and
confirmed via experiment. However, the understanding of several consequential
phenomena, such as the Many-Body Localization (MBL), has been obstructed by the
lack of a systematic approach to obtain many-body entanglement dynamics. This
paper introduces the Quantum Correlation Transfer Function (QCTF) approach to
entanglement dynamics in many-body quantum systems and employs this new
framework to demonstrate the mechanism of MBL in disordered spin chains. We
show that in the QCTF framework, the entanglement dynamics of two-level
constituent particles of a many-body quantum system can be fully characterized
directly from the system's Hamiltonian, which circumvents the bottleneck of
calculating the many-body system's time-evolution. By employing the QCTF-based
approach to entanglement dynamics, we demonstrate MBL dynamics in disordered
Heisenberg spin chains through the suppressed quasi-periodic spin's
entanglement evolution after a quench from an anti-ferromagnetic state.
Furthermore, we prove the validity of a previous fundamental conjecture
regarding the MBL phase by showing that in strongly-disordered spin chains with
short-range interactions, the quantum correlation between particles is
exponentially attenuated with respect to the site-to-site distance. Moreover,
we obtain the lowest possible amplitude of the quasi-periodic spin's
entanglement as a function of disorder in the chain. The QCTF analysis is
verified by exact numerical simulation of the system's evolution. We also show
that QCTF provides a new foundation to study the Eigenstate Thermalization
Hypothesis (ETH). The QCTF methodology can be extended in various ways to
address general issues regarding non-equilibrium quantum thermodynamics in spin
lattices with different geometries.",2201.11223v1
2023-09-19,Dynamics of inhomogeneous spin ensembles with all-to-all interactions: breaking permutational invariance,"We investigate the consequences of introducing non-uniform initial conditions
in the dynamics of spin ensembles characterized by all-to-all interactions.
Specifically, our study involves the preparation of a set of semi-classical
spin ensembles with varying orientations. Through this setup, we explore the
influence of such non-uniform initial states on the disruption of permutational
invariance. Comparing this approach to the traditional scenario of initializing
with spins uniformly aligned, we find that the dynamics of the spin ensemble
now spans a more expansive effective Hilbert space. This enlargement arises due
to the inclusion of off-diagonal coherences between distinct total angular
momentum subspaces - an aspect typically absent in conventional treatments of
all-to-all spin dynamics. Conceptually, the dynamic evolution can be understood
as a composite of multiple homogeneous sub-ensembles navigating through
constrained subspaces. Notably, observables that are sensitive to the
non-uniformity of initial conditions exhibit discernible signatures of these
off-diagonal coherences. We adopt this fresh perspective to reexamine the
relaxation phenomena exhibited by the Dicke model, as well as a prototypical
example of a boundary time crystal. Intriguingly, ensembles initialized with
inhomogeneous initial conditions can show distinctive behaviors when contrasted
with canonical instances of collective dynamics. These behaviors encompass the
emergence of novel gapless excitations, the manifestation of limit-cycles
featuring dressed frequencies due to superradiance, instances of frequency
locking or beating synchronizations, and even the introduction of ``extra''
dimensions within the dynamics. In closing, we provide a brief overview of the
potential implications of our findings in the context of modern cavity quantum
electrodynamics (QED) platforms.",2309.10746v1
2009-07-15,Long-term Dynamics of the Electron-nuclear Spin System of a Semiconductor Quantum Dot,"A quasi-classical theoretical description of polarization and relaxation of
nuclear spins in a quantum dot with one resident electron is developed for
arbitrary mechanisms of electron spin polarization. The dependence of the
electron-nuclear spin dynamics on the correlation time $\tau_c$ of electron
spin precession, with frequency $\Omega$, in the nuclear hyperfine field is
analyzed. It is demonstrated that the highest nuclear polarization is achieved
for a correlation time close to the period of electron spin precession in the
nuclear field. For these and larger correlation times, the indirect hyperfine
field, which acts on nuclear spins, also reaches a maximum. This maximum is of
the order of the dipole-dipole magnetic field that nuclei create on each other.
This value is non-zero even if the average electron polarization vanishes. It
is shown that the transition from short correlation time to $\Omega\tau_c>1$
does not affect the general structure of the equation for nuclear spin
temperature and nuclear polarization in the Knight field, but changes the
values of parameters, which now become functions of $\Omega\tau_c$. For
correlation times larger than the precession time of nuclei in the electron
hyperfine field, it is found that three thermodynamic potentials ($\chi$,
$\bm{\xi}$, $\varsigma$) characterize the polarized electron-nuclear spin
system. The values of these potentials are calculated assuming a sharp
transition from short to long correlation times, and the relaxation mechanisms
of these potentials are discussed. The relaxation of the nuclear spin potential
is simulated numerically showing that high nuclear polarization decreases
relaxation rate.",0907.2661v1
2010-08-16,Phase transitions in random Potts systems and the community detection problem: spin-glass type and dynamic perspectives,"Phase transitions in spin glass type systems and, more recently, in related
computational problems have gained broad interest in disparate arenas. In the
current work, we focus on the ""community detection"" problem when cast in terms
of a general Potts spin glass type problem. As such, our results apply to
rather broad Potts spin glass type systems. Community detection describes the
general problem of partitioning a complex system involving many elements into
optimally decoupled ""communities"" of such elements. We report on phase
transitions between solvable and unsolvable regimes. Solvable region may
further split into ""easy"" and ""hard"" phases. Spin glass type phase transitions
appear at both low and high temperatures (or noise). Low temperature
transitions correspond to an ""order by disorder"" type effect wherein
fluctuations render the system ordered or solvable. Separate transitions appear
at higher temperatures into a disordered (or an unsolvable) phase. Different
sorts of randomness lead to disparate behaviors. We illustrate the spin glass
character of both transitions and report on memory effects. We further relate
Potts type spin systems to mechanical analogs and suggest how chaotic-type
behavior in general thermodynamic systems can indeed naturally arise in
hard-computational problems and spin-glasses. The correspondence between the
two types of transitions (spin glass and dynamic) is likely to extend across a
larger spectrum of spin glass type systems and hard computational problems. We
briefly discuss potential implications of these transitions in complex many
body physical systems.",1008.2699v3
2012-02-03,Prototype effective-one-body model for nonprecessing spinning inspiral-merger-ringdown waveforms,"We first use five non-spinning and two mildly spinning (chi_i \simeq -0.44,
+0.44) numerical-relativity waveforms of black-hole binaries and calibrate an
effective-one-body (EOB) model for non-precessing spinning binaries, notably
its dynamics and the dominant (2,2) gravitational-wave mode. Then, we combine
the above results with recent outcomes of small-mass-ratio simulations produced
by the Teukolsky equation and build a prototype EOB model for detection
purposes, which is capable of generating inspiral-merger-ringdown waveforms for
non-precessing spinning black-hole binaries with any mass ratio and individual
black-hole spins -1 \leq chi_i \lesssim 0.7. We compare the prototype EOB model
to two equal-mass highly spinning numerical-relativity waveforms of black holes
with spins chi_i = -0.95, +0.97, which were not available at the time the EOB
model was calibrated. In the case of Advanced LIGO we find that the mismatch
between prototype-EOB and numerical-relativity waveforms is always smaller than
0.003 for total mass 20-200 M_\odot, the mismatch being computed by maximizing
only over the initial phase and time. To successfully generate merger waveforms
for individual black-hole spins chi_i \gtrsim 0.7, the prototype-EOB model
needs to be improved by (i) better modeling the plunge dynamics and (ii)
including higher-order PN spin terms in the gravitational-wave modes and
radiation-reaction force.",1202.0790v2
2013-04-10,Magnetization and spin dynamics of the spin S=1/2 hourglass nanomagnet Cu5(OH)2(NIPA)4*10H2O,"We report a combined experimental and theoretical study of the spin S=1/2
nanomagnet Cu5(OH)2(NIPA)4*10H2O (Cu5-NIPA). Using thermodynamic, electron spin
resonance and 1H nuclear magnetic resonance measurements on one hand, and ab
initio density-functional band-structure calculations, exact diagonalizations
and a strong coupling theory on the other, we derive a microscopic magnetic
model of Cu5-NIPA and characterize the spin dynamics of this system. The
elementary five-fold Cu2+ unit features an hourglass structure of two
corner-sharing scalene triangles related by inversion symmetry. Our microscopic
Heisenberg model comprises one ferromagnetic and two antiferromagnetic exchange
couplings in each triangle, stabilizing a single spin S=1/2 doublet ground
state (GS), with an exactly vanishing zero-field splitting (by Kramer's
theorem), and a very large excitation gap of \Delta~68 K. Thus, Cu5-NIPA is a
good candidate for achieving long electronic spin relaxation (T1) and coherence
(T2) times at low temperatures, in analogy to other nanomagnets with low-spin
GS's. Of particular interest is the strongly inhomogeneous distribution of the
GS magnetic moment over the five Cu2+ spins. This is a purely
quantum-mechanical effect since, despite the non-frustrated nature of the
magnetic couplings, the GS is far from the classical collinear ferrimagnetic
configuration. Finally, Cu5-NIPA is a rare example of a S=1/2 nanomagnet
showing an enhancement in the nuclear spin-lattice relaxation rate 1/T1 at
intermediate temperatures.",1304.2826v1
2017-03-20,Hierarchical analysis of gravitational-wave measurements of binary black hole spin-orbit misalignments,"Binary black holes may form both through isolated binary evolution and
through dynamical interactions in dense stellar environments. The formation
channel leaves an imprint on the alignment between the black hole spins and the
orbital angular momentum. Gravitational waves from these systems directly
encode information about the spin--orbit misalignment angles, allowing them to
be (weakly) constrained. Identifying sub-populations of spinning binary black
holes will inform us about compact binary formation and evolution. We simulate
a mixed population of binary black holes with spin--orbit misalignments
modelled under a range of assumptions. We then develop a hierarchical analysis
and apply it to mock gravitational-wave observations of these populations.
Assuming a population with dimensionless spin magnitudes of $\chi = 0.7$, we
show that tens of observations will make it possible to distinguish the
presence of subpopulations of coalescing binary black holes based on their spin
orientations. With $100$ observations it will be possible to infer the relative
fraction of coalescing binary black holes with isotropic spin directions
(corresponding to dynamical formation in our models) with a fractional
uncertainty of $\sim 40\%$. Meanwhile, only $\sim 5$ observations are
sufficient to distinguish between extreme models---all binary black holes
either having exactly aligned spins or isotropic spin directions.",1703.06873v2
2017-08-30,Gate-Control of Anisotropic Spin Transport and Spin Helix Dynamics in a Modulation-Doped GaAs Quantum Well,"Electron spin transport and dynamics are investigated in a single,
high-mobility, modulation-doped, GaAs quantum well using ultrafast two-color
Kerr-rotation micro-spectroscopy, supported by qualitative kinetic theory
simulations of spin diffusion and transport. Evolution of the spins is governed
by the Dresselhaus bulk and Rashba structural inversion asymmetries, which
manifest as an effective magnetic field that can be extracted directly from the
experimental coherent spin precession. A spin precession length L-SOI is
defined as one complete precession in the effective magnetic field. It is
observed that application of (a) an out-of-plane electric field changes the
spin decay time and L-SOI through the Rashba component of the spin-orbit
coupling, (b) an in-plane magnetic field allows for extraction of the
Dresselhaus and Rashba parameters, and (c) an in-plane electric field markedly
modifies both the L-SOI and diffusion coefficient. While simulations reproduce
the main features of the experiments, the latter results exceed the
corresponding simulations and extend previous studies of
drift-current-dependent spin-orbit interactions.",1708.09150v2
2018-02-13,Efficient conversion of anti-phase spin order of protons into 15N magnetization using SLIC-SABRE,"SABRE (Signal Amplification By Reversible Exchange) is a technique for
enhancement of NMR (Nuclear Magnetic Resonance) signals, which utilizes
parahydrogen (pH2, the H2 molecule in its nuclear spin state) as a source of
non-thermal spin order. In SABRE experiments, pH2 binds to an organometallic
complex with a to-be-polarized substrate; subsequently, spin order transfer
takes place and the substrate acquires non-thermal spin polarization resulting
in strong NMR signal enhancement. In this work we argue that the spin order of
H2 in SABRE experiments performed at high magnetic fields is not necessarily
the singlet order but rather anti-phase polarization, $S_{1z}S_{2z}$. Although
SABRE exploits pH2, i.e., the starting spin order of H2 is supposed to be the
singlet order, in solution S-T0 conversion becomes efficient once pH2 binds to
a complex. Such a variation of the spin order, which becomes $S_{1z}S_{2z}$,
has an important consequence: NMR methods used for transferring SABRE
polarization need to be modified. Here we demonstrate that methods proposed for
the initial singlet order may not work for the S_1z S_2z order; however, a
simple modification makes them efficient again. A theoretical treatment of the
problem under consideration is proposed; these considerations are supported by
high-field SABRE experiments. Hence, for efficient use of SABRE one should note
that polarization formation is a complex multi-stage process: careful
optimization of this process may not only deal with chemical aspects but also
with the spin dynamics, including the spin dynamics of H2.",1802.04471v1
2016-05-16,A new and simple model for magneto-optics uncovers an unexpected spin switching,"In magneto-optics the spin angular momentum $S_z$ of a sample is indirectly
probed by the rotation angle and ellipticity, which are mainly determined by
the off-diagonal susceptibility $\chi^{(1)}_{xy}$. A direct and analytic
relation between $S_z$ and $\chi^{(1)}_{xy}$ is necessary and of paramount
importance to the success of magneto-optics, but is often difficult to acquire
since quantum mechanically the relation is hidden in the sum-over-states. Here
we propose a new and simple model to establish such a much needed relation. Our
model is based on the Hookean model, but includes spin-orbit coupling. Under cw
excitation, we show that $\chi^{(1)}_{xy}(\omega)$ is indeed directly
proportional to $S_z$ for a fixed photon frequency $\omega$. Such an elegant
relation is encouraging, and we wonder whether our model can describe spin
dynamics as well. By allowing the spin to change dynamically, to our surprise,
our model predicts that an ultrafast laser pulse can induce a spin precession;
with appropriate parameters, the laser can even reverse spin from one direction
to another. This works for both the circularly and linearly polarized light.
The spin reversal window is narrow. These unexpected results closely resemble
all-optical helicity-dependent magnetic switching found in much more
complicated ferrimagnetic rare earth compounds. Therefore, we believe that our
spin-orbit coupled model may find some important applications in spin switching
processes, a hot topic in femtomagnetism.",1605.04847v1
2019-09-16,"Test black holes, scattering amplitudes and perturbations of Kerr spacetime","It has been suggested that amplitudes for quantum higher-spin massive
particles exchanging gravitons lead, via a classical limit, to results for
scattering of spinning black holes in general relativity, when the massive
particles are in a certain way minimally coupled to gravity. Such limits of
such amplitudes suggest, at least at lower orders in spin, up to second order
in the gravitational constant $G$, that the classical aligned-spin scattering
function for an arbitrary-mass-ratio two-spinning-black-hole system can be
obtained by a simple kinematical mapping from that for a spinning test black
hole scattering off a stationary background Kerr black hole. Here we test these
suggestions, at orders beyond the reach of the post-Newtonian and
post-Minkowskian results used in their initial partial verifications, by
confronting them with results from general-relativistic ""self-force""
calculations of the linear perturbations of a Kerr spacetime sourced by a small
orbiting body, here considering only results for circular orbits in the
equatorial plane. We translate between scattering and circular-orbit results by
assuming the existence of a local-in-time canonical Hamiltonian governing the
conservative dynamics of generic (bound and unbound) aligned-spin orbits, while
employing the associated first law of spinning binary mechanics. We confirm,
through linear order in the mass ratio, some previous conjectures which would
begin to fill in the spin-dependent parts of the conservative dynamics for
arbitrary-mass-ratio aligned-spin binary black holes at the fourth-and-a-half
and fifth post-Newtonian orders.",1909.07361v1
2020-12-11,The semiclassical theory for spin dynamics in a disordered system,"We investigate the Drude model of spin dynamics in two-dimensional spin-orbit
coupled systems. In the absence of an applied electric field, the spin aligns
with the k-dependent effective magnetic field. The influence of disorder (the
momentum relaxation time $\tau$) on the system is considered. In the presence
of an electric field, the change in momentum causes a change in the effective
magnetic field. The in-plane spin can precess around the successive change in
the orientation of the effective magnetic field. We find that up to the linear
order of the electric field, the spin orientation undergoes Larmor-like and
non-Larmor like precession. Furthermore, we find that the non-Larmor motion
over a very short time ($t\ll\tau$) exactly equals the result obtained from the
Kubo formula. This means that the Kubo formula only captures the system's
response over a very short evolution. The spin-Hall conductivity for Larmor and
non-Larmor precession in the Rashba system is analytically calculated. We find
that the intrinsic spin-Hall current is not a universal constant and correctly
drops to zero when the Rashba spin-orbit coupling drops to zero. We also
calculate the time-averaged Larmor and non-Larmor spin-Hall conductivities
(SHCs) for the k-cubic Rashba system and compare them to experimental values.
The time-averaged Larmor SHC vanishes and the non-Larmor SHC is given by
$2.1(q/8\pi)$ which is very close to the experimental value $2.2(q/8\pi)$ by
Wunderlich et al. [Phys. Rev. Lett. {\bf 94}, 047204 (2005)].",2012.06053v1
2021-06-08,Particle-hole asymmetry in the dynamical spin and charge structure factors of the corner-shared one-dimensional cuprates,"The collective spin and charge excitations of doped cuprates and their
relationship to superconductivity are not yet fully understood, particularly in
the case of the charge excitations. Here, we study the doping-dependent
dynamical spin and charge structure factors of single and multi-orbital models
for the one-dimensional corner shared spin-chain cuprates using several
numerically exact methods. We find that the singleband Hubbard model can
describe the spin and charge excitations of the $pd$-model in the low-energy
region, including the particle-hole asymmetry in the spin response. However,
our results also reveal that the weight of the interorbital spin excitations
between Cu and O orbitals is comparable to the weight of the spin excitations
between two Cu orbitals. This finding elucidates the microscopic nature of the
spin excitations in the 1D cuprates and sheds light on the spin properties of
other oxides. Importantly, we find a particle-hole asymmetry in the
orbital-resolved charge excitations, which cannot be described by the
singleband Hubbard model and is relevant to resonant inelastic x-ray scattering
experiments. Our results imply that the explicit inclusion of the oxygen
degrees of freedom may be required to understand experimental observations.",2106.04017v1
2022-03-06,Spin-Dependent Graph Neural Network Potential for Magnetic Materials,"The development of machine learning interatomic potentials has immensely
contributed to the accuracy of simulations of molecules and crystals. However,
creating interatomic potentials for magnetic systems that account for both
magnetic moments and structural degrees of freedom remains a challenge. This
work introduces SpinGNN, a spin-dependent interatomic potential approach that
employs the graph neural network (GNN) to describe magnetic systems. SpinGNN
consists of two types of edge GNNs: Heisenberg edge GNN (HEGNN) and
spin-distance edge GNN (SEGNN). HEGNN is tailored to capture Heisenberg-type
spin-lattice interactions, while SEGNN accurately models multi-body and
high-order spin-lattice coupling. The effectiveness of SpinGNN is demonstrated
by its exceptional precision in fitting a high-order spin Hamiltonian and two
complex spin-lattice Hamiltonians with great precision. Furthermore, it
successfully models the subtle spin-lattice coupling in BiFeO3 and performs
large-scale spin-lattice dynamics simulations, predicting its antiferromagnetic
ground state, magnetic phase transition, and domain wall energy landscape with
high accuracy. Our study broadens the scope of graph neural network potentials
to magnetic systems, serving as a foundation for carrying out large-scale
spin-lattice dynamic simulations of such systems.",2203.02853v2
2022-04-12,Rapid Spin Up and Spin Down of Flow Along Slopes,"The near-bottom mixing that allows abyssal waters to upwell tilts isopycnals
and spins up flow over the flanks of mid-ocean ridges. Meso- and large-scale
currents along sloping topography are subjected to a delicate balance of Ekman
arrest and spin down. These two seemingly disparate oceanographic phenomena
share a common theory, which is based on a one-dimensional model of rotating,
stratified flow over a sloping, insulated boundary. This commonly used model,
however, lacks rapid adjustment of interior flows, limiting its ability to
capture the full physics of spin up and spin down of along-slope flow.
Motivated by two-dimensional dynamics, the present work extends the
one-dimensional model by constraining the vertically integrated cross-slope
transport and allowing for a barotropic cross-slope pressure gradient. This
produces a closed secondary circulation by forcing Ekman transport in the
bottom boundary layer to return in the interior. The extended model can thus
capture Ekman spin up and spin down physics: the interior return flow is turned
by the Coriolis acceleration, leading to rapid \linelabel{ll:slowdiff}rather
than slow diffusive adjustment of the along-slope flow. This
transport-constrained one-dimensional model accurately describes
two-dimensional mixing-generated spin up over an idealized ridge and provides a
unified framework for understanding the relative importance of Ekman arrest and
spin down of flow along a slope.",2204.05943v1
2022-06-22,Probing Laser-Induced Spin-Current Generation in Synthetic Ferrimagnets Using Spin Waves,"Several rare-earth transition-metal ferrimagnetic systems exhibit all-optical
magnetization switching upon excitation with a femtosecond laser pulse.
Although this phenomenon is very promising for future opto-magnetic data
storage applications, the role of non-local spin transport in these systems is
scarcely understood. Using Co/Gd and Co/Tb bilayers we isolate the contribution
of the rare-earth materials to the generated spin currents by using the
precessional dynamics they excite in an adjacent ferromagnetic layer as a
probe. By measuring THz standing spin-waves as well as GHz homogeneous
precessional modes, we probe both the high- and low-frequency components of
these spin currents. The low-frequency homogeneous mode indicates a significant
contribution of Gd to the spin current, but not from Tb, consistent with the
difficulty in achieving all-optical switching in Tb-containing systems.
Measurements on the THz frequency spin waves reveal the inability of the
rare-earth generated spin currents to excite dynamics at the sub-ps timescale.
We present modelling efforts using the $s$-$d$ model, which effectively
reproduce our results and allow us to explain the behavior in terms of the
temporal profile of the spin current.",2206.10934v1
2022-12-25,Theory of superdiffusive spin transport in noncollinear magnetic multilayers,"Ultrafast demagnetization induced by femtosecond laser pulses in thin
metallic layers is caused by the outflow of spin-polarized hot electron
currents describable by the superdiffusive transport model. These
laser-generated spin currents can cross the interface into another magnetic
layer and give rise to magnetization dynamics in magnetic spin valves with
noncollinear magnetizations. To describe ultrafast transport and spin dynamics
in such nanostructures we develop here the superdiffusive theory for general
noncollinear magnetic multilayers. Specifically, we introduce an Al/Ni/Ru/Fe/Ru
multilayer system with noncollinear Ni and Fe magnetic moments and analyze how
the ultrafast demagnetization and spin-transfer torque depend on the
noncollinearity. We employ ab initio calculations to compute the spin- and
energy-dependent transmissions of hot electrons at the interfaces of the
multilayer. Taking into account multiple electron scattering at interfaces and
spin mixing in the spacer layer we find that the laser-induced demagnetization
of the Ni layer and magnetization change of the Fe layer strongly depend on the
angle between their magnetizations. Similarly, the spin-transfer torques on the
Ni and Fe layers and the total spin momentum absorbed in the Ni and Fe layer
are found to vary markedly with the amount of noncollinearity.
  These results suggest that changing the amount of noncollinearity in magnetic
multilayers one can efficiently control the hot electron spin transport, which
may open a way toward achieving fast, laser-driven spintronic devices.",2212.12961v1
2023-05-24,Charged spinning and magnetized test particles orbiting quantum improved charged black holes,"In the present work, we aimed to investigate the dynamics of spinning charged
and magnetized test particles around both electrically and magnetically charged
quantum-improved black holes. We derive the equations of motion for charged
spinning test particles using the Mathisson-Papapetrou-Dixon equations with the
Lorentz coupling term. The radius of innermost stable circular orbits (ISCOs),
specific angular momentum, and energy for charged spinless, uncharged spinning,
and charged spinning test particles around the charged and non-charged
quantum-improved black holes are analyzed separately. We found that the quantum
parameter increases the maximum spin value, $s_\text{max}$, which leads to the
nonphysical motion (superluminal motion) of the charged spinning test particle,
whereas the black hole charge decreases its value. We also found that, in
contrast to the Reissner Nordstr\""om black hole, spinning charged test
particles in the quantum-improved charged black hole have higher
$s_\text{max}$; moreover, positively charged spinning particles can have higher
values of $s_\text{max}$ near the extreme black hole cases when compared with
uncharged spinning particles. Finally, we investigate the magnetized test
particle's dynamics around a quantum-improved magnetically charged black hole
in Quantum Einstein Gravity using the Hamilton-Jacobi equation. We show that
the presence of $\omega$ increases the maximum value of the effective potential
and decreases the minimum energy and angular momentum of magnetized particles
at their circular orbits. We found an upper constraint in the black hole charge
at the ISCO.",2305.15350v1
2023-06-27,"Three-dimensional spin-wave dynamics, localization and interference in a synthetic antiferromagnet","Spin waves are collective perturbations in the orientation of the magnetic
moments in magnetically ordered materials. Their rich phenomenology is
intrinsically three dimensional, from the trajectory of the spin precession
during their propagation, to the profiles of the spin-wave mode throughout the
volume of the magnetic system. This gives rise to novel complex phenomena with
high potential for applications in the field of magnonics. However, the
three-dimensional imaging of spin waves, key to understanding and harnessing
these phenomena, has so far not been possible. Here, we image the
three-dimensional dynamics of spin waves excited in a synthetic
antiferromagnet, with nanoscale spatial resolution and sub-ns temporal
resolution, using time-resolved magnetic laminography. In this way, we map the
distribution of the spin-wave modes throughout the volume of the structure,
revealing unexpected depth-dependent profiles originating from the interlayer
dipolar interaction. We experimentally demonstrate the existence of complex
three-dimensional interference patterns, and analyze them via micromagnetic
modelling. We find that these patterns are generated by the superposition of
spin waves with non-uniform amplitude profiles, and that their features can be
controlled by tuning the composition and structure of the magnetic system. Our
results open unforeseen possibilities for the study of complex spin-wave modes
and their interaction within nanostructures, and for the generation and
manipulation of three-dimensional spin-wave landscapes for the design of novel
functions in magnonic devices.",2306.15404v1
2023-07-19,Entanglement and replica symmetry breaking in a driven-dissipative quantum spin glass,"We describe simulations of the quantum dynamics of a confocal cavity QED
system that realizes an intrinsically driven-dissipative spin glass. A close
connection between open quantum dynamics and replica symmetry breaking is
established, in which individual quantum trajectories are the replicas. We
observe that entanglement plays an important role in the emergence of replica
symmetry breaking in a fully connected, frustrated spin network of up to
fifteen spin-1/2 particles. Quantum trajectories of entangled spins reach
steady-state spin configurations of lower energy than that of semiclassical
trajectories. Cavity emission allows monitoring of the continuous stochastic
evolution of spin configurations, while backaction from this projects entangled
states into states of broken Ising and replica symmetry. The emergence of spin
glass order manifests itself through the simultaneous absence of magnetization
and the presence of nontrivial spin overlap density distributions among
replicas. Moreover, these overlaps reveal incipient ultrametric order, in line
with the Parisi RSB solution ansatz for the Sherrington-Kirkpatrick model. A
nonthermal Parisi order parameter distribution, however, highlights the
driven-dissipative nature of this quantum optical spin glass. This practicable
system could serve as a testbed for exploring how quantum effects enrich the
physics of spin glasses.",2307.10176v2
2018-09-07,Dynamical coupling between Ising and FK percolation,"We investigate the problem of constructing a dynamics on edge--spin
configurations which realizes a coupling between a Glauber dynamics of the
Ising model and a dynamical evolution of the percolation configurations. We
dream of constructing a Markov process on edge--spin configurations which is
reversible with respect to the Ising--FK coupling measure, and such that the
marginal on the spins is a Glauber dynamics, while the marginal on the edges is
a Markovian evolution. We present two local dynamics, one which fulfills only
the first condition and one which fulfills the first two conditions. We show
next that our dream process is not feasible in general. We present a third
dynamics, which is non local and fulfills the first and the third conditions.
We finally present a localized version of this third dynamics, which can be
seen as a contraction of the first dynamics.",1809.02330v1
1996-12-02,Domain wall roughening in disordered media: From local spin dynamics to a continuum description of the interface,"We study the kinetic roughening of a driven domain wall between spin-up and
spin-down domains for a model with non-conserved order parameter and quenched
disorder. To understand the scaling behavior of this interface we construct an
equation of motion and study it theoretically.",9612015v1
2003-12-17,Recent Progress in Spin Glasses,"We review recent findings on spin glass models. Both the equilibrium
properties and the dynamic properties are covered. We focus on progress in
theoretical, in particular numerical, studies, while its relationship to real
magnetic materials is also mentioned.",0312432v2
2001-03-05,A generating formulation for free higher spin massless fields,"An action describing the dynamics of an infinite collection of massless
integer spin fields with spin s=0,1,2,3, ...$\infty$ corresponding to totally
symmetric Young tableaux representations of Poincare and anti-de Sitter groups
is constructed, in any dimension d, in terms of two functions on a
2d-dimensional manifold. The action is represented by an integral localized on
a 2d-1-dimensional hypersurface.",0103028v1
2003-04-24,The spin contribution to the form factor of quantum graphs,"Following the quantisation of a graph with the Dirac operator (spin-1/2) we
explain how additional weights in the spectral form factor K(\tau) due to spin
propagation around orbits produce higher order terms in the small-\tau
asymptotics in agreement with symplectic random matrix ensembles. We determine
conditions on the group of spin rotations sufficient to generate CSE
statistics.",0304046v1
2007-07-25,Study of the spin-$\frac32$ Hubbard-Kondo lattice model by means of the Composite Operator Method,"We study the spin-$\frac32$ Hubbard-Kondo lattice model by means of the
Composite Operator Method, after applying a Holstein-Primakov transformation.
The spin and particle dynamics in the ferromagnetic state are calculated by
taking into account strong on-site correlations between electrons and
antiferromagnetic exchange among $\frac32$ spins, together with usual Hund
coupling between electrons and spins.",0707.3822v1
2007-11-13,The Commutativity of Integrals of Motion for Quantum Spin Chains and Elliptic Functions Identities,"We prove the commutativity of the first two nontrivial integrals of motion
for quantum spin chains with elliptic form of the exchange interaction. We also
show thair linear independence for the numbers of spins larger than 4. As a
byproduct, we obtained several identities between elliptic Weierstrass
functions of three and four arguments.",0711.1973v1
2008-05-18,Effect of spin diffusion on spin torque in magnetic nanopillars,"We present systematic magnetoelectronic measurements of magnetic nanopillars
with different structures of polarizing magnetic layers. The magnetic reversal
at small magnetic field, the onset of magnetic dynamics at larger field, and
the magnetoresistance exhibit a significant dependence on the type of the
polarizing layer. We performed detailed quantitative modeling showing that the
differences can be explained by the effects of spin-dependent electron
diffusion.",0805.2706v1
2009-05-25,LQG propagator from the new spin foams,"We compute metric correlations in loop quantum gravity with the dynamics
defined by the new spin foam models. The analysis is done at the lowest order
in a vertex expansion and at the leading order in a large spin expansion. The
result is compared to the graviton propagator of perturbative quantum gravity.",0905.4082v1
2010-04-28,Quark spin in the proton,"The proton spin puzzle has challenged our understanding of QCD for the last
20 years. We survey new developments in theory and experiment. The proton spin
puzzle seems to be telling us about the interplay of valence quarks with chiral
dynamics and the complex vacuum structure of QCD.",1004.4977v1
2012-09-28,Generic examples of PT-symmetric qubit (spin 1/2) Liouvillians,"We outline two general classes of examples of PT-symmetric quantum
Liouvillian dynamics of open many qubit systems, namely interacting hard-core
bosons (or more general XYZ-type spin 1/2 systems) with, either (i) pure
dephasing noise, or (ii) having solely single particle/spin
injection/absorption incoherent processes.",1209.6588v1
2013-12-29,The spin-orbit resonances of the Solar system: A mathematical treatment matching physical data,"In the mathematical framework of a restricted, slightly dissipative
spin-orbit model, we prove the existence of periodic orbits for astronomical
parameter values corresponding to all satellites of the Solar system observed
in exact spin-orbit resonance.",1312.7544v1
2015-06-15,Helicity-0 spinning particles,"We show that a self-consistent classical theory of the spin, based on a very
general Lagrangian extending the Newtonian dynamics, does predict the special
case of helicity-0 particles, which at the same time are endowed with nonzero
spin and zero intrinsic angular momentum.",1506.04471v1
2016-06-24,Spin-liquid Mott quantum criticality in two dimensions: Destabilization of a spinon Fermi surface and emergence of one-dimensional spin dynamics,"Resorting to a recently developed theoretical device called dimensional
regularization for quantum criticality with a Fermi surface, we examine a
metal-insulator quantum phase transition from a Landau's Fermi-liquid state to
a U(1) spin-liquid phase with a spinon Fermi surface in two dimensions.
Unfortunately, we fail to approach the spin-liquid Mott quantum critical point
from the U(1) spin-liquid state within the dimensional regularization
technique. Self-interactions between charge fluctuations called holons are not
screened, which shows a run-away renormalization group flow, interpreted as
holons remain gapped. This leads us to consider another fixed point, where the
spinon Fermi surface can be destabilized across the Mott transition. Based on
this conjecture, we reveal the nature of the spin-liquid Mott quantum critical
point: Dimensional reduction to one dimension occurs for spin dynamics
described by spinons. As a result, Landau damping for both spin and charge
dynamics disappear in the vicinity of the Mott quantum critical point. When the
flavor number of holons is over its critical value, an interacting fixed point
appears to be identified with an inverted XY universality class, controlled
within the dimensional regularization technique. On the other hand, a
fluctuation-driven first order metal-insulator transition results when it is
below the critical number. We propose that the destabilization of a spinon
Fermi surface and the emergence of one-dimensional spin dynamics near the
spin-liquid Mott quantum critical point can be checked out by spin
susceptibility with a $2 k_{F}$ transfer momentum, where $k_{F}$ is a Fermi
momentum in the U(1) spin-liquid state: The absence of Landau damping in U(1)
gauge fluctuations gives rise to a divergent behavior at zero temperature while
it vanishes in the presence of a spinon Fermi surface.",1606.07544v3
2012-04-24,Recent positivity constraints for spin observables and parton distributions,"Spin observables allow a deeper understanding of the nature of the underlying
dynamics and positivity reduces substantially their allowed domains. We will
present some new positivity constraints for spin observables and their
implications for parton distributions. We will also make some comparisons with
recent data.",1204.5279v1
2019-03-30,Spin in gravitational and electromagnetic fields,"A unified approach to the study of classical and quantum spin in external
fields is developed. Understanding the dynamics of particles with spin and
dipole moments in arbitrary gravitational, inertial and electromagnetic fields
is important in astrophysics and high-energy and heavy-ion experimental
physics.",1904.00181v1
1997-02-02,Effect of spin-glass order on magnetic polarons in semimagnetic semiconductors,"A theory accounting for the specific features of magnetic polarons (MP) in
the presence of spin glass order is presented. We derive and solve
selfconsistent equations for i) the polaron magnetisation, ii) the
thermodynamically averaged carrier--spin, and iii) for the spin glass order
parameter. The temperature dependence of these quantities is analysed in
detail. The modification of the spin glass phase due to the presence of the
exchange field of the carrier inside the magnetic polaron volume is
investigated. The onset of spin glass order leads to a plateau--like flattening
in the temperature dependence of the MP energy at low temperatures. It is found
that solutions of spin glass equations are needed to optimally fit the
experimental data of the temperature dependence of the exciton magnetic polaron
(EMP) energy in (Cd,Mn)Te. Moreover, the dynamical aspects of the MP formation
are discussed. Our model predicts qualitatively different temperature
dependences of the MP formation time in different dynamical scenarios.",9702013v1
1999-08-24,Spin Dynamics of Rare Earth Ions in Phosphate Laser Glasses,"The spin dynamics of rare earth ions (Er, Nd, Sm and Gd) in heavily doped
phosphate glasses have been investigated using 31P NMR. Correlation times in
the range 10^-2 to 10^-12 s have been obtained for temperatures between 4 K and
100 K. No evidence of spin-spin coupling between the ions has been found and
spin relaxation occurs via conventional phonon processes, including the Orbach
process.
  A model involving inhomogeneous broadening of the NMR resonance lines, with
distinct sample regions corresponding to the presence or absence of nuclear
spin diffusion, has been used in extracting the electron spin correlation times
from the NMR measurements.",9908333v1
2001-02-21,Spin Diffusion in the S=1/2 Quasi One-Dimensional Antiferromagnet α-VO(PO_3)_2 via 31P NMR,"Low-frequency spin dynamics in the S=1/2 antiferromagnetic spin-chain
compound \alpha-VO(PO_3)_2 has been studied by means of 31P NMR. The nuclear
spin-lattice relaxation rate 1/T_1 at the P site exhibits H^{-1/2} dependence
on the applied magnetic field (H) at temperatures (T) well above the intrachain
coupling strength J/k_{B} = 3.50 K indicating one-dimensional diffusive spin
dynamics. The diffusive contribution to 1/T_1 decreases on cooling as
electronic spins acquire short-range antiferromagnetic correlations within the
chain, and vanishes almost entirely around T \approx J/k_{B}. This is
accompanied by an apparent increase of the spin-diffusion constant from the
value expected in the classical limit. On the other hand, the field-independent
part of 1/T_1 increases with decreasing temperature, which may be a precursor
for the true long-range antiferromagnetic ordering found below T_{N} = 1.93 \pm
0.01 K.",0102365v2
2001-09-05,"Slow Spin Dynamics in Non-Fermi-Liquid UCu_{5-x}Pd_x, x = 1.0 and 1.5","Low-temperature muon spin-lattice relaxation measurements in the
non-Fermi-liquid heavy-fermion alloys UCu_{5-x}Pd_x, x = 1.0 and 1.5, indicate
inhomogeneously distributed f-electron spin fluctuation rates, and exhibit a
time-field scaling of the muon relaxation function indicative of long-lived
spin correlations. In UCu_4Pd the scaling exponent \gamma is small and
temperature independent. In UCu_{3.5}Pd_{1.5} \gamma varies with temperature,
increasing with decreasing temperature similar to spin-glass AgMn. This
suggests that the spin-glass state found for x \gtrsim 2 in UCu_{5-x}Pd_x
modifies the low-frequency spin dynamics in UCu_{3.5}Pd_{1.5}.",0109070v1
2002-08-13,Electron Spin Dynamics in Semiconductors without Inversion Symmetry,"We present a microscopic analysis of electron spin dynamics in the presence
of an external magnetic field for non-centrosymmetric semiconductors in which
the D'yakonov-Perel' spin-orbit interaction is the dominant spin relaxation
mechanism. We implement a fully microscopic two-step calculation, in which the
relaxation of orbital motion due to electron-bath coupling is the first step
and spin relaxation due to spin-orbit coupling is the second step. On this
basis, we derive a set of Bloch equations for spin with the relaxation times
T_1 and T_2 obtained microscopically. We show that in bulk semiconductors
without magnetic field, T_1 = T_2, whereas for a quantum well with a magnetic
field applied along the growth direction T_1 = T_2/2 for any magnetic field
strength.",0208261v1
2003-04-22,Dynamic scaling in spin glasses,"We present new Neutron Spin Echo (NSE) results and a revisited analysis of
historical data on spin glasses, which reveal a pure power-law time decay of
the spin autocorrelation function $s(Q,t) = S(Q,t)/S(Q)$ at the glass
temperature $T_g$, each power law exponent being in excellent agreement with
that calculated from dynamic and static critical exponents deduced from
macroscopic susceptibility measurements made on a quite different time scale.
It is the first time that this scaling relation involving exponents of
different physical quantities determined by completely independent experimental
methods is stringently verified experimentally in a spin glass. As spin glasses
are a subgroup of the vast family of glassy systems also comprising structural
glasses, other non-crystalline systems living matter the observed strict
critical scaling behaviour is important. Above the phase transition the
strikingly non-exponential relaxation, best fitted by the Ogielski (power-law
times stretched exponential) function, appears as an intrinsic, homogeneous
feature of spin glasses.",0304493v2
2003-07-25,Dynamics of a magnetic moment induced by a spin-polarized current,"Effects of an incoming spin-polarized current on a magnetic moment are
explored. We found that the spin torque occurs only when the incoming spin
changes as a function of time inside of the magnetic film. This implies that
some modifications are necessary in a phenomenological model where the
coefficient of the spin torque term is a constant, and the coefficient is
determined by dynamics instead of geometrical details. The precession of the
magnetization reversal depends on the incoming energy of electrons in the
spin-polarized current. If the incoming energy is smaller than the interaction
energy, the magnetization does not precess while reversing its direction. We
also found that the relaxation time associated with the reversal depends on the
incoming energy. The coupling between an incoming spin and a magnetic moment
can be estimated by measuring the relaxation time.",0307633v1
2003-10-27,Transverse spin dynamics in a spin-polarized Fermi liquid,"The linear equations for transverse spin dynamics in weakly polarised
degenerate Fermi liquid with arbitrary relationship between temperature and
polarization are derived from Landau-Silin phenomenological kinetic equation
with general form of two-particle collision integral. The temperature and
polarization dependence of the spin current relaxation time is established. It
is found in particular that at finite polarization transverse spin wave damping
has a finite value at T=0. The analogy between temperature dependences of spin
waves attenuation and ultrasound absorption in degenerate Fermi liquid at
arbitrary temperature is presented. We also discuss spin-polarized Fermi liquid
in the general context of the Fermi-liquid theory and compare it with ""Fermi
liquid"" with spontaneous magnetization.",0310620v2
2006-02-20,"Relaxation, dephasing, and quantum control of electron spins in double quantum dots","Recent experiments have demonstrated quantum manipulation of two-electron
spin states in double quantum dots using electrically controlled exchange
interactions. Here, we present a detailed theory for electron spin dynamics in
two-electron double dot systems that was used to guide these experiments and
analyze experimental results. The theory treats both charge and spin degrees of
freedom on an equal basis. Specifically, we analyze the relaxation and
dephasing mechanisms that are relevant to experiments and discuss practical
approaches for quantum control of two-electron system. We show that both charge
and spin dephasing play important roles in the dynamics of the two-spin system,
but neither represents a fundamental limit for electrical control of spin
degrees of freedom in semiconductor quantum bits.",0602470v2
2007-02-07,Effect of structure anisotropy on low temperature spin dynamics in quantum wells,"Spin dynamics of two-dimensional electron gas confined in an asymmetrical
quantum well is studied theoretically in the regime where the scattering
frequency is comparable with the spin precession frequency due to the
conduction band spin splitting. The spin polarization is shown to demonstrate
quantum beats. If the spin splitting is determined by both bulk and structural
asymmetry mechanisms the beats are damped at zero temperature even in the
absence of a scattering. We calculate the decay of spin beats due to the
thermal broadening of the electron distribution function and electron
scattering. The magnetic field applied along the structure growth axis is shown
to increase the frequency of the beats and shift system towards the collision
dominated regime.",0702167v1
2003-05-01,Spin effects and baryon resonance dynamics in phi-meson photoproduction at few GeV,"The diffractive $\phi$-meson photoproduction amplitude is dominated by the
Pomeron exchange process and contains the terms that govern the spin-spin and
spin-orbital interactions.
  We show that these terms are responsible for the spin-flip transitions at
forward photoproduction angles and appear in the angular distributions of
$\phi\to K^+K^-$ -decay in reactions with unpolarized and polarized photon
beams.
  At large momentum transfers, the main contribution to the $\phi$-meson
photoproduction is found to be due to the excitation of nucleon resonances.
  Combined analysis of $\omega$ and $\phi$ photoproduction indicates strong
OZI-rule violation in $\phi NN^*$ - couplings.
  We also show that the spin observables are sensitive to the dynamics of
$\phi$-meson photoproduction at large angles and could help distinguish
different theoretical models of nucleon resonances.
  Predictions for spin effects in $\phi$-meson photoproduction are presented
for future experimental tests.",0305002v2
2007-05-31,Rapid Diffusion of dipolar order enhances dynamic nuclear polarization,"In a dynamic nuclear polarization experiment on a 40 mM solution of
4-amino-TEMPO in a 40:60 water/glycerol mixture, we have observed that the bulk
dipolar reservoir is cooled to a spin temperature of 15.5 micro-K, following
microwave irradiation for 800 s. This is significantly cooler than the 35 mK
spin temperature of the Zeeman reservoir. Equilibration of the two reservoirs
results in a 50 % increase in the NMR signal intensity, corresponding to a
Zeeman spin temperature of 23 mK. In order to achieve this polarization
directly, it was necessary to irradiate the sample with microwaves for 1500 s.
Cooling of the dipolar reservoir occurs during polarization transport through
the magnetic field gradient around the paramagnetic impurity, and is rapidly
communicated to the bulk by dipolar spin diffusion. As dipolar spin diffusion
is significantly faster than Zeeman spin diffusion, the bulk dipolar reservoir
cools faster than the Zeeman reservoir. This process can be exploited to
rapidly polarize the nuclear spins, by repeatedly cooling the dipolar system
and transferring the polarization to the Zeeman reservoir.",0705.4671v1
2007-08-21,Long nuclear spin decay times controlled by optical pumping in individual quantum dots,"Nuclear polarization dynamics are measured in the nuclear spin bi-stability
regime in a single optically pumped InGaAs/GaAs quantum dot. The controlling
role of nuclear spin diffusion from the dot into the surrounding material is
revealed in pump-probe measurements of the non-linear nuclear spin dynamics. We
measure nuclear spin decay times in the range 0.2-5 sec, strongly dependent on
the optical pumping time. The long nuclear spin decay arises from polarization
of the material surrounding the dot by spin diffusion for long (>5sec) pumping
times. The time-resolved methods allow the detection of the unstable nuclear
polarization state in the bi-stability regime otherwise undetectable in cw
experiments.",0708.2792v2
2007-08-27,Spin dynamics in a one-dimensional ferromagnetic Bose gas,"We investigate the propagation of spin excitations in a one-dimensional (1D)
ferromagnetic Bose gas. While the spectrum of longitudinal spin waves in this
system is sound-like, the dispersion of transverse spin excitations is
quadratic making a direct application of the Luttinger Liquid (LL) theory
impossible. By using a combination of different analytic methods we derive the
large time asymptotic behavior of the spin-spin dynamical correlation function
for strong interparticle repulsion. The result has an unusual structure
associated with a crossover from the regime of trapped spin wave to an open
regime and does not have analogues in known low-energy universality classes of
quantum 1D systems.",0708.3638v2
2008-12-22,Spin-wave contributions to current-induced domain wall dynamics,"We examine theoretically the role of spin-waves on current-induced domain
wall dynamics in a ferromagnetic wire. At room temperature, we find that an
interaction between the domain wall and the spin waves appears when there is a
finite difference between the domain wall velocity $\dot{x}_0$ and the spin
current $u$. Three important consequences of this interaction are found.
Firstly, spin-wave emission leads to a Landau-type damping of the
current-induced domain wall motion towards restoring the solution $\dot{x}_0 =
u$, where spin angular momentum is perfectly transfered from the conduction
electrons to the domain wall. Secondly, the interaction leads to a modification
of the domain wall width and mass, proportional to the kinetic energy of the
domain wall. Thirdly, the coupling by the electrical current between the domain
wall and the spin waves leads to temperature-dependent effective wall mass.",0812.4084v1
2009-04-16,Antiferromagnetism in the magnetoelectric effect single crystal LiMnPO$_4$,"Elastic and inelastic neutron scattering studies reveal details of the
antiferromagnetic tansition and intriguing spin-dynamics in the
magneto-electric effect single crystal LiMnPO$_4$. The elastic scattering
studies confirm the system is antiferromagnetic (AFM) below $T_N$=33.75 K with
local magnetic moments (Mn$^{2+}$; $S = 5/2$) that are aligned along the
crystallographic a-axis. The spin-wave dispersion curves propagating along the
three principal axes, determined by inelastic scattering, are adequately
modeled in the linear spin-wave framework assuming a spin-Hamiltonian that is
parameterized by inter- and in-plane nearest- and next-nearest-neighbor
interactions, and by easy-plane anisotropy. The temperature dependence of the
spin dynamics makes this an excellent model many-body spin system to address
the question of the relationship between spin-wave excitations and the order
parameter.",0904.2580v1
2009-09-16,The spin Sutherland model of D_N type and its associated spin chain,"In this paper we study the su(m) spin Sutherland (trigonometric) model of D_N
type and its related spin chain of Haldane-Shastry type obtained by means of
Polychronakos's freezing trick. As in the rational case recently studied by the
authors, we show that these are new models, whose properties cannot be simply
deduced from those of their well-known BC_N counterparts by taking a suitable
limit. We identify the Weyl-invariant extended configuration space of the spin
dynamical model, which turns out to be the N-dimensional generalization of a
rhombic dodecahedron. This is in fact one of the reasons underlying the greater
complexity of the models studied in this paper in comparison with both their
rational and BC_N counterparts. By constructing a non-orthogonal basis of the
Hilbert space of the spin dynamical model on which its Hamiltonian acts
triangularly, we compute its spectrum in closed form. Using this result and
applying the freezing trick, we derive an exact expression for the partition
function of the associated Haldane-Shastry spin chain of D_N type.",0909.2968v3
2009-11-09,What relaxes muon spins in molecular nanomagnets?,"We address the cause of the unusual muon spin relaxation (muSR) results on
molecular nanomagnets (MNMs). Through measurements on protonated and deuterated
samples of the MNMs Cr7Mn (S=1) and Cr8 (S=0), we show that the muon spin for
$S \neq 0$ MNMs is relaxed via dynamic fluctuations of the electronic spins. A
freezing out of dynamic processes occurs on cooling and at low temperatures the
muon spins are relaxed by the electronic spins which themselves are dephased by
incoherent nuclear field fluctuations.We observe a transition to a state of
static magnetic order of the MNM electronic spins in Cr7Mn below 2 K.",0911.1693v1
2009-11-25,Semiclassical dynamics and transport of the Dirac spin,"A semiclassical theory of spin dynamics and transport is formulated using the
Dirac electron model. This is done by constructing a wavepacket from the
positive-energy electron band, and studying its structure and center of mass
motion. The wavepacket has a minimal size equal to the Compton wavelength, and
has self-rotation about the average spin angular momentum, which gives rise to
the spin magnetic moment. Geometric gauge structure in the center of mass
motion provides a natural explanation of the spin-orbit coupling and various
Yafet terms. Applications of the spin-Hall and spin-Nernst effects are
discussed.",0911.4760v1
2010-10-20,Electron spin decoherence in diluted magnetic quantum wells,"We study electron spin dynamics in diluted magnetic quantum wells. The
electrons are coupled by exchange interaction with randomly distributed
magnetic ions polarized by magnetic field. This coupling leads to both spin
relaxation and spin decoherence. We demonstrate that even very small spatial
fluctuations of quantum well width dramatically increase rate of decoherence.
Depending on the strength of exchange interaction and the amplitude of the
fluctuations the decoherence can be homogeneous or inhomogeneous. In the
homogeneous regime, the transverse (with respect to magnetic field) component
of the electron spin decays on the short time scale exponentialy, while the
long-time spin dynamics is non-exponential demonstrating long-lived power law
tail. In the inhomogeneous case, the transverse spin component decays
exponentially with the exponent quadratic in time.",1010.4284v1
2010-12-25,Screw-pitch effect and velocity oscillation of domain-wall in ferromagnetic nanowire driven by spin-polarized current,"We investigate the dynamics of domain wall in ferromagnetic nanowire with
spin-transfer torque. The critical current condition is obtained analytically.
Below the critical current, we get the static domain wall solution which shows
that the spin-polarized current can't drive domain wall moving continuously. In
this case, the spin-transfer torque plays both the anti-precession and
anti-damping roles, which counteracts not only the spin-precession driven by
the effective field but also Gilbert damping to the moment. Above the critical
value, the dynamics of domain wall exhibits the novel screw-pitch effect
characterized by the temporal oscillation of domain wall velocity and width,
respectively. Both the theoretical analysis and numerical simulation
demonstrate that this novel phenomenon arise from the conjunctive action of
Gilbert-damping and spin-transfer torque. We also find that the roles of
spin-transfer torque are entirely contrary for the cases of below and above the
critical current.",1012.5473v1
2012-06-01,Dynamical Self-Quenching of Spin Pumping into Double Quantum Dots,"Nuclear spin polarization can be pumped into spin-blocked quantum dots by
multiple Landau- Zener passages through singlet-triplet anticrossings. By
numerical simulations of realistic systems including approximately $10^7$
nuclear spins during $10^5$ sweeps, we uncover a mechanism of dynamical
self-quenching which results in a fast saturation of the nuclear polarization
under stationary pumping. This is caused by screening of the field of the
nuclear spins. In systems with moderate spin-orbit coupling, self-quenching
also screens the spin-orbit interaction. The mechanism is generic and remains
robust under a moderate noise. Our finding explains low polarization levels
achieved experimentally and calls for developing new protocols that break the
self-quenching limitations.",1206.0100v3
2012-09-03,Dynamical Jahn-Teller Effect in Spin-Orbital Coupled System,"Dynamical Jahn-Teller (DJT) effect in a spin-orbital coupled system on a
honeycomb lattice is examined, motivated from recently observed spin-liquid
behavior in Ba$_3$CuSb$_2$O$_9$. An effective vibronic Hamiltonian, where the
superexchange interaction and the DJT effect are taken into account, is
derived. We find that the DJT effect induces a spin-orbital resonant state
where local spin-singlet states and parallel orbital configurations are
entangled with each other. This spin-orbital resonant state is realized in
between an orbital ordered state, where spin-singlet pairs are localized, and
an antiferromagnetic ordered state. Based on the theoretical results, a
possible scenario for Ba$_3$CuSb$_2$O$_9$ is proposed.",1209.0239v2
2012-10-23,Spatial distribution of dynamically polarized nuclear spins in electron spin domains in the $ν= 2/3$ fractional quantum Hall state studied by nuclear electric resonance,"Nuclear electric resonance (NER) is based on nuclear magnetic resonance
mediated by spatial oscillations of electron spin domains excited by a radio
frequency (RF) electric field, and it allows us to investigate the spatial
distribution of the nuclear spin polarization around domain walls (DWs). Here,
NER measurements were made of the dynamic nuclear spin polarization (DNP) at
the spin phase transition of the fractional quantum Hall state at a Landau
level filling factor of $\nu=2/3$. From the RF pulse power and pulse duration
dependence of the NER spectrum, we show that the DNP occurs only within $\sim
100$ nm around DWs, and that it does not occur in DWs. We also show that DWs
are pinned by the hyperfine field from polarized nuclear spins.",1210.6223v2
2012-11-14,The center of mass and center of charge of the electron,"If the assumption that the center of mass(CM) and the center of charge(CC) of
the electron are two different points was stated 100 years ago, our conceptual
ideas about elementary particles would be different. This assumption is only
compatible with a relativistic description. It suggests, from the classical
point of view, that the angular momentum of the electron has to have a unique
value. In the free motion, the CC follows a helix at the speed of light. The
spin with respect to CC and to CM satisfy two different dynamical equations
which shows that Dirac spin operator in the quantum case satisfies the same
dynamical equation as the classical spin with respect to the CC. This means,
among other things, that the addition of the three Dirac's spin operators of
the three quarks can never give rise to the spin of the proton, so that the
proton spin crisis could be related to this incompleteness in the addition of
the quark's angular momenta. Some other effects related to spinning particles
like the concept of gyromagnetic ratio, a classical description of tunneling
and the formation of bound pairs of electrons, are analized.",1211.3253v2
2012-11-21,Quantum and classical correlations in high temperature dynamics of two coupled large spins,"We study dynamical correlations of two coupled large spins depending on the
time and on the spin quantum numbers. In the high-temperature approximation, we
obtain analytical expressions for the mutual informations, quantum and
classical parts of correlations. The latter was obtained performing the
non-orthogonal projective (POVM) measurements onto the spin coherent states of
two spins or one spin, as well as by means of the orthogonal projective
measurement of von Neumann. Contribution from quantum correlations is much less
than that from classical ones and decreasing with the increase in spin quantum
numbers at short times. However, it is not so in a time equal to half of the
quantum period.",1211.4923v2
2013-01-04,Observation of Zitterbewegung in a spin-orbit coupled Bose-Einstein condensate,"Spin-orbit coupled ultra-cold atoms provide an intriguing new avenue for the
study of rich spin dynamics in superfluids. In this Letter, we observe
Zitterbewegung, the simultaneous velocity (thus position) and spin
oscillations, of neutral atoms between two spin-orbit coupled bands in a
Bose-Einstein condensate (BEC) through sudden quantum quenches of the
Hamiltonian. The observed Zitterbewegung oscillations are perfect on a short
time scale but gradually damp out on a long time scale, followed by sudden and
strong heating of the BEC. As an application, we also demonstrate how
Zitterbewegung oscillations can be exploited to populate the upper spin-orbit
band, and observe a subsequent dipole motion. Our experimental results are
corroborated by a theoretical and numerical analysis and showcase the great
flexibility that ultra-cold atoms provide for investigating rich spin dynamics
in superfluids.",1301.0658v2
2013-03-24,Spin-Transfer Torques in Helimagnets,"We theoretically investigate current-induced magnetization dynamics in
chiral-lattice helimagnets. Spin-orbit coupling in non-centrosymmetric crystals
induces a reactive spin-transfer torque that has not been previously
considered. We demonstrate how the torque is governed by the crystal symmetry
and acts as an effective magnetic field along the current direction in cubic
B20-type crystals. The effects of the new torque are computed for
current-induced dynamics of spin-spirals and the Doppler shift of spin waves.
In current-induced spin-spiral motion, the new torque tilts the spiral
structure. The spin waves of the spiral structure are initially displaced by
the new torque, while the dispersion relation is unaffected.",1303.5921v2
2013-03-31,Electrical current and coupled electron-nuclear spin dynamics in double quantum dots,"We examine electronic transport in a spin-blockaded double quantum dot. We
show that by tuning the strength of the spin-orbit interaction the current
flowing through the double dot exhibits a dip at zero magnetic field or a peak
at a magnetic field for which the two-electron energy levels anticross. This
behaviour is due to the dependence of the singlet-triplet mixing on the field
and spin-orbit amplitude. We derive approximate expressions for the current as
a function of the amplitudes of the states involved in the transport. We also
consider an alternative model that takes into account a finite number of
nuclear spins and study the resulting coupled dynamics between electron and
nuclear spins. We show that if the spin ensemble is in a thermal state there
are regular oscillations in the transient current followed by quasi-chaotic
revivals akin to those seen in a thermal Jaynes-Cummings model.",1304.0169v1
2013-11-28,Dynamic Spin Fluctuations at $T\rightarrow 0$ in a Spin-1/2 Ferromagnetic Kagome Lattice,"We report magnetization, electron spin resonance (ESR), and muon spin
relaxation ($\mu $SR) measurements on single crystals of the $S=1/2$ (Cu$%
^{+2}$) kagom\'{e} compound Cu(1,3-benzendicarboxylate). The $\mu $SR is
carried to temperatures as low as 45 mK. The spin Hamiltonian parameters are
determined from the analysis of the magnetization and ESR data. We find that
this compound has anisotropic ferromagnetic interactions. Nevertheless, no spin
freezing is observed even at temperatures two orders of magnitude lower than
the coupling constants. In light of this finding, the relation between
persistent spin dynamics and spin liquid are reexamined.",1311.7411v1
2014-07-30,Dipolar atomic spin ensembles in a double-well potential,"We experimentally study the spin dynamics of mesoscopic ensembles of
ultracold magnetic spin-3 atoms located in two separated wells of an optical
dipole trap. We use a radio-frequency sweep to selectively flip the spin of the
atoms in one of the wells, which produces two separated spin domains of
opposite polarization. We observe that these engineered spin domains are
metastable with respect to the long-range magnetic dipolar interactions between
the two ensembles. The absence of inter-cloud dipolar spin-exchange processes
reveals a classical behavior, in contrast to previous results with atoms loaded
in an optical lattice. When we merge the two subsystems, we observe
spin-exchange dynamics due to contact interactions which enable the first
determination of the s-wave scattering length of 52Cr atoms in the S=0
molecular channel a_0=13.5^{+11}_{-10.5}a_B (where a_B is the Bohr radius).",1407.8130v1
2014-09-17,Bosonic Many-body Theory of Quantum Spin Ice,"We carry out an analytical study of quantum spin ice, a U$(1)$ quantum spin
liquid close to the classical spin ice solution for an effective spin $1/2$
model with anisotropic exchange couplings $J_{zz}$, $J_{\pm}$ and $J_{z\pm}$ on
the pyrochlore lattice. Starting from the quantum rotor model introduced by
Savary and Balents in Phys. Rev. Lett. 108, 037202 (2012), we retain the
dynamics of both the spinons and gauge field sectors in our treatment. The
spinons are described by a bosonic representation of quantum XY rotors while
the dynamics of the gauge field is captured by a phenomenological Hamiltonian.
By calculating the one-loop spinon self-energy, which is proportional to
$J_{z\pm}^2$, we determine the stability region of the U$(1)$ quantum spin
liquid phase in the $J_{\pm}/J_{zz}$ vs $J_{z\pm}/J_{zz}$ zero temperature
phase diagram. From these results, we estimate the location of the boundaries
between the spin liquid phase and classical long-range ordered phases.",1409.5127v2
2015-01-19,Stabilizing nuclear spins around semiconductor electrons via the interplay of optical coherent population trapping and dynamic nuclear polarization,"We experimentally demonstrate how coherent population trapping (CPT) for
donor-bound electron spins in GaAs results in autonomous feedback that prepares
stabilized states for the spin polarization of nuclei around the electrons. CPT
was realized by excitation with two lasers to a bound-exciton state.
Transmission studies of the spectral CPT feature on an ensemble of electrons
directly reveal the statistical distribution of prepared nuclear spin states.
Tuning the laser driving from blue to red detuned drives a transition from one
to two stable states. Our results have importance for ongoing research on
schemes for dynamic nuclear spin polarization, the central spin problem and
control of spin coherence.",1501.04524v2
2015-02-13,Antiferromagnet-Mediated Spin Transfer Between Metal and Ferromagnet,"We develop a theory for spin transported by coherent Neel dynamics through an
antiferromagnetic insulator coupled to a ferromagnetic insulator on one side
and a current-carrying normal metal with strong spin-orbit coupling on the
other. The ferromagnet is considered within the mono-domain limit and we assume
its coupling to the local antiferromagnet Neel order at the
ferromagnet|antiferromagnet interface through exchange coupling. Coupling
between the charge current and the local Neel order at the other interface is
described using spin Hall phenomenology. Spin transport through the
antiferromagnet, assumed to possess an easy-axis magnetic anisotropy, is solved
within the adiabatic approximation and the effect of spin current flowing into
the ferromagnet on its resonance linewidth is evaluated. Onsager reciprocity is
used to evaluate the inverse spin Hall voltage generated across the metal by a
dynamic ferromagnet as a function the antiferromagnet thickness.",1502.04128v1
2015-02-28,Electron-spin to Phonon Coupling in Graphene Decorated with Heavy Adatoms,"The naturally weak spin-orbit coupling in Graphene can be largely enhanced by
adatom deposition (e.g. Weeks et al. Phys. Rev. X 1, 021001 (2011)). However,
the dynamics of the adatoms also induces a coupling between phonons and the
electron spin. Using group theory and a tight-binding model, we systematically
investigate the coupling between the low-energy in-plane phonons and the
electron spin in single-layer graphene uniformly decorated with heavy adatoms.
Our results provide the foundation for future investigations of spin transport
and superconductivity in this system. In order to quantify the effect of the
coupling to the lattice on the electronic spin dynamics, we compute the
spin-flip rate of electrons and holes. We show that the latter exhibits a
strong dependence on the quasi-particle energy and system temperature.",1503.00092v1
2014-08-26,Post-Newtonian dynamics basing on Mathisson-Papapetrou equations with Corinaldesi-Papapetrou condition in Kerr spacetime,"We derive the post-Newtonian dynamics for a spinning body with
Corinaldesi-Papapetrou spin supplementary condition in Kerr spacetime. Both the
equations of motion for the center-of-mass of body and the spin evolution are
obtained. For the non-relativistic case, our calculations show that the
magnitude of spin measured in the rest frame of the body's center-of-mass does
not change with time, though the center-of-mass does not move along the
geodesic. Moreover, we find that the effects of the spin-orbit and spin-spin
couplings will be suppressed by the Lorentz factor when the body has a
relativistic velocity.",1504.02049v3
2015-05-20,Effect of Transverse Magnetic Field on Dynamics of Current Driven Domain Wall Motion in the Presence of Spin-Hall Effect,"Theoretically, we study the dynamics of a current induced domain wall in the
bi-layer structure consists of a ferromagnetic layer and a non-magnetic metal
layer with strong spin-orbit coupling in the presence of spin-Hall effect. The
analytical expressions for the velocity and width of the domain wall interms of
excitation angle are obtained by solving the Landau-Lifshitz-Gilbert equation
with adiabatic, nonadiabatic and spin Hall effect-spin transfer torques using
Schryers and Walker's method. Numerical results show that the occurance of
polarity switching in the domain wall is observed only above the threshold
current density. The presence of transverse magnetic field along with spin Hall
effect-spin transfer torque enchances the value of the threshold current
density, and the corresponding saturated velocity at the threshold current
density is also increased.",1505.05249v1
2015-09-22,Long-lived Neel states in antiferromagnetic quantum spin chains with strong uniaxial anisotropy for atomic-scale antiferromagnetic spintronics,"It has been experimentally established that magnetic adatoms on surfaces can
be arranged to form antiferromagnetic quantum spin chains with strong uniaxial
anisotropy and Neel states in such spin systems can be used to realize
information storage. Here, we investigate eigen states, quantum spin dynamics,
and life times of Neel states in short antiferromagnetic quantum spin chains
with strong uniaxial anisotropy on the basis of numerical exact diagonalization
method. We show rigorously that as long as the uniaxial anisotropy is very
strong, the ground state and the first excitation state, being nearly
degenerate, are safely separated from the other states and thus dominate the
quantum dynamics of the Neel states. Through further numerical analysis, we
achieve a powerful life-time expression of the Neel states for arbitrary spin
and model parameters. It is interesting that for the famous Fe adatom chains on
Cu$_2$N surface, 14 or 16 Fe adatoms are enough to obtain a practical long
life-time for Neel state storage of information. These should be applicable to
other similar antiferromagnetic spin systems for atomic-scale antiferromagnetic
spintronics.",1509.06597v1
2016-02-05,Thermalization and many-body localization in systems under dynamic nuclear polarization,"We study the role of dipolar interactions in the standard protocol used to
achieve dynamic nuclear polarization (DNP). In the so-called spin-temperature
regime, where the interactions establish an effective thermodynamic behavior in
the out-of-equilibrium stationary state, we provide numerical predictions for
the level of hyperpolarization. We show that nuclear spins equilibrate to the
effective spin-temperature established among the electron spins of radicals, as
expected from the quantum theory of thermalization. Moreover, we present an
analytical technique to estimate the spin temperature, and thus, the nuclear
hyperpolarization in the steady state, as a function of interaction strength
and quenched disorder. This reproduces both our numerical data and experimental
results. Our central finding is that the nuclear hyperpolarization increases
steadily upon reducing the interaction strength (by diluting the radical
density). Interestingly, the highest polarization is reached at a point where
the establishment of a spin temperature is just about to break down due to the
incipient many-body localization transition in the electron spin system.",1602.01931v1
2016-03-28,Spin dynamics of hopping electrons in quantum wires: algebraic decay and noise,"We study theoretically spin decoherence and intrinsic spin noise in
semiconductor quantum wires caused by an interplay of electron hopping between
the localized states and the hyperfine interaction of electron and nuclear
spins. At a sufficiently low density of localization sites the hopping rates
have an exponentially broad distribution. It allows the description of the spin
dynamics in terms of closely-situated ""pairs"" of sites and single ""reaching""
states, from which the series of hops result in the electron localized inside a
""pair"". The developed analytical model and numerical simulations demonstrate
disorder-dependent algebraic tails in the spin decay and power-law
singularity-like features in the low-frequency part of the spin noise spectrum.",1603.08381v1
2016-04-05,Designing spin channel geometries for entanglement distribution,"We investigate different geometries of spin-1/2 nitrogen impurity channels
for distributing entanglement between pairs of remote nitrogen vacancy centers
(NVs) in diamond. To go beyond the system size limits imposed by directly
solving the master equation, we implement a matrix product operator method to
describe the open system dynamics. In so doing, we provide an early
demonstration of how this technique can be used for simulating real systems.
For a fixed NV separation there is an interplay between incoherent impurity
spin decay and coherent entanglement transfer: Long transfer time, few-spin
systems experience strong dephasing that can be overcome by increasing the
number of spins in the channel. We examine how missing spins and disorder in
the coupling strengths affect the dynamics, finding that in some regimes a spin
ladder is a more effective conduit for information than a single spin chain.",1604.01297v1
2016-04-06,Antiferromagnetic domain wall motion driven by spin-orbit torques,"We theoretically investigate dynamics of antiferromagnetic domain walls
driven by spin-orbit torques in antiferromagnet/heavy metal bilayers. We show
that spin-orbit torques drive antiferromagnetic domain walls much faster than
ferromagnetic domain walls. As the domain wall velocity approaches the maximum
spin-wave group velocity, the domain wall undergoes Lorentz contraction and
emits spin-waves in the terahertz frequency range. The interplay between spin
orbit torques and the relativistic dynamics of antiferromagnetic domain walls
leads to the efficient manipulation of antiferromagnetic spin textures and
paves the way for the generation of high frequency signals in antiferromagnets.",1604.01473v1
2016-04-11,All-Optical Study of Tunable Ultrafast Spin Dynamics in [Co/Pd]-NiFe Systems: The Role of Spin-Twist Structure on Gilbert Damping,"We investigate optically induced ultrafast magnetization dynamics in [Co(0.5
nm)/Pd(1 nm)]x5/NiFe(t) exchange-spring samples with tilted perpendicular
magnetic anisotropy using a time-resolved magneto-optical Kerr effect
magnetometer. The competition between the out-of-plane anisotropy of the hard
layer, the in-plane anisotropy of the soft layer and the applied bias field
reorganizes the spins in the soft layer, which are modified further with the
variation in t. The spin-wave spectrum, the ultrafast demagnetization time, and
the extracted damping coefficient all depend on the spin distribution in the
soft layer, while the latter two also depend on the spin-orbit coupling between
the Co and Pd layers. The spin-wave spectra change from multimode to
single-mode as t increases. At the maximum field reached in this study, H=2.5
kOe, the damping shows a nonmonotonic dependence on t with a minimum at t=7.5
nm. For t<7.5 nm, intrinsic effects dominate, whereas for t>7.5 nm, extrinsic
effects govern the damping mechanisms.",1604.02998v1
2016-04-25,Increased coherence time in narrowed bath states in quantum dots,"We study the influence of narrowed distributions of the nuclear Overhauser
field on the decoherence of a central electron spin in quantum dots. We
describe the spin dynamics in quantum dots by the central spin model. We use
analytic solutions for uniform couplings and the time dependent density-matrix
renormalization group (tDMRG) for nonuniform couplings. With these tools we
calculate the dynamics of the central spin for large baths of nuclear spins
with or without external magnetic field applied to the central spin. The focus
of our study is the influence of initial mixtures with narrowed distributions
of the Overhauser field and of applied magnetic fields on the decoherence of
the central spin.",1604.07165v2
2016-07-26,Spin-orbit signatures in the dynamics of singlet-triplet qubits in double quantum dots,"We characterize numerically and analytically the signatures of the spin-orbit
interaction in a two-electron GaAs double quantum dot in the presence of an
external magnetic field. In particular, we obtain the return probability of the
singlet state by simulating Landau-Zener voltage detuning sweeps which traverse
the singlet-triplet ($S-T_+$) resonance. Our results indicate that
non-spin-conserving interdot tunneling processes arising from the spin-orbit
interaction have well defined signatures. These allow direct access to the
spin-orbit interaction scales and are characterized by a frequency shift and
Fourier amplitude modulation of the Rabi flopping dynamics of the
singlet-triplet qubits $S-T_0$ and $S-T_+$. By applying the Bloch-Feshbach
projection formalism, we demonstrate analytically that the aforementioned
effects originate from the interplay between spin-orbit interaction and
processes driven by the hyperfine interaction between the electron spins and
those of the GaAs nuclei.",1607.07852v3
2016-09-07,Spin excitations in the quasi-two-dimensional charge-ordered insulator $α$-(BEDT-TTF)$_2$I$_3$ probed via $^{13}$C NMR,"The spin excitations from the nonmagnetic charge-ordered insulating state of
$\alpha$-(BEDT-TTF)$_2$I$_3$ at ambient pressure have been investigated by
probing the static and low-frequency dynamic spin susceptibilities via
site-selective nuclear magnetic resonance at $^{13}$C sites. The site-dependent
values of the shift and the spin-lattice relaxation rate $1/T_1$ below the
charge-ordering transition temperature ($T_{CO} \approx$ 135 K) demonstrate a
spin density imbalance in the unit cell, in accord with the charge-density
ratio reported earlier. The shift and $1/T_1$ show activated temperature
dependence with a static (shift) gap $\Delta_S \approx$ 47-52 meV and a dynamic
($1/T_1$) gap $\Delta_R \approx$ 40 meV. The sizes of the gaps are well
described in terms of a localized spin model, where spin one-half
antiferromagnetic dimer chains are weakly coupled with each other.",1609.01906v1
2017-02-03,Research Note: The Expected Spins of Gravitational Wave Sources With Isolated Field Binary Progenitors,"We explore the consequences of dynamical evolution of field binaries composed
of a primary black hole (BH) and a Wolf-Rayet (WR) star in the context of
gravitational wave (GW) source progenitors. We argue, from general
considerations, that the spin of the WR-descendent BH will be maximal in a
significant number of cases due to dynamical effects. In other cases, the spin
should reflect the natal spin of the primary BH which are currently
theoretically unconstrained. We argue that the three currently published LIGO
systems (GW150914, GW151226, LVT151012) suggest that this spin is small. The
resultant effective spin distribution of gravitational wave sources should thus
be bi-model if this classic GW progenitor channel is indeed dominant. While
this is consistent with the LIGO detections thus far, it is in contrast to the
three best-measured high-mass x-ray binary (HMXB) systems. A comparison of the
spin distribution of HMXBs and GW sources should ultimately reveal whether or
not these systems arise from similar astrophysical channels.",1702.00885v1
2017-02-14,Spin diffusion from an inhomogeneous quench in an integrable system,"Generalised hydrodynamics predicts universal ballistic transport in
integrable lattice systems when prepared in generic inhomogeneous initial
states. However, the ballistic contribution to transport can vanish in systems
with additional discrete symmetries. Here we perform large scale numerical
simulations of spin dynamics in the anisotropic Heisenberg $XXZ$ spin $1/2$
chain starting from an inhomogeneous mixed initial state which is symmetric
with respect to a combination of spin-reversal and spatial reflection. In the
isotropic and easy-axis regimes we find non-ballistic spin transport which we
analyse in detail in terms of scaling exponents of the transported
magnetisation and scaling profiles of the spin density. While in the easy-axis
regime we find accurate evidence of normal diffusion, the spin transport in the
isotropic case is clearly super-diffusive, with the scaling exponent very close
to $2/3$, but with universal scaling dynamics which obeys the diffusion
equation in nonlinearly scaled time.",1702.04210v2
2017-08-06,Chiral spin currents in a trapped-ion quantum simulator using Floquet engineering,"The most typical ingredient of topologically protected quantum states are
magnetic fluxes. In a system of spins, complex-valued interaction parameters
give rise to a flux, if their phases do not add up to zero along a closed loop.
Here we apply periodic driving, a powerful tool for quantum engineering, to a
trapped-ion quantum simulator in order to generate such spin-spin interactions.
We consider a simple driving scheme, consisting of a repeated series of locally
quenched fields, and demonstrate the feasibility of this approach by studying
the dynamics of a small system. An emblematic hallmark of the flux, accessible
in experiments, is the appearance of chiral spin currents. Strikingly, we find
that in parameter regimes where, in the absence of fluxes, phonon excitations
dramatically reduce the fidelity of the spin model simulation, the spin
dynamics remains widely unaffected by the phonons when fluxes are present.",1708.01882v1
2018-02-16,Dephasing mechanisms of diamond-based nuclear-spin memories for quantum networks,"We probe dephasing mechanisms within a quantum network node consisting of a
single nitrogen-vacancy centre electron spin that is hyperfine coupled to
surrounding $^{13} \text{C}$ nuclear-spin quantum memories. Previous studies
have analysed memory dephasing caused by the stochastic electron-spin reset
process, which is a component of optical internode entangling protocols. Here,
we find, by using dynamical decoupling techniques and exploiting phase matching
conditions in the electron-nuclear dynamics, that control infidelities and
quasi-static noise are the major contributors to memory dephasing induced by
the entangling sequence. These insights enable us to demonstrate a 19-fold
improved memory performance which is still not limited by the electron
reinitialization process. We further perform pump-probe studies to investigate
the spin-flip channels during the optical electron spin reset. We find that
spin-flips occur via decay from the meta-stable singlet states with a branching
ratio of 8(1):1:1, in contrast with previous work. These results allow us to
formulate straightforward improvements to diamond-based quantum networks and
similar architectures.",1802.05996v1
2020-07-20,Regulating spin dynamics of graphene flakes,"A method of regulating spin dynamics of the so-called magnetic graphene is
analyzed. Magnetic moments can be incorporated into graphene flakes and
graphene ribbons through defects, such as adatoms and vacancies. Local spins
can also be attached to graphene at hydrogenated zigzag edges. Spin flips can
be produced by transverse pulses and by connecting the sample to a resonance
electric coil. The action of the resonator feedback field strongly accelerates
spin reversal. The possibility of fast spin reversal is important for
spintronics and for quantum information processing allowing for an efficient
functioning of spin registers.",2007.10217v1
2014-03-14,Spin noise in a quantum dot ensemble: from a quantum mechanical to a semi-classical description,"Spin noise spectroscopy is a promising technique for revealing the
microscopic nature of spin dephasing processes in quantum dots. We compare the
spin-noise in an ensemble of singly charged quantum dots calculated by two
complementary approaches. The Chebyshev polynomial expansion technique (CET)
accounts for the full quantum mechanical fluctuation of the nuclear spin bath
and a semi-classical approach (SCA) is based on the averaging the electron spin
dynamics over all different static Overhauser field configurations.
  We observe a remarkable agreement between both methods in the high-frequency
part of the spectra, while the low-frequency part is determined by the long
time fluctuations of the Overhauser field. We find small differences in the
spectra depending on the distribution of hyperfine couplings. The spin-noise
spectra in strong enough magnetic fields where the nuclear dynamics is quenched
calculated by two complimentary approaches are in perfect agreement.",1403.3550v1
2018-05-19,Optically driven spin pumping mediating collective magnetization dynamics in a spin valve structure,"We demonstrate spin pumping, i.e. the generation of a pure spin current by
precessing magnetization, without application of microwave radiation commonly
used in spin pumping experiments. We use femtosecond laser pulses to
simultaneously launch the magnetization precession in each of two ferromagnetic
layers of a Galfenol-based spin valve and monitor the temporal evolution of the
magnetizations. The spin currents generated by the precession cause a dynamic
coupling of the two layers. This coupling has dissipative character and is
especially efficient when the precession frequencies in the two layers are in
resonance, where coupled modes with strongly different decay rates are formed.",1805.07669v1
2012-01-03,Coherent spin dynamics of electrons and excitons in nanostructures,"The studies of spin phenomena in semiconductor low dimensional systems have
grown into the rapidly developing area of the condensed matter physics:
spintronics. The most urgent problems in this area, both fundamental and
applied, are the creation of charge carrier spin polarization and its detection
as well as electron spin control by nonmagnetic methods. Here we present a
review of recent achievements in the studies of spin dynamics of electrons,
holes and their complexes in the pump-probe method. The microscopic mechanisms
of spin orientation of charge carriers and their complexes by short circularly
polarized optical pulses and the formation processes of the spin signals of
Faraday and Kerr rotation of the probe pulse polarization plane as well as
induced ellipticity are discussed. A special attention is paid to the
comparison of theoretical concepts with experimental data obtained on the
n-type quantum well and quantum dot array samples.",1201.0604v1
2014-06-03,Spin-orbital dynamics in a system of polar molecules,"Spin-orbit coupling (SOC) in solids normally originates from the electron
motion in the electric field of the crystal. It is key to understanding a
variety of spin-transport and topological phenomena, such as Majorana fermions
and recently discovered topological insulators. Implementing and controlling
spin-orbit coupling is thus highly desirable and could open untapped
opportunities for the exploration of unique quantum physics. Here, we show that
dipole-dipole interactions can produce an effective SOC in two-dimensional
ultracold polar molecule gases. This SOC generates chiral excitations with a
non-trivial Berry phase $2\pi$. These excitations, which we call
\emph{chirons}, resemble low-energy quasiparticles in bilayer graphene and
emerge regardless of the quantum statistics and for arbitrary ratios of kinetic
to interaction energies. Chirons manifest themselves in the dynamics of the
spin density profile, spin currents, and spin coherences, even for molecules
pinned in a deep optical lattice and should be observable in current
experiments.",1406.0570v2
2016-12-08,Spin relaxation in a one-dimensional large-spin degenerate Fermi gas,"In this work, we study the dynamics of an atomic harmonically trapped
large-spin Fermi gas in one dimension (1D). We investigate the interplay of
different collision processes. Coherent spin oscillations, driven by
spin-changing forward scattering are captured by a mean-field description and
scale linearly with density regardless of the dimension of the system.
Conversely, ""incoherent"" collision processes which e.g. lead to the damping of
spin oscillations, behave differently. In the usual three-dimensional (3D)
case, the rate of incoherent processes increases faster with density than
mean-field effects, but in 1D it increases slower. This means, that in the 1D
case, incoherent collisions become more important at lower densities. We study
these effects by deriving and integrating a quantum Boltzmann equation. We
demonstrate that the well known fact that in one dimension, interaction-induced
correlations become more dominant at low densities can be observed in
far-from-equilibrium spin dynamics.",1612.02618v2
2016-12-21,Spin transitions driven by electric dipole spin resonance in fluorinated single- and bilayer-graphene quantum dots,"Spin transitions driven by a periodically varying electric potential in
dilute fluorinated graphene quantum dots are investigated. Flakes of monolayer
graphene are considered as well as electrostatic electron traps induced in
bilayer graphene. The stationary states are obtained within the tight-binding
approach and are used to the basis of eigenstates to describe the system
dynamics. The dilute fluorination of the top layer lifts the valley degeneracy
of the confined states and attenuates the orbital magnetic dipole moments due
to current circulation within the flake. Moreover, the spin-orbit coupling
introduced by the surface deformation of the top layer induced by the adatoms
allows spin flips to be driven by the AC electric field. For the bilayer
quantum dots the spin flip times is substantially shorter than the experimental
spin relaxation. Dynamical effects including many-photon and multilevel
transitions are also discussed.",1612.07001v1
2017-06-02,Closing the gap between spatial and spin dynamics of electrons at the metal-to-insulator transition,"We combine extensive precision measurements of the optically detected spin
dynamics and magneto-transport measurements in a contiguous set of n-doped bulk
GaAs structures in order to unambiguously unravel the intriguing but complex
contributions to the spin relaxation at the metal-to-insulator transition
(MIT). Just below the MIT, the interplay between hopping induced loss of spin
coherence and hyperfine interaction yields a maximum spin lifetime exceeding
800~ns. At slightly higher doping concentrations, however, the spin relaxation
deviates from the expected Dyakonov-Perel mechanism which is consistently
explained by a reduction of the effective motional narrowing with increasing
doping concentration. The reduction is attributed to the change of the dominant
momentum scattering mechanism in the metallic impurity band where scattering by
local conductivity domain boundaries due to the intrinsic random distribution
of donors becomes significant. Here, we fully identify and model all intricate
contributions of the relevant microscopic scattering mechanisms which allows
the complete quantitative modeling of the electron spin relaxation in the
entire regime from weakly interacting up to fully delocalized electrons.",1706.00615v1
2017-07-02,Dynamics of one-dimensional electrons with broken spin-charge separation,"Spin-charge separation is known to be broken in many physically interesting
one-dimensional (1D) and quasi-1D systems with spin-orbit interaction because
of which spin and charge degrees of freedom are mixed in collective
excitations. Mixed spin-charge modes carry an electric charge and therefore can
be investigated by electrical means. We explore this possibility by studying
the dynamic conductance of a 1D electron system with image-potential-induced
spin-orbit interaction. The real part of the admittance reveals an oscillatory
behavior versus frequency that reflects the collective excitation resonances
for both modes at their respective transit frequencies. By analyzing the
frequency dependence of the conductance the mode velocities can be found and
their spin-charge structure can be determined quantitatively.",1707.00316v3
2018-10-24,Photoinduced topological spin texture in a metallic ferromagnet,"Photoinduced nonequilibrium spin structure is examined in the double-exchange
model, in which itinerant electrons couple with localized spins through the
ferromagnetic Hund coupling. In particular, we focus on the transient spin
structure from the initial ferromagnetic metallic state to the steady
antiferromagnetic ordered state reported in [Phys. Rev. Lett. 119, 207202
(2017)]. By solving the Schr\""odinger equation combined with the
Landau-Lifshitz-Gilbert equation, we find finite winding number and chirality,
which implies emergence of topological chiral spin textures. These observations
are reproduced by a calculation where spin dynamics after sudden quench of the
chemical potential are examined in larger clusters. A possible mechanism of the
topological spin texture in the transient dynamics is discussed.",1810.10244v1
2020-01-10,Transport-induced suppression of nuclear field fluctuations in multi-quantum-dot systems,"Magnetic noise from randomly fluctuating nuclear spin ensembles is the
dominating source of decoherence for many multi-quantum-dot multielectron spin
qubits. Here we investigate in detail the effect of a DC electric current on
the coupled electron-nuclear spin dynamics in double and triple quantum dots
tuned to the regime of Pauli spin blockade. We consider both systems with and
without significant spin-orbit coupling and find that in all cases the flow of
electrons can induce a process of dynamical nuclear spin polarization that
effectively suppresses the nuclear polarization gradients over neighboring
dots. Since exactly these gradients are the components of the nuclear fields
that act harmfully in the qubit subspace, we believe that this presents a
straightforward way to extend coherence times in multielectron spin qubits by
at least one order of magnitude.",2001.03481v1
2020-02-06,Rashba controlled two-electron spin-charge qubits as building blocks of a quantum computer,"The spin-sensitive charge oscillation, controlled by an external magnetic
field, was recently proposed as a mechanism of transformations of qubits,
defined as two-electron spin-charge Wannier molecules in a square quantum dot.
The paper expands this idea by including the effects of Rashba type spin-orbit
coupling. The problem is studied theoretically by mapping the system to an
analytic effective Hamiltonian for 8 low energy states, comprising singlet and
triplet on each dot diagonal. The validity of the mapping is confirmed by
comparing the energy and spin of full and mapped system, and also by the
reproduction of charge-oscillation dynamics in the presence of magnetic flux.
The newly introduced Rashba coupling significantly enriches the system
dynamics, affecting the magnitude of charge oscillations and allowing the
controlled transitions between singlet and triplet states due to the spin
rotations, induced by spin-orbit coupling. The results indicate the possibility
for use of the studied system for quantum information processing, while
possible extensions of the system to serve as a qubit in a universal quantum
computer, fulfilling all five DiVincenzo criteria, are also discussed.",2002.02426v1
2020-12-23,Spin noise spectroscopy of a noise-squeezed atomic state,"Spin noise spectroscopy is emerging as a powerful technique for studying the
dynamics of various spin systems also beyond their thermal equilibrium and
linear response. Here, we study spin fluctuations of room-temperature neutral
atoms in a Bell-Bloom type magnetometer. Driven by indirect pumping and
undergoing a parametric excitation, this system is known to produce
noise-squeezing. Our measurements not only reveal a strong asymmetry in the
noise distribution of the atomic signal quadratures at the magnetic resonance,
but also provide insight into the mechanism behind its generation and
evolution. In particular, a structure in the spectrum is identified which
allows to investigate the main dependencies and the characteristic timescales
of the noise process. The results obtained are compatible with parametrically
induced noise squeezing. Notably, the noise spectrum provides information on
the spin dynamics even in regimes where the macroscopic atomic coherence is
lost, effectively enhancing the sensitivity of the measurements. Our work
promotes spin noise spectroscopy as a versatile technique for the study of
noise squeezing in a wide range of spin based magnetic sensors.",2012.12617v1
2012-05-15,Dynamic Critical Scaling of the Holographic Spin Fluctuations,"Criticality with strong coupling is described by a theory in the vicinity of
a non-Gaussian fixed point. The holographic duality conjectures that a theory
at a non-Gaussian fixed point with strong coupling is dual to a gravitational
theory. In this paper, we present a holographic theory in treating the strongly
coupled critical spin fluctuations in quasi-2-dimension. We show that a
universal frequency over temperature scaling law is a rather general property
of the critical ac spin susceptibility at strongly coupled limit. Explicit
results for the dynamic scaling of spin susceptibility are obtained in large-N
and large 't Hooft limit. We argue that such critical scaling are in good
agreement with a number of experiments, some of which can not be explained by
any perturbative spin-density-wave theory. Our results strongly suggest that
the anomalous behavior of non-Fermi liquids in materials is closely related to
the spin fluctuations described through the non-Gaussian fixed point. The
exotic properties of non-Fermi liquids can be viewed as the Fermi liquids
coupling to strongly coupled critical spin fluctuations.",1205.3267v2
2017-09-29,Designing Magnetic Droplet Soliton Nucleation Employing Spin Polarizer,"We show by means of micromagnetic simulations that spin polarizer in
nano-contact spin torque oscillators (NC-STOs) as the representative of the
fixed layer in an orthogonal pseudo-spin valve (P-SV) can be employed to design
and to control magnetic droplet soliton nucleation and dynamics. We found that
using a tilted spin polarizer layer decreases the droplet nucleation time which
is more suitable for high speed applications. However, a tilted spin polarizer
increases the nucleation current and decreases the frequency stability of the
droplet. Additionally, by driving the magnetization inhomogenously at the
nano-contact region, it is found that a tilted spin polarizer reduces the
precession angle of the droplet and through an interplay with the Oersted field
of the DC current, it breaks the spatial symmetry of the droplet profile. Our
findings explore fundamental insight into nano-scale magnetic droplet soliton
dynamics with potential tunability parameters for future microwave electronics.",1709.10325v3
2017-11-27,Surprises from the spins: astrophysics and relativity with detections of spinning black-hole mergers,"Measurements of black-hole spins are of crucial importance to fulfill the
promise of gravitational-wave astronomy. On the astrophysics side, spins are
perhaps the cleanest indicator of black-hole evolutionary processes, thus
providing a preferred way to discriminate how LIGO's black holes form. On the
relativity side, spins are responsible for peculiar dynamical phenomena (from
precessional modulations in the long inspiral to gravitational-wave recoils at
merger) which encode precious information on the underlying astrophysical
processes. I present some examples to explore this deep and fascinating
interplay between spin dynamics (relativity) and environmental effects
(astrophysics). Black-hole spins indeed hide remarkable surprises on both
fronts: morphologies, resonances, constraints on supernova kicks, multiple
merger generations and more...",1711.10038v1
2018-06-06,Effect of electron correlations on spin excitation bandwidth in Ba$_{0.75}$K$_{0.25}$Fe$_{2}$As$_{2}$ as seen via time-of-flight inelastic neutron scattering,"We use inelastic neutron scattering (INS) to investigate the effect of
electron correlations on spin dynamics in the iron-based superconductor
Ba$_{0.75}$K$_{0.25}$Fe$_{2}$As$_{2}$. Our INS data show a spin-wave-like
dispersive feature, with a zone boundary energy of 200 meV. A first principles
analysis of dynamical spin susceptibility, incorporating the mass
renormalization factor of 3, as determined by angle-resolved photoemission
spectroscopy, provides a reasonable description of the observed spin
excitations. This analysis shows that electron correlations in the Fe-3$d$
bands yield enhanced effective electron masses, and consequently, induce
substantial narrowing of the spin excitation bandwidth. Our results highlight
the importance of electron correlations in an itinerant description of the spin
excitations in iron-based superconductors.",1806.02097v1
2018-06-06,Variational Renormalization Group for Dissipative Spin-Cavity Systems: Periodic Pulses of Nonclassical Photons from Mesoscopic Spin Ensembles,"Mesoscopic spin ensembles coupled to a cavity offer the exciting prospect of
observing complex nonclassical phenomena that pool the microscopic features
from a few spins with those of macroscopic spin ensembles. Here, we demonstrate
how the collective interactions in an ensemble of as many as hundred spins can
be harnessed to obtain a periodic pulse train of nonclassical light. To unravel
the full quantum dynamics and photon statistics, we develop a time-adaptive
variational renormalization group method that accurately captures the
underlying Lindbladian dynamics of the mesoscopic spin-cavity system.",1806.02394v2
2018-07-12,Dynamics of entanglement creation between two spins coupled to a chain,"We study the dynamics of entanglement between two spins which is created by
the coupling to a common thermal reservoir. The reservoir is a
spin-$\frac{1}{2}$ Ising transverse field chain thermally excited, the two
defect spins couple to two spins of the chain which can be at a macroscopic
distance. In the weak-coupling and low-temperature limit the spin chain is
mapped onto a bath of linearly interacting oscillators using the
Holstein-Primakoff transformation. We analyse the time evolution of the density
matrix of the two defect spins for transient times and deduce the entanglement
which is generated by the common reservoir. We discuss several scenarios for
different initial states of the two spins and for varying distances.",1807.04507v2
2018-08-08,Analog Quantum Simulation of Extremely Sub-Ohmic Spin-Boson Models,"We propose a scheme for the quantum simulation of sub-Ohmic spin--boson
models by color centers in free-standing hexagonal boron nitride (h-BN)
membranes. The electronic spin of a color center that couples to the membrane
vibrational spectrum constitute the physical model. The spin-motion coupling is
provided by an external magnetic field gradient. In this study, we show that a
class of spectral densities can be attained by engineering geometry and
boundary conditions of the h-BN resonator. We then put our focus on two extreme
cases, i.e. $1/f$- and white-noise spectral densities. Spin coherence and
polarization dynamics are studied. Our calculations show coherence revivals at
periods set by the bath characteristic frequency signaling the non-Markovian
nature of the baths. The nonequilibrium dynamics of the spin polarization
exhibits a coherent localization, a property peculiar to the quantum phase
transition in extremely sub-Ohmic spin-boson models. Our scheme may find
application in understanding sources of decoherence in solid-state quantum
bits.",1808.02916v1
2019-02-20,Persistent spin dynamics in the pressurized spin-liquid candidate YbMgGaO$_4$,"Single-crystal x-ray diffraction, density-functional band-structure
calculations, and muon spin relaxation ($\mu$SR) are used to probe pressure
evolution of the triangular spin-liquid candidate YbMgGaO$_4$. The rhombohedral
crystal structure is retained up to at least 10 GPa and shows a nearly uniform
compression along both in-plane and out-of-plane directions, whereas local
distortions caused by the random distribution of Mg$^{2+}$ and Ga$^{3+}$ remain
mostly unchanged. The $\mu$SR data confirm persistent spin dynamics up to 2.6
GPa and down to 250 mK with no change in the muon relaxation rate.
Longitudinal-field $\mu$SR reveals power-law behavior of the spin-spin
autocorrelation function, both at ambient pressure and upon compression.",1902.07749v2
2019-04-10,Dimension transcendence and anomalous charge transport in magnets with moving multiple-$Q$ spin textures,"Multiple-$Q$ spin textures, such as magnetic bubble and skyrmion lattices,
can be driven into motion by external stimuli. The motion of spin textures
affects the electronic states. Here we show that to describe correctly the
electronic dynamics, the momentum space needs to be transcended to higher
dimensions by including the ancillary dimensions associated with phason modes
of the translational motion of the spin textures. The electronic states have
non-trivial topology characterized by the first and second Chern numbers in the
high dimensional hybrid momentum space. This gives rise to an anomalous
electric charge transport due to the motion of spin textures. By deforming the
spin textures, a nonlinear response associated with the second Chern number can
be induced. The charge transport is derived from the semi-classical equation of
motion of electrons that depends on the Berry curvature in the hybrid momentum
space. Our results suggest that the motion of multiple-$Q$ spin textures has
significant effects on the electronic dynamics and provides a new platform to
explore high dimensional topological physics.",1904.05473v3
2020-06-02,Dynamic magnetization in non-Hermitian quantum spin system,"We report a global effect induced by the local complex field, associated with
the spin-exchange interaction. High-order exceptional point up to ($N+1$)-level
coalescence is created at the critical local complex field applied to the
$N$-size quantum spin chain. The ($N+1$)-order coalescent level is a saturated
ferromagnetic ground state in the isotropic spin system. Remarkably, the final
state always approaches the ground state for an arbitrary initial state with
any number of spin flips; even if the initial state is orthogonal to the ground
state. Furthermore, the switch of macroscopic magnetization is solely driven by
the time and forms a hysteresis loop in the time domain. The retentivity and
coercivity of the hysteresis loop mainly rely on the non-Hermiticity. Our
findings highlight the cooperation of non-Hermiticity and the interaction in
quantum spin system, suggest a dynamical framework to realize magnetization,
and thus pave the way for the non-Hermitian quantum spin system.",2006.01324v1
2020-06-07,Quantum Dynamics of Collective Spin States in a Thermal Gas,"Ensembles of alkali or noble-gas atoms at room temperature and above are
widely applied in quantum optics and metrology owing to their long-lived spins.
Their collective spin states maintain nonclassical nonlocal correlations,
despite the atomic thermal motion in the bulk and at the boundaries. Here we
present a stochastic, fully-quantum description of the effect of atomic
diffusion in these systems. We employ the Bloch-Heisenberg-Langevin formalism
to account for the quantum noise originating from diffusion and from various
boundary conditions corresponding to typical wall coatings, thus modeling the
dynamics of nonclassical spin states with spatial inter-atomic correlations. As
examples, we apply the model to calculate spin noise spectroscopy, temporal
relaxation of squeezed spin states, and the coherent coupling between two spin
species in a hybrid system.",2006.04243v2
2020-06-23,Dynamic polarization of electron spins interacting with nuclei in semiconductor nanostructures,"We suggest a new spin orientation mechanism for localized electrons:
$dynamic~electron~spin~polarization~provided~by~nuclear~spin~fluctuations$. The
angular momentum for the electrons is gained from the nuclear spin system via
the hyperfine interaction in a weak magnetic field. For this the sample is
illuminated by an unpolarized light, which directly polarizes neither the
electrons nor the nuclei. We predict, that for the electrons bound in localized
excitons 100% spin polarization can be reached in longitudinal magnetic fields
of a few millitesla. The proof of principle experiment is performed on
momentum-indirect excitons in (In,Al)As/AlAs quantum dots, where in a magnetic
field of 17 mT the electron spin polarization of 30% is measured.",2006.13263v1
2020-06-30,Multi-solitons of the half-wave maps equation and Calogero-Moser spin-pole dynamics,"We consider the half-wave maps (HWM) equation which provides a continuum
description of the classical Haldane-Shastry spin chain on the real line. We
present exact multi-soliton solutions of this equation. Our solutions describe
solitary spin excitations that can move with different velocities and interact
in a non-trivial way. We make an ansatz for the solution allowing for an
arbitrary number of solitons, each described by a pole in the complex plane and
a complex spin variable, and we show that the HWM equation is satisfied if
these poles and spins evolve according to the dynamics of an exactly solvable
spin Calogero-Moser (CM) system with certain constraints on initial conditions.
We also find first order equations providing a B\""acklund transformation of
this spin CM system, generalize our results to the periodic HWM equation, and
provide plots that visualize our soliton solutions.",2006.16826v1
2020-11-03,Fractional Spin fluctuations and quantum liquid signature in Gd2ZnIrO6,"Hitherto, the discrete identification of quantum spin liquid phase, holy
grail of condensed matter physics, remains a challenging task experimentally.
However, the precursor of quantum spin liquid state may reflect in the spin
dynamics even in the paramagnetic phase over a wide temperature range as
conjectured theoretically. Here we report comprehensive inelastic light (Raman)
scattering measurements on the Ir based double perovskite, Gd2ZnIrO6, as a
function of different incident photon energies and polarization in a broad
temperature range. Our results evidenced the spin fractionalization within the
paramagnetic phase reflected in the emergence of a polarization independent
quasi-elastic peak at low energies with lowering temperature. Also, the
fluctuating scattering amplitude measured via dynamic Raman susceptibility
increases with lowering temperature and decreases mildly upon entering into
long-range magnetic ordering phase, below 23 K, suggesting the magnetic origin
of these fluctuations. This anomalous scattering response is thus indicative of
fluctuating fractional spin evincing the quantum spin liquid phase in a
three-dimensional double perovskite system.",2011.01470v2
2021-02-05,Symmetry-Driven Spin-Wave Gap Modulation in Nanolayered SrRuO3/SrTiO3 Heterostructures: Implications for Spintronic Applications,"A strong correlation between magnetic interaction and topological symmetries
leads to unconventional magneto-transport behavior. Weyl fermions induce
topologically protected spin-momentum locking, which is closely related to
spin-wave gap formation in magnetic crystals. Ferromagnetic SrRuO3, regarded as
a strong candidate for Weyl semimetal, inherently possesses a nonzero spin-wave
gap owing to its strong magnetic anisotropy. In this paper, we propose a method
to control the spin-wave dynamics by nanolayer designing of the SrRuO3/SrTiO3
superlattices. In particular, the six-unit-cell-thick SrRuO3 layers within the
superlattices undergo a phase transition in crystalline symmetry from
orthorhombic to tetragonal, as the thickness of the SrTiO3 layers is modulated
with atomic-scale precision. Consequently, the magnetic anisotropy, anomalous
Hall conductivity, and spin-wave gap could be systematically manipulated. Such
customization of magnetic anisotropy via nanoscale heterostructuring offers a
novel control knob to tailor the magnon excitation energy for future spintronic
applications, including magnon waveguides and filters. Our nanolayer approach
unveils the important correlation between the tunable lattice degrees of
freedom and spin dynamics in topologically non-trivial magnetic materials.",2102.03008v1
2021-04-14,Spin waves propagating through a stripe magnetic domain structure and their applications to reservoir computing,"Spin waves propagating through a stripe domain structure and reservoir
computing with their spin dynamics have been numerically studied with focusing
on the relation between physical phenomena and computing capabilities. Our
system utilizes a spin-wave-based device that has a continuous magnetic garnet
film and 1-input/72-output electrodes on the top. To control
spatially-distributed spin dynamics, a stripe magnetic domain structure and
amplitude-modulated triangular input waves were used. The spatially-arranged
electrodes detected spin vector outputs with various nonlinear characteristics
that were leveraged for reservoir computing. By moderately suppressing
nonlinear phenomena, our system achieves 100$\%$ prediction accuracy in
temporal exclusive-OR (XOR) problems with a delay step up to 5. At the same
time, it shows perfect inference in delay tasks with a delay step more than 7
and its memory capacity has a maximum value of 21. This study demonstrated that
our spin-wave-based reservoir computing has a high potential for edge-computing
applications and also can offer a rich opportunity for further understanding of
the underlying nonlinear physics.",2104.06794v1
2021-05-11,Symmetry-Induced Universal Momentum-Transfer Dependencies for Inelastic Neutron Scattering on Anisotropic Spin Clusters,"Inelastic neutron scattering (INS) is a key method for studying magnetic
excitations in spin systems, including molecular spin clusters. The method has
significantly advanced in recent years and now permits to probe the scattering
intensity as a function of the energy transfer and the momentum-transfer vector
Q. It was recently shown that high molecular symmetry facilitates the analysis
of spectra. Point-group symmetry imposes selection rules in isotropic as well
as anisotropic spin models. Furthermore, the Q-dependence of the INS intensity
may be completely determined by the point-group symmetry of the states involved
in a transition, thereby affording a clear separation of dynamics (energies,
transition strengths) and geometrical features (Q-dependencies). The present
work addresses this issue for anisotropic spin models. We identify a number of
cases where the Q-dependence is completely fixed by the point-group symmetry.
For six- and eight-membered planar spin rings and two polyhedra (the cube and
the icosahedron) we tabulate and plot the corresponding powder-averaged
universal intensity functions. The outlined formalism straightforwardly applies
to other highly-symmetric systems and should be useful for future analyses of
INS spectra by focusing on those features that contain information on either
spin dynamics or the point-group symmetry of states.",2105.04853v1
2021-09-08,Chirality Induced Propagation Velocity Asymmetry,"The spin-dependent propagation of electrons in helical nanowires is
investigated. We show that the interplay of spin angular momentum and nanowire
chirality, under spin-orbit interaction, lifts the symmetry between left and
right propagating electrons, giving rise to a velocity asymmetry. The study is
based on a microscopic tight-binding model that takes into account the
spin-orbit interaction. The continuity equation for the spin-dependent
probability density is derived, including the spin non-conserving terms, and
quantum dynamics calculations are performed to obtain the electron propagating
dynamics. The calculations are applied to the inorganic double-helix SnIP, a
quasi-1D material that constitutes a semiconductor with a band gap of ~ 1.9 eV.
The results, nevertheless, have general validity due to symmetry
considerations. The relation of the propagation velocity asymmetry with the
phenomena ascribed to the chiral-induced spin selectivity (CISS) effect is
examined.",2109.03629v2
2021-09-08,Gravity with a Dynamical Spinning Aether,"Einstein-aether theory is extended by allowing for spinning degrees of
freedom of the aether. In addition to the acceleration, shear, expansion, and
vorticity of the aether velocity field, a spin rotation describing the dynamics
of a classical intrinsic angular momentum of the aether is introduced as a
kinematic quantity. The action of Einstein-aether theory is augmented by a term
quadratic in the spin rotation and by coupling terms with the vorticity and the
acceleration. Besides breaking the Lorentz boost invariance, the theory breaks
the invariance under spatial rotations in the direction of the aether velocity.
In the weak field limit, there is a linear relationship between the spin
rotation, the vorticity, and the acceleration. Linearized wave solutions
correspond to the ones of Einstein-aether theory where the speeds of the spin 0
and spin 1 mode are modified. The extension of Einstein-aether theory has a
natural formulation in the framework of a teleparallel geometry where the
kinematic quantities become torsion fields.",2109.03700v1
2021-10-26,"Structure and magnetic studies of geometrically frustrated disordered pyrochlores A$_{2}$Zr$_{2}$O$_{7}$: (A = Eu, Gd, Er)","The spin ice system Dy$_{2}$Ti$_{2}$O$_{7}$ exhibits strong
frequency-dependent spin-freezing at $\sim$ 16 K temperature. Although it has
been a matter of discussion for years, the origin of this unusual spin freezing
is still unknown. The replacement of Ti with isovalent Zr leads to the dynamic
magnetic ground state at low temperatures in Dy$_{2}$Zr$_{2}$O$_{7}$ and
prevents the formation of high-temperature spin freezing. Interestingly the
high-temperature spin freezing re-emerges in the presence of the magnetic
field. In this direction, we have studied a series of disordered pyrochlore
oxides A$_{2}$Zr$_{2}$O$_{7}$ (A = Eu, Gd, Er) and compared their crystal
structure, magnetic, and heat capacity behavior with that of
Dy$_{2}$Zr$_{2}$O$_{7}$ and Ho$_{2}$Zr$_{2}$O$_{7}$ systems. Our study shows
that depending on the disordered parameter, the spin-freezing behavior can be
retained by slowing down the spin dynamic with a suitable choice of the
magnetic field. We observe that unlike titanates, modification at the rare
earth site does not make considerable change in the magnetic ground state of
these zirconates compounds.",2110.13573v1
2021-11-15,Phase diagram and post-quench dynamics in a double spin-chain system in transverse fields,"We propose and explore the physics of a toy multiferroic model by coupling
two distinct dipolar XXZ models in transverse fields. We determine first the
rich ground-state phase diagram of the model using density matrix
renormalization group techniques. Then, we explore the dynamics of the system
after global and local quenches, using the time-evolving block decimation
algorithm. After a global quench, the system displays decaying coupled
oscillations of the electric and magnetic spins, in agreement with the
Eigenstate Thermalization Hypothesis (ETH) for many-body interacting quantum
systems. Notably, the spin-spin interactions lead to a sizeable quadratic shift
in the oscillation frequency as the inter-chain coupling is increased. Local
quenches lead to a light-cone-like propagation of excitations. In this case,
the inter-chain coupling drives a transfer of energy between the chains that
generates a novel fast spin-wave mode along the 'magnetic' chain at the speed
of the 'electric' spin-wave. This suggests a limited control mechanism for
faster information transfer in magnetic spin chains using electric fields that
harnesses the electric dipoles as intermediaries.",2111.07831v1
2021-11-24,Distinguishing multi-spin interactions from lower-order effects,"Multi-spin interactions can be engineered with artificial quantum spins.
However, it is challenging to verify such interactions experimentally. Here we
describe two methods to characterize the $n$-local coupling of $n$ spins.
First, we analyze the variation of the transition energy of the static system
as a function of local spin fields. Standard measurement techniques are
employed to distinguish $n$-local interactions between up to five spins from
lower-order contributions in the presence of noise and spurious fields and
couplings. Second, we show a detection technique that relies on time dependent
driving of the coupling term. Generalizations to larger system sizes are
analyzed for both static and dynamic detection methods, and we find that the
dynamic method is asymptotically optimal when increasing the system size. The
proposed methods enable robust exploration of multi-spin interactions across a
broad range of both coupling strengths and qubit modalities.",2111.12717v1
2021-11-27,Active Magnetoelectric Control of Terahertz Spin Current,"Electrical control of photogenerated THz spin current pulses from a
spintronic emitter has been at the forefront for the development of scalable,
cost-efficient, wideband opto-spintronics devices. Artificially combined
ferroelectric and ferromagnet heterostructure provides the potential avenue to
control the spin dynamics efficiently utilizing the magnetoelectric coupling.
The demonstration of the electric field control of spin dynamics has so far
been limited up to gigahertz frequencies. Here, we demonstrate the electric
field mediated piezoelectric strain control of photogenerated THz spin current
pulse from a multiferroic spintronic emitter. The phase reversal of the THz
spin current pulse is obtained from the combined effect of piezoelectric strain
and a small constant magnetic field applied opposite to the initial
magnetization of the ferromagnet. The piezoelectric strain-controlled phase
switching of THz spin current thus opens a door to develop efficient strain
engineered scalable on-chip THz spintronics devices.",2111.13823v1
2021-12-08,Giant Resonant Self-Blocking in Magnetophononically Driven Quantum Magnets,"Magnetophononics, the modulation of magnetic interactions by driven
infrared-active lattice excitations, is emerging as a key mechanism for the
ultrafast dynamical control of both semiclassical and quantum spin systems by
coherent light. We demonstrate that, in a quantum magnetic material with strong
spin-phonon coupling, resonances between the driven phonon and the spin
excitation frequencies exhibit a giant self-blocking effect. Instead of
absorbing more energy, the spin system acts as a strong brake on the driven
phonon, causing it to absorb only a tiny fraction of the power available from
the laser. Using the quantum master equations governing the nonequilibrium
steady states of the coupled spin-lattice system, we show how self-blocking
dominates the dynamics, demonstrate the creation of mutually repelling hybrid
spin-phonon states, and control the nonequilibrium renormalization of the
lattice-driven spin excitation band.",2112.04508v1
2022-02-07,Nonequilibrium topological spin textures in momentum space,"Nonequilibrium quantum dynamics of many-body systems is the frontier of
condensed matter physics; recent advances in various time-resolved
spectroscopic techniques continue to reveal rich phenomena. Angle-resolved
photoemission spectroscopy (ARPES) as one powerful technique can resolve
electronic energy, momentum, and spin along the time axis after excitation.
However, dynamics of spin textures in momentum space remains mostly unexplored.
Here we demonstrate theoretically that the photoexcited surface state of
genuine or magnetically doped topological insulators shows novel topological
spin textures, i.e., tornado-like patterns, in the spin-resolved ARPES. We
systematically reveal its origin as a unique nonequilibrium photoinduced
topological winding phenomenon. As all intrinsic and extrinsic topological
helicity factors of both material and light are embedded in a robust and
delicate manner, the tornado patterns not only allow a remarkable tomography of
such important system information, but also enable various unique dichroic
topological switchings of the momentum-space spin texture. These results open a
new direction of nonequilibrium topological spin states in quantum materials.",2202.02917v2
2022-06-29,The role of electron polarization on nuclear spin diffusion,"Dynamic nuclear polarization (DNP) is capable of boosting signals in nuclear
magnetic resonance by orders of magnitude by creating out-of-equilibrium
nuclear spin polarization. The diffusion of nuclear spin polarization in the
vicinity of paramagnetic dopants is a crucial step for DNP and remains yet not
well understood. In this Letter, we show that the polarization of the electron
spin controls the rate of proton spin diffusion in a DNP sample at 1.2 K and 7
T; at increasingly high electron polarization, spin diffusion vanishes. We
rationalize our results using a 2 nucleus - 1 electron model and Lindblad s
Master equation, which generalizes preexisting models in the literature and
qualitatively accounts for the experimental observed spin diffusion dynamics.",2206.14771v1
2022-08-02,Fluctuating Fractionalized Spins in Quasi Two-dimensional Magnetic V0.85PS3,"Quantum spin liquid (QSL), a state characterized by exotic low energy
fractionalized excitations and statistics is still elusive experimentally and
may be gauged via indirect experimental signatures. Remnant of QSL phase may
reflect in the spin dynamics as well as quanta of lattice vibrations, i.e.,
phonons, via the strong coupling of phonons with the underlying fractionalized
excitations i.e., Majorana fermions. Inelastic light scattering (Raman) studies
on V1-xPS3 single crystals evidences the spin fractionalization into Majorana
fermions deep into the paramagnetic phase reflected in the emergence of a low
frequency quasielastic response along with a broad magnetic continuum marked by
a crossover temperature T* ~ 200 K from a pure paramagnetic state to
fractionalized spins regime qualitatively gauged via dynamic Raman
susceptibility. We further evidenced anomalies in the phonons self-energy
parameters in particular phonon line broadening and line asymmetry evolution at
this crossover temperature, attributed to the decaying of phonons into
itinerant Majorana fermions. This anomalous scattering response is thus
indicative of fluctuating fractionalized spins suggesting a phase proximate to
the quantum spin liquid state in this quasi two-dimensional (2D) magnetic
system.",2208.01550v1
2022-10-01,Spin dynamics of the generalized quantum spin compass chain,"We calculate the dynamical spin structure factor of the generalized
spin-$1/2$ compass spin chain using the density matrix renormalization group.
The model, also known as the twisted Kitaev spin chain, was recently proposed
to be relevant for the description of the spin chain compound CoNb$_2$O$_6$. It
features bond-dependent interactions and interpolates between an Ising chain
and a one-dimensional variant of Kitaev's honeycomb spin model. The structure
factor, in turn, is found to interpolate from gapped and non-dispersive in the
Ising limit to gapless with non-trivial continua in the Kitaev limit. In
particular, the component of the structure factor perpendicular to the Ising
directions changes abruptly at the Kitaev point into a dispersionless continuum
due to the emergence of an extensive groundstate degeneracy. We show this
continuum is consistent with analytical Jordan-Wigner results. We also discuss
implications for future inelastic scattering experiments and applications to
materials, particularly CoNb$_2$O$_6$.",2210.00357v2
2022-12-18,Exact Entanglement Dynamics of Two Spins in Finite Baths,"We consider the buildup and decay of two-spin entanglement through phase
interactions in a finite environment of surrounding spins, as realized in
quantum computing platforms based on arrays of atoms, molecules, or nitrogen
vacancy centers. The non-Markovian dephasing caused by the spin environment
through Ising-type phase interactions can be solved exactly and compared to an
effective Markovian treatment based on collision models. In a first case study
on a dynamic lattice of randomly hopping spins, we find that non-Markovianity
boosts the dephasing rate caused by nearest neighbour interactions with the
surroundings, degrading the maximum achievable entanglement. However, we also
demonstrate that additional three-body interactions can mitigate this
degradation, and that randomly timed reset operations performed on the two-spin
system can help sustain a finite average amount of steady-state entanglement.
In a second case study based on a model nuclear magnetic resonance system, we
elucidate the role of bath correlations at finite temperature on non-Markovian
dephasing. They speed up the dephasing at low temperatures while slowing it
down at high temperatures, compared to an uncorrelated bath, which is related
to the number of thermally accessible spin configurations with and without
interactions.",2212.09151v1
2022-12-30,Unique determination of localized basis in molecular spin,"Localized basis plays an important role in comprehending the magnetic
dynamics in molecular spins from a physics perspective. Nonetheless, the
uniqueness and rigor of its determination have received limited attention. In
this study, we propose a new determination of the localized basis applicable to
both non-Kramers and Kramers molecular spin systems, leveraging the
time-reversal symmetry of the spin Hamiltonian and the molecular spin's main
magnetic axis. By introducing this, we establish a distinct and practical means
of determining the localized basis, enabling the association of a molecular
spin wave function with either an ""up"" or ""down"" magnetic moment orientation in
molecular spins. This finding facilitates a comprehensive interpretation of
magnetic dynamics and simplifies the construction of theoretical models for
materials analysis.",2212.14639v3
2023-02-02,Phonon Dynamics in the Generalized Kitaev Spin Liquid,"Candidate materials for the Kitaev spin liquid generically have residual
interactions beyond the Kitaev coupling. It therefore becomes necessary to
understand how signatures of the quantum spin liquid, e.g., fractionalization
of the spin excitations, are affected by the presence of these interactions.
Recently it was shown that phonon dynamics is an indirect but effective probe
to study fractionalized excitations in the Kitaev spin liquid. Ultrasound
experiments can measure sound attenuation, which should show characteristic
temperature and angular dependence of the sound attenuation coefficient if the
scattering of phonons happens predominantly on Majorana fermions. So far the
computation of the sound attenuation was only done in the pure spin-phonon
coupled Kitaev model, without taking into account residual interactions. In
order to understand experimental signatures, here we present a mean-field study
of the sound attenuation in the generalized $J$-$K$-$\Gamma$ model, which is
relevant to candidate materials. Our findings show that as long as the system
is in the spin liquid phase, characteristic features of the sound attenuation
remain observable even in the presence of residual interactions.",2302.01254v2
2023-03-08,Andreev spin qubit: A nonadiabatic geometric gate,"We study a hybrid structure of a ferromagnetic-insulator and a superconductor
connected by a weak link, which accommodates Andreev bound states whose spin
degeneracy is lifted due to the exchange interaction with the ferromagnet. The
resultant spin-resolved energy levels realize a two-state quantum system,
provided that a single electron is trapped in the bound state, i.e., an Andreev
spin qubit. The qubit state can be manipulated by controlling the magnetization
dynamics of the ferromagnet, which mediates the coupling between external
fields and the qubit. In particular, our hybrid structure provides a simple
platform to manipulate and control the spin qubit using spintronic techniques.
By employing a modified Hahn spin echo protocol for the magnetization dynamics,
we show that our Andreev spin qubit can realize a nonadiabatic geometric gate.",2303.04344v1
2023-03-24,Effects of orbital selective dynamical correlation on the spin susceptibility and superconducting symmetries in Sr$_2$RuO$_4$,"We investigate the connection between the local electron correlation and the
momentum dependence of the spin susceptibility and the superconducting gap
functions in Sr$_2$RuO$_4$, using density-functional theory combined with
dynamical mean-field theory. Adopting frequency-dependent twoparticle vertex
moves the zero energy spin susceptibility peaks towards the Brillouin zone
center, compared with random-phase approximation which basically retains the
peak positions closer to the Brillouin zone boundary as determined by the
Fermi-surface nesting. We find that dxy orbital plays a central role here via
its enhanced correlation strength. Solving the linearized Eliashberg equation
from this spin susceptibility, prime candidates of the superconducting gap
symmetry are a s-wave, along with a nearly degenerate d-wave solution, all in
spin singlet. Furthermore, another set of degenerate spin singlet gap functions
emerges, odd with respect to k-point as well as orbital exchanges. We show that
the stability of these gap functions are strongly dependent on the peak
position of the spin susceptibility in the Brillouin zone.",2303.13910v1
2023-06-17,Coherent two-dimensional THz magnetic resonance spectroscopies for molecular magnets: Analysis of Dzyaloshinskii-Moriya interaction,"To investigate the novel quantum dynamic behaviors of magnetic materials that
arise from complex spin-spin interactions, it is necessary to probe the
magnetic response at a speed greater than the spin-relaxation and dephasing
processes. Recently developed two-dimensional (2D) terahertz magnetic resonance
(THz-MR) spectroscopy techniques use the magnetic components of laser pulses,
and this allows investigation of the details of the ultrafast dynamics of spin
systems. For such investigations, quantum treatment -- not only of the spin
system itself but also of the environment surrounding the spin system -- is
important. In our method, based on the theory of multidimensional optical
spectroscopy, we formulate nonlinear THz-MR spectra using an approach based on
the numerically rigorous hierarchical equations of motion. We conduct numerical
calculations of both linear (1D) and 2D THz-MR spectra for a linear chiral spin
chain. The pitch and direction of chirality (clockwise or anticlockwise) are
determined by the strength and sign of the Dzyaloshinskii-Moriya interaction
(DMI). We show that not only the strength but also the sign of the DMI can be
evaluated through the use of 2D THz-MR spectroscopic measurements, while 1D
measurements allow us to determine only the strength.",2306.10222v1
2023-09-06,Creation and dynamics of spin fluctuations in a noisy magnetic field,"We theoretically and numerically investigate the spin fluctuations induced in
a thermal atomic ensemble by an external fluctuating uniaxial magnetic field,
in the context of a standard spin noise spectroscopy (SNS) experiment. We show
that additional spin noise is excited, which dramatically depends on the
magnetic noise variance and bandwidth, as well as on the power of the probe
light and its polarization direction. We develop an analytical perturbative
model proving that this spin noise first emerges from the residual optical
pumping in the medium, which is then converted into spin fluctuations by the
magnetic noise and eventually detected using SNS. The system studied is a
spin-1 system, which thus shows both Faraday rotation and ellipticity noises
induced by the random magnetic fluctuations. The analytical model gives results
in perfect agreement with the numerical simulations, with potential
applications in future experimental characterization of stray field properties
and their influence on spin dynamics.",2309.02916v1
2023-09-14,Paramagnon Heat Capacity and Anomalous Thermopower in Anisotropic Magnetic Systems: Understanding Inter-Layer Spin Correlations in a Magnetically Disordered Phase,"The interplay between entropy transport and charge carriers-paramagnon
interaction in the Onsager linear system has been a subject of debate due to
the limited theoretical and experimental understanding of paramagnon heat
capacity. In this study, we investigate this interplay in an anisotropic
layered magnetic system using cluster mean-field theory with spin quantum
correlations. By examining spin correlation functions between different spins
with various types of clustering, we derive the spin correlation function as a
function of distance and temperature for the inter-layer clusters both below
and above the magnetic order phase transition. Our analysis reveals that
paramagnons characterized by pronounced spin correlations among inter-layer
nearest-neighbor spins exhibit a non-zero heat capacity, providing valuable
insights into the dynamics of entropy transport. The findings align with
experimental observations, lending strong support to the validity of the
paramagnon drag thermopower concept. This study sheds light on the intricate
dynamics and thermodynamic properties of paramagnons, advancing our
understanding of entropy transport in complex systems.",2309.07646v1
2023-10-06,Spin-vibronic dynamics in open-shell systems beyond the spin Hamiltonian formalism,"Vibronic coupling has a dramatic influence over a large number of molecular
processes, ranging from photo-chemistry, to spin relaxation and electronic
transport. The simulation of vibronic coupling with multi-reference
wavefunction methods has been largely applied to organic compounds, and only
early efforts are available for open-shell systems such as transition metal and
lanthanide complexes. In this work, we derive a numerical strategy to
differentiate the molecular electronic Hamiltonian in the context of
multi-reference ab initio methods and inclusive of spin-orbit coupling effects.
We then provide a formulation of open quantum system dynamics able to predict
the time evolution of the electrons' density matrix under the influence of a
Markovian phonon bath up to fourth-order perturbation theory. We apply our
method to Co(II) and Dy(III) molecular complexes exhibiting long spin
relaxation times and successfully validate our strategy against the use of an
effective spin Hamiltonian. Our study shed light on the nature of vibronic
coupling, the importance of electronic excited states in spin relaxation, and
the need for high-level computational chemistry to quantify it.",2310.04278v2
2023-10-18,Zigzag materials: selective interchain couplings control the coexistence of one-dimensional physics and deviations from it,"The coexistence in the low-temperature spin-conducting phases of the zigzag
materials BaCo2V2O8 and SrCo2V2O8 of one-dimensional (1D) physics with
important deviations from it is not well understood. The studies of this paper
account for an important selection rule that follows from interchain spin
states being coupled more strongly within the spin dynamical structure factor
of such zigzag materials whenever they are connected by a specific symmetry
operation of the underlying lattice. In the case of excited states, this
symmetry operation is only a symmetry in spin-space ifno electronic spin flip
is performed within the generation of such states. Our results on both the role
of selective interchain couplings in protecting the 1D physics and being behind
deviations from it and on the dynamical properties being controlled by
scattering of singlet pairs of physical spins 1/2 open the door to a key
advance in the understanding of the physics of the spin chains in BaCo2V2O8 and
SrCo2V2O8.",2310.12099v1
2021-07-22,When can localized spins interacting with conduction electrons in ferro- or antiferromagnets be described classically via the Landau-Lifshitz equation: Transition from quantum many-body entangled to quantum-classical nonequilibrium states,"Experiments in spintronics and magnonics operate with macroscopically large
number of localized spins within ferromagnetic (F) or antiferromagnetic (AF)
materials, so that their nonequilibrium dynamics is standardly described by the
Landau-Lifshitz (LL) equation treating localized spins as classical vectors of
fixed length. However, spin is a genuine quantum degree of freedom, and even
though quantum effects become progressively less important for spin value
$S>1$, they exist for all $S < \infty$. While this has motivated exploration of
limitations/breakdown of the LL equation, by using examples of F insulators,
analogous comparison of fully quantum many-body vs. quantum (for
electrons)-classical (for localized spins) dynamics in systems where
nonequilibrium conduction electrons are present is lacking. Here we employ
quantum Heisenberg F or AF chains of $N=4$ sites, whose localized spins
interact with conduction electrons via $sd$ exchange interaction, to perform
such comparison by starting from unentangled pure (at zero temperature) or
mixed (at finite temperature) quantum state of localized spins as the initial
condition. This reveals that quantum-classical dynamics can faithfully
reproduce fully quantum dynamics in the F metallic case, but only when spin
$S$, Heisenberg exchange between localized spins and $sd$ exchange are
sufficiently small. Increasing any of these three parameters can lead to
substantial deviations, which are explained by the dynamical buildup of
entanglement between localized spins and/or between them and electrons. In the
AF metallic case, substantial deviations appear even at early times, despite
starting from unentangled N\'{e}el state, which therefore poses a challenge on
how to rigorously justify wide usage of the LL equation in phenomenological
modeling of antiferromagnetic spintronics experiments.",2107.10776v3
1996-01-31,Berry's phase and Quantum Dynamics of Ferromagnetic Solitons,"We study spin parity effects and the quantum propagation of solitons (Bloch
walls) in quasi-one dimensional ferromagnets. Within a coherent state path
integral approach we derive a quantum field theory for nonuniform spin
configurations. The effective action for the soliton position is shown to
contain a gauge potential due to the Berry phase and a damping term caused by
the interaction between soliton and spin waves. For temperatures below the
anisotropy gap this dissipation reduces to a pure soliton mass renormalization.
The gauge potential strongly affects the quantum dynamics of the soliton in a
periodic lattice or pinning potential. For half-integer spin, destructive
interference between soliton states of opposite chirality suppresses nearest
neighbor hopping. Thus the Brillouin zone is halved, and for small mixing of
the chiralities the dispersion reveals a surprising dynamical correlation: Two
subsequent band minima belong to different chirality states of the soliton. For
integer spin, the Berry phase is inoperative and a simple tight-binding
dispersion is obtained. Finally it is shown that external fields can be used to
interpolate continuously between the Bloch wall dispersions for half-integer
and integer spin.",9601153v1
1999-01-28,From Magnons to the Resonance Peak: Spin Dynamics in High-T_C Superconducting Cuprates by Inelastic Neutron Scattering,"The spin dynamics of high temperature superconductors measured by inelastic
neutron scattering is reviewed. The spin susceptibility evolves a lot with
increasing doping from the undoped insulating state to the overdoped metallic
state. In the superconducting state, a strong magnetic resonance peak occurs in
the spin excitation spectrum whose energy is proportional to the
superconducting temperature. In underdoped and optimally doped regimes, normal
state antiferromagnetic fluctuations are observed, proving the existence of
strong electronic correlations in cuprates. They are characterized by a spin
pseudo-gap. In contrast, these dynamical spin correlations vanish in overdoped
samples.",9901333v2
1999-08-04,Nonlinear Dynamics of Nuclear-Electronic Spin Processes in Ferromagnets,"Spin dynamics is considered in ferromagnets consisting of electron and
nuclear subsystems interacting with each other through hyperfine forces. In
addition, the ferromagnetic sample is coupled with a resonance electric
circuit. Under these conditions, spin relaxation from a strongly nonequilibrium
initial state displays several peculiarities absent for the standard set-up in
studying spin relaxation. The main feature of the nonlinear spin dynamics
considered in this communication is the appearance of ultrafast coherent
relaxation, with characteristic relaxation times several orders shorter than
the transverse relaxation time $T_2$. This type of coherent spin relaxation can
be used for extracting additional information on the intrinsic properties of
ferromagnetic materials and also can be employed for different technical
applications.",9908072v1
2003-08-20,Domain wall dynamics of the Ising chains in a transverse field,"We show that the dynamics of an Ising spin chain in a transverse field
conserves the number of domains (strings of down spins in an up-spin
background) at discrete times. This enables the determination of the
eigenfunctions of the time-evolution operator, and the dynamics of initial
states with domains. The transverse magnetization is shown to be identically
zero in all sectors with a fixed number of domains. For an initial state with a
single string of down spins, the local magnetization, the equal-time and
double-time spin-spin correlation functions, are calculated analytically as
functions of time and the initial string size. The domain size distribution
function can be expressed as a simple integral involving Bessel functions.",0308393v1
2004-03-12,"Disordered, Spin Liquid and Valence-Bond Ordered Phases of the Kagome Lattice Quantum Ising Models With Transverse Field and XXZ Dynamics","General conditions in which disordered, spin liquid, and valence-bond ordered
phases occur in quantum Ising antiferromagnets are studied using the prototype
Kagome lattice spin models. A range of quantum dynamical processes in the Ising
model, with and without total Ising spin conserved, are analytically shown to
yield all three characteristic quantum paramagnetic phases in the Kagome
system. Special emphasis is given to the XXZ model that can be sensibly
compared to the Kagome lattice Heisenberg antiferromagnet. It is explicitly
demonstrated that the total-spin-conserving dynamics can yield a resonant
valence bond (RVB) liquid phase with very short-ranged correlations, but also a
valence-bond ordered phase compatible with the one proposed to explain the
seemingly gapless singlet states of the Heisenberg antiferromagnet on the
Kagome lattice. Likely consequences for generic spin models are discussed. The
analysis combines compact U(1) gauge theory, duality transformations,
lattice-field-theoretical methods, and variational approach.",0403332v1
2004-12-16,Spin and Spin-Wave Dynamics in Josephson Junctions,"We extend the Keldysh formulation to quantum spin systems and derive exact
equations of motion. This allows us to explore the dynamics of single spins and
of ferromagnets when these are inserted between superconducting leads. Several
new effects are reported. Chief amongst these are nutations of single S=1/2
spins in Josephson junctions. These nutations are triggered by the
superconducting pairing correlations in the leads. Similarly, we find that on
rather universal grounds, magnets display unconventional spin wave dynamics
when placed in Josephson junctions. These lead to modifications in the
tunneling current.",0412410v4
2005-06-07,Semiclassical theory of weak antilocalization and spin relaxation in ballistic quantum dots,"We develop a semiclassical theory for spin-dependent quantum transport in
ballistic quantum dots. The theory is based on the semiclassical Landauer
formula, that we generalize to include spin-orbit and Zeeman interaction.
Within this approach, the orbital degrees of freedom are treated
semiclassically, while the spin dynamics is computed quantum mechanically.
Employing this method, we calculate the quantum correction to the conductance
in quantum dots with Rashba and Dresselhaus spin-orbit interaction. We find a
strong sensitivity of the quantum correction to the underlying classical
dynamics of the system. In particular, a suppression of weak antilocalization
in integrable systems is observed. These results are attributed to the
qualitatively different types of spin relaxation in integrable and chaotic
quantum cavities.",0506171v1
2005-07-28,Theory of transverse spin dynamics in a polarized Fermi liquid and an itinerant ferromagnet,"The linear equations for transverse spin dynamics in a weakly polarized
degenerate Fermi liquid with arbitrary relationship between temperature and
polarization are derived from Landau-Silin phenomenological kinetic equation
with general form of two-particle collision integral. Unlike the previous
treatment where Fermi velocity and density of states have been taken as
constants independent of polarization here we made derivation free from this
assumption. The obtained equations are applicable for description of spin
dynamics in paramagnetic Fermi liquid with finite polarization as well in an
itinerant ferromagnet. In both cases transverse spin wave frequency is found to
be proportional to the square of the wave vector with complex constant of
proportionality (diffusion coefficient) such that the damping has a finite
value at T=0. The polarization dependence of the diffusion coefficient is found
to be different for a polarized Fermi liquid and for an itinerant ferromagnet.
These conclusions are confirmed by derivation of transverse spin wave
dispersion law in frame of field theoretical methods from the integral equation
for the vortex function. It is shown that similar derivation taking into
consideration the divergency of static transverse susceptibility also leads to
the same attenuating spin wave spectrum.",0507675v1
2005-09-19,Enhancement of Spin Coherence using Q-factor Engineering in Semiconductor Microdisk Lasers,"Semiconductor microcavities offer unique means of controlling light-matter
interactions, which have led to the development of a wide range of applications
in optical communications and inspired proposals for quantum information
processing and computational schemes. Studies of spin dynamics in microcavities
- a new and promising research field - have revealed novel effects such as
polarization beats, stimulated spin scattering, and giant Faraday rotation.
Here, we study the electron spin dynamics in optically-pumped GaAs microdisk
lasers with quantum wells (QWs) and interface-fluctuation quantum dots (QDs) in
the active region. In particular, we address the question of how the electron
spin dynamics are modified by the stimulated emission in the disks, and observe
an enhancement of the spin lifetime when the optical excitation is in resonance
with a high quality (Q ~ 5000) lasing mode. This resonant enhancement, contrary
to what is expected from the Purcell effect observed in the cavities, is then
manipulated by altering the cavity design and dimensions.",0509500v1
2006-01-17,Spin dynamics of low-dimensional excitons due to acoustic phonons,"We investigate the spin dynamics of excitons interacting with acoustic
phonons in quantum wells, quantum wires and quantum disks by employing a
multiband model based on the $4\times4$ Luttinger Hamiltonian. We also use the
Bir-Pikus Hamiltonian to model the coupling of excitons to both longitudinal
acoustic phonons and transverse acoustic phonons, thereby providing us with a
realistic framework in which to determine details of the spin dynamics of
excitons. We use a fractional dimensional formulation to model the excitonic
wavefunctions and we demonstrate explicitly the decrease of spin relaxation
time with dimensionality. Our numerical results are consistent with
experimental results of spin relaxation times for various configurations of the
GaAs/Al$_{0.3}$Ga$_{0.7}$As material system. We find that longitudinal and
transverse acoustic phonons are equally significant in processes of exciton
spin relaxations involving acoustic phonons.",0601361v1
2006-12-15,Exact dynamics in the inhomogeneous central-spin model,"We study the dynamics of a single spin-1/2 coupled to a bath of spins-1/2 by
inhomogeneous Heisenberg couplings including a central magnetic field. This
central-spin model describes decoherence in quantum bit systems. An exact
formula for the dynamics of the central spin is presented, based on the Bethe
ansatz. This formula is evaluated explicitly for initial conditions such that
the bath spins are completely polarized at the beginning. For this case we
find, after an initial decay, a persistent oscillatory behaviour of the central
spin. For a large number of bath spins $N_b$, the oscillation frequency is
proportional to $N_b$, whereas the amplitude behaves like $1/N_b$, to leading
order. No asymptotic decay due to the non-uniform couplings is observed, in
contrast to some recent studies.",0612382v3
2007-01-10,Disorder effects in the quantum Heisenberg model: An Extended Dynamical mean-field theory analysis,"We investigate a quantum Heisenberg model with both antiferromagnetic and
disordered nearest-neighbor couplings. We use an extended dynamical mean-field
approach, which reduces the lattice problem to a self-consistent local impurity
problem that we solve by using a quantum Monte Carlo algorithm. We consider
both two- and three-dimensional antiferromagnetic spin fluctuations and
systematically analyze the effect of disorder. We find that in three dimensions
for any small amount of disorder a spin-glass phase is realized. In two
dimensions, while clean systems display the properties of a highly correlated
spin-liquid (where the local spin susceptibility has a non-integer power-low
frequency and/or temperature dependence), in the present case this behavior is
more elusive unless disorder is very small. This is because the spin-glass
transition temperature leaves only an intermediate temperature regime where the
system can display the spin-liquid behavior, which turns out to be more
apparent in the static than in the dynamical susceptibility.",0701211v1
2004-01-09,Non-Markovian dynamics in a spin star system: Exact solution and approximation techniques,"The reduced dynamics of a central spin coupled to a bath of N spin-1/2
particles arranged in a spin star configuration is investigated. The exact time
evolution of the reduced density operator is derived, and an analytical
solution is obtained in the limit of an infinite number of bath spins, where
the model shows complete relaxation and partial decoherence. It is demonstrated
that the dynamics of the central spin cannot be treated within the Born-Markov
approximation. The Nakajima-Zwanzig and the time-convolutionless projection
operator technique are applied to the spin star system. The performance of the
corresponding perturbation expansions of the non-Markovian equations of motion
is examined through a comparison with the exact solution.",0401051v2
2007-06-07,An Analytic Perturbation Approach for Classical Spinning Particle Dynamics,"A perturbation method to analytically describe the dynamics of a classical
spinning particle, based on the Mathisson-Papapetrou-Dixon (MPD) equations of
motion, is presented. By a power series expansion with respect to the
particle's spin magnitude, it is shown how to obtain in general form an
analytic representation of the particle's kinematic and dynamical degrees of
freedom that is formally applicable to infinite order in the expansion. Within
this formalism, it is possible to identify a classical analogue of radiative
corrections to the particle's mass and spin due to spin-gravity interaction.
The robustness of this approach is demonstrated by showing how to explicitly
compute the first-order momentum and spin tensor components for arbitrary
particle motion in a general space-time background. Potentially interesting
applications based on this perturbation approach are outlined.",0706.0928v3
2007-06-16,Realizable spin models and entanglement dynamics in superconducting flux qubit systems,"Realizable spin models are investigated in a two superconducting flux qubit
system. It is shown that a specific adjustment of system parameters in the two
flux qubit system makes it possible to realize an artificial two-spin system
that cannot be found naturally. For the artificial two-spin systems, time
evolution of a prepared quantum state is discussed to quantify quantum
entanglement dynamics. The concurrence and fidelity as a function of time are
shown to reveal a characteristic entanglement dynamics of the artificial spin
systems. It is found that the unentangled input state can evolute to be a
maximally entangled output state periodically due to the exchange interactions
induced by two-qubit flipping tunneling processes while single-qubit flipping
tunneling processes plays a role of magnetic fields for the artificial spins.",0706.2402v1
2008-02-18,Nuclear spin dynamics and Zeno effect in quantum dots and defect centers,"We analyze nuclear spin dynamics in quantum dots and defect centers with a
bound electron under electron-mediated coupling between nuclear spins due to
the hyperfine interaction (""J-coupling"" in NMR). Our analysis shows that the
Overhauser field generated by the nuclei at the position of the electron has
short-time dynamics quadratic in time for an initial nuclear spin state without
transverse coherence. The quadratic short-time behavior allows for an extension
of the Overhauser field lifetime through a sequence of projective measurements
(quantum Zeno effect). We analyze the requirements on the repetition rate of
measurements and the measurement accuracy to achieve such an effect. Further,
we calculate the long-time behavior of the Overhauser field for effective
electron Zeeman splittings larger than the hyperfine coupling strength and
find, both in a Dyson series expansion and a generalized master equation
approach, that for a nuclear spin system with a sufficiently smooth
polarization the electron-mediated interaction alone leads only to a partial
decay of the Overhauser field by an amount on the order of the inverse number
of nuclear spins interacting with the electron.",0802.2463v1
2008-03-29,Tunnel-barrier-enhanced dc voltage signals induced by magnetization dynamics in magnetic tunnel junctions,"We theoretically study the recently observed tunnel-barrier-enhanced dc
voltage signals generated by magnetization precession in magnetic tunnel
junctions. While the spin pumping is suppressed by the high tunneling
impedance, two complimentary processes are predicted to result in a sizable
voltage generation in ferromagnet (F)|insulator (I)|normal-metal (N) and F|I|F
junctions, with one ferromagnet being resonantly excited. Magnetic dynamics in
F|I|F systems induces a robust charge pumping, translating into voltage in open
circuits. In addition, dynamics in a single ferromagnetic layer develops
longitudinal spin accumulation inside the ferromagnet. A tunnel barrier then
acts as a nonintrusive probe that converts the spin accumulation into a
measurable voltage. Neither of the proposed mechanisms suffers from spin
relaxation, which is typically fast on the scale of the exponentially slow
tunneling rates. The longitudinal spin-accumulation buildup, however, is very
sensitive to the phenomenological ingredients of the spin-relaxation picture.",0803.4228v2
2008-11-02,Micromagnetic simulations of persistent oscillatory modes excited by spin-polarized current in nanoscale exchange-biased spin valves,"We perform 3D micromagnetic simulations of current-driven magnetization
dynamics in nanoscale exchange biased spin-valves that take account of (i) back
action of spin-transfer torque on the pinned layer, (ii) non-linear damping and
(iii) random thermal torques. Our simulations demonstrate that all these
factors significantly impact the current-driven dynamics and lead to a better
agreement between theoretical predictions and experimental results. In
particular, we observe that, at a non-zero temperature and a sub-critical
current, the magnetization dynamics exhibits nonstationary behaviour in which
two independent persistent oscillatory modes are excited which compete for the
angular momentum supplied by spin-polarized current. Our results show that this
multi-mode behaviour can be induced by combined action of thermal and spin
transfer torques.",0811.0173v1
2009-06-12,NMR multiple quantum coherences in quasi-one-dimensional spin systems: Comparison with ideal spin-chain dynamics,"The 19F spins in a crystal of fluorapatite have often been used to
experimentally approximate a one-dimensional spin system. Under suitable
multi-pulse control, the nuclear spin dynamics may be modeled to first
approximation by a double-quantum one-dimensional Hamiltonian, which is
analytically solvable for nearest-neighbor couplings. Here, we use solid-state
nuclear magnetic resonance techniques to investigate the multiple quantum
coherence dynamics of fluorapatite, with an emphasis on understanding the
region of validity for such a simplified picture. Using experimental,
numerical, and analytical methods, we explore the effects of long-range
intra-chain couplings, cross-chain couplings, as well as couplings to a spin
environment, all of which tend to damp the oscillations of the multiple quantum
coherence signal at sufficiently long times. Our analysis characterizes the
extent to which fluorapatite can faithfully simulate a one-dimensional quantum
wire.",0906.2434v1
2009-11-20,Spin Transfer Dynamics in Spin Valves with Out-of-plane Magnetized CoNi Free Layers,"We have measured spin transfer-induced dynamics in magnetic nanocontact
devices having a perpendicularly magnetized Co/Ni free layer and an in-plane
magnetized CoFe fixed layer. The frequencies and powers of the excitations
agree well with the predictions of the single-domain model and indicate that
the excited dynamics correspond to precessional orbits with angles ranging from
zero to 90 degrees as the applied current is increased at a fixed field. From
measurements of the onset current as a function of applied field strength we
estimate the magnitude of the spin torque asymmetry parameter lambda ~ 1.5. By
combining these with spin torque ferromagnetic resonance measurements, we also
estimate the spin wave radiation loss in these devices.",0911.4077v1
2010-01-19,Spin dynamics of electrons and holes in InGaAs/GaAs quantum wells at milliKelvin temperatures,"The carrier spin dynamics in a n-doped (In,Ga)As/GaAs quantum well has been
studied by time-resolved Faraday rotation and ellipticity techniques in the
temperature range down to 430 milliKelvin. These techniques give data with very
different spectral dependencies, from which nonetheless consistent information
on the spin dynamics can be obtained, in agreement with theoretical
predictions. The mechanisms of long-lived spin coherence generation are
discussed for the cases of trion and exciton resonant excitation. We
demonstrate that carrier localization leads to a saturation of spin relaxation
times at 45 ns for electrons below 4.5 K and at 2 ns for holes below 2.3 K. The
underlying spin relaxation mechanisms are discussed.",1001.3228v1
2010-02-10,Reduced Hamiltonian for next-to-leading order Spin-Squared Dynamics of General Compact Binaries,"Within the post Newtonian framework the fully reduced Hamiltonian (i.e., with
eliminated spin supplementary condition) for the next-to-leading order
spin-squared dynamics of general compact binaries is presented. The Hamiltonian
is applicable to the spin dynamics of all kinds of binaries with
self-gravitating components like black holes and/or neutron stars taking into
account spin-induced quadrupolar deformation effects in second post-Newtonian
order perturbation theory of Einstein's field equations. The corresponding
equations of motion for spin, position and momentum variables are given in
terms of canonical Poisson brackets. Comparison with a nonreduced potential
calculated within the Effective Field Theory approach is made.",1002.2093v2
2010-07-16,"Dynamics, Synchronization and Quantum Phase Transitions of Two Dissipative Spins","We analyze the static and dynamical properties of two Ising-coupled quantum
spins embedded in a common bosonic bath as an archetype of dissipative quantum
mechanics. First, we elucidate the ground state phase diagram for an ohmic and
a subohmic bath using a combination of bosonic numerical renormalization group
(NRG), analytical techniques and intuitive arguments. Second, employing the
time-dependent NRG we investigate the system's rich dynamical behavior arising
from the complex interplay between spin-spin and spin-bath interactions.
Interestingly, spin oscillations can synchronize due to the proximity of the
common non-Markovian bath and the system displays highly entangled steady
states for certain nonequilibrium initial preparations. We complement our
non-perturbative numerical results by exact analytical solutions when available
and provide quantitative limits on the applicability of the perturbative
Bloch-Redfield approach at weak coupling.",1007.2857v2
2011-08-04,Melting artificial spin ice,"Artificial spin ice arrays of micromagnetic islands are a means of
engineering additional energy scales and frustration into magnetic materials.
Despite much progress in elucidating the properties of such arrays, the `spins'
in the systems studied so far have no thermal dynamics as the kinetic
constraints are too high. Here we address this problem by using a material with
an ordering temperature near room temperature. By measuring the temperature
dependent magnetization in different principal directions, and comparing with
simulations of idealized statistical mechanical models, we confirm a dynamical
`pre-melting' of the artificial spin ice structure at a temperature well below
the intrinsic ordering temperature of the island material. We thus create a
spin ice array that has real thermal dynamics of the artificial spins over an
extended temperature range.",1108.1092v2
2011-12-16,Dissipationless dynamics of randomly coupled spins at high temperatures,"We develop a technique to compute the high-frequency asymptotics of spin
correlators in weakly interacting disordered spin systems. We show that the
dynamical spin correlator decreases exponentially at high frequencies, $<
SS>_{\omega}\sim\exp(-\tau_{*}\omega)$ and compute the characteristic time
$\tau^{*}$ of this dependence. In a typical random configuration, some fraction
of spins form strongly coupled pairs, which behave as two-level systems. Their
switching dynamics is driven by the high-frequency noise from the surrounding
spins, resulting in low-frequency $1/f$ noise in the magnetic susceptibility
and other physical quantities. We discuss application of these results to the
problem of susceptibility and flux noise in superconducting circuits at mK
temperatures.",1112.3855v1
2012-08-14,Chaos-driven dynamics in spin-orbit coupled atomic gases,"The dynamics, appearing after a quantum quench, of a trapped, spin-orbit
coupled, dilute atomic gas is studied. The characteristics of the evolution is
greatly influenced by the symmetries of the system, and we especially compare
evolution for an isotropic Rashba coupling and for an anisotropic spin-orbit
coupling. As we make the spin-orbit coupling anisotropic, we break the
rotational symmetry and the underlying classical model becomes chaotic; the
quantum dynamics is affected accordingly. Within experimentally relevant
time-scales and parameters, the system thermalizes in a quantum sense. The
corresponding equilibration time is found to agree with the Ehrenfest time,
i.e. we numerically verify a ~log(1/h) scaling. Upon thermalization, we find
the equilibrated distributions show examples of quantum scars distinguished by
accumulation of atomic density for certain energies. At shorter time-scales we
discuss non-adiabatic effects deriving from the spin-orbit coupled induced
Dirac point. In the vicinity of the Dirac point, spin fluctuations are large
and, even at short times, a semi-classical analysis fails.",1208.2923v2
2012-08-24,Spin-echo dynamics of a heavy hole in a quantum dot,"We develop a theory for the spin-echo dynamics of a heavy hole in a quantum
dot, accounting for both hyperfine- and electric-field-induced fluctuations. We
show that a moderate applied magnetic field can drive this system to a
motional-averaging regime, making the hyperfine interaction ineffective as a
decoherence source. Furthermore, we show that decay of the spin-echo envelope
is highly sensitive to the geometry. In particular, we find a specific choice
of initialization and {\pi}-pulse axes which can be used to study intrinsic
hyperfine-induced hole-spin dynamics, even in systems with substantial
electric-field-induced dephasing. These results point the way to designed
hole-spin qubits as a robust and long-lived alternative to electron spins.",1208.4898v2
2012-11-02,Dynamic Spin Injection into Chemical Vapor Deposited Graphene,"We demonstrate dynamic spin injection into chemical vapor deposition (CVD)
grown graphene by spin pumping from permalloy (Py) layers. Ferromagnetic
resonance measurements at room temperature reveal a strong enhancement of the
Gilbert damping at the Py/graphene interface, exceeding that observed in even
Py/platinum interfaces. Similar results are also shown on Co/graphene layers.
This enhancement in the Gilbert damping is understood as the consequence of
spin pumping at the interface driven by magnetization dynamics. Our
observations suggest a strong enhancement of spin-orbit coupling in CVD
graphene, in agreement with earlier spin valve measurements.",1211.0492v1
2013-06-12,Dissipative dynamics of a driven quantum spin coupled to a bath of ultracold fermions,"We explore the dynamics and the steady state of a driven quantum spin coupled
to a bath of fermions, which can be realized with a strongly imbalanced mixture
of ultracold atoms using currently available experimental tools.
Radio-frequency driving can be used to induce tunneling between the spin
states. The Rabi oscillations are modified due to the coupling of the quantum
spin to the environment, which causes frequency renormalization and damping.
The spin-bath coupling can be widely tuned by adjusting the scattering length
through a Feshbach resonance. When the scattering potential creates a bound
state, by tuning the driving frequency it is possible to populate either the
ground state, in which the bound state is filled, or a metastable state in
which the bound state is empty. In the latter case, we predict an emergent
inversion of the steady-state magnetization. Our work shows that different
regimes of dissipative dynamics can be explored with a quantum spin coupled to
a bath of ultracold fermions.",1306.2947v2
2013-10-08,Unified Dynamics of Electrons and Photons via Zitterbewegung and Spin-Orbit Interaction,"We show that when an electron or photon propagates in a cylindrically
symmetric waveguide, it experiences both a zitterbewegung effect and a
spin-orbit interaction leading to identical propagation dynamics for both
particles. Applying a unified perturbative approach to both particles
simultaneously, we find that to first-order in perturbation theory their
Hamiltonians each contain identical Darwin (zitterbewegung) and spin-orbit
terms, resulting in the unification of their dynamics. The presence of the
zitterbewegung effect may be interpreted physically as the delocalization of
the electron on the scale of its Compton wavelength, or the delocalization of
the photon on the scale of its wavelength in the waveguide. The presence of the
spin-orbit interaction leads to the prediction of several rotational effects:
the spatial or time evolution of either particle's spin/polarization vector is
controlled by the sign of its orbital angular momentum quantum number, or
conversely, its spatial wave function is controlled by its spin angular
momentum.",1310.1995v1
2013-10-16,Terahertz out-of-plane resonances due to spin-orbit coupling,"A microscopic kinetic theory is developed which allows to investigate
non-Abelian SU(2) systems interacting with meanfields and spin-orbit coupling
under magnetic fields in one, two, and three dimensions. The coupled kinetic
equations for the scalar and spin components are presented and linearized with
respect to an external electric field. The dynamical classical and quantum Hall
effect are described in this way as well as the anomalous Hall effect where a
new symmetric dynamical contribution to the conductivity is presented. The
coupled density and spin response functions to an electric field are derived
including arbitrary magnetic fields. The magnetic field induces a staircase
structure at frequencies of the Landau levels. It is found that for linear
Dresselhaus and Rashba spin-orbit coupling a dynamical out-of-plane spin
response appears at these Landau level frequencies establishing terahertz
resonances.",1310.4405v1
2013-12-23,Relaxation dynamics of an isolated large-spin Fermi gas far from equilibrium,"A fundamental question in many-body physics is how closed quantum systems
reach equilibrium. We address this question experimentally and theoretically in
an ultracold large-spin Fermi gas where we find a complex interplay between
internal and motional degrees of freedom. The fermions are initially prepared
far from equilibrium with only a few spin states occupied. The subsequent
dynamics leading to redistribution among all spin states is observed
experimentally and simulated theoretically using a kinetic Boltzmann equation
with full spin coherence. The latter is derived microscopically and provides
good agreement with experimental data without any free parameters. We identify
several collisional processes, which occur on different time scales. By varying
density and magnetic field, we control the relaxation dynamics and are able to
continuously tune the character of a subset of spin states from an open to a
closed system.",1312.6704v3
2014-02-03,Self-induced Spatial Dynamics to Enhance Spin-Squeezing via One-Axis Twisting in a Two-Component Bose-Einstein Condensate,"We theoretically investigate a scheme to enhance spin squeezing in a
two-component Bose-Einstein condensate (BEC) by utilizing the inherent
mean-field dynamics of the condensate. Due to the asymmetry in the scattering
lengths, the two components exhibit density oscillations where they spatially
separate and recombine. The effective non-linearity responsible for spin
squeezing is increased by up to three orders of magnitude when the two
components spatially separate \cite{treutlein2010}. We perform a multi-mode
simulation of the system using the truncated Wigner method, and show that this
method can be used to create significant spin squeezing in systems where the
effective nonlinearity would ordinarily be too small, and that strong spatial
dynamics resulting from large particle numbers aren't necessarily detrimental
to generating spin-squeezing. We develop a simplified semi-analytic model that
gives good agreement with our multi-mode simulation, and will be useful for
predicting spin-squeezing in a range of different systems.",1402.0307v3
2015-02-25,Observation of a phononic Mollow triplet in a hybrid spin-nanomechanical system,"Reminiscent of the bound character of a qubit's dynamics confined on the
Bloch sphere, the observation of a Mollow triplet in the resonantly driven
qubit fluorescence spectrum represents one of the founding signatures of
Quantum Electrodynamics. Here we report on its observation in a hybrid
spin-nanomechanical system, where a Nitro-gen Vacancy spin qubit is
magnetically coupled to the vibrations of a Silicon Carbide nanowire. A
resonant microwave field turns the originally parametric hybrid interac-tion
into a resonant process, where acoustic phonons are now able to induce
transitions between the dressed qubit states, leading to synchronized
spin-oscillator dynamics. We further explore the vectorial character of the
hybrid coupling to the bidimensional de-formations of the nanowire. The
demonstrated microwave assisted synchronization of the spin-oscillator dynamics
opens novel perspectives for the exploration of spin-dependent forces, the
key-ingredient for quantum state transfer.",1502.07071v1
2015-03-12,Density Functional plus Dynamical Mean-Field Theory of the Spin-Crossover Molecule Fe(phen)$_2$(NCS)$_2$,"We study the spin-crossover molecule Fe(phen)$_2$(NCS)$_2$ using density
functional theory (DFT) plus dynamical mean-field theory, which allows access
to observables not attainable with traditional quantum chemical or electronic
structure methods. The temperature dependent magnetic susceptibility, electron
addition and removal spectra, and total energies are calculated and compared to
experiment. We demonstrate that the proper quantitative energy difference
between the high-spin and low-spin state, as well as reasonably accurate values
of the magnetic susceptibility can be obtained when using realistic interaction
parameters. Comparisons to DFT and DFT+U calculations demonstrate that
dynamical correlations are critical to the energetics of the low-spin state.
Additionally, we elucidate the differences between DFT+U and spin density
functional theory (SDFT) plus U methodologies, demonstrating that DFT+U can
recover SDFT+U results for an appropriately chosen on-site exchange
interaction.",1503.03547v1
2016-06-29,The dynamics of a spinning particle in a linear in spin Hamiltonian approximation,"We investigate for order and chaos the dynamical system of a spinning test
particle of mass $m$ moving in the spacetime background of a Kerr black hole of
mass M. This system is approximated in our investigation by the linear in spin
Hamiltonian function provided in [E. Barausse, and A. Buonanno, Phys.Rev. D 81,
084024 (2010)]. We study the corresponding phase space by using 2D projections
on a surface of section and the method of color and rotation on a 4D Poincar\'e
section. Various topological structures coming from the non-integrability of
the linear in spin Hamiltonian are found and discussed. Moreover, an
interesting result is that from the value of the dimensionless spin $S/(m
M)=10^{-4}$ of the particle and below, the impact of the non-integrability of
the system on the motion of the particle seems to be negligible.",1606.09171v1
2016-09-07,Mutual synchronization of nano-oscillators driven by pure spin current,"We report the experimental observation of mutual synchronization of magnetic
nanooscillators driven by pure spin current generated by nonlocal spin
injection. We show that the oscillators efficiently synchronize due to the
direct spatial overlap of the dynamical modes excited by spin current, which is
facilitated by the large size of the auto-oscillation area inherent to these
devices. The synchronization occurs within an interval of the driving current
determined by the competition between the dynamic nonlinearity that facilitates
synchronization, and the short-wavelength magnetic fluctuations enhanced by the
spin current that suppress synchronization. The demonstrated synchronization
effects can be utilized to control the spatial and spectral characteristics of
the dynamical states induced by spin currents.",1609.01879v1
2016-09-29,Rattleback: a model of how geometric singularity induces dynamic chirality,"The rattleback is a boat-shaped top with an asymmetric preference in spin.
Its dynamics can be described by nonlinearly coupled pitching, rolling, and
spinning modes. The chirality, designed into the body as a skewed mass
distribution, manifests itself in the quicker transition of $+$spin
$\rightarrow$ pitch $\rightarrow$ $-$spin than that of $-$spin $\rightarrow$
roll $\rightarrow$ $+$spin. The curious guiding idea of this work is that we
can formulate the dynamics as if a symmetric body were moving in a chiral
space. By elucidating the duality of matter and space in the Hamiltonian
formalism, we attribute asymmetry to space. The rattleback is shown to live in
the space dictated by the Bianchi type ${\rm VI}_{h < -1}$ (belonging to class
B) algebra; this particular algebra is used here for the first time in a
mechanical example. The class B algebra has a singularity that separates the
space (Poisson manifold) into mirror-asymmetric subspaces, breaking the
time-reversal symmetry of nearby orbits.",1609.09223v2
2018-04-05,Spin dynamics of the block orbital-selective Mott phase,"Iron-based superconductors display a variety of magnetic phases originating
in the competition between electronic, orbital, and spin degrees of freedom.
Previous theoretical investigations of the multi-orbital Hubbard model in one
dimension revealed the existence of an orbital-selective Mott phase (OSMP) with
block spin order. Recent inelastic neutron scattering (INS) experiments on the
BaFe$_2$Se$_3$ ladder compound confirmed the relevance of the block-OSMP.
Moreover, the powder INS spectrum reveled an unexpected structure, containing
both low-energy acoustic and high-energy optical modes. Here we present the
theoretical prediction for the dynamical spin structure factor within a
block-OSMP regime using the density-matrix renormalization group method. In
agreement with experiments we find two dominant features: low-energy dispersive
and high-energy dispersionless modes. We argue that the former represents the
spin-wave-like dynamics of the block ferromagnetic islands, while the latter is
attributed to a novel type of local on-site spin excitations controlled by the
Hund coupling.",1804.01959v2
2018-04-09,General method for atomistic spin-lattice dynamics with first principles accuracy,"We present a computationally efficient general first-principles based method
for spin-lattice simulations for solids. Our method is based on a combination
of atomistic spin dynamics and molecular dynamics, expressed through a
spin-lattice Hamiltonian where the bilinear magnetic term is expanded to second
order in displacement, and all parameters are computed using density functional
theory. The effect of first-order spin-lattice coupling on the magnon and
phonon dispersion in bcc Fe is reported as an example, and is seen to be in
good agreement with previous simulations performed with an empirical potential
approach. In addition, we also illustrate the abilities of our method on a more
conceptual level, by exploring dissipation-free spin and lattice motion in
small magnetic clusters (a dimer, trimer and quadmer). Our method opens the
door for quantitative description and understanding of the microscopic origin
of many fundamental phenomena of contemporary interest, such as ultrafast
demagnetization, magnetocalorics, and spincaloritronics.",1804.03119v2
2010-05-14,Spin Torque Dynamics with Noise in Magnetic Nano-System,"We investigate the role of equilibrium and nonequilibrium noise in the
magnetization dynamics on mono-domain ferromagnets. Starting from a microscopic
model we present a detailed derivation of the spin shot noise correlator. We
investigate the ramifications of the nonequilibrium noise on the spin torque
dynamics, both in the steady state precessional regime and the spin switching
regime. In the latter case we apply a generalized Fokker-Planck approach to
spin switching, which models the switching by an Arrhenius law with an
effective elevated temperature. We calculate the renormalization of the
effective temperature due to spin shot noise and show that the nonequilibrium
noise leads to the creation of cold and hot spot with respect to the noise
intensity.",1005.2439v3
2013-08-09,Topological excitations and the dynamic structure factor of spin liquids on the kagome lattice,"Recent neutron scattering experiments on the spin-1/2 kagome lattice
antiferromagnet ZnCu3(OH)6Cl2 (Herbertsmithite) provide the first evidence of
fractionalized excitations in a quantum spin liquid state in two spatial
dimensions. In contrast to existing theoretical models of spin liquids, the
measured dynamic structure factor reveals an excitation continuum which is
remarkably flat as a function of frequency and has almost no momentum
dependence along several high-symmetry directions. Here we show that many
experimentally observed features can be explained by the presence of
topological vison excitations in a Z2 spin liquid. These visons form flat bands
on the kagome lattice, and thus act as a momentum sink for spin-carrying
excitations which are probed by neutron scattering. We compute the dynamic
structure factor for two different Z2 spin liquids and find that one of them
describes Herbertsmithite well above a very low energy cutoff.",1308.2222v1
2018-05-27,Dynamical structure factors in the nematic phase of frustrated ferromagnetic spin chains,"Frustrated spin systems can show phases with spontaneous breaking of
spin-rotational symmetry without the formation of local magnetic order. We
study the dynamic response of the spin-nematic phase of one-dimensional
spin-1/2 systems, characterized by slow large-distance decay of quadrupolar
correlations, by numerically computing one-spin and two-spin dynamical
structure factors at zero temperature using time-dependent density matrix
renormalization group methods. We interpret the results in terms of an
effective theory of gapped magnon excitations interacting with a
quasi-condensate of bound magnon pairs. This employs an extension of the
well-known Tomonaga-Luttinger liquid theory which includes the magnon states as
a mobile impurity. A good qualitative understanding of the characteristic
thresholds and their intensity in the structure factors is obtained this way.
Our results are useful in the interpretation of inelastic neutron scattering
and resonant inelastic x-ray scattering experiments.",1805.10612v2
2011-11-18,Disentanglement dynamics of interacting two qubits and two qutrits in an XY spin-chain environment with the Dzyaloshinsky-Moriya interaction,"We investigate disentanglement dynamics of two coupled qubits and qutrits
which interact uniformly to a general XY spin-chain environment with the
Dzyaloshinsky-Moriya (DM) interaction. We obtained exact expression of the time
evolution operator and analyzed the dynamical process of the decoherence
factors. Through explicitly calculating the concurrence and the negativity, we
examined disentanglement behaviors of two coupled central spins evolve from
different initial pure states, which are found to be nontrivially different
from those of the uncorrelated ones, in particular, the enhanced decay of the
entanglement induced by quantum criticality of the surrounding environment may
be broken by introducing self-Hamiltonian of the central spin system. Moreover,
the DM interaction may have different influences on decay of the entanglement
depending on the strength of the system-environment coupling, the anisotropy of
the environmental spin chain and the intensity of the transverse magnetic
field, as well as the explicit form of the initial states of the central spin
system.",1111.4274v1
2011-11-22,Magnetic Dynamics and Spin Freezing in the Ferromagnetic Phase of Ba-Doped Perovskite Cobaltites,"The magnetic properties of polycrystaline La0.5Ba0.5CoO2.5+d (d = 0.44 and
0.485) where investigated using muon spin relaxation and bulk magnetization
experiments. Below a Curie temperature of T_C = 160 K and 180 K, respectively,
a magnetic phase with a macroscopic ferromagnetic moment forms. muSR proves
that the full volume inhomogeneously orders at T_C but that there is
microscopically a phase separation into phase volumes possessing a fully static
and a slow magnetic dynamic behavior. A peak in the dynamic relaxation rate 35
K respectively 55 K below the Curie temperature indicates the freezing of spin
components. The spin fluctuations are thermally activated with a typical
Jahn-Teller like phonon energy of E_a = 340 K. Together with co-operative
Jahn-Teller distortions appearing below the spin freezing temperature, this
points to a strong magneto elastic coupling as the cause for the magnetic
fluctuations and the spin freezing.",1111.5232v1
2017-12-12,Dynamical Negative Differential Resistance in Antiferromagnetically Coupled Few-Atom Spin-Chains,"We present the appearance of negative differential resistance (NDR) in
spin-dependent electron transport through a few-atom spin-chain. A chain of
three antiferromagnetically coupled Fe atoms(Fe trimer) was positioned on a
Cu2N/Cu(100) surface and contacted with the spin-polarized tip of a scanning
tunneling microscope, thus coupling the Fe trimer to one non-magnetic and one
magnetic lead. Pronounced NDR appears at the low bias of 7 mV where inelastic
electron tunneling dynamically locks the atomic spin in a long-lived excited
state. This causes a rapid increase of the magnetoresistance between
spin-polarized tip and Fe trimer and quenches elastic tunneling. By varying the
coupling strength between tip and Fe trimer we find that in this transport
regime the dynamic locking of the Fe trimer competes with magnetic exchange
interaction, which statically forces the Fe trimer into the
high-magnetoresistance state and removes the NDR.",1712.04213v1
2017-12-25,"Magnon and Phonon Dispersion, Lifetime and Thermal Conductivity of Iron from Spin-Lattice Dynamics Simulations","In recent years, the fundamental physics of spin-thermal (i.e.,
magnon-phonon) interaction has attracted significant experimental and
theoretical interests given its potential paradigm-shifting impacts in areas
like spin-thermoelectrics, spin-caloritronics and spintronics. Modelling
studies of the transport of magnons and phonons in magnetic crystals are very
rare. In this paper, we use spin-lattice dynamics (SLD) simulations to model
ferromagnetic crystalline iron, where the spin and lattice systems are coupled
through the atomic position-dependent exchange function, and thus the
interaction between magnon and phonon is naturally considered. We then present
a method combining SLD simulations with spectral energy analysis to calculate
the magnon and phonon harmonic (e.g., dispersion, specific heat, group
velocity) and anharmonic (e.g., scattering rate) properties, based on which
their thermal conductivity values are calculated. This work represents an
example of using SLD simulations to understand the transport properties
involving coupled magnon and phonon dynamics.",1712.09002v1
2018-01-11,Dynamics of a quantum spin liquid beyond integrability $-$ the Kitaev-Heisenberg-$Γ$ model in an augmented parton mean-field theory,"We present an augmented parton mean-field theory which (i) reproduces the
$exact$ ground state, spectrum, and dynamics of the quantum spin liquid phase
of Kitaev's honeycomb model; and (ii) is amenable to the inclusion of
integrability breaking terms, allowing a perturbation theory from a controlled
starting point. Thus, we exemplarily study dynamical spin correlations of the
honeycomb Kitaev quantum spin liquid within the $K-J-\Gamma$ model which
includes Heisenberg and symmetric-anisotropic (pseudo-dipolar) interactions.
This allows us to trace changes of the correlations in the regime of slowly
moving fluxes, where the theory captures the dominant deviations when
integrability is lost. These include an asymmetric shift together with a
broadening of the dominant peak in the response as a function of frequency; the
generation of further-neighbour correlations and their structure in real- and
spin-space; and a resulting loss of an approximate rotational symmetry of the
structure factor in reciprocal space. We discuss the limitations of this
approach, and also view the neutron scattering experiments on the putative
proximate quantum spin liquid material, $\alpha$-RuCl$_3$, in the light of the
results from this extended parton theory.",1801.03774v1
2019-07-25,Order out of a Coulomb phase and Higgs transtion: frustrated transverse interactions of Nd2Zr2O7,"The pyrochlore material Nd$_2$Zr$_2$O$_7$ with an ""all-in-all-out"" (AIAO)
magnetic order shows novel quantum moment fragmentation with gapped flat
dynamical spin ice modes. The parameterized spin Hamiltonian with a dominant
frustrated ferromagnetic transverse term reveals a proximity to a U(1) spin
liquid. Here we study magnetic excitations of Nd$_2$Zr$_2$O$_7$ above the
ordering temperature ($T_\text{N}$) using high-energy-resolution inelastic
neutron scattering. We find strong spin ice correlations at zero energy with
the disappearance of gapped magnon excitations of the AIAO order. It seems that
the gap to the dynamical spin ice closes above $T_\text{N}$ and the system
enters a quantum spin ice state competing with and suppressing the AIAO order.
Classical Monte Carlo, molecular dynamics and quantum boson calculations
support the existence of a Coulombic phase above $T_\text{N}$. Our findings
relate the magnetic ordering of Nd$_2$Zr$_2$O$_7$ with the Higgs mechanism and
provide explanations for several previously reported experimental features.",1907.11056v1
2019-09-10,Anisotropic magnetic excitations of a frustrated bilinear-biquadratic spin model -- Implications for spin waves of detwinned iron pnictides,"Elucidating the nature of spin excitations is important to understanding the
mechanism of superconductivity in the iron pnictides. Motivated by recent
inelastic neutron scattering measurements in the nearly 100% detwinned
BaFe$_{2}$As$_{2}$, we study the spin dynamics of an $S=1$ frustrated
bilinear-biquadratic Heisenberg model in the antiferromagnetic phase with
wavevector $(\pi,0)$. The biquadratic interactions are treated in a dynamical
way using a flavor-wave theory in an $SU(3)$ representation. Besides the magnon
(dipolar) excitations, the biquadratic interactions give rise to quadrupolar
excitations at high energies. We find that the quadrupolar wave significantly
influences, in an energy dependent way, the anisotropy between the spin
excitation spectra along the $(\pi,0)$ and $(0,\pi)$ directions in the wave
vector space. Our theoretical results capture the essential behavior of the
spin dynamics measured in the antiferromagnetic phase of the detwinned
BaFe$_2$As$_2$. More generally, our results underscore the importance of
electron correlation effects for the microscopic physics of the iron pnictides.",1909.04555v2
2019-09-11,Spin dynamics of the planar kagome lattice ferromagnet with four-site ring exchange processes,"By means of quantum Monte Carlo simulations, combined with a stochastic
analytic continuation, we examine the spin dynamics of the spin-1/2 planar (XY)
ferromagnet on the kagome lattice with additional four-site ring exchange
terms. Such exchange processes were previously considered to lead into an
extended $Z_2$ quantum spin liquid phase beyond a quantum critical point from
the XY-ferromagnet. We examine the dynamical spin structure factor in the
non-magnetic regime and probe for signatures of spin fractionalization.
Furthermore, we contrast our findings and the corresponding energy scales of
the excitation gaps in the ring exchange model to those emerging in a related
Balents-Fisher-Girvin model with a $Z_2$ quantum spin liquid phase, and monitor
the softening of the magnon mode upon approaching the quantum critical point
from the XY-ferromagnetic regime.",1909.04877v1
2020-01-13,Gate-tunable spin waves in antiferromagnetic atomic bilayers,"The emergence of two-dimensional (2D) layered magnetic materials has opened
an exciting playground for both fundamental studies of magnetism in 2D and
explorations of spinbased applications. Remarkable properties, including spin
filtering in magnetic tunnel junctions and gate control of magnetic states,
have recently been demonstrated in 2D magnetic materials. While these studies
focus on the static properties, dynamic magnetic properties such as excitation
and control of spin waves have remained elusive. Here we excite spin waves and
probe their dynamics in antiferromagnetic CrI3 bilayers by employing an
ultrafast optical pump/magneto-optical Kerr probe technique. We identify
sub-terahertz magnetic resonances under an in-plane magnetic field, from which
we determine the anisotropy and interlayer exchange fields and the spin damping
rates. We further show tuning of antiferromagnetic resonances by tens of
gigahertz through electrostatic gating. Our results shed light on magnetic
excitations and spin dynamics in 2D magnetic materials, and demonstrate their
unique potential for applications in ultrafast data storage and processing.",2001.04044v1
2017-05-23,Spin mixing and protection of ferromagnetism in a spinor dipolar condensate,"We study spin mixing dynamics in a chromium dipolar Bose-Einstein Condensate,
after tilting the atomic spins by an angle $\theta$ with respect to the
magnetic field. Spin mixing is triggered by dipolar coupling, but, once
dynamics has started, it is mostly driven by contact interactions. For the
particular case $\theta=\pi/2$, an external spin-orbit coupling term induced by
a magnetic gradient is required to enable the dynamics. Then the initial
ferromagnetic character of the gas is locally preserved, an unexpected feature
that we attribute to large spin-dependent contact interactions.",1705.08358v1
2018-03-06,Coupled charge and spin dynamics in a photo-excited Mott insulator,"Using a nonequilibrium implementation of the extended dynamical mean field
theory (EDMFT) we simulate the relaxation after photo excitation in a strongly
correlated electron system with antiferromagnetic spin interactions. We
consider the $t$-$J$ model and focus on the interplay between the charge- and
spin-dynamics in different excitation and doping regimes. The appearance of
string states after a weak photo excitation manifests itself in a nontrivial
scaling of the relaxation time with the exchange coupling and leads to a
correlated oscillatory evolution of the kinetic energy and spin-spin
correlation function. A strong excitation of the system, on the other hand,
suppresses the spin correlations and results in a relaxation that is controlled
by hole scattering. We discuss the possibility of detecting string states in
optical and cold atom experiments.",1803.02071v1
2018-03-12,Probing ultrafast spin-relaxation and precession dynamics in a cuprate Mott insulator with 7-fs optical pulses,"A charge excitation in a two-dimensional Mott insulator is strongly coupled
with the surrounding spins, which is observed as magnetic-polaron formations of
doped carriers and a magnon sideband in the Mott-gap transition spectrum.
However, the dynamics related to the spin sector are difficult to measure.
Here, we show that pump-probe reflection spectroscopy with 7-fs laser pulses
can detect the optically induced spin dynamics in Nd$_2$CuO$_4$, a cuprate Mott
insulator. The bleaching signal at the Mott-gap transition is enhanced at
$\sim$18 fs, which corresponds to the spin-relaxation time in magnetic-polaron
formations and is characterized by the exchange interaction. More importantly,
ultrafast coherent oscillations appear in the time evolutions of the
reflectivity changes, and their frequencies (1400-2700 cm$^{-1}$) are equal to
the probe energy measured from the Mott-gap transition peak. These oscillations
originate from interferences between charge excitations with two magnons and
provide direct evidence for charge-spin coupling.",1803.04158v1
2019-11-05,Exceptional points in dissipatively coupled spin dynamics,"We theoretically investigate dynamics of classical spins exchange-coupled
through an isotropic medium. The coupling is treated at the adiabatic level of
the medium's response, which mediates a first-order in frequency dissipative
interaction along with an instantaneous Heisenberg exchange. The resultant
damped spin precession yields exceptional points (EPs) in the coupled spin
dynamics, which should be experimentally accessible with the existing magnetic
heterostructures. In particular, we show that an EP is naturally approached in
an antiferromagnetic dimer by controlling local damping, while the same is
achieved by tuning the dissipative coupling between spins in the ferromagnetic
case. Extending our treatment to one-dimensional spin chains, we show how EPs
can emerge within the magnonic Brillouin zone by tuning the dissipative
properties. The critical point, at which an EP pair emerges out of the
Brillouin zone center, realizes a gapless Weyl point in the magnon spectrum.
Tuning damping beyond this critical point produces synchronization (level
attraction) of magnon modes over a finite range of momenta, both in ferro- and
antiferromagnetic cases. We thus establish that damped magnons can generically
yield singular points in their band structure, close to which their kinematic
properties, such as group velocity, become extremely sensitive to the control
parameters.",1911.01619v2
2020-02-28,Vibrational dressing in Kinetically Constrained Rydberg Spin Systems,"Quantum spin systems with kinetic constraints have become paradigmatic for
exploring collective dynamical behaviour in many-body systems. Here we discuss
a facilitated spin system which is inspired by recent progress in the
realization of Rydberg quantum simulators. This platform allows to control and
investigate the interplay between facilitation dynamics and the coupling of
spin degrees of freedom to lattice vibrations. Developing a minimal model, we
show that this leads to the formation of polaronic quasiparticle excitations
which are formed by many-body spin states dressed by phonons. We investigate in
detail the properties of these quasiparticles, such as their dispersion
relation, effective mass and the quasiparticle weight. Rydberg lattice quantum
simulators are particularly suited for studying this phonon-dressed kinetically
constrained dynamics as their exaggerated length scales permit the
site-resolved monitoring of spin and phonon degrees of freedom.",2003.00034v2
2020-06-28,Level-crossing induced spin phenomena in SiC: a theoretical study,"A theoretical approach is proposed to treat the spin dynamics in defect color
centers. The method explicitly takes into account the spin dynamics in the
ground state and excited state of the defect center as well as spin state
dependent transitions involving the ground state and excited state, as well as
an additional intermediate state. The proposed theory is applied to treat
spin-dependent phenomena is silicon carbide, namely, in spin-3/2
silicon-vacancy centers, VSi or V2 centers. Theoretical predictions of magnetic
field dependent photoluminescence intensity and optically detected magnetic
resonance spectra demonstrate an important role of level crossing phenomena in
the spin dynamics of the ground state and excited state. The results are in
good agreement with previously published experimental data [Phys. Rev. X, 6
(2016) 031014].",2006.15542v1
2020-08-12,Spin dynamics during chirped pulses: applications to homonuclear decoupling and broadband excitation,"Swept-frequency pulses have found applications in a wide range of areas
including spectroscopic techniques where efficient control of spins is
required. For many of these applications, a good understanding of the evolution
of spin systems during these pulses plays a vital role, not only in describing
the mechanism of techniques, but also in enabling new methodologies. In
magnetic resonance spectroscopy, broadband inversion, refocusing, and
excitation using these pulses are among the most used applications in NMR, ESR,
MRI, and $in$ $vivo$ MRS. In the present survey, a general expression for
chirped pulses will be introduced, and some numerical approaches to calculate
the spin dynamics during chirped pulses via solutions of the well-known
Liouville-von Neumann equation and the lesser-explored Wei-Norman Lie algebra
along with comprehensive examples are presented. In both cases, spin state
trajectories are calculated using the solution of differential equations.
Additionally, applications of the proposed methods to study the spin dynamics
during the PSYCHE pulse element for broadband homonuclear decoupling and the
CHORUS sequence for broadband excitation will be presented.",2008.05380v1
2020-09-14,Many-Body Phases of a Planar Bose-Einstein Condensate with Cavity-Induced Spin-Orbit Coupling,"We explore the many-body phases of a two-dimensional Bose-Einstein condensate
with cavity-mediated dynamic spin-orbit coupling. By the help of two transverse
non-interfering, counterpropagating pump lasers and a single standing-wave
cavity mode, two degenerate Zeeman sub-levels of the quantum gas are Raman
coupled in a double-$\Lambda$-configuration. Beyond a critical pump strength
the cavity mode is populated via coherent superradiant Raman scattering from
the two pump lasers, leading to the appearance of a dynamical spin-orbit
coupling for the atoms. We identify three quantum phases with distinct atomic
and photonic properties: the normal ``homogeneous'' phase, the superradiant
``spin-helix'' phase, and the superradiant ``supersolid spin-density-wave''
phase. The latter exhibits an emergent periodic atomic density distribution
with an orthorhombic centered rectangular-lattice structure due to the
interplay between the coherent photon scattering into the resonator and the
collision-induced momentum coupling. The transverse lattice spacing of the
emergent crystal is set by the dynamic spin-orbit coupling.",2009.06475v1
2020-11-19,Phase-Space Methods for Simulating the Dissipative Many-Body Dynamics of Collective Spin Systems,"We describe an efficient numerical method for simulating the dynamics and
steady states of collective spin systems in the presence of dephasing and
decay. The method is based on the Schwinger boson representation of spin
operators and uses an extension of the truncated Wigner approximation to map
the exact open system dynamics onto stochastic differential equations for the
corresponding phase space distribution. This approach is most effective in the
limit of very large spin quantum numbers, where exact numerical simulations and
other approximation methods are no longer applicable. We benchmark this
numerical technique for known superradiant decay and spin-squeezing processes
and illustrate its application for the simulation of non-equilibrium phase
transitions in dissipative spin lattice models.",2011.10049v4
2021-02-08,Non-equilibrium criticality and efficient exploration of glassy landscapes with memory dynamics,"Spin glasses are notoriously difficult to study both analytically and
numerically due to the presence of frustration and metastability. Their highly
non-convex landscapes require collective updates to explore efficiently.
Currently, most state-of-the-art algorithms rely on stochastic spin clusters to
perform non-local updates, but such ""cluster algorithms"" lack general
efficiency. Here, we introduce a non-equilibrium approach for simulating spin
glasses based on classical dynamics with memory. By simulating various classes
of 3d spin glasses (Edwards-Anderson, partially-frustrated, and
fully-frustrated models), we find that memory dynamically promotes critical
spin clusters during time evolution, in a self-organizing manner. This
facilitates an efficient exploration of the low-temperature phases of spin
glasses.",2102.04557v3
2021-08-09,The role of spin-lattice coupling for ultrafast magnetization changes in rare earth metals,"By comparing femtosecond laser-pulse-induced spin dynamics in the surface
state of the rare earth metals Gd and Tb we show that the spin polarization of
the valence states in both materials decays with significantly different time
constants of 15\,ps and 400\,fs, respectively. The distinct spin polarization
dynamics in Gd and Tb are opposed by similar exchange splitting dynamics in the
two materials. The different time scales observed in our experiment can be
attributed to weak and strong $4f$ spin to lattice coupling in Gd and Tb
suggesting an intimate coupling of spin polarization and 4f magnetic moment.
While in Gd the lattice mainly acts as a heat sink, it contributes
significantly to ultrafast demagnetization of Tb. This helps explain why all
optical switching is observed in FeGd -- but rarely in FeTb-based compounds.",2108.04380v2
2021-09-22,Engineering infinite-range SU($n$) interactions with spin-orbit-coupled fermions in an optical lattice,"We study multilevel fermions in an optical lattice described by the Hubbard
model with on site SU($n$)-symmetric interactions. We show that in an
appropriate parameter regime this system can be mapped onto a spin model with
all-to-all SU($n$)-symmetric couplings. Raman pulses that address internal spin
states modify the atomic dispersion relation and induce spin-orbit coupling,
which can act as a synthetic inhomogeneous magnetic field that competes with
the SU($n$) exchange interactions. We investigate the mean-field dynamical
phase diagram of the resulting model as a function of $n$ and different initial
configurations that are accessible with Raman pulses. Consistent with previous
studies for $n=2$, we find that for some initial states the spin model exhibits
two distinct dynamical phases that obey simple scaling relations with $n$.
Moreover, for $n>2$ we find that dynamical behavior can be highly sensitive to
initial intra-spin coherences. Our predictions are readily testable in current
experiments with ultracold alkaline-earth(-like) atoms.",2109.11019v1
2021-10-01,Thermalization of nuclear spins in lanthanide molecular magnets,"Single molecule magnets distinguish themselves in the field of quantum
magnetism through the ability to combine fundamental research with promising
applications, the evolution of quantum spintronics in the last decade
exemplifying the potential held by molecular based quantum devices. Notably,
the read-out and manipulation of the embedded nuclear spin states was used in
proof of principle studies of quantum computation at the single molecule level.
In this paper we study the relaxation dynamics of the $^{159}$Tb nuclear spins
in a diluted molecular crystal by using recently acquired understanding of the
nonadiabatic dynamics of TbPc$_2$ molecules. We find that phonon modulated
hyperfine interaction opens a direct relaxation channel between the nuclear
spins and the phonon bath. We highlight the potential importance of the
discovered mechanism for the theory of spin bath and the relaxation dynamics of
the molecular spins at crossover temperatures.",2110.00161v1
2021-10-07,Unraveling higher-order corrections in the spin dynamics of RIXS spectra,"Resonant inelastic x-ray scattering (RIXS) is an evolving tool for
investigating spin dynamics of strongly correlated materials, which complements
inelastic neutron scattering. Both techniques have found that
non-spin-conserving (NSC) excitations in quasi-1D isotropic quantum
antiferromagnets are confined to the two-spinon phase space. Outside this phase
space, only spin-conserving (SC) four-spinon excitations have been detected
using O $K$-edge RIXS. Here, we investigate SrCuO$_2$ and find four-spinon
excitations outside the two-spinon phase space at both O $K$- and Cu
$L_3$-edges. Using the Kramers-Heisenberg formalism, we demonstrate that the
four-spinon excitations arise from both SC and NSC processes at Cu $L_3$-edge.
We show that these new excitations only appear in the second-order terms of the
ultra-fast core-hole lifetime expansion and arise from long-range spin
fluctuations. These results thus open a new window to the spin dynamics of
quantum magnets.",2110.03186v1
2022-01-22,Microwave-free dynamic nuclear polarization via sudden thermal jumps,"Dynamic Nuclear Polarization (DNP) presently stands as the preferred strategy
to enhance the sensitivity of nuclear magnetic resonance measurements, but its
application relies on the use of high-frequency microwave to manipulate
electron spins, an increasingly demanding task as the applied magnetic field
grows. Here we investigate the dynamics of a system hosting a polarizing agent
formed by two distinct paramagnetic centers near a level anti-crossing. We
theoretically show that nuclear spins polarize efficiently under a cyclic
protocol that combines alternating thermal jumps and radio-frequency pulses
connecting hybrid states with opposite nuclear and electronic spin alignment.
Central to this process is the difference between the spin-lattice relaxation
times of either electron spin species, transiently driving the electronic spin
bath out of equilibrium after each thermal jump. Without the need for microwave
excitation, this route to enhanced nuclear polarization may prove convenient,
particularly if the polarizing agent is designed to feature electronic level
anti-crossings at high magnetic fields.",2201.09092v1
2022-01-31,Electrochemical characterisation of ionic dynamics resulting from spin conversion of water isomers,"Para- and ortho- isomers of water have different chemical and physical
properties. Excitations by magnetic field, laser emission or hydrodynamic
cavitation are reported to change energetic levels and spin configurations of
water molecules that in turn change macroscopically measurable properties of
aqueous solutions. Similar scheme is also explored for dissolved molecular
oxygen, where physical excitations form singlet oxygen with different spin
configurations and generate a long chain of ionic and free-radical reactions.
This work utilizes electrochemical impedance spectroscopy (EIS) to characterize
ionic dynamics of proposed spin conversion methods applied to dissolving of
carbon dioxide CO$_2$ and hydrogen peroxide H$_2$O$_2$ in pure water excited by
fluctuating weak magnetic field in uT range. Measurement results demonstrate
different ionic reactivities and surface tension effects triggered by
excitations at 10$^{-8}$J/mL. The CO$_2$- and O$_2$-related reaction pathways
are well distinguishable by EIS. Control experiments without CO$_2$/H$_2$O$_2$
input show no significant effects. Dynamics of electrochemical impedances and
temperature of fluids indicates anomalous quasi-periodical fluctuations
pointing to possible carbonate-induced cyclic reactions or cyclical spin
conversion processes. This approach can underlay development of affordable
sensors operating with spin conversion technologies.",2202.00526v1
2022-06-01,Exceptional spin wave dynamics in an antiferromagnetic honeycomb lattice,"We theoretically investigate possible effects of electric current on the spin
wave dynamics for the N\'{e}el-type antiferromagnetic order in a honeycomb
lattice. Based on a general vector decomposition of the spin polarization of
conduction electrons, we find that there can exist reciprocal and nonreciprocal
terms in the current-induced torque acting on the local spins in the system.
Furthermore, we show that the reciprocal terms will cause the spin wave Doppler
effect, while the nonreciprocal terms can induce rich non-Hermitian topological
phenomena in the spin wave dynamics, including exceptional points, bulk Fermi
arc, non-Hermitian skin effect, etc. Our results indicate the capability to
manipulate non-Hermitian magnons in magnetic materials by electric current,
which could be important for both fundamental physics and technology
applications.",2206.00723v1
2022-10-03,Dynamics of mixed quantum-classical spin systems,"Mixed quantum-classical spin systems have been proposed in spin chain theory
and, more recently, in magnon spintronics. However, current models of
quantum-classical dynamics beyond mean-field approximations typically suffer
from long-standing consistency issues, and, in some cases, invalidate
Heisenberg's uncertainty principle. Here, we present a fully Hamiltonian theory
of quantum-classical spin dynamics that appears to be the first to ensure an
entire series of consistency properties, including positivity of both the
classical and the quantum density, so that Heisenberg's principle is satisfied
at all times. We show how this theory may connect to recent energy-balance
considerations in measurement theory and we present its Poisson bracket
structure explicitly. After focusing on the simpler case of a classical Bloch
vector interacting with a quantum spin observable, we illustrate the extension
of the model to systems with several spins, and restore the presence of orbital
degrees of freedom.",2210.00988v2
2023-01-12,Inelastic Neutron Scattering Study of the Spin Dynamics in the Breathing Pyrochlore System LiGa0.95In0.05Cr4O8,"The A-site ordered chromate spinels LiGa1-xInxCr4O8 host a network of
size-alternating spin-3/2 Cr3+ tetrahedra known as a 'breathing' pyrochlore
lattice. For the x=0.05 composition, the complex magneto-structural ordering
observed in the parent x=0 material is replaced by a single transition at Tf=11
K, ascribed to the collinear nematic order caused by strong spin-lattice
coupling. We present here an inelastic neutron scattering study of the spin
dynamics in this composition. Above Tf , the dynamical scattering function
S(Q,E) is ungapped and quasi-elastic, similar to undoped LiGaCr4O8. Below Tf ,
the spectral weight splits between a broad inelastic feature at 5.8 meV and
toward the elastic line. The former feature can be ascribed to spin precessions
within antiferromagnetic loops, lifted to finite energy by the effective
biquadratic spin-lattice term in the spin Hamiltonian.",2301.05064v1
2023-02-03,Linear Absorption Spectrum of the Spin-Boson Model Studied by Extended Hierarchical Equations of Motion,"With a decomposition scheme for the bath correlation function, the
hierarchical equations of motion (HEOM) are extended to the zero-temperature
sub-Ohmic and Ohmic spin-boson model. We investigate the linear absorption
spectrum of the sub-Ohmic and Ohmic spin-boson model at zero temperature. By
applying the extended HEOM, the equilibrium spin dynamics are obtained
approximately. Then the linear response function is calculated according to the
Kubo formula rewritten in Liouville space. To explore the essence of phase
transition, we compute the linear absorption spectrum defined by the linear
response function of a dipole moment. By analyzing the peak structure of the
linear response spectrum, we get the dependence of linear absorption spectrum
with Kondo parameter and different bath exponents. The spin relaxation dynamics
are also calculated to explore the coherent-incoherent dynamic transition (CI)
and delocalizedlocalized phase transition (DL). The corresponding phase diagram
of DL and CI transition are also obtained. We pose a energy level picture to
understand the different mechanism of DL phase transition between the deep
sub-Ohmic and Ohmic spin-boson model.",2302.01908v1
2023-02-07,Decoherence of Nuclear Spins in the Proximity of Nitrogen Vacancy Centers in Diamond,"Nuclear spins in the proximity of electronic spin defects in solids are
promising platforms for quantum information processing due to their ability to
preserve quantum states for a remarkably long time. Here we report a
comprehensive study of the nuclear decoherence processes in the vicinity of the
nitrogen-vacancy (NV) center in diamond. We simulate from first principles the
change in the dynamics of nuclear spins as a function of distance and state of
the NV center and validate our results with experimental data. Our simulations
reveal nontrivial oscillations in the Hahn echo signal, pointing to a new
sensing modality of dynamical-decoupling spectroscopy, and show how
hybridization of the electronic states suppresses the coherence time of
strongly coupled nuclear spins. The computational framework developed in our
work is general and can be broadly applied to predict the dynamical properties
of nuclear spins.",2302.03257v1
2023-09-11,Room Temperature Dynamics of an Optically Addressable Single Spin in Hexagonal Boron Nitride,"Hexagonal boron nitride (h-BN) hosts pure single-photon emitters that have
shown evidence of optically detected electronic spin dynamics. However, the
electrical and chemical structure of these optically addressable spins is
unknown, and the nature of their spin-optical interactions remains mysterious.
Here, we use time-domain optical and microwave experiments to characterize a
single emitter in h-BN exhibiting room temperature optically detected magnetic
resonance. Using dynamical simulations, we constrain and quantify transition
rates in the model, and we design optical control protocols that optimize the
signal-to-noise ratio for spin readout. This constitutes a necessary step
towards quantum control of spin states in h-BN.",2309.05604v2
2023-10-12,Time-resolved Broadband Spectroscopy of Coherent Lattice Dynamics in a Rashba Material,"Spintronics aims at establishing an information technology relying on the
spins of electrons. Key to this vision is the spin-to-charge conversion (and
vice versa) enabled by spin-orbit coupling, which represents the intimate bond
between spins and charges. Here, we set the foundations to manipulate the
spin-orbit coupling in Rashba systems in a coherent way at THz frequencies
without parasitic electronic dissipation. Our approach relies on the generation
of coherent lattice dynamics in BiTeI. Using ultrashort laser pulses ranging
from the visible to the mid-infrared spectral range we establish quantitatively
the conditions for an effective generation of coherent THz phonons, with the
required symmetry for a manipulation of the Rashba coupling. Furthermore, we
conclude an open discussion on the possibility of photoinducing of a spin
current in BiTeI, proving that this is not the case. We envision a direct
application of our pumping scheme in a photoemission experiment, which can
directly disclose the THz dynamics of the Rashba splitting.",2310.08411v1
2023-11-06,Direct Observation of Chirality-Induced Spin Selectivity in Electron Donor-Acceptor Molecules,"The role of chirality in determining the spin dynamics of photoinduced
electron transfer in donor-acceptor molecules remains an open question.
Although chirality-induced spin selectivity (CISS) has been demonstrated in
molecules bound to substrates, experimental information about whether this
process influences spin dynamics in the molecules themselves is lacking. Here
we use time-resolved electron paramagnetic resonance spectroscopy to show that
CISS strongly influences the spin dynamics of isolated covalent donor-chiral
bridge-acceptor (D-B$\chi$-A) molecules in which selective photoexcitation of D
is followed by two rapid, sequential electron transfer events to yield
D$^+$-B$\chi$-A$^-$. Exploiting this phenomenon affords the possibility of
using chiral molecular building blocks to control electron spin states in
quantum information applications.",2311.03599v1
2023-12-05,Quantum spin probe of single charge dynamics,"Electronic defects in semiconductors form the basis for many emerging quantum
technologies. Understanding defect spin and charge dynamics in solid state
platforms is crucial to developing these building blocks, but many defect
centers are difficult to access at the single-particle level due to the lack of
sensitive readout techniques. A method for probing optically inactive spin
defects would reveal semiconductor physics at the atomic scale and advance the
study of new quantum systems. We exploit the intrinsic correlation between the
charge and spin states of defect centers to measure defect charge populations
and dynamics through the steady-state spin population, read-out at the
single-defect level with a nearby optically active qubit. We directly measure
ionization and charge relaxation of single dark defects in diamond, effects we
do not have access to with traditional coherence-based quantum sensing. These
spin resonance-based methods generalize to other solid state defect systems in
relevant materials.",2312.02894v1
2023-12-16,Spin-torque nano-oscillator based on two in-plane magnetized synthetic ferrimagnets,"We report the dynamic characterization of the spin-torque-driven in-plane
precession modes of a spin-torque nano-oscillator based on two different
synthetic ferrimagnets: a pinned one characterized by a strong RKKY interaction
which is exchange coupled to an antiferromagnetic layer; and a second one,
non-pinned characterized by weak RKKY coupling. The microwave properties
associated with the steady-state precession of both SyFs are characterized by
high spectral purity and power spectral density. However, frequency dispersion
diagrams of the damped and spin transfer torque modes reveal drastically
different dynamical behavior and microwave emission properties in both SyFs. In
particular, the weak coupling between the magnetic layers of the non-pinned SyF
raises discontinuous dispersion diagrams suggesting a strong influence of mode
crossing. An interpretation of the different dynamical features observed in the
damped and spin torque modes of both SyF systems was obtained by solving
simultaneously, in a macrospin approach, a linearized version of the
Landau-Lifshitz-Gilbert equation including the spin transfer torque term.",2312.10451v2
2023-12-22,Exact numerical solution of the classical and quantum Heisenberg spin glass,"We present the mean field solution of the quantum and classical Heisenberg
spin glasses, using the combination of a high precision numerical solution of
the Parisi full replica symmetry breaking equations and a continuous time
Quantum Monte Carlo. We characterize the spin glass order and its low-energy
excitations down to zero temperature. The Heisenberg spin glass has a rougher
energy landscape than its Ising analogue, and exhibits a very slow temperature
evolution of its dynamical properties. We extend our analysis to the doped,
metallic Heisenberg spin glass, which displays an unexpectedly slow spin
dynamics reflecting the proximity to the melting quantum critical point and its
associated Sachdev-Ye-Kitaev Planckian dynamics.",2312.14598v2
2024-03-25,Spin-charge separation in the quantum boomerang effect,"We study the localization dynamics of a SU(2) fermionic wavepacket launched
in a (pseudo)random potential. We show that in the limit of strong
inter-component repulsions, the total wavepacket exhibits a boomerang-like
dynamics, returning near its initial position as expected for non-interacting
particles, while separately each spin-component does not. This spin-charge
separation effect occurs both in the infinite repulsive limit and at finite
interactions. At infinite interactions, the system is integrable and
thermalization cannot occur: the two spin-components push each other during the
dynamics and their centers of mass stop further from each other than their
initial position. At finite interactions, integrability is broken, the two
spin-components oscillate and mix, with their center-of-mass positions
converging very slowly to the center of mass of the whole system. This is a
signature that the final localized state is a fully spin-mixed thermalized
state.",2403.16923v1
1999-05-20,Spin dynamics simulation of the three-dimensional XY model: Structure factor and transport properties,"We present extensive Monte-Carlo spin dynamics simulations of the classical
XY model in three dimensions on a simple cubic lattice with periodic boundary
conditions. A recently developed efficient integration algorithm for the
equations of motion is used, which allows a substantial improvement of
statistics and large integration times. We find spin wave peaks in a wide range
around the critical point and spin diffusion for all temperatures. At the
critical point we find evidence for a violation of dynamic scaling in the sense
that independent components of the dynamic structure factor S(q,w) require
different dynamic exponents in order to obtain scaling. Below the critical
point we investigate the dispersion relation of the spin waves and the
linewidths of S(q,w) and find agreement with mode coupling theory. Apart from
strong spin wave peaks we observe additional peaks in S(q,w) which can be
attributed to two-spin wave interactions. The overall lineshapes are also
discussed and compared to mode coupling predictions. Finally, we present first
results for the transport coefficient D(q,w) of the out-of-plane magnetization
component at the critical point, which is related to the thermal conductivity
of He4 near the superfluid-normal transition.",9905295v1
2004-10-26,Aging dynamics across a dynamic Almeida-Thouless line in three dimensional short-range Issuing spin glass Cu$_{0.5}$Co$_{0.5}$Cl$_{2}$-FeCl$_{3}$ graphite bi-intercalation compound,"Cu$_{0.5}$Co$_{0.5}$Cl$_{2}$-FeCl$_{3}$ graphite intercalation compound is a
three-dimensional short-range Ising spin glass with a spin freezing temperature
$T_{c}$ ($= 3.92 \pm 0.11$ K). The stability of the spin glass phase in the
presence of a magnetic field $H$ is examined from (i) the spin freezing
temperature $T_{f}(\omega,H)$ at which the differential field-cooled (FC)
susceptibility $\partial M_{FC}(T,H)/\partial H$ coincides with the dispersion
$\chi^{\prime}(\omega,T,H=0)$ with the angular frequency $\omega$, and (ii) the
time dependence of zero-field cooled (ZFC) susceptibility $\chi_{ZFC}$ after a
ZFC aging protocol with a wait time $t_{W}$ ($= 1.0 \times 10^{4}$). The
relaxation rate $S(t)$ (= d$\chi_{ZFC}$/d$\ln t$) exhibits a local maximum at a
characteristic time $t_{cr}$, reflecting non-equilibrium aging dynamics. The
peak time $t_{cr}(T,H)$ decreases with increasing $H$ at the fixed temperature
$T$ (2.9 K $\leq T<T_{c}$). The spin freezing temperature $T_{f}(\omega,H)$
provides evidence for the instability of the spin glass phase in thermal
equilibrium in a finite magnetic field. Both $t_{cr}(T,H)$ and
$T_{f}(\omega,H)$ exhibit certain scaling behavior predicted from the droplet
picture, suggesting a dynamic crossover from SG dynamics to paramagnetic
behavior in the presence of $H$.",0410676v2
2006-04-21,Spin Precession and Real Time Dynamics in the Kondo Model: A Time-Dependent Numerical Renormalization-Group Study,"A detailed derivation of the recently proposed time-dependent numerical
renormalization-group (TD-NRG) approach to nonequilibrium dynamics in quantum
impurity systems is presented. We demonstrate that the method is suitable for
fermionic as well as bosonic baths. A comparison with exact analytical results
for the charge relaxation in the resonant-level model and for dephasing in the
spin-boson model establishes the accuracy of the method. The real-time dynamics
of a single spin coupled to both types of baths is investigated. We use the
TD-NRG to calculate the spin relaxation and spin precession of a single Kondo
impurity. The short- and long-time dynamics is studied as a function of
temperature in the ferromagnetic and antiferromagnetic regimes. The short-time
dynamics agrees very well with analytical results obtained at second order in
the exchange coupling $J$. In the ferromagnetic regime, the long-time spin
decay is described by the scaling variable $x = 2\rho_F J(T) T t$. In the
antiferromagnetic regime it is governed for $T < T_K$ by the Kondo time scale
$1/T_K$. Here $\rho_F$ is the conduction-electron density of states and $T_K$
is the Kondo temperature. Results for spin precession are obtained by rotating
the external magnetic field from the x axis to the z axis.",0604517v1
2011-01-27,Phenomenological Study of Decoherence in Solid-State Spin Qubits due to Nuclear Spin Diffusion,"We present a study of the prospects for coherence preservation in solid-state
spin qubits using dynamical decoupling protocols. Recent experiments have
provided the first demonstrations of multipulse dynamical decoupling sequences
in this qubit system, but quantitative analyses of potential coherence
improvements have been hampered by a lack of concrete knowledge of the relevant
noise processes. We present simulations of qubit coherence under the
application of arbitrary dynamical decoupling pulse sequences based on an
experimentally validated semiclassical model. This phenomenological approach
bundles the details of underlying noise processes into a single experimentally
relevant noise power spectral density. Our results show that the dominant
features of experimental measurements in a two-electron singlet-triplet spin
qubit can be replicated using a $1/\omega^{2}$ noise power spectrum associated
with nuclear-spin-flips in the host material. Beginning with this validation we
address the effects of nuclear programming, high-frequency nuclear-spin
dynamics, and other high-frequency classical noise sources, with conjectures
supported by physical arguments and microscopic calculations where relevant.
Our results provide expected performance bounds and identify diagnostic metrics
that can be measured experimentally in order to better elucidate the underlying
nuclear spin dynamics.",1101.5189v2
2017-03-20,Spin-Wave Dynamics in the Presence of Magnetic Vortices,"This chapter describes spin-wave excitations in nanosized dots and rings in
the presence of the vortex state. The special attention is paid to the
manifestation of the competition between exchange and dipolar interactions in
the spin-wave spectrum as well as the correlation between the spectrum and the
stability of the vortex. The calculation method uses the dynamic matrix for an
all-discrete system, the numerical diagonalization of which yields the spectrum
of frequencies and spin-wave profiles of normal modes of the dot. We study
in-plane vortices of two types: a circular magnetization in circular dots and
rings and the Landau state in square rings. We examine the influence of the
dipolar-exchange competition and the geometry of the dot on the stability of
the vortex and on the spectrum of spin waves. We show that the lowest-frequency
mode profile proves to be indicative of the dipolar-to-exchange interaction
ratio and the vortex stability is closely related to the spin-wave profile of
the soft mode. The negative dispersion relation is also shown. Our results
obtained for in-plane vortices are in qualitative agreement with results for
core-vortices obtained from experiments, micromagnetic simulations, and
analytical calculations.",1703.06668v1
2017-04-26,Dynamics and thermodynamics of a central spin immersed in a spin bath,"An exact reduced dynamical map along with its operator sum representation is
derived for a central spin interacting with a thermal spin environment. The
dynamics of the central spin shows high sustainability of quantum traits such
as coherence and entanglement in the low-temperature regime. However, for
sufficiently high temperature and when the number of bath particles approaches
the thermodynamic limit, this feature vanishes and the dynamics closely mimics
Markovian evolution. The properties of the long-time-averaged state and the
trapped information of the initial state for the central qubit are also
investigated in detail, confirming that the nonergodicity of the dynamics can
be attributed to the finite temperature and finite size of the bath. It is
shown that if a certain stringent resonance condition is satisfied, the
long-time-averaged state retains quantum coherence, which can have far reaching
technological implications in engineering quantum devices. An exact time-local
master equation of the canonical form is derived. With the help of this master
equation, the nonequilibrium properties of the central spin system are studied
by investigating the detailed balance condition and irreversible entropy
production rate. The result reveals that the central qubit thermalizes only in
the limit of very high temperature and large number of bath spins.",1704.08291v2
2008-07-08,Static and dynamical properties of elliptic quantum corrals,"Due to their focalizing properties, elliptic quantum corrals present very
interesting physical behaviors. In this work, we analyze static and dynamical
properties of these systems. Results are presented for realistic values of the
parameters, which might be useful for comparison with experiments. We study
noninteracting corrals and their response to several kinds of external
perturbations, observing that, for realistic values of the Fermi level, the
dynamics involves only a few number of excited states, making the system quite
robust with respect to possible sources of decoherence. We also study the
system in the presence of two S=1/2 impurities located at its foci, which
interact with the electrons of the ellipse via a superexchange interaction J.
This system is diagonalized numerically and properties such as the spin gap and
spin-spin static and dynamical correlations are studied. We find that, for
small J, both spins are locked in a singlet or triplet state, for even or odd
filling, respectively, and its spin dynamics consists mainly of a single peak
above the spin gap. In this limit, we can define an effective Heisenberg
Hamiltonian to describe the low-energy properties. For larger J, more states
are involved and the localized spins decorrelate in a manner similar to the
Ruderman-Kittel-Kasuya-Yosida-Kondo transition for the two-impurity problem.",0807.1146v1
2018-06-06,Non-equilibrium Quantum Spin Dynamics from 2PI Functional Integral Techniques in the Schwinger Boson Representation,"We present a non-equilibrium quantum field theory approach to the
initial-state dynamics of spin models based on two-particle irreducible (2PI)
functional integral techniques. It employs a mapping of spins to Schwinger
bosons for arbitrary spin interactions and spin lengths. At next-to-leading
order (NLO) in an expansion in the number of field components, a wide range of
non-perturbative dynamical phenomena are shown to be captured, including
relaxation of magnetizations in a 3D long-range interacting system with
quenched disorder, different relaxation behaviour on both sides of a quantum
phase transition and the crossover from relaxation to arrest of dynamics in a
disordered spin chain previously shown to exhibit many-body-localization. Where
applicable, we employ alternative state-of-the-art techniques and find rather
good agreement with our 2PI NLO results. As our method can handle large system
sizes and converges relatively quickly to its thermodynamic limit, it opens the
possibility to study those phenomena in higher dimensions in regimes in which
no other efficient methods exist. Furthermore, the approach to classical
dynamics can be investigated as the spin length is increased.",1806.02347v2
2020-03-25,Spin Dynamics in the t-t'-J Model: Dynamical Density-Matrix Renormalization Group Study,"The ground state of a hole-doped t-t'-J ladder with four legs favors a
striped charge distribution. Spin excitation from the striped ground state is
known to exhibit incommensurate spin excitation near q=(pi,pi) along the leg
direction (qx direction). However, an outward dispersion from the
incommensurate position toward q=(0,pi) is strong in intensity, inconsistent
with inelastic neutron scattering (INS) experiment in hole-doped cuprates.
Motivated by this inconsistency, we use the t-t'-J model with m x n=96 lattice
sites by changing lattice geometry from four-leg (24x4) to rectangle (12x8)
shape and investigate the dynamical spin structure factor by using the
dynamical density matrix renormalization group. We find that the outward
dispersion has weak spectral weights in the 12x8 lattice, accompanied with the
decrease of excitation energy close to q=(pi,pi), being consistent with the INS
data. In the 12x8 lattice, weakening of incommensurate spin correlation is
realized even in the presence of the striped charge distribution. For further
investigation of geometry related spin dynamics, we focus on direction
dependent spin excitation reported by recent resonant inelastic x-ray
scattering (RIXS) for cuprate superconductors and obtain a consistent result
with RIXS by examining an 8x8 t-t'-J square lattice.",2003.11161v2
2023-04-28,Persistent dynamic magnetic state in artificial honeycomb spin ice,"Topological magnetic charges, arising due to the non-vanishing magnetic flux
on spin ice vertices, serve as the origin of magnetic monopoles that traverse
the underlying lattice effortlessly. Unlike spin ice materials of atomic
origin, the dynamic state in artificial honeycomb spin ice is conventionally
described in terms of finite size domain wall kinetics that require magnetic
field or current application. Contrary to this common understanding, here we
show that thermally tunable artificial permalloy honeycomb lattice manifests a
perpetual dynamic state due to self-propelled magnetic charge defect relaxation
in the absence of any external tuning agent. Quantitative investigation of
magnetic charge defect dynamics using neutron spin echo spectroscopy reveals
sub-ns relaxation times that are comparable to monopole's relaxation in bulk
spin ices. Most importantly, the kinetic process remains unabated at low
temperature where thermal fluctuation is negligible. This suggests that dynamic
phenomena in honeycomb spin ice are mediated by quasi-particle type entities,
also confirmed by quantum Monte-Carlo simulations that replicate the kinetic
behavior. Our research unveils a new `macroscopic' magnetic particle that
shares many known traits of quantum particles, namely magnetic monopole and
magnon.",2305.00093v1
2023-05-24,Non-Gaussian dynamics of quantum fluctuations and mean-field limit in open quantum central spin systems,"Central spin systems, in which a {\it central} spin is singled out and
interacts nonlocally with several {\it bath} spins, are paradigmatic models for
nitrogen-vacancy centers and quantum dots. They show complex emergent dynamics
and stationary phenomena which, despite the collective nature of their
interaction, are still largely not understood. Here, we derive exact results on
the emergent behavior of open quantum central spin systems. The latter
crucially depends on the scaling of the interaction strength with the bath
size. For scalings with the inverse square root of the bath size (typical of
one-to-many interactions), the system behaves, in the thermodynamic limit, as
an open quantum Jaynes-Cummings model, whose bosonic mode encodes the quantum
fluctuations of the bath spins. In this case, non-Gaussian correlations are
dynamically generated and persist at stationarity. For scalings with the
inverse bath size, the emergent dynamics is instead of mean-field type. Our
work provides a fundamental understanding of the different dynamical regimes of
central spin systems and a simple theory for efficiently exploring their
nonequilibrium behavior. Our findings may become relevant for developing fully
quantum descriptions of many-body solid-state devices and their applications.",2305.15547v2
2024-03-12,Discrete Laplacian thermostat for flocks and swarms: the fully conserved Inertial Spin Model,"Experiments on bird flocks and midge swarms reveal that these natural systems
are well described by an active theory in which conservation laws play a
crucial role. By building a symplectic structure that couples the particles'
velocities to the generator of their internal rotations (spin), the Inertial
Spin Model (ISM) reinstates a second-order temporal dynamics that captures many
phenomenological traits of flocks and swarms. The reversible structure of the
ISM predicts that the total spin is a constant of motion, the central
conservation law responsible for all the novel dynamical features of the model.
However, fluctuations and dissipation introduced in the original model to make
it relax, violate the spin conservation law, so that the ISM aligns with the
biophysical phenomenology only within finite-size regimes, beyond which the
overdamped dynamics characteristic of the Vicsek model takes over. Here, we
introduce a novel version of the ISM, in which the irreversible terms needed to
relax the dynamics strictly respect the conservation of the spin. We perform a
numerical investigation of the fully conservative model, exploring both the
fixed-network case, which belongs to the equilibrium class of Model G, and the
active case, characterized by self-propulsion of the agents and an
out-of-equilibrium reshuffling of the underlying interaction network. Our
simulations not only capture the correct spin wave phenomenology of the ordered
phase, but they also yield dynamical critical exponents in the near-ordering
phase that agree very well with the theoretical predictions.",2403.07644v1
2022-06-12,Exchange-enhancement of the ultrafast magnetic order dynamics in antiferromagnets,"We theoretically demonstrate that the ultrafast magnetic order dynamics in
antiferromagnets is exchange-enhanced in comparison to their ferromagnetic
counterparts. We provide an equation of motion for the magnetic order dynamics
validated by computer simulations using atomistic spin dynamics methods. The
exchange of angular momentum between sublattices speeds up the dynamics in
antiferromagnets, a process absent in ferromagnets.",2206.05783v1
2015-11-17,"Spin Dynamics of Complex Oxides, Bismuth-Antimony Alloys, and Bismuth Chalcogenides","This thesis predicts that two types of material families could be a solution
to the challenges in spintronics: complex oxides and bismuth based materials.
We derive a general approach for constructing an effective spin-orbit
Hamiltonian, which applies to all nonmagnetic materials. We also verify this
formalism through comparisons with other approaches for III-V semiconductors.
Its general applicability is illustrated by deriving the spin-orbit interaction
and predicting spin lifetimes for strained SrTiO$_3$ and a two-dimensional
electron gas (such as at the LaAlO$_3$/SrTiO$_3$ interface). Our results
suggest robust spin coherence and spin transport properties in SrTiO$_3$
related materials. In the second part, we calculate intrinsic spin Hall
conductivities for Bi$_{1-x}$Sb$_x$ semimetals with strong spin-orbit
couplings, from the Kubo formula and using Berry curvatures evaluated from a
tight-binding Hamiltonian. Nearly crossing bands with strong spin-orbit
interaction generate giant spin Hall conductivities in these materials, ranging
from 474 ($\hbar/e)( \Omega^{-1}cm^{-1}$) for bismuth to 96($\hbar/e)(
\Omega^{-1}cm^{-1}$) for antimony; the value for bismuth is more than twice
that of platinum. The large spin Hall conductivities persist for alloy
compositions corresponding to a three-dimensional topological insulator state,
such as Bi$_{0.83}$Sb$_{0.17}$. The spin Hall conductivity could be changed by
a factor of 5 for doped Bi, or for Bi$_{0.83}$Sb$_{0.17}$, by changing the
chemical potential, suggesting the potential for doping or voltage tuned spin
Hall current. We also calculate intrinsic spin Hall conductivities of
Bi$_2$Se$_3$ and Bi$_2$Te$_3$ topological insulators from an effective
tight-binding Hamiltonian. We conclude that bismuth-antimony alloys and bismuth
chalcogenides are primary candidates for efficiently generating spin currents
through the spin Hall effect.",1511.05276v1
2012-04-12,Quantum Decoherence of the Central Spin in a Sparse System of Dipolar Coupled Spins,"The central spin decoherence problem has been researched for over 50 years in
the context of both nuclear magnetic resonance and electron spin resonance.
Until recently, theoretical models have employed phenomenological stochastic
descriptions of the bath-induced noise. During the last few years, cluster
expansion methods have provided a microscopic, quantum theory to study the
spectral diffusion of a central spin. These methods have proven to be very
accurate and efficient for problems of nuclear-induced electron spin
decoherence in which hyperfine interactions with the central electron spin are
much stronger than dipolar interactions among the nuclei. We provide an
in-depth study of central spin decoherence for a canonical scale-invariant
all-dipolar spin system. We show how cluster methods may be adapted to treat
this problem in which central and bath spin interactions are of comparable
strength. Our extensive numerical work shows that a properly modified cluster
theory is convergent for this problem even as simple perturbative arguments
begin to break down. By treating clusters in the presence of energy detunings
due to the long-range (diagonal) dipolar interactions of the surrounding
environment and carefully averaging the effects over different spin states, we
find that the nontrivial flip-flop dynamics among the spins becomes effectively
localized by disorder in the energy splittings of the spins. This localization
effect allows for a robust calculation of the spin echo signal in a dipolarly
coupled bath of spins of the same kind, while considering clusters of no more
than 6 spins. We connect these microscopic calculation results to the existing
stochastic models. We, furthermore, present calculations for a series of
related problems of interest for candidate solid state quantum bits including
donors and quantum dots in silicon as well as nitrogen-vacancy centers in
diamond.",1204.2834v2
2019-10-22,A Spin Quintet in a Silicon Double Quantum Dot: Spin Blockade and Relaxation,"Spins in gate-defined silicon quantum dots are promising candidates for
implementing large-scale quantum computing. To read the spin state of these
qubits, the mechanism that has provided the highest fidelity is spin-to-charge
conversion via singlet-triplet spin blockade, which can be detected in-situ
using gate-based dispersive sensing. In systems with a complex energy spectrum,
like silicon quantum dots, accurately identifying when singlet-triplet blockade
occurs is hence of major importance for scalable qubit readout. In this work,
we present a description of spin blockade physics in a tunnel-coupled silicon
double quantum dot defined in the corners of a split-gate transistor. Using
gate-based magnetospectroscopy, we report successive steps of spin blockade and
spin blockade lifting involving spin states with total spin angular momentum up
to $S=3$. More particularly, we report the formation of a hybridized spin
quintet state and show triplet-quintet and quintet-septet spin blockade. This
enables studies of the quintet relaxation dynamics from which we find $T_1 \sim
4 ~\mu s$. Finally, we develop a quantum capacitance model that can be applied
generally to reconstruct the energy spectrum of a double quantum dot including
the spin-dependent tunnel couplings and the energy splitting between different
spin manifolds. Our results open for the possibility of using Si CMOS quantum
dots as a tuneable platform for studying high-spin systems.",1910.10118v1
2013-05-22,Self-consistent calculation of spin transport and magnetization dynamics,"A spin-polarized current transfers its spin-angular momentum to a local
magnetization, exciting current-induced magnetization dynamics. So far, most
studies in this field have focused on the direct effect of spin transport on
magnetization dynamics, but ignored the feedback from the magnetization
dynamics to the spin transport and back to the magnetization dynamics. Although
the feedback is usually weak, there are situations when it can play an
important role in the dynamics. In such situations, self-consistent
calculations of the magnetization dynamics and the spin transport can
accurately describe the feedback. This review describes in detail the feedback
mechanisms, and presents recent progress in self-consistent calculations of the
coupled dynamics. We pay special attention to three representative examples,
where the feedback generates non-local effective interactions for the
magnetization. Possibly the most dramatic feedback example is the dynamic
instability in magnetic nanopillars with a single magnetic layer. This
instability does not occur without non-local feedback. We demonstrate that full
self-consistent calculations generate simulation results in much better
agreement with experiments than previous calculations that addressed the
feedback effect approximately. The next example is for more typical spin valve
nanopillars. Although the effect of feedback is less dramatic because even
without feedback the current can induce magnetization oscillation, the feedback
can still have important consequences. For instance, we show that the feedback
can reduce the linewidth of oscillations, in agreement with experimental
observations. Finally, we consider nonadiabatic electron transport in narrow
domain walls. The non-local feedback in these systems leads to a significant
renormalization of the effective nonadiabatic spin transfer torque.",1305.5087v1
2014-10-07,Quantum model of a solid-state spin qubit: Ni cluster on a silicon surface by the generalized spin Hamiltonian and X-ray absorption spectroscopy investigations,"We present here the quantum model of a Ni solid-state electron spin qubit on
a silicon surface with the use of a density functional scheme for calculation
of the exchange integrals in the non-collinear spin configurations in the
generalized spin Hamiltonian (GSH) with the anisotropic exchange couplings
parameters linking the nickel ions with a silicon substrate. In this article we
offer the model of the quantum solid-state N-spin qubit based on the studying
of the spin structure and the spin-dynamics simulations of the 3d-metal Ni
clusters on a silicon surface. The solution of the problem of the entanglement
between a spin states in N-spin systems is becoming more interesting when
considering clusters or molecules with a spectral gap in their density of
states. For quantifying the distribution of the entanglement between the
individual spin eigenvalues (modes) in the spin structure of the N-spin system
we use the density of entanglement. We have studied the Rabi oscillations to
evaluate the N-spin qubits system as a function of the time and the magnetic
field. We have observed the stabilized Rabi oscillations and have stabilized
the quantum dynamical qubit state and Rabi driving after a fixed time. The
comparison of the energy pattern with the anisotropic exchange models
conventionally used for the analysis of this system and, with the results of
the experimental XANES spectra, shows that our complex investigations provide a
good description of the pattern of the spin levels and the spin structures of
the nanomagnetic Ni7 qubit. The results are discussed in the view of the
general problem of the solid state spin qubits and the spin structure of the Ni
cluster.",1410.1658v1
1996-02-22,Exact Solution of an Irreversible One-Dimensional Model with Fully Biased Spin Exchanges,"We introduce a model with conserved dynamics, where nearest neighbor pairs of
spins $\uparrow \downarrow (\downarrow \uparrow)$ can exchange to assume the
configuration $\downarrow \uparrow (\uparrow \downarrow)$, with rate $\beta
(\alpha)$, through energy decreasing moves only. We report exact solution for
the case when one of the rates, $\alpha$ or $\beta$, is zero. The
irreversibility of such dynamics results in strong dependence on the initial
conditions. Domain wall arguments suggest that for more general models with
steady states the dynamical critical exponent for the anisotropic spin exchange
is different from the isotropic value.",9602122v1
2000-12-05,Algorithm for molecular dynamics simulations of spin liquids,"A new symplectic time-reversible algorithm for numerical integration of the
equations of motion in magnetic liquids is proposed. It is tested and applied
to molecular dynamics simulations of a Heisenberg spin fluid. We show that the
algorithm exactly conserves spin lengths and can be used with much larger time
steps than those inherent in standard predictor-corrector schemes. The results
obtained for time correlation functions demonstrate the evident dynamic
interplay between the liquid and magnetic subsystems.",0012059v1
2001-08-14,Glassy dynamics in granular compaction: sand on random graphs,"We discuss the use of a ferromagnetic spin model on a random graph to model
granular compaction. A multi-spin interaction is used to capture the
competition between local and global satisfaction of constraints characteristic
for geometric frustration. We define an athermal dynamics designed to model
repeated taps of a given strength. Amplitude cycling and the effect of
permanently constraining a subset of the spins at a given amplitude is
discussed. Finally we check the validity of Edwards' hypothesis for the
athermal tapping dynamics.",0108225v2
2002-02-07,Anomalously Soft Droplets and Aging in Short-ranged Spin Glasses,"We extend the standard droplet scaling theory for isothermal aging in spin
glasses assuming that the effective stiffness constant of droplets as large as
extended defects is vanishingly small. A novel dynamical order parameter and
the associated dynamical susceptibility emerge. Breaking of the fluctuation
dissipation theorem takes place at the dynamical order parameter well below the
equilibrium Edwards-Anderson order parameter at which the time translational
invariance is strongly broken. The scenario is examined numerically in a 4
dimensional EA Ising spin glass model.",0202110v2
2002-05-06,Low-temperature dynamics of spin glasses: Walking in the energy landscape,"We analyse the relationship between dynamics and configuration space
structure of Ising spin glass systems. The exact knowledge of the structure of
the low--energy landscape is used to study the relaxation of the system by
random walk in the configuration space. The influence of the size of the
valleys, clusters and energy barriers and the connectivity between them on the
spin correlation function is shown.",0205093v2
2003-08-15,Current-Driven Magnetization Dynamics in Magnetic Multilayers,"We develop a quantum analog of the classical spin-torque model for
current-driven magnetic dynamics. The current-driven magnetic excitation at
finite field becomes significantly incoherent. This excitation is described by
an effective magnetic temperature rather than a coherent precession as in the
spin-torque model. However, both the spin-torque and effective temperature
approximations give qualitatively similar switching diagrams in the
current-field coordinates, showing the need for detailed experiments to
establish the proper physical model for current-driven dynamics.",0308320v2
2003-09-11,Spin Dynamics of t-J Model on Triangular Lattice,"We study the spin dynamics of t-J model on triangular lattice in the
Slave-Boson-RPA scheme in light of the newly discovered superconductor
Na$_{x}$CoO$_{2}$. We find resonant peak in the dynamic spin susceptibility in
the $d+id^{^{\prime}}$-wave superconducting state for both hole and electron
doping in large doping range. We find the geometrical frustration inherent of
the triangular lattice provide us a unique opportunity to discriminate the
SO(5) and RPA-like intepretation of the origin of the resonant peak.",0309275v1
2004-06-21,Entanglement dynamics in the Lipkin-Meshkov-Glick model,"The dynamics of the one-tangle and the concurrence is analyzed in the
Lipkin-Meshkov-Glick model which describes many physical systems such as the
two-mode Bose-Einstein condensates. We consider two different initial states
which are physically relevant and show that their entanglement dynamics are
very different. A semiclassical analysis is used to compute the one-tangle
which measures the entanglement of one spin with all the others, whereas the
frozen-spin approximation allows us to compute the concurrence using its
mapping onto the spin squeezing parameter.",0406481v2
2005-12-08,Physics of Complex Magnetic Materials: Quasiparticle Many-Body Dynamics,"A brief survey of the author's works on the quantum theory of magnetism.
Theoretical foundation and applications of the generalized spin-fermion (sp-d)
exchange lattice model to various magnetic systems, e.g., rare-earth metals and
compounds, and magnetic and diluted magnetic semiconductors are discussed
briefly. The main emphasis is put on the dynamic behavior of two interacting
subsystems, the localized spins and spin density of itinerant carriers. A
nonperturbative many-body approach was used to describe the quasiparticle
dynamics. The approach permits to investigate and clarify the role of various
interactions and disorder effects in combined quantum models of magnetism in
unified and coherent fashion.",0512183v1
2000-04-07,Quantum ergodicity for Pauli Hamiltonians with spin 1/2,"Quantum ergodicity, which expresses the semiclassical convergence of almost
all expectation values of observables in eigenstates of the quantum Hamiltonian
to the corresponding classical microcanonical average, is proven for
non-relativistic quantum particles with spin 1/2. It is shown that quantum
ergodicity holds, if a suitable combination of the classical translational
dynamics and the spin dynamics along the trajectories of the translational
motion is ergodic.",0004007v1
2007-04-23,Dynamical stability for finite quantum spin chains against a time-periodic inhomogeneous perturbation,"We investigate dynamical stability of the ground state against a
time-periodic and spatially-inhomogeneous magnetic field for finite quantum XXZ
spin chains. We use the survival probability as a measure of stability and
demonstrate that it decays as $P(t) \propto t^{-1/2}$ under a certain
condition. The dynamical properties should also be related to the level
statistics of the XXZ spin chains with a constant spatially-inhomogeneous
magnetic field. The level statistics depends on the anisotropy parameter and
the field strength. We show how the survival probability depends on the
anisotropy parameter, the strength and frequency of the field.",0704.2922v1
2009-01-22,Monopole and Topological Electron Dynamics in Adiabatic Spintronic and Graphene Systems,"A unified theoretical treatment is presented to describe the physics of
electron dynamics in semiconductor and graphene systems. Electron spin fast
alignment with the Zeeman magnetic field (physical or effective) is treated as
a form of adiabatic spin evolution which necessarily generates a monopole in
magnetic space. One could transform this monopole into the physical and
intuitive topological magnetic fields in the useful momentum (K) or real spaces
(R). The physics of electron dynamics related to spin Hall, torque,
oscillations and other technologically useful spinor effects can be inferred
from the topological magnetic fields in spintronic, graphene and other SU(2)
systems.",0901.3411v1
2009-05-05,Markovian and Post-Markovian dynamics of nonequilibrium thermal entanglement,"The dynamics of two spins coupled to bosonic baths at different temperatures
is studied. The analytical solution for the reduced density matrix of the
system in the Markovian and Post-Markovian case with exponential memory kernel
is found. The dynamics and temperature dependence of spin-spin entanglement is
analyzed.",0905.0544v2
2011-04-03,Chaotic dynamics and spin correlation functions in a chain of nanomagnets,"We study a chain of coupled nanomagnets in a classical approximation. We show
that the infinitely long chain of coupled nanomagnets can be equivalently
mapped onto an effective one-dimensional Hamiltonian with a fictitious
time-dependent perturbation. We establish a connection between the dynamical
characteristics of the classical system and spin correlation time. The decay
rate for the spin correlation functions turns out to depend logarithmically on
the maximal Lyapunov exponent. Furthermore, we discuss the non-trivial role of
the exchange anisotropy within the chain.",1104.0371v1
2011-04-11,Spin segregation via dynamically induced long-range interaction in a system of ultracold fermions,"We investigate theoretically the time evolution of a one-dimensional system
of spin-1/2 fermions in a harmonic trap after, initially, a spiral spin
configuration far-from equilibrium is created. We predict a spin segregation
building up in time already for weak interaction under realistic experimental
conditions. The effect relies on the interplay between exchange interaction and
the harmonic trap, and it is found for a wide range of parameters. It can be
understood as a consequence of an effective, dynamically induced long-range
interaction that is derived by integrating out the rapid oscillatory dynamics
in the trap.",1104.1965v2
2011-05-24,Constrained Dynamics of an Anomalous $(g/neq 2)$ Relativistic Spinning Particle in Electromagnetic Background,"In this paper we have considered the dynamics of an anomalous ($g\neq 2$)
charged relativistic spinning particle in the presence of an external
electromagnetic field. The constraint analysis is done and the complete set of
Dirac brackets are provided that generate the canonical Lorentz algebra and
dynamics through Hamiltonian equations of motion. The spin-induced effective
curvature of spacetime and its possible connection with Analogue Gravity models
are commented upon.",1105.4691v2
2012-06-11,Scaling in Dynamic Susceptibility of Herbertsmithite and Heavy-Fermion Metals,"We present a theory of the dynamic magnetic susceptibility of quantum spin
liquid. The obtained results are in good agreement with experimental facts
collected on herbertsmithite ZnCu3(OH)6Cl2 and on heavy-fermion metals, and
allow us to predict a new scaling in magnetic fields in the dynamic
susceptibility. Under the application of strong magnetic fields quantum spin
liquid becomes completely polarized. We show that this polarization can be
viewed as a manifestation of gapped excitations when investigating the
spin-lattice relaxation rate.",1206.2324v2
2012-07-13,Magnetic relaxation in bilayers of yttrium iron garnet/platinum due to the dynamic coupling at the interface,"We show that in ferromagnetic (FM)/normal metal (NM) bilayers the dynamic
coupling at the interface transfers an additional magnetic relaxation from the
heavily damped motion of the conduction electron spins in the NM layer to the
FM spins. While the FM relaxation rates due to two-magnon scattering and spin
pumping decrease rapidly with increasing FM film thickness, the damping due to
the dynamic coupling does not depend on the FM film thickness. The proposed
mechanism explains the very large broadening of ferromagnetic resonance lines
in thick films of yttrium iron garnet after deposition of a Pt layer.",1207.3330v1
2013-01-19,Observation of the Quantum Zeno Effect on a Single Solid State Spin,"The quantum Zeno effect, i.e. the inhibition of coherent quantum dynamics by
projective measurements is one of the most intriguing predictions of quantum
mechanics. Here we experimentally demonstrate the quantum Zeno effect by
inhibiting the microwave driven coherent spin dynamics between two ground state
spin levels of the nitrogen vacancy center in diamond nano-crystals. Our
experiments are supported by a detailed analysis of the population dynamics via
a semi-classical model.",1301.4544v2
2013-04-09,Defects dynamics following thermal quenches in square spin-ice,"We present a study of the single spin flip stochastic dynamics of the two
dimensional sixteen vertex model. We single out several dynamic regimes
controlled by different processes that we describe. We analyse the emergence of
very long-lived metastable states and their dependence on the system size,
boundary conditions, and working parameters. We investigate the coarsening
process after quenches into the ordered ferromagnetic and antiferromagnetic
phases. We discuss our results in the context of artificial spin ice on square
lattices.",1304.2595v1
2013-10-06,Gravitational radiation and angular momentum flux from a spinning dynamical black hole,"A four-dimensional asymptotic expansion scheme is used to study the next
order effects of the nonlinearity near a spinning dynamical black hole. The
angular momentum flux and energy flux formula are then obtained by asymptotic
expansion and the compatibility of the coupling Newman-Penrose equations. After
constructing the reference frame in terms of the compatible constant spinors,
the energy-momentum flux is derived and it is related to the black hole area
growth. Directly from the flux formula of the spinning dynamical horizon, we
find that the physically reasonable condition on the positivity of the
gravitational energy flux yields that the shear will monotonically decrease
with time.",1310.1602v1
2013-10-23,Dynamics of the Dicke model close to the classical limit,"We study the dynamical properties of the Dicke model for increasing spin
length, as the system approaches the limit of a classical spin. First, we
describe the emergence of collective excitations above the groundstate that
converge to the coupled spin-oscillator oscillations found in the classical
limit. The corresponding Green functions reveal quantum dynamical signatures
close to the superradiant quantum phase transition. Second, we identify
signatures of classical quasi-periodic orbits in the quantum time evolution
using numerical time-propagation of the wave function. The resulting phase
space plots are compared to the classical trajectories. We complete our study
with the analysis of individual eigenstates close to the quasi-periodic orbits.",1310.6140v1
2014-10-23,Quantum spin dynamics,"The classical Landau-Lifshitz equation has been derived from quantum
mechanics. Starting point is the assumption of a non-Hermitian Hamilton
operator to take the energy dissipation into account. The corresponding quantum
mechanical time dependent Schr\""odinger, Liouville and Heisenberg equation have
been described and the similarities and differences between classical and
quantum mechanical spin dynamics have been discussed. Furthermore, a time
dependent Schr\""odinger equation corresponding to the classical
Landau-Lifshitz-Gilbert equation and two ways to include temperature into the
quantum mechanical spin dynamics have been proposed.",1410.6383v1
2015-09-03,Dynamic Entanglement Evolution of Two-qubit XYZ Spin Chain in Markovian Environment,"We propose a new approach called Ket-Bra Entangled State (KBES) Method for
converting master equation into Schr\""{o}dinger-like equation. With this
method, we investigate decoherence process and entanglement dynamics induced by
a $2$-qubit spin chain that each qubit coupled with reservoir. The spin chain
is an anisotropy $XYZ$ Heisenberg model in the external magnetic field $B$, the
corresponding master equation is solved concisely by KBES method; Furthermore,
the effects of anisotropy, temperature, external field and initial state on
concurrence dynamics is analyzed in detail for the case that initial state is
Extended Wenger-Like(EWL) state. Finally we research the coherence and
concurrence of the final state (namely the density operator for time tend to
infinite)",1509.01001v1
2016-09-05,Trace formula for spin chains,"While detailed information about the semiclassics for single-particle systems
is available, much less is known about the connection between quantum and
classical dynamics for many-body systems. As an example, we focus on spin
chains which are of considerable conceptual and practical importance. We derive
a trace formula for coupled spin $j$ particles which relates the quantum energy
levels to the classical dynamics. Our derivation is valid in the limit
$j\rightarrow\infty$ with $j\hbar={\rm const.}$ and applies to time-continuous
as well as to periodically driven dynamics. We provide a simple explanation why
the Solari-Kochetov phase can be omitted if the correct classical Hamiltonian
is chosen.",1609.01191v1
2018-11-30,Dynamical spin effects within the pseudo scalar nonet within holographic QCD,"We investigate the importance of dynamical spin effects in the holographic
light-front wavefunctions of the pseudoscalar mesons. We find that these
effects are crucial to describe the pion data while they are not necessary to
describe the available kaon data. For $\eta-\eta^\prime$ system, we find that
dynamical spin effects are required to describe their transition form factors
data.",1811.12886v1
2008-07-22,Fingerprints for spin-selection rules in the interaction dynamics of O2 at Al(111),"We performed mixed quantum-classical molecular dynamics simulations based on
first-principles potential-energy surfaces to demonstrate that the scattering
of a beam of singlet O2 molecules at Al(111) will enable an unambiguous
assessment of the role of spin-selection rules for the adsorption dynamics. At
thermal energies we predict a sticking probability that is substantially less
than unity, with the repelled molecules exhibiting characteristic kinetic,
vibrational and rotational signatures arising from the non-adiabatic spin
transition.",0807.3557v1
2018-09-28,Dynamical Gibbs-non-Gibbs transitions in Curie-Weiss Widom-Rowlinson models,"We consider the Curie-Weiss Widom-Rowlinson model for particles with spins
and holes, with a repulsion strength beta between particles of opposite spins.
We provide a closed solution of the model, and investigate dynamical
Gibbs-non-Gibbs transitions for the time-evolved model under independent
stochastic symmetric spin-flip dynamics. We show that, for sufficiently large
beta after a transition time, continuously many bad empirical measures appear.
These lie on (unions of) curves on the simplex whose time-evolution we
describe.",1809.11014v1
2020-01-13,Dynamics of laterally-coupled pairs of spin-VCSELs,"A newly-developed normal mode model of laser dynamics in a generalised array
of waveguides is applied to extend the spin-flip model (SFM) to pairs of
evanescently-coupled spin-VCSELS. The effect of high birefringence is explored,
revealing new dynamics and regions of bistability. It is shown that optical
switching of the polarisation states of the lasers may be controlled through
the optical pump and that, under certain conditions, the polarisation of one
laser may be switched by controlling the intensity and polarisation in the
other.",2001.04531v1
2018-12-17,Dynamics of relativistic spin-polarized fluids,"We briefly review the foundations of a new relativistic fluid dynamics
framework for polarized systems of particles with spin one half. Using this
approach we numerically study the dynamics of the spin polarization of a
rotating medium resembling the ones created in high-energy heavy-ion
collisions.",1812.06801v1
2019-01-17,Dynamics of noncollinear antiferromagnetic textures driven by spin current injection,"We present a theoretical formalism to address the dynamics of textured,
noncolliear antiferromagnets subject to spin current injection. We derive
sine-Gordon type equations of motion for the antiferromagnets, which are
applicable to technologically important antiferromagnets such as Mn3Ir and
Mn3Sn, and enables an analytical approach to domain wall dynamics in those
materials. We obtain the expression for domain wall velocity, which is
estimated to reach around 1 km/s in Mn3Ir by exploiting spin Hall effect with
electric current density around 10^11A/m^2.",1901.05684v1
2020-03-10,Spin dynamics of a hydrogen atom in a periodic magnetic structure,"The spin dynamics of a hydrogen atom during the passage of a periodic
magnetic structure is discussed. The occupation numbers of the components of
the hyperfine structure are considered as a function of time. The
characteristic low-frequency oscillations are visible, which have a direct
analogue in the effect of nuclear magnetic resonance. An envelope forms of
these oscillations are found using the Krylov-Bogolyubov-Mitropol'skii method.
The dependence of spin dynamics on the parameters of the magnetic structure is
investigated. It is shown that this dependence is very sensitive to the
structure of the magnetic field.",2003.04653v1
2020-06-14,Ideal memristor based on viscous magnetization dynamics driven by spin torque,"We show that ideal memristors - devices whose resistance is proportional to
the charge that flows through them - can be realized using spin torque-driven
viscous magnetization dynamics. The latter can be accomplished in the spin
liquid state of thin-film heterostructures with frustrated exchange, where
memristive response is tunable by proximity to the glass transition, while
current-induced Joule heating facilitates nonvolatile operation and
second-order memristive functionality beneficial for neuromorphic applications.
Ideal memristive behaviors can be achieved in other systems characterized by
viscous dynamics of physical, electronic, or magnetic degrees of freedom.",2006.07996v1
2020-09-13,Hydrodynamics formalism with Spin dynamics,"We review the key steps of the relativistic fluid dynamics formalism with
spin degrees of freedom initiated recently. We obtain equations of motion of
the expansion of the system from the underlying definitions of quantum kinetic
theory for the equilibrium phase space distribution functions. We investigate
the dynamics of spin polarization of the system in the Bjorken hydrodynamical
background.",2009.07067v2
2020-10-02,Dynamic Phase Diagram of an Orthogonal Spin Torque device: Topological Category,"The magnetization evolution of the free layer in an orthogonal spin-torque
device is studied based on a macrospin model. The trajectory of magnetization
vector under various conditions has shown rich nonlinear properties. The phase
diagram is obtained in the parameter spaces of current density and the
polarization distribution (the ratio of in-plane and out-of-plane polarizers).
These dynamic phases can be classified according to their nonlinear behaviors
which are topologically different, namely limit point and/or limit cycle. The
topological classification is meaningful to design the ultra-fast spin-torque
devices under different dynamic conditions towards various applications such as
memory and oscillators.",2010.00749v1
2020-10-27,Quantum chaos in the spin coherent state representation,"We use spin coherent states to compare classical and quantum evolution of a
simple paradigmatic, discrete-time quantum dynamical system exhibiting chaotic
behavior in the classical limit. The spin coherent states are employed to
define a phase-space quasidistribution for quantum states (P-representation).
It can be, in principle, used for a direct comparison of the quantum and
classical dynamics, where on the classical level one deals with the classical
distribution function on the classical phase space. In the paper, we presented
a different way by comparing evolution of appropriately defined moments of
classical and quantum distributions, in particular the one-step propagators of
the moments.",2010.14509v1
2008-09-26,Ultra-fast spin dynamics: the effect of colored noise,"Recent experimental results have pushed the limits of magnetization dynamics
to pico- and femtosecond timescales. This ultra-fast spin dynamics occurs in
extreme conditions of strong and rapidly varying fields and high temperatures.
This situation requires new description of magnetization dynamics, even on a
phenomenological level of the atomistic Landau-Lifshitz-Gilbert equation,
taking into account that the correlation time for electron system could be of
the order of the inverse characteristic spin frequency. For this case we
introduce the thermodynamically correct phenomenological approach for spin
dynamics based on the Landau-Lifshitz-Miyasaki-Seki equation. The influence of
the noise correlation time on longitudinal and transverse magnetization
relaxation is investigated. We also demonstrate the effect of the noise
correlation time on demagnetisation rate of different materials during
laser-induced dynamics.",0809.4595v1
2013-03-14,"Decoherence, relaxation and chaos in a kicked-spin ensemble","We study the dynamics of a quantum spin ensemble controlled by trains of
ultrashort pulses. To model disturbances of the kicks, we consider that the
spins are submitted to different kick trains which follow regular, random,
stochastic or chaotic dynamical processes. These are described by dynamical
systems on a torus. We study the quantum decoherence and the population
relaxation of the spin ensemble induced by these classical dynamical processes
disturbing the kick trains. For chaotic kick trains we show that the
decoherence and the relaxation processes exhibit a signature of chaos directly
related to the Lyapunov exponents of the dynamical system. This signature is a
horizon of coherence, i.e. a preliminary duration without decoherence followed
by a rapid decoherence process.",1303.3412v2
2014-09-12,A New and Unifying Approach to Spin Dynamics and Beam Polarization in Storage Rings,"With this paper we extend our studies [1] on polarized beams by distilling
tools from the theory of principal bundles. Four major theorems are presented,
one which ties invariant fields with the notion of normal form, one which
allows one to compare different invariant fields, and two that relate the
existence of invariant fields to the existence of certain invariant sets and
relations between them. We then apply the theory to the dynamics of spin-1/2
and spin-1 particles and their density matrices describing statistically the
particle-spin content of bunches. Our approach thus unifies the spin-vector
dynamics from the T-BMT equation with the spin-tensor dynamics and other
dynamics. This unifying aspect of our approach relates the examples elegantly
and uncovers relations between the various underlying dynamical systems in a
transparent way.",1409.4373v2
2014-10-30,Nonadiabatic multichannel dynamics of a spin-orbit coupled condensate,"We investigate the nonadiabatic dynamics of a driven spin-orbit-coupled
Bose-Einstein condensate in both weak and strong driven force. It is shown that
the standard Landau-Zener (LZ) tunneling fails in the regime of weak driven
force and/or strong spin-orbital coupling, where the full nonadiabatic dynamics
requires a new mechanism through multichannel effects. Beyond the semiclassical
approach, our numerical and analytical results show an oscillating power-law
decay in the quantum limit, different from the exponential decay in the
semiclassical limit of the LZ effect. Furthermore, the condensate density
profile is found to be dynamically fragmented by the multichannel effects and
enhanced by interaction effects. Our work therefore provides a complete picture
to understand the nonadiabatic dynamics of a spin-orbit coupled condensate,
including various range of driven force and interaction effects through
multichannel interference. The experimental indication of these nonadiabatic
dynamics is also discussed.",1410.8444v2
2014-12-09,Glauber Dynamics of colorings on trees,"The mixing time of the Glauber dynamics for spin systems on trees is closely
related to reconstruction problem. Martinelli, Sinclair and Weitz established
this correspondence for a class of spin systems with soft constraints bounding
the log-Sobolev constant by a comparison with the block dynamics. However, when
there are hard constraints, the block dynamics may be reducible.
  We introduce a variant of the block dynamics extending these results to a
wide class of spin systems with hard constraints. This applies for essentially
any spin system that has non-reconstruction provided that on average the root
is not locally frozen in a large neighborhood. In particular we prove that the
mixing time of the Glauber dynamics for colorings on the regular tree is
$O(n\log n)$ in the entire known non-reconstruction regime.",1412.3156v1
2015-05-25,Dynamics of the two-dimensional directed Ising model: zero-temperature coarsening,"We investigate the laws of coarsening of a two-dimensional system of Ising
spins evolving under single-spin-flip irreversible dynamics at low temperature
from a disordered initial condition. The irreversibility of the dynamics comes
from the directedness, or asymmetry, of the influence of the neighbours on the
flipping spin. We show that the main characteristics of phase ordering at low
temperature, such as self-similarity of the patterns formed by the growing
domains, and the related scaling laws obeyed by the observables of interest,
which hold for reversible dynamics, are still present when the dynamics is
directed and irreversible, but with different scaling behaviour. In particular
the growth of domains, instead of being diffusive as is the case when dynamics
is reversible, becomes ballistic. Likewise, the autocorrelation function and
the persistence probability (the probability that a given spin keeps its sign
up to time $t$) have still power-law decays but with different exponents.",1505.06587v2
2013-08-03,Monte Carlo simulation of classical spin models with chaotic billiards,"It has recently been shown that the computing abilities of Boltzmann
machines, or Ising spin-glass models, can be implemented by chaotic billiard
dynamics without any use of random numbers. In this paper, we further
numerically investigate the capabilities of the chaotic billiard dynamics as a
deterministic alternative to random Monte Carlo methods by applying it to
classical spin models in statistical physics. First, we verify that the
billiard dynamics can yield samples that converge to the true distribution of
the Ising model on a small lattice, and we show that it appears to have the
same convergence rate as random Monte Carlo sampling. Second, we apply the
billiard dynamics to finite-size scaling analysis of the critical behavior of
the Ising model and show that the phase transition point and the critical
exponents are correctly obtained. Third, we extend the billiard dynamics to
spins that take more than two states and show that it can be applied
successfully to the Potts model. We also discuss the possibility of extensions
to continuous-valued models such as the XY model.",1308.0660v2
2017-01-27,Collective dynamics in atomistic models with coupled translational and spin degrees of freedom,"Using an atomistic model that simultaneously treats the dynamics of
translational and spin degrees of freedom, we perform combined molecular and
spin dynamics simulations to investigate the mutual influence of the phonons
and magnons on their respective frequency spectra and lifetimes in
ferromagnetic bcc iron. By calculating the Fourier transforms of the space- and
time-displaced correlation functions, the characteristic frequencies and the
linewidths of the vibrational and magnetic excitation modes were determined.
Comparison of the results with that of the stand-alone molecular dynamics and
spin dynamics simulations reveals that the dynamic interplay between the
phonons and magnons leads to a shift in the respective frequency spectra and a
decrease in the lifetimes. Moreover, in the presence of lattice vibrations,
additional longitudinal magnetic excitations were observed with the same
frequencies as the longitudinal phonons.",1701.07906v1
2019-06-24,Slow propagation in some disordered quantum spin chains,"We introduce the notion of transmission time to study the dynamics of
disordered quantum spin chains and prove results relating its behavior to
many-body localization properties. We also study two versions of the so-called
Local Integrals of Motion (LIOM) representation of spin chain Hamiltonians and
their relation to dynamical many-body localization. We prove that
uniform-in-time dynamical localization expressed by a zero-velocity
Lieb-Robinson bound implies the existence of a LIOM representation of the
dynamics as well as a weak converse of this statement. We also prove that for a
class of spin chains satisfying a form of exponential dynamical localization,
sparse perturbations result in a dynamics in which transmission times diverge
at least as a power law of distance, with a power for which we provide lower
bound that diverges with increasing sparseness of the perturbation.",1906.10167v3
2020-01-02,Three-dimensional dynamics of magnetic hopfion driven by spin transfer torque,"Magnetic hopfion is three-dimensional (3D) topological soliton with novel
spin structure that would enable exotic dynamics. Here we study the current
driven 3D dynamics of a magnetic hopfion with unit Hopf index in a frustrated
magnet. Attributed to spin Berry phase and symmetry of the hopfion, the phase
space entangles multiple collective coordinates, thus the hopfion exhibits rich
dynamics including longitudinal motion along the current direction, transverse
motion perpendicular to the current direction, rotational motion and dilation.
Furthermore, the characteristics of hopfion dynamics is determined by the ratio
between the non-adiabatic spin transfer torque parameter and the damping
parameter. Such peculiar 3D dynamics of magnetic hopfion could shed light on
understanding the universal physics of hopfions in different systems and boost
the prosperous development of 3D spintronics.",2001.00417v1
2018-12-07,Flat bands and dynamical localization of spin-orbit coupled Bose-Einstein condensates,"Flat bands and dynamical localization of binary mixtures of Bose-Einstein
condensates, with spin-orbit coupling subjected to a deep optical lattice which
is shaking in time and to a periodic time modulation of the Zeeman field, are
investigated. In contrast with usual dynamical localization in the absence of
spin-orbit coupling, we find that to fully suppress the tunneling in the system
the optical lattice shaking is not enough, and a proper tuning of the
spin-orbit term, achievable via the Zeeman field modulation, is also required.
This leads to a sequence of Zeeman parameter values where energy bands become
flat, the tunneling in the system is suppressed, and the dynamical localization
phenomenon occurs. Exact wave functions at the dynamical localization points
show that the binary mixture localizes on a dimer with the two components
occupying different sites. This type of localization occurs in exact form also
for the ground state of the system at the dynamical localization points in the
presence of nonlinearity and remains valid, although in approximate form, for a
wide range of the Zeeman parameter around these points. The possibility of
observing the above phenomena in real experiments is also briefly discussed.",1812.03164v1
2019-11-18,Universality for Langevin-like spin glass dynamics,"We study dynamics for asymmetric spin glass models, proposed by Hertz et al.
and Sompolinsky et al. in the 1980's in the context of neural networks:
particles evolve via a modified Langevin dynamics for the
Sherrington--Kirkpatrick model with soft spins, whereby the disorder is i.i.d.
standard Gaussian rather than symmetric. Ben Arous and Guionnet (1995),
followed by Guionnet (1997), proved for Gaussian interactions that as the
number of particles grows, the short-term empirical law of this dynamics
converges a.s. to a non-random law $\mu_\star$ of a ``self-consistent single
spin dynamics,'' as predicted by physicists. Here we obtain universality of
this fact:
  For asymmetric disorder given by i.i.d. variables of zero mean, unit variance
and exponential or better tail decay, at every temperature, the empirical law
of sample paths of the
  Langevin-like dynamics in a fixed time interval has the same a.s. limit
$\mu_\star$.",1911.08001v2
2020-09-07,Topological edge modes without symmetry in quasiperiodically driven spin chains,"We construct an example of a 1$d$ quasiperiodically driven spin chain whose
edge states can coherently store quantum information, protected by a
combination of localization, dynamics, and topology. Unlike analogous behavior
in static and periodically driven (Floquet) spin chains, this model does not
rely upon microscopic symmetry protection: Instead, the edge states are
protected purely by emergent dynamical symmetries. We explore the dynamical
signatures of this Emergent Dynamical Symmetry-Protected Topological (EDSPT)
order through exact numerics, time evolving block decimation, and analytic
high-frequency expansion, finding evidence that the EDSPT is a stable dynamical
phase protected by bulk many-body localization up to (at least)
stretched-exponentially long time scales, and possibly beyond. We argue that
EDSPTs are special to the quasiperiodically driven setting, and cannot arise in
Floquet systems. Moreover, we find evidence of a new type of boundary
criticality, in which the edge spin dynamics transition from quasiperiodic to
chaotic, leading to bulk thermalization.",2009.03314v1
2022-09-16,Is the relaxation dynamics of spatially disordered quantum spin systems universal?,"A major goal toward understanding far-from-equilibrium dynamics of quantum
many-body systems consists in finding indications of universality in the sense
that the dynamics no longer depends on microscopic details of the system. We
realize a large range of many-body spin systems on a Rydberg atom quantum
simulator by choosing appropriate Rydberg state combinations. We use this
platform to compare the magnetization relaxation dynamics of disordered
Heisenberg XX-, XXZ- and Ising Hamiltonians in a scalable fashion. After
appropriate rescaling of evolution time, all the dynamics collapse onto a
single curve, indicative of universal relaxation behavior. We find that this
dynamics is approximately captured by an integrable model that only considers
local pairs of spins. A detailed examination of the pair approximation not only
facilitates a comprehensive discussion of the experimental data within the
framework of prethermalization but also establishes in which sense the
relaxation in disordered spin systems can be regarded as universal.",2209.08080v3
2024-02-08,Absence of breakdown of ferrodark solitons exhibiting snake instability,"We investigate the dynamical stability and real time dynamics of the
two-types of ferrodark solitons (FDSs) which occur as topological magnetic
domain walls in the easy-plane phase of a quasi-two-dimensional (2D)
ferromagnetic spin-1 Bose-Einstein condensate. The type-I FDS has positive
inertial mass and exhibits a single dynamical instability that generates in
plane spin winding, causing polar-core spin vortex dipoles. The positive
inertial mass leads to the elastic oscillations of the soliton under transverse
perturbations. The type-II FDS has negative inertial mass and exhibits a snake
instability and a spin-twist instability, with the latter involving the
generation of out of plane spin winding. Distinct from the normal dynamics of
negative mass solitons under long wave length transverse perturbations, the
snake instability does not lead to the type-II FDS breaking down. Instead,
segments of the type-II FDS convert to type-I and mass vortex dipoles are
produced. The resulting hybridized-chain of the two soliton types and vortices
exhibits complex 2D soliton dynamics at long times while the vortices remain
confined and the topological structure of a magnetic domain wall is preserved.",2402.05351v1
2006-08-24,Equation-of-motion treatment of hyperfine interaction in a quantum dot,"Isolated electron spins in semiconductor nanostructures are promising qubit
candidates for a solid state quantum computer, There have seen truly impressive
experimental progresses in the study of single spins in the past two years. In
this paper we analytically solve the {\it Non-Markovian} single electron spin
dynamics due to inhomogeneous hyperfine couplings with surrounding nuclei in a
quantum dot. We use the equation-of-motion method assisted with a large field
expansion in a full quantum mechanical treatment. We recover the exact solution
for fully polarized nuclei. By considering virtual nuclear spin flip-flops
mediated by the electron, which generate fluctuations in the Overhauser field
(the nuclear field) for the electron spin, we find that the decay amplitude of
the transverse electron spin correlation function for partially polarized
nuclear spin configurations is of the order unity instead of $\text{O}(1/N)$
($N$ being the number of nuclei in the dot) obtained in previous studies. We
show that the complete amplitude decay can be understood with the spectrum
broadening of the correlation function near the electron spin Rabi frequency
induced by nuclear spin flip-flops. Our results show that a 90% nuclear
polarization can enhance the electron spin $T_2$ time by more than one order of
magnitude in some parameter regime. In the long time limit, the envelope of the
transverse electron spin correlation function has a non-exponential $1/t^2$
decay in the presence of both polarized and unpolarized nuclei.",0608544v1
2013-03-18,"Hanle effect in (In,Ga)As quantum dots: Role of nuclear spin fluctuations","The role of nuclear spin fluctuations in the dynamic polarization of nuclear
spins by electrons is investigated in (In,Ga)As quantum dots. The
photoluminescence polarization under circularly polarized optical pumping in
transverse magnetic fields (Hanle effect) is studied. A weak additional
magnetic field parallel to the optical axis is used to control the efficiency
of nuclear spin cooling and the sign of nuclear spin temperature. The shape of
the Hanle curve is drastically modified with changing this control field, as
observed earlier in bulk semiconductors and quantum wells. However, the
standard nuclear spin cooling theory, operating with the mean nuclear magnetic
field (Overhauser field), fails to describe the experimental Hanle curves in a
certain range of control fields. This controversy is resolved by taking into
account the nuclear spin fluctuations owed to the finite number of nuclei in
the quantum dot. We propose a model describing cooling of the nuclear spin
system by electron spins experiencing fast vector precession in the random
Overhauser fields of nuclear spin fluctuations. The model allows us to
accurately describe the measured Hanle curves and to determine the parameters
of the electron-nuclear spin system of the studied quantum dots.",1303.4192v1
2013-06-20,"Magnetic orders, excitations, and phase transitions in Fe_1+yTe","We study the magnetic properties of Fe_1+y Te, a parent compound of the
iron-based high-temperature superconductors. Motivated by recent neutron
scattering experiments, we show that a spin-1 exchange model, supplemented by a
single-ion spin anisotropy, accounts well for the experimentally observed low
temperature magnetic phase diagram, that exhibits a commensurate bicollinear
order at low Fe dopings (y < 0.12) and an incommensurate spin-spiral order at
high Fe dopings (y > 0.12). We suggest that the commensurate-incommensurate
transition at y = 0.12 is due to the competition between the exchange
interaction and the local spin anisotropy. At low Fe dopings, the single-ion
spin anisotropy is strong and pins the spins along the easy axis, which,
together with the spatially anisotropic exchanges, induces a unusual
bicollinear commensurate magnetic order. The low-energy spin-wave excitation is
gapped due to the explict breaking of spin-rotational symmetry by the local
spin anisotropy. At high Fe dopings, the single-ion anisotropy is weak, and the
exchange favors an incommensurate coplanar state. The incommensurate magnetic
wavevector averages out the spin anisotropy so that a gapless low-energy
spin-wave excitation is obtained. We also analyze the low-energy hydrodynamic
model and use it to describe the magneto-structural transition and the static
and dynamical spin structure factors across the magnetic ordering transitions.",1306.4730v2
2014-07-08,An improved semiclassical theory of radical pair recombination reactions,"We present a practical semiclassical method for computing the electron spin
dynamics of a radical in which the electron spin is hyperfine coupled to a
large number of nuclear spins. This can be used to calculate the singlet and
triplet survival probabilities and quantum yields of radical recombination
reactions in the presence of magnetic fields. Our method differs from the early
semiclassical theory of Schulten and Wolynes [J. Chem. Phys. 68, 3292 (1978)]
in allowing each individual nuclear spin to precess around the electron spin,
rather than assuming that the hyperfine coupling-weighted sum of nuclear spin
vectors is fixed in space. The downside of removing this assumption is that one
can no longer obtain a simple closed-form expression for the electron spin
correlation tensor: our method requires a numerical calculation. However, the
computational effort increases only linearly with the number of nuclear spins,
rather than exponentially as in an exact quantum mechanical calculation. The
method is therefore applicable to arbitrarily large radicals. Moreover, it
approaches quantitative agreement with quantum mechanics as the number of
nuclear spins increases and the environment of the electron spin becomes more
complex, owing to the rapid quantum decoherence in complex systems. Unlike the
Schulten-Wolynes theory, the present semiclassical theory predicts the correct
long-time behaviour of the electron spin correlation tensor, and it therefore
correctly captures the low magnetic field effect in the singlet yield of a
radical recombination reaction with a slow recombination rate.",1407.2139v1
2015-08-31,Spin Response to Localized Pumps: Exciton Polaritons Versus Electrons and Holes,"Polariton polarization can be described in terms of a pseudospin which can be
oriented along the $x,\,y,$ or $z$ axis, similarly to electron and hole spin.
Unlike electrons and holes where time-reversal symmetry requires that the
spin-orbit interaction be odd in the momentum, the analogue of the spin-orbit
interaction for polaritons, the so-called TE-TM splitting, is even in the
momentum. We calculate and compare spin transport of polariton, electron, and
hole systems, in the diffusive regime of many scatterings. After dimensional
rescaling diffusive systems with spatially uniform particle densities have
identical dynamics, regardless of the particle type. Differences between the
three particles appear in spatially non-uniform systems, with pumps at a
specific localized point. We consider both oscillating pumps and transient
(delta-function) pumps. In such systems each particle type produces distinctive
spin patterns. The particles can be distinguished by their differing spatial
multipole character, their response and resonances in a perpendicular magnetic
field, and their relative magnitude which is largest for electrons and weakest
for holes. These patterns are manifested both in response to unpolarized pumps
which produce in-plane and perpendicular spin signals, and to polarized pumps
where the spin precesses from in-plane to out-of-plane and vice versa. These
results will be useful for designing systems with large spin polarization
signals, for identifying the dominant spin-orbit interaction and measuring
subdominant terms in experimental devices, and for measuring the scattering
time and the spin-orbit coupling's magnitude.",1508.07863v2
2016-09-22,Magnetization oscillations and waves driven by pure spin currents,"Recent advances in the studies of pure spin currents - flows of angular
momentum (spin) not accompanied by the electric currents - have opened new
horizons for the emerging technologies based on the electron's spin degree of
freedom, such as spintronics and magnonics. The main advantage of pure spin
current, as compared to the spin-polarized electric current, is the possibility
to exert spin transfer torque on the magnetization in thin magnetic films
without electrical current flow through the material. In addition to minimizing
Joule heating and electromigration effects, this characteristic enables the
implementation of spin torque devices based on the low-loss insulating magnetic
materials, and offers an unprecedented geometric flexibility. Here we review
the recent experimental achievements in investigations of magnetization
oscillations excited by pure spin currents in different magnetic nanosystems
based on metallic and insulating magnetic materials. We discuss the spectral
properties of spin-current nano-oscillators, and relate them to the spatial
characteristics of the excited dynamic magnetic modes determined by the
spatially-resolved measurements. We also show that these systems support
locking of the oscillations to external microwave signals, as well as their
mutual synchronization, and can be used as efficient nanoscale sources of
propagating spin waves.",1609.06899v1
2018-02-06,Magnetic oscillations Excited by Concurrent Spin Injection from a Tunneling Current and a Spin Hall Current,"In this paper, a 3-terminal spin-transfer torque nano-oscillator (STNO) is
studied using the concurrent spin injection of a spin-polarized tunneling
current and a spin Hall current exciting the free layer into dynamic regimes
beyond what is achieved by each individual mechanism. The pure spin injection
is capable of inducing oscillations in the absence of charge currents
effectively reducing the critical tunneling current to zero. This reduction of
the critical charge currents can improve the endurance of both STNOs and
non-volatile magnetic memories (MRAM) devices. It is shown that the system
response can be described in terms of an injected spin current density $J_s$
which results from the contribution of both spin injection mechanisms, with the
tunneling current polarization $p$ and the spin Hall angle $\theta$ acting as
key parameters determining the efficiency of each injection mechanism. The
experimental data exhibits an excellent agreement with this model which can be
used to quantitatively predict the critical points ($J_s = -2.26\pm 0.09 \times
10^9 \hbar/e$ A/m$^2$) and the oscillation amplitude as a function of the input
currents. In addition, the fitting of the data also allows an independent
confirmation of the values estimated for the spin Hall angle and tunneling
current polarization as well as the extraction of the damping $\alpha = 0.01$
and non-linear damping $Q = 3.8\pm 0.3$ parameters.",1802.02224v1
2018-11-02,Spinning superconductors and ferromagnets,"When a magnetic field is applied to a ferromagnetic body it starts to spin
(Einstein-de Haas effect). This demonstrates the intimate connection between
the electron's magnetic moment $\mu_B=e\hbar/2m_ec$, associated with its spin
angular momentum $S=\hbar/2$, and ferromagnetism. When a magnetic field is
applied to a superconducting body it also starts to spin (gyromagnetic effect),
and when a normal metal in a magnetic field becomes superconducting and expels
the magnetic field (Meissner effect) the body also starts to spin. Yet
according to the conventional theory of superconductivity the electron's spin
only role is to label states, and the electron's magnetic moment plays no role
in superconductivity. Instead, within the unconventional theory of hole
superconductivity, the electron's spin and associated magnetic moment play a
fundamental role in superconductivity. Just like in ferromagnets the
magnetization of superconductors is predicted to result from an aggregation of
magnetic moments with angular momenta $\hbar/2$. This gives rise to a ""Spin
Meissner effect"", the existence of a spin current in the ground state of
superconductors. The theory explains how a superconducting body starts spinning
when it expels magnetic fields, it provides a dynamical explanation for the
Meissner effect, and it explains how supercurrents stop without dissipation,
all of which we argue the conventional theory fails to explain. Essential
elements of the theory of hole superconductivity are that superconductivity is
driven by lowering of kinetic energy, which we have also proposed is true for
ferromagnets], that the normal state charge carriers in superconducting
materials are holes, and that the spin-orbit interaction plays a key role in
superconductivity. The theory is proposed to apply to all superconductors.",1811.03938v1
2010-05-17,Long coherence of electron spins coupled to a nuclear spin bath,"Qubits, the quantum mechanical bits required for quantum computing, must
retain their fragile quantum states over long periods of time. In many types of
electron spin qubits, the primary source of decoherence is the interaction
between the electron spins and nuclear spins of the host lattice. For electrons
in gate defined GaAs quantum dots, previous spin echo measurements have
revealed coherence times of about 1 $\mu$s at low magnetic fields below 100 mT.
Here, we show that coherence in such devices can actually survive to much
longer times, and provide a detailed understanding of the measured nuclear spin
induced decoherence. At fields above a few hundred millitesla, the coherence
time measured using a single-pulse spin echo extends to 30 $\mu$s. At lower
magnetic fields, the echo first collapses, but then revives at later times
given by the period of the relative Larmor precession of different nuclear
species. This behavior was recently predicted, and as we show can be
quantitatively accounted for by a semi-classical model for the electron spin
dynamics in the presence of a nuclear spin bath. Using a multiple-pulse
Carr-Purcell-Meiboom-Gill echo sequence, the decoherence time can be extended
to more than 200 $\mu$s, which represents an improvement by two orders of
magnitude compared to previous measurements. This demonstration of effective
methods to mitigate nuclear spin induced decoherence puts the quantum error
correction threshold within reach.",1005.2995v1
2017-07-11,Tilting Styx and Nix but not Uranus with a Spin-Precession-Mean-motion resonance,"A Hamiltonian model is constructed for the spin axis of a planet perturbed by
a nearby planet with both planets in orbit about star. We expand the
planet-planet gravitational potential perturbation to first order in orbital
inclinations and eccentricities, finding terms describing spin resonances
involving the spin precession rate and the two planetary mean motions.
Convergent planetary migration allows the spinning planet to be captured into
spin resonance. With initial obliquity near zero, the spin resonance can lift
the planet's obliquity to near 90 or 180 degrees depending upon whether the
spin resonance is first or zero-th order in inclination. Past capture of Uranus
into such a spin resonance could give an alternative non-collisional scenario
accounting for Uranus's high obliquity. However we find that the time spent in
spin resonance must be so long that this scenario cannot be responsible for
Uranus's high obliquity. Our model can be used to study spin resonance in
satellite systems. Our Hamiltonian model explains how Styx and Nix can be
tilted to high obliquity via outward migration of Charon, a phenomenon
previously seen in numerical simulations.",1707.03180v2
2020-08-21,Correlation of interface transmission in THz spintronic emitters with spin mixing conductance in spin pumping experiments,"The field of THz spintronics is a novel direction in the research field of
spintronics that combines magnetism with optical physics and ultrafast
photonics. The experimental scheme of the field involves the use of femtosecond
laser pulses to trigger ultrafast spin and charge dynamics in bilayers composed
of ferromagnetic (FM) and non-magnetic (NM) thin films where the NM layer
features a strong spin-orbit coupling. The key technological and scientific
challenges of THz spintronic emitters is to increase their intensity and
frequency bandwidth. To achieve this the control of the source of the
radiation, namely the transport of the ultrafast spin current is required.
However, the transfer of a spin current from a FM to a NM layer is a highly
interface-sensitive effect. In this work we study the properties of the spin
current transport through the interface measuring the strength of the THz
emission and compare it to the effective spin mixing conductance, one of the
key concepts in the spin current transport through interfaces. The results show
an enhancement of the spin mixing conductance for interfaces with higher degree
of epitaxy similarly to the improvement of the THz emission. The
proportionality between spin mixing conductance and THz emission can define new
directions in engineering the emission of spintronic THz emitters.",2008.09537v1
2021-11-21,Flying electron spin control gates,"The control of ""flying"" (or moving) spin qubits is an important functionality
for the manipulation and exchange of quantum information between remote
locations on a chip. Typically, gates based on electric or magnetic fields
provide the necessary perturbation for their control either globally or at
well-defined locations. Here, we demonstrate the dynamic control of moving
electron spins via contactless gates that move together with the spin. The
concept is realized using electron spins trapped and transported by moving
potential dots defined by a surface acoustic wave (SAW). The SAW strain at the
electron trapping site, which is set by the SAW amplitude, acts as a
contactless, tunable gate that controls the precession frequency of the flying
spins via the spin-orbit interaction. We show that the degree of precession
control in moving dots exceeds previously reported results for unconstrained
transport by an order of magnitude and is well accounted for by a theoretical
model for the strain contribution to the spin-orbit interaction. This flying
spin gate permits the realization of an acoustically driven optical
polarization modulator based on electron spin transport, a key element for
on-chip spin information processing with a photonic interface.",2111.10808v1
1998-08-04,Spin-only approach to quantum magnetism in the ordered stripe state,"It has been argued that the spin-dynamics in cuprate superconductors is
governed by the proximity to a zero-temperature critical point. This critical
point would be related to a transition from the superconducting phase to an
ordered stripe state. Using a coupled spin-ladder model, we investigate to what
extent the strong quantum spin-fluctuations in the ordered stripe state can be
attributed to the spin sector. For the bond-centered stripes, we find that our
spin-only model can account for the observed spin-fluctuations. For
site-ordered stripes, coupling of the spin and charge sector is needed.",9808034v1
1998-09-11,Spin-glass model with partially annealed asymmetric bonds,"We have considered the two-spin interaction spherical spin-glass model with
asymmetric bonds (coupling constants). Besides the usual interactions between
spins and bonds and between the spins and a thermostat with temperature
$T_{\sigma}$ there is also an additional factor: the bonds are not assumed
random {\it a priori} but interact with some other thermostat at the
temperature $T_{J}$. We show that when the bonds are frozen with respect to the
spins a first order phase transition to a spin-glass phase occurs, and the
temperature of this transition tends to zero if $T_J$ is large. Our analytical
results show that a spin-glass phase can exist in mean-field models with
nonrelaxational dynamics.",9809170v1
1999-09-06,Excitation Spectra of Structurally Dimerized and Spin-Peierls Chains in a Magnetic Field,"The dynamical spin structure factor and the Raman response are calculated for
structurally dimerized and spin-Peierls chains in a magnetic field, using exact
diagonalization techniques. In both cases there is a spin liquid phase composed
of interacting singlet dimers at small fields h < h_c1, an incommensurate
regime (h_c1 < h < h_c2) in which the modulation of the triplet excitation
spectra adapts to the applied field, and a fully spin polarized phase above an
upper critical field h_c2. For structurally dimerized chains, the spin gap
closes in the incommensurate phase, whereas spin-Peierls chains remain gapped.
In the spin liquid regimes, the dominant feature of the triplet spectra is a
one-magnon bound state, separated from a continuum of states at higher
energies. There are also indications of a singlet bound state above the
one-magnon triplet.",9909093v1
2000-11-03,Coupled dynamics of fast spins and slow exchange interactions in the XY spin-glass,"We investigate an XY spin-glass model in which both spins and interactions
(or couplings) evolve in time, but with widely separated time-scales. For large
times this model can be solved using replica theory, requiring two levels of
replicas, one level for the spins and one for the couplings. We define the
relevant order parameters, and derive a phase diagram in the replica-symmetric
approximation, which exhibits two distinct spin-glass phases. The first phase
is characterized by freezing of the spins only, whereas in the second phase
both spins and couplings are frozen. A detailed stability analysis leads also
to two distinct corresponding de Almeida-Thouless lines, each marking
continuous replica-symmetry breaking. Numerical simulations support our
theoretical study.",0011065v1
2001-02-13,Isotopically engineered silicon/silicon-germanium nanostructures as basic elements for a nuclear spin quantum computer,"The idea of quantum computation is the most promising recent developments in
the high-tech domain, while experimental realization of a quantum computer
poses a formidable challenge. Among the proposed models especially attractive
are semiconductor based nuclear spin quantum computer's (S-NSQC), where nuclear
spins are used as quantum bistable elements, ''qubits'', coupled to the
electron spin and orbital dynamics. We propose here a scheme for implementation
of basic elements for S-NSQC's which are realizable within achievements of the
modern nanotechnology. These elements are expected to be based on a
nuclear-spin-controlled isotopically engineered Si/SiGe heterojunction, because
in these semiconductors one can vary the abundance of nuclear spins by
engineering the isotopic composition. A specific device is suggested, which
allows one to model the processes of recording, reading and information
transfer on a quantum level using the technique of electrical detection of the
magnetic state of nuclear spins. Improvement of this technique for a
semiconductor system with a relatively small number of nuclei might be applied
to the manipulation of nuclear spin ''qubits'' in the future S-NSQC.",0102228v1
2002-12-19,Non-ideality of quantum operations with the electron spin of a 31P donor in a Si crystal due to interaction with a nuclear spin system,"We examine a 31P donor electron spin in a Si crystal to be used for the
purposes of quantum computation. The interaction with an uncontrolled system of
29Si nuclear spins influences the electron spin dynamics appreciably. The
hyperfine field at the 29Si nuclei positions is non-collinear with the external
magnetic field. Quantum operations with the electron wave function, i.e. using
magnetic field pulses or electrical gates, change the orientation of hyperfine
field and disturb the nuclear spin system. This disturbance produces a
deviation of the electron spin qubit from an ideal state, at a short time scale
in comparison with the nuclear spin diffusion time. For H_ext=9 T, the
estimated error rate is comparable to the threshold value required by the
quantum error correction algorithms. The rate is lower at higher external
magnetic fields.",0212501v2
2003-04-24,Ferromagnetism in a dilute magnetic semiconductor -- Generalized RKKY interaction and spin-wave excitations,"Carrier-mediated ferromagnetism in a dilute magnetic semiconductor has been
studied using i) a single-impurity based generalized RKKY approach which goes
beyond linear response theory, and ii) a mean-field-plus-spin-fluctuation
(MF+SF) approach within a (purely fermionic) Hubbard-model representation of
the magnetic impurities, which incorporates dynamical effects associated with
finite frequency spin correlations in the ordered state. Due to a competition
between the magnitude of the carrier spin polarization and its oscillation
length scale, the ferromagnetic spin coupling is found to be optimized with
respect to both hole doping concentration and impurity-carrier spin coupling
energy $J$ (or equivalently $U$). The ferromagnetic transition temperature
$T_c$, deteremined within the spin-fluctuation theory, corresponds closely with
the observed $T_c$ values. Positional disorder of magnetic impurities causes
significant stiffening of the high-energy magnon modes. We also explicitly
study the stability/instability of the mean-field ferromagnetic state, which
highlights the role of competing AF interactions causing spin twisting and
noncollinear ferromagnetic ordering.",0304557v2
2004-04-16,Slowing down of spin relaxation in two dimensional systems by quantum interference effects,"The effect of weak localization on spin relaxation in a two-dimensional
system with a spin-split spectrum is considered. It is shown that the spin
relaxation slows down due to the interference of electron waves moving along
closed paths in opposite directions. As a result, the averaged electron spin
decays at large times as $1/t$. It is found that the spin dynamics can be
described by a Boltzmann-type equation, in which the weak localization effects
are taken into account as nonlocal-in-time corrections to the collision
integral. The corrections are expressed via a spin-dependent return
probability. The physical nature of the phenomenon is discussed and it is shown
that the ""nonbackscattering"" contribution to the weak localization plays an
essential role. It is also demonstrated that the magnetic field, both
transversal and longitudinal, suppresses the power tail in the spin
polarization.",0404391v2
2004-06-03,Qubit coherence control in a nuclear spin bath,"Coherent dynamics of localized spins in semiconductors is limited by spectral
diffusion arising from dipolar fluctuation of lattice nuclear spins. Here we
extend the semiclassical theory of spectral diffusion for nuclear spins I=1/2
to the high nuclear spins relevant to the III-V materials and show that
applying successive qubit pi-rotations at a rate approximately proportional to
the nuclear spin quantum number squared (I^2) provides an efficient method for
coherence enhancement. Hence robust coherent manipulation in the large spin
environments characteristic of the III-V compounds is possible without
resorting to nuclear spin polarization, provided that the pi-pulses can be
generated at intervals scaling as I^{-2}.",0406090v3
2004-09-13,DC Spin Current Generation in a Rashba-type Quantum Channel,"We propose and demonstrate theoretically that resonant inelastic scattering
(RIS) can play an important role in dc spin current generation. The RIS makes
it possible to generate dc spin current via a simple gate configuration: a
single finger-gate that locates atop and orients transversely to a quantum
channel in the presence of Rashba spin-orbit interaction. The ac biased
finger-gate gives rise to a time-variation in the Rashba coupling parameter,
which causes spin-resolved RIS, and subsequently contributes to the dc spin
current. The spin current depends on both the static and the dynamic parts in
the Rashba coupling parameter, $\alpha_0$ and $\alpha_1$, respectively, and is
proportional to $\alpha_0 \alpha_1^2$. The proposed gate configuration has the
added advantage that no dc charge current is generated. Our study also shows
that the spin current generation can be enhanced significantly in a double
finger-gate configuration.",0409291v3
2004-12-08,Generation of spin current and polarization under dynamic gate control of spin-orbit interaction in low-dimensional semiconductor systems,"Based on the Keldysh formalism, the Boltzmann kinetic equation and the drift
diffusion equation have been derived for studying spin polarization flow and
spin accumulation under effect of the time dependent Rashba spin-orbit
interaction in a semiconductor quantum well. The time dependent Rashba
interaction is provided by time dependent electric gates of appropriate shapes.
Several examples of spin manipulation by gates have been considered. Mechanisms
and conditions for obtaining the stationary spin density and the induced
rectified DC spin current are studied.",0412181v3
2004-12-21,Theory of spin-polarized transport in semiconductor heterojunctions: Proposal for spin injection and detection in silicon,"Spin injection and detection in silicon is a difficult problem, in part
because the weak spin-orbit coupling and indirect gap preclude using standard
optical techniques. We propose two ways to overcome this difficulty, and
illustrate their operation by developing a model for spin-polarized transport
across a heterojunction. We find that equilibrium spin polarization of holes
leads to a strong modification of the spin and charge dynamics of electrons,
and we show how the symmetry properties of the charge current can be exploited
to detect spin injection in silicon using currently available techniques.",0412580v2
2005-02-24,Non-exponential spin relaxation in magnetic field in quantum wells with random spin-orbit coupling,"We investigate the spin dynamics of electrons in quantum wells where the
Rashba type of spin-orbit coupling is present in the form of random nanosize
domains. We study the effect of magnetic field on the spin relaxation in these
systems and show that the spatial randomness of spin-orbit coupling limits the
minimum relaxation rate and leads to a Gaussian time-decay of spin polarization
due to memory effects. In this case the relaxation becomes faster with increase
of the magnetic field in contrast to the well known magnetic field suppression
of spin relaxation.",0502593v3
2005-11-11,"Spin amplification, reading, and writing in transport through anisotropic magnetic molecules","Inelastic transport through a single magnetic molecule weakly coupled to
metallic leads is studied theoretically. We consider dynamical processes that
are relevant for writing, storing, and reading spin information in molecular
memory devices. Magnetic anisotropy is found to be crucial for slow spin
relaxation. In the presence of anisotropy we find giant spin amplification: The
spin accumulated in the leads if a bias voltage is applied to a molecule
prepared in a spin-polarized state can be made exponentially large in a
characteristic energy divided by temperature. For one ferromagnetic and one
paramagnetic lead the molecular spin can be reversed by applying a bias voltage
even in the absence of a magnetic field. We propose schemes for reading and
writing spin information based on our findings.",0511291v2
2005-12-14,Spin and charge excitations in the anisotropic Hubbard ladder at quarter filling with charge-ordering instability,"Quantum Monte Carlo and density-matrix renormalization group methods are used
to study the coupled spin-pseudospin Hamiltonian in one-dimension (1D) that
models the charge-ordering instability of the anisotropic Hubbard ladder at
quarter filling. We calculate the temperature dependence of the uniform spin
susceptibility and specific heat as well as the spin and charge excitation
spectra of the system. We thereby show that there is a parameter and
temperature region where the spin degrees of freedom are separated from the
charge degrees of freedom and behave like a 1D antiferromagnetic Heisenberg
model, and that, outside this parameter region and above a crossover
temperature, the spin excitations are largely affected by the charge
fluctuations. We argue that observed anomalous spin dynamics in the disorder
phase of a typical charge-ordered material $\alpha'$-NaV$_2$O$_5$ may possibly
be a consequence of this type of spin-charge coupling.",0512310v1
2006-05-30,Electric Dipole Induced Spin Resonance in Disordered Semiconductors,"One of the hallmarks of spintronics is the control of magnetic moments by
electric fields enabled by strong spin-orbit interaction (SOI) in
semiconductors. A powerful way of manipulating spins in such structures is
electric dipole induced spin resonance (EDSR), where the radio-frequency fields
driving the spins are electric, and not magnetic like in standard paramagnetic
resonance. Here, we present a theoretical study of EDSR for a two-dimensional
electron gas in the presence of disorder where random impurities not only
determine the electric resistance but also the spin dynamics via SOI.
Considering a specific geometry with the electric and magnetic fields parallel
and in-plane, we show that the magnetization develops an out-of-plane component
at resonance which survives the presence of disorder. We also discuss the spin
Hall current generated by EDSR. These results are derived in a diagrammatic
approach with the dominant effects coming from the spin vertex correction, and
the optimal parameter regime for observation is identified.",0605735v1
2006-07-15,Degradation of electron-hole entanglement by spin-orbit coupling,"Electron-hole pairs produced by tunneling in a degenerate electron gas lose
their spin entanglement by spin-orbit coupling, which transforms the fully
entangled Bell state into a partially entangled mixed density matrix of the
electron and hole spins. We calculate the dependence of the entanglement
(quantified by the concurrence) on the spin-orbit coupling time tau_so and on
the diffusion time (or dwell time) tau_dwell of electron and hole in the
conductors (with conductances >> e^2/h) at the two sides of the tunnel barrier
(with conductance << e^2/h). The entanglement disappears when the ratio
tau_dwell/tau_so exceeds a critical value of order unity. The results depend on
the type of conductor (disordered wire or chaotic quantum dot), but they are
independent of other microscopic parameters (number of channels, level
spacing). Our analytical treatment relies on an ""isotropy approximation"" (no
preferential basis in spin space), which allows us to express the concurrence
entirely in terms of spin correlators. We test this approximation for the case
of chaotic dynamics with a computer simulation (using the spin kicked rotator)
and find good agreement.",0607395v2
1998-08-24,Spin effects in gravitational radiation backreaction III. Compact binaries with two spinning components,"The secular evolution of a spinning, massive binary system in eccentric orbit
is analyzed, expanding and generalizing our previous treatments of the
Lense-Thirring motion and the one-spin limit. The spin-orbit and spin-spin
effects up to the 3/2 post-Newtonian order are considered, both in the
equations of motion and in the radiative losses. The description of the orbit
in terms of the true anomaly parametrization provides a simple averaging
technique, based on the residue theorem, over eccentric orbits. The evolution
equations of the angle variables characterizing the relative orientation of the
spin and orbital angular momenta reveal a speed-up effect due to the
eccentricity. The dissipative evolutions of the relevant dynamical and angular
variables is presented in the form of a closed system of differential
equations.",9808063v1
1999-11-22,Spin-spin effects in radiating compact binaries,"The dynamics of a binary system with two spinning components on an eccentric
orbit is studied, with the inclusion of the spin-spin interaction terms
appearing at the second post-Newtonian order. A generalized true anomaly
parametrization properly describes the radial component of the motion. The
average over one radial period of the magnitude of the orbital angular momentum
$\bar{L}$ is found to have no nonradiative secular change. All spin-spin terms
in the secular radiative loss of the energy and magnitude of orbital angular
momentum are given in terms of $\bar{L}$ and other constants of the motion.
Among them, self-interaction spin effects are found, representing the second
post-Newtonian correction to the 3/2 post-Newtonian order Lense-Thirring
approximation.",9911082v1
2004-04-22,Spin Hall effect and Berry phase of spinning particles,"We consider the adiabatic evolution of the Dirac equation in order to compute
its Berry curvature in momentum space. It is found that the position operator
acquires an anomalous contribution due to the non Abelian Berry gauge
connection making the quantum mechanic algebra noncommutative. A generalization
to any known spinning particles is possible by using the Bargmann-Wigner
equation of motions. The noncommutativity of the coordinates is responsible of
the topological spin transport of spinning particle similarly to the spin Hall
effect in spintronic physics or the Magnus effect in optics. As an application
we predict new dynamics for nonrelativistic particles in an electric field and
for photons in a gravitational field.",0404165v5
2002-07-09,Suppression of decoherence via strong intra-environmental coupling,"We examine the effects of intra-environmental coupling on decoherence by
constructing a low temperature spin--spin-bath model of an atomic impurity in a
Debye crystal. The impurity interacts with phonons of the crystal through
anti-ferromagnetic spin-spin interactions. The reduced density matrix of the
central spin representing the impurity is calculated by dynamically integrating
the full Schroedinger equation for the spin--spin-bath model for different
thermally weighted eigenstates of the spin-bath. Exact numerical results show
that increasing the intra-environmental coupling results in suppression of
decoherence. This effect could play an important role in the construction of
solid state quantum devices such as quantum computers.",0207051v1
2004-10-01,Modeling and Simulations of a Single-Spin Measurement using MRFM,"We review the quantum theory of a single spin magnetic resonance force
microscopy (MRFM). We concentrate on the novel technique called oscillating
cantilever-driven adiabatic reversals (OSCAR), which has been used for a single
spin detection (Dan Rugar, Talk on the 2004 IEEE NTC Quantum Device Technology
Workshop). First we describe the quantum dynamics of the cantilever-spin system
using simple estimates in the spirit of the mean field approximation. Then we
present the results of our computer simulations of the Schrodinger equation for
the wave function of the cantilever-spin system and of the master equation for
the density matrix of the system. We demonstrate that the cantilever behaves
like a quasi-classical measurement device which detects the spin projection
along the effective magnetic field. We show that the OSCAR technique provides
continuous monitoring of the single spin, which could be used to detect the
mysterious quantum collapses of the wave function of the cantilever-spin
system.",0410002v1
2005-02-28,Control of Local Relaxation Behavior in Closed Bipartite Quantum Systems,"We investigate the decoherence of a spin 1/2 subsystem weakly coupled to an
environment of many spins 1/2 with and without mutual coupling. The total
system is closed, its state is pure and evolves under Schroedinger dynamics.
Nevertheless, the considered spin typically reaches a quasi-stationary
equilibrium state. Here we show that this state depends strongly on the
coupling to the environment on the one hand and on the coupling within the
environmental spins on the other. In particular we focus on spin star and spin
ring-star geometries to investigate the effect of intra-environmental coupling
on the central spin. By changing the spectrum of the environment its effect as
a bath on the central spin is changed also and may even be adjustable to some
degree. We find that the relaxation behavior is related to the distribution of
the energy eigenstates of the total system. For each of these relaxation modes
there is a dual mode for which the resulting subsystem approaches an inverted
state occupation probability (negative temperature).",0502181v2
2007-02-05,Decoherence of two-electron spin states in quantum dots,"The time evolution of spin states of two electrons interacting with a nuclear
spin bath in a quantum dot system is studied. The hyperfine interaction between
the electrons and the nuclear spins is modeled by an isotropic Heisenberg
interaction, and the interaction between the electron spins by Heisenberg
exchange. Depending on the extent of the overlap between the spatial wave
functions of the electrons, there are two physically different cases, namely
the two qubits either interact with the same set of nuclear spins or they see
different nuclear spin environment. In the two cases, the decoherence of the
two-qubit state is studied analytically. We have identified a class of
two-qubit states which have a rich dynamics when the exchange interaction
between the qubits becomes large in comparison to the hyperfine interaction
strengths. The decoherence time scale is determined as a function of the
bath-spin distribution and the polarizations of the initial two-qubit state.
States with large decoherence times are identified by performing a minimization
over all the two-qubit pure states.",0702035v1
2007-06-28,Simple Two-Dimensional Model for the Elastic Origin of Cooperativity among Spin States of Spin-Crossover Complexes,"We study the origin of the cooperative nature of spin crossover (SC) between
low spin (LS) and high spin (HS) states from the view point of elastic
interactions among molecules. As the size of each molecule changes depending on
its spin state, the elastic interaction among the lattice distortions provides
the cooperative interaction of the spin states. We develop a simple model of SC
with intra and intermolecular potentials which accounts for the elastic
interaction including the effect of the inhomogeneity of the spin states, and
apply constant temperature molecular dynamics based on the Nos\'e-Hoover
formalism. We demonstrate that, with increase of the strength of the
intermolecular interactions, the temperature dependence of the HS component
changes from a gradual crossover to a first-order transition.",0706.4135v1
2007-07-31,Coherent spin rotations in open driven double quantum dots,"We analyze the charge and spin dynamics in a DC biased double quantum dot
driven by crossed DC and AC magnetic fields. In this configuration, spatial
delocalization due to inter-dot tunnel competes with intra-dot spin rotations
induced by the time dependent magnetic field, giving rise to a complicated time
dependent behavior of the tunnelling current. When the Zeeman splitting has the
same value in both dots and spin flip is negligible, the electrons remain in
the triplet subspace (dark subspace) performing coherent spin rotations and the
current does not flow. This electronic trapping is removed either by finite
spin relaxation or when the Zeeman splitting is different in each quantum dot.
In the first case, our results show that measuring the current will allow to
get information on the spin relaxation time. In the last case, we will show
that applying a resonant bichromatic magnetic field, the electrons become
trapped in a coherent superposition of states and electronic transport is
blocked. Then, manipulating AC magnetic fields, electrons are driven to perform
coherent spin rotations which can be unambiguously detected by direct
measurement of the tunneling current.",0707.4636v2
2007-08-13,Current-induced non-adiabatic spin torques and domain wall motion with spin relaxation in a ferromagnetic metallic wire,"Within the s-d model description, we derive the current-driven spin torque in
a ferromagnet, taking explicitly into account a spin-relaxing Caldeira-Leggett
bath coupling to the s-electrons. We derive Bloch-Redfield equations of motion
for the s-electron spin dynamics, and formulate a systematic gradient expansion
to obtain non-adiabatic (higher-order) corrections to the well-known adiabatic
(first-order) spin torque. We provide simple analytical expressions for the
second-order spin torque. The theory is applied to current-driven domain wall
motion. Second-order contributions imply a deformation of a transverse
tail-to-tail domain wall. The wall center still moves with a constant velocity
that now depends on the spin-polarized current in a non-trivial manner.",0708.1684v2
2007-09-24,Estimating the final spin of a binary black hole coalescence,"We present a straightforward approach for estimating the final black hole
spin of a binary black hole coalescence with arbitrary initial masses and
spins. Making some simple assumptions, we estimate the final angular momentum
to be the sum of the individual spins plus the orbital angular momentum of a
test particle orbiting at the last stable orbit around a Kerr black hole with a
spin parameter of the final black hole. The formula we obtain is able to
reproduce with reasonable accuracy the results from available numerical
simulations, but, more importantly, it can be used to investigate what
configurations might give rise to interesting dynamics. In particular, we
discuss scenarios which might give rise to a ``flip'' in the direction of the
total angular momentum of the system. By studying the dependence of the final
spin upon the mass ratio and initial spins we find that our simple approach
suggests that it is not possible to spin-up a black hole to extremal values
through merger scenarios irrespective of the mass ratio of the objects
involved.",0709.3839v1
2007-11-29,Quantum and classical multiple scattering effects in spin dynamics of cavity polaritons,"The transport properties of exciton-polaritons are studied with allowance for
their polarization. Both classical multiple scattering effects and quantum
effects such as weak localization are taken into account in the framework of a
generalized kinetic equation. The longitudinal-transverse (TE-TM) splitting of
polariton states which plays role analogous to the spin-orbit splitting in
electron systems is taken into account. The developed formalism is applied to
calculate the particle and spin diffusion coefficients of exciton-polaritons,
spin relaxation rates and the polarization conversion efficiency under the
conditions of the optical spin Hall effect. In contrast to the electron
systems, strong spin splitting does not lead to the antilocalization behavior
of the particle diffusion coefficient, while quantum corrections to spin
diffusion and polarization conversion can be both negative and positive
depending on the spin splitting value.",0711.4702v1
2008-01-25,Electrical generation of pure spin currents in a two-dimensional electron gas,"Pure spin currents are measured in micron-wide channels of GaAs
two-dimensional electron gas (2DEG). Spins are injected and detected using
quantum point contacts, which become spin polarized at high magnetic field.
High sensitivity to the spin signal is achieved in a nonlocal measurement
geometry, which dramatically reduces spurious signals associated with charge
currents. Measured spin relaxation lengths range from 30 to 50 microns, much
longer than has been reported in GaAs 2DEG's. The technique developed here
provides a flexible tool for the study of spin polarization and spin dynamics
in mesoscopic structures defined in 2D semiconductor systems.",0801.4021v4
2008-04-28,Coherent spin relaxation in molecular magnets,"Numerical modelling of coherent spin relaxation in nanomagnets, formed by
magnetic molecules of high spins, is accomplished. Such a coherent spin
dynamics can be realized in the presence of a resonant electric circuit coupled
to the magnet. Computer simulations for a system of a large number of
interacting spins is an efficient tool for studying the microscopic properties
of such systems. Coherent spin relaxation is an ultrafast process, with the
relaxation time that can be an order shorter than the transverse spin dephasing
time. The influence of different system parameters on the relaxation process is
analysed. The role of the sample geometry on the spin relaxation is
investigated.",0804.4368v1
2008-06-27,Spin-flip scattering in time-dependent transport through a quantum dot: Enhanced spin-current and inverse tunneling magnetoresistance,"We study the effects of spin-flip scatterings on the time-dependent transport
properties through a magnetic quantum dot attached to normal and ferromagnetic
leads. The transient spin-dynamics as well as the steady-state tunneling
magnetoresistance (TMR) of the system are investigated. The absence of a
definite spin quantization axis requires the time-propagation of two-component
spinors. We present numerical results in which the electrodes are treated both
as one-dimensional tight-binding wires and in the wide-band limit
approximation. In the latter case we derive a transparent analytic formula for
the spin-resolved current, and transient oscillations damped over different
time-scales are identified. We also find a novel regime for the TMR inversion.
For any given strength of the spin-flip coupling the TMR becomes negative
provided the ferromagnetic polarization is larger than some critical value.
Finally we show how the full knowledge of the transient response allows for
enhancing the spin-current by properly tuning the period of a pulsed bias.",0806.4480v1
2008-08-01,Dynamic polarization of single nuclear spins by optical pumping of NV color centers in diamond at room temperature,"We report a versatile method to efficiently polarize single nuclear spins in
diamond, which is based on optical pumping of a single NV color center and
mediated by a level-anti crossing in its excited state. A nuclear spin
polarization higher than 98% is achieved at room temperature for the 15N
nuclear spin associated to the NV center, corresponding to $\mu$K effective
nuclear spin temperature. We then show simultaneous deterministic
initialization of two nuclear spins (13C and 15N) in close vicinity to a NV
defect. Such robust control of nuclear spin states is a key ingredient for
further scaling up of nuclear-spin based quantum registers in diamond.",0808.0154v3
2008-11-06,Unconventional spin freezing and fluctuations in the frustrated antiferromagnet NiGa2S4,"Muon spin rotation (muSR) experiments reveal unconventional spin freezing and
dynamics in the two-dimensional (2D) triangular lattice antiferromagnet
NiGa2S4. Long-lived disordered Ni-spin freezing (correlation time > 10-6 s at 2
K) sets in below T_f = 8.5 +- 0.5 K with a mean-field-like temperature
dependence. The observed exponential temperature dependence of the muon spin
relaxation above T_f is strong evidence for 2D critical spin fluctuations. Slow
Ni spin fluctuations coexist with quasistatic magnetism at low temperatures but
are rapidly suppressed for fields > 10 mT, in marked contrast with the
field-independent specific heat. The muSR and bulk susceptibility data indicate
a well-defined 2D phase transition at T_f, below which NiGa2S4 is neither a
conventional magnet nor a singlet spin liquid.",0811.1057v1
2009-09-14,Collective modes of a helical liquid,"We study low energy collective modes and transport properties of the ""helical
metal"" on the surface of a topological insulator. At low energies, electrical
transport and spin dynamics at the surface are exactly related by an operator
identity equating the electric current to the in-plane components of the spin
degrees of freedom. From this relation it follows that an undamped spin wave
always accompanies the sound mode in the helical metal -- thus it is possible
to `hear' the sound of spins. In the presence of long range Coulomb
interactions, the surface plasmon mode is also coupled to the spin wave, giving
rise to a hybridized ""spin-plasmon"" mode. We make quantitative predictions for
the spin-plasmon in ${\rm Bi}_2{\rm Se}_3$, and discuss its detection in a
spin-grating experiment.",0909.2477v2
2009-10-15,Cyclotron effect on coherent spin precession of two-dimensional electrons,"We investigate the spin dynamics of high-mobility two-dimensional electrons
in GaAs/AlGaAs quantum wells grown along the $[001]$ and $[110]$ directions by
time-resolved Faraday rotation at low temperatures. In measurements on the
$(001)$-grown structures without external magnetic fields, we observe coherent
oscillations of the electron spin polarization about the effective spin-orbit
field. In non-quantizing magnetic fields applied normal to the sample plane,
the cyclotron motion of the electrons rotates the effective spin-orbit field.
This rotation leads to fast oscillations in the spin polarization about a
non-zero value and a strong increase in the spin dephasing time in our
experiments. These two effects are absent in the $(110)$-grown structure due to
the different symmetry of its effective spin-orbit field. The measurements are
in excellent agreement with our theoretical model.",0910.2847v1
2010-04-05,Multiple quantum NMR of spin-carrying molecules in nanopores: high order corrections to the two-spin/two-quantum Hamiltonian,"This paper is devoted to the multiple-quantum (MQ) NMR spectroscopy in
nanopores filled by a gas of spin-carrying molecules (s=1/2) in a strong
external magnetic field. It turned out that the high symmetry of the spin
system in nanopores yields a possibility to overcome the problem of the
exponential growth of the Hilbert space dimension with an increase in the
number of spins and to investigate MQ NMR dynamics in systems consisting of
several hundred spins. We investigate the dependence of the MQ coherence
intensities on their order (the profile of the MQ coherence intensities) for a
spin system governed by the standard MQ NMR Hamiltonian (the nonsecular
two-quantum/two-spin Hamiltonian) together with the second order correction of
the average Hamiltonian theory. It is shown that the profile depends on the
value of this correction and varies from the exponential to the logarithmic
one.",1004.0566v3
2010-10-20,Aharonov-Casher oscillations of spin current through a multichannel mesoscopic ring,"The Aharonov-Casher (AC) oscillations of spin current through a 2D ballistic
ring in the presence of Rashba spin-orbit interaction and external magnetic
field has been calculated using the semiclassical path integral method. For
classically chaotic trajectories the Fokker-Planck equation determining
dynamics of the particle spin polarization has been derived. On the basis of
this equation an analytic expression for the spin conductance has been obtained
taking into account a finite width of the ring arms carrying large number of
conducting channels. It was shown that the finite width results in a broadening
and damping of spin current AC oscillations. We found that an external magnetic
field leads to appearance of new nondiagonal components of the spin
conductance, allowing thus by applying a rather weak magnetic field to change a
direction of the transmitted spin current polarization.",1010.4197v1
2011-02-17,SU(2)-invariant spin liquids on the triangular lattice with spinful Majorana excitations,"We describe a new class of spin liquids with global SU(2) spin rotation
symmetry in spin 1/2 systems on the triangular lattice, which have real
Majorana fermion excitations carrying spin S = 1. The simplest
translationally-invariant mean-field state on the triangular lattice breaks
time-reversal symmetry and is stable to fluctuations. It generically possesses
gapless excitations along 3 Fermi lines in the Brillouin zone. These intersect
at a single point where the excitations scale with a dynamic exponent z = 3. An
external magnetic field has no orbital coupling to the SU(2) spin
rotation-invariant fermion bilinears that can give rise to a transverse thermal
conductivity, thus leading to the absence of a thermal Hall effect. The Zeeman
coupling is found to gap out two-thirds of the z = 3 excitations near the
intersection point and this leads to a suppression of the low temperature
specific heat, the spin susceptibility and the Wilson ratio. We also compute
physical properties in the presence of weak disorder and discuss possible
connections to recent experiments on organic insulators.",1102.3690v2
2011-05-28,Relaxation of Electron Spin during High-Field Transport in GaAs Bulk,"A semiclassical Monte Carlo approach is adopted to study the multivalley spin
depolarization of drifting electrons in a doped n-type GaAs bulk semiconductor,
in a wide range of lattice temperature ($40<T_L<300$ K) and doping density
($10^{13}<n<10^{16}$cm$^{-3}$). The decay of the initial non-equilibrium spin
polarization of the conduction electrons is investigated as a function of the
amplitude of the driving static electric field, ranging between 0.1 and 6
kV/cm, by considering the spin dynamics of electrons in both the $\Gamma$ and
the upper valleys of the semiconductor. Doping density considerably affects
spin relaxation at low temperature and weak intensity of the driving electric
field. At high values of the electric field, the strong spin-orbit coupling of
electrons in the $L$-valleys significantly reduces the average spin
polarization lifetime, but, unexpectedly, for field amplitudes greater than 2.5
kV/cm, the spin lifetime increases with the lattice temperature. Our numerical
findings are validated by a good agreement with the available experimental
results and with calculations recently obtained by a different theoretical
approach.",1105.5716v2
2011-07-26,Extended loop algorithm for pyrochlore Heisenberg spin models with spin-ice type degeneracy: application to spin-glass transition in antiferromagnets coupled to local lattice distortions,"For Ising spin models which bear the spin-ice type macroscopic
(quasi-)degeneracy, conventional classical Monte Carlo (MC) simulation using
single spin flips suffers from dynamical freezing at low temperatures ($T$). A
similar difficulty is seen also in a family of Heisenberg spin models with
easy-axis anisotropy or biquadratic interactions. In the Ising case, the
difficulty is avoided by introducing a non-local update based on the loop
algorithm. We present an extension of the loop algorithm to the Heisenberg
case. As an example of its application, we review our recent study on
spin-glass (SG) transition in a bond-disordered Heisenberg antiferromagnet
coupled to local lattice distortions.",1107.5103v1
2011-09-13,Thickness-dependent magnetic structure of ultrathin Fe/Ir(001) films: from spin-spiral states towards ferromagnetic order,"We present a detailed study of the ground-state magnetic structure of
ultrathin Fe films on the surface of fcc Ir(001). We use the spin-cluster
expansion technique in combination with the relativistic disordered local
moment scheme to obtain parameters of spin models and then determine the
favored magnetic structure of the system by means of a mean field approach and
atomistic spin dynamics simulations. For the case of a single monolayer of Fe
we find that layer relaxations very strongly influence the ground-state spin
configurations, whereas Dzyaloshinskii-Moriya (DM) interactions and biquadratic
couplings also have remarkable effects. To characterize the latter effect we
introduce and analyze spin collinearity maps of the system. While for two
monolayers of Fe we find a single-q spin spiral as ground state due to DM
interactions, for the case of four monolayers the system shows a noncollinear
spin structure with nonzero net magnetization. These findings are consistent
with experimental measurements indicating ferromagnetic order in films of four
monolayers and thicker.",1109.2721v1
2011-12-12,Spin-blockade effect and coherent control of DNA-damage by free radicals: a proposal on bio-spintronics,"Coherent control of OH-free radicals interacting with the spin-triplet state
of a DNA molecule is investigated. A model Hamiltonian for molecular spin
singlet-triplet resonance is developed. We illustrate that the spin-triplet
state in DNA molecules can be efficiently populated, as the spin-injection rate
can be tuned to be orders of magnitudes greater than the decay rate due to
small spin-orbit coupling in organic molecules. Owing to the nano-second
life-time of OH free radicals, a non-equilibrium free energy barrier induced by
the injected spin triplet state that lasts approximately longer than one-micro
second in room temperature can efficiently block the initial Hydrogen
abstraction and DNA damage. For a direct demonstration of the spin-blockade
effect, a molecular simulation based on an {\em ab-initio} Car-Parrinello
molecular dynamics is deployed.",1112.2733v1
2012-02-19,Hot spin spots in the laser-induced demagnetization,"Laser-induced femtosecond magnetism or femtomagnetism simultaneously relies
on two distinctive contributions: (a) the optical dipole interaction (ODI)
between a laser field and a magnetic system and (b) the spin expectation value
change (SEC) between two transition states. Surprisingly, up to now, no study
has taken both contributions into account simultaneously. Here we do so by
introducing a new concept of the optical spin generator, a product of SEC and
ODI between transition states. In ferromagnetic nickel, our first-principles
calculation demonstrates that the larger the value of optical spin generator
is, the larger the dynamic spin moment change is. This simple generator
directly links the time-dependent spin moment change {\Delta}Mk z (t) at every
crystal- momentum k point to its intrinsic electronic structure and magnetic
properties. Those hot spin spots are a direct manifestation of the optical spin
generator, and should be the focus of future research.",1202.4155v1
2012-06-22,Optically induced nuclear spin polarization in a single GaAs/AlGaAs quantum well probed by a resistance detection method in the fractional quantum Hall regime,"We study the optically pumped nuclear spin polarization in a single
GaAs/AlGaAs quantum well in the quantum Hall system. We apply resistive
detection via the contact hyperfine interaction, which provides high
sensitivity and selectivity, to probe a small amount of polarized nuclear spins
in a single well. The properties of the optical nuclear spin polarization are
clearly observed. We theoretically discuss the nuclear spin dynamics
accompanied with doped electrons to analyze the experimental data. The optical
nuclear polarization spectra exhibit electron-spin-resolved lowest Landau level
interband transitions. We find that the phonon emission process, which normally
assists the optical pumping process, influences the optical nuclear spin
polarization. We also discuss that the electron-electron interaction can play
an important role in the optical nuclear spin polarization.",1206.5227v3
2012-08-20,Reversal and Termination of Current-Induced Domain Wall Motion via Magnonic Spin-Transfer Torque,"We investigate the domain wall dynamics of a ferromagnetic wire under the
combined influence of a spin-polarized current and magnonic spin-transfer
torque generated by an external field, taking also into account Rashba
spin-orbit coupling interactions. It is demonstrated that current-induced
motion of the domain wall may be completely reversed in an oscillatory fashion
by applying a magnonic spin-transfer torque as long as the spin-wave velocity
is sufficiently high. Moreover, we show that the motion of the domain wall may
be fully terminated by means of the generation of spin-waves, suggesting the
possibility to pin the domain-walls to predetermined locations. We also discuss
how strong spin-orbit interactions modify these results.",1208.4108v1
2012-10-09,Spectral Characteristics of the Microwave Emission by the Spin Hall Nano-Oscillator,"We utilized microwave spectroscopy to study the magnetization oscillations
locally induced in a Permalloy film by a pure spin current, which is generated
due to the spin Hall effect in an adjacent Pt layer. The oscillation frequency
is lower than the ferromagnetic resonance of Permalloy, indicating that the
oscillation forms a self-localized nonpropagating spin-wave soliton. At
cryogenic temperatures, the spectral characteristics are remarkably similar to
the traditional spin-torque nano-oscillators driven by spin-polarized currents.
However, the linewidth of the oscillation increases exponentially with
temperature and an additional peak appears in the spectrum below the
ferromagnetic resonance, suggesting that the spectral characteristics are
determined by interplay between two localized dynamical states.",1210.2758v2
2013-05-16,Interplay between spin-orbit interactions and a time-dependent electromagnetic field in monolayer graphene,"We apply a circularly and linearly polarized terahertz field on a monolayer
of graphene taking into account spin-orbit interactions of the intrinsic and
Rashba type. It turns out that the field can not only be used to induce a gap
in the energy spectrum, but also to close an existing gap due to the different
reaction of the spin components on circularly polarized light. Signatures of
spin-orbit coupling on the density of states of the driven system can be
observed even for energies where the static density of states is independent of
spin-orbit interactions. Furthermore it is shown that the time evolution of the
spin polarization and the orbital dynamics of an initial wave packet can be
modulated by varying the ratio of the spin-orbit coupling parameters. Assuming
that the system acquires a quasi stationary state, the optical conductivity of
the irradiated sample is calculated. Our results confirm the multi step nature
of the conductivity obtained recently, where the number of intermediate steps
can be changed by adjusting the spin-orbit coupling parameters and the
orientation of the field.",1305.3810v2
2013-07-17,Spin-orbit interaction induced spin selective transmission through a multi-terminal mesoscopic ring,"Spin dependent transport in a multi-terminal mesoscopic ring is investigated
in presence of Rashba and Dresselhaus spin-orbit interactions. Within a
tight-binding framework we use a general spin density matrix formalism to
evaluate all three components ($P_x$, $P_y$ and $P_z$) of the polarization
vector associated with the charge current through the outgoing leads. It
explores the dynamics of the spin polarization vector of current propagating
through the system subjected to the Rashba and/or the Dresselhaus spin-orbit
couplings. The sensitivity of the polarization components on the electrode-ring
interface geometry is discussed in detail. Our present analysis provides an
understanding of the coupled spin and electron transport in mesoscopic bridge
systems.",1307.4506v2
2013-10-28,Coulomb-driven organization and enhancement of spin-orbit fields in collective spin excitations,"Spin-orbit (SO) fields in a spin-polarized electron gas are studied by
angle-resolved inelastic light scattering on a CdMnTe quantum well. We
demonstrate a striking organization and enhancement of SO fields acting on the
collective spin excitation (spin-flip wave). While individual electronic SO
fields have a broadly distributed momentum dependence, giving rise to
D'yakonov-Perel' dephasing, the collective spin dynamics is governed by a
single collective SO field which is drastically enhanced due to many-body
effects. The enhancement factor is experimentally determined. These results
provide a powerful indication that these constructive phenomena are universal
to collective spin excitations of conducting systems.",1310.7613v1
2013-11-06,Observation of zero-point quantum fluctuations of a single-molecule magnet through the relaxation of its nuclear spin bath,"A single-molecule magnet placed in a magnetic field perpendicular to its
anisotropy axis can be truncated to an effective two-level system, with easily
tunable energy splitting. The quantum coherence of the molecular spin is
largely determined by the dynamics of the surrounding nuclear spin bath. Here
we report the measurement of the nuclear spin--lattice relaxation in a single
crystal of the single-molecule magnet Mn$_{12}$-ac, at $T \approx 30$ mK in
perpendicular fields $B_{\perp}$ up to 9 T. Although the molecular spin is in
its ground state, we observe an increase of the nuclear relaxation rates by
several orders of magnitude up to the highest $B_{\perp}$. This unique finding
is a consequence of the zero-point quantum fluctuations of the Mn$_{12}$-ac
spin, which allow it to efficiently transfer energy from the excited nuclear
spin bath to the lattice. Our experiment highlights the importance of quantum
fluctuations in the interaction between an `effective two-level system' and its
surrounding spin bath.",1311.1373v1
2013-11-08,Spin wave nonreciprocity for logic device applications,"The utilization of spin waves as eigenmodes of the magnetization dynamics for
information processing and communication has been widely explored recently due
to its high operational speed with low power consumption and possible
applications for quantum computations. Previous proposals of spin wave
Mach-Zehnder devices were based on the spin wave phase, a delicate entity which
can be easily disrupted. Here, we propose a complete logic system based on the
spin wave amplitude utilizing the nonreciprocal spin wave behavior excited by
microstrip antennas. The experimental data reveal that the nonreciprocity of
magnetostatic surface spin wave can be tuned by the bias magnetic field.
Furthermore, engineering of the device structure could result in a high
nonreciprocity factor for spin wave logic applications.",1311.1881v1
2013-11-12,Leggett's Modes in Magnetic Systems with Jahn-Teller distortion,"Leggett's mode is a collective excitation corresponding to the oscillation of
the relative phase of the order parameters in a two band superconductor, with
frequency proportional to interband coupling. We report on the existence of
modes, similar to Leggett's mode, in magnetic systems with Jahn-Teller
distortion. The minimal Kugel-Khomskii model, which describes simultaneously
both the spin and the orbital order, is studied. The dynamical degrees of
freedom are spin-$s$ operators of localized spins and pseudospin-$\tau$
operators, which respond to the orbital degeneracy and satisfy the similar
commutation relation with those of the spin operators. In the case of
""antiferro"" spin and pseudospin order the system possesses two
antiferromagnetic magnons with equal spin-wave velocities and two Leggett's
modes with equal gaps proportional to the square root of the spin-pseudospin
interaction constant. In the case of ""ferro"" spin and pseudospin order the
system possesses one ferromagnetic magnon and one Leggett's mode with gap
proportional to the spin-pseudospin interaction constant.",1311.2733v3
2013-12-06,Magnetic Field Effect on Electron Spin Dynamics in (110) GaAs Quantum wells,"We study the electron spin relaxation in both symmetric and asymmetric
GaAs/AlGaAs quantum wells (QWs) grown on (110) substrates in an external
magnetic field B applied along the QW normal. The spin polarization is induced
by circularly polarized light and detected by time-resolved Kerr rotation
technique. In the asymmetric structure, where a {\delta}-doped layer on one
side of the QW produces the Rashba contribution to the conduction-band
spin-orbit splitting, the lifetime of electron spins aligned along the growth
axis exhibits an anomalous dependence on B in the range 0<B<0.5 T; this results
from the interplay between the Dresselhaus and Rashba effective fields which
are perpendicular to each other. For larger magnetic fields, the spin lifetime
increases, which is the consequence of the cyclotron motion of the electrons
and is also observed in (001)-grown quantum wells. The experimental results are
in agreement with the calculation of the spin lifetimes in (110)- grown
asymmetric quantum wells described by the point group Cs where the growth
direction is not the principal axis of the spin-relaxation-rate tensor.",1312.1807v1
2014-01-05,Dynamics of spin-flip photon-assisted tunneling,"We present time-resolved measurements of spin-flip photon-assisted tunneling
and spin-flip relaxation in a doubly occupied double quantum dot. The
photon-assisted excitation rate as a function of magnetic field indicates that
spin-orbit coupling is the dominant mechanism behind the spin-flip under the
present conditions. We are able to extract the resulting effective `spin-flip
tunneling' energy, which is found to be three orders of magnitude smaller than
the regular spin-conserving tunneling energy. We also measure the relaxation
and dephasing times of a qubit formed out of two two-electron states with
different spin and charge configurations.",1401.0881v1
2014-02-11,Information transmission and control in a chaotically kicked spin chain,"We study spin chains submitted to disturbed kick trains described by
classical dynamical processes. The spin chains are coupled by Heisenberg and
Ising-Z models. We consider chaotic processes by using the kick irregularity in
the multipartite system (the spin chain). We show that the both couplings
transmit differently the chaos disorder along the spin chain but conserve the
horizon of coherence (when the disorder into the kick bath is transmitted to
the spin chain). An example of information transmission between the spins of
the chain coupled by a Heisenberg interaction shows the interest of the horizon
of coherence. The use of some chosen stationary kicks disturbed by a chaotic
environment allows to modify the information transmission between the spins and
to perform a free control during the horizon of coherence.",1402.2411v3
2014-02-27,On the longitudinal spin current induced by a temperature gradient in a ferromagnetic insulator,"Based on the solution of the stochastic Landau-Lifshitz-Gilbert equation
discretized for a ferromagnetic chain subject to a uniform temperature
gradient, we present a detailed numerical study of the spin dynamics with a
focus particularly on finite-size effects. We calculate and analyze the net
longitudinal spin current for various temperature gradients, chain lengths, and
external static magnetic fields. In addition, we model an interface formed by a
nonuniformly magnetized finite-size ferromagnetic insulator and a normal metal
and inspect the effects of enhanced Gilbert damping on the formation of the
space-dependent spin current within the chain. A particular aim of this study
is the inspection of the spin Seebeck effect beyond the linear response regime.
We find that within our model the microscopic mechanism of the spin Seebeck
current is the magnon accumulation effect quantified in terms of the exchange
spin torque. According to our results, this effect drives the spin Seebeck
current even in the absence of a deviation between the magnon and phonon
temperature profiles. Our theoretical findings are in line with the recently
observed experimental results by M. Agrawal et al., Phys. Rev. Lett. 111,
107204 (2013).",1402.6899v1
2014-08-15,Separated spin-up and spin-down evolution of degenerated electrons in two dimensional systems: Dispersion of longitudinal collective excitations in plane and nanotube geometry,"Applying the separated spin evolution quantum hydrodynamics to
two-dimensional electron gas in plane samples and nanotubes located in external
magnetic fields we find new kind of wave in electron gas, which is called the
spin-electron acoustic wave. Separate spin-up electrons and spin-down electrons
evolution reveals in replacement of the Langmuir wave by the couple of hybrid
waves. One of two hybrid waves is the modified Langmuir wave. Another hybrid
wave is the spin-electron acoustic wave. We study dispersion of these waves in
two dimensional structures of electrons. We also consider dependence of
dispersion properties on spin polarisation of electrons in external magnetic
field.",1408.3662v1
2014-10-06,Surprisingly large inverse spin Hall effect and systematic variation of spin-orbit coupling with d-orbital filling in 3d transition metals,"It is generally believed that spin-orbit coupling (SOC) follows Z4 (atomic
number) dependence and becomes significant only in heavy elements.
Consequently, SOC in 3d transition metals should be negligible given their
small Z. Using dynamic spin pumping of Y3Fe5O12-based structures, we uncover a
systematic evolution of spin Hall angle with d-orbital filling in a series of
3d metals, reminiscent of behavior observed in 5d metals. In particular, Cr and
Ni show very large spin Hall angle (half of that for Pt), indicating that
d-orbital filling rather than Z plays a dominant role in spin Hall effect (SHE)
in 3d metals. This result enriches our understanding of SHE and broadens the
scope of materials available for exploring the rich phenomena enabled by SOC as
well as presenting a guidepost for testing theoretical models of spin-orbit
coupling in transition metals.",1410.1590v1
2015-04-10,Proton and neutron correlations in $^{10}$B,"We investigate positive-parity states of $^{10}$B with the calculation of
antisymmetrized molecular dynamics focusing on $pn$ pair correlations. We
discuss effects of the spin-orbit interaction on energy spectra and $pn$
correlations of the $J^\pi T=1^+_10$, $=3^+_10$, and $0^+_11$ states. The
$1^+_10$ state has almost no energy gain of the spin-orbit interaction, whereas
the $3^+_10$ state gains the spin-orbit interaction energy largely to come down
to the ground state. We interpret a part of the two-body spin-orbit interaction
in the adopted effective interactions as a contribution of the genuine $NNN$
force, and find it to be essential for the level ordering of the $3^+_10$ and
$1^+_10$ states in $^{10}$B. We also apply a $2\alpha+pn$ model to discuss
effects of the spin-orbit interaction on $T=0$ and $T=1$ $pn$ pairs around the
2$\alpha$ core. In the spin-aligned $J^\pi T=3^+0$ state, the spin-orbit
interaction affects the $(ST)=(10)$ pair attractively and keeps the pair close
to the core, whereas, in the $1^+0$ state, it gives a minor effect to the
$(ST)=(10)$ pair. In the $0^+1$ state, the $(ST)=(01)$ pair is somewhat
dissociated by the spin-orbit interaction.",1504.02594v1
2015-04-28,Influcence of the nuclear electric quadrupolar interaction on the coherence time of hole- and electron-spins confined in semiconductor quantum dots,"The real-time spin dynamics and the spin noise spectra are calculated for p
and n-charged quantum dots within an anisotropic central spin model extended by
additional nuclear electric quadrupolar interactions (QC) and augmented by
experimental data studied using identical excitation conditions. Using
realistic estimates for the distribution of coupling constants including an
anisotropy parameter, we show that the characteristic long time scale is of the
same order for electron and hole spins strongly determined by the QC even
though the analytical form of the spin decay differs significantly consistent
with our measurements. The low frequency part of the electron spin noise
spectrum is approximately $1/3$ smaller than those for hole spins as a
consequence of the spectral sum rule and the different spectral shapes. This is
confirmed by our experimental spectra measured on both types of quantum dot
ensembles in the low power limit of the probe laser.",1504.07417v1
2015-06-15,Spin flips in generic black hole binaries,"We study the spin dynamics of individual black holes in a binary system. In
particular we focus on the polar precession of spins and the possibility of a
complete flip of spins with respect to the orbital plane. We perform a full
numerical simulation that displays these characteristics. We evolve equal mass
binary spinning black holes for $t=20,000M$ from an initial proper separation
of $d=25M$ down to merger after 48.5 orbits. We compute the gravitational
radiation from this system and compare it to 3.5 post-Newtonian generated
waveforms finding close agreement. We then further use 3.5 post-Newtonian
evolutions to show the extension of this spin {flip-flop} phenomenon to unequal
mass binaries. We also provide analytic expressions to approximate the maximum
{flip-flop} angle and frequency in terms of the binary spins and mass ratio
parameters at a given orbital radius. Finally we discuss the effect this spin
{flip-flop} would have on accreting matter and other potential observational
effects.",1506.04768v2
2015-07-07,Robust micro-magnet design for fast electrical manipulations of single spins in quantum dots,"Tailoring spin coupling to electric fields is central to spintronics and
spin-based quantum information processing. We present an optimal micromagnet
design that produces appropriate stray magnetic fields to mediate fast
electrical spin manipulations in nanodevices. We quantify the practical
requirements for spatial field inhomogeneity and tolerance for misalignment
with spins, and propose a design scheme to improve the spin-rotation frequency
(to exceed 50MHz in GaAs nanostructures). We then validate our design by
experiments in separate devices. Our results will open a route to rapidly
control solid-state electron spins with limited lifetimes and to study coherent
spin dynamics in solids.",1507.01765v1
2015-08-01,Exchange-driven spin relaxation in ferromagnet/oxide/semiconductor heterostructures,"We investigate electron spin relaxation in GaAs in the proximity of a Fe/MgO
layer using spin-resolved optical pump-probe spectroscopy, revealing a strong
dependence of the spin relaxation time on the strength of an exchange-driven
hyperfine field. The temperature dependence of this effect reveals a strong
correlation with carrier freeze out, implying that at low temperatures the free
carrier spin lifetime is dominated by inhomogeneity in the local hyperfine
field due to carrier localization. This result resolves a long-standing and
contentious question of the origin of the spin relaxation in GaAs at low
temperature when a magnetic field is present. Further, this improved
fundamental understanding paves the way for future experiments exploring the
time-dependent exchange interaction at the ferromagnet/semiconductor interface
and its impact on spin dissipation and transport in the regime of
dynamically-driven spin pumping.",1508.00164v1
2015-08-17,Magnetization dynamics driven by angle-dependent spin-orbit spin transfer torque,"Spin-orbit spin transfer torque allows an efficient control of magnetization
by an in-plane current. Recent experiments found that the spin-orbit torque has
strong dependence on the magnetization angle [Garello et al., Nature
Nanotechnol. 8, 587 (2013); Qiu et al., Sci. Rep. 4, 4491 (2014)]. We
theoretically investigate magnetization switching and domain wall motion in a
perpendicularly magnetized layer, induced by angle-dependent spin-orbit torque.
We obtain analytic expressions of the switching current and domain wall
velocity, in agreement with numerical results. Based on the expressions, we
find that the spin-orbit torque increasing with the polar angle of
magnetization is beneficial for both switching and domain wall motion. Our
result will serve as a guideline to design and interpret switching and domain
wall experiments based on spin-orbit torque.",1508.04067v2
2015-09-11,Non-perturbative Correlation Effects in Diluted Magnetic Semiconductors,"The effects of carrier-impurity correlations due to a Kondo-like spin-spin
interaction in diluted magnetic semiconductors are investigated. These
correlations are not only responsible for a transfer of spins between the
carriers and the impurities, but also produce non-perturbative effects in the
spin dynamics such as renormalization of the precession frequency of the
carrier spins, which can reach values of several percent in CdMnTe quantum
wells. In two-dimensional systems, the precession frequency renormalization for
a single electron spin with defined wave vector shows logarithmic divergences
similar to those also known from the Kondo problem in metals. For smooth
electron distributions, however, the divergences disappear due to the
integrability of the logarithm. A possible dephasing mechanism caused by the
wave-vector dependence of the electron spin precession frequencies is found to
be of minor importance compared to the spin transfer from the carrier to the
impurity system. In the Markov limit of the theory, a quasi-equilibrium
expression for the carrier-impurity correlation energy can be deduced
indicating the formation of strongly correlated carrier-impurity states for
temperatures in the mK range.",1509.03442v1
2015-10-20,Using Majorana spin-1/2 representation for the spin-boson model,"The Majorana representation for spin operators enables efficient application
of field-theoretical methods for the analysis of spin dynamics. Moreover, a
wide class of spin correlation functions can be reduced to Majorana
correlations of the same order, simplifying their calculation. For the
spin-boson model, direct application of this method in the lowest order allows
for a straightforward computation of the transverse-spin correlations, however,
for the longitudinal-spin correlations it apparently fails in the long-time
limit. Here we indicate the reason and discuss, how this method can be used as
a convenient and accurate tool for generic spin correlations. Specifically, we
demonstrate that accurate results are obtained by avoiding the use of the
longitudinal Majorana fermion, and that correlations of the remaining
transverse Majorana fermions can be easily evaluated using an effective
Gaussian action.",1510.05838v2
2015-11-04,Enhanced strain coupling of nitrogen vacancy spins to nanoscale diamond cantilevers,"Nitrogen vacancy (NV) centers can couple to confined phonons in diamond
mechanical resonators via the effect of lattice strain on their energy levels.
Access to the strong spin-phonon coupling regime with this system requires
resonators with nanoscale dimensions in order to overcome the weak strain
response of the NV ground state spin sublevels. In this work, we study NVs in
diamond cantilevers with lateral dimensions of a few hundred nm. Coupling of
the NV ground state spin to the mechanical mode is detected in electron spin
resonance (ESR), and its temporal dynamics are measured via spin echo. Our
small mechanical mode volume leads to a 10-100X enhancement in spin-phonon
coupling strength over previous NV-strain coupling demonstrations. This is an
important step towards strong spin-phonon coupling, which can enable
phonon-mediated quantum information processing and quantum metrology.",1511.01548v1
2016-03-08,Spin slush in an extended spin ice model,"We introduce a new classical spin liquid on the pyrochlore lattice by
extending spin ice with further neighbour interactions. We find that this
disorder free spin model exhibits a form of dynamical heterogeneity with
extremely slow relaxation for some spins while others fluctuate quickly down to
zero temperature. We thus call this state ""spin slush"", in analogy to the
heterogeneous mixture of solid and liquid water. This behaviour is driven by
the structure of the ground state manifold which extends the celebrated the
two-in/two-out ice states to include branching structures built from
three-in/one-out, three-out/one-in and all-in/all-out tetrahedra defects.
Distinctive liquid-like patterns in the spin correlations serve as a signature
of this intermediate range order. Possible applications to materials as well
the effects of quantum tunneling are discussed.",1603.02683v1
2016-03-26,Direct coupling between charge current and spin polarization by extrinsic mechanisms in graphene,"Spintronics---the all-electrical control of the electron spin for quantum or
classical information storage and processing---is one of the most promising
applications of the two-dimensional material graphene. Although pristine
graphene has negligible spin-orbit coupling (SOC), both theory and experiment
suggest that SOC in graphene can be substantially enhanced by extrinsic means,
such as functionalization by adatom impurities. We present a theory of
transport in graphene that accounts for the full spin-coherent dynamics of the
carriers, including hitherto-neglected spin precession processes during
resonant scattering with dilute impurities. We identify a novel ""anisotropic
spin precession scattering"" process, specific to two dimensions and extrinsic
SOC, which contributes to a large current-induced spin polarization in
graphene. The theory also yields a comprehensive description of the spin
relaxation mechanisms in impurity-decorated graphene: the Elliot-Yafet and
Dyakonov-Perel relaxation rates are both present, and we find that the latter
can dominate for some choices of carrier density and impurity strength. This
provides theoretical foundations for designing future graphene-based integrated
spintronic devices.",1603.08107v2
2016-04-28,Chirality-driven Hall Transport Phenomena of Spins,"Experimental and theoretical aspects of Hall-type transport of spins in
magnetic insulators are reviewed, with emphasis on their spin chirality origin.
A general formalism for linear response theory of thermal Hall transport in the
spin model is developed, which can be applied to both the magnon and the
paramagnetic, spin-liquid regimes. Recent experiments on magnon-mediated
thermal Hall transport in the two-dimensional kagome, and three-dimensional
pyrochlore ferromagnetic insulators are reviewed in light of the multi-band
magnon theory of Hall transport, and compared to the more mysterious thermal
Hall transport found in the putative quantum spin ice material. As realizations
of spin-chirality driven magnon transport in the real space, we review the
general theory of emergent gauge fields governing the magnon dynamics in the
textured magnet, and discuss its application to the magnon-Skyrmion scattering
problem. Topological magnon Hall effect driven by the Skyrmion texture is
discussed.",1604.08290v2
2016-06-25,Photo-creating supercooled spiral-spin states in a multiferroic manganite,"We demonstrate that dynamics of the ab-spiral-spin order in a magnetoelectric
multiferroic Eu0.55Y0.45MnO3 can be unambiguously probed through optical second
harmonic signals, generated via the spin-induced ferroelectric polarization. In
the case of relatively weak photoexcitation,the ferroelectric and the
spiral-spin order remains interlocked, both relaxing through spin-lattice
relaxation in the non-equilibrium state. When the additional optical pulse
illuminating sample is intense enough to induced a local phase transition
thermally, the system creates a metastable state of the bc-spiral-spin order
(with the electric polarization P//c) via supercooling across the first-order
phase transition between ab- and bc-spiral. The supercooled state of bc-spiral
spin is formed in the thermodynamical ground state of ab-spiral (P//a),
displaying a prolonged lifetime with strong dependence on the magnetic field
along the a-axis. The observed photo-switching between the two distinct
multiferroic states sheds light on novel photoinduced phenomena in spiral-spin
multiferroics.",1606.07922v1
2016-07-15,Theory of spin-coherent transport through a defect spin state in a metal/ferromagnet tunnel junction during ferromagnetic resonance,"We describe the coherent interaction between a defect spin at the interface
of a ferromagnet and a non-magnetic material, under bias and when the
magnetization of the ferromagnetic contact precesses during ferromagnetic
resonance. The magnet filters charge carriers by preferentially allowing in
parallel spins, which leads to a dynamic spin accumulation on the defect. Local
effective fields acting on the defect spin site modify the defect spin's
precession, which also modifies the charge current through the defect. This new
form of current-detected spin resonance reveals the local environment of the
defect, and thus can yield the defect identity.",1607.04535v2
2016-07-16,Measurement of spin pumping voltage separated from extrinsic microwave effects,"Conversions between spin and charge currents are core technologies in recent
spintronics. In this article, we provide methods for estimating inverse spin
Hall effects (ISHEs) induced by using microwave-driven spin pumping (SP) as a
spin-current generator. ISHE and SP induce an electromotive force at the
ferromagnetic or spin-wave resonance, which offers a valuable electric way to
study spin physics in materials. At the resonance, a microwave for exciting the
magnetization dynamics induces an additional electromotive force via rf-current
rectification and thermoelectric effects. We discuss methods to separate the
signals generated from such extrinsic microwave effects by controlling sample
structures and configurations. These methods are helpful in performing accurate
measurements on ISHE induced by SP, enabling quantitative studies on the
conversion between spin and charge currents on various kinds of materials.",1607.04716v1
2016-10-27,Purification of an unpolarized spin ensemble into entangled singlet pairs,"Dynamical polarization of nuclear spin ensembles is of central importance for
magnetic resonance studies, precision sensing and for applications in quantum
information theory. Here we propose a scheme to generate long-lived singlet
pairs in an unpolarized nuclear spin ensemble which is dipolar coupled to the
electron spins of a Nitrogen Vacancy center in diamond. The quantum mechanical
back-action induced by frequent spin-selective readout of the NV centers allows
the nuclear spins to pair up into maximally entangled singlet pairs.
Counterintuitively, the robustness of the pair formation to dephasing noise
improves with increasing size of the spin ensemble. We also show how the paired
nuclear spin state allows for enhanced sensing capabilities of NV centers in
diamond.",1610.08886v2
2017-02-05,Chiral Spin Condensation in a One-Dimensional Optical Lattice,"We study a spinor (two-component) Bose gas confined in a one-dimensional
double-valley optical lattice which has a double-well structure in momentum
space. Based on field theory analysis, it is found that spinor bosons in the
double-valley band may form a spin-charge mixed chiral spin quasicondensate
under certain conditions. Our numerical calculations in a concrete $\pi$-flux
triangular ladder system confirm the robustness of the chiral spin order
against interactions and quantum fluctuations. This exotic atomic Bose-Einstein
condensate exhibits spatially staggered spin loop currents without any charge
dynamics despite the complete absence of spin-orbit coupling in the system,
creating an interesting approach to atom spintronics. The entanglement entropy
scaling allows us to extract conformal-field-theory central charge and
establish the low-energy effective field theory for the chiral spin condensate
as a two-component Luttinger liquid. Our predictions should be detectable in
atomic experiments through spin-resolved time-of-flight techniques.",1702.01439v2
2017-02-13,Inter-valley dark trion states with spin lifetimes of 150 ns in WSe$_2$,"We demonstrate long trion spin lifetimes in a WSe$_2$ monolayer of up to 150
ns at 5 K. Applying a transverse magnetic field in time-resolved Kerr-rotation
measurements reveals a complex composition of the spin signal of up to four
distinct components. The Kerr rotation signal can be well described by a model
which includes inhomogeneous spin dephasing and by setting the trion spin
lifetimes to the measured excitonic recombination times extracted from
time-resolved reflectivity measurements. We observe a continuous shift of the
Kerr resonance with the probe energy, which can be explained by an
adsorbate-induced, inhomogeneous potential landscape of the WSe$_2$ flake. A
further indication of extrinsic effects on the spin dynamics is given by a
change of both the trion spin lifetime and the distribution of g-factors over
time. Finally, we detect a Kerr rotation signal from the trion's higher-energy
triplet state when the lower-energy singlet state is optically pumped by
circularly polarized light. We explain this by the formation of dark trion
states, which are also responsible for the observed long trion spin lifetimes.",1702.03712v1
2017-02-15,Topological Properties of a Coupled Spin-Photon System Induced by Damping,"We experimentally examine the topological nature of a strongly coupled
spin-photon system induced by damping. The presence of both spin and photonic
losses results in a non-Hermitian system with a variety of exotic phenomena
dictated by the topological structure of the eigenvalue spectra and the
presence of an exceptional point (EP), where the coupled spin-photon
eigenvectors coalesce. By controlling both the spin resonance frequency and the
spin-photon coupling strength we observe a resonance crossing for
cooperativities above one, suggesting that the boundary between weak and strong
coupling should be based on the EP location rather than the cooperativity.
Furthermore we observe dynamic mode switching when encircling the EP and
identify the potential to engineer the topological structure of coupled
spin-photon systems with additional modes. Our work therefore further
highlights the role of damping within the strong coupling regime, and
demonstrates the potential and great flexibility of spin-photon systems for
studies of non-Hermitian physics.",1702.04797v2
2017-02-22,Is spin superfluidity possible in YIG films?,"Recently it was suggested that stationary spin supercurrents (spin
superfluidity) are possible in the magnon condensate observed in
yttrium-iron-garnet (YIG) magnetic films under strong external pumping. Here we
analyze this suggestion. From topology of the equilibrium order parameter in
YIG one must not expect energetic barriers making spin supercurrents
metastable. However some small barriers of dynamical origin are possible
nevertheless. The critical phase gradient (analog of the Landau critical
velocity in superfluids) is proportional to intensity of the coherent spin wave
(number of condensed magnons). The conclusion is that although spin
superfluidity in YIG films is possible in principle, the published claim of its
observation is not justified.
  The analysis revealed that the widely accepted spin-wave spectrum in YIG
films with magnetostatic and exchange interaction required revision. This led
to revision of non-linear corrections, which determine stability of the magnon
condensate with and without spin supercurrents.",1702.06994v2
2017-03-21,Spin in the extended electron model,"It has been found that a model of extended electrons is more suited to
describe theoretical simulations and experimental results obtained via scanning
tunnelling microscopes, but while the dynamic properties are easily
incorporated, magnetic properties, and in particular electron spin properties
pose a problem due to their conceived isotropy in the absence of measurement.
The spin of an electron reacts with a magnetic field and thus has the
properties of a vector. However, electron spin is also isotropic, suggesting
that it does not have the properties of a vector. This central conflict in the
description of an electron's spin, we believe, is the root of many of the
paradoxical properties measured and postulated for quantum spin particles.
Exploiting a model in which the electron spin is described consistently in real
three-dimensional space - an extended electron model - we demonstrate that spin
may be described by a vector and still maintain its isotropy. In this
framework, we re-evaluate the Stern-Gerlach experiments, the
Einstein-Podolsky-Rosen experiments, and the effect of consecutive measurements
and find in all cases a fairly intuitive explanation.",1703.08076v1
2019-05-07,Spin Berry phase in a helical edge state: Sz nonconservation and transport signatures,"Topological protection of edge state in quantum spin Hall systems relies only
on time-reversal symmetry. Hence, S z conservation on the edge can be relaxed
which can have an interferometric manifestation in terms of spin Berry phase.
Primarily it could lead to the generation of spin Berry phase arising from a
closed loop dynamics of electrons. Our work provides a minimal framework to
generate and detect these effects by employing both spin-unpolarized and
spin-polarized leads. We show that spin-polarized leads could lead to
resonances or anti-resonances in the two-terminal conductance of the
interferometer. We further show that the positions of these anti-resonances (as
a function of energy of the incident electron) get shifted owing to the
presence of spin Berry phase. Finally, we present simulations of a device setup
using KWANTpackage which put our theoretical predictions on firm footing.",1905.02801v2
2013-08-14,Excitation- and state-transfer through spin chains in the presence of spatially correlated noise,"We investigate the influence of environmental noise on spin networks and spin
chains. In addition to the common model of an independent bath for each spin in
the system we also consider noise with a finite spatial correlation length. We
present the emergence of new dynamics and decoherence-free subspaces with
increasing correlation length for both dephasing and dissipating environments.
This leads to relaxation blocking of one spin by uncoupled surrounding spins.
We then consider perfect state transfer through a spin chain in the presence of
decoherence and discuss the dependence of the transfer quality on spatial noise
correlation length. We identify qualitatively different features for dephasing
and dissipative environments in spin-transfer problems.",1308.3042v1
2013-08-16,Tunable critical supercurrent and spin-asymmetric Josephson effect in superlattices,"Combining the Josephson effect with magnetism, or spin dependence in general,
creates novel physical phenomena. The spin-asymmetric Josephson effect is a
predicted phenomenon where a spin-dependent potential applied across a
Josephson junction induces a spin-polarized Josephson current. Here, we propose
an approach to observe the spin-asymmetric Josephson effect with spin-dependent
superlattices, realizable, e.g., in ultracold atomic gases. We show that
observing this effect is feasible by studying numerically the quantum dynamics
of the system in one dimension. Furthermore, we show that the enhancement, or
tunability, of the critical supercurrent in ferromagnetic Josephson junctions
[F. S. Bergeret, A. F. Volkov, and K. B. Efetov, Phys. Rev. Lett. 86, 3140
(2001)] can be explained by the spin-asymmetric Josephson effect.",1308.3626v3
2018-05-03,Sculpting the Spin-Wave Response of Artificial Spin Ice via Microstate Selection,"The spin-wave dynamics of the ferromagnetic nanoarrays termed artificial spin
ice (ASI) are known to vary depending on their magnetic microstate. However,
little work has been done to characterise this relationship. Recent advances in
control over the magnetic configuration of ASI bring designs harnessing the
interplay between spin-wave eigenmodes and the microstate within reach,
offering diverse applications including reconfigurable magnonic crystals,
microwave filters and microstate read-out probes. These designs hinge on a
strong understanding of the underlying spin wave-microstate correspondence.
  Here, we analyse the effects of the magnetic microstate on spin-wave spectra
of honeycomb ASI systems via micromagnetic simulation. We find the spin-wave
spectrum to be highly-tunable via the microstate to an enhanced degree relative
to existing magnonic crystals, with mode shifting and (de)activation realised
by reversing individual nanoislands. Symmetries of ASI systems and the
chirality of magnetic defects are found to play important roles in determining
the high-frequency response.",1805.01397v3
2011-11-15,Dynamical spin Hall conductivity in a magnetic disordered system,"We investigate the intrinsic spin Hall effect in a quantum well semiconductor
doped with magnetic impurities, as a means to manipulate the carriers' spin.
Using a simple Hamiltonian with Rashba spin-orbit coupling and exchange
interactions, we analytically compute the spin Hall conductivity. It is
demonstrated that using the appropriate order of limits, one recovers the
intrinsic universal value. Numerical computations on a tight-binding model, in
the weak disorder regime, confirm that the spin Hall effect is preserved in the
presence of magnetic impurities. The optical spin conductivity shows large
sample to sample fluctuations in the low frequency region. As a consequence,
for weak disorder, the static spin conductivity is found to follow a wide
Gaussian distribution with its mean value near the intrinsic clean value.",1111.3575v1
2012-01-03,Quantum Simulation of Spin Models on an Arbitrary Lattice with Trapped Ions,"A collection of trapped atomic ions represents one of the most attractive
platforms for the quantum simulation of interacting spin networks and quantum
magnetism. Spin-dependent optical dipole forces applied to an ion crystal
create long-range effective spin-spin interactions and allow the simulation of
spin Hamiltonians that possess nontrivial phases and dynamics. Here we show how
appropriate design of laser fields can provide for arbitrary multidimensional
spin-spin interaction graphs even for the case of a linear spatial array of
ions. This scheme uses currently existing trap technology and is scalable to
levels where classical methods of simulation are intractable.",1201.0776v1
2012-04-26,High fidelity optical preparation and coherent Larmor precession of a single hole in an InGaAs quantum dot molecule,"We employ ultrafast pump-probe spectroscopy with photocurrent readout to
directly probe the dynamics of a single hole spin in a single, electrically
tunable self-assembled quantum dot molecule formed by vertically stacking
InGaAs quantum dots. Excitons with defined spin configurations are initialized
in one of the two dots using circularly polarized picosecond pulses. The
time-dependent spin configuration is probed by the spin selective optical
absorption of the resulting few Fermion complex. Taking advantage of sub-5 ps
electron tunneling to an orbitally excited state of the other dot, we
initialize a single hole spin with a purity of >96%, i.e., much higher than
demonstrated in previous single dot experiments. Measurements in a lateral
magnetic field monitor the coherent Larmor precession of the single hole spin
with no observable loss of spin coherence within the ~300 ps hole lifetime.
Thereby, the purity of the hole spin initialization remains unchanged for all
investigated magnetic fields.",1204.5899v1
2014-05-06,Influence of Nuclear Quadrupole Moments on Electron Spin Coherence in Semiconductor Quantum Dots,"We theoretically investigate the influence of the fluctuating Overhauser
field on the spin of an electron confined to a quantum dot (QD). The
fluctuations arise from nuclear angular momentum being exchanged between
different nuclei via the nuclear magnetic dipole coupling. We focus on the role
of the nuclear electric quadrupole moments (QPMs), which generally cause a
reduction in internuclear spin transfer efficiency in the presence of electric
field gradients. The effects on the electron spin coherence time are studied by
modeling an electron spin echo experiment. We find that the QPMs cause an
increase in the electron spin coherence time and that an inhomogeneous
distribution of the quadrupolar shift, where different nuclei have different
shifts in energy, causes an even larger increase in the electron coherence time
than a homogeneous distribution. Furthermore, a partial polarization of the
nuclear spin ensemble amplifies the effect of the inhomogeneous quadrupolar
shifts, causing an additional increase in electron coherence time, and provides
an alternative to the experimentally challenging suggestion of full dynamic
nuclear spin polarization.",1405.1329v1
2014-05-13,From Spin Glass to Quantum Spin Liquid Ground States in Molybdate Pyrochlores,"We present new magnetic heat capacity and neutron scattering results for two
magnetically frustrated molybdate pyrochlores: $S=1$ oxide Lu$_2$Mo$_2$O$_7$
and $S={\frac{1}{2}}$ oxynitride Lu$_2$Mo$_2$O$_5$N$_2$. Lu$_2$Mo$_2$O$_7$
undergoes a transition to an unconventional spin glass ground state at $T_f
{\sim} 16$ K. However, the preparation of the corresponding oxynitride tunes
the nature of the ground state from spin glass to quantum spin liquid. The
comparison of the static and dynamic spin correlations within the oxide and
oxynitride phases presented here reveals the crucial role played by quantum
fluctuations in the selection of a ground state. Furthermore, we estimate an
upper limit for a gap in the spin excitation spectrum of the quantum spin
liquid state of the oxynitride of ${\Delta} {\sim} 0.05$ meV or
${\frac{\Delta}{|\theta|}}\sim0.004$, in units of its antiferromagnetic Weiss
constant ${\theta} {\sim}-121$ K.",1405.3172v1
2017-10-07,Coupled spin-charge dynamics in helical Fermi liquids beyond the random phase approximation,"We consider a helical system of fermions with a generic spin (or pseudospin)
orbit coupling. Using the equation of motion approach for the single-particle
distribution functions, and a mean-field decoupling of the higher order
distribution functions, we find a closed form for the charge and spin density
fluctuations in terms of the charge and spin density linear response functions.
Approximating the nonlocal exchange term with a Hubbard-like local-field
factor, we obtain coupled spin and charge density response matrix beyond the
random phase approximation, whose poles give the dispersion of four collective
spin-charge modes. We apply our generic technique to the well-explored
two-dimensional system with Rashba spin-orbit coupling and illustrate how it
gives results for the collective modes, Drude weight, and spin-Hall
conductivity which are in very good agreement with the results obtained from
other more sophisticated approaches.",1710.02712v1
2017-12-13,Coupled spin and electron-phonon dynamics at the relativistic Tl/Si(111) surface,"We investigate the role played by the electron spin and the spin-orbit
interaction on the exceptional electronphonon coupling at the Tl/Si(111)
surface. Our first-principles calculations demonstrate that the particular spin
pattern of this system dominates the whole low-energy electron-phonon physics,
which is remarkably explained by forbidden spin-spin scattering channels. In
particular, we show that the strength of the electron-phonon coupling appears
drastically weakened for surface states close to the K and K' valleys, which is
unambiguously attributed to the spin polarization through the associated
modulation due to the spinor overlaps. However, close to the {\Gamma} point,
the particular spin pattern in this area is less effective in damping the
electron-phonon matrix elements, and the result is an exceptional strength of
electron-phonon coupling parameter {\lambda} ~ 1.4. These results are
rationalized by a simple model for the electron-phonon matrix elements
including the spinor terms.",1712.04868v3
2018-01-11,Blind quantum computation using the central spin Hamiltonian,"Blindness is a desirable feature in delegated computation. In the classical
setting, blind computations protect the data or even the program run by a
server. In the quantum regime, blind computing may also enable testing
computational or other quantum properties of the server system. Here we propose
a scheme for universal blind quantum computation using a quantum simulator
capable of emulating Heisenberg-like Hamiltonians. Our scheme is inspired by
the central spin Hamiltonian in which a single spin controls dynamics of a
number of bath spins. We show how, by manipulating this spin, a client that
only accesses the central spin can effectively perform blind computation on the
bath spins. Remarkably, two-way quantum communication mediated by the central
spin is sufficient to ensure security in the scheme. Finally, we provide
explicit examples of how our universal blind quantum computation enables
verification of the power of the server from classical to stabilizer to full
BQP computation.",1801.04006v1
2018-01-29,Ab initio calculation of the spin lattice relaxation time $T_1$ for nitrogen-vacancy centers in diamond,"We investigate the fundamental mechanism of spin phonon coupling in the
negatively charged nitrogen vacancy center $(\mathrm{NV}^-)$ in diamond in
order to calculate the spin lattice relaxation time $T_1$ and its temperature
dependence from first principles. Starting from the dipolar spin-spin
interaction between two electrons, we couple the spins of the electrons to the
movements of the ions and end up with an effective spin-phonon interaction
potential $V_{s-ph}$. Taking this time dependent potential as a perturbation of
the system, a Fermi's golden rule expression for transition rates is obtained
which allows to calculate the spin lattice relaxation time $T_1$. We simulate
the color center with the Vienna Ab initio Simulation Package (VASP) to extract
the figures necessary to quantify $T_1$. We investigate on the local phonon
modes of the color center within the harmonic approximation using the small
displacement method and extract the phononic density of states and
bandstructure by diagonalizing the dynamical matrix using the phononpy package.
We show that our model allows to calculate $T_1$ in good agreement with
experimental observations.",1801.09529v2
2019-07-01,Spin currents driven by the Higgs mode in magnetic superconductors,"Higgs mode in superconducting materials describes slowly-decaying
oscillations of the order parameter amplitude. We demonstrate that in magnetic
superconductors with built-in spin-splitting field Higgs mode is strongly
coupled to the spin degrees of freedom allowing for the generation of
time-dependent spin currents.
  Converting such spin currents to electric signals by spin-filtering elements
provides a tool for the second-harmonic generation and the electrical detection
of the Higgs mode generated by the external irradiation. The non-adiabatic spin
torques generated by these spin currents allow for the magnetic detection of
the Higgs mode by measuring the precession of magnetic moment in the adjacent
ferromagnet. We discuss also the reciprocal effect which is the generation of
the Higgs mode by the magnetic precession. Coupling the collective modes in
superconductors to light and magnetic dynamics opens the new direction of
superconducting optospintronics.",1907.00539v1
2019-09-11,Real-time observation of spin-resolved plexcitons between metal plasmons and excitons of WS$_2$,"Strong light-matter interactions between resonantly coupled metal plasmons
and spin decoupled bright excitons from two dimensional (2D) transition metal
dichalcogenides (TMDs) can produce discrete spin-resolved exciton-plasmon
polariton (plexciton). A few efforts have been made to perceive the spin
induced exciton-polaritons in nanocavities at cryogenic conditions, however,
successful realization of spin-resolved plexciton in time-domain is still
lacking. Here, we are able to identify both the spin-resolved plexcitons
discretely at room temperature and investigate their ultrafast temporal
dynamics in size-tunable $Au-WS_{2}$ hybrid nanostructures using femtosecond
pump-probe spectroscopy technique. Furthermore, we attribute that zero detuning
between the excitons and plasmons is achieved at $\sim$7.0 ps along with
transient Rabi-splitting energy exceeding $\sim$250 meV for both the
spin-plexcitons, validating the strong-coupling conditions of polariton
formation. Realization of these novel spin-plexcitons in the metal-TMDs
platform is, therefore, interesting for both fundamental understanding and
their possible futuristic applications in quantum photonics operating at room
temperature.",1909.05290v1
2019-09-24,Theoretical study on the slit experiments in the Rashba electron systems,"We develop a theory of designing slit experiments in two-dimensional electron
systems with the Rashba spin-orbit interaction. By simulating the
spatiotemporal dynamics of electrons passing through a single slit or a double
slit, we find that the interference fringes of the electron probability density
attain specific spin orientations via the precession of spins around effective
magnetic fields mediated by the Rashba spin-orbit interaction whose directions
are determined by the propagation path. The spin orientations of the fringes
can be controlled by tuning the Rashba spin-orbit parameter, which can be
achieved by applying an electric gate voltage. This phenomenon can be exploited
to implement electrically tunable transmission of spin information and to
generate spin-polarized currents.",1909.10725v1
2020-04-23,Nanoscale Detection of Magnon Excitations with Variable Wavevectors Through a Quantum Spin Sensor,"We report the optical detection of magnons with a broad range of wavevectors
in magnetic insulator Y3Fe5O12 thin films by proximate nitrogen-vacancy (NV)
single-spin sensors. Through multi-magnon scattering processes, the excited
magnons generate fluctuating magnetic fields at the NV electron spin resonance
frequencies, which accelerate the relaxation of NV spins. By measuring the
variation of the emitted spin-dependent photoluminescence of the NV centers,
magnons with variable wavevectors up to ~ 5 x 10^7 m-1 can be optically
accessed, providing an alternative perspective to reveal the underlying spin
behaviors in magnetic systems. Our results highlight the significant
opportunities offered by NV single-spin quantum sensors in exploring nanoscale
spin dynamics of emergent spintronic materials.",2004.11067v1
2020-12-16,Spin-dependent tunneling between individual superconducting bound states,"Magnetic impurities on superconductors induce discrete bound levels inside
the superconducting gap, known as Yu-Shiba-Rusinov (YSR) states. YSR levels are
fully spin-polarized such that the tunneling between YSR states depends on
their relative spin orientation. Here, we use scanning tunneling spectroscopy
to resolve the spin dynamics in the tunneling process between two YSR states by
experimentally extracting the angle between the spins. To this end, we exploit
the ratio of thermally activated and direct spectral features in the
measurement to directly extract the relative spin orientation between the two
YSR states. We find freely rotating spins down to 7mK, indicating a purely
paramagnetic nature of the impurities. Such a non-collinear spin alignment is
essential not only for producing Majorana bound states but also as an outlook
manipulating and moving the Majorana state onto the tip.",2012.09257v1
2000-06-05,Spin tunneling and topological selection rules for integer spins,"We present topological interference effects for the tunneling of a single
large spin, which are caused by the symmetry of a general class of magnetic
anisotropies. The interference originates from spin Berry phases associated
with different tunneling paths exposed to the same dynamics. Introducing a
generalized path integral for coherent spin states, we evaluate transition
amplitudes between ground as well as low-lying excited states. We show that
these interference effects lead to topological selection rules and spin-parity
effects for integer spins that agree with quantum selection rules and which
thus provide a generalization of the Kramers degeneracy to integer spins. Our
results apply to the molecular magnets Mn12 and Fe8.",0006075v2
2012-05-10,"Multiboson spin-wave theory for Ba2CoGe2O7, a spin-3/2 easy-plane Neel antiferromagnet with strong single-ion anisotropy","We consider the square-lattice antiferromagnetic Heisenberg Hamiltonian
extended with a single-ion axial anisotropy term as a minimal model for the
multiferroic Ba2CoGe2O7. Developing a multiboson spin-wave theory, we
investigate the dispersion of the spin excitations in this spin-3/2 system. As
a consequence of a strong single-ion anisotropy, a stretching (longitudinal)
spin-mode appears in the spectrum. The inelastic neutron scattering spectra of
Zheludev et al. [Phys. Rev. B 68, 024428 (2003)] are successfully reproduced by
the low energy modes in the multiboson spin-wave theory, and we anticipate the
appearance of the spin stretching modes at 4meV that can be identified using
the calculated dynamical spin structure factors. We expect the appearance of
spin stretching modes for any S>1/2 compound where the single-ion anisotropy is
significant.",1205.2196v2
2012-05-15,Dissipative Phase Transition in Central Spin Systems,"We investigate dissipative phase transitions in an open central spin system.
In our model the central spin interacts coherently with the surrounding
many-particle spin environment and is subject to coherent driving and
dissipation. We develop analytical tools based on a self-consistent
Holstein-Primakoff approximation that enable us to determine the complete phase
diagram associated with the steady states of this system. It includes first and
second-order phase transitions, as well as regions of bistability, spin
squeezing and altered spin pumping dynamics. Prospects of observing these
phenomena in systems such as electron spins in quantum dots or NV centers
coupled to lattice nuclear spins are briefly discussed.",1205.3341v2
2012-05-30,Circuit Quantum Electrodynamics with a Spin Qubit,"Circuit quantum electrodynamics allows spatially separated superconducting
qubits to interact via a ""quantum bus"", enabling two-qubit entanglement and the
implementation of simple quantum algorithms. We combine the circuit quantum
electrodynamics architecture with spin qubits by coupling an InAs nanowire
double quantum dot to a superconducting cavity. We drive single spin rotations
using electric dipole spin resonance and demonstrate that photons trapped in
the cavity are sensitive to single spin dynamics. The hybrid quantum system
allows measurements of the spin lifetime and the observation of coherent spin
rotations. Our results demonstrate that a spin-cavity coupling strength of 1
MHz is feasible.",1205.6767v1
2017-05-22,Out-of-Equilibrium Spin Transport in Mesoscopic Superconductors,"The excitations in conventional superconductors, Bogoliubov quasiparticles,
are spin-1/2 fermions but their charge is energy-dependent and, in fact, zero
at the gap edge. Therefore, in superconductors (unlike normal metals) the spin
and charge degrees of freedom may be separated. In this article, we review spin
injection into conventional superconductors and focus on recent experiments on
mesoscopic superconductors. We show how quasiparticle spin transport and
out-of-equilibrium spin dependent superconductivity can be triggered using the
Zeeman splitting of the quasiparticle density of states in thin-film
superconductors with small spin-mixing scattering. Finally, we address the spin
dynamics and the feedback of quasiparticle spin imbalances on the strength of
the superconducting energy gap.",1705.07770v2
2017-11-10,How many spin liquids are there in Ca$_{10}$Cr$_7$O$_{28}$?,"The search for novel phases of matter is a central theme of modern physics,
with some of the most intriguing examples provided by the spin liquids found in
magnets with competing, or ""frustrated"" interactions. Ca$_{10}$Cr$_7$O$_{28}$,
a novel spin-$1/2$ magnet with a bilayer breathing-kagome lattice, has
properties which differ from from any known spin liquid. However, understanding
Ca$_{10}$Cr$_7$O$_{28}$ presents a significant challenge, because of its
complex frustration. Here we use large-scale molecular-dynamics simulation to
explore the origin of spin-liquid behaviour in Ca$_{10}$Cr$_7$O$_{28}$. We
uncover qualitatively different behaviour on different timescales, and argue
that ground state of Ca$_{10}$Cr$_7$O$_{28}$ is born out of a
slowly-fluctuating ""spiral spin liquid"", while faster fluctuations echo the
U(1) spin liquid found in the kagome antiferromagnet. These results provide a
concrete scenario for spin-liquid behaviour in Ca$_{10}$Cr$_7$O$_{28}$, and
highlight the possibility of spin liquids existing on multiple timescales.",1711.03778v1
2018-03-28,Persistent Spin Helix Manipulation by Optical Doping of a CdTe Quantum Well,"Time-resolved Kerr-rotation microscopy explores the influence of optical
doping on the persistent spin helix in a [001]-grown CdTe quantum well at
cryogenic temperatures. Electron spin diffusion dynamics reveal a
momentum-dependent effective magnetic field providing SU(2) spin-rotation
symmetry, consistent with kinetic theory. The Dresselhaus and Rashba spin-orbit
coupling parameters are extracted independently from rotating the spin helix
with external magnetic fields applied parallel and perpendicular to the
effective magnetic field. Most importantly, a non-uniform spatiotemporal
precession pattern is observed. The kinetic theory framework of spin diffusion
allows for modeling of this finding by incorporating the photocarrier density
into the Rashba ($\alpha$) and the Dresselhaus ($\beta_3$) parameters.
Corresponding calculations are further validated by an excitation-density
dependent measurement. This work shows universality of the persistent spin
helix by its observation in a II-VI compound and the ability to fine-tune it by
optical doping.",1803.10644v1
2018-03-30,Gate-controlled anisotropy in Aharonov-Casher spin interference: signatures of Dresselhaus spin-orbit inversion and spin phases,"The coexistence of Rashba and Dresselhaus spin-orbit interactions (SOIs) in
semiconductor quantum wells leads to an anisotropic effective field coupled to
carriers' spins. We demonstrate a gate-controlled anisotropy in Aharonov-Casher
(AC) spin interferometry experiments with InGaAs mesoscopic rings by using an
in-plane magnetic field as a probe. Supported by a perturbation-theory
approach, we find that the Rashba SOI strength controls the AC resistance
anisotropy via spin dynamic and geometric phases and establish ways to
manipulate them by employing electric and magnetic tunings. Moreover, assisted
by two-dimensional numerical simulations, we identify a remarkable anisotropy
inversion in our experiments attributed to a sign change in the renormalized
linear Dresselhaus SOI controlled by electrical means, which would open a door
to new possibilities for spin manipulation.",1803.11371v2
2018-06-05,Decoherence assisted spin squeezing generation in superposition of tripartite GHZ and W states,"In the present paper, we study spin squeezing under decoherence in the
superposition of tripartite maximally entangled GHZ and W states. Here we use
amplitude damping, phase damping and depolarisation channel. We have
investigated the dynamics of spin squeezing with the interplay of superposition
and decoherence parameters with different directions of the mean spin vector.
We have found the mixture of GHZ and W states is robust against spin squeezing
generation for amplitude damping and phase damping channels for certain
directions of the mean spin vector. However, the depolarisation channel
performs well for spin squeezing generation and generates permanent spin
squeezing in the superposition of GHZ and W states.",1806.01730v1
2018-06-13,Phase-locking between different partial-waves in atom-ion spin-exchange collisions,"We present a joint experimental and theoretical study of spin dynamics of a
single $^{88}$Sr$^+$ ion colliding with an ultracold cloud of Rb atoms in
various hyperfine states. While spin-exchange between the two species occurs
after 9.1(6) Langevin collisions on average, spin-relaxation of the Sr$^+$ ion
Zeeman qubit occurs after 48(7) Langevin collisions which is significantly
slower than in previously studied systems due to a small second-order
spin-orbit coupling. Furthermore, a reduction of the endothermic spin-exchange
rate was observed as the magnetic field was increased. Interestingly, we found
that, while the phases acquired when colliding on the spin singlet and triplet
potentials vary largely between different partial waves, the singlet-triplet
phase difference, which determines the spin-exchange cross-section, remains
locked to a single value over a wide range of partial-waves which leads to
quantum interference effects.",1806.05150v2
2018-08-21,Recent advances in spin-orbit torques: Moving towards device applications,"The ability of spintronic devices to utilize an electric current for
manipulating the magnetization has resulted in large-scale developments, such
as, magnetic random access memories and boosted the spintronic research area.
In this regard, over the last decade, magnetization manipulation using
spin-orbit torque has been devoted a lot of research attention as it shows a
great promise for future ultrafast and power efficient magnetic memories. In
this review, we summarize the latest advancements in spin-orbit torque research
and highlight some of the technical challenges for practical spin-orbit torque
devices. We will first introduce the basic concepts and highlight the latest
material choices for spin-orbit torque devices. Then, we will summarize the
important advancements in the study of magnetization switching dynamics using
spin-orbit torque, which are important from scientific as well as technological
aspect. The final major section focuses on the concept of external assist field
free spin-orbit torque switching which is a requirement for practical
spin-orbit torque devices.",1808.06829v1
2019-02-17,Numerical Investigation of Spin Excitations in a Doped Spin Chain,"We study the doping evolution of spin excitations in a 1D Hubbard model and
its downfolded spin Hamiltonians, by using exact diagonalization combined with
cluster perturbation theory. In all models, we observe hardening (softening) of
spin excitations upon electron (hole) doping, which are reminiscent of recent
experiments on 2D cuprate materials. We also find that the 3-site and even
higher-order terms are crucial for the low-energy effective spin models to
reproduce the magnetic spectra of doped Hubbard systems at a quantitative
level. To interpret the numerical results, we further employ a strong coupling
slave-boson mean-field theory. The mean-field theory provides an intuitive
understanding of the overall compact support of dynamic spin structure factors,
including the shift of zero-energy modes and change of spin excitation
bandwidth with doping. Our results can serve as predictive benchmarks for
future inelastic x-ray or neutron scattering experiments on doped 1D
antiferromagnetic Mott insulators.",1902.06311v3
2019-02-27,Optimal photon energies for initialization of hybrid spin quantum registers of NV centers in diamond,"Initializing quantum registers with high fidelity is a fundamental
precondition for many applications like quantum information processing and
sensing. The electronic and nuclear spins of a Nitrogen-Vacancy (NV) center in
diamond form an interesting hybrid quantum register that can be initialized by
a combination of laser, microwave, and radio-frequency pulses. However, the
laser illumination, which is necessary for achieving electron spin
polarization, also has the unwanted side-effect of depolarizing the nuclear
spin. Here, we study how the depolarization dynamics of the $^{14}$N nuclear
spin depends on the laser wavelength. We show experimentally that excitation
with an orange laser (594 nm) causes significantly less nuclear spin
depolarization compared to the green laser (532 nm) typically used for
excitation and hence leads to higher nuclear spin polarization. This could be
because orange light excitation inhibits ionization of NV$^{0}$ into NV$^{-}$
and therefore suppresses one source of noise acting on the nuclear spin.",1902.10513v2
2019-04-04,Neural network agent playing spin Hamiltonian games on a quantum computer,"Quantum computing is expected to provide new promising approaches for solving
the most challenging problems in material science, communication, search,
machine learning and other domains. However, due to the decoherence and gate
imperfection errors modern quantum computer systems are characterized by a very
complex, dynamical, uncertain and fluctuating computational environment. We
develop an autonomous agent effectively interacting with such an environment to
solve magnetism problems. By using the reinforcement learning the agent is
trained to find the best-possible approximation of a spin Hamiltonian ground
state from self-play on quantum devices. We show that the agent can learn the
entanglement to imitate the ground state of the quantum spin dimer. The
experiments were conducted on quantum computers provided by IBM. To compensate
the decoherence we use local spin correction procedure derived from a general
sum rule for spin-spin correlation functions of a quantum system with even
number of antiferromagnetically-coupled spins in the ground state. Our study
paves a way to create a new family of the neural network eigensolvers for
quantum computers.",1904.02467v2
2020-05-03,Subterahertz spin pumping from an insulating antiferromagnet,"Spin-transfer torque and spin Hall effects combined with their reciprocal
phenomena, spin-pumping and inverse spin Hall (ISHE) effects, enable the
reading and control of magnetic moments in spintronics. The direct observation
of these effects remains elusive in antiferromagnetic-based devices. We report
sub-terahertz spin-pumping at the interface of a uniaxial insulating
antiferromagnet MnF2 and platinum. The measured ISHE voltage arising from
spin-charge conversion in the platinum layer depends on the chirality of the
dynamical modes of the antiferromagnet, which is selectively excited and
modulated by the handedness of the circularly polarized sub-THz irradiation.
Our results open the door to the controlled generation of coherent pure spin
currents at THz frequencies.",2005.01203v1
2020-06-11,Observation of a strongly ferromagnetic spinor Bose-Einstein condensate,"We report the observation of strongly ferromagnetic $F=1$ spinor
Bose-Einstein condensates of $^7$Li atoms. The condensates are generated in an
optical dipole trap without using magnetic Feshbach resonances, so that the
condensates have internal spin degrees of freedom. Studying the non-equilibrium
spin dynamics, we have measured the ferromagnetic spin interaction energy and
determined the $s$-wave scattering length difference among total spin $f$
channels to be $a_{f=2}-a_{f=0} =-18(3)$ Bohr radius. This strong
collision-channel dependence leads to a large variation in the condensate size
with different spin composition. We were able to excite a radial monopole mode
after a spin-flip transition between the $|m_F=0\rangle$ and $|m_F=1\rangle$
spin states. From the experiments, we estimated the scattering length ratio
$a_{f=2}/a_{f=0}=0.27(6)$, and determined $a_{f=2}$ = 7(2) and $a_{f=0}$ =
25(5) Bohr radii, respectively. The results indicate the spin-dependent
interaction energy of our system is as large as 46$\%$ of the condensate
chemical potential.",2006.06228v1
2020-06-24,Magnetic order and ballistic spin transport in a sine-Gordon spin chain,"We report the results of muon-spin spectroscopy ($\mu^+$SR) measurements on
the staggered molecular spin chain [pym-Cu(NO$_3$)$_2$(H$_2$O)$_2$] (pym =
pyrimidine), a material previously described using sine-Gordon field theory.
Zero-field $\mu^+$SR reveals a long range magnetically-ordered ground state
below a transition temperature $T_\mathrm{N}=0.22(1)$ K. Using
longitudinal-field (LF) $\mu^+$SR we investigate the dynamic response in
applied magnetic fields $0< B < 500$ mT and find evidence for ballistic spin
transport. Our LF $\mu^+$SR measurements on the chiral spin chain
[Cu(pym)(H$_2$O)$_4$]SiF$_6 \cdot $H$_2$O instead demonstrate one-dimensional
spin diffusion and the distinct spin transport in these two systems likely
reflects differences in their magnetic excitations.",2006.13743v1
2020-08-19,Non-axisymmetric flow characteristics in Head-on Collision of Spinning Droplets,"Effects of spinning motion on the bouncing and coalescence between a spinning
droplet and a non-spinning droplet undergoing the head-on collision were
numerically studied by using a Volume-of-Fluid method. A prominent discovery is
that the spinning droplet can induce significant non-axisymmetric flow features
for the head-on collision of equal-size droplets composed of the same liquid.
Specifically, a non-axisymmetric bouncing was observed, and it is caused by the
conversion of the spinning angular momentum into the orbital angular momentum.
This process is accompanied by the rotational kinetic energy loss due to the
interaction between the rotational and radial flows of the droplets. A
non-axisymmetric internal flow and a delayed separation after temporary
coalescence were also observed, and they are caused by the enhanced interface
oscillation and internal-flow-induced viscous dissipation. The spinning motion
can also promote the mass interminglement of droplets because the locally
non-uniform mass exchange occurs at the early collision stage by
non-axisymmetric flow and is further stretched along the filament at later
collision stages. In addition, it is found that the non-axisymmetric flow
features increase with increasing the orthogonality of the initial
translational motion and the spinning motion of droplets.",2008.08343v1
2020-08-24,Wigner negativity in spin-$j$ systems,"The nonclassicality of simple spin systems as measured by Wigner negativity
is studied on a spherical phase space. Several SU(2)-covariant states with
common qubit representations are addressed: spin coherent, spin cat (GHZ/N00N),
and Dicke ($\textsf{W}$). We derive a bound on the Wigner negativity of spin
cat states that rapidly approaches the true value as spin increases beyond $j
\gtrsim 5$. We find that spin cat states are not significantly Wigner-negative
relative to their Dicke state counterparts of equal dimension. We also find, in
contrast to several entanglement measures, that the most Wigner-negative Dicke
basis element is spin-dependent, and not the equatorial state $| j,0 \rangle$
(or $|j,\pm 1/2 \rangle$ for half-integer spins). These results underscore the
influence that dynamical symmetry has on nonclassicality, and suggest a guiding
perspective for finding novel quantum computational applications.",2008.10167v1
2020-08-27,Incommensurate Spin Fluctuations in the Spin-triplet Superconductor Candidate UTe$_2$,"Spin-triplet superconductors are of extensive current interest because they
can host topological state and Majorana ferimons important for quantum
computation. The uranium based heavyfermion superconductor UTe$_2$ has been
argued as a spin-triplet superconductor similar to UGe$_2$, URhGe, and UCoGe,
where the superconducting phase is near (or coexists with) a ferromagnetic (FM)
instability and spin-triplet electron pairing is driven by FM spin
fluctuations. Here we use neutron scattering to show that although UTe$_2$
exhibits no static magnetic order down to 0.3 K, its magnetism is dominated by
incommensurate spin fluctuations near antiferromagnetic (AF) ordering wave
vector and extends to at least 2.6 meV. We are able to understand the dominant
incommensurate spin fluctuations of UTe$_2$ in terms of its electronic
structure calculated using a combined density functional and dynamic mean field
theory.",2008.12377v1
2020-09-09,Superconductivity-enhanced spin pumping: Role of Andreev resonances,"We describe a simple hybrid superconductor$|$ferromagnetic-insulator
structure manifesting spin-resolved Andreev bound states in which dynamic
magnetization is employed to probe spin related physics. We show that, at low
bias and below $T_c$, the transfer of spin angular momentum pumped by an
externally driven ferromagnetic insulator is greatly affected by the formation
of spin-resolved Andreev bound states. Our results indicate that these bound
states capture the essential physics of condensate-facilitated spin flow. For
finite thicknesses of the superconducting layer, comparable to the coherence
length, resonant Andreev bound states render highly transmitting subgap spin
transport channels. We point out that the resonant enhancement of the subgap
transport channels establishes a prototype Fabry-P\'erot resonator for spin
pumping.",2009.04423v4
2020-10-15,Emergent Bloch oscillations in a kinetically constrained Rydberg spin lattice,"We explore the relaxation dynamics of elementary spin clusters of a
kinetically constrained spin system. Inspired by experiments with Rydberg
lattice gases, we focus on the situation in which an excited spin leads to a
""facilitated"" excitation of a neighboring spin. We show that even weak
interactions that extend beyond nearest neighbors can have a dramatic impact on
the relaxation behavior: they generate a linear potential, which under certain
conditions leads to the onset of Bloch oscillations of spin clusters. These
hinder the expansion of a cluster and more generally the relaxation of
many-body states towards equilibrium. This shows that non-ergodic behavior in
kinetically constrained systems may occur as a consequence of the interplay
between reduced connectivity of many-body states and weak interparticle
interactions. We furthermore show that the emergent Bloch oscillations
identified here can be detected in experiment through measurements of the
Rydberg atom density, and discuss how spin-orbit coupling between internal and
external degrees of freedom of spin clusters can be used to control their
relaxation behavior.",2010.07825v2
2020-11-07,A hydrodynamic study of hyperon spin polarization in relativistic heavy ion collisions,"We perform a systematic study of the spin polarization of hyperons in
heavy-ion collisions using the MUSIC hydrodynamic model with A Multi-Phase
Transport (AMPT) pre-equilibrium dynamics. Our model calculations nicely
describe the measured collision-energy, centrality, rapidity, and $p_T$
dependence of $\Lambda$ polarization. We also study and predict the global spin
polarization of $\Xi^-$ and $\Omega^-$ as a function of collision energy, which
provides a baseline for the studies of the magnetic moment, spin, and mass
dependence of the spin polarization. For the local spin polarization, we
calculate the radial and azimuthal components of the transverse $\Lambda$
polarization and find specific modulating behavior which could reflect the
circular vortical structure. However, our model fails to describe the
azimuthal-angle dependence of the longitudinal and transverse $\Lambda$
polarization, which indicates that the hydrodynamic framework with the spin
Cooper-Frye formula under the assumption of thermal equilibrium of spin degree
of freedom needs to be improved.",2011.03740v2
2021-02-08,"Deep optical cooling of coupled nuclear spin-spin and quadrupole reservoirs in a GaAs/(Al,Ga)As quantum well","The selective cooling of $^{75}$As spins by optical pumping followed by
adiabatic demagnetization in the rotating frame is realized in a nominally
undoped GaAs/(Al,Ga)As quantum well. The rotation of 6 kG strong Overhauser
field at the $^{75}$As Larmor frequency of 5.5 MHz is evidenced by the dynamic
Hanle effect. Despite the presence of the quadrupole induced nuclear spin
splitting, it is shown that the rotating $^{75}$As magnetization is uniquely
determined by the spin temperature of coupled spin-spin and quadrupole
reservoirs. The dependence of heat capacity of these reservoirs on the external
magnetic field direction with respect to crystal and structure axes is
investigated. The lowest nuclear spin temperature achieved is 0.54 $\mu$K,
which is the record low value for semiconductors and semiconductor
nanostructures.",2102.04153v1
2021-03-01,Electron-induced nuclear magnetic ordering in n-type semiconductors,"Nuclear magnetism in n-doped semiconductors with positive hyperfine constant
is revisited. Two kinds of nuclear magnetic ordering can be induced by resident
electrons in a deeply cooled nuclear spin system. At positive nuclear spin
temperature below a critical value, randomly oriented nuclear spin polarons
similar to that predicted by I. Merkulov [I. Merkulov, Physics of the Solid
State 40, 930 (1998)] should emerge. These polarons are oriented randomly and
within each polaron nuclear and electron spins are aligned
antiferromagnetically. At negative nuclear spin temperature below a critical
value we predict another type of magnetic ordering - dynamically induced
nuclear ferromagnet. This is a long-range ferromagnetically ordered state
involving both electrons and nuclei. It can form if electron spin relaxation is
dominated by the hyperfine coupling, rather than by the spin-orbit interaction.
Application of the theory to the n-doped GaAs suggests that the ferromagnetic
order may be reached at experimentally achievable nuclear spin temperature
$\Theta_N \approx 0.5$ $\mu$K and lattice temperature $T_L \approx 5$ K.",2103.01120v1
2021-03-26,Gravitational radiation from inspiralling compact objects: Spin-spin effects completed at the next-to-leading post-Newtonian order,"Using the gravitational potential and source multipole moments bilinear in
the spins, first computed to next-to-leading order (NLO) in the post-Newtonian
(PN) expansion within the effective field theory (EFT) framework, we complete
here the derivation of the dynamical invariants and flux-balance equations,
including energy and angular momentum. We use these results to calculate
spin-spin effects in the orbital frequency and accumulated phase to NLO for
circular orbits. We also derive the linear momentum and center-of-mass fluxes
and associated kick-velocity, to the highest relevant PN order. We explicitly
demonstrate the equivalence between the quadratic-in-spin source multipoles
obtained using the EFT formalism and those rederived later with more
traditional tools, leading to perfect agreement for spin-spin radiative
observables to NLO among both approaches.",2103.14612v1
2021-03-29,Photonic spin lattices: symmetry constraints for skyrmion and meron topologies,"Symmetry governs many electronic and photonic phenomena in optics and
condensed matter physics. Skyrmions and merons are prominent topological
structures in magnetic materials, with the topological features determined by
the interplay between anisotropy of a material and its magnetization. Here we
theoretically show and experimentally demonstrate that the symmetry of the
electromagnetic field determines the spin topological properties of the guided
modes via spin-orbit coupling and may only result in either hexagonal
spin-skyrmion or square spin-meron lattices. We also show that in the absence
of spin-orbit coupling these spin topologies are degenerated in dynamic
field-skyrmions, unifying description of electromagnetic field topologies. The
results provide new understanding of electromagnetic field topology and its
transformations as well as new opportunities for applications in quantum
optics, spin-optics and topological photonics.",2103.15366v1
2021-03-29,Spin Dynamics of Extrasolar Giant Planets in Planet-Planet Scattering,"Planet-planet scattering best explains the eccentricity distribution of
extrasolar giant planets. Past literature showed that the orbits of planets
evolve due to planet-planet scattering. This work studies the spin evolution of
planets in planet-planet scattering in 2-planet systems. Spin can evolve
dramatically due to spin-orbit coupling made possible by the evolving spin and
orbital precession during the planet-planet scattering phase. The main source
of torque to planet spin is the stellar torque, and the total planet-plane
torque contribution is negligible. As a consequence of the evolution of the
spin, planets can end up with significant obliquity (the angle between a
planet's own orbit normal and spin axis) like planets in our Solar System.",2103.15902v1
2021-04-07,Acoustically induced coherent spin trapping,"Hybrid spin-optomechanical quantum systems offer high flexibility,
integrability and applicability for quantum science and technology.
Particularly, on-chip surface acoustic waves (SAWs) can efficiently drive spin
transitions in the ground states (GSs) of atomic-scale, color centre qubits,
which are forbidden in case of the more frequently used electromagnetic fields.
Here, we demonstrate that strain-induced spin interactions within their
optically excited state (ES) can exceed by two orders of magnitude the ones
within the GS. This gives rise to novel physical phenomena, such as the
acoustically induced coherent spin trapping (CST) unvealed here. The CST
manifests itself as the spin preservation along one particular direction under
the coherent drive of the GS and ES by the same acoustic field. Our findings
provide new opportunities for the coherent control of spin qubits with
dynamically generated strain fields that can lead towards the realization of
future spin-acoustic quantum devices.",2104.03011v1
2021-04-21,Spin-wave driven bidirectional domain wall motion in kagome antiferromagnets,"We predict a mechanism to controllably manipulate domain walls in kagome
antiferromagnets via a single linearly polarized spin-wave source. We show by
means of atomistic spin dynamics simulations of antiferromagnets with kagome
structure that the speed and direction of the domain wall motion can be
regulated by only tuning the frequency of the applied spin-wave. Starting from
microscopics, we establish an effective action and derive the corresponding
equations of motion for the spin-wave-driven domain wall. Our analytical
calculations reveal that the coupling of two spin-wave modes inside the domain
wall explains the frequency-dependent velocity of the spin texture. Such a
highly tunable spin-wave-induced domain wall motion provides a key component
toward next-generation fast, energy-efficient, and Joule-heating-free
antiferromagnetic insulator devices.",2104.10460v2
2021-04-30,Unstable binary black-hole spins: post-Newtonian theory and numerical relativity,"Spin precession occurs in binary black holes whose spins are misaligned with
the orbital angular momentum. Otherwise, the spin configuration is constant and
the subsequent binary dynamics and gravitational-wave emission are much
simpler. We summarize a series of works which has shown that, while three of
the aligned configurations are stable equilibria, the `up-down' configuration,
in which the heavier (lighter) black hole is (anti) aligned with the orbital
angular momentum, is unstable when perturbed; at a critical point in the
inspiral the black hole spins begin to tilt wildly as precession takes over. We
present two equivalent approaches to derive the instability onset based on
multitimescale post-Newtonian techniques, and point out that the instability
has a predictable endpoint. Finally, we demonstrate the presence of this
precessional instability in the strong-field regime of numerical relativity
with simulations of aligned-spin binaries lasting $\sim100$ orbits before
merger. The spins of up-down systems can tilt by $\sim90^\circ$, leaving a
notable imprint in the emitted gravitational-wave signals and providing a
possible mechanism to form precessing systems in astrophysical environments
from which sources are preferentially born with (anti) aligned spins.",2104.15011v1
2021-05-12,Probing Strong Coupling between a Microwave Cavity and a Spin Ensemble with Raman Heterodyne Spectroscopy,"Raman heterodyne spectroscopy is a powerful tool for characterizing the
energy and dynamics of spins. The technique uses an optical pump to transfer
coherence from a spin transition to an optical transition where the coherent
emission is more easily detected.
  Here Raman heterodyne spectroscopy is used to probe an isotopically purified
ensemble of erbium dopants, in a yttrium orthosilicate (Y$_2$SiO$_5$) crystal
coupled to a microwave cavity. Because the erbium electron spin transition is
strongly coupled to the microwave cavity, we observed Raman heterodyne signals
at the resonant frequencies of the hybrid spin-cavity modes (polaritons) rather
than the bare erbium spin transition frequency. Using the coupled system, we
made saturation recovery measurements of the ground state spin relaxation time
T$_1$ = 10$\pm$3 seconds, and also observed Raman heterodyne signals using an
excited state spin transition. We discuss the implications of these results for
efforts towards converting microwave quantum states to optical quantum states.",2105.05387v1
2021-06-05,Extraordinary transverse spin: Hidden vorticity of the energy flow and momentum distributions in propagating light fields,"Spatially inhomogeneous fields of electromagnetic guided modes exhibit a
complex of extraordinary dynamical properties such as the
polarization-dependent transverse momentum, helicity-independent transverse
spin, spin-associated non-reciprocity and unidirectional propagation, etc.
Recently, the remarkable relationship has been established between the spin and
propagation features of such fields, expressed through the spin-momentum
equations [Proc. Natl. Acad. Sci. 118 (2021) e2018816118] connecting the wave
spin with the curl of momentum. Here, the meaning, limitations and specific
forms of this correspondence are further investigated, involving the physically
transparent and consistent examples of paraxial light fields, plane-wave
superpositions and evanescent waves. The conclusion is inferred that the
spin-momentum equation is an attribute of guided waves with well defined
direction of propagation, and it unites the helicity-independent
""extraordinary"" transverse spin with the spatially-inhomogeneous longitudinal
field momentum (energy flow) density. Physical analogies with the layered
hydrodynamic flows and possible generalizations for other wave fields are
discussed. The results can be useful in optical trapping, manipulation and the
data processing techniques.",2106.02849v1
2021-06-07,"Binding Sites, Vibrations and Spin-Lattice Relaxation Times in Europium(II)-based Metallofullerene Spin Qubits","To design molecular spin qubits with enhanced quantum coherence, a control of
the coupling between the local vibrations and the spin states is crucial, which
could be realized in principle by engineering molecular structures via
coordination chemistry. To this end, understanding the underlying structural
factors that govern the spin relaxation is a central topic. Here, we report the
investigation of the spin dynamics in a series of chemically-designed
europium(II)-based endohedral metallofullerenes (EMFs). By introducing a unique
structural difference, i.e. metal-cage binding site, while keeping other
molecular parameters constant between different complexes, these manifest the
key role of the three low energy metal-based vibrations in mediating the
spin-lattice relaxation times (T1). The temperature dependence of T1 can thus
be normalized by the frequencies of these low energy vibrations to show an
unprecedentedly universal behavior for EMFs in frozen CS2 solution. Our
theoretical analysis indicates that this structural difference determines not
only the vibrational rigidity but also spin-vibration coupling in these
EMF-based qubit candidates.",2106.03633v1
2021-06-11,The origin of chirality induced spin selectivity in photo-induced electron transfer,"Here we propose a mechanism by which spin polarization can be generated
dynamically in chiral molecular systems undergoing photo-induced electron
transfer. The proposed mechanism explains how spin polarization emerges in
systems where charge transport is dominated by incoherent hopping, mediated by
spin orbit and electronic exchange couplings through an intermediate charge
transfer state. We derive a simple expression for the spin polarization that
predicts a non-monotonic temperature dependence consistent with recent
experiments. We validate this theory using approximate quantum master equations
and the numerically exact hierarchical equations of motion. The proposed
mechanism of chirality induced spin selectivity should apply to many chiral
systems, and the ideas presented here have implications for the study of spin
transport at temperatures relevant to biology, and provide simple principles
for the molecular control of spins in fluctuating environments.",2106.06554v1
2021-07-01,Van der Waals Magnet based Spin-Valve Devices at Room Temperature,"The discovery of van der Waals (vdW) magnets opened up a new paradigm for
condensed matter physics and spintronic technologies. However, the operations
of active spintronic devices with vdW magnets are so far limited to cryogenic
temperatures, inhibiting its broader practical applications. Here, for the
first time, we demonstrate room temperature spin-valve devices using vdW
itinerant ferromagnet Fe5GeTe2 in heterostructures with graphene. The tunnel
spin polarization of the Fe5GeTe2/graphene vdW interface is detected to be
significantly large ~ 45 % and negative at room temperature. Lateral spin-valve
device design enables electrical control of spin signal and realization of
basic building blocks for device application such as efficient spin injection,
transport, precession, and detection functionalities. Furthermore, measurements
with different magnetic orientations provide unique insights into the magnetic
anisotropy of Fe5GeTe2 and its relation with spin polarization and dynamics in
the heterostructure. These findings open opportunities for the applications of
vdW magnet-based all-2D spintronic devices and integrated spin circuits at
ambient temperatures.",2107.00310v1
2021-07-16,Spinning test particle motion around a traversable wormhole,"The motion of spinning test particles around a traversable wormhole is
investigated using the Mathisson Papapetrous Dixon equations, which couple the
Riemann tensor with the antisymmetric tensor $S^{ab}$, related to the spin of
the particle. Hence, we study the effective potential, circular orbits, and
innermost stable circular orbit ISCO of spinning particles. We found that the
spin affects significantly the location of the ISCO, in contrast with the
motion of nonspinning particles, where the ISCO is the same in both the upper
and lower universes. On the other hand, since the dynamical fourmomentum and
kinematical fourvelocity of the spinning particle are not always parallel, we
also consider a superluminal bound on the particles motion. In the case of
circular orbits at the ISCO, we found that the motion of particles with an
adimensional spin parameter lower greater than $s=-1.5$ $(1.5)$ is forbidden.
The spin interaction becomes important for Kerr black hole orbiting super
massive wormholes SMWH.",2107.07998v1
2021-07-19,Dimensional reduction by geometrical frustration in a cubic antiferromagnet composed of tetrahedral clusters,"Dimensionality is a critical factor in determining the properties of solids
and is an apparent built-in character of the crystal structure. However, it can
be an emergent and tunable property in geometrically frustrated spin systems.
Here, we study the spin dynamics of the tetrahedral cluster antiferromagnet,
pharmacosiderite, via muon spin resonance and neutron scattering. We find that
the spin correlation exhibits a two-dimensional characteristic despite the
isotropic connectivity of tetrahedral clusters made of spin 5/2 Fe3+ ions in
the three-dimensional cubic crystal, which we ascribe to two-dimensionalisation
by geometrical frustration based on spin wave calculations. Moreover, we
suggest that even one-dimensionalisation occurs in the decoupled layers,
generating low-energy and one-dimensional excitation modes, causing large spin
fluctuation in the classical spin system. Pharmacosiderite facilitates studying
the emergence of low-dimensionality and manipulating anisotropic responses
arising from the dimensionality using an external magnetic field.",2107.08735v1
2021-07-21,Nonmonotonic quantum phase gathering in curved spintronic circuits,"Spin carriers propagating along quantum circuits gather quantum spin phases
depending on the circuit's size, shape, and spin-orbit coupling (SOC) strength.
These phases typically grow monotonically with the SOC strength, as found in
Rashba quantum wires and rings. In this work we show that the spin-phase
gathering can be engineered by geometric means, viz. by the geometric curvature
of the circuits, to be non-monotonic. We demonstrate this peculiar property by
using one-dimensional polygonal models where flat segments alternate with
highly curved vertices. The complex interplay between dynamic and geometric
spin-phase components -- triggered by a series of emergent spin degeneracy
points -- leads to bounded, global spin phases. Moreover, we show that the
particulars of the spin-phase gathering have observable consequences in the
Aharonov-Casher conductance of Rashba loops, a connection that passed unnoticed
in previous works.",2107.10192v4
2021-10-06,Dissipation-assisted preparation of steady spin-squeezed states of SiV centers,"We propose an efficient scheme for generating spin-squeezed states at steady
state in a spin-mechanical hybrid system, where an ensemble of SiV centers are
coupled to a strongly damped nanomechanical resonator. We show that,there
exists a collective steady state in the system, which is exactly formed by the
collective spin states plus the zero excitation state of the mechanical mode.
The generation of the steady spin-squeezed state is based on a dissipative
quantum dynamical process in which the mechanical dissipation plays a positive
role but without destroying the target state. We demonstrate that the
spin-squeezed steady state can be deterministically prepared via dissipative
means, with the optimal spin squeezing up to 4/N in the ideal case, where N is
the number of spins. This work provides a promising platform for quantum
information processing and quantum metrology.",2110.02837v1
2021-10-24,Spin dynamics in the skyrmion-host lacunar spinel GaV4S8,"In the lacunar spinel GaV4S8, the interplay of spin, charge, and orbital
degrees of freedom produces a rich phase diagram that includes an unusual
Neel-type skyrmion phase composed of molecular spins. To provide insight into
the interactions underlying this complex phase diagram, we study the spin
excitations in GaV4S8 through inelastic neutron scattering measurements on
polycrystalline and single-crystal samples. Using linear spin-wave theory, we
describe the spin-wave excitations using a model where V4 clusters decorate an
FCC lattice. The effective cluster model includes a ferromagnetic interaction
and a weaker antisymmetric Dzyaloshinskii-Moriya (DM) interaction between the
neighboring molecular spins. Our work clarifies the spin interactions in GaV4S8
and supports the picture of interacting molecular clusters.",2110.12322v2
2021-12-03,Spin polarization dynamics in the non-boost-invariant background,"Space-time evolution of spin polarization within the framework of
hydrodynamics with spin based on de Groot - van Leeuwen - van Weert forms of
energy-momentum and spin tensors is studied. Due to the non-boost invariant
flow in the system the spin polarization components couple to each other
implying some effects on the spin polarization observables. We study
transverse-momentum and rapidity dependence of mean spin polarization vector
for $\Lambda$ hyperons. Our results show qualitative agreement for rapidity
dependence of the global spin polarization with the experiments and other
models. The quadrupole structure of the longitudinal component at midrapidity
is not found, however, as compared to the results for Bjorken expansion, some
non-trivial signal at forward rapidities is observed.",2112.01856v2
2021-12-22,Modified coherence of quantum spins in a damped pure-dephasing model,"We consider a spin-$j$ particle coupled to a structured bath of bosonic modes
that decay into thermal baths. We obtain an analytic expression for the reduced
spin state and use it to investigate non-Markovian spin dynamics. In the
heavily overdamped regime, spin coherences are preserved due to a quantum Zeno
affect. We extend the solution to two spins and include coupling between the
modes, which can be leveraged for preservation of the symmetric spin subspace.
For many spins, we find that inter-mode coupling gives rise to a privileged
symmetric mode gapped from the other modes. This provides a handle to
selectively address that privileged mode for quantum control of the collective
spin. Finally, we show that our solution applies to defects in solid-state
systems, such as NV$^{-}$ centres in diamond.",2112.11711v2
2021-12-28,Superfluid Spin Transistor,"We propose to use the Hall response of topological defects, such as merons
and antimerons, to spin currents in 2D magnetic insulator with in-plane
anisotropy for identification of the Berezinskii-Kosterlitz-Thouless (BKT)
transition in a transistor-like geometry. Our numerical results relying on a
combination of Monte Carlo and spin dynamics simulations show transition from
spin superfluidity to conventional spin transport, accompanied by the universal
jump of the spin stiffness and exponential growth of the transverse vorticity
current. We propose a superfluid spin transistor in which the spin and
vorticity currents are modulated by tuning the in-plane magnet across BKT
transition, e.g., by changing the exchange interaction, magnetic anisotropy, or
temperature.",2112.14241v2
2022-01-14,An Anderson impurity interacting with the helical edge states in a quantum spin Hall insulator,"Using the natural orbitals renormalization group (NORG) method, we have
investigated the screening of the local spin of an Anderson impurity
interacting with the helical edge states in a quantum spin Hall insulator. We
find that there is a local spin formed at the impurity site and the local spin
is completely screened by electrons in the quantum spin Hall insulator.
Meanwhile, the local spin is screened dominantly by a single active natural
orbital. We then show that the Kondo screening mechanism becomes transparent
and simple in the framework of natural orbitals formalism. We project the
active natural orbital respectively into real space and momentum space to
characterize its structure. And we confirm the spin-momentum locking property
of the edge states based on the occupancy of a Bloch state in the edge to which
the impurity couples. Furthermore, we study the dynamical property of the
active natural orbital represented by the local density of states, from which
we observe the Kondo resonance peak.",2201.05308v1
2022-01-22,Elasto-Dynamical Induced Spin and Charge Pumping in Bulk Heavy Metals,"Analogous to the Spin-Hall Effect (SHE), {\it ab initio} electronic structure
calculations reveal that acoustic phonons can induce charge (spin) current
flowing along (normal to) its propagation direction. Using Floquet approach we
have calculated the elastodynamical-induced charge and spin pumping in bulk Pt
and demonstrate that: (i) While the longitudinal charge pumping is an intrinsic
observable, the transverse pumped spin-current has an extrinsic origin that
depends strongly on the electronic relaxation time; (ii) The longitudinal
charge current
  is of nonrelativstic origin, while the transverse spin current is a
relativistic effect that to lowest order scales linearly with the spin-orbit
coupling strength; (iii) both charge and spin pumped currents have parabolic
dependence on the amplitude of the elastic wave.",2201.09121v1
2022-04-19,Effects of spin-exchange collisions on the fluctuation spectra of hot alkali-metal vapors,"We present a first-principles analysis of the noise spectra of
alkali-metal-metal vapors in and out of the spin-exchange-relaxation-free
(SERF) regime, and we predict non-intuitive features with a potential to
further improve the sensitivity of SERF media, and which must be taken into
account in their use in quantum optical applications. Studying the process of
spin-noise spectroscopy (SNS), we derive analytic formulas for the observable
noise spectra, and for the correlation functions among different hyperfine
components, which give additional insight into the spin dynamics. The analytic
results indicate a variety of distortions of the spin-noise spectrum relative
to simpler models, including a broad spectral background that mimics optical
shot noise, interference of noise contributions from the two ground-state
hyperfine levels, noise reduction at the spin-precession frequency, and
``hiding'' of spin-noise power that can introduce a systematic error in
noise-based calibrations, e.g., for spin-squeezing experiments.",2204.08748v3
2022-06-23,Anisotropic magnon damping by zero-temperature quantum fluctuations in ferromagnetic CrGeTe$_3$,"Spin and lattice are two fundamental degrees of freedom in a solid, and their
fluctuations about the equilibrium values in a magnetic ordered crystalline
lattice form quasiparticles termed magnons (spin waves) and phonons (lattice
waves), respectively. In most materials with strong spin-lattice coupling
(SLC), the interaction of spin and lattice induces energy gaps in the spin wave
dispersion at the nominal intersections of magnon and phonon modes. Here we use
neutron scattering to show that in the two-dimensional (2D) van der Waals
honeycomb lattice ferromagnetic CrGeTe3, spin waves propagating within the 2D
plane exhibit an anomalous dispersion, damping, and break-down of quasiparticle
conservation, while magnons along the c axis behave as expected for a local
moment ferromagnet. These results indicate the presence of dynamical SLC
arising from the zero-temperature quantum fluctuations in CrGeTe3, suggesting
that the observed in-plane spin waves are mixed spin and lattice quasiparticles
fundamentally different from pure magnons and phonons.",2206.11962v1
2022-07-06,Microscopic origin of the effective spin-spin interaction in a semiconductor quantum dot ensemble,"We present a microscopic model for a singly charged quantum dot (QD) ensemble
to reveal the origin of the long-range effective interaction between the
electron spins in the QDs. Wilson's numerical renormalization group (NRG) is
used to calculate the magnitude and the spatial dependency of the effective
spin-spin interaction mediated by the growth induced wetting layer.
Surprisingly, we found an antiferromagnetic Heisenberg coupling for very short
inter-QD distances that is caused by the significant particle-hole asymmetry of
the wetting layer band at very low filling. Using the NRG results obtained from
realistic parameters as input for a semiclassical simulation for a large QD
ensemble, we demonstrate that the experimentally reported phase shifts in the
coherent spin dynamics between single and two color laser pumping can be
reproduced by our model, solving a longstanding mystery of the microscopic
origin of the inter QD electron spin-spin interaction.",2207.02707v2
2022-07-06,Electron induced nanoscale nuclear spin relaxation probed by hyperpolarization injection,"We report on experiments that quantify the role of a central electronic spin
as a relaxation source for nuclear spins in its nanoscale environment. Our
strategy exploits hyperpolarization injection from the electron as a means to
controllably probe an increasing number of nuclear spins in the bath, and
subsequently interrogate them with high fidelity. Our experiments are focused
on a model system of a nitrogen vacancy (NV) center electronic spin surrounded
by several hundred 13C nuclear spins. We observe that the 13C transverse spin
relaxation times vary significantly with the extent of hyperpolarization
injection, allowing the ability to measure the influence of electron mediated
relaxation extending over several nanometers. These results suggest interesting
new means to spatially discriminate nuclear spins in a nanoscale environment,
and have direct relevance to dynamic nuclear polarization and quantum sensors
and memories constructed from hyperpolarized nuclei.",2207.02827v2
2022-07-14,Dzyaloshinskii-Moriya spin density by skew scattering,"Anisotropic exchange couplings, such as the Dzyaloshinskii-Moriya interaction
(DMI), have played a vital role in the formation and dynamics of spin textures.
This work predicts an anisotropic conduction electron spin density in metals
with heavy magnetic impurities. The polarization of this
$Dzyaloshinskii$-$Moriya$ $spin$ $density$ (DM-SD) is not collinear to the
localized magnetic moments but rotated by the spin-dependent skew scattering of
heavy atoms. The DM-SD induces the DMI between magnetic moments in metals and,
therefore, it is the anisotropic extension of the
Rutherman-Kittel-Kasuya-Yoshida spin density. Our model consists of two
localized magnetic moments, one with a large spin-orbit coupling (a lanthanide
or rare earth), in a free electron gas. The lanthanide spin controls the DM-SD
strength and polarization, promising a flexible control mechanism for
anisotropic couplings.",2207.06842v2
2022-11-07,Determining Perpendicular Magnetic Anisotropy in Fe/MgO/Fe Magnetic Tunnel Junction: A DFT-Based Spin-Orbit Torque Method,"In our JunPy package, we have combined the first-principles calculated
self-consistent Hamiltonian with divide-and-conquer technique to successfully
determine the magnetic anisotropy (MA) in an Fe/MgO/Fe magnetic tunnel junction
(MTJ). We propose a comprehensive analytical derivation to clarify the crucial
roles of spin-orbit coupling that mediates the exchange and spin-orbit
components of spin torque, and the kinetic and spin-orbit components of spin
current accumulation. The angular dependence of cumulative spin-orbit torque
(SOT) indicates a uniaxial MA corresponding to the out-of-plane rotations of
magnetic moments of the free Fe layers. Different from the conventional MA
energy calculation and the phenomenological theory for a whole MTJ, our results
provide insight into the orbital-resolved SOT for atomistic spin dynamics
simulation in emergency complex magnetic heterojunctions.",2211.03603v3
2022-12-14,Spin singlet topological superconductivity in the attractive Rashba Hubbard model,"Fully gapped, spin singlet superconductors with antisymmetric spin-orbit
coupling in a Zeeman magnetic field provide a promising route to realize
superconducting states with non-Abelian topological order and therefore
fault-tolerant quantum computation. Here we use a quantum Monte Carlo dynamical
cluster approximation to study the superconducting properties of a doped
two-dimensional attractive Hubbard model with Rashba spin-orbit coupling in a
Zeeman magnetic field. We generally find that the Rashba coupling has a
beneficial effect towards s-wave superconductivity. In the presence of a finite
Zeeman field, when superconductivity is suppressed by Pauli pair-breaking, the
Rashba coupling counteracts the spin imbalance created by the Zeeman field by
mixing the spins, and thus restores superconductivity at finite temperatures.
We show that this favorable effect of the spin-orbit coupling is traced to a
spin-flip driven enhancement of the amplitude for the propagation of a pair of
electrons in time-reversed states. Moreover, by inspecting the Fermi surface of
the interacting model, we show that for sufficiently large Rashba coupling and
Zeeman field, the superconducting state is expected to be topologically
non-trivial.",2212.07251v1
2022-12-15,Identification of acoustically induced spin resonances of Si vacancy centers in 4H-SiC,"The long-lived and optically addressable spin states of silicon vacancies
($\mathrm{V}_\mathrm{Si}$) in 4H-SiC make them promising qubits for quantum
communication and sensing. These color centers can be created in both the
hexagonal (V1) and in the cubic (V2) local crystallographic environments of the
4H-SiC host. While the spin of the V2 center can be efficiently manipulated by
optically detected magnetic resonance at room temperature, spin control of the
V1 centers above cryogenic temperatures has so far remained elusive. Here, we
show that the dynamic strain of surface acoustic waves can overcome this
limitation and efficiently excite magnetic resonances of V1 centers up to room
temperature. Based on the width and temperature dependence of the acoustically
induced spin resonances of the V1 centers, we attribute them to transitions
between spin sublevels in the excited state. The acoustic spin control of both
kinds of $\mathrm{V}_\mathrm{Si}$ centers in their excited states opens new
ways for applications in quantum technologies based on spin-optomechanics.",2212.07704v2
2023-04-03,Relativistic second-order spin hydrodynamics: an entropy-current analysis,"We present a new derivation of Israel-Stewart-like relativistic second-order
dissipative spin hydrodynamic equations using the entropy current approach. In
our analysis, we consider a general energy-momentum tensor with symmetric and
anti-symmetric parts. Moreover, the spin tensor, which is not separately
conserved, has a simple phenomenological form that is antisymmetric only in the
last two indices. Apart from the evolution equations for energy density, fluid
flow, and spin density, we also find relaxation-type dynamical equations for
various dissipative currents. The latter are consistently derived within the
second-order theory as gradient corrections to the energy-momentum and spin
tensors. We argue that this approach correctly reproduces the corresponding
Navier-Stokes limit of spin hydrodynamic equations. Throughout our analysis,
the spin chemical potential is considered a $\mathcal{O}(\partial)$ quantity in
the hydrodynamic gradient expansion and reduces to thermal vorticity in the
global equilibrium. New coefficients appearing in the generalized spin
hydrodynamic equations are undetermined and can only be evaluated within a
proper underlying microscopic theory of a given system.",2304.01009v1
2023-04-09,Spin alignment of vector mesons by glasma fields,"We explain how spin alignment of vector mesons can be induced by background
fields, such as electromagnetic fields or soft gluon fields. Our study is based
on the quantum kinetic theory of spinning quarks and antiquarks and
incorporates the relaxation of the dynamically generated spin polarization. The
spin density matrix of vector mesons is obtained by quark coalescence via the
Wigner function and kinetic equation. Our approach predicts a local spin
correlation that is distinct from the non-local expressions previously obtained
in phenomenological derivations. We estimate the magnitude of such local
correlations in the glasma model of the preequilibrium phase of relativistic
heavy ion collisions. It is found that the resulting spin alignment could be
greatly enhanced and may be comparable to the experimental measurement in order
of magnitude. We further propose new phenomenological scenarios to
qualitatively explain the transverse-momentum and centrality dependence of spin
alignment in a self-consistent framework.",2304.04181v2
2023-04-10,"Intrinsic persistent spin helix in 2D T-XY (X$\neq$Y=P, As, Sb and Bi)","The persistent spin helix (PSH) is robust against spin-independent scattering
and renders an extremely long spin lifetime, which can improve the performance
of potential spintronic devices. To achieve the PSH, a unidirectional spin
configuration is required in the momentum space. Here, T-XY (X$\neq$Y=P, As, Sb
and Bi) monolayers with dynamical, mechanical and thermal stabilities are
predicted to intrinsically possess PSH. Due to the $C_{2\upsilon}$ point-group
symmetry, a unidirectional spin configuration is preserved in the out-of-plane
direction for both conduction and valence bands around the high-symmetry
$\Gamma$ point. That is, the expectation value of the spin $S$ only has the
out-of-plane component $S_z$. The application of an out-of-plane external
electric field can induce in-plane components $S_x$ and $S_y$, thus offering a
promising platform for the on-off logical functionality of spin devices. Our
work reveals a new family of T-phase two-dimensional (2D) materials, which
could provide promising applications in spintronic devices.",2304.04393v3
2023-05-04,Quarkonium spin alignment in a vortical medium,"We use a potential model to investigate the phenomenology of quarkonium in a
thermal rotating medium, where vorticity and spin density are not necessarily
in equilibrium. We find that the quarkonium spin density matrix, as well as the
binding energy and melting temperature, are sensitive to both the vorticity and
the lack of equilibrium between vorticity and spin. This means that quarkonium
spin alignment is a sensitive probe for vorticity and spin within the
hydrodynamic phase. Information unequivocably pointing to spin-orbit
non-equilibrium dynamics can be obtained from a combined study of quarkonium
relative abundance and spin alignment, as well as experimentally obtainable
off-diagonal density matrix elements.",2305.02985v2
2023-05-11,Nonmonotonic buildup of spin-singlet correlations in a double quantum dot,"Dynamical buildup of spin-singlet correlations between the two quantum dots
is investigated by means of the time-dependent numerical renormalization group
method. By calculating the timeevolution of the spin-spin expectation value
upon a quench in the hopping between the quantum dots, we examine the time
scales associated with the development of an entangled spin-singlet state in
the system. Interestingly, we find that in short time scales the effective
exchange interaction between the quantum dots is of ferromagnetic type,
favoring spin-triplet correlations, as opposite to the long time limit, when
strong antiferromagnetic correlations develop and eventually an entangled
spin-singlet state is formed between the dots. We also numerically determine
the relevant time scales and show that the physics is generally governed by the
interplay between the Kondo correlations on each dot and exchange interaction
between the spins of both quantum dots.",2305.06734v1
2023-06-03,Quasicrystalline Spin Foam with Matter: Definitions and Examples,"In this work, we define quasicrystalline spin networks as a subspace within
the standard Hilbert space of loop quantum gravity, effectively constraining
the states to coherent states that align with quasicrystal geometry structures.
We introduce quasicrystalline spin foam amplitudes, a variation of the EPRL
spin foam model, in which the internal spin labels are constrained to
correspond to the boundary data of quasicrystalline spin networks. Within this
framework, the quasicrystalline spin foam amplitudes encode the dynamics of
quantum geometries that exhibit aperiodic structures. Additionally, we
investigate the coupling of fermions within the quasicrystalline spin foam
amplitudes. We present calculations for three-dimensional examples and then
explore the 600-cell construction, which is a fundamental component of the
four-dimensional Elser-Sloane quasicrystal derived from the E8 root lattice.",2306.01964v1
2023-07-05,Kinetic theory for spin-polarized relativistic plasmas,"The investigation of spin and polarization effects in ultra-high intensity
laser-plasma and laser-beam interactions has become an emergent topic in
high-field science recently. In this paper we derive a relativistic kinetic
description of spin-polarized plasmas, where QED effects are taken into account
via Boltzmann-type collision operators under the local constant field
approximation. The emergence of anomalous precession is derived from one-loop
self-energy contributions in a strong background field. We are interested, in
particular, in the interplay between radiation reaction effects and the spin
polarization of the radiating particles. For this we derive equations for
spin-polarized quantum radiation reaction from moments of the spin-polarized
kinetic equations. By comparing with the classical theory, we identify and
discuss the spin-dependent radiation reaction terms, and radiative
contributions to spin dynamics.",2307.02114v2
2023-09-26,Constraining the LIGO/Virgo AGN channel with black hole spins,"Merging black holes (BH) are expected to produce remnants with large
dimensionless spin parameters ($a_{\rm spin} \sim 0.7$). However, gravitational
wave (GW) observations with LIGO/Virgo suggest that merging BH are consistent
with modestly positive but not high spin ($a_{\rm spin} \sim 0.2$), causing
tension with models suggesting that high mass mergers are produced by
hierarchical merger channels. Some BH also show evidence for strong in-plane
spin components. Here we point out that \emph{spin down} of BH due to eccentric
prograde post-merger orbits within the gas of an active galactic nucleus (AGN)
disk can yield BH with masses in the upper mass gap, but only modestly positive
$a_{\rm spin}$, and thus observations of BH with low spin \emph{do not} rule
out hierarchical models. We also point out that the fraction of BBH mergers
with significant in-plane spin components is a strong test of interactions
between disk binary black holes (BBH) and nuclear spheroid orbiters. Spin
magnitude and spin tilt constraints from LIGO/Virgo observations of BBH are an
excellent test of dynamics of black holes in AGN disks, disk properties and the
nuclear clusters interacting with AGN.",2309.15213v1
2023-10-15,A singlet-triplet hole-spin qubit in MOS silicon,"Holes in silicon quantum dots are promising for spin qubit applications due
to the strong intrinsic spin-orbit coupling. The spin-orbit coupling produces
complex hole-spin dynamics, providing opportunities to further optimize spin
qubits. Here, we demonstrate a singlet-triplet qubit using hole states in a
planar metal-oxide-semiconductor double quantum dot. We observe rapid qubit
control with singlet-triplet oscillations up to 400 MHz. The qubit exhibits
promising coherence, with a maximum dephasing time of 600 ns, which is enhanced
to 1.3 us using refocusing techniques. We investigate the magnetic field
anisotropy of the eigenstates, and determine a magnetic field orientation to
improve the qubit initialisation fidelity. These results present a step forward
for spin qubit technology, by implementing a high quality singlet-triplet
hole-spin qubit in planar architecture suitable for scaling up to 2D arrays of
coupled qubits.",2310.09722v1
2023-10-24,Measuring nuclear spin qubits by qudit-enhanced spectroscopy in Silicon Carbide,"Nuclear spins with hyperfine coupling to single electron spins are highly
valuable quantum bits. In this work we probe and characterise the particularly
rich nuclear spin environment around single silicon vacancy color-centers (V2)
in 4H-SiC. By using the electron spin-3/2 qudit as a 4 level sensor, we
identify several groups of $^{29}$Si and $^{13}$C nuclear spins through their
hyperfine interaction. We extract the major components of their hyperfine
coupling via optical detected nuclear resonance, and assign them to shell
groups in the crystal via the DFT simulations. We utilise the ground state
level anti-crossing of the electron spin for dynamic nuclear polarization and
achieve a nuclear spin polarization of up to $98\pm6\,\%$. We show that this
scheme can be used to detect the nuclear magnetic resonance signal of
individual spins and demonstrate their coherent control. Our work provides a
detailed set of parameters for future use of SiC as a multi-qubit memory and
quantum computing platform.",2310.15557v1
2023-11-09,Exciton Spin Hall Effect In Arc-Shaped Strained WSe$_2$,"Generating a pure spin current using electrons, which have degrees of freedom
beyond spin, such as electric charge and valley index, presents challenges. In
response, we propose a novel mechanism based on intervalley exciton dynamics in
{\em arc-shaped} strained transition metal dichalcogenides (TMDs) to achieve
the {\em exciton spin Hall effect} in an electrically insulating regime,
without the need for an external electric field. The interplay between strain
gradients and strain-induced pseudomagnetic fields results in a net Lorentz
force on long-lived intervalley excitons in WSe$_2$, carrying non-zero spin
angular momentum. This process generates an exciton-mediated pure spin Hall
current, resulting in opposite-sign spin accumulations and local magnetization
on the two sides of the single-layer arc-shaped TMD. We demonstrate that the
magnetic field induced by spin accumulation, at approximately $\sim {\rm mT}$,
can be detected using techniques such as superconducting quantum interference
magnetometry or spatially-resolved magneto-optical Faraday and Kerr rotations.",2311.05242v1
2023-11-15,Chirality-induced emergent spin-orbit coupling in topological atomic lattices,"Spin-orbit coupled dynamics are of fundamental interest in both quantum
optical and condensed matter systems alike. In this work, we show that photonic
excitations in pseudospin-1/2 atomic lattices exhibit an emergent spin-orbit
coupling when the geometry is chiral. This spin-orbit coupling arises naturally
from the electric dipole interaction between the lattice sites and leads to
spin polarized excitation transport. Using a general quantum optical model, we
determine analytically the conditions that give rise to spin-orbit coupling and
characterize the behavior under various symmetry transformations. We show that
chirality-induced spin textures are associated with a topologically nontrivial
Zak phase that characterizes the chiral setup. Our results demonstrate that
chiral atom arrays are a robust platform for realizing spin-orbit coupled
topological states of matter.",2311.09303v1
2023-12-02,Understanding central spin decoherence due to interacting dissipative spin baths,"We propose a new approach to simulate the decoherence of a central spin
coupled to an interacting dissipative spin bath with cluster-correlation
expansion techniques. We benchmark the approach on generic 1D and 2D spin baths
and find excellent agreement with numerically exact simulations. Our
calculations show a complex interplay between dissipation and coherent spin
exchange, leading to increased central spin coherence in the presence of fast
dissipation. Finally, we model near-surface NV centers in diamond and show that
accounting for bath dissipation is crucial to understanding their decoherence.
Our method can be applied to a variety of systems and provides a powerful tool
to investigate spin dynamics in dissipative environments.",2312.01205v1
2023-12-08,Large Spin Stern-Gerlach Interferometry for Gravitational Entanglement,"Recently, there has been a proposal to test the quantum nature of gravity in
the laboratory by witnessing the growth of entanglement between two masses in
spatial quantum superpositions. The required superpositions can be created via
Stern-Gerlach interferometers, which couple an embedded spin qubit quantum
state to the spatial dynamics of each mass. The masses would entangle only if
gravity is quantum in nature. Here, we generalise the experiment to an
arbitrary spin $j$ or equivalently to an ensemble of uniformly coupled spins.
We first exemplify how to create a generalized Stern-Gerlach interferometer,
which splits the mass into $2j+1$ trajectories. This shows that a controlled
protocol can be formulated to encode the amplitudes of any spin state to a
spatial superposition. Secondly, two masses in spatial superpositions of the
above form are left to interact via gravity, and the entanglement is computed.
Different families of initial spin states are varied to find the optimal spin
state that maximizes the entanglement. We conclude that larger spins can offer
a modest advantage in enhancing gravity-induced entanglement.",2312.05170v1
2024-01-25,Magnon dispersion and spin transport in CrCl$_3$ bilayers under different strain-induced magnetic states,"Atomically-thin van der Waals magnetic materials offer exceptional
opportunities to mechanically and electrically manipulate magnetic states and
spin textures. The possibility of efficient spin transport in these materials
makes them promising for the development of novel nanospintronics technology.
Using atomistic spin dynamics simulations, we investigate magnetic ground
state, magnon dispersion, critical temperature, and magnon spin transport in
CrCl$_3$ bilayers in the absence and presence of compressive and tensile
strains. We show that in the presence of mechanical strain, the magnon band gap
at the $\Gamma$ point and the critical temperature of the bilayer are
increased. Furthermore, our simulations show that the magnon diffusion length
is reduced in the presence of strain. Moreover, by exciting magnons through the
spin Seebeck effect and spin Hall-induced torque, we illustrate distinctions
between magnon spin transport in the antiferromagnetic state, under compressive
strains, and ferromagnetic states, under tensile strains or in the unstrained
case.",2401.13984v1
2024-02-05,On the integrability of extended test body dynamics around black holes,"In general relativity, the motion of an extended test body is influenced by
its proper rotation, or spin. We present a covariant and physically
self-consistent Hamiltonian framework to study this motion, up to quadratic
order in the body's spin, including a spin-induced quadrupole, and in an
arbitrary background spacetime. The choice of spin supplementary condition and
degeneracies associated with local Lorentz invariance are treated rigorously
with adapted tools from Hamiltonian mechanics. Applying the formalism to a
background space-time described by the Kerr metric, we prove that the motion of
any test compact object around a rotating black hole defines an integrable
Hamiltonian system to linear order in the body's spin. Moreover, this
integrability still holds at quadratic order in spin when the compact object
has the deformability expected for an isolated black hole. Our analytical
results shed light on longstanding numerical conjectures regarding spin-induced
chaos in the motion of asymmetric compact binaries, and provides a powerful
framework to improve current gravitational waveform modelling to account for
spin-induced extended body effects.",2402.02670v2
2024-02-21,Global quark spin correlations in relativistic heavy ion collisions,"The observation of the vector meson's global spin alignment by the STAR
Collaboration reveals that strong spin correlations may exist for quarks and
antiquarks in relativistic heavy-ion collisions in the normal direction of the
reaction plane. We propose a systematic method to describe such correlations in
the quark matter. The correlations can be classified as local and long range
types. We show in particular that the effective quark spin correlations contain
the genuine spin correlations originated directly from the dynamical process as
well as those induced by averaging over other degrees of freedom. We also show
that such correlations can be studied by measuring the vector meson's spin
density matrix and hyperon-hyperon and hyperon-anti-hyperon spin correlations.
We present the relationships between these measurable quantities and spin
correlations of quarks and antiquarks.",2402.13721v2
1997-08-21,Attenuation of polarization echoes in NMR: A study of the emergence of dynamical irreversibility in many-body quantum systems,"The reversal of the time evolution of the local polarization in an
interacting spin system involves a sign change of the effective dipolar
Hamiltonian which refocuses the 'spin diffusion' process generating a
polarization echo. Here, the attenuation of these echo amplitudes as a function
of evolution time is presented for cymantrene and ferrocene polycrystalline
samples, involving one and two five spin rings per molecule respectively. We
calculate the fraction of polarization which is not refocused because only the
secular part of the dipolar Hamiltonian is inverted. The results indicate that,
as long as the spin dynamics is restricted to a single ring, the non-inverted
part of the Hamiltonian is notable by itself to explain the whole decay of the
polarization echoes. A cross over from exponential (cymantrene) to Gaussian
(ferrocene) attenuation is experimentally observed. This is attributed to an
increase of the relative importance of the spin dynamics, as compared with
irreversible interactions, which favors dynamical irreversibility.",9708172v2
1999-01-28,Doped bilayer antiferromagnets: Hole dynamics on both sides of a magnetic ordering transition,"The two-layer square lattice quantum antiferromagnet with spins 1/2 shows a
magnetic order-disorder transition at a critical ratio of the interplane to
intraplane couplings. We investigate the dynamics of a single hole in a bilayer
antiferromagnet described by a t-J Hamiltonian. To model the spin background we
propose a ground-state wave function for the undoped system which covers both
magnetic phases and includes transverse as well as longitudinal spin
fluctuations. The photoemission spectrum is calculated using the spin-polaron
picture for the whole range of the ratio of the magnetic couplings. This allows
for the study of the hole dynamics of both sides of the magnetic order-disorder
transition. For small interplane coupling we find a quasiparticle with
properties known from the single-layer antiferromagnet, e.g., the dispersion
minimum is at (pi/2,pi/2). For large interplane coupling the hole dispersion is
similar to that of a free fermion (with reduced bandwidth). The cross-over
between these two scenarios occurs inside the antiferromagnetic phase which
indicates that the hole dynamics is governed by the local environment of the
hole.",9901326v2
2001-03-21,Aging dynamics of quantum spin glasses of rotors,"We study the long time dynamics of quantum spin glasses of rotors using the
non-equilibrium Schwinger-Keldysh formalism. These models are known to have a
quantum phase transition from a paramagnetic to a spin glass phase, which we
approach by looking at the divergence of the spin relaxation rate at the
transition point. In the aging regime, we determine the dynamical equations
governing the time evolution of the spin response and correlation functions,
and show that all terms in the equations that arise solely from quantum effects
are irrelevant at long times under time reparametrization group (RpG)
transformations. At long times, quantum effects enter only through the
renormalization of the parameters in the dynamical equations for the classical
counterpart of the rotor model. Consequently, quantum effects only modify the
out of equilibrium fluctuation dissipation relation (OEFDR), i.e. the ratio X
between the temperature and the effective temperature, but not the form of the
classical OEFDR.",0103428v1
2003-03-31,Spin-lattice models: inhomogeneity and diffusion,"In spin-lattice models with order parameter conserved, we generalize the idea
of spin diffusion incorporating a variety factors as possible driving forces,
including the external field and the temperature. The Kawasaki dynamics in the
Gaussian model and the one-dimensional Ising model are studied. The Gaussian
model is rigorously treated and the critical exponent $\gamma =1$ is obtained.
The competition of the internal and the external inhomogeneities may lead to
interesting and rich dynamic behavior. The diffusion induced by the
inhomogeneity of the magnetization itself is believed to vanish near the
critical point, meanwhile the nonvanishing diffusion induced by the
inhomogeneity of the environment may be coupled to the spin configuration and
weakened by thermal noise. Several interesting examples are visualized, and the
concept of local hysteresis is proposed in this spin-conserved dynamics. A
dynamic phase transition is observed in the one-dimensional Ising model subject
to an electromagnetic wave.",0303638v2
2003-09-26,Explicit and Hidden Symmetries in Quantum Dots and Quantum Ladders,"The concept of dynamical hidden symmetries in the physics of electron
tunneling through composite quantum dots (CQD) and quantum ladders (QL) is
developed and elucidated. Quite generally, dynamical symmetries are realizable
in the space of low energy excited states in a given charge sector of
nanoobjects, which involve spin variables and/or electron-hole pairs. While
spin multiplets in an individual rung of a QL or in an isolated CQD form a
representation space of the usual rotation group, this SU(2) symmetry is broken
due to spin transfer (in QL) electron cotunneling through CQD. Dynamical
symmetries in the space of spin multiplets are then unravelled in these
processes. The corresponding symmetry groups are described by SO(n) or SU(n)
depending on the origin of rotation group symmetry breaking. The effective spin
Hamiltonians of QL and CQD are derived and expressed in terms of the pertinent
group generators. We employ fermionization procedure for analyzing the physical
content of these dynamical symmetries, including Kondo tunneling through CQD
and Haldane gap formation in QL.",0309606v1
2003-10-05,Dynamical Symmetry Enlargement Versus Spin-Charge Decoupling in the One-Dimensional SU(4) Hubbard Model,"We investigate dynamical symmetry enlargement in the half-filled SU(4)
Hubbard chain using non-perturbative renormalization group and Quantum Monte
Carlo techniques. A spectral gap is shown to open for arbitrary Coulombic
repulsion $U$. At weak coupling, $U \lesssim 3t$, a SO(8) symmetry between
charge and spin-orbital excitations is found to be dynamically enlarged at low
energy. At strong coupling, $U \gtrsim 6t$, the charge degrees of freedom
dynamically decouple and the resulting effective theory in the spin-orbital
sector is that of the SO(6) antiferromagnetic Heisenberg model. Both regimes
exhibit spin-Peierls order. However, although spin-orbital excitations are
$incoherent$ in the SO(6) regime they are $coherent$ in the SO(8) one. The
cross-over between these regimes is discussed.",0310090v1
2004-11-18,Optoelectronic control of spin dynamics at near-THz frequencies in magnetically doped quantum wells,"We use time-resolved Kerr rotation to demonstrate the optical and electronic
tuning of both the electronic and local moment (Mn) spin dynamics in
electrically gated parabolic quantum wells derived from II-VI diluted magnetic
semiconductors. By changing either the electrical bias or the laser energy, the
electron spin precession frequency is varied from 0.1 to 0.8 THz at a magnetic
field of 3 T and at a temperature of 5 K. The corresponding range of the
electrically-tuned effective electron g-factor is an order of magnitude larger
compared with similar nonmagnetic III-V parabolic quantum wells. Additionally,
we demonstrate that such structures allow electrical modulation of local moment
dynamics in the solid state, which is manifested as changes in the amplitude
and lifetime of the Mn spin precession signal under electrical bias. The large
variation of electron and Mn-ion spin dynamics is explained by changes in
magnitude of the sp&#8722;d exchange overlap.",0411492v1
2005-04-04,Dynamical scaling in Ising and vector spin glasses,"We have studied numerically the dynamics of spin glasses with Ising and XY
symmetry (gauge glass) in space dimensions 2, 3, and 4. The nonequilibrium
spin-glass susceptibility and the nonequilibrium energy per spin of samples of
large size L_b are measured as a function of anneal time t_w after a quench to
temperatures T. The two observables are compared to the equilibrium spin-glass
susceptibility and the equilibrium energy, respectively, measured as functions
of temperature T and system size L for a range of system sizes. For any time
and temperature a nonequilibrium time-dependent length scale L*(t_w,T) can be
defined by comparing equilibrium and nonequilibrium quantities. Our analysis
shows that for all systems studied, an ""effective dynamical critical exponent""
parametrization L*(t_w,T) = A(T) t^(1/z(T)) fits the data well at each
temperature within the whole temperature range studied, which extends from well
above the critical temperature to near T = 0 for dimension 2, or to well below
the critical temperature for the other space dimensions studied. In addition,
the data suggest that the dynamical critical exponent z varies smoothly when
crossing the transition temperature.",0504082v2
2005-06-24,Spin dynamics of the quasi two dimensional spin-1/2 quantum magnet Cs_2CuCl_4,"We study dynamical properties of the anisotropic triangular quantum
antiferromagnet Cs_2CuCl_4. Inelastic neutron scattering measurements have
established that the dynamical spin correlations cannot be understood within a
linear spin wave analysis. We go beyond linear spin wave theory by taking
interactions between magnons into account in a 1/S expansion. We determine the
dynamical structure factor and carry out extensive comparisons with
experimental data. We find that compared to linear spin wave theory a
significant fraction of the scattering intensity is shifted to higher energies
and strong scattering continua are present. However, the 1/S expansion fails to
account for the experimentally observed large quantum renormalization of the
exchange energies.",0506667v1
2005-11-07,Signature of the Ground-State Topology in the Low-Temperature Dynamics of Spin Glasses,"We numerically address the issue of how the ground state topology is
reflected in the finite temperature dynamics of the $\pm J$ Edwards-Anderson
spin glass model. In this system a careful study of the ground state
configurations allows to classify spins into two sets: solidary and
non-solidary spins. We show that these sets quantitatively account for the
dynamical heterogeneities found in the mean flipping time distribution at
finite low temperatures. The results highlight the relevance of taking into
account the ground state topology in the analysis of the finite temperature
dynamics of spin glasses.",0511157v2
2006-06-23,Dynamical spin chirality and spin anisotropy in gapped S=1/2 quantum systems,"We have studied the spin anisotropy in spin-singlet ground state compounds
and the magnetic chirality, as measured by inelastic polarized neutron
scattering techniques, in the chain-sublattice of Sr14Cu24O41. In-plane and out
of plane magnetic fluctuations are measured to be anisotropic and further
discussed in the light of the current hypothesis of spin-orbit coupling. We
show that under appropriate conditions of magnetic field and neutron
polarization, the \textit{trivial} magnetic chirality selects only one of the
Zeeman splitted triplet states for scattering and erases the other one that
posses opposite helicity. Our analysis pertains to previous studies on
dynamical magnetic chirality and chiral critical exponents, where the ground
state is chiral itself, the so-called \textit{non-trivial} dynamical magnetic
chirality. As it turns out, both \textit{trivial} and \textit{non-trivial}
dynamical magnetic chirality have identical selection rules for inelastic
polarized neutron scattering experiments and it is not at all evident that they
can be distinguished in a paramagnetic compound.",0606598v1
2005-01-01,Equatorial and related non-equilibrium states in magnetization dynamics of ferromagnets: Generalization of Suhl's spin-wave instabilities,"We investigate the nonlinear dynamics underlying the evolution of a 2-D
nanoscale ferromagnetic film with uniaxial anisotropy in the presence of
perpendicular pumping. Considering the associated Landau-Lifshitz spin
evolution equation with Gilbert damping together with Maxwell equation for the
demagnetization field, we study the dynamics in terms of the stereographic
variable. We identify several new fixed points for suitable choice of external
field in a rotating frame of reference. In particular, we identify explicit
equatorial and related fixed points of the spin vector in the plane transverse
to the anisotropy axis when the pumping frequency coincides with the amplitude
of the static parallel field. We then study the linear stability of these novel
fixed points under homogeneous and spin wave perturbations and obtain a
generalized Suhl's instability criterion, giving the condition for exponential
growth of P-modes under spin wave perturbations. Two parameter phase diagrams
(in terms of amplitudes of static parallel and oscillatory perpendicular
magnetic fields) for stability are obtained, which differ qualitatively from
those for the conventional ferromagnetic resonance near thermal equilibrium and
are amenable to experimental tests.",0501002v2
2001-12-03,The dynamical equation of the spinning electron,"We obtain by invariance arguments the relativistic and non-relativistic
invariant dynamical equations of a classical model of a spinning electron. We
apply the formalism to a particular classical model which satisfies Dirac's
equation when quantised. It is shown that the dynamics can be described in
terms of the evolution of the point charge which satisfies a fourth order
differential equation or, alternatively, as a system of second order
differential equations by describing the evolution of both the center of mass
and center of charge of the particle. As an application of the found dynamical
equations, the Coulomb interaction between two spinning electrons is
considered. We find from the classical viewpoint that these spinning electrons
can form bound states under suitable initial conditions. Since the classical
Coulomb interaction of two spinless point electrons does not allow for the
existence of bound states, it is the spin structure that gives rise to new
physical phenomena not described in the spinless case. Perhaps the paper may be
interesting from the mathematical point of view but not from the point of view
of physics.",0112005v2
2007-10-02,The Effect of Pure State Structure on Nonequilibrium Dynamics,"Motivated by short-range Ising spin glasses, we review some rigorous results
and their consequences for the relation between the number/nature of
equilibrium pure states and nonequilibrium dynamics. Two of the consequences
for spin glass dynamics following a deep quench to a temperature with broken
spin flip symmetry are: (1) Almost all initial configurations lie on the
boundary between the basins of attraction of multiple pure states. (2) Unless
there are uncountably many pure states with almost all pairs having zero
overlap, there can be no equilibration to a pure state as time goes to
infinity. We discuss the relevance of these results to the difficulty of
equilibration of spin glasses. We also review some results concerning the
``nature vs. nurture'' problem of whether the large-time behavior of both
ferromagnets and spin glasses following a deep quench is determined more by the
initial configuration or by the dynamics realization.",0710.0633v1
2008-10-09,Atomistic spin dynamics of the CuMn spin glass alloy,"We demonstrate the use of Langevin spin dynamics for studying dynamical
properties of an archetypical spin glass system. Simulations are performed on
CuMn (20% Mn) where we study the relaxation that follows a sudden quench of the
system to the low temperature phase. The system is modeled by a Heisenberg
Hamiltonian where the Heisenberg interaction parameters are calculated by means
of first-principles density functional theory. Simulations are performed by
numerically solving the Langevin equations of motion for the atomic spins. It
is shown that dynamics is governed, to a large degree, by the damping parameter
in the equations of motion and the system size. For large damping and large
system sizes we observe the typical aging regime.",0810.1645v1
2009-03-10,Dynamical coupling and separation of multiple degrees of freedom in a photoexcited double-exchange system,"We present a theory of ultrafast photo-induced dynamics in a spin-charge
coupled system, motivated by pump-probe experiments in perovskite manganites. A
microscopic picture for multiple dynamics in spin and charge degrees is focused
on. Real-time simulations are carried out by two complimentary methods. Our
calculation demonstrates that electron motion governs a short-time scale where
charge and spin dynamics are combined strongly, while, in a long-time scale
controlled by spin relaxation, charge sector does not follow remarkable change
in spin sector. Present results are in contrast to a conventional
double-exchange picture in equilibrium states.",0903.1715v2
2009-06-13,Coevolution of Glauber-like Ising dynamics and topology,"We study the coevolution of a generalized Glauber dynamics for Ising spins,
with tunable threshold, and of the graph topology where the dynamics takes
place. This simple coevolution dynamics generates a rich phase diagram in the
space of the two parameters of the model, the threshold and the rewiring
probability. The diagram displays phase transitions of different types: spin
ordering, percolation, connectedness. At variance with traditional coevolution
models, in which all spins of each connected component of the graph have equal
value in the stationary state, we find that, for suitable choices of the
parameters, the system may converge to a state in which spins of opposite sign
coexist in the same component, organized in compact clusters of like-signed
spins. Mean field calculations enable one to estimate some features of the
phase diagram.",0906.2471v2
2009-07-27,Stochastic dynamics and control of a driven nonlinear spin chain: the role of Arnold diffusion,"We study a chain of non-linear, interacting spins driven by a static and a
time-dependent magnetic field. The aim is to identify the conditions for the
locally and temporally controlled spin switching. Analytical and full numerical
calculations show the possibility of stochastic control if the underlying
semi-classical dynamics is chaotic. This is achievable by tuning the external
field parameters according to the method described in this paper. We show
analytically for a finite spin chain that Arnold diffusion is the underlying
mechanism for the present stochastic control. Quantum mechanically we consider
the regime where the classical dynamics is regular or chaotic. For the latter
we utilize the random matrix theory. The efficiency and the stability of the
non-equilibrium quantum spin-states are quantified by the time-dependence of
the Bargmann angle related to the geometric phases of the states.",0907.4717v1
2010-07-13,Asymmetric optical nuclear spin pumping in a single uncharged quantum dot,"A highly asymmetric dynamic nuclear spin pumping is observed in a single self
assembled InGaAs quantum dot subject to resonant optical pumping of the neutral
exciton transition leading to a large maximum polarization of 54%. This dynamic
nuclear polarization is found to be much stronger following pumping of the
higher energy Zeeman state. Time-resolved measurements allow us to directly
monitor the buildup of the nuclear spin polarization in real time and to
quantitatively study the dynamics of the process. A strong dependence of the
observed dynamic nuclear polarization on the applied magnetic field is found,
with resonances in the pumping efficiency being observed for particular
magnetic fields. We develop a model that fully accounts for the observed
behaviour, where the pumping of the nuclear spin system is due to
hyperfine-mediated spin flip transitions between the states of the neutral
exciton manifold.",1007.2145v2
2010-09-24,Photoinduced dynamics in quantum rings,"We investigate the spin-dependent dynamical response of a semiconductor
quantum ring with a spin orbit interaction (SOI) upon the application of a
single and two linearly polarized, picosecond, asymmetric electromagnetic
pulses in the presence of a static magnetic flux. We find that the
pulse-generated electric dipole moment is spin dependent. It is also shown that
the SOI induces an extra SU(2) effective flux in addition to the static
external magnetic flux which is reflected in an additional periodicity of the
spin-dependent dipole moment. Furthermore, the pulses may induce a net
dynamical charge currents (CC) and dynamical spin currents (SC) when the
clockwise and anti-clockwise symmetry of the carrier is broken upon the pulse
application.",1009.4809v1
2010-10-05,Magnetic Monopole Dynamics in Spin Ice,"One of the most remarkable examples of emergent quasi-particles, is that of
the ""fractionalization"" of magnetic dipoles in the low energy configurations of
materials known as ""spin ice"", into free and unconfined magnetic monopoles
interacting via Coulomb's 1/r law [Castelnovo et. al., Nature, 451, 42-45
(2008)]. Recent experiments have shown that a Coulomb gas of magnetic charges
really does exist at low temperature in these materials and this discovery
provides a new perspective on otherwise largely inaccessible phenomenology. In
this paper, after a review of the different spin ice models, we present
detailed results describing the diffusive dynamics of monopole particles
starting both from the dipolar spin ice model and directly from a Coulomb gas
within the grand canonical ensemble. The diffusive quasi-particle dynamics of
real spin ice materials within ""quantum tunneling"" regime is modeled with
Metropolis dynamics, with the particles constrained to move along an underlying
network of oriented paths, which are classical analogues of the Dirac strings
connecting pairs of Dirac monopoles.",1010.0970v1
2011-03-16,The multiple quantum NMR dynamics in systems of equivalent spins with the dipolar ordered initial state,"The multiple quantum (MQ) NMR dynamics in the system of equivalent spins with
the dipolar ordered initial state is considered. The high symmetry of the MQ
Hamiltonian is used in order to develop the analytical and numerical methods
for an investigation of the MQ NMR dynamics in the systems consisting of
hundreds of spins from ""the first principles"". We obtain the dependence of the
intensities of the MQ NMR coherences on their orders (profiles of the MQ NMR
coherences) for the systems of $200 - 600$ spins. It is shown that these
profiles may be well approximated by the exponential distribution functions. We
also compare the MQ NMR dynamics in the systems of equivalent spins having two
different initial states, namely the dipolar ordered state and the thermal
equilibrium state in the strong external magnetic field.",1103.3108v2
2011-07-13,Long timescale dynamics of spin textures in a degenerate F=1 $^{87}$ Rb spinor Bose gas,"We investigate the long-term dynamics of spin textures prepared by cooling
unmagnetized spinor gases of F=1 $^{87}$Rb to quantum degeneracy, observing
domain coarsening and a strong dependence of the equilibration dynamics on the
quadratic Zeeman shift $q$. For small values of $|q|$, the textures arrive at a
configuration independent of the initial spin-state composition, characterized
by large length-scale spin domains, and the establishment of easy-axis
(negative $q$) or easy-plane (positive $q$) magnetic anisotropy. For larger
$|q|$, equilibration is delayed as the spin-state composition of the degenerate
spinor gas remains close to its initial value. These observations support the
mean-field equilibrium phase diagram predicted for a ferromagnetic spinor
Bose-Einstein condensate, but also illustrate that equilibration is achieved
under a narrow range of experimental settings, making the F=1 $^{87}$Rb gas
more suitable for studies of nonequilibrium quantum dynamics.",1107.2672v1
2012-08-22,Transport through single-level systems: Spin dynamics in the nonadiabatic regime,"We investigate the Fano-Anderson model coupled to a large ensemble of spins
under the influence of an external magnetic field. The interaction between the
two spin systems is treated within a meanfield-approach and we assume an
anisotropic coupling between these two systems. By using a nonadiabatic
approach, we make no further approximations in the theoretical description of
our system, apart from the semiclassical treatment. Therewith, we can include
the short-time dynamics as well as the broadening of the energy levels arising
due to the coupling to the external electronic reservoirs. We study the spin
dynamics in the regime of low and high bias. For the infinite bias case, we
compare our results to those obtained from a simpler rate equation approach,
where higher-order transitions are neglected. We show, that these higher-order
terms are important in the range of low magnetic field. Additionally, we
analyze extensively the finite bias regime with methods from nonlinear
dynamics, and we discuss the possibility of switching of the large spin.",1208.4574v2
2012-09-13,Self-sustaining dynamical nuclear polarization oscillations in quantum dots,"Early experiments on spin-blockaded double quantum dots revealed surprising
robust, large-amplitude current oscillations in the presence of a static (dc)
source-drain bias [see e.g. K. Ono, S. Tarucha, Phys. Rev. Lett. 92, 256803
(2004)]. Experimental evidence strongly indicates that dynamical nuclear
polarization plays a central role, but the mechanism has remained a mystery.
Here we introduce a minimal albeit realistic model of coupled electron and
nuclear spin dynamics which supports robust self-sustained oscillations. Our
mechanism relies on a nuclear-spin analog of the tunneling magnetoresistance
phenomenon (spin-dependent tunneling rates in the presence of an inhomogeneous
Overhauser field) and nuclear spin diffusion, which governs dynamics of the
spatial profile of nuclear polarization. The extremely long oscillation periods
(up to hundreds of seconds) observed in experiments as well as the differences
in phenomenology between vertical and lateral quantum dot structures are
naturally explained in the proposed framework.",1209.2997v1
2013-05-29,Hydrodynamic theory of coupled current and magnetization dynamics in spin-textured antiferromagnets,"Antiferromagnets with vanishingly small (or zero) magnetization are
interesting candidates for spintronics applications. In the present paper we
propose two models for description of the current-induced phenomena in
antiferromagnetic textures. We show that the magnetization that originates from
rotation or oscillations of antiferromagnetic vector can, via $sd$-exchange
coupling, polarize the current and give rise to adiabatic and nonadiabatic spin
torques. Due to the Lorentz-type dynamics of antiferromagnetic moments (unlike
the Galilenian-like dynamics in ferromagnets), the adiabatic spin torque
affects the characteristic lengthscale of the moving texture. Nonadiabatic spin
torque contributes to the energy pumping and can induce the stable motion of
antiferromagnetic texture, but, in contrast to ferromagnets, has pure dynamic
origin. We also consider the current-induced phenomena in artificial
antiferromagnets where the current maps the staggered magnetization of the
structure. In this case the effect of nonadiabatic spin torque is similar to
that in ferromagnetic constituents of the structure. In particular, the current
can remove degeneracy of the translational antiferromagnetic domains
indistinguishable in the external magnetic field and thus can set into motion
the 180$^\circ$ domain wall.",1305.6734v2
2015-06-09,Strain induced coherent dynamics of coupled carriers and Mn spins in a quantum dot,"We report on the coherent dynamics of the spin of an individual magnetic atom
coupled to carriers in a semiconductor quantum dot which has been investigated
by resonant photoluminescence of the positively charged exciton (X+). We
demonstrate that a positively charged CdTe/ZnTe quantum dot doped with a single
Mn atom forms an ensemble of optical Lambda systems which can be addressed
independently. We show that the spin dynamics of the X+Mn complex is dominated
by the electron-Mn exchange interaction and report on the coherent dynamics of
the electron-Mn spin system that is directly observed in the time domain.
Quantum beats reflecting the coherent transfer of population between
electron-Mn spin states, which are mixed by an anisotropic strain in the plane
of the quantum dot, are clearly observed. We finally highlight that this strain
induced coherent coupling is tunable with an external magnetic field.",1506.02821v1
2016-01-06,All-electrical detection of spin dynamics in magnetic antidot lattices by the inverse spin Hall effect,"The understanding of spin dynamics in laterally confined structures on
sub-micron length scales has become a significant aspect of the development of
novel magnetic storage technologies. Numerous ferromagnetic resonance
measurements, optical characterization by Kerr microscopy and Brillouin light
scattering spectroscopy and x-ray studies were carried out to detect the
dynamics in patterned magnetic antidot lattices. Here, we investigate
Oersted-field driven spin dynamics in rectangular Ni80Fe20/Pt antidot lattices
with different lattice parameters by electrical means and compare them to
micromagnetic simulations. When the system is driven to resonance, a dc voltage
across the length of the sample is detected that changes its sign upon field
reversal, which is in agreement with a rectification mechanism based on the
inverse spin Hall effect. Furthermore, we show that the voltage output scales
linearly with the applied microwave drive in the investigated range of powers.
Our findings have direct implications on the development of engineered
magnonics applications and devices.",1601.01221v1
2016-06-16,Spin dynamics of counterrotating Kitaev spirals via duality,"Incommensurate spiral order is a common occurrence in frustrated magnetic
insulators. Typically, all magnetic moments rotate uniformly, through the same
wavevector. However the honeycomb iridates family Li2IrO3 shows an
incommensurate order where spirals on neighboring sublattices are
counter-rotating, giving each moment a different local environment.
Theoretically describing its spin dynamics has remained a challenge: the Kitaev
interactions proposed to stabilize this state, which arise from strong
spin-orbit effects, induce magnon umklapp scattering processes in spin-wave
theory. Here we propose an approach via a (Klein) duality transformation into a
conventional spiral of a frustrated Heisenberg model, allowing a direct
derivation of the dynamical structure factor. We analyze both Kitaev and
Dzyaloshinskii-Moriya based models, both of which can stabilize counterrotating
spirals, but with different spin dynamics, and we propose experimental tests to
identify the origin of counterrotation.",1606.05356v2
2016-07-10,Crossover from collisionless to collisional spin dynamics of polarized fermions,"We study the transverse spin dynamics of trapped polarized Fermi gases in the
high temperature limit. In the non-interacting collisionless regime, a magnetic
field gradient induces collective spin wave oscillations. In the strongly
interacting collisional regime, the dynamics are governed by spin diffusion.
These two limits have been extensively studied both experimentally and
theoretically, but the crossover between them has received less attention. In
this paper, we use a quantum Boltzmann equation to study transverse spin
dynamics and show how the excitations evolve from dispersive to diffusive in
the high temperature limit. We provide analytical solutions in the two limiting
regimes, which agree well with our numerical results.",1607.02764v4
2016-09-07,Motion of solitons in one-dimensional spin-orbit-coupled Bose-Einstein condensates,"Solitons play a fundamental role in dynamics of nonlinear excitations. Here
we explore the motion of solitons in one-dimensional uniform Bose-Einstein
condensates subjected to a spin-orbit coupling (SOC). We demonstrate that the
spin dynamics of solitons is governed by a nonlinear Bloch equation. The spin
dynamics influences the orbital motion of the solitons leading to the
spin-orbit effects in the dynamics of the macroscopic quantum objects
(mean-field solitons). The latter perform oscillations with a frequency
determined by the SOC, Raman coupling, and intrinsic nonlinearity. These
findings reveal unique features of solitons affected by the SOC, which is
confirmed by analytical considerations and numerical simulations of the
underlying Gross-Pitaevskii equations.",1609.02164v1
2018-11-20,Dynamics and energy landscape of the jammed spin-liquid,"We study the low temperature static and dynamical properties of the classical
bond-disordered antiferromagnetic Heisenberg model on the kagome lattice. This
model has recently been shown to host a new type of spin liquid exhibiting an
exponentially large number of discrete ground states. Surprisingly, despite the
rigidity of the groundstates, we establish the vanishing of the corresponding
spin stiffness. Locally, the low-lying eigenvectors of the Hessian appear to
exhibit a fractal inverse participation ratio. Its spin dynamics resembles that
of Coulomb Heisenberg spin liquids, but exhibits a new low-temperature
dynamically arrested regime, which however gets squeezed out with increasing
system size. We also probe the properties of the energy landscape underpinning
this behaviour, and find energy barriers between distinct ground states
vanishing with system size. In turn the local minima appear highly connected
and the system tends to lose memory of its inital state in an accumulation of
soft directions.",1811.08452v2
2011-11-20,Topological insulator ribbon: Surface states and dynamical response,"We study theoretically the distributions of charge and spin polarization of a
topological insulator ribbon, with a realistic rectangular cross section. Due
to constriction in two lateral directions, the surface states discretize into a
series of subbands inside of the bulk band gap. The charge and spin
distribution show interesting characters which are different from an ideal
topological surface state. The effect of merging of four different surface
states into the new one as an entity are analyzed. Optical conductivity and
dynamical spin susceptibility of the ribbon are studied. Different from a
single ideal surface, the optical response and dynamical spin susceptibility of
a ribbon do not have a clear correspondence. The dynamical spin susceptibility
could be used to identify the more adequate model for Bi$_2$Se$_3$.",1111.4614v2
2016-05-17,Direct observation of dynamic modes excited in a magnetic insulator by pure spin current,"Excitation of magnetization dynamics by pure spin currents has been recently
recognized as an enabling mechanism for spintronics and magnonics, which allows
implementation of spin-torque devices based on low-damping insulating magnetic
materials. Here we report the first spatially-resolved study of the dynamic
modes excited by pure spin current in nanometer-thick microscopic insulating
Yttrium Iron Garnet disks. We show that these modes exhibit nonlinear
self-broadening preventing the formation of the self-localized magnetic bullet,
which plays a crucial role in the stabilization of the single-mode
magnetization oscillations in all-metallic systems. This peculiarity associated
with the efficient nonlinear mode coupling in low-damping materials can be
among the main factors governing the interaction of pure spin currents with the
dynamic magnetization in high-quality magnetic insulators.",1605.05211v1
2019-10-14,Markovian and non-Markovian dynamics from probability amplitudes perspective,"One-spin and two-spin in a thermodynamic limit spin-1/2 chain as open quantum
systems are considered. The dynamics of system is generated by XX Heisenberg
interaction and three-spin interaction (TSI) among all the nearest three spins
in the chain. Two variety Hamiltonians of the three-spin interaction are
considered. Using the fermionization technique and calculating the trace
distance, non-Markovianity as a function of the TSI is evaluated, and the
results for the two different open quantum systems are compared. In addition,
the time behavior of the probability amplitudes are studied. The results show
that if all probability amplitudes except one of them will almost vanish after
some time, the dynamics of the open quantum system will be Markovian. In the
non-Markovian dynamics, more than one of the probability amplitudes fluctuate
in time and will never reach zero value.",1910.05951v2
2021-01-22,Spin dynamics and unconventional Coulomb phase in Nd$_2$Zr$_2$O$_7$,"We investigate the temperature dependence of the spin dynamics in the
pyrochlore magnet Nd$_2$Zr$_2$O$_7$ by neutron scattering experiments. At low
temperature, this material undergoes a transition towards an ""all in - all out""
antiferromagnetic phase and the spin dynamics encompass a dispersion-less mode,
characterized by a dynamical spin ice structure factor. Unexpectedly, this mode
is found to survive above $T_{\rm N} \approx 300$ mK. Concomitantly, elastic
correlations of the spin ice type develop. These are the signatures of a
peculiar correlated paramagnetic phase which can be considered as a new example
of Coulomb phase. Our observations near $T_{\rm N}$ do not reproduce the
signatures expected for a Higgs transition, but show reminiscent features of
the ""all in - all out"" order superimposed on a Coulomb phase.",2101.09049v2
2018-03-01,Trochoidal motion and pair generation in skyrmion and antiskyrmion dynamics under spin-orbit torques,"Skyrmions and antiskyrmions in magnetic ultrathin films are characterised by
a topological charge describing how the spins wind around their core. This
topology governs their response to forces in the rigid core limit. However,
when internal core excitations are relevant, the dynamics become far richer. We
show that current-induced spin-orbit torques can lead to phenomena such as
trochoidal motion and skyrmion-antiskyrmion pair generation that only occurs
for either the skyrmion or antiskyrmion, depending on the symmetry of the
underlying Dzyaloshinskii-Moriya interaction. Such dynamics are induced by core
deformations, leading to a time-dependent helicity that governs the motion of
the skyrmion and antiskyrmion core. We compute the dynamical phase diagram
through a combination of atomistic spin simulations, reduced-variable
modelling, and machine learning algorithms. It predicts how spin-orbit torques
can control the type of motion and the possibility to generate skyrmion
lattices by antiskyrmion seeding.",1803.00534v2
2018-03-12,Analytical results for the quantum non-Markovianity of spin ensembles undergoing pure dephasing dynamics,"We study analytically the non-Markovianity of a spin ensemble, with arbitrary
number of spins and spin quantum number, undergoing a pure dephasing dynamics.
The system is considered as a part of a larger spin ensemble of any geometry
with pairwise interactions. We derive exact formulas for the reduced dynamics
of the system and for its non-Markovianity as assessed by the witness of
Lorenzo \emph{et al.} [Phys.~Rev.~A \textbf{88}, 020102(R) (2013)]. The
non-Markovianity is further investigated in the thermodynamic limit when the
environment's size goes to infinity. In this limit and for finite-size systems,
we find that the Markovian's character of the system's dynamics crucially
depends on the range of the interactions. We also show that, when the system
and its environment are initially in a separable state, the appearance of
non-Markovianity is independent of the entanglement generation between the
system and its environment.",1803.04519v2
2018-08-15,Effect of initial system-environment correlations with spin environments,"Understanding the dynamics of open quantum systems is a highly important task
for the implementation of emerging quantum technologies. To make the problem
tractable theoretically, it is common to neglect initial system-environment
correlations. However, this assumption is questionable in situations where the
system is interacting strongly with the environment. In particular, the system
state preparation can then influence the dynamics of the system via the
system-environment correlations. To gain insight into the effect of these
correlations, we solve an exactly solvable model of a quantum spin interacting
with a spin environment both with and without initial correlations for
arbitrary system-environment coupling strengths. We show that the effect of the
system state preparation may or may not be significant in the strong
system-environment coupling regime at low temperatures. We also study the
dynamics of the entanglement between two spins interacting with a common spin
environment with and without initial system-environment correlations to
demonstrate that the correlations can play a significant role in the dynamics
of two-qubit systems as well.",1808.04988v1
2018-12-17,Phonon-induced quantum ratchet in the exciton spin dynamics in diluted magnetic semiconductors in a magnetic field,"Magnetically doped semiconductors are well known for their giant Zeeman
splittings which can reach several meV even in relatively small external
magnetic fields. After preparing a nonequilibrium exciton distribution via
optical excitation, the spin dynamics in diluted magnetic semiconductor quantum
wells is typically governed by spin-flip scattering processes due to the
exciton-impurity exchange interaction. Our theoretical calculations show that
the giant Zeeman splitting in these materials in combination with the influence
of longitudinal acoustic phonons lead to a quantum ratchet-type dynamics,
resulting in an almost complete reversal of the carrier spin polarization at
very low temperatures. Furthermore, we find that the predictions of a much
simpler rate-equation approach qualitatively agree with a more advanced and
numerically demanding quantum kinetic description of the spin dynamics for a
wide range of temperatures, although quantitative difference are noticeable.",1812.06734v2
2019-03-25,Quench dynamics of spin in quantum dots coupled to spin-polarized leads,"We investigate the quench dynamics of a quantum dot strongly coupled to
spin-polarized ferromagnetic leads. The real-time evolution is calculated by
means of the time-dependent density-matrix numerical renormalization group
method implemented within the matrix product states framework. We examine the
system's response to a quench in the spin-dependent coupling strength to
ferromagnetic leads as well as in the position of the dot's orbital level. The
spin dynamics is analyzed by calculating the time-dependent expectation values
of the quantum dot's magnetization and occupation. Based on these, we determine
the time-dependence of a ferromagnetic-contact-induced exchange field and
predict its nonmonotonic build-up. In particular, two time scales are
identified, describing the development of the exchange field and the dot's
magnetization sign change. Finally, we study the effects of finite temperature
on the dynamical behavior of the system.",1903.10381v1
2019-08-01,Theory of current-driven dynamics of spin textures on a surface of topological insulators,"Spin-transfer torque is one of the important physical quantities to
understand for successful application of topological insulators to spintronics.
In this paper, we present analytical expressions of the spin-transfer torques
on a surface of a magnetic topological insulator by including the higher-order
contributions of momentum, $k^2$-term and the hexagonal warping. We obtain six
different types of the spin-transfer torque including both the field-like and
the damping-like torques; the four of them appear only when the higher-order
momentum contributions are included. In addition, we discuss the dynamics of
magnetic skyrmions driven by the spin-transfer torques on the surface of the
topological insulator. Unlike the skyrmion dynamics in conventional metals, we
find that the dynamics significantly depends on the internal structure of
magnetic textures.",1908.00152v1
2019-11-04,Ultrafast demagnetization dynamics in Ni: role of electron correlations,"Experimental observations of the ultrafast (less than 50 fs) demagnetization
of Ni have so far defied theoretical explanations particularly since its
spin-flipping time is much less than that resulting from spin-orbit and
electron-lattice interactions. Through the application of an approach that
benefits from spin-flip time-dependent density-functional theory and dynamical
mean-field theory, we show that proper inclusion of electron correlations and
memory (time-dependence of electron-electron interaction) effects leads to
demagnetization at the femtosecond scale, in good agreement with experimental
observations. Furthermore, our calculations reveal that this ultrafast
demagnetization results mainly from spin-flip transitions from occupied to
unoccupied orbitals implying a dynamical reduction of exchange splitting. These
conclusions are found to be valid for a wide range of laser pulse amplitudes.
They also pave the way for ab initio investigations of ultrafast charge and
spin dynamics in a variety of quantum materials in which electron correlations
may play a definitive role.",1911.01147v1
2020-03-31,Probing Environmental Spin Polarization with Superconducting Flux Qubits,"We present measurements of the dynamics of a polarized magnetic environment
coupled to the flux degree of freedom of rf-SQUID flux qubits. The qubits are
used as both sources of polarizing field and detectors of the environmental
polarization. We probe dynamics at timescales from 5 $\mu$s to 5 ms and at
temperatures between 12.5 and 22 mK. The measured polarization versus
temperature provides strong evidence for a phase transition at a temperature of
$5.7\pm 0.3$ mK. Furthermore, the environmental polarization grows initially as
$\sqrt{t}$, consistent with spin diffusion dynamics. However, spin diffusion
model deviates from data at long timescales, suggesting that a different
phenomenon is responsible for the low-frequency behavior. A simple $1/f$ model
can fit the data at all time scales but it requires empirical low- and
high-frequency cutoffs. We argue that these results are consistent with an
environment comprised of random clusters of spins, with fast spin diffusion
dynamics within the clusters and slow fluctuations of the total moments of the
clusters.",2003.14244v2
2020-06-19,Spin-glass thermo-remanent magnetization revisited: a numerical and analytical study,"Thermoremanent magnetization data for the 3D Edwards-Anderson spin glass are
generated using the Waiting Time Method as simulational tool and interpreted
using Record Dynamics. We verify that clusters of contiguous spins are
overturned by quakes, non-equilibrium events linked to record sized energy
fluctuations and show that quaking is a log-Poisson process, i.e. a Poisson
process whose average depends on the logarithm of the system age, counted from
the initial quench. Our results compare favorably with experimental
thermoremanent magnetization findings and with the spontaneous fluctuation
dynamics of the E-A model.
  The logarithm growth of the size of overturned clusters is related to similar
experimental results and to the growing length scale of the spin-spin spatial
correlation function. The analysis buttresses the applicability of the Waiting
Time Method as a simulational tool and of Record Dynamics as coarse-graining
method for aging dynamics.",2006.11214v2
2020-08-25,Phase-adaptive dynamical decoupling methods for robust spin-spin dynamics in trapped ions,"Quantum platforms based on trapped ions are main candidates to build a
quantum hardware with computational capacities that largely surpass those of
classical devices. Among the available control techniques in these setups,
pulsed dynamical decoupling (pulsed DD) revealed as a useful method to process
the information encoded in ion registers, whilst minimising the environmental
noise over them. In this work, we incorporate a pulsed DD technique that uses
random pulse phases, or correlated pulse phases, to significantly enhance the
robustness of entangling spin-spin dynamics in trapped ions. This procedure was
originally conceived in the context of nuclear magnetic resonance for nuclear
spin detection purposes, and here we demonstrate that the same principles apply
for robust quantum information processing in trapped-ion settings.",2008.10933v2
2021-07-05,Adiabatic Dynamical-Decoupling Based Control of Nuclear Spin Registers,"The use of the nuclear spins surrounding electron spin qubits as quantum
registers and long-lived memories opens the way to new applications in quantum
information and biological sensing. Hence, there is a need for generic and
robust forms of control of the nuclear registers. Although adiabatic gates are
widely used in quantum information, they can become too slow to outpace
decoherence. Here, we introduce a technique whereby adiabatic gates arise from
the dynamical decoupling protocols that simultaneously extend coherence. We
illustrate this pulse-based adiabatic control for nuclear spins around NV
centers in diamond. We obtain a closed-form expression from Landau-Zener theory
and show that it reliably describes the dynamics. By identifying robust Floquet
states, we show that the technique enables polarisation, one-shot flips and
state storage for nuclear spins. These results introduce a new control paradigm
that combines dynamical decoupling with adiabatic evolution.",2107.01931v1
2021-08-28,Rolling spinners on the water surface,"Angular momentum of spinning bodies leads to their remarkable interactions
with fields, waves, fluids, and solids. Orbiting celestial bodies, balls in
sports, liquid droplets above a hot plate, nanoparticles in optical fields, and
spinning quantum particles exhibit nontrivial rotational dynamics. Here, we
report self-guided propulsion of magnetic fast-spinning particles on a liquid
surface in the presence of a solid boundary. Above some critical spinning
frequency (higher rotational Reynolds numbers), such particles generate
localized 3D vortices and form composite 'spinner-vortex' quasi-particles with
nontrivial, yet robust dynamics. Such spinner-vortices are attracted and
dynamically trapped near the boundaries, propagating along the wall of any
shape similarly to 'liquid wheels'. The propulsion velocity and the distance to
the wall are controlled by the angular velocity of the spinner via the balance
between the Magnus and wall-repulsion forces. Our results offer a new type of
surface vehicles and provide a powerful tool to manipulate spinning objects in
fluids.",2108.12578v1
2022-04-25,Quantum kinetic theory for dynamical spin polarization from QED-type interaction,"We investigate the dynamical spin polarization of a massless electron probing
an electron plasma in locally thermal equilibrium via the Moller scattering
from the quantum kinetic theory. We derive an axial kinetic equation
delineating the dynamical spin evolution in the presence of the collision term
with quantum corrections up to $\mathcal{O}(\hbar)$ and the leading-logarithmic
order in coupling by using the hard-thermal-loop (HTL) approximation, from
which we extract the spin-polarization rate induced by the spacetime gradients
of the medium. When the electron probe approaches local equilibrium, we further
simplify the collision term into a relaxation-time expression. Our kinetic
equation may be implemented in the future numerical simulations for dynamical
spin polarization.",2204.11519v2
2023-01-09,X-ray detected ferromagnetic resonance techniques for the study of magnetization dynamics,"Element-specific spectroscopies using synchrotron-radiation can provide
unique insights into materials properties. The recently developed technique of
X-ray detected ferromagnetic resonance (XFMR) allows studying the magnetization
dynamics of magnetic spin structures. Magnetic sensitivity in XFMR is obtained
from the X-ray magnetic circular dichroism (XMCD) effect, where the phase of
the magnetization precession of each magnetic layer with respect to the
exciting radio frequency is obtained using stroboscopic probing of the spin
precession. Measurement of both amplitude and phase response in the magnetic
layers as a function of bias field can give a clear signature of spin-transfer
torque (STT) coupling between ferromagnetic layers due to spin pumping. Over
the last few years, there have been new developments utilizing X-ray scattering
techniques to reveal the precessional magnetization dynamics of ordered spin
structures in the GHz frequency range. The techniques of diffraction and
reflectometry ferromagnetic resonance (DFMR and RFMR) provide novel ways for
the probing of the dynamics of chiral and multilayered magnetic materials,
thereby opening up new pathways for the development of high-density and
low-energy consumption data processing solutions.",2301.03256v1
2023-01-22,Fast-forward adiabatic quantum dynamics of XY spin model on three spin system,"We discussed a method to accelerate an adiabatic quantum dynamics of XY spin
model by using the fast-forward method proposed by Masuda and Nakamura. The
Accelerated scheme is constructed by adding the driving Hamiltonian to the
original Hamiltonian and speeding it up with a large time-scaling factor and an
adiabatic parameter that realizes adiabatic quantum dynamics in a shortened
time. Accelerated adiabatic dynamics start by assuming the candidate of driving
Hamiltonian consists of the pair-wise exchange interaction and magnetic field.
The driving Hamiltonian terms multiplied by the velocity function together with
the original Hamiltonian give fast-forward driving for adiabatic states. We
apply our method to XY spin model by considering three spin systems on the
Kagome lattice. In this model, we obtained the XY pair-wise exchange
interaction of nearest neighbors and next-nearest neighbors should be added to
the original Hamiltonian as a driving interaction to accelerate the adiabatic
motion. This pair-wise driving interaction in the fast-forward scheme
guarantees the complete fidelity of accelerated states.",2301.09039v1
2023-05-03,An overview of the spin dynamics of antiferromagnetic Mn$_5$Si$_3$,"The metallic compound Mn$_5$Si$_3$ hosts a series of antiferromagnetic phases
which can be controlled by external stimuli such as temperature and magnetic
field. In this work, we investigate the spin-excitation spectrum of bulk
Mn$_5$Si$_3$ by combining inelastic neutron scattering measurements and density
functional theory calculations. We study the evolution of the dynamical
response under external parameters and demonstrate that the spin dynamics of
each phase is robust against any combination of temperature and magnetic field.
In particular, the high-energy spin dynamics is very characteristic of the
different phases consisting of either spin waves or broad fluctuations
patterns.",2305.02409v2
2023-11-01,Coupled spin-lattice dynamics from the tight-binding electronic structure,"We developed a method which performs the coupled adiabatic spin and lattice
dynamics based on the tight-binding electronic structure model, where the
intrinsic magnetic field and ionic forces are calculated from the converged
self-consistent electronic structure at every time step. By doing so, this
method allows us to explore limits where the physics described by a
parameterized spin-lattice Hamiltonian is no longer accurate. We demonstrate
how the lattice dynamics is strongly influenced by the underlying magnetic
configuration, where disorder is able to induce significant lattice
distortions. The presented method requires significantly less computational
resources than ab initio methods, such as time-dependent density functional
theory (TD-DFT). Compared to parameterized Hamiltonian-based methods, it also
describes more accurately the dynamics of the coupled spin and lattice degrees
of freedom, which becomes important outside of the regime of small lattice and
spin fluctuations.",2311.00765v1
2023-11-20,Bulk photovoltaic effect in antiferromagnet: Role of collective spin dynamics,"Inspired by recent advancements in the bulk photovoltaic effect which can
extend beyond the independent particle approximation (IPA), this study delves
into the influence of collective spin dynamics in an antiferromagnetic on
photocurrent generation using a time domain calculation. In the linear and
photocurrent conductivity spectra, we observe peaks below the bandgap regime,
attributed to the resonant contributions of collective modes, alongside
broadband modifications resulting from off-resonant spin dynamics. Notably, the
emergence of spin dynamics allows various types of photocurrent, which are
absent in the IPA framework. Furthermore, we emphasize the importance of energy
scale proximity between electronic and spin degrees of freedom in enabling
efficient feedback between them. These findings offer new avenues for efficient
energy harvesting and optoelectronic applications.",2311.12212v2
2017-02-05,Spin-Diffusions and Diffusive Molecular Dynamics,"Metastable condensed matter typically fluctuates about local energy minima at
the femtosecond time scale before transitioning between local minima after
nanoseconds or microseconds. This vast scale separation limits the
applicability of classical molecular dynamics methods and has spurned the
development of a host of approximate algorithms. One recently proposed method
is diffusive molecular dynamics which aims to integrate a system of ordinary
differential equations describing the likelihood of occupancy by one of two
species, in the case of a binary alloy, while quasistatically evolving the
locations of the atoms. While diffusive molecular dynamics has shown to be
efficient and provide agreement with observations, it is fundamentally a model,
with unclear connections to classical molecular dynamics.
  In this work, we formulate a spin-diffusion stochastic process and show how
it can be connected to diffusive molecular dynamics. The spin-diffusion model
couples a classical overdamped Langevin equation to a kinetic Monte Carlo model
for exchange amongst the species of a binary alloy. Under suitable assumptions
and approximations, spin-diffusion can be shown to lead to diffusive molecular
molecular dynamics type models. The key assumptions and approximations include
a well defined time scale separation, a choice of spin exchange rates, a low
temperature approximation, and a mean field type approximation. We derive
several models from different assumptions and show their relationship to
diffusive molecular dynamics. Differences and similarities amongst the models
are explored in a simple test problem.",1702.01469v4
1995-05-30,On the dynamics of a spherical spin-glass,"We carry out an analysis of the effect of a quenched magnetic field on the
dynamics of the spherical Sherrington-Kirkpatrick spin-glass model. We show
that there is a characteristic time introduced by the presence of the field.
Firstly, for times sufficiently small the dynamic scenario of the zero field
case - with aging effects - is reproduced. Secondly, for times larger than the
characteristic time one sees equilibrium dynamics. This dynamical behaviour is
reconciled with the geometry of the energy landscape of the model. We compare
this behaviour with experimental observations at a finite applied field.",9505149v1
1995-08-01,Analytical solution of the Monte Carlo dynamics of a simple spin-glass model,"In this note we present an exact solution of the Monte Carlo dynamics of the
spherical Sherrington-Kirkpatrick spin-glass model. We obtain the dynamical
equations for a generalized set of moments which can be exactly closed. Only in
a certain particular limit the dynamical equation of the energy coincides with
that of the Langevin dynamics.",9508004v1
1995-11-17,Dynamics within metastable states in a mean-field spin glass,"In this letter we present a dynamical study of the structure of metastable
states (corresponding to TAP solutions) in a mean-field spin-glass model. After
reviewing known results of the statical approach, we use dynamics: starting
from an initial condition thermalized at a temperature between the statical and
the dynamical transition temperatures, we are able to study the relaxational
dynamics within metastable states and we show that they are characterized by a
true breaking of ergodicity and exponential relaxation.",9511089v1
2005-09-14,On the dynamics of the glass transition on Bethe lattices,"The Glauber dynamics of disordered spin models with multi-spin interactions
on sparse random graphs (Bethe lattices) is investigated. Such models undergo a
dynamical glass transition upon decreasing the temperature or increasing the
degree of constrainedness. Our analysis is based upon a detailed study of large
scale rearrangements which control the slow dynamics of the system close to the
dynamical transition. Particular attention is devoted to the neighborhood of a
zero temperature tricritical point.
  Both the approach and several key results are conjectured to be valid in a
considerably more general context.",0509366v1
2002-05-16,A sufficient criterion for integrability of stochastic many-body dynamics and quantum spin chains,"We propose a dynamical matrix product ansatz describing the stochastic
dynamics of two species of particles with excluded-volume interaction and the
quantum mechanics of the associated quantum spin chains respectively. Analyzing
consistency of the time-dependent algebra which is obtained from the action of
the corresponding Markov generator, we obtain sufficient conditions on the
hopping rates for identifing the integrable models. From the dynamical algebra
we construct the quadratic algebra of Zamolodchikov type, associativity of
which is a Yang Baxter equation. The Bethe ansatz equations for the spectra are
obtained directly from the dynamical matrix product ansatz.",0205169v1
2008-08-11,Propagation and Ghosts in the Classical Kagome Antiferromagnet,"We investigate the classical spin dynamics of the kagome antiferromagnet by
combining Monte Carlo and spin dynamics simulations. We show that this model
has two distinct low temperature dynamical regimes, both sustaining propagative
modes. The expected gauge invariance type of the low energy low temperature out
of plane excitations is also evidenced in the non linear regime. A detailed
analysis of the excitations allows to identify ghosts in the dynamical
structure factor, i.e propagating excitations with a strongly reduced spectral
weight. We argue that these dynamical extinction rules are of geometrical
origin.",0808.1406v1
2009-04-09,Spin Dynamics in Pyrochlore Heisenberg Antiferromagnets,"We study the low temperature dynamics of the classical Heisenberg
antiferromagnet with nearest neighbour interactions on the pyrochlore lattice.
We present extensive results for the wavevector and frequency dependence of the
dynamical structure factor, obtained from simulations of the precessional
dynamics. We also construct a solvable stochastic model for dynamics with
conserved magnetisation, which accurately reproduces most features of the
precessional results. Spin correlations relax at a rate independent of
wavevector and proportional to temperature.",0904.1541v1
2018-02-22,Chaotic dynamics in spin-vortex pairs,"We report on spin-vortex pair dynamics measured at temperatures low enough to
suppress stochastic core motion, thereby uncovering the highly non-linear
intrinsic dynamics of the system. Our analysis shows that the decoupling of the
two vortex cores is resonant and can be enhanced by dynamic chaos. We detail
the regions of the relevant parameter space, in which the various mechanisms of
the resonant core-core dynamics are activated. We show that the presence of
chaos can reduce the thermally-induced spread in the switching time by up to
two orders of magnitude.",1802.08271v1
2020-08-03,Robust dynamics of antiferromagnetic skyrmion driven by spin-polarized current in small thin disks,"We investigate skyrmion configuration and dynamics in antiferromagnetic thin
disks. It is shown that the skyrmion acquires oscillatory dynamics with
well-defined amplitude and frequency which may be controlled on demand by the
spin-polarized current. Such dynamics are robust in the sense that an interface
between two half-disks cannot change the dynamics appreciably. Indeed, the
skyrmion keeps its oscillatory despite crossing this interface. The way
skyrmion found to do that is by modifying its core region shape so that its
total energy is unaltered for several cycles.",2008.01061v1
2023-03-22,Fidelity Out-of-Time-Order Correlator in the Spin-Boson Model,"In this article, using the numerically exact time-evolving matrix product
operators method, we study the fidelity out-of-time-order correlator (FOTOC) in
the unbiased spin-boson model at zero temperature. It is found that after the
initial exponential growth of FOTOC, the information of the system dynamics
will adulterate into the FOTOC. This makes the FOTOC an advanced epitome of the
system dynamics, i.e., the FOTOC shows similar behavior to that of system
dynamics within a shorter time interval. Eventually the progress of the FOTOC
is ahead of the system dynamics, which can provide a prediction of the system
dynamics.",2303.12276v1
2012-05-17,A stochastic opinion dynamics model with domain size dependent dynamic evolution,"We introduce a stochastic model of binary opinion dynamics in one dimension.
The binary opinions $\pm 1$ are analogous to up and down Ising spins and in the
equivalent spin system, only the spins at the domain boundary can flip. The
probability that a spin at the boundary is up is taken as $P_{up} = \frac
{s_{up}} {s_{up} + \delta s_{down}}$ where $s_{up} (s_{down})$ denotes the size
of the domain with up (down) spins neighbouring it. With $x$ fraction of up
spins initially, a phase transition is observed in terms of the exit
probability and the phase boundary is obtained in the $\delta -x$ plane. In
addition, we investigate the coarsening behaviour starting from a completely
random state; conventional scaling is observed only at the phase transition
point $\delta = 1$. The scaling behaviour is compared to other dynamical
phenomena; the model apparently belongs to a new dynamical universility class
as far as persistence is concerned although the dynamical exponent, equal to
one, is identical to a similar model with no stochasticity.",1205.3943v3
2018-07-25,Impact of non-equilibrium fluctuations on pre-thermal dynamical phase transitions in long-range interacting spin chains,"We study the non-equilibrium phase diagram and the dynamical phase
transitions occurring during the pre-thermalization of non-integrable quantum
spin chains, subject to either quantum quenches or linear ramps of a relevant
control parameter. We consider spin systems in which long-range ferromagnetic
interactions compete with short-range, integrability-breaking terms. We capture
the pre-thermal stages of the non-equilibrium evolution via a time-dependent
spin wave expansion at leading order in the spin waves density. In order to
access regimes with strong integrability breaking, instead, we perform
numerical simulations based on the time-dependent variational principle with
matrix product states. By investigating a large class of quantum spin models,
we demonstrate that non-equilibrium fluctuations can significantly affect the
dynamics near critical points of the phase diagram, resulting in a chaotic
evolution of the collective order parameter, akin to the dynamics of a
classical particle in a multiple-well potential subject to quantum friction. We
also elucidate the signature of this novel dynamical phase on the
time-dependent correlation functions of the local order parameter. We finally
establish a connection with the notion of dynamical quantum phase transition
associated with a possible non-analytic behavior of the return probability
amplitude, or Loschmidt echo, showing that the latter displays cusps whenever
the order parameter vanishes during its real-time evolution.",1807.09797v2
2020-03-15,An Emergent Autonomous Flow for Mean-Field Spin Glasses,"We study the dynamics of symmetric and asymmetric spin-glass models of size
$N$. The analysis is in terms of the double empirical process: this contains
both the spins, and the field felt by each spin, at a particular time (without
any knowledge of the correlation history). It is demonstrated that in the large
$N$ limit, the dynamics of the double empirical process becomes deterministic
and autonomous over finite time intervals. This does not contradict the
well-known fact that SK spin-glass dynamics is non-Markovian (in the large $N$
limit) because the empirical process has a topology that does not discern
correlations in individual spins at different times. In the large $N$ limit,
the evolution of the density of the double empirical process approaches a
nonlocal autonomous PDE operator $\Phi_t$. Because the emergent dynamics is
autonomous, in future work one will be able to apply PDE techniques to analyze
bifurcations in $\Phi_t$. Preliminary numerical results for the SK Glauber
dynamics suggest that the `glassy dynamical phase transition' occurs when a
stable fixed point of the flow operator $\Phi_t$ destabilizes.",2003.06741v4
2020-08-12,Mean-field spin-oscillation dynamics beyond the single-mode approximation for a harmonically trapped spin-1 Bose-Einstein condensate,"Compared to single-component Bose-Einstein condensates, spinor Bose-Einstein
condensates display much richer dynamics. In addition to density oscillations,
spinor Bose-Einstein condensates exhibit intriguing spin dynamics that is
associated with population transfer between different hyperfine components.
This work analyzes the validity of the widely employed single-mode
approximation when describing the spin dynamics in response to a quench of the
system Hamiltonian. The single-mode approximation assumes that the different
hyperfine states all share the same time-independent spatial mode. This implies
that the resulting spin Hamiltonian only depends on the spin interaction
strength and not on the density interaction strength. Taking the spinor sodium
Bose-Einstein condensate in the $f=1$ hyperfine manifold as an example and
working within the mean-field theory framework, it is found numerically that
the single-mode approximation misses, in some parameter regimes, intricate
details of the spin and spatial dynamics. We develop a physical picture that
explains the observed phenomenon. Moreover, using that the population
oscillations described by the single-mode approximation enter into the
effective potential felt by the mean-field spinor, we derive a
semi-quantitative condition for when dynamical mean-field induced corrections
to the single-mode approximation are relevant. Our mean-field results have
implications for a variety of published and planned experimental studies.",2008.05118v2
2022-03-04,From spin foams to area metric dynamics to gravitons,"Although spin foams arose as quantizations of the length metric degrees of
freedom, the quantum configuration space is rather based on areas as more
fundamental variables. This is also highlighted by the semi-classical limit of
four-dimensional spin foam models, which is described by the Area Regge action.
Despite its central importance to spin foams the dynamics encoded by the Area
Regge action is only poorly understood, in particular in the continuum limit.
We perform here a systematic investigation of the dynamics defined by the Area
Regge action on a regular centrally subdivided hypercubical lattice. This
choice of lattice avoids many problems of the non-subdivided hypercubical
lattice, for which the Area Regge action is singular. The regularity of the
lattice allows to extract the continuum limit and its corrections, order by
order in the lattice constant. We show that, contrary to widespread
expectations which arose from the so-called flatness problem of spin foams, the
continuum limit of the Area Regge action does describe to leading order the
same graviton dynamics as general relativity. The next-to-leading order
correction to the effective action for the length metric is of second order in
the lattice constant, and is given by a quadratic term in the Weyl curvature
tensor. This correction can be understood to originate from an underlying
dynamics of area metrics. This suggests that the continuum limit of spin foam
dynamics does lead to massless gravitons, and that the leading order quantum
corrections can be understood to emerge from a generalization of the
configuration space from length to area metrics.",2203.02409v1
2021-08-02,Engineering an Effective Three-spin Hamiltonian in Trapped-ion Systems for Applications in Quantum Simulation,"Trapped-ion quantum simulators, in analog and digital modes, are considered a
primary candidate to achieve quantum advantage in quantum simulation and
quantum computation. The underlying controlled ion-laser interactions induce
all-to-all two-spin interactions via the collective modes of motion through
Cirac-Zoller or Molmer-Sorensen schemes, leading to effective two-spin
Hamiltonians, as well as two-qubit entangling gates. In this work, the
Molmer-Sorensen scheme is extended to induce three-spin interactions via
tailored first- and second-order spin-motion couplings. The scheme enables
engineering single-, two-, and three-spin interactions, and can be tuned via an
enhanced protocol to simulate purely three-spin dynamics. Analytical results
for the effective evolution are presented, along with detailed numerical
simulations of the full dynamics to support the accuracy and feasibility of the
proposed scheme for near-term applications. With a focus on quantum simulation,
the advantage of a direct analog implementation of three-spin dynamics is
demonstrated via the example of matter-gauge interactions in the U(1) lattice
gauge theory within the quantum link model. The mapping of degrees of freedom
and strategies for scaling the three-spin scheme to larger systems, are
detailed, along with a discussion of the expected outcome of the simulation of
the quantum link model given realistic fidelities in the upcoming experiments.
The applications of the three-spin scheme go beyond the lattice gauge theory
example studied here and include studies of static and dynamical phase diagrams
of strongly interacting condensed-matter systems modeled by two- and three-spin
Hamiltonians.",2108.01022v1
2006-05-29,Spin polarization and chiral symmetry breaking at finite density,"We investigate the possibility of the spin polarization of quark matter at
zero temperature and moderate baryon density.The Nambu-Jona-Lasinio (NJL) model
including interactions in vector and axial-vector channel (coupling constant
$G_2$) as well as scalar and pseudoscalar channel (coupling constant $G_1$) is
used, and the self consistent equations for the spin polarization and chiral
condensate are solved numerically in the framework of the Hartree
approximation. Numerical calculations show that in the one flavor model the
spin polarization is possible at finite density if the ratio $G_2/G_1$ is
larger than O(1).We find that the interplay between the spin polarization and
the chiral symmetry plays an important role.If the chemical potential of quarks
reaches a certain finite value, the spin polarization begins to occur because
the quark still has relatively large dynamical mass, which is generated by
spontaneous chiral symmetry breaking.On the other hand, when the spin
polarization occurs, it operates to lower the dynamical quark mass a little.If
one increases the chemical potential furthermore, the spin polarization becomes
weaker and finally disappears because the dynamical quark mass is reduced by
restoring gradually the chiral symmetry.",0605311v4
2008-11-17,A slave-fermion gauge-theory approach of the t-J model: Doping-induced complex magnetic structure and Z$_{2}$ spin-gapped anomalous metal in an antiferromagnetic doped Mott insulator,"We reinvestigate a doped antiferromagnetic Mott insulator based on the
slave-fermion approach of the t-J model, where antiferromagnetic spin
fluctuations and doped holes are described by bosonic spinons and fermionic
holons, respectively. Earlier studies have shown that an effective field theory
for the doped antiferromagnetic Mott insulator is given by a non-relativistic
fermion (holon) U(1) gauge theory for charge dynamics and a relativistic boson
(spinon) U(1) gauge theory for spin dynamics, thus allowing an anomalous
metallic phase where bosonic spinons are gapped away from an antiferromagnetic
state, analogous to the U(1) spin liquid phase in the slave-boson approach of
the t-J model. We argue that the emergent U(1) gauge structure in this approach
is based on a simplified picture for antiferromagnetic correlations.
Considering that dynamics of doped holes frustrates a collinear
antiferromagnetic spin configuration, we show that doped holes enhance
ferromagnetic spin correlations and result in a complex magnetic structure. The
presence of such a complex spin texture reduces the U(1) gauge structure down
to Z$_{2}$, thus a different effective field theory results for the spin-gapped
non-Fermi liquid metal at low temperatures because there are no gapless U(1)
gauge fluctuations.",0811.2626v1
2010-07-09,Muon-spin-relaxation study of the Cu-spin dynamics in electron-doped high-T_c_ superconductor Pr_0.86_LaCe_0.14_Cu_1-y_Zn_y_O_4_,"Muon-spin-relaxation (muSR) measurements have been performed for the
partially Zn-substituted electron-doped high-T_c_ superconductor
Pr_0.86_LaCe_0.14_Cu_1-y_Zn_y_O_4+alpha-delta_ with y=0-0.05 and the reduced
oxygen content delta=0-0.09, in order to investigate nonmagnetic Zn-impurity
effects on the Cu-spin dynamics. For all the measured samples with
delta=0.01-0.09, it has been found that a fast depolarization of muon spins is
observed below 100 K due to the effect of Pr^3+^ moments and that the muSR time
spectrum in the long-time region above 5 mu-sec increases with decreasing
temperature at low temperatures below 30 K possibly due to slowing down of the
Cu-spin fluctuations assisted by Pr^3+^ moments. No Zn-induced slowing down of
the Cu-spin fluctuations has been observed for moderately oxygen-reduced
samples with delta=0.04-0.09, which is very different from the muSR results of
La_2-x_Sr_x_Cu_1-y_Zn_y_O_4_. The possible reason may be that there are no
dynamical stripe correlations of spins and electrons in the electron-doped
high-T_c_ cuprates or that the effect of Pr^3+^ moments on the muSR spectra is
stronger than that of a small amount of Zn impurities.",1007.1603v1
2012-09-29,Emergence and Frustration of Magnetic Order with Variable-Range Interactions in a Trapped Ion Quantum Simulator,"Frustration, or the competition between interacting components of a network,
is often responsible for the complexity of many body systems, from social and
neural networks to protein folding and magnetism. In quantum magnetic systems,
frustration arises naturally from competing spin-spin interactions given by the
geometry of the spin lattice or by the presence of long-range antiferromagnetic
couplings. Frustrated magnetism is a hallmark of poorly understood systems such
as quantum spin liquids, spin glasses and spin ices, whose ground states are
massively degenerate and can carry high degrees of quantum entanglement. The
controlled study of frustrated magnetism in materials is hampered by short
dynamical time scales and the presence of impurities, while numerical modeling
is generally intractable when dealing with dynamics beyond N~30 particles.
Alternatively, a quantum simulator can be exploited to directly engineer
prescribed frustrated interactions between controlled quantum systems, and
several small-scale experiments have moved in this direction. In this article,
we perform a quantum simulation of a long-range antiferromagnetic quantum Ising
model with a transverse field, on a crystal of up to N = 16 trapped Yb+ atoms.
We directly control the amount of frustration by continuously tuning the range
of interaction and directly measure spin correlation functions and their
dynamics through spatially-resolved spin detection. We find a pronounced
dependence of the magnetic order on the amount of frustration, and extract
signatures of quantum coherence in the resulting phases.",1210.0142v1
2014-08-27,Dynamics of a mesoscopic nuclear spin ensemble interacting with an optically driven electron spin,"The ability to discriminate between simultaneously occurring noise sources in
the local environment of semiconductor InGaAs quantum dots, such as electric
and magnetic field fluctuations, is key to understanding their respective
dynamics and their effect on quantum dot coherence properties. We present a
discriminatory approach to all-optical sensing based on two-color resonance
fluorescence of a quantum dot charged with a single electron. Our measurements
show that local magnetic field fluctuations due to nuclear spins in the absence
of an external magnetic field are described by two correlation times, both in
the microsecond regime. The nuclear spin bath dynamics show a strong dependence
on the strength of resonant probing, with correlation times increasing by a
factor of four as the optical transition is saturated. We interpret the
behavior as motional averaging of both the Knight field of the resident
electron spin and the hyperfine-mediated nuclear spin-spin interaction due to
optically-induced electron spin flips.",1408.6437v2
2014-11-15,Cubic order spin effects in the dynamics and gravitational wave energy flux of compact object binaries,"We investigate cubic-in-spin effects for inspiralling compact objects
binaries, both in the dynamics and the energy flux emitted in gravitational
waves, at the leading post-Newtonian order. We use a Lagrangian formalism to
implement finite-size effects, and extend it at cubic order in the spins, which
corresponds to the octupolar order in a multipolar decomposition. This
formalism allows us to derive the equation of motion, equations of precession
for the spin, and stress-energy tensor of each body in covariant form, and
admits a formal generalization to any multipolar order. For spin-induced
multipoles, i.e. in the case where the rotation of the compact object is sole
responsible for the additional multipole moments, we find a unique structure
for the octupolar moment representing cubic-in-spin effects. We apply these
results to compute the associated effects in the dynamics of compact binary
systems, and deduce the corresponding terms in the energy loss rate due to
gravitational waves. These effects enter at the third-and-a-half post-Newtonian
order, and can be important for binaries involving rapidly spinning black
holes. We provide simplified results for spin-aligned, circular orbits, and
discuss the quantitative importance of the new contributions.",1411.4118v2
2015-11-05,Spinor Bose-Einstein gases,"In a spinor Bose-Einstein gas, the non-zero hyperfine spin of the gas becomes
an accessible degree of freedom. At low temperature, such a gas shows both
magnetic and superfluid order, and undergoes both density and spin dynamics.
These lecture notes present a general overview of the properties of spinor
Bose-Einstein gases. The notes are divided in five sections. In the first, we
summarize basic properties of multi-component quantum fluids, focusing on the
specific case of spinor Bose-Einstein gases and the role of rotational symmetry
in defining their properties. Second, we consider the magnetic state of a
spinor Bose-Einstein gas, highlighting effects of thermodynamics and
Bose-Einstein statistics and also of spin-dependent interactions between atoms.
In the third section, we discuss methods for measuring the properties of
magnetically ordered quantum gases and present newly developed schemes for
spin-dependent imaging. We then discuss the dynamics of spin mixing in which
the spin composition of the gas evolves through the spin-dependent interactions
within the gas. We discuss spin mixing first from a microscopic perspective,
and then advance to discussing collective and beyond-mean-field dynamics. The
fifth section reviews recent studies of the magnetic excitations of
quantum-degenerate spinor Bose gases. We conclude with some perspectives on
future directions for research.",1511.01575v1
2016-02-29,Metastability for Glauber dynamics on random graphs,"In this paper we study metastable behaviour at low temperature of Glauber
spin-flip dynamics on random graphs. We fix a large number of vertices and
randomly allocate edges according to the Configuration Model with a prescribed
degree distribution. Each vertex carries a spin that can point either up or
down. Each spin interacts with a positive magnetic field, while spins at
vertices that are connected by edges also interact with each other via a
ferromagnetic pair potential. We start from the configuration where all spins
point down, and allow spins to flip up or down according to a Metropolis
dynamics at positive temperature. We are interested in the time it takes the
system to reach the configuration where all spins point up. In order to achieve
this transition, the system needs to create a sufficiently large droplet of
up-spins, called critical droplet, which triggers the crossover.
  In the limit as the temperature tends to zero, and subject to a certain
\emph{key hypothesis} implying metastable behaviour, the average crossover time
follows the classical \emph{Arrhenius law}, with an exponent and a prefactor
that are controlled by the \emph{energy} and the \emph{entropy} of the critical
droplet. The crossover time divided by its average is exponentially
distributed. We study the scaling behaviour of the exponent as the number of
vertices tends to infinity, deriving upper and lower bounds. We also identify a
regime for the magnetic field and the pair potential in which the key
hypothesis is satisfied. The critical droplets, representing the saddle points
for the crossover, have a size that is of the order of the number of vertices.
This is because the random graphs generated by the Configuration Model are
expander graphs.",1602.08900v1
2016-03-03,The Fock Space of Loopy Spin Networks for Quantum Gravity,"In the context of the coarse-graining of loop quantum gravity, we introduce
loopy and tagged spin networks, which generalize the standard spin network
states to account explicitly for non-trivial curvature and torsion. Both
structures relax the closure constraints imposed at the spin network vertices.
While tagged spin networks merely carry an extra spin at every vertex encoding
the overall closure defect, loopy spin networks allow for an arbitrary number
of loops attached to each vertex. These little loops can be interpreted as
local excitations of the quantum gravitational field and we discuss the
statistics to endow them with. The resulting Fock space of loopy spin networks
realizes new truncation of loop quantum gravity, allowing to formulate its
graph-changing dynamics on a fixed background graph plus local degrees of
freedom attached to the graph nodes. This provides a framework for
re-introducing a non-trivial background quantum geometry around which we would
study the effective dynamics of perturbations. We study how to implement the
dynamics of topological BF theory in this framework. We realize the projection
on flat connections through holonomy constraints and we pay special attention
to their often overlooked non-trivial flat solutions defined by higher
derivatives of the $\delta$-distribution.",1603.01117v2
2016-10-28,Insulating nanomagnets driven by spin torque,"Magnetic insulators, such as yttrium iron garnet (Y$_3$Fe$_5$O$_{12}$), are
ideal materials for ultra-low power spintronics applications due to their low
energy dissipation and efficient spin current generation and transmission.
Recently, it has been realized that spin dynamics can be driven very
effectively in micrometer-sized Y$_3$Fe$_5$O$_{12}$/Pt heterostructures by
spin-Hall effects. We demonstrate here the excitation and detection of spin
dynamics in Y$_3$Fe$_5$O$_{12}$/Pt nanowires by spin-torque ferromagnetic
resonance. The nanowires defined via electron-beam lithography are fabricated
by conventional room temperature sputtering deposition on Gd$_3$Ga$_5$O$_{12 }$
substrates and lift-off. We observe field-like and anti-damping-like torques
acting on the magnetization precession, which are due to simultaneous
excitation by Oersted fields and spin-Hall torques. The Y$_3$Fe$_5$O$_{12}$/Pt
nanowires are thoroughly examined over a wide frequency and power range. We
observe a large change in the resonance field at high microwave powers, which
is attributed to a decreasing effective magnetization due to microwave
absorption. These heating effects are much more pronounced in the investigated
nanostructures than in comparable micron-sized samples. By comparing different
nanowire widths, the importance of geometrical confinements for magnetization
dynamics becomes evident: quantized spin-wave modes across the width of the
wires are observed in the spectra. Our results are the first stepping stones
toward the realization of integrated magnonic logic devices based on
insulators, where nanomagnets play an essential role.",1610.09360v1
2016-08-18,Spin drift and diffusion in one- and two-subband helical systems,"The theory of spin drift and diffusion in two-dimensional electron gases is
developed in terms of a random walk model incorporating Rashba, linear and
cubic Dresselhaus, and intersubband spin-orbit couplings. The additional
subband degree of freedom introduces new characteristics to the persistent spin
helix (PSH) dynamics. As has been described before, for negligible intersubband
scattering rates, the sum of the magnetization of independent subbands leads to
a checkerboard pattern of crossed PSHs with long spin lifetime. For strong
intersubband scattering we model the fast subband dynamics as a new random
variable, yielding a dynamics set by averaged spin-orbit couplings of both
subbands. In this case the crossed PSH becomes isotropic, rendering circular
(Bessel) patterns with short spin lifetime. Additionally, a finite drift
velocity breaks the symmetry between parallel and transverse directions,
distorting and dragging the patterns. We find that the maximum spin lifetime
shifts away from the PSH regime with increasing drift velocity. We present
approximate analytical solutions for these cases and define their domain of
validity. Effects of magnetic fields and initial package broadening are also
discussed.",1608.05437v2
2017-12-02,Coherent excitation of heterosymmetric spin waves with ultrashort wavelengths,"In the emerging field of magnonics, spin waves are foreseen as signal
carriers for future spintronic information processing and communication
devices, owing to both the very low power losses and a high device
miniaturisation potential predicted for short-wavelength spin waves. Yet, the
efficient excitation and controlled propagation of nanoscale spin waves remains
a severe challenge. Here, we report the observation of high-amplitude,
ultrashort dipole-exchange spin waves (down to 80 nm wavelength at 10 GHz
frequency) in a ferromagnetic single layer system, coherently excited by the
driven dynamics of a spin vortex core. We used time-resolved x-ray microscopy
to directly image such propagating spin waves and their excitation over a wide
range of frequencies. By further analysis, we found that these waves exhibit a
heterosymmetric mode profile, involving regions with anti-Larmor precession
sense and purely linear magnetic oscillation. In particular, this mode profile
consists of dynamic vortices with laterally alternating helicity, leading to a
partial magnetic flux closure over the film thickness, which is explained by a
strong and unexpected mode hybridisation. This spin-wave phenomenon observed is
a general effect inherent to the dynamics of sufficiently thick ferromagnetic
single layer films, independent of the specific excitation method employed.",1712.00681v3
2017-12-04,Trend reversal in the magnetic-field dependence of exciton spin-transfer rates in diluted magnetic semiconductors due to non-Markovian dynamics,"We investigate theoretically the influence of an external magnetic field on
the spin dynamics of excitons in diluted magnetic semiconductor quantum wells.
To this end, we apply a quantum kinetic theory beyond the Markov approximation
which reveals that non-Markovian effects can significantly influence the
exciton spin dynamics. If the magnetic field is oriented parallel to the growth
direction of the well, the Markovian spin-transfer rate decreases monotonically
with increasing field as predicted by Fermi's golden rule. The quantum kinetic
theory follows this result qualitatively but predicts pronounced quantitative
differences in the spin-transfer rate as well as in the long-time spin
polarization. However, for an in-plane magnetic field, where the Markovian
spin-transfer rate first drops and then increases again, quantum kinetic
effects become so pronounced that the Markovian trend is completely reversed.
This is made evident by a distinct maximum of the rate followed by a monotonic
decrease. The deviations can be traced back to a redistribution of carriers in
energy space caused by correlations between excitons and magnetic dopants. The
same effect leads to a finite electron-spin polarization at long times in
longitudinal as well as transverse fields which is much larger than the
corresponding Markovian prediction.",1712.00978v2
2018-07-09,Cavity-induced emergent topological spin textures in a Bose Einstein condensate,"The coupled nonlinear dynamics of ultracold quantum matter and
electromagnetic field modes in an optical resonator exhibits a wealth of
intriguing collective phenomena. Here we study a $\Lambda$-type,
three-component Bose-Einstein condensate coupled to four dynamical running-wave
modes of a ring cavity, where only two of the modes are externally pumped.
However, the unpumped modes play a crucial role in the dynamics of the system
due to coherent back-scattering of photons. On a mean- field level we identify
three fundamentally different steady-state phases with distinct characteristics
in the density and spatial spin textures: a combined density and spin wave, a
continuous spin spiral with a homogeneous density, and a spin spiral with a
modulated density. The spin-spiral states, which are topological, are
intimately related to cavity-induced spin-orbit coupling emerging beyond a
critical pump power. The topologically trivial density-wave--spin-wave state
has the characteristics of a supersolid with two broken continuous symmetries.
The transitions between different phases are either simultaneously topological
and first order, or second order. The proposed setup allows the simulation of
intriguing many-body quantum phenomena by solely tuning the pump amplitudes and
frequencies, with the cavity output fields serving as a built-in nondestructive
observation tool.",1807.03316v1
2021-06-23,Correlation Between Spin and Orbital Dynamics During Laser-Induced Femtosecond Demagnetization,"Spin and orbital angular momenta are two intrinsic properties of an electron
and are responsible for the physics of a solid. How the spin and orbital evolve
with respect to each other on several hundred femtoseconds is largely unknown,
but it is at the center of laser-induced ultrafast demagnetization. In this
paper, we introduce a concept of the spin-orbital correlation diagram, where
spin angular momentum is plotted against orbital angular momentum, much like
the position-velocity phase diagram in classical mechanics. We use four sets of
highly accurate time-resolved x-ray magnetic circular dichroism (TR-XMCD) data
to construct four correlation diagrams for iron and cobalt. To our surprise, a
pattern emerges. The trace on the correlation diagram for iron is an arc, and
at the end of demagnetization, it has a pronounced cusp. The correlation
diagram for cobalt is different and appears more linear, but with kinks. We
carry out first-principles calculations with two different methods:
time-dependent density functional theory (TDDFT) and time-dependent Liouville
density functional theory (TDLDFT). These two methods agree that the
experimental findings for both Fe and Co are not due t experimental errors. It
is the spin-orbit coupling that correlates the spin dynamics to the orbital
dynamics.Microscopically, Fe and Co have different orbital occupations, which
leads to distinctive correlation diagrams. We believe that this correlation
diagram presents a useful tool to better understand spin and orbital dynamics
on an ultrafast time scale. A brief discussion on the magnetic anisotropy
energy is also provided.",2106.12679v1
2021-12-10,"Observation and control of collective spin-wave mode-hybridisation in chevron arrays and square, staircase and brickwork artificial spin ices","Dipolar magnon-magnon coupling has long been predicted in nano-patterned
artificial spin systems. However, observation of such phenomena and related
collective spin-wave signatures have until recently proved elusive or limited
to low-power edge-modes which are difficult to measure experimentally. Here we
describe the requisite conditions for dipolar mode-hybridisation, how it may be
controlled, why it was not observed earlier and how strong coupling may occur
between nanomagnet bulk-modes. We experimentally investigate four
nano-patterned artificial spin system geometries: `chevron' arrays, `square',
`staircase' and `brickwork' artificial spin ices. We observe significant
dynamic dipolar-coupling in all systems with relative coupling strengths and
avoided-crossing gaps supported by micromagnetic-simulation results. We
demonstrate reconfigurable mode-hybridisation regimes in each system via
microstate control, and in doing so elucidate the underlying dynamics governing
dynamic dipolar-coupling with implications across reconfigurable magnonics. We
demonstrate that confinement of the bulk-modes via edge effects play a critical
role in dipolar hybridised-modes, and treating nanoislands as a coherently
precessing macro-spins or standing spin-waves are insufficient to capture
experimentally-observed coupling phenomena. Finally, we present a
parameter-space search detailing how coupling strength may be tuned via
nanofabrication-dimensions and material properties.",2112.05354v1
2022-03-17,Precise control of entanglement in multinuclear spin registers coupled to defects,"Quantum networks play an indispensable role in quantum information tasks such
as secure communications, enhanced quantum sensing, and distributed computing.
Among the most mature and promising platforms for quantum networking are
nitrogen-vacancy centers in diamond and other color centers in solids. One of
the challenges in using these systems for networking applications is to
controllably manipulate entanglement between the electron and the nuclear spin
register despite the always-on nature of the hyperfine interactions, which
makes this an inherently many-body quantum system. Here, we develop a general
formalism to quantify and control the generation of entanglement in an
arbitrarily large nuclear spin register coupled to a color center electronic
spin. We provide a reliable measure of nuclear spin selectivity, by exactly
incorporating into our treatment the dynamics with unwanted nuclei. We also
show how to realize direct multipartite gates through the use of dynamical
decoupling sequences, drastically reducing the total gate time compared to
protocols based on sequential entanglement with individual nuclear spins. We
quantify the performance of such gate operations in the presence of unwanted
residual entanglement links, capturing the dynamics of the entire nuclear spin
register. Finally, using experimental parameters of a well-characterized 27
nuclear spin register device, we show how to prepare with high fidelity
entangled states for quantum error correction.",2203.09459v2
2022-04-22,Controlling magnetism with light in a zero orbital angular momentum antiferromagnet,"Antiferromagnetic materials feature intrinsic ultrafast spin dynamics, making
them ideal candidates for future magnonic devices operating at THz frequencies.
A major focus of current research is the investigation of optical methods for
the efficient generation of coherent magnons in antiferromagnetic insulators.
In magnetic lattices endowed with orbital angular momentum, spin-orbit coupling
enables spin dynamics through the resonant excitation of low-energy electric
dipoles such as phonons and orbital resonances which interact with spins.
However, in magnetic systems with zero orbital angular momentum, microscopic
pathways for the resonant and low-energy optical excitation of coherent spin
dynamics are lacking. Here, we consider experimentally the relative merits of
electronic and vibrational excitations for the optical control of zero orbital
angular momentum magnets, focusing on a limit case: the antiferromagnet
manganese thiophoshate (MnPS3), constituted by orbital singlet Mn2+ ions. We
study the correlation of spins with two types of excitations within its band
gap: a bound electron orbital excitation from the singlet orbital ground state
of Mn2+ into an orbital triplet state, which causes coherent spin precession,
and a vibrational excitation of the crystal field that causes thermal spin
disorder. Our findings cast orbital transitions as key targets for magnetic
control in insulators constituted by magnetic centers of zero orbital angular
momentum.",2204.10574v1
2023-08-16,Accelerating micromagnetic and atomistic simulations using multiple GPUs,"It is shown micromagnetic and atomistic spin dynamics simulations can use
multiple GPUs in order to reduce computation time, but also to allow for a
larger simulation size than is possible on a single GPU. Whilst interactions
which depend on neighbouring spins, such as exchange interactions, may be
implemented efficiently by transferring data between GPUs using halo regions,
or alternatively using direct memory accesses, implementing the long-range
demagnetizing interaction is the main difficulty in achieving good performance
scaling, where the data transfer rate between GPUs is a significant bottleneck.
A multi-GPU convolution algorithm is developed here, which relies on single-GPU
FFTs executed in parallel. It is shown that even for micromagnetic simulations
where the demagnetizing interaction computation time dominates, good
performance scaling may be achieved, with speedup factors up to 1.8, 2.5, and
3.1, for 2, 3, and 4 GPUs respectively. The code developed here can be used for
any number of GPUs in parallel, with performance scaling strongly dependent on
inter-GPU data transfer rate and connection topology. This is further improved
in micromagnetic simulations which include a spin transport solver, obtaining
speedup factors up to 1.96, 2.8, and 3.7, for 2, 3, and 4 GPUs respectively.
The best case scenario is obtained for atomistic spin dynamics simulations,
where the demagnetizing interaction is implemented with spin-averaged cells.
Using a single workstation with 4 GPUs, it is shown atomistic spin dynamics
simulations with up to 1 billion spins, and atomistic Monte Carlo simulations
with up to 2 billion spins are possible, with a near-ideal performance scaling.",2308.08447v2
2023-09-20,Hybrid Quantum-Classical Stochastic Approach to Spin-Boson Models,"Interacting spin-boson models encompass a large class of physical systems,
spanning models with a single spin interacting with a bosonic bath -- a
paradigm of quantum impurity problems -- to models with many spins interacting
with a cavity mode -- a paradigm of quantum optics. Such models have emerged in
various quantum simulation platforms which are further subject to noise and
lossy dynamics. As generic many-body systems, dynamics of spin-boson models
constitutes a challenging problem. In this paper, we present an exact hybrid
quantum-classical stochastic approach to different spin-boson models which are
typically treated using distinct techniques. In this approach, the solution of
a classical stochastic equation (mimicking the bosonic modes) is input into a
quantum stochastic equation for the spins. Furthermore, the spins are
effectively decoupled for each stochastic realization, but this comes at the
expense of sampling over unphysical states. Remarkably, the dynamics remains
Markovian in our approach even in the strong coupling regime. Moreover, we
utilize Markovian dissipation to make \textit{causality} manifest, thus
ensuring hermiticity (though not positivity) of the density matrix for each
realization. Finally, in contrast with many existing methods, we place no
restriction on the initial state, and further argue that an intrinsic
nonlinearity of the bosonic modes can be tackled within this framework. We
benchmark and showcase the utility of our approach in several examples,
specifically in cases where an exact numerical calculation is far from reach.",2309.11553v1
2024-01-24,Magnetism and spin dynamics of an S=3/2 frustrated trillium lattice antiferromagnet K2CrTi(PO4)3,"Competing magnetic interactions, frustration driven quantum fluctuations, and
spin correlations offer an ideal route for the experimental realization of
emergent quantum phenomena and exotic quasi particle excitations in 3D
frustrated magnets. In this context, trillium lattice, wherein magnetic ions
decorate a three-dimensional chiral network of corner-shared equilateral
triangular motifs, provides a viable ground. Herein, we present the crystal
structure, magnetic susceptibility, specific heat, electron spin-resonance,
muSR results on the polycrystalline samples of K2CrTi(PO4)3 wherein the Cr3+
ions form a perfect trillium lattice without any detectable anti-site disorder.
The Curie-Weiss fit of the magnetic susceptibility data above 100 K yields a
Curie-Weiss temperature of -23 K, which indicates the presence of dominant
antiferromagnetic interactions between Cr3+ (S=3/2) moments. The specific heat
measurements reveal the occurrence of two consecutive phase transitions, at
temperatures TL = 4.3 K and TH = 8 K, corresponding to two different magnetic
phases and it unveils the existence of short-range spin correlations above the
ordering temperature TH. The power-law behavior of ESR linewidth suggests the
persistence of short-range spin correlations over a relatively wide critical
region in agreement with the specific heat results. The muSR resultsprovide
concrete evidence of two different phases corresponding to two transitions,
coupled with thecritical slowing down of spin fluctuations above TL and
persistent spin dynamics below TL, consistent with the thermodynamic results.
Moreover, the muSR results reveal the coexistence of static and dynamic local
magnetic fields below TL, signifying the presence of complex magnetic phases
owing to the entwining of spin correlations and competing magnetic interactions
in this three-dimensional frustrated magnet.",2401.13445v1
2007-06-19,Dynamics and thermalization of the nuclear spin bath in the single-molecule magnet Mn12-ac: test for the theory of spin tunneling,"The description of the tunneling of a macroscopic variable in the presence of
a bath of localized spins is a subject of great fundamental and practical
interest, and is relevant for many solid-state qubit designs. Instead of
focusing on the the ""central spin"" (as is most often done), here we present a
detailed study of the dynamics of the nuclear spin bath in the Mn12-ac
single-molecule magnet, probed by NMR experiments down to very low temperatures
(T = 20 mK). We find that the longitudinal relaxation rate of the 55Mn nuclei
in Mn12-ac becomes roughly T-independent below T = 0.8 K, and can be strongly
suppressed with a longitudinal magnetic field. This is consistent with the
nuclear relaxation being caused by quantum tunneling of the molecular spin, and
we attribute the tunneling fluctuations to the minority of fast-relaxing
molecules present in the sample. The transverse nuclear relaxation is also
T-independent for T < 0.8 K, and can be explained qualitatively and
quantitatively by the dipolar coupling between like nuclei in neighboring
molecules. We also show that the isotopic substitution of 1H by 2H leads to a
slower nuclear longitudinal relaxation, consistent with the decreased tunneling
probability of the molecular spin. Finally, we demonstrate that, even at the
lowest temperatures, the nuclear spins remain in thermal equilibrium with the
lattice phonons, and we investigate the timescale for their thermal
equilibration. After a review of the theory of macroscopic spin tunneling in
the presence of a spin bath, we argue that most of our experimental results are
consistent with that theory, but the thermalization of the nuclear spins is
not.",0706.2760v2
2013-05-24,Realizing a lattice spin model with polar molecules,"With the recent production of polar molecules in the quantum regime,
long-range dipolar interactions are expected to facilitate the understanding of
strongly interacting many-body quantum systems and to realize lattice spin
models for exploring quantum magnetism. In atomic systems, where interactions
require wave function overlap, effective spin interactions on a lattice can be
realized via superexchange; however, the coupling is weak and limited to
nearest-neighbor interactions. In contrast, dipolar interactions exist in the
absence of tunneling and extend beyond nearest neighbors. This allows coherent
spin dynamics to persist even at high entropy and low lattice filling. Effects
of dipolar interactions in ultracold molecular gases have so far been limited
to the modification of chemical reactions. We now report the observation of
dipolar interactions of polar molecules pinned in a 3D optical lattice. We
realize a lattice spin model with spin encoded in rotational states, prepared
and probed by microwaves. This spin-exchange interaction arises from the
resonant exchange of rotational angular momentum between two molecules. We
observe clear oscillations in the evolution of the spin coherence in addition
to an overall decay. The frequency of these oscillations, the strong dependence
of the spin coherence time on the lattice filling, and the effect of a
multi-pulse sequence designed to reverse dynamics due to two-body exchange
interactions all provide evidence of dipolar interactions. We also demonstrate
suppression of loss in weak lattices due to a quantum Zeno mechanism.
Measurements of these tunneling-induced losses allow us to independently
determine the lattice filling factor. These results comprise an initial
exploration of the behavior of many-body spin models with direct, long-range
spin interactions and lay the groundwork for future studies of many-body
dynamics in spin lattices.",1305.5598v1
2019-04-23,Spin injection and pumping generated by a direct current flowing through a magnetic tunnel junction,"A charge flow through a magnetic tunnel junction (MTJ) leads to the
generation of a spin-polarized current which exerts a spin-transfer torque
(STT) on the magnetization. When the density of applied direct current exceeds
some critical value, the STT excites high-frequency magnetization precession in
the ""free"" electrode of MTJ. Such precession gives rise to microwave output
voltage and, furthermore, can be employed for spin pumping into adjacent normal
metal or semiconductor. Here we describe theoretically the spin dynamics and
charge transport in the CoFeB/MgO/CoFeB/Au tunneling heterostructure connected
to a constant-current source. The magnetization dynamics in the free CoFeB
layer with weak perpendicular anisotropy is calculated by numerical integration
of the Landau-Lifshitz-Gilbert-Slonczewski equation accounting for both STT and
voltage controlled magnetic anisotropy associated with the CoFeB|MgO interface.
It is shown that a large-angle magnetization precession, resulting from
electrically induced dynamic spin reorientation transition, can be generated in
a certain range of relatively low current densities. An oscillating spin
current, which is pumped into the Au overlayer owing to such precession, is
then evaluated together with the injected spin current. Considering both the
driving spin-polarized charge current and the pumped spin current, we also
describe the charge transport in the CoFeB/Au bilayer with the account of
anomalous and inverse spin Hall effects. An electric potential difference
between the lateral sides of the CoFeB/Au bilayer is calculated as a function
of distance from the CoFeB|MgO interface. It is found that this transverse
voltage signal in Au is large enough for experimental detection, which
indicates significant efficiency of the proposed current-driven spin injector.",1904.10361v1
2021-11-23,Wavelet-resolved coherence beats in the Overhauser field of a thermal nuclear spin ensemble,"This work introduces the so-called synchrosqueezed wavelet transform, to shed
light on the dipolar fluctuations of a thermal ensemble of nuclear spins in a
diamond crystal structure, hyperfine-coupled to a central spin. The raw time
series of the nuclear spin bath coherent dynamics is acquired through the
two-point correlation function computed using the cluster correlation expansion
method. The dynamics can be conveniently analyzed according to zero-, single-,
and double-quantum transitions derived from the dipolar pairwise spin flips. We
show that in the early-time behavior when the coherence is preserved in the
spin ensemble, the Overhauser field fluctuations are modulated by
dipole-dipole-induced small inhomogeneous detunings of nearly resonant
transitions within the bath. The resulting beating extending over relatively
longer time intervals is featured on the scalograms where both temporal and
spectral behaviors of nuclear spin noise are unveiled simultaneously. Moreover,
a second kind of beating that affects faster dynamics is readily discernible,
originating from the inhomogeneous spread of the hyperfine coupling of each
nucleus with the central spin. Additionally, any quadrupolar nuclei within the
bath imprint as beating residing in the zero-quantum channel. The nuclear spin
environment can be directionally probed by orienting the hyperfine axis.
Thereby, crucial spatial information about the closely separated spin clusters
surrounding the central spin are accessible. Thus, a wavelet-based post
processing can facilitate the identification of proximal nuclear spins as
revealed by their unique beating patterns on the scalograms. Finally, when
these features are overwhelmed by either weakly or strongly coupled classical
noise sources, we demonstrate the efficacy of thresholding techniques in the
wavelet domain in denoising contaminated scalograms.",2111.11812v2
2022-12-11,Layer-dependent optically-induced spin polarization in InSe,"Optical control of spin in semiconductors has been pioneered using
nanostructures of III-V and II-VI semiconductors, but the emergence of
two-dimensional van der Waals materials offers an alternative low-dimensional
platform for spintronic phenomena. Indium selenide (InSe), a group-III
monochalcogenide van der Waals material, has shown promise for opto-electronics
due to its high electron mobility, tunable direct bandgap, and quantum
transport. There are predictions of spin-dependent optical selection rules
suggesting potential for all-optical excitation and control of spin in a
two-dimensional layered material. Despite these predictions, layer-dependent
optical spin phenomena in InSe have yet to be explored. Here, we present
measurements of layer-dependent optical spin dynamics in few-layer and bulk
InSe. Polarized photoluminescence reveals layer-dependent optical orientation
of spin, thereby demonstrating the optical selection rules in few-layer InSe.
Spin dynamics are also studied in many-layer InSe using time-resolved Kerr
rotation spectroscopy. By applying out-of-plane and in-plane static magnetic
fields for polarized emission measurements and Kerr measurements, respectively,
the $g$-factor for InSe was extracted. Further investigations are done by
calculating precession values using a $\textbf{k} \cdot \textbf{p}$ model,
which is supported by \textit{ab-initio} density functional theory. Comparison
of predicted precession rates with experimental measurements highlights the
importance of excitonic effects in InSe for understanding spin dynamics.
Optical orientation of spin is an important prerequisite for opto-spintronic
phenomena and devices, and these first demonstrations of layer-dependent
optical excitation of spins in InSe lay the foundation for combining
layer-dependent spin properties with advantageous electronic properties found
in this material.",2212.05423v1
1997-04-14,Dynamics of PSR J0045-7319/B-star Binary and Neutron Star Formation,"Recent timing observations have revealed the presence of orbital precession
due to spin-orbit coupling and rapid orbital decay due to dynamical tidal
interaction in the PSR J0045-7319/B-star binary system. They can be used to put
concrete constraints on the age, initial spin and velocity of the neutron star.",9704134v1
1994-05-16,Bifurcations of two coupled classical spin oscillators,"Two classical, damped and driven spin oscillators with an isotropic exchange
interaction are considered. They represent a nontrivial physical system whose
equations of motion are shown to allow for an analytic treatment of local
codimension 1 and 2 bifurcations. In addition, numerical results are presented
which exhibit a Feigenbaum route to chaos.",9405011v1
1994-02-23,Statistical mechanics of one-dimensional s=1/2 anisotropic XY model in transverse field with Dzyaloshinskii-Moriya interaction,"For 1D s=1/2 anisotropic XY model in transverse field with
Dzyaloshinskii-Moriya interaction using Jordan-Wigner transformation the
thermodynamical functions, static spin correlation functions, transverse
dynamical spin correlation function and connected with it transverse dynamical
susceptibility have been obtained. It has been shown that Dzyaloshinskii-Moriya
interaction essentially influences the calculated quantities.",9402098v1
1998-07-08,Integrability and Quantum Chaos in Spin Glass Shards,"We study spin glass clusters (""shards"") in a random transverse magnetic
field, and determine the regime where quantum chaos and random matrix level
statistics emerge from the integrable limits of weak and strong field.
Relations with quantum phase transition are also discussed.",9807123v1
1999-01-20,Stabilizing Role of Mesoscopic Fluctuations in Spin Systems,"The occurrence of mesoscopic fluctuations in statistical systems implies,
from the point of view of dynamical theory, the existence of local
instabilities. However, the presence of such fluctuations can make a system, as
a whole, more stable from the thermodynamic point of view. Thus, in many cases,
a local dynamic instability is a requisite for the global thermodynamic
stability. This idea is illustrated by several spin models.",9901199v1
2001-10-19,Spin-models of granular compaction: From one-dimensional models to random graphs,"We discuss two athermal types of dynamics suitable for spin-models designed
to model repeated tapping of a granular assembly. These dynamics are applied to
a range of models characterised by a 3-spin Hamiltonian aiming to capture the
geometric frustration in packings of granular matter.",0110413v1
2002-05-29,On controlling simple dynamics by a disagreement function,"We introduce a formula for the disagreement function which is used to control
a recently proposed dynamics of the Ising spin system. This leads to four
different phases of the Ising spin chain in a zero temperature. One of these
phases is doubly degenerated (anti- and ferromagnetic states are equally
probable). On the borders between the phases two types of transitions are
observed: infinite degeneration and instability lines. The relaxation of the
system depends strongly on the phase.",0205614v1
2004-02-07,Eigen model as a quantum spin chain: exact dynamics,"We map Eigen model of biological evolution [Naturwissenschaften {\bf 58}, 465
(1971)] into a one-dimensional quantum spin model with non-Hermitean
Hamiltonian. Based on such a connection, we derive exact relaxation periods for
the Eigen model to approach static energy landscape from various initial
conditions. We also study a simple case of dynamic fitness function.",0402212v1
2005-09-11,Spin Dynamics for the Lebwohl-Lasher Model,"A spin dynamics algorithm, combining checkerboard updating and a rotation
algorithm based on the local second-rank ordering field, is developed for the
Lebwohl-Lasher model of liquid crystals. The method is shown to conserve energy
well and to generate simulation averages which are consistent with those
obtained by Monte Carlo simulation. However, care must be taken to avoid the
undesirable effects of director rotation, and a method for doing this is
proposed.",0509271v1
1996-01-05,Directly Interacting Massless Particles - a Twistor Approach,"Twistor phase spaces are used to provide a general description of the
dynamics of a finite number of directly interacting massless spinning particles
forming a closed relativistic massive and spinning system with an internal
structure. A Poincare invariant canonical quantization of the so obtained
twistor phase space dynamics is performed.",9601017v1
2004-07-13,Dynamical correlation functions of the XXZ spin-1/2 chain,"We derive a master equation for the dynamical spin-spin correlation functions
of the XXZ spin-1/2 Heisenberg finite chain in an external magnetic field. In
the thermodynamic limit, we obtain their multiple integral representation.",0407108v1
2005-04-04,Dynamical Theory of Generalized Matrices,"We propose a generalization of spin algebra using multi-index objects, and a
dynamical system analogous to matrix theory. The system has a solution
described by generalized spin representation matrices and possesses a symmetry
similar to the volume preserving diffeomorphism in the p-brane action.",0504017v1
2002-07-03,What's Wrong with these Observables?,"An imprecise measurement of a dynamical variable (such as a spin component)
does not, in general, give the value of another dynamical variable (such as a
spin component along a slightly different direction). The result of the
measurement cannot be interpreted as the value of any observable that has a
classical analogue.",0207020v1
2007-10-01,Next to leading order gravitational wave emission and dynamical evolution of compact binary systems with spin,"Compact binary systems with spinning components are considered. Finite size
effects due to rotational deformation are taken into account. The dynamical
evolution and next to leading order gravitational wave forms are calculated,
taking into account the orbital motion up to the first post-Newtonian
approximation.",0710.0258v2
2011-10-24,Grassmann dynamics of classical spin in nonabelian gauge fields,"Using Grassmann variant of classical mechanics, we construct Lagrangian
dynamics of classical spinning particle in (possibly non-abelian) gauge fields.
Quantization of this model is briefly discussed.",1110.5185v1
2015-10-21,Gacs Algorithmic Complexity on Hilbert Spaces and Some of its Applications,"We extend the notion of Gacs quantum algorithmic entropy, originally
formulated for finitely many qubits, to infinite dimensional quantum spin
chains and investigate the relation of this extension with two quantum
dynamical entropies that have been proposed in recent years. Further, we prove
an extension of Brudno's theorem in quantum spin chains with shift dynamics.",1511.00635v1
2016-09-22,Manipulation of magnetic Skyrmions with a Scanning Tunneling Microscope,"The dynamics of a single magnetic Skyrmion in an atomic spin system under the
influence of Scanning Tunneling Microscope is investigated by computer
simulations solving the Landau-Lifshitz-Gilbert equation. Two possible
scenarios are described: manipulation with aid of a spin-polarized tunneling
current and by an electric field created by the scanning tunneling microscope.
The dynamics during the creation and annihilation process is studied and the
possibility to move single Skyrmions is showed.",1609.06797v1
2017-02-16,Driven dissipative dynamics and topology of quantum impurity systems,"In this review, we provide an introduction and overview to some more recent
advances in real-time dynamics of quantum impurity models and their
realizations in quantum devices. We focus on the Ohmic spin-boson and related
models, which describes a single spin-1/2 coupled to an infinite collection of
harmonic oscillators. The topics are largely drawn from our efforts over the
past years, but we also present a few novel results. In the first part of this
review, we begin with a pedagogical introduction to the real-time dynamics of a
dissipative spin at both high and low temperatures. We then focus on the driven
dynamics in the quantum regime beyond the limit of weak spin-bath coupling. In
these situations, the non-perturbative stochastic Schroedinger equation method
is ideally suited to numerically obtain the spin dynamics as it can incorporate
bias fields $h_z(t)$ of arbitrary time-dependence in the Hamiltonian. We
present different recent applications of this method: (i) how topological
properties of the spin such as the Berry curvature and the Chern number can be
measured dynamically, and how dissipation affects the topology and the
measurement protocol, (ii) how quantum spin chains can experience
synchronization dynamics via coupling to a common bath. In the second part of
this review, we discuss quantum engineering of spin-boson and related models in
circuit quantum electrodynamics (cQED), quantum electrical circuits and
cold-atoms architectures. In different realizations, the Ohmic environment can
be represented by a long (microwave) transmission line, a Luttinger liquid, a
one-dimensional Bose-Einstein condensate, a chain of superconducting Josephson
junctions. We show that the quantum impurity can be used as a quantum sensor to
detect properties of a bath at minimal coupling, and how dissipative spin
dynamics can lead to new insight in the Mott-Superfluid transition.",1702.05135v3
2017-08-22,Dynamics of X-state in anisotropic Heisenberg spin with magnetic field,"We study the dynamics of X-state for anisotropic Heisenberg spin system using
quantum fidelity. It is shown that while Bell diagonal state, a special class
of X-state, is stationary, there exists a set of two parametric states which
are stationary in presence of external uniform magnetic field.",1708.06632v1
2008-07-01,The su(2|3) Undynamic Spin Chain,"The integrable spin chain found in perturbative planar N=4 supersymmetric
gauge theory is dynamic. Here we propose a reformulation which removes the
dynamic effects in order to make the model more accessible to an algebraic
treatment.",0807.0099v2
2017-12-06,QCD-constrained dynamical spin effects in the pion holographic light-front wavefunction,"Using light-front holography, we predict simultaneously the pion decay
constant and the pion charge radius by taking into account (higher twist)
dynamical spin effects whose relative importance is constrained by QCD.",1712.02263v1
2019-10-18,Neutron spin dynamics in polarized targets,"We present neutron elastic scattering amplitude for arbitrary polarized
target in irreducible spherical tensor representation. The general approach for
the description of neutron spin dynamics for the propagation trough the medium
with an arbitrary polarization is discussed in a relation to the search for
time reversal invariance violation in neutron scattering.",1910.08598v2
2018-06-27,Time discretization of the spin Calogero-Moser model and the semi-discrete matrix KP hierarchy,"We introduce the discrete time version of the spin Calogero-Moser system. The
equations of motion follow from the dynamics of poles of rational solutions to
the matrix KP hierarchy with discrete time. The dynamics of poles is derived
using the auxiliary linear problem for the discrete flow.",1806.10525v1
2018-08-07,Dynamics of quantum measurements employing two Curie-Weiss apparatuses,"Two types of quantum measurements, measuring the spins of an entangled pair
and attempting to measure a spin at either of two positions, are analysed
dynamically by apparatuses of the Curie-Weiss type. The outcomes comply with
the standard postulates.",1808.02421v1
2019-12-09,Dynamics of classical and quantum spin in external fields: A general formalism,"We study the dynamics of classical and quantum particles with spin and dipole
moments in external fields within the framework of the general approach by
making use of the projection technique. Applications include the neutrino
physics in matter, polarization phenomena in astrophysics, high-energy and
heavy-ion physics.",1912.04985v1
2021-11-24,Spin dynamics simulation of the $Z_2$-vortex fluctuations,"Motivated by the recent quasi-elastic neutron scattering experiment, we
extend the spin-dynamics simulation on the triangular-lattice Heisenberg
antiferromagnet, to observe a sharp central peak of its energy width $\sim
0.001J$ ($J$ the exchange coupling) of the $Z_2$-vortex origin, consistently
with the experiment.",2111.12271v1
2022-11-02,Light-induced ultrafast dynamics of spin crossovers in LaCoO3,"Ultrafast quantum dynamics relaxation of a photoexcited state in a strongly
correlated spin crossover system LaCoO3 under a sudden perturbation is
considered with the density matrix generalized master equation. The
magnetization and cobalt-oxygen bond length oscillations were found. The
evolution of the electronic band structure during relaxation is calculated in
the framework of the LDA+GTB method.",2211.01300v1
2014-06-26,"Spin Supercurrent, Magnetization Dynamics, and Phi-State in Spin-Textured Josephson Junctions","The prospect of combining the dissipationless nature of superconducting
currents with the spin-polarization of magnetic materials is interesting with
respect to exploring superconducting analogues of topics in spintronics. In
order to accomplish this aim, it is pivotal to understand how
spin-supercurrents interact dynamically with magnetization textures. We
investigate the appearance of a spin-supercurrent and the resulting
magnetization dynamics in a textured magnetic Josephson current by using three
experimentally relevant models: i) a S/F/S junction with spin-active
interfaces, ii) a S/F1/F2/F3/S Josephson junction with a ferromagnetic
trilayer, and iii) a Josephson junction containing a domain wall. In all of
these cases, the supercurrent is spin-polarized and exerts a spin-transfer
torque on the ferromagnetic interlayers which causes magnetization dynamics.
Using a scattering matrix formalism in the clean limit, we compute the
Andreev-bound states and free energy of the system which is used to solve the
Landau-Lifshiftz-Gilbert equation. We compute both how the inhomogeneous
magnetism influences the phase-dependence of the charge supercurrent as well as
the magnetization dynamics caused by the spin-supercurrent. Using a realistic
experimental parameter set, we find that the supercurrent can induce
magnetization switching that is controlled by the superconducting phase
difference. Moreover, we demonstrate that the combined effect of chiral spin
symmetry breaking and interface scattering causes the system to act as a phase
battery that may supply any superconducting phase difference phi in the ground
state. Such a phi junction is accompanied by an anomalous supercurrent
appearing even at zero phase difference, and we demonstrate that the flow
direction of this current is controlled by the chirality of the magnetization
configuration.",1406.7016v1
2022-05-05,Parity Violation in Spin-Precessing Binaries: Gravitational Waves from the Inspiral of Black Holes in Dynamical Chern-Simons Gravity,"Spin precession in compact binaries is intricately tuned to the multipole
structure of the underlying bodies. For black holes, violations of the no-hair
theorems induced by modifications to general relativity correct the precession
dynamics, which in turn imprints onto the amplitude and phase modulations of
the gravitational waves emitted by the binary. Recently, the spin precession
equations were derived up to second order in spin for dynamical Chern-Simons
gravity, a parity violating modified theory of gravity. We here solve these
equations and construct, for the first time, analytic expressions for the time-
and frequency-domain gravitational waves emitted in the quasi-circular inspiral
of spin-precessing black hole binaries in a modified theory of gravity using
the post-Newtonian approximation. Working within the small coupling
approximation and using multiple scale analysis, we show that the corrections
to the nutation phase enter at relative 1PN order, and the corrections to the
precession angle and Thomas phase enter at relative 0PN order. Making use of
the stationary phase approximation and shifted uniform asymptotics, we find
that the Fourier phase of the waveform is characterized by three modifications,
two due to the back-reaction of the precession dynamics onto the spin-orbit and
spin-spin couplings that enter at 1.5PN and 2PN orders, and a 2PN modification
due to the emission of dipole radiation. We also find that back-reaction of the
precession dynamics forces the dCS corrections to the Fourier amplitude to
enter at 0PN order, as opposed to 2PN order, as expected for spin-aligned
binaries. Our work lays the first foundational stones to build an
inspiral-merger-ringdown phenomenological model for spin-precessing binaries in
a modified theory of gravity.",2205.02675v2
2023-07-06,Finding the Dynamics of an Integrable Quantum Many-Body System via Machine Learning,"We study the dynamics of the Gaudin magnet (""central-spin model"") using
machine-learning methods. This model is of practical importance, e.g., for
studying non-Markovian decoherence dynamics of a central spin interacting with
a large bath of environmental spins and for studies of nonequilibrium
superconductivity. The Gaudin magnet is also integrable, admitting many
conserved quantities: For $N$ spins, the model Hamiltonian can be written as
the sum of $N$ independent commuting operators. Despite this high degree of
symmetry, a general closed-form analytic solution for the dynamics of this
many-body problem remains elusive. Machine-learning methods may be well suited
to exploiting the high degree of symmetry in integrable problems, even when an
explicit analytic solution is not obvious. Motivated in part by this intuition,
we use a neural-network representation (restricted Boltzmann machine) for each
variational eigenstate of the model Hamiltonian. We then obtain accurate
representations of the ground state and of the low-lying excited states of the
Gaudin-magnet Hamiltonian through a variational Monte Carlo calculation. From
the low-lying eigenstates, we find the non-perturbative dynamic transverse spin
susceptibility, describing the linear response of a central spin to a
time-varying transverse magnetic field in the presence of a spin bath. Having
an efficient description of this susceptibility opens the door to improved
characterization and quantum control procedures for qubits interacting with an
environment of quantum two-level systems. These systems include electron-spin
and hole-spin qubits interacting with environmental nuclear spins via hyperfine
interactions or qubits with charge or flux degrees of freedom interacting with
coherent charge or paramagnetic impurities.",2307.03310v2
2008-06-23,Spin-resolved quantum-dot resonance fluorescence,"In the quest for physically realizable quantum information science (QIS)
primitives, self-assembled quantum dots (QDs) serve a dual role as sources of
photonic (flying) qubits and traps for electron spin; the prototypical
stationary qubit. Here we demonstrate the first observation of spin-selective,
near background-free and transform-limited photon emission from a resonantly
driven QD transition. The hallmark of resonance fluorescence, i.e. the Mollow
triplet in the scattered photon spectrum when an optical transition is driven
resonantly, is presented as a natural way to spectrally isolate the photons of
interest from the original driving field. We go on to demonstrate that the
relative frequencies of the two spin-tagged photon states are tuned independent
of an applied magnetic field via the spin-selective dynamic Stark effect
induced by the very same driving laser. This demonstration enables the
realization of challenging QIS proposals such as heralded single photon
generation for linear optics quantum computing, spin-photon entanglement, and
dipolar interaction mediated quantum logic gates. From a spectroscopy
perspective, the spin-selective dynamic Stark effect tunes the QD spin-state
splitting in the ground and excited states independently, thus enabling
previously inaccessible regimes for controlled probing of mesoscopic spin
systems.",0806.3707v1
2008-11-07,Electrically driven magnetization of diluted magnetic semiconductors actuated by Overhauser effect,"It is well-known that the Curie temperature, and hence the magnetization, in
diluted magnetic semiconductor (DMS) like Ga$_{1-x}$Mn$_x$As can be controlled
by changing the equilibrium density of holes in the material. Here, we propose
that even with a constant hole density, large changes in the magnetization can
be obtained with a relatively small imbalance in the quasi-Fermi levels for
up-spin and down-spin electrons. We show, by coupling mean field theory of
diluted magnetic semiconductor ferromagnetism with master equations governing
the Mn spin-dynamics, that a mere splitting of the up-spin and down-spin
quasi-Fermi levels by 0.1 meV will produce the effect of an external magnetic
field as large as 1 T as long as the alternative relaxation paths for Mn spins
(i.e. spin-lattice relaxation) can be neglected. The physics is similar to the
classic Overhauser effect, also called the dynamic nuclear polarization, with
the Mn impurities playing the role of the nucleus. We propose that a lateral
spin-valve structure in anti-parallel configuration with a DMS as the channel
can be used to demonstrate this effect as quasi-Fermi level splitting of such
magnitude, inside the channel of similar systems, have already been
experimentally demonstrated to produce polarization of paramagnetic impurity
spins.",0811.1225v2
2010-04-26,Symplectic structure of post-Newtonian Hamiltonian for spinning compact binaries,"The phase space of a Hamiltonian system is symplectic. However, the
post-Newtonian Hamiltonian formulation of spinning compact binaries in existing
publications does not have this property, when position, momentum and spin
variables $[X, P, S_1, S_2]$ compose its phase space. This may give a
convenient application of perturbation theory to the derivation of the
post-Newtonian formulation, but also makes classic theories of a symplectic
Hamiltonian system be a serious obstacle in application, especially in
diagnosing integrability and nonintegrability from a dynamical system theory
perspective. To completely understand the dynamical characteristic of the
integrability or nonintegrability for the binary system, we construct a set of
conjugate spin variables and reexpress the spin Hamiltonian part so as to make
the complete Hamiltonian formulation symplectic. As a result, it is directly
shown with the least number of independent isolating integrals that a
conservative Hamiltonian compact binary system with both one spin and the pure
orbital part to any post-Newtonian order is typically integrable and not
chaotic. And conservative binary system consisting of two spins restricted to
the leading order spin-orbit interaction and the pure orbital part at all
post-Newtonian orders is also integrable, independently on the mass ratio. For
all other various spinning cases, the onset of chaos is possible.",1004.4549v1
2012-06-11,Photon and spin dependence of the resonance lines shape in the strong coupling regime,"We study the quantum dynamics of a spin ensemble coupled to cavity photons.
Recently, related experimental results have been reported, showing the
existence of the strong coupling regime in such systems. We study the
eigenenergy distribution of the multi-spin system (following the Tavis-Cummings
model) which shows a peculiar structure as a function of the number of cavity
photons and of spins. We study how this structure causes changes in the
spectrum of the admittance in the linear response theory, and also the
frequency dependence of the excited quantities in the stationary state under a
probing field. In particular, we investigate how the structure of the higher
excited energy levels changes the spectrum from a double-peak structure (the
so-called vacuum field Rabi splitting) to a single peak structure. We also
point out that the spin dynamics in the region of the double-peak structure
corresponds to recent experiments using cavity ringing while in region of the
single peak structure, it corresponds to the coherent Rabi oscillation in a
driving electromagnetic filed. Using a standard Lindblad type mechanism, we
study the effect of dissipations on the line width and separation in the
computed spectra. In particular, we study the relaxation of the total spin in
the general case of a spin ensemble in which the total spin of the system is
not specified. The theoretical results are correlated with experimental
evidence of the strong coupling regime, achieved with a spin 1/2 ensemble.",1206.2394v1
2014-10-16,Three stage decoherence dynamics of electron spin qubits in an optically active quantum dot,"The control of discrete quantum states in solids and their use for quantum
information processing is complicated by the lack of a detailed understanding
of the mechanisms responsible for qubit decoherences. For spin qubits in
semiconductor quantum dots, phenomenological models of decoherence currently
recognize two Basic stages; fast ensemble dephasing due to the coherent
precession of spin qubits around nearly static but randomly distributed
hyperfine fields and a much slower process of irreversible relaxation of spin
qubit polarization due to dynamics of the nuclear spin bath induced by complex
many-body interaction effects. We unambiguosly demonstrate that such a view on
decoherence is greatly oversimplified; the relaxation of a spin qubit state is
determined by three rather than two basic stages. The additional stage
corresponds to the effect of coherent dephasing processes that occur in the
nuclear spin bath that manifests itself by a relatively fast but incomplete
non-monotonous relaxation of the central spin polarization at intermediate
timescales. This observation changes our understanding of the electron spin
qubit decoherence mechanisms in solid state systems.",1410.4316v2
2015-03-06,Ultrafast spin dynamics in II-VI diluted magnetic semiconductors with spin-orbit interaction,"We study theoretically the ultrafast spin dynamics of II-VI diluted magnetic
semiconductors in the presence of spin-orbit interaction. Our goal is to
explore the interplay or competition between the exchange $sd$-coupling and the
spin-orbit interaction in both bulk and quantum well systems. For bulk
materials we concentrate on Zn$_{1-x}$Mn$_x$Se and take into account the
Dresselhaus interaction, while for quantum wells we examine
Hg$_{1-x-y}$Mn$_x$Cd$_y$Te systems with a strong Rashba coupling. Our
calculations were performed with a recently developed formalism which
incorporates electronic correlations beyond mean-field theory originated from
the exchange $sd$-coupling. For both bulk and quasi-two-dimensional systems we
find that, by varying the system parameters within realistic ranges, both
interactions can be chosen to play a dominant role or to compete on an equal
footing with each other. The most notable effect of the spin-orbit interaction
in both types of systems is the appearance of strong oscillations where the
exchange $sd$-coupling by itself only causes an exponential decay of the mean
electronic spin components. The mean-field approximation is also studied and it
is interpreted analytically why it shows a strong suppression of the
spin-orbit-induced dephasing of the spin component parallel to the Mn magnetic
field.",1503.01937v2
2015-05-07,The classical nature of nuclear spin noise near clock transitions of Bi donors in silicon,"Whether a quantum bath can be approximated as classical noise is a
fundamental issue in central spin decoherence and also of practical importance
in designing noise-resilient quantum control. Spin qubits based on bismuth
donors in silicon have tunable interactions with nuclear spin baths and are
first-order insensitive to magnetic noise at so-called clock-transitions (CTs).
This system is therefore ideal for studying the quantum/classical nature of
nuclear spin baths since the qubit-bath interaction strength determines the
back-action on the baths and hence the adequacy of a classical noise model. We
develop a Gaussian noise model with noise correlations determined by quantum
calculations and compare the classical noise approximation to the full quantum
bath theory. We experimentally test our model through dynamical decoupling
sequence of up to 128 pulses, finding good agreement with simulations and
measuring electron spin coherence times approaching one second - notably using
natural silicon. Our theoretical and experimental study demonstrates that the
noise from a nuclear spin bath is analogous to classical Gaussian noise if the
back-action of the qubit on the bath is small compared to the internal bath
dynamics, as is the case close to CTs. However, far from the CTs, the
back-action of the central spin on the bath is such that the quantum model is
required to accurately model spin decoherence.",1505.01604v1
2015-06-14,Few-second-long correlation times in a quantum dot nuclear spin bath probed by frequency-comb NMR spectroscopy,"One of the key challenges in spectroscopy is inhomogeneous broadening that
masks the homogeneous spectral lineshape and the underlying coherent dynamics.
A variety of techniques including four-wave mixing and spectral hole-burning
are used in optical spectroscopy while in nuclear magnetic resonance (NMR)
spin-echo is the most common way to counteract inhomogeneity. However, the
high-power pulses used in spin-echo and other sequences often create spurious
dynamics obscuring the subtle spin correlations that play a crucial role in
quantum information applications. Here we develop NMR techniques that allow the
correlation times of the fluctuations in a nuclear spin bath of individual
quantum dots to be probed. This is achieved with the use of frequency comb
excitation which allows the homogeneous NMR lineshapes to be measured avoiding
high-power pulses. We find nuclear spin correlation times exceeding 1 s in
self-assembled InGaAs quantum dots - four orders of magnitude longer than in
strain-free III-V semiconductors. The observed freezing of the nuclear spin
fluctuations opens the way for the design of quantum dot spin qubits with a
well-understood, highly stable nuclear spin bath.",1506.04412v1
2016-01-22,Optically induced dynamic nuclear spin polarisation in diamond,"The sensitivity of Magnetic Resonance Imaging (MRI) depends strongly on
nuclear spin polarisation and, motivated by this observation, dynamical nuclear
spin polarisation has recently been applied to enhance MRI protocols
(Kurhanewicz, J., et al., Neoplasia 13, 81 (2011)). Nuclear spins associated
with the 13 C carbon isotope (nuclear spin I = 1/2) in diamond possess uniquely
long spin lattice relaxation times (Reynhardt, E.C. and G.L. High, Prog. in
Nuc. Mag. Res. Sp. 38, 37 (2011)) If they are present in diamond nanocrystals,
especially when strongly polarised, they form a promising contrast agent for
MRI. Current schemes for achieving nuclear polarisation, however, require
cryogenic temperatures. Here we demonstrate an efficient scheme that realises
optically induced 13 C nuclear spin hyperpolarisation in diamond at room
temperature and low ambient magnetic field. Optical pumping of a
Nitrogen-Vacancy (NV) centre creates a continuously renewable electron spin
polarisation which can be transferred to surrounding 13 C nuclear spins.
Importantly for future applications we also realise polarisation protocols that
are robust against an unknown misalignment between magnetic field and crystal
axis.",1601.05967v1
2018-11-14,Acceleration of the precession frequency for optically-oriented electron spins in ferromagnetic/semiconductor hybrids,"Time-resolved Kerr rotation measurements were performed in InGaAs/GaAs
quantum wells nearby a doped Mn delta layer. Our magneto-optical results show a
typical time evolution of the optically-oriented electron spin in the quantum
well. Surprisingly, this is strongly affected by the Mn spins, resulting in an
increase of the spin precession frequency in time. This increase is attributed
to the variation in the effective magnetic field induced by the dynamical
relaxation of the Mn spins. Two processes are observed during electron spin
precession: a quasi-instantaneous alignment of the Mn spins with photo-excited
holes, followed by a slow alignment of Mn spins with the external transverse
magnetic field. The first process leads to an equilibrium state imprinted in
the initial precession frequency, which depends on pump power, while the second
process promotes a linear frequency increase, with acceleration depending on
temperature and external magnetic field. This observation yields new
information about exchange process dynamics and on the possibility of
constructing spin memories, which can rapidly respond to light while retaining
information for a longer period.",1811.06095v2
2014-03-24,Spin wave imaging in atomically designed nanomagnets,"The spin dynamics of all ferromagnetic materials are governed by two types of
collective excitations: spin waves and domain walls. The fundamental processes
underlying these collective modes, such as exchange interactions and magnetic
anisotropy, all originate at the atomic scale; yet, conventional probing
techniques, based on neutron and photon scattering, provide high resolution in
reciprocal space, and thereby poor spatial resolution. Here we present direct
imaging of spin waves in individual chains of ferromagnetically coupled $S=2$
Fe atoms, assembled one by one on a Cu$_2$N surface using a scanning tunnelling
microscope. We are able to map the spin dynamics of these designer nanomagnets
with atomic resolution, in two complementary ways. First, atom to atom
variations of the amplitude of the quantized spin wave excitations, predicted
by theory, are probed using inelastic electron tunnelling spectroscopy. Second,
we observe slow stochastic switching between two opposite magnetisation states,
whose rate varies strongly depending on the location of the tip along the
chain. Our observations, combined with model calculations, reveal that switches
of the chain are initiated by a spin wave excited state which has its antinodes
at the edges of the chain, followed by a domain wall shifting through the chain
from one end to the other. This approach opens the way towards atomic scale
imaging of other types of spin excitations, such as spinons and fractional
end-states, in engineered spin chains.",1403.5890v1
2012-01-06,Experimental observation of the optical spin transfer torque,"The spin transfer torque is a phenomenon in which angular momentum of a spin
polarized electrical current entering a ferromagnet is transferred to the
magnetization. The effect has opened a new research field of electrically
driven magnetization dynamics in magnetic nanostructures and plays an important
role in the development of a new generation of memory devices and tunable
oscillators. Optical excitations of magnetic systems by laser pulses have been
a separate research field whose aim is to explore magnetization dynamics at
short time scales and enable ultrafast spintronic devices. We report the
experimental observation of the optical spin transfer torque, predicted
theoretically several years ago building the bridge between these two fields of
spintronics research. In a pump-and-probe optical experiment we measure
coherent spin precession in a (Ga,Mn)As ferromagnetic semiconductor excited by
circularly polarized laser pulses. During the pump pulse, the spin angular
momentum of photo-carriers generated by the absorbed light is transferred to
the collective magnetization of the ferromagnet. We interpret the observed
optical spin transfer torque and the magnetization precession it triggers on a
quantitative microscopic level. Bringing the spin transfer physics into optics
introduces a fundamentally distinct mechanism from the previously reported
thermal and non-thermal laser excitations of magnets. Bringing optics into the
field of spin transfer torques decreases by several orders of magnitude the
timescales at which these phenomena are explored and utilized.",1201.1436v1
2018-10-09,Coherent spin dynamics of electrons and holes in CsPbBr$_3$ perovskite crystals,"The lead halide perovskites demonstrate huge potential for optoelectronic
applications, high energy radiation detectors, light emitting devices and solar
energy harvesting. Those materials exhibit strong spin-orbit coupling enabling
efficient optical orientation of carrier spins in perovskite-based devices with
performance controlled by a magnetic field. Perovskites are promising for
spintronics due to substantial bulk and structure inversion asymmetry, however,
their spin properties are not studied in detail. Here we show that elaborated
time-resolved spectroscopy involving strong magnetic fields can be successfully
used for perovskites. We perform a comprehensive study of high-quality
CsPbBr$_3$ crystals by measuring the exciton and charge carrier $g$-factors,
spin relaxation times and hyperfine interaction of carrier and nuclear spins by
means of coherent spin dynamics. Owing to their ""inverted"" band structure,
perovskites represent appealing model systems for semiconductor spintronics
exploiting the valence band hole spins, while in conventional semiconductors
the conduction band electrons are considered for spin functionality.",1810.04081v1
2018-10-15,Enhancement of nuclear spin coherence times by driving dynamic nuclear polarization at defect centers in solids,"The hyperpolarization of nuclear spins can enable powerful imaging and
sensing techniques provided the hyperpolarization is sufficiently long-lived.
Recent experiments on nanodiamond $^{13}$C nuclear spins demonstrate that
relaxation times can be extended by three orders of magnitude by building up
dynamic nuclear polarization (DNP) through the driving of electron-nuclear
flip-flop processes at defect centers. This finding raises the question of
whether the nuclear spin coherence times are also impacted by this
hyperpolarization process. Here, we theoretically examine the effect of DNP on
the nuclear spin coherence times as a function of the hyperpolarization drive
time. We do this by developing a microscopic theory of DNP in a nuclear spin
ensemble coupled to microwave-driven defect centers in solids and subject to
spin diffusion mediated by internuclear dipolar interactions. We find that,
similarly to relaxation times, the nuclear spin coherence times can be
increased substantially by a few orders of magnitude depending on the driving
time. Our theoretical model and results will be useful for current and future
experiments on enhancing nuclear spin coherence times via DNP.",1810.06542v2
2019-07-25,Controllable freezing of the nuclear spin bath in a single-atom spin qubit,"The quantum coherence and gate fidelity of electron spin qubits in
semiconductors is often limited by noise arising from coupling to a bath of
nuclear spins. Isotopic enrichment of spin-zero nuclei such as $^{28}$Si has
led to spectacular improvements of the dephasing time $T_2^*$ which,
surprisingly, can extend two orders of magnitude beyond theoretical
expectations. Using a single-atom $^{31}$P qubit in enriched $^{28}$Si, we show
that the abnormally long $T_2^*$ is due to the controllable freezing of the
dynamics of the residual $^{29}$Si nuclei close to the donor. Our conclusions
are supported by a nearly parameter-free modeling of the $^{29}$Si nuclear spin
dynamics, which reveals the degree of back-action provided by the electron spin
as it interacts with the nuclear bath. This study clarifies the limits of
ergodic assumptions in analyzing many-body spin-problems under conditions of
strong, frequent measurement, and provides novel strategies for maximizing
coherence and gate fidelity of spin qubits in semiconductors.",1907.11032v1
2020-12-04,Stability of supercurrents in a superfluid phase of spin-1 bosons in an optical lattice,"We study collective modes and superfluidity of spin-1 bosons with
antiferromagnetic interactions in an optical lattice based on the
time-dependent Ginzburg-Landau (TDGL) equation derived from the spin-1
Bose-Hubbard model. Specifically, we examine the stability of supercurrents in
the polar phase in the vicinity of the Mott insulating phase with even filling
factors. Solving the linearized TDGL equation, we obtain gapless spin-nematic
modes and gapful spin-wave modes in the polar phase that arise due to the
breaking of $S^2$ symmetry in spin space. Supercurrents exhibit dynamical
instabilities induced by growing collective modes. In contrast to the
second-order phase transition, the critical momentum of mass currents is finite
at the phase boundary of the first-order superfluid-Mott insulator (SF-MI)
phase transition. Furthermore, the critical momentum remains finite throughout
the metastable SF phase and approaches zero towards the phase boundary, at
which the metastable SF state disappears. We also study the stability of spin
currents motivated by recent experiments for spinor gases. The critical
momentum of spin currents is found to be zero, where a spin-nematic mode causes
the dynamical instability. We investigate the origin of the zero critical
momentum of spin currents and find it attributed to the fact that the polar
state becomes energetically unstable even in the presence of an infinitesimal
spin current. We discuss implications of the zero critical momentum of spin
currents for the stability of the polar state.",2012.02501v2
2017-05-03,Current driven second harmonic domain wall resonance in ferromagnetic metal/ nonmagnetic metal bilayer: a field-free method for spin Hall angle measurements,"We study the ac current-driven domain wall motion in bilayer ferromagnetic
metal (FM)/nonmagnetic metal (NM) nanowire. The solution of the modified
Landau-Lifshitz-Gilbert equation including all the spin transfer torques is
used to describe motion of the domain wall in presence of the spin Hall effect.
We show that the domain wall center has second harmonic frequency response in
addition to the known first harmonic excitation. In contrast to the
experimentally observed second harmonic response in harmonic Hall measurements
of spin-orbit torque in magnetic thin films, this second harmonic response
directly originates from spin-orbit torque driven domain wall dynamics. Based
on the spin current generated by domain wall dynamics, the longitudinal spin
motive force generated voltage across the length of the nanowire is determined.
The second harmonic response introduces additionally a new practical field-free
and all-electrical method to probe the effective spin Hall angle for FM/NM
bilayer structures that could be applied in experiments. Our results also
demonstrate the capability of utilizing FM/NM bilayer structure in domain wall
based spin torque signal generators and resonators.",1705.01355v5
2017-09-18,"Scattering of two spinning black holes in post-Minkowskian gravity, to all orders in spin, and effective-one-body mappings","We demonstrate equivalences, under simple mappings, between the dynamics of
three distinct systems---(i) an arbitrary-mass-ratio two-spinning-black-hole
system, (ii) a spinning test black hole in a background Kerr spacetime, and
(iii) geodesic motion in Kerr---when each is considered in the first
post-Minkowskian (1PM) approximation to general relativity, i.e. to linear
order $G$ but to all orders in $1/c$, and to all orders in the black holes'
spins, with all orders in the multipole expansions of their linearized
gravitational fields. This is accomplished via computations of the net results
of weak gravitational scattering encounters between two spinning black holes,
namely the net $O(G)$ changes in the holes' momenta and spins as functions of
the incoming state. The results are given in remarkably simple closed forms,
found by solving effective Mathisson-Papapetrou-Dixon-type equations of motion
for a spinning black hole in conjunction with the linearized Einstein equation,
with appropriate matching to the Kerr solution. The scattering results fully
encode the gauge-invariant content of a canonical Hamiltonian governing
binary-black-hole dynamics at 1PM order, for generic (unbound and bound) orbits
and spin orientations. We deduce one such Hamiltonian, which reproduces and
resums the 1PM parts of all such previous post-Newtonian results, and which
directly manifests the equivalences with the test-body limits via simple
effective-one-body mappings.",1709.06016v2
2020-06-03,"Emergence of quantum critical charge and spin-state fluctuations near the pressure-induced Mott transition in MnO, FeO, CoO, and NiO","We perform a comprehensive theoretical study of the pressure-induced
evolution of the electronic structure, magnetic state, and phase stability of
the late transition metal monoxides MnO, FeO, CoO, and NiO using a fully charge
self-consistent DFT+dynamical mean-field theory method. Our results reveal that
the pressure-induced Mott insulator-to-metal phase transition in MnO-NiO is
accompanied by a simultaneous collapse of local magnetic moments and lattice
volume, implying a complex interplay between chemical bonding and electronic
correlations. We compute the pressure-induced evolution of relative weights of
the different valence states and spin-state configurations. Employing the
concept of fluctuating valence in a correlated solid, we demonstrate that in
MnO, FeO, and CoO a Mott insulator-metal transition and collapse of the local
moments is accompanied by a sharp crossover of the spin-state and valence
configurations. Our microscopic explanation of the magnetic collapse differs
from the accepted picture and points out a remarkable dynamical coexistence
(frustration) of the high-, intermediate-, and low-spin states. In particular,
in MnO, the magnetic collapse is found to be driven by the appearance of the
intermediate-spin state (IS), competing with the low-spin (LS) state; in FeO,
we observe a conventional high-spin to low-spin (HS-LS) crossover. Most
interestingly, in CoO, we obtain a remarkable (dynamical) coexistence of the HS
and LS states, i.e., a HS-LS frustration, up to high pressure. Our results
demonstrate the importance of quantum fluctuations of the valence and spin
states for the understanding of quantum criticality of the Mott transitions.",2006.02406v1
2021-02-26,Spin relaxation in radical pairs from the stochastic Schrödinger equation,"We show that the stochastic Schr\""odinger equation (SSE) provides an ideal
way to simulate the quantum mechanical spin dynamics of radical pairs. Electron
spin relaxation effects arising from fluctuations in the spin Hamiltonian are
straightforward to include in this approach, and their treatment can be
combined with a highly efficient stochastic evaluation of the trace over
nuclear spin states that is required to compute experimental observables. These
features are illustrated in example applications to a flavin-tryptophan radical
pair of interest in avian magnetoreception, and to a problem involving
spin-selective radical pair recombination along a molecular wire. In the first
of these examples, the SSE is shown to be both more efficient and more widely
applicable than a recent stochastic implementation of the Lindblad equation,
which only provides a valid treatment of relaxation in the extreme-narrowing
limit. In the second, the exact SSE results are used to assess the accuracy of
a recently-proposed combination of Nakajima-Zwanzig theory for the spin
relaxation and Schulten-Wolynes theory for the spin dynamics, which is
applicable to radical pairs with many more nuclear spins. An appendix analyses
the efficiency of trace sampling in some detail, highlighting the particular
advantages of sampling with SU(N) coherent states.",2102.13430v1
2021-03-15,Tomography of time-dependent quantum spin networks with machine learning,"Interacting spin networks are fundamental to quantum computing. Data-based
tomography of time-independent spin networks has been achieved, but an open
challenge is to ascertain the structures of time-dependent spin networks using
time series measurements taken locally from a small subset of the spins.
Physically, the dynamical evolution of a spin network under time-dependent
driving or perturbation is described by the Heisenberg equation of motion.
Motivated by this basic fact, we articulate a physics-enhanced machine learning
framework whose core is Heisenberg neural networks. In particular, we develop a
deep learning algorithm according to some physics motivated loss function based
on the Heisenberg equation, which ""forces"" the neural network to follow the
quantum evolution of the spin variables. We demonstrate that, from local
measurements, not only the local Hamiltonian can be recovered but the
Hamiltonian reflecting the interacting structure of the whole system can also
be faithfully reconstructed. We test our Heisenberg neural machine on spin
networks of a variety of structures. In the extreme case where measurements are
taken from only one spin, the achieved tomography fidelity values can reach
about 90%. The developed machine learning framework is applicable to any
time-dependent systems whose quantum dynamical evolution is governed by the
Heisenberg equation of motion.",2103.08645v1
2021-10-23,Auger and spin dynamics in a self-assembled quantum dot,"The Zeeman-split spin states of a single quantum dot can be used together
with its optical trion transitions to form a spin-photon interface between a
stationary (the spin) and a flying (the photon) quantum bit. Besides long
coherence times of the spin state itself, the limiting decoherence mechanisms
of the trion states are of central importance. We investigate here in
time-resolved resonance fluorescence the electron and trion dynamics in a
single self-assembled quantum dot in an applied magnetic field of up to $B =
10\,$T. The quantum dot is only weakly coupled to an electron reservoir with
tunneling rates of about $1\,$ms$^{-1}$. Using this sample structure, we can
measure, in addition to the spin-flip rate of the electron and the spin-flip
Raman rate of the trion transition, the Auger recombination process, that
scatters an Auger electron into the conduction band. The Auger effect destroys
the radiative trion transition and leaves the quantum dot empty until an
electron tunnels from the reservoir into the dot. The Auger recombination rate
decreases by a factor of three from $\gamma_A=3\,\mu$s$^{-1}$ down to
$1\,\mu$s$^{-1}$ in an applied magnetic field of $10\,$T in Faraday geometry.
The combination of an Auger recombination event with subsequent electron
tunneling from the reservoir can flip the electron spin and thus constitutes a
previously unaccounted mechanism that limits spin coherence, an important
resource for quantum technologies.",2110.12213v1
2022-05-17,Spin dynamics of positively charged excitons in Cr$^+$-doped quantum dots probed by resonant photoluminescence,"We study the dynamics of the spin system that consist of a positively charged
II-VI semiconductor quantum dot doped with a single Cr$^+$ ion. The resonant
photoluminescence (PL) of the positively charged exciton coupled with the
Cr$^+$ spin is used to analyze the main spin relaxation channels. The intensity
of the resonant PL is reduced by an optical pumping of the spin of the resident
hole-Cr$^+$ complex that can be seen as a nano-magnet. The spin memory can be
partially erased by a non-resonant optical excitation. This leads to an
increase of the resonant PL signal. The resonant PL is co-circularly polarized
and corresponds to relaxation channels that conserve the Cr$^+$ spin $\vert S_z
\vert$. The observation in the resonant-PL excitation spectra of optical
transitions with a change of the Cr$^+$ spin permits to determine the magnetic
anisotropy of the magnetic atom. Optical pumping, auto-correlation measurements
and the power dependence of the PL intensity distribution show that the
effective temperature of the hole-Cr$^+$ spin system is affected by the optical
excitation through the local generation of phonons.",2205.08122v1
2022-09-06,The population properties of spinning black holes using Gravitational-wave Transient Catalog 3,"Binary black holes formed via different pathways are predicted to have
distinct spin properties. Measuring these properties with gravitational waves
provides an opportunity to unveil the origins of binary black holes. Recent
work draws conflicting conclusions regarding the spin distribution observed by
LIGO--Virgo--KAGRA (LVK). Some analyses suggest that a fraction of the observed
black-hole spin vectors are significantly misaligned (by $>90^\circ$) relative
to the orbital angular momentum. This has been interpreted to mean that some
binaries in the LVK dataset are assembled dynamically in dense stellar
environments. Other analyses find support for a sub-population of binaries with
negligible spin and no evidence for significantly misaligned spin -- a result
consistent with the field formation scenario. In this work, we study the spin
properties of binary black holes in the third LVK gravitational-wave transient
catalog. We find that there is insufficient data to resolve the existence of a
sub-population of binaries with negligible black-hole spin (the presence of
this sub-population is supported by a modest Bayes factor of 1.7). We find
modest support for the existence of mergers with extreme spin tilt angles $>
90^\circ$ (the presence of extreme-tilt binaries is favored by a Bayes factor
of 10.1). Only one thing is clear: at least some of the LVK binaries formed in
the field. At most $89\%$ of binaries are assembled dynamically (99\%
credibility), though, the true branching fraction could be much lower, even
negligible.",2209.02206v2
2022-11-10,Static and dynamic magnetic properties of the spin-5/2 triangle lattice antiferromagnet Na3Fe(PO4)2 studied by 31P NMR,"$^{31}$P nuclear magnetic resonance (NMR) measurements have been carried out
to investigate the magnetic properties and spin dynamics of Fe$^{3+}$ ($S$ =
5/2) spins in the two-dimensional triangular lattice (TL) compound
Na$_3$Fe(PO$_4$)$_2$. The temperature ($T$) dependence of nuclear spin-lattice
relaxation rates ($1/T_1$) shows a clear peak around N\'eel temperature,
$T_{\rm N} = 10.9$~K, corresponding to an antiferromagnetic (AFM) transition.
From the temparature dependence of NMR shift ($K$) above $T_{\rm N}$, an
exchange coupling between Fe$^{3+}$ spins was estimated to be $J/k_{\rm
B}\simeq 1.9$~K using the spin-5/2 Heisenberg isotropic-TL model. The
temperature dependence of $1/T_1T$ divided by the magnetic susceptibility
($\chi$), $1/T_1T\chi$, above $T_{\rm N}$ proves the AFM nature of spin
fluctuations below $\sim$ 50 K in the paramagnetic state. In the magnetically
ordered state below $T_{\rm N}$, the characteristic rectangular shape of the
NMR spectra is observed, indicative of a commensurate AFM state in its ground
state. The strong temperature dependence of 1/$T_1$ in the AFM state is well
explained by the two-magnon (Raman) process of the spin waves in a 3D
antiferromagnet with a spin-anisotropy energy gap of 5.7 K. The temperature
dependence of sublattice magnetization is also well reproduced by the spin
waves. Those results indicate that the magnetically ordered state of
Na$_3$Fe(PO$_4$)$_2$ is a conventional 3D AFM state, and no obvious spin
frustration effects were detected in its ground state.",2211.05921v1
2023-05-25,Nonlinear spin dynamics of ferromagnetic ring in the vortex state and its application for spin-transfer nano-oscillator,"We study a nonlinear spin dynamics of a ferromagnetic ring in a vortex state
induced by the spin-polarized current. We also suggest to use the ferromagnetic
ring as a free layer of a coreless vortex spin-transfer nano-oscillator. The
calculated working frequency is about several GHz, that is much higher than the
gyromode frequency of the disk-based vortex oscillator. The response of the
vortex-state ring to the spin-polarized current has hysteretic behavior with
the reasonable values of the thresholds current densities: ignition threshold
is about $10^{8} \text{A}\text{cm}^{-2}$, and elimination current to maintain
the oscillations has much lower values about $10^{6} \text{A} \text{cm}^{-2}$.
The output signal can be extracted by the help of the inverse spin Hall effect
or by the giant magnetoresistance. The output electromotive force averaged over
all sample vanishes, and we suggest to use a ferromagnetic ring or disk in a
vortex state as a GMR analyzer. For an inverse spin Hall analyser we advise to
use two heavy metals with different signs of Spin-Hall angle. The ring-based
STNO is supposed to increase the areas of practical application of the STNOs.",2305.16019v2
2023-10-18,New Black Hole Spin Values for Sagittarius A* Obtained with the Outflow Method,"Six archival Chandra observations are matched with eight sets of radio data
and studied in the context of the outflow method to measure and study the spin
properties of $\rm{Sgr ~A^*}$. Three radio and X-ray data sets obtained
simultaneously, or partially simultaneously, are identified as preferred for
the purpose of measuring the spin properties of $\rm{Sgr ~A^*}$. Similar
results are obtained with other data sets. Results obtained with the preferred
data sets are combined and indicate a weighted mean value of the spin function
of $\rm{F} = 0.62 \pm 0.10$ and dimensionless spin angular momentum of
$\rm{a_*} = 0.90 \pm 0.06$. The spin function translates into measurements of
the black hole rotational mass, $\rm{M_{rot}}$, irreducible mass,
$\rm{M_{irr}}$, and spin mass-energy available for extraction, $\rm{M_{spin}}$,
relative to the total black hole dynamical mass, $\rm{M_{dyn}}$. Weighted mean
values of $\rm{(M_{rot}/M_{dyn}) = (0.53 \pm 0.06)}$, $\rm{({M_{irr}/M_{dyn})}
= (0.85 \pm 0.04)}$, $\rm{({M_{spin}/M_{dyn})} = (0.15 \pm 0.04)}$,
$\rm{{M_{rot}} = (2.2 \pm 0.3) \times 10^6 ~M_{\odot}}$, $\rm{{M_{irr}} = (3.5
\pm 0.2) \times 10^6 ~M_{\odot}}$, and $\rm{{M_{spin}} = (6.2 \pm 1.6) \times
10^5 ~M_{\odot}}$ are obtained; of course $\rm{{(M_{rot}/M_{irr})} = (0.62 \pm
0.10)}$ since $\rm{{(M_{rot}/M_{irr})} = F}$. Values obtained for $\rm{Sgr
~A^*}$ are compared with those obtained for M87 based on the published spin
function which indicate that M87 carries substantially more rotational energy
and spin mass-energy relative to the total (i.e., dynamical) black hole mass,
the irreducible black hole mass, and in absolute terms.",2310.12108v1
2024-04-09,Excited-State Dynamics and Optically Detected Magnetic Resonance of Solid-State Spin Defects from First Principles,"Optically detected magnetic resonance (ODMR) is an efficient and reliable
method that enables initialization and readout of spin states through
spin-photon interface. In general, high quantum efficiency and large
spin-dependent photoluminescence (PL) contrast are desirable for reliable
quantum information readout. However, reliable prediction of the ODMR contrast
from first-principles requires accurate description of complex spin
polarization mechanisms of spin defects. These mechanisms often include
multiple radiative and nonradiative processes in particular intersystem
crossing (ISC) among multiple excited electronic states. In this work we
present our implementation of the first-principles ODMR contrast, by solving
kinetic master equation with calculated rates from ab initio electronic
structure methods then benchmark the implementation on the case of the
negatively-charged nitrogen vacancy (NV) center in diamond. We show the
importance of correct description of multi-reference electronic states for
accurate prediction of excitation energy, spin-orbit coupling, and the rate of
ISC. Moreover, we underscore the importance of pseudo Jahn-Teller effect for
the spin-orbit coupling, and the dynamical Jahn-Teller effect for
electron-phonon coupling, key factors determining ISC rates and ODMR contrast.
We show good agreement between our first-principles calculations and the
experimental ODMR contrast under magnetic field. We then demonstrate reliable
predictions of magnetic field direction, pump power, and microwave frequency
dependency, as important parameters for ODMR experiments. Our work clarifies
the important excited-state relaxation mechanisms determining ODMR contrast and
provides a predictive computational platform for spin polarization and optical
readout of solid-state quantum defects from first principles.",2404.05917v1
2009-04-08,First observation of spin-helical Dirac fermions and topological phases in undoped and doped Bi2Te3 demonstrated by spin-ARPES spectroscopy,"Electron systems that possess light-like dispersion relations or the conical
Dirac spectrum, such as graphene and bismuth, have recently been shown to
harbor unusual collective states in high magnetic fields. Such states are
possible because their light-like electrons come in spin pairs that are
chiral,which means that their direction of propagation is tied to a quantity
called pseudospin that describes their location in the crystal lattice. An
emerging direction in quantum materials research is the manipulation of atomic
spin-orbit coupling to simulate the effect of a spin dependent magnetic
field,in attempt to realize novel spin phases of matter. This effect has been
proposed to realize systems consisting of unpaired Dirac cones that are
helical, meaning their direction of propagation is tied to the electron spin
itself, which are forbidden to exist in graphene or bismuth. The experimental
existence of topological order can not be determined without spin-resolved
measurements. Here we report a spin-and angle-resolved photoemission study of
the hexagonal surface of the Bi2Te3 and Bi{2-x}MnxTe3 series, which is found to
exhibit a single helical Dirac cone that is fully spin-polarized. Our
observations of a gap in the bulk spin-degenerate band and a spin-resolved
surface Dirac node close to the chemical potential show that the low energy
dynamics of Bi2Te3 is dominated by the unpaired spin-helical Dirac modes. Our
spin-texture measurements prove the existence of a rare topological phase in
this materials class for the first time, and suggest its suitability for novel
2D Dirac spin device applications beyond the chiral variety or traditional
graphene.",0904.1260v1
2019-10-25,Spatiotemporal electronic spin fluctuations in random nuclear fields in n-CdTe,"We report on the dynamics of electron spins in n-doped CdTe layers that
differs significantly from the expected response derived from the studies
dedicated to electron spin relaxation in n-GaAs. At zero magnetic field, the
electron spin noise spectra exhibit a two-peak structure - a zero-frequency
line and a satellite - that we attribute to the electron spin precession in a
frozen random nuclear spin distribution. This implies a surprisingly long
electron spin correlation time whatever the doping level, even above the Mott
transition. Using spatiotemporal spin noise spectroscopy, we demonstrate that
the observation of a satellite in the spin noise spectra and a fast spin
diffusion are mutually exclusive. This is consistent with a shortening of the
electron spin correlation time due to hopping between donors. We interpret our
data via a model assuming that the low temperature spin relaxation is due to
hopping between donors in presence of hyperfine and anisotropic exchange
interactions. Most of our results can be interpreted in this framework. First,
a transition from inhomogeneous to homogeneous broadening of the spin noise
peaks and the disappearance of the satellite are observed when the hopping rate
becomes larger than the Larmor period induced by the local nuclear fields. In
the regime of homogeneous broadening the ratio between the spin diffusion
constant and the spin relaxation rate has a value in good agreement with the
Dresselhaus constant. In the regime of inhomogeneous broadening, most of the
samples exhibit a broadening consistent with the distribution of local nuclear
fields. We obtain a new estimate of the hyperfine constants in CdTe and a value
of 0.10 Tesla for the maximum nuclear field. Finally, our study also reveals a
puzzle as our samples behave as if the active donor concentration was reduced
by several orders of magnitudes with respect to the nominal values.",1910.11805v1
2004-08-10,"Collective Spin Dynamics in the ""Coherence Window"" for Quantum Nanomagnets","The spin coherence phenomena and the possibility of their observation in
nanomagnetic insulators attract more and more attention in the last several
years. Recently it has been shown that in these systems in large transverse
magnetic field there can be a fairly narrow ""coherence window"" for phonon and
nuclear spin-mediated decoherence. What kind of spin dynamics can then be
expected in this window in a crystal of magnetic nanomolecules coupled to
phonons, to nuclear spin bath and it to each other via dipole-dipole
interactions? Studying multispin correlations, we determine the region of
parameters where ""coherent clusters"" of collective spin excitations can appear.
Although two particular systems, namely crystals of $Fe_8$-triazacyclonane and
$Mn_{12}$-acetate molecules, are used in this work to illustrate the results,
here we are not trying to predict an existence of collective coherent dynamics
in some particular system. Instead, we discuss the way how any crystalline
system of dipole-dipole coupled nanomolecules can be analyzed to decide whether
this system is suitable for attempts to observe coherent dynamics. The
presented analysis can be useful in the search for magnetic systems showing the
spin coherence phenomena.",0408220v3
2004-02-19,Dissipative quantum dynamics with the Surrogate Hamiltonian approach. A comparison between spin and harmonic baths,"The dissipative quantum dynamics of an anharmonic oscillator coupled to a
bath is studied with the purpose of elucidating the differences between the
relaxation to a spin bath and to a harmonic bath. Converged results are
obtained for the spin bath by the Surrogate Hamiltonian approach. This method
is based on constructing a system-bath Hamiltonian, with a finite but large
number of spin bath modes, that mimics exactly a bath with an infinite number
of modes for a finite time interval. Convergence with respect to the number of
simultaneous excitations of bath modes can be checked. The results are compared
to calculations that include a finite number of harmonic modes carried out by
using the multi-configuration time-dependent Hartree method of Nest and Meyer,
[J. Chem. Phys. 119, 24 (2003)]. In the weak coupling regime, at zero
temperature and for small excitations of the primary system, both methods
converge to the Markovian limit. When initially the primary system is
significantly excited, the spin bath can saturate restricting the energy
acceptance. An interaction term between bath modes that spreads the excitation
eliminates the saturation. The loss of phase between two cat states has been
analyzed and the results for the spin and harmonic baths are almost identical.
For stronger couplings, the dynamics induced by the two types of baths deviate.
The accumulation and degree of entanglement between the bath modes have been
characterized. Only in the spin bath the dynamics generate entanglement between
the bath modes.",0402144v1
2009-05-19,Dynamical spin-spin correlation functions in the Kondo model out of equilibrium,"We calculate the dynamical spin-spin correlation functions of a Kondo dot
coupled to two noninteracting leads held at different chemical potentials. To
this end we generalize a recently developed real-time renormalization group
method in frequency space (RTRG-FS) to allow the calculation of dynamical
correlation functions of arbitrary dot operators in systems describing spin
and/or orbital fluctuations. The resulting two-loop RG equations are
analytically solved in the weak-coupling regime. This implies that the method
can be applied provided either the voltage $V$ through the dot or the external
magnetic field $h_0$ are sufficiently large, $\max\{V,h_0\}\gg T_K$, where the
Kondo temperature $T_K$ is the scale where the system enters the
strong-coupling regime. Explicitly, we calculate the longitudinal and
transverse spin-spin correlation and response functions as well as the
resulting fluctuation-dissipation ratios. The correlation functions in
real-frequency space can be calculated in Matsubara space without the need of
any analytical continuation. We obtain analytic results for the line-shape, the
small- and large-frequency limits and several other features like the height
and width of the peak in the transverse susceptibility at
$\Omega\approx\tilde{h}$, where $\tilde{h}$ denotes the reduced magnetic field.
Furthermore, we discuss how the developed method can be generalized to
calculate dynamical correlation functions of other operators involving
reservoir degrees of freedom as well.",0905.3095v2
2018-02-02,Electrically tunable dynamic nuclear spin polarization in GaAs quantum dots at zero magnetic field,"In III-V semiconductor nano-structures the electron and nuclear spin dynamics
are strongly coupled. Both spin systems can be controlled optically. The
nuclear spin dynamics is widely studied, but little is known about the
initialization mechanisms. Here we investigate optical pumping of carrier and
nuclear spins in charge tunable GaAs dots grown on 111A substrates. We
demonstrate dynamic nuclear polarization (DNP) at zero magnetic field in a
single quantum dot for the positively charged exciton X$^+$ state transition.
We tune the DNP in both amplitude and sign by variation of an applied bias
voltage V$_g$. Variation of $\Delta$V$_g$ of the order of 100 mV changes the
Overhauser splitting (nuclear spin polarization) from -30 $\mu$eV (-22 %) to
+10 $\mu$eV (+7 %), although the X$^+$ photoluminescence polarization does not
change sign over this voltage range. This indicates that absorption in the
structure and energy relaxation towards the X$^+$ ground state might provide
favourable scenarios for efficient electron-nuclear spin flip-flops, generating
DNP during the first tens of ps of the X$^+$ lifetime which is of the order of
hundreds of ps. Voltage control of DNP is further confirmed in Hanle
experiments.",1802.00629v2
2013-09-25,Sensing and atomic-scale structure analysis of single nuclear spin clusters in diamond,"Single-molecule nuclear magnetic resonance (NMR) is a crown-jewel challenge
in the field of magnetic resonance spectroscopy and has important applications
in chemical analysis and in quantum computing. Recently, it becomes possible to
tackle this grand challenge thanks to experimental advances in preserving
quantum coherence of nitrogen-vacancy (NV) center spins in diamond as a
sensitive probe and theoretical proposals on atomic-scale magnetometry via
dynamical decoupling control. Through decoherence measurement of NV centers
under dynamical decoupling control, sensing of single $^{13}\textbf{C}$ at
nanometer distance has been realized. Toward the ultimate goal of structure
analysis of single molecules, it is highly desirable to directly measure the
interactions within single nuclear spin clusters. Here we sensed a single
$^{13}\textbf{C}$-$^{13}\textbf{C}$ nuclear spin dimer located about 1 nm from
the NV center and characterized the interaction between the two nuclear spins,
by measuring NV center spin decoherence under various dynamical decoupling
control. From the measured interaction we derived the spatial configuration of
the dimer with atomic-scale resolution. These results demonstrate that central
spin decoherence under dynamical decoupling control is a feasible probe for NMR
structure analysis of single molecules.",1309.6548v1
2019-06-11,Fast-forward approach to adiabatic quantum dynamics of regular spin clusters: nature of geometry-dependent driving interactions,"The fast forward scheme of adiabatic quantum dynamics is applied to finite
regular spin clusters with various geometries and the nature of driving
interactions is elucidated. The fast forward is the quasi-adiabatic dynamics
guaranteed by regularization terms added to the reference Hamiltonian, followed
by a rescaling of time with use of a large scaling factor. With help of the
regularization terms consisting of pair-wise and 3-body interactions, we apply
the proposed formula (Phys. Rev.A 96, 052106(2017)) to regular triangle and
open linear chain for N = 3 spin systems, and to triangular pyramid, square,
primary star graph and open linear chain for N = 4 spin systems. The
geometry-induced symmetry greatly decreases the rank of coefficient matrix of
the linear algebraic equation for regularization terms. Choosing a transverse
Ising Hamiltonian as a reference, we find: (1) for N = 3 spin clusters, the
driving interaction consists of only the geometry-dependent pairwise
interactions and there is no need for the 3-body interaction; (2) for N = 4
spin clusters, the geometry-dependent pair-wise interactions again constitute
major part of the driving interaction, whereas the universal 3-body interaction
free from the geometry is necessary but plays a subsidiary role. Our scheme
predicts the practical driving interaction in accelerating the adiabatic
quantum dynamics of structured regular spin clusters.",1906.04433v1
2018-03-30,Dynamical DMRG study of spin and charge excitations in the four-leg t-t'-J ladder,"The ground state of the t-t'-J ladder with four legs favors a striped charge
distribution for the parameters corresponding to hole-doped cuprate
superconductors. We investigate the dynamical spin and charge structure factors
of the model by using the dynamical density matrix renormalization group (DMRG)
and clarify the influence of the stripe on the structure factors. The dynamical
charge structure factor along the momentum direction from q=(0,0) to (pi,0)
clearly shows low-energy excitations corresponding to the stripe order in hole
doping. On the other hand, the stripe order weakens in electron doping,
resulting in fewer low-energy excitations in the charge channel. In the spin
channel, we find incommensurate spin excitations near q=(pi,pi) forming an
hourglass behavior in hole doping, while in electron doping we find clearly
spin-wave-like dispersions starting from q=(pi,pi). Along the (0,0)-(pi,0)
direction, the spin excitations are strongly influenced by the stripes in hole
doping, resulting in two branches that form a discontinuous behavior in the
dispersion. In contrast, the electron-doped systems show a downward shift in
energy toward (pi,0). These behaviors along the (0,0)-(pi,0) direction are
qualitatively similar to momentum-dependent spin excitations recently observed
by resonant inelastic x-ray scattering experiments in hole- and electron-doped
cuprate superconductors.",1803.11342v2
2022-06-20,First-principles calculation of the parameters used by atomistic magnetic simulations,"While the ground state of magnetic materials is in general well described on
the basis of spin density functional theory (SDFT), the theoretical description
of finite-temperature and non-equilibrium properties require an extension
beyond the standard SDFT. Time-dependent SDFT (TD-SDFT), which give for example
access to dynamical properties are computationally very demanding and can
currently be hardly applied to complex solids. Here we focus on the alternative
approach based on the combination of a parameterized phenomenological spin
Hamiltonian and SDFT-based electronic structure calculations, giving access to
the dynamical and finite-temperature properties for example via spin-dynamics
simulations using the Landau-Lifshitz-Gilbert (LLG) equation or Monte Carlo
simulations. We present an overview on the various methods to calculate the
parameters of the various phenomenological Hamiltonians with an emphasis on the
KKR Green function method as one of the most flexible band structure methods
giving access to practically all relevant parameters. Concerning these, it is
crucial to account for the spin-orbit coupling (SOC) by performing relativistic
SDFT-based calculations as it plays a key role for magnetic anisotropy and
chiral exchange interactions represented by the DMI parameters in the spin
Hamiltonian. This concerns also the Gilbert damping parameters characterizing
magnetization dissipation in the LLG equation, chiral multispin interaction
parameters of the extended Heisenberg Hamiltonian, as well as spin-lattice
interaction parameters describing the interplay of spin and lattice dynamics
processes, for which an efficient computational scheme has been developed
recently by the present authors.",2206.09969v1
2022-10-04,The BKT Transition and its Dynamics in a Spin Fluid,"We study the effect of particle mobility on phase transitions in a spin fluid
in two dimensions. The presence of a phase transition of the BKT universality
class is shown in an off-lattice model of particles with purely repulsive
interaction employing computer simulations. A critical spin wave region $0 < T
< T_{\textrm{BKT}}$ is found with a non-universal exponent $\eta(T)$ that
follows the shape suggested by BKT theory, including a critical value
consistent with $\eta_{\textrm{BKT}} = 1/4$. One can observe a transition from
power-law decay to exponential decay in the static correlation functions at the
transition temperature $T_{\textrm{BKT}}$, which is supported by finite-size
scaling analysis. A critical temperature $T_{\textrm{BKT}} = 0.17(1)$ is
suggested. Investigations into the dynamic aspects of the phase transition are
carried out. The short-time behavior of the incoherent spin autocorrelation
function agrees with the Nelson-Fisher prediction, whereas the long-time
behavior differs from the finite-size scaling known for the static XY model.
Analysis of coherent spin wave dynamics shows that the spin wave peak is a
propagating mode that can be reasonably well fitted by hydrodynamic theory. The
mobility of the particles strongly enhances damping of the spin waves, but the
model lies still within the dynamic universality class of the standard XY
model.",2210.01838v1
2024-02-06,A metronome spin stabilizes time-crystalline dynamics,"We investigate a disorder-free quantum Ising chain subject to a time-periodic
drive that rotates each spin by an angle $\pi(1-\epsilon_i)$. In case all spins
experience the same deviation $\epsilon$ and the system is initialized in a
fully polarized state, the dynamics is known to be time-crystalline: the
magnetization of the system exhibits period-doubled oscillations for timescales
that grow exponentially with the length of the chain. In this work, we study
the effect of a deviation $\epsilon$ that differs between spins. We find that
reducing $\epsilon$ for a single spin drastically enhances the lifetime of
spatio-temporal order, suggesting the name ``metronome"" spin. Employing
perturbative arguments in an average Hamiltonian picture, we explain this
observation for initial states with macroscopic bulk magnetization.
Furthermore, in the case of random bitstring initial states, we report the
enhancement of the lifetime of a topological edge mode, which can also be
understood in the same picture. Finally, we discuss an altered geometry in
which the metronome spin is not directly part of the chain, affecting the
dynamics in different ways in the two scenarios considered. Our findings unveil
the intricate dynamics that emerge in Floquet systems under the influence of a
spatially varying drive, thereby uncovering new avenues for Floquet
engineering.",2402.04078v1
2017-02-01,Coherent Rabi dynamics of a superradiant spin ensemble in a microwave cavity,"We achieve the strong coupling regime between an ensemble of phosphorus donor
spins in a highly enriched $^{28}$Si crystal and a 3D dielectric resonator.
Spins were polarized beyond Boltzmann equilibrium using spin selective optical
excitation of the no-phonon bound exciton transition resulting in $N$ =
$3.6\cdot10^{13}$ unpaired spins in the ensemble. We observed a normal mode
splitting of the spin ensemble-cavity polariton resonances of 2$g\sqrt{N}$ =
580 kHz (where each spin is coupled with strength $g$) in a cavity with a
quality factor of 75,000 ($\gamma \ll \kappa \approx$ 60 kHz where $\gamma$ and
$\kappa$ are the spin dephasing and cavity loss rates, respectively). The spin
ensemble has a long dephasing time (T$_2^*$ = 9 $\mu$s) providing a wide window
for viewing the dynamics of the coupled spin ensemble-cavity system. The free
induction decay shows up to a dozen collapses and revivals revealing a coherent
exchange of excitations between the superradiant state of the spin ensemble and
the cavity at the rate $g\sqrt{N}$. The ensemble is found to evolve as a single
large pseudospin according to the Tavis-Cummings model due to minimal
inhomogeneous broadening and uniform spin-cavity coupling. We demonstrate
independent control of the total spin and the initial Z-projection of the
psuedospin using optical excitation and microwave manipulation respectively. We
vary the microwave excitation power to rotate the pseudospin on the Bloch
sphere and observe a long delay in the onset of the superradiant emission as
the pseudospin approaches full inversion. This delay is accompanied by an
abrupt $\pi$ phase shift in the peusdospin microwave emission. The scaling of
this delay with the initial angle and the sudden phase shift are explained by
the Tavis-Cummings model.",1702.00504v1
2013-09-02,Periastron advance in spinning black hole binaries: comparing effective-one-body and Numerical Relativity,"We compute the periastron advance using the effective-one-body formalism for
binary black holes moving on quasi-circular orbits and having spins collinear
with the orbital angular momentum. We compare the predictions with the
periastron advance recently computed in accurate numerical-relativity
simulations and find remarkable agreement for a wide range of spins and mass
ratios. These results do not use any numerical-relativity calibration of the
effective-one-body model, and stem from two key ingredients in the
effective-one-body Hamiltonian: (i) the mapping of the two-body dynamics of
spinning particles onto the dynamics of an effective spinning particle in a
(deformed) Kerr spacetime, fully symmetrized with respect to the two-body
masses and spins, and (ii) the resummation, in the test-particle limit, of all
post-Newtonian (PN) corrections linear in the spin of the particle. In fact,
even when only the leading spin PN corrections are included in the
effective-one-body spinning Hamiltonian but all the test-particle corrections
linear in the spin of the particle are resummed we find very good agreement
with the numerical results (within the numerical error for equal-mass binaries
and discrepancies of at most 1% for larger mass ratios). Furthermore, we
specialize to the extreme mass-ratio limit and derive, using the equations of
motion in the gravitational skeleton approach, analytical expressions for the
periastron advance, the meridional Lense-Thirring precession and spin
precession frequency in the case of a spinning particle on a nearly circular
equatorial orbit in Kerr spacetime, including also terms quadratic in the spin.",1309.0544v3
2020-09-24,Quantum spin torque driven transmutation of antiferromagnetic Mott insulator,"The standard model of spin-transfer torque (STT) in antiferromagnetic
spintronics considers exchange of angular momentum between quantum spins of
flowing electrons and noncollinear-to-them localized spins treated as classical
vectors. These vectors are assumed to realize N\'{e}el order in equilibrium,
$\uparrow \downarrow \ldots \uparrow \downarrow$, and their STT-driven dynamics
is described by the Landau-Lifshitz-Gilbert (LLG) equation. However, many
experimentally employed materials (such as archetypal NiO) are strongly
electron-correlated antiferromagnetic Mott insulators (AFMI) where localized
spins form a ground state quite different from the unentangled N\'{e}el state
$|\!\! \uparrow \downarrow \ldots \uparrow \downarrow \rangle$. The true ground
state is entangled by quantum spin fluctuations, leading to expectation value
of all localized spins being zero, so that LLG dynamics of classical vectors of
fixed length rotating due to STT cannot even be initiated. Instead, a fully
quantum treatment of both conduction electrons and localized spins is necessary
to capture exchange of spin angular momentum between them, denoted as quantum
STT. We use a recently developed time-dependent density matrix renormalization
group approach to quantum STT to predict how injection of a spin-polarized
current pulse into a normal metal layer coupled to AFMI overlayer via exchange
interaction and possibly small interlayer hopping -- which mimics, e.g.,
topological-insulator/NiO bilayer employed experimentally -- will induce
nonzero expectation value of AFMI localized spins. This new nonequilibrium
phase is a spatially inhomogeneous ferromagnet with zigzag profile of localized
spins. The total spin absorbed by AFMI increases with electron-electron
repulsion in AFMI, as well as when the two layers do not exchange any charge.",2009.11833v3
2023-10-09,Nanoscale engineering and dynamical stabilization of mesoscopic spin textures,"Thermalization phenomena, while ubiquitous in quantum systems, have
traditionally been viewed as obstacles to be mitigated. In this study, we
demonstrate the ability, instead, to harness thermalization to dynamically
engineer and stabilize structured quantum states in a mesoscopically large
ensemble of spins. Specifically, we showcase the capacity to generate, control,
stabilize, and read out 'shell-like' spin texture with interacting $ {}^{
13}\mathrm{C}$ nuclear spins in diamond, wherein spins are polarized oppositely
on either side of a critical radius. The texture spans several nanometers and
encompasses many hundred spins. We capitalize on the thermalization process to
impose a quasi-equilibrium upon the generated texture; as a result, it is
highly stable, immune to spin diffusion, and endures over multiple-minute long
periods -- over a million times longer than the intrinsic interaction scale of
the spins. Additionally, the texture is created and interrogated without
locally controlling or probing the nuclear spins. These features are
accomplished using an electron spin as a nanoscale injector of spin
polarization, and employing it as a source of spatially varying dissipation,
allowing for serial readout of the emergent spin texture. Long-time
stabilization is achieved via prethermalization to a Floquet-induced
Hamiltonian under the electronic gradient field. Our work presents a new
approach to robust nanoscale spin state engineering and paves the way for new
applications in quantum simulation, quantum information science, and nanoscale
imaging.",2310.05635v1
2022-11-02,Quantum Spin Puddles and Lakes: NISQ-Era Spin Liquids from Non-Equilibrium Dynamics,"While many-body systems can host long-ranged entangled quantum spin liquids
(QSLs), the ingredients for realizing these as ground states can be
prohibitively difficult. In many circumstances, one requires (i) a constrained
Hilbert space and (ii) an extensive quantum superposition. The paradigmatic
example is the toric code, or $\mathbb{Z}_2$ spin liquid, which is a
superposition of closed loop states. We show how non-equilibrium Hamiltonian
dynamics can provide a streamlined route toward creating such QSLs. Rather than
cooling into the ground state of a Hamiltonian, we show how a simple parameter
sweep can dynamically project a family of initial product states into the
constrained space, giving rise to a QSL. For the toric code, this is achieved
in systems with a separation in energy scales between the $e$- and $m$-anyons,
where one can sweep in a way that is adiabatic (sudden) with respect to the
former (latter). Although this separation of scales does not extend to the
thermodynamic limit, we analytically and numerically show that this method
efficiently prepares a spin liquid in finite-sized regions, which we brand
``quantum spin lakes.'' This mechanism elucidates recent experimental and
numerical observations of the dynamical state preparation of the ruby lattice
spin liquid in Rydberg atom arrays. In fact, the slow dynamics of $m$-anyons
suggest that we can capture spin lake preparation by simulating the dynamics on
tree lattices, which we confirm with tensor network simulations. Finally, we
use this mechanism to propose new experiments, e.g., for preparing a
finite-sized $U(1)$ spin liquid as a honeycomb Rokhsar-Kivelson dimer model
using Rydberg atoms -- which is remarkable given its equilibrium counterpart is
unstable in $2 + 1$D. Our work opens up a new avenue in the study of
non-equilibrium physics, as well as the exploration of exotic states of finite
extent in NISQ devices.",2211.01381v2
2009-08-19,Ultraslow quantum dynamics in a sub-Ohmic heat bath,"We show that the low-frequency modes of a sub-Ohmic bosonic heat bath
generate an effective dynamical asymmetry for an intrinsically symmetric
quantum spin -1/2. An initially fully polarized spin first decays towards a
quasiequilibrium determined by the dynamical asymmetry, thereby showing
coherent damped oscillations on the (fast) time scale of the spin splitting. On
top of this, the dynamical asymmetry itself decays on an ultraslow time scale
and vanishes asymptotically since the global equilibrium phase is symmetric. We
quantitatively study the nature of the initial fast decay to the
quasiequilibrium and discuss the features of ultraslow dynamics of the
quasiequilibrium itself. The dynamical asymmetry is more pronounced for smaller
values of the sub-Ohmic exponent and for lower temperatures, which emphasizes
the quantum many-body nature of the effect. The symmetry breaking is related to
the dynamic crossover between coherent and overdamped relaxation of the spin
polarization and is not connected to the localization quantum phase transition.
In addition to this delocalized phase, we identify a novel phase which is
characterized by damped coherent oscillations in the localized phase. This
allows for a sketch of the zero-temperature phase diagram of the sub-Ohmic
spin-boson model with four distinct phases.",0908.2749v2
2013-12-19,Theory of dynamic nuclear polarization and feedback in quantum dots,"An electron confined in a quantum dot interacts with its local nuclear spin
environment through the hyperfine contact interaction. This interaction
combined with external control and relaxation or measurement of the electron
spin allows for the generation of dynamic nuclear polarization. The quantum
nature of the nuclear bath, along with the interplay of coherent external
fields and incoherent dynamics in these systems renders a wealth of intriguing
phenomena seen in recent experiments such as electron Zeeman frequency
focusing, hysteresis, and line dragging. We develop in detail a fully quantum,
self-consistent theory that can be applied to such experiments and that
moreover has predictive power. Our theory uses the operator sum representation
formalism in order to incorporate the incoherent dynamics caused by the
additional, Markovian bath, which in self-assembled dots is the vacuum field
responsible for electron-hole optical recombination. The beauty of this
formalism is that it reduces the complexity of the problem by encoding the
joint dynamics of the external coherent and incoherent driving in an effective
dynamical map that only acts on the electron spin subspace. This together with
the separation of timescales in the problem allows for a tractable and
analytically solvable formalism. The key role of entanglement between the
electron spin and the nuclear spins in the formation of dynamic nuclear
polarization naturally follows from our solution. We demonstrate the theory in
detail for an optical pulsed experiment and present an in-depth discussion and
physical explanation of our results.",1312.5741v2
2013-09-18,Tunable non-equilibrium dynamics: field quenches in spin ice,"We present non-equilibrium physics in spin ice as a novel setting which
combines kinematic constraints, emergent topological defects, and magnetic long
range Coulomb interactions. In spin ice, magnetic frustration leads to highly
degenerate yet locally constrained ground states. Together, they form a highly
unusual magnetic state -- a ""Coulomb phase"" -- whose excitations are pointlike
defects -- magnetic monopoles -- in the absence of which effectively no
dynamics is possible. Hence, when they are sparse at low temperature, dynamics
becomes very sluggish. When quenching the system from a monopole-rich to a
monopole-poor state, a wealth of dynamical phenomena occur the exposition of
which is the subject of this article. Most notably, we find reaction diffusion
behaviour, slow dynamics due to kinematic constraints, as well as a regime
corresponding to the deposition of interacting dimers on a honeycomb lattice.
We also identify new potential avenues for detecting the magnetic monopoles in
a regime of slow-moving monopoles. The interest in this model system is further
enhanced by its large degree of tunability, and the ease of probing it in
experiment: with varying magnetic fields at different temperatures, geometric
properties -- including even the effective dimensionality of the system -- can
be varied. By monitoring magnetisation, spin correlations or zero-field Nuclear
Magnetic Resonance, the dynamical properties of the system can be extracted in
considerable detail. This establishes spin ice as a laboratory of choice for
the study of tunable, slow dynamics.",1309.4676v2
2021-11-15,Critical spin dynamics of Heisenberg ferromagnets revisited,"We calculate the dynamic structure factor $S (\boldsymbol{k},\omega)$ in the
paramagnetic regime of quantum Heisenberg ferromagnets for temperatures $T$
close to the critical temperature $T_c$ using our recently developed functional
renormalization group approach to quantum spin systems. In $d=3$ dimensions we
find that for small momenta $\boldsymbol{k}$ and frequencies $\omega$ the
dynamic structure factor assumes the scaling form $S(\boldsymbol{k},\omega) =
(\tau T G (\boldsymbol{k})/\pi)\Phi (k\xi, \omega\tau)$, where $ G
(\boldsymbol{k})$ is the static spin-spin correlation function, $\xi$ is the
correlation length, and the characteristic time-scale $\tau$ is proportional to
$\xi^{5/2}$. We explicitly calculate the dynamic scaling function $\Phi (x,y)$
and find satisfactory agreement with neutron scattering experiments probing the
critical spin dynamics in EuO and EuS. Precisely at the critical point where
$\xi = \infty$ our result for the dynamic structure factor can be written as $S
(\boldsymbol{k},\omega) = (\pi\omega_k)^{-1} T_c G (\boldsymbol{k}) \Psi_c
(\omega/\omega_k)$, where $\omega_k \propto k^{5/2}$. We find that
$\Psi_c(\nu)$ vanishes as $\nu^{-13/5}$ for large $\nu$, and as $\nu^{3/5}$ for
small $\nu$. While the large-frequency behavior of $\Psi_c (\nu)$ is consistent
with calculations based on mode-coupling theory and with perturbative
renormalization group calculations to second order in $\epsilon = 6-d$, our
result for small frequencies disagrees with previous calculations. We argue
that up until now neither experiments nor numerical simulations are
sufficiently accurate to determine the low-frequency behavior of $\Psi_c
(\nu)$. We also calculate the low-temperature behavior of $S (
\boldsymbol{k},\omega)$ in one- and two dimensional ferromagnets and find that
it satisfies dynamic scaling with exponent $z=2$ and exhibits a pseudogap for
small frequencies.",2111.07621v2
2007-10-09,NMR Time Reversal as a Probe of Incipient Turbulent Spin Dynamics,"We demonstrate time reversal of nuclear spin dynamics in highly magnetized
dilute liquid 3He-4He mixtures through effective inversion of long-range
dipolar interactions. These experiments, which involve using magic sandwich NMR
pulse sequences to generate spin echoes, probe the spatiotemporal development
of turbulent spin dynamics and promise to serve as a versatile tool for the
study and control of dynamic magnetization instabilities. We also show that a
repeated magic sandwich pulse sequence can be used to dynamically stabilize
modes of nuclear precession that are otherwise intrinsically unstable. To date,
we have extended the effective precession lifetimes of our magnetized samples
by more than three orders of magnitude.",0710.1765v1
2007-12-20,Dynamic probes of quantum spin chains with the Dzyaloshinskii-Moriya interaction,"We consider the spin-1/2 anisotropic XY chain in a transverse (z) field with
the Dzyaloshinskii-Moriya interaction directed along z-axis in spin space to
examine the effect of the Dzyaloshinskii-Moriya interaction on the zz, xx and
yy dynamic structure factors. Using the Jordan-Wigner fermionization approach
we analytically calculate the dynamic transverse spin structure factor. It is
governed by a two-fermion excitation continuum. We analyze the effect of the
Dzyaloshinskii-Moriya interaction on the two-fermion excitation continuum.
Other dynamic structure factors which are governed by many-fermion excitations
are calculated numerically. We discuss how the Dzyaloshinskii-Moriya
interaction manifests itself in the dynamic properties of the quantum spin
chain at various fields and temperatures.",0712.3361v1
2008-05-01,Chaotic Spin Dynamics of a Long Nanomagnet Driven by a Current,"We study the spin dynamics of a long nanomagnet driven by an electrical
current. In the case of only DC current, the spin dynamics has a sophisticated
bifurcation diagram of attractors. One type of attractors is a weak chaos. On
the other hand, in the case of only AC current, the spin dynamics has a rather
simple bifurcation diagram of attractors. That is, for small Gilbert damping,
when the AC current is below a critical value, the attractor is a limit cycle;
above the critical value, the attractor is chaotic (turbulent). For normal
Gilbert damping, the attractor is always a limit cycle in the physically
interesting range of the AC current. We also developed a Melnikov integral
theory for a theoretical prediction on the occurrence of chaos. Our Melnikov
prediction seems performing quite well in the DC case. In the AC case, our
Melnikov prediction seems predicting transient chaos. The sustained chaotic
attractor seems to have extra support from parametric resonance leading to a
turbulent state.",0805.0147v1
2008-11-17,Dynamical properties of the one-dimensional spin-1/2 Bose-Hubbard model near Mott-insulator to ferromagnetic liquid transition,"We investigate the dynamics of the one-dimensional strongly repulsive
spin-1/2 Bose-Hubbard model for filling $\nu\le1.$ While at $\nu=1$ the system
is a Hubbard-Mott insulator exhibiting dynamical properties of the Heisenberg
ferromagnet, at $\nu<1$ it is a ferromagnetic liquid with complex spin
dynamics. We find that close to the insulator-liquid transition the system
admits for a complete separation of spin and density degrees of freedom valid
at {\it all} energy and momentum scales within the $t-J$ approximation. This
allows us to derive the propagator of transverse spin waves and the shape of
the magnon peak in the dynamic spin structure factor.",0811.2676v2
2013-03-22,Quantum loss of synchronization in the dynamics of two spins,"Motivated by the spin self-rephasing recently observed in an atomic clock, we
introduce a simple dynamical model to study the competition between dephasing
and synchronization. Two spins $S$ are taken to be initially parallel and in
the plane perpendicular to an inhomogeneous magnetic field $\Delta$ that tends
to dephase them. In addition, the spins are coupled by exchange interaction $J$
that tries to keep them locked. The analytical solution of the classical
dynamics shows that, there is a phase transition to a synchronized regime for
sufficiently large exchange interaction $J>\Delta$ compared to the
inhomogeneity. The quantum dynamics is solved analytically in four limits --
large/small $J/\Delta$ and large/small $S$ -- and numerically in between. In
sharp contrast to the classical case, the quantum solution features very rich
$S$-dependent multiscale dynamics. For any finite $S$, there is no
synchronization but a crossover around $J=\Delta$ between two regimes. The
synchronization transition is only recovered when $S\to \infty$, approaching
the classical solution in a non-trivial way. Quantum effects therefore suppress
the synchronization transition.",1303.5564v2
2013-10-28,Interaction-Tuned Dynamical Transitions in a Rashba Spin-Orbit Coupled Fermi Gas,"We consider the time evolution of the magnetization in a Rashba
spin-orbit-coupled Fermi gas, starting from a fully-polarized initial state. We
model the dynamics using a Boltzmann equation, which we solve in the
Hartree-Fock approximation. The resulting non-linear system of equations gives
rise to three distinct dynamical regimes with qualitatively different
asymptotic behaviors of the magnetization at long times. The distinct regimes
and the transitions between them are controlled by the interaction strength:
for weakly interacting fermions, the magnetization decays to zero. For
intermediate interactions, it displays undamped oscillations about zero and for
strong interactions, a partially magnetized state is dynamically stabilized.
The dynamics we find is a spin analog of interaction induced self-trapping in
double-well Bose Einstein condensates. The predicted phenomena can be realized
in trapped Fermi gases with synthetic spin-orbit interactions.",1310.7639v1
2015-04-29,Dynamical instability in the S=1 Bose-Hubbard model,"We study the dynamical instabilities of superfluid flows in the S=1
Bose-Hubbard model. The time evolution of each spin component in a condensate
is calculated based on the dynamical Gutzwiller approximation for a wide range
of interactions, from a weakly correlated regime to a strongly correlated
regime near the Mott-insulator transition. Owing to the spin-dependent
interactions, the superfluid flow of the spin-1 condensate decays at a
different critical momentum from a spinless case when the interaction strength
is the same. We furthermore calculate the dynamical phase diagram of this model
and clarify that the obtained phase boundary has very different features
depending on whether the average number of particles per site is even or odd.
Finally, we analyze the density and spin modulations that appear in association
with the dynamical instability. We find that spin modulations are highly
sensitive to the presence of a uniform magnetic field.",1504.07847v3
2016-07-11,Non-Markovian dynamics in the extended cluster spin-1/2 XX chain,"We study the dynamics of entanglement in the extended cluster spin-1/2 XX
chain, equivalent to a 1D spin-1/2 XX model with three-spin interaction (TSI).
Selecting the nearest neighbor pair spins as an open quantum system, the rest
of the chain plays the role of environment. The two-spin Heisenberg and the TSI
interaction are responsible for coupling between system and environment. We
show the existence of a critical value in the TSI, where the dynamics of
concurrence changes from Markovian to the non-Markovian. In the region with the
non-Markovian dynamics, entanglement sudden death in the system is observed. By
focusing on the nearest neighbor pair spins of the environment, we have showed
that the dynamics of entanglement in the environment is sensitive to the
Markovian and non-Markovian regions.",1607.02837v1
2018-11-01,Performance of trajectory surface hopping method in the treatment of ultrafast intersystem crossing dynamics,"We carried out extensive studies to examine the performance of the
fewest-switches surface hopping method in the description of the ultrafast
intersystem crossing dynamic of various singlet-triplet (S-T) models by
comparison with the results of the exact full quantum dynamics. Different
implementation details and some derivative approaches were examined. As
expected, it is better to perform the trajectory surface hopping calculations
in the spin-adiabatic representation or by the local diabatization approach,
instead of in the spin-diabatic representation. The surface hopping method
provides reasonable results for the short-time dynamics in the S-T model with
weak spin-orbital coupling (diabatic coupling), although it does not perform
well in the models with strong spin-orbital coupling (diabatic coupling). When
the system accesses the S-T potential energy crossing with rather high kinetic
energy, the trajectory surface hopping method tends to produce the good
description of the nonadiabatic intersystem crossing dynamics. The impact of
the decoherence correction on the performance of the trajectory surface hopping
is system dependent. It improves the result accuracy in many cases, while its
influence may also be minor for other cases.",1811.00254v2
2009-12-01,Hyperfine induced spin and entanglement dynamics in Double Quantum Dots: A homogeneous coupling approach,"We investigate hyperfine induced electron spin and entanglement dynamics in a
system of two quantum dot spin qubits. We focus on the situation of zero
external magnetic field and concentrate on approximation-free theoretical
methods. We give an exact solution of the model for homogeneous hyperfine
coupling constants (with all coupling coefficients being equal) and varying
exchange coupling, and we derive the dynamics therefrom. After describing and
explaining the basic dynamical properties, the decoherence time is calculated
from the results of a detailed investigation of the short time electron spin
dynamics. The result turns out to be in good agreement with experimental data.",0912.0154v2
2017-07-18,Uncovering nonperturbative dynamics of the biased sub-Ohmic spin-boson model with variational Matrix Product States,"We study the dynamics of the biased sub-Ohmic spin-boson model by means of a
time-dependent variational matrix product state (TDVMPS) algorithm. The
evolution of both the system and the environment is obtained in the weak- and
the strong-coupling regimes, respectively characterized by damped spin
oscillations and by a nonequilibrium process where the spin freezes near its
initial state, which are explicitly shown to arise from a variety of reactive
environmental quantum dynamics. We also explore the rich phenomenology of the
intermediate-coupling case, a nonperturbative regime where the system shows a
complex dynamical behavior, combining features of both the weakly and the
strongly coupled case in a sequential, time-retarded fashion. Our work
demonstrates the potential of TDVMPS methods for exploring otherwise elusive,
nonperturbative regimes of complex open quantum systems, and points to the
possibilities of exploiting the qualitative, real-time modification of quantum
properties induced by nonequilibrium bath dynamics in ultrafast transient
processes.",1707.05524v2
2020-02-25,Effect of chemical structure on the ultrafast spin dynamics in core-excited states,"Recent developments of the sources of intense and ultrashort X-ray pulses
stimulate theoretical studies of phenomena occurring on ultrafast timescales.
In the present study, spin-flip dynamics in transition metal complexes
triggered by sub-femtosecond X-ray pulses are addressed theoretically using a
density matrix-based time-dependent configuration interaction approach. The
influence of different central metal ions and ligands on the character and
efficiency of spin-flip dynamics is put in focus. According to our results,
slight variations in the coordination sphere do not lead to qualitative
differences in dynamics, whereas the nature of the central ion is more
critical. However, the behavior in a row of transition metals demonstrates
trends that are not consistent with general expectations. Thus, the
peculiarities of spin dynamics have to be analyzed on a case-to-case basis.",2002.11032v1
2018-07-27,Dynamical detection of topological charges,"We propose a generic scheme to characterize topological phases via detecting
topological charges by quench dynamics. A topological charge is defined as the
chirality of a monopole at Dirac or Weyl point of spin-orbit field, and
topological phases can be classified by total charges in the region enclosed by
the so-called band-inversion surfaces (BISs). We show that both the topological
monopoles and BISs can be identified by non-equilibrium spin dynamics caused by
a sequence of quenches. From an emergent dynamical field given by time-averaged
spin textures, the topological charges, as well as the topological invariant,
can be readily obtained. An explicit advantage in this scheme is that only a
single spin component needs to be measured to detect all the information of the
topological phase. We numerically examine two realistic models, and propose a
feasible experimental setup for the measurement. This work opens a new way to
dynamically classify topological phases.",1807.10782v2
2021-03-15,Evolution of concentration under lattice spin-flip dynamics,"We consider spin-flip dynamics of configurations in
$\{-1,1\}^{\mathbb{Z}^d}$, and study the time evolution of concentration
inequalities. For ""weakly interacting"" dynamics we show that the Gaussian
concentration bound is conserved in the course of time and it is satisfied by
the unique stationary Gibbs measure. Next we show that, for a general class of
translation-invariant spin-flip dynamics, it is impossible to evolve in finite
time from a low-temperature Gibbs state towards a measure satisfying the
Gaussian concentration bound. Finally, we consider the time evolution of the
weaker uniform variance bound, and show that this bound is conserved under a
general class of spin-flip dynamics.",2103.08264v2
2021-07-23,Anomalous magnetic noise in imperfect flat bands in the topological magnet Dy2Ti2O7,"The spin ice compound Dy_2Ti_2O_7 stands out as the first topological magnet
in three dimensions, with its tell-tale emergent fractionalized magnetic
monopole excitations. Its real-time dynamical properties have been an enigma
from the very beginning. Using ultrasensitive, non-invasive SQUID measurements,
we show that Dy_2Ti_2O_7 exhibits a highly anomalous noise spectrum, in three
qualitatively different regimes: equilibrium spin ice, a `frozen' regime
extending to ultra-low temperatures, as well as a high-temperature `anomalous'
paramagnet. We show that in the simplest model of spin ice, the dynamics is not
anomalous, and we present several distinct mechanisms which give rise to a
coloured noise spectrum. In addition, we identify the structure of the
single-ion dynamics as a crucial ingredient for any modelling. Thus, the
dynamics of spin ice Dy_2Ti_2O_7 reflects the interplay of local dynamics with
emergent topological degrees of freedom and a frustration-generated imperfectly
flat energy landscape, and as such should be relevant for a broad class of
magnetic materials.",2107.11379v1
2022-10-27,Electron-phonon mediated spin-flip as driving mechanism for ultrafast magnetization dynamics in 3$d$ ferromagnets,"Despite intense experimental effort, theoretical proposals and modeling
approaches, a lack of consensus exists about the intrinsic mechanisms driving
ultrafast magnetization dynamics in 3$d$ ferromagnets. In this work, we find
evidence of electron-phonon mediated spin-flip as the driving mechanism for the
ultrafast magnetization dynamics in all three 3$d$ ferromagnets; nickel, iron
and cobalt. We use a microscopic three temperature model with parameters
calculated from first-principles, which has been validated by direct comparison
to the electron and lattice dynamics extracted from previous experiments. By
direct comparison to the experimentally measured magnetization dynamics for
different laser fluence, we determine the spin-flip probability of each
material. In contrast to previous findings but in agreement to ab-initio
predictions, we find that relatively small values of the spin-flip probability
enable ultrafast demagnetization in all three 3$d$ ferromagnets.",2210.15269v1
2023-03-25,Equilibrium via multi-spin-flip Glauber dynamics in Ising Model,"Notwithstanding great strides that statistical mechanics has made in recent
decades, an analytic solution of arguably the simplest model of relaxation
dynamics, the Ising model in an applied external field remains elusive even in
$1d$. Extant studies are based on numerics using single-spin-flip Glauber
dynamics. There is no reason why this algorithm should lead to the global
minimum energy state of the system. With this in mind, we explore
multi-spin-flip parallel and sequential Glauber dynamics of Ising spins in $1d$
and also on a regular random graph of coordination number $z=3$. We view our
study as a small initial step to test the generally implied hypothesis that the
equilibrium is independent of the relaxational dynamics or if it carries some
signature of it.",2303.14380v1
2008-04-06,Fermionization for charge degrees of freedom and bosonization of spin degrees of freedom in the SU(2) slave-boson theory,"Fermionizing the charge sector and bosonizing the spin part in the SU(2)
slave-boson theory, we derive an effective field theory for dynamics of doped
holes in the antiferromagnetically correlated spin background, where spin
fluctuations are described by an SO(5) Wess-Zumino-Witten (WZW) theory while
dynamics of doped holes is characterized by QED$_{3}$ with a chemical potential
term. An important feature of our effective field theory is the coupling term
between valance bond fluctuations and doped holes. Considering that valance
bond fluctuations are deeply related with monopole excitations of staggered
U(1) gauge fields in the bosonic field theory for spin fluctuations, we
demonstrate that hole dynamics helps deconfinement of bosonic spinons near the
quantum critical point of the SO(5) WZW theory. We solve this effective field
theory in the Eliashberg framework, and find non-Fermi liquid physics in
thermodynamics and transport, where $z = 3$ criticality with dynamical exponent
$z$ plays an important role for hole dynamics. We discuss validity of our field
theory, applying it to a doped spin chain and comparing it with the
slave-fermion framework. Furthermore, we discuss instability of the anomalous
metallic phase against superconductivity and density waves of doped holes,
resulting from competition between gauge and valance bond fluctuations.",0804.0895v3
2010-04-09,A kinetic Ising model study of dynamical correlations in confined fluids: Emergence of both fast and slow time scales,"Experiments and computer simulation studies have revealed existence of rich
dynamics in the orientational relaxation of molecules in confined systems such
as water in reverse micelles, cyclodextrin cavities and nano-tubes. Here we
introduce a novel finite length one dimensional Ising model to investigate the
propagation and the annihilation of dynamical correlations in finite systems
and to understand the intriguing shortening of the orientational relaxation
time that has been reported for small sized reverse micelles. In our finite
sized model, the two spins at the two end cells are oriented in the opposite
directions, to mimic the effects of surface that in real system fixes water
orientation in the opposite directions. This produces opposite polarizations to
propagate inside from the surface and to produce bulk-like condition at the
centre. This model can be solved analytically for short chains. For long chains
we solve the model numerically with Glauber spin flip dynamics (and also with
Metropolis single-spin flip Monte Carlo algorithm). We show that model nicely
reproduces many of the features observed in experiments. Due to the destructive
interference among correlations that propagate from the surface to the core,
one of the rotational relaxation time components decays faster than the bulk.
In general, the relaxation of spins is non-exponential due to the interplay
between various interactions. In the limit of strong coupling between the spins
or in the limit of low temperature, the nature of relaxation of the spins
undergoes a qualitative change with the emergence of a homogeneous dynamics
where decay is predominantly exponential, again in agreement with experiments.",1004.1471v2
2015-02-20,Keeping a spin qubit alive in natural silicon: Comparing optimal working points and dynamical decoupling,"There are two distinct techniques of proven effectiveness for extending the
coherence lifetime of spin qubits in environments of other spins. One is
dynamical decoupling, whereby the qubit is subjected to a carefully timed
sequence of control pulses; the other is tuning the qubit towards 'optimal
working points' (OWPs), which are sweet-spots for reduced decoherence in
magnetic fields. By means of quantum many-body calculations, we investigate the
effects of dynamical decoupling pulse sequences far from and near OWPs for a
central donor qubit subject to decoherence from a nuclear spin bath. Key to
understanding the behavior is to analyse the degree of suppression of the
usually dominant contribution from independent pairs of flip-flopping spins
within the many-body quantum bath. We find that to simulate recently measured
Hahn echo decays at OWPs (lowest-order dynamical decoupling), one must consider
clusters of three interacting spins, since independent pairs do not even give
finite $T_2$ decay times. We show that while operating near OWPs, dynamical
decoupling sequences require hundreds of pulses for a single order of magnitude
enhancement of $T_2$, in contrast to regimes far from OWPs, where only about
ten pulses are required.",1502.05951v3
2015-08-31,Dynamical structure factors and excitation modes of the bilayer Heisenberg model,"Using quantum Monte Carlo simulations along with higher-order spin-wave
theory, bond-operator and strong-coupling expansions, we analyse the dynamical
spin structure factor of the spin-half Heisenberg model on the square-lattice
bilayer. We identify distinct contributions from the low-energy Goldstone modes
in the magnetically ordered phase and the gapped triplon modes in the quantum
disordered phase. In the antisymmetric (with respect to layer inversion)
channel, the dynamical spin structure factor exhibits a continuous evolution of
spectral features across the quantum phase transition, connecting the two types
of modes. Instead, in the symmetric channel we find a depletion of the spectral
weight when moving from the ordered to the disordered phase. While the
dynamical spin structure factor does not exhibit a well-defined distinct
contribution from the amplitude (or Higgs) mode in the ordered phase, we
identify an only marginally-damped amplitude mode in the dynamical singlet
structure factor, obtained from interlayer bond correlations, in the vicinity
of the quantum critical point. These findings provide quantitative information
in direct relation to possible neutron or light scattering experiments in a
fundamental two-dimensional quantum-critical spin system.",1508.07816v1
2008-07-08,Funnel landscape and mutational robustness as a result of evolution under thermal noise,"In biological systems, expression dynamics to shape a fitted phenotype for
function has evolved through mutations to genes, as observed in the evolution
of funnel landscape in protein. We study this evolutionary process with a
statistical-mechanical model of interacting spins, where the fitted phenotype
is represented by a configuration of a given set of ""target spins"" and
interaction matrix J among spins is genotype evolving over generations. The
expression dynamics is given by stochastic process with temperature T_S to
decrease energy for a given set of J. The evolution of J is also stochastic
with temperature T_J, following mutation in J and selection based on a fitness
given by configurations of the target spins. Below a certain temperature
T_S^{c2}, the highly adapted J evolves, whereasanother phase transition
characterised by frustration occurs at T_S^{c1}<T_S^{c2}. At temperature lower
than T_S^{c1}, the Hamiltonian exhibits a spin-glass like phase, where the
dynamics requires long time steps to produce the fitted phenotype, and the
fitness often decreases drastically by single mutation. In contrast, in the
intermediate temperature phase between T_S^{c1} and T_S^{c2}, the evolved
genotypes, that have no frustration around the target spins (we call ""local
Mattis state""), give a funnel-like rapid expression dynamics and are robust to
mutation. These results imply that evolution under thermal noise beyond a
certain level leads to funnel dynamics and mutational robustness. We will
explain its mechanism with the statistical-mechanical method.",0807.1216v3
2018-03-03,Evidence for a dynamical ground state in a frustrated pyrohafnate Tb2Hf2O7,"We report the physical properties of Tb2Hf2O7 based on ac magnetic
susceptibility \chi_ac(T), dc magnetic susceptibility \chi(T), isothermal
magnetization M(H), and heat capacity C_p(T) measurements combined with muon
spin relaxation (\muSR) and neutron powder diffraction measurements. No
evidence for long-range magnetic order is found down to 0.1 K. However,
\chi_ac(T) data present a frequency-dependent broad peak (near 0.9 K at 16 Hz)
indicating slow spin dynamics. The slow spin dynamics is further evidenced from
the \muSR data (characterized by a stretched exponential behavior) which show
persistent spin fluctuations down to 0.3 K. The neutron powder diffraction data
collected at 0.1 K show a broad peak of magnetic origin (diffuse scattering)
but no magnetic Bragg peaks. The analysis of the diffuse scattering data
reveals a dominant antiferromagnetic interaction in agreement with the negative
Weiss temperature. The absence of long-range magnetic order and the presence of
slow spin dynamics and persistent spin fluctuations together reflect a
dynamical ground state in Tb2Hf2O7.",1803.01193v1
2020-11-25,Spin dynamics in bulk MnNiGa and Mn$_{1.4}$Pt$_{0.9}$Pd$_{0.1}$Sn investigated by muon spin relaxation,"We report muon spin relaxation and magnetometry studies of bulk
Mn$_{1.4}$Pt$_{0.9}$Pd$_{0.1}$Sn and MnNiGa, two materials which have recently
been proposed to host topological magnetic states in thin lamella
(antiskyrmions for Mn$_{1.4}$Pt$_{0.9}$Pd$_{0.1}$Sn and biskyrmions for
MnNiGa), and show spin reorientation transitions in bulk. These measurements
shed light on the magnetic dynamics surounding the two magnetic phase
transitions in each material. In particular, we demonstrate that the behaviour
approaching the higher temperature transition in both samples is best
understood by considering a slow decrease in the frequency of dynamics with
temperature, rather than the sharp critical slowing down typical of second
order transitions. Furthermore, at low temperatures the two samples both show
spin dynamics over a broad range of frequencies that persist below the spin
reorienation transition. The dynamic behavior we identify gives new insight
into the bulk magnetism of these materials that may help underpin the
stabilization of the topologically non-trivial phases that are seen in thin
lamellae.",2011.12994v2
2021-11-01,Dynamics of position disordered Ising spins with a soft-core potential,"We theoretically study magnetization relaxation of Ising spins distributed
randomly in a $d$-dimension homogeneous and Gaussian profile under a soft-core
two-body interaction potential $\propto1/[1+(r/R_c)^\alpha]$ ($\alpha\ge d$),
where $r$ is the inter-spin distance and $R_c$ is the soft-core radius. The
dynamics starts with all spins polarized in the transverse direction. In the
homogeneous case, an analytic expression is derived at the thermodynamic limit,
which starts as $\propto\exp(-t^2)$ and follows a stretched-exponential law
asymptotically at long time with an exponent $\beta=d/\alpha$. In between an
oscillating behaviour is observed with a damping amplitude. For Gaussian
samples, the degree of disorder in the system can be controlled by the ratio
$l_\rho/R_c$ with $l_\rho$ the mean inter-spin distance and the magnetization
dynamics is investigated numerically. In the limit of $l_\rho/R_c\ll1$, a
coherent many-body dynamics is recovered for the total magnetization despite of
the position disorder of spins. In the opposite limit of $l_\rho/R_c\gg1$, a
similar dynamics as that in the homogeneous case emerges at later time after a
initial fast decay of the magnetization. We obtain a stretched exponent of
$\beta\approx0.18$ for the asymptotic evolution with $d=3, \alpha=6$, which is
different from that in the homogeneous case ($\beta=0.5$).",2111.00779v1
2022-07-27,Quantum critical dynamics in a 5000-qubit programmable spin glass,"Experiments on disordered alloys suggest that spin glasses can be brought
into low-energy states faster by annealing quantum fluctuations than by
conventional thermal annealing. Due to the importance of spin glasses as a
paradigmatic computational testbed, reproducing this phenomenon in a
programmable system has remained a central challenge in quantum optimization.
Here we achieve this goal by realizing quantum critical spin-glass dynamics on
thousands of qubits with a superconducting quantum annealer. We first
demonstrate quantitative agreement between quantum annealing and time-evolution
of the Schr\""odinger equation in small spin glasses. We then measure dynamics
in 3D spin glasses on thousands of qubits, where simulation of many-body
quantum dynamics is intractable. We extract critical exponents that clearly
distinguish quantum annealing from the slower stochastic dynamics of analogous
Monte Carlo algorithms, providing both theoretical and experimental support for
a scaling advantage in reducing energy as a function of annealing time.",2207.13800v2
2023-06-20,Convolutional neural networks for large-scale dynamical modeling of itinerant magnets,"Complex spin textures in itinerant electron magnets hold promises for
next-generation memory and information technology. The long-ranged and often
frustrated electron-mediated spin interactions in these materials give rise to
intriguing localized spin structures such as skyrmions. Yet, simulations of
magnetization dynamics for such itinerant magnets are computationally difficult
due to the need for repeated solutions to the electronic structure problems. We
present a convolutional neural network (CNN) model to accurately and
efficiently predict the electron-induced magnetic torques acting on local
spins. Importantly, as the convolutional operations with a fixed kernel
(receptive field) size naturally take advantage of the locality principle for
many-electron systems, CNN offers a scalable machine learning approach to spin
dynamics. We apply our approach to enable large-scale dynamical simulations of
skyrmion phases in itinerant spin systems. By incorporating the CNN model into
Landau-Lifshitz-Gilbert dynamics, our simulations successfully reproduce the
relaxation process of the skyrmion phase and stabilize a skyrmion lattice in
larger systems. The CNN model also allows us to compute the effective receptive
fields, thus providing a systematic and unbiased method for determining the
locality of the original electron models.",2306.11833v1
2023-08-21,Dynamic evolution of S$_0$-S$_3$ at the oxygen evolving complex with spin markers under photoelectric polarization,"Water oxidation at the oxygen evolving complex (OEC) of the photosystem II is
catalyzed by the core cluster CaMn$_4$O$_5$ which was projected to experience
five intermediate states S$\rm_i$ in the Kok's cycle since 1970's. However, the
detailed dynamics of state evolutions still remains unclear, albeit with the
general fact that the process is initiated by the transfer of photoelectrons
with the steady electron donors of the water molecules. Based on density
functional simulations, we find that the spin flips of Manganese atoms between
the consecutive states in the electric polarization field can be used as a
marker to uncover the intricate dynamic evolutions and the underlying dynamics.
The dynamic electron and proton transfers and water insertion and dissociation
are traced to reveal the evolution pathways of S$_0$-S$_3$ with commensurate
spin flips towards the exact spin configuration of the next state. In
particular, the various water insertions and dissociations at coordination
sites of the S$_2$ open and closed cubane isomers are predicted with
constraints on the necessary spin flips. Our study paves a way to uncover the
animated OEC evolutions with the spin flips that await for more experimental
verifications and lays a solid ground for revealing the mechanism of dioxygen
generation via the pending S$_4$ state.",2308.10769v2
2004-08-05,Spectroscopy of spontaneous spin noise as a probe of spin dynamics and magnetic resonance,"Not all noise in experimental measurements is unwelcome. Certain fundamental
noise sources contain valuable information about the system itself -- a notable
example being the inherent voltage fluctuations that exist across any resistor
(Johnson noise), from which temperature may be determined[1,2]. In magnetic
systems, fundamental noise can exist in the form of random spin
fluctuations[3,4]. Felix Bloch noted in 1946 that statistical fluctuations of N
paramagnetic spins should generate measurable noise of order \sqrt{N} spins,
even in zero magnetic field[5,6]. Here we address precisely these same spin
fluctuations, using off-resonant Faraday rotation to passively[7,8] ""listen"" to
the magnetization noise in an equilibrium ensemble of paramagnetic alkali
atoms. These random fluctuations generate spontaneous spin coherences which
precess and decay with the same characteristic energy and time scales as the
macroscopic magnetization of an intentionally polarized or driven ensemble.
Correlation spectra of the measured spin noise reveals g-factors, nuclear spin,
isotope abundance ratios, hyperfine splittings, nuclear moments, and spin
coherence lifetimes -- without having to excite, optically pump, or otherwise
drive the system away from thermal equilibrium. These noise signatures scale
inversely with interaction volume, suggesting routes towards non-perturbative,
sourceless magnetic resonance of small systems.",0408107v1
2005-12-08,Statistical Theory of Spin Relaxation and Diffusion in Solids,"A comprehensive theoretical description is given for the spin relaxation and
diffusion in solids. The formulation is made in a general
statistical-mechanical way. The method of the nonequilibrium statistical
operator (NSO) developed by D. N. Zubarev is employed to analyze a relaxation
dynamics of a spin subsystem. Perturbation of this subsystem in solids may
produce a nonequilibrium state which is then relaxed to an equilibrium state
due to the interaction between the particles or with a thermal bath (lattice).
The generalized kinetic equations were derived previously for a system weakly
coupled to a thermal bath to elucidate the nature of transport and relaxation
processes. In this paper, these results are used to describe the relaxation and
diffusion of nuclear spins in solids. The aim is to formulate a successive and
coherent microscopic description of the nuclear magnetic relaxation and
diffusion in solids. The nuclear spin-lattice relaxation is considered and the
Gorter relation is derived. As an example, a theory of spin diffusion of the
nuclear magnetic moment in dilute alloys (like Cu-Mn) is developed. It is shown
that due to the dipolar interaction between host nuclear spins and impurity
spins, a nonuniform distribution in the host nuclear spin system will occur and
consequently the macroscopic relaxation time will be strongly determined by the
spin diffusion. The explicit expressions for the relaxation time in certain
physically relevant cases are given.",0512182v2
2006-08-10,The origin of the spin glass transition in a model geometrically frustrated magnet,"Highly frustrated systems have macroscopically degenerate ground states that
lead to novel properties. In magnetism its consequences underpin exotic and
technologically important effects, such as, high temperature superconductivity,
colossal magnetoresistence, and the anomalous Hall effect. One of the enduring
mysteries of frustrated magnetism is why certain experimental systems have a
spin glass transition and its exact nature, given that it is not determined by
the strength of the dominant magnetic interactions. There have been some
suggestions that real systems possess disorder of the magnetic sites or bonds
that are responsible. We show that the spin glass transition in the model
kagome antiferromagnet hydronium jarosite arises from a spin anisotropy. This
weaker energy scale is much smaller than that of the magnetic exchange, yet it
is responsible for the energy barriers that are necessary to stabilise a glassy
magnetic phase at finite temperature. The resultant glassy phase is quite
unlike those found in conventional disordered spin glasses as it is based on
complex collective rearrangements of spins called ""spin folds"". This simplifies
hugely theoretical treatment of both the complex dynamics characteristic of a
spin glass and the microscopic nature of the spin glass transition itself.",0608234v1
2007-02-15,Theory of Nonequilibrium Spin Transport and Spin Transfer Torque in Superconducting-Ferromagnetic Nanostructures,"Spin transport currents and the spin-transfer torques in voltage-biased
superconducting-ferromagnetic nanopillars (SFNFS point contacts) are computed.
We develop and implement an algorithm based on the Ricatti formulation of the
quasiclassical theory of superconductivity to solve the time-dependent boundary
conditions for the nonequilibrium Green's functions for spin transport through
the ferromagnetic interfaces. A signature of the nonequilibrium torque is a
component perpendicular to the plane spanned by the two ferromagnetic moments.
The perpendicular component is absent in normal-metal-ferromagnetic nanopillars
(NFNFN) contacts, but is shown to have the same order of magnitude as the
in-plane torque for non-equilibrium SFNFS contacts. The out-of-plane torque is
due to the rotation of quasiparticle spin by the exchange fields of the
ferromagnetic layers. In the ballistic limit the equilibrium torque is related
to the spectrum of spin-polarized Andreev bound states, while the {\sl ac}
component, for small bias voltages, is determined by the nearly adiabatic
dynamics of the Andreev bound states. The nonlinear voltage dependence of the
non-equilibrium torque, including the subharmonic gap structure and the
high-voltage asymptotics, is attributed to the interplay between multiple
Andreev reflections, spin filtering and spin mixing. These properties of spin
angular momentum transport may be exploited to control the state of
nanomagnets.",0702371v3
2004-07-27,Domain wall dynamics driven by adiabatic spin transfer torques,"In a first approximation, known as the adiabatic process, the direction of
the spin polarization of currents is parallel to the local magnetization vector
in a domain wall. Thus the spatial variation of the direction of the spin
current inside the domain wall results in an adiabatical spin transfer torque
on the magnetization. We show that domain wall motion driven by this spin
torque has many unique features that do not exist in the conventional wall
motion driven by a magnetic field. By analytically and numerically solving the
Landau-Lifshitz-Gilbert equation along with the adiabatic spin torque in
magnetic nanowires, we find the domain wall has its maximum velocity at the
initial application of the current but the velocity decreases to zero as the
domain wall begins to deform during its motion. We have computed domain wall
displacement and domain wall deformation of nanowires, and concluded that the
spin torque based on the adiabatic propagation of the spin current in the
domain wall is unable to maintain wall movement. We also introduce a novel
concept of domain wall inductance to characterize the capacity of the
spin-torque induced magnetic energy stored in a domain wall. In the presence of
domain wall pinning centers, we construct a phase diagram for the domain wall
depinning by the combined action of the magnetic field and the spin current.",0407064v1
2009-05-14,Orbitally induced string formation in the spin-orbital polarons,"We study the spectral function of a single hole doped into the (a,b) plane of
the Mott insulator LaVO$_3$, with antiferromagnetic (AF) spin order of S=1
spins accompanied by alternating orbital (AO) order of active
$\{d_{yz},d_{zx}\}$ orbitals. Starting from the respective t-J model, with
spin-orbital superexchange and effective three-site hopping terms, we derive
the polaron Hamiltonian and show that a hole couples simultaneously to the
collective excitations of the AF/AO phase, magnons and orbitons. Next, we solve
this polaron problem using the self-consistent Born approximation and find a
stable quasiparticle solution -- a spin-orbital polaron. We show that the
spin-orbital polaron resembles the orbital polaron found in $e_g$ systems, as
e.g. in K$_2$CuF$_4$ or (to some extent) in LaMnO$_3$, and that the hole may be
seen as confined in a string-like potential. However, the spins also play a
crucial role in the formation of this polaron -- we explain how the orbital
degrees of freedom: (i) confine the spin dynamics acting on the hole as the
classical Ising spins, and (ii) generate the string potential which is of the
joint spin-orbital character. Finally, we discuss the impact of the results
presented here on the understanding of the phase diagrams of the lightly doped
cubic vanadates.",0905.2380v1
2011-01-10,Spin precession and inverted Hanle effect in a semiconductor near a finite-roughness ferromagnetic interface,"Although the creation of spin polarization in various non-magnetic media via
electrical spin injection from a ferromagnetic tunnel contact has been
demonstrated, much of the basic behavior is heavily debated. It is reported
here for semiconductor/Al2O3/ferromagnet tunnel structures based on Si or GaAs
that local magnetostatic fields arising from interface roughness dramatically
alter and even dominate the accumulation and dynamics of spins in the
semiconductor. Spin precession in the inhomogeneous magnetic fields is shown to
reduce the spin accumulation up to tenfold, and causes it to be inhomogeneous
and non-collinear with the injector magnetization. The inverted Hanle effect
serves as experimental signature. This interaction needs to be taken into
account in the analysis of experimental data, particularly in extracting the
spin lifetime and its variation with different parameters (temperature, doping
concentration). It produces a broadening of the standard Hanle curve and
thereby an apparent reduction of the spin lifetime. For heavily doped n-type Si
at room temperature it is shown that the spin lifetime is larger than
previously determined, and a new lower bound of 0.29 ns is obtained. The
results are expected to be general and occur for spins near a magnetic
interface not only in semiconductors but also in metals, organic and
carbon-based materials including graphene, and in various spintronic device
structures.",1101.1691v2
2011-08-05,Magnons and electromagnons in a spin-lattice-coupled frustrated magnet CuFeO2 as seen via inelastic neutron scattering,"We have investigated spin-wave excitations in a four-sublattice (4SL)
magnetic ground state of a frustrated magnet CuFeO2, in which `electromagnon'
(electric-field-active magnon) excitation has been discovered by recent
terahertz time-domain spectroscopy [Seki et al. Phys. Rev. Lett. 105 097207
(2010)]. In previous study, we have identified two spin-wave branches in the
4SL phase by means of inelastic neutron scattering measurements under applied
uniaxial pressure. [T. Nakajima et al. J. Phys. Soc. Jpn. 80 014714 (2011) ] In
the present study, we have performed high-energy-resolution inelastic neutron
scattering measurements in the 4SL phase, resolving fine structures of the
lower-energy spin-wave branch near the zone center. Taking account of the
spin-driven lattice distortions in the 4SL phase, we have developed a model
Hamiltonian to describe the spin-wave excitations. The determined Hamiltonian
parameters have successfully reproduced the spin-wave dispersion relations and
intensity maps obtained in the inelastic neutron scattering measurements. The
results of the spin-wave analysis have also revealed physical pictures of the
magnon and electromagnon modes in the 4SL phase, suggesting that collinear and
noncollinear characters of the two spin-wave modes are the keys to understand
the dynamical coupling between the spins and electric dipole moments in this
system.",1108.1297v1
2012-09-02,Nanoscale magnetic imaging of a single electron spin under ambient conditions,"The detection of ensembles of spins under ambient conditions has
revolutionized the biological, chemical, and physical sciences through magnetic
resonance imaging and nuclear magnetic resonance. Pushing sensing capabilities
to the individual-spin level would enable unprecedented applications such as
single molecule structural imaging; however, the weak magnetic fields from
single spins are undetectable by conventional far-field resonance techniques.
In recent years, there has been a considerable effort to develop nanoscale
scanning magnetometers, which are able to measure fewer spins by bringing the
sensor in close proximity to its target. The most sensitive of these
magnetometers generally require low temperatures for operation, but measuring
under ambient conditions (standard temperature and pressure) is critical for
many imaging applications, particularly in biological systems. Here we
demonstrate detection and nanoscale imaging of the magnetic field from a single
electron spin under ambient conditions using a scanning nitrogen-vacancy (NV)
magnetometer. Real-space, quantitative magnetic-field images are obtained by
deterministically scanning our NV magnetometer 50 nanometers above a target
electron spin, while measuring the local magnetic field using dynamically
decoupled magnetometry protocols. This single-spin detection capability could
enable single-spin magnetic resonance imaging of electron spins on the nano-
and atomic scales and opens the door for unique applications such as mechanical
quantum state transfer.",1209.0203v1
2012-11-29,Solid-state electronic spin coherence time approaching one second,"Solid-state electronic spin systems such as nitrogen-vacancy (NV) color
centers in diamond are promising for applications of quantum information,
sensing, and metrology. However, a key challenge for such solid-state systems
is to realize a spin coherence time that is much longer than the time for
quantum spin manipulation protocols. Here we demonstrate an improvement of more
than two orders of magnitude in the spin coherence time ($T_2$) of NV centers
compared to previous measurements: $T_2 \approx 0.5$ s at 77 K, which enables
$\sim 10^7$ coherent NV spin manipulations before decoherence. We employed
dynamical decoupling pulse sequences to suppress NV spin decoherence due to
magnetic noise, and found that $T_2$ is limited to approximately half of the
longitudinal spin relaxation time ($T_1$) over a wide range of temperatures,
which we attribute to phonon-induced decoherence. Our results apply to
ensembles of NV spins and do not depend on the optimal choice of a specific NV,
which could advance quantum sensing, enable squeezing and many-body
entanglement in solid-state spin ensembles, and open a path to simulating a
wide range of driven, interaction-dominated quantum many-body Hamiltonians.",1211.7094v2
2013-01-08,Magnetic anisotropy in hole-doped superconducting Ba 0.67K 0.33Fe 2As2 probed by polarized inelastic neutron scattering,"We use polarized inelastic neutron scattering (INS) to study spin excitations
of optimally hole-doped superconductor Ba$_{0.67}$K$_{0.33}$Fe$_2$As$_{2}$
($T_c=38$ K).
  In the normal state, the imaginary part of the dynamic susceptibility,
$\chi^{\prime\prime}(Q,\omega)$, shows magnetic anisotropy for energies below
$\sim$7 meV with c-axis polarized spin excitations larger than that of the
in-plane component. Upon entering into the superconducting state, previous
unpolarized INS experiments have shown that spin gaps at $\sim$5 and 0.75 meV
open at wave vectors $Q=(0.5,0.5,0)$ and $(0.5,0.5,1)$, respectively, with a
broad neutron spin resonance at $E_r=15$ meV. Our neutron polarization analysis
reveals that the large difference in spin gaps is purely due to different spin
gaps in the c-axis and in-plane polarized spin excitations, resulting resonance
with different energy widths for the c-axis and in-plane spin excitations. The
observation of spin anisotropy in both opitmally electron and hole-doped
BaFe$_2$As$_2$ is due to their proximity to the AF ordered BaFe$_2$As$_2$ where
spin anisotropy exists below $T_N$.",1301.1397v1
2013-07-22,Topological quantum phase transition in Kane-Mele-Kondo lattice model,"We systematically explore the ground-state phase diagram of the
Kane-Mele-Kondo lattice model on the honeycomb lattice, in particular, we focus
on its magnetic properties which has not been studied in the previous
publication[Feng, Dai, Chung, and Si, Phys. Rev. Lett. \textbf{111}, 016402
(2013)]. Beside the Kondo insulator found in that paper, two kinds of
antiferromagnetic spin-density-wave phases are identified. One is the normal
antiferromagnetic spin-density-wave state and the other is a nontrivial
topological antiferromagnetic spin-density-wave state with a quantized spin
Hall conductance and a helical edge-state. The quantum spin Hall insulator is
found to be absent since it is always unstable to antiferromagnetic
spin-density-wave states at least at the mean-field level in our model.
Furthermore, the transition between the two spin-density-wave phases are
topological quantum phase transition described by the three-dimensional quantum
electrodynamics, in which conduction electrons contribute to the low-energy
Dirac fermions while the spin-wave fluctuation of local spins gives rise to an
effective dynamic U(1) gauge-field. Such nontrivial transition shows radical
critical thermodynamic, transport and single-particle behaviors, which provide
a fingerprint for this transition. Additionally, the transition of
antiferromagnetic spin-density-wave states to the Kondo insulator is found to
be first-order. The introduction of two novel magnetic phases and their
topological quantum phase transition show rich and intrinsic physics involving
in the Kane-Mele-Kondo lattice model.",1307.5627v2
2013-07-23,Harnessing nuclear spin polarization fluctuations in a semiconductor nanowire,"Soon after the first measurements of nuclear magnetic resonance (NMR) in a
condensed matter system, Bloch predicted the presence of statistical
fluctuations proportional to $1/\sqrt{N}$ in the polarization of an ensemble of
$N$ spins. First observed by Sleator et al., so-called ""spin noise"" has
recently emerged as a critical ingredient in nanometer-scale magnetic resonance
imaging (nanoMRI). This prominence is a direct result of MRI resolution
improving to better than 100 nm^3, a size-scale in which statistical spin
fluctuations begin to dominate the polarization dynamics. We demonstrate a
technique that creates spin order in nanometer-scale ensembles of nuclear spins
by harnessing these fluctuations to produce polarizations both larger and
narrower than the natural thermal distribution. We focus on ensembles
containing ~10^6 phosphorus and hydrogen spins associated with single InP and
GaP nanowires (NWs) and their hydrogen-containing adsorbate layers. We monitor,
control, and capture fluctuations in the ensemble's spin polarization in
real-time and store them for extended periods. This selective capture of large
polarization fluctuations may provide a route for enhancing the weak magnetic
signals produced by nanometer-scale volumes of nuclear spins. The scheme may
also prove useful for initializing the nuclear hyperfine field of electron spin
qubits in the solid-state.",1307.6007v1
2014-04-27,Spin dynamics in semiconductors in the streaming regime,"We present results of a cross-disciplinary theoretical research at the
interface of spin physics and hot-electron transport. A moderately strong
electric field is assumed to provide the streaming regime where each free
charge carrier, an electron or a hole, accelerates quasiballistically in the
""passive"" region until reaching the optical-phonon energy, then emits an
optical phonon and starts the next period of acceleration. The inclusion of
spin degree of freedom into the streaming-regime kinetics gives rise to rich
and interesting spin-related phenomena. Firstly, in the streaming regime the
spin relaxation is substantially modified, and the current-induced spin
orientation is remarkably increased. Under short-pulsed photoexcitation at the
bottom of conduction band the photoelectrons execute a periodic damped motion
in the energy space with the period equal to the free flight time of an
electron in the passive region. If the short optical pulse is circularly
polarized so that the photocarriers are spin oriented, then the spin energy
distribution is oscillating in time as well, which can be detected in the
pump-probe time-resolved experiments. We show that the spin-orbit splitting of
the conduction band becomes a source for additional spin oscillations, periodic
or aperiodic depending on the value of electric field.",1404.6755v1
2014-07-11,Atomic-scale nuclear spin imaging using quantum-assisted sensors in diamond,"Nuclear spin imaging at the atomic level is essential for the understanding
of fundamental biological phenomena and for applications such as drug
discovery. The advent of novel nano-scale sensors has given hope of achieving
the long-standing goal of single-protein, high spatial-resolution structure
determination in their natural environment and ambient conditions. In
particular, quantum sensors based on the spin-dependent photoluminescence of
Nitrogen Vacancy (NV) centers in diamond have recently been used to detect
nanoscale ensembles of external nuclear spins. While NV sensitivity is
approaching single-spin levels, extracting relevant information from a very
complex structure is a further challenge, since it requires not only the
ability to sense the magnetic field of an isolated nuclear spin, but also to
achieve atomic-scale spatial resolution. Here we propose a method that, by
exploiting the coupling of the NV center to an intrinsic quantum memory
associated with the Nitrogen nuclear spin, can reach a tenfold improvement in
spatial resolution, down to atomic scales. The spatial resolution enhancement
is achieved through coherent control of the sensor spin, which creates a
dynamic frequency filter selecting only a few nuclear spins at a time. We
propose and analyze a protocol that would allow not only sensing individual
spins in a complex biomolecule, but also unraveling couplings among them, thus
elucidating local characteristics of the molecule structure.",1407.3134v1
2014-07-23,Effect of magnetoelastic coupling on spin-glass behavior in Heisenberg pyrochlore antiferromagnets with bond disorder,"Motivated by puzzling aspects of spin-glass behavior reported in frustrated
magnetic materials, we theoretically investigate effects of magnetoelastic
coupling in geometrically frustrated classical spin models. In particular, we
consider bond-disordered Heisenberg antiferromagnets on a pyrochlore lattice
coupled to local lattice distortions. By integrating out the lattice degree of
freedom, we derive an effective spin-only model, the bilinear-biquadratic model
with bond disorder, which is analyzed by classical Monte Carlo simulations.
First, we discuss the phase diagrams as well as thermodynamic and magnetic
properties. We show that the spin-glass transition temperature is largely
enhanced by the spin-lattice coupling $b$ in the weakly disordered regime. This
enhancement is ascribed to the suppression of thermal fluctuations in
semidiscrete degenerate manifold formed in the presence of the spin-lattice
coupling. We also find that, as increasing the strength of disorder, the system
shows a concomitant transition of the nematic order and spin glass at a
temperature determined by $b$, being almost independent of bond disorder.
Although further-neighbor exchange interactions originating in the cooperative
lattice distortions result in the spin-lattice order in the weakly disordered
regime, the concomitant transition remains robust. We investigate the nature of
the concomitant transition by analyzing the hysteresis of the magnetic
susceptibility, the nonlinear susceptibility, and the specific heat.
Furthermore, we discuss linear and nonlinear magnetic susceptibilities in the
high-temperature paramagnetic phase as well as single-spin flip dynamics in the
nematic phase. All these results are discussed in comparison with experiments
for typical pyrochlore magnets, such as Y2Mo2O7 and ZnCr2O4.",1407.6158v1
2014-08-31,Effect of the spin-orbit interaction on flows in heavy-ion collisions at intermediate energies,"The effect of the spin-orbit coupling in heavy ion collisions is investigated
based on an updated version of the ultra-relativistic quantum molecular
dynamics (UrQMD) model, in which the Skyrme potential energy density functional
is employed. And in special, the spin-orbit coupling effects on the directed
and elliptic flows of free nucleons emitted from $^{197}$Au+$^{197}$Au
collisions as functions of both the beam energy and the impact parameter are
studied. Our results show that the net contribution of the spin-orbit term to
flows of nucleons is negligible, whereas a directed flow splitting between
spin-up and spin-down nucleons is visible especially at large impact parameters
and a peak of the splitting is found at the beam energy around 150
MeV$/$nucleon. We also found that the directed flow splitting between spin-up
and spin-down neutrons is comparable with the neutron directed flow difference
calculated by a soft and a stiff symmetry energy, indicating that the directed
flow of neutrons cannot be used to pin down the stiffness of symmetry energy
any more without considering the spin degree of freedom in models in case of
spin polarization.",1409.0188v1
2015-04-07,Hexagonal Plaquette Spin-spin Interactions and Quantum Magnetism in a Two-dimensional Ion Crystal,"We propose a trapped ion scheme en route to realize spin Hamiltonians on a
Kagome lattice which, at low energies, are described by emergent Z2 gauge
fields, and support a topological quantum spin liquid ground state. The
enabling element in our scheme is the hexagonal plaquette spin-spin
interactions in a 2D ion crystal. For this, the phonon-mode spectrum of the
crystal is engineered by standing-wave optical potentials or by using Rydberg
excited ions, thus generating localized phonon-modes around a hexagon of ions
selected out of the entire two-dimensional crystal. These tailored modes can
mediate spin-spin interactions between ion-qubits on a hexagonal plaquette when
subject to state-dependent optical dipole forces. We discuss how these
interactions can be employed to emulate a generalized Balents-Fisher-Girvin
model in minimal instances of one and two plaquettes. This model is an
archetypical Hamiltonian in which gauge fields are the emergent degrees of
freedom on top of the classical ground state manifold. Under realistic
situations, we show the emergence of a discrete Gauss's law as well as the
dynamics of a deconfined charge excitation on a gauge-invariant background
using the two-plaquettes trapped ions spin-system. The proposed scheme in
principle allows further scaling in a future trapped ion quantum simulator, and
we conclude that our work will pave the way towards the simulation of emergent
gauge theories and quantum spin liquids in trapped ion systems.",1504.01474v1
2015-08-09,Dynamic detection of electron spin accumulation in ferromagnet-semiconductor devices by ferromagnetic resonance,"A distinguishing feature of spin accumulation in ferromagnet-semiconductor
devices is precession of the non-equilibrium spin population of the
semiconductor in a magnetic field. This is the basis for detection techniques
such as the Hanle effect, but these approaches become less effective as the
spin lifetime in the semiconductor decreases. For this reason, no electrical
Hanle measurement has been demonstrated in GaAs at room temperature. We show
here that by forcing the magnetization in the ferromagnet (the spin injector
and detector) to precess at the ferromagnetic resonance frequency, an
electrically generated spin accumulation can be detected from 30 to 300 K. At
low temperatures, the distinct Larmor precession of the spin accumulation in
the semiconductor can be detected by ferromagnetic resonance in an oblique
field. We verify the effectiveness of this new spin detection technique by
comparing the injection bias and temperature dependence of the measured spin
signal to the results obtained using traditional methods. We further show that
this new approach enables a measurement of short spin lifetimes (< 100 psec), a
regime that is not accessible in semiconductors using traditional Hanle
techniques.",1508.02093v1
2016-10-21,An electric-field representation of the harmonic XY model,"The two-dimensional harmonic XY (HXY) model is a spin model in which the
classical spins interact via a piecewise parabolic potential. We argue that the
HXY model should be regarded as the canonical classical lattice spin model of
phase fluctuations in two-dimensional condensates, as it is the simplest model
that guarantees the modular symmetry of the experimental systems. Here we
formulate a lattice electric-field representation of the HXY model and contrast
this with an analogous representation of the Villain model and the
two-dimensional Coulomb gas with a purely rotational auxiliary field. We find
that the HXY model is a spin-model analogue of a lattice electric-field model
of the Coulomb gas with an auxiliary field, but with a temperature-dependent
vacuum (electric) permittivity that encodes the coupling of the spin vortices
to their background spin-wave medium. The spin vortices map to the Coulomb
charges, while the spin-wave fluctuations correspond to auxiliary-field
fluctuations. The coupling explains the striking differences in the
high-temperature asymptotes of the specific heats of the HXY model and the
Coulomb gas with an auxiliary field. Our results elucidate the propagation of
effective long-range interactions throughout the HXY model (whose interactions
are purely local) by the lattice electric fields. They also imply that global
spin-twist excitations (topological-sector fluctuations) generated by local
spin dynamics are ergodically excluded in the low-temperature phase. We discuss
the relevance of these results to condensate physics.",1610.06692v2
2018-02-04,MOCCA-SURVEY Database I: Assessing GW kick retention fractions for BH-BH mergers in globular clusters,"Anisotropy of gravitational wave (GW) emission results in a net momentum
gained by the black hole (BH) merger product, leading to a recoil velocity up
to $\sim10^3\text{ km s}^{-1}$, which may kick it out of a globular cluster
(GC). We estimate GW kick retention fractions of merger products assuming
different models for BH spin magnitude and orientation (MS0 - random, MS1 -
spin as a function of mass and metalicity, MS2 - constant value of $0.5$). We
check how they depend on BH-BH merger time and properties of the cluster. We
analyze the implications of GW kick retention fractions on intermediate massive
BH (IMBH) formation by repeated mergers in a GC. We also calculate final spin
of the merger product, and investigate how it correlates with effective spin of
the binary. We used data from MOCCA (MOnte Carlo Cluster simulAtor) GC
simulations to get a realistic sample of BH-BH mergers, assigned each BH spin
value according to a studied model, and calculated recoil velocity and final
spin based on most recent theoretical formulas. We discovered that for
physically motivated models, GW kick retention fractions are about $30\%$ and
display small dependence on assumptions about spin, but are much more prone to
cluster properties. In particular, we discovered a strong dependence of GW kick
retention fractions on cluster density. We also show that GW kick retention
fractions are high in final life stages of the cluster, but low at the
beginning. Finally, we derive formulas connecting final spin with effective
spin for primordial binaries, and with maximal effective spin for dynamical
binaries.",1802.01192v2
2019-05-06,Search of the ground state(s) of spin glasses and quantum annealing,"We review our earlier studies on the order parameter distribution of the
quantum Sherrington-Kirkpatrick (SK) model. Through Monte Carlo technique, we
investigate the behavior of the order parameter distribution at finite
temperatures. The zero temperature study of the spin glass order parameter
distribution is made by the exact diagonalization method. We find in
low-temperature (high-transverse-field) spin glass region, the tail (extended
up to zero value of order parameter) and width of the order parameter
distribution become zero in thermodynamic limit. Such observations clearly
suggest the existence of a low-temperature (high-transverse-field) ergodic
region. We also find in high-temperature (low-transverse-field) spin glass
phase the order parameter distribution has nonzero value for all values of the
order parameter even in infinite system size limit, which essentially indicates
the nonergodic behavior of the system. We study the annealing dynamics by the
paths which pass through both ergodic and nonergodic spin glass regions. We
find the average annealing time becomes system size independent for the paths
which pass through the quantum-fluctuation-dominated ergodic spin glass region.
In contrast to that, the annealing time becomes strongly system size dependent
for annealing down through the classical-fluctuation-dominated nonergodic spin
glass region. We investigate the behavior of the spin autocorrelation in the
spin glass phase. We observe that the decay rate of autocorrelation towards its
equilibrium value is much faster in the ergodic region with respect to the
nonergodic region of the spin glass phase.",1905.01946v2
2020-07-07,Spin shuttling in a silicon double quantum dot,"The transport of quantum information between different nodes of a quantum
device is among the challenging functionalities of a quantum processor. In the
context of spin qubits, this requirement can be met by coherent electron spin
shuttling between semiconductor quantum dots. Here we theoretically study a
minimal version of spin shuttling between two quantum dots. To this end, we
analyze the dynamics of an electron during a detuning sweep in a silicon double
quantum dot (DQD) occupied by one electron. Possibilities and limitations of
spin transport are investigated. Spin-orbit interaction and the Zeeman effect
in an inhomogeneous magnetic field play an important role for spin shuttling
and are included in our model. Interactions that couple the position, spin and
valley degrees of freedom open a number of avoided crossings in the spectrum
allowing for diabatic transitions and interfering paths. The outcomes of single
and repeated spin shuttling protocols are explored by means of numerical
simulations and an approximate analytical model based on the solution of the
Landau--Zener problem. We find that a spin infidelity as low as $1-F_s\lesssim
0.002$ with a relatively fast level velocity of $\alpha = 600\, {\mu}$eV/ns is
feasible for optimal choices of parameters or by making use of constructive
interference.",2007.03598v1
2010-05-06,Spin Foams and Noncommutative Geometry,"We extend the formalism of embedded spin networks and spin foams to include
topological data that encode the underlying three-manifold or four-manifold as
a branched cover. These data are expressed as monodromies, in a way similar to
the encoding of the gravitational field via holonomies. We then describe
convolution algebras of spin networks and spin foams, based on the different
ways in which the same topology can be realized as a branched covering via
covering moves, and on possible composition operations on spin foams. We
illustrate the case of the groupoid algebra of the equivalence relation
determined by covering moves and a 2-semigroupoid algebra arising from a
2-category of spin foams with composition operations corresponding to a fibered
product of the branched coverings and the gluing of cobordisms. The spin foam
amplitudes then give rise to dynamical flows on these algebras, and the
existence of low temperature equilibrium states of Gibbs form is related to
questions on the existence of topological invariants of embedded graphs and
embedded two-complexes with given properties. We end by sketching a possible
approach to combining the spin network and spin foam formalism with matter
within the framework of spectral triples in noncommutative geometry.",1005.1057v1
2017-04-12,Absorption and generation of femtosecond laser-pulse excited spin currents in non-collinear magnetic bilayers,"Spin currents can be generated on an ultrafast timescale by excitation of a
ferromagnetic (FM) thin film with a femtosecond laser-pulse. Recently, it has
been demonstrated that these ultrafast spin currents can transport angular
momentum to neighbouring FM layers, being able to change both the magnitude and
orientation of the magnetization in the adjacent layer. In this work, both the
generation and absorption of these optically excited spin currents are
investigated. This is done using non-collinear magnetic bilayers, i.e. two FM
layers separated by a conductive spacer. Spin currents are generated in a Co/Ni
multilayer with out-of-plane (OOP) anisotropy, and absorbed by a Co layer with
an in-plane (IP) anisotropy. This behaviour is confirmed by careful analysis of
the laser-pulse induced magnetization dynamics, whereafter it is demonstrated
that the transverse spin current is absorbed very locally near the injection
interface of the IP layer (90% within the first approx. 2 nm). Moreover, it
will also be shown that this local absorption results in the excitation of THz
standing spin waves within the IP layer. The dispersion measured for these high
frequency spin waves shows a discrepancy with respect to the theoretical
predictions, for which a first explanation involving intermixed interface
regions is proposed. Lastly, the spin current generation is investigated using
different number of repeats for the Co/Ni multilayer, which proves to be of
great relevance for identifying the optical spin current generation mechanism.",1704.03746v1
2017-10-07,Dissecting spin-phonon equilibration in ferrimagnetic insulators by ultrafast lattice excitation,"To gain control over magnetic order on ultrafast time scales, a fundamental
understanding of the way electron spins interact with the surrounding crystal
lattice is required. However, measurement and analysis even of basic collective
processes such as spin-phonon equilibration have remained challenging. Here, we
directly probe the flow of energy and angular momentum in the model insulating
ferrimagnet yttrium iron garnet. Following ultrafast resonant lattice
excitation, we observe that magnetic order reduces on distinct time scales of 1
ps and 100 ns. Temperature-dependent measurements, a spin-coupling analysis and
simulations show that the two dynamics directly reflect two stages of
spin-lattice equilibration. On the 1-ps scale, spins and phonons reach
quasi-equilibrium in terms of energy through phonon-induced modulation of the
exchange interaction. This mechanism leads to identical demagnetization of the
ferrimagnet's two spin-sublattices and a novel ferrimagnetic state of increased
temperature yet unchanged total magnetization. Finally, on the much slower,
100-ns scale, the excess of spin angular momentum is released to the crystal
lattice, resulting in full equilibrium. Our findings are relevant for all
insulating ferrimagnets and indicate that spin manipulation by phonons,
including the spin Seebeck effect, can be extended to antiferromagnets and into
the terahertz frequency range.",1710.02700v2
2017-12-08,Numerical Relativity Simulations of Precessing Binary Neutron Star Mergers,"We present the first set of numerical relativity simulations of binary
neutron mergers that include spin precession effects and are evolved with
multiple resolutions. Our simulations employ consistent initial data in general
relativity with different spin configurations and dimensionless spin magnitudes
$\sim 0.1$. They start at a gravitational-wave frequency of $\sim392$~Hz and
cover more than $1$ precession period and about 15 orbits up to merger. We
discuss the spin precession dynamics by analyzing coordinate trajectories,
quasi-local spin measurements, and energetics, by comparing spin aligned,
antialigned, and irrotational configurations. Gravitational waveforms from
different spin configuration are compared by calculating the mismatch between
pairs of waveforms in the late inspiral. We find that precession effects are
not distinguishable from nonprecessing configurations with aligned spins for
approximately face-on binaries, while the latter are distinguishable from a
nonspinning configurations. Spin precession effects are instead clearly visible
for approximately edge-on binaries.
  For the parameters considered here, precession does not significantly affect
the characteristic postmerger gravitational-wave frequencies nor the mass
ejection. Our results pave the way for the modeling of spin precession effects
in the gravitational waveform from binary neutron star events.",1712.02992v1
2019-06-18,Nuclear magnetic resonance spectroscopy with a superconducting flux qubit,"We theoretically analyze the performance of the nuclear magnetic resonance
(NMR) spectroscopy with a superconducting flux qubit (FQ). Such NMR with the FQ
is attractive because of the possibility to detect the relatively small number
of nuclear spins in a local region ($\sim\mu$m) with low temperatures ($\sim$
mK) and low magnetic fields ($\sim$ mT), in which other types of quantum
sensing schemes cannot easily access. A sample containing nuclear spins is
directly attached on the FQ, and the FQ is used as a magnetometer to detect
magnetic fields from the nuclear spins. Especially, we consider two types of
approaches to NMR with the FQ. One of them is to use spatially inhomogeneous
excitations of the nuclear spins, which are induced by a spatially asymmetric
driving with radio frequency~(RF) pulses. Such an inhomogeneity causes a change
in the DC magnetic flux penetrating a loop of the FQ, which can be detected by
a standard Ramsey measurement on the FQ. The other approach is to use a
dynamical decoupling on the FQ to measure AC magnetic fields induced by Larmor
precession of the nuclear spins. In this case, neither a spin excitation nor a
spin polarization is required since the signal comes from fluctuating magnetic
fields of the nuclear spins. We calculate the minimum detectable density
(number) of the nuclear spins for the FQ with experimentally feasible
parameters. We show that the minimum detectable density (number) of the nuclear
spins with these approaches is around $10^{21}$ /cm$^3$ ($10^8$) with an
accumulation time of a second.",1906.07386v1
2019-07-11,Anomalous anisotropic behaviour of spin-triplet proximity effect in Au/SrRuO$_3$/Sr$_2$RuO$_4$ junctions,"Spin-polarized supercurrents can be generated with magnetic inhomogeneity at
a ferromagnet/spin-singlet-superconductor interface. In such systems, complex
magnetic inhomogeneity makes it difficult to functionalise the spin-polarized
supercurrents. However, spin-polarized supercurrents in
ferromagnet/spin-triplet-superconductor junctions can be controlled by angle
between magnetization and spin of Copper pairs ($d$-vector), that can
effectively be utilized in developing of a field of research known as
superconducting spintronics. Recently, we found induction of spin-triplet
correlation into a ferromagnet SrRuO$_3$ epitaxially deposited on a
spin-triplet superconductor Sr$_2$RuO$_4$, without any electronic spin-flip
scattering. Here, we present systematic magnetic field dependence of the
proximity effect in Au/SrRuO$_3$/ Sr$_2$RuO$_4$ junctions. It is found that
induced triplet correlations exhibit strong anisotropic field response. Such
behaviour attributes to the rotation of the $d$-vector of Sr$_2$RuO$_4$. This
anisotropic behaviour is in contrast with the vortex dynamic. Our results will
stimulate study of interaction between ferromagnetism and unconventional
superconductivity.",1907.05175v2
2017-04-29,Competing spin liquids and hidden nematic order in spin ice with frustrated transverse exchange,"Frustration in magnetic interactions can give rise to disordered ground
states with subtle and beautiful properties. The spin ices Ho2Ti2O7 and
Dy2Ti2O7 exemplify this phenomenon, displaying a classical spin liquid state,
with fractionalized magnetic--monopole excitations. Recently there has been
great interest in closely-related ""quantum spin ice"" materials, following the
realization that anisotropic exchange interactions could convert spin ice into
a massively-entangled, quantum, spin liquid, where magnetic monopoles become
the charges of an emergent quantum electrodynamics. Here we show that even the
simplest model of a quantum spin ice, the XXZ model on the pyrochlore lattice,
can realise a still-richer scenario. Using a combination of classical Monte
Carlo simulation, semi--classical molecular--dynamics simulation, and analytic
field theory, we explore the properties of this model for frustrated transverse
exchange. We find not one, but three, competing forms of spin liquid, as well
as a phase with hidden, spin-nematic, order. We explore the experimental
signatures of each of these different states, making explicit predictions for
inelastic neutron scattering. These results show an intriguing similarity to
experiments on a range of pyrochlore oxides.",1705.00148v2
2017-11-10,All-optical control of long-lived nuclear spins in rare-earth doped nanoparticles,"Nanoscale systems offer key capabilities for quantum technologies that
include single qubit control and readout, multiple qubit gate operation,
extremely sensitive and localized sensing and imaging, as well as the ability
to build hybrid quantum systems. To fully exploit these functionalities,
multiple degrees of freedom are highly desirable: in this respect, nanoscale
systems that coherently couple to light and possess spins, allow for storage of
photonic qubits or light-matter entanglement together with processing
capabilities. In addition, all-optical control of spins can be possible for
faster gate operations and higher spatial selectivity compared to direct RF
excitation. Such systems are therefore of high interest for quantum
communications and processing. However, an outstanding challenge is to preserve
properties, and especially optical and spin coherence lifetimes, at the
nanoscale. Indeed, interactions with surfaces related perturbations strongly
increase as sizes decrease, although the smallest objects present the highest
flexibility for integration with other systems. Here, we demonstrate optically
controlled nuclear spins with long coherence lifetimes (T2) in rare earth doped
nanoparticles. We observed spins echoes and measured T2 of 2.9 +/- 0.3 ms at 5
K and under a magnetic field of 9 mT, a value comparable to those obtained in
bulk single crystals. Moreover, we achieve, for the first time, spin T2
extension using all-optical spin dynamical decoupling and observe high fidelity
between excitation and echo phases. Rare-earth doped nanoparticles are thus the
only reported nano-materials in which optically controlled spins with
millisecond coherence lifetimes have been observed. These results open the way
to providing quantum light-atom-spin interfaces with long storage time within
hybrid architectures.",1711.03934v1
2018-03-02,Coherent electron transport in silicon quantum dots,"With silicon being the go-to material for spin qubits, and motivated by the
demand of a scalable quantum computer architecture for fast and reliable
quantum information transfer on-chip, we study coherent electron transport in a
silicon double quantum dot. We first examine the valley-orbital dynamics in a
silicon double dot, and discuss how to properly measure the tunnel couplings as
well as the valley phase difference between two quantum dots. We then focus on
possible phase and spin flip errors during spin transport across a silicon
double dot. In particular, we clarify correction on the effective $g$-factor
for the electron spin from the double dot confinement potential, and quantify
the resulting phase error. We then study spin fidelity loss due to spin-valley
mixing, which is a unique feature of silicon quantum dots. We show that a small
phase correction between valleys can cause a significant coherence loss. We
also investigate spin flip errors caused by either an external inhomogeneous
magnetic field or the intrinsic spin-orbit coupling. We show that the presence
of valleys makes it possible to have much broader (in terms of interdot
detuning) level anti-crossings compared to typical anti-crossings in, for
example, a GaAs double dot, and such broad anti-crossings lead to amplification
of spin flip errors. Lastly, we design a pulse sequence to suppress various
possible spin flip errors by taking advantage of the multiple level
anti-crossings in a silicon double dot and employing Landau-Zener transitions.",1803.00749v3
2019-01-06,Asymmetric dynamics of edge exchange spin waves in honeycomb nanoribbons with zigzag and bearded edges boundaries,"We report on the theoretical prediction of asymmetric edge spin waves,
propagating in opposite directions on the edges of honeycomb nanoribbons with
zigzag and bearded edges boundaries. The simultaneous propagation of edge spin
waves in the same direction on both edges of these nanoribbons is hence
predicted to be forbidden. These asymmetric edge exchange spin waves are
analogous to the nonreciprocal surface spin waves reported in magnetic thin
films. Their existence is related to the nontrivial symmetry underlying the
nanoribbons under study. The edge and discretized bulk exchange spin waves are
calculated in the long wavelength part of the Brillouin zone using the
classical spin wave theory approach and appropriate boundary conditions. In the
absence of an external magnetic field in our study, the asymmetric edge spin
waves propagate with equal frequencies and opposite directions, since the
energy dispersion relation is independent of the sign of the wavevector
components in the long wavelength part of the Brillouin zone. The edge spin
waves are characterized by linear dispersion relations for magnetically
isotropic nanoribbons. Introducing magnetic anisotropy in the calculation
significantly enhances the energy gap between the edge and bulk spin waves in
both types of nanoribbons. Based on our calculation, the large energy gap
allows separate excitation of bulk and edge modes as their energies are no more
overlapping.",1901.01617v1
2020-08-06,Paramagnetic spin Hall magnetoresistance,"Spin Hall magnetoresistance (SMR) refers to a resistance change in a metallic
film reflecting the magnetization direction of a magnet attached to the film.
The mechanism of this phenomenon is spin exchange between conduction-electron
spins and magnetization at the interface. SMR has been used to read out
information written in a small magnet and to detect magnetization dynamics, but
it has been limited to magnets; magnetic ordered phases or instability of
magnetic phase transition has been believed to be indispensable. Here, we
report the observation of SMR in a paramagnetic insulator
Gd$_{3}$Ga$_{5}$O$_{12}$ (GGG) without spontaneous magnetization combined with
a Pt film. The paramagnetic SMR can be attributed to spin-transfer torque
acting on localized spins in GGG. We determine the efficiencies of spin torque
and spin-flip scattering at the Pt/GGG interface, and demonstrate these
quantities can be tuned with external magnetic fields. The results clarify the
mechanism of spin-transport at a metal/paramagnetic insulator interface, which
gives new insight into the spintronic manipulation of spin states in
paramagnetic systems.",2008.02446v2
2021-03-11,Long-range spin transport on the surface of topological Dirac semimetal,"We theoretically propose the long-range spin transport mediated by the
gapless surface states of topological Dirac semimetal (TDSM). Low-dissipation
spin current is a building block of next-generation spintronics devices. While
conduction electrons in metals and spin waves in ferromagnetic insulators
(FMIs) are the major carriers of spin current, their propagation length is
inevitably limited due to the Joule heating or the Gilbert damping. In order to
suppress dissipation and realize long-range spin transport, we here make use of
the spin-helical surface states of TDSMs, such as $\mathrm{Cd_3 As_2}$ and
$\mathrm{Na_3 Bi}$, which are robust against disorder. Based on a junction of
two FMIs connected by a TDSM, we demonstrate that the magnetization dynamics in
one FMI induces a spin current on the TDSM surface flowing to the other FMI. By
both the analytical transport theory on the surface and the numerical
simulation of real-time evolution in the bulk, we find that the induced spin
current takes a universal semi-quantized value that is insensitive to the
microscopic coupling structure between the FMI and the TDSM. We show that this
surface spin current is robust against disorder over a long range, which
indicates that the TDSM surface serves as a promising system for realizing
spintronics devices.",2103.06519v1
2021-08-02,Quantum Computation Protocol for Dressed Spins in a Global Field,"Spin qubits are contenders for scalable quantum computation because of their
long coherence times demonstrated in a variety of materials, but individual
control by frequency-selective addressing using pulsed spin resonance creates
severe technical challenges for scaling up to many qubits. This individual
resonance control strategy requires each spin to have a distinguishable
frequency, imposing a maximum number of spins that can be individually driven
before qubit crosstalk becomes unavoidable. Here we describe a complete
strategy for controlling a large array of spins in quantum dots dressed by an
on-resonance global field, namely a field that is constantly driving the spin
qubits, to dynamically decouple from the effects of background magnetic field
fluctuations. This approach -- previously implemented for the control of single
electron spins bound to electrons in impurities -- is here harmonized with all
other operations necessary for universal quantum computing with spins in
quantum dots. We define the logical states as the dressed qubit states and
discuss initialization and readout utilizing Pauli spin blockade, as well as
single- and two-qubit control in the new basis. Finally, we critically analyze
the limitations imposed by qubit variability and potential strategies to
improve performance.",2108.00798v2
2021-08-14,Dissipation-relaxation dynamics of a spin-1/2 particle with a Rashba-type spin-orbit coupling in an ohmic heat bath,"Spin-orbit coupling (SOC), which is inherent to a Dirac particle that moves
under the influence of electromagnetic fields, manifests itself in a variety of
physical systems including non-relativistic ones. For instance, it plays an
essential role in spintronics developed in the past few decades, particularly
by controlling spin current generation and relaxation. In the present work, by
using an extended Caldeira-Leggett model, we elucidate how the interplay
between spin relaxation and momentum dissipation of an open system of a single
spin-$1/2$ particle with a Rashba type SOC is induced by the interactions with
a spinless, three-dimensional environment. Staring from the path integral
formulation for the reduced density matrix of the system, we have derived a set
of coupled nonlinear equations that consists of a quasi-classical Langevin
equation for the momentum with a frictional term and a spin precession
equation. The spin precesses around the effective magnetic field generated by
both the SOC and the frictional term. It is found from analytical and numerical
solutions to these equations that a spin torque effect included in the
effective magnetic field causes a spin relaxation and that the spin and
momentum orientations after a long time evolution are largely controlled by the
Rashba coupling strength. Such a spin relaxation mechanism is qualitatively
different from, e.g., the one encountered in semiconductors where essentially
no momentum dissipation occurs due to the Pauli blocking.",2108.06465v1
2021-09-29,Prospects for measuring off-axis spins of binary black holes with Plus-era gravitational-wave detectors,"The mass and spin properties of binary black holes (BBHs) inferred from their
gravitational-wave signatures reveal important clues about how these systems
form. BBHs originating from isolated binary evolution are expected to have
spins preferentially aligned with their orbital angular momentum, whereas there
is no such preference in binaries formed via dynamical assembly. The fidelity
with which near-future gravitational-wave detectors can measure off-axis spins
will have implications for the study of BBH formation channels. In this work,
we examine the degree to which the Advanced LIGO Plus (A+) and Advanced Virgo
Plus (AdV+) interferometric detectors can measure both aligned and misaligned
spins. We compare spin resolution between the LIGO-Virgo network operating at
either A+/AdV+ (""Plus"") sensitivity or Advanced-era design (""Design"")
sensitivity using simulated BBH gravitational-wave signals injected into
synthetic detector noise. The signals are distributed over the mass-spin
parameter space of likely BBH systems, accounting for the effects of precession
and higher-order modes. We find that the Plus upgrades yield significant
improvements in spin estimation for systems with unequal masses and moderate or
large spins. Using simulated signals modelled after different types of
hierarchical BBH mergers, we also conclude that the Plus detector network will
yield substantially improved spin estimates for 1G+2G binaries compared to the
Design network.",2109.14571v2
2021-12-14,Rapidly enhanced spin polarization injection in an optically pumped spin ratchet,"Rapid injection of spin polarization into an ensemble of nuclear spins is a
problem of broad interest, spanning dynamic nuclear polarization (DNP) to
quantum information science. We report on a strategy to boost the spin
injection rate by exploiting electrons that can be rapidly polarized via
high-power optical pumping. We demonstrate this in a model system of Nitrogen
Vacancy center electrons injecting polarization into a bath of 13C nuclei in
diamond. We deliver >20W of continuous, nearly isotropic, optical power to the
sample, constituting a substantially higher power than in previous experiments.
Through a spin-ratchet polarization transfer mechanism, we show boosts in spin
injection rates by over two orders of magnitude. Our experiments elucidate
bottlenecks in the DNP process caused by rates of electron polarization,
polarization transfer to proximal nuclei, and spin diffusion. This work
demonstrates opportunities for rapid spin injection employing non-thermally
generated electron polarization, and has relevance to a broad class of
experimental systems including in DNP, quantum sensing, and spin-based MASERs.",2112.07223v3
2022-03-03,Anisotropic deconfined criticality in Dirac spin liquids,"We analyze a Higgs transition from a U(1) Dirac spin liquid to a gapless
$\mathbb{Z}_2$ spin liquid. This $\mathbb{Z}_2$ spin liquid is of relevance to
the spin $S=1/2$ square lattice antiferromagnet, where recent numerical studies
have given evidence for such a phase existing in the regime of high frustration
between nearest neighbor and next-nearest neighbor antiferromagnetic
interactions (the $J_1$-$J_2$ model), appearing in a parameter regime between
the vanishing of N\'eel order and the onset of valence bond solid ordering. The
proximate Dirac spin liquid is unstable to monopole proliferation on the square
lattice, ultimately leading to N\'eel or valence bond solid ordering. As such,
we conjecture that this Higgs transition describes the critical theory
separating the gapless $\mathbb{Z}_2$ spin liquid of the $J_1$-$J_2$ model from
one of the two proximate ordered phases. The transition into the other ordered
phase can be described in a unified manner via a transition into an unstable
SU(2) spin liquid, which we have analyzed in prior work. By studying the
deconfined critical theory separating the U(1) Dirac spin liquid from the
gapless $\mathbb{Z}_2$ spin liquid in a $1/N_f$ expansion, with $N_f$
proportional to the number of fermions, we find a stable fixed point with an
anisotropic spinon dispersion and a dynamical critical exponent $z \neq 1$. We
analyze the consequences of this anisotropic dispersion by calculating the
angular profiles of the equal-time N\'eel and valence bond solid correlation
functions, and we find them to be distinct. We also note the influence of the
anisotropy on the scaling dimension of monopoles.",2203.01962v1
2022-03-08,Cavity Quantum Electrodynamics Effects of Optically Cooled Nitrogen-Vacancy Centers Coupled to a High Frequency Microwave Resonator,"Recent experiments demonstrated the cooling of a microwave mode of a
high-quality dielectric resonator coupled to optically cooled nitrogen-vacancy
(NV) spins in diamond. Our recent theoretical study [arXiv:2110.10950] pointed
out the cooled NV spins can be used to realize cavity quantum electrodynamics
effects (C-QED) at room temperature. In this article, we propose to modify the
setup used in a recent diamond maser experiment [Nature 55, 493-496 (2018)],
which features a higher spin transition frequency, a lower spin-dephasing rate
and a stronger NV spins-resonator coupling, to realize better microwave mode
cooling and the room-temperature CQED effects. To describe more precisely the
optical spin cooling and the collective spin-resonator coupling, we extend the
standard Jaynes-Cumming model to account for the rich electronic and spin
levels of the NV centers. Our calculations show that for the proposed setup it
is possible to cool the microwave mode from $293$ K (room temperature) to $116$
K, which is about $72$ K lower than the previous records, and to study the
intriguing dynamics of the CQED effects under the weak-to-strong coupling
transition by varying the laser power. With simple modifications, our model can
be applied to, e.g., other solid-state spins or triplet spins of pentacene
molecules, and to investigate other effects, such as the operations of pulsed
and continuous-wave masing.",2203.04102v1
2022-03-21,Large anomalous Hall effect and anisotropic magnetoresistance in intrinsic nanoscale spin-valve-type structure of an antiferromagnet,"A spin valve is a prototype of spin-based electronic devices found on
ferromagnets, in which an antiferromagnet plays a supporting role. Recent
findings in antiferromagnetic spintronics show that an antiferromagnetic order
in single-phase materials solely governs dynamic transport, and
antiferromagnets are considered promising candidates for spintronic technology.
In this work, we demonstrated antiferromagnet-based spintronic functionality on
an itinerant Ising antiferromagnet of Ca0.9Sr0.1Co2As2 by integrating nanoscale
spin-valve-type structure and investigating anisotropic magnetic properties
driven by spin-flips. Multiple stacks of 1 nm thick spin-valve-like unit are
intrinsically embedded in the antiferromagnetic spin structure. In the presence
of a rotating magnetic field, a new type of the spin-valve-like operation was
observed for large anomalous Hall conductivity and anisotropic
magnetoresistance, whose effects are maximized above the spin-flip transition.
In addition, a joint experimental and theoretical study provides an efficient
tool to read out various spin states, which scheme can be useful for
implementing extensive spintronic applications.",2203.10952v1
2022-04-25,Scattering phenomena for spin transport in Kitaev spin liquid,"The Kitaev model exhibits a canonical quantum spin liquid as a ground state
and hosts two fractional quasiparticles, itinerant Majorana fermion and
localized flux excitation. The former can carry heat and spin modulations in
the quantum spin liquid, but the role of the latter remains unknown for the
transport phenomena. Here, we focus on spin transport in the presence of
excited fluxes and report that they yield strong interference in the
propagation of the Majorana fermions, which feel gauge-like potential emergent
around the fluxes. We examine the transient spin dynamics triggered by a pulsed
magnetic field at an edge. In the absence of excited fluxes, the magnetic-field
pulse creates the plane wave of the Majorana fermions, which flows in the
quantum spin liquid. Although this wave does not accompany the change of local
spin moments in bulk, it induces local moments at the side opposite to the edge
under the magnetic-field pulse. We observe the spatial modulation of induced
spin moments when fluxes are excited in the bulk region. This behavior is more
striking than the case of lattice defects. Moreover, we find that, although the
amplitude of the spatial change is almost independent of the distance between
lattice defects, it is strongly enhanced by increasing the distance for the
case of excited fluxes. The difference is understood from the influence on the
itinerant Majorana fermions; the lattice defects change the system locally, but
flux excitations alter all the transfer integrals on the string connecting
them. The present results will provide another route to observing intrinsic
flux excitations distinguished from extrinsic effects such as lattice defects.",2204.11578v1
2022-05-24,Spinning test particle motion around a rotating wormhole,"In this work, we investigated the motion of spinning test particles around a
rotating wormhole, extending, in this way, the previous work of
Benavides-Gallego et al. in [Phys. Rev. D 101, no.12, 124024] to the general
case. Using the Mathisson-Papapetrous-Dixon equations, we study the effective
potential, circular orbits, and the innermost stable circular orbit (ISCO) of
spinning test particles. We found that both the particle and wormhole spins
affect the location of the ISCO significantly. On the other hand, Similar to
the non-rotating case, we also found two possible configurations in the
effective potential: plus and minus. Furthermore, the minimum value of the
effective potential is not at the throat due to its spin, in contrast to the
motion of the non-spinning test particles in a non-rotating wormhole, where the
effective potential is symmetric, and its minimum value is at the throat. In
the case of the ISCO, we found that it increases as the spin of the wormhole a
increases, in contrast to black holes where the presence of spin decreases the
value of the ISCO. Finally, since the dynamical four-momentum and kinematical
four-velocity of the spinning particle are not always parallel, we consider the
superluminal bound, finding that the allowed values of s change as the
wormhole's spin a increases.",2205.11727v1
2022-06-11,Chirality as Generalized Spin-Orbit Interaction in Spintronics,"This review focuses on the chirality observed in the excited states of the
magnetic order, dielectrics, and conductors that hold transverse spins when
they are evanescent. Even without any relativistic effect, the transverse spin
of the evanescent waves are locked to the momentum and the surface normal of
their propagation plane. This chirality thereby acts as a generalized
spin-orbit interaction, which leads to the discovery of various chiral
interactions between magnetic, phononic, electronic, photonic, and plasmonic
excitations in spintronics that mediate the excitation of quasiparticles into a
single direction, leading to phenomena such as chiral spin and phonon pumping,
chiral spin Seebeck, spin skin, magnonic trap, magnon Doppler, and spin diode
effects. Intriguing analogies with electric counterparts in the nano-optics and
plasmonics exist. After a brief review of the concepts of chirality that
characterize the ground state chiral magnetic textures and chirally coupled
magnets in spintronics, we turn to the chiral phenomena of excited states. We
present a unified electrodynamic picture for dynamical chirality in spintronics
in terms of generalized spin-orbit interaction and compare it with that in
nano-optics and plasmonics. Based on the general theory, we subsequently review
the theoretical progress and experimental evidence of chiral interaction, as
well as the near-field transfer of the transverse spins, between various
excitations in magnetic, photonic, electronic and phononic nanostructures at
GHz time scales. We provide a perspective for future research before concluding
this article.",2206.05535v2
2022-07-13,Chaos motion and Periastron precession of spinning test particles moving in the vicinage of a Schwarzschild black hole surrounded by a quintessence matter field,"In the present work, our main objective is to investigate the orbits of
spinning test particles around a Schwarzschild black hole under the influence
of a quintessence matter field (SQBH). We begin with the dynamics of the
spinning test particles around SQBH which is governed by the
Mathisson-Papapetrou-Dixon (MPD) equations under the pole-dipole approximation,
where the gravitational field and the higher multipoles of the particle are
neglected. Depending on the types of saddle points,the effective potential are
classified and the possibility of chaotic orbits is discussed. The inner most
stable circular orbits (ISCOs) of the spinning particle around SQBH are
addressed, as are the effects of the parameters $S$ (particles' spin) and
$\epsilon$ (equation of state parameter). Later, Periastron precession is
investigated up to the first-order spin correction for a spinning particle
moving in nearly circular orbits around SQBH. It is noted that the addition of
particle's spin revamps the results obtained for the non-spinning particles and
also articulates the some interesting observational properties of the SQBH.
Additionally, we discuss the ramifications of employing first-order spin
corrections for analysing ISCOs, as well as compare our results to the
Schwarzschild black hole to ensure that they are consistent in the limit when
equation of state parameter $\epsilon=-1/3$ and normalization factor $\alpha
\to 0$.",2207.06007v1
2022-09-12,Coherent control of a nuclear spin via interactions with a rare-earth ion in the solid-state,"Individually addressed Er$^{3+}$ ions in solid-state hosts are promising
resources for quantum repeaters, because of their direct emission in the
telecom band and compatibility with silicon photonic devices. While the
Er$^{3+}$ electron spin provides a spin-photon interface, ancilla nuclear spins
could enable multi-qubit registers with longer storage times. In this work, we
demonstrate coherent coupling between the electron spin of a single Er$^{3+}$
ion and a single $I=1/2$ nuclear spin in the solid-state host crystal, which is
a fortuitously located proton ($^1$H). We control the nuclear spin using
dynamical decoupling sequences applied to the electron spin, implementing one-
and two-qubit gate operations. Crucially, the nuclear spin coherence time
exceeds the electron coherence time by several orders of magnitude, because of
its smaller magnetic moment. These results provide a path towards combining
long-lived nuclear spin quantum registers with telecom-wavelength emitters for
long-distance quantum repeaters.",2209.05631v1
2022-10-07,Colloquium: Spin-orbit effects in superconducting hybrid structures,"Spin-orbit coupling (SOC) describes the interaction between an electron's
motion and its spin, and is ubiquitous in condensed matter systems. The
interplay of SOC with superconductivity has attracted significant interest over
the past decade and understanding has substantially progressed, both
experimentally and theoretically. Even with well-understood materials,
conventional $s$-wave superconducting hybrid structures with SOC provide a
platform for realizing exotic phenomena and counterparts in the normal state.
Understanding the emergent phenomena in such systems is an important aim in
condensed matter physics. One such area relates to the generation and interplay
of spin-polarized spin-triplet Cooper pairs in superconducting structures with
magnetic interfaces. It is established that certain forms of magnetic
inhomogeneity at an $s$-wave superconductor interface with a ferromagnet can
transform spin-singlet Cooper pairs into a spin-polarized spin-triplet Cooper
pairs, enabling transformative concepts for cryogenic computing. Recently,
theory and experiments have demonstrated singlet-to-triplet pair conversion via
SOC in $s$-wave superconducting structures with or without magnetic layers.
Moreover, the spin-dependent properties of quasiparticles and their
non-equilibrium behavior also change in the presence of SOC. These
breakthroughs create the potential for energy-efficient control of static and
dynamic spin phenomena in superconducting structures and devices. This article
reviews progress in superconducting spintronics with a focus on the coupling of
superconductivity and SOC in hybrid structures and devices, and outlines
directions that are critical for future device development and fundamental
understanding.",2210.03549v1
2022-10-24,Spin State Evolution of (99942) Apophis during its 2029 Earth Encounter,"We explore the effects of the 2029 Earth encounter on asteroid (99942)
Apophis' non-principal axis spin state, leveraging refined orbit, spin state,
and inertia information provided by more recent optical and radar observations.
Propagating the asteroids' coupled orbit and rigid body attitude dynamics
through the flyby, we present the range of possible post-flyby spin states.
These spin state distributions will be valuable for planning Apophis
observation campaigns and spacecraft missions, most notably OSIRIS-APEX. The
simulations indicate that gravitationally induced changes to the asteroid's
tumbling periods and rotational angular momentum direction (pole) will likely
be significant and measurable. For the current spin state and inertia estimates
and their uncertainties, Apophis is likely to remain in a short axis mode (SAM)
tumbling state but its effective spin rate could halve or double. Its pole is
likely to shift by 10 degrees or more and increase in longitude while moving
closer to the ecliptic plane. These spin state changes are very sensitive to
the asteroid's close approach attitude and mass distribution. With ground-based
tracking of the asteroid's spin state through the encounter, this sensitivity
will help refine mass distribution knowledge. We also discuss the implications
of this abrupt spin state alteration for Apophis' Yarkovsky acceleration and
geophysical properties, identifying possible pathways for surface and internal
changes, most notably if Apophis is a contact binary. Comparison of the pre and
post-flyby inertia estimates obtained from the ground-based observations will
help assess the extent of possible geophysical changes.",2210.13365v1
2023-01-18,Charged magnons on the surface of a topological insulator,"We study a system of two-dimensional Dirac electrons (as is realized on the
surface of a 3D topological insulator) coupled to an array of localized spins.
The spins are coupled ferromagnetically to each other, forming an ordered
ground state with low-energy spin-wave excitations (magnons). The Dirac
electrons couple to the spins through a spin-dependent effective Zeeman field.
The out-of-plane effective Zeeman field therefore serves as a Dirac mass that
gaps the electronic spectrum. Once a spin is flipped, it creates a surrounding
domain in which the sign of the Dirac mass is opposite to that of the rest of
the sample. Therefore, an electronic bound state appears on the domain wall, as
predicted by Jackiw and Rebbi. However, in a quantum magnet, a localized spin
flip does not produce an eigenstate. Instead, the eigenstates correspond to
delocalized spin waves (magnons). As in the case of the single flipped spin,
the delocalized magnon also binds an in-gap electronic state. We name this
excitation a `Jackiw-Rebbi-Magnon' (JRM) and study its signature in the dynamic
spin susceptibility. When the sample is tunnel-coupled to an electronic
reservoir, a magnon produced in a system without any electrons hybridizes with
a JRM (which binds a single electron), producing magnon-JRM polaritons. For
such a system, we identify a quantum phase transition when the magnon-JRM
polariton energy falls below that of the fully polarized ferromagnetic ground
state.",2301.07754v2
2024-04-08,Effect of collective spin excitation on electronic transport in topological spin texture,"We develop an efficient real-time simulation method for the spin-charge
coupled system in the velocity gauge. This method enables us to compute the
real-time simulation for the two-dimensional system with the complex spin
texture. We focus on the effect of the collective excitation of the localized
spins on the electronic transport properties of the non-trivial topological
state in real space. To investigate this effect, we calculate the linear
optical conductivity by calculating the real-time evolution of the Kondo
lattice model on the triangular lattice, which hosts an all-in/all-out magnetic
structure. In the linear conductivity spectra, we observe multiple peaks below
the bandgap regime, attributed to the resonant contributions of collective
modes similar to the skyrmionic system, alongside broadband modifications
resulting from off-resonant spin dynamics. The result shows that the collective
excitation, similar to the skyrmionic system, influences the optical response
of the electron systems based on symmetry analysis. We elucidate the
interference between the contributions from the different spin excitations to
the optical conductivity in the multiple spin texture, pointing out the
mode-dependent electrical activity. We show the complex interplay between the
complex spin texture and the itinerant electrons in the two-dimensional
spin-charge coupled system.",2404.05204v1
2019-05-14,Dynamics of an itinerant spin-3 atomic dipolar gas in an optical lattice,"Arrays of ultra-cold dipolar gases loaded in optical lattices are emerging as
powerful quantum simulators of the many-body physics associated with the rich
interplay between long-range dipolar interactions, contact interactions,
motion, and quantum statistics. In this work we report on our investigation of
the quantum many-body dynamics of a large ensemble of bosonic magnetic chromium
atoms with spin S = 3 in a three-dimensional lattice as a function of lattice
depth. Using extensive theory and experimental comparisons we study the
dynamics of the population of the different Zeeman levels and the total
magnetization of the gas across the superfluid to the Mott insulator
transition. We are able to identify two distinct regimes: At low lattice
depths, where atoms are in the superfluid regime, we observe that the spin
dynamics is strongly determined by the competition between particle motion,
onsite interactions and external magnetic field gradients. Contact spin
dependent interactions help to stabilize the collective spin length, which sets
the total magnetization of the gas. On the contrary, at high lattice depths,
transport is largely frozen out. In this regime, while the spin populations are
mainly driven by long range dipolar interactions, magnetic field gradients also
play a major role in the total spin demagnetization. We find that dynamics at
low lattice depth is qualitatively reproduced by mean-field calculations based
on the Gutzwiller ansatz; on the contrary, only a beyond mean-field theory can
account for the dynamics at large lattice depths. While the cross-over between
these two regimes does not correspond to sharp features in the observed
dynamical evolution of the spin components, our simulations indicate that it
would be better revealed by measurements of the collective spin length.",1905.06123v1
2007-05-15,Decoherence of many-spin systems in NMR: From molecular characterization to an environmentally induced quantum dynamical phase transition,"The control of open quantum systems has a fundamental relevance for fields
ranging from quantum information processing to nanotechnology. Typically, the
system whose coherent dynamics one wants to manipulate, interacts with an
environment that smoothly degrades its quantum dynamics. Thus, a precise
understanding of the inner mechanisms of this process, called ""decoherence"", is
critical to develop strategies to control the quantum dynamics. In this thesis
we solved the generalized Liouville-von Neumann quantum master equation to
obtain the dynamics of many-spin systems interacting with a spin bath. We also
solve the spin dynamics within the Keldysh formalism. Both methods lead to
identical solutions and together gave us the possibility to obtain numerous
physical predictions that contrast well with Nuclear Magnetic Resonance
experiments. We applied these tools for molecular characterizations,
development of new numerical methodologies and the control of quantum dynamics
in experimental implementations. But, more important, these results contributed
to fundamental physical interpretations of how quantum dynamics behaves in open
systems. In particular, we found a manifestation of an environmentally induced
quantum dynamical phase transition.",0705.2350v1
2014-08-07,Regular and irregular dynamics of Dirac-Weyl wavepackets in a mesoscopic quantum dot at the edge of topological insulator,"The dynamics of Dirac-Weyl spin-polarized wavepackets driven by periodic
electric field is considered for the electrons in a mesoscopic quantum dot
formed at the edge of two-dimensional HgTe/CdTe topological insulator with
Dirac-Weyl massless energy spectra, where the motion of carriers is less
sensitive to disorder and impurity potentials. It was observed that the
interplay of strongly coupled spin and charge degrees of freedom creates the
regimes of irregular dynamics both in coordinate and spin channels. The border
between the regular and irregular regimes determined by the strength and
frequency of the driving field is found analytically within the quasiclassical
approach by means of the Ince-Strutt diagram for Mathieu equation, and is
supported by full quantum mechanical simulations of the driven dynamics. The
investigation of quasienergy spectrum by Floquet approach reveals the presence
of non-Poissonian level statistics which indicates the possibility of chaotic
quantum dynamics and corresponds to the areas of parameters for irregular
regimes within the quasiclassical approach. We found that the influence of weak
disorder leads to partial suppression of the dynamical chaos. Our findings are
of interest both for progress in a fundamental field of quantum chaotic
dynamics and for further experimental and technological applications of
spin-dependent phenomena in nanostructures based on topological insulators.",1408.1544v4
2016-03-04,Novel Dynamical Phenomena in Magnetic systems,"Dynamics of Ising models is a much studied phenomenon and has emerged as a
rich field of present-day research. An important dynamical feature commonly
studied is the quenching phenomenon below the critical temperature. In this
thesis we have studied the zero temperature quenching dynamics of different
Ising spin systems. First we have studied the zero temperature quenching
dynamics of two dimensional Ising spin system with competating interactions.
Then we have studied the effect of randomness or disorder on the quenching
dynamics of Ising spin system. We have studied the effect of the nature of
randomness on zero temperature quenching dynamics of one dimensional Ising
model on two type of complex networks. A model for opinion dynamics also has
been proposed in this thesis, in which the binary opinions of the individuals
are determined according to the size of their neighboring domains. This model
can be equivalently defined in terms of Ising spin variables and the various
quantities studied have one to one correspondence with magnetic systems.
Introducing disorder in this model through a parameter called rigidity
parameter $\rho$ (probability that people are completely rigid and never change
their opinion), the transition to a heterogeneous society at $\rho = 0^{+}$ is
obtained. The Model (Model I) has been generalized introducing a parameter
named as size sensitivity parameter to modify the dynamics of the proposed
model and a macroscopic crossover in time is observed for the intermediate
values of this parameter.",1603.01646v1
1994-01-12,Strong-Coupling Behavior of Two $t-J$ Chains with Interchain Single-Electron Hopping,"Using the fermion-spin transformation to implement spin-charge separation of
constrained electrons, a model of two $t-J$ chains with interchain
single-electron hopping is studied by abelian bosonization. After spin-charge
decoupling the charge dynamics can be trivially solved, while the spin dynamics
is determined by a strong-coupling fixed point where the correlation functions
can be calculated explicitly. This is a generalization of the Luther-Emery line
for two-coupled $t-J$ chains. The interchain single-electron hopping changes
the asymptotic behavior of the interchain spin-spin correlation functions and
the electron Green function, but their exponents are independent of the
coupling strength.",9401024v2
1997-11-25,Nonlinear Spin Dynamics in Nuclear Magnets,"A method is developed for solving nonlinear systems of differential, or
integrodifferential, equations with stochastic fields. The method makes it
possible to give an accurate solution for an interesting physical problem: What
are the peculiarities of nonlinear spin dynamics in nonequilibrium nuclear
magnets coupled with a resonator? Evolution equations for nuclear spins are
derived basing on a Hamiltonian with dipole interactions. The ensemble of spins
is coupled with a resonator electric circuit. Seven types of main relaxation
regimes are found: free induction, collective induction, free relaxation,
collective relaxation, weak superradiance, pure superradiance, and triggered
superradiance. The initial motion of spins can be originated by two reasons,
either by an imposed initial coherence or by local spin fluctuations due to
nonsecular dipole interactions. The relaxation regimes caused by the second
reason cannot be described by the Bloch equations. Numerical estimates show
good agreement with experiment.",9711259v1
1999-04-20,Dynamical studies of the response function in a Spin Glass,"Experiments on the time dependence of the response function of a Ag(11 at%Mn)
spin glass at a temperature below the zero field spin glass temperature are
used to explore the non-equilibrium nature of the spin glass phase. It is found
that the response function is only governed by the thermal history in the very
neighbourhood of the actual measurement temperature. The thermal history
outside this narrow region is irrelevant to the measured response. A result
that implies that the thermal history during cooling (cooling rate, wait times
etc.) is imprinted in the spin structure and is always retained when any higher
temperature is recovered. The observations are discussed in the light of a real
space droplet/domain phenomenology. The results also emphasise the importance
of using controlled cooling procedures to acquire interpretable and
reproducible experimental results on the non-equilibrium dynamics in spin
glasses.",9904281v1
1999-12-06,Coherent spin dynamics in diluted-magnetic quantum wells,"Spins of charge carriers, paramagnetic centers, and nuclei in semiconductor
structures are known to be oriented if circular-polarized light is shined upon
the structure. This is due to transfer of angular momentum from photons to
various excitations in the semiconductor. What would happen if the structure is
anisotropic, so that the angular momentum is not conserved? Experiments
performed on diluted-magnetic II-VI quantum wells (such as CdMnTe/CdMgTe) show
that at some conditions the effect of light upon the spin state of the
semiconductor structure can be greatly amplified. Exchange field of
photoexcited heavy holes initiates a coherent evolution of a great number of
localized spins of Mn-ions. In the simplest case, it is just a precession in an
effective field, but generally the spin dynamics is more intricate. It shows
up, for instance, in long sequences of spin-flip peaks in Raman spectra, in
enhanced magnetic-polaron effect, and in modulation of optical response within
the picosecond time scale.",9912084v1
2000-01-11,Dynamical aspects of a three-dimensional Heisenberg spin glass,"Spin-glass and chiral-glass orderings of a three-dimensional isotropic
Heisenberg spin glass are studied both by equilibrium and off-equilibrium Monte
Carlo simulations with emphasis on their dynamical aspects. The model is found
to exhibit a finite-temperature chiral-glass transition without the
conventional spin-glass order. Although chirality is an Ising-like quantity
from symmetry, universality class of the chiral-glass transition appears to be
different from that of the standard Ising spin glass. In the off-equilibrium
simulation, while the spin autocorrelation exhibits only an interrupted aging,
the chirality autocorrelation persists to exhibit a pronounced aging effect
reminiscent of the one observered in the mean-field model.",0001126v1
2000-04-26,Lattice dynamical effects on the Peierls transition in one-dimensional metals and spin chains,"The interplay of charge, spin and lattice degrees of freedom is studied for
quasi-one-dimensional electron and spin systems coupled to quantum phonons.
Special emphasis is put on the influence of the lattice dynamics on the Peierls
transition. Using exact diagonalization techniques the ground-state and
spectral properties of the Holstein model of spinless fermions and of a
frustrated Heisenberg model with magneto-elastic coupling are analyzed on
finite chains. In the non-adiabatic regime a (T=0) quantum phase transition
from a gapless Luttinger-liquid/spin-fluid state to a gapped dimerized phase
occurs at a nonzero critical value of the electron/spin-phonon interaction. To
study the nature of the spin-Peierls transition at finite temperatures for the
infinite system, an alternative Green's function approach is applied to the
magnetostrictive XY model. With increasing phonon frequency the structure
factor shows a remarkable crossover from soft-mode to central-peak behaviour.
The results are discussed in relation to recent experiments on $\rm CuGeO_3$.",0004426v1
2003-02-20,Dynamical Nuclear Polarization by Electrical Spin Injection in Ferromagnet-Semiconductor Heterostructures,"Electrical spin injection from Fe into Al$_x$Ga$_{1-x}$As quantum well
heterostructures is demonstrated in small (< 500 Oe) in-plane magnetic fields.
The measurement is sensitive only to the component of the spin that precesses
about the internal magnetic field in the semiconductor. This field is much
larger than the applied field and depends strongly on the injection current
density. Details of the observed hysteresis in the spin injection signal are
reproduced in a model that incorporates the magnetocrystalline anisotropy of
the epitaxial Fe film, spin relaxation in the semiconductor, and the dynamical
polarization of nuclei by the injected spins.",0302391v1
2003-02-20,Simulations of a classical spin system with competing superexchange and double-exchange interactions,"Monte-Carlo simulations and ground-state calculations have been used to map
out the phase diagram of a system of classical spins, on a simple cubic
lattice, where nearest-neighbor pairs of spins are coupled via competing
antiferromagnetic superexchange and ferromagnetic double-exchange interactions.
For a certain range of parameters, this model is relevant for some magnetic
materials, such as doped manganites, which exhibit the remarkable colossal
magnetoresistance effect. The phase diagram includes two regions in which the
two sublattice magnetizations differ in magnitude. Spin-dynamics simulations
have been used to compute the time- and space-displaced spin-spin correlation
functions, and their Fourier transforms, which yield the dynamic structure
factor $S(q,\omega)$ for this system. Effects of the double-exchange
interaction on the dispersion curves are shown.",0302397v1
2003-07-25,Spin Glasses: A Ghost Story,"Extensive experimental and numerical studies of the non-equilibrium dynamics
of spin glasses subjected to temperature or bond perturbations have been
performed to investigate chaos and memory effects in selected spin glass
systems. Temperature shift and cycling experiments were performed on the
strongly anisotropic Ising-like system {\ising} and the weakly anisotropic
Heisenberg-like system {\AgMn}, while bond shift and cycling simulations were
carried out on a 4 dimensional Ising Edwards-Anderson spin glass. These spin
glass systems display qualitatively the same characteristic features and the
observed memory phenomena are found to be consistent with predictions from the
ghost domain scenario of the droplet scaling model.",0307640v2
2004-03-08,Mean-field magnetization relaxation in conducting ferromagnets,"Collective ferromagnetic motion in a conducting medium is damped by the
transfer of the magnetic moment and energy to the itinerant carriers. We
present a calculation of the corresponding magnetization relaxation as a
linear-response problem for the carrier dynamics in the effective exchange
field of the ferromagnet. In electron systems with little intrinsic spin-orbit
interaction, a uniform magnetization motion can be formally eliminated by going
into the rotating frame of reference for the spin dynamics. The ferromagnetic
damping in this case grows linearly with the spin-flip rate when the latter is
smaller than the exchange field and is inversely proportional to the spin-flip
rate in the opposite limit. These two regimes are analogous to the
""spin-pumping"" and the ""breathing Fermi-surface"" damping mechanisms,
respectively. In diluted ferromagnetic semiconductors, the hole-mediated
magnetization can be efficiently relaxed to the itinerant-carrier degrees of
freedom due to the strong spin-orbit interaction in the valence bands.",0403224v2
2004-03-24,Spin facilitated Ising model with long range interaction,"We study the dynamics of a spin facilitated Ising model with long range
kinetic constraints. To formulate those restrictions within an analytical
approach we introduce the size of a kinetic active environment of a given spin.
Based on a Master equation in second quantized form, the spin-autocorrelation
function is calculated. It exhibits a pronounced slow dynamics, manifested by a
logarithmic decay law of the spin-autocorrelation function. In case of an
infinite kinetic interaction the mean field solution yields an asymptotic exact
expression for the autocorrelation function which is in excellent agreement
with Monte Carlo Simulations for finite interaction lengths. With increasing
size of the active zone the cooperative processes, characterizing the
facilitated model with short range kinetic interaction, become irrelevant. We
demonstrate that the long range kinetic interaction dominates the actual spin
configurations of the whole system and the mean field solution is the exact
one.",0403619v1
2004-06-21,Basic considerations for magnetization dynamics in the combined presence of spin-transfer torques and thermal fluctuations,"This article reviews basic theoretical features of Gilbert magnetization
dynamics of a single domain magnetic film in the presence of Slonczewski
spin-transfer torques, with and without thermal fluctuations taken into
account. Rather than showing results of detailed numerical calculations, the
discussion here is restricted to basic analytical results and conclusions which
can mostly be derived from simply the form of the equations of motion, as well
as elementary considerations based on classical stability analysis and the
fluctuation-dissipation theorem. The presents work describes how interesting
features of spin-transfer may be viewed as arising from non-equilibrium
thermodynamics that are a direct consequence of the nonreciprocal nature of
spin-transfer torques. The present article discusses fairly general results for
spin-torque induced instability without thermal fluctuations, as well as the
case of thermally activated magnetization reversal in uniaxial devices in the
combined presence of external fields, thermal fluctuations, and spin-transfer
torques. The results will be discussed and briefly compared and contrasted with
that of prior work.",0406486v1
2005-03-10,Dynamics of a domain wall and spin-wave excitations driven by a mesoscopic current,"The dynamics of a domain wall driven by a spin-polarized current in a
mesoscopic system is studied numerically. Spin-mixing in the states of the
conduction electrons is fully taken into account. When the Fermi energy of the
electrons is larger than the exchange energy ($E_{\rm F}>J_{\rm sd}$), the spin
precession induces spin wave excitations in the local spins which contribute
towards the displacement of the domain wall. The resulting average velocity is
found to be much smaller than the one obtained in the adiabatic limit. For
$E_{\rm F}<J_{\rm sd}$, the results are consistent with the adiabatic
approximation except for the region below the critical current where a residual
domain wall velocity is found.",0503247v1
2005-07-15,2D Kagome Ordering in the 3D Frustrated Spinel Li2Mn2O4,"muSR experiments on the geometrically frustrated spinel oxide, Li2Mn2O4, show
the development of spin correlations over a range of length scales with
decreasing temperature. Increased relaxation below 150 K is consistent with the
onset of spin correlations. Below 50 K, spin order on a length scale, which is
long range for the muSR probe, appears abruptly in temperature, consistent with
prior neutron diffraction results. The oscillations in the zero field asymmetry
are analyzed using a three frequency model. By locating the muon site this is
shown to be consistent with the unexpected 2D q = root 3 x root 3 structure on
the Kagome planes proposed originally from neutron data. Longitudinal field
data demonstrate that some spin dynamics persist even at 2 K. Thus, a very
complex magnetic ground state, featuring the co-existence of long length scale
2D ordering and significant spin dynamics, is proposed. This is unusual
considering the 3D topology of the Mn3+ spins in this material.",0507355v1
2005-10-07,"muSR study of the Cu-spin dynamics in the electron-doped high-Tc cuprate of Pr0.86LaCe0.14Cu1-y(Zn,Ni)yO4","Effects of the Zn- and Ni-substitution on the Cu-spin dynamics in the
electron-doped Pr0.86LaCe0.14Cu1-y(Zn,Ni)yO4+a-d with y = 0, 0.01, 0.02, 0.05
and different values of the reduced oxygen content d have been studied using
zero-field muon-spin-relaxation (muSR) measurements at temperatures down to 2
K. For the as-grown sample (d = 0, y = 0) and the sample with a very small d
value (d < 0.01, y = 0), a muon-spin precession due to long-range
antiferromagnetic order has been observed. On the other hand, no precession has
been observed for moderately oxygen-reduced samples (0.01 < d < 0.09). It has
been found that for all the samples of 0.01 < d < 0.09 the asymmetry A(t) (muSR
time spectrum) in the long-time region increases with decreasing temperature at
low temperatures, suggesting possible slowing-down of the Cu-spin fluctuations.
On the other hand, no significant difference between Zn- and Ni-substitution
effects on the slowing down of the Cu-spin fluctuations has been observed.",0510159v1
2005-11-09,Current driven magnetization dynamics in helical spin density waves,"A mechanism is proposed for manipulating the magnetic state of a helical spin
density wave using a current. In this paper, we show that a current through a
bulk system with a helical spin density wave induces a spin transfer torque,
giving rise to a rotation of the order parameter.The use of spin transfer
torque to manipulate the magnetization in bulk systems does not suffer from the
obstacles seen for magnetization reversal using interface spin transfer torque
in multilayered systems. We demonstrate the effect by a quantitative
calculation of the current induced magnetization dynamics of Erbium. Finally we
propose a setup for experimental verification.",0511224v2
2006-01-27,Dynamics of thin-film spin-flip transistors with perpendicular source-drain magnetizations,"A ""spin-flip transistor"" is a lateral spin valve consisting of ferromagnetic
source drain contacts to a thin-film normal-metal island with an electrically
floating ferromagnetic base contact on top. We analyze the
\emph{dc}-current-driven magnetization dynamics of spin-flip transistors in
which the source-drain contacts are magnetized perpendicularly to the device
plane by magnetoelectronic circuit theory and the macrospin
Landau-Lifshitz-Gilbert equation. Spin flip scattering and spin pumping effects
are taken into account. We find a steady-state rotation of the base
magnetization at GHz frequencies that is tuneable by the source-drain bias. We
discuss the advantages of the lateral structure for high-frequency generation
and actuation of nanomechanical systems over recently proposed nanopillar
structures.",0601630v1
2006-03-28,Solving spin quantum-master equations with matrix continued-fraction methods: application to superparamagnets,"We implement continued-fraction techniques to solve exactly quantum master
equations for a spin with arbitrary S coupled to a (bosonic) thermal bath. The
full spin density matrix is obtained, so that along with relaxation and
thermoactivation, coherent dynamics is included (precession, tunnel, etc.). The
method is applied to study isotropic spins and spins in a bistable anisotropy
potential (superparamagnets). We present examples of static response, the
dynamical susceptibility including the contribution of the different relaxation
modes, and of spin resonance in transverse fields.",0603730v2
2006-04-27,Ferromagnetic - spin glass transition induced by pressure in the geometrically frustrated pyrochlore (Tb$_{1-x}$La$_x$)$_2$Mo$_2$O$_7$,"We have studied (Tb$_{1-x}$La$_x$)$_2$Mo$_2$O$_7$ pyrochlores by neutron
diffraction and $\mu$SR at ambient and under applied pressure. Substitution of
Tb for La expands the lattice and induces a change from a spin-glass like state
({\itshape x}=0) to a non collinear ferromagnet ({\itshape x}=0.2). In the
ferromagnetic structure, the Tb moments orient close to their local anisotropy
axis as for an ordered spin ice, while the Mo moments orient close to the net
moment. The $\mu$SR dynamical relaxation rate shows a cusp-like peak at the
Curie temperature T$_C$ and a broad anomaly at T$^\star$$<$T$_C$, suggesting a
second transition of local or dynamical nature. Under pressure, the long range
order breaks down and a spin glass-like state is recovered. The whole set of
data provide a microscopic picture of the spin correlations and fluctuations in
the region of the ferromagnetic-spin glass threshold.",0604627v1
2006-09-15,Towards Microscopic Understanding of the Phonon Bottleneck,"The problem of the phonon bottleneck in the relaxation of two-level systems
(spins) to a narrow group of resonant phonons via emission-absorption processes
is investigated from the first principles. It is shown that the kinetic
approach based on the Pauli master equation is invalid because of the narrow
distribution of the phonons exchanging their energy with the spins. This
results in a long-memory effect that can be best taken into account by
introducing an additional dynamical variable corresponding to the nondiagonal
matrix elements responsible for spin-phonon correlation. The resulting system
of dynamical equations describes the phonon-bottleneck plateau in the spin
excitation, as well as a gap in the spin-phonon spectrum for any finite
concentration of spins. On the other hand, it does not accurately render the
lineshape of emitted phonons and still needs improving.",0609379v2
2007-02-09,Magnetic vortex oscillator driven by dc spin-polarized current,"Transfer of angular momentum from a spin-polarized current to a ferromagnet
provides an efficient means to control the dynamics of nanomagnets. A peculiar
consequence of this spin-torque, the ability to induce persistent oscillations
of a nanomagnet by applying a dc current, has previously been reported only for
spatially uniform nanomagnets. Here we demonstrate that a quintessentially
nonuniform magnetic structure, a magnetic vortex, isolated within a nanoscale
spin valve structure, can be excited into persistent microwave-frequency
oscillations by a spin-polarized dc current. Comparison to micromagnetic
simulations leads to identification of the oscillations with a precession of
the vortex core. The oscillations, which can be obtained in essentially zero
magnetic field, exhibit linewidths that can be narrower than 300 kHz, making
these highly compact spin-torque vortex oscillator devices potential candidates
for microwave signal-processing applications, and a powerful new tool for
fundamental studies of vortex dynamics in magnetic nanostructures.",0702253v1
2002-03-09,Semiclassical theory of spin-orbit interactions using spin coherent states,"We formulate a semiclassical theory for systems with spin-orbit interactions.
Using spin coherent states, we start from the path integral in an extended
phase space, formulate the classical dynamics of the coupled orbital and spin
degrees of freedom, and calculate the ingredients of Gutzwiller's trace formula
for the density of states. For a two-dimensional quantum dot with a spin-orbit
interaction of Rashba type, we obtain satisfactory agreement with fully
quantum-mechanical calculations. The mode-conversion problem, which arose in an
earlier semiclassical approach, has hereby been overcome.",0203015v2
2006-02-10,Electron Spin Dynamics in a Quantum Dot due to Hyperfine Coupling with Nuclei in the Dot - An Exact Analysis,"The time-dependent Schrodinger equation of a many particle spin system
consisting of an electron in a quantum dot interacting with the spins of the
nuclei (N) in the dot due to hyperfine interaction is solved exactly for a
given arbitrary initial state. The electron spin dynamics is then expressed in
terms of the reduced density matrix of the composite system by computing the
marginal density matrix of the electron. This is accomplished by classifying
states of the system by the total spin of the coupled electron and nuclear
system that commutes with the system Hamiltonian. These states are used in
enumerating and finding the exact solution of the time-dependent Schrodinger
equation. In each sector of the total spin, the problem reduces to solving a
linear simultaneous set of equations that are solved by matrix inversion. Such
solutions enable one to make a reliable approximate scheme for purposes of
numerical estimation of the various physical quantities. A methematical and
physical discussion of this procedure with the density matrix approach to this
problem is given here. To elucidate the procedure and its advantages, special
cases of N=3,4 are given in some detail in an Appendix.",0602092v1
2007-04-26,Transient Charging and Discharging of Spin-polarized Electrons in a Quantum Dot,"We study spin-polarized transient transport in a quantum dot coupled to two
ferromagnetic leads subjected to a rectangular bias voltage pulse.
Time-dependent spin-resolved currents, occupations, spin accumulation, and
tunneling magnetoresistance (TMR) are calculated using both nonequilibrium
Green function and master equation techniques. Both parallel and antiparallel
leads' magnetization alignments are analyzed. Our main findings are: a
dynamical spin accumulation that changes sign in time, a short-lived pulse of
spin polarized current in the emitter lead (but not in the collector lead), and
a dynamical TMR that develops negative values in the transient regime. We also
observe that the intra-dot Coulomb interaction can enhance even further the
negative values of the TMR.",0704.3598v2
2007-05-24,Local spin dynamic arising from the non-perturbative SU(2) gauge field of the spin orbit effect,"We use the non-perturbative gauge field approach to study the effects of spin
orbit coupling on the dynamic of magnetic moment. We present a general equation
of motion (EOM) which unifies i) the spin orbit coupling effect derived from
the SU(2) spin gauge field, and ii) the moment chirality effect previously
derived from the topological U(1)xU(1) rotation gauge under the adiabatic
condition. We present a modified Landau-Liftshitz-Gilbert equation and discuss
the implication of the modified EOM in various technological applications, such
as current-induced switching and trajectory of magnetic moments in spin-valve
multilayers, magnetic memory and diluted magnetic semiconductor.",0705.3502v1
2007-07-23,Cu-spin dynamics in the overdoped regime of La_2-x_Sr_x_Cu_1-y_Zn_y_O_4_ probed by muon spin relaxation,"Muon-spin-relaxation measurements have been performed for the partially
Zn-substituted La_2-x_Sr_x_Cu_1-y_Zn_y_O_4_ with y=0-0.10 in the overdoped
regime up to x=0.30. In the 3 % Zn-substituted samples up to x=0.27,
exponential-like depolarization of muon spins has been observed at low
temperatures, indicating Zn-induced slowing-down of the Cu-spin fluctuations.
The depolarization rate decreases with increasing x and almost no fast
depolarization of muon spins has been observed for x=0.30 where
superconductivity disappears. The present results suggest that the dynamical
stripe correlations exist in the whole superconducting regime of
La_2-x_Sr_x_CuO_4_ and that there is no quantum critical point at x~0.19.",0707.3322v1
2007-09-26,Two-phonon assisted exciton spin relaxation due to exchange interaction in spherical quantum dots,"Spin relaxation in undoped quasi-spherical CdS quantum dots at zero magnetic
fields is investigated using time- and polarization-resolved transient
absorption measurements. Unlike in previous studies of these systems, the
measured signals were corrected for spin-insensitive contributions to the
exciton bleaching dynamics, {allowing us to determine} the pure spin-related
exciton dynamics. To explain the observed room-temperature spin-relaxation time
of several nanoseconds, we propose a novel mechanism based on intralevel
exciton transitions with the emission of one LO phonon, the absorption of
another LO phonon, and an electron spin flip, which is driven by the
electron-hole exchange interaction. The transition rates, calculated in the
present work for different sizes of quantum dots and temperatures, are in fair
agreement with our experimental results.",0709.4168v1
2007-12-10,Chirality tunneling and quantum dynamics for domain walls in mesoscopic ferromagnets,"We studied the quantum dynamics of ferromagnetic domain walls (topological
kink-type solitons) in one dimensional ferromagnetic spin chains. We show that
the tunneling probability does not depend on the number of spins in a domain
wall; thus, this probability can be large even for a domain wall containing a
large number of spins. We also predict that there is a strong interplay between
the tunneling of a wall from one lattice site to another (tunneling of the kink
coordinate) and the tunneling of the kink topological charge (so-called
chirality). Both of these elementary processes are suppressed for kinks in
one-dimensional ferromagnets with half-integer spin. The dispersion law (i.e.,
the domain wall energy versus momentum) is essentially different for chains
with either integer or half-integer spins. The predicted quantum effects could
be observed for mesoscopic magnetic structures, e.g., chains of magnetic
clusters, large-spin molecules, or nanosize magnetic dots.",0712.1392v1
2008-02-08,Quantum Communication through Spin Chain Dynamics: an Introductory Overview,"We present an introductory overview of the use of spin chains as quantum
wires, which has recently developed into a topic of lively interest. The
principal motivation is in connecting quantum registers without resorting to
optics. A spin chain is a permanently coupled 1D system of spins. When one
places a quantum state on one end of it, the state will be dynamically
transmitted to the other end with some efficiency if the spins are coupled by
an exchange interaction. No external modulations or measurements on the body of
the chain, except perhaps at the very ends, is required for this purpose. For
the simplest (uniformly coupled) chain and the simplest encoding (single qubit
encoding), however, dispersion reduces the quality of transfer. We present a
variety of alternatives proposed by various groups to achieve perfect quantum
state transfer through spin chains. We conclude with a brief discussion of the
various directions in which the topic is developing.",0802.1224v1
2008-04-09,Dynamics of large anisotropic spin in a sub-ohmic dissipative environment close to a quantum-phase transition,"We investigate the dynamics of a large anisotropic spin whose easy-axis
component is coupled to a bosonic bath with a spectral function $J(\w)\propto
\omega^s$. Such a spin complex might be realized in a single-molecular magnet.
Using the non-perturbative renormalization group, we calculate the line of
quantum-phase transitions in the sub-ohmic regime ($s<1$). These quantum-phase
transitions only occur for integer spin $J$. For half-integer $J$, the low
temperature fixed-point is identical to the fixed-point of the spin-boson model
without quantum-tunneling between the two levels. Short-time coherent
oscillations in the spin decay prevail even into the localized phase in the
sub-ohmic regime. The influence of the reorganization energy and the recurrence
time on the decoherence in the absence of quantum-tunneling is discussed.",0804.1457v1
2008-05-31,Single spin optical read-out in CdTe/ZnTe quantum dot studied by photon correlation spectroscopy,"Spin dynamics of a single electron and an exciton confined in CdTe/ZnTe
quantum dot is investigated by polarization-resolved correlation spectroscopy.
Spin memory effects extending over at least a few tens of nanoseconds have been
directly observed in magnetic field and described quantitatively in terms of a
simple rate equation model. We demonstrate an effective (68%) all-optical
read-out of the single carrier spin state through probing the degree of
circular polarization of exciton emission after capture of an oppositely
charged carrier. The perturbation introduced by the pulsed optical excitation
serving to study the spin dynamics has been found to be the main source of the
polarization loss in the read-out process. In the limit of low laser power the
read-out efficiency extrapolates to a value close to 100%. The measurements
allowed us as well to determine neutral exciton spin relaxation time ranging
from 3.4 +/- 0.1 ns at B = 0 T to 16 +/- 3 ns at B = 5 T.",0806.0077v1
2008-09-30,Investigation of the magnetic fluctuations in Tb$_2$Sn$_2$O$_7$ ordered spin ice by high resolution energy-resolved neutron scattering,"We have studied magnetically frustrated Tb$_2$Sn$_2$O$_7$ by neutron
diffraction and high resolution energy-resolved neutron scattering. At 0.1 K,
we observe short range magnetic correlations with a typical scale of 4 \AA,
close to the near neighbor distance between Tb$^{3+}$ ions. %(3.686 \AA), This
short range order coexists with ferromagnetic correlations and long range spin
ice order at the scales of 18 and 190 \AA, respectively. Spin dynamics was
investigated at a time scale down to 10$^{-9}$s, by energy-resolved experiments
on a backscattering spectrometer. We observe a freezing of the spin dynamics
for all length-scales, with a strong slowing down of the spin fluctuations when
long range order settles in. We discuss the spin fluctuations remaining in the
ground state in comparison with previous data obtained by muon spectroscopy.",0809.5241v1
2008-11-20,Dynamical Behavior of Spins in the Rare-Earth Kagomé Pr$_3$Ga$_5$SiO$_{14}$,"We report on the use of $^{69,71}$Ga nuclear magnetic resonance to probe spin
dynamics in the rare-earth kagom\'{e} system Pr$_3$Ga$_5$SiO$_{14}$. We find
that the spin-lattice relaxation rate $^{69}1/T_1$ exhibits a maximum around 30
K, below which the Pr$^{3+}$ spin correlation time $\tau$ shows novel
field-dependent behavior consistent with a field-dependent gap in the
excitation spectrum. The spin-spin relaxation rate $^{69}1/T_{2}$ exhibits a
peak at a lower temperature (10 K) below which field-dependent power-law
behavior close to $T^{2}$ is observed. These results point to field-induced
formation of nanoscale magnetic clusters consistent with recent neutron
scattering measurements.",0811.3367v1
2009-06-02,Manipulation of double-dot spin qubit by continuous noisy measurement,"We consider evolution of a double quantum dot (DQD) two-electron spin qubit
which is continuously weakly measured with a linear charge detector (quantum
point contact). Since the interaction between the spins of two electrons
depends on their charge state, the charge measurement affects the state of two
spins, and induces non-trivial spin dynamics. We consider the regimes of strong
and weak coupling to the detector, and investigate the measurement-induced spin
dynamics both analytically and numerically. We observe emergence of the
negative-result evolution and the system stabilization due to an analog of
quantum Zeno effect. Moreover, unitary evolution between the triplet and a
singlet state is induced by the negative-result measurement. We demonstrate
that these effects exist for both strong and weak coupling between the detector
and the DQD system.",0906.0425v1
2009-07-13,A topological gauge field in nanomagnets: spin wave excitations over a slowly moving magnetization background,"We introduce a topological gauge vector potential which influences spin wave
excitations over arbitrary non-uniform, slowly moving magnetization
distribution. The time-component of the gauge potential plays a principal role
in magnetization dynamics, whereas its spatial components can be often
neglected for typical magnetic nanostructures. As an example, we consider spin
modes excited in the vortex state magnetic dots. It is shown that the vortex/
spin wave interaction can be described as a consequence of the gauge field
arising due to non uniform moving vortex magnetization distribution. The
coupled equations of motion of the vortex and spin waves are solved within
small excitation amplitude approximation. The model yields a giant frequency
splitting of the spin wave modes having non-zero overlapping with the vortex
mode as well as a finite vortex mass of dynamical origin.",0907.2226v1
2009-08-19,Holonomic Quantum Computation with Electron Spins in Quantum Dots,"With the help of the spin-orbit interaction, we propose a scheme to perform
holonomic single qubit gates on the electron spin confined to a quantum dot.
The manipulation is done in the absence (or presence) of an applied magnetic
field. By adiabatic changing the position of the confinement potential, one can
rotate the spin state of the electron around the Bloch sphere in semiconductor
heterostructures. The dynamics of the system is equivalent to employing an
effective non-Abelian gauge potential whose structure depends on the type of
the spin-orbit interaction. As an example, we find an analytic expression for
the electron spin dynamics when the dot is moved around a circular path (with
radius R) on the two dimensional electron gas (2DEG), and show that all single
qubit gates can be realized by tuning the radius and orientation of the
circular paths. Moreover, using the Heisenberg exchange interaction, we
demonstrate how one can generate two-qubit gates by bringing two quantum dots
near each other, yielding a scalable scheme to perform quantum computing on
arbitrary N qubits.
  This proposal shows a way of realizing holonomic quantum computers in
solid-state systems.",0908.2800v2
2009-10-09,Anomalous Hanle Effect in Quantum Dots : Evidence for Strong Dynamical Nuclear Polarization in Transverse Magnetic Field,"Hanle effect is ubiquitous in the study of spin-related phenomena and has
been used to determine spin lifetime, precession and transport in
semiconductors. Here, we report an experimental observation of anomalous Hanle
effect in individual self-assembled InAs/GaAs quantum dots where we find that a
sizeable photo-created electron spin polarization can be maintained in
transverse fields as high as 1T until it abruptly collapses. The striking
broadening of the Hanle curve by a factor of ~20 and its bistability upon
reversal of the magnetic sweep direction points to a novel dynamical nuclear
spin polarization mechanism where the effective nuclear magnetic field
compensates the transverse applied field. This interpretation is further
supported by the measurement of actual electron Zeeman splitting which exhibits
an abrupt increase at the Hanle curve collapse. Strong inhomogeneous
quadrupolar interactions typical for strained quantum dots are likely to play a
key role in polarizing nuclear spins perpendicular to the optically injected
spin orientation.",0910.1744v1
2010-09-24,Fast optical control of spin dynamics in a quantum wire,"The spin dynamics in a quantum wire with a Rashba spin orbit interaction
(SOI) is shown to be controllable via sub-picosecond electromagnetic pulses
shaped appropriately. If the light polarization vector is along the wire's
direction, the carriers experience a momentum boost while the phase coherence
in different spin channels is maintained, a fact exploitable to control the
speed of a photo-driven spin field effect transistor. A photon pulse with a
polarization vector perpendicular to the wire results in a spin precession
which is comparable to that due to the Rashba SOI and is tunable by the pulse
field parameters, an effect utilizable in optically controlled spintronics
devices.",1009.4819v2
2010-11-11,Interaction between hopping and static spins in a discrete network,"We consider a process where a spin hops across a discrete network and at
certain sites couples to static spins. While this setting is implementable in
various scenarios (e.g quantum dots or coupled cavities) the physics of such
processes is still basically unknown. Here, we take a first step along this
line by scrutinizing a two-site and a three-site lattices, each with two static
spins. Despite a generally complex dynamics occurs, we show a regime such that
the spin dynamics is described by an effective three-spin chain. Tasks such as
entanglement generation and quantum state transfer can be achieved accordingly.",1011.2734v2
2011-01-18,Spin dynamics in triangular lattice antiferromagnets CuCr$_{1-x}$Mg$_x$O$_2$,"The electron spin resonance (ESR) spectroscopy was employed to investigate
the spin dynamics in triangular lattice antiferromagnets
CuCr$_{1-x}$Mg$_{x}$O$_2$ with $x =$ 0 and 0.02. All spectra can be well fitted
by a single Lorentzian lineshape. The analysis of the $g$ factor, the linewidth
$\bigtriangleup H$, and the ESR intensity $I$ as a function of temperature
suggests the development of significant antiferromagnetic (AFM) spin
fluctuations at temperature well above $T_N$ in both samples. However, the
evolution of the AFM spin fluctuations is different for each sample. For
undoped sample the ESR intensity $I$ is almost temperature independent between
$\sim$ 100 K and 50 K and then drops rapidly below 50 K. But for $x =$ 0.02,
the $I$ monotonously increases with cooling and reduces rapidly only below
$T_N$. These results indicate that the AFM spin fluctuations are extremely
strong in the undoped sample and appear to be suppressed upon Mg doping.",1101.3367v1
2011-01-31,Swapping and entangling hyperfine coupled nuclear spin baths,"We numerically study the hyperfine induced nuclear spin dynamics in a system
of two coupled quantum dots in zero magnetic field. Each of the electron spins
is considered to interact with an individual bath of nuclear spins via
homogeneous coupling constants (all coupling coefficients being equal). In
order to lower the dimension of the problem, the two baths are approximated by
two single long spins. We demonstrate that the hyperfine interaction enables to
utilize the nuclear baths for quantum information purposes. In particular, we
show that it is possible to swap the nuclear ensembles on time scales of
seconds and indicate that it might even be possible to fully entangle them. As
a key result, it turns out that the larger the baths are, the more useful they
become as a resource of quantum information. Interestingly, the nuclear spin
dynamics strongly benefits from combining two quantum dots of different
geometry to a double dot set up.",1101.6011v2
2011-04-27,Spin Density Waves and Domain Wall Interactions in Nanowires,"We investigated how the dynamics of a domain wall are affected by the
presence of spin density waves in a ferromagnetic wire. Domain walls and other
scattering centres can cause coherent spin density waves to propagate through a
wire when a current is applied. In some cases the spin torque due to these
scattered electrons can be enhanced such that it is on a par with the exchange
and anisotropy energies controlling the shape and dynamics of the domain wall.
In such a case we find that the spin density waves enhance the current induced
domain wall motion, allowing for domain wall motion with smaller current
pulses. Here we consider a system involving two domain walls and focus on how
the motion of the second domain wall is modified by the spin density waves
caused by the presence of the first domain wall.",1104.5175v1
2011-08-01,Charge and spin criticality for the continuous Mott transition in a two-dimensional organic conductor,"We study the continuous bandwidth-controlled Mott transition in the
two-dimensional single-band Hubbard model with a focus on the critical scaling
behavior of charge and spin degrees of freedom. Using plaquette cluster
dynamical mean-field theory, we find charge and spin criticality consistent
with experimental results for organic conductors. In particular, the charge
degree of freedom measured via the local density of states at the Fermi level
shows a smoother transition than expected for the Ising universality class and
in single-site dynamical mean-field theory, revealing the importance of
short-ranged nonlocal correlations in two spatial dimensions. The spin
criticality measured via the local spin susceptibility agrees quantitatively
with nuclear magnetic resonance measurements of the spin-lattice relaxation
rate.",1108.0428v1
2011-09-09,Dynamics of Spin-Polarized Electron Liquid and Spin Pendulum,"We investigate the dynamics of spin-nonequilibrium electron systems for the
case when normal electron collisions prevail over the other scattering
processes and the ""hydrodynamic flow"" regime is realized. The hydrodynamic
equations for the electron liquid have been obtained and analyzed. We
demonstrate that oscillations of the spin polarization are possible in a
conducting ring with inhomogeneous magnetic properties. These low-decay
oscillations are accompanied by the oscillations of the drift current in the
ring. We demonstrate also that the spin polarization of the electron density
may be revealed via the voltage between the ends of the open circuit with an
inhomogeneous spin polarization. The effect may be observed both in the
hydrodynamic and diffusive regimes.",1109.1872v1
2011-10-16,Spin Hall Effect-driven Spin Torque in Magnetic Texture,"Current-induced spin torque and magnetization dynamics in the presence of
spin Hall effect in magnetic textures is studied theoretically. The local
deviation of the charge current gives rise to a current-induced spin torque of
the form (1-\beta{\bf M})x[({\bf u}_0+\alpha_H{\bf u}_0x\bf M})\cdot{\bm
\nabla}]{\bf M}, where {\bf u}_0 is the direction of the injected current,
\alpha_H is the Hall angle and \beta is the non-adiabaticity parameter due to
spin relaxation. Since \alpha_H and \beta can have a comparable order of
magnitude, we show that this torque can significantly modify the
current-induced dynamics of both transverse and vortex walls.",1110.3485v1
2011-10-17,Vortical Dynamics of spinning quantum plasmas - Helicity Conservation,"It is shown that a vorticity, constructed from spin field of a quantum
spinning plasma, combines with the classical generalized vorticity
(representing the magnetic and the velocity fields) to yield a new grand
generalized vorticity that obeys the standard vortex dynamics. Expressions for
the quantum or spin vorticity, and for the resulting generalized helicity
invariant are derived. Reduction of the rather complex spinning quantum system
to a well known and highly investigated classical form opens familiar channels
for the delineation of physics peculiar to dense plasmas spanning solid state
to astrophysical objects. A simple example is worked out to show that the
magnetics of a spinning plasma can be much richer than that of the
corresponding classical system.",1110.3685v1
2012-02-24,Interacting spins in a cavity: finite size effects and symmetry-breaking dynamics,"We calculate the ground state and simulate the dynamics of a finite chain of
spins with Ising nearest-neighbor interactions and a Dicke collective spin
interaction with a single mode cavity field. We recover the signatures of first
and second order phase transitions predicted by mean field theory, while for
small chains, we find significant and non-trivial finite size effects. Below
the first order phase transition, even quite large spin chains of 30-40 spins
give rise to a mean photon number and number fluctuations significantly above
the mean field vacuum result. Near the second order phase critical point, our
calculations reveal photon number fluctuations that grow beyond Poisson
statistics with the size of the spin chain. We simulate the stochastic
evolution of the system when the cavity output field is subject to homodyne
detection. For an initial state close to the first order phase-transition the
random character of the measurement process causes a measurement-induced
symmetry-breaking in the system. This symmetry-breaking occurs on the
time-scale needed for an observer to gather sufficient information to
distinguish between the two possible (mean-field) symmetry-broken states.",1202.5397v1
2012-08-30,Quantum-critical spin dynamics in quasi-one-dimensional antiferromagnets,"By means of nuclear spin-lattice relaxation rate 1/T1, we follow the spin
dynamics as a function of the applied magnetic field in two gapped
one-dimensional quantum antiferromagnets: the anisotropic spin-chain system
NiCl2-4SC(NH2)2 and the spin-ladder system (C5H12N)2CuBr4. In both systems,
spin excitations are confirmed to evolve from magnons in the gapped state to
spinons in the gapples Tomonaga-Luttinger-liquid state. In between, 1/T1
exhibits a pronounced, continuous variation, which is shown to scale in
accordance with quantum criticality. We extract the critical exponent for 1/T1,
compare it to the theory, and show that this behavior is identical in both
studied systems, thus demonstrating the universality of quantum critical
behavior.",1208.6117v1
2012-09-29,Brownian Motion and Quantum Dynamics of Magnetic Monopoles in Spin Ice,"Spin ice illustrates many unusual magnetic properties, including zero point
entropy, emergent monopoles and a quasi liquid-gas transition. To reveal the
quantum spin dynamics that underpin these phenomena is an experimental
challenge. Here we show how crucial information is contained in the frequency
dependence of the magnetic susceptibility and in its high frequency or
adiabatic limit. These measures indicate that monopole diffusion is strictly
Brownian but is underpinned by spin tunnelling and is influenced by collective
monopole interactions. We also find evidence of driven monopole plasma
oscillations in weak applied field, and unconventional critical behaviour in
strong applied field. Our results resolve contradictions in the present
understanding of spin ice, reveal unexpected physics and establish adiabatic
susceptibility as a revealing characteristic of exotic spin systems.",1210.0106v1
2012-10-19,Avoided ferromagnetic quantum critical point: Unusual short-range ordered state in CeFePO,"Cerium 4f electronic spin dynamics in single crystals of the heavy-fermion
system CeFePO is studied by means of ac-susceptibility, specific heat and
muon-spin relaxation ($\mu$SR). Short-range static magnetism occurs below the
freezing temperature Tg ~ 0.7 K, which prevents the system from accessing the
putative ferromagnetic quantum critical point. In the $\mu$SR, the
sample-averaged muon asymmetry function is dominated by strongly inhomogeneous
spin fluctuations below 10 K and exhibits a characteristic time-field scaling
relation expected from glassy spin dynamics, strongly evidencing cooperative
and critical spin fluctuations. The overall behavior can be ascribed neither to
canonical spin glasses nor other disorder-driven mechanisms.",1210.5463v1
2012-10-24,"Dynamics, crystallization and structures in colloid spin coating","Spin coating is an out-of-equilibrium technique for producing polymer films
and colloidal crystals quickly and reproducibly. In this review, we present an
overview of theoretical and experimental studies of the spin coating of
colloidal suspensions. The dynamics of the spin coating process is discussed
first, and we present insights from both theory and experiment. A key
difference between spin coating with polymer solutions and with monodisperse
colloidal suspensions is the emergence of long range (centimeter scale)
orientational correlations in the latter. We discuss experiments in different
physical regimes that shed light on the many unusual partially-ordered
structures that have long-range orientational order, but no long-range
translational order. The nature of these structures can be tailored by adding
electric or magnetic fields during the spin coating procedure. These
partially-ordered structures can be considered as model systems for studying
the fundamentals of poorly crystalline and defect-rich solids, and they can
also serve as templates for patterned and/or porous optical and magnetic
materials.",1210.6662v2
2012-12-13,Dynamical Spin Injection into p-type Germanium at Room Temperature,"We demonstrate dynamical spin injection into p-type germanium (Ge) at room
temperature (RT) using spin pumping. The generated pure spin current is
converted to a charge current by the inverse spin-Hall effect (ISHE) arising in
the p-type Ge sample. A clear electromotive force due to the ISHE is detected
at RT. The spin-Hall angle for p-type Ge is estimated to be {\theta}SHE =
2.6x10-3 at RT, which is much larger than that for p-type Si.",1212.3089v3
2012-12-13,Large nuclear spin polarization in gate-defined quantum dots using a single-domain nanomagnet,"The electron-nuclei (hyperfine) interaction is central to spin qubits in
solid state systems. It can be a severe decoherence source but also allows
dynamic access to the nuclear spin states. We study a double quantum dot
exposed to an on-chip single-domain nanomagnet and show that its inhomogeneous
magnetic field crucially modifies the complex nuclear spin dynamics such that
the Overhauser field tends to compensate external magnetic fields. This turns
out to be beneficial for polarizing the nuclear spin ensemble. We reach a
nuclear spin polarization of ~50%, unrivaled in lateral dots, and explain our
manipulation technique using a comprehensive rate equation model.",1212.3140v1
2013-01-09,Interplay between lattice and spin states degree of freedom in the FeSe superconductor: dynamic spin state instabilities,"Polarized Raman-scattering spectra of superconducting, single-crystalline
FeSe evidence pronounced phonon anomalies with temperature reduction. A large
6.5% hardening of the B_1g(Fe) phonon mode is attributed to the suppression of
local fluctuations of the iron spin state with the gradual decrease of the iron
paramagnetic moment. The ab-initio lattice dynamic calculations support this
conclusion. The enhancement of the low-frequency spectral weight above the
structural phase transition temperature T_s and its change below T_s is
discussed in relation with the opening of an energy gap between low (S=0) and
higher spin states which prevents magnetic order in FeSe. The very narrow
phonon line widths compared to observations in FeTe suggests the absence of
intermediate spin states in the fluctuating spin state manifold in FeSe.",1301.1960v1
2013-01-16,NMR Investigation of the Low Temperature Dynamics of solid 4He doped with 3He impurities,"The lattice dynamics of solid 4He has been explored using pulsed NMR methods
to study the motion of 3He impurities in the temperature range where
experiments have revealed anomalies attributed to superflow or unexpected
viscoelastic properties of the solid 4He lattice. We report the results of
measurements of the nuclear spin-lattice and spin-spin relaxation times that
measure the fluctuation spectrum at high and low frequencies, respectively, of
the 3He motion that results from quantum tunneling in the 4He matrix. The
measurements were made for 3He concentrations 16<x_3<2000 ppm. For 3He
concentrations x_3 = 16 ppm and 24 ppm, large changes are observed for both the
spin-lattice relaxation time T_1 and the spin-spin relaxation time T_2 at
temperatures close to those for which the anomalies are observed in
measurements of torsional oscillator responses and the shear modulus. These
changes in the NMR relaxation rates were not observed for higher 3He
concentrations.",1301.3929v1
2013-02-09,Current-driven dynamics of chiral ferromagnetic domain walls,"In most ferromagnets the magnetization rotates from one domain to the next
with no preferred handedness. However, broken inversion symmetry can lift the
chiral degeneracy, leading to topologically-rich spin textures such as
spin-spirals and skyrmions via the Dzyaloshinskii-Moriya interaction (DMI).
Here we show that in ultrathin metallic ferromagnets sandwiched between a heavy
metal and an oxide, the DMI stabilizes chiral domain walls (DWs) whose spin
texture enables extremely efficient current-driven motion. We show that spin
torque from the spin Hall effect drives DWs in opposite directions in
Pt/CoFe/MgO and Ta/CoFe/MgO, which can be explained only if the DWs assume a
N\'eel configuration with left-handed chirality. We directly confirm the DW
chirality and rigidity by examining current-driven DW dynamics with magnetic
fields applied perpendicular and parallel to the spin spiral. This work
resolves the origin of controversial experimental results and highlights a new
path towards interfacial design of spintronic devices.",1302.2257v1
2013-03-04,Inhomogeneous dynamic nuclear polarization and suppression of electron-polarization decay in a quantum dot,"We investigate the dynamic nuclear polarization process by frequently
injecting polarized electron spins into a quantum dot. Due to the suppression
of the direct dipolar and indirect electron-mediated nuclear spin interactions,
by the frequently injected electron spins, the analytical predictions under the
independent spin approximation agree well with quantum numerical simulations.
Our results show that the acquired nuclear polarization is highly
inhomogeneous, proportional to the square of the local electron-nuclear
hyperfine interaction constant, if the injection frequency is high. Utilizing
the inhomogeneously polarized nuclear spins as an initial state, we further
show that the electron-polarization decay time can be extended 100 times even
at a relatively low nuclear polarization (<20%), without much suppression of
the fluctuation of the Overhauser field. Our results lay the foundation for
future investigations of the effect of DNP in more complex spin systems, such
as double quantum dots and nitrogen vacancy centers in diamonds.",1303.0590v1
2013-04-01,Extending the Electron Spin Coherence Time of Atomic Hydrogen by Dynamical Decoupling,"We study the electron spin decoherence of encapsulated atomic hydrogen in
octasilsesquioxane cages induced by the 1H and 29Si nuclear spin bath. By
applying the Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence we significantly
suppress the low-frequency noise due to nuclear spin flip-flops up to the point
where a maximum T2 = 56 us is observed. Moreover, dynamical decoupling with the
CPMG sequence reveals the existence of two sources of high-frequency noise:
first, a fluctuating magnetic field with the proton Larmor frequency,
equivalent to classical magnetic field noise imposed by the 1H nuclear spins of
the cage organic substituents, and second, decoherence due to entanglement
between the electron and the inner 29Si nuclear spin of the cage.",1304.0418v1
2013-06-28,Dynamical polarization of nuclear spins by acceptor-bound holes in a zinc blende semiconductor,"The ground state of an acceptor-bound hole in a zinc-blende semiconductor is
formed by four eigenstates of the total angular momentum, which is a vector sum
of spin and orbital moment of the hole. As a result, the hyperfine interaction
of the hole with lattice nuclei becomes anisotropic and coordinate-dependent.
We develop a theory of dynamic polarization of nuclear spins by the
acceptor-bound hole, giving full account for its complex spin structure. The
rate of hole-nuclear flip-flop transitions is shown to depend on the angle
between the total angular momentum of the hole and the position vector of the
nucleus with respect to the acceptor center. The resulted spatially
inhomogeneous spin polarization of nuclei gives rise to non-equidistant spin
splitting of the hole, which can be detected by methods of optical or microwave
spectroscopy.",1306.6787v2
2013-10-09,Chargeless spin current for switching and coupling of domain walls in magnetic nanowires,"The demonstration of the generation and control of a pure spin current
(without net charge flow) by electric fields and/or temperature gradient has
been an essential leap in the quest for low-power consumption electronics. The
key issue of whether and how such a current can be utilized to drive and
control information stored in magnetic domain walls (DWs) is still outstanding
and is addressed here. We demonstrate that pure spin current acts on DWs in a
magnetic stripe with an effective spin-transfer torque resulting in a mutual
DWs separation dynamics and picosecond magnetization reversal. In addition,
long-range ($\sim$ mm) antiferromagnetic DWs coupling emerges. If one DW is
pinned by geometric constriction, the spin current induces a dynamical spin
orbital interaction that triggers an internal electric field determined by
$\vec{E} \sim \hat{e}_{x} \cdot (\vec{n}_{1} \times \vec{n}_{2})$ where
$\vec{n}_{1/2}$ are the effective DWs orientations and $\hat{e}_{x} $ is their
spatial separation vector. This leads to charge accumulation or persistent
electric current in the wire. As DWs are routinely realizable and tuneable, the
predicted effects bear genuine potential for power-saving spintronics devices.",1310.2331v1
2013-10-16,Non-Linear Spin Dynamics Of The Electron Liquid In Nanosystems,"We investigate the dynamics of spin-nonequilibrium electron systems in the
hydrodynamic flow regime, when the normal scattering processes, which conserve
the total quasi-momentum of the system of electrons and quasi-particles that
interact with them, dominate over other scattering processes. We obtain a set
of spin-hydrodynamic equations for the case of an arbitrary electron spectrum
that varies slowly with the coordinates. Solving the one-dimensional non-linear
problem we found the exact solutions both for the electrical potential in the
open-ends circuit and for the spin-electrical oscillation in an inhomogeneous
conducting ring. As we demonstrate, the oscillation characteristics are
different in the cases of a magnetic ring and a non-magnetic ring to which the
spin polarization was injected. We found also that a voltage between the ends
of the open circuit may reveal the presence of an inhomogeneous spin
polarization of the electron density.",1310.4238v1
2013-11-13,Thermally activated in-plane magnetization rotation induced by spin torque,"We study the role of thermal fluctuations on the spin dynamics of a thin
permalloy film with a focus on the behavior of spin torque and find that the
thermally assisted spin torque results in new aspects of the magnetization
dynamics. In particular, we uncover the formation of a finite, spin
torque-induced, in-plane magnetization component. The orientation of the
in-plane magnetization vector depends on the temperature and the spin-torque
coupling. We investigate and illustrate that the variation of the temperature
leads to a thermally-induced rotation of the in-plane magnetization.",1311.3120v1
2014-04-24,Decoherence of an exchange qubit by hyperfine interaction,"We study three-electron-spin decoherence in a semiconductor triple quantum
dot with a linear geometry. The three electron spins are coupled by exchange
interactions J_{12} and J_{23}, and we clarify inhomogeneous and homogeneous
dephasing dynamics for a logical qubit encoded in the (S=1/2,S_{z} =1/2)
subspace. We first justify that qubit leakage via the fluctuating Overhauser
field can be effectively suppressed by sufficiently large Zeeman and exchange
splittings. For J_{12}=J_{23} and the case of J_{12} and J_{23} being
different, we construct an effective pure dephasing Hamiltonian with the Zeeman
splitting much larger than the exchange splitting. Both effective Hamiltonians
have the same order of magnitude as that for a single-spin qubit, and the
relevant dephasing time scales are of the same order as those for a single
spin. We provide estimates of the dynamics of three-spin free induction decay,
the decay of a Hahn spin echo, and the decay of echoes from a CPMG pulse
sequence for GaAs quantum dots.",1404.6220v2
2014-10-14,Flip-flopping binary black holes,"We study binary spinning black holes to display the long term individual spin
dynamics. We perform a full numerical simulation starting at an initial proper
separation of $d\approx25M$ between equal mass holes and evolve them down to
merger for nearly 48 orbits, 3 precession cycles, and half of a flip-flop
cycle. The simulation lasts for $t=20000M$ and displays a total change in the
orientation of the spin of one of the black holes from initially aligned with
the orbital angular momentum to a complete anti-alignment after half of a
flip-flop cycle. We compare this evolution with an integration of the 3.5
Post-Newtonian equations of motion and spin evolution to show that this process
continuously flip-flops the spin during the lifetime of the binary until
merger. We also provide lower order analytic expressions for the maximum
flip-flop angle and frequency. We discuss the effects this dynamics may have on
spin growth in accreting binaries and on the observational consequences for
galactic and supermassive binary black holes.",1410.3830v2
2014-11-14,Spinning compact binary dynamics and chameleon orbits,"We analyse the conservative evolution of spinning compact binaries to second
post-Newtonian (2PN) order accuracy, with leading order spin-orbit, spin-spin
and mass quadrupole-monopole contributions included. As a main result we derive
a closed system of first order differential equations in a compact form, for a
set of dimensionless variables encompassing both orbital elements and spin
angles. These evolutions are constrained by conservation laws holding at 2PN
order. As required by the generic theory of constrained dynamical systems we
perform a consistency check and prove that the constraints are preserved by the
evolution. We apply the formalism to show the existence of chameleon orbits,
whose local, orbital parameters evolve from elliptic (in the Newtonian sense)
near pericenter, towards hyperbolic at large distances. This behavior is
consistent with the picture that General Relativity predicts stronger gravity
at short distances than Newtonian theory does.",1411.4057v2
2015-02-12,Unusual spin dynamics in topological insulators,"The dynamic spin susceptibility (DSS) has a ubiquitous Lorentzian form in
conventional materials with weak spin orbit coupling, whose spectral width
characterizes the spin relaxation rate. We show that DSS has an unusual
non-Lorentzian form in topological insulators, which are characterized by
strong SOC. At zero temperature, the high frequency part of DSS is universal
and increases in certain directions as $\omega^{d-1}$ with $d=2$ and 3 for
surface states and Weyl semimetals, respectively, while for helical edge
states, the interactions renormalize the exponent as $d=2K-1$ with $K$ the
Luttinger-liquid parameter. As a result, spin relaxation rate cannot be deduced
from the DSS in contrast to the case of usual metals, which follows from the
strongly entangled spin and charge degrees of freedom in these systems. These
parallel with the optical conductivity of neutral graphene.",1502.03680v1
2015-03-06,Spin-Motive Forces and Current-Induced Torques in Ferromagnets,"In metallic ferromagnets, the spin-transfer torque and spin-motive force are
known to exhibit a reciprocal relationship. Recent experiments on ferromagnets
with strong spin-orbit coupling have revealed a rich complexity in the
interaction between itinerant charge carriers and magnetization, but a full
understanding of this coupled dynamics is lacking. Here, we develop a general
phenomenology of the two reciprocal processes of charge pumping by spin-motive
forces and current-driven magnetization dynamics. The formalism is valid for
spin-orbit coupling of any strength and presents a systematic scheme for
deriving all possible torque and charge-pumping terms that obey the symmetry
requirements imposed by the point group of the system. We demonstrate how the
different charge pumping and torque contributions are connected via the Onsager
reciprocal relations. The formalism is applied to two important classes of
systems: isotropic ferromagnets with non-uniform magnetization and homogeneous
ferromagnets described by the point group $C_{2v}$.",1503.01899v2
2015-07-14,Influence of impurity spin dynamics on quantum transport in epitaxial graphene,"Experimental evidence from both spin-valve and quantum transport measurements
points towards unexpectedly fast spin relaxation in graphene. We report
magnetotransport studies of epitaxial graphene on SiC in a vector magnetic
field showing that spin relaxation, detected using weak-localisation analysis,
is suppressed by an in-plane magnetic field, $B_{\parallel}$, and thereby
proving that it is caused at least in part by spinful scatterers. A
non-monotonic dependence of effective decoherence rate on $B_{\parallel}$
reveals the intricate role of scatterers' spin dynamics in forming the
interference correction to conductivity, an effect that has gone unnoticed in
earlier weak localisation studies",1507.03841v1
2015-08-04,Stochastic Ising model with flipping sets of spins and fast decreasing temperature,"This paper deals with the stochastic Ising model with a temperature shrinking
to zero as time goes to infinity. A generalization of the Glauber dynamics is
considered, on the basis of the existence of simultaneous flips of some spins.
Such dynamics act on a wide class of graphs which are periodic and embedded in
$\mathbb{R}^d$. The interactions between couples of spins are assumed to be
quenched i.i.d. random variables following a Bernoulli distribution with
support $\{-1,+1\}$. The specific problem here analyzed concerns the assessment
of how often (finitely or infinitely many times, almost surely) a given spin
flips. Adopting the classification proposed in \cite{GNS}, we present
conditions in order to have models of type $\mathcal{F}$ (any spin flips
finitely many times), $\mathcal{I}$ (any spin flips infinitely many times) and
$\mathcal{M}$ (a mixed case). Several examples are provided in all dimensions
and for different cases of graphs. The most part of the obtained results holds
true for the case of zero-temperature and some of them for the cubic lattice
$\mathbb{L}_d=(\mathbb{Z}^d, \mathbb{E}_d)$ as well.",1508.00850v2
2015-09-01,Spin dynamics of antiferromagnetically coupled bilayers - the case of Cr_2TeO_6,"Understanding the dynamics of interacting quantum spins has been one of the
active areas of condensed matter physics research. Recently, extensive
inelastic neutron scattering measurements have been carried out in an
interesting class of systems, Cr_2(W, Te, Mo)O_6. These systems consist of
bilayers of Cr^{3+} spins (S=3/2) with strong antiferromagnetic inter-bilayer
coupling (J) and tuneable intra-bilayer coupling (j) from ferro (for W and Mo)
to antiferro (for Te). In the limit when J>|j|, the system reduces to weakly
interacting quantum spin-3/2 dimers. In this paper we discuss the
low-temperature magnetic properties of Cr_2TeO_6 systems where both intra-layer
and inter-layer exchange couplings are antiferromagnetic, i.e. J,j>0. Using
linear spin-wave theory we obtain the magnon dispersion, sublattice
magnetization, two-magnon density of states, and longitudinal spin-spin
correlation function.",1509.00101v3
2015-09-17,The impact of nuclear spin dynamics on electron transport through donors,"We present an analysis of electron transport through two weakly coupled
precision placed phosphorus donors in silicon. In particular, we examine the
(1,1) to (0,2) charge transition where we predict a new type of current
blockade driven entirely by the nuclear spin dynamics. Using this nuclear spin
blockade mechanism we devise a protocol to readout the state of single nuclear
spins using electron transport measurements only. We extend our model to
include realistic effects such as Stark shifted hyperfine interactions and
multi-donor clusters. In the case of multi-donor clusters we show how nuclear
spin blockade can be alleviated allowing for low magnetic field electron spin
measurements.",1509.05407v1
2015-11-03,Nd2Sn2O7: an all-in-all-out pyrochlore magnet with no divergence-free field and anomalously slow paramagnetic spin dynamics,"We report measurements performed on a polycrystalline sample of the
pyrochlore compound Nd2Sn2O7. It undergoes a second order magnetic phase
transition at Tc ~ 0.91 K to a noncoplanar all-in-all-out magnetic structure of
the Nd3+ magnetic moments. The thermal behavior of the low temperature specific
heat fingerprints excitations with linear dispersion in a three-dimensional
lattice. The temperature independent spin-lattice relaxation rate measured
below Tc and the anomalously slow paramagnetic spin dynamics detected up to ~
30 Tc are suggested to be due to magnetic short-range correlations in
unidimensional spin clusters, i.e., spin loops. The observation of a
spontaneous field in muon spin relaxation measurements is associated with the
absence of a divergence-free field for the ground state of an all-in-all-out
pyrochlore magnet as predicted recently.",1511.00987v1
2015-11-03,Spin-Orbit Coupling Induced Back-action Cooling in Cavity-Optomechanics with a Bose-Einstein Condensate,"We report a spin-orbit coupling induced back-action cooling in an
optomechanical system, composed of a spin-orbit coupled Bose-Einstein
condensate trapped in an optical cavity with one movable end mirror, by
suppressing heating effects of quantum noises. The collective density
excitations of the spin-orbit coupling mediated hyperfine states - serving as
atomic oscillators equally coupled to the cavity field - trigger strongly
driven atomic back-action. We find that the back-action not only revamps
low-temperature dynamics of its own but also provides an opportunity to cool
the mechanical mirror to its quantum mechanical ground state. Further, we
demonstrate that the strength of spin-orbit coupling also superintends dynamic
structure factor and squeezes nonlinear quantum noises, like thermo-mechanical
and photon shot noise, which enhances optomechanical features of hybrid cavity
beyond the previous investigations. Our findings are testable in a realistic
setup and enhance the functionality of cavity-optomechanics with spin-orbit
coupled hyperfine states in the field of quantum optics and quantum
computation.",1511.01109v2
2015-11-10,Unraveling photoinduced spin dynamics in topological insulator Bi2Se3,"We report on time-resolved ultrafast optical spectroscopy study of the
topological insulator (TI) Bi$_2$Se$_3$. We unravel that a net spin
polarization can not only be generated using circularly polarized light via
interband transitions between topological surface states (SSs), but also via
transitions between SSs and bulk states. Our experiment demonstrates that
tuning photon energy or temperature can essentially allow for photoexcitation
of spin-polarized electrons to unoccupied topological SSs with two distinct
spin relaxation times ($\sim$25 fs and $\sim$300 fs), depending on the coupling
between SSs and bulk states. The intrinsic mechanism leading to such
distinctive spin dynamics is the scattering in SSs and bulk states which is
dominated by $E_g^2$ and $A_{1g}^1$ phonon modes, respectively. These findings
are suggestive of novel ways to manipulate the photoinduced coherent spins in
TIs.",1511.02994v2
2016-02-24,Preferential rotation of chiral dipoles in isotropic turbulence,"Particles in the shape of chiral dipoles show a preferential rotation in
three dimensional homogeneous isotropic turbulence. A chiral dipole consists of
a rod with two helices of opposite handedness, one at each end. We can use 3d
printing to fabricate these particles with length in the inertial range and
track their rotations in a turbulent flow between oscillating grids. High
aspect ratio chiral dipoles will align with the extensional eigenvectors of the
strain rate tensor and the helical ends will respond to the strain field by
spinning around its long axis. The mean of the measured spinning rate is
non-zero and reflects the average stretching the particles experience. We use
Stokesian dynamics simulations of chiral dipoles in pure strain flow to
quantify the dependence of spinning on particle shape. Based on the known
response to pure strain, we build a model that gives the spinning rate of small
chiral dipoles using Lagrangian velocity gradients from high resolution direct
numerical simulations. The statistics of chiral dipole spinning determined with
this model show surprisingly good agreement with the measured spinning of much
larger chiral dipoles in the experiments.",1602.07413v1
2016-04-14,THz-driven ultrafast spin-lattice scattering in amorphous metallic ferromagnets,"We use single-cycle THz fields and the femtosecond magneto-optical Kerr
effect to respectively excite and probe the magnetization dynamics in two
thin-film ferromagnets with different lattice structure: crystalline Fe and
amorphous CoFeB. We observe Landau-Lifshitz-torque magnetization dynamics of
comparable magnitude in both systems, but only the amorphous sample shows
ultrafast demagnetization caused by the spin-lattice depolarization of the
THz-induced ultrafast spin current. Quantitative modelling shows that such
spin-lattice scattering events occur on similar time scales than the
conventional spin conserving electronic scattering ($\sim30$ fs). This is
significantly faster that optical laser-induced demagnetization. THz
conductivity measurements point towards the influence of lattice disorder in
amorphous CoFeB as the driving force for enhanced spin-lattice scattering.",1604.04077v1
2016-07-29,Exchange interaction-driven dynamic nuclear polarization in Mn-doped InGaAs/GaAs quantum dots,"We investigated optical spin orientation and dynamic nuclear polarization
(DNP) in individual self-assembled InGaAs/GaAs quantum dots (QDs) doped by a
single Mn atom, a magnetic impurity providing a neutral acceptor A$^0$ with an
effective spin $J=1$. We find that the spin of an electron photo-created in
such a quantum dot can be efficiently oriented by a quasi-resonant
circularly-polarized excitation. For the electron spin levels which are made
quasi-degenerate by a magnetic field compensating the exchange interaction
$\Delta_e$ with A$^0$, there is however a full depolarization due the
anisotropic part of the exchange. Still, in most studied QDs, the spin
polarized photo-electrons give rise to a pronounced DNP which grows with a
longitudinal magnetic field until a critical field where it abruptly vanishes.
For some QDs, several replica of such DNP sequence are observed at different
magnetic fields. This striking behavior is qualitatively discussed as a
consequence of different exchange interactions experienced by the electron,
driving the DNP rate via the energy cost of electron-nucleus spin flip-flops.",1607.08870v2
2017-02-27,Persistent low-temperature spin dynamics in the mixed-valence iridate Ba$_{3}$InIr$_{2}$O$_{9}$,"Using thermodynamic measurements, neutron diffraction, nuclear magnetic
resonance, and muon spin relaxation, we establish putative quantum spin-liquid
behavior in Ba$_3$InIr$_2$O$_9$, where unpaired electrons are localized on
mixed-valence Ir$_2$O$_9$ dimers with Ir$^{4.5+}$ ions. Despite the
antiferromagnetic Curie-Weiss temperature on the order of 10 K, neither
long-range magnetic order nor spin freezing are observed down to at least 20
mK, such that spins are short-range correlated and dynamic over nearly three
decades in temperature. Quadratic power-law behavior of both the spin-lattice
relaxation rate and specific heat indicates the gapless nature of the ground
state. We envisage that this exotic behavior may be related to an unprecedented
combination of the triangular and buckled honeycomb geometries of
nearest-neighbor exchange couplings in the mixed-valence setting.",1702.08305v3
2017-08-03,Spin and reoccupation noise in a single quantum dot beyond the fluctuation-dissipation theorem,"We report on the nonequilibrium spin noise of a single InGaAs quantum dot
charged by a single hole under strong driving by a linearly polarized probe
light field. The spectral dependency of the spin noise power evidences a
homogeneous broadening and negligible charge fluctuations in the environment of
the unbiased quantum dot. Full analysis of the spin noise spectra beyond the
fluctuation-dissipation theorem yields the heavy-hole spin dynamics as well as
the trion spin dynamics. Moreover, the experiment reveals an additional much
weaker noise contribution in the Kerr rotation noise spectra. This additional
noise contribution has a maximum at the quantum dot resonance and shows a
significantly longer correlation time. Magnetic-field-dependent measurements in
combination with theoretical modeling prove that this additional noise
contribution unveils a charge reoccupation noise which is intrinsic in
naturally charged quantum dots.",1708.01245v2
2018-02-01,GPU accelerated manifold correction method for spinning compact binaries,"The conservative Post-Newtonian (PN) Hamiltonian formulation of spinning
compact binaries has six integrals of motion including the total energy, the
total angular momentum and the constant unit lengths of spins. The manifold
correction method can effectively eliminate the integration errors accumulation
in a long time. In this paper, the accelerated manifold correction method based
on graphics processing unit (GPU) is designed to simulate the dynamic evolution
of spinning compact binaries. The feasibility and the efficiency of parallel
computation on GPU for spinning compact binaries have been confirmed by various
numerical experiments. The numerical comparisons show that the accuracy on GPU
execution of manifold corrections method has a good agreement with the
execution of codes on merely central processing unit (CPU-based) method. The
acceleration ability when the codes are implemented on GPU can increase
enormously through the use of shared memory and register optimization
techniques without additional hardware costs, implying that the speedup is
nearly 13 times as compared with the codes executed on CPU for phase space scan
(including orbits). In addition, GPU-accelerated manifold correction method is
used to numerically study how dynamics are affected by the spin-induced
quadrupole-monopole interaction for black hole binary system.",1802.00147v1
2019-05-06,Elementary excitation in the spin-stripe phase in quantum chains,"Elementary excitations in condensed matter capture the complex many-body
dynamics of interacting basic entities in a simple quasiparticle picture. In
magnetic systems the most established quasiparticles are magnons, collective
excitations that reside in ordered spin structures, and spinons, their
fractional counterparts that emerge in disordered, yet correlated spin states.
Here we report on the discovery of elementary excitation inherent to
spin-stripe order that represents a bound state of two phason quasiparticles,
resulting in a wiggling-like motion of the magnetic moments. We observe these
excitations, which we dub ""wigglons"", in the frustrated zigzag spin-1/2 chain
compound $\beta$-TeVO$_4$, where they give rise to unusual low-frequency spin
dynamics in the spin-stripe phase. This result provides insights into the
stripe physics of strongly-correlated electron systems.",1905.02079v1
2019-05-27,Critical spin fluctuation mechanism for the spin Hall effect,"We propose mechanisms for the spin Hall effect in metallic systems arising
from the coupling between conduction electrons and local magnetic moments that
are dynamically fluctuating. Both a side-jump-type mechanism and a
skew-scattering-type mechanism are considered. In either case, dynamical spin
fluctuation gives rise to a nontrivial temperature dependence in the spin Hall
conductivity. This leads to the enhancement in the spin Hall conductivity at
nonzero temperatures near the ferromagnetic instability. The proposed
mechanisms could be observed in $4d$ or $5d$ metallic compounds.",1905.10929v3
2018-05-21,Dynamical suppression of tunneling and spin switching of a spin-orbit-coupled atom in a double-well trap,"We predict wide-band suppression of tunneling of spin-orbit-coupled atoms (or
noninteracting Bose-Einstein condensate) in a double-well potential with
periodically varying depths of the potential wells. The suppression of
tunneling is possible for a single state and for superposition of two states,
i.e. for a qbit. By varying spin-orbit coupling one can drastically increase
the range of modulation frequencies in which an atom remains localized in one
of the potential wells, the effect connected with crossing of energy levels.
This range of frequencies is limited because temporal modulation may also
excite resonant transitions between lower and upper states in different wells.
The resonant transitions enhance tunneling and are accompanied by pseudo-spin
switching. Since the frequencies of the resonant transitions are independent of
potential modulation depth, in contrast to frequencies at which suppression of
tunneling occurs, by varying this depth one can dynamically control both
spatial localization and pseudo-spin of the final state.",1805.07961v1
2018-05-28,Gravitational spin-orbit coupling in binary systems at the second post-Minkowskian approximation,"We compute the rotations, during a scattering encounter, of the spins of two
gravitationally interacting particles at second-order in the gravitational
constant (second post-Minkowskian order). Following a strategy introduced in
Phys. Rev. D {\bf 96}, 104038 (2017), we transcribe our result into a
correspondingly improved knowledge of the spin-orbit sector of the Effective
One-Body (EOB) Hamiltonian description of the dynamics of spinning binary
systems. We indicate ways of resumming our results for defining improved
versions of spinning EOB codes which might help in providing a better
analytical description of the dynamics of coalescing spinning binary black
holes.",1805.10809v1
2012-01-27,Enhanced solid-state multi-spin metrology using dynamical decoupling,"We use multi-pulse dynamical decoupling to increase the coherence lifetime
(T2) of large numbers of nitrogen-vacancy (NV) electronic spins in room
temperature diamond, thus enabling scalable applications of multi-spin quantum
information processing and metrology. We realize an order-of-magnitude
extension of the NV multi-spin T2 for diamond samples with widely differing
spin environments. For samples with nitrogen impurity concentration <~1 ppm, we
find T2 > 2 ms, comparable to the longest coherence time reported for single NV
centers, and demonstrate a ten-fold enhancement in NV multi-spin sensing of AC
magnetic fields.",1201.5686v2
2012-04-01,Growth Direction Dependence of the Electron Spin Dynamics in {111} GaAs Quantum Wells,"The electron spin dynamics is studied by time-resolved Kerr rotation in
GaAs/AlGaAs quantum wells embedded in a negatively doped-intrinsic-positively
doped structures grown on (111)A or (111)B-oriented substrates. In both cases
the spin lifetimes are significantly increased by applying an external electric
field but this field has to point along the growth direction for structures
grown on (111)A and opposite to it for the ones grown on (111)B. This extended
electron spin lifetime is the result of the suppression of the D'yakonov-Perel
spin relaxation mechanism [Sov. Phys. Solid State 13, 3023 (1972)] due to the
cancellation effect of the internal Dresselhaus term [Phys. Rev. 100, 580
(1955)] with the external electric field induced Rashba one [J. Phys. C 17,
6039 (1984)], both governing the conduction band spin-orbit splitting. These
results demonstrate the key role played by the growth direction in the design
of spintronic devices.",1204.0154v2
2013-09-23,Quench Induced Growth of Distant Entanglement from Product and Locally Entangled States in Spin Chains,"We study the problem of entangling two spins at the distant ends of a spin
chain by exploiting the nonequilibrium dynamics of the system after a sudden
global quench. As initial states we consider a canted/spiral order product
state of the spins, and singlets of neighboring pairs of spins. We find that
within the class of canted order initial states, no entanglement is generated
at any time except for the special case of the Neel state. While an earlier
work had shown that the Neel state is indeed an excellent starting resource for
the dynamical generation of long distance entanglement, the curious fact that
this is the sole point within a large class of initial product states of the
spins was not noted. On the other hand, we find that an initial state which is
a series of nearest neighbor Bell states, and well motivated by some physical
realizations, is also a good starting resource for end to end entanglement in a
similar way to the Neel state.",1309.5756v2
2014-05-09,Magnetization dynamics and damping due to electron-phonon scattering in a ferrimagnetic exchange model,"We present a microscopic calculation of magnetization damping for a magnetic
""toy model."" The magnetic system consists of itinerant carriers coupled
antiferromagnetically to a dispersionless band of localized spins, and the
magnetization damping is due to coupling of the itinerant carriers to a phonon
bath in the presence of spin-orbit coupling. Using a mean-field approximation
for the kinetic exchange model and assuming the spin-orbit coupling to be of
the Rashba form, we derive Boltzmann scattering integrals for the distributions
and spin coherences in the case of an antiferromagnetic exchange splitting,
including a careful analysis of the connection between lifetime broadening and
the magnetic gap. For the Elliott-Yafet type itinerant spin dynamics we extract
dephasing and magnetization times T_1 and T_2 from initial conditions
corresponding to a tilt of the magnetization vector, and draw a comparison to
phenomenological equations such as the Landau-Lifshitz or the Gilbert damping.
We also analyze magnetization precession and damping for this system including
an anisotropy field and find a carrier mediated dephasing of the localized spin
via the mean-field coupling.",1405.2347v1
2014-06-19,Probing the dynamics of a nuclear spin bath in diamond through time-resolved central spin magnetometry,"Using fast electron spin resonance spectroscopy of a single nitrogen-vacancy
defect in diamond, we demonstrate real-time readout of the Overhauser field
produced by its nuclear spin environment under ambient conditions. These
measurements enable narrowing the Overhauser field distribution by
post-selection, corresponding to a conditional preparation of the nuclear spin
bath. Correlations of the Overhauser field fluctuations are quantitatively
inferred by analysing the Allan deviation over consecutive measurements. This
method allows to extract the dynamics of weakly coupled nuclear spins of the
reservoir.",1406.5077v2
2016-08-13,Topological transport of sound mediated by spin-redirection geometric phase,"When a dynamic system undergoes a cyclic evolution, a geometric phase that
depends only on the path traversed in parameter space can arise in addition to
the normal dynamical phase. These geometric phases have profound impacts in
both quantum and classical physics. In addition to the geometric phase
associated with band structures in reciprocal space that has led to the
discovery of topological insulators, the spin-redirection geometric phase
induced by the $SO$(3) rotation of states in real space can also give rise to
intriguing phenomena such as the photonic analog of the spin Hall effect. By
exploiting the orbital angular momentum of sound vortices, we theoretically and
experimentally demonstrate the spin-redirection geometric phase effects in
airborne sound, which is a scalar wave without spin. We show that these
effects, associated with the helical transport of sound, can be used to control
the flow of sound. This finding opens new possibilities for the manipulation of
scalar wave propagation by exploiting spin-redirection geometric phases.",1608.03976v3
2016-12-09,Open spin chains with dynamic lattice supersymmetry,"The quantum spin $1/2$ XXZ chain with anisotropy parameter $\Delta=-1/2$
possesses a dynamic supersymmetry on the lattice. This supersymmetry and a
generalisation to higher spin are investigated in the case of open spin chains.
A family of non-diagonal boundary interactions that are compatible with the
lattice supersymmetry and depend on several parameters is constructed. The
cohomology of the corresponding supercharges is explicitly computed as a
function of the parameters and the length of the chain. For certain specific
values of the parameters, this cohomology is shown to be non-trivial. This
implies that the spin-chain ground states are supersymmetry singlets. Special
scalar products involving an arbitrary number of these supersymmetry singlets
for chains of different lengths are exactly computed. As a physical
application, the logarithmic bipartite fidelity of the open quantum spin $1/2$
XXZ chain with $\Delta=-1/2$ and special diagonal boundary interactions is
determined.",1612.02951v1
2017-06-01,Spin-density fluctuations and the fluctuation-dissipation theorem in 3d ferromagnetic metals,"Spatial and time scales of spin density fluctuations (SDF) were analyzed in
3d ferromagnets using ab initio linear response calculations of complete
wavevector and energy dependence of the dynamic spin susceptibility tensor. We
demonstrate that SDF are spread continuously over the entire Brillouin zone and
while majority of them reside within the 3d bandwidth, a significant amount
comes from much higher energies. A validity of the adiabatic approximation in
spin dynamics is discussed. The SDF spectrum is shown to have two main
constituents: a minor low-energy spin wave contribution and a much larger
high-energy component from more localized excitations. Using the
fluctuation-dissipation theorem (FDT), the on-site spin correlator (SC) and the
related effective fluctuating moment were properly evaluated and their
universal dependence on the 3d band population is further discussed.",1706.00512v2
2017-10-23,Frequency and wavenumber selective excitation of spin waves through coherent energy transfer from elastic waves,"Using spin-wave tomography (SWaT), we have investigated the excitation and
the propagation dynamics of optically-excited magnetoelastic waves, i.e.
hybridized modes of spin waves and elastic waves, in a garnet film. By using
time-resolved SWaT, we reveal the excitation dynamics of magnetoelastic waves
through coherent-energy transfer between optically-excited pure-elastic waves
and spin waves via magnetoelastic coupling. This process realizes frequency and
wavenumber selective excitation of spin waves at the crossing of the dispersion
relations of spin waves and elastic waves. Finally, we demonstrate that the
excitation mechanism of the optically-excited pure-elastic waves, which are the
source of the observed magnetoelastic waves, is dissipative in nature.",1710.08087v2
2017-12-13,Mobile bound states of Rydberg excitations in a lattice,"Spin lattice models play central role in the studies of quantum magnetism and
non-equilibrium dynamics of spin excitations -- magnons. We show that a spin
lattice with strong nearest-neighbor interactions and tunable long-range
hopping of excitations can be realized by a regular array of laser driven
atoms, with an excited Rydberg state representing the spin-up state and a
Rydberg-dressed ground state corresponding to the spin-down state. We find
exotic interaction-bound states of magnons that propagate in the lattice via
the combination of resonant two-site hopping and non-resonant second-order
hopping processes. Arrays of trapped Rydberg-dressed atoms can thus serve as a
flexible platform to simulate and study fundamental few-body dynamics in spin
lattices.",1712.04713v1
2018-09-08,A strategy for solving difficulties in spin-glass simulations,"A spin-glass transition has been investigated for a long time but we have not
yet reached a conclusion due to difficulties in the simulations. They are slow
dynamics, strong finite-size effects, and sample-to-sample dependences. We
clarified that these difficulties are mainly caused by a competition between
the spin-glass order and the boundary conditions. We also found that the
spin-glass order grows fast and reaches the lattice boundary within a very
short Monte Carlo step. A key to solve the difficulties is to eliminate the
boundary effect first. It was made possible by a dynamic scaling analysis on
nonequilibrium relaxation functions in a large-size and short-time regime. The
observed quantity was also found to be self-averaging in a limit of large
replica number. The spin-glass transition and the chiral-glass transition was
clarified to occur at the same temperature in the Heisenberg spin-glass model
in three dimensions. The estimated critical exponent $\nu$ agrees with the
experimental result.",1809.02739v2
2018-10-01,Synchronization of strongly interacting alkali-metal spins,"The spins of gaseous alkali atoms are commonly assumed to oscillate at a
constant hyperfine frequency, which for many years has been used to define the
Second. Indeed, under standard experimental conditions, the spins oscillate
independently, only weakly perturbed and slowly decaying due to random
spin-spin collisions. Here we consider a different, unexplored regime of very
dense gas, where collisions, more frequent than the hyperfine frequency,
dominate the dynamics. Counter-intuitively, we find that the hyperfine
oscillations become significantly longer-lived, and their frequency becomes
dependent on the state of the ensemble, manifesting strong nonlinear dynamics.
We reveal that the nonlinearity originates from a many-body interaction which
synchronizes the electronic spins, driving them into a single collective mode.
The conditions for experimental realizations of this regime are outlined.",1810.00570v1
2018-10-30,Destabilization of local minima in analog spin systems by correction of amplitude heterogeneity,"The relaxation of binary spins to analog values has been the subject of much
debate in the field of statistical physics, neural networks, and more recently
quantum computing, notably because the benefits of using an analog state for
finding lower energy spin configurations are usually offset by the negative
impact of the improper mapping of the energy function that results from the
relaxation. We show that it is possible to destabilize trapping sets of analog
states that correspond to local minima of the binary spin Hamiltonian by
extending the phase space to include error signals that correct amplitude
inhomogeneity of the analog spin states and controlling the divergence of their
velocity. Performance of the proposed analog spin system in finding lower
energy states is competitive against state-of-the-art heuristics.",1810.12565v3
2019-07-04,Domain wall dynamics due to femtosecond laser-induced superdiffusive spin transport,"Manipulation of magnetic domain walls via a helicity-independent laser pulse
has recently been experimentally demonstrated and various physical mechanisms
leading to domain wall dynamics have been discussed. Spin-dependent
superdiffusive transport of hot electrons has been identified as one of the
possible ways how to affect a magnetic domain wall. Here, we develop a model
based on superdiffusive spin-dependent transport to study the laser-induced
transport of hot electrons through a smooth magnetic domain wall. We show that
the spin transfer between neighboring domains can enhance ultrafast
demagnetization in the domain wall. More importantly, our calculations reveal
that when the laser pulse is properly focused on to the vicinity of the domain
wall, it can excite sufficiently strong spin currents to generate a
spin-transfer torque that can rapidly move the magnetic domain wall by several
nanometers in several hundreds of femtoseconds, leading to a huge
nonequilibrium domain wall velocity.",1907.02419v1
2019-07-28,Universal spin dynamics in infinite-temperature one-dimensional quantum magnets,"We address the nature of spin dynamics in various integrable and
non-integrable, isotropic and anisotropic quantum spin-$S$ chains, beyond the
paradigmatic $S=1/2$ Heisenberg model. In particular, we investigate the
algebraic long-time decay $\propto t^{-1/z}$ of the spin-spin correlation
function at infinite temperature, using state-of-the-art simulations based on
tensor network methods. We identify three universal regimes for the spin
transport, independent of the exact microscopic model: (i) superdiffusive with
$z=3/2$, as in the Kardar-Parisi-Zhang universality class, when the model is
integrable with extra symmetries such as spin isotropy that drive the Drude
weight to zero, (ii) ballistic with $z=1$ when the model is integrable with a
finite Drude weight, and (iii) diffusive with $z=2$ with easy-axis anisotropy
or without integrability, at variance with previous observations.",1907.12115v3
2019-07-30,Microscopic dynamics of electron hopping in a semiconductor quantum well probed by spin-dependent photon echoes,"Spin-dependent photon echoes in combination with pump-probe Kerr rotation are
used to study the microscopic electron spin transport in a CdTe/(Cd,Mg)Te
quantum well in the hopping regime. We demonstrate that independent of the
particular spin relaxation mechanism, hopping of resident electrons leads to a
shortening of the photon echo decay time, while the transverse spin relaxation
time evaluated from pump-probe transients increases due to motional narrowing
of spin dynamics in the fluctuating effective magnetic field of the lattice
nuclei.",1907.12811v1
2019-09-30,Coherent spin mixing via spin-orbit coupling in Bose gases,"We study beyond-mean-field properties of interacting spin-1 Bose gases with
synthetic Rashba-Dresselhaus spin-orbit coupling at low energies. We derive a
many-body Hamiltonian following a tight-binding approximation in quasi-momentum
space, where the effective spin dependence of the collisions that emerges from
spin-orbit coupling leads to dominant correlated tunneling processes that
couple the different bound states. We discuss the properties of the spectrum of
the derived Hamiltonian and its experimental signatures. In a certain region of
the parameter space, the system becomes integrable, and its dynamics becomes
analogous to that of a spin-1 condensate with spin-dependent collisions.
Remarkably, we find that such dynamics can be observed in existing experimental
setups through quench experiments that are robust against magnetic
fluctuations.",1909.13840v1
2020-02-09,Walker-like Domain Wall breakdown in layered Antiferromagnets driven by staggered spin-orbit fields,"Within linear continuum theory, no magnetic texture can propagate faster than
the maximum group velocity of its spin waves. Here we report a transient regime
due to the appearance of additional antiferromagnetic textures that breaks the
Lorentz translational invariance of the magnetic system by atomistic spin
dynamics simulations. This dynamical regime is akin to domain wall
Walker-breakdown in ferromagnets and involves the nucleation of an
antiferromagnetic domain wall pair. Subsequently, one of the nucleated
180$^{\circ}$ domain wall creates with the original domain wall a 360$^{\circ}$
spin-rotation which remains static even under the action of the spin-orbit
field. The other 180$^{\circ}$ domain wall becomes accelerated to
super-magnonic speeds. Under large spin-orbit fields, multiple domain wall
generation and recombination is obtained which may explain the recently
experimentally observed current pulse induce shattering of large domain
structures into small fragmented domains and the subsequent slow recreation of
large-scale domain formation prior current pulse.",2002.03332v1
2020-02-17,Linear resistivity and Sachdev-Ye-Kitaev (SYK) spin liquid behavior in a quantum critical metal with spin-$1/2$ fermions,"`Strange metals' with resistivity depending linearly on temperature $T$ down
to low-$T$ have been a long-standing puzzle in condensed matter physics. Here,
we consider a model of itinerant spin-$1/2$ fermions interacting via on-site
Hubbard interaction and random infinite-ranged spin-spin interaction. We show
that the quantum critical point associated with the melting of the spin-glass
phase by charge fluctuations displays non-Fermi liquid behaviour, with local
spin dynamics identical to that of the Sachdev-Ye-Kitaev family of models. This
extends the quantum spin liquid dynamics previously established in the
large-$M$ limit of $SU(M)$ symmetric models, to models with physical $SU(2)$
spin-$1/2$ electrons. Remarkably, the quantum critical regime also features a
Planckian linear-$T$ resistivity associated with a $T$-linear scattering rate
and a frequency dependence of the electronic self-energy consistent with the
Marginal Fermi Liquid phenomenology.",2002.07181v1
2020-12-16,Observation of non-Hermitian topology with non-unitary dynamics of solid-state spins,"Non-Hermitian topological phases exhibit a number of exotic features that
have no Hermitian counterparts, including the skin effect and breakdown of the
conventional bulk-boundary correspondence. Here, we implement the non-Hermitian
Su-Schrieffer-Heeger (SSH) Hamiltonian, which is a prototypical model for
studying non-Hermitian topological phases, with a solid-state quantum simulator
consisting of an electron spin and a $^{13}$C nuclear spin in a
nitrogen-vacancy (NV) center in a diamond. By employing a dilation method, we
realize the desired non-unitary dynamics for the electron spin and map out its
spin texture in the momentum space, from which the corresponding topological
invariant can be obtained directly. Our result paves the way for further
exploiting and understanding the intriguing properties of non-Hermitian
topological phases with solid-state spins or other quantum simulation
platforms.",2012.09191v1
2021-01-20,Dynamical preparation of stripe states in spin-orbit coupled gases,"In spinor Bose-Einstein condensates, spin-changing collisions are a
remarkable proxy to coherently realize macroscopic many-body quantum states.
These processes have been, e.g., exploited to generate entanglement, to study
dynamical quantum phase transitions, and proposed for realizing nematic phases
in atomic condensates. In the same systems dressed by Raman beams, the coupling
between spin and momentum induces a spin dependence in the scattering processes
taking place in the gas. Here we show that, at weak couplings, such modulation
of the collisions leads to an effective Hamiltonian which is equivalent to the
one of an artificial spinor gas with spin-changing collisions that are tunable
with the Raman intensity. By exploiting this dressed-basis description, we
propose a robust protocol to coherently drive the spin-orbit coupled condensate
into the ferromagnetic stripe phase via crossing a quantum phase transition of
the effective low-energy model in an excited-state.",2101.08253v3
2017-05-05,Unexpected Enhancement of Three-Dimensional Low-Energy Spin Correlations in Quasi-Two-Dimensional Fe$_{1+y}$Te$_{1-x}$Se$_{x}$ System at High Temperature,"We report inelastic neutron scattering measurements of low energy ($\hbar
\omega < 10$ meV) magnetic excitations in the ""11"" system
Fe$_{1+y}$Te$_{1-x}$Se$_{x}$. The spin correlations are two-dimensional (2D) in
the superconducting samples at low temperature, but appear much more
three-dimensional when the temperature rises well above $T_c \sim 15$ K, with a
clear increase of the (dynamic) spin correlation length perpendicular to the Fe
planes. The spontaneous change of dynamic spin correlations from 2D to 3D on
warming is unexpected and cannot be naturally explained when only the spin
degree of freedom is considered. Our results suggest that the low temperature
physics in the ""11"" system, in particular the evolution of low energy spin
excitations towards %better satisfying the nesting condition for mediating
superconducting pairing, is driven by changes in orbital correlations.",1705.02324v1
2017-05-26,Static and Dynamic Magnetic Properties of FeMn/Pt Multilayers,"Recently we have demonstrated the presence of spin-orbit toque in FeMn/Pt
multilayers which, in combination with the anisotropy field, is able to rotate
its magnetization consecutively from 0o to 360o without any external field.
Here, we report on an investigation of static and dynamic magnetic properties
of FeMn/Pt multilayers using combined techniques of magnetometry, ferromagnetic
resonance, inverse spin Hall effect and spin Hall magnetoresistance
measurements. The FeMn/Pt multilayer was found to exhibit ferromagnetic
properties, and its temperature dependence of saturation magnetization can be
fitted well using a phenomenological model by including a finite distribution
in Curie temperature due to subtle thickness variations across the multilayer
samples. The non-uniformity in static magnetic properties is also manifested in
the ferromagnetic resonance spectra, which typically exhibit a broad resonance
peak. A damping parameter of around 0.106 is derived from the frequency
dependence of ferromagnetic resonance linewidth, which is comparable to the
reported values for other types of Pt-based multilayers. Clear inverse spin
Hall signals and spin Hall magnetoresistance have been observed in all samples
below the Curie temperature, which corroborate the strong spin-orbit torque
effect observed previously.",1705.09423v1
2017-09-04,Electron spin dynamics of Ce$^{3+}$ ions in YAG crystals studied by pulse-EPR and pump-probe Faraday rotation,"The spin relaxation dynamics of Ce$^{3+}$ ions in heavily cerium-doped YAG
crystals is studied using pulse-electron paramagnetic resonance and
time-resolved pump-probe Faraday rotation. Both techniques address the 4$f$
ground state, while pump-probe Faraday rotation provides also access to the
excited 5$d$ state. We measure a millisecond spin-lattice relaxation time
$T_1$, a microsecond spin coherence time $T_2$ and a $\sim 10$ ns inhomogeneous
spin dephasing time $T_2^*$ for the Ce$^{3+}$ ground state at low temperatures.
The spin-lattice relaxation of Ce$^{3+}$ ions is due to modified Raman
processes involving the optical phonon mode at 125 cm$^{-1}$. The relaxation at
higher temperature goes through a first excited level of the $^{2}$F$_{5/2}$
term at about $\hbar \omega \approx 228$ cm$^{-1}$. Effects provided by the
hyperfine interaction of the Ce$^{3+}$ with the $^{27}$Al nuclei are observed.",1709.01997v1
2017-11-23,Chaos in two-dimensional Kepler problem with spin-orbit coupling,"We consider classical two-dimensional Kepler system with spin-orbit coupling
and show that at a sufficiently strong coupling it demonstrates a chaotic
behavior. The chaos emerges since the spin-orbit coupling reduces the number of
the integrals of motion as compared to the number of the degrees of freedom.
This reduction is manifested in the equations of motion as the emergence of the
anomalous velocity determined by the spin orientation. By using analytical and
numerical arguments, we demonstrate that the chaotic behavior, being driven by
this anomalous term, is related to the system energy dependence on the initial
spin orientation. We observe the critical dependence of the dynamics on the
initial conditions, where system can enter and exit a stability domain by very
small changes in the initial spin orientation. Thus, this system can
demonstrate a reentrant order-from-disorder transition driven by very small
variations in the initial conditions.",1711.08773v1
2018-03-04,Spin hydrodynamics in amorphous magnets,"Spin superfluidity, i.e., coherent spin transport mediated by topologically
stable textures, is limited by parasitic anisotropies rooted in relativistic
interactions and spatial inhomogeneities. Since structural disorder in
amorphous magnets can average out the effect of these undesired couplings, we
propose this class of materials as platforms for superfluid spin transport. We
establish nonlinear equations describing the hydrodynamics of spin in
insulating amorphous magnets, where the currents are defined in terms of
coherent rotations of a noncollinear texture. Our theory includes dissipation
and nonequilibrium torques at the interface with metallic reservoirs. This
framework allows us to determine different regimes of coherent dynamics and
their salient features in nonlocal magneto-transport measurements. Our work
paves the way for future studies on macroscopic spin dynamics in materials with
frustrated interactions.",1803.01309v2
2018-03-22,Time-resolved quantum spin transport through an Aharonov-Casher ring,"After obtaining an exact analytical time-varying solution for the
Aharonov-Casher conducting ring embedded in a textured static/dynamic electric
field, we investigate the spin-resolved quantum transport in the structure. It
is shown that the interference patterns are governed by not only the
Aharonov-Casher geometry phase but also the instantaneous phase difference of
spin precession through different traveling paths. This dynamic phase is
determined by the strength of applied electric field and can have substantial
effects on the charge/spin conductances, especially in the weak field regime as
the period of spin precession comparable to that of the orbital motion. Our
studies suggest that a low-frequency normal electric field with moderate
strength possesses more degrees of freedom for manipulating the spin
interference of incident electrons.",1803.08246v3
2018-06-07,Accessing eigenstate spin-glass order from reduced density matrices,"Many-body localized phases may not only be characterized by their ergodicity
breaking, but can also host ordered phases such as the many-body localized
spin-glass (MBL-SG). The MBL-SG is challenging to access in a dynamical
measurement and therefore experimentally since the conventionally used
Edwards-Anderson order parameter is a two-point correlation function in time.
In this work, we show that many-body localized spin-glass order can also be
detected from two-site reduced density matrices, which we use to construct an
eigenstate spin-glass order parameter. We find that this eigenstate spin-glass
order parameter captures spin-glass phases in random Ising chains both in
many-body eigenstates as well as in the nonequilibrium dynamics from a local in
time measurement. We discuss how our results can be used to observe MBL-SG
order within current experiments in Rydberg atoms and trapped ion systems.",1806.02571v1
2018-07-13,Spinor self-ordering of a quantum gas in a cavity,"We observe the joint spin-spatial (spinor) self-organization of a
two-component BEC strongly coupled to an optical cavity. This unusual
nonequilibrium Hepp-Lieb-Dicke phase transition is driven by an off-resonant
two-photon Raman transition formed from a classical pump field and the emergent
quantum dynamical cavity field. This mediates a spinor-spinor interaction that,
above a critical strength, simultaneously organizes opposite spinor states of
the BEC on opposite checkerboard configurations of an emergent 2D lattice. The
resulting spinor density-wave polariton condensate is observed by directly
detecting the atomic spin and momentum state and by holographically
reconstructing the phase of the emitted cavity field. The latter provides a
direct measure of the spin state, and a spin-spatial domain wall is observed.
The photon-mediated spin interactions demonstrated here may be engineered to
create dynamical gauge fields and quantum spin glasses.",1807.04915v1
2018-08-30,Dynamical spin-spin susceptibility of Silicene,"We present a detailed study of the imaginary and real parts of the
spin-susceptibility of silicene which can be generalized to other buckled
honeycomb structure. We find that while the off-diagonal components are
non-zero in individual valleys, they add up to zero upon including
contributions from both the valleys. We investigate the interplay of the
spin-orbit interaction and an external electric field applied perpendicular to
the substrate and find that although the xx and yy components of the
susceptibility are identical, they differ from the zz-component. The external
electric field plays an important role in modifying the allowed inter-subband
regions. In the dynamic limit, the real part of the susceptibility exhibits
log-divergence, position of which can be tuned by the electric field and
therefore has implications for spin-collective excitations. The effect of the
electric field on the static part of the susceptibility and its consequence for
the long distance decay of the spin-susceptibility have been explored.",1808.10176v1
2019-01-07,Stabilisation of an optical transition energy via nuclear Zeno dynamics in quantum dot-cavity systems,"We investigate the effect of nuclear spins on the phase shift and
polarisation rotation of photons scattered off a quantum dot-cavity system. We
show that as the phase shift depends strongly on the resonance energy of an
electronic transition in the quantum dot, it can provide a sensitive probe of
the quantum state of nuclear spins that broaden this transition energy. By
including the electron-nuclear spin coupling at a Hamiltonian level within an
extended input-output formalism, we show how a photon scattering event acts as
a nuclear spin measurement, which when rapidly applied leads to an inhibition
of the nuclear spin dynamics via the quantum Zeno effect, and a corresponding
stabilisation of the optical resonance. We show how such an effect manifests in
the intensity autocorrelation $g^{(2)}(\tau)$ of scattered photons, whose
long-time bunching behaviour changes from quadratic decay for low photon
scattering rates (weak laser intensities), to ever slower exponential decay for
increasing laser intensities as optical measurements impede the nuclear spin
evolution.",1901.01962v2
2019-02-02,Bloch oscillations of spin-orbit-coupled cold atoms in an optical lattice and spin current generation,"We study the Bloch oscillation dynamics of a spin-orbit-coupled cold atomic
gas trapped inside a one-dimensioanl optical lattice. The eigenspectra of the
system is identified as two interpenetrating Wannier-Stark ladder. Based on
that, we carefully analyzed the Bloch oscillation dynamics and found out that
intraladder coupling between neighboring rungs of Wannier-Stark ladder give
rise to ordinary Bloch oscillation while interladder coupling lead to small
amplitude high frequency oscillation superimposed on it. Specifically
spin-orbit interaction breaks Galilean invariance, which can be reflected by
out-of-phase oscillation of the two spin components in the accelerated frame.
The possibility of generating spin current in this system are also explored.",1902.00634v1
2019-02-13,Origins of overshoots in the exciton spin dynamics in semiconductors,"We investigate the origin of overshoots in the exciton spin dynamics after
resonant optical excitation. As a material system, we focus on diluted magnetic
semiconductor quantum wells as they provide a strong spin-flip scattering for
the carriers. Our study shows that overshoots can appear as a consequence of
radiative decay even on the single-particle level in a theory without any
memory. The magnitude of the overshoots in this case depends strongly on the
temperature as well as the doping fraction of the material. If many-body
effects beyond the single-particle level become important so that a
quantum-kinetic description is required, a spin overshoot appears already
without radiative decay and is much more robust against variations of system
parameters. We show that the origin of the spin overshoot can be determined
either via its temperature dependence or via its behavior for different doping
fractions. The results can be expected to apply to a wide range of
semiconductors as long as radiative decay and a spin-flip mechanism are
present.",1902.04921v2
2019-03-20,Spin dynamics of antiferromagnetically coupled ferromagnetic bilayers -- the case of Cr$_2$WO$_6$ and Cr$_2$MoO$_6$,"Recent inelastic neutron diffraction measurements on Cr$_2$(Te, W, Mo)O$_6$
have revealed that these systems consist of bilayers of spin-3/2 Cr$^{3+}$ ions
with strong antiferromagnetic inter-bilayer coupling and tuneable intra-bilayer
coupling from ferro (for W and Mo) to antiferro (for Te). These measurements
have determined the ground state spin structure and the values of sublattice
magnetization, which shows significant reduction of sublattice magnetization
from the atomic spin value of 3.0$\mu_B$ for Cr$^{3+}$ atoms. In an earlier
paper we theoretically investigated the low temperature spin dynamics of
Cr$_2$TeO$_6$ bilayer system where both the intra and inter-bilayer couplings
are antiferromagnetic. In this paper we investigate Cr$_2$WO$_6$ and
Cr$_2$MoO$_6$ systems where intra-bilayer exchange couplings are ferromagnetic
but the inter-bilayer exchange couplings are antiferromagnetic. We obtain the
magnon dispersion, sublattice magnetization, two-magnon density of states,
longitudinal spin-spin correlation function, and its powder average and compare
the results for these systems with results for Cr$_2$TeO$_6$.",1903.08512v1
2019-04-10,Radiofrequency driving of coherent electron spin dynamics in $n$-GaAs detected by Faraday rotation,"We suggest a new pump-probe method for studying semiconductor spin dynamics
based on pumping of carrier spins by a pulse of oscillating radiofrequency (rf)
magnetic field and probing by measuring the Faraday rotation of a short laser
pulse. We demonstrate this technique on $n$-GaAs and observe the onset and
decay of coherent spin precession during and after the course of rf pulse
excitation. We show that the rf field resonantly addresses the electron spins
with Larmor frequencies close to that of the rf field. This opens the
opportunity to determine the homogeneous spin coherence time $T_2$, that is
inaccessible directly in standard all-optical pump-probe experiments.",1904.05398v2
2019-11-18,Influence of non-equilibrium phonons on the spin dynamics of a single Cr atom,"We analyse the influence of optically generated non-equilibrium phonons on
the spin relaxation and effective spin temperature of an individual Cr atom
inserted in a quantum dot. Using a three pulses pump-probe technique, we show
that the spin relaxation measured in resonant optical pumping experiments
strongly depends on the optical excitation conditions. We observe for an
isolated Cr in the dark a heating time shorter than a few hundreds $ns$ after
an initial high power non-resonant excitation pulse. A cooling time larger than
a few tens of $\mu s$, independent on the excitation, is obtained in the same
experimental conditions. We show that a tunable spin-lattice coupling dependent
on the density of non-equilibrium phonons can explain the observed dynamics.
Low energy excitation conditions are found where the Cr spin states
S$_z$=$\pm$1 can be efficiently populated by a non-resonant optical excitation,
prepared and read-out by resonant optical pumping and conserved in the dark
during a few $\mu$s.",1911.07639v1
2019-12-20,Efficient Ab-initio Multiplet Calculations for Magnetic Adatoms on MgO,"Scanning probe microscopy and spectroscopy, and more recently in combination
with electron spin resonance, have allowed the direct observation of electron
dynamics on the single-atom limit. The interpretation of data is strongly
depending on model Hamiltonians. However, fitting effective spin Hamiltonians
to experimental data lacks the ability to explore a vast number of potential
systems of interest. By using plane-wave density functional theory (DFT) as
starting point, we build a multiplet Hamiltonian making use of
maximally-localized Wannier functions. The Hamiltonian contains spin-orbit and
electron-electron interactions needed to obtain the relevant spin dynamics. The
resulting reduced Hamiltonian is solved by exact diagonalization. We compare
three prototypical cases of 3d transition metals Mn (total spin $S=5/2$), Fe
($S=2$) and Co ($S=3/2$) on MgO with experimental data and find that our
calculations can accurately predict the spin orientation and anisotropy of the
magnetic adatom. Our method does not rely on experimental input and permits us
to explore and predict the fundamental magnetic properties of adatoms on
surfaces.",1912.09793v1
2020-03-28,Acoustic spin transfer to a subwavelength spheroidal particle,"We demonstrate that the acoustic spin of a first-order Bessel beam can be
transferred to a subwavelength (prolate) spheroidal particle at the beam axis
in a viscous fluid. The induced radiation torque is proportional to the
acoustic spin, which scales with the beam energy density. The analysis of the
particle rotational dynamics in a Stokes' flow regime reveals that its angular
velocity varies linearly with the acoustic spin. Asymptotic expressions of the
radiation torque and angular velocity are obtained for a quasispherical and
infinitely thin particle. Excellent agreement is found between the theoretical
results of radiation torque and finite element simulations. The induced
particle spin is predicted and analyzed using the typical parameter values of
the acoustical vortex tweezer and levitation devices. We discuss how the beam
energy density and fluid viscosity can be assessed by measuring the induced
spin of the particle.",2003.12784v1
2020-05-06,Relativistic electron spin dynamics in a strong unipolar laser field,"The behavior of an electron spin interacting with a linearly polarized laser
field is analyzed. In contrast to previous considerations of the problem, the
initial state of the electron represents a localized wave packet, and a spatial
envelope is introduced for the laser pulse, which allows one to take into
account the finite size of both objects. Special attention is paid to
ultrashort pulses possessing a high degree of unipolarity. Within a classical
treatment (both nonrelativistic and relativistic), proportionality between the
change of the electron spin projections and the electric field area of the
pulse is clearly demonstrated. We also perform calculations of the electron
spin dynamics according to the Dirac equation. Evolving the electron wave
function in time, we compute the mean values of the spin operator in various
forms. It is shown that the classical relativistic predictions are accurately
reproduced when using the Foldy-Wouthuysen operator. The same results are
obtained when using the Lorentz transformation and the nonrelativistic (Pauli)
spin operator in the particle's rest frame.",2005.02839v1
2020-05-28,Nonequilibrium quasistationary spin disordered state in the Kitaev-Heisenberg magnet $α$-RuCl$_3$,"Excitation by light pulses enables the manipulation of phases of quantum
condensed matter. Here, we photoexcite high-energy holon-doublon pairs as a way
to alter the magnetic free energy landscape of the Kitaev-Heisenberg magnet
$\alpha$-RuCl$_3$, with the aim to dynamically stabilize a proximate spin
liquid phase. The holon-doublon pair recombination through multimagnon emission
is tracked through the time-evolution of the magnetic linear dichroism
originating from the competing zigzag spin ordered ground state. A small
holon-doublon density suffices to reach a spin disordered state. The phase
transition is described within a dynamic Ginzburg-Landau framework,
corroborating the quasistationary nature of the transient spin disordered
phase. Our work provides insight into the coupling between the electronic and
magnetic degrees of freedom in $\alpha$-RuCl$_3$ and suggests a new route to
reach a proximate spin liquid phase in Kitaev-Heisenberg magnets.",2005.14189v1
2020-09-20,Non-classical spin transfer effects in an antiferromagnet,"We simulate scattering of electrons by a chain of antiferromagnetically
coupled quantum Heisenberg spins, to analyze spin-transfer effects not
described by the classical models of magnetism. Our simulations demonstrate
efficient excitation of dynamical states that would be forbidden by the
semiclassical symmetries, such as generation of multiple magnetic excitation
quanta by a single electron. Furthermore, quantum interference of spin
wavefunctions enables generation of magnetization dynamics with amplitudes
exceeding the transferred magnetic moment. The efficiency of excitation is
almost independent of the electron spin polarization, and is governed mainly by
the transfer of energy. Non-classical spin transfer may thus enable efficient
electronic control of antiferromagnets not limited by the classical
constraints.",2009.09540v2
2020-09-30,Dynamical properties of a driven dissipative dimerized $S = 1/2$ chain,"We consider the dynamical properties of a gapped quantum spin system coupled
to the electric field of a laser, which drives the resonant excitation of
specific phonon modes that modulate the magnetic interactions. We deduce the
quantum master equations governing the time-evolution of both the lattice and
spin sectors, by developing a Lindblad formalism with bath operators providing
an explicit description of their respective phonon-mediated damping terms. We
investigate the nonequilibrium steady states (NESS) of the spin system
established by a continuous driving, delineating parameter regimes in driving
frequency, damping, and spin-phonon coupling for the establishment of
physically meaningful NESS and their related non-trivial properties. Focusing
on the regime of generic weak spin-phonon coupling, we characterize the NESS by
their frequency and wave-vector content, explore their transient and relaxation
behavior, and discuss the energy flow, the system temperature, and the critical
role of the type of bath adopted. Our study lays a foundation for the
quantitative modelling of experiments currently being designed to control
coherent many-body spin states in quantum magnetic materials.",2009.14805v2
2020-11-13,Suppression of nuclear spin fluctuations in an InGaAs quantum dot ensemble by GHz-pulsed optical excitation,"The coherent electron spin dynamics of an ensemble of singly charged
(In,Ga)As/GaAs quantum dots in a transverse magnetic field is driven by
periodic optical excitation at 1 GHz repetition frequency. Despite the strong
inhomogeneity of the electron $g$ factor, the spectral spread of optical
transitions, and the broad distribution of nuclear spin fluctuations, we are
able to push the whole ensemble of excited spins into a single Larmor
precession mode that is commensurate with the laser repetition frequency.
Furthermore, we demonstrate that an optical detuning of the pump pulses from
the probed optical transitions induces a directed dynamic nuclear polarization
and leads to a discretization of the total magnetic field acting on the
electron ensemble. Finally, we show that the highly periodic optical excitation
can be used as universal tool for strongly reducing the nuclear spin
fluctuations and preparation of a robust nuclear environment for subsequent
manipulation of the electron spins, also at varying operation frequencies.",2011.06869v2
2021-06-25,Energy balance and energy correction in dynamics of classical spin systems,"Energy-correction method is proposed as an addition to mainstream integrators
for equations of motion of systems of classical spins. This solves the problem
of non-conservation of energy in long computations and makes mainstream
integrators competitive with symplectic integrators for spin systems that for
different-site interactions conserve the energy explicitly. The proposed method
is promising for spin systems with single-site interactions for which
symplectic integrators do not conserve energy and thus have no edge against
mainstream integrators. From the energy balance in the spin system with a
phenomenological damping and Langevin fields, a formula for the dynamical spin
temperature in the presence of single-site anisotropy is obtained.",2106.14689v2
2021-10-19,Analytical Estimations of the Chromaticity and Corrections to the Spin Precession Frequency in Weak Focusing Magnetic Storage Rings,"Understanding beam and spin dynamics are fundamental in accelerator physics,
and there has been growing interest in having more precise estimations of the
beam and spin dynamics variables, as more high precision particle physics
experiments in the Intensity Frontier appear. The present paper provides
analytical estimations of some of the important variables such as beam
transverse chromaticities and the spin precession frequency bias in the
simplest type of particle accelerator: a circular magnetic storage ring with
weak vertical focusing. We attempt to precisely obtain the next order
approximations from the small betatron oscillations or the momentum dispersion,
verified by high precision spin tracking simulation. We also discuss a
potential way to suppress the spin precession frequency bias which relevant
experiments may find beneficial.",2110.10003v2
2021-10-26,Ultrafast signatures of spin and orbital order in antiferromagnetic $α$-Sr$_2$CrO$_4$,"We used femtosecond optical spectroscopy to study ultrafast spin and orbital
ordering dynamics in the antiferromagnetic Mott insulator
$\alpha$-Sr$_2$CrO$_4$. This chromate system possesses multiple spin and
orbital ordered phases, and therefore could enable us to study the unique
interplay between these collective phases through their non-equilibrium
response to photoexcitation. Here, by varying the pump photon energy, we
selectively drove inter-site spin hopping between neighboring Cr $t_{2g}$
orbitals and charge transfer-type transitions between oxygen 2$p$ and Cr
$e_{g}$ orbitals. The resulting transient reflectivity dynamics revealed
temperature-dependent anomalies across the N${\textrm{\'e}}$el temperature for
spin ordering as well as the transition temperatures linked to different types
of orbital order. Our results reveal distinct relaxation timescales for spin
and orbital orders in $\alpha$-Sr$_2$CrO$_4$ and provide experimental evidence
for the phase transition at $T_\textrm{O}$, possibly related to antiferro-type
orbital ordering.",2110.14004v1
2021-12-23,NMR evidence against a spin-nematic nature of the presaturation phase in the frustrated magnet SrZnVO(PO4)2,"Using $^{31}$P nuclear magnetic resonance (NMR) we investigate the recently
discovered presaturation phase in the highly frustrated two-dimensional spin
system SrZnVO(PO$_4$)$_2$ [F. Landolt et al., Phys. Rev. B 104, 224435 (2021)].
Our data provide two pieces of evidence against the presumed spin-nematic
character of this phase: i) NMR spectra reveal that it hosts a dipolar spin
order and ii) the 1/$T_1$ relaxation rate data recorded above the saturation
field can be fitted by the sum of a single-magnon term, exponential in the gap,
and a critical second-order term, exponential in the triple gap, leaving no
space for a nematic spin dynamics, characterized by a double-gap exponential.
We explain the unexpectedly broad validity of the simple fit and the related
critical spin dynamics.",2112.12603v2
2022-03-11,Rotational viscosity in spin resonance of hydrodynamic electrons,"In novel ultra-pure materials electrons can form a viscous fluid, which is
fundamentally different by its dynamics from the electron gas in ordinary
conductors with significant density of defects. The shape of the non-stationary
flow of such electron fluid is similar to the alternating flow of blood in
large-radius arteries [J. R. Womersley, J. Physiol. 127, 552 (1955)]. The
rotational viscosity effect is responsible for interconnection between the
dynamics of electron spins and flow inhomogeneities. In particular, it induces
the spin polarization of electrons in a curled flow via an internal spin-orbit
torque acting on electron spins. Here we show that this effect in an electron
fluid placed in a magnetic field leads to a correction to the ac sample
impedance, which has a resonance at the Larmor frequency of electrons. In this
way, via the electrically detected spin resonance the Womersley flow of an
electron fluid can be visualized and the rotational viscosity can be measured.",2203.06070v4
2022-04-20,Controlling atomic spin-mixing via multiphoton transitions in a cavity,"We propose to control spin-mixing dynamics in a gas of spinor atoms, via the
combination of two off-resonant Raman transition pathways, enabled by a common
cavity mode and a bichromatic pump laser. The mixing rate, which is
proportional to the synthesized spin-exchange interaction strength, and the
effective atomic quadratic Zeeman shift (QZS), can both be tuned by changing
the pump laser parameters. Quench and driving dynamics of the atomic collective
spin are shown to be controllable on a faster time scale than in existing
experiments based on inherent spin-exchange collision interactions. The results
we present open a promising avenue for exploring spin-mixing physics of atomic
ensembles accessible in current experiments.",2204.09609v1
2022-06-13,Vanadium in Silicon Carbide: Telecom-ready spin centres with long relaxation lifetimes and hyperfine-resolved optical transitions,"Vanadium in silicon carbide (SiC) is emerging as an important candidate
system for quantum technology due to its optical transitions in the telecom
wavelength range. However, several key characteristics of this defect family
including their spin relaxation lifetime (T1), charge state dynamics, and level
structure are not fully understood. In this work, we determine the T1 of an
ensemble of vanadium defects, demonstrating that it can be greatly enhanced at
low temperature. We observe a large spin contrast exceeding 90% and long
spin-relaxation times of up to 25s at 100mK, and of order 1s at 1.3K. These
measurements are complemented by a characterization of the ensemble charge
state dynamics. The stable electron spin furthermore enables high-resolution
characterization of the systems' hyperfine level structure via two-photon
magneto-spectroscopy. The acquired insights point towards high-performance
spin-photon interfaces based on vanadium in SiC.",2206.06240v1
2022-07-07,Towards effective actions for the continuum limit of spin foams,"Spin foams arise from a quantization of classical gravity expressed via the
Plebanski action. Key open questions related to the continuum limit of spin
foams are whether general relativity is reproduced and what type of corrections
could emerge. As a central component for spin foam dynamics, recent results on
the continuum limit of the Area Regge action suggest a close relation with
actions for area metrics instead of a length metric. Inspired by these results,
within the framework of modified Plebanski theory we construct a family of
candidate actions for area metrics. These actions are expected to describe the
continuum limit of spin foams and provide a starting point to explore
phenomenological aspects of the large-scale dynamics of spin foams. More
generally, they set the stage for exploring consequences of an enlargement of
the configuration space for gravity from length to area metrics. The actions we
construct lead to an effective action for the length metric, describing a
non-local and ghost-free version of Einstein-Weyl gravity.",2207.03307v2
2022-11-24,Elliptic soliton solutions of the spin non-chiral intermediate long-wave equation,"We construct elliptic multi-soliton solutions of the spin non-chiral
intermediate long-wave (sncILW) equation with periodic boundary conditions.
These solutions are obtained by a spin-pole ansatz including a dynamical
background term; we show that this ansatz solves the periodic sncILW equation
provided the spins and poles satisfy the elliptic $A$-type spin Calogero-Moser
(sCM) system with certain constraints on the initial conditions. The key to
this result is a B\""{a}cklund transformation for the elliptic sCM system which
includes a non-trivial dynamical background term. We also present solutions of
the sncILW equation on the real line and of the spin Benjamin-Ono equation
which generalize previously obtained solutions by allowing for a non-trivial
background term.",2211.13791v1
2023-02-20,Spin squeezing in open Heisenberg spin chains,"Spin squeezing protocols successfully generate entangled many-body quantum
states, the key pillars of the second quantum revolution. In our recent work
[Phys. Rev. Lett. 129, 090403 (2022)] we showed that spin squeezing described
by the one-axis twisting model could be generated in the Heisenberg spin-1/2
chain with periodic boundary conditions when accompanied by a
position-dependent spin-flip coupling induced by a single laser field. This
work shows analytically that the change of boundary conditions from the
periodic to the open ones significantly modifies spin squeezing dynamics. A
broad family of twisting models can be simulated by the system in the weak
coupling regime, including the one- and two-axis twisting under specific
conditions, providing the Heisenberg level of squeezing and acceleration of the
dynamics. Full numerical simulations confirm our analytical findings.",2302.09829v2
2023-02-21,Micromagnetic study of inertial spin waves in ferromagnetic nanodots,"Here we report the possibility to excite ultra-short spin waves in
ferromagnetic thin-films by using time-harmonic electromagnetic fields with
terahertz frequency. Such ultra-fast excitation requires to include inertial
effects in the description of magnetization dynamics. In this respect, we
consider the inertial Landau-Lifshitz-Gilbert (iLLG) equation and develop
analytical theory for exchange-dominated inertial spin waves. The theory
predicts a finite limit for inertial spin wave propagation velocity, as well as
spin wave spatial decay and lifetime as function of material parameters. Then,
guided by the theory, we perform numerical micromagnetic simulations that
demonstrate the excitation of ultra-short inertial spin waves (20 nm long)
propagating at finite speed in a confined magnetic nanodot. The results are in
agreement with the theory and provide the order of magnitude of quantities
observable in realistic ultra-fast dynamics experiments.",2302.10759v2
2023-03-13,Intrinsic spin-orbit torque mechanism for deterministic all-electric switching of noncollinear antiferromagnets,"Using a pure electric current to control kagome noncollinear antiferromagnets
is promising in information storage and processing, but a full description is
still lacking, in particular, on intrinsic (i.e., no external magnetic fields
or external spin currents) spin-orbit torques. In this work, we
self-consistently describe the relations among the electronic structure,
magnetic structure, spin accumulations, and intrinsic spin-orbit torques, in
the magnetic dynamics of a noncollinear antiferromagnet driven by a pure
electric current. Our calculation can yield a critical current density
comparable with those in the experiments, when considering the boost from the
out-of-plane magnetic dynamics induced by the current-driven spin accumulation
on individual magnetic moments. We stress the parity symmetry breaking in
deterministic switching among magnetic structures. This work will be helpful
for future applications of noncollinear antiferromagnets.",2303.06929v2
2023-04-11,Observation of orbital pumping,"Harnessing spin and orbital angular momentum is a fundamental concept in
condensed matter physics, materials science, and quantum-device applications.
In particular, the search for new phenomena that generate a flow of spin
angular momentum, a spin current, has led to the development of spintronics,
advancing the understanding of angular momentum dynamics at the nanoscale. In
contrast to this success, the generation and detection of orbital currents, the
orbital counterpart of spin currents, remains a significant challenge. Here, we
report the observation of orbital pumping, a phenomenon in which magnetization
dynamics pumps an orbital current, a flow of orbital angular momentum. The
orbital pumping is the orbital counterpart of the spin pumping, which is one of
the most versatile and powerful mechanisms for spin-current generation. We show
that the orbital pumping in Ni/Ti bilayers injects an orbital current into the
Ti layer, which is detected through the inverse orbital Hall effect. Our
findings provide a promising approach for generating orbital currents and pave
the way for exploring the physics of orbital transport in solids.",2304.05266v2
2023-05-03,"Impacts of the half-skyrmion spin topology, spin-orbit torque, and dynamic symmetry breaking on the growth of magnetic stripe domains","We have performed an experimental and modeling-based study of the spin-orbit
torque-induced growth of magnetic stripe domains in heavy metal/ferromagnet
thin-film heterostructures that possess chiral N\'eel-type domain walls due to
an interfacial Dzyaloshinskii-Moriya interaction. In agreement with previous
reports, the stripe domains stabilized in these systems exhibit a significant
transverse growth velocity relative to the applied current axis. This behavior
has previously been attributed to the Magnus force-like skyrmion Hall effect of
the stripe domain spin topology, which is analogous to that of a half-skyrmion.
However, through analytic modeling of the in-plane torques generated by
spin-orbit torque, we find that a dynamical reconfiguration of the domain wall
magnetization profile is expected to occur - promoting motion with similar
directionality and symmetry as the skyrmion Hall effect. These results further
highlight the sensitivity of spin-orbit torque to the local orientation of the
domain wall magnetization profile and its contribution to domain growth
directionality.",2305.02181v1
2023-07-10,Angular dependence of spin-orbit torque in monolayer $Fe_3GeTe_2$,"In ferromagnetic systems lacking inversion symmetry, an applied electric
field can control the ferromagnetic order parameters through the spin-orbit
torque. The prototypical example is a bilayer heterostructure composed of a
ferromagnet and a heavy metal that acts as a spin current source. In addition
to such bilayers, spin-orbit coupling can mediate spin-orbit torques in
ferromagnets that lack bulk inversion symmetry. A recently discovered example
is the two-dimensional monolayer ferromagnet $Fe_3GeTe_2$. In this work, we use
first-principles calculations to study the spin-orbit torque and ensuing
magnetic dynamics in this material. By expanding the torque versus
magnetization direction as a series of vector spherical harmonics, we find that
higher order terms (up to $\ell=4$) are significant and play important roles in
the magnetic dynamics. They give rise to deterministic, magnetic field-free
electrical switching of perpendicular magnetization.",2307.04900v2
2023-07-24,Spin-dependent gain and loss in photonic quantum spin Hall systems,"Topological phases are greatly enriched by including non-Hermiticity. While
most works focus on the topology of the eigenvalues and eigenstates, how
topologically nontrivial non-Hermitian systems behave in dynamics has only
drawn limited attention. Here, we consider a breathing honeycomb lattice known
to emulate the quantum spin Hall effect and exhibits higher-order corner modes.
We find that non-reciprocal intracell couplings introduce gain in one
pseudo-spin subspace while loss with the same magnitude in the other. In
addition, non-reciprocal intracell couplings can also suppress the spin mixture
of the edge modes at the boundaries and delocalize the higher-order corner
mode. Our findings deepen the understanding of non-Hermitian topological phases
and bring in the spin degree of freedom in manipulating the dynamics in
non-Hermitian systems.",2307.12503v1
2023-07-31,Persistent spin dynamics in magnetically ordered honeycomb cobalt oxides,"In the quest to find quantum spin liquids, layered cobalt oxides Na2Co2TeO6
and Na3Co2SbO6 have been proposed as promising candidates for approximating the
Kitaev honeycomb model. Yet, their suitability has been thrown into question
due to observed long-range magnetic order at low temperatures and indications
of easy-plane, rather than Kitaev-type, spin anisotropy. Here we use muon spin
relaxation to reveal an unexpected picture: contrary to the anticipated static
nature of the long-range order, the systems show prevalent spin dynamics with
spatially uneven distribution and varied correlation times. This underlines
that the magnetic ground states cannot be solely described by the long-range
order, suggesting a significant role of quantum fluctuations. Our findings not
only shed new light on the complex physics of these systems but also underscore
the need for a refined approach in the search for realizable quantum spin
liquids.",2307.16451v1
2023-10-25,Photo-induced electronic and spin topological phase transitions in monolayer bismuth,"Ultrathin bismuth exhibits rich physics including strong spin-orbit coupling,
ferroelectricity, nontrivial topology, and light-induced structural dynamics.
We use \textit{ab initio} calculations to show that light can induce structural
transitions to four transient phases in bismuth monolayers. These light-induced
phases exhibit nontrivial topological character, which we illustrate using the
recently introduced concept of spin bands and spin-resolved Wilson loops.
Specifically, we find that the topology changes via the closing of the electron
and spin band gaps during photo-induced structural phase transitions, leading
to distinct edge states. Our study provides strategies to tailor electronic and
spin topology via ultrafast control of photo-excited carriers and associated
structural dynamics.",2310.16886v2
2023-11-27,Analysis of spin-squeezing generation in cavity-coupled atomic ensembles with continuous measurements,"We analyze the generation of spin-squeezed states by coupling three-level
atoms to an optical cavity and continuously measuring the cavity transmission
in order to monitor the evolution of the atomic ensemble. Using analytical
treatment and microscopic simulations of the dynamics, we show that one can
achieve significant spin squeezing even without the continuous feedback that is
proposed in optimal approaches. In the adiabatic cavity removal approximation
and large number of atoms $N$ limit, we find the scaling exponents $N^{-2/3}$
for spin squeezing and $N^{-1/3}$ for the corresponding protocol duration,
which are crucially impacted by the collective Bloch sphere curvature. With
full simulations, we characterize how spin-squeezing generation depends on the
system parameters and departs from the bad cavity regime, by gradually mixing
with cavity-filling dynamics until metrological advantage is lost. Finally, we
discuss the relevance of this spin-squeezing protocol to state-of-the-art
optical clocks.",2311.15725v2
2023-12-13,Hubbard physics with Rydberg atoms: using a quantum spin simulator to simulate strong fermionic correlations,"We propose a hybrid quantum-classical method to investigate the equilibrium
physics and the dynamics of strongly correlated fermionic models with
spin-based quantum processors. Our proposal avoids the usual pitfalls of
fermion-to-spin mappings thanks to a slave-spin method which allows to
approximate the original Hamiltonian into a sum of self-correlated
free-fermions and spin Hamiltonians. Taking as an example a Rydberg-based
analog quantum processor to solve the interacting spin model, we avoid the
challenges of variational algorithms or Trotterization methods. We explore the
robustness of the method to experimental imperfections by applying it to the
half-filled, single-orbital Hubbard model on the square lattice in and out of
equilibrium. We show, through realistic numerical simulations of current
Rydberg processors, that the method yields quantitatively viable results even
in the presence of imperfections: it allows to gain insights into equilibrium
Mott physics as well as the dynamics under interaction quenches. This method
thus paves the way to the investigation of physical regimes -- whether
out-of-equilibrium, doped, or multiorbital -- that are difficult to explore
with classical processors.",2312.08065v2
2024-01-08,Composite cores of monopoles and Alice rings in spin-2 Bose-Einstein condensates,"We show that energy relaxation causes a point defect in the uniaxial-nematic
phase of a spin-2 Bose-Einstein condensate to deform into a spin-Alice ring
that exhibits a composite core structure with distinct topology at short and
long distances from the singular line. An outer biaxial-nematic core exhibits a
spin half-quantum vortex structure with a uniaxial-nematic inner core. By
numerical simulation we demonstrate a dynamical oscillation between the
spin-Alice ring and a split-core hedgehog configuration via the appearance of
ferromagnetic rings with associated vorticity inside an extended core region.
We further show that a similar dynamics is exhibited by a spin-Alice ring
surrounding a spin-vortex line resulting from the relaxation of a monopole
situated on a spin-vortex line in the biaxial-nematic phase. In the cyclic
phase similar states are shown instead to form extended phase-mixing cores
containing rings with fractional mass circulation or cores whose spatial shape
reflect the order-parameter symmetry of cyclic inner core, depending on the
initial configuration.",2401.04103v1
2024-01-22,Active Inference Demonstrated with Artificial Spin Ice,"A numerical model of interacting nanomagnetic elements is used to demonstrate
active inference with a three dimensional Artificial Spin Ice structure. It is
shown that thermal fluctuations can drive this magnetic spin system to evolve
under dynamic constraints imposed through interactions with an external
environment as predicted by the neurological free energy principle and active
inference. The structure is defined by two layers of magnetic nanoelements
where one layer is a square Artificial Spin Ice geometry. The other magnetic
layer functions as a sensory filter that mediates interaction between the
external environment and the hidden Artificial Spin Ice layer. Spin dynamics
displayed by the bilayer structure are shown to be well described using a
continuous form of a neurological free energy principle that has been
previously proposed as a high level description of certain biological neural
processes. Numerical simulations demonstrate that this proposed bilayer
geometry is able to reproduce theoretical results derived previously for
examples of active inference in neurological contexts.",2401.12211v4
2008-12-26,Thermalization dynamics close to a quantum phase transition,"We investigate the dissipative dynamics of a quantum critical system in
contact with a thermal bath. In analogy with the standard protocol employed to
analyze aging, we study the response of a system to a sudden change of the bath
temperature. The specific example of the XY model in a transverse magnetic
field whose spins are locally coupled to a set of bosonic baths is considered.
The peculiar nature of the dynamics is encoded in the correlations developing
out of equilibrium. By means of a kinetic equation we analyze the spin-spin
correlations and block correlations. We identify some universal features in the
out-of-equilibrium dynamics. Two distinct regimes, characterized by different
time and length scales, emerge. During the initial transient the dynamics is
characterized by the same critical exponents as those of the equilibrium
quantum phase transition and resembles the dynamics of thermal phase
transitions. At long times equilibrium is reached through the propagation along
the chain of a thermal front in a manner similar to the classical Glauber
dynamics.",0812.4717v2
2013-06-04,Dynamic susceptibility and dynamic correlations in spin ice,"Here we calculate the dynamic susceptibility and dynamic correlation function
in spin ice using the model of emergent magnetic monopoles. Calculations are
based on a method originally suggested for the description of dynamic processes
in water ice (non-equilibrium thermodynamics approach). We show that for zero
temperature the dynamic correlation function reproduces the transverse dipole
correlations (static correlation function) characteristic of spin ice in its
ground state. At non-zero temperatures the dynamic correlation function
includes an additional longitudinal component which decreases as the
temperature decreases. Both terms (transverse and longitudinal) exhibit
identical Debye-like dependences on frequency but with different relaxation
times: the magnetic Coulomb interaction of monopoles reduces the longitudinal
relaxation time with respect to the transverse one. We calculate the dielectric
function for the magnetic monopole gas and discuss how the non-equilibrium
thermodynamics approach exposes corrections to the Debye-Huckel theory of
magnetic monopoles and the concept of ""entropic charge"".",1306.0653v1
2019-08-23,Massively parallel atomistic simulation of ultrafast thermal spin dynamics of a permalloy vortex,"Ultrafast magnetization dynamics probes the most fundamental properties of
magnetic materials, exploring questions about the fundamental interactions
responsible for magnetic phenomena. Thermal effects are known to be extremely
important for laser-induced dynamics in metallic systems, but the dynamics of
topological magnetic structures are little understood. Here we apply a
massively parallel atomistic spin dynamics simulation to study the response of
a permalloy vortex to a 50 fs laser pulse. We find that macroscopically the
short timescale dynamics are indistinguishable from the bulk, but that strong
edge spin waves lead to a complex time evolution of the magnetic structure and
long-lived oscillations on the nanosecond timescale. In the near future such
simulations will provide unprecedented insight into the dynamics of magnetic
materials and devices beyond the approximations of continuum micromagnetics.",1908.08885v1
2020-06-22,The dynamics of a driven harmonic oscillator coupled to independent Ising spins in random fields,"We aim at an understanding of the dynamical properties of a periodically
driven damped harmonic oscillator coupled to a Random Field Ising Model (RFIM)
at zero temperature, which is capable to show complex hysteresis. The system is
a combination of a continuous (harmonic oscillator) and a discrete (RFIM)
subsystem, which classifies it as a hybrid system. In this paper we focus on
the hybrid nature of the system and consider only independent spins in quenched
random local fields, which can already lead to complex dynamics such as chaos
and multistability. We study the dynamic behavior of this system by using the
theory of piecewise-smooth dynamical systems and discontinuity mappings.
Specifically, we present bifurcation diagrams, Lyapunov exponents as well as
results for the shape and the dimensions of the attractors and the
self-averaging behavior of the attractor dimensions and the magnetization.
Furthermore we investigate the dynamical behavior of the system for an
increasing number of spins and the transition to the thermodynamic limit, where
the system behaves like a driven harmonic oscillator with an additional
nonlinear smooth external force.",2006.12588v2
2020-10-23,Dynamical replica analysis of quantum annealing,"Quantum annealing aims to provide a faster method for finding the minima of
complicated functions, compared to classical computing, so there is an
increasing interest in the relaxation dynamics of quantum spin systems.
Moreover, it is known that problems in quantum annealing caused by first order
phase transitions can be reduced via appropriate temporal adjustment of control
parameters, aimed at steering the system away from local minima. To do this
optimally, it would be helpful to predict the evolution of the system at the
level of macroscopic observables. Solving the dynamics of a quantum ensemble is
nontrivial, as it requires modelling not just the quantum spin system itself
but also its interaction with the environment, with which it exchanges energy.
An interesting alternative approach to the dynamics of quantum spin systems was
proposed about a decade ago. It involves creating a stochastic proxy dynamics
via the Suzuki-Trotter mapping of the quantum ensemble to a classical one (the
quantum Monte Carlo method), and deriving from this new dynamics closed
macroscopic equations for macroscopic observables, using the dynamical replica
method. In this chapter we give an introduction to this approach, focusing on
the ideas and assumptions behind the derivations, and on its potential and
limitations.",2010.12334v1
2022-05-04,Exceptional points as signatures of dynamical magnetic phase transitions,"One of the most fascinating and puzzling aspects of non-Hermitian systems is
their spectral degeneracies, i.e., exceptional points (EPs), at which both
eigenvalues and eigenvectors coalesce to form a defective state space. While
coupled magnetic systems are natural hosts of EPs, the relation between the
linear and nonlinear spin dynamics in the proximity of EPs remains relatively
unexplored. Here we theoretically investigate the spin dynamics of easy-plane
magnetic bilayers in the proximity of exceptional points. We show that the
interplay between the intrinsically dissipative spin dynamics and external
drives can yield a rich dynamical phase diagram. In particular, we find that,
in antiferromagnetically coupled bilayers, a periodic oscillating dynamical
phase emerges in the region enclosed by EPs. Our results not only offer a
pathway for probing magnetic EPs and engineering magnetic nano-oscillators with
large-amplitude oscillations, but also uncover the relation between exceptional
points and dynamical phase transitions in systems displaying non-linearities.",2205.02308v2
2013-01-14,Polarised Electromagnetic wave propagation through the ferromagnet: Phase boundary of dynamic phase transition,"The dynamical responses of ferromagnet to the propagating electromagnetic
field wave passing through it are modelled and studied here by Monte Carlo
simulation in two dimensional Ising ferromagnet. Here, the electromagnetic wave
is linearly polarised in such a way that the direction of magnetic field is
parallel to that of the magnetic momemts (spins). The coherent propagating mode
of spin-clusters is observed. The time average magnetisation over the full
cycle (time) of the field defines the order parameter of the dynamic
transition. Depending on the value of the temperature and the amplitude of the
propagating magnetic field wave, a dynamical phase transition is observed. The
dynamic transition was detected by studying the temperature dependences of the
dynamic order parameter, the variance of the dynamic order parameter, the
derivative of the dynamic order parameter and the dynamic specific heat. The
phase boundaries of the dynamic transitions were drawn for two different values
of the wave lengths of the propagating magnetic field wave. The phase boundary
was observed to shrink (inward) for lower speed of propagation of the EM wave.
The divergence of the releavant length scale was observed at the transition
point.",1301.3071v2
2019-05-09,Dynamical Topological Phase Transition in a Bose-Einstein Condensate,"We study a Bose-Einstein condensate (BEC) at low energy limit and show that
their collective dynamics exhibit interesting topological behavior. The system
undergoes dynamical topological phase transition at its global periods if its
dispersion relation is strictly linear and when all of the bosonic mode are
properly displaced from their equilibrium position. We corroborate the
occurrence of dynamical phase transition by calculating Fisher zeros of the
Loschmidt amplitude for sudden quench dynamics. A connection is established
between the order of nonanalycity in the accumulated geometric phase and the
spectral density of the system. Furthermore, it is shown that a power law
scaling holds at all critical times for various displacement spectra, whose
dynamical exponent equals unity. Eventually, a scheme for the quantum
simulation of such dynamical phase transition is proposed. The scheme is based
on the vibrational spectrum of a free-standing membrane of a two-dimensional
material. To induce a displacement in the system and for tracking its
collective geometrical dynamics, we propose to employ a spin that properly
couples to the modes. When appropriate geometrical and boundary conditions are
applied to the membrane, a spectrum with linear dispersion is attainable, then
decoherence dynamics of the spin unveils occurrence of a dynamical topological
phase transition.",1905.03455v1
2004-10-14,The distribution and cosmic evolution of massive black hole spins,"We study the expected distribution of massive black hole (MBH) spins and its
evolution with cosmic time in the context of hierarchical galaxy formation
theories. Our model uses Monte Carlo realizations of the merger hierarchy in a
LCDM cosmology, coupled to semi-analytical recipes, to follow the merger
history of dark matter halos, the dynamics of the MBHs they host, and their
growth via gas accretion and binary coalescences. The coalescence of comparable
mass holes increases the spin of MBHs, while the capture of smaller companions
in randomly-oriented orbits acts to spin holes down. We find that, given the
distribution of MBH binary mass ratios in hierarchical models, binary
coalescences alone do not lead to a systematic spin-up or spin-down of MBHs
with time: the spin distribution retains memory of its initial conditions. By
contrast, because of the Bardeen-Petterson effect, gas accretion via a thin
disk tends to spin holes up even if the direction of the spin axis changes
randomly in time. In our models, accretion dominates over black hole captures
and efficiently spins holes up. The spin distribution is heavily skewed towards
fast-rotating Kerr holes, is already in place at early epochs, and does not
change much below redshift 5. If accretion is via a thin disk, about 70% of all
MBHs are maximally rotating and have radiative efficiencies approaching 30%
(assuming a ""standard'' spin-efficiency conversion). Even in the conservative
case where accretion is via a geometrically thick disk, about 80% of all MBHs
have spin parameters a/m > 0.8 and accretion efficiencies > 12%. Rapidly
spinning holes with high radiative efficiencies may satisfy constraints based
on comparing the local MBH mass density with the mass density inferred from
luminous quasars (Soltan's argument).",0410342v1
2015-03-12,Theory of box-model hyperfine couplings and transport signatures of long-range nuclear-spin coherence in a quantum-dot spin valve,"We have theoretically analyzed coherent nuclear-spin dynamics induced by
electron transport through a quantum-dot spin valve. The hyperfine interaction
between electron and nuclear spins in a quantum dot allows for the transfer of
angular momentum from spin-polarized electrons injected from ferromagnetic or
half-metal leads to the nuclear spin system under a finite voltage bias.
Accounting for a local nuclear-spin dephasing process prevents the system from
becoming stuck in collective dark states, allowing a large nuclear polarization
to be built up in the long-time limit. After reaching a steady state, reversing
the voltage bias induces a transient current response as the nuclear
polarization is reversed. Long-range nuclear-spin coherence leads to a strong
enhancement of spin-flip transition rates (by an amount proportional to the
number of nuclear spins) and is revealed by an intense current burst, analogous
to superradiant light emission. The crossover to a regime with incoherent spin
flips occurs on a relatively long time scale, on the order of the
single-nuclear-spin dephasing time, which can be much longer than the time
scale for the superradiant current burst. This conclusion is confirmed through
a general master equation. For the two limiting regimes (coherent/incoherent
spin flips) the general master equation recovers our simpler treatment based on
rate equations, but is also applicable at intermediate dephasing. Throughout
this work we assume uniform hyperfine couplings, which yield the strongest
coherent enhancement. We propose realistic strategies, based on isotopic
modulation and wavefunction engineering in core-shell nanowires, to realize
this analytically solvable ""box-model"" of hyperfine couplings.",1503.03645v2
2020-07-20,Kinetic approach to the nuclear-spin polaron formation,"Under optical cooling of nuclei, a strongly correlated nuclear-spin polaron
state can form in semiconductor nanostructures with localized charge carriers
due to the strong hyperfine interaction of the localized electron spin with the
surrounding nuclear spins. Here we develop a kinetic-equation formalism
describing the nuclear-spin polaron formation. We present a derivation of the
kinetic equations for an electron-nuclear spin system coupled to reservoirs of
different electron and nuclear spin temperatures which generate the exact
thermodynamic steady state for equal temperatures independent of the system
size. We illustrate our approach using the analytical solution of the central
spin model in the limit of an Ising form of the hyperfine coupling. For
homogeneous hyperfine coupling constants, i.e., the box model, the model is
reduced to an analytically solvable form. Based on the analysis of the
nuclear-spin distribution function and the electron-nuclear spin correlators,
we derive a relation between the electron and nuclear spin temperatures, where
the correlated nuclear-spin polaron state is formed. In the limit of large
nuclear baths, this temperature line coincides with the critical temperature of
the mean-field theory for polaron formation. The criteria of the polaron
formation in a finite-size system are discussed. We demonstrate that the
system's behavior at the transition temperature does not depend on details of
the hyperfine-coupling distribution function but only on the effective number
of coupled bath spins. In addition, the kinetic equations enable the analysis
of the temporal formation of the nuclear-polaron state, where we find the
build-up process predominated by the nuclear spin-flip dynamics.",2007.10138v2
2018-09-28,Engineering long spin coherence times of spin-orbit systems,"Spin-orbit coupling fundamentally alters spin qubits, opening pathways to
improve the scalability of quantum computers via long distance coupling
mediated by electric fields, photons, or phonons. It also allows for new
engineered hybrid and topological quantum systems. However, spin qubits with
intrinsic spin-orbit coupling are not yet viable for quantum technologies due
to their short ($\sim1~\mu$s) coherence times $T_2$, while qubits with long
$T_2$ have weak spin-orbit coupling making qubit coupling short-ranged and
challenging for scale-up. Here we show that an intrinsic spin-orbit coupled
""generalised spin"" with total angular momentum $J=\tfrac{3}{2}$, which is
defined by holes bound to boron dopant atoms in strained $^{28}\mathrm{Si}$,
has $T_2$ rivalling the electron spins of donors and quantum dots in
$^{28}\mathrm{Si}$. Using pulsed electron paramagnetic resonance, we obtain
$0.9~\mathrm{ms}$ Hahn-echo and $9~\mathrm{ms}$ dynamical decoupling $T_2$
times, where strain plays a key role to reduce spin-lattice relaxation and the
longitudinal electric coupling responsible for decoherence induced by electric
field noise. Our analysis shows that transverse electric dipole can be
exploited for electric manipulation and qubit coupling while maintaining a weak
longitudinal coupling, a feature of $J=\tfrac{3}{2}$ atomic systems with a
strain engineered quadrupole degree of freedom. These results establish
single-atom hole spins in silicon with quantised total angular momentum, not
spin, as a highly coherent platform with tuneable intrinsic spin-orbit coupling
advantageous to build artificial quantum systems and couple qubits over long
distances.",1809.10859v2
2017-09-22,Using spin to understand the formation of LIGO's black holes,"With the detection of four candidate binary black hole (BBH) mergers by the
Advanced LIGO detectors thus far, it is becoming possible to constrain the
properties of the BBH merger population in order to better understand the
formation of these systems. Black hole (BH) spin orientations are one of the
cleanest discriminators of formation history, with BHs in dynamically formed
binaries in dense stellar environments expected to have spins distributed
isotropically, in contrast to isolated populations where stellar evolution is
expected to induce BH spins preferentially aligned with the orbital angular
momentum. In this work we propose a simple, model-agnostic approach to
characterizing the spin properties of LIGO's BBH population. Using measurements
of the effective spin of the binaries, which is LIGO's best constrained spin
parameter, we introduce a simple parameter to quantify the fraction of the
population that is isotropically distributed, regardless of the spin magnitude
distribution of the population. Once the orientation characteristics of the
population have been determined, we show how measurements of effective spin can
be used to directly constrain the underlying BH spin magnitude distribution.
Although we find that the majority of the current effective spin measurements
are too small to be informative, with LIGO's four BBH candidates we find a
slight preference for an underlying population with aligned spins over one with
isotropic spins (with an odds ratio of 1.1). We argue that it will be possible
to distinguish symmetric and anti-symmetric populations at high confidence with
tens of additional detections, although mixed populations may take
significantly more detections to disentangle. We also derive preliminary spin
magnitude distributions for LIGO's black holes, under the assumption of aligned
or isotropic populations.",1709.07896v1
2018-06-06,"Decay and revival of electron spin polarization in an ensemble of (In,Ga)As quantum dots","The periodic optical orientation of electron spins in (In,Ga)As/GaAs quantum
dots leads to the formation of electron spin precession modes about an external
magnetic field which are resonant with the pumping periodicity. As the electron
spin is localized within a nuclear spin bath, its polarization imprints onto
the spin polarization of the bath. The latter acts back on the electron spin
polarization. We implement a pulse protocol where a train of laser pulses is
followed by a long, dark gap. It allows us to obtain a high-resolution
precession mode spectrum from the free evolution of the electron spin
polarization. Additionally, we vary the number of pump pulses in a train to
investigate the build-up of the precession modes. To separate out nuclear
effects, we suppress the nuclear polarization by using a radio-frequency field.
We find that a long-living nuclear spin polarization imprinted by the periodic
excitation significantly speeds up the buildup of the electron spin
polarization and induces the formation of additional electron spin precession
modes. To interpret these findings, we extend an established dynamical nuclear
polarization model to take into account optically detuned quantum dots for
which nuclear spins activate additional electron spin precession modes.",1806.02268v2
2019-11-18,Optical control of an individual Cr spin in a semiconductor quantum dot,"We demonstrate that the spin of a Cr atom in a quantum dot (QD) can be
controlled optically and we discuss the main properties of this single spin
system. The photoluminescence of individual Cr-doped QDs and their evolution in
magnetic field reveal a large magnetic anisotropy of the Cr spin induced by
local strain. This results in a splitting of the Cr spin states and in a
thermalization on the lower energy states states S$_z$=0 and S$_z$=$\pm$1. The
magneto-optical properties of Cr-doped QDs can be modelled by an effective spin
Hamiltonian including the spin to strain coupling and the influence of the QD
symmetry. We also show that a single Cr spin can be prepared by resonant
optical pumping. Monitoring the intensity of the resonant fluorescence of the
QD during this process permits to probe the dynamics of the optical
initialization of the spin. Hole-Cr flip-flops induced by an interplay of the
hole-Cr exchange interaction and the coupling with acoustic phonons are the
main source of relaxation that explains the efficient resonant optical pumping.
The Cr spin relaxation time is measured in the $\mu s$ range. We evidence that
a Cr spin couples to non-equilibrium acoustic phonons generated during the
optical excitation inside or near the QD). Finally we show that the energy of
any spin state of an individual Cr atom can be independently tuned by a
resonant single mode laser through the optical Stark effect. All these
properties make Cr-doped QDs very promising for the development of hybrid
spin-mechanical systems where a coherent mechanical driving of an individual
spin in an oscillator is required.",1911.08572v1
2021-09-03,Building better spin models for merging binary black holes: Evidence for non-spinning and rapidly spinning nearly aligned sub-populations,"Recent work paints a conflicting portrait of the distribution of black hole
spins in merging binaries measured with gravitational waves. Some analyses find
that a significant fraction of merging binaries contain at least one black hole
with a spin tilt $>90^\circ$ with respect to the orbital angular momentum
vector, which has been interpreted as a signature for dynamical assembly. Other
analyses find the data are consistent with a bimodal population in which some
binaries contain black holes with negligible spin while the rest contain black
holes with spin vectors preferentially aligned with the orbital angular
momentum vector. In this work, we scrutinize models for the distribution of
black hole spins to pinpoint possible failure modes in which the model yields a
faulty conclusion. We reanalyze data from the second LIGO--Virgo
gravitational-wave transient catalog (GWTC-2) using a revised spin model, which
allows for a sub-population of black holes with negligible spins. In agreement
with recent results by Roulet et al., we show that the GWTC-2 detections are
consistent with two distinct sub-populations. We estimate that $29-75\%$ (90\%
credible interval) of merging binaries contain black holes with negligible spin
$\chi \approx 0$. The remaining binaries are part of a second sub-population in
which the spin vectors are preferentially (but not exactly) aligned to the
orbital angular momentum. The black holes in this second sub-population are
characterized by spins of $\chi\sim0.45$. We suggest that the inferred spin
distribution is consistent with the hypothesis that all merging binaries form
via the field formation scenario.",2109.02424v3
2022-12-10,Nuclear spin relaxation in cold atom-molecule collisions,"We explore the quantum dynamics of nuclear spin relaxation in cold collisions
of $^1\Sigma^+$ molecules with structureless atoms in an external magnetic
field. To this end, we develop a rigorous coupled-channel methodology, which
accounts for rotational and nuclear spin degrees of freedom of $^1\Sigma^+$
molecules, their interaction with an external magnetic field, as well as for
anisotropic atom-molecule interactions. We apply the methodology to study
collisional relaxation of the nuclear spin sublevels of $^{13}$CO molecules
immersed in a cold buffer gas of $^4$He atoms. We find that nuclear spin
relaxation in the ground rotational manifold of CO occurs extremely slowly due
to the absence of direct couplings between the nuclear spin sublevels. The
rates of collisional transitions between the $N=1$ nuclear spin states of CO
are generally much higher due to the direct nuclear spin-rotation coupling
between the states. These transitions obey selection rules, which depend on the
values of space-fixed projections of rotational and nuclear spin angular
momenta for the initial and final molecular states. For some initial states, we
also observe a strong magnetic field dependence, which can be understood using
the first Born approximation. We use our calculated nuclear spin relaxation
rates to investigate the thermalization of a single nuclear spin state of
CO$(N=0)$ immersed in a cold buffer gas of He. The calculated nuclear spin
relaxation times ($T_1\simeq 0.5$ s at $T=1$ K) display a steep temperature
dependence decreasing rapidly at elevated temperatures due to the increased
population of rotationally excited states, which undergo nuclear spin
relaxation at a much faster rate. Thus, long relaxation times of $N=0$ nuclear
spin states in cold collisions with buffer gas atoms can only be maintained at
sufficiently low temperatures ($kT\ll 2B_e$), where $B_e$ is the rotational
constant.",2212.05363v2
2016-02-02,Carrier-impurity spin transfer dynamics in paramagnetic II-VI diluted magnetic semiconductors in the presence of a wave-vector-dependent magnetic field,"Quantum kinetic equations of motion for carrier and impurity spins in
paramagnetic II-VI diluted magnetic semiconductors in a $\mathbf{k}$-dependent
effective magnetic field are derived, where the carrier-impurity correlations
are taken into account. In the Markov limit, rates for the electron-impurity
spin transfer can be derived for electron spins parallel and perpendicular to
the impurity spins corresponding to measurable decay rates in Kerr experiments
in Faraday and Voigt geometry. Our rigorous microscopic quantum kinetic
treatment automatically accounts for the fact that, in an individual spin
flip-flop scattering process, a spin flip of an electron is necessarily
accompanied by a flop of an impurity spin in the opposite direction and the
corresponding change of the impurity Zeeman energy influences the final energy
of the electron after the scattering event. This shift in the electron energies
after a spin flip-flop scattering processes, which usually has been overlooked
in the literature, turns out to be especially important in the case of
extremely diluted magnetic semiconductors in an external magnetic field. As a
specific example for a $\mathbf{k}$-dependent effective magnetic field the
effects of a Rashba field on the dynamics of the carrier-impurity correlations
in a Hg$_{1-x-y}$Cd$_y$Mn$_x$Te quantum well are described. It is found that,
although accounting for the Rashba interaction in the dynamics of the
correlations leads to a modified $\mathbf{k}$-space dynamics, the time
evolution of the total carrier spin is not significantly influenced.
Furthermore, a connection between the present theory and the description of
collective carrier-impurity precession modes is presented.",1602.00911v2
2021-03-23,Probing spin dynamics on diamond surfaces using a single quantum sensor,"Understanding the dynamics of a quantum bit's environment is essential for
the realization of practical systems for quantum information processing and
metrology. We use single nitrogen-vacancy (NV) centers in diamond to study the
dynamics of a disordered spin ensemble at the diamond surface. Specifically, we
tune the density of ""dark"" surface spins to interrogate their contribution to
the decoherence of shallow NV center spin qubits. When the average surface spin
spacing exceeds the NV center depth, we find that the surface spin contribution
to the NV center free induction decay can be described by a stretched
exponential with variable power n. We show that these observations are
consistent with a model in which the spatial positions of the surface spins are
fixed for each measurement, but some of them reconfigure between measurements.
In particular, we observe a depth-dependent critical time associated with a
dynamical transition from Gaussian (n=2) decay to n=2/3, and show that this
transition arises from the competition between the small decay contributions of
many distant spins and strong coupling to a few proximal spins at the surface.
These observations demonstrate the potential of a local sensor for
understanding complex systems and elucidate pathways for improving and
controlling spin qubits at the surface.",2103.12757v1
2010-02-22,Transport and magnetization dynamics in a superconductor/single-molecule magnet/superconductor junction,"We study dc-transport and magnetization dynamics in a junction of arbitrary
transparency consisting of two spin-singlet superconducting leads connected via
a single classical spin precessing at the frequency $\Omega$. The presence of
the spin in the junction provides different transmission amplitudes for spin-up
and spin-down quasiparticles as well as a time-dependent spin-flip transmission
term. For a phase biased junction, we show that a steady-state superconducting
charge current flows through the junction and that an out-of-equilibrium
circularly polarized spin current, of frequency $\Omega$, is emitted in the
leads. Detailed understanding of the charge and spin currents is obtained in
the entire parameter range. In the adiabatic regime, $\hbar \Omega \ll 2\Delta$
where $\Delta$ is the superconducting gap, and for high transparencies of the
junction, a strong suppression of the current takes place around $\vp \approx
0$ due to an abrupt change in the occupation of the Andreev bound-states. At
higher values of the phase and/or precession frequency, extended
(quasi-particle like) states compete with the bound-states in order to carry
the current. Well below the superconducting transition, these results are shown
to be weakly affected by the back-action of the spin current on the dynamics of
the precessing spin. Indeed, we show that the Gilbert damping due to the
quasi-particle spin current is strongly suppressed at low-temperatures, which
goes along with a shift of the precession frequency due to the condensate. The
results obtained may be of interest for on-going experiments in the field of
molecular spintronics.",1002.3929v4
2020-10-22,Spin-Orbit Misalignments in Tertiary-Induced Black-Hole Binary Mergers: Theoretical Analysis,"Black-hole (BH) binary mergers driven by gravitational perturbations of
tertiary companions constitute an important class of dynamical formation
channels for compact binaries detected by LIGO/VIRGO. Recent works have
examined numerically the combined orbital and spin dynamics of BH binaries that
undergo large Lidov-Kozai (LK) eccentricity oscillations induced by a highly
inclined companion and merge via gravitational wave radiation. However, the
extreme eccentricity variations make such systems difficult to characterize
analytically. In this paper, we develop an analytical formalism for
understanding the spin dynamics of binary BHs undergoing LK-induced mergers. We
show that, under certain conditions, the eccentricity oscillations of the
binary can be averaged over to determine the long-term behavior of the BH spin
in a smooth way. In particular, we demonstrate that the final spin-orbit
misalignment angle $\theta_{\rm sl}$ is often related to the binary's
primordial spin orientation through an approximate adiabatic invariant. Our
theory explains the ""$90^\circ$ attractor"" (as found in recent numerical
studies) for the evolution of $\theta_{\rm sl}$ when the initial BH spin is
aligned with the orbital axis and the octupole LK effects are negligible --
such a ""$90^\circ$ attractor"" would lead to a small binary effective spin
parameter $\chi_{\rm eff}\sim 0$ even for large intrinsic BH spins. We
calculate the deviation from adiabaticity in closed form as a function of the
initial conditions. We also place accurate constraints on when this adiabatic
invariant breaks down due to resonant spin-orbit interactions. We consider both
stellar-mass and supermassive BH tertiary companions, and provide simple
prescriptions for determining analytically the final spin-orbit misalignment
angles of the merging BH binaries.",2010.11951v2
2022-12-05,Spin excitation continuum to topological magnon crossover and thermal Hall conductivity in Kitaev magnets,"There has been great interest in identifying a Kitaev quantum spin liquid
state in frustrated magnets with bond-dependent interactions. In particular,
the experimental report of a half-quantized thermal Hall conductivity in
$\alpha$-RuCl$_3$ in the presence of a magnetic field has generated excitement
as it could be strong evidence for a field-induced chiral spin liquid. More
recent experiments, however, provide a conflicting interpretation advocating
for topological magnons in the field-polarized state as the origin of the
non-quantized thermal Hall conductivity observed in their experiments. An
inherent difficulty in distinguishing between the two scenarios is the phase
transition between a putative two-dimensional spin liquid and the
field-polarized state exists only at zero temperature, while the behaviour at
finite temperature is mostly crossover phenomena. In this work, we provide
insights into the finite temperature crossover behavior between the spin
excitation continuum in a quantum spin liquid and topological magnons in the
field-polarized state in three different theoretical models with large Kitaev
interactions. These models allow for a field-induced phase transition from a
spin liquid (or an intermediate field-induced spin liquid) to the
field-polarized state in the quantum model. We obtain the dynamical spin
structure factor as a function of magnetic field using molecular dynamics
simulations and compute thermal Hall conductivity in the field-polarized
regime. We demonstrate the gradual evolution of the dynamical spin structure
factor exhibiting crossover behaviour near magnetic fields where
zero-temperature phase transitions occur in the quantum model. We also examine
nonlinear effects on topological magnons and the validity of thermal Hall
conductivity computed using linear spin wave theory. We discuss the
implications of our results to existing and future experiments.",2212.02516v1
1995-11-27,Multimode electron-phonon interactions in the 2-dimensional t-J-Holstein model,"Polaronic effects are investigated in the two dimensional t--J model
(describing Cu spins and holes of the planes in high-$T_c$ cuprates) in the
presence of in-plane dynamic oxygen breathing modes. We focus on the effect of
dynamic multi-phonon modes. Spin and charge structure factors are computed. We
found evidence for self-localisation of the holes and {\it increased} short
range antiferromagnetic spin-spin correlations between the remaining spins.
This effect persists when all the in-plane oxygen vibration degrees of freedom
are taken into account. This suggests that dynamic phonons could play a key
role in stabilizing inhomogeneous stripe phases or domain wall structures.",9511125v2
1997-05-14,Anisotropic dynamical scaling in a spin model with competing interactions,"Results are presented for the kinetics of domain growth of a two-dimensional
Ising spin model with competing interactions quenched from a disordered to a
striped phase. The domain growth exponent are $\beta=1/2$ and $\beta=1/3$ for
single-spin-flip and spin-exchange dynamics, as found in previous simulations.
However the correlation functions measured in the direction parallel and
transversal to the stripes are different as suggested by the existence of
different interface energies between the ground states of the model. In the
case of single-spin-flip dynamics an anisotropic version of the
Ohta-Jasnow-Kawasaki theory for the pair scaling function can be used to fit
our data.",9705135v1
1997-07-19,Dynamic Spin Response for Heisenberg Ladders,"We employ the recently proposed plaquette basis to investigate static and
dynamic properties of isotropic 2-leg Heisenberg spin ladders. Simple
non-interacting multi-plaquette states provide a remarkably accurate picture of
the energy/site and dynamic spin response of these systems. Insights afforded
by this simple picture suggest a very efficient truncation scheme for more
precise calculations. When the small truncation errors are accounted for using
recently developed Contractor Renormalization techniques, very accurate results
requiring a small fraction of the computational effort of exact calculations
are obtained. These methods allow us to determine the energy/site, gap, and
spin response of 2x16 ladders. The former two values are in good agreement with
density matrix renormalization group results. The spin response calculations
show that nearly all the strength is concentrated in the lowest triplet level
and that coherent many-body effects enhance the response/site by nearly a
factor of 1.6 over that found for 2x2 systems.",9707207v1
1999-11-18,Time-resolved optical observation of spin-wave dynamics,"We have created a nonequilibrium population of antiferromagnetic spin-waves
in Cr2O3, and characterized its dynamics, using frequency- and time-resolved
nonlinear optical spectroscopy of the exciton-magnon transition. We observe a
time-dependent pump-probe line shape, which results from excitation induced
renormalization of the spin-wave band structure. We present a model that
reproduces the basic characteristics of the data, in which we postulate the
optical nonlinearity to be dominated by interactions with long-wavelength
spin-waves, and the dynamics to be due to spin-wave thermalization.",9911294v1
2000-12-20,"Glassy Spin Dynamics in Non-Fermi-Liquid UCu_{5-x}Pd_x, x = 1.0 and 1.5","Local f-electron spin dynamics in the non-Fermi-liquid heavy-fermion alloys
UCu_{5-x}Pd_x, x = 1.0 and 1.5, have been studied using muon spin-lattice
relaxation. The sample-averaged asymmetry function Gbar(t) indicates strongly
inhomogeneous spin fluctuations, and exhibits the scaling Gbar(t,H) =
Gbar(t/H^\gamma) expected from glassy dynamics. At 0.05 K \gamma(x=1.0) = 0.35
\pm 0.1, but \gamma(x=1.5) = 0.7 \pm 0.1. This is in contrast to inelastic
neutron scattering results, which yield \gamma = 0.33 for both concentrations.
There is no sign of static magnetism \gtrsim 10^{-3} \mu_B/U ion in either
material above 0.05 K. Our results strongy suggest that both alloys are quantum
spin glasses.",0012389v2
2002-07-08,Static and Dynamical Dzyaloshinsky-Moriya interactions in gapped spin systems,"Anisotropic spin-spin interactions of Dzyaloshinsky and Moriya symmetry are
generally considered weak, as they depend on the spin-orbit couplings. In spin
systems with gapped ground states they can, however, have rather strong
effects. We will discuss recent results related to the results of neutron
scattering and ESR for $\rm SrCu_2(BO_3)_2$. Inclusion of the
Dzyaloshinsky-Moriya interactions can explain much of the dynamics of the
systems discussed, in particular the splitting and dispersion of the triplet
modes. Some effects remain to be explained, however. Symmetries of the crystal
lead to the prediction of zero intensity for transitions, for example between
the ground state and the triplets observed in ESR.
  We present recent calculations of the effects of anisotropic terms generated
dynamically, ie linearly in the phonon coordinates. We discuss how this leads
to a novel mechanism to explain the ESR intensities. For polarized neutron
scattering experiments, we can calculate the mixing of nuclear and magnetic
scattering amplitudes by such a term and how such mixing should be observed.",0207191v1
2003-05-01,Spin dynamics from Majorana fermions,"Using the Majorana fermion representation of spin-1/2 local moments, we show
how it is possible to directly read off the dynamic spin correlation and
susceptibility from the one-particle propagator of the Majorana fermion. We
illustrate our method by applying it to the spin dynamics of a non-equilibrium
quantum dot, computing the voltage-dependent spin relaxation rate and showing
that, at weak coupling, the fluctuation-dissipation relation for the spin of a
quantum dot is voltage-dependent. We confirm the voltage-dependent Curie
susceptibility recently found by Parcollet and Hooley [Phys. Rev. B {\bf 66},
085315 (2002)].",0305001v3
2003-09-19,Quantum Dissipative Dynamics of the Magnetic Resonance Force Microscope in the Single-Spin Detection Limit,"We study a model of a magnetic resonance force microscope (MRFM) based on the
cyclic adiabatic inversion technique as a high-resolution tool to detect single
electron spins. We investigate the quantum dynamics of spin and cantilever in
the presence of coupling to an environment. To obtain the reduced dynamics of
the combined system of spin and cantilever, we use the Feynman-Vernon influence
functional and get results valid at any temperature as well as at arbitrary
system-bath coupling strength. We propose that the MRFM can be used as a
quantum measurement device, i.e., not only to detect the modulus of the spin
but also its direction.",0309456v1
2004-08-18,Spin-Fermion Model of Magnetism: Quasi-particle Many-Body Dynamics,"Theoretical foundations and applications of the generalized spin-fermion
(sp-d) exchange lattice model to various magnetic systems, e.g. rare-earth
metals and compounds and magnetic semiconductors are discussed. The
capabilities of the model to describe spin quasi-particle spectra are
investigated. The main emphasis is made on the dynamical behavior of two
interacting subsystems, the localized spins and spin density of itinerant
carriers. A nonperturbative many-body approach, the Irreducible Green Functions
(IGF) method, is used to describe the quasi-particle dynamics.
  Scattering states are investigated and three branches of magnetic excitations
are calculated in the regime characteristic of a magnetic semiconductor. For a
simplified version of the model (Kondo lattice model) we study the spectra of
quasi-particle excitations with special attention given to diluted magnetic
semiconductors in simple approximation, to demonstrate the possibilities of the
IGF approach. For this, to include the effects of disorder, a modified mean
fields are determined self-consistently. The approach permits to investigate
and clarify the role of various interactions and disorder effects in unified
and coherent fashion.",0408406v1
2004-10-28,Heterogeneous slow dynamics in a two dimensional doped classical antiferromagnet,"We introduce a lattice model for a classical doped two dimensional
antiferromagnet which has no quenched disorder, yet displays slow dynamics
similar to those observed in supercooled liquids. We calculate two-time spatial
and spin correlations via Monte Carlo simulations and find that for
sufficiently low temperatures, there is anomalous diffusion and
stretched-exponential relaxation of spin correlations. The relaxation times
associated with spin correlations and diffusion both diverge at low
temperatures in a sub-Arrhenius fashion if the fit is done over a large
temperature-window or an Arrhenius fashion if only low temperatures are
considered. We find evidence of spatially heterogeneous dynamics, in which
vacancies created by changes in occupation facilitate spin flips on
neighbouring sites. We find violations of the Stokes-Einstein relation and
Debye-Stokes-Einstein relation and show that the probability distributions of
local spatial correlations indicate fast and slow populations of sites, and
local spin correlations indicate a wide distribution of relaxation times,
similar to observ ations in other glassy systems with and without quenched
disorder.",0410734v2
2005-07-29,Spin dynamics in electrochemically charged CdSe quantum dots,"We use time-resolved Faraday rotation to measure coherent spin dynamics in
colloidal CdSe quantum dots charged in an electrochemical cell at room
temperature. Filling of the 1Se electron level is demonstrated by the bleaching
of the 1Se-1S3/2 absorption peak. One of the two Lande g-factors observed in
uncharged quantum dots disappears upon filling of the 1Se electron state. The
transverse spin coherence time, which is over 1 ns and is limited by
inhomogeneous dephasing, also appears to increase with charging voltage. The
amplitude of the spin precession signal peaks near the half-filling potential.
Its evolution at charging potentials without any observable bleaching of the
1Se-1S3/2 transition suggests that the spin dynamics are influenced by
low-energy surface states.",0507699v1
2006-01-17,Surfaces of Constant Temperature for Glauber Dynamics,"The wavefunction of a single spin system in a prepared initial state evolves
to equilibrium with a heat bath. The average spin $$q(t) = p_{\uparrow}(t) -
p_{\downarrow}(t)$$ exhibits a characteristic time for this evolution. With the
proper choice of spin flip rates, a dynamical Ising model (Glauber) can be
constructed with the same characteristic time for transition of the average
spin to equilibrium. The Glauber dynamics are expressed as a Markoff process
that possesses many of the same physical characteristics as its quantum
mechanical counterpart. In addition, since the classical trajectories are those
of an ergodic process (the time averages of a single trajectory are equivalent
to the ensemble averages), the surfaces of constant temperature, in terms of
the model parameters, may be derived for the single spin system.",0601387v1
2006-05-12,Comment on Frequency response and origin of the spin-1/2 photolumines-cence-detected magnetic resonance in a pi-conjugated polymer,"In a recent paper Segal et al. [1] attempted to explain the dynamics of spin
1/2 photoluminescence detected magnetic resonance (PLDMR) in films of a
pi-conjugated polymer, namely a soluble de-rivative of poly(phenylene-vinylene)
[MEH-PPV] using a model (dubbed TPQ), in which the PLDMR is due to spin
dependent triplet-polaron interactions that reduce the polarons density and
consequent quenching of singlet excitons. We studied the full PLDMR and
photoinduced ab-sorption (PA) dynamics of MEH-PPV films as a function of
microwave power at various tempera-tures. We show, firstly, that the TPQ model
is incompatible with the full frequency dependent spin 1/2 PLDMR response;
secondly, it is not in agreement with the spin-1 PLDMR temperature dependence;
thirdly, it predicts a much shorter triplet exciton lifetime than that obtained
experimentally; and fourthly, that is in contradiction with the temperature
dependencies of spin 1/2 PLDMR and triplet exciton PA. In contrast, an
alternative model, namely the spin dependent re-combination of polarons, is
capable of explaining the whole body of experimental results, and in particular
the PLDMR dynamics.",0605322v1
2006-06-09,Spin wave dynamics and the determination of intrinsic Gilbert damping in locally-excited Permalloy thin films,"Time-resolved scanning Kerr effect microscopy has been used to study
magnetization dynamics in Permalloy thin films excited by transient magnetic
pulses generated by a micrometer-scale transmission line structure. The results
are consistent with magnetostatic spin wave theory and are supported by
micromagnetic simulations. Magnetostatic volume and surface spin waves are
measured for the same specimen using different bias field orientations and can
be accurately calculated by k-space integrations over all excited plane wave
components. A single damping constant of Gilbert form is sufficient to describe
both scenarios. The nonuniform pulsed field plays a key role in the spin wave
dynamics, with its Fourier transform serving as a weighting function for the
participating modes. The intrinsic Gilbert damping parameter $\alpha$ is most
conveniently measured when the spin waves are effectively stationary.",0606235v3
2006-07-18,Exact spin dynamics of the 1/r^2 supersymmetric t-J model in a magnetic field,"The dynamical spin structure factor S^{zz}(Q,omega) in the small momentum
region is derived analytically for the one-dimensional supersymmetric t-J model
with 1/r^2 interaction. Strong spin-charge separation is found in the spin
dynamics. The structure factor S^{zz}(Q,omega) with a given spin polarization
does not depend on the electron density in the small momentum region. In the
thermodynamic limit, only two spinons and one antispinon (magnon) contribute to
S^{zz}(Q,omega). These results are derived via solution of the SU(2,1)
Sutherland model in the strong coupling limit.",0607444v1
2007-01-21,Dynamical control of electron spin coherence in a quantum dot,"We investigate the performance of dynamical decoupling methods at suppressing
electron spin decoherence from a low-temperature nuclear spin reservoir in a
quantum dot. The controlled dynamics is studied through exact numerical
simulation, with emphasis on realistic pulse delays and long-time limit. Our
results show that optimal performance for this system is attained by a periodic
protocol exploiting concatenated design, with control rates substantially
slower than expected from the upper spectral cutoff of the bath. For a known
initial electron spin state, coherence can saturate at long times, signaling
the creation of a stable ``spin-locked'' decoherence-free subspace. Analytical
insight on saturation is obtained for a simple echo protocol, in good agreement
with numerical results.",0701507v1
2006-09-07,Single-Spin Observables and Orbital Structures in Hadronic Distributions,"Within the light-quark sector of the standard model, P-odd observables are
generated from point-like electroweak processes while A_t- odd observables
(neglecting quark mass parameters) come from dynamic spin-orbit correlations
within hadrons or within larger composite systems, such as nuclei. The effects
of A_t-odd dynamics can be inserted into transverse-momentum dependent
constituent distribution functions and, in this paper, we construct the
contribution from an orbital quark to the A_t odd quark parton distribution.
Using this distribution, we examine the crucial role of initial- and
final-state interactions in the observation of the scattering asymmetries in
different hard-scattering processes. This construction provides a geometrical
and dynamical interpretation of the Collins conjugation relation between
single-spin asymmetries in semi-inclusive deep inelastic scattering and the
asymmetries in Drell-Yan production. Finally, our construction allows us to
display a significant difference between the calculation of a spin asymmetry
generated by a hard scattering mechanism involving color-singlet exchange (such
as a photon) and a calculation of an asymmetry with a hard-scattering exchange
involving gluons. This leads to an appreciation of the process dependence
inherent in measurements of single-spin observables.",0609080v1
2004-03-12,Continuous Weak Measurement and Nonlinear Dynamics in a Cold Spin Ensemble,"A weak continuous quantum measurement of an atomic spin ensemble can be
implemented via Faraday rotation of an off-resonance probe beam, and may be
used to create and probe nonclassical spin states and dynamics. We show that
the probe light shift leads to nonlinearity in the spin dynamics and limits the
useful Faraday measurement window. Removing the nonlinearity allows a
non-perturbing measurement on the much longer timescale set by decoherence. The
nonlinear spin Hamiltonian is of interest for studies of quantum chaos and
real-time quantum state estimation.",0403096v2
2007-07-12,Stochastic analysis and simulation of spin star systems,"We discuss two methods of an exact stochastic representation of the
non-Markovian quantum dynamics of open systems. The first method employs a pair
of stochastic product vectors in the total system's state space, while the
second method uses a pair of state vectors in the open system's state space and
a random operator acting on the state space of the environment. Both techniques
lead to an exact solution of the von Neumann equation for the density matrix of
the total system. Employing a spin star model describing a central spin coupled
to bath of surrounding spins, we perform Monte Carlo simulations for both
variants of the stochastic dynamics. In addition, we derive analytical
expression for the expectation values of the stochastic dynamics to obtain the
exact solution for the density matrix of the central spin.",0707.1795v1
2007-08-30,Multiple Quantum NMR Dynamics in Dipolar Ordered Spin Systems,"We investigate analytically and numerically the Multiple Quantum (MQ) NMR
dynamics in systems of nuclear spins 1/2 coupled by the dipole-dipole
interactions in the case of the dipolar ordered initial state. We suggest two
different methods of MQ NMR. One of them is based on the measurement of the
dipolar temperature in the quasi-equilibrium state which establishes after the
time of order T2 after the MQ NMR experiment. The other method uses an
additional resonance 45^0 -pulse after the preparation period of the standard
MQ NMR experiment in solids. Many-spin clusters and correlations are created
faster in such experiments than in the usual MQ NMR experiments and can be used
for the investigation of many-spin dynamics of nuclear spins in solids.",0708.4085v2
2007-11-30,"Effective action, magnetic excitations and quantum fluctuations in lightly doped single layer cuprates","We consider the extended 2D $t-t'-t''-J$ model at zero temperature.
Parameters of the model corresponds to doping by holes. Using the low doping
effective action we demonstrate that the system can 1) preserve the long range
collinear antiferromagnetic order, 2) lead to a spin spiral state (static or
dynamic), 3) lead to the phase separation instability. We show that at
parameters of the effective action corresponding to the single layer cuprate
La$_{2-x}$Sr$_x$CuO$_4$ the spin spiral ground state is realized. We derive
properties of magnetic excitations and calculate quantum fluctuations. Quantum
fluctuations destroy the static spin spiral at the critical doping $x_c\approx
0.11$. This is the point of the quantum phase transition to the spin-liquid
state (dynamic spin spiral). The state is still double degenerate with respect
to the direction of the dynamic spiral, so this is a ``directional nematic''.
The superconducting pairing exists throughout the phase diagram and is not
sensitive to the quantum phase transition. We also compare the calculated
neutron scattering spectra with experimental data.",0711.4865v1
2008-01-30,Femtosecond Control of the Magnetization in Ferromagnetic Semiconductors,"We develop a theory of collective spin dynamics triggered by ultrafast
optical excitation of ferromagnetic semiconductors. Using the density matrix
equations of motion in the mean field approximation and including magnetic
anisotropy and hole spin dephasing effects, we predict the development of a
light--induced magnetization tilt during ultra--short time intervals comparable
to the pulse duration. This femtosecond dynamics in the coherent temporal
regime is governed by the interband nonlinear optical polarizations and is
followed by a second temporal regime governed by the magnetic anisotropy of the
Fermi sea. We interpret our numerical results by deriving a
Landau--Gilbert--like equation for the collective spin, which demonstrates an
ultrafast correction to the magnetic anisotropy effective field due to second
order coherent nonlinear optical processes. Using the Lindblad semigroup
method, we also derive a contribution to the interband polarization dephasing
determined by the Mn spin and the hole spin dephasing. Our predicted
magnetization tilt and subsequent nonlinear dynamics due to the magnetic
anisotropy can be controlled by varying the optical pulse intensity, duration,
and helicity and can be observed with pump--probe magneto--optical
spectroscopy.",0801.4641v1
2008-03-08,Energy-Dependent Electron-Electron Scattering and Spin Dynamics in a Two Dimensional Electron Gas,"Measurements of spin dynamics of electrons in a degenerate two dimensional
electron gas, where the Dyakonov-Perel mechanism is dominant, have been used to
investigate the electron scattering time (tp*) as a function of energy near the
Fermi energy. Close to the Fermi energy the spin evolution is oscillatory,
indicating a quasi-collision-free regime of spin dynamics. As the energy is
increased a transition to exponential, collision-dominated, spin decay occurs.
The frequency and the value of tp* are extracted using a Monte Carlo simulation
method. At the Fermi energy tp* is very close to the ensemble momentum
relaxation time (tp) obtained from the electron mobility. For higher energies
tp* falls quadratically, consistent with theoretical expectations for the onset
of electron-electron scattering which is inhibited by the Pauli principle at
the Fermi energy.",0803.1230v1
2008-04-01,Dynamics of Collective Decoherence and Thermalization,"We analyze the dynamics of N interacting spins (quantum register)
collectively coupled to a thermal environment. Each spin experiences the same
environment interaction, consisting of an energy conserving and an energy
exchange part.
  We find the decay rates of the reduced density matrix elements in the energy
basis. We show that if the spins do not interact among each other, then the
fastest decay rates of off-diagonal matrix elements induced by the energy
conserving interaction is of order N^2, while that one induced by the energy
exchange interaction is of the order N only. Moreover, the diagonal matrix
elements approach their limiting values at a rate independent of N.
  For a general spin system the decay rates depend in a rather complicated (but
explicit) way on the size N and the interaction between the spins.
  Our method is based on a dynamical quantum resonance theory valid for small,
fixed values of the couplings. We do not make Markov-, Born- or weak coupling
(van Hove) approximations.",0804.0243v1
2008-04-21,Anisotropic plasmons in a two-dimensional electron gas with spin-orbit interaction,"Spin-orbit coupling induced anisotropies of plasmon dynamics are investigated
in two-dimensional semiconductor structures. The interplay of the linear
Bychkov-Rashba and Dresselhaus spin-orbit interactions drastically affects the
plasmon spectrum: the dynamical structure factor exhibits variations over
several decades, prohibiting plasmon propagation in specific directions. While
this plasmon filtering makes the presence of spin-orbit coupling in plasmon
dynamics observable, it also offers a control tool for plasmonic devices.
Remarkably, if the strengths of the two interactions are equal, not only the
anisotropy, but all the traces of the linear spin-orbit coupling in the
collective response disappear.",0804.3366v3
2008-08-19,Magnetization and spin dynamics of a Cr-based magnetic cluster: Cr$_{7}$Ni,"We study the magnetization and the spin dynamics of the Cr$_7$Ni ring-shaped
magnetic cluster. Measurements of the magnetization at high pulsed fields and
low temperature are compared to calculations and show that the spin Hamiltonian
approach provides a good description of Cr$_7$Ni magnetic molecule. In
addition, the phonon-induced relaxation dynamics of molecular observables has
been investigated. By assuming the spin-phonon coupling to take place through
the modulation of the local crystal fields, it is possible to evaluate the
decay of fluctuations of two generic molecular observables. The nuclear
spin-lattice relaxation rate $1/T_1$ directly probes such fluctuations, and
allows to determine the magnetoelastic coupling strength.",0808.2621v1
2008-12-26,Normal State Spin Dynamics of Five-band Model for Iron-pnictides,"Normal state spin dynamics of the recently discovered iron-pnictide
superconductors is discussed by calculating spin structure factor S(q, omega)
in an itinerant five-band model within RPA approximation. Due to the
characteristic Fermi surface structure of iron-pnictide, column like response
is found at (pi, 0) in extended Brillouin zone in the undoped case, which is
consistent with the recent neutron scattering experiment. This indicates that
the localized spin model is not necessary to explain the spin dynamics of this
system. Furthermore, we show that the temperature dependence of inelastic
neutron scattering intensity can be well reproduced in the itinerant model. We
also study NMR 1/T_1T in the same footing calculation and show that the
itinerant model can capture the magnetic property of iron-pnictide
superconductors.",0812.4664v1
2009-07-24,Large-scale dynamical simulations of the three-dimensional XY spin glass,"Large-scale simulations have been performed in the current-driven
three-dimensional XY spin glass with resistively-shunted junction dynamics for
sample sizes up to $64^3$. It is observed that the linear resistivity at low
temperatures tends to zero, providing a strong evidence of a finite temperature
phase-coherence (i.e. spin-glass) transition. Dynamical scaling analysis
demonstrates that a perfect collapse of current-voltage data can be achieved.
The obtained critical exponents agree with those in equilibrium Monte Carlo
simulations, and are compatible with those observed in various experiments on
high-T$_c$ cuprate superconductors. It is suggested that the spin and the
chirality order simultaneously. A genuine continuous depinning transition is
found at zero temperature. For low temperature creep motion, critical exponents
are evaluated, and a non-Arrhenius creep motion is observed in the low
temperature ordered phase. It is proposed that the XY spin glass gives an
effective description of the transport properties in high-T$_c$ superconductors
with d-wave symmetry.",0907.4220v1
2010-03-23,Low frequency spin dynamics in the quantum magnet copper pyrazine dinitrate,"The S=1/2 antiferromagnetic Heisenberg chain exhibits a magnetic field driven
quantum critical point. We study the low frequency spin dynamics in copper
pyrazine dinitrate (CuPzN), a realization of this model system of quantum
magnetism, by means of $^{13}$C-NMR spectroscopy. Measurements of the nuclear
spin-lattice relaxation rate $T_1^{-1}$ in the vicinity of the saturation field
are compared with quantum Monte Carlo calculations of the dynamic structure
factor. Both show a strong divergence of low energy excitations at temperatures
in the quantum regime. The analysis of the anisotropic $T_1^{-1}$-rates and
frequency shifts allows one to disentangle the contributions from transverse
and longitudinal spin fluctuations for a selective study and to determine the
transfer of delocalized spin moments from copper to the neighboring nitrogen
atoms.",1003.4535v1
2010-04-21,Numerical Study of Photo-Induced Dynamics in Double-Exchange Model,"Photo-induced spin and charge dynamics in double-exchange model are
numerically studied. The Lanczos method and the density-matrix
renormalization-group method are applied to one-dimensional finite-size
clusters. By photon irradiation in a charge ordered (CO) insulator associated
with antiferromagnetic (AFM) correlation, both the CO and AFM correlations
collapse rapidly, and appearances of new peaks inside of an insulating gap are
observed in the optical spectra and the one-particle excitation spectra. Time
evolutions of the spin correlation and the in-gap state are correlated with
each other, and are governed by the transfer integral of conduction electrons.
Results are interpreted by the charge kink/anti-kink picture and their
effective motions which depend on the localized spin correlation. Pump-photon
density dependence of spin and charge dynamics are also studied. Roles of spin
degree of freedom are remarkable in a case of weak photon density. Implications
of the numerical results for the pump-probe experiments in perovskite
manganites are discussed.",1004.3680v1
2010-06-11,Chaos and dynamics of spinning particles in Kerr spacetime,"We study chaos dynamics of spinning particles in Kerr spacetime of rotating
black holes use the Papapetrou equations by numerical integration. Because of
spin, this system exists many chaos solutions, and exhibits some exceptional
dynamic character. We investigate the relations between the orbits chaos and
the spin magnitude S, pericenter, polar angle and Kerr rotation parameter a by
means of a kind of brand new Fast Lyapulov Indicator (FLI) which is defined in
general relativity. The classical definition of Lyapulov exponent (LE) perhaps
fails in curve spacetime. And we emphasize that the Poincar\'e sections cannot
be used to detect chaos for this case. Via calculations, some new interesting
conclusions are found: though chaos is easier to emerge with bigger S, but not
always depends on S monotonically; the Kerr parameter a has a contrary action
on the chaos occurrence. Furthermore, the spin of particles can destroy the
symmetry of the orbits about the equatorial plane. And for some special initial
conditions, the orbits have equilibrium points.",1006.2229v1
2011-02-20,Mean-field Dynamics of Spin-Orbit Coupled Bose-Einstein Condensates,"Spin-orbit coupling (SOC), the interaction between the spin and momentum of a
quantum particle, is crucial for many important condensed matter phenomena. The
recent experimental realization of SOC in neutral bosonic cold atoms provides a
new and ideal platform for investigating spin-orbit coupled quantum many-body
physics. In this Letter, we derive a generic Gross-Pitaevskii equation as the
starting point for the study of many-body dynamics in spin-orbit coupled
Bose-Einstein condensates. We show that different laser setups for realizing
the same SOC may lead to different mean field dynamics. Various ground state
phases (stripe, phase separation, etc.) of the condensate are found in
different parameter regions. A new oscillation period induced by the SOC,
similar to the Zitterbewegung oscillation, is found in the center of mass
motion of the condensate.",1102.4045v3
2011-04-06,Hyperfine interaction dominated dynamics of nuclear spins in self-assembled quantum dots,"We measure the dynamics of nuclear spins in a self-assembled quantum dot at a
magnetic field of 5 Tesla and identify two distinct mechanisms responsible for
the decay of the Overhauser field. We attribute a temperature-independent decay
which lasts ~100 seconds to intra-dot diffusion induced by hyperfine-mediated
indirect nuclear spin interaction. In addition, we observe a gate-voltage and
temperature dependent decay stemming from co-tunneling mediated nuclear spin
flip processes. By adjusting the gate-voltage and lowering the electron
temperature to ~200 milliKelvin, we prolong the corresponding decay time to ~30
hours. Our measurements indicate possibilities for exploring quantum dynamics
of the central spin model using a single self-assembled quantum dot.",1104.1111v1
2011-09-30,Charge localization and dynamical spin locking in double quantum dots driven by ac magnetic fields,"We investigate electron localization and dynamical spin locking induced by ac
magnetic fields in double quantum dots. We demonstrate that by tuning the ac
magnetic fields parameters, i.e., the field intensity, frequency, and the phase
difference between the fields within each dot, coherent destruction of
tunneling (and thus charge localization) can be achieved. We show that in
contrast with ac electric fields, ac magnetic fields are able to induce spin
locking, i.e., to freeze the electronic spin, at certain field parameters. We
show how the symmetry of the Hamiltonian determines the quasienergy spectrum
which presents degeneracies at certain field parameters, and how it is
reflected in the charge and spin dynamics.",1109.6934v1
2011-10-30,Chaotic spin-dependent electron dynamics in a field-driven double dot potential,"We study the nonlinear classical dynamics of an electron confined in a double
dot potential and subjected to a spin-orbit coupling and a constant external
magnetic field. It is shown that due to the spin orbit coupling, the energy can
be transferred from the spin to the orbital motion. This naturally heats up the
orbital motion which, due to the presence of the separatrix line in the phase
space of the system, results in a motion of the electron between the dots. It
is shown that depending on the strength of the spin orbit coupling and the
energy of the system, the electronic orbital motion undergoes a transition from
the regular to the chaotic regime.",1110.6597v1
2012-02-23,Entanglement dynamics via semiclassical propagators in systems of two spins,"We analyze the dynamical generation of entanglement in systems of two
interacting spins initially prepared in a product of spin coherent states. For
arbitrary time-independent Hamiltonians, we derive a semiclassical expression
for the purity of the reduced density matrix as function of time. The final
formula, subsidiary to the linear entropy, shows that the short-time dynamics
of entanglement depends exclusively on the stability of trajectories governed
by the underlying classical Hamiltonian. Also, this semiclassical measure is
shown to reproduce the general properties of its quantum counterpart and give
the expected result in the large spin limit. The accuracy of the semiclassical
formula is further illustrated in a problem of phase exchange for two particles
of spin $j$.",1202.5144v1
2013-02-14,Faithful Solid State Optical Memory with Dynamically Decoupled Spin Wave Storage,"We report an optical memory in a rare earth doped crystal with long storage
times, up to 20 ms, together with an optical bandwidth of 1.5 MHz. This is
obtained by transferring optical coherences to nuclear spin coherences, which
were then protected against environmental noise by dynamical decoupling. With
this approach, we achieved a 33 fold increase in spin wave storage time over
the intrinsic spin coherence lifetime. Comparison between different decoupling
sequences indicates that sequences insensitive to initial spin coherence
increase retrieval efficiency. Finally, an interference experiment shows that
relative phases of input pulses are preserved through the whole storage process
with a visibility close to 1, demonstrating the usefulness of dynamical
decoupling for extending the storage time of quantum memories.",1302.3358v1
2013-03-28,Spin Torque on Magnetic Textures Coupled to the Surface of a Three-Dimensional Topological Insulator,"We investigate theoretically the spin torque and magnetization dynamic in a
thin ferromagnetic (FM) layer with spatially varying magnetization. The FM
layer is deposited on the surface of a topological insulator (TI). In the limit
of the adiabatic relaxation of electron spin along the magnetization, the
interaction between the exchange interaction and the Rashba-like surface
texture of a TI yields a topological gauge field. Under the gauge field and an
applied current, spin torque is induced according to the direction of the
current. We derived the corresponding effective anisotropy field and hence the
modified Landau-Lifshitz-Gilbert equation, which describes the spin torque and
the magnetization dynamic. In addition, we study the effective field for
exemplary magnetic textures, such as domain wall, skyrmion, and vortex
configurations. The estimated strength of the effective field is comparable to
the switching fields of typical FM materials, and hence can significantly
influence the dynamics of the FM layer.",1303.7031v1
2013-04-08,Study of unconventional superfluid phases and the phase dynamics in spin-orbit coupled bose system,"We study the phase distribution and its dynamics in spin-orbit coupled two
component ultracold Bosons for finite size system. Using an inhomogeneous
meanfield analysis we demonstrate how phase distribution evolves as we tune the
spin-orbit coupling $\gamma$ and $t$, the spin-independent hopping. For
$t>>\gamma$ we find the homogeneous superfluid phase. As we increase $\gamma$,
differences in the phases of the order parameter grows leading to twisted
superfluid phase. For $t \sim \gamma$ competing orderings in the phase
distribution is observed. At large $\gamma$ limit a Ferro-Magnetic stripe
ordering appears along the diagonal. We explain that this is due to the
frustration bought in by the spin-orbit interaction. Isolated vortex formation
is also shown to appear. We also investigate the possible collective modes. In
deep superfluid regime we derive the equation of motion for the phases
following a semi-classical approximation. Imaginary frequencies indicating the
damped modes are seen to appear and the dynamics of lowest normal modes are
discussed.",1304.2098v1
2013-04-09,Exchange randomness and spin dynamics in the frustrated magnetic Keplerate {W72V30},"The magnetic properties and spin dynamics of the spin frustrated
polyoxometalate {W72V30}, where 30 V^{4+} ions (s = 1/2) occupy the sites of an
icosidodecahedron, have been investigated by low temperature magnetization,
magnetic susceptibility, proton and vanadium nuclear magnetic resonance, and
theoretical studies. The field-dependent magnetization at 0.5 K increases
monotonically up to 50 T without any sign of staircase behavior. This
low-temperature behavior cannot be explained by a Heisenberg model based on a
single value of the nearest-neighbor exchange coupling. We analyze this
behavior upon assuming a rather broad distribution of nearest-neighbor exchange
interactions. Slow spin dynamics of {W72V30} at low temperatures is observed
from the magnetic field and temperature dependence of nuclear spin-lattice
relaxation rate 1/T_1 measurements.",1304.2603v1
2013-04-30,GPU accelerated Trotter-Suzuki solver for quantum spin dynamics,"The resolution of dynamics in out of equilibrium quantum spin systems lies at
the heart of fundamental questions among Quantum Information Processing,
Statistical Mechanics and Nano-Technologies. Efficient computational
simulations of interacting many-spin systems are extremely valuable tools for
tackling such questions. Here, we use the Trotter-Suzuki (TS) algorithm, a
well-known strategy that provides the evolution of quantum systems, to address
the spin dynamics. We present a GPU implementation of a particular TS version,
which has been previously implemented on single cores in CPUs. We develop a
massive parallel version of this algorithm and compare the efficiency between
CPU and GPU implementations. This method reduces the execution time
considerably and is capable of dealing with systems of up to 27 spins (only
limited by GPU memory).",1305.0036v2
2013-07-23,Exact Real Time Dynamics of Quantum Spin Systems Using the Positive-P Representation,"We discuss a scheme for simulating the real time quantum quench dynamics of
interacting quantum spin systems within the positive-P formalism. As model
systems we study the transverse field Ising model as well as the Heisenberg
model undergoing a quench away from the classical ferromagnetic ordered state
and antiferromagnetic Neel state, depending on the sign of the Heisenberg
exchange interaction. The connection to the positive-P formalism as it is used
in quantum optics is established by mapping the spin operators on to Schwinger
bosons. In doing so, the dynamics of the interacting quantum spin system is
mapped onto a set of Ito stochastic differential equations (SDEs) the number of
which scales linearly with the number of spins, N, compared to an exact
solution through diagonalization that in the case of the Heisenberg model would
require matrices exponentially large in N . This mapping is exact and can be
extended to higher dimensional interacting systems as well as to systems with
an explicit coupling to the environment.",1307.6267v1
2013-12-22,Dynamical Skyrmion State in a Spin Current Nano-Oscillator with Perpendicular Magnetic Anisotropy,"We study the spectral characteristics of spin current nano-oscillators based
on the Pt/[Co/Ni] magnetic multilayer with perpendicular magnetic anisotropy.
By varying the applied magnetic field and current, both localized and
propagating spin wave modes of the oscillation are achieved. At small fields,
we observe an abrupt onset of the modulation sidebands. We use micromagnetic
simulations to identify this state as a dynamical magnetic skyrmion stabilized
in the active device region by spin current injection, whose current-induced
dynamics is accompanied by the gyrotropic motion of the core due to the skew
deflection. Our results demonstrate a practical route for controllable skyrmion
manipulation by spin current in magnetic thin films.",1312.6343v2
2014-04-15,Spectroscopy of Surface-Induced Noise Using Shallow Spins in Diamond,"We report on the noise spectrum experienced by few nanometer deep
nitrogen-vacancy centers in diamond as a function of depth, surface coating,
magnetic field and temperature. Analysis reveals a double-Lorentzian noise
spectra consistent with a surface electronic spin bath, with slower dynamics
due to spin-spin interactions and faster dynamics related to phononic coupling.
These results shed new light on the mechanisms responsible for surface noise
affecting shallow spins at semiconductor interfaces, and suggests possible
directions for further studies. We demonstrate dynamical decoupling from the
surface noise, paving the way to applications ranging from nanoscale NMR to
quantum networks.",1404.3879v2
2014-04-16,"Fractional Revivals, Multiple-Cat States and Quantum Carpets in the Interaction of a Qubit with $N$ Qubits","We study the dynamics of a system comprising a single qubit interacting
equally with $N$ qubits (a ""spin star"" system). Although this model can be
solved exactly, the exact solution does not give much intuition for the
dynamics of the model. Here, we find an approximation that gives some insight
into the dynamics for a particular class of initial spin coherent states of the
$N$ qubits. We find an effective Hamiltonian for the system that is a finite
Kerr (one-axis twisting) Hamiltonian for the $N+1$ qubits. The initial spin
coherent state evolves to spin squeezed states on short timescales, and to
""multiple-cat"" states (superpositions of many spin coherent states) on longer
timescales, a manifestation of the phenomenon of fractional revivals of the
initial state. The evolution of the system is visualised with phase space plots
($Q$-functions) that, when plotted against time, reveal a ""quantum carpet""
pattern. Of particular interest is the fact that our approximation captures the
qualitative features of the model even for small values of $N$. This suggests
the possibility of observing the phenomenon of fractional revival in this model
for systems of few qubits.",1404.4296v2
2014-09-14,"Comment on ""Topological excitations and the dynamic structure factor of spin liquids on the kagome lattice"" (Punk, M., Chowdhury, D. & Sachdev, S. Nature Physics 10, 289-293 (2014))","The authors of a recent paper evidently take the view that the whole of
progress made toward a theoretical understanding of the physics of quantum spin
liquids (QSL) is associated with models of the kind proposed and applied in
their present work. As motivation for this work, they observe that in contrast
to existing theoretical models of both gapped and gapless spin liquids, which
give rise to sharp dispersive features in the dynamic structure factor, the
measured dynamic structure factor reveals an excitation continuum that is
remarkably flat as a function of frequency. They go on to assert that ""so far,
the only theoretical model for a spin liquid state on the kagome lattice which
naturally gives rise to a flat excitation band at low energies consists of the
$Z_2$ spin liquids"". Here we point out that there already exists a different
and demonstrably successful approach to the QSL problem that does naturally
feature a flat band.",1409.4034v1
2014-10-21,Dissipation dynamics and spin-orbit force in time-dependent Hartree-Fock theory,"We investigate the one-body dissipation dynamics in heavy-ion collisions of
$^{16}{\rm O}$+$^{16}{\rm O}$ using a fully three-dimensional time-dependent
Hartree-Fock (TDHF) theory with the modern Skyrme energy functional and without
any symmetry restrictions. The energy dissipation is revealed to decrease in
deep-inelastic collisions of the light systems as the bombarding energy
increases owing to the competition between collective motion and
single-particle degrees of freedom. The role of spin-orbit force is given
particular emphasis in deep-inelastic collisions. The spin-orbit force causes a
significant enhancement of the dissipation. The time-even coupling of
spin-orbit force plays a dominant role at low energies, while the influence of
time-odd terms is notable at high energies. About 40-65\% of the total
dissipation depending on the different parameter sets is predicted to arise
from the spin-orbit force. The theoretical fusion cross section has a
reasonably good agreement with the experimental data, considering that no free
parameters are adjusted to reaction dynamics in the TDHF approach.",1410.5573v1
2014-12-08,Magnetization Dynamics driven by Non-equilibrium Spin-Orbit Coupled Electron Gas,"The dynamics of magnetization coupled to an electron gas via s-d exchange
interaction is investigated by using density matrix technique. Our theory shows
that non-equilibrium spin accumulation induces a spin torque and the electron
bath leads to a damping of the magnetization. For the two-dimensional
magnetization thin film coupled to the electron gas with Rashba spin-orbit
coupling, the result for the spin-orbit torques is consistent with the previous
semi-classical theory. Our theory predicts a damping of the magnetization,
which is absent in the semi-classical theory. The magnitude of the damping due
to the electron bath is comparable to the intrinsic Gilbert damping and may be
important in describing the magnetization dynamics of the system.",1412.2479v1
2014-12-18,Effective Equations for the Precession Dynamics of Electron Spins and Electron-Impurity Correlations in Diluted Magnetic Semiconductors,"Starting from a quantum kinetic theory for the spin dynamics in diluted
magnetic semiconductors, we derive simplified equations that effectively
describe the spin transfer between carriers and magnetic impurities for an
arbitrary initial impurity magnetization. Taking the Markov limit of these
effective equations, we obtain good quantitative agreement with the full
quantum kinetic theory for the spin dynamics in bulk systems at high magnetic
doping. In contrast, the standard rate description where the carrier-dopant
interaction is treated according to Fermi's golden rule, which involves the
assumption of a short memory as well as a perturbative argument, has been shown
previously to fail if the impurity magnetization is non-zero. The Markov limit
of the effective equations is derived, assuming only a short memory, while
higher order terms are still accounted for. These higher order terms represent
the precession of the carrier-dopant correlations in the effective magnetic
field due to the impurity spins. Numerical calculations show that the Markov
limit of our effective equations reproduces the results of the full quantum
kinetic theory very well. Furthermore, this limit allows for analytical
solutions and for a physically transparent interpretation.",1412.5898v1
2015-01-13,Dynamics and Correlations among Soft Excitations in Marginally Stable Glasses,"Marginal stability is the notion that stability is achieved, but only barely
so. This property constrains the ensemble of configurations explored at low
temperature in a variety of systems, including spin, electron and structural
glasses. A key feature of marginal states is a (saturated) pseudo-gap in the
distribution of soft excitations. We study how such a pseudo-gap appears
dynamically in the case of the Sherrington-Kirkpatrick (SK) spin glass. After
revisiting and correcting the multi-spin-flip criterion for local stability, we
show that stationarity along the hysteresis loop requires that soft spins are
frustrated among each other, with a correlation that diverges as
$C(\lambda)\sim 1/\lambda$, where $\lambda$ is the larger of two considered
local fields. We explain how this arises spontaneously in a marginal system and
develop an analogy between the spin dynamics in the SK model and random walks
in two dimensions. We discuss the applicability of these findings to hard
sphere packings.",1501.03017v1
2015-02-16,Cyclotron Dynamics of a Kondo Singlet in a Spin-Orbit-Coupled Alkaline-Earth Atomic Gas,"We propose a scheme to investigate the interplay between Kondo-exchange
interaction and quantum spin Hall effect with ultracold fermionic
alkaline-earth atoms trapped in two-dimensional optical lattices using
ultracold collision and laser-assisted tunneling. In the strong Kondo-coupling
regime, though the loop trajectory of the mobile atom disappears, collective
dynamics of an atom pair in two clock states can exhibit an unexpected
spin-dependent cyclotron orbit in a plaquette, realizing the quantum spin Hall
effect of the Kondo singlet. We demonstrate that the collective cyclotron
dynamics of the spin-zero Kondo singlet is governed by an effective
Harper-Hofstadter model in addition to second-order diagonal tunneling.",1502.04422v1
2015-02-24,Digital quantum simulation of spin models with circuit quantum electrodynamics,"Systems of interacting quantum spins show a rich spectrum of quantum phases
and display interesting many-body dynamics. Computing characteristics of even
small systems on conventional computers poses significant challenges. A quantum
simulator has the potential to outperform standard computers in calculating the
evolution of complex quantum systems. Here, we perform a digital quantum
simulation of the paradigmatic Heisenberg and Ising interacting spin models
using a two transmon-qubit circuit quantum electrodynamics setup. We make use
of the exchange interaction naturally present in the simulator to construct a
digital decomposition of the model-specific evolution and extract its full
dynamics. This approach is universal and efficient, employing only resources
which are polynomial in the number of spins and indicates a path towards the
controlled simulation of general spin dynamics in superconducting qubit
platforms.",1502.06778v1
2015-02-28,Dissipative dynamics of entangled finite-spin systems with non-competitive external fields,"We apply a new method based upon thermofield dynamics (TFD) to study
entanglement of finite-spin systems with non-competitive external fields for
both equilibrium and non-equilibrium cases. For the equilibrium finite-spin
systems, the temperature dependence of the extended density matrices is derived
using this method, and the effect of non-competitive external field is
demonstrated. For the non-equilibrium finite-spin systems, the time dependence
of the extended density matrices and the extended entanglement entropies is
derived in accordance with von Noumann equation, and the dissipative dynamics
of the finite-spin systems is argued. Consequently, the applicability of the
TFD-based method to describe entanglement is confirmed in both equilibrium and
non-equilibrium cases with the external fieds.",1503.00052v5
2015-06-16,Resolving Remoter Nuclear Spins in a Noisy Bath by Dynamical Decoupling Design,"We experimentally resolve several weakly coupled nuclear spins in diamond
using a series of novelly designed dynamical decoupling controls. Some nuclear
spin signals, hidden by decoherence under ordinary dynamical decoupling
controls, are shifted forward in time domain to the coherence time range and
thus rescued from the fate of being submerged by the noisy spin bath. In this
way, more and remoter single nuclear spins are resolved. Additionally, the
field of detection can be continuously tuned on sub-nanoscale. This method
extends the capacity of nanoscale magnetometry and may be applicable in other
systems for high-resolution noise spectroscopy.",1506.04826v1
2015-09-10,Ultrafast cooling and heating scenarios for the laser induced phase transition in CuO,"The multiferroic compound CuO exhibits low temperature magnetic properties
similar to antiferromagnetic iron oxides, while the electronic properties have
much more in common with the high $T_c$ cuprate superconductors. This suggests
novel possibilities for the ultrafast optical excitation of magnetism. On the
basis on atomistic spin dynamics simulations, we study the effect of
phonon-assisted multimagnon absorption and photodoping on the spin dynamics in
the vicinity of the first-order phase transition from collinear to spin-spiral
magnetic order. Similar as in recent experiments, we find that for both
excitations the phase transition can proceed on the picosecond timescale.
Interestingly, however, these excitation mechanisms display very distinct
dynamics. Following photodoping, the spin system first cools down on sub-ps
timescales, which we explain as an ultrafast magnetocaloric effect. Opposed to
this, following phonon-assisted multimagnon excitation the spin systems rapidly
heats up and subsequently evolves to the noncollinear phase even under the
influence of isotropic exchange interactions alone.",1509.03202v2
2015-09-15,Dynamical current-induced ferromagnetic and antiferromagnetic resonances,"We demonstrate that ferromagnetic and antiferromagnetic excitations can be
triggered by the dynamical spin accumulations induced by the bulk and surface
contributions of the spin Hall effect. Due to the spin-orbit interaction, a
time-dependent spin density is generated by an oscillatory electric field
applied parallel to the atomic planes of Fe/W(110) multilayers. For symmetric
trilayers of Fe/W/Fe in which the Fe layers are ferromagnetically coupled, we
demonstrate that only the collective out-of-phase precession mode is excited,
while the uniform (in-phase) mode remains silent. When they are
antiferromagnetically coupled, the oscillatory electric field sets the Fe
magnetizations into elliptical precession motions with opposite angular
velocities. The manipulation of different collective spin-wave dynamical modes
through the engineering of the multilayers and their thicknesses may be used to
develop ultrafast spintronics devices. Our work provides a general framework
that probes the realistic responses of materials in the time or frequency
domain.",1509.04599v2
2016-01-06,Mutual synchronization of spin torque nano-oscillators through a non-local and tunable electrical coupling,"The concept of spin torque driven high frequency magnetization dynamics has
opened up the field of spintronics to non-linear physics, potentially in
complex networks of dynamical systems. In the scarce demonstrations of
synchronized spin-torque oscillators, the local nature of the magnetic coupling
that is used have largely hampered a good understanding and thus the control of
the synchronization process. Here we take advantage of the non-local nature of
an electrical coupling to mutually synchronize spin-torque oscillators through
their self-emitted microwave currents. The control of the synchronized state is
achieved at the nanoscale through two active components of spin transfer
torques, but also externally through an electrical delay line. These additional
levels of control of the synchronization capability provide new approaches to
underlie a large variety of nanoscale collective dynamics in complex networks.",1601.01247v1
2016-01-11,Bose-Fermi Mapping and Multi-Branch Spin Chain Model for Strongly Interacting Quantum Gases in One-Dimension: Dynamics and Collective Excitations,"We show that the wave function of a one dimensional spinor gas with contact
$s$-wave interaction, either bosonic or fermionic, can be mapped to the direct
product of the wave function of a spinless Fermi gas with short-range $p$-wave
interaction and that of a spin system governed by spin parity projection
operators. Applying this mapping to strongly interacting spinor gases, we
obtain a generalized spin chain model that captures both the static and
dynamics properties of the system. Using this spin chain model, we investigate
the breathing mode frequency and the quench dynamics of strongly interacting
harmonically trapped spinor gases.",1601.02556v2
2016-01-19,Solid effect DNP polarization dynamics in a system of many spins,"We discuss the polarization dynamics during solid effect dynamic nuclear
polarization (DNP) in a central spin model that consists of an electron
surrounded by many nuclei. To this end we use a recently developed formalism
and validate first its performance by comparing its predictions to results
obtained by solving the Liouville von Neumann master equation. The use of a
Monte Carlo method in our formalism makes it possible to significantly increase
the number of spins considered in the model system. We then analyse the
dependence of the nuclear bulk polarization on the presence of nuclei in the
vicinity of the electron and demonstrate that increasing the minimal distance
between nuclei and electrons leads to a rise of the nuclear bulk polarization.
These observations have implications for the design of radicals that can lead
to impoved values of nuclear spin polarization. Furthermore, we discuss the
potential to extend our formalism for more complex spin systems such as cross
effect DNP.",1601.04921v1
2016-02-13,Spin transport in n-type single-layer transition metal dichalcogenides,"Valley asymmetry of the electron spectrum in transition metal dichalcogenides
(TMDs) originates from the spin-orbit coupling. Presence of spin-orbit fields
of opposite signs for electrons in K and K' valleys in combination with
possibility of intervalley scattering result in a nontrivial spin dynamics.
This dynamics is reflected in the dependence of nonlocal resistance on external
magnetic field (the Hanle curve). We calculate theoretically the Hanle shape in
TMDs. It appears that, unlike conventional materials without valley asymmetry,
the Hanle shape in TMDs is different for normal and parallel orientations of
the external field. For normal orientation, it has two peaks for slow
intervalley scattering, while, for fast intervalley scattering the shape is
usual. For parallel orientation, the Hanle curve exhibits a cusp at zero field.
This cusp is a signature of a slow-decaying valley-asymmetric mode of the spin
dynamics.",1602.04276v1
2016-04-18,Majorana spectroscopy of 3D Kitaev spin-liquids,"We analyse the dynamical response of a range of 3D Kitaev quantum
spin-liquids, using lattice models chosen to explore the different possible
low-energy spectra for gapless Majorana fermions, with either Fermi surfaces,
nodal lines or Weyl points. We find that the behaviour of the dynamical
structure factor is distinct in all three cases, reflecting the quasiparticle
density of states in two fundamentally different ways. First, the low-energy
response is either straightforwardly related to the power with which the
low-energy density of states vanishes; or for a non-vanishing density of
states, to the phase shifts encountered in the corresponding X-ray edge
problem, whose phenomenology we extend to the case of Majorana fermions.
Second, at higher energies, there is a rich fine-structure, determined by
microscopic features of the Majorana spectrum. Our theoretical results test the
usefulness of inelastic neutron scattering as a probe of these quantum spin
liquids: we find that although spin flips fractionalise, the main features of
the dynamical spin response nevertheless admit straightforward interpretations
in terms of Majorana and flux loop excitations.",1604.05199v2
2016-09-27,Steady State and Dynamics of Joule Heating in Magnetic Tunnel Junctions Observed via the Temperature Dependence of RKKY Coupling,"Understanding quantitatively the heating dynamics in magnetic tunnel
junctions (MTJ) submitted to current pulses is very important in the context of
spin-transfer-torque magnetic random access memory development. Here we provide
a method to probe the heating of MTJ using the RKKY coupling of a synthetic
ferrimagnetic storage layer as a thermal sensor. The temperature increase
versus applied bias voltage is measured thanks to the decrease of the spin-flop
field with temperature. This method allows distinguishing spin transfer torque
(STT) effects from the influence of temperature on the switching field. The
heating dynamics is then studied in real-time by probing the conductance
variation due to spin-flop rotation during heating. This approach provides a
new method for measuring fast heating in spintronic devices, particularly
magnetic random access memory (MRAM) using thermally assisted or spin transfer
torque writing.",1609.08385v1
2017-02-01,Ab initio dynamical exchange interactions in frustrated anti-ferromagnets,"The ultrafast response to an optical pulse excitation of the spin-spin
exchange interaction in transition metal anti-ferromagnets is studied within
the framework of the time-dependent spin-density functional theory. We propose
a formulation for the purely dynamical exchange interaction, which is non-local
in space, and it is derived starting from {\it ab initio} arguments. Then, we
investigate the effect of the laser pulse on the onset of the dynamical
process. It is found that we can distinguish two types of excitations, both
activated immediately after the action of the laser pulse. While the first one
can be associated to a Stoner-like excitation and involves the transfer of spin
from one site to another, the second one is related to the ultrafast
modification of a Heisenberg-like exchange interaction and can trigger the
formation of spin waves in the first few hundred femtoseconds of the time
evolution.",1702.00375v1
2017-02-06,Spin resonance under topological driving fields,"We study the dynamics of a localized spin-1/2 driven by a time-periodic
magnetic field that undergoes a topological transition. Despite the strongly
non-adiabatic effects dominating the spin dynamics, we find that the field's
topology appears clearly imprinted in the Floquet spin states through an
effective Berry phase emerging in the quasienergy. This has remarkable
consequences on the spin resonance condition suggesting a whole new class of
experiments to spot topological transitions in the dynamics of spins and other
two-level systems, from nuclear magnetic resonance to strongly-driven
superconducting qubits.",1702.01781v2
2017-03-28,Configuration Memory in Patchwork Dynamics for Low-dimensional Spin Glasses,"A patchwork method is used to study the dynamics of loss and recovery of an
initial configuration in spin glass models in dimensions d=1 and d=2. The
patchwork heuristic is used to accelerate the dynamics to investigate how
models might reproduce the remarkable memory effects seen in experiment.
Starting from a ground state configuration computed for one choice of nearest
neighbor spin couplings, the sample is aged up to a given scale under new
random couplings, leading to the partial erasure of the original ground state.
The couplings are then restored to the original choice and patchwork coarsening
is again applied, in order to assess the recovery of the original state.
Eventual recovery of the original ground state upon coarsening is seen in
two-dimensional Ising spin glasses and one-dimensional Potts models, while
one-dimensional Ising glasses neither lose nor gain overlap with the ground
state during the recovery stage. The recovery for the two-dimensional Ising
spin glasses suggests scaling relations that lead to a recovery length scale
that grows as a power of the aging length scale.",1703.09806v2
2018-02-26,Unusual spin-wave dynamics in core-shell magnetic nanodisks,"We investigated the spin dynamics of a vortex state in a core-shell magnetic
nanodisk driven by an oscillating field applied perpendicular to the disk plane
by means of micromagnetic simulations. The nanodisk comprises a Py (Fe0.2Ni0.8)
core of 100 nm in radius, surrounded by a 50 nm thick Fe shell. Fourier
transform analyses show that the Py core and the Fe shell dominate spin-wave
oscillation at the fundamental and higher order radial modes, respectively. For
oscillating driving field tuned to the fundamental eigenfrequency, the Py/Fe
interface effectively confines spin-wave excitation in the Py core region. This
effect leads to significantly more rapid vortex core (VC) reversal in
comparison to homogeneous disks. Our work demonstrates that the higher order
modes can drive much faster VC reversal than the fundamental mode, in sharp
contrast to the results obtained in homogeneous disks. With excitation levels
up to 30 mT, we find strong nonlinear spin-wave dynamics in the system, which
results in mode frequency redshifting, therefore the observation of the most
rapid VC reversals below eigenfrequencies and VC switching in wide ranges of
frequencies.",1802.09181v1
2018-02-28,Distinctive Picosecond Spin Polarization Dynamics in Bulk Half-Metals,"Femtosecond laser excitations in half-metal (HM) compounds are theoretically
predicted to induce an exotic picosecond spin dynamics. In particular,
conversely to what is observed in conventional metals and semiconductors, the
thermalization process in HMs leads to a long living partially thermalized
configuration characterized by three Fermi--Dirac distributions for the
minority, majority conduction and majority valence electrons respectively.
Remarkably, these distributions have the same temperature but different
chemical potentials. This unusual thermodynamics state causes a persistent
non-equilibrium spin polarization only well above the Fermi energy. Femtosecond
spin dynamics experiments performed on Fe$_3$O$_4$ by time-, spin-, and
angle-resolved photoelectron spectroscopy confirm our model. Furthermore, the
spin polarization response proves to be very robust and it can be adopted to
selectively test the bulk HM character in a wide range of compounds.",1802.10356v1
2018-11-30,Subsecond nuclear spin dynamics in $n$-GaAs,"We use time-resolved detection of the Hanle effect and polarized
photoluminescence with dark intervals to investigate the buildup and decay of
the spin polarization of nuclei interacting with donor-bound electrons in
$n$-doped GaAs. Strong hyperfine coupling defines the millisecond timescale of
the spin dynamics of these nuclei, as distinct from the nuclei far from
impurity centers, characterized by a thousand times longer spin-relaxation
time. The dynamics of spin polarization and relaxation attributed to the nuclei
inside the donor orbit is observed on the time scale from 200 to 425 ms.",1811.12885v2
2019-05-27,Phase Diagram and Quench Dynamics in a Spinful Interacting Kitaev Chain,"We consider an exact solvable interacting spinful Kitaev chain which is a
generalization of the Mattis-Nam model. A nearest-neighbor dimerized
interaction favoring the production of disjoint molecules drives the quantum
phase into an insulating one. The phases are characterized statically and
dynamically in terms of magnetization and spin-singlet correlations by using
the exact solution. The model is shown to be exactly solvable also in the
presence of boundary interactions which are originated from a spin-singlet
superconducting pairing and a magnetic field. We exploit the exact solution to
investigate the out-of-equilibrium dynamics as due to a quench at the boundary.
The propagation of the disturbance in nearest-neighbor magnetic and
spin-singlet pairing displays a ballistic behavior for long times with
different velocities.",1905.11090v3
2013-08-13,Non-equilibrium finite temperature dynamics of magnetic quantum systems: Applications to spin-polarized scanning tunneling microscopy,"We calculate the real time non-equilibrium dynamics of quantum spin systems
at finite temperatures. The mathematical framework originates from the
$C^*$-approach to quantum statistical mechanics and is applied to samples
investigated by means of spin-polarized scanning tunneling microscopy. Quantum
fluctuations around thermal equilibrium are analyzed and calculated. The time
averaged expectation values agree with the time averaged experimental data for
magnetization curves. The method is used to investigate the dynamics of a
sample for shorter times than the resolution time of the experimental setup.
Furthermore, predictions for relaxation times of single spins on metallic and
semiconductor surfaces are made. To check the validity of our model we compare
our results with experimental data obtained from Fe adatoms on InSb and Co
adatoms on Pt(111) and find good agreement. Approximated thermalization is
found numerically for the expectation values of the spin operators.",1308.2875v1
2011-12-30,How do spins interact coherently with ultrashort laser pulses ?,"We investigate the interaction of femtosecond laser pulses with spins
including relativistic corrections. The time-ordered magneto-optical signals
corresponding to a pump-probe configuration are calculated in the case of one
electron submitted to a magnetic field and evolving in eight levels of the fine
structure of a hydrogen-like atom. Our simulations explain the origin of the
coherent magneto-optical response and ultrafast spin dynamics in ferromagnets
excited by intense laser pulses as recently reported in Ni and CoPt3
ferromagnetic thin films. Our detailed analysis allows identifying the
respective roles of the coherent spin-photon interaction and spin dynamics
unraveling recent controversies about the laser induced ultrafast magnetization
dynamics.",1201.0166v1
2012-03-31,Spin Squeezing under Non-Markovian Channels by Hierarchy Equation Method,"We study spin squeezing under non-Markovian channels, and consider an
ensemble of $N$ independent spin-1/2 particles with exchange symmetry. Each
spin interacts with its own bath, and the baths are independent and identical.
For this kind of open system, the spin squeezing under decoherence can be
investigated from the dynamics of the local expectations, and the multi-qubit
dynamics can be reduced into the two-qubit one. The reduced dynamics is
obtained by the hierarchy equation method, which is a exact without
rotating-wave and Born-Markov approximation. The numerical results show that
the spin squeezing displays multiple sudden vanishing and revival with lower
bath temperature, and it can also vanish asymptotically.",1204.0093v1
2014-05-04,Spin Torque Oscillators with Thermal Noise: A Constant Energy Orbit Approach,"We consider a biaxial macrospin with an easy and hard axis, and study its
dynamical evolution under the combined effects of thermal noise and spin
transfer torque. The spin-torque is associated with both a perpendicularly
magnetized polarizer and an in-plane magnetized reference layer, leading to an
effective tilt between the easy and spin polarization axes. Using techniques
based on energy averaging over the relevant dynamical trajectories, we analyze
the effects of tilt on the dynamics and derive the conditions for the
occurrence of stable out-of-plane precessionary states. The presence of these
states and their predicted stability boundaries can be tested in experiments on
orthogonal spin-transfer devices, and may also serve as a test of the
applicability of the macrospin model to real devices, which have internal
magnetic degrees of freedom.",1405.0731v3
2014-05-29,From quantum-mechanical to classical dynamics in the central-spin model,"We discuss the semiclassical and classical character of the dynamics of a
single spin 1/2 coupled to a bath of noninteracting spins 1/2. On the
semiclassical level, we extend our previous approach presented in D. Stanek, C.
Raas, and G. S. Uhrig, Phys. Rev. B 88, 155305 (2013) by the explicit
consideration of the conservation of the total spin. On the classical level, we
compare the results of the classical equations of motions in absence and
presence of an external field to the full quantum result obtained by
density-matrix renormalization (DMRG). We show that for large bath sizes and
not too low magnetic field the classical dynamics, averaged over Gaussian
distributed initial spin vectors, agrees quantitatively with the
quantum-mechanical one. This observation paves the way for an efficient
approach for certain parameter regimes.",1405.7594v2
2014-06-18,Quantum magnetism with ultracold molecules,"This article gives an introduction to the realization of effective quantum
magnetism with ultracold molecules in an optical lattice, reviews experimental
and theoretical progress, and highlights future opportunities opened up by
ongoing experiments. Ultracold molecules offer capabilities that are otherwise
difficult or impossible to achieve in other effective spin systems, such as
long-ranged spin-spin interactions with controllable degrees of spatial and
spin anisotropy and favorable energy scales. Realizing quantum magnetism with
ultracold molecules provides access to rich many-body behaviors, including many
exotic phases of matter and interesting excitations and dynamics.
Far-from-equilibrium dynamics plays a key role in our exposition, just as it
did in recent ultracold molecule experiments realizing effective quantum
magnetism. In particular, we show that dynamical probes allow the observation
of correlated many-body spin physics, even in polar molecule gases that are not
quantum degenerate. After describing how quantum magnetism arises in ultracold
molecules and discussing recent observations of quantum magnetism with polar
molecules, we survey prospects for the future, ranging from immediate goals to
long-term visions.",1406.4758v1
2014-06-30,Dynamical topological quantum computation using spin pulse control in the Heisenberg model,"Hamiltonian engineering is an important approach for quantum information
processing, when appropriate materials do not exist in nature or are unstable.
So far there is no stable material for the Kitaev spin Hamiltonian with
anisotropic interactions on a honeycomb lattice (A. Kitaev, Annals of Physics
vol 321, 2 (2006)), which plays a crucial role in the realization of both
Abelian and non-Abelian anyons. Here, we show how to dynamically realize the
Kitaev spin Hamiltonian from the conventional Heisenberg spin Hamiltonian using
a pulse-control technique. By repeating the same pulse sequence, the quantum
state is dynamically preserved. The effects of the spin-orbit interaction and
the hyperfine interaction are also investigated.",1406.7631v1
2019-06-30,"Non-linear spin torque, pumping and cooling in superconductor/ferromagnet systems","We study the effects of the coupling between magnetization dynamics and the
electronic degrees of freedom in a heterostructure of a metallic nanomagnet
with dynamic magnetization coupled with a superconductor containing a steady
spin-splitting field. We predict how this system exhibits a non-linear spin
torque, which can be driven either with a temperature difference or a voltage
across the interface. We generalize this notion to arbitrary magnetization
precession by deriving a Keldysh action for the interface, describing the
coupled charge, heat and spin transport in the presence of a precessing
magnetization. We characterize the effect of superconductivity on the
precession damping and the anti-damping torques. We also predict the full
non-linear characteristic of the Onsager counterparts of the torque, showing up
via pumped charge and heat currents. For the latter, we predict a spin-pumping
cooling effect, where the magnetization dynamics can cool either the nanomagnet
or the superconductor.",1907.00424v2
2019-10-10,Slow Nonthermalizing Dynamics in a Quantum Spin Glass,"Spin glasses and many-body localization (MBL) are prime examples of
ergodicity breaking, yet their physical origin is quite different: the former
phase arises due to rugged classical energy landscape, while the latter is a
quantum-interference effect. Here we study quantum dynamics of an isolated 1d
spin-glass under application of a transverse field. At high energy densities,
the system is ergodic, relaxing via resonance avalanche mechanism, that is also
responsible for the destruction of MBL in non-glassy systems with power-law
interactions. At low energy densities, the interaction-induced fields obtain a
power-law soft gap, making the resonance avalanche mechanism inefficient. This
leads to the persistence of the spin-glass order, as demonstrated by resonance
analysis and by numerical studies. A small fraction of resonant spins forms a
thermalizing system with long-range entanglement, making this regime distinct
from the conventional MBL. The model considered can be realized in systems of
trapped ions, opening the door to investigating slow quantum dynamics induced
by glassiness.",1910.04421v2
2019-10-25,Nutation Wave as a Platform for Ultrafast Spin Dynamics in Ferromagnets,"At short time scales the inertia term becomes relevant for the magnetization
dynamics of ferromagnets and leads to nutation for the magnetization vector.
For the case of spatially extended magnetic systems, for instance Heisenberg
spin chains with isotropic spin-exchange interaction, this leads to the
appearance of a novel collective excitation, the ""nutation wave"", whose
properties are elucidated by analytic arguments and numerical studies. The
one--particle excitations can be identified as relativistic massive particles.
These particles, the ""nutatons"", acquire their mass via the Brout-Englert-Higgs
mechanism, through the interaction of the wave with an emergent topological
gauge field. This spin excitation would appear as a peak in the spectrum of the
scattering structure factor in inelastic neutron scattering experiments. The
high frequency and speed of the nutation wave can open new paths for realizing
ultrafast spin dynamics.",1910.11897v3
2019-10-29,A hierarchical mean field model of interacting spins,"We consider a system of hierarchical interacting spins under dynamics of
spin-flip type with a ferromagnetic mean field interaction, scaling with the
hierarchical distance, coupled with a system of linearly interacting
hierarchical diffusions of Ornstein-Uhlenbeck type. In particular, the
diffusive variables enter in the spin-flip rates, effectively acting as
dynamical magnetic fields. In absence of the diffusions, the spin-flip dynamics
can be thought of as a modification of the Curie--Weiss model. We study the
mean field and the two-level hierarchical model, in the latter case restricting
to a subcritical regime, corresponding to high temperatures, obtaining
macroscopic limits at different spatio-temporal scales and studying the phase
transitions in the system. We also formulate a generalization of our results to
the $k$-th level hierarchical case, for any $k$ finite, in the subcritical
regime. We finally address the supercritical regime, in the zero-temperature
limit, for the two-level hierarchical case, proceeding heuristically with the
support of numerics.",1910.13469v1
2020-04-23,Quantum mechanical spin dynamics of a molecular magnetoreceptor,"Radical pair recombination reactions are known to be sensitive to extremely
weak magnetic fields, and can therefore be said to function as molecular
magnetoreceptors. The classic example is a carotenoid-porphyrin-fullerene
(C+PF-) radical pair that has been shown to provide a ""proof-of-principle"" for
the operation of a chemical compass [K. Maeda et al., Nature 453, 387 (2008)].
Previous simulations of this radical pair have employed semiclassical
approximations, which are routinely applicable to its 47 coupled electronic and
nuclear spins. However, calculating the exact quantum mechanical spin dynamics
presents a significant challenge, and has not been possible before now. Here we
use a recently developed method to perform numerically converged simulations of
the C+PF- quantum mechanical spin dynamics, including all coupled spins.
Comparison of these quantum mechanical simulations with various semiclassical
approximations reveals that, while it is not perfect, the best semiclassical
approximation does capture essentially all of the relevant physics in this
problem.",2004.11261v1
2020-12-10,Estimating the black hole spin for the X-ray binary MAXI J1820+070,"MAXI J1820+070 is a newly-discovered black hole X-ray binary, whose dynamical
parameters, namely the black hole mass, the inclination angle and the source
distance, have been estimated recently. \emph{Insight}-HXMT have observed its
entire outburst from March 14th, 2018. In this work, we attempted to estimate
the spin parameter~$a_*$, using the continuum-fitting method and applying a
fully-relativistic thin disk model to the soft-state spectra obtained by
\emph{Insight}-HXMT. It is well know that $a_*$ is strongly dependent on three
dynamical parameters in this method, and we have examined two sets of
parameters. Adopting our preferred parameters: $M$ =
$8.48^{+0.79}_{-0.72}~M_\odot$, $i=63^\circ\pm3^\circ$ and $D=2.96\pm0.33$ kpc,
we found a slowly-spinning black hole of $a_*=0.14 \pm 0.09$ ($1\sigma$), which
give a prograde spin parameter as majority of other systems show. While it is
also possible for the black hole to have a retrograde spin (less than 0) if
different dynamical parameters are taken.",2012.05544v2
2021-01-18,Quantum-accurate magneto-elastic predictions with classical spin-lattice dynamics,"A data-driven framework is presented for building magneto-elastic
machine-learning interatomic potentials (ML-IAPs) for large-scale spin-lattice
dynamics simulations. The magneto-elastic ML-IAPs are constructed by coupling a
collective atomic spin model with an ML-IAP. Together they represent a
potential energy surface from which the mechanical forces on the atoms and the
precession dynamics of the atomic spins are computed. Both the atomic spin
model and the ML-IAP are parametrized on data from first-principles
calculations. We demonstrate the efficacy of our data-driven framework across
magneto-structural phase transitions by generating a magneto-elastic ML-IAP for
{\alpha}-iron. The combined potential energy surface yields excellent agreement
with first-principles magneto-elastic calculations and quantitative predictions
of diverse materials properties including bulk modulus, magnetization, and
specific heat across the ferromagnetic-paramagnetic phase transition.",2101.07332v3
2000-06-16,Spin fluctuations in nearly magnetic metals from ab-initio dynamical spin susceptibility calculations:application to Pd and Cr95V5,"We describe our theoretical formalism and computational scheme for making
ab-initio calculations of the dynamic paramagnetic spin susceptibilities of
metals and alloys at finite temperatures. Its basis is Time-Dependent Density
Functional Theory within an electronic multiple scattering, imaginary time
Green function formalism. Results receive a natural interpretation in terms of
overdamped oscillator systems making them suitable for incorporation into spin
fluctuation theories. For illustration we apply our method to the nearly
ferromagnetic metal Pd and the nearly antiferromagnetic chromium alloy Cr95V5.
We compare and contrast the spin dynamics of these two metals and in each case
identify those fluctuations with relaxation times much longer than typical
electronic `hopping times'",0006268v1
2017-11-22,Irreversible Markov chains in spin models: Topological excitations,"We analyze the convergence of the irreversible event-chain Monte Carlo
algorithm for continuous spin models in the presence of topological
excitations. In the two-dimensional XY model, we show that the local nature of
the Markov-chain dynamics leads to slow decay of vortex-antivortex correlations
while spin waves decorrelate very quickly. Using a Frechet description of the
maximum vortex-antivortex distance, we quantify the contributions of
topological excitations to the equilibrium correlations, and show that they
vary from a dynamical critical exponent z \sim 2 at the critical temperature to
z \sim 0 in the limit of zero temperature. We confirm the event-chain
algorithm's fast relaxation (corresponding to z = 0) of spin waves in the
harmonic approximation to the XY model. Mixing times (describing the approach
towards equilibrium from the least favorable initial state) however remain much
larger than equilibrium correlation times at low temperatures. We also describe
the respective influence of topological monopole-antimonopole excitations and
of spin waves on the event-chain dynamics in the three-dimensional Heisenberg
model.",1711.08375v1
2017-11-24,Coherence of a dynamically decoupled quantum-dot hole spin,"A heavy hole confined to an InGaAs quantum dot promises the union of a stable
spin and optical coherence to form a near perfect, high-bandwidth spin-photon
interface. Despite theoretical predictions and encouraging preliminary
measurements, the dynamic processes determining the coherence of the hole spin
are yet to be understood. Here, we establish the regimes that allow for a
highly coherent hole spin in these systems, recovering a crossover from
hyperfine to electrical-noise dominated decoherence with a few-Tesla external
magnetic field. Dynamical decoupling allows us to reach the longest
ground-state coherence time, T2, of 4.4 $\mu$s, observed in this system. The
improvement of coherence we measure is quantitatively supported by an
independent analysis of the local electrical environment.",1711.09169v1
2018-06-07,Terahertz Emission from Compensated Magnetic Heterostructures,"Terahertz emission spectroscopy (TES) has recently played an important role
in unveiling the spin dynamics at a terahertz (THz) frequency range. So far,
ferromagnetic (FM)/nonmagnetic (NM) heterostructures have been intensively
studied as THz sources. Compensated magnets such as a ferrimagnet (FIM) and
antiferromagnet (AFM) are other types of magnetic materials with interesting
spin dynamics. In this work, we study TES from compensated magnetic
heterostructures including CoGd FIM alloy or IrMn AFM layers. Systematic
measurements on composition and temperature dependences of THz emission from
CoGd/Pt bilayer structures are conducted. It is found that the emitted THz
field is determined by the net spin polarization of the laser induced spin
current rather than the net magnetization. The temperature robustness of the
FIM based THz emitter is also demonstrated. On the other hand, an AFM plays a
different role in THz emission. The IrMn/Pt bilayer shows negligible THz
signals, whereas Co/IrMn induces sizable THz outputs, indicating that IrMn is
not a good spin current generator, but a good detector. Our results not only
suggest that a compensated magnet can be utilized for robust THz emission, but
also provide a new approach to study the magnetization dynamics especially near
the magnetization compensation point.",1806.02517v1
2018-06-26,Probing quantum thermalization of a disordered dipolar spin ensemble with discrete time-crystalline order,"We investigate thermalization dynamics of a driven dipolar many-body quantum
system through the stability of discrete time crystalline order. Using periodic
driving of electronic spin impurities in diamond, we realize different types of
interactions between spins and demonstrate experimentally that the interplay of
disorder, driving and interactions leads to several qualitatively distinct
regimes of thermalization. For short driving periods, the observed dynamics are
well described by an effective Hamiltonian which sensitively depends on
interaction details. For long driving periods, the system becomes susceptible
to energy exchange with the driving field and eventually enters a universal
thermalizing regime, where the dynamics can be described by interaction-induced
dephasing of individual spins. Our analysis reveals important differences
between thermalization of long-range Ising and other dipolar spin models.",1806.10169v1
2018-07-14,Quantum continuum fluctuations in glassy perovskite Ca(Co$_{0.15}$Ru$_{0.85}$)O$_{3}$,"The quantum spin continuum and classical spin freezing, associated with a
glassy state, represent two opposite extremes of a correlated electronic
material. Here, we report the coexistence of a quantum spin continuum with a
weak spin glass order in Co-doped CaRuO$_{3}$ perovskite near the chemical
doping dependent metal-insulator transition boundary. Inelastic neutron
measurements on Ca(Co$_{0.15}$Ru$_{0.85}$)O$_{3}$ at low temperature, $T$ = 1.5
K, reveal a continuum spectrum in the $Q-E$ space due to uncorrelated spin
fluctuations. This persists across the glass transition at $T_G \simeq$23 K.
Furthermore, scaling of the dynamic susceptibility yields a very small scaling
coefficient $\alpha$ $\simeq$ 0.1, suggesting extreme locality of the dynamic
properties. The experimental results indicate the realization of a narrow
regime where the distinction between continuum dynamic behavior and glass-like
regimes is reduced.",1807.05404v1
2018-12-22,Atomic antiferromagnetic domain wall propagation beyond the relativistic limit,"We theoretically investigate the dynamics of atomic domain walls (DWs) in
antiferromagnets driven by a spin-orbit field. For a DW with the width of a few
lattice constants, we identify a Peierls-like pinning effect, with the
depinning field exponentially decaying with the DW width, so that a spin-orbit
field moderately larger than the threshold can drive the propagation of an
atomic DW in a step-wise manner. For a broad DW, the Peierls pinning is
negligibly small. However, the external spin-orbit field can induce a fast DW
propagation, accompanied by a significant shrinking of its width down to atomic
scales. Before stepping into the pinning region, noticeable spin waves are
emitted at the tail of the DW. The spin-wave emission event not only broadens
the effective width of the DW, but also pushes the DW velocity over the
magnonic barrier, which is generally believed to be the relativistic limit of
the DW speed. While the existing dynamic theory based on the continuum
approximation fails in the atomic scale, we develop an energy conversion theory
to interpret the DW dynamics beyond the relativistic limit.",1812.09540v1
2019-03-03,Dynamical mode coupling and coherence in spin Hall nano-oscillator with perpendicular magnetic anisotropy,"We experimentally study the dynamical modes excited by spin current in Spin
Hall nano-oscillators based on the Pt/[Co/Ni] multilayers with perpendicular
magnetic anisotropy. Both propagating spin wave and localized solitonic modes
of the oscillation are achieved and controlled by varying the applied magnetic
field and current. At room temperature, the generation linewidth broadening
associated with mode hopping was observed at currents close to the transition
between different modes and in the mode coexistence regimes. The mode hopping
was suppressed at cryogenic temperatures, confirming that the coupling between
modes is mediated by thermal magnons. We also demonstrate that coherent
single-mode oscillations with linewidth of 5 MHz can be achieved without
applying external magnetic field. Our results provide insight into the
mechanisms controlling the dynamical coherence in nanomagnetic oscillators, and
guidance for optimizing their applications in spin wave-based electronics.",1903.00822v1
2019-03-16,Critical phenomena and nonlinear dynamics in a spin ensemble strongly coupled to a cavity. II. Semiclassical-to-quantum boundary,"We numerically study the dynamics and stationary states of a spin ensemble
strongly coupled to a single-mode resonator subjected to loss and external
driving. Employing a generalized cumulant expansion approach we analyze
finite-size corrections to a semiclassical description of amplitude
bistability, which is a paradigm example of a driven-dissipative phase
transition. Our theoretical model allows us to include inhomogeneous broadening
of the spin ensemble and to capture in which way the quantum corrections
approach the semiclassical limit for increasing ensemble size $N$. We set up a
criterion for the validity of the Maxwell-Bloch equations and show that close
to the critical point of amplitude bistability even very large spin ensembles
consisting of up to $10^4$ spins feature significant deviations from the
semiclassical theory.",1903.06893v2
2019-03-20,Investigating ultrafast quantum magnetism with machine learning,"We investigate the efficiency of the recently proposed Restricted Boltzmann
Machine (RBM) representation of quantum many-body states to study both the
static properties and quantum spin dynamics in the two-dimensional Heisenberg
model on a square lattice. For static properties we find close agreement with
numerically exact Quantum Monte Carlo results in the thermodynamical limit. For
dynamics and small systems, we find excellent agreement with exact
diagonalization, while for systems up to N=256 spins close consistency with
interacting spin-wave theory is obtained. In all cases the accuracy converges
fast with the number of network parameters, giving access to much bigger
systems than feasible before. This suggests great potential to investigate the
quantum many-body dynamics of large scale spin systems relevant for the
description of magnetic materials strongly out of equilibrium.",1903.08482v3
2019-03-29,Ultra-fast electric field controlled spin-fluctuations in the Hubbard model,"Highly intense electric field pulses can move the electronic momentum
occupation in correlated metals over large portions of the Brillouin zone,
leading to phenomena such as dynamic Bloch oscillations. Using the
non-equilibrium fluctuation-exchange approximation for the two-dimensional
Hubbard model, we study how such non-thermal electron-distributions drive
collective spin and charge fluctuations. Suitable pulses can induce a highly
anisotropic modification of the occupied momenta, and the corresponding spin
dynamics results in a transient change from antiferromagnetic to anisotropic
ferromagnetic correlations. To good approximation this behavior is understood
in terms of an instantaneous response of the spin fluctuations to the
single-particle properties, opposite to the conventional time-scale separation
between spin and electron dynamics.",1904.00098v1
2019-04-08,Impact of high spins on the ejection of mass in GW170817,"Following the detection of GW170817 and the accompanying kilonova AT2017gfo,
it has become crucial to model and understand the various channels through
which mass is ejected in neutron-star binary mergers. We discuss the impact
that high stellar spins prior to merger have on the ejection of mass focussing,
in particular, on the dynamically ejected mass by performing
general-relativistic magnetohydrodynamic simulations employing
finite-temperature equations of state and neutrino-cooling effects. Using eight
different models with dimensionless spins ranging from $\chi\simeq-0.14$ to
$\chi\simeq0.29$ we discuss how the presence of different spins affects the
angular distribution and composition of the ejected matter. Most importantly,
we find that the dynamical component of the ejected mass can be strongly
suppressed in the case of high spins aligned with the orbital angular momentum.
In this case, in fact, the merger remnant has an excess angular momentum
yielding a more extended and ""colder"" object, with reduced ability to shed mass
dynamically. We discuss how this result impacts the analysis of the recent
merger event GW170817 and its kilonova afterglow.",1904.04220v2
2019-04-17,Controlling Dipolar Exchange Interactions in a Dense 3D Array of Large Spin Fermions,"Dipolar interactions are ubiquitous in nature and rule the behavior of a
broad range of systems spanning from energy transfer in biological systems to
quantum magnetism. Here, we study magnetization-conserving dipolar induced
spin-exchange dynamics in dense arrays of fermionic erbium atoms confined in a
deep three-dimensional lattice. Harnessing the special atomic properties of
erbium, we demonstrate control over the spin dynamics by tuning the dipole
orientation and changing the initial spin state within the large 20 spin
hyperfine manifold. Furthermore, we demonstrate the capability to quickly turn
on and off the dipolar exchange dynamics via optical control. The experimental
observations are in excellent quantitative agreement with numerical
calculations based on discrete phase-space methods, which capture entanglement
and beyond-mean field effects. Our experiment sets the stage for future
explorations of rich magnetic behaviors in long-range interacting dipoles,
including exotic phases of matter and applications for quantum information
processing.",1904.08262v1
2019-04-18,Radical pair intersystem crossing: Quantum dynamics or incoherent kinetics?,"Magnetic field effects on radical pair reactions arise due to the interplay
of coherent electron spin dynamics and spin relaxation effects, a rigorous
treatment of which requires the solution of the Liouville-von Neumann equation.
However, it is often found that simple incoherent kinetic models of the radical
pair singlet-triplet intersystem crossing provide an acceptable description of
experimental measurements. In this paper we outline the theoretical basis for
this incoherent kinetic description, elucidating its connection to exact
quantum mechanics. We show in particular how the finite lifetime of the radical
pair spin states, as well as any additional spin-state dephasing, leads to
incoherent intersystem crossing. We arrive at simple expressions for the
radical pair spin state interconversion rates to which the functional form
proposed recently by Steiner et al. [J. Phys. Chem. C 122, 11701 (2018)] can be
regarded as an approximation. We also test the kinetic master equation against
exact quantum dynamical simulations for a model radical pair and for a series
of $\text{PTZ}^{\bullet+}\text{-Ph}_\text{n}\text{-PDI}^{\bullet-}$ molecular
wires.",1904.09025v1
2019-11-05,Engineering the dynamics of topological spin textures by anisotropic spin-orbit torques,"Integrating topologically stabilized magnetic textures such as skyrmions as
nanoscale information carriers into future technologies requires the reliable
control by electric currents. Here, we uncover that the relevant skyrmion Hall
effect, which describes the deflection of moving skyrmions from the current
flow direction, acquires important corrections owing to anisotropic spin-orbit
torques that alter the dynamics of topological spin structures. Thereby, we
propose a viable means for manipulating the current-induced motion of skyrmions
and antiskyrmions. Based on these insights, we demonstrate by first-principles
calculations and symmetry arguments that the motion of spin textures can be
tailored by materials design in magnetic multilayers of Ir/Co/Pt and Au/Co/Pt.
Our work advances the understanding of the current-induced dynamics of these
magnetic textures, which underlies a plethora of memory and logic applications.",1911.01987v1
2019-12-27,Dynamical spin-to-charge conversion on the edge of quantum spin Hall insulator,"We theoretically manifest that the edge of a quantum spin Hall insulator
(QSHI), attached to an insulating ferromagnet (FM), can realize a highly
efficient spin-to-charge conversion. Based on a one-dimensional QSHI-FM
junction, the electron dynamics on the QSHI edge is analyzed, driven by a
magnetization dynamics in the FM. Under a large gap opening on the edge from
the magnetic exchange coupling, we find that the spin injection into the QSHI
edge gets suppressed while the charge current driven on the edge gets
maximized, demanded by the band topology of the one-dimensional helical edge
states.",1912.11957v2
2020-05-18,Dynamical decoupling of spin ensembles with strong anisotropic interactions,"Ensembles of dopants have widespread applications in quantum technology. The
miniaturization of corresponding devices is however hampered by dipolar
interactions that reduce the coherence at increased dopant density. We
theoretically and experimentally investigate this limitation. We find that
dynamical decoupling can alleviate, but not fully eliminate, the decoherence in
crystals with strong anisotropic spin-spin interactions. Our findings can be
generalized to all quantum systems with anisotropic g-factor used for quantum
sensing, microwave-to-optical conversion, and quantum memory.",2005.08822v2
2020-09-01,Quantum Brownian Motion for Magnets,"Spin precession in magnetic materials is commonly modelled with the classical
phenomenological Landau-Lifshitz-Gilbert (LLG) equation. Based on a quantized
spin+environment Hamiltonian, we here derive a general spin operator equation
of motion that describes three-dimensional precession and damping and
consistently accounts for effects arising from memory, coloured noise and
quantum statistics. The LLG equation is recovered as its classical, Ohmic
approximation. We further introduce resonant Lorentzian system--reservoir
couplings that allow a systematic comparison of dynamics between Ohmic and
non--Ohmic regimes. Finally, we simulate the full non-Markovian dynamics of a
spin in the semi--classical limit. At low temperatures, our numerical results
demonstrate a characteristic reduction and flattening of the steady state spin
alignment with an external field, caused by the quantum statistics of the
environment. The results provide a powerful framework to explore general
three-dimensional dissipation in quantum thermodynamics.",2009.00600v2
2020-09-27,Dynamical spin susceptibility in La2CuO4 studied by resonant inelastic x-ray scattering,"Resonant inelastic X-ray scattering (RIXS) is a powerful probe of elementary
excitations in solids. It is now widely applied to study magnetic excitations.
However, its complex cross-section means that RIXS has been more difficult to
interpret than inelastic neutron scattering (INS). Here we report
high-resolution RIXS measurements of magnetic excitations of La2CuO4, the
antiferromagnetic parent of one system of high-temperature superconductors. At
high energies (~2 eV), the RIXS spectra show angular-dependent dd orbital
excitations which are found to be in good agreement with single-site multiplet
calculations. At lower energies (<0.3 eV), we show that the
wavevector-dependent RIXS intensities are proportional to the product of the
single-ion spin-flip cross section and the dynamical susceptibility of the
spin-wave excitations. When the spin-flip crosssection is dividing out, the
RIXS magnon intensities show a remarkable resemblance to INS data. Our results
show that RIXS is a quantitative probe the dynamical spin susceptibility in
cuprate and therefore should be used for quantitative investigation of other
correlated electron materials.",2009.12925v1
2020-10-13,Information Processing Capacity of Spin-Based Quantum Reservoir Computing Systems,"The dynamical behaviour of complex quantum systems can be harnessed for
information processing. With this aim, quantum reservoir computing (QRC) with
Ising spin networks was recently introduced as a quantum version of classical
reservoir computing. In turn, reservoir computing is a neuro-inspired machine
learning technique that consists in exploiting dynamical systems to solve
nonlinear and temporal tasks. We characterize the performance of the spin-based
QRC model with the Information Processing Capacity (IPC), which allows to
quantify the computational capabilities of a dynamical system beyond specific
tasks. The influence on the IPC of the input injection frequency, time
multiplexing, and different measured observables encompassing local spin
measurements as well as correlations, is addressed. We find conditions for an
optimum input driving and provide different alternatives for the choice of the
output variables used for the readout. This work establishes a clear picture of
the computational capabilities of a quantum network of spins for reservoir
computing. Our results pave the way to future research on QRC both from the
theoretical and experimental points of view.",2010.06369v1
2020-10-21,A Frustrated Bimeronium: Static Structure and Dynamics,"We show a topological spin texture called ""bimeronium"" in magnets with
in-plane magnetization. It is a topological counterpart of skyrmionium in
perpendicularly magnetized magnets and can be seen as a combination of two
bimerons with opposite topological charges. We report the static structure and
spin-orbit-torque-induced dynamics of an isolated bimeronium in a magnetic
monolayer with frustrated exchange interactions. We study the anisotropy and
magnetic field dependences of a static bimeronium. We also explore the
bimeronium dynamics driven by the damping-like spin-orbit torque. We find that
the bimeronium shows steady rotation when the spin polarization direction is
parallel to the easy axis. Moreover, we demonstrate the annihilation of the
bimeronium when the spin polarization direction is perpendicular to the easy
axis. Our results are useful for understanding fundamental properties of
bimeronium structures and may offer an approach to build bimeronium-based
spintronic devices.",2010.10822v2
2020-10-29,Collective spin dynamics under dissipative spin Hall torque,"Current-induced spin torques in layered magnetic heterostructures have many
commonalities across broad classes of magnetic materials. These include not
only collinear ferromagnets, ferrimagnets, and antiferromagnets, but also more
complex noncollinear spin systems. We develop a general Lagrangian-Rayleigh
approach for studying the role of dissipative torques, which can pump energy
into long-wavelength magnetic dynamics, causing dynamic instabilities. While
the Rayleigh structure of such torques is similar for different magnetic
materials, their consequences depend sensitively on the nature of the order
and, in particular, on whether there is a net magnetic moment. The latter
endows the system with a unipolar switching capability, while magnetically
compensated materials tend to evolve towards limit cycles, at large torques,
with chirality dependent on the torque sign. Apart from the ferromagnetic and
antiferromagnetic cases, we discuss ferrimagnets, which display an intricate
competition between switching and limit cycles. As a simple case for
compensated noncollinear order, we consider isotropic spin glasses, as well as
a scenario of their coexistence with a collinear magnetic order.",2010.15994v1
2020-11-10,Shortcuts to Dynamic Polarization,"Dynamic polarization protocols aim to hyperpolarize a spin bath by
transferring spin polarization from a well-controlled qubit such as a quantum
dot or a color defect. Building on techniques from shortcuts to adiabaticity,
we design fast and efficient dynamic polarization protocols in central spin
models that apply to dipolarly interacting systems. The protocols maximize the
transfer of polarization via bright states at a nearby integrable point,
exploit the integrability-breaking terms to reduce the statistical weight on
dark states that do not transfer polarization, and realize experimentally
accessible local counterdiabatic driving through Floquet-engineering. A master
equation treatment suggests that the protocol duration scales linearly with the
number of bath spins with a prefactor that can be orders of magnitude smaller
than that of unassisted protocols. This work opens new pathways to cool spin
baths and extend qubit coherence times for applications in quantum information
processing and metrology.",2011.05349v2
2020-11-16,Dynamical generation of spin squeezing in ultra-cold dipolar molecules,"We study a bulk fermionic dipolar molecular gas in the quantum degenerate
regime confined in a two-dimensional geometry. We consider two rotational
states that encode a spin 1/2 degree of freedom. We derive a long-range
interacting XXZ model describing the many-body spin dynamics of the molecules
valid in the regime where motional degrees of freedom are frozen. Due to the
spatially extended nature of the harmonic oscillator modes, the interactions in
the spin model are very long-ranged and the system behaves close to the
collective limit, resulting in robust dynamics and generation of entanglement
in the form of spin squeezing even at finite temperature and in presence of
dephasing and chemical reactions. We demonstrate how the internal state
structure can be exploited to realise time-reversal and enhanced metrological
sensing protocols.",2011.08202v2
2021-04-12,Strongly anisotropic spin dynamics in magnetic topological insulators,"The recent discovery of magnetic topological insulators has opened new
avenues to explore exotic states of matter that can emerge from the interplay
between topological electronic states and magnetic degrees of freedom, be it
ordered or strongly fluctuating. Motivated by the effects that the dynamics of
the magnetic moments can have on the topological surface states, we investigate
the magnetic fluctuations across the
(MnBi$_{\text{2}}$Te$_{\text{4}}$)(Bi$_{\text{2}}$Te$_{\text{3}}$)$_{\text{n}}$
family. Our paramagnetic electron spin resonance experiments reveal contrasting
Mn spin dynamics in different compounds, which manifests in a strongly
anisotropic Mn spin relaxation in MnBi$_{\text{2}}$Te$_{\text{4}}$ while being
almost isotropic in MnBi$_{\text{4}}$Te$_{\text{7}}$. Our density-functional
calculations explain these striking observations in terms of the sensitivity of
the local electronic structure to the Mn spin-orientation, and indicate that
the anisotropy of the magnetic fluctuations can be controlled by the carrier
density, which may directly affect the electronic topological surface states.",2104.05659v1
2021-05-19,Particle creation in the spin modes of a dynamically oscillating two-component Bose-Einstein condensate,"We investigate the parametric amplification of the zero-point fluctuations in
the spin modes of a two-component Bose-Einstein condensate, triggered by the
dynamical evolution of the condensate density. We first make use of a
Thomas-Fermi approximation to develop a tractable theoretical model of the
quantum dynamics of the Bogoliubov excitations in a harmonically trapped
condensate with a time-dependent trapping frequency. The predictions of this
model are then compared to an ab-initio numerical study of the correlation
functions of density and spin fluctuations for general spatially inhomogeneous
configurations. Results are shown for the two cases of expanding and
oscillating condensates: while the quantum excitation of spin modes remains
weak and relatively featureless in the case of an expanding condensate, clear
and experimentally promising signatures of particle creation are anticipated
for the oscillating case under suitable resonance conditions between the
density and the spin modes.",2105.09349v2
2021-07-01,Novel elementary excitations in spin-1/2 antiferromagnets on the triangular lattice,"We discuss spin-$\frac12$ Heisenberg antiferromagnet on the triangular
lattice using the recently proposed bond-operator technique (BOT). We use the
variant of the BOT which takes into account all spin degrees of freedom in the
magnetic unit cell containing three spins. Apart from conventional magnons
known from the spin-wave theory (SWT), there are novel high-energy collective
excitations in the BOT which are built from high-energy excitations of the
magnetic unit cell. We obtain also another novel high-energy quasiparticle
which has no counterpart not only in the SWT but also in the harmonic
approximation of the BOT. All observed elementary excitations produce visible
anomalies in dynamical spin correlators. We show that quantum fluctuations
considerably change properties of conventional magnons predicted by the SWT.
The effect of a small easy-plane anisotropy is discussed. The anomalous spin
dynamics with multiple peaks in the dynamical structure factor is explained
that was observed recently experimentally in $\rm Ba_3CoSb_2O_9$ and which the
SWT could not describe even qualitatively.",2107.00256v5
2021-09-08,Melting a Rydberg ice to a topological spin liquid with cavity vacuum fluctuation,"Quantum spin liquids are exotic phases of matter that are prevented from
being frozen even at zero temperature, and appear disordered by local probes
that monitor the subsystems. Driven by quantum fluctuations, topological spin
liquids are manifested by their long-range entanglement, and are characterized
by quasiparticles with fractional statistics. Here, we make contact of a 2D
Rydberg ice to a QED vacuum of an ultra-high-finesse optical cavity, and
dynamically promote the frustrated background field of the spin ice to a
$\mathbb{Z}_2$ spin liquid. We characterize the deconfined nature of the
dynamical gauge theory residing in the strongly-correlated Rydberg matter with
Wilsonian loops. We observe the proliferation of vison and spinon pairs by
site-resolved fluorescence imaging, and detect the exchange statistical angle
$\theta_{\text{top}}\sim\pi/2$ between the two anyons by monitoring the
dynamical correlators of the fluctuating cavity photons. Our work provides the
first microscopic detection of anyons in a topological quantum matter, and
heralds the arrival of strongly-coupled many-body QED, where interacting matter
and light are put on equal footing at the level of individual quanta.",2109.03741v2
2021-12-02,Arresting dynamics in hardcore spin models,"We study the dynamics of hardcore spin models on the square and triangular
lattice, constructed by analogy to hard spheres, where the translational
degrees of freedom of the spheres are replaced by orientational degrees of
freedom of spins on a lattice and the packing fraction as a control parameter
is replaced by an exclusion angle. In equilibrium, models on both lattices
exhibit a Kosterlitz-Thouless transition at an exclusion angle $\Delta_{\rm
KT}$. We devise compression protocols for hardcore spins and find that {\it
any} protocol that changes the exclusion angle nonadiabatically, if endowed
with only local dynamics, fails to compress random initial states beyond an
angle $\Delta_{\rm J}> \Delta_{\rm KT}$. This coincides with a doubly algebraic
divergence of the relaxation time of compressed states towards equilibrium. We
identify a remarkably simple mechanism underpinning this divergent timescale:
topological defects involved in the phase ordering kinetics of the system
become incompatible with the hardcore spin constraint, leading to a vanishing
defect mobility as $\Delta\rightarrow\Delta_{\rm J}$.",2112.01553v2
2022-03-29,Spontaneous spinning of a dichloromethane drop on an aqueous surfactant solution,"We report a series of experiments carried out with a dichloromethane drop
deposited on the surface of an aqueous solution containing a surfactant,
cetyltrimethylammonium bromide. After an induction stage during which the drop
stays axisymmetric, oscillations occur along the contact line. These
oscillations are succeeded by a spectacular spontaneous spinning of the drop.
The latter quickly takes the form of a two-tip `rotor' and the spinning rate
stabilizes at a constant value, no longer varying despite the gradual changes
of the drop shape and size. The drop eventually disappears due to the continual
dissolution and evaporation of dichloromethane. Schlieren visualizations and
particle image velocimetry are used to establish a consistent scenario capable
of explaining the evolution of the system. The Marangoni effect induced by the
dissolution of dichloromethane in the drop vicinity is shown to be responsible
for the observed dynamics. Arguments borrowed from dynamical systems theory and
from an existing low-order model allow us to explain qualitatively why the
system selects the spinning configuration. The geometry of the immersed part of
the drop is shown to play a crucial role in this selection process, as well as
in the regulation of the spinning rate.",2203.15606v1
2022-03-30,Atomistic modeling of spin and electron dynamics in two-dimensional magnets switched by two-dimensional topological insulators,"To design fast memory devices, we need material combinations which can
facilitate fast read and write operation. We present a heterostructure
comprising a two-dimensional (2D) magnet and a 2D topological insulator (TI) as
a viable option for designing fast memory devices. We theoretically model
spin-charge dynamics between the 2D magnets and 2D TIs. Using the adiabatic
approximation, we combine the non-equilibrium Green's function method for
spin-dependent electron transport, and time-quantified Monte-Carlo for
simulating magnetization dynamics. We show that it is possible to switch the
magnetic domain of a ferromagnet using spin-torque from spin-polarized edge
states of 2D TI. We further show that the switching between TIs and 2D magnets
is strongly dependent on the interface exchange ($J_{\mathrm{int}}$), and an
optimal interface exchange depending on the exchange interaction within the
magnet is required for efficient switching. Finally, we compare the
experimentally grown Cr-compounds and show that Cr-compounds with higher
anisotropy (such as $\rm CrI_3$) results in lower switching speed but more
stable magnetic order.",2203.16008v1
2022-05-10,A Machine-Learned Spin-Lattice Potential for Dynamic Simulations of Defective Magnetic Iron,"A machine-learned spin-lattice interatomic potential (MSLP) for magnetic iron
is developed and applied to mesoscopic scale defects. It is achieved by
augmenting a spin-lattice Hamiltonian with a neural network term trained to
descriptors representing a mix of local atomic configuration and magnetic
environments. It reproduces the cohesive energy of BCC and FCC phases with
various magnetic states. It predicts the formation energy and complex magnetic
structure of point defects in quantitative agreement with density functional
theory (DFT) including the reversal and quenching of magnetic moments near the
core of defects. The Curie temperature is calculated through spin-lattice
dynamics showing good computational stability at high temperature. The
potential is applied to study magnetic fluctuations near sizable dislocation
loops. The MSLP transcends current treatments using DFT and molecular dynamics,
and surpasses other spin-lattice potentials that only treat near-perfect
crystal cases.",2205.04732v1
2022-10-04,Dissipative dynamics of an impurity with spin-orbit coupling,"Brownian motion of a mobile impurity in a bath is affected by spin-orbit
coupling (SOC). Here, we discuss a Caldeira-Leggett-type model that can be used
to propose and interpret quantum simulators of this problem in cold Bose gases.
First, we derive a master equation that describes the model and explore it in a
one-dimensional (1D) setting. To validate the standard assumptions needed for
our derivation, we analyze available experimental data without SOC; as a
byproduct, this analysis suggests that the quench dynamics of the impurity is
beyond the 1D Bose-polaron approach at temperatures currently accessible in a
cold-atom laboratory -- motion of the impurity is mainly driven by dissipation.
For systems with SOC, we demonstrate that 1D spin-orbit coupling can be 'gauged
out' even in the presence of dissipation -- the information about SOC is
incorporated in the initial conditions. Observables sensitive to this
information (such as spin densities) can be used to study formation of steady
spin polarization domains during quench dynamics.",2210.01829v2
2022-12-15,Many-body slow quench dynamics and nonadiabatic characterization of topological phases,"Previous studies have shown that the bulk topology of single-particle systems
can be captured by the band inversion surface or by the spin inversion surface
emerged on the time-averaged spin polarization. Most of the studies, however,
are based on the single-particle picture even though the systems are fermionic
and of multi-bands. Here, we study the many-body quench dynamics of topological
systems with all the valence bands fully occupied, and show that the concepts
of band inversion surface and spin inversion surface are still valid. More
importantly, the many-body quench dynamics is shown to be reduced to a
nontrivial three-level Landau-Zener model, which can be solved exactly. Based
on the analytical results, the topological spin texture revealed by the
time-averaged spin polarization can be applied to characterize the bulk
topology and thus provides a direct comparison for future experiments.",2301.04534v1
2023-03-03,Spin alignment of vector mesons from quark dynamics in a rotating medium,"Vorticities in heavy-ion collisions (HICs) are supposed to induce spin
alignment and polarization phenomena of quarks and mesons. In this work, we
analyze the spin alignment of vector mesons $\phi$ and $\rho$ induced by
rotation from quark dynamics in the framework of the Nambu-Jona-Lasinio (NJL)
model. The rotating angular velocity induces mass splitting of spin components
for vector $\phi,\rho$ mesons $M_{\phi,\rho}(\Omega)\simeq
M_{\phi,\rho}(\Omega=0)-s_{z}\Omega$. This behavior contributes to the spin
alignment of vector mesons $\phi,\rho$ in an equilibrium medium and naturally
explains the negative deviation of $\rho_{00}-1/3$ for vector mesons.
Incidentally, the positive deviation of $\rho_{00}-1/3$ under the magnetic
field can also be easily understood from quark dynamics.",2303.01897v1
2023-04-03,Magnetic resonance in the quasi-2D square lattice easy-plane antiferromagnet Ba$_2$MnGe$_2$O$_7$,"We report results of a multi-frequency (0.8-60 GHz) electron spin resonance
study of the spin dynamics in the quasi-2D square lattice antiferromagnet
Ba$_2$MnGe$_2$O$_7$ both in antiferromagnetically ordered and paramagnetic
phases. We directly observe two zero-field gaps in the excitation spectrum of
the ordered phase, the larger one being due to easy-plane anisotropy, and the
smaller one indicates the presence of fourth-order in-plane anisotropy probably
related to the multiferroic properties of this compound. We observe effects of
hyperfine interaction on the electron spin resonance spectra in the
antiferromagnetically ordered state, which turns out to be comparable with
in-plane anisotropy. The hyperfine field strength is found from the observed
low-temperature electron spin resonance data. The spin dynamics of the
paramagnetic phase is characterized by strong broadening of the ESR absorption
line, which can be ascribed to the vortex dynamics of a 2D magnet.",2304.01280v1
2023-07-25,The silicon vacancy centers in SiC: determination of intrinsic spin dynamics for integrated quantum photonics,"The negatively-charged silicon vacancy center ($\rm V_{Si}^-$) in silicon
carbide (SiC) is an emerging color center for quantum technology covering
quantum sensing, communication, and computing. Yet, limited information
currently available on the internal spin-optical dynamics of these color
centers prevents us achieving the optimal operation conditions and reaching the
maximum performance especially when integrated within quantum photonics. Here,
we establish all the relevant intrinsic spin dynamics of negatively charged
$\rm V_{Si}^-$ center in 4H-SiC by an in-depth electronic fine structure
modeling including intersystem-crossing and deshelving mechanisms. With
carefully designed spin-dependent measurements, we obtain all previously
unknown spin-selective radiative and non-radiative decay rates. To showcase the
relevance of our work for integrated quantum photonics, we use the obtained
rates to propose a realistic implementation of time-bin entangled multi-photon
GHZ and cluster state generation. We find that up to 3-photon GHZ/cluster
states are readily within reach using the existing nanophotonic cavity
technology.",2307.13648v1
2023-08-01,Field and Polarization Dependent Quantum Spin Dynamics in Honeycomb Magnet Na$_2$Co$_2$TeO$_6$: Magnetic Excitations and Continuum,"We report terahertz spectroscopic measurements of quantum spin dynamics in
the spin-1/2 honeycomb magnet Na$_2$Co$_2$TeO$_6$ as a function of applied
magnetic field with different terahertz polarizations. Distinct field
dependencies of the resolved spin dynamics are identified in three regimes,
which are separated by two critical fields at $B_{c1}\approx 7$ and
$B_{c2}\approx 10$ T. A polarization selective continuum is observed in the
intermediate phase, featuring spin fluctuations of a proximate quantum spin
liquid.",2308.00631v2
2023-09-11,Classification of dynamical Lie algebras for translation-invariant 2-local spin systems in one dimension,"Much is understood about 1-dimensional spin chains in terms of entanglement
properties, physical phases, and integrability. However, the Lie algebraic
properties of the Hamiltonians describing these systems remain largely
unexplored. In this work, we provide a classification of all Lie algebras
generated by translation-invariant 2-local spin chain Hamiltonians, or
so-called dynamical Lie algebras. We consider chains with open and periodic
boundary conditions and find 17 unique dynamical Lie algebras. Our
classification covers some well-known models such as the transverse-field Ising
model and the Heisenberg chain, and we also find more exotic classes of
Hamiltonians that cannot be identified easily. In addition to the closed and
open spin chains, we consider systems with a fully connected topology, which
may be relevant for quantum machine learning approaches. We discuss the
practical implications of our work in the context of quantum control,
variational quantum computing, and the spin chain literature.",2309.05690v2
2023-12-20,Excitations and phase ordering of the spin-stripe phase of a binary dipolar condensate,"We consider the ground states, excitations and dynamics of a
quasi-two-dimensional binary dipolar Bose-Einstein condensate. Our focus is on
the transition to a spin-stripe ground state in which the translational
invariance is spontaneously broken by a striped immiscible pattern of the
alternating components. We develop a ground state phase diagram showing the
parameter regime where the spin-stripe state occurs. Using Bogoliubov theory we
calculate the excitation spectrum and structure factors. We identify a balanced
regime where the system has a $\mathbb{Z}_2$ symmetry, and in the spin-stripe
state this yields a nonsymmorphic symmetry. We consider the evolution of the
system following a quench from the uniform to spin-stripe state, revealing
novel ordering dynamics involving defects of the stripe order. Using an order
parameter to characterize the orientational order of the stripes, we show that
the phase ordering exhibits dynamic scaling.",2312.12695v1
2015-02-16,Aging of the Metropolis dynamics on the Random Energy Model,"We study the Metropolis dynamics of the simplest mean-field spin glass model,
the Random Energy Model. We show that this dynamics exhibits aging by showing
that the properly rescaled time change process between the Metropolis dynamics
and a suitably chosen `fast' Markov chain converges in distribution to a stable
subordinator. The rescaling might depend on the realization of the environment,
but we show that its exponential growth rate is deterministic.",1502.04535v1
2015-08-31,Hydrostatics and dynamical large deviations for a reaction-diffusion model,"We consider the superposition of a symmetric simple exclusion dynamics,
speeded-up in time, with a spin-flip dynamics in a one-dimensional interval
with periodic boundary conditions. We prove the hydrostatics and the dynamical
large deviation principle.",1508.07818v2
1995-12-01,The Non Linear Sigma Model and Spin Ladders,"The well known Haldane map from spin chains into the $O(3)$ non linear sigma
model is generalized to the case of spin ladders. This map allows us to explain
the different qualitative behaviour between even and odd ladders, exactly in
the same way it explains the difference between integer and half-integer spin
chains. Namely, for even ladders the topological term in the sigma model action
is absent, while for odd ladders the $\theta$ parameter, which multiplies the
topological term, is equal to $2 \pi S$, where $S$ is the spin of the ladder.
Hence even ladders should have a dynamically generated spin gap, while odd
ladders with half-integer spin should stay gapless, and physically equivalent
to a perturbed $SU(2)_1$ Wess-Zumino -Witten model in the infrared regime. We
also derive some consequences from the dependence of the sigma model coupling
constant on the ladder Heisenberg couplings constants.",9512007v2
1996-09-11,Cumulant approach to weakly doped antiferromagnets,"We present a new approach to static and dynamical properties of holes and
spins in weakly doped antiferromagnets in two dimensions. The calculations are
based on a recently introduced cumulant approach to ground--state properties of
correlated electronic systems. The present method allows to evaluate hole and
spin--wave dispersion relations by considering hole or spin excitations of the
ground state. Usually, these dispersions are found from time--dependent
correlation functions. To demonstrate the ability of the approach we first
derive the dispersion relation for the lowest single hole excitation at
half--filling. However, the main purpose of this paper is to focus on the
mutual influence of mobile holes and spin waves in the weakly doped system. It
is shown that low-energy spin excitations strongly admix to the ground--state.
The coupling of spin waves and holes leads to a strong suppression of the
staggered magnetization which can not be explained by a simple rigid--band
picture for the hole quasiparticles. Also the experimentally observed doping
dependence of the spin--wave excitation energies can be understood within our
formalism.",9609098v1
1999-03-12,Observation of spin freezing and relaxation at microwave frequencies in the spin ladder compound $Sr_{14-x}Ca_{x}Cu_{24}O_{41}$,"We report the observation of a frequency ($\omega $) and temperature (T)
-dependent loss peak in $\chi''$ and accompanying dispersion in $\chi'$ from
microwave (2-18GHz) measurements of the complex susceptibility
$\tilde{\chi}(\omega, T)=\chi'+i\chi''$ of $Sr_{14-x}Ca_{x}Cu_{24}O_{41}$. We
associate this phenomenon with a rapid decrease of spin disorder and
corresponding spin relaxation rate, representing a ``spin freezing transition''
accompanying charge ordering which occurs at temperatures $\sim 250K$. Our
results enable direct quantitative measurements of the spin relaxation rate,
and yield information on spin dynamics in these materials and the related
compounds $SrCuO_{2}$ and $Sr_{2}CuO_{3}$.",9903198v1
2000-11-20,Spin correlations in the two-leg antiferromagnetic ladder in a magnetic field,"We study the ground-state spin correlations in the gapless incommensurate
regime of a S=1/2 XXZ chain and a two-leg antiferromagnetic ladder under a
magnetic field, in which the gapless excitations form a Tomonaga-Luttinger (TL)
liquid. We calculate numerically the two-spin correlation functions and the
local magnetization in the two models using the density-matrix
renormalization-group method. By fitting the numerical results for an open XXZ
chain of 100 spins to correlation functions of a Gaussian model, we determine
the TL-liquid parameter K and the amplitudes of the correlation functions. The
value of K estimated from the fits is in excellent agreement with the exact
value obtained from the Bethe ansatz. We apply the same method to the open
ladder consisting of 200 spins and determine the dependence of K on the
magnetization M. The K-M relation changes drastically depending on the ratio of
the coupling constants in the leg and rung directions. We also discuss
implications of these results to experiments on the nuclear spin relaxation
rate 1/T_1 and dynamical spin structure factors.",0011320v1
2001-07-10,Cu NQR study of host and guest spin dynamics in impurity-doped YBa2Cu4O8,"We present the planar 63Cu nuclear spin-lattice relaxation study of
impurity-doped YBa2(Cu1-xMx)4O8 (M=Ni, Zn) at T=4.2-300 K with Cu nuclear
quadrupole resonance (NQR) spin-echo technique. In the light of an
impurity-induced NQR relaxation theory, we estimated the host Cu nuclear
spin-lattice relaxation time (T1)HOST, the impurity-induced Cu nuclear
spin-lattice relaxation time (t1), and the wipeout region around the impurity
in the superconducting state. The pseudo spin-gap behavior of the host Cu
antiferromagnetic spin fluctuation above Tc is not readily removed by a small
amount of the impurity. The Zn-induced non-Korringa behavior of (T1)HOST below
Tc is in sharp contrast to the doping effect of the magnetic impurity Ni.",0107186v1
2001-07-12,Neutron scattering study of dipolar spin ice Ho_2Sn_2O_7: Frustrated pyrochlore magnet,"By means of neutron scattering techniques we have investigated the frustrated
pyrochlore magnet Ho_2Sn_2O_7, which was found to show a ferromagnetic spin-ice
behavior below T \simeq 1.4 K by susceptibility measurements. High-resolution
powder-neutron-diffraction shows no detectable disorder of the lattice, which
implies appearance of a random magnetic state solely by frustrated geometry,
i.e., the corner sharing tetrahedra. Magnetic inelastic-scattering spectra show
that Ho magnetic moments behave as an Ising spin system at low temperatures,
and that the spin fluctuation has static character. The system remains in a
short-range ordered state down to T = 0.4 K. By analyzing the wave-number
dependence of the magnetic scattering using a mean field theory, it is
clarified that the Ising spins interact via the dipolar interaction. Therefore
we conclude that Ho_2Sn_2O_7 belongs to the dipolar-spin-ice family. Slow spin
dynamics is exhibited as thermal hysteresis and time dependence of the magnetic
scattering.",0107278v2
2002-02-04,Electronic theory for the normal state spin dynamics in Sr$_2$RuO$_4$: anisotropy due to spin-orbit coupling,"Using a three-band Hubbard Hamiltonian we calculate within the
random-phase-approximation the spin susceptibility, $\chi({\bf q},\omega)$, and
NMR spin-lattice relaxation rate, 1/T$_1$, in the normal state of the triplet
superconductor Sr$_2$RuO$_4$ and obtain quantitative agreement with
experimental data. Most importantly, we find that due to spin-orbit coupling
the out-of-plane component of the spin susceptibility $\chi^{zz}$ becomes at
low temperatures two times larger than the in-plane one. As a consequence
strong incommensurate antiferromagnetic fluctuations of the
quasi-one-dimensional $xz$- and $yz$-bands point into the $z$-direction. Our
results provide further evidence for the importance of spin fluctuations for
triplet superconductivity in Sr$_2$RuO$_4$.",0202051v2
2002-04-10,Spin dynamics in semiconductor nanocrystals,"Time-resolved Faraday rotation is used to study both transverse and
longitudinal spin relaxation in chemically-synthesized CdSe nanocrystals (NCs)
22-80 Angstroms in diameter. The precession of optically-injected spins in a
transverse magnetic field occurs at distinct frequencies whose assignment to
electron and exciton spins is developed through systematic studies of the
size-dependence and theoretical calculations. It is shown that the transverse
spin lifetime is limited by inhomogeneous dephasing to a degree that cannot be
accounted for by the NC size distribution alone. Longitudinal spin relaxation
in these NCs occurs on several distinct timescales ranging from 100 ps-10
microseconds and exhibits markedly different dependencies on temperature and
field in comparison to transverse spin relaxation.",0204235v1
2002-12-27,Semiclassical Monte Carlo Model for In-Plane Transport of Spin-Polarized Electrons in III-V Heterostructures,"We study the in-plane transport of spin-polarized electrons in III-V
semiconductor quantum wells. The spin dynamics is controlled by the spin-orbit
interaction, which arises via the Dresselhaus (bulk asymmetry) and Rashba (well
asymmetry) mechanisms. This interaction, owing to its momentum dependence,
causes rotation of the spin polarization vector, and also produces effective
spin dephasing. The density matrix approach is used to describe the evolution
of the electron spin polarization, while the spatial motion of the electrons is
treated semiclassically. Monte Carlo simulations have been carried out for
temperatures in the range 77-300 K.",0212610v2
2003-08-07,Spin-Fermion model of $UGe_2$,"It is assumed that U atoms in $UGe_2$ have a number of $f$ electrons
appropriate to give them each a spin $s=1$ as well as one extra itinerant
electron which may equally well be on one or other U atom. The dynamical
degrees of freedom are spin-s operators of localized spins and spin-1/2 fermi
operators of itinerant electrons. Applying hydrostatic pressure changes the
bandwidths of spin-up and spin-down itinerant electrons in different way, which
leads to decreasing of the contribution of the fermions to the magnetization
keeping the spin-fermion interaction unchanged. In turn the local spin-fermion
interaction leads to ferromagnetic superconductivity. The model accounts, in a
quantitative and natural way, for the characteristics of the coexistence of
superconductivity and ferromagnetism in $UGe_2$, including many of the key
experimental results: metamagnetic transitions, quantum transition from
ferromagnetism to ferromagnetic superconductivity, the position of the highest
superconducting critical temperature etc.",0308134v1
2003-09-29,Magnons in CMR pyrochlore Tl2Mn2O7,"Well defined spin waves were observed when the spin dynamics of Tl2Mn2O7, the
first pyrochlore compound found to exhibit colossal magnetoresistance, was
measured [J.W.Lynn et al., Phys.Rev.Lett. 80,4582(1998)], in stark contrast
with the experimental results on the larger family of magnetoresistive
manganites with perovskite structure. In this work, we present our calculation
for the spin waves in Tl2Mn2O7, which we described using the microscopic
generic model proposed recently for this compound [C.I.Ventura and M.A.Gusmao,
Phys.Rev.B 65, 14422(2002)]. We have employed a canonical transformation to
determine perturbatively the effective spin-wave Hamiltonian, obtaining
therefrom the renormalization of the ferromagnetic spin waves related to the
localized Mn$^{4+}$ spins, due to their coupling with the conduction electrons
present. We have calculated the magnon dispersion relations along different
paths in the first Brillouin zone, comparing them with those which are obtained
for an ideal isotropic ferromagnet. This comparison evidences an agreement
between the ferromagnetic magnons obtained from the generic model and the bare
spin waves, such as had been found in neutron scattering experiments.",0309684v1
2004-06-25,Excitations of incoherent spin-waves due to spin-transfer torque,"As predicted by Slonczewski and Berger, the possibility of exciting microwave
oscillations in a nanomagnet by a spin-polarized current has been recently
demonstrated. This observation opens very important perspectives of
applications in RF components. However, some unresolved inconsistencies are
found when interpreting the magnetization dynamics results within the coherent
spin-torque model (CSM). In some cases, the telegraph noise caused by
spin-currents could not be described quantitatively by the CSM. This led to
controversies about the need of an effective magnetic temperature model (ETM).
Here we interpret the experimental results of Kiselev et al. [Nature 425, 380
(2003)] using micromagnetic simulations. We point out the key role played by
incoherent spin-waves excitation due to spin-transfer effects. The incoherence
is caused by the spatial inhomogeneities of the local fields, generating a
distribution of local precession frequencies. It results in telegraph noise at
zero temperature associated with transitions between attraction wells in phase
space.",0406628v3
2004-06-29,"Aging, rejuvenation and memory phenomena in spin glasses","In this paper, we review several important features of the out-of-equilibrium
dynamics of spin glasses. Starting with the simplest experiments, we discuss
the scaling laws used to describe the isothermal aging observed in spin glasses
after a quench down to the low temperature phase. We report in particular new
results on the sub-aging behaviour of spin glasses. We then discuss the
rejuvenation and memory effects observed when a spin glass is submitted to
temperature variations during aging, from the point of view of both energy
landscape pictures and of real space pictures. We highlight the fact that both
approaches point out the necessity of hierarchical processes involved in aging.
Finally, we report an investigation of the effect of small temperature
variations on aging in spin glass samples with various anisotropies which
indicates that this hierarchy depends on the spin anisotropy.",0406721v2
2004-07-06,Suppression of Dyakonov-Perel Spin Relaxation in high mobility n-GaAs,"We report a large and unexpected suppression of the free electron spin
relaxation in lightly-doped n-GaAs bulk crystals. The spin relaxation rate
shows weak mobility dependence and saturates at a level 30 times less then that
predicted by the Dyakonov-Perel theory. The dynamics of the spin-orbit field
differs substantially from the usual scheme: although all the experimental data
can be self-consistently interpreted as a precessional spin relaxation induced
by a random spin-orbit field, the correlation time of this random field,
surprisingly, is much shorter than, and is independent of, the momentum
relaxation time determined from transport measurements. Understanding of this
phenomenon could lead to high temperature engineering of the electron spin
memory.",0407133v1
2004-07-26,Control of Electron Spin Coherence Using Landau Level Quantization in a Two-Dimensional Electron Gas,"Time-resolved optical measurements of electron spin dynamics in modulation
doped InGaAs quantum wells are used to explore electron spin coherence times
and spin precession frequencies in a regime where an out of plane magnetic
field quantizes the states of a two-dimensional electron gas into Landau
levels. Oscillatory features in the transverse spin coherence time and
effective g-factor as a function of applied magnetic field exhibit a
correspondence with Shubnikov-de Haas oscillations, illustrating a coupling
between spin and orbital eigenstates. We present a theoretical model in which
inhomogeneous dephasing due to the population of different Landau levels limits
the spin coherence time and captures the essential experimental results.",0407681v1
2005-01-09,Nonequilibrium Kondo Effect in a Quantum Dot Coupled to Ferromagnetic Leads,"We study the Kondo effect in the electron transport through a quantum dot
coupled to ferromagnetic leads, using a real-time diagrammatic technique which
provides a systematic description of the nonequilibrium dynamics of a system
with strong local electron correlations. We evaluate the theory in an extension
of the `resonant tunneling approximation', introduced earlier, by introducing
the self-energy of the off-diagonal component of the reduced propagator in spin
space. In this way we develop a charge and spin conserving approximation that
accounts not only for Kondo correlations but also for the spin splitting and
spin accumulation out of equilibrium. We show that the Kondo resonances, split
by the applied bias voltage, may be spin polarized. A left-right asymmetry in
the coupling strength and/or spin polarization of the electrodes significantly
affects both the spin accumulation and the weight of the split Kondo resonances
out of equilibrium. The effects are observable in the nonlinear differential
conductance. We also discuss the influence of decoherence on the Kondo
resonance in the frame of the real-time formulation.",0501172v1
2005-05-02,Absence of spin superradiance in resonatorless magnets,"A spin system is considered with a Hamiltonian typical of molecular magnets,
having dipole-dipole interactions and a single-site magnetic anisotropy. In
addition, spin interactions through the common radiation field are included. A
fully quantum-mechanical derivation of the collective radiation rate is
presented. An effective narrowing of the dipole-dipole attenuation, due to high
spin polarization is taken into account. The influence of the radiation rate on
spin dynamics is carefully analysed. It is shown that this influence is
completely negligible. No noticeable collective effects, such as superradiance,
can appear in molecular magnets, being caused by electromagnetic spin
radiation. Spin superradiance can arise in molecular magnets only when these
are coupled to a resonant electric circuit, as has been suggested earlier by
one of the authors in Laser Phys. {\bf 12}, 1089 (2002).",0505024v1
2005-08-09,Spin-dependent recombination in GaAsN alloys,"The spin-dependent recombination (SDR) has been observed in GaAs_{1-x}N_{x}
(x = 2.1, 2.7, 3.4%) at room temperature. It reveals itself in a decrease of
the edge photoluminescence (PL) intensity by more than a factor of 3 when
either the polarization of the exciting light is changed from circular to
linear or the transverse magnetic field of ~300 gauss (G) is applied. The
interband absorption of the circularly polarized light results in a spin
polarization of conduction electrons, which reaches 35% with increasing the
pump intensity. The effects observed are explained by dynamical polarization of
deep paramagnetic centers and spin-dependent capture of conduction electrons by
these centers. The PL depolarization in a transverse magnetic field (Hanle
effect) allows us to estimate the electron spin relaxation time in the range of
1 ns. Theoretically, it has been concluded that, due to the SDR, this long time
is controlled by slow spin relaxation of bound electrons. In all the three
alloy samples, a positive sign of the bound-electron g-factor is determined
experimentally from the direction of their mean spin rotation in the magnetic
field.",0508222v1
2005-09-05,Unified description of bulk and interface-enhanced spin pumping,"The dynamics of non-equilibrium spin accumulation generated in metals or
semiconductors by rf magnetic field pumping is treated within a diffusive
picture. The dc spin accumulation produced in a uniform system by a rotating
applied magnetic field or by a precessing magnetization of a weak ferromagnet
is in general given by a (small) fraction of hbar omega, where omega is the
rotation or precession frequency. With the addition of a neighboring,
field-free region and allowing for the diffusion of spins, the spin
accumulation is dramatically enhanced at the interface, saturating at the
universal value hbar omega in the limit of long spin relaxation time. This
effect can be maximized when the system dimensions are of the order of sqrt(2pi
D omega), where D is the diffusion constant. We compare our results to the
interface spin pumping theory of A. Brataas et al. [Phys. Rev. B 66, 060404(R)
(2002)].",0509100v1
2005-10-18,Spin excitations in fluctuating stripe phases of doped cuprate superconductors,"Using a phenomenological lattice model of coupled spin and charge modes, we
determine the spin susceptibility in the presence of fluctuating stripe charge
order. We assume the charge fluctuations to be slow compared to those of the
spins, and combine Monte Carlo simulations for the charge order parameter with
exact diagonalization of the spin sector. Our calculations unify the spin
dynamics of both static and fluctuating stripe phases and support the notion of
a universal spin excitation spectrum in doped cuprate superconductors.",0510448v4
2006-10-31,Effect of random interactions in spin baths on decoherence,"We study the decoherence of a central spin 1/2 induced by a spin bath with
intrabath interactions. Since we are interested in the cumulative effect of
interaction and disorder, we study baths comprising Ising spins with random
ferro- and antiferromagnetic interactions between the spins. Using the
resolvent operator method which goes beyond the standard Born-Markov master
equation approach, we show that, in the weak coupling regime, the decoherence
of the central spin at all times is entirely determined by the local-field
distribution or equivalently, the dynamical structure factor of the Ising bath.
We present analytic results for the Ising spin chain bath at arbitrary
temperature for different distributions of the intrabath interaction strengths.
We find clear evidence of non-Markovian behavior in the low temperature regime.
We also consider baths described by Ising models on higher-dimensional
lattices. We find that interactions lead to a significant reduction of the
decoherence. An important feature of interacting spinbaths is the saturation of
the asymptotic Markovian decay rate at high temperatures, as opposed to the
conventional Ohmic boson bath.",0610874v1
2007-01-10,Electron Density Dependence of in-plane Spin Relaxation Anisotropy in GaAs/AlGaAs Two-Dimensional Electron Gas,"We investigated the spin dynamics of two-dimensional electrons in (001)
GaAs/AlGaAs heterostructure using the time resolved Kerr rotation technique
under a transverse magnetic field. The in-plane spin lifetime is found to be
anisotropic below 150k due to the interference of Rashba and Dresselhaus
spin-orbit coupling and D'yakonov-Perel' spin relaxation. The ratio of in-plane
spin lifetimes is measured directly as a function of temperature and pump
power, showing that the electron density in 2DEG channel strongly affects the
Rashba spin-orbit coupling.",0701195v2
2007-01-24,Charge and spin excitation spectra in the one-dimensional Hubbard model with next-nearest-neighbor hopping,"The dynamical density-matrix renormalization group technique is used to
calculate spin and charge excitation spectra in the one-dimensional (1D)
Hubbard model at quarter filling with nearest-neighbor $t$ and
next-nearest-neighbor $t'$ hopping integrals. We consider a case where $t$
($>0$) is much smaller than $t'$ ($>0$). We find that the spin and charge
excitation spectra come from the two nearly independent $t'$-chains and are
basically the same as those of the 1D Hubbard (and t-J) chain at quarter
filling. However, we find that the hopping integral $t$ plays a crucial role in
the short-range spin and charge correlations; i.e., the ferromagnetic spin
correlations between electrons on the neighboring sites is enhanced and
simultaneously the spin-triplet pairing correlations is induced, of which the
consequences are clearly seen in the calculated spin and charge excitation
spectra at low energies.",0701579v1
2007-02-03,Nuclear spin effects in singly negatively charged InP quantum dots,"Experimental investigation of nuclear spin effects on the electron spin
polarization in singly negatively charged InP quantum dots is reported.
Pump-probe photoluminescence measurements of electron spin relaxation in the
microsecond timescale are used to estimate the time-period $T_{N}$ of the
Larmor precession of nuclear spins in the hyperfine field of electrons. We find
$T_{N}$ to be $\sim 1$ $\mu$s at $T \approx 5$ K, under the vanishing external
magnetic field. From the time-integrated measurements of electron spin
polarization as a function of a longitudinally applied magnetic field at $T
\approx 5$ K, we find that the Overhauser field appearing due to the dynamic
nuclear polarization increases linearly with the excitation power, though its
magnitude remains smaller than 10 mT up to the highest excitation power (50 mW)
used in these experiments. The effective magnetic field of the frozen
fluctuations of nuclear spins is found to be 15 mT, independent of the
excitation power.",0702063v1
2007-02-05,Nuclear spin population and its control toward initialization using an all-electrical sub-micron scale nuclear magnetic resonance device,"We study the nuclear spin population in a GaAs quantum well structure and
demonstrate its initialization using an all-electrical nuclear magnetic
resonance (NMR) device. In our device, nuclear spins are dynamically polarized
in a sub-micron scale region defined by split gates. The nuclear spin
populations under various polarization conditions are estimated from
resistively-detected pulsed NMR spectra. We find that nuclear spin populations
are determined by electron spin configurations. By applying radio frequency
pulses to the strongly polarized nuclear spins, we demonstrate the creation of
two-qubit effective pure states, which is a crucial step toward NMR quantum
computation.",0702086v1
1998-04-24,Proton Structure Functions from Chiral Dynamics and QCD Constraints,"The spin fractions and deep inelastic structure functions of the proton are
analyzed using chiral field theory involving Goldstone bosons. A detailed
comparison with recent chiral models sheds light on their successful
description of the spin fractions of the proton as being due to neglecting
helicity non-flip chiral transitions. This approximation is valid for zero mass
quarks but not for constituent quarks. Since the chiral spin fraction models
with the pure spin-flip approximation reproduce the measured spin fractions of
the proton, axialvector constituent-quark-Goldstone boson coupling is found to
be inconsistent with the proton spin data. Initial quark valence distributions
are then constructed using quark counting constraints at Bjorken $x \to 1$ and
Regge behavior at $x \to 0$. Sea quark distributions predicted by chiral field
theory on this basis have correct order of magnitude and shape. The spin
fractions agree with the data.",9804394v2
2004-06-22,Master equation for spin-spin correlation functions of the XXZ chain,"We derive a new representation for spin-spin correlation functions of the
finite XXZ spin-1/2 Heisenberg chain in terms of a single multiple integral,
that we call the master equation. Evaluation of this master equation gives rise
on the one hand to the previously obtained multiple integral formulas for the
spin-spin correlation functions and on the other hand to their expansion in
terms of the form factors of the local spin operators. Hence, it provides a
direct analytic link between these two representations of the correlation
functions and a complete re-summation of the corresponding series. The master
equation method also allows one to obtain multiple integral representations for
dynamical correlation functions.",0406190v1
2004-08-11,The Spin Interaction of a Dirac Particle in an Aharonov-Bohm Potential in First Order Scattering,"For a Dirac particle in an Aharonov-Bohm (AB) potential, it is shown that the
spin interaction (SI) operator which governs the transitions in the spin sector
of the first order S-matrix is related to one of the generators of rotation in
the spin space of the particle. This operator, which is given by the projection
of the spin operator $\mathbf{\Sigma}$ along the direction of the total
momentum of the system, and the two operators constructed from the projections
of the $\mathbf{\Sigma}$ operator along the momentum transfer and the
z-directions close the SU(2) algebra.It is suggested, then, that these two
directions of the total momentum and the momentum transfer form some sort of
natural intrinsic directions in terms of which the spin dynamics of the
scattering process at first order can be formulated conveniently. A formulation
and an interpretation of the conservation of helicity at first order using the
spin projection operators along these directions is presented .",0408093v2
2004-10-21,BRST approach to Lagrangian construction for fermionic massless higher spin fields,"We develop the BRST approach to Lagrangian formulation for all massless
half-integer higher spin fields on an arbitrary dimensional flat space. General
procedure of Lagrangian construction describing the dynamics of fermionic field
with any spin is given. It is shown that in fermionic case the higher spin
field model is a reducible gauge theory and the order of reducibility grows
with the value of spin. No off-shell constraints on the fields and the gauge
parameters are used. We prove that in four dimensions after partial gauge
fixing the Lagrangian obtained can be transformed to Fang-Fronsdal form
however, in general case, it includes the auxiliary fields and possesses the
more gauge symmetries in compare with Fang-Fronsdal Lagrangian. As an example
of general procedure, we derive the new Lagrangian for spin 5/2 field
containing all set of auxiliary fields and gauge symmetries of free fermionic
higher spin field theory.",0410215v4
2006-01-11,Massive higher spins and holography,"We review recent progress towards the understanding of higher spin gauge
symmetry breaking in AdS space from a holographic vantage point. According to
the AdS/CFT correspondence, N=4 SYM theory at vanishing coupling constant
should be dual to a theory in AdS which exhibits higher spin gauge symmetry
enhancement. When the SYM coupling is non-zero, all but a handful of HS
currents are violated by anomalies, and correspondingly local higher spin
symmetry in the bulk gets spontaneously broken. In agreement with previous
results and holographic expectations, we find that, barring one notable
exception (spin 1 eating spin 0), the Goldstone modes responsible for HS
symmetry breaking in AdS have non-vanishing mass even in the limit in which the
gauge symmetry is restored. We show that spontaneous breaking a' la
Stueckelberg implies that the mass of the relevant spin s'=s-1 Goldstone field
is exactly the one predicted by the correspondence.",0601071v1
1994-07-01,"Relativistic treatment of spin-transfer observables in quasielastic $(\vec{\bf p},\vec{\bf n})$ scattering","We calculate all spin-transfer observables for the quasielastic
$(\vec{p},\vec{n})$ reaction in a relativistic plane-wave impulse
approximation. The nuclear-structure information is contained in a large set of
nuclear-response functions that are computed in nuclear matter using a
relativistic random-phase approximation to the Walecka model. A reduced value
of the nucleon mass in the medium induces important dynamical changes in the
residual isovector interaction relative to its nonrelativistic counterpart. As
a result, good agreement is found for all spin observables --- including the
spin-longitudinal to spin-transverse ratio --- when compared to the original
($q=1.72$~fm$^{-1}$) NTOF experiment. In contrast, the spin-longitudinal to
spin-transverse ratio is underpredicted at $q=1.2$~fm$^{-1}$ and overpredicted
at $q=2.5$~fm$^{-1}$. We comment on the role of distortions as a possible
solution to this discrepancy.",9407001v1
2001-02-13,Equilibrium sizes of jellium metal clusters in the stabilized spin-polarized jellium model,"We have used the stabilized spin-polarized jellium model to calculate the
equilibrium sizes of metal clusters. Our self-consistent calculations in the
local spin-density approximation show that for an $N$-electron cluster, the
equilibrium is achieved for a configuration in which the difference in the
numbers of up-spin and down-spin electrons is zero or unity, depending on the
total number of electrons. That is, a configuration in which the spins are
maximally compensated. This maximum spin-compensation results in both the
alternation in the average distance between the nearest neighbor ions and the
odd-even alternations in the ionization energies of alkali metal clusters, in a
good agreement with the molecular dynamics findings and the experiment. These
suggest a realistic and more accurate method for calculating the properties of
metal clusters in the context of jellium model than previous jellium model
methods.",0102037v1
2004-09-12,Energy levels and decoherence properties of single electron and nuclear spins in a defect center in diamond,"The coherent behavior of the single electron and single nuclear spins of a
defect center in diamond and a 13C nucleus in its vicinity, respectively, are
investigated. The energy levels associated with the hyperfine coupling of the
electron spin of the defect center to the 13C nuclear spin are analyzed.
Methods of magnetic resonance together with optical readout of single defect
centers have been applied in order to observe the coherent dynamics of the
electron and nuclear spins. Long coherence times, in the order of microseconds
for electron spins and tens of microseconds for nuclear spins, recommend the
studied system as a good experimental approach for implementing a 2-qubit gate.",0409067v1
2007-04-18,A Luttinger Liquid Coupled to a Quantum Spin Bath: Flow Equation Approach to the Kondo Necklace Model,"We study a lattice realization of a Luttinger liquid interacting with a bath
of quantum spins in terms of an antiferromagnetic S=1/2 Heisenberg chain, where
each spin is also coupled to a \sigma=1/2 Kondo spin degree of freedom. This
model describes the low-energy spin dynamics in quasi one dimensional
materials, where the electronic spins of the magnetic ions interact with those
of impurities, nuclei and possibly other spin species present in their
environment. For large ferromagnetic and antiferromagnetic Kondo interaction J'
there are two phases corresponding to an effective spin-1 Heisenberg chain and
a dimerised spin-1/2 ladder, respectively. For weak Kondo interaction we
establish that the Kondo interaction drives the system to a strong coupling
regime. This suggests that J'=0 is the only critical point in the system.",0704.2343v2
2007-05-23,Recent results of the STAR high-energy polarized proton-proton program at RHIC at BNL,"The STAR experiment at the Relativistic Heavy-Ion Collider (RHIC) at
Brookhaven National Laboratory (BNL) is carrying out a spin physics program
colliding transverse or longitudinal polarized proton beams at
$\sqrt{s}=200-500 $GeV to gain a deeper insight into the spin structure and
dynamics of the proton. These studies provide fundamental tests of Quantum
Chromodynamics (QCD).
  One of the main objectives of the STAR spin physics program is the
determination of the polarized gluon distribution function through a
measurement of the longitudinal double-spin asymmetry, $A_{LL}$, for various
processes. Recent results will be shown on the measurement of $A_{LL}$ for
inclusive jet production, neutral pion production and charged pion production
at $\sqrt{s}=200 $GeV. In addition to these measurements involving longitudinal
polarized proton beams, the STAR collaboration has performed several important
measurements employing transverse polarized proton beams. New results on the
measurement of the transverse single-spin asymmetry, $A_{N}$, for forward
neutral pion production and the first measurement of $A_{N}$ for mid-rapidity
di-jet production will be discussed.",0705.3483v1
2007-06-13,Mapping of spin lifetimes to electronic states in n-type GaAs near the metal-insulator transition,"The longest spin lifetimes in bulk n-GaAs exceed 100 ns for doping
concentrations near the metal-insulator transition (J.M. Kikkawa, D.D.
Awschalom, Phys. Rev. Lett. 80, 4313 (1998)). The respective electronic states
have yet not been identified. We therefore investigate the energy dependence of
spin lifetimes in n-GaAs by time-resolved Kerr rotation. Spin lifetimes vary by
three orders of magnitude as a function of energy when occupying donor and
conduction band states. The longest spin lifetimes (>100 ns) are assigned to
delocalized donor band states, while conduction band states exhibit shorter
spin lifetimes. The occupation of localized donor band states is identified by
short spin lifetimes (~300 ps) and a distinct Overhauser shift due to dynamic
nuclear polarization.",0706.1884v1
2007-07-09,Coherence of an optically illuminated single nuclear spin qubit,"We investigate the coherence properties of individual nuclear spin quantum
bits in diamond [Dutt et al., Science, 316, 1312 (2007)] when a proximal
electronic spin associated with a nitrogen-vacancy (NV) center is being
interrogated by optical radiation. The resulting nuclear spin dynamics are
governed by time-dependent hyperfine interaction associated with rapid
electronic transitions, which can be described by a spin-fluctuator model. We
show that due to a process analogous to motional averaging in nuclear magnetic
resonance, the nuclear spin coherence can be preserved after a large number of
optical excitation cycles. Our theoretical analysis is in good agreement with
experimental results. It indicates a novel approach that could potentially
isolate the nuclear spin system completely from the electronic environment.",0707.1341v2
2007-08-10,Geometry and dynamics of higher-spin frame fields,"We give a systematic account of unconstrained free bosonic higher-spin fields
on D-dimensional Minkowski and (Anti-)de Sitter spaces in the frame formalism.
The generalized spin connections are determined by solving a chain of
torsion-like constraints. Via a generalization of the vielbein postulate these
allow to determine higher-spin Christoffel symbols, whose relation to the de
Wit--Freedman connections is discussed. We prove that the generalized Einstein
equations, despite being of higher-derivative order, give rise to the AdS
Fronsdal equations in the compensator formulation. To this end we derive
Damour-Deser identities for arbitrary spin on AdS. Finally we discuss the
possibility of a geometrical and local action principle, which is manifestly
invariant under unconstrained higher-spin symmetries.",0708.1391v2
2007-10-15,"Model for a collimated spin wave beam generated by a single layer, spin torque nanocontact","A model of spin torque induced magnetization dynamics based upon
semi-classical spin diffusion theory for a single layer nanocontact is
presented. The model incorporates effects due to the current induced Oersted
field and predicts the generation of a variety of spatially dependent,
coherent, precessional magnetic wave structures. Directionally controllable
collimated spin wave beams, vortex spiral waves, and localized standing waves
are found to be excited by the interplay of the Oersted field and the
orientation of an applied field. These fields act as a spin wave ``corral''
around the nanocontact that controls the propagation of spin waves in certain
directions.",0710.2890v3
2007-11-29,A study of polarization buildup by spin filtering,"Many sets of polarization evolution equations have been suggested to describe
the method of polarization buildup by spin filtering in storage rings. In this
paper a generic system of polarization evolution equations describing spin
filtering is derived and solved, then we compare and contrast this system to
other descriptions of spin filtering appearing in the literature. This is of
interest to projects planning to produce a polarized antiproton beam by spin
filtering, and to any project utilizing spin filtering in storage rings. The
physical processes responsible for spin filtering are analysed and their
contributions to the dynamics of polarization buildup are highlighted. It is
hoped that this will shed light on some of the confusion in the literature.",0711.4819v1
2008-01-28,Modulated spin waves and robust quasi-solitons in classical Heisenberg rings,"We investigate the dynamical behavior of finite rings of classical spin
vectors interacting via nearest-neighbor isotropic exchange in an external
magnetic field. Our approach is to utilize the solutions of a continuum version
of the discrete spin equations of motion (EOM) which we derive by assuming
continuous modulations of spin wave solutions of the EOM for discrete spins.
This continuous EOM reduces to the Landau-Lifshitz equation in a particular
limiting regime. The usefulness of the continuum EOM is demonstrated by the
fact that the time-evolved numerical solutions of the discrete spin EOM closely
track the corresponding time-evolved solutions of the continuum equation. Of
special interest, our continuum EOM possesses soliton solutions, and we find
that these characteristics are also exhibited by the corresponding solutions of
the discrete EOM. The robustness of solitons is demonstrated by considering
cases where initial states are truncated versions of soliton states and by
numerical simulations of the discrete EOM equations when the spins are coupled
to a heat bath at finite temperatures.",0801.4262v1
2008-08-06,Electron spin resonance in Kondo systems,"We calculate the dynamical spin response of Kondo impurity and Kondo lattice
systems within a semiphenomenological Fermi liquid description, at low
temperatures $T<T_K$, the Kondo temperature, and low magnetic fields $B \ll k_B
T_K/g\mu_B$. Fermi liquid parameters are determined by comparison (i) with
microscopic theory (numerical renormalization group) for the impurity model and
(ii) with experiment for the lattice model. We find in the impurity case that
the true impurity spin resonance has a width of the order of $T_K$ and
disappears altogether if the $g$-factors of impurity spin and conduction
electron spin are equal. However, there is an impurity-induced resonance
contribution at the conduction electron resonance. The latter is broadened by
spin lattice relaxation and is usually unobservable. In contrast, for the
Anderson lattice in the Kondo regime we find a \textit{sharp} ESR resonance
line only slightly shifted from the local resonance and broadened by spin
lattice relaxation, the latter significantly reduced by both the effects of
heavy fermion physics and ferromagnetic fluctuations. We conjecture that our
findings explain the sharp ESR-lines recently observed in several heavy fermion
compounds.",0808.0892v2
2008-08-14,Co-resonant enhancement of spin-torque critical currents in spin-valves with synthetic-ferrimagnet free-layer,"It is experimentally shown that the critical current for onset of spin-torque
instability in current-perpendicular-to-plane spin-valves can be strongly
enhanced using ""synthetic ferrimagnet"" free-layers of form FM1/Ru/FM2
(FM=ferrromagnet). However, this enhancement occurs for only one polarity of
bias current. A two-macrospin model is shown to reproduce the observations. The
model suggests that this phenomenon is related to a polarity-dependent,
spin-torque induced co-resonance between the two natural dynamic modes of the
FM1/FM2 couple. The resonance condition facilitates energy transfer out of the
spin-torque destabilized mode into the other stable mode whose effective
damping is actually enhanced by spin-torques, thereby delaying the onset of
instability of this coupled system to larger critical currents.",0808.2015v2
2008-08-27,The entanglement in one-dimensional random XY spin chain with Dzyaloshinskii-Moriya interaction,"The impurities of exchange couplings, external magnetic fields and
Dzyaloshinskii--Moriya (DM) interaction considered as Gaussian distribution,
the entanglement in one-dimensional random $XY$ spin systems is investigated by
the method of solving the different spin-spin correlation functions and the
average magnetization per spin. The entanglement dynamics at central locations
of ferromagnetic and antiferromagnetic chains have been studied by varying the
three impurities and the strength of DM interaction. (i) For ferromagnetic spin
chain, the weak DM interaction can improve the amount of entanglement to a
large value, and the impurities have the opposite effect on the entanglement
below and above critical DM interaction. (ii) For antiferromagnetic spin chain,
DM interaction can enhance the entanglement to a steady value. Our results
imply that DM interaction strength, the impurity and exchange couplings (or
magnetic field) play competing roles in enhancing quantum entanglement.",0808.3682v1
2008-09-17,Spin-transfer torque induced reversal in magnetic domains,"Using the complex stereographic variable representation for the macrospin,
from a study of the nonlinear dynamics underlying the generalized
Landau-Lifshitz(LL) equation with Gilbert damping, we show that the
spin-transfer torque is effectively equivalent to an applied magnetic field. We
study the macrospin switching on a Stoner particle due to spin-transfer torque
on application of a spin polarized current. We find that the switching due to
spin-transfer torque is a more effective alternative to switching by an applied
external field in the presence of damping. We demonstrate numerically that a
spin-polarized current in the form of a short pulse can be effectively employed
to achieve the desired macro-spin switching.",0809.2910v1
2008-10-27,Anisotropic itinerant magnetism and spin fluctuations in BaFe2As2: A neutron scattering study,"Neutron scattering measurements were performed to investigate magnetic
excitations in a single-crystal sample of the ternary iron arsenide BaFe2As2, a
parent compound of a recently discovered family of Fe-based superconductors. In
the ordered state, we observe low energy spin-wave excitations with a gap
energy of 9.8(4) meV. The in-plane spin-wave velocity v_ab and out-of-plane
spin-wave velocity v_c measured at 12 meV are 280(150) and 57(7) meV A,
respectively. At high energy, we observe anisotropic scattering centered at the
antiferromagnetic wave vectors. This scattering indicates two-dimensional spin
dynamics, which possibly exist inside the Stoner continuum. At T_N=136(1) K,
the gap closes, and quasi-elastic scattering is observed above T_N, indicative
of short-range spin fluctuations. In the paramagnetic state, the scattering
intensity along the L direction becomes ""rodlike,"" characteristic of
uncorrelated out-of-plane spins, attesting to the two-dimensionality of the
system.",0810.4790v2
2008-11-17,Spin fluctuations probed by NMR in paramagnetic spinel LiV$_2$O$_4$: a self-consistent renormalization theory,"Low frequency spin fluctuation dynamics in paramagnetic spinel LiV$_2$O$_4$,
a rare 3$d$-electron heavy fermion system, is investigated. A parametrized
self-consistent renormalization (SCR) theory of the dominant AFM spin
fluctuations is developed and applied to describe temperature and pressure
dependences of the low-$T$ nuclear spin-lattice relaxation rate $1/T_1$ in this
material. The experimental data for $1/T_1$ available down to $\sim 1$K are
well reproduced by the SCR theory, showing the development of AFM spin
fluctuations as the paramagnetic metal approaches a magnetic instability under
the applied pressure. The low-$T$ upturn of $1/T_1T$ detected below 0.6 K under
the highest applied pressure of 4.74 GPa is explained as the nuclear spin
relaxation effect due to the spin freezing of magnetic defects unavoidably
present in the measured sample of LiV$_2$O$_4$.",0811.2665v1
2008-12-19,Spin-bias driven magnetization reversal and nondestructive detection in a single molecular magnet,"The magnetization reversal in a single molecular magnet (SMM) weakly coupled
to an electrode with spin-dependent splitting of chemical potentials (spin
bias) is theoretically investigated by means of the rate equation. A
microscopic mechanism for the reversal is demonstrated by the avalanche
dynamics at the reversal point. The magnetization as a function of the spin
bias shows hysteresis loops tunable by the gate voltage and varying with
temperature. The nondestructive measurement to the orientation of giant spin in
SMM is presented by measuring the fully polarized electric current in the
response to a small spin bias. For Mn$_{12}$ac molecule, its small transverse
anisotropy only slightly violates the results above. The situation when there
is an angle between the easy axis of the SMM and the spin quantization
direction of the electrode is also studied.",0812.3713v2
2009-02-19,Kondo screening suppression by spin-orbit interaction in quantum dots,"We study the transport properties of a quantum dot embedded in an
Aharonov-Bohm ring in the presence of spin-orbit interactions. Using a
numerical renormalization group analysis of the system in the Kondo regime, we
find that the competition of Aharonov-Bohm and spin-orbit dynamical phases
induces a strong suppression of the Kondo state singlet, somewhat akin to an
effective intrinsic magnetic field in the system. This effective field breaks
the spin degeneracy of the localized state and produces a finite magnetic
moment in the dot. By introducing an {\em in-plane} Zeeman field we show that
the Kondo resonance can be fully restored, reestablishing the spin singlet and
a desired spin filtering behavior in the Kondo regime, which may result in full
spin polarization of the current through the ring.",0902.3310v1
2009-06-12,Magnetic dynamics with spin transfer torques near the Curie temperature,"We use atomistic stochastic Landau-Lifshitz-Slonczewski simulations to study
the interaction between large thermal fluctuations and spin transfer torques in
the magnetic layers of spin valves. At temperatures near the Curie temperature
$T_{\rm C}$, spin currents measurably change the size of the magnetization
(i.e. there is a {\it longitudinal} spin transfer effect). The change in
magnetization of the free magnetic layer in a spin valve modifies the
temperature dependence of the applied field-applied current phase diagram for
temperatures near $T_{\rm C}$. These atomistic simulations can be accurately
described by a Landau-Lifshitz-Bloch + Slonczewski equation, which is a
thermally averaged mean field theory. Both the simulation and the mean field
theory show that a longitudinal spin transfer effect can be a substantial
fraction of the magnetization close to $T_{\rm C}$.",0906.2423v1
2009-07-08,Decoherence of a quantum memory coupled to a collective spin bath,"We study the quantum dynamics of a single qubit coupled to a bath of
interacting spins as a model for decoherence in solid state quantum memories.
The spin bath is described by the Lipkin-Meshkov-Glick model and the bath spins
are subjected to a transverse magnetic field. We investigate the qubit
interacting via either an Ising- or an XY-type coupling term to subsets of bath
spins of differing size. The large degree of symmetry of the bath allows us to
find parameter regimes where the initial qubit state is revived at well defined
times after the qubit preparation. These times may become independent of the
bath size for large baths and thus enable faithful qubit storage even in the
presence of strong coupling to a bath. We analyze a large range of parameters
and identify those which are best suited for quantum memories. In general we
find that a small number of links between qubit and bath spins leads to less
decoherence and that systems with Ising coupling between qubit and bath spins
are preferable.",0907.1399v2
2009-07-09,Excitation spectrum and magnetic field effects in a quantum critical spin-orbital system:FeSc$_2$S$_4$,"The orbitally degenerate A-site spinel compound FeSc2S4 has been
experimentally identified as a ``spin-orbital liquid'', with strong
fluctuations of both spins and orbitals. Assuming that the second neighbor spin
exchange J2 is the dominant one, we argued in a recent theoretical study [Chen
et al., Phys. Rev. Lett. 102, 096406 (2009)] that FeSc2S4 is in a local
``spin-orbital singlet'' state driven by spin orbit coupling, close to a
quantum critical point, which separates the ``spin-orbital singlet'' phase from
a magnetically and orbitally ordered phase. In this paper, we refine further
and develop this theory of FeSc2S4 . First, we show that inclusion of a small
first neighbor exchange J1 induces a narrow region of incommensurate phase near
the quantum critical point. Next, we derive the phase diagram in the presence
of an external magnetic field B, and show that the latter suppresses the
ordered phase. Lastly, we compute the field dependent dynamical magnetic
susceptibility $\chi(k, \omega; B)$, from which we extract a variety of
physical quantities. Comparison with and suggestions for experiment are
discussed.",0907.1692v1
2009-08-03,Direct Measurement of Quantum Dot Spin Dynamics using Time-Resolved Resonance Fluorescence,"We temporally resolve the resonance fluorescence from an electron spin
confined to a single self-assembled quantum dot to measure directly the spin's
optical initialization and natural relaxation timescales. Our measurements
demonstrate that spin initialization occurs on the order of microseconds in the
Faraday configuration when a laser resonantly drives the quantum dot
transition. We show that the mechanism mediating the optically induced
spin-flip changes from electron-nuclei interaction to hole-mixing interaction
at 0.6 Tesla external magnetic field. Spin relaxation measurements result in
times on the order of milliseconds and suggest that a $B^{-5}$ magnetic field
dependence, due to spin-orbit coupling, is sustained all the way down to 2.2
Tesla.",0908.0292v1
2010-07-22,Quantized Lattice Dynamic Effects on the Spin-Peierls Transition,"The density matrix renormalization group method is used to investigate the
spin-Peierls transition for Heisenberg spins coupled to quantized phonons. We
use a phonon spectrum that interpolates between a gapped, dispersionless
(Einstein) limit to a gapless, dispersive (Debye) limit. A variety of
theoretical probes are used to determine the quantum phase transition,
including energy gap crossing, a finite size scaling analysis, bond order
auto-correlation functions, and bipartite quantum entanglement. All these
probes indicate that in the antiadiabatic phonon limit a quantum phase
transition of the Berezinskii-Kosterlitz-Thouless type is observed at a
non-zero spin-phonon coupling, $g_{\text c}$. An extrapolation from the
Einstein limit to the Debye limit is accompanied by an increase in $g_{\text
c}$ for a fixed optical ($q=\pi $) phonon gap. We therefore conclude that the
dimerized ground state is more unstable with respect to Debye phonons, with the
introduction of phonon dispersion renormalizing the effective spin-lattice
coupling for the Peierls-active mode. We also show that the staggered spin-spin
and phonon displacement order parameters are unreliable means of determining
the transition.",1007.3860v2
2010-08-06,Multifrequency spin resonance in diamond,"Magnetic resonance techniques provide a powerful tool for controlling spin
systems, with applications ranging from quantum information processing to
medical imaging. Nevertheless, the behavior of a spin system under strong
excitation remains a rich dynamical problem. In this paper, we examine spin
resonance of the nitrogen-vacancy center in diamond under conditions outside
the regime where the usual rotating wave approximation applies, focusing on
effects of multifrequency excitation and excitation with orientation parallel
to the spin quantization axis. Strong-field phenomena such as multiphoton
transitions and coherent destruction of tunneling are observed in the spectra
and analyzed via numerical and analytic theory. In addition to illustrating the
response of a spin system to strong multifrequency excitation, these
observations may inform techniques for manipulating electron-nuclear spin
quantum registers.",1008.1103v1
2010-08-10,Spin Fluid Dynamics Observed by Magnetic Fountain Effect and Mechano-Spin Effect in the Ferromagnetic Superfluid $^3$He A$_1$ Phase,"Systematic observations of the magnetically generated fountain pressure in
the superfluid $^3$He A$_1$ have been carried out in a newly built apparatus
designed to reduce the effect of thermal gradients. In the same apparatus,
mechanical pumping and filtering of polarized nuclear spins were realized by
the pneumatic pumping action of an electrostatically actuated membrane. In both
experiments, the measured induced pressure was observed to decay at all
temperatures where the A$_1$ phase appeared in magnetic fields up to 13 T and
liquid pressures between 1 and 29 bar. The inferred spin relaxation rate tended
to increase as the low temperature phase boundary with the A$_2$ phase
(T$_{C2}$) was approached. The increase in spin relaxation rate near T$_{C2}$
can be explained by the presence of a minority spin condensate in the A$_1$
phase as predicted by Monien and Tewordt and by the application of the
Leggett-Takagi theory of spin relaxation in superfluid $^3$He.",1008.1780v1
2010-09-27,Hybridization and spin decoherence in heavy-hole quantum dots,"We theoretically investigate the spin dynamics of a heavy hole confined to an
unstrained III-V semiconductor quantum dot and interacting with a narrowed
nuclear-spin bath. We show that band hybridization leads to an exponential
decay of hole-spin superpositions due to hyperfine-mediated nuclear pair flips,
and that the accordant single-hole-spin decoherence time T2 can be tuned over
many orders of magnitude by changing external parameters. In particular, we
show that, under experimentally accessible conditions, it is possible to
suppress hyperfine-mediated nuclear-pair-flip processes so strongly that
hole-spin quantum dots may be operated beyond the `ultimate limitation' set by
the hyperfine interaction which is present in other spin-qubit candidate
systems.",1009.5195v2
2010-11-04,Spin polarization phenomena in dense neutron matter at a strong magnetic field,"Spin polarized states in neutron matter at strong magnetic fields up to
$10^{18}$ G are considered in the model with the Skyrme effective interaction.
Analyzing the self-consistent equations at zero temperature, it is shown that a
thermodynamically stable branch of solutions for the spin polarization
parameter as a function of density corresponds to the negative spin
polarization when the majority of neutron spins are oriented oppositely to the
direction of the magnetic field. Besides, it is found that in a strong magnetic
field the state with the positive spin polarization can be realized as a
metastable state at the high density region in neutron matter. At finite
temperature, the entropy of the thermodynamically stable branch demonstrates
the unusual behavior being larger than that for the nonpolarized state (at
vanishing magnetic field) above certain critical density which is caused by the
dependence of the entropy on the effective masses of neutrons in a spin
polarized state.",1011.1244v1
2010-11-23,Correlation Effects in Quantum Spin-Hall Insulators: A Quantum Monte Carlo Study,"We consider the Kane-Mele model with spin-orbit coupling supplemented by a
Hubbard U term. On the basis of projective auxiliary field quantum Monte Carlo
simulations on lattice sizes up to 15 x 15, we map out the phase diagram. The
quantum spin-liquid state found in the Hubbard model is shown to be robust
against weak spin-orbit interaction, and is not adiabatically connected to the
spin-Hall insulating state. Beyond a critical value of U > U_c both states are
unstable toward magnetic ordering. Within the quantum spin-Hall state we study
the spin, charge and single-particle dynamics of the helical Luttinger liquid
by retaining the Hubbard interaction only on the edge of a ribbon. The Hubbard
interaction greatly suppresses charge currents along the edge, promotes edge
magnetism, but leaves the single-particle signatures of the helical liquid
intact.",1011.5063v3
2011-02-09,Observation of intrinsic inverse spin Hall effect,"We report observation of intrinsic inverse spin Hall effect in un-doped GaAs
multiple quantum wells with a sample temperature of 10 K. A transient ballistic
pure spin current is injected by a pair of laser pulses through quantum
interference. By time-resolving the dynamics of the pure spin current, the
momentum relaxation time is deduced, which sets the lower limit of the
scattering time between electrons and holes. The transverse charge current
generated by the pure spin current via the inverse spin Hall effect is
simultaneously resolved. We find that the charge current is generated well
before the first electron-hole scattering event. Generation of the transverse
current in the scattering-free ballistic transport regime provides unambiguous
evidence for the intrinsic inverse spin Hall effect.",1102.1958v2
2011-03-22,Ultrafast mapping of optical polarization states onto spin coherence of localized electrons in a semiconductor,"We experimentally demonstrate an ultrafast method for preparing spin states
of donor-bound electrons in GaAs with single laser pulses. Each polarization
state of a preparation pulse has a direct mapping onto a spin state, with
bijective correspondence between the Poincar\'{e}-sphere (for photon
polarization) and Bloch-sphere (for spin) state representations. The
preparation is governed by a stimulated Raman process and occurs orders of
magnitude faster than the spontaneous emission and spin dephasing. Similar
dynamics governs our ultrafast optical Kerr detection of the spin coherence,
thus getting access to spin state tomography. Experiments with double
preparation pulses show an additive character for the preparation method.
Utilization of these phenomena is of value for quantum information schemes.",1103.4307v2
2011-04-06,"Magnetic transition, long-range order, and moment fluctuations in the pyrochlore iridate Eu2Ir2O7","Muon spin rotation and relaxation experiments in the pyrochlore iridate
Eu2Ir2O7 yield a well-defined muon spin precession frequency below the
metal-insulator/antiferromagnetic transition temperature TM = 120 K, indicative
of long-range commensurate magnetic order and thus ruling out quantum spin
liquid and spin-glass-like ground states. The dynamic muon spin relaxation rate
is temperature-independent between 2 K and ~TM and yields an anomalously long
Ir^{4+} spin correlation time, suggesting a singular density of low-lying spin
excitations. Similar behavior is found in other pyrochlores and geometrically
frustrated systems, but also in the unfrustrated iridate BaIrO3. Eu2Ir2O7 may
be only weakly frustrated; if so, the singularity might be associated with the
small-gap insulating state rather than frustration.",1104.1213v1
2011-04-13,The diamond Nitrogen-Vacancy center as a probe of random fluctuations in a nuclear spin ensemble,"New schemes that exploit the unique properties of Nitrogen-Vacancy (NV)
centers in diamond are presently being explored as a platform for
high-resolution magnetic sensing. Here we focus on the ability of a NV center
to monitor an adjacent mesoscopic nuclear spin bath. For this purpose, we
conduct comparative experiments where the NV spin evolves under the influence
of surrounding 13C nuclei or, alternatively, in the presence of asynchronous AC
fields engineered to emulate bath fluctuations. Our study reveals substantial
differences that underscore the limitations of the semi-classical picture when
interpreting and predicting the outcome of experiments designed to probe small
nuclear spin ensembles. In particular, our study elucidates the NV center
response to bath fluctuations under common pulse sequences, and explores a
detection protocol designed to probe time correlations of the nuclear spin bath
dynamics. Further, we show that the presence of macroscopic nuclear spin order
is key to the emergence of semi-classical spin magnetometry.",1104.2546v1
2011-04-18,Enhanced photon-assisted spin transport in a quantum dot attached to ferromagnetic leads,"We investigate real-time dynamics of spin-polarized current in a quantum dot
coupled to ferromagnetic leads in both parallel and antiparallel alignments.
While an external bias voltage is taken constant in time, a gate terminal,
capacitively coupled to the quantum dot, introduces a periodic modulation of
the dot level. Using non equilibrium Green's function technique we find that
spin polarized electrons can tunnel through the system via additional
photon-assisted transmission channels. Owing to a Zeeman splitting of the dot
level, it is possible to select a particular spin component to be
photon-transfered from the left to the right terminal, with spin dependent
current peaks arising at different gate frequencies. The ferromagnetic
electrodes enhance or suppress the spin transport depending upon the leads
magnetization alignment. The tunnel magnetoresistance also attains negative
values due to a photon-assisted inversion of the spin-valve effect.",1104.3483v2
2011-04-30,Entangled spinning particles in charged and rotating black holes,"Spin precession for an EPR pair of spin-1/2 particles in equatorial orbits
around a Kerr-Newman black hole is studied. Hovering observers are introduced
to ensure fixed reference frames in order to perform the Wigner rotation. These
observers also guarantee a reliable direction to compare spin states in
rotating black holes. The velocity of the particle due frame-dragging is
explicitly incorporated by addition of velocities with respect the hovering
observers and the corresponding spin precession angle is computed. The
spin-singlet state is observed to be mixed with the spin-triplet by dynamical
and gravity effects, thus it is found that a perfect anti-correlation of
entangled states for these observers is deteriorated. Finally, an analysis
concerning the different limit cases of parameters of spin precession including
the frame-dragging effects is carried out.",1105.0094v3
2011-05-17,Magnetic Resonance Force Microscopy of paramagnetic electron spins at millikelvin temperatures,"Magnetic Resonance Force Microscopy (MRFM) is a powerful technique to detect
a small number of spins that relies on force-detection by an ultrasoft
magnetically tipped cantilever and selective magnetic resonance manipulation of
the spins. MRFM would greatly benefit from ultralow temperature operation,
because of lower thermomechanical noise and increased thermal spin
polarization. Here, we demonstrate MRFM operation at temperatures as low as 30
mK, thanks to a recently developed SQUID-based cantilever detection technique
which avoids cantilever overheating. In our experiment, we detect dangling bond
paramagnetic centers on a silicon surface down to millikelvin temperatures.
Fluctuations of such kind of defects are supposedly linked to 1/f magnetic
noise and decoherence in SQUIDs as well as in several superconducting and
single spin qubits. We find evidence that spin diffusion plays a key role in
the low temperature spin dynamics.",1105.3395v3
2011-06-06,Quantum Spin Hall Insulators with Interactions and Lattice Anisotropy,"We investigate the interplay between spin-orbit coupling and
electron-electron interactions on the honeycomb lattice combining the cellular
dynamical mean-field theory and its real space extension with analytical
approaches. We provide a thorough analysis of the phase diagram and temperature
effects at weak spin-orbit coupling. We systematically discuss the stability of
the quantum spin Hall phase toward interactions and lattice anisotropy
resulting in the plaquette-honeycomb model. We also show the evolution of the
helical edge states characteristic of quantum spin Hall insulators as a
function of Hubbard interaction and anisotropy. At very weak spin-orbit
coupling and intermediate electron-electron interactions, we substantiate the
existence of a quantum spin liquid phase.",1106.0943v2
2011-07-07,Initial data for binary neutron stars with arbitrary spins,"In general neutron stars in binaries are spinning. Due to the existence of
millisecond pulsars we know that these spins can be substantial. We argue that
spins with periods on the order a few dozen milliseconds could influence the
late inspiral and merger dynamics. Thus numerical simulations of the last few
orbits and the merger should start from initial conditions that allow for
arbitrary spins. We discuss quasi-equilibrium approximations one can make in
the construction of binary neutron star initial data with spins. Using these
approximations we are able to derive two new matter equations. As in the case
of irrotational neutron star binaries one of these equations is algebraic and
the other elliptic. If these new matter equations are solved together with the
equations for the metric variables following the Wilson-Mathews or conformal
thin sandwich approach one can construct neutron star initial data. The spin of
each star is described by a rotational velocity that can be chosen freely so
that one can create stars in arbitrary rotation states. Our new matter
equations reduce to the well known limits of both corotating and irrotational
neutron star binaries.",1107.1440v1
2011-08-09,AC Susceptibility and Electron Spin Resonance Studies of Spin Dynamics in n Ba$_3$NbFe$_3$Si$_2$O$_{14}$: A Geometrically Frustrated Lattice,"We report ac susceptibility and high-frequency electron spin resonance (ESR)
measurements on the geometrically frustrated compound
Ba$_3$NbFe$_3$Si$_2$O$_{14}$ with the N\'{e}el temperature $T_N=27 K$. An
unusually large frequency-dependence of ac susceptibility in the temperature
range of 20 - 100 K reveals a spin-glass-like behavior, signalling the presence
of frustration related slow magnetic fluctuations. ESR experiments show a
multi-step magnetic and spin chirality ordering process. For temperatures above
30 K, the weak temperature dependence of the ESR linewidth $\Delta
H_{pp}\propto T^{-p}$ with $p=0.8$ evidences the development of short-range
correlated spin clusters. The critical broadening with $p =1.8$, persisting
down to 14 K, indicates the coexistence of the short-range ordered spin
clusters within a helically ordered state. Below 9.5 K, the anomalously large
decrease of the linewidth reveals the stabilization of a long-range ordered
state with one chirality.",1108.1853v1
2011-09-09,Spin dynamics in the ordered spin ice Tb$_2$Sn$_2$O$_7$,"Geometrical frustration is a central challenge in contemporary condensed
matter physics, a crucible favourable to the emergence of novel physics. The
pyrochlore magnets, with rare earth magnetic moments localized at the vertices
of corner-sharing tetrahedra, play a prominent role in this field, with a rich
variety of exotic ground states ranging from the ""spin ices"" \hoti\ and \dyti\
to the ""spin liquid"" and ""ordered spin ice"" ground states in \tbti\ and \tbsn.
Inelastic neutron scattering provides valuable information for understanding
the nature of these ground states, shedding light on the crystal electric field
(CEF) level scheme and on the interactions between magnetic moments. We have
performed such measurements with unprecedented neutron flux and energy
resolution, in the ""ordered spin ice"" \tbsn. We argue that a new interaction,
which involves the spin lattice coupling through a low temperature distortion
of the trigonal crystal field, is necessary to account for the data.",1109.1960v1
2011-09-19,Spin dynamics in finite cyclic XY model,"Evolution of the z-component of a single spin in the finite cyclic XY spin
1/2 chain is studied. Initially one selected spin is polarized while other
spins are completely unpolarized and uncorrelated. Polarization of the selected
spin as a function of time is proportional to the autocorrelation function at
infinite temperature. Initialization of the selected spin gives rise to two
wave packets moving in opposite directions and winding over the circle. We
express the correlation function as a series in winding number and derive
tractable approximations for each term. This allows to give qualitative
explanation and quantitative description to various finite-size effects such as
partial revivals and transition from regular to erratic behavior.",1109.4127v3
2011-10-16,Spin Torque in Anisotropic Tunneling Junctions,"Spin transport in magnetic tunnel junctions comprising a single magnetic
layer in the presence of interfacial spin-orbit interaction (SOI) is
investigated theoretically. Due to the presence of interfacial SOI, a
current-driven spin torque can be generated at the second order in SOI, even in
the absence of an external spin polarizer. This torque possesses two
components, in-plane and perpendicular to the plane of rotation, that can
induce either current-driven {\em magnetization switching} from in-plane to
out-of-plane configuration or {\em magnetization precessions}, similarly to
Spin Transfer Torque in spin-valves. Consequently, it appears that it is
possible to control the magnetization steady state and dynamics by either
varying the bias voltage or electrically modifying the SOI at the interface.",1110.3488v1
2011-10-31,Spin excitations and mechanisms of superconductivity in cuprates,"A microscopic theory of spin excitations in strongly-correlated electronic
systems within the t-J model is discussed. An exact representation for the
dynamic spin susceptibility is derived. In the normal state, the excitation
spectrum reveals a crossover from spin-wave-like excitations at low doping to
overdamped paramagnons above the optimal doping. At low temperatures, the
resonance mode at the antiferromagnetic wave vector Q = \pi(1,1) emerges which
is explained by a strong suppression of the spin excitation damping caused by a
spin gap at Q rather than by opening of a superconducting gap. A major role of
spin excitations in the d-wave superconducting pairing in cuprates is stressed
in discussing mechanisms of high-Tc superconductivity within the Hubbard model
in the limit of strong correlations, while electron-phonon interaction and a
well-screened weak Coulomb interaction are not essential.",1110.6715v1
2012-06-20,Free induction decay of single spins in diamond,"We study both theoretically and experimentally the free induction decay (FID)
of the electron spin associated with a single nitrogen-vacancy defect in high
purity diamond, where the main source of decoherence is the hyperfine
interaction with a bath of $^{13}$C nuclear spins. In particular, we report a
systematic study of the FID signal as a function of the strength of a magnetic
field oriented along the symmetry axis of the defect. On average, an increment
of the coherence time by a factor of $\sqrt{5/2}$ is observed at high magnetic
field in diamond samples with a natural abundance of $^{13}$C nuclear spins, in
agreement with numerical simulations and theoretical studies. Further
theoretical analysis shows that this enhancement is independent of the
concentration of nuclear spin impurities. By dividing the nuclear spin bath
into shells and cones, we theoretically identify which nuclear spins are
responsible for the observed dynamics.",1206.4575v2
2012-07-30,"Aligned Spins: Orbital Elements, Decaying Orbits, and Last Stable Circular Orbit to high post-Newtonian Orders","In this article the quasi-Keplerian parameterisation for the case that spins
and orbital angular momentum in a compact binary system are aligned or
anti-aligned with the orbital angular momentum vector is extended to 3PN
point-mass, next-to-next-to-leading order spin-orbit, next-to-next-to-leading
order spin(1)-spin(2), and next-to-leading order spin-squared dynamics in the
conservative regime. In a further step, we use the expressions for the
radiative multipole moments with spin to leading order linear and quadratic in
both spins to compute radiation losses of the orbital binding energy and
angular momentum. Orbital averaged expressions for the decay of energy and
eccentricity are provided. An expression for the last stable circular orbit is
given in terms of the angular velocity type variable $x$.",1207.6961v2
2012-08-27,Probing dynamics of an electron-spin ensemble via a superconducting resonator,"We study spin relaxation and diffusion in an electron-spin ensemble of
nitrogen impurities in diamond at low temperature (0.25-1.2 K) and polarizing
magnetic field (80-300 mT). Measurements exploit mode- and
temperature-dependent coupling of hyperfine-split sub-ensembles to the
resonator. Temperature-independent spin linewidth and relaxation time suggest
that spin diffusion limits spin relaxation. Depolarization of one sub-ensemble
by resonant pumping of another indicates fast cross-relaxation compared to spin
diffusion, with implications on use of sub-ensembles as independent quantum
memories.",1208.5473v1
2012-09-07,Chiral Spin Waves in Fermi Liquids with Spin-Orbit Coupling,"We predict the existence of chiral spin waves collective modes in a
two-dimensional Fermi liquid with the Rashba or Dresselhaus spin-orbit
coupling. Starting from the phenomenological Landau theory, we show that the
long-wavelength dynamics of magnetization is governed by the Klein- Gordon
equations. The standing-wave solutions of these equations describe ""particles""
with effective masses, whose magnitudes and signs depend on the strength of the
electron-electron interaction. The spectrum of the spin-chiral modes for
arbitrary wavelengths is determined from the Dyson equation for the interaction
vertex. We propose to observe spin-chiral modes via microwave absorption of
standing waves confined by an in-plane profile of the spin-orbit splitting.",1209.1647v1
2012-10-03,Waves of spin-current in magnetized dielectrics,"Spin-current is an important physical quantity in present day spintronics and
it might be very usefull in the physics of quantum plasma of spinning
particles. Thus it is important to have an equation of the spin-current
evolution. This equation naturally appears as a part of a set of the quantum
hydrodynamics (QHD) equations. Consequently, we present the set of the QHD
equations derived from the many-particle microscopic Schrodinger equation,
which consists of the continuity equation, the Euler equation, the Bloch
equation and equation of the spin-current evolution. We use these equations to
study dispersion of the collective excitations in the three dimensional samples
of the magnetized dielectrics. We show that dynamics of the spin-current leads
to formation of new type of the collective excitations in the magnetized
dielectrics, which we called spin-current waves.",1210.1090v2
2013-01-18,Influences of Topological Defect on Spin Hall Effect,"We study the influence of topological defect on the spin current as well as
the spin Hall effect. We find that the nontrivial deformation of the space-time
due to topological defect can generate a spin dependent current which then
induces an imbalanced accumulation of spin states on the edges of sample. The
corresponding spin-Hall conductivity has also been calculated for the
topological defect of a cosmic string. Comparing to the ordinary value, a
correction which is linear with mass density of the cosmic string appears. Our
approach to the dynamics of non-relativistic spinor in the presence of a
topological defect is based on the Foldy-Wouthuysen transformation. The spin
current is obtained in by using the extended Drude model which is independent
of the scattering mechanism.",1301.4363v2
2013-01-23,"The effect of inertia on the Dirac electron, the spin Hall current and the momentum space Berry curvature","We have studied the spin dependent force and the associated momentum space
Berry curvature in an accelerating system. The results are derived by taking
into consideration the non relativistic limit of a generally covariant Dirac
equation under the presence of electromagnetic field where the methodology of
Foldy-Wouthuysen transformation is applied to achieve the non relativistic
limit. Spin currents appear due to the combined action of the external electric
field, crystal field and the induced inertial electric field via the total
effective spin-orbit interaction. In an accelerating frame, the crucial role of
momentum space Berry curvature in the spin dynamics has also been addressed
from the perspective of spin Hall conductivity. For time dependent
acceleration, the expression for the spin polarization has been derived.",1301.5431v1
2013-05-05,Cavity cooling of an ensemble spin system,"We describe how sideband cooling techniques may be applied to large spin
ensembles in magnetic resonance. Using the Tavis-Cummings model in the presence
of a Rabi drive, we solve a Markovian master equation describing the joint
spin-cavity dynamics to derive cooling rates as a function of ensemble size.
Our calculations indicate that the coupled angular momentum subspaces of a spin
ensemble containing roughly $10^{11}$ electron spins may be polarized in a time
many orders of magnitude shorter than the typical thermal relaxation time. The
described techniques should permit efficient removal of entropy for spin-based
quantum information processors and fast polarization of spin samples. The
proposed application of a standard technique in quantum optics to magnetic
resonance also serves to reinforce the connection between the two fields, which
has recently begun to be explored in further detail due to the development of
hybrid designs for manufacturing noise-resilient quantum devices.",1305.1029v2
2013-06-28,Spin-flip transitions and departure from the Rashba model in the Au(111) surface,"We present a detailed analysis of the spin-flip excitations induced by a
periodic time-dependent electric field in the Rashba prototype Au(111) noble
metal surface. Our calculations incorporate the full spinor structure of the
spin-polarized surface states and employ a Wannier-based scheme for the
spin-flip matrix elements. We find that the spin-flip excitations associated
with the surface states exhibit an important angular modulation which is
completely absent in the standard Rashba model \cite{rashba}. Furthermore, we
demonstrate that the maximum of the calculated spin-flip absorption rate is
about twice the model prediction. These results show that although the Rashba
model accurately describes the spectrum and spin polarization, it does not
fully account for the dynamical properties of the surface states.",1306.6831v2
2013-07-31,Giant spin oscillations in an ultracold Fermi sea,"Collective behavior in many-body systems is the origin of many fascinating
phenomena in nature ranging from swarms of birds and modeling of human behavior
to fundamental magnetic properties of solids. We report on the first
observation of collective spin dynamics in an ultracold Fermi sea with large
spin: We observe long-lived and large-amplitude coherent spin oscillations,
driven by local spin interactions. At ultralow temperatures, Pauli blocking
stabilizes the collective behavior and the Fermi sea behaves as a single entity
in spin space. With increasing temperature, we observe a stronger damping
associated with particle-hole excitations. As a striking feature, we find a
high-density regime where excited spin configurations are collisionally
stabilized.",1307.8392v1
2013-10-13,Optically-driven nuclear-spin-selective Rabi oscillations of single electron spins in diamond,"Optically-driven Rabi oscillations of single electron spins in a diamond
nitrogen vacancy center are realized with two Raman-resonant optical pulses
that are detuned from the respective dipole optical transitions. The Rabi
oscillations are nuclear-spin selective and are robust against rapid
decoherence of the underlying optical transitions, opening the door to
generating phonon-mediated spin entanglement in an optically-driven spin-phonon
system. A direct comparison between the Rabi oscillations and simulated Raman
adiabatic passage along with a detailed theoretical analysis provide a wealth
of information on the coherent spin dynamics and in particular reveal that
decoherence and environmental fluctuations associated with the optical
transitions affect the fidelity of the Rabi oscillations through relatively
large jumps in the transition frequencies.",1310.3525v1
2013-11-06,Magnetization dynamics of cobalt grown on graphene,"Ferromagnetic resonance (FMR) spin pumping is a rapidly growing field which
has demonstrated promising results in a variety of material systems. This
technique utilizes the resonant precession of magnetization in a ferromagnet to
inject spin into an adjacent non-magnetic material. Spin pumping into graphene
is attractive on account of its exceptional spin transport properties. This
article reports on FMR characterization of cobalt grown on CVD graphene and
examines the validity of linewidth broadening as an indicator of spin pumping.
In comparison to cobalt samples without graphene, direct contact
cobalt-on-graphene exhibits increased FMR linewidth--an often used signature of
spin pumping. Similar results are obtained in Co/MgO/graphene structures, where
a 1nm MgO layer acts as a tunnel barrier. However, SQUID, MFM, and Kerr
microscopy measurements demonstrate increased magnetic disorder in cobalt grown
on graphene, perhaps due to changes in the growth process and an increase in
defects. This magnetic disorder may account for the observed linewidth
enhancement due to effects such as two-magnon scattering or mosaicity. As such,
it is not possible to conclude successful spin injection into graphene from FMR
linewidth measurements alone.",1311.1441v1
2013-11-20,On higher spin extension of the Jackiw-Teitelboim gravity model,"We formulate AdS_2 higher spin gravity as BF theory with fields taking values
in sl(N,R) algebra treated as higher spin algebra. The theory is topological
and naturally extends the Jackiw-Teitelboim gravity model so as to include
higher spin fields. The BF equations linearized about AdS_2 background are
interpreted as describing higher spin partially-massless fields of maximal
depth along with dilaton fields. It is shown that there are dual metric-like
formulations following from the original linearized BF higher spin theory. The
duality establishes a dynamical equivalence of the metric-like field equations
that can be given either as massive scalar field equations or as conservation
conditions for higher spin currents.",1311.5119v3
2013-12-17,Low energy magnetic excitations in the spin-orbital Mott insulator Sr$_2$IrO$_4$,"We report a high-field electron spin resonance study in the sub-THz frequency
domain of a single crystal of Sr$_2$IrO$_4$ that has been recently proposed as
a prototypical spin-orbital Mott insulator. In the antiferromagnetically (AFM)
ordered state with noncollinear spin structure that occurs in this material at
$T_{\rm N} \approx 240$ K we observe both the ""low"" frequency mode due to the
precession of weak ferromagnetic moments arising from a spin canting, and the
""high"" frequency modes due to the precession of the AFM sublattices.
Surprisingly, the energy gap for the AFM excitations appears to be very small,
amounting to 0.83 meV only. This suggests a rather isotropic Heisenberg
dynamics of interacting Ir$^{4+}$ effective spins despite the spin-orbital
entanglement in the ground state.",1312.4847v2
2014-02-25,Unusual Two-stage Dynamics of the Spin-Lattice Polaron Formation,"We follow the formation of a spin-lattice polaron after a quantum quench that
simulates absorption of the pump{pulse in the time-resolved experiments. We
discover a two-stage relaxation where spin and lattice degrees of freedom
represent an integral part of the relaxation mechanism. In the first stage the
kinetic energy of the spin-lattice polaron relaxes towards its ground state
value while relaxation processes via spin and phonon degrees of freedom remain
roughly independent. In the second, typically much longer stage, a subsequent
energy transfer between lattice and spin degrees of freedom via the charge
carrier emerges. The excess local spin energy radiates away via magnon
excitations.",1402.6104v1
2014-07-23,Anomalous organic magnetoresistance from competing carrier-spin-dependent interactions with localized electronic and nuclear spins,"We describe a new regime for low-field magnetoresistance in organic
semiconductors, in which the spin-relaxing effects of localized nuclear spins
and electronic spins interfere. The regime is studied by the controlled
addition of localized electronic spins to a material that exhibits substantial
room-temperature magnetoresistance ($\sim 20$\%). Although initially the
magnetoresistance is suppressed by the doping, at intermediate doping there is
a regime where the magnetoresistance is insensitive to the doping level. For
much greater doping concentrations the magnetoresistance is fully suppressed.
The behavior is described within a theoretical model describing the effect of
carrier spin dynamics on the current.",1407.6313v1
2014-08-20,Analyses of the transmission of the disorder from a disturbed environment to a spin chain,"We study spin chains submitted to disturbed kick trains described by
classical dynamical processes. The spin chains are described by Heisenberg and
Ising models. We consider decoherence, entanglement and relaxation processes
induced by the kick irregularity in the multipartite system (the spin chain).
We show that the different couplings transmit the disorder along the chain
differently and also to each spin density matrix with different efficiencies.
In order to analyze and to interpret the observed effects we use a
semi-classical analysis across the Husimi distribution. It consists to consider
the classical spin orientation movements. A possibility of conserving the order
into the spin chain is finally analyzed.",1408.4570v2
2014-09-02,Quantum spin coherence in halogen-modified Cr$_7$Ni molecular nanomagnets,"Among the factors determining the quantum coherence of the spin in molecular
magnets is the presence and the nature of nuclear spins in the molecule. We
have explored modifying the nuclear spin environment in Cr$_7$Ni-based
molecular nanomagnets by replacing hydrogen atoms with deuterium or the halogen
atoms, fluorine or chlorine. We find that the spin coherence, studied at low
temperatures by pulsed electron spin resonance, is modified by a range of
factors, including nuclear spin and magnetic moment, changes in dynamics owing
to nuclear mass, and molecular morphology changes.",1409.0821v2
2014-09-08,Two-dimensional nanoscale imaging of gadolinium spins via scanning probe relaxometry with a single spin in diamond,"Spin-labeling of molecules with paramagnetic ions is an important approach
for determining molecular structure, however current ensemble techniques lack
the sensitivity to detect few isolated spins. In this Letter, we demonstrate
two-dimensional nanoscale imaging of paramagnetic gadolinium compounds using
scanning relaxometry of a single nitrogen vacancy (NV) center in diamond.
Gadopentetate dimeglumine attached to an atomic force microscope tip is
controllably interacted with and detected by the NV center, by virtue of the
fact that the NV exhibits fast relaxation in the fluctuating magnetic field
generated by electron spin flips in the gadolinium. Using this technique, we
demonstrate a reduction in the $T_1$ relaxation time of the NV center by over
two orders of magnitude, probed with a spatial resolution of 20 nm. Our result
exhibits the viability of the technique for imaging individual spins attached
to complex nanostructures or biomolecules, along with studying the magnetic
dynamics of isolated spins.",1409.2422v1
2014-09-16,Phonon-modulated magnetic interactions and spin Tomonaga-Luttinger liquid in the p-orbital antiferromagnet CsO2,"The magnetic response of antiferromagnetic CsO2, coming from the p-orbital
S=1/2 spins of anionic O2- molecules, is followed by 133Cs nuclear magnetic
resonance across the structural phase transition occuring at Ts1=61 K on
cooling. Above Ts1, where spins form a square magnetic lattice, we observe a
huge, nonmonotonic temperature dependence of the exchange coupling originating
from thermal librations of O2- molecules. Below Ts1, where antiferromagnetic
spin chains are formed as a result of p-orbital ordering, we observe a spin
Tomonaga-Luttinger-liquid behavior of spin dynamics. These two interesting
phenomena, which provide rare simple manifestations of the coupling between
spin, lattice and orbital degrees of freedom, establish CsO2 as a model system
for molecular solids.",1409.4818v2
2014-10-01,Near-Earth Asteroid Satellite Spins Under Spin-Orbit Coupling,"We develop a fourth-order numerical integrator to simulate the coupled spin
and orbital motions of two rigid bodies having arbitrary mass distributions
under the influence of their mutual gravitational potential. We simulate the
dynamics of components in well-characterized binary and triple near-Earth
asteroid systems and use surface of section plots to map the possible spin
configurations of the satellites. For asynchronous satellites, the analysis
reveals large regions of phase space where the spin state of the satellite is
chaotic. For synchronous satellites, we show that libration amplitudes can
reach detectable values even for moderately elongated shapes. The presence of
chaotic regions in the phase space has important consequences for the evolution
of binary asteroids. It may substantially increase spin synchronization
timescales, explain the observed fraction of asynchronous binaries, delay
BYORP-type evolution, and extend the lifetime of binaries. The variations in
spin rate due to large librations also affect the analysis and interpretation
of lightcurve and radar observations.",1410.0082v3
2014-10-23,Gravitational waves from spinning compact binaries in hyperbolic orbits,"Compact binaries in hyperbolic orbits are plausible gravitational wave (GW)
sources for the upcoming and planned GW observatories. We develop an efficient
prescription to compute post-Newtonian (PN) accurate ready-to-use GW
polarization states for spinning compact binaries, influenced by the dominant
order spin-orbit interactions, in hyperbolic orbits. This is achieved by
invoking the 1.5PN accurate quasi-Keplerian parameterization for the radial
sector of the orbital dynamics. We probe the influences of spins and
gravitational radiation reaction on $h_+$ and $h_{\times}$ during the
hyperbolic passage. It turns out that both polarization states exhibit the
memory effect for GWs from spinning compact binaries in hyperbolic orbits. In
contrast, only cross polarization state exhibits the memory effect for GWs from
non-spinning compact binaries. Additionally, we compute 1PN accurate amplitude
corrected GW polarization states for hyperbolic non-spinning compact binaries
in a fully parametric manner and perform initial comparisons with the existing
waveforms.",1410.6311v3
2014-11-14,Quantum discord in the central spin model,"The quantum properties of dynamic correlations in a system of an electron
spin surrounded by nuclear spins under the conditions of free induction decay
(FID) and spin echo have been studied. Analytical results for the time
evolution of mutual information, classical part of correlations, and quantum
part characterized by quantum discord have been obtained within the central
spin model in the high-temperature approximation. The same formulas describe
the quantum discord in both the FID and the spin echo although the forms of the
dependences are different because of difference in the parameters entering into
the formulas. Discord of the spin echo compared with the FID has a strong
dependence on time at short times, and it tends to zero with decreasing of the
magnetic field, whereas in the case of the FID it reaches a plateau.",1411.3782v1
2014-12-17,Topological transitions in spin interferometers,"We show that topological transitions in electronic spin transport are
feasible by a controlled manipulation of spin-guiding fields. The transitions
are determined by the topology of the fields texture through an effective Berry
phase (related to the winding parity of spin modes around poles in the Bloch
sphere), irrespective of the actual complexity of the nonadiabatic spin
dynamics. This manifests as a distinct dislocation of the interference pattern
in the quantum conductance of mesoscopic loops. The phenomenon is robust
against disorder, and can be experimentally exploited to determine the
magnitude of inner spin-orbit fields.",1412.5487v3
2015-01-14,Accurate and efficient spin integration for particle accelerators,"Accurate spin tracking is a valuable tool for understanding spin dynamics in
particle accelerators and can help improve the performance of an accelerator.
In this paper, we present a detailed discussion of the integrators in the spin
tracking code gpuSpinTrack. We have implemented orbital integrators based on
drift-kick, bend-kick, and matrix-kick splits. On top of the orbital
integrators, we have implemented various integrators for the spin motion. These
integrators use quaternions and Romberg quadratures to accelerate both the
computation and the convergence of spin rotations. We evaluate their
performance and accuracy in quantitative detail for individual elements as well
as for the entire RHIC lattice. We exploit the inherently data-parallel nature
of spin tracking to accelerate our algorithms on graphics processing units.",1501.03450v1
2015-02-05,Nonlinear analysis of magnetization dynamics excited by spin Hall effect,"We investigate the possibility of exciting self-oscillation in a
perpendicular ferromagnet by the spin Hall effect on the basis of a nonlinear
analysis of the Landau-Lifshitz-Gilbert (LLG) equation. In the self-oscillation
state, the energy supplied by the spin torque during a precession on a constant
energy curve should equal the dissipation due to damping. Also, the current to
balance the spin torque and the damping torque in the self-oscillation state
should be larger than the critical current to destabilize the initial state. We
find that the second condition in the spin Hall system is not satisfied by
deriving analytical solutions of the energy supplied by the spin transfer
effect and the dissipation due to the damping from the nonlinear LLG equation.
This indicates that the self-oscillation of a perpendicular ferromagnet cannot
be excited solely by the spin Hall torque.",1502.01420v2
2015-02-25,Parallelized Traveling Cluster Approximation to Study Numerically Spin-Fermion Models on Large Lattices,"Lattice spin-fermion models are important to study correlated systems where
quantum dynamics allows for a separation between slow and fast degrees of
freedom. The fast degrees of freedom are treated quantum mechanically while the
slow variables, generically refereed to as the ""spins"", are treated
classically. At present, exact diagonalization coupled with classical Monte
Carlo (ED+MC) is extensively used to solve numerically a general class of
lattice spin-fermion problems. In this common setup, the classical variables
(spins) are treated via the standard MC method while the fermion problem is
solved by exact diagonalization. The ""Traveling Cluster Approximation"" (TCA) is
a real space variant of the ED+MC method that allows to solve spin-fermion
problems on lattice sizes with up to $10^3$ sites. In this publication, we
present a novel reorganization of the TCA algorithm in a manner that can be
efficiently parallelized. This allows us to solve generic spin-fermion models
easily on $10^4$ lattice sites and with some effort on $10^5$ lattice sites,
representing the record lattice sizes studied for this family of models.",1502.07028v1
2015-06-02,Spin Superfluidity in the $ν=0$ Quantum Hall State of Graphene,"A proposal to detect the purported canted antiferromagnet order for the
$\nu=0$ quantum Hall state of graphene based on a two-terminal spin transport
setup is theoretically discussed. In the presence of a magnetic field normal to
the graphene plane, a dynamic and inhomogeneous texture of the N\'eel vector
lying within the plane should mediate (nearly dissipationless) superfluid
transport of spin angular momentum polarized along the $z$ axis, which could
serve as a strong support for the canted antiferromagnet scenario. Spin
injection and detection can be achieved by coupling two spin-polarized edge
channels of the $|\nu|=2$ quantum Hall state on two opposite ends of the
$\nu=0$ region. A simple kinetic theory and Onsager reciprocity are invoked to
model the spin injection and detection processes, and the transport of spin
through the antiferromagnet is accounted for using the Landau-Lifshitz-Gilbert
phenomenology.",1506.01061v1
2015-06-15,Neutrino electromagnetic properties: new approach to oscillations in magnetic fields,"Several new and interesting aspects of neutrino oscillations in a magnetic
field are considered: 1) We develop a standard usually used approach to the
neutrino spin oscillations in the neutrino mass basis and obtain the effective
neutrino spin (and ""spin-mass"") oscillation Hamiltonian that can be used for
description of the neutrino oscillations between different pairs of neutrino
states with different masses and helicities; 2) We derive the exact solution of
the Dirac equation for a massive neutrino with nonzero magnetic moment in the
presence of a constant transversal magnetic field that is rotating along the
direction of the neutrino propagation (the twisting magnetic field) and on the
basis of the obtained energy spectrum the neutrino spin oscillation effective
Hamiltonian is derive; 3) We develop a new approach to neutrino spin
oscillations that is based on the description of the neutrino spin states with
the corresponding spin operator that commutes with the neutrino dynamics
Hamiltonian in the magnetic field. The obtained new results can have important
phenomenological applications.",1506.05311v1
2015-06-22,Heat transport between antiferromagnetic insulators and normal metals,"Antiferromagnetic insulators can become active spintronics components by
controlling and detecting their dynamics via spin currents in adjacent metals.
This cross-talk occurs via spin-transfer and spin-pumping, phenomena that have
been predicted to be as strong in antiferromagnets as in ferromagnets. Here, we
demonstrate that a temperature gradient drives a significant heat flow from
magnons in antiferromagnetic insulators to electrons in adjacent normal metals.
The same coefficients as in the spin-transfer and spin-pumping processes also
determine the thermal conductance. However, in contrast to ferromagnets, the
heat is not transferred via a spin Seebeck effect which is absent in
antiferromagnetic insulator-normal metal systems. Instead, the heat is
transferred via a large staggered spin Seebeck effect.",1506.06705v1
2015-06-30,On the action for Weyssenhoff spin fluid and the Barbero-Immirzi parameter,"It was showed by Perez and Rovelli in 2006 that the Holst action in gravity
with torsion with massless and minimally coupling Dirac fermions gives rise to
the four-fermion coupling term, whose coefficient is a function of the
Barbero-Immirzi (BI) parameter. This parameter is present in the Holst action,
which is an object of investigation in a non-perturbative formalism of quantum
gravity. The key feature is the torsion because its absence implies no effect
from Holst term in dynamical equations. In this paper we consider a spin fluid
(also called Weyssenhoff fluid), which is a perfect fluid that has intrinsic
spin. We study the Host action in gravity with torsion and spin fluid, and we
include, for completeness, minimaly coupling massive fermions.We find the
equivalent action containing the same four-fermion interaction term previously
calculated by Perez and Rovelli without the spin fluid, also the quadratic spin
tensor term and finally an interaction term between the axial current and the
spin tensor, which can be relevant for new effects and features in Cosmology.
In all three cases, the dependence on BI parameter is the same.",1506.09071v1
2015-07-21,Generation and Detection of Atomic Spin Entanglement in Optical Lattices,"Ultracold atoms in optical lattices offer a great promise to generate
entangled states for scalable quantum information processing owing to the
inherited long coherence time and controllability over a large number of
particles. We report on the generation, manipulation and detection of atomic
spin entanglement in an optical superlattice. Employing a spin-dependent
superlattice, atomic spins in the left or right sites can be individually
addressed and coherently manipulated by microwave pulses with near unitary
fidelities. Spin entanglement of the two atoms in the double wells of the
superlattice is generated via dynamical evolution governed by spin
superexchange. By observing collisional atom loss with in-situ absorption
imaging we measure spin correlations of atoms inside the double wells and
obtain the lower boundary of entanglement fidelity as $0.79\pm0.06$, and the
violation of a Bell's inequality with $S=2.21\pm 0.08$. The above results
represent an essential step towards scalable quantum computation with ultracold
atoms in optical lattices.",1507.05937v1
2015-08-06,Interface-driven spin-torque ferromagnetic resonance by Rashba coupling at the interface between non-magnetic materials,"The Rashba-Edelstein effect stems from the interaction between the electron's
spin and its momentum induced by spin-orbit interaction at an interface or a
surface. It was shown that the inverse Rashba-Edelstein effect can be used to
convert a spin- into a charge current. Here, we demonstrate that a Bi/Ag Rashba
interface can even drive an adjacent ferromagnet to resonance. We employ a
spin-torque ferromagnetic resonance excitation/detection scheme which was
developed originally for a bulk spin-orbital effect, the spin Hall effect. In
our experiment, the direct Rashba-Edelstein effect generates an oscillating
spin current from an alternating charge current driving the magnetization
precession in a neighboring permalloy (Py, Ni80Fe20) layer. Electrical
detection of the magnetization dynamics is achieved by a rectification
mechanism of the time dependent multilayer resistance arising from the
anisotropic magnetoresistance.",1508.01410v1
2015-08-12,Spin orbit splitting of the photon induced Fano Resonance in an oscillating graphene electrostatic barrier,"We investigate theoretically the effect of a time dependent oscillating
potential on the transport property of the Dirac Fermion through a monolayer
graphene electrostatic barrier under the influence of the Rashba spin orbit
interaction. The time dependent problem is solved in the frame work of the non
perturbative Floquet approach. It is noted that the dynamic condition of the
barrier may be controlled by tuning the Rashba parameter. Introduction of the
spin orbit interaction causes splitting of the Fano resonance(FR), a
characteristic feature in photon assisted tunneling. The separation between the
spin split FR gives an indirect measure of the fine structure of the quasihole
bound state inside the barrier. The present findings on the Rashba splitting of
the FR and its external control by tuning the oscillating field parameters
might have potential for applications in spintronic devices, especially in the
spin field effect transistors. The spin polarization of different Floquet
sidebands is found to be quite sensitive to the spin pseudospin interaction.",1508.02888v1
2015-09-04,Versatile microwave-driven trapped ion spin system for quantum information processing,"Using trapped atomic ions we demonstrate a tailored and versatile effective
spin-system suitable for quantum simulations and universal quantum computation.
By simply applying microwave pulses, selected spins can be decoupled from the
remaining system and thus can serve as a quantum memory, while simultaneously,
other coupled spins perform conditional quantum dynamics. Also, microwave
pulses can change the sign of spin-spin couplings, as well as their effective
strength, even during the course of a quantum algorithm. Taking advantage of
the simultaneous long-range coupling between three spins a coherent quantum
Fourier transform -- an essential building block for many quantum algorithms --
is efficiently realized. This approach, which is based on microwave-driven
trapped ions and is complementary to laser-based methods, opens a new route to
overcoming technical and physical challenges in the quest for a quantum
simulator and a quantum computer.",1509.01478v2
2015-10-23,"Fast, nanoscale addressability of nitrogen-vacancy spins via coupling to a dynamic ferromagnetic vortex","The core of a ferromagnetic vortex domain creates a strong, localized
magnetic field which can be manipulated on nanosecond timescales, providing a
platform for addressing and controlling individual nitrogen-vacancy center
spins in diamond at room temperature, with nanometer-scale resolution. First,
we show that the ferromagnetic vortex can be driven into proximity with a
nitrogen-vacancy defect using small applied magnetic fields, inducing
significant nitrogen-vacancy spin splitting. Second, we find that the magnetic
field gradient produced by the vortex is sufficient to address spins separated
by nanometer length scales. By applying a microwave-frequency magnetic field,
we drive both the vortex and the nitrogen-vacancy spins, resulting in enhanced
coherent rotation of the spin state. Finally we demonstrate that by driving the
vortex on fast timescales, sequential addressing and coherent manipulation of
spins is possible on $\sim100$ ns timescales.",1510.07073v2
2016-01-04,Influence of magnetic quantum confined Stark effect on the spin lifetime of indirect excitons,"We report on the unusual and counter-intuitive behaviour of spin lifetime of
excitons in coupled semiconductor quantum wells (CQWs) in the presence of
in-plane magnetic field. Instead of conventional acceleration of spin
relaxation due to the Larmor precession of electron and hole spins we observe a
strong increase of the spin relaxation time at low magnetic fields followed by
saturation and decrease at higher fields. We argue that this non-monotonic spin
relaxation dynamics is a fingerprint of the magnetic quantum confined Stark
effect. In the presence of electric field along the CQW growth axis, an applied
magnetic field efficiently suppresses the exciton spin coherence, due to
inhomogeneous broadening of the $g$-factor distribution.",1601.00427v1
2016-02-18,Locking of electron spin coherence over fifty milliseconds in natural silicon carbide,"We demonstrate that silicon carbide (SiC) with natural isotope abundance can
preserve a coherent spin superposition in silicon vacancies over unexpectedly
long time approaching 0.1 seconds. The spin-locked subspace with drastically
reduced decoherence rate is attained through the suppression of heteronuclear
spin cross-talking by applying a moderate magnetic field in combination with
dynamic decoupling from the nuclear spin baths. We identify several
phonon-assisted mechanisms of spin-lattice relaxation, ultimately limiting
quantum coherence, and find that it can be extremely long at cryogenic
temperature, equal or even longer than 8 seconds. Our approach may be extended
to other polyatomic compounds and open a path towards improved qubit memory for
wafer-scale quantum techmologies.",1602.05775v2
2016-02-27,Nonlinear separate spin evolution in degenerate electron-positron-ion plasmas,"The non-linear evolution of spin-electron acoustic, positron-acoustic, and
spin-electron-positron acoustic waves is considered. It is demonstrated that
weakly nonlinear dynamics of each wave leads to the soliton formation.
Altogether, we report on existence of three different solitons. The
spin-electron acoustic soliton known for electron-ion plasmas is described for
electron-positron-ion plasmas for the first time. The existence of the
spin-electron-positron acoustic soliton is reported for the first time. The
positron-acoustic soliton and the spin-electron-positron acoustic soliton arise
as the areas of a positive electric potential. The spin-electron acoustic
soliton behaves as the area of a negative electric potential at the relatively
small positron imbalance $n_{0p}/n_{0e}=0.1$ and as the area of a positive
electric potential at the relatively large positron imbalance
$n_{0p}/n_{0e}=0.5$.",1602.08640v1
2016-03-10,Spin Dynamics in Bilayer Graphene : Role of Electron-Hole Puddles and the Dyakonov-Perel Mechanism,"We report on spin transport features which are unique to high quality bilayer
graphene, in absence of magnetic contaminants and strong intervalley mixing.
The time-dependent spin polarization of propagating wavepacket is computed
using an efficient quantum transport method. In the limit of vanishing effects
of substrate and disorder, the energy-dependence of spin lifetime is similar to
monolayer graphene with a M-shape profile and minimum value at the charge
neutrality point, but with an electron-hole asymmetry fingerprint. In sharp
contrast, the incorporation of substrate-induced electron-hole puddles
(characteristics of supported graphene either on SiO2 orhBN) surprisingly
results in a large enhancement of the low-energy spin lifetime and a lowering
of its high-energy values. Such feature, unique to bilayer, is explained in
terms of a reinforced Dyakonov-Perel mechanism at the Dirac point, whereas spin
relaxation at higher energies is driven by pure dephasing effects. This
suggests further electrostatic control of the spin transport length scales in
graphene devices.",1603.03263v2
2016-04-10,Measurement of spin coherence using Raman scattering,"Ramsey interferometry provides a natural way to determine the coherence time
of most qubit systems. Recent experiments on quantum dots however, demonstrated
that dynamical nuclear spin polarization can strongly influence the measurement
process, making it difficult to extract the $T_2^*$ coherence time using
optical Ramsey pulses. Here, we demonstrate an alternative method for spin
coherence measurement that is based on first-order coherence of photons
generated in spin-flip Raman scattering. We show that if a quantum emitter is
driven by a weak monochromatic laser, Raman coherence is determined exclusively
by spin coherence, allowing for a direct determination of spin $T_2^*$ time.
When combined with coherence measurements on Rayleigh scattered photons, our
technique enables us to identify coherent and incoherent contributions to
resonance fluorescence, and to minimize the latter. We verify the validity of
our technique by comparing our results to those determined from Ramsey
interferometry for electron and heavy-hole spins.",1604.02685v1
2016-04-18,Spin-transfer torques in antiferromagnets: efficiency and quantification method,"We formulate a theory of spin-transfer torques in antiferromagnets, which
covers the small to large limits of the exchange coupling energy relative to
the kinetic energy of the inter-sublattice electron dynamics. Our theory
suggests a natural definition of the efficiency of spin-transfer torques in
antiferromagnets in terms of well-defined material parameters, revealing that
the charge current couples predominantly to the antiferromagnetic order
parameter and the sublattice-canting moment in, respectively, the limits of
large and small exchange coupling. The effects can be quantified by analyzing
the antiferromagnetic spin-wave dispersions in the presence of charge current:
in the limit of large exchange coupling the spin-wave Doppler shift always
occurs, whereas, in the opposite limit, the only spin-wave modes to react to
the charge current are ones that carry a pronounced sublattice-canting moment.
The findings offer a framework for understanding and designing spin-transfer
torques in antiferromagnets belonging to different classes of sublattice
structures such as, e.g., bipartite and layered antiferromagnets.",1604.05277v2
2016-06-03,Enhanced spin-orbit coupling in core/shell nanowires,"The spin-orbit coupling (SOC) in semiconductors is strongly influenced by
structural asymmetries, as prominently observed in bulk crystal structures that
lack inversion symmetry. Here, we study an additional effect on the SOC: the
asymmetry induced by the large interface area between a nanowire core and its
surrounding shell. Our experiments on purely wurtzite GaAs/AlGaAs core/shell
nanowires demonstrate optical spin injection into a single free-standing
nanowire and determine the effective electron g-factor of the hexagonal GaAs
wurtzite phase. The spin relaxation is highly anisotropic in time-resolved
micro-photoluminescence measurements on single nanowires, showing a significant
increase of spin relaxation in external magnetic fields. This behavior is
counterintuitive compared to bulk wurtzite crystals. We present a model for the
observed electron spin dynamics highlighting the dominant role of the
interface-induced SOC in these core/shell nanowires. This enhanced SOC may
represent an interesting tuning parameter for the implementation of
spin-orbitronic concepts in semiconductor-based structures.",1606.01135v1
2016-06-10,Quantum decoherence dynamics of divacancy spins in silicon carbide,"Long coherence times are key to the performance of quantum bits (qubits).
Here, we experimentally and theoretically show that the Hahn-echo coherence
time (T2) of electron spins associated with divacancy defects in 4H-SiC reaches
1.3 ms, one of the longest T2 times of an electron spin in a naturally isotopic
crystal. Using a first-principles microscopic quantum-bath model, we find that
two factors determine the unusually robust coherence. First, in the presence of
moderate magnetic fields (300 G and above), the 29Si and 13C paramagnetic
nuclear spin baths are decoupled. In addition, because SiC is a binary crystal,
homo-nuclear spin pairs are both diluted and forbidden from forming strongly
coupled, nearest-neighbor spin pairs. Longer neighbor distances result in fewer
nuclear spin flip-flops, a less fluctuating intra-crystalline magnetic
environment, and thus a longer T2 time. Our results point to polyatomic
crystals as promising hosts for coherent qubits in the solid state.",1606.03354v2
2016-06-14,Modulation instability in quasi two-dimensional spin-orbit coupled Bose-Einstein condensates,"We theoretically investigate the dynamics of modulation instability (MI) in
two-dimensional spin-orbit coupled Bose-Einstein condensates (BECs). The
analysis is performed for equal densities of pseudo-spin components. Different
combination of the signs of intra- and inter-component interaction strengths
are considered, with a particular emphasize on repulsive interactions. We
observe that the unstable modulation builds from originally miscible
condensates, depending on the combination of the signs of the intra- and
inter-component interaction strengths. The repulsive intra- and inter-component
interactions admit instability and the MI immiscibility condition is no longer
significant. Influence of interaction parameters such as spin-orbit and Rabi
coupling on MI are also investigated. The spin-orbit coupling (SOC) inevitably
contributes to instability regardless of the nature of the interaction. In the
case of attractive interaction, SOC manifest in enhancing the MI. Thus, a
comprehensive study of MI in two-dimensional spin-orbit coupled binary BECs of
pseudo-spin components is presented.",1606.04426v2
2016-06-17,Symmetry protected gapless $Z_2$ spin liquids,"Despite rapid progress in understanding gapped topological states, much less
is known about gapless topological phases of matter, especially in strongly
correlated electrons. In this work we discuss a large class of robust gapless
quantum spin liquids in frustrated magnets made of half-integer spins, which
are described by gapless fermionic spinons coupled to dynamical $Z_2$ gauge
fields. Requiring $U(1)$ spin conservation, time reversal and certain space
group symmetries, we show that certain spinon symmetry fractionalization class
necessarily leads to a gapless spectrum. These gapless excitations are stable
against any perturbations, as long as the required symmetries are preserved.
Applying these gapless criteria to spin one-half systems on square, triangular
and kagome lattices, we show that all gapped symmetric $Z_2$ spin liquids in
Abrikosov-fermion representation can also be realized in Schwinger-boson
representation. This leads to 64 gapped $Z_2$ spin liquids on square lattice,
and 8 gapped states on both kagome and triangular lattices.",1606.05652v3
2016-07-12,$μ$SR evidence for the U(1) quantum spin liquid ground state in the triangular antiferromagnet YbMgGaO$_4$,"Muon spin relaxation and rotation ($\mu$SR) experiments on single crystals of
the structurally perfect triangular antiferromagnet YbMgGaO$_4$ indicate the
absence of both static long-range magnetic order and spin freezing down to
0.048 K in zero field. Below 0.4 K, the $\mu^{+}$ spin relaxation rates, which
are proportional to the dynamic correlation function of the Yb$^{3+}$
spins,exhibit temperature-independent plateaus. Same behavior is revealed by
temperature-independent local susceptibilities extracted from the Knight shifts
of the $\mu^{+}$ spin rotation frequencies under a transverse field of 20 Oe.
All these $\mu$SR results unequivocally support the formation of a gapless U(1)
quantum spin liquid ground state in the triangular antiferromagnet YbMgGaO$_4$.",1607.03298v1
2016-09-28,A Bilocal Model for the Relativistic Spinning Particle,"In this work we show that a relativistic spinning particle can be described
at the classical and the quantum level as being composed of two physical
constituents which are entangled and separated by a fixed distance. This
bilocal model for spinning particles allows for a natural description of
particle interactions as a local interaction at each of the constituents. This
form of the interaction vertex provides a resolution to a long standing issue
on the nature of relativistic interactions for spinning objects in the context
of the worldline formalism. It also potentially brings a dynamical explanation
for why massive fundamental objects are naturally of lowest spin. We analyze
first a non-relativistic system where spin is modeled as an entangled state of
two particles with the entanglement encoded into a set of constraints. It is
shown that these constraints can be made relativistic and that the resulting
description is isomorphic to the usual description of the phase space of
massive relativistic particles with the restriction that the quantum spin has
to be an integer.",1609.09110v1
2016-10-17,Spin blockade and coherent dynamics of high-spin states in a three-electron double quantum dot,"Asymmetry in a three-electron double quantum dot (DQD) allows spin blockade,
when spin-3/2 (quadruplet) states and spin-1/2 (doublet) states have different
charge configurations. We have observed this DQD spin blockade near the
(1,2)-(2,1) charge transition using a pulsed-gate technique and a charge
sensor. We then use this spin blockade to detect Landau-Zener-St\""uckelberg
(LZS) interference and coherent oscillations between the spin quadruplet and
doublet states. Such studies add to our understandings of coherence and control
properties of three-spin states in a double dot, which in turn would benefit
the explorations into various qubit encoding schemes in semiconductor
nanostructures.",1610.04940v1
2017-02-09,Electron spin polarization in strong-field ionization of Xenon atoms,"As a fundamental property of the electron, the spin plays a decisive role in
the electronic structure of matter from solids to molecules and atoms, e.g.
causing magnetism. Yet, despite its importance, the spin dynamics of electrons
released during the interaction of atoms with strong ultrashort laser pulses
has remained unexplored. Here we report on the experimental detection of
electron spin polarization by strong-field ionization of Xenon atoms and
support our results by theoretical analysis. We found up to 30% spin
polarization changing its sign with electron energy. This work opens the new
dimension of spin to strong-field physics. It paves the way to production of
subfemtosecond spin polarized electron pulses with applications ranging from
probing magnetic properties of matter at ultrafast time scales to testing
chiral molecular systems with subfemtosecond temporal and sub-{\AA}ngstr\""om
spatial resolution.",1702.02778v1
2017-03-13,Role of Spin Flips versus Spin Transport in Non Thermal Electrons Excited by Ultrashort Optical Pulses in Transition Metals,"A joint theoretical and experimental investigation is performed to understand
the underlying physics of laser-induced demagnetization in Ni and Co films.
Experimentally dynamics of spins is studied by determining the time-dependent
amplitude of the Voigt vector and theoretically ab-initio calculations are
performed using time-dependent density functional theory. We demonstrate that
overall spin-orbit induced spin-flips are the most significant contributors
with super-diffusive spin transport playing very limited to no role. Our study
highlights the material dependent nature of the demagnetization during the
process of thermalization of non-equilibrium spins.",1703.06756v1
2017-07-31,High-efficiency optical pumping of nuclear polarization in a GaAs quantum well,"The dynamic polarization of nuclear spins by photoexcited electrons is
studied in a high quality GaAs/AlGaAs quantum well. We find a surprisingly high
efficiency of the spin transfer from the electrons to the nuclei as reflected
by a maximum nuclear field of 0.9 T in a tilted external magnetic field of 1 T
strength only. This high efficiency is due to a low leakage of spin out of the
polarized nuclear system, because mechanisms of spin relaxation other than the
hyperfine interaction are strongly suppressed, leading to a long nuclear
relaxation time of up to 1000 s. A key ingredient to that end is the low
impurity concentration inside the heterostructure, while the electrostatic
potential from charged impurities in the surrounding barriers becomes screened
through illumination by which the spin relaxation time is increased compared to
keeping the system in the dark. This finding indicates a strategy for obtaining
high nuclear spin polarization as required for long-lasting carrier spin
coherence.",1708.00053v2
2018-04-16,Calculation of impurity density and electron-spin relaxation times in p-type GaAs:Mn,"Magnetic semiconductors have aroused interest due to their various
functionalities related to spintronic devices. Manganese (Mn) as a
substitutional impurity in A3B5 semiconductors supplies not only holes, but
also localized spins. The ejection of Mn atoms with an uncompensated magnetic
moment leads to the appearance of ferromagnetic properties. The most suitable
material characterized by long-term spin dynamics is n-type GaAs. In p-type
GaAs, the spin relaxation time of electrons is generally much shorter. For
purposes of this research, electron-spin relaxation times in 3D and 2D p-type
GaAs were studied. Calculation of impurity densities and charge state of
magnetic acceptors demonstrate the essential composition of the material.
Comparison of theoretical and experimental data in optical-spin orientation of
electrons reveal the longest spin relaxation time of 77 ns in 2D GaAs:Mn, less
than twice the best time in the p-type 3D GaAs material.",1804.05581v2
2020-07-02,Magnetic-field-induced reorientation in the SDW and the spin-stripe phases of the frustrated spin-1/2 chain compound $β$-TeVO$_4$,"$\beta$-TeVO$_4$ is a frustrated spin 1/2 zig-zag chain system,where
spin-density-wave (SDW), vector chiral (VC)and an exotic dynamic spin-stripe
phase compete at low temperatures. Here we use torque magnetometry to study the
anisotropy of these phases in magnetic fields of up to 5 T. Our results show
that the magnetic-field-induced spin reorientation occurs in the SDW and in the
spin stripe phases for $\mu_0 H \geq 2$~T. The observed spin reorientation is a
new element of the anisotropic phase diagram for the field directions in the
$ac$ and $a^*b$ crystallographic planes. The presented results should help
establishing the model of anisotropic magnetic interactions, which are
responsible for the formation of complex magnetic phases in $\beta$-TeVO$_4$
and similar quantum systems.",2007.00932v1
2010-05-26,Decoherence and Thermalization of Quantum Spin Systems,"In this review, we discuss the decoherence and thermalization of a quantum
spin system interacting with a spin bath environment, by numerically solving
the time-dependent Schr\""{o}dinger equation of the whole system. The effects of
the topologic structure and the initial state of the environment on the
decoherence of the two-spin and many-spin system are discussed. The role of
different spin-spin coupling is considered. We show under which conditions the
environment drives the reduced density matrix of the system to a fully
decoherent state, and how the diagonal elements of the reduced density matrix
approach those expected for the system in the microcanonical or canonical
ensemble, depending on the character of the additional integrals of motion. Our
demonstration does not rely on time-averaging of observables nor does it assume
that the coupling between system and bath is weak. Our findings show that the
microcanonical distribution (in each eigenenergy subspace) and canonical
ensemble are states that may result from pure quantum dynamics, suggesting that
quantum mechanics may be regarded as the foundation of quantum statistical
mechanics. Furthermore, our numerical results show that a fully decoherent
quantum system prefers to stay in an equilibrium state with a maximum entropy,
indicating the validity of the second law of thermodynamics in the decoherence
process.",1005.4776v1
2014-03-27,Tight-binding simulations of electrically driven spin-valley transitions in carbon nanotube quantum dots,"We describe dynamics of spin and valley transitions driven by alternating
electric fields in quantum dots defined electrostatically within semiconducting
carbon nanotubes (CNT). We use the tight-binding approach to describe the
states localized within a quantum dot taking into account the circumferential
spin-orbit interaction due to the s-p hybridization and external fields. The
basis of eigenstates localized in the quantum dot is used in the solution of
the time-dependent Schroedinger equation for description of spin flips and
inter-valley transitions that are driven by periodic perturbation in the
presence of coupling between the spin, valley and orbital degrees of freedom.
Besides the first order transitions we find also fractional resonances. We
discuss the transition rates with selection rules that are lifted by atomic
disorder and the bend of the tube. We demonstrate that the electric field
component perpendicular to the axis of the CNT activates spin transitions which
are otherwise absent and that the resonant spin-flip time scales with the
inverse of the electric field.",1403.6970v3
2012-01-05,Temperature dependence of electron-spin relaxation in a single InAs quantum dot at zero applied magnetic field,"The temperature-dependent electron spin relaxation of positively charged
excitons in a single InAs quantum dot (QD) was measured by time-resolved
photoluminescence spectroscopy at zero applied magnetic fields. The
experimental results show that the electron-spin relaxation is clearly divided
into two different temperature regimes: (i) T < 50 K, spin relaxation depends
on the dynamical nuclear spin polarization (DNSP) and is approximately
temperature-independent, as predicted by Merkulov et al. (ii) T > about 50 K,
spin relaxation speeds up with increasing temperature. A model of two LO phonon
scattering process coupled with hyperfine interaction is proposed to account
for the accelerated electron spin relaxation at higher temperatures.",1201.1125v1
2012-04-09,Spin-Orbit Coupled Degenerate Fermi Gases,"Spin-orbit coupling plays an increasingly important role in the modern
condensed matter physics. For instance, it gives birth to topological
insulators and topological superconductors. Quantum simulation of spin-orbit
coupling using ultracold Fermi gases will offer opportunities to study these
new phenomena in a more controllable setting. Here we report the first
experimental study of a spin-orbit coupled Fermi gas. We observe spin dephasing
in spin dynamics and momentum distribution asymmetry in the equilibrium state
as hallmarks of spin-orbit coupling. We also observe evidences of Lifshitz
transition where the topology of Fermi surfaces change. This serves as an
important first step toward finding Majorana fermions in this system.",1204.1887v1
2012-04-20,Topological Invariant and Quantum Spin Models from Magnetic π Fluxes in Correlated Topological Insulators,"The adiabatic insertion of a \pi flux into a quantum spin Hall insulator
gives rise to localized spin and charge fluxon states. We demonstrate that \pi
fluxes can be used in exact quantum Monte Carlo simulations to identify a
correlated Z_2 topological insulator using the example of the Kane-Mele-Hubbard
model. In the presence of repulsive interactions, a \pi flux gives rise to a
Kramers doublet of spinon states with a Curie law signature in the magnetic
susceptibility. Electronic correlations also provide a bosonic mode of magnetic
excitons with tunable energy that act as exchange particles and mediate a
dynamical interaction of adjustable range and strength between spinons. \pi
fluxes can therefore be used to build models of interacting spins. This idea is
applied to a three-spin ring and to one-dimensional spin chains. Due to the
freedom to create almost arbitrary spin lattices, correlated topological
insulators with \pi fluxes represent a novel kind of quantum simulator
potentially useful for numerical simulations and experiments.",1204.4728v3
2012-04-22,Spin Hall effect versus Rashba torque: a Diffusive Approach,"Current-driven magnetization dynamics of single ferromagnets in heavy
metal/ferromagnet bilayers has been recently realized. In this work, spin
torque induced by so-called Rashba spin-orbit coupling and spin Hall effect are
considered within a diffusive model. The dependence of the resulting torque as
a function of the thicknesses of the ferromagnet and heavy metal is analyzed.
We show that (i) both torques are on the form ${\bf T}=T_{||}{\bf m}\times{\bf
y}+T_\bot{\bf m}\times({\bf y}\times{\bf m})$, (ii) the ratio $T_{||}/T_\bot$
strongly depends on the thickness of the layers and (iii) the thickness
dependence of the spin torque provides an indication of the origin of the
(Rashba- or spin Hall effect-induced) spin torque .",1204.4869v1
2014-05-26,Chiral spin superfluidity and spontaneous spin Hall effect of interacting bosons,"Recent experiments on ultracold atoms in optical lattices have synthesized a
variety of tunable bands with degenerate double-well structures in momentum
space. Such degeneracies in the single particle spectrum strongly enhance
quantum fluctuations, and may lead to exotic many-body ground states. Here we
consider weakly interacting spinor Bose gases in such bands, and discover a
universal quantum ""order by disorder"" phenomenon which selects a novel chiral
spin superfluid with remarkable properties such as spontaneous anomalous spin
Hall effect and momentum space antiferromagnetism. For bosons in the excited
Dirac band of a hexagonal lattice, such a state supports staggered spin loop
currents in real space. We show that Bloch oscillations provide a powerful
dynamical route to quantum state preparation of such a chiral spin superfluid.
Our predictions can be readily tested in spin resolved time-of-flight
experiments.",1405.6715v1
2014-05-27,Anisotropy of the molecular magnet V$_{15}$ spin Hamiltonian detected by high-field electron spin resonance,"The molecular compound K$_6$[V$^{IV}_{15}$As$^{III}_6$O$_{42}$(H$_2$O)]
$\cdot$ 8H$_2$O, in short V$_{15}$, has shown important quantum effects such as
coherent spin oscillations. The details of the spin quantum dynamics depend on
the exact form of the spin Hamiltonian. In this study, we present a precise
analysis of the intramolecular interactions in V$_{15}$. To that purpose, we
performed high-field electron spin resonance measurements at 120 GHz and
extracted the resonance fields as a function of crystal orientation and
temperature. The data are compared against simulations using exact
diagonalization to obtain the parameters of the molecular spin Hamiltonian.",1405.7000v1
2014-05-28,Conditional control of donor nuclear spins in silicon using Stark shifts,"Electric fields can be used to tune donor spins in silicon using the Stark
shift, whereby the donor electron wave function is displaced by an electric
field, modifying the hyperfine coupling between the electron spin and the donor
nuclear spin. We present a technique based on dynamic decoupling of the
electron spin to accurately determine the Stark shift, and illustrate this
using antimony donors in isotopically purified silicon-28. We then demonstrate
two different methods to use a DC electric field combined with an applied
resonant radio-frequency (RF) field to conditionally control donor nuclear
spins. The first method combines an electric-field induced conditional phase
gate with standard RF pulses, and the second one simply detunes the spins
off-resonance. Finally, we consider different strategies to reduce the effect
of electric field inhomogeneities and obtain above 90% process fidelities.",1405.7420v1
2014-06-17,Spectral function of the $U \rightarrow \infty$ one dimensional Hubbard model at finite temperature and the crossover to the spin incoherent regime,"The physics of the strongly interacting Hubbard chain (with $t/U \ll 1$) at
finite temperatures undergoes a crossover to a spin incoherent regime when the
temperature is very small relative to the Fermi energy, but larger than the
characteristic spin energy scale. This crossover can be understood by means of
Ogata and Shiba's factorized wave function, where charge and spin are totally
decoupled, and assuming that the charge remains in the ground state, while the
spin is thermally excited and at an effective ""spin temperature"". We use the
time-dependent density matrix renormalization group method (tDMRG) to calculate
the dynamical contributions of the spin, to reconstruct the single-particle
spectral function of the electrons. The crossover is characterized by a
redistribution of spectral weight both in frequency and momentum, with an
apparent shift by $k_F$ of the minimum of the dispersion.",1406.4471v1
2015-12-28,Hamiltonian systems and semiclassical dynamics for interacting spins in QED,"In this article, we consider fixed spin-1/2 particles interacting through the
quantized electromagnetic field in a constant magnetic field. We give
approximate evolutions of coherent states. This uses spins-photon classical
Hamiltonian mechanics. These approximations enable to derive that the
approximate average fields and spins follow Maxwell-Bloch equations with a
current density coming from spins. In addition, we obain a law concerning the
evolution of the approximate average number of photons. Next, we provide
stationary points of the spins-photon Hamiltonian when the spin particles
belong to an orthogonal plane to the constant magnetic field. This allows for
the construction of quasimodes with spins colinear to the constant magnetic
field. Finally, a quasimode with an arbitrary high accuracy is built up and its
first order radiative correction is computed.",1512.08429v1
2016-05-16,Spin-polarization in the vicinity of quantum point contact with spin-orbit interaction,"We have developed a novel technique for detection of spin polarization with a
quantum dot weakly coupled to the objective device. The disturbance to the
object in this technique is very small since the detection is performed through
sampling of single electrons in the object with very slow rate. We have applied
the method to a quantum point contact (QPC) under a spin-orbit interaction. A
high degree of spin polarization in the vicinity of the QPC was detected when
the conductance stayed on a plateau at a half of the unit conductance quantum
($G_{\rm q}/2\equiv e^2/h$), and also on another plateau at $2e^2/h$. On the
half-quantum plateau, the degree of polarization $P$ decreased with the bias
source-drain voltage of the QPC while $P$ increased on the single-quantum
plateau, manifesting that different mechanisms of polarization were working on
these plateaus. Very long spin relaxation times in the detector quantum dot
probably due to dynamical nuclear spin polarization were observed. Anomalous
decrease of $P$ around zero-bias was observed at a Kondo-like resonance peak.",1605.04685v1
2016-12-23,Single-Shot Readout of a Nuclear Spin Weakly Coupled to a Nitrogen-Vacancy Center,"Single-shot readout of qubits is required for scalable quantum computing.
Nuclear spins are superb quantum memories due to their long coherence times but
are difficult to be read out in single shot due to their weak interaction with
probes. Here we demonstrate single-shot readout of a weakly coupled $^{13}$C
nuclear spin, which is unresolvable in traditional protocols. We use dynamical
decoupling pulse sequences to selectively enhance the entanglement between the
nuclear spin and a nitrogen-vacancy center electron spin, tuning the weak
measurement of the nuclear spin to a strong, projective one. A nuclear spin
coupled to the NV center with strength 330 kHz is read out in 200 ms with
fidelity 95.5\%. This work provides a general protocol for single-shot readout
of weakly coupled qubits and therefore largely extends the range of physical
systems for scalable quantum computing.",1612.07944v1
2017-06-12,Microscopic Theory of Spin Toroidization in Periodic Crystals,"Using the semiclassical theory of electron dynamics, we derive a
gauge-invariant expression for the spin toroidization in a periodical crystal.
We show that the spin toroidization is comprised of two contributions: one is
due to the configuration of a classical spin array, while the other comes from
the coordinate shift of the electron as spin carrier in response to the
inhomogeneous magnetic field. We then establish a direct and elengant relation
between our spin toroidization and the antisymmetric magnetoelectric
polarizability in insulators. Finally, we demonstrate our spin toroidization in
a tight-binding model and show that it is a genuine bulk quantity.",1706.03685v3
2017-06-28,Spin correlation and entanglement detection in Cooper pair splitters by current measurements using magnetic detectors,"We analyze a model of double quantum dot Cooper pair splitter coupled to two
ferromagnetic detectors, and demonstrate the possibility of determination of
spin correlation by current measurements. We use perturbation theory taking
account of the exchange interaction with the detectors, which leads to complex
spin dynamics in the dots. This affects the measured spin and restricts the use
of ferromagnetic detectors to the nonlinear current-voltage characteristic
regime at current plateau, where the relevant spin projection is conserved, in
contrast to the linear current-voltage characteristic regime, in which the spin
information is distorted. Moreover, we show that for separable states the spin
correlation can only be determined in a limited parameter regime, much more
restricted than in the case of entangled states. We propose an entanglement
test based on the Bell inequality.",1706.09472v3
2017-07-17,"Ab initio calculation of spin fluctuation spectra using time dependent density functional perturbation theory, planewaves, and pseudopotentials","We present an implementation of time-dependent density functional
perturbation theory for spin fluctuations, based on planewaves and
pseudopotentials. We compute the dynamic spin susceptibility self-consistently
by solving the time-dependent Sternheimer equation, within the adiabatic local
density approximation to the exchange and correlation kernel. We demonstrate
our implementation by calculating the spin susceptibility of representative
elemental transition metals, namely bcc Fe, fcc Ni and bcc Cr. The calculated
magnon dispersion relations of Fe and Ni are in agreement with previous work.
The calculated spin susceptibility of Cr exhibits a soft-paramagnon
instability, indicating the tendency of the Cr spins to condense in a
incommensurate spin density wave phase, in agreement with experiment.",1707.05219v1
2017-07-19,Controllable electron spin dephasing due to phonon state distinguishability in a coupled quantum dot system,"We predict a spin pure dephasing channel in electron relaxation between
states with unequal Zeeman splittings, exemplified by a spin-preserving
electron tunneling between quantum dots in a magnetic field. The dephasing is
caused by a mismatch in electron $g$-factors in the dots leading to
distinguishability of phonons emitted during tunneling with opposite spins.
Combining multiband $\boldsymbol{k}{\cdot}\boldsymbol{p}$ modeling and
dynamical simulations via a Master equation we show that this fundamental
effect of spin measurement effected by the phonon bath may be widely controlled
by the size and composition of the dots or on demand, via tuning of external
fields. By comparing the numerically simulated degree of dephasing with the
predictions of general theory based on distinguishability of environment
states, we show that the proposed mechanism is the dominant phonon-related spin
dephasing channel and may limit spin coherence time in tunnel-coupled
structures at cryogenic temperatures.",1707.06155v4
2017-10-11,Perturbed Kitaev model: excitation spectrum and long-ranged spin correlations,"We developed general approach to the calculation of power-law infrared
asymptotics of spin-spin correlation functions in the Kitaev honeycomb model
with different types of perturbations. We have shown that in order to find
these correlation functions, one can perform averaging of some bilinear forms
composed out of free Majorana fermions, and we presented the method for
explicit calculation of these fermionic densities. We demonstrated how to
derive an effective Hamiltonian for the Majorana fermions, including the
effects of perturbations. For specific application of the general theory, we
have studied the effect of the Dzyaloshinskii-Moriya anisotropic spin-spin
interaction; we demonstrated that it leads, already in the second order over
its relative magnitude $D/K$, to a power-law spin correlation functions, and
calculated dynamical spin structure factor of the system. We have shown that an
external magnetic field $h$ in presence of the DM interaction, opens a gap in
the excitation spectrum of magnitude $\Delta \propto D h$.",1710.04138v1
2017-12-02,Using Programmable Graphene Channels as Weights in Spin-Diffusive Neuromorphic Computing,"A graphene-based spin-diffusive (GrSD) neural network is presented in this
work that takes advantage of the locally tunable spin transport of graphene and
the non-volatility of nanomagnets. By using electrostatically gated graphene as
spintronic synapses, a weighted summation operation can be performed in the
spin domain while the weights can be programmed using circuits in the charge
domain. Four-component spin/charge circuit simulations coupled to magnetic
dynamics are used to show the feasibility of the neuron-synapse functionality
and quantify the analog weighting capability of the graphene under different
spin relaxation mechanisms. By realizing transistor-free weight implementation,
the graphene spin-diffusive neural network reduces the energy consumption to
0.08-0.32 fJ per cell-synapse and achieves significantly better scalability
compared to its digital counterparts, particularly as the number and bit
accuracy of the synapses increases.",1712.00550v1
2017-12-14,Synthesis of antisymmetric spin exchange interaction and entanglement generation with chiral spin states in a superconducting circuit,"We have synthesized the anti-symmetric spin exchange interaction (ASI), which
is also called the Dzyaloshinskii-Moriya interaction, in a superconducting
circuit containing five superconducting qubits connected to a bus resonator, by
periodically modulating the transition frequencies of the qubits with different
modulation phases. This allows us to show the chiral spin dynamics in three-,
four- and five-spin clusters. We also demonstrate a three-spin chiral logic
gate and entangle up to five qubits in Greenberger-Horne-Zeilinger states. Our
results pave the way for quantum simulation of magnetism with ASI and quantum
computation with chiral spin states.",1712.05261v2
2018-10-16,On-chip detection of spin-selective routing in plasmonic nanocircuits,"On-chip manipulating and controlling the temporal and spatial evolution of
light is of crucial importance for information processing in future planar
integrated nanophotonics. The spin and orbital angular momentum of light, which
can be treated independently in classical macroscopic geometrical optics,
appear to be coupled on subwavelength scales. We use spin-orbit interactions in
a plasmonic achiral nano-coupler to unidirectionally excite surface plasmon
polariton modes propagating in seamlessly integrated plasmonic slot waveguides.
The spin-dependent flow of light in the proposed nanophotonic circuit allows
on-chip electrical detection of the spin state of incident photons by
integrating two germanium-based plasmonic-waveguide photodetectors.
Consequently, our device serves as a compact ($\sim$ 6 $\times$ 18 $\mu$m$^2$)
electrical sensor for photonic spin Hall dynamics. The demonstrated
configuration opens new avenues for developing highly-integrated
polarization-controlled optical devices that would exploit the spin-degree of
freedom for manipulating and controlling subwavelength optical modes in
nanophotonic systems.",1810.06922v1
2019-07-04,Self-induced spin glass state in elemental and crystalline neodymium,"Spin glasses are a highly complex magnetic state of matter, intricately
linked to spin frustration and structural disorder. They exhibit no long-range
order and exude aging phenomena, distinguishing them from quantum spin liquids.
We report a new type of spin glass state, the spin-Q glass, observable in
bulk-like crystalline metallic neodymium thick films. Using spin-polarized
scanning tunneling microscopy combined with ab initio calculations and
atomistic spin-dynamics simulations, we visualize the variations in
atomic-scale non-collinear order and its response to magnetic field and
temperature. We quantify the aging phenomena relating the glassiness to
crystalline symmetry and the energy landscape. This result not only resolves
the long-standing debate of the magnetism of neodymium, but also suggests that
glassiness may arise in other magnetic solids lacking extrinsic disorder.",1907.02295v2
2019-07-13,Non-classicality of spin structures in condensed matter: An analysis of Sr$_{14}$Cu$_{24}$O$_{41}$,"When two quantum systems are coupled via a mediator, their dynamics has
traces of non-classical properties of the mediator. We show how this
observation can be effectively utilised to study the quantum nature of
materials without well-established structure. A concrete example considered is
Sr$_{14}$Cu$_{24}$O$_{41}$. Measurements of low temperature magnetic and
thermal properties of this compound were explained with long-range coupling of
unpaired spins through dimerised spin chains. We first show that the required
coupling is not provided by the spin chain alone and give alternative compact
two-dimensional spin structures compatible with the experimental results. Then
we argue that any mediator between the unpaired spins must share with them
quantum correlations in the form of quantum discord and in many cases quantum
entanglement. In conclusion, present data witnesses quantum mediators between
unpaired spins in Sr$_{14}$Cu$_{24}$O$_{41}$.",1907.06027v2
2020-02-04,Precise high-fidelity electron-nuclear spin entangling gates in NV centers via hybrid dynamical decoupling sequences,"Color centers in solids, such as the nitrogen-vacancy center in diamond,
offer well-protected and well-controlled localized electron spins that can be
employed in various quantum technologies. Moreover, the long coherence time of
the surrounding spinful nuclei can enable a robust quantum register controlled
through the color center. We design pulse sequence protocols that drive the
electron spin to generate robust entangling gates with these nuclear memory
qubits. We find that compared to using Carr-Purcell-Meiboom-Gill (CPMG) alone,
Uhrig decoupling sequence and hybrid protocols composed of CPMG and Uhrig
sequences improve these entangling gates in terms of fidelity, spin control
range, and spin selectivity. We provide analytical expressions for the sequence
protocols and also show numerically the efficacy of our method on
nitrogen-vacancy centers in diamond. Our results are broadly applicable to
color centers weakly coupled to a small number of nuclear spin qubits.",2002.01480v2
2020-04-10,Sub-wavelength spin excitations in ultracold gases created by stimulated Raman transitions,"Raman transitions are used in quantum simulations with ultracold atoms for
cooling, spectroscopy and creation of artificial gauge fields. Spatial shaping
of the Raman fields allows local control of the effective Rabi frequency, which
can be mapped to the atomic spin. Evanescent Raman fields are of special
interest as they can provide a new degree of control emanating from their
rapidly decaying profile and for their ability to generate features below the
diffraction limit. This opens the door to the formation of sub-wavelength spin
textures. In this work, we present a theoretical and numerical study of Raman
Rabi frequency in the presence of evanescent driving fields. We show how spin
textures can be created by spatially varying driving fields and demonstrate a
skyrmionium lattice - a periodic array of topological spin excitations, each of
which is composed of two skyrmions with opposite topological charges. Our
results pave the way to quantum simulation of spin excitation dynamics in
magnetic materials, especially of itinerant spin models.",2004.05044v1
2020-12-04,Pulsed-gate spectroscopy of single-electron spin states in bilayer graphene quantum dots,"Graphene and bilayer graphene quantum dots are promising hosts for spin
qubits with long coherence times. Although recent technological improvements
make it possible to confine single electrons electrostatically in bilayer
graphene quantum dots, and their spin and valley texture of the single particle
spectrum has been studied in detail, their relaxation dynamics remains still
unexplored. Here, we report on transport through a high-frequency gate
controlled single-electron bilayer graphene quantum dot. By transient current
spectroscopy of single-electron spin states, we extract a lower bound of the
spin relaxation time of 0.5~$\mu$s. This result represents an important step
towards the investigation of spin coherence times in graphene-based quantum
dots and the implementation of spin-qubits.",2012.02555v2
2020-12-08,Pure spin current injection of single-layer monochalcogenides,"We compute the spectrum of pure spin current injection in ferroelectric
single-layer SnS, SnSe, GeS, and GeSe. The formalism takes into account the
coherent spin dynamics of optically excited conduction states split in energy
by spin orbit coupling. The velocity of spins is calculated as a function of
incoming photon energy and angle of linearly polarized light within a full
electronic band structure scheme using density functional theory. We find peak
speeds of 250, 210, 180 and 154 Km/s for SnS, SnSe, GeS and GeSe, respectively
which are an order of magnitude larger than those found in bulk semiconductors,
e.g., CdSe and GaAs. Interestingly, the spin velocity is independent of the
direction of polarization of light in a range of photon energies. Our results
demonstrate that single-layer SnS, SnSe, GeS and GeSe are candidates to produce
on demand spin-velocity injection for spintronics applications.",2012.04604v1
2021-01-21,A Mapping between the Spin and Fermion Algebra,"We derive a formalism to express the spin algebra $\mathfrak{su}(2)$ in a
spin $s$ representation in terms of the algebra of $L$ fermionic operators that
obey the Canonical Anti-commutation Relations. We also give the reverse
direction of expressing the fermionic operators as polynomials in the spin
operators of a single spin. We extend here to further spin values the previous
investigations by Dobrov [J.Phys.A: Math. Gen 36 L503, (2003)] who in turn
clarified on an inconsistency within a similar formalism in the works of
Batista and Ortiz [Phys.\ Rev.\ Lett. 86, 1082 (2001)]. We then consider a
system of $L$ fermion flavors and apply our mapping in order to express it in
terms of the spin algebra. Furthermore we investigate a possibility to simplify
certain Hamiltonian operators by means of the mapping.",2101.10119v2
2021-01-26,Free coherent evolution of a coupled atomic spin system initialized by electron scattering,"Full insight into the dynamics of a coupled quantum system depends on the
ability to follow the effect of a local excitation in real-time. Here, we trace
the coherent evolution of a pair of coupled atomic spins by means of scanning
tunneling microscopy. We use a pump-probe scheme to detect the local
magnetization following a current-induced excitation performed on one of the
spins. Making use of magnetic interaction with the probe tip, we are able to
tune the relative precession of the spins. We show that only if their Larmor
frequencies match, the two spins can entangle, causing the excitation to be
swapped back and forth. These results provide insight into the locality of
electron-spin scattering, and set the stage for controlled migration of a
quantum state through an extended spin lattice.",2101.10765v1
2017-05-24,Covariant conservation laws and the spin Hall effect in Dirac-Rashba systems,"We present a theoretical analysis of two-dimensional Dirac-Rashba systems in
the presence of disorder and external perturbations. We unveil a set of exact
symmetry relations (Ward identities) that impose strong constraints on the spin
dynamics of Dirac fermions subject to proximity-induced interactions. This
allows us to demonstrate that an arbitrary dilute concentration of scalar
impurities results in the total suppression of nonequilibrium spin Hall
currents when only Rashba spin-orbit coupling is present. Remarkably, a finite
spin Hall conductivity is restored when the minimal Dirac-Rashba model is
supplemented with a spin-valley interaction. The Ward identities provide a
systematic way to predict the emergence of the spin Hall effect in a wider
class of Dirac-Rashba systems of experimental relevance and represent an
important benchmark for testing the validity of numerical methodologies.",1705.08898v2
2017-05-31,Giant Spin Lifetime Anisotropy in Graphene Induced by Proximity Effects,"We report on fundamental aspects of spin dynamics in graphene interfaced with
transition metal dichalcogenides (TMDCs). By using realistic models derived
from first principles we compute the spin lifetime anisotropy, defined as the
ratio of lifetimes for spins pointing out of the graphene plane to those
pointing in the plane. In the presence of strong intervalley scattering the
anisotropy can reach unprecedented values of tens to hundreds, while it reduces
to 1/2 for weak disorder. This behavior is mediated by spin-valley locking,
which is strong in TMDCs and is imprinted onto graphene. Such giant spin
transport anisotropy, driven by proximity effects, provides an exciting
paradigm for designing novel spin device functionalities.",1705.10972v2
2017-09-07,Tunable spin pumping in exchange coupled magnetic trilayers,"Magnetic thin films at ferromagnetic resonance (FMR) leak angular momentum,
which may be absorbed by adjacent layers. This phenomenon, known as spin
pumping, is manifested by an increase in the resonance linewidth ($\Delta H$),
and the closely related Gilbert damping. Another effect of this transfer of
spin currents is a dynamical and long-range coupling that can drive two
magnetic layers into a collective precession when their FMR frequencies
coincide. A collective behavior is also found in magnetic trilayers with
interlayer exchange coupling (IEC). In this study we investigate the interplay
between IEC and spin pumping, using Co/Cu/Py pseudo-spin values. We employ
broadband FMR spectroscopy to explore both the frequency and coupling-strength
dependence of $\Delta H$. Our observations show that there exists a cut-off
frequency, set by the IEC strength, below which the precession is truly
collective and the spin pumping is suppressed. These results demonstrate that
it is possible to control the spin pumping efficiency by varying the frequency
or the interlayer exchange coupling.",1709.02295v1
2018-03-08,Competing spin transfer and dissipation at Co/Cu(001) interfaces on femtosecond timescales,"By combining interface-sensitive non-linear magneto-optical experiments with
femtosecond time resolution and ab-initio time-dependent density functional
theory, we show that optically excited spin dynamics at Co/Cu(001) interfaces
proceeds via spin-dependent charge transfer and backtransfer between Co and Cu.
This ultrafast spin transfer competes with dissipation of spin angular momentum
mediated by spin-orbit coupling already on sub 100 fs timescales. We thereby
identify the fundamental microscopic processes during laser-induced spin
transfer at a model interface for technologically relevant ferromagnetic
heterostructures.",1803.03090v3
2018-06-12,Spin-orbit effects at chiral surfaces,"Two-dimensional hexagonal and oblique lattices were investigated
theoretically with the aim of observing differences in the spin expectation
values between chiral and achiral systems. The spinresolved band structures
were derived from the energy eigenvalues and eigenfunctions of a Hamiltonian
that includes the lattice potential and the spin-orbit interaction. The spin
texture of the achiral hexagonal system was shown to have two non-zero
components of the spin polarisation, whereas all three components were
calculated to be non-zero for the chiral system. The longitudinal component,
found to be zero in the achiral lattice, was observed to invert between the
enantiomorphs of the chiral lattice. A heuristic model was introduced to
discern the origin of this inverting spin polarisation by considering the
dynamics of an electron in chiral and achiral lattices. This model was further
used to demonstrate the change in magnitude of the spin polarisation as a
function of the lattice parameters and an electric field perpendicular to the
lattice.",1806.04372v1
2018-07-05,Mesonic excited states of magnetic monopoles in quantum spin ice,"Spin ice magnetic monopoles are fractionalized emergent excitations in a
class of frustrated magnets called spin ices. The classical spin ice model has
an extensive number of ground state spin configurations, whereas magnetic
monopoles can be thought of as the endpoints of string operators applied to
these ground states. Introducing quantum fluctuations into the model induces
monopoles with dynamics, which would normally lift the degeneracy of the
two-monopole energy level at the linear order of the perturbation. Contrary to
this expectation, we find that quantum fluctuations in the form of a locally
transverse field term partially preserve the extensive degeneracy of the
monopole pairs up to the much weaker splitting of the background monopole-free
spin ice configurations. Each of these approximately degenerate excited states,
termed mesons, can be represented as a bound monopole-antimonopole pair
delocalized in a classical spin ice background.",1807.02193v1
2018-07-13,Dynamical decoupling of interacting dipolar spin ensembles,"We demonstrate that CPMG and XYXY decoupling sequences with non-ideal $\pi$
pulses can reduce dipolar interactions between spins of the same species in
solids. Our simulations of pulsed electron spin resonance (ESR) experiments
show that $\pi$ rotations with small ($<$~10\%) imperfections refocus
instantaneous diffusion. Here, the intractable N-body problem of interacting
dipoles is approximated by the average evolution of a single spin in a changing
mean field. These calculations agree well with experiments and do not require
powerful hardware. Our results add to past attempts to explain similar
phenomena in solid state nuclear magnetic resonance (NMR). Although the
fundamental physics of NMR are similar to ESR, the larger linewidths in ESR and
stronger dipolar interactions between electron spins compared to nuclear spins
preclude drawing conclusions from NMR studies alone. For bulk spins, we also
find that using XYXY results in less inflation of the deduced echo decay times
as compared to decays obtained with CPMG.",1807.04908v1
2018-12-01,Quantitative quantum mechanical approach to SABRE hyperpolarization at high magnetic fields,"A theoretical approach is proposed for quantitative modeling of SABRE (Signal
Amplification By Reversible Exchange) experiments performed at a high magnetic
field of an NMR spectrometer. SABRE is a method, which exploits the spin order
of parahydrogen (the H$_2$ molecule in its nuclear singlet state) for
hyper-polarizing the spins of various substrates to enhance their NMR signals.
An important feature of SABRE is that the substrate is not modified chemically:
instead spin order transfer takes place in a transient complex with
parahydrogen. In high-field SABRE experiments, such a transfer is achieved by
using suitable NMR excitation schemes. The approach presented here can
explicitly treat the spin dynamics in the SABRE complex as well as the kinetics
of substrate exchange (between the free and bound form) and complex interplay
of spin evolution and chemical processes. One more important effect included in
the model is the alteration of the spin state of parahydrogen giving rise to
the formation of anti-phase spin order from the initial singlet order. Such a
treatment enables a detailed analysis of known high-field SABRE schemes,
quantitative comparison with experiments and elucidation of the key factors
that limit the resulting NMR signal enhancement.",1812.00206v1
2018-12-20,Unidirectional spin-wave channeling along magnetic domain walls of Bloch type,"From the pioneering work of Winter [Phys. Rev. 124, 452 (1961)], a magnetic
domain wall of Bloch type is known to host a special wall-bound spin-wave mode,
which corresponds to spin-waves being channeled along the magnetic texture.
Using micromagnetic simulations, we investigate spin-waves travelling inside
Bloch walls formed in thin magnetic media with perpendicular-to-plane magnetic
anisotropy and we show that their propagation is actually strongly
nonreciprocal, as a result of dynamic dipolar interactions. We investigate
spin-wave non-reciprocity effects in single Bloch walls, which allows us to
clearly pinpoint their origin, as well as in arrays of parallel walls in stripe
domain configurations. For such arrays, a complex domain-wall-bound spin-wave
band structure develops, some aspects of which can be understood qualitatively
from the single-wall picture by considering that a wall array consists of a
sequence of up/down and down/up walls with opposite non-reciprocities.
Circumstances are identified in which the non-reciprocity is so extreme that
spin-wave propagation inside individual walls becomes unidirectional.",1812.08741v1
2019-01-01,The dynamics of bimeron skyrmions in easy-plane magnets induced by a spin supercurrent,"We theoretically study the interaction of an isolated bimeron skyrmion in
quasi-two-dimensional easy-plane magnets with a surrounding spin superfluid
associated with spontaneously broken U(1) spin-rotational symmetry, revealing
that skyrmion energy depends on the local spin current flowing in its
background. The finding leads us to propose to manipulate a skyrmion energy
landscape via a spin supercurrent, which can be controlled non-locally by
varying the magnitudes of spin-current injection and ejection through the
boundaries. Two exemplary cases are discussed: a steady-state motion of a
skyrmion induced by a uniform force and a skyrmion motion localized along a
one-dimensional racetrack. We envision that a skyrmion interacting with a spin
superfluid can serve as a robust point-like information carrier that can be
operated with minimal dissipation.",1901.00094v2
2019-02-10,Spin asymmetry in single pion production induced by weak interactions of neutrinos with polarized nucleons,"The single pion production (SPP) in the charged-current neutrino
(antineutrino) scattering off the polarized nucleon is discussed. The spin
asymmetry is predicted within two approaches. The spin polarizations of the
target nucleon that are longitudinal and perpendicular to the neutrino momentum
are considered. It is shown, in several examples, that information about the
SPP dynamics coming from the spin asymmetry is complementary to information
obtained from measurements of spin averaged cross section. Indeed, the spin
asymmetry is sensitive to the nonresonance background description of the SPP
model. For the normal polarization of the target, the spin asymmetry is given
by the interference between the resonance and the nonresonance contributions.",1902.03671v2
2019-02-21,Conformal geometry and (super)conformal higher-spin gauge theories,"We develop a manifestly conformal approach to describe linearised
(super)conformal higher-spin gauge theories in arbitrary conformally flat
backgrounds in three and four spacetime dimensions. Closed-form expressions in
terms of gauge prepotentials are given for gauge-invariant higher-spin (super)
Cotton and (super) Weyl tensors in three and four dimensions, respectively. The
higher-spin (super) Weyl tensors are shown to be conformal primary
(super)fields in arbitrary conformal (super)gravity backgrounds, however they
are gauge invariant only if the background (super) Weyl tensor vanishes. The
proposed higher-spin actions are (super) Weyl-invariant on arbitrary curved
backgrounds, however the appropriate higher-spin gauge invariance holds only in
the conformally flat case. We also describe conformal models for generalised
gauge fields that are used to describe partially massless dynamics in three and
four dimensions. In particular, generalised higher-spin Cotton and Weyl tensors
are introduced.",1902.08010v2
2019-02-25,Steering of the Skyrmion Hall Angle By Gate Voltage,"Magnetic skyrmions can be driven by an applied spin-polarized electron
current which exerts a spin-transfer torque on the localized spins constituting
the skyrmion. However, the longitudinal dynamics is plagued by the skyrmion
Hall effect which causes the skyrmions to acquire a transverse velocity
component. We show how to use spin-orbit interaction to control the skyrmion
Hall angle and how the interplay of spin-transfer and spin-orbit torques can
lead to a complete suppression of the transverse motion. Since the spin-orbit
torques can be controlled all-electronically by a gate voltage, the skyrmion
motion can be steered all-electronically on a broad racetrack at high speed and
conceptually new writing and gating operations can be realized.",1902.09521v2
2019-03-03,Theory for spin torque in Weyl semimetal with magnetic texture,"The spin-transfer torque is a fundamental physical quantity to operate the
spintronics devices such as racetrack memory. We theoretically study the
spin-transfer torque and analyze the dynamics of the magnetic domain walls in
magnetic Weyl semimetals. Owing to the strong spin-orbit coupling in Weyl
semimetals, the spin-transfer torque can be significantly enhanced, because of
which they can provide a more efficient means of controlling magnetic textures.
We derive the analytical expression of the spin-transfer torque and find that
the velocity of the domain wall is one order of magnitude greater than that of
conventional ferromagnetic metals. Furthermore, due to the suppression of
longitudinal conductivity in the thin domain-wall configuration, the
dissipation due to Joule heating for the spin-transfer torque becomes much
smaller than that in bulk metallic ferromagnets. Consequently, the fast-control
of the domain wall can be achieved with smaller dissipation from Joule heating
in the Weyl semimetals as required for application to low-energy-consumption
spintronics devices.",1903.00849v1
2019-03-07,Nonlocal Spin Transport as a Probe of Viscous Magnon Fluids,"Magnons in ferromagnets behave as a viscous fluid over a length scale, the
momentum-relaxation length, below which momentum-conserving scattering
processes dominate. We show theoretically that in this hydrodynamic regime
viscous effects lead to a sign change in the magnon chemical potential, which
can be detected as a sign change in the nonlocal resistance measured in spin
transport experiments. This sign change is observable when the
injector-detector distance becomes comparable to the momentum-relaxation
length. Taking into account momentum- and spin-relaxation processes, we
consider the quasiconservation laws for momentum and spin in a magnon fluid.
The resulting equations are solved for nonlocal spin transport devices in which
spin is injected and detected via metallic leads. Because of the finite
viscosity we also find a backflow of magnons close to the injector lead. Our
work shows that nonlocal magnon spin transport devices are an attractive
platform to develop and study magnon-fluid dynamics.",1903.02790v2
2019-03-27,Observing Black Holes Spin,"The spin of a black hole retains the memory of how the black hole grew, and
can be a potent source of energy for powering relativistic jets. To understand
the diagnostic power and astrophysical significance of black hole spin,
however, we must first devise observational methods for measuring spin. Here, I
describe the current state of black hole spin measurements, highlighting the
progress made by X-ray astronomers, as well as the current excitement of
gravitational wave and radio astronomy based techniques. Today's spin
measurements are already constraining models for the growth of supermassive
black holes and giving new insights into the dynamics of stellar core-collapse,
as well as hinting at the physics of relativistic jet production. Future X-ray,
radio, and gravitational wave observatories will transform black hole spin into
a precision tool for astrophysics and test fundamental theories of gravity.",1903.11704v1
2019-04-01,51V-NMR study on the S=1/2 square lattice antiferromagnet K2V3O8,"Static and dynamic properties of the quasi-two-dimensional antiferromagnet
K$_2$V$_3$O$_8$ have been investigated by $^{51}$V-NMR experiments on
nonmagnetic V$^{5+}$ sites. Above the structural transition temperature
$T_{\rm{S}}$ = 115 K, NMR spectra are fully compatible with the $P4bm$ space
group symmetry. The formation of superstructure below $T_{\rm{S}}$ causes
splitting of the NMR lines, which get broadened at lower temperatures so that
individual peaks are not well resolved. Evolution of NMR spectra with magnetic
field along $c$-axis below the magnetic transition temperature $T_{\rm{N}} \sim
4$ K is qualitatively consistent with a simple N\'{e}el order and a spin flop
transition. However, broad feature of the spectra does not rule out possible
incommensurate spin structure. The spin-lattice relaxation rate $1/T_1$ below
$T_{\rm{N}}$ shows huge enhancement for a certain range of magnetic field,
which is independent of temperature and attributed to cross relaxation due to
anomalously large nuclear spin-spin coupling between V$^{5+}$ and magnetic
V$^{4+}$ sites. The results indicate strong gapless spin fluctuations, which
could arise from incommesurate orders or complex spin textures.",1904.00909v1
2019-11-03,Magnetic damping modulation in $IrMn_{3}/Ni_{80}Fe_{20}$ via the magnetic spin Hall effect,"Non-collinear antiferromagnets can have additional spin Hall effects due to
the net chirality of their magnetic spin structure, which provides for more
complex spin-transport phenomena compared to ordinary non-magnetic materials.
Here we investigated how ferromagnetic resonance of permalloy
($Ni_{80}Fe_{20}$) is modulated by spin Hall effects in adjacent epitaxial
$IrMn_{3}$ films. We observe a large dc modulation of the ferromagnetic
resonance linewidth for currents applied along the [001] $IrMn_{3}$ direction.
This very strong angular dependence of spin-orbit torques from dc currents
through the bilayers can be explained by the magnetic spin Hall effect where
$IrMn_{3}$ provides novel pathways for modulating magnetization dynamics
electrically.",1911.00943v1
2019-12-13,"Spin-, time- and angle-resolved photoemission spectroscopy on WTe$_2$","We combined a spin-resolved photoemission spectrometer with a high-harmonic
generation (HHG) laser source in order to perform spin-, time- and
angle-resolved photoemission spectroscopy (STARPES) experiments on the
transition metal dichalcogenide bulk WTe$_2$, a possible Weyl type-II
semimetal. Measurements at different femtosecond pump-probe delays and
comparison with spin-resolved one-step photoemission calculations provide
insight into the spin polarization of electrons above the Fermi level in the
region where Weyl points of WTe$_2$ are expected. We observe a spin
accumulation above the Weyl points region, that is consistent with a
spin-selective bottleneck effect due to the presence of spin polarized
cone-like electronic structure. Our results support the feasibility of STARPES
with HHG, which despite being experimentally challenging provides a unique way
to study spin dynamics in photoemission.",1912.06572v1
2020-03-06,Spin-accumulation induced magnetic texture in a metal-insulator bilayer,"We consider the influence of a spin accumulation in a normal metal on the
magnetic statics and dynamics in an adjacent magnetic insulator. In particular,
we focus on arbitary angles between the spin accumulation and the easy-axis of
the magnetic insulator. Based on Landau-Lifshitz-Gilbert phenomenology
supplemented with magnetoelectronic circuit theory, we find that the magnetic
texture twists into a stable configuration that turns out to be described by a
virtual, or image, domain wall configuration, i.e., a domain wall outside the
ferromagnet. We show that even when the spin accumulation is perpendicular to
the anisotropy axis, the magnetic texture develops a component parallel to the
spin accumulation for sufficiently large spin bias. The emergence of this
parallel component gives rise to threshold behavior in the spin Hall
magnetoresistance and nonlocal magnon transport. This threshold can be used to
design novel spintronic and magnonic devices that can be operated without
external magnetic fields.",2003.03226v1
2020-05-06,"Spinning Black Hole Binary Dynamics, Scattering Amplitudes and Effective Field Theory","We describe a systematic framework for finding the conservative potential of
compact binary systems with spin based on scattering amplitudes of particles of
arbitrary spin and effective field theory. An arbitrary-spin formalism is
generally required in the classical limit. By matching the tree and one-loop
amplitudes of four spinning particles with those of a suitably-chosen effective
field theory, we obtain the spin1-spin2 terms of a two-body effective
Hamiltonian through O(G^2) and valid to all orders in velocity. Solving
Hamilton's equations yields the impulse and spin changes of the individual
bodies. We write them in a surprisingly compact form as appropriate derivatives
of the eikonal phase obtained from the amplitude. It seems likely this
structure persists to higher orders. We also point out various double-copy
relations for general spin.",2005.03071v1
2020-05-06,Sub-Nanosecond Spin-Transfer Torque in an Ensemble of Superparamagnetic-Like Nanomagnets,"Spin currents can exert spin-transfer torques on magnetic systems even in the
limit of vanishingly small net magnetization, as is the case for
antiferromagnets. Here, we experimentally show that a spin-transfer torque is
operative in a material with weak, short-range magnetic order -- namely, a
macroscopic ensemble of superparamagnetic-like Co nanomagnets. We employ
element- and time-resolved X-ray ferromagnetic resonance (XFMR) spectroscopy to
directly detect sub-ns dynamics of the Co nanomagnets, excited into precession
with cone angle $\geq$0.003$^{\circ}$ by an oscillating spin current. XFMR
measurements reveal that as the net moment of the ensemble decreases, the
strength of the spin-transfer torque increases relative to those of magnetic
field torques. Our findings point to spin-transfer torque as an effective way
to manipulate the state of nanomagnet ensembles at sub-ns timescales.",2005.03081v1
2020-05-15,Direct imaging of the ac component of the pumped spin polarization with element specificity,"Spin pumping in a ferromagnet/nonferromagnet heterostructure is directly
imaged with spatial resolution as well as element selectivity. The
time-resolved detection in scanning transmission x-ray microscopy allows to
directly probe the spatial extent of the ac spin polarization in Co-doped ZnO
which is generated by spin pumping from an adjacent permalloy microstrip.
Comparing the relative phases of the dynamic magnetization component of the two
constituents is possible and found to be antiphase. The correlation between the
distribution of the magnetic excitation in the permalloy and the Co-doped ZnO
reveals that laterally there is no one-to-one correlation. The observed
distribution is rather complex, but integrating over larger areas clearly
demonstrates that the spin polarization in the nonferromagnet extends laterally
beyond the region of the ferromagnetic microstrip. Therefore the observations
are better explained by a local spin pumping efficieny and a lateral
propagation of the ac spin polarization in the nonferromagnet over the range of
a few micrometers.",2005.08728v1
2020-06-15,Magnetic Droplet Solitons,"Magnetic droplet solitons are dynamical magnetic textures that form due to an
attractive interaction between spin waves in thin films with perpendicular
magnetic anisotropy. Spin currents and the spin torques associated with these
currents enable their formation as they provide a means to excite
non-equilibrium spin wave populations and compensate their decay. Recent years
have seen rapid advances in experiments that realize and study magnetic
droplets. Important advances include the first direct x-ray images of droplets,
determination of their threshold and sustaining currents, measurement of their
generation and annihilation time and evidence for drift instabilities, which
can limit their lifetime in spin-transfer nanocontacts. This article reviews
these studies and contrasts these solitons to other types of spin-current
excitations such as spin-wave bullets, and static magnetic textures, including
magnetic vortices and skyrmions. Magnetic droplet solitons can also serve as
current controlled microwave frequency oscillators with potential applications
in neuromorphic chips as nonlinear oscillators with memory.",2006.08808v2
2020-09-03,"Odd-spin glueballs, AdS/QCD and information entropy","Odd-spin glueballs in the dynamical AdS/QCD model are scrutinized, in the
paradigm of the configurational entropy (CE). Configurational-entropic Regge
trajectories, that relate the CE underlying odd-spin glueballs to their mass
spectra and spin, are then engendered. They predict the mass spectra of
odd-spin glueballs, besides pointing towards the configurational stability of
odd-spin glueball resonances. The exponential modified dilaton with logarithmic
anomalous dimensions comprises the most suitable choice to derive the mass
spectra of odd-spin glueballs, compatible to lattice QCD. It is then used in a
hybrid paradigm that takes both lattice QCD and the AdS/QCD correspondence into
account.",2009.01890v2
2020-10-21,Spontaneous Chiral-Spin Ordering in Spin-Orbit Coupled Honeycomb Magnets,"Frustrated magnets with highly degenerate ground states are at the heart of
hunting exotic states of matter. Recent studies in spin-orbit coupled honeycomb
magnets have generated immense interest in bond-dependent interactions,
appreciating a symmetric off-diagonal $\Gamma$ interaction which exhibits a
macroscopic degeneracy in the classical limit. Here, we study a generic spin
model and discover a novel chiral-spin ordering with spontaneously broken
time-reversal symmetry near the dominant $\Gamma$ region. The chiral-spin phase
is demonstrated to possess a staggered chirality relation in different
sublattices, and it exhibits gapless excitations as revealed by the vanishing
energy gap and the finite central charge on cylinders. Although there is a
vestige of a tiny peak in the corner of the second Brillouin zone, the magnetic
order is likely to vanish as the system size increases. Finally, we also
attempt to gain insight into the possible topological signature of the
chiral-spin phase by calculating the dynamic structure factor and the modular
$\mathcal{S}$ matrix.",2010.11233v2
2020-11-02,Spin-orbital magnetic response of relativistic fermions with band hybridization,"Spins of relativistic fermions are related to their orbital degrees of
freedom. In order to quantify the effect of hybridization between relativistic
and nonrelativistic degrees of freedom on spin-orbit coupling, we focus on the
spin-orbital (SO) crossed susceptibility arising from spin-orbit coupling. The
SO crossed susceptibility is defined as the response function of their spin
polarization to the ""orbital"" magnetic field, namely the effect of magnetic
field on the orbital motion of particles as the vector potential. Once
relativistic and nonrelativistic fermions are hybridized, their SO crossed
susceptibility gets modified at the Fermi energy around the band hybridization
point, leading to spin polarization of nonrelativistic fermions as well. These
effects are enhanced under a dynamical magnetic field that violates thermal
equilibrium, arising from the interband process permitted by the band
hybridization. Its experimental realization is discussed for Dirac electrons in
solids with slight breaking of crystalline symmetry or doping, and also for
quark matter including dilute heavy quarks strongly hybridized with light
quarks, arising in a relativistic heavy-ion collision process.",2011.00882v2
2020-11-16,Can discovery of hidden charm strange pentaquark states help determine the spins of $P_c(4440)$ and $P_c(4457)$?,"The pentaquark states, $P_{c}(4312)$, $P_{c}(4440)$ and $P_{c}(4457)$, could
be nicely arranged into a multiplet of seven molecules of
$\bar{D}^{(\ast)}\Sigma_{c}^{(\ast)}$ dictated by heavy quark spin symmetry.
However, the spins of $P_c(4440)$ and $P_c(4457)$ are not yet fully determined.
In this work we employ the contact-range effective field theory to investigate
the $SU(3)$-flavor counterparts of $\bar{D}^{(\ast)}\Sigma_{c}^{(\ast)}$, and
study the possibility whether their discovery can help determine the spins of
$P_c(4457)$ and $P_c(4440)$. We find the existence of a complete hidden charm
strange multiplet of $\bar{D}^{(\ast)}\Xi_{c}^{(\prime\ast)}$ molecules
irrespective of the spins of $P_c(4440)$ and $P_c(4457)$. On the other hand, we
find that although molecules of $\bar{D}^{(\ast)}\Xi_{c}$ are also likely,
depending on the realization of the underlying dynamics, their discovery can be
more useful to determine the spins of $P_{c}(4440)$ and $P_{c}(4457)$ and to
tell how the heavy quark and light quark interaction depends on the spin of the
light quark pair.",2011.07935v1
2021-03-02,Long-lived electron spin coherence in Ga-doped crystals at room temperature,"Electron spin dynamics are studied in Ga-doped ZnO single crystals by
time-resolved Faraday and Kerr rotation spectroscopies. Long-lived spin
coherence with two dephasing processes is discovered where the characteristic
time is up to 5.2 ns at room temperature. Through the dependence measurements
of laser wavelength and temperature, the room-temperature long-lived spin
signal is attributed to localized electrons. The spin dephasing (relaxation)
processes are independent of transverse (longitudinal) magnetic fields,
indicating the spin dephasing not resulting from the g-factor inhomogeneity and
electron-nuclear hyperfine interaction. It reveals that the two spin dephasing
processes originate from two types of localized electrons, both of which are
dominated by the anisotropic exchange Dzyaloshinskii-Moriya interaction between
adjacent localized electrons.",2103.01673v1
2021-05-07,Two-Orders-of-Magnitude Improvement in the Total Spin Angular Momentum of 131Xe Nuclei Using Spin Exchange Optical Pumping,"We report on hyperpolarization of quadrupolar (I=3/2) 131Xe via spin-exchange
optical pumping. Observations of the 131Xe polarization dynamics show that the
effective alkali-metal/131Xe spin-exchange cross-sections are large enough to
compete with 131Xe spin relaxation. 131Xe polarization up to 7.6 p/m 1.5
percent was achieved in ca. 8.5EE20 spins--a ca. 100-fold improvement in the
total spin angular momentum--enabling applications including measurement of
spin-dependent neutron-131Xe s-wave scattering and sensitive searches for
time-reversal violation in neutron-131Xe interactions beyond the Standard
Model.",2105.03076v1
2021-05-10,Role of Majorana fermions in spin transport of anisotropic Kitaev model,"We study a quantum spin Kitaev model with zigzag edges to clarify the effects
of anisotropy in the exchange couplings on the spin propagation. We simulate
the spin and Majorana dynamics triggered by a magnetic pulse, using the
real-space time-dependent Majorana mean-field theory. When the anisotropy is
small, the dispersion of the itinerant Majorana fermions remains gapless, where
the velocity of the spin propagation matches the group velocity of the
itinerant Majorana fermions at the nodal points. On the other hand, in the
gapped system with a large anisotropy, the spin propagation is strongly
suppressed although its nature depends on the shape of the pulse. The spin
transport in the junction system described by the Kitaev models with distinct
anisotropies is also dressed.",2105.04094v1
2021-07-27,Spin transport-induced damping of coherent THz spin dynamics in iron,"We study the damping of perpendicular standing spin-waves (PSSWs) in
ultrathin Fe films at frequencies up to 2.4 THz. The PSSWs are excited by
optically generated ultrashort spin current pulses, and probed optically in the
time domain. Analyzing the wavenumber and thickness dependence of the damping,
we demonstrate that at sufficiently large wave vectors $k$ the damping is
dominated by spin transport effects scaling with k^4 and limiting the frequency
range of observable PSSWs. Although this contribution is known to originate in
the spin diffusion, we argue that at moderate and large k a more general
description is necessary and develop a model where the 'transverse spin mean
free path' is the a key parameter, and estimate it to be ~0.5 nm.",2107.12812v2
2021-09-21,Spin-induced motion in black hole spacetime,"Based on the covariant hamiltonian formalism, we study the dynamics of
spinning test bodies in the Kerr and Schwarzschild spacetimes. For the first
time, we derive the exact solution of circular orbits in the Kerr plane without
truncating the spin of the particle or black hole. A large class of noncircular
bound orbits has been developed by using the world line perturbation theory. It
is found that the spinning body possesses a double frequency, and thus, in
addition to the angular shift, the periastron varies radially proportional to
the alignment and magnitude of spins. By using the method of stability
analysis, we predict the radius of the innermost stable circular orbit (ISCO)
as a function of particle and black hole spin. Furthermore, extending the
perturbative technique for generic orientation of spin in Schwarzschild
spacetime leads to the development of nonplanar bound orbits and the prediction
of fully relativistic precessional frequency of the orbital plane.",2109.10022v1
2021-11-09,Dynamics of hole singlet triplet qubits with large g-factor differences,"The spin-orbit interaction is the key element for electrically tunable spin
qubits. Here we probe the effect of cubic Rashba spin-orbit interaction on
mixing of the spin states by investigating singlet-triplet oscillations in a
planar Ge hole double quantum dot. By varying the magnetic field direction we
find an intriguing transformation of the funnel into a butterfly-shaped
pattern. Landau-Zener sweeps disentangle the Zeeman mixing effect from the
spin-orbit induced coupling and show that large singlet-triplet avoided
crossings do not imply a strong spin-orbit interaction. Our work emphasizes the
need for a complete knowledge of the energy landscape when working with hole
spin qubits.",2111.05130v1
2021-12-16,Decoupling of Spin Decoherence Paths near Zero Magnetic Field,"We demonstrate a method to quantify and manipulate nuclear spin decoherence
mechanisms that are active in zero to ultralow magnetic fields. These include:
(i) non-adiabatic switching of spin quantization axis, due to residual
background fields; (ii) scalar pathways due to through-bond couplings between
$^1$H and heteronuclear spin species, such as $^2$H used partially as an
isotopic substitute for $^1$H. Under conditions of free evolution, scalar
relaxation due to $^2$H can significantly limit nuclear spin polarization
lifetimes and thus the scope of magnetic resonance procedures near zero field.
It is shown that robust trains of pulsed dc magnetic fields that apply $\pi$
flip angles to one or multiple spin species may switch effective symmetry of
the nuclear spin Hamiltonian, imposing decoupled or coupled dynamic regimes on
demand. The method should broaden the spectrum of hyperpolarized biomedical
contrast-agent compounds and hyperpolarization procedures that are used near
zero field.",2112.08536v1
2022-02-06,Ab initio calculations of spin-nonconserving exciton-phonon scattering in monolayer transition metal dichalcogenides,"We investigate the spin-nonconserving relaxation channel of excitons by their
couplings with phonons in two-dimensional transition metal dichalcogenides
using $\textit{ab initio}$ approaches. Combining $\text{GW}$-Bethe-Salpeter
equation method and density functional perturbation theory, we calculate the
electron-phonon and exciton-phonon coupling matrix elements for the spin-flip
scattering in monolayer WSe$_{\text{2}}$, and further analyze the microscopic
mechanisms influencing these scattering strengths. We find that phonons could
produce effective in-plane magnetic fields which flip spin of excitons, giving
rise to relaxation channels complimentary to the spin-conserving relaxation.
Finally, we calculate temperature-dependent spin-flip exciton-phonon relaxation
times. Our method and analysis can be generalized to study other
two-dimensional materials and would stimulate experimental measurements of
spin-flip exciton relaxation dynamics.",2202.02866v1
2022-02-08,"Spin-Phonon Relaxation in Magnetic Molecules: Theory, Predictions and Insights","Magnetic molecules have played a central role in the development of magnetism
and coordination chemistry and their study keeps leading innovation in
cutting-edge scientific fields such as magnetic resonance, magnetism,
spintronics, and quantum technologies. Crucially, a long spin lifetime well
above cryogenic temperature is a stringent requirement for all these
applications. In this chapter we review the foundations of spin relaxation
theory and provide a detailed overview of first-principles strategies applied
to the problem of spin-phonon relaxation in magnetic molecules. Firstly, we
present a rigorous formalism of spin-phonon relaxation based on open quantum
systems theory. These results are then used to derive classical
phenomenological relations based on the Debye model. Finally, we provide a
prescription of how to map the relaxation formalism onto existing electronic
structure methods to obtain a quantitative picture of spin-phonon relaxation.
Examples from the literature, including both transition metals and lanthanides
compounds, will be discussed in order to illustrate how Direct, Orbach and
Raman relaxation mechanisms can affect spin dynamics for this class of
compounds.",2202.03776v1
2022-07-06,Chaotic spin precession in antiferromagnetic domain walls,"In contrast with rich investigations about the translation of an
antiferromagnetic (AFM) texture, spin precession in an AFM texture is seldom
concerned for lacking an effective driving method. In this work, however, we
show that under an alternating spin-polarized current with spin along the AFM
anisotropy axis, spin precession can be excited in an AFM DW. Especially,
chaotic spin precession occurs at moderate interfacial Dzyaloshinskii-Moriya
interaction (DMI), which contributes to a nonlinear term in the dynamic
equation of DW precession. Also, crisis-induced intermittent chaos appears when
the current density is higher than a critical value. This work not only paves a
way to unravel rich spin precession behaviors in an AFM texture but also
provides guidelines for developing ultrafast spintronic devices based on new
physical principles.",2207.02492v1
2022-07-14,Spin relaxation dynamics of radical-pair processes at low magnetic fields,"We report measurements of room-temperature spin-relaxation times $T_1$ and
$T_2$ of charge-carrier spins in a $\pi$-conjugated polymer thin film under
bipolar injection and low ($1\mbox{ mT}\lesssim B_0\lesssim 10\mbox{ mT}$)
static magnetic fields, using electrically detected magnetic resonant Hahn-echo
and inversion-recovery pulse sequences. The experiments confirm the correlation
between the magnetic-field sensitive observables of radical-pair processes,
which include both the spin-dependent recombination currents in organic
semiconductors and the associated spin-relaxation times when random local
hyperfine fields and external magnetic fields compete in magnitude. Whereas a
striking field dependence of spin-lattice relaxation exists in the low-field
regime, the apparent spin decoherence time remains field independent as the
distinction between the two is lifted at low fields.",2207.07086v1
2022-08-11,Spin functional renormalization group for the $J_{1}J_{2}J_{3}$ quantum Heisenberg model,"We use our recently developed functional renormalization group (FRG) approach
for quantum spin systems to investigate the phase diagram of the frustrated
$J_{1}J_{2}J_{3}$ quantum Heisenberg model on a cubic lattice. From a simple
truncation of the hierarchy of FRG flow equations for the irreducible
spin-vertices which retains only static spin fluctuations and neglects the flow
of the four-spin interaction, we can estimate the critical temperature with a
similar accuracy as the numerically more expensive pseudofermion FRG. In the
regime where the ground state exhibits either ferromagnetic or
antiferromagnetic order, a more sophisticated truncation including the
renormalization of the four-spin interaction as well as dynamic spin
fluctuations reveals the underlying renormalization group fixed point and
yields critical temperatures which deviate from the accepted values by at most
4 %.",2208.05741v3
2022-09-01,Spin contributions to the gravitational-waveform modes for spin-aligned binaries at the 3.5PN order,"We complete the post-Newtonian (PN) prediction at the 3.5PN order for the
spin contributions to the gravitational waveforms emitted by inspiraling
compact binaries, in the case of quasi-circular, equatorial orbits, where both
spins are aligned with the orbital angular momentum. Using results from the
multipolar post-Minkowskian wave generation formalism, we extend previous works
that derived the dynamics and gravitational-wave energy flux and phasing, by
computing the full waveform decomposed in spin-weighted spherical harmonics.
This new calculation requires the computation of multipolar moments of higher
multipolar order, new quadratic-in-spin contributions to the hereditary tail
terms entering at the 3.5PN order, as well as other non-linear interactions
between moments. When specialized to the test-mass limit, our results are
equivalent to those obtained in the literature for the waveform emitted by a
test-mass in equatorial, circular orbits around a Kerr black hole. We also
compute the factorized modes for use in effective-one-body waveform models,
correcting the 2.5PN nonspinning and 3PN quadratic-in-spin terms in the (2,1)
mode used in current models.",2209.00374v2
2022-09-08,Kramers Fulde-Ferrell state and superconducting spin diode effect,"We study a novel Fulde-Ferrell equal-spin pairing state with opposite center
of mass Cooper pair momentum for each spin polarization. This state respects
time-reversal symmetry and is dubbed a Kramers Fulde-Ferrell (KFF) state. It
can be realized in a one-dimensional system with spin-orbit coupling and
nearest neighbor attraction. We find that the KFF state supports nonreciprocal
spin transport for both bulk superconductor and Josephson junctions when
inversion symmetry is broken. In addition to the spin Josephson diode effect,
the charge transport is controlled by intriguing dynamics of bound states whose
transitions can be manipulated by the length of the KFF superconductor. We
discuss the relevance of the effective theory to the novel physics observed in
monolayer Fe-based superconductor along line defects and domain walls, and the
potential for using spins to make dissipationless superconducting spintronics.",2209.03520v3
2022-12-20,Spin dynamics in quantum dots on liquid helium,"Liquid He-4 is free from magnetic defects, making it an ideal substrate for
electrons with long-lived spin states. Such states can serve as qubit states.
Here we consider the spin states of electrons electrostatically localized in
quantum dots on a helium surface. Efficient gate operations in this system
require spin-orbit coupling. It can be created by a nonuniform magnetic field
from a current-carrying wire, can be turned on and off, and allows one to
obtain large electro-dipole moment and comparatively fast coupling of spins in
neighboring dots. Of central importance is to understand the spin decay due to
the spin-orbit coupling. We establish the leading mechanism of such decay and
show that the decay is sufficiently slow to enable high-fidelity single- and
two-qubit gate operations",2212.10683v1
2023-01-23,Nearest-neighbor approximation in one-excitation state evolution along spin-1/2 chain governed by XX-Hamiltonian,"The approximation of nearest neighbor interaction (NNI) is widely used in
short-time spin dynamics with dipole-dipole interactions (DDI) when the
intensity of spin-spin interaction is $\sim 1/r^3$, where $r$ is a distance
between those spins. However, NNI can not approximate the long time evolution
in such systems. We consider the system with the intensity of the spin-spin
interaction $\sim 1/r^{\alpha}$, $\alpha\ge 3$, and find the low boundary
$\alpha_c$ of applicability of the NNI to the evolution of an arbitrary
one-excitation initial quantum state in the homogeneous spin chain governed by
the $XX$-Hamiltonian. We obtain the logarithmic dependence of $\alpha_c$ on the
chain length.",2301.09469v1
2023-02-09,Calorimetric measurement of nuclear spin-lattice relaxation rate in metals,"The quasiparticle density of states in correlated and quantum-critical metals
directly probes the effect of electronic correlations on the Fermi surface.
Measurements of the nuclear spin-lattice relaxation rate provide one such
experimental probe of quasiparticle mass through the electronic density of
states. By far the most common way of accessing the spin-lattice relaxation
rate is via nuclear magnetic resonance and nuclear quadrupole resonance
experiments, which require resonant excitation of nuclear spin transitions.
Here we report non-resonant access to spin-lattice relaxation dynamics in
AC-calorimetric measurements. The nuclear spin-lattice relaxation rate is
inferred in our measurements from its effect on the frequency dispersion of the
thermal response of the calorimeter-sample assembly. We use fast,
lithographically-defined nanocalorimeters to access the nuclear spin-lattice
relaxation times in metallic indium from 0.3~K to 7~K and in magnetic fields up
to 35~T.",2302.04442v2
2023-03-13,Towards a unified picture of polarization transfer -- pulsed DNP and chemically equivalent PHIP,"Nuclear spin hyperpolarization techniques, such as dynamic nuclear
polarization (DNP) and parahydrogen-induced polarization (PHIP), have
revolutionized nuclear magnetic resonance and magnetic resonance imaging. In
these methods, a readily available source of high spin order, either electron
spins in DNP or singlet states in hydrogen for PHIP, is brought into close
proximity with nuclear spin targets, enabling efficient transfer of spin order
under external quantum control. Despite vast disparities in energy scales and
interaction mechanisms between electron spins in DNP and nuclear singlet states
in PHIP, a pseudo-spin formalism allows us to establish an intriguing
equivalence. As a result, the important low-field polarization transfer regime
of PHIP can be mapped onto an analogous system equivalent to pulsed-DNP. This
establishes a correspondence between key polarization transfer sequences in
PHIP and DNP, facilitating the transfer of sequence development concepts. This
promises fresh insights and significant cross-pollination between DNP and PHIP
polarization sequence developers.",2303.07478v2
2023-04-04,Geometrical torque on magnetic moments coupled to a correlated antiferromagnet,"The geometrical spin torque mediates an indirect interaction of magnetic
moments, which are weakly exchange coupled to a system of itinerant electrons.
It originates from a finite spin-Berry curvature and leads to a non-Hamiltonian
magnetic-moment dynamics. We demonstrate that there is an unprecedentedly
strong geometrical spin torque in case of an electron system, where
correlations cause antiferromagnetic long-range order. The key observation is
that the anomalous torque is strongly boosted by low-energy magnon modes
emerging in the two-electron spin-excitation spectrum due to spontaneous
breaking of SU(2) spin-rotation symmetry. As long as single-electron
excitations are gapped out, the effect is largely universal, i.e., essentially
independent of the details of the electronic structure, but decisively
dependent on the lattice dimension and spatial and spin anisotropies. Analogous
to the reasoning that leads to the Mermin-Wagner theorem, there is a lower
critical dimension at and below which the spin-Berry curvature diverges.",2304.02071v1
2023-05-18,Giant optical orientation of exciton spins in lead halide perovskite crystals,"Optical orientation of carrier spins by circularly polarized light is the
basis of spin physics in semiconductors. Here, we demonstrate strong optical
orientation of 85\%, approaching the ultimate limit of unity, for excitons in
FA$_{0.9}$Cs$_{0.1}$PbI$_{2.8}$Br$_{0.2}$ lead halide perovskite bulk crystals.
Time-resolved photoluminescence allows us to distinguish excitons with 60~ps
lifetime from electron-hole recombination in the spin dynamics detected via
coherent spin quantum beats in magnetic field. We reveal electron-hole spin
correlations through linear polarization beats after circularly polarized
excitation. Detuning of the excitation energy from the exciton resonance up to
0.5~eV does not reduce the optical orientation, evidencing clean chiral
selection rules in agreement with atomistic calculations, and suppressed spin
relaxation of electrons and holes even with large kinetic energies.",2305.10875v1
2023-06-22,Control of Spin Polarization through Recollisions,"Using only linearly polarized light, we study the possibility of generating
spin-polarized photoelectrons from xenon atoms. No net spin polarization is
possible, since the xenon ground state is spin-less, but when the photoelectron
are measured in coincidence with the residual ion, spin polarization emerges.
Furthermore, we show that ultrafast dynamics of the recolliding photoelectrons
contribute to an apparent flipping of the spin of the photoelectron, a process
that has been completely neglected so far in all analyses of recollision-based
processes. We link this phenomenon to the ``spin--orbit clock'' of the
remaining ion. These effects arise already in dipole approximation.",2306.12823v3
2023-10-08,Nonlinear Orbital and Spin Edelstein Effect in Centrosymmetric Metals,"Nonlinear spintronics combines nonlinear dynamics with spintronics, opening
up new possibilities beyond linear responses. A recent theoretical work [Xiao
et al., Phys. Rev. Lett. 130, 166302 (2023)] predicts the nonlinear generation
of spin density [nonlinear spin Edelstein effect (NSEE)] in centrosymmetric
metals based on symmetry analysis combined with first principle calculation.
However, its microscopic mechanism is limited to a specific set of materials
with local inversion symmetry breaking and is not applicable to general
materials. This paper focuses on the fundamental role of orbital degrees of
freedom for the nonlinear generation in centrosymmetric systems. Using a
combination of tight-binding model and density functional theory calculations,
we demonstrate that nonlinear orbital density can arise independently of
spin-orbit coupling. In contrast, spin density follows through spin-orbit
coupling. We further elucidate the microscopic mechanism responsible for this
phenomenon, which involves the NSEE induced by electric-field-induced orbital
Rashba texture. In addition, we also explore the potential applications of the
nonlinear orbital and spin Edelstein effect for field-free switching of
magnetization.",2310.05113v4
2023-10-26,Full-magnetic implementation of a classical Toffoli gate,"The Toffoli gate is the essential ingredient for reversible computing, an
energy efficient classical computational paradigm that evades the energy
dissipation resulting from Landauer's principle. In this paper we analyze
different setups to realize a magnetic implementation of the Toffoli gate using
three interacting classical spins, each one embodying one of the three bits
needed for the Toffoli gate. In our scheme, different control-spins
configurations produce an effective field capable of conditionally flipping the
target spin. We study what are the experimental requirements for the
realization of our scheme, focusing on the degree of local control, the ability
to dynamically switch the spin-spin interactions, and the required single-spin
anisotropies to make the classical spin stable, showing that these are
compatible with current technology.",2310.17422v3
2023-11-10,Spin noise of a halide perovskite,"We report on first observation of spin noise in a strongly birefringent
semiconductor -- halide perovskite single crystal MAPbI$_3$. The observed spin
noise resonance is ascribed to free holes with a record spin dephasing time of
4 ns. The spin dynamics is found to be affected by the residual light
absorption of the crystal providing renormalization of the Larmor frequency.
Extended spin noise spectroscopy with rotating magnetic field allowed us not
only to evaluate the $g$-factor anisotropy, but also to distinguish two
different spin subsystems tentatively associated to twinning of the crystal.",2311.06077v1
2024-01-12,Fidelity of photon-mediated entanglement between remote nuclear-spin multi-qubit registers,"The electron spin of a nitrogen-vacancy center in diamond lends itself to the
control of proximal $^{13}$C nuclear spins via dynamical decoupling methods,
possibly combined with radio-frequency driving. Long-lived single-qubit states
and high-fidelity electron-nuclear gates required for the realization of a
multiqubit register have already been demonstrated. Towards the goal of a
scalable architecture, linking multiple such registers in a photonic network
represents an important step. Multiple pairs of remotely entangled qubits can
enable advanced algorithms or error correction protocols. We investigate how a
photonic architecture can be extended from the intrinsic nitrogen spin to
multiple $^{13}$C spins per node. Applying decoherence-protected gates
sequentially, we simulate the fidelity of creating multiple pairs of remotely
entangled qubits. Even though the currently achieved degree of control of
$^{13}$C spins might not be sufficient for large-scale devices, the two schemes
are compatible in principle. One requirement is the correction of unconditional
phases acquired by unaddressed nuclear spins during a decoupling sequence.",2401.06705v1
2024-01-30,Multi-Camera Asynchronous Ball Localization and Trajectory Prediction with Factor Graphs and Human Poses,"The rapid and precise localization and prediction of a ball are critical for
developing agile robots in ball sports, particularly in sports like tennis
characterized by high-speed ball movements and powerful spins. The Magnus
effect induced by spin adds complexity to trajectory prediction during flight
and bounce dynamics upon contact with the ground. In this study, we introduce
an innovative approach that combines a multi-camera system with factor graphs
for real-time and asynchronous 3D tennis ball localization. Additionally, we
estimate hidden states like velocity and spin for trajectory prediction.
Furthermore, to enhance spin inference early in the ball's flight, where
limited observations are available, we integrate human pose data using a
temporal convolutional network (TCN) to compute spin priors within the factor
graph. This refinement provides more accurate spin priors at the beginning of
the factor graph, leading to improved early-stage hidden state inference for
prediction. Our result shows the trained TCN can predict the spin priors with
RMSE of 5.27 Hz. Integrating TCN into the factor graph reduces the prediction
error of landing positions by over 63.6% compared to a baseline method that
utilized an adaptive extended Kalman filter.",2401.17185v1
2024-02-19,Photoelectron Polarization Vortexes in Strong-Field Ionization,"The spin polarization of photoelectrons induced by an intense linearly
polarized laser field is investigated using numerical solutions of the
time-dependent Schr\""odinger equation in companion with our analytic treatment
via the spin-resolved strong-field approximation and classical trajectory Monte
Carlo simulations. We demonstrate that, even though the total polarization
vanishes upon averaging over the photoelectron momentum, momentum-resolved spin
polarization is significant, typically exhibiting a vortex structure relative
to the laser polarization axis. The polarization arises from the transfer of
spin-orbital coupling in the bound state to the spin-correlated quantum orbits
in the continuum. The rescattering of photoelectrons at the atomic core plays
an important role in forming the polarization vortex structure, while there is
no significant effect of the spin-orbit coupling during the continuum dynamics.
Furthermore, spin-polarized electron holography is demonstrated, feasible for
extracting fine structural information about the atom.",2402.11825v1
2024-02-28,Simulating decoherence of coupled two spin qubits using generalized cluster correlation expansion,"We study the coherence of two coupled spin qubits in the presence of a bath
of nuclear spins simulated using generalized cluster correlation expansion
(gCCE) method. In our model, two electron spin qubits coupled with isotropic
exchange or magnetic dipolar interactions interact with an environment of
random nuclear spins. We study the time-evolution of the two-qubit reduced
density matrix (RDM) and resulting decay of the off diagonal elements,
corresponding to decoherence, which allows us to calculate gate fidelity in the
regime of pure dephasing. We contrast decoherence when the system undergoes
free evolution and evolution with dynamical decoupling pulses applied.
Moreover, we study the dependence of decoherence on external magnetic field and
system parameters which mimic realistic spin qubits, emphasizing magnetic
molecules. Lastly, we comment on the application and limitations of gCCE in
simulating nuclear-spin induced two-qubit relaxation processes.",2402.18722v1
2024-03-04,Realization of a Spin Glass in a two-dimensional van der Waals material,"Recent advances in van der Waals (vdW) materials have sparked renewed
interest in the impact of dimensionality on magnetic phase transitions. While
ordered magnetic phases have been demonstrated to survive in the
two-dimensional (2D) limit, the quest for a spin-glass with quenched magnetic
disorder in lower dimensions has proven elusive. Here we show evidence of a
spin-glass emerging from randomly distributed Fe atoms in Fe3GeTe2, the first
time such a state has been reported in a vdW material. AC magnetic
susceptibility displays a strong frequency dependence indicative of slow spin
dynamics. Additional distinctive phenomena, including ageing, chaos, and memory
effects, further substantiate the existence of a glassy state. Remarkably, we
find that this state persists even in single-unit-cell thick Fe3GeTe2, thereby
confirming the existence of a 2D spin-glass. The formation of spin-glass states
via intercalation in vdW systems allows for highly tunable spin-glass states
that are otherwise difficult to realize.",2403.02088v1
2024-04-07,Spin-lattice relaxation with non-linear couplings: Comparison between Fermi's golden rule and extended dissipaton equation of motion,"Fermi's golden rule (FGR) offers an empirical framework for understanding the
dynamics of spin-lattice relaxation in magnetic molecules, encompassing
mechanisms like direct (one-phonon) and Raman (two-phonon) processes. These
principles effectively model experimental longitudinal relaxation rates,
denoted as $T_1^{-1}$. However, under scenarios of increased coupling strength
and nonlinear spin-lattice interactions, FGR's applicability may diminish. This
paper numerically evaluates the exact spin-lattice relaxation rate kernels,
employing the extended dissipaton equation of motion (DEOM) formalism. Our
calculations reveal that when quadratic spin-lattice coupling is considered,
the rate kernels exhibit a free induction decay-like feature, and the damping
rates depend on the interaction strength. We observe that the temperature
dependence predicted by FGR significantly deviates from the exact results since
FGR ignores the non-Markovian nature of spin-lattice relaxation. Our methods
can be readily applied to other systems with nonlinear spin-lattice
interactions and provide valuable insights into the temperature dependence of
$T_1$ in molecular qubits.",2404.04803v2
1995-08-09,Weak Interactions in Supernova Cores and Saturation of Nucleon Spin Fluctuations,"Extrapolation of perturbative nucleon spin fluctuation rates seems to suggest
a strong suppression of weak interactions in supernova cores. We derive a new
sum rule for the dynamical spin-density structure function which relates the
spin fluctuation rate to the average nuclear interaction energy. For a
bremsstrahlung like structure function profile we show that instead of strongly
decreasing, the neutrino scattering cross section is roughly density
independent and axion emission rates increase somewhat slower than the lowest
order emissivities towards the center of a hot supernova core.",9508046v1
2006-08-13,Dynamics of Extended Spinning Masses in a Gravitational Field,"We develop a first-order approximation method for the influence of spin on
the motion of extended spinning test masses in a gravitational field. This
approach is illustrated for approximately circular equatorial motion in the
exterior Kerr spacetime. In this case, the analytic results for the first-order
approximation are compared to the numerical integration of the exact system and
the limitations of the first-order results are pointed out. Furthermore, we
employ our analytic results to illustrate the gravitomagnetic clock effect for
spinning particles.",0608278v2
1994-11-03,Monte Carlo Studies of Ising Spin Glasses and Random Field Systems,"We review recent numerical progress in the study of finite dimensional
strongly disordered magnetic systems like spin glasses and random field
systems. In particular we report in some details results for the critical
properties and the non-equilibrium dynamics of Ising spin glasses. Furthermore
we present an overview over recent investigations on the random field Ising
model and finally of quantum spin glasses.",9411017v1
1995-03-09,Spin Dynamics of the Triangular Heisenberg Antiferromagnet: A Schwinger Boson Approach,"We have analyzed the two-dimensional antiferromagnetic Heisenberg model on
the triangular lattice using a Schwinger boson mean-field theory. By expanding
around a state with local $120^\circ$ order, we obtain, in the limit of
infinite spin, results for the excitation spectrum in complete agreement with
linear spin wave theory (LSWT). In contrast to LSWT, however, the modes at the
ordering wave vectors acquire a mass for finite spin. We discuss the origin of
this effect.",9503048v1
1995-11-03,Quantum Coherence in Magnetic Grains,"We consider a model of the dynamics of a magnetic grain, incorporating
interactions with nuclear and paramagnetic spins, conduction electrons, and
phonons. Decoherence comes both from the spins and the electrons, although
electron effects can be neglected if the substrate is insulating, and the grain
has spin $S \le 10^5$. A successful experiment will require both isotopic and
chemical purification, if coherence is to be seen; we suggest a ""spin echo""
arrangement to do this.",9511015v1
1995-12-04,Spin dynamics of SrCu$_2$O$_3$ and the Heisenberg ladder,"The $S=1/2$ Heisenberg antiferromagnet in the ladder geometry is studied as a
model for the spin degrees of freedom of SrCu$_2$O$_3$. The susceptibility and
the spin echo decay rate are calculated using a quantum Monte Carlo technique,
and the spin-lattice relaxation rate is obtained by maximum entropy analytic
continuation of imaginary time correlation functions. All calculated quantities
are in reasonable agreement with experimental results for SrCu$_2$O$_3$ if the
exchange coupling $J \approx 850$K, i.e. significantly smaller than in
high-T$_c$ cuprates.",9512026v1
1997-01-23,Magnetic Excitations in the Spin-Peierls System $CuGeO_3$,"We have calculated the magnetic excitation spectrum in frustrated and
dimerized spin 1/2 Heisenberg chains for model parameters which describe the
thermodynamics and low frequency spin dynamics in the spin--Peierls system
$CuGeO_{3}$. As a test the chosen model is found to reproduce the lowest Raman
excitation energy near $30 cm^{-1}$ in the dimerized phase. We establish the
elementary triplet and singlet excitation branches below the continuum and
estimate the interchain coupling effects on the dimerization parameter.",9701176v1
1998-08-26,Orbital Ordering Induced Antiferromagnetic Spin Fluctuations in the Ferromagnetic State of 50 % Hole-doped Manganites: Pr{1/2}Sr{1/2}MnO3 and Nd{1/2}Sr{1/2}MnO3,"We report inelastic neutron scattering results on the spin dynamics in the 50
% hole-doped manganites, Pr{1/2}Sr{1/2}MnO3 and Nd{1/2}Sr{1/2}MnO3. In the
paramagnetic phase, these systems exhibit a ridge-type diffuse scattering,
indicating a two-dimensional ferromagnetic (FM) correlation. With decreasing
temperature, the systems enter the FM state, but simultaneously they develop
A-type antiferromagnetic spin fluctuations. The spin wave dispersion in the FM
state is strongly anisotropic. These behaviors can be consistently interpreted
from a viewpoint of the underlying orbital ordering.",9808286v1
1998-10-27,Spin relaxation of conduction electrons in polyvalent metals: A realistic calculation,"Relaxation of electronic spins in metals is significantly enhanced whenever a
Fermi surface crosses Brillouin zone boundaries, special symmetry points, or
lines of accidental degeneracy. A realistic calculation shows that if aluminum
had one valence electron, its spin relaxation would be slower by nearly two
orders of magnitude. This not only solves a longstanding experimental puzzle,
but also provides a way of tailoring spin dynamics of electrons in a conduction
band.",9810375v1
1999-04-13,Spin dynamics of quantum and classical Heisenberg dimers,"Analytical solutions for the time-dependent autocorrelation function of the
classical and quantum mechanical spin dimer with arbitrary spin are presented
and compared. For large spin quantum numbers or high temperature the classical
and the quantum dimer become more and more similar, yet with the major
difference that the quantum autocorrelation function is periodic in time
whereas the classical is not.",9904170v1
1999-04-22,Orbital order out of spin disorder: How to measure the orbital gap,"The interplay between spin and orbital degrees of freedom in the Mott-Hubbard
insulator is studied by considering an orbitally degenerate superexchange
model. We argue that orbital order and the orbital excitation gap in this model
are generated through the order-from-disorder mechanism known previously from
frustrated spin models. We propose that the orbital gap should show up
indirectly in the dynamical spin structure factor; it can therefore be measured
using the conventional inelastic neutron scattering method.",9904318v1
1999-05-10,Mixed Charge-Spin Response Functions of an Arbitrarily Polarized Electron Gas,"In this paper, using different approaches we demonstrate the equality of the
two mixed charge-spin response functions of a spin-polarized electron gas when
orbital effects are negligible. Within a generalized STLS approximation we show
that the two mixed responses are equal. We also present arguments for the
equality of the two dynamic responses by considering a symmetry of the
effective screened interaction between two opposite spin electrons.
Furthermore, using the reflection symmetry of the system and the fact that the
hamiltonian is real we prove rigorously that the two responses coincide
identically.",9905117v1
1999-05-27,Universal conductance fluctuations and low temperature 1/f noise in mesoscopic AuFe spin glasses,"We report on intrinsic time-dependent conductance fluctuations observed in
mesoscopic AuFe spin glass wires. These dynamical fluctuations have a 1/f-like
spectrum and appear below the measured spin glass freezing temperature of our
samples. The dependence of the fluctuation amplitude on temperature, magnetic
field, voltage and Fe concentration allows a consistent interpretation in terms
of quantum interference effects which are sensitive to the slowly fluctuating
spin configuration.",9905402v1
1999-10-04,Longitudinal magnetic excitations in classical spin systems,"Using spin dynamics simulations we predict the splitting of the longitudinal
spin wave peak in all antiferromagnets with single site anisotropy into two
peaks separated by twice the energy gap at the Brillouin zone center. This
phenomenon has yet to be observed experimentally but can be easily investigated
through neutron scattering experiments on MnF$_2$ and FeF$_2$. We have also
determined that for all classical Heisenberg models the longitudinal
propagative excitations are entirely multiple spin-wave in nature.",9910031v1
1999-10-06,Nonlinear response scaling of the two-dimensional XY spin glass in the Coulomb-gas representation,"Vortex critical dynamics of the two dimensional XY spin glass is studied by
Monte Carlo methods in the Coulomb-gas representation. A scaling analysis of
the nonlinear response is used to calculate the correlation length exponent
$\nu $ of the zero-temperature glass transition. The estimate, $\nu =1.3(2)$,
is in agreement witth a recent estimate in the phase representation using the
same analysis and indicates that the relevant length scale for vortex motion is
set by the spin-glass correlation length and that spin and chiralities may
order with different correlation length exponents.",9910075v2
2000-05-26,Spin and charge excitations in incommensurate spin density waves,"Collective excitations both for spin- and charge-channels are investigated in
incommensurate spin density wave (or stripe) states on two-dimensional Hubbard
model. By random phase approximation, the dynamical susceptibility
\chi(q,\omega) is calculated for full range of (q,\omega) with including all
higher harmonics components. An intricate landscape of the spectra in
\chi(q,\omega) is obtained. We discuss the anisotropy of the dispersion cones
for spin wave excitations, and for the phason excitation related to the motion
of the stripe line. Inelastic neutron experiments on Cr and its alloys and
stripe states of underdoped cuprates are proposed.",0005466v1
2000-07-03,Charge Ordering and Spin Dynamics in NaV2O5,"We report high-resolution neutron inelastic scattering experiments on the
spin excitations of NaV2O5. Below Tc, two branches associated with distinct
energy gaps are identified. From the dispersion and intensity of the spin
excitation modes, we deduce the precise zig-zag charge distribution on the
ladder rungs and the corresponding charge order (about 0.6). We argue that the
spin gaps observed in the low-T phase of this compound are primarily due to the
charge transfer.",0007025v2
2000-11-13,Phase Transition of a Heisenberg Spin-Glass Model in Three Dimensions,"We study the phase transition of the $\pm J$ Heisenberg model in three
dimensions. Using a dynamical simulation method that removes a drift of the
system, the existence of the spin-glass (SG) phase at low temperatures is
suggested. The transition temperature is estimated to be $T_{\rm SG} \sim
0.18J$ from both equilibrium and off-equilibrium Monte-Carlo simulations. Our
result contradicts the chirality mechanism of the phase transition reported
recently by Kawamura which claims that it is not the spins but the chiralities
of the spins that are ordered in Heisenberg SG systems.",0011218v1
2001-02-13,Nuclear spin driven quantum relaxation in LiY_0.998Ho_0.002F_4,"Staircase hysteresis loops of the magnetization of a LiY_0.998Ho_0.002F_4
single crystal are observed at subkelvin temperatures and low field sweep
rates. This behavior results from quantum dynamics at avoided level crossings
of the energy spectrum of single Ho^{3+} ions in the presence of hyperfine
interactions. Enhanced quantum relaxation in constant transverse fields allows
the study of the relative magnitude of tunnel splittings. At faster sweep
rates, non-equilibrated spin-phonon and spin-spin transitions, mediated by weak
dipolar interactions, lead to magnetization oscillations and additional steps.",0102231v2
2001-07-17,Two-hole dynamics in spin ladders,"We present an analytic theory for the energy spectrum of a two-leg spin
ladder doped with two holes. Starting from a pseudo-fermion-bond-boson
representation of the corresponding $t_{1,2}-J_{1,2}$ Hamiltonian we apply a
diagrammatic approach adapted to the limit of strong rung coupling, which
includes both, the coupling of holes to the spin background as well as the
two-hole interactions. The two-hole spectrum is calculated and the formation of
bound states is discussed. Additionally the evolution of the spin gap of the
ladder upon doping is analyzed. A comparison with existing exact
diagonalization data is presented and good agreement is found.",0107365v2
2001-09-26,Observation of anomalous spin-state segregation in a trapped ultra-cold vapor,"We observe counter-intuitive spin segregation in an inhomogeneous sample of
ultra-cold, non-condensed Rubidium atoms in a magnetic trap. We use spatially
selective microwave spectroscopy to verify a model that accounts for the
differential forces on two internal spin states. In any simple understanding of
the cloud dynamics, the forces are far too small to account for the dramatic
transient spin polarizations observed. The underlying mechanism remains to be
elucidated.",0109476v1
2002-01-08,Spin dynamics of the S=1/2 antiferromagnetic zig-zag ladder with anisotropy,"We use exact diagonalization and the modified Lanczos method to study the
finite energy and finite momentum spectral weight of the longitudinal and
transverse spin excitations of the anisotropic zig-zag ladder. We find that the
spin excitations form continua of gapless or gapped spinons in the different
regions of the phase diagram. The results obtained are consistent with a
picture previously proposed that in the anisotropic case there is a transition
from a gapped regime to a gapless regime, for small interchain coupling. In
this regime we find a sharp low-energy peak in the structure function for the
transverse spin excitations, consistent with a finite stiffness.",0201098v1
2002-11-13,Spin-fluctuations in the quarter-filled Hubbard ring : significances to LiV$_2$O$_4$,"Using the quantum Monte Carlo method, we investigate the spin dynamics of
itinerant electrons in the one-dimensional Hubbard system. Based on the model
calculation, we have studied the spin-fluctuations in the quarter-filled
metallic Hubbard ring, which is aimed at the vanadium ring or chain defined
along corner-sharing tetrahedra of LiV$_2$O$_4$, and found the dramatic changes
of magnetic responses and spin-fluctuation characteristics with the
temperature. Such results can explain the central findings in the recent
neutron scattering experiment for LiV$_2$O$_4$.",0211261v1
2003-03-18,Transport equations for a two-dimensional electron gas with spin-orbit interaction,"The transport equations for a two-dimensional electron gas with spin-orbit
interaction are presented. The distribution function is a 2x2-matrix in the
spin space. Particle and energy conservation laws determine the expressions for
the electric current and the energy flow. The derived transport equations are
applied to the spin-splitting of a wave packed and to the calculation of the
structure factor and the dynamic conductivity.",0303362v2
2003-03-26,Chern Numbers for Spin Models of Transition Metal Nanomagnets,"We argue that ferromagnetic transition metal nanoparticles with fewer than
approximately 100 atoms can be described by an effective Hamiltonian with a
single giant spin degree of freedom. The total spin $S$ of the effective
Hamiltonian is specified by a Berry curvature Chern number that characterizes
the topologically non-trivial dependence of a nanoparticle's many-electron
wavefunction on magnetization orientation. The Berry curvatures and associated
Chern numbers have a complex dependence on spin-orbit coupling in the
nanoparticle and influence the semiclassical Landau-Liftshitz equations that
describe magnetization orientation dynamics.",0303555v1
2003-04-02,Magnetic orderings in Al nanowires suspended between electrodes,"A theoretical analysis of a relation between atomic and spin-electronic
structures for the ground state of single-row aluminum nanowires suspended
between Al(001) electrodes is demonstrated using first-principles
molecular-dynamics simulations. We obtain a unusual result that a
3-aluminum-atom nanowire sandwiched between the electrodes does not manifest
magnetic ordering although an isolated aluminum trimer molecule in a straight
line is spin-polarized. On the other hand, a 5-atom nanowire exhibits
ferromagnetic ordering, where three central atoms form a spin-polarized trimer.
Moreover, in the case of an 8-atom nanowire, the middle atoms in the nanowire
form two spin-polarized trimers with antiferromagnetic ordering.",0304060v1
2003-05-22,Coherent Spin Oscillations in a Disordered Magnet,"Most materials freeze when cooled to sufficiently low temperature. We find
that magnetic dipoles randomly distributed in a solid matrix condense into a
spin liquid with spectral properties on cooling that are the diametric opposite
of those for conventional glasses. Measurements of the non-linear magnetic
dynamics in the low temperature liquid reveal the presence of coherent spin
oscillations composed of hundreds of spins with lifetimes up to ten seconds.
These excitations can be labeled by frequency, manipulated by the magnetic
fields from a loop of wire, and permit the encoding of information at multiple
frequencies simultaneously.",0305541v1
2003-06-20,Quantum dynamics of tunneling between ferromagnets,"We study the Josephson-like spin currents between two ferromagnetic metals by
deriving the effective action of the junction. A DC spin Josephson current with
the full O(3) symmetry is obtained. By the analogy to the superconducting
junctions, we have shown that a time-independent uniform magnetic field can
serve as the source of the AC spin Josephson effect. That is, the spin current
becomes a periodic function of the time with the period proportional to the
inverse of the magnitude of the external magnetic field.",0306518v2
2003-08-23,Non-Unitary Spin-Charge Separation in One-Dimensional Fermion Gas,"In this Letter we report exact results on the infrared asymptotics of
one-particle dynamical correlation function of the gas of impenetrable spin 1/2
fermions at infinitesimal temperature. The correlation function shows signs of
spin-charge separation with scaling behavior in the charge part and exponential
decay as a function of the space coordinate in the spin part. Surprisingly, the
anomalous dimensions in the charge part do not correspond to any unitary
conformal field theory. We find that the fermion spectral weight has a power
law divergency at low energy with the anomalous exponent $-1/2.$",0308470v1
2003-12-01,Full Counting Statistics of Spin Currents,"We discuss how to detect fluctuating spin currents and derive full counting
statistics of electron spin transfers. It is interesting to consider several
detectors in series that simultaneously monitor different components of the
spins transferred. We have found that in general the statistics of the
measurement outcomes cannot be explained with the projection postulate and
essentially depends on the quantum dynamics of the detectors.",0312045v1
2003-12-02,Itineracy Effects on Spin Correlations in 1D Mott Insulators,"We consider spin correlations in the one dimensional half filled repulsive
Hubbard model. For very large values of the on-site repulsion U the spin
correlations are dominated by virtual hopping processes of electrons and are
described in terms of a spin-1/2 Heisenberg chain. As U is decreased real
hopping processes of electrons become important and eventually dominate the
spin response. We discuss the evolution of the dynamical structure factor as a
function of U. We comment on the relevance of our results for inelastic neutron
scattering experiments on quasi-1D materials.",0312055v1
2004-05-14,Dynamical AC study of the critical behavior in Heisenberg spin glasses,"We present some numerical results for the Heisenberg spin-glass model with
Gaussian interactions, in a three dimensional cubic lattice. We measure the AC
susceptibility as a function of temperature and determine an apparent finite
temperature transition which is compatible with the chiral-glass temperature
transition for this model. The relaxation time diverges like a power law
$\tau\sim (T-T_c)^{-z\nu}$ with $T_c=0.19(4)$ and $z\nu=5.0(5)$. Although our
data indicates that the spin-glass transition occurs at the same temperature as
the chiral glass transition, we cannot exclude the possibility of a chiral-spin
coupling scenario for the lowest frequencies investigated.",0405308v1
2004-06-21,"Magnetic susceptibility, exchange interactions and spin-wave spectra in the local spin density approximation","Starting from exact expression for the dynamical spin susceptibility in the
time-dependent density functional theory a controversial issue about exchange
interaction parameters and spin-wave excitation spectra of itinerant electron
ferromagnets is reconsidered. It is shown that the original expressions for
exchange integrals based on the magnetic force theorem (J. Phys. F14 L125
(1984)) are optimal for the calculations of the magnon spectrum whereas static
response function is better described by the ``renormalized'' magnetic force
theorem by P. Bruno (Phys. Rev. Lett. 90, 087205 (2003)). This conclusion is
confirmed by the {\it ab initio} calculations for Fe and Ni.",0406488v1
2004-07-06,Spin characterization and control over the regime of radiation-induced zero-resistance states,"Over the regime of the radiation-induced zero-resistance states and
associated oscillatory magnetoresistance, we propose a low magnetic field
analog of quantum-Hall-limit techniques for the electrical detection of
electron spin- and nuclear magnetic- resonance, dynamical nuclear polarization
via electron spin resonance, and electrical characterization of the nuclear
spin polarization via the Overhauser shift. In addition, beats observed in the
radiation-induced oscillatory-magnetoresistance are developed into a method to
measure and control the zero-field spin splitting due to the Bychkov-Rashba and
bulk inversion asymmetry terms in the high mobility GaAs/AlGaAs system.",0407143v1
2005-02-02,Spin-fluctuation mechanism of superconductivity in cuprates,"The theory of superconductivity within the t-J model, as relevant for
cuprates, is developed. It is based on the equations of motion for projected
fermionic operators and the mode-coupling approximation for the self-energy
matrix. The dynamical spin susceptibility at various doping is considered as an
input, extracted from experiments. The analysis shows that the
superconductivity onset is dominated by the spin-fluctuation contribution. We
show that T_c is limited by the spin-fluctuation scale $\Gamma$ and shows a
pronounced dependence on the next-nearest-neighbor hopping t'. The latter can
offer an explanation for the variation of T_c among different families of
cuprates.",0502044v1
2005-02-25,Room temperature spin coherence in ZnO,"Time-resolved optical techniques are used to explore electron spin dynamics
in bulk and epilayer samples of n-type ZnO as a function of temperature and
magnetic field. The bulk sample yields a spin coherence time T2* of 20 ns at T
= 30 K. Epilayer samples, grown by pulsed laser deposition, show a maximum T2*
of 2 ns at T = 10 K, with spin precession persisting up to T = 280 K.",0502620v1
2005-05-20,Spin noise spectroscopy in GaAs,"We observe the noise spectrum of electron spins in bulk GaAs by Faraday
rotation noise spectroscopy. The experimental technique enables the undisturbed
measurement of the electron spin dynamics in semiconductors. We measure
exemplarily the electron spin relaxation time and the electron Lande g-factor
in n-doped GaAs at low temperatures and find good agreement of the measured
noise spectrum with an unpretentious theory based on Poisson distribution
probability.",0505495v1
2005-06-09,Screening in the two-dimensional electron gas with spin-orbit coupling,"We study the interplay between electron-electron interaction and Rashba
spin-orbit coupling in the two-dimensional electron gas. Using the random phase
approximation we predict new screening properties of the electron gas which
result in extension of the region of particle-hole excitations and in
spin-orbit induced suppression of collective modes. In particular, we observe
that the spin-orbit coupling gives a finite lifetime to plasmons and
longitudinal optical phonons, which can be resolved in inelastic Raman
scattering. We evaluate the experimentally measurable dynamic structure factor
and estimate the range of parameters where the described phenomena are mostly
pronounced.",0506227v2
2005-11-28,Spin susceptibility of underdoped cuprates: the case of Ortho-II YBa_2Cu_3O_{6.5},"Recent inelastic neutron scattering measurements found that the spin
susceptibility of detwinned and highly ordered ortho-II YBa_2Cu_3O_{6.5}
exhibits, in both the normal and superconducting states, one-dimensional
incommensurate modulations at low energies which were interpreted as a
signature of dynamic stripes. We propose an alternative model based on
quasiparticle transitions between the arcs of a truncated Fermi surface. Such
transitions are resonantly enhanced by scattering to the triplet spin
resonance. We show that the anisotropy in the experimental spin response is
consistent with this model if the gap at the saddle points is anisotropic.",0511661v1
2006-02-06,Suppression of Spin Relaxation in Submicron InGaAs Wires,"We investigate electron spin dynamics in narrow two-dimensional n-InGaAs
channels as a function of the channel width. The spin relaxation times increase
with decreasing channel width, in accordance with recent theoretical
predictions based on the dimensionally-constrained D'yakonov-Perel' mechanism.
Surprisingly, the suppression of the relaxation rate, which is anticipated for
the one-dimensional limit, is observed for widths that are an order of
magnitude larger than the electron mean free path. We find the spin precession
length and the channel width to be the relevant length scales for interpreting
these results.",0602155v1
2006-04-18,Spin-Orbital Entanglement and Violation of the Goodenough-Kanamori Rules,"We point out that large composite spin-orbital fluctuations in Mott
insulators with $t_{2g}$ orbital degeneracy are a manifestation of quantum
entanglement of spin and orbital variables. This results in a dynamical nature
of the spin superexchange interactions, which fluctuate over positive and
negative values, and leads to an apparent violation of the Goodenough-Kanamori
rules. [{\it Published in Phys. Rev. Lett. {\bf 96}, 147205 (2006).}]",0604417v1
2006-05-06,Evidence for multimagnon-mediated nuclear spin relaxation in the intertwining double-cain ferrimagnet $Ca_3 Cu_3 (PO_4)_4$,"The nuclear spin-lattice relaxation time $T_1$ of $^{31}P$ nuclei in the
title compound is measured for the first time and interpreted in terms of a
modified spin-wave theory. We establish a novel scenario for one-dimensional
ferrimagnetic spin dynamics -- it is three-magnon processes enhanced by
exchange scattering, rather than Raman processes, that make the major
contribution to $1/T_1$.",0605157v2
2006-05-08,Microscopic Calculation of Spin Torques in Disordered Ferromagnets,"Effects of conduction electrons on magnetization dynamics, represented by
spin torques, are calculated microscopically in the first order in spatial
gradient and time derivative of magnetization. Special attention is paid to the
so-called $\beta$-term and the Gilbert damping, $\alpha$, in the presence of
electrons' spin-relaxation processes, which are modeled by quenched magnetic
(and spin-orbit) impurities. The obtained results such as $\alpha \ne \beta$
hold for localized as well as itinerant ferromagnetism.",0605186v1
2006-05-29,Pair-wise decoherence in coupled spin qubit networks,"Experiments involving phase coherent dynamics of networks of spins, such as
echo experiments, will only work if decoherence can be suppressed. We show
here, by analyzing the particular example of a crystalline network of Fe8
molecules, that most decoherence typically comes from pairwise interactions
(particularly dipolar interactions) between the spins, which cause `correlated
errors'. However at very low T these are strongly suppressed. These results
have important implications for the design of quantum information processing
systems using electronic spins.",0605709v3
2006-08-02,Nuclear spin effects in negatively charged InP quantum dots,"Effects of both the dynamic nuclear polarization (DNP) created by circularly
polarized light and the fluctuations of average nuclear spin in a quantum dot
(QD) on the electron spin orientation are studied for singly negatively charged
InP QDs. From the dependence of the negative circular polarization of
photoluminescence on the applied longitudinal magnetic field, the hyperfine
field B_N of a few mT appearing due to DNP and the effective magnetic field B_f
of a few tens of mT arising from nuclear spin fluctuations (NSF) are estimated.
A lifetime of about 1 microsecond is estimated for NSF.",0608043v1
2006-08-04,"An electron spin injection driven, paramagnetic solid-state MASER device","In response to an external, microwave-frequency magnetic field, a
paramagnetic medium will absorb energy from the field that drives the
magnetization dynamics. Here we describe a new process by which an external
spin injection source, when combined with the microwave field spin-pumping, can
drive the paramagnetic medium from one that absorbs microwave energy to one
that emits microwave energy. We derive a simple condition for the crossover
from absorptive to emissive behavior. Based on this process, we propose a spin
injection-driven paramagnetic MASER device.",0608111v1
2006-08-22,Clustering induced suppression of ferromagnetism in diluted magnets,"Ferromagnetism in diluted magnets in the compensated regime p << x is shown
to be suppressed by the formation of impurity spin clusters. The majority bulk
spin couplings are shown to be considerably weakened by the preferential
accumulation of holes in spin clusters, resulting in low-energy magnon
softening and enhanced low-temperature decay of magnetic order. A locally
self-consistent magnon renormalization analysis of spin dynamics shows that
although strong intra-cluster correlations tend to prolong global order, T_c is
still reduced compared to the ordered case.",0608474v2
2006-08-31,Quantum Spin Dynamics of Spin-1 Bose Gas,"We show that the quantum evolution of a spin-1 Bose gas with nearly all
bosons initially in the $F_z = 0$ state has a ""quantum carpet"" {\em spin-time}
structure with self-similar properties. The system continuously evolves into
""multi-peaked"" Schr\""odinger cat like states, returning occasionally to
coherent structures, which leads to large number fluctuations (as seen in
recent experiments). The self similar behavior allows one to reveal the quantum
evolution as a set of peaks in the number probability distribution of a spin
component at times {\em much shorter} than the quantum revival time. We also
show that these features survive small number fluctuations among spin
components up to a few percent.",0608732v1
2006-09-05,Out-of-plane spin polarization from in-plane electric and magnetic fields,"We show that the joint effect of spin-orbit and magnetic fields leads to a
spin polarization perpendicular to the plane of a two-dimensional electron
system with Rashba spin-orbit coupling and in-plane parallel dc magnetic and
electric fields, for angle-dependent impurity scattering or nonparabolic energy
spectrum, while only in-plane polarization persists for simplified models. We
derive Bloch equations, describing the main features of recent experiments,
including the magnetic field dependence of static and dynamic responses.",0609078v1
2006-09-19,Spin echo without an external permanent magnetic field,"The spin echo techniques aim at the elimination of the effect of a random
magnetic field on the spin evolution. These techniques conventionally utlize
the application of a permanent field which is much stronger than the random
one. The strong field, however, may also modify the magnetic response of the
medium containing the spins, thus altering their ``natural'' dynamics. We
suggest an iterative scheme for generating a sequence of pulses which create an
echo without an external permanent field. The approximation to the ideal echo
improves with the sequence length.",0609490v1
2006-11-27,Microscopic Calculation of Spin Torques and Forces,"Spin torques, that is, effects of conduction electrons on magnetization
dynamics, are calculated microscopically in the first order in spatial gradient
and time derivative of magnetization. Special attention is paid to the
so-called \beta-term and the Gilbert damping, \alpha, in the presence of
electrons' spin-relaxation processes, which are modeled by quenched magnetic
impurities. Two types of forces that the electric/spin current exerts on
magnetization are identified based on a general formula relating the force to
the torque.",0611669v1
2006-11-27,Probing $n$-Spin Correlations in Optical Lattices,"We propose a technique to measure multi-spin correlation functions of
arbitrary range as determined by the ground states of spinful cold atoms in
optical lattices. We show that an observation of the atomic version of the
Stokes parameters, using focused lasers and microwave pulsing, can be related
to $n$-spin correlators. We discuss the possibility of detecting not only
ground state static spin correlations, but also time-dependent spin wave
dynamics as a demonstrative example using our proposed technique.",0611689v2
2006-12-19,Effect of spin-orbit coupling on the excitation spectrum of Andreev billiards,"We consider the effect of spin-orbit coupling on the low energy excitation
spectrum of an Andreev billiard (a quantum dot weakly coupled to a
superconductor), using a dynamical numerical model (the spin Andreev map).
Three effects of spin-orbit coupling are obtained in our simulations: In zero
magnetic field: (1) the narrowing of the distribution of the excitation gap;
(2) the appearance of oscillations in the average density of states. In strong
magnetic field: (3) the appearance of a peak in the average density of states
at zero energy. All three effects have been predicted by random-matrix theory.",0612501v1
2003-04-22,Gravitomagnetic Moments and Dynamics of Dirac's (spin 1/2) fermions in flat space-time Maxwellian Gravity,"The gravitational effects in the relativistic quantum mechanics are
investigated in a relativistically derived version of Heaviside's speculative
Gravity (in flat space-time) named here as Maxwellian Gravity. The standard
Dirac's approach to the intrinsic spin in the fields of Maxwellian Gravity
yields the gravitomagnetic moment of a Dirac (spin 1/2) particle exactly equals
to its intrinsic spin. Violation of The Equivalence Principle (both at
classical and quantum mechanical level) in the relativistic domain has also
been reported in this work.",0304084v2
1992-05-09,Ising Model Coupled to Three-Dimensional Quantum Gravity,"We have performed Monte Carlo simulations of the Ising model coupled to
three-dimensional quantum gravity based on a summation over dynamical
triangulations. These were done both in the microcanonical ensemble, with the
number of points in the triangulation and the number of Ising spins fixed, and
in the grand canoncal ensemble. We have investigated the two possible cases of
the spins living on the vertices of the triangulation (``diect'' case) and the
spins living in the middle of the tetrahedra (``dual'' case). We observed phase
transitions which are probably second order, and found that the dual
implementation more effectively couples the spins to the quantum gravity.",9205009v1
1994-03-22,How to probe the spin-dependent gluon distributions,"Two-spin asymmetries $A_{LL}^{\pi^0}$ are calculated for various types of
spin-dependent gluon distributions. It is concluded that the E581/704 data on
$A_{LL}^{\pi^0}$ do not necessarily rule out the large gluon polarization but
restrict severely the $x$ dependence of its distribution. Moreover,
$A_{LL}^{J/\psi}$ are calculated for the forthcoming test of spin-dependent
gluon distributions.",9403334v1
2000-07-05,Nucleon Spin Structure Functions,"The review of the nucleon spin structure functions problems is presented. The
perturbative QCD predictions for the small x behaviour of the nucleon spin
structure functions are discussed. The role of the resummation of the ln^2 1/x
terms is emphasized. Predictions for the nonsinglet structure function g_1 in
case of a flat as well as a dynamical input are given. The so called ""spin
crisis"" on the context of both theoretical and experimental future hopes are
also briefly discussed.",0007042v1
2005-10-12,Alternative approaches to transversity: how convenient and feasible are they?,"The complete knowledge of the nucleon spin structure at leading twist
requires also addressing the transverse spin distribution of quarks, or
transversity, which is yet unexplored because of its chiral-odd nature.
Elaborating strategies to extract it from (spin) asymmetry data represents a
unique opportunity to explore more generally the transverse spin structure of
the nucleon and the transverse momentum dynamics of partons inside it. Here, we
critically review some of the most promising approaches.",0510165v2
2007-02-27,Polarisation Observables in Antiproton Proton to Lepton Antilepton Reactions,"The electromagnetic form factors of hadrons as measured both in the space
like and time like domains provide fundamental information on the nucleon
structure and internal dynamics. General expressions, including the lepton
mass, for the spin averaged differential cross section for the annihilation
reaction lepton antilepton to proton antiproton are given, as well as general
formulae for the single and double spin asymmetries. The time reversed reaction
would involve a kinematic factor. We also present general expressions for the
helicity amplitudes for this reaction.",0702276v1
1994-11-18,Spin in the path integral: anti-commuting versus commuting variables,"We discuss the equivalence between the path integral representations of spin
dynamics for anti-commuting (Grassmann) and commuting variables and establish a
bosonization dictionary for both generators of spin and single fermion
operators. The content of this construction in terms of the representations of
the spin algebra is discussed in the path integral setting. Finally it is shown
how a `free field realization' (Dyson mapping) can be constructed in the path
integral.",9411142v1
2005-05-12,Non-planar spin bits beyond two loops,"We study higher-loop orders of spin bit models underlying the non-planar
dynamics of $\mathcal{N}=4$ SYM gauge theory. In particular, we derive a
''tower'' of non-planar identities involving products of site permutation
operators. Such identities are then applied in the formulation of planarly
consistent, testable conjectures for the full non-planar, higher-loop
Hamiltonian of the $su(2)$ spin-chain.",0505106v2
2006-08-03,Anomalous Dimensions from a Spinning D5-Brane,"We consider the anomalous dimension of a certain twist two operator in N=4
super Yang-Mills theory. At strong coupling and large-N it is captured by the
classical dynamics of a spinning D5-brane. The present calculation generalizes
the result of Gubser, Klebanov and Polyakov (hep-th/0204051): in order to
calculate the anomalous dimension of a bound state of k coincident strings, the
spinning closed string is replaced by a spinning D5 brane that wraps an S4
inside the S5 part of the AdS5 times S5 metric.",0608026v2
2002-10-08,Parity of the spin structure defined by a quadratic differential,"According to the work of Kontsevich-Zorich, the invariant that classifies
non-hyperelliptic connected components of the moduli spaces of Abelian
differentials with prescribed singularities,is the parity of the spin
structure.
  We show that for the moduli space of quadratic differentials, the spin
structure is constant on every stratum where it is defined. In particular this
disproves the conjecture that it classifies the non-hyperelliptic connected
components of the strata of quadratic differentials with prescribed
singularities. An explicit formula for the parity of the spin structure is
given.",0210116v2
2005-06-10,A Family of Hyperbolic Spin Calogero-Moser Systems and the Spin Toda Lattices,"In this paper, we continue to develop a general scheme to study a broad class
of integrable systems naturally associated with the coboundary dynamical Lie
algebroids. In particular, we present a factorization method for solving the
Hamiltonian flows. We also present two important class of new examples, a
family of hyperbolic spin Calogero-Moser systems and the spin Toda lattices. To
illustrate our factorization theory, we show how to solve these Hamiltonian
systems explicitly.",0506028v1
2003-02-06,Semiclassical theory of spin-orbit interaction in the extended phase space,"We consider the semiclassical theory in a joint phase space of spin and
orbital degrees of freedom. The method is developed from the path integrals
using the spin-coherent-state representation, and yields the trace formula for
the density of states. We discuss special cases, such as weak and strong
spin-orbit coupling, and relate the present theory to the earlier approaches.",0302011v2
2003-09-02,Periodic orbit theory including spin degrees of freedom,"We summarize recent developments of the semiclassical description of shell
effects in finite fermion systems with explicit inclusion of spin degrees of
freedom, in particluar in the presence of spin-orbit interactions. We present a
new approach that makes use of spin coherent states and a correspondingly
enlarged classical phase space. Taking suitable limits, we can recover some of
the earlier approaches. Applications to some model systems are presented.",0309006v1
2006-06-02,Controlling electronic spin relaxation of cold molecules with electric fields,"We present a theoretical study of atom - molecule collisions in superimposed
electric and magnetic fields and show that dynamics of electronic spin
relaxation in molecules at temperatures below 0.5 K can be manipulated by
varying the strength and the relative orientation of the applied fields. The
mechanism of electric field control of Zeeman transitions is based on an
intricate interplay between intramolecular spin-rotation couplings and
molecule-field interactions. We suggest that electric fields may affect
chemical reactions through inducing nonadiabatic spin transitions and
facilitate evaporative cooling of molecules in a magnetic trap.",0606027v2
2004-01-19,Effective quantum spin systems with ion traps,"We show that the physical system consisting of trapped ions interacting with
lasers may undergo a rich variety of quantum phase transitions. By changing the
laser intensities and polarizations the dynamics of the internal states of the
ions can be controlled, in such a way that an Ising or Heisenberg-like
interaction is induced between effective spins. Our scheme allows us to build
an analogue quantum simulator of spin systems with trapped ions, and observe
and analyze quantum phase transitions with unprecedent opportunities for the
measurement and manipulation of spins.",0401102v1
2004-04-20,Wave function collapses in a single spin magnetic resonance force microscopy,"We study the effects of wave function collapses in the oscillating cantilever
driven adiabatic reversals (OSCAR) magnetic resonance force microscopy (MRFM)
technique. The quantum dynamics of the cantilever tip (CT) and the spin is
analyzed and simulated taking into account the magnetic noise on the spin. The
deviation of the spin from the direction of the effective magnetic field causes
a measurable shift of the frequency of the CT oscillations. We show that the
experimental study of this shift can reveal the information about the average
time interval between the consecutive collapses of the wave function",0404105v1
2005-04-08,Geometric Effects and Computation in Spin Networks,"When initially introduced, a Hamiltonian that realises perfect transfer of a
quantum state was found to be analogous to an x-rotation of a large spin. In
this paper we extend the analogy further to demonstrate geometric effects by
performing rotations on the spin. Such effects can be used to determine
properties of the chain, such as its length, in a robust manner. Alternatively,
they can form the basis of a spin network quantum computer. We demonstrate a
universal set of gates in such a system by both dynamical and geometrical
means.",0504063v1
2005-06-21,Controlled Flow of Spin-Entangled Electrons via Adiabatic Quantum Pumping,"We propose a method to dynamically generate and control the flow of
spin-entangled electrons, each belonging to a spin-singlet, by means of
adiabatic quantum pumping. The pumping cycle functions by periodic time
variation of localized two-body interactions. We develop a generalized approach
to adiabatic quantum pumping as traditional methods based on scattering matrix
in one dimension cannot be applied here. We specifically compute the flow of
spin-entangled electrons within a Hubbard-like model of quantum dots, and
discuss possible implementations and identify parameters that can be used to
control the singlet flow.",0506172v1
2007-01-10,Experimental demonstration of stimulated polarization wave in a chain of nuclear spins,"A stimulated wave of polarization, which implements a simple mechanism of
quantum amplification, is experimentally demonstrated in a chain of four
J-coupled nuclear spins, irradiated by a weak radio-frequency transverse field.
The ""quantum domino"" dynamics, a wave of flipped spins triggered by a flip of
the first spin, has been observed in fully $^{13}$C-labeled sodium butyrate.",0701056v1
2007-09-12,Two Ferromagnetic Phases in Spin-Fermion Systems,"We consider spin-fermion systems which get their magnetic properties from a
system of localized magnetic moments being coupled to conducting electrons. The
dynamical degrees of freedom are spin-$s$ operators of localized spins and
spin-1/2 fermi operators of itinerant electrons. We develop modified spin-wave
theory and obtain that system has two ferromagnetic phases. At the
characteristic temperature T* the magnetization of itinerant electrons becomes
zero, and high temperature ferromagnetic phase (T*<T<T_C) is a phase where only
localized electrons give contribution to the magnetization of the system. An
anomalous increasing of magnetization below T* is obtained in a good agrement
with experimental measurements of the ferromagnetic phase of UGe2.",0709.1759v2
2008-06-04,External magnetic field effects on a distorted kagome antiferromagnet,"We report bulk magnetization, and elastic and inelastic neutron scattering
measurements under an external magnetic field, $H$, on the weakly coupled
distorted kagome system, Cu_{2}(OD)_3Cl. Our results show that the ordered
state below 6.7 K is a canted antiferromagnet and consists of large
antiferromagnetic $ac$-components and smaller ferromagnetic $b$-components. By
first-principle calculations and linear spin wave analysis, we present a simple
spin hamiltonian with non-uniform nearest neighbor exchange interactions
resulting in a system of coupled spin trimers with a single-ion anisotropy that
can qualitatively reproduce the spin dynamics of Cu_{2}(OD)_3Cl.",0806.0767v1
2008-06-10,Amplification of Fluctuations in a Spinor Bose Einstein Condensate,"Dynamical instabilities due to spin-mixing collisions in a $^{87}$Rb F=1
spinor Bose-Einstein condensate are used as an amplifier of quantum spin
fluctuations. We demonstrate the spectrum of this amplifier to be tunable, in
quantitative agreement with mean-field calculations. We quantify the
microscopic spin fluctuations of the initially paramagnetic condensate by
applying this amplifier and measuring the resulting macroscopic magnetization.
The magnitude of these fluctuations is consistent with predictions of a
beyond-mean-field theory. The spinor-condensate-based spin amplifier is thus
shown to be nearly quantum-limited at a gain as high as 30 dB.",0806.1553v1
2008-06-19,Dirac particle in gravitational field,"Classical dynamics of spinning zero-size objects in an external gravitational
field is derived from the conservation law of the stress-energy and spin
tensors. The resulting world line equations differ from those in the existing
literature. In particular, the spin of the Dirac particle does not couple to
the background curvature. As a check of consistency, the wave packet solution
of the free Dirac equation is considered. The resulting equations are shown to
include a constraint that relates the wave packet spin to its orbital angular
momentum. In the zero-size limit, both contributions to the total angular
momentum disappear simultaneously.",0806.3228v1
2008-09-24,Exactly solvable D_N-type quantum spin models with long-range interaction,"We derive the spectra of the D_N-type Calogero (rational) su(m) spin model,
including the degeneracy factors of all energy levels. By taking the strong
coupling limit of this model, in which its spin and dynamical degrees of
freedom decouple, we compute the exact partition function of the su(m)
Polychronakos-Frahm spin chain of D_N type. With the help of this partition
function we study several statistical properties of the chain's spectrum, such
as the density of energy levels and the distribution of spacings between
consecutive levels.",0809.4234v1
2008-10-24,Polarization and entanglement in spin systems,"We established important relationships between entanglement measures and the
order parameter (spin polarization) in nuclear spin systems controlled by the
nuclear magnetic resonance (NMR) technique. Since spin polarization can be
easily manipulated by the NMR technique, experimentalists are presented with an
opportunity to study the dynamic properties of entanglement, i.e., the creation
and evolution of entangled states. Our approach may constitute the basis for
researching the relations between the entanglement measures and measurable
parameters of order in other quantum systems.",0810.4388v1
2008-11-04,\muSR-dtected Soft mode toward a Possible Phase Transition in disordered spin gap system (CH3)2CHNH3-Cu(ClxBr1-x)3,"Measurements of macroscopic properties have indicated that the
bond-disordered spin-gap system (CH3)2CHNH3-Cu(ClxBr1-x)3 is gapless when x is
between 0.44 and 0.87. Using muon spin relaxation to investigate microscopic
properties of sample with x=0.35, we observed a dynamical spin fluctuation,
whose characteristic frequency decreases with decreasing temperature,
indicating a magnetic ground state.",0811.0386v1
2009-03-07,Impurity effects in multiferroic compounds,"We investigate the effect of impurities in multiferroic materials using an
equation of motion approach for the spin dynamics of the host multiferroic
compound. We model the impurities as a two-level system and focus on the regime
where the impurity spins relax slowly. When the impurity strength is weak the
host spins oscillate with no decay and the electric polarization is not
affected. However as the impurity strength is increased the host spin
components get damped and the electrion polarization is suppressed. Since
polarization in multiferroic materials is driven by magnetic ordering we
conclude that the presence of impurities is detrimental to multiferroicity.",0903.1319v1
2009-03-16,Controlled multiqubit entangled states and quantum transmission in quantum molecule-spin systems,"he multiqubit entangled states are coherently controlled in the quantum spin
systems composed of $N+1$ interacting antiferromagnetic molecular rings. The
tunable intermolecular couplings arise from the local exchange interactions
between electron spins of $N$ circumjacent magnets and those of one central
molecular ring. The quantum dynamics of such system is analytically deduced by
the effective spin hamiltonian with anisotropic Heisenberg couplings. It is
found that entangled $W$ states can be generated with a high precision under
the circumstance of quantum fluctuations. The multiqubit entangled state is
also transferred from some molecular rings to others by the selection of
intermolecular couplings.",0903.2705v1
2009-03-22,Anomalous Magnetic Susceptibility in Iron Pnictides: Paramagnetic Phase,"Observation of an anomalous temperature dependence of the spin
susceptibility, along with a spin gap in NMR, in the quantum paramagnetic
normal state of Iron Pnictides is a signature of an unusual metallic state. We
argue that both these anomalous features are associated with a wide
fluctuational regime dominated by dynamical, short-ranged and frustrated spin
correlations in a strongly correlated metal. Using LDA+DMFT, we show that both
these features can be quantitatively undertstood in the doped Fe-pnictides. We
argue that such spin correlations naturally arise in a Mottness scenario, where
an effective, dualistic description involves coexisting renormalized
quasiparticles and effectively localized moments, arising from the same set of
d bands.",0903.3732v1
2009-04-22,Current-induced nuclear-spin activation in a two-dimensional electron gas,"Electrically detected nuclear magnetic resonance was studied in detail in a
two-dimensional electron gas as a function of current bias and temperature. We
show that applying a relatively modest dc-current bias, I_dc ~ 0.5 microAmps,
can induce a re-entrant and even enhanced nuclear spin signal compared with the
signal obtained under similar thermal equilibrium conditions at zero current
bias. Our observations suggest that dynamic nuclear spin polarization by small
current flow is possible in a two-dimensional electron gas, allowing for easy
manipulation of the nuclear spin by simple switching of a dc current.",0904.3405v1
2009-07-17,Glassy Spin Freezing and Gapless Spin Dynamics in a Spatially Anisotropic Triangular Antiferromagnet Ag2MnO2,"Using elastic and inelastic neutron scattering techniques, we show that upon
cooling a spatially anisotropic triangular antiferromagnet Ag$_2$MnO$_2$
freezes below $T_f ~\sim 50$ K into short range collinear state. The static
spin correlations are extremely two-dimensional, and the spin fluctuations are
gapless with two characteristic relaxation rates that behave linearly with
temperature.",0907.3157v1
2009-08-21,Spin-transfer torque in disordered weak ferromagnets,"We study theoretically the spin transfer effect on a domain wall in
disordered weak ferromagnets. We have identified the adiabatic condition for
the disordered case as $\lambda \gg \lambda_{\rm D}\equiv \sqrt{{\hbar
D}/{\spol}}$, where $D$ and $\spol$ are the diffusion constant and the spin
splitting energy due to the $s$-$d$ type exchange interaction, respectively,
and found out that perfect spin-transfer effect occurs even in weak
ferromagnets as long as this condition is satisfied. The effective $\beta$ term
arising from the force turns out to govern the wall dynamics, and therefore,
the wall motion can be as efficient as in strong ferromagnets even if $\spol$
is small.",0908.3048v1
2009-09-08,"Memory, Aging and Spin Glass Nature: A Study of NiO Nanoparticles","We report studies on magnetization dynamics in NiO nanoparticles of average
size 5 nm. Temperature and time dependence of dc magnetization, wait time
dependence of magnetic relaxation (aging) and memory phenomena in the dc
magnetization are studied with various temperature and field protocols. We
observe that the system shows memory and aging in field cooled and zero field
cooled magnetization measurements. These experiments show that the magnetic
behavior of NiO nanoparticles is similar to spin glasses. We argue that the
spin glass behavior originates from the freezing of spins at the surface of the
individual particles.",0909.1391v2
2010-01-14,State transfer in static and dynamic spin chains with disorder,"We examine the speed and fidelity of several protocols for state or single
excitation transfer in finite spin chains subject to diagonal and off-diagonal
disorder. We find that, for a given chain length and maximal achievable
inter-spin exchange (XY) coupling strength, the optimal static spin-coupling
protocol, implementing the fastest state transfer between the two ends of the
chain, is more susceptible to off-diagonal (XY coupling) disorder, as compared
to a much slower but robust adiabatic transfer protocol with time-dependent
coupling strengths.",1001.2444v1
2010-02-16,ADM canonical formulation with spin and application to post-Newtonian approximations,"Recently, different methods succeeded in calculating the spin dynamics at
higher orders in the post-Newtonian (PN) approximation. This is an essential
step toward the determination of more accurate templates for gravitational
waves, to be used in future gravitational wave astronomy. We focus on the
extension of the ADM canonical formalism to spinning binary black holes. Using
the global Poincare invariance of asymptotically flat spacetimes as the most
important guiding consistency condition, this extension can be constructed
order by order in the PN approximation. We were able to reach a high order both
in the spin power and the PN counting.",1002.3057v1
2010-07-26,Entanglement Routers Using Macroscopic Singlets,"We propose a mechanism where high entanglement between very distant boundary
spins is generated by suddenly connecting two long Kondo spin chains. We show
that this procedure provides an efficient way to route entanglement between
multiple distant sites. We observe that the key features of the entanglement
dynamics of the composite spin chain are remarkably well described using a
simple model of two singlets, each formed by two spins. The proposed
entanglement routing mechanism is a footprint of the emergence of a Kondo cloud
in a Kondo system and can be engineered and observed in varied physical
settings.",1007.4516v2
2010-07-29,Magnetic domain walls displacement : automotion vs. spin-transfer torque,"The magnetization dynamics equation predicts that a domain wall that changes
structure should undergo a displacement by itself - automotion - due to the
relaxation of the linear momentum that is associated with the wall structure.
We experimentally demonstrate this effect in soft nanostrips,transforming under
spin transfer torque a metastable asymmetric transverse wall into a vortex
wall. Displacements more than three times as large as under spin transfer
torque only are measured for 1~ns pulses. The results are explained by
analytical and numerical micromagnetics. Their relevance to domain wall motion
under spin transfer torque is emphasized.",1007.5233v1
2010-08-02,Chern number spins of Mn acceptor magnets in GaAs,"We determine the effective total spin $J$ of local moments formed from
acceptor states bound to Mn ions in GaAs by evaluating their magnetic Chern
numbers. We find that when individual Mn atoms are close to the sample surface,
the total spin changes from $J = 1$ to $J = 2$, due to quenching of the
acceptor orbital moment. For Mn pairs in bulk, the total $J$ depends on the
pair orientation in the GaAs lattice and on the separation between the Mn
atoms. We point out that Berry curvature variation as a function of local
moment orientation can profoundly influence the quantum spin dynamics of these
magnetic entities.",1008.0275v1
2010-08-06,Spin Resonance and dc Current Generation in a Quantum Wire,"We show that in a quantum wire the spin-orbit interaction leads to a narrow
spin resonance at low temperatures, even in the absence of an external magnetic
field. A relatively weak dc magnetic field of a definite direction strongly
increases the resonance absorption. Linearly polarized resonance radiation
produces dynamic magnetization as well as electric and spin currents. The
effect strongly depends on the external magnetic field.",1008.1225v1
2010-08-09,Efficient Data Averaging for Spin Noise Spectroscopy in Semiconductors,"Spin noise spectroscopy (SNS) is the perfect tool to investigate electron
spin dynamics in semiconductors at thermal equilibrium. We simulate SNS
measurements and show that ultrafast digitizers with low bit depth enable
sensitive, high bandwidth SNS in the presence of strong optical background shot
noise. The simulations reveal that optimized input load at the digitizer is
crucial for efficient spin noise detection while the bit depth influences the
sensitivity rather weakly.",1008.1474v2
2010-09-21,Electron Spin Resonance of the ferromagnetic Kondo lattice CeRuPO,"The spin dynamics of the ferromagnetic Kondo lattice CeRuPO is investigated
by Electron Spin Resonance (ESR) at microwave frequencies of 1, 9.4, and
34~GHz. The measured resonance can be ascribed to a rarely observed bulk Ce3+
resonance in a metallic Ce compound and can be followed below the ferromagnetic
transition temperature Tc=14 K. At T>Tc the interplay between the RKKY-exchange
interaction and the crystal electric field anisotropy determines the ESR
parameters. Near Tc the spin relaxation rate is influenced by the critical
fluctuations of the order parameter.",1009.4108v1
2011-03-22,Exact solution of the Schrodinger equation with the spin-boson Hamiltonian,"We address the problem of obtaining the exact reduced dynamics of the
spin-half (qubit) immersed within the bosonic bath (enviroment). An exact
solution of the Schrodinger equation with the paradigmatic spin-boson
Hamiltonian is obtained. We believe that this result is a major step ahead and
may ultimately contribute to the complete resolution of the problem in
question. We also construct the constant of motion for the spin-boson system.
In contrast to the standard techniques available within the framework of the
open quantum systems theory, our analysis is based on the theory of block
operator matrices.",1103.4383v1
2011-03-29,Spin waves in the block checkerboard antiferromagnetic phase,"Motivated by the discovery of new family 122 iron-based superconductors, we
present the theoretical results on the ground state phase diagram, spin wave
and dynamic structure factor of the extended $J_{1}-J_{2}$ Heisenberg model. In
the reasonable physical parameter region of $K_{2}Fe_{4}Se_{5}$, we fi{}nd the
block checkerboard antiferromagnetic order phase is stable. There are two
acoustic branches and six optical branches spin wave in the block checkerboard
antiferromagnetic phase, which has analytic expression in the high symmetry
points. To compare the further neutron scattering experiments, we discuss the
saddlepoint structure in the magnetic excitation spectrum and calculate the
predicted inelastic neutron scattering pattern based on linear spin wave
theory.",1103.5521v1
2011-08-09,Spin-orbit coupling and $g$-factor of $X$-valley in cubic GaN,"We report our theoretically investigation on the spin-orbit coupling and
$g$-factor of the $X$-valley in cubic GaN. We find that the spin-orbit coupling
coefficient from $sp^3d^5s^\ast$ tight-binding model is 0.029\,eV$\cdot${\AA},
which is comparable with that in cubic GaAs. By employing the ${\bf k}\cdot{\bf
p}$ theory, we find that the $g$-factor in this case is only slightly different
from the free electron $g$-factor. These results are expected to be important
for the on-going study on spin dynamics far away from equilibrium in cubic GaN.",1108.2059v1
2011-10-07,Spin-orbit splittings in heavy-light mesons and Dirac equation,"The spin-orbit splitting in heavy-light mesons is seen to be suppressed
experimentally. It is shown that it can be understood qualitatively in the
frame work of Dirac theory. An alternative derivation of a relativistic
dynamical symmetry for the Dirac Hamiltonian, which suppresses spin orbit
splitting, is also given. However it is shown that such a symmetry is not
needed since the spin-orbit splitting in Dirac theory with Coulomb like
potential (as is the case for the one gluon exchange potential in pQCD) is
small anyway.",1110.1451v1
2012-06-15,Optical control of the spin state of two Mn atoms in a quantum dot,"We report on the optical spectroscopy of the spin of two magnetic atoms (Mn)
embedded in an individual quantum dot interacting with either a single
electron, a single exciton and single trion. As a result of their interaction
to a common entity, the Mn spins become correlated. The dynamics of this
process is probed by time resolved spectroscopy, that permits to determine the
optical orientation time in the range of a few tens of $ns$. In addition, we
show that the energy of the collective spin states of the two Mn atoms can be
tuned through the optical Stark effect induced by a resonant laser field.",1206.3491v1
2012-09-19,Dynamical evolution of an inverted spin ensemble in a cavity: Inhomogeneous broadening as a stabilizing mechanism,"We study the evolution of an inverted spin ensemble coupled to a cavity. The
inversion itself presents an inherent instability of the system; however, the
inhomogeneous broadening of spin-resonance frequencies presents a stabilizing
mechanism, and a stability criterion is derived. The detailed behavior of mean
values and variances of the spin components and of the cavity field is
accounted for under both stable and unstable conditions.",1209.4167v1
2012-09-19,Spin-orbit coupling assisted by flexural phonons in graphene,"We analyze the couplings between spins and phonons in graphene. We present a
complete analysis of the possible couplings between spins and flexural, out of
plane, vibrations. From tight-binding models we obtain analytical and numerical
estimates of their strength. We show that dynamical effects, induced by quantum
and thermal fluctuations, significantly enhance the spin-orbit gap.",1209.4382v2
2012-11-02,Ripples in a graphene membrane coupled to Glauber spins,"We propose a theory of ripples in suspended graphene sheets based on
two-dimensional elasticity equations that are made discrete on the honeycomb
lattice and then periodized. At each point carbon atoms are coupled to Ising
spins whose values indicate the atoms local trend to move vertically off-plane.
The Ising spins are in contact with a thermal bath and evolve according to
Glauber dynamics. In the limit of slow spin flip compared to membrane
vibrations, ripples with no preferred orientation appear as long-lived
metastable states for any temperature. Numerical solutions confirm this
picture.",1211.0541v1
2012-11-18,Controlling the Spin Torque Efficiency with Ferroelectric Barriers,"Non-equilibrium spin-dependent transport in magnetic tunnel junctions
comprising a ferroelectric barrier is theoretically investigated. The exact
solutions of the free electron Schr\""odinger equation for electron tunneling in
the presence of interfacial screening are obtained by combining Bessel and Airy
functions. We demonstrate that the spin transfer torque efficiency, and more
generally the bias-dependence of tunneling magneto- and electroresistance, can
be controlled by switching the ferroelectric polarization of the barrier. This
effect provides a supplementary way to electrically control the current-driven
dynamic states of the magnetization and related magnetic noise in spin transfer
devices.",1211.4196v1
2012-11-29,Pumping $ac$ Josephson current in the Single Molecular Magnets by spin nutation,"We demonstrate that an {\it ac} Josephson current is pumped through the
Single Molecular Magnets (SMM) by the spin nutation. The spin nutation is
generated by applying a time dependent magnetic field to the SMM. We obtain the
flowing charge current through the junction by working in the tunneling limit
and employing Green's function technique. At the resonance conditions some
discontinuities and divergencies are appeared in the normal and Josephson
currents, respectively. Such discontinuities and divergencies reveal themselves
when the absorbed/emitted energy, owing to the interaction of the
quasiparticles with the spin dynamics are in the range of the superconducting
gap.",1211.6879v1
2012-12-12,Spin diffusion in one-dimensional classical Heisenberg mode,"The problem of spin diffusion is studied numerically in one-dimensional
classical Heisenberg model using a deterministic odd even spin precession
dynamics. We demonstrate that spin diffusion in this model, like energy
diffusion, is normal and one obtains a long time diffusive tail in the decay of
autocorrelation function (ACF). Some variations of the model with different
coupling schemes and with anisotropy are also studied and we find normal
diffusion in all of them. A systematic finite size analysis of the Heisenberg
model also suggests diffusive spreading of fluctuation, contrary to previous
claims of anomalous diffusion.",1212.2829v1
2013-02-22,Anderson Localization of cold atomic gases with effective spin-orbit interaction in a quasiperiodic optical lattice,"We theoretically investigate the localization properties of a spin-orbit
coupled spin-1/2 particle moving in a one-dimensional quasiperiodic potential,
which can be experimentally implemented using cold atoms trapped in a
quasiperiodic optical lattice potential and external laser fields. We present
the phase diagram in the parameter space of the disorder strength and those
related to the spin-orbit coupling. The phase diagram is verified via
multifractal analysis of the atomic wavefunctions and the numerical simulation
of diffusion dynamics. We found that spin-orbit coupling can lead to the
spectra mixing (coexistence of extended and localized states) and the
appearance of mobility edges.",1302.5465v1
2013-03-10,Spin Dynamics of Trimers on a Distorted Kagomé Lattice,"We treat the ground state, elementary excitations, and neutron scattering
cross section for a system of trimers consisting of three tightly bound spins
1/2 on a distorted Kagom\'e lattice, subject to isotropic nearest neighbor
(usually antiferromagnetic) Heisenberg interactions. The interactions between
trimers are assumed to be weak compared to the intra trimer interactions. We
compare the spin-wave excitation spectrum of trimers with that obtained from
standard spin-wave theory and attribute the differences at low energy to the
fact that the trimer formulation includes exactly the effects of intra-trimer
zero point motion. Application to existing systems is briefly discussed.",1303.2320v1
2013-05-08,Spontaneous synchronization and quantum correlation dynamics of open spin systems,"We discuss the emergence of spontaneous synchronization for an open spin-pair
system interacting only via a common environment. Under suitable conditions,
and even in the presence of detuning between the natural precession frequencies
of the two spins, they are shown to reach a long-lasting transient behavior
where they oscillate in phase. We explore the connection between the emergence
of such a behavior and the establishment of robust quantum correlations between
the two spins, analyzing differences between dissipative and dephasing effects.",1305.1816v2
2013-07-28,Real Time Electrical Detection of Coherent Spin Oscillations,"We demonstrate that the bandwidth of pulsed electrically detected magnetic
resonance can be increased to at least 80 MHz using a radio
frequency-reflectometry detection scheme. Using this technique, we measure
coherent spin oscillations in real time during a resonant microwave pulse. We
find that the observed signal is in quantitative agreement with simulations
based on rate equations modeling the recombination dynamics of the spin system
under study. The increased bandwidth opens the way to electrically study faster
spin-dependent recombination processes, e.g., in direct semiconductors which so
far have almost exclusively been studied by optically detected magnetic
resonance.",1307.7413v1
2013-07-30,Spin-dependent shot noise enhancement in a quantum dot,"The spin-dependent dynamical blockade was investigated in a lateral quantum
dot in a magnetic field. Spin-polarized edge channels in the two-dimensional
leads and the spatial distribution of Landau orbitals in the dot modulate the
tunnel coupling of the quantum dot level spectrum. In a measurement of the
electron shot noise we observe a pattern of super-Poissonian noise which is
correlated to the spin-dependent competition between different transport
channels.",1307.8165v1
2013-12-03,Covariant Map Between Ramond-Neveu-Schwarz and Pure Spinor Formalisms for the Superstring,"A covariant map between the Ramond-Neveu-Schwarz (RNS) and pure spinor
formalisms for the superstring is found which transforms the RNS and pure
spinor BRST operators into each other. The key ingredient is a dynamical
twisting of the ten spin-half RNS fermions into five spin-one and five
spin-zero fermions using bosonic pure spinors that parameterize an SO(10)/U(5)
coset. The map relates massless vertex operators in the two formalisms, and
gives a new description of Ramond states which does not require spin fields. An
argument is proposed for relating the amplitude prescriptions in the two
formalisms.",1312.0845v2
2013-12-05,Radial quantization of the 3d CFT and the higher spin/vector model duality,"We study the radial quantization of the 3d O(N) vector model. We calculate
the higher spin charges whose commutation relations give the higher spin
algebra. The Fock states of higher spin gravity in AdS_{4} are realized as the
states in the 3d CFT. The inner products between these states encode dynamical
information. The construction of bulk operators from CFT is discussed as well.
This serves as the simplest explicit demonstration of the CFT definition for
the quantum gravity.",1312.1545v2
2014-02-25,Spin state in the propagation of quantum relativistic particles along classical trajectories,"We address the propagation of the spin along classical trajectories for a
1/2-spin particle obeying the Dirac equation with scalar potentials. Focusing
on classical trajectories as the exact propagation of wave-function
discontinuities we find an explicit spin-transport law for the case of the
Dirac oscillator. In the general case we examine the spin propagation along
classical trajectories emerging as an approximation of the quantum dynamics via
the mechanical analog of the optical eikonal asymptotic approach. Throughout we
establish as many parallels as possible with the equivalent situation for the
electromagnetic field.",1402.6063v2
2014-04-26,Excitation of spin density and current by coherent light pulses in QWs,"We study the orbital and spin dynamics of charge carriers induced by
non-overlapping linearly polarized light pulses in semiconductor quantum wells
(QWs). It is shown that such an optical excitation with coherent pulses leads
to a spin orientation of photocarriers and an electric current. The effects are
caused by the interference of optical transitions driven by individual pulses.
The distribution of carriers in the spin and momentum spaces depends on the QW
crystallographic orientation and can be efficiently controlled by the pulse
polarizations, time delay and phase shift between the pulses, as well as an
external magnetic field.",1404.6675v1
2014-08-09,Mutual Phase Locking of Very Nonidentical Spin Torque Nanooscillators via Spin Wave Interaction,"In this paper the mutual phase locking theory of very nonidentical
spin-torque nanooscillators, which is based on the Slavin-Tiberkevich model,
considering the theory of nonlinear oscillations, is developed. Using
generalized Adler equation we calculate phase-locking region of the system with
spinwave coupling in the parameter plane - distance between nanocontacts and
radii difference. We describe trajectories of such a system in the phase space
and show the effect of a broadband synchronization. We introduce a
generalization of this approach to the ensembles of spin-torque nanooscillators",1408.2141v1
2014-08-20,Detecting two-site spin-entanglement in many-body systems with local particle-number fluctuations,"We derive experimentally measurable lower bounds for the two-site
entanglement of the spin-degrees of freedom of many-body systems with local
particle-number fluctuations. Our method aims at enabling the spatially
resolved detection of spin-entanglement in Hubbard systems using
high-resolution imaging in optical lattices. A possible application is the
observation of entanglement generation and spreading during spin impurity
dynamics, for which we provide numerical simulations. More generally, the
scheme can simplify the entanglement detection in ion chains, Rydberg atoms, or
similar atomic systems.",1408.4672v1
2014-09-16,Sensitivity to small perturbations in systems of large quantum spins,"We investigate the sensitivity of nonintegrable large-spin quantum lattices
to small perturbations with a particular focus on the time reversal experiments
known in statistical physics as ""Loschmidt echoes"" and in nuclear magnetic
resonance (NMR) as ""magic echoes"". Our numerical simulations of quantum
spin-$7\frac{1}{2}$ clusters indicate that there is a regime, where Loschmidt
echoes exhibit nearly exponential sensitivity to small perturbations with
characteristic constant approximately equal to twice the value of the largest
Lyapunov exponent of the corresponding classical spin clusters. The above
theoretical results are verifiable by NMR experiments on solids containing
large-spin nuclei.",1409.4763v1
2014-10-13,Vortex gyration mediated by spin waves driven by an out-of-plane oscillating magnetic field,"In this letter we address the vortex core dynamics involved in gyration
excitation and damping change by out-of-plane oscillating magnetic fields. When
the vortex core is at rest under the effect of in-plane bias magnetic fields,
the spin waves excited by the perpendicular magnetic field can induce obvious
vortex gyration. When simultaneously excite spin waves and vortex gyrotropic
motion, the gyration damping changes. Analysis of the system energy allows us
to explain the origin of the spin-wave-mediated vortex gyration.",1410.3230v1
2014-11-10,Classical and quantum chaotic angular-momentum pumps,"We study directed transport of charge and intrinsic angular momentum by
periodically driven scattering in the regime of fast and strong driving. A
spin-orbit coupling through a kicked magnetic field confined to a compact
region in space leads to irregular scattering and triggers spin flips in a
spatially asymmetric manner which allows to generate polarized currents. The
dynamical mechanisms responsible for the spin separation carry over to the
quantum level and give rise to spin pumping. Our theory, based on the Floquet
formalism, is confirmed by numerical solutions of the time-dependent
inhomogeneous Schr\""{o}dinger equation with a continuous source term.",1411.2659v2
2014-12-08,Refocusing dipolar interactions between electronic spins of donors in silicon,"We note the existence of a set of magnetic field values where a simple Hahn
echo sequence refocuses the dynamics of the full dipolar interaction, for spin
systems of electron donors in silicon. As the refocussing occurs for both
arbitrary coupling strengths and arbitrary times, these dipolar refocusing
points (DRPs) offer new possibilities for regulating entanglement due to the
always-on spin dipolar interaction. While the experimental effects of DRPs will
be strongly diluted in the measured coherences of thermal (unpolarized) spin
ensembles, we investigate possible signatures in coherence decays arising from
a study of the combined effects of decoherence arising from instantaneous
diffusion and direct flip-flops",1412.2645v1
2015-01-25,Integrable non-equilibrium steady state density operators for boundary driven XXZ spin chains: observables and full counting statistics,"We will review some known exact solutions for the steady state of the open
quantum Heisenberg $XXZ$ spin chain coupled to a pair of baths [Phys. Rev.
Lett. 107, 137201 (2011).]. The dynamics is modelled by the Lindblad master
equation. We also review how to calculate some relevant physical observables
and provide the statistics of spin current assuming the spin chain is weakly
coupled to the baths [Phys. Rev. Lett. 112, 067201 (2014).].",1501.06156v1
2015-05-27,Acoustic waves generated by the spin precession,"We study generation of acoustic waves by a precessing spin of a nanoparticle
deposited on the surface of a solid. Our approach elucidates macroscopic
dynamics of the Einstein - de Haas effect. It is based upon solution of
parameter-free equations of motion mandated by the conservation of the total
angular momentum: spin + mechanical. We show that the amplitude of the acoustic
waves generated by the spin precession may be sufficient for detection by a
tunneling electron microscope.",1505.07373v1
2015-07-02,Spin-dependent tunneling in semiconductor heterostructures with a magnetic layer,"We present a theory that describes the appearance of circular polarization of
the photoluminescence (PL) in ferromagnet-semiconductor hybrid heterostructures
due to spin-dependent tunneling of photoexcited carriers from a quantum well
into a magnetic layer. The theory succeeds in explaining the experimental data
on time-resolved PL for heterostructures consisting of InGaAs-based quantum
well (QW) and a spatially separated Mn $\delta$-layer. We show that the
circular polarization of the PL originates from dynamic spin polarization of
electrons due to spin-dependent leakage from the QW onto Mn donor states split
by the exchange field of the ferromagnetic Mn delta-layer.",1507.00585v1
2015-07-27,Dynamics of extended bodies in a Kerr spacetime with spin-induced quadrupole tensor,"The features of equatorial motion of an extended body in Kerr spacetime are
investigated in the framework of the Mathisson-Papapetrou-Dixon model. The body
is assumed to stay at quasi-equilibrium and respond instantly to external
perturbations. Besides the mass, it is completely determined by its spin, the
multipolar expansion being truncated at the quadrupole order, with a
spin-induced quadrupole tensor. The study of the radial effective potential
allows to analytically determine the ISCO shift due to spin and the associated
frequency of the last circular orbit.",1507.07441v1
2015-10-04,Spinon walk in quantum spin ice,"We study a minimal model for the dynamics of spinons in quantum spin ice. The
model captures the essential strong coupling between the spinon and the
disordered background spins. We demonstrate that the spinon motion can be
mapped to a random walk with an entropy-induced memory in imaginary time. Our
numerical simulation of the spinon walk indicates that the spinon propagates as
a massive quasiparticle at low energy despite its strong coupling to the spin
background at the microscopic energy scale. We discuss the experimental
implications of our findings.",1510.00979v2
2015-10-18,Two-Fluid Theory for Spin Superfluidity in Magnetic Insulators,"We investigate coupled spin and heat transport in easy-plane magnetic
insulators. These materials display a continuous phase transition between
normal and condensate states that is controlled by an external magnetic field.
Using hydrodynamic equations supplemented by Gross-Pitaevski phenomenology and
magnetoelectric circuit theory, we derive a two-fluid model to describe the
dynamics of thermal and condensed magnons, and the appropriate boundary
conditions in a hybrid normal-metal|magnetic-insulator|normal-metal
heterostructure. We discuss how the emergent spin superfluidity can be
experimentally probed via a spin Seebeck effect measurement.",1510.05316v2
2016-02-22,Exchange magnon induced resistance asymmetry in permalloy spin-Hall oscillators,"We investigate magnetization dynamics in a spin-Hall oscillator using a
direct current measurement as well as conventional microwave spectrum analysis.
When the current applies an anti-damping spin-transfer torque, we observe a
change in resistance which we ascribe to the excitation of incoherent exchange
magnons. A simple model is developed based on the reduction of the effective
saturation magnetization, quantitatively explaining the data. The observed
phenomena highlight the importance of exchange magnons on the operation of
spin-Hall oscillators.",1602.06710v1
2016-02-29,Emergent interacting spin islands in a depleted strong-leg Heisenberg ladder,"Properties of the depleted Heisenberg spin ladder material series
(C$_7$H$_{10}$N)$_2$Cu$_{1-z}$Zn$_{z}$Br$_4$ have been studied by the
combination of magnetic measurements and neutron spectroscopy. Disorder-induced
degrees of freedom lead to a specific magnetic response, described in terms of
emergent strongly interacting ""spin island"" objects. The structure and dynamics
of the spin islands is studied by high-resolution inelastic neutron scattering.
This allows to determine their spatial shape and to observe their mutual
interactions, manifested by strong spectral in-gap contributions.",1603.00070v1
2016-04-15,Electron magnetic resonance in magnetic nanoparticles: dependence on the particle size and applicability of the modified giant spin model,"Superparamagnetic nanoparticles containing hundreds and thousands of coupled
electron spins are on the boundary between classical and quantum behavior, and
demonstrate features which are typical for paramagnetic spins and absent in
macroscopic ferromagnetic systems. In order to better understand the evolution
of magnetization dynamics from quantum to classical behavior with the increase
in the system size, we study the electron magnetic resonance signal in
suspensions of iron oxide nanoparticles as the function of the particle size.
The experimental data are compared with numerical simulations based on the
giant spin approach.",1604.04594v2
2016-06-16,Quantum atomistic approach for interacting spins,"The phenomenological Landau theory of the spin precession has been used to
reproduce the out-of-equilibrium properties of many magnetic systems. However,
such an approach suffers from some serious limitations. The main reason is that
the spin and the angular momentum of the atoms are described by the classical
theory of the angular momentum. We derive a discrete model that extends the
Landau theory to the quantum mechanical framework. Our approach is based on the
application of the quantification procedure to the classical hamiltonian of an
array of interacting spins. The connection with the classical dynamics is
discussed.",1606.05368v1
2016-06-30,Spinning particles moving around black holes: integrability and chaos,"The motion of a stellar compact object around a supermassive black hole can
be approximated by the motion of a spinning test particle. The equations of
motion describing such systems are in general non-integrable, and therefore,
chaotic motion should be expected. This article discusses the integrability
issue of the spinning particle for the cases of Schwarzschild and Kerr
spacetime, and then it focuses on a canonical Hamiltonian formalism where the
spin of the particle is included only up to the linear order.",1606.09430v1
2016-10-31,Strong non-equilibrium effects in spin torque systems,"We consider a problem of persistent magnetization precession in a single
domain ferromagnetic nano particle under the driving by the spin-transfer
torque. We find that the adjustment of the electronic distribution function in
the particle renders this state unstable. Instead, abrupt switching of the spin
orientation is predicted upon increase of the spin-transfer torque current. On
the technical level, we derive an effective action of the type of
Ambegaokar-Eckern-Sch\""on action for the coupled dynamics of magnetization
(gauge group $SU(2)$) and voltage (gauge group $U(1)$).",1610.09944v2
2014-03-03,Nuclear Spin Diffusion Mediated by Heavy Hole Hyperfine Non-Collinear Interactions,"We show that the hyperfine mediated dynamics of heavy hole states confined in
neutral self- assembled quantum dots leads to a nuclear spin diffusion
mechanism. It is found that the oftentimes neglected effective heavy hole
hyperfine non-collinear interaction is responsible for the low degree of
nuclear spin polarization in neutral quantum dots. Moreover, our results
demonstrate that after pumping the nuclear spin state is left in a complex
mixed state, from which it is not straightforward to deduce the sign of the
Ising-like interactions.",1403.0490v1
2014-03-18,31P NMR Investigation of the Superconductor LiFeP (Tc = 5 K),"We investigate the static and dynamic spin susceptibility of the 111 type
Fe-based superconductor LiFeP with Tc ~ 5 K through the measurement of Knight
shift 31K and the spin-lattice relaxation rate 1/T1 at 31P site by nuclear
magnetic resonance. The constant 31K, small magnitudes of 1/T1T, along with the
resistivity rho ~ T^2 all point to the weak spin correlations in LiFeP. 1/T1T
display small enhancement toward Tc, indicating that the superconductivity is
intimately correlated with the antiferromagnetic spin fluctuations.",1403.4458v1
2008-07-20,$^{77}$Se NMR investigation of the field-induced spin-density-wave transitions in (TMTSF)$_2$ClO$_4$,"Complementary $^{77}$Se nuclear magnetic resonance (NMR) and electrical
transport have been used to correlate the spin density dynamics with the
subphases of the field-induced spin density wave (FISDW) ground state in \tmt.
We find that the peaks in the spin-lattice relaxation rate 1/T$_1$ appear
within the metal-FISDW phase boundary and/or at first-order subphase
transitions. In the quantum limit above 25 T, the NMR data gives an insight
into the FISDW electronic structure.",0807.3119v1
2008-07-22,Spinning fluid cosmology,"The dynamics of a spinning fluid in a flat cosmological model is
investigated. The space-time is itself generated by the spinning fluid which is
characterized by an energy-momentum tensor consisting a sum of the usual
perfect-fluid energy-momentum tensor and some Belinfante-Rosenfeld tensors. It
is shown that the equations of motion admit a solution for which the fluid
four-velocity and four-momentum are not co-linear in general. The momentum and
spin densities of the fluid are expressed in terms of the scale factor.",0807.3389v1
2011-11-24,Replica symmetry breaking in an adiabatic spin-glass model of adaptive evolution,"We study evolutionary canalization using a spin-glass model with replica
theory, where spins and their interactions are dynamic variables whose
configurations correspond to phenotypes and genotypes, respectively. The spins
are updated under temperature T_S, and the genotypes evolve under temperature
T_J, according to the evolutionary fitness. It is found that adaptation occurs
at T_S < T_S^{RS}, and a replica symmetric phase emerges at T_S^{RSB} < T_S <
T_S^{RS}. The replica symmetric phase implies canalization, and replica
symmetry breaking at lower temperatures indicates loss of robustness.",1111.5770v1
2012-01-02,Temperature dependence of the paramagnetic spin susceptibility of doped graphene,"In this work, we present a semi-analytical expression for the temperature
dependence of a spin-resolved dynamical density-density response function of
massless Dirac fermions within the Random Phase Approximation. This result is
crucial in order to describe thermodynamic properties of the interacting
systems. In particular, we use it to make quantitative predictions for the
paramagnetic spin susceptibility of doped graphene sheets. We find that, at low
temperatures, the spin susceptibility behaves like $T^{-2}$ which is completely
different from the temperature dependence of the magnetic susceptibility in
undoped graphene sheets.",1201.0434v1
2012-01-25,Quantum strings in quantum spin ice,"We study quantum spin ice in an external magnetic field applied along a
$<100>$ direction. When quantum spin fluctuations are weak, elementary
excitations are quantum strings with monopoles at their ends manifested as
multiple spin-wave branches in the dynamical structure factor. Strong quantum
fluctuations make the string tension negative and give rise to the
deconfinement of monopoles. We discuss our results in the light of recent
neutron scattering experiments in $\mathrm{Yb_2Ti_2O_7}$",1201.5314v3
2013-09-07,Fast spin control in a two-electron double quantum dot by dynamical invariants,"Inverse engineering of electric fields has been recently proposed to achieve
fast and robust spin control in a single-electron quantum dot with spin-orbit
coupling. In this paper we design, by inverse engineering based on
Lewis-Riesenfeld invariants, time-dependent electric fields to realize fast
transitions in the selected singlet-triplet subspace of a two-electron double
quantum dot. We apply two-mode driving schemes, directly employing the
Lewis-Riesenfeld phases, to minimize the electric field necessary to design
flexible protocols and perform spin manipulation on the chosen timescale.",1309.1916v1
2013-09-19,Quantum Fisher information and spin squeezing in one-axis twisting model,"We consider the quantum Fisher information and spin squeezing in one-axis
twisting model with a coherent spin state $|\theta_{0},\phi_{0}\rangle$. We
analytically discuss the dependence of the two parameters: spin squeezing
parameter $\xi^2_{K}$ and the average parameter estimation precision $\chi^2$
on the polar angle $\theta_{0}$ and the azimuth angle $\phi_0$. Moreover, we
discuss the effects of the collisional dephasing on the dynamics of the two
parameters. In this case, the analytical solution of $\xi^2_K$ is also
obtained.",1309.4842v2
2014-05-13,Nuclear Magnetometry Study of Spin Dynamics in Bilayer Quantum Hall Systems,"We performed a nuclear magnetometry study on quantum Hall ferromagnet with a
bilayer total filling factor of $\nu_{\rm{tot}} = 2$. We found not only a rapid
nuclear relaxation but also a sudden change in the nuclear spin polarization
distribution after a one-second interaction with a canted antiferromagnetic
phase. We discuss the possibility of observing cooperative phenomena coming
from nuclear spin ensemble triggered by electrons with collective spin
interactions.",1405.3015v2
2014-05-30,Real-Time Simulation of Large Open Quantum Spin Systems driven by Measurements,"We consider a large quantum system with spins $\frac{1}{2}$ whose dynamics is
driven entirely by measurements of the total spin of spin pairs. This gives
rise to a dissipative coupling to the environment. When one averages over the
measurement results, the corresponding real-time path integral does not suffer
from a sign problem. Using an efficient cluster algorithm, we study the
real-time evolution of a 2-d Heisenberg antiferromagnet, which is driven to a
disordered phase, either by sporadic measurements or by continuous monitoring
described by Lindblad evolution.",1405.7882v1
2014-06-26,An intrinsic way to control E-sail spin,"We show that by having the auxtethers made partly or completely of conducting
material and by controlling their voltages, it is possible to control the spin
rate of the electric solar wind sail by using the electric sail effect itself.
The proposed intrinsic spin rate control scheme has enough control authority to
overcome the secular change of the spin rate due to orbital Coriolis effect.",1406.6847v1
2015-12-28,Dynamical Quantum Phase Transitions in presence of a spin bath,"We derive an effective time independent Hamiltonian for the transverse Ising
model coupled to a spin bath, in the presence of a high frequency AC magnetic
field. We show that the spin blocking mechanism that removes the quantum phase
transition can be suppressed by the AC field, allowing high tunability of the
quantum critical point. Finally, we calculate the phase diagram within the RPA
approximation for the case of spin $7/2$ nuclei, appropriate to the
$LiHo_{x}Y_{1-x}F_{4}$ system.",1512.08315v3
2017-12-19,Spin generalization of the Calogero-Moser hierarchy and the matrix KP hierarchy,"We establish a correspondence between rational solutions to the matrix KP
hierarchy and the spin generalization of the Calogero-Moser system on the level
of hierarchies. Namely, it is shown that the rational solutions to the matrix
KP hierarchy appear to be isomorphic to the spin Calogero-Moser system in a
sense that the dynamics of poles of solutions to the matrix KP hierarchy in the
higher times is governed by the higher Hamiltonians of the spin Calogero-Moser
integrable hierarchy with rational potential.",1712.06943v3
2018-09-07,Optimal Spin Squeezed Steady State induced by the dynamics of non-hermtian hamiltonians,"In this work, we study the time evolution of a coherent spin state under the
action of a non-hermitian hamiltonian. The hamiltonian is modeled by a one-axis
twisting term plus a Lipkin-type interaction. We show that when the Lipkin
interaction is switched on, depending on the relative values of the coupling
constants, the initial state evolves into a steady squeezed state which
minimizes the Uncertainty Relations, Intelligent Spin State. We apply this
result to look for the generation of an steady intelligent spin state from an
ensemble of nitrogen vacancy colour centers in diamond coupled to a mechanical
resonator.",1809.02683v1
2018-10-29,Nonlinear Semi-Classical 3D Quantum Spin,"In an effort to provide an alternative method to represent a quantum spin, a
precise 3D nonlinear dynamics method is used. A two-sided torque function is
created to mimic the unique behavior of the quantum spin. A full 3D
representation of the magnetic field of a Stern-Gerlach device was used as in
the original experiment. Furthermore, the temporarily driven nonlinear damped
model exhibits chaos, but struggles to be consistent through azimuthal angles
in reproducing the quantum spin statistics.",1810.12424v1
2020-01-28,Spin-dependent two-photon Bragg scattering in the Kapitza-Dirac effect,"We present the possibility of spin-dependent Kapitza-Dirac scattering based
on a two-photon interaction only. The interaction scheme is inspired from a
Compton scattering process, for which we explicitly show the mathematical
correspondence to the spin-dynamics of an electron diffraction process in a
standing light wave. The spin effect has the advantage that it already appears
in a Bragg scattering setup with arbitrary low field amplitudes, for which we
have estimated the diffraction count rate in a realistic experimental setup at
available X-ray free-electron laser facilities.",2001.10177v2
2020-04-01,Entropy and specific heat of the infinite-dimensional three-orbital Hubbard model,"The Hund coupling in multiorbital Hubbard systems induces spin freezing and
associated Hund metal behavior. Using dynamical mean field theory, we explore
the effect of local moment formation, spin and charge excitations on the
entropy and specific heat of the three-orbital model. In particular, we
demonstrate a substantial enhancement of the entropy in the spin-frozen metal
phase at low temperatures, and peaks in the specific heat associated with the
activation of spin and charge fluctuations at high temperature. We also clarify
how these temperature scales depend on the interaction parameters and filling.",2004.00471v1
2020-04-30,Magnon Current Generation by Dynamical Distortion,"The interaction between spin and nanomechanical degrees of freedom attracts
interest from the viewpoint of basic science and device applications. We study
the magnon current induced by the torsional oscillation of ferromagnetic
nanomechanical cantilever. We find that a finite Dzyaloshinskii-Moriya (DM)
interaction emerges by the torsional oscillation, which is described by the
spin gauge field, and the DM interaction leads to the detectably-large magnon
current with frequency same as that of the torsional oscillation. Our theory
paves the way for studying torsional spin-nanomechanical phenomena by using the
spin gauge field.",2004.14707v1
2012-05-14,BRST-BV approach to cubic interaction vertices for massive and massless higher-spin fields,"Using BRST-BV formulation of relativistic dynamics, we study arbitrary spin
massive and massless fields propagating in flat space. Generating functions of
gauge invariant off-shell cubic interaction vertices for mixed-symmetry and
totally symmetric fields are obtained. For the case of totally symmetric
fields, we derive restrictions on the allowed values of spins and the number of
derivatives, which provide a classification of cubic interaction vertices for
such fields. As by product, we present simple expressions for the Yang-Mills
and gravitational interactions of massive totally symmetric arbitrary spin
fields.",1205.3131v1
2017-11-06,Exact spin-orbit qubit manipulation,"We consider exactly solvable manipulation of spin-qubits confined in a moving
harmonic trap and in the presence of the time dependent Rashba interaction.
Non-adiabatic Anandan phase for cyclic time evolution is compared to the
Wilczek-Zee adiabatic counterpart. It is shown that the ratio of these two
phases can for a chosen system be any real number. Next we demonstrate the
possibility of arbitrary qubit transformation in a ring with spin-orbit
interaction. Finally, we present an example of exact analysis of spin-orbit
dynamics influenced by the Ornstein-Uhlenbeck coloured noise.",1711.02134v1
2018-06-19,Scalar Tops and Perturbed Quadrupoles: Probing Fundamental Physics with Spin-Precessing Binaries,"Parity violation in the gravitational interaction has an important impact on
fundamental observables and the evolution of the universe. We here investigate
for the first time our ability to probe the parity violating nature of the
gravitational interaction using gravitational waves from spin-precessing
binaries. Focusing on dynamical Chern-Simons gravity, we derive the
spin-precession equations, calculate the gravitational waves emitted by
spin-precessing, quasi-circular black hole binaries and estimate the level to
which the theory could be constrained with future gravitational wave
observations.",1806.07425v1
2018-08-23,Conformal Higher-Spin Gravity: Linearized Spectrum = Symmetry Algebra,"The linearized spectrum and the algebra of global symmetries of conformal
higher-spin gravity decompose into infinitely many representations of the
conformal algebra. Their characters involve divergent sums over spins. We
propose a suitable regularization adapted to their evaluation and observe that
their characters are actually equal. This result holds in the case of type-A
and type-B (and their higher-depth generalizations) theories and confirms
previous observations on a remarkable rearrangement of dynamical degrees of
freedom in conformal higher-spin gravity after regularization.",1808.07728v2
2018-12-05,Magnetic control of polariton spin transport,"We show the full control of the polarization dynamics of a propagating
exciton-polariton condensate in a planar microcavity by using a magnetic field
applied in the Voigt geometry. The change of the spin-beat frequency, the
suppression of the optical spin Hall effect and the rotation of the
polarization pattern by the magnetic field are theoretically reproduced by
accounting for the magneto-induced mixing of exciton-polariton and dark, spin
forbidden, exciton states.",1812.01919v1
2019-01-02,Relativistic fluid dynamics of spin-polarized systems of particles,"We review basic ingredients of the recently introduced perfect-fluid
hydrodynamic equations for particles with spin one-half. For a quasi-realistic
setup, first numerical solutions for various hydrodynamic variables including
the spin polarization tensor are presented. Our results indicate that the
initial spin polarization of the hottest region may play a dominant role in the
polarization of particles at freeze-out.",1901.00352v1
2019-04-05,Microwave Scattering in the Subohmic Spin-Boson Systems of Superconducting Circuits,"We study quantum critical phenomena in the microwave scattering of the
subohmic spin-boson system, which exhibits a quantum phase transition at a
critical system-reservoir coupling. By relating the reflection coefficient of a
microwave with the dynamic susceptibility of the subohmic spin-boson system, we
clarify the appearance of quantum critical phenomena in microwave scattering.
Further, we propose experimental setups to realize the subohmic spin-boson
system in a superconducting circuit composed of a charge qubit and a
dissipative transmission line.",1904.03051v3
2020-10-05,Localized excitations and scattering of spin waves in ferromagnetic chains containing magnetic nanoclusters,"The spectrum of localized excitations in an anisotropic one-dimensional
ferromagnet containing a spin cluster of arbitrary size is found exactly within
the framework of the discrete Takeno-Homma model. The boundaries of stability
of spin nanoclusters are determined, depending on their size, and the exchange
and the anisotropy parameter of the ferromagnet. The problem of the spin waves
scattering against nanoclusters is solved and explicit analytical expressions
for their reflection and transmission coefficients are obtained. A model of a
metamaterial consisting of weakly interacting magnetic molecular nanoclusters
and possessing revealed dynamic properties is proposed.",2010.01861v1
2021-03-31,Spin charge conversion in Rashba split ferromagnetic interfaces,"We show here theoretically and experimentally that a Rashba-split electron
state inside a ferromagnet can efficiently convert a dynamical spin
accumulation into an electrical voltage. The effect is understood to stem from
the Rashba splitting but with a symmetry linked to the magnetization direction.
It is experimentally measured by spin pumping in a CoFeB/MgO structure where it
is found to be as efficient as the inverse spin Hall effect at play when Pt
replaces MgO, with the extra advantage of not affecting the damping in the
ferromagnet.",2103.16867v1
2021-09-07,Creating moving gap solitons in spin-orbit-coupled Bose-Einstein condensates,"A simple and efficient method to create gap solitons is proposed in a
spin-orbit-coupled spin-1 Bose-Einstein condensate. We find that a free
expansion along the spin-orbit coupling dimension can generate two moving gap
solitons, which are identified from a generalized massive Thirring model. The
dynamics of gap solitons can be controlled by adjusting spin-orbit coupling
parameters.",2109.02871v1
2021-09-21,Torque-free manipulation of nanoparticle rotations via embedded spins,"Spin angular momentum and mechanical rotation both contribute to the total
angular momentum of rigid bodies, leading to spin-rotational coupling via the
Einstein-de Haas and Barnett effects. Here we show that the revolutions of
symmetric nanorotors can be strongly affected by a small number of intrinsic
spins. The resulting dynamics are observable with freely rotating nanodiamonds
with embedded nitrogen-vacancy centers and persist for realistically-shaped
near-symmetric particles, opening the door to torque-free schemes to control
their rotations at the quantum level.",2109.10340v2
2021-10-06,Superfield approach to interacting N=2 massive and massless supermultiplets in 3d flat space,"Massive arbitrary spin supermultiplets and massless (scalar and spin
one-half) supermultiplets of the N=2 Poincare superalgebra in three-dimensional
flat space are considered. Both the integer spin and half-integer spin
supermultiplets are studied. For such massive and massless supermultiplets, a
formulation in terms of light-cone gauge unconstrained superfields defined in a
momentum superspace is developed. For the supermultiplets under consideration a
superspace first derivative representation for all cubic interaction vertices
is obtained. A superspace representation for dynamical generators of the N=2
Poincare superalgebra is also found.",2110.02696v1
2022-07-15,Target normal single-spin asymmetry in inclusive electron-nucleon scattering with two-photon exchange: Analysis using $1/N_c$ expansion,"We calculate the target normal single-spin asymmetry caused by two-photon
exchange in inclusive electron-nucleon scattering in the resonance region. Our
analysis uses the $1/N_c$ expansion of low-energy QCD and combines $N$ and
$\Delta$ intermediate and final states using the contracted $SU(4)$ spin-flavor
symmetry. The normal spin asymmetry obtained in leading-order accuracy in
$1/N_c$ has magnitude $\sim 10^{-2}$ and different sign in $ep$ and $en$
scattering. It can be measured in electron scattering at lab energies $\sim$
0.5-1.5 GeV and provides a clean probe of two-photon exchange dynamics.",2207.07588v1
2022-07-26,Rectification of the spin Seebeck current in noncollinear antiferromagnets,"In the absence of an external magnetic field and a spin-polarized charge
current, an antiferromagnetic system supports two degenerate magnon modes. An
applied thermal bias activates the magnetic dynamics, leading to a magnon flow
from the hot to the cold edge (magnonic spin Seebeck current). Both degenerate
bands contribute to the magnon current but the orientations of the magnetic
moments underlying the magnons are opposite in different bands. Therefore,
while the magnon current is nonzero, the net spin current is zero.",2207.12890v1
2023-01-08,Prethermal time-crystalline spin ice and monopole confinement in a driven magnet,"Studies on systems far from equilibrium open up new avenues for investigating
exotic phases of matter. A driven-dissipative frustrated spin system is
examined in this study, and we suggest an out-of-equilibrium non-magnetic phase
where the spins do not order but adhere to the ice rule in space and establish
a long-range crystalline order in time. In contrast to the conventional spin
ice, the dynamics of monopoles is confined due to the nonequilibrium feature of
our model. Possible experimental realizations of our model has been discussed.",2301.03054v3
2023-05-25,Vortex spin in a superfluid,"General relativity predicts that the curvature of spacetime induces spin
rotations on a parallel transported particle. We deploy Unruh's analogue
gravity picture and consider a quantised vortex embedded in a two-dimensional
superfluid Bose--Einstein condensate. We show that such a vortex behaves
dynamically like a charged particle with a spin in a gravitational field. The
existence of a vortex spin in a superfluid complements Onsager's prediction of
the quantisation of circulation, and is suggestive of potential quantum
technology applications of rotating superfluids.",2305.16016v1
2023-05-31,Hidden covalent insulator and spin excitations in SrRu$_2$O$_6$,"The density functional plus dynamical mean-field theory is used to study the
spin excitation spectra of SrRu$_2$O$_6$. A good quantitative agreement with
experimental spin excitation spectra is found. Depending on the size of the
Hund's coupling $J_H$ the systems chooses either Mott insulator or covalent
insulator state when magnetic ordering is not allowed. We find that the nature
of the paramagnetic state has negligible influence on the charge and spin
excitation spectra. We find that antiferromagnetic correlations hide the
covalent insulator state for realistic choices of the interaction parameters.",2305.19826v2
2023-07-22,Spin-orbit-coupling-induced phase separation in trapped Bose gases,"In a trapped spin-1/2 Bose-Einstein condensate with miscible interactions, a
two-dimensional spin-orbit coupling can introduce an unconventional spatial
separation between the two components. We reveal the physical mechanism of such
a spin-orbit-coupling-induced phase separation. Detailed features of the phase
separation are identified in a trapped Bose-Einstein condensate. We further
analyze differences of phase separation in Rashba and anisotropic
spin-orbit-coupled Bose gases. An adiabatic splitting dynamics is proposed as
an application of the phase separation.",2307.12177v2
2023-11-30,Antiferromagnetic droplet soliton driven by spin current,"We demonstrate that a spin current flowing through a nano-contact into a
uniaxial antiferromagnet with first- and second-order anisotropy can excite a
self-localized dynamic magnetic soliton, known as a spin-wave droplet in
ferromagnets. The droplet nucleates at a certain threshold current with the
frequency of the N\'eel vector precession laying below the antiferromagnetic
resonance. The frequency exhibits nonlinear behavior with the increasing of
applied current. At the high value of applied torque, the soliton mode
transforms, and the oscillator emits spin waves propagating in the
antiferromagnetic layer.",2311.18583v1
2014-01-08,Dynamic exchange via spin currents in acoustic and optical modes of ferromagnetic resonance in spin-valve structures,"Two ferromagnetic layers magnetically decoupled by a thick normal metal
spacer layer can be, nevertheless, dynamically coupled via spin currents
emitted by the spin-pump and absorbed through the spin-torque effects at the
neighboring interfaces. A decrease of damping in both layers due to a partial
compensation of the angular momentum leakage in each layer was previously
observed at the coincidence of the two ferromagnetic resonances. In case of
non-zero magnetic coupling, such a dynamic exchange will depend on the mutual
precession of the magnetic moments in the layers. A difference in the linewidth
of the resonance peaks is expected for the acoustic and optical regimes of
precession. However, the interlayer coupling hybridizes the resonance responses
of the layers and therefore can also change their linewidths. The interplay
between the two mechanisms has never been considered before. In the present
work, the joint influence of the hybridization and non-local damping on the
linewidth has been studied in weakly coupled NiFe/CoFe/Cu/CoFe/MnIr spin-valve
multilayers. It has been found that the dynamic exchange by spin currents is
different in the optical and acoustic modes, and this difference is dependent
on the interlayer coupling strength. In contrast to the acoustic precession
mode, the dynamic exchange in the optical mode works as an additional damping
source. A simulation in the framework of the Landau-Lifshitz-Gilbert formalism
for two ferromagnetic layers coupled magnetically and by spin currents has been
done to separate the effects of the non-local damping from the resonance modes
hybridization. In our samples both mechanisms bring about linewidth changes of
the same order of magnitude, but lead to a distinctly different angular
behavior. The obtained results are relevant for a broad class of coupled
magnetic multilayers with ballistic regime of the spin transport.",1401.1672v1
2015-01-12,A detailed and unified treatment of spin-orbit systems using tools distilled from the theory of bundles,"We return to our study \cite{BEH} of invariant spin fields and spin tunes for
polarized beams in storage rings but in contrast to the continuous-time
treatment in \cite{BEH}, we now employ a discrete-time formalism, beginning
with the $\rm{Poincar\acute{e}}$ maps of the continuous time formalism. We then
substantially extend our toolset and generalize the notions of invariant spin
field and invariant frame field. We revisit some old theorems and prove several
theorems believed to be new. In particular we study two transformation rules,
one of them known and the other new, where the former turns out to be an
$SO(3)$-gauge transformation rule. We then apply the theory to the dynamics of
spin-$1/2$ and spin-$1$ particle bunches and their density matrix functions,
describing semiclassically the particle-spin content of bunches. Our approach
thus unifies the spin-vector dynamics from the T-BMT equation with the
spin-tensor dynamics and other dynamics. This unifying aspect of our approach
relates the examples elegantly and uncovers relations between the various
underlying dynamical systems in a transparent way. As in \cite{BEH}, the
particle motion is integrable but we now allow for nonlinear particle motion on
each torus. Since this work is inspired by notions from the theory of bundles,
we also provide insight into the underlying bundle-theoretic aspects of the
well-established concepts of invariant spin field, spin tune and invariant
frame field. Since we neglect, as is usual, the Stern-Gerlach force, the
underlying principal bundle is of product formso that we can present the theory
in a fashion which does not use bundle theory. Nevertheless we occasionally
mention the bundle-theoretic meaningof our concepts and we also mention the
similarities with the geometrical approach to Yang-Mills Theory.",1501.02747v1
2021-04-21,"Spin dynamics in the Kitaev model with disorder: Quantum Monte Carlo study of dynamical spin structure factor, magnetic susceptibility, and NMR relaxation rate","We investigate the impact of two types of disorder, bond randomness and site
dilution, on the spin dynamics in the Kitaev model on a honeycomb lattice. The
ground state of this model is a canonical quantum spin liquid with spin
fractionalization into two types of quasiparticles, itinerant Majorana fermions
and localized fluxes. Using unbiased quantum Monte Carlo simulations, we
calculate the temperature evolution of the dynamical spin structure factor, the
magnetic susceptibility, and the NMR relaxation rate. In the dynamical spin
structure factor, we find that the two types of disorder affect seriously the
low-energy peak dominantly originating from the flux excitations, rather than
the high-energy continuum from the Majorana excitations, in a different way:
The bond randomness softens the peak to the lower energy with broadening,
whereas the site dilution smears the peak and in addition develops the other
sharp peaks inside the spin gap including the zero energy. We show that the
zero-energy spin excitations, which originate from the Majorana zero modes
induced around the site vacancies, survive up to the temperature comparable to
the energy scale of the Kitaev interaction. For the bond randomness, the
low-temperature susceptibility does not show any qualitative change against the
weak disorder, but it changes to divergent behavior while increasing the
strength of disorder. Similar distinct behaviors for the weak and strong
disorder are observed also in the NMR relaxation rate; an exponential decay
changes into a power-law decay. In contrast, for the site dilution, we find no
such crossover; divergent behavior in the susceptibility and a power-law decay
in the NMR relaxation rate appear immediately with the introduction of the site
dilution. We discuss the relevance of our results to experiments for the Kitaev
candidate materials with disorders.",2104.10549v1
1995-08-25,Dynamics of quantum spin systems in dimer and valence-bond solid ground states stabilized by competing interactions,"For special coupling ratios, the one-dimensional (1D) s=1/2 Heisenberg model
with antiferromagnetic nearest and next-nearest neighbor interactions has a
pure dimer ground state, and the 1D s=1 Heisenberg model with antiferromagnetic
bilinear and biquadratic interactions has an exact valence-bond-solid ground
state. The recursion method is used to calculate the T=0 spin dynamic structure
factor for both models and, for the s=1/2 model, also the dimer dynamic
structure factor. New results for line shapes and dynamically relevant
dispersions are obtained.",9508124v1
1996-01-23,Equilibrium dynamics of the dissipative two-state system,"Wilson's momentum shell renormalization group method is used to solve for the
dynamics of the dissipative two--state system. We utilize the mapping of the
spin--boson model onto the anisotropic Kondo model (AKM) and solve for the
dynamics of the latter. We find that the AKM captures the physics of the
dissipative two--state system for dissipation strength $0\leq\alpha\leq 4$
corresponding to $\infty\geq J_{\parallel}\geq -\infty$ in the AKM. The
dynamics of the AKM shows a smooth crossover between two strong coupling
regimes corresponding to weak and strong dissipation in the spin--boson model.",9601107v1
1997-05-02,High-Temperature Dynamics of Spin Glasses,"We develop a systematic expansion method of physical quantities for the SK
model and the finite-dimensional $\pm J$ model of spin glasses in
non-equilibrium states. The dynamical probability distribution function is
derived from the master equation using a high temperature expansion. We
calculate the expectation values of physical quantities from the dynamical
probability distribution function. The theoretical curves show satisfactory
agreement with Monte Carlo simulation results in the appropriate temperature
and time regions. A comparison is made with the results of a dynamics theory by
Coolen, Laughton and Sherrington.",9705019v1
1999-09-09,Application of the Projected Dynamics Method to an Anisotropic Heisenberg Model,"The Projected Dynamics method was originally developed to study metastable
decay in ferromagnetic discrete spin models. Here, we apply it to a classical,
continuous Heisenberg model with anisotropic ferromagnetic interactions, which
evolves under a Monte Carlo dynamic. The anisotropy is sufficiently large to
allow comparison with the Ising model. We describe the Projected Dynamics
method and how to apply it to this continuous-spin system. We also discuss how
to extract metastable lifetimes and how to extrapolate from small systems to
larger systems.",9909142v1
1999-10-15,Different Scenarios for Critical Glassy Dynamics,"We study the role of different terms in the $N$-body potential of glass
forming systems on the critical dynamics near the glass transition. Using a
simplified spin model with quenched disorder, where the different terms of the
real $N$-body potential are mapped into multi-spin interactions, we identified
three possible scenarios. For each scenario we introduce a ``minimal'' model
representative of the critical glassy dynamics near, both above and below, the
critical transition lin e. For each ``minimal'' model we discuss the low
temperature equilibrium dynamics.",9910235v2
2002-04-25,Dynamical Properties of One-Dimensional Multicomponent Quantum Liquids in Metallic Phase,"We investigate low-energy dynamical properties of one-dimensional
multicomponent quantum liquids with the short-range interaction as well as the
$1/x$-type long-range interaction. By calculating the single-particle spectrum
and the dynamical spin susceptibility by means of the bosonization method, we
discuss how the orbital degeneracy and the band splitting affect the dynamical
response functions. The effect of the long-range interaction is also addressed.
Although the long-range interaction suppresses charge fluctuations, it
effectively enhances spin fluctuations via the formation of the Wigner crystal.",0204567v1
2004-06-21,Dynamics and thermodynamics in spinor quantum gases,"We discuss magnetism in spinor quantum gases theoretically and experimentally
with emphasis on temporal dynamics of the spinor order parameter in the
presence of an external magnetic field. In a simple coupled Gross-Pitaevskii
picture we observe a dramatic suppression of spin dynamics due to quadratic
Zeeman ''dephasing''. In view of an inhomogeneous density profile of the
trapped condensate we present evidence of spatial variations of spin dynamics.
In addition we study spinor quantum gases as a model system for thermodynamics
of Bose-Einstein condensation. As a particular example we present measurements
on condensate magnetisation due to the interaction with a thermal bath.",0406485v1
2005-06-24,Lifetime of dynamic heterogeneity in strong and fragile kinetically constrained spin models,"Kinetically constrained spin models are schematic coarse-grained models for
the glass transition which represent an efficient theoretical tool to study
detailed spatio-temporal aspects of dynamic heterogeneity in supercooled
liquids. Here, we study how spatially correlated dynamic domains evolve with
time and compare our results to various experimental and numerical
investigations. We find that strong and fragile models yield different results.
In particular, the lifetime of dynamic heterogeneity remains constant and
roughly equal to the alpha relaxation time in strong models, while it increases
more rapidly in fragile models when the glass transition is approached.",0506629v1
2006-06-29,Spin and charge dynamics of the one-dimensional extended Hubbard model,"We investigate the dynamical spin and charge structure factors and the
one-particle spectral function of the one-dimensional extended Hubbard model at
half band-filling using the dynamical density-matrix renormalization group
method. The influence of the model parameters on these frequency- and
momentum-resolved dynamical correlation functions is discussed in detail for
the Mott-insulating regime. We find quantitative agreement between our
numerical results and experiments for the optical conductivity, resonant
inelastic X-ray scattering, neutron scattering, and angle-resolved
photoemission spectroscopy in the quasi-one-dimensional Mott insulator
SrCuO$_2$.",0606748v1
2002-03-19,Transfer operators and dynamical zeta functions for a class of lattice spin models,"We investigate the location of zeros and poles of a dynamical zeta function
arizing in a class of lattice spin models introduced in the 60-ties by M. Kac.
The transfer operator method allows us to prove the xistence of infinitely
nontrivial zeros of this function on the real line. For certain parameter
values there exist also infinitely many trivial equally spaced zeros on a line
parallel to the imaginary axis. Hence also for this kind of dynamical zeta
function some kind of Riemann hypothesis seems to hold.",0203191v1
2007-01-03,Meromorphic continuation of dynamical zeta functions via transfer operators,"We describe a general method to prove meromorphic continuation of dynamical
zeta functions to the entire complex plane under the condition that the
corresponding partition functions are given via a dynamical trace formula from
a family of transfer operators. Further we give general conditions for the
partition functions associated with general spin chains to be of this type and
provide various families of examples for which these conditions are satisfied.
  Keywords: Dynamical zeta function, transfer operator, trace formulae,
thermodynamic formalism, spin chain, Fock space, regularized determinants,
weighted composition operator.",0701097v1
2000-01-13,Propagation of Molecular Chaos by Quantum Systems and the Dynamics of the Curie-Weiss Model,"The propagation of molecular chaos, a tool of classical kinetic theory, is
generalized to apply to quantum systems of distinguishable particles. We prove
that the Curie-Weiss model of ferromagnetism propagates molecular chaos and
derive the effective dynamics of a single-spin state in the mean-field limit.
Our treatment differs from the traditional approach to mean-field spin models
in that it concerns the dynamics of single-particle states instead of the
dynamics of infinite-particle states.",0001018v1
2007-10-18,Dynamics in One-Dimensional Spin Systems - Density-Matrix Renormalization Group Study,"We study the one-dimensional $S=1/2$ Heisenberg model with a uniform and a
staggered magnetic fields, using the dynamical density-matrix renormalization
group (DDMRG) technique. The DDMRG enables us to investigate the dynamical
properties of chain with lengths up to a few hundreds, and the results are
numerically exact in the same sense as 'exact diagonalization' results are.
Thus, we can analyze the low-energy spectrum almost in the thermodynamic limit.
In this work, we calculate the dynamical spin structure factor and demonstrate
the performance of the DDMRG method applying the open-end boundary condition as
well as the periodic boundary condition.",0710.3506v1
2007-12-15,Dynamic structure factors of the spin-1/2 XX chain with Dzyaloshinskii-Moriya interaction,"We consider the spin-1/2 isotropic XY chain in a (z) transverse magnetic
field with the Dzyaloshinskii-Moriya interaction directed along the z-axis in
spin space and examine the effects of the latter interaction on the zz, xx (yy)
and xy (yx) dynamic structure factors. The Dzyaloshinskii-Moriya interaction
does not manifest itself in the zz dynamic quantities. In contrast, the xx (yy)
and xy (yx) dynamic structure factors show dramatical changes owing to the
Dzyaloshinskii-Moriya interaction. Implications of our results for electron
spin resonance experiments are briefly discussed.",0712.2507v1
2009-07-10,Parallel dynamics of disordered Ising spin systems on finitely connected directed random graphs with arbitrary degree distributions,"We study the stochastic parallel dynamics of Ising spin systems defined on
finitely connected directed random graphs with arbitrary degree distributions,
using generating functional analysis. For fully asymmetric graphs the dynamics
of the system can be completely solved, due to the asymptotic absence of loops.
For arbitrary graph symmetry, we solve the dynamics exactly for the first few
time steps, and we construct approximate stationary solutions.",0907.1699v2
2010-10-06,Theory of Local Dynamical Magnetic Susceptibilities from the Korringa-Kohn-Rostoker Green Function Method,"Within the framework of time-dependent density functional theory combined
with the Korringa-Kohn-Rostoker Green function formalism, we present a real
space methodology to investigate dynamical magnetic excitations from
first-principles. We set forth a scheme which enables one to deduce the correct
effective Coulomb potential needed to preserve the spin-invariance signature in
the dynamical susceptibilities, i.e. the Goldstone mode. We use our approach to
explore the spin dynamics of 3d adatoms and different dimers deposited on a
Cu(001) with emphasis on their decay to particle-hole pairs.",1010.1293v1
2011-02-14,Application of Resonance Perturbation Theory to Dynamics of Magnetization in Spin Systems Interacting with Local and Collective Bosonic Reservoirs,"We apply our recently developed resonance perturbation theory to describe the
dynamics of magnetization in paramagnetic spin systems interacting
simultaneously with local and collective bosonic environments. We derive
explicit expressions for the evolution of the reduced density matrix elements.
This allows us to calculate explicitly the dynamics of the macroscopic
magnetization, including characteristic relaxation and dephasing time-scales.
We demonstrate that collective effects (i) do not influence the character of
the relaxation processes but merely renormalize the relaxation times, and (ii)
significantly modify the dephasing times, leading in some cases to a
complicated (time inhomogeneous) dynamics of the transverse magnetization,
governed by an effective time-dependent magnetic field.",1102.2847v1
2011-03-29,Transfer operator analysis of the parallel dynamics of disordered Ising chains,"We study the synchronous stochastic dynamics of the random field and random
bond Ising chain. For this model the generating functional analysis methods of
De Dominicis leads to a formalism with transfer operators, similar to transfer
matrices in equilibrium studies, but with dynamical paths of spins and
(conjugate) fields as arguments, as opposed to replicated spins. In the
thermodynamic limit the macroscopic dynamics is captured by the dominant
eigenspace of the transfer operator, leading to a relative simple and
transparent set of equations that are easy to solve numerically. Our results
are supported excellently by numerical simulations.",1103.5595v1
2013-05-25,Thermally-Assisted Spin-Transfer Torque Dynamics in Energy Space,"We consider the general Landau-Lifshitz-Gilbert theory underlying the
magnetization dynamics of a macrospin magnet subject to spin-torque effects and
thermal fluctuations. Thermally activated dynamical properties are analyzed by
averaging the full magnetization equations over constant- energy orbits. After
averaging, all the relevant dynamical scenarios are a function of the ratio
between hard and easy axis anisotropies. We derive analytically the range of
currents for which limit cycles exist and discuss the regimes in which the
constant energy orbit averaging technique is applicable.",1305.5945v2
2013-12-13,Multi-channel Kondo impurity dynamics in a Majorana device,"We study the multi-channel Kondo impurity dynamics realized in a mesoscopic
superconducting island connected to metallic leads. The effective 'impurity
spin' is non-locally realized by Majorana bound states and strongly coupled to
lead electrons by non-Fermi liquid correlations. We explore the spin dynamics
and its observable ramifications near the low-temperature fixed point. The
topological protection of the system raises the perspective to observe
multi-channel Kondo impurity dynamics in experimentally realistic environments.",1312.3802v3
2015-09-14,Same-spin dynamical correlation effects on the electron localization,"The Electron Localization Function (ELF) -- as proposed originally by Becke
and Edgecombe -- has been widely adopted as a descriptor of atomic shells and
covalent bonds. The ELF takes into account the antisymmetry of Fermions but it
neglects the multi-reference character of a truly interacting many-electron
state. Electron-electron interactions induce, schematically, different kind of
correlations: non-dynamical correlations mostly affect stretched molecules and
strongly correlated systems; dynamical correlations dominate in weakly
correlated systems. Here, within an affordable computational effort, we
estimate the effects of same-spin dynamical correlations on the electron
localization by means of a simple modification of the ELF.",1509.04089v1
2013-09-17,Cavity-Assisted Dynamical Spin-Orbit Coupling in Cold Atoms,"We consider ultracold atoms subjected to a cavity-assisted two-photon Raman
transition. The Raman coupling gives rise to effective spin-orbit interaction
which couples atom's center-of-mass motion to its pseudospin degrees of
freedom. Meanwhile, the cavity photon is dynamically affected by the atom. This
feedback between atom and photon leads to a dramatic modification of the atomic
dispersion relation, and further leads to dynamical instability of the system.
We propose to detect the change of cavity photon number as a direct way to
demonstrate dynamical instability.",1309.4369v2
2018-10-04,Domain wall dynamics in easy-cone magnets,"We theoretically and numerically investigate magnetic domain wall dynamics in
a nanowire of easy-cone magnet. The easy-cone domain wall exhibits several
distinguishing dynamic features in comparison to the easy-axis domain wall. The
features of easy-cone domain wall are related to the generation of additional
chiral spin textures due to the domain wall precession, which is common for
various driving sources such as magnetic fields and spin-transfer torques. The
unique easy-cone domain wall dynamics could enrich magnetic domain wall study
and find use in device applications based on easy-cone domain walls.",1810.02216v1
2019-07-29,Magnetization Dynamics in Holographic Ferromagnets: Landau-Lifshitz Equation from Yang-Mills Fields,"We introduce a new approach to understand magnetization dynamics in
ferromagnets based on the holographic realization of ferromagnets. A
Landau-Lifshitz equation describing the magnetization dynamics is derived from
a Yang-Mills equation in the dual gravitational theory, and temperature
dependences of the spin-wave stiffness and spin transfer torque appearing in
the holographic Landau-Lifshitz equation are investigated by the holographic
approach. The results are consistent with the known properties of magnetization
dynamics in ferromagnets with conduction electrons.",1907.12306v1
2018-06-05,Dynamic structure factor of disordered quantum spin ladders,"We investigate the impact of quenched disorder on the dynamical correlation
functions of two-leg quantum spin ladders. Perturbative continuous unitary
transformations with the help of white graphs and bond-operator mean-field
theory are used to calculate the one- and two-triplon contribution of the
zero-temperature dynamical structure factor. Disorder results in huge effects
on quasi-particles as well as composite bound states due to localization. This
leads to intriguing quantum structures in dynamical correlation functions well
observable in spectroscopic experiments.",1806.01717v1
2020-03-02,SU$(2|1)$ supersymmetric spinning models of chiral superfields,"We construct SU$(2|1)$, $d=1$ supersymmetric models based on the coupling of
dynamical and semi-dynamical (spin) multiplets, where the interaction term of
both multiplets is defined on the generalized chiral superspace. The dynamical
multiplet is defined as a chiral multiplet ${\bf (2,4,2)}$, while the
semi-dynamical multiplet is associated with a multiplet ${\bf (4,4,0)}$ of the
mirror type.",2003.01023v3
2003-06-06,Non-Ergodic Nuclear Depolarization in Nano-Cavities,"Recently, it has been observed that the effective dipolar interactions
between nuclear spins of spin-carrying molecules of a gas in a closed
nano-cavities are independent of the spacing between all spins. We derive exact
time-dependent polarization for all spins in spin-1/2 ensemble with spatially
independent effective dipolar interactions. If the initial polarization is on a
single (first) spin,$P_1(0)= 1$ then the exact spin dynamics of the model is
shown to exhibit a periodical short pulses of the polarization of the first
spin, the effect being typical of the systems having a large number, $N$, of
spins. If $N \gg 1$, then within the period $4\pi/g$ ($2\pi/g$) for odd (even)
$N$-spin clusters, with $g$ standing for spin coupling, the polarization of
spin 1 switches quickly from unity to the time independent value, 1/3, over the
time interval about $(g\sqrt{N})^{-1}$, thus, almost all the time, the spin 1
spends in the time independent condition $P_1(t)= 1/3$. The period and the
width of the pulses determine the volume and the form-factor of the ellipsoidal
cavity. The formalism is adopted to the case of time varying nano-fluctuations
of the volume of the cavitation nano-bubbles. If the volume $V(t)$ is varied by
the Gaussian-in-time random noise then the envelope of the polarization peaks
goes irreversibly to 1/3. The polarization dynamics of the single spin exhibits
the Gaussian (or exponential) time dependence when the correlation time of the
fluctuations of the nano-volume is larger (or smaller) than the $<(\delta g)^2
>^{-1/2} $, where the $<(\delta g)^2>$ is the variance of the $g(V(t))$
coupling. Finally, we report the exact calculations of the NMR line shape for
the $N$-spin gaseous aggregate.",0306055v2
2007-12-31,"Spin dynamics and spin freezing behavior in the two-dimensional antiferromagnet NiGa$_{2}$S$_{4}$ revealed by Ga-NMR, NQR and $μ$SR measurements","We have performed $^{69,71}$Ga nuclear magnetic resonance (NMR) and nuclear
quadrupole resonance (NQR) and muon spin rotation/resonance on the quasi
two-dimensional antiferromagnet (AFM) NiGa$_2$S$_4$, in order to investigate
its spin dynamics and magnetic state at low temperatures. Although there exists
only one crystallographic site for Ga in NiGa$_2$S$_4$, we found two distinct
Ga signals by NMR and NQR. The origin of the two Ga signals is not fully
understood, but possibly due to stacking faults along the c axis which induce
additional broad Ga NMR and NQR signals with different local symmetries. We
found the novel spin freezing occurring at $T_{\rm f}$, at which the specific
heat shows a maximum, from a clear divergent behavior of the nuclear
spin-lattice relaxation rate $1/T_{1}$ and nuclear spin-spin relaxation rate
$1/T_{2}$ measured by Ga-NQR as well as the muon spin relaxation rate
$\lambda$. The main sharp NQR peaks exhibit a stronger tendency of divergence,
compared with the weak broader spectral peaks, indicating that the spin
freezing is intrinsic in NiGa$_2$S$_4$. The behavior of these relaxation rates
strongly suggests that the Ni spin fluctuations slow down towards $T_{\rm f}$,
and the temperature range of the divergence is anomalously wider than that in a
conventional magnetic ordering. A broad structureless spectrum and
multi-component $T_1$ were observed below 2 K, indicating that a static
magnetic state with incommensurate magnetic correlations or inhomogeneously
distributed moments is realized at low temperatures. However, the wide
temperature region between 2 K and $T_{\rm f}$, where the NQR signal was not
observed, suggests that the Ni spins do not freeze immediately below $T_{\rm
f}$, but keep fluctuating down to 2 K with the MHz frequency range.",0801.0190v1
2018-04-22,Spontaneous spinning of a rattleback placed on vibrating platform,"The spontaneous spinning of a rattleback placed on a vibrating platform is
investigated. The rattleback is a toy with some curious properties. When placed
on a surface with reasonable friction, the rattleback has a preferred direction
of spin. If rotated anti to it, longitudinal vibrations are set up and spin
direction is reversed.
  In this paper, the dynamics of a rattleback placed on a sinusoidally
vibrating platform are simulated. We can expect base vibrations to excite the
pitch motion of the rattleback, which, because of the coupling between pitch
and spin motion, should cause the rattleback to spin. Results are presented
which show that this indeed is the case- the rattleback has a mono-peak spin
resonance with respect to base vibrations. The rattleback, thus, transduces
translating vibrations into continuous rotary motion and, therefore, is ideal
for applications in Energy harvesting and Vibration sensing.
  The dynamic response of the rattleback was found to be composed of two
principal frequencies that appeared in the pitch and rolling motions. One of
the frequencies was found to have a large coupling with the spin of the
rattleback. Spin resonance was found to occur when the base oscillatory
frequency was twice the value of the coupled frequency. A linearized model is
developed which can predict the values of the two frequencies accurately and
analytical expressions for the same in terms of the parameters of the
rattleback have been derived. The analysis, thus, forms an effective and easy
method for obtaining the spin resonant frequency of a given rattleback.
  Novel ideas for applications utilizing the phenomenon of spin resonance, for
example, an energy harvester composed of a magnetized rattleback surrounded by
ferromagnetic walls and a small scale vibration sensor comprising an array of
several magnetized rattlebacks, are included.",1804.08163v1
2016-11-13,Electron-nuclear spin dynamics of Ga$^{2+}$ paramagnetic centers probed by spin dependent recombination: A master equation approach,"Similar to nitrogen-vacancy centers in diamond and impurity atoms in silicon,
interstitial gallium deep paramagnetic centers in GaAsN have been proven to
have useful characteristics for the development of spintronic devices. Among
other interesting properties, under circularly polarized light, gallium centers
in GaAsN act as spin filters that dynamically polarize free and bound electrons
reaching record spin polarizations (100\%). Furthermore, the recent observation
of the amplification of the spin filtering effect under a Faraday configuration
magnetic field has suggested that the hyperfine interaction that couples bound
electrons and nuclei permits the optical manipulation of its nuclear spin
polarization. Even though the mechanisms behind the nuclear spin polarization
in gallium centers are fairly well understood, the origin of nuclear spin
relaxation and the formation of an Overhauser-like magnetic field remain
elusive. In this work we develop a model based on the master equation approach
to describe the evolution of electronic and nuclear spin polarizations of
gallium centers interacting with free electrons and holes. Our results are in
good agreement with existing experimental observations. In regard to the
nuclear spin relaxation, the roles of nuclear dipolar and quadrupolar
interactions are discussed. Our findings show that, besides the hyperfine
interaction, the spin relaxation mechanisms are key to understand the
amplification of the spin filtering effect and the appearance of the
Overhauser-like magnetic field. Based on our model's results we propose an
experimental protocol based on time resolved spectroscopy. It consists of a
pump-probe photoluminescence scheme that would allow the detection and the
tracing of the electron-nucleus flip-flops through time resolved PL
measurements.",1611.04200v1
2019-07-20,DFT+DMFT study of spin-charge-lattice coupling in covalent LaCoO$_3$,"We study energetics and the nature of both homogeneous and mixed spin (MS)
states in LaCoO$_3$ incorporating structural changes of the crystal volume
expansion and the Co-O bond disproportionation (BD) during the spin-state
transition using the density functional theory plus dynamical mean field theory
(DFT+DMFT) method. DFT+DMFT predicts that energetics of both excited spin
states are almost the same while DFT+U calculations of the same structures
energetically favor the MS states and produce various metastable solutions
whose energetics depend sensitively on final spin states. Within DFT+DMFT, the
homogeneous spin state in the expanded crystal volume shows the
multiconfigurational nature with non-negligible occupancy probabilities of both
high spin (HS) and low spin (LS) states along with $d^6$ and $d^7$ charge
configurations indicating the dynamically fluctuating nature of spin and charge
states due to the Co-O covalency. The nature of the MS state under the BD
structure reveals that Co sites with the long Co-O bonds develop a Mott
insulating state and favor HS with a $d^6$ configuration, while more covalent
Co sites with the short Co-O bonds occupy more LS states with a $d^7$
configuration and behave as a band insulator, as a result, charge ordering is
induced in the BD structure from the spin-state ordering. We also find that
both energetics and electronic structure sensitively depend on the Co-O
covalency effect, which can be tuned by changing the double counting potential
and the resulting $d-$occupancy ($N_d$), and $N_d$ close to 6.7 is consistent
with the nature of the spin-state transition. Our results show that structural
changes during the spin-state transition can play an important role in
understanding energetics and electronic structure of LaCoO$_3$.",1907.08780v2
2020-12-17,Energy-efficient spin injector into semiconductors driven by elastic waves,"Generation of spin imbalance in nonmagnetic semiconductors is crucial for the
functioning of many spintronic devices. An attractive design of spin injectors
into semiconductors is based on a spin pumping from a precessing ferromagnet,
typically excited by a microwave magnetic field leading to a high power
consumption of the device. Here we describe theoretically a spin injector with
greatly reduced energy losses, in which the magnetic dynamics is excited by an
elastic wave injected into a ferromagnet-semiconductor heterostructure. To
demonstrate the efficient functioning of such an injector, we perform
micromagnetoelastic simulations of the coupled elastic and magnetic dynamics in
Ni films and Ni/GaAs bilayers. For thick Ni films, it is shown that a
monochromatic acoustic wave generates a spin wave with the same frequency and
wavelength, which propagates over distances of several micrometers at the
excitation frequencies close to the frequency of ferromagnetic resonance. The
simulations of Ni/GaAs bilayers with Ni thicknesses comparable to the
wavelength of the injected acoustic wave demonstrate the development of a
steady-state magnetization precession at the Ni/GaAs interface. The amplitude
of such a precession has a maximum at Ni thickness amounting to three quarters
of the wavelength of the elastic wave, which is explained by an analytical
model. Using simulation data obtained for the magnetization precession at the
Ni/GaAs interface, we evaluate the spin current pumped into GaAs and calculate
the spin accumulation in it by solving the spin diffusion equation. Then the
electrical signals resulting from the spin flow and the inverse spin Hall
effect are determined via the numerical solution of the Laplace's equation. It
is shown that amplitudes of these ac signals are large enough for experimental
measurement, which indicates an efficient acoustically driven spin pumping into
GaAs.",2012.09531v1
2003-03-17,Glassy dynamics in the East model,"We study the dynamics of the East model, comprising a chain of uncoupled
spins in a downward-pointing field. Glassy effects arise at low temperatures
$T$ from the kinetic constraint that spins can only flip if their left
neighbour is up. We give details of our previous solution of the
non-equilibrium coarsening dynamics after a quench to low $T$ (Phys. Rev.\
Lett. 83:3238, 1999), including the anomalous coarsening of down-spin domains
with typical size $\bar{d} \sim t^{T \ln 2}$, and the pronounced `fragile
glass'-divergence of equilibration times as $t_*=\exp(1/T^2\ln 2)$. We also
link the model to the paste-all coarsening model, defining a family of
interpolating models that all have the same scaling distribution of domain
sizes. We then proceed to the problem of equilibrium dynamics at low $T$. Based
on a scaling hypothesis for the relation between timescales and lengthscales,
we propose a model for the dynamics of `superdomains' which are bounded by
up-spins that are frozen on long timescales. From this we deduce that the
equilibrium spin correlation and persistence functions should exhibit identical
scaling behaviour for low $T$, decaying as $g(\tilde{t})$. The scaling variable
is $\tilde{t}=(t/t_*)^{T\ln 2}$, giving strongly stretched behaviour for low
$T$. The scaling function $g(\cdot)$ decays faster than exponential, however,
and in the limit $T\to 0$ at fixed $\tilde{t}$ reaches zero at a {\em finite}
value of $\tilde{t}$.",0303318v2
2008-12-25,Dynamic properties of the spin-1/2 XY chain with three-site interactions,"We consider a spin-1/2 XY chain in a transverse (z) field with multi-site
interactions. The additional terms introduced into the Hamiltonian involve
products of spin components related to three adjacent sites. A Jordan-Wigner
transformation leads to a simple bilinear Fermi form for the resulting
Hamiltonian and hence the spin model admits a rigorous analysis. We point out
the close relationships between several variants of the model which were
discussed separately in previous studies. The ground-state phases (ferromagnet
and two kinds of spin liquid) of the model are reflected in the dynamic
structure factors of the spin chains, which are the main focus in this study.
First we consider the zz dynamic structure factor reporting for this quantity a
closed-form expression and analyzing the properties of the two-fermion
(particle-hole) excitation continuum which governs the dynamics of transverse
spin component fluctuations and of some other local operator fluctuations. Then
we examine the xx dynamic structure factor which is governed by many-fermion
excitations, reporting both analytical and numerical results. We discuss some
easily recognized features of the dynamic structure factors which are
signatures for the presence of the three-site interactions.",0812.4601v1
2009-06-08,Multiple quantum NMR dynamics of spin-1/2 carrying molecules of a gas in nanopores,"We consider the multiple quantum (MQ) NMR dynamics of a gas of spin carrying
molecules in nanocavities.
  MQ NMR dynamics is determined by the residual dipole-dipole interactions
which are not averaged completely due to the molecular diffusion in nanopores.
  Since the averaged non-secular Hamiltonian describing MQ NMR dynamics depends
on only one coupling constant, this Hamiltonian commutes with the square of the
total spin angular momentum $\hat I^2$.
  We use the basis of common eigenstates of $\hat I^2$ and the projection of
$I$ on the external magnetic field for investigation of MQ NMR dynamics.
  This approach allows us to study MQ NMR dynamics in systems consisting of
several hundreds of spins. The analytical approximation of the stationary
profile of MQ coherences is obtained.
  The analytical expressions for MQ NMR coherence intensities of the five-spin
system in a nanopore are found.
  Numerical investigations allow us to find the dependencies of intensities of
MQ coherences on their orders (the profiles of MQ coherences) in systems
consisting of 600 spins and even more.
  It is shown that the stationary MQ coherence profile in the considered system
is an exponential one.",0906.1413v1
2017-07-07,Gapless quantum spin chains: multiple dynamics and conformal wavefunctions,"We study gapless quantum spin chains with spin 1/2 and 1: the Fredkin and
Motzkin models. Their entangled groundstates are known exactly but not their
excitation spectra. We first express the groundstates in the continuum which
allows for the calculation of spin and entanglement properties in a unified
fashion. Doing so, we uncover an emergent conformal-type symmetry, thus
consolidating the connection to a widely studied family of Lifshitz quantum
critical points in 2d. We then obtain the low lying excited states via
large-scale DMRG simulations and find that the dynamical exponent is z = 3.2 in
both cases. Other excited states show a different z, indicating that these
models have multiple dynamics. Moreover, we modify the spin-1/2 model by adding
a ferromagnetic Heisenberg term, which changes the entire spectrum. We track
the resulting non-trivial evolution of the dynamical exponents using DMRG.
Finally, we exploit an exact map from the quantum Hamiltonian to the
non-equilibrium dynamics of a classical spin chain to shed light on the quantum
dynamics.",1707.02317v2
2012-05-09,Non-equilibrium dynamics of an unstable quantum pendulum,"A pendulum prepared perfectly inverted and motionless is a prototype of
unstable equilibria and corresponds to an unstable hyperbolic fixed point in
the dynamical phase space. Unstable fixed points are central to understanding
Hamiltonian chaos in classical systems. In many-body quantum systems,
mean-field approximations fail in the vicinity of unstable fixed points and
lead to dynamics driven by quantum fluctuations. Here, we measure the
non-equilibrium dynamics of a many-body quantum pendulum initialized to a
hyperbolic fixed point of the phase space. The experiment uses a spin-1 Bose
condensate, which exhibits Josephson dynamics in the spin populations that
correspond in the mean-field limit to motion of a non-rigid mechanical
pendulum. The condensate is initialized to a minimum uncertainty spin state,
and quantum fluctuations lead to non-linear spin evolution along a separatrix
and non-Gaussian probability distributions that are measured to be in good
agreement with exact quantum calculations up to 0.25 s. At longer times, atomic
loss due to the finite lifetime of the condensate leads to larger spin
oscillation amplitudes compared to no loss case as orbits depart from the
separatrix. This demonstrates how decoherence of a many-body system can result
in more apparent coherent behaviour. This experiment provides new avenues for
studying macroscopic spin systems in the quantum limit and for investigations
of important topics in non-equilibrium quantum dynamics.",1205.2121v1
2017-05-25,Spin-orbit torque-driven skyrmion dynamics revealed by time-resolved X-ray microscopy,"Magnetic skyrmions are topologically-protected spin textures with attractive
properties suitable for high-density and low-power spintronic device
applications. Much effort has been dedicated to understanding the dynamical
behaviours of the magnetic skyrmions. However, experimental observation of the
ultrafast dynamics of this chiral magnetic texture in real space, which is the
hallmark of its quasiparticle nature, has so far remained elusive. Here, we
report nanosecond-dynamics of a 100 nm-size magnetic skyrmion during a current
pulse application, using a time-resolved pump-probe soft X-ray imaging
technique. We demonstrate that distinct dynamic excitation states of magnetic
skyrmions, triggered by current-induced spin-orbit torques, can be reliably
tuned by changing the magnitude of spin-orbit torques. Our findings show that
the dynamics of magnetic skyrmions can be controlled by the spin-orbit torque
on the nanosecond time scale, which points to exciting opportunities for
ultrafast and novel skyrmionic applications in the future.",1705.09019v1
2003-10-29,Superparamagnetism and Spin Glass Dynamics of Interacting Magnetic Nanoparticle Systems,"The physical properties of magnetic nanoparticles have been investigated with
focus on the influence of dipolar interparticle interaction. For weakly coupled
nanoparticles, thermodynamic perturbation theory is employed to derive
analytical expressions for the linear equilibrium susceptibility, the
zero-field specific heat and averages of the local dipolar fields. By
introducing the averages of the dipolar fields in an expression for the
relaxation rate of a single particle, a nontrivial dependence of the
superparamagnetic blocking on the damping coefficient is evidenced. This
damping dependence is interpreted in terms of the nonaxially symmetric
potential created by the transverse component of the dipolar field.
  Strongly interacting nanoparticle systems are investigated experimentally in
terms of spin glass behavior. Disorder and frustration arise in samples
consisting of frozen ferrofluids from the randomness in particle position and
anisotropy axis orientation. A strongly interacting FeC system is shown to
exhibit critical dynamics characteristic of a spin glass phase transition.
Aging, memory and rejuvenation phenomena similar to those of conventional spin
glasses are observed, albeit with much weaker rejuvenation effects than in both
a Ag(11 at% Mn) Heisenberg and an Fe_{0.5}Mn_{0.5}TiO_3 Ising spin glass.
Differences in the nonequilibrium dynamics of the strongly interacting
nanoparticle system and the two spin glass samples are discussed in terms of
anisotropy and different timescales, due to the much longer microscopic flip
time of a magnetic moment than of an atomic spin.",0310684v2
2006-07-25,Spin dynamics in the diluted ferromagnetic Kondo lattice model,"The interplay of disorder and competing interactions is investigated in the
carrier-induced ferromagnetic state of the Kondo lattice model within a
numerical finite-size study in which disorder is treated exactly. Competition
between impurity spin couplings, stability of the ferromagnetic state, and
magnetic transition temperature are quantitatively investigated in terms of
magnon properties for different models including dilution, disorder, and
weakly-coupled spins. A strong optimization is obtained for T_c at hole doping
p << x, highlighting the importance of compensation in diluted magnetic
semiconductors. The estimated T_c is in good agreement with experimental
results for Ga_{1-x}Mn_x As for corresponding impurity concentration, hole
bandwidth, and compensation. Finite-temperature spin dynamics is quantitatively
studied within a locally self-consistent magnon renormalization scheme, which
yields a substantial enhancement in T_c due to spin clustering, and highlights
the nearly-paramagnetic spin dynamics of weakly-coupled spins. The large
enhancement in density of low-energy magnetic excitations due to disorder and
competing interactions results in a strong thermal decay of magnetization,
which fits well with the Bloch form M_0(1-BT^{3/2}) at low temperature, with B
of same order of magnitude as obtained in recent squid magnetization
measurements on Ga_{1-x}Mn_x As samples.",0607633v1
2005-10-19,Massive relativistic particle model with spin from free two-twistor dynamics and its quantization,"We consider a relativistic particle model in an enlarged relativistic phase
space M^{18} = (X_\mu, P_\mu, \eta_\alpha, \oeta_\dalpha, \sigma_\alpha,
\osigma_\dalpha, e, \phi), which is derived from the free two-twistor dynamics.
The spin sector variables (\eta_\alpha, \oeta_\dalpha, \sigma_\alpha,\
osigma_\dalpha) satisfy two second class constraints and account for the
relativistic spin structure, and the pair (e,\phi) describes the electric
charge sector. After introducing the Liouville one-form on M^{18}, derived by a
non-linear transformation of the canonical Liouville one-form on the
two-twistor space, we analyze the dynamics described by the first and second
class constraints. We use a composite orthogonal basis in four-momentum space
to obtain the scalars defining the invariant spin projections. The
first-quantized theory provides a consistent set of wave equations, determining
the mass, spin, invariant spin projection and electric charge of the
relativistic particle. The wavefunction provides a generating functional for
free, massive higher spin fields.",0510161v2
2002-03-01,Baryon resonances and strong QCD,"Light-baryon resonances (with u,d, and s quarks in the SU(3) classification)
fall on Regge trajectories. When their squared masses are plotted against the
intrinsic orbital angular momenta {\rm L}, $\Delta^*$'s with even and odd
parity can be described by the same Regge trajectory. For a given {\rm L},
nucleon resonances with spin {\rm S}=3/2 are approximately degenerate in mass
with $\Delta$ resonances. To which total angular momentum {\rm L} and {\rm S}
couple has no significant impact on the baryon mass. Nucleons with spin 1/2 are
shifted in mass; the shift is - in units of squared masses - proportional to
the component in the wave function which is antisymmetric in spin and flavor.
Based on these observations, a new baryon mass formula is proposed which
reproduces nearly all known baryon masses. It is shown that the masses are
compatible with a quark-diquark picture while the richness of the
experimentally known states require three particles to participate in the
dynamics. This conflict is resolved by proposing that quarks polarize the QCD
condensates and are surrounded by a polarization cloud shielding the color. A
new interpretation of constituent quarks as colored quark clusters emerges;
their interaction is responsible for the mass spectrum. Fast flavor exchange
between the colored quark clusters exhausts the dynamical richness of the
three-particle dynamics. The colored-quark-cluster model provides a mechanism
in which the linear confinement potential can be traced to the increase of the
volume in which the condensates are polarized. The quark-spin magnetic moment
induces currents in the polarized condensates which absorb the quark-spin
angular momentum: the proton spin is not carried by quark spins. The model
provides a new picture of hybrids and glueballs.",0203002v1
2008-03-25,Spin Dynamics in the Second Subband of a Quasi Two Dimensional System Studied in a Single Barrier Heterostructure by Time Resolved Kerr Rotation,"By biasing a single barrier heterostructure with a 500nm-thick GaAs layer as
the absorption layer, the spin dynamics for both of the first and second
subband near the AlAs barrier are examined. We find that when simultaneously
scanning the photon energy of both the probe and pump beams, a sign reversal of
the Kerr rotation (KR) takes place as long as the probe photons break away the
first subband and probe the second subband. This novel feature, while stemming
from the exchange interaction, has been used to unambiguously distinguish the
different spin dynamics ($T_2^{1*}$ and $T_2^{2*}$) for the first and second
subbands under the different conditions by their KR signs (negative for
$1^{st}$ and positive for $2^{nd}$). In the zero magnetic field, by scanning
the wavelength towards the short wavelength, $T_2^{1*}$ decreases in accordance
with the D'yakonov-Perel' (DP) spin decoherence mechanism. At 803nm,
$T_2^{2*}$(450ps) becomes ten times longer than $T_2^{1*}$(50ps). However, the
value of $T_2^{2*}$ at 803nm is roughly the same as the value of $T_2^{1*}$ at
815nm. A new feature has been disclosed at the wavelength of 811nm under the
bias of -0.3V (807nm under the bias of -0.6V) that the spin coherence times
($T_2^{1*}$ and $T_2^{2*}$) and the effective $g^*$ factors ($|g^*(E1)|$ and
$|g^*(E2)|$) all display a sudden change, due to the ""resonant"" spin exchange
coupling between two spin opposite bands.",0803.3579v1
2013-10-14,High temperature expansion for dynamical correlation functions in the infinite-U Hubbard Model,"We develop a diagrammatic approach for calculating the high temperature
expansion of dynamic correlation functions, such as the electron Green's
function and the time-dependent density-density and spin-spin correlation
functions, for the infinite-U Hubbard Model with any number of spin species.
The formalism relies on the use of restricted lattice sums, in which distinct
vertices of the diagram represent distinct sites on the lattice. We derive a
new formula for the restricted lattice sum of a disconnected diagram consisting
of several connected components, and use it to prove the linked cluster theorem
with respect to ""generalized connected diagrams"", formed by overlapping the
original connected components on the lattice. This enables us to express all
quantities as a sum over these generalized connected diagrams. We compute the
Green's function to 4th order in \beta t for the case of m spin species on a
d-dimensional hypercube by hand. We take the m\to\infty limit, enabling us to
obtain expressions for the Dyson-Mori self-energy to 4th order in \beta t for
the case of an infinite number of spin species. This may have connections to
slave boson techniques used for the study of this model. Our approach is
computationally more efficient than any used previously for the calculation of
the high temperature expansion of dynamic correlation functions, and high order
results for both the Green's function and the time-dependent density-density
and spin-spin correlation functions shall be presented in a separate paper
[25].",1310.3797v1
2014-07-08,Dynamical competition between Quantum Hall and Quantum Spin Hall effects,"In this paper we investigate the occurrence of quantum phase transitions in
topological systems out of equi- librium. More specifically, we consider
graphene with a sizable spin-orbit coupling, irradiated by circularly-
polarized light. In the absence of light, the spin-orbit coupling drives a
quantum spin Hall phase where edge currents with opposite spins
counter-propagate. On the other hand, the light generates a time-dependent
vector potential, which leads to a hopping parameter with staggered
time-dependent phases around the benzene ring. The model is a dynamical version
of the Haldane model, which considers a static staggered flux with zero total
flux through each plaquette. Since the light breaks time-reversal symmetry, a
quantum Hall phase protected by an integer topological invariant arises. By
numerically solving the complete problem, with spin-orbit coupling and light,
and investigating different values of the driving frequency {\omega}, we show
that the spectrum exhibits non-trivial gaps not only at zero energy, but also
at {\omega}/2. This additional gap is created by photon resonances between the
valence and conduction band of graphene, and the symmetry of the spectrum
forces it to lie at {\omega}/2. By increasing the intensity of the irradiation,
the topological state in the zero energy gap undergoes a dynamical phase
transition from a quantum spin Hall to a quantum Hall phase, whereas the gap
around {\omega}/2 remains in the quantum Hall regime.",1407.2152v3
2014-07-08,Asymmetric recombination and electron spin relaxation in the semiclassical theory of radical pair reactions,"We describe how the semiclassical theory of radical pair recombination
reactions recently introduced by two of us [D. E. Manolopoulos and P. J. Hore,
J. Chem. Phys. 139, 124106 (2013)] can be generalised to allow for different
singlet and triplet recombination rates. This is a non-trivial generalisation
because when the recombination rates are different the recombination process is
dynamically coupled to the coherent electron spin dynamics of the radical pair.
Furthermore, because the recombination operator is a two-electron operator, it
is no longer sufficient simply to consider the two electrons as classical
vectors: one has to consider the complete set of 16 two-electron spin operators
as independent classical variables. The resulting semiclassical theory is first
validated by comparison with exact quantum mechanical results for a model
radical pair containing 12 nuclear spins. It is then used to shed light on the
spin dynamics of a carotenoid-porphyrin-fullerene (CPF) triad containing
considerably more nuclear spins which has recently been used to establish a
'proof of principle' for the operation of a chemical compass [K. Maeda et al.,
Nature 453, 387 (2008)]. We find in particular that the intriguing biphasic
behaviour that has been observed in the effect of an Earth-strength magnetic
field on the time-dependent survival probability of the photo-excited C+PF-
radical pair arises from a delicate balance between its asymmetric
recombination and the relaxation of the electron spin in the carotenoid
radical.",1407.2162v1
2014-08-29,Hole dynamics and spin currents after ionization in strong circularly polarized laser fields,"We apply the time-dependent analytical R-matrix theory to develop a movie of
hole motion in a Kr atom upon ionization by strong circularly polarized field.
We find rich hole dynamics, ranging from rotation to swinging motion. The
motion of the hole depends on the final energy and the spin of the
photoelectron and can be controlled by the laser frequency and intensity.
Crucially, hole rotation is a purely non-adiabatic effect, completely missing
in the framework of quasistatic (adiabatic) tunneling theories. We explore the
possibility to use hole rotation as a clock for measuring ionization time.
Analysing the relationship between the relative phases in different ionization
channels we show that in the case of short-range electron-core interaction the
hole is always initially aligned along the instantaneous direction of the laser
field, signifying zero delays in ionization. Finally, we show that strong-field
ionization in circular fields creates spin currents (i.e. different flow of
spin-up and spin-down density in space) in the ions. This phenomenon is
intimately related to the production of spin-polarized electrons in strong
laser fields [Barth I and Smirnova O 2013 Phys. Rev. A 88 013401]. We
demonstrate that rich spin dynamics of electrons and holes produced during
strong field ionization can occur in typical experimental conditions and does
not require relativistic intensities or strong magnetic fields.",1408.6961v1
2015-05-21,Theoretical model of the dynamic spin polarization of nuclei coupled to paramagnetic point defects in diamond and silicon carbide,"Dynamic nuclear spin polarization (DNP) mediated by paramagnetic point
defects in semiconductors is a key resource for both initializing nuclear
quantum memories and producing nuclear hyperpolarization. DNP is therefore an
important process in the field of quantum-information processing,
sensitivity-enhanced nuclear magnetic resonance, and nuclear-spin-based
spintronics. DNP based on optical pumping of point defects has been
demonstrated by using the electron spin of nitrogen-vacancy (NV) center in
diamond, and more recently, by using divacancy and related defect spins in
hexagonal silicon carbide (SiC). Here, we describe a general model for these
optical DNP processes that allows the effects of many microscopic processes to
be integrated. Applying this theory, we gain a deeper insight into dynamic
nuclear spin polarization and the physics of diamond and SiC defects. Our
results are in good agreement with experimental observations and provide a
detailed and unified understanding. In particular, our findings show that the
defects' electron spin coherence times and excited state lifetimes are crucial
factors in the entire DNP process.",1505.05651v2
2017-03-03,Correlations and dynamics of spins in an XY-like spin-glass (Ni0.4Mn0.6)TiO3 single crystal system,"Elastic and inelastic neutron scattering (ENS and INS) experiments were
performed on a single crystal of (Ni0.4Mn0.6)TiO3 (NMTO) to study the spatial
correlations and dynamics of spins in the XY-like spin-glass (SG) state.
Magnetization measurements reveal signatures of SG behavior in NMTO with a
freezing temperature of TSG ~ 9.1 K. The ENS experiments indicated that the
intensity of magnetic diffuse scattering starts to increase around 12 K, which
is close to TSG. Also, spin-spin correlation lengths (zeta) at 1.5 K are
approximately (21) and (73) angstrom in the interlayer and the in-plane
directions, respectively, demonstrating that magnetic correlations in NMTO
exhibit quasi two-dimensional antiferromagnetic order. In addition, critical
exponent (beta) is determined to be 0.37 from the intensity of magnetic diffuse
scattering confirms the XY-like SG state of NMTO. INS results show
quasi-elastic neutron scattering (QENS) profiles below TSG. The life-time of
dynamic correlations obtained from the half width at half maximum of the
Lorentzian QENS profiles, are approximately 16 and 16 ps at 10 K for two
positions (0.00, 0.00, 1.52) and (0.01, 0.01, 1.50), respectively. Therefore,
our experimental findings demonstrate that short-range-ordered
antiferromagnetic clusters with short-lived spin correlations are present in
the XY-like SG state of NMTO.",1703.09773v1
2017-08-08,Spin-orbit-torque driven magnetoimpedance in Pt-layer/magnetic-ribbon heterostructures,"When a flow of electron passes through a paramagnetic layer with strong
spin-orbit-coupling such as platinum (Pt), a net spin current is produced via
spin Hall effect (SHE). This spin current can exert a torque on the
magnetization of an adjacent ferromagnetic layer which can be probed via
magnetization dynamic response, e.g. spin-torque ferromagnetic resonance
(ST-FMR). Nevertheless, that effect in lower frequency magnetization dynamic
regime (MHz) where skin effect occurs in high permeability ferromagnetic
conductors namely the magneto-impedance (MI) effect can be fundamentally
important which has not been studied so far. Here, by utilizing the MI effect
in magnetic-ribbon/Pt heterostructure with high magnetic permeability that
allows the ac current effectively confined at the skin depth of ~100 nm
thickness, the effect of spin-orbit-torque (SOT) induced by the SHE probed via
MI measurement is investigated. We observed a systematic MI frequency shift
that increases by increasing the applied current amplitude and thickness of the
Pt layer (varying from 0 nm to 20 nm). In addition, the role of Pt layer in
ribbon/Pt heterostructure is evaluated with ferromagnetic resonance (FMR)
effect representing standard Gilbert damping increase as the result of presence
of the SHE. Our results unveil the role of SOT in dynamic control of the
transverse magnetic permeability probed with impedance spectroscopy as useful
and valuable technique for detection of future SHE devices.",1708.02402v2
2018-04-13,Tuning Spin Dynamics and Localization Near the Metal-Insulator Transition in Fe/GaAs heterostructures,"We present a simultaneous investigation of coherent spin dynamics in both
localized and itinerant carriers in Fe/GaAs heterostructures using ultrafast
and spin-resolved pump-probe spectroscopy. We find that for excitation
densities that push the transient Fermi energy of photocarriers above the
mobility edge there exist two distinct precession frequencies in the ob-served
spin dynamics, allowing us to simultaneously monitor both localized and
itinerant states. For low magnetic fields (below 3 T) the beat frequency
between these two excitations evolves linearly, indicating that the nuclear
polarization is saturated almost immediately and that the hyperfine coupling to
these two states is comparable, despite the 100x enhancement in nuclear
polarization provided by the presence of the Fe layer. At higher magnetic
fields (above 3 T) the Zeeman energy drives reentrant localization of the
photocarriers. Subtracting the constant hyperfine contribution from both sets
of data allows us to extract the Lande g-factor for each state and estimate
their energy relative to the bottom of the conduction band, yielding -2.16 meV
and 17 meV for localized and itinerant states, respectively. This work advances
our fundamental understanding of spin-spin interactions between electron and
nuclear spin species, as well as between localized and itinerant electronics
states, and therefore has implications for future work in both spintronics and
quantum information/computation.",1804.04761v1
2016-08-02,RESPECT: Neutron Resonance Spin-Echo Spectrometer for Extreme Studies,"We propose the design of a Resonance SPin-echo spECtrometer for exTreme
studies, RESPECT, that is ideally suited for the exploration of non-dispersive
processes such as diffusion, crystallization, slow dynamics, tunneling
processes, crystal electric field excitations, and spin fluctuations. It is a
variant of the conventional neutron spin-echo technique (NSE) by i) replacing
the long precession coils by pairs of longitudinal neutron spin-echo coils
combined with RF-spin flippers and ii) by stabilizing the neutron polarization
with small longitudinal guide fields that can in addition be used as field
subtraction coils thus allowing to adjust the field integrals over a range of 8
orders of magnitude. Therefore, the dynamic range of RESPECT can in principle
be varied over 8 orders of magnitude in time, if neutrons with the required
energy are made available. Similarly as for existing NSE-spectrometers, spin
echo times of up to approximately 1 microsecond can be reached if the
divergence and the correction elements are properly adjusted. Thanks to the
optional use of neutron guides and the fact that the currents for the
correction coils are much smaller than in standard NSE, intensity gains of at
least one order of magnitude are expected , making the concept of RESPECT also
competitive for operation at medium flux neutron sources. RESPECT can also be
operated in a MIEZE configuration allowing the investigation of relaxation
processes in depolarizing environments as they occur when magnetic fields are
applied at the sample position, i.e. for the investigation of the dynamics of
flux lines in superconductors, magnetic fluctuations in ferromagnetic
materials, and samples containing hydrogen.",1608.00836v1
2017-12-07,Narrow-band tunable THz detector in antiferromagnets via Néel spin-orbit torque and spin-transfer torque,"We study dynamics of antiferromagnets induced by simultaneous application of
dc spin current and ac charge current, motivated by the requirement of
all-electrically controlled devices in THz gap (0.1-30 THz). We show that ac
electric current, via N\'eel spin orbit torques, can lock the phase of a steady
rotating N\'eel vector whose precession is controlled by a dc spin current. In
the phase-locking regime the frequency of the incoming ac signal coincides with
the frequency of autooscillations which for typical antiferromagnets fall into
the THz range. The frequency of autooscillations is proportional to the
precession-induced tilting of the magnetic sublattices related to the so-called
dynamical magnetization. We show how the incoming ac signal can be detected
from the measurement of the dc-current dependencies of the constant dynamical
magnetization. We formulate the conditions of phase-locking based on relations
between parameters of an antiferromagnet and the characteristics of the
incoming signal (frequency, amplitude, bandwidth, duration). We also show that
the rotating N\'eel vector can generate ac electrical current via inverse
N\'eel spin-orbit torque. Hence, antiferromagnets driven by dc spin current can
be used as tunable detectors and emitters of narrow-band signals operating in
the THz range.",1712.02686v1
2019-06-03,Single-atom quantum probes for ultracold gases using nonequilibrium spin dynamics,"Quantum probes are atomic-sized devices mapping information of their
environment to quantum mechanical states. By improving measurements and at the
same time minimizing perturbation of the environment, they form a central asset
for quantum technologies. We realize spin-based quantum probes by immersing
individual Cs atoms into an ultracold Rb bath. Controlling inelastic
spin-exchange processes between probe and bath allows mapping motional and
thermal information onto quantum-spin states. We show that the steady-state
spin-population is well suited for absolute thermometry, reducing temperature
measurements to detection of quantum spin distributions. Moreover, we find that
the information gain per inelastic collision can be maximized by accessing the
nonequilibrium spin dynamic. The sensitivity of nonequilibrium quantum probing
effectively beats the steady-state Cram\'er Rao limit of quantum probing by
almost an order of magnitude, while reducing the perturbation of the bath to
only three quanta of angular momentum. Our work paves the way for local probing
of quantum systems at the Heisenberg limit, and moreover for optimizing
measurement strategies via control of nonequilibrium dynamics.",1906.00844v1
2019-10-17,Unusual slow magnetic fluctuations and critical slowing down in Sr$_{2}$Ir$_{1-x}$Rh$_{x}$O$_{4}$,"Hidden magnetic order of Sr$_2$Ir$_{1-x}$Rh$_x$O$_4$, $x = 0.05$ and 0.1, has
been studied using muon spin relaxation spectroscopy. In zero applied field and
weak longitudinal fields ($\mu_0H_L \lesssim 2$~mT), muon spin relaxation data
can be well described by exponentially-damped static Lorentzian Kubo-Toyabe
functions, indicating that static and dynamic local fields coexist at each muon
site. For $\mu_0H_L \gtrsim 2$~mT, the static rate is completely decoupled, and
the exponential decay is due to dynamic spin fluctuations. In both zero field
and $\mu_0H_L = 1$--2~mT, the temperature dependencies of the exponential muon
spin relaxation rate exhibit maxima at 215~K for $x = 0.05$ and 175~K for $x =
0.1$, suggesting critical slowing down of electronic spin fluctuations. The
field dependencies of the dynamic spin fluctuation rates can be well described
by the Redfield relation. The correlation time of this electronic spin
fluctuation is in the range of~2--5~ns for Sr$_2$Ir$_{0.9}$Rh$_{0.1}$O$_4$, and
shorter than 2~ns for Sr$_2$Ir$_{0.95}$Rh$_{0.05}$O$_4$. The rms fluctuating
field is on the order of 1 mT, which is consistent with the polarized neutron
diffraction cross-section.",1910.07759v2
2021-01-29,Dynamically stable negative-energy states induced by spin-transfer torques,"We investigate instabilities of the magnetic ground state in ferromagnetic
metals that are induced by uniform electrical currents, and, in particular, go
beyond previous analyses by including dipolar interactions. These instabilities
arise from spin-transfer torques that lead to Doppler shifted spin waves. For
sufficiently large electrical currents, spin-wave excitations have negative
energy with respect to the uniform magnetic ground state, while remaining
dynamically stable due to dissipative spin-transfer torques. Hence, the uniform
magnetic ground state is energetically unstable, but is not able to dynamically
reach the new ground state. We estimate this to happen for current densities $
j\gtrsim (1-D/D_c)10^{13} \mathrm{A/m^2} $ in typical thin film experiments,
with $ D $ the Dzyaloshinskii-Moriya interaction constant, and $ D_c $ the
Dzyaloshinskii-Moriya interaction that is required for spontaneous formation of
spirals or skyrmions. These current densities can be made arbitrarily small for
ultrathin film thicknesses at the order of nanometers, due to surface- and
interlayer effects. From an analogue gravity perspective, the stable negative
energy states are an essential ingredient to implement event horizons for
magnons -- the quanta of spin waves -- giving rise to e.g. Hawking radiation
and can be used to significantly amplify spin waves in a so-called black-hole
laser.",2101.12544v1
2020-05-01,Optically pumped spin polarization as a probe of many-body thermalization,"The interplay between disorder and transport is a problem central to the
understanding of a broad range of physical processes, most notably the ability
of a system to reach thermal equilibrium. Disorder and many body interactions
are known to compete, with the dominance of one or the other giving rise to
fundamentally different dynamical phases. Here we investigate the spin
diffusion dynamics of 13C in diamond, which we dynamically polarize at room
temperature via optical spin pumping of engineered color centers. We focus on
low-abundance, strongly hyperfine-coupled nuclei, whose role in the
polarization transport we expose through the integrated impact of variable
radio-frequency excitation on the observable bulk 13C magnetic resonance
signal. Unexpectedly, we find good thermal contact throughout the nuclear spin
bath, virtually independent of the hyperfine coupling strength, which we
attribute to effective carbon-carbon interactions mediated by the electronic
spin ensemble. In particular, observations across the full range of hyperfine
couplings indicate the nuclear spin diffusion constant takes values up to two
orders of magnitude greater than that expected from homo-nuclear spin
couplings. Our results open intriguing opportunities to study the onset of
thermalization in a system by controlling the internal interactions within the
bath.",2005.00647v1
2020-05-16,Balancing coherent and dissipative dynamics in a central-spin system,"The average time required for an open quantum system to reach a steady state
(the steady-state time) is generally determined through a competition of
coherent and incoherent (dissipative) dynamics. Here, we study this competition
for a ubiquitous central-spin system, corresponding to a `central' spin-1/2
coherently coupled to ancilla spins and undergoing dissipative spin relaxation.
The ancilla system can describe $N$ spins-1/2 or, equivalently, a single large
spin of length $I=N/2$. We find exact analytical expressions for the
steady-state time in terms of the dissipation rate, resulting in a minimal
(optimal) steady-state time at an optimal value of the dissipation rate,
according to a universal curve. Due to a collective-enhancement effect, the
optimized steady-state time grows only logarithmically with increasing $N=2I$,
demonstrating that the system size can be grown substantially with only a
moderate cost in steady-state time. This work has direct applications to the
rapid initialization of spin qubits in quantum dots or bound to donor
impurities, to dynamic nuclear-spin polarization protocols, and may provide key
intuition for the benefits of error-correction protocols in quantum annealing.",2005.08023v2
2020-10-15,Spin injection characteristics of Py/graphene/Pt by gigahertz and terahertz magnetization dynamics driven by femtosecond laser pulse,"Spin transport characteristics of graphene has been extensively studied so
far. The spin transport along c-axis is however reported by rather limited
number of papers. We have studied spin transport characteristics through
graphene along c-axis with permalloy(Py)/graphene(Gr)/Pt by gigahertz (GHz) and
terahertz (THz) magnetization dynamics driven by femtosecond laser pulses. The
relatively simple sample structure does not require electrodes on the sample.
The graphene layer was prepared by chemical vapor deposition and transferred on
Pt film. The quality of graphene layer was characterized by Raman microscopy.
Time resolved magneto-optical Kerr effect is used to characterize gigahertz
magnetization dynamics. Magnetization precession is clearly observed both for
Pt/Py and Pt/Gr/Py. The Gilbert damping constant of Pt/Py was 0.015, indicates
spin pumping effect from Py to Pt. The Gilbert damping constant of Pt/Gr/Py is
found to be 0.011, indicates spin injection is blocked by graphene layer. We
have also performed the measurement of THz emission for Pt/Py and Pt/Gr/Py.
While the THz emission is clearly observed for Pt/Py, a strong reduction of THz
emission is observed for Pt/Gr/Py. With these two different experiments, and
highly anisotropic resistivity of graphite, we conclude that the vertical spin
transport is strongly suppressed by the graphene layer.",2010.07694v1
2021-02-19,Spin Effects in the Effective Field Theory Approach to Post-Minkowskian Conservative Dynamics,"Building upon the worldline effective field theory (EFT) formalism for
spinning bodies developed for the Post-Newtonian regime, we generalize the EFT
approach to Post-Minkowskian (PM) dynamics to include rotational degrees of
freedom in a manifestly covariant framework. We introduce a systematic
procedure to compute the total change in momentum and spin in the gravitational
scattering of compact objects. For the special case of spins aligned with the
orbital angular momentum, we show how to construct the radial action for
elliptic-like orbits using the Boundary-to-Bound correspondence. As a
paradigmatic example, we solve the scattering problem to next-to-leading PM
order with linear and bilinear spin effects and arbitrary initial conditions,
incorporating for the first time finite-size corrections. We obtain the
aligned-spin radial action from the resulting scattering data, and derive the
periastron advance and binding energy for circular orbits. We also provide the
(square of the) center-of-mass momentum to ${\cal O}(G^2)$, which may be used
to reconstruct a Hamiltonian. Our results are in perfect agreement with the
existent literature, while at the same time extend the knowledge of the PM
dynamics of compact binaries at quadratic order in spins.",2102.10059v2
2021-04-09,Dissipative spin dynamics in hot quantum paramagnets,"We use the functional renormalization approach for quantum spin systems
developed by Krieg and Kopietz [Phys. Rev. B $\mathbf{99}$, 060403(R) (2019)]
to calculate the spin-spin correlation function $G (\boldsymbol{k}, \omega )$
of quantum Heisenberg magnets at infinite temperature. For small wavevectors
$\boldsymbol{k} $ and frequencies $\omega$ we find that $G ( \boldsymbol{k},
\omega )$ assumes in dimensions $d > 2$ the diffusive form predicted by
hydrodynamics. In three dimensions our result for the spin-diffusion
coefficient ${\cal{D}}$ is somewhat smaller than previous theoretical
predictions based on the extrapolation of the short-time expansion, but is
still about $30 \%$ larger than the measured high-temperature value of
${\cal{D}}$ in the Heisenberg ferromagnet Rb$_2$CuBr$_4\cdot$2H$_2$O. In
reduced dimensions $d \leq 2$ we find superdiffusion characterized by a
frequency-dependent complex spin-diffusion coefficient ${\cal{D}} ( \omega )$
which diverges logarithmically in $d=2$, and as a power-law ${\cal{D}} ( \omega
) \propto \omega^{-1/3}$ in $d=1$. Our result in one dimension implies scaling
with dynamical exponent $z =3/2$, in agreement with recent calculations for
integrable spin chains. Our approach is not restricted to the hydrodynamic
regime and allows us to calculate the dynamic structure factor $S (
\boldsymbol{k} , \omega )$ for all wavevectors. We show how the
short-wavelength behavior of $S ( \boldsymbol{k}, \omega )$ at high
temperatures reflects the relative sign and strength of competing exchange
interactions.",2104.04270v2
2021-07-09,Emergence of Dynamical Coherence in a Driven One-dimensional Interacting Rotor Model,"In order to understand the dynamics of active matter, we examine a
minimalistic model where interacting spins on a one-dimensional lattice are
driven by a self-propelled spin at the centre with a fixed rotational velocity
$({\omega}_{0})$. The other spins execute rotational Brownian motion by
following the Shore-Zwanzig model of rotational dynamics. The simplicity of the
model allows us to inquire about several relevant microscopic quantities. The
continuous 'active' torque on the central spin is propagated through nearest
neighbour interactions with a uniform coupling parameter, J. We have found a
bounded region in the J-${\omega}_{0}$ plane where the system exhibits 'active
matter like behaviour'. Interestingly, in the limits of large J and
${\omega}_{0}$, we observe a 'slipping behaviour'. The site specific average
rotational velocity of the spin, as one moves away from the central spin
exhibits a nearly exponential decay with distance, allowing the definition of a
correlation length $({\xi})$ which grows rapidly with an increase of the
coupling (J) between the spins. Site specific average velocity exhibits a
change from a single exponential to biexponential decay pattern as the system
enters the active region of the phase diagram, accompanied by a non-monotonic
behavior of the correlation length. We conclude that a macroscopic coherent
state can emerge in the presence of a small concentration of active molecules.
We discuss experimental relevance of our results.",2107.04215v1
2021-10-13,Spin-lasing in bimodal quantum dot micropillar cavities,"Spin-controlled lasers are highly interesting photonic devices and have been
shown to provide ultra-fast polarization dynamics in excess of 200 GHz. In
contrast to conventional semiconductor lasers their temporal properties are not
limited by the intensity dynamics, but are governed primarily by the
interaction of the spin dynamics with the birefringent mode splitting that
determines the polarization oscillation frequency. Another class of modern
semiconductor lasers are high-beta emitters which benefit from enhanced
light-matter interaction due to strong mode confinement in low-mode-volume
microcavities. In such structures, the emission properties can be tailored by
the resonator geometry to realize for instance bimodal emission behavior in
slightly elliptical micropillar cavities. We utilize this attractive feature to
demonstrate and explore spin-lasing effects in bimodal high-beta quantum dot
micropillar lasers. The studied microlasers with a beta-factor of 4% show
spin-laser effects with experimental polarization oscillation frequencies up to
15 GHz and predicted frequencies up to about 100 GHz which are controlled by
the ellipticity of the resonator. Our results reveal appealing prospects for
very compact, ultra-fast and energy-efficient spin-lasers and can pave the way
for future purely electrically injected spin-lasers enabled by short injection
path lengths.",2110.06960v1
2022-01-12,Efficient Spin-Orbit Torques in an Antiferromagnetic Insulator with Tilted Easy Plane,"Electrical manipulation of spin textures inside antiferromagnets represents a
new opportunity for developing spintronics with superior speed and high device
density. Injecting spin currents into antiferromagnets and realizing efficient
spin-orbit-torque-induced switching is however still challenging due to the
complicated interactions from different sublattices. Meanwhile, because of the
diminishing magnetic susceptibility, the nature and the magnitude of
current-induced magnetic dynamics remain poorly characterized in
antiferromagnets, whereas spurious effects further complicate experimental
interpretations. In this work, by growing a thin film antiferromagnetic
insulator, {\alpha}-Fe2O3, along its non-basal plane orientation, we realize a
configuration where an injected spin current can robustly rotate the N\'eel
vector within the tilted easy plane, with an efficiency comparable to that of
classical ferromagnets. The spin-orbit torque effect stands out among other
competing mechanisms and leads to clear switching dynamics. Thanks to this new
mechanism, in contrast to the usually employed orthogonal switching geometry,
we achieve bipolar antiferromagnetic switching by applying positive and
negative currents along the same channel, a geometry that is more practical for
device applications. By enabling efficient spin-orbit torque control on the
antiferromagnetic ordering, the tilted easy plane geometry introduces a new
platform for quantitatively understanding switching and oscillation dynamics in
antiferromagnets.",2201.04732v1
2022-12-04,Superradiant Masing with Solid-state Spins at Room Temperature,"Steady-state superradiance and superradiant lasing attract significant
attentions in the field of optical lattice clocks, but have not been achieved
so far due to the technical challenges and atom loss problem. In this article,
we propose that their counter-part may be observed in the microwave domain with
solid-state spins-microwave resonator systems at room temperature with
realistic technical restrictions. To validate our proposal, we investigate
systematically the system dynamics and steady-state by solving quantum master
equations for the multi-level and multi-process dynamic of trillions of spins.
To this end, we employ a mean-field approach, and convert the mean-field
dynamics of the spin ensemble into the one in a more intuitive Dicke state
picture. Our calculations show that for systems with nitrogen vacancy center
spins and pentacene molecular spins the superradiant Rabi oscillations occur
firstly due to transitions among different Dicke states, and the subsequent
continuous-wave superradiant masing can achieve a linewidth well below
millihertz. Our work may guide further exploration of transient and
steady-state superradiant masing with the mentioned and other solid-state spins
systems, such as silicon vacancy centers in silicon carbide and boron vacancy
centers in hexagonal boron nitride, where the coherent radiation with
ultra-narrow linewidth may find applications in deep-space communications,
radio astronomy and high-precision metrology.",2212.01864v1
2023-02-14,On the Likely Dynamical Origin of GW191109 and of Binary Black Hole Mergers with Negative Effective Spin,"With the growing number of binary black hole (BBH) mergers detected by
LIGO/Virgo/KAGRA, several systems have become difficult to explain via isolated
binary evolution, having components in the pair-instability mass gap, high
orbital eccentricities, and/or spin-orbit misalignment. Here, we focus on
GW191109\_010717, a BBH merger with component masses of $65^{+11}_{-11}$ and
$47^{+15}_{-13}$ $\rm M_{\odot}$, and effective spin $-0.29^{+0.42}_{-0.31}$,
which could imply a spin-orbit misalignment of more than $\pi/2$ radians for at
least one of its components. Besides its component masses being in the
pair-instability mass gap, we show that isolated binary evolution is unlikely
to reproduce the proposed spin-orbit misalignment of GW191109 with high
confidence. On the other hand, we demonstrate that BBHs dynamically assembled
in dense star clusters would naturally reproduce the spin-orbit misalignment
and the masses of GW191109, and the rates of GW191109-like events, if at least
one of the components were to be a second-generation BH. Finally, we generalize
our results to all the events with a measured negative effective spin, arguing
that GW200225 also has a likely dynamical origin.",2302.07284v2
2023-02-26,Spin-Orbit Coupling of Europa's Ice Shell and Interior,"Europa is an icy ocean world, differentiated into a floating ice shell and
solid interior, separated by a global ocean. The classical spin-orbit coupling
problem considers a satellite as a single rigid body, but in the case of
Europa, the existence of the subsurface ocean enables independent motion of the
ice shell and solid interior. This paper explores the spin-orbit coupling
problem for Europa from a dynamical perspective, yielding illuminating
analytical and numerical results. We determine that the spin behavior of Europa
is influenced by processes not captured by the classical single rigid body
spin-orbit coupling analysis. The tidal locking process for Europa is governed
by the strength of gravity-gradient coupling between the ice shell and solid
interior, with qualitatively different behavior depending on the scale of this
effect. In this coupled rigid model, the shell can potentially undergo large
angular displacements from the solid interior, and the coupling plays an
outsize role in the dynamical evolution of the moon, even without incorporating
the dissipative effects of shell non-rigidity. We additionally discuss the
effects of a realistic viscoelastic shell, and catalogue other torques that we
expect to be sub-dominant in Europa's spin dynamics, or whose importance is
unknown. Finally, we explore how the choice of tidal model affects the
resulting equilibrium spin state.",2302.13226v3
2023-06-09,Secular dynamics of stellar spin driven by planets inside Kozai-Lidov resonance,"In many exoplanetary systems with `hot Jupiters', it is observed that the
spin axes of host stars are highly misaligned to planetary orbital axes. In
this study, a possible channel is investigated for producing such a
misalignment under a hierarchical three-body system where the evolution of
stellar spin is subjected to the gravitational torque induced from the planet
inside Kozai--Lidov (KL) resonance. In particular, two special configurations
are explored in detail. The first one corresponds to the configuration with
planets at KL fixed points, and the second one corresponds to the
configurations with planets moving on KL librating cycles. When the planet is
located at the KL fixed point, the corresponding Hamiltonian model is of one
degree of freedom and there are three branches of libration centres for stellar
spin. When the planet is moving on KL cycles, the technique of Poincar\'e
section is taken to reveal global structures of stellar spin in phase space. To
understand the complex structures, perturbative treatments are adopted to study
rotational dynamics. It shows that analytical structures in phase portraits
under the resonant model can agree well with numerical structures arising in
Poincar\'e sections, showing that the complicated dynamics of stellar spin are
governed by the primary resonance under the unperturbed Hamiltonian model in
combination with the 2:1 (high-order and/or secondary) spin-orbit resonances.",2306.05639v1
2023-11-22,Spin-orbit interaction driven terahertz nonlinear dynamics in transition metals,"The interplay of electric charge, spin, and orbital polarizations, coherently
driven by picosecond long oscillations of light fields in spin-orbit coupled
systems, is the foundation of emerging terahertz spintronics and orbitronics.
The essential rules for how terahertz light interacts with these systems in a
nonlinear way are still not understood. In this work, we demonstrate a
universally applicable electronic nonlinearity originating from spin-orbit
interactions in conducting materials, wherein the interplay of light-induced
spin and orbital textures manifests. We utilized terahertz harmonic generation
spectroscopy to investigate the nonlinear dynamics over picosecond timescales
in various transition metal films. We found that the terahertz harmonic
generation efficiency scales with the spin Hall conductivity in the studied
films, while the phase takes two possible values (shifted by {\pi}), depending
on the d-shell filling. These findings elucidate the fundamental mechanisms
governing non-equilibrium spin and orbital polarization dynamics at terahertz
frequencies, which is relevant for potential applications of terahertz spin-
and orbital-based devices.",2311.13272v1
2023-12-07,Nonlinear dielectric response in glasses: restoring forces and avoided spin-glass criticality,"Experimental measurements of nonlinear dielectric response in glassformers
like supercooled glycerol or propylene carbonate have been interpreted as
providing evidence for a growing thermodynamic length scale when lowering
temperature. A heuristic picture based on coherently flipping `superdipoles'
with disordered internal structure has been argued to capture the essence of
the experimentally reported behavior, pointing to the key role of effectively
disordered interactions in structural glasses. We test these ideas by devising
an explicit one-dimensional model of interacting spins incorporating both the
spin-glass spirit of the superdipole argument, and the necessary long-time
decorrelation of structural disorder, encoded here in a slow dynamics of the
coupling constants. The frequency-dependent third-order response of the model
qualitatively reproduces the typical humped shape reported in experiments. The
temperature dependence of the maximum value is also qualitatively reproduced.
In contrast, the humped shape of the third-order response is not reproduced by
a simple kinetically constrained spin model with non-interacting spins. To
rationalize these results, we propose a two-length-scale scenario by
distinguishing between the characteristic length of dynamical heterogeneities
and a coherence length that monitors the effect of interactions. We show that
both length scales are identical in the kinetically constrained spin model,
while they have significantly different dynamics in the model of interacting
spins.",2312.04267v1
1995-07-13,Spin Fluctuations in an Itinerant Heisenberg System: Naive Rpa Treatment,"The dynamical spin fluctuations in a two-dimensional square lattice in its
paramagnetic phase are examined within the framework of Random Phase
Approximation(RPA). Itinerant carriers with spin interact with each other via
an antiferromagnetic Heisenberg interaction. Then there appear three
fundamental scattering processes;a) scattering between parallel spins,b)
scattering between antiparallel spins and c) scattering with spin-flip. To
examine how these scattering processes affect the dynamical spin fluctuations,
we pick up carefully all possible combination of RPA diagrams in a consistent
manner and take the spin rotational symmetry into account. Then it becomes
clear that we have to take up a sequence of the irreducible single loop which
in itself is modified due to the particle-hole ladder type vertex correction.We
set up the Bethe-Salpeter equation for the vertex correction and show that this
can be solved in a closed form due to separable nature of the antiferromagnetic
interaction. We evaluated numerically the effectof the vertex correction and
found that the correction is negligibly small. Therefore we propose that in an
itinerant Heisenberg system, including the $t$-$J$ model as its derivertive,
the simplified RPA, where the irreducible single loop is unrenormalized, works
very well. This conclusion strongly support the simplified treatment which is
widely used in High-$T_{c}$ problem. Moreover the present formalism enables us
to proceed further microscopic calculations on the magnetic properties in the
current High-$T_{c}$ problem.",9507042v2
1998-06-30,Structure and Spin Dynamics of La$_{0.85}$Sr$_{0.15}$MnO$_3$,"Neutron scattering has been used to study the structure and spin dynamics of
La$_{0.85}$Sr$_{0.15}$MnO$_3$. The magnetic structure of this system is
ferromagnetic below T_C = 235 K. We see anomalies in the Bragg peak intensities
and new superlattice peaks consistent with the onset of a spin-canted phase
below T_{CA} = 205 K, which appears to be associated with a gap at q = (0, 0,
0.5) in the spin-wave spectrum. Anomalies in the lattice parameters indicate a
concomitant lattice distortion. The long-wavelength magnetic excitations are
found to be conventional spin waves, with a gapless (< 0.02 meV) isotropic
dispersion relation $E = Dq^2$. The spin stiffness constant D has a $T^{5/2}$
dependence at low T, and the damping at small q follows $q^4T^{2}$. An
anomalously strong quasielastic component, however, develops at small wave
vector above 200 K and dominates the fluctuation spectrum as T -> T_C. At
larger q, on the other hand, the magnetic excitations become heavily damped at
low temperatures, indicating that spin waves in this regime are not eigenstates
of the system, while raising the temperature dramatically increases the
damping. The strength of the spin-wave damping also depends strongly on the
symmetry direction in the crystal. These anomalous damping effects are likely
due to the itinerant character of the $e_g$ electrons.",9806381v1
2002-07-04,"Dynamics, Selection Rules and Dzyaloshinsky-Moriya interactions in Strongly Frustrated Magnets","Anisotropic spin-spin interactions of the symmetry described by Dzyaloshinsky
and Moriya are generally considered weak, as they depend on the spin-orbit
couplings. In frustrated spin systems with singlet ground states they can,
however, have rather strong effects. We discuss recent results related to two
gapped spin systems: $\rm CuGeO_3$ and $\rm SrCu_2(BO_3)_2$ in particular. In
the first compound the Dzyaloshinsky-Moriya interactions effectively lower the
symmetry of the magnetic unit cell and this leads to doubling of the low
frequency mode. In the second case, the Dzyaloshinsky-Moriya interactions also
split the lowest magnon mode linearly in the spin-orbit coupling. In addition,
the relatively weak Dzyaloshinsky-Moriya interactions can dominate the
dispersion.
  Consideration of the selection rules for optical transitions show that while
the Dzyaloshinsky-Moriya interactions can explain much of the dynamics, they do
not explain the observed transition amplitudes. This leads to a review of
recent calculations of anisotropic spin-phonon couplings. We discuss how this
leads to a novel mechanism to explain the ESR intensities in the spin gap
systems discussed. Selection rules for this novel mechanism involving coupling
to the electric field of the resonant probe are discussed and relation to
polarised neutron experiments briefly mentioned.",0207116v1
2006-09-29,Bosonization approach to charge and spin dynamics of 1D fermions with band-curvature,"We consider one-dimensional (1D) spin-1/2 fermions in a clean quantum wire,
with forward scattering interactions and a non-linear single-particle spectrum,
$\xi_k = v|k| + k^2/2m$ where $v$ is the Fermi velocity and $1/m$ is the
band-curvature. We calculate the dynamical structure factor (DSF) of the model
at small wave-vector $q$ with the help of the bosonization technique. For
spinless fermions, we show that, starting from the single-parametric spectrum:
$\om = u |q|$, bosonization emulates the 2-parametric excitation spectrum: $\om
= u |q| \pm q^2/2m^*$, where $m^*$ decreases with increasing repulsive
interactions. Moreover, away from the excitation-cone, {\it i.e.} $\om \gg u
|q|$, bosonization yields the 2-pair excitation continuum of the DSF. For
spinful fermions, we show that the spin-charge coupling (SCC) due to
band-curvature affects charge and spin DSF in an asymmetric way. For the charge
DSF, SCC manifests as a two-peak structure: a charge peak at $\om = u_\rho |q|$
but also a spin peak at $\om = u_\sigma |q|$, as charge fluctuations may decay
via chargeless spin-singlet excitations. For the magnetic DSF, SCC manifests as
a continuous transfer of magnetic spectral weight to frequencies $\om >
u_\sigma |q|$, as spin fluctuations decay via pairs of chargeless spin and
spinless charge-neutral excitations.",0609754v2
2001-01-07,Formation and Dynamics of a Schrödinger-Cat State in Continuous Quantum Measurement,"We consider the process of a single-spin measurement using magnetic resonance
force microscopy (MRFM) as an example of a truly continuous measurement in
quantum mechanics. This technique is also important for different applications,
including a measurement of a qubit state in quantum computation. The
measurement takes place through the interaction of a single spin with a
quasi-classical cantilever, modeled by a quantum oscillator in a coherent state
in a quasi-classical region of parameters. The entire system is treated
rigorously within the framework of the Schr\""odinger equation, without any
artificial assumptions. Computer simulations of the spin-cantilever dynamics,
where the spin is continuously rotated by means of cyclic adiabatic inversion,
show that the cantilever evolves into a Schr\""odinger-cat state: the
probability distribution for the cantilever position develops two asymmetric
peaks that quasi-periodically appear and vanish. For a many-spin system our
equations reduce to the classical equations of motion, and we accurately
describe conventional MRFM experiments involving cyclic adiabatic inversion of
the spin system. We surmise that the interaction of the cantilever with the
environment would lead to a collapse of the wave function; however, we show
that in such a case the spin does not jump into a spin eigenstate.",0101035v1
2007-05-10,Observation of extremely slow hole spin relaxation in self-assembled quantum dots,"We report the measurement of extremely slow hole spin relaxation dynamics in
small ensembles of self-assembled InGaAs quantum dots. Individual spin
orientated holes are optically created in the lowest orbital state of each dot
and read out after a defined storage time using spin memory devices. The
resulting luminescence signal exhibits a pronounced polarization memory effect
that vanishes for long storage times. The hole spin relaxation dynamics are
measured as a function of external magnetic field and lattice temperature. We
show that hole spin relaxation can occur over remarkably long timescales in
strongly confined quantum dots (up to ~270 us), as predicted by recent theory.
Our findings are supported by calculations that reproduce both the observed
magnetic field and temperature dependencies. The results suggest that hole spin
relaxation in strongly confined quantum dots is due to spin orbit mediated
phonon scattering between Zeeman levels, in marked contrast to higher
dimensional nanostructures where it is limited by valence band mixing.",0705.1466v4
2008-06-28,Suppression of quantum tunneling for all spins for easy-axis systems,"The semi-classical limit of quantum spin systems corresponds to a dynamical
Lagrangian which contains the usual kinetic energy, the couplings and
interactions of the spins and an additional, first order kinematical term which
corresponds to the Wess-Zumino-Novikov-Witten (WZNW) term for the spin degree
of freedom \cite{og}. It was shown that in the case of the kinetic dynamics
determined only by the WZNW term, half odd integer spin systems show a lack of
tunneling phenomena whereas integer spin systems are subject to it \cite{l} in
the case of potentials with easy-plane easy-axis symmetry. Here we prove, for
the theory with a normal quadratic kinetic term of arbitrary strength or the
first order theory with azimuthal symmetry (which is equivalently the so-called
easy-axis situation), that the tunneling is in fact suppressed for all non-zero
values of spin. This model exemplifies the concept that in the presence of
complex Euclidean action, it is necessary to use the ensuing complex critical
points in order to define the quantum (perturbation) theory \cite{ampr}. In the
present example, if we do not do so, exactly the opposite, erroneous
conclusion, that the tunneling is unsuppressed for all spins, is reached.",0806.4692v1
2009-06-30,Exact Algorithm for Sampling the 2D Ising Spin Glass,"A sampling algorithm is presented that generates spin glass configurations of
the 2D Edwards-Anderson Ising spin glass at finite temperature, with
probabilities proportional to their Boltzmann weights. Such an algorithm
overcomes the slow dynamics of direct simulation and can be used to study
long-range correlation functions and coarse-grained dynamics. The algorithm
uses a correspondence between spin configurations on a regular lattice and
dimer (edge) coverings of a related graph: Wilson's algorithm [D. B. Wilson,
Proc. 8th Symp. Discrete Algorithms 258, (1997)] for sampling dimer coverings
on a planar lattice is adapted to generate samplings for the dimer problem
corresponding to both planar and toroidal spin glass samples. This algorithm is
recursive: it computes probabilities for spins along a ""separator"" that divides
the sample in half. Given the spins on the separator, sample configurations for
the two separated halves are generated by further division and assignment. The
algorithm is simplified by using Pfaffian elimination, rather than Gaussian
elimination, for sampling dimer configurations. For n spins and given floating
point precision, the algorithm has an asymptotic run-time of O(n^{3/2}); it is
found that the required precision scales as inverse temperature and grows only
slowly with system size. Sample applications and benchmarking results are
presented for samples of size up to n=128^2, with fixed and periodic boundary
conditions.",0906.5519v2
2010-06-08,Dynamic spin susceptibility of superconducting cuprates: A microscopic theory of the magnetic resonance mode,"A microscopic theory of the dynamic spin susceptibility (DSS) in the
superconducting state within the t-J model is presented. It is based on an
exact representation for the DSS obtained by applying the Mori-type projection
technique for the relaxation function in terms of Hubbard operators. The static
spin susceptibility is evaluated by a sum-rule-conserving generalized
mean-field approximation, while the self-energy is calculated in the
mode-coupling approximation. The spectrum of spin excitations is studied in the
underdoped and optimally doped regions. The DSS reveals a resonance mode (RM)
at the antiferromagnetic wave vector Q = \pi(1,1) at low temperatures due to a
strong suppression of the damping of spin excitations. This is explained by an
involvement of spin excitations in the decay process besides the particle-hole
continuum usually considered in random-phase-type approximations. The spin gap
in the spin-excitation spectrum at Q plays a dominant role in limiting the
decay in comparison with the superconducting gap which results in the
observation of the RM even above $T_c$ in the underdoped region. A good
agreement with inelastic neutron-scattering experiments on the RM in YBCO
compounds is found.",1006.1525v2
2010-08-25,Doping dependence of spin dynamics of drifting electrons in GaAs bulks,"We study the effect of the impurity density on lifetimes and relaxation
lengths of electron spins in the presence of a static electric field in a
n-type GaAs bulk. The transport of electrons and the spin dynamics are
simulated by using a semiclassical Monte Carlo approach, which takes into
account the intravalley scattering mechanisms of warm electrons in the
semiconductor material. Spin relaxation is considered through the
D'yakonov-Perel mechanism, which is the dominant mechanism in III-V
semiconductors. The evolution of spin polarization is analyzed by computing the
lifetimes and depolarization lengths as a function of the doping density in the
range 10^{13} - 10^{16} cm^{-3}, for different values of the amplitude of the
static electric field (0.1 - 1.0 kV/cm). We find an increase of the electron
spin lifetime as a function of the doping density, more evident for lattice
temperatures lower than 150 K. Moreover, at very low intensities of the driving
field, the spin depolarization length shows a nonmonotonic behaviour with the
density. At the room temperature, the spin lifetimes and depolarization lengths
are nearly independent on the doping density. The underlying physics is
analyzed.",1008.4228v6
2012-09-16,Glass-like recovery of antiferromagnetic spin ordering and dimensional crossover in a photo-excited manganite Pr$_{0.7}$Ca$_{0.3}$MnO$_3$,"Electronic orderings of charges, orbitals and spins are observed in many
strongly correlated electron materials, and revealing their dynamics is a
critical step toward understanding the underlying physics of important emergent
phenomena. Here we use time-resolved resonant soft x-ray scattering
spectroscopy to probe the dynamics of antiferromagnetic spin ordering in the
manganite Pr$_{0.7}$Ca$_{0.3}$MnO$_3$ following ultrafast photo-exitation. Our
studies reveal a glass-like recovery of the spin ordering and a crossover in
the dimensionality of the restoring interaction from quasi-1D at low pump
fluence to 3D at high pump fluence. This behavior arises from the metastable
state created by photo-excitation, a state characterized by spin disordered
metallic droplets within the larger charge- and spin-ordered insulating
domains. Comparison with time-resolved resistivity measurements suggests that
the collapse of spin ordering is correlated with the insulator-to-metal
transition, but the recovery of the insulating phase does not depend on the
re-establishment of the spin ordering.",1209.3452v2
2013-05-13,Absence of exponential sensitivity to small perturbations in nonintegrable systems of spins 1/2,"We show that macroscopic nonintegrable lattices of spins 1/2, which are often
considered to be chaotic, do not exhibit the basic property of classical
chaotic systems, namely, exponential sensitivity to small perturbations. We
compare chaotic lattices of classical spins and nonintegrable lattices of spins
1/2 in terms of their magnetization responses to imperfect reversal of spin
dynamics known as Loschmidt echo. In the classical case, magnetization exhibits
exponential sensitivity to small perturbations of Loschmidt echoes, which is
characterized by twice the value of the largest Lyapunov exponent of the
system. In the case of spins 1/2, magnetization is only power-law sensitive to
small perturbations. Our findings imply that it is impossible to define
Lyapunov exponents for lattices of spins 1/2 even in the macroscopic limit. At
the same time, the above absence of exponential sensitivity to small
perturbations is an encouraging news for the efforts to create quantum
simulators. The power-law sensitivity of spin 1/2 lattices to small
perturbations is predicted to be measurable in nuclear magnetic resonance
experiments.",1305.2817v2
2013-05-14,Long-range FMR driven spin pumping through a nonmagnetic insulator,"Ferromagnetic resonance (FMR) driven spin pumping is an emerging technique
for injection of a pure spin current from a ferromagnet (FM) into a
non-magnetic (NM) material without an accompanying charge current. It is widely
believed that this pumping proceeds exclusively via a short-range exchange
interaction at the FM/NM interface. Here we report robust, long-range spin
pumping from the ferrimagnetic double perovskite Sr2FeMoO6 (SFMO) into Pt
across an insulating barrier up to 200 nm thick, and systematically rule out
all known spurious effects. This result demonstrates dynamic spin injection
over a distance far beyond the coupling range of the exchange interaction,
exposing the need to consider other coupling mechanisms. The characteristic
length scale for magnetic textures in Sr2FeMoO6 is approximately 150 nm,
resulting from structural antiphase boundaries, thus raising the possibility
that magnetic dipole coupling underlies the observed long range spin transfer.
This discovery reveals a route to dynamic angular momentum transfer between a
FM and a NM in the absence of mediation by itinerant electrons and promises new
spin-functional devices employing long-range spin pumping.",1305.3016v2
2016-07-14,Spin dynamics of diamond nitrogen-vacancy centres at the ground state level anti-crossing and all-optical low frequency magnetic field sensing,"We investigate the photo-induced spin dynamics of single nitrogen-vacancy
(NV) centres in diamond near the electronic ground state level anti-crossing
(GSLAC), which occurs at an axial magnetic field around 1024 G. Using optically
detected magnetic resonance spectroscopy, we first find that the electron spin
transition frequency can be tuned down to 100 kHz for the \NV{14} centre, while
for the \NV{15} centre the transition strength vanishes for frequencies below
about 2 MHz owing to the GSLAC level structure. Using optical pulses to prepare
and readout the spin state, we observe coherent spin oscillations at 1024 G for
the \NV{14}, which originate from spin mixing induced by residual transverse
magnetic fields. This effect is responsible for limiting the smallest
observable transition frequency, which can span two orders of magnitude from
100 kHz to tens of MHz depending on the local magnetic noise. A similar feature
is observed for the \NV{15} centre at 1024 G. As an application of these
findings, we demonstrate all-optical detection and spectroscopy of
externally-generated fluctuating magnetic fields at frequencies from 8 MHz down
to 500 kHz, using a \NV{14} centre. Since the Larmor frequency of most nuclear
spin species lies within this frequency range near the GSLAC, these results
pave the way towards all-optical, nanoscale nuclear magnetic resonance
spectroscopy, using longitudinal spin cross-relaxation.",1607.04006v1
2016-07-14,Complete conservative dynamics for inspiralling compact binaries with spins at the fourth post-Newtonian order,"In this work we complete the spin-dependent conservative dynamics of
inspiralling compact binaries at the fourth post-Newtonian order, and in
particular the derivation of the next-to-next-to-leading order spin-squared
interaction potential. We derive the physical equations of motion of the
position and the spin from a direct variation of the action. Further, we derive
the quadratic-in-spin Hamiltonians, as well as their expressions in the
center-of-mass frame. We construct the conserved integrals of motion, which
form the Poincar\'e algebra. This construction provided a consistency check for
the validity of our result, which is crucial in particular in the current
absence of another independent derivation of the next-to-next-to-leading order
spin-squared interaction. Finally, we provide here the complete gauge-invariant
relations among the binding energy, angular momentum, and orbital frequency of
an inspiralling binary with generic compact spinning components to the fourth
post-Newtonian order. These high post-Newtonian orders, in particular taking
into account the spins of the binary constituents, will enable to gain more
accurate information on the constituents from even more sensitive
gravitational-wave detections to come.",1607.04252v2
2016-09-08,Influence of non-magnetic impurity scattering on the spin dynamics in diluted magnetic semiconductors,"The doping of semiconductors with magnetic impurities gives rise not only to
a spin-spin interaction between quasi-free carriers and magnetic impurities,
but also to a local spin-independent disorder potential for the carriers. Based
on a quantum kinetic theory for the carrier and impurity density matrices as
well as the magnetic and non-magnetic carrier-impurity correlations, the
influence of the non-magnetic scattering potential on the spin dynamics in DMS
after optical excitation with circularly polarized light is investigated using
the example of Mn-doped CdTe. It is shown that non-Markovian effects, which are
predicted in calculations where only the magnetic carrier-impurity interaction
is accounted for, can be strongly suppressed in the presence of non-magnetic
impurity scattering. This effect can be traced back to a significant
redistribution of carriers in $\mathbf{k}$-space which is enabled by the
build-up of large carrier-impurity correlation energies. A comparison with the
Markov limit of the quantum kinetic theory shows that, in the presence of an
external magnetic field parallel to the initial carrier polarization, the
asymptotic value of the spin polarization at long times is significantly
different in the quantum kinetic and the Markovian calculations. This effect
can also be attributed to the formation of strong correlations which
invalidates the semiclassical Markovian picture and it is stronger when the
non-magnetic carrier-impurity interaction is accounted for. In an external
magnetic field perpendicular to the initial carrier spin, the correlations are
also responsible for a renormalization of the carrier spin precession
frequency.",1609.02582v1
2017-03-14,Waveform measurement of charge- and spin-density wave packets in a Tomonaga-Luttinger liquid,"In contrast to a free electron system, a Tomonaga-Luttinger (TL) liquid in a
one dimensional (1D) electron system hosts charge and spin excitations as
independent entities. When an electron wave packet is injected into a TL
liquid, it transforms into wave packets carrying either charge or spin that
propagate at different group velocities and move away from each other. This
process, known as spin-charge separation, is the hallmark of TL physics. While
the existence of these TL eigenmodes has been identified in momentum- or
frequency-resolved measurements, their waveforms, which are a direct
manifestation of 1D electron dynamics, have been long awaited to be measured.
In this study, we present a time domain measurement for the
spin-charge-separation process in an asymmetric chiral TL liquid comprising
quantum Hall (QH) edge channels. We measure the waveforms of both charge and
spin excitations by combining a spin filter with a time-resolved charge
detector. Spatial separation of charge- and spin-wave packets over a distance
exceeding 200 um was confirmed. In addition, we found that the 1D electron
dynamics can be controlled by tuning the electric environment. These
experimental results provide fundamental information about non-equilibrium
phenomena in actual 1D electron systems.",1703.04833v1
2018-11-26,A solvable quantum model of dynamic nuclear polarization in quantum dots,"We present a quantum mechanical theory of optically induced dynamic nuclear
polarization applicable to quantum dots and other interacting spin systems. The
exact steady state of the optically driven coupled electron-nuclear system is
calculated under the assumption of uniform hyperfine coupling strengths (box
model) for an arbitrary number of nuclear spins. This steady state is given by
a tractable expression that allows for an intuitive interpretation in terms of
spin-flip rates. Based on this result, we investigate the nuclear spin
behaviour for different experimental parameter regimes and find that our model
reproduces the flat-top and triangular absorption line shapes seen in various
experiments (line dragging) under the assumption of fast electron spin
dephasing due to phonons and co-tunneling. The mechanism responsible for line
dragging has been a matter of controversy so far; in contrast with previous
works, we show that the effect can be explained solely in terms of the contact
hyperfine interaction, without the need to introduce non-collinear terms or
other types of electron-nuclear interactions. Furthermore we predict a novel
nuclear spin polarization effect: under particular, experimentally realistic
conditions, the nuclear spin system tends to become sharply polarized in such a
way as to cancel the effect of the external magnetic field. This effect can
therefore suppress electron spin dephasing due to inhomogeneous broadening,
which could have important repercussions for quantum technological
applications.",1811.10491v2
2019-05-31,Fingerprints of Kitaev physics in the magnetic excitations of honeycomb iridates,"In the quest for realizations of quantum spin liquids, the exploration of
Kitaev materials - spin-orbit entangled Mott insulators with strong
bond-directional exchanges - has taken center stage. However, in these
materials the local spin-orbital j=1/2 moments typically show long-range
magnetic order at low temperature, thus defying the formation of a spin-liquid
ground state. Using resonant inelastic x-ray scattering (RIXS), we here report
on a proximate spin liquid regime with clear fingerprints of Kitaev physics in
the magnetic excitations of the honeycomb iridates alpha-Li2IrO3 and Na2IrO3.
We observe a broad continuum of magnetic excitations that persists up to at
least 300K, more than an order of magnitude larger than the magnetic ordering
temperatures. We prove the magnetic character of this continuum by an analysis
of the resonance behavior. RIXS measurements of the dynamical structure factor
for energies within the continuum show that dynamical spin-spin correlations
are restricted to nearest neighbors. Notably, these spectroscopic observations
are also present in the magnetically ordered state for excitation energies
above the conventional magnon excitations. Phenomenologically, our data agree
with inelastic neutron scattering results on the related honeycomb compound
RuCl3, establishing a common ground for a proximate Kitaev spin-liquid regime
in these materials.",1905.13590v1
2016-11-23,X-ray imaging of spin currents and magnetisation dynamics at the nanoscale,"Understanding how spins move in time and space is the aim of both fundamental
and applied research in modern magnetism. Over the past three decades, research
in this field has led to technological advances that have had a major impact on
our society, while improving the understanding of the fundamentals of spin
physics. However, important questions still remain unanswered, because it is
experimentally challenging to directly observe spins and their motion with a
combined high spatial and temporal resolution. In this article, we present an
overview of the recent advances in X-ray microscopy that allow researchers to
directly watch spins move in time and space at the microscopically relevant
scales. We discuss scanning X-ray transmission microscopy (STXM) at resonant
soft X-ray edges, which is available at most modern synchrotron light sources.
This technique measures magnetic contrast through the X-ray magnetic circular
dichroism (XMCD) effect at the resonant absorption edges, while focusing the
X-ray radiation at the nanometre scale, and using the intrinsic pulsed
structure of synchrotron-generated X-rays to create time-resolved images of
magnetism at the nanoscale. In particular, we discuss how the presence of spin
currents can be detected by imaging spin accumulation, and how the
magnetisation dynamics in thin ferromagnetic films can be directly imaged. We
discuss how a direct look at the phenomena allows for a deeper understanding of
the the physics at play, that is not accessible to other, more indirect
techniques. Finally, we present an overview of the exciting opportunities that
lie ahead to further understand the fundamentals of novel spin physics,
opportunities offered by the appearance of diffraction limited storage rings
and free electron lasers.",1611.07691v2
2017-01-12,Dynamic coupling of ferromagnets via spin Hall magnetoresistance,"The synchronized magnetization dynamics in ferromagnets on a nonmagnetic
heavy metal caused by the spin Hall effect is investigated theoretically. The
direct and inverse spin Hall effects near the ferromagnetic/nonmagnetic
interface generate longitudinal and transverse electric currents. The
phenomenon is known as the spin Hall magnetoresistance effect, whose magnitude
depends on the magnetization direction in the ferromagnet due to the spin
transfer effect. When another ferromagnet is placed onto the same nonmagnet,
these currents are again converted to the spin current by the spin Hall effect
and excite the spin torque to this additional ferromagnet, resulting in the
excitation of the coupled motions of the magnetizations. The in-phase or
antiphase synchronization of the magnetization oscillations, depending on the
value of the Gilbert damping constant and the field-like torque strength, is
found in the transverse geometry by solving the Landau-Lifshitz-Gilbert
equation numerically. On the other hand, in addition to these synchronizations,
the synchronization having a phase difference of a quarter of a period is also
found in the longitudinal geometry. The analytical theory clarifying the
relation among the current, frequency, and phase difference is also developed,
where it is shown that the phase differences observed in the numerical
simulations correspond to that giving the fixed points of the energy supplied
by the coupling torque.",1701.03201v2
2012-04-05,Seeing the light : experimental signatures of emergent electromagnetism in a quantum spin ice,"The ""spin ice"" state found in the rare earth pyrochlore magnets Ho2Ti2O7 and
Dy2Ti2O7 offers a beautiful realisation of classical magnetostatics, complete
with magnetic monopole excitations. It has been suggested that in ""quantum spin
ice"" materials, quantum-mechanical tunnelling between different ice
configurations could convert the magnetostatics of spin ice into a quantum spin
liquid which realises a fully dynamical, lattice-analogue of quantum
electromagnetism. Here we explore how such a state might manifest itself in
experiment, within the minimal microscopic model of a such a quantum spin ice.
We develop a lattice field theory for this model, and use this to make explicit
predictions for the dynamical structure factor which would be observed in
neutron scattering experiments on a quantum spin ice. We find that ""pinch
points"", seen in quasi-elastic scattering, which are the signal feature of a
classical spin ice, fade away as a quantum ice is cooled to its
zero-temperature ground state. We also make explicit predictions for the
ghostly, linearly dispersing magnetic excitations which are the ""photons"" of
this emergent electromagnetism. The predictions of this field theory are shown
to be in quantitative agreement with Quantum Monte Carlo simulations at zero
temperature.",1204.1325v2
2015-12-06,Intrinsic limit to electron spin coherence in InGaAs quantum dots featuring strain-induced nuclear dispersion,"The Zeeman-split spin-states of a single electron confined in a
self-assembled quantum dot provide an optically-accessible spin qubit. For
III-V materials the nuclear spins of the solid-state host provide an intrinsic
noise source, resulting in electron-spin dephasing times of few nanoseconds.
While a comprehensive study of electron-spin dynamics at low magnetic field has
recently been carried out, what limits the electron coherence in these systems
remains unclear, in part due to the dominant effect of measurement-induced
dynamic polarisation of the nuclear bath. We develop an all-optical method to
access the quantum dot spin-state without perturbing the nuclear environment.
We use this method to implement Hahn-echo decoupling and reach the intrinsic
limit to coherence set by inhomogeneous strain fields coupling to quadrupolar
moments of the nuclear bath. These results indicate that the extension of
electron spin coherence beyond this few-microsecond limit necessitates the
reduction of strain-induced quadrupolar broadening in these materials.",1512.01811v2
2018-10-04,Ultrafast Spin-To-Charge Conversion at the Surface of Topological Insulator Thin Films,"Strong spin-orbit coupling, resulting in the formation of
spin-momentum-locked surface states, endows topological insulators with
superior spin-to-charge conversion characteristics, though the dynamics that
govern it have remained elusive. Here, we present an all-optical method that
enables unprecedented tracking of the ultrafast dynamics of spin-to-charge
conversion in a prototypical topological insulator Bi$_2$Se$_3$/ferromagnetic
Co heterostructure, down to the sub-picosecond timescale. Compared to pure
Bi$_2$Se$_3$ or Co, we observe a giant terahertz emission in the
heterostructure than originates from spin-to-charge conversion, in which the
topological surface states play a crucial role. We identify a 0.12-picosecond
timescale that sets a technological speed limit of spin-to-charge conversion
processes in topological insulators. In addition, we show that the
spin-to-charge conversion efficiency is temperature independent in Bi$_2$Se$_3$
as expected from the nature of the surface states, paving the way for designing
next-generation high-speed opto-spintronic devices based on topological
insulators at room temperature.",1810.02253v1
2019-06-18,Noninertial and spin effects on the 2D Dirac oscillator in the magnetic cosmic string background,"In this work, we analyze the influence of noninertial and spin effects on the
dynamics of the 2D Dirac oscillator in the magnetic cosmic string background.
To model this background, we consider a uniform magnetic field, the
Aharonov-Bohm effect, and a parameter $\eta$ generated by a cosmic string.
Posteriorly, we determine the bound-state solutions of the system: the Dirac
spinor and the relativistic energy spectrum. We verified that this spinor is
written in terms of the generalized Laguerre polynomials and this spectrum
depends on the effective quantum number $N_r$, angular velocity $\Omega$ and
parameter $s$ associated to the noninertial and spin effects, magnetic flux
$\Phi$, cyclotron frequency $\omega_c$, zero-point energy $E_0$, and on the
deficit angle $\eta$. In particular, we note that besides this spectrum to be a
periodic function and asymmetric, its values infinitely increase when $\eta\to
0$ or $N_r=\omega_c=\Omega\to\infty$. We also note that the energies of the
antiparticle with spin down are larger than of the particle with spin up or
down. In the nonrelativistic limit, we get the Schr\""{o}dinger-Pauli oscillator
with two types of couplings: the spin-orbit coupling and the spin-rotation
coupling, and two Hamiltonians: one quantum harmonic oscillator-type and other
Zeeman-type. Finally, we compare our results with other works, where we
verified that our problem generalizes some particular cases of the literature
when $\Omega$, $\omega_c$, $\Phi$, $s$ or $\eta$ are excluded from the system.",1906.07369v2
2019-07-29,Anomalous diffusion and localization in a positionally disordered quantum spin array,"Disorder in quantum systems can lead to the disruption of long-range order in
the ground state and to the localization of the elementary excitations - famous
examples thereof being the Bose glass of interacting bosons in a disordered or
quasi-periodic environment, or the localized phase of spin chains mapping onto
fermions. Here we present a two-dimensional quantum Ising model - relevant to
the physics of Rydberg-atom arrays - in which positional disorder of the spins
induces a randomization of the spin-spin couplings and of an on-site
longitudinal field. This form of disorder preserves long-range order in the
ground state, while it localizes the elementary excitations above it,
faithfully described as spin waves: the spin-wave spectrum is partially
localized for weak disorder (seemingly exhibiting mobility edges between
localized and extended, yet non-ergodic states), while it is fully localized
for strong disorder. The regime of partially localized excitations exhibits a
very rich non-equilibrium dynamics following a low-energy quench: correlations
and entanglement spread with a power-law behavior whose exponent is a
continuous function of disorder, interpolating between ballistic and arrested
transport. Our findings expose a stark dichotomy between static and dynamical
properties of disordered quantum spin systems, which is readily accessible to
experimental verification using quantum simulators of closed quantum many-body
systems.",1907.12511v1
2019-10-30,On decoherence induced by a spin chain: role of initial prepared states,"We study the decoherence process induced by a spin chain environment on a
central spin consisting of R spins and we apply it on the dynamics of quantum
correlations (QCs) of three interacting qubits. In order to see the impact of
the initial prepared state of the spin chain environment on the decoherence
process, we assume the spin chain environment prepared in two main ways,
namely, either the ground state or the vacuum state in the momentum space. We
develop a general heuristic analysis when the spin chain environment in
prepared in these states, in order to understand the decoherence process
against the physical parameters. We show that the decoherence process is mainly
determined by the choice of the initial prepared state, the number of spin of
the chain, the coupling strength, the anisotropy parameter and the position
from the quantum critical point. In fact, in the strong coupling regime, the
decoherence process does not appear for the environment prepared in the vacuum
state and it behaves oscillatory in the case of evolution from ground state. On
the other hand, in the weak coupling regime and far from the quantum critical
point, decoherence induced by the ground state is weaker than that of the
vacuum state. Finally, we show that, QCs are completely shielded from
decoherence in the case of evolution from the W state and obey the same
dynamics as the decoherence factors for the GHZ state.",1910.13661v1
2020-01-14,Decoherence dynamics of entangled quantum states in the $XXX$ central spin model,"Maintaining coherence of a qubit is of vital importance for realizing a
large-scale quantum computer in practice. In this work, we study the central
spin decoherence problem in the $XXX$ central spin model (CSM) and focus on the
quantum states with different initial entanglement, namely intra-bath
entanglement or system-bath entanglement. We analytically obtain their
evolutions of fidelity, entanglement, and quantum coherence. When the initial
bath spins constitute an $N$-particle entangled state (the
Greenberger-Horne-Zeilinger-bath or the $W$-bath), the leading amplitudes of
their fidelity evolutions both scale as $\mathcal O(1/N)$, which is the same as
the case of a fully polarized bath. However, when the central spin is maximally
entangled with one of the bath spins, the amplitude scaling of its fidelity
evolution declines from $\mathcal O(1/N)$ to $\mathcal O(1/N^2)$. That implies
appropriate initial system-bath entanglement is contributive to suppress
central spin decoherence. In addition, with the help of system-bath
entanglement, we realize quantum coherence-enhanced dynamics for the central
spin where the consumption of bath entanglement is shown to play a central
role.",2001.04772v2
2017-09-03,Femtosecond formation dynamics of the spin Seebeck effect revealed by terahertz spectroscopy,"Understanding the transfer of spin angular momentum is essential in modern
magnetism research. A model case is the generation of magnons in magnetic
insulators by heating an adjacent metal film. Here, we reveal the initial steps
of this spin Seebeck effect with <27fs time resolution using terahertz
spectroscopy on bilayers of ferrimagnetic yttrium-iron garnet and platinum.
Upon exciting the metal with an infrared laser pulse, a spin Seebeck current
$j_\textrm{s}$ arises on the same ~100fs time scale on which the metal
electrons thermalize. This observation highlights that efficient spin transfer
critically relies on carrier multiplication and is driven by conduction
electrons scattering off the metal-insulator interface. Analytical modeling
shows that the electrons' dynamics are almost instantaneously imprinted onto
$j_\textrm{s}$ because their spins have a correlation time of only ~4fs and
deflect the ferrimagnetic moments without inertia. Applications in material
characterization, interface probing, spin-noise spectroscopy and terahertz spin
pumping emerge.",1709.00768v5
2019-03-11,Giant spin-orbit torque in a single ferrimagnetic metal layer,"Antiferromagnets and compensated ferrimagnets offer opportunities to
investigate spin dynamics in the 'terahertz gap' because their resonance modes
lie in the 0.3 THz to 3 THz range. Despite some inherent advantages when
compared to ferromagnets, these materials have not been extensively studied due
to difficulties in exciting and detecting the high-frequency spin dynamics,
especially in thin films. Here we show that spin-obit torque in a single layer
of the highly spin-polarized compensated ferrimagnet Mn2RuxGa is remarkably
efficient at generating spin-orbit fields \mu_0H_eff, which approach 0.1x10-10
T m2/A in the low-current density limit -- almost a thousand times the Oersted
field, and one to two orders of magnitude greater than the effective fields in
heavy metal/ferromagnet bilayers. From an analysis of the harmonic Hall effect
which takes account of the thermal contributions from the anomalous Nernst
effect, we show that the antidamping component of the spin-orbit torque is
sufficient to sustain self-oscillation. Our study demonstrates that spin
electronics has the potential to underpin energy-frugal, chip-based solutions
to the problem of ultra high-speed information transfer.",1903.04432v3
2019-04-15,Spin-boson model as a simulator of non-Markovian multiphoton Jaynes-Cummings models,"The paradigmatic spin-boson model considers a spin degree of freedom
interacting with an environment typically constituted by a continuum of bosonic
modes. This ubiquitous model is of relevance in a number of physical systems
where, in general, one has neither control over the bosonic modes, nor the
ability to tune distinct interaction mechanisms. Despite this apparent lack of
control, we present a suitable transformation that approximately maps the
spin-boson dynamics into that of a tunable multiphoton Jaynes-Cummings model
undergoing dissipation. Interestingly, the latter model describes the coherent
interaction between a spin and a single bosonic mode via the simultaneous
exchange of n bosons per spin excitation. Resorting to the so-called reaction
coordinate method, we identify a relevant collective bosonic mode in the
environment which is then used to generate multiphoton interactions following
the proposed theoretical framework. Moreover, we show that spin-boson models
featuring structured environments can lead into non-Markovian multiphoton
Jaynes-Cummings dynamics. We discuss the validity of the proposed method
depending on the parameters and analyze its performance, which is supported by
numerical simulations. In this manner, the spin-boson model serves as a good
analog quantum simulator for the inspection and realization of multiphoton
Jaynes-Cummings models as well as the interplay of non-Markovian effects, and
thus, as a simulator of light-matter systems with tunable interaction
mechanisms.",1904.07037v2
2019-04-25,Zero-temperature Glauber dynamics on the 3-regular tree and the median process,"In zero-temperature Glauber dynamics, vertices of a graph are given
i.i.d.~initial spins $\sigma_x(0)$ from $\{-1,+1\}$ with
$\mathbb{P}_p(\sigma_x(0) = +1)=p$, and they update their spins at the arrival
times of i.i.d. Poisson processes to agree with a majority of their neighbors.
We study this process on the 3-regular tree $\mathbb{T}_3$, where it is known
that the critical threshold $p_c$, below which $\mathbb{P}_p$-a.s. all spins
fixate to $-1$, is strictly less than $1/2$. Defining $\theta(p)$ to be the
$\mathbb{P}_p$-probability that a vertex fixates to $+1$, we show that $\theta$
is a continuous function on $[0,1]$, so that, in particular, $\theta(p_c)=0$.
To do this, we introduce a new continuous-spin process we call the median
process, which gives a coupling of all the measures $\mathbb{P}_p$. Along the
way, we study the time-infinity agreement clusters of the median process, show
that they are a.s. finite, and deduce that all continuous spins flip finitely
often. In the second half of the paper, we show a correlation decay statement
for the discrete spins under $\mathbb{P}_p$ for a.e. value of $p$. The proof
relies on finiteness of a vertex's ""trace"" in the median process to derive a
stability of discrete spins under finite resampling. Last, we use our methods
to answer a question of C. Howard (2001) on the emergence of spin chains in
$\mathbb{T}_3$ in finite time.",1904.11625v1
2019-08-29,Enhancement of ultrafast demagnetization rate and Gilbert damping driven by femtosecond laser-induced spin currents in Fe81Ga19/Ir20Mn80 bilayers,"In spintronics applications, ultrafast spin dynamics have to be controlled at
femtosecond (fs) timescales via fs-laser radiation. At such ultrafast
timescales, the effect of the Gilbert damping factor {\alpha} on ultrafast
demagnetization time should be considered. In previous explorations for the
relationship between these two parameters, it was found that the theoretical
calculations based on the local spin-flip scattering model do not agree with
the experimental results. Here, we find that in Fe81Ga19(FeGa)/Ir20Mn80(IrMn)
bilayers, the unconventional IrMn thickness dependence of {\alpha} results from
the competition between spin currents pumped from the ferromagnetic (FM) FeGa
layer to the antiferromagnetic (AFM) IrMn layer and those pumped from the AFM
layer to the FM layer. More importantly, we establish a proportional
relationship between the change of the ultrafast demagnetization rate and the
enhancement of Gilbert damping induced by the spin currents via interfacial
spin chemical potential . Our work builds a bridge to connect the ultrafast
demagnetization time and Gilbert damping in ultrafast photo-induced spin
currents dominated systems, which not only explains the disagreement between
experimental and theoretical results in the relation of {\tau}_M with {\alpha},
but provides further insight into ultrafast spin dynamics as well.",1908.11084v1
2020-03-02,Signatures of associative memory behavior in a multi-mode spin-boson model,"Spin-boson models can describe a variety of physical systems, such as atoms
in a cavity or vibrating ion chains. In equilibrium these systems often feature
a radical change in their behavior when switching from weak to strong
spin-boson interaction. This usually manifests in a transition from a ""dark"" to
a ""superradiant"" phase. However, understanding the out-of-equilibrium physics
of these models is extremely challenging, and even more so for strong
spin-boson coupling. Here we show that non-equilibrium strongly interacting
spin-boson systems can mimic some fundamental properties of an associative
memory - a system which permits the recognition of patterns, such as letters of
an alphabet. Patterns are encoded in the couplings between spins and bosons,
and we discuss the dynamics of the spins from the perspective of pattern
retrieval in associative memory models. We identify two phases, a
""paramagnetic"" and a ""ferromagnetic"" one, and a crossover behavior between
these regimes. The ""ferromagnetic"" phase is reminiscent of pattern retrieval.
We highlight similarities and differences with the thermal dynamics of a
Hopfield associative memory and show that indeed elements of ""machine learning
behavior"" emerge in strongly coupled spin-boson systems.",2003.01004v1
2020-05-11,Photoinduced electronic and spin properties of two-dimensional electron gases with Rashba spin-orbit coupling under perpendicular magnetic fields,"We theoretically investigate photoinduced phenomena induced by time-periodic
driving fields in two-dimensional electron gases under perpendicular magnetic
fields with Rashba spin-orbit coupling. Using perturbation theory, we provide
analytical results for the Floquet-Landau energy spectrum appearing due to THz
radiation. By employing the resulting photo-modulated states, we compute the
dynamical evolution of the spin polarization function for an initially prepared
coherent state. We find that the interplay of the magnetic field, Rashba
spin-orbit interaction and THz radiation can lead to inversion of the spin
polarization. The dynamics also induces fractional revivals and non-trivial
beating patterns in the autocorrelation function due to interference of the
photo-modulated quantum states. We also calculate the transverse photo-assisted
conductivity in the linear response regime using Kubo formalism and analyze the
impact of the radiation field and Rashba spin-orbit interaction. In the static
limit, we find that our results reduce to well-known expressions of the
conductivity in non-relativistic and quasi-relativistic (topological insulator
surfaces) two-dimensional electron gas thoroughly described in the literature.
We discuss the possible experimental detection of our theoretical prediction
and their relevance for spin-orbit physics at high magnetic fields.",2005.05450v2
2020-09-22,Dynamic $^{14}\rm N$ nuclear spin polarization in nitrogen-vacancy centers in diamond,"We studied the dynamic nuclear spin polarization of nitrogen in negatively
charged nitrogen-vacancy (NV) centers in diamond both experimentally and
theoretically over a wide range of magnetic fields from 0 to 1100 G covering
both the excited-state level anti-crossing and the ground-state level
anti-crossing magnetic field regions. Special attention was paid to the less
studied ground-state level anti-crossing region. The nuclear spin polarization
was inferred from measurements of the optically detected magnetic resonance
signal. These measurements show that a very large (up to $96 \pm 2\%$) nuclear
spin polarization of nitrogen can be achieved over a very broad range of
magnetic field starting from around 400 G up to magnetic field values
substantially exceeding the ground-state level anti-crossing at 1024 G. We
measured the influence of angular deviations of the magnetic field from the NV
axis on the nuclear spin polarization efficiency and found that, in the
vicinity of the ground-state level anti-crossing, the nuclear spin polarization
is more sensitive to this angle than in the vicinity of the excited-state level
anti-crossing. Indeed, an angle as small as a tenth of a degree of arc can
destroy almost completely the spin polarization of a nitrogen nucleus. In
addition, we investigated theoretically the influence of strain and optical
excitation power on the nuclear spin polarization.",2009.10516v1
2022-01-03,Uncovering footprints of dipolar-octupolar quantum spin ice from neutron scattering signatures,"Recent experiments on Ce$_2$Zr$_2$O$_7$ suggest that this material may host a
novel form of quantum spin ice, a three-dimensional quantum spin liquid with an
emergent photon. The Ce$^{3+}$ local moments on the pyrochlore lattice are
described by pseudospin 1/2 degrees of freedom, whose components transform as
dipolar and octupolar moments under symmetry operations. In principle, there
exist four possible quantum spin ice regimes, depending on whether the Ising
component is in the dipolar/octupolar channel, and two possible flux
configurations of the emergent gauge field. In this work, using exact
diagonalization and molecular dynamics, we investigate the equal-time and
dynamical spin structure factors in all four quantum spin ice regimes using
quantum and classical computations. Contrasting the distinct signatures of
quantum and classical results for the four possible quantum spin ice regimes
and elucidating the role of quantum fluctuations, we show that the quantum
structure factor computed for the $\pi$-flux octupolar quantum spin ice regime
is most compatible with the neutron scattering results on Ce$_2$Zr$_2$O$_7$.",2201.00828v3
2022-06-27,Local spin dynamics in geometrically frustrated Mo pyrochlore antiferromagnet Lu$_2$Mo$_2$O$_{5-y}$N$_2$,"The magnetic ground state of oxynitride pyrochlore
Lu$_2$Mo$_2$O$_{5-y}$N$_2$, a candidate compound for the quantum spin liquid
($S=1/2$, Mo$^{5+}$), was studied by muon spin rotation/relaxation experiment.
In contrast to Lu$_2$Mo$_2$O$_7$ ($S=1$, Mo$^{4+}$) which exhibits the
spin-glass behavior with a freezing temperature $T_g\simeq16$ K, no such spin
freezing or long range magnetic order was observed down to 0.3 K. Moreover, two
separate magnetic domains were detected below $\sim$13 K, which were
characterized by differences in spin dynamics. The first is the ""sporadic"" spin
fluctuation seen in frustrated antiferromagnets, where the amplitude of the
hyperfine fields suggests that the excitation comprises a local cluster of
unpaired spins. The other is rapid paramagnetic fluctuation, which is only
weakly suppressed at low temperatures. In place of the paramagnetic
fluctuation, the volume fraction for the sporadic fluctuation steadily
increases with decreasing temperature, indicating the formation of an
excitation gap with a broad distribution of the gap energy involving null gap.",2206.13049v4
2022-07-11,Magnetic structure and spin dynamics of the quasi-2D antiferromagnet Zn-doped copper pyrovanadate,"Magnetic properties of the antiferromagnet Zn$_{0.15}$Cu$_{1.85}$V$_2$O$_7$
(ZnCVO) have been thoroughly investigated on powder and single-crystal samples.
The crystal structure determination using powder x-ray and neutron diffraction
confirms that ZnCVO with Zn = 0.15 is isostructural with
$\beta$-Cu$_{2}$V$_2$O$_7$ ($\beta$-CVO) with small deviation in the lattice
parameters. Macroscopic magnetic properties measurements also confirm the
similarity between the two compounds. The Cu$^{2+}$ spins were found to align
along the crystallographic $c$-axis, antiparallel to their nearest neighbors
connected by the leading exchange interaction $J_1$. Spin dynamics reveals a
typical symmetric spin-wave dispersion with strong interactions in the
$bc$-plane and weak interplane coupling. The exchange interaction analysis
indicates that the spin network of ZnCVO is topologically consistent with the
previous DFT prediction but the values of leading exchange interactions are
contradictory. Furthermore, rather than the predicted 2D honeycomb structure,
the spin network in ZnCVO could be better described by the anisotropic 2D spin
network composing of $J_1$, $J_5$, and $J_6$ interactions, four bonds per one
spin site, coupled by weak interplane interactions.",2207.04618v2
2022-09-21,Spin current driven by ultrafast magnetization of FeRh,"Laser-induced ultrafast demagnetization is an important phenomenon that
probes arguably ultimate limits of the angular momentum dynamics in solid.
Unfortunately, many aspects of the dynamics remain unclear except that the
demagnetization transfers the angular momentum eventually to the lattice. In
particular, roles of electron-carried spin current are debated. Here we
experimentally probe the spin current in the opposite phenomenon, i.e.,
laser-induced ultrafast magnetization of FeRh, where the laser pump pulse
initiates the angular momentum build-up rather than its dissipation. Using the
time-resolved magneto-optical Kerr effect, we directly measure the
ultrafast-magnetization-driven spin current in a FeRh/Cu heterostructure.
Strong correlation between the spin current and the net magnetization change
rate of FeRh is found even though the spin filter effect is negligible in this
opposite process. This result implies that the angular momentum build-up is
achieved by an angular momentum transfer from the electron bath (supplier) to
the magnon bath (receiver) and followed by the spatial transport of angular
momentum (spin current) and dissipation of angular momentum to the phonon bath
(spin relaxation).",2209.10290v1
2022-12-19,Machine learning assisted derivation of effective low energy models for metallic magnets,"We consider the problem of extracting an effective low-energy spin model from
a Kondo Lattice Model (KLM) with classical localized moments. The non-analytic
dependence of the effective spin-spin interactions on the Kondo exchange $J$
excludes the possibility of using perturbation theory beyond the second order
Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction at zero temperature. Here we
introduce a Machine Learning (ML) assisted protocol to extract effective two-
and four-spin interactions by integrating out the conduction electrons of the
original KLM. The resulting effective spin model reproduces the phase diagram
obtained with the original KLM as a function of magnetic field and easy-axis
anisotropy and reveals the effective four-spin interactions that are
responsible for the field induced skyrmion crystal phase. Moreover, this
minimal spin model enables an efficient computation of static and dynamical
properties with a much lower numerical cost relative to the original KLM. A
comparison of the dynamical spin structure factor in the fully polarized phase
computed with the effective model and the original KLM reveals a good agreement
for the magnon dispersion despite the fact that this information was not
included in the training data set.",2212.09796v2
2023-01-11,Evolution of the spin dynamics during freezing in the spin-glass Fe$_{x}$Cr$_{1-x}$,"In the iron--chromium system, Fe$_{x}$Cr$_{1-x}$, a wide dome of spin-glass
behavior emerges when the ferromagnetism of iron is suppressed and the
antiferromagnetism of chromium emerges as a function of increasing iron content
$x$. As both, the high-temperature state and the characteristic cluster size
vary as a function of $x$, different regimes of spin-glass behavior may be
compared in a single, isostructural material system. Here, we report a study of
the spin dynamics across the freezing process into the spin-glass state for
different iron concentrations ($x = 0.145$, $0.175$, $0.21$) using Modulation
of IntEnsity with Zero Effort (MIEZE) spectroscopy. In the parameter range
studied, the relaxation process observed experimentally may be described well
in terms of a stretched exponential. In the reentrant cluster-glass regime, $x
= 0.145$, this behavior persists up to high temperatures. In comparison, in the
superparamagnetic regime, $x = 0.175$ and $x = 0.21$, a single relaxation time
at elevated temperatures is observed. For all samples studied, the spin
relaxation exhibits a momentum dependence consistent with a power law,
providing evidence of a dispersive character of the spin relaxation.",2301.04495v1
2023-02-01,Spin relaxation dynamics with a continuous spin environment: the dissipaton equation of motion approach,"We present the quantum dynamics of a spin coupling to a bath of independent
spins via the dissipaton equation of motion (DEOM) approach. The bath,
characterized by a continuous spectral density function, is composed of spins
that are independent level systems described by the su(2) Lie algebra. This
represents an extreme class of anharmonic environment. Based on the conclusion
drawn by Suarez and Silbey [J. Chem. Phys. 95, 9115 (1991)] and Makri [J. Chem.
Phys. 111, 6164 (1999)] that the spin bath can be mapped to a Gaussian
environment under its linear response limit, we derive the
fluctuation-dissipation theorem (FDT) of the spin bath from a microscopic
perspective, and generalize the discussion to the case of arbitrary bath spin
quantum number S. Next, the time-domain Prony fitting decomposition scheme is
applied to the bare-bath time correlation function (TCF) given by FDT to
generate the exponential decay basis (or pseudo modes) for DEOM construction.
The accuracy and efficiency of this strategy has been justified by a variety of
numerical results. We envision this work provides new insights to extend the
hierarchical equations of motion (HEOM) and DEOM approach to certain types of
anharmonic enviroments with arbitrary TCF or spectral density",2302.00215v1
2023-03-13,Fractionalization induced structural domain patterns in U(1) quantum spin liquids,"The emergence of fractionalized quasiparticles in quantum spin liquids has
served a wealth of unconventional phenomena in frustrated magnets. In our work,
we explore the various domain patterns of such fractionalized quasiparticles,
especially focusing on charge defects in U(1) quantum spin liquids. We claim
that emergent long range interaction between charge defects leads to
characteristic structures with distinct length scales, where they can be
controlled via the ratio of interaction strengths. In this context, the spin
ice phase is the dilute gas of weakly interacting charges, whereas, the
macroscopic population of charge defects naturally develops charge ordering for
large Coulomb interaction limit. Interestingly, we find that the competing spin
interactions could naturally give rise to stabilize the mosaic structure of
charge defects in the absence of uniform ordering. They are characterized by
liquid-like correlations having a finite length scale. The emergence of such
intermediate order in the mosaic structure is confirmed by both dynamical and
static correlations. By establishing the microscopic spin Hamiltonian, we also
present the distinctive signatures in static spin correlation to detect such
spatial structure of charge defects. We speculate that the domain pattern of
defect population might be a potential hallmark to reveal unusual dynamical
properties observed in spin liquids.",2303.07341v1
2023-03-15,Rapid in-situ quantification of rheo-optic evolution for cellulose spinning in ionic solvents,"It is critical to monitor the structural evolution during deformation of
complex fluids for the optimization of many manufacturing processes, including
textile spinning. However, in situ measurements in a textile spinning process
suffer from paucity of non-destructive instruments and interpretations of the
measured data. In this work, kinetic and rheo-optic properties of a
cellulose/ionic liquid solution were measured simultaneously while fibers were
regenerated in aqueous media from a miniature wet spinline equipped with a
customized polarized microscope. This system enables to control key spinning
parameters, while capturing and processing the geometrical and structural
information of the spun fiber in a real-time manner. We identified complex flow
kinematics of a deformed fiber during the coagulation process via feature
tracking methods, and visualized its morphology and birefringent responses
before and during regeneration at varying draw ratios and residence time.
Meanwhile, a three-dimensional physical rheological model was applied to
describe the non-linear viscoelastic behavior in a complex wet-spinning process
incorporating both shear and extensional flows. We subsequently compared the
birefringent responses of fibers under coagulation with the transient
orientation inferred from the rheological model, and identified a superposed
structure-optic relationship under varying spinning conditions. Such structural
characterizations inferred from the flow dynamics of spinning dopes are readily
connected with key mechanical properties of fully-regenerated fibers, thus
enabling to predict the spinning performance in a non-destructive protocol.",2303.08573v1
2023-03-28,Generation of third-harmonic spin oscillation from strong spin precession induced by terahertz magnetic near fields,"The ability to drive a spin system to state far from the equilibrium is
indispensable for investigating spin structures of antiferromagnets and their
functional nonlinearities for spintronics. While optical methods have been
considered for spin excitation, terahertz (THz) pulses appear to be a more
convenient means of direct spin excitation without requiring coupling between
spins and orbitals or phonons. However, room-temperature responses are usually
limited to small deviations from the equilibrium state because of the
relatively weak THz magnetic fields in common approaches. Here, we studied the
magnetization dynamics in a HoFeO3 crystal at room temperature. A custom-made
spiral-shaped microstructure was used to locally generate a strong multicycle
THz magnetic near field perpendicular to the crystal surface; the maximum
magnetic field amplitude of about 2 T was achieved. The observed time-resolved
change in the Faraday ellipticity clearly showed second- and third-order
harmonics of the magnetization oscillation and an asymmetric oscillation
behaviour. Not only the ferromagnetic vector M but also the antiferromagnetic
vector L plays an important role in the nonlinear dynamics of spin systems far
from equilibrium.",2303.16016v1
2023-05-25,Optically controlling the competition between spin flips and intersite spin transfer in a Heusler half-metal on sub-100 fs timescales,"The direct manipulation of spins via light may provide a path toward
ultrafast energy-efficient devices. However, distinguishing the microscopic
processes that can occur during ultrafast laser excitation in magnetic alloys
is challenging. Here, we study the Heusler compound Co2MnGa, a material that
exhibits very strong light-induced spin transfers across the entire M-edge. By
combining the element-specificity of extreme ultraviolet high harmonic probes
with time-dependent density functional theory, we disentangle the competition
between three ultrafast light-induced processes that occur in Co2MnGa:
same-site Co-Co spin transfer, intersite Co-Mn spin transfer, and ultrafast
spin-flips mediated by spin-orbit coupling. By measuring the dynamic magnetic
asymmetry across the entire M-edges of the two magnetic sublattices involved,
we uncover the relative dominance of these processes at different probe energy
regions and times during the laser pulse. Our combined approach enables a
comprehensive microscopic interpretation of laser-induced magnetization
dynamics on timescales shorter than 100 fs.",2305.16455v2
2024-04-06,Consistent Second-Order Treatment of Spin-Orbit Coupling and Dynamic Correlation in Quasidegenerate N-Electron Valence Perturbation Theory,"We present a formulation and implementation of second-order quasidegenerate
N-electron valence perturbation theory (QDNEVPT2) that provides a balanced and
accurate description of spin-orbit coupling and dynamic correlation effects in
multiconfigurational electronic states. In our approach, the energies and
wavefunctions of electronic states are computed by treating electron repulsion
and spin-orbit coupling operators as equal perturbations to the
non-relativistic complete active-space wavefunctions and their contributions
are incorporated fully up to the second order. The spin-orbit effects are
described using the Breit-Pauli (BP) or exact two-component Douglas-Kroll-Hess
(DKH) Hamiltonians within spin-orbit mean-field approximation. The resulting
second-order methods (BP2- and DKH2-QDNEVPT2) are capable of treating
spin-orbit coupling effects in nearly degenerate electronic states by
diagonalizing an effective Hamiltonian expanded in a compact non-relativistic
basis. For a variety of atoms and small molecules across the entire periodic
table, we demonstrate that DKH2-QDNEVPT2 is competitive in accuracy with
variational two-component relativistic theories. BP2-QDNEVPT2 shows high
accuracy for the second- and third-period elements, but its performance
deteriorates for heavier atoms and molecules. We also consider the first-order
spin-orbit QDNEVPT2 approximations (BP1- and DKH1-QDNEVPT2), among which
DKH1-QDNEVPT2 is reliable but less accurate than DKH2-QDNEVPT2. Both DKH1- and
DKH2-QDNEVPT2 hold promise as efficient and accurate electronic structure
methods for treating electron correlation and spin-orbit coupling in a variety
of applications.",2404.04716v1
1999-05-16,Experimental Generation and Observation of Intrinsic Localized Spin Wave Modes in an Antiferromagnet,"By driving with a microwave pulse the lowest frequency antiferromagnetic
resonance of the quasi 1-D biaxial antiferromagnet (C_2 H_5 NH_3)_2 CuCl_4 into
an unstable region intrinsic localized spin waves have been generated and
detected in the spin wave gap. These findings are consistent with the
prediction that nonlinearity plus lattice discreteness can lead to localized
excitations with dimensions comparable to the lattice constant.",9905025v1
1995-08-16,Spin Dynamics of Hole Doped ${\rm Y_{2-x} Ca_x Ba Ni O_5}$,"We propose an electronic model for the recently discovered hole doped
compound ${\rm Y_{2-x} Ca_x Ba Ni O_5 }$. From a multiband Hamiltonian with
oxygen and nickel orbitals, a one band model is derived. Holes are described
using Zhang-Rice-like S=1/2 states at the nickels propagating on a S=1 spin
chain. Using numerical techniques to calculate the dynamical spin structure
factor ${\rm S(q,\omega)}$ in a realistic regime of couplings, spectral weight
in the Haldane gap is observed in agreement with neutron scattering data. Low
energy states with S=3/2 appear in the model. Several predictions are made to
test these ideas.",9508061v1
1995-08-29,Impact of criticality and phase separation on the spin dynamics of the one-dimensional t-J model,"The recursion method is used to determine the T=0 spin dynamic structure
factor S_{zz}(q,\omega) in the Luttinger liquid state and in the
phase-separated state of the one-dimensional t-J model. As the exchange
coupling increases from zero, the dispersions and line shapes of the dominant
spin excitations are observed to undergo a major metamorphosis between the
free-fermion limit and the onset of phase separation. The familiar two-spinon
spectrum of the Heisenberg antiferromagnetic chain emerges gradually in the
strongly phase-separated state.",9508134v1
1996-04-03,Quantum Dynamical Echoes in the Spin 'Diffusion' in Mesoscopic Systems,"The evolution of local spin polarization in finite systems involves
interference phenomena that give rise to {\bf quantum dynamical echoes }and
non-ergodic behavior. We predict the conditions to observe these echoes by
exploiting the NMR sequences devised by Zhang et al. [Phys. Rev. Lett. {\bf %
69}, 2149 (1992)], which uses a rare $^{13}$C as {\bf local probe }for a
dipolar coupled $^1$H spin system. The non-ideality of this probe when testing
mesoscopic systems is carefully analyzed revealing the origin of various
striking experimental features.",9604019v1
1996-06-26,Dynamic Behavior of Spin Glass Systems on Quenched Phi-3 Graphs,"We study the dynamical out-of-equilibrium behavior of a $J = \pm 1$ Ising
spin glass on quenched $\phi^{3}$ graphs. We show that magnetization and energy
decay with a power law behavior, with exponents that are linear in
$\frac{T}{T_{c}}$. Quenched $\phi^{3}$ graphs turn out to be a very effective
way to study numerically mean field spin glasses.",9606194v1
1996-07-24,Long Wavelength Anomalous Diffusion Mode in the 2D XY Dipole Magnet,"In 2D XY ferromagnet the dipole force induces a strong interaction between
spin-waves in the long-wavelength limit. The major effect of this interaction
is the transformation of a propagating spin-wave into a diffusion mode. We
study the anomalous dynamics of such diffusion modes. We find that the
Janssen-De Dominics functional, which governs this dynamics, approaches the
non-Gaussian fixed-point. A spin-wave propagates by an anomalous anisotropic
diffusion with the dispersion relation: $i\omega{\sim}k_{y}^{\Delta_y}$ and
$i\omega{\sim}k_{x}^{\Delta_x}$, where ${\Delta_y}=47/27$ and
${\Delta_x}=47/36$. The low-frequency response to the external magnetic field
is found.",9607168v1
1996-12-02,Spin dynamics of dimerized Heisenberg chains,"We study numerically the dimerized Heisenberg model with frustration
appropriate for the quasi-1D spin-Peierls compound CuGeO$_3$. We present
evidence for a bound state in the dynamical structure factor for any finite
dimerization $\delta$ and estimate the respective spectral weight. For the
homogeneous case ($\delta=0$) we show that the spin-wave velocity $v_s$ is
renormalized by the n.n.n. frustration term $\alpha$ as $v_s=\pi/2
J(1-b\alpha)$ with $b\approx1.12$",9612013v1
1997-03-24,Kawasaki dynamics and equilibrium distributions in simulations of phase separating systems,"We compare equilibrium probability distributions obtained from Monte Carlo
simulations for different spin exchange dynamics with the exact Boltzmann
distribution for the fixed magnetization Ising model on small lattices. We
present simple arguments and numerical evidence in order to show that
""efficient"" Kawasaki exchange does not lead to Boltzmann equilibrium
distributions and that nearest-neighbour equal spin-exchange must be
considered. Arbitrary distance opposite spin interchange is indicated as an
alternative to obtaining the full phase diagram with phase separation.",9703198v2
1997-05-22,Dynamical properties of the hypercell spin glass model,"The spreading of damage technique is used to study the sensibility to initial
conditions in a heath bath Monte Carlo simulation of the spin glass hypercubic
cell model. Since the hypercubic cell in dimension 2D and the hypercubic
lattice in dimension D resemble each other closely at finite dimensions and
both converge to mean field when dimension goes to infinity, it allows us to
study the effect of dimensionality on the dynamical behavior of spin glasses.",9705229v1
1997-12-12,Dynamical Spin Response Functions for Heisenberg Ladders,"We present the results of a numerical study of the 2 by L spin 1/2 Heisenberg
ladder. Ground state energies and the singlet-triplet energy gaps for L =
(4-14) and equal rung and leg interaction strengths were obtained in a Lanczos
calculation and checked against earlier calculations by Barnes et al. (even L
up to 12). A related moments technique is then employed to evaluate the
dynamical spin response for L=12 and a range of rung to leg interaction
strength ratios (0 - 5). We comment on two issues, the need for
reorthogonalization and the rate of convergence, that affect the numerical
utility of the moments treatment of response functions.",9712131v1
1997-12-15,Pressure Effects in Manganites with Layered Perovskite Structure,"Pressure effects on the charge and spin dynamics in the bilayer manganite
compounds $La_{2-2x}Sr_{1+2x}Mn_2O_7$ are studied theoretically by taking into
account the orbital degrees of freedom. The orbital degrees are active in the
layered crystal structure, and applied hydrostatic pressure stabilizes the
$3d_{x^2-y^2}$ orbital in comparison with $3d_{3z^2-r^2}$. The change of the
orbital states weakens the interlayer charge and spin couplings, and suppresses
the three dimensional ferromagnetic transition. Numerical results, based on an
effective Hamiltonian which includes the energy level difference of the
orbitals, show that the applied pressure controls the dimensionality of the
spin and charge dynamics through changes of the orbital states.",9712162v1
1998-01-30,Dynamical Mean-Field Theory for Doped Antiferromagnets,"We have generalized the dynamical mean-field theory to study the doping
dependence of the crossover from antiferromagnetic to short-range order
modelled by an incommensurate spin density wave in the Hubbard model. The local
selfenergy which includes spin fluctuations gives quasiparticle weights and
spectral properties in good agreement with quantum Monte Carlo and exact
diagonalization data in two dimensions. The spectra at finite doping are
characterized by a Mott-Hubbard `gap' accompanied by a pseudogap induced by the
local spin order.",9801325v1
1998-10-28,Spin dynamics of hole doped Y2BaNiO5,"Starting from a multiband Hamiltonian containing the relevant Ni and O
orbitals, we derive an effective Hamiltonian $H_{eff}$ for the low energy
physics of doped Y$_{2}$BaNiO$_{5}.$ For hole doping, $H_{eff}$ describes O
fermions interacting with S=1 Ni spins in a chain, and cannot be further
reduced to a simple one-band model. Using numerical techniques, we obtain a
dynamical spin structure factor with weight inside the Haldane gap. The nature
of these low-energy excitations is identified and the emerging physical picture
is consistent with most of the experimental information in Y%
$_{2-x}$Ca$_{x}$BaNiO$_{5}$",9810387v1
1999-01-11,Theory of spin wave excitation in manganites,"The role of the orbital degrees of freedom is studied theoretically for the
spin dynamics of $R_{1-x}A_x$MnO$_3$. Based on the meanfield solution, an RPA
calculation has been done and it is found that the $d_{x^2-y^2}$-type orbital
is essential for the double-exchange (DE) interactions, i.e., the DE is
basically two-dimensional interaction. Based on this results compared with
experiments, we propose that the orbital wavefunction is $d_{x^2-y^2}$-type
locally even in the metallic ferromagnetic state, which fluctuate quantum
mechanically. Well agreement of the estimation with experiments suggest that
the Jahn-Teller phonon has less importance on the spin dynamics.",9901076v2
1999-05-04,Quantum spin ladder with dynamic phonons. Bound states of magnons and phonons,"We consider the two-chain Heisenberg ladder with antiferromagnetic
interactions. Our approach is based on the description of spin excitations as
triplets above a strong-coupling singlet ground state. It is shown that
interaction with dynamic phonons drastically changes the dispersion of the
elementary triplet excitation (magnon) and the spin structure factor. It is
also shown that a new triplet excitation appears in the spectrum: the bound
state of a magnon and a phonon.",9905030v1
1999-07-23,A Unified Theory of Dynamical Mean Field and Spin Fluctuations,"A new approach is proposed which encompasses the dynamical mean field theory
(DMFT) for strongly correlated electron systems and the self-consistent
renormalization (SCR) theory of spin fluctuations. The latter is incorporated
into DMFT as a $O(1/d)$ correction, where $d$ is the spatial dimensionality,
but in a phenomenological way. The DMFT is completely recovered when the effect
of spin fluctuation is omitted, whereas the properties at the quantum critical
point (QCP) is the same as the SCR theory. An example of calculation is
presented for the single band Hubbard model and the non-Fermi liquid behavior
is demonstrated at QCP.",9907354v2
1999-08-20,Dynamical correlation functions of the spin Calogero-Sutherland model,"The thermodynamic limit of the dynamical density and spin-density two-point
correlation functions for the spin Calogero-Sutherland model are derived from
Uglov's finite-size results. The resultant formula for the density two-point
correlation function is consistent with the previous conjecture on the basis of
the minimal number of elementary excitations.",9908290v1
1999-08-28,Domain Wall Motion in the Presence of Nuclear Spins,"We investigate the motion of a domain wall in the presence of a dynamical
hyperfine field. At temperature T high compared to the hyperfine coupling, the
nuclear spins create a spatially random potential landscape, with dynamics
dictated by the nuclear relaxation time $T_2$. The distribution of the domain
wall relaxation times (both in the thermal and quantum regimes) can show a long
tail, characteristic of stochastic processes where rare events are important.
Here, these are due to occasional strong fluctuations in the nuclear spin
polarisation.",9908423v1
2000-03-17,Glassy Dynamics in a Frustrated Spin System: Role of Defects,"In an effort to understand the glass transition, the kinetics of a spin model
with frustration but no quenched randomness has been analyzed. The
phenomenology of the spin model is remarkably similiar to that of structural
glasses. Analysis of the model suggests that defects play a major role in
dictating the dynamics as the glass transition is approached.",0003306v1
2000-11-13,Spin Excitations in Localized and Itinerant Magnets,"Collective excitations in magnetic materials can be investigated by means of
inelastic neutron scattering. We show that this experimental method gives
access to the complete spectrum of magnetic fluctuations through the energy-
and momentum-dependence of the dynamical susceptibility. We focus on the
dynamical properties of magnets with localized spin densities and of metals.
  From such studies, microscopic parameters like exchange integrals, spin-wave
stiffness and relaxation times can be determined. This is of great help to test
current theories in magnetism.",0011220v1
2000-12-19,Significance of the direct relaxation process in the low-energy spin dynamics of a one-dimensional ferrimagnet NiCu(C_7H_6N_2O_6)(H_2O)_3 2H_2O,"In response to recent nuclear-magnetic-resonance measurements on a
ferrimagnetic chain compound NiCu(C_7H_6N_2O_6)(H_2O)_3 2H_2O [Solid State
Commun. {\bf 113} (2000) 433], we calculate the nuclear spin-lattice relaxation
rate 1/T_1 in terms of a modified spin-wave theory. Emphasizing that the
dominant relaxation mechanism arises from the direct (single-magnon) process
rather than the Raman (two-magnon) one, we explain the observed temperature and
applied-field dependences of 1/T_1. Ferrimagnetic relaxation phenomena are
generally discussed and novel ferrimagnets with extremely slow dynamics are
predicted.",0012342v1
2000-12-22,Signatures of Spin Degrees of Freedom in Charge Dynamics of YBa_2Cu_3O_6.95,"Charge carrier-spin excitation spectral densities constructed from optical
data and varying with temperature are used to calculate various properties of
the charge carrier dynamics. Temperature (T) variations of such properties are
sensitive to the changes in the spectral density brought about by the growth in
the 41 meV spin resonance as T is lowered. The microwave conductivity and the
thermal conductivity are stressed and comparison with experiment is given. The
imaginary part of the conductivity as a function of frequency \omega is also
featured.",0012425v1
2001-06-14,Non-gaussian Noise in Quantum Spin Glasses and Interacting Two-level Systems,"We study a general model for non-gaussian $1/f$ noise based on an infinite
range quantum Ising spin system in the paramagnetic state, or equivalently,
interacting two-level classical fluctuators. We identify a dilatation
interaction term in the dynamics which survives the thermodynamic limit and
circumvents the central limit theorem to produce non-gaussian noise even when
the equilibrium distribution is that of {\em non-interacting} spins. The
resulting second spectrum (`noise of the noise') itself has a universal $1/f$
form which we analyze within a dynamical mean field approximation.",0106283v1
2001-11-19,Phase transitions in the steady state behavior of mechanically perturbed spin glasses and ferromagnets,"We analyze the steady state regime of systems interpolating between spin
glasses and ferromagnets under a tapping dynamics recently introduced by
analogy with the dynamics of mechanically perturbed granular media. A crossover
from a second order to first order ferromagnetic transition as a function of
the spin coupling distribution is found. The flat measure over blocked states
introduced by Edwards for granular media is used to explain this scenario.
Annealed calculations of the Edwards entropy are shown to qualitatively explain
the nature of the phase transitions. A Monte-Carlo construction of the Edwards
measure confirms that this explanation is also quantitatively accurate.",0111331v1
2002-03-25,Dynamic nonlinear (cubic) susceptibility in quantum Ising spin glass,"Dynamic nonlinear (cubic) susceptibility in quantum d-dimensional Ising spin
glass with short-range interactions is investigated on the basis of quantum
droplet model and quantum-mechanical nonlinear response theory. Nonlinear
response depends on the tunneling rate for a droplet which regulates the
strength of quantum fluctuations. It shows a strong dependence on the
distribution of droplet free energies and on the droplet length scale average.
Comparison with recent experiments on quantum spin glasses like disordered
dipolar quantum Ising magnet is discussed.",0203501v1
2002-04-17,Non-Markoffian effects of a simple nonlinear bath,"We analyze a model of a nonlinear bath consisting of a single two-level
system coupled to a linear bath (a classical noise force in the limit
considered here). This allows us to study the effects of a nonlinear,
non-Markoffian bath in a particularly simple situation. We analyze the effects
of this bath onto the dynamics of a spin by calculating the decay of the
equilibrium correlator of the spin's z-component. The exact results are
compared with those obtained using three commonly used approximations: a
Markoffian master equation for the spin dynamics, a weak-coupling
approximation, and the substitution of a linear bath for the original nonlinear
bath.",0204372v1
2002-08-21,The spin angular gradient approximation in the density functional theory,"A spin angular gradient approximation for the exchange correlation magnetic
field in the density functional formalism is proposed. The usage of such
corrections leads to a consistent spin dynamical approach beyond the local
approximation. The proposed technique does not contain any approximations for
the form of potential and can be used in modern full potential band structure
methods. The obtained results indicate that the direct 'potential' exchange in
3d magnets is rather small compared to the indirect 'kinetic' exchange, thus
justifies the dynamical aspect of the local density approximation in 3d metals.",0208420v1
2002-10-26,Dynamic exchange coupling in magnetic bilayers,"A long-ranged dynamic interaction between ferromagnetic films separated by
normal-metal spacers is reported, which is communicated by nonequilibrium spin
currents. It is measured by ferromagnetic resonance (FMR) and explained by an
adiabatic spin-pump theory. In FMR the spin-pump mechanism of spatially
separated magnetic moments leads to an appreciable increase in the FMR line
width when the resonance fields are well apart, and results in a dramatic
line-width narrowing when the FMR fields approach each other.",0210588v2
2002-11-01,Exploring dynamical magnetism with time-dependent density-functional theory: from spin fluctuations to Gilbert damping,"We use time-dependent spin-density-functional theory to study dynamical
magnetic phenomena. First, we recall that the local-spin-density approximation
(LSDA) fails to account correctly for magnetic fluctuations in the paramagnetic
state of iron and other itinerant ferromagnets. Next, we construct a
gradient-dependent density functional that does not suffer from this problem of
the LSDA. This functional is then used to derive, for the first time, the
phenomenological Gilbert equation of micromagnetics directly from
time-dependent density-functional theory. Limitations and extensions of Gilbert
damping are discussed on this basis, and some comparisons with phenomenological
theories and experiments are made.",0211021v1
2003-03-08,Transition rates via Bethe ansatz for the spin-1/2 planar XXZ antiferromagnet,"A novel determinantal representation for matrix elements of local spin
operators between Bethe wave functions of the one-dimensional s=1/2 XXZ model
is used to calculate transition rates for dynamic spin structure factors in the
planar regime. In a first application, high-precision numerical data are
presented for lineshapes and band edge singularities of the in-plane (xx)
two-spinon dynamic spin structure factor.",0303147v1
2003-04-22,Optical spin transfer in ferromagnetic semiconductors,"Circularly polarized laser pulses that excite electron-hole pairs across the
band gap of (III,Mn)V ferromagnetic semiconductors can be used to manipulate
and to study collective magnetization dynamics. The initial spin orientation of
a photocarrier in a (III,V) semiconductors is determined by the polarization
state of the laser. We show that the photocarrier spin can be irreversibly
transferred to the collective magnetization, whose dynamics can consequently be
flexibly controlled by suitably chosen laser pulses. As illustrations we
demonstrate the feasibility of all optical ferromagnetic resonance and optical
magnetization reorientation.",0304492v2
2003-07-18,Dynamics of a nanoparticle as a one-spin system and beyond,"We review some recent results beyond the now established theory of
magnetization switching of a nanoparticle within the single-spin approximation.
The first extension is that of the Stoner-Wohlfarth model for magnetization
static switching under applied magnetic field including the effect of
temperature at long-time scales. The second concerns a generalization of the
N\'eel-Brown model for thermoactivated dynamic magnetization switching to
include the effect of exchange interaction in the framework of Langer's theory
in the intermediate-to-high damping limit. We finally argue why the single-spin
approximation is not appropriate for very small nanoparticles.",0307457v1
2003-10-09,Rejuvenation and Memory in Migdal-Kadanoff Spin Glasses,"We study aging phenomena of Migdal-Kadanoff spin glasses in order to clarify
relevancy of temperature chaos to rejuvenation and memory. By exploiting
renormalization, we do efficient dynamical simulations in very wide time/length
scales including the chaos length. As a consequence, we find that temperature
chaos and temperature dependence of speed of equilibration cause two
significantly different effects against temperature variations, i.e.,
rejuvenation for positive temperature variation and memory for negative
temperature variation, as are observed experimentally in spin glasses.",0310198v1
2004-01-14,"Correlation, excitation, and relaxation of the antiferromagnetic nanoparticle","We study the dynamics of spins in the canted antiferromagnetic hematite
nanoparticles $\alpha$-Fe$_2$O$_3$. The system includes an antiferromagnetic
exchange ($J$) between two sublattices as well as the potential dominated by a
uniaxial anisotropy and dissipates through the thermally triggered spin-phonon
mechanism. The exchange $J$ is found to reduce the superparamagnetic relaxation
and drive the incoherent relaxation of transverse spins in the low temperature.
Dynamical properties are semi-quantitatively understood within a role of the
exchange interaction $J$ and agree well with recent inelastic neutron
scattering experiments.",0401247v1
2004-01-23,Dynamical Spin-Blockade in a quantum dot with paramagnetic leads,"We investigate current fluctuations in a three-terminal quantum dot in the
sequential tunneling regime. Dynamical spin blockade can be induced when the
spin-degeneracy of the dot states is lifted by a magnetic field. This results
in super-Poissonian shot noise and positive zero-frequency cross-correlations.
Our proposed setup can be realized with semiconductor quantum dots.",0401456v2
2004-01-24,Static and Dynamic Properties of Antiferromagnetic Heisenberg Ladders: Fermionic versus Bosonic Approaches,"In terms of spinless fermions via the Jordan-Wigner transformation along a
snake-like path and spin waves modified so as to restore the sublattice
symmetry, we investigate static and dynamic properties of two-leg
antiferromagnetic Heisenberg ladders. The specific heat is finely reproduced by
the spinless fermions, whereas the magnetic susceptibility is well described by
the modified spin waves. The nuclear spin-lattice relaxation rate is discussed
in detail with particular emphasis on its novel field dependence.",0401477v1
2004-06-21,Spin dynamics for bosons in an optical lattice,"We study the internal dynamics of bosonic atoms in an optical lattice. Within
the regime in which the atomic crystal is a Mott insulator with one atom per
well, the atoms behave as localized spins which interact according to some spin
Hamiltonian. The type of Hamiltonian (Heisenberg, Ising), and the sign of
interactions may be tuned by changing the properties of the optical lattice, or
applying external magnetic fields. When, on the other hand, the number of atoms
per lattice site is unknown, we can still use the bosons to perform general
quantum computation.",0406468v1
2004-08-21,Phenomenological lattice model for dynamic spin and charge fluctuations in the cuprates,"Motivated by recent neutron scattering experiments on the cuprate
superconductors, we present a phenomenological framework describing the
dynamics of collective spin excitations coupled to charge/bond order
fluctuations. Our quantum lattice model contains two order parameter fields,
and can capture spin excitations both in broken-symmetry states with static
lattice modulations, as well as in homogeneous states where the charge/bond
order is fluctuating. We present results for different types of static
charge/bond order, namely site- and bond-centered stripes, and plaquette
modulation.",0408461v1
2004-12-01,Exact calculation of the energy contributions to the T=0 random-field Ising model with metastable dynamics on the Bethe lattice,"We analyze the energy terms corresponding to the spin-spin exchange and
spin-random field coupling of the zero temperature random-field Ising model on
the Bethe lattice driven by an external field with metastable dynamics. Exact
results are calculated as a function of the standard deviation of the disorder
and the coordination number z, and compared with numerical simulations on
random graphs for z=4, for which a disorder-induced transition takes place.",0412007v1
2005-02-02,Coherent spin mixing dynamics in a spin-1 atomic condensate,"We study the coherent off-equilibrium spin mixing inside an atomic
condensate. Using mean field theory and adopting the single spatial mode
approximation (SMA), the condensate spin dynamics is found to be well described
by that of a nonrigid pendulum, and displays a variety of periodic oscillations
in an external magnetic field. Our results illuminate several recent
experimental observations and provide critical insights into the observation of
coherent interaction-driven oscillations in a spin-1 condensate.",0502061v2
2005-03-04,Dynamic Spin Structure Factor of SrCu2(BO3)2 at Finite Temperatures,"Using finite temperature Lanczos technique on finite clusters we calculate
dynamical spin structure factor of the quasi-two-dimensional dimer spin liquid
SrCu2(BO3)2 as a function of wavevector and temperature. Unusual temperature
dependence of calculated spectra is in agreement with inelastic neutron
scattering measurements. Normalized peak intensities of the single-triplet peak
are q-independent, their unusual temperature dependence is analyzed in terms of
thermodynamic quantities.",0503098v2
2005-08-07,Ultrafast light-induced magnetization dynamics in ferromagnetic semiconductors,"We develop a theory of the magnetization dynamics triggered by ultrafast
optical excitation of ferromagnetic semiconductors. We describe the effects of
the strong carrier spin relaxation on the nonlinear optical response by using
the Lindblad semigroup method. We demonstrate magnetization control during
femtosecond timescales via the interplay between circularly polarized optical
excitation, hole-spin damping, polarization dephasing, and the Mn-hole spin
interactions. Our results show a light-induced magnetization precession and
relaxation for the duration of the optical pulse.",0508178v1
2005-08-30,Current induced transverse spin-wave instability in thin ferromagnets: beyond linear stability analysis,"A sufficiently large unpolarized current can cause a spin-wave instability in
thin nanomagnets with asymmetric contacts. The dynamics beyond the instability
is understood in the perturbative regime of small spin-wave amplitudes, as well
as by numerically solving a discretized model. In the absence of an applied
magnetic field, our numerical simulations reveal a hierarchy of instabilities,
leading to chaotic magnetization dynamics for the largest current densities we
consider.",0508732v1
2005-12-16,Studies of R2Ti2O7 (R=Gd and Yb); new results,"Specific heat and muon spin rotation and relaxation data are presented for
two geometrically frustrated systems: Gd2Ti2O7 which antiferromagnetically
orders and Yb2Ti2O7 which presents dynamical short range correlations at low
temperature. The muon data help to characterize the spin dynamics of these two
compounds.",0512389v1
2006-01-14,Monte-Carlo simulation of supercooled liquids using a self-consistent local temperature,"We combine Creutz energy conservation with Kawasaki spin exchange to simulate
the microcanonical dynamics of a system of interacting particles. Relaxation
occurs via Glauber spin-flip activation using a self-consistent temperature.
Heterogeneity in the dynamics comes from finite-size constraints on the spin
exchange that yield a distribution of correlated regions. The simulation
produces a high-frequency response that can be identified with the boson peak,
and a lower-frequency peak that contains non-Debye relaxation and non-Arrhenius
activation, similar to the primary response of supercooled liquids.",0601313v1
2006-09-08,Dynamics of photoexcited states in one-dimensional dimerized Mott insulators,"Dynamical properties of photoexcited states are theoretically studied in a
one-dimensional Mott insulator dimerized by the spin-Peierls instability.
Numerical calculations combined with a perturbative analysis have revealed that
the lowest photoexcited state without nearest-neighbor interaction corresponds
to an interdimer charge transfer excitation that belongs to dispersive
excitations. This excited state destabilizes the dimerized phase, leading to a
photoinduced inverse spin-Peierls transition. We discuss the purely electronic
origin of midgap states that are observed in a latest photoexcitation
experiment of an organic spin-Peierls compound, K-TCNQ
(potassium-tetracyanoquinodimethane).",0609186v1
2006-09-08,Quantum Dynamics of Molecular Nanomagnets in a Resonant Cavity and the Maser Effect,"We study the dynamics of molecular nanomagnets through a fully quantum
mechanical model describing high-spin and high-anisotropy magnetic molecules
subjected to a time-dependent magnetic field along the quantization axis, which
continuously inverts the population of spin states. Crystals of molecular
nanomagnets placed inside a resonant cavity interact with a quantized
electromagnetic field. Relaxation of excited states takes place by means of
spin-photon interaction, allowing stimulated emission of radiation and creating
a maser effect.",0609205v1
2006-09-19,Solitons in a trapped spin-1 atomic condensate,"We numerically investigate a particular type of spin solitons inside a
trapped atomic spin-1 Bose-Einstein condensate (BEC) with ferromagnetic
interactions. Within the mean field theory approximation, our study of the
solitonic dynamics shows that the solitonic wave function, its center of mass
motion, and the local spin evolutions are stable and are intimately related to
the domain structures studied recently in spin-1 $^{87}$Rb condensates. We
discuss a rotating reference frame wherein the dynamics of the solitonic local
spatial spin distribution become time independent.",0609468v3
1999-10-12,"Gravity Waves, Chaos, and Spinning Compact Binaries","Spinning compact binaries are shown to be chaotic in the Post-Newtonian
expansion of the two body system. Chaos by definition is the extreme
sensitivity to initial conditions and a consequent inability to predict the
outcome of the evolution. As a result, the spinning pair will have
unpredictable gravitational waveforms during coalescence. This poses a
challenge to future gravity wave observatories which rely on a match between
the data and a theoretical template.",9910040v3
1993-05-18,Spin Structure of the Pion in a Light-Cone Representation,"The spin structure of the pion is discussed by transforming the wave function
for the pion in the naive quark model into a light-cone representation. It is
shown that there are higher helicity ($\lambda_{1}+\lambda_{2}=\pm1$) states in
the full light-cone wave function for the pion besides the ordinary helicity
($\lambda_{1}+\lambda_{2}=0$) component wave functions as a consequence from
the Melosh rotation relating spin states in light-front dynamics and those in
instant-form dynamics. Some low energy properties of the pion, such as the
electromagnetic form factor, the charged mean square radius, and the weak decay
constant, could be interrelated in this representation with reasonable
parameters.",9305283v1
2002-11-11,Transversity in Exclusive and Inclusive Processes,"Both meson photoproduction and semi-inclusive deep inelastic scattering can
potentially probe transversity properties of the nucleon. We explore how that
potential can be realized dynamically. The role of rescattering in both
exclusive and inclusive meson production as a source for single spin
asymmetries is examined. Using a dynamical model, we evaluate the spin
independent $\cos 2\phi$ asymmetry associated with transversity of quarks
inside unpolarized hadrons, at HERMES kinematics. We also explore the effects
of rescattering on the transversity distribution of the nucleon.",0211155v1
1993-09-06,Motion of Wavefunction Zeros in Spin-Boson Systems,"In the analytic-Bargmann representation associated with the harmonic
oscillator and spin coherent states, the wavefunction as entire complex
functions can be factorized in terms of their zeros in a unique way. The
Schr\""odinger equation of motion for the wavefunction is turned to a system of
equations for its zeros. The motion of these zeros as a non-linear flow of
points is studied and interpreted for linear and non-linear bosonic and spin
Hamiltonians. Attention is given to the study of the zeros of the
Jaynes-Cummings model and to its finite analoque. Numerical solutions are
derived and discussed.",9309032v1
1999-02-20,Massless and spinning particles as dynamics in one dimensional (super)diffeomorphism groups,"It is shown that dynamics of D+2 elements of the (super)diffeomorphism group
in one (1+1 for the super) dimension describes the D - dimensional (spinning)
massless relativistic particles. The coordinates of this elements (D+2
einbeins, D+2 connections and 1 additional common coordinate of higher
dimensionality) play the role of coordinates, momenta and Lagrange multiplier,
needed for the manifestly conformal and reparametrization invariant description
of the D - dimensional (spinning) particle in terms of the D+2 - dimensional
spacetime.",9902143v2
2003-06-05,Understanding visual map formation through vortex dynamics of spin Hamiltonian models,"The pattern formation in orientation and ocular dominance columns is one of
the most investigated problems in the brain. From a known cortical structure,
we build spin-like Hamiltonian models with long-range interactions of the
Mexican hat type. These Hamiltonian models allow a coherent interpretation of
the diverse phenomena in the visual map formation with the help of relaxation
dynamics of spin systems. In particular, we explain various phenomena of
self-organization in orientation and ocular dominance map formation including
the pinwheel annihilation and its dependency on the columnar wave vector and
boundary conditions.",0306047v2
2001-05-06,Spin-orbit pendulum in Dirac oscillator,"The dynamics of wavepackets in a relativistic Dirac oscillator (DO) is
considered. A comparison to nonrelativistic spin-orbit pendulum effect is
discussed. Particular relativistic effects, like Zitterbewegung in spin motion,
are found in Dirac representation. This trembling motion disappears in
Foldy-Wouthuysen representation. A substantial difference between the dynamics
of wavepackets corresponding to circular and linear orbits of a particle is
obtained and discussed.",0105021v1
2004-09-08,Transport of Entanglement Through a Heisenberg-XY Spin Chain,"The entanglement dynamics of spin chains is investigated using Heisenberg-XY
spin Hamiltonian dynamics. The various measures of two-qubit entanglement are
calculated analytically in the time-evolved state starting from initial states
with no entanglement and exactly one pair of maximally-entangled qubits. The
localizable entanglement between a pair of qubits at the end of chain captures
the essential features of entanglement transport across the chain, and it
displays the difference between an initial state with no entanglement and an
initial state with one pair of maximally-entangled qubits.",0409048v1
2005-04-30,Spin dynamics in a dissipative environment: from quantal to classical,"We address the problem of spin dynamics in the presence of a thermal bath, by
solving exactly the appropriate quantum master equations with
continued-fraction methods. The crossover region between the quantum and
classical domains is studied by increasing the spin value S, and the asymptote
for the classical absorption spectra is eventually recovered. Along with the
recognized relevance of the coupling strength, we show the critical role played
by the structure of the system-environment interaction in the emergence of
classical phenomenology.",0505002v2
2006-11-20,Bopp operators and phase-space spin dynamics: Application to rotational quantum brownian motion,"As already known for nonrelativistic spinless particles, Bopp operators give
an elegant and simple way to compute the dynamics of quasiprobability
distributions in the phase space formulation of Quantum Mechanics. In this
work, we present a generalization of Bopp operators for spins and apply our
results to the case of open spin systems. This approach allows to take the
classical limit in a transparent way, recovering the corresponding
Fokker-Planck equation.",0611194v2
2007-02-28,"Creating, distributing and freezing entanglement with spin chains","We show how branching spin chains can be used to both generate and distribute
entanglement from their natural dynamics. Such entanglement provides a useful
resource, for example for teleportation or distributed quantum processing. Once
distributed, this resource can be isolated through mapping or swapping the
entanglement into specific qubits at the ends of branches. Alternatively, as we
demonstrate for distributed bipartite entanglement, applying simple
single-qubit operations to the end spin of one or more branches can dynamically
freeze the entanglement at the branch ends.",0702269v2
2007-07-27,Excitation of spin dynamics by spin-polarized current in vortex state disks,"A spin-polarized current with the polarization perpendicular to the plane of
a vortex-state disk results in renormalization of the effective damping for a
given magnetization mode, and the effective damping becomes zero if the current
exceeds a threshold value. The lowest threshold current corresponds to the
lowest frequency vortex gyroscopic mode. For larger values of the current the
dynamic magnetization state is characterized by precession of the vortex around
the dot center with non-small amplitude and higher frequency.",0707.4128v1
2007-07-30,Gap function symmetry and spin dynamics in electron-doped cuprate superconductor,"An antiferromagnetic (AF) spin fluctuation induced pairing model is proposed
for the electron-doped cuprate superconductors. It suggests that, similar to
the hole-doped side, the superconducting gap function is monotonic
d_{x^2-y^2}-wave and explains why the observed gap function has a nonmonotonic
d_{x^2-y^2}-wave behavior when an AF order is taken into account. Dynamical
spin susceptibility is calculated and shown to be in good agreement with the
experiment. This gives a strong support to the proposed model.",0707.4348v1
2007-10-24,Spin dynamics of a trapped spin-1 Bose Gas above the Bose-Einstein transition temperature,"We study collective spin oscillations in a spin-1 Bose gas above the
Bose-Einstein transition temperature. Starting from the Heisenberg equation of
motion, we derive a kinetic equation describing the dynamics of a thermal gas
with the spin-1 degree of freedom. Applying the moment method to the kinetic
equation, we study spin-wave collective modes with dipole symmetry. The dipole
modes in the spin-1 system are found to be classified into the three type of
modes. The frequency and damping rate are obtained as functions of the peak
density. The damping rate is characterized by three relaxation times associated
with collisions.",0710.4419v2
2007-10-29,Cyclotron motion and magnetic focusing in semiconductor quantum wells with spin-orbit coupling,"We investigate the ballistic motion of electrons in III-V semiconductor
quantum wells with Rashba spin-orbit coupling in a perpendicular magnetic
field. Taking into account the full quantum dynamics of the problem, we explore
the modifications of classical cyclotron orbits due to spin-orbit interaction.
As a result, for electron energies comparable with the cyclotron energy the
dynamics are particularly rich and not adequately described by semiclassical
approximations. Our study is complementary to previous semiclassical approaches
concentrating on the regime of weaker fields.",0710.5395v2
2007-11-26,Dynamic Nuclear Polarization in Silicon Microparticles,"We report record high Si-29 spin polarization obtained using dynamic nuclear
polarization in microcrystalline silicon powder. Unpaired electrons in this
silicon powder are due to dangling bonds in the amorphous region of this
intrinsically heterogeneous sample. Si-29 nuclei in the amorphous region become
polarized by forced electron-nuclear spin flips driven by off-resonant
microwave radiation while nuclei in the crystalline region are polarized by
spin diffusion across crystalline boundaries. Hyperpolarized silicon
microparticles have long T1 relaxation times and could be used as tracers for
magnetic resonance imaging.",0711.4076v2
2008-01-11,Thermal Dynamics in Symmetric Magnetic Nanopillars Driven by Spin Transfer,"We study the effects of spin transfer on thermally activated dynamics of
magnetic nanopillars with identical thicknesses of the magnetic layers. The
symmetric nanopillars exhibit anomalous dependencies of switching statistics on
magnetic field and current. We interpret our data in terms of simultaneous
current-induced excitation of both layers. We also find evidence for coupling
between the fluctuations of the layers due to the spin transfer.",0801.1807v1
2008-01-23,Theory of Domain Wall Dynamics under Current,"Microscopic theory of domain wall dynamics under electric current is
reviewed. Domain wall is treated as rigid and planar. The spin-transfer torque
and forces on the wall are derived based on the $s$-$d$ exchange interaction
between localized spins and conduction electrons, treating non-adiabaticity
expressed by the gauge field perturbatively. Effect of spin relaxation is also
studied.",0801.3517v1
2008-02-13,FMR induced Josephson Current in a Superconductor/Ferromagnet/Superconductor Junction,"We propose the phase dynamics induced by spin waves in a
superconductor/ferromagnet/superconductor (SC/FM/SC) Josephson junction. The
resistively shunted junction (RSJ) model, which describes the dynamics of
superconducting phase difference, is extended to include the spin wave
excitation by ferromagnetic resonance (FMR) using the gauge invariant phase
difference between two s-wave superconductors. The current-voltage
characteristics show step structures when the magnetization in FM is driven by
tuning the microwave frequency to FMR in the SC/FM/SC junction. The result
presents a new route to observe the spin wave excitation using the Josephson
effect.",0802.1755v2
2008-10-14,Exactly solvable model for the dynamics of two spin-1/2 particles embedded in separate spin star environments,"Exact analytical results for the dynamics of two interacting qubits each of
which is embedded in its own spin star bath are presented. The time evolution
of the concurrence and the purity of the two-qubit system is investigated for
finite and infinite numbers of environmental spins. The effect of qubit-qubit
interactions on the steady state of the central system is investigated",0810.2532v1
2009-02-03,Freezing of spin dynamics in underdoped cuprates,"The Mori's memory function approach to spin dynamics in doped
antiferromagnetic insulator combined with the assumption of temperature
independent static spin correlations and constant collective mode damping leads
to w/T scaling in a broad range. The theory involving a nonuniversal scaling
parameter is used to analyze recent inelastic neutron scattering results for
underdoped cuprates. Adopting modified damping function also the emerging
central peak in low-doped cuprates at low temperatures can be explained within
the same framework.",0902.0546v1
2009-07-16,Influence of magnetic viscosity on domain wall dynamics under spin-polarized currents,"We present a theoretical study of the influence of magnetic viscosity on
current-driven domain wall dynamics. In particular we examine how domain wall
depinning transitions, driven by thermal activation, are influenced by the
adiabatic and nonadiabatic spin-torques. We find the Arrhenius law that
describes the transition rate for activation over a single energy barrier
remains applicable under currents but with a current-dependent barrier height.
We show that the effective energy barrier is dominated by a linear current
dependence under usual experimental conditions, with a variation that depends
only on the nonadiabatic spin torque coefficient beta.",0907.2867v1
2009-09-01,Spin transfer and current-induced switching in antiferromagnets,"We present theoretical description of the precessional switching processes
induced by simultaneous application of spin-polarized current and external
magnetic field to antiferromagnetic component of the ""pinned"" layer. We found
stability ranges of different static and dynamic regimes. We showed the
possibility of steady current-induced precession of antiferromagnetic vector
with frequency that linearly depends on the bias current. Furthermore, we found
an optimal duration of current pulse required for switching between different
orientations of antiferromagnetic vector and current and field dependence of
switching time. Our results reveal the difference between dynamics of ferro-
and antiferromagnets subjected to spin transfer torques.",0909.0234v2
2009-10-30,Dissipative dynamics of magnetic solitons in metals,"Soliton dynamics in spin-textured metals generate electrical currents, which
produce backaction through spin torques. We modify the Landau-Lifshitz-Gilbert
equation and the corresponding solitonic equations of motion to include such
higher-order texture effects. We also find a quasistatic equation for the
induced electrochemical potential, which needs to be solved for
self-consistently, in the incompressible limit. As an example, we consider the
orbital motion of a vortex in a point-contact spin valve, and discuss
modifications of orbit radius, frequency, and dissipation power.",0910.5912v2
2010-06-21,Dynamics of magnetic charges in artificial spin ice,"Artificial spin ice has been recently implemented in two-dimensional arrays
of mesoscopic magnetic wires. We propose a theoretical model of magnetization
dynamics in artificial spin ice under the action of an applied magnetic field.
Magnetization reversal is mediated by domain walls carrying two units of
magnetic charge. They are emitted by lattice junctions when the the local field
exceeds a critical value $H_c$ required to pull apart magnetic charges of
opposite sign. Positive feedback from Coulomb interactions between magnetic
charges induces avalanches in magnetization reversal.",1006.4075v2
2010-07-01,Photo-induced insulator-metal transition of a spin-electron coupled system,"The photo-induced metal-insulator transition is studied by the numerical
simulation of real-time quantum dynamics of a double-exchange model. The
spatial and temporal evolutions of the system during the transition have been
revealed including (i) the threshold behavior with respect to the intensity and
energy of light, (ii) multiplication of particle-hole (p-h) pairs by a p-h pair
of high energy, and (iii) the space-time pattern formation such as (a) the
stripe controlled by the polarization of light, (b) coexistence of metallic and
insulating domains, and (c) dynamical spontaneous symmetry-breaking associated
with the spin spiral formation imposed by the conservation of total spin for
small energy-dissipation rates.",1007.0061v1
2011-01-24,Some circumstances where extra updates can delay mixing,"Peres and Winkler proved a ""censoring"" inequality for Glauber dynamics on
monotone spins systems such as the Ising model. Specifically, if, starting from
a constant-spin configuration, the spins are updated at some sequence of sites,
then inserting another site into this sequence brings the resulting
configuration closer in total variation to the stationary distribution. We show
by means of simple counterexamples that the analogous statements fail for
Glauber dynamics on proper colorings of a graph, and for lazy transpositions on
permutations, answering two questions of Peres. It is not known whether the
censoring property holds in other natural settings such as the Potts model.",1101.4690v1
2011-08-17,Quantum phases and dynamics of geometric phase in a quantum spin chain system under linear quench,"We study the quantum phases of anisotropic XY spin chain system in presence
and absence of adiabatic quench. A connection between geometric phase and
criticality is established from the dynamical behaviour of the geometric phase
for a quench induced quantum phase transition in a quantum spin chain. We
predict XX criticality associated with a sequence of non-contractible geometric
phases.",1108.3406v2
2011-12-14,Quenched Slonczewski-Windmill in Spin-Torque Vortex-Oscillators,"We present a combined analytical and numerical study on double-vortex
spin-torque nano-oscillators and describe a mechanism that suppresses the
windmill modes. The magnetization dynamics is dominated by the gyrotropic
precession of the vortex in one of the ferromagnetic layers. In the other layer
the vortex gyration is strongly damped. The dominating layer for the
magnetization dynamics is determined by the current polarity. Measurements on
Fe/Ag/Fe nano-pillars support these findings. The results open up a new
perspective for building high quality-factor spin-torque oscillators operating
at selectable, well-separated frequency bands.",1112.3163v1
2012-07-08,The excitation operator method in the spin dynamics of the one-dimensional XXZ model,"We develop the excitation operator method, which is designed to solve the
Heisenberg equation of motion by constructing the excitation operators. We use
it to study the spin dynamics in the one-dimensional XXZ model. We find the
diffusive spin transport in the gapped phase at the high temperature limit.",1207.1861v2
2012-11-28,Spin Josephson vortices in two tunnel coupled spinor Bose gases,"We study topological excitations in spin-1 Bose-Einstein condensates trapped
in an elongated double-well optical potential. This system hosts a new
topological defect, the spin Josephson vortex (SJV), which forms due to the
competition between the inter-well atomic tunneling and short-range
ferromagnetic two-body interaction. We identify the spin structure and
formation dynamics of the SJV and determine the phase diagram of the system. By
exploiting the intrinsic stability of the SJV, we propose a dynamical method to
create SJVs under realistic experimental conditions.",1211.6609v2
2013-02-16,Quantum dynamics of a nano-rod under compression,"A nano-rod under compression, which is capacitively coupled to a Cooper-pair
box, can be modeled in terms of a quartic oscillator linearly interacting with
a tunnelling pseudo-spin. We have integrated numerically the quantum dynamics
of this system in the partial Wigner representation and calculated the
pseudo-spin population difference. Depending on the coupling, we have verified
that the quantum tunnelling of the oscillator can lead to a more effective
reduction of the Rabi oscillation amplitude of the pseudo-spin. Such findings
suggests an experimental set-up that might be able to discriminate between the
quantum and the classical motion of a nano-rod.",1302.3951v1
2013-03-06,Mixed-State Effect on the Low-Energy Spin Dynamics in Optimally-doped Iron Pnictide Superconductors,"Based on a phenomenological model with $s_{\pm}$ or s-wave pairing symmetry,
the mixed-state effect on the low-energy spin dynamics in optimally-doped iron
pnictide superconductors is studied by solving Bogoliubov-de Gennes equations.
Our results of the spin susceptibility at $\mathbf{q}=\mathbf{Q}$ in the
normal, superconducting and mixed states agree qualitatively with recent
neutron scattering experiments. We also propose that the field-induced
intensity change shows different behaviors between the $s_{\pm}$ and s-wave
symmetries in both momentum and real space, thus it can be used to distinguish
these two pairing symmetries.",1303.1557v1
2013-05-03,Dynamical twisting and the b ghost in the pure spinor formalism,"After adding an RNS-like fermionic vector \psi^m to the pure spinor
formalism, the non-minimal b ghost takes a simple form similar to the pure
spinor BRST operator. The N=2 superconformal field theory generated by the b
ghost and the BRST current can be interpreted as a ""dynamical twisting"" of the
RNS formalism where the choice of which spin half \psi^m variables are twisted
into spin 0 and spin 1 variables is determined by the pure spinor variables
that parameterize the coset SO(10)/U(5).",1305.0693v1
2013-06-14,Quantum Dynamics in Classical Spin Baths,"A formalism for studying the dynamics of quantum systems embedded in
classical spin baths is introduced. The theory is based on generalized
antisymmetric brackets and predicts the presence of open-path off-diagonal
geometric phases in the evolution of the density matrix. The weak coupling
limit of the equation can be integrated by standard algorithms and provides a
non-Markovian approach to the computer simulation of quantum systems in
classical spin environments. It is expected that the theory and numerical
schemes presented here have a wide applicability.",1306.3299v1
2013-12-03,Dynamical properties of three terminal magnetic tunnel junctions: spintronics meets spin-orbitronics,"This letter introduces a micromagnetic model able to characterize the
magnetization dynamics in three terminal magnetic tunnel junctions, where the
effects of spin-transfer torque and spin-orbit torque are taken into account.
Our results predict that the possibility to separate electrically those two
torque sources is very promising from a technological point of view for both
next generation of nanoscale spintronic oscillators and microwave detectors. A
scalable synchronization scheme based on the parallel connection of those three
terminal devices is also proposed.",1312.0806v1
2014-01-10,Nonequilibrium thermal entanglement for three-spin chain,"The dynamics of a chain of three spins coupled at both ends to separate
bosonic baths at different temperatures is studied. An exact analytical so-
lution of the master equation in the Born-Markov approximation for the reduced
density matrix of the chain is constructed. It is shown that for long times the
reduced density matrix converges to the non-equilibrium steady- state.
Dynamical and steady state properties of the concurrence between the first and
the last spin are studied.",1401.2302v1
2014-11-25,Comparison of Spin Dynamics in the Cylindrical and Frenet-Serret Coordinate Systems,"A comparative analysis of a description of spin dynamics in the cylindrical
and Frenet-Serret coordinate systems is carried out. An equivalence of these
two systems is shown. A possibility of efficient use of the cylindrical
coordinate system for a calculation of spin evolution of particles and nuclei
in accelerators and storage rings is caused by an immobility of its coordinate
axes relative to stationary detectors.",1502.05970v1
2015-04-23,Magnetization damping in noncollinear spin valves with antiferromagnetic interlayer couplings,"We study the magnetic damping in the simplest of synthetic antiferromagnets,
i.e. antiferromagnetically exchange-coupled spin valves in which applied
magnetic fields tune the magnetic configuration to become noncollinear. We
formulate the dynamic exchange of spin currents in a noncollinear texture based
on the spindiffusion theory with quantum mechanical boundary conditions at the
ferrromagnet|normal-metal interfaces and derive the Landau-Lifshitz-Gilbert
equations coupled by the static interlayer non-local and the dynamic exchange
interactions. We predict non-collinearity-induced additional damping that can
be sensitively modulated by an applied magnetic field. The theoretical results
compare favorably with published experiments.",1504.06042v1
2015-06-20,Spin and orbital exchange interactions from Dynamical Mean Field Theory,"We derive a set of equations expressing the parameters of the magnetic
interactions characterizing a strongly correlated electronic system in terms of
single-electron Green's functions and self-energies. This allows to establish a
mapping between the initial electronic system and a spin model including up to
quadratic interactions between the effective spins, with a general interaction
(exchange) tensor that accounts for anisotropic exchange, Dzyaloshinskii-Moriya
interaction and other symmetric terms such as dipole-dipole interaction. We
present the formulas in a format that can be used for computations via
Dynamical Mean Field Theory algorithms.",1506.06209v1
2015-08-24,Learning of couplings for random asymmetric kinetic Ising models revisited: random correlation matrices and learning curves,"We study analytically the performance of a recently proposed algorithm for
learning the couplings of a random asymmetric kinetic Ising model from finite
length trajectories of the spin dynamics. Our analysis shows the importance of
the nontrivial equal time correlations between spins induced by the dynamics
for the speed of learning. These correlations become more important as the
spin's stochasticity is decreased. We also analyse the deviation of the
estimation error from asymptotic optimality.",1508.05865v2
2016-02-19,Digital-Analog Quantum Simulation of Spin Models in Trapped Ions,"We propose a method to simulate spin models in trapped ions using a
digital-analog approach, consisting in a suitable gate decomposition in terms
of analog blocks and digital steps. In this way, we show that the quantum
dynamics of an enhanced variety of spin models could be implemented with
substantially less number of gates than a fully digital approach. Typically,
analog blocks are built of multipartite dynamics providing the complexity of
the simulated model, while the digital steps are local operations bringing
versatility to it. Finally, we describe a possible experimental implementation
in trapped-ion technologies.",1602.06248v2
2016-04-21,Non-equilibrium magnetic fields in ab initio spin dynamics,"Starting from the continuity equation for the magnetization in time-dependent
spin-density functional theory, we derive an expression for the effective
time-dependent magnetic fields driving the out-of-equilibrium spin dynamics in
magnetic systems. We evaluate these, so called, kinetic magnetic fields in the
ultrafast demagnetization response to optical pulse excitations of
ferromagnetic iron-based materials, namely Fe$_6$ cluster and bulk bcc Fe. We
identify spatial ""hot spots"" where the demagnetization is particularly enhanced
as a result of the increased kinetic torque.",1604.06262v2
2016-06-06,Dissipative Entanglement of Quantum Spin Fluctuations,"We consider two non-interacting infinite quantum spin chains immersed in a
common thermal environment and undergoing a local dissipative dynamics of
Lindblad type. We study the time evolution of collective mesoscopic quantum
spin fluctuations that, unlike macroscopic mean-field observables, retain a
quantum character in the thermodynamical limit. We show that the microscopic
dissipative dynamics is able to entangle these mesoscopic degrees of freedom,
through a purely mixing mechanism. Further, the behaviour of the dissipatively
generated quantum correlations between the two chains is studied as a function
of temperature and dissipation strength.",1606.01733v1
2016-09-21,Finite speed heat transport in a quantum spin chain after quenched local cooling,"We study the dynamics of an initially thermalized spin chain in the quantum
XY-model, after sudden coupling to a heat bath of lower temperature at one end
of the chain. In the semi-classical limit we see an exponential decay of the
system-bath heatflux by exact solution of the reduced dynamics. In the full
quantum description however, we numerically find the heatflux to reach
intermediate plateaus where it is approximately constant -- a phenomenon that
we attribute to the finite speed of heat transport via spin waves.",1609.06483v2
2017-02-28,Simultaneous tracking of spin angle and amplitude beyond classical limits,"We show how simultaneous, back-action evading tracking of non-commuting
observables can be achieved in a widely-used sensing technology, atomic
interferometry. Using high-dynamic-range dynamically-decoupled quantum
non-demolition (QND) measurements on a precessing atomic spin ensemble, we
track the collective spin angle and amplitude with negligible effects from back
action, giving steady-state tracking sensitivity 2.9 dB beyond the standard
quantum limit and 7.0 dB beyond Poisson statistics.",1702.08888v1
2019-05-21,Collective spin dynamics of Z2 vortex crystals in triangular Kitaev-Heisenberg antiferromagnets,"We show that the mesoscopic incommensurate $\mathbb{Z}_2$ vortex crystals
proposed for layered triangular anisotropic magnets can be most saliently
identified by two distinctive signatures in dynamical spin response
experiments: The presence of pseudo-Goldstone `phonon' modes at low frequencies
$\omega$, associated with the collective vibrations of the vortex cores, and a
characteristic multi-scattered intensity profile at higher $\omega$, arising
from a large number of Bragg reflections and magnon bandgaps. These are direct
fingerprints of the large vortex sizes and magnetic unit cells and the
solitonic spin profile around the vortex cores.",1905.08694v2
2014-03-18,Optimizing phase estimation algorithms for diamond spin magnetometry,"We present a detailed theoretical and numerical study discussing the
application and optimization of phase estimation algorithms (PEAs) to diamond
spin magnetometry. We compare standard Ramsey magnetometry, the non-adaptive
PEA (NAPEA) and quantum PEA (QPEA) incorporating error-checking. Our results
show that the NAPEA requires lower measurement fidelity, has better dynamic
range, and greater consistency in sensitivity. We elucidate the importance of
dynamic range to Ramsey magnetic imaging with diamond spins, and introduce the
application of PEAs to time-dependent magnetometry.",1403.4506v3
2008-07-11,Probing the spin polarization of current by soft X-ray imaging of current-induced magnetic vortex dynamics,"Time-resolved soft X-ray transmission microscopy is applied to image the
current-induced resonant dynamics of the magnetic vortex core realized in a
micronsized Permalloy disk. The high spatial resolution better than 25 nm
enables us to observe the resonant motion of the vortex core. The result also
provides the spin polarization of the current to be 0.67 +/-0.16 for Permalloy
by fitting the experimental results with an analytical model in the framework
of the spin-transfer torque.",0807.1782v1
2012-01-27,Quantum spin mixing in a binary mixture of spin-1 atomic condensates,"We study quantum spin mixing in a binary mixture of spin-1 condensates
including coherent interspecies mixing process, using the familiar spinor
condensates of $^{87}$Rb and $^{23}$Na atoms in the ground lower hyperfine F=1
manifolds as prototype examples. Within the single spatial mode approximation
for each of the two spinor condensates, the mixing dynamics reduce to that of
three coupled nonlinear pendulums with clear physical interpretations. Using
suitably prepared initial states, it is possible to determine the interspecies
singlet-pairing as well as spin-exchange interactions from the subsequent
mixing dynamics.",1201.5711v1
2012-04-12,Spin-orbit coupled cold exciton condensates,"We analyze theoretically the dynamics of degenerate condensate of cold
indirect excitons. We account for both linear spin dependent terms arising from
spin-orbit interaction of Rashba and Dresselhaus types and non-linear terms
transforming a pair of bright excitons into a pair of dark ones. We show that
both terms should lead to the qualitative changes in the dynamics of cold
exciton droplets in the real space and time.",1204.2721v1
2014-06-18,Spin-lattice coupling induced weak dynamical magnetism in EuTiO_3 at high temperatures,"EuTiO_3, which is a G-type antiferromagnet below T_N = 5.5 K, has some
fascinating properties at high temperatures, suggesting that macroscopically
hidden dynamically fluctuating weak magnetism exists at high temperatures. This
conjecture is substantiated by magnetic field dependent magnetization
measurements, which exhibit pronounced anomalies below 200 K becoming more
distinctive with increasing magnetic field strength. Additional results from
muon spin rotation (${\mu}$SR) experiments provide evidence for weak
fluctuating bulk magnetism induced by spin-lattice coupling which is strongly
supported in increasing magnetic field.",1406.4915v1
2014-06-30,Monte Carlo simulations for Ising spins with spin greater than 1/2 applied to the square and triangular lattices with antiferromagnetic interactions and comparing results using Kawasaki and Glauber dynamics,"This paper has a pedagogical introduction. We describe the correct method for
performing Monte Carlo simulations of Ising model systems with spin greater
than one half. Correct and incorrect procedures are clearly outlined and the
consequences of using the incorrect procedure are shown. The difference between
Kawasaki and Glauber dynamics is then outlined and both methods are applied to
the antiferromagnetic square and triangular lattices for S =1.",1406.7816v1
2016-08-23,Dynamic dependence to domain wall propagation through artificial spin ice,"Domain wall propagation dynamics have been studied in nanostructured
artificial kagome spin ice structures. A stripline circuit has been used to
provide localised pulsed magnetic fields within the artificial spin ice
structure. This provides control of the system through electrically assisted
domain wall nucleation events. Synchronisation of the pulsed fields with
additional global magnetic fields and the use of a focussed magneto-optical
Kerr effect magnetometer allows our experiments to probe the domain wall
transit through an extended ASI structure. We find that the propagation
distance depends on the driving field revealing field driven properties of
domain walls below their intrinsic nucleation field.",1608.06436v1
2017-07-28,Moving obstacle potential in a spin-orbit-coupled Bose-Einstein condensate,"We investigate the dynamics around an obstacle potential moving in the
plane-wave state of a pseudospin-$1/2$ Bose-Einstein condensate with Rashba
spin-orbit coupling. We numerically investigate the dynamics of the system and
find that it depends not only on the velocity of the obstacle but also
significantly on the direction of obstacle motion, which are verified by a
Bogoliubov analysis. The excitation diagram with respect to the velocity and
direction is obtained. The dependence of the critical velocity on the strength
of the spin-orbit coupling and the size of the obstacle is also investigated.",1707.09136v1
2017-12-06,Thermal contact through a two-temperature kinetic Ising chain,"We consider a model for thermal contact through a diathermal interface
between two macroscopic bodies at different temperatures: an Ising spin chain
with nearest neighbor interactions is endowed with a Glauber dynamics with
different temperatures and kinetic parameters on alternating sites. The
inhomogeneity of the kinetic parameter is a novelty with respect to the model
of Ref.[1] and we exhibit its influence upon the stationary non equilibrium
values of the two-spin correlations at any distance. By mapping to the dynamics
of spin domain walls and using free fermion techniques, we determine the scaled
generating function for the cumulants of the exchanged heat amounts per unit of
time in the long time limit.",1712.02273v1
2019-06-22,Dynamics and correlations in Motzkin and Fredkin spin chains,"The Motzkin and Fredkin quantum spin chains are described by frustration-free
Hamiltonians recently introduced and studied because of their anomalous
behaviors in the correlation functions and in the entanglement properties. In
this paper we analyze their quantum dynamical properties, focusing in
particular on the time evolution of the excitations driven by a quantum quench,
looking at the correlations functions of spin operators defined along different
directions, and discussing the results in relation with the cluster
decomposition property.",1906.09515v1
2020-02-04,Lorentz symmetry violation and the tunneling radiation of fermions with spin $1/2$ for Kerr Anti-de-Sitter black hole,"We studied the correction of the quantum tunneling radiation of fermions with
spin $1/2$ in Kerr Anti-de-Sitter black hole. First, the dynamic equation of
spin $1/2$ fermions was corrected using Lorentz's violation theory. Second, the
new expressions of the fermions quantum tunneling rate, the Hawking temperature
of the black hole and the entropy of the black hole were obtained according to
the corrected fermions dynamic equation. At last, some comments are made on the
results of our work.",2002.01148v1
2012-05-25,Emergence of a common energy scale close to the orbital-selective Mott transition,"We calculate the spectra and spin susceptibilities of a Hubbard model with
two bands having different bandwidths but the same on-site interaction, with
parameters close to the orbital-selective Mott transition, using dynamical
mean-field theory. If the Hund's rule coupling is sufficiently strong, one
common energy scale emerges which characterizes both the location of kinks in
the self-energy and extrema of the diagonal spin susceptibilities. A physical
explanation of this energy scale is derived from a Kondo-type model. We infer
that for multi-band systems local spin dynamics rather than spectral functions
determine the location of kinks in the effective band structure.",1205.5782v1
2017-09-22,Quantum Biomimetic Modeling of Diamond NV$^{-}$ Center Spin Dynamics,"The spin dynamics of the diamond NV$^{-}$ center turns out to be similar to
that of the chemical compass responsible for avian magnetoreception. We present
a simulation framework based on quantum master equation for the former that is
based upon the Radical Pair model of the latter. We show that this framework
captures all the experimentally studied behavior of the NV$^{-}$ center spin
system and can therefore be a predictive modeling tool.",1709.07632v1
2017-11-08,Revealing the internal spin dynamics in a double quantum dot by periodic voltage modulation,"The paper proposes the method to analyze the internal dynamics of nanoscopic
systems by periodic modulation of the electrochemical potentials of the
attached leads and measuring the time-averaged current. The idea is presented
using the example of the a double quantum dot coupled to one nonmagnetic and
one spin-polarized lead. The current flowing through the molecule is shown to
depend on both the frequency of the modulation and the exchange coupling
between the electrons occupying the molecule. In particular, one can observe a
pronounced oscillatory behavior of the current-frequency dependence, which
reveals the coherent oscillations between the spin states of the system.",1711.02873v1
2017-11-14,Vortex dipole precession in a Fermi superfluid with Rashba spin-orbit coupling,"We present a closed-form expression for the time dynamics of a balanced Fermi
superfluid with s-wave pairing and Rashba spin-orbit (SO) coupling. Solving the
associated self-consistency conditions for an initial number density given by a
Gaussian and an initial gap containing a vortex dipole, we show that Rashba SO
coupling results in precession of the vortex dipole. The integrated
self-consistent gap decays as a function of time, characterising a ""transient
Fermi superfluid"". Our analytic solution forms a starting point for studies of
vortex dynamics -- in particular braiding of Majorana fermions -- in Fermi
superfluids in the presence of spin population imbalance and two-dimensional SO
coupling, which are both required to realize a topological atomic Fermi gas in
experiments.",1711.04970v1
2018-06-20,Configuration Interaction Singles with Spin-Orbit Coupling: Constructing Spin-Adiabatic States and Their Analytical Nuclear Gradients,"For future use in modeling photoexcited dynamics and intersystem crossing, we
calculate spin-adiabatic states and their analytical nuclear gradients within
CIS the- ory. These energies and forces should be immediately useful for
surface hopping dynamics, which are natural within an adiabatic framework. The
resulting code has been implemented within the Q-Chem software and preliminary
results suggest that the additional cost of including SOC within the
singles-singles block is not large.",1806.07835v1
2019-02-19,Exact generation of quantum states by the dynamics of spin chains,"We design a quasi-one dimensional spin chain with engineered coupling
strengths such that the natural dynamics of the spin chain evolves a single
excitation localized at the left hand site to any specified single particle
state on the whole chain. Our treatment is an exact solution to a problem which
has already been addressed in approximate ways. As two important examples, we
study the $W$ states and Gaussian states with arbitrary width.",1902.07295v2
2019-04-01,Synchrony breakdown and noise-induced oscillation death in ensembles of serially connected spin-torque oscillators,"We consider collective dynamics in the ensemble of serially connected
spin-torque oscillators governed by the Landau-Lifshitz-Gilbert-Slonczewski
magnetization equation. Proximity to homoclinicity hampers synchronization of
spin-torque oscillators: when the synchronous ensemble experiences the
homoclinic bifurcation, the Floquet multiplier, responsible for the temporal
evolution of small deviations from the ensemble mean, diverges. Depending on
the configuration of the contour, sufficiently strong common noise, exemplified
by stochastic oscillations of the current through the circuit, may suppress
precession of the magnetic field for all oscillators. We derive the explicit
expression for the threshold amplitude of noise, enabling this suppression.",1904.00897v1
2019-04-17,Orientation dependent current-induced motion of skyrmions with various topologies,"We study the current-driven motion of metastable localized spin structures
with various topological charges in a (Pt$_{1-x}$Ir$_{x}$)/Fe bilayer on a
Pd(111) surface by combining atomistic spin model simulations with an approach
based on the generalized Thiele equation. We demonstrate that besides a
distinct dependence on the topological charge itself the dynamic response of
skyrmionic structures with topological charges $\mathrm{Q} = -1$ and
$\mathrm{Q}= 3$ to a spin-polarized current exhibits an orientation dependence.
We further show that such an orientation dependence can be induced by applying
an in-plane external field, possibly opening up a new pathway to the
manipulation of skyrmion dynamics.",1904.08198v1
2019-12-03,Ferromagnetic spin correlations in the two-dimensional Hubbard model,"We analyze the dynamical nearest-neighbor and next-nearest-neighbor spin
correlations in the 4-site and 8-site dynamical cluster approximation to the
two-dimensional Hubbard model. Focusing on the robustness of these correlations
at long imaginary times, we reveal enhanced ferromagnetic correlations on the
lattice diagonal, consistent with the emergence of composite spin-1 moments at
a temperature scale that essentially coincides with the pseudo-gap temperature
$T^*$. We discuss these results in the context of the spin-freezing theory of
unconventional superconductivity.",1912.01260v1
2019-12-10,Holographic Map for Cosmological Horizons,"We propose a holographic map between Einstein gravity coupled to matter in a
de Sitter background and large N quantum mechanics of a system of spins.
Holography maps a spin model with a finite dimensional Hilbert space defined on
a version of the stretched horizon into bulk gravitational dynamics. The full
Hamiltonian of the spin model contains a non-local piece which generates
chaotic dynamics, widely conjectured to be a necessary part of quantum gravity,
and a local piece which recovers the perturbative spectrum in the bulk.",1912.04864v1
2019-12-19,Markovianity of an emitter coupled to a structured spin chain bath,"We analyze the dynamics of a spin 1/2 subsystem coupled to a spin chain. We
simulate numerically the full quantum many-body system for various sets of
parameters and initial states of the chain, and characterize the divisibility
of the subsystem dynamics, i.e. whether it is Markovian and can be described by
a (time dependent) master equation. We identify regimes in which the subsystem
admits such Markovian description, despite the many-body setting, and provide
insight about why the same is not possible in other regimes. Interestingly,
coupling the subsystem at the edge, instead of the center, of the chain gives
rise to qualitatively distinct behavior.",1912.09151v1
2020-10-15,Equilibrium Dynamics of the Sub-Ohmic Spin-boson Model At Finite Temperature,"We use the full-density matrix (FDM) numerical renormalization group (NRG)
method to calculate the equilibrium dynamical correlation function $C(\omega)$
of the spin operator $\sigma_z$ at finite temperature for the sub-Ohmic
spin-boson model. A peak is observed at the frequency $\omega_{T}\sim T$ in the
curve of $C(\omega)$. The curve merges with the zero temperature $C(\omega)$ in
$\omega \gg \omega_{T}$ and deviate significantly from the power-law form
$\omega^{\pm s}$ of the zero temperature curve in $\omega \ll\omega_{T}$.",2010.07471v1
2021-05-27,"Curvature-induced long ranged supercurrents in diffusive SFS Josephson Junctions, with dynamic $0-π$ transition","We report that spin supercurrents can be induced in diffusive SFS Josephson
junctions without any magnetic misalignment or intrinsic spin orbit coupling.
Instead, the pathway to spin triplet generation is provided via geometric
curvature, and results in a long ranged Josephson effect. In addition, the
curvature is shown to induce a dynamically tunable $0-\pi$ transition in the
junction. We provide the analytic framework and discuss potential experimental
and innovation implications.",2105.13372v2
2021-12-07,Bogoliubov spectrum and the dynamic structure factor in a quasi-two-dimensional spin-orbit coupled BEC,"We compute the the Bogoliubov-de-Gennes excitation spectrum in a trapped
two-component spin-orbit-coupled (SOC) Bose-Einstein condensate (BEC) in
quasi-two-dimensions as a function of linear and angular momentum and analyse
them. The excitation spectrum exhibits a minima-like feature at finite momentum
for the immiscible SOC-BEC configuration. We augment these results by computing
the dynamic structure factor in the density and pseudo-spin sector, and discuss
its interesting features that can be experimentally measured through Bragg
spectroscopy of such ultra cold-condensate.",2112.03505v1
2022-05-20,Spin dynamics in the topological elemental gray Tin from first principles perspective,"Gray Tin is attracting much more interest as a topological quantum material,
which has a precisely controlled composition and can be a material for
spintronic devices. However, the spin dynamics in gray Tin is largely unknown.
In this paper, we calculate the topological surface state of gray Tin by
combining density functional theory and a tight-bind model, also propose an
electromagnetics -- quantum mechanics hybrid approach on how to enhance with
metastructures the spin polarized photocurrent in gray Tin, which was
experimentally measured recently.",2205.09919v2
2023-07-28,Berezinskii approach to disordered spin systems with asymmetric scattering and application to the quantum boomerang effect,"We extend the Berezinskii diagrammatic technique to one-dimensional
disordered spin systems, in which time-reversal invariance is broken due to a
spin-orbit coupling term inducing left-right asymmetric scattering. We then use
this formalism to theoretically describe the dynamics of the quantum boomerang
effect, a recently discovered manifestation of Anderson localization. The
theoretical results are confirmed by exact numerical simulations of wave-packet
dynamics in a random potential.",2307.15354v1
2023-10-19,Crossover from string to cluster dynamics following a field quench in spin ice,"We investigate quench dynamics of spin ice after removal of a strong magnetic
field along the [100] crystal direction, using Monte Carlo simulations and
theoretical arguments. We show how the early-time relaxation of the
magnetization can be understood in terms of nucleation and growth of strings of
flipped spins, in agreement with an effective stochastic model that we
introduce and solve analytically. We demonstrate a crossover at longer times to
a regime dominated by approximately isotropic clusters, which we characterize
in terms of their morphology, and present evidence for a percolation transition
as a function of magnetization.",2310.12410v2
2023-11-23,Supercurrent-carrying supersolid in spin-orbit-coupled Bose-Einstein condensates,"One of brilliant achievements in spin-orbit-coupled Bose-Einstein condensates
is the discovery and observation of the supersolid stripe states. So far, all
studied supersolid stripe states do not carry supercurrent. In this work, we
reveal the existence of novel supercurrent-carrying supersolids in
spin-orbit-coupled Bose-Einstein condensates. The supersolid family has a
parabolic-like dispersion relation and carries supercurrent which is
proportional to the quasimomentum. Energetic and dynamical instabilities can
break supercurrent-carrying ability of this supersolid family. An insightful
interpretation of the dynamical instability of supercurrent-carrying
supersolids from the pure plane-wave phase is provided.",2311.13786v1
2023-12-07,Thermomagnetic Anomalies by Magnonic Criticality in Ultracold Atomic Transport,"We investigate thermomagnetic transport in an ultracold atomic system with
two ferromagnets linked via a magnetic quantum point contact. Using
nonequilibrium Green's function approach, we show a divergence in spin
conductance and a slowing down of spin relaxation that manifest in the weak
effective-Zeeman-field limit. These anomalous spin dynamics result from the
magnonic critical point at which magnons become gapless due to spontaneous
magnetization. Our findings unveil untapped dynamics in ultracold atomic
systems, opening new avenues in thermomagnetism.",2312.04280v1
2023-12-10,Polarization dynamics from moment equations,"We derive an expression for the local transverse polarization of a
boost-invariant expanding system of massive particles, which involves a set of
dynamical spin moments. Starting from spin kinetic theory, we obtain a closed
set of equations of motion for these spin moments. These equations are valid
during the full evolution of the system, from free streaming to local
equilibrium, and can be used to study polarization phenomena in relativistic
heavy-ion collisions.",2312.05917v1
2023-12-22,Magnetic droplet solitons,"Magnetic droplets are nanoscale, non-topological, dynamical solitons that can
be nucleated in different spintronic devices, such as spin torque
nano-oscillators (STNOs) and spin Hall nano-oscillators (SHNOs). This chapter
first briefly discusses the theory of spin current driven dissipative magnetic
droplets in ferromagnetic thin films with uniaxial anisotropy. We then
thoroughly review the research literature on magnetic droplets and their
salient features, as measured using electrical, microwave, and synchrotron
techniques, and as envisaged by micromagnetic simulations. We also touch upon a
closely related soliton, the dynamical skyrmion. Finally, we present an outlook
of new routes in droplet science.",2312.14621v1
2024-01-01,Exotic synchronization in continuous time crystals outside the symmetric subspace,"Exploring continuous time crystals (CTCs) within the symmetric subspace of
spin systems has been a subject of intensive research in recent times. Thus
far, the stability of the time-crystal phase outside the symmetric subspace in
such spin systems has gone largely unexplored. Here, we investigate the effect
of including the asymmetric subspaces on the dynamics of CTCs in a driven
dissipative spin model. This results in multistability, and the dynamics
becomes dependent on the initial state. Remarkably, this multistability leads
to exotic synchronization regimes such as chimera states and cluster
synchronization in an ensemble of coupled identical CTCs.",2401.00675v1
2024-01-08,Steering spin fluctuations in lattice systems via two-tone Floquet engineering,"We report on the controlled creation and destruction of antiferromagnetic
dimers using two-tone Floquet engineering. We consider a one-dimensional
spin-1/2 lattice with periodically modulated bonds using parametric resonances.
The stroboscopic dynamics generated from distributed bond modulations lead to
pair correlation between spins. Consequently, subharmonic response in local
observables breaks discrete time translational symmetry and leads to the
emergence of Floquet dynamical dimerisation. We present a protocol allowing the
control of local spin-correlated pairs driven by one-period evolution
operators, providing significant insight into new nonequilibrium states of
matter that can be feasibly implemented in current quantum simulator platforms.",2401.03889v1
2024-01-26,Collective dynamical Fermi suppression of optically-induced inelastic scattering,"We observe strong dynamical suppression of optically-induced loss in a weakly
interacting Fermi gas as the $s$-wave scattering length is increased. The
single, cigar-shaped cloud behaves as a large spin lattice in energy space with
a tunable Heisenberg Hamiltonian. The loss suppression occurs as the lattice
transitions into a magnetized state, where the fermionic nature of the atoms
inhibits interactions. The data are quantitatively explained by incorporating
spin-dependent loss into a quasi-classical collective spin vector model, the
success of which enables the application of optical control of effective
long-range interactions to this system.",2401.15162v2
2017-05-19,Sub-picosecond spin dynamics of excited states in the topological insulator Bi$_2$Te$_3$,"Using time-, spin- and angle-resolved photoemission, we investigate the
ultrafast spin dynamics of hot electrons on the surface of the topological
insulator Bi$_2$Te$_3$ following optical excitation by fs-infrared pulses. We
observe two surface-resonance states above the Fermi level coexisting with a
transient population of Dirac fermions that relax in about $\sim$2 ps. One
state is located below $\sim$0.4 eV just above the bulk continuum, the other
one at $\sim$0.8 eV inside a projected bulk band gap. At the onset of the
excitation, both states exhibit a reversed spin texture with respect to that of
the transient Dirac bands, in agreement with our one-step photoemission
calculations. Our data reveal that the high-energy state undergoes spin
relaxation within $\sim$0.5 ps, a process that triggers the subsequent spin
dynamics of both the Dirac cone and the low-energy state, which behave as two
dynamically-locked electron populations. We discuss the origin of this behavior
by comparing the relaxation times observed for electrons with opposite spins to
the ones obtained from a microscopic Boltzmann model of ultrafast band cooling
introduced into the photoemission calculations. Our results demonstrate that
the nonequilibrium surface dynamics is governed by electron-electron rather
than electron-phonon scattering, with a characteristic time scale unambiguously
determined by the complex spin texture of excited states above the Fermi level.
Our findings reveal the critical importance of detecting momentum and
energy-resolved spin textures with fs resolution to fully understand the sub-ps
dynamics of transient electrons on the surface of topological insulators.",1705.07071v1
2017-05-30,"Dipolar spin ice states with fast monopole hopping rate in CdEr$_2$X$_4$ (X = Se, S)","Excitations in a spin ice behave as magnetic monopoles, and their population
and mobility control the dynamics of a spin ice at low temperature.
CdEr$_2$Se$_4$ is reported to have the Pauling entropy characteristic of a spin
ice, but its dynamics are three-orders of magnitude faster than the canonical
spin ice Dy$_2$Ti$_2$O$_7$. In this letter we use diffuse neutron scattering to
show that both CdEr$_2$Se$_4$ and CdEr$_2$S$_4$ support a dipolar spin ice
state -- the host phase for a Coulomb gas of emergent magnetic monopoles. These
Coulomb gases have similar parameters to that in Dy$_2$Ti$_2$O$_7$, i.e. dilute
and uncorrelated, so cannot provide three-orders faster dynamics through a
larger monopole population alone. We investigate the monopole dynamics using ac
susceptometry and neutron spin echo spectroscopy, and verify the crystal
electric field Hamiltonian of the Er$^{3+}$ ions using inelastic neutron
scattering. A quantitative calculation of the monopole hopping rate using our
Coulomb gas and crystal electric field parameters shows that the fast dynamics
in CdEr$_2$X$_4$ (X = Se, S) are primarily due to much faster monopole hopping.
Our work suggests that CdEr$_2$X$_4$ offer the possibility to study alternative
spin ice ground states and dynamics, with equilibration possible at much lower
temperatures than the rare earth pyrochlore examples.",1705.10737v3
2020-09-02,Enhancing associative memory recall and storage capacity using confocal cavity QED,"We introduce a near-term experimental platform for realizing an associative
memory. It can simultaneously store many memories by using spinful bosons
coupled to a degenerate multimode optical cavity. The associative memory is
realized by a confocal cavity QED neural network, with the cavity modes serving
as the synapses, connecting a network of superradiant atomic spin ensembles,
which serve as the neurons. Memories are encoded in the connectivity matrix
between the spins, and can be accessed through the input and output of patterns
of light. Each aspect of the scheme is based on recently demonstrated
technology using a confocal cavity and Bose-condensed atoms. Our scheme has two
conceptually novel elements. First, it introduces a new form of random spin
system that interpolates between a ferromagnetic and a spin-glass regime as a
physical parameter is tuned---the positions of ensembles within the cavity.
Second, and more importantly, the spins relax via deterministic
steepest-descent dynamics, rather than Glauber dynamics. We show that this
nonequilibrium quantum-optical scheme has significant advantages for
associative memory over Glauber dynamics: These dynamics can enhance the
network's ability to store and recall memories beyond that of the standard
Hopfield model. Surprisingly, the cavity QED dynamics can retrieve memories
even when the system is in the spin glass phase. Thus, the experimental
platform provides a novel physical instantiation of associative memories and
spin glasses as well as provides an unusual form of relaxational dynamics that
is conducive to memory recall even in regimes where it was thought to be
impossible.",2009.01227v1
2023-03-21,Spin-motion coupling in a circular Rydberg state quantum simulator: case of two atoms,"Rydberg atoms are remarkable tools for the quantum simulation of spin arrays.
Circular Rydberg atoms open the way to simulations over very long time scales,
using a combination of laser trapping of the atoms and spontaneous-emission
inhibition, as shown in the proposal of a XXZ spin-array simulator based on
chains of trapped circular atoms [T.L. Nguyen $\textit{et al.}$, Phys. Rev. X
8, 011032 (2018)]. Such simulators could reach regimes (thermalization, glassy
dynamics) that are out of the reach of those based on ordinary,
low-angular-momentum short-lived Rydberg atoms. Over the promised long time
scales, the unavoidable coupling of the spin dynamics with the atomic motion in
the traps may play an important role. We study here the interplay between the
spin exchange and motional dynamics in the simple case of two interacting
circular Rydberg atoms confined in harmonic traps. The time evolution is solved
exactly when the position dependence of the dipole-dipole interaction terms can
be linearized over the extension of the atomic motion. We present numerical
simulations in more complex cases, using the realistic parameters of the
simulator proposal. We discuss three applications. First, we show that
realistic experimental parameters lead to a regime in which atomic and spin
dynamics become fully entangled, generating interesting non-classical motional
states. We also show that, in other parameter regions, the spin dynamics
notably depends on the initial temperature of the atoms in the trap, providing
a sensitive motional thermometry method. Last, and most importantly, we discuss
the range of parameters in which the motion has negligible influence over the
spin dynamics.",2303.12150v2
2004-10-21,A Note on Edwards' Hypothesis for Zero-Temperature Ising Dynamics,"We give a simple criterion for checking the so called Edwards' hypothesis in
certain zero-temperature, ferromagnetic spin-flip dynamics and use it to
invalidate the hypothesis in various examples in dimension one and higher.",0410543v1
1996-10-28,The Renormalization Group and Dynamical Triangulations,"A block spin renormalization group approach is introduced which can be
applied to dynamical triangulations in any dimension.",9610037v1
2009-04-28,"2H and 13C NMR studies on the temperature-dependent water and protein dynamics in hydrated elastin, myoglobin and collagen","2H NMR spin-lattice relaxation and line-shape analyses are performed to study
the temperature-dependent dynamics of water in the hydration shells of
myoglobin, elastin, and collagen.",0904.4424v1
2012-02-20,Variational description of Gibbs-non-Gibbs dynamical transitions for the Curie-Weiss model,"We perform a detailed study of Gibbs-non-Gibbs transitions for the
Curie-Weiss model subject to independent spin-flip dynamics
(""infinite-temperature"" dynamics). We show that, in this setup, the program
outlined in van Enter, Fern\'andez, den Hollander and Redig can be fully
completed, namely that Gibbs-non-Gibbs transitions are equivalent to
bifurcations in the set of global minima of the large-deviation rate function
for the trajectories of the magnetization conditioned on their endpoint. As a
consequence, we show that the time-evolved model is non-Gibbs if and only if
this set is not a singleton for some value of the final magnetization. A
detailed description of the possible scenarios of bifurcation is given, leading
to a full characterization of passages from Gibbs to non-Gibbs -and vice versa-
with sharp transition times (under the dynamics Gibbsianness can be lost and
can be recovered).
  Our analysis expands the work of Ermolaev and Kulske who considered zero
magnetic field and finite-temperature spin-flip dynamics. We consider both zero
and non-zero magnetic field but restricted to infinite-temperature spin-flip
dynamics. Our results reveal an interesting dependence on the interaction
parameters, including the presence of forbidden regions for the optimal
trajectories and the possible occurrence of overshoots and undershoots in the
optimal trajectories. The numerical plots provided are obtained with the help
of MATHEMATICA.",1202.4205v2
2013-09-14,Variational description of Gibbs-non-Gibbs dynamical transitions for spin-flip systems with a Kac-type interaction,"We continue our study of Gibbs-non-Gibbs dynamical transitions. In the
present paper we consider a system of Ising spins on a large discrete torus
with a Kac-type interaction subject to an independent spin-flip dynamics
(infinite-temperature Glauber dynamics). We show that, in accordance with the
program outlined in \cite{vEFedHoRe10}, in the thermodynamic limit
Gibbs-non-Gibbs dynamical transitions are \emph{equivalent} to bifurcations in
the set of global minima of the large-deviation rate function for the
trajectories of the empirical density \emph{conditional} on their endpoint.
More precisely, the time-evolved measure is non-Gibbs if and only if this set
is not a singleton for \emph{some} value of the endpoint. A partial description
of the possible scenarios of bifurcation is given, leading to a
characterization of passages from Gibbs to non-Gibbs and vice versa, with sharp
transition times.
  Our analysis provides a conceptual step-up from our earlier work on
Gibbs-non-Gibbs dynamical transitions for the Curie-Weiss model, where the
mean-field interaction allowed us to focus on trajectories of the empirical
magnetization rather than the empirical density.",1309.3667v1
2011-09-15,Dynamic mean-field and cavity methods for diluted Ising systems,"We compare dynamic mean-field and dynamic cavity as methods to describe the
stationary states of dilute kinetic Ising models. We compute dynamic mean-field
theory by expanding in interaction strength to third order, and compare to the
exact dynamic mean-field theory for fully asymmetric networks. We show that in
diluted networks the dynamic cavity method generally predicts magnetizations of
individual spins better than both first order (""naive"") and second order
(""TAP"") dynamic mean field theory.",1109.3399v3
1997-11-30,Dynamics of spin ladders,"We derive an approximate theory for Heisenberg spin ladders with two legs by
mapping the spin dynamics onto the problem of hard-core `bond-Bosons'. The
parameters of the Bosonic Hamiltonian are obtained by matching anomalous
Green's functions to Lanczos results and we find evidence for a strong
renormalization due to quantum fluctuations. Various dynamical spin correlation
functions are calculated and found to be in good agreement with Lanczos
results. We then enlarge the effective Hamiltonian to describe the coupling of
the bond-Bosons to a single hole injected into the system and treat the
hole-dynamics within the `rainbow-diagram' approximation by Schmidt-Rink et.
al. Theoretical predictions for the single hole spectral function are obtained
and found to be in good agreement with Lanczos results.",9712003v1
1999-04-22,Non-equilibrium dynamics of simple spherical spin models,"We investigate the non-equilibrium dynamics of spherical spin models with
two-spin interactions. For the exactly solvable models of the d-dimensional
spherical ferromagnet and the spherical Sherrington-Kirkpatrick model the
asymptotic dynamics has for large times and for large waiting times the same
formal structure. In the limit of large waiting times we find in both models an
intermediate time scale, scaling as a power of the waiting time with an
exponent smaller than one, and thus separating the time-translation invariant
short-time dynamics from the aging regime. It is this time scale on which the
fluctuation-dissipation regime is violated. Aging in these models is similar to
that observed in spin glasses at the level of correlation functions, but
different at the level of response functions, and thus different at the level
of experimentally accessible quantities like the thermoremanent magnetization.",9904329v1
2000-04-05,Low-frequency spin dynamics in the orthorombic phase of La_2CuO_4,"An effective field theory is derived that describes the low-frequency spin
dynamics in the low-temperature orthorombic phase of La_2CuO_4. Restricted to a
single CuO_2 layer the effective theory is a simple generalization of the
relativistic nonlinear sigma model to include all spin interactions allowed by
symmetry. Incorporating a weak interlayer interaction leads to two coupled
nonlinear sigma models which provide an efficient description of the complete
bilayer dynamics. Particular attention is paid to the weak-ferromagnetic and
spin-flop transitions induced by external magnetic fields. The main features of
the observed (covert) weak ferromagnetism are thus accounted for in a
straightforward manner but some of the finer theoretical predictions would
require further experimental investigation. The derived framework is also
suitable for the study of the structure and dynamics of magnetic domains in
undoped La_2CuO_4.",0004071v1
2001-02-08,Real space application of the mean-field description of spin glass dynamics,"The out of equilibrium dynamics of finite dimensional spin glasses is
considered from a point of view going beyond the standard `mean-field theory'
versus `droplet picture' debate of the last decades. The main predictions of
both theories concerning the spin glass dynamics are discussed. It is shown, in
particular, that predictions originating from mean-field ideas concerning the
violations of the fluctuation-dissipation theorem apply quantitatively,
provided one properly takes into account the role of the spin glass coherence
length which plays a central role in the droplet picture. Dynamics in a uniform
magnetic field is also briefly discussed.",0102151v2
2001-05-10,Expectation bubbles in a spin model of markets: Intermittency from frustration across scales,"A simple spin model is studied, motivated by the dynamics of traders in a
market where expectation bubbles and crashes occur. The dynamics is governed by
interactions which are frustrated across different scales: While ferromagnetic
couplings connect each spin to its local neighborhood, an additional coupling
relates each spin to the global magnetization. This new coupling is allowed to
be anti-ferromagnetic. The resulting frustration causes a metastable dynamics
with intermittency and phases of chaotic dynamics. The model reproduces main
observations of real economic markets as power-law distributed returns and
clustered volatility.",0105224v2
2004-03-05,Parallel dynamics of disordered Ising spin systems on finitely connected random graphs,"We study the dynamics of bond-disordered Ising spin systems on random graphs
with finite connectivity, using generating functional analysis. Rather than
disorder-averaged correlation and response functions (as for fully connected
systems), the dynamic order parameter is here a measure which represents the
disorder averaged single-spin path probabilities, given external perturbation
field paths. In the limit of completely asymmetric graphs our macroscopic laws
close already in terms of the single-spin path probabilities at zero external
field. For the general case of arbitrary graph symmetry we calculate the first
few time steps of the dynamics exactly, and we work out (numerical and
analytical) procedures for constructing approximate stationary solutions of our
equations. Simulation results support our theoretical predictions.",0403172v1
2006-01-10,Engineering of spin-lattice relaxation dynamics by digital growth of diluted magnetic semiconductor CdMnTe,"The technological concept of ""digital alloying"" offered by molecular-beam
epitaxy is demonstrated to be a very effective tool for tailoring static and
dynamic magnetic properties of diluted magnetic semiconductors. Compared to
common ""disordered alloys"" with the same Mn concentration, the spin-lattice
relaxation dynamics of magnetic Mn ions has been accelerated by an order of
magnitude in (Cd,Mn)Te digital alloys, without any noticeable change in the
giant Zeeman spin splitting of excitonic states, i.e. without effect on the
static magnetization. The strong sensitivity of the magnetization dynamics to
clustering of the Mn ions opens a new degree of freedom for spin engineering.",0601194v1
2002-12-19,Spacetime diffeomorphisms and the geodesic approximation,"We present a spacetime diffeomorphism invariant formulation of the geodesic
approximation to soliton dynamics.",0212249v1
2007-04-27,Dynamics of Quantum Dot Nuclear Spin Polarization Controlled by a Single Electron,"We present an experimental study of the dynamics underlying the buildup and
decay of dynamical nuclear spin polarization in a single semiconductor quantum
dot. Our experiment shows that the nuclei can be polarized on a time scale of a
few milliseconds, while their decay dynamics depends drastically on external
parameters. We show that a single electron can very efficiently depolarize the
nuclear spins and discuss two processes that can cause this depolarization.
Conversely, in the absence of a quantum dot electron, the lifetime of nuclear
spin polarization is on the time scale of a second, most likely limited by the
non-secular terms of the nuclear dipole-dipole interaction. We can further
suppress this depolarization rate by 1-2 orders of magnitude by applying an
external magnetic field exceeding 1 mT.",0704.3684v1
2007-07-16,Importance of bath dynamics for decoherence in spin systems,"We study the decoherence of two coupled spins that interact with a chaotic
spin-bath environment. It is shown that connectivity of spins in the bath is of
crucial importance for the decoherence of the central system. The previously
found phenomenon of two-step decoherence (Phys. Rev. Lett. {\bf 90}, 210401
(2003)) turns out to be typical for the bath with a slow enough dynamics or no
dynamics. For a generic random system with chaotic dynamics a conventional
exponential relaxation to the pointer states takes place. Our results confirm a
conjecture of Paz and Zurek (Phys. Rev. Lett. {\bf 82}, 5181 (1999)) that for
weak enough interactions the pointer states are eigenstates of the central
system.",0707.2372v1
2007-08-15,Density-Profile Processes Describing Biological Signaling Networks: Almost Sure Convergence to Deterministic Trajectories,"We introduce jump processes in R^k, called density-profile process, to model
biological signaling networks. They describe the macroscopic evolution of
finite-size spin-flip models with k types of spins interacting through a
non-reversible Glauber dynamics. We focus on the the k-dimensional
empirical-magnetization vector in the thermodynamic limit, and prove that,
within arbitrary finite time-intervals, its path converges almost surely to a
deterministic trajectory determined by a first-order (non-linear) differential
equation. As parameters of the spin-flip dynamics change, the associated
dynamical system may go through bifurcations, associated to phase transitions
in the statistical mechanical setting. We present a simple example of spin-flip
stochastic model leading to a dynamical system with Hopf and pitchfork
bifurcations; depending on the parameter values, the magnetization random path
can either converge to a unique stable fixed point, converge to one of a pair
of stable fixed points, or asymptotically evolve close to a deterministic orbit
in R^k.",0708.2044v1
2007-09-25,Spin dynamics with non-abelian Berry gauge fields as a semiclassical constrained hamiltonian system,"The dynamics of observables which are matrices depending on \hbar and taking
values in classical phase space is defined retaining the terms up to the first
order in \hbar of the Moyal bracket. Within this semiclassical approach a first
order lagrangian involving gauge fields is studied as a constrained hamiltonian
system. This provides a systematic study of spin dynamics in the presence of
non-abelian Berry gauge fields. We applied the method to various types of
dynamical spin systems and clarified some persisting discussions. In particular
employing the Berry gauge field which generates the Thomas precession, we
calculated the force exerted on an electron in the external electric and
magnetic fields. Moreover, a simple semiclassical formulation of the spin Hall
effect is accomplished.",0709.3908v4
2007-12-17,Dynamics of an Ising Spin Glass on the Bethe Lattice,"We study the dynamical low temperature behaviour of the Ising spin glass on
the Bethe lattice. Starting from Glauber dynamics we propose a cavity like
Ansatz that allows for the treatment of the slow (low temperature) part of
dynamics. Assuming a continuous phase transitions and ultrametricity with
respect to long time scales we approach the problem perturbatively near the
critical temperature. The theory is formulated in terms of
correlation-response-functions of arbitrary order. They can, however, be broken
down completely to products of pair functions depending on two time arguments
only. For binary couplings $J=\pm I$ a spin glass solution is found which
approaches the corresponding solution for the SK-model in the limit of high
connectivity. For more general distributions $P(J)$ no stable or marginal
solution of this type appears to exist. The nature of the low temperature phase
in this more general case is unclear.",0712.2658v1
2008-02-22,From particles to spins: Eulerian formulation of supercooled liquids and glasses,"The dynamics of supercooled liquid and glassy systems are usually studied
within the Lagrangian representation, in which the positions and velocities of
distinguishable interacting particles are followed. Within this representation,
however, it is difficult to define measures of spatial heterogeneities in the
dynamics, as particles move in and out of any one given region within long
enough times. It is also non-transparent how to make connections between the
structural glass and the spin glass problems within the Lagrangian formulation.
We propose an Eulerian formulation of supercooled liquids and glasses that
allows for a simple connection between particle and spin systems, and that
permits the study of dynamical heterogeneities within a fixed frame of
reference similar to the one used for spin glasses. We apply this framework to
the study of the dynamics of colloidal particle suspensions for packing
fractions corresponding to the supercooled and glassy regimes, which are probed
via confocal microscopy.",0802.3297v1
2009-03-16,Non-stationary magnetization dynamics driven by spin transfer torque,"This paper shows that the presence of two dynamical regimes, characterized by
different precessional-axis, is the origin of the non-monotonic behavior of the
output integrated power for large-amplitude magnetization precession driven by
spin-polarized current in nanoscale exchange biased spin-valves. In particular,
at the transition current between those two regimes exists an abruptly loss in
the integrated output power. After the introduction of a time-frequency
analysis of magnetization dynamics based on the wavelet transform, we performed
a numerical experiment by means of micromagnetic simulations. Our results
predicted that, together with a modulation of the frequency of the main excited
mode of the magnetization precession, at high non-linear dynamical regime the
instantaneous output power of the spin-torque oscillator can disappear and then
reappear at nanosecond scale.",0903.2751v1
2010-06-25,Spin and charge dynamics in [TbPc$_2$]$^0$ and [DyPc$_2$]$^0$ single molecule magnets,"Magnetization, AC susceptibility and $\mu$SR measurements have been performed
in neutral phthalocyaninato lanthanide ([LnPc$_2]^0$) single molecule magnets
in order to determine the low-energy levels structure and to compare the
low-frequency spin excitations probed by means of macroscopic techniques, such
as AC susceptibility, with the ones explored by means of techniques of
microscopic character, such as $\mu$SR. Both techniques show a high temperature
thermally activated regime for the spin dynamics and a low temperature
tunneling one. While in the activated regime the correlation times for the spin
fluctuations estimated by AC susceptibility and $\mu$SR basically agree, clear
discrepancies are found in the tunneling regime. In particular, $\mu$SR probes
a faster dynamics with respect to AC susceptibility. It is argued that the
tunneling dynamics probed by $\mu$SR involves fluctuations which do not yield a
net change in the macroscopic magnetization probed by AC susceptibiliy. Finally
resistivity measurements in [TbPc$_2]^0$ crystals show a high temperature
nearly metallic behaviour and a low temperature activated behaviour.",1006.4919v1
2010-09-06,Spin Dynamics of a $J_1-J_2$ Antiferromagnet and its Implications for Iron Pnictides,"Motivated by the recent observation of antiferromagnetic correlations in the
paramagnetic phase of iron pnictides, we study the finite-temperature spin
dynamics of a two-dimensional $J_1-J_2$ antiferromagnet. We consider the
paramagnetic phase in the $J_2>J_1$ regime of a $(\pi,0)$ collinear ground
state, using the modified spin wave theory. Below the mean-field Ising
transition temperature, we identify short-range anisotropic antiferromagnetic
correlations. We show that the dynamical structure factor
$\mathcal{S}(\mathbf{q},\omega)$ contains elliptic features in the momentum
space, and determine its variation with temperature and energy. Implications
for the spin-dynamical experiments in the iron pnictides are discussed.",1009.1111v3
2010-11-25,Controllable coupling and quantum correlation dynamics of two double quantum dots coupled via a transmission line resonator,"We propose a theoretical scheme to generate a controllable and switchable
coupling between two double-quantum-dot (DQD) spin qubits by using a
transmission line resonator (TLR) as a bus system. We study dynamical behaviors
of quantum correlations described by entanglement correlation (EC) and discord
correlation (DC) between two DQD spin qubits when the two spin qubits and the
TLR are initially prepared in $X$-type quantum states and a coherent state,
respectively. We demonstrate that in the EC death regions there exist DC
stationary states in which the stable DC amplification or degradation can be
generated during the dynamical evolution. It is shown that these DC stationary
states can be controlled by initial-state parameters, the coupling, and
detuning between qubits and the TLR. We reveal the full synchronization and
anti-synchronization phenomena in the EC and DC time evolution, and show that
the EC and DC synchronization and anti-synchronization depends on the
initial-state parameters of the two DQD spin qubits. These results shed new
light on dynamics of quantum correlations.",1011.5621v1
2012-02-06,Spin Dynamics at Very Low Temperature in Spin Ice Dy$_2$Ti$_2$O$_7$,"We have performed AC susceptibility and DC magnetic relaxation measurements
on the spin ice system Dy$_2$Ti$_2$O$_7$ down to 0.08 K. The relaxation time of
the magnetization has been estimated below 2 K down to 0.08 K. The spin
dynamics of Dy$_2$Ti$_2$O$_7$ is well described by using two relaxation times
($\tau_{\rm S}$ (short time) and $\tau_{\rm L}$ (long time)). Both $\tau_{\rm
S}$ and $\tau_{\rm L}$ increase on cooling. Assuming the Arrhenius law in the
temperature range 0.5-1 K, we obtained an energy barrier of 9 K. Below 0.5 K,
both $\tau_{\rm S}$ and $\tau_{\rm L}$ show a clear deviation from the thermal
activated dynamics toward temperature independent relaxation, suggesting a
quantum dynamics.",1202.1107v1
2012-08-31,Dynamics and hysteresis in square lattice artificial spin-ice,"Dynamical effects under geometrical frustration are considered in a model for
artificial spin ice on a square lattice in two dimensions. Each island of the
spin ice has a three-component Heisenberg-like dipole moment subject to shape
anisotropies that influence its direction. The model has real dynamics,
including rotation of the magnetic degrees of freedom, going beyond the
Ising-type models of spin ice. The dynamics is studied using a Langevin
equation solved via a second order Heun algorithm. Thermodynamic properties
such as the specific heat are presented for different couplings. A peak in
specific heat is related to a type of melting-like phase transition present in
the model. Hysteresis in an applied magnetic field is calculated for model
parameters where the system is able to reach thermodynamic equilibrium.",1208.6557v2
2013-11-28,Conservative effects in spin-transfer-driven magnetization dynamics,"It is shown that under appropriate conditions spin-transfer-driven
magnetization dynamics in a single-domain nanomagnet is conservative in nature
and admits a specific integral of motion, which is reduced to the usual
magnetic energy when the spin current goes to zero. The existence of this
conservation law is connected to the symmetry properties of the dynamics under
simultaneous inversion of magnetisation and time. When one applies an external
magnetic field parallel to the spin polarization, the dynamics is transformed
from conservative into dissipative. More precisely, it is demonstrated that
there exists a state function such that the field induces a monotone relaxation
of this function toward its minima or maxima, depending on the field
orientation. These results hold in the absence of intrinsic damping effects.
When intrinsic damping is included in the description, a competition arises
between field-induced and damping-induced relaxations, which leads to the
appearance of limit cycles, that is, of magnetization self-oscillations.",1311.7344v1
2015-04-29,The connection between statics and dynamics of spin glasses,"We present results of numerical simulations on a one-dimensional Ising spin
glass with long-range interactions. Parameters of the model are chosen such
that it is a proxy for a short-range spin glass above the upper critical
dimension (i.e. in the mean-field regime). The system is quenched to a
temperature well below the transition temperature $T_c$ and the growth of
correlations is observed. The spatial decay of the correlations at distances
less than the dynamic correlation length $\xi(t)$ agrees quantitatively with
the predictions of a static theory, the ""metastate"", evaluated according to the
replica symmetry breaking (RSB) theory. We also compute the dynamic exponent
$z(T)$ defined by $\xi(t) \propto t^{1/z(T)}$ and find that it is compatible
with the mean-field value of the critical dynamical exponent for short range
spin glasses.",1504.07709v2
2015-08-19,Chiral Magnetic Effect and Anomalous Hall Effect in Antiferromagnetic Insulators with Spin-Orbit Coupling,"We search for dynamical magnetoelectric phenomena in three-dimensional
correlated systems with spin-orbit coupling. We focus on the antiferromagnetic
insulator phases where the dynamical axion field is realized by the fluctuation
of the antiferromagnetic order parameter. It is shown that the dynamical chiral
magnetic effect, an alternating current generation by magnetic fields, emerges
due to the time dependences of the order parameter such as antiferromagnetic
resonance. It is also shown that the anomalous Hall effect arises due to the
spatial variations of the order parameter such as antiferromagnetic domain
walls. Our study indicates that spin excitations in antiferromagnetic
insulators with spin-orbit coupling can result in nontrivial charge responses.
Moreover, observing the chiral magnetic effect and anomalous Hall effect in our
system is equivalent to detecting the dynamical axion field in condensed
matter.",1508.04590v2
2016-03-25,The influence of the structural transition on magnetic fluctuations in NaFeAs,"NaFeAs belongs to a class of Fe-based superconductors which parent compounds
show separated structural and magnetic transitions. Effects of the structural
transition on spin dynamics therefore can be investigated separately from the
magnetic transition. A plateau in dynamic spin response is observed in a
critical region around the structural transition temperature T_S. It is
interpreted as due to the stiffening of spin fluctuations along the in-plane
magnetic hard axis due to the dxz and dyz orbital ordering. The appearance of
anisotropic spin dynamics in the critical region above the T_S at T* offers a
dynamic magnetic scattering mechanism for anisotropic electronic properties in
the commonly referred ""nematic phase"".",1603.07873v2
2016-10-03,Quench dynamics of spin-imbalanced Fermi-Hubbard model in one dimension,"We study a nonequilibrium dynamics of a one-dimensional spin-imbalanced
Fermi-Hubbard model following a quantum quench of on-site interaction,
realizable, for example, in Feshbach-resonant atomic Fermi gases. We focus on
the post-quench evolution starting from the initial BCS and
FuldeFerrell-Larkin-Ovchinnikov (FFLO) ground states and analyze the
corresponding spin-singlet, spin-triplet, density-density, and
magnetization-magnetization correlation functions. We find that beyond a
light-cone crossover time, rich post-quench dynamics leads to thermalized and
pre-thermalized stationary states that display strong dependence on the initial
ground state. For initially gapped BCS state, the long-time stationary state
resembles thermalization with the effective temperature set by the initial
value of the Hubbard interaction. In contrast, while the initial gapless FFLO
state reaches a stationary pre-thermalized form, it remains far from
equilibrium. We suggest that such post-quench dynamics can be used as a
fingerprint for identification and study of the FFLO phase.",1610.00670v2
2017-08-01,Manifestations of dynamical localization in the disordered XXZ spin chain,"We study disordered XXZ spin chains in the Ising phase exhibiting droplet
localization, a single cluster localization property we previously proved for
random XXZ spin chains. It holds in an energy interval $I$ near the bottom of
the spectrum, known as the droplet spectrum. We establish dynamical
manifestations of localization in the energy window $I$, including
non-spreading of information, zero-velocity Lieb-Robinson bounds, and general
dynamical clustering. Our results do not rely on knowledge of the dynamical
characteristics of the model outside the droplet spectrum. A byproduct of our
analysis is that for random XXZ spin chains this droplet localization can
happen only inside the droplet spectrum.",1708.00474v1
2018-04-06,Floquet prethermalization in periodically driven classical spin systems,"It is proved that the energy absorption in a periodically driven classical
spin system is exponentially slow in frequency, which results in a two-step
relaxation called the Floquet prethermalization. This result is shown by
establishing the classical limit of the quantum spin dynamics. The Floquet
prethermal state is well described by the Gibbs ensemble with respect to the
static effective Hamiltonian obtained by a truncation of the Floquet-Magnus
expansion. On the other hand, the same effective Hamiltonian does not reproduce
the local dynamics for an exponentially long time. This is due to the
chaoticity of classical dynamics, and in stark contrast to quantum spin
systems, in which the effective Hamiltonian well reproduces the exact quantum
dynamics up to an exponentially long time.",1804.02165v3
2020-07-03,Dynamic spin-triplet order induced by alternating electric fields in superconductor-ferromagnet-superconductor Josephson junctions,"Dynamic states offer extended possibilities to control the properties of
quantum matter. Recent efforts are focused on studying the ordered states which
appear exclusively under the time-dependent drives. Here we demonstrate a class
of systems which feature dynamic spin-triplet superconducting order stimulated
by the alternating electric field. The effect is based on the interplay of
ferromagnetism, interfacial spin-orbital coupling (SOC) and the condensate
motion driven by the field, which converts hidden static p-wave order, produced
by the joint action of the ferromagnetism and the SOC, into dynamical s-wave
equal-spin triplet correlations. We demonstrate that the critical current of
Josephson junctions hosting these states is proportional to the electromagnetic
power, supplied either by the external irradiation or by the ac current source.
Based on these unusual properties we propose the scheme of a Josephson
transistor which can be switched by the ac voltage and demonstrates an
even-numbered sequence of Shapiro steps. Combining the photo-active Josephson
junctions with recently discovered Josephson phase batteries we find
photo-magnetic SQUID devices which can generate spontaneous magnetic fields
while being exposed to irradiation.",2007.01805v2
2016-11-27,Different growth rates for spin and superfluid order in a quenched spinor condensate,"In this paper we study the coarsening dynamics of a spinor condensate
quenched into an easy-axis ferromagnetic phase by a sudden change in the
quadratic Zeeman energy. We show that applying a spin rotation prior to
changing the Zeeman energy accelerates the development of local order and
reduces heating. We examine the longitudinal spin ordering and the superfluid
ordering of the system and show that the respective order parameter correlation
functions exhibit dynamic scaling in the late time dynamics. Our results also
demonstrate that these two types of order grow at different rates, i.e.~with
different dynamic critical exponents. The spin domain area distribution is
calculated and is shown to have power law scaling behavior expected from
percolation theory.",1611.08922v1
2017-04-13,From Coarse-Graining to Holography in Loop Quantum Gravity,"We discuss the relation between coarse-graining and the holographic principle
in the framework of loop quantum gravity and ask the following question: when
we coarse-grain arbitrary spin network states of quantum geometry, are we
integrating out physical degrees of freedom or gauge degrees of freedom?
Focusing on how bulk spin network states for bounded regions of space are
projected onto boundary states, we show that all possible boundary states can
be recovered from bulk spin networks with a single vertex in the bulk and a
single internal loop attached to it. This partial reconstruction of the bulk
from the boundary leads us to the idea of realizing the Hamiltonian constraints
at the quantum level as a gauge equivalence reducing arbitrary spin network
states to one-loop bulk states. This proposal of ""dynamics through
coarse-graining"" would lead to a one-to-one map between equivalence classes of
physical states under gauge transformations and boundary states, thus defining
holographic dynamics for loop quantum gravity.",1704.04067v2
2012-01-17,Electron Dynamics in Slowly Varying Antiferromagnetic Texture,"Effective dynamics of conduction electrons in antiferromagnetic (AFM)
materials with slowly varying spin texture is developed via non-Abelian gauge
theory. Quite different from the ferromagnetic (FM) case, the spin of a
conduction electron does not follow the background texture even in the
adiabatic limit due to the accumulation of a SU(2) non-Abelian Berry phase.
Correspondingly, it is found that the orbital dynamics becomes spin-dependent
and is affected by two emergent gauge fields. While one of them is the
non-Abelian generalization of what has been discovered in FM systems, the other
leads to an anomalous velocity that has no FM counterpart. Two examples are
provided to illustrate the distinctive spin dynamics of a conduction electron.",1201.3523v4
2012-04-19,Nahm equations in supersymmetric mechanics,"We elaborate on a novel model of N=4 supersymmetric mechanics with extra spin
variables. A dynamical linear (1,4,3) multiplet is coupled to a
""semi-dynamical"" linear (3,4,1) multiplet representing spin degrees of freedom
in a Wess-Zumino action. The unique coupling of these two multiplets relates
the dynamical bosonic variable to an arbitrary harmonic function of the SU(2)
triplet of spin variables. As we prove at the classical and quantum level, N=4
supersymmetry is equivalent to the Nahm equations for the spin variables, with
the dynamical boson as evolution parameter. We treat in detail the one- and
two-monopole as well as some special multi-monopole configurations. While one
monopole exhibits superconformal OSp(4|2) symmetry and was worked out
previously, only N=4, d=1 Poincare supersymmetry survives for multi-monopole
configurations.",1204.4474v1
2014-05-01,Analytical approach to the dynamics of facilitated spin models on random networks,"Facilitated spin models were introduced some decades ago to mimic systems
characterized by a glass transition. Recent developments have shown that a
class of facilitated spin models is also able to reproduce characteristic
signatures of the structural relaxation properties of glass-forming liquids.
While the equilibrium phase diagram of these models can be calculated
analytically, the dynamics are usually investigated numerically. Here we
propose a new network-based approach, called approximate master equation (AME),
to the dynamics of the Fredrickson-Andersen model. The approach correctly
predicts the critical temperature at which the glass transition occurs. We also
find excellent agreement between the theory and the numerical simulations for
the transient regime, except in close proximity of the liquid-glass transition.
Finally, we analytically characterize the critical clusters of the model and
show that the departures between our AME approach and the Monte Carlo can be
related to the large interface between frozen and unfrozen spins at
temperatures close to the glass transition.",1405.0195v2
2014-05-09,Low-temperature dynamics of Long-Ranged Spin-Glasses : full hierarchy of relaxation times via real-space renormalization,"We consider the long-ranged Ising spin-glass with random couplings decaying
as a power-law of the distance, in the region of parameters where the
spin-glass phase exists with a positive droplet exponent. For the Metropolis
single-spin-flip dynamics near zero temperature, we construct via real-space
renormalization the full hierarchy of relaxation times of the master equation
for any given realization of the random couplings. We then analyze the
probability distribution of dynamical barriers as a function of the spatial
scale. This real-space renormalization procedure represents a simple explicit
example of the droplet scaling theory, where the convergence towards local
equilibrium on larger and larger scales is governed by a strong hierarchy of
activated dynamical processes, with valleys within valleys.",1405.2179v2
2014-05-25,Spin Hall phenomenology of magnetic dynamics,"We study the role of spin-orbit interactions in the coupled magnetoelectric
dynamics of a ferromagnetic film coated with an electrical conductor. While the
main thrust of this work is phenomenological, several popular simple models are
considered microscopically in some detail, including Rashba and Dirac
two-dimensional electron gases coupled to a magnetic insulator, as well as a
diffusive spin Hall system. We focus on the long-wavelength magnetic dynamics
that experiences current-induced torques and produces fictitious electromotive
forces. Our phenomenology provides a suitable framework for analyzing
experiments on current-induced magnetic dynamics and reciprocal charge pumping,
including the effects of magnetoresistance and Gilbert-damping anisotropies,
without a need to resort to any microscopic considerations or modeling.
Finally, some remarks are made regarding the interplay of spin-orbit
interactions and magnetic textures.",1405.6354v2
2016-12-17,The effect of Chern-Simons dynamics on the energy of electrically charged and spinning vortices,"We study the effect of a Chern-Simons term on the electrically charged and
spinning solitons of several $U(1)$ gauged models in $2+1$ dimensions. These
are vortices of complex scalar field theories, both with and without symmetry
breaking dynamics, and the $O(3)$ Skyrme model. In all cases the gauge
decoupling limits are also considered. It is well known that the effect of the
Chern-Simons dynamics is to endow vortices with electric charge $Q_e$ and spin
$J$, but our main aim here is to reveal a new feature: that the mass-energy $E$
of the electrically charged vortex can be lower than that of the electrically
neutral one, in contrast to the usual monotonic increase of $E$ with $Q_e$.
These effects of Chern-Simons dynamics were observed previously in $3+1$
dimensional systems, and the present results can be viewed as corroborating the
latter. Moreover, the usual energy-spin relationship is likewise altered. We
carry out a detailed quantitative analysis of azimuthally symmetric vortices
and describe their qualitative features by constructing the solutions
numerically.",1612.05835v2
2017-06-18,Neutron star dynamics under time dependent external torques,"The two component model describes neutron star dynamics incorporating the
response of the superfluid interior. Conventional solutions and applications
involve constant external torques, as appropriate for radio pulsars on
dynamical timescales. We present the general solution of two component dynamics
under arbitrary time dependent external torques, with internal torques that are
linear in the rotation rates, or with the extremely non-linear internal torques
due to vortex creep. The two-component model incorporating the response of
linear or nonlinear internal torques can now be applied not only to radio
pulsars but also to magnetars and to neutron stars in binary systems, with
strong observed variability and noise in the spin-down or spin-up rates. Our
results allow the extraction of the time dependent external torques from the
observed spin-down (or spin-up) time series, $\dot{\Omega}(t)$. Applications
are discussed.",1706.05662v2
2017-06-21,Uniform magnetization dynamics of a submicron ferromagnetic coin driven by the spin-orbit coupled spin torque,"A simple model of magnetization dynamics in a ferromagnet/doped semiconductor
hybrid structure with Rashba spin-orbit interaction (SOI) driven by an applied
pulse of the electric field is proposed. The electric current excited by the
applied field is spin-polarized due to the SOI and therefore it induces the
magnetization rotation in the ferromagnetic layer via s-d exchange coupling.
Magnetization dynamics dependence on the electric pulse shape and magnitude is
analyzed for realistic values of parameters. We show that it is similar to the
dynamics of a damped nonlinear oscillator with the time-dependent frequency
proportional to the square root of the applied electric field. The
magnetization switching properties of an elliptic magnetic element are examined
as a function of the applied field magnitude and direction.",1706.06909v1
2017-07-31,Orbital-selective thermalization plateau in the mass imbalanced Hubbard model,"We use time-dependent non-equilibrium dynamical mean-field theory with
weak-coupling auxiliary-field continuous time quantum Monte Carlo as an
impurity solver to study the thermalization behavior of the mass-imbalanced
single-band Hubbard model after a quench of the Coulomb interaction from the
non-interacting limit to a finite positive value. By contrast, when the Coulomb
interaction in our model is increased under equilibrium conditions, the
quasi-particle weight for spin-up and spin-down (the mass imbalance) electrons
approach zero simultaneously, indicating the absence of an orbital selective
Mott transition. Our out-of-equilibrium study suggests that there exists a time
window where an orbital selective dynamical phase transition occurs. The
dynamical phase transition is characterized by the relaxation behavior of
energy (kinetic and Coulomb interaction) and the spin-resolved
momentum-dependent occupation. To make connection with possible experiments, we
calculate the spin-resolved two-time optical conductivity, which confirms the
orbital-selective thermalization plateau. We find the time window for the
orbital selective dynamical phase transition grows as the mass imbalance
increases.",1707.09692v2
2017-12-01,Relativistic Dynamics of Point Magnetic Moment,"The covariant motion of a classical point particle with magnetic moment in
the presence of (external) electromagnetic fields is revisited. We are
interested in understanding Lorentz force extension involving point particle
magnetic moment (Stern-Gerlach force) and how the spin precession dynamics is
modified for consistency. We introduce spin as a classical particle property
inherent to Poincare\'e symmetry of space-time. We propose a covariant
formulation of the magnetic force based on a \lq magnetic\rq\ 4-potential and
show how the point particle magnetic moment relates to the Amperian (current
loop) and Gilbertian (magnetic monopole) description. We show that covariant
spin precession lacks a unique form and discuss connection to $g-2$ anomaly. We
consider variational action principle and find that a consistent extension of
Lorentz force to include magnetic spin force is not straightforward. We look at
non-covariant particle dynamics, and present a short introduction to dynamics
of (neutral) particles hit by a laser pulse of arbitrary shape.",1712.01825v1
2018-10-22,Dynamical structure factor of the three-dimensional quantum spin liquid candidate NaCaNi$_2$F$_7$,"We study the spin-1 pyrochlore material NaCaNi$_2$F$_7$ with a combination of
molecular dynamics simulations, stochastic dynamical theory and linear spin
wave theory. The dynamical structure factor from inelastic neutron scattering
is well described with a near-ideal Heisenberg Hamiltonian incorporating small
anisotropic terms {and weak second-neighbor interactions}. We find that all
three approaches reproduce remarkably well the momentum dependence of the
scattering intensity as well as its energy dependence with the exception of the
lowest energies. These results are notable in that (i) the data show a complete
lack of sharp quasiparticle excitations in momentum space over much, if not
all, of the energy range; (ii) linear spin-wave theory appears to apply in a
regime where it would be expected to fail for a number of reasons. We elucidate
what underpins these surprises, and note that basic questions about the nature
of quantum spin liquidity in such systems pose themselves as a result.",1810.09481v1
2018-10-26,Phonon impact on the dynamics of resonantly excited and hot excitons in diluted magnetic semiconductors,"Phonons are well known to be the main mechanism for the coupling between
bright and dark excitons in nonmagnetic semiconductors. Here, we investigate
diluted magnetic semiconductors where this process is in direct competition
with the scattering at localized magnetic impurities. To this end, a recently
developed quantum kinetic description of the exciton spin dynamics in diluted
magnetic semiconductor quantum wells is extended by the scattering with
longitudinal acoustic phonons. A strong phonon impact is found in the
redistribution of exciton momenta on the exciton parabola that becomes
especially prominent for high temperatures and exciton distributions further
away from the exciton resonance which are optically dark. Despite their impact
on the energetic redistribution, acoustic phonons virtually do not affected the
exciton spin dynamics as the exciton-impurity interaction always dominates.
Furthermore, it turns out that the exciton spin lifetime increases by roughly
one order of magnitude for nonequilibrium hot exciton distributions and, in
addition, pronounced quantum kinetic signatures in the exciton spin dynamics
appearing after resonant optical excitation are drastically reduced.",1810.11241v2
2019-06-28,Dynamical $t/U$ Expansion of the Doped Hubbard Model,"We construct a new $U(1)$ slave spin representation for the single band
Hubbard model in the large-$U$ limit. The mean-field theory in this
representation is more amenable to describe both the spin-charge-separation
physics of the Mott insulator at half-filling and the strange metal behavior at
finite doping. By employing a dynamical Green's function theory for slave
spins, we calculate the single-particle spectral function of electrons, and the
result is comparable to that in dynamical mean field theories. We then
formulate a dynamical $t/U$ expansion for the doped Hubbard model that
reproduces the mean-field results at the lowest order of expansion. To the next
order of expansion, it naturally yields an effective low-energy theory of a
$t-J$ model for spinons self-consistently coupled to n $XXZ$ model for the
slave spins. We show that the superexchange $J$ is renormalized by doping, in
agreement with the Gutzwiller approximation. Surprisingly, we find a new
ferromagnetic channel of exchange interactions which survives in the infinite
$U$ limit, as a manifestation of the Nagaoka ferromagnetism.",1906.12071v2
2018-03-16,Dynamically enhanced magnetic incommensurability: Effects of local dynamics on non-local spin-correlations in a strongly correlated metal,"We compute the spin susceptibility of the two-dimensional Hubbard model away
from half-filling, and analyze the impact of frequency dependent vertex
corrections as obtained from the dynamical mean field theory (DMFT). We find
that the local dynamics captured by the DMFT vertex strongly affects non-local
spin correlations, and thus the momentum dependence of the spin susceptibility.
While the widely used random phase approximation yields commensurate
N\'eel-type antiferromagnetism as the dominant instability over a wide doping
range, the vertex corrections favor incommensurate ordering wave vectors away
from $(\pi,\pi)$. Our results indicate that the connection between the magnetic
ordering wave vector and the Fermi surface geometry, familiar for weakly
interacting systems, can hold in a strongly correlated metal, too.",1803.06175v1
2019-03-16,Critical phenomena and nonlinear dynamics in a spin ensemble strongly coupled to a cavity. I. Semiclassical approach,"We present a theoretical study on the nonlinear dynamics and stationary
states of an inhomogeneously broadened spin ensemble coupled to a single-mode
cavity driven by an external drive with constant amplitude. Assuming a sizeable
number of constituents within the ensemble allows us to use a semiclassical
approach and to formally reduce the theoretical description to the
Maxwell-Bloch equations for the cavity and spin amplitudes. We explore the
critical slowing-down effect, quench dynamics, and asymptotic behavior of the
system near a steady-state dissipative phase transition accompanied by a
bistability effect. Some of our theoretical findings have recently been
successfully verified in a specific experimental realization based on a spin
ensemble of negatively charged nitrogen-vacancy centers in diamond strongly
coupled to a single-mode microwave cavity (see Science Adv. 3, e1701626
(2017)).",1903.06892v2
2019-04-17,Spin-mapping approach for nonadiabatic molecular dynamics,"We propose a trajectory-based method for simulating nonadiabatic dynamics in
molecular systems with two coupled electronic states. Employing a
quantum-mechanically exact mapping of the two-level problem to a spin-1/2
coherent state, we construct a classical phase space of a spin vector
constrained to a spherical surface with a radius consistent with the quantum
magnitude of the spin. In contrast with the singly-excited harmonic oscillator
basis used in Meyer-Miller-Stock-Thoss (MMST) mapping, the theory requires no
additional projection operators onto the space of physical states. When treated
under a quasiclassical approximation, we show that the resulting dynamics is
equivalent to that generated by the MMST Hamiltonian. What differs is the value
of the zero-point energy parameter as well as the initial distribution and the
measurement operators. For various spin-boson models the results of our method
are seen to be a significant improvement compared to both standard Ehrenfest
dynamics and linearized semiclassical MMST mapping, without adding any
computational complexity.",1904.08293v1
2020-05-27,Spin-valley dynamics in alloy-based transition metal dichalcogenide heterobilayers,"Van der Waals heterobilayers based on 2D transition metal dichalcogenides
have been recently shown to support robust and long-lived valley polarization
for potential valleytronic applications. However, the role of the band
structure and alignment of the constituent layers in the underlying dynamics
remains largely unexplored. Here we study spin--valley relaxation dynamics in
heterobilayers with different band structures engineered via the use of alloyed
monolayer semiconductors. Through a combination of time-resolved Kerr rotation
spectroscopic measurements and theoretical modelling for
Mo$_{1-x}$W$_{x}$Se$_2$/WSe$_2$ samples with different chemical compositions
and stacking angles, we uncover the roles of interlayer exciton recombination
and charge carrier spin depolarization in the overall valley dynamics. Our
results provide insights into the microscopic spin--valley polarization
mechanisms in van der Waals heterostructures for the development of future 2D
valleytronic devices.",2005.13306v2
2020-06-23,Magnetization dynamics in synthetic antiferromagnets: Role of dynamical energy and mutual spin pumping,"We investigate magnetization dynamics in asymmetric interlayer exchange
coupled Py/Ru/Py trilayers using both vector network analyzer-based and
electrically detected ferromagnetic resonance techniques. Two different
ferromagnetic resonance modes, in-phase and out-of-phase, are observed across
all three regimes of the static magnetization configurations, through
antiparallel alignment at low fields, the spin-flop transition at intermediate
fields, and parallel alignment at high fields. The nonmonotonic behavior of the
modes as a function of the external field is explained in detail by analyzing
the interlayer exchange and Zeeman energies and is found to be solely governed
by the interplay of their dynamical components. In addition, the linewidths of
both modes were determined across the three regimes and the different behaviors
of the linewidths versus external magnetic field are attributed to mutual spin
pumping induced in the samples. Interestingly, the difference between the
linewidths of the out-of-phase and in-phase modes decreases at the spin-flop
transition and is reversed between the antiparallel and parallel aligned
magnetization states.",2006.13031v1
2021-04-19,Chaotic Antiferromagnetic Nano-Oscillator driven by Spin-Torque,"We theoretically describe the behavior of a terahertz nano-oscillator based
on an anisotropic antiferromagnetic dynamical element driven by spin torque. We
consider the situation when the polarization of the spin-current is
perpendicular to the external magnetic field applied along the anisotropy
easy-axis. We determine the domain of the parametric space (field, current)
where the oscillator demonstrates chaotic dynamics. Characteristics of the
chaotic regimes are analyzed using conventional techniques such as spectra of
the Lyapunov exponents. We show that the threshold current of the chaos
appearance is particularly low in the vicinity of the spin-flop transition. In
this regime, we consider the mechanism of the chaos appearance in detail when
the field is fixed and the current density increases. We show that the
appearance of chaos is preceded by a regime of quasiperiodic dynamics on the
surface of a two-frequency torus arising in phase space as a result of the
Neimark-Sacker bifurcation.",2104.09195v1
2021-08-05,Spin-valley relaxation dynamics of Landau-quantized electrons in MoSe$_2$ monolayer,"Non-equilibrium dynamics of strongly correlated systems constitutes a
fascinating problem of condensed matter physics with many open questions. Here
we investigate the relaxation dynamics of Landau-quantized electron system into
spin-valley polarized ground state in a gate-tunable MoSe$_2$ monolayer
subjected to a strong magnetic field. The system is driven out of equilibrium
with optically injected excitons that depolarize the electron spins and the
subsequent electron spin-valley relaxation is probed in time-resolved
experiments. We demonstrate that the relaxation rate at millikelvin
temperatures sensitively depends on the Landau level filling factor: it becomes
faster whenever the electrons form an integer quantum Hall liquid and slows
down appreciably at non-integer fillings. Our findings evidence that valley
relaxation dynamics may be used as a tool to investigate the interplay between
the effects of disorder and strong interactions in the electronic ground state.",2108.02767v1
2021-08-13,Optical signatures of the coupled spin-mechanics of a levitated magnetic microparticle,"We propose a platform that combines the fields of cavity optomagnonics and
levitated optomechanics in order to control and probe the coupled
spin-mechanics of magnetic dielectric particles. We theoretically study the
dynamics of a levitated Faraday-active dielectric microsphere serving as an
optomagnonic cavity, placed in an external magnetic field and driven by an
external laser. We find that the optically driven magnetization dynamics
induces angular oscillations of the particle with low associated damping.
Further, we show that the magnetization and angular motion dynamics can be
probed via the power spectrum of the outgoing light. Namely, the characteristic
frequencies attributed to the angular oscillations and the spin dynamics are
imprinted in the light spectrum by two main resonance peaks. Additionally, we
demonstrate that a ferromagnetic resonance setup with an oscillatory
perpendicular magnetic field can enhance the resonance peak corresponding to
the spin oscillations and induce fast rotations of the particle around its
anisotropy axis.",2108.06214v1
2021-11-29,Element selective ultrafast magnetization dynamics of hybrid Stoner-Heisenberg magnets,"Stoner and Heisenberg excitations in magnetic materials are inherently
different. The former involves an effective reduction of the exchange
splitting, whereas the latter comprises excitation of spin-waves. In this work,
we test the impact of these two excitations in the hybrid Stoner-Heisenberg
system FePd. We present a microscopic picture of ultrafast demagnetization
dynamics in this alloy, which represents both components of strong local
exchange splitting in Fe, and induced polarization in Pd. We identify
spin-orbit coupling and optical inter-site spin transfer as the two dominant
factors for demagnetization at ultrashort timescales. By tuning the external
laser pulse, the extrinsic inter-site spin transfer can be manipulated for site
selective demagnetization on femtosecond time scales providing the fastest way
for optical and selective control of the magnetization dynamics in alloys.
Remarkably, the drastic difference in origin of the magnetic moment of the Fe
and Pd species is not deciding the initial magnetization dynamics in this
alloy.",2111.14607v1
2021-12-15,Mixed states driven by Non-Hermitian Hamiltonians of a nuclear spin ensemble,"We study the quantum dynamics of a non-interacting spin ensemble under the
effect of a reservoir by applying the framework of the non-Hermitian
Hamiltonian operators. Theoretically, the two-level model describes the quantum
spin system and the Bloch vector to establish the dynamical evolution.
Experimentally, phosphorous ($^{31}$P) nuclei with spin $I=1/2$ are used to
represent the two-level system and the magnetization evolution is measured and
used to compare with the theoretical prediction. At room temperature, the
composite dynamics of the radio-frequency pulse plus field inhomogeneities (or
unknown longitudinal fluctuations) along the $z$-axis transform the initial
quantum state and drives it into a mixed state at the end of the dynamics. The
experimental setup shows a higher accuracy when compared with the theoretical
prediction (>98\%), ensuring the relevance and effectiveness of the
non-Hermitian theory at a high-temperature regime.",2112.08169v1
2022-02-10,Dynamical quantum phase transition in diamond: applications in quantum metrology,"Nonequilibrium dynamics is a paramount scenario for studying quantum systems.
The emergence of new features with no equilibrium counterpart, such as
dynamical quantum phase transition (DQPT), has attracted wide attention. In
this work, we depart from the well known Ising model and showcase an
experimentally accessible configuration of a negatively charged
Nitrogen-Vacancy center that interacts with nearby Carbon-13 nuclear spins. We
provide new insights into this system in the context of DQPT. We show that
nuclear spins undergo DQPT by appropriately choosing the relation between the
transverse and longitudinal components of an external magnetic field.
Furthermore, we can steer the DQPT via a time-dependent longitudinal magnetic
field and apply this control to enhance the estimation of the coupling strength
between the nuclear spins. Moreover, we propose a novel quenched dynamics that
originates from the rotation of the central electron spin, which controls the
DQPT relying on the anisotropy of the hyperfine coupling.",2202.05216v1
2022-04-11,Accelerating the approach of dissipative quantum spin systems towards stationarity through global spin rotations,"We consider open quantum systems whose dynamics is governed by a
time-independent Markovian Lindblad Master equation. Such systems approach
their stationary state on a timescale that is determined by the spectral gap of
the generator of the Master equation dynamics. In the recent paper [Carollo et
al., Phys. Rev. Lett. 127, 060401 (2021)] it was shown that under certain
circumstances it is possible to exponentially accelerate the approach to
stationarity by performing a unitary transformation of the initial state. This
phenomenon can be regarded as the quantum version of the so-called Mpemba
effect. The transformation of the initial state removes its overlap with the
dynamical mode of the open system dynamics that possesses the slowest decay
rate and thus determines the spectral gap. While this transformation can be
exactly constructed in some cases, it is in practice challenging to implement.
Here we show that even far simpler transformations constructed by a global
unitary spin rotation allow to exponentially speed up relaxation. We
demonstrate this using simple dissipative quantum spin systems, which are
relevant for current quantum simulation and computation platforms based on
trapped atoms and ions.",2204.05339v1
2022-04-02,Understanding the Spin Crossover Dynamical Effects of the Dioxygen Binding and Activation on HOD enzyme,"For the cofactor-free 1-H-3-hydroxy-4-oxoquinaldine-2,4-dioxygenase (HOD),
the dioxygen (O2) dependent steps are rate-limiting along with a spin state
crossover to the singlet spin state. Here, the primary triplet O2 molecule
activation on the 2-methyl-3-hydroxy-4(1H)-quinolone (MHQ) is investigated, and
the catalytic role of the intersystem crossing effects is highlighted by
directly comparing results from the Born-Oppenheimer dynamics and non-adiabatic
surface hopping dynamics. This work confirms non-adiabatic dynamical effects
are essential to modulate the O2 activation on the substrate MHQ. The time
scale of the equilibration and conversion from triplet to singlet state should
be in the range of a few hundreds of femtoseconds. We hope this work provides
us a fresh look at the underlying physics of dioxygen activation reactions
involving more than one spin state.",2204.06524v1
2022-09-02,tqix.pis: A toolbox for quantum dynamics simulation of spin ensembles in Dicke basis,"We introduce tqix.pis, a library of tqix, for quantum dynamics simulation of
spin ensembles. The library emulates a dynamic process by a quantum circuit,
including initializing a quantum state, executing quantum operators, and
measuring the final state. It utilizes collective processes in spin ensembles
to reduce the dimension from exponentially to quadratically with the number of
particles, i.e., the quantum state spans in Dicke basis. It also facilitates
the simulation time with multi-core processors and Graphics Processing Units.
The library is thus applicable for the simulation of ensembles of large number
of particles that have collective properties. Various phenomena, such as spin
squeezing, variational quantum squeezing, quantum phase transition, and
many-body quantum dynamics, can be simulated using the library.",2209.01168v2
2022-10-18,Dynamics of Stripe Patterns in Supersolid Spin-Orbit-Coupled Bose Gases,"Despite ground-breaking observations of supersolidity in spin-orbit-coupled
Bose-Einstein condensates, until now the dynamics of the emerging spatially
periodic density modulations has been vastly unexplored. Here, we demonstrate
the nonrigidity of the density stripes in such a supersolid condensate and
explore their dynamic behavior subject to spin perturbations. We show both
analytically in infinite systems and numerically in the presence of a harmonic
trap how spin waves affect the supersolid's density profile in the form of
crystal waves, inducing oscillations of the periodicity as well as the
orientation of the fringes. Both these features are well within reach of
present-day experiments. Our results show that this system is a paradigmatic
supersolid, featuring superfluidity in conjunction with a fully dynamic
crystalline structure.",2210.10064v2
2022-11-15,Nonlinear sub-switching regime of magnetization dynamics in photo-magnetic garnets,"We analyze, both experimentally and numerically, the nonlinear regime of the
photo-induced coherent magnetization dynamics in cobalt-doped yttrium iron
garnet films. Photo-magnetic excitation with femtosecond laser pulses reveals a
strongly nonlinear response of the spin subsystem with a significant increase
of the effective Gilbert damping. By varying both laser fluence and the
external magnetic field, we show that this nonlinearity originates in the
anharmonicity of the magnetic energy landscape. We numerically map the
parameter workspace for the nonlinear photo-induced spin dynamics below the
photo-magnetic switching threshold. Corroborated by numerical simulations of
the Landau-Lifshitz-Gilbert equation, our results highlight the key role of the
cubic symmetry of the magnetic subsystem in reaching the nonlinear spin
precession regime. These findings expand the fundamental understanding of
laser-induced nonlinear spin dynamics as well as facilitate the development of
applied photo-magnetism.",2211.08048v2
2022-12-16,Relaxation dynamics of an unlike spin pair system,"Redfield master equation was applied to study the dynamics of an ensemble of
interacting pair of unlike spins at room temperature. This spin quantum system
is a workbench quantum model to analyze the relaxation dynamics of a
heteronuclear two-level spin system interacting by a pure dipole-dipole
coupling. Expressions for the density matrix elements and their relaxation rate
constants of each coherence order were computed. In addition, the solutions
were evaluated considering three initial quantum states, and the theoretical
predictions, such as multi-exponential evolutions and enhancement, are
behaviors that the solutions preserve and agree with previous studies performed
for magnetization time evolutions. Moreover, the solutions computed to predict
the dynamics of the longitudinal magnetization avoid the disagreement reported
by I. Solomon.",2212.08747v2
2023-03-06,Spin-Polarized Extended Lagrangian Born-Oppenheimer Molecular Dynamics,"We present a generalization of Extended Lagrangian Born-Oppenheimer molecular
dynamics [Phys. Rev. Lett. vol. 100, 123004 (2008); Eur. Phys. J. B vol. 94,
164 (2021)] that also includes the electronic spin-degrees of freedom as
extended dynamical variables. To integrate the combined spin and charge degrees
of freedom, we use a preconditioned low-rank Krylov subspace approximation. Our
approach is demonstrated for quantum-mechanical molecular dynamics simulations
of iron, using spin-polarized self-consistent charge density functional
tight-binding theory. We also show how the low-rank Krylov subspace
approximation can be used to accelerate the self-consistent field convergence.",2303.03529v1
2023-03-31,Characterization and Coherent Control of Spin Qubits with Modulated Electron Beam and Resonator,"The coherent dynamics and control of spin qubits are essential requirements
for quantum technology. A prominent challenge for coherent control of a spin
qubit in a set of qubits is the destructive effect of the applied magnetic
field on the coherent dynamics of neighbouring qubits due to its spatial
extension. We propose a novel scheme to characterize the coherent dynamics of
these quantum systems and to coherently control them using a magnetic field.
Our scheme consists of a resonator that encompasses the desired quantum system
and a modulated electron beam that passes through the resonator in close
proximity to the quantum system of interest. The dynamics of the system is
obtained by solving the Lindblad master equation. To verify the reliability of
our model, we tested the model on a Potassium atom, $^{41}$K and NV$^-$ centre
in Diamond. The results show that by properly controlling the parameters of the
resonator and the electron beam, the coherence and decoherence rates of these
quantum systems can be improved. Our model has the potential to be used for
characterizing different types of spin-based quantum systems, and implementing
quantum logic gates for quantum computation.",2303.17952v1
2023-05-25,Crystallization dynamics of magnetic skyrmions in a frustrated itinerant magnet,"We investigate the phase ordering kinetics of skyrmion lattice (SkL) in a
metallic magnet. The SkL can be viewed as a superposition of magnetic stripes
whose periods are determined by the quasi-nesting wave vectors of the
underlying Fermi surface. An effective magnetic Hamiltonian that describes the
electron-mediated spin-spin interaction is obtained for a two-dimensional s-d
model with the Rashba spin-orbit coupling. Large-scale Landau-Lifshitz-Gilbert
dynamics simulations based on the effective spin Hamiltonian reveal a two-stage
phase ordering of the SkL phase after a thermal quench. The initial fast
crystallization of skyrmions is followed by a slow relaxation dominated by the
annihilation dynamics of dislocations, which are topological defects of the
constituent magnetic stripe orders. The late-stage phase ordering also exhibits
a dynamical scaling symmetry. We further show that the annihilation of
dislocations follows a power-law time dependence with a logarithmic correction
that depends on magnetic fields. Implications of our results for SkL phases in
magnetic materials are also discussed.",2305.16182v1
2023-06-11,Spin-flip dynamics in core-excited states in the basis of irreducible spherical tensor operators,"Recent experimental advances in ultrafast science put different processes
occurring on the electronic timescale below a few femtoseconds in focus. In the
present theoretical work, we demonstrate how the transformation and propagation
of the density matrix in the basis of irreducible spherical tensors can be
conveniently used to study sub-few fs spin-flip dynamics in the core-excited
transition metal compounds. With the help of the Wigner-Eckart theorem, such a
transformation separates the essential dynamical information from the geometric
factors governed by the angular momentum algebra. We show that an additional
reduction can be performed by the physically motivated truncation of the
spherical tensor basis. In particular, depending on the degree of coherence,
the ultrafast dynamics can be considered semi-quantitative in the notably
reduced spherical basis when only total populations of the basis states of the
given spin are of interest. Such truncation should be especially beneficial
when the number of the high-spin basis states is vast, as it substantially
reduces computational costs.",2306.06737v1
2023-07-25,Effective Hamiltonian approach to the quantum phase transitions in the extended Jaynes-Cummings model,"The study of phase transitions in dissipative quantum systems based on the
Liouvillian is often hindered by the difficulty of constructing a time-local
master equation when the system-environment coupling is strong. To address this
issue, the complex discretization approximation for the environment is proposed
to study the quantum phase transition in the extended Jaynes-Cumming model with
an infinite number of boson modes. This approach yields a non-Hermitian
effective Hamiltonian that can be used to simulate the dynamics of the spin. It
is found that the ground state of this effective Hamiltonian determines the
spin dynamics in the single-excitation subspace. Depending on the opening of
the energy gap and the maximum population of excitations on the spin degree of
freedom, three distinct phases can be identified: fast decaying, localized, and
stretched dynamics of the spin. This approach can be extended to multiple
excitations, and similar dynamics were found in the double-excitation subspace,
indicating the robustness of the single-excitation phase.",2307.13518v3
2024-01-19,Diversity of Ultrafast Spin Dynamics Near the Tricritical Point in a Ferrimagnetic Gd/FeCo Multilayer,"It is found that subtle changes in the external magnetic field and
temperature result in dramatic changes in the ultrafast response of spins to a
femtosecond laser excitation in a ferrimagnetic Gd/FeCo multilayer. A total of
six distinct types of spin dynamics were observed and explained by considering
the spin-flop transition to the noncollinear phase and the concept of a
tricritical point in the $H$-$T$ phase diagram. A particularly interesting type
of dynamics is the exchange-driven reversal. These exchange-driven dynamics
provide new insights into the tricritical point, which is shown to separate two
thermodynamically distinct noncollinear phases with the transition-metal
magnetization pointing on adjacent sides of the anisotropy plane.",2401.10671v1
2024-02-27,Semiclassical approach to spin dynamics of a ferromagnetic S=1 chain,"Motivated by recent experimental progress in the quasi-one-dimensional
quantum magnet NiNb$_2$O$_6$, we study the spin dynamics of an S=1
ferromagnetic Heisenberg chain with single-ion anisotropy by using a
semiclassical molecular dynamics approach. This system undergoes a quantum
phase transition from a ferromagnetic to a paramagnetic state under a
transverse magnetic field, and the magnetic responses reflecting this
transition is well described by our semiclassical method. We show that at
low-temperature the transverse component of the dynamical structure factor
depicts clearly the magnon dispersion, and the longitudinal component exhibits
two continua associated with single- and two-magnon excitations, respectively.
These spin excitation spectra show interesting temperature dependence as
effects of magnon interactions.Our findings shed light on experimental
detection of spin excitations in a large class of quasi-one-dimensional
magnets.",2402.17416v1
2003-06-26,Kondo effect in systems with dynamical symmetries,"This paper is devoted to a systematic exposure of the Kondo physics in
quantum dots for which the low energy spin excitations consist of a few
different spin multiplets $|S_{i}M_{i}>$. Under certain conditions (to be
explained below) some of the lowest energy levels $E_{S_{i}}$ are nearly
degenerate. The dot in its ground state cannot then be regarded as a simple
quantum top in the sense that beside its spin operator other dot (vector)
operators ${\bf R}_{n}$ are needed (in order to fully determine its quantum
states), which have non-zero matrix elements between states of different spin
multiplets $<S_{i}M_{i} |{\bf R}_{n}|S_{j}M_{j} > \ne 0$. These ""Runge-Lenz""
operators do not appear in the isolated dot-Hamiltonian (so in some sense they
are ""hidden""). Yet, they are exposed when tunneling between dot and leads is
switched on. The effective spin Hamiltonian which couples the metallic electron
spin ${\bf s}$ with the operators of the dot then contains new exchange terms,
$J_{n} {\bf s} \cdot {\bf R}_{n}$ beside the ubiquitous ones $J_{i} {\bf
s}\cdot {\bf S}_{i}$. The operators ${\bf S}_{i}$ and ${\bf R}_{n}$ generate a
dynamical group (usually SO(n)). Remarkably, the value of $n$ can be controlled
by gate voltages, indicating that abstract concepts such as dynamical symmetry
groups are experimentally realizable. Moreover, when an external magnetic field
is applied then, under favorable circumstances, the exchange interaction
involves solely the Runge-Lenz operators ${\bf R}_{n}$ and the corresponding
dynamical symmetry group is SU(n). For example, the celebrated group SU(3) is
realized in triple quantum dot with four electrons.",0306670v2
2009-05-07,Amplified Quantum Dynamics and Enhanced Parameter Sensitivity via Coherent Feedback in Collective Atomic Spin Systems,"We consider the effective dynamics obtained by double-passing a far-detuned
laser probe through a large atomic spin system. The net result of the
atom-field interaction is a type of coherent positive feedback that amplifies
the values of selected spin observables. An effective equation of motion for
the atomic system is presented, and an approximate 2-parameter model of the
dynamics is developed that should provide a viable approach to modeling even
the extremely large spin systems, with N>>1 atoms, encountered under typical
laboratory conditions.
  Combining the nonlinear dynamics that result from the positive feedback with
continuous observation of the atomic spin offers an improvement in quantum
parameter estimation. We explore the possibility of reaching the Heisenberg
uncertainty scaling in atomic magnetometry without the need for any appreciable
spin-squeezing by analyzing our system via the quantum Cramer-Rao inequality.
Finally, we develop a realistic quantum parameter estimator for atomic
magnetometry that is based on a two-parameter family of Gaussian states and
investigate the performance of this estimator through numerical simulations. In
doing so, we identify several issues, such as numerical convergence and the
reduction of estimator bias, that must be addressed when incorporating our
parameter estimation methods into an actual laboratory setting.",0905.0931v1
2015-06-04,Spin dynamics in the presence of competing ferro- and antiferro-magnetic correlations in Yb2Ti2O7,"In this work, we show that the zero field excitation spectra in the quantum
spin ice candidate pyrochlore compound \ybti\ is a continuum characterized by a
very broad and almost flat dynamical response which extends up to $1-1.5$ meV,
coexisting or not with a quasi-elastic response depending on the wave-vector.
The spectra do not evolve between 50 mK and 2 K, indicating that the spin
dynamics is only little affected by the temperature in both the short-range
correlated and ordered regimes. Although classical spin dynamics simulations
qualitatively capture some of the experimental observations, we show that they
fail to reproduce this broad continuum. In particular, the simulations predict
an energy scale twice smaller than the experimental observations. This analysis
is based on a careful determination of the exchange couplings, able to
reproduce both the zero field diffuse scattering and the spin wave spectrum
rising in the field polarized state. According to this analysis, \ybti\ lies at
the border between a ferro and an antiferromagnetic phase. These results
suggest that the unconventional ground state of \ybti\ is governed by strong
quantum fluctuations arising from the competition between those phases. The
observed spectra may correspond to a continuum of deconfined spinons as
expected in quantum spin liquids.",1506.01729v1
2016-02-02,Non-Markovian Dynamics in Chiral Quantum Networks with Spins and Photons,"We study the dynamics of chiral quantum networks consisting of nodes coupled
by unidirectional or asymmetric bidirectional quantum channels. In contrast to
familiar photonic networks where driven two-level atoms exchange photons via 1D
photonic nanostructures, we propose and study a setup where interactions
between the atoms are mediated by spin excitations (magnons) in 1D $XX$ spin
chains representing spin waveguides. While Markovian quantum network theory
eliminates quantum channels as structureless reservoirs in a Born-Markov
approximation to obtain a master equation for the nodes, we are interested in
non-Markovian dynamics. This arises from the nonlinear character of the
dispersion with band-edge effects, and from finite spin propagation velocities
leading to time delays in interactions. To account for the non-Markovian
dynamics we treat the quantum degrees of freedom of the nodes and connecting
channels as a composite spin system with the surrounding of the quantum network
as a Markovian bath, allowing for an efficient solution with time-dependent
density matrix renormalization group techniques. We illustrate our approach
showing non-Markovian effects in the driven-dissipative formation of quantum
dimers, and we present examples for quantum information protocols involving
quantum state transfer with engineered elements as basic building blocks of
quantum spintronic circuits.",1602.00926v2
2016-09-19,"Secular precessing compact binary dynamics, spin and orbital angular momentum flip-flops","We derive the conservative secular evolution of precessing compact binaries
to second post-Newtonian order accuracy, with leading-order spin-orbit,
spin-spin and mass quadrupole-monopole contributions included. The emerging
closed system of first-order differential equations evolves the pairs of polar
and azimuthal angles of the spin and orbital angular momentum vectors together
with the periastron angle. In contrast with the instantaneous dynamics, the
secular dynamics is autonomous. This secular dynamics reliably characterizes
the system over timescales starting from a few times the radial period to
several precessional periods, but less than the radiation reaction timescale.
We numerically compare the instantaneous and secular evolutions and estimate
the number of periods for which dissipation has no significant effect, e.g. the
conservative timescale. We apply the analytic equations to study the spin
flip-flop effect, recently found by numerical relativity methods. Our
investigations show that the effect does not generalize beyond its original
parameter settings, although we reveal distinct configurations exhibiting one
half flip-flops. In addition, we find a flip-flopping evolution of the orbital
angular momentum vector, which ventures from one pole to another through
several precessional periods. This is a new effect, occurring for mass ratios
much less than one.",1609.05915v1
2017-02-24,Einstein-aether theory: Dynamics of relativistic particles with spin or polarization in a Gödel-type universe,"In the framework of the Einstein-aether theory we consider a cosmological
model, which describes the evolution of the unit dynamic vector field with
activated rotational degree of freedom. We discuss exact solutions of the
Einstein-aether theory, for which the space-time is of the G\""odel-type, the
velocity four-vector of the aether motion is characterized by a non-vanishing
vorticity, thus the rotational vectorial modes can be associated with the
source of the universe rotation. The main goal of our paper is to study the
motion of test relativistic particles with vectorial internal degree of freedom
(spin or polarization), which is coupled to the unit dynamic vector field. The
particles are considered as the test ones in the given space-time background of
the G\""odel-type; the spin (polarization) coupling to the unit dynamic vector
field is modeled using exact solutions of three types. The first exact solution
describes the aether with arbitrary Jacobson's coupling constants; the second
one relates to the case, when the Jacobson's constant responsible for the
vorticity is vanishing; the third exact solution is obtained using three
constraints for the coupling constants. The analysis of the exact expressions,
which are obtained for the particle momentum and for the spin (polarization)
four-vector components, shows that the interaction of the spin (polarization)
with the unit vector field induces a rotation, which is additional to the
geodesic precession of the spin (polarization) associated with the universe
rotation as a whole.",1702.07607v1
2017-03-22,Time evolution of a pair of distinguishable interacting spins subjected to controllable and noisy magnetic fields,"The quantum dynamics of a
$\hat{\mathbf{J}}^2=(\hat{\mathbf{j}}_1+\hat{\mathbf{j}}_2)^2$-conserving
Hamiltonian model describing two coupled spins $\hat{\mathbf{j}}_1$ and
$\hat{\mathbf{j}}_2$ under controllable and fluctuating time-dependent magnetic
fields is investigated. Each eigenspace of $\hat{\mathbf{J}}^2$ is dynamically
invariant and the Hamiltonian of the total system restricted to any one of such
$(j_1+j_2)-|j_1-j_2|+1$ eigenspaces, possesses the SU(2) structure of the
Hamiltonian of a single fictitious spin acted upon by the total magnetic field.
We show that such a reducibility holds regardless of the time dependence of the
externally applied field as well as of the statistical properties of the noise,
here represented as a classical fluctuating magnetic field. The time evolution
of the joint transition probabilities of the two spins $\hat{\mathbf{j}}_1$ and
$\hat{\mathbf{j}}_2$ between two prefixed factorized states is examined,
bringing to light peculiar dynamical properties of the system under scrutiny.
When the noise-induced non-unitary dynamics of the two coupled spins is
properly taken into account, analytical expressions for the joint Landau-Zener
transition probabilities are reported. The possibility of extending the
applicability of our results to other time-dependent spin models is pointed
out.",1703.07673v3
2018-02-23,Quantum spin dynamics of individual neutral impurities coupled to a Bose-Einstein condensate,"We report on spin dynamics of individual, localized neutral impurities
immersed in a Bose-Einstein condensate. Single Cesium atoms are transported
into a cloud of Rubidium atoms, thermalize with the bath, and the ensuing
spin-exchange between localized impurities with quasi-spin $F_i=3$ and bath
atoms with $F_b=1$ is resolved. Comparing our data to numerical simulations of
spin dynamics we find that, for gas densities in the BEC regime, the dynamics
is dominated by the condensed fraction of the cloud. We spatially resolve the
density overlap of impurities and gas by the spin-population of impurities.
Finally we trace the coherence of impurities prepared in a coherent
superposition of internal states when coupled to a gas of different densities.
For our choice of states we show that, despite high bath densities and thus
fast thermalization rates, the impurity coherence is not affected by the bath,
realizing a regime of sympathetic cooling while maintaining internal state
coherence. Our work paves the way toward non-destructive probing of quantum
many-body systems via localized impurities.",1802.08702v2
2012-04-06,Electron-nuclei spin dynamics in II-VI semiconductor quantum dots,"We report on the dynamics of optically induced nuclear spin polarization in
individual CdTe/ZnTe quantum dots loaded with one electron by modulation
doping. The fine structure of the hot trion (charged exciton $X^-$ with an
electron in the $P$-shell) is identified in photoluminescence excitation
spectra. A negative polarisation rate of the photoluminescence, optical pumping
of the resident electron and the built-up of dynamic nuclear spin polarisation
(DNSP) are observed in time-resolved optical pumping experiments when the
quantum dot is excited at higher energy than the hot trion triplet state. The
time and magnetic field dependence of the polarisation rate of the $X^-$
emission allows to probe the dynamics of formation of the DNSP in the optical
pumping regime. We demonstrate using time-resolved measurements that the
creation of a DNSP at B=0T efficiently prevents longitudinal spin relaxation of
the electron caused by fluctuations of the nuclear spin bath. The DNSP is built
in the microsecond range at high excitation intensity. A relaxation time of the
DNSP in about 10 microseconds is observed at $B=0T$ and significantly increases
under a magnetic field of a few milli-Tesla. We discuss mechanisms responsible
for the fast initialisation and relaxation of the diluted nuclear spins in this
system.",1204.1469v1
2016-12-08,Landauer-Büttiker approach for hyperfine mediated electronic transport in the integer quantum Hall regime,"The interplay of spin-polarized electronic edge states with the dynamics of
the host nuclei in quantum Hall systems presents rich and non-trivial transport
physics. Here, we develop a Landauer-B\""uttiker approach to understand various
experimental features observed in the integer quantum Hall set ups featuring
quantum point contacts. The approach developed here entails a phenomenological
description of spin resolved inter-edge scattering induced via hyperfine
assisted electron-nuclear spin flip-flop processes. A self-consistent
simulation framework between the nuclear spin dynamics and edge state
electronic transport is presented in order to gain crucial insights into the
dynamic nuclear polarization effects on electronic transport and in turn the
electron-spin polarization effects on the nuclear spin dynamics. In particular,
we show that the hysteresis noted experimentally in the conductance-voltage
trace as well as in the resistively detected NMR lineshape results from a lack
of quasi-equilibrium between electronic transport and nuclear polarization
evolution. In addition, we present circuit models to emulate such hyperfine
mediated transport effects to further facilitate a clear understanding of the
electronic transport processes occurring around the quantum point contact.
Finally, we extend our model to account for the effects of quadrupolar
splitting of nuclear levels and also depict the electronic transport signatures
that arise from single and multi-photon processes.",1612.02584v2
2019-07-25,Magnetic memory effect in ensembles of interacting anisotropic magnetic nanoparticles,"We explore the influence of demagnetization interaction on magnetic memory
effect by varying organization geometry of anisotropic ZnFe$_2$O$_4$
nanoparticles in an ensemble. The static and dynamic behaviour of two
differently organized ensembles, compact ensemble (CE) and hollow core ensemble
(HCE), are extensively studied by both dc and ac susceptibility, magnetic
memory effect and spin relaxation. The frequency-dependence peak shifting of
freezing temperature in both the systems is analyzed properly with the help of
two dynamic scaling models: Vogel-Fulcher law and power law. Presence of
cluster spin-glass phase is reflected from Vogel-Fulcher temperature $T_0$
$\simeq$ 142.58 K for CE, $\simeq$ 97 K for HCE and characteristic time
constant $\tau_0$ $\simeq$ $8.85\times10^{-9}$ s for CE, $\simeq$
$3.8\times10^{-10}$ s for HCE; along with $\delta$T$_{Th}$ $\sim$ 0.1 for CE
and 0.2 for HCE. The power law fitting with dynamic exponent $zv'$ = 6.2 $\pm$
1.1 for CE, 6.3 $\pm$ 0.5 for HCE and single spin flip $\tau^*$ $\simeq$
$7.7\times10^{-11}$ s for CE, $\simeq$ $1.3\times10^{-10}$ s for HCE provide
firm confirmation of cluster spin-glass phase. The progressive spin freezing
across multiple metastable states with prominent memory effects is reflected in
both the systems via nonequilibrium dynamics study. The hollow core geometry
with anisotropic nanoparticles on surface with closer proximity leads to
complex anisotropy energy landscape with enhanced demagnetizing field resulting
highly frustrated surface spins. As a consequence, more prominent magnetic
memory effect is observed in HCE with higher activation energy, reduced
blocking temperature and enhanced coercivity than that of CE.",1907.11116v2
2020-01-22,The dynamics of a domain wall in ferrimagnets driven by spin-transfer torque,"The spin-transfer-torque-driven (STT-driven) dynamics of a domain wall in an
easy-axis rare-earth transition-metal ferrimagnet is investigated theoretically
and numerically in the vicinity of the angular momentum compensation point
$T_A$, where the net spin density vanishes. The particular focus is given on
the unusual interaction of the antiferromagnetic dynamics of a ferrimagnetic
domain wall and the adiabatic component of STT, which is absent in
antiferromagnets but exists in the ferrimagnets due to the dominant coupling of
conduction electrons to transition-metal spins. Specifically, we first show
that the STT-induced domain-wall velocity changes its sign across $T_A$ due to
the sign change of the net spin density, giving rise to a phenomenon unique to
ferrimagnets that can be used to characterize $T_A$ electrically. It is also
shown that the frequency of the STT-induced domain-wall precession exhibits its
maximum at $T_A$ and it can approach the spin-wave gap at sufficiently high
currents. Lastly, we report a numerical observation that, as the current
density increases, the domain-wall velocity starts to deviate from the
linear-response result, calling for a more comprehensive theory for the
domain-wall dynamics in ferrimagnets driven by a strong current.",2001.08037v1
2017-11-01,Dynamical Jahn-Teller effect of fullerene anions,"The dynamical Jahn-Teller effect of C$_{60}^{n-}$ anions ($n = $ 1-5) is
studied using the numerical diagonalization of the linear $p^n \otimes 8d$
Jahn-Teller Hamiltonian with the currently established coupling parameters. It
is found that in all anions the Jahn-Teller effect stabilizes the low-spin
states, resulting in the violation of Hund's rule. The energy gain due to the
Jahn-Teller dynamics is found to be comparable to the static Jahn-Teller
stabilization. The Jahn-Teller dynamics influences the thermodynamic properties
via strong variation of the density of vibronic states with energy. Thus, the
large vibronic entropy in the low-spin states enhances the effective spin gap
of C$_{60}^{3-}$ quenching the spin crossover. From the calculations of the
effective spin gap in function of the Hund's rule coupling, we found that the
latter should amount 40 $\pm$ 5 meV in order to cope with the violation of
Hund's rule and to reproduce the large spin gap. With the obtained numerical
solutions the matrix elements of electronic operators for the low-lying
vibronic levels and the vibronic reduction factors are calculated for all
anions.",1711.00340v3
2018-06-24,Nanoscopic time crystal obtained by nonergodic spin dynamics,"We study the far-from-equilibrium properties of quenched magnetic nanoscopic
classical spin systems. In particular, we focus on the interplay between
lattice vibrations and magnetic frustrations induced by surface effects typical
of an antiferromagnet. We use a combination of Monte Carlo simulations and
explore the dynamical behaviours by solving the stochastic
Landau-Lifshitz-Gilbert equation at finite temperature. The Monte Carlo
approach treats both the ionic degrees of freedom and spin variables on the
same footing, via an extended Lennard-Jones Hamiltonian with a spin-lattice
coupling. The zero temperature phase diagram of the finite size nanoscopic
systems with respect to the range of the Heisenberg interaction and the
Lennard-Jones coupling constant shows two main structures with non-trivial
magnetisation triggered by antiferromagnetism: a simple cubic and a
body-centred cubic. At non zero temperature, the competition between spins and
the ionic vibrations considerably affects the magnetization of the system.
Exploring the dynamics reveals a non-trivial structural induced behaviour in
the spin relaxation with a concomitant memory of the initially applied
ferromagnetic quench. We report the observation of a non-trivial dynamical
scenario, obtained after a ferromagnetic magnetic quench at low temperature.
Furthermore, we observe long-lived non-thermal states which could open new
avenues for nano-technology.",1806.09130v4
2018-08-18,Dynamic Hamiltonian engineering of 2D rectangular lattices in a one-dimensional ion chain,"Controlling the interaction graph between spins or qubits in a quantum
simulator allows user-controlled tailoring of native interactions to achieve a
target Hamiltonian. The flexibility of engineering long-ranged phonon-mediated
spin-spin interactions in a trapped ion quantum simulator offers such a
possibility. Trapped ions, a leading candidate for simulating computationally
hard quantum many-body dynamics, are most readily trapped in a linear 1D chain,
limiting their utility for readily simulating higher dimensional spin models.
In this work, we introduce a hybrid method of analog-digital simulation for
simulating 2D spin models and dynamically changing interactions to achieve a
new graph using a linear 1D chain. The method relies on time domain Hamiltonian
engineering through a successive application of Stark shift gradient pulses,
and wherein the pulse sequence can simply be obtained from a Fourier series
decomposition of the target Hamiltonian over the space of lattice couplings. We
focus on engineering 2D rectangular nearest-neighbor spin lattices,
demonstrating that the required control parameters scale linearly with ion
number. This hybrid approach offers compelling possibilities for the use of 1D
chains in the study of Hamiltonian quenches, dynamical phase transitions, and
quantum transport in 2D and 3D. We discuss a possible experimental
implementation of this approach using real experimental parameters.",1808.06124v1
2020-05-12,Spin crossovers and superdiffusion in the one-dimensional Hubbard model,"We use tools from integrability and generalized hydrodynamics to study
finite-temperature dynamics in the one-dimensional Hubbard model. First, we
examine charge, spin, and energy transport away from half-filling and zero
magnetization, focusing on the strong coupling regime where we identify a rich
interplay of temperature and energy scales, with crossovers between distinct
dynamical regimes. We identify an intermediate-temperature regime analogous to
the spin-incoherent Luttinger liquid, where spin degrees of freedom are hot but
charge degrees of freedom are at low temperature. We demonstrate that the spin
Drude weight exhibits sharp features at the crossover between this regime and
the low-temperature Luttinger liquid regime, that are absent in the charge and
energy response, and rationalize this behavior in terms of the properties of
Bethe ansatz quasiparticles. We then turn to the dynamics along special lines
in the phase diagram corresponding to half-filling and/or zero magnetization
where on general grounds we anticipate that the transport is sub-ballistic but
superdiffusive. We provide analytical and numerical evidence for
Kardar-Parisi-Zhang (KPZ) dynamical scaling (with length and time scales
related via $x\sim t^{2/3}$) along both lines and at the $SO(4)$-symmetric
point where they intersect. Our results suggest that both spin-coherence
crossovers and KPZ scaling may be accessed in near-term experiments with
optical lattice Hubbard emulators.",2005.05984v2
2020-06-11,Coupling a mobile hole to an antiferromagnetic spin background: Transient dynamics of a magnetic polaron,"Understanding the interplay between charge and spin and its effects on
transport is a ubiquitous challenge in quantum many-body systems. In the
Fermi-Hubbard model, this interplay is thought to give rise to magnetic
polarons, whose dynamics may explain emergent properties of quantum materials
such as high-temperature superconductivity. In this work, we use a cold-atom
quantum simulator to directly observe the formation dynamics and subsequent
spreading of individual magnetic polarons. Measuring the density- and
spin-resolved evolution of a single hole in a 2D Hubbard insulator with
short-range antiferromagnetic correlations reveals fast initial delocalization
and a dressing of the spin background, indicating polaron formation. At long
times, we find that dynamics are slowed down by the spin exchange time, and
they are compatible with a polaronic model with strong density and spin
coupling. Our work enables the study of out-of-equilibrium emergent phenomena
in the Fermi-Hubbard model, one dopant at a time.",2006.06672v2
2022-06-06,Probing spin dynamics of ultra-thin van der Waals magnets via photon-magnon coupling,"Layered van der Waals (vdW) magnets can maintain a magnetic order even down
to the single-layer regime and hold promise for integrated spintronic devices.
While the magnetic ground state of vdW magnets was extensively studied, key
parameters of spin dynamics, like the Gilbert damping, crucial for designing
ultra-fast spintronic devices, remains largely unexplored. Despite recent
studies by optical excitation and detection, achieving spin wave control with
microwaves is highly desirable, as modern integrated information technologies
predominantly are operated with these. The intrinsically small numbers of
spins, however, poses a major challenge to this.
  Here, we present a hybrid approach to detect spin dynamics mediated by
photon-magnon coupling between high-Q superconducting resonators and ultra-thin
flakes of Cr$_2$Ge$_2$Te$_6$ (CGT) as thin as 11\,nm. We test and benchmark our
technique with 23 individual CGT flakes and extract an upper limit for the
Gilbert damping parameter. These results are crucial in designing on-chip
integrated circuits using vdW magnets and offer prospects for probing spin
dynamics of monolayer vdW magnets.",2206.02460v2
2022-09-06,Dynamic coupling and spin-wave dispersions in a magnetic hybrid system made of an artificial spin-ice structure and an extended NiFe underlayer,"We present a combined experimental and numerical study of the spin-wave
dispersion in NiFe artificial spin-ice (ASI) system consisting of an array of
stadium-shaped nanoislands deposited on the top of a continuous NiFe film with
nonmagnetic spacer layers of varying thickness. The spin-wave dispersion,
measured by wavevector resolved Brillouin light scattering spectroscopy in the
Damon-Eshbach configuration, consists of a rich number of modes, with either
stationary or propagating character. We find that the lowest frequency mode
displays a bandwidth of approximately 0.5 GHz, which is independent of the
presence of the film underneath. On the contrary, the BLS intensity of some of
the detected modes strongly depends on the presence of the extended thin-film
underlayer. Micromagnetic simulations unveil the details of the dynamic
coupling between ASI lattice and film underlayer. Interestingly, the ASI
lattice facilitates dynamics of the film either specific wavelengths or
intensity modulation peculiar to the modes of the ASI elements imprinted in the
film. Our results demonstrate that propagating spin waves can be modulated at
the nanometer length scale by harnessing the dynamic mode coupling in the
vertical, i.e., the out-of-plane direction of suitably designed magnonic
structures.",2209.02783v1
2023-02-18,Entangling dynamics from effective rotor/spin-wave separation in U(1)-symmetric quantum spin models,"The non-equilibrium dynamics of quantum spin models is a most challenging
topic, due to the exponentiality of Hilbert space; and it is central to the
understanding of the many-body entangled states that can be generated by
state-of-the-art quantum simulators. A particularly important class of
evolutions is the one governed by U(1) symmetric Hamiltonians, initialized in a
state which breaks the U(1) symmetry -- the paradigmatic example being the
evolution of the so-called one-axis-twisting (OAT) model, featuring
infinite-range interactions between spins. In this work we show that the
dynamics of the OAT model can be closely reproduced by systems with
power-law-decaying interactions, thanks to an effective separation between the
zero-momentum degrees of freedom, associated with the so-called Anderson tower
of states, and reconstructing a OAT model; and finite-momentum ones, associated
with spin-wave excitations. This mechanism explains quantitatively the recent
numerical observation of spin squeezing and Schr\""odinger-cat generation in the
dynamics of dipolar Hamiltonians; and it paves the way for the extension of
this observation to a much larger class of models of immediate relevance for
quantum simulations.",2302.09271v1
2023-07-17,Slonczewski-spin-current driven dynamics of 180$^{\circ}$ domain walls in spin valves with interfacial Dzyaloshinskii-Moriya interaction,"Steady-flow dynamics of ferromagnetic 180$^{\circ}$ domain walls (180DWs) in
long and narrow spin valves (LNSVs) with interfacial Dzyaloshinskii-Moriya
interaction (IDMI) under spin currents with Slonczewski $g-$factor are
examined. Depending on the magnetization orientation of polarizers (pinned
layers of LNSVs), dynamics of 180DWs in free layers of LNSVs are subtly
manipulated: (i) For parallel polarizers, stronger spin polarization leads to
higher Walker limit thus ensures the longevity of faster steady flows.
Meantime, IDMI induces both the stable-region flapping and its width
enlargement. (ii) For perpendicular polarizers, a wandering of 180DWs between
bi- and tri-stability persists with the criticality adjusted by the IDMI. (iii)
For planar-transverse polarizers, IDMI makes the stable region of steady flows
completely asymmetric and further imparts a high saturation wall velocity under
large current density. Under the last two polarizers, the ultrahigh
differential mobility of 180DWs survives. The combination of Slonczewski spin
current and IDMI provides rich possibilities of fine controlling on 180DW
dynamics, hence opens avenues for magnetic nanodevices with rich functionality
and high robustness.",2307.08419v1
2023-10-17,RelativisticDynamics.jl: Relativistic Spin-Orbital Dynamics in Julia,"RelativisticDynamics.jl is an open-source Julia package for relativistic
spin-orbital dynamics in the gravitational strong-field of a Kerr spacetime.
Existing codes for modelling the dynamics of spinning objects like pulsars in
the strong-field regime are generally lacking, since such systems occupy an
intermediate regime that is generally overlooked. At the ""low"" end of this
regime there are post-Newtonian descriptions which neglect the influence of the
pulsar spin on the underlying spacetime metric (""spin-curvature"" coupling). At
the ""high"" end there are the full numerical relativity solutions which are
primarily applicable toe two black holes with a mass ratio $\mathcal{O}(1)$,
and are computationally intractable for pulsar systems observed over a large
number of orbital cycles. RelativisticDynamics.jl aims to bridge this gap by
providing a modern, fast code for accurate numerical evolution of spinning
relativistic systems via the Mathisson-Papetrou-Dixon formalism. Julia is a
modern language that solves the ""two language problem"", enabling fast dynamic
typing and JIT compilation on conjunction with petaflop performance, comparable
with numerical languages that are better known in the astrophysics community
such as C or Fortran. RelativisticDynamics.jl is written to be fully type
flexible, being able to support arbitrary number formats, and fully
differentiable via automatic differentiation.",2310.11002v1
2023-11-22,Quantum spin dynamics due to strong Kitaev interactions in the triangular-lattice antiferromagnet CsCeSe$_2$,"The extraordinary properties of the Kitaev model have motivated an intense
search for new physics in materials that combine geometrical and bond
frustration. In this work, we employ inelastic neutron scattering, spin wave
theory, and exact diagonalization to study the spin dynamics in the perfect
triangular-lattice antiferromagnet (TLAF) CsCeSe$_2$. This material orders into
a stripe phase, which is demonstrated to arise as a consequence of the
off-diagonal bond-dependent terms in the spin Hamiltonian. By studying the spin
dynamics at intermediate fields, we identify an interaction between the
single-magnon state and the two-magnon continuum that causes decay of coherent
magnon excitations, level repulsion, and transfer of spectral weight to the
continuum that are controlled by the strength of the magnetic field. Our
results provide a microscopic mechanism for the stabilization of the stripe
phase in TLAF and show how complex many-body physics can be present in the spin
dynamics in a magnet with strong Kitaev coupling even in an ordered ground
state.",2311.13146v2
2023-12-28,Anisotropic skyrmion and multi-$q$ spin dynamics in centrosymmetric Gd$_2$PdSi$_3$,"Skyrmions are particle-like vortices of magnetization with non-trivial
topology, which are usually stabilized by Dzyaloshinskii-Moriya interactions
(DMI) in noncentrosymmetric bulk materials. Exceptions are centrosymmetric Gd-
and Eu-based skyrmion-lattice (SkL) hosts with net-zero DMI, where both the SkL
stabilization mechanisms and magnetic ground states remain controversial. We
address these by investigating both static and dynamic spin properties of the
centrosymmetric SkL host Gd$_2$PdSi$_3$ using muon spectroscopy ($\mu$SR). We
find that spin fluctuations in its non-coplanar SkL phase are highly
anisotropic, implying that spin anisotropy plays a prominent role in
stabilizing this phase. We also observe strongly-anisotropic spin dynamics in
the ground-state (IC-1) incommensurate magnetic phase of the material,
indicating that it is a meron-like multi-$q$ structure. In contrast, the
higher-field, coplanar IC-2 phase is found to be single-$q$ with
nearly-isotropic spin dynamics.",2312.17323v2
2003-04-17,Dynamic heterogeneities in the out-of-equilibrium dynamics of simple spherical spin models,"The response of spherical two-spin interaction models, the spherical
ferromagnet (s-FM) and the spherical Sherrington-Kirkpatrick (s-SK) model, is
calculated for the protocol of the so-called nonresonant hole burning
experiment (NHB) for temperatures below the respective critical temperatures.
It is shown that it is possible to select dynamic features in the
out-of-equilibrium dynamics of both models, one of the hallmarks of dynamic
heterogeneities. The behavior of the s-SK model and the s-FM in three
dimensions is very similar, showing dynamic heterogeneities in the long time
behavior, i.e. in the aging regime. The appearence of dynamic heterogeneities
in the s-SK model explicitly demonstrates that these are not necessarily
related to {\it spatial} heterogeneities. For the s-FM it is shown that the
nature of the dynamic heterogeneities changes as a function of dimensionality.
With incresing dimension the frequency selectivity of the NHB diminishes and
the dynamics in the mean-field limit of the s-FM model becomes homogeneous.",0304396v2
1998-04-30,Ergodicity properties of energy conserving single spin flip dynamics in the XY model,"A single spin flip stochastic energy conserving dynamics for the XY model is
considered. We study the ergodicity properties of the dynamics. It is shown
that phase space trajectories densely fill the geometrically connected parts of
the energy surface. We also show that while the dynamics is discrete and the
phase point jumps around, it cannot make transitions between closed
disconnected parts of the energy surface. Thus the number of distinct sectors
depends on the number of geometrically disconnected parts of the energy
surface. Information on the connectivity of the surfaces is obtained by
studying the critical points of the energy function. We study in detail the
case of two spins and find that the number of sectors can be either one or two,
depending on the external fields and the energy. For a periodic lattice in $d$
dimensions, we find regions in phase space where the dynamics is non-ergodic
and obtain a lower bound on the number of disconnected sectors. We provide some
numerical evidence which suggests that such regions might be of small measure
so that the dynamics is effectively ergodic.",9804327v1
2003-08-23,On the universality of the fluctuation-dissipation ratio in non-equilibrium critical dynamics,"The two-time nonequilibrium correlation and response functions in 1D kinetic
classical spin systems with non-conserved dynamics and quenched to their
zero-temperature critical point are studied. The exact solution of the kinetic
Ising model with Glauber dynamics for a wide class of initial states allows for
an explicit test of the universality of the non-equilibrium limit
fluctuation-dissipation ratio X_{\infty}. It is shown that the value of
X_{\infty} depends on whether the initial state has finitely many domain walls
or not and thus two distinct dynamic universality classes can be identified in
this model. Generic 1D kinetic spin systems with non-conserved dynamics fall
into the same universality classes as the kinetic Glauber-Ising model provided
the dynamics is invariant under the C-symmetry of simultaneous spin and
magnetic-field reversal. While C-symmetry is satisfied for magnetic systems, it
need not be for lattice gases which may therefore display hitherto unexplored
types of non-universal kinetics.",0308466v2
2005-02-04,Static and dynamic lengthscales in a simple glassy plaquette model,"We study static and dynamic spatial correlations in a two-dimensional spin
model with four-body plaquette interactions and standard Glauber dynamics by
means of analytic arguments and Monte Carlo simulations. We study in detail the
dynamical behaviour which becomes glassy at low temperatures due to the
emergence of effective kinetic constraints in a dual representation where spins
are mapped to plaquette variables. We study the interplay between non-trivial
static correlations of the spins and the dynamic `four-point' correlations
usually studied in the context of supercooled liquids. We show that slow
dynamics is spatially heterogeneous due to the presence of diverging
lengthscales and scaling, as is also found in kinetically constrained models.
This analogy is illustrated by a comparative study of a froth model where the
kinetic constraints are imposed.",0502120v2
2006-09-11,Fluctuation-dissipation relations in plaquette spin systems with multi-stage relaxation,"We study aging dynamics in two non-disordered spin models with multi-spin
interactions, following a sudden quench to low temperature. The models are
relevant to the physics of supercooled liquids. Their low temperature dynamics
resemble those of kinetically constrained models, and obey dynamical scaling,
controlled by zero-temperature critical points. Dynamics in both models are
thermally activated, resulting in multi-stage relaxation towards equilibrium.
We study several two-time correlation and response functions. We find that
equilibrium fluctuation-dissipation relations are generically not satisfied
during the aging regime, but deviations from them are well described by
fluctuation-dissipation ratios, as found numerically in supercooled liquids.
These ratios are purely dynamic objects, containing information about the
nature of relaxation in the models. They are non-universal, and can even be
negative as a result of activated dynamics. Thus, effective temperatures are
not well-defined in these models.",0609257v1
2011-08-18,Dynamical Localization in Disordered Quantum Spin Systems,"We say that a quantum spin system is dynamically localized if the
time-evolution of local observables satisfies a zero-velocity Lieb-Robinson
bound. In terms of this definition we have the following main results: First,
for general systems with short range interactions, dynamical localization
implies exponential decay of ground state correlations, up to an explicit
correction. Second, the dynamical localization of random xy spin chains can be
reduced to dynamical localization of an effective one-particle Hamiltonian. In
particular, the isotropic xy chain in random exterior magnetic field is
dynamically localized.",1108.3811v2
2017-06-13,Dynamic phase transition features of the cylindrical nanowire driven by a propagating magnetic field,"Magnetic response of the spin-$1/2$ cylindrical nanowire to the propagating
magnetic field wave has been investigated by means of Monte Carlo simulation
method based on Metropolis algorithm. The obtained microscopic spin
configurations suggest that the studied system exhibits two types of dynamical
phases depending on the considered values of system parameters: Coherent
propagation of spin bands and spin-frozen or pinned phases, as in the case of
the conventional bulk systems under the influence of a propagating magnetic
field. By benefiting from the temperature dependencies of variances of dynamic
order parameter, internal energy and the derivative of dynamic order parameter
of the system, dynamic phase diagrams are also obtained in related planes for
varying values of the wavelength of the propagating magnetic field. Our
simulation results demonstrate that as the strength of the field amplitude is
increased, the phase transition points tend to shift to the relatively lower
temperature regions. Moreover, it has been observed that dynamic phase boundary
line shrinks inward when the value of wavelength of the external field
decreases.",1706.04089v1
2019-07-18,Dynamical formation of a magnetic polaron in a two-dimensional quantum antiferromagnet,"We numerically study the real-time dynamics of a single hole created in the
$t-J$ model on a square lattice. Initially, the hole spreads ballistically with
a velocity proportional to the hopping matrix element. At intermediate to long
times, the dimensionality as well as the spin background determine the hole
dynamics. A hole created in the ground state of a two dimensional quantum
antiferromagnet propagates again ballistically at long times but with a
velocity proportional to the spin exchange coupling, showing the formation of a
magnetic polaron. We provide an intuitive explanation of this dynamics in terms
of a parton construction, which leads to a good quantitative agreement with the
numerical simulations. In the limit of infinite temperature and no spin
exchange couplings, the dynamics can be approximated by a quantum random walk
on the Bethe lattice. Adding Ising interactions corresponds to an effective
disordered potential, which can dramatically slow down the hole propagation,
consistent with subdiffusive dynamics.",1907.08214v1
2019-07-24,Approximate dynamical eigenmodes of the Ising model with local spin-exchange moves,"We establish that the Fourier modes of the magnetization serve as the
dynamical eigenmodes for the two-dimensional Ising model at the critical
temperature with local spin-exchange moves, i.e., Kawasaki dynamics. We obtain
the dynamical scaling properties for these modes, and use them to calculate the
time evolution of two dynamical quantities for the system, namely the
autocorrelation function and the mean-square deviation of the line
magnetizations. At intermediate times $1 \lesssim t \lesssim L^{z_c}$, where
$z_c=4-\eta=15/4$ is the dynamical critical exponent of the model, we find that
the line magnetization undergoes anomalous diffusion. Following our recent work
on anomalous diffusion in spin models, we demonstrate that the Generalized
Langevin Equation (GLE) with a memory kernel consistently describes the
anomalous diffusion, verifying the corresponding fluctuation-dissipation
theorem with the calculation of the force autocorrelation function.",1907.10296v1
2020-12-08,The effect of active photons on dynamical frustration in cavity QED,"We study the far-from-equilibrium dynamical regimes of a many-body spin boson
model with disordered couplings relevant for cavity QED and trapped ions
experiments, using the discrete truncated Wigner approximation (DTWA). We focus
on the dynamics of spin observables upon varying the disorder strength and the
frequency of the photons, finding that the latter can considerably alter the
structure of the system's dynamical responses. When the photons evolve at a
similar rate as the spins, they can induce qualitatively distinct frustrated
dynamics characterized by either logarithmic or algebraically slow relaxation.
The latter illustrates resilience of glassy-like dynamics in the presence of
active photonic degrees of freedom, suggesting that disordered quantum many
body systems with resonant photons or phonons can display a rich diagram of
non-equilibrium responses, with near future applications for quantum
information science.",2012.04660v3
2017-11-01,Dynamics influencing ordering of a s=3 Ising antiferromagnetic on a triangular lattice,"Antiferromagnetically coupled Ising s =3 spins on a triangular lattice are
very close to ordering at zero temperature. The low temperature behaviour of a
triangular lattice with Ising spins s =3 has been simulated by using both
Glauber and Kawasaki dynamics. The formation of misfit clusters, which are
essential for destabilizing the ordered state, are inhibited by the use of
Kawasaki dynamics. The sublattice susceptibilities and the sublattice order
parameter are found to depend qualitatively on the dynamics used so that robust
ordering occurs when Kawasaki dynamics are employed. The thermal behaviour that
is found for the spin model with Kawasaki dynamics gives insight into the
observed ordering of side chains seen in a tetraphilic liquid crystal.",1711.00297v1
2019-08-06,A Construction of Dynamical Entropy on CAR Algebras,"The dynamical entropy on von Neumann algebras defined by Accardi, Ohya and
Watanabe (AOW entropy) is a natural noncommutative extension of the classical
dynamical entropy. On the other hand, quantum spin lattice systems currently
used in quantum computing and communication processes are mathematically
described by $C^*$-algebras called CAR algebras. Therefore, in order to obtain
the average amount of quantum information and to calculate the uncertainty of
the dynamics of quantum spin systems, it is necessary to define dynamical
entropy on CAR algebras. In this paper, we formulate dynamical entropy on CAR
algebras based on the construction of the AOW entropy. Moreover, we compute the
introduced entropy for a $2 \times 2$ matrix algebra case which has relation to
the quantum spin system.",1908.01955v1
2020-05-01,Self-duality triggered dynamical transition,"A basic result about the dynamics of spinless quantum systems is that the
Maryland model exhibits dynamical localization in any dimension. Here we
implement mathematical spectral theory and numerical experiments to show that
this result does not hold, when the 2-dimensional Maryland model is endowed
with spin 1/2 -- hereafter dubbed spin-Maryland (SM) model. Instead, in a
family of SM models, tuning the (effective) Planck constant drives dynamical
localization{delocalization transitions of topological nature. These
transitions are triggered by the self-duality, a symmetry generated by some
transformation in the parameter -- the inverse Planck constant -- space. This
provides significant insights to new dynamical phenomena such as what occur in
the spinful quantum kicked rotor.",2005.00232v1
2020-11-18,Temperature chaos is present in off-equilibrium spin-glass dynamics,"We find a dynamic effect in the non-equilibrium dynamics of a spin glass that
closely parallels equilibrium temperature chaos. This effect, that we name
dynamic temperature chaos, is spatially heterogeneous to a large degree. The
key controlling quantity is the time-growing spin-glass coherence length. Our
detailed characterization of dynamic temperature chaos paves the way for the
analysis of recent and forthcoming experiments. This work has been made
possible thanks to the most massive simulation to date of non-equilibrium
dynamics, carried out on the Janus~II custom-built supercomputer.",2011.09419v2
2021-10-13,Eigenvalue-based micromagnetic analysis of switching in spin-torque-driven structures,"We present an eigenvalue-based approach for studying the magnetization
dynamics in magnetic nanostructures driven by spintronic excitations, such as
spin transfer torque and spin orbit torque. The approach represents the system
dynamics in terms of normal oscillation modes (eigenstates) with corresponding
complex eigenfrequencies. The dynamics is driven by a small number of active
eigenstates and often considering just a single eigenstate is sufficient. We
develop a perturbation theory that provides semi-analytical dynamic solutions
by using eigenstates for the case in the absence of damping and spintronic
excitations as a basis. The approach provides important insights into dynamics
in such systems and allows solving several difficulties in their modeling, such
as extracting the switching current in magnetic random access memories (MRAM)
and understanding switching mechanisms. We show that the presented approach
directly predicts the critical switching current, i.e., switching current for
an infinite time. The approach also provides solutions for the switching
dynamics allowing obtaining the switching current for a finite switching time,
provided that the system symmetry is broken, e.g., by tilting the polarizer, so
that switching by a finite pulse is possible.",2110.07085v2
2022-09-14,Full investigation of nonadiabatic dynamical characterization in arbitrary quenching process,"Recently, dynamical characterization of bulk topology has been experimentally
realized under nonadiabatic sudden quench dynamics. However, it has been shown
that only the topology of final phase can be characterized when the system is
quenched from initial topologically trivial phase. In this paper, taking the
two-dimensional Chern insulator as an example, we make a thorough investigation
of different types of quenching processes under nonadiabatic slow quench
dynamics, and study not only the processes between nontrivial phase and trivial
phase, but also between the phases with different topological invariants. We
find that, under slow quench dynamics, both the initial and final topological
phase can be characterized and the topological invariant can be captured by
time-averaged spin polarization. Moreover, different types of processes can be
distinguished from the special regions where the time-averaged spin
polarization vanishes. All the dynamical characterization schemes are entirely
based on the experimentally measurable quantity time-averaged spin
polarization, and thus one can expect our findings may provide reference for
future experiments.",2209.06380v3
2022-11-10,Constructing Dynamical Systems to Model Higher Order Ising Spin Interactions and their Application in Solving Combinatorial Optimization Problems,"The Ising model provides a natural mapping for many computationally hard
combinatorial optimization problems (COPs). Consequently, dynamical
system-inspired computing models and hardware platforms that minimize the Ising
Hamiltonian, have recently been proposed as a potential candidate for solving
COPs, with the promise of significant performance benefit. However, the Ising
model, and consequently, the corresponding dynamical system-based computational
models primarily consider quadratic interactions among the nodes. Computational
models considering higher order interactions among Ising spins remain largely
unexplored. Therefore, in this work, we propose dynamical-system-based
computational models to consider higher order (>2) interactions among the Ising
spins, which subsequently, enables us to propose computational models to
directly solve many COPs that entail such higher order interactions (COPs on
hypergraphs). Specifically, we demonstrate our approach by developing dynamical
systems to compute the solution for the Boolean NAE-K-SAT (K is greater than 3)
problem as well as solve the Max-K-Cut of a hypergraph. Our work advances the
potential of the physics-inspired 'toolbox' for solving COPs.",2211.05365v1
2023-01-16,Dynamical mean-field driven spinor condensate physics beyond the single-mode approximation,"$^{23}$Na spin-1 Bose-Einstein condensates are used to experimentally
demonstrate that mean-field physics beyond the single-mode approximation can be
relevant during the non-equilibrium dynamics. The experimentally observed spin
oscillation dynamics and associated dynamical spatial structure formation
confirm theoretical predictions that are derived by solving a set of coupled
mean-field Gross-Pitaevskii equations [J. Jie et al., Phys. Rev. A 102, 023324
(2020)]. The experiments rely on microwave dressing of the $f=1$ hyperfine
states, where $f$ denotes the total angular momentum of the $^{23}$Na atom. The
fact that beyond single-mode approximation physics at the mean-field level,
i.e., spatial mean-field dynamics that distinguishes the spatial density
profiles associated with different Zeeman levels, can -- in certain parameter
regimes -- have a pronounced effect on the dynamics when the spin healing
length is comparable to or larger than the size of the Bose-Einstein condensate
has implications for using Bose-Einstein condensates as models for quantum
phase transitions and spin squeezing studies as well as for non-linear SU(1,1)
interferometers.",2301.06461v1
2009-03-12,Pure quantum dephasing of a solid state electron spin qubit in a large nuclear spin bath coupled by long-range hyperfine-mediated interactions,"We investigate decoherence due to pure dephasing of a localized spin qubit
interacting with a nuclear spin bath. Although in the limit of a very large
magnetic field the only decoherence mechanism is spectral diffusion due to
dipolar flip-flops of nuclear spins, with decreasing field the
hyperfine-mediated interactions between the nuclear spins become important. We
take advantage of their long-range nature, and resum the leading terms in an
1/N expansion of the decoherence time-evolution function (N, being the number
of nuclear spins interacting appreciably with the electron spin, is large). For
the case of the thermal uncorrelated bath we show that our theory is applicable
down to low magnetic fields (~10 mT for a large dot with N=10^6) allowing for
comparison with recent experiments in GaAs quantum dot spin qubits. Within this
approach we calculate the free induction decay and spin echo decoherence in
GaAs and InGaAs as a function of the number of the nuclei in the bath (i.e. the
quantum dot size) and the magnetic field. Our theory for free induction decay
in a narrowed nuclear bath is shown to agree with the exact solution for
decoherence due to hyperfine-mediated interaction which can be obtained when
all the nuclei-electron coupling constants are identical. For the spin echo
evolution we show that the dominant decoherence process at low fields is due to
interactions between nuclei having significantly different Zeeman energies
(i.e. nuclei of As and two isotopes of Ga in GaAs), and we compare our results
with recent measurements of spin echo signal of a single spin confined in a
GaAs quantum dot. For the same set of parameters we perform calculations of
decoherence under various dynamical decoupling pulse sequences, and predict the
effect of these sequences in low B regime in GaAs.",0903.2256v3
2010-07-07,Hole spin relaxation in intrinsic and $p$-type bulk GaAs,"We investigate hole spin relaxation in intrinsic and $p$-type bulk GaAs from
a fully microscopic kinetic spin Bloch equation approach. In contrast to the
previous study on hole spin dynamics, we explicitly include the intraband
coherence and the nonpolar hole-optical-phonon interaction, both of which are
demonstrated to be of great importance to the hole spin relaxation. The
relative contributions of the D'yakonov-Perel' and Elliott-Yafet mechanisms on
hole spin relaxation are also analyzed. In our calculation, the screening
constant, playing an important role in the hole spin relaxation, is treated
with the random phase approximation. In intrinsic GaAs, our result shows good
agreement with the experiment data at room temperature, where the hole spin
relaxation is demonstrated to be dominated by the Elliott-Yafet mechanism. We
also find that the hole spin relaxation strongly depends on the temperature and
predict a valley in the density dependence of the hole spin relaxation time at
low temperature due to the hole-electron scattering. In $p$-type GaAs, we
predict a peak in the spin relaxation time against the hole density at low
temperature, which originates from the distinct behaviors of the screening in
the degenerate and nondegenerate regimes. The competition between the screening
and the momentum exchange during scattering events can also lead to a valley in
the density dependence of the hole spin relaxation time in the low density
regime. At high temperature, the effect of the screening is suppressed due to
the small screening constant. Moreover, we predict a nonmonotonic dependence of
the hole spin relaxation time on temperature associated with the screening
together with the hole-phonon scattering. Finally, we find that the
D'yakonov-Perel' mechanism can markedly contribute to the .... (omitted due to
the limit of space)",1007.1134v3
2015-10-09,Limits On The Spin Up Of Stellar-Mass Black Holes Through A Spiral Stationary Accretion Shock Instability,"The spin of a number of black holes (BHs) in binary systems has been
measured. In the case of BHs found in low-mass X-ray binaries (LMXBs) the
observed values are in agreement with some theoretical predictions based on
binary stellar evolution. However, using the same evolutionary models, the
calculated spins of BHs in high-mass X-ray binaries (HMXBs) fall short compared
to the observations. A possible solution to this conundrum is the accretion of
high-specific-angular-momentum material after the formation of the BH, although
this requires accretion above the Eddington limit. Another suggestion is that
the observed high values of the BHs spin could be the result of an asymmetry
during Core Collapse (CC). The only available energy to spin up the compact
object during CC is its binding energy. A way to convert it to rotational
kinetic energy is by using a Standing Accretion Shock Instability (SASI), which
can develop during CC and push angular momentum into the central compact object
through a spiral mode ($m = 1$). Here we study the CC-SASI scenario and
discuss, in the case of LMXBs and HMXBs, the limits for the spin of a
stellar-mass BHs. Our results predict a strong dichotomy in the maximum spin of
low-mass compact objects and massive BHs found in HMXBs. The maximum spin value
($|a_\star|$) for a compact object near the mass boundary between BHs and NSs
is found to be somewhere between 0.27 and 0.38, depending on whether secular or
dynamical instabilities limit the efficiency of the spin up process. For more
massive BHs, such as those found in HMXBs, the natal spin is substantially
smaller and for $M_{\rm BH}\!>\!8~M_\odot$ spin is limited to values
$|a_\star|\!\lesssim\!0.05$. Therefore we conclude that the observed high spins
of BHs in HMXBs cannot be the result of a CC-SASI spin up.",1510.02805v1
2017-06-05,Robust techniques for polarization and detection of nuclear spin ensembles,"Highly sensitive nuclear spin detection is crucial in many scientific areas
including nuclear magnetic resonance spectroscopy (NMR), imaging (MRI) and
quantum computing. The tiny thermal nuclear spin polarization represents a
major obstacle towards this goal which may be overcome by Dynamic Nuclear Spin
Polarization (DNP) methods. The latter often rely on the transfer of the
thermally polarized electron spins to nearby nuclear spins, which is limited by
the Boltzmann distribution of the former. Here we demonstrate the polarization
and read out of a nuclear spin bath consisting of $^{13}$C nuclear spins in
diamond by using a single nitrogen-vacancy (NV) center. Our method utilizes
microwave dressed states to transfer the NV's high ($>$~92~\%) non-equilibrium
electron spin polarization induced by short laser pulses to the surrounding
carbon nuclear spins, where the NV is repeatedly repolarized optically, thus
providing an effectively infinite polarization reservoir. A saturation of the
polarization in the nuclear ""frozen core"" is achieved, which is confirmed by
the decay of the polarization transfer signal and shows an excellent agreement
with theoretical simulations. Hereby we introduce the Polarization Read Out by
Polarization Inversion (PROPI) method as a quantitative magnetization measure
of the nuclear spin bath. Moreover, we show that using the integrated solid
effect both for single and double quantum transitions a nuclear spin
polarization can be achieved even when the static magnetic field is not aligned
along the NV's crystal axis. This opens a path for the application of our DNP
technique to spins in and outside of nanodiamonds, enabling their application
as MRI tracers.",1706.01315v2
2018-12-19,"Nonlinear-in-spin effects in effective-one-body waveform models of spin-aligned, inspiralling, neutron star binaries","Spinning neutron stars acquire a quadrupole moment due to their own rotation.
This quadratic-in-spin, self-spin effect depends on the equation of state (EOS)
and affects the orbital motion and rate of inspiral of neutron star binaries.
We incorporate the EOS-dependent self-spin (or monopole-quadrupole) terms in
the spin-aligned effective-one-body (EOB) waveform model TEOBResumS at
next-to-next-to-leading (NNLO) order, together with other (bilinear, cubic and
quartic) nonlinear-in-spin effects (at leading order, LO). The structure of the
Hamiltonian of TEOBResumS is such that it already incorporates, in the binary
black hole case, the recently computed quartic-in-spin LO term. Using the
gauge-invariant characterization of the phasing provided by the function
$Q_\omega=\omega^2/\dot{\omega}$ of $\omega=2\pi f$ , where $f$ is the
gravitational wave frequency, we study the EOS dependence of the self-spin
effects and show that: (i) the next-to-leading order (NLO) and NNLO
monopole-quadrupole corrections yield increasingly phase-accelerating effects
compared to the corresponding LO contribution; (ii) the standard TaylorF2
post-Newtonian (PN) treatment of NLO (3PN) EOS-dependent self-spin effects
makes their action stronger than the corresponding EOB description; (iii) the
addition to the standard 3PN TaylorF2 post-Newtonian phasing description of
self-spin tail effects at LO allows one to reconcile the self-spin part of the
TaylorF2 PN phasing with the corresponding TEOBResumS one up to dimensionless
frequencies $M\omega\simeq 0.04-0.06$. By generating the inspiral dynamics
using the post-adiabatic approximation, incorporated in a new implementation of
TEOBResumS, one finds that the computational time needed to obtain a typical
waveform (including all multipoles up to $\ell=8$) from 10 Hz is of the order
of 0.4 sec.",1812.07923v1
2019-04-22,Colloquium: Atomic spin chains on surfaces,"In the present Colloquium, we focus on the properties of 1-D magnetic systems
on solid surfaces. From the emulation of 1-D quantum phases to the potential
realization of Majorana edge states, spin chains are unique systems to study.
The advent of scanning tunnelling microscope (STM) based techniques has
permitted us to engineer spin chains in an atom-by-atom fashion via atom
manipulation and to access their spin states on the ultimate atomic scale.
Here, we present the current state of research on spin correlations and
dynamics of atomic spin chains as studied by the STM. After a brief review of
the main properties of spin chains on solid surfaces, we classify spin chains
according to the coupling of their magnetic moments with the holding substrate.
This classification scheme takes into account that the nature and lifetimes of
the spin-chain excitation intrinsically depend on the holding substrate. We
first show the interest of using insulating layers on metals, which generally
results in an increase in the spin state's lifetimes such that their quantized
nature gets evident and they are individually accessible. Next, we show that
the use of semiconductor substrates promises additional control through the
tunable electron density via doping. When the coupling to the substrate is
increased for spin chains on metals, the substrate conduction electron mediated
interactions can lead to emergent exotic phases of the coupled spin
chain-substrate conduction electron system. A particularly interesting example
is furnished by superconductors. Magnetic impurities induce states in the
superconducting gap. Due to the extended nature of the spin chain, the in-gap
states develop into bands that can lead to the emergence of 1-D topological
superconductivity and, consequently to the appearance of Majorana edge states.",1904.09941v1
2022-03-15,Dressed-state control of effective dipolar interaction between strongly-coupled solid-state spins,"Strong interactions between spins in many-body solid-state quantum system is
a crucial resource for exploring and applying non-classical states. In
particular, electronic spins associated with defects in diamond system are a
leading platform for the study of collective quantum phenomena and for quantum
technology applications. While such solid-state quantum defect systems have the
advantage of scalability and operation under ambient conditions, they face the
key challenge of controlling interactions between the defects spins, since the
defects are spatially fixed inside the host lattice with relative positions
that cannot be well controlled during fabrication. In this work, we present a
dressed-state approach to control the effective dipolar coupling between
solid-state spins; and then demonstrate this scheme experimentally using two
strongly-coupled nitrogen vacancy (NV) centers in diamond. Including Rabi
driving terms between the m$_s$ = 0 and $\pm$1 states in the NV spin
Hamiltonian allows us to turn on and off or tune the effective dipolar coupling
between two NV spins. Through Ramsey spectroscopy, we detect the change of the
effective dipolar field generated by the control NV spin prepared in different
dressed states. To observe the change of interaction dynamics, we then deploy
spin-lock-based polarization transfer measurements via a Hartmann-Hahn matching
condition between two NV spins in different dressed states. We perform
simulations that indicate the promise for this robust scheme to control the
distribution of interaction strengths in strongly-interacting spin systems,
including interaction strength homogenization in a spin ensemble, which can be
a valuable tool for studying non-equilibrium quantum phases and generating high
fidelity multi-spin correlated states for quantum-enhanced sensing.",2203.07610v2
2022-07-14,Neutron Scattering Study of Fluctuating and Static Spin Correlations in the Anisotropic Spin Glass Fe$_2$TiO$_5$,"The anisotropic spin glass transition, in which spin freezing is observed
only along the c-axis in pseudobrookite Fe$_2$TiO$_5$, has long been perplexing
because the Fe$^{3+}$ moments (d$^5$) are expected to be isotropic. Recently,
neutron diffraction demonstrated that surfboard-shaped antiferromagnetic
nanoregions coalesce above the glass transition temperature, T$_g$ $\approx$ 55
K, and a model was proposed in which the freezing of the fluctuations of the
surfboards' magnetization leads to the anisotropic spin glass state. Given this
new model, we have carried out high resolution inelastic neutron scattering
measurements of the spin-spin correlations to understand the temperature
dependence of the intra-surfboard spin dynamics on neutron (picosecond)
time-scales. Here, we report on the temperature-dependence of the spin
fluctuations measured from single crystal Fe$_2$TiO$_5$. Strong quasi-elastic
magnetic scattering, arising from intra-surfboard correlations, is observed
well above T$_g$. The spin fluctuations possess a steep energy-wave vector
relation and are indicative of strong exchange interactions, consistent with
the large Curie-Weiss temperature. As the temperature approaches T$_g$ from
above, a shift in spectral weight from inelastic to elastic scattering is
observed. At various temperatures between 4 K and 300 K, a characteristic
relaxation rate of the fluctuations is determined. Despite the freezing of the
majority of the spin correlations, an inelastic contribution remains even at
base temperature, signifying the presence of fluctuating intra-surfboard spin
correlations to at least T/T$_g$ $\approx$ 0.1 consistent with a description of
Fe$_2$TiO$_5$ as a hybrid between conventional and geometrically frustrated
spin glasses.",2207.07085v1
2023-12-12,Supermassive black hole spin evolution in cosmological simulations with OpenGadget3,"Mass and spin of massive black holes (BHs) at the centre of galaxies evolve
due to gas accretion and mergers with other BHs. Besides affecting e.g. the
evolution of relativistic jets, the BH spin determines the efficiency with
which the BH radiates energy. Using cosmological, hydrodynamical simulations,
we investigate the evolution of the BH spin across cosmic time and its role in
controlling the joint growth of supermassive BHs and their host galaxies. We
implement a sub-resolution prescription that models the BH spin, accounting for
both BH coalescence and misaligned accretion through a geometrically thin,
optically thick disc. We investigate how BH spin evolves in two idealised
setups, in zoomed-in simulations, and in a cosmological volume. The latter
simulation allows us to retrieve statistically robust results as for the
evolution and distribution of BH spins as a function of BH properties. We find
that BHs with $M_{\rm BH}\lesssim 2 \times 10^{7}\;{\rm M}_{\odot}$ grow
through gas accretion, occurring mostly in a coherent fashion that favours
spin-up. Above $M_{\rm BH}\gtrsim 2 \times 10^{7}~{\rm M}_{\odot}$ the gas
angular momentum directions of subsequent accretion episodes are often
uncorrelated with each other. The probability of counter-rotating accretion and
hence spin-down increases with BH mass. In the latter mass regime, BH
coalescence plays an important role. The spin magnitude displays a wide variety
of histories, depending on the dynamical state of the gas feeding the BH and
the relative contribution of mergers and gas accretion. As a result of their
combined effect, we observe a broad range of values of the spin magnitude at
the high-mass end. Our predictions for the distributions of BH spin and
spin-dependent radiative efficiency as a function of BH mass are in very good
agreement with observations.",2312.07657v1
2020-05-31,Exact dynamics of the homogeneous two-qubit $XXZ$ central spin model with the spin bath prepared in superpositions of symmetric Dicke states,"We obtain exact dynamics of a two-qubit central spin model (CSM) consisting
of two interacting qubits homogeneously coupled to a spin bath via the
$XXZ$-type coupling, with the bath initially prepared in linear superpositions
of the symmetric Dicke states. Using the interaction picture Hamiltonian with
respect to the non-spin-flipping part of the model, we derive a sequence of
equations of motion within each magnetization sector satisfied by the
probability amplitudes of the time-evolved state. These equations of motion
admit analytical solutions for the single-qubit CSM in which one of the two
central qubits decouples from the rest of the system. Based on this, we provide
a quantitative interpretation to the observed collapse-revival phenomena in the
single-qubit Rabi oscillations when the bath is prepared in the spin coherent
state. We then study the disentanglement and coherence dynamics of two
initially entangled noninteracting qubits when the two qubits interact with
individual baths or with a common bath. For individual baths the coherent
dynamics is found to positively correlated to the single-qubit purity dynamics,
and entanglement sudden disappearance and revivals are observed in both cases.
The entanglement creation of two initially separable qubits coupled to a common
bath is also studied and collapse and revival behaviors in the entanglement
dynamics are observed. Choosing the equally weighted state and the $W$-class
states as the bath initial states, we finally study the dynamics of
entanglement between two individual bath spins and demonstrate the entanglement
sharing mechanism in such a system.",2006.00550v2
2006-03-07,Zero Point Entropy in Stuffed Spin Ice,"The third law of thermodynamics dictates that the entropy of a system in
thermal equilibrium goes to zero as its temperature approaches absolute zero.
In ice, however, a ""zero point"" or residual entropy can be measured -
attributable to a high degeneracy in the energetically preferred positions of
the hydrogen ions associated with the so-called ""ice rules"".1,2 Remarkably, the
spins in certain magnetic materials with the pyrochlore structure of
corner-sharing tetrahedra, called ""spin ice"", have an equivalent degeneracy of
energetically preferred states and also have been shown to display a zero point
entropy.3,4,5,6,7 Here we report that we have chemically altered Ho2Ti2O7 spin
ice by stuffing extra Ho magnetic moments into normally non-magnetic Ti sites
surrounding the Ho tetrahedra. The resulting series, Ho2(Ti2-xHox)O7-x/2,
provides a unique opportunity to study the effects of increased connectivity
between spins on a frustrated lattice. Surprisingly, the measured zero point
entropy per spin appears unchanged by these excess spins, and the dynamic
freezing of the spins is suppressed to lower temperatures. The results
challenge our understanding of the spin ice state, and suggest a new avenue for
using chemistry to study both ice-like frustration and the properties of the
broad family of geometrically frustrated magnets based on the pyrochlore
structure.",0603146v1
2009-03-03,Detecting and Switching Magnetization of Stoner Nanograin in Non-local Spin Valve,"The magnetization detection and switching of an ultrasmall Stoner nanograin
in a non-local spin valve (NLSV) device is studied theoretically. With the help
of the rate equations, a unified description can be presented on the same
footing for the NLSV signal that reads out the magnetization, and for the
switching process. The setup can be viewed as that the grain is connected to
two non-magnetic leads via sequential tunneling. In one lead, the chemical
potentials for spin-up and -down electrons are split due to the spin injection
in the NLSV. This splitting (or the spin bias) is crucial to the NLSV signal
and the critical condition to the magnetization switching. By using the
standard spin diffusion equation and parameters from recent NLSV device, the
magnitude of the spin bias is estimated, and found large enough to drive the
magnetization switching of the cobalt nanograin reported in earlier
experiments. A microscopic interpretation of NLSV signal in the sequential
tunneling regime is thereby raised, which show properties due to the ultrasmall
size of the grain. The dynamics at the reversal point shows that there may be a
spin-polarized current instead of the anticipated pure spin current flowing
during the reversal due to the electron accumulation in the floating lead used
for the readout of NLSV signal.",0903.0456v2
2009-03-26,A model independent spin analysis of fundamental particles using azimuthal asymmetries,"Exploiting the azimuthal angle dependence of the density matrices we
construct observables that directly measure the spin of a heavy unstable
particle. A novelty of the approach is that the analysis of the azimuthal angle
dependence in a frame other than the usual helicity frame offers an independent
cross-check on the extraction of the spin. Moreover, in some instances when the
transverse polarisation tensor of highest rank is vanishing, for an accidental
or dynamical reason, the standard azimuthal asymmetries vanish and would lead
to a measurement with a wrong spin assignment. In a frame such as the one we
construct, the correct spin assignment would however still be possible. The
method gives direct information about the spin of the particle under
consideration and the same event sample can be used to identify the spins of
each particle in a decay chain. A drawback of the method is that it is
instrumental only when the momenta of the test particle can be reconstructed.
However we hope that it might still be of use in situations with only partial
reconstruction. We also derive the conditions on the production and decay
mechanisms for the spins, and hence the polarisations, to be measured at a
collider experiment. As an example for the use of the method we consider the
simultaneous reconstruction, at the partonic level, of the spin of both the top
and the $W$ in top pair production in $e^+ e^-$ in the semi-leptonic channel.",0903.4705v1
2010-06-22,Loop algorithm for classical Heisenberg models with spin-ice type degeneracy,"In many frustrated Ising models, a single-spin flip dynamics is frozen out at
low temperatures compared to the dominant interaction energy scale because of
the discrete ""multiple valley"" structure of degenerate ground-state manifold.
This makes it difficult to study low-temperature physics of these frustrated
systems by using Monte Carlo simulation with the standard single-spin flip
algorithm. A typical example is the so-called spin ice model, frustrated
ferromagnets on the pyrochlore lattice. The difficulty can be avoided by a
global-flip algorithm, the loop algorithm, that enables to sample over the
entire discrete manifold and to investigate low-temperature properties. We
extend the loop algorithm to Heisenberg spin systems with strong easy-axis
anisotropy in which the ground-state manifold is continuous but still retains
the spin-ice type degeneracy. We examine different ways of loop flips and
compare their efficiency. The extended loop algorithm is applied to the
following two models, a Heisenberg antiferromagnet with easy-axis anisotropy
along the z axis, and a Heisenberg spin ice model with the local <111>
easy-axis anisotropy. For both models, we demonstrate high efficiency of our
loop algorithm by revealing the low-temperature properties which were hard to
access by the standard single-spin flip algorithm. For the former model, we
examine the possibility of order-from-disorder and critically check its
absence. For the latter model, we elucidate a gas-liquid-solid transition,
namely, crossover or phase transition among paramagnet, spin-ice liquid, and
ferromagnetically-ordered ice-rule state.",1006.4300v2
2010-08-05,Nuclear Feedback in a Single Electron-Charged Quantum Dot under Pulsed Optical Control,"Electron spins in quantum dots under coherent control exhibit a number of
novel feedback processes. Here, we present experimental and theoretical
evidence of a feedback process between nuclear spins and a single electron spin
in a single charged InAs quantum dot, controlled by the coherently modified
probability of exciting a trion state. We present a mathematical model
describing competition between optical nuclear pumping and nuclear
spin-diffusion inside the quantum dot. The model correctly postdicts the
observation of a hysteretic sawtooth pattern in the free-induction-decay of the
single electron spin, hysteresis while scanning a narrowband laser through the
quantum dot's optical resonance frequency, and non-sinusoidal fringes in the
spin echo. Both the coherent electron-spin rotations, implemented with
off-resonant ultrafast laser pulses, and the resonant narrow-band optical
pumping for spin initialization interspersed between ultrafast pulses, play a
role in the observed behavior. This effect allows dynamic tuning of the
electron Larmor frequency to a value determined by the pulse timing,
potentially allowing more complex coherent control operations.",1008.0912v2
2010-10-30,Spin-orbit qubit in a semiconductor nanowire,"Motion of electrons can influence their spins through a fundamental effect
called spin-orbit interaction. This interaction provides a way to electrically
control spins and as such lies at the foundation of spintronics. Even at the
level of single electrons, spin-orbit interaction has proven promising for
coherent spin rotations. Here we report a spin-orbit quantum bit implemented in
an InAs nanowire, where spin-orbit interaction is so strong that spin and
motion can no longer be separated. In this regime we realize fast qubit
rotations and universal single qubit control using only electric fields. We
enhance coherence by dynamically decoupling the qubit from the environment. Our
qubits are individually addressable: they are hosted in single-electron quantum
dots, each of which has a different Land\'e g-factor. The demonstration of a
nanowire qubit opens ways to harness the advantages of nanowires for use in
quantum computing. Nanowires can serve as one-dimensional templates for
scalable qubit registers. Unique to nanowires is the possibility to easily vary
the material even during wire growth. Such flexibility can be used to design
wires with suppressed decoherence and push semiconductor qubit fidelities
towards error-correction levels. Furthermore, electrical dots can be integrated
with optical dots in p-n junction nanowires. The coherence times achieved here
are sufficient for the conversion of an electronic qubit into a photon, the
flying qubit, for long-distance quantum communication.",1011.0064v1
2011-01-03,The building blocks of magnonics,"Novel material properties can be realized by designing waves' dispersion
relations in artificial crystals. The crystal's structural length scales may
range from nano- (light) up to centimeters (sound waves). Because of their
emergent properties these materials are called metamaterials. Different to
photonics, where the dielectric constant dominantly determines the index of
refraction, in a ferromagnet the spin-wave index of refraction can be
dramatically changed already by the magnetization direction. This allows a
different flexibility in realizing dynamic wave guides or spin-wave switches.
The present review will give an introduction into the novel functionalities of
spin-wave devices, concepts for spin-wave based computing and magnonic
crystals. The parameters of the magnetic metamaterials are adjusted to the
spin-wave k-vector such that the magnonic band structure is designed. However,
already the elementary building block of an antidot lattice, the singular hole,
owns a strongly varying internal potential determined by its magnetic dipole
field and a localization of spin-wave modes. Photo-magnonics reveal a way to
investigate the control over the interplay between localization and
delocalization of the spin-wave modes using femtosecond lasers, which is a
major focus of this review. We will discuss the crucial parameters to realize
free Bloch states and how, by contrast, a controlled localization might allow
to gradually turn on and manipulate spin-wave interactions in spin-wave based
devices in the future.",1101.0479v2
2011-01-04,Universal Spin Transport in a Strongly Interacting Fermi Gas,"Transport of fermions is central in many fields of physics. Electron
transport runs modern technology, defining states of matter such as
superconductors and insulators, and electron spin, rather than charge, is being
explored as a new carrier of information [1]. Neutrino transport energizes
supernova explosions following the collapse of a dying star [2], and
hydrodynamic transport of the quark-gluon plasma governed the expansion of the
early Universe [3]. However, our understanding of non-equilibrium dynamics in
such strongly interacting fermionic matter is still limited. Ultracold gases of
fermionic atoms realize a pristine model for such systems and can be studied in
real time with the precision of atomic physics [4, 5]. It has been established
that even above the superfluid transition such gases flow as an almost perfect
fluid with very low viscosity [3, 6] when interactions are tuned to a
scattering resonance. However, here we show that spin currents, as opposed to
mass currents, are maximally damped, and that interactions can be strong enough
to reverse spin currents, with opposite spin components reflecting off each
other. We determine the spin drag coeffcient, the spin diffusivity, and the
spin susceptibility, as a function of temperature on resonance and show that
they obey universal laws at high temperatures. At low temperatures, the spin
diffusivity approaches a minimum value set by the ratio of the reduced Planck's
constant to the atomic mass. For repulsive interactions, our measurements
appear to exclude a metastable ferromagnetic state [7-9].",1101.0780v1
2013-07-25,Next-to-leading tail-induced spin-orbit effects in the gravitational radiation flux of compact binaries,"The imprint of non-linearities in the propagation of gravitational waves ---
the tail effect --- is responsible for new spin contributions to the energy
flux and orbital phasing of spinning black hole binaries. The spin-orbit
(linear in spin) contribution to this effect is currently known at leading
post-Newtonian order, namely 3PN for maximally spinning black holes on
quasi-circular orbits. In the present work, we generalize these tail-originated
spin-orbit terms to the next-to-leading 4PN order. This requires in particular
extending previous results on the dynamical evolution of precessing compact
binaries. We show that the tails represent the only spin-orbit terms at that
order for quasi-circular orbits, and we find perfect agreement with the known
result for a test particle around a Kerr black hole, computed by perturbation
theory. The BH-horizon absorption terms have to be added to the PN result
computed here. Our work completes the knowledge of the spin-orbit effects to
the phasing of compact binaries up to the 4PN order, and will allow the
building of more faithful PN templates for the inspiral phase of black hole
binaries, improving the capabilities of ground-based and space-based
gravitational wave detectors.",1307.6793v2
2013-12-03,Quantum group spin nets: refinement limit and relation to spin foams,"So far spin foam models are hardly understood beyond a few of their basic
building blocks. To make progress on this question, we define analogue spin
foam models, so called spin nets, for quantum groups $\text{SU}(2)_k$ and
examine their effective continuum dynamics via tensor network renormalization.
In the refinement limit of this coarse graining procedure, we find a vast
non-trivial fixed point structure beyond the degenerate and the $BF$ phase. In
comparison to previous work, we use fixed point intertwiners, inspired by
Reisenberger's construction principle [1] and the recent work [2], as the
initial parametrization. In this new parametrization fine tuning is not
required in order to flow to these new fixed points. Encouragingly, each fixed
point has an associated extended phase, which allows for the study of phase
transitions in the future. Finally we also present an interpretation of spin
nets in terms of melonic spin foams. The coarse graining flow of spin nets can
thus be interpreted as describing the effective coupling between two spin foam
vertices or space time atoms.",1312.0905v2
2013-12-17,Measurement of the magnetic interaction between two electrons,"Electrons have an intrinsic, indivisible, magnetic dipole aligned with their
internal angular momentum (spin). The magnetic interaction between two
electrons can therefore impose a change in their spin orientation. This
process, however, was never observed in experiment. The challenge is two-fold.
At the atomic scale, where the coupling is relatively large, the magnetic
interaction is often overshadowed by the much larger coulomb exchange
counterpart. In typical situations where exchange is negligible, magnetic
interactions are also very weak and well below ambient magnetic noise. Here we
report on the first measurement of the magnetic interaction between two
electronic spins. To this end, we used the ground state valence electrons of
two $^{88}$Sr$^+$ ions, co-trapped in an electric Paul trap and separated by
more than two micrometers. We measured the weak, millihertz scale
(alternatively $10^{-18}$ eV or $10^{-14}$ K), magnetic interaction between
their electronic spins. This, in the presence of magnetic noise that was six
orders of magnitude larger than the respective magnetic fields the electrons
apply on each other. Cooperative spin dynamics was kept coherent for 15 s
during which spin-entanglement was generated. The sensitivity necessary for
this measurement was provided by restricting the spin evolution to a
Decoherence-Free Subspace (DFS) which is immune to collective magnetic field
noise. Finally, by varying the separation between the two ions, we were able to
recover the inverse cubic distance dependence of the interaction. The reported
method suggests an alternative route to the search of long-range anomalous
spin-spin forces and can be generalized to include Quantum Error Correction
codes for other cases of extremely weak signal detection.",1312.4881v1
2014-12-31,Hyperfine spin qubits in irradiated malonic acid: heat-bath algorithmic cooling,"The ability to perform quantum error correction is a significant hurdle for
scalable quantum information processing. A key requirement for multiple-round
quantum error correction is the ability to dynamically extract entropy from
ancilla qubits. Heat-bath algorithmic cooling is a method that uses quantum
logic operations to move entropy from one subsystem to another, and permits
cooling of a spin qubit below the closed system (Shannon) bound.
Gamma-irradiated, $^{13}$C-labeled malonic acid provides up to 5 spin qubits: 1
spin-half electron and 4 spin-half nuclei. The nuclei are strongly hyperfine
coupled to the electron and can be controlled either by exploiting the
anisotropic part of the hyperfine interaction or by using pulsed
electron-nuclear double resonance (ENDOR) techniques. The electron connects the
nuclei to a heat-bath with a much colder effective temperature determined by
the electron's thermal spin polarization. By accurately determining the full
spin Hamiltonian and performing realistic algorithmic simulations, we show that
an experimental demonstration of heat-bath algorithmic cooling beyond the
Shannon bound is feasible in both 3-qubit and 5-qubit variants of this spin
system. Similar techniques could be useful for polarizing nuclei in molecular
or crystalline systems that allow for non-equilibrium optical polarization of
the electron spin.",1501.00082v2
2015-03-23,Strong mechanical driving of a single electron spin,"Quantum devices for sensing and computing applications require coherent
quantum systems which can be manipulated in a fast and robust way. Such quantum
control is typically achieved using external electric or magnetic fields which
drive the system's orbital or spin degrees of freedom. However, most of these
approaches require complex and unwieldy antenna or gate structures, and with
few exceptions are limited to the regime of weak driving. Here, we present a
novel approach to strongly and coherently drive a single electron spin in the
solid state using internal strain fields in an integrated quantum device.
Specifically, we study individual Nitrogen-Vacancy (NV) spins embedded in
diamond mechanical oscillators and exploit the intrinsic strain coupling
between spin and oscillator to strongly drive the spins. As hallmarks of the
strong driving regime, we directly observe the energy spectrum of the emerging
phonon-dressed states and employ our strong, continuous driving for enhancement
of the NV spin coherence time. Our results constitute a first step towards
strain-driven, integrated quantum devices and open new perspectives to
investigate unexplored regimes of strongly driven multi-level systems and to
study exotic spin dynamics in hybrid spin-oscillator devices.",1503.06793v1
2015-08-25,On Testing the Kerr Metric of the Massive Black Hole in the Galactic Center via Stellar Orbital Motion: Full General Relativistic Treatment,"The S-stars in the Galactic center (GC) are anticipated to provide unique
dynamical constraint on the spin of the GC massive black hole (MBH). In this
paper, we develop a fast full general relativistic method to simultaneously
constrain the MBH mass, spin, and spin direction by considering both the motion
of a star and the propagation of photons from the star to a distant observer.
Assuming some example stars, we demonstrate that the spin-induced effects on
the projected trajectory and redshift curve of a star depend on both the value
and the direction of the spin. The maximum effects over a full orbit can differ
by a factor upto more than one order of magnitude for cases with significantly
different spin directions. Adopting the Markov Chain Monte Carlo fitting
technique, we illustrate that the spin of the GC MBH is likely to be well
constrained by using the motion of S0-2/S2 over a period of ~45yr if it is
close to one and the astrometric and spectroscopic precisions (sigma_p,sigma_Z)
can be as high as (10muas, 1km/s). In the mean time, the distance from the sun
to the GC and the MBH mass can also be constrained to an unprecedented accuracy
(0.01%-0.1%). If there exists a star with semimajor axis significantly smaller
than that of S0-2/S2 and eccentricity larger than that of S0-2/S2, the MBH spin
can be constrained with high accuracy over a period of <~10yr for
(sigma_p,sigma_Z) ~ (10muas,1km/s), even if the spin is only moderately large
(>~0.2).",1508.06293v1
2016-09-28,Correlation induced out-of-phase plasmon in an electron liquid,"We derive from first principles the existence of a low-frequency plasmon in a
strongly coupled three-dimensional homogeneous electron gas (HEG). From its
dispersion and its satisfaction of the 3rd frequency sum rule we identify it
with the conjectured magnetic excitation in the HEG. This excitation, is
maintained by the out-of-phase oscillations of the spin-up and spin-down
densities of the electron liquid, but governed solely by the Coulomb
interaction between the particles. The frequency square of this mode is
proportional to the overlap ($r=0$) (absolute) value of the spin-up/spin-down
correlation function, and thus slightly affected by, but not contingent upon
the degree of polarization of the electron liquid. We estimate the spectral
weight of the mode: it is expected to be governed by electron-electron
collision induced spin drag. The spectral weight is manifest in the partial
spin-resolved dynamical structure functions and it is proportional to the
product of the densities of the two spin components. An independent derivation
based on a generalized Feynman Ansatz corroborates our result. The relationship
to the recently identified ""spin plasmon"" excitation is discussed. It is
pointed out that a scattering experiment with polarized neutrons or polarized
X-rays may be possible avenues to observe equilibrium fluctuations associated
with these modes and also to provide information on the spin drag coefficient
in the HEG.",1609.09029v3
2017-02-16,Theory of current-induced spin polarizations in an electron gas,"We derive the Bloch equations for the spin dynamics of a two-dimensional
electron gas in the presence of spin-orbit coupling. For the latter we consider
both the intrinsic mechanisms of structure inversion asymmetry (Rashba) and
bulk inversion asymmetry (Dresselhaus), and the extrinsic ones arising from the
scattering from impurities. The derivation is based on the SU(2) gauge-field
formulation of the Rashba-Dresselhaus spin-orbit coupling. Our main result is
the identification of a new spin-generation torque arising from the
Elliot-Yafet process, which opposes a similar term arising from the
Dyakonov-Perel process. The new spin-generation torque contributes to the
current-induced spin polarization (CISP) -- also known as the Edelstein or
inverse spin-galvanic effect. As a result, the behavior of the CISP turns out
to be more complex than one would surmise from consideration of the internal
Rashba-Dresselhaus fields alone. In particular, the symmetry of the
current-induced spin polarization does not necessarily coincide with that of
the internal Rashba-Dresselhaus field, and an out-of-plane component of the
CISP is generally predicted, as observed in recent experiments. We also discuss
the extension to the three-dimensional electron gas, which may be relevant for
the interpretation of experiments in thin films.",1702.04887v1
2017-03-01,Optimized Quantification of Spin Relaxation Times in the Hybrid State,"Purpose: The analysis of optimized spin ensemble trajectories for relaxometry
in the hybrid state.
  Methods: First, we constructed visual representations to elucidate the
differential equation that governs spin dynamics in hybrid state. Subsequently,
numerical optimizations were performed to find spin ensemble trajectories that
minimize the Cram\'er-Rao bound for $T_1$-encoding, $T_2$-encoding, and their
weighted sum, respectively, followed by a comparison of the Cram\'er-Rao bounds
obtained with our optimized spin-trajectories, as well as Look-Locker and
multi-spin-echo methods. Finally, we experimentally tested our optimized spin
trajectories with in vivo scans of the human brain.
  Results: After a nonrecurring inversion segment on the southern hemisphere of
the Bloch sphere, all optimized spin trajectories pursue repetitive loops on
the northern half of the sphere in which the beginning of the first and the end
of the last loop deviate from the others. The numerical results obtained in
this work align well with intuitive insights gleaned directly from the
governing equation. Our results suggest that hybrid-state sequences outperform
traditional methods. Moreover, hybrid-state sequences that balance $T_1$- and
$T_2$-encoding still result in near optimal signal-to-noise efficiency. Thus,
the second parameter can be encoded at virtually no extra cost.
  Conclusion: We provide insights regarding the optimal encoding processes of
spin relaxation times in order to guide the design of robust and efficient
pulse sequences. We find that joint acquisitions of $T_1$ and $T_2$ in the
hybrid state are substantially more efficient than sequential encoding
techniques.",1703.00481v2
2017-03-11,Magnonic crystals - prospective structures for shaping spin waves in nanoscale,"We have investigated theoretically band structure of spin waves in magnonic
crystals with periodicity in one-(1D), two- (2D) and three-dimensions (3D). We
have solved Landau-Lifshitz equation with the use of plane wave method, finite
element method in frequency domain and micromagnetic simulations in time domain
to find the dynamics of spin waves and spectrum of their eigenmodes. The spin
wave spectra were calculated in linear approximation. In this paper we show
usefulness of these methods in calculations of various types of spin waves. We
demonstrate the surface character of the Damon-Eshbach spin wave in 1D magnonic
crystals and change of its surface localization with the band number and
wavenumber in the first Brillouin zone. The surface property of the spin wave
excitation is further exploited by covering plate of the magnonic crystal with
conductor. The band structure in 2D magnonic crystals is complex due to
additional spatial inhomogeneity introduced by the demagnetizing field. This
modifies spin wave dispersion, makes the band structure of magnonic crystals
strongly dependent on shape of the inclusions and type of the lattice. The
inhomogeneity of the internal magnetic field becomes unimportant for magnonic
crystals with small lattice constant, where exchange interactions dominate. For
3D magnonic crystals, characterized by small lattice constant, wide magnonic
band gap is found. We show that the spatial distribution of different materials
in magnonic crystals can be explored for tailored effective damping of spin
waves.",1703.04012v1
2018-11-02,Anatomy of electrical signals and dc-voltage lineshape in spin torque ferromagnetic resonance,"The electrical detection of spin torque ferromagnetic resonance (st-FMR) is
becoming a popular method for measuring the spin-Hall angle of heavy metals
(HM). However, various sensible analysis on the same material with either the
same or different experimental setups yielded different spin-Hall angles with
large discrepancy, indicating some missing ingredients in our current
understanding of st-FMR. Here we carry out a careful analysis of electrical
signals of the st-FMR in a HM/ferromagnet (HM/FM) bilayer with an arbitrary
magnetic anisotropy. The FM magnetization is driven by two radio-frequency (rf)
forces: the rf Oersted field generated by an applied rf electric current and
the so called rf spin-orbit torque from the spin current flowing
perpendicularly from the HM to the FM due to the spin-Hall effect. By using the
universal form of the dynamic susceptibility matrix of magnetic materials at
the st-FMR, the electrical signals originated from the anisotropic
magnetoresistance, anomalous Hall effect and inverse spin-Hall effect are
analysed and dc-voltage lineshape near the st-FMR are obtained.
Angle-dependence of dc-voltage is given for two setups. A way of experimentally
extracting the spin-Hall angle of a HM is proposed.",1811.00810v1
2013-08-13,Exploring Boolean and Non-Boolean Computing Applications of Spin Torque Devices,"In this paper we discuss the potential of emerging spintorque devices for
computing applications. Recent proposals for spinbased computing schemes may be
differentiated as all-spin vs. hybrid, programmable vs. fixed, and, Boolean vs.
non-Boolean. All spin logic-styles may offer high area-density due to small
form-factor of nano-magnetic devices. However, circuit and system-level design
techniques need to be explored that leverage the specific spin-device
characteristics to achieve energy-efficiency, performance and reliability
comparable to those of CMOS. The non-volatility of nanomagnets can be exploited
in the design of energy and area-efficient programmable logic. In such
logic-styles, spin-devices may play the dual-role of computing as well as
memory-elements that provide field-programmability. Spin-based threshold logic
design is presented as an example (dynamic resisitve threshold logic and
magnetic threshold logic). Emerging spintronic phenomena may lead to ultralow-
voltage, current-mode, spin-torque switches that can offer attractive computing
capabilities, beyond digital switches. Such devices may be suitable for
non-Boolean data-processing applications which involve analog processing.
Integration of such spin-torque devices with charge-based devices like CMOS and
resistive memory can lead to highly energy-efficient information processing
hardware for applications like pattern-matching, neuromorphic-computing,
image-processing and data-conversion. Towards the end, we discuss the
possibility of applying emerging spin-torque switches in the design of
energy-efficient global interconnects, for future chip multiprocessors.",1308.2745v2
2009-12-15,Towards an Effective Spin Hamiltonian of the Pyrochlore Spin Liquid Tb2Ti2O7,"Tb2Ti2O7 is a pyrochlore antiferromagnet that has dynamical spins and only
short-range correlations even at 50 mK; the lowest temperature explored so far,
which is much smaller than the scale set by the Curie-Weiss temperature
T_{CW}~14 K. The absence of long-range order in this material is not
understood. Recently, virtual crystal field excitations (VCFEs) have been shown
to be significant in Tb2Ti2O7. While previous work found that VCFEs-induced
renormalization of the nearest neighbor Ising exchange leads to spin ice
correlations on a single tetrahedron, their effect on spin correlations has not
been fully explored. In this paper, we construct an effective spin-1/2
low-energy theory for Tb2Ti2O7 on the pyrochlore lattice. We determine
semiclassical ground states on a lattice that allow us to see how the physics
of spin ice is connected to the possible physics of Tb2Ti2O7. We observe a
shift in the phase boundaries with respect to those of the dipolar spin ice
model as the quantum corrections become more significant. In addition to the
familiar classical dipolar spin ice model phases, we see a stabilization of a q
= 0 ordered ice phase over a large part of the phase diagram; ferromagnetic
correlations being preferred by quantum corrections in spite of an
antiferromagnetic nearest neighbor exchange in the microscopic model.
Frustration is hence seen to arise from virtual crystal field excitations over
and above the effect of dipolar interactions in spin ice in inducing ice-like
correlations.",0912.2957v1
2015-12-27,Quantum Spin Liquid State in the Disordered Triangular Lattice Sc2Ga2CuO7,"We present microscopic magnetic properties of a two dimensional triangular
lattice Sc2Ga2CuO7, consisting of single and double triangular Cu planes. A
Curie-Weiss temperature theta_CW = --44 K and an antiferromagnetic (AFM)
exchange interaction J/KB = 35 K between Cu2+ (S = 1/2) spins in the triangular
bi-plane are obtained from the analysis of magnetic susceptibility data. The
intrinsic magnetic susceptibility extracted from 71Ga NMR shift data displays
the presence of AFM short range spin correlations and remains finite down to 50
mK suggesting an non-singlet ground state. The nuclear spin-lattice relaxation
rate (1/T1) reveals a slowing down of Cu2+ spin fluctuations with decreasing T
down to 100 mK. Magnetic specific heat (Cm) and 1/T1 exhibit a power law
behavior at low temperatures implying gapless nature of the spin excitation
spectrum. Absence of long range magnetic ordering down to ~ J/700, nonzero spin
susceptibility at low T, and power law behavior of Cm and 1/T1 suggest a
gapless quantum spin liquid (QSL) state. Our results demonstrate that
persistent spin dynamics induced by frustration maintain a quantum-disordered
state at T -> 0 in this triangular lattice antiferromagnet. This suggests that
the low energy modes are dominated by spinon excitations in the QSL state due
to randomness engendered by disorder and frustration.",1512.08273v2
2016-05-09,Electron doping evolution of the magnetic excitations in NaFe$_{1-x}$Co$_x$As,"We use time-of-flight (ToF) inelastic neutron scattering (INS) spectroscopy
to investigate the doping dependence of magnetic excitations across the phase
diagram of NaFe$_{1-x}$Co$_x$As with $x=0, 0.0175, 0.0215, 0.05,$ and $0.11$.
The effect of electron-doping by partially substituting Fe by Co is to form
resonances that couple with superconductivity, broaden and suppress low energy
($E\le 80$ meV) spin excitations compared with spin waves in undoped NaFeAs.
However, high energy ($E> 80$ meV) spin excitations are weakly Co-doping
dependent. Integration of the local spin dynamic susceptibility
$\chi^{\prime\prime}(\omega)$ of NaFe$_{1-x}$Co$_x$As reveals a total
fluctuating moment of 3.6 $\mu_B^2$/Fe and a small but systematic reduction
with electron doping. The presence of a large spin gap in the Co-overdoped
nonsuperconducting NaFe$_{0.89}$Co$_{0.11}$As suggests that Fermi surface
nesting is responsible for low-energy spin excitations. These results parallel
Ni-doping evolution of spin excitations in BaFe$_{2-x}$Ni$_x$As$_2$, confirming
the notion that low-energy spin excitations coupling with itinerant electrons
are important for superconductivity, while weakly doping dependent high-energy
spin excitations result from localized moments.",1605.02695v1
2016-08-29,Multi-fractal Geometry of Finite Networks of Spins,"Quantum spin networks overcome the challenges of traditional charge-based
electronics by encoding the information into spin degrees of freedom. Although
beneficial for transmitting information with minimal losses when compared to
their charge-based counterparts, the mathematical formalization of the
information propagation in a spin(tronic) network is challenging due to its
complicated scaling properties. In this paper, we propose a geometric
approach---specific to finite networks---for unraveling the
information-theoretic phenomena of spin chains and rings by abstracting them as
weighted graphs, where the vertices correspond to the spin excitation states
and the edges represent the information theoretic distance between pair of
nodes. The weighted graph representation of the quantum spin network dynamics
exhibits a complex self-similar structure (where subgraphs repeat to some
extent over various space scales). To quantify this complex behavior, we
develop a new box counting inspired algorithm which assesses the mono-fractal
versus multi-fractal properties of quantum spin networks. Besides specific to
finite networks, multi-fractality is further compounded by ""engineering"" or
""biasing"" the network for selective transfer, as selectivity makes the network
more heterogeneous. To demonstrate criticality in finite size systems, we
define a thermodynamics inspired framework for describing information
propagation and show evidence that some spin chains and rings exhibit an
informational phase transition phenomenon, akin to the metal-to-insulator phase
transition in Anderson localization in finite media.}",1608.08192v1
2017-06-05,Distinguishing Spin-Aligned and Isotropic Black Hole Populations With Gravitational Waves,"The first direct detections of gravitational waves from merging binary black
holes open a unique window into the binary black hole formation environment.
One promising environmental signature is the angular distribution of the black
hole spins; systems formed through dynamical interactions among already-compact
objects are expected to have isotropic spin orientations whereas binaries
formed from pairs of stars born together are more likely to have spins
preferentially aligned with the binary orbital angular momentum. We consider
existing gravitational wave measurements of the binary effective spin, the
best-measured combination of spin parameters, in the four likely binary black
hole detections GW150914, LVT151012, GW151226, and GW170104. If binary black
hole spin magnitudes extend to high values we show that the data exhibit a
$2.4\sigma$ ($0.015$ odds ratio) preference for an isotropic angular
distribution over an aligned one. By considering the effect of 10 additional
detections, we show that such an augmented data set would enable in most cases
a preference stronger than $5\sigma$ ($2.9 \times 10^{-7}$ odds ratio). The
existing preference for either an isotropic spin distribution or low spin
magnitudes for the observed systems will be confirmed (or overturned)
confidently in the near future.",1706.01385v2
2017-10-05,Transport theory for femtosecond laser-induced spin-transfer torques,"Ultrafast demagnetization of magnetic layers pumped by a femtosecond laser
pulse is accompanied by a nonthermal spin-polarized current of hot electrons.
These spin currents are studied here theoretically in a spin valve with
noncollinear magnetizations. To this end, we introduce an extended model of
superdiffusive spin transport that enables to treat noncollinear magnetic
configurations, and apply it to the perpendicular spin valve geometry. We show
how spin-transfer torques arise due to this mechanism and calculate their
action on the magnetization present, as well as how the latter depends on the
thicknesses of the layers and other transport parameters. We demonstrate that
there exists a certain optimum thickness of the out-of-plane magnetized
spin-current polarizer such that the torque acting on the second magnetic layer
is maximal. Moreover, we study the magnetization dynamics excited by the
superdiffusive spin-transfer torque due to the flow of hot electrons employing
the Landau-Lifshitz-Gilbert equation. Thereby we show that a femtosecond laser
pulse applied to one magnetic layer can excite small-angle precessions of the
magnetization in the second magnetic layer. We compare our calculations with
recent experimental results.",1710.02083v2
2019-10-29,Imaging and control of critical spin fluctuations in two-dimensional magnets,"Strong spin fluctuations are expected near the thermodynamic critical point
of a continuous magnetic phase transition. Such critical spin fluctuations are
highly correlated and in principle can occur at any time- and length-scales;
they govern critical phenomena and potentially can drive new phases. Although
theoretical studies have been made for decades, direct observation of critical
spin fluctuations remains elusive. The recent discovery of two-dimensional (2D)
layered magnets, in which spin fluctuations significantly modify magnetic
properties as compared to their bulk counterparts and integration into
heterostructures and devices can be easily achieved, provides an ideal platform
to investigate and harness critical spin phenomena. Here we develop a fast and
sensitive magneto-optical imaging microscope to achieve wide-field, real-time
monitoring of critical spin fluctuations in single-layer CrBr3, which is a 2D
ferromagnetic insulator. We track the critical phenomena directly from the
fluctuation correlations and observe both slowing-down dynamics and enhanced
correlation length. Through real-time feedback control of critical spin
fluctuations, we further achieve switching of magnetic states solely by
electrostatic gating without applying a magnetic field or a Joule current. The
ability to directly image and control critical spin fluctuations in 2D magnets
opens up exciting opportunities to explore critical phenomena and develop
applications in nanoscale engines and information science.",1910.13023v1
2020-01-20,Spin Dynamics Investigation of Quasi-Frozen Spin Lattice for EDM Searches,"The Quasi-Frozen Spin (QFS) method was proposed by Yu. Senichev et al. in [1]
as an alternative to the Frozen Spin (FS) method [2] for the search of deuteron
electric dipole moment (dEDM). The QFS approach simplifies the design of the
lattice. In particular, small changes to the currently operating COSY storage
ring will satisfy the QFS condition. Spin decoherence and systematic errors
fundamentally limit EDM signal detection and measurement. Our QFS
implementation method includes measurement of spin precession in (1) the
horizontal plane to calibrate the magnetic field when changing field polarity
and (2) the vertical plane to search for EDM. To address systematic errors due
to element misalignments, we track particle bunches in forward and reverse
directions. We modeled and tracked two QFS and one FS lattice in COSY INFINITY.
The models include normally distributed random variate spin kicks in magnetic
dipoles and combined electrostatic and magnetic field elements. We used Wolfram
Mathematica programs to partially automate lattice input file generation and
tracking output data analysis. We observed indications that the QFS method is a
viable alternative to the FS method.
  [1] Y. Senichev, A. Lehrach, B. Lorentz, R. Maier, S. Andrianov, A. Ivanov,
S. Chekmenev, M. Berz, and E. Valetov (on behalf of the JEDI Collaboration), in
Proceedings of IPAC 2015, Richmond, VA (2015) MOPWA044. [2] D. Anastassopoulos
et al., AGS Proposal: Search for a Permanent Electric Dipole Moment of the
Deuteron Nucleus at the $10^{-29}\:e\cdot\mathrm{cm}$ Level, BNL Report,
Brookhaven National Laboratory, Upton, NY (2008).",2001.07062v1
2020-02-05,Spin Resonances in Iron-Selenide High-Tc Superconductors by Proximity to Hidden Spin Density Wave,"Recent inelastic neutron scattering studies by Pan et al., Nature
Communications 8, 123 (2017), find evidence for spin excitations at energies
above the quasi-particle gap in an iron-selenide high-Tc superconductor. The
momenta of the spin excitations form a diamond around the checkerboard
wavevector, Q_AF, that is associated with the square lattice of iron atoms that
makes up the system. It has been suggested that such a ""hollowed-out""
spin-excitation spectrum is due to hidden Neel order. We study such a hidden
spin-density wave (hSDW) state that results from nested Fermi surfaces at the
center and at the corner of the unfolded Brillouin zone. It emerges within mean
field theory from an extended Hubbard model over a square lattice of iron atoms
that contain the minimal d_xz and d_yz orbitals. Opposing Neel order exists
over the isotropic d+ = d_xz + i d_yz and d- = d_xz - i d_yz orbitals. The
dynamical spin susceptibility of the hSDW is computed within the random phase
approximation, at perfect nesting. Unobservable Goldstone modes that disperse
acoustically are found at Q_AF. A threshold is found in the spectrum of
observable spin excitations that forms a ""floating ring"" at Q_AF also. The ring
threshold moves down in energy toward zero with increasing Hund's Rule
coupling, while it moves up in energy with increasing magnetic frustration.
Comparison with the normal-state features of the spin-excitation spectrum shown
by electron-doped iron selenide is made. Also, recent predictions of a Lifshitz
transition from the nested Fermi surfaces to Fermi surface pockets at the
corner of the folded Brillouin zone will be discussed.",2002.01732v2
2021-01-27,Broad-band spectroscopy of a vanadyl porphyrin: a model electronuclear spin qudit,"We explore how to encode more than a qubit in vanadyl porphyrin molecules
hosting a electronic spin 1/2 coupled to a nuclear spin 7/2. The spin
Hamiltonian and its parameters, as well as the spin dynamics, have been
determined via a combination of electron paramagnetic resonance, heat capacity,
magnetization and on-chip magnetic spectroscopy experiments performed on single
crystals. We find low temperature spin coherence times of micro-seconds and
spin relaxation times longer than a second. For sufficiently strong magnetic
fields (B larger than 0.1 T, corresponding to resonance frequencies of 9 to 10
GHz) these properties make vanadyl porphyrin molecules suitable qubit
realizations. The presence of multiple equispaced nuclear spin levels then
merely provides 8 alternatives to define the 0 and 1 basis states. For lower
magnetic fields (below 0.1 T), and lower frequencies (smaller than 2 GHz), we
find spectroscopic signatures of a sizeable electronuclear entanglement. This
effect generates a larger set of allowed transitions between different
electronuclear spin states and removes their degeneracies. Under these
conditions, we show that each molecule fulfills the conditions to act as a
universal 4-qubit processor or, equivalently, as a d = 16 qudit. These findings
widen the catalogue of chemically designed systems able to implement
non-trivial quantum functionalities, such as quantum simulations and,
especially, quantum error correction at the molecular level.",2101.11650v1
2017-11-28,Spin-lattice relaxation of individual solid-state spins,"Understanding the effect of vibrations on the relaxation process of
individual spins is crucial for implementing nano systems for quantum
information and quantum metrology applications. In this work, we present a
theoretical microscopic model to describe the spin-lattice relaxation of
individual electronic spins associated to negatively charged nitrogen-vacancy
centers in diamond, although our results can be extended to other spin-boson
systems. Starting from a general spin-lattice interaction Hamiltonian, we
provide a detailed description and solution of the quantum master equation of
an electronic spin-one system coupled to a phononic bath in thermal
equilibrium. Special attention is given to the dynamics of one-phonon processes
below 1 K where our results agree with recent experimental findings and
analytically describe the temperature and magnetic-field scaling. At higher
temperatures, linear and second-order terms in the interaction Hamiltonian are
considered and the temperature scaling is discussed for acoustic and
quasi-localized phonons when appropriate. Our results, in addition to
confirming a $T^5$ temperature dependence of the longitudinal relaxation rate
at higher temperatures, in agreement with experimental observations, provide a
theoretical background for modeling the spin-lattice relaxation at a wide range
of temperatures where different temperature scalings might be expected.",1711.10280v1
2018-06-08,Magnetic field dependence of the electron spin revival amplitude in periodically pulsed quantum dots,"Periodic laser pulsing of singly charged semiconductor quantum dots in an
external magnetic field leads to a synchronization of the spin dynamics with
the optical excitation. The pumped electron spins partially rephase prior to
each laser pulse, causing a revival of electron spin polarization with its
maximum at the incidence time of a laser pulse. The amplitude of this revival
is amplified by the frequency focusing of the surrounding nuclear spins. Two
complementary theoretical approaches for simulating up to 20 million laser
pulses are developed and employed that are able to bridge between 11 orders of
magnitude in time: a fully quantum mechanical description limited to small
nuclear bath sizes and a technique based on the classical equations of motion
applicable for a large number of nuclear spins. We present experimental data of
the nonmonotonic revival amplitude as function of the magnetic field applied
perpendicular to the optical axis. The dependence of the revival amplitude on
the external field with a profound minimum at $4\;$T is reproduced by both of
our theoretical approaches and is ascribed to the nuclear Zeeman effect. Since
the nuclear Larmor precession determines the electronic resonance condition, it
also defines the number of electron spin revolutions between pump pulses, the
orientation of the electron spin at the incidence time of a pump pulse, and the
resulting revival amplitude. The magnetic field of $4\;$T, for example,
corresponds to half a revolution of nuclear spins between two laser pulses.",1806.03109v2
2018-06-25,Spin relaxation due to the D'yakonov-Perel' mechanism in 2D semiconductors with an elliptic band structure,"D'yakonov-Perel' (DP) mechanism describes the dynamics of non-equilibrium
spin distribution in a two-dimensional (2D) system in the presence of Rashba
spin-orbit coupling. In this paper, we study the anisotropy of spin relaxation
via the DP mechanism for a 2D semiconductor with an elliptic band structure.
Within the effective-mass approximation, the low-energy band structure is
described using anisotropic in-plane effective mass of free carriers. Spin
relaxation time of free carriers is calculated theoretically using the time
evolution equation of the density matrix of a polarized spin ensemble in the
strong momentum scattering regime. Results are obtained for scattering
potential due to both Coulomb interaction and neutral defects in the sample. We
show that the ratio of spin relaxation time in the y- and x-direction within
the 2D plane displays a power-law dependence on the effective mass ratio, while
the exponent captures the details of the scattering potential. The model is
applied to study electron spin relaxation in monolayer black phosphorus, which
is known to exhibit significant band structure ellipticity. The model can also
predict spin relaxation anisotropy in mechanically strained 2D materials in
which elliptic band structure emerges as a consequence of the modification of
the lattice constants.",1806.09488v3
2019-01-07,Spin dynamics of edge-sharing spin chains in SrCa13Cu24O41,"The low-energy magnetic excitation from the highly Ca-doped
quasi-one-dimensional magnet SrCa13Cu24O41 was studied in the magnetic ordered
state by using inelastic neutron scattering. We observed the gapless spin-wave
excitation, dispersive along the a and c axes but nondispersive along the b
axis. Such excitations are attributed to the spin wave from the spin-chain
sublattice. Model fitting to the experimental data gives the nearest-neighbour
interaction Jc as 5.4 meV and the interchain interaction Ja = 4.4 meV. Jc is
antiferromagnetic and its value is close to the nearest-neighbour interactions
of the similar edge-sharing spin-chain systems such as CuGeO3. Comparing with
the hole-doped spin chains in Sr14Cu24O41, which shows a spin gap due to spin
dimers formed around Zhang-Rice singlets, the chains in SrCa13Cu24O41 show a
gapless excitation in this study. We ascribe such a change from gapped to
gapless excitations to holes transferring away from the chain sublattice into
the ladder sublattice upon Ca doping.",1901.02102v1
2019-03-09,Spin-wave thermodynamics of square-lattice antiferromagnets revisited,"Modifying the conventional spin-wave theory in a novel manner based on the
Wick decomposition, we present an elaborate thermodynamics of square-lattice
quantum antiferromagnets. Our scheme is no longer accompanied by the notorious
problem of an artificial transition to the paramagnetic state inherent in
modified spin waves in the Hartree-Fock approximation. In the cases of spin
$\frac{1}{2}$ and spin $1$, various modified-spin-wave findings for the
internal energy, specific heat, static uniform susceptibility, and dynamic
structure factor are not only numerically compared with quantum Monte Carlo
calculations and Lanczos exact diagonalizations but also analytically expanded
into low-temperature series. Modified spin waves interacting via the Wick
decomposition provide reliable thermodynamics over the whole temperature range
of absolute zero to infinity. Adding higher-order spin couplings such as ring
exchange interaction to the naivest Heisenberg Hamiltonian, we precisely
reproduce inelastic-neutron-scattering measurements of the
high-temperature-superconductor-parent antiferromagnet
$\mathrm{La}_2\mathrm{CuO}_4$. Modifying Dyson-Maleev bosons combined with
auxiliary pseudofermions also yields thermodynamics of square-lattice
antiferromagnets free from thermal breakdown, but it is less precise unless
temperature is sufficiently low. Applying all the schemes to layered
antiferromagnets as well, we discuss the advantages and disadvantages of
modified spin-wave and combined boson-pseudofermion representations.",1903.03769v1
2019-04-03,Collective spinon spin wave in a magnetized U(1) spin liquid,"We study the transverse dynamical spin susceptibility of the two dimensional
U(1) spinon Fermi surface spin liquid in a small applied Zeeman field. We show
that both short-range interactions, present in a generic Fermi liquid, as well
as gauge fluctuations, characteristic of the U(1) spin liquid, qualitatively
change the result based on the frequently assumed non-interacting spinon
approximation. Short-range interaction leads to a new collective mode: a
""spinon spin wave"" which splits off from the two-spinon continuum at small
momentum and disperses downward. Gauge fluctuations renormalize the
susceptibility, providing non-zero power law weight in the region outside the
spinon continuum and giving the spin wave a finite lifetime, which scales as
momentum squared. We also study the effect of Dzyaloshinskii-Moriya anisotropy
on the zero momentum susceptibility, which is measured in electron spin
resonance (ESR), and obtain a resonance linewidth linear in temperature and
varying as $B^{2/3}$ with magnetic field $B$ at low temperature. Our results
form the basis for a theory of inelastic neutrons scattering, ESR, and resonant
inelastic x-ray scattering (RIXS) studies of this quantum spin liquid state.",1904.02117v2
2020-05-07,Spin caloritronics in a CrBr$_3$-based magnetic van der Waals heterostructure,"The recently reported magnetic ordering in insulating two-dimensional (2D)
materials, such as chromium triiodide (CrI$_3$) and chromium tribromide
(CrBr$_3$), opens new possibilities for the fabrication of magneto-electronic
devices based on 2D systems. Inevitably, the magnetization and spin dynamics in
2D magnets are strongly linked to Joule heating. Therefore, understanding the
coupling between spin, charge and heat, i.e. spin caloritronic effects, is
crucial. However, spin caloritronics in 2D ferromagnets remains mostly
unexplored, due to their instability in air. Here we develop a fabrication
method that integrates spin-active contacts with 2D magnets through hBN
encapsulation, allowing us to explore the spin caloritronic effects in these
materials. The angular dependence of the thermal spin signal of the CrBr$_3$/Pt
system is studied, for different conditions of magnetic field and heating
current. We highlight the presence of a significant magnetic proximity effect
from CrBr$_3$ on Pt revealed by an anomalous Nernst effect in Pt, and suggest
the contribution of the spin Seebeck effect from CrBr$_3$. These results pave
the way for future magnonic devices using air-sensitive 2D magnetic insulators.",2005.03561v1
2020-06-12,Spin Excitations and Spin Wave Gap in the Ferromagnetic Weyl Semimetal Co$_3$Sn$_2$S$_2$,"We report a comprehensive neutron scattering study on the spin excitations in
the magnetic Weyl semimetal Co$_3$Sn$_2$S$_2$ with quasi-two-dimensional
structure. Both in-plane and out-of-plane dispersions of the spin waves are
revealed in the ferromagnetic state, similarly dispersive but damped spin
excitations persist into the paramagnetic state. The effective exchange
interactions have been estimated by a semi-classical Heisenberg model to
consistently reproduce the experimental $T_C$ and spin stiffness. However, a
full spin wave gap below $E_g=2.3$ meV is observed at $T=4$ K, much larger than
the estimated magnetic anisotropy energy ($\sim0.6$ meV), while its temperature
dependence indicates a significant contribution from the Weyl fermions. These
results suggest that Co$_3$Sn$_2$S$_2$ is a three-dimensional correlated system
with large spin stiffness, and the low-energy spin dynamics could interplay
with the topological electron states.",2006.07339v2
2021-05-06,Tunable spin polarization and electronic structure of bottom-up synthesized MoSi$_2$N$_4$ materials,"Manipulation of spin-polarized electronic states of two-dimensional (2D)
materials under ambient conditions is necessary for developing new quantum
devices with small physical dimensions. Here, we explore spin-dependent
electronic structures of ultra-thin films of recently introduced 2D synthetic
materials MSi$_2$Z$_4$ (M = Mo or W and Z = N or As) using first-principles
modeling. Stacking of MSi$_2$Z$_4$ monolayers is found to generate dynamically
stable bilayer and bulk materials with thickness-dependent properties. When
spin-orbit coupling (SOC) is included in the computations, MSi$_2$N$_4$
monolayers display indirect bandgaps and large spin-split states at the $K$ and
$K'$ symmetry points at the corners of the Brillouin zone with nearly 100\%
spin polarization. The spins are locked in opposite directions along an
out-of-the-plane direction at $K$ and $K'$, leading to spin-valley coupling
effects. As expected, spin polarization is absent in the pristine bilayers due
to the presence of inversion symmetry, but it can be induced via an external
out-of-plane electric field much like the case of Mo(W)S$_2$ bilayers. A
transition from an indirect to a direct bandgap can be driven by replacing N by
As in MSi$_2$(N, As)$_4$ monolayers. Our study indicates that the MSi$_2$Z$_4$
materials can provide a viable alternative to the MoS$_2$ class of 2D materials
for valleytronics and optoelectronics applications.",2105.02739v2
2021-06-01,Quantum control of the tin-vacancy spin qubit in diamond,"Group-IV color centers in diamond are a promising light-matter interface for
quantum networking devices. The negatively charged tin-vacancy center (SnV) is
particularly interesting, as its large spin-orbit coupling offers strong
protection against phonon dephasing and robust cyclicity of its optical
transitions towards spin-photon entanglement schemes. Here, we demonstrate
multi-axis coherent control of the SnV spin qubit via an all-optical stimulated
Raman drive between the ground and excited states. We use coherent population
trapping and optically driven electronic spin resonance to confirm coherent
access to the qubit at 1.7 K, and obtain spin Rabi oscillations at a rate of
$\Omega/2\pi$=3.6(1) MHz. All-optical Ramsey interferometry reveals a spin
dephasing time of $T_2^*$=1.3(3)$\mu$s and two-pulse dynamical decoupling
already extends the spin coherence time to $T_2$=0.33(14) ms. Combined with
transform-limited photons and integration into photonic nanostructures, our
results make the SnV a competitive spin-photon building block for quantum
networks.",2106.00723v1
2021-06-21,Local non-linear excitation of sub-100 nm bulk-type spin waves by edge-localized spin waves in magnetic films,"The excitation of high-frequency short-wavelength spin waves is a challenge
limiting the application of these propagating magnetization disturbances in
information processing systems. We propose a method of local excitation of the
high-frequency spin waves using the non-linear nature of magnetization
dynamics. We demonstrate with numeric simulations that an edge-localized spin
wave can be used to excite plane waves propagating obliquely from the film's
edge at a doubled frequency and over twice shorter in wavelength. The
excitation mechanism is a direct result of the ellipticity of the magnetic
moments precession that is related to the edge-mode propagation. As a
consequence, the magnetization component tangential to the equilibrium
orientation oscillates with doubled temporal and spatial frequencies, which
leads to efficient excitation of the plane spin waves. Threshold-less
non-linear process of short-wavelength spin-wave excitation proposed in our
study is promising for integration with an inductive or point-like spin-torque
source of edge spin waves.",2106.11114v1
2021-09-23,Large Exotic Spin Torques in Antiferromagnetic Iron Rhodium,"Spin torque is a promising tool for driving magnetization dynamics for novel
computing technologies. These torques can be easily produced by spin-orbit
effects, but for most conventional spin source materials, a high degree of
crystal symmetry limits the geometry of the spin torques produced. Magnetic
ordering is one way to reduce the symmetry of a material and allow exotic
torques, and antiferromagnets are particularly promising because they are
robust against external fields. We present spin torque ferromagnetic resonance
measurements and second harmonic Hall measurements characterizing the spin
torques in antiferromagnetic iron rhodium alloy. We report extremely large,
strongly temperature-dependent exotic spin torques with a geometry apparently
defined by the magnetic ordering direction. We find the spin torque efficiency
of iron rhodium to be (330$\pm$150) % at 170 K and (91$\pm$32) % at room
temperature. We support our conclusions with theoretical calculations showing
how the antiferromagnetic ordering in iron rhodium gives rise to such exotic
torques.",2109.11108v1
2021-10-25,Spin relaxation in a single-electron graphene quantum dot,"The relaxation time of a single-electron spin is an important parameter for
solid-state spin qubits, as it directly limits the lifetime of the encoded
information. Thanks to the low spin-orbit interaction and low hyperfine
coupling, graphene and bilayer graphene (BLG) have long been considered
promising platforms for spin qubits. Only recently, it has become possible to
control single-electrons in BLG quantum dots (QDs) and to understand their
spin-valley texture, while the relaxation dynamics have remained mostly
unexplored. Here, we report spin relaxation times ($T_1$) of single-electron
states in BLG QDs. Using pulsed-gate spectroscopy, we extract relaxation times
exceeding 200 $\mu$s at a magnetic field of 1.9 T. The $T_1$ values show a
strong dependence on the spin splitting, promising even longer $T_1$ at lower
magnetic fields, where our measurements are limited by the signal-to-noise
ratio. The relaxation times are more than two orders of magnitude larger than
those previously reported for carbon-based QDs, suggesting that graphene is a
potentially promising host material for scalable spin qubits.",2110.13051v3
2021-11-07,Impact of gigahertz and terahertz transport regimes on spin propagation and conversion in the antiferromagnet IrMn,"Control over spin transport in antiferromagnetic systems is essential for
future spintronic applications with operational speeds extending to ultrafast
time scales. Here, we study the transition from the gigahertz (GHz) to
terahertz (THz) regime of spin transport and spin-to-charge current conversion
(S2C) in the prototypical antiferromagnet IrMn by employing spin pumping and
THz spectroscopy techniques. We reveal a factor of 4 shorter characteristic
propagation lengths of the spin current at THz frequencies (~ 0.5 nm) as
compared to the GHz regime (~ 2 nm) which may be attributed to the ballistic
and diffusive nature of electronic spin transport, respectively. The conclusion
is supported by an extraction of sub-picosecond temporal dynamics of the THz
spin current. We also report on a significant impact of the S2C originating
from the IrMn/non-magnetic metal interface which is much more pronounced in the
THz regime and opens the door for optimization of the spin control at ultrafast
time scales.",2111.04191v2
2022-03-17,Quantum Sensors for High Precision Measurements of Spin-dependent Interactions,"The applications of spin-based quantum sensors to measurements probing
fundamental physics are surveyed. Experimental methods and technologies
developed for quantum information science have rapidly advanced in recent
years, and these tools enable increasingly precise control and measurement of
spin dynamics. Theories of beyond-the-Standard-Model physics predict, for
example, symmetry violating electromagnetic moments aligned with particle
spins, exotic spin-dependent forces, coupling of spins to ultralight bosonic
dark matter fields, and changes to the local environment that affect spins.
Spin-based quantum sensors can be used to search for these myriad phenomena,
and offer a methodology for tests of fundamental physics that is complementary
to particle colliders and large scale particle detectors. Areas of
technological development that can significantly enhance the sensitivity of
spin-based quantum sensors to new physics are highlighted.",2203.09488v2
2022-03-31,Constraining black-hole binary spin precession and nutation with sequential prior conditioning,"We investigate the detectability of sub-dominant spin effects in merging
black-hole binaries using current gravitational-wave data. Using a
phenomenological model that separates the spin dynamics into precession
(azimuthal motion) and nutation (polar motion), we present constraints on the
resulting amplitudes and frequencies. We also explore current constraints on
the spin morphologies, indicating if binaries are trapped near spin-orbit
resonances. We dissect such weak effects from the signals using a sequential
prior conditioning approach, where parameters are progressively re-sampled from
their posterior distribution. This allows us to investigate whether the data
contain additional information beyond what is already provided by quantities
that are better measured, namely the masses and the effective spin. For the
current catalog of events, we find no significant measurements of weak spin
effects such as nutation and spin-orbit locking. We synthesize a source with a
high nutational amplitude and show that near-future detections will allow us to
place powerful constraints, hinting that we may be at the cusp of detecting
spin nutations in gravitational-wave data.",2204.00026v3
2022-04-22,Quantum-classical correspondence in spin-boson equilibrium states at arbitrary coupling,"The equilibrium properties of nanoscale systems can deviate significantly
from standard thermodynamics due to their coupling to an environment. For the
generalised $\theta$-angled spin-boson model, we first derive a compact and
general form of the classical equilibrium state including environmental
corrections to all orders. Secondly, for the quantum spin-boson model we prove,
by carefully taking a large spin limit, that Bohr's quantum-classical
correspondence persists at all coupling strengths. This correspondence gives
insight into the conditions for a coupled quantum spin to be well-approximated
by a coupled classical spin-vector. Thirdly, we demonstrate that previously
identified environment-induced 'coherences' in the equilibrium state of weakly
coupled quantum spins, do not disappear in the classical case. Finally, we
provide the first classification of the coupling parameter regimes for the
spin-boson model, from weak to ultrastrong, both for the quantum case and the
classical setting. Our results shed light on the interplay of quantum and mean
force corrections in equilibrium states of the spin-boson model, and will help
draw the quantum to classical boundary in a range of fields, such as magnetism
and exciton dynamics.",2204.10874v3
2022-04-27,Spin liquid state in a rare-earth hyperkagome lattice,"Quantum fluctuations enhanced by frustration and subtle interplay between
competing degrees of freedom offer an ideal ground to realize novel states with
fractional quantum numbers in quantum materials that defy standard theoretical
paradigms. Quantum spin liquid (QSL) is a highly entangled state wherein
frustration induced strong quantum fluctuations preclude symmetry breaking
phase transitions down to zero temperature without any order parameter.
Experimental realizations of QSL in quantum materials with spin dimensionality
greater than one is very rare. Here, we present our thermodynamic, nuclear
magnetic resonance, muon spin relaxation and inelastic neutron scattering
studies of a new rare-earth hyperkagome compound Li3Yb3Te2O12 in which Yb3+
ions constitute a three dimensional spin-lattice without any detectable
disorder. Our comprehensive experiments evince neither signature of magnetic
ordering nor spin freezing down to 38 mK that suggest the realization of
dynamic liquid-like ground state in this antiferromagnet. The ground state of
this material is interpreted by a low energy Jeff = 1/2 degrees of freedom with
short range spin correlations. The present results demonstrate a viable basis
to explore spin-orbit driven enigmatic correlated quantum states in a new class
of rare-earth based three dimensional frustrated magnets that may open new
avenues in theoretical and experimental search for spin liquids.",2204.12813v1
2022-05-08,Robustness of Kardar-Parisi-Zhang scaling in a classical integrable spin chain with broken integrability,"Recent investigations have observed superdiffusion in integrable classical
and quantum spin chains. An intriguing connection between these spin chains and
Kardar-Parisi-Zhang (KPZ) universality class has emerged. Theoretical
developments (e.g. generalized hydrodynamics) have highlighted the role of
integrability as well as spin-symmetry in KPZ behaviour. However understanding
their precise role on superdiffusive transport still remains a challenging
task. The widely used quantum spin chain platform comes with severe numerical
limitations. To circumvent this barrier, we focus on a classical integrable
spin chain which was shown to have deep analogy with the quantum
spin-$\frac{1}{2}$ Heisenberg chain. Remarkably, we find that KPZ behaviour
prevails even when one considers integrability-breaking but spin-symmetry
preserving terms, strongly indicating that spin-symmetry plays a central role
even in the non-perturbative regime. On the other hand, in the non-perturbative
regime, we find that energy correlations exhibit clear diffusive behaviour. We
also study the classical analog of out-of-time-ordered correlator (OTOC) and
Lyapunov exponents. We find significant presence of chaos for the
integrability-broken cases even though KPZ behaviour remains robust. The
robustness of KPZ behaviour is demonstrated for a wide class of spin-symmetry
preserving integrability-breaking terms.",2205.03858v1
2022-09-18,The causality and stability of relativistic spin-hydrodynamics,"We study the causality and stability of relativistic hydrodynamics with the
inclusion of the spin degree of freedom as a hydrodynamic field. We consider
two specific models of spin-hydrodynamics for this purpose. A linear mode
analysis for static background shows that a first-order dissipative
spin-hydrodynamics remains acausal and admits instabilities. Besides, it is
found that the inclusion of the spin field in hydrodynamics leads to new kinds
of linear modes in the system. These new modes also exhibit instability and
acausal behavior. The second model of the spin-hydrodynamics that we have
considered here is equivalent to a particular second-order conventional
hydrodynamics with no dissipative effects. For a static background, it is found
that the linear modes of this model support the sound waves only. However, when
the background has constant vorticity, then the model admits instability and
acausality in certain situations. It is found that the spin-dynamics have an
effect on the hydrodynamic response of the fluid. These findings point toward
the need for a causal and stable theory with spin as a hydrodynamic field to
describe the spin-polarized fluid.",2209.08652v2
2022-10-01,"Stability analysis of the spin evolution fix points in inspiraling compact binaries with black hole, neutron star, gravastar, or boson star components","Based on the secular spin evolution of black holes, neutron stars,
gravastars, or boson stars in precessing compact binaries on eccentric orbit,
we identify the aligned and more generic coplanar configurations of the spins
and orbital angular momentum as fix points. Through a dynamical system
analysis, we investigate their linear stability as function of the mass
quadrupole parameter. Marginal stability holds for the binary configurations
with both spins antialigned to the orbital angular momentum, for both spins
aligned to the orbital angular momentum (with the exception of certain
quadrupolar parameter ranges of neutron stars and boson stars), and for the
extremal mass ratio. For equal masses, the configurations of one of the spins
aligned and the other antialigned is stable for gravastar binaries, for neutron
star binaries in the high quadrupolar parameter range, and for boson star
binaries. For some unequal mass gravastar binaries, black hole binaries or
neutron star binaries, a transition from stability to instability can occur
during the inspiral, when one of the spins is aligned, while the other is
antialigned to the orbital angular momentum. We discover a transitional
instability regime during the inspiral of certain gravastar, neutron star, or
boson star binaries with opposing spins. For coplanar configurations we find
instabilities only for the gravastar - gravastar, boson star - boson star and
black hole - boson star binaries. For a given spin configuration, marginal
stability strongly depends on the value of the quadrupolar parameters. The
stability region is larger for neutron star binaries than for black hole
binaries, while the mixed systems have a restricted stability parameter region.",2210.00285v1
2022-10-19,Improving the spin-down limits of the continuous gravitational waves emitted from rotating triaxial pulsars,"The spin-down limit of the continuous gravitational wave strain from pulsars
assumed to be triaxial stars rotating about a principal moment of inertia axis
depends upon the value of the intrinsic spin frequency derivative of the
pulsar, among other parameters. In order to get more accurate intrinsic spin
frequency derivative values, dynamical effects contributing to the measured
spin frequency derivative values must be estimated via more realistic
approaches. In this work, we calculated improved values for the spin-down limit
of the continuous gravitational wave strain (assuming that pulsars are triaxial
stars rotating about a principal moment of inertia axis) for a set of 237
pulsars for which a targeted search for continuous gravitational waves was
recently carried out by the LIGO-Virgo-KAGRA (LVK) Collaboration. We used
`GalDynPsr', a Python-based public package, to calculate more realistic values
for the intrinsic spin frequency derivatives and, consequently, we get more
realistic values of the spin-down limit. The realistic values that we obtain
for the intrinsic spin frequency derivatives can also provide a valuable
contribution to improving the sensitivity of searches for continuous
gravitational waves from known pulsars.",2210.10355v2
2022-12-16,Spin excitations in the kagome-lattice metallic antiferromagnet Fe$_{0.89}$Co$_{0.11}$Sn,"Kagome-lattice materials have attracted tremendous interest due to the broad
prospect for seeking superconductivity, quantum spin liquid states, and
topological electronic structures. Among them, the transition-metal kagome
lattices are high-profile objects for the combination of topological
properties, rich magnetism, and multiple-orbital physics. Here we report an
inelastic neutron scattering study on the spin dynamics of a kagome-lattice
antiferromagnetic metal Fe$_{0.89}$Co$_{0.11}$Sn. Although the magnetic
excitations can be observed up to $\sim$250 meV, well-defined spin waves are
only identified below $\sim$90 meV and can be modeled using Heisenberg exchange
with ferromagnetic in-plane nearest-neighbor coupling $J_1$, in-plane
next-nearest-neighbor coupling $J_2$, and antiferromagnetic (AFM) interlayer
coupling $J_c$ under linear spin-wave theory. Above $\sim$90 meV, the spin
waves enter the itinerant Stoner continuum and become highly damped
particle-hole excitations. At the K point of the Brillouin zone, we reveal a
possible band crossing of the spin wave, which indicates a potential Dirac
magnon. Our results uncover the evolution of the spin excitations from the
planar AFM state to the axial AFM state in Fe$_{0.89}$Co$_{0.11}$Sn, solve the
magnetic Hamiltonian for both states, and confirm the significant influence of
the itinerant magnetism on the spin excitations.",2212.08590v2
2023-02-28,"Strong-coupling magnetophononics: Self-blocking, phonon-bitriplons, and spin-band engineering","Magnetophononics, the modulation of magnetic interactions by driving
infrared-active lattice excitations, is emerging as a key mechanism for the
ultrafast dynamical control of both semiclassical and quantum spin systems by
coherent light. We demonstrate that, in a quantum magnet with strong
spin-phonon coupling, resonances between the driven phonon and the spin
excitation frequencies exhibit an intrinsic self-blocking effect, whereby only
a fraction of the available laser power is absorbed by the phonon. Using the
quantum master equations governing the nonequilibrium steady states of the
coupled spin-lattice system, we show how self-blocking arises from the
self-consistent alteration of the resonance frequencies. We link this to the
appearance of mutually repelling collective spin-phonon states, which in the
regime of strong hybridization become composites of a phonon and two triplons.
We then identify the mechanism and optimal phonon frequencies by which to
control a global nonequilibrium renormalization of the lattice-driven spin
excitation spectrum and demonstrate that this effect should be observable in
ultrafast THz experiments on a number of known quantum magnetic materials.",2303.00125v1
2023-07-26,Giant spin-charge conversion in ultrathin films of the MnPtSb half-Heusler compound,"Half-metallic half-Heusler compounds with strong spin-orbit-coupling and
broken inversion symmetry in their crystal structure are promising materials
for generating and absorbing spin-currents, thus enabling the electric
manipulation of magnetization in energy-efficient spintronic devices. In this
work, we report the spin-to-charge conversion in sputtered ultrathin films of
the half-Heusler compound MnPtSb with thickness (t) in the range from 1 to 6
nm. A combination of X-ray and transmission electron microscopy measurements
evidence the epitaxial nature of these ultrathin non-centrosymmetric MnPtSb
films, with a clear (111)-orientation obtained on top of (0001) single-crystal
sapphire substrates. The study of the thickness (t)-dependent magnetization
dynamics of the MnPtSb(t)/Co(5nm)/Au(5nm) heterostructure revealed that the
MnPtSb compound can be used as an efficient spin current generator, even at
film thicknesses as low as 1 nm. By making use of spin pumping FMR, we measure
a remarkable t-dependent spin-charge conversion in the MnPtSb layers, which
clearly demonstrate the interfacial origin of the conversion. When interpreted
as arising from the inverse Edelstein effect (IEE), the spin-charge conversion
efficiency extracted at room temperature for the thinnest MnPtSb layer reaches
{\lambda}IEE~3 nm, representing an extremely high spin-charge conversion
efficiency at room temperature. The still never explored ultrathin regime of
the MnPtSb films studied in this work and the discover of their outstanding
functionality are two ingredients which demonstrate the potentiality of such
materials for future applications in spintronics.",2307.14516v1
2023-10-09,Mapping of Spin-Wave Transport in Thulium Iron Garnet Thin Films Using Diamond Quantum Microscopy,"Spin waves, collective dynamic magnetic excitations, offer crucial insights
into magnetic material properties. Rare-earth iron garnets offer an ideal
spin-wave (SW) platform with long propagation length, short wavelength,
gigahertz frequency, and applicability to magnon spintronic platforms. Of
particular interest, thulium iron garnet (TmIG) has attracted a huge interest
recently due to its successful growth down to a few nanometers, observed
topological Hall effect and spin orbit torque-induced switching effects.
However, there is no direct spatial measurement of its SW properties. This work
uses diamond nitrogen vacancy (NV) magnetometry in combination with SW
electrical transmission spectroscopy to study SW transport properties in TmIG
thin films. NV magnetometry allows probing spin waves at the sub-micrometer
scale, seen by the amplification of the local microwave magnetic field due to
the coupling of NV spin qubits with the stray magnetic field produced by the
microwave-excited spin waves. By monitoring the NV spin resonances, the SW
properties in TmIG thin films are measured as function of the applied magnetic
field, including their amplitude, decay length (~ 50 um), and wavelength (0.8 -
2 um). These results pave the way for studying spin qubit-magnon interactions
in rare-earth magnetic insulators, relevant to quantum magnonics applications.",2310.06188v4
2023-11-03,Magnetic properties and spin dynamics in a spin-orbit driven Jeff= 1/2 triangular lattice antiferromagnet,"Frustration-induced strong quantum fluctuations accompanied by spin-orbit
coupling and crystal electric field can give rise to rich and diverse magnetic
phenomena associated with unconventional low-energy excitations in rare-earth
based quantum magnets. Herein, we present crystal structure, magnetic
susceptibility, specific heat, muon spin relaxation(muSR), and electron spin
resonance (ESR) studies on the polycrystalline samples of Ba6Yb2Ti4O17 in which
Yb3+ ions constitute a perfect triangular lattice in ab-plane without
detectable anti-site disorder between atomic sites. The Curie-Weiss fit of
low-temperature magnetic susceptibility data suggest the spin-orbit entangled
Jeff = 1/2 degrees of freedom of Yb3+ spin with weak antiferromagnetic exchange
interactions in the Kramers doublet ground state. The zero-field specific heat
data reveal the presence of long-range magnetic order at TN = 77 mK which is
suppressed in a magnetic field 1 T. The broad maximum in specific heat is
attributed to the Schottky anomaly implying the Zeeman splitting of the Kramers
doublet ground state. The ESR measurements suggest the presence of anisotropic
exchange interaction between the moments of Yb3+ spins and the well separated
Kramers doublet state. muSR experiments reveal a fluctuating state of Yb3+
spins in the temperature range 0.1 K-100 K owing to depopulation of crystal
electric field levels, which suggests that the Kramers doublets are well
separated consistent with thermodynamic and ESR results. In addition to the
intraplane nearest-neighbor superexchange interaction, the interplane exchange
interaction and anisotropy are expected to stabilize the long-range ordered
state in this triangular lattice antiferromagnet.",2311.01858v1
2024-03-01,Microwave Control of the Tin-Vacancy Spin Qubit in Diamond with a Superconducting Waveguide,"Group-IV color centers in diamond are promising candidates for quantum
networks due to their dominant zero-phonon line and symmetry-protected optical
transitions that connect to coherent spin levels. The negatively charged
tin-vacancy (SnV) center possesses long electron spin lifetimes due to its
large spin-orbit splitting. However, the magnetic dipole transitions required
for microwave spin control are suppressed, and strain is necessary to enable
these transitions. Recent work has shown spin control of strained emitters
using microwave lines that suffer from Ohmic losses, restricting coherence
through heating. We utilize a superconducting coplanar waveguide to measure SnV
centers subjected to strain, observing substantial improvement. A detailed
analysis of the SnV center electron spin Hamiltonian based on the
angle-dependent splitting of the ground and excited states is performed. We
demonstrate coherent spin manipulation and obtain a Hahn echo coherence time of
up to $T_2 = 430\,\mu$s. With dynamical decoupling, we can prolong coherence to
$T_2 = 10\,$ms, about six-fold improved compared to earlier works. We also
observe a nearby coupling $^{13}\mathrm{C}$ spin which may serve as a quantum
memory. This substantiates the potential of SnV centers in diamond and
demonstrates the benefit of superconducting microwave structures.",2403.00521v1
2020-11-11,Destruction of long-range magnetic order in an external magnetic field and the associated spin dynamics in Cu2GaBO5 and Cu2AlBO5 ludwigites,"The quantum spin systems Cu$_2$M'BO$_5$ (M' = Al, Ga) with the ludwigite
crystal structure consist of a structurally ordered Cu$^{2+}$ sublattice in the
form of three-leg ladders, interpenetrated by a structurally disordered
sublattice with a statistically random site occupation by magnetic Cu$^{2+}$
and nonmagnetic Ga$^{3+}$ or Al$^{3+}$ ions. A microscopic analysis based on
density-functional-theory calculations for Cu$_2$GaBO$_5$ reveals a frustrated
quasi-two-dimensional spin model featuring five inequivalent antiferromagnetic
exchanges. A broad low-temperature $^{11}$B nuclear magnetic resonance points
to a considerable spin disorder in the system. In zero magnetic field,
antiferromagnetic order sets in below $T_\text{N}$ $\approx$ 4.1 K and ~2.4 K
for the Ga and Al compounds, respectively. From neutron diffraction, we find
that the magnetic propagation vector in Cu$_2$GaBO$_5$ is commensurate and lies
on the Brillouin-zone boundary in the (H0L) plane, $\mathbf{q}_\text{m}$ =
(0.45 0 -0.7), corresponding to a complex noncollinear long-range ordered
structure with a large magnetic unit cell. Muon spin relaxation is monotonic,
consisting of a fast static component typical for complex noncollinear spin
systems and a slow dynamic component originating from the relaxation on
low-energy spin fluctuations. Gapless spin dynamics in the form of a diffuse
quasielastic peak is also evidenced by inelastic neutron scattering. Most
remarkably, application of a magnetic field above 1 T destroys the static
long-range order, which is manifested in the gradual broadening of the magnetic
Bragg peaks. We argue that such a crossover from a magnetically long-range
ordered state to a spin-glass regime may result from orphan spins on the
structurally disordered magnetic sublattice, which are polarized in magnetic
field and thus act as a tuning knob for field-controlled magnetic disorder.",2011.05819v1
2022-02-09,Emergent Non-Abelian Gauge Theory in Coupled Spin-Electron Dynamics,"A clear separation of the time scales governing the dynamics of ""slow"" and
""fast"" degrees of freedom often serves as a prerequisite for the emergence of
an independent low-energy theory. Here, we consider (slow) classical spins
exchange coupled to a tight-binding system of (fast) conduction electrons. The
effective equations of motion are derived under the constraint that the quantum
state of the electron system at any instant of time $t$ lies in the
$n$-dimensional low-energy subspace for the corresponding spin configuration at
$t$. The effective low-energy theory unfolds itself straightforwardly and takes
the form of a non-abelian gauge theory with the gauge freedom given by the
arbitrariness of the basis spanning the instantaneous low-energy sector. The
holonomic constraint generates a gauge covariant spin-Berry curvature tensor in
the equations of motion for the classical spins. In the non-abelian theory for
$n>1$, opposed to the $n=1$ adiabatic spin dynamics theory, the spin-Berry
curvature is generically nonzero, even for time-reversal symmetric systems. Its
expectation value with the representation of the electron state is gauge
invariant and gives rise to an additional {\em geometrical} spin torque.
Besides anomalous precession, the $n\ge 2$ theory also captures the spin
nutational motion, which is usually considered as a retardation effect. This is
demonstrated by proof-of-principle numerical calculations for a minimal model
with a single classical spin. Already for $n=2$ and in parameter regimes where
the $n=1$ adiabatic theory breaks down, we find good agreement with results
obtained from the full (unconstrained) theory.",2202.04694v2
2004-06-10,Spin dynamics in a doped-Mott-insulator superconductor,"We present a systematic study of spin dynamics in a superconducting ground
state, which itself is a doped-Mott-insulator and can correctly reduce to an
antiferromagnetic (AF) state at half-filling with an AF long-range order
(AFLRO). Such a doped Mott insulator is described by a mean-field theory based
on the phase string formulation of the t-J model. We show that the spin wave
excitation in the AFLRO state at half-filling evolves into a resonancelike peak
at a finite energy in the superconducting state, which is located around the AF
wave vectors. The width of such a resonancelike peak in momentum space decides
a spin correlation length scale which is inversely proportional to the square
root of doping concentration, while the energy of the resonancelike peak scales
linearly with the doping concentration at low doping. An important prediction
of the theory is that, while the total spin sum rule is satisfied at different
doping concentrations, the weight of the resonancelike peak does not vanish,
but is continuously saturated to the weight of the AFLRO at zero-doping limit.
Besides the low-energy resonancelike peak, we also show that the high-energy
excitations still track the spin wave dispersion in momentum space,
contributing to a significant portion of the total spin sum rule. The
fluctuational effect beyond the mean-field theory is also examined, which is
related to the broadening of the resonancelike peak in energy space. In
particular, we discuss the incommensurability of the spin dynamics by pointing
out that its visibility is strongly tied to the low-energy fluctuations below
the resonancelike peak. We finally investigate the interlayer coupling effect
on the spin dynamics as a function of doping, by considering a bilayer system.",0406239v2
2020-12-29,Coherent single-spin electron resonance spectroscopy manifested at an exceptional-point singularity in a doped polyacetylene,"Spin-dependent charge transfer decay in an alkali atom doped polyacetylene is
studied in terms of the complex spectral analysis, revealing the single-spin
Zeeman splitting influenced by the spin-orbit interaction. Nonhermitian
effective Hamiltonian has been derived from the total system hermitian
Hamiltonian using Brillouin-Wigner-Feshbach projection method, where the
microscopic spin-dependent dissipation effect is correctly incorporated in the
energy-dependent self-energy. Since the present method maintains the dynamical
and chiral symmetries of the total system, we discovered two types of
exceptional point (EP) singularities in a unified perspective: the EP surface
and EP ring are attributed to the dynamical and chiral symmetry breaking,
respectively. We have revealed that the coherent single-spin electron resonance
(SSESR) spectrum reflects the complex eigenenergy spectrum of the system. We
have formulated the SSESR spectrum in terms of the nonlinear response function
in the Liouville-space pathway approach, where we have constructed the
Liouville space basis using the complex eigenstates of the total Hamiltonian.
We have calculated the one- and two-dimensional Fourier transform SSESR (1DFT
and 2DFT) spectra reflecting the spin-relaxation dynamics at the donor site.
While the 1DFT SSESR spectrum reflects the complex eigenenergy spectrum, the
2DFT gives detailed information on the quantum coherence in the spin-relaxation
dynamics as a cross-correlation between the two frequencies. We found a giant
response of the coherent SSESR around the EP ring singularity due to the
vanishing normalization factors at the EP ring and the resonance effect. We
have discovered that the giant response is much larger in magnitudes in the
2DFT spectrum than in the 1DFT spectrum, which promises the 2DFT SSESR a useful
tool to observe the single-spin response in a molecule.",2012.14655v1
2020-03-21,First-principles perspective on magnetic second sound,"The fluctuations of the magnetic order parameter, or longitudinal spin
excitations, are investigated theoretically in the ferromagnetic Fe and Ni as
well as in the antiferromagnetic phase of the pnictide superconductor FeSe. The
charge and spin dynamics of these systems is described by evaluating the
generalized charge and spin density response function calculated from
first-principles linear response time dependent density functional theory
within adiabatic local spin density approximation. We observe that the formally
non-interacting Kohn-Sham system features strong coupling between the
magnetization and charge dynamics in the longitudinal channel and that the
coupling is effectively removed upon the inclusion of the Coulomb interaction
in the charge channel and the resulting appearance of plasmons. The
longitudinal spin fluctuations acquire a collective character without the
emergence of the Goldstone boson, similar to the case of paramagnon excitations
in non-magnetic metals like Pd. In ferromagnetic Fe and Ni the longitudinal
spin dynamics is governed by interactions between low-energy intraband
electron-hole pairs while in quasi two dimensional antiferromagnet FeSe it is
dominated by the interband transitions with energies of the order of exchange
splitting. In the later material, the collective longitudinal magnetization
fluctuations feature well defined energies and long life times for small
momenta and appear below the particle-hole continuum. The modes become strongly
Landau-damped for growing wave-vectors. We relate our theoretical findings to
existing experimental spin-polarized electron energy loss spectroscopy results.
In bulk bcc Fe, the longitudinal magnetic modes appear above the typical
energies of transverse spin-waves, have energies comparable with the Stoner
spin-flip excitation continuum, and are order of magnitude less energetic than
the charge dynamics.",2003.09735v3
2021-09-23,Dynamic Parallel Spin Stripes from the 1/8 anomaly to the End of Superconductivity in La$_{1.6-x}$Nd$_{0.4}$Sr$_x$CuO$_4$,"We have carried out new neutron spectroscopic measurements on single crystals
of La$_{1.6-x}$Nd$_{0.4}$Sr$_x$CuO$_4$ from 0.12 to 0.26 using time-of-flight
techniques. These measurements allow us to follow the evolution of parallel
spin stripe fluctuations with energies less than 33 meV, from x=0.12 to 0.26.
Samples at these hole-doping levels are known to display static (on the neutron
scattering time scale) parallel spin stripes at low temperature, with onset
temperatures and intensities which decrease rapidly with increasing x.
Nonetheless, we report remarkably similar dynamic spectral weight for the
corresponding dynamic parallel spin stripes, between 5 meV to 33 meV, from the
1/8 anomaly near x=0.12, to optimal doping near x=0.19 to the quantum critical
point for the pseudogap phase near x=0.24, and finally to the approximate end
of superconductivity near x=0.26. This observed dynamic magnetic spectral
weight is structured in energy with a peak near 17 meV at all dopings studied.
Earlier neutron and resonant x-ray scattering measurements on related cuprate
superconductors have reported both a disappearance with increasing doping of
magnetic fluctuations at ($\pi$, $\pi$) wavevectors characterizing parallel
spin stripe structures, and persistant paramagnon scattering away from this
wavevector, respectively. Our new results on
La$_{1.6-x}$Nd$_{0.4}$Sr$_x$CuO$_4$ from 0.12 < x <0.26 clearly show persistent
parallel spin stripe fluctuations at and around at ($\pi$, $\pi$), and across
the full range of doping studied. These results are also compared to recent
theory. Together with a rapidly declining x-dependence to the static parallel
spin stripe order, the persistent parallel spin stripe fluctuations show a
remarkable similarity to the expectations of a quantum spin glass, random t-J
model, recently introduced to describe strong local correlations in cuprates.",2109.11570v2
2022-09-14,Collapse and revival structure of information backflow for a central spin coupled to a finite spin bath,"The Markovianity of quantum dynamics is an important property of open quantum
systems determined by various ingredients of the system and bath. Apart from
the system-bath interaction, the initial state of the bath, etc., the dimension
of the bath plays a critical role in determining the Markovianity of quantum
dynamics, as a strict decay of the bath correlations requires an infinite
dimension for the bath. In this work, we investigate the role of finite bath
dimension in the Markovianity of quantum dynamics by considering a simple but
nontrivial model in which a central spin is isotropically coupled to a finite
number of bath spins, and show how the dynamics of the central spin transits
from non-Markovian to Markovian as the number of the bath spins increases. The
non-Markovianity is characterized by the information backflow from the bath to
the system in terms of the trace distance of the system states. We derive the
time evolution of the trace distance analytically, and find periodic
collapse-revival patterns in the information flow. The mechanism underlying
this phenomenon is investigated in detail, and it shows that the period of the
collapse-revival pattern is determined by the competition between the number of
the bath spins, the system-bath coupling strength, and the frequency detuning.
When the number of bath spins is sufficiently large, the period of the
collapse-revival structure as well as the respective collapse and revival times
increase in proportion to the number of the bath spins, which characterizes how
the information backflow decays with a large dimension of the bath. We also
analyze the effect of the system-bath interaction strength and frequency
detuning on the collapse-revival patterns of the information flow, and obtain
the condition for the existence of the collapse-revival structure. The results
are illustrated by numerical computation.",2209.06541v2
2023-05-30,Nonlinear dynamics for the Ising model,"We introduce and analyze a natural class of nonlinear dynamics for spin
systems such as the Ising model. This class of dynamics is based on the
framework of mass action kinetics, which models the evolution of systems of
entities under pairwise interactions, and captures a number of important
nonlinear models from various fields, including chemical reaction networks,
Boltzmann's model of an ideal gas, recombination in population genetics and
genetic algorithms. In the context of spin systems, it is a natural
generalization of linear dynamics based on Markov chains, such as Glauber
dynamics and block dynamics, which are by now well understood. However, the
inherent nonlinearity makes the dynamics much harder to analyze, and rigorous
quantitative results so far are limited to processes which converge to
essentially trivial stationary distributions that are product measures. In this
paper we provide the first quantitative convergence analysis for natural
nonlinear dynamics in a combinatorial setting where the stationary distribution
contains non-trivial correlations, namely the Ising model at high temperatures.
We prove that nonlinear versions of both the Glauber dynamics and the block
dynamics converge to the Gibbs distribution of the Ising model (with given
external fields) in times $O(n\log n)$ and $O(\log n)$ respectively, where $n$
is the size of the underlying graph (number of spins). Given the lack of
general analytical methods for such nonlinear systems, our analysis is
unconventional, and combines tools such as information percolation (due in the
linear setting to Lubetzky and Sly), a novel coupling of the Ising model with
Erd\H{o}s-R\'enyi random graphs, and non-traditional branching processes
augmented by a fragmentation process.",2305.18788v1
2008-05-31,Quantum many-body theory of qubit decoherence in a finite-size spin bath,"Decoherence of a center spin or qubit in a spin bath is essentially
determined by the many-body bath evolution. We develop a cluster-correlation
expansion (CCE) theory for the spin bath dynamics relevant to the qubit
decoherence problem. A cluster correlation term is recursively defined as the
evolution of a group of bath spins divided by the cluster correlations of all
the subgroups. The so-defined correlation accounts for the authentic collective
excitations within a given group. The bath propagator is the product of all
possible cluster correlation terms. For a finite-time evolution as in the qubit
decoherence problem, a convergent result can be obtained by truncating the
expansion up to a certain cluster size. The two-spin cluster truncation of the
CCE corresponds to the pair-correlation approximation [PRB 74,195301(2006)]. In
terms of the standard linked cluster expansion, a cluster correlation term is
the infinite summation of all the connected diagrams with all and only the
spins in the group flip-flopped, and thus the expansion is exact whenever
converges. When the individual contribution of each higher-order correlation
term to the decoherence is small, as the usual case for relatively large baths
where the decoherence could complete well within the bath spin flip-flop time,
the CCE coincides with the cluster expansion [PRB 74,035322(2006)]. For small
baths, however, the qubit decoherence may not complete within the bath spin
flip-flop timescale and thus individual higher-order cluster correlations could
grow significant. In such cases, only the CCE converges to the exact coherent
dynamics of multi-spin clusters. We check the accuracy of the CCE in an exactly
solvable spin-chain model.",0806.0098v1
2013-12-19,Black hole binary remnant mass and spin: A new phenomenological formula,"We perform a set of 38 numerical simulations of equal-mass BH binaries in a
configuration where the BH spins in the binary are equal in both magnitude and
direction, to study precession effects. We vary the initial direction of the
total spin S with respect to the orbital angular momentum L, covering the 2
dimensional space of orientation angles with 38 configurations consisting of 36
configurations distributed in the azimuthal angle phi and polar angle theta,
and two configurations on the poles. In all cases, we set the initial
dimensionless BH spins to 0.8. We observe that during the late-inspiral stage,
the total angular momentum of the system J remains within 5 deg of its original
direction, with the largest changes in direction occurring when the spins are
nearly counter-aligned with the orbital angular momentum. We also observe that
the angle between S and L is nearly conserved during the inspiral phase. These
two dynamical properties allow us to propose a new phenomenological formula for
the final mass and spin of merged BHs in terms of the individual masses and
spins of the progenitor binary at far separations. We determine coefficients of
this formula (in the equal-mass limit) using a least-squares fit to the results
of this new set of 38 runs, an additional set of five new configurations with
spins aligned/counteraligned with the orbital angular momentum, and over 100
recent simulations. We find that our formulas reproduce the remnant mass and
spin of these simulations to within a relative error of 2.5%. We discuss the
region of validity of this dynamical picture for precessing unequal-mass
binaries. Finally, we perform a statistical study to see the consequence of
this new formula for distributions of spin-magnitudes and remnant masses with
applications to BH-spin distributions and gravitational radiation in
cosmological scenarios involving several mergers.",1312.5775v3
2018-07-27,Detection of Rashba spin splitting in 2D organic-inorganic perovskite via precessional carrier spin relaxation,"The strong spin-orbit interaction in the organic-inorganic perovskites tied
to the incorporation of heavy elements (\textit{e.g.} Pb, I) makes these
materials interesting for applications in spintronics. Due to a lack of
inversion symmetry associated with distortions of the metal-halide octahedra,
the Rashba effect (used \textit{e.g.} in spin field-effect transistors and spin
filters) has been predicted to be much larger in these materials than in
traditional III-V semiconductors such as GaAs, supported by the recent
observation of a near record Rashba spin splitting in CH$_3$NH$_3$PbBr$_3$
using angle-resolved photoemission spectroscopy (ARPES). More experimental
studies are needed to confirm and quantify the presence of Rashba effects in
the organic-inorganic perovskite family of materials. Here we apply
time-resolved circular dichroism techniques to the study of carrier spin
dynamics in a 2D perovskite thin film [(BA)$_2$MAPb$_2$I$_7$; BA =
CH$_3$(CH$_2$)$_3$NH$_3$, MA = CH$_3$NH$_3$]. Our findings confirm the presence
of a Rashba spin splitting via the dominance of precessional spin relaxation
induced by the Rashba effective magnetic field. The size of the Rashba spin
splitting in our system was extracted from simulations of the measured spin
dynamics incorporating LO-phonon and electron-electron scattering, yielding a
value of 10 meV at an electron energy of 50 meV above the band gap,
representing a 20 times larger value than in GaAs quantum wells.",1807.10803v1
2020-05-08,Nanoscale Spin Injector Driven by a Microwave Voltage,"We propose an electrically driven spin injector into normal metals and
semiconductors, which is based on a magnetic tunnel junction (MTJ) subjected to
a microwave voltage. Efficient functioning of such an injector is provided by
electrically induced magnetization precession in the ""free"" layer of MTJ, which
generates the spin pumping into a metallic or semiconducting overlayer. We
theoretically describe the spin and charge dynamics in the
CoFeB/MgO/CoFeB/Au(GaAs) heterostructures. First, the magnedynamics in the free
CoFeB layer is quantified with the account of a spin-transfer torque and a
voltage-controlled magnetic anisotropy. By numerically solving the
magnetodynamics equation, we determine dependences of the precession amplitude
on the frequency $f$ and magnitude $V_\mathrm{max}$ of the ac voltage applied
to the MTJ. It is found that the frequency dependence changes drastically above
the threshold amplitude $V_\mathrm{max} \approx 200$mV, exhibiting a break at
the resonance frequency $f_\mathrm{res}$ due to nonlinear effects. The results
obtained for the magnetization dynamics are used to describe the spin injection
and pumping into the Au and GaAs overlayers. Since the generated spin current
creates additional charge current owing to the inverse spin Hall effect, we
also calculate distribution of the electric potential in the thick Au
overlayer. The calculations show that the arising transverse voltage becomes
experimentally measurable at $f = f_\mathrm{res}$. Finally, we evaluate the
spin accumulation in a long n$^+$-GaAs bar coupled to the MTJ and determine its
temporal variation and spatial distribution along the bar. It is found that the
spin accumulation under resonant excitation is large enough for experimental
detection even at micrometer distances from the MTJ. This result demonstrates
high efficiency of the described nanoscale spin injector.",2005.03896v1
2021-10-11,Transition of laser-induced terahertz spin currents from torque- to conduction-electron-mediated transport,"Spin transport is crucial for future spintronic devices operating at
bandwidths up to the terahertz (THz) range. In F|N thin-film stacks made of a
ferro/ferrimagnetic layer F and a normal-metal layer N, spin transport is
mediated by (1) spin-polarized conduction electrons and/or (2) torque between
electron spins. To identify a cross-over from (1) to (2), we study laser-driven
spin currents in F|Pt stacks where F consists of model materials with different
degrees of electrical conductivity. For the magnetic insulators YIG, GIG and
maghemite, identical dynamics is observed. It arises from the THz interfacial
spin Seebeck effect (SSE), is fully determined by the relaxation of the
electrons in the metal layer and provides an estimate of the spin-mixing
conductance of the GIG/Pt interface. Remarkably, in the half-metallic
ferrimagnet Fe3O4 (magnetite), our measurements reveal two spin-current
components with opposite direction. The slower, positive component exhibits SSE
dynamics and is assigned to torque-type magnon excitation of the A- and B-spin
sublattices of Fe3O4. The faster, negative component arises from the
pyro-spintronic effect and can consistently be assigned to ultrafast
demagnetization of e-sublattice minority-spin hopping electrons. This
observation supports the magneto-electronic model of Fe3O4. In general, our
results provide a new route to the contact-free separation of torque- and
conduction-electron-mediated spin currents.",2110.05462v2
2022-07-20,Flux noise in disordered spin systems,"Impurity spins randomly distributed at the surfaces and interfaces of
superconducting wires are known to cause flux noise in Superconducting Quantum
Interference Devices, providing a mechanism for decoherence in superconducting
qubits. While flux noise is well characterised experimentally, the microscopic
model underlying spin dynamics remains unknown. First-principles theories are
too computationally expensive to capture spin diffusion over large length
scales, third-principles approaches lump spin dynamics into a single
phenomenological spin-diffusion operator that is not able to describe the
quantum noise regime and connect to microscopic models and disorder scenarios.
Here we propose an intermediate ""second principles"" method to describe general
spin dissipation and flux noise in the quantum regime. It leads to the
interpretation that flux noise arises from the density of paramagnon
excitations at the edge of the wire, with paramagnon-paramagnon interactions
leading to spin diffusion, and interactions between paramagnons and other
degrees of freedom leading to spin energy relaxation. At high frequency we
obtain an upper bound for flux noise, showing that the (super)Ohmic noise
observed in experiments does not originate from interacting spin impurities. We
apply the method to Heisenberg models in two dimensional square lattices with
random distribution of vacancies and nearest-neighbour spins coupled by
constant exchange. Numerical calculations of flux noise show that it follows
the observed power law $A/\omega^{\alpha}$, with amplitude $A$ and exponent
$\alpha$ depending on temperature and inhomogeneities. These results are
compared to experiments in niobium and aluminium devices. The method
establishes a connection between flux noise experiments and microscopic
Hamiltonians identifying relevant microscopic mechanisms and guiding strategies
for reducing flux noise.",2207.10033v3
2024-03-18,Tuning of the ultrafast demagnetization by ultrashort spin polarized currents in multi-sublattice ferrimagnets,"Femtosecond laser pulses can be used to induce ultrafast changes of the
magnetization in magnetic materials. Several microscopic mechanisms have been
proposed to explain the observations, including the transport of ultrashort
spin-polarized hot-electrons (SPHE). Such ultrafast spin currents find growing
interest because of the recent challenges in ultrafast spintronics however they
are only poorly characterized. One of the key challenges is to characterize the
spin-polarized ultrafast currents and the microscopic mechanisms behind SPHE
induced manipulation of the magnetization, especially in the case of
technologically relevant ferrimagnetic alloys. Here, we have used a combined
approach using time- and element-resolved X-ray magnetic circular dichroism and
theoretical calculations based on atomistic spin-dynamics simulations to
address the ultrafast transfer of the angular momentum from spin-polarized
currents into ferrimagnetic Fe74Gd26 films and the concomitant reduction of
sub-lattice magnetization. Our study shows that using a Co/Pt multilayer as a
polarizer in a spin-valve structure, the SPHE drives the demagnetization of the
two sub-lattices of the Fe74Gd26 film. This behaviour is explained based on two
physical mechanisms, i.e., spin transfer torque and thermal fluctuations
induced by the SPHE. We provide a quantitative description of the heat transfer
of the ultrashort SPHE pulse to the Fe74Gd26 films, as well as the degree of
spin-polarization of the SPHE current density responsible for the observed
magnetization dynamics. Our work finally characterizes the spin-polarization of
the SPHEs revealing unexpected opposite spin polarization to the Co
magnetization, explaining our experimental results.",2403.11739v2
2008-08-28,"Effects of Zn and Ni substitution on the Cu-spin dynamics and superconductivity in La_2-x_Sr_x_Cu_1-y_(Zn,Ni)_y_O_4_ with x=0.15-0.20 studied by the muon spin relaxation and magnetic susceptibility","We have investigated effects of Zn and Ni on the Cu-spin dynamics and
superconductivity from the zero-field muon-spin-relaxation (ZF-muSR) and
magnetic-susceptibility, chi, measurements for
La_2-x_Sr_x_Cu_1-y_(Zn,Ni)_y_O_4_ with x=0.15-0.20, changing y up to 0.10 in
fine step. In the optimally doped x=0.15, it has been concluded that the
formation of a magnetic order requires a larger amount of Ni than that of Zn,
which is similar to our previous results of x=0.13. From the estimation of
volume fractions of superconducting (SC) and magnetic regions, it has been
found for x=0.15 that the SC region is in rough correspondence to the region
where Cu spins fluctuate fast beyond the muSR frequency window for both Zn- and
Ni-substituted samples. According to the stripe model, it follows that, even
for x=0.15, the dynamical stripe correlations of spins and holes are pinned and
localized around Zn and Ni, leading to the formation of the static stripe order
and the suppression of superconductivity. These may indicate an importance of
the dynamical stripe in the appearance of the high-T_c_ superconductivity in
the hole-doped cuprates. In the overdoped regime of x=0.18 and 0.20, on the
other hand, the SC region seems to be in rough correspondence to the region
where Cu spins fluctuate fast beyond the muSR frequency window, though it
appears that the Cu-spin dynamics and superconductivity are affected by the
phase separation into SC and normal-state regions.",0808.3871v2
2022-05-08,Ground-state and dynamical properties of a spin-$S$ Heisenberg star,"We generalize the Heisenberg star consisting of a spin-1/2 central spin and a
homogeneously coupled spin bath modeled by the XXX ring [Richter J and Voigt A
1994 \emph{J. Phys. A: Math. Gen.} \textbf{27} 1139-1149] to the case of
arbitrary central-spin size $S<N/2$, where $N$ is the number of bath spins. We
describe how to block-diagonalize the model based on the Bethe ansatz solution
of the XXX ring, with the dimension of each block Hamiltonian $\leq 2S+1$. We
obtain all the eigenenergies and explicit expressions of the sub-ground states
in each $l$-subspace with $l$ being the total angular momentum of the bath.
Both the eigenenergies and the sub-ground states have distinct structures
depending whether $S\leq l$ or $l<S$. The absolute ground-state energy and the
corresponding $l$ as functions of the intrabath coupling are numerically
calculated for $N=16$ and $S=1,2,\cdots,7$ and their behaviors are
quantitatively explained in the weak and strong intrabath coupling limits. We
then study the dynamics of the antiferromagnetic order within an XXX bath
prepared in the N\'eel state. Effects of the initial state of the central spin,
the value of $S$, and the system-bath coupling strength on the staggered
magnetization dynamics are investigated. By including a Zeeman term for the
central spin and the anisotropy in the intrabath coupling, we also study the
polarization dynamics of the central spin for a bath prepared in the spin
coherent state. Under the resonant condition and at the isotropic point of the
bath, the polarization dynamics for $S>1/2$ exhibits collapse-revival behaviors
with fine structures. However, the collapse-revival phenomena is found to be
fragile with respect to anisotropy of the intrabath coupling.",2205.03808v2
2001-06-16,Statics and Dynamics of the 10-state mean-field Potts glass model: A Monte Carlo study,"We investigate by means of Monte Carlo simulations the fully connected
p-state Potts model for different system sizes in order to see how the static
and dynamic properties of a finite model compare with the, exactly known,
behavior of the system in the thermodynamic limit. Using p=10 we are able to
study the equilibrium dynamics for system sizes as large as N=2560. We find
that the static quantities, such as the energy, the entropy, the spin glass
susceptibility as well as the distribution of the order parameter P(q) show
very strong finite size effects. From P(q) we calculate the forth order
cumulant g_4(N,T) and the Guerra parameter G(N,T) and show that these
quantities cannot be used to locate the static transition temperature for the
system sizes investigated. Also the spin-autocorrelation function C(t) shows
strong finite size effects in that it does not show a plateau even for
temperatures around the dynamical critical temperature T_D. We show that the
N-and T-dependence of the \alpha-relaxation time can be understood by means of
a dynamical finite size scaling Ansatz. C(t) does not obey the time-temperature
superposition principle for temperatures around T_D, but does so for
significantly lower T. Finally we study the relaxation dynamics of the
individual spins and show that their dependence on time depends strongly on the
chosen spin, i.e. that the system is dynamically very heterogeneous, which
explains the non-exponentiality of C(t).",0106314v1
2009-06-04,A statistical-mechanical study of evolution of robustness in noisy environment,"In biological systems, expression dynamics that can provide fitted phenotype
patterns with respect to a specific function have evolved through mutations.
This has been observed in the evolution of proteins for realizing folding
dynamics through which a target structure is shaped. We study this evolutionary
process by introducing a statistical-mechanical model of interacting spins,
where a configuration of spins and their interactions $\bm{J}$ represent a
phenotype and genotype, respectively. The phenotype dynamics are given by a
stochastic process with temperature $T_{S}$ under a Hamiltonian with $\bm{J}$.
The evolution of $\bm{J}$ is also stochastic with temperature $T_{J}$ and
follows mutations introduced into $\bm{J}$ and selection based on a fitness
defined for a configuration of a given set of target spins. Below a certain
temperature $T_{S}^{c2}$, the interactions $\bm{J}$ that achieve the target
pattern evolve, whereas another phase transition is observed at
$T_{S}^{c1}<T_{S}^{c2}$. At low temperatures $T_{S}<T_{S}^{c1}$, the
Hamiltonian exhibits a spin-glass like phase, where the dynamics toward the
target pattern require long time steps, and the fitness often decreases
drastically as a result of a single mutation to $\bm{J}$. In the
intermediate-temperature region, the dynamics to shape the target pattern
proceed rapidly and are robust to mutations of $\bm{J}$. The interactions in
this region have no frustration around the target pattern and results in
funnel-type dynamics. We propose that the ubiquity of funnel-type dynamics, as
observed in protein folding, is a consequence of evolution subjected to thermal
noise beyond a certain level; this also leads to mutational robustness of the
fitness.",0906.0900v3
2018-05-15,Coarsening and percolation in the kinetic $2d$ Ising model with spin exchange updates and the voter model,"We study the early time dynamics of bimodal spin systems on $2d$ lattices
evolving with different microscopic stochastic updates. We treat the
ferromagnetic Ising model with locally conserved order parameter (Kawasaki
dynamics), the same model with globally conserved order parameter (nonlocal
spin exchanges), and the voter model. As already observed for non-conserved
order parameter dynamics (Glauber dynamics), in all the cases in which the
stochastic dynamics satisfy detailed balance, the critical percolation state
persists over a long period of time before usual coarsening of domains takes
over and eventually takes the system to equilibrium. By studying the
geometrical and statistical properties of time-evolving spin clusters we are
able to identify a characteristic length $\ell_p(t)$, different from the usual
length $\ell_d(t) \sim t^{1/z_{d}}$ that describes the late time coarsening,
that is involved in all scaling relations in the approach to the critical
percolation regime. We find that this characteristic length depends on the
particular microscopic dynamics and the lattice geometry. In the case of the
voter model, we observe that the system briefly passes through a critical
percolation state, to later approach a dynamical regime in which the scaling
behaviour of the geometrical properties of the ordered domains can be ascribed
to a different criticality.",1805.05775v2
2016-05-18,Standing magnetic wave on Ising ferromagnet: Nonequilibrium phase transition,"The dynamical response of an Ising ferromagnet to a plane polarised standing
magnetic field wave is modelled and studied here by Monte Carlo simulation in
two dimensions. The amplitude of standing magnetic wave is modulated along the
direction x. We have detected two main dynamical phases namely, pinned and
oscillating spin clusters. Depending on the value of field amplitude the system
is found to undergo a phase transition from oscillating spin cluster to pinned
as the system is cooled down. The time averaged magnetisation over a full cycle
of magnetic field oscillations is defined as the dynamic order parameter. The
transition is detected by studying the temperature dependences of the variance
of the dynamic order parameter, the derivative of the dynamic order parameter
and the dynamic specific heat. The dependence of the transition temperature on
the magnetic field amplitude and on the wavelength of the magnetic field wave
is studied at a single frequency. A comprehensive phase boundary is drawn in
the plane described by the temperature and field amplitude for two different
wavelengths of the magnetic wave. The variation of instantaneous line
magnetisation during a period of magnetic field oscillation for standing wave
mode is compared to those for the propagating wave mode. Also the probability
that a spin at any site, flips, is calculated. The above mentioned variations
and the probability of spin flip clearly distinguish between the dynamical
phases formed by propagating magnetic wave and by standing magnetic wave in an
Ising ferromagnet.",1605.05643v2
2019-03-31,Relaxation to equilibrium in models of classical spins with long-range interactions,"For a model long-range interacting system of classical Heisenberg spins, we
study how fluctuations, such as those arising from having a finite system size
or through interaction with the environment, affect the dynamical process of
relaxation to Boltzmann-Gibbs equilibrium. Under deterministic spin
precessional dynamics, we unveil the full range of quasistationary behavior
observed during relaxation to equilibrium, whereby the system is trapped in
nonequilibrium states for times that diverge with the system size. The
corresponding stochastic dynamics, modeling interaction with the environment
and constructed in the spirit of the stochastic Landau-Lifshitz-Gilbert
equation, however shows a fast relaxation to equilibrium on a size-independent
timescale and no signature of quasistationarity, provided the noise is strong
enough. Similar fast relaxation is also seen in Glauber Monte Carlo dynamics of
the model, thus establishing the ubiquity of what has been reported earlier in
particle dynamics (hence distinct from the spin dynamics considered here) of
long-range interacting systems, that quasistationarity observed in
deterministic dynamics is washed away by fluctuations induced through contact
with the environment.",1904.00432v2
2020-09-21,Influence of spin and orbital fluctuations on Mott-Hubbard exciton dynamics in LaVO${}_{3}$ Thin Films,"Recent optical conductivity measurements reveal the presence of Hubbard
excitons in certain Mott insulators. In light of these results, it is important
to revisit the dynamics of these materials to account for excitonic
correlations. We investigate time-resolved excitation and relaxation dynamics
as a function of temperature in perovskite-type LaVO${}_{3}$ thin films using
ultrafast optical pump-probe spectroscopy. LaVO${}_{3}$ undergoes a series of
phase transitions at roughly the same critical temperature $T_C\cong 140\ K$,
including a second-order magnetic phase transition (PM $\xrightarrow{}$ AFM)
and a first-order structural phase transition, accompanied by \textit{C}-type
spin order (SO) and \textit{G}-type orbital order (OO). Ultrafast optical
pump-probe spectroscopy at 1.6 eV monitors changes in the spectral weight of
the Hubbard exciton resonance which serves as a sensitive reporter of spin and
orbital fluctuation dynamics. We observe dramatic slowing down of the spin, and
orbital dynamics in the vicinity of $T_C\cong 140$ K, reminiscent of a
second-order phase transition, despite the (weakly) first-order nature of the
transition. We emphasize that since it is spectral weight changes that are
probed, the measured dynamics are not reflective of conventional exciton
generation and recombination, but are related to the dynamics of Hubbard
exciton formation in the presence of a fluctuating many-body environment.",2009.10219v1
2024-03-13,On sampling diluted Spin Glasses using Glauber dynamics,"Spin-glasses are Gibbs distributions that have been studied in CS for many
decades. Recently, they have gained renewed attention as they emerge naturally
in learning, inference, optimisation etc.
  We consider the Edwards-Anderson (EA) spin-glass distribution at inverse
temperature $\beta$ when the underlying graph is an instance of $G(n,d/n)$.
This is the random graph on $n$ vertices where each edge appears independently
with probability $d/n$ and $d=\Theta(1)$. We study the problem of approximate
sampling from this distribution using Glauber dynamics.
  For a range of $\beta$ that depends on $d$ and for typical instances of the
EA model on $G(n,d/n)$, we show that the corresponding Glauber dynamics
exhibits mixing time $O(n^{2+\frac{3}{\log^2 d}})$.
  The range of $\beta$ for which we obtain our rapid-mixing results correspond
to the expected influence being $<1/d$; we conjecture that this is the best
possible.
  Unlike the mean-field spin-glasses, where the problem has been studied
before, the diluted case has not.
  We utilise the well-known path-coupling technique. In the standard Glauber
dynamics on $G(n,d/n)$, one has to deal with the so-called effect of high
degree vertices. Here, rather than considering degrees, it is more natural to
use a different measure on the vertices called aggregate influence.
  We build on the block-construction approach proposed by [Dyer et al. 2006] to
circumvent the problem of high-degree vertices. Specifically, we first
establish rapid mixing for an appropriately defined block-dynamics. We design
this dynamics such that vertices of large aggregate influence are placed deep
inside their blocks. Then, we obtain rapid mixing for the Glauber dynamics
utilising a comparison argument.",2403.08921v1
1997-08-25,Effects of Phonons and Nuclear Spins on the Tunneling of a Domain Wall,"We consider the quantum dynamics of a magnetic domain wall at low
temperatures, where dissipative couplings to magnons and electrons are very
small. The wall motion is then determined by its coupling to phonons and
nuclear spins, and any pinning potentials. In the absence of nuclear spins
there is a dominant superOhmic 1-phonon coupling to the wall velocity, plus a
strongly T-dependent Ohmic coupling to pairs of phonons. There is also a
T-independent Ohmic coupling between single phonons and the wall chirality,
which suppresses ``chirality tunneling''. We calculate the effect of these
couplings on the T-dependent tunneling rate of a wall out of a pinning
potential. Nuclear spins have a very strong and hitherto unsuspected influence
on domain wall dynamics, coming from a hyperfine-mediated coupling to the
domain wall position. For $k_B T \gg \omega_{0}$ this coupling yields a
spatially random potential, fluctuating at a rate governed by the nuclear
$T_2$. When $k_B T \ll \omega_{0}$, the hyperfine potential fluctuates around a
linear binding potential. The wall dynamics is influenced by the fluctuations
of this potential, ie., by the nuclear spin dynamics. Wall tunneling can occur
when fluctuations open an occasional ``tunneling window''. This changes the
crossover to tunneling and also causes a slow ""wandering"", in time, of the
energy levels associated with domain wall motion inside the pinning potential.
This effect is fairly weak in $Ni$- and $Fe$- based magnets, and we give an
approximate treatment of its effect on the tunneling dynamics, as well as a
discussion of the relationship to recent domain wall tunneling experiments.",9708191v1
2003-12-15,Statics and Dynamics of Quantum XY and Heisenberg Systems on Graphs,"We consider the statics and dynamics of distinguishable spin-1/2 systems on
an arbitrary graph G with N vertices. In particular, we consider systems of
quantum spins evolving according to one of two hamiltonians: (i) the XY
hamiltonian H_XY, which contains an XY interaction for every pair of spins
connected by an edge in G; and (ii) the Heisenberg hamiltonian H_Heis, which
contains a Heisenberg interaction term for every pair of spins connected by an
edge in G. We find that the action of the XY (respectively, Heisenberg)
hamiltonian on state space is equivalent to the action of the adjacency matrix
(respectively, combinatorial laplacian) of a sequence G_k, k=0,..., N of graphs
derived from G (with G_1=G). This equivalence of actions demonstrates that the
dynamics of these two models is the same as the evolution of a free particle
hopping on the graphs G_k. Thus we show how to replace the complicated dynamics
of the original spin model with simpler dynamics on a more complicated
geometry. A simple corollary of our approach allows us to write an explicit
spectral decomposition of the XY model in a magnetic field on the path
consisting of N vertices. We also use our approach to utilise results from
spectral graph theory to solve new spin models: the XY model and heisenberg
model in a magnetic field on the complete graph.",0312126v3
2007-10-31,Spin-Torque Driven Magnetization Dynamics: Micromagnetic Modelling,"In this paper we present an overview of recent progress made in the
understanding of the spin-torque induced magnetization dynamics in nanodevices
using mesoscopic micromagnetic simulations. We first specify how a spin-torque
term may be added to the usual Landau-Lifshitz-Gilbert equation of
magnetization motion and detail its physical meaning. After a brief description
of spin-torque driven dynamics in the macrospin approximation, we discuss the
validity of this approximation for various experimentally relevant geometries.
Next, we perform a detailed comparison between accurate experimental data
obtained from nanopillar devices and corresponding numerical modelling. We show
that, on the one hand, many qualitatively important features of the observed
magnetization dynamics (e.g., non-linear frequency shift and frequency jumps
with increasing current) can be satisfactory explained by sophisticated
micromagnetic models, but on the other hand, understanding of these experiments
is still far from being complete. We proceed with the numerical analysis of
point-contact experiments, where an even more complicated magnetization
dynamics is observed. Simulations reveal that such a rich behaviour is due to
the formation of several strongly non-linear oscillation modes. In the last
part of the paper we emphasize the importance of sample characterization and
conclude with some important remarks concerning the relation between
micromagnetic modelling and real experiments.",0710.5924v1
2009-09-24,Quantum control and measurement of atomic spins in polarization spectroscopy,"Quantum control and measurement are two sides of the same coin. To affect a
dynamical map, well-designed time-dependent control fields must be applied to
the system of interest. To read out the quantum state, information about the
system must be transferred to a probe field. We study a particular example of
this dual action in the context of quantum control and measurement of atomic
spins through the light-shift interaction with an off-resonant optical probe.
By introducing an irreducible tensor decomposition, we identify the coupling of
the Stokes vector of the light field with moments of the atomic spin state.
This shows how polarization spectroscopy can be used for continuous weak
measurement of atomic observables that evolve as a function of time.
Simultaneously, the state-dependent light shift induced by the probe field can
drive nonlinear dynamics of the spin, and can be used to generate arbitrary
unitary transformations on the atoms. We revisit the derivation of the master
equation in order to give a unified description of spin dynamics in the
presence of both nonlinear dynamics and photon scattering. Based on this
formalism, we review applications to quantum control, including the design of
state-to-state mappings, and quantum-state reconstruction via continuous weak
measurement on a dynamically controlled ensemble.",0909.4506v1
2009-11-30,Large deviation principle for one-dimensional random walk in dynamic random environment: attractive spin-flips and simple symmetric exclusion,"Consider a one-dimensional shift-invariant attractive spin-flip system in
equilibrium, constituting a dynamic random environment, together with a
nearest-neighbor random walk that on occupied sites has a local drift to the
right but on vacant sites has a local drift to the left. In previous work we
proved a law of large numbers for dynamic random environments satisfying a
space-time mixing property called cone-mixing. If an attractive spin-flip
system has a finite average coupling time at the origin for two copies starting
from the all-occupied and the all-vacant configuration, respectively, then it
is cone-mixing.
  In the present paper we prove a large deviation principle for the empirical
speed of the random walk, both quenched and annealed, and exhibit some
properties of the associated rate functions. Under an exponential space-time
mixing condition for the spin-flip system, which is stronger than cone-mixing,
the two rate functions have a unique zero, i.e., the slow-down phenomenon known
to be possible in a static random environment does not survive in a fast mixing
dynamic random environment. In contrast, we show that for the simple symmetric
exclusion dynamics, which is not cone-mixing (and which is not a spin-flip
system either), slow-down does occur.",0911.5629v1
2011-12-20,Spin Dynamics of a J1-J2-K Model for the Paramagnetic Phase of Iron Pnictides,"We study the finite-temperature spin dynamics of the paramagnetic phase of
iron pnictides within an antiferromagnetic J_1-J_2 Heisenberg model on a square
lattice with a biquadratic coupling $-K (S_i \cdot S_j)^2$ between the
nearest-neighbor spins. Our focus is on the paramagnetic phase in the parameter
regime of this J_1-J_2-K model where the ground state is a (\pi,0) collinear
antiferromagnet. We treat the biquadratic interaction via a
Hubbard-Stratonovich decomposition, and study the resulting effective
quadratic-coupling model using both modified spin wave and Schwinger boson
mean-field theories; the results for the spin dynamics derived from the two
methods are very similar. We show that the spectral weight of dynamical
structure factor S(q,\omega) is peaked at ellipses in the momentum space at low
excitation energies. With increasing energy, the elliptic features expand
towards the zone boundary, and gradually split into two parts, forming a
pattern around (\pi,\pi). Finally, the spectral weight is anisotropic, being
larger along the major axis of the ellipse than along its minor axis. These
characteristics of the dynamical structure factor are consistent with the
recent measurements of the inelastic neutron scattering spectra on BaFe_2As_2
and SrFe_2As_2.",1112.4785v3
2013-12-03,Lattice-site-specific spin-dynamics in double perovskite Sr2CoOsO6,"We have studied the magnetic properties and spin-dynamics of the
structurally-ordered double perovskite Sr$_2$CoOsO$_6$. Our neutron
diffraction, muon spin relaxation and ac-susceptibility measurements reveal two
antiferromagnetic (AFM) phases on cooling from room temperature down to 2 K. In
the first AFM phase, with transition temperature $T_{\mathrm{N}}=108$ K, cobalt
(3$d^7$, $S=3/2$) and osmium (5$d^2$, $S=1$) moments fluctuate dynamically,
while their \textit{average} effective moments undergo long-range order. In the
second AFM phase with $T_{\mathrm{N}}=67$ K, cobalt moments first become frozen
and induce a noncollinear spin-canted AFM state, while dynamically fluctuating
osmium moments are later frozen into a randomly canted state at $T\approx 5$ K.
Our \textit{ab initio} calculations indicate that the effective exchange
coupling between cobalt and osmium sites is rather weak, so that cobalt and
osmium sublattices exhibit different ground states and spin-dynamics, making
Sr$_2$CoOsO$_6$ distinct from previously reported double-perovskite compounds.",1312.0767v2
2016-04-20,Emergence of a low spin phase in group field theory condensates,"Recent results have shown how quantum cosmology models can be derived from
the effective dynamics of condensate states in group field theory (GFT), where
'cosmology is the hydrodynamics of quantum gravity': the classical Friedmann
dynamics for homogeneous, isotropic universes, as well as loop quantum
cosmology (LQC) corrections to general relativity have been shown to emerge
from fundamental quantum gravity. We take one further step towards
strengthening the link with LQC and show, in a class of GFT models for gravity
coupled to a free massless scalar field and for generic initial conditions,
that GFT condensates dynamically reach a low spin phase of many quanta of
geometry, in which all but an exponentially small number of quanta are
characterised by a single spin $j_0$ (i.e. by a constant volume per quantum).
As the low spin regime is reached, GFT condensates expand to exponentially
large volumes, and the dynamics of the total volume follows precisely the
classical Friedmann equations. This behaviour follows from a single requirement
on the couplings in the GFT model under study. We present one particular simple
case in which the dominant spin is the lowest one: $j_0=0$ or, if this is
excluded, $j_0=1/2$. The type of quantum state usually assumed in the
derivation of LQC is hence derived from the quantum dynamics of GFT. These
results confirm and extend recent results by Oriti, Sindoni and Wilson-Ewing in
the same setting.",1604.06023v2
2010-05-02,A large-deviation view on dynamical Gibbs-non-Gibbs transitions,"We develop a space-time large-deviation point of view on Gibbs-non-Gibbs
transitions in spin systems subject to a stochastic spin-flip dynamics. Using
the general theory for large deviations of functionals of Markov processes
outlined in Feng and Kurtz [11], we show that the trajectory under the
spin-flip dynamics of the empirical measure of the spins in a large block in
Z^d satisfies a large deviation principle in the limit as the block size tends
to infinity. The associated rate function can be computed as the action
functional of a Lagrangian that is the Legendre transform of a certain
non-linear generator, playing a role analogous to the moment-generating
function in the Gartner-Ellis theorem of large deviation theory when this is
applied to finite-dimensional Markov processes. This rate function is used to
define the notion of ""bad empirical measures"", which are the discontinuity
points of the optimal trajectories (i.e., the trajectories minimizing the rate
function) given the empirical measure at the end of the trajectory. The
dynamical Gibbs-non-Gibbs transitions are linked to the occurrence of bad
empirical measures: for short times no bad empirical measures occur, while for
intermediate and large times bad empirical mea- sures are possible. A future
research program is proposed to classify the various possible scenarios behind
this crossover, which we refer to as a ""nature-versus-nurture"" transition.",1005.0147v1
2018-05-17,An experiment-oriented analysis of 2D spin-glass dynamics: a twelve time-decades scaling study,"Recent high precision experimental results on spin-glass films ask for a
detailed understanding of the domain-growth dynamics of two-dimensional spin
glasses. To achieve this goal, we numerically simulate the out-equilibrium
dynamics of the Ising spin glass for a time that spans close to twelve orders
of magnitude (from picoseconds to order of a second), in systems large enough
to avoid finite-size effects. We find that the time-growth of the size of the
glassy domains is excellently described by a single scaling function. A single
time-scale $\tau(T)$ controls the dynamics. $\tau(T)$ diverges upon approaching
the $T=0$ critical point. The divergence of $\tau(T\to 0)$ is Arrhenius-like,
with a barrier height that depends very mildly on temperature. The growth of
this barrier-height is best described by critical dynamics. As a side product
we obtain an impressive confirmation of universality of the equilibrium
behavior of two-dimensional spin-glasses.",1805.06738v4
2018-01-11,Anomalous quantum-critical spin dynamics in YFe2Al10,"We report results of a muon spin relaxation ($\mu$SR) study of
YFe$_2$Al$_{10}$, a quasi-2D nearly-ferromagnetic metal in which unconventional
quantum critical behavior is observed. No static Fe$^{2+}$ magnetism, with or
without long-range order, is found down to 19~mK\@. The dynamic muon spin
relaxation rate~$\lambda$ exhibits power-law divergences in temperature and
magnetic field, the latter for fields that are too weak to affect the
electronic spin dynamics directly. We attribute this to the proportionality of
$\lambda(\omega_\mu,T)$ to the dynamic structure factor~$S(\omega_\mu,T)$,
where $\omega_\mu \approx 10^5$--$10^7~\mathrm{s}^{-1}$ is the muon Zeeman
frequency. These results suggest critical divergences of $S(\omega_\mu,T)$ in
both temperature and frequency. Power-law scaling and a 2D dissipative quantum
XY (2D-DQXY) model both yield forms for $S(\omega,T)$ that agree with neutron
scattering data ($\omega \approx 10^{12}~\mathrm{s}^{-1}$). Extrapolation to
$\mu$SR frequencies agrees semi-quantitatively with the observed temperature
dependence of $\lambda(\omega_\mu,T)$, but predicts frequency independence for
$\omega_\mu \ll T$ in extreme disagreement with experiment. We conclude that
the quantum critical spin dynamics of YFe$_2$Al$_{10}$ are not well understood
at low frequencies.",1801.03659v2
2019-01-09,Secular spin-axis dynamics of exoplanets,"Context: Seasonal variations and climate stability of a planet are very
sensitive to the planet obliquity and its evolution. This is of particular
interest for the emergence and sustainability of land-based life, but orbital
and rotational parameters of exoplanets are still poorly constrained. Numerical
explorations usually realised in this situation are thus in heavy contrast with
the uncertain nature of the available data.
  Aims: We aim to provide an analytical formulation of the long-term spin-axis
dynamics of exoplanets, linking it directly to physical and dynamical
parameters, but still giving precise quantitative results if the parameters are
well known. Together with bounds for the poorly constrained parameters of
exoplanets, this analysis is designed to allow a quick and straightforward
exploration of the spin-axis dynamics.
  Methods: The long-term orbital solution is decomposed in quasi-periodic
series and the spin-axis Hamiltonian is expanded in powers of eccentricity and
inclination. Chaotic zones are measured by the resonance overlap criterion.
Bounds for the poorly known parameters of exoplanets are obtained from physical
grounds (rotational breakup) and dynamical considerations (equipartition of
AMD).
  Results: This method gives accurate results when the orbital evolution is
well known. The chaotic zones for planets of the Solar System can be retrieved
in details from simple analytical formulas. For less constrained planetary
systems, the maximal extent of the chaotic regions can be computed, requiring
only the mass, the semi-major axis and the eccentricity of the planets present
in the system. Additionally, some estimated bounds of the precession constant
allow to classify which observed exoplanets are necessarily out of major
spin-orbit secular resonances (unless the precession rate is affected by the
presence of massive satellites).",1901.02831v1
2019-04-24,Integrable and chaotic dynamics of spins coupled to an optical cavity,"We show that a class of random all-to-all spin models, realizable in systems
of atoms coupled to an optical cavity, gives rise to a rich dynamical phase
diagram due to the pairwise separable nature of the couplings. By controlling
the experimental parameters, one can tune between integrable and chaotic
dynamics on the one hand, and between classical and quantum regimes on the
other hand. For two special values of a spin-anisotropy parameter, the model
exhibits rational-Gaudin type integrability and it is characterized by an
extensive set of spin-bilinear integrals of motion, independent of the spin
size. More generically, we find a novel integrable structure with conserved
charges that are not purely bilinear. Instead, they develop `dressing tails' of
higher-body terms, reminiscent of the dressed local integrals of motion found
in Many-Body Localized phases. Surprisingly, this new type of integrable
dynamics found in finite-size spin-1/2 systems disappears in the large-$S$
limit, giving way to classical chaos. We identify parameter regimes for
characterizing these different dynamical behaviors in realistic experiments, in
light of the limitations set by cavity dissipation.",1904.10966v3
2021-03-12,Mapping quantum chemical dynamics problems onto spin-lattice simulators,"The accurate computational determination of chemical, materials, biological,
and atmospheric properties has critical impact on a wide range of health and
environmental problems, but is deeply limited by the computational scaling of
quantum-mechanical methods. The complexity of quantum-chemical studies arises
from the steep algebraic scaling of electron correlation methods, and the
exponential scaling in studying nuclear dynamics and molecular flexibility. To
date, efforts to apply quantum hardware to such quantum chemistry problems have
focused primarily on electron correlation. Here, we provide a framework which
allows for the solution of quantum chemical nuclear dynamics by mapping these
to quantum spin-lattice simulators. Using the example case of a short-strong
hydrogen bonded system, we construct the Hamiltonian for the nuclear degrees of
freedom on a single Born-Oppenheimer surface and show how it can be transformed
to a generalized Ising model Hamiltonian. We then demonstrate a method to
determine the local fields and spin-spin couplings needed to identically match
the molecular and spin-lattice Hamiltonians. We describe a protocol to
determine the on-site and inter-site coupling parameters of this Ising
Hamiltonian from the Born-Oppenheimer potential and nuclear kinetic energy
operator. Our approach represents a paradigm shift in the methods used to study
quantum nuclear dynamics, opening the possibility to solve both electronic
structure and nuclear dynamics problems using quantum computing systems.",2103.07420v2
2021-10-25,Gravitational spin-orbit dynamics at the fifth-and-a-half post-Newtonian order,"Accurate waveform models are crucial for gravitational-wave data analysis,
and since spin has a significant effect on the binary dynamics, it is important
to improve the spin description in these models. In this paper, we derive the
spin-orbit (SO) coupling at the fifth-and-a-half post-Newtonian (5.5PN) order.
The method we use splits the conservative dynamics into local and
nonlocal-in-time parts, then relates the local-in-time part to gravitational
self-force results by exploiting the simple mass-ratio dependence of the
post-Minkowskian expansion of the scattering angle. We calculate the nonlocal
contribution to the 5.5PN SO dynamics to eighth order in the small-eccentricity
expansion for bound orbits, and to leading order in the large-eccentricity
expansion for unbound orbits. For the local contribution, we obtain all the
5.5PN SO coefficients from first-order self-force results for the redshift and
spin-precession invariants, except for one unknown that could be fixed in the
future by second-order self-force results. However, by incorporating our 5.5PN
results in the effective-one-body formalism and comparing its binding energy to
numerical relativity, we find that the remaining unknown has a small effect on
the SO dynamics, demonstrating an improvement in accuracy at that order.",2110.12813v2
2022-10-03,Slow semiclassical dynamics of a two-dimensional Hubbard model in disorder-free potentials,"The quench dynamics of the Hubbard model in tilted and harmonic potentials is
discussed within the semiclassical picture. Applying the fermionic truncated
Wigner approximation (fTWA), the dynamics of imbalances for charge and spin
degrees of freedom is analyzed and its time evolution is compared with the
exact simulations in one-dimensional lattice. Quench from charge or spin
density wave is considered. We show that introduction of harmonic and
spin-dependent linear potentials sufficiently validates fTWA for longer times.
Such an improvement of fTWA is also obtained for the higher order correlations
in terms of quantum Fisher information for charge and spin channels. This
allows us to discuss the dynamics of larger system sizes and connect our
discussion to the recently introduced Stark many-body localization. In
particular, we focus on a finite two-dimensional system and show that at
intermediate linear potential strength, the addition of a harmonic potential
and spin dependence of the tilt, results in subdiffusive dynamics, similar to
that of disordered systems. Moreover, for specific values of harmonic
potential, we observed phase separation of ergodic and non-ergodic regions in
real space. The latter fact is especially important for ultracold atom
experiments in which harmonic confinement can be easily imposed, causing a
significant change in relaxation times for different lattice locations.",2210.01082v2
2023-07-02,Rapid mixing of global Markov chains via spectral independence: the unbounded degree case,"We consider spin systems on general $n$-vertex graphs of unbounded degree and
explore the effects of spectral independence on the rate of convergence to
equilibrium of global Markov chains. Spectral independence is a novel way of
quantifying the decay of correlations in spin system models, which has
significantly advanced the study of Markov chains for spin systems. We prove
that whenever spectral independence holds, the popular Swendsen--Wang dynamics
for the $q$-state ferromagnetic Potts model on graphs of maximum degree
$\Delta$, where $\Delta$ is allowed to grow with $n$, converges in $O((\Delta
\log n)^c)$ steps where $c > 0$ is a constant independent of $\Delta$ and $n$.
We also show a similar mixing time bound for the block dynamics of general spin
systems, again assuming that spectral independence holds. Finally, for monotone
spin systems such as the Ising model and the hardcore model on bipartite
graphs, we show that spectral independence implies that the mixing time of the
systematic scan dynamics is $O(\Delta^c \log n)$ for a constant $c>0$
independent of $\Delta$ and $n$. Systematic scan dynamics are widely popular
but are notoriously difficult to analyze. Our result implies optimal $O(\log
n)$ mixing time bounds for any systematic scan dynamics of the ferromagnetic
Ising model on general graphs up to the tree uniqueness threshold. Our main
technical contribution is an improved factorization of the entropy functional:
this is the common starting point for all our proofs. Specifically, we
establish the so-called $k$-partite factorization of entropy with a constant
that depends polynomially on the maximum degree of the graph.",2307.00683v2
2023-08-29,Relativistic and Spin-Orbit Dynamics at Non-Relativistic Intensities in Strong-Field Ionization,"Spin-orbit dynamics and relativistic corrections to the kinetic energy in
strong-field dynamics, have long been ignored for near- and mid-IR fields with
intensities $10^{13}$--$10^{14}$ W/cm$^2$, as the final photoelectron energies
are considered too low for these effects to play a role. However, using a
precise and flexible path-integral formalism, we include all correction terms
from the fine-structure, Breit-Pauli Hamiltonian. This enables a treatment of
spin, through coherent spin-states, which is the first model to use this
approach in strong-field physics. We are able to show that the most
energetically rescattered wavepackets, undergo huge momentum transfer and
briefly reach relativistic velocities, which warrants relativistic kinetic
energy corrections. We probe these effects and show that they yield notable
differences for a $1600$ nm wavelength laser field on the dynamics and the
photoelectron spectra. Furthermore, we find that the dynamical spin-orbit
coupling is strongly overestimated if relativistic corrections to kinetic
energy are not considered. Finally, we derive a new condition that demonstrates
that relativistic effects begin to play a role at intensities orders of
magnitude lower than expected. Our findings may have important implication for
imaging processes such as laser-induced electron diffraction, which includes
high-energy photoelectron recollisions.",2308.15374v1
2021-03-23,Probing many-body dynamics in a two dimensional dipolar spin ensemble,"The most direct approach for characterizing the quantum dynamics of a
strongly-interacting system is to measure the time-evolution of its full
many-body state. Despite the conceptual simplicity of this approach, it quickly
becomes intractable as the system size grows. An alternate framework is to
think of the many-body dynamics as generating noise, which can be measured by
the decoherence of a probe qubit. Our work centers on the following question:
What can the decoherence dynamics of such a probe tell us about the many-body
system? In particular, we utilize optically addressable probe spins to
experimentally characterize both static and dynamical properties of
strongly-interacting magnetic dipoles. Our experimental platform consists of
two types of spin defects in diamond: nitrogen-vacancy (NV) color centers
(probe spins) and substitutional nitrogen impurities (many-body system). We
demonstrate that signatures of the many-body system's dimensionality, dynamics,
and disorder are naturally encoded in the functional form of the NV's
decoherence profile. Leveraging these insights, we directly characterize the
two-dimensional nature of a nitrogen delta-doped diamond sample. In addition,
we explore two distinct facets of the many-body dynamics: First, we address a
persistent debate about the microscopic nature of spin dynamics in
strongly-interacting dipolar systems. Second, we demonstrate direct control
over the correlation time of the many-body system. Finally, we demonstrate
polarization exchange between NV and P1 centers, opening the door to quantum
sensing and simulation using two-dimensional spin-polarized ensembles.",2103.12742v3
2023-01-11,Entangling spins using cubic nonlinear dynamics,"Entangled states with a large number of $N$ atomic spins are a key ingredient
for quantum information processing and quantum metrology. Nowadays, the
preparation of such states has mainly relied on the quadratic nonlinear
dynamics. Here, we investigate the preparation of spin-spin multipartite
entanglement, witnessed by quantum Fisher information, by using the cubic
nonlinear dynamics. We find that, in the regime of weak coupling, the cubic
scheme can greatly speed up the rate of entanglement generation as compared to
the quadratic scheme (about $N$ times faster). In the strong coupling regime,
the cubic nonlinear dynamics enables the periodic in time generation of a broad
variety of new-type macroscopic superposition states, which allow us to realize
near-Heisenberg-limit phase sensitivity. In addition, we also reveal an
interesting feature that the amount of entanglement generated by the cubic
scheme has a macroscopic sensitivity to the parity of $N$, which has no
counterpart in quadratic nonlinear dynamics and can be exploited for sensing
the parity of $N$ at the single-spin level. We also propose a new approach for
a fast and high-fidelity generation of maximally entangled
Greenberger-Horne-Zeilinger (GHZ) states. By using an alternative
cubic-quadratic-admixture type of nonlinear interaction, we show that one may
accelerate the procedure of GHZ-state generation. The realization of the cubic
nonlinear dynamics is also considered, showing that the cubic nonlinear
dynamics can be realized by either repeatedly using linear- and
quadratic-nonlinear dynamics or utilizing light-mediated interactions in just
one step. Finally, by taking realistic imperfections into account, we find that
the cubic scheme is sensitivity to the single-spin decay in the strong coupling
regime, while is robust against the collective dephasing.",2301.04520v1
2004-09-12,Stochastic Resonance and Nonequilibrium Dynamic Phase Transition of Ising Spin System Driven by a Joint External Field,"We studied the dynamic response and stochastic resonance of kinetic Ising
spin system (ISS), subject to the joint external field of weak sinusoidal
modulation and stochastic white-noise, through solving the mean-field equation
of motion based on Glauber dynamics. The periodically driven stochastic ISS
shows the occurrence of characteristic stochastic resonance as well as
nonequilibrium dynamic phase transition (NDPT) when the frequency and amplitude
h0 of driving field, the temperature t of the system and noise intensity D
attain a specific accordance in quantity. There exist in the system two typical
dynamic phases, referred to as dynamic disordered paramagnetic and ordered
ferromagnetic phases respectively, corresponding to zero and unit dynamic order
parameter. We also figured out the NDPT boundary surface of the system which
separates the dynamic paramagnetic and dynamic ferromagnetic phase in the 3D
parameter space of h0~t~D. An intriguing dynamical ferromagnetic phase with an
intermediate order parameter at 0.66 was revealed for the first time in the ISS
subject to the perturbation of a joint determinant and stochastic field. Our
primary result indicates that the intermediate order dynamical ferromagnetic
phase is dynamic metastable in nature and owns a peculiar characteristic in its
stability and response to external driving field when compared with fully order
dynamic ferromagnetic phase.",0409306v1
1997-05-05,Dynamical properties of low dimensional CuGeO3 and NaV2O5 systems,"Properties of low-dimensional spin-Peierls systems are described by using a
one dimensional S=1/2 antiferromagnetic Heisenberg chain linearly coupled to a
single phonon mode of wave vector pi (whose contribution is expected to be
dominant). By exact diagonalizations of small rings with up to 24 sites
supplemented by a finite size scaling analysis, static and dynamical properties
are investigated. Numerical evidences are given for a spontaneous discrete
symmetry breaking towards a spin gapped phase with a frozen lattice
dimerization. Special emphasis is put on the comparative study of the two
inorganic spin-Peierls compounds CuGeO3 and NaV2O5 and the model parameters are
determined from a fit of the experimental spin gaps. We predict that the
spin-phonon coupling is 2 or 3 times larger in NaV2O5 than in CuGeO3. Inelastic
neutron scattering spectra are calculated and similar results are found in the
single phonon mode approximation and in the model including a static
dimerization. In particular, the magnon S=1 branch is clearly separated from
the continuum of triplet excitations by a finite gap.",9705032v2
1997-09-17,Muon Spin Relaxation Study of Reentrant Spin Glasses: Amorphous-Fe_{1-x}Mn_x,"We have performed an extensive muon spin relaxation study of the well known
(Fe$_{1-x}$Mn$_{x}$)$_{75}$P$_{16}$B$_6$Al$_3$ reentrant spin glass. We find a
strong increase of the dynamic as well as static muon depolarization rate at
the paramagnetic to ferromagnetic transition temperature, $T_c$, and at $T_f$
($T_f<T_c$) that corresponds to the onset of strong bulk magnetic
irreversabilities. We find no critical dynamic signature of a freezing of the
transverse $XY$ spin components at an intermediate temperature $T_{xy}$ ($T_f <
T_{xy} < T_c$) where extra static order not contributing to the magnetization
starts developping.",9709190v1
1997-11-06,"The Spin Dynamics of the Spin Ladder, Dimer Chain Material Sr14Cu24O41","We have performed inelastic neutron scattering on a single crystal sample of
Sr14Cu24O41 to study the spin dynamics of the Cu2O3 spin ladder layers, and
CuO2 chains. Data collected with incident energies of 50 meV, 200 meV, 350 meV
and 500 meV are best fitted with a dispersion with a spin gap of 32.5+/-0.1 meV
and a maximum of 193.52.4 meV, consistent with a coupling along the ladders,
J|| = 130 meV and a rung coupling J^=72 meV. We find that excitations with an
energy transfer of approximately 11.5 meV can be described solely in terms of a
dimer chain with an antiferromagnetic intra-dimer coupling, J1 = 11.2 meV,
between next-nearest-neighbour Cu ions and a ferromagnetic inter-dimer
coupling, J2 = -1.1 meV. The dimers are separated by two Cu ions providing a
periodicity for the dimer chain of five units.",9711053v1
1998-04-06,Effect of next-nearest neighbor hopping on the spin dynamics in antiferromagnets,"Recently, inelastic neutron scattering (INS) experiments on the insulating
parent compounds of high-T_c materials were analyzed to extract the value of
the superexchange constant $J$. Starting point of the analysis was the
nearest-neighbor Heisenberg model. Motivated by recent ARPES experiments, we
consider the effects of a next-nearest neighbor hopping, $t'$ in the strong
coupling limit of the spin-density wave formalism, where it leads to an
antiferromagnetic exchange $J'>0$ between next-nearest neighbor spins. We show
that a finite $J'$ (a) changes the spin-wave velocity and thus the value of $J$
extracted from the INS data, yielding almost identical values for $J$ in
La_2CuO_4 and YBa_2Cu_3O_{6.15}, and (b) leads to a considerable change in the
high-frequency spin-dynamics. Finally, we calculate the 1/S quantum corrections
in the presence of $J'$ and discuss their relevance for the INS data.",9804069v2
1998-08-27,Mean-Field Theory for Spin Ladders Using Angular-Momentum Coupled Bases,"We study properties of two-leg Heisenberg spin ladders in a mean-field
approximation using a variety of angular-momentum coupled bases. The mean-field
theory proposed by Gopalan, Rice, and Sigrist, which uses a rung basis, assumes
that the mean-field ground state consists of a condensate of spin-singlets
along the rungs of the ladder. We generalize this approach to larger
angular-momentum coupled bases which incorporate---by their mere definition---a
substantial fraction of the important short-range structure of these materials.
In these bases the mean-field ground-state remains a condensate of spin
singlet---but now with each involving a larger fraction of the spins in the
ladder. As expected, the ``purity'' of the ground-state, as judged by the
condensate fraction, increases with the size of the elementary block defining
the basis. Moreover, the coupling to quasiparticle excitations becomes weaker
as the size of the elementary block increases. Thus, the weak-coupling limit of
the theory becomes an accurate representation of the underlying mean-field
dynamics. We illustrate the method by computing static and dynamic properties
of two-leg ladders in the various angular-momentum coupled bases.",9808310v1
1999-07-19,Renormalization of the Spin-Peierls Transition due to Phonon Dynamics,"We report results from a systematic strong-coupling expansion of a spin-1/2
Heisenberg chain coupled to Einstein phonons. In the non-adiabatic regime this
model is used to describe zero temperature properties of CuGeO3. The linked
cluster expansion allows the determination of observables in the thermodynamic
limit preserving the full lattice dynamics without a truncation of the phononic
Hilbert space. In particular, the spin gap and the dispersion of the elementary
triplet excitation are calculated up to 10th order in a dimer expansion. The
magnetic structure factor of the ground state is evaluated up to 6th order. We
show that the spin-phonon coupling leads to a renormalization of the elementary
triplet dispersion. Surprisingly in the non-adiabatic regime a substantial
renormalization of the spin gap only sets in at much larger couplings than
those proposed for CuGeO3. The ground state magnetic correlations are found to
be hardly effected by the spin-phonon coupling, but dominated by the
frustrating magnetic interaction in the parameter regime relevant for CuGeO3.",9907266v1
1999-07-19,Optically Pumped NMR Studies of Electron Spin Polarization and Dynamics: New Constraints on the Composite Fermion Description of nu = 1/2,"The Knight shift and the nuclear spin-lattice relaxation rate 1/T1 of Ga-71
nuclei are measured in GaAs quantum wells at Landau level filling factor nu =
1/2 using optically pumped NMR. The temperature dependences of these data are
compared with predictions of a weakly-interacting composite fermion model. Our
measurements of the electron spin polarization and spin dynamics near the
transition between fully and partially spin-polarized ground states provide new
constraints on the theoretical description of nu = 1/2.",9907280v1
1999-11-17,Inhomogeneous Low Frequency Spin Dynamics in La_{1.65}Eu_{0.2}Sr_{0.15}CuO_4,"We report Cu and La nuclear magnetic resonance (NMR) measurements in the
title compound that reveal an inhomogeneous glassy behavior of the spin
dynamics. A low temperature peak in the La spin lattice relaxation rate and the
``wipeout'' of Cu intensity both arise from these slow electronic spin
fluctuations that reveal a distribution of activation energies. Inhomogeneous
slowing of spin fluctuations appears to be a general feature of doped lanthanum
cuprate.",9911268v3
1999-11-22,Zero-Temperature Dynamics of Ising Spin Systems Following a Deep Quench: Results and Open Problems,"We consider zero-temperature, stochastic Ising models with nearest-neighbor
interactions and an initial spin configuration chosen from a symmetric
Bernoulli distribution (corresponding physically to a deep quench). Whether a
final state exists, i.e., whether each spin flips only finitely many times as
time goes to infinity (for almost every initial spin configuration and
realization of the dynamics), or if not, whether every spin - or only a
fraction strictly less than one - flips infinitely often, depends on the nature
of the couplings, the dimension, and the lattice type. We review results,
examine open questions, and discuss related topics.",9911353v1
2000-01-12,Incommensurate and Commensurate Antiferromagnetic Spin Fluctuations in Cr and Cr Alloys from Ab Initio Dynamical Spin Susceptibility Calculations,"A scheme for making ab-initio calculations of the dynamic paramagnetic spin
susceptibilities of solids at finite temperatures is described. It is based on
Time-Dependent Density Functional Theory and employs an electronic multiple
scattering formalism. Incommensurate and commensurate anti-ferromagnetic spin
fluctuations in paramagnetic Cr and compositionally disordered Cr95V5 and
Cr95Re5 alloys are studied together with the connection with the nesting of
their Fermi surfaces. We find that the spin fluctuations can be described
rather simply in terms of an overdamped oscillator model. Good agreement with
inelastic neutron scattering data is obtained.",0001160v1
2000-01-19,Critical Dynamics of Singlet Excitations in a Frustrated Spin System,"We construct and analyze a two-dimensional frustrated quantum spin model with
plaquette order, in which the low-energy dynamics is controlled by spin
singlets. At a critical value of frustration the singlet spectrum becomes
gapless, indicating a quantum transition to a phase with dimer order. This T=0
transition belongs to the 3D Ising universality class, while at finite
temperature a 2D Ising critical line separates the plaquette and dimerized
phases.
  The magnetic susceptibility has an activated form throughout the phase
diagram, whereas the specific heat exhibits a rich structure and a power law
dependence on temperature at the quantum critical point.
  We argue that the novel quantum critical behavior associated with singlet
criticality discussed in this work can be relevant to a wide class of quantum
spin systems, such as antiferromagnets on Kagome and pyrochlore lattices, where
the low-energy excitations are known to be spin singlets, as well as to the
CAVO lattice and several recently discovered strongly frustrated square-lattice
antiferromagnets.",0001282v2
2000-11-10,Temperature Dependence of Spin Correlation and Charge Dynamics in the Stripe Phase of High-T_c Superconductors,"We examine the temperature dependence of the electronic states in the stripe
phase of high-Tc cuprates by using the t-J model with a potential that
stabilizes vertical charge stripes. Charge and spin-correlation functions and
optical conductivity are calculated by using finite-temperature Lanczos method.
At zero temperature, the antiferromagnetic correlation between a spin in a
charge stripe and that in a spin domain adjacent to the stripe is weak, since
the charge stripe and the spin domain are almost separated. With increasing
temperature, the correlation increases and then decreases toward high
temperature. This is in contrast to other correlations that decrease
monotonically. From the examination of the charge dynamics, we find that this
anomalous temperature dependence of the correlation is the consequence of a
crossover from one-dimensional electronic states to two-dimensional ones.",0011185v2
2001-05-03,Zero-field Time Correlation Functions of Four Classical Heisenberg Spins on a Ring,"A model relevant for the study of certain molecular magnets is the ring of
N=4 classical spins with equal near-neighbor isotropic Heisenberg exchange
interactions. Assuming classical Heisenberg spin dynamics, we solve explicitly
for the time evolution of each of the spins. Exact triple integral
representations are derived for the auto, near-neighbor, and
next-nearest-neighbor time correlation functions for any temperature. At
infinite temperature, the correlation functions are reduced to quadrature. We
then evaluate the Fourier transforms of these functions in closed form, which
are double integrals. At low temperatures, the Fourier transform functions
explicitly demonstrate the presence of magnons. Our exact results for the
infinite temperature correlation functions in the long-time asymptotic limit
differ qualitatively from those obtained assuming diffusive spin dynamics.
Whether such explicitly non-hydrodynamic behavior would be maintained for
large-N rings is discussed.",0105050v1
2001-10-17,Dynamics at T -> 0 in the half-integer isotropic high spin molecules,"We investigate the dynamical spin-spin auto-correlation function of the
isotropic high spin molecules CrCu$_{6}$ (S=9/2), CrNi$_{6}$ (S=15/2) and
CrMn$_{6}$ (S=27/2), using magnetization, $\mu$SR and NMR measurements. We find
that the field autocorrelation time $\tau$ of the molecule's spin at zero and
low fields is nearly temperature independent as $T\to 50$ mK. The high
temperatures $\tau$ is very different between the molecules. Surprisingly, it
is identical ($\sim$ 10 nsec) at low temperature. This suggests that $\tau$ is
governed by hyperfine interactions.",0110347v2
2001-11-14,Ultrafast Spin Dynamics in GaAs/GaSb/InAs Heterostructures Probed by Second Harmonic Generation,"We report the first application of pump-probe second harmonic generation
(SHG) measurements to characterize optically-induced magnetization in
non-magnetic multilayer semiconductors. In the experiment, coherent spins are
selectively excited by a pump beam in the GaAs layer of GaAs/GaSb/InAs
structures. However, the resulting net magnetization manifests itself through
the induced SHG probe signal from the GaSb/InAs interface, thus indicating a
coherent spin transport across the heterostructure. We find that the
magnetization dynamics is governed by an interplay between the spin density
evolution at the interfaces and the spin dephasing.",0111266v1
2002-05-08,"Interplay of charge, spin, orbital and lattice correlations in colossal magnetoresistance manganites","We derive a realistic microscopic model for doped colossal magnetoresistance
manganites, which includes the dynamics of charge, spin, orbital and lattice
degrees of freedom on a quantum mechanical level. The model respects the SU(2)
spin symmetry and the full multiplet structure of the manganese ions within the
cubic lattice. Concentrating on the hole doped domain ($0\le x\le 0.5$) we
study the influence of the electron-lattice interaction on spin and orbital
correlations by means of exact diagonalisation techniques. We find that the
lattice can cause a considerable suppression of the coupling between spin and
orbital degrees of freedom and show how changes in the magnetic correlations
are reflected in dynamic phonon correlations. In addition, our calculation
gives detailed insights into orbital correlations and demonstrates the
possibility of complex orbital states.",0205150v2
2003-12-24,Dynamic generation of spin orbit coupling,"Spin-orbit coupling plays an important role in determining the properties of
solids, and is crucial for spintronics device applications. Conventional
spin-orbit coupling arises microscopically from relativistic effects described
by the Dirac equation, and is described as a single particle band effect. In
this work, we propose a new mechanism in which spin-orbit coupling can be
generated dynamically in strongly correlated, non-relativistic systems as the
result of fermi surface instabilities in higher angular momentum channels.
Various known forms of spin-orbit couplings can emerge in these new phases, and
their magnitudes can be continuously tuned by temperature or other quantum
parameters.",0312632v4
2004-03-03,Nuclear spin dynamics in the quantum regime of a single-molecule magnet,"We show that the nuclear spin dynamics in the single-molecule magnet Mn12-ac
below 1 K is governed by quantum tunneling fluctuations of the cluster spins,
combined with intercluster nuclear spin diffusion. We also obtain the first
experimental proof that - surprisingly - even deep in the quantum regime the
nuclear spins remain in good thermal contact with the lattice phonons. We
propose a simple model for how T-independent tunneling fluctuations can relax
the nuclear polarization to the lattice, that may serve as a framework for more
sophisticated theories.",0403107v2
2004-03-25,Ab-initio spin dynamics applied to nanoparticles: canted magnetism of a finite Co chain along a Pt(111) surface step edge,"In order to search for the magnetic ground state of surface nanostructures we
extended first principles adiabatic spin dynamics to the case of fully
relativistic electron scattering. Our method relies on a constrained density
functional theory whereby the evolution of the orientations of the spin-moments
results from a semi-classical Landau-Lifshitz equation. This approach is
applied to a study of the ground state of a finite Co chain placed along a step
edge of a Pt(111) surface. As far as the ground state spin orientation is
concerned we obtain excellent agreement with the experiment. Furthermore we
observe noncollinearity of the atom-resolved spin and orbital moments. In terms
of magnetic force theorem calculations we also demonstrate how a reduction of
symmetry leads to the existence of canted magnetic states.",0403637v1
2004-05-14,Evolution of a localized electron spin in a nuclear spin environment,"Motivated by recent interest in the role of the hyperfine interaction in
quantum dots we study the dynamics of a localized electron spin coupled to many
nuclei. An important feature of the model is that the coupling to an individual
nuclear spin depends on its position in the quantum dot. We introduce a
semi-classical description of the system valid in the limit of a large number
of nuclei and analyze the resulting classical dynamics. Contrary to a natural
assumption, the correlation functions of electron spin with an arbitrary
initial condition show no decay in time. Rather, they exhibit complicated
undamped oscillations. This may be attributed to the fact that the system has
many integrals of motion and is close to an integrable one. The ensemble
averaged correlation functions do exhibit a slow decay (1/ln(t)) for t ->
\infty.",0405318v1
2004-07-16,Interaction and dynamical binding of spin waves or excitons in quantum Hall systems,"Interaction between spin waves (or excitons) moving in the lowest Landau
level is studied using numerical diagonalization. Becuse of complicated
statistics obeyed by these composite particles, their effective interaction is
completely different from the dipole-dipole interaction predicted in the model
of independent (bosonic) waves. In particular, spin waves moving in the same
direction attract one another which leads to their dynamical binding. The
interaction pseudopotentials V_[up,up](k) and V_[up,down](k) for two spin waves
with equal wavevectors k and moving in the same or opposite directions have
been calculated and shown to obey power laws V(k) ~ k^alpha at small k. A high
value of alpha_[up,up]~4 explains the occurrence of linear bands in the spin
excitation spectra of quantum Hall droplets.",0407449v1
2004-10-15,Matter-Wave Solitons in an F=1 Spinor Bose-Einstein Condensate,"Following our previous work [J. Ieda, T. Miyakawa, M. Wadati,
cond-mat/0404569] on a novel integrable model describing soliton dynamics of an
F=1 spinor Bose--Einstein condensate, we discuss in detail the properties of
the multi-component system with spin-exchange interactions. The exact multiple
bright soliton solutions are obtained for the system where the mean-field
interaction is attractive (c_0 < 0) and the spin-exchange interaction is
ferromagnetic (c_2 < 0). A complete classification of the one-soliton solution
with respect to the spin states and an explicit formula of the two-soliton
solution are presented. For solitons in polar state, there exists a variety of
different shaped solutions including twin peaks. We show that a ""singlet pair""
density can be used to distinguish those energetically degenerate solitons. We
also analyze collisional effects between solitons in the same or different spin
state(s) by computing the asymptotic forms of their initial and final states.
The result reveals that it is possible to manipulate the spin dynamics by
controlling the parameters of colliding solitons.",0410384v1
2004-11-10,Dynamical nuclear polarization and nuclear magnetic fields in semiconductor nanostructures,"We investigate the dynamic nuclear polarization from the hyperfine
interaction between nonequilibrium electronic spins and nuclear spins coupled
to them in semiconductor nanostructures. We derive the time and position
dependence of the induced nuclear spin polarization and dipolar magnetic
fields. In GaAs/AlGaAs parabolic quantum wells the nuclear spin polarization
can be as high as 80% and the induced nuclear magnetic fields can approach a
few gauss with an associated nuclear resonance shift of the order of kHz when
the electronic system is 100% spin polarized. These fields and shifts can be
tuned using small electric fields. We discuss the implications of such control
for optical nuclear magnetic resonance experiments in low-dimensional
semiconductor nanostructures.",0411277v1
2004-12-22,Topology and spin dynamics in magnetic molecules,"We investigate the role of topology and distortions in the quantum dynamics
of magnetic molecules, using a cyclic spin system as reference. We consider
three variants of antiferromagnetic molecular ring, i.e. Cr$_8$, Cr$_7$Zn and
Cr$_7$Ni, characterized by low lying states with different total spin $S$. We
theoretically and experimentally study the low-temperature behavior of the
magnetic torque as a function of the applied magnetic field. Near level
crossings, this observable selectively probes quantum fluctuations of the total
spin (''$S$ mixing"") induced by lowering of the ideal ring symmetry. We show
that while a typical distortion of a model molecular structure is very
ineffective in opening new $S$-mixing channels, the spin topology is a major
ingredient to control the degree of $S$ mixing. This conclusion is further
substantiated by low-temperature heat capacity measurements.",0412628v1
2005-03-03,Transport properties of diluted magnetic semiconductors: Dynamical mean field theory and Boltzmann theory,"The transport properties of diluted magnetic semiconductors (DMS) are
calculated using dynamical mean field theory (DMFT) and Boltzmann transport
theory. Within DMFT we study the density of states and the dc-resistivity,
which are strongly parameter dependent such as temperature, doping, density of
the carriers, and the strength of the carrier-local impurity spin exchange
coupling. Characteristic qualitative features are found distinguishing weak,
intermediate, and strong carrier-spin coupling and allowing quantitative
determination of important parameters defining the underlying ferromagnetic
mechanism. We find that spin-disorder scattering, formation of bound state, and
the population of the minority spin band are all operational in DMFT in
different parameter range. We also develop a complementary Boltzmann transport
theory for scattering by screened ionized impurities. The difference in the
screening properties between paramagnetic ($T>T_c$) and ferromagnetic ($T<T_c$)
states gives rise to the temperature dependence (increase or decrease) of
resistivity, depending on the carrier density, as the system goes from the
paramagnetic phase to the ferromagnetic phase. The metallic behavior below
$T_c$ for optimally doped DMS samples can be explained in the Boltzmann theory
by temperature dependent screening and thermal change of carrier spin
polarization.",0503077v1
2005-04-06,Macrospin Models of Spin Transfer Dynamics,"The current-induced magnetization dynamics of a spin valve are studied using
a macrospin (single domain) approximation and numerical solutions of a
generalized Landau-Lifshitz-Gilbert equation. For the purpose of quantitative
comparison with experiment [Kiselev {\it et al.} Nature {\bf 425}, 380 (2003)],
we calculate the resistance and microwave power as a function of current and
external field including the effects of anisotropies, damping, spin-transfer
torque, thermal fluctuations, spin-pumping, and incomplete absorption of
transverse spin current. While many features of experiment appear in the
simulations, there are two significant discrepancies: the current dependence of
the precession frequency and the presence/absence of a microwave quiet magnetic
phase with a distinct magnetoresistance signature. Comparison is made with
micromagnetic simulations designed to model the same experiment.",0504142v1
2005-07-19,Energy-resolved inelastic electron scattering off a magnetic impurity,"We study inelastic scattering of energetic electrons off a Kondo impurity. If
the energy E of the incoming electron (measured from the Fermi level) exceeds
significantly the Kondo temperature T_K, then the differential inelastic
cross-section \sigma (E,w), i.e., the cross-section characterizing scattering
of an electron with a given energy transfer w, is well-defined. We show that
\sigma (E,w) factorizes into two parts. The E-dependence of \sigma (E,w) is
logarithmically weak and is due to the Kondo renormalization of the effective
coupling. We are able to relate the w-dependence to the spin-spin correlation
function of the magnetic impurity. Using this relation, we demonstrate that in
the absence of magnetic field the dynamics of the impurity spin causes the
electron scattering to be inelastic at any temperature. Quenching of the spin
dynamics by an applied magnetic field results in a finite elastic component of
the electron scattering cross-section. The differential scattering
cross-section may be extracted from the measurements of relaxation of hot
electrons injected in conductors containing localized spins.",0507431v2
2005-09-13,Coherent spinor dynamics in a spin-1 Bose condensate,"Collisions in a thermal gas are perceived as random or incoherent as a
consequence of the large numbers of initial and final quantum states accessible
to the system. In a quantum gas, e.g. a Bose-Einstein condensate or a
degenerate Fermi gas, the phase space accessible to low energy collisions is so
restricted that collisions be-come coherent and reversible. Here, we report the
observation of coherent spin-changing collisions in a gas of spin-1 bosons.
Starting with condensates occupying two spin states, a condensate in the third
spin state is coherently and reversibly created by atomic collisions. The
observed dynamics are analogous to Josephson oscillations in weakly connected
superconductors and represent a type of matter-wave four-wave mixing. The
spin-dependent scattering length is determined from these oscillations to be
-1.45(18) Bohr. Finally, we demonstrate coherent control of the evolution of
the system by applying differential phase shifts to the spin states using
magnetic fields.",0509341v2
2006-01-02,Three--body Correlation Effects on the Spin Dynamics of Double--Exchange Ferromagnets,"We present a variational calculation of the spin wave excitation spectrum of
double--exchange ferromagnets in different dimensions. Our theory recovers the
Random Phase approximation and 1/S expansion results as limiting cases and can
be used to study the intermediate exchange coupling and electron concentration
regime relevant to the manganites. In particular, we treat exactly the long
range three--body correlations between a Fermi sea electron--hole pair and a
magnon excitation and show that they strongly affect the spin dynamics in the
parameter range relevant to experiments in the manganites. The manifestations
of these correlations are many-fold. We demonstrate that they significantly
change the ferromagnetic phase boundary. In addition to a decrease in the
magnon stiffness, we obtain an instability of the ferromagnetic state against
spin wave excitations close to the Brillouin zone boundary.Within a range of
intermediate concentrations, we find a strong softening of the spin wave
dispersion as compared to the Heisenberg ferromagnet with the same stiffness,
which changes into hardening for other concentrations. We discuss the relevance
of these results to experiments in colossal magnetoresistance ferromagnets.",0601025v2
2006-01-12,Aging behavior of spin glasses under bond and temperature perturbations from laser illumination,"We have studied the nonequilibrium dynamics of spin glasses subjected to bond
perturbation, which was based on the direct change in the spin-spin interaction
$\Delta J$, using photo illumination in addition to temperature change $\Delta
T$. Differences in time-dependent magnetization are observed between that under
$\Delta T+\Delta J$ and $\Delta T$ perturbations with the same $\Delta T$. This
differences shows the contribution of $\Delta J$ to spin-glass dynamics through
the decrease in the overlap length. That is, the overlap length $L_{\Delta
T+\Delta J}$ under $\Delta T+\Delta J$ perturbation is less than $L_{\Delta T}$
under $\Delta T$ perturbation. Furthermore, we observe the crossover between
weakly and strongly perturbed regimes under bond cycling accompanied by
temperature cycling. These effects of bond perturbation strongly indicates the
existence of both chaos and the overlap length.",0601248v3
2006-09-01,Spin dynamics of $Yb Rh_2 Si_2$ observed by Electron Spin Resonance,"Below the Kondo temperature $T_{\rm K}$ electron spin resonance (ESR) usually
is not observable from the Kondo-ion itself because the characteristic spin
fluctuation energy results in a huge width of the ESR line. The heavy fermion
metal YbRh$_{2}$Si$_{2}$ seems to be an exceptional case where definite ESR
spectra show characteristic properties of the Kondo-ion Yb$^{3+}$ well
\textit{below} $T_{\rm K}$. We found that the spin dynamics of
YbRh$_{2}$Si$_{2}$, as determined by its ESR relaxation, is spatially
characterized by an anisotropy of the zero temperature residual relaxation
only.",0609020v1
2006-09-07,Hyperfine interaction induced decoherence of electron spins in quantum dots,"We investigate in detail, using both analytical and numerical tools, the
decoherence of electron spins in quantum dots (QDs) coupled to a bath of
nuclear spins in magnetic fields or with various initial bath polarizations,
focusing on the longitudinal relaxation in low and moderate field/polarization
regimes. An increase of the initial polarization of nuclear spin bath has the
same effect on the decoherence process as an increase of the external magnetic
field, namely, the decoherence dynamics changes from smooth decay to damped
oscillations. This change can be observed experimentally for a single QD and
for a double-QD setup. Our results indicate that substantial increase of the
decoherence time requires very large bath polarizations, and the use of other
methods (dynamical decoupling or control of the nuclear spins distribution) may
be more practical for suppressing decoherence of QD-based qubits.",0609185v2
2007-02-17,"Low Field, Current-Hysteretic Oscillations in Spin Transfer Nanocontacts","We have measured spin-transfer-driven, large amplitude, current hysteretic,
low frequency (< 500 MHz), narrowband oscillations in nanocontacts made to spin
valve structures. The oscillations occur in zero field, persist up to 5 mT for
in plane applied fields, and to beyond 400 mT for out of plane fields. Unlike
previous measurements, the oscillation frequency is well below that for
uniform-mode ferromagnetic resonance, is only a weak function of applied field,
and is highly anharmonic. The oscillations are hysteretic with applied dc
current, appearing at high currents but persisting to lower currents upon
decrease of the current. We suggest that these observations are consistent with
the dynamics of a nonuniform magnetic state in the vicinity of the contact
nucleated by both the spin transfer torque and dc current-generated Oersted
fields, with the dynamics driven by spin transfer. The electrical oscillation
amplitudes are large and narrowband, with the largest amplitudes on the order
of 1 mV and the narrowest linewidths below 1 MHz.",0702416v1
1996-06-29,Quantum Spin Dynamics (QSD),"An anomaly-free operator corresponding to the Wheeler-DeWitt constraint of
Lorentzian, four-dimensional, canonical, non-perturbative vacuum gravity is
constructed in the continuum. This operator is entirely free of factor ordering
singularities and can be defined in symmetric and non-symmetric form. We work
in the real connection representation and obtain a well-defined quantum theory.
We compute the complete solution to the Quantum Einstein Equations for the
non-symmetric version of the operator and a physical inner product thereon. The
action of the Wheeler-DeWitt constraint on spin-network states is by
annihilating, creating and rerouting the quanta of angular momentum associated
with the edges of the underlying graph while the ADM-energy is essentially
diagonalized by the spin-network states. We argue that the spin-network
representation is the ``non-linear Fock representation"" of quantum gravity,
thus justifying the term ``Quantum Spin Dynamics (QSD)"".",9606089v1
2000-08-09,Polyakov's spin factor and new algorithms for efficient perturbative computations in QCD,"Polyakov's spin factor enters as a weight in the path-integral description of
particle-like modes propagating in Euclidean space-times, accounting for
particle spin. The Fock-Feynman-Schwinger path integral applied to QCD
accomodates Polyakov's spin factor in a natural manner while, at the same time,
it identifies Wilson line (loop) operators as sole agents of interaction
dynamics among matter and gauge field quanta. A direct application of such a
separation between spin content and dynamics is the emergence of master
expressions for the perturbative series involving either open or closed
fermionic lines which provide new, comprehensive approaches to perturbative
QCD.",0008078v2
2003-10-28,The su(2|3) Dynamic Spin Chain,"The complete one-loop, planar dilatation operator of the N=4 superconformal
gauge theory was recently derived and shown to be integrable. Here, we present
further compelling evidence for a generalisation of this integrable structure
to higher orders of the coupling constant. For that we consider the su(2|3)
subsector and investigate the restrictions imposed on the spin chain
Hamiltonian by the symmetry algebra. This allows us to uniquely fix the energy
shifts up to the three-loop level and thus prove the correctness of a
conjecture in hep-th/0303060. A novel aspect of this spin chain model is that
the higher-loop Hamiltonian, as for N=4 SYM in general, does not preserve the
number of spin sites. Yet this dynamic spin chain appears to be integrable.",0310252v2
2005-01-14,Dynamics of Higher Spin Fields and Tensorial Space,"The structure and the dynamics of massless higher spin fields in various
dimensions are reviewed with an emphasis on conformally invariant higher spin
fields. We show that in D=3,4,6 and 10 dimensional space-time the conformal
higher spin fields constitute the quantum spectrum of a twistor-like particle
propagating in tensorial spaces of corresponding dimensions. We give a detailed
analysis of the field equations of the model and establish their relation with
known formulations of free higher spin field theory.",0501113v3
2006-08-04,Spin-field Interaction Effects and Loop Dynamics in AdS/CFT Duality,"The spin-field interaction is considered, in the context of the gauge
fields/string correspondence, in the large 't Hooft coupling limit. The latter
can be viewed as a WKB-type approximation to the AdS/CFT duality conjecture.
Basic theoretical objects entering the present study are (a) the Wilson loop
functional, on the gauge field side and (b) the sigma model action for the
string propagating in AdS$_5$. Spin effects are introduced in a worldline
setting, via the spin factor for a particle entity propagating on a Wilson loop
contour. The computational tools employed for conducting the relevant analysis,
follow the methodological guidelines introduced in two papers by Polyakov and
Rychkov. The main result is expressed in terms of the modification of the spin
factor brought about by dynamical effects, both perturbative and
non-perturbative, according to AdS/CFT in the considered limit.",0608030v1
2003-12-18,Frustrated quantum-spin system on a triangle coupled with $e_g$ lattice vibrations - Correspondence to Longuet-Higgins et al.'s Jahn-Teller model -,"We investigate the quantum three spin model $({\bf S_1},{\bf S_2},{\bf S_3})$
of spin$=1/2$ on a triangle, in which spins are coupled with
lattice-vibrational modes through the exchange interaction depending on
distances between spin sites. The present model corresponds to the dynamic
Jahn-Teller system $E_g\otimes e_g$ proposed by Longuet-Higgins {\it et al.},
Proc.R.Soc.A.{\bf 244},1(1958). This correspondence is revealed by using the
transformation to Nakamura-Bishop's bases proposed in Phys.Rev.Lett.{\bf
54},861(1985). Furthermore, we elucidate the relationship between the behavior
of a chiral order parameter ${\hat \chi}={\bf S_1\cdot(S_2\times S_3)}$ and
that of the electronic orbital angular momentum ${\hat \ell_z}$ in $E_g\otimes
e_g$ vibronic model: The regular oscillatory behavior of the expectation value
$<{\hat \ell_z}>$ for vibronic structures with increasing energy can also be
found in that of $<{\hat \chi}>$. The increase of the additional
anharmonicity(chaoticity) is found to yield a rapidly decaying irregular
oscillation of $<{\hat \chi}>$.",0312039v1
2004-11-16,Polarized Proton and Deuteron Beams at COSY,"Aim of this paper is to present a brief and basic introduction to polarized
beams and the behaviour of a particle's spin in an electromagnetic field. It is
not intended to give a complete presentation of the spin dynamic theory.
Instead the most importa nt features are given without proof and details not
absolutely necessary are left out. Spin depolarizing mechanisms are discussed
and the cures against depolarizing especially during acceleration as utilized
at COSY are outlined. A list of references is given at the end to help the
reader to find more deep details on spin dynamic theory [1].",0411148v1
2000-01-14,Spin dynamics of wave packets evolving with the Dirac Hamiltonian in atoms with high Z,"The motion of circular WP for one electron in central Coulomb field with high
Z is calculated. The WP is defined in terms of solutions of the Dirac equation
in order to take into account all possible relevant effects in particular the
spin-orbit potential. A time scale is defined within which spin dynamics must
be taken into account mainly in the atoms with high Z. Within this time scale
there exists a mechanism of collapses and revivals of the spin already shown by
the authors for harmonic oscillator potential and called the 'spin-orbit
pendulum'. However this effect has not the exact periodicity of the simpler
model, but the WP's spatial motion is nevertheless quite similar.",0001051v2
2007-09-05,Time-Domain Studies of Very-Large-Angle Magnetization Dynamics Excited by Spin Transfer Torques,"We describe time-domain measurements which provide new information about the
large-angle nonlinear dynamics of nanomagnets excited by spin-transfer torque
from a spin-polarized current. Sampling-oscilloscope measurements, which
average over thousands of experimental time traces, show that the mean reversal
time for spin-transfer-driven magnetic switching has a step-like dependence on
magnetic field, because an integer number of precession cycles is required for
reversal. Storage-oscilloscope measurements of individual experimental traces
reveal non-periodic large-amplitude resistance variations at values of magnetic
field and current in a crossover region between the regimes of
spin-transfer-driven switching and steady-state precession. We also observe
directly the existence of time-dependent switching, on the nanosecond scale,
between different precessional modes and between a precessional mode and a
static state, at particular values of magnetic field and current bias.",0709.0560v1
2007-09-08,Transition rates for a S \ge 1 model coupled to a phonon bath,"We investigate transition rates between different spin configurations for $S
\ge 1$ spins weakly coupled to a $d$-dimensional phonon bath. This study is
motivated by understanding observed magnetization relaxation as a function of
temperature in diverse magnetic systems such as arrays of magnetic
nanoparticles and magnetic molecules. We assume that the magnetization of the
spin system relaxes through consecutive emission or absorption of a single
phonon. From a weak, linear spin-phonon coupling Hamiltonian, we derive
transition rates that would be used to examine dynamic properties of the system
in kinetic Monte Carlo simulations. Although the derived phonon-assisted
transition rates satisfy detailed balance, in the case of two and three
dimensional phonon baths, transitions between degenerate states are not
allowed. Thus, if there are no alternative paths along which the spin system
can relax, the relaxation time diverges. Otherwise, the system finds other
paths, which leads to an increase in the relaxation time and energy barrier.
However, when higher-order phonon processes are included in the transition
rates, it is found that the system can reach the states which were inaccessible
due to the forbidden transitions. As a result, the system recovers some of the
dynamic properties obtained using the Glauber transition rate.",0709.1237v1
2008-02-16,"Hysteresis, transient oscillations, and nonhysteretic switching in resonantly modulated large-spin systems","We study the classical dynamics of resonantly modulated large-spin systems in
a strong magnetic field. We show that these systems have special symmetry. It
leads to characteristic nonlinear effects. They include abrupt switching
between magnetization branches with varying modulating field without hysteresis
and a specific pattern of switching in the presence of multistability and
hysteresis. Along with steady forced vibrations the transverse spin components
can display transient vibrations at a combination of the Larmor frequency and a
slower frequency determined by the anisotropy energy. The analysis is based on
a microscopic theory that takes into account relaxation mechanisms important
for single-molecule magnets and other large-spin systems. We find how the
Landau-Lifshitz model should be modified in order to describe the classical
spin dynamics. The occurrence of transient oscillations depends on the
interrelation between the relaxation parameters.",0802.2304v1
2008-06-01,Accelerating the spin-up of Ensemble Kalman Filtering,"A scheme is proposed to improve the performance of the ensemble-based Kalman
Filters during the initial spin-up period. By applying the no-cost ensemble
Kalman Smoother, this scheme allows the model solutions for the ensemble to be
""running in place"" with the true dynamics, provided by a few observations.
  Results of this scheme are investigated with the Local Ensemble Transform
Kalman Filter (LETKF) implemented in a Quasi-geostrophic model, whose original
framework requires a very long spin-up time when initialized from a cold start.
Results show that it is possible to spin up the LETKF and have a fast
convergence to the optimal level of error. The extra computation is only
required during the initial spin-up since this scheme resumes to the original
LETKF after the ""running in place"" is achieved.",0806.0180v1
2008-06-15,Low-lying excitations of the three-leg spin tube using the density-matrix renormalization group method,"Using the (dynamical) density-matrix renormalization group method, we study
the low-energy physics of three-leg antiferromagnetic Heisenberg model where
the periodic boundary conditions are applied in the rung direction. We confirm
that the spin excitations are always gapped as long as the intra-ring couplings
form a regular triangle. From precise finite-size-scaling analyses of the spin
gap and dimerization order parameter, we also find that the spin gap is
collapsed by very small asymmetric modulation of the intra-ring couplings.
Moreover, the dynamical spin structure factors on the intra- and inter-leg
correlations are calculated. It is demonstrated that the low-lying structure of
the inter-leg spectra is particularly affected by the asymmetric modulation.",0806.2474v1
2008-06-24,Spin Glass Order Induced by Dynamic Frustration,"Spin glasses are systems whose magnetic moments freeze at low temperature
into random orientations without long-range order. It is generally accepted
that both frustration and disorder are essential ingredients in all spin
glasses, so it was surprising that PrAu2Si2, a stoichiometric compound with a
well-ordered crystal structure, was reported to exhibit spin glass freezing. In
this article, we report on inelastic neutron scattering measurements of the
crystal field excitations, which show that PrAu2Si2 has a singlet ground state
and that the exchange coupling is very close to the critical value to induce
magnetic order. We propose that spin glass freezing results from dynamic
fluctuations of the crystal field levels that destabilize the induced moments
and frustrate the development of long-range magnetic correlations. This novel
mechanism for producing a frustrated ground state could provide a method of
testing the concept of `avoided criticality' in glassy systems.",0806.3935v1
2008-12-18,A geometrical approach to the dynamics of spinor condensates I: Hydrodynamics,"In this work, we derive the equations of motion governing the hydrodynamics
of spin-F spinor condensates. We pursue a description based on standard
physical variables (total density and superfluid velocity), alongside 2F
`spin-nodes': unit vectors that describe the spin F state, and also exhibit the
point-group symmetry of a spinor condensate's mean-field ground state. The
hydrodynamic equations of motion consist of a mass continuity equation, 2F
Landau-Lifshitz equations for the spin-nodes, and a modified Euler equation. In
particular, we provide a generalization of the Mermin-Ho relation to spin one,
and find an analytic solution for the skyrmion texture in the incompressible
regime of a spin-half condensate. These results exhibit a beautiful geometrical
structure that underlies the dynamics of spinor condensates.",0812.3403v3
2009-02-21,Inelastic Neutron Scattering Studies of the Spin and Lattice Dynamics in Iron Arsenide Compounds,"Neutrons have played an important role in advancing our understanding of the
pairing mechanism and the symmetry of the superconducting energy gap in the
iron arsenide compounds. Neutron measurements of the phonon density-of-state
are in good agreement with ab initio calculations, provided the magnetism of
the iron atoms is taken into account. However, the predicted superconducting
transition temperatures are less than 1 K, making a conventional phononic
mechanism for superconductivity highly unlikely. Measurements of the spin
dynamics within the spin density wave phase of the parent compounds show
evidence of strongly dispersive spin waves with exchange interactions
consistent with the observed magnetic order. Antiferromagnetic fluctuations
persist in the normal phase of the superconducting compounds, but they are more
diffuse. Below Tc, there is evidence compounds that these fluctuations condense
into a resonant spin excitation at the antiferromagnetic wavevector with an
energy that scales with Tc, consistent with unconventional superconductivity of
extended-s+/- wave symmetry.",0902.3760v1
2009-07-10,On the cosmological effects of the Weyssenhoff spinning fluid in the Einstein-Cartan framework,"The effects of non-Riemannian structures in Cosmology have been studied long
ago and are still a relevant subject of investigation. In the seventies, it was
discovered that singularity avoidance and early accelerated expansion can be
induced by torsion in the Einstein-Cartan theory. In this framework, torsion is
not dynamical and is completely expressed by means of the spin sources. Thus,
in order to study the effects of torsion in the Einstein-Cartan theory, one has
to introduce matter with spin. In principle, this can be done in several ways.
In this work we consider the cosmological evolution of the universe in the
presence of a constant isotropic and homogeneous axial current and the
Weyssenhoff spinning fluid. We analyse possible solutions of this model, with
and without the spinning fluid.",0907.1701v2
2009-07-24,Spin dynamics in gravitational fields of rotating bodies and the equivalence principle,"We discuss the quantum and classical dynamics of a particle with spin in the
gravitational field of a rotating source. A relativistic equation describing
the motion of classical spin in curved spacetimes is obtained. We demonstrate
that the precession of the classical spin is in a perfect agreement with the
motion of the quantum spin derived from the Foldy-Wouthuysen approach for the
Dirac particle in a curved spacetime. We show that the precession effect
depends crucially on the choice of a tetrad. The results obtained are compared
to the earlier computations for different tetrad gauges.",0907.4367v2
2009-08-27,Nonequilibrium dynamics in a two-channel Kondo system due to a quantum quench,"Recent experiments by Potok et al. have demonstrated a remarkable tunability
between a single-channel Fermi liquid fixed point and a two-channel non-Fermi
liquid fixed point. Motivated by this we study the nonequilibrium dynamics due
to a sudden quench of the parameters of a Hamiltonian from a single-channel to
a two-channel anisotropic Kondo system. We find a distinct difference between
the long time behavior of local quantities related to the impurity spin as
compared to that of bulk quantities related to the total (conduction electrons
+ impurity) spin of the system. In particular, the local impurity spin and the
local spin susceptibility are found to equilibrate, but in a very slow
power-law fashion which is peculiar to the non-Fermi liquid properties of the
Hamiltonian. In contrast, we find a lack of equilibration in the two particle
expectation values related to the total spin of the system.",0908.4058v2
2009-11-25,Griffiths-like phase in the three-dimensional $\pm J$ Edwards-Anderson spin-glass model,"Using information of the ground state topology and the damage spreading
technique we show a Griffiths-like phase is present in the three-dimensional
$\pm J$ Edwards-Anderson spin glass model. With spin-flipping dynamics damage
spreads for temperatures larger than $T_{\mathrm{g}}$, the glass transition
temperature. With spin-orienting dynamics and for temperatures in
$T_{\mathrm{g}} < T < T_{\mathrm{d}}$, damage spreads over a finite region of
the system, composed of finite clusters of ferromagnetic character.
$T_{\mathrm{d}}$ is the spin-orienting damage critical temperature, which is of
the same order as the critical temperature of the ferromagnetic Ising model,
$T_{\mathrm{c}}$. The present results allow us to identify the clusters which
originate the Griffiths-like phase in the present model.",0911.4837v1
2010-08-12,Universal dynamical decoupling of a single solid-state spin from a spin bath,"Controlling the interaction of a single quantum system with its environment
is a fundamental challenge in quantum science and technology. We dramatically
suppress the coupling of a single spin in diamond with the surrounding spin
bath by using double-axis dynamical decoupling. The coherence is preserved for
arbitrary quantum states, as verified by quantum process tomography. The
resulting coherence time enhancement is found to follow a general scaling with
the number of decoupling pulses. No limit is observed for the decoupling action
up to 136 pulses, for which the coherence time is enhanced more than 25 times
compared to spin echo. These results uncover a new regime for experimental
quantum science and allow to overcome a major hurdle for implementing quantum
information protocols.",1008.2119v2
2010-09-27,Universal quantum control of two-electron spin quantum bits using dynamic nuclear polarization,"One fundamental requirement for quantum computation is to perform universal
manipulations of quantum bits at rates much faster than the qubit's rate of
decoherence. Recently, fast gate operations have been demonstrated in logical
spin qubits composed of two electron spins where the rapid exchange of the two
electrons permits electrically controllable rotations around one axis of the
qubit. However, universal control of the qubit requires arbitrary rotations
around at least two axes. Here we show that by subjecting each electron spin to
a magnetic field of different magnitude we achieve full quantum control of the
two-electron logical spin qubit with nanosecond operation times. Using a single
device, a magnetic field gradient of several hundred milliTesla is generated
and sustained using dynamic nuclear polarization of the underlying Ga and As
nuclei. Universal control of the two-electron qubit is then demonstrated using
quantum state tomography. The presented technique provides the basis for single
and potentially multiple qubit operations with gate times that approach the
threshold required for quantum error correction.",1009.5343v1
2010-11-04,Low-energy spin dynamics in the [YPc2]0 S=1/2 antiferromagnetic chain,"1H nuclear magnetic resonance (NMR) measurements in [YPc2]0, an organic
compound formed by radicals stacking along chains, are presented. The
temperature dependence of the macroscopic susceptibility, of the NMR shift and
of the spin-lattice relaxation rate 1/T1 indicate that the unpaired electron
spins are not delocalized but rather form a S=1/2 antiferromagnetic chain. The
exchange couplings estimated from those measurements are all in quantitative
agreement. The low-energy spin dynamics can be described in terms of diffusive
processes and the temperature dependence of the corresponding diffusion
constant suggests that a spin-gap around 1 K might be present in this compound.",1011.1141v2
2010-11-21,Optical detection of spin transport in non-magnetic metals,"We determine the dynamic magnetization induced in non-magnetic metal wedges
composed of silver, copper and platinum by means of Brillouin light scattering
(BLS) microscopy. The magnetization is transferred from a ferromagnetic
Ni80Fe20 layer to the metal wedge via the spin pumping effect. The spin pumping
efficiency can be controlled by adding an insulating but transparent interlayer
between the magnetic and non-magnetic layer. By comparing the experimental
results to a dynamical macroscopic spin-transport model we determine the
transverse relaxation time of the pumped spin current which is much smaller
than the longitudinal relaxation time.",1011.4656v2
2011-03-04,Observation of Hysteretic Transport Due to Dynamic Nuclear Spin Polarization in a GaAs Lateral Double Quantum Dot,"We report a new transport feature in a GaAs lateral double quantum dot that
emerges only for magnetic field sweeps and shows hysteresis due to dynamic
nuclear spin polarization (DNP). This DNP signal appears in the Coulomb
blockade regime by virtue of the finite inter-dot tunnel coupling and
originates from the crossing between ground levels of the spin triplet and
singlet extensively used for nuclear spin manipulations in pulsed gate
experiments. The unexpectedly large signal intensity is suggestive of
unbalanced DNP between the two dots, which opens up the possibility of
controlling electron and nuclear spin states via DC transport.",1103.0827v3
2011-03-13,Micromagnetic understanding of stochastic resonance driven by spin-transfertorque,"In this paper, we employ micromagnetic simulations to study non-adiabatic
stochastic resonance (NASR) excited by spin-transfer torque in a
super-paramagnetic free layer nanomagnet of a nanoscale spin valve. We find
that NASR dynamics involves thermally activated transitions among two static
states and a single dynamic state of the nanomagnet and can be well understood
in the framework of Markov chain rate theory. Our simulations show that a
direct voltage generated by the spin valve at the NASR frequency is at least
one order of magnitude greater than the dc voltage generated off the NASR
frequency. Our computations also reproduce the main experimentally observed
features of NASR such as the resonance frequency, the temperature dependence
and the current bias dependence of the resonance amplitude. We propose a simple
design of a microwave signal detector based on NASR driven by spin transfer
torque.",1103.2536v1
2011-06-30,Spin dynamics in the pressure-induced two-leg ladder cuprate superconductor Sr$_{14-x}$Ca$_{x}$Cu$_{24}$O$_{41}$,"Within the two-leg $t$-J ladder, the spin dynamics of the pressure-induced
two-leg ladder cuprate superconductor Sr$_{14-x}$Ca$_{x}$Cu$_{24}$O$_{41}$ is
studied based on the kinetic energy driven superconducting mechanism. It is
shown that in the pressure-induced superconducting state, the incommensurate
spin correlation appears in the underpressure regime, while the commensurate
spin fluctuation emerges in the optimal pressure and overpressure regimes. In
particular, the spin-lattice relaxation time is dominated by a temperature
linear dependence term at low temperature followed by a peak developed below
the superconducting transition temperature, in qualitative agreement with the
experimental observation on Sr$_{14-x}$Ca$_{x}$Cu$_{24}$O$_{41}$.",1106.6187v2
2011-06-30,Spin Liquid Ground State in the Frustrated Kagome Antiferromagnet MgCu3(OH)6Cl2,"We report muSR experiments on Mg{x}Cu{4-x}(OH)6Cl2 with x \sim 1, a new
material isostructural to Herbertsmithite exhibiting regular kagome planes of
spin 1/2 (Cu^{2+}), and therefore a candidate for a spin liquid ground state.
We evidence the absence of any magnetic ordering down to 20 mK (\sim J/10^4).
We investigate in detail the spin dynamics on well characterized samples in
zero and applied longitudinal fields and propose a low T defect based
interpretation to explain the unconventional dynamics observed in the quantum
spin liquid phase.",1106.6309v2
2011-07-01,Semiclassical Description of Relativistic Spin without use of Grassmann variables and the Dirac equation,"We propose a relativistic particle model without Grassmann variables which,
being canonically quantized, leads to the Dirac equation. Both
$\Gamma$\,-matrices and the relativistic spin tensor are produced through the
canonical quantization of the classical variables which parametrize the
properly constructed relativistic spin surface. Although there is no mass-shell
constraint in our model, our particle's speed cannot exceed the speed of light.
The classical dynamics of the model is in correspondence with the dynamics of
mean values of the corresponding operators in the Dirac theory. In particular,
the position variable experiences {\it Zitterbewegung} in noninteracting
theory. The classical equations for the spin tensor are the same as those of
the Barut-Zanghi model of a spinning particle.",1107.0273v4
2011-08-12,Universal spatial correlations in random spinor fields,"We identify universal spatial fluctuations in systems with non trivial spin
dynamics. To this end we calculate by exact numerical diagonalization a variety
of experimentally relevant correlations between spinor amplitudes, spin
polarizations and spin currents both in the bulk and near the boundary of a
confined two-dimensional clean electron gas in the presence of spin-orbit
interaction and a single magnetic impurity. We support or claim of universality
with the excellent agreement between the numerical results and
system-independent spatial correlations of a random field defined on both the
spatial and spin degrees of freedom. A rigorous identity relating our universal
predictions with response functions provides a direct physical interpretation
of our results in the framework of linear response theory.",1108.2652v1
2011-08-29,Domain Wall Spin Dynamics in Kagome Antiferromagnets,"We report magnetization and neutron scattering measurements down to 60 mK on
a new family of Fe based kagome antiferromagnets, in which a strong local spin
anisotropy combined with a low exchange path network connectivity lead to
domain walls intersecting the kagome planes through strings of free spins.
These produce unfamiliar slow spin dynamics in the ordered phase, evolving from
exchange-released spin-flips towards a cooperative behavior on decreasing the
temperature, probably due to the onset of long-range dipolar interaction. A
domain structure of independent magnetic grains is obtained that could be
generic to other frustrated magnets.",1108.5540v2
2012-02-10,Charmed and strange baryon resonances with heavy-quark spin symmetry,"We study charmed and strange baryon resonances that are generated dynamically
by a unitary baryon-meson coupled-channel model which incorporates heavy-quark
spin symmetry. This is accomplished by extending the SU(3) Weinberg-Tomozawa
chiral Lagrangian to SU(8) spin-flavor symmetry plus a suitable symmetry
breaking. The model produces resonances with negative parity from s-wave
interaction of pseudoscalar and vector mesons with $1/2^+$ and $3/2^+$ baryons.
Resonances in all the isospin, spin, and strange sectors with one, two, and
three charm units are studied. Our results are compared with experimental data
from several facilities, such as the CLEO, Belle or BaBar Collaborations, as
well as with other theoretical models. Some of our dynamically generated states
can be readily assigned to resonances found experimentally, while others do not
have a straightforward identification and require the compilation of more data
and also a refinement of the model. In particular, we identify the
$\Xi_c(2790)$ and $\Xi_c(2815)$ resonances as possible candidates for a
heavy-quark spin symmetry doublet.",1202.2239v2
2012-03-13,Dynamical lattice instability versus spin liquid state in a frustrated spin chain system,"The low-dimensional s=1/2 compound (NO)[Cu(NO3)3] has recently been suggested
to follow the Nersesyan-Tsvelik model of coupled spin chains. Such a system
shows unbound spinon excitations and a resonating valence bond ground state due
spin frustration. Our Raman scattering study demonstrates phonon anomalies as
well as the suppression of a broad magnetic scattering continuum for
temperatures below a characteristic temperature, T<T*=100K. We interpret these
effects as evidence for a dynamical interplay of spin and lattice degrees of
freedom that might lead to a further transition into a dimerized or
structurally distorted phase at lower temperatures.",1203.2818v1
2012-03-21,Protecting and Enhancing Spin Squeezing via Continuous Dynamical Decoupling,"Realizing useful quantum operations with high fidelity is a two-task quantum
control problem wherein decoherence is to be suppressed and desired unitary
evolution is to be executed. The dynamical decoupling (DD) approach to
decoherence suppression has been fruitful but synthesizing DD fields with
certain quantum control fields may be experimentally demanding. In the context
of spin squeezing, here we explore an unforeseen possibility that continuous DD
fields may serve dual purposes at once. In particular, it is shown that a
rather simple configuration of DD fields can suppress collective decoherence
and yield a 1/N scaling of the squeezing performance (N is the number of
spins), thus making spin squeezing more robust to noise and much closer to the
so-called Heisenberg limit. The theoretical predictions should be within the
reach of current spin squeezing experiments.",1203.4631v1
2012-06-20,Long-lived driven solid-state quantum memory,"We investigate the performance of inhomogeneously broadened spin ensembles as
quantum memories under continuous dynamical decoupling. The role of the
continuous driving field is two-fold: first, it decouples individual spins from
magnetic noise; second and more important, it suppresses and reshapes the
spectral inhomogeneity of spin ensembles. We show that a continuous driving
field, which itself may also be inhomogeneous over the ensemble, can enhance
the decay of the tails of the inhomogeneous broadening distribution
considerably. This fact enables a spin ensemble based quantum memory to exploit
the effect of cavity protection and achieve a much longer storage time. In
particular, for a spin ensemble with a Lorentzian spectral distribution, our
calculations demonstrate that continuous dynamical decoupling has the potential
to improve its storage time by orders of magnitude for the state-of-art
experimental parameters.",1206.4430v2
2012-07-02,Spin chains with dynamical lattice supersymmetry,"Spin chains with exact supersymmetry on finite one-dimensional lattices are
considered. The supercharges are nilpotent operators on the lattice of
dynamical nature: they change the number of sites. A local criterion for the
nilpotency on periodic lattices is formulated. Any of its solutions leads to a
supersymmetric spin chain. It is shown that a class of special solutions at
arbitrary spin gives the lattice equivalents of the N=(2,2) superconformal
minimal models. The case of spin one is investigated in detail: in particular,
it is shown that the Fateev-Zamolodchikov chain and its off-critical extension
admits a lattice supersymmetry for all its coupling constants. Its
supersymmetry singlets are thoroughly analysed, and a relation between their
components and the weighted enumeration of alternating sign matrices is
conjectured.",1207.0357v2
2012-08-29,Persistent spin dynamics intrinsic to amplitude-modulated long-range magnetic order,"An incommensurate elliptical helical magnetic structure in the frustrated
coupled-spin-chain system FeTe2O5Br is surprisingly found to persist down to
53(3) mK (T/T_N ~ 1/200), according to neutron scattering and muon spin
relaxation. In this state, finite spin fluctuations at T -> 0 are evidenced by
muon depolarization, which is in agreement with specific-heat data indicating
the presence of both gapless and gapped excitations. We thus show that the
amplitude-modulated magnetic order intrinsically accommodates contradictory
persistent spin dynamics and long-range order and can serve as a model
structure to investigate their coexistence.",1208.5843v2
2012-12-10,Antiferromagnetic Spatial Ordering in a Quenched One-dimensional Spinor Gas,"We have experimentally observed the emergence of spontaneous
antiferromagnetic spatial order in a sodium spinor Bose-Einstein condensate
that was quenched through a magnetic phase transition. For negative values of
the quadratic Zeeman shift, a gas initially prepared in the F = 1, mF = 0 state
collapsed into a dynamically evolving superposition of all 3 spin projections,
mF = 0, +/-1. The quench gave rise to rich, nonequilibrium behavior where both
nematic and magnetic spin waves were generated. We characterized the
spatiotemporal evolution through two particle correlations between atoms in
each pair of spin states. These revealed dramatic differences between the
dynamics of the spin correlations and those of the spin populations.",1212.2233v1
2013-01-11,"Neutron Scattering Study on Spin Dynamics in Superconducting (Tl,Rb)2Fe4Se5","We observed in superconducting (Tl,Rb)2Fe4Se5 spin-wave branches that span an
energy range from 6.5 to 209 meV. Spin dynamics are successfully described by a
Heisenberg localized spin model whose dominant in-plane interactions include
only the nearest (J1 and J1') and next nearest neighbor (J2 and J2') exchange
terms within and between the tetramer spin blocks, respectively. These
experimentally determined exchange constants would crucially constrain the
theoretical viewpoints on magnetism and superconductivity in the Fe-based
materials.",1301.2413v1
2013-01-29,Creation and dynamics of remote spin-entangled pairs in the expansion of strongly correlated fermions in an optical lattice,"We consider the nonequilibrium dynamics of an interacting spin-1/2 fermion
gas in a one-dimensional optical lattice after switching off the confining
potential. In particular, we study the creation and the time evolution of
spatially separated, spin-entangled fermionic pairs. The time-dependent
density-matrix renormalization group is used to simulate the time evolution and
evaluate the two-site spin correlation functions, from which the concurrence is
calculated. We find that the typical distance between entangled fermions
depends crucially on the onsite interaction strength, and that a time-dependent
modulation of the tunneling amplitude can enhance the production of
spin-entanglement. Moreover, we discuss the prospects of experimentally
observing these phenomena using spin-dependent single-site detection.",1301.6951v3
2013-01-31,Resistive detection of nuclear spins in a single quantum dot under Kondo effect regime,"We study dynamic polarization and resistive detection of nuclear spins in a
semiconductor quantum dot (QD) under the Kondo effect regime. We find that the
differential conductance spectra of the QD exhibit hysteresis under the Kondo
effect regime in magnetic fields. Relevance of nuclear spins to the hysteresis
is confirmed by the detection of nuclear magnetic resonance signals by
monitoring the differential conductance. We attribute the origin of the
hysteresis to the dynamic nuclear spin polarization (DNP) induced in the QD.
Using the DNP, we demonstrate nuclear spin relaxation rate measurements in the
QD under the Kondo effect regime.",1301.7730v1
2013-06-12,Coarse graining of spin net models: dynamics of intertwiners,"Spin foams are models of quantum gravity and therefore quantum space time. A
key open issue is to determine the possible continuum phases of these models.
Progress on this issue has been prohibited by the complexity of the full
four--dimensional models. We consider here simplified analogue models, so
called spin nets, that retain the main dynamical ingredient of spin foams, the
simplicity constraints. For a certain class of these spin net models we
determine the phase diagram and therefore the continuum phases via a coarse
graining procedure based on tensor network renormalization. This procedure will
also reveal an unexpected fixed point, which turns out to define a new
triangulation invariant vertex model.",1306.2987v1
2013-06-24,Spinon confinement: dynamics of weakly coupled Hubbard chains,"Using large-scale determinant quantum Monte Carlo simulations in combination
with the stochastic analytical continuation, we study two-particle dynamical
correlation functions in the anisotropic square lattice of weakly coupled
one-dimensional (1D) Hubbard chains at half-filling and in the presence of weak
frustration. The evolution of the static spin structure factor upon increasing
the interchain coupling is suggestive of the transition from the power-law
decay of spin-spin correlations in the 1D limit to long-range antiferromagnetic
order in the quasi-1D regime and at $T=0$. In the numerically accessible regime
of interchain couplings, the charge sector remains gapped. The low-energy
momentum dependence of the spin excitations is well described by the linear
spin-wave theory with the largest intensity located around the
antiferromagnetic wave vector. This magnon mode corresponds to a bound state of
two spinons. At higher energies the spinons deconfine and we observe signatures
of the two-spinon continuum which progressively fade away as a function of
interchain hopping.",1306.5775v2
2013-07-09,Converting a real quantum bath to an effective classical noise,"We present a cluster expansion method for approximating quantum spin-bath
dynamics in terms of a classical Gaussian stochastic process. The cluster
expansion produces the two-point correlation function of the approximate
classical bath, permitting rapid evaluation of noise-mitigating quantum control
strategies without resorting to computationally intensive dynamical decoupling
models. Our approximation is valid for the wide class of models possessing
negligible back-action and nearly-Gaussian noise. We study several instances of
the central spin decoherence problem in which the central spin and
randomly-located bath spins are alike and dipolarly coupled. For various pulse
sequences, we compare the coherence echo decay computed explicitly quantum
mechanically versus those computed using our approximate classical model, and
obtain agreement in most, but not all, cases. We demonstrate the utility of
these classical noise models by efficiently searching for the 4-pulse sequences
that maximally mitigate decoherence in each of these cases, a computationally
expensive task in the explicit quantum model.",1307.2597v2
2013-10-14,Synchronizing the dynamics of a single NV spin qubit on a parametrically coupled radio-frequency field through microwave dressing,"A hybrid spin-oscillator system in parametric interaction is experimentally
emulated using a single NV spin qubit immersed in a radio frequency (RF) field
and probed with a quasi resonant microwave (MW) field. We report on the MW
mediated locking of the NV spin dynamics onto the RF field, appearing when the
MW driven Rabi precession frequency approaches the RF frequency and for
sufficiently large RF amplitudes. These signatures are analog to a phononic
Mollow triplet in the MW rotating frame for the parametric interaction and
promise to have impact in spin-dependent force detection strategies.",1310.3789v1
2013-10-28,Maximal Rabi frequency of an electrically driven spin in a disordered magnetic field,"We present a theoretical study of the spin dynamics of a single electron
confined in a quantum dot. Spin dynamics is induced by the interplay of
electrical driving and the presence of a spatially disordered magnetic field,
the latter being transverse to a homogeneous magnetic field. We focus on the
case of strong driving, i.e., when the oscillation amplitude $A$ of the
electron's wave packet is comparable to the quantum dot length $L$. We show
that electrically driven spin resonance can be induced in this system by
subharmonic driving, i.e., if the excitation frequency is an integer fraction
(1/2, 1/3, etc) of the Larmor frequency. At strong driving we find that (i) the
Rabi frequencies at the subharmonic resonances are comparable to the Rabi
frequency at the fundamental resonance, and (ii) at each subharmonic resonance,
the Rabi frequency can be maximized by setting the drive strength to an
optimal, finite value. Our simple model is applied to describe electrical
control of a spin-valley qubit in a weakly disordered carbon nanotube.",1310.7350v2
2014-01-11,Near-band-gap photo-induced nuclear spin dynamics in semi-insulating GaAs: Hyperfine- and quadrupolar-driven relaxation,"Understanding and manipulating spin polarization and transport in the
vicinity of semiconductor-hosted defects is a problem of present technological
and fundamental importance. Here, we use high-field magnetic resonance to
monitor the relaxation dynamics of spin-3/2 nuclei in semi-insulating GaAs. Our
experiments benefit from the conditions created in the limit of low
illumination intensities, where intermittent occupation of the defect site by
photo-excited electrons leads to electric field gradient fluctuations and
concomitant spin relaxation of the neighboring quadrupolar nuclei. We find
indication of a heterogeneous distribution of polarization, governed by
different classes of defects activated by either weak or strong laser
excitation. Upon application of a train of light pulses of variable repetition
rate and on/off ratio, we uncover an intriguing regime of mesoscale nuclear
spin diffusion restricted by long-range, non-uniform electric field gradients.
Given the slow time scale governing nuclear spin evolution, such
optically-induced polarization patterns could be exploited as a contrast
mechanism to expose dark lattice defects or localized charges with nanoscale
resolution.",1401.2534v1
2014-01-23,The suppression of electron correlations in the collapsed tetragonal phase of CaFe2As2 under ambient pressure demonstrated by 75As NMR-NQR measurements,"The static and the dynamic spin correlations in the low temperature collapsed
tetragonal and the high temperature tetragonal phase in CaFe2As2 have been
investigated by 75As nuclear magnetic resonance (NMR) and nuclear quadrupole
resonance (NQR) measurements.
  Through the temperature (T) dependence of the nuclear spin lattice relaxation
rates (1/T1) and the Knight shifts, although stripe-type antiferromagnetic
(AFM) spin correlations are realized in the high temperature tetragonal phase,
no trace of the AFM spin correlations can be found in the non-superconducting,
low temperature, collapsed tetragonal (cT) phase.
  Given that there is no magnetic broadening in 75As NMR spectra, together with
the T-independent behavior of magnetic susceptibility (x) and the T dependence
of 1/T1Tx, we conclude that Fe spin correlations are completely quenched
statically and dynamically in the non-superconducting cT phase in CaFe2As2.",1401.6191v1
2014-01-29,Josephson physics of spin-orbit coupled elongated Bose-Einstein condensates,"We consider an ultracold bosonic binary mixture confined in a one-dimensional
double-well trap. The two bosonic components are assumed to be two hyperfine
internal states of the same atom. We suppose that these two components are
spin-orbit coupled between each other. We employ the two-mode approximation
starting from two coupled Gross-Pitaevskii equations and derive a system of
ordinary differential equations governing the temporal evolution of the
inter-well population imbalance of each component and that between the two
bosonic species. We study the Josephson oscillations of these spin-orbit
coupled Bose-Einstein condensates by analyzing the interplay between the
interatomic interactions and the spin-orbit coupling and the self-trapped
dynamics of the inter-species imbalance. We show that the dynamics of this
latter variable is crucially determined by the relationship between the
spin-orbit coupling, the tunneling energy, and the interactions.",1401.7693v1
2014-09-06,Three-level spin system under decoherence-minimizing driving fields: Application to nitrogen-vacancy spin dynamics,"Within the framework of a general three-level problem, the dynamics of the
nitrogen-vacancy (NV) spin is studied for the case of a special type of
external driving consisting of a set of continuous fields with decreasing
intensities. Such a set has been proposed for minimizing coherence losses. Each
new driving field with smaller intensity is designed to protect against the
fluctuations induced by the driving field at the preceding step with larger
intensity. We show that indeed this particular type of external driving
minimizes the loss of coherence, using purity and entropy as quantifiers for
this purpose. As an illustration, we study the coherence loss of an NV spin due
to a surrounding spin bath of $^{13}$C nuclei.",1409.2005v1
2014-09-10,Chaotic Dynamics of Stellar Spin in Binaries and the Production of Misaligned Hot Jupiters,"Many exoplanetary systems containing hot Jupiters are observed to have highly
misaligned orbital axes relative to the stellar spin axes. Kozai-Lidov
oscillations of orbital eccentricity/inclination induced by a binary companion,
in conjunction with tidal dissipation, is a major channel for the production of
hot Jupiters. We demonstrate that gravitational interaction between the planet
and its oblate host star can lead to chaotic evolution of the stellar spin axis
during Kozai cycles. As parameters such as the planet mass and stellar rotation
period vary, periodic islands can appear in an ocean of chaos, in a manner
reminiscent of other dynamical systems. In the presence of tidal dissipation,
the complex spin evolution can leave an imprint on the final spin-orbit
misalignment angles.",1409.3247v1
2014-12-23,Current-induced spin torque resonance of a magnetic insulator,"Pure spin currents transport angular momentum without an associated charge
flow. This unique property makes them attractive for spintronics applications,
such as torque induced magnetization control in nanodevices that can be used
for sensing, data storage, interconnects and logics. Up to now, however, most
spin transfer torque studies focused on metallic ferromagnets, while magnetic
insulators were largely ignored, in spite of superior magnetic quality factors.
Here, we report the observation of spin torque-induced magnetization dynamics
in a magnetic insulator. Our experiments show that in ultrathin magnetic
insulators the spin torque induced magnetization dynamics can be substantially
larger than those generated by the Oersted field. This opens new perspectives
for the efficient integration of ferro-, ferri-, and antiferromagnetic
insulators into electronic devices.",1412.7460v1
2015-01-22,Relativistic dynamical spin excitations of magnetic adatoms,"We present a first-principles theory of dynamical spin excitations in the
presence of spin-orbit coupling. The broken global spin rotational invariance
leads to a new sum rule. We explore the competition between the magnetic
anisotropy energy and the external magnetic field, as well as the role of
electron-hole excitations, through calculations for 3$d$-metal adatoms on the
Cu(111) surface. The spin excitation resonance energy and lifetime display
non-trivial behavior, establishing the strong impact of relativistic effects.
We legitimate the use of the Landau-Lifshitz-Gilbert equation down to the
atomic limit, but with parameters that differ from a stationary theory.",1501.05509v1
2015-03-06,Standing spin wave mode in RFIM at T=0: Patterns and nonequilibrium phases,"The dynamical responses of random field Ising model at zero temperature,
driven by standing magnetic field wave, is studied by Monte Carlo simulation in
two dimensions. The three different kinds of distribution of quenched random
field are used here, uniform, bimodal and Gaussian. In all cases, three
distinct dynamical phases were observed, namely, the pinned, structured and
random. In the pinned phase no spin flip is observed. In the structured phase
standing spin wave modes are observed. The random phase is shown no regular
pattern. For a fixed value of the amplitude of the standing magnetic field
wave, in the region of small quenched field, the system remains in a pinned
phase. In the intermediate range of values of random field, a standing spin
wave mode (structured phase) is observed. The regular pattern of this spin wave
mode disappears for higher values of random field yielding a random phase. The
comprehensive phase baundaries are drawn in all three cases. The boundary of
pinned phase are analytically calculated for uniform and bimodal types of
quenched random fields.",1503.01861v2
2015-03-29,Energy landscape in three-dimensional Heisenberg spin glasses,"Recent work suggests that Heisenberg spin glasses may belong to the same
universality class than structural glasses. Indeed, finding a lattice
equivalent for supercooled liquids would probably allow easier numerical and
analytical studies, that may help to answer long-standing questions on the
glass transition. Supercooled liquids have many peculiar behaviors that should
be found in the paramagnetic phase of Heisenberg spin glasses if the analogy
between the two systems holds. It is with this motivation that we undertake a
study of the paramagnetic phase of Heisenberg spin glasses. We shall emphasize
the role of the energy landscape, with a detailed study of the properties of
the inherent structures (by analogy with supercooled liquids, we name inherent
structure the local minimum of the energy function which is closest to the
current spin configuration). Finding inherent structures will require the
development of a new search algorithm. We shall investigate as well the
existence of a dynamic transition in the paramagnetic phase. As a matter of
fact, both the existence of a complex energy landscape, as well as the
existence of a dynamic transition, are distinguished features of the Physics of
supercooled liquids.",1503.08409v1
2015-04-02,Electron-Magnon Scattering in Magnetic Heterostructures Far Out-of-Equilibrium,"We present a theory of out-of-equilibrium ultrafast spin dynamics in magnetic
heterostructures based on the s-d model of ferromagnetism. Both in the bulk and
across interfaces, the exchange processes between the itinerant s and the
localized d electrons are described by kinetic rate equations for
electron-magnon spin-flop scattering. The principal channel for dissipation of
angular momentum is provided by spin relaxation of the itinerant electrons. Our
theory extends interfacial spin phenomena such as torques, pumping, and the
Peltier and Seebeck effects to address laser-induced rapid spin dynamics, in
which the effective electron temperature may approach or even exceed the Curie
temperature.",1504.00511v1
2015-04-27,Exciton spin dynamics in GaSe,"We analyze exciton spin dynamics in GaSe under nonresonant circularly
polarized optical pumping with an exciton spin-flip rate-equation model. The
model reproduces polarized time-dependent photoluminescence measurements in
which the initial circular polarization approaches unity even when pumping with
0.15 eV excess energy. At T = 10 K, the exciton spin relaxation exhibits a
biexponential decay with a sub-20 ps and a >500 ps time constants, which are
also reproduced by the rate-equation model assuming distinct spin-relaxation
rates for hot (nonequilibrium) and cold band-edge excitons.",1504.07147v2
2015-04-30,Generalized mean-field approach to simulate large dissipative spin ensembles with long range interactions,"We simulate the collective dynamics in spin lattices with long range
interactions and collective decay in one, two and three dimensions. Starting
from a dynamical mean-field approach derived by local factorization of the
density operator we improve the numerical approximation of the full master
equation by including pair correlations at any distance. This truncations
enable us to drastically increase the number of spins in our numerical
simulations from about ten spins in case of the full quantum model to several
ten-thousands in the mean-field approximation and a few hundreds if pair
correlations are included. Extensive numerical tests help us identify
interaction strengths and geometric configurations where these approximations
perform well and allow us to state fairly simple error estimates. By simulating
systems of increasing size we show that in one and two dimensions we can
include as many spins as needed to capture the properties of infinite size
systems with high accuracy, while in 3D the method does not converge to desired
accuracy within the system sizes we can currently implement. Our approach is
well suited to give error estimates of magic wavelength optical lattices for
atomic clock applications and corresponding super radiant lasers.",1504.08279v2
2015-06-15,Detection of topological states in two-dimensional Dirac systems by the dynamic spin susceptibility,"We discuss dynamic spin susceptibility (DSS) in two-dimensional (2D) Dirac
electrons with spin-orbit interactions to characterize topological insulators.
The imaginary part of the DSS appears as an absorption rate in response to a
transverse ac magnetic field, just as in an electron spin resonance experiment
for localized spin systems. We found that when the system is in a static
magnetic field, the topological state can be identified by an anomalous
resonant peak of the imaginary part of the DSS as a function of the frequency
of the transverse magnetic field $\omega$. In the absence of a static magnetic
field, the imaginary part of the DSS becomes a continuous function of $\omega$
with a threshold frequency $\omega_{\rm c}$. In this case, the topological and
the trivial phases can also be distinguished by the values of $\omega_{\rm c}$
and by the line shapes. Thus the DSS is an experimentally observable physical
quantity to characterize a topological insulator directly from bulk properties,
without observing a topological transition.",1506.04691v2
2015-07-10,Dynamics of Fractionalization in Quantum Spin Liquids,"We present the theory of dynamical spin-response for the Kitaev honeycomb
model, obtaining exact results for the structure factor (SF) in gapped and
gapless, Abelian and non-Abelian quantum spin-liquid (QSL) phases. We also
describe the advances in methodology necessary to compute these results. The
structure factor shows signatures of spin-fractionalization into emergent
quasiparticles -- Majorana fermions and fluxes of $Z_2$ gauge field. In
addition to a broad continuum from spin-fractionalization, we find sharp
($\delta$-function) features in the response. These arise in two distinct ways:
from excited states containing only (static) fluxes and no (mobile) fermions;
and from excited states in which fermions are bound to fluxes. The SF is
markedly different in Abelian and non-Abelian QSLs, and bound fermion-flux
composites appear only in the non-Abelian phase.",1507.02865v1
2015-09-11,Comparison between a quantum kinetic theory of spin transfer dynamics in Mn doped bulk semiconductors and its Markov limit for non-zero Mn magnetization,"We investigate the transfer between carrier and Mn spins due to the
s-d-exchange interaction in a Mn doped bulk semiconductor within a microscopic
quantum kinetic theory. We demonstrate that the spin transfer dynamics is
qualitatively different for components of the carrier spin parallel and
perpendicular to the Mn magnetization. From our quantum kinetic equations we
have worked out the corresponding Markov limit which is equivalent to rate
equations based on Fermi's golden rule. The resulting equations resemble the
widely used Landau-Lifshitz-Gilbert-equations, but also describe genuine spin
transfer due to quantum corrections. Although it is known that the Markovian
rate description works well for bulk systems when the initial Mn magnetization
is zero, we find large qualitative deviations from the full quantum kinetic
theory for finite initial Mn magnetizations. These deviations mainly reflect
corrections of higher than leading order in the interaction which are not
accounted for in golden rule-type rates.",1509.03479v1
2015-10-02,Evidence for unidimensional low-energy excitations as the origin of persistent spin dynamics in geometrically frustrated magnets,"We report specific heat, magnetic, and muon spin relaxation measurements
performed on a polycrystalline sample of the normal spinel CdHo2S4. The
rare-earth ions sit on a lattice of corner-sharing regular tetrahedra as in
pyrochlore compounds. Magnetic ordering is detected at Tc ~ 0.87 K. From
spin-lattice relaxation rate measurements on both sides of Tc we uncover
similar magnetic excitation modes driving the so-called persistent spin
dynamics at T < Tc. Unidimensional excitations are argued to be at its origin.
Often observed spin loop structures are suggested to support these excitations.
The possibility of a generic mechanism for their existence is discussed.",1510.00544v1
2016-01-12,Spin-dependent Bragg spectroscopy of a spinor Bose gas,"We develop a general theory of spin-dependent Bragg spectroscopy for spinor
Bose-Einstein condensates. This spectroscopy involves using a density and
spin-coupled optical probe to excite the system. We show that within the linear
response regime the momentum or energy transferred by the probe is determined
by a set of density and spin-density dynamic structure factors. We derive a set
of $f$-sum rules that provide rigorous constraints for the first energy moments
of these structure factors. As an application we compute the dynamic structure
factors for cases within all four distinct phases of a spin-1 condensate using
Bogoliubov theory. Our results demonstrate that spin-dependent Bragg
spectroscopy can be used to selectively investigate the various phonon and
magnon excitation branches and will be a useful tool for advancing our
understanding of spinor condensates.",1601.02716v2
2016-02-12,Versatile Approach to the Spin Dynamics in Correlated Electron Systems,"Time-dependent spin phenomena in condensed matter are most often either
described in the weakly correlated limit of metallic Stoner/Slater-like
magnetism via band theory or in the strongly correlated limit of
Heisenberg-like interacting spins in an insulator. However many experimental
studies, e.g. of (de)magnetization processes, focus on itinerant local-moment
materials such as transition metals and various of their compounds. We here
present a general theoretical framework that is capable of addressing
correlated spin dynamics, also in the presence of a vanishing charge gap. A
real-space implementation of the time-dependent rotational-invariant slave
boson methodology allows to treat non-equilibrium spins numerically fast and
efficiently beyond linear response as well as beyond the band-theoretical or
Heisenberg limit.",1602.04141v3
2016-02-15,Polariton Spin Whirls,"We report on the observation of spin whirls in a radially expanding polariton
condensate formed under non-resonant optical excitation. Real space imaging of
polarization- and time-resolved photoluminescence reveal a spiralling
polarization pattern in the plane of the microcavity. Simulations of the
spatiotemporal dynamics of a spinor condensate reveal the crucial role of
polariton interactions with a spinor exciton reservoir. Harnessing spin
dependent interactions between the exciton reservoir and polariton condensates
allows for the manipulation of spin currents and the realization of dynamic
collective spin effects in solid state systems.",1602.04757v1
2016-04-03,Spin relaxation signature of colossal magnetic anisotropy in platinum atomic chains,"Recent experimental data demonstrate emerging magnetic order in platinum
atomically thin nanowires. Furthermore, an unusual form of magnetic anisotropy
-- colossal magnetic anisotropy (CMA) -- was earlier predicted to exist in
atomically thin platinum nanowires. Using spin dynamics simulations based on
first-principles calculations, we here explore the spin dynamics of atomically
thin platinum wires to reveal the spin relaxation signature of colossal
magnetic anisotropy, comparing it with other types of anisotropy such as
uniaxial magnetic anisotropy (UMA). We find that the CMA alters the spin
relaxation process distinctly and, most importantly, causes a large speed-up of
the magnetic relaxation compared to uniaxial magnetic anisotropy. The magnetic
behavior of the nanowire exhibiting CMA should be possible to identify
experimentally at the nanosecond time scale for temperatures below 5 K. This
time-scale is accessible in e.g., soft x-ray free electron laser experiments.",1604.00626v1
2016-06-25,Spin structure factors of chiral quantum spin liquids on the kagome lattice,"We calculate dynamical spin structure factors for gapped chiral spin liquid
states in the spin-1/2 Heisenberg antiferromagnet on the kagome lattice using
Schwinger-boson mean-field theory. In contrast to static (equal-time) structure
factors, the dynamical structure factor shows clear signatures of time-reversal
symmetry breaking for chiral spin liquid states. In particular, momentum
inversion $\bm{k} \to -\bm{k}$ symmetry as well as the six-fold rotation
symmetry around the $\Gamma$-point are lost. We highlight other interesting
features, such as a relatively flat onset of the two-spinon continuum for the
\emph{cuboc1} state. Our work is based on the projective symmetry group
classification of time-reversal symmetry breaking Schwinger-boson mean-field
states by Messio, Lhuillier, and Misguich.",1606.07856v2
2016-06-29,"Kinetics of local $""$magnetic$""$ moment and non-stationary spin-polarized current in the single impurity Anderson-model","We perform theoretical investigation of the localized state dynamics in the
presence of interaction with the reservoir and Coulomb correlations. We analyze
kinetic equations for electron occupation numbers with different spins taking
into account high order correlation functions for the localized electrons. We
reveal that in the stationary state electron occupation numbers with the
opposite spins always have the same value - the stationary state is a
$""$paramagnetic$""$ one. $""$Magnetic$""$ properties can appear only in the
non-stationary characteristics of the single-impurity Anderson model and in the
dynamics of the localized electrons second order correlation functions. We
found, that for deep energy levels and strong Coulomb correlations, relaxation
time for initial $""$magnetic$""$ state can be several orders larger than for
$""$paramagnetic$""$ one. So, long-living $""$magnetic$""$ moment can exist in the
system. We also found non-stationary spin polarized currents flowing in
opposite directions for the different spins in the particular time interval.",1606.08975v1
2017-02-15,Solution of the Lindblad equation for spin helix states,"Using Lindblad dynamics we study quantum spin systems with dissipative
boundary dynamics that generate a stationary nonequilibrium state with a
non-vanishing spin current that is locally conserved except at the boundaries.
We demonstrate that with suitably chosen boundary target states one can solve
the many-body Lindblad equation exactly in any dimension. As solution we obtain
pure states at any finite value of the dissipation strength and any system
size. They are characterized by a helical stationary magnetization profile and
a superdiffusive ballistic current of order one, independent of system size
even when the quantum spin system is not integrable. These results are derived
in explicit form for the one-dimensional spin-1/2 Heisenberg chain and its
higher-spin generalizations (which include for spin-1 the integrable
Zamolodchikov-Fateev model and the bi-quadratic Heisenberg chain). The
extension of the results to higher dimensions is straightforward.",1702.04586v1
2017-08-03,Spin Resonance in the New-Structure-Type Iron-Based Superconductor CaKFe4As4,"The dynamical spin susceptibility in the new-structure-type iron-based
superconductor CaKFe$_4$As$_4$ was investigated by using a combination of
inelastic neutron scattering (INS) measurements and random phase approximation
(RPA) calculations. Powder INS measurements show that the spin resonance at
$Q_\text{res}=1.17(1)$~$\text{\AA}^{-1}$, corresponding to the $(\pi,\pi)$
nesting wave vector in tetragonal notation, evolves below $T_\text{c}$. The
characteristic energy of the spin resonance $E_\text{res}=12.5$~meV is smaller
than twice the size of the superconducting gap ($2\Delta$). The broad energy
feature of the dynamical susceptibility of the spin resonance can be explained
by the RPA calculations, in which the different superconducting gaps on
different Fermi surfaces are taken into account. Our INS and PRA studies
demonstrate that the superconducting pairing nature in CaKFe$_4$As$_4$ is the
$s_\pm$ symmetry.",1708.01006v2
2017-08-18,General treatment of quantum and classical spinning particles in external fields,"We develop the general theory of spinning particles with electric and
magnetic dipole moments moving in arbitrary electromagnetic, inertial and
gravitational fields. Both the quantum-mechanical and classical dynamics is
investigated. We start from the covariant Dirac equation extended to a
spin-${\frac 12}$ fermion with anomalous magnetic and electric dipole moments
and then perform the relativistic Foldy-Wouthuysen transformation. This
transformation allows us to obtain the quantum-mechanical equations of motion
for the physical operators in the Schr\""odinger form and to establish the
classical limit of relativistic quantum mechanics. The results obtained are
then compared to the general classical description of the spinning particle
interacting with electromagnetic, inertial and gravitational fields. The
complete agreement between the quantum mechanics and the classical theory is
proven in the general case. As an application of the results obtained, we
consider the dynamics of a spinning particle in a gravitational wave and
analyze the prospects of using the magnetic resonance setup to find possible
manifestations of the gravitational wave on spin.",1708.05601v2
2018-02-07,Excitonic magnet in external field: complex order parameter and spin currents,"We investigate spin-triplet exciton condensation in the two-orbital Hubbard
model close to half filling by means of dynamical mean-field theory. Employing
an impurity solver that handles complex off-diagonal hybridization functions,
we study the behavior of excitonic condensate in stoichiometric and doped
systems subject to external magnetic field. We find a general tendency of the
triplet order parameter to lay perpendicular with the applied field and
identify exceptions from this rule. For solutions exhibiting k-odd spin
textures, we discuss the Bloch theorem which, in the absence of spin-orbit
coupling, forbids the appearance of spontaneous net spin current. We
demonstrate that the Bloch theorem is not obeyed by the dynamical mean-field
theory.",1802.02387v1
2018-02-12,Dynamics of a magnetic skyrmionium driven by spin waves,"The magnetic skyrmionium is a skyrmion-like structure but carries a zero net
skyrmion number, which can be used as a building block for non-volatile
information processing devices. Here, we study the dynamics of a magnetic
skyrmionium driven by propagating spin waves. It is found that the skyrmionium
can be effectively driven into motion by spin waves showing tiny skyrmion Hall
effect, of which the mobility is much better than that of the skyrmion at the
same condition. We also show that the skyrmionium mobility depends on the
nanotrack width and damping coefficient, and can be controlled by an external
out-of-plane magnetic field. Besides, we demonstrate the skyrmionium motion
driven by spin waves is inertial. Our results indicate that the skyrmionium is
a promising building block for building spin-wave spintronic devices.",1802.03868v2
2018-04-02,Importance of orbital fluctuations for the magnetic dynamics in heavy-fermion compound SmB$_6$,"The emergent dynamical processes associated with magnetic excitations in
heavy-fermion SmB$_6$ are investigated. By imposing multiorbital interactions
on a first-principles model, we find the interplay between spin and orbital
fluctuations in the $f$ manifold is highly sensitive to local correlations. The
magnetic phase diagram constructed at zero temperature reveals quantum critical
features with the existence of several competing phases. Within the random
phase approximation, we perform a comprehensive study of the spin-spin
correlation function, and our results agree with neutron scattering
experiments. Spectral weight analysis shows the low energy spin excitations are
selectively accompanied by orbital fluctuations, indicating a non-trivial
entanglement between the spin and orbital degree of freedom driven by
relativistic couplings.",1804.00674v2
2018-11-05,Quantum spin liquid at finite temperature: proximate dynamics and persistent typicality,"Quantum spin liquids are long-range entangled states of matter with emergent
gauge fields and fractionalized excitations. While candidate materials, such as
the Kitaev honeycomb ruthenate $\alpha$-RuCl$_3$, show magnetic order at low
temperatures $T$, here we demonstrate numerically a dynamical crossover from
magnon-like behavior at low $T$ and frequencies $\omega$ to long-lived
fractionalized fermionic quasiparticles at higher $T$ and $\omega$. This
crossover is akin to the presence of spinon continua in quasi-1D spin chains.
It is further shown to go hand in hand with persistent typicality down to very
low $T$. This aspect, which has also been observed in the spin-1/2 kagome
Heisenberg antiferromagnet, is a signature of proximate spin liquidity and
emergent gauge degrees of freedom more generally, and can be the basis for the
numerical study of many finite-$T$ properties of putative spin liquids.",1811.01671v2
2018-11-05,Vison-Majorana complex zero-energy resonance in Kitaev's spin liquid,"We study the effect of site dilution in Kitaev's model. We derive an
analytical solution of the dynamical spin correlation functions for arbitrary
configurations of $Z_2$ fluxes. By incorporating this solution into classical
Monte Carlo scheme, we address how a site vacancy affects the experimental
observables, such as the static spin susceptibility and the spin lattice
relaxation rate, $1/T_1$. As a result, we found an enhancement of dynamical
magnetic response in the vicinity of vacancy, which leads to Friedel-like
oscillation in local $1/T_1$, in contrast to limited influences on the static
susceptibility. Furthermore, we found a sharp zero-energy peak in the magnetic
excitation spectrum, which is attributed to the Vison & Majorana zero mode
trapped near the site vacancy. This zero mode can be interpreted as
fractionalized spin hole into an Ising triplet with differentiated magnetic
axes, which leads to the characteristic temperature and field-orientational
dependence of $1/T_1$.",1811.02092v1
2018-11-14,Dynamics of a tensor polarization of particles and nuclei and its influence on the spin motion in external fields,"The tensor polarization of particles and nuclei is constant in a coordinate
system rotating with the same angular velocity as the spin. In the laboratory
frame, it rotates with this angular velocity. The general equation defining the
evolution of the tensor polarization is derived. An explicit form of the
dynamics of this polarization is given in the case when the angular velocity of
the spin precession is constant and vertical. It is shown that the spin tensor
interactions result in mutual transformations of the vector and tensor
polarizations. These interactions can influence the spin motion.",1811.06377v1
2018-11-16,"Spin-models, dynamics and criticality with atoms in tilted optical superlattices","We show that atoms in tilted optical superlattices provide a platform for
exploring coupled spin chains of forms that are not present in other systems.
In particular, using a period-2 superlattice in 1D, we show that coupled Ising
spin chains with XZ and ZZ spin coupling terms can be engineered. We use
optimized tensor network techniques to explore the criticality and
non-equilibrium dynamics in these models, finding a tricritical Ising point in
regimes that are accessible in current experiments. These setups are ideal for
studying low-entropy physics, as initial entropy is ""frozen-out"" in realizing
the spin models, and provide an example of the complex critical behaviour that
can arise from interaction-projected models.",1811.06995v2
2020-07-24,Quantum point particle approximation of spinning black holes and compact stars,"Gravitational wave observatories targeted for compact binary coalescence,
such as LIGO and VIRGO, require various theoretical inputs for their efficient
detection. One of such inputs are analytical description of binary dynamics at
sufficiently separated orbital scales, commonly known as post-Newtonian
dynamics. One approach for determining such two-body effective Hamiltonians is
to use quantum scattering amplitudes.
  This dissertation aims at an improved understanding of classical physics of
spinning bodies in quantum scattering amplitudes, for application to the
problem of effective two-body Hamiltonians. The main focus will be on
spin-induced higher-order multipole moments. In this dissertation results for
the first post-Minkowskian order (linear in Newton's constant $G$ and to all
orders in relative momentum $p^2$) Hamiltonian that is valid for arbitrary
compact spinning bodies to all orders in spin is presented. Next, obstruction
and prospects for the formulation's extension to second post-Minkowskian order
is discussed, based on an equivalent loop order quantum field theory
computations.
  This dissertation is based on the works [1-4].",2007.12398v1
2020-07-27,Non-local SPDE limits of spatially-correlated-noise driven spin systems derived to sample a canonical distribution,"We study the macroscopic behavior of a stochastic spin ensemble driven by a
discrete Markov jump process motivated by the Metropolis-Hastings algorithm
where the proposal is made with spatially correlated (colored) noise, and hence
fails to be symmetric. However, we demonstrate a scenario where the failure of
proposal symmetry is a higher order effect. Hence, from these microscopic
dynamics we derive as a limit as the proposal size goes to zero and the number
of spins to infinity, a non-local stochastic version of the harmonic map heat
flow (or overdamped Landau-Lipshitz equation). The equation is both
mathematically well-posed and samples the canonical/Gibbs distribution related
to the kinetic energy. The failure of proposal symmetry due to interaction
between the confining geometry of the spin system and the colored noise is in
contrast to the uncorrelated, white-noise, driven system. Specifically, the
choice of projection of the noise to conserve the magnitude of the spins is
crucial to maintaining the proper equilibrium distribution. Numerical
simulations are included to verify convergence properties and demonstrate the
dynamics.",2007.13612v1
2020-07-29,Orbital and Spin Dynamics of Single Neutrally-Charged Nitrogen-Vacancy Centers in Diamond,"The neutral charge state plays an important role in quantum information and
sensing applications based on nitrogen-vacancy centers. However, the orbital
and spin dynamics remain unexplored. Here, we use resonant excitation of single
centers to directly reveal the fine structure, enabling selective addressing of
spin-orbit states. Through pump-probe experiments, we find the orbital
relaxation time (430ns at 4.7K) and measure its temperature-dependence up to
11.8K. Finally we reveal the spin relaxation time (1.5s), and realize
projective high-fidelity single-shot readout of the spin state ($\geq98\%$).",2007.14673v1
2010-05-31,Next to leading order spin-orbit effects in the motion of inspiralling compact binaries,"Using effective field theory (EFT) techniques we calculate the
next-to-leading order (NLO) spin-orbit contributions to the gravitational
potential of inspiralling compact binaries. We use the covariant spin
supplementarity condition (SSC), and explicitly prove the equivalence with
previous results by Faye et al. in arXiv:gr-qc/0605139. We also show that the
direct application of the Newton-Wigner SSC at the level of the action leads to
the correct dynamics using a canonical (Dirac) algebra. This paper then
completes the calculation of the necessary spin dynamics within the EFT
formalism that will be used in a separate paper to compute the spin
contributions to the energy flux and phase evolution to NLO.",1005.5730v2
2013-08-08,Dynamics of a two-level system under the simultaneous influence of a spin bath and a boson bath,"We study dynamics of a two-level system coupled simultaneously to a pair of
dissimilar reservoirs, namely, a spin bath and a boson bath, which are
connected via finite interbath coupling. It is found that the steady-state
energy transfer in the two-level system increases with its coupling to the spin
bath while optimal transfer occurs at intermediate coupling in the transient
process. If the two-level system is strongly coupled to the spin bath, the
population transfer is unidirectional barring minor population oscillations of
minute amplitudes. If the spin bath is viewed as an atomic ensemble, robust
generation of macroscopic superposition states exists against parameter
variations of the two-level system and the boson bath.",1308.1764v1
2014-03-24,Spin-orbit and impurity scattering in an integrable electron model: Exact results for dynamic correlations,"We introduce an integrable model of spin-polarized interacting electrons
subject to a spin-conserving spin-orbit interaction. Using Bethe Ansatz and
conformal field theory we calculate the exact large-time single-electron and
density correlations and find that while the spin-orbit interaction enhances
the single-electron Green's function, the density correlations get suppressed.
Adding a localized impurity and coupling it to the electrons so that
integrability is preserved, the dynamic correlations are found to change
significantly after a quantum quench with the impurity interaction switched on
suddenly. When the electrons are confined to a periodic structure, the
correlations are indifferent to the location of the impurity and only carry an
imprint of its intrinsic properties. We conjecture that this unusual feature
originates from the integrability of the model.",1403.6091v2
2014-03-27,Driving spin and charge in quantum wells by surface acoustic waves,"Recent experiments have shown the potential of surface acoustic waves as a
mean for transporting charge and spin in quantum wells. In particular, they
have proven highly effective for the coherent transport of spin-polarized wave
packets, suggesting their potential in spintronics applications. Motivated by
these experimental observations, we have theoretically studied the spin and
charge dynamics in a quantum well under surface acoustic waves. We show that
the dynamics acquires a simple and transparent form in a reference frame
co-moving with the surface acoustic wave. Our results, e.g., the calculated
spin relaxation and precession lengths, are in excellent agreement with recent
experimental observations.",1403.6960v2
2017-01-21,Controlling electron spin dynamics in bichromatic Kapitza-Dirac scattering by the laser field polarization,"Spin-dependent Kapitza-Dirac scattering of electron beams from
counterpropagating bichromatic laser waves in various polarization geometries
is studied. The corresponding scattering probabilities are obtained by
analytical and numerical solutions of the time-dependent Dirac equation,
assuming a field frequency ratio of 2. When the fundamental field mode is
circular-polarized, we show that spin dynamics are generally suppressed at low
intensities, but can become distinct at high intensities. Conversely, when a
linearly or elliptically polarized fundamental mode is combined with a second
harmonic of circular polarization, strong spin effects arise already at low
field intensities. In particular, a polarization configuration is identified
which acts as a spin filter for free electrons.",1701.05951v2
2008-07-16,Dynamics of Photo-excited Spins in InSb Based Quantum Wells,"We report time resolved measurements of spin relaxation in doped and undoped
InSb quantum wells using degenerate and two-color magneto-optical Kerr effect
techniques. We observed that the photo-excited spin dynamics are strongly
influenced by laser excitation fluence and the doping profile of the samples.
In the low fluence regime, an oscillatory pattern was observed at low
temperatures ($\leq$ 77 K) in the samples with an asymmetric doping profile
which might be attributed to the quasi-collision-free spin relaxation regime.
Our measurements also suggest the influence of the barrier materials
(Al$_{x}$In$_{1-x}$Sb) on the spin relaxation in these material systems.",0807.2660v1
2011-11-11,Near-Earth Binaries and Triples: Origin and Evolution of Spin-Orbital Properties,"In the near-Earth asteroid population, binary and triple systems have been
discovered with mutual orbits that have significant eccentricities as well as
large semi-major axes. All known systems with eccentric orbits and all
widely-separated primary-satellite pairs have rapidly rotating satellites. Here
we study processes that can elucidate the origin of these spin-orbital
properties. Binary formation models based on rotational fissioning can
reproduce asynchronous satellites on orbits with high eccentricities and a wide
range of separations, but do not match observed properties. We explore whether
any evolutionary mechanisms can link the spin and orbital parameters expected
from post-fission dynamics to those observed today. We investigate four
processes: tidal torques, radiative perturbations (BYORP), close planetary
encounters, and Kozai oscillations. We find that a combination of post-fission
dynamics and tidal evolution can explain nearly all the spin-orbit properties
in a sample of nine well-characterized near-Earth binaries and triples. The
other mechanisms may act but are not required to explain the observed data.
Lastly, we describe evolutionary pathways between observed spin-orbital states
including synchronous and circular, asynchronous and circular, and asynchronous
and eccentric configurations.",1111.2794v1
2012-01-09,Manipulating dipolar and spin-exchange interactions in spin-1 Bose-Einstein condensates,"It remains a challenge to independently manipulate the magnetic dipolar and
the spin-exchange interactions, which are entangled in many spin systems,
particularly in spin-1 Bose-Einstein condensates. For this purpose, we put
forward a sequence of rf pulses and the periodic dynamical decoupling sequence
of optical Feshbach resonance pulses to control the dipolar and the
spin-exchange interactions, respectively. Our analytic results and the
numerical simulations demonstrate that either of the two interactions can be
suppressed to make the other dominate the spin dynamics; furthermore, both of
the interactions can be simultaneously suppressed to realize
spinor-condensate-based magnetometers with a higher sensitivity. This
manipulation method may find its wide applications in magnetic resonance and
spintronics.",1201.1779v3
2013-08-31,Ballistic quantum state transfer in spin chains: general theory for quasi-free models and arbitrary initial states,"Ballistic quantum-information transfer through spin chains is based on the
idea of making the spin dynamics ruled by collective excitations with linear
dispersion relation. Unlike perfect state transfer schemes, a ballistic
transmission requires only a minimal engineering of the interactions; in fact,
for most practical purposes, the optimization of the couplings to the ends of
the chain is sufficient to obtain an almost perfect transmission. In this work
we review different ballistic quantum-state transfer protocols based on the
dynamics of quasi-free spin chains, and further generalize them both at zero
and finite temperature. In particular, besides presenting novel analytical
results for XX, XY, and Ising spin models, it is shown how, via a complete
control on the first and last two qubits of the chain, destructive thermal
effects can be cancelled, leading to a high-quality state transmission
irrespective of the temperature.",1309.0069v2
2013-09-03,Non-abelian Gauge Fields from Defects in Spin-Networks,"\emph{Effective} gauge fields arise in the description of the dynamics of
defects in lattices of graphene in condensed matter. The interactions between
neighboring nodes of a lattice/spin-network are described by the Hubbard model
whose effective field theory at long distances is given by the Dirac equation
for an \emph{emergent} gauge field. The spin-networks in question can be used
to describe the geometry experienced by a non-inertial observer in flat
spacetime moving at a constant acceleration in a given direction. We expect
such spin-networks to describe the structure of quantum horizons of black holes
in loop quantum gravity. We argue that the abelian and non-abelian gauge fields
of the Standard Model can be identified with the emergent degrees of freedom
required to describe the dynamics of defects in symmetry reduced spin-networks.",1309.0652v1
2016-08-17,Quantum-critical spin dynamics in a Tomonaga-Luttinger liquid studied with muon-spin relaxation,"We demonstrate that quantum-critical spin dynamics can be probed in high
magnetic fields using muon-spin relaxation ($\mu^{+}$SR). Our model system is
the strong-leg spin ladder bis(2,3-dimethylpyridinium) tetrabromocuprate
(DIMPY). In the gapless Tomonaga-Luttinger liquid phase we observe
finite-temperature scaling of the $\mu^{+}$SR $1/T_1$ relaxation rate which
allows us to determine the Luttinger parameter $K$. We discuss the benefits and
limitations of local probes compared with inelastic neutron scattering.",1608.05059v3
2017-06-02,Coherent Terahertz Spin-Wave Emission Associated with Ferrimagnetic Domain Wall Dynamics,"We theoretically study the dynamics of ferrimagnetic domain walls in the
presence of Dzyaloshinskii-Moriya interaction. We find that an application of a
DC magnetic field can induce terahertz spin-wave emission by driving
ferrimagnetic domain walls, which is not possible for ferromagnetic or
antiferromagnetic domain walls. Dzyaloshinskii-Moriya interaction is shown to
facilitate the teraherz spin-wave emission in wide ranges of net angular
momentum by increasing the Walkerbreakdown field. Moreover, we show that
spin-orbit torque combined with Dzyaloshinskii-Moriya interaction also drives a
fast ferrimagnetic domain wall motion with emitting terahertz spin-waves in
wide ranges of net angular momentum.",1706.00549v1
2017-06-09,Controlling Spin-flips of Molecules in an Electromagnetic Trap,"Doubly dipolar molecules exhibit complex internal spin-dynamics when electric
and magnetic fields are both applied. Near magnetic trap minima, these
spin-dynamics lead to enhancements in Majorana spin-flip transitions by many
orders of magnitude relative to atoms, and are thus an important obstacle for
progress in molecule trapping and cooling. We conclusively demonstrate and
address this with OH molecules in a trap geometry where spin-flip losses can be
tuned from over $200 \text{ s}^{-1} $ to below our $2\text{ s}^{-1}$ vacuum
limited loss rate with only a simple external bias coil and with minimal impact
on trap depth and gradient.",1706.02806v2
2017-06-10,Spin wave nonreciprocity and magnonic band structure in thin permalloy film induced by dynamical coupling with an array of Ni stripes,"An efficient way for the control of spin wave propagation in a magnetic
medium is the use of periodic patterns known as magnonic crystals (MCs).
However, the fabrication of MCs especially bi-components, with periodicity on
nanoscale, is a challenging task due to the requirement for sharp interfaces.
An alternative method to circumvent this problem is to use homogeneous
ferromagnetic film with modified periodically surrounding. The structure is
also suitable for exploiting nonreciprocal properties of the surface spin
waves. In this work, we demonstrate that the magnonic band structure forms in
thin permalloy film due to dynamical magnetostatic coupling with Ni stripes
near its surface. We show, that the band gap width can be systematically tuned
by the changing interlayer thickness between film and stripes. We show also the
effect of nonreciprocity, which is seen at the band gap edge shifted from the
Brillouin zone boundary and also in nonreciprocal interaction of propagating
spin waves in Py film with the standing spin waves in Ni stripes. Our findings
open possibility for further investigation and exploitation of the
nonreciprocity and band structure in magnonic devices.",1706.03202v1
2017-06-13,Stochastic dissipative quantum spin chains (I) : Quantum fluctuating discrete hydrodynamics,"Motivated by the search for a quantum analogue of the macroscopic fluctuation
theory, we study quantum spin chains dissipatively coupled to quantum noise.
The dynamical processes are encoded in quantum stochastic differential
equations. They induce dissipative friction on the spin chain currents. We show
that, as the friction becomes stronger, the noise induced dissipative effects
localize the spin chain states on a slow mode manifold, and we determine the
effective stochastic quantum dynamics of these slow modes. We illustrate this
approach by studying the quantum stochastic Heisenberg spin chain.",1706.03984v4
2017-07-11,Putative spin liquid in the triangle-based iridate Ba$_3$IrTi$_2$O$_9$,"We report on thermodynamic, magnetization, and muon spin relaxation
measurements of the strong spin-orbit coupled iridate Ba$_3$IrTi$_2$O$_9$,
which constitutes a new frustration motif made up a mixture of edge- and
corner-sharing triangles. In spite of strong antiferromagnetic exchange
interaction of the order of 100~K, we find no hint for long-range magnetic
order down to 23 mK. The magnetic specific heat data unveil the $T$-linear and
-squared dependences at low temperatures below 1~K. At the respective
temperatures, the zero-field muon spin relaxation features a persistent spin
dynamics, indicative of unconventional low-energy excitations. A comparison to
the $4d$ isostructural compound Ba$_3$RuTi$_2$O$_9$ suggests that a concerted
interplay of compass-like magnetic interactions and frustrated geometry
promotes a dynamically fluctuating state in a triangle-based iridate.",1707.03140v1
2017-07-25,Cavity QED engineering of spin dynamics and squeezing in a spinor gas,"We propose a method for engineering spin dynamics in ensembles of
integer-spin atoms confined within a high-finesse optical cavity. Our proposal
uses cavity-assisted Raman transitions to engineer a Dicke model for
integer-spin atoms, which, in a dispersive limit, reduces to effective
atom-atom interactions within the ensemble. This scheme offers a promising and
flexible new avenue for the exploration of a wide range of spinor many-body
physics. As an example of this, we present results showing that this method can
be used to generate spin-nematic squeezing in an ensemble of spin-1 atoms. With
realistic parameters the scheme should enable substantial squeezing on time
scales much shorter than current experiments with spin-1 Bose-Einstein
condensates.",1707.07793v2
2017-10-12,Magnetic droplet solitons generated by pure spin currents,"Magnetic droplets are dynamical solitons that can be generated by locally
suppressing the dynamical damping in magnetic films with perpendicular
anisotropy. To date, droplets have been observed only in nanocontact
spin-torque oscillators operated by spin-polarized electrical currents. Here,
we experimentally demonstrate that magnetic droplets can be nucleated and
sustained by pure spin currents in nanoconstriction-based spin Hall devices.
Micromagnetic simulations support our interpretation of the data, and indicate
that in addition to the stationary droplets, propagating solitons can be also
generated in the studied system, which can be utilized for the information
transmission in spintronic applications.",1710.04430v1
2017-12-13,"Post-Newtonian Dynamics in Dense Star Clusters: Highly-Eccentric, Highly-Spinning, and Repeated Binary Black Hole Mergers","We present models of realistic globular clusters with post-Newtonian dynamics
for black holes. By modeling the relativistic accelerations and
gravitational-wave emission in isolated binaries and during three- and
four-body encounters, we find that nearly half of all binary black hole mergers
occur inside the cluster, with about 10% of those mergers entering the
LIGO/Virgo band with eccentricities greater than 0.1. In-cluster mergers lead
to the birth of a second generation of black holes with larger masses and high
spins, which, depending on the black hole natal spins, can sometimes be
retained in the cluster and merge again. As a result, globular clusters can
produce merging binaries with detectable spins regardless of the birth spins of
black holes formed from massive stars. These second-generation black holes
would also populate any upper mass gap created by pair-instability supernovae.",1712.04937v3
2018-01-19,Nonabelian magnonics in antiferromagnets,"We present a semiclassical formalism for antiferromagnetic (AFM) magnonics
which promotes the central ingredient of spin wave chirality, encoded in a
quantity called magnonic isospin, to a first-class citizen of the theory. We
use this formalism to unify results of interest from the field under a single
chirality-centric formulation. Our main result is that the isospin is governed
by unitary time evolution, through a Hamiltonian projected down from the full
spin wave dynamics. Because isospin is SU(2)-valued, its dynamics on the Bloch
sphere are precisely rotations - which, in general, do not commute.
Consequently, the induced group of operations on AFM spin waves is nonabelian.
This is a paradigmatic departure from ferromagnetic magnonics, which operates
purely within the abelian group generated by spin wave phase and amplitude. Our
investigation of this nonabelian magnonics in AFM insulators focuses on
studying several simple gate operations, and offering in broad strokes a
program of study for interesting new logic families in antiferromagnetic spin
wave systems",1801.06535v3
2018-09-29,Dynamical decoupling protocols with nuclear spin state selectivity,"The ability to initialise nuclear spins, which are typically in a mixed state
even at low temperature, is a key requirement of many protocols used in quantum
computing and simulations as well as in magnetic resonance spectroscopy and
imaging. Yet, it remains a challenging task that typically involves complex and
inefficient protocols, limiting the fidelity of ensuing operations or the
measurement sensitivity. We introduce here a class of dynamical nuclear spin
state selective (DNSS) protocols which, when applied to a polarised electron
spin such as the nitrogen-vacancy (NV) centre in diamond, permit the addressing
of selected nuclear states of the mixture. It works by splitting the underlying
eigenstates into two distinct symmetries dependent on the nuclear spin state,
and independent of the electron-nuclear coupling strength. As a particular
example, we show that DNSS is achievable by simply introducing a detuning in
the common Carr-Purcell-Meiboom-Gill (CPMG) protocol, where the state selection
is then controlled by the inter-pulse spacing. This approach offers advantages
in ultra-high fidelity initialisation of nuclear registers, ensemble
polarisation and single-gate manipulation of nuclei.",1810.00174v1
2019-06-25,Melting of Spin Ice state through structural disorder in Dy2Zr2O7,"Neutron scattering, a.c. magnetic susceptibility and specific heat studies
have been carried out on polycrystalline Dy2Zr2O7. Unlike the pyrochlore spin
ice Dy2Ti2O7, Dy2Zr2O7 crystallizes into the fluorite structure and the
magnetic Dy3+ moments randomly reside on the corner-sharing tetrahedral
sublattice with non-magnetic Zr ions. Antiferromagnetic spin correlations
develop below 10 K but remain dynamic down to 40 mK. These correlations extend
over the length of two tetrahedra edges and grow to 6 nearest neighbors with
the application of a 20 kOe magnetic field. No Pauling's residual entropy was
observed and by 8 K the full entropy expected for a two level system is
released. We propose that the disorder melts the spin ice state seen in the
chemically ordered Dy2Ti2O7 compound, but the spins remain dynamic in a
disordered, liquid-like state and do not freeze into a glass-like state that
one might intuitively expect.",1906.10738v1
2019-09-12,Perspectives on spin hydrodynamics in ferromagnetic materials,"The field of spin hydrodynamics aims to describe magnetization dynamics from
a fluid perspective. For ferromagnetic materials, there is an exact mapping
between the Landau-Lifshitz equation and a set of dispersive hydrodynamic
equations. This analogy provides ample opportunities to explore novel
magnetization dynamics and magnetization states that can lead to applications
relying entirely upon magnetic materials, for example, long-distance transport
of information. This article provides an overview of the theoretical
foundations of spin hydrodynamics and their physical interpretation in the
context of spin transport. We discuss other proposed applications for spin
hydrodynamics as well as our view on challenges and future research directions.",1909.05756v1
2020-02-04,Superradiant-like dynamics by electron shuttling on a nuclear-spin island,"We investigate superradiant-like dynamics of the nuclear-spin bath in a
single-electron quantum dot, by considering electrons cyclically shuttling
on/off an isotopically enriched `nuclear-spin island'. Assuming a uniform
hyperfine interaction, we discuss in detail the nuclear spin evolution under
shuttling and its relation to superradiance. We derive the minimum shuttling
time which allows to escape the adiabatic spin evolution. Furthermore, we
discuss slow/fast shuttling under the inhomogeneous field of a nearby
micromagnet. Finally, by comparing our scheme to a model with stationary
quantum dot, we stress the important role played by non-adiabatic shuttling in
lifting the Coulomb blockade and thus establishing the superradiant-like
behavior.",2002.01219v1
2020-02-26,Magnon dispersion and dynamic spin response in three-dimensional spin models for $α$-RuCl$_3$,"In the search for experimental realizations of bond-anisotropic Kitaev
interactions and resulting spin-liquid phases, the layered magnet
$\alpha$-RuCl$_3$ is a prime candidate. Its modelling typically involves
Heisenberg, Kitaev, and symmetric off-diagonal $\Gamma$ interactions on the
two-dimensional honeycomb lattice. However, recent neutron-scattering
experiments point towards a sizeable magnetic interlayer coupling. Here we
study three-dimensional exchange models for $\alpha$-RuCl$_3$, for both
possible $R\bar{3}$ and $C2/m$ crystal structures. We discuss the symmetry
constraints on the interlayer couplings, construct minimal models, and use them
to compute the magnetic mode dispersion and the dynamical spin structure
factor, in both the zero-field zigzag phase and the paramagnetic high-field
phase. Our predictions for the interlayer mode dispersion shall guide future
experiments; they also call for a reevaluation of the quantitative model
parameters relevant for $\alpha$-RuCl$_3$.",2002.11727v2
2020-04-01,"The mass gap, the spin gap, and the origin of merging binary black holes","Two of the dominant channels to produce the black-hole binary mergers
observed by LIGO and Virgo are believed to be the isolated evolution of stellar
binaries in the field and dynamical formation in star clusters. Their relative
efficiency can be characterized by a ""mixing fraction."" Pair instabilities
prevent stellar collapse from generating black holes more massive than about
$45 M_\odot$. This ""mass gap"" only applies to the field formation scenario, and
it can be filled by repeated mergers in clusters. A similar reasoning applies
to the binary's effective spin. If black holes are born slowly rotating, the
high-spin portion of the parameter space (the ""spin gap"") can only be populated
by black hole binaries that were assembled dynamically. Using a semianalytical
cluster model, we show that future gravitational-wave events in either the mass
gap, the spin gap, or both can be leveraged to infer the mixing fraction
between the field and cluster formation channels.",2004.00650v2
2020-04-22,Polarized proton spin filter for epithermal neutron based on dynamic nuclear polarization using photo-excited triplet electron spins,"For the polarization of neutrons with an energy level of
\textcolor{black}{$>0.1$ eV}, we developed a novel polarized proton spin filter
based on dynamic nuclear polarization using photo-excited triplet electron
spins. The spin filter consists of a single crystal of naphthalene doped with
deuterated pentacene and has a size of $\phi15\times4$ ${\rm mm}^3$, allowing
it to cover a wide beam diameter. It was operated in 0.35 T and at 90 K. We
succeeded in polarizing neutrons in the energy range $0.1-10$ eV using a RIKEN
accelerator-driven compact neutron source. The averaged values of the proton
and neutron polarization were $0.250\pm0.050$ and $0.076\pm0.015$,
respectively.",2004.10370v2
2020-04-28,Enhancement of acoustic spin pumping by acoustic distributed Bragg reflector cavity,"Surface acoustic waves (SAWs) in the GHz frequency range can inject spin
currents dynamically into adjacent nonmagnetic layers via spin pumping effect
associated with ferromagnetic resonance. Here, we demonstrate an enhancement of
acoustic ferromagnetic resonance and spin current generation by a pair of SAW
reflector gratings, which form an acoustic analogue of the distributed Bragg
reflector cavity. In the experiment, we confirmed 2.04 $\pm$ 0.02 times larger
SAW power absorption in a device with cavity than in case of no acoustic
cavity. We confirmed up to 2.96 $\pm$ 0.02 times larger spin current generation
by measuring electric voltages generated by the inverse Edelstein effect (IEE)
at the interface between Cu and Bi$_2$O$_3$. The results suggest that acoustic
cavities would be useful to enhance the conversion efficiency in SAW driven
coupled magnon-phonon dynamics.",2004.13885v3
2020-04-29,Dynamics of Colombo's Top: Generating Exoplanet Obliquities from Planet-Disk Interactions,"Large planetary spin-orbit misalignments (obliquities) may strongly influence
atmospheric circulation and tidal heating in the planet. A promising avenue to
generate obliquities is via spin-orbit resonances, where the spin and orbital
precession frequencies of the planet cross each other as the system evolves in
time. One such mechanism involves a dissipating (mass-losing) protoplanetary
disk that drives orbital precession of an interior planet. We study this
scenario analytically in this paper, and obtain the mapping between the general
initial spin orientation and the final obliquity. We show that (i) under
adiabatic evolution (i.e. the disk dissipates at a sufficiently slow rate), the
final planetary obliquity as a function of the initial spin orientation
bifurcates into distinct tracks governed by interactions with the resonance;
(ii) under nonadiabatic evolution, a broad range of obliquities can be excited.
We obtain analytical expressions for the final obliquities for various regimes
of parameter space. The dynamical system studied in this paper is an example of
""Colombo's top"", and our analysis and results can be adapted to other
applications.",2004.14380v3
2020-12-10,Structure Preserving Reduced Attitude Control of Gyroscopes,"We design a reduced attitude controller for reorienting the spin axis of a
gyroscope in a geometric control framework. The proposed controller preserves
the inherent gyroscopic stability associated with a spinning axis-symmetric
rigid body. The equations of motion are derived in two frames: a non-spinning
frame to show the gyroscopic stability, and a body-fixed spinning frame for
deriving the controller. The proposed controller is designed such that it
retains the gyroscopic stability structure in the closed loop and renders the
desired equilibrium almost-globally asymptotically stable. Due to the
time-critical nature of the control input, in particular its sensitivity with
respect to delays/neglected dynamics, the controller is extended to incorporate
the effect of actuator dynamics for practical implementation. Thereafter, a
comparison in performance is shown between the proposed controller and a
conventional reduced attitude geometric controller with numerical simulation.
The controller is validated experimentally on a spinning tricopter.",2012.05468v1
2020-12-22,Geometric transitions with Spin(7) holonomy via a dynamical system,"We clarify the global geometry of two 1-parameter families of cohomogeneity
one Spin(7) holonomy metrics with generic orbit the Aloff--Wallach space
$N(1,-1) \cong \mathrm{SU}(3)/\mathrm{U}(1)$ and singular orbits $S^5$ and
$\mathbb{C}P^2$, which at short distance were shown to exist by Reidegeld. The
two families fit into the geography of previously known families of
cohomogeneity one metrics with exceptional holonomy and provide a Spin(7)
analogue of the well-known conifold transition in the setting of Calabi--Yau
3-folds. Furthermore, we discover that there is another transition to families
of Spin(7) holonomy metrics which have a similar asymptotic behaviour on one
end, but are singular on the other end. We obtain our results by relating the
Spin(7)-equations to a simple dynamical system on a 3-dimensional cube.",2012.11758v1
2021-01-08,Hawking radiation by spherically-symmetric static black holes for all spins: I -- Teukolsky equations and potentials,"In the context of the dynamics and stability of black holes in modified
theories of gravity, we derive the Teukolsky equations for massless fields of
all spins in general spherically-symmetric and static metrics. We then compute
the short-ranged potentials associated with the radial dynamics of spin 1 and
spin 1/2 fields, thereby completing the existing literature on spin 0 and 2.
These potentials are crucial for the computation of Hawking radiation and
quasi-normal modes emitted by black holes. In addition to the Schwarzschild
metric, we apply these results and give the explicit formulas for the radial
potentials in the case of charged (Reissner--Nordstr\""om) black holes,
higher-dimensional black holes, and polymerized black holes arising from loop
quantum gravity. These results are in particular relevant and applicable to a
large class of regular black hole metrics. The phenomenological applications of
these formulas will be the subject of a companion paper.",2101.02951v2
2012-05-29,Thermally-Assisted Spin-Transfer Torque Magnetization Reversal in Uniaxial Nanomagnets,"We simulate the stochastic Landau-Lifshitz-Gilbert (LLG) dynamics of a
uniaxial nanomagnet out to sub-millisecond timescales using a graphical
processing unit based micromagnetic code and determine the effect of
geometrical tilts between the spin-current and uniaxial anisotropy axes on the
thermally assisted reversal dynamics. The asymptotic behavior of the switching
time ($I\rightarrow 0$, $<\tau>\propto\exp(-\xi(1-I)^2)$) is approached
gradually, indicating a broad crossover regime between ballistic and thermally
assisted spin transfer reversal. Interestingly, the mean switching time is
shown to be nearly independent of the angle between the spin current and
magnet's uniaxial axes. These results have important implications for modeling
the energetics of thermally assisted magnetization reversal of spin transfer
magnetic random access memory bit cells.",1205.6509v1
2017-04-30,Angular Dependent Magnetization Dynamics of Kagome Artificial Spin Ice Incorporating Topological Defects,"We report angular-dependent spin-wave spectroscopy on kagome artificial spin
ice made of large arrays of interconnected Ni80Fe20 nanobars. Spectra taken in
saturated and disordered states exhibit a series of resonances with
characteristic in-plane angular dependencies. Micromagnetic simulations allow
us to interpret characteristic resonances of a two-step magnetization reversal
of the nanomagnets. The dynamic properties are consistent with topological
defects that are provoked via a magnetic field applied at specific angles.
Simulations that we performed on previously investigated kagome artificial spin
ice consisting of isolated nanobars show characteristic discrepancies in the
spin wave modes which we explain by the absence of vertices.",1705.00270v1
2017-05-04,"Physics of the Kitaev model: fractionalization, dynamical correlations, and material connections","Quantum spin liquids have fascinated condensed matter physicists for decades
because of their unusual properties such as spin fractionalization and
long-range entanglement. Unlike conventional symmetry breaking the topological
order underlying quantum spin liquids is hard to detect experimentally. Even
theoretical models are scarce for which the ground state is established to be a
quantum spin liquid. The Kitaev honeycomb model and its generalizations to
other tri-coordinated lattices are chief counterexamples --- they are exactly
solvable, harbor a variety of quantum spin liquid phases, and are also relevant
for certain transition metal compounds including the polymorphs of
(Na,Li)$_2$IrO$_3$ Iridates and RuCl$_3$. In this review, we give an overview
of the rich physics of the Kitaev model, including 2D and 3D fractionalization
as well as dynamical correlations and behavior at finite temperatures. We
discuss the different materials, and argue how the Kitaev model physics can be
relevant even though most materials show magnetic ordering at low temperatures.",1705.01740v1
2017-05-10,Spin-tensor--momentum-coupled Bose-Einstein condensates,"The recent experimental realization of spin-orbit coupling for ultracold
atomic gases provides a powerful platform for exploring many interesting
quantum phenomena. In these studies, spin represents spin vector (spin-1/2 or
spin-1) and orbit represents linear momentum. Here we propose a scheme to
realize a new type of spin-tensor--momentum coupling (STMC) in spin-1 ultracold
atomic gases. We study the ground state properties of interacting Bose-Einstein
condensates (BECs) with STMC and find interesting new types of stripe
superfluid phases and multicritical points for phase transitions. Furthermore,
STMC makes it possible to study quantum states with dynamical stripe orders
that display density modulation with a long tunable period and high visibility,
paving the way for direct experimental observation of a new dynamical
supersolid-like state.. Our scheme for generating STMC can be generalized to
other systems and may open the door for exploring novel quantum physics and
device applications.",1705.03920v3
2017-05-12,Spin dynamics of close-in planets exhibiting large TTVs,"We study the spin evolution of close-in planets in compact multi-planetary
systems. The rotation period of these planets is often assumed to be
synchronous with the orbital period due to tidal dissipation. Here we show that
planet-planet perturbations can drive the spin of these planets into
non-synchronous or even chaotic states. In particular, we show that the transit
timing variation (TTV) is a very good probe to study the spin dynamics, since
both are dominated by the perturbations of the mean longitude of the planet. We
apply our model to KOI-227b and Kepler-88b, which are both observed undergoing
strong TTVs. We also perform numerical simulations of the spin evolution of
these two planets. We show that for KOI-227b non-synchronous rotation is
possible, while for Kepler-88b the rotation can be chaotic.",1705.04460v1
2017-05-17,Nonequilibrium dynamics of spin-boson models from phase space methods,"An accurate description of the nonequilibrium dynamics of systems with
coupled spin and bosonic degrees of freedom remains theoretically challenging,
especially for large system sizes and in higher than one dimension. Phase space
methods such as the Truncated Wigner Approximation (TWA) have the advantage of
being easily scalable and applicable to arbitrary dimensions. In this work we
adapt the TWA to generic spin-boson models by making use of recently developed
algorithms for discrete phase spaces [Schachenmayer, PRX 5, 011022 (2015)].
Furthermore we go beyond the standard TWA approximation by applying a scheme
based on the Bogoliubov-Born-Green-Kirkwood-Yvon (BBGKY) hierarchy of equations
[Pucci, PRB 93, 174302 (2016)] to our coupled spin-boson model. This allows in
principle to study how systematically adding higher order corrections improves
the convergence of the method. To test various levels of approximation we study
an exactly solvable spin-boson model which is particularly relevant for
trapped-ion arrays. Using TWA and its BBGKY extension we accurately reproduce
the time evolution of a number of one- and two-point correlation functions in
several dimensions and for arbitrary number of bosonic modes.",1705.06203v1
2017-05-18,Flat spin connections in the Teleparallel equivalent of General Relativity,"This work generalizes the treatment of flat spin connections in the
teleparallel equivalent of general relativity. It is shown that a general flat
spin connection form a subspace in the affine space of spin connections which
is dynamically decoupled from the tetrad and the matter fields. A translation
in the affine subspace introduces a torsion term without changing the tetrad.
Instead, the change in the torsion is related to the introduction of a global
acceleration field term that introduces Lorentz inertial effects in the
reference frame. The dynamics of the gravitationally coupled matter fields
remains however equivalent regardless of the flat spin connection chosen. The
implications of the break of this invariance by a general $f(T)$ and $f(R)$ is
discussed.",1705.06585v3
2017-09-01,Amplified Sensitivity of Nitrogen-Vacancy Spins in Nanodiamonds using All-Optical Charge Readout,"Nanodiamonds containing nitrogen-vacancy (NV) centers offer a versatile
platform for sensing applications spanning from nanomagnetism to in-vivo
monitoring of cellular processes. In many cases, however, weak optical signals
and poor contrast demand long acquisition times that prevent the measurement of
environmental dynamics. Here, we demonstrate the ability to perform fast,
high-contrast optical measurements of charge distributions in ensembles of NV
centers in nanodiamonds and use the technique to improve the spin readout
signal-to-noise ratio through spin-to-charge conversion. A study of 38
nanodiamonds, each hosting 10-15 NV centers with an average diameter of 40 nm,
uncovers complex, multiple-timescale dynamics due to radiative and
non-radiative ionization and recombination processes. Nonetheless, the
nanodiamonds universally exhibit charge-dependent photoluminescence contrasts
and the potential for enhanced spin readout using spin-to-charge conversion. We
use the technique to speed up a $T_1$ relaxometry measurement by a factor of
five.",1709.00465v1
2017-11-06,Dynamic Nuclear Polarization from Topological Insulator Helical Edge States,"Topological insulators are promising for spintronics and related technologies
due to their spin-momentum-locked edge states, which are protected by
time-reversal symmetry. In addition to the unique fundamental physics that
arises in these systems, the potential technological applications of these
protected states has also been driving TI research over the past decade.
However, most known topological insulator materials naturally contain spinful
nuclei, and their hyperfine coupling to helical edge states intrinsically
breaks time-reversal symmetry, removing the topological protection and enabling
the buildup of dynamic nuclear spin polarization through hyperfine-assisted
backscattering. Here, we calculate scattering probabilities and nuclear
polarization for edge channels containing up to $34$ nuclear spins using a
numerically exact analysis that exploits the symmetries of the problem to
drastically reduce the computational complexity. We then show the emergence of
universal scaling properties that allow us to extrapolate our findings to
vastly larger and experimentally relevant system sizes. We find that
significant nuclear polarization can result from relatively weak helical edge
currents, suggesting that it may be an important factor affecting spin
transport in topological insulator devices.",1711.01712v3
2017-11-27,Characterization of Spin-Transfer-Torque effect induced magnetization dynamics driven by short current pulses,"We present a time-resolved study of the magnetization dynamics in a
microstructured Cr$|$Heusler$|$Pt waveguide driven by the Spin-Hall-Effect and
the Spin-Transfer-Torque effect via short current pulses. In particular, we
focus on the determination of the threshold current at which the spin-wave
damping is compensated. We have developed a novel method based on the temporal
evolution of the magnon density at the beginning of an applied current pulse at
which the magnon density deviates from the thermal level. Since this method
does not depend on the signal-to-noise ratio, it allows for a robust and
reliable determination of the threshold current which is important for the
characterization of any future application based on the Spin-Transfer-Torque
effect.",1711.09647v1
2018-06-05,Multi-orbital nature of the spin fluctuations in Sr$_2$RuO$_4$,"The spin susceptibility of strongly correlated Sr$_2$RuO$_4$ is known to
display a rich structure in reciprocal space, with a prominent peak at ${\bf
Q}_i$=$(0.3,0.3,0)$. It is still debated if the resulting incommensurate
spin-density-wave fluctuations foster unconventional superconductivity at low
temperature or compete therewith. By means of density functional theory
combined with dynamical mean-field theory, we reveal the realistic
multi-orbital signature of the (dynamic) spin susceptibility beyond existing
weak-coupling approaches. The experimental fluctuation spectrum up to 80 meV is
confirmed by theory. Furthermore, the peak at ${\bf Q}_i$ is shown to carry
nearly equal contributions from each of the Ru$(4d)$-$t_\mathrm{2g}$ orbitals,
pointing to a cooperative effect resulting in the dominant spin fluctuations.",1806.01511v2
2018-06-11,Spin dynamics of coupled spin ladders near quantum criticality in Ba2CuTeO6,"We report inelastic neutron scattering measurements of the magnetic
excitations in Ba2CuTeO6, proposed by ab initio calculations to magnetically
realize weakly coupled antiferromagnetic two-leg spin-1/2 ladders. Isolated
ladders are expected to have a singlet ground state protected by a spin gap.
Ba2CuTeO6 orders magnetically, but with a small Neel temperature relative to
the exchange strength, suggesting that the interladder couplings are relatively
small and only just able to stabilize magnetic order, placing Ba2CuTeO6 close
in parameter space to the critical point separating the gapped phase and Neel
order. Through comparison of the observed spin dynamics with linear spin wave
theory and quantum Monte Carlo calculations, we propose values for all relevant
intra- and interladder exchange parameters, which place the system on the
ordered side of the phase diagram in proximity to the critical point. We also
compare high field magnetization data with quantum Monte Carlo predictions for
the proposed model of coupled ladders.",1806.04052v2
2018-06-25,Hybrid quantum-classical method for simulating high-temperature dynamics of nuclear spins in solids,"First-principles calculations of high-temperature spin dynamics in solids in
the context of nuclear magnetic resonance (NMR) is a long-standing problem,
whose conclusive solution can significantly advance the applications of NMR as
a diagnostic tool for material properties. In this work, we propose a new
hybrid quantum-classical method for computing NMR free induction decay(FID) for
spin $1/2$ lattices. The method is based on the simulations of a finite cluster
of spins $1/2$ coupled to an environment of interacting classical spins via a
correlation-preserving scheme. Such simulations are shown to lead to accurate
FID predictions for one-, two- and three-dimensional lattices with a broad
variety of interactions. The accuracy of these predictions can be efficiently
estimated by varying the size of quantum clusters used in the simulations.",1806.09355v2
2018-07-18,Spin-orbit coupled soliton in a random potential,"We investigate theoretically the dynamics of a spin-orbit coupled soliton
formed by a self- interacting Bose-Einstein condensate immersed in a random
potential, in the presence of an artificial magnetic field. We find that due to
the anomalous spin-dependent velocity, the synthetic Zeeman coupling can play a
critical role in the soliton dynamics by causing its localization or
delocalization, depending on the coupling strength and on the parameters of the
random potential. The observed effects of the Zeeman coupling qualitatively
depend on the type of self-interaction in the condensate since the spin state
and the self-interaction energy of the condensate are mutually related if the
invariance of the latter with respect to the spin rotation is lifted.",1807.06794v2
2018-08-10,Fast and sensitive detection of hemoglobin and other paramagnetic species using coupled charge and spin dynamics in strongly fluorescent nanodiamonds,"Sensing of a few unpaired electron spins, such as metal ions and radicals, is
a useful but difficult task in nanoscale physics, biology, and chemistry.
Single nitrogen-vacancy (NV) centers in diamond offer high sensitivity and
spatial resolution in the optical detection of weak magnetic fields produced by
a spin bath, but often require long acquisition times, of the order of seconds.
Here we use a novel approach, based on coupled spin and charge dynamics in
dense NV ensembles in strongly fluorescent nanodiamonds (NDs) to sense external
magnetic dipoles. We apply this approach to various paramagnetic species,
including gadolinium complexes, magnetite nanoparticles and hemoglobin in whole
blood. Taking advantage of the high NV density, we demonstrate detection of
subnanomolar amounts of Gd spins with ultrashort acquisition time approaching
10 ms. Strong luminescence, high sensitivity and short acquisition time make
dense NV- ensembles in NDs a powerful tool for biosensing and bioimaging
applications.",1808.03525v1
2018-12-14,Metallic Spin Liquid-like Behavior of LiV$_2$O$_4$,"LiV$_2$O$_4$ spinel is known to exhibit heavy fermion-like behavior below a
characteristic temperature $T_K\simeq 20$ K, while it preserves a paramagnetic
state down to $T\sim10^{-2}$ K due to geometrical frustration. Here, it is
shown that the dynamical spin susceptibility $\chi({\bf q},\omega)$ in
LiV$_2$O$_4$ exhibits anomalous duality which is modeled as a sum of itinerant
($\chi_{\rm F}$) and local ($\chi_{\rm L}$) components,and that the local spin
dynamics inferred from $\chi_{\rm L}({\bf q},\omega)$ is qualitatively
different from that expected from time-averaged bulk properties. The anomaly
coexists with the marginal Fermi liquid behavior inferred from the $-\ln T$
dependence of the electronic specific heat over a wide temperature range below
$T_K$. We argue that such unusual properties of LiV$_2$O$_4$ can be attributed
to the putative metallic spin liquid state emerging near the quantum critical
point between spin glass and Fermi liquid states.",1812.05843v1
2019-03-07,Interplay between spin dynamics and crystal field in multiferroic compound HoMnO$_3$,"In the multiferroic hexagonal manganite HoMnO3, inelastic neutron scattering
and synchrotron based THz spectroscopy have been used to investigate the spin
waves associated to the Mn order together with Ho crystal field excitations.
While the Mn order sets in first below 80 K, a spin reorientation occurs below
37 K, a rare feature in the rare earth manganites. We show that severalHo
crystal field excitations are present in the same energy range as the magnons,
and that they are all affected by the spin reorientation. Moreover, several
anomalous features are observed in the excitations at low temperature. Our
analysis and calculations for the Mn spin waves and Ho crystal field
excitations support Mn-Ho coupling mechanisms as well as coupling to the
lattice affecting the dynamics.",1903.03009v1
2019-04-24,Magnetic Susceptibility and Simulated Neutron Signal in the 2D Hubbard Model,"We compute dynamic spin susceptibilities in the two-dimensional Hubbard model
using the method of Dual Fermions and provide comparison to lattice Monte Carlo
and cluster dynamical mean field theory. We examine the energy dispersion
identified by peaks in ${\rm Im}\chi(\omega,q)$ which define spin modes and
compare the exchange scale and magnon dispersion to neutron experiments on the
parent La$_2$CuO$_4$ cuprate. We present the evolution of the spin excitations
as a function of Hubbard interaction strengths and doping and explore the
particle-hole asymmetry of the spin excitations. We also study the correlation
lengths and the spin excitation dispersion peak structure and find a `Y'-shaped
dispersion similar to neutron results on doped HgBa$_2$CuO$_{4+\delta}$.",1904.10782v1
2019-04-25,Spin-wave propagation in metallic CoFe films determined by microfocused frequency-resolved magneto-optic Kerr effect,"We investigated the magnetization dynamics of a patterned
Co$_{25}$Fe$_{75}$-based heterostructure with a novel optical measurement
technique that we call microfocused frequency-resolved magneto optic Kerr
effect ($\mu$FR-MOKE). We measured the magnetic field dependence of the
dynamical spin-wave susceptibility and recorded a spatial map of the spin-waves
excited by a microwave antenna. We compare these results to those obtained on
the same sample with the established microfocused Brillouin light scattering
technique. With both techniques, we find a spin-wave propagation length of
5.6$\mu$m at 10GHz. Furthermore, we measured the dispersion of the wavevector
and the spin-wave propagation length as a function of the external magnetic
field. These results are in good agreement with existing literature and with
the employed Kalinkos-Slavin model.",1904.11273v1
2019-08-01,Spin dynamics investigations for the EDM experiment at COSY,"Precision experiments, such as the search for a deuteron electric dipole
moments using a storage rings like COSY, demand for an understanding of the
spin dynamics with unprecedented accuracy. In such an enterprise, numerical
predictions play a crucial role for the development and later application of
spin-tracking algorithms. Various measurement concepts involving polarization
effects induced by an RF Wien filter and static solenoids in COSY are
discussed. The matrix formalism, applied here, deals \textit{solely} with spin
rotations \textit{on the closed orbit} of the machine, and is intended to
provide \textit{numerical} guidance for the development of beam and
spin-tracking codes for rings that employ realistic descriptions of the
electric and magnetic bending and focusing elements, solenoids etc., and a
realistically-modeled RF Wien filter.",1908.00350v1
2019-08-15,Analytic Solutions to Compact Binary Inspirals With Leading Order Spin-Orbit Contribution Using The Dynamical Renormalization Group,"We calculate the real-space trajectory and spin precession of a generic
spinning compact binary inspiral at any time instant using the dynamical
renormalization group formalism. This method leads to closed-form analytic
solutions to the binary motion through treating radiation reaction as
perturbations and resumming the secular growth of perturbative terms. We
consider the spin-orbit effects at leading order and the 2.5PN radiation
reaction without orbit averaging or precession averaging for arbitrary
individual masses and spin magnitudes and orientations. The solutions are
written in a moving reference frame, with the orbital angular momentum and
binary radial directions aligned along two of the axes. The resummed solutions
show improved accuracy compared to adiabatic solutions while also being an
order of magnitude faster computationally compared to numerical integration
methods.",1908.05688v1
2019-08-23,Damping enhancement in coherent ferrite/insulating-paramagnet bilayers,"High-quality epitaxial ferrites, such as low-damping MgAl-ferrite (MAFO), are
promising nanoscale building blocks for all-oxide heterostructures driven by
pure spin current. However, the impact of oxide interfaces on spin dynamics in
such heterostructures remains an open question. Here, we investigate the spin
dynamics and chemical and magnetic depth profiles of 15-nm-thick MAFO
coherently interfaced with an isostructural $\approx$1-8-nm-thick overlayer of
paramagnetic CoCr$_2$O$_4$ (CCO) as an all-oxide model system. Compared to MAFO
without an overlayer, effective Gilbert damping in MAFO/CCO is enhanced by a
factor of $>$3, irrespective of the CCO overlayer thickness. We attribute this
damping enhancement to spin scattering at the $\sim$1-nm-thick chemically
disordered layer at the MAFO/CCO interface, rather than spin pumping or
proximity-induced magnetism. Our results indicate that damping in ferrite-based
heterostructures is strongly influenced by interfacial chemical disorder, even
if the thickness of the disordered layer is a small fraction of the ferrite
thickness.",1908.08629v2
2019-12-04,Effective Spin-1/2 Moments on a Yb$^{3+}$ Triangular Lattice: an ESR Study,"We investigated the spin dynamics by electron spin resonance (ESR) of the
Yb-based, effective spin-1/2 delafossites NaYbO$_{2}$, AgYbO$_{2}$,
LiYbS$_{2}$, NaYbS$_{2}$, and NaYbSe$_{2}$ which all show an absence of
magnetic order down to lowest reachable temperatures and thus are prime
candidates to host a quantum spin-liquid ground state in the vicinity of long
range magnetic order. Clearly resolved ESR spectra allow to obtain well-defined
$g$ values which are determined by the crystal field of the distorted
octahedral surrounding of the Yb-ions in trigonal symmetry. This local crystal
field information provides important input to characterize the effective $S =
1/2$ Kramers doublet as well as the anisotropic exchange coupling between the
Yb ions which is crucial for the nature of the groundstate. The ESR linewidth
$\Delta B$ is characterised by the spin dynamics and is mainly determined by
the anisotropic exchange coupling. We discuss and compare $\Delta B$ of the
above mentioned delafossites focussing on the low temperature behaviour which
is dominated by the growing influence of spin correlations.",1912.01868v1
2019-12-07,Mechanical rotation via optical pumping of paramagnetic impurities,"Hybrid quantum systems exhibiting coupled optical, spin, and mechanical
degrees of freedom can serve as a platform for sensing, or as a bus to mediate
interactions between qubits with disparate energy scales. These systems are
also creating opportunities to test foundational ideas in quantum mechanics,
including direct observations of the quantum regime in macroscopic objects.
Here, we make use of angular momentum conservation to study the dynamics of a
pair of paramagnetic centers featuring different spin numbers in the presence
of a properly tuned external magnetic field. We examine the interplay between
optical excitation, spin evolution, and mechanical motion, and theoretically
show that in the presence of continuous optical illumination, inter-spin
cross-relaxation must induce rigid rotation of the host crystal. The system
dynamics is robust to scattering of spin-polarized phonons, a result we build
on to show this form of angular momentum transfer should be observable using
state-of-the-art torsional oscillators or trapped nanoparticles.",1912.03524v1
2019-12-23,Optical Phase Transitions in Photonic Networks: A Spin System Formulation,"We investigate the collective dynamics of nonlinearly interacting modes in
multimode photonic settings with long-range couplings. To this end, we have
established a connection with the theory of spin networks. The emerging
""photonic spins"" are complex, soft (their size is not fixed) and their dynamics
has two constants of motion. Our analysis shed light on the nature of the
thermal equilibrium states and reveals the existence of optical
phase-transitions which resemble a paramagnetic to a ferromagnetic and to a
spin-glass phase transitions occurring in spin networks. We show that, for
fixed average optical power, these transitions are driven by the type (constant
or random couplings) of the network connectivity and by the total energy of the
optical signal.",1912.10569v1
2020-05-14,Harmonic fine tuning and triaxial spatial anisotropy of dressed atomic spins,"The addition of a weak oscillating field modifying strongly dressed spins
enhances and enriches the system quantum dynamics. Through low-order harmonic
mixing the bichromatic driving generates additional rectified static field
acting on the spin system. The secondary field allows for a fine tuning of the
atomic response and produces effects not accessible with a single dressing
field, such as a spatial triaxial anisotropy of the spin coupling constants and
acceleration of the spin dynamics. This tuning-dressed configuration introduces
an extra handle for the system full engineering for quantum control
applications. Tuning amplitude, harmonic content, spatial orientation and phase
relation are control parameters. A theoretical analysis, based on perturbative
approach, is experimentally validated by applying a bichromatic radiofrequency
field to an optically pumped Cs atomic vapour. We measure the resonance shifts
produced by tuning fields up to the third harmonic.",2005.07279v3
2020-05-31,Ultrafast dynamics of light-induced spin crossovers under high pressure,"Within the multielectron model of magnetic insulator with spin crossover
under high pressure we have studied the mean field phase diagrams in pressure
temperature plane and dynamics of a sudden excited non equilibrium spin state.
We obtain the different relaxation of the magnetization, high spin/low spin
occupation numbers, and the metal oxygen bond length for different values of
the external pressure. We found the long living oscillations of magnetization
without pressure and at small external pressure. Close to crossover pressure
the smooth relaxation is accompanied with a set of sharp strongly non linear
oscillations of magnetization and HS/LS occupation numbers that are accompanied
by the Franck Condon resonances.",2006.00539v1
2020-06-23,Doping-induced quantum spin Hall insulator to superconductor transition,"A unique property of a dynamically generated quantum spin Hall state are
Goldstone modes that correspond to the long-wavelength fluctuations of the
spin-orbit coupling order parameter whose topological Skyrmion excitations
carry charge 2$e$. Within the model considered here, upon varying the chemical
potential, we observe two transitions: An s-wave superconducting order
parameter develops at a critical chemical potential $\mu_{c1}$, corresponding
to the excitation gap of pairs of fermions, and at $\mu_{c2}$ the SO(3) order
parameter of the quantum spin Hall state vanishes. Using negative-sign-free,
large-scale quantum Monte Carlo simulations, we show that $\mu_{c1}=\mu_{c2}$
within our accuracy -- we can resolve dopings away from half filling down to
$\delta = 0.0017$. The length scale associated with the fluctuations of the
quantum spin Hall order parameter grows down to our lowest doping, suggesting
either a continuous or a weakly first-order transition. Contrary to mean-field
expectations, the doping versus chemical potential curve is not linear,
indicating a dynamical critical exponent $z > 2$ if the transition is
continuous.",2006.13239v2
2020-09-10,Distinct Critical Behaviors from the Same State in Quantum Spin and Population Dynamics Perspectives,"There is a deep connection between the ground states of transverse-field spin
systems and the late-time distributions of evolving viral populations -- within
simple models, both are obtained from the principal eigenvector of the same
matrix. However, that vector is the wavefunction amplitude in the quantum spin
model, whereas it is the probability itself in the population model. We show
that this seemingly minor difference has significant consequences: phase
transitions which are discontinuous in the spin system become continuous when
viewed through the population perspective, and transitions which are continuous
become governed by new critical exponents. We introduce a more general class of
models which encompasses both cases, and that can be solved exactly in a
mean-field limit. Numerical results are also presented for a number of
one-dimensional chains with power-law interactions. We see that well-worn spin
models of quantum statistical mechanics can contain unexpected new physics and
insights when treated as population-dynamical models and beyond, motivating
further studies.",2009.05064v1
2020-09-30,Quantum hydrodynamics of spin winding,"An easy-plane spin winding in a quantum spin chain can be treated as a
transport quantity, which propagates along the chain but has a finite lifetime
due to phase slips. In a hydrodynamic formulation for the winding dynamics, the
quantum continuity equation acquires a source term due to the transverse
vorticity flow. The latter reflects the phase slips and generally compromises
the global conservation law. A linear-response formalism for the nonlocal
winding transport then reduces to a Kubo response for the winding flow along
the spin chain, in conjunction with the parasitic vorticity flow transverse to
it. One-dimensional topological hydrodynamics can be recovered when the
vorticity flow is asymptotically small. Starting with a microscopic spin-chain
formulation, we focus on the asymptotic behavior of the winding transport based
on the renormalized sine-Gordon equation, incorporating phase slips as well as
Gilbert damping. A generic electrical device is proposed to manifest this
physics. We thus suggest winding conductivity as a tangible concept that can
characterize low-energy dynamics in a broad class of quantum magnets.",2010.00144v1
2020-10-13,Quantum operator growth bounds for kicked tops and semiclassical spin chains,"We present a framework for understanding the dynamics of operator size, and
bounding the growth of out-of-time-ordered correlators, in models of large-$S$
spins. Focusing on the dynamics of a single spin, we show the finiteness of the
Lyapunov exponent in the large-$S$ limit; our bounds are tighter than the best
known Lieb-Robinson-type bounds on these systems. We numerically find our upper
bound on Lyapunov exponents is within an order of magnitude of numerically
computed values in classical and quantum kicked top models. Generalizing our
results to coupled large-$S$ spins on lattices, we show that the butterfly
velocity, which characterizes the spatial speed of quantum information
scrambling, is finite as $S\rightarrow\infty$. We emphasize qualitative
differences between operator growth in semiclassical large-spin models, and
quantum holographic systems including the Sachdev-Ye-Kitaev model.",2010.06592v3
2020-11-26,From modeling of political opinion formation to two-spin statistical physics model,"A two-spin system based on the idea used to formulate the dynamical model
simulating the process of opinion spreading in a society, where people adopt
one of the four social attitudes [Physica A 351, 593 (2005)] is studied. The
model is made of chains with two species of spins S and V at each site coupled
by an insite interaction ~M0 and interacting in different way with nearest (NN)
and next-nearest (NNN) neighbors. The one-dimensional model with only NN
interaction of the S spins and both NN and NNN interactions of the V spins
(ACLS model) is analyzed. Using the linear renormalization group (LRG) the
dependences of the specific heat and correlation functions on temperature and
~M0 are calculated. The roles of the insite and NNN interactions are
considered. The usefulness of the ACLS model to define stable states of the
dynamical model describing opinion spreading in a society, which members
represent four different attitudes to the level of freedom in two areas:
personal and economic is discussed. It is pointed out that the difficulties in
organizing modern societies can result from an internal con ict between these
two areas. 1",2011.13269v1
2021-02-11,Magnonics in collinear magnetic insulating systems,"In the last decades, collinear magnetic insulating systems have emerged as
promising energy-saving information carriers. Their elementary collective spin
excitations, i.e., magnons, can propagate for long distances bypassing the
Joule heating effects that arise from electron scattering in metal-based
devices. This tutorial article provides an introduction to theoretical and
experimental advances in the study of magnonics in collinear magnetic
insulating systems. We start by outlining the quantum theory of spin waves in
ferromagnetic and antiferromagnetic systems and we discuss their quantum
statistics. We review the phenomenology of spin and heat transport of the
coupled coherent and incoherent spin dynamics and the interplay between
magnetic excitations and lattice degrees of freedom. Finally, we introduce the
reader to the key ingredients of two experimental probes of magnetization
dynamics, spin transport and NV-center relaxometry setups, and discuss
experimental findings relevant to the outlined theory.",2102.08829v1
2021-03-01,Electron Tunneling Spectroscopy of the Anisotropic Kitaev Quantum Spin Liquid Sandwiched with Superconductors,"We present the electron tunneling transport and spectroscopic characters of a
superconducting {\it Josephson} junction with a barrier of single anisotropic
Kitaev quantum spin liquid (QSL) layer. We find that the dynamical spin
correlation features are well reflected in the direct-current differential
conductance $dI^{c}/dV$ of the single-particle tunneling, including the unique
spin gap and dressed itinerant Majorana dispersive band, in addition to an
energy shift $2\Delta$ of two-lead superconducting gaps. From the spectral
characters, we identify different topological quantum phases of the anisotropic
Kitaev QSL. We also present the zero-voltage {\it Josephson} current $I^{s}$
which displays residual features of the anisotropic Kitaev QSL. These results
pave a new way to measure the dynamical spinon or Majorana fermion spectroscopy
of the Kitaev and other spin liquid materials.",2103.01003v3
2021-03-24,Variational study of the Kitaev-Heisenberg-Gamma model,"We compute the low-energy excitation spectrum and the dynamical spin
structure factor of the Kitaev-Heisenberg-Gamma model through a variational
approach based on the exact fractionalized excitations of the pure Kitaev
honeycomb model. This novel approach reveals the physical reason for the
asymmetric stability of the Kitaev spin liquid phases around the ferromagnetic
and antiferromagnetic Kitaev limits. Moreover, we demonstrate that the
fractionalized excitations form bound states in specific regions of each Kitaev
spin liquid phase and that certain phase transitions induced by Heisenberg and
Gamma interactions are driven by the condensation of such a bound state.
Remarkably, this bound state appears as a sharp mode in the dynamical spin
structure factor, while its condensation patterns at the appropriate phase
transitions provide a simple explanation for the magnetically ordered phases
surrounding each Kitaev spin liquid phase.",2103.13274v2
2021-06-23,"Stable spin Hall-Littlewood symmetric functions, combinatorial identities, and half-space Yang-Baxter random field","Stable spin Hall-Littlewood symmetric polynomials labeled by partitions were
recently introduced by Borodin and Wheeler in the context of higher spin six
vertex models, which are one-parameter deformation of the Hall-Littlewood
polynomials. We present a new combinatorial definition for the stable spin
Hall-Littlewood polynomials, and derive a series of new combinatorial
identities, including the skew Littlewood identity, refined Cauchy identity and
refined Littlewood identity.
  Employing bijectivisation of summation identities, Bufetov and Petrov
introduced local stochastic moves based on the Yang-Baxter equation. Combining
the skew Littlewood identity and these moves, we introduce the half-space
Yang-Baxter random field for stable spin Hall-Littlewood polynomials. We match
the lengths of the partitions in this field with a new dynamic version of
stochastic six vertex model in the half-quadrant, which can be mapped to a
dynamic version of discrete-time interacting particle system on the half-line
with an open boundary.",2106.12557v1
2021-07-16,Dynamic mean-field theory for dense spin systems at infinite temperature,"A dynamic mean-field theory for spin ensembles (spinDMFT) at infinite
temperatures on arbitrary lattices is established. The approach is introduced
for an isotropic Heisenberg model with $S = \tfrac12$ and external field. For
large coordination numbers, it is shown that the effect of the environment of
each spin is captured by a classical time-dependent random mean-field which is
normally distributed. Expectation values are calculated by averaging over these
mean-fields, i.e., by a path integral over the normal distributions. A
self-consistency condition is derived by linking the moments defining the
normal distributions to spin autocorrelations. In this framework, we explicitly
show how the rotating wave approximation becomes a valid description for
increasing magnetic field. We also demonstrate that the approach can easily be
extended. Exemplarily, we employ it to reach a quantitative understanding of a
dense ensemble of spins with dipolar interaction which are distributed randomly
on a plane including static Gaussian noise as well.",2107.07821v2
2021-09-27,Subdiffusive hydrodynamics of nearly-integrable anisotropic spin chains,"We address spin transport in the easy-axis Heisenberg spin chain subject to
integrability-breaking perturbations. We find that spin transport is
subdiffusive with dynamical exponent $z=4$ up to a timescale that is
parametrically long in the anisotropy. In the limit of infinite anisotropy,
transport is subdiffusive at all times; for large finite anisotropy, one
eventually recovers diffusion at late times, but with a diffusion constant
independent of the strength of the integrability breaking perturbation. We
provide numerical evidence for these findings, and explain them by adapting the
generalized hydrodynamics framework to nearly integrable dynamics. Our results
show that the diffusion constant of near-integrable interacting spin chains is
generically not perturbative in the integrability breaking strength.",2109.13251v2
2021-09-28,Spin oscillations of a single-mode polariton system driven by a plane wave,"Theoretical study is performed of a single-mode polariton system with linear
coupling of spin components. When combined with an ordinary two-particle
interaction, the spin coupling involves a spontaneous symmetry breaking
accompanied by a switch from linear to circular polarization under resonant
driving. The asymmetric steady states can also lose stability, giving way to
oscillatory and chaotic dynamics. Here, we explore a continuous transformation
between the multistable regime, where the system is steady and locked in phase
to the pump but has a broken spin symmetry, and full-span oscillations of the
circular-polarization degree, owing to which the symmetry is effectively
reestablished. Such oscillations are analogous to the intrinsic Josephson
effect and prove to be robust against arbitrarily strong perturbations.
Transitional phenomena include the Hopf bifurcation, spin bistability of limit
cycles, and continuous transitions to and from dynamical chaos through series
of period doubling/halving events.",2109.13775v3
2021-10-19,Dynamical Signatures of Rank-2 $U(1)$ Spin Liquids,"Emergent $U(1)$ gauge theories and artificial photons in frustrated magnets
are outstanding examples of many-body collective phenomena. The classical and
quantum regimes of these systems provide platforms for classical and quantum
spin liquids, and are the subject of current active theoretical and
experimental investigations. Recently, realizations of rank-2 $U(1)$ (R2-U1)
gauge theories in three-dimensional frustrated magnets have been proposed. Such
systems in the quantum regime may lead to the so-called fracton ordered phases
-- a new class of topological order that has been associated with quantum
stabilizer codes and holography. However, there exist few distinguishing
characteristics of these states for their detection in real materials. Here we
focus on the classical limit, and present the dynamical spin structure factor
for a R2-U1 spin liquid state on a breathing pyrochlore lattice. Remarkably, we
find unique signatures of the R2-U1 state, and we contrast them with the
results obtained from a more conventional $U(1)$ spin liquid. These results
provide a new path of investigation for future inelastic neutron scattering
experiments on candidate materials.",2110.10180v1
2021-10-22,Catching Bethe phantoms and quantum many-body scars: Long-lived spin-helix states in Heisenberg magnets,"Exact solutions for quantum many-body systems are rare and provide valuable
insight to universal phenomena. Here we show experimentally in anisotropic
Heisenberg chains that special helical spin patterns can have very long
lifetimes. This finding confirms the recent prediction of phantom Bethe states,
exact many-body eigenstates carrying finite momenta yet no energy. We
theoretically find analogous stable spin helices in higher dimensions and in
other non-integrable systems, where they imply non-thermalizing dynamics
associated with quantum many-body scars. We use phantom spin helices to
directly measure the interaction anisotropy which has a major contribution from
short-range off-site interactions that have not been observed before. Phantom
helix states open new opportunities for quantum simulations of spin physics and
studies of many-body dynamics.",2110.12043v1
2021-11-17,Dynamical anyon generation in Kitaev honeycomb non-Abelian spin liquids,"Relativistic Mott insulators known as 'Kitaev materials' potentially realize
spin liquids hosting non-Abelian anyons. Motivated by fault-tolerant
quantum-computing applications in this setting, we introduce a dynamical
anyon-generation protocol that exploits universal edge physics. The setup
features holes in the spin liquid, which define energetically cheap locations
for non-Abelian anyons, connected by a narrow bridge that can be tuned between
spin liquid and topologically trivial phases. We show that modulating the
bridge from trivial to spin liquid over intermediate time scales -- quantified
by analytics and extensive simulations -- deposits non-Abelian anyons into the
holes with O(1) probability. The required bridge manipulations can be
implemented by integrating the Kitaev material into magnetic tunnel junction
arrays that engender locally tunable exchange fields. Combined with existing
readout strategies, our protocol reveals a path to topological qubit
experiments in Kitaev materials at zero applied magnetic field.",2111.09325v1
2021-12-28,Spin-orbit coupling for close-in planets,"We study the spin evolution of close-in planets in multi-body systems and
present a very general formulation of the spin-orbit problem. This includes a
simple way to probe the spin dynamics from the orbital perturbations, a new
method for computing forced librations and tidal deformation, and general
expressions for the tidal torque and capture probabilities in resonance. We
show that planet-planet perturbations can drive the spin of Earth-size planets
into asynchronous or chaotic states, even for nearly circular orbits. We apply
our results to Mercury and to the KOI-1599 system of two super-Earths in a 3/2
mean motion resonance.",2112.14335v1
2021-12-31,Higher spin dynamics in gravity and $w_{1 + \infty}$ celestial symmetries,"In this paper we extract from a large-$r$ expansion of the vacuum Einstein's
equations a dynamical system governing the time evolution of an infinity of
higher-spin charges. Upon integration, we evaluate the canonical action of
these charges on the gravity phase space. The truncation of this action to
quadratic order and the associated charge conservation laws yield an infinite
tower of soft theorems. We show that the canonical action of the higher spin
charges on gravitons in a conformal primary basis, as well as conformally soft
gravitons reproduces the higher spin celestial symmetries derived from the
operator product expansion. Finally, we give direct evidence that these charges
form a canonical representation of a $w_{1+\infty}$ loop algebra on the
gravitational phase space.",2112.15573v2
2022-01-14,Spinning Driven Dynamic Nuclear Polarization with Optical Pumping,"We propose a new, more efficient, and potentially cost effective, solid-state
nuclear spin hyperpolarization method combining the Cross Effect mechanism and
electron spin optical hyperpolarization in rotating solids. We first
demonstrate optical hyperpolarization in the solid state at low temperature and
low field, and then investigate its field dependence to obtain the optimal
condition for high-field electron spin hyperpolarization. The results are then
incorporated into advanced Magic Angle Spinning Dynamic Nuclear Polarization
(MAS-DNP) numerical simulations that show that optically pumped MAS-DNP could
yield breakthrough enhancements at very high magnetic fields. Based on these
investigations, enhancements greater than the ratio of electron to nucleus
magnetic moments (>658 for 1H) are possible without microwave irradiation. This
could solve at once the MAS-DNP performance decrease with increasing field and
the high cost of MAS-DNP instruments at very high fields.",2201.05703v2
2022-02-15,Analysis of the robustness and dynamics of spin-locking preparations for the detection of oscillatory magnetic fields,"Extracting quantitative information of neuronal signals by non-invasive
imaging is an outstanding challenge for understanding brain function and
pathology. However, state-of-the-art techniques offer low sensitivity to deep
electrical sources. Stimulus induced rotary saturation (SIRS) is a recently
proposed magnetic resonance imaging (MRI) sequence that detects oscillatory
magnetic fields using a spin-lock preparation. Phantom experiments and
simulations proved its efficiency and sensitivity, but the susceptibility of
the method to field inhomogeneities is still not well understood. In this
study, we simulated and analyzed the dynamic of three spin-lock preparations
and their response to field inhomogeneities in the presence of a resonant
oscillating field. We show that the composite spin-lock preparation is more
robust against field variations within the double resonance effect. In
addition, we tested the capability of the chosen composite spin-lock
preparation to recover information about the spectral components of a composite
signal. This study sets the bases to move one step further towards the clinical
application of MR-based neuronal current imaging.",2202.07705v2
2022-03-10,Ultrafast optically induced magnetic state transition in 2D antiferromagnets,"Manipulating spin in antiferromagnetic (AFM) materials has great potential in
AFM opto-spintronics. Laser pulses can induce a transient ferromagnetic (FM)
state in AFM metallic systems, but have never been proven in two-dimensional
(2D) AFM semiconductors and related van der Waals (vdW) heterostructures. Here,
using 2D vdW heterostructures of FM MnS2 and AFM MXenes as prototypes, we
investigated optically induced interlayer spin transfer dynamics based on the
real-time time-dependent density functional theory (rt-TDDFT). We observed that
laser pulses induce significant spin injection and the interfacial
atom-mediated spin transfer from MnS2 to Cr2CCl2. In particular, we first
demonstrated the transient FM state in semiconducting AFM/FM heterostructures
during photoexcited processes. Because the proximity magnetism breaks the
magnetic symmetry of Cr2CCl2 in heterostructures. Our results provide the
microscopic understanding for optically controlled interlayer spin dynamics in
2D magnetic heterostructures and open a new way to manipulate magnetic orders
in ultrafast opto-spintronics.",2203.05124v1
2022-03-30,Topological Burning Glass Effect,"We reveal a topological burning glass effect, where the local response of a
system exhibits a topological quantization that is enhanced by an integer due
to its environmental coupling. As a paradigmatic platform for this intriguing
phenomenon, we study a central spin that is quasiperiodically driven by two
incommensurate frequencies, and statically coupled to $N-1$ surrounding spins.
In the strong coupling regime, the adiabatic dynamics of the total system is
readily understood to imprint on the central spin an $N$-fold enhanced
topological frequency conversion between the two driving frequencies. We argue
that the topological burning glass effect is induced by the non-unitary
dynamics of the central spin, which locally involves the collective motion of
the surrounding spins. Our results are derived in the framework of adiabatic
perturbation theory and fully corroborated by exact numerical simulations.",2203.16382v2
2022-04-05,Periodic solutions of the non-chiral intermediate Heisenberg ferromagnet equation described by elliptic spin Calogero-Moser dynamics,"We present a class of periodic solutions of the non-chiral intermediate
Heisenberg ferromagnet (ncIHF) equation, which was recently introduced by the
authors together with Langmann as a classical, continuum limit of an
Inozemtsev-type spin chain. These exact analytic solutions are constructed via
a spin-pole ansatz written in terms of certain elliptic functions. The
dynamical parameters in our solutions solve an elliptic spin Calogero-Moser
(CM) system subject to certain constraints. In the course of our construction,
we establish a novel B\""acklund transformation for this constrained elliptic
spin CM system.",2204.02182v1
2022-05-10,Spectra of a Gapped Quantum Spin Liquid with a Strong Chiral Excitation on the Triangular Lattice,"While a quantum spin liquid (QSL) phase has been identified in the
$J_1$-$J_2$ Heisenberg model on a triangular lattice via numerical
calculations, debate persists about whether or not such a QSL is gapped or
gapless, with contradictory conclusions from different techniques. Moreover,
information about excitations and dynamics is crucial for the experimental
detection of such a phase. In this work, we use exact diagonalization to
characterize signatures of a QSL phase on the triangular lattice through the
dynamical spin structure factor $\mathcal{S}(q,\omega)$ and Raman
susceptibility $\mathcal{\chi}(\omega)$. We find that spectra for the QSL phase
show distinct features compared to those of neighboring phases; and both the
Raman spectra and spin structure factor show gapped behaviour in the QSL phase.
Interestingly, there is a prominent excitation mode in the Raman $A_2$ channel,
indicating a strong subleading tendency toward a chiral spin liquid phase.",2205.04727v2
2022-06-13,Quasiballistic transport in long-range anisotropic Heisenberg model,"Purely ballistic transport is a rare feature even for integrable models. By
numerically studying the Heisenberg chain with the power-law exchange,
\mbox{$J\propto1/r^\alpha$}, where $r$ is a distance, we show that for spin
anisotropy $\Delta \simeq \exp(-\alpha+2)$ the system exhibits a quasiballistic
spin transport and the presence of fermionic excitation which do not decay up
to extremely long times $\sim10^3/J$. This conclusion is reached on the base of
the dynamics of spin domains, the dynamical spin conductivity, inspecting the
matrix elements of the spin-current operator, and by the analysis of most
conserved operators. Our results smoothly connects two models where fully
ballistic transport is present: free particles with nearest-neighbor hopping
and the isotropic Haldane-Shastry model.",2206.05960v3
2022-08-30,Phonons and phase symmetries in bulk $CrCl_3$ from scattering measurements and theory,"Phonon-derived behaviors are important indicators of novel phenomena in
transition metal trihalides, including spin liquid behavior, two-dimensional
magnetism, and spin-lattice coupling. However, phonons and their dependence on
spin structure and excitations have not been adequately explored. In this work,
we probe and critically examine the vibrational properties of bulk $CrCl_3$
using inelastic neutron scattering and density functional theory. We
demonstrate that magnetic and van der Waals interactions are essential to
describing the structure and phonons in $CrCl_3$; however, the specific spin
configuration is unimportant. This provides context for understanding thermal
transport measurements as governed by dynamical spin-lattice couplings. More
importantly, we introduce an efficient dynamic method that exploits
translational symmetries in large conventional unit cells that generates
insights into phonon dispersions, interactions, and measured spectra in terms
of quantum phase interference conditions. This work opens new avenues for
understanding phonons in layered magnets and more generally in conventional
cell geometries of a variety of materials.",2209.02394v1
2022-10-06,Magnetic excitations in the helical Rashba superconductor,"We investigate the magnetic excitation spectrum in the helical state of a
noncentrosymmetric superconductor with inversion symmetry breaking and strong
Rashba spin-orbit coupling. For this purpose, we derive the general expressions
of the dynamical spin response functions under the presence of strong Rashba
splitting of conduction bands, superconducting gap, and external field which
lead to stabilization of Cooper pairs with finite overall momentum in a helical
state. The latter is characterized by momentum space regions of paired and
unpaired states with different quasiparticle dispersions. The magnetic response
is determined by i) excitations within and between both paired and unpaired
regions ii) anomalous coherence factors and iii) additional spin matrix
elements due to helical Rashba spin texture of bands. We show that as a
consequence typical correlated real space and spin space anisotropies appear in
the dynamical susceptibility which would be observable as a characteristic
fingerprint for a helical superconducting state in inelastic neutron scattering
investigations.",2210.03059v1
2022-10-26,"The Biological Qubit: Calcium Phosphate Dimers, not Trimers","The Posner molecule (calcium phosphate trimer), has been hypothesized to
function as a biological quantum information processor due to its supposedly
long-lived entangled $^{31}$P nuclear spin states. This hypothesis was
challenged by our recent finding that the molecule lacks a well-defined
rotational axis of symmetry -- an essential assumption in the proposal for
Posner-mediated neural processing -- and exists as an asymmetric dynamical
ensemble. Following up, we investigate here the spin dynamics of the molecule's
entangled $^{31}$P nuclear spins within the asymmetric ensemble. Our
simulations show that entanglement between two nuclear spins prepared in a Bell
state in separate Posner molecules decays on a sub-second timescale -- much
faster than previously hypothesized, and not long enough for super-cellular
neuronal processing. Calcium phosphate dimers however, are found to be
surprisingly resilient to decoherence and are able to preserve entangled
nuclear spins for hundreds of seconds, suggesting that neural processing might
occur through them instead.",2210.14812v3
2022-11-23,Anatomy of spin wave driven magnetic texture motion via magnonic torques,"The interplay between spin wave and magnetic texture represents the
information exchange between the fast and slow dynamical parts of magnetic
systems. Here we formulate a set of magnonic torques acting on background
magnetic texture, by extracting time-invariant information from the fast
precessing spin waves. Under the frame of magnonic torques, we use theoretical
formulations and micromagnetic simulations to investigate the spin wave driven
domain wall motion in two typical symmetry-breaking situations: the rotational
symmetry broken by the Dzyaloshinkii-Moriya interaction, and the translational
symmetry broken by magnetic damping. The torque-based microscopic analyses
provide compact yet quantitative tools to reinterpret the magnetic texture
dynamics induced by spin wave, beyond the conventional framework of global
momentum conservation.",2211.12958v1
2023-03-22,Kerr binary dynamics from minimal coupling and double copy,"We construct a new Yang-Mills Lagrangian based on a notion of minimal
coupling that incorporates classical spin effects. The construction relies on
the introduction of a new covariant derivative, which we name ""classical spin
covariant derivative"", that is compatible with the three-point interaction of
the $\sqrt{\mathrm{Kerr}}$ solution with the gauge field. The resulting
Lagrangian, beside the correct three-point coupling, predicts a unique choice
for contact terms and therefore it can be used to compute higher-point
amplitudes such as the Compton, unaffected by spurious poles. Using double-copy
techniques we use this theory to extract gravity amplitudes and observables
that are relevant to describe Kerr binary dynamics to all orders in the spin.
In particular, we compute the 2PM ($\mathcal{O}(G^2_N)$) $2\rightarrow 2$
scattering amplitude between two classically spinning objects to all orders in
the spin and use it to extract the 2PM scattering angle.",2303.12784v4
2023-04-09,Charge transport modulation by a redox supramolecular spin-filtering chiral crystal,"The chirality induced spin selectivity (CISS) effect is a fascinating
phenomena correlating molecular structure with electron spin-polarisation in
excited state measurements. Experimental procedures to quantify the
spin-filtering magnitude relies generally on averaging data sets, especially
those from magnetic field dependent conductive-AFM. We investigate the
underlying observed disorder in the IV spectra and the origin of spikes
superimposed. We demonstrate and explain that a dynamic, voltage sweep rate
dependent, phenomena can give rise to complex IV curves for chiral crystals of
coronene bisimide. The redox group, able to capture localized charge states,
acts as an impurity state interfering with a continuum, giving rise to Fano
resonances. We introduce a novel mechanism for the dynamic transport which
might also provide insight into the role of spin-polarization. Crucially,
interference between charge localisation and delocalisation during transport
may be important properties into understanding the CISS phenomena.",2304.04215v1
2023-04-13,Finite Temperature Dynamics of Spin Solitons with Applications in Thermocouples and Refrigerators,"The exploitation of spin Berry phases to generate emergent fields for
producing miniaturized and high-quality inductors has enjoyed considerable
popularity among proponents of quantum technologies [Nature 586, 202 (2020)}].
Inspired by this breakthrough, we extend its mechanism to spin thermoelectrics
by probing responses of ferrimagnetic domain walls (DWs) to thermal gradients.
Similarly, voltages here stem from DW-spin collective motion, in contrast to
normal electron transport phenomena. We further develop finite-temperature
dynamics to investigate thermoelectric figures of merit and attribute
corresponding quantum superiority to ultrafast spin evolution of ferrimagnetism
with tunable non-Abelian phases. We propose a more likely cause of DW motion
towards hot or cold regions (contrary to conclusions of previous reports) and
verify existence of efficient magnon-momentum transfers. These findings deepen
our understanding of heat-driven DW kinetics and suggest profitable new
directions in an emerging realm of spincaloritronics.",2304.06608v1
2023-04-27,Coherent magnetization dynamics in strongly quenched Ni thin films,"The remagnetization process after ultrafast demagnetization can be described
by relaxation mechanisms between the spin, electron, and lattice reservoirs.
Thereby, collective spin excitations in form of spin waves and their angular
momentum transfer play an important role on the longer timescales. In this
work, we address the question whether the strength of demagnetization affects
the coherency and the phase of the excited spin waves. We present a study of
coherent magnetization dynamics in thin nickel films after ultrafast
demagnetization using the all-optical, time-resolved magneto-optical
Kerr-effect (tr-MOKE) technique. The largest coherent oscillation amplitude was
observed for strongly quenched systems, showing the conservation of coherency
for demagnetizations of up to 90%. Moreover, the phase of the excited
spin-waves increases with pump power, indicating a delayed start of the
precession during the remagnetization.",2304.14325v1
2023-07-13,Tracking Berry curvature effect in molecular dynamics by ultrafast magnetic x-ray scattering,"The spin-dependent Berry force is a genuine effect of Berry curvature in
molecular dynamics, which can dramatically result in spatial spin separation
and change of reaction pathways. However, the way to probe the effect of Berry
force remains challenging, because the time-reversal (TR) symmetry required for
opposite Berry forces conflicts with TR symmetry breaking spin alignment needed
to observe the effect, and the net effect could be transient for a molecular
wave packet. We demonstrate that in molecular photodissociation, the
dissociation rates can be different for molecules with opposite initial spin
directions due to Berry force. We showcase that the spatially separated spin
density, which is transiently induced by Berry force as the molecular wave
packet passes through conical intersection, can be reconstructed from the
circular dichroism (CD) of ultrafast non-resonant magnetic x-ray scattering
using free electron lasers.",2307.06523v1
2023-07-26,Spatial orientation of the fission fragment intrinsic spins and their correlations,"New experimental and theoretical results obtained in 2021 made it acutely
clear that more than 80 years after the discovery of nuclear fission we do not
understand the generation and dynamics of fission fragment (FF) intrinsic spins
well, in particular their magnitudes, their spatial orientation, and their
correlations. The magnitude and orientation of the primary FFs have a crucial
role in defining the angular distribution and correlation between the emitted
prompt neutrons, and subsequent emission of statistical (predominantly E1) and
stretched E2 {\gamma}-rays, and their correlations with the final fission
fragments. Here we present detailed microscopic evaluations of the FF intrinsic
spins, for both even- and odd-mass FFs, and of their spatial correlations.
These point to a well-defined 3D FF intrinsic spin dynamics, characteristics
absent in semi-phenomenological studies, due to the presence of the twisting
spin modes, which artificially were suppressed in semi-phenomenological
studies.",2307.14455v2
2023-08-25,Realtime dynamics of hyperon spin correlations from string fragmentation in a deformed four-flavor Schwinger model,"Self-polarizing weak decays of $\Lambda$-hyperons provide unique insight into
the role of entanglement in the fragmentation of QCD strings through
measurements of the spin correlations of $\Lambda{\bar \Lambda}$-pairs produced
in collider experiments. The simplest quantum field theory representing the
underlying parton dynamics is the four-flavor massive Schwinger model plus an
effective spin-flip term, where the flavors are mapped to light (up/down) and
heavy (strange) quarks and their spins. This construction provides a novel way
to explore hyperon spin-correlations in 1+1-dimensions. We investigate the
evolution of these correlations for different string configurations that are
sensitive to the rich structure of the model Hamiltonian.",2308.13596v2
2023-09-18,Rapid spin depolarization in the layered 2D Ruddlesden Popper perovskite (BA)(MA)PbI,"We report temperature-dependent spectroscopy on the layered (n=4)
two-dimensional (2D) Ruddlesden-Popper perovskite (BA)(MA)PbI.
Helicity-resolved steady-state photoluminescence (PL) reveals no optical degree
of polarization. Time-resolved PL shows a photocarrier lifetime on the order of
nanoseconds. From simultaneaously recorded time-resolved differential
reflectivity (TR$\Delta$R) and time-resolved Kerr ellipticity (TRKE), a
photocarrier lifetime of a few nanoseconds and a spin dephasing time on the
order of picoseconds was found. This stark contrast in lifetimes clearly
explains the lack of spin polarization in steady-state PL. While we observe
clear temperature-dependent effects on the PL dynamics that can be related to
structural dynamics, the spin dephasing is nearly T-independent. Our results
highlight that spin dephasing in 2D (BA)(MA)PbI occurs at time scales faster
than the exciton recombination time, which poses a bottleneck for applications
aimingto utilize this degree of freedom.",2309.09784v1
2023-10-31,Coherent spin-phonon scattering in facilitated Rydberg lattices,"We investigate the dynamics of a spin system with facilitation constraint
that can be studied using Rydberg atoms in arrays of optical tweezer traps. The
elementary degrees of freedom of the system are domains of Rydberg excitations
that expand ballistically through the lattice. Due to mechanical forces,
Rydberg excited atoms are coupled to vibrations within their traps. At zero
temperature and large trap depth, it is known that virtually excited lattice
vibrations only renormalize the timescale of the ballistic propagation.
However, when vibrational excitations are initially present -- i.e., when the
external motion of the atoms is prepared in an excited Fock state, coherent
state or thermal state -- resonant scattering between spin domain walls and
phonons takes place. This coherent and deterministic process, which is free
from disorder, leads to a reduction of the power-law exponent characterizing
the expansion of spin domains. Furthermore, the spin domain dynamics is
sensitive to the coherence properties of the atoms' vibrational state, such as
the relative phase of coherently superimposed Fock states. Even for a
translationally invariant initial state the latter manifests macroscopically in
a phase-sensitive asymmetric expansion.",2311.00064v1
2023-11-09,Dynamics of spin glass formation under tunable fluctuations in frustrated cavity QED experiments,"We solve the dynamics of multi-mode cavity QED with frustrated atom-photon
couplings using non-perturbative diagrammatics. Our technique enables a
thorough investigation of the nature of the spin glass transition hosted in
these platforms. We focus in particular on the role of quantum correlations in
each of the atomic ensembles which form the frustrated spin network modeling
the experiment. We report on the stabilizing effect of strong quantum
fluctuations in fostering a glassy phase over extended time scales. At variance
with this behaviour, in the semi-classical limit, spin glass order is
pre-thermally obstructed by the ferromagnetic correlations present at the level
of individual atomic ensembles, which substantially delay spin glass formation,
acting as competing order. Our results set the stage for studying cavity QED
experiments with tunable quantum fluctuations, and accompanying them in the
transition from semi-classical to strongly correlated operational regimes.",2311.05682v2
2024-02-13,Self-Induced Superradiant Masing,"We study superradiant masing in a hybrid system composed of nitrogen-vacancy
center spins in diamond coupled to a superconducting microwave cavity. After
the first fast superradiant decay we observe transient pulsed and then
quasi-continuous masing. This emission dynamics can be described by a
phenomenological model incorporating the transfer of inverted spin excitations
into the superradiant window of spins resonant with the cavity. After
experimentally excluding cQED effects associated with the pumping of the masing
transition we conjecture that direct higher-order spin-spin interactions are
responsible for creating the dynamics and the transition to the sustained
masing. Our experiment thus opens up a novel way to explore many-body physics
in disordered systems through cQED and superradiance.",2402.08537v1
2024-02-28,Two-mode Squeezing in Floquet Engineered Power-law Interacting Spin Models,"We study the non-equilibrium dynamics of a quantum spin 1/2 XXZ model
confined in a two-dimensional bi-layer system, with couplings mediated by
inverse power-law interactions, falling off with distance $r$ as
$1/r^{\alpha}$, and spatio-temporal control of the spins enabled via local
fields. An initial state of spins with opposite magnetization in the two layers
is dynamically unstable resulting in exponential generation of correlated pairs
of excitations. We find that scalable generation of entanglement in the form of
two-mode squeezing between the layers can generically be achieved in powerlaw
models. We further demonstrate that spatially-temporally engineered
interactions allow to significantly increase the generated entanglement and in
fact achieve Heisenberg limited scaling. This work is relevant to a wide
variety of experimental atomic, molecular, and optical platforms, which realize
powerlaw spin models, and demonstrates the advantage of spatio-temporal control
to maximize the generation of metrologically useful entanglement, with
potential applications in quantum-enhanced sensing.",2402.18642v1
2024-03-11,"Exploring spin-squeezing in the Mott insulating regime: role of anisotropy, inhomogeneity and hole doping","Spin-squeezing in systems with single-particle control is a well-established
resource of modern quantum technology. Applied in an optical lattice clock can
reduce the statistical uncertainty of spectroscopic measurements. Here, we
consider dynamic generation of spin-squeezing with ultra-cold bosonic atoms
with two internal states loaded into an optical lattice in the strongly
interacting regime as realized with state-of-the-art experiments using a
quantum gas microscope. We show that anisotropic interactions and inhomogeneous
magnetic fields generate scalable spin-squeezing if their magnitudes are
sufficiently small, but not negligible. The effect of non-uniform filling
caused by hole doping, non-zero temperature and external confinement is studied
at a microscopic level demonstrating their limiting role in the dynamics and
scaling of spin squeezing.",2403.06521v1
2024-03-18,Fractionalization Signatures in the Dynamics of Quantum Spin Liquids,"We investigate the signatures of fractionalization in quantum spin liquids by
studying different phases of the Kitaev honeycomb model in the presence of an
out-of-plane magnetic field through which the model becomes non-integrable.
Using the infinite Projected Entangled Pair States (iPEPS) ansatz, along with
analytical calculations and exact diagonalization, we calculate dynamical
signatures of fractionalized particles through spin-spin and dimer-dimer
correlations. Our analysis demonstrates the ability of these correlations to
discern distinct fractionalized quantum sectors, namely Majorana fermions and
the emergent $Z_2$ fluxes, in both the chiral spin liquid (CSL) phase under
weak field and the emergent intermediate gapless phase (IGP) under moderate
field. Importantly, our calculation reveals the nature of IGP observed at
moderate fields, a region of ongoing debate, indicating that this phase is a
Majorana metal induced by strong flux fluctuations.",2403.12141v2
2024-03-25,Parity-sensitive inhomogeneous dephasing of macroscopic spin ensembles,"Spin ensembles play a pivotal role in various quantum applications such as
metrology and simulating many-body physics. Recent research has proposed
utilizing spin cat states to encode logical quantum information, with
potentially logical lifetimes on the order of seconds via enhanced collective
interactions that scale with system size. We investigate the dynamics of spin
cat states under inhomogeneous broadening, revealing a phenomenon termed
`parity-sensitive inhomogeneous dephasing': odd cat states are significantly
more susceptible to inhomogeneous dephasing compared to even cat states due to
parity symmetry. Additionally, from a mean-field analysis of the
driven-dissipative dynamics, we identify a synchronization phase transition
wherein the ensemble becomes completely dephased beyond a critical
inhomogeneous linewidth. Our findings shed light on the stability of collective
spin states, important for advancing quantum technologies.",2403.16491v1
2006-06-07,Dynamic crossover in the spin-glass phase,"Dynamic scaling analyses are performed in the spin-glass phase of the $\pm J$
Ising, the {\it XY}, and the Heisenberg models in three dimensions. We found a
crossover from the critical dynamics to the ground-state dynamics in the Ising
model and the Heisenberg model. The ground-state dynamics of the Ising model is
characterized by an activation law with a finite energy gap: the typical time
diverges exponentially. On the other hand, the typical time in the Heisenberg
model diverges algebraically with the inverse temperature. Algebraic relaxation
with a finite dynamic exponent is observed after the typical time in both
models. The ground-state dynamic exponent is estimated to be $z_0\simeq 13$,
which is common to both models. There is no crossover in the {\it XY} model.
The critical dynamics is considered to continue to the ground-state.",0606181v1
2019-04-19,Experimental observation of dynamical bulk-surface correspondence for topological phases,"We experimentally demonstrate a dynamical classification approach for
investigation of topological quantum phases using a solid-state spin system
through nitrogen-vacancy (NV) center in diamond. Similar to the bulkboundary
correspondence in real space at equilibrium, we observe a dynamical
bulk-surface correspondence in the momentum space from a dynamical quench
process. An emergent dynamical topological invariant is precisely measured in
experiment by imaging the dynamical spin-textures on the recently defined
band-inversion surfaces, with high topological numbers being implemented.
Importantly, the dynamical classification approach is shown to be independent
of quench ways and robust to the decoherence effects, offering a novel and
practical strategy for dynamical topology characterization, especially for high
dimensional gapped topological phases.",1904.09065v1
2020-09-11,Classical Dynamics Generated by Long-Range Interactions for Lattice Fermions and Quantum Spins,"We study the macroscopic dynamical properties of fermion and quantum-spin
systems with long-range, or mean-field, interactions. The results obtained are
far beyond previous ones and require the development of a mathematical
framework to accommodate the macroscopic long-range dynamics, which corresponds
to an intricate combination of classical and short-range quantum dynamics. In
this paper we focus on the classical part of the long-range, or mean-field,
macroscopic dynamics, but we already introduce the full framework. The quantum
part of the macroscopic dynamics is studied in a subsequent paper. We show that
the classical part of the macroscopic dynamics results from self-consistency
equations within the (quantum) state space. As is usual, the classical dynamics
is driven by Liouville's equation.",2009.05315v1
2023-01-04,Reduced dynamics with Poincaré symmetry in an open quantum system,"We consider how the reduced dynamics of an open quantum system coupled to an
environment admits the Poincar\'e symmetry. The reduced dynamics is described
by a dynamical map, which is given by tracing out the environment from the
total unitary evolution without initial correlations. We investigate the
dynamical map which is invariant under the Poincar\'e group. Based on the
unitary representation theory of the Poincar\'e group, we develop a systematic
way to give such a dynamical map. Using this way, we derive the dynamical map
of a massive particle with a finite spin and a massless particle with a finite
spin and a nonzero momentum. The dynamical map of a spinless massive particle
is exemplified and the conservation of the Poincar\'e generators is discussed.
We then find the map with the Poincar\'e invariance and the four-momentum
conservation. Further, we show that the conservation of the angular momentum
and the boost operator makes the map of a spinless massive particle unitary",2301.01451v3
2020-06-29,"Octonions, trace dynamics and non-commutative geometry: a case for unification in spontaneous quantum gravity","We have recently proposed a new matrix dynamics at the Planck scale, building
on the theory of trace dynamics. This is a Lagrangian dynamics in which the
matrix degrees of freedom are made from Grassmann numbers, and the Lagrangian
is trace of a matrix polynomial. Matrices made from even grade elements of the
Grassmann algebra are called bosonic, and those made from odd grade elements
are called fermionic: together they describe an `aikyon'. In the present
article we provide a basic definition of spin angular momentum in this matrix
dynamics, and introduce a bosonic (fermionic) configuration variable conjugate
to the spin of a boson (fermion). We then show that at energies below Planck
scale, where the matrix dynamics reduces to quantum theory, fermions have
half-integer spin (in multiples of Planck's constant), and bosons have integral
spin. We also show that this definition of spin agrees with the conventional
understanding of spin in relativistic quantum mechanics. Consequently, we
obtain an elementary proof for the spin-statistics connection. We then motivate
why an octonionic space is the natural space in which an aikyon evolves. The
group of automorphisms in this space is the exceptional Lie group $G_2$ which
has fourteen generators [could they stand for the twelve vector bosons and two
degrees of freedom of the graviton? ]. The aikyon also resembles a closed
string, and it has been suggested in the literature that 10-D string theory can
be represented as a 2-D string in the 8-D octonionic space. From the work of
Cohl Furey and others it is known that the Dixon algebra made from the four
division algebras [real numbers, complex numbers, quaternions and octonions]
can possibly describe the symmetries of the standard model. In the present
paper we outline how in our work the Dixon algebra arises naturally, and could
lead to a unification of gravity with the standard model.",2006.16274v3
2000-05-16,Mesoscopic Spin Tunneling in Molecular Crystals,"The phenomenon of Quantum Tunneling of Mesoscopic Spins is reviewed in the
light of the behavior of the archetype of these systems: the molecular complex
Mn12-ac. Most observations can be understood in the framework of the reduced
Hilbert space dimension 2S+1=21. Due to the large spin S=10, the energy barrier
preventing spin rotation is large, and as a consequence, quantum relaxation is
very slow. The application of a magnetic field of a few Tesla below 1 K allows
to observe tunneling (i) between the states m=-10 and m=10-n with n=8 to 11 if
the field is longitudinal, or (ii) between the two ground-states m~-10 and m~10
if the field is transverse. The crossover temperature between ground-state and
thermally assisted tunneling in a longitudinal field extrapolates in zero field
at ~1.7 K. The observation of square root relaxation at
short-times/low-temperatures and of exponential relaxation at
long-times/high-temperatures, as observed previously above 1.5 K, confirms the
important role of the spin bath dynamics which is out of equilibrium in the
first regime and at equilibrium in the second one. In a second part of this
paper a new molecule, so-called V15, with resultant spin S=1/2 is investigated.
Contrary to high spin molecules, the energy barrier of low spin molecules is
small or null, and the splitting between the symmetrical and anti-symmetrical
states is sufficiently large to allow spin-phonon transitions during spin
rotation. In low spin molecules the coupling to the environment is quite
different from the one found in large spin molecules in low fields.",0005268v1
2008-03-13,Solid state quantum memory using the 31P nuclear spin,"The transfer of information between different physical forms is a central
theme in communication and computation, for example between processing entities
and memory. Nowhere is this more crucial than in quantum computation, where
great effort must be taken to protect the integrity of a fragile quantum bit.
Nuclear spins are known to benefit from long coherence times compared to
electron spins, but are slow to manipulate and suffer from weak thermal
polarisation. A powerful model for quantum computation is thus one in which
electron spins are used for processing and readout while nuclear spins are used
for storage. Here we demonstrate the coherent transfer of a superposition state
in an electron spin 'processing' qubit to a nuclear spin 'memory' qubit, using
a combination of microwave and radiofrequency pulses applied to 31P donors in
an isotopically pure 28Si crystal. The electron spin state can be stored in the
nuclear spin on a timescale that is long compared with the electron decoherence
time and then coherently transferred back to the electron spin, thus
demonstrating the 31P nuclear spin as a solid-state quantum memory. The overall
store/readout fidelity is about 90%, attributed to systematic imperfections in
radiofrequency pulses which can be improved through the use of composite
pulses. We apply dynamic decoupling to protect the nuclear spin quantum memory
element from sources of decoherence. The coherence lifetime of the quantum
memory element is found to exceed one second at 5.5K.",0803.2021v2
2017-06-13,"Evolution of Spin, Orbital, and Superorbital Modulations of 4U 0114+650","We report a systematic analysis of the spin, orbital, and superorbital
modulations of 4U 0114+650, a high-mass X-ray binary consists of one of the
slowest spinning neutron stars. Utilizing the dynamic power spectrum, we found
that the spin period varied dramatically and anti-correlated with the long-term
X-ray flux variation that can be observed using RXTE ASM, Swift BAT, and MAXI.
The spin-up rate over the entire dataset is consistent with previously reported
values; however, the local spin-up rate is considerably higher. The
corresponding local spin-up timescale is comparable to the local spin-up rate
of OAO 1657-415, indicating that 4U 0114+650 could also have a transient disk.
Moreover, the spin period evolution shows two ~1000-day spin-down/random-walk
epochs that appeared together with depressions of the superorbital modulation
amplitude. This implies that the superorbital modulation was closely related to
the presence of the accretion disk, which is not favored in the
spin-down/random-walk epochs because the accretion is dominated by the direct
wind accretion.The orbital period is stable during the entire time span;
however, the orbital profile changes with time significantly. We found that the
depth of the dip near the inferior conjunction of the companion is highly
variable, which disfavors the eclipsing scenario. Moreover, the dip was less
obvious during the spin-down/random-walk epochs, indicating its correlation
with the accretion disk. Further monitoring in both X-ray and optical bands
could reveal the establishment of the accretion disk in this system.",1706.03902v2
2019-12-19,Magnon-driven chiral charge and spin pumping and electron-magnon scattering from time-dependent quantum transport combined with atomistic spin dynamics theory,"Using newly developed quantum-classical hybrid framework, we investigate
interaction between spin-polarized conduction electrons and a single spin wave
(SW) coherently excited within a metallic ferromagnetic nanowire. When the
nanowire hosting SW is attached to two normal metal (NM) leads, with no dc bias
voltage applied between them, the SW pumps chiral electronic charge and spin
currents into the leads---their direction is tied to the direction of SW
propagation and they scale linearly with the frequency of the precession. This
is in contrast to: standard pumping by the uniform precession mode with
identical spin currents flowing in both directions and no accompanying charge
current; or experimentally observed [C.~Ciccarelli et al., Nat. Nanotech. 10,
50 (2014); M.~Evelt et al., Phys. Rev. B 95, 024408 (2017)] magnonic charge
pumping which requires spin-orbit coupling spin-orbit coupling. The mechanism
behind our prediction is nonadiabaticity due to time-retardation
effects---motion of localized magnetic moment affects conduction electron spin
in a retarded way, so that it takes a finite time until the electron spin
reacts to the motion of the classical vector. Upon injecting dc spin-polarized
charge current from the left NM lead, electrons interact with SW where
outflowing charge and spin current into the right NM lead are changed due to
both scattering off time-dependent potential generated by the SW and
superposition with the currents pumped by the SW itself. Using Lorentzian
voltage pulse to excite leviton out of the Fermi sea, which carries one
electron charge with no accompanying electron-hole pairs and behaves as
soliton-like quasiparticle, we describe how a single electron interacts with a
single SW.",1912.09452v2
2020-09-16,Entanglement robustness and spin relaxation in thermal states of two-dimensional dissipative spin system in an inhomogeneous magnetic field,"We consider a finite two-dimensional Heisenberg triangular spin lattice at
different degrees of anisotropy coupled to a dissipative Lindblad environment
obeying the Born-Markovian constrain at finite temperature. We show how
applying an inhomogeneous magnetic field to the system may significantly affect
the entanglement distribution and properties among the spins in the asymptotic
steady state of the system. Particularly, applying an inhomogeneous field with
an inward (growing) gradient toward the central spin is found to considerably
enhance the nearest neighbor entanglement and its robustness to the thermal
dissipative decay effect in the completely anisotropic (Ising) system, whereas
all the beyond nearest neighbor entanglements vanish entirely. Applying the
same field to a partially anisotropic (XYZ) system, does not only enhance the
nearest neighbor entanglements and their robustness but also all the beyond
nearest neighbor ones. Nevertheless, the inhomogeneity of the field shows no
effect on the asymptotic behavior of the entanglement in the isotropic (XXX)
system, which vanishes under any system configuration. Moreover, the same
inhomogeneous field exhibits the most influential impact, compared with the
other ones, on the the spin dynamics as well. Although in the isotropic system
the spins relax to a separable (disentangled) steady state with all the spins
reaching a common spin state regardless of the field inhomogeneity, the spins
in the steady state of the completely anisotropic system reach different
distinguished spin states depending on their positions in the lattice. However,
in the XYZ system, though the anisotropy is lower, the spin states become even
more distinguished, accompanying the long range quantum correlation across the
system, which is a sign of a critical behavior taking place at this combination
of system anisotropy and field inhomogeneity.",2009.07878v1
2021-07-27,Quantum control of nuclear spin qubits in a rapidly rotating diamond,"Nuclear spins in certain solids couple weakly to their environment, making
them attractive candidates for quantum information processing and inertial
sensing. When coupled to the spin of an optically-active electron, nuclear
spins can be rapidly polarized, controlled and read via lasers and
radiofrequency fields. Possessing coherence times of several milliseconds at
room temperature, nuclear spins hosted by a nitrogen-vacancy center in diamond
are thus intriguing systems to observe how classical physical rotation at
quantum timescales affects a quantum system. Unlocking this potential is
hampered by precise and inflexible constraints on magnetic field strength and
alignment in order to optically induce nuclear polarization, which restricts
the scope for further study and applications. In this work, we demonstrate
optical nuclear spin polarization and rapid quantum control of nuclear spins in
a diamond physically rotating at $1\,$kHz, faster than the nuclear spin
coherence time. Free from the need to maintain strict field alignment, we are
able to measure and control nuclear spins in hitherto inaccessible regimes,
such as in the presence of a large, time-varying magnetic field that makes an
angle of more than $100^\circ$ to the nitrogen-lattice vacancy axis. The field
induces spin mixing between the electron and nuclear states of the qubits,
decoupling them from oscillating rf fields. We are able to demonstrate that
coherent spin state control is possible at any point of the rotation, and even
for up to six rotation periods. We combine continuous dynamical decoupling with
quantum feedforward control to eliminate decoherence induced by imperfect
mechanical rotation. Our work liberates a previously inaccessible degree of
freedom of the NV nuclear spin, unlocking new approaches to quantum control and
rotation sensing.",2107.12577v1
2021-08-14,"Relativistic Mechanics Theory for Electrons that Exhibits Spin, Zitterbewegung, Superposition and Produces Dirac's Wave Equation","A neo-classical relativistic mechanics theory is presented where the spin of
an electron is a natural part of its space-time path as a point particle. The
fourth-order equation of motion corresponds to the same Lagrangian function in
proper time as in special relativity except for an additional spin energy term.
The total motion can be decomposed into a sum of a local spin motion about a
point and a global motion of this point, called the spin center. The global
motion is sub-luminal and obeys Newton's second law in proper time, the time
for a clock fixed at the spin center, while the total motion occurs at the
speed of light c, consistent with the eigenvalues of Dirac's velocity operators
having magnitude c. The local spin motion corresponds to Schr\""odinger's
zitterbewegung and is a perpetual motion, which for a free electron has a
circular path in the spin-center frame. In an electro-magnetic field, this spin
motion generates magnetic and electric dipole energies through the Lorentz
force on the electron's point charge. The corresponding electric dipole energy
is consistent with the spin-orbit coupling term in the corrected Pauli
non-relativistic Hamiltonian but the magnetic dipole energy is one half of that
in Dirac's theory. By defining a spin tensor as the angular momentum of the
electron's total motion about its spin center, the fundamental equations of
motion can be re-written in an identical form to those of the Barut-Zanghi
electron theory. These equations of motion can then be expressed using
operators applied to a state function of proper time satisfying a
Dirac-Schr\""odinger spinor equation. The operators produce dynamic variables
without any probability implications. For the free electron, the state function
satisfies Dirac's relativistic wave equation when the Lorentz transformation is
applied to express proper time in terms of an observer's space-time
coordinates.",2108.07267v3
2022-10-01,"Spin and quadrupolar effects in the secular evolution of precessing compact binaries with black hole, neutron star, gravastar, or boson star components","We discuss precessing compact binaries on eccentric orbit with gravastar,
black hole, neutron star, or boson star components. We derive secular evolution
equations to second post-Newtonian--order accuracy, with leading-order
spin-orbit, spin-spin, and mass quadrupole-monopole contributions. The emerging
closed system of first-order differential equations evolves the pairs of polar
and azimuthal angles of the spin and orbital angular momentum vectors together
with the periastron angle. The secular dynamics is autonomous. We confirm
numerically, that secular evolutions look like smoothed-out instantaneous
evolutions over timescales where radiation reaction is negligible. The secular
evolution of the spin polar angles and the difference of their azimuthal angles
generates a closed subsystem. We study analytically this system for the
particular cases of one spin dominating over the other and for black hole -
boson star binaries of equal masses. In the first case known large flip-flops
of the smaller spin are reproduced, when the larger spin is almost coplanar
with the orbit. We also find new, quadrupole-induced flip-flops occurring when
the neutron star with dominant spin has a quadrupolar parameter $w_1\approx 3$.
Finally we analyze the evolutions of the spin angles numerically by comparing
the cases when the black hole companion is either a gravastar, another black
hole or a boson star with identical mass. We find that both the amplitude and
period of the flip-flop are the largest, when the companion is a black hole. In
the case of a boson star companion the frequency of the flip-flop increases
significantly. Further, while in the case of gravastars and black holes a
swinging-type azimuthal evolution occurs, with the spins of the components
periodically overpassing each other, their sequence is conserved when the
companion is a boson star.",2210.00284v1
2023-10-24,Revisiting spin ice physics in the ferromagnetic Ising pyrochlore Pr$_2$Sn$_2$O$_7$,"Pyrochlore materials are characterized by their hallmark network of
corner-sharing rare-earth tetrahedra, which can produce a wide array of complex
magnetic ground states. Ferromagnetic Ising pyrochlores often obey the
""two-in-two-out"" spin ice rules, which can lead to a highly-degenerate spin
structure. Large moment systems, such as Ho$_2$Ti$_2$O$_7$ and
Dy$_2$Ti$_2$O$_7$, tend to host a classical spin ice state with low-temperature
spin freezing and emergent magnetic monopoles. Systems with smaller effective
moments, such as Pr$^{3+}$-based pyrochlores, have been proposed as excellent
candidates for hosting a ""quantum spin ice"" characterized by entanglement and a
slew of exotic quasiparticle excitations. However, experimental evidence for a
quantum spin ice state has remained elusive. Here, we show that the
low-temperature magnetic properties of Pr$_2$Sn$_2$O$_7$ satisfy several
important criteria for continued consideration as a quantum spin ice. We find
that Pr$_2$Sn$_2$O$_7$ exhibits a partially spin-frozen ground state with a
large volume fraction of dynamic magnetism. Our comprehensive bulk
characterization and neutron scattering measurements enable us to map out the
magnetic field-temperature phase diagram, producing results consistent with
expectations for a ferromagnetic Ising pyrochlore. We identify key hallmarks of
spin ice physics, and show that the application of small magnetic fields
($\mu_0 H_c \sim$0.75T) suppresses the spin ice state and induces a long-range
ordered magnetic structure. Together, our work clarifies the current state of
Pr$_2$Sn$_2$O$_7$ and encourages future studies aimed at exploring the
potential for a quantum spin ice ground state in this system.",2310.16180v1
1996-04-20,Spin Fluctuations in Magnetically Coupled Bi-layer Cuprates,"We propose a possible mechanism of pseudo spin gap anomaly(PSGA) in
magnetically coupled bi-layer cuprates without any fermion pairing instability.
In our proposal PSGA does not necessarily require the spin-charge separation or
the breakdown of the Fermi liquid description of a normal state of the cuprate
superconductor.The low energy magnetic excitations are mainly governed by the
{\it itinerant nature of the intra-layer system} and {\it the inter-layer
antiferromagnetic coupling}. No matter how weak the bare inter-layer coupling
is, it can be dramatically enhanced due to the intra-layerspin fluctuations. As
the temperature decreases near the antiferromagnetic phase boundary the
strongly enhanced inter-layer correlation induces the inter-layer particle-hole
exchange scattering processes that tend to enhance the inter-layer spin singlet
formation and kill the triplet formation. We propose that the coupling of spin
fluctuations on the adjacend layers via the strong repulsive interaction
between parallel spins travelling on each layer give rise to the dynamical
screening effects. As a result the low energy part of the spin excitation
spectrum is strongly suppressed as the temperature decreases near the
antiferromagnetic phase boundary. We ascribe PSGA to this dynamical screening
effects.",9604128v3
1998-04-29,"Magnetic correlations and quantum criticality in the insulating antiferromagnetic, insulating spin liquid, renormalized Fermi liquid, and metallic antiferromagnetic phases of the Mott system V_2O_3","Magnetic correlations in all four phases of pure and doped vanadium
sesquioxide V_2O_3 have been examined by magnetic thermal neutron scattering.
While the antiferromagnetic insulator can be accounted for by a Heisenberg
localized spin model, the long range order in the antiferromagnetic metal is an
incommensurate spin-density-wave, resulting from a Fermi surface nesting
instability. Spin dynamics in the strongly correlated metal are dominated by
spin fluctuations in the Stoner electron-hole continuum. Furthermore, our
results in metallic V_2O_3 represent an unprecedentedly complete
characterization of the spin fluctuations near a metallic quantum critical
point, and provide quantitative support for the SCR theory for itinerant
antiferromagnets in the small moment limit. Dynamic magnetic correlations for
energy smaller than k_BT in the paramagnetic insulator carry substantial
magnetic spectral weight. However, the correlation length extends only to the
nearest neighbor distance. The phase transition to the antiferromagnetic
insulator introduces a sudden switching of magnetic correlations to a different
spatial periodicity which indicates a sudden change in the underlying spin
Hamiltonian. To describe this phase transition and also the unusual short range
order in the paramagnetic state, it seems necessary to take into account the
orbital degrees of freedom associated with the degenerate d-orbitals at the
Fermi level in V_2O_3.",9804320v3
2001-04-26,"Bond operator theory of doped antiferromagnets: from Mott insulators with bond-centered charge order, to superconductors with nodal fermions","The ground states and excitations of two-dimensional insulating and doped
Mott insulators are described by a bond operator formalism. While the method
represents the degrees of freedom of an arbitrary antiferromagnet exactly, it
is especially suited to systems in which there is a natural pairing of sites
into bonds, as in states with spontaneous or explicit spin-Peierls order (or
bond-centered charge order). In the undoped insulator, as discussed previously,
we obtain both paramagnetic and magnetically-ordered states. We describe the
evolution of superconducting order in the ground state with increasing
doping--at low doping, the superconductivity is weak, can co-exist with
magnetic order, and there are no gapless spin 1/2 fermionic excitations; at
high doping, the magnetic order is absent and we obtain a BCS d-wave
superconductor with gapless spin 1/2, nodal fermions. We present the critical
theory describing the onset of these nodal fermionic excitations. We discuss
the evolution of the spin spectrum, and obtain regimes where a spin 1 exciton
contributes a sharp resonance in the dynamic spin susceptiblity. We also
discuss the experimental consequences of low-energy, dynamically fluctuating,
spin-Peierls order in an isotropic CuO_2 plane--we compute consequences for the
damping and dispersion of an optical phonon involving primarily the O ions, and
compare the results with recent neutron scattering measurements of phonon
spectra.",0104519v4
2004-10-25,Spin Dynamics of Half-Doped La3/2Sr1/2NiO4,"We report polarized- and unpolarized- neutron inelastic scattering
measurements of the magnetic excitation spectrum in the spin-charge ordered
phase of La3/2Sr1/2NiO4. Up to energies of ~30 meV we observe broad magnetic
modes characteristic of a near checkerboard ordering. A linear spin-wave model
for an ideal checkerboard ordering with a single antiferromagnetic exchange
interaction J' = 5.8 +/- 0.5 meV between next-nearest-neighbour spins on Ni2+
sites, together with a small XY-like single-ion anisotropy, provides a
reasonable description of the measured dispersion. Above 30 meV the excitations
are not fully consistent with the linear spin-wave model, with modes near the
two-dimensional reciprocal space wavevector (0.5,0.5) having an anomalously
large intensity. Furthermore, two additional dispersive modes not predicted by
spin wave theory were observed, both of which are probably magnetic. One
disperses away from (0.5,0.5) in the energy range between 50-56 meV, and the
other appears around (h,k) type positions (h,k = integer) in the energy range
31-39 meV. We propose a model in which these anomalous features are explained
by the existence of discommensurations in the checkerboard ordering. At low
energies there is additional diffuse scattering centred on the magnetic
ordering wavevector. We associate this diffuse scattering with dynamic
antiferromagnetic correlations between spins attached to the doped holes.",0410636v1
2005-02-14,1/S-expansion study of spin waves in a two-dimensional Heisenberg antiferromagnet,"We study the effects of quantum fluctuations on excitation spectra in the
two-dimensional Heisenberg antiferromagnet by means of the 1/S expansion. We
calculate the spin-wave dispersion and the transverse dynamical structure
factor up to the second order of 1/S in comparison with inelastic neutron
scattering experiments. The spin-wave energy at momentum $(\pi,0)$ is found to
be about 2% smaller than that at $(\pi/2,\pi/2)$ due to the second-order
correction. In addition, we study the dimensional crossover from two dimensions
to one dimension by weakening exchange couplings in one direction. It is found
that the second-order correction becomes large with approaching the quasi-one
dimensional situation and makes the spin-wave energy approach to the des
Cloizeaux-Pearson boundary for $S=1/2$. The transverse dynamical structure
factor is also calculated up to the second order of 1/S. It is shown that the
intensity of spin-wave peak is strongly reduced while the intensity of
three-spin-wave continuum becomes large and exceeds that of the spin-wave peak
in the quasi-one dimensional situation.",0502318v2
2005-07-29,Frustrated two-level impurities in two-dimensional antiferromagnets,"Dynamical properties of the impurity spin-$\frac12$ in 2D and quasi-2D
Heisenberg antiferromagnets (AFs) at $T\ge0$ are discussed. The specific case
of an impurity coupled symmetrically to two neighboring host spins is
considered. The specific feature of this problem is that the defect is
degenerate (frustrated) being located in zero molecular field. It is shown that
this problem can be described by spin-boson model without tunneling term and
with a more complex interaction. We demonstrate that the effect of the host
system on the defect is completely described by the spectral function. It is
found within the spin-wave approximation that for not too small $\omega$ the
spectral function is proportional to $\omega^2/J^3$, where $J$ is the exchange
constant between the host spins. The defect dynamical susceptibility is derived
using Abrikosov's pseudofermion technique and diagrammatic expansion. The
calculations are performed within the fourth order of the dimensionless
coupling parameter $f$. It is found that transverse impurity susceptibility
$\chi_\perp(\omega)$ has a Lorenz peak with the width proportional to
$f^4J(T/J)^3$ which disappears at T=0, and a non-resonant term. The later term
diverges logarithmically as $\omega,T \to 0$. The static susceptibility
$\chi(0)$ has the free-spin-like contribution $1/(4T)$, and a logarithmic
correction proportional to $f^2\ln(J/T)$. The influence of finite concentration
of the defects $n$ on the low-temperature properties of AF is also
investigated. A logarithmic correction to spin-wave velocity of the form
$nf^4\ln|J/\omega|$ and an anomalous damping of spin waves proportional to
$nf^4|\omega|$ are obtained.",0507704v2
2004-07-25,The dynamics of precessing binary black holes using the post-Newtonian approximation,"We investigate the (conservative) dynamics of binary black holes using the
Hamiltonian formulation of the post-Newtonian (PN) equations of motion. The
Hamiltonian we use includes spin-orbit coupling, spin-spin coupling, and mass
monopole/spin-induced quadrupole interaction terms. In the case of both
quasi-circular and eccentric orbits, we search for the presence of chaos (using
the method of Lyapunov exponents) for a large variety of initial conditions.
For quasi-circular orbits, we find no chaotic behavior for black holes with
total mass 10 - 40 solar masses when initially at a separation corresponding to
a Newtonian gravitational-wave frequency less than 150 Hz. Only for rather
small initial radial distances, for which spin-spin induced oscillations in the
radial separation are rather important, do we find chaotic solutions, and even
then they are rare. Moreover, these chaotic quasi-circular orbits are of
questionable astrophysical significance, since they originate from direct
parametrization of the equations of motion rather than from widely separated
binaries evolving to small separations under gravitational radiation reaction.
In the case of highly eccentric orbits, which for ground-based interferometers
are not astrophysically favored, we again find chaotic solutions, but only at
pericenters so small that higher order PN corrections, especially higher spin
PN corrections, should also be taken into account.",0407091v2
2006-12-14,Quantum dynamics of double-qubits in a spin star lattice with an XY interaction,"The dynamics of two coupled spins-1/2 interacting with a spin-bath via the
quantum Heisenberg XY coupling is studied. The pair of central spins served as
a quantum open subsystem are initially prepared in two types of states: the
product states and the Bell states. The bath, which consists of $N$ (in the
thermodynamic limit $N\to\infty$) mutually coupled spins-1/2, is in a thermal
state at the beginning. By the Holstein-Primakoff transformation, the model can
be treated effectively as two spin qubits embedded in a single mode cavity. The
time-evolution of the purity, z-component summation and the concurrence of the
central spins can be determined by a Laguerre polynomial scheme. It is found
that (i) at a low temperature, the uncoupled subsystem in a product state can
be entangled due to the interaction with bath, which is tested by the
Peres-Horodecki separability; however, at a high temperature, the bath produces
a stronger destroy effect on the purity and entanglement of the subsystem; (ii)
when the coupling strength between the two central spins is large, they are
protected strongly against the bath; (iii) when the interaction between the
subsystem and the bath is strong, the collapse of the two spin qubits from
their initial entangled state is fast.",0612115v2
2008-11-24,Dynamics of Black Hole Pairs II: Spherical Orbits and the Homoclinic Limit of Zoom-Whirliness,"Spinning black hole pairs exhibit a range of complicated dynamical behaviors.
An interest in eccentric and zoom-whirl orbits has ironically inspired the
focus of this paper: the constant radius orbits. When black hole spins are
misaligned, the constant radius orbits are not circles but rather lie on the
surface of a sphere and have acquired the name ""spherical orbits"". The
spherical orbits are significant as they energetically frame the distribution
of all orbits. In addition, each unstable spherical orbit is asymptotically
approached by an orbit that whirls an infinite number of times, known as a
homoclinic orbit. A homoclinic trajectory is an infinite whirl limit of the
zoom-whirl spectrum and has a further significance as the separatrix between
inspiral and plunge for eccentric orbits. We work in the context of two
spinning black holes of comparable mass as described in the 3PN Hamiltonian
with spin-orbit coupling included. As such, the results could provide a testing
ground of the accuracy of the PN expansion. Further, the spherical orbits could
provide useful initial data for numerical relativity. Finally, we comment that
the spinning black hole pairs should give way to chaos around the homoclinic
orbit when spin-spin coupling is incorporated.",0811.3798v1
2009-07-21,Normal-State Spin Dynamics and Temperature-Dependent Spin Resonance Energy in an Optimally Doped Iron Arsenide Superconductor,"The proximity of superconductivity and antiferromagnetism in the phase
diagram of iron arsenides, the apparently weak electron-phonon coupling and the
""resonance peak"" in the superconducting spin excitation spectrum have fostered
the hypothesis of magnetically mediated Cooper pairing. However, since most
theories of superconductivity are based on a pairing boson of sufficient
spectral weight in the normal state, detailed knowledge of the spin excitation
spectrum above the superconducting transition temperature Tc is required to
assess the viability of this hypothesis. Using inelastic neutron scattering we
have studied the spin excitations in optimally doped BaFe1.85Co0.15As2 (Tc = 25
K) over a wide range of temperatures and energies. We present the results in
absolute units and find that the normal state spectrum carries a weight
comparable to underdoped cuprates. In contrast to cuprates, however, the
spectrum agrees well with predictions of the theory of nearly antiferromagnetic
metals, without complications arising from a pseudogap or competing
incommensurate spin-modulated phases. We also show that the temperature
evolution of the resonance energy follows the superconducting energy gap, as
expected from conventional Fermi-liquid approaches. Our observations point to a
surprisingly simple theoretical description of the spin dynamics in the iron
arsenides and provide a solid foundation for models of magnetically mediated
superconductivity.",0907.3632v1
2010-06-08,Engineering Long Range Distance Independent Entanglement through Kondo Impurities in Spin Chains,"We investigate the entanglement properties of the Kondo spin chain when it is
prepared in its ground state as well as its dynamics following a single bond
quench. We show that a true measure of entanglement such as negativity enables
to characterize the unique features of the gapless Kondo regime. We determine
the spatial extent of the Kondo screening cloud and propose an ansatz for the
ground state in the Kondo regime accessible to this spin chain; we also
demonstrate that the impurity spin is indeed maximally entangled with the Kondo
cloud. We exploit these features of the entanglement in the gapless Kondo
regime to show that a single local quench at one end of a Kondo spin chain may
always induce a fast and long lived oscillatory dynamics, which establishes a
high quality entanglement between the individual spins at the opposite ends of
the chain. This entanglement is a footprint of the presence of the Kondo cloud
and may be engineered so as to attain - even for very large chains- a constant
high value independent of the length; in addition, it is thermally robust. To
better evidence the remarkable peculiarities of the Kondo regime, we carry a
parallel analysis of the entanglement properties of the Kondo spin chain model
in the gapped dimerised regime where these remarkable features are absent.",1006.1422v1
2010-11-29,Effect of pulse error accumulation on dynamical decoupling of the electron spins of phosphorus donors in silicon,"Dynamical decoupling (DD) is an efficient tool for preserving quantum
coherence in solid-state spin systems. However, the imperfections of real
pulses can ruin the performance of long DD sequences. We investigate the
accumulation and compensation of different pulse errors in DD using the
electron spins of phosphorus donors in silicon as a test system. We study
periodic DD sequences (PDD) based on spin rotations about two perpendicular
axes, and their concatenated and symmetrized versions. We show that pulse
errors may quickly destroy some spin states, but maintain other states with
high fidelity over long times. Pulse sequences based on spin rotations about
$x$ and $y$ axes outperform those based on $x$ and $z$ axes due to the
accumulation of pulse errors. Concatenation provides an efficient way to
suppress the impact of pulse errors, and can maintain high fidelity for all
spin components: pulse errors do not accumulate (to first order) as the
concatenation level increases, despite the exponential increase in the number
of pulses. Our theoretical model gives a clear qualitative picture of the error
accumulation, and produces results in quantitative agreement with the
experiments.",1011.6417v2
2012-10-01,51V-NMR study of antiferromagnetic state and spin dynamics in the quasi-one-dimensional BaCo2V2O8,"We report on our 51V-NMR study of static and dynamical magnetic properties in
the quasi-one-dimensional antiferromagnet BaCo2V2O8. Although the NMR spectrum
shows well-defined antiferromagnetic (AF) order in the N\'eel ground state, the
AF characteristic from the NMR spectrum is incomplete between 3.5 K and TN= 5.4
K, which could be affected by quantum spin fluctuations. The AF NMR spectrum
indicates two V sites experiencing different magnetic field magnitudes, HA1=2.1
kOe and HA2=3.8 kOe. These internal fields could be explained by accounting for
the classical and the pseudo-dipolar fields from Co2+ spins with a proposed
magnetic structure based on the neutron diffraction measurements. In the
paramagnetic state, the nuclear spin relaxation is dominated by AF spin
fluctuations through the dipolar-type coupling between V and surrounding Co2+
ions. The linear relation between the nuclear spin-lattice relaxation rate
1/T1T and the magnetic susceptibility chi indicates that the Q component of
magnetic susceptibility chi(Q) is roughly proportional to chi, where Q is the
AF wave number. A change in slope of 1/T1T with respect to \chi around 150 K
suggests a change in the AF spin fluctuation spectrum.",1210.0272v1
2013-11-18,Mergers of binary neutron stars with realistic spin,"Simulations of binary neutron stars have seen great advances in terms of
physical detail and numerical quality. However, the spin of the neutron stars,
one of the simplest global parameters of binaries, remains mostly unstudied. We
present the first, fully nonlinear general relativistic dynamical evolutions of
the last three orbits for constraint satisfying initial data of spinning
neutron star binaries, with astrophysically realistic spins aligned and
anti-aligned to the orbital angular momentum. The initial data is computed with
the constant rotational velocity approach. The dynamics of the systems is
analyzed in terms of gauge-invariant binding energy vs. orbital angular
momentum curves. By comparing to a binary black hole configuration we can
estimate the different tidal and spin contributions to the binding energy for
the first time. First results on the gravitational wave forms are presented.
The phase evolution during the orbital motion is significantly affected by
spin-orbit interactions, leading to delayed or early mergers. Furthermore, a
frequency shift in the main emission mode of the hyper massive neutron star is
observed. Our results suggest that a detailed modeling of merger waveforms
requires the inclusion of spin, even for the moderate magnitudes observed in
binary neutron star systems.",1311.4443v2
2013-12-04,Long-lived selective spin echoes in dipolar solids under periodic and aperiodic pi-pulse trains,"The application of Carr-Purcell-Meiboom-Gill (CPMG) $\pi-$trains for
dynamically decoupling a system from its environment has been extensively
studied in a variety of physical systems. When applied to dipolar solids,
recent experiments have demonstrated that CPMG pulse trains can generate
long-lived spin echoes. While there still remains some controversy as to the
origins of these long-lived spin echoes under the CPMG sequence, there is a
general agreement that pulse errors during the $\pi-$pulses are a necessary
requirement. In this work, we develop a theory to describe the spin dynamics in
dipolar coupled spin-1/2 system under a CPMG($\phi_{1},\phi_{2}$) pulse train,
where $\phi_{1}$ and $\phi_{2}$ are the phases of the $\pi-$pulses. From our
theoretical framework, the propagator for the CPMG($\phi_{1},\phi_{2}$) pulse
train is equivalent to an effective ``pulsed'' spin-locking of single-quantum
coherences with phase $\pm\frac{\phi_{2}-3\phi_{1}}{2}$, which generates a
periodic quasiequilibrium that corresponds to the long-lived echoes. Numerical
simulations, along with experiments on both magnetically dilute, random spin
networks found in C$_{60}$ and C$_{70}$ and in non-dilute spin systems found in
adamantane and ferrocene, were performed and confirm the predictions from the
proposed theory.",1312.0996v1
2014-12-01,Experimental and Numerical Understanding of Localized Spin Wave Mode Behavior in Broadly Tunable Spatially Complex Magnetic Configurations,"Spin wave modes confined in a ferromagnetic film by the spatially
inhomogeneous magnetic field generated by a scanned micromagnetic tip of a
ferromagnetic resonance force microscope (FMRFM) enable microscopic imaging of
the internal fields and spin dynamics in nanoscale magnetic devices. Here we
report a detailed study of spin wave modes in a thin ferromagnetic film
localized by magnetic field configurations frequently encountered in FMRFM
experiments, including geometries in which the probe magnetic moment is both
parallel and antiparallel to the applied uniform magnetic field. We demonstrate
that characteristics of the localized modes, such as resonance field and
confinement radius, can be broadly tuned by controlling the orientation of the
applied field relative to the film plane. Micromagnetic simulations accurately
reproduce our FMRFM spectra allowing quantitative understanding of the
localized modes. Our results reveal a general method of generating tightly
confined spin wave modes in various geometries with excellent spatial
resolution that significantly facilitates the broad application of FMRFM. This
paves the way to imaging of magnetic properties and spin wave dynamics in a
variety of contexts for uncovering new physics of nanoscale spin excitations.",1412.0726v1
2015-03-24,Micro-focused Brillouin light scattering study of the magnetization dynamics driven by Spin Hall effect in a transversely magnetized NiFe nanowire,"We employed micro-focused Brillouin light scattering to study the
amplification of the thermal spin wave eigenmodes by means of a pure spin
current, generated by the spin-Hall effect, in a transversely magnetized
Pt(4nm)/NiFe(4nm)/SiO2(5nm) layered nanowire with lateral dimensions 500x2750
nm2. The frequency and the cross section of both the center (fundamental) and
the edge spin wave modes have been measured as a function of the intensity of
the injected dc electric current. The frequency of both modes exhibits a clear
redshift while their cross section is greatly enhanced on increasing the
intensity of the injected dc. A threshold-like behavior is observed for a value
of the injected dc of 2.8 mA. Interestingly an additional mode, localized in
the central part of the nanowire, appears at higher frequency on increasing the
intensity of the injected dc above the threshold value. Micromagnetic
simulations were used to quantitatively reproduce the experimental results and
to investigate the complex non-linear dynamics induced by the spin-Hall effect,
including the modification of the spatial profile of the spin wave modes and
the appearance of the extra mode above the threshold.",1503.06968v1
2015-05-04,Optimizing a Dynamical Decoupling Protocol for Solid-State Electronic Spin Ensembles in Diamond,"We demonstrate significant improvements of the spin coherence time of a dense
ensemble of nitrogen-vacancy (NV) centers in diamond through optimized
dynamical decoupling (DD). Cooling the sample down to $77$ K suppresses
longitudinal spin relaxation $T_1$ effects and DD microwave pulses are used to
increase the transverse coherence time $T_2$ from $\sim 0.7$ ms up to $\sim 30$
ms. We extend previous work of single-axis (CPMG) DD towards the preservation
of arbitrary spin states. Following a theoretical and experimental
characterization of pulse and detuning errors, we compare the performance of
various DD protocols. We identify that the optimal control scheme for
preserving an arbitrary spin state is a recursive protocol, the concatenated
version of the XY8 pulse sequence. The improved spin coherence might have an
immediate impact on improvements of the sensitivities of AC magnetometry.
Moreover, the protocol can be used on denser diamond samples to increase
coherence times up to NV-NV interaction time scales, a major step towards the
creation of quantum collective NV spin states.",1505.00636v3
2016-03-31,Dynamical spin properties of confined Fermi and Bose systems in presence of spin-orbit coupling,"Due to the recent experimental progress, tunable spin-orbit (SO) interactions
represent ideal candidates for the control of polarization and dynamical spin
properties in both quantum wells and cold atomic systems. A detailed
understanding of spin properties in SO coupled systems is thus a compelling
prerequisite for possible novel applications or improvements in the context of
spintronics and quantum computers. Here we analyze the case of equal Rashba and
Dresselhaus couplings in both homogeneous and laterally confined
two-dimensional systems. Starting from the single-particle picture and
subsequently introducing two-body interactions we observe that periodic spin
fluctuations can be induced and maintained in the system. Through an analytical
derivation we show that the two-body interaction does not involve decoherence
effects in the bosonic dimer, and, in the repulsive homogeneous Fermi gas it
may be even exploited in combination with the SO coupling to induce and tune
standing currents. By further studying the effects of a harmonic lateral
confinement --a particularly interesting case for Bose condensates-- we
evidence the possible appearance of non-trivial {\it spin textures}, whereas
the further application of a small Zeeman-type interaction can be exploited to
fine-tune the system polarizability.",1603.09604v1
2017-08-24,Black Hole Spin Axis in Numerical Relativity,"Colliding black holes are systems of profound interest in both gravitational
wave astronomy and in gravitation theory, and a variety of methods have been
developed for modeling their dynamics in detail. The features of these dynamics
are determined by the masses of the holes and by the magnitudes and axes of
their spins. While masses and spin magnitudes can be defined in reasonably
unambiguous ways, the spin axis is a concept which despite great physical
importance is seriously undermined by the coordinate freedom of general
relativity. Despite a great wealth of detailed numerical simulations of generic
spinning black hole collisions, very little attention has gone into defining or
justifying the definitions of the spin axis used in the numerical relativity
literature. In this paper, we summarize and contrast the various spin direction
measures available in the SpEC code, including a comparison with a method
common in other codes, we explain why these measures have shown qualitatively
different nutation features than one would expect from post-Newtonian theory,
and we derive and implement new measures that give much better agreement.",1708.07325v2
2018-11-05,A Bound on Massive Higher Spin Particles,"According to common lore, massive elementary higher spin particles lead to
inconsistencies when coupled to gravity. However, this scenario was not
completely ruled out by previous arguments. In this paper, we show that in a
theory where the low energy dynamics of the gravitons are governed by the
Einstein-Hilbert action, any finite number of massive elementary particles with
spin more than two cannot interact with gravitons, even classically, in a way
that preserves causality. This is achieved in flat spacetime by studying
eikonal scattering of higher spin particles in more than three spacetime
dimensions. Our argument is insensitive to the physics above the effective
cut-off scale and closes certain loopholes in previous arguments. Furthermore,
it applies to higher spin particles even if they do not contribute to
tree-level graviton scattering as a consequence of being charged under a global
symmetry such as $\mathbb{Z}_2$. We derive analogous bounds in anti-de Sitter
spacetime from analyticity properties of correlators of the dual CFT in the
Regge limit. We also argue that an infinite tower of fine-tuned higher spin
particles can still be consistent with causality. However, they necessarily
affect the dynamics of gravitons at an energy scale comparable to the mass of
the lightest higher spin particle. Finally, we apply the bound in de Sitter to
impose restrictions on the structure of three-point functions in the squeezed
limit of the scalar curvature perturbation produced during inflation.",1811.01952v2
2018-11-30,Spin excitation spectra of the two dimensional $S=1/2$ Heisenberg model with a checkerboard structure,"We study the spin excitation spectra of the two-dimensional spin-$1/2$
Heisenberg model with a checkerboard structures using stochastic analytic
continuation of the imaginary-time correlation function obtained from a quantum
Monte Carlo simulation. The checkerboard models have two different
antiferromagnetic nearest-neighbor interactions $J_{1}$ and $J_{2}$, and the
tuning parameter $g$ is defined as $J_{2}/J_{1}$. The dynamic spin structure
factors are systematically calculated in all phases of the models as well as at
the critical points. To give a full understanding of the dynamic spectra, spin
wave theory is employed to explain some features of numerical results,
especially for the low-energy part. When $g$ is close to $1$, the features of
the spin excitation spectra of each checkerboard model are roughly the same as
those of the original square lattice antiferromagnetic Heisenberg model, and
the high-energy continuum among them is discussed. In contrast to the other
checkerboard structures investigated in this paper, the $3\times 3$
checkerboard model has distinctive excitation features, such as a gap between a
low-energy gapless branch and a gapped high-energy part that exists when $g$ is
small. The gapless branch in this case can be regarded as a spin wave in
N$\mathrm{\acute{e}}$el order formed by a ""block spin"" in each $3\times 3$
plaquette with an effective exchange interaction originating from
renormalization. One unexpected finding is that the continuum also appears in
this low-energy branch.",1811.12753v2
2017-04-24,Spin partners of the $Z_b(10610)$ and $Z_b(10650)$ revisited,"We study the implications of the heavy-quark spin symmetry for the possible
spin partners of the exotic states $Z_b(10610)$ and $Z_b(10650)$ in the
spectrum of bottomonium. We formulate and solve numerically the coupled-channel
equations for the $Z_b$ states that allow for a dynamical generation of these
states as hadronic molecules. The force includes short-range contact terms and
the one-pion exchange potential, both treated fully nonperturbatively. The
strength of the potential at leading order is fixed completely by the pole
positions of the $Z_b$ states such that the mass and the most prominent
contributions to the width of the isovector heavy-quark spin partner states
$W_{bJ}$ with the quantum numbers $J^{++}$ ($J=0,1,2$) come out as predictions.
Since the accuracy of the present experimental data does not allow one to fix
the pole positions of the $Z_b$'s reliably enough, we also study the pole
trajectories of their spin partner states as functions of the $Z_b$ binding
energies. It is shown that, once the heavy-quark spin symmetry is broken by
means of the physical $B$ and $B^*$ masses, especially the pion tensor force
has a significant impact on the location of the partner states clearly
demonstrating the need of a coupled-channel treatment of pion dynamics to
understand the spin multiplet pattern of hadronic molecules.",1704.07332v2
2018-05-31,Unusual double-peak specific heat and spin freezing in a spin-2 triangular lattice antiferromagnet FeAl$_{2}$Se$_{4}$,"We report the properties of a triangular lattice iron-chalcogenide
antiferromagnet FeAl$_{2}$Se$_{4}$. The spin susceptibility reveals a
significant antiferromagnetic interaction with a Curie-Weiss temperature
{\Theta}$_{CW}$ ~ -200K and a spin-2 local moment. Despite a large spin and a
large |{\Theta}$_{CW}$|, the low-temperature behaviors are incompatible with
conventional classical magnets. No long-range order is detected down to 0.4K.
Similar to the well-known spin-1 magnet NiGa$_{2}$S$_{4}$, the specific heat of
FeAl$_{2}$Se$_{4}$ exhibits an unusual double-peak structure and a T$^{2}$
power law at low temperatures, which are attributed to the underlying
quadrupolar spin correlations and the Halperin-Saslow modes, respectively. The
spin freezing occurs at ~ 14K, below which the relaxation dynamics is probed by
the ac susceptibility. Our results are consistent with the early theory for the
spin-1 system with Heisenberg and biquadratic spin interactions. We argue that
the early proposal of the quadrupolar correlation and gauge glass dynamics may
be well extended to FeAl$_{2}$Se$_{4}$. Our results provide useful insights
about the magnetic properties of frustrated quantum magnets with high spins.",1805.12569v1
2014-06-12,Spin diffusion in the low-dimensional molecular quantum Heisenberg antiferromagnet Cu(pyz)(NO$_{3}$)$_{2}$ detected with implanted muons,"We present the results of muon-spin relaxation measurements of spin
excitations in the one-dimensional quantum Heisenberg antiferromagnet
Cu(pyz)(NO$_{3}$)$_{2}$. Using density-functional theory we propose muon sites
and assess the degree of perturbation the muon probe causes on the system. We
identify a site involving the muon forming a hydroxyl-type bond with an oxygen
on the nitrate group that is sensitive to the characteristic spin dynamics of
the system. Our measurements of the spin dynamics show that in the temperature
range $T_{\mathrm{N}}<T<J$ (between the ordering temperature $T_{\mathrm{N}}$
and the exchange energy scale $J$) the field-dependent muon spin relaxation is
characteristic of diffusive transport of spin excitations over a wide range of
applied fields. We also identify a possible crossover at higher applied fields
in the muon probe's response to the fluctuation spectrum, to a regime where the
muon detects early-time transport with a ballistic character. This behavior is
contrasted with that found for $T>J$ and that in the related two-dimensional
system Cu(pyz)$_2$(ClO$_4$)$_{2}$.",1406.3202v2
2016-05-06,Nanosecond-timescale low error switching of in-plane magnetic tunnel junctions through dynamic Oersted-field assisted spin-Hall effect,"We investigate fast-pulse switching of in-plane-magnetized magnetic tunnel
junctions (MTJs) within 3-terminal devices in which spin-transfer torque is
applied to the MTJ by the giant spin Hall effect. We measure reliable
switching, with write error rates down to $10^{-5}$, using current pulses as
short as just 2 ns in duration. This represents the fastest reliable switching
reported to date for any spin-torque-driven magnetic memory geometry, and
corresponds to a characteristic time scale that is significantly shorter than
predicted possible within a macrospin model for in-plane MTJs subject to
thermal fluctuations at room temperature. Using micromagnetic simulations, we
show that in the 3-terminal spin-Hall devices the Oersted magnetic field
generated by the pulse current strongly modifies the magnetic dynamics excited
by the spin-Hall torque, enabling this unanticipated performance improvement.
Our results suggest that in-plane MTJs controlled by Oersted-field-assisted
spin-Hall torque are a promising candidate for both cache memory applications
requiring high speed and for cryogenic memories requiring low write energies.",1605.02104v2
2018-10-13,Dynamics of spin-orbit-coupled cold atomic gases in a Floquet lattice with an impurity,"In this study, we have studied the quantum tunneling of a single
spin-orbit-coupled atom held in a periodically modulated optical lattice with
an impurity. At the pseudocollapse points of quasienergy bands, where the
dynamical localization takes place globally, two types of local second-order
tunneling processes appear beyond expectation between the two nearest-neighbor
sites of the impurity with the spin unchanged and with impurity site population
negligible all the time, when the impurity potential is far off-resonant with
the driving field. Though tunneling behaviors of the two types seem to be the
same, they are believed to involve two distinct mechanisms: one is related to
spin-independent process, while the other is to spin-dependent tunneling
process. The two types of second-order processes can be identified by means of
resonant tunneling with or without spin-flipping by tuning the impurity
potential to be in resonance with the driving field. In the Floquet picture,
the second-order processes are manifested as subtle and fine avoided crossings
of quasienergy spectrums near the pseudocollapse region. These results are
confirmed analytically on the basis of effective three-site model and
multiple-time-scale asymptotic perturbative method, and may be exploited for
engineering the spin-dependent quantum transport in realistic experiments.",1810.05854v1
2019-09-30,"High-harmonic generation by electric polarization, spin current, and magnetization","High-harmonic generation (HHG), a typical nonlinear optical effect, has been
actively studied in electron systems such as semiconductors and
superconductors. As a natural extension, we theoretically study HHG from
electric polarization, spin current and magnetization in magnetic insulators
under terahertz (THz) or gigahertz (GHz) electromagnetic waves. We use simple
one-dimensional spin chain models with or without multiferroic coupling between
spins and the electric polarization, and study the dynamics of the spin chain
coupled to an external ac electric or magnetic field. We map spin chains to
two-band fermions and invoke an analogy of semiconductors and superconductors.
With a quantum master equation and Lindblad approximation, we compute the time
evolution of the electric polarization, spin current, and magnetization,
showing that they exhibit clear harmonic peaks. We also show that the
even-order HHG by magnetization dynamics can be controlled by static magnetic
fields in a wide class of magnetic insulators. We propose experimental setups
to observe these HHG, and estimate the required strength of the ac electric
field $E_0$ for detection as $E_0\sim100$kV/cm--1MV/cm, which corresponds to
the magnetic field $B_0\sim0.1$T--1T. The estimated strength would be relevant
also for experimental realizations of other theoretically-proposed nonlinear
optical effects in magnetic insulators such as Floquet engineering of magnets.",1910.00146v3
2020-02-07,Effective quantum kinetic theory for spin transport of fermions with collsional effects,"We systematically derive the collision term for the axial kinetic theory, a
quantum kinetic theory delineating the coupled dynamics of the vector/axial
charges and spin transport carried by the massive spin-1/2 fermions traversing
a medium. We employ the Wigner-function approach and propose a consistent
power-counting scheme where the axial-charge distribution function, a
non-conserved quantity for massive particles, is accounted as the first-order
quantity in the $ \hbar $ expansion, while the vector-charge distribution
function the zeroth-order quantity. This specific power-counting scheme allows
us to organize a reduced $ \hbar$ expansion for the collision term and to
formally identity the spin-diffusion effect and the spin-polarization effect at
the same order. We confirm that the obtained collisional axial kinetic theory
smoothly reduces to the chiral kinetic theory in the massless limit, serving as
a consistency check. In the absence of electromagnetic fields, we further
present the simplified axial kinetic equations suitable for tracking dynamical
spin polarization of heavy and light fermions, respectively. As an application
to the weakly coupled quark-gluon plasma at high temperature, we compute the
spin-diffusion term for massive quarks within the leading-log approximation.
The formal expression for the first-order terms provides a path toward
evaluation of the spin polarization effect in quantum chromodynamics.",2002.02612v4
2020-04-09,Analyzing photon-count heralded entanglement generation between solid-state spin qubits by decomposing the master equation dynamics,"We analyze and compare three different schemes that can be used to generate
entanglement between spin qubits in optically-active single solid-state quantum
systems. Each scheme is based on first generating entanglement between the spin
degree of freedom and either the photon number, the time bin, or the
polarization degree of freedom of photons emitted by the systems. We compute
the time evolution of the entanglement generation process by decomposing the
dynamics of a Markovian master equation into a set of propagation
superoperators conditioned on the cumulative detector photon count. We then use
the conditional density operator solutions to compute the efficiency and
fidelity of the final spin-spin entangled state while accounting for spin
decoherence, optical pure dephasing, spectral diffusion, photon loss, phase
errors, detector dark counts, and detector photon number resolution
limitations. We find that the limit to fidelity for each scheme is restricted
by the mean wavepacket overlap of photons from each source, but that these
bounds are different for each scheme. We also compare the performance of each
scheme as a function of the distance between spin qubits.",2004.04786v2
2020-12-23,Maximising Dynamic Nuclear Polarisation via Selective Hyperfine Tuning,"Dynamic nuclear polarisation (DNP) refers to a class of techniques used to
increase the signal in nuclear magnetic resonance measurements by transferring
spin polarisation from ensembles of highly polarised electrons to target
nuclear analytes. These techniques, however, require the application of strong
magnetic fields to maximise electron spin polarisation, limiting pathways for
electron-nuclear (hyperfine) spin coupling and transfer. In this work we show
that, for systems of electronic spin $S\geq1$ possessing an intrinsic
zero-field splitting, a separate class of stronger hyperfine interactions based
on lab-frame cross relaxation may be utilised to improve DNP efficiency and
yield, whilst operating at moderate fields. We analytically review existing
methods, and determine that this approach increases the rate of polarisation
transfer to the nuclear ensemble by up to an order of magnitude over existing
techniques. This result is demonstrated experimentally at room temperature
using the optically polarisable $S=1$ electron spin system of the nitrogen
vacancy (NV) defect in diamond as the source of electron spin polarisation.
Finally we assess the utility of these NV-based approaches for the polarisation
of macroscopic quantities of molecular spins external to the diamond for NMR
and MRI applications.",2012.12508v1
2018-06-07,Dynamics and Spin-Valley Locking Effects in Monolayer Transition Metal Dichalcogenides,"Transition metal dichalcogenides have been the primary materials of interest
in the field of valleytronics for their potential in information storage, yet
the limiting factor has been achieving long valley decoherence times. We
explore the dynamics of four monolayer TMDCs (MoS$_2$, MoSe$_2$, WS$_2$,
WSe$_2$) using ab initio calculations to describe electron-electron and
electron-phonon interactions. By comparing calculations which both omit and
include relativistic effects, we isolate the impact of spin-resolved spin-orbit
coupling on transport properties. In our work, we find that spin-orbit coupling
increases carrier lifetimes at the valence band edge by an order of magnitude
due to spin-valley locking, with a proportional increase in the hole mobility
at room temperature. At temperatures of 50~K, we find intervalley scattering
times on the order of 100 ps, with a maximum value ~140 ps in WSe$_2$. Finally,
we calculate excited-carrier generation profiles which indicate that direct
transitions dominate across optical energies, even for WSe$_2$ which has an
indirect band gap. Our results highlight the intriguing interplay between spin
and valley degrees of freedom critical for valleytronic applications. Further,
our work points towards interesting quantum properties on-demand in transition
metal dichalcogenides that could be leveraged via driving spin, valley and
phonon degrees of freedom.",1806.02673v1
2018-07-30,Ground-state cooling of a nanomechanical oscillator with N spins,"Typical of modern quantum technologies employing nanomechanical oscillators
is to demand few mechanical quantum excitations, for instance, to prolong
coherence times of a particular task or, to engineer a specific non-classical
state. For this reason, we devoted the present work to exhibit how to bring an
initial thermalized nanomechanical oscillator near to its ground state.
Particularly, we focus on extending the novel results of D. D. B. Rao
\textit{et al.}, Phys. Rev. Lett. \textbf{117}, 077203 (2016), where a
mechanical object can be heated up, squeezed, or cooled down near to its ground
state through conditioned single-spin measurements. In our work, we study a
similar iterative spin-mechanical system when $N$ spins interact with the
mechanical oscillator. Here, we have also found that the postselection
procedure acts as a discarding process, i.e., we steer the mechanics to the
ground state by dynamically filtering its vibrational modes. We show that when
considering symmetric collective spin postselection, the inclusion of $N$ spins
into the quantum dynamics results highly beneficial. In particular, decreasing
the total number of iterations to achieve the ground-state, with a success rate
of probability comparable with the one obtained from the single-spin case.",1807.11600v2
2018-08-29,Fast spin exchange between two distant quantum dots,"The Heisenberg exchange interaction between neighboring quantum dots allows
precise voltage control over spin dynamics, due to the ability to precisely
control the overlap of orbital wavefunctions by gate electrodes. This allows
the study of fundamental electronic phenomena and finds applications in quantum
information processing. Although spin-based quantum circuits based on
short-range exchange interactions are possible, the development of scalable,
longer-range coupling schemes constitutes a critical challenge within the
spin-qubit community. Approaches based on capacitative coupling and
cavity-mediated interactions effectively couple spin qubits to the charge
degree of freedom, making them susceptible to electrically-induced decoherence.
The alternative is to extend the range of the Heisenberg exchange interaction
by means of a quantum mediator. Here, we show that a multielectron quantum dot
with 50-100 electrons serves as an excellent mediator, preserving speed and
coherence of the resulting spin-spin coupling while providing several
functionalities that are of practical importance. These include speed (mediated
two-qubit rates up to several gigahertz), distance (of order of a micrometer),
voltage control, possibility of sweet spot operation (reducing susceptibility
to charge noise), and reversal of the interaction sign (useful for dynamical
decoupling from noise).",1808.09736v1
2019-11-25,Quantum field theory of topological spin dynamics,"We develop a field theory of quantum magnets and magnetic (semi)metals, which
is suitable for the analysis of their universal and topological properties. The
systems of interest include collinear, coplanar and general non-coplanar
magnets. At the basic level, we describe the dynamics of magnetic moments using
smooth vector fields in the continuum limit. Dzyaloshinskii-Moriya interaction
is captured by a non-Abelian vector gauge field, and chiral spin couplings
related to topological defects appear as higher-rank antisymmetric tensor gauge
fields. We distinguish type-I and type-II magnets by their equilibrium response
to the non-Abelian gauge flux, and characterize the resulting lattices of
skyrmions and hedgehogs, the spectra of spin waves, and the chiral response to
external perturbations. The general spin-orbit coupling of electrons is
similarly described by non-Abelian gauge fields, including higher-rank tensors
related to the electronic Berry flux. Itinerant electrons and local moments
exchange their gauge fluxes through Kondo and Hund interactions. Hence, by
utilizing gauge fields, this theory provides a unifying physical picture of
``intrinsic'' and ``topological'' anomalous Hall effects, spin-Hall effects,
and other correlations between the topological properties of electrons and
moments. We predict ``topological'' magnetoelectric effect in materials prone
to hosting hedgehogs. Links to experiments and model calculations are provided
by deriving the couplings and gauge fields from generic microscopic models,
including the Hubbard model with spin-orbit interactions. We establish the
possible existence of novel quantum spin liquids that exhibit a fractional
magnetoelectric effect, and discuss a few applications to topological magnetic
conductors like Mn$_3$Sn and Pr$_2$Ir$_2$O$_7$.",1911.11155v2
2020-06-16,Block orbital-selective Mott insulators: a spin excitation analysis,"We present a comprehensive study of the spin excitations - as measured by the
dynamical spin structure factor $S(q,\omega)$ - of the so-called block-magnetic
state of low-dimensional orbital-selective Mott insulators. We realize this
state via both a multi-orbital Hubbard model and a generalized Kondo-Heisenberg
Hamiltonian. Due to various competing energy scales present in the models, the
system develops periodic ferromagnetic islands of various shapes and sizes,
which are antiferromagnetically coupled. The 2$\times$2 particular case was
already found experimentally in the ladder material BaFe$_2$Se$_3$ that becomes
superconducting under pressure. Here we discuss the electronic density as well
as Hubbard and Hund coupling dependence of $S(q,\omega)$ using density matrix
renormalization group method. Several interesting features were identified: (1)
An acoustic (dispersive spin-wave) mode develops. (2) The spin-wave bandwidth
establishes a new energy scale that is strongly dependent on the size of the
magnetic island and becomes abnormally small for large clusters. (3) Optical
(dispersionless spin excitation) modes are present for all block states studied
here. In addition, a variety of phenomenological spin Hamiltonians have been
investigated but none matches entirely our results that were obtained primarily
at intermediate Hubbard $U$ strengths. Our comprehensive analysis provides
theoretical guidance and motivation to crystal growers to search for
appropriate candidate materials to realize the block states, and to neutron
scattering experimentalists to confirm the exotic dynamical magnetic properties
unveiled here, with a rich mixture of acoustic and optical features.",2006.09495v2
2020-08-06,Antiferromagnetic Switching Driven by the Collective Dynamics of a Coexisting Spin Glass,"The theory behind the electrical switching of antiferromagnets is premised on
the existence of a well defined broken symmetry state that can be rotated to
encode information. A spin glass is in many ways the antithesis of this state,
characterized by an ergodic landscape of nearly degenerate magnetic
configurations, choosing to freeze into a distribution of these in a manner
that is seemingly bereft of information. In this study, we show that the
coexistence of spin glass and antiferromagnetic order allows a novel mechanism
to facilitate the switching of the antiferromagnet Fe$_{1/3+\delta}$NbS$_2$,
which is rooted in the electrically-stimulated collective winding of the spin
glass. The local texture of the spin glass opens an anisotropic channel of
interaction that can be used to rotate the equilibrium orientation of the
antiferromagnetic state. The use of a spin glass' collective dynamics to
electrically manipulate antiferromagnetic spin textures has never been applied
before, opening the field of antiferromagnetic spintronics to many more
material platforms with complex magnetic textures.",2008.02795v1
2020-09-08,Role of an additional interfacial spin-transfer torque for current-driven skyrmion dynamics in chiral magnetic layers,"Skyrmions can be driven by spin-orbit torques as a result of the spin Hall
effect. Here we model an additional contribution in ultra-thin multilayers,
arising from the spin accumulation at heavy metal / ferromagnetic interfaces
and observe the effects on a large range of skyrmion diameters. The combination
of the interfacial spin-transfer torque and the spin-orbit torque results in
skyrmion motion which helps to explain the observation of small skyrmion Hall
angles for skyrmion diameters less than 100 nm. We show that this additional
term has a significant effect on the skyrmion dynamics and leads to rapidly
decreasing skyrmion Hall angles for small skyrmion diameters, as well as a
skyrmion Hall angle versus skyrmion velocity dependence nearly independent of
the surface roughness characteristics. Also, the effect of various disordered
energy landscapes, in the form of surface roughness, on the skyrmion Hall angle
and velocity is shown to be largely drive-dependent. Our results show good
agreement with those found in experiments thus concluding that the interfacial
spin-transfer torque should be included in micromagnetics simulations for the
reproduction of experimental results.",2009.03751v2
2020-11-09,Classical many-body chaos with and without quasiparticles,"We study correlations, transport and chaos in a Heisenberg magnet as a
classical model many-body system. By varying temperature and dimensionality, we
can tune between settings with and without symmetry breaking and accompanying
collective modes or quasiparticles. We analyse both conventional and
out-of-time-ordered spin correlators (`decorrelators') to track the spreading
of a spatiotemporally localised perturbation -- the wingbeat of the butterfly
-- as well as transport coefficients and Lyapunov exponents. We identify a
number of qualitatively different regimes. Trivially, at $T=0$, there is no
dynamics at all. In the limit of low temperature, $T=0^+$, integrability
emerges, with infinitely long-lived magnons; here the wavepacket created by the
perturbation propagates ballistically, yielding a lightcone at the spin wave
velocity which thus subsumes the butterfly velocity; inside the lightcone, a
pattern characteristic of the free spin wave spectrum is visible at short
times. On top of this, residual interactionslead to spin wave lifetimes which,
while divergent in this limit, remain finite at any nonzero $T$. At the longest
times, this leads to a `standard' chaotic regime; for this regime, we show that
the Lyapunov exponent is simply proportional to the inverse spin-wave lifetime.
Visibly strikingly, between this and the `short-time' integrable regimes, a
scarred regime emerges: here, the decorrelator is spatiotemporally highly
non-uniform, being dominated by rare and random scattering events seeding
secondary lightcones. As the spin correlation length decreases with increasing
$T$, the distinction between these regimes disappears and at high temperature
the previously studied chaotic paramagnetic regime emerges. For this, we
elucidate how, somewhat counterintuitively, the ballistic butterfly velocity
arises from a diffusive spin dynamics.",2011.04700v1
2020-11-23,Response of a strongly interacting spin-orbit coupling system to a Zeeman field,"A strongly spin-orbital coupled systems could be in a magnetic ordered phase
at zero field. However, a Zeeman field could drive it into different quantum or
topological phases. In this work, starting from general symmetry principle, we
construct various effective actions to study all these quantum phases and phase
transitions which take different forms depending on the condensation momenta
are commensurate or in-commensurate.
  We not only recover all these quantum phases and their excitations achieved
by the microscopic calculations, but also discover several novel classes of
quantum phase transitions with dynamic exponents $ z=1, z=2 $ and anisotropic
ones $ (z_x=3/2, z_y=3) $ respectively. We determine the relations between the
quantum spin and the order parameters of the effective actions which display
rich spin-orbital structures. We find a new type of dangerously irrelevant
operator we name type-II, in distinction from the known one we name type-I. We
explore a new phenomena called order parameter fractionization where one
complex order parameter split into two which is different than quantum spin
fractionization into a spinon and a $ Z_2 $ flux. Finite temperature
transitions are presented. The dynamic spin-spin correlation functions are
evaluated. Thermal Hall conductivities are discussed. The cases with the $
U(1)_{soc} $ symmetry explicitly broken are briefly outlined. In view of recent
experimental advances in generating 2d SOC for cold atoms in optical lattices,
these new many-body phenomena can be explored in the near future cold atom
experiments. Implications to various SOC materials such as MnSi,
Fe$_{0.5}$Co$_{0.5}$Si, especially 4d Kitaev materials $\alpha$-RuCl$_3$ in a
Zeeman field are outlined.",2011.11287v2
2021-03-10,"Spin texture induced by non-magnetic doping and spin dynamics in 2D triangular lattice antiferromagnet h-Y(Mn,Al)O3","Novel effects induced by nonmagnetic impurities in frustrated magnets and
quantum spin liquid represent a highly nontrivial and interesting problem. A
theoretical proposal of extended modulated spin structures induced by doping of
such magnets, distinct from the well-known skyrmions has attracted significant
interest. Here, we demonstrate that nonmagnetic impurities can produce such
extended spin structures in h-YMnO3, a triangular antiferromagnet with
noncollinear magnetic order. Using inelastic neutron scattering (INS), we
measured the full dynamical structure factor in Al-doped h-YMnO3 and confirmed
the presence of magnon damping with a clear momentum dependence. Our
theoretical calculations can reproduce the key features of the INS data,
supporting the formation of the proposed spin textures. As such, our study
provides the first experimental confirmation of the impurity-induced spin
textures. It offers new insights and understanding of the impurity effects in a
broad class of noncollinear magnetic systems.",2103.05936v2
2021-03-12,Atomic-layer Rashba-type superconductor protected by dynamic spin-momentum locking,"Spin-momentum locking is essential to the spin-split Fermi surfaces of
inversion-symmetry broken materials, which are caused by either Rashba-type or
Zeeman-type spin-orbit coupling (SOC). While the effect of Zeeman-type SOC on
superconductivity has experimentally been shown recently, that of Rashba-type
SOC remains elusive. Here we report on convincing evidence for the critical
role of the spin-momentum locking on crystalline atomic-layer superconductors
on surfaces, for which the presence of the Rashba-type SOC is demonstrated.
In-situ electron transport measurements reveal that in-plane upper critical
magnetic field is anomalously enhanced, reaching approximately three times the
Pauli limit at $T = 0$. Our quantitative analysis clarifies that dynamic
spin-momentum locking, a mechanism where spin is forced to flip at every
elastic electron scattering, suppresses the Cooper pair-breaking parameter by
orders of magnitude and thereby protects superconductivity. The present result
provides a new insight into how superconductivity can survive the detrimental
effects of strong magnetic fields and exchange interactions.",2103.07143v1
2021-04-30,A numerical exploration of signal detector arrangement in a spin-wave reservoir computing device,"This paper studies numerically how the signal detector arrangement influences
the performance of reservoir computing using spin waves excited in a
ferrimagnetic garnet film. This investigation is essentially important since
the input information is not only conveyed but also transformed by the spin
waves into high-dimensional information space when the waves propagate in the
film in a spatially distributed manner. This spatiotemporal dynamics realizes a
rich reservoir-computational functionality. First, we simulate spin waves in a
rectangular garnet film with two input electrodes to obtain spatial
distributions of the reservoir states in response to input signals, which are
represented as spin vectors and used for a machine-learning waveform
classification task. The detected reservoir states are combined through readout
connection weights to generate a final output. We visualize the spatial
distribution of the weights after training to discuss the number and positions
of the output electrodes by arranging them at grid points, equiangularly
circular points or at random. We evaluate the classification accuracy by
changing the number of the output electrodes, and find that a high accuracy
($>$ 90\%) is achieved with only several tens of output electrodes regardless
of grid, circular or random arrangement. These results suggest that the spin
waves possess sufficiently complex and rich dynamics for this type of tasks.
Then we investigate in which area useful information is distributed more by
arranging the electrodes locally on the chip. Finally, we show that this device
has generalization ability for input wave-signal frequency in a certain
frequency range. These results will lead to practical design of spin-wave
reservoir devices for low-power intelligent computing in the near future.",2104.14915v1
2021-07-02,Quantum spin solver near saturation: QS$^3_{~}$,"We develop a program package named QS$^{3}$ [\textipa{kj\'u:-\'es-kj\'u:b}]
based on the (thick-restart) Lanczos method for analyzing spin-1/2 XXZ-type
quantum spin models on spatially uniform/non-uniform lattices near fully
polarized states, which can be mapped to dilute hardcore Bose systems. All
calculations in QS$^{3}$, including eigenvalue problems, expectation values for
one/two-point spin operators, and static/dynamical spin structure factors, are
performed in the symmetry-adapted bases specified by the number
$N_{\downarrow}$ of down spins and the wave number $\boldsymbol{k}$ associated
with the translational symmetry without using the bit representation for
specifying spin configurations. Because of these treatments, QS$^{3}$ can
support large-scale quantum systems containing more than 1000 sites with dilute
$N_{\downarrow}$. We show the benchmark results of QS$^{3}$ for the low-energy
excitation dispersion of the isotropic Heisenberg model on the
$10\times10\times10$ cubic lattice, the static and dynamical spin structure
factors of the isotropic Heisenberg model on the $10\times10$ square lattice,
and the open-MP parallelization efficiency on the supercomputer (Ohtaka) based
on AMD Epyc 7702 installed at the Institute for the Solid State Physics (ISSP).
Theoretical backgrounds and the user interface of QS$^{3}$ are also described.",2107.00872v1
2021-07-26,"Terrain-perception-free Quadrupedal Spinning Locomotion on Versatile Terrains: Modeling, Analysis, and Experimental Validation","Dynamic quadrupedal locomotion over rough terrains reveals remarkable
progress over the last few decades. Small-scale quadruped robots are adequately
flexible and adaptable to traverse uneven terrains along sagittal direction,
such as slopes and stairs. To accomplish autonomous locomotion navigation in
complex environments, spinning is a fundamental yet indispensable functionality
for legged robots. However, spinning behaviors of quadruped robots on uneven
terrain often exhibit position drifts. Motivated by this problem, this study
presents an algorithmic method to enable accurate spinning motions over uneven
terrain and constrain the spinning radius of the Center of Mass (CoM) to be
bounded within a small range to minimize the drift risks. A modified spherical
foot kinematics representation is proposed to improve the foot kinematic model
and rolling dynamics of the quadruped during locomotion. A CoM planner is
proposed to generate stable spinning motion based on projected stability
margins. Accurate motion tracking is accomplished with Linear Quadratic
Regulator (LQR) to bound the position drift during the spinning movement.
Experiments are conducted on a small-scale quadruped robot and the
effectiveness of the proposed method is verified on versatile terrains
including flat ground, stairs and slopes.",2107.12479v4
2021-08-30,On the large apparent black hole spin-orbit misalignment angle in GW200115,"GW200115 is one of the first two confidently detected gravitational-wave
events of neutron star-black hole mergers. An interesting property of this
merger is that the black hole, if spinning rapidly, has its spin axis
negatively aligned (with a misalignment angle $> 90^{\circ}$) with the binary
orbital angular momentum vector. Although such a large spin-orbit misalignment
angle naturally points toward a dynamical origin, the measured neutron
star-black hole merger rate exceeds theoretical predictions of the dynamical
formation channel. In the canonical isolated binary formation scenario, the
immediate progenitor of GW200115 is likely to be a binary consisting of a black
hole and a helium star, with the latter forming a neutron star during a
supernova explosion. Since the black hole is generally expected to spin along
the pre-supernova binary orbital angular momentum axis, a large neutron star
natal kick is required to produce the observed misalignment angle. Using simple
kinematic arguments, we find that a misalignment angle $> 90^{\circ}$ in
GW200115-like systems implies a kick velocity $\sim 600\, \text{km/s}$ and a
kick direction within $\approx 30 ^{\circ}$ of the pre-supernova orbital plane.
We discuss different interpretations of the large apparent black hole
spin-orbit misalignment angle, including a non-spinning black hole.",2108.13540v2
2022-03-07,Manipulating quantum impurity spins via dynamical modes of nanomagnets,"Quantum impurity (QI) spins offer promising information processing and
sensing applications by harnessing up to room-temperature quantum coherence.
Challenged by the requirement of designing local coherent drives and improving
sensitivity to various signals for such applications, the search of hybrid
systems coupling QI spins with matter excitations have garnered significant
recent interest. We propose and theoretically study a hybrid system that
couples spin-1 QI with the dynamical excitations of nanomagnets, which are
controlled by mechanisms uncovered in classical spintronics. We show that in
such systems the QI-spin decoherence, due to coupling to thermally excited
modes of the nanomagnet, can be designed across a wide range by exploiting the
control over nanomagnet's mode ellipticity and the chiral nature of the
coupling between the QI spin and nanomagnet. On the other hand, when activated
electrically via voltage-induced torques, we demonstrate that QI spins can be
driven coherently with large quality factors at room temperature by leveraging
inherent non-linear precessional modes of the nanomagnet. Our results provide
theoretical guidance for enabling unique quantum spintronic functionalities,
such as local coherent driving of QI spins up to ambient conditions, and the
design of nanomagnet-enhanced QI-based hybrid sensors.",2203.03652v1
2022-05-08,Multipartite entangled states in dipolar quantum simulators,"The scalable production of multipartite entangled states in ensembles of
qubits is a fundamental function of quantum devices, as such states are an
essential resource both for fundamental studies on entanglement, as well as for
applied tasks. Here we focus on the $U(1)$ symmetric Hamiltonians for qubits
with dipolar interactions -- a model realized in several state-of-the-art
quantum simulation platforms for lattice spin models, including Rydberg-atom
arrays with resonant interactions. Making use of exact and variational
simulations, we theoretically show that the non-equilibrium dynamics generated
by this lattice spin Hamiltonian shares fundamental features with that of the
one-axis-twisting model, namely the simplest interacting collective-spin model
with $U(1)$ symmetry. The evolution governed by the dipolar Hamiltonian
generates a cascade of multipartite entangled states -- spin-squeezed states,
Schr\""odinger's cat states, and multi-component superpositions of coherent spin
states. Investigating systems with up to $N=144$ qubits, we observe full
scalability of the entanglement features of these states directly related to
metrology, namely scalable spin squeezing at an evolution time ${\cal
O}(N^{1/3})$; and Heisenberg scaling of sensitivity of the spin parity to
global rotations for cat states reached at times ${\cal O}(N)$. Our results
suggest that the native Hamiltonian dynamics of state-of-the-art quantum
simulation platforms, such as Rydberg-atom arrays, can act as a robust source
of multipartite entanglement.",2205.03910v1
2022-06-15,Bond Ordering and Molecular Spin-Orbital Fluctuations in the Cluster Mott Insulator GaTa$_4$Se$_8$,"For materials where spin-orbit coupling is competitive with electronic
correlations, the spatially anisotropic spin-orbital wavefunctions can
stabilize degenerate states that lead to many and diverse quantum phases of
matter. Here, we find evidence for a dynamical spin-orbital state preceding a
T$^*$=50 K order-disorder spin-orbital ordering transition in the $j\!=\!3/2$
lacunar spinel GaTa$_4$Se$_8$. Above T$^*$, GaTa$_4$Se$_8$ has an average cubic
crystal structure, but total scattering measurements indicate local non-cubic
distortions of Ta$_4$ tetrahedral clusters for all measured temperatures $2 < T
< 300$ K. Inelastic neutron scattering measurements reveal the dynamic nature
of these local distortions through symmetry forbidden optical phonon modes that
modulate $j\!=\!3/2$ molecular orbital occupation as well as intercluster Ta-Se
bonds. Spin-orbital ordering at T$^*$ cannot be attributed to a classic
Jahn-Teller mechanism and based on our findings, we propose that intercluster
interactions acting on the scale of T$^*$ act to break global symmetry. The
resulting staggered intercluster dimerization pattern doubles the unit cell,
reflecting a spin-orbital valence bond ground state.",2206.07738v1
2022-06-20,Effect of internal magnetic flux on a relativistic spin-1 oscillator in the spinning point source-generated spacetime,"We consider a charged relativistic spin-1 oscillator under the influence of
an internal magnetic flux in a 2+1 dimensional spacetime induced by a spinning
point source. In order to analyze the effects of the internal magnetic flux and
spin of the point source on the relativistic dynamics of such a vector field,
we seek a non-perturbative solution of the associated spin-1 equation derived
as an excited state of Zitterbewegung. By performing an analytical solution of
the resulting equation, we determine exact results for the system in question.
Accordingly, we analyze the effects of spin of the point source and internal
magnetic flux on the relativistic dynamics of the considered test field. We see
that the spin of such a field can be altered by the magnetic flux and this
means that the considered system may behave as a fermion or boson according to
the varying values of the magnetic flux, in principle. We observe that the
internal magnetic flux and the spin of the point source impact on the
relativistic energy levels and probability density functions. Also, our results
indicate that the spin of the point source breaks the symmetry of the energy
levels corresponding to particle-antiparticle states.",2206.09898v3
2022-12-21,Charge transfer and disorder-induced spin relaxation in La2NiMnO6 crystallites,"Investigation of the electronic and spin structure in double perovskites is
recently attracting significant attention, mainly driven by their unique
multifunctional properties and other underlying charge and spin dynamics.
Herein, using X-ray photoelectron spectroscopy (XPS), we explore the influence
of variable fractions of Mn3+/Mn4+ cation in different crystallite sizes of
La2NiMnO6 that control the various completing exchange interactions of Ni/Mn
cations responsible for multiple magnetic transitions. The enhanced itinerant
electron due to Mn4+ + Ni2+ to Mn3+ + Ni3+ charge transfer emerged as a
shoulder like characteristics at the low binding energy in the Mn-2P core-level
spectrum. The various approaches such as difference in saturation
magnetization, presence of multiple charge valance, and magnetic entropy
calculations confirm the presence of antisites disorder and it varies as a
function of milling. As milling provides excess energy that helps with
nucleation or cation ordering. Competing magnetic interactions driven by mixed
valences and disorder were established across a cluster glassy phase in the
crystallites. Electron spin resonance spectroscopy (ESR) was utilized to probe
the temperature-driven ferromagnetic-cluster spin-glass transition with
modified g-factor ranging from 2.050 to 2.037. The line width of the ESR
signals increases across the ferromagnetic to cluster-glass phase transition
due to spin freezing. This phase transition is further characterized by
temperature-dependent ac-magnetic susceptibility measurements. Argand diagram
for the ac-susceptibility of the interacting crystallites suggests a collective
magnetization relaxation dynamic in the proximity of spin-glass freezing
temperature of La2NiMnO6.",2212.10845v2
2022-12-29,Inelastic Neutron Scattering in Weakly Coupled Triangular Spin Tubes CsCrF$_4$,"We performed inelastic neutron scattering (INS) experiments to measure spin
dynamics on a polycrystalline sample of a spin tube candidate CsCrF$_{4}$. The
compound exhibits a successive phase transition from a paramagnetic phase
through an intermediate temperature (IT) phase of a 120$^{\circ}$ structure to
a low temperature (LT) phase of another 120$^{\circ}$ structure. Elaborate
comparison between observed and calculated neutron spectra in LT phase reveals
that the spin Hamiltonian is identified as antiferromagnetic spin tubes
including perturbative terms of intertube interaction, Dzyaloshinskii-Moriya
interaction, and single ion anisotropy. A phase diagram for the ground state is
classically calculated. A set of parameters in the spin Hamiltonian obtained
from the INS spectra measured in LT phase is quite close to a boundary to the
phase of the 120$^{\circ}$ structure of IT phase. The INS spectra measured in
IT phase is, surprisingly, the same as those in LT phase in the level of powder
averaged spectra, even though the magnetic structures in IT and LT phases are
different. Identical dynamical structures compatible with two different static
structures are observed. No difference in the observed spectra indicates no
change of the spin Hamiltonian with the temperature, suggesting that the origin
of the successive phase transition being order-by-disorder mechanism.",2212.14280v1
2023-02-04,Multi-Stability in Cavity QED with Spin-Orbit Coupled Bose-Einstein Condensate,"We investigate the occurrence of steady-state multi-stability in a cavity
system containing spin-orbit coupled Bose-Einstein condensate and driven by a
strong pump laser. The applied magnetic field splits the Bose-Einstein
condensate into pseudo-spin states, which then became momentum sensitive with
two counter propagating Raman lasers directly interacting with ultra-cold
atoms. After governing the steady-state dynamics for all associated subsystems,
we show the emergence of multi-stable behavior of cavity photon number, which
is unlike with previous investigation on cavity-atom systems. However, this
multi-stability can be tuned with associated system parameters. Further, we
illustrate the occurrence of mixed-stability behavior for atomic population of
the pseudo spin-$\uparrow$ amd spin-$\downarrow$ states, which are appearing in
so-called bi-unstable form. The collective behavior of these atomic number
states interestingly possesses a transitional interface among the population of
both spin states, which can be enhance and controlled by spin-orbit coupling
and Zeeman field effects. Furthermore, we illustrate the emergence of secondary
interface mediated by increasing the mechanical dissipation rate of the
pseudo-spin states. These interfaces could be cause by the non-trivial behavior
of synthetic spin state mediated by cavity. Our findings are not only crucial
for the subject of optical switching, but also could provide foundation for
future studies on mechanical aspect of synthetic atomic states with cavity
quantum electrodynamics.",2302.02147v1
2023-08-10,Spinning magnetized particles orbiting magnetized Schwarzschild black holes,"A way to test electromagnetic field and spacetime properties around black
holes is by considering the dynamics of test particles. In fact, in real
astrophysical scenarios, it is hard to determine spacetime geometry which is
dominating due to degeneracy gravitational effects in parameters of gravity
theories. In this work, we study for the first time the dynamics of spinning
particles that have magnetic dipole moments around Schwarzschild black holes
immersed in an external asymptotically uniform magnetic field using the
Mathisson-Papapetrou-Dixon (MPD) equation. There are two combined interactions:
gravitational interaction between the spin of the particle and
(electro)magnetic interaction between the external magnetic field and the
magnetic dipole moment of the particle to be taken into account. First, we
derive the effective potential of the test spinning magnetized particles in
motion around the black hole. We also study the combined effects of spin and
magnetic interactions on innermost stable circular orbits (ISCOs), the energy,
and angular momentum of the particles at ISCO together with superluminal
bounds. We investigated the collision of the particles and evaluated the
center-of-mass energy in the collisions. Finally, we consider various cases in
which neutron stars and rotating stellar mass black holes can be treated as
spinning magnetized particles, evaluating the effects of the spin and magnetic
moment of objects around supermassive and intermediate-mass black holes.",2308.05392v1
1994-12-12,Spin diffusion of the t-J model,"The spin-diffusion constant of the 2D $t-J$ model is calculated for the first
time using an analytical approach at high temperatures and a recently-developed
numerical method based on the Lanczos technique combined with random sampling
in the intermediate temperature regime. A simple relation, $\sigma = D_s\chi$,
between spin conductivity and spin diffusion is established and used to
calculate the latter. In the high-temperature and low-doping limit the
calculated diffusion constant agrees with known results for the Heisenberg
model. At small hole doping, $D_s$ increases approximately linearly with
doping, which leads us to an important conclusion that hopping processes
enhance spin diffusion at high temperatures. At modest hole doping, $\delta\sim
0.25$, diffusion exhibits a nonmonotonic temperature dependence, which
indicates anomalous spin dynamics at small frequencies.",9412055v2
1997-01-07,The p-spin spherical spin glass model,"This review presents various aspects of a mean-field spin glass model known
as the p-spin spherical spin glass model, which has raised a lot of interest in
the study of spin glasses, and also for its possible links with a mean-field
theory of structural glasses.
  This preprint contains no new results and is therefore not intended to be
published, but its aim is to present a collection of results and formulas
concerning this very rich model. It is in fact the english translation of one
of the chapters of my PhD thesis (``Quelques aspects de la dynamique hors
d'equilibre des verres de spin'', ``Some aspects of the out of equilibrium
dynamics of spin glasses''). A postscript version (in french) of this PhD
thesis will soon be available at http://www.lpt.ens.fr .",9701031v1
1997-05-29,Quantum Critical Behavior of the Infinite-range Transverse Ising Spin Glass : An Exact Numerical Diagonalization Study,"We report exact numerical diagonalization results of the infinite-range Ising
spin glass in a transverse field $\Gamma$ at zero temperature. Eigenvalues and
eigenvectors are determined for various strengths of $\Gamma$ and for system
sizes $N \le 16$. We obtain the moments of the distribution of the spin-glass
order parameter, the spin-glass susceptibility and the mass gap at different
values of $\Gamma$. The disorder averaging is done typically over 1000
configurations. Our finite size scaling analysis indicates a spin glass
transition at $\Gamma_c \simeq 1.5$. Our estimates for the exponents at the
transition are in agreement with those known from other approaches. For the
dynamic exponent, we get $z=2.1 \pm 0.1$ which is in contradiction with a
recent estimate ($z=4$). Our cumulant analysis indicates the existence of a
replica symmetric spin glass phase for $\Gamma < \Gamma_c$.",9705297v1
1998-01-15,Obervation of non-linear stationary spin waves in superfluid 3He-B,"Due to its broken spin and orbit rotation symmetries, superfluid $^3$He plays
a unique role for testing rotational quantum properties on a macroscopic scale.
In this system the orbital momentum forms textures that provide an effective
potential well for the creation of stationary spin waves. In the limit of the
lowest temperatures presently attainable, we observe by NMR techniques a
profound change in the spin dynamics. The NMR line shape becomes asymmetric,
strongly hysteretic and displays substantial frequency shifts. This behavior,
quantitatively described by an anharmonic oscillator model, indicates that the
parameters of the potential well depend on the spin waves amplitude, and
therefore that the orbital motion is not damped in this new regime, not
considered by the standard Leggett-Takagi theory. This regime of non-linear
stationary spin waves is shown to give rise to the pulsed NMR ""Persistent
Signals"" reported recently.",9801159v1
1998-11-04,Simulation of Spin Glass with a Variable-system-size Ensemble,"In this paper, we introduce a dynamical Monte Carlo algorithm for spin models
in which the number of the spins fluctuates from zero to a given number by
addition and deletion of spins with a probabilistic rule. Such simulations are
realized with a variable-system-size ensemble, a mixture of canonical ensembles
each of which corresponds to a system with different size. The weight of each
component of the mixture is controlled by a penalty term and systematically
tuned in a preliminary run in a way similar to the multicanonical algorithm. In
a measurement run, the system grows and shrinks without violating the detailed
balance condition and we can obtain the correct canonical averages if physical
quantities is measured only when its size is equal to the prescribed maximum
size. The mixing of Markov chain is facilitated by the fast relaxation at small
system sizes. The algorithm is implemented for the SK model of spin glass and
shows better performance than that of a conventional heat bath algorithm.",9811053v1
1998-12-17,Spin Maser under Stationary Pumping,"Spin dynamics of a polarized spin system is studied when the latter is
coupled with a resonant electric circuit and is under the action of an external
pumping supporting a stationary nonequilibrium magnetization. A complete
classification of possible regimes of spin motion is given. In addition to
seven regimes considered earlier, two other transient regimes are found and
thoroughly described: One is an oscillatory regime, when spins always move
coherently but the degree of coherence fluctuates with time. Another is a
pulsing regime, when spins reveal coherent motion during short pulses separated
from each other by intervals of incoherent motion. These regimes are, in
principle, transient, although may be extremely long lasting; their duration
may be several orders longer than the transverse relaxation time and twice
longer than the longitudinal relaxation time. Both transient regimes end with a
coherent quasistationary regime.",9812298v1
1999-01-25,Quantum lattice fluctuations in a frustrated Heisenberg spin-Peierls chain,"As a simple model for spin-Peierls systems we study a frustrated Heisenberg
chain coupled to optical phonons. In view of the anorganic spin-Peierls
compound CuGeO3 we consider two different mechanisms of spin-phonon coupling.
Combining variational concepts in the adiabatic regime and perturbation theory
in the anti-adiabatic regime we derive effective spin Hamiltonians which cover
the dynamical effect of phonons in an approximate way. Ground-state phase
diagrams of these models are determined, and the effect of frustration is
discussed. Comparing the properties of the ground state and of low-lying
excitations with exact diagonalization data for the full quantum spin phonon
models, good agreement is found especially in the anti-adiabatic regime.",9901262v1
1999-04-20,Nuclear spin-spin coupling in La_{2-x}Sr_{x}CuO_{4} studied by stimulated echo decay,"We have performed copper NQR experiments in high temperature superconductors
YBa_{2}Cu_{4}O_{8}, YBa_{2}Cu_{3}O_{7}, and La_{2-x}Sr_{x}CuO_{4} (x=0.12 and
0.15), using the stimulated echo technique. The stimulated echo intensity is
analyzed by a model that includes the spin-lattice relaxation process (T_ {1
}-process) and the fluctuating local field due to nuclear spin-spin coupling.
The model gives quantitative account of the experimental results in Y-based
compounds using the known values of 1/T_{1} and 1/T_{2G}, the gaussian decay
rate of the spin echo intensity. The same model applied to LSCO enables us to
extract the value of T_{2G}. Our results indicate that T_{1}T/T_{2G} is
independent of temperature, implying that the dynamic exponent is one in
La_{2-x}Sr_{x}CuO_{4}.",9904275v2
1999-11-17,Spin Dynamics in the LTT Phase of ~1/8 Doped Single Crystal La_{1.67}Eu_{0.2}Sr_{0.13}CuO_4,"We present La and Cu NMR relaxation measurements in single crystal
La_{1.67}Eu_{0.2}Sr_{0.13}CuO_4. A strong peak in the La spin-lattice
relaxation rate observed in the spin ordered state is well-described by the BPP
mechanism[1] and arises from continuous slowing of electronic spin fluctuations
with decreasing temperature; these spin fluctuations exhibit XY-like anisotropy
in the ordered state. The spin pseudogap is enhanced by the static
charge-stripe order in the LTT phase.",9911272v2
2000-02-23,Nuclear Spin Qubit Dephasing Time in the Integer Quantum Hall Effect Regime,"We report the first theoretical estimate of the nuclear-spin dephasing time
T_2 owing to the spin interaction with the two-dimensional electron gas, when
the latter is in the integer quantum Hall state, in a two-dimensional
heterojunction or quantum well at low temperature and in large applied magnetic
field. We establish that the leading mechanism of dephasing is due to the
impurity potentials that influence the dynamics of the spin via virtual
magnetic spin-exciton scattering. Implications of our results for
implementation of nuclear spins as quantum bits (qubits) for quantum computing
are discussed.",0002350v2
2000-11-03,Spin-Glass State in $\rm CuGa_2O_4$,"Magnetic susceptibility, magnetization, specific heat and positive muon spin
relaxation (\musr) measurements have been used to characterize the magnetic
ground-state of the spinel compound $\rm CuGa_2O_4$. We observe a spin-glass
transition of the S=1/2 $\rm Cu^{2+}$ spins below $\rm T_f=2.5K$ characterized
by a cusp in the susceptibility curve which suppressed when a magnetic field is
applied. We show that the magnetization of $\rm CuGa_2O_4$ depends on the
magnetic histo Well below $\rm T_f$, the muon signal resembles the dynamical
Kubo-Toyabe expression reflecting that the spin freezing process in $\rm
CuGa_2O_4$ results Gaussian distribution of the magnetic moments. By means of
Monte-Carlo simulati we obtain the relevant exchange integrals between the $\rm
Cu^{2+}$ spins in this compound.",0011055v1
2000-11-28,Spin wave dispersion softening in the ferromagnetic Kondo lattice model for manganites,"Spin dynamics is calculated in the ferromagnetic (FM) state of the
generalized Kondo lattice model taking into account strong on-site correlations
between e_g electrons and antiferromagnetic (AFM) exchange among t_{2g} spins.
Our study suggests that competing FM double-exchange and AFM super-exchange
interaction lead to a rather nontrivial spin-wave spectrum. While spin
excitations have a conventional Dq^2 spectrum in the long-wavelength limit,
there is a strong deviation from the spin-wave spectrum of the isotropic
Heisenberg model close to the zone boundary. The relevance of our results to
the experimental data are discussed.",0011464v1
2000-11-28,Skyrmions in a ferromagnetic Bose-Einstein condensate,"The recently realized multicomponent Bose-Einstein condensates provide
opportunities to explore the rich physics brought about by the spin degrees of
freedom. For instance, we can study spin waves and phase separation,
macroscopic quantum tunneling, Rabi oscillations, the coupling between spin
gradients and superfluid flow, squeezed spin states, vortices and other
topological excitations. Theoretically, there have been already some studies of
the ground-state properties of these systems and their line-like vortex
excitations. In analogy with nuclear physics or the quantum Hall effect, we
explore here the possibility of observing point-like topological excitations or
skyrmions. These are nontrivial spin textures that in principle can exist in a
spinor Bose-Einstein condensate. In particular, we investigate the stability of
skyrmions in a fictitious spin-1/2 condensate of Rb87 atoms. We find that
skyrmions can exist in this case only as a metastable state, but with a
lifetime of the order of, or even longer than, the typical lifetime of the
condensate itself. In addition to determining the size and the lifetime of the
skyrmion, we also present its spin texture and finally briefly consider its
dynamical properties.",0011471v1
2000-12-21,Spin-stiffness and topological defects in two-dimensional frustrated spin systems,"Using a {\it collective} Monte Carlo algorithm we study the low-temperature
and long-distance properties of two systems of two-dimensional classical tops.
Both systems have the same spin-wave dynamics (low-temperature behavior) as a
large class of Heisenberg frustrated spin systems. They are constructed so that
to differ only by their topological properties. The spin-stiffnesses for the
two systems of tops are calculated for different temperatures and different
sizes of the sample. This allows to investigate the role of topological defects
in frustrated spin systems. Comparisons with Renormalization Group results
based on a Non Linear Sigma model approach and with the predictions of some
simple phenomenological model taking into account the topological excitations
are done.",0012397v2
2001-06-12,Steady State Behavior of Mechanically Perturbed Spin Glasses and Ferromagnets,"A zero temperature dynamics of Ising spin glasses and ferromagnets on random
graphs of finite connectivity is considered, like granular media these systems
have an extensive entropy of metastable states. We consider the problem of what
energy a randomly prepared spin system falls to before becoming stuck in a
metastable state. We then introduce a tapping mechanism, analogous to that of
real experiments on granular media, this tapping, corresponding to flipping
simultaneously any spin with probability $p$, leads to stationary regime with a
steady state energy $E(p)$. We explicitly solve this problem for the one
dimensional ferromagnet and $\pm J$ spin glass and carry out extensive
numerical simulations for spin systems of higher connectivity. The link with
the density of metastable states at fixed energy and the idea of Edwards that
one may construct a thermodynamics with a flat measure over metastable states
is discussed. In addition our simulations on the ferromagnetic systems reveal a
novel first order transition, whereas the usual thermodynamic transition on
these graphs is second order.",0106220v1
2001-08-17,"17O NMR study of q=0 spin excitations in a nearly ideal S=1/2 1D Heisenberg antiferromagnet, Sr2CuO3, up to 800 K","We used 17O NMR to probe the uniform (wavevector q=0) electron spin
excitations up to 800 K in Sr2CuO3 and separate the q=0 from the q=\pm\pi/a
staggered components. Our results support the logarithmic decrease of the
uniform spin susceptibility below T ~ 0.015J, where J=2200 K. From measurement
of the dynamical spin susceptibility for q=0 by the spin-lattice relaxation
rate 1/T_{1}, we demonstrate that the q=0 mode of spin transport is ballistic
at the T=0 limit, but has a diffusion-like contribution at finite temperatures
even for T << J.",0108272v1
2002-01-19,Spontaneous Spin Coherence in n-GaAs Produced by Ferromagnetic Proximity Polarization,"We find that photoexcited electrons in an n-GaAs epilayer rapidly (< 50 ps)
spin-polarize due to the proximity of an epitaxial ferromagnetic metal.
Comparison between MnAs/GaAs and Fe/GaAs structures reveals that this coherent
spin polarization is aligned antiparallel and parallel to their magnetizations,
respectively. In addition, the GaAs nuclear spins are dynamically polarized
with a sign determined by the spontaneous electron spin orientation. In
Fe/GaAs, competition between nuclear hyperfine and applied magnetic fields
results in complete quenching of electron spin precession.",0201350v1
2002-08-29,Emergent excitations in a geometrically frustrated magnet,"Frustrated systems are ubiquitous and interesting because their behavior is
difficult to predict. Magnetism offers extreme examples in the form of spin
lattices where all interactions between spins cannot be simultaneously
satisfied. Such geometrical frustration leads to macroscopic degeneracies, and
offers the possibility of qualitatively new states of matter whose nature has
yet to be fully understood. Here we have discovered how novel composite spin
degrees of freedom can emerge from frustrated interactions in the cubic spinel
ZnCr2O4. Upon cooling, groups of six spins self-organize into weakly
interacting antiferromagnetic loops whose directors, defined as the unique
direction along which the spins are aligned parallel or antiparallel, govern
all low temperature dynamics. The experimental evidence comes from a
measurement of the magnetic form factor by inelastic neutron scattering. While
the data bears no resemblance to the atomic form factor for chromium, they are
perfectly consistent with the form factor for hexagonal spin loop directors.
The hexagon directors are to a first approximation decoupled from each other
and hence their reorientations embody the long-sought local zero energy modes
for the pyrochlore lattice.",0208587v1
2002-09-10,New Evidence for Zero-Temperature Relaxation in a Spin-Polarized Fermi Liquid,"Spin-echo experiments are reported for 3He-4He solutions under extremely high
B/T conditions, B=14.75 T and T >= 1.73 mK. The 3He concentration x_3 was
adjusted close to the value x_c = 3.8% at which the spin rotation parameter
muM_0 vanishes. In this way the transverse and longitudinal spin diffusion
coefficients D_perp, D_parallel were measured while keeping |muM_0| < 1. It is
found that the temperature dependence of D_perp deviates strongly from 1/T^2,
with anisotropy temperature T_a = 4.26 +/- 0.18 mK. This value is close to the
theoretical prediction for dilute solutions, and suggests that spin current
relaxation remains finite as the temperature tends to zero.",0209222v2
2002-09-17,Optical response and spin relaxation in semiconductor systems under excitation with arbitrary polarization,"The equations-of-motion for the density matrix are derived in a multiband
model to describe the response of semiconductors (bulk or quantum well
structures) under optical excitation with arbitrary polarization. The multiband
model used, comprising the twofold conduction band and the fourfold topmost
valence band (or heavy- and light-hole states), incorporates spin-splitting of
the single-particle states. The interaction terms include besides the direct
Coulomb coupling between carriers also the electron-hole exchange interaction,
which together with the spin-splitting terms is responsible for spin
relaxation. Applying the Hartree-Fock truncation scheme leads to a set of
coherent semiconductor Bloch equations for the multiband case. This concept
provides the theoretical frame for describing phenomena connected with optical
response under excitation with arbitrary light polarization and spin
relaxation: polarized optical response, polarization dynamics of VCSELs, spin
relaxation, and the circular photovoltaic effect.",0209389v1
2002-09-20,Theoretical $T_1$ Calculation for Isotropic High Spin Molecules,"We calculate the molecular-spin ($S$), temperature ($T$), and field ($H$)
dependence of $1/T_1$ for a local magnetic probe coupled to an isotropic high
spin molecule, based on spin-phonon interaction. We compare the calculation to
recent NMR and $\mu$SR experiments in CrCu$_6$ ($S = 9/2$), CrNi$_6$ ($S =
15/2$) and CrMn$_6$ ($S = 27/2$). Although we can account for the high and
intermediate temperature regimes, the calculation is fundamentally different
from the data at $T \longrightarrow 0$. Since $1/T_1$ must be due to coupling
of the molecular spin to an external heat bath, and since phonon contribution
is ruled out at low $T$, we conclude that at these temperatures hyperfine
interactions must play an important role in the molecular spin dynamic.",0209497v2
2003-10-14,Spin resonance peak in Na$_{x}$CoO$_{2}\cdot y$H$_{2}$O superconductors: A probe of the pairing symmetry,"Motivated by the recent discovery of superconductivity in layered
Na$_{x}$CoO$_{2}\cdot y$H$_{2}$O compound, we investigate theoretically the
spin dynamics in the superconducting state with three possible $p_{x}+ip_{y}$-,
$d+id'$-, and $f$-wave pairing symmetries in two-dimensional triangular
lattices. We find that a spin resonance peak, which is elaborated to have a
close relevance to the relative phase of the gap function and the geometry of
the Fermi surface, appears in both in-plane and out-of-plane components of the
spin susceptibility $\chi$ for the spin-singlet $d+id'$-wave pairing, while
only in the out-of-plane(in-plane) component of $\chi$ for the spin-triplet
$p_{x}+ip_{y}$-wave ($f$-wave) pairing. Because the pairing symmetry in this
compound is still hotly debated at present, this distinct feature may be used
to probe or determine it unambiguously with future neutron scattering
experiments.",0310308v1
2003-12-11,Nondemolition measurements of a single quantum spin using Josephson oscillations,"We consider a Josephson junction containing a single localized spin 1/2
between conventional singlet superconducting electrodes. We study the spin
dynamics and measurements when a dc-magnetic field ${\bf B}\parallel z$ acts on
the spin and the junction is embedded into a dissipative circuit. We show that
when tunneling or a voltage are turned on at time $t=0$ the Josephson current
starts to oscillate with an amplitude depending on the initial ($t=0$) value of
the spin $z$-component, $S_z= \pm 1/2$. At low temperatures, when effects of
quasiparticles may be neglected, this procedure realizes a
quantum-non-demolition (QND) measurement of $S_z$.",0312274v2
2004-03-05,Crossover to non-Fermi-liquid spin dynamics in cuprates,"The antiferromagnetic spin correlation function $S_{\bf Q}$, the staggered
spin susceptibility $\chi_{\bf Q}$ and the energy scale $\omega_{FL}=S_{\bf
Q}/\chi_{\bf Q}$ are studied numerically within the t-J model and the Hubbard
model, as relevant to cuprates. It is shown that $\omega_{FL}$, related to the
onset of the non-Fermi-liquid spin response at $T>\omega_{FL}$, is very low in
the regime below the 'optimum' hole doping $c_h < c_h^* \sim 0.16$, while it
shows a steep increase in the overdoped regime. A quantitative analysis of NMR
spin-spin relaxation-rate $1/T_{2G}$ for various cuprates reveals a similar
behavior, indicating on a sharp, but continuous, crossover between a
Fermi-liquid and a non-Fermi-liquid behavior as a function of doping.",0403165v1
2004-11-08,A spin pump turnstile: parametric pumping of a spin-polarized current through a nearly-closed quantum dot,"We investigate parametric pumping of a spin-polarized current through a
nearly-closed quantum dot in a perpendicular magnetic field. Pumping is
achieved by tuning the tunnel couplings to the left and right lead - thereby
operating the quantum dot as a turnstile - and changing either the magnetic
field or a gate-voltage. We analyze the quantum dynamics of a pumping cycle and
the limiting time scales for operating the quantum dot turnstile as a pure spin
pump. The proposed device can be used as a fully controllable double-sided and
bipolar spin filter and to inject spins ""on demand"".",0411193v2
2005-03-01,Dynamic spin Jahn-Teller effect in small magnetic clusters,"We study the effect of spin-phonon coupling in small magnetic clusters,
concentrating on a S=1/2 ring of 4 spins coupled antiferromagnetically. If the
phonons are treated as classical variables, there is a critical value of the
spin-phonon coupling above which a static distortion occurs. This is a good
approximation if the zero point energy is small compared to the energy gain due
to the distortion, which is true for large exchange interactions compared to
the phonons energy ($J\gg\hbar\omega$). In the opposite limit, one can
integrate out the phonon degrees of freedom and get an effective spin
hamiltonian. Using exact diagonalizations to include the quantum nature of both
spins and phonons, we obtain the spectrum in the whole range of parameters and
explicit the crossover between the classical and quantum regimes. We then
establish quantitatively the limits of validity of two widely used approaches
(one in the quantum and one in the classical limits) and show that they are
quite poor for small magnetic clusters. We also show that upon reducing
$\hbar\omega/J$ the first excitation of a 4-site cluster becomes a singlet, a
result that could be relevant for Cu$_2$Te$_2$O$_5$Br$_2$.",0503017v1
2005-08-25,Energy-resolved electron-spin dynamics at surfaces of p-doped GaAs,"Electron-spin relaxation at different surfaces of p-doped GaAs is
investigated by means of spin, time and energy resolved 2-photon photoemission.
These results are contrasted with bulk results obtained by time-resolved
Faraday rotation measurements as well as calculations of the Bir-Aronov-Pikus
spin-flip mechanism. Due to the reduced hole density in the band bending region
at the (100) surface the spin-relaxation time increases over two orders of
magnitude towards lower energies. At the flat-band (011) surface a constant
spin relaxation time in agreement with our measurements and calculations for
bulk GaAs is obtained.",0508601v1
2005-10-07,Theory of orbital state and spin interactions in ferromagnetic titanates,"A spin-orbital superexchange Hamiltonian in a Mott insulator with $t_{2g}$
orbital degeneracy is investigated. More specifically, we focus on a spin
ferromagnetic state of the model and study a collective behavior of orbital
angular momentum. Orbital order in the model occurs in a nontrivial way -- it
is stabilized exclusively by quantum effects through the order-from-disorder
mechanism. Several energetically equivalent orbital orderings are identified.
Some of them are specified by a quadrupole ordering and have no unquenched
angular momentum at low energy. Other states correspond to a noncollinear
ordering of the orbital angular momentum and show the magnetic Bragg peaks at
specific positions. Order parameters are unusually small because of strong
quantum fluctuations. Orbital contribution to the resonant x-ray scattering is
discussed. The dynamical magnetic structure factor in different ordered states
is calculated. Predictions made should help to observe elementary excitations
of orbitals and also to identify the type of the orbital order in ferromagnetic
titanates. Including further a relativistic spin-orbital coupling, we derive an
effective low-energy spin Hamiltonian and calculate a spin-wave spectrum, which
is in good agreement with recent experimental observations in YTiO$_3$.",0510175v1
2005-10-14,Analytical Solution of Electron Spin Decoherence Through Hyperfine Interaction in a Quantum Dot,"We analytically solve the {\it Non-Markovian} single electron spin dynamics
due to hyperfine interaction with surrounding nuclei in a quantum dot. We use
the equation-of-motion method assisted with a large field expansion, and find
that virtual nuclear spin flip-flops mediated by the electron contribute
significantly to a complete decoherence of transverse electron spin correlation
function. Our results show that a 90% nuclear polarization can enhance the
electron spin $T_2$ time by almost two orders of magnitude. In the long time
limit, the electron spin correlation function has a non-exponential $1/t^2$
decay in the presence of both polarized and unpolarized nuclei.",0510379v3
2006-01-30,Multiple transfer of angular momentum quanta from a spin-polarized hole to magnetic ions in ZnMnSe/ZnBeSe quantum wells,"The magnetization kinetics in (Zn,Mn)Se/(Zn,Be)Se quantum wells has been
studied on a ps-time scale after pulsed laser excitation. The magnetization
induced by an external magnetic field is reduced by up to 30% during ~100 ps
due to spin and energy transfer from photocarriers to Mn spin system. The giant
Zeeman splitting leads to a complete spin polarization of the carriers,
resulting in a strong suppression of flip-flop processes between carriers and
magnetic ions. Therefore a multiple angular momentum transfer from each
spin-polarized hole to the Mn ions becomes the dominant mechanism in the
magnetization dynamics. A model based on spin-momentum coupling in the valence
band is suggested for explaining this transfer.",0601661v1
2006-02-18,Spin waves in quasi-equilibrium spin systems,"Using the Landau Fermi liquid theory we have discovered a new regime for the
propagation of spin waves in a quasi-equilibrium spin systems. We have
determined the dispersion relation for the transverse spin waves and found that
one of the modes is gapless. The gapless mode corresponds to the precessional
mode of the magnetization in a paramagnetic system in the absence of an
external magnetic field. One of the other modes is gapped which is associated
with the precession of the spin current around the internal field. The gapless
mode has a quadratic dispersion leading to some interesting thermodynamic
properties including a $T^{3/2}$ contribution to the specific heat. We also
show that these modes make significant contributions to the dynamic structure
function.",0602435v1
2006-07-04,The Compressible Ising Spin Glass: Simulation Results,"This paper reports numerical studies of a compressible version of the Ising
spin glass in two dimensions. Compressibility is introduced by adding a term
that couples the spin-spin interactions and local lattice deformations to the
standard Edwards-Anderson model. The relative strength of this coupling is
controlled by a single dimensionless parameter, mu. The timescale associated
with the dynamics of the system grows exponentially as mu is increased, and the
energy of the compressible system is shifted downward by an amount proportional
to mu times the square of the uncoupled energy. This result leads to the
formulation of a simplified model that depends solely on spin variables;
analysis and numerical simulations of the simplified model predict a critical
value of the coupling strength above which the spin-glass transition cannot
exist at any temperature.",0607089v2
2006-10-21,Enhanced spin relaxation time due to electron-electron scattering in semiconductors,"We present a detailed experimental and theoretical analysis of the spin
dynamics of two-dimensional electron gases (2DEGs) in a series of n-doped
GaAs/AlGaAs quantum wells. Picosecond-resolution polarized pump-probe
reflection techniques were applied in order to study in detail the
temperature-, concentration- and quantum-well-width- dependencies of the spin
relaxation rate of a small photoexcited electron population. A rapid
enhancement of the spin life-time with temperature up to a maximum near the
Fermi temperature of the 2DEG was demonstrated experimentally. These
observations are consistent with the D'yakonov-Perel' spin relaxation mechanism
controlled by electron-electron collisions. The experimental results and
theoretical predictions for the spin relaxation times are in good quantitative
agreement.",0610587v1
2006-12-31,Algebraic vortex liquid theory of a quantum antiferromagnet on the kagome lattice,"There is growing evidence from both experiment and numerical studies that low
half-odd integer quantum spins on a kagome lattice with predominant
antiferromagnetic near neighbor interactions do not order magnetically or break
lattice symmetries even at temperatures much lower than the exchange
interaction strength. Moreover, there appear to be a plethora of low energy
excitations, predominantly singlets but also spin carrying, which suggest that
the putative underlying quantum spin liquid is a gapless ``critical spin
liquid'' rather than a gapped spin liquid with topological order. Here, we
develop an effective field theory approach for the spin-1/2 Heisenberg model
with easy-plane anisotropy on the kagome lattice. By employing a vortex duality
transformation, followed by a fermionization and flux-smearing, we obtain
access to a gapless yet stable critical spin liquid phase, which is described
by (2+1)-dimensional quantum electrodynamics (QED$_3$) with an emergent
$\mathrm{SU}(8)$ flavor symmetry. The specific heat, thermal conductivity, and
dynamical structure factor are extracted from the effective field theory, and
contrasted with other theoretical approaches to the kagome antiferromagnet.",0701020v3
2007-02-01,Stabilizing effect of nuclear quadrupole interaction on the polarization of electron-nuclear spin system in a quantum dot,"Nuclear quadrupole interaction extends the limits imposed by hyperfine
interaction on the spin coherence of the electron and nuclei in a quantum dot.
The strain-induced nuclear quadrupole interaction suppresses the nuclear spin
flip and makes possible the zero-field dynamic nuclear polarization in
self-organized InP/InGaP quantum dots. The direction of the effective nuclear
magnetic field is fixed in space, thus quenching the magnetic depolarization of
the electron spin in the quantum dot. The quadrupole interaction suppresses the
zero-field electron spin decoherence also for the case of non-polarized nuclei.
These results provide a new vision of the role of the nuclear quadrupole
interaction in nanostructures: it elongates the spin memory of the
electron-nuclear system.",0702010v4
2007-02-02,Quantum fluctuation-induced uniaxial and biaxial spin nematics,"It is shown that zero point quantum fluctuations (ZPQFs) completely lift the
accidental continuous degeneracy that is found in mean field analysis of
quantum spin nematic phases of hyperfine spin 2 cold atoms. The result is two
distinct ground states which have higher symmetries: a uniaxial spin nematic
and a biaxial spin nematic with dihedral symmetry ${Dih}_4$. There is a novel
first order quantum phase transition between the two phases as atomic
scattering lengths are varied. We find that the ground state of $^{87}Rb$ atoms
should be a uniaxial spin nematic. We note that the energy barrier between the
phases could be observable in dynamical experiments.",0702052v3
2007-02-26,Spin-gapped incoherent metal with preformed pairing in the doped antiferromagnetic Mott insulator,"We investigate how the antiferromagnetic Mott insulator evolves into the
d-wave BCS superconductor through hole doping. Allowing spin fluctuations in
the strong coupling approach, we find a spin-gapped incoherent metal with
preformed pairing as an intermediate phase between the antiferromagnetic Mott
insulator and d-wave superconductor. This non-Fermi liquid metal is identified
with an infrared stable fixed point in the spin-decomposition gauge theory,
analogous to the spin liquid insulator in the slave-boson gauge theory. We
consider the single particle spectrum and dynamical spin susceptibility in the
anomalous metallic phase, and discuss physical implications.",0702586v3
1998-10-07,Propagating spin modes in canonical quantum gravity,"One of the main results in canonical quantum gravity is the introduction of
spin network states as a basis on the space of kinematical states. To arrive at
the physical state space of the theory though we need to understand the
dynamics of the quantum gravitational states. To this aim we study a model in
which we allow for the spins, labeling the edges of spin networks, to change
according to simple rules. The gauge invariance of the theory, restricting the
possible values for the spins, induces propagating modes of spin changes. We
investigate these modes under various assumptions about the parameters of the
model.",9810024v1
2006-05-27,Higher-order spin effects in the dynamics of compact binaries I. Equations of motion,"We derive the equations of motion of spinning compact binaries including the
spin-orbit (SO) coupling terms one post-Newtonian (PN) order beyond the
leading-order effect. For black holes maximally spinning this corresponds to
2.5PN order. Our result for the equations of motion essentially confirms the
previous result by Tagoshi, Ohashi and Owen. We also compute the spin-orbit
effects up to 2.5PN order in the conserved (Noetherian) integrals of motion,
namely the energy, the total angular momentum, the linear momentum and the
center-of-mass integral. We obtain the spin precession equations at 1PN order
beyond the leading term, as well. Those results will be used in a future paper
to derive the time evolution of the binary orbital phase, providing more
accurate templates for LIGO-Virgo-LISA type interferometric detectors.",0605139v4
1998-05-20,Higher Spin N=8 Supergravity,"The product of two N=8 supersingletons yields an infinite tower of massless
states of higher spin in four dimensional anti de Sitter space. All the states
with spin s > 1/2 correspond to generators of Vasiliev's super higher spin
algebra shs^E (8|4) which contains the D=4, N=8 anti de Sitter superalgebra
OSp(8|4). Gauging the higher spin algebra and introducing a matter multiplet in
a quasi-adjoint representation leads to a consistent and fully nonlinear
equations of motion as shown sometime ago by Vasiliev. We show the embedding of
the N=8 AdS supergravity equations of motion in the full system at the
linearized level and discuss the implications for the embedding of the
interacting theory. We furthermore speculate that the boundary N=8 singleton
field theory yields the dynamics of the N=8 AdS supergravity in the bulk,
including all higher spin massless fields, in an unbroken phase of M-theory.",9805125v2
2002-02-13,On the Sutherland Spin Model of B_N Type and its Associated Spin Chain,"The B_N hyperbolic Sutherland spin model is expressed in terms of a suitable
set of commuting Dunkl operators. This fact is exploited to derive a complete
family of commuting integrals of motion of the model, thus establishing its
integrability. The Dunkl operators are shown to possess a common flag of
invariant finite-dimensional linear spaces of smooth scalar functions. This
implies that the Hamiltonian of the model preserves a corresponding flag of
smooth spin functions. The discrete spectrum of the restriction of the
Hamiltonian to this spin flag is explicitly computed by triangularization. The
integrability of the hyperbolic Sutherland spin chain of B_N type associated
with the dynamical model is proved using Polychronakos's ""freezing trick"".",0202080v3
2004-07-21,Superfield Theories in Tensorial Superspaces and the Dynamics of Higher Spin Fields,"We present the superfield generalization of free higher spin equations in
tensorial superspaces and analyze tensorial supergravities with GL(n) and SL(n)
holonomy as a possible framework for the construction of a non-linear higher
spin field theory. Surprisingly enough, we find that the most general solution
of the supergravity constraints is given by a class of superconformally flat
and OSp(1|n)-related geometries. Because of the conformal symmetry of the
supergravity constraints and of the higher spin field equations such geometries
turn out to be trivial in the sense that they cannot generate a `minimal'
coupling of higher spin fields to their potentials even in curved backgrounds
with a non-zero cosmological constant. This suggests that the construction of
interacting higher spin theories in this framework might require an extension
of the tensorial superspace with additional coordinates such as twistor-like
spinor variables which are used to construct the OSp(1|2n) invariant
(`preonic') superparticle action in tensorial superspace.",0407180v2
2006-03-28,Gauge invariant Lagrangian construction for massive higher spin fermionic fields,"We formulate a general gauge invariant Lagrangian construction describing the
dynamics of massive higher spin fermionic fields in arbitrary dimensions.
Treating the conditions determining the irreducible representations of Poincare
group with given spin as the operator constraints in auxiliary Fock space, we
built the BRST charge for the model under consideration and find the gauge
invariant equations of motion in terms of vectors and operators in the Fock
space. It is shown that like in massless case hep-th/0410215, the massive
fermionic higher spin field models are the reducible gauge theories and the
order of reducibility grows with the value of spin. In compare with all
previous approaches, no off-shell constraints on the fields and the gauge
parameters are imposed from the very beginning, all correct constraints emerge
automatically as the consequences of the equations of motion. As an example, we
derive a gauge invariant Lagrangian for massive spin 3/2 field.",0603212v3
2000-11-14,The Isospin Asymmetry in the Pseudo-spin Dynamical Symmetry,"Pseudo-spin symmetry in nuclei is investigated considering the Dirac equation
with a Lorentz structured Woods-Saxon potential. The isospin correlation of the
energy splittings of pseudo-spin partners with the nuclear potential parameters
is studied. We show that in an isotopic chain, the pseudo-spin symmetry is
better realized for neutrons than for protons. This behavior comes from balance
effects amongst the central nuclear potential parameters. In general, we found
an isospin asymmetry of the nuclear pseudo-spin interaction, opposed to the
nuclear spin-orbit interaction which is quasi isospin symmetric.",0011053v3
1999-02-16,"Spin systems, spin coherent states and quasi-exactly solvable models","Spin coherent states play a crucial role in defining QESM (quasi-exactly
solvable models) establishing a strict correspondence between energy spectra of
spin systems and low-lying quantum states for a particle moving in a potential
field of a certain form. Spin coherent states are also used for finding the
Wigner-Kirkwood expansion and quantum corrections to energy quantization rules.
The closed equation which governs dynamics of a quantum system is obtained in
the spin coherent representation directly for observable quantities.",9902058v1
2003-05-27,Spin squeezing as a measure of entanglement in a two qubit system,"We show that two definitions of spin squeezing extensively used in the
literature [M. Kitagawa and M. Ueda, Phys. Rev. A {\bf 47}, 5138 (1993) and
D.J. Wineland {\it et al.}, Phys. Rev. A {\bf 50}, 67 (1994)] give different
predictions of entanglement in the two-atom Dicke system. We analyze
differences between the definitions and show that the Kitagawa and Ueda's spin
squeezing parameter is a better measure of entanglement than the commonly used
spectroscopic spin squeezing parameter. We illustrate this relation by
examining different examples of a driven two-atom Dicke system in which spin
squeezing and entanglement arise dynamically. We give an explanation of the
source of the difference in the prediction of entanglement using the negativity
criterion for entanglement. For the examples discussed, we find that the
Kitagawa and Ueda's spin squeezing parameter is the sufficient and necessary
condition for entanglement.",0305166v1
2005-08-05,Resurrection of Schrodinger Cat,"Quantum decoherence is the major obstacle in using the potential of
engineered quantum dynamics to revolutionize high-precision measurements,
sensitive detection, or information processing. Here we experimentally
demonstrate that quantum state of a system can be recovered after the state is
destroyed by uncontrollable natural decoherence. Physical system is a cluster
of seven dipolar-coupled nuclear spins of single-labeled 13C-benzene in liquid
crystal. 13C spin plays a role of a device for measuring protons' ""cat"" state,
a superposition of states with six spins up (alive) and six spins down (dead).
Information about the state, stored in the 13C spin, is used to bring the
protons' subsystem into the alive state, while the excess entropy produced by
decoherence is transferred to the ""measuring device"", the 13C spin.",0508052v1
2006-12-11,Quantum chaos with spin-chains in pulsed magnetic fields,"Recently it was found that the dynamics in a Heisenberg spin-chain subjected
to a sequence of periodic pulses from an external, parabolic, magnetic field
can have a close correspondence with the quantum kicked rotor (QKR). The QKR is
a key paradigm of quantum chaos; it has as its classical limit the well-known
Standard Map. It was found that a single spin excitation could be converted
into a pair of non-dispersive, counter-propagating spin coherent states
equivalent to the accelerator modes of the Standard Map. Here we consider how
other types of quantum chaotic systems such as a double-kicked quantum rotor or
a quantum rotor with a double-well potential might be realized with spin
chains; we discuss the possibilities regarding manipulation of the one-magnon
spin waves.",0612074v1
2007-06-01,Weak measurement of quantum dot spin qubits,"The theory of weak quantum measurements is developed for quantum dot spin
qubits. Building on recent experiments, we propose a control cycle to prepare,
manipulate, weakly measure, and perform quantum state tomography. This is
accomplished using a combination of the physics of electron spin resonance,
spin blockade, and Coulomb blockade, resulting in a charge transport process.
We investigate the influence of the surrounding nuclear spin environment, and
find a regime where this environment significantly simplifies the dynamics of
the weak measurement process, making this theoretical proposal realistic with
existing experimental technology. We further consider spin-echo refocusing to
combat dephasing, as well as discuss a realization of ""quantum undemolition"",
whereby the effects of quantum state disturbance are undone.",0706.0180v1
2007-06-01,Systematic analysis of a spin-susceptibility representation of the pairing interaction in the 2D Hubbard model,"A dynamic cluster quantum Monte Carlo algorithm is used to study a spin
susceptibility representation of the pairing interaction for the
two-dimensional Hubbard model with an on-site Coulomb interaction equal to the
bandwidth for various doping levels. We find that the pairing interaction is
well approximated by ${3/2}\Ub(T)^2\chi(K-K')$ with an effective temperature
and doping dependent coupling $\Ub(T)$ and the numerically calculated spin
susceptibility $\chi(K-K')$. We show that at low temperatures, $\Ub$ may be
accurately determined from a corresponding spin susceptibility based
calculation of the single-particle self-energy. We conclude that the strength
of the d-wave pairing interaction, characterized by the mean-field transition
temperature, can be determined from a knowledge of the dressed spin
susceptibility and the nodal quasiparticle spectral weight. This has important
implications with respect to the questions of whether spin fluctuations are
responsible for pairing in the high-T$_c$ cuprates.",0706.0241v1
2007-06-07,Influence of an external magnetic field on the decoherence of a central spin coupled to an antiferromagnetic environment,"Using the spin wave approximation, we study the decoherence dynamics of a
central spin coupled to an antiferromagnetic environment under the application
of an external global magnetic field. The external magnetic field affects the
decoherence process through its effect on the antiferromagnetic environment. It
is shown explicitly that the decoherence factor which displays a Gaussian decay
with time depends on the strength of the external magnetic field and the
crystal anisotropy field in the antiferromagnetic environment. When the values
of the external magnetic field is increased to the critical field point at
which the spin-flop transition (a first-order quantum phase transition) happens
in the antiferromagnetic environment, the decoherence of the central spin
reaches its highest point. This result is consistent with several recent
quantum phase transition witness studies. The influences of the environmental
temperature on the decoherence behavior of the central spin are also
investigated.",0706.0934v1
2007-06-11,Theory of Neutron Scattering in High-T$_c$ Cuprates: Two Component Spin-Fermion Model,"Recent neutron scattering experiments have revealed that the generic form of
the magnetic excitations in the high-Tc cuprates of wide range of doping has
the so-called ""hourglass"" shape; it features both upward and downward
excitations at the incommensurate (IC) momenta spanning from the resonance peak
at the commensurate momentum $(\pi,\pi)$. We propose the two-component
spin-fermion model as a minimal phenomenological model which has both local
spins and itinerant fermions as independent degrees of freedom. Our
calculations of the dynamic spin correlation function provide good agreement
with experiments and show: (1) the upward dispersion branch of magnetic
excitations is mostly due to the local spin excitations; (2) the downward
dispersion branch is from collective spin excitations of fermions; (3) the
resonance mode is a mixture of both degrees of freedom.",0706.1387v2
2007-08-16,Spin-transfer torques in anti-ferromagnetic metals from first principles,"In spite of the absence of a macroscopic magnetic moment, an anti-ferromagnet
is spin-polarized on an atomic scale. The electric current passing through a
conducting anti-ferromagnet is polarized as well, leading to spin-transfer
torques when the order parameter is textured, such as in anti-ferromagnetic
non-collinear spin valves and domain walls. We report a first principles study
on the electronic transport properties of anti-ferromagnetic systems. The
current-induced spin torques acting on the magnetic moments are comparable with
those in conventional ferromagnetic materials, leading to measurable angular
resistances and current-induced magnetization dynamics. In contrast to
ferromagnets, spin torques in anti-ferromagnets are very nonlocal. The torques
acting far away from the center of an anti-ferromagnetic domain wall should
facilitate current-induced domain wall motion.",0708.2143v2
2007-10-10,Time evolution and decoherence of a spin-1/2 particle coupled to a spin bath in thermal equilibrium,"The time evolution of a spin-1/2 particle under the influence of a locally
applied external magnetic field, and interacting with anisotropic spin
environment in thermal equilibrium at temperature $T$ is studied. The exact
analytical form of the reduced density matrix of the central spin is calculated
explicitly for finite number of bath spins. The case of an infinite number of
environmental spins is investigated using the convergence of the rescaled bath
operators to normal Gaussian random variables. In this limit, we derive the
analytical form of the components of the Bloch vector for antiferromagnetic
interactions within the bath, and we investigate the short-time and long-time
behavior of reduced dynamics. The effect of the external magnetic field, the
anisotropy and the temperature of the bath on the decoherence of the central
spin is discussed.",0710.2001v1
2007-10-19,Exponential decay in a spin bath,"We show that the coherence of an electron spin interacting with a bath of
nuclear spins can exhibit a well-defined purely exponential decay for special
(`narrowed') bath initial conditions in the presence of a strong applied
magnetic field. This is in contrast to the typical case, where spin-bath
dynamics have been investigated in the non-Markovian limit, giving
super-exponential or power-law decay of correlation functions. We calculate the
relevant decoherence time T_2 explicitly for free-induction decay and find a
simple expression with dependence on bath polarization, magnetic field, the
shape of the electron wave function, dimensionality, total nuclear spin I, and
isotopic concentration for experimentally relevant heteronuclear spin systems.",0710.3762v2
2007-10-25,Optical detection of single electron spin resonance in a quantum dot,"We demonstrate optically detected spin resonance of a single electron
confined to a self-assembled quantum dot. The dot is rendered dark by resonant
optical pumping of the spin with a coherent laser. Contrast is restored by
applying a radio frequency (rf) magnetic field at the spin resonance. The
scheme is sensitive even to rf fields of just a few micro-T. In one case, the
spin resonance behaves exactly as a driven 3-level quantum system (a
lambda-system) with weak damping. In another, the dot exhibits remarkably
strong (67% signal recovery) and narrow (0.34 MHz) spin resonances with
fluctuating resonant positions, evidence of unusual dynamic processes of
non-Markovian character.",0710.4901v1
2007-12-02,Electrical detection of spin echoes for phosphorus donors in silicon,"The electrical detection of spin echoes via echo tomography is used to
observe decoherence processes associated with the electrical readout of the
spin state of phosphorus donor electrons in silicon near a SiO$_2$ interface.
Using the Carr-Purcell pulse sequence, an echo decay with a time constant of
$1.7\pm0.2 \rm{\mu s}$ is observed, in good agreement with theoretical modeling
of the interaction between donors and paramagnetic interface states. Electrical
spin echo tomography thus can be used to study the spin dynamics in realistic
spin qubit devices for quantum information processing.",0712.0141v1
2007-12-06,Energy Level Lifetimes in the Single-Molecule Magnet Fe_8 : Experiments and Simulations,"We present pump-probe measurements on the single-molecule magnet Fe_8 with
microwave pulses having a length of several nanoseconds. The microwave
radiation in the experiments is located in the frequency range between 104 GHz
and 118 GHz. The dynamics of the magnetization of the single Fe_8 crystal is
measured using micrometer-sized Hall sensors. This technique allows us to
determine the level lifetimes of excited spin states, that are found to be in
good agreement with theoretical calculations. The theory, to which we compare
our experimental results, is based on a general spin-phonon coupling formalism,
which involves spin transitions between nearest and next-nearest energy levels.
We show that good agreement between theory and experiments is only obtained
when using both the Delta m_S = +-1 transition as well as Delta m_S = +-2,
where Delta m_S designates a change in the spin quantum number m_S. Temperature
dependent studies of the level lifetimes of several spin states allow us
finally to determine experimentally the spin-phonon coupling constants.",0712.0931v1
2008-01-16,Intrinsic Cutoff and Acausality for Massive Spin 2 Fields Coupled to Electromagnetism,"We couple a massive spin 2 particle to electromagnetism. By introducing new,
redundant degrees of freedom using the Stueckelberg formalism, we extract an
intrinsic, model independent UV cutoff of the effective field theory describing
this system. The cutoff signals both the onset of a strongly interacting
dynamical regime and a finite size for the spin 2 particle. We show that the
existence of a cutoff is strictly connected to other pathologies of interacting
high-spin fields, such as the Velo-Zwanziger acausality. We also briefly
comment on implications of this result for the detection of high spin states
and on its possible generalization to arbitrary spin.",0801.2581v3
2008-02-29,Classical and Quantum Spins in Curved Spacetimes,"A comparative analysis of the Mathisson-Papapetrou and Pomeransky-Khriplovich
equations is presented. Motion of spinning particles and their spins in
gravitational fields and noninertial frames is considered. The angular velocity
of spin precession defined by the Pomeransky-Khriplovich equations depends on
the choice of the tetrad. The connection of such a dependence with the Thomas
precession is established. General properties of spin interactions with
gravitational fields are discussed. It is shown that dynamics of classical and
quantum spins in curved spacetimes is identical. A manifestation of the
equivalence principle in an evolution of the helicity is analyzed.",0802.4443v1
2008-03-10,Electrodynamics of spin currents in superconductors,"In recent work we formulated a new set of electrodynamic equations for
superconductors as an alternative to the conventional London equations,
compatible with the prediction of the theory of hole superconductivity that
superconductors expel negative charge from the interior towards the surface.
Charge expulsion results in a macroscopically inhomogeneous charge distribution
and an electric field in the interior, and because of this a spin current is
expected to exist. Furthermore, we have recently shown that a dynamical
explanation of the Meissner effect in superconductors leads to the prediction
that a spontaneous spin current exists near the surface of superconductors. In
this paper we extend the electrodynamic equations proposed earlier for the
charge density and charge current to describe also the space and time
dependence of the spin density and spin current. This allows us to determine
the magnitude of the expelled negative charge and interior electric field as
well as of the spin current in terms of other measurable properties of
superconductors. We also provide a 'geometric' interpretation of the difference
between type I and type II superconductors, discuss the relationship between
our model and Slater's seminal work on superconductivity, and discuss the
magnitude of the expected novel effects for elemental and other
superconductors.",0803.1198v1
2008-05-02,Electron spin decoherence of single Nitrogen-Vacancy defects in diamond,"We present a theoretical analysis of the electron spin decoherence in single
Nitrogen-Vacancy defects in ultra-pure diamond. The electron spin decoherence
is due to the interactions with Carbon-13 nuclear spins in the diamond lattice.
Our approach takes advantage of the low concentration (1.1%) of Carbon-13 and
their random distribution in the diamond lattice by an algorithmic aggregation
of spins into small, strongly interacting groups. By making use of this
\emph{disjoint cluster} approach, we demonstrate a possibility of non-trival
dynamics of the electron spin that can not be described by a single time
constant. This dependance is caused by a strong coupling between the electron
and few nuclei and results, in particular, in a substantial echo signal even at
microsecond time scales. Our results are in good agreement with recent
experimental observations.",0805.0327v1
2008-05-29,Wave packet dynamics in 2DEG with spin orbit coupling: splitting and zitterbewegung,"We study the effect of splitting and zitterbewegung of 1D and 2D electron
wave packets in the semiconductor quantum well under the influence of the
Rashba spin orbit coupling. Results of our investigations show that the spin
orbit interaction induces dramatic qualitative changes in the evolution of spin
polarized wave packet. The initial wave packet splits into two parts with
different spin polarization propagating with unequal group velocity. This
splitting appears due to the presence of two branches of electron spectrum
corresponding to the stationary states with different chirality. It is
demonstrated also that in the presence of external magnetic field B$
perpendicular to the electron gas plane the wave packet splits into two parts
which rotates with different cyclotron frequencies. It was shown that after
some periods the electron density distributes around cyclotron orbit and the
motion acquire an irregular character. Our calculations were made for both
cases of weak and strong spin orbit coupling.",0805.4489v2
2008-06-19,Coherent optical control of correlation waves of spins in semiconductors,"We calculate the dynamical fluctuation spectrum of electronic spins in a
semiconductor under a steady-state illumination by light containing
polarization squeezing correlations. Taking into account quasi-particle
lifetime and spin relaxation for this non-equilibrium situation we consider up
to fourth order optical effects which are sensitive to the squeezing phases.
  We demonstrate the possibility to control the spin fluctuations by optically
modulating these phases as a function of frequency, leading to a non-Lorentzian
spectrum which is very different from the thermal equilibrium fluctuations in
n-doped semiconductors. Specifically, in the time-domain spin-spin correlation
can exhibit time delays and sign flips originating from the phase modulations
and correlations of polarizations, respectively. For higher light intensity we
expect a regime where the squeezing correlations will dominate the spectrum.",0806.3291v1
2008-08-21,Theory of Electron Spin Relaxation in ZnO,"Doped ZnO is a promising material for spintronics applications. For such
applications, it is important to understand the spin dynamics and particularly
the spin coherence of this II-VI semiconductor. The spin lifetime $\tau_{s}$
has been measured by optical orientation experiments, and it shows a surprising
non-monotonic behavior with temperature. We explain this behavior by invoking
spin exchange between localized and extended states. Interestingly, the effects
of spin-orbit coupling are by no means negligible, in spite of the relatively
small valence band splitting. This is due to the wurtzite crystal structure of
ZnO. Detailed analysis allows us to characterize the impurity binding energies
and densities, showing that optical orientation experiments can be used as a
characterization tool for semiconductor samples.",0808.2913v3
2008-08-22,Weak quasistatic magnetism in the frustrated Kondo lattice Pr_2Ir_2O_7,"Muon spin relaxation experiments have been performed in the pyrochlore
iridate Pr_2Ir_2O_7 for temperatures in the range 0.025-250 K. Kubo-Toyabe
relaxation functions are observed up to > 200 K, indicating static magnetism
over this temperature range. The T -> 0 static muon spin relaxation rate
Delta(0) ~ 8 mus^-1 implies a weak quasistatic moment (~0.1 mu_B). The
temperature dependence of Delta is highly non-mean-field-like, decreasing
smoothly by orders of magnitude but remaining nonzero below ~150 K. The data
rule out ordering of the full Pr^3+ CEF ground-state moment (3.0 mu_B) down to
0.025 K. The weak static magnetism is most likely due to hyperfine-enhanced
^141Pr nuclear magnetism. The dynamic relaxation rate lambda increases markedly
below ~20 K, probably due to slowing down of spin fluctuations in the
spin-liquid state. At low temperatures lambda is strong and
temperature-independent, indicative of a high density of low-lying spin
excitations as is common in frustrated antiferromagnets.",0808.3142v1
2008-10-12,Geometrodynamics of Spinning Light,"The semiclassical evolution of spinning particles has recently been
re-examined in condensed matter physics, high energy physics, and optics,
resulting in the prediction of the intrinsic spin Hall effect associated with
the Berry phase. A fundamental nature of this effect is related to the
spin-orbit interaction and topological monopoles. Here we report a unified
theory and a direct observation of two mutual phenomena: a spin-dependent
deflection (the spin Hall effect) of photons and the precession of the Stokes
vector along the coiled ray trajectory of classical geometrical optics. Our
measurements are in perfect agreement with theoretical predictions, thereby
verifying the dynamical action of the topological Berry-phase monopole in the
evolution of light. These results may have promising applications in
nano-optics and can be immediately extrapolated to the evolution of massless
particles in a variety of physical systems.",0810.2136v1
2008-11-18,Optical manipulation of a single Mn spin in a CdTe-based quantum dot,"A system of two coupled CdTe quantum dots, one of them containing a single Mn
ion, was studied in continuous wave and modulated photoluminescence,
photoluminescence excitation, and photon correlation experiments. Optical
writing of information in the spin state of the Mn ion has been demonstrated,
using orientation of the Mn spin by spin-polarized carriers transferred from
the neighbor quantum dot. Mn spin orientation time values from 20 ns to 100 ns
were measured, depending on the excitation power. Storage time of the
information in the Mn spin was found to be enhanced by application of a static
magnetic field of 1 T, reaching hundreds of microseconds in the dark. Simple
rate equation models were found to describe correctly static and dynamical
properties of the system.",0811.2898v1
2009-01-30,Anomalous Spin segregation in a weakly interacting two-component Fermi gas,"We explain the spin segregation seen at Duke in a two-component gas of 6Li
[Du, Luo, Clancy and Thomas, Phys. Rev. Lett. 101,150401 (2008)] as a
mean-field effect describable via a collisionless Boltzmann equation. As seen
in experiments, we find that slight differences in the trapping potentials in
the two spin states drive small spin currents. Hartree-Fock type interactions
convert these currents into a redistribution of populations in energy space,
and consequently a long lived spin texture develops. We explore the interaction
strength dependence of these dynamics, finding close agreement with experiment.",0901.4808v2
2009-02-02,Stationary Spinning Strings and Symmetries of Classical Spacetimes,"We explore the symmetries of classical stationary spacetimes in terms of the
dynamics of a spinning string described by a worldsheet supersymmetric action.
We show that for stationary configurations of the string, the action reduces to
that for a pseudo-classical spinning point particle in an effective space,
which is a conformally scaled quotient space of the original spacetime. As an
example, we consider the stationary spinning string in the Kerr-Newman
spacetime, whose motion is equivalent to that of the spinning point particle in
the three-dimensional effective space. We present the Killing tensor as well as
the spin-valued Killing vector of this space. However, the nongeneric
supersymmetry corresponding to the Killing-Yano tensor of the Kerr-Newman
spacetime is lost in the effective space.",0902.0258v1
2009-02-03,Spin relaxation in sub-monolayer and monolayer InAs structures grown in GaAs matrix,"Electron spin dynamics in InAs/GaAs heterostructures consisting of a single
layer of InAs (1/3$\sim$1 monolayer) embeded in (001) and (311)A GaAs matrix
was studied by means of time-resolved Kerr rotation spectroscopy. The spin
relaxation time of the sub-monolayer InAs samples is significantly enhanced,
compared with that of the monolayer InAs sample. We attributed the slowing of
the spin relaxation to dimensionally constrained
D\textquoteright{}yakonov-Perel\textquoteright{} mechanism in the motional
narrowing regime. The electron spin relaxation time and the effective g-factor
in sub-monolayer samples were found to be strongly dependent on the
photon-generated carrier density. The contribution from both
D\textquoteright{}yakonov-Perel\textquoteright{} mechanism and Bir-Aronov-Pikus
mechanism were discussed to interpret the temperature dependence of spin
decoherence at various carrier densities.",0902.0484v1
2009-05-11,"Hyperfine interaction mediated exciton spin relaxation in (In,Ga)As quantum dots","The population dynamics of dark and bright excitons in (In,Ga)As/GaAs quantum
dots is studied by two-color pump-probe spectroscopy in an external magnetic
field. With the field applied in Faraday geometry and at T<20 K, the dark
excitons decay on a ten nanoseconds time scale unless the magnetic field
induces a resonance with a bright exciton state. At these crossings their
effective lifetime is drastically shortened due to spin flips of either
electron or hole by which the dark excitons are converted into bright ones. Due
to the quasielastic character we attribute the origin of these flips to the
hyperfine interaction with the lattice nuclei. We compare the exciton spin
relaxation times in the two resonances and find that the spin flip involving an
electron is approximately 25 times faster than the one of the hole. A
temperature increase leads to a considerable, nonmonotonic decrease of the dark
exciton lifetime. Here phonon-mediated spin flips due to the spin-orbit
interaction gradually become more important.",0905.1586v2
2009-05-27,Exciton spin-flip rate in quantum dots determined by a modified local density of optical states,"The spin-flip rate that couples dark and bright excitons in self-assembled
quantum dots is obtained from time-resolved spontaneous emission measurements
in a modified local density of optical states. Employing this technique, we can
separate effects due to non-radiative recombination and unambiguously record
the spin-flip rate. The dependence of the spin-flip rate on emission energy is
compared in detail to a recent model from the literature, where the spin flip
is due to the combined action of short-range exchange interaction and acoustic
phonons. We furthermore observe a surprising enhancement of the spin-flip rate
close to a semiconductor-air interface, which illustrates the important role of
interfaces for quantum dot based nanophotonic structures. Our work is an
important step towards a full understanding of the complex dynamics of quantum
dots in nanophotonic structures, such as photonic crystals, and dark excitons
are potentially useful for long-lived coherent storage applications.",0905.4493v1
2009-07-20,Computational study of microwave oscillations in absence of external field in nonstandard spin valves in the diffusive transport limit,"An anomalous (inverse) spin accumulation in the nonmagnetic spacer may build
up when the spin valve consists of magnetic films having different spin
symmetries. This leads to wavy-like dependence of spin-transfer torque on the
angle between magnetizations, as predicted by spin-dependent diffusive
transport model, and also confirmed experimentally. Making use of these
predictions, we have numerically studied the magnetization dynamics in presence
of such a wavy-torque in Co(8 nm)/Cu(10 nm)/Py(8 nm) nanopillar, considering
geometry with extended and etched Co layer. In both cases we specify conditions
for the out-of-plane precession to appear in absence of external magnetic field
and neglecting thermal fluctuations. We prove the assumption of wavy-like
torque angular dependence to be fully consistent with experimental
observations. We also show that some features reported experimentally, like
nonlinear slope of frequency vs. current behavior, are beyond the applicability
range of macrospin approximation and can be explained only by means of full
micromagnetic analysis.",0907.3384v1
2009-08-06,Finite temperature spin-dynamics and phase transitions in spin-orbital models,"We study finite temperature properties of a generic spin-orbital model
relevant to transition metal compounds, having coupled quantum Heisenberg-spin
and Ising-orbital degrees of freedom. The model system undergoes a phase
transition, consistent with that of a 2D Ising model, to an orbitally ordered
state at a temperature set by short-range magnetic order. At low temperatures
the orbital degrees of freedom freeze-out and the model maps on to a quantum
Heisenberg model. The onset of orbital excitations causes a rapid scrambling of
the spin spectral weight away from coherent spin-waves, which leads to a sharp
increase in uniform magnetic susceptibility just below the phase transition,
reminiscent of the observed behavior in the Fe-pnictide materials.",0908.0800v2
2009-08-07,Spin-orbit coupling and semiclassical electron dynamics in noncentrosymmetric metals,"Spin-orbit coupling of electrons with the crystal lattice plays a crucial
role in materials without inversion symmetry, lifting spin degeneracy of the
Bloch states and endowing the resulting nondegenerate bands with complex spin
textures and topologically nontrivial wavefunctions. We present a detailed
symmetry-based analysis of the spin-orbit coupling and the band degeneracies in
noncentrosymmetric metals. We systematically derive the semiclassical equations
of motion for fermionic quasiparticles near the Fermi surface, taking into
account both the spin-orbit coupling and the Zeeman interaction with an applied
magnetic field. Some of the lowest-order quantum corrections to the equations
of motions can be expressed in terms of a fictitious ""magnetic field"" in the
momentum space, which is related to the Berry curvature of the band
wavefunctions. The band degeneracy points or lines serve as sources of a
topologically nontrivial Berry curvature. We discuss the observable effects of
the wavefunction topology, focusing, in particular, on the modifications to the
Lifshitz-Onsager semiclassical quantization condition and the de Haas-van
Alphen effect in noncentrosymmetric metals.",0908.1105v1
2009-09-04,Quantum Imaging of Topologically Unpaired Spin-Polarized Dirac Fermions,"The motion of a relativistic particle is linked to its spin by the Dirac
equation. Remarkably, electrons in two-dimensional materials can mimic such
Dirac particles but must always appear in pairs of opposite spin chirality.
Using topological ideas of chiral boundary electrons wrapping a
three-dimensional crystal with tuned spin-orbit coupling, we show that elusive
unpaired Dirac fermions exist on the surface of a topological insulator parent
matrix, pure antimony. Using scanning tunneling microscopy and angle-resolved
photoemission spectroscopy we image coherent quantum interference between these
particles, map their helical spin texture, and ultimately observe a transition
to a single Dirac fermion distinguished by backscattering suppression via Berry
phase interference. The robust dynamics of these unique spin-polarized carriers
envisage future applications in spintronics and topological quantum
computation.",0909.0921v2
2010-01-22,Spin-flip M1 giant resonance as a challenge for Skyrme forces,"Despite a great success of the Skyrme mean-field approach in exploration of
nuclear dynamics, it seems to fail in description of the spin-flip M1 giant
resonance. The results for different Skyrme parameterizations are contradictory
and poorly agree with experiment. In particular, there is no parameterization
which simultaneously describes the one-peak gross structure of M1 strength in
doubly magic nuclei and two-peak structure in heavy deformed nuclei. The reason
of this mismatch could lie in an unsatisfactory treatment of spin correlations
and spin-orbit interaction. We discuss the present status of the problem and
possible ways of its solution. In particular, we inspect i) the interplay of
the collective shift and spin-orbit splitting, ii) the isovector M1 response
versus isospin-mixed responses, and iii) the role of tensor and isovector
spin-orbit interaction.",1001.3965v1
2010-02-04,Neutron scattering and muSR investigations of the spin liquid state with quenched disorder in LuCuGaO4,"LuCuGaO4 has magnetic Cu2+ and diamagnetic Ga3+ ions distributed on a
triangular bilayer and is suggested to undergo a spin-glass transition with T_g
approximately 0.4 K. Using muSR and neutron scattering measurements, we show
that at low temperature the spins form a short-range correlated state with spin
fluctuations detectable over a wide range of timescales: at 0.05 K magnetic
fluctuations can be detected in both the muSR time window and also extending
beyond 7 meV in the inelastic neutron scattering response, indicating magnetic
fluctuations spanning timescales between 1E-5 and 1E-10 seconds. The dynamical
susceptibility scales according to the form \chi''(\omega)T^\alpha, with
\alpha=1, throughout the measured temperature range (0.05 - 50 K). These
effects are associated with quantum fluctuations and some degree of structural
disorder in ostensibly quite different materials, including certain heavy
fermion alloys, kagome spin liquids, quantum spin glasses, and valence bond
glasses. We therefore suggest LuCuGaO4 is an interesting model compound for the
further examination of disorder and quantum magnetism.",1002.0975v2
2010-04-23,Electron spin relaxation in intrinsic bulk InP semiconductor,"Electron spin dynamics in intrinsic bulk Indium Phosphide (InP) semiconductor
is studied by time resolved pump probe reflectivity (TRPPR) technique using the
co- and counter-circularly polarized femtosecond pulses at room temperature and
70 K. The reflectivity change from bleaching into absorption is observed with
increasing pump photon energy, which can be explained in terms of the spin
sensitive band filling and band gap renormalization effects. Density dependence
of electron spin relaxation time shows similar tendency at room temperature and
70 K. With increasing carrier density, the electron spin relaxation time
increases and then decreases after reaching a maximum value. Our experimental
results agree well with the recent theoretical prediction [Jiang and Wu, Phys.
Rev. B 79, 125206 (2009)] and D'yakonov-Perel' mechanism is considered as a
dominating contribution to the electron spin relaxation in intrinsic bulk InP
semiconductor.",1004.4048v2
2010-06-08,Effects of impurities and vortices on the low-energy spin excitations in high-Tc materials,"We review a theoretical scenario for the origin of the spin-glass phase of
underdoped cuprate materials. In particular it is shown how disorder in a
correlated d-wave superconductor generates a magnetic phase by inducing local
droplets of antiferromagnetic order which eventually merge and form a
quasi-long range ordered state. When correlations are sufficiently strong,
disorder is unimportant for the generation of static magnetism but plays an
additional role of pinning disordered stripe configurations. We calculate the
spin excitations in a disordered spin-density wave phase, and show how disorder
and/or applied magnetic fields lead to a slowing down of the dynamical spin
fluctuations in agreement with neutron scattering and muon spin rotation (muSR)
experiments.",1006.1483v1
2010-06-09,Electron energy spectrum of the spin-liquid state in a frustrated Hubbard model,"Non-local correlation effects in the half-filled Hubbard model on an
isotropic triangular lattice are studied within a spin polarized extension of
the dual fermion approach. A competition between the antiferromagnetic
non-collinear and the spin liquid states is strongly enhanced by an
incorporation of a k-dependent self-energy beyond the local dynamical
mean-field theory. The dual fermion correc- tions drastically decrease the
energy of a spin liquid state while leaving the non-collinear magnetic states
almost non-affected. This makes the spin liquid to become a preferable state in
a certain interval of interaction strength of an order of the magnitude of a
bandwidth. The spectral function of the spin-liquid Mott insulator is
determined by a formation of local singlets which results in the energy gap of
about twice larger than that of the 120 degrees antiferromagnetic Neel state.",1006.1855v2
2010-08-04,Spin relaxation due to electron-electron magnetic interaction in high Lande g-factor semiconductors,"We investigate spin transport in InSb/InAlSb heterostructure using the Monte
Carlo approach, generalized by including density matrix description of spin for
taking spin dynamics into account. In addition to the dominant Dyakonov-Perel
(DP) mechanism for spin control and relaxation, we consider magnetic
interaction between electrons which assumes importance due to high electronic
Lande g-factor in the material. It is found that while the effect of magnetic
interaction is not important at low densities, it reduces the spin relaxation
length by as much as 50% at higher densities. We also present a calculation
which elucidates the suppression of decoherence attributed to wave vector
dependent magnetic field in the DP relaxation mechanism. We note that magnetic
interaction is a general relaxation mechanism which may assume importance in
materials with high electronic Lande g-factor.",1008.0739v1
2010-09-27,Spin-transfer pulse switching: From the dynamic to the thermally activated regime,"The effect of thermal fluctuations on spin-transfer switching has been
studied for a broad range of time scales (sub-ns to seconds) in a model system,
a uniaxial thin film nanomagnet. The nanomagnet is incorporated into a
spin-valve nanopillar, which is subject to spin-polarized current pulses of
variable amplitude and duration. Two physical regimes are clearly
distinguished: a long pulse duration regime, in which reversal occurs by
spin-transfer assisted thermal activation over an energy barrier, and a short
time large pulse amplitude regime, in which the switching probability is
determined by the spin angular momentum in the current pulse.",1009.5240v1
2010-10-12,Optical control of coherent interactions between quantum dot electron spins,"Coherent interactions between spins in quantum dots are a key requirement for
quantum gates. We have performed pump-probe experiments in which pulsed lasers
emitting at different photon energies manipulate two distinct subsets of
electron spins within an inhomogeneous InGaAs quantum dot ensemble. The spin
dynamics are monitored through their precession about an external magnetic
field. These measurements demonstrate spin precession phase shifts and
modulations of the magnitude of one subset of oriented spins after optical
orientation of the second subset. The observations are consistent with results
from a model using a Heisenberg-like interaction with microeV-strength.",1010.2523v2
2010-12-04,Algebraic Properties of a Disordered Asymmetric Glauber Model,"We consider a variant of Glauber dynamics of Ising spins on a one-dimensional
lattice, where each spin flips according to the relative state of the spin to
its left. Moreover, each bond allows for two rates; flips which equalize
nearest neighbor spins, and flips which ""unequalize"" them. In addition, the
leftmost spin flips depending on the spin at that site. We explicitly calculate
all eigenvalues of the transition matrix for all system sizes and conjecture a
formula for the normalization factor of the model. We then analyze two limits
of this model, which are analogous to ferromagnetic and antiferromagnetic
behavior in the Ising model for which we are able to prove an analogous formula
for the normalization factor.",1012.0875v1
2010-12-13,Cold and ultracold NH--NH collisions in magnetic fields,"Elastic and spin-changing inelastic collision cross sections are presented
for cold and ultracold magnetically trapped NH. The cross sections are obtained
from coupled-channel scattering calculations as a function of energy and
magnetic field. We specifically investigate the influence of the intramolecular
spin-spin, spin-rotation, and intermolecular magnetic dipole coupling on the
collision dynamics. It is shown that $^{15}$NH is a very suitable candidate for
evaporative cooling experiments. The dominant trap-loss mechanism in the
ultracold regime originates from the intermolecular dipolar coupling term. At
higher energies and fields, intramolecular spin-spin coupling becomes
increasingly important. Our qualitative results and conclusions are fairly
independent of the exact form of the potential and of the size of the channel
basis set.",1012.2814v1
2011-01-12,Dynamics of a driven spin coupled to an antiferromagnetic spin bath,"We study the behavior of the Rabi oscillations of a driven central spin
(qubit) coupled to an antiferromagnetic spin bath (environment). It is found
that the decoherence behavior of the central spin depends on the detuning,
driving strength, the qubit-bath coupling and an important factor, associated
with the number of the coupled atoms, the detailed lattice structure, and the
temperature of the environment. If the detuning exists, the Rabi oscillations
may show the behavior of collapses and revivals; however, if the detuning is
zero, such a behavior will not appear. We investigate the weighted frequency
distribution of the time evolution of the central spin inversion and give this
phenomenon of collapses and revivals a reasonable explanation. We also discuss
the decoherence and the pointer states of the qubit from the perspectives of
the von Neumann entropy. It is found that the eigenstates of the qubit
self-Hamiltonian emerge as the pointer states in the weak system-environment
coupling limit.",1101.2386v1
2011-02-16,A semi-classical approach to electron spin resonance in quantum spin systems,"We develop a semi-classical approximation to electron spin resonance in
quantum spin systems, based on the rotor or non-linear sigma model. The
classical time evolution is studied using molec- ular dynamics while random
initial conditions are sampled using classical Monte Carlo methods. Although
the approximation may be especially powerful in two dimensions, we apply it
here to one- dimensional systems of large spin at intermediate temperatures, in
the presence of staggered and uniform magnetic fields. We first test the
validity of the semi-classical approximation by comparing the magnetization to
quantum Monte Carlo results on S = 2 chains. Then we calculate the ESR
spectrum, finding broad coexisting paramagnetic and spin wave resonances.",1102.3239v1
2011-02-25,Highlights from RHIC Spin Physics Program,"The Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory
delivers the world's highest energy polarized proton-proton collisions at a
center of mass energy up to 500 GeV and provides a unique opportunity to study
the quark and gluon spin structure of the proton and QCD dynamics at high
energy scale. RHIC has produced many exiting physics results in recent years.
The latest data from RHIC significantly constrain the gluon spin contribution
to the proton spin, and the parity violating single spin asymmetry are observed
for the first time in W production by both the PHENIX and STAR collaborations.
In this report, I present the latest results from the PHENIX and STAR
experiments, followed by a brief discussion of the future prospects of
transverse physics, particularly on the importance of the unique measurements
of Drell-Yan single spin asymmetry.",1102.5371v1
2011-03-28,Ultrafast transport of laser-excited spin polarized carriers in Au/Fe/MgO(001),"A time domain approach to probe hot carrier-induced spin dynamics is
demonstrated. The experiments are performed in epitaxial Au/Fe/MgO(001), where
spin-polarized hot carriers are excited in the Fe layer by 35 fs laser pulses.
They propagate to the Au surface where the transient spin polarization is
detected by magneto-induced second harmonic generation. Different energies of
majority and minority hot carriers excited in the exchange-split Fe band
structure lead to their spindependent lifetimes in Au. Accordingly, two
spin-polarized current contributions which propagate superdiffusively at
different velocities result in a spin current pulse of about 100 fs duration.",1103.5310v1
2011-05-26,Bloch-oscillations of exciton-polaritons and photons for the generation of an alternating terahertz spin current,"We analyze theoretically the spin dynamics of exciton-polaritons and photons
during their Bloch oscillations in a one-dimensional microwire. The wire
geometry induces an energy splitting between the longitudinal and transverse
electric polarized eigenmodes. We show analytically that a synchronized regime
between the Bloch oscillations in space and the precession of the pseudospin
can be achieved. This synchronization results in the formation of a THz
alternating spin current which can be extracted out of the confinement region
by the Landau-Zener tunneling towards the second allowed miniband. Finally we
show how the spin signal can be maintained despite of the lifetime of the
particles for the case of exciton-polaritons both in a resonant and non
resonant pumping schemes. The structure therefore acts as a Spin-optronic
device able to convert the polarization and emit spin polarized pulses.",1105.5278v1
2011-06-15,Spin-flip induced magnetoresistance in positionally disordered organic solids,"A model for magnetoresistance in positionally disordered organic materials is
presented and solved using percolation theory. The model describes the effects
of spin flips on hopping transport by considering the effect of spin dynamics
on an effective density of hopping sites. Faster spin-flip transitions open up
`spin-blocked' pathways to become viable conduction channels and hence produces
magnetoresistance. The magnetoresistance can be found analytically in several
regimes, including when the spin-flip time is slower than the hopping time. The
ratio of hopping time to the hyperfine precession time is a crucial quantity in
determining the shape of magnetoresistance curves. Studies of magnetoresistance
in known systems with controllable positional disorder would provide a
stringent test of this model.",1106.3040v1
2011-06-17,Exact spin-spin correlation function for the zero-temperature random-field Ising model,"An exact expression for the spin-spin correlation function is derived for the
zero-temperature random-field Ising model defined on a Bethe lattice of
arbitrary coordination number. The correlation length describing dynamic
spin-spin correlations and separated from the intrinsic topological length
scale of the Bethe lattice is shown to diverge as a power law at the critical
point. The critical exponents governing the behaviour of the correlation length
are consistent with the mean-field values found for a hypercubic lattice with
dimension greater than the upper critical dimension.",1106.3424v2
2011-07-17,Spin current induced magnetization oscillations in a paramagnetic disc,"When electron spins are injected uniformly into a paramagnetic disc, they can
precess along the demagnetizing field induced by the resulting magnetic moment.
Normally this precession damps out by virtue of the spin relaxation which is
present in paramagnetic materials. We propose a new mechanism to excite a
steady-state form of this dynamics by injecting a constant spin current into
this paramagnetic disc. We show that the rotating magnetic field generated by
the eddy currents provide a torque which makes this possible. Unlike the
ferromagnetic equivalent, the spin-torque-oscillator, the oscillation frequency
is fixed and determined by the dimensions and intrinsic parameters of the
paramagnet. The system possesses an intrinsic threshold for spin injection
which needs to be overcome before steady-state precession is possible. The
additional application of a magnetic field lowers this threshold. We discuss
the feasibility of this effect in modern materials. Transient analysis using
pump-probe techniques should give insight in the physical processes which
accompany this effect.",1107.3288v1
2011-08-05,Frustration and glassiness in spin models with cavity-mediated interactions,"We show that the effective spin-spin interaction between three-level atoms
confined in a multimode optical cavity is long-ranged and sign-changing, like
the RKKY interaction; therefore, ensembles of such atoms subject to frozen-in
positional randomness can realize spin systems having disordered and frustrated
interactions. We argue that, whenever the atoms couple to sufficiently many
cavity modes, the cavity-mediated interactions give rise to a spin glass. In
addition, we show that the quantum dynamics of cavity-confined spin systems is
that of a Bose-Hubbard model with strongly disordered hopping but no on-site
disorder; this model exhibits a random-singlet glass phase, absent in
conventional optical-lattice realizations. We briefly discuss experimental
signatures of the realizable phases.",1108.1400v2
2011-09-13,Interplay between non equilibrium and equilibrium spin torque using synthetic ferrimagnets,"We discuss the current induced magnetization dynamics of spin valves F0|N|SyF
where the free layer is a synthetic ferrimagnet SyF made of two ferromagnetic
layers F1 and F2 coupled by RKKY exchange coupling. In the interesting
situation where the magnetic moment of the outer layer F2 dominates the
magnetization of the ferrimagnet, we find that the sign of the effective spin
torque exerted on the free middle layer F1 is controlled by the strength of the
RKKY coupling: for weak coupling one recovers the usual situation where spin
torque tends to, say, anti-align the magnetization of F1 with respect to the
pinned layer F0. However for large coupling the situation is reversed and the
spin torque tends to align F1 with respect to F0. Careful numerical simulations
in the intermediate coupling regime reveal that the competition between these
two incompatible limits leads generically to spin torque oscillator (STO)
behavior. The STO is found in the absence of magnetic field, with very
significant amplitude of oscillations and frequencies up to 50 GHz or higher.",1109.2705v2
2011-10-05,Charmonium potential from full lattice QCD,"We present both spin-independent and -dependent parts of a central interquark
potential for charmonium states, which is calculated in 2+1 flavor dynamical
lattice QCD using the PACS-CS gauge configurations with a lattice cutoff of
a^{-1}~2.2 GeV. Our simulations are performed with a relativistic heavy quark
action for the charm quark at the lightest pion mass, M_\pi=156(7) MeV, in a
spatial volume of 3fm^3. We observe that the spin-independent charmonium
potential obtained from lattice QCD with almost physical quark masses is quite
similar to the Conrnell potential used in non-relativistic potential models.
The spin-spin potential properly exhibits the short range repulsive
interaction, while its r-dependence is different from either a point-like
spin-spin potential generated by one-gluon exchange or a phenomenological
finite-range one adopted in quark potential models.",1110.0888v2
2011-10-12,Femtosecond Laser-induced Crystallization of Amorphous Sb2Te3 film and Coherent Phonon Spectroscopy Characterization and Optical Injection of Electron Spins,"A femtosecond laser-irradiated crystallizing technique is tried to convert
amorphous Sb2Te3 film into crystalline film. Sensitive coherent phonon
spectroscopy (CPS) is used to monitor the crystallization of amorphous Sb2Te3
film at the original irradiation site. The CPS reveals that the vibration
strength of two phonon modes that correspond to the characteristic phonon modes
of crystalline Sb2Te3, enhances with increasing laser irradiation fluence
(LIF), showing the rise of the degree of crystallization with LIF and that
femtosecond laser irradiation is a good post-treatment technique. Time-resolved
circularly polarized pump-probe spectroscopy is used to investigate electron
spin relaxation dynamics of the laser-induced crystallized Sb2Te3 film. Spin
relaxation process indeed is observed, confirming the theoretical predictions
on the validity of spin-dependent optical transition selection rule and the
feasibility of transient spin-grating-based optical detection scheme of
spin-plasmon collective modes in Sb2Te3-like topological insulators.",1110.2551v1
2011-10-12,Spin supercurrent in Josephson contacts with noncollinear ferromagnets,"We present a theoretical study of the Josephson coupling of two s-wave
superconductors which are connected through a diffusive contact consisting of
noncollinear ferromagnetic domains. First, we consider a contact with two
domains with magnetization vectors misoriented by an angle $\theta$. Using the
quantum circuit theory, we find that in addition to the charge supercurrent, a
spin supercurrent, which is even in $\phi$ and odd in $\theta$, with a spin
polarization normal to the magnetization vectors flows between the domains.
Furthermore, with asymmetric insulating barriers at the interfaces of the
junction, the system may experience an antiferromagnetic-ferromagnetic phase
transition for $\phi=\pi$. Secondly, we discuss the spin supercurrent in an
extended magnetic texture with multiple domainwalls. We find the
position-dependent spin supercurrent. The magnitude of the spin supercurrent
strongly depends on the phase difference between the superconductors and the
number of domain walls. Our results demonstrate the possibility to couple the
superconducting phase to the magnetization dynamics.",1110.2568v1
2011-10-27,Magnetically Controlling the Explosion of Dirac Fermions during the Oxidation of Graphene,"The different physical properties of multilayered graphene or graphite
relative to single layer graphene result from the Dirac spins symmetry in
graphene and the Pauli spin symmetry in graphite. The Dirac symmetry in
multilayers of graphene (graphite) is hindered by interlayer interactions.
Different magnetizations, electronics and chemistry of graphite and graphene
follow from absence of interlayer interactions in graphene. The distinct
kinetics and dynamics of graphite and graphene by oxidation by the Hummer's
method in weak external magnetic field are observed in this work. Graphite
manifest enhanced non-explosive oxidation of Pauli spins in weak magnetic field
with background paramagnetic oxygen slowing the magnetic acceleration. Graphene
and graphite oxide manifest explosive oxidation and magnetically decelerated
explosive oxidation of Dirac spins in weak magnetic field for temperatures
below 20 oCelsius. The explosive oxidation of graphene and its deceleration in
weak external magnetic field are interpreted resulting from the giant
nonlocality and spin Hall Effect in the chemically reacting graphene. This is
the first identification, analysis and interpretation of the chemistry of the
Dirac spins and the magnetochemistry of relativistic electrons.",1110.6060v1
2011-12-12,Counterflow instability and turbulence in a spin-1 spinor Bose--Einstein condensate,"We theoretically study counterflow instability and turbulence in a spin-1
spinor Bose--Einstein condensate by the Gross--Pitaevskii equation and the
Bogoliubov--de Gennes equation. Our study considers (i) the dynamics induced by
the counterflow of two components with different magnetic quantum numbers,
which leads to turbulence with spin degrees of freedom, and (ii) the properties
of the turbulence. For (i), the behavior of the condensate induced by the
counterflow strongly depends on whether the spin-dependent interaction is
ferromagnetic or antiferromagnetic, leading to different behaviors for the
dispersion relation and the spin density vector, $etc$. For (ii), we
numerically calculate the spectrum of the spin-dependent interaction energy,
which also depends on the spin-dependent interaction. The spectrum of the
spin-dependent interaction energy in the ferromagnetic case exhibits a -7/3
power law, whereas that in the antiferromagnetic case does not. The -7/3 power
law can be explained by scaling analysis.",1112.2443v1
2011-12-13,Pressure-Driven Orbital Selective Insulator to Metal Transition and Spin State Crossover in Cubic CoO,"The metal-insulator and spin state transitions of CoO under high pressure are
studied by using density functional theory combined with dynamical mean-field
theory. Our calculations predict that the metal-insulator transition in CoO is
a typical orbital selective Mott transition, where the $t_{2g}$ orbitals of Co
3d shell become metallic firstly around 60 GPa while the $e_g$ orbitals still
remain insulating until 170 GPa. Further studies of the spin states of Co 3d
shell reveal that the orbital selective Mott phase in the intermediate pressure
regime is mainly stabilized by the high-spin state of the Co 3d shell and the
transition from this phase to the full metallic state is driven by the
high-spin to low-spin transition of the Co$^{2+}$ ions. Our results are in good
agreement with the most recent transport and x-ray emission experiments under
high pressure.",1112.2790v1
2012-02-01,Field dependence of the Eu2+ spin relaxation in EuFe(2-x)CoxAs2,"The layered compound EuFe2As2 is an interesting model system to investigate
the effects of well defined local Eu2+ 4f states on the itinerant electronic
and magnetic properties of the FeAs layers. To address this subject, we
investigated the series EuFe2-xCoxAs2 (0.1 <= x <=0.75) by electron spin
resonance (ESR) of Eu2+ to probe the spin dynamics of the itinerant subsystem.
We relate the results to dc-susceptibility measurements and band structure
calculations. As a consequence of the weak coupling between the local and
itinerant subsystems we found that the spin relaxation is well understood in
terms of the exchange coupling among the local Eu2+ spins. A pronounced field
dependence of the Eu2+ spin relaxation demonstrates the direct influence of
magnetic fluctuations at the Fe2-xCoxAs2 layers.",1202.0221v2
2012-02-08,Spin-spin correlations of entangled qubit pairs in the Bohm interpretation of quantum mechanics,"A general entangled qubit pair is analyzed in the de Broglie-Bohm formalism
corresponding to two spin-1/2 quantum rotors. Several spin-spin correlators of
Bohm's hidden variables are analyzed numerically and a detailed comparison with
results obtained by standard quantum mechanics is outlined. In addition to
various expectation values the Bohm interpretation allows also a study of the
corresponding probability distributions, which enables a novel understanding of
entangled qubit dynamics. In particular, it is shown how the angular momenta of
two qubits in this formalism can be viewed geometrically and characterized by
their relative angles. For perfectly entangled pairs, for example, a compelling
picture is given, where the qubits exhibit a unison precession making a
constant angle between their angular momenta. It is also demonstrated that the
properties of standard quantum mechanical spin-spin correlators responsible for
the violation of Bell's inequalities are identical to their counterparts
emerging from the probability distributions obtained by the Bohmian approach.",1202.1695v1
2012-03-28,Nonperturbative master equation solution of central spin dephasing dynamics,"We solve the long-standing central spin problem for a general set of
inhomogeneous bath couplings and a large class of initial bath states. We
compute the time evolution of the coherence of a central spin coupled to a spin
bath by resumming all orders of the time-convolutionless master equation, thus
avoiding the need to assume weak coupling to the bath. The fully quantum,
non-Markovian solution is obtained in the large-bath limit and is valid up to a
timescale set by the largest coupling constant. Our result captures the full
decoherence of an electron spin qubit coupled to a nuclear spin bath in a GaAs
quantum dot for experimentally relevant parameters. In addition, our solution
is quite compact and can readily be used to make quantitative predictions for
the decoherence process and to guide the design of nuclear state preparation
protocols.",1203.6355v2
2012-06-09,Spin-Electromagnetic Hydrodynamics and Magnetization Induced by Spin-Magnetic Interaction,"The hydrodynamic model including the spin degree of freedom and the
electromagnetic field was discussed. In this derivation, we applied
electromagnetism for macroscopic medium proposed by Minkowski. For the equation
of motion of spin, we assumed that the hydrodynamic representation of the Pauli
equation is reproduced when the many-body effect is neglected. Then the
spin-magnetic interaction in the Pauli equation was converted to a part of the
magnetization. The fluid and spin stress tensors induced by the many-body
effect were obtained by employing the algebraic positivity of the entropy
production in the framework of the linear irreversible thermodynamics,
including the mixing effect of the irreversible currents. We further
constructed the constitutive equation of the polarization and the
magnetization. Our polarization equation is more reasonable compared to another
result obtained using electromagnetism for macroscopic medium proposed by de
Groot-Mazur.",1206.1976v3
2012-07-13,Resolving Spin-Orbit and Hyperfine Mediated Electric Dipole Spin Resonance in a Quantum Dot,"We investigate the electric manipulation of a single electron spin in a
single gate-defined quantum dot. We observe that so-far neglected differences
between the hyperfine and spin-orbit mediated electric dipole spin resonance
conditions have important consequences at high magnetic fields. In experiments
using adiabatic rapid passage to invert the electron spin, we observe an
unusually wide and asymmetric response as a function of magnetic field.
Simulations support the interpretation of the lineshape in terms of four
different resonance conditions. These findings may lead to isotope-selective
control of dynamic nuclear polarization in quantum dots.",1207.3331v2
2012-08-16,Holonomy Spin Foam Models: Definition and Coarse Graining,"We propose a new holonomy formulation for spin foams, which naturally extends
the theory space of lattice gauge theories. This allows current spin foam
models to be defined on arbitrary two-complexes as well as to generalize
current spin foam models to arbitrary, in particular finite groups. The
similarity with standard lattice gauge theories allows to apply standard coarse
graining methods, which for finite groups can now be easily considered
numerically. We will summarize other holonomy and spin network formulations of
spin foams and group field theories and explain how the different
representations arise through variable transformations in the partition
function. A companion paper will provide a description of boundary Hilbert
spaces as well as a canonical dynamic encoded in transfer operators.",1208.3388v1
2012-09-07,Lyapunov instabilities in lattices of interacting classical spins at infinite temperature,"We numerically investigate Lyapunov instabilities for one-, two- and
three-dimensional lattices of interacting classical spins at infinite
temperature. We obtain the largest Lyapunov exponents for a very large variety
of nearest-neighbor spin-spin interactions and complete Lyapunov spectra in a
few selected cases. We investigate the dependence of the largest Lyapunov
exponents and whole Lyapunov spectra on the lattice size and find that both
quickly become size-independent. Finally, we analyze the dependence of the
largest Lyapunov exponents on the anisotropy of spin-spin interaction with the
particular focus on the difference between bipartite and nonbipartite lattices.",1209.1468v2
2012-09-19,Quantum correlations in a system of nuclear s=1/2 spins in a strong magnetic field,"Entanglement and quantum discord for a pair of nuclear spins $s=1/2$ in a
nanopore filled with a gas of spin-carrying molecules (atoms) are studied. The
correlation functions describing dynamics of dipolar coupled spins in a
nanopore are found. The dependence of spin-pair entanglement on the temperature
and the number of spins is obtained from the reduced density matrix, which is
centrosymmetric (CS). An analytic expression for the concurrence is obtained
for an arbitrary CS density matrix. It is shown that the quantum discord as a
measure of quantum correlations attains a significant value at low
temperatures. It is shown also that the discord in the considered model has
""flickering"" character and disappears periodically in the course of the time
evolution of the system. The geometric discord is studied for arbitrary
$4\times 4$ CS density matrices.",1209.4166v1
2012-10-09,"Spin Wave Excitations in AFe$_{1.5}$Se$_2$ (A=K, Tl): Analytical Study","We have analytically solved the spin wave excitations for the intercalated
ternary iron-selenide AFe$_{1.5}$Se$_2$ (A=K, Tl) in the $4\times 2$ collinear
antiferromagnetic order. It is found that there are one acoustic branch
(gapless Goldstone mode) and two gapful optical branches of spin wave
excitations with each in double degeneracy. By examining the non-imaginary
excitation frequency condition, we can determine the corresponding phase
boundary. The exchange couplings between Fe moments in AFe$_{1.5}$Se$_2$ are
derived based on the first-principles total energy calculations. The Fe spin is
found to be $S=3/2$ through computing the antiferromagnetic quantum
fluctuation. And it is further found that a very small spin-orientation
anisotropy can remarkably suppress the antiferromagnetic quantum fluctuation.
The spin dynamical structure factors are calculated and discussed in
association with neutron inelastic scattering experiment.",1210.2668v1
2012-11-09,Metal-insulator transition in three-band Hubbard model with strong spin-orbit interaction,"Recent investigations suggest that both spin-orbit coupling and electron
correlation play very crucial roles in the $5d$ transition metal oxides. By
using the generalized Gutzwiller variational method and dynamical mean-field
theory with the hybridization expansion continuous time quantum Monte Carlo as
impurity solver, the three-band Hubbard model with full Hund's rule coupling
and spin-orbit interaction terms, which contains the essential physics of
partially filled $t_{2g}$ sub-shell of $5d$ materials, is studied
systematically. The calculated phase diagram of this model exhibits three
distinct phase regions, including metal, band insulator and Mott insulator
respectively. We find that the spin-orbit coupling term intends to greatly
enhance the tendency of the Mott insulator phase. Furthermore, the influence of
the electron-electron interaction on the effective strength of spin-orbit
coupling in the metallic phase is studied in detail. We conclude that the
electron correlation effect on the effective spin-orbit coupling is far beyond
the mean-field treatment even in the intermediate coupling region.",1211.2055v1
2012-11-13,Spin decoherence due to Fluctuating Fields,"The dynamics of a spin in the presence of a deterministic and a fluctuating
magnetic field is solved for analytically to obtain the averaged value of the
spin as a function of time for various kinds of fluctuations (noise).
Specifically, analytic results are obtained for the time dependence of the
expectation value of the spin, averaged over fluctuations, for Gaussian white
noise and Guassian colored noise, as well as non-Gaussian telegraph noise.
Fluctuations cause the decay of the average spin vector (decoherence). For
noise with finite temporal correlation time, a deterministic component of the
field can suppress decoherence of the spin component along the field. Hence,
decoherence can be manipulated by controlling the deterministic magnetic field.
A simple universal physical picture emerges which explains the mechanism of the
suppression of the decay.",1211.3032v2
2012-11-13,Quenched binary Bose-Einstein condensates: spin domain formation and coarsening,"We explore the time evolution of quasi-1D two component Bose-Einstein
condensates (BEC's) following a quench from one component BEC's with a ${\rm
U}(1)$ order parameter into two component condensates with a ${\rm
U}(1)\shorttimes{\rm Z}_2$ order parameter. In our case, these two spin
components have a propensity to phase separate, i.e., they are immiscible.
Remarkably, these spin degrees of freedom can equivalently be described as a
single component attractive BEC. A spatially uniform mixture of these spins is
dynamically unstable, rapidly amplifing any quantum or pre-existing classical
spin fluctuations. This coherent growth process drives the formation of
numerous spin polarized domains, which are far from the system's ground state.
At much longer times these domains grow in size, coarsening, as the system
approaches equilibrium. The experimentally observed time evolution is fully
consistent with our stochastic-projected Gross-Pitaevskii calculation.",1211.3127v2
2012-11-29,Topological transport in a spin-orbit coupled bosonic Mott insulator,"We investigate topological transport in a spin-orbit coupled bosonic Mott
insulator. We show that interactions can lead to anomalous quasi-particle
dynamics even when the spin-orbit coupling is abelian. To illustrate the
latter, we consider the spin-orbit coupling realized in the experiment of Lin
\textit{et al}. [Nature (London) \textbf{471}, 83 (2011)]. For this spin-orbit
coupling, we compute the quasiparticle dispersions and spectral weights, the
interaction-induced momentum space Berry curvature, and the momentum space
distribution of spin density, and propose experimental signatures. Furthermore,
we find that in our approximation for the single-particle propagator, the
ground state can in principle support an integer Hall conductivity if the sum
of the Chern numbers of the hole bands is nonzero.",1211.6924v2
2012-12-21,Mixing time bounds for oriented kinetically constrained spin models,"We analyze the mixing time of a class of oriented kinetically constrained
spin models (KCMs) on a d-dimensional lattice of $n^d$ sites. A typical example
is the North-East model, a 0-1 spin system on the two-dimensional integer
lattice that evolves according to the following rule: whenever a site's
southerly and westerly nearest neighbours have spin 0, with rate one it resets
its own spin by tossing a p-coin, at all other times its spin remains frozen.
Such models are very popular in statistical physics because, in spite of their
simplicity, they display some of the key features of the dynamics of real
glasses. We prove that the mixing time is O(n log n) whenever the relaxation
time is O(1). Our study was motivated by the ""shape"" conjecture put forward by
G. Kordzakhia and S.P. Lalley.",1212.5425v2
2013-02-19,Chirality Sensitive Domain Wall Motion in Spin-Orbit Coupled Ferromagnets,"Using the Lagrangian formalism, we solve analytically the equations of motion
for current-induced domain-wall dynamics in a ferromagnet with Rashba
spin-orbit coupling. An exact solution for the domain wall velocity is
provided, including the effect of non-equilibrium conduction electron
spin-density, Gilbert damping, and the Rashba interaction parameter. We
demonstrate explicitly that the influence of spin-orbit interaction can be
qualitatively different from the role of non-adiabatic spin-torque in the sense
that the former is sensitive to the chirality of the domain wall whereas the
latter is not: the domain wall velocity shows a reentrant behavior upon
changing the chirality of the domain wall. This could be used to experimentally
distinguish between the spin-orbit and non-adiabatic contribution to the wall
speed. A quantitative estimate for the attainable domain wall velocity is
given, based on an experimentally relevant set of parameters for the system.",1302.4744v1
2013-02-19,Optimization of spin-torque switching using AC and DC pulses,"We explore spin-torque induced magnetic reversal in magnetic tunnel junctions
using combined AC and DC spin-current pulses. We calculate the optimal pulse
times and current strengths for both AC and DC pulses as well as the optimal AC
signal frequency, needed to minimize the Joule heat lost during the switching
process. The results of this optimization are compared against numeric
simulations. Finally we show how this optimization leads to different dynamic
regimes, where switching is optimized by either a purely AC or DC spin-current,
or a combination AC/DC spin-current, depending on the anisotropy energies and
the spin-current polarization.",1302.4770v4
2013-02-28,Spin-polarized Shapiro steps and spin-precession-assisted multiple Andreev reflection,"We investigate the charge and spin transport of a voltage-biased
superconducting point contact coupled to a nanomagnet. The magnetization of the
nanomagnet is assumed to precess with the Larmor frequency, $\omega_L$, due to
ferromagnetic resonance. The interplay between the ac Josephson current and the
magnetization dynamics leads to spin-polarized Shapiro steps at voltages
$|V|=\hbar \omega_L/2en$ for $n=1,2,...$ and the subharmonic steps with $n>1$
are a consequence of multiple Andreev reflection (MAR). Moreover, the
spin-precession-assisted MAR generates quasiparticle scattering amplitudes
that, due to interference, lead to current-voltage characteristics of the dc
charge and spin currents with subharmonic gap structures displaying an even-odd
effect.",1302.7107v1
2013-03-01,Spontaneous and resonant lifting of the spin blockade in nanowire quantum dots,"A complete numerical description of the charge and spin dynamics of a
two-electron system confined in narrow nanowire quantum dots under oscillating
electric field is presented in the context of recent electric dipole spin
resonance experiments. We find that the spin-orbit coupling results in lifting
the spin blockade by phonon mediated relaxation provided that the initially
occupied state is close in energy to the ground state. This leads to
suppression of the blockade from the triplet state with spins polarized
parallel to the external magnetic field B. At higher B, after singlet-triplet
ground-state transition a new channel for lifting the Pauli blockade opens
which results in an appearance of additional resonance lines. The calculated
signatures of this transition are consistent with recent experimental results
[S. M. Frolov et al., Phys. Rev. Lett. 109, 236805 (2012)].",1303.0211v2
2013-03-27,Fluorescence thermometry enhanced by the quantum coherence of single spins in diamond,"We demonstrate fluorescence thermometry techniques with sensitivities
approaching 10 mK Hz^(-1/2) based on the spin-dependent photoluminescence of
nitrogen vacancy (NV) centers in diamond. These techniques use dynamical
decoupling protocols to convert thermally induced shifts in the NV center's
spin resonance frequencies into large changes in its fluorescence. By
mitigating interactions with nearby nuclear spins and facilitating selective
thermal measurements, these protocols enhance the spin coherence times
accessible for thermometry by 45x, corresponding to a 7x improvement in the NV
center's temperature sensitivity. Moreover, we demonstrate these techniques can
be applied over a broad temperature range and in both finite and near-zero
magnetic field environments. This versatility suggests that the quantum
coherence of single spins could be practically leveraged for sensitive
thermometry in a wide variety of biological and microscale systems.",1303.6730v2
2013-04-21,On a consistent macroscopic description for a spin quantum plasma with interparticle interactions,"Quantum mechanical averaging of the particle concentration operator is an
effective starting point for derivation of the many-particle quantum
hydrodynamic equations. In many-particle quantum systems, we have to separate
the ordered motion of the local center of mass (velocity field), the thermal,
and the quantum motion. The quantum mechanical average process, invoked here,
is completely determined, and is different from the usual averaging processes
that introduces undefined probabilities for quantum states. It is shown that
the Madelung decomposition for the $N$-particle spinor wave function allows the
correct introduction of the velocity field, and gives explicit expressions for
the quantum contributions to both the momentum, and the spin flux. The
formalism also contains plasma effects produced by the Coulomb and spin-spin
interparticle interactions. It is shown that both interactions appear in plasma
dynamics as effective electric and magnetic fields. As result we find a fully
coherent description for spin quantum plasma in the self-consistent field
approximation for interparticle interactions. A simple consequence - the change
brought about by interparticle correlations on the propagation of electrostatic
waves in a spin quantum plasma - is discussed.",1304.5780v1
2013-05-22,Spin-wave nonreciprocity based on interband magnonic transitions,"We theoretically demonstrate linear spin-wave nonreciprocity in a Ni80Fe20
nanostripe waveguide, based on interband magnonic transitions induced by a
time-reversal and spatialinversion symmetry breaking magnetic field. An
analytical coupled-mode theory of spin waves, developed to describe the
transitions which are accompanied by simultaneous frequency and wavevector
shifts of the coupled spin waves, is well corroborated by numerical
simulations. Our findings could pave the way for the realization of spin-wave
isolation and the dynamic control of spin-wave propagation in nanoscale
magnonic integrated circuits via an applied magnetic field.",1305.5018v3
2013-05-24,Spin-dependent phenomena in semiconductors in strong electric fields,"We develop a theory of spin-dependent phenomena in the streaming regime
characterized by ballistic acceleration of electrons in the moderate electric
field until they achieve the optical phonon energy and abruptly emit the
phonons. It is shown that the Dyakonov-Perel spin relaxation is drastically
modified in this regime, the current-induced spin orientation remarkably
increases, reaches a high value ~2% in the electric field ~1kV/cm and falls
with the further increase in the field. The spin polarization enhancement is
caused by squeezing of the electron momentum distribution in the direction of
drift. We also predict field-induced oscillatory dynamics of spin polarization
of the photocarriers excited into the conduction band by a short
circularly-polarized optical pulse.",1305.5680v1
2013-06-06,Large-Amplitude Superexchange of High-Spin Fermions in Optical Lattices,"We show that fermionic high-spin systems with spin-changing collisions allow
to monitor superexchange processes in optical superlattices with large
amplitudes and strong spin fluctuations. By investigating the non-equilibrium
dynamics, we find a superexchange dominated regime at weak interactions. The
underlying mechanism is driven by an emerging tunneling-energy gap in shallow
few-well potentials. As a consequence, the interaction-energy gap that is
expected to occur only for strong interactions in deep lattices is
reestablished. By tuning the optical lattice depth, a crossover between two
regimes with negligible particle number fluctuations is found: first, the
common regime with vanishing spin-fluctuations in deep lattices and, second, a
novel regime with strong spin fluctuations in shallow lattices. We discuss the
possible experimental realization with ultracold 40K atoms and observable
quantities in double wells and two-dimensional plaquettes.",1306.1330v2
2013-06-09,Entanglement of spins under a strong laser influence,"The fate of entanglement of spins for two heavy constituents of a bound state
moving in a strong laser field is analyzed within the semiclassical approach.
The bound state motion as a whole is considered classically beyond the dipole
approximation and taking into account the magnetic field effect by using the
exact solution to the Newton equation. At the same time the evolution of
constituent spins under the laser influence is studied quantum mechanically.
The spin density matrix is determined as solution to the von Neumann equation
with the effective Hamiltonian, describing spin-laser interaction along the
bound state classical trajectory. Based on the solution, the dynamics of
concurrence of spins is calculated for the maximally entangled Werner states as
well as for an initially uncorrelated state.",1306.2074v1
2013-07-11,Strong Hyperfine-Induced Modulation of an Optically-Driven Hole Spin in an InAs Quantum Dot,"Compared to electrons, holes in InAs quantum dots have a significantly weaker
hyperfine interaction that leads to less dephasing from nuclear spins. Thus
many recent studies have suggested that nuclear spins are unimportant for hole
spin dynamics compared to electric field fluctuations. We show that the hole
hyperfine interaction can have a strong effect on hole spin coherence
measurements through a nuclear feedback effect. The nuclear polarization is
generated through a unique process that is dependent on the anisotropy of the
hole hyperfine interaction and the coherent precession of nuclear spins, giving
rise to strong modulation at the nuclear precession frequency.",1307.3260v2
2013-10-23,Exchange-dominated Standing Spin Wave Excitations under microwave irradiation in Ni80Fe20 Thin Films,"We investigated the microwave-assisted DC voltages of ferromagnetic
resonances and exchangedominated standing spin wave excitations in two
different in-plane magnetized permalloy thin films via homodyne detection. The
line shapes of ferromagnetic resonance spectra and the dispersion curves of
ferromagnetic resonance and standing spin wave are in agreement of previous
studies, while further investigations of DC voltage spectra for these two
excitations reveal that 1. unlike ferromagnetic resonance signals, the
anti-symmetrical line shapes of standing spin wave excitations are not depend
on the electromagnetic relative phase of assisted microwave, and 2. linewidths
of their DC voltage spectra are distinct. The complicated spin dynamics of
standing spin wave is consequently discussed by applying
Landau-Lifshitz-Gilbert equation in term of exchange interaction.",1310.6108v1
2013-11-01,Coherent Magnetism and Spin-Orbit Interaction in Garnet Films Probed with Femtosecond Magneto-Optical Four Wave Mixing,"We report about the dephasing of the spins states in a Garnet film excited by
femtosecond laser pulses. It is shown that magneto-optical four-wave-mixing
signals are efficiently generated and controlled with an external static
magnetic field. The self-diffraction of either two or three femtosecond pulses
allows us determining independently the coherent response time ($T_2$ < 50 fs)
and the population relaxation, which occurs in several steps. After the laser
induced demagnetization, the spin-lattice relaxation is the dominant mechanism
($T_{1,spin-lat}$ < 1.35 ps) and the precession of the magnetization takes
place at later times ($T_{1,prec}$ < 150 ps). The coherent response of the
spins states is modeled with a multi-level hydrogen-like system, taking into
account the fundamental relativistic quantum dynamics of the spins. Our
experimental approach is general and opens the way to investigating quantum
magnetism in ordered magnetic systems useful for applications in information
and communications technologies.",1311.0080v1
2013-11-29,Resonant optical pumping of a Mn spin in a strain free quantum dot,"We report on the spin properties of individual Mn atoms in II-VI
semiconductor strain free quantum dots. Strain free Mn-doped CdTe quantum dots
are formed by width fluctuations in thin quantum wells lattice matched on a
CdTe substrate. These quantum dots permit to optically probe and address any
spin state of a Mn atom in a controlled strain environment. The absence of
strain induced magnetic anisotropy prevents an optical pumping of the Mn spin
at zero magnetic field. Thus, a large photoluminescence is obtained under
resonant optical excitation of the exciton-Mn complex. An efficient optical
pumping of the coupled electronic and nuclear spins of the Mn is restored under
a weak magnetic field. The observed reduction of the resonant photoluminescence
intensity under magnetic field is well described by a model including the
hyperfine coupling and a residual crystal field splitting of the Mn atom.
Finally, we show that the second order correlation function of the resonant
photoluminescence presents a large photon bunching at short delay which is a
probe of the dynamics of coupled electronic and nuclear spins of the Mn atom.",1311.7622v1
2014-01-03,Spin-Transfer-Torque Driven Magneto-Logic Gates Using Nano Spin-Valve Pillars,"We propose model magneto-logic NOR and NAND gates using a spin valve pillar,
wherein the logical operation is induced by spin-polarized currents which also
form the logical inputs. The operation is facilitated by the simultaneous
presence of a constant controlling magnetic field. The same spin-valve assembly
can also be used as a magnetic memory unit. We identify regions in the
parameter space of the system where the logical operations can be effectively
performed. The proposed gates retain the non-volatility of a magnetic random
access memory,(MRAM). We verify the functioning of the gate by numerically
simulating its dynamics, governed by the appropriate Landau-Lifshitz-Gilbert
equation with the spin-transfer torque term. The flipping time for the logical
states is estimated to be within nano seconds.",1401.0723v1
2014-01-24,Wavenumber-dependent Gilbert damping in metallic ferromagnets,"New terms to the dynamical equation of magnetization motion, associated with
spin transport, have been reported over the past several years. Each newly
identified term is thought to possess both a real and an imaginary effective
field leading to fieldlike and dampinglike torques on magnetization. Here we
show that three metallic ferromagnets possess an imaginary effective-field term
which mirrors the well-known real effective-field term associated with exchange
in spin waves. Using perpendicular standing spin wave resonance between 2-26
GHz, we evaluate the magnitude of the finite-wavenumber ($k$) dependent Gilbert
damping $\alpha$ in three typical device ferromagnets, Ni$_{79}$Fe$_{21}$, Co,
and Co$_{40}$Fe$_{40}$B$_{20}$, and demonstrate for the first time the presence
of a $k^2$ term as $\Delta\alpha=\Delta\alpha_0+A_{k}\cdot k^2$ in all three
metals. We interpret the new term as the continuum analog of spin pumping,
predicted recently, and show that its magnitude, $A_{k}$=0.07-0.1 nm$^2$, is
consistent with transverse spin relaxation lengths as measured by conventional
(interlayer) spin pumping.",1401.6467v2
2014-02-02,The Low-Spin Black Hole in LMC X-3,"Building upon a new dynamical model for the X-ray binary LMC X-3, we measure
the spin of its black hole primary via the continuum-fitting method. We
consider over one thousand thermal-state RXTE X-ray spectra of LMC X-3. Using a
large subset of these spectra, we constrain the spin parameter of the black
hole to be spin = 0.21(+0.18,-0.22), 90% confidence. Our estimate of the
uncertainty in spin takes into account a wide range of systematic errors. We
discuss evidence for a correlation between a black hole's spin and the
complexity of its X-ray spectrum.",1402.0148v1
2014-02-17,Derivation of Electron Spin Relaxation Rate by Electron-Phonon Interaction Using a New Diagram Method,"A formula for the electron spin relaxation rate of an electron-phonon system
is derived using a new spring-loop diagram method. The result contains the
distribution functions for the electrons and phonons properly. Therefore, all
the spin flip and conserving processes are explained from a microscopic point
of view, and a physical insight of the quantum dynamics of electron spin in a
solid is obtained from the diagram. Photons and phonons are classified
according to the spin flip and conserving processes. The formula is used to
calculate the electron spin relaxation rate in GaAs. The temperature dependence
of the relaxation rate is obtained by a comparison with the experimental
result.",1402.3888v1
2014-02-25,Flux $1/f^α$ noise in 2D Heisenberg spin glasses: effects of weak anisotropic interactions,"We study the dynamics of a two-dimensional ensemble of randomly distributed
classical Heisenberg spins with isotropic RKKY and weaker anisotropic
dipole-dipole couplings. Such ensembles may give rise to the flux noise
observed in SQUIDs with a $1/f^{\alpha}$ power spectrum ($\alpha \lesssim 1$).
We solve numerically the Landau-Lifshiftz-Gilbert equations of motion in the
dissipationless limit. We find that Ising type fluctuators, which arise from
spin clustering close to a spin-glass critical behavior with $T_c =0$, give
rise to $1/f^{\alpha}$ noise. Even weak anisotropic interactions lead to a
crossover from the Heisenberg-type criticality to the much stronger Ising-type
criticality. The temperature dependent exponent $\alpha(T) \lesssim 1$ grows
and approaches unity when the temperature is lowered. This mechanism acts in
parallel to the spin diffusion mechanism. Whereas the latter is sensitive to
the device geometry, the spin-clustering mechanism is largely geometry
independent.",1402.6229v2
2014-07-21,Electron Spin Dephasing and Optical Pumping of Nuclear Spins in GaN,"We have measured the donor-bound electron spin dynamics in cubic GaN by
time-resolved Kerr rotation experiments. The ensemble electron spin dephasing
time in this quantum dot like system characterized by a Bohr radius of 2.5 nm
is of the order of 1.5 ns as a result of the interaction with the fluctuating
nuclear spins. It increases drastically when an external magnetic field as
small as 10 mT is applied. We extract a dispersion of the nuclear hyperfine
field {\delta}Bn $\sim$ 4 mT, in agreement with calculations. We also
demonstrate for the first time in GaN based systems the optical pumping of
nuclear spin yielding the build-up of a significant nuclear polarization.",1407.5540v1
2014-08-10,Coherent precession of an individual 5/2 spin,"We present a direct observation of a coherent spin precession of an
individual Mn$^{2+}$ ion, having both electronic and nuclear spins equal to
5/2, embedded in a CdTe quantum dot and placed in magnetic field. The spin
state evolution is probed in a time-resolved pump-probe measurement of
absorption of the single dot. The experiment reveals subtle details of the
large-spin coherent dynamics, such as non-sinusoidal evolution of states
occupation, and beatings caused by the strain-induced differences in energy
levels separation. Sensitivity of the large-spin impurity on the crystal strain
opens the possibility of using it as a local strain probe.",1408.2263v1
2014-08-19,Quantum Spin Dimers from Chiral Dissipation in Cold-Atom Chains,"We consider the non-equilibrium dynamics of a driven dissipative spin chain
with chiral coupling to a 1D bosonic bath, and its atomic implementation with a
two-species mixture of cold quantum gases. The reservoir is represented by a
spin-orbit coupled 1D quasi-condensate of atoms in a magnetized phase, while
the spins are identified with motional states of a separate species of atoms in
an optical lattice. The chirality of reservoir excitations allows the spins to
couple differently to left and right moving modes, which in our atomic setup
can be tuned from bidirectional to purely unidirectional. Remarkably, this
leads to a pure steady state in which pairs of neighboring spins form dimers
that decouple from the remainder of the chain. Our results also apply to
current experiments with two-level emitters coupled to photonic waveguides.",1408.4357v3
2014-09-30,Charge ordering in a pure spin model: dipolar spin-ice,"We study the dipolar spin-ice model at fixed density of single excitations,
$\rho$, using a Monte Carlo algorithm where processes of creation and
annihilation of such excitations are banned. In the limit of $\rho$ going to
zero, this model coincides with the usual dipolar spin-ice model at low
temperatures, with the additional advantage that a negligible number of
monopoles allows for equilibration even at the lowest temperatures. Thus, the
transition to the ordered fundamental state found by Melko et al. in 2001 is
reached using simple local spin flip dynamics. As the density is increased, the
monopolar nature of the excitations becomes apparent: the system shows a rich
$\rho$ vs. $T$ phase diagram with ""charge"" ordering transitions analogous to
that observed for Coulomb charges in lattices. A further layer of complexity is
revealed by the existence of order both within the charges and their associated
vacuum, which can only be described in terms of spins --the true microscopic
degrees of freedom of the system.",1410.1430v1
2014-10-10,A convex solution to Psiaki's first joint attitude and spin-rate estimation problem,"We consider the problem of jointly estimating the attitude and spin-rate of a
spinning spacecraft. Psiaki (J. Astronautical Sci., 57(1-2):73--92, 2009) has
formulated a family of optimization problems that generalize the classical
least-squares attitude estimation problem, known as Wahba's problem, to the
case of a spinning spacecraft. If the rotation axis is fixed and known, but the
spin-rate is unknown (such as for nutation-damped spin-stabilized spacecraft)
we show that Psiaki's problem can be reformulated exactly as a type of
tractable convex optimization problem called a semidefinite optimization
problem. This reformulation allows us to globally solve the problem using
standard numerical routines for semidefinite optimization. It also provides a
natural semidefinite relaxation-based approach to more complicated variations
on the problem.",1410.2841v1
2014-10-24,Memory effect from spinning unbound binaries,"We present a recently developed prescription to obtain ready-to-use
gravitational wave (GW) polarization states for spinning compact binaries on
hyperbolic orbits. We include leading order spin-orbit interactions, invoking
1.5PN-accurate quasi-Keplerian parametrization for the radial part of the
orbital dynamics. We also include radiation reaction effects on $h_+$ and
$h_{\times}$ during the interaction. In the GW signals from spinning binaries
there is evidence of the memory effect in both polarizations, in contrast to
the non-spinning case, where only the cross polarizations exhibits
non-vanishing amplitudes at infinite time. We also compute 1PN-accurate GW
polarization states for non-spinning compact binaries in unbound orbits in a
fully parametric way, and compare them with existing waveforms.",1410.6605v1
2015-01-22,Incoherent excitation and switching of spin states in exciton-polariton condensates,"We investigate, theoretically and numerically, the spin dynamics of a
two-component exciton-polariton condensate created and sustained by
non-resonant spin-polarized optical pumping of a semiconductor microcavity.
Using the open-dissipative mean-field model, we show that the existence of well
defined phase-locked steady states of the condensate may lead to efficient
switching and control of spin (polarization) states with a non-resonant
excitation. Spatially inhomogeneous pulsed excitations can cause symmetry
breaking in the pseudo-spin structure of the condensate and lead to formation
of non-trivial spin textures. Our model is universally applicable to two weakly
coupled polariton condensates, and therefore can also describe the behaviour of
condensate populations and phases in 'double-well' type potentials.",1501.05355v1
2015-01-30,Phase diagram and optimal switching induced by spin Hall effect in a perpendicular magnetic layer,"In a ferromagnet/heavy-metal bilayer device with strong spin Hall effect an
in-plane current excites magnetic dynamics through spin torque. We analyze
bilayers with perpendicular magnetization and calculate three-dimensional phase
diagrams describing switching by external magnetic field at a fixed current. We
then concentrate on the case of a field applied in the plane formed by the film
normal and the current direction. Here we analytically study the evolution of
both the conventional ""up""/""down"" magnetic equilibria and the additional
equilibria created by the spin torque. Expressions for the stability regions of
all equilibria are derived, and the nature of switching at each critical
boundary is discussed. The qualitative picture obtained this way predicts
complex hysteresis patterns that should occur in bilayers. By analyzing the
phase portraits of the system we show that when the spin torque induced
equilibrium exists, switching between ""up"" and ""down"" states proceeds through
it as an intermediate state. Using numeric simulations we analyze the switching
time and compare it to that of a conventional spin torque device with collinear
magnetizations of the polarizer and the free layer.",1501.07787v1
2015-02-13,Spin-current injection and detection in strongly correlated organic conductor,"Spin-current injection into an organic semiconductor
$\rm{\kappa\text{-}(BEDT\text{-}TTF)_2Cu[N(CN)_2]Br}$ film induced by the spin
pumping from an yttrium iron garnet (YIG) film. When magnetization dynamics in
the YIG film is excited by ferromagnetic or spin-wave resonance, a voltage
signal was found to appear in the
$\rm{\kappa\text{-}(BEDT\text{-}TTF)_2Cu[N(CN)_2]Br}$ film.
Magnetic-field-angle dependence measurements indicate that the voltage signal
is governed by the inverse spin Hall effect in
$\rm{\kappa\text{-}(BEDT\text{-}TTF)_2Cu[N(CN)_2]Br}$. We found that the
voltage signal in the $\rm{\kappa\text{-}(BEDT\text{-}TTF)_2Cu[N(CN)_2]Br}$/YIG
system is critically suppressed around 80 K, around which magnetic and/or glass
transitions occur, implying that the efficiency of the spin-current injection
is suppressed by fluctuations which critically enhanced near the transitions.",1502.05244v1
2015-02-19,Using coherent dynamics to quantify spin-coupling within triplet-exciton/polaron complexes in organic diodes,"Quantifying the spin-spin interactions which influence electronic transitions
in organic semiconductors is crucial for understanding their
magneto-optoelectronic properties. By combining a theoretical model for three
spin interactions in the coherent regime with pulsed electrically detected
magnetic resonance experiments on MEH-PPV diodes, we quantify the spin-coupling
within complexes comprising three spin-half particles. We determine that these
particles form triplet-exciton:polaron pairs, where the polaron:exciton
exchange is over 5 orders of magnitude weaker (less than 170 MHz) than that
within the exciton. This approach providing a direct spectroscopic approach for
distinguishing between coupling regimens, such as strongly bound trions, which
have been proposed to occur in organic devices.",1502.05471v1
2015-04-14,Magnetic charges and magnetoelectricity in hexagonal rare-earth manganites and ferrites,"Magnetoelectric (ME) materials are of fundamental interest and show broad
potential for technological applications. Commonly the dominant contribution to
the ME response is the lattice-mediated one, which is proportional to both the
Born electric charge $Z^{\rm e}$ and its analogue, the dynamical magnetic
charge $Z^{\rm m}$. Our previous study has shown that exchange striction acting
on noncollinear spins induces much larger magnetic charges than those that
depend on spin-orbit coupling. The hexagonal manganites $R$MnO$_3$ and ferrites
$R$FeO$_3$ ($R$ = Sc, Y, In, Ho-Lu) exhibit strong couplings between electric,
magnetic and structural degrees of freedom, with the transition-metal ions in
the basal plane antiferromagnetically coupled through super-exchange so as to
form a 120$^\circ$ noncollinear spin arrangement. Here we present a theoretical
study of the magnetic charges, and of the spin-lattice and spin-electronic ME
constants, in these hexagonal manganites and ferrites, clarifying the
conditions under which exchange striction leads to an enhanced $Z^{\rm m}$
values and anomalously large in-plane spin-lattice ME effects.",1504.03405v1
2015-04-30,Ab initio calculation of Spin-Polarized Low-Energy Electron Diffraction Pattern for the systems Fe(001) and Fe(001)-p(1x1)-O,"The construction of a multi-channel vector spin polarimeter requires the
development of a new detector type, which works as a spin polarizing mirror
with high reflectivity and asymmetry properties to guarantee for a high figure
of merit. Technical realizations are found by spin polarized electron
scattering from a surface at low energies. A very promising candidate for such
a detector suitable material consists of an oxygen passivated iron surface, as
for example a Fe(001)-p(1x1)-O surface. We investigate in detail the electronic
structure of this adsorbate system and calculate the corresponding
spin-polarized low-energy electron scattering. Our theoretical study is based
on the fully relativistic SPRKKR-method in the framework of density functional
theory. Furthermore, we use the local spin-density approximation in combination
with dynamical mean field theory to determine the electronic structure of
Fe(001)-p(1x1)-O and demonstrate that a significant impact of correlation
effects occurs in the calculated figure of merit.",1504.08198v2
2015-05-20,Intrinsic life-time and external manipulation of Neel states in antiferromagnetic adatom spins on semiconductor surfaces,"It has been proposed that antiferromagnetic Fe adatom spins on semiconductor
Cu-N surfaces can be used to store information [S. Loth {\it et al}, Science
\textbf{335}, 196 (2012)]. Here, we investigate spin dynamics of such
antiferromagnetic systems through Monte Carlo simulations. We find out the
temperature and size laws of switching rates of N\'{e}el states and show that
the N\'{e}el states can become stable enough for the information storage when
the number of spins reaches to one or two dozens of the Fe spins. We also
explore promising methods for manipulating the N\'{e}el states. These could
help realize information storage with such antiferromagnetic spin systems.",1505.05261v1
2015-08-03,Spin-Spin Coupling in the Solar System,"The richness of dynamical behavior exhibited by the rotational states of
various solar system objects has driven significant advances in the theoretical
understanding of their evolutionary histories. An important factor that
determines whether a given object is prone to exhibiting non-trivial rotational
evolution is the extent to which such an object can maintain a permanent
aspheroidal shape, meaning that exotic behavior is far more common among the
small body populations of the solar system. Gravitationally bound binary
objects constitute a substantial fraction of asteroidal and TNO populations,
comprising systems of triaxial satellites that orbit permanently deformed
central bodies. In this work, we explore the rotational evolution of such
systems with specific emphasis on quadrupole-quadrupole interactions, and show
that for closely orbiting, highly deformed objects, both prograde and
retrograde spin-spin resonances naturally arise. Subsequently, we derive
capture probabilities for leading order commensurabilities and apply our
results to the illustrative examples of (87) Sylvia and (216) Kleopatra
asteroid systems. Cumulatively, our results suggest that spin-spin coupling may
be consequential for highly elongated, tightly orbiting binary objects.",1508.00616v1
2015-09-18,Atomic-scale positioning of single spins via multiple nitrogen-vacancy centers,"We present a scheme of positioning a single electron spin with sub-nanometer
resolution through multiple nitrogen-vacancy centers in diamond. With unwanted
noise suppressed by dynamical decoupling, the spin coherence of each center
develops characteristic oscillations due to a single electron spin located
$4{\sim20}$ nm away from the centers. We can extract the position information
from the characteristic electron spin-coherence oscillations of each center.
This scheme is useful for high-resolution nanoscale magnetometry and spin-based
quantum computing.",1509.05558v2
2015-10-15,Shaped electric fields for fast optimal manipulation of electron spin and position in a double quantum dot,"We use quantum optimal control theory algorithms to design external electric
fields that drive the coupled spin and orbital dynamics of an electron in a
double quantum dot, subject to the spin-orbit interaction and Zeeman magnetic
fields. We obtain time-profiles of multi-frequency electric pulses which
increase the rate of spin-flip transitions by several orders of magnitude in
comparison with monochromatic fields, where the spin Rabi oscillations were
predicted to be very slow. This precise, with the accuracy higher than
$10^{-4}$, and fast, at the timescale of the order of 0.1 ns, simultaneous
control of the electron spin orientation and position is achieved while keeping
the electron in the four lowest tunneling- and Zeeman-split levels through the
duration of the pulse, facilitating high fidelity and suggesting useful
applications in spintronics and quantum information devices.",1510.04502v2
2015-11-12,Thermally-driven spin torques in layered magnetic insulators,"Thermally-driven spin-transfer torques have recently been reported in
electrically insulating ferromagnet$|$normal-metal heterostructures. In this
paper, we propose two physically distinct mechanisms for such torques. The
first is a local effect: out-of-equilibrium, thermally-activated magnons in the
ferromagnet, driven by a spin Seebeck effect, exert a torque on the
magnetization via magnon-magnon scattering with coherent dynamics. The second
is a nonlocal effect which requires an additional magnetic layer to provide the
symmetry breaking necessary to realize a thermal torque. The simplest structure
in which to induce a nonlocal thermal torque is a spin valve composed of two
insulating magnets separated by a normal metal spacer; there, a thermal flux
generates a pure spin current through the spin valve, which results in a torque
when the magnetizations of the layers are misaligned.",1511.04104v1
2016-01-21,Nuclear spin correlations and collective excitations in supercritical H$_2$,"Nuclear spins are known to experience spontaneous long-range correlations
only below 2.5 mili-Kelvin in superfluid $^3$He. Here we present the first
evidence of nuclear spin coupling in molecular hydrogen (H$_2$) at 74-92 Kelvin
using neutron scattering, showing a fundamental change in nature from the
incoherent scattering universally expected from hydrogen, which reflects single
particle properties of uncorrelated nuclear spins, to coherent, with a peak
materializing on the elastic line, indicating H$_2$-H$_2$ nuclear spin
correlations. In this novel phase, the dynamic response of the system also
changes nature, and collective excitations with an effective mass of nine H$_2$
are observed with inelastic scattering at momentum transfers up to 37
\AA$^{-1}$, corresponding to length scales smaller than the H-H bond, where
previous experiments have always found single atom excitations. This novel
behavior has only been observed from H$_2$ within the subnanometer sized
graphitic pores of a carbon material, marking the first demonstration that a
confined materials environment can be used to control nuclear spin
correlations.",1602.01811v1
2016-02-11,Laser-Driven Multiferroics and Ultrafast Spin Current Generation,"We propose an ultrafast way to generate spin chirality and spin current in a
class of multiferroic magnets using a terahertz circularly polarized laser.
Using the Floquet formalism for periodically driven systems, we show that it is
possible to dynamically control the Dzyaloshinskii-Moriya interaction in
materials with magnetoelectric coupling. This is supported by numerical
calculations, by which additional resonant phenomena are found. Specifically,
when a static magnetic field is applied in addition to the circularly polarized
laser, a large resonant enhancement of spin chirality is observed resembling
the electron spin resonance. Spin current is generated when the laser is
spatially modulated by chiral plasmonic structures and could be detected using
optospintronic devices.",1602.03702v2
2016-02-12,High-precision force sensing using a single trapped ion,"We introduce quantum sensing schemes for measuring very weak forces with a
single trapped ion. They use the spin-motional coupling induced by the
laser-ion interaction to transfer the relevant force information to the
spin-degree of freedom. Therefore, the force estimation is carried out simply
by observing the Ramsey-type oscillations of the ion spin states. Three quantum
probes are considered, which are represented by systems obeying the
Jaynes-Cummings, quantum Rabi (in 1D) and Jahn-Teller (in 2D) models. By using
dynamical decoupling schemes in the Jaynes-Cummings and Jahn-Teller models, our
force sensing protocols can be made robust to the spin dephasing caused by the
thermal and magnetic field fluctuations. In the quantum-Rabi probe, the
residual spin-phonon coupling vanishes, which makes this sensing protocol
naturally robust to thermally-induced spin dephasing. We show that the proposed
techniques can be used to sense the axial and transverse components of the
force with a sensitivity beyond the yN $/\sqrt{\text{Hz}}$ range, i.e. in the
xN$ /\sqrt{\text{Hz}}$ (xennonewton, $10^{-27}$). The Jahn-Teller protocol, in
particular, can be used to implement a two-channel vector spectrum analyzer for
measuring ultra-low voltages.",1602.04072v1
2016-02-26,Criticality and Energy Landscapes in Spin Glasses,"Despite the extreme simplicity in their definition, spin glasses disclose a
wide variety of non-trivial behaviors that are not yet fully understood. In
this thesis we try to shed light on some of them, focusing on one hand on the
search of phase transitions under perturbations of the Hamiltonian, and on the
other hand on the zero-temperature properties and responses to external
stimuli. After introducing spin glasses through a historiographical review, and
useful concepts on phase transitions and numerics, the results of two massive
Monte Carlo campaigns on three-dimensional systems are shown. In the first one
the de Almeida-Thouless transition is studied, and a new finite-size scaling
ansatz is proposed, that accelerates the convergence to the thermodynamic
limit. In the second one the phase diagram of the Heisenberg spin glass with
random exchange anisotropy is reconstructed. In the following part of the
manuscript, surprising features of zero-temperature statics and dynamics of
several spin glass models are found. Among them, correlations between soft
spins that arise spontaneously during avalanches, and the discovery of
localized states that involve the presence of two-level systems.",1602.08239v2
2016-02-26,Gate fidelity and coherence of an electron spin in a Si/SiGe quantum dot with micromagnet,"The gate fidelity and the coherence time of a qubit are important benchmarks
for quantum computation. We construct a qubit using a single electron spin in a
Si/SiGe quantum dot and control it electrically via an artificial spin-orbit
field from a micromagnet. We measure an average single-qubit gate fidelity of
$\approx$ 99$\%$ using randomized benchmarking, which is consistent with
dephasing from the slowly evolving nuclear spins in substrate. The coherence
time measured using dynamical decoupling extends up to $\approx$ 400 $\mu$s for
128 decoupling pulses, with no sign of saturation. We find evidence that the
coherence time is limited by noise in the 10 kHz $-$ 1 MHz range, possibly
because charge noise affecting the spin via the micromagnet gradient. This work
shows that an electron spin in a Si/SiGe quantum dot is a good candidate for
quantum information processing as well as for a quantum memory, even without
isotopic purification.",1602.08334v1
2016-03-25,Effect of quantum phase transition in the disentanglement of three spins coupled to an XY spin chain,"Recently, along with the development of quantum information, quantum
entanglemant became a hot topic of people. Quantum entanglemant is one of the
most amazing phenomenon in quantum mechanics that is totally different from
classical physics. However, system would interact with environment in the
practical quantum information process. The entanglement would be broken. In
this paper, we study the disentanglement evolution of three spin qubits in an
XY spin-chain environment. The dynamical process of the disentanglement is
investigated. We found the exact expression of the coherence factor. We discuss
the coherence factor and the parameters, and then we illustrate that the
disentanglement of central spins is best enhanced by the quantum critical
behavior of the environmental spin chain. Furthermore, a scaling rule is
obtained.",1603.08555v1
2016-04-01,Topological edge Mott insulating state in two dimensions at finite temperatures -bulk and edge analysis-,"We study a bilayer Kane-Mele-Hubbard model with lattice distortion and
inter-layer spin exchange interaction under cylinder geometry. Our analysis
based on real-space dynamical mean field theory with continuous-time quantum
Monte Carlo demonstrates the emergence of a topological edge Mott insulating
(TEMI) state which hosts gapless edge modes only in collective spin
excitations. This is confirmed by the numerical calculations at finite
temperatures for the spin-Hall conductivity and the single-particle excitation
spectrum; the spin Hall conductivity is almost quantized,
$\sigma^{xy}_\mathrm{spin}\sim2(e/2\pi)$, predicting gapless edge modes
carrying the spin current, while the helical edge modes in the single-particle
spectrum are gapped out with respecting symmetry. It is clarified how the TEMI
state evolves from the ordinary spin Hall insulating state with increasing the
Hubbard interaction at a given temperature and then undergoes a phase
transition to a trivial Mott insulating state. With a bosonization approach at
zero temperature, we further address which collective modes host gapless edge
modes in the TEMI state.",1604.00122v1
2016-07-03,Spin waves and magnetic exchange interactions in the spin ladder compound RbFe$_2$Se$_3$,"We report an inelastic neutron scattering study of the spin waves of the
one-dimensional antiferromagnetic spin ladder compound RbFe$_2$Se$_3$. The
results reveal that the products, $SJ$'s, of the spin $S$ and the magnetic
exchange interactions $J$'s along the antiferromagnetic (leg) direction and the
ferromagnetic (rung) direction are comparable with those for the stripe ordered
phase of the parent compounds of the iron-based superconductors. The
universality of the $SJ$'s implies nearly universal spin wave dynamics and the
irrelevance of the fermiology for the existence of the stripe antiferromagnetic
order among various Fe-based materials.",1607.00639v1
2016-07-08,Supercurrent-induced Skyrmion dynamics and Tunable Weyl points in Chiral Magnet with Superconductivity,"Recent studies show superconductivity provides new perspectives on
spintronics. We study a heterostructure composed of an s-wave superconductor
and a cubic chiral-magnet that can stabilize a topological spin texture, a
skyrmion. We propose a supercurrent-induced spin torque that originates from
the spin-orbit coupling, and we show that the spin torque can drive a skyrmion
in an efficient way that reduces Joule heating. We also study the band
structure of Bogoliubov quasiparticles and show the existence of Weyl points,
whose positions can be controlled by the direction of the magnetization. This
results in an effective magnetic field acting on the quasiparticles in the
presence spin textures. Furthermore, the tilt of the Weyl cones can also be
tuned by the strength of the spin-orbit coupling, and we propose a possible
realization of type-II Weyl points.",1607.02336v4
2016-07-26,Multitude of phases in correlated lattice fermion systems with spin-dependent disorder,"The magnetic phases induced by the interplay between disorder acting only on
particles with a given spin projection (""spin-dependent disorder"") and a local
repulsive interaction is explored. To this end the magnetic ground state phase
diagram of the Hubbard model at half-filling is computed within dynamical
mean-field theory combined with the geometric average over disorder, which is
able to describe Anderson localization. Five distinct phases are identified: a
ferromagnetically polarized metal, two types of insulators, and two types of
spin-selective localized phases. The latter four phases possess different
long-range order of the spins. The predicted phase diagram may be tested
experimentally using cold fermions in optical lattices subject to
spin-dependent random potentials.",1607.07708v2
2016-07-27,Cavity-assisted measurement and coherent control of collective atomic spin oscillators,"We demonstrate continuous measurement and coherent control of the collective
spin of an atomic ensemble undergoing Larmor precession in a high-finesse
optical cavity. The coupling of the precessing spin to the cavity field yields
phenomena similar to those observed in cavity optomechanics, including cavity
amplification, damping, and optical spring shifts. These effects arise from
autonomous optical feedback onto the atomic spin dynamics, conditioned by the
cavity spectrum. We use this feedback to stabilize the spin in either its high-
or low-energy state, where, in equilibrium with measurement back-action
heating, it achieves a steady-state temperature, indicated by an asymmetry
between the Stokes and anti-Stokes scattering rates. For sufficiently large
Larmor frequency, such feedback stabilizes the spin ensemble in a nearly pure
quantum state, in spite of continuous measurement by the cavity field.",1607.07941v2
2016-09-05,Spin excitations in optimally P-doped BaFe2(As0.7P0.3)2superconductor,"We use inelastic neutron scattering to study temperature and energy
dependence of spin excitations in optimally P-doped BaFe2(As0.7P0.3)2
superconductor (Tc = 30 K) throughout the Brillouin zone. In the undoped state,
spin waves and paramagnetic spin excitations of BaFe2As2 stem from
antiferromagnetic (AF) ordering wave vector QAF= (1/-1,0) and peaks near zone
boundary at (1/-1,1/-1) around 180 meV. Replacing 30% As by smaller P to induce
superconductivity, low-energy spin excitations of BaFe2(As0.7P0.3)2form a
resonance in the superconducting state and high-energy spin excitations now
peaks around 220 meV near (1/-1,1/-1). These results are consistent with
calculations from a combined density functional theory and dynamical mean field
theory, and suggest that the decreased average pnictogen height in
BaFe2(As0.7P0.3)2 reduces the strength of electron correlations and increases
the effective bandwidth of magnetic excitations.",1609.01021v1
2016-10-18,Spin Relaxation in GaAs: Importance of Electron-Electron Interactions,"We study spin relaxation in n-type bulk GaAs, due to the Dyakonov--Perel
mechanism, using ensemble Monte Carlo methods. Our results confirm that spin
relaxation time increases with the electronic density in the regime of moderate
electronic concentrations and high temperature. We show that the
electron-electron scattering in the non-degenerate regime significantly slows
down spin relaxation. This result supports predictions by Glazov and Ivchenko.
Most importantly, our findings highlight the importance of many-body
interactions for spin dynamics: we show that only by properly taking into
account electron-electron interactions within the simulations, results for the
spin relaxation time---with respect to both electron density and
temperature---will reach good {\it quantitative} agreement with corresponding
experimental data. Our calculations contain no fitting parameters.",1610.05698v1
2017-02-09,Magnetic charge injection in spin ice: a new way to fragmentation,"The complexity embedded in condensed matter fertilizes the discovery of new
states of matter, enriched by ingredients like frustration. Illustrating
examples in magnetic systems are Kitaev spin liquids, skyrmions phases, or spin
ices. These unconventional ground states support exotic excitations, for
example the magnetic charges in spin ices, also called monopoles. Beyond their
discovery, an important challenge is to be able to control and manipulate them.
Here, we propose a new mechanism to inject monopoles in a spin ice through a
staggered magnetic field. We show theoretically, and demonstrate experimentally
in the Ho$_2$Ir$_2$O$_7$ pyrochlore iridate, that it results in the
stabilization of a monopole crystal, which exhibits magnetic fragmentation. In
this new state of matter, the magnetic moment fragments into an ordered part
and a persistently fluctuating one. Compared to conventional spin ices, the
different nature of the excitations in this fragmented state opens the way to
novel tunable field-induced and dynamical behaviors.",1702.02864v1
2017-02-14,Electron-nuclear coherent spin oscillations probed by spin dependent recombination,"We demonstrate the detection of coherent electron-nuclear spin oscillations
related to the hyperfine interaction and revealed by the band-to-band
photoluminescence (PL) in zero external magnetic field. On the base of a
pump-probe PL experiment we measure, directly in the temporal domain, the
hyperfine constant of an electron coupled to a gallium defect in GaAsN by
tracing the dynamical behavior of the conduction electron spin-dependent
recombination to the defect site. The hyperfine constants and the relative
abundance of the nuclei isotopes involved can be determined without the need of
electron spin resonance technique and in the absence of any magnetic field.
Information on the nuclear and electron spin relaxation damping parameters can
also be estimated from the oscillations damping and the long delay behavior.",1702.04129v1
2017-03-21,Large anisotropic spin relaxation time of exciton bound to donor states in triple quantum wells,"We have studied the spin dynamics of a dense two-dimensional electron gas
confined in a GaAs/AlGaAs triple quantum well by using time-resolved Kerr
rotation and resonant spin amplification. Strong anisotropy of the spin
relaxation time up to a factor of 10 was found between the electron spins
oriented in-plane and out-of-plane when the excitation energy is tuned to an
exciton bound to neutral donor transition. We model this anisotropy using an
internal magnetic field and the inhomogeneity of the electron g-factor. The
data analysis allows us to determine the direction and magnitude of this
internal field in the range of a few mT for our studied structure, which
decreases with the sample temperature and optical power. The dependence of the
anisotropic spin relaxation was directly measured as a function of several
experimental parameters: excitation wavelength, sample temperature, pump-probe
time delay, and pump power.",1703.07156v2
2017-08-06,Disorder and Quantum spin ice,"We report on diffuse neutron scattering experiments providing evidence for
the presence of random strains in the quantum spin ice candidate Pr2Zr2O7.
Since Pr is a non-Kramers ion, the strain deeply modifies the picture of Ising
magnetic moments governing the low temperature properties of this material. It
is shown that the derived strain distribution accounts for the temperature
dependence of the specific heat and of the spin excitation spectra. Taking
advantage of mean field and spin dynamics simulations, we argue that the
randomness in Pr2Zr2O7, promotes a new state of matter, which is disordered,
yet characterized by short range antiferroquadrupolar correlations, and from
which emerge spin-ice like excitations. This study thus opens an original
research route in the field of quantum spin ice.",1708.01845v1
2018-02-27,Spin Transport in a Mott Insulator of Ultracold Fermions,"Strongly correlated materials are expected to feature unconventional
transport properties, such that charge, spin, and heat conduction are
potentially independent probes of the dynamics. In contrast to charge
transport, the measurement of spin transport in such materials is highly
challenging. We observed spin conduction and diffusion in a system of ultracold
fermionic atoms that realizes the half-filled Fermi-Hubbard model. For strong
interactions, spin diffusion is driven by super-exchange and
doublon-hole-assisted tunneling, and strongly violates the quantum limit of
charge diffusion. The technique developed in this work can be extended to
finite doping, which can shed light on the complex interplay between spin and
charge in the Hubbard model.",1802.10018v2
2018-02-28,Beliaev Damping in Spin-$\frac{1}{2}$ Interacting Bosons with Spin-Orbit Coupling,"Beliaev damping provides one of the most important mechanisms for dissipation
of quasiparticles through beyond-mean-field effects at zero temperature. Here
we present the first analytical result of Beliaev damping in low-energy
excitations of spin-$\frac{1}{2}$ interacting bosons with equal Rashba and
Dresslhaus spin-orbit couplings. We identify novel features of Beliaev decay
rate due to spin-orbit coupling, in particular, it shows explicit dependence on
the spin-density interaction and diverges at the interaction-modified phase
boundary between the zero-momentum and plane-wave phases. This represents a
manifestation of the effect of spin-orbit coupling in the beyond-mean-field
regime, which by breaking Galilean invariance couples excitations in the
density- and spin-channels. By describing the Beliaev damping in terms of the
observable dynamic structure factors, our results allow direct experimental
access within current facilities.",1802.10295v1
2018-04-13,Finite-temperature properties of the extended Heisenberg model on a triangular lattice,"We present numerical results for the $J_1$-$J_2$ Heisenberg model on a
triangular lattice at finite temperatures $T>0$. In contrast to unfrustrated
lattices we reach much lower $T \sim 0.15 J_1$. In static quantities the novel
feature is a quite sharp low-$T$ maximum in the specific heat. Dynamical spin
structure factor $S({\bf q},\omega)$ allows for the extraction of the effective
spin-wave energies $\omega_{\bf q}(T)$ and their damping $\gamma_{\bf q}(T)$.
While for $J_2=0$ our results are consistent with $T=0$ spin ordering, $J_2/J_1
\sim 0.1 $ induces additional frustration with a signature of spin liquid
ground state. In the latter case, results for spin-lattice relaxation rate
indicate in the low-$T$ accesible regime on $1/T_1 \propto T^{\alpha}$ with
$\alpha \geq 1$, as observed in recent spin-liquid materials on a triangular
lattice.",1804.04819v1
2018-04-19,Non-classical measurement statistics induced by a coherent spin environment,"We demonstrate the role of measurement back-action of a coherent spin
environment on the dynamics of a spin (qubit) coupled to it, by inducing
non-classical (Quantum Random Walk like) statistics on its measurement
trajectory. We show how the long-life time of the spin-bath allows it to
correlate measurements of the qubit over many repetitions. We have used
Nitrogen Vacancy centers in diamond as a model system, and the projective
single-shot readout of the electron spin at low temperatures to simulate these
effects. We show that the proposed theoretical model, explains the
experimentally observed statistics and their application for quantum state
engineering of spin ensembles towards desired states.",1804.07111v1
2020-07-25,Using a Lindbladian approach to model decoherence in two coupled nuclear spins via correlated phase-damping and amplitude damping noise channels,"In this work, we studied the relaxation dynamics of coherences of different
order present in a system of two coupled nuclear spins. We used a previously
designed model for intrinsic noise present in such systems which considers the
Lindblad master equation for Markovian relaxation. We experimentally created
zero-, single- and double- quantum coherences in several two-spin systems and
performed a complete state tomography and computed state fidelity. We
experimentally measured the decay of zero- and double- quantum coherences in
these systems. The experimental data fitted well to a model that considers the
main noise channels to be a correlated phase damping channel acting
simultaneously on both spins in conjunction with a generalized amplitude
damping channel acting independently on both spins. The differential relaxation
of multiple-quantum coherences can be ascribed to the action of a correlated
phase damping channel acting simultaneously on both the spins.",2007.12972v1
2010-05-03,Collective spin mode in a multi-component system of coupled itinerant and localized electrons,"We study collective spin excitations of a magnetically ordered state in a
multi-component system composed of both itinerant electrons and local moments.
Here the induced spin-density-wave (SDW) ordering of itinerant electrons and
the collinear antiferromangetic (AF) ordering of local moments are locked
together via a Hund's rule coupling. We show that the Goldstone theorem still
holds at the RPA level with the gapless spin wave protected inside the small
SDW gap of itinerant electrons, which, however, is fragile in the presence of
ion-anisotropy. A gapped out-of-phase spin mode extending over a much wider
energy scale above the SDW gap is found to be more robust against the
ion-anisotropy, which is mainly contributed by the local moment fluctuations.
While the scattering between the Goldstone mode and itinerant electrons
diminishes within the SDW gap, the out-of-phase mode will strongly interact
with itinerant electrons and thus dominate the spin and charge dynamics in such
an ordered phase. Possible relevance of such a model to the iron-pnictides will
be also discussed.",1005.0421v1
2010-05-26,Phase Transitions in Dissipative Quantum Transport and Mesoscopic Nuclear Spin Pumping,"Topological phase transitions can occur in the dissipative dynamics of a
quantum system when the ratio of matrix elements for competing transport
channels is varied. Here we establish a relation between such behavior in a
class of non-Hermitian quantum walk problems [M. S. Rudner and L. S. Levitov,
Phys. Rev. Lett. 102, 065703 (2009)] and nuclear spin pumping in double quantum
dots, which is mediated by the decay of a spin-blockaded electron triplet state
in the presence of spin-orbit and hyperfine interactions. The transition occurs
when the strength of spin-orbit coupling exceeds the strength of the net
hyperfine coupling, and results in the complete suppression of nuclear spin
pumping. Below the transition point, nuclear pumping is accompanied by a strong
reduction in current due to the presence of non-decaying ""dark states"" in this
regime. Due to its topological character, the transition is expected to be
robust against dephasing of the electronic degrees of freedom.",1005.4809v1
2013-08-02,Extraordinary momentum and spin in evanescent waves,"Momentum and spin represent fundamental dynamical properties of quantum
particles and fields. In particular, propagating optical waves (photons) carry
momentum and longitudinal spin determined by the wave vector and circular
polarization, respectively. Here we show that exactly the opposite can be the
case for evanescent optical waves. A single evanescent wave possesses a spin
component, which is independent of the polarization and is orthogonal to the
wave vector. Furthermore, such a wave carries a momentum component, which is
determined by the circular polarization and is also orthogonal to the wave
vector. We show that these extraordinary properties reveal a fundamental
Belinfante's spin momentum, known in field theory and unobservable in
propagating fields. We demonstrate that the transverse momentum and spin push
and twist a probe Mie particle in an evanescent field. This allows the
observation of `impossible' properties of light and of a fundamental
field-theory quantity, which was previously considered as `virtual'.",1308.0547v3
2013-08-06,Chirality from interfacial spin-orbit coupling effects in magnetic bilayers,"As nanomagnetic devices scale to smaller sizes, spin-orbit coupling due to
the broken structural inversion symmetry at interfaces becomes increasingly
important. Here we study interfacial spin-orbit coupling effects in magnetic
bilayers using a simple Rashba model. The spin-orbit coupling introduces
chirality into the behavior of the electrons and through them into the
energetics of the magnetization. In the derived form of the magnetization
dynamics, all of the contributions that are linear in the spin-orbit coupling
follow from this chirality, considerably simplifying the analysis. For these
systems, an important consequence is a correlation between the
Dzyaloshinskii-Moriya interaction and the spin-orbit torque. We use this
correlation to analyze recent experiments.",1308.1198v2
2013-08-16,Persistent spin excitations in doped antiferromagnets revealed by resonant inelastic light scattering,"How coherent quasiparticles emerge by doping quantum antiferromagnets is a
key question in correlated electron systems, whose resolution is needed to
elucidate the phase diagram of copper oxides. Recent resonant inelastic X-ray
scattering (RIXS) experiments in hole-doped cuprates have purported to measure
high-energy collective spin excitations that persist well into the overdoped
regime and bear a striking resemblance to those found in the parent compound,
challenging the perception that spin excitations should weaken with doping and
have a diminishing effect on superconductivity. Here we show that RIXS at the
Cu L3-edge indeed provides access to the spin dynamical structure factor once
one considers the full influence of light polarization. Further we demonstrate
that high-energy spin excitations do not correlate with the doping dependence
of Tc, while low-energy excitations depend sensitively on doping and show
ferromagnetic correlations. This suggests that high-energy spin excitations are
marginal to pairing in cuprate superconductors.",1308.3717v2
2013-08-22,Magnetization oscillations by vortex-antivortex dipoles,"A vortex-antivortex dipole can be generated due to current with in-plane
spin-polarization, flowing into a magnetic element, which then behaves as a
spin transfer oscillator. Its dynamics is analyzed using the Landau-Lifshitz
equation including a Slonczewski spin-torque term. We establish that the vortex
dipole is set in steady state rotational motion due to the interaction between
the vortices, while an external in-plane magnetic field can tune the frequency
of rotation. The rotational motion is linked to the nonzero skyrmion number of
the dipole. The spin-torque acts to stabilize the vortex dipole at a definite
vortex-antivortex separation distance. In contrast to a free vortex dipole, the
rotating pair under spin-polarized current is an attractor of the motion,
therefore a stable state. Three types of vortex-antivortex pairs are obtained
as we vary the external field and spin-torque strength. We give a guide for the
frequency of rotation based on analytical relations.",1308.4805v1
2014-03-03,Relativistic spin operators in various electromagnetic environments,"Different operators have been suggested in the literature to describe the
electron's spin degree of freedom within the relativistic Dirac theory. We
compare concrete predictions of the various proposed relativistic spin
operators in different physical situations. In particular, we investigate the
so-called Pauli, Foldy-Wouthuysen, Czachor, Frenkel, Chakrabarti, Pryce, and
Fradkin-Good spin operators. We demonstrate that when a quantum system
interacts with electromagnetic potentials the various spin operators predict
different expectation values. This is explicitly illustrated for the scattering
dynamics at a potential step and in a standing laser field and also for energy
eigenstates of hydrogenic ions. Therefore, one may distinguish between the
proposed relativistic spin operators experimentally.",1403.0550v2
2014-03-05,Role of dual nuclear baths on spin blockade leakage current bistabilities,"Spin-blockaded electronic transport across a double quantum dot (DQD) system
represents an important advancement in the area of spin-based quantum
information. The basic mechanism underlying the blockade is the formation of a
blocking triplet state. The bistability of the leakage current as a function of
the applied magnetic field in this regime is believed to arise from the effect
of nuclear Overhauser fields on spin-flip transitions between the blocking
triplet and the conducting singlet states. The objective of this paper is to
present the nuances of considering a two bath model on the experimentally
observed current bistability by employing a self consistent simulation of the
nuclear spin dynamics coupled with the electronic transport of the DQD set up.
In doing so, we first discuss the important subtleties involved in the
microscopic derivation of the hyperfine mediated spin flip rates. We then give
insights as to how the differences between the two nuclear baths and the
resulting difference Overhauser field affect the two-electron states of the
DQD, and their connection with the experimentally observed current hysteresis
curve.",1403.1090v2
2014-03-25,Decay of the rotary echoes for the spin of a nitrogen-vacancy center in diamond,"We study dynamics of the electron spin of a nitrogen-vacancy (NV) center
subjected to a strong driving field with periodically reversed direction (train
of rotary echoes). We use analytical and numerical tools to analyze in detail
the form and timescales of decay of the rotary echo train, modeling the
decohering spin environment as a random magnetic field. We demonstrate that the
problem can be exactly mapped onto a model of spin 1 coupled to a single
bosonic mode with imaginary frequency. This mapping allows comprehensive
analytical investigation beyond the standard Bloch-Redfield-type approaches. We
explore the decay of the rotary echo train under assumption of strong driving,
and identify the most important regimes of the decay. The analytical results
are compared with the direct numerical simulations to confirm quantitative
accuracy of our study. We present the results for realistic environment of
substitutional nitrogen atoms (P1 centers), and provide a simplified but
accurate description for decay of the rotary echo train of the NV center's
spin. The approach presented here can also be used to study decoherence and
longitudinal relaxation of other spin systems under conditions of strong
driving.",1403.6446v1
2016-11-28,Nuclear scissors modes and hidden angular momenta,"The coupled dynamics of low lying modes and various giant resonances are
studied with the help of the Wigner Function Moments method generalized to take
into account spin degrees of freedom and pair correlations simultaneously. The
method is based on Time Dependent Hartree-Fock-Bogoliubov equations. The model
of the harmonic oscillator including spin-orbit potential plus
quadrupole-quadrupole and spin-spin interactions is considered. New low lying
spin dependent modes are analyzed. Special attention is paid to the scissors
modes. A new source of nuclear magnetism, connected with counter-rotation of
spins up and down around the symmetry axis (hidden angular momenta), is
discovered. Its inclusion into the theory allows one to improve substantially
the agreement with experimental data in the description of energies and
transition probabilities of scissors modes.",1611.09037v1
2017-01-05,Chiral spin liquid on kagome antiferromagnet induced by Dzyaloshinskii-Moriya interaction,"The quantum spin liquid material herbertsmithite is described by an
antiferromagnetic Heisenberg model on the kagome lattice with non-negligible
Dzyaloshinskii-Moriya interaction~(DMI). A well established phase transition to
the $\mathbf q=0$ long-range order occurs in this model when the DMI strength
increases, but the precise nature of a small-DMI phase remains controversial.
Here, we describe a new phase obtained from Schwinger-boson mean-field theory
that is stable at small DMI, and which can explain the dispersionless spectrum
seen in inelastic neutron scattering experiment by Han et al (Nature (London)
492, 406 (2012)}). It is a time-reversal symmetry breaking $\mathbb Z_2$ spin
liquid, with the unique property of a small and constant spin gap in an
extended region of the Brillouin zone. The phase diagram as a function of DMI
and spin size is given, and dynamical spin structure factors are presented.",1701.01243v2
2017-04-04,A method for solving gyroscopic equations with operators,"The dynamics of a set of identical spins interacting with another one through
a time-dependent coupling gives rise to a gyroscopic equation with a variable
Larmor frequency and, more importantly, with an operator playing the role a
Larmor vector. The subsequent technical complexity is due to non-trivial
algebraic relations between multiple inner products coming from the
non-commutative algebra of the angular momenta. A general formalism is derived
giving the integrated solution valid for all values of the involved spins, and
several applications of the formalism are treated in details. Among other
results, it is seen that, starting from a fully polarised state for the set of
identical spins, their total spin can at most only partially flip (in the
mean); this somewhat surprising fact means that the memory of the initial state
is kept for ever but varying the coupling constant allows to adjust at will the
possible polarisation of the final state. The robustness of the initial state
is shown to depend on the nature fermionic or bosonic of the perturbing spin
and also on the size of the collection of identical spins.",1704.01063v1
2017-04-13,Majorana flipping of quarkonium spin states in transient magnetic field,"We demonstrate that spin flipping transitions occur between various
quarkonium spin states due to transient magnetic field produced in non central
heavy ion collisions (HICs). The inhomogeneous nature of the magnetic field
results in \textit{non adiabatic evolution} of (spin)states of quarkonia moving
inside the transient magnetic environment. Our calculations explicitly show
that the consideration of azimuthal inhomogeneity gives rise to dynamical
mixing between different spin states owing to Majorana spin flipping. Notably,
this effect of non-adiabaticity is novel and distinct from previously predicted
mixing of the singlet and one of the triplet states of quarkonia in the
presence of a static and homogeneous magnetic field.",1704.04094v2
2018-05-15,Emergence of a Field-Driven U(1) Spin Liquid in the Kitaev Honeycomb Model,"In the field of quantum magnetism, the exactly solvable Kitaev honeycomb
model serves as a paradigm for the fractionalization of spin degrees of freedom
and the formation of $\mathbb{Z}_2$ quantum spin liquids. An intense
experimental search has led to the discovery of a number of spin-orbit
entangled Mott insulators that realize its characteristic bond-directional
interactions and, in the presence of magnetic fields, exhibit no indications of
long-range order. Here, we map out the complete phase diagram of the Kitaev
model in tilted magnetic fields and report the emergence of a distinct gapless
quantum spin liquid at intermediate field strengths. Analyzing a number of
static, dynamical, and finite temperature quantities using numerical exact
diagonalization techniques, we find strong evidence that this phase exhibits
gapless fermions coupled to a massless $U(1)$ gauge field. We discuss its
stability in the presence of perturbations that naturally arise in spin-orbit
entangled candidate materials.",1805.05953v4
2008-07-07,Hole - Nuclear Spin Interaction in Quantum Dots,"We have measured the carrier spin dynamics in p-doped InAs/GaAs quantum dots
by pump-probe photo-induced circular dichroism and time-resolved
photoluminescence experiments. We show that the hole spin dephasing is
controlled by the hyperfine interaction between hole and nuclear spins. In the
absence of external magnetic field, we find a characteristic hole spin
dephasing time of 15 ns, in close agreement with our calculations based on
dipole-dipole coupling between the hole and the quantum dot nuclei. Finally we
demonstrate that a small external magnetic field, typically 10 mT instead of
200 mT for the case of electrons, quenches the hyperfine hole spin dephasing.",0807.0968v2
2011-11-06,Two component spin-fermion model for high-$T_c$ cuprates: Applications to neutron scattering and ARPES experiments,"Motivated by neutron scattering experiments in the high-$T_c$ cuprates, we
propose the two-component spin-fermion model as a minimal phenomenological
model which has both local spins and itinerant fermions as independent degrees
of freedom. Our calculations of the dynamic spin correlation function provide a
successful description of the puzzling neutron experiment data and show that:
(1) the upward dispersion branch of magnetic excitations is mostly due to the
local spin excitations; (2) the downward dispersion branch is from collective
particle-hole excitations of fermions; and (3) the resonance mode is a mixture
of both degrees of freedom. Using the same model with the same set of
parameters we calculated the renormalized quasiparticle dispersion and
successfully reproduced one of the key features of the angle resolved
photoemission spectroscopy (ARPES) experiments, i.e., the high energy kink
structure in the fermion quasiparticle dispersion, hence further support the
two component spin-fermion phenomenology.",1111.1372v1
2012-01-12,Environment Assisted Metrology with Spin Qubit,"We investigate the sensitivity of a recently proposed method for precision
measurement [Phys. Rev. Lett. 106, 140502 (2011)], focusing on an
implementation based on solid-state spin systems. The scheme amplifies a
quantum sensor response to weak external fields by exploiting its coupling to
spin impurities in the environment. We analyze the limits to the sensitivity
due to decoherence and propose dynamical decoupling schemes to increase the
spin coherence time. The sensitivity is also limited by the environment spin
polarization; therefore we discuss strategies to polarize the environment spins
and present a method to extend the scheme to the case of zero polarization. The
coherence time and polarization determine a figure of merit for the
environment's ability to enhance the sensitivity compared to echo-based sensing
schemes. This figure of merit can be used to engineer optimized samples for
high-sensitivity nanoscale magnetic sensing, such as diamond nanocrystals with
controlled impurity density.",1201.2684v1
2012-01-18,Crossover from coherent to incoherent scattering in spin-orbit dominated Sr2IrO4,"Strong spin-orbit interaction in the two dimensional compound Sr2IrO4 leads
to the formation of Jeff=1/2 isospins with unprecedented dynamics. In Raman
scattering a continuum attributed to double spin scattering is observed. With
higher excitation energy of the incident Laser this signal crosses over to an
incoherent background. The characteristic energy scale of this cross over is
identical to that of intensity resonance effects in phonon scattering. It is
related to exciton-like orbital excitations that are also evident in resonant
X-Ray scattering. The crossover and evolution of incoherent excitations are
proposed to be due to their coupling to spin excitations. This signals a
spin-orbit induced entanglement of spin, lattice and charge degrees of freedoms
in Sr2IrO4.",1201.3841v1
2013-09-05,Nuclear magnetization in gallium arsenide quantum dots at zero magnetic field,"Optical and electrical control of the nuclear spin system allows enhancing
the sensitivity of NMR applications and spin-based information storage and
processing. Dynamic nuclear polarization in semiconductors is commonly achieved
in the presence of a stabilizing external magnetic field. Here we report
efficient optical pumping of nuclear spins at zero magnetic field in strain
free GaAs quantum dots. The strong interaction of a single, optically injected
electron spin with the nuclear spins acts as a stabilizing, effective magnetic
field (Knight field) on the nuclei. We optically tune the Knight field
amplitude and direction. In combination with a small transverse magnetic field,
we are able to control the longitudinal and transverse component of the nuclear
spin polarization in the absence of lattice strain i.e. nuclear quadrupole
effects, as reproduced by our model calculations.",1309.1288v1
2014-05-04,Decoherence of a quantum system coupled to an XY spin chain: Role of the initial state of the spin chain,"We study the decoherence of a coupled quantum system consisting of a central
spin and its correlated environment described by a general $XY$ spin-chain
model. We make it clear that the evolution of the coherence factor sensitively
depends on the initial states of the environment spin-chain. Specially, the
dynamical evolution of the coherence factor of the central spin is numerically
and analytically investigated in both weak and strong coupling cases for
different initial states including thermal equilibrium state. In both weak and
strong coupling regimes, the decay of the coherence factor can be approximated
by a Gaussian and in the strong coupling regime the coherence factor oscillate
rapidly under a Gaussian envelope. The width of the Gaussian decay (envelope)
has been studied in details and we explained the origin of the so-called
universal regime.",1405.0635v1
2014-05-21,Spin-orbit coupled Bose-Einstein condensates in a double well,"We study the quantum dynamics of a spin-orbit (SO) coupled Bose-Einstein
condensate (BEC) in a double-well potential inspired by the experimental
protocol recently developed by NIST group. We focus on the regime where the
number of atoms is very large and perform a two-mode approximation. An
analytical solution of the two-site Bose-Hubbard-like Hamiltonian is found for
several limiting cases, which range from a strong Raman coupling to a strong
Josephson coupling, ending with the complete model in the presence of weak
nonlinear interactions. Depending on the particular limit, different approaches
are chosen: a mapping onto an SU(2) spin problem together with a
Holstein-Primakoff transformation in the first two cases and a rotating wave
approximation (RWA) when dealing with the complete model. The quantum evolution
of the number difference of bosons with equal or different spin between the two
wells is investigated in a wide range of parameters; finally the corresponding
total atomic current and the spin current are computed. We show a spin
Josephson effect which could be detected in experiments and employed to build
up realistic devices.",1405.5356v1
2014-06-15,Direct and inverse spin-orbit torques,"In collinear magnets lacking inversion symmetry application of electric
currents induces torques on the magnetization and conversely magnetization
dynamics induces electric currents. The two effects, which both rely on
spin-orbit interaction (SOI), are reciprocal to each other and denoted direct
spin-orbit torque (SOT) and inverse spin-orbit torque (ISOT), respectively. We
derive expressions for SOT and ISOT within the Kubo linear response formalism.
We show that expressions suitable for density-functional theory calculations
can be derived either starting from a Kohn-Sham Hamiltonian with time-dependent
exchange field or by expressing general susceptibilities in terms of the
Kohn-Sham susceptibilities. For the case of magnetic bilayer systems we derive
the general form of the ISOT current induced under ferromagnetic resonance.
Using \textit{ab initio} calculations within density-functional theory we
investigate SOT and ISOT in Co/Pt(111) magnetic bilayers. We determine the
spatial distribution of spin and charge currents as well as torques in order to
expose the mechanisms underlying SOT and ISOT and to highlight their
reciprocity on the microscopic level. We find that the spin Hall effect is
position-dependent close to interfaces.",1406.3866v2
2015-12-15,Long-lived nanosecond spin coherence in high-mobility 2DEGs confined in double and triple quantum wells,"We investigated the spin coherence of high-mobility two-dimensional electron
gases confined in multilayer GaAs quantum wells. The dynamics of the spin
polarization was optically studied using pump-probe techniques: time-resolved
Kerr rotation and resonant spin amplification. For double and triple quantum
wells doped beyond the metal-to-insulator transition, the spin-orbit
interaction was tailored by the sample parameters of structural symmetry
(Rashba constant), width and electron density (Dresselhaus linear and cubic
constants) which allows us to attain long dephasing times in the nanoseconds
range. The determination of the scales: transport scattering time,
single-electron scattering time, electron-electron scattering time, and spin
polarization decay time further supports the possibility of using n-doped
multilayer systems for developing spintronic devices.",1512.04759v3
2015-12-16,Kagome spin liquid: a deconfined critical phase driven by $U(1)$ gauge fluctuation,"We investigate the nature of quantum spin liquid (QSL) phase of the
spin-$1/2$ nearest-neighbor XXZ antiferromagnet on the kagome lattice. Recent
numerical calculations suggest that such a kagome spin liquid is insensitive to
the XXZ anisotropy and is adjacent to a chiral spin liquid phase. Reformulating
the problem in terms of a $U(1)$ lattice gauge theory with dynamical bosonic
spinons, we propose that the kagome spin liquid can be understood as a
deconfined critical phase extended by the $U(1)$ gauge fluctuation from a
deconfined critical point between a symmetry-protected topological phase and a
superfluid phase. Crucially, the stability of this QSL is ensured by the gauge
fluctuation and hence our description necessarily falls beyond the conventional
mean-field constructions of QSLs. Our work also makes an interesting connection
between the critical spin liquid, deconfined criticality, symmetry protected
topological phase and topological order.",1512.05381v2
2016-08-04,Doping induced spin state transition in Li$_x$CoO$_2$ as studied by the GGA+DMFT calculations,"Magnetic properties of Li$_x$CoO$_2$ for $x = 0.94, 0.75, 0.66$ and $0.51$
were investigated in frames of method combining Generalized Gradient
Approximation with Dynamical Mean--Field Theory (GGA+DMFT). We found that a
delicate interplay between Hund's exchange energy and $t_{2g}-e_g$ crystal
field splitting is responsible for the high spin to low spin state transition
for Co$^{4+}$ ions. The GGA+DMFT calculations show that at small doping level
the Co$^{4+}$ ions adopt high spin state, while delithiation results in
increase of the crystal field splitting and low spin state becomes preferable.
The Co$^{3+}$ ions were found to stays in the low spin configuration for any
$x$.",1608.01475v1
2016-08-17,Ultrafast spin-flip dynamics in transition metal complexes triggered by soft X-ray light,"Recent advances in attosecond physics provide access to the correlated motion
of valence and core electrons on their intrinsic timescales. For valence
excitations, processes related to the electron spin are usually driven by
nuclear motion. For core-excited states, where the core hole has a nonzero
angular momentum, spin-orbit coupling is strong enough to drive spin-flips on a
much shorter time scale. Here, unprecedented short spin-crossover driven by
spin-orbit coupling is demonstrated for L-edge (2p$\rightarrow$3d) excited
states of a prototypical Fe(II) complex. It occurs on a time scale, which is
faster than the core hole lifetime of about 4~fs. A detailed analysis of such
phenomena will",1608.04979v1
2016-12-30,Impurity-Induced Environmental Quantum Phase Transitions in the Quadratic-Coupling Spin-Boson Model,"We study the zero temperature properties of the sub-Ohmic spin-boson model
with quadratic spin-boson coupling. This model describes experimental set ups
at the optimal working point where the linear-coupling between the qubit (spin)
and the environmental noise (bosons) is zero and the leading coupling is
quadratic. In the strong coupling regime, we find that the existence of spin
induces quantum phase transitions (QPTs) between two states of environment: the
normal state and a state with local distortions. The phase diagram contains
both continuous and the first-order QPTs, with non-trivial critical properties
obtained exactly. At the QPTs, the equilibrium state spin dynamics bears
power-law $\omega$ dependence in the small frequency limit and a robust
coherent Rabi oscillation at high frequency. We discuss the feasibility of
observing such environmental QPTs in the qubit-related experiments.",1612.09437v2
2017-06-06,Long-lived spin polarization in n-doped MoSe$_2$ monolayers,"Transition metal dichalcogenide monolayers are highly interesting for
potential valleytronic applications due to the coupling of spin and valley
degrees of freedom and valley-selective excitonic transitions. However,
ultrafast recombination of excitons in these materials poses a natural limit
for applications, so that a transfer of polarization to resident carriers is
highly advantageous. Here, we study the low-temperature spin-valley dynamics in
nominally undoped and n-doped MoSe$_2$ monolayers using time-resolved Kerr
rotation. In the n-doped MoSe$_2$, we find a long-lived component of the Kerr
signal which we attribute to the spin polarization of resident carriers. This
component is absent in the nominally undoped MoSe$_2$. The long-lived spin
polarization is stable under applied in-plane magnetic fields. Spatially
resolved measurements allow us to determine an upper boundary for the electron
spin diffusion constant in MoSe$_2$.",1706.01802v2
2017-06-07,Spin-Orbit Misalignment of Merging Black-Hole Binaries with Tertiary Companions,"We study the effect of external companion on the orbital and spin evolution
of merging black-hole (BH) binaries. An sufficiently close by and inclined
companion can excite Lidov-Kozai (LK) eccentricity oscillations in the binary,
thereby shortening its merger time. During such LK-enhanced orbital decay, the
spin axis of the BH generally exhibits chaotic evolution, leading to a wide
range ($0^\circ$-$180^\circ$) of final spin-orbit misalignment angle from an
initially aligned configuration. For systems that do not experience
eccentricity excitation, only modest ($\lesssim 20^\circ$) spin-orbit
misalignment can be produced, and we derive an analytic expression for the
final misalignment using the principle of adiabatic invariance. The spin-orbit
misalignment directly impacts the gravitational waveform, and can be used to
constrain the formation scenarios of BH binaries and dynamical influences of
external companions.",1706.02309v2
2017-06-20,Tuning an effective spin chain of three strongly interacting one-dimensional fermions with the transversal confinement,"Strongly interacting one-dimensional fermions form an effective spin chain in
the absence of an external lattice potential. We show that the exchange
coefficients of such a chain may be locally tuned by properly tailoring the
transversal confinement. In particular, in the vicinity of a
confinement-induced resonance (CIR) the exchange coefficients may have
simultaneously opposite ferromagnetic and antiferromagnetic characters at
different locations along the trap axis. Moreover, the local exchanges may be
engineered to induce avoided crossings between spin states at the CIR, and
hence a ramp across the resonance may be employed to create different spin
states and to induce spin dynamics in the chain. We show that such unusual spin
chains have already been realized in the experiment of Murmann et al. [Phys.
Rev. Lett. 115, 215301 (2015)].",1706.06513v2
2017-07-18,Spin and optical properties of silicon vacancies in silicon carbide (a review),"We discuss the fine structure and spin dynamics of spin-3/2 centers
associated with silicon vacancies in silicon carbide. The centers have
optically addressable spin states which makes them highly promising for quantum
technologies. The fine structure of the spin centers turns out to be highly
sensitive to mechanical pressure, external magnetic and electric fields,
temperature variation, etc., which can be utilized for efficient
room-temperature sensing, particularly by purely optical means or through the
optically detected magnetic resonance. We discuss the experimental achievements
in magnetometry and thermometry based on the spin state mixing at level
anticrossings in an external magnetic field and the underlying microscopic
mechanisms. We also discuss spin fluctuations in an ensemble of vacancies
caused by interaction with environment.",1707.05503v1
2017-07-28,Measurement back-action and spin noise spectroscopy in a charged cavity-QED device in the strong coupling regime,"We study theoretically the spin-induced and photon-induced fluctuations of
optical signals from a singly-charged quantum dot-microcavity structure. We
identify the respective contributions of the photon-polariton interactions, in
the strong light-matter coupling regime, and of the quantum back-action induced
by photon detection on the spin system. Strong spin projection by a single
photon is shown to be achievable, allowing the initialization and measurement
of a fully-polarized Larmor precession. The spectrum of second-order
correlations is deduced, displaying information on both spin and quantum
dot-cavity dynamics. The presented theory thus bridges the gap between the
fields of spin noise spectroscopy and quantum optics.",1707.09342v1
2017-10-16,Carrier and Spin Coherent Dynamics in Strained Germanium-Tin Semiconductor on Silicon,"Germanium-Tin is emerging as a material exhibiting excellent photonic
properties. Here we demonstrate optical initialization and readout of spins in
this intriguing group IV semiconductor alloy and report on spin quantum beats
between Zeeman-split levels under an external magnetic field. Our optical
experiments reveal robust spin orientation in a wide temperature range and a
persistent spin lifetime that approaches the ns regime at room temperature.
Besides important insights into nonradiative recombination pathways, our
findings disclose a rich spin physics in novel epitaxial structures directly
grown on a conventional Si substrate. This introduces a viable route towards
the synergic enrichment of the group IV semiconductor toolbox with advanced
spintronics and photonic capabilities.",1710.05792v1
2017-10-17,"Fast, low-current spin-orbit torque switching of magnetic tunnel junctions through atomic modifications of the free layer interfaces","Future applications of spin-orbit torque will require new mechanisms to
improve the efficiency for switching nanoscale magnetic tunnel junctions
(MTJs), while also controlling the magnetic dynamics to achieve fast,
nanosecond scale performance with low write error rates. Here we demonstrate a
strategy to simultaneously enhance the interfacial magnetic anisotropy energy
and suppress interfacial spin memory loss by introducing sub-atomic and
monatomic layers of Hf at the top and bottom interfaces of the ferromagnetic
free layer of an in-plane magnetized three-terminal MTJ device. When combined
with a beta-W spin Hall channel that generates spin-orbit torque, the
cumulative effect is a switching current density of 5.4 x 106 A/cm2, more than
a factor of 3 lower than demonstrated in any other spin-orbit-torque magnetic
memory device at room temperature, and highly reliable switching with current
pulses only 2 ns long.",1710.06391v1
2017-12-08,Infinite coherence time of edge spins in finite-length chains,"Motivated by the recent observation that exponentially long coherence times
can be achieved for edge spins in models with strong zero modes, we study the
impact of level crossings in finite-length spin chains on the dynamics of the
edge spins. Focussing on the XY spin-1=2 chain with transverse or longitudinal
magnetic field, two models relevant to understand recent experimental results
on cobalt adatoms, we show that the edge spins can remain coherent for an
infinite time even for a finite-length chain if the magnetic field is tuned to
a value at which there is a level crossing. Furthermore, we show that the edge
spins remain coherent for any initial state for the integrable case of
transverse field because all states have level crossings at the same value of
the field, while the coherence time is increasingly large for lower
temperatures in the case of longitudinal field, which is non-integrable.",1712.03165v1
2018-01-04,Protecting solid-state spins from strongly coupled environment,"Quantum memories are critical for solid-state quantum computing devices and a
good quantum memory requires both long storage time and fast read/write
operations. A promising system is the Nitrogen-Vacancy (NV) center in diamond,
where the NV electronic spin serves as the computing qubit and a nearby nuclear
spin as the memory qubit. Previous works used remote, weakly coupled $^{13}$C
nuclear spins, trading read/write speed for long storage time. Here we focus
instead on the intrinsic strongly coupled $^{14}$N nuclear spin. We first
quantitatively understand its decoherence mechanism, identifying as its source
the electronic spin that acts as a quantum fluctuator. We then propose a scheme
to protect the quantum memory from the fluctuating noise by applying dynamical
decoupling on the environment itself. We demonstrate a factor of $3$
enhancement of the storage time in a proof-of-principle experiment, showing the
potential for a quantum memory that combines fast operation with long coherence
time.",1801.01375v2
2018-01-08,Low frequency spin dynamics in XY quantum spin ice Yb$_2$Pt$_2$O$_7$,"The XY pyrochlore Yb$_2$Ti$_2$O$_7$, with pseudo spin 1/2 at the Yb$^{3+}$
site, has been celebrated as potential host for the quantum spin ice state. The
substitution of non-magnetic Ti with Pt gives Yb$_2$Pt$_2$O$_7$, a system with
remarkably similar magnetic properties. The large nuclear gyromagnetic ratio
($\gamma_{n}/2 \pi = 9.15$~MHz/T) of $^{195}$Pt makes Yb$_2$Pt$_2$O$_7$ an
ideal material for NMR investigation of its unconventional magnetic properties.
Based on the $^{195}$Pt nuclear spin-lattice relaxation rate $1/T_1$ and the
magnetic specific heat $C_{p}$ measured in a broad range of magnetic field
$B_{ext}$, we demonstrate that the field-induced magnon gap linearly decreases
with $B_{ext}$ but additional low energy mode of spin excitations emerge below
$\sim 0.5$~T.",1801.02724v2
2018-01-10,Spin dynamics and Andreev-Bashkin effect in mixtures of one-dimensional Bose gases,"We investigate the propagation of spin waves in two-component mixtures of
one-dimensional Bose gases interacting through repulsive contact potentials. By
using quantum Monte Carlo methods we calculate static ground-state properties,
such as the spin susceptibility and the spin structure factor, as a function of
both the intra-species and inter-species coupling strength and we determine the
critical parameters for phase separation. In homogeneous mixtures, results of
the velocity of spin waves and of its softening close to the critical point of
phase separation are obtained by means of a sum-rule approach. We quantify the
non-dissipative drag effect, resulting from the Andreev-Bashkin current-current
interaction between the two components of the gas, and we show that in the
regime of strong coupling it causes a significant suppression of the spin-wave
velocity.",1801.03446v2
2018-09-27,Spin wave radiation from vortices in $^3$He-B,"We consider a vortex line in the B phase of superfluid $^3$He under uniformly
precessing magnetization. The magnetization exerts torque on the vortex,
causing its order parameter to oscillate. These oscillations generate spin
waves, which is analogous to an oscillating charge generating electromagnetic
radiation. The spin waves carry energy, causing dissipation in the system.
Solving the equations of spin dynamics, we calculate the energy dissipation
caused by spin wave radiation for arbitrary tipping angles of the magnetization
and directions of the magnetic field, and for both vortex types of $^3$He-B.
For the double-core vortex we also consider the anisotropy of the radiation and
the dependence of the dissipation on twisting of the half cores. The radiated
energy is compared with experiments in the mid-temperature range $T \sim 0.5
T_c$. The dependence of the calculated dissipation on several parameters is in
good agreement with the experiments. Combined with numerically calculated
vortex structure, the radiation theory produces the order of magnitude of the
experimental dissipation. The agreement with the experiments indicates that
spin wave radiation is the dominant dissipation mechanism for vortices in
superfluid $^3$He-B in the mid-temperature range.",1809.10484v1
2019-06-23,Probing magnetism via spin dynamics in graphene/2D-ferromagnet heterostructures,"The recent discovery of two-dimensional magnetic insulators has generated a
great deal of excitement over their potential for nanoscale manipulation of
spin or magnetism. One intriguing use for these materials is to put them in
contact with graphene, with the goal of making graphene magnetic while
maintaining its unique electronic properties. Such a system could prove useful
in applications such as magnetic memories, or could serve as a host for exotic
states of matter. Proximity to a magnetic insulator will alter the spin
transport properties of graphene, and the strength of this interaction can be
probed with Hanle spin precession experiments. To aid in the analysis of such
experiments, in this work we derive an explicit expression for Hanle spin
precession in graphene interfaced with a ferromagnetic insulator whose
magnetization points perpendicular to the graphene plane. We find that this
interface results in a shifted and asymmetric Hanle response, and we discuss
how this behavior can be used to interpret measurements of spin transport in
these systems.",1906.09568v2
2019-09-26,Spin current as a probe of the $\mathbb{Z}_2$-vortex topological transition in the classical Heisenberg antiferromagnet on the triangular lattice,"We have theoretically investigated transport properties of the classical
Heisenberg antiferromagnet on the triangular lattice in which a
binding-unbinding topological transition of $\mathbb{Z}_2$ vortices is
predicted to occur at a finite temperature $T_v$. It is shown by means of the
hybrid Monte-Carlo and spin-dynamics simulations that the longitudinal
spin-current conductivity exhibits a divergence at $T_v$, while the thermal
conductivity only shows a monotonic temperature dependence with no clear
anomaly at $T_v$. The significant enhancement of the spin-current conductivity
is found to be due to the rapid growth of the spin-current-relaxation time
toward $T_v$, which can be understood as a manifestation of the topological
nature of the free $\mathbb{Z}_2$ vortex whose lifetime gets longer toward
$T_v$. The result suggests that the spin-current measurement is a promising
probe to detect the $\mathbb{Z}_2$-vortex topological transition which has
remained elusive in experiments.",1909.12750v2
2019-10-15,Spin Polarizations in a Covariant Angular-Momentum-Conserved Chiral Transport Model,"Using a covariant and angular-momentum-conserved chiral transport model,
which takes into account the spin-orbit interactions of chiral fermions in
their scatterings via the side jumps, we study the quark spin polarization in
quark matter. For a system of rotating and unpolarized massless quarks in an
expanding box, we find that side jumps can dynamically polarize the quark spin
and result in a final quark spin polarization consistent with that of thermally
equilibrated massless quarks in a self-consistent vorticity field. For the
quark matter produced in noncentral relativistic heavy ion collisions, we find
that in the medium rest frame both the quark local spin polarizations in the
direction perpendicular to the reaction plane and along the longitudinal beam
direction show an azimuthal angle dependence in the transverse plane similar to
those observed in experiments for the Lambda hyperon.",1910.06774v2
2019-10-22,Electron spin relaxation in radical pairs: Beyond the Redfield approximation,"Relaxation processes can have a large effect on the spin selective electron
transfer reactions of radical pairs. These processes are often treated using
phenomenological relaxation superoperators or with some model for the
microscopic relaxation mechanism treated within Bloch-Redfield-Wangsness
theory. Here, we demonstrate that an alternative perturbative relaxation
theory, based on the Nakajima-Zwanzig equation, has certain advantages over
Redfield theory. In particular, the Nakajima-Zwanzig equation does not suffer
from the severe positivity problem of Redfield theory in the static disorder
limit. Combining the Nakajima-Zwanzig approach consistently with the
Schulten-Wolynes semiclassical method, we obtain an efficient method for
modeling the spin dynamics of radical pairs containing many hyperfine-coupled
nuclear spins. This is then used to investigate the spin-dependent electron
transfer reactions and intersystem crossing of
dimethyljulolidine-naphthalenediimide (DMJ-NDI) radical ion pairs. By comparing
our simulations with experimental data, we find evidence for a
field-independent contribution to the triplet quantum yields of these reactions
which cannot be explained by electron spin relaxation alone.",1910.09870v1
2020-01-02,Self-Supervised Learning of Generative Spin-Glasses with Normalizing Flows,"Spin-glasses are universal models that can capture complex behavior of
many-body systems at the interface of statistical physics and computer science
including discrete optimization, inference in graphical models, and automated
reasoning. Computing the underlying structure and dynamics of such complex
systems is extremely difficult due to the combinatorial explosion of their
state space. Here, we develop deep generative continuous spin-glass
distributions with normalizing flows to model correlations in generic discrete
problems. We use a self-supervised learning paradigm by automatically
generating the data from the spin-glass itself. We demonstrate that key
physical and computational properties of the spin-glass phase can be
successfully learned, including multi-modal steady-state distributions and
topological structures among metastable states. Remarkably, we observe that the
learning itself corresponds to a spin-glass phase transition within the layers
of the trained normalizing flows. The inverse normalizing flows learns to
perform reversible multi-scale coarse-graining operations which are very
different from the typical irreversible renormalization group techniques.",2001.00585v2
2020-02-05,From Chiral Kinetic Theory To Spin Hydrodynamics,"The total angular momentum is conserved in the evolution of the Quark-Gluon
Plasma (QGP) created in heavy-ion collision, and consists of two sectors: the
orbital angular momentum (OAM) caused by kinetic motion, and the spin, an
intrinsic degree of freedom of quarks and gluons. Microscopic scattering
processes allow the conversion between these two components, hence the spin
density could eventually have non-trivial influence on the QGP evolution. A
hydrodynamic theory, with the spin polarization effect properly taken into
account, is required to quantitatively study the polarization rate for observed
hadrons, e.g. the $\Lambda$-hyperon. In this work, we start with chiral kinetic
theory and construct the spin hydrodynamic framework for a chiral spinor
system. We obtain the equations of motion of second-order dissipative
relativistic fluid dynamics with non-trivial spin polarization density.",2002.01911v1
2020-02-06,On BF-type higher-spin actions in two dimensions,"We propose a non-abelian higher-spin theory in two dimensions for an infinite
multiplet of massive scalar fields and infinitely many topological higher-spin
gauge fields together with their dilaton-like partners. The spectrum includes
local degrees of freedom although the field equations take the form of flatness
and covariant constancy conditions because fields take values in a suitable
extension of the infinite-dimensional higher-spin algebra $hs[\lambda]$. The
corresponding action functional is of BF-type and generalizes the known
topological higher-spin Jackiw-Teitelboim gravity.",2002.02387v3
2020-02-13,Thermal effects on a nonadiabatic spin-flip protocol of spin-orbit qubits,"We study the influence of a thermal environment on a non-adiabatic spin-flip
driving protocol of spin-orbit qubits. The driving protocol operates by moving
the qubit, trapped in a harmonic potential, along a nanowire in the presence of
a time-dependent spin-orbit interaction. We consider the harmonic degrees of
freedom to be weakly coupled to a thermal bath. We find an analytical
expression for the Floquet states and derive the Lindblad equation for a
strongly non-adiabatically driven qubit. The Lindblad equation corrects the
dynamics of an isolated qubit with Lamb shift terms and a dissipative
behaviour. Using the Lindblad equation, the influence of a thermal environment
on the spin-flip protocol is analysed.",2002.05548v1
2020-12-29,Incoherent transport in a classical spin liquid,"We study the energy and spin transport of the classical spin liquid hosted by
the pyrochlore Heisenberg antiferromagnet in the large $S$ limit. Molecular
dynamics calculation suggests that both the energy and spin diffusion constants
approach finite limits as the temperature tends to zero. We explain our results
in terms of an effective disorder model, where the energy/spin-carrying normal
modes propagate in a quasi-static disordered spin background. The finite zero
temperature limits of the diffusion constants are then naturally understood as
a result of the finite mean free path of the normal modes due to the effective
disorder.",2012.14565v3
2021-01-06,Dimerization and spin-decoupling in two-leg Heisenberg ladder with frustrated trimer rungs,"We study the antiferromagnetic spin-half Heisenberg ladder in the presence of
an additional frustrating rung spin which is motivated and relevant also for
the description of real two-dimensional materials such as the two-dimensional
trimer magnet Ba$_4$Ir$_3$O$_{10}$. We study the zero-temperature phase
diagram, where we combine numerical and analytical methods into an overall
consistent description. All numerical simulations are also accompanied by
studies of the dynamical spin structure factor obtained via the density matrix
renormalization group. Overall, we find in the regime of strong rung coupling a
gapped dimerized phase related to competing symmetry sectors in Hilbert space
that ultimately results in frustration-driven spin-Peierls transition. In the
weak rung-coupling regime, the system is uniform, yet shows a gapped spinon
continuum together with a sharp coherent low-energy branch which renders the
system critical overall. In either case, the additional rung spin quickly get
sidelined and nearly decouple once their bare coupling to the ladder drops
somewhat below the direct Heisenberg coupling of the legs.",2101.02135v2
2021-01-07,Nanoscale spin detection of copper ions using double electron-electron resonance at room temperature,"We report the nanoscale spin detection and electron paramagnetic resonance
(EPR) spectrum of copper (Cu$^{2+}$) ions via double electron-electron
resonance with single spins in diamond at room temperature and low magnetic
fields. We measure unexpectedly narrow EPR resonances with linewidths $\sim
2-3$ MHz from copper-chloride molecules dissolved in poly-lysine. We also
observe coherent Rabi oscillations and hyperfine splitting from single
Cu$^{2+}$ ions, which could be used for dynamic nuclear spin polarization and
higher sensitivity of spin detection. We interpret and analyze these
observations using both spin hamiltonian modeling of the copper-chloride
molecules and numerical simulations of the predicted DEER response, and obtain
a sensing volume $\sim (250 \text{nm})^3$. This work will open the door for
copper-labeled EPR measurements under ambient conditions in bio-molecules and
nano-materials.",2101.02650v2
2021-01-12,Double Nuclear Spin Relaxation in Hybrid Quantum Hall Systems,"Recent advances in quantum engineering have given us the ability to design
hybrid systems with novel properties normally not present in the regime they
operate in. The coupling of spin ensembles and magnons to microwave resonators
has for instance lead to a much richer understanding of collective effects in
these systems and their potential quantum applications. We can also hybridize
electron and nuclear spin ensembles together in the solid-state regime to
investigate collective effects normally only observed in the atomic, molecular
and optical world. Here we explore in the solid state regime the dynamics of a
double domain nuclear spin ensemble coupled to the Nambu-Goldstone boson in
GaAs semiconductors and show it exhibits both collective and individual
relaxation (thermalization) on very different time scales. Further the
collective relaxation of the nuclear spin ensemble is what one would expect
from superradiant decay. This opens up the possibility for the exploration of
novel collective behaviour in solid state systems where the natural energies
associated with those spins are much less than the thermal energy.",2101.04433v1
2012-05-10,"Bose Hubbard Models with Synthetic Spin-Orbit Coupling: Mott Insulators, Spin Textures and Superfluidity","Motivated by the experimental realization of synthetic spin-orbit coupling
for ultracold atoms, we investigate the phase diagram of the Bose Hubbard model
in a non-abelian gauge field in two dimensions. Using a strong coupling
expansion in the combined presence of spin-orbit coupling and tunable
interactions, we find a variety of interesting magnetic Hamiltonians in the
Mott insulator (MI), which support magnetic textures such as spin spirals and
vortex and Skyrmion crystals. An inhomogeneous mean field treatment shows that
the superfluid (SF) phases inherit these exotic magnetic orders from the MI and
display, in addition, unusual modulated current patterns. We present a slave
boson theory which gives insight into such intertwined spin-charge orders in
the SF, and discuss signatures of these orders in Bragg scattering, in situ
microscopy, and dynamic quench experiments.",1205.2319v1
2017-04-27,Relativistic fluid dynamics with spin,"Using the conservation laws for charge, energy, momentum, and angular
momentum, we derive hydrodynamic equations for the charge density, local
temperature, and fluid velocity, as well as for the spin tensor, starting from
local equilibrium distribution functions for particles and antiparticles with
spin 1/2. The resulting set of differential equations extend the standard
picture of perfect-fluid hydrodynamics with a conserved entropy current in a
minimal way. This framework can be used in space-time analyzes of the evolution
of spin and polarization in various physical systems including high-energy
nuclear collisions. We demonstrate that a stationary vortex, which exhibits
vorticity-spin alignment, corresponds to a special solution of the
spin-hydrodynamical equations.",1705.00587v4
2017-05-10,Long-time coherence in fourth-order spin correlation functions,"We study the long-time decay of fourth-order electron spin correlation
functions for an isolated singly charged semi-conductor quantum dot. The
electron spin dynamics is governed by the applied external magnetic field as
well as the hyperfine interaction. While the long-time coherent oscillations in
the correlation functions can be understood within an semi-classical approach
treating the Overhauser field as frozen, the field dependent decay of its
amplitude reported in different experiments cannot be explained by the
central-spin model indicating the insufficiency of such a description. By
incorporating the nuclear Zeeman splitting and the strain induced
nuclear-electric quadrupolar interaction, we find the correct crossover from a
fast decay in small magnetic fields to a slow exponential asymptotic in large
magnetic fields. It originates from a competition between the quadrupolar
interaction inducing an enhanced spin decay and the nuclear Zeeman term that
suppressed the spin-flip processes. We are able to explain the magnetic field
dependency of the characteristic long-time decay time $T_2$ depending on the
experimental setups. The calculated asymptotic values of $T_2 = 3 -4\,\mu$s
agree qualitatively well with the experimental data.",1705.03712v2
2017-09-08,Connecting nth order generalised quantum Rabi models: Emergence of nonlinear spin-boson coupling via spin rotations,"We establish an approximate equivalence between a generalised quantum Rabi
model and its nth order counterparts where spin-boson interactions are
nonlinear as they comprise a simultaneous exchange of $n$ bosonic excitations.
Although there exists no unitary transformation between these models, we
demonstrate their equivalence to a good approximation in a wide range of
parameters. This shows that nonlinear spin-boson couplings, i.e. nth order
quantum Rabi models, are accessible to quantum systems with only linear
coupling between boson and spin modes by simply adding spin rotations and after
an appropriate transformation. Furthermore, our result prompts novel
approximate analytical solutions to the dynamics of the quantum Rabi model in
the ultrastrong coupling regime improving previous approaches.",1709.02714v2
2017-09-14,Electric power transfer in spin pumping experiments,"Spin pumping is becoming an established method to generate voltages from
magnetic dynamics. The standard detection method of spin pumping is based on
open circuit voltage measurement across ferromagnetic (FM) and non-magnetic
(NM) bi-layers, where the inverse spin-Hall effect (ISHE) can convert spin
currents into electrical charge accumulation. In this paper, we present that it
is also possible to measure the associated electric charge current generated in
FM/NM bi-layers, by using a macroscopic closed circuitry detection method.
Using variable load resistors connected in series to the sample, we quantified
charge currents and associated electric power dissipation as a function of the
load resistance. By using basic circuit analysis, we are able to describe spin
pumping cells as a non-ideal voltage source or equivalent current source with
an internal resistor.",1709.04690v2
2017-11-09,Spin effects on the semiclassical trajectories of Dirac electrons,"The relativistic semiclassical evolution of the position of an electron in
the presence of an external electromagnetic field is studied in terms of a
Newton equation that incorporates spin effects directly. This equation emerges
from the Dirac equation and allows the identification of scenarios where spin
effects are necessary to understand the main characteristics of the electron
trajectories. It involves the eigenvalues of the non-Hermitian operator
$\Sigma_{\mu\nu}F^{\mu\nu}$ with $\Sigma_{\mu\nu}$ and $F^{\mu\nu}$ as the spin
and electromagnetic tensors. The formalism allows a deeper understanding on the
physics behind known analytical solutions of the Dirac equation when
translational dynamics decouples from spin evolution. As an illustrative
example, it is applied to an electron immersed in an electromagnetic field
which exhibits chiral symmetry and optical vortices. It is shown that the
polarization of intense structured light beams can be used to suppress or
enhance spin effects on the electron semiclassical trajectory; the latter case
yields a realization of a Stern-Gerlach apparatus for an electron",1711.03546v1
2018-03-12,Rotation-symmetry-enforced coupling of spin and angular momentum for p-orbital bosons,"Intrinsic spin angular-momentum coupling of an electron has a relativistic
quantum origin with the coupling arising from charged-orbits, which does not
carry over to charge-neutral atoms. Here we propose a mechanism of spontaneous
generation of spin angular-momentum coupling with spinor atomic bosons loaded
into $p$-orbital bands of a two-dimensional optical-lattice. This spin
angular-momentum coupling originates from many-body correlations and
spontaneous symmetry breaking in a superfluid, with the key ingredients
attributed to spin-channel quantum fluctuations and an approximate rotation
symmetry. The resultant spin angular-momentum intertwined superfluid has Dirac
excitations. In presence of a chemical potential difference for adjacent sites,
it provides a bosonic analogue of a symmetry-protected-topological insulator.
Through a dynamical mean-field calculation, this novel superfluid is found to
be a generic low-temperature phase, and it gives way to Mott localization only
at strong interactions and even-integer fillings. We show the temperature to
reach this order is accessible with present experiments.",1803.04429v2
2018-06-15,Dynamically Polarizing Spin Register of NV Centers in Diamond using Chopped Laser Pulses,"Nuclear spins nearby nitrogen-vacancy (NV) centers in diamond are excellent
quantum memory for quantum computing and quantum sensing, but are difficult to
be initialized due to their weak interactions with the environment. Here we
propose and demonstrate a magnetic-field-independent, deterministic and highly
efficient polarization scheme by introducing chopped laser pulses into the
double-resonance initialization method. With this method, we demonstrate
initialization of single-nuclear-spin approaching $98.1\%$ and a
$^{14}N$-$^{13}C$ double-nuclear-spin system approaching $96.8\%$ at room
temperature. The initialization is limited by a nuclear-spin depolarization
effect due to chopped laser excitation. Our approach could be extended to NV
systems with more nuclear spins and would be a useful tool in future
applications such as nano-MRI and single-cell NMR.",1806.05881v2
2018-06-16,Decoherence in a quantum neural network,"In this study, we propose a spin-star model for spin-(1/2) particles in order
to examine the coherence dynamics of a quantum neural network (QNN) unit. Since
quantum computing paradigm promises advantages over their classical
counterparts, quantum versions of neural networks can be examined in this
context. We focus on quantum coherence as a natural resource for quantum
computing and investigate the central spin coherence of a spin star model in
the time domain in a dissipative environment. More particularly, we investigate
the extend to which the central spin coherence time would be prolonged under
specific parameters and spin-coupling Hamiltonians in a Markov environment. We
show that Ising-type spin coupling is not desirable since it rapidly diminishes
the coherence time in a dissipative environment.",1806.07251v1
2018-07-24,Improving spin-based noise sensing by adaptive measurements,"Localized spins in the solid state are attracting widespread attention as
highly sensitive quantum sensors with nanoscale spatial resolution and
fascinating applications. Recently, adaptive measurements were used to improve
the dynamic range for spin-based sensing of deterministic Hamiltonian
parameters. Here we explore a very different direction -- spin-based adaptive
sensing of random noises. First, we identify distinguishing features for the
sensing of magnetic noises compared with the estimation of deterministic
magnetic fields, such as the different dependences on the spin decoherence, the
different optimal measurement schemes, the absence of the modulo-2\pi phase
ambiguity, and the crucial role of adaptive measurement. Second, we perform
numerical simulations that demonstrate significant speed up of the
characterization of the spin decoherence time via adaptive measurements. This
paves the way towards adaptive noise sensing and coherence protection.",1807.09233v1
2018-07-31,Terahertz Spin Transfer Torque Oscillator Based on a Synthetic Antiferromagnet,"Bloch-Bloembergen-Slonczewski equation is adopted to simulate magnetization
dynamics in spin-valve based spin-transfer torque oscillator with synthetic
antiferromagnet acting as a free magnetic layer. High frequency up to the
terahertz scale is predicted in synthetic antiferromagnet spin-transfer torque
oscillator with no external magnetic field if the following requirements are
fulfilled: antiferromagnetic coupling between synthetic antiferromagnetic
layers is sufficiently strong, and the thickness of top (bottom) layer of
synthetic antiferromagnet is sufficiently thick (thin) to achieve a wide
current density window for the high oscillation frequency. Additionally, the
transverse relaxation time of the free magnetic layer should be sufficiently
larger compared with the longitudinal relaxation time. Otherwise, stable
oscillation cannot be sustained or scenarios similar to regular spin
valve-based spin-transfer torque oscillator with relatively low frequency will
occur. Our calculations pave a new way for exploring THz spintronics devices.",1807.11633v1
2018-08-06,Formation of Spatial Patterns by Spin-selective Excitations of Interacting Fermions,"We describe the formation of charge- and spin-density patterns induced by
spin-selective photoexcitations of interacting fermionic systems in the
presence of a microstructure. As an example, we consider a one-dimensional
Hubbard-like system with a periodic magnetic microstructure, which has a
uniform charge distribution in its ground state, and in which a long-lived
charge-density pattern is induced by the spin-selective photoexcitation. Using
tensor-network methods, we study the full quantum dynamics in the presence of
electron-electron interactions and identify doublons as the main decay channel
for the induced charge pattern. Our setup is compared to the OISTR mechanism,
in which ultrafast optically induced spin transfer in Heusler and magnetic
compounds is associated to the difference of the local density of states of the
different elements in the alloys. We find that applying a spin-selective
excitation there induces spatially periodic patterns in local observables.
Implications for pump-probe experiments on correlated materials and experiments
with ultracold gases on optical lattices are discussed.",1808.02138v3
2018-08-30,Influence of spin glass-like magnetic relaxation on the zero-field-cooled exchange bias effect,"The zero-field-cooled exchange bias (ZEB) effect is a remarkable phenomenon
recently reported for some reentrant spin glass-like compounds. In this work,
the time-evolution of magnetization is thoroughly investigated for two ZEB
materials in order to figure out the role played by the spin glass-like phase
on such effect. La$_{1.5}$Sr$_{0.5}$CoMnO$_{6}$ and
La$_{1.5}$Ca$_{0.5}$CoMnO$_{6}$ were chosen as representative samples of ZEB
systems, since the former compound presents the largest ZEB reported so far,
while the second has a much smaller effect, despite being
structurally/chemically similar. Comprehensive magnetic measurements were
carried on both samples, and the results are discussed in terms of the amount
and time-evolution of the spin glass-like phase under the influence of a
varying field. We also propose a phenomenological model, based on the pinning
of spin glass-like moments and on the dynamics of their magnetic relaxation, to
explain the asymmetry observed in the hysteresis loops. The good agreement
between the simulated and experimental results confirms our hypothesis that the
spin glass-like phase is key to the ZEB effect.",1808.10305v1
2018-12-19,Electron Spin Resonance on the spin-1/2 triangular magnet NaYbS2,"The delafossite structure of NaYbS2 contains a planar spin-1/2 triangular
lattice of Yb3+ ions and features a possible realisation of a quantum
spin-liquid state. We investigated the Yb3+ spin dynamics by Electron Spin
Resonance (ESR) in single-crystalline samples of NaYbS2. Very clear spectra
with a well-resolved and large anisotropy could be observed down to the lowest
accessible temperature of 2.7 K. In contrast to the ESR properties of other
known spin-liquid candidate systems, the resonance seen in NaYbS2 is accessible
at low fields (< 1T) and is narrow enough for accurate characterisation of the
relaxation rate as well as the g factor of the Yb3+ spins.",1812.07871v1
2019-01-20,Fate of spin polarization in a relativistic fluid: An entropy-current analysis,"We derive relativistic hydrodynamic equations with a dynamical spin degree of
freedom on the basis of an entropy-current analysis. The first and second laws
of local thermodynamics constrain possible structures of the constitutive
relations including a spin current and the antisymmetric part of the
(canonical) energy-momentum tensor. Solving the obtained hydrodynamic equations
within the linear-mode analysis, we find spin-diffusion modes, indicating that
spin density is damped out after a characteristic time scale controlled by
transport coefficients introduced in the antisymmetric part of the
energy-momentum tensor in the entropy-current analysis. This is a consequence
of mutual convertibility between spin and orbital angular momentum.",1901.06615v2
2019-01-21,Natural orbital functional for spin-polarized periodic systems,"Natural orbital functional theory is considered for systems with one or more
unpaired electrons. An extension of the Piris natural orbital functional (PNOF)
based on electron pairing approach is presented, specifically, we extend the
independent pair model, PNOF5, and the interactive pair model PNOF7 to describe
spin-uncompensated systems. An explicit form for the two-electron cumulant of
high-spin cases is only taken into account, so that singly occupied orbitals
with the same spin are solely considered. The rest of electron pairs with
opposite spins remain paired. The reconstructed two-particle reduced density
matrix fulfills certain N-representability necessary conditions, as well as
guarantees the conservation of the total spin. The theory is applied to model
systems with strong non-dynamic (static) electron correlation, namely, the
one-dimensional Hubbard model with periodic boundary conditions and hydrogen
rings. For the latter, PNOF7 compares well with exact diagonalization results
so the model presented here is able to provide a correct description of the
strong-correlation effects.",1901.06942v1
2019-03-06,Effects of geometry on spin-orbit Kramers states in semiconducting nanorings,"The holonomic manipulation of spin-orbital degenerate states, encoded in the
Kramers doublet of narrow semiconducting channels with spin-orbit interaction,
is shown to be intimately intertwined with the geometrical shape of the
nanostructures. The presence of doubly degenerate states is not sufficient to
guarantee a non-trivial mixing by only changing the Rashba spin-orbit coupling.
We demonstrate that in nanoscale quantum rings the combination of arbitrary
inhomogeneous curvature and adiabatic variation of the spin-orbit amplitude,
e.g. through electric-field gating, can be generally employed to get
non-trivial combinations of the degenerate states. Shape symmetries of the
nanostructure act to constrain the adiabatic quantum evolution. While for
circular rings the geometric phase is not generated along a non-cyclic path in
the parameters space, remarkably, for generic mirror-symmetric shape deformed
rings the spin-orbit driving can lead to a series of dynamical quantum phase
transitions. We explicitly show this occurrence and propose a route to detect
such topological transitions by measuring a variation of the electron tunneling
amplitude into the semiconducting channel.",1903.02455v1
2019-03-19,Broadband magnetoelastic coupling in magphonic crystals for high-frequency nanoscale spin wave generation,"Spin waves are promising candidates for information carriers in advanced
technology. The interactions between spin waves and acoustic waves in magnetic
nanostructures are of much interest because of their potential application for
spin wave generation, amplification and transduction. We investigate
numerically the dynamics of magnetoelastic excitations in a one-dimensional
magphonic crystal consisting of alternating layers of permalloy and cobalt. We
use the plane wave method and the finite element method for frequency- and
time-domain simulations, respectively. The studied structure is optimized for
hybridization of specific spin-wave and acoustic dispersion branches in the
entire Brillouin zone in a broad frequency range. We show that this type of
periodic structure can be used for efficient generation of high-frequency spin
waves.",1903.08024v1
2019-03-25,Effect of disorder on the collective excitations of the chiral spin soliton lattice,"We assess the impact of magnetic disorder on the spin excitation spectra of
the chiral helimagnetic crystal $\mathrm{CrNb_3S_6}$ using microwave resonance
spectroscopy. The chiral spin soliton lattice phase (CSL), which is a prototype
of a noncollinear spin system that forms periodically over a macroscopic length
scale, exhibited three resonance modes over a wide frequency range. We found
that the predominance of these modes depended on the degree of magnetic
disorder and that disorder can be suppressed by sweeping the external field via
an ideal helical state at 0~T. The macroscopic coherence of the CSL can be
clearly observed through its collective dynamic behavior. Our study suggests
that magnetic disorder can be used as a mechanism to control spin wave
excitation in noncollinear spin systems.",1903.10129v1
2019-04-11,Spin-exchange-induced exotic superfluids in a Bose-Fermi spinor mixture,"We consider a mixture of spin-1/2 bosons and fermions, where only the bosons
are subjected to the spin-orbit coupling induced by Raman beams. The fermions,
although not directly coupled to the Raman lasers, acquire an effective
spin-orbit coupling through the spin-exchange interaction between the two
species. Our calculation shows that this is a promising way of obtaining
spin-orbit coupled Fermi gas without Raman-induced heating, where the
long-sought topological Fermi superfluids and topological bands can be
realized. Conversely, we find that the presence of fermions not only provides a
new way to create the supersolid stripe phase of the bosons, but more
strikingly it can also greatly increase the spatial period of the bosonic
density stripes, and hence makes this phase directly observable in the
experiment. This system provides a new and practical platform to explore the
physics of spin-orbit coupling, which possesses a dynamic nature through the
interaction between the two species.",1904.05486v2
2019-08-16,Emergent Snake Magnetic Domains in Canted Kagome Ice,"We study the two-dimensional kagome-ice model derived from a pyrochlore
lattice with second- and third-neighbor interactions. The canted moments align
along the local $\langle 111 \rangle$ axes of the pyrochlore and respond to
both in-plane and out-of-plane external fields. We find that the combination of
further-neighbor interactions together with the external fields introduces a
rich phase diagram with different spin textures. Close to the phase boundaries,
metastable $\textit{""snake""}$ domains emerge with extremely long relaxation
time. Our kinetic Monte Carlo analysis of the magnetic-field quench process
from saturated state shows unusually slow dynamics. Despite that the interior
spins are almost frozen in snake domains, the spins on the edge are free to
fluctuate locally, leading to frequent creation and annihilation of
monopole-anti-monopole bound states. Once the domains are formed, these
excitations are localized and can hardly propagate due to the energy barrier of
snakes. The emergence of such snake domains may shed light on the experimental
observation of dipolar spin ice under tilted fields, and provide a new strategy
to manipulate both spin and charge textures in artificial spin ice.",1908.05872v1
2019-08-27,Broadband Optical Detection using the Spin Seebeck Effect,"The generation, control, and detection of spin currents in solid-state
devices are critical for Joule-heating minimization, spin-based computation,
and electrical energy generation from thermal gradients. Although incorporation
of spin functionality into technologically important architectures is still in
its infancy, advantages over all-electric devices are increasingly becoming
clear. Here, we utilize the spin Seebeck effect (SSE) in Pt/Y3Fe5O12 devices to
detect light from 390 to 2200 nm. We find the device responsivity is remarkably
flat across this technologically important wavelength range, closely following
the Pt absorption coefficient. As expected from a SSE-generation mechanism, we
observe that the photovoltage and Pt heating dynamics are in strong agreement.
To precisely determine the optically created thermal gradient produced from a
point-like heat source, we introduce a field-modulation method for measuring
the SSE. Our results show broadband optical detection can be performed with
devices based solely on spin current generation and detection.",1908.10472v1
2019-11-12,Iridium Enabled Field-free Spin-orbit Torque Switching of Perpendicular Magnetic Tunnel Junction Device,"Writing magnetic bits by spin-orbit torques (SOTs) arising from spin Hall
effect creates new possibilities for ultrafast and low-power magnetoresistive
random access memory (MRAM). For perpendicular MRAM, an extra in-plane field is
required to break the symmetry for the deterministic SOT writing of the
perpendicular storage layer. Although schemes have been demonstrated in
external-field-free SOT switching of a perpendicular layer, practically
integrating them with perpendicular MTJs still appears to be challenging. Here,
we present experimental demonstration of spin-orbit torques (SOTs) switching a
perpendicular magnetic tunnel junction (MTJ) device without applying an
external magnetic field. An Ir layer is used to serve dual-purpose of both
injecting the pure spin current via spin Hall effect and mediating an in-plane
exchange field to the perpendicular free layer of the MTJ. Robust field-free
SOT switching with pulsed write path current is demonstrated for various MTJ
sizes ranging from 50 nm to 500 nm. The effect of MTJ size and pulse width on
the critical switching current is studied. Combined micromagnetic simulations
are carried out to provide in-depth analysis of the switching dynamics as well
as the thermal effect on the switching.",1911.05007v1
2019-12-17,Three Jahn-Teller states of matter in the spin-crossover system Mn(taa),"Three high-spin phases recently discovered in the spin-crossover system
Mn(taa) are identified through analysis by a combination of first-principles
calculations and Monte Carlo simulation as a low-temperature Jahn-Teller
ordered (solid) phase, an intermediate-temperature dynamically correlated
(liquid) phase, and an uncorrelated (gas) phase. In particular, the Jahn-Teller
liquid phase arises from competition between mixing with low-spin impurities,
which drive the disorder, and inter-molecular strain interactions. The latter
are a key factor in both the spin-crossover phase transition and the
magnetoelectric coupling. Jahn-Teller liquids may exist in other spin-crossover
materials and materials that have multiple equivalent Jahn-Teller axes.",1912.07770v2
2020-03-09,Colossal quasiparticle radiation in the Lifshitz spin liquid phase of a two-dimensional quantum antiferromagnet,"Strong quantum fluctuations in magnetic systems can create disordered quantum
spin liquid phases of matter which are not predicted by classical physics. The
complexity of the exotic phenomena on display in spin liquids has led to a
great deal of theoretical and experimental interest. However, understanding the
fundamental nature of the excitations in these systems remains challenging. In
this work, we consider the Lifshitz quantum critical point in a two-dimensional
frustrated $XY$ antiferromagnet. At this point, quantum fluctuations destroy
long range order, leading to the formation of an algebraic Lifshitz spin
liquid. We demonstrate that the bosonic magnon excitations are long-lived and
well-defined in the Lifshitz spin liquid phase, though paradoxically, the
dynamic structure factor has a broad non-Lorentzian frequency distribution with
no single-particle weight. We resolve this apparent contradiction by showing
that the Lifshitz spin liquid suffers from an infrared catastrophe: An external
physical probe always excites an infinite number of arbitrarily low energy
quasiparticles, which leads to significant radiative broadening of the
spectrum.",2003.03936v1
2020-03-25,Gravitational spin-orbit coupling through third-subleading post-Newtonian order: from first-order self-force to arbitrary mass ratios,"Exploiting simple yet remarkable properties of relativistic gravitational
scattering, we use first-order self-force (linear-in-mass-ratio) results to
obtain arbitrary-mass-ratio results for the complete third-subleading
post-Newtonian (4.5PN) corrections to the spin-orbit sector of spinning-binary
conservative dynamics, for generic (bound or unbound) orbits and spin
orientations. We thereby improve important ingredients of models of
gravitational waves from spinning binaries, and we demonstrate the improvement
in accuracy by comparing against aligned-spin numerical simulations of binary
black holes.",2003.11391v2
2020-03-25,Transparent Spin Method for Spin Control of Hadron Beams in Colliders,"We present a concept for control of the ion polarization, called a
transparent spin method. The spin transparency is achieved by designing such a
synchrotron structure that the net spin rotation angle in one particle turn is
zero. The polarization direction of any ions including deuterons can be
efficiently controlled using weak quasi-static fields. These fields allow for
dynamic adjustment of the polarization direction during an experiment. The main
features of the Transparent Spin method are illustrated in a figure-8 collider.
The results are relevant to the Electron-Ion Collider considered in the US, the
ion-ion collider NICA constructed in Russia, and a polarized Electron-ion
collider planned in China.",2003.11469v2
2020-03-27,Spectral characteristics of the antiferromagnetic spin-1/2 Heisenberg model on the square lattice in a magnetic field,"We predict that spin-waves in an ordered square quantum antiferromagnet in a
transverse magnetic field (h) may demonstrate three modes of spin excitations.
Starting from the self-consistent rotation-invariant Green's function method, a
new mean-field theory is constructed for h not equal to 0. The method preserves
the translational and the axial symmetries, and provides exact fulfillment of
the single-site constraint for each of the three modes. We examine the
dynamical structure factors S(aa)(k,w), a= x, y, z. It is shown, that the
introduction of h leads to the hybridization of two degenerate spin modes due
to the appearance of a nondiagonal on a, b spin-spin Green's functions. The
comparison of the theory with the exact diagonalization study and with results
on inelastic neutron scattering experiments is discussed at T = 0. We discuss
also the correspondence of the theory to the existing theories, which allow
only two spin excitations modes for the total S(k,w).",2003.12387v1
2020-05-07,U(1) spin Chern-Simons theory and Arf invariants in two dimensions,"The level-k U(1) Chern-Simons theory is a spin topological quantum field
theory for k odd. Its dynamics is captured by the 2d CFT of a compact boson
with a certain radius. Recently it was recognized that a dependence on the 2d
spin structure can be given to the CFT by modifying it using the so-called Arf
invariant. We demonstrate that one can reorganize the torus partition function
of the modified CFT into a finite sum involving a finite number of conformal
blocks. This allows us to reproduce the modular matrices of the spin theory. We
use the modular matrices to calculate the partition function of the spin
Chern-Simons theory on the lens space $L(a,\pm 1)$, and demonstrate the
expected dependence on the 3d spin structure.",2005.03203v2
2020-05-15,Recent results on cold-QCD from RHIC,"Polarized proton-proton collisions at the Relativistic Heavy Ion Collider
(RHIC) provide unique opportunities to study the spin structure of the nucleon.
We will highlight recent results on the nucleon spin structure from the STAR
and PHENIX experiments at RHIC: (1) A sizable gluon polarization in the proton
is measured with longitudinal double spin asymmetries of jet and hadron
production; (2) Longitudinal single spin asymmetries in W boson production
improve constraints on the sea quark polarization. The new spin asymmetry
results for W boson confirmed the SU(2) flavor asymmetry of the light sea quark
polarization in the proton; (3) Transverse spin effects in hadronic systems
offer new implications on parton distribution functions in the collinear and
transverse momentum dependent frameworks. We will also discuss near term plans
for the STAR forward detector upgrade and prospects for proton-proton and
proton-ion collisions in the years beyond 2021 at STAR.",2005.07345v1
2020-05-15,Generation of Multipeak Spectrum of Spin Torque Oscillator in Non-linear Regime,"We investigate the spectral characteristics of spin torque oscillator (STO)
excited by the spin Hall-induced spin current. We observe that the modest spin
current injection triggers the conventional single peak oscillating behavior of
STO. As the spin current is further increased to enter the non-linear regime,
we find the transition of the spectrum from a single peak to multipeak
structure whose frequency spacing is constant. This behavior can be primarily
explained by the extremely broadened peak of the STO, which is accompanied by
the frequency-dependent filtering by the transmission line. To explain the
observation more quantitatively, we also discuss that the multipeak may reflect
the characteristics of the intrinsic dynamics of STO in the non-linear regime.",2005.07434v1
2020-05-20,Quark spin and orbital angular momentum from proton GPDs,"We calculate the leading-twist helicity-dependent generalized parton
distributions (GPDs) of the proton at finite skewness in the
Nambu--Jona-Lasinio (NJL) model of quantum chromodynamics (QCD). From these
(and previously calculated helicity-independent GPDs) we obtain the spin
decomposition of the proton, including predictions for quark intrinsic spin and
orbital angular momentum. The inclusion of multiple species of diquarks is
found to have a significant effect on the flavor decomposition, and resolving
the internal structure of these dynamical diquark correlations proves essential
for the mechanical stability of the proton. At a scale of $Q^2=4\,$GeV$^2$ we
find that the up and down quarks carry an intrinsic spin and orbital angular
momentum of $S_u=0.534$, $S_d=-0.214$, $L_u=-0.189$, and $L_d=0.210$, whereas
the gluons have a total angular momentum of $J_g=0.151$. The down quark is
therefore found to carry almost no total angular momentum due to cancellations
between spin and orbital contributions. Comparisons are made between these spin
decomposition results and lattice QCD calculations.",2005.10286v1
2020-05-21,Chemical Reaction Rates for Systems with Spin-Orbit Coupling and an Odd Number of Electrons: Does Berry's Phase Lead to Meaningful Spin-Dependent Nuclear Dynamics for a Two State Crossing?,"Within the context of very simple avoided crossing, we investigate the
investigate the effect of a complex diabatic coupling in determining
spin-dependent rate constants and scattering states. We find that, if the
molecular geometry is not linear and the Berry force is not zero, one can find
significant spin polarization of the products. This study emphasizes that, when
analyzing nonadiabatic reactions with spin orbit coupling (and a complex
Hamiltonian), one must consider how Berry force affects nuclear motion -- at
least in the context of gas phase reactions. Work is currently ongoing as far
as extrapolating these conclusions to the condensed phase where interesting
spin selection has been observed in recent years.",2005.10424v1
2020-06-01,Scalable spin-glass optical simulator,"Many developments in science and engineering depend on tackling complex
optimizations on large scales. The challenge motivates intense search for
specific computing hardware that takes advantage from quantum features,
nonlinear dynamics, or photonics. A paradigmatic optimization problem is
finding low-energy states in classical spin systems with fully-random
interactions. To date no alternative computing platform can address such
spin-glass problems on a large scale. Here we propose and realize an optical
scalable spin-glass simulator based on spatial light modulation and multiple
light scattering. By tailoring optical transmission through a disordered
medium, we optically accelerate the computation of the ground state of large
spin networks with all-to-all random couplings. Scaling of the operation time
with the problem size demonstrates optical advantage over conventional
computing. Our results point out optical vector-matrix multiplication as a tool
for spin-glass problems and provide a general route towards large-scale
computing that exploits speed, parallelism and coherence of light.",2006.00828v2
2020-06-02,Coherence Revivals of a Spinor Polariton Condensate from Self-induced Larmor Precession,"First order coherence measurements of a polariton condensate, reveal a regime
where the condensate pseudo-spin precesses persistently within the driving
optical pulse. Within a single 20 $\mu$s optical pulse the condensate
pseudo-spin performs over $10^5$ precessions with striking frequency stability.
The condensate maintains its phase coherence even after a complete precession
of the spin vector, making the observed state by a definition a spin coherent
state. The emergence of the precession is traced to the polariton interactions
that give rise to a self-induced out-of-plane magnetic field that in turn
drives the spin dynamics. We find that the Larmor oscillation frequency scales
with the condensate density, enabling external tuning of this effect by optical
means. The stability of the system allows for the realization of integrated
optical magnetometry devices with the use of materials with enhanced exciton
$g$-factor and can facilitate spin squeezing effects and active coherent
control on the Bloch sphere in polariton condensates.",2006.01741v1
2020-06-02,Parallel single-shot measurement and coherent control of solid-state spins below the diffraction limit,"Solid-state spin defects are a promising platform for quantum science and
technology, having realized demonstrations of a variety of key components for
quantum information processing, particularly in the area of quantum networks.
An outstanding challenge for building larger-scale quantum systems with
solid-state defects is realizing high-fidelity control over multiple defects
with nanoscale separations, which is required to realize strong spin-spin
interactions for multi-qubit logic and the creation of entangled states. In
this work, we experimentally demonstrate an optical frequency-domain
multiplexing technique, allowing high-fidelity initialization and single-shot
spin measurement of six rare earth (Er$^{3+}$) ions, within the sub-wavelength
volume of a single, silicon photonic crystal cavity. We also demonstrate
sub-wavelength control over coherent spin rotations using an optical AC Stark
shift. The demonstrated approach may be scaled to large numbers of ions with
arbitrarily small separation, and is a significant step towards realizing
strongly interacting atomic defect arrays with applications to quantum
information processing and fundamental studies of many-body dynamics.",2006.01823v1
2020-06-07,Anomalous magnetic suppression of spin relaxation in a two-dimensional electron gas in a GaAs/AlGaAs quantum well,"We study the spin dynamics in a high-mobility two-dimensional electron gas
confined in a GaAs/AlGaAs quantum well. An unusual magnetic field dependence of
the spin relaxation is found: as the magnetic field becomes stronger, the spin
relaxation time first increases quadratically but then changes to a linear
dependence, before it eventually becomes oscillatory, whereby the longitudinal
and transverse times reach maximal values at even and odd filling Landau level
factors, respectively. We show that the suppression of spin relaxation is due
to the effect of electron gyration on the spin-orbit field, while the
oscillations correspond to oscillations of the density of states appearing at
low temperatures and high magnetic fields. The transition from quadratic to
linear dependence can be related to a transition from classical to Bohm
diffusion and reflects an anomalous behavior of the two-dimensional electron
gas analogous to that observed in magnetized plasmas.",2006.04110v1
2020-06-10,Controlling spin without magnetic fields -- the Bloch-Rashba rotator,"We consider the dynamics of a quantum particle held in a lattice potential,
and subjected to a time-dependent spin-orbit coupling. Tilting the lattice
causes the particle to perform Bloch oscillations, and by suitably changing the
Rashba interaction during its motion, the spin of the particle can be gradually
rotated. Even if the Rashba coupling can only be altered by a small amount,
large spin-rotations can be obtained by accumulating the rotation from
successive oscillations. We show how the time-dependence of the spin-orbit
coupling can be chosen to maximize the rotation per cycle, and thus how this
method can be used to produce a precise and controllable spin-rotator, the
Bloch-Rashba rotator, without requiring an applied magnetic field.",2006.06046v2
2020-06-12,Symmetry Approach to Chiral Optomagnonics in Antiferromagnetic Insulators,"We discuss several aspects of chiral optomagnonics in antiferromagnetic
insulators by considering common symmetries between the electromagnetic field
and spin excitations. This approach allows us to look at optical and magnetic
materials from similar perspectives, and discuss useful analogies between them.
We show that spin waves in collinear antiferromagnets and the electromagnetic
field in vacuum are both invariant under the same eight-dimensional algebra of
symmetry transformations. By such analogy, we can extend the concept of optical
chirality to antiferromagnetic insulators, and demonstrate that the spin-wave
dynamics in these materials in the presence of a spin current is similar to
that of the light inside chiral metamaterials. Photo-excitation of magnonic
spin currents is also discussed from the symmetry point of view. It is
demonstrated that a direct magnonic spin photocurrent can be exited by
circularly polarized light, which can be considered as a magnonic analogue of
the photogalvanic effect. We also note that the Zitterbewegung process should
appear and may play a role in photo-excitation processes.",2006.07399v1
2020-06-16,Gravity Probe Spin: Prospects for measuring general-relativistic precession of intrinsic spin using a ferromagnetic gyroscope,"An experimental test at the intersection of quantum physics and general
relativity is proposed: measurement of relativistic frame dragging and geodetic
precession using intrinsic spin of electrons. The behavior of intrinsic spin in
spacetime dragged and warped by a massive rotating body is an experimentally
open question, hence the results of such a measurement could have important
theoretical consequences. Such a measurement is possible by using mm-scale
ferromagnetic gyroscopes in orbit around the Earth. Under conditions where the
rotational angular momentum of a ferromagnet is sufficiently small, a
ferromagnet's angular momentum is dominated by atomic electron spins and is
predicted to exhibit macroscopic gyroscopic behavior. If such a ferromagnetic
gyroscope is sufficiently isolated from the environment, rapid averaging of
quantum uncertainty via the spin-lattice interaction enables readout of the
ferromagnetic gyroscope dynamics with sufficient sensitivity to measure both
the Lense-Thirring (frame dragging) and de Sitter (geodetic precession) effects
due to the Earth.",2006.09334v1
2020-06-23,Nature of the Spin Glass Phase in Finite Dimensional (Ising) Spin Glasses,"Spin glasses are the paradigm of complex systems. These materials present
really slow dynamics. However, the nature of the spin glass phase in finite
dimensional systems is still controversial. Different theories describing the
low temperature phase have been proposed: droplet, replica symmetry breaking
and chaotic pairs. We present analytical studies of critical properties of spin
glasses, in particular, critical exponents at and below the phase transition,
existence of a phase transition in a magnetic field, computation of the lower
critical dimension (in presence/absence of a magnetic field). We also introduce
some rigorous results based on the concept of metastate. Finally, we report
some numerical results regarding the construction of the Aizenman-Wehr
metastate, scaling of the correlation functions in the spin glass phase and
existence of a phase transition in a field, confronting these results with the
predictions of different theories.",2006.12930v1
2020-06-29,Collective excitations in spin-polarized bilayer graphene,"We calculate the plasmon frequency and damping rate of plasma oscillations in
a spin-polarized BLG system. Using the long wavelength approximation for
dynamical dielectric function, we obtain an analytical expression for plasmon
frequency showing that the degree of spin polarization P has negligible effect
on the long wavelength plasmon frequency. Numerical calculations demonstrate
that the degree of spin polarization affects slightly (strongly) plasmon
frequency at small (large) wave-vectors and the maximum value of damping rate
increases with increasing P. We also study the effects of carrier density and
substrate dielectric constant on plasmon properties for different value of spin
polarization. The numerically calculated critical wave-vector, at which the
plasmon dispersion curve hits the edge of electron-hole continuum, decreases
with P and can be used to determine experimentally the degree of spin
polarization.",2006.16042v2
2020-08-21,Quantum Fourier transform for quantum sensing,"The Quantum Fourier Transformation ($QFT$) is a key building block for a
whole wealth of quantum algorithms.
  Despite its proven efficiency, only a few proof-of-principle demonstrations
have been reported.
  Here we utilize $QFT$ to enhance the performance of a quantum sensor.
  We implement the $QFT$ algorithm in a hybrid quantum register consisting of a
nitrogen-vacancy (NV) center electron spin and three nuclear spins.
  The $QFT$ runs on the nuclear spins and serves to process the sensor - NV
electron spin signal.
  We demonstrate $QFT$ for quantum (spins) and classical signals (radio
frequency (RF) ) with near Heisenberg limited precision scaling.
  We further show the application of $QFT$ for demultiplexing the nuclear
magnetic resonance (NMR) signal of two distinct target nuclear spins.
  Our results mark the application of a complex quantum algorithm in sensing
which is of particular interest for high dynamic range quantum sensing and
nanoscale NMR spectroscopy experiments.",2008.09716v1
2020-11-05,Experimental Observation of Phase Transitions in Spatial Photonic Ising Machine,"Statistical spin dynamics plays a key role to understand the working
principle for novel optical Ising machines. Here we propose the gauge
transformations for spatial photonic Ising machine, where a single spatial
phase modulator simultaneously encodes spin configurations and programs
interaction strengths. Thanks to gauge transformation, we experimentally
evaluate the phase diagram of high-dimensional spin-glass equilibrium system
with $100$ fully-connected spins. We observe the presence of paramagnetic,
ferromagnetic as well as spin-glass phases and determine the critical
temperature $T_c$ and the critical probability ${{p}_{c}}$ of phase
transitions, which agree well with the mean-field theory predictions. Thus the
approximation of the mean-field model is experimentally validated in the
spatial photonic Ising machine. Furthermore, we discuss the phase transition in
parallel with solving combinatorial optimization problems during the cooling
process and identify that the spatial photonic Ising machine is robust with
sufficient many-spin interactions, even when the system is associated with the
optical aberrations and the measurement uncertainty.",2011.02771v2
2021-02-24,Spin waves and high-frequency response in layered superconductors with helical magnetic structure,"We evaluate the spin-wave spectrum and dynamic susceptibility in a layered
superconductors with helical interlayer magnetic structure. We especially focus
on the structure in which the moments rotate 90$^{\circ}$ from layer to layer
realized in the iron pnictide RbEuFe$_{4}$As$_{4}$. The spin-wave spectrum in
superconductors is strongly renormalized due to the long-range electromagnetic
interactions between the oscillating magnetic moments. This leads to strong
enhancement of the frequency of the mode coupled with uniform field and this
enhancement exists only within a narrow range of the c-axis wave vectors of the
order of the inverse London penetration depth. The key feature of materials
like RbEuFe$_{4}$As$_{4}$ is that this uniform mode corresponds to the maximum
frequency of the spin-wave spectrum with respect to c-axis wave vector. As a
consequence, the high-frequency surface resistance acquires a very distinct
asymmetric feature spreading between the bare and renormalized frequencies. We
also consider excitation of spin waves with Josephson effect in a tunneling
contact between helical-magnetic and conventional superconductors and study the
interplay between the spin-wave features and geometrical cavity resonances in
the current-voltage characteristics.",2102.12445v2
2021-03-12,Superconductivity provides a giant enhancement to the spin battery effect,"We develop a theory of the spin battery effect in
superconductor/ferromagnetic insulator (SC/FI) systems taking into account the
magnetic proximity effect. We demonstrate that the spin-energy mixing enabled
by the superconductivity leads to the enhancement of spin accumulation by
several orders of magnitude relative to the normal state. This finding can
explain the recently observed giant inverse spin Hall effect generated by
thermal magnons in the SC/FI system. We suggest a non-local electrical
detection scheme which can directly probe the spin accumulation driven by the
magnetization dynamics. We predict a giant Seebeck effect converting the magnon
temperature bias into the non-local voltage signal. We also show how this can
be used to enhance the sensitivity of magnon detection even up to the
single-magnon level.",2103.07412v1
2021-03-16,Effect of spin-orbit coupling on the high harmonics from the topological Dirac semimetal Na3Bi,"In this work, we performed extensive first-principles simulations of
high-harmonic generation in the topological Diract semimetal Na3Bi using a
time-dependent density functional theory framework, focusing on the effect of
spin-orbit coupling (SOC) on the harmonic response. We also derived a general
analytical model describing the microscopic mechanism of strong-field dynamics
in presence of spin-orbit coupling, starting from a locally U(1)xSU(2)
gauge-invariant Hamiltonian. Our results reveal that SOC: (i) affects the
strong-field ionization by modifying the bandstructure of Na3Bi, (ii) modifies
the electron velocity, making each spin channel to react differently to the
pump laser field, (iii) changes the emission timing of the emitted harmonics.
Moreover, we show that the SOC affects the harmonic emission by directly
coupling the charge current to the spin currents, paving the way to the
high-harmonic spectroscopy of spin currents in solids.",2103.09322v1
2021-03-17,Molecular spin qudits for quantum simulation of light-matter interactions,"We show that molecular spin qudits provide an ideal platform to simulate the
quantum dynamics of photon fields strongly interacting with matter. The basic
unit of the proposed molecular quantum simulator can be realized by a simple
dimer of a spin 1/2 and a spin $S$ transition metal ion, solely controlled by
microwave pulses. The spin $S$ ion is exploited to encode the photon field in a
flexible architecture, which enables the digital simulation of a wide range of
spin-boson models much more efficiently than by using a multi-qubit register.
The effectiveness of our proposal is demonstrated by numerical simulations
using realistic molecular parameters, whose prerequisites delineating possible
chemical approaches are also discussed.",2103.09706v1
2021-03-17,Micromagnetic description of twisted spin spirals in the B20 chiral magnet FeGe from first principles,"Using the model of classical Heisenberg exchange and Dzyaloshinskii-Moriya
(DM) interaction we show that the ground state of B20 FeGe chiral magnet is a
superposition of twisted helical spin-density waves formed by different
sublattices of the crystal. Such twisted spin-density waves propagate in the
same direction but with different phases and different directions of the
rotation axes. We derive an advanced micromagnetic expression describing the
exchange and DM interaction for such magnetic structures. By employing
first-principles calculations based on density functional theory and using our
micromagnetic model we show that the magnitude of the spin-spiral twist in B20
FeGe is of the same order as global spiraling. While the energy difference
between the ground state of twisted spirals and the FM state is in good
agreement with the experimental results, for the spin spirals without a twist
it is smaller by factor three. In addition, we verify our results by employing
spin dynamics simulations. This calls for new experiments exploring the ground
state properties of B20 chiral magnets.",2103.09800v2
2021-04-01,Accretion induced black hole spin up revised by numerical GR MHD simulations,"We investigate the accretion induced spin up of the black hole via numerical
simulations. Our method is based on general-relativistic magneto-hydrodynamics
of the slowly-rotating flows in the Kerr metric, where possibly transonic shock
fronts may form. We account for the changing black hole mass and spin during
accretion which enforces dynamical evolution of the space-time metric. We first
study non-magnetized flows with shocks, and we also include magnetic field
endowed in the gas. The aim of this study is to verify whether the high mass
black holes may be produced with large spins, even though at birth the
collapsars might have contained slowly, or moderately spinning cores. In this
way, we put constraints on the content of angular momentum in the collapsing
massive stars. Our studies are also showing that shock fronts and magnetic
fields may halt accretion and limit the black hole spin-up in the exploding
supernovae.",2104.00741v1
2021-04-12,Spin-orbit torque switching of Néel order in two-dimensional CrI$_3$,"Spin-orbit torque enables electrical control of the magnetic state of
ferromagnets or antiferromagnets. In this work we consider the spin-orbit
torque in the 2-d Van der Waals antiferromagnetic bilayer CrI$_3$, in the
$n$-doped regime. In the purely antiferromagnetic state, two individually
inversion-symmetry broken layers of CrI$_3$ form inversion partners, like the
well-studied CuMnAs and Mn$_2$Au. However, the exchange and anisotropy energies
are similar in magnitude, unlike previously studied antiferromagnets, which
leads to qualitatively different behaviors in this material. Using a
combination of first-principles calculations of the spin-orbit torque and an
analysis of the ensuing spin dynamics, we show that the deterministic
electrical switching of the N\'eel vector is the result of dampinglike
spin-orbit torque, which is staggered on the magnetic sublattices.",2104.05155v1
2021-05-26,Gapless Spin Liquid and Non-local Corner Excitation in the Spin-1/2 Heisenberg Antiferromagnet on Fractal,"Motivated by the mathematical beauty and the recent experimental realizations
of fractal systems, we study the spin-$1/2$ antiferromagnetic Heisenberg model
on a Sierpi\'nski gasket. The fractal porous feature generates new kinds of
frustration to exhibit exotic quantum states. Using advanced tensor network
techniques, we identify a quantum gapless-spin-liquid ground state in
fractional spatial dimension. This fractal spin system also demonstrates
nontrivial non-local properties. While the extremely short-range correlation
causes a highly degenerate spin form factor, the entanglement in this fractal
system suggests scaling behaviors significantly different from those in integer
dimensions. We also study the dynamic structure factor and clearly identify the
gapless excitation with a stable corner excitation emerged from the
ground-state entanglement. Our results unambiguously point out multiple
essential properties of this fractal spin system, and open a new route to
explore spin liquid and frustrated magnetism.",2105.12487v1
2021-08-31,Achieving spin-squeezed states by quench dynamics in a quantum chain,"We study the time evolution of spin squeezing in the one-dimensional spin-1/2
XY model subject to a sudden quantum quench of a transverse magnetic field. The
initial state is selected from the ground state phase diagram of the model,
consisting of ferro- and paramagnetic phases separated by a critical value of
the transverse field. Our analysis, based on exact results for the model,
reveals that by a proper choice of protocol, a quantum quench from an
unsqueezed state can create spin squeezed nonequilibrium states. We also
identify a nonanalyticity in the long-time average of the spin-squeezing
parameter when quenching to the equilibrium quantum critical point. This
suggests that the ferro- and paramagnetic phases also define distinct phases
for how the transverse field redistributes quantum fluctuations among the spin
components away from equilibrium.",2108.13805v2
2021-09-17,Current-Induced Spin-Wave Doppler Shift in Antiferromagnets,"We theoretically study the spin dynamics in antiferromagnets (AFs)under the
influence of an electric current. We identify two different sources of
spin-transfer torques that stem from uniform (${\boldsymbol v}_n$) and
staggered (${\boldsymbol v}_\ell$) electron spin densities. While the former is
well recognized, the latter is often overlooked. We show that both
${\boldsymbol v}_n$ and ${\boldsymbol v}_\ell$ contribute equally to the
spin-wave Doppler shift. Microscopic calculations are presented for electrons
on a two-dimensional square lattice with nearest-neighbor ($t$) and
next-nearest-neighbor ($t'$) hopping, which interpolate two opposite transport
regimes of strongly-coupled AF ($t'/t \ll 1$) and two weakly coupled
ferromagnets ($t'/t \gg 1$). In the AF transport regime ($t'/t \ll 1$),
${\boldsymbol v}_n$ and ${\boldsymbol v}_\ell$ have opposite signs, and the
sign of the Doppler shift depends on band filling; ${\boldsymbol v}_n$
(${\boldsymbol v}_\ell$) is dominant near the AF gap (near the band bottom or
the top). As $t'/t$ is increased, ${\boldsymbol v}_n$ undergoes a sign change
whereas ${\boldsymbol v}_\ell$ does not. In the limit of vanishing $t$,
${\boldsymbol v}_n$ and ${\boldsymbol v}_\ell$ coincide and the spin-transfer
torque reduces to that of ferromagnets.",2109.08432v1
2021-10-11,Simulating two-dimensional dynamics within a large-size atomic spin,"Encoding a dimension in the internal degree of freedom of an atom provides an
interesting tool for quantum simulation, facilitating the realization of
artificial gauge fields. We propose an extension of the synthetic dimension
toolbox, making it possible to encode two dimensions within a large atomic
spin. The protocol combines first- and second-order spin couplings, such that
the spin projection $m$ and the remainder $r=m$ (mod 3) of its Euclidian
division by 3 act as orthogonal coordinates on a synthetic cylinder. It is
suited for an implementation with lanthanide atoms, which feature a large
electronic spin and narrow optical transitions for applying the required spin
couplings. This method is useful for simulating geometries with periodic
boundary conditions, and engineering various types of topological systems
evolving in high dimensions.",2110.05269v1
2021-10-17,Ising Machine Based on Electrically Coupled Spin Hall Nano-Oscillators,"The Ising machine is an unconventional computing architecture that can be
used to solve NP-hard combinatorial optimization problems more efficiently than
traditional von Neumann architectures. Fast, compact oscillator networks which
provide programmable connectivities among arbitrary pairs of nodes are highly
desirable for the development of practical oscillator-based Ising machines.
Here we propose using an electrically coupled array of GHz spin Hall
nano-oscillators to realize such a network. By developing a general analytical
framework that describes injection locking of spin Hall oscillators with large
precession angles, we explicitly show the mapping between the coupled
oscillators' properties and the Ising model. We integrate our analytical model
into a versatile Verilog-A device that can emulate the coupled dynamics of spin
Hall oscillators in circuit simulators. With this abstract model, we analyze
the performance of the spin Hall oscillator network at the circuit level using
conventional electronic components and considering phase noise and scalability.
Our results provide design insights and analysis tools toward the realization
of a CMOS-integrated spin Hall oscillator Ising machine operating with a high
degree of time, space, and energy efficiency.",2110.08885v2
2021-10-25,Thermodynamics of spin crossover in ferropericlase: an improved LDA+$U_{sc}$ calculation,"We present LDA+$U_{sc}$ calculations of high-spin (HS) and low-spin (LS)
states in ferropericlase (fp) with an iron concentration of 18.75$\%$. The
Hubbard parameter $U$ is determined self-consistently with structures optimized
at arbitrary pressures. We confirm a strong dependence of $U$ on the pressure
and spin state. Static calculations confirm that the antiferromagnetic
configuration is more stable than the ferromagnetic one in the HS state,
consistent with low-temperature measurements. Phonon calculations guarantee the
dynamical stability of HS and LS states throughout the pressure range of the
Earth mantle. Compression curves for HS and LS states agree well with
experiments. Using a non-ideal mixing model for the HS to LS states solid
solution, we obtain a crossover starting at $\sim$45 GPa at room temperature
and considerably broader than previous results. The spin-crossover phase
diagram is calculated, including vibrational, magnetic, electronic, and
non-ideal HS-LS entropic contributions. Our results suggest the mixed-spin
state predominates in fp in most of the lower mantle.",2110.12637v2
2021-11-12,Whirling interlayer fields as a source of stable topological order in moiré CrI3,"The moir\'e engineering of two-dimensional magnets opens unprecedented
opportunities to design novel magnetic states with promises for spintronic
device applications. The possibility of stabilizing skyrmions in these
materials without chiral spin-orbit couplings or dipolar interactions is yet to
be explored. Here, we investigate the formation and control of ground state
topological spin textures (TSTs) in moir\'e CrI3 using stochastic
Landau-Lifshitz-Gilbert simulations. We unveil the emergence of interlayer
vortex and antivortex Heisenberg exchange fields, stabilizing spontaneous and
field-assisted ground state TSTs with various topologies. The developed study
accounts for the full bilayer spin dynamics, thermal fluctuations, and
intrinsic spin-orbit couplings. By examining the effect of the Kitaev
interaction and the next nearest-neighbor Dzyaloshinskii-Moriya interaction, we
propose the latter as the unique spin-orbit coupling mechanism compatible with
experiments on monolayer and twisted CrI3. Our findings contribute to the
current knowledge about moir\'e skyrmionics and uncover the nature of
spin-orbit coupling in CrI3.",2111.06936v2
2021-11-24,Spin Polarization through A Molecular Junction Based on Nuclear Berry Curvature Effects,"We explore the effects of spin-orbit coupling on nuclear wave packet motion
near an out-of-equilibrium molecular junction, where nonzero Berry curvature
emerges as the antisymmetric part of the electronic friction tensor. The
existence of nonzero Berry curvature mandates that different nuclear wave
packets (associated with different electronic spin states) experience different
nuclear Berry curvatures, i.e. different pseudo-magnetic fields. Furthermore,
for a generic, two-orbital two-lead model (representing the simplest molecular
junction), we report significant spin polarization of the {\em electronic}
current with decaying and oscillating signatures in the large voltage limit --
all as a result of {\em nuclear} motion. These results are consistent with
magnetic AFM chiral-induced spin selectivity experiments. Altogether, our
results highlight an essential role for Berry curvature in condensed phase
dynamics, where spin separation survives dissipation to electron-hole pair
creation and emerges as one manifestation of nuclear Berry curvature.",2111.12815v2
2021-11-29,Tailoring High-Frequency Magnonics in Monolayer Chromium Trihalides,"Monolayer chromium trihalides, the archetypal two dimensional (2D) magnetic
materials, are readily suggested as a promising platform for high frequency
magnonics. Here we detail the spin wave properties of monolayer CrBr$_3$ and
CrI$_3$, using spin dynamics simulations parametrized from the first
principles. We reveal that spin wave dispersion can be tuned in a broad range
of frequencies by strain, paving the way towards flexo magnonic applications.
We further show that ever present halide vacancies in these monolayers host
sufficiently strong Dzyaloshinskii Moriya interaction to scatter spin waves,
which promotes design of spin-wave guides by defect engineering. Finally we
discuss the spectra of spin-waves propagating across a moir\'e periodic
modulation of magnetic parameters in a van der Waals heterobilayer, and show
that the nanoscale moir\'e periodicities in such samples are ideal for
realization of a magnonic crystal in the terahertz frequency range. Recalling
the additional tunability of magnetic 2D materials by electronic gating, our
results situate these systems among the front-runners for prospective high
frequency magnonic applications.",2111.14305v1
2021-11-29,Interface-Induced Conservation of Momentum Leads to Chiral-Induced Spin Selectivity,"We study the non-equilibrium dynamics of electron transmission from a
straight waveguide to a helix with spin-orbit coupling. Transmission is found
to be spin-selective and can lead to large spin polarizations of the itinerant
electrons. The degree of spin selectivity depends on the width of the interface
region, and no polarization is found for single-point couplings. We show that
this is due to momentum conservation conditions arising from extended
interfaces. We therefore identify interface structure and conservation of
momentum as crucial ingredients for chiral-induced spin selectivity, and
confirm that this mechanism is robust against static disorder.",2111.14770v1
2021-12-17,Multi-qudit interactions in molecular spins,"We study photon-mediated interactions between molecular spin qudits in the
dispersive regime of operation. We derive from a microscopic model the
effective interaction between molecular spins, including their crystal field
anisotropy (i.e., the presence of non-linear spin terms) and their multi-level
structure. Finally, we calculate the long time dynamics for a pair of
interacting molecular spins using the method of multiple scales analysis. This
allows to find the set of 2-qudit gates that can be realized for a specific
choice of molecular spins and to determine the time required for their
implementation. Our results are relevant for the implementation of logical
gates in general systems of qudits with unequally spaced levels or to determine
an adequate computational subspace to encode and process the information.",2112.09714v2
2022-01-04,Enhanced coupling of electron and nuclear spins by quantum tunneling resonances,"Noble-gas spins feature hours long coherence times owing to their great
isolation from the environment, and find practical usage in various
applications. However, this isolation leads to extremely slow preparation
times, relying on weak spin transfer from an electron-spin ensemble. Here we
propose a controllable mechanism to enhance this transfer rate. We analyze the
spin dynamics of helium-3 atoms with hot, optically-excited potassium atoms and
reveal the formation of quasi-bound states in resonant binary collisions. We
find a resonant enhancement of the spin-exchange cross section by up to six
orders of magnitude and two orders of magnitude enhancement for the thermally
averaged, polarization rate-coefficient. We further examine the effect for
various other noble gases and find that the enhancement is universal. We
outline feasible conditions under which the enhancement may be experimentally
observed and practically utilized.",2201.01255v1
2022-01-05,Electrical readout microwave-free sensing with diamond,"While nitrogen-vacancy (NV-) centers have been extensively investigated in
the context of spin-based quantum technologies, the spin-state readout is
conventionally performed optically, which may limit miniaturization and
scalability. Here, we report photoelectric readout of ground-state
cross-relaxation features, which serves as a method for measuring electron spin
resonance spectra of nanoscale electronic environments and also for
microwave-free sensing. As a proof of concept, by systematically tuning NV
centers into resonance with the target electronic system, we extracted the
spectra for the P1 electronic spin bath in diamond. Such detection may enable
probing optically inactive defects and the dynamics of local spin environment.
We also demonstrate a magnetometer based on photoelectric detection of the
ground-state level anticrossings (GSLAC), which exhibits a favorable detection
efficiency as well as magnetic sensitivity. This approach may offer potential
solutions for determining spin densities and characterizing local environment.",2201.01801v1
2022-01-18,Measuring correlations from the collective spin fluctuations of a large ensemble of lattice-trapped dipolar spin-3 atoms,"We perform collective spin measurements to study the buildup of two-body
correlations between $\approx10^4$ spin $s=3$ chromium atoms pinned in a 3D
optical lattice. The spins interact via long range and anisotropic dipolar
interactions. From the fluctuations of total magnetization, measured at the
standard quantum limit, we estimate the dynamical growth of the connected
pairwise correlations associated with magnetization. The quantum nature of the
correlations is assessed by comparisons with short and long time expansions,
and numerical simulations. Our work shows that measuring fluctuations of spin
populations provides new ways to characterize correlations in quantum many-body
systems, for $s>1/2$ spins",2201.07277v1
2022-01-19,Conservative and radiative dynamics of spinning bodies at third post-Minkowskian order using worldline quantum field theory,"Using the spinning worldline quantum field theory formalism we calculate the
quadratic-in-spin momentum impulse $\Delta p_i^\mu$ and spin kick $\Delta
a_i^\mu$ from a scattering of two arbitrarily oriented spinning massive bodies
(black holes or neutron stars) in a weak gravitational background up to third
post-Minkowskian (PM) order ($G^3$). Two-loop Feynman integrals are performed
in the potential region, yielding conservative results. For spins aligned to
the orbital angular momentum we find a conservative scattering angle that is
fully consistent with state-of-the-art post-Newtonian results. Using the 2PM
radiated angular momentum previously obtained by Plefka, Steinhoff and the
present authors we generalize the angle to include radiation-reaction effects,
in which case it avoids divergences in the high-energy limit.",2201.07778v3
2022-03-10,Experimental realization of a fermionic spin-momentum lattice,"We experimentally realize a spin-momentum lattice with a homogeneously
trapped Fermi gas. The lattice is created via cyclically-rotated atom-laser
couplings between three bare atomic spin states, and are such that they form a
triangular lattice in a synthetic spin-momentum space. We demonstrate the
lattice and explore its dynamics with spin- and momentum-resolved absorption
imaging. This platform will provide new opportunities for synthetic spin
systems and the engineering of topological bands. In particular, the use of
three spin states in two spatial dimensions would allow the simulation of
synthetic magnetic fields of high spatial uniformity, which would lead to
ultra-narrow Chern bands that support robust fractional quantum Hall states.",2203.05543v1
2022-03-15,Optimal mixing for two-state anti-ferromagnetic spin systems,"We prove an optimal $\Omega(n^{-1})$ lower bound for modified log-Sobolev
(MLS) constant of the Glauber dynamics for anti-ferromagnetic two-spin systems
with $n$ vertices in the tree uniqueness regime. Specifically, this optimal MLS
bound holds for the following classes of two-spin systems in the tree
uniqueness regime:
  $\bullet$ all strictly anti-ferromagnetic two-spin systems (where both edge
parameters $\beta,\gamma<1$), which cover the hardcore models and the
anti-ferromagnetic Ising models;
  $\bullet$ general anti-ferromagnetic two-spin systems on regular graphs.
  Consequently, an optimal $O(n\log n)$ mixing time holds for these
anti-ferromagnetic two-spin systems when the uniqueness condition is satisfied.
These MLS and mixing time bounds hold for any bounded or unbounded maximum
degree, and the constant factors in the bounds depend only on the gap to the
uniqueness threshold. We prove this by showing a boosting theorem for MLS
constant for distributions satisfying certain spectral independence and
marginal stability properties.",2203.07771v1
2022-03-28,Semi-classical kinetic theory for massive spin-half fermions with leading-order spin effects,"We consider the quantum kinetic-theory description for interacting massive
spin-half fermions using the Wigner function formalism. We derive a general
kinetic theory description assuming that the spin effects appear at the
classical and quantum level. To track the effect of such different
contributions we use the semi-classical expansion method to obtain the
generalized dynamical equations including spin, analogous to classical
Boltzmann equation. This approach can be used to obtain a collision kernel
involving local as well as non-local collisions among the microscopic
constituent of the system and eventually, a framework of spin hydrodynamics
ensuring the conservation of the energy-momentum tensor and total angular
momentum tensor.",2203.15562v2
2022-04-27,Elastic Spin and Orbital Angular Momenta,"Motivated by recent theoretical and experimental interest in the spin and
orbital angular momenta of elastic waves, we revisit canonical wave momentum,
spin, and orbital angular momentum in isotropic elastic media. We show that
these quantities are described by simple universal expressions, which differ
from the results of [G. J. Chaplain et al., Phys. Rev. Lett. 128, 064301
(2022)] and do not require separation of the longitudinal and transverse parts
of the wavefield. For cylindrical elastic modes, the normalized z-component of
the total (spin+orbital) angular momentum is quantized and equals the azimuthal
quantum number of the mode, while the orbital and spin parts are not quantized
due to the spin-orbit geometric-phase effects. In contrast to the claims of the
above article, longitudinal, transverse, and `hybrid' contributions to the
angular momenta are equally important and cannot be neglected. As another
application of the general formalism, we calculate the transverse spin angular
momentum of a surface Rayleigh wave.",2204.13037v3
2022-07-21,Influence of nonuniform magnetization reorientation on spin-orbit torque measurements,"Measurements of spin-orbit torques in a ferromagnetic/nonmagnetic multilayer
are typically based on an assumption that the entire ferromagnetic layer
uniformly responds to the spin-orbit torque. This assumption breaks down when
the thickness of the ferromagnetic layer is comparable to the dynamic exchange
coupling length, which can be as short as a few nanometers in certain
measurement geometries. The nonuniform magnetization reorientation coupled with
nonuniform contribution of each magnetic sublayer to the magnetoresistance or
the Kerr effect may impact the accuracy in the extrapolation of spin-orbit
torque, particularly if a thick ferromagnetic layer is used. In this paper, we
use numerical models to investigate such an impact in three different
techniques: the magneto-optic-Kerr-effect method, the second-harmonic method
and the spin torque ferromagnetic resonance method. We show that the
second-harmonic and magneto-optic-Kerr-effect methods are prone to be
influenced by the nonuniform magnetization reorientation, while the spin torque
ferromagnetic resonance method is much less impacted.",2207.10349v1
2022-09-16,Pseudo-PT symmetric Dirac equation : effect of a new mean spin angular momentum operator on Gilbert damping,"The pseudo-PT symmetric Dirac equation is proposed and analyzed by using a
non-unitary Foldy-Wouthuysen transformations. A new spin operator PT symmetric
expectation value (called the mean spin operator) for an electron interacting
with a time-dependent electromagnetic field is obtained. We show that spin
magnetization - which is the quantity usually measured experimentally - is not
described by the standard spin operator but by this new mean spin operator to
properly describe magnetization dynamics in ferromagnetic materials and the
corresponding equation of motion is compatible with the phenomenological model
of the Landau-Lifshitz-Gilbert equation (LLG).",2209.07908v1
2022-10-10,Strong coupling of a Gd$^{3+}$ multilevel spin system to an on-chip superconducting resonator,"We report the realization of a strong coupling between a Gd$^{3+}$ spin
ensemble hosted in a scheelite (CaWO$_4$) single crystal and the resonant mode
of a coplanar stripline superconducting cavity leading to a large separation of
spin-photon states of 146 MHz. The interaction is well described by the Dicke
model and the crystal-field Hamiltonian of the multilevel spin system. We
observe a change of the crystal-field parameters due to the presence of photons
in the cavity that generates a significant perturbation of the crystal ground
state. Using finite-element calculations, we numerically estimate the cavity
sensing volume as well as the average spin-photon coupling strength of
$g_0\approx$ 620 Hz. Lastly, the dynamics of the spin-cavity states are
explored via pulsed measurements by recording the cavity ring-down signal as a
function of pulse length and amplitude. The results indicate a potential method
to initialize this multilevel system in its ground state via an active cooling
process.",2210.05053v2
2022-10-17,Ultrafast laser-driven topological spin textures on a 2D magnet,"Ultrafast laser excitations provide an efficient and low-power consumption
alternative since different magnetic properties and topological spin states can
be triggered and manipulated at the femtosecond (fs) regime. However, it is
largely unknown whether laser excitations already used in data information
platforms can manipulate the magnetic properties of recently discovered
two-dimensional (2D) van der Waals (vdW) materials. Here we show that
ultrashort laser pulses (30$-$85 fs) can not only manipulate magnetic domains
of 2D-XY CrCl$_3$ ferromagnets, but also induce the formation and control of
topological nontrivial meron and antimeron spin textures. We observed that
these spin quasiparticles are created within $\sim$100 ps after the excitation
displaying rich dynamics through motion, collision and annihilation with
emission of spin waves throughout the surface. Our findings highlight
substantial opportunities of using photonic driving forces for the exploration
of spin textures on 2D magnetic materials towards magneto-optical topological
applications.",2210.09210v1
2022-10-25,Exact solutions for a spin-orbit coupled bosonic double-well system,"Exact solutions for spin-orbit (SO) coupled cold atomic systems are very
important and rare in physics. In this paper, we propose a simple method of
combined modulations to generate the analytic exact solutions for an SO-coupled
boson held in a driven double well. For the cases of synchronous combined
modulations and the spin-conserving tunneling, we obtain the general analytical
accurate solutions of the system respectively. For the case of spin-flipping
tunneling under asynchronous combined modulations, we get the special exact
solutions in simple form when the driving parameters satisfy certain
conditions. Based on these obtained exact solutions, we reveal some intriguing
quantum spin dynamical phenomena, for instance, the arbitrary population
transfer (APT) with and/or without spin-flipping, the controlled coherent
population conservation (CCPC), and the controlled coherent population
inversion (CCPI). The results may have potential applications in the
preparation of accurate quantum entangled states and quantum information
processing.",2210.13724v1
2022-10-28,Stripe order and spin dynamics in triangular-lattice antiferromagnet KErSe$_{2}$: A single-crystal study with a theoretical description,"The rare-earth triangular-lattice chalcogenide is a great platform for
exploring both spin liquids and novel magnetic orders with anisotropic spin
interactions and magnetic frustrations. Here, we report the thermodynamic and
neutron scattering measurements of rare-earth triangular-lattice chalcogenide
KErSe$_{2}$, using single-crystal samples. Our experiments revealed a
long-range stripe order below 0.2 K. Although the magnetic order was
three-dimensional, magnetic excitations exhibited negligible modulation along
the z direction, indicating very weak interlayer coupling. Furthermore,
magnetic excitation developed a well-defined spin-wave dispersion with a gap of
$\sim$0.03 meV at M points. Both the stripe order and spin-wave excitations
could be quantitatively understood from the anisotropic spin interactions of
the Er$^{3+}$ Kramers doublets.",2210.15867v1
2022-11-07,Interaction of gapless spin waves and a domain wall in an easy-cone ferromagnet,"We theoretically study the interaction of spin waves and a domain wall in a
quasi-one-dimensional easy-cone ferromagnet. The gapless spin waves on top of a
domain wall are found to exhibit finite reflection in contrast to the
well-known perfect transmission of gapful spin waves in easy-axis magnets.
Based on the obtained scattering properties, we study the thermal-magnon-driven
dynamics of a domain wall subjected to a thermal bias within the
Landau-B\""uttiker formalism, where transmitted magnons are shown to exert the
magnonic torque on the domain wall and thereby drive it with the velocity
linear to the applied thermal bias. The peculiar gapless nature of spin waves
in easy-cone magnets enables the thermally-driven domain-wall motion even at
low temperatures, differing from the easy-axis case where the domain-wall
velocity is exponentially suppressed at low temperatures. Our work suggests
that easy-cone magnets can serve as a useful platform to study the interaction
of gapless spin waves and nonlinear excitations and thereby realize
low-temperature magnon-related phenomena.",2211.03331v1
2022-11-20,Long-distance propagation of high-velocity antiferromagnetic spin waves,"We report on coherent propagation of antiferromagnetic (AFM) spin waves over
a long distance ($\sim$10 $\mu$m) at room temperature in a canted AFM
$\alpha$-Fe$_2$O$_3$ with the Dzyaloshinskii-Moriya interaction (DMI).
Unprecedented high group velocities (up to 22.5 km/s) are characterized by
microwave transmission using all-electrical spin wave spectroscopy. We derive
analytically AFM spin-wave dispersion in the presence of the DMI which accounts
for our experimental results. The AFM spin waves excited by nanometric coplanar
waveguides with large wavevectors enter the exchange regime and follow a
quasi-linear dispersion relation. Fitting of experimental data with our
theoretical model yields an AFM exchange stiffness length of 1.7 angstrom. Our
results provide key insights on AFM spin dynamics and demonstrate high-speed
functionality for AFM magnonics.",2211.10989v1
2022-11-30,"Universal Relations of Energy Flow, Acoustic Spin and Torque for Near-Field Acoustic Tweezers","Acoustic spin, radiation torque, energy flow, and reactive power are of
significant importance from both fundamental and practical aspects, responsible
for flexible tweezer manipulations and near-field sound directionality.
Nevertheless, the intrinsic relations among these physical quantities are far
from clear. Here, we prove the universal geometric relations among them in
acoustics, independent on wave structure details. Particularly, we connect
acoustic spin and torque to the cross product of time-averaged energy flow and
reactive power, as well as to the local vorticity of energy flow. These
relations are universally valid, verified in a variety of different acoustic
systems. We also demonstrate the multipole mechanical torques and forces
generated in three acoustic near-field sources: Janus, Huygens and Spin
sources, applying on small lossy particles. These universal geometric relations
uncover hidden locking relations beyond simple spin-momentum locking of
near-field waves, and show the basic principles between the acoustic spin,
radiation torque, and energy flow, reactive power.",2212.00028v1
2022-12-08,Dynamic generation of spin spirals of moiré trapped carriers via exciton mediated spin interactions,"Stacking transition metal dichalcogenides (TMDs) to form moir\'e
superlattices has provided exciting opportunities to explore many-body
correlation phenomena of the moir\'e trapped carriers. TMDs bilayers, on the
other hand, host long-lived interlayer exciton (IX), an elementary excitation
of long spin-valley lifetime that can be optically or electrically injected.
Here we find that, through the Coulomb exchange between mobile IXs and
carriers, the IX bath can mediate both Heisenberg and Dzyaloshinskii-Moriya
type spin interactions between moir\'e trapped carriers, controllable by
exciton density and exciton spin current respectively. We show the strong
Heisenberg interaction, and the extraordinarily long-ranged
Dzyaloshinskii-Moriya interaction here can jointly establish robust spin spiral
magnetic orders in Mott-Wigner crystal states at various filling factors, with
spiral direction controlled by exciton current.",2212.04021v1
2022-12-09,Pure gauge theory for the gravitational spin connection,"The gravitational spin connection appears in gravity as a non-Abelian gauge
field for the Lorentz group $SO(3,1)$, which is non-compact. The action for
General Relativity is linear in the field strength associated to the spin
connection, and its equation of motion corresponds to the standard metricity
constraint. Consequently, the zero-torsion spin connection is never realized as
an independent degree of freedom and is determined by the vierbein field. In
this work, we take a different perspective and consider a pure Yang-Mills
theory for the spin connection coupled to Dirac fermions, resulting in the
former being a dynamical field. After discussing various approaches towards
managing the pathologies associated with non-compact gauge theories, we compute
the tree-level amplitude for fermion scattering via a spin connection exchange.
In contrast to integrating out torsion in the presence of fermions, the model
induces a chiral four-Fermi like term that involves a right-right current
interaction, which is not present in the Standard Model.",2212.05069v2
2022-12-14,All-Optical Nuclear Quantum Sensing using Nitrogen-Vacancy Centers in Diamond,"Solid state spins have demonstrated significant potential in quantum sensing
with applications including fundamental science, medical diagnostics and
navigation. The quantum sensing schemes showing best performance under ambient
conditions all utilize microwave or radio-frequency driving, which poses a
significant limitation for miniaturization, energy-efficiency and
non-invasiveness of quantum sensors. We overcome this limitation by
demonstrating a purely optical approach to coherent quantum sensing. Our scheme
involves the $^{15}$N nuclear spin of the Nitrogen-Vacancy (NV) center in
diamond as a sensing resource, and exploits NV spin dynamics in oblique
magnetic fields near the NV's excited state level anti-crossing to optically
pump the nuclear spin into a quantum superposition state. We demonstrate
all-optical free-induction decay measurements - the key protocol for
low-frequency quantum sensing - both on single spins and spin ensembles. Our
results pave the way for highly compact quantum sensors to be employed for
magnetometry or gyroscopy applications in challenging environments.",2212.07093v1
2022-12-21,Heisenberg Spin Chain And Supersymmetric Gauge Theory,"We show how a Heisenberg spin chain emerges from the two-dimensional
${\mathcal N}$=(2,2) gauge theory at an intermediate scale, which relies on the
renormalization group flow guided by the global symmetries and the dynamics of
domain walls. The discussion of higher-dimensional gauge theories with four
supercharges is similar by compactifying them into two dimensions. Instead of
utilizing the bosonic fields solely in the literature, adopting the fermionic
degrees of freedom of gauge theory is a crucial step in our construction. From
the perspective of the spin chain, we observe that the Seiberg(-like) duality
between two gauge theories is manifest since it is a finite symmetry in the
closed spin chain. Based on this, we further conjecture gauge theories with the
same global symmetries could be unified into a single system: the Heisenberg
spin chain. At least, we prove this conjecture at the intermediate scale.
Finally, we also comment on other formulations of an integrable system centered
on the Heisenberg spin chain.",2212.11288v1
2023-02-10,Approaching a fully-polarized state of nuclear spins in a semiconductor quantum dot,"Magnetic noise of atomic nuclear spins is a major problem for solid state
spin qubits. Highly-polarized nuclei would not only overcome this obstacle, but
also make nuclear spins a useful quantum information resource. However,
achieving sufficiently high nuclear polarizations has remained an evasive goal.
Here we implement a nuclear spin polarization protocol which combines strong
optical pumping and fast electron tunneling. Polarizations well above 95% are
generated in GaAs semiconductor quantum dots on a timescale of 1 minute. The
technique is compatible with standard quantum dot device designs, where
highly-polarized nuclear spins can simplify implementations of quantum bits and
memories, as well as offer a testbed for studies of many-body quantum dynamics
and magnetism.",2302.05489v1
2023-02-20,Motion of a spinning particle under the conservative piece of the self-force is Hamiltonian to first order in mass and spin,"We consider the motion of a point particle with spin in a stationary
spacetime. We define, following Witzany (2019) and later Ramond (2022), a
twelve dimensional Hamiltonian dynamical system whose orbits coincide with the
solutions of the Mathisson-Papapetrou-Dixon equations of motion with the
Tulczyjew-Dixon spin supplementary condition, to linear order in spin. We then
perturb this system by adding the conservative pieces of the leading order
gravitational self-force and self-torque sourced by the particle's mass and
spin. We show that this perturbed system is Hamiltonian and derive expressions
for the Hamiltonian function and symplectic form. This result extends our
previous result for spinless point particles.",2302.10233v2
2023-03-06,Resolving the stellar-collapse and hierarchical-merger origins of the coalescing black holes,"Spin and mass properties provide essential clues in distinguishing the
formation channels for coalescing binary black holes (BBHs). With a dedicated
non-parametric population model for the joint distributions of mass, spin
magnitude, and spin orientation of the black holes (BHs) in the coalescing
binaries, we find two distinct categories of BHs among the GWTC-3 events with
considerably different spin and mass distributions. One category, with a mass
ranging from $\sim 25M_\odot$ to $\sim 80M_\odot$, is distinguished by the high
spin-magnitudes and consistent with the (hierarchical) merger origin. The other
category, characterized by low spins, has a sharp mass cutoff at $\sim
40M_\odot$ ($<56.8M_{\odot}$ at 90\% credible level), which is natural for the
stellar-collapse origin. In particular, such a mass cutoff is expected for the
pair-instability explosion of massive stars. The stellar-collapse category is
estimated to consist of $\sim 70\%$ filed binaries and $\sim 30\%$ dynamical
assembly from star clusters (mostly globular clusters); while the merger-origin
category may contain comparable amounts of events from the Active Galactic
Nuclei disks and star clusters.",2303.02973v1
2023-03-06,Phase driving hole spin qubits,"The spin-orbit interaction in spin qubits enables spin-flip transitions,
resulting in Rabi oscillations when an external microwave field is resonant
with the qubit frequency. Here, we introduce an alternative driving mechanism
of hole spin qubits, where a far-detuned oscillating field couples to the qubit
phase. Phase driving at radio frequencies, orders of magnitude slower than the
microwave qubit frequency, induces highly non-trivial spin dynamics, violating
the Rabi resonance condition. By using a qubit integrated in a silicon fin
field-effect transistor (Si FinFET), we demonstrate a controllable suppression
of resonant Rabi oscillations, and their revivals at tunable sidebands. These
sidebands enable alternative qubit control schemes using global fields and
local far-detuned pulses, facilitating the design of dense large-scale qubit
architectures with local qubit addressability. Phase driving also decouples
Rabi oscillations from noise, an effect due to a gapped Floquet spectrum and
can enable Floquet engineering high-fidelity gates in future quantum
processors.",2303.03350v1
2023-05-03,One- and two-particle correlation functions in the cluster perturbation theory for cuprates,"Physics of high-$T_c$ superconducting cuprates is obscured by the effect of
strong electronic correlations. One way to overcome the problem is to seek for
an exact solution at least within the small cluster and expand it to the whole
crystal. Such an approach is in the heart of the cluster perturbation theory
(CPT). Here we develop CPT for the dynamic spin and charge susceptibilities
(spin-CPT and charge-CPT), within which the correlation effects are explicitly
taken into account by the exact diagonalization. We apply spin-CPT and
charge-CPT to the effective two-band Hubbard model for the cuprates obtained
from the three-band Emery model and calculate one- and two-particle correlation
functions, namely, spectral function and spin and charge susceptibilities.
Doping dependence of the spin susceptibility was studied within spin-CPT and
CPT-RPA that is the CPT generalization of the random phase approximation (RPA).
Both methods produce the low energy response at four incommensurate wave
vectors in qualitative agreement to the results of the inelastic neutron
scattering on overdoped cuprates.",2305.01882v1
2023-05-05,A new microscopic representation of the spin dynamics in quantum systems with the Coulomb exchange interactions,"There is a version of the Landau-Lifshitz equation that takes into account
the Coulomb exchange interactions between atoms, expressed by the term
$\sim\bm{s}\times\triangle\bm{s}$. On the other hand, ions in the magnetic
materials have several valence electrons on the $d$-shell, and therefore the
Hamiltonian of many-electron atoms with spins $S>1$ should include a
biquadratic exchange interaction. We first propose a new fundamental
microscopic derivation of the spin density evolution equation with an explicit
form of biquadratic exchange interaction using the method of many-particle
quantum hydrodynamics. The equation for the evolution of the spin density is
obtained from the many-particle Schrodinger-Pauli equation and contains the
contributions of the usual Coulomb exchange interaction and the biquadratic
exchange. Furthermore, the derived biquadratic exchange torque in the spin
density evolution equation is proportional to the nematic tensor for the medium
of atoms with spin $\textit{S = 1}$. Our method may be very attractive for
further studies of the magnetoelectric effect in multiferroics.",2305.03826v3
2023-05-08,Phonon-Induced Decoherence in Color-Center Qubits,"Electron spin states of solid-state defects such as Nitrogen- and
Silicon-vacancy {\em color centers} in diamond are a leading quantum-memory
candidate for quantum communications and computing. Via open-quantum-systems
modeling of spin-phonon coupling -- the major contributor of decoherence -- at
a given temperature, we derive the time dynamics of the density operator of an
electron-spin qubit. We use our model to corroborate experimentally-measured
decoherence rates. We further derive the temporal decay of distillable
entanglement in spin-spin entangled states heralded via photonic Bell-state
measurements. Extensions of our model to include other decoherence mechanisms,
e.g., undesired hyperfine couplings to the neighboring nuclear-spin
environment, will pave the way to a rigorous predictive model for engineering
artificial-atom qubits with desirable properties.",2305.05049v2
2023-05-17,Spin-wave dynamics controlled by tunable ac magnonic crystal,"The magnonic crystal, which has a spatial modulation wave vector $q$, couples
the spin wave with wave vector $k$ to the one with wave vector $k-q$. For a
conventional magnonic crystal with direct current (dc) supply, the spin waves
around $q/2$ are resonantly coupled to the waves near $-q/2$, and a band gap is
opened at $k=\pm q/2$. If instead of the dc current the magnonic crystal is
supplied with an alternating current (ac), then the band gap is \emph{shifted}
to $k$ satisfying $|\omega_{s}(k)-\omega_{s}(k-q)|=\omega_{ac}$; here
$\omega_{s}(k)$ is the dispersion of the spin wave, while $\omega_{ac}$ is the
frequency of the ac modulation. The resulting gap in the case of the ac
magnonic crystal is the half of the one caused by the dc with the same
amplitude of modulation. The time evolution of the resonantly coupled spin
waves controlled by properly suited ac pulses can be well interpreted as the
motion on a Bloch sphere. The tunability of the ac magnonic crystal broadens
the perspective of spin-wave computing.",2305.09876v1
2023-05-24,Superdiffusion from nonabelian symmetries in nearly integrable systems,"The Heisenberg spin chain is a canonical integrable model. As such, it
features stable ballistically propagating quasiparticles, but spin transport is
sub-ballistic at any nonzero temperature: an initially localized spin
fluctuation spreads in time $t$ to a width $t^{2/3}$. This exponent, as well as
the functional form of the dynamical spin correlation function, suggest that
spin transport is in the Kardar-Parisi-Zhang (KPZ) universality class. However,
the full counting statistics of magnetization is manifestly incompatible with
KPZ scaling. A simple two-mode hydrodynamic description, derivable from
microscopic principles, captures both the KPZ scaling of the correlation
function and the coarse features of the full counting statistics, but remains
to be numerically validated. These results generalize to any integrable spin
chain invariant under a continuous nonabelian symmetry, and are surprisingly
robust against moderately strong integrability-breaking perturbations that
respect the nonabelian symmetry.",2305.15463v1
2023-05-24,Unraveling spin dynamics from charge fluctuations,"The use of single electron spins in quantum dots as qubits requires detailed
knowledge about the processes involved in their initialization and operation as
well as their relaxation and decoherence. In optical schemes for such spin
qubits, spin-flip Raman as well as Auger processes play an important role, in
addition to environment-induced spin relaxation. In this paper, we demonstrate
how to quantitatively access all the spin-related processes in one go by
monitoring the charge fluctuations of the quantum dot. For this, we employ
resonance fluorescence and analyze the charge fluctuations in terms of
waiting-time distributions and full counting statistics characterized by
factorial cumulants.",2305.15502v1
2023-06-05,Spin network Entanglement and Bulk-Boundary Map in Loop Quantum Gravity,"This thesis is dedicated to the study of open spin networks. We formulate
quasi-local descriptions of loop quantum gravity. We investigate the
coarse-graining procedure via tracing over bulk degrees of freedom, which
encodes all that we can know about the quantum state of geometry from probing
the boundary. We prove a boundary-to bulk universal reconstruction procedure,
to be understood as a purification of the mixed boundary state into a pure bulk
state. We then move to define multipartite entanglement in spin networks, and
show the computation of entanglement excitation from holonomy operator, which
also allows us to glimpse bulk curvature from entanglement. Moreover, by
investigating another coarse-graining procedure - via gauge-fixing, which does
not trace over any bulk degrees of freedom, we show a new interesting
connection between bulk geometry and boundary observables via the dynamics of
entanglement. Finally, we define the spin network entanglement between spin
sub-networks, which correspond to spatial sub-regions. We then generalize the
coarse-graining approach, and prove that the entanglement between spin
sub-networks is preserved under the coarse-graining (via gauge-fixing).",2306.02789v1
2023-06-06,Ultrafast Hidden Spin Polarization Dynamics of Bright and Dark Excitons in 2H-WSe$_2$,"We performed spin-, time- and angle-resolved extreme ultraviolet
photoemission spectroscopy (STARPES) of excitons prepared by photoexcitation of
inversion-symmetric 2H-WSe$_2$ with circularly polarized light. The very short
probing depth of XUV photoemission permits selective measurement of
photoelectrons originating from the top-most WSe$_2$ layer, allowing for direct
measurement of hidden spin polarization of bright and momentum-forbidden dark
excitons. Our results reveal efficient chiroptical control of bright excitons'
hidden spin polarization. Following optical photoexcitation, intervalley
scattering between nonequivalent K-K' valleys leads to a decay of bright
excitons' hidden spin polarization. Conversely, the ultrafast formation of
momentum-forbidden dark excitons acts as a local spin polarization reservoir,
which could be used for spin injection in van der Waals heterostructures
involving multilayer transition metal dichalcogenides.",2306.03610v2
2023-07-19,"Dark Matter Halo Spin of the Dwarf Galaxy UGC 5288: Insights from Observations, N-body and Cosmological Simulations","Dark matter (DM) halo angular momentum is very challenging to determine from
observations of galaxies. In this study, we present a new hybrid method of
estimating the dimensionless halo angular momentum, halo spin of a gas-rich
dwarf barred galaxy UGC5288 using N-Body/SPH simulations. We forward model the
galaxy disk properties: stellar and gas mass, surface densities, disk
scalelengths, bar length and bar ellipticity from observations. We use the HI
rotation curve to constrain the DM halo density profile and further use the bar
properties to determine the models that best represent the observed baryonic
disk. We compare the halo spin profile from our models to the halo spin
profiles of similar mass dwarf galaxy analogues of UGC5288 in the TNG50
simulations. The halo spin profile from our simulated models matches within
ballpark values of the median spin profile of UGC5288 analogues in the TNG50
simulations, although there are some uncertainties due to the DM halo
evolutionary history.",2307.09952v1
2023-07-27,Spin Coupling Effect on Geometry-Dependent X-ray Absorption of Diradicals,"We theoretically investigate the influence of diradical electron spin
coupling on the time-resolved X-ray absorption spectra of the photochemical
ring opening of furanone. We predict geometry dependent carbon K-edge signals
involving transitions from core orbitals to both singly and unoccupied
molecular orbitals. The most obvious features of the ring opening come from the
carbon atom directly involved in the bond breaking, through its transition to
both the newly formed SOMO and the available LUMO state. In addition to this
primary feature, the singlet spin coupling of four unpaired electrons that
arises in the core-to-LUMO states creates additional geometry dependence in
some spectral features, with both oscillator strengths and relative excitation
energies varying observably as a function of the ring opening. We attribute
this behavior to a spin-occupancy-induced selection rule, which occurs when
singlet spin coupling is enforced in the diradical state. Notably, one of these
geometry-sensitive core-to-LUMO transitions excites core electrons from a
backbone carbon not involved in the bond breaking, providing a novel non-local
X-ray probe of chemical dynamics arising from electron spin coupling.",2307.15207v1
2023-08-10,Protocols to measure the non-Abelian Berry phase by pumping a spin qubit through a quantum-dot loop,"A quantum system constrained to a degenerate energy eigenspace can undergo a
nontrival time evolution upon adiabatic driving, described by a non-Abelian
Berry phase. This type of dynamics may provide logical gates in quantum
computing that are robust against timing errors. A strong candidate to realize
such holonomic quantum gates is an electron or hole spin qubit trapped in a
spin-orbit-coupled semiconductor, whose twofold Kramers degeneracy is protected
by time-reversal symmetry. Here, we propose and quantitatively analyze
protocols to measure the non-Abelian Berry phase by pumping a spin qubit
through a loop of quantum dots. One of these protocols allows to characterize
the local internal Zeeman field directions in the dots of the loop. We expect a
near-term realisation of these protocols, as all key elements have been already
demonstrated in spin-qubit experiments. These experiments would be important to
assess the potential of holonomic quantum gates for spin-based quantum
information processing.",2308.05455v1
2023-08-22,Dissipative scattering of spinning black holes at fourth post-Minkowskian order,"We compute the radiation reacted momentum impulse $\Delta p_i^\mu$, spin kick
$\Delta S_i^\mu$, and scattering angle $\theta$ between two scattered spinning
massive bodies (black holes or neutron stars) using the $\mathcal{N}=1$
supersymmetric worldline quantum field theory formalism up to fourth
post-Minkowskian (4PM) order. Our calculation confirms the state-of-the-art
non-spinning results, and extends them to include spin-orbit effects. Advanced
multi-loop Feynman integral technology including differential equations and the
method of regions are applied and extended to deal with the retarded
propagators arising in a causal description of the scattering dynamics. From
these results we determine a complete set of radiative fluxes at sub-leading PM
order: the 4PM radiated four-momentum and, via linear response, the 3PM
radiated angular momentum, both again including spin-orbit effects.",2308.11514v1
2023-08-27,How to produce spin-splitting in antiferromagnetic materials,"Antiferromagnetic (AFM) materials have potential advantages for spintronics
due to their robustness, ultrafast dynamics, and magnetotransport effects.
However, the missing spontaneous polarization and magnetization hinders the
efficient utilization of electronic spin in these AFM materials. Here, we
propose a simple way to produce spin-splitting in AFM materials by making the
magnetic atoms with opposite spin polarization locating in the different
environment (surrounding atomic arrangement), which does not necessarily
require the presence of spin-orbital coupling (SOC). We confirm our proposal by
four different types of two-dimensional (2D) AFM materials within the
first-principles calculations. Our works provide a intuitional design principle
to find or produce spin-splitting in AFM materials.",2308.14097v1
2023-08-29,Probing quantum spin liquids with a quantum twisting microscope,"The experimental characterization of quantum spin liquids poses significant
challenges due to the absence of long-range magnetic order, even at absolute
zero temperature. The identification of these states of matter often relies on
the analysis of their excitations. In this paper, we propose a method for
detecting the signatures of the fractionalized excitations in quantum spin
liquids using a tunneling spectroscopy setup. Inspired by the recent
development of the quantum twisting microscope, we consider a planar tunneling
junction, in which a candidate quantum spin liquid material is placed between
two graphene layers. By tuning the relative twist angle and voltage bias
between the leads, we can extract the dynamical spin structure factor of the
tunneling barrier with momentum and energy resolution. Our proposal presents a
promising tool for experimentally characterizing quantum spin liquids in
two-dimensional materials.",2308.15533v2
2023-09-06,Equilibrium dynamics of infinite-range quantum spin glasses in a field,"We determine the low-energy spectrum and Parisi replica symmetry breaking
function for the spin glass phase of the quantum Ising model with
infinite-range random exchange interactions and transverse and longitudinal
($h$) fields. We show that, for all $h$, the spin glass state has full replica
symmetry breaking, and the local spin spectrum is gapless with a spectral
density which vanishes linearly with frequency. These results are obtained
using an action functional$\unicode{x2014}$argued to yield exact results at low
frequencies$\unicode{x2014}$that expands in powers of a spin glass order
parameter, which is is bilocal in time, and a matrix in replica space. We also
present the exact solution of the infinite-range spherical quantum $p$-rotor
model at nonzero $h$: here, the spin glass state has one-step replica symmetry
breaking, and gaplessness only appears after imposition of an additional
marginal stability condition. Possible connections to experiments on random
arrays of trapped Rydberg atoms are noted.",2309.03255v1
2023-09-15,Charge pumping with strong spin-orbit coupling: Fermi surface breathing and higher harmonic generation,"Spin and charge pumping induced by a precessing magnetization has been
instrumental to the development of spintronics. Nonetheless, most theoretical
studies so far treat the spin-orbit coupling as a perturbation, which
disregards the dynamical competition between exchange and spin-orbit fields. In
this work, based on Keldysh formalism and Wigner expansion, we develop an
adiabatic theory of spin and charge pumping adapted to multiorbital systems
with arbitrary spin-orbit coupling. We apply this theory to the magnetic Rashba
gas and magnetic graphene cases and discuss the pumped ac and dc current. We
show that the pumped current possesses both intrinsic and extrinsic
contributions, akin to the magnetic damping. In addition, we find that higher
harmonics can be generated under large angle precession and we propose a couple
of experimental setups where such an effect could be experimentally observed.",2309.08597v1
2023-09-17,Long Electron Spin Coherence Times of Atomic Hydrogen Trapped in Silsesquioxane Cages,"Encapsulated atomic hydrogen in cube-shaped octa-silsesquioxane (POSS) cages
of the Si$_8$O$_{12}$R$_8$ type (where R is an organic group) is the simplest
alternative stable system to paramagnetic endohedral fullerenes (N@C$_{60}$ or
P@C$_{60}$) that have been regarded as key elements of spin-based quantum
technologies. Apart from common sources of decoherence like nuclear spin and
spectral diffusion, all H@POSS species studied so far suffer from additional
shortening of $T_2$ at low temperatures due to methyl group rotations. Here we
eliminate this factor for the first time by studying the relaxation properties
of the smallest methyl-free derivative of this family with R=H, namely
H@T$_8$H$_8$. We suppress nuclear spin diffusion by applying dynamical
decoupling methods and we measure electron spin coherence times $T_2$ up to 280
$\pm$ 76 $\mu$s at $T=90$ K. We observe a linear dependence of the decoherence
rate $1/T_2$ on trapped hydrogen concentrations ranging between 9$\times
10^{14}$ cm$^{-3}$ and 5$\times 10^{15}$ cm$^{-3}$ which we attribute to the
spin dephasing mechanism of instantaneous diffusion and a nonuniform spatial
distribution of encapsulated H atoms.",2309.09365v1
2023-10-17,Quantum spin chains with bond dissipation,"We study the effect of bond dissipation on the one-dimensional
antiferromagnetic spin-$1/2$ Heisenberg model. In analogy to the spin-Peierls
problem, the dissipative bath is described by local harmonic oscillators that
modulate the spin exchange coupling, but instead of a single boson frequency we
consider a continuous bath spectrum $\propto \omega^s$. Using an exact quantum
Monte Carlo method for retarded interactions, we show that for $s<1$ any finite
coupling to the bath induces valence-bond-solid order, whereas for $s>1$ the
critical phase of the isolated chain remains stable up to a finite critical
coupling. We find that, even in the presence of the gapless bosonic spectrum,
the spin-triplet gap remains well defined for any system size, from which we
extract a dynamical critical exponent of $z=1$. We provide evidence for a
Berezinskii-Kosterlitz-Thouless quantum phase transition that is governed by
the SU(2)$_1$ Wess-Zumino-Witten model. Our results suggest that the critical
properties of the dissipative system are the same as for the spin-Peierls
model, irrespective of the different interaction range, i.e., power-law vs.
exponential decay, of the retarded dimer-dimer interaction, indicating that the
spin-Peierls criticality is robust with respect to the bosonic density of
states.",2310.11525v1
2023-10-18,Generalized phantom helix states in quantum spin graphs,"In general, the summation of a set of sub-Hamiltonians cannot share a common
eigenstate of each one, only if it is an unentangled product state, such as a
phantom helix state in quantum spin system. Here we present a method, referred
to as the building block method (BBM), for constructing possible spin-1/2 XXZ
Heisenberg lattice systems possessing phantom helix states. We focus on two
types of XXZ dimers as basic elements, with a non-Hermitian parity-time (PT )
field and Hermitian Dzyaloshinskii-Moriya interaction (DMI), which share the
same degenerate eigenstates. Based on these two building blocks, one can
construct a variety of Heisenberg quantum spin systems, which support helix
states with zero energy. The underlying mechanism is the existence of a set of
degenerate eigenstates. Furthermore, we show that such systems act as quantum
spin graphs since they obey the analogs of Kirchhoff's laws for sets of spin
helix states when the non-Hermitian PT fields cancel each other out. In
addition, the dynamic response of the helix states for three types of
perturbations is also investigated analytically and numerically. Our findings
provide a way to study quantum spin systems with irregular geometries beyond
the Bethe ansatz approach.",2310.11786v1
2023-10-25,Spin-eccentricity interplay in merging binary black holes,"Orbital eccentricity and spin precession are precious observables to infer
the formation history of binary black holes with gravitational-wave data. We
present a post-Newtonian, multi-timescale analysis of the binary dynamics able
to capture both precession and eccentricity over long inspirals. We show that
the evolution of an eccentric binary can be reduced that of effective source on
quasi-circular orbits, coupled to a post-Newtonian prescription for the secular
evolution of the eccentricity. Our findings unveil an interplay between
precession and eccentricity: the spins of eccentric binaries precess on shorter
timescales and their nutation amplitude is altered compared to black holes on
quasi-circular orbits, consequently affecting the so-called spin morphology.
Even if binaries circularize by the time they enter the sensitivity window of
our detectors, their spin orientations retain some memory of the past evolution
on eccentric orbits, thus providing a new link between gravitational-wave
detection and astrophysical formation. At the same time, we point out that
residual eccentricity should be considered a source of systematics when
reconstructing the past history of black-hole binaries using the spin
orientations.",2310.16893v2
2023-12-13,Spin relaxation rate for baryons in thermal pion gas,"We study the relaxation dynamics of the spin polarization of baryons (nucleon
and $\Lambda$-baryon), in a thermal pion gas as a simple model of the hadronic
phase of the QCD plasma produced in relativistic heavy-ion collisions. For this
purpose, we formulate the quantum kinetic theory for the spin density matrix of
baryons in the leading order of the gradient expansion. Considering the
baryon-pion elastic scattering processes as the dominant interaction between
baryons and thermal pions, we compute the spin relaxation rate of nucleons and
$\Lambda$-baryons in a pion gas up to temperature 200 MeV. In the case of
nucleons, we evaluate the spin relaxation rate in the $s$-channel resonance
approximation, based on the known experimental data on $\Delta$-resonances. We
also estimate the spin relaxation rate for $\Lambda$-baryons, based on
experimental inputs and theoretical models for the low-energy $\Lambda$$\pi$
scattering, including the chiral perturbation theory.",2312.08266v1
2024-01-10,Self-generated spin-orbit torque driven by anomalous Hall current,"Spin-orbit torques enable energy-efficient manipulation of magnetization by
electric current and hold promise for applications ranging from nonvolatile
memory to neuromorphic computing. Here we report the discovery of a giant
spin-orbit torque induced by anomalous Hall current in ferromagnetic
conductors. This anomalous Hall torque is self-generated as it acts on
magnetization of the ferromagnet that engenders the torque. The magnitude of
the anomalous Hall torque is sufficiently large to fully negate magnetic
damping of the ferromagnet, which allows us to implement a microwave spin
torque nano-oscillator driven by this torque. The peculiar angular symmetry of
the anomalous Hall torque favors its use over the conventional spin Hall torque
in coupled nano-oscillator arrays. The universal character of the anomalous
Hall torque makes it an integral part of the description of coupled spin
transport and magnetization dynamics in magnetic nanostructures.",2401.05006v1
2024-01-18,Observing Topological Insulator Phases with a Programmable Quantum Simulator,"Topological insulators exhibit fascinating properties such as the appearance
of edge states protected by symmetries. The Su-Schrieffer-Heeger (SSH) model is
a canonical description of a one-dimensional quantum topological insulator. We
experimentally implement a modified SSH model with long-range interacting spin
systems in one-dimensional trapped ion crystals of up to $22$ spins. An array
of tightly focused laser beams generates site-specific Floquet fields that
control the bond dimerization of the spins, which when subject to reflection
symmetry, exhibit signatures of topologically-protected edge states. We study
the evolution of highly excited configurations with various ranges of the
spin-spin interaction, revealing the nontrivial role of many-body
fermionic-interaction terms on the resulting dynamics. These results allow
direct quantum simulations of topological quantum degrees of freedom expected
in exotic materials, but here with high control of individual spins and their
interaction range.",2401.10362v1
2024-02-01,Enhancement of Chiral-Induced Spin Selectivity via Circularly Polarized Light,"The notion of chiral-induced spin selectivity (CISS) has attracted intensive
research interest recently. However, the practical applications of the CISS
effects face challenges due to relatively low spin polarization. In this
Letter, we propose a non-perturbative theory illustrating how circularly
polarized (CP) light enhances CISS effects through strong light-matter
interactions. We introduce a Floquet electronic friction model to study the
nonadiabatic dynamics and spin transport through a chiral molecule in a
molecule junction subjected to external driving. Our results show that the
interplay of the nonadiabatic effects and light-matter interactions can
significantly ($>90\%$) enhance electron spin polarization under CP light. Our
predictions can be very useful in experiments for using CP light to control
spin current in chiral molecular junctions.",2402.00903v1
2024-03-07,Stability of low-momentum rest frame modes in first- and second-order spin hydrodynamics,"The low-momentum rest frame stability of the second-order spin hydrodynamics
is analyzed in detail. A truncation scheme of the Israel-Stewart formalism
derived in our earlier work is proposed that extends the minimal causal
formulation. It consists of altogether 40 interconnected relaxation-type
dynamical equations -- 16 (24) of them correspond to the independent components
of the energy-momentum (spin) tensor. Similarly to previous studies, we find
that the stability of the perturbations depends on the form of the spin
equation of state. The stability is achieved if the equation of state satisfies
the generalized Frenkel condition demanding that the ""electric"" and ""magnetic""
components of the spin density tensor have opposite signs. We then re-examine
the study of the first-order (Navier-Stokes) dissipative spin hydrodynamics and
find a similar type of behavior, which is consistent with the overall stability
of low-momentum rest frame modes in conventional relativistic hydrodynamics.",2403.04711v1
2024-03-25,Vector Ising Spin Annealer for Minimizing Ising Hamiltonians,"We introduce the Vector Ising Spin Annealer (VISA), a framework in gain-based
computing that harnesses light-matter interactions to solve complex
optimization problems encoded in spin Hamiltonians. Traditional
driven-dissipative systems often select excited states due to limitations in
spin movement. VISA transcends these constraints by enabling spins to operate
in a three-dimensional space, offering a robust solution to minimize Ising
Hamiltonians effectively. Our comparative analysis reveals VISA's superior
performance over conventional single-dimension spin optimizers, demonstrating
its ability to bridge substantial energy barriers in complex landscapes.
Through detailed studies on cyclic and random graphs, we show VISA's
proficiency in dynamically evolving the energy landscape with time-dependent
gain and penalty annealing, illustrating its potential to redefine optimization
in physical systems.",2403.16608v1
1998-03-04,In an Ising model with spin-exchange dynamics damage always spreads,"We investigate the spreading of damage in Ising models with Kawasaki
spin-exchange dynamics which conserves the magnetization. We first modify a
recent master equation approach to account for dynamic rules involving more
than a single site. We then derive an effective-field theory for damage
spreading in Ising models with Kawasaki spin-exchange dynamics and solve it for
a two-dimensional model on a honeycomb lattice. In contrast to the cases of
Glauber or heat-bath dynamics, we find that the damage always spreads and never
heals. In the long-time limit the average Hamming distance approaches that of
two uncorrelated systems. These results are verified by Monte-Carlo
simulations.",9803053v2
2000-04-27,Slow dynamics of Ising models with energy barriers,"Using Monte Carlo simulations we study the dynamics of three-dimensional
Ising models with nearest-, next-nearest-, and four-spin (plaquette)
interactions. During coarsening, such models develop growing energy barriers,
which leads to very slow dynamics at low temperature. As already reported, the
model with only the plaquette interaction exhibits some of the features
characteristic of ordinary glasses: strong metastability of the supercooled
liquid, a weak increase of the characteristic length under cooling,
stretched-exponential relaxation and aging. The addition of two-spin
interactions, in general, destroys such behaviour: the liquid phase loses
metastability and the slow-dynamics regime terminates well below the melting
transition, which is presumably related with a certain corner-rounding
transition. However, for a particular choice of interaction constants, when the
ground state is strongly degenerate, our simulations suggest that the
slow-dynamics regime extends up to the melting transition. The analysis of
these models leads us to the conjecture that in the four-spin Ising model
domain walls lose their tension at the glassy transition and that they are
basically tensionless in the glassy phase.",0004466v1
2001-01-08,Critical dynamics of a spin-5/2 2D isotropic antiferromagnet,"We report a neutron scattering study of the dynamic spin correlations in
Rb$_2$MnF$_4$, a two-dimensional spin-5/2 antiferromagnet. By tuning an
external magnetic field to the value for the spin-flop line, we reduce the
effective spin anisotropy to essentially zero, thereby obtaining a nearly ideal
two-dimensional isotropic antiferromagnet. From the shape of the quasielastic
peak as a function of temperature, we demonstrate dynamic scaling for this
system and find a value for the dynamical exponent $z$. We compare these
results to theoretical predictions for the dynamic behavior of the
two-dimensional Heisenberg model, in which deviations from $z=1$ provide a
measure of the corrections to scaling.",0101097v1
2002-06-06,Dynamic linear response of the SK spin glass coupled microscopically to a bath,"The dynamic linear response theory of a general Ising model weakly coupled to
a heat bath is derived employing the quantum statistical theory of Mori,
treating the Hamiltonian of the spin bath coupling as a perturbation, and
applying the Markovian approximation. Both the dynamic susceptibility and the
relaxation function are expressed in terms of the static susceptibility and the
static internal field distribution function. For the special case of the SK
spin glass this internal field distribution can be related to the solutions of
the TAP equations in the entire temperature region. Application of this new
relation and the use of numerical solutions of the modified TAP equations leads
for finite but large systems to explicit results for the distribution function
and for dynamic linear response functions. A detailed discussion is presented
which includes finite size effects. Due to the derived temperature dependence
of the Onsager-Casimir coefficients a frequency-dependent shift of the cusp
temperature of the real part of the dynamic susceptibility is found.",0206090v2
2002-10-11,Dynamics of spin-2 Bose condensate driven by external magnetic fields,"Dynamic response of the F=2 spinor Bose-Einstein condensate (BEC) under the
influence of external magnetic fields is studied. A general formula is given
for the oscillation period to describe population transfer from the initial
polar state to other spin states. We show that when the frequency and the
reduced amplitude of the longitudinal magnetic field are related in a specific
manner, the population of the initial spin-0 state will be dynamically
localized during time evolution. The effects of external noise and nonlinear
spin exchange interaction on the dynamics of the spinor BEC are studied. We
show that while the external noise may eventually destroy the Rabi oscillations
and dynamic spin localization, these coherent phenomena are robust against the
nonlinear atomic interaction.",0210252v1
2003-06-13,Glassy phase in the Hamiltonian Mean Field model,"We study the relaxation dynamics of a Hamiltonian system of
  N fully-coupled XY spins. The thermodynamics of the system predicts a
ferromagnetic and a paramagnetic phase. Starting from out-of-equilibrium
initial conditions, the dynamics at constant energy drives the system into
quasi-stationary states (QSS) characterized by dynamical frustration. We
introduce the spin polarization as a new order parameter which allows to
interpret the dynamically generated QSS regime as a glassy phase of the model.",0306374v4
2004-09-07,Spin Dynamics of Layered Triangular Antiferromagnets with Uniaxial Anisotropy,"The spin dynamics of the semiclassical Heisenberg model with uniaxial
anisotropy, on the layered triangular lattice with antiferromagnetic coupling
for both intralayer nearest neighbor interaction and interlayer interaction is
studied both in the ordered phase and in the paramagnetic phase, using the
Monte Carlo-molecular dynamics technique. The important quantities calculated
are the full dynamic structure function $S(\bf q, \omega)$, the chiral dynamic
structure function $S_{chi}(\omega)$, the static order parameter and some
thermodynamic quantities. Our results show the existence of propagating modes
corresponding to both $S(\bf q, \omega)$ and $S_{chi}(\omega)$ in the ordered
phase, supporting the recent conjectures. Our results for the static properties
show the magnetic ordering in each layer to be of coplanar 3-sublattice type
deviating from 120 degree structure. In the presence of magnetic trimerization
however, we find the 3-sublattice structure to be weakened alongwith the
tendency towards non-coplanarity of the spins.",0409151v1
2006-06-15,On Equilibrium Dynamics of Spin-Glass Systems,"We present a critical analysis of the Sompolinsky theory of equilibrium
dynamics. By using the spherical $2+p$ spin glass model we test the asymptotic
static limit of the Sompolinsky solution showing that it fails to yield a
thermodynamically stable solution. We then present an alternative formulation,
based on the Crisanti, H\""orner and Sommers [Z. f\""ur Physik {\bf 92}, 257
(1993)] dynamical solution of the spherical $p$-spin spin glass model,
reproducing a stable static limit that coincides, in the case of a one step
Replica Symmetry Breaking Ansatz, with the solution at the dynamic free energy
threshold at which the relaxing system gets stuck off-equilibrium. We formally
extend our analysis to any number of Replica Symmetry Breakings $R$. In the
limit $R\to\infty$ both formulations lead to the Parisi anti-parabolic
differential equation. This is the special case, though, where no dynamic
blocking threshold occurs. The new formulation does not contain the additional
order parameter $\Delta$ of the Sompolinsky theory.",0606425v2
2010-01-26,Quantum-tunneling dynamics of a spin-polarized Fermi gas in a double-well potential,"We study the exact dynamics of a one-dimensional spin-polarized gas of
fermions in a double-well potential at zero and finite temperature. Despite the
system is made of non-interacting fermions, its dynamics can be quite complex,
showing strongly aperiodic spatio-temporal patterns during the tunneling. The
extension of these results to the case of mixtures of spin-polarized fermions
in interaction with self-trapped Bose-Einstein condensates (BECs) at zero
temperature is considered as well. In this case we show that the fermionic
dynamics remains qualitatively similar to the one observed in absence of BEC
but with the Rabi frequencies of fermionic excited states explicitly depending
on the number of bosons and on the boson-fermion interaction strength. From
this, the possibility to control quantum fermionic dynamics by means of
Feshbach resonances is suggested.",1001.4615v1
2010-04-27,Signature of a Z_2 vortex in the dynamical correlations of the triangular-lattice Heisenberg antiferromagnet,"Dynamical properties of the classical Heisenberg antiferromagnet on the
triangular lattice are investigated by means of a spin-dynamics simulation and
an analytical calculation. While the model was suggested to exhibit a
topological transition driven by the Z_2-vortex binding-unbinding, weakness of
the associated thermodynamic singularity has made it difficult to observe the
evidence of the Z_2 vortex experimentally so far, only some indirect support.
Here, we show that the signature of the Z_2-vortex excitation and the
vortex-induced topological transition can be captured from the dynamical spin
correlations. In particular, the dynamical spin structure factor exhibits a
characteristic central peak around the Z_2-vortex transition, and this central
peak will be a fingerprint of the Z_2-vortex excitation.",1004.4730v2
2010-11-25,Memory-keeping effects and forgetfulness in the dynamics of a qubit coupled to a spin chain,"Using recently proposed measures for non-Markovianity [H. P. Breuer, E. M.
Laine, and J. Piilo, Phys. Rev. Lett. {\bf 103}, 210401 (2009)], we study the
dynamics of a qubit coupled to a spin environment via an energy-exchange
mechanism. We show the existence of a point, in the parameter space of the
system, where the qubit dynamics is effectively Markovian and that such a point
separates two regions with completely different dynamical behaviors. Indeed,
our study demonstrates that the qubit evolution can in principle be tuned from
a perfectly forgetful one to a deep non-Markovian regime where the qubit is
strongly affected by the dynamical back-action of the environmental spins. By
means of quantum process tomography, we provide a complete and intuitive
characterization of the qubit channel.",1011.5653v2
2011-04-05,Emergent gauge dynamics of highly frustrated magnets,"Condensed matter exhibits a wide variety of exotic emergent phenomena such as
the fractional quantum Hall effect and the low temperature cooperative behavior
of highly frustrated magnets. I consider the classical Hamiltonian dynamics of
spins of the latter phenomena using a method introduced by Dirac in the 1950s
by assuming they are constrained to their lowest energy configurations as a
simplifying measure. Focusing on the kagome antiferromagnet as an example, I
find it is a gauge system with topological dynamics and non-locally connected
edge states for certain open boundary conditions similar to doubled
Chern-Simons electrodynamics expected of a $Z_2$ spin liquid. These dynamics
are also similar to electrons in the fractional quantum Hall effect. The
classical theory presented here is a first step towards a controlled
semi-classical description of the spin liquid phases of many pyrochlore and
kagome antiferromagnets and towards a description of the low energy classical
dynamics of the corresponding unconstrained Heisenberg models.",1104.0721v3
2011-05-02,Magnetization Oscillation of a Spinor Condensate Induced by Magnetic Field Gradient,"We study the spin mixing dynamics of ultracold spin-1 atoms in a weak
non-uniform magnetic field with field gradient $G$, which can flip the spin
from +1 to -1 so that the magnetization $m=\rho_{+}-\rho_{-}$ is not any more a
constant. The dynamics of $m_F=0$ Zeeman component $\rho_{0}$, as well as the
system magnetization $m$, are illustrated for both ferromagnetic and polar
interaction cases in the mean-field theory. We find that the dynamics of system
magnetization can be tuned between the Josephson-like oscillation similar to
the case of double well, and the interesting self-trapping regimes, i.e. the
spin mixing dynamics sustains a spontaneous magnetization. Meanwhile the
dynamics of $\rho_0$ may be sufficiently suppressed for initially imbalanced
number distribution in the case of polar interaction. A ""beat-frequency""
oscillation of the magnetization emerges in the case of balanced initial
distribution for polar interaction, which vanishes for ferromagnetic
interaction.",1105.0280v1
2012-03-24,Non-perturbative Dynamical Decoupling Control: A Spin Chain Model,"This paper considers a spin chain model by numerically solving the exact
model to explore the non-perturbative dynamical decoupling regime, where an
important issue arises recently (J. Jing, L.-A. Wu, J. Q. You and T. Yu,
arXiv:1202.5056.). Our study has revealed a few universal features of
non-perturbative dynamical control irrespective of the types of environments
and system-environment couplings. We have shown that, for the spin chain model,
there is a threshold and a large pulse parameter region where the effective
dynamical control can be implemented, in contrast to the perturbative
decoupling schemes where the permissible parameters are represented by a point
or converge to a very small subset in the large parameter region admitted by
our non-perturbative approach. An important implication of the non-perturbative
approach is its flexibility in implementing the dynamical control scheme in a
experimental setup. Our findings have exhibited several interesting features of
the non-perturbative regimes such as the chain-size independence, pulse
strength upper-bound, noncontinuous valid parameter regions, etc. Furthermore,
we find that our non-perturbative scheme is robust against randomness in model
fabrication and time-dependent random noise.",1203.5400v1
2012-03-29,Facilitated spin models of dissipative quantum glasses,"We introduce a class of dissipative quantum spin models with local
interactions and without quenched disorder that show glassy behaviour. These
models are the quantum analogs of the classical facilitated spin models. Just
like their classical counterparts, quantum facilitated models display complex
glassy dynamics despite the fact that their stationary state is essentially
trivial. In these systems, dynamical arrest is a consequence of kinetic
constraints and not of static ordering. These models display a quantum version
of dynamic heterogeneity: the dynamics towards relaxation is spatially
correlated despite the absence of static correlations. Associated dynamical
fluctuation phenomena such as decoupling of timescales is also observed.
Moreover, we find that close to the classical limit quantum fluctuations can
enhance glassiness, as recently reported for quantum liquids.",1203.6585v1
2013-06-05,Dynamical structure factor of triangular-lattice antiferromagnet,"We elucidate the role of magnon interaction and spontaneous decays in the
spin dynamics of the triangular-lattice Heisenberg antiferromagnet by
calculating its dynamical structure factor within the spin-wave theory.
Explicit theoretical results for neutron-scattering intensity are provided for
spins S=1/2 and S=3/2. The dynamical structure factor exhibits unconventional
features such as quasiparticle peaks broadened by decays, non-Lorentzian
lineshapes, and significant spectral weight redistribution to the two-magnon
continuum. This rich excitation spectrum illustrates the complexity of the
triangular-lattice antiferromagnet and provides distinctive qualitative and
quantitative fingerprints for experimental observation of decay-induced magnon
dynamics.",1306.1231v3
2013-10-15,Noise-resilient quantum evolution steered by dynamical decoupling,"Realistic quantum computing is subjected to noise. A most important frontier
in research of quantum computing is to implement noise-resilient quantum
control over qubits. Dynamical decoupling can protect coherence of qubits. Here
we demonstrate non-trivial quantum evolution steered by dynamical decoupling
control, which automatically suppresses the noise effect. We designed and
implemented a self-protected controlled-NOT gate on the electron spin of a
nitrogen-vacancy centre and a nearby carbon-13 nuclear spin in diamond at room
temperature, by employing an engineered dynamical decoupling control on the
electron spin. Final state fidelities of 0.91 and 0.88 were observed even with
imperfect initial states. In the mean time, the qubit coherence time has been
elongated by at least 30 folds. The design scheme does not require that the
dynamical decoupling control commute with the qubit interaction and works for
general systems. This work marks a step toward realistic quantum computing.",1310.4120v1
2013-10-29,Group field theory as the 2nd quantization of Loop Quantum Gravity,"We construct a 2nd quantized reformulation of canonical Loop Quantum Gravity
at both kinematical and dynamical level, in terms of a Fock space of spin
networks, and show in full generality that it leads directly to the Group Field
Theory formalism. In particular, we show the correspondence between canonical
LQG dynamics and GFT dynamics leading to a specific GFT model from any
definition of quantum canonical dynamics of spin networks. We exemplify the
correspondence of dynamics in the specific example of 3d quantum gravity. The
correspondence between canonical LQG and covariant spin foam models is obtained
via the GFT definition of the latter.",1310.7786v2
2015-07-21,Probing molecular dynamics at the nanoscale via an individual paramagnetic center,"Understanding the dynamics of molecules adsorbed to surfaces or confined to
small volumes is a matter of increasing scientific and technological
importance. Here, we demonstrate a pulse protocol using individual paramagnetic
nitrogen vacancy (NV) centers in diamond to observe the time evolution of 1H
spins from organic molecules located a few nanometers from the diamond surface.
The protocol records temporal correlations among the interacting 1H spins, and
thus is sensitive to the local system dynamics via its impact on the nuclear
spin relaxation and interaction with the NV. We are able to gather information
on the nanoscale rotational and translational diffusion dynamics by carefully
analyzing the time dependence of the NMR signal. Applying this technique to
various liquid and solid samples, we find evidence that liquid samples form a
semi-solid layer of 1.5 nm thickness on the surface of diamond, where
translational diffusion is suppressed while rotational diffusion remains
present. Extensions of the present technique could be adapted to highlight the
chemical composition of molecules tethered to the diamond surface or to
investigate thermally or chemically activated dynamical processes such as
molecular folding.",1507.05921v1
2016-01-29,Spin torque driven dynamics of a coupled two layer structure: interplay between conservative and dissipative coupling,"In this manuscript the general concepts of spin wave theory are adapted to
the dynamics of a self-polarized system based on two layers coupled via
interlayer exchange (conservative coupling) and mutual spin torque (dissipative
coupling). An analytical description of the non-linear dynamics is proposed and
validated through numerical simulations. In contrast to the single layer model,
the phase equation of the coupled system has a contribution coming from the
dissipative part of the LLGS equation. It is shown that this is a major
contribution to the frequency mandatory to describe well the most basic
features of the dynamics of coupled systems. Using the proposed model a
specific feature of coupled dynamics is addressed: the redshift to blueshift
transition observed in the frequency current dependence of this kind of
exchange coupled systems upon increasing the applied field. It is found that
the blueshift regime can only occur in a region of field where the two linear
eigenmodes contribute equally to the steady state mode (i.e. high mode
hybridization). Finally, a general perturbed Hamiltonian equation for the
coupled system is proposed.",1601.08150v1
2016-03-27,"A Model of Charge Transfer Excitons: Diffusion, Spin Dynamics, and Magnetic Field Effects","In this letter we explore how the microscopic dynamics of charge transfer
(CT) excitons are influenced by the presence of an external magnetic field in
disordered molecular semiconductors. This influence is driven by the dynamic
interplay between the spin and spatial degrees of freedom of the electron-hole
pair. To account for this interplay we have developed a numerical framework
that combines a traditional model of quantum spin dynamics with a
coarse-grained model of stochastic charge transport. This combination provides
a general and efficient methodology for simulating the effects of magnetic
field on CT state dynamics, therefore providing a basis for revealing the
microscopic origin of experimentally observed magnetic field effects. We
demonstrate that simulations carried out on our model are capable of
reproducing experimental results as well as generating theoretical predictions
related to the efficiency of organic electronic materials.",1603.08160v2
2016-06-22,Thermally induced magnetic relaxation in square artificial spin ice,"The properties of natural and artificial assemblies of interacting elements,
ranging from Quarks to Galaxies, are at the heart of Physics. The collective
response and dynamics of such assemblies are dictated by the intrinsic
dynamical properties of the building blocks, the nature of their interactions
and topological constraints. Here we report on the relaxation dynamics of the
magnetization of artificial assemblies of mesoscopic spins. In our model
nano-magnetic system - square artificial spin ice - we are able to control the
geometrical arrangement and interaction strength between the magnetically
interacting building blocks by means of nano-lithography. Using time resolved
magnetometry we show that the relaxation process can be described using the
Kohlrausch law and that the extracted temperature dependent relaxation times of
the assemblies follow the Vogel-Fulcher law. The results provide insight into
the relaxation dynamics of mesoscopic nano-magnetic model systems, with
adjustable energy and time scales, and demonstrates that these can serve as an
ideal playground for the studies of collective dynamics and relaxations.",1606.06899v1
2016-10-25,Quantum spin dynamics in Fock space following quenches: Caustics and vortices,"Caustics occur widely in dynamics and take on shapes classified by
catastrophe theory. At finite wavelengths they produce interference patterns
containing networks of vortices (phase singularities). Here we investigate
caustics in quantized fields, focusing on the collective dynamics of quantum
spins. We show that, following a quench, caustics are generated in the Fock
space amplitudes specifying the many-body configuration and which are
accessible in experiments with cold atoms, ions or photons. The granularity of
quantum fields removes all singularities, including phase singularities,
converting point vortices into nonlocal vortices that annihilate in pairs as
the quantization scale is increased. Furthermore, the continuous scaling laws
of wave catastrophes are replaced by discrete versions. Such `quantum
catastrophes' are expected to be universal dynamical features of quantized
fields.",1610.08031v2
2017-03-09,Dynamics and inertia of a skyrmion in chiral magnets and interfaces: A linear response approach based on magnon excitations,"Taking all the magnon modes into account, we derive the skyrmion dynamics in
response to a weak external drive. A skyrmion has rotational symmetry and the
magnon modes can be characterized by an angular momentum. For a weak distortion
of a skyrmion, only the magnon modes with an angular momentum $|m|=1$ govern
the dynamics of skyrmion topological center. The skyrmion inertia is determined
by the magnon modes in the continuum spectrum. For a skyrmion driven by a
magnetic field gradient or by a spin transfer torque generated by a current,
the dynamical response is practically instantaneous. This justifies the rigid
skyrmion approximation used in Thiele's collective coordinate approach. For a
skyrmion driven by a spin Hall torque, the torque couples to the skyrmion
motion through the magnons in the continuum and damping, therefore the skyrmion
dynamics shows sizable inertia in this case. The trajectory of a skyrmion is an
ellipse for an ac drive of spin Hall torque.",1703.03099v2
2008-07-18,Microscopic approach to current-driven domain wall dynamics,"This review describes in detail the essential techniques used in microscopic
theories on spintronics. We have investigated the domain wall dynamics induced
by electric current based on the $s$-$d$ exchange model. The domain wall is
treated as rigid and planar and is described by two collective coordinates: the
position and angle of wall magnetization. The effect of conduction electrons on
the domain wall dynamics is calculated in the case of slowly varying spin
structure (close to the adiabatic limit) by use of a gauge transformation. The
spin-transfer torque and force on the wall are expressed by Feynman diagrams
and calculated systematically using non-equilibrium Green's functions, treating
electrons fully quantum mechanically. The wall dynamics is discussed based on
two coupled equations of motion derived for two collective coordinates. The
force is related to electron transport properties, resistivity, and the Hall
effect. Effect of conduction electron spin relaxation on the torque and wall
dynamics is also studied.",0807.2894v2
2018-10-10,Magnetization Dynamics,"Magnetism primarily describes the physics and materials science of systems
presenting a magnetization -- a macroscopic order parameter characterizing
electron angular momentum. The order parameter is associated with the
electronic exchange interactions, which is fundamentally quantum mechanical.
Its dynamic behavior bridges the macroscopic and the microscopic worlds. On
macroscopic length and time-scales, it interacts with electromagnetic fields
dictated by the Maxwells equations. On a microscopic scale, it involves the
quantum-mechanical electronic states both in spin-space and momentum space,
thus giving rise to a wide range of behavior that extend down to femtoseconds.
Thanks to the development of modern metrology, there have been many new and
noteworthy observations of magnetism-related phenomena across the entire range
-- from spin-torque induced antidamping dynamics, to ultrafast laser induced
femtosecond electron dynamics that involve spin current and angular momentum
conservation. In this review we introduce some observations on magnetodynamics,
and the scientific subjects these new results give rise to.",1810.04591v1
2019-09-26,Glassy dynamics in a disordered Heisenberg quantum spin system,"Understanding the dynamics of strongly interacting disordered quantum systems
is one of the most challenging problems in modern science, due to features such
as the breakdown of thermalization and the emergence of glassy phases of
matter. We report on the observation of anomalous relaxation dynamics in an
isolated XXZ quantum spin system realized by an ultracold gas of atoms
initially prepared in a superposition of two-different Rydberg states. The
total magnetization is found to exhibit sub-exponential relaxation analogous to
classical glassy dynamics, but in the quantum case this relaxation originates
from the build-up of non-classical correlations. In both experiment and
semi-classical simulations, we find the evolution towards a randomized state is
independent of the strength of disorder up to a critical value. This hints
towards a unifying description of relaxation dynamics in disordered isolated
quantum systems, analogous to the generalization of statistical mechanics to
out-of-equilibrium scenarios in classical spin glasses.",1909.11959v3
2019-09-26,Non-equilibrium criticality in quench dynamics of infinite-range spin models,"Long-range interacting spin systems are ubiquitous in physics and exhibit a
variety of ground state disorder-to-order phase transitions. We consider a
prototype of infinite-range interacting models known as the
Lipkin-Meshkov-Glick (LMG) model describing the collective interaction of $N$
spins, and investigate the dynamical properties of fluctuations and
correlations after a sudden quench of the Hamiltonian. Specifically, we focus
on critical quenches, where the initial state and/or the quench Hamiltonian are
critical. Depending on the type of quench, we identify three distinct behaviors
where both the short-time dynamics and the stationary state at long times are
effectively thermal, quantum, and genuinely non-equilibrium, characterized by
distinct universality classes and static and dynamical critical exponents.
These behaviors can be identified by an infrared effective temperature that is
finite, zero, and infinite (the latter scaling with the system size as
$N^{1/3}$), respectively. The quench dynamics is studied through a combination
of exact numerics and analytical calculations utilizing the non-equilibrium
Keldysh field theory. Our results are amenable to realization in experiments
with trapped-ion experiments where long-range interactions naturally arise.",1909.12311v1
2020-02-07,Laser pulse driven control of charge and spin order in the two-dimensional Kondo lattice,"Fast and dynamical control of quantum phases is highly desired in the
application of quantum phenomena in devices. On the experimental side,
ultrafast laser pulses provide an ideal platform to induce femtosecond dynamics
in a variety of materials. Here, we show that a laser pulse driven heavy
fermion system, can be tuned to dynamically evolve into a phase, which is not
present in equilibrium. Using the state-of-the-art time-dependent variational
Monte Carlo method, we perform numerical simulations of realistic laser pulses
applied to the Kondo Lattice model. By tracking spin and charge degrees of
freedom we identify a dynamical phase transition from a charge ordered into a
metallic state, while preserving the spin order of the system. We propose to
use higher harmonic generation to identify the dynamical phase transition in an
ultrafast experiment.",2002.03023v1
2021-01-26,Nonergodic dynamics in disorder-free potentials,"We review the dynamics of interacting particles in disorder-free potentials
concentrating on a combination of a harmonic binding with a constant tilt. We
show that a simple picture of an effective local tilt describes a variety of
cases. Our examples include spinless fermions (as modeled by Heisenberg spin
chain in a magnetic field), spinful fermions as well as bosons that enjoy a
larger local on-site Hilbert space. We also discuss the domain-wall dynamics
that reveals nonergodic features even for a relatively weak tilt as suggested
by Doggen et. al. [arXiv:2012.13722]. By adding a harmonic potential on top of
the static field we confirm that the surprizing regular dynamics is not
entirely due to Hilbert space shuttering. It seems better explained by the
inhibited transport within the domains of identically oriented spins. Once the
spin-1/2 restrictions are lifted as, e.g., for bosons, the dynamics involve
stronger entanglement generation. Again for domain wall melting, the effect of
the harmonic potential is shown to lead mainly to an effective local tilt.",2101.11061v2
2019-02-19,Spin bath dynamics and dynamical Renormalization Group,"Abstract We discuss the quantum dynamics of the central spin model in a
regime where the central spin and bath are slaved to each other. The exact
solution is found when the bath is static, and is compared with the effect of
an external field, finding that they are inequivalent due to the quantum nature
of the environment. When the bath has dynamics, we analyze the differences
between the numerical simulation using time-dependent perturbation theory and
the equation of motion technique, which shows better accuracy. We demonstrate
that the use of dynamical Renormalization Group (dRG), simultaneously with the
equation of motion technique, provides a suitable analytical tool to understand
the physics, to capture the main physical processes, and a powerful method to
eliminate secular terms. In addition, this approach allows to separate
classical non-linear behavior from corrections due to quantum correlations.",1902.07338v2
2020-11-10,Ultrafast high-harmonic nanoscopy of magnetization dynamics,"Light-induced magnetization changes, such as all-optical switching, skyrmion
nucleation, and intersite spin transfer, unfold on temporal and spatial scales
down to femtoseconds and nanometers, respectively. Pump-probe spectroscopy and
diffraction studies indicate that spatio-temporal dynamics may drastically
affect the non-equilibrium magnetic evolution. Yet, direct real-space magnetic
imaging on the relevant timescale has remained challenging. Here, we
demonstrate ultrafast high-harmonic nanoscopy employing circularly polarized
high-harmonic radiation for real-space imaging of femtosecond magnetization
dynamics. We observe the reversible and irreversible evolution of nanoscale
spin textures following femtosecond laser excitation. Specifically, we map
quenched magnetic domains and localized spin structures in Co/Pd multilayers
with a sub-wavelength spatial resolution down to 16 nm, and strobosocopically
trace the local magnetization dynamics with 40 fs temporal resolution. Our
approach enables the highest spatio-temporal resolution of magneto-optical
imaging to date. Facilitating ultrafast imaging with an extreme sensitivity to
various microscopic degrees of freedom expressed in chiral and linear
dichroism, we envisage a wide range of applications spanning magnetism, phase
transitions, and carrier dynamics.",2011.05450v1
2022-05-12,Dynamics and entanglement in quantum and quantum-classical systems: lessons for gravity,"Motivated by quantum gravity, semi-classical theory, and quantum theory on
curved spacetimes, we study the system of an oscillator coupled to two spin-1/2
particles. This model provides a prototype for comparing three types of
dynamics: the full quantum theory, the classical oscillator with spin
backreaction, and spins propagating on a fixed oscillator background. From
nonperturbative calculations of oscillator and entanglement entropy dynamics,
we find that entangled tripartite states produce novel oscillator trajectories,
and that the three systems give equivalent dynamics for sufficiently weak
oscillator-spin couplings, but deviate significantly for intermediate
couplings. These results suggest that semiclassical dynamics with back reaction
does not provide a suitable intermediate regime between quantum gravity and
quantum theory on curved spacetime.",2205.06388v2
2023-01-26,Generalised Jeffery's equations for rapidly spinning particles. Part 1: Spheroids,"The observed behaviour of passive objects in simple flows can be surprisingly
intricate, and is complicated further by object activity. Inspired by the
motility of bacterial swimmers, in this two-part study we examine the
three-dimensional motion of rigid active particles in shear Stokes flow,
focusing on bodies that induce rapid rotation as part of their activity. Here,
in Part 1, we develop a multiscale framework to investigate these emergent
dynamics and apply it to simple spheroidal objects. In Part 2
(arXiv:2301.11032), we apply our framework to understand the emergent dynamics
of more complex shapes; helicoidal objects with chirality. Via a
multiple-scales asymptotic analysis for nonlinear systems, we systematically
derive emergent equations of motion for long-term trajectories that explicitly
account for the strong (leading-order) effects of fast spinning. Supported by
numerical examples, we constructively link these effective dynamics to the
well-known Jeffery's orbits for passive spheroids, deriving an explicit
closed-form expression for the effective shape of the active particle,
broadening the scope of Jeffery's seminal study to spinning spheroids.",2301.11311v3
2023-06-09,Interplay between Markovianity and Progressive Quenching,"Progressive quenching (PQ) is a process in which we sequentially fix a
system's degrees of freedom, which would otherwise evolve according to their
stochastic dynamics. Previous studies have discovered what we refer to as the
hidden martingale property in PQ. Here, we first attribute this martingale
property to the canonicity of the two-layer ensemble comprising quenched and
thermal ensembles and demonstrate that the Markovian property, coupled with the
detailed balance (DB) of the evolution dynamics, underpins this canonicity. We
then expand the PQ to the Markovian dynamics on the transition network where
the DB is locally upheld. Additionally, we examine the PQ of the systems that
evolve through non-Markovian dynamics between consecutive quenching. When
non-Markovian dynamics ensure a trajectory-wise DB, such as in an equilibrium
spin system with a hidden part, the PQ can occasionally maintain the canonical
structure of the overall statistical ensemble, but not always. Lastly, we
analytically and numerically investigate the PQ of a non-Markovian spin system
with delayed interaction and illustrate how the reduction of spin correlations
due to the delay can be compensated by the PQ.",2306.05831v2
2023-11-15,Probing Iron in Earth's Core With Molecular-Spin Dynamics,"Dynamic compression of iron to Earth-core conditions is one of the few ways
to gather important elastic and transport properties needed to uncover key
mechanisms surrounding the geodynamo effect. Herein a new machine-learned
ab-initio derived molecular-spin dynamics (MSD) methodology with explicit
treatment for longitudinal spin-fluctuations is utilized to probe the dynamic
phase-diagram of iron. This framework uniquely enables an accurate resolution
of the phase-transition kinetics and Earth-core elastic properties, as
highlighted by compressional wave velocity and adiabatic bulk moduli
measurements. In addition, a unique coupling of MSD with time-dependent density
functional theory enables gauging electronic transport properties, critically
important for resolving geodynamo dynamics.",2311.08737v1
2024-02-27,Expansion dynamics of Bose-Einstein condensates in a synthetic magnetic field,"We investigate the expansion dynamics of spin-orbit-coupled Bose-Einstein
condensates subjected to a synthetic magnetic field, after their release from
an external harmonic trap. Our findings reveal that the condensate experiences
a spin-dependent rotation and separation due to the rigid-like rotational
velocity field, which leads to a spin density deflection. The deflection angle
reaches a peak at a time that is inversely related to the frequency of the
harmonic trap. When the detuning gradient is below a critical value for vortex
nucleation, our analytical results derived from a spinor hydrodynamic theory
align closely with numerical results using the coupled Gross-Pitaevskii
equations. Beyond this critical value, we also numerically simulated the
expansion dynamics of the condensates containing vortices with negative
circulation. Our findings highlight the pivotal role of the rigid-like
rotational velocity field on the dynamics of the condensate and may stimulate
further experimental investigations into the rich superfluid dynamics induced
by synthetic magnetic fields.",2402.17691v1
2001-11-01,Exact Persistence Exponent for One-dimensional Potts Models with Parallel Dynamics,"We obtain \theta_p(q) = 2\theta_s(q) for one-dimensional q-state
ferromagnetic Potts models evolving under parallel dynamics at zero temperature
from an initially disordered state, where \theta_p(q) is the persistence
exponent for parallel dynamics and \theta_s(q) = -{1/8}+
\frac{2}{\pi^2}[cos^{-1}{(2-q)/q\sqrt{2}}]^2 [PRL, {\bf 75}, 751, (1995)], the
persistence exponent under serial dynamics. This result is a consequence of an
exact, albeit non-trivial, mapping of the evolution of configurations of Potts
spins under parallel dynamics to the dynamics of two decoupled reaction
diffusion systems.",0111013v1
2005-01-31,Voter Dynamics on an Ising Ladder: Coarsening and Persistence,"Coarsening and persistence of Ising spins on a ladder is examined under voter
dynamics. The density of domain walls decreases algebraically with time as
$t^-{1/2}$ for sequential as well as parallel dynamics. The persistence
probability decreases as $t^{-\theta_{s}}$ under sequential dynamics, and as
$t^{-\theta_{p}}$ under parallel dynamics where $\theta_{p} = 2 \theta_{s}
\approx .88$. Numerical values of the exponents are explained. The results are
compared with the voter model on one and two dimensional lattices, as well as
Ising model on a ladder under zero-temperature Glauber dynamics.",0501754v2
2005-02-17,Onset of slow dynamics in difluorotetrachloroethane glassy crystal,"Complementary Neutron Spin Echo and X-ray experiments and Molecular Dynamics
simulations have been performed on difluorotetrachloroethane (CFCl2-CFCl2)
glassy crystal. Static, single-molecule reorientational dynamics and collective
dynamics properties are investigated. The orientational disorder is
characterized at different temperatures and a change in nature of rotational
dynamics is observed. We show that dynamics can be described by some scaling
predictions of the Mode Coupling Theory (MCT) and a critical temperature
$T_{c}$ is determined. Our results also confirm the strong analogy between
molecular liquids and plastic crystals for which $\alpha$-relaxation times and
non-ergodicity parameters are controlled by the non trivial static correlations
as predicted by MCT.",0502416v1
2007-09-06,Dynamic Multiscaling in Turbulence,"We give an overview of the progress that has been made in recent years in
understanding the dynamic multiscaling of homogeneous, isotropic turbulence and
related problems. We emphasise the similarity of this problem with the dynamic
scaling of time-dependent correlation functions in the vicinity of a critical
point in, e.g., a spin system. The universality of dynamic-multiscaling
exponents in fluid turbulence is explored by detailed simulations of the GOY
shell model for fluid turbulence.",0709.0893v1
2017-05-30,Perturbative Dynamics of Open Quantum Systems by Renormalization Group Method,"We analyze perturbative dynamics of a composite system consisting of a
quantum mechanical system and an environment by the renormalization group (RG)
method. The solution obtained from the RG method has no secular terms and
approximates the exact solution for a long time interval. Moreover, the RG
method causes a reduction of the dynamics of the composite system under some
assumptions. We show that this reduced dynamics is closely related to a quantum
master equation for the quantum mechanical system. Then, we compare this
dynamics with the exact dynamics in an exactly solvable spin-boson model.",1705.10522v1
2023-10-07,Baxterization for the dynamical Yang-Baxter equation,"The Baxterization process for the dynamical Yang-Baxter equation is studied.
We introduce the local dynamical Hecke ,Temperley-Lieb and
Birman-Murakami-Wenzl operators, then by inserting spectral parameters, from
each representation of these operators, we get dynamical R matrix under some
conditions. As applications, we reformulate trigonometric degeneration of
elliptic quantum group representations and also get dynamical R matrix for
critical ADE integrable lattice models. Through Baxterization, we construct
some one dimensional integrable systems that are dynamical version of the
Heisenberg spin chain.",2310.04728v2
2023-10-18,"Mean-field dynamics of an infinite-range interacting quantum system: chaos, dynamical phase transition, and localisation","We investigate the dynamical properties of the XY spin 1/2 chain with
infinite-range transverse interactions and find a dynamical phase transition
with a chaotic dynamical phase. In the latter, we find non-vanishing
finite-time Lyapunov exponents and intermittent behavior signaled by fast and
slow entropy growth periods. Further, we study the XY chain with a local
self-consistent transverse field and observe a localization phase transition.
We show that localization stabilizes the chaotic dynamical phase.",2310.11947v2
2024-02-03,Finite temperature dynamics in a polarized sub-Ohmic heat bath: a hierarchical equations of motion-tensor train study,"Dynamics of the sub-Ohmic spin-boson model under polarized initial conditions
at finite temperature is investigated by employing both analytical tools and
the numerically accurate hierarchical equations of motion-tensor train method.
By analyzing the features of nonequilibrium dynamics, we discovered a
bifurcation phenomenon which separates two regimes of the dynamics. It is found
that before the bifurcation time, increasing temperature slows down the
population dynamics, while the opposite effect occurs after the bifurcation
time. The dynamics is highly sensitive to both initial preparation of the bath
and thermal effects.",2402.02138v1
1995-01-27,Fractal Spectrum of a Quasi_periodically Driven Spin System,"We numerically perform a spectral analysis of a quasi-periodically driven
spin 1/2 system, the spectrum of which is Singular Continuous. We compute
fractal dimensions of spectral measures and discuss their connections with the
time behaviour of various dynamical quantities, such as the moments of the
distribution of the wave packet. Our data suggest a close similarity between
the information dimension of the spectrum and the exponent ruling the algebraic
growth of the 'entropic width' of wavepackets.",9501013v1
1995-06-29,Theory for the Interdependence of High-T$_c$ Superconductivity and Dynamical Spin Fluctuations,"The doping dependence of the superconducting state for the 2D one-band
Hubbard Hamiltonian is determined. By using an Eliashberg-type theory, we find
that the gap function $\Delta_{\bf k}$ has a $d_{x^2-y^2}$ symmetry in momentum
space and T$_c$ becomes maximal for $13 \; \%$ doping. Since we determine the
dynamical excitations directly from real frequency axis calculations, we obtain
new structures in the angular resolved density of states related to the
occurrence of {\it shadow states} below T$_c$. Explaining the anomalous
behavior of photoemission and tunneling experiments in the cuprates, we find a
strong interplay between $d$-wave superconductivity and dynamical spin
fluctuations.",9506136v1
1995-10-13,Phase space geometry and slow dynamics,"We describe a non-Arrhenius mechanism for slowing down of dynamics that is
inherent to the high dimensionality of the phase space. We show that such a
mechanism is at work both in a family of mean-field spin-glass models without
any domain structure and in the case of ferromagnetic domain growth. The
marginality of spin-glass dynamics, as well as the existence of a `quasi
equilibrium regime' can be understood within this scenario. We discuss the
question of ergodicity in an out-of equilibrium situation.",9510079v1
1996-04-29,Percolation and cluster Monte Carlo dynamics for spin models,"A general scheme for devising efficient cluster dynamics proposed in a
previous letter [Phys.Rev.Lett. 72, 1541 (1994)] is extensively discussed. In
particular the strong connection among equilibrium properties of clusters and
dynamic properties as the correlation time for magnetization is emphasized. The
general scheme is applied to a number of frustrated spin model and the results
discussed.",9604169v1
1996-07-31,Slow dynamics and aging in spin-glasses,"Contribution presented by Eric Vincent in the Conference `Complex Behaviour
of Glassy Systems', Sitges, Barcelona, Spain, June, 1996. It contains a review
of the experimental results on Slow dynamics and aging in spin-glasses. It also
presents their comparison with recent theoretical developments in the
description of the out of equilibrium dynamics of disordered systems; namely,
the trap model and the mean-field theory.",9607224v1
1997-03-26,Spreading of Damage in the SK Spherical Spin Glass,"By considering the Langevin dynamics of the SK spin glass with a spherical
constraint we calculate the asymptotic distance between two real replicas that
evolve with the same thermal noise from different initial conditions. Despite
the simplicity of the model its dynamics is known to be non trivial and
presents aging phenomena. We find that the asymptotic distance between two
replicas is maximal for a whole family of initial conditions that are
arbitrarily close at t=0 . The asymptotic distance presents a dynamical
transition at a temperature equal to the static phase transition one.",9703225v1
1997-04-07,Study of the ultrametric structure of Finite Dimensional Spin Glasses throught a constrained Monte Carlo dynamics,"We report a very detailed relation about the study, by a constrained Monte
Carlo dynamic, of a 4D EA spin glass model (J=+/- 1). In particular we
concentrate our attention on the behaviour of the system under different bounds
imposed in order to optimize the dynamic and try to understand the low energy
states structure. We find that in the thermodynamic limit this structure is
clearly ultrametric as already established for the SK model.",9704053v1
1998-08-17,Competing Glauber and Kawasaki Dynamics,"Using a quantum formulation of the master equation we study a kinetic Ising
model with competing stochastic processes: the Glauber dynamics with
probability $p$ and the Kawasaki dynamics with probability $1 - p$. Introducing
explicitely the coupling to a heat bath and the mutual static interaction of
the spins the model can be traced back exactly to a Ginzburg Landau functional
when the interaction is of long range order. The dependence of the correlation
length on the temperature and on the probability $p$ is calculated. In case
that the spins are subject to flip processes the correlation length disappears
for each finite temperature. In the exchange dominated case the system is
strongly correlated for each temperature.",9808172v1
1999-04-15,Instantons in the Langevin dynamics: an application to spin glasses,"We develop a general technique to calculate the probability of transitions
over the barriers in spin-glasses in the framework of the dynamical theory. We
use Lagrangian formulation of the instanton dynamics in which the transitions
are represented by instantons. We derive the full set of the equations that
determine the instantons but instead of solving them directly we prove that an
instanton process can be mapped into a usual process going back in time which
simplifies the problem significantly. We apply this general considerations to a
simple example of the spherical Sherrington-Kirkpatrick model and we find the
probability of the transition between the metastable states which is in
agreement with physical expectations.",9904219v1
1999-04-22,"Comment on ""Numerical Study on Aging Dynamics in the 3D Ising Spin Glass Model""","We show that the dynamical behavior of the 3D Ising spin glass with Gaussian
couplings is not compatible with a droplet dynamics. We show that this is
implied from the data of reference cond-mat/9904143, that, when analyzed in an
accurate way, give multiple evidences of this fact. Our study is based on the
analysis of the overlap-overlap correlation function, at different values of
the separation r and of the time t.",9904321v1
1999-09-10,Advanced Dynamic Algorithms for the Decay of Metastable Phases in Discrete Spin Models: Bridging Disparate Time Scales,"An overview of advanced dynamical algorithms capable of spanning the widely
disparate time scales that govern the decay of metastable phases in discrete
spin models is presented. The algorithms discussed include constrained
transfer-matrix, Monte Carlo with Absorbing Markov Chains (MCAMC), and
projective dynamics (PD) methods. The strengths and weaknesses of each of these
algorithms are discussed, with particular emphasis on identifying the parameter
regimes (system size, temperature, and field) in which each algorithm works
best.",9909158v1
1999-09-22,The Critical Exponent $θ'$ in Spin Glasses,"Short-time dynamic scaling behavior of the 3D $\pm J$ Ising spin glass is
studied by Monte Carlo methods. Starting the replicas with independent initial
configurations with a small pseudo magnetization, the dynamic evolution of the
overlap q(t) between two replicas is measured. The initial increase of the
overlap q(t) is observed and the corresponding exponent $\theta'$ is obtained.
  From the scaling relation $\lambda =d/z-\theta'$, the dynamic exponent z is
estimated.",9909325v1
2000-04-10,Charge dynamics in doped triangular antiferromagnets,"Within the framework of the fermion-spin theory based on the charge-spin
separation, the charge dynamics of the doped antiferromagnet on a triangular
lattice is studied. The holon part is treated by using the loop expansion to
the second order. It is shown that the charge dynamics is mainly caused by
charged holons moving in the background of spinon excitations. The optical
conductivity spectrum shows an unusual behavior at low energies and an
anomalous midinfrared band, while the resistivity exhibits a nonlinearity in
temperatures.",0004130v1
2000-05-29,Dynamically Induced Multi-Channel Kondo Effect,"We study how the multi-channel Kondo effect is dynamically induced to affect
the photoemission and the inverse photoemission spectrum when an electron is
emitted from (or added to) the completely screened Kondo impurity with spin
$S>1/2$. The spectrum thereby shows a power-law edge singularity characteristic
of the multi-channel Kondo model. We discuss this anomalous behavior by using
the exact solution of the multi-channel Kondo model and boundary conformal
field theory. The idea is further applied to the photoemission for quantum spin
systems, in which the edge singularity is controlled by the dynamically induced
overscreening effect with a mobile Kondo impurity.",0005495v1
2000-10-31,Dynamic ultrametricity in finite dimensional spin glasses,"We show results of simulations of a weakly driven four dimensional Edwards-
Anderson spin glass, which presents clear signatures of dynamical
ultrametricity at low temperatures. The presence of a hierarchical organization
of time scales is evident from the appearance of a triangular relation between
correlations at three characteristic long times in the asymptotic limit of
small drive, and also in the scaling form of stationary correlations in this
regime. The differences between this scenario and known results of the aging
dynamics of the model are also analyzed.",0010495v2
2002-11-19,Quantum dot ground state energies and spin polarizations: soft versus hard chaos,"We consider how the nature of the dynamics affects ground state properties of
ballistic quantum dots. We find that ``mesoscopic Stoner fluctuations'', that
arise from the residual screened Coulomb interaction, are very sensitive to the
degree of chaos. It leads to ground state energies and spin-polarizations whose
fluctuations strongly increase as a system becomes less chaotic. The crucial
features are illustrated with a model that depends on a parameter that tunes
the dynamics from nearly integrable to mostly chaotic.",0211412v1
2003-02-11,Monte Carlo Study of Four-Spinon Dynamic Structure Function in Antiferromagnetic Heisenberg Model,"Using Monte Carlo integration methods, we describe the behavior of the exact
four-spinon dynamic structure function $S_{4}$ in the antiferromagnetic spin
1/2 Heisenberg quantum spin chain as a function of the neutron energy $\omega$
and momentum transfer $k$. We also determine the four-spinon continuum, the
extent of the region in the $(k,\omega)$ plane outside which $S_{4}$ is
identically zero. In each case, the behavior of $S_{4}$ is shown to be
consistent with the four-spinon continuum and compared to the one of the exact
two-spinon dynamic structure function $S_{2}$. Overall shape similarity is
noted.",0302219v1
2003-11-24,Simulating spin-boson dynamics with stochastic Liouville-von Neumann equations,"Based on recently derived exact stochastic Liouville-von Neumann equations,
several strategies for the efficient simulation of open quantum systems are
developed and tested on the spin-boson model. The accuracy and efficiency of
these simulations is verified for several test cases including both coherent
and incoherent dynamics, involving timescales differing by several orders of
magnitude. Using simulations with a time-dependent field, the time evolution of
coherences in the reduced density matrix is investigated. Even in the case of
weak damping, pronounced preparation effects are found. These indicate hidden
coherence in the interacting system which can only be indirectly observed in
the basis of the reduced quantum dynamics.",0311544v1
2004-03-03,Current-Induced Nanomagnet Dynamics for Magnetic Fields Perpendicular to the Sample Plane,"We present electrical measurements of high-frequency magnetic dynamics
excited by spin-polarized currents in Co/Cu/Ni80Fe20 nanopillar devices, with a
magnetic field applied perpendicular to the sample layers. As a function of
current and magnetic field, the dynamical phase diagram contains several
distinguishable precessional modes and also static magnetic states. Using
detailed comparisons with numerical simulations, we provide rigorous tests of
the theory of spin-transfer torques.",0403100v1
2004-12-01,From Large Scale Rearrangements to Mode Coupling Phenomenology,"We consider the equilibrium dynamics of Ising spin models with multi-spin
interactions on sparse random graphs (Bethe lattices). Such models undergo a
mean field glass transition upon increasing the graph connectivity or lowering
the temperature. Focusing on the low temperature limit, we identify the large
scale rearrangements responsible for the dynamical slowing-down near the
transition. We are able to characterize exactly the dynamics near criticality
by analyzing the statistical properties of such rearrangements. Our approach
can be generalized to a large variety of glassy models on sparse random graphs,
ranging from satisfiability to kinetically constrained models.",0412023v2
2005-06-30,Dynamic critical behaviour in Ising spin glasses,"The critical dynamics of Ising spin glasses with Bimodal, Gaussian, and
Laplacian interaction distributions are studied numerically in dimensions 3 and
4. The data demonstrate that in both dimensions the critical dynamic exponent
$z_{\rm c}$, the non-equilibrium autocorrelation decay exponent
$\lambda_c/z_{\rm c}$, and the critical fluctuation-dissipation ratio
$X_{\infty}$ all vary strongly and systematically with the form of the
interaction distribution.",0506795v3
2006-02-28,Statics and dynamics of the Lebwohl-Lasher model in the Bethe approximation,"We study the Lebwohl-Lasher model for systems in which spin are arranged on
random graph lattices. At equilibrium our analysis follows the theory of
spin-systems on random graphs which allows us to derive exact bifurcation
conditions for the phase diagram. We also study the dynamics of this model
using a variant of the dynamical replica theory. Our results are tested against
simulations.",0602666v3
2006-05-25,Time Quantified Monte Carlo Algorithm for Interacting Spin Array Micromagnetic Dynamics,"In this paper, we reexamine the validity of using time quantified Monte Carlo
(TQMC) method [Phys. Rev. Lett. 84, 163 (2000); Phys. Rev. Lett. 96, 067208
(2006)] in simulating the stochastic dynamics of interacting magnetic
nanoparticles. The Fokker-Planck coefficients corresponding to both TQMC and
Langevin dynamical equation (Landau-Lifshitz-Gilbert, LLG) are derived and
compared in the presence of interparticle interactions. The time quantification
factor is obtained and justified. Numerical verification is shown by using TQMC
and Langevin methods in analyzing spin-wave dispersion in a linear array of
magnetic nanoparticles.",0605621v1
2006-08-10,Spin Dynamics of a Magnetic Antivortex,"We report on a study of the dynamics of a magnetic antivortex in a submicron,
asteroid shaped, permalloy ferromagnet using micromagnetic simulations. As with
vortex states in disk and square geometries, a gyrotropic mode was found in
which a shifted antivortex core orbits about the center of the asteroid. Pulsed
magnetic fields were used to generate azimuthal or radial spin wave modes,
depending on the field orientation. The degeneracy of low frequency azimuthal
mode frequencies is lifted by gyrotropic motion of the antivortex core, and
restored by inserting a hole in the center of the particle to suppress this
motion. We briefly compare the dynamics of the vortex state of the asteroid to
the antivortex. The size dependence of the antivortex modes is reported.",0608245v1
2007-03-27,Critical Scattering and Dynamical Scaling in an Heisenberg Ferromagnet Neutron Spin Echo versus Renormalization Group Theory,"High resolution Neutron Spin Echo (NSE) spectroscopy was used to investigate
the dynamics of an 3D Heisenberg ferromagnet in the exchange-controlled regime
over a broad range of temperatures and momentum transfer. These results allow
for the first time an extensive comparison between the experimental dynamical
critical behavior and the predictions of the Renormalization Group (RG) theory.
The agreement is exhaustive and surprising as the RG theory accounts not only
for the critical relaxation but also for the shape crossover towards an
exponential diffusive relaxation when moving from the critical to the
hydrodynamic regime above $T_C$.",0703702v1
1995-05-16,"Orbits, forces and accretion dynamics near spinning black holes","We analyze the relativistic dynamical properties of Keplerian and
non-Keplerian circular orbits in a general axisymmetric and stationary
gravitational field, and discuss the implications for the stability of co- and
counter-rotating accretion disks and tori surrounding a spinning black hole.
Close to the horizon there are orbital peculiarities which can seem
counterintuitive, but are elucidated by formulating the dynamics in terms of
the orbital velocity actually measured by a local, zero-angular-momentum
observer.",9505025v1
2006-12-21,Hyperon-Nucleon Scattering from Fully-Dynamical Lattice QCD,"We present results of the first fully-dynamical lattice QCD determination of
hyperon-nucleon scattering. One s-wave phase shift was determined for n Lambda
scattering in both spin-channels at pion masses of 350, 490, and 590 MeV, and
for n Sigma- scattering in both spin channels at pion masses of 490, and 590
MeV. The calculations were performed with domain-wall valence quarks on
dynamical, staggered gauge configurations with a lattice spacing of b ~ 0.125
fm.",0612026v1
1993-07-20,Ising (anti-)ferromagnet on dynamical triangulations and quadrangulations,"We write down matrix models for Ising spins with zero external field on the
vertices of dynamical triangulated random surfaces (DTRS) and dynamically
quadrangulated random surfaces (DQRS) and compare these with the standard
matrix model approach which places the spins on the dual $\phi^3$ and $\phi^4$
graphs. We show that the critical temperatures calculated in the DTRS and DQRS
models agree with those deduced from duality arguments in the standard
approach. Using the DQRS model we observe that the Ising antiferromagnet still
undergoes a phase transition to a Neel (checkerboard) ordered ground state
which is absent because of frustration in the other cases.",9307125v1
1994-11-28,N-point matrix elements of dynamical vertex operators of the higher spin XXZ model,"We extend the concept of conjugate vertex operators, first introduced by
Dotsenko in the case of the bosonization of the $su(2)$ conformal field theory,
to the bosonization of the dynamical vertex operators (type II in the
classification of the Kyoto school) of the higher spin XXZ model. We show that
the introduction of the conjugate vertex operators leads to simpler expressions
for the N-point matrix elements of the dynamical vertex operators, that is,
without redundant Jackson integrals that arise from the insertion of screening
charges. In particular, the two-point matrix element can be represented without
any integral.",9411207v1
1995-08-17,Twistor Phase Space Dynamics and the Lorentz Force Equation,"Using Lorentz force equation as an input a Hamiltonian mechanics on the
non-projective two twistor phase space TxT is formulated. Such a construction
automatically reproduces dynamics of the intrinsic classical relativistic spin.
The charge appears as a dynamical variable. It is also shown that if the
classical relativistic spin function on TxT vanishes, the natural conformally
invariant symplectic structure on TxT reduces to the natural symplectic
structure on the cotangent bundle of the Kaluza-Klein space.",9508083v1
2005-11-18,Spin Calogero models and dynamical r-matrices,"The main point of the construction of spin Calogero type classical integrable
systems based on dynamical r-matrices, developed by L.-C. Li and P. Xu, is
reviewed. It is shown that non-Abelian dynamical r-matrices with variables in a
reductive Lie algebra ${\cal F}$ and their Abelian counterparts with variables
in a Cartan subalgebra of ${\cal F}$ lead essentially to the same models.",0511059v2
2006-12-06,Chiral pion-nucleon dynamics in finite nuclei: spin-isospin excitations,"The nuclear density functional framework, based on chiral dynamics and the
symmetry breaking pattern of low-energy QCD, is extended to the description of
collective nuclear excitations. Starting from the relativistic point-coupling
Lagrangian previously introduced [Nucl. Phys. A770 (2006) 1], the
proton-neutron (quasiparticle) random phase approximation is formulated and
applied to investigate the role of chiral pion-nucleon dynamics in excitation
modes involving spin and isospin degrees of freedom, e.g. isobaric analog
states and Gamow-Teller resonances.",0612026v2
1999-04-29,Semiclassical dynamics of a spin-1/2 in an arbitrary magnetic field,"The spin coherent state path integral describing the dynamics of a
spin-1/2-system in a magnetic field of arbitrary time-dependence is considered.
Defining the path integral as the limit of a Wiener regularized expression, the
semiclassical approximation leads to a continuous minimal action path with
jumps at the endpoints. The resulting semiclassical propagator is shown to
coincide with the exact quantum mechanical propagator. A non-linear
transformation of the angle variables allows for a determination of the
semiclassical path and the jumps without solving a boundary-value problem. The
semiclassical spin dynamics is thus readily amenable to numerical methods.",9904102v1
2001-01-07,Evolution of entanglement for spin-flip dynamics,"A model of evolution of bipartite quantum state entanglement is studied. It
involves recently introduced quantum block spin-flip dynamics on a lattice. We
find that for initially separable states the considered evolution leads, in
general, to entangled states. We also present a complete characterization of
two-point correlation functions for that type of dynamics to confirm
enhancement of quantum correlations for the considered system.",0101033v3
2004-02-20,Zitterbewegung and semiclassical observables for the Dirac equation,"In a semiclassical context we investigate the Zitterbewegung of relativistic
particles with spin 1/2 moving in external fields. It is shown that the
analogue of Zitterbewegung for general observables can be removed to arbitrary
order in \hbar by projecting to dynamically almost invariant subspaces of the
quantum mechanical Hilbert space which are associated with particles and
anti-particles. This not only allows to identify observables with a
semiclassical meaning, but also to recover combined classical dynamics for the
translational and spin degrees of freedom. Finally, we discuss properties of
eigenspinors of a Dirac-Hamiltonian when these are projected to the almost
invariant subspaces, including the phenomenon of quantum ergodicity.",0402154v1
2005-10-20,Entanglement dynamics for two interacting spins,"We study the dynamical generation of entanglement for a very simple system: a
pair of interacting spins, s1 and s2, in a constant magnetic field. Two
different situations are considered:(a) s1 ->\infty, s2 = 1/2 and (b) s1 = s2
->\infty, corresponding, respectively, to a quantum degree of freedom coupled
to a semiclassical one (a qubit in contact with an environment) and a fully
semiclassical system, which in this case displays chaotic behavior. Relations
between quantum entanglement and classical dynamics are investigated.",0510162v1
2006-10-10,Effective Quantum Dynamics of Interacting Systems with Inhomogeneous Coupling,"We study the quantum dynamics of a single mode/particle interacting
inhomogeneously with a large number of particles and introduce an effective
approach to find the accessible Hilbert space where the dynamics takes place.
Two relevant examples are given: the inhomogeneous Tavis-Cummings model (e.g.,
N atomic qubits coupled to a single cavity mode, or to a motional mode in
trapped ions) and the inhomogeneous coupling of an electron spin to N nuclear
spins in a quantum dot.",0610078v2
2007-09-06,Brownian dynamics of a microswimmer,"We report on dynamic properties of a simple model microswimmer composed of
three spheres and propelling itself in a viscous fluid by spinning motion of
the spheres under zero net torque constraint. At a fixed temperature and
increasing the spinning frequency, the swimmer demonstrates a transition from
dissipation-dominated to a pumping-dominated motion regime characterized by
negative effective friction coefficient. In the limit of high frequencies, the
diffusion of the swimmer can be described by a model of an active particle with
constant velocity.",0709.0792v1
2008-01-09,The limiting nuclear polarization in a quantum dot under optical electron-spin orientation and applicability of the box-model of the electron-nuclear dynamics,"For the model Hamiltonian describing the electron-nuclear dynamics of a
quantum dot, we obtained an exact expression for the limiting nuclear
polarization as a function of the number of groups of equivalent nuclei. It is
shown that the refinement of the model Hamiltonian by increasing the number of
the groups results in a slow growth of the limiting nuclear polarization. This
allowed us to put forward arguments in favor of applicability of the box-model
(with all the nuclei being equivalent) for description of the electron-nuclear
spin dynamics within the time intervals of around hundreds of periods of the
optical orientation.",0801.1391v1
2008-01-19,The invariant manifold approach applied to nonlinear dynamics of a rotor-bearing system,"The invariant manifold approach is used to explore the dynamics of a
nonlinear rotor, by determining the nonlinear normal modes, constructing a
reduced order model and evaluating its performance in the case of response to
an initial condition. The procedure to determine the approximation of the
invariant manifolds is discussed and a strategy to retain the speed dependent
effects on the manifolds without solving the eigenvalue problem for each spin
speed is presented. The performance of the reduced system is analysed in
function of the spin speed.",0801.3020v1
2008-02-12,Dynamical Coupling Between Ferromagnets Due to Spin Transfer Torque,"We use a combination of analytic calculations and numerical simulations to
demonstrate that electrical current flowing through a magnetic bilayer induces
dynamical coupling between the layers. The coupling originates from the
dependence of the spin transfer torque exerted on the layers on the relative
orientations of their magnetic moments. We demonstrate that such coupling
modifies the behaviors of both layers, significantly affecting the the
stability of the current-induced dynamical regimes and the efficiency of
current-induced magnetic reversal.",0802.1560v1
2008-06-21,Limiting Dynamics for Spherical Models of Spin Glasses with Magnetic Field,"We study the Langevin dynamics for the family of spherical spin glass models
of statistical physics, in the presence of a magnetic field. We prove that in
the limit of system size N approaching infinity, the empirical state
correlation, the response function, the overlap and the magnetization for these
N-dimensional coupled diffusions converge to the non-random unique strong
solution of four explicit non-linear integro-differential equations, that
generalize the system proposed by Cugliandolo and Kurchan in the presence of a
magnetic field. We then analyze the system and provide a rigorous derivation of
the FDT regime in a large area of the temperature-magnetization plane.",0806.3519v1
2009-01-23,Quantum jumps and spin dynamics of interacting atoms in a strongly coupled atom-cavity system,"We experimentally investigate the spin dynamics of one and two neutral atoms
strongly coupled to a high finesse optical cavity. We observe quantum jumps
between hyperfine ground states of a single atom. The interaction-induced
normal mode splitting of the atom-cavity system is measured via the atomic
excitation. Moreover, we observe evidence for conditional dynamics of two atoms
simultaneously coupled to the cavity mode. Our results point towards the
realization of measurement-induced entanglement schemes for neutral atoms in
optical cavities.",0901.3738v2
2009-10-23,Hamiltonian reduction for the magnetic dynamics in antiferromagnetic crystals,"The nonlinear spin dynamics in antiferromagnetic crystals is studied for the
magnetic structures similar to that of hematite. For the case when only two
magnetization vectors are non-zero and the Hamiltonian has an axial symmetry, a
reduction to a Hamiltonian system with one degree of freedom is performed,
based on the corresponding conservation law. The analysis of the phase
portraits of this system provides tractable analytical and geometric
descriptions of the regimes of nonlinear spin dynamics in the crystal.",0910.4527v3
2010-06-08,Quench Dynamics of Entanglement in an Opened Anisotropic Spin-1/2 Heisenberg Chain,"The quantum entanglement dynamics of a one-dimensional spin-1/2 anisotropic
XXZ model is studied using the method of the adaptive time-dependent
density-matrix renormalization-group when two cases of quenches are performed
in the system. An anisotropic interaction quench and the maximum number of
domain walls of staggered magnetization quench are considered. The dynamics of
pairwise entanglement between the nearest two qubits in the spin chain is
investigated. The entanglement of the two-spin qubits can be created and
oscillates in both cases of the quench. The anisotropic interaction has a
strong influence on the oscillation frequency of entanglement.",1006.1417v1
2010-06-24,Field-induced decay dynamics in square-lattice antiferromagnet,"Dynamical properties of the square-lattice Heisenberg antiferromagnet in
applied magnetic field are studied for arbitrary value S of the spin. Above the
threshold field for two-particle decays, the standard spin-wave theory yields
singular corrections to the excitation spectrum with logarithmic divergences
for certain momenta. We develop a self-consistent approximation applicable for
S >= 1, which avoids such singularities and provides regularized magnon decay
rates. Results for the dynamical structure factor obtained in this approach are
presented for S = 1 and S = 5/2.",1006.4838v2
2010-09-23,Revisiting Kawasaki dynamics in one dimension,"Critical exponents of the Kawasaki dynamics in the Ising chain are
re-examined numerically through the spectrum gap of evolution operators
constructed both in spin and domain wall representations. At low temperature
regimes the latter provides a rapid finite-size convergence to these exponents,
which tend to $z \simeq 3.11$ for instant quenches under ferromagnetic
couplings, while approaching to $z \simeq 2$ in the antiferro case. The spin
representation complements the evaluation of dynamic exponents at higher
temperature scales, where the kinetics still remains slow.",1009.4511v1
2011-02-12,Two-step spacetime deformation induced dynamical torsion,"We extend the geometrical ideas of the spacetime deformations to study the
physical foundation of the post-Riemannian geometry. To this aim, we construct
the theory of 'two-step spacetime deformation' as a guiding principle. We
address the theory of teleparallel gravity and construct a consistent
Einstein-Cartan (EC) theory with the 'dynamical torsion'. We show that the
equations of the standard EC theory, in which the equation defining torsion is
the algebraic type and, in fact, no propagation of torsion is allowed, can be
equivalently replaced by the set of 'modified EC equations' in which the
torsion, in general, is dynamical. The special physical constraint imposed upon
the spacetime deformations yields the short-range propagating spin-spin
interaction.",1102.2491v1
2011-03-05,Dynamical TAP equations for non-equilibrium Ising spin glasses,"We derive and study dynamical TAP equations for Ising spin glasses obeying
both synchronous and asynchronous dynamics using a generating functional
approach. The system can have an asymmetric coupling matrix, and the external
fields can be time-dependent. In the synchronously updated model, the TAP
equations take the form of self consistent equations for magnetizations at time
$t+1$, given the magnetizations at time $t$. In the asynchronously updated
model, the TAP equations determine the time derivatives of the magnetizations
at each time, again via self consistent equations, given the current values of
the magnetizations. Numerical simulations suggest that the TAP equations become
exact for large systems.",1103.1044v1
2011-04-08,High-accuracy approximation of binary-state dynamics on networks,"Binary-state dynamics (such as the susceptible-infected-susceptible (SIS)
model of disease spread, or Glauber spin dynamics) on random networks are
accurately approximated using master equations. Standard mean-field and
pairwise theories are shown to result from seeking approximate solutions of the
master equations. Applications to the calculation of SIS epidemic thresholds
and critical points of non-equilibrium spin models are also demonstrated.",1104.1537v3
2011-07-01,Current induced magnetization reversal on the surface of a topological insulator,"We study dynamics of the magnetization coupled to the surface Dirac fermions
of a three di- mensional topological insulator. By solving the
Landau-Lifshitz-Gilbert equation in the presence of charge current, we find
current induced magnetization dynamics and discuss the possibility of mag-
netization reversal. The torque from the current injection depends on the
transmission probability through the ferromagnet and shows nontrivial
dependence on the exchange coupling. The mag- netization dynamics is a direct
manifestation of the inverse spin-galvanic effect and hence another ferromagnet
is unnecessary to induce spin transfer torque in contrast to the conventional
setup.",1107.0116v1
2011-07-13,Out of equilibrium dynamics in the bidimensional spin-ice model,"We study the dynamics of 2d spin-ice following a quench from a fully
disordered initial condition (equilibrium at infinite temperature) into its
disordered, ferromagnetic and antiferromagnetic phases. We analyze the
evolution of the density of topological defects and we show that these take
finite density over very long periods of time in all kinds of quenches. We
identify the leading mechanisms for the growth of domains in the ordered phases
and we evaluate the (anisotropically) growing lengths involved in dynamic
scaling.",1107.2528v2
2012-02-24,Phase locking dynamics of dipolarly coupled vortex-based spin transfer oscillators,"Phase locking dynamics of dipolarly coupled vortices excited by
spin-polarized current in two identical nanopillars is studied as a function of
the interpillar distance L. Numerical study and analytical model have proved
the remarkable efficiency of magneto-static interaction to achieve phase
locking. Investigating the dynamics in the transient regime towards phase
locking, we extract the evolution of the locking time \tau, the coupling
strength {\mu} and the interaction energy W. Finally, we compare this coupling
energy with the one obtained by simple model.",1202.5499v1
2012-10-15,Optimal Control of Stochastic Magnetization Dynamics by Spin Current,"Fluctuation-induced stochastic magnetization dynamics plays an important role
in magnetic recording and writing. Here we propose that the magnetization
dynamics can be optimally controlled by the spin current to minimize or
maximize the Freidlin-Wentzell action functional of the system hence to
increase or decrease the happening probability of the rare event. We apply this
method to study thermal-driven magnetization switching problem and to
demonstrate the advantage of the optimal control strategy.",1210.4036v1
2012-12-18,Skyrmion dynamics and disintegration in a spin-1 Bose-Einstein condensate,"Dynamics of skyrmionic spin texture in the spin-1 Bose-Einstein condensate is
examined by analytical and numerical means. We show the skyrmion (coreless
vortex) to be inherently unstable in the sense that the state initially
prepared purely within the antiferromagnetic (ferromagnetic) order parameter
manifold inevitably evolves into a mixture of both. The vorticity-dependent
drift in the presence of the trapping potential also contributes to the
disintegration of the initial spin texture manifold. We argue that the notion
of a skyrmion as a topologically protected entity becomes ill defined during
the dynamical evolution process.",1212.4224v1
2013-05-16,The dynamics of a rotating ellipsoid,"An interesting physical phenomenon, which contradicts our common sense, is
concerned with the dynamics of motion of a spinning ellipsoid in a non smooth
surface. A hard-boiled egg spinning on a table with a rough surface is an
example. In this article, we present a theoretical explanation, of the dynamics
of motion of this ellipsoid, that describes the axis raising phenomenon, from
the horizontal to the vertical. The equations of motion were obtained with
Lagrangian formalism.",1305.3898v1
2016-07-22,Spin and spatial dynamics in electron-impact scattering off S-wave He using R-matrix with Time-Dependence theory,"R-matrix with time-dependence theory is applied to electron-impact ionisation
processes for He in the S-wave model. Cross sections for electron-impact
excitation, ionisation and ionisation with excitation for impact energies
between 25 and 225 eV are in excellent agreement with benchmark cross sections.
Ultra-fast dynamics induced by a scattering event is observed through
time-dependent signatures associated with autoionisation from doubly excited
states. Further insight into dynamics can be obtained through examination of
the spin components of the time-dependent wavefunction.",1607.06723v1
2017-03-13,Effects of boundary conditions on irreversible dynamics,"We present a simple one-dimensional Ising-type spin system on which we define
a completely asymmetric Markovian single spin-flip dynamics. We study the
system at a very low, yet non-zero, temperature and we show that for empty
boundary conditions the Gibbs measure is stationary for such dynamics, while
introducing in a single site a $+$ condition the stationary measure changes
drastically, with macroscopical effects. We achieve this result defining an
absolutely convergent series expansion of the stationary measure around the
zero temperature system. Interesting combinatorial identities are involved in
the proofs.",1703.04511v1
2018-02-01,Exploring the diluted ferromagnetic p-spin model with a Cavity Master Equation,"We introduce a new solution to Glauber multi-spin dynamics on random graphs.
The solution is based on the recently introduced Cavity Master Equation (CME),
a time-closure turning the in principle exact Dynamic Cavity Method into a
practical method of analysis and of fast simulation.
  Running CME once is of comparable computational complexity as one Monte Carlo
run on the same problem. We show that CME correctly models the ferromagnetic
$p$-spin Glauber dynamics from high temperatures down to and below the
spinoidal transition. We also show that CME allows a novel exploration of the
low-temperature spin-glass phase of the model.",1802.00298v1
2018-05-21,Operational Dynamical Modeling of spin 1/2 relativistic particles: the Dirac equation and its classical limit,"The formalism of Operational Dynamical Modeling [Phys. Rev. Lett. {\bf 109},
190403 (2012)] is employed to analyze dynamics of spin half relativistic
particles. We arrive at the Dirac equation from specially constructed
relativistic Ehrenfest theorems by assuming that the coordinates and momenta do
not commute. Forbidding creation of antiparticles and requiring the
commutativity of the coordinates and momenta lead to classical Spohn's equation
[Ann. Phys. {\bf 282}, 420 (2000)]. Moreover, Spohn's equation turns out to be
the classical Koopman-von Neumann theory underlying the Dirac equation.",1805.08243v1
2012-01-04,Adjacent Spin Operator Dynamical Structure Factor of the S=1/2 Heisenberg Chain,"Considering the adjacent spin operators $S^z_jS^z_{j+1}$ and $S^-_jS^-_{j+1}$
in the S=1/2 Heisenberg chain, we give a determinant representation of their
form factors. The dynamical structure factors of the respective operators are
computed over the whole Brillouin zone in several magnetic fields and the
resulting signal is analyzed in terms of excitation types. Among other results,
we find that the $S^z_jS^z_{j+1}$ dynamical structure factor carries a large
weight of the 4-spinon excitations which are distinguishable from the 2-spinon
signal because they are located outside the 2-spinon spectrum.",1201.0867v1
2012-04-14,Optical conductivity for a dimer in the Dynamic Hubbard model,"The Dynamic Hubbard Model represents the physics of a multi-band Hubbard
model by using a pseudo-spin degree of freedom to dynamically modify the
on-site Coulomb interaction. Here we use a dimer system to obtain analytical
results for this model. The spectral function and the optical conductivity are
calculated analytically for any number of electrons, and the distribution of
optical spectral weight is analyzed in great detail. The impact of polaron-like
effects due to overlaps between pseudo-spin states on the optical spectral
weight distribution is derived analytically. Our conclusions support results
obtained previously with different models and techniques: holes are less mobile
than electrons.",1204.3219v1
2016-12-05,Dynamical realization of magnetic states in a strongly interacting Bose mixture,"We describe the dynamical preparation of magnetic states in a strongly
interacting two-component Bose gas in a harmonic trap. By mapping this system
to an effective spin chain model, we obtain the dynamical spin densities and
the fidelities for a few-body system. We show that the spatial profiles transit
between ferromagnetic and antiferromagnetic states as the intraspecies
interaction parameter is slowly increased.",1612.01570v4
2018-09-22,Modulation instability associated nonlinear dynamics of spin-orbit coupled Bose-Einstein condensates,"We study pattern-forming nonlinear dynamics starting from a continuous wave
state of quasi-one-dimensional two-component Bose-Einstein condensates with
synthetic spin-orbit coupling induced by Raman lasers. Modulation instability
can occur even when the miscibility condition due to the interatomic
interactions is satisfied. We find that the initial stage of the nonlinear
development is consistent with the prediction of modulation instability, where
the two primary and secondary instability bands lead to the spontaneous growth
of the modulation and the subsequent complicated dynamics of pattern formation.
At later stages of the evolution, the wave functions undergo clear separation
in the momentum space, reflected in the dispersion of the single particle
Hamiltonian.",1809.08491v2
2020-02-05,A non-perturbative analysis of spin-boson interactions using the Weyl relations,"We perform a non-perturbative analysis of the dynamics of a two-level quantum
system subjected to repeated interactions with a bosonic environment when these
interactions are intense and localized in time. We use the Weyl relations to
obtain a closed expression for the resulting state of the spin despite the
non-perturbative nature of the problem. Furthermore, we study divisibility and
memory effects in the dynamics and draw conclusions about the role that the
quantum-mechanical features of the environment play on the dynamics of the
two-level system.",2002.01994v1
2021-01-15,Spin dynamics from a constrained magnetic Tight-Binding model,"A dynamics of the precession of coupled atomic moments in the tight-binding
(TB) approximation is presented. By implementing an angular penalty functional
in the energy that captures the magnetic effective fields self-consistently,
the motion of the orientation of the local magnetic moments is observed faster
than the variation of their magnitudes. This allows the computation of the
effective atomic magnetic fields that are found consistent with the
Heisenberg's exchange interaction, by comparison with classical atomistic spin
dynamics on Fe, Co and Ni magnetic clusters.",2101.06121v2
2017-05-11,Tunable spin dynamics in chiral soliton lattice,"We study dynamics of a chiral soliton lattice (CSL) in a classical
one-dimensional spin chain coupled to the conduction electrons under an
electric field. The CSL has attracted much interest because its period can be
easily controlled by an external magnetic field. We clarify the dependence of
the CSL dynamics on its period. A collective coordinate and an SU(2) gauge
method are used for the analysis. It turns out that the velocity of the CSL
becomes slower as the period becomes longer. We also mention a relation between
the velocity and the magnetic resistance.",1705.04086v2
2017-05-29,"Part of a collection of reviews on antiferromagnetic spintronics. Antiferromagnetic dynamics, spin-texures, and nanostructures","Antiferromagnets as active elements of spintronics can be faster than their
ferromagnetic counterparts and more robust to magnetic noise. Owing to the
strongly exchange-coupled magnetic sublattice structure, antiferromagnetic
order parameter dynamics are qualitatively different and thus capable of
engendering novel device functionalities. In this review, we discuss
antiferromagnetic textures -- nanoparticles, domain walls, and skyrmions, --
under the action of different spin torques. We contrast the antiferromagnetic
and ferromagnetic dynamics, with a focus on the features that can be relevant
for applications.",1705.10377v1
2018-06-28,Machine learning with controllable quantum dynamics of a nuclear spin ensemble in a solid,"We experimentally demonstrate quantum machine learning using NMR based on a
framework of quantum reservoir computing. Reservoir computing is for exploiting
natural nonlinear dynamics with large degrees of freedom, which is called a
reservoir, for a machine learning purpose. Here we propose a concrete physical
implementation of a quantum reservoir using controllable dynamics of a nuclear
spin ensemble in a molecular solid. In this implementation, we demonstrate
learning of nonlinear functions with binary or continuous variable inputs with
low mean squared errors. Our implementation and demonstration paves a road
toward exploiting quantum computational supremacy in NMR ensemble systems for
information processing with reachable technologies.",1806.10910v1
2018-08-01,Long range dynamical coupling between magnetic adatoms mediated by a 2D topological insulator,"We study the spin excitation spectra and the dynamical exchange coupling
between iron adatoms on a Bi bilayer nanoribbon. We show that the topological
character of the edge states is preserved in the presence of the magnetic
adatoms. Nevertheless, they couple significantly to the edge spin currents, as
witnessed by the large and long-ranged dynamical coupling we obtain in our
calcula- tions. The large effective magnetocrystalline anisotropy of the
magnetic adatoms combined with the transport properties of the topologically
protected edge states make this system a strong candidate for implementation of
spintronics devices and quantum information and/or computation protocols.",1808.00347v1
2018-12-18,Predicted antiferromagnetic-vortex dynamics driven by spin polarized current in thin discs,"We investigate vortex configuration in antiferromagnetic thin discs. It is
shown that the vortex acquires oscillatory dynamics with well-defined amplitude
and frequency which may be controlled on demand by an alternating spin
polarized current. These findings may be useful for the emerging field of
antiferromagnetic topological spintronics, once vortex dynamics may be
controlled by purely electric means.",1812.07537v1
2019-03-06,Cluster multipole dynamics in non-collinear antiferromagnets,"A systematic framework to investigate spin dynamics in non-collinear
antiferromagnet is proposed. Taking Mn$_3$Sn as a representative example, we
derive an effective low energy model based on the multipole expansion of the
magnetic structure, and investigate the uniform precession and the domain wall
dynamics. We show that the solution for the effective model accurately
reproduces the numerical calculation of the Landau-Lifshitz-Gilbert equations.
Our results indicate that Mn$_3$Sn has preferable properties for applications
to a racetrack memory and a spin torque oscillator, and thus, is a promising
candidate for new devices by using the multipole degrees of freedom.",1903.02259v1
2020-05-04,A Dynamical Mean-Field Theory for Learning in Restricted Boltzmann Machines,"We define a message-passing algorithm for computing magnetizations in
Restricted Boltzmann machines, which are Ising models on bipartite graphs
introduced as neural network models for probability distributions over spin
configurations. To model nontrivial statistical dependencies between the spins'
couplings, we assume that the rectangular coupling matrix is drawn from an
arbitrary bi-rotation invariant random matrix ensemble. Using the dynamical
functional method of statistical mechanics we exactly analyze the dynamics of
the algorithm in the large system limit. We prove the global convergence of the
algorithm under a stability criterion and compute asymptotic convergence rates
showing excellent agreement with numerical simulations.",2005.01560v1
2020-06-16,Dynamical response and competing orders in two-band Hubbard model,"We present a dynamical mean-field study of two-particle dynamical response
functions in two-band Hubbard model across several phase transitions. We
observe that the transition between theexcitonic condensate and spin-state
ordered state is continuous with a narrow strip of supersolidphase separating
the two. Approaching transition from the excitonic condensate is announced
bysoftening of the excitonic mode at theMpoint of the Brillouin zone. Inside
the spin-state orderedphase there is a magnetically ordered state with 2x2
periodicity, which has no precursor in thenormal phase.",2006.09058v1
2020-08-07,Anisotropic Ultrafast Spin Dynamics in Epitaxial Cobalt,"We investigate the ultrafast spin dynamics in an epitaxial hcp(1100) cobalt
thin film. By performing pump-probe magneto-optical measurements with the
magnetization along either the easy or hard magnetic axis, we determine the
demagnetization and recovery times for the two axes. We observe a 35% slower
dynamics along the easy magnetization axis, which we attribute to
magneto-crystalline anisotropy of the electron-phonon coupling, supported by
our ab initio calculations. This points towards an unambiguous and previously
undisclosed role of anisotropic electron-lattice coupling in ultrafast
magnetism.",2008.03119v1
2021-11-22,Counting edge modes via dynamics of boundary spin impurities,"We study dynamics of the one-dimensional Ising model in the presence of
static symmetry-breaking boundary field via the two-time autocorrelation
function of the boundary spin. We find that the correlations decay as a power
law. We uncover a dynamical phase diagram where, upon tuning the strength of
the boundary field, we observe distinct power laws that directly correspond to
changes in the number of edge modes as the boundary and bulk magnetic field are
varied. We suggest how the universal physics can be demonstrated in current
experimental setups, such as Rydberg chains.",2111.11428v2
2022-08-08,Accelerating many-body entanglement generation by dipolar interactions in the Bose-Hubbard model,"The spin squeezing protocols allow the dynamical generation of massively
correlated quantum many-body states, which can be utilized in
entanglement-enhanced metrology and technologies. We study a quantum simulator
generating twisting dynamics realized in a two-component Bose-Hubbard model
with dipolar interactions. We show that the interplay of contact and long-range
dipolar interactions between atoms in the superfluid phase activates the
anisotropic two-axis counter-twisting mechanism, accelerating the spin
squeezing dynamics and allowing the Heisenberg-limited accuracy in
spectroscopic measurements.",2208.04019v1
2023-03-24,Total Angular Momentum Conservation in Ab Initio Born-Oppenheimer Molecular Dynamics,"We prove both analytically and numerically that the total angular momentum of
a molecular system undergoing adiabatic Born-Oppenheimer dynamics is conserved
only when pseudo-magnetic Berry forces are taken into account. This finding
sheds light on the nature of Berry forces for molecular systems with spin-orbit
coupling and highlights how ab initio Born-Oppenheimer molecular dynamics
simulations can successfully capture the entanglement of spin and nuclear
degrees of freedom as modulated by electronic interactions.",2303.13787v1
2023-06-15,Robust gates with spin-locked superconducting qubits,"Dynamical decoupling is effective in reducing gate errors in most quantum
computation platforms and is therefore projected to play an essential role in
future fault-tolerant constructions. In superconducting circuits, however, it
has proven difficult to utilize the benefits of dynamical decoupling. In this
work, we present a theoretical proposal that incorporates a continuous version
of dynamical decoupling, namely spin locking, with a coupler-based CZ gate for
transmons and provide analytical and numerical results that demonstrate its
effectiveness.",2306.09149v3
2023-09-03,Dirac hydrodynamics in 19 forms,"We consider the relativistic spinor field theory re-formulated in polar
variables so to allow for the interpretation given in terms of fluid variables.
After that the dynamics of spinor fields is converted as dynamics of a special
type of spin fluid, we demonstrate that such conversion into dynamical spin
fluid is not unique but it can be obtained through $19$ different
rearrangements, by explicitly showing the $19$ minimal systems of hydrodynamic
equations that are equivalent to the Dirac equations.",2309.00617v1
2023-09-27,Regulating spin dynamics in magnetic nanomaterials,"Magnetic nanomaterials can be used in the construction of devices for
information processing and memory storage. For this purpose, they have to enjoy
two contradictory properties, from one side being able of keeping for long time
magnetization frozen, hence information stored, and from the other side
allowing for quick change of magnetization required for fast erasing of memory
and rewriting new information. Methods of resolving this dilemma are suggested
based on triggering resonance, dynamic resonance tuning, and on quadratic
Zeeman effect. These methods make it possible to realize effective regulation
of spin dynamics in such materials as magnetic nanomolecules and magnetic
nanoclusters.",2309.15568v1
2023-12-11,Asymptotical dynamics of askew-polarized spinning top under the radiation reaction torque,"Rotary dynamics of polarized composite particles as dipole rigid bodies is
considered. It is described the Euler equations singularly perturbed by the
radiation reaction torque. The Schott term is taken into account, and the
reduction procedure lowering higher derivatives is applied. Asymptotic methods
of nonlinear mechanics are used to analyze the rotary dynamics of
askew-polarized spinning top. Numerical estimates are relevant to the
hypothetical DAST-nanocrystals that might possess a huge dipole moment.",2401.02970v1
2024-02-16,Spin-Orbit Synchronization and Singular Perturbation Theory,"In this study, we formulate a set of differential equations for a binary
system to describe the secular-tidal evolution of orbital elements, rotational
dynamics, and deformation (flattening), under the assumption that one body
remains spherical while the other is slightly aspherical throughout the
analysis. By applying singular perturbation theory, we analyze the dynamics of
both the original and secular equations. Our findings indicate that the secular
equations serve as a robust approximation for the entire system, often
representing a slow-fast dynamical system. Additionally, we explore the
geometric aspects of spin-orbit resonance capture, interpreting it as a
manifestation of relaxation oscillations within singularly perturbed systems.",2402.10880v1
2024-03-01,Quantum spin representation for the Navier-Stokes equation,"We develop a quantum representation for Newtonian viscous fluid flows by
establishing a mapping between the Navier-Stokes equation (NSE) and the
Schr\""odinger-Pauli equation (SPE). The proposed nonlinear SPE incorporates the
two-component wave function and the imaginary diffusion. Consequently,
classical fluid flow can be interpreted as a non-Hermitian quantum spin system.
Using the SPE-based numerical simulation of viscous flows, we demonstrate the
quantum/wave-like behavior in flow dynamics. Furthermore, the SPE equivalent to
the NSE can facilitate the quantum simulation of fluid dynamics.",2403.00596v1
2004-04-06,Anomalous scaling behavior of the dynamical spin susceptibility of Ce$_{0.925}$La$_{0.075}$Ru$_{2}$Si$_{2}$,"Inelastic neutron scattering measurements have been performed on single
crystals of the heavy fermion compound Ce$_{0.925}$La$_{0.075}$Ru$_{2}$Si$_{2}$
in broad energy [0.1, 9.5 meV] and temperature [40 mK, 294 K] ranges in order
to address the question of scaling behavior of the dynamical spin
susceptibility at the quantum critical point of an itinerant magnetic system.
For two wavevectors $\mathbf{Q}$ corresponding to uncorrelated and
antiferromagnetically correlated spin fluctuations, it is found that the
dynamical spin susceptibility $\chi''(\mathbf{Q},E,T)$ is independent of
temperature below a cut-off temperature $T_{\mathbf{Q}}$: the spin fluctuation
amplitude saturates at low temperatures contrarily to its expected divergence
at a quantum critical point. Above $T_{\mathbf{Q}}$, a $\mathbf{Q}$-dependent
scaling behavior of the form $T\chi''(\mathbf{Q},E,T) =
C_{\mathbf{Q}}f[E/(a_{\mathbf{Q}}T^{\beta_{\mathbf{Q}}})]$ with
$\beta_{\mathbf{Q}}<1$ is obtained. This scaling does not enter the general
framework of quantum phase transition theories, since it is obtained in a high
temperature range, where Kondo spin fluctuations depend strongly on
temperature.",0404124v2
2004-09-09,Nonlocal magnetization dynamics in ferromagnetic heterostructures,"Two complementary effects modify the GHz magnetization dynamics of nanoscale
heterostructures of ferromagnetic and normal materials relative to those of the
isolated magnetic constituents: On the one hand, a time-dependent ferromagnetic
magnetization pumps a spin angular-momentum flow into adjacent materials and,
on the other hand, spin angular momentum is transferred between ferromagnets by
an applied bias, causing mutual torques on the magnetizations. These phenomena
are manifestly nonlocal: they are governed by the entire spin-coherent region
that is limited in size by spin-flip relaxation processes. We review recent
progress in understanding the magnetization dynamics in ferromagnetic
heterostructures from first principles, focusing on the role of spin pumping in
layered structures. The main body of the theory is semiclassical and based on a
mean-field Stoner or spin-density--functional picture, but quantum-size effects
and the role of electron-electron correlations are also discussed. A growing
number of experiments support the theoretical predictions. The formalism should
be useful to understand the physics and to engineer the characteristics of
small devices such as magnetic random-access memory elements.",0409242v3
2000-04-05,Monopole Chern-Simons Term: Charge-Monopole System as a Particle with Spin,"The topological nature of Chern-Simons term describing the interaction of a
charge with magnetic monopole is manifested in two ways: it changes the plane
dynamical geometry of a free particle for the cone dynamical geometry without
distorting the free (geodesic) character of the motion, and in the limit of
zero charge's mass it describes a spin system. This observation allows us to
interpret the charge-monopole system alternatively as a free particle of fixed
spin with translational and spin degrees of freedom interacting via the
helicity constraint, or as a symmetric spinning top with dynamical moment of
inertia and ""isospin"" U(1) gauge symmetry, or as a system with higher
derivatives. The last interpretation is used to get the twistor formulation of
the system. We show that the reparametrization and scale invariant monopole
Chern-Simons term supplied with the kinetic term of the same invariance gives
rise to the alternative description for the spin, which is related to the
charge-monopole system in a spherical geometry. The relationship between the
charge-monopole system and (2+1)-dimensional anyon is discussed in the light of
the obtained results.",0004032v3
2007-04-09,Spin Dynamics Of $qqq$ Wave Function On Light Front In High Momentum Limit Of QCD : Role Of $qqq$ Force,"The contribution of a spin-rich $qqq$ force (in conjunction with pairwise
$qq$ forces) to the analytical structure of the $qqq$ wave function is worked
out in the high momentum regime of QCD where the confining interaction may be
ignored, so that the dominant effect is $Coulombic$. A distinctive feature of
this study is that the spin-rich $qqq$ force is generated by a $ggg$ vertex (a
genuine part of the QCD Lagrangian) wherein the 3 radiating gluon lines end on
as many quark lines, giving rise to a (Mercedes-Benz type) $Y$-shaped diagram.
The dynamics is that of a Salpeter-like equation (3D support for the kernel)
formulated covariantly on the light front, a la Markov-Yukawa Transversality
Principle (MYTP) which warrants a 2-way interconnection between the 3D and 4D
Bethe-Salpeter (BSE) forms for 2 as well as 3 fermion quarks. With these
ingredients, the differential equation for the 3D wave function $\phi$ receives
well-defined contributions from the $qq$ and $qqq$ forces. In particular a
$negative$ eigenvalue of the spin operator $i \sigma_1.\sigma_2\times \sigma_3$
which is an integral part of the $qqq$ force, causes a characteristic
singularity in the differential equation, signalling the dynamical effect of a
spin-rich $qqq$ force not yet considered in the literature. The potentially
crucial role of this interesting effect vis-a-vis the so-called `spin anomaly'
of the proton, is a subject of considerable physical interest.",0704.1103v1
2010-04-19,Phase transitions in a mechanical system coupled to Glauber spins,"A harmonic oscillator linearly coupled with a linear chain of Ising spins is
investigated. The $N$ spins in the chain interact with their nearest neighbours
with a coupling constant proportional to the oscillator position and to
$N^{-1/2}$, are in contact with a thermal bath at temperature $T$, and evolve
under Glauber dynamics. The oscillator position is a stochastic process due to
the oscillator-spin interaction which produces drastic changes in the
equilibrium behaviour and the dynamics of the oscillator. Firstly, there is a
second order phase transition at a critical temperature $T_c$ whose order
parameter is the oscillator stable rest position: this position is zero above
$T_c$ and different from zero below $T_c$. This transition appears because the
oscillator moves in an effective potential equal to the harmonic term plus the
free energy of the spin system at fixed oscillator position. Secondly, assuming
fast spin relaxation (compared to the oscillator natural period), the
oscillator dynamical behaviour is described by an effective equation containing
a nonlinear friction term that drives the oscillator towards the stable
equilibrium state of the effective potential. The analytical results are
compared with numerical simulation throughout the paper.",1004.3215v2
2010-07-11,Nonequilibrium dynamics of a fast oscillator coupled to Glauber spins,"A fast harmonic oscillator is linearly coupled with a system of Ising spins
that are in contact with a thermal bath, and evolve under a slow Glauber
dynamics at dimensionless temperature $\theta$. The spins have a coupling
constant proportional to the oscillator position. The oscillator-spin
interaction produces a second order phase transition at $\theta=1$ with the
oscillator position as its order parameter: the equilibrium position is zero
for $\theta>1$ and non-zero for $\theta< 1$. For $\theta<1$, the dynamics of
this system is quite different from relaxation to equilibrium. For most initial
conditions, the oscillator position performs modulated oscillations about one
of the stable equilibrium positions with a long relaxation time. For random
initial conditions and a sufficiently large spin system, the unstable zero
position of the oscillator is stabilized after a relaxation time proportional
to $\theta$. If the spin system is smaller, the situation is the same until the
oscillator position is close to zero, then it crosses over to a neighborhood of
a stable equilibrium position about which keeps oscillating for an
exponentially long relaxation time. These results of stochastic simulations are
predicted by modulation equations obtained from a multiple scale analysis of
macroscopic equations.",1007.1806v1
2010-09-07,A general and solvable random matrix model for spin decoherence,"We propose and solve a simple but very general quantum model of an SU(2) spin
interacting with a large external system with N states. The coupling is
described by a random hamiltonian in a new general gaussian SU(2)xU(N) random
matrix ensemble, that we introduce in this paper. We solve the model in the
large N limit, for any value of the spin j and for any choice of the coupling
matrix element distributions in the different possible angular momentum
channels l (and provided that the internal dynamics of the spin is slow).
Besides its mathematical interest as a non-trivial random matrix model, it
allows to study and illustrate in a simple framework various phenomena: the
decoherence dynamics, the conditions of emergence of the classical phase space
for the spin, the properties quantum diffusion in phase space. The large time
evolution for the spin is shown to be non-Markovian in general, the Markov
property emerging in some specific case for the dynamics and the initial
conditions.",1009.1282v2
2011-01-11,Single-Spin Addressing in an Atomic Mott Insulator,"Ultracold atoms in optical lattices are a versatile tool to investigate
fundamental properties of quantum many body systems. In particular, the high
degree of control of experimental parameters has allowed the study of many
interesting phenomena such as quantum phase transitions and quantum spin
dynamics. Here we demonstrate how such control can be extended down to the most
fundamental level of a single spin at a specific site of an optical lattice.
Using a tightly focussed laser beam together with a microwave field, we were
able to flip the spin of individual atoms in a Mott insulator with
sub-diffraction-limited resolution, well below the lattice spacing. The Mott
insulator provided us with a large two-dimensional array of perfectly arranged
atoms, in which we created arbitrary spin patterns by sequentially addressing
selected lattice sites after freezing out the atom distribution. We directly
monitored the tunnelling quantum dynamics of single atoms in the lattice
prepared along a single line and observed that our addressing scheme leaves the
atoms in the motional ground state. Our results open the path to a wide range
of novel applications from quantum dynamics of spin impurities, entropy
transport, implementation of novel cooling schemes, and engineering of quantum
many-body phases to quantum information processing.",1101.2076v1
2011-02-16,Experimental characterization of coherent magnetization transport in a one-dimensional spin system,"We experimentally characterize the non-equilibrium, room-temperature
magnetization dynamics of a spin chain evolving under an effective
double-quantum Hamiltonian. We show that the Liouville space operators
corresponding to the magnetization and the two-spin correlations evolve 90
degrees out of phase with each other, and drive the transport dynamics. For a
nearest-neighbor-coupled N-spin chain, the dynamics are found to be restricted
to a Liouville operator space whose dimension scales only as N^2, leading to a
slow growth of multi-spin correlations. Even though long-range couplings are
present in the real system, we find excellent agreement between the analytical
predictions and our experimental results, confirming that leakage out of the
restricted Liouville space is slow on the timescales investigated. Our results
indicate that the group velocity of the magnetization is 6.04 +/- 0.38 um/s,
corresponding to a coherent transport over N ~ 26 spins on the experimental
timescale. As the double-quantum Hamiltonian is related to the standard
one-dimensional XX Hamiltonian by a similarity transform, our results can be
directly extended to XX quantum spin chains, which have been extensively
studied in the context of both quantum magnetism and quantum information
processing.",1102.3400v2
2013-05-28,Microscopic observation of magnon bound states and their dynamics,"More than eighty years ago, H. Bethe pointed out the existence of bound
states of elementary spin waves in one-dimensional quantum magnets. To date,
identifying signatures of such magnon bound states has remained a subject of
intense theoretical research while their detection has proved challenging for
experiments. Ultracold atoms offer an ideal setting to reveal such bound states
by tracking the spin dynamics after a local quantum quench with single-spin and
single-site resolution. Here we report on the direct observation of two-magnon
bound states using in-situ correlation measurements in a one-dimensional
Heisenberg spin chain realized with ultracold bosonic atoms in an optical
lattice. We observe the quantum walk of free and bound magnon states through
time-resolved measurements of the two spin impurities. The increased effective
mass of the compound magnon state results in slower spin dynamics as compared
to single magnon excitations. In our measurements, we also determine the decay
time of bound magnons, which is most likely limited by scattering on thermal
fluctuations in the system. Our results open a new pathway for studying
fundamental properties of quantum magnets and, more generally, properties of
interacting impurities in quantum many-body systems.",1305.6598v2
2013-06-03,Dynamic nuclear polarization in InGaAs/GaAs and GaAs/AlGaAs quantum dots under non-resonant ultra-low power optical excitation,"We study experimentally the dependence of dynamic nuclear spin polarization
on the power of non-resonant optical excitation in two types of individual
neutral semiconductor quantum dots: InGaAs/GaAs and GaAs/AlGaAs. We show that
the mechanism of nuclear spin pumping via second order recombination of
optically forbidden (''dark'') exciton states recently reported in InP/GaInP
quantum dots [Phys. Rev. B 83, 125318 (2011)] is relevant for material systems
considered in this work. In the InGaAs/GaAs dots this nuclear spin polarization
mechanism is particularly pronounced, resulting in Overhauser shifts up to ~80
micro-eV achieved at optical excitation power ~1000 times smaller than the
power required to saturate ground state excitons. The Overhauser shifts
observed at low-power optical pumping in the interface GaAs/AlGaAs dots are
generally found to be smaller (up to ~40 micro-eV). Furthermore in GaAs/AlGaAs
we observe dot-to-dot variation and even sign reversal of the Overhauser shift
which is attributed to dark-bright exciton mixing originating from
electron-hole exchange interaction in dots with reduced symmetry. Nuclear spin
polarization degrees reported in this work under ultra-low power optical
pumping are comparable to those achieved by techniques such as resonant optical
pumping or above-gap pumping with high power circularly polarized light.
Dynamic nuclear polarization via second-order recombination of ''dark''
excitons may become a useful tool in single quantum dot applications, where
manipulation of the nuclear spin environment or electron spin is required.",1306.0469v1
2013-11-05,Spin dynamics and an orbital-antiphase pairing symmetry in iron-based superconductors,"The symmetry of the wave function describing the Cooper pairs is one of the
most fundamental quantities in a superconductor but its measurement in the
iron-based superconductors has proved to be very difficult. The complex
multi-band nature of these materials makes the interplay of superconductivity
with spin and orbital dynamics very intriguing, leading to very material
dependent magnetic excitations, and pairing symmetries. Here we use
first-principles many-body method, including ab initio determined two-particle
vertex function, to study the spin dynamics and superconducting pairing
symmetry in a large number of iron-based superconductors. In iron compounds
with high transition temperature, we find both the dispersive high-energy spin
excitations, and very strong low energy commensurate or nearly commensurate
spin response, suggesting that these low energy spin excitations play the
dominate role in cooper pairing. We find three closely competing types of
pairing symmetries, which take a very simple form in the space of active iron
$3d$ orbitals, and differ only in the relative quantum mechanical phase of the
$xz$, $yz$ and $xy$ orbital contributions. The extensively discussed s$^{+-}$
symmetry appears when contributions from all orbitals have equal sign, while
the opposite sign in $xz$ and $yz$ orbitals leads to the $d$ wave symmetry. A
novel orbital antiphase $s^{+-}$ symmetry emerges when $xy$ orbital has
opposite sign to $xz$ and $yz$ orbitals. We propose that this orbital-antiphase
pairing symmetry explains the puzzling variation of the experimentally observed
superconducting gaps on all the Fermi surfaces of LiFeAs. This novel symmetry
of the order parameter may be realized in other iron superconductors.",1311.1188v1
2015-01-26,Dynamics of correlations in two-dimensional quantum spin models with long-range interactions: A phase-space Monte-Carlo study,"Interacting quantum spin models are remarkably useful for describing
different types of physical, chemical, and biological systems. Significant
understanding of their equilibrium properties has been achieved to date,
especially for the case of spin models with short-range couplings. However,
progress towards the development of a comparable understanding in long-range
interacting models, in particular out-of-equilibrium, remains limited. In a
recent work, we proposed a semiclassical numerical method to study spin models,
the discrete truncated Wigner approximation (DTWA), and demonstrated its
capability to correctly capture the dynamics of one- and two-point correlations
in one dimensional (1D) systems. Here we go one step forward and use the DTWA
method to study the dynamics of correlations in 2D systems with many spins and
different types of long-range couplings, in regimes where other numerical
methods are generally unreliable. We compute spatial and time-dependent
correlations for spin-couplings that decay with distance as a power-law and
determine the velocity at which correlations propagate through the system.
Sharp changes in the behavior of those velocities are found as a function of
the power-law decay exponent. Our predictions are relevant for a broad range of
systems including solid state materials, atom-photon systems and ultracold
gases of polar molecules, trapped ions, Rydberg, and magnetic atoms. We
validate the DTWA predictions for small 2D systems and 1D systems, but
ultimately, in the spirt of quantum simulation, experiments will be needed to
confirm our predictions for large 2D systems.",1501.06593v2
2015-05-19,4D Higher Spin Gravity with Dynamical Two-Form as a Frobenius--Chern--Simons Gauge Theory,"We provide an off-shell formulation of four-dimensional higher spin gravity
based on a covariant Hamiltonian action on an open nine-dimensional Poisson
manifold whose boundary consists of the direct product of spacetime and a
noncommutative twistor space of S^2 x S^2 topology. The fundamental field is a
superconnection consisting of even and odd differential forms valued in the odd
and even sectors of a 3-graded associative algebra given by the direct product
of an eight-dimensional Frobenius algebra and a higher spin algebra extended by
inner Klein operators. The superconnection consists of two one-forms gauging
the one-sided actions of the higher spin algebra, two bi-fundamental real forms
given by the Weyl zero-form and a new dynamical two-form, an additional set of
forms providing a maximal duality extension, and, finally, the Lagrange
multipliers required for the covariant Hamiltonian action. In a particular
two-form background, the model yields Vasiliev's recently proposed extended
higher spin gravity equations, whose interaction terms are accounted for by de
Rham closed globally defined forms arising in the dynamical two-form.",1505.04957v2
2015-10-14,Field-induced dynamical properties of the $XXZ$ model on a honeycomb lattice,"We present a comprehensive $1/S$ study of the field-induced dynamical
properties of the nearest-neighbor $XXZ$ antiferromagnet on a honeycomb lattice
using the formalism of the nonlinear spin-wave theory developed for this model.
The external magnetic field controls spin frustration in the system and induces
non-collinearity of the spin structure, which is essential for the two-magnon
decay processes. Our results include an intriguing field-evolution of the
regions of the Brillouin zone wherein decays of spin excitations are prominent,
a detailed classification of the decay channels involving magnons from both
excitation branches, and a thorough analysis of the singularities in the magnon
spectra due to coupling to the two magnon continuum, all of which are
illustrated for several field and anisotropy values. We highlight a number of
features related to either the non-Bravais nature of the lattice, or the
existence of the Dirac-like points in the spectrum. In addition, the asymptotic
behavior of the decay rates near high-symmetry points is analyzed in detail.
The inelastic neutron-scattering spin-spin structure factor is obtained in the
leading $1/S$ order and is shown to exhibit qualitatively distinct fingerprints
of the decay-induced magnon dynamics such as quasiparticle peaks broadened by
decays and strong spectral weight redistribution.",1510.04275v2
2016-03-07,Superfluidity and spin superfluidity in spinor Bose gases,"We show that spinor Bose gases subject to a quadratic Zeeman effect exhibit
coexisting superfluidity and spin superfluidity, and study the interplay
between these two distinct types of superfluidity. To illustrate that the basic
principles governing these two types of superfluidity are the same, we describe
the magnetization and particle-density dynamics in a single hydrodynamic
framework. In this description spin and mass supercurrents are driven by their
respective chemical potential gradients. As an application, we propose an
experimentally accessible stationary state, where the two types of
supercurrents counterflow and cancel each other, thus resulting in no mass
transport. Furthermore, we propose a straightforward setup to probe spin
superfluidity by measuring the in-plane magnetization angle of the whole cloud
of atoms. We verify the robustness of these findings by evaluating the
four-magnon collision time, and find that the time scale for coherent
(superfluid) dynamics is separated from that of the slower incoherent dynamics
by one order of magnitude. Comparing the atom and magnon kinetics reveals that
while the former can be hydrodynamic, the latter is typically collisionless
under most experimental conditions. This implies that, while our
zero-temperature hydrodynamic equations are a valid description of spin
transport in Bose gases, a hydrodynamic description that treats both mass and
spin transport at finite temperatures may not be readily feasible.",1603.01996v2
2019-05-22,Current-Induced Dynamics and Chaos of Antiferromagnetic Bimerons,"A magnetic bimeron is a topologically non-trivial spin texture carrying an
integer topological charge, which can be regarded as the counterpart of
skyrmion in easy-plane magnets. The controllable creation and manipulation of
bimerons are crucial for practical applications based on topological spin
textures. Here, we analytically and numerically study the dynamics of an
antiferromagnetic bimeron driven by a spin current. Numerical simulations
demonstrate that the spin current can create an isolated bimeron in the
antiferromagnetic thin film via the damping-like spin torque. The spin current
can also effectively drive the antiferromagnetic bimeron without a transverse
drift. The steady motion of an antiferromagnetic bimeron is analytically
derived and is in good agreement with the simulation results. Also, we find
that the alternating-current-induced motion of the antiferromagnetic bimeron
can be described by the Duffing equation due to the presence of the nonlinear
boundary-induced force. The associated chaotic behavior of the bimeron is
analyzed in terms of the Lyapunov exponents. Our results demonstrate the
inertial dynamics of an antiferromagnetic bimeron, and may provide useful
guidelines for building future bimeron-based spintronic devices.",1905.09007v2
2016-12-22,Imaging Magnetization Structure and Dynamics in Ultrathin YIG/Pt Bilayers with High Sensitivity Using the Time-Resolved Longitudinal Spin Seebeck Effect,"We demonstrate an instrument for time-resolved magnetic imaging that is
highly sensitive to the in-plane magnetization state and dynamics of thin-film
bilayers of yttrium iron garnet (Y3Fe5O12,YIG)/Pt: the time-resolved
longitudinal spin Seebeck (TRLSSE) effect microscope. We detect the local,
in-plane magnetic orientation within the YIG by focusing a picosecond laser to
generate thermally-driven spin current from the YIG into the Pt by the spin
Seebeck effect, and then use the inverse spin Hall effect in the Pt to
transduce this spin current to an output voltage. To establish the time
resolution of TRLSSE, we show that pulsed optical heating of patterned YIG (20
nm)/Pt(6 nm)/Ru (2 nm) wires generates a magnetization-dependent voltage pulse
of less than 100 ps. We demonstrate TRLSSE microscopy to image both static
magnetic structure and gigahertz-frequency magnetic resonance dynamics with
sub-micron spatial resolution and a sensitivity to magnetic orientation below
0.3$^{\circ}/\sqrt{\text{Hz}}$ in ultrathin YIG.",1612.07610v2
2018-10-15,Steering Magnetic Skyrmions with Nonequilibrium Green's Functions,"Magnetic skyrmions, topologically protected vortex-like configurations in
spin textures, are of wide conceptual and practical appeal for quantum
information technologies, notably in relation to the making of so-called
race-track memory devices. Skyrmions can be created, steered and destroyed with
magnetic fields and/or (spin) currents. Here we focus on the latter mechanism,
analyzed via a microscopic treatment of the skyrmion-current interaction. The
system we consider is an isolated skyrmion in a square-lattice cluster,
interacting with electrons spins in a current-carrying quantum wire. For the
theoretical description, we employ a quantum formulation of spin-dependent
currents via nonequilibrium Green's functions (NEGF) within the generalized
Kadanoff-Baym ansatz (GKBA). This is combined with a treatment of skyrmions
based on classical localized spins, with the skyrmion motion described via
Ehrenfest dynamics. With our mixed quantum-classical scheme, we assess how
time-dependent currents can affect the skyrmion dynamics, and how this in turn
depends on electron-electron and spin-orbit interactions in the wire. Our study
shows the usefulness of a quantum-classical treatment of skyrmion steering via
currents, as a way for example to validate/extract an effective,
classical-only, description of skyrmion dynamics from a microscopic quantum
modeling of the skyrmion-current interaction.",1810.06212v1
2019-06-26,Strong ergodicity breaking in aging of mean field spin glasses,"Out of equilibrium relaxation processes show aging if they become slower as
time passes. Aging processes are ubiquitous and play a fundamental role in the
physics of glasses and spin glasses and in other applications (e.g. in
algorithms minimizing complex cost/loss functions). The theory of aging in the
out of equilibrium dynamics of mean-field spin glass models has achieved a
fundamental role, thanks to the asymptotic analytic solution found by
Cugliandolo and Kurchan. However this solution is based on assumptions (e.g.
the weak ergodicity breaking hypothesis) which have never been put under a
strong test until now. In the present work we present the results of an
extraordinary large set of numerical simulations of the prototypical mean-field
spin glass models, namely the Sherrington-Kirkpatrick and the Viana-Bray
models. Thanks to a very intensive use of GPUs, we have been able to run the
latter model for more than $2^{64}$ spin updates and thus safely extrapolate
the numerical data both in the thermodynamical limit and in the large times
limit. The measurements of the two-times correlation functions in isothermal
aging after a quench from a random initial configuration to a temperature
$T<T_c$ provides clear evidence that, at large times, such correlations do not
decay to zero as expected by assuming weak ergodicity breaking. We conclude
that strong ergodicity breaking takes place in mean-field spin glasses aging
dynamics which, asymptotically, takes place in a confined configurational
space. Theoretical models for the aging dynamics need to be revised
accordingly.",1906.11195v1
2021-01-13,Spin pumping between noncollinear ferromagnetic insulators through thin superconductors,"Dynamical magnets can pump spin currents into superconductors. To understand
such a phenomenon, we develop a method utilizing the generalized Usadel
equation to describe time-dependent situations in superconductors in contact
with dynamical ferromagnets. Our proof-of-concept theory is valid when there is
sufficient dephasing at finite temperatures, and when the ferromagnetic
insulators are weakly polarized. We derive the effective equation of motion for
the Keldysh Green's function focusing on a thin film superconductor sandwiched
between two noncollinear ferromagnetic insulators of which one is dynamical. In
turn, we compute the spin currents in the system as a function of the
temperature and the magnetizations' relative orientations. When the induced
Zeeman splitting is weak, we find that the spin accumulation in the
superconducting state is smaller than in the normal states due to the lack of
quasiparticle states inside the gap. This feature gives a lower backflow spin
current from the superconductor as compared to a normal metal. Furthermore, in
superconductors, we find that the ratio between the backflow spin current in
the parallel and anti-parallel magnetization configuration depends strongly on
temperature, in contrast to the constant ratio in normal metals.",2101.05128v1
2018-03-01,Quantum Interference Controls the Electron Spin Dynamics in n-GaAs,"Manifestations of quantum interference effects in macroscopic objects are
rare. Weak localization is one of the few examples of such effects showing up
in the electron transport through solid state. Here we show that weak
localization becomes prominent also in optical spectroscopy via detection of
the electron spin dynamics. In particular, we find that weak localization
controls the free electron spin relaxation in semiconductors at low
temperatures and weak magnetic fields by slowing it down by almost a factor of
two in $n$-doped GaAs in the metallic phase. The weak localization effect on
the spin relaxation is suppressed by moderate magnetic fields of about 1 T,
which destroy the interference of electron trajectories, and by increasing the
temperature. The weak localization suppression causes an anomalous decrease of
the longitudinal electron spin relaxation time $T_1$ with magnetic field, in
stark contrast with well-known magnetic field induced increase in $T_1$. This
is consistent with transport measurements which show the same variation of
resistivity with magnetic field. Our discovery opens a vast playground to
explore quantum magneto-transport effects optically in the spin dynamics.",1803.00352v2
2019-02-12,Effective field analysis using the full angular spin-orbit torque magnetometry dependence,"Spin-orbit torques promise ultra-efficient magnetization switching used for
advanced devices based on emergent quasi-particles such as domain walls and
skyrmions. Recently, the spin structure dynamics, materials and systems with
tailored spin-orbit torques are being developed. A method, which allows one to
detect the acting torques in a given system as a function of the magnetization
direction is the torque-magnetometry method based on a higher harmonics
analysis of the anomalous Hall-effect. Here we show that the effective fields
acting on magnetic domain walls that govern the efficiency of their dynamics
require a sophisticated analysis taking into account the full angular
dependence of the torques. Using a 1-D model we compared the spin orbit torque
efficiencies by depinning measurements and spin torque magnetometry. We show
that the effective fields can be accurately determined and we find good
agreement. Thus our method allows us now to rapidly screen materials and
predict the resulting quasi-particle dynamics.",1902.04665v2
2019-02-27,Anomalous phase ordering of a quenched ferromagnetic superfluid,"Coarsening dynamics, the canonical theory of phase ordering following a
quench across a symmetry breaking phase transition, is thought to be driven by
the annihilation of topological defects. Here we show that this understanding
is incomplete. We simulate the dynamics of an isolated spin-1 condensate
quenched into the easy-plane ferromagnetic phase and find that the mutual
annihilation of spin vortices does not take the system to the equilibrium
state. A nonequilibrium background of long wavelength spin waves remain at the
Berezinskii-Kosterlitz-Thouless temperature, an order of magnitude hotter than
the equilibrium temperature. The coarsening continues through a second much
slower scale invariant process with a length scale that grows with time as
$t^{1/3}$. This second regime of coarsening is associated with spin wave energy
transport from low to high wavevectors, bringing about the the eventual
equilibrium state. Because the relevant spin waves are noninteracting, the
transport occurs through a dynamic coupling to other degrees of freedom of the
system. The transport displays features of a spin wave energy cascade,
providing a potential profitable connection with the emerging field of spin
wave turbulence. Strongly coupling the system to a reservoir destroys the
second regime of coarsening, allowing the system to thermalise following the
annihilation of vortices.",1902.10792v4
2019-11-28,Manipulating Spin Chirality of Magnetic Skyrmion Bubbles by In-Plane Re-versed Magnetic Fields in (Mn$_{1-x}$Ni$_x$)$_{65}$Ga$_{35}$ ($x = 0.45$) magnet,"Understanding the dynamics of the magnetic skyrmion, a particle-like
topologically stable spin texture, and its response dynamics to external fields
are indis-pensable for the applications in spintronic devices. In this letter,
the Lorentz transmis-sion electron microscopy (LTEM) was used to investigate
the spin chirality of the mag-netic skyrmion bubbles (SKBs) in the
centrosymmetric magnet MnNiGa at room tem-perature. The reversal of SKBs
excited by the in-plane magnetic field has been revealed. Moreover, the
collective behavior of interacting spin chirality can be manipulated by
reversing the directions of the magnetic fields on a wedge-shaped thin plate.
The dy-namic behavior of the bubbles at different position of the thin plate
has been explored with the micromagnetic simulation, indicating a non-uniform
and nontrivial dynamic magnetization on the surfaces and center of the thin
plate during the spin chirality re-versal. The results suggest that the
controllable symmetry breaking of the SKBs arising from thickness variation
provides an ability to manipulate the collective behavior of the spin chirality
with small external fields, leading to a promising application in nonvola-tile
spintronic devices for magnetic skyrmions.",1911.12497v1
2020-05-19,Spin transport in a tunable Heisenberg model realized with ultracold atoms,"Simple models of interacting spins play an important role in physics. They
capture the properties of many magnetic materials, but also extend to other
systems, such as bosons and fermions in a lattice, systems with gauge fields,
high-Tc superconductors, and systems with exotic particles such as anyons and
Majorana fermions. In order to study and compare these models, a versatile
platform is needed. Realizing such a system has been a long-standing goal in
the field of ultracold atoms. So far, spin transport has only been studied in
the isotropic Heisenberg model. Here we implement the Heisenberg XXZ model with
adjustable anisotropy and use this system to study spin transport far from
equilibrium after quantum quenches from imprinted spin helix patterns. In the
non-interacting XX model, we find ballistic behavior of spin dynamics, while in
the isotropic XXX model, we find diffusive behavior. For positive anisotropies,
the dynamics ranges from anomalous super-diffusion to sub-diffusion depending
on anisotropy, whereas for negative anisotropies, we observe a crossover in the
time domain from ballistic to diffusive transport. This behavior contrasts with
expectations for the linear response regime and raises new questions in
understanding quantum many-body dynamics far away from equilibrium.",2005.09549v1
2020-05-30,Dzyaloshinskii-Moriya and dipole-dipole interactions affect coupling-based Landau-Majorana-Stückelberg-Zener transitions,"It has been theoretically demonstrated that two spins (qubits or qutrits),
coupled by exchange interaction only, undergo a coupling-based joint
Landau-Majorana-St\""uckelberg-Zener (LMSZ) transition when a linear ramp acts
upon one of the two spins. Such a transition, under appropriate conditions on
the parameters, drives the two-spin system toward a maximally entangled state.
In this paper, effects on the quantum dynamics of the two qudits, stemming from
the Dzyaloshinskii-Moriya (DM) and dipole-dipole (d-d) interactions, are
investigated qualitatively and quantitatively. The enriched Hamiltonian model
of the two spins, shares with the previous microscopic one the same C2-symmetry
which once more brings about an exact treatment of the new quantum dynamical
problem. This paper transparently reveals that the DM and d-d interactions
generate independent, enhancing or hindering, modifications in the dynamical
behaviour predicted for the two spins coupled exclusively by the exchange
interaction. It is worthy noticing that, on the basis of the theory here
developed, the measurement of the time evolution of the magnetization in a
controlled LMSZ scenario, can furnish information on the relative weights of
the three kinds of couplings describing the spin system. This possibility is
very important since it allows in principle to legitimate the choice of the
microscopic model to be adopted in a given physical scenario.",2006.00229v1
2020-08-19,Dynamical decoupling in interacting systems: applications to signal-enhanced hyperpolarized readout,"Methods that preserve coherence broadly impact all quantum information
processing and metrology applications. Dynamical decoupling methods accomplish
this by protecting qubits in noisy environments but are typically constrained
to the limit where the qubits themselves are non-interacting. Here we consider
the alternate regime wherein the inter-qubit couplings are of the same order as
dephasing interactions with the environment. We propose and demonstrate a
multi-pulse protocol that protects transverse spin states by suitably
Hamiltonian engineering the inter-spin coupling while simultaneously
suppressing dephasing noise on the qubits. We benchmark the method on 13C
nuclear spin qubits in diamond, dipolar coupled to each other and embedded in a
noisy electronic spin bath, and hyperpolarized via optically pumped NV centers.
We observe effective state lifetimes of 13C nuclei $T_2^{\prime}\approx$2.5s at
room temperature, an extension of over 4700-fold over the conventional
$T_2^{\ast}$ free induction decay. The spins are continuously interrogated
during the applied quantum control, resulting in 13C NMR line narrowing and an
$>$500-fold boost in SNR due to the lifetime extension. Together with
hyperpolarization spin interrogation is accelerated by $>10^{11}$ over
conventional 7T NMR. This work suggests strategies for the dynamical decoupling
of coupled qubit systems with applications in a variety of experimental
platforms.",2008.08323v1
2020-09-18,Floquet dynamical quantum phase transition in the extended XY model: nonadiabatic to adiabatic topological transition,"We investigate both pure and mixed states Floquet dynamical quantum phase
transition (DQPT) in the periodically time-dependent extended XY model. We
exactly show that the proposed Floquet Hamiltonian of interacting spins can be
expressed as a sum of noninteracting quasi-spins imposed by an effective time
dependent magnetic field (Schwinger-Rabi model). The calculated Chern number
indicates that there is a topological transition from nonadiabatic to adiabatic
regime. In the adiabatic regime, the quasi-spins trace the time dependent
effective magnetic field and then oscillate between spin up and down states.
While in the nonadiabatic regime, the quasi-spins cannot follow the time
dependent effective magnetic field and feel an average magnetic field. We find
the range of driving frequency over which the quasi-spins experience adiabatic
cyclic processes. Moreover, we obtain the exact expression of the Loschmidt
amplitude and generalized Loschmidt amplitude of the proposed Floquet system.
The results represent that both pure and mixed states dynamical phase
transition occurs when the system evolves adiabatically. In other words, the
minimum required driving frequency for the appearance of Floquet DQPT is equal
to the threshold frequency needed for transition from nonadiabatic to adiabatic
regime.",2009.09008v1
2021-03-12,Robust spin squeezing from the tower of states of $U(1)$-symmetric spin Hamiltonians,"Spin squeezing - a central resource for quantum metrology - can be generated
via the non-linear, entangling evolution of an initially factorized spin state.
Here we show that robust (i.e. persistent) squeezing dynamics is generated by a
very large class of $S=1/2$ spin Hamiltonians with axial symmetry, in
relationship with the existence of a peculiar structure of the low-lying
Hamiltonian eigenstates - the so-called Anderson's tower of states. Such states
are fundamentally related to the appearance of spontaneous symmetry breaking in
quantum systems; and, for models with sufficiently high connectivity, they are
parametrically close to the eigenstates of a planar rotor (Dicke states), in
that they feature an anomalously large value of the total angular momentum. Our
central insight is that, starting from a coherent spin state, a generic
$U(1)$-symmetric Hamiltonian featuring the Anderson's tower of states generates
the same squeezing evolution at short times as the one governed by the
paradigmatic one-axis-twisting (or planar-rotor) model of squeezing dynamics.
The full squeezing evolution of the planar-rotor model is seemingly reproduced
for interactions decaying with distance $r$ as $r^{-\alpha}$ when $\alpha <
5d/3$ in $d$ dimensions. Our results connect quantum simulation with quantum
metrology by unveiling the squeezing power of a large variety of Hamiltonian
dynamics that are currently implemented by different quantum simulation
platforms.",2103.07354v2
2021-03-16,Theory of Ca$_{10}$Cr$_7$O$_{28}$ as a bilayer breathing-kagome magnet: Classical thermodynamics and semi-classical dynamics,"Ca$_{10}$Cr$_7$O$_{28}$ is a novel spin-$1/2$ magnet exhibiting spin liquid
behaviour which sets it apart from any previously studied model or material.
However, understanding Ca$_{10}$Cr$_7$O$_{28}$ presents a significant
challenge, because the low symmetry of the crystal structure leads to very
complex interactions, with up to seven inequivalent coupling parameters in the
unit cell. Here we explore the origin of the spin-liquid behaviour in
Ca$_{10}$Cr$_7$O$_{28}$, starting from the simplest microscopic model
consistent with experiment - a Heisenberg model on a single bilayer of the
breathing-kagome (BBK) lattice. We use a combination of classical Monte Carlo
(MC) simulation and (semi-)classical Molecular Dynamics (MD) simulation to
explore the thermodynamic and dynamic properties of this model, and compare
these with experimental results for Ca$_{10}$Cr$_7$O$_{28}$. We uncover
qualitatively different behaviours on different timescales, and argue that the
ground state of Ca$_{10}$Cr$_7$O$_{28}$ is born out of a slowly-fluctuating
""spiral spin liquid"", while faster fluctuations echo the U(1) spin liquid found
in the kagome antiferromagnet. We also identify key differences between
longitudinal and transverse spin excitations in applied magnetic field, and
argue that these are a distinguishing feature of the spin liquid in the BBK
model.",2103.08790v2
2021-04-22,Dynamic Spin Fluctuations in the Frustrated Spin Chain Compound Li$_3$Cu$_2$SbO$_6$,"We report the signatures of dynamic spin fluctuations in the layered
honeycomb Li$_3$Cu$_2$SbO$_6$ compound, with a 3$d$ S = 1/2 $d^9$ Cu$^{2+}$
configuration, through muon spin rotation and relaxation ($\mu$SR) and neutron
scattering studies. Our zero-field (ZF) and longitudinal-field (LF)-$\mu$SR
results demonstrate the slowing down of the Cu$^{2+}$ spin fluctuations below
4.0 K. The saturation of the ZF relaxation rate at low temperature, together
with its weak dependence on the longitudinal field between 0 and 3.2 kG,
indicates the presence of dynamic spin fluctuations persisting even at 80 mK
without static order. Neutron scattering study reveals the gaped magnetic
excitations with three modes at 7.7, 13.5 and 33 meV. Our DFT calculations
reveal that the next nearest neighbors (NNN) AFM exchange ($J_{AFM}$ = 31 meV)
is stronger than the NN FM exchange ($J_{FM}$ = -21 meV) indicating the
importance of the orbital degrees of freedom. Our results suggest that the
physics of Li$_3$Cu$_2$SbO$_6$ can be explained by an alternating AFM chain
rather than the honeycomb lattice.",2104.10859v1
2021-06-23,Spin dynamics of itinerant electrons: local magnetic moment formation and Berry phase,"The state-of-the-art theoretical description of magnetic materials relies on
solving effective Heisenberg spin problems or their generalizations to
relativistic or multi-spin-interaction cases that explicitly assume the
presence of local magnetic moments in the system. We start with a general
interacting fermionic model that is often obtained in ab initio electronic
structure calculations and show that the corresponding spin problem can be
introduced even in the paramagnetic regime, which is characterized by a zero
average value of the magnetization. Further, we derive a physical criterion for
the formation of the local magnetic moment and confirm that the latter exists
already at high temperatures well above the transition to the ordered magnetic
state. The use of path-integral techniques allows us to disentangle spin and
electronic degrees of freedom and to carefully separate rotational dynamics of
the local magnetic moment from Higgs fluctuations of its absolute value. It
also allows us to accurately derive the topological Berry phase and relate it
to a physical bosonic variable that describes dynamics of the spin degrees of
freedom. As the result, we demonstrate that the equation of motion in the case
of a large magnetic moment takes a conventional Landau-Lifshitz form that
explicitly accounts for the Gilbert damping due to itinerant nature of the
original electronic model.",2106.12462v3
2021-12-30,Probing Majorana Modes via Local Spin Dynamics,"We investigate Majorana modes in a quantum spin chain with bond-dependent
exchange interactions by studying its dynamics. Specifically, we consider
two-time correlations for the Kitaev-Heisenberg (KH) Hamiltonian close to the
so-called Kitaev critical point. Here, the model coincides with a phase
boundary of two uncoupled instances of Kitaev's model for p-wave
superconductors, together supporting a degenerate ground state characterized by
multiple Majorana modes. In this regime, the real-time dynamics of local spins
reveal a set of strong zero modes, corresponding to a set of protruding
frequencies in the two-time correlation function. We derive perturbative
interactions that map the KH spin chain onto the topological regime of Kitaev's
fermionic model, thus opening up a bulk gap whilst retaining almost degenerate
modes in the mesoscopic regime, i.e., for finite system sizes. This showcases
the emergence of Majorana modes in a chain of effective dimers. Here, the
binding energy within each unit cell competes with the inter-dimer coupling to
generate a finite size energy gap, in analogy with local energy terms in the
transverse-field Ising model. These modes give rise to long coherence times of
local spins located at the system edges. By breaking the local symmetry in each
dimer, one can also observe a second class of Majorana modes in terms of a
beating frequency in the two-time correlations function of the edge spin.
Furthermore, we develop a scenario for realizing these model predictions in
ion-trap quantum simulators with collective addressing of the ions.",2112.15033v1
2022-05-24,Emission of coherent THz magnons in an antiferromagnetic insulator triggered by ultrafast spin-phonon interactions,"Antiferromagnetic materials have been proposed as new types of narrowband THz
spintronic devices owing to their ultrafast spin dynamics. Manipulating
coherently their spin dynamics, however, remains a key challenge that is
envisioned to be accomplished by spin-orbit torques or direct optical
excitations. Here, we demonstrate the combined generation of broadband THz
(incoherent) magnons and narrowband (coherent) magnons at 1 THz in low damping
thin films of NiO/Pt. We evidence, experimentally and through modelling, two
excitation processes of magnetization dynamics in NiO, an off-resonant
instantaneous optical spin torque and a strain-wave-induced THz torque induced
by ultrafast Pt excitation. Both phenomena lead to the emission of a THz signal
through the inverse spin Hall effect in the adjacent heavy metal layer. We
unravel the characteristic timescales of the two excitation processes found to
be < 50 fs and > 300 fs, respectively, and thus open new routes towards the
development of fast opto-spintronic devices based on antiferromagnetic
materials.",2205.11965v1
2022-06-30,Origin and dynamics of umbrella states in rare-earth iron garnets,"Rare-earth iron garnets $R_{3}$Fe$_{5}$O$_{12}$ are fascinating insulators
with very diverse magnetic phases. Their strong potential in spintronic devices
has encouraged a renewal of interest in the study of their low temperature spin
structures and spin wave dynamics. A striking feature of rare-earth garnets
with $R$-ions exhibiting strong crystal-field effects like Tb-, Dy-, Ho-, and
Er-ions is the observation of low-temperature non-collinear magnetic structures
featuring ""umbrella-like"" arrangements of the rare-earth magnetic moments. In
this study, we demonstrate that such umbrella magnetic states are naturally
emerging from the crystal-field anisotropies of the rare-earth ions. By means
of a general model endowed with only the necessary elements from the crystal
structure, we show how umbrella-like spin structures can take place and
calculate the canting-angle as a result of the competition between the
exchange-interaction of the rare-earth and the iron ions as well as the
crystal-field anisotropy. Our results are compared to experimental data, and a
study of the polarised spin wave dynamics is presented. Our study improves the
understanding of umbrella-like spin structures and paves the way for more
complex spin wave calculations in rare-earth iron garnets with non-collinear
magnetic phases.",2207.00017v2
2022-09-29,Spin Dynamics in Patterned Magnetic Multilayers with Perpendicular Magnetic Anisotropy,"The magnetization dynamics in nanostructures has been extensively studied in
the last decades, and nanomagnetism has evolved significantly over that time,
discovering new effects, developing numerous applications, and identifying
promising new directions. This includes magnonics, an emerging research field
oriented on the study of spin-wave dynamics and their applications. In this
context, thin ferromagnetic films with perpendicular magnetic anisotropy (PMA)
offer interesting opportunities to study spin waves, in particular, due to
out-of-plane magnetization in remanence or at relatively weak external magnetic
fields. This is the only magnetization configuration offering isotropic
in-plane spin-wave propagation within the sample plane, the forward volume
magnetostatic spin-wave geometry. The isotropic dispersion relation is highly
important in designing signal-processing devices, offering superior prospects
for direct replicating various concepts from photonics into magnonics.
Analogous to photonic or phononic crystals, which are the building blocks of
optoelectronics and phononics, magnonic crystals are considered as key
components in magnonics applications. Arrays of nanodots and structured
ferromagnetic thin films with a periodic array of holes, popularly known as
antidot lattices based on PMA multilayers have been recently studied. Novel
magnonic properties related to propagating spin-wave modes, exploitation of the
band gaps, and confined modes, were demonstrated. Also, the existence of
nontrivial magnonic band topologies has been shown. Moreover, the combination
of PMA and Dzyaloshinskii-Moriya interaction leads to the formation of chiral
magnetization states, including N\'eel domain walls, skyrmions, and skyrmionium
states.",2209.14824v2
2022-11-30,Unconventional spin dynamics in the non-collinear phase of a ferrimagnet,"Ferrimagnets containing several partially compensated magnetic sublattices
are considered the most promising materials for all-optical data storage and
for ultrafast communications based on spin waves. There are two magnetic phases
of the ferrimagnets: collinear and non-collinear ones. Up to now spin dynamics
in ferrimagnets has been studied mostly in the collinear state without paying
much attention to the kind of the magnetic phase. Here we investigate laser
induced ultrafast spin dynamics in a rare-earth iron garnet film in the
noncollinear phase as well. We identify a crucial influence of the magnetic
phase on the excited spin modes which allowed us to discover several prominent
effects previously overlooked. In particular, the non-collinearity makes the
quasi-antiferromagnetic mode sensitive to the external magnetic field and
brings its frequency close to the frequency of the quasiferromagnetic mode. The
latter maximizes near the magnetization compensation point and vanishes towards
the collinear phase. Spectacularly, at the phase transition the
quasiferromagnetic mode becomes soft and its amplitude significantly increases
reaching 7{\deg}. This opens new opportunities for the ultrafast control of
spins in ferrimagnets for nonthermal data storage and data processing.",2212.00085v2
2023-01-22,Easy-plane spin Hall oscillator,"Spin Hall oscillators (SHOs) based on bilayers of a ferromagnet (FM) and a
non-magnetic heavy metal (HM) are electrically tunable nanoscale microwave
signal generators. Achieving high output power in SHOs requires driving
large-amplitude magnetization dynamics by a direct spin Hall current. The
maximum possible amplitude of such oscillations with the precession cone angle
nearing $90^\circ$ is predicted for FM layers with easy-plane magnetic
anisotropy and spin Hall current polarization perpendicular to the easy plane.
While many FMs exhibit natural easy-plane anisotropy in the FM film plane, the
spin Hall current in a HM|FM bilayer is polarized in this plane and thus cannot
drive large-amplitude magneto-dynamics. Here we present a new type of SHO
engineered to have the easy-plane anisotropy oriented normal to the film plane,
enabling large-amplitude easy-plane dynamics driven by spin Hall current. Our
experiments and micromagnetic simulations demonstrate that the desired
easy-plane anisotropy can be achieved by tuning the magnetic shape anisotropy
and perpendicular magnetic anisotropy in a nanowire SHO, leading to a
significant enhancement of the generated microwave power. The easy-plane SHO
experimentally demonstrated here is an ideal candidate for realization of a
spintronic spiking neuron. Our results provide a new approach to design of
high-power SHOs for wireless communications, neuromorphic computing, and
microwave assisted magnetic recording.",2301.09228v1
2023-09-06,Spin-lattice couplings in a skyrmion multilayers of Pd-Fe/Ir(111),"Pd-Fe/Ir(111) has attracted tremendous attention for next-generation
spintronics devices due to existence of magnetic skyrmions with the external
magnetic field. Our density functional theoretical calculations in combination
with spin dynamics simulation suggest that the spin spiral phase in fcc stacked
Pd-Fe/Ir(111) flips into the skyrmion lattice phase around B$_{ext} \sim$ 6 T.
This leads to the microscopic understanding of the thermodynamic and kinetic
behaviours affected by the intrinsic spin-lattice couplings (SLCs) in this
skyrmion material for magneto-mechanical properties. Here we calculate fully
relativistic SLC parameters from first principle computations and investigate
the effect of SLC on dynamical magnetic interactions in skyrmion multilayers
Pd-Fe/Ir(111). The exchange interactions arising from next nearest-neighbors
(NN) in this material are highly frustrated and responsible for enhancing
skyrmion stability. We report the larger spin-lattice effect on both dynamical
Heisenberg exchanges and Dzyaloshinskii-Moriya interactions for next NN
compared to NN which is in contrast with recently observed spin-lattice effect
in bulk bcc Fe and CrI$_3$ monolayer. Based on our analysis, we find that the
effective measures of SLCs in fcc (hcp) stacking of Pd-Fe/Ir(111) are $\sim
2.71 ( \sim 2.36)$ and $\sim 14.71 ( \sim21.89)$ times stronger for NN and next
NN respectively, compared to bcc Fe. The linear regime of displacement for SLC
parameters is $\leq$ 0.02 {\AA} which is 0.72\% of the lattice constant for
Pd-FeIr(111). The microscopic understanding of SLCs provided by our current
study could help in designing spintronic devices based on thermodynamic
properties of skyrmion multilayers.",2309.03074v1
2023-12-12,The hardness of quantum spin dynamics,"Recent experiments demonstrated quantum computational advantage in random
circuit sampling and Gaussian boson sampling. However, it is unclear whether
these experiments can lead to practical applications even after considerable
research effort. On the other hand, simulating the quantum coherent dynamics of
interacting spins has been considered as a potential first useful application
of quantum computers, providing a possible quantum advantage. Despite evidence
that simulating the dynamics of hundreds of interacting spins is challenging
for classical computers, concrete proof is yet to emerge. We address this
problem by proving that sampling from the output distribution generated by a
wide class of quantum spin Hamiltonians is a hard problem for classical
computers. Our proof is based on the Taylor series of the output probability,
which contains the permanent of a matrix as a coefficient when bipartite spin
interactions are considered. We devise a classical algorithm that extracts the
coefficient using an oracle estimating the output probability. Since
calculating the permanent is #P-hard, such an oracle does not exist unless the
polynomial hierarchy collapses. With an anticoncentration conjecture, the
hardness of the sampling task is also proven. Based on our proof, we estimate
that an instance involving about 200 spins will be challenging for classical
devices but feasible for intermediate-scale quantum computers with
fault-tolerant qubits.",2312.07658v1
2017-03-03,Quantum Surface and Intertwiner Dynamics in Loop Quantum Gravity,"We introduce simple generic models of surface dynamics in loop quantum
gravity (LQG). A quantum surface is defined as a set of elementary patches of
area glued together. We provide it with an extra structure of locality (nearest
neighbors), thought of as induced by the whole spin network state defining the
3d bulk geometry around the quantum surface. Here, we focus on classical
surface dynamics, using a spinorial description of surface degrees of freedom.
We introduce two classes of dynamics, to be thought as templates for future
investigation of LQG dynamics with in mind the dynamics of quantum black holes.
The first defines global dynamics of the closure defect of the surface, with
two basic toy-models, either a dissipative dynamics relaxing towards the
closure constraint or a Hamiltonian dynamics precessing the closure defect. The
second class of dynamics describes the isolated regime, when both area and
closure defect are conserved throughout the evolution. The surface dynamics is
implemented through U(N) transformations and generalizes to a Bose-Hubbard
Hamiltonian with a local quadratic potential interaction. We briefly discuss
the implications of modeling the quantum black hole dynamics by a surface
Bose-Hubbard model.",1703.01156v1
1995-04-25,High Temperature Expansions and Dynamical Systems,"We develop a resummed high-temperature expansion for lattice spin systems
with long range interactions, in models where the free energy is not, in
general, analytic. We establish uniqueness of the Gibbs state and exponential
decay of the correlation functions. Then, we apply this expansion to the
Perron-Frobenius operator of weakly coupled map lattices.",9504015v1
1995-03-17,Density matrix algorithm for the calculation of dynamical properties of low dimensional systems,"I extend the scope of the density matrix renormalization group technique
developed by White to the calculation of dynamical correlation functions. As an
application and performance evaluation I calculate the spin dynamics of the 1D
Heisenberg chain.",9503094v1
1994-12-29,Dynamical Supersymmetry of a Vortex System with $1/r^{2}$ Potential,"The Pauli Hamiltonian for a spin $\frac{1}{2}$ charged particle interacting
with a point magnetic vortex and $1/r^{2}$ potential exhibits a dynamical
supersymmetry $Osp(1,1)$ on the plane except at the origin. Using this
symmetry, the spectrum and the wave functions have been obtained. And, the
dynamical supersymmetry could be imported to the case when an external harmonic
potential is added.",9412225v1
1997-06-19,Classical dynamical r-matrices for Calogero-Moser systems and their generalizations,"We present a derivation of the dynamical r-matrices of the Calogero-Moser
models using the Hamiltonian reduction procedure to get general formulae. We
describe the dynamical r-matrices thus found for spin Calogero-Moser models and
relativistic Ruijsenaars-Schneider models",9706024v1
2006-06-01,"Dynamical Entanglement in Non-Relativistic, Elastic Scattering","This article considers dynamical entanglement in non-relativistic particle
scattering. Three questions are explored: what kinds of entanglement occur in
this system, how do global symmetries constrain entanglement, and how do the
boundary conditions of scattering affect dynamical entanglement? First, a
simple model of scattering spin systems is considered, then the full system is
discussed.",0606011v1
2014-12-28,Reversibility of dynamics and multiple-quantum coherences,"In spin systems, the decay of the Loschmidt echo in the time-reversal
experiment (evolution, perturbation, time-reversed evolution) is linked to the
generation of multiple-quantum coherences. The approach is extended to other
systems, and the general problem of reversibility of quantum dynamics is
analyzed.",1412.8199v1
2017-03-22,The dynamics of critical fluctuations in asymmetric Curie-Weiss models,"We study the dynamics of fluctuations at the critical point for two
time-asymmetric version of the Curie-Weiss model for spin systems that, in the
macroscopic limit, undergo a Hopf bifurcation. The fluctuations around the
macroscopic limit reflect the type of bifurcation, as they exhibit observables
whose fluctuations evolve at different time scales. The limiting dynamics of
fluctuations of slow observable is obtained via an averaging principle.",1703.07572v1
1999-09-16,Semiclassical form factor for chaotic systems with spin 1/2,"We study the properties of the two-point spectral form factor for classically
chaotic systems with spin 1/2 in the semiclassical limit, with a suitable
semiclassical trace formula as our principal tool. To this end we introduce a
regularized form factor and discuss the limit in which the so-called diagonal
approximation can be recovered. The incorporation of the spin contribution to
the trace formula requires an appropriate variant of the equidistribution
principle of long periodic orbits as well as the notion of a skew product of
the classical translational and spin dynamics. Provided this skew product is
mixing, we show that generically the diagonal approximation of the form factor
coincides with the respective predictions from random matrix theory.",9909026v1
1996-11-11,Dynamic correlations of antiferromagnetic spin-1/2 XXZ chains at arbitrary temperature from complete diagonalization,"All eigenstates and eigenvalues are determined for the spin- 1/2 $XXZ$ chain
$H = 2J \sum_i ( S_{i}^{x} S_{i + 1}^{x} + S_{i}^{y} S_{i + 1}^{y} + \Delta
S_i^z S_{i + 1}^{z})$ for rings with up to N=16 spins, for anisotropies
$\Delta=0 , \cos(0.3\pi)$, and 1. The dynamic spin pair correlations $<
S_{l+n}^{\mu}(t) S_l^{\mu} > , (\mu=x,z)$, the dynamic structure factors
$S^{\mu}(q,\omega)$, and the intermediate structure factors $I^{\mu}(q,t)$ are
calculated for arbitrary temperature T. It is found, that for all T,
$S^{z}(q,\omega)$ is mainly concentrated on the region $|\omega| <
\varepsilon_2(q)$, where $\varepsilon_2(q)$ is the upper boundary of the
two-spinon continuum, although excited states corresponding to a much broader
frequency spectrum contribute. This is also true for the Haldane-Shastry model
and the frustrated Heisenberg model. The intermediate structure factors
$I^{\mu}(q,t)$ for $\Delta \neq 0$ show exponential decay for high T and large
q. Within the accessible time range, the time-dependent spin correlation
functions do not display the long-time signatures of spin diffusion.",9611077v1
1997-04-02,Dynamical properties of the spin-Peierls compound α'--NaV2O5,"Dynamical properties of the novel inorganic spin-Peierls compound
\alpha'--NaV2O5 are investigated using a one-dimensional dimerized Heisenberg
model. By exact diagonalizations of chains with up to 28 sites, supplemented by
a finite-size scaling analysis, the dimerization parameter \delta is determined
by requiring that the model reproduces the experimentally observed spin gap
\Delta. The dynamical and static spin structure factors are calculated. As for
CuGeO3, the existence of a low energy magnon branch separated from the
continuum is predicted. The present calculations also suggest that a large
magnetic Raman scattering intensity should appear above an energy threshold of
1.9 \Delta. The predicted photoemission spectrum is qualitatively similar to
results for an undimerized chain due to the presence of sizable short-range
antiferromagnetic correlations.",9704015v3
1998-03-20,Dynamic Spin Correlation Function near the Antiferromagnetic Quantum Phase Transition of Heavy-Fermions,"The dynamical spin susceptibility is studied in the magnetically-disordered
phase of heavy-Fermion systems near the antiferromagnetic quantum phase
transition. In the framework of the $S=1/2$ Kondo lattice model, we introduce a
perturbative expansion treating the spin and Kondo-like degrees of freedom on
an equal footing. The dynamical spin susceptibility displays a two-component
behaviour in agreement with the inelastic neutron scattering (INS) experiments
performed in $CeCu_{6}$, $Ce_{1-x}La_{x}Ru_{2}Si_{2}$ and $UPt_{3}$: a
quasielastic q-independent peak as in a Fermi liquid theory, and a strongly
q-dependent inelastic peak typical of a non-Fermi liquid behaviour. Very
strikingly, the position of the inelastic peak is found to be pushed to zero at
the antiferromagnetic transition. The picture is consistent with the neutron
cross sections observed in INS experiments.",9803255v3
1998-05-18,Fast spin dynamics algorithms for classical spin systems,"We have proposed new algorithms for the numerical integration of the
equations of motion for classical spin systems. In close analogy to symplectic
integrators for Hamiltonian equations of motion used in Molecular Dynamics
these algorithms are based on the Suzuki-Trotter decomposition of exponential
operators and unlike more commonly used algorithms exactly conserve spin length
and, in special cases, energy. Using higher order decompositions we investigate
integration schemes of up to fourth order and compare them to a well
established fourth order predictor-corrector method. We demonstrate that these
methods can be used with much larger time steps than the predictor-corrector
method and thus may lead to a substantial speedup of computer simulations of
the dynamical behavior of magnetic materials.",9805214v1
1998-09-18,Extraction of the Spin Glass Correlation Length,"The peak of the spin glass relaxation rate, S(t)=d{-M_{TRM}(t,t_w)}/H/{d ln
t}, is directly related to the typical value of the free energy barrier which
can be explored over experimental time scales. A change in magnetic field H
generates an energy E_z={N_s}{X_fc}{H^2} by which the barrier heights are
reduced, where X_{fc} is the field cooled susceptibility per spin, and N_s is
the number of correlated spins. The shift of the peak of S(t) gives E_z,
generating the correlation length, Ksi(t,T), for Cu:Mn 6at.% and
CdCr_{1.7}In_{0.3}S_4. Fits to power law dynamics, Ksi(t,T)\propto
{t}^{\alpha(T)} and activated dynamics Ksi(t,T) \propto {ln t}^{1/psi} compare
well with simulation fits, but possess too small a prefactor for activated
dynamics.",9809246v2
1998-11-26,Spin Dynamics near the Quantum Critical Point of Heavy-Fermions,"The dynamical spin susceptibility is studied in the magnetically-disordered
phase of heavy-Fermion systems near the antiferromagnetic quantum phase
transition. In the framework of the $S=1/2$ Kondo lattice model, we introduce a
perturbative expansion treating the spin and Kondo-like degrees of freedom on
an equal footing. The general expression of the dynamical spin susceptibility
that we derive presents a two-component behaviour: a quasielastic peak as in a
Fermi liquid theory, and a strongly q-dependent inelastic peak typical of a
non-Fermi liquid behaviour. Very strikingly, the position of the inelastic peak
is found to be pushed to zero at the antiferromagnetic transition with a
vanishing relaxation rate. The comparison has been quantitatively made with
Inelastic Neutron Scattering (INS) experiments performed in $CeCu_{6}$ and
$Ce_{1-x}La_{x}Ru_{2}Si_{2}$. The excellent agreement that we have found gives
strong support to a two-band model with new prospects for the study of the
quantum critical phenomena in the vicinity of the magnetic phase transition.",9811379v1
1999-03-31,Spin dynamics and magnetic correlation length in two-dimensional quantum Heisenberg antiferromagnets,"The correlated spin dynamics and the temperature dependence of the
correlation length $\xi(T)$ in two-dimensional quantum ($S=1/2$) Heisenberg
antiferromagnets (2DQHAF) on square lattice are discussed in the light of
experimental results of proton spin lattice relaxation in copper formiate
tetradeuterate (CFTD). In this compound the exchange constant is much smaller
than the one in recently studied 2DQHAF, such as La$_2$CuO$_4$ and
Sr$_2$CuO$_2$Cl$_2$. Thus the spin dynamics can be probed in detail over a
wider temperature range. The NMR relaxation rates turn out in excellent
agreement with a theoretical mode-coupling calculation. The deduced temperature
behavior of $\xi(T)$ is in agreement with high-temperature expansions, quantum
Monte Carlo simulations and the pure quantum self-consistent harmonic
approximation. Contrary to the predictions of the theories based on the
Non-Linear $\sigma$ Model, no evidence of crossover between different quantum
regimes is observed.",9903450v1
1999-04-21,Dynamics and Transport in Random Antiferromagnetic Spin Chains,"We present the first results on the low-frequency dynamical and transport
properties of random antiferromagnetic spin chains at low temperature ($T$). We
obtain the momentum and frequency dependent dynamic structure factor in the
Random Singlet (RS) phases of both spin-1/2 and spin-1 chains, as well as in
the Random Dimer phase of spin-1/2 chains. We also show that the RS phases are
unusual `spin-metals' with divergent low-frequency conductivity at T=0, and
follow the spin conductivity through `metal-insulator' transitions tuned by the
strength of dimerization or Ising anisotropy in the spin-1/2 case, and by the
strength of disorder in the spin-1 case.",9904290v2
1999-11-07,ESR investigation on the Breather mode and the Spinon-Breather dynamical crossover in Cu Benzoate,"A new elementary-excitation, the so called ""breather excitation"", is observed
directly by millimeter-submillimeter wave electron spin resonance (ESR) in the
Heisenberg quantum spin-chain Cu benzoate, in which a field-induced gap is
found recently by specific heat and neutron scattering measurements. Distinct
anomalies were found in line width and in resonance field around the ""dynamical
crossover"" regime between the gap-less spinon-regime and the gapped
breather-regime. When the temperature becomes sufficiently lower than the
energy gap, a new ESR-line with very narrow line-width is found, which is the
manifestation of the breather excitation. The non-linear field dependence of
the resonance field agrees well with the theoretical formula of the first
breather-excitation proposed by Oshikawa and Affleck. The present work
establishes experimentally for the first time that a sine-Gordon model is
applicable to explain spin dynamics in a S=1/2 Heisenberg spin chain subjected
to staggered field even in high fields.",9911094v2
2000-03-30,Spin Dynamics of Cavity Polaritons,"We have studied polariton spin dynamics in a GaAs/AlGaAs microcavity by means
of polarization- and time-resolved photoluminescence spectroscopy as a function
of excitation density and normal mode splitting. The experiments reveal a novel
behavior of the degree of polarization of the emission, namely the existence of
a finite delay to reach its maximum value. We have also found that the
stimulated emission of the lower polariton branch has a strong influence on
spin dynamics: in an interval of $\sim$150 ps the polarization changes from
+100% to negative values as high as -60%. This strong modulation of the
polarization and its high speed may open new possibilities for spin-based
devices.",0003491v1
2001-04-30,Out of equilibrium dynamics of a Quantum Heisenberg Spin Glass,"We study the out of equilibrium dynamics of the infinite range quantum
Heisenberg spin glass model coupled to a thermal relaxation bath. The SU(2)
spin algebra is generalized to SU(N) and we analyse the large-N limit. The
model displays a dynamical phase transition between a paramagnetic and a glassy
phase. In the latter, the system remains out of equilibrium and displays an
aging phenomenon, which we characterize using both analytical and numerical
methods. In the aging regime, the quantum fluctuation-dissipation relation is
violated and replaced at very long time by its classical generalization, as in
models involving simple spin algebras studied previously. We also discuss the
effect of a finite coupling to the relaxation baths and their possible forms.
This work completes and justifies previous studies on this model using a static
approach.",0105001v3
2002-02-26,"Jamming, freezing and metastability in one-dimensional spin systems","We consider in parallel three one-dimensional spin models with kinetic
constraints: the paramagnetic constrained Ising chain, the ferromagnetic Ising
chain with constrained Glauber dynamics, and the same chain with constrained
Kawasaki dynamics. At zero temperature the dynamics of these models is fully
irreversible, leading to an exponentially large number of blocked states. Using
a mapping of these spin systems onto sequential adsorption models of,
respectively, monomers, dimers, and hollow trimers, we present exact results on
the statistics of blocked states. We determine the distribution of their energy
or magnetization, and in particular the large-deviation function describing its
exponentially small tails. The spin and energy correlation functions are also
determined. The comparison with an approach based on a priori statistics
reveals systematic discrepancies with the Edwards hypothesis, concerning in
particular the fall-off of correlations.",0202465v2
2002-05-16,Low Frequency Spin Dynamics in the CeMIn_5 Materials,"We measure the spin lattice relaxation of the In(1) nuclei in the CeMIn_5
materials, extract quantitative information about the low energy spin dynamics
of the lattice of Ce moments in both CeRhIn_5 and CeCoIn_5, and identify a
crossover in the normal state. Above a temperature T* the Ce lattice exhibits
""Kondo gas"" behavior characterized by local fluctuations of independently
screened moments; below T* both systems exhibit a ""Kondo liquid"" regime in
which interactions between the local moments contribute to the spin dynamics.
Both the antiferromagnetic and superconducting ground states in these systems
emerge from the ""Kondo liquid"" regime. Our analysis provides strong evidence
for quantum criticality in CeCoIn_5.",0205354v2
2003-04-15,On the stochastic dynamics of disordered spin models,"In this article we discuss several aspects of the stochastic dynamics of spin
models. The paper has two independent parts. Firstly, we explore a few
properties of the multi-point correlations and responses of generic systems
evolving in equilibrium with a thermal bath. We propose a fluctuation principle
that allows us to derive fluctuation-dissipation relations for many-time
correlations and linear responses. We also speculate on how these features will
be modified in systems evolving slowly out of equilibrium, as
finite-dimensional or dilute spin-glasses. Secondly, we present a formalism
that allows one to derive a series of approximated equations that determine the
dynamics of disordered spin models on random (hyper) graphs.",0304333v1
2003-08-14,Dynamics of F=2 Spinor Bose-Einstein Condensates,"We experimentally investigate and analyze the rich dynamics in F=2 spinor
Bose-Einstein condensates of Rb87. An interplay between mean-field driven spin
dynamics and hyperfine-changing losses in addition to interactions with the
thermal component is observed. In particular we measure conversion rates in the
range of 10^-12 cm^3/s for spin changing collisions within the F=2 manifold and
spin-dependent loss rates in the range of 10^-13 cm^3/s for hyperfine-changing
collisions. From our data we observe a polar behavior in the F=2 ground state
of Rb87, while we measure the F=1 ground state to be ferromagnetic. Furthermore
we see a magnetization for condensates prepared with non-zero total spin.",0308281v1
2003-10-07,Dynamics of the spin-boson model with a structured environment,"We investigate the dynamics of the spin-boson model when the spectral density
of the boson bath shows a resonance at a characteristic frequency $\Omega$ but
behaves Ohmically at small frequencies. The time evolution of an initial state
is determined by making use of the mapping onto a system composed of a quantum
mechanical two-state system (TSS) which is coupled to a harmonic oscillator
(HO) with frequency $\Omega$. The HO itself is coupled to an Ohmic environment.
The dynamics is calculated by employing the numerically exact quasiadiabatic
path-integral propagator technique. We find significant new properties compared
to the Ohmic spin-boson model. By reducing the TSS-HO system in the dressed
states picture to a three-level system for the special case at resonance, we
calculate the dephasing rates for the TSS analytically. Finally, we apply our
model to experimentally realized superconducting flux qubits coupled to an
underdamped dc-SQUID detector.",0310140v1
2003-12-18,Current induced magnetization dynamics in current perpendicular to the plane spin valves,"We observe magnetization dynamics induced by spin momentum transfer in the
noise spectra of current perpendicular to the plane giant magnetoresistance
spin valves. The dynamics are observable only for those combinations of current
direction and magnetic configuration in which spin transfer acts to reorient
the free layer magnetization away from the direction set by the net magnetic
field. Detailed measurements as a function of magnetic configuration reveal an
evolution of the noise spectra, going from a spectrum with a well-defined noise
peak when the free layer is roughly collinear with the pinned layer to a
spectrum dominated by 1/f noise when the free layer is in an orthogonal
configuration. Finally, the amplitude of the corresponding resistance noise
increases rapidly with increasing current until it saturates at a value that is
a substantial fraction of the magnetoresistance between parallel and
antiparallel states.",0312504v2
2004-08-18,Electron spin tomography through counting statistics: a quantum trajectory approach,"We investigate the dynamics of electron spin qubits in quantum dots.
Measurement of the qubit state is realized by a charge current through the dot.
The dynamics is described in the framework of the quantum trajectory approach,
widely used in quantum optics, and we show that it can be applied successfully
to problems in condensed matter physics. The relevant master equation dynamics
is unravelled to simulate stochastic tunneling events of the current through
the dot.Quantum trajectories are then used to extract the counting statistics
of the current. We show how, in combination with an electron spin resonance
(ESR) field, counting statistics can be employed for quantum state tomography
of the qubit state. Further, it is shown how decoherence and relaxation time
scales can be estimated with the help of counting statistics, in the time
domain. Finally, we discuss a setup for single shot measurement of the qubit
state without the need for spin-polarized leads.",0408412v1
2004-12-22,Modulation of dephasing due to a spin-boson environment,"We study the reduced dynamics of a spin (qubit) coupled to a spin-boson
environment in the case of pure dephasing. We derive formal exact expressions
which can be cast in terms of exact integro-differential master equations. We
present results for a SB environment with ohmic dissipation at finite
temperatures. For the special value of the ohmic damping strength K=1/2 the
reduced dynamics is found in analytic form. For K<<1 we discuss the possibility
of modulating the effect of the SB environment on the qubit. In particular we
study the effect of the crossover to a slow environment dynamics, which may be
triggered by changing both the temperature and the system-environment coupling.",0412615v1
2005-05-19,Spin-lattice relaxation of Mn-ions in ZnMnSe/ZnBeSe quantum wells measured under pulsed photoexcitation,"The dynamics of spin-lattice relaxation of the Mn-ions in (Zn,Mn)Se-based
diluted-magnetic-semiconductor quantum wells is studied by time-resolved
photoluminescence. The spin-lattice relaxation time varies by five orders of
magnitude from 10-3 down to 10-8 s, when the Mn content increases from 0.4 up
to 11%. Free carriers play an important role in this dynamics. Hot carriers
with excess kinetic energy contribute to heating of the Mn system, while
cooling of the Mn system occurs in the presence of cold background carriers
provided by modulation doping. In a Zn0.89Mn0.11Se quantum well structure,
where the spin-lattice relaxation process is considerably shorter than the
characteristic lifetime of nonequilibrium phonons, also the phonon dynamics and
its contribution to heating of the Mn system are investigated.",0505485v1
2006-03-22,"Aging, rejuvenation and memory : the example of spin glasses","In this paper, we review the general features of the out-of-equilibrium
dynamics of spin glasses. We use this example as a guideline for a brief
description of glassy dynamics in other disordered systems like structural and
polymer glasses, colloids, gels etc. Starting with the simplest experiments, we
discuss the scaling laws used to describe the isothermal aging observed in spin
glasses after a quench down to the low temperature phase (these scaling laws
are the same as established for polymer glasses). We then discuss the
rejuvenation and memory effects observed when a spin glass is submitted to
temperature variations during aging, and show some examples of similar
phenomena in other glassy systems. The rejuvenation and memory effects and
their implications are analyzed from the point of view of both energy landscape
pictures and of real space pictures. We highlight the fact that both approaches
point out the necessity of hierarchical processes involved in aging. We
introduce the concept of a slowly growing and strongly temperature dependent
dynamical correlation length, which is discussed at the light of a large panel
of experiments.",0603583v1
2006-05-10,Spin-flip processes and ultrafast magnetization dynamics in Co - unifying the microscopic and macroscopic view of femtosecond magnetism,"The femtosecond magnetization dynamics of a thin cobalt film excited with
ultrashort laser pulses has been studied using two complementary pump-probe
techniques, namely spin-, energy- and time-resolved photoemission and
time-resolved magneto-optical Kerr effect. Combining the two methods it is
possible to identify the microscopic electron spin-flip mechanisms responsible
for the ultrafast macroscopic magnetization dynamics of the cobalt film. In
particular, we show that electron-magnon excitation does not affect the overall
magnetization even though it is an efficient spin-flip channel on the sub-200
fs timescale. Instead we find experimental evidence for the relevance of
Elliott-Yafet type spin-flip processes for the ultrafast demagnetization taking
place on a time scale of 300 fs.",0605272v2
2006-08-28,Strong Dynamical Heterogeneities in the Violation of the Fluctuation-Dissipation Theorem in Spin Glasses,"We analyze numerically the violation of the fluctuation-dissipation theorem
(FDT) in the $\pm J$ Edwards-Anderson (EA) spin glass model. Using single spin
probability densities we reveal the presence of strong dynamical
heterogeneities, which correlate with ground state information. The physical
interpretation of the results shows that the spins in the EA model can be
divided in two sets. In 3D, one set forms a compact structure which presents a
coarsening-like behavior with its characteristic violation of the FDT, while
the other asymptotically follows the FDT. Finally, we compare the dynamical
behavior observed in 3D with 2D.",0608603v2
2002-10-14,Dynamics of spinning test particles in Kerr spacetime,"We investigate the dynamics of relativistic spinning test particles in the
spacetime of a rotating black hole using the Papapetrou equations. We use the
method of Lyapunov exponents to determine whether the orbits exhibit sensitive
dependence on initial conditions, a signature of chaos. In the case of
maximally spinning equal-mass binaries (a limiting case that violates the
test-particle approximation) we find unambiguous positive Lyapunov exponents
that come in pairs +/- lambda, a characteristic of Hamiltonian dynamical
systems. We find no evidence for nonvanishing Lyapunov exponents for physically
realistic spin parameters, which suggests that chaos may not manifest itself in
the gravitational radiation of extreme mass-ratio binary black-hole inspirals
(as detectable, for example, by LISA, the Laser Interferometer Space Antenna).",0210042v8
2001-01-23,Effective field theory and the quark model,"We analyze the connections between the quark model (QM) and the description
of hadrons in the low-momentum limit of heavy-baryon effective field theory in
QCD. By using a three-flavor-index representation for the effective baryon
fields, we show that the ``nonrelativistic'' constituent QM for baryon masses
and moments is completely equivalent through O(m_s) to a parametrization of the
relativistic field theory in a general spin--flavor basis. The flavor and spin
variables can be identified with those of effective valence quarks. Conversely,
the spin-flavor description clarifies the structure and dynamical
interpretation of the chiral expansion in effective field theory, and provides
a direct connection between the field theory and the semirelativistic models
for hadrons used in successful dynamical calculations. This allows dynamical
information to be incorporated directly into the chiral expansion. We find, for
example, that the striking success of the additive QM for baryon magnetic
moments is a consequence of the relative smallness of the non-additive
spin-dependent corrections.",0101267v1
2004-03-16,Semiclassical propagation of coherent states with spin-orbit interaction,"We study semiclassical approximations to the time evolution of coherent
states for general spin-orbit coupling problems in two different semiclassical
scenarios: The limit \hbar to zero is first taken with fixed spin quantum
number s and then with \hbar*s held constant. In these two cases different
classical spin-orbit dynamics emerge. We prove that a coherent state propagated
with a suitable classical dynamics approximates the quantum time evolution up
to an error of size \sqrt{\hbar} and identify an Ehrenfest time scale.
Subsequently an improvement of the semiclassical error to an arbitray order
\hbar^{N/2} is achieved by a suitable deformation of the state that is
propagated classically.",0403030v1
1997-02-21,New mechanism of collapse and revival in wave packet dynamics due to spin-orbit interaction,"The article discusses the properties of time evolution of wave packets in a
few systems. Dynamics of wave packet motion for Rydberg atoms with the
hierarchy of collapses and revivals is briefly reviewed. The main part of the
paper focuses on the new mechanism of quantum reccurrences in wave packet
dynamics. This mechanism can occur (in principle) in any physical system with
strong enough spin-orbit interaction. We discuss here the SPIN_ORBIT PENDULUM
effect that consists in different motions of subpackets possessing different
spin fields and results in oscillations of a fraction of average angular
momentum between spin and ordinary subspaces. The evolution of localized wave
packet into toroidal objects and backwards (for other class of initial
conditions) is also subject to discussion.",9702044v1
2006-06-04,Dynamic generation of entangling wave packets in XY spin system with decaying long range couplings,"We study the dynamic generation of spin entanglement between two distant
sites in an XY model with $1/r^{2}$-decay long range couplings. Due to the
linear dispersion relation $\epsilon (k)\sim |k|$ of magnons in such model, we
show that a well-located spin state can be dynamically split into two moving
entangled local wave packets without changing their shapes. Interestingly, when
such two wave packets meet at the diametrically opposite site after the fast
period $\tau =\pi $, the initial well-located state can be recurrent
completely. Numerical calculation is performed to confirm the analytical result
even the ring system of sizes $N$ up to several thousands are considered. The
truncation approximation for the coupling strengths is also studied. Numerical
simulation shows that the above conclusions still hold even the range of the
coupling strength is truncated at a relative shorter scale comparing to the
size of the spin system.",0606029v1
2007-01-10,Engineering correlation and entanglement dynamics in spin systems,"We show that the correlation and entanglement dynamics of spin systems can be
understood in terms of propagation of spin waves. This gives a simple, physical
explanation of the behaviour seen in a number of recent works, in which a
localised, low-energy excitation is created and allowed to evolve. But it also
extends to the scenario of translationally invariant systems in states far from
equilibrium, which require less local control to prepare. Spin-wave evolution
is completely determined by the system's dispersion relation, and the latter
typically depends on a small number of external, physical parameters.
Therefore, this new insight into correlation dynamics opens up the possibility
not only of predicting but also of controlling the propagation velocity and
dispersion rate, by manipulating these parameters. We demonstrate this
analytically in a simple, example system.",0701053v1
2007-07-07,Concatenated dynamical decoupling in a solid-state spin bath,"Concatenated dynamical decoupling (CDD) pulse sequences hold much promise as
a strategy to mitigate decoherence in quantum information processing. It is
important to investigate the actual performance of these dynamical decoupling
strategies in real systems that are promising qubit candidates. In this Rapid
Communication, we compute the echo decay of concatenations of the Hahn echo
sequence for a solid-state electronic spin qubit in a nuclear spin bath using a
cluster expansion technique. We find that each level of concatenation reverses
the effect of successive levels of intrabath fluctuations. On the one hand,
this advances CDD as a versatile and realistic decoupling strategy. On the
other hand, this invalidates, as overly optimistic, results of the simple pair
approximation used previously to study restoration, through CDD, of coherence
lost to a mesoscopic spin bath.",0707.1037v2
2007-10-26,Absorption Effects due to Spin in the Worldline Approach to Black Hole Dynamics,"We generalize the effective point particle approach to black hole dynamics to
include spin. In this approach dissipative effects are captured by degrees of
freedom localized on the wordline. The absorptive properties of the black hole
are determined by correlation functions which can be matched with the graviton
absorption cross section in the long wavelength approximation. For rotating
black holes, superradiance is responsible for the leading contribution. The
effective theory is then used to predict the power loss due to spin in the
dynamics of non-relativistic binary systems. An enhancement of three powers of
the relative velocity is found with respect to the non-rotating case. Then we
generalize the results to other type of constituents in the binary system, such
as rotating neutron stars. Finally we compute the power loss absorbed by a test
spinning black hole in a given spacetime background.",0710.5150v2
2007-12-04,Signature of the Overhauser field on the coherent spin dynamics of donor-bound electron in a single CdTe quantum well,"We have studied the coherent spin dynamics in an oblique magnetic field of
electrons localized on donors and placed in the middle of a single CdTe quantum
well, by using a time-resolved optical technique: the photo-induced Faraday
rotation. We showed that this dynamics is affected by a weak Overhauser field
created via the hyperfine interaction of optically spin-polarized donor-bound
electrons with the surrounding nuclear isotopes carrying non-zero spins. We
have measured this nuclear field, which is on the order of a few mT and can
reach a maximum experimental value of 9.4 mT. This value represents 13 % of the
maximal nuclear polarization, and corresponds also to 13 % of maximal
electronic polarization.",0712.0559v1
2007-12-18,Dynamics Of Proton Spin : Role Of $qqq$ Force,"The analytic structure of the $qqq$ wave function, obtained recently in the
high momentum regime of QCD, is employed for the formulation of baryonic
transition amplitudes via quark loops. A new aspect of this study is the role
of a direct ($Y$-shaped, Mercedes-Benz type) $qqq$ force in generating the
$qqq$ wave function. The dynamics is that of a Salpeter-like equation (3D
support for the kernel) formulated covariantly on the light front, a la
Markov-Yukawa Transversality Principle (MYTP) which warrants a 2-way
interconnection between the 3D and 4D Bethe-Salpeter (BSE) forms for 2 as well
as 3 fermion quarks. The dynamics of this 3-body force shows up through a
characteristic singularity in the hypergeometric differential equation for the
3D wave function $\phi$, corresponding to a $negative$ eigenvalue of the spin
operator $i \sigma_1.\sigma_2\times \sigma_3$ which is an integral part of the
$qqq$ force. As a first application of this wave function to the problem of the
proton spin anomaly, the two-gluon contribution to the anomaly yields an
estimate of the right sign, although somewhat smaller in magnitude.
  Keywords: 3bodyforce; proton-spin; 2gluon anomaly; fractional correction
$\theta$",0712.2896v1
2008-03-27,Effect of cluster size of chalcogenide glass nanocolloidal solutions on the surface morphology of spin-coated amorphous films,"Amorphous chalcogenide thin film deposition can be achieved by a spin-coating
technique from proper solutions of the corresponding glass. Films produced in
this way exhibit certain grain texture, which is presumably related to the
cluster size in solution. This paper deals with the search of such a
correlation between grain size of surface morphology of as-deposited
spin-coated As33S67 chalcogenide thin films and cluster size of the glass in
butylamine solutions. Optical absorption spectroscopy and dynamic light
scattering were employed to study optical properties and cluster size
distributions in the solutions at various glass concentrations. Atomic force
microscopy is used to study the surface morphology of the surface of
as-deposited and thermally stabilized spin-coated films. Dynamic light
scattering revealed a concentration dependence of cluster size in solution.
Spectral-dependence dynamic light scattering studies showed an interesting
athermal photo-aggregation effect in the liquid state.",0803.3989v1
2008-06-03,Growth of a dynamical correlation length in an aging superspin glass,"We report on zero field cooled magnetization relaxation experiments on a
concen- trated frozen ferrofluid exhibiting a low temperature superspin glass
transition. With a method initially developed for spin glasses, we investigate
the field dependence of the relaxations that take place after different aging
times. We extract the typical number of correlated spins involved in the aging
dynamics. This brings important insights into the dynamical correlation length
and its time growth. Our results, consistent with expressions obtained for spin
glasses, extend the generality of these behaviours to the class of superspin
glasses. Since the typical flipping time is much larger for superspins than for
atomic spins, our experiments probe a time regime much closer to that of
numerical simulations.",0806.0564v2
2008-06-04,Modeling And Simulation Of Prolate Dual-Spin Satellite Dynamics In An Inclined Elliptical Orbit: Case Study Of Palapa B2R Satellite,"In response to the interest to re-use Palapa B2R satellite nearing its End of
Life (EOL) time, an idea to incline the satellite orbit in order to cover a new
region has emerged in the recent years. As a prolate dual-spin vehicle, Palapa
B2R has to be stabilized against its internal energy dissipation effect. This
work is focused on analyzing the dynamics of the reusable satellite in its
inclined orbit. The study discusses in particular the stability of the prolate
dual-spin satellite under the effect of perturbed field of gravitation due to
the inclination of its elliptical orbit. Palapa B2R physical data was
substituted into the dual-spin's equation of motion. The coefficient of zonal
harmonics J2 was induced into the gravity-gradient moment term that affects the
satellite attitude. The satellite's motion and attitude were then simulated in
the perturbed gravitational field by J2, with the variation of orbit's
eccentricity and inclination. The analysis of the satellite dynamics and its
stability was conducted for designing a control system for the vehicle in its
new inclined orbit.",0806.0740v1
2008-10-24,Spin Dynamics in the Magnetoelectric Effect LiCoPO$_4$ Compound,"Inelastic neutron scattering (INS) experiments were performed to investigate
the spin dynamics in magnetoelectric effect (ME) LiCoPO$_4$ single crystals.
Weak dispersion was detected in the magnetic excitation spectra along the three
principal crystallographic axes measured around the (0 1 0) magnetic
reflection. Analysis of the data using linear spin-wave theory indicate that
single-ion anisotropy in LiCoPO$_4$ is as important as the strongest
nearest-neighbor exchange coupling. Our results suggest that Co$^{2+}$
single-ion anisotropy plays an important role in the spin dynamics of
LiCoPO$_4$ and must be taken into account in understanding its physical
properties. High resolution INS measurements reveal an anomalous low energy
excitation that we hypothesize may be related to the magnetoelectric effect of
LiCoPO$_4$.",0810.4471v1
2008-11-21,Numerical Study of Current-Induced Domain-Wall Dynamics: Crossover from Spin Transfer to Momentum Transfer,"We study current-induced dynamics of a magnetic domain wall by solving a
time-dependent Schr\""{o}dinger equation combined with Landau-Lifshitz-Gilbert
equation in a one-dimensional electron system coupled to localized spins. Two
types of domain-wall motions are observed depending on the hard-axis
anisotropy, $K_{\perp}$, of the localized spin system. For small values of
$K_{\perp}$, the magnetic domain wall shows a streaming motion driven by spin
transfer. In contrast, for large values of $K_{\perp}$, a stick-slip motion
driven by momentum transfer is obtained. We clarify the origin of these
characters of domain-wall motions in terms of the dynamics of one-particle
energy levels and distribution functions.",0811.3545v2
2009-04-27,Gate control of low-temperature spin dynamics in two-dimensional hole systems,"We have investigated spin and carrier dynamics of resident holes in
high-mobility two-dimensional hole systems in GaAs/Al$_{0.3}$Ga$_{0.7}$As
single quantum wells at temperatures down to 400 mK. Time-resolved Faraday and
Kerr rotation, as well as time-resolved photoluminescence spectroscopy are
utilized in our study. We observe long-lived hole spin dynamics that are
strongly temperature dependent, indicating that in-plane localization is
crucial for hole spin coherence. By applying a gate voltage, we are able to
tune the observed hole g factor by more than 50 percent. Calculations of the
hole g tensor as a function of the applied bias show excellent agreement with
our experimental findings.",0904.4111v2
2009-09-19,Thermal quenches in spin ice,"We study the diffusion annihilation process which occurs when spin ice is
quenched from a high temperature paramagnetic phase deep into the spin ice
regime, where the excitations -- magnetic monopoles -- are sparse. We find that
due to the Coulomb interaction between the monopoles, a dynamical arrest
occurs, in which `non-universal' lattice-scale constraints impede the complete
decay of charge fluctuations. This phenomenon is outside the reach of universal
mean-field theory for a two-component Coulomb liquid. We identify the relevant
timescales for the dynamical arrest and propose an experiment for detecting
monopoles and their dynamics in spin ice based on this non-equilibrium
phenomenon.",0909.3605v2
2009-10-10,Temperature Dependence of Fluctuation Time Scales in Spin Glasses,"Using a series of fast cooling protocols we have probed aging effects in the
spin glass state as a function of temperature. Analyzing the logarithmic decay
found at very long time scales within a simple phenomenological barrier model,
leads to the extraction of the fluctuation time scale of the system at a
particular temperature. This is the smallest dynamical time-scale, defining a
lower-cut off in a hierarchical description of the dynamics. We find that this
fluctuation time scale, which is approximately equal to atomic spin fluctuation
time scales near the transition temperature, follows ageneralized Arrhenius
law. We discuss the hypothesisthat, upon cooling to a measuring temperature
within the spin glass state, there is a range of dynamically in-equivalent
configurations in which the system can be trapped, and check within a numerical
barrier model simulation, that this leads to sub-aging behavior in scaling aged
TRM decay curves, as recently discussed theoretically, see arXiv:0902.3556 .",0910.1924v1
2010-01-11,Magnon softening in a ferromagnetic monolayer: a first-principles spin dynamics study,"We study the Fe/W(110) monolayer system through a combination of first
principles calculations and atomistic spin dynamics simulations. We focus on
the dispersion of the spin waves parallel to the [001] direction. Our results
compare favorably with the experimental data of Prokop et al. [Phys. Rev. Lett.
102, 177206], and correctly capture a drastic softening of the magnon spectrum,
with respect to bulk bcc Fe. The suggested shortcoming of the itinerant
electron model, in particular that given by density functional theory, is
refuted. We also demonstrate that finite temperature effects are significant,
and that atomistic spin dynamics simulations represent a powerful tool with
which to include these.",1001.1669v2
2010-07-21,Dynamics of a Heisenberg spin chain in the quantum critical regime: NMR experiment versus effective field theory,"A comprehensive comparison between the magnetic field- and
temperature-dependent low frequency spin dynamics in the antiferromagnetic
spin-1/2 Heisenberg chain (AFHC) system copper pyrazine dinitrate, probed via
the 13C-nuclear magnetic resonance (NMR) relaxation rate 1/T1, and the field
theoretical approach in the Luttinger liquid (LL) regime has been performed. We
have found a very good agreement between the experiment and theory in the
investigated temperature and field range. Our results demonstrate how strongly
the quantum critical point affects the spin dynamics of Heisenberg spin chain
compounds.",1007.3608v2
2011-06-14,Dissipative spin dynamics near a quantum critical point: Numerical Renormalization Group and Majorana diagrammatics,"We provide an extensive study of the sub-ohmic spin-boson model with power
law density of states J(\omega)=\omega^s (with 0<s<1), focusing on the
equilibrium dynamics of the three possible spin components, from very weak
dissipation to the quantum critical regime. Two complementary methods, the
bosonic Numerical Renormalization Group (NRG) and Majorana diagrammatics, are
used to explore the physical properties in a wide range of parameters. We show
that the bosonic self-energy is the crucial ingredient for the description of
critical fluctuations, but that many-body vertex corrections need to be
incorporated as well in order to obtain quantitative agreement of the
diagrammatics with the numerical simulations. Our results suggest that the
out-of-equilibrium dynamics in dissipative models beyond the Bloch-Redfield
regime should be reconsidered in the long-time limit. Regarding also the
spin-boson Hamiltonian as a toy model of quantum criticality, some of the
insights gained here may be relevant for field theories of electrons coupled to
bosons in higher dimensions.",1106.2655v2
2011-10-20,Core-Core Dynamics in Spin Vortex Pairs,"We investigate magnetic nano-pillars, in which two thin ferromagnetic
nanoparticles are separated by a nanometer thin nonmagnetic spacer and can be
set into stable spin vortex-pair configurations. The 16 ground states of the
vortex-pair system are characterized by parallel or antiparallel chirality and
parallel or antiparallel core-core alignment. We detect and differentiate these
individual vortex-pair states experimentally and analyze their dynamics
analytically and numerically. Of particular interest is the limit of strong
core-core coupling, which we find can dominate the spin dynamics in the system.
We observe that the 0.2 GHz gyrational resonance modes of the individual
vortices are replaced with 2-6 GHz range collective rotational and vibrational
core-core resonances in the configurations where the cores form a bound pair.
These results demonstrate new opportunities in producing and manipulating spin
states on the nanoscale and may prove useful for new types of ultra-dense
storage devices where the information is stored as multiple vortex-core
configurations.",1110.4430v1
2012-02-06,Symmetries on Spin Chains: Limited Controllability and Minimal Controls for Full Controllability,"Symmetry is a fundamentally important concept in many branches of physics. In
this work, we discuss two types of symmetries, external symmetry and internal
symmetry, which appear frequently in controlled quantum spin chains and apply
them to study various controllability problems. For spin chains under single
local end control when external symmetries exists, we can rigorously prove that
the system is controllable in each of the invariant subspaces for both XXZ and
XYZ chains, but not for XX or Ising chains. Such results have direct
applications in controlling antiferromagnetic Heisenberg chains when the
dynamics is naturally confined in the largest excitation subspace. We also
address the theoretically important question of minimal control resources to
achieve full controllability over the entire spin chain space. In the process
we establish a systematic way of evaluating the dynamical Lie algebras and
using known symmetries to help identify the dynamical Lie algebra.",1202.1033v1
2012-11-28,A radiating spin chain as a model of irreversible dynamics,"We construct a finite spin-1/2 chain model (quantum domino) interacting with
a Fermi field, capable of emitting a scalar fermion from the last spin in the
chain. The chain with dynamics gradually reversing the neighbouring spins emits
eventually a fermion which escapes then to infinity, and the chain converges to
a stationary state. We determine the rate of convergence of the system for
large time to a different ""macroscopic"" state connected with the emission of a
fermion. We prove that the probability of fermion emission as a function of
time t approaches to unity ""almost exponentially"". We propose that this fast
rate of convergence could serve as an approximate theoretical possibility for
the ""effective"" description of the quantum measurement process in the sense
proposed by K. Hepp. This all will be preceded by an outline of explicitly
solvable dynamics of infinite version of the spin chain which exhibits
transition from a locally perturbed unstable stationary state to a truly
macroscopically different (i.e. disjoint) state, but with slow convergence for
t approaching to infinity.",1211.6783v1
2013-01-08,Kinematical and Dynamical Aspects of Higher-Spin Bound-State Equations in Holographic QCD,"In this paper we derive holographic wave equations for hadrons with arbitrary
spin starting from an effective action in a higher-dimensional space asymptotic
to anti-de Sitter (AdS) space. Our procedure takes advantage of the local
tangent frame, and it applies to all spins, including half-integer spins. An
essential element is the mapping of the higher-dimensional equations of motion
to the light-front Hamiltonian, thus allowing a clear distinction between the
kinematical and dynamical aspects of the holographic approach to hadron
physics. Accordingly, the non-trivial geometry of pure AdS space encodes the
kinematics, and the additional deformations of AdS space encode the dynamics,
including confinement. It thus becomes possible to identify the features of
holographic QCD which are independent of the specific mechanisms of conformal
symmetry breaking. In particular, we account for some aspects of the striking
similarities and differences observed in the systematics of the meson and
baryon spectra.",1301.1651v1
2013-03-05,Dynamics and relaxation in spin nematics,"We study dynamics and relaxation of elementary excitations (magnons) in the
spin nematic (quadrupole ordered) phase of S=1 magnets. We develop a general
phenomenological theory of spin dynamics and relaxation for spin-1 systems.
Results of the phenomenological approach are compared to those obtained by
microscopic calculations for the specific S=1 model with isotropic bilinear and
biquadratic exchange interactions. This model exhibits a rich behavior
depending on the ratio of bilinear and biquadratic exchange constants,
including several points with an enhanced symmetry. It is shown that symmetry
plays an important role in relaxation. Particularly, at the SU(3) ferromagnetic
point the magnon damping $\Gamma$ depends on its wavevector k as $\Gamma\propto
k^{4}$, while a deviation from the high-symmetry point changes the behavior of
the leading term to $\Gamma\propto k^{2}$. We point out a similarity between
the behavior of magnon relaxation in spin nematics to that in an isotropic
ferromagnet.",1303.1194v2
2013-03-21,Spin dynamics of two bosons in an optical lattice site: a role of anharmonicity and anisotropy of the trapping potential,"We study a spin dynamics of two magnetic Chromium atoms trapped in a single
site of a deep optical lattice in a resonant magnetic field. Dipole-dipole
interactions couple spin degrees of freedom of the two particles to their
motion in the site. The motion is quantized, therefore a trap geometry combined
with two-body contact s-wave interactions influence a spin dynamics through the
energy spectrum of the two atom system. Anharmonicity and anisotropy of the
site results in a `fine' structure of two body eigenenergies. The structure can
be easily resolved by a weak magnetic dipole-dipole interactions. As an example
we examine the effect of anharmonicity and anisotropy of the binding potential
on the Einstein-de Haas effect. We show that the weak dipolar interactions
provide a perfect tool for a precision spectroscopy of the energy spectrum of
the interacting few particle system.",1303.5232v2
2013-03-23,The dynamics of Bianchi I universes in $R^n$ cosmologies with torsion,"We analyze the phase space of Bianchi I cosmologies filled by a spin fluid in
the framework of $f(R)$-gravity with torsion using a combination of the
dynamical systems approach and the 1+3 covariant formalism. In the simple case
of $f(R)=R^n$ our results allow a quantification of the role of torsion and the
spin of the cosmic fluid in the evolution of the cosmology. While torsion is
able to modify the cosmological dynamics with respect to the purely metric
case, the spin has little influence on the cosmology. We argue that this is due
to the different symmetries of the tensor characterizing the anisotropies and
the spin tensor. The cosmological model we analyzed presents isotropization for
a wide set of initial conditions and values of the parameters and allows for
two types of exotic bounce solutions.",1303.5828v1
2013-07-14,Simulation of the Dynamics of Many-Body Quantum Spin Systems Using Phase-Space Techniques,"We reformulate the full quantum dynamics of spin systems using a phase space
representation based on SU(2) coherent states which generates an exact mapping
of the dynamics of any spin system onto a set of stochastic differential
equations. The new representation is superior in practice to an earlier phase
space approach based on Schwinger bosons, with the numerical effort scaling
only linearly with system size. By also implementing extrapolation techniques
from quasiclassical equations to the full quantum limit, we are able to extend
useful simulation times several fold. This approach is applicable in any
dimension including cases where frustration is present in the spin system. The
method is demonstrated by simulating quenches in the transverse field Ising
model in one and two dimensions",1307.3786v1
2013-12-20,SU(2s+1) symmetry and nonlinear dynamic equations of spin s magnets,"The article is devoted to the description of dynamics of magnets with
arbitrary spin on the basis of the Hamiltonian formalism. The relationship
between the magnetic ordering and Poisson bracket subalgebras of the magnetic
degrees of freedom for spin s=1/2; 1; 3/2 has been established. We have been
obtained non-linear dynamic equations without damping for normal and degenerate
non-equilibrium states of high-spin magnets with the properties of the SO(3),
SU(4), SU(2)$\times$SU(2), SU(3), SO(4), SO(5) symmetry of exchange
interaction. The connection between models of the magnetic exchange energy and
the Casimir invariants has been discussed.",1312.5828v2
2014-07-23,Modulating spin transfer torque switching dynamics with two orthogonal spin-polarizers by varying the cell aspect ratio,"We study in-plane magnetic tunnel junctions with additional perpendicular
polarizer for subnanosecond-current-induced switching memories. The
spin-transfer-torque switching dynamics was studied as a function of the cell
aspect ratio both experimentally and by numerical simulations using the
macrospin model. We show that the anisotropy field plays a significant role in
the dynamics, along with the relative amplitude of the two spin-torque
contributions. This was confirmed by micromagnetic simulations. Real-time
measurements of the reversal were performed with samples of low and high aspect
ratio. For low aspect ratios, a precessional motion of the magnetization was
observed and the effect of temperature on the precession coherence was studied.
For high aspect ratios, we observed magnetization reversals in less than 1 ns
for high enough current densities, the final state being controlled by the
current direction in the magnetic tunnel junction cell.",1407.6240v2
2014-08-05,Coherent Excitation Transfer in a Spin Chain of Three Rydberg Atoms,"We study coherent excitation hopping in a spin chain realized using highly
excited individually addressable Rydberg atoms. The dynamics are fully
described in terms of an XY spin Hamiltonian with a long range resonant
dipole-dipole coupling that scales as the inverse third power of the lattice
spacing, $C_3/R^3$. The experimental data demonstrate the importance of next
neighbor interactions which are manifest as revivals in the excitation
dynamics. The results suggest that arrays of Rydberg atoms are ideally suited
to large scale, high-fidelity quantum simulation of spin dynamics.",1408.1055v2
2014-09-25,Quantum versus classical annealing: insights from scaling theory and results for spin glasses on 3-regular graphs,"We discuss an Ising spin glass where each $S=1/2$ spin is coupled
antiferromagnetically to three other spins (3-regular graphs). Inducing quantum
fluctuations by a time-dependent transverse field, we use out-of-equilibrium
quantum Monte Carlo simulations to study dynamic scaling at the quantum glass
transition. Comparing the dynamic exponent and other critical exponents with
those of the classical (temperature-driven) transition, we conclude that
quantum annealing is less efficient than classical simulated annealing in
bringing the system into the glass phase. Quantum computing based on the
quantum annealing paradigm is therefore inferior to classical simulated
annealing for this class of problems. We also comment on previous simulations
where a parameter is changed with the simulation time, which is very different
from the true Hamiltonian dynamics simulated here.",1409.7192v2
2014-10-14,Spin precession mapping at ferromagnetic resonance via nuclear resonant scattering,"We probe the spin dynamics in a thin magnetic film at ferromagnetic resonance
by nuclear resonant scattering of synchrotron radiation at the 14.4 keV
resonance of $^{57}$Fe. The precession of the magnetization leads to an
apparent reduction of the magnetic hyperfine field acting at the $^{57}$Fe
nuclei. The spin dynamics is described in a stochastic relaxation model adapted
to the ferromagnetic resonance theory by Smit and Beljers to model the decay of
the excited nuclear state. From the fits of the measured data the shape of the
precession cone of the spins is determined. Our results open a new perspective
to determine magnetization dynamics in layered structures with very high depth
resolution by employing ultrathin isotopic probe layers.",1410.3689v1
2014-10-22,Resonating Valence-Bond State in an Orbitally Degenerate Quantum Magnet with Dynamical Jahn-Teller Effect,"Short-range resonating-valence bond states in an orbitally degenerate magnet
on a honeycomb lattice is studied. A quantum-dimer model is derived from the
Hamiltonian which represents the superexchange interaction and the dynamical
Jahn-Teller (JT) effect. We introduce two local units termed ""spin-orbital
singlet dimer"", where two spins in a nearest-neighbor bond form a singlet state
associated with an orbital polarization along the bond, and ""local JT singlet"",
where an orbital polarization is quenched due to the dynamical JT effect. A
derived quantum-dimer model consists of the hopping of the spin-orbital singlet
dimers and the JT singlets, and the chemical potential of the JT singlets. We
analyze the model by the mean-field approximation, and find that a
characteristic phase, termed ""JT liquid phase"", where both the spin-orbital
singlet dimers and the JT singlets move quantum mechanically, is realized.
Possible scenarios for the recently observed non magnetic-ordered state in
Ba$_3$CuSb$_2$O$_9$ are discussed.",1410.6009v1
2014-12-03,Spin dynamics of the bilinear-biquadratic $S=1$ Heisenberg model on the triangular lattice: a quantum Monte Carlo study,"We study thermodynamic properties as well as the dynamical spin and
quadrupolar structure factors of the O(3)-symmetric spin-1 Heisenberg model
with bilinear-biquadratic exchange interactions on the triangular lattice.
Based on a sign-problem-free quantum Monte Carlo approach, we access both the
ferromagnetic and the ferroquadrupolar ordered, spin nematic phase as well as
the SU(3)-symmetric point which separates these phases. Signatures of Goldstone
soft-modes in the dynamical spin and the quadrupolar structure factors are
identified, and the properties of the low-energy excitations are compared to
the thermodynamic behavior observed at finite temperatures as well as to
Schwinger-boson flavor-wave theory.",1412.1225v1
2015-01-09,Optimized dynamical control of state transfer through noisy spin chains,"We propose a method of optimally controlling the tradeoff of speed and
fidelity of state transfer through a noisy quantum channel (spin-chain). This
process is treated as qubit state-transfer through a fermionic bath. We show
that dynamical modulation of the boundary-qubits levels can ensure state
transfer with the best tradeoff of speed and fidelity. This is achievable by
dynamically optimizing the transmission spectrum of the channel. The resulting
optimal control is robust against both static and fluctuating noise in the
channel's spin-spin couplings. It may also facilitate transfer in the presence
of diagonal disorder (on site energy noise) in the channel.",1501.02133v1
2015-01-26,Dynamics of magnon fluid in Dzyaloshinskii-Moriya magnet and its manifestation in magnon-Skyrmion scattering,"We construct Holstein-Primakoff Hamiltonian for magnons in arbitrary slowly
varying spin background, for a microscopic spin Hamiltonian consisting of
ferromagnetic spin exchange,Dzyaloshinskii-Moriya exchange, and the Zeeman
term. The Gross-Pitaevskii-type equation for magnon dynamics contains several
background gauge fields pertaining to local spin chirality, inhomogeneous
potential, and anomalous scattering that violates the boson number
conservation. Non-trivial corrections to previous formulas derived in the
literature are given. Subsequent mapping to hydrodynamic fields yields the
continuity equation and the Euler equation of the magnon fluid dynamics. Magnon
wave scattering off a localized Skyrmion is examined numerically based on our
Gross-Pitaevskii formulation. Dependence of the effective flux experienced by
the impinging magnon on the Skyrmion radius is pointed out, and compared with
analysis of the same problem using the Landau-Lifshitz-Gilbert equation.",1501.06467v1
2015-01-30,Improved spectral stability in spin transfer nano-oscillators: single vortex versus coupled vortices dynamics,"We perform a comparative study of spin transfer induced excitation of the
gyrotropic motion of a vortex core with either uniform or vortex spin
polarizers. The microwave output voltage associated with the vortex dynamics,
detected in both cases, displays a strong reduction of phase fluctuations in
the case of the vortex polarizer, with a decrease of the peak linewidth by one
order of magnitude down to 200kHz at zero field. A thorough study of rf
emission features for the different accessible vortex configurations shows that
this improvement is related to the excitation of coupled vortex dynamics by
spin transfer torques.",1501.07839v1
2015-03-26,Mott physics and spin fluctuations: a unified framework,"We present a formalism for strongly correlated electrons systems which
consists in a local approximation of the dynamical three-leg interaction
vertex. This vertex is self-consistently computed with a quantum impurity model
with dynamical interactions in the charge and spin channels, similar to
dynamical mean field theory (DMFT) approaches. The electronic self-energy and
the polarization are both frequency and momentum dependent. The method
interpolates between the spin-fluctuation or GW approximations at weak coupling
and the atomic limit at strong coupling. We apply the formalism to the Hubbard
model on a two-dimensional square lattice and show that as interactions are
increased towards the Mott insulating state, the local vertex acquires a strong
frequency dependence, driving the system to a Mott transition, while at low
enough temperatures the momentum-dependence of the self-energy is enhanced due
to large spin fluctuations. Upon doping, we find a Fermi arc in the
one-particle spectral function, which is one signature of the pseudo-gap state.",1503.07724v1
2015-03-27,Dynamic nuclear polarization and the paradox of Quantum Thermalization,"Dynamic Nuclear Polarization (DNP) is to date the most effective technique to
increase the nuclear polarization up to a factor $100,000$ opening disruptive
perspectives for medical applications. In DNP, the nuclear spins are driven to
an - out of equilibrium - hyperpolarized state by microwave saturation of the
electron spins in interaction with them. Here we show that the electron dipolar
interactions compete with the local magnetic fields resulting in two distinct
dynamical phases: for strong interactions the electron spins equilibrate to an
extremely low effective temperature that boosts DNP efficiency. For weak
interaction this spin temperature is not defined and the polarization profile
has an 'hole burning' shape characteristic of the non interacting case. The
study of the many-body eigenstates reveals that these two phases are intimately
related to the problem of thermalization in closed quantum systems where
breaking of ergodicity is expected varying the strength of the interactions.",1503.08181v2
2015-04-09,Spin-transfer torque effects in the dynamic forced response of the magnetization of nanoscale ferromagnets in superimposed ac and dc bias fields in the presence of thermal agitation,"Spin-transfer torque (STT) effects on the stationary forced response of
nanoscale ferromagnets subject to thermal fluctuations and driven by an ac
magnetic field of arbitrary strength and direction are investigated via a
generic nanopillar model of a spin-torque device comprising two ferromagnetic
strata representing the free and fixed layers and a nonmagnetic conducting
spacer all sandwiched between two ohmic contacts. The STT effects are treated
via the Brown magnetic Langevin equation generalized to include the Slonczewski
STT term thereby extending the statistical moment method [Y. P. Kalmykov et
al., Phys. Rev. B 88, 144406 (2013)] to the forced response of the most general
version of the nanopillar model. The dynamic susceptibility, nonlinear
frequency-dependent dc magnetization, dynamic magnetic hysteresis loops, etc.
are then evaluated highlighting STT effects on both the low-frequency thermal
relaxation processes and the high-frequency ferromagnetic resonance, etc.,
demonstrating a pronounced dependence of these on the spin polarization current
and facilitating interpretation of STT experiments.",1504.02319v2
2015-04-13,Insensitivity of spin dynamics to the orbital angular momentum transferred from twisted light to extended semiconductors,"We study the spin dynamics of carriers due to the Rashba interaction in
semiconductor quantum disks and wells after excitation with light with orbital
angular momentum. We find that although twisted light transfers orbital angular
momentum to the excited carriers and the Rashba interaction conserves their
total angular momentum, the resulting electronic spin dynamics is essentially
the same for excitation with light with orbital angular momentum $l=+|l|$ and
$l=-|l|$. The differences between cases with different values of $|l|$ are due
to the excitation of states with slightly different energies and not to the
different angular momenta per se, and vanish for samples with large radii where
a $k$-space quasi-continuum limit can be established. These findings apply not
only to the Rashba interaction but also to all other envelope-function
approximation spin-orbit Hamiltonians like the Dresselhaus coupling.",1504.03098v1
2015-05-04,Numerical study of the dynamics of some long range spin glass models,"We present results of a Monte Carlo study of the equilibrium dynamics of the
one dimensional long-range Ising spin glass model. By tuning a parameter
$\sigma$, this model interpolates between the mean field
Sherrington-Kirkpatrick model and a proxy of the finite dimensional
Edward-Anderson model. Activated scaling fits for the behavior of the
relaxation time $\tau$ as a function of the number of spins $N$ (Namely
$\ln(\tau)\propto N^{\psi}$) give values of $\psi$ that are not stable against
inclusion of subleading corrections. Critical scaling ($\tau\propto N^{\rho}$)
gives more stable fits, at least in the non mean field region. We also present
results on the scaling of the time decay of the critical remanent magnetization
of the Sherrington-Kirkpatrick model, a case where the simulation can be done
with quite large systems and that shows the difficulties in obtaining precise
values for dynamical exponents in spin glass models.",1505.00676v3
2015-07-01,Dynamical spin-density waves in a spin-orbit-coupled Bose-Einstein condensate,"Synthetic spin-orbit (SO) coupling, an important ingredient for quantum
simulation of many exotic condensed matter physics, has recently attracted
considerable attention. The static and dynamic properties of a SO coupled
Bose-Einstein condensate (BEC) have been extensively studied in both theory and
experiment. Here we numerically investigate the generation and propagation of a
\textit{dynamical} spin-density wave (SDW) in a SO coupled BEC using a fast
moving Gaussian-shaped barrier. We find that the SDW wavelength is sensitive to
the barrier's velocity while varies slightly with the barrier's peak potential
or width. We qualitatively explain the generation of SDW by considering a
rectangular barrier in a one dimensional system. Our results may motivate
future experimental and theoretical investigations of rich dynamics in the SO
coupled BEC induced by a moving barrier.",1507.00318v1
2015-07-15,Probing spin dynamics from the Mott insulating to the superfluid regime in a dipolar lattice gas,"We analyze the spin dynamics of an out-of-equilibrium large spin dipolar
atomic Bose gas in an optical lattice. We observe a smooth crossover from a
complex oscillatory behavior to an exponential behavior throughout the Mott to
superfluid transition. While both of these regimes are well described by our
theoretical models, we provide data in the intermediate regime where dipolar
interactions, contact interactions, and super-exchange mechanisms compete. In
this strongly correlated regime, spin dynamics and transport are coupled, which
challenges theoretical models for quantum magnetism.",1507.04273v1
2016-03-03,Scaling analysis and instantons for thermally-assisted tunneling and Quantum Monte Carlo simulations,"We develop an instantonic calculus to derive an analytical expression for the
thermally-assisted tunneling decay rate of a metastable state in a fully
connected quantum spin model. The tunneling decay problem can be mapped onto
the Kramers escape problem of a classical random dynamical field. This
dynamical field is simulated efficiently by path integral Quantum Monte Carlo
(QMC). We show analytically that the exponential scaling with the number of
spins of the thermally-assisted quantum tunneling rate and the escape rate of
the QMC process are identical. We relate this effect to the existence of a
dominant instantonic tunneling path. The instanton trajectory is described by
nonlinear dynamical mean-field theory equations for a single site magnetization
vector, which we solve exactly. Finally, we derive scaling relations for the
""spiky"" barrier shape when the spin tunnelling and QMC rates scale polynomially
with the number of spins $N$ while a purely classical over-the-barrier
activation rate scales exponentially with $N$.",1603.01293v2
2016-09-19,Illuminating Black Hole Binary Formation Channels with Spins in Advanced LIGO,"The recent detections of the binary black hole mergers GW150914 and GW151226
have inaugurated the field of gravitational-wave astronomy. For the two main
formation channels that have been proposed for these sources, isolated binary
evolution in galactic fields and dynamical formation in dense star clusters,
the predicted masses and merger rates overlap significantly, complicating any
astrophysical claims that rely on measured masses alone. Here, we examine the
distribution of spin- orbit misalignments expected for binaries from the field
and from dense star clusters. Under standard assumptions for black-hole natal
kicks, we find that black-hole binaries similar to GW150914 could be formed
with significant spin-orbit misalignment only through dynamical processes. In
particular, these heavy-black-hole binaries can only form with a significant
spin-orbit anti-alignment in the dynamical channel. Our results suggest that
future detections of merging black hole binaries with measurable spins will
allow us to identify the main formation channel for these systems.",1609.05916v2
2016-10-12,Quantum Critical Point revisited by the Dynamical Mean Field Theory,"Dynamical mean field theory is used to study the quantum critical point (QCP)
in the doped Hubbard model on a square lattice. The QCP is characterized by a
universal scaling form of the self energy and a spin density wave instability
at an incommensurate wave vector. The scaling form unifies the low energy kink
and the high energy waterfall feature in the spectral function, while the spin
dynamics includes both the critical incommensurate and high energy
antiferromagnetic paramagnons. We use the frequency dependent four-point
correlation function of spin operators to calculate the momentum dependent
correction to the electron self energy. Our results reveal a substantial
difference with the calculations based on the Spin-Fermion model which
indicates that the frequency dependence of the the quasiparitcle-paramagnon
vertices is an important factor.",1610.03720v1
2017-02-27,Dynamics of Bound Magnon Pairs in the Quasi-One-Dimensional Frustrated Magnet LiCuVO_4,"We report on the dynamics of the spin-1/2 quasi-one-dimensional frustrated
magnet LiCuVO$\mathrm{_4}$ measured by nuclear spin relaxation in high magnetic
fields 10--34 T, in which the ground state has spin-density-wave order. The
spin fluctuations in the paramagnetic phase exhibit striking anisotropy with
respect to the magnetic field. The transverse excitation spectrum probed by
$^{51}$V nuclei has an excitation gap, which increases with field. On the other
hand, the gapless longitudinal fluctuations sensed by $^7$Li nuclei grow with
lowering temperature, but tend to be suppressed with increasing field. Such
anisotropic spin dynamics and its field dependence agree with the theoretical
predictions and are ascribed to the formation of bound magnon pairs, a
remarkable consequence of the frustration between ferromagnetic nearest
neighbor and antiferromagnetic next-nearest-neighbor interactions.",1702.08573v2
2017-03-13,A model for the neutron resonance in HgBa$_{2}$CuO$_{4+δ}$,"We study the spin dynamics of the Resonant Excitonic State (RES) proposed,
within the theory of an emergent SU(2) symmetry, to explain some properties of
the pseudo-gap phase of cuprate superconductors. The RES can be described as a
proliferation of particle-hole patches with an internal modulated structure. We
model the RES modes as a charge order with multiple $2{\bf {p}}_{\text{F}}$
ordering vectors, where $2{\bf {p}}_{\text{F}}$ connects two opposite side of
the Fermi surface. This simple modelization enables us to propose a
comprehensive study of the collective mode observed at the antiferromagnetic
(AF) wave vector $\mathbf{Q}=(\pi,\pi)$ by Inelastic Neutron Scattering (INS)
in both superconducting state (SC), but also in the Pseudogap regime. In this
regime, we show that the dynamic spin susceptibility accuses a loss of
coherence terms except at special wave vectors commensurate with the lattice.
We argue that this phenomenon could explain the change of the spin response
shape around $\mathbf{Q}$. We demonstrate that the hole dependence of the RES
spin dynamics is in agreement with the experimental data in
HgBa$_{2}$CuO$_{4+\delta}$.",1703.04442v1
2017-03-17,Dynamic nuclear spin polarization in self-assembled quantum dots under zero magnetic field,"We studied the zero-field dynamic nuclear spin polarization in a single
In$_{0.75}$Al$_{0.25}$As/Al$_{0.3}$Ga$_{0.7}$As quantum dot. Even without any
external magnetic field, the positive trion excited by the circularly-polarized
light generated an Overhauser field of up to $\sim$0.8 T. From the excitation
power dependences of the Overhauser field and degree of circular polarization
of the photoluminescence spectra, the relation between the Overhauser field and
Knight field under zero external magnetic field was revealed clearly. In
addition, we found that the nuclear depolarization rate decreased as the
magnitude of the longitudinal magnetic field increased, which seemed to be
caused by the influence of the quadrupolar interaction of nuclear spins.
Further, the key parameters describing the dynamics of a coupled
electron-nuclear spin system, the electron g-factor and the fluctuation of the
Overhauser field, were evaluated in a typical single InAlAs quantum dot.",1703.06046v1
2018-02-22,Chaos in Dirac electron optics: Emergence of a relativistic quantum chimera,"We uncover a remarkable quantum scattering phenomenon in two-dimensional
Dirac material systems where the manifestations of both classically integrable
and chaotic dynamics emerge simultaneously and are electrically controllable.
The distinct relativistic quantum fingerprints associated with different
electron spin states are due to a physical mechanism analogous to chiroptical
effect in the presence of degeneracy breaking. The phenomenon mimics a chimera
state in classical complex dynamical systems but here in a relativistic quantum
setting - henceforth the term ""Dirac quantum chimera,"" associated with which
are physical phenomena with potentially significant applications such as
enhancement of spin polarization, unusual coexisting quasibound states for
distinct spin configurations, and spin selective caustics. Experimental
observations of these phenomena are possible through, e.g., optical
realizations of ballistic Dirac fermion systems.",1802.08197v1
2018-04-22,Magnetic Droplet Soliton Nucleation in Oblique Fields,"We study the auto-oscillating magnetodynamics in orthogonal spin torque
nano-oscillators (STNOs) as a function of the out-of-plane (OOP) magnetic field
angle. In perpendicular fields and at OOP field angles down to approximately 50
degrees we observe the nucleation of a droplet. However, for field angles below
50 degrees, experiments indicate that the droplet gives way to propagating spin
waves, in agreement with our micromagnetic simulations. Theoretical
calculations show that the physical mechanism behind these observations is the
sign changing of spin-wave nonlinearity (SWN) by angle. In addition, we show
that the presence of a strong perpendicular magnetic anisotropy (PMA) free
layer in the system reverses the angular dependence of the SWN and dynamics in
STNOs with respect to the known behavior determined for the in-plane magnetic
anisotropy free layer. Our results are of fundamental interest in understanding
the rich dynamics of nanoscale solitons and spin-wave dynamics in STNOs.",1804.08047v2
2018-04-27,Observation of Floquet Raman transition in a driven solid-state spin system,"We experimentally observe Floquet Raman transitions in the weakly driven
solid state spin system of nitrogen-vacancy center in diamond. The periodically
driven spin system simulates a two-band Wannier-Stark ladder model, and allows
us to observe coherent spin state transfer arising from Raman transition
mediated by Floquet synthetic levels. It also leads to the prediction of analog
photon-assisted Floquet Raman transition and dynamical localisation in a driven
two-level quantum system. The demonstrated rich Floquet dynamics offers new
capabilities to achieve effective Floquet coherent control of a quantum system
with potential applications in various types of quantum technologies based on
driven quantum dynamics. In particular, the Floquet-Raman system may be used as
a quantum simulator for the physics of periodically driven systems.",1804.10492v2
2020-07-03,Emergence of Intra-Particle Entanglement and Time-Varying Violation of Bell's Inequality in Dirac Matter,"We demonstrate the emergence and dynamics of intra-particle entanglement in
massless Dirac fermions. This entanglement, generated by spin-orbit coupling,
arises between the spin and sublattice pseudospin of electrons in graphene. The
entanglement is a complex dynamic quantity but is generally large, independent
of the initial state. Its time dependence implies a dynamical violation of a
Bell inequality, while its magnitude indicates that large intra-particle
entanglement is a general feature of graphene on a substrate. These features
are also expected to impact entanglement between pairs of particles, and may be
detectable in experiments that combine Cooper pair splitting with nonlocal
measurements of spin-spin correlation in mesoscopic devices based on Dirac
materials.",2007.01584v2
2020-07-07,Unveiling operator growth in SYK quench dynamics,"We study non-equilibrium dynamics induced by a sudden quench of strongly
correlated Hamiltonians with all-to-all interactions. By relying on a
Sachdev-Ye-Kitaev (SYK) based quench protocol, we show that the time evolution
of simple spin-spin correlation functions is highly sensitive to the degree of
locality of the corresponding operators, once an appropriate set of fundamental
fields is identified. By tracking the time-evolution of specific spin-spin
correlation functions and their decay, we argue that it is possible to
distinguish between operator hopping and operator growth dynamics; the latter
being a hallmark of quantum chaos in many-body quantum systems. Such
observation, in turn, could constitute a promising tool to probe the emergence
of chaotic behavior, rather accessible in state-of-the-art quench setups.",2007.03551v2
2020-07-28,Dynamic modulation of phonon-assisted transitions in quantum defects in monolayer transition-metal dichalcogenide semiconductors,"Quantum localization via atomic point defects in semiconductors is of
significant fundamental and technological importance. Quantum defects in
monolayer transition-metal dichalcogenide semiconductors have been proposed as
stable and scalable optically-addressable spin qubits. Yet, the impact of
strong spin-orbit coupling on their dynamical response, for example under
optical excitation, has remained elusive. In this context, we study the effect
of spin-orbit coupling on the electron-phonon interaction in a single chalcogen
vacancy defect in monolayer transition metal dichalcogenides, molybdenum
disulfide (MoS$_2$) and tungsten disulfide (WS$_2$). From ab initio electronic
structure theory calculations, we find that spin-orbit interactions tune the
magnitude of the electron-phonon coupling in both optical and charge-state
transitions of the defect, modulating their respective efficiencies. This
observation opens up a promising scheme of dynamically modulating material
properties to tune the local behavior of a quantum defect.",2007.14399v1
2014-03-24,"Nuclear Spin Dynamics in Double Quantum Dots: Multi-Stability, Dynamical Polarization, Criticality and Entanglement","We theoretically study the nuclear spin dynamics driven by electron transport
and hyperfine interaction in an electrically-defined double quantum dot (DQD)
in the Pauli-blockade regime. We derive a master-equation-based framework and
show that the coupled electron-nuclear system displays an instability towards
the buildup of large nuclear spin polarization gradients in the two quantum
dots. In the presence of such inhomogeneous magnetic fields, a quantum
interference effect in the collective hyperfine coupling results in sizable
nuclear spin entanglement between the two quantum dots in the steady state of
the evolution. We investigate this effect using analytical and numerical
techniques, and demonstrate its robustness under various types of
imperfections.",1403.6145v2
2016-11-29,Dynamical Shiba states by precessing magnetic moments in an s-wave superconductor,"We study theoretically the dynamics of a Shiba state forming around
precessing classical spin in an s-wave superconductor. Utilizing a rotating
wave description for the precessing magnetic impurity, we find the resulting
Shiba bound state quasi-energy and the spatial extension of the Shiba
wavefunction. We show that such a precession pertains to dc charge and spin
currents flowing through a normal STM tip tunnel coupled to the superconductor
in the vicinity of the impurity. We calculate these currents and find that they
strongly depend on the magnetic impurity precession frequency, precession
angle, and on the position of the Shiba energy level in the superconducting
gap. The resulting charge current is found to be proportional to the difference
between the electron and hole wavefunctions of the Shiba state, being a direct
measure for such an asymmetry. By dynamically driving the impurity one can
infer the spin dependence of the Shiba states in the absence of a
spin-polarized STM tip",1611.09722v1
2017-01-26,Antiferromagnetic textures and dynamics on the surface of a heavy metal,"We investigate the formation and dynamics of spin textures in
antiferromagnetic insulators adjacent to a heavy-metal substrate with strong
spin-orbit interactions. Exchange coupling to conduction electrons engenders an
effective anisotropy, Dzyaloshinskii-Moriya interactions, and a magnetoelectric
effect for the N\'{e}el order, which can conspire to produce nontrivial
antiferromagnetic textures. Current-driven spin transfer enabled by the heavy
metal, furthermore, triggers ultrafast (THz) oscillations of the N\'{e}el order
for dc currents exceeding a critical threshold, opening up the possibility of
Terahertz spin-torque self-oscillators. For a commonly invoked
antidamping-torque geometry, however, the instability current scales with the
energy gap of the antiferromagnetic insulator and, therefore, may be
challenging to reach experimentally. We propose an alternative generic geometry
for inducing ultrafast autonomous antiferromagnetic dynamics.",1701.07863v2
2008-07-30,Dynamics revealed by correlations of time-distributed weak measurements of a single spin,"We show that the correlations in stochastic outputs of time-distributed weak
measurements can be used to study the dynamics of an individual quantum object,
with a proof-of-principle setup based on small Faraday rotation caused by a
single spin in a quantum dot. In particular, the third order correlation can
reveal the ""true"" spin decoherence, which would otherwise be concealed by the
inhomogeneous broadening effect in the second order correlations. The viability
of such approaches lies in that (1) in weak measurement the state collapse
which would disturb the system dynamics occurs at a very low probability, and
(2) a shot of measurement projecting the quantum object to a known basis state
serves as a starter or stopper of the evolution without pumping or coherently
controlling the system as otherwise required in conventional spin echo.",0807.4779v2
2012-01-30,Quantitative MRFM characterization of the autonomous and forced dynamics in a spin transfer nano-oscillator,"Using a magnetic resonance force microscope (MRFM), the power emitted by a
spin transfer nano-oscillator consisting of a normally magnetized Py$|$Cu$|$Py
circular nanopillar is measured both in the autonomous and forced regimes. From
the power behavior in the subcritical region of the autonomous dynamics, one
obtains a quantitative measurement of the threshold current and of the noise
level. Their field dependence directly yields both the spin torque efficiency
acting on the thin layer and the nature of the mode which first
auto-oscillates: the lowest energy, spatially most uniform spin-wave mode. From
the MRFM behavior in the forced dynamics, it is then demonstrated that in order
to phase-lock this auto-oscillating mode, the external source must have the
same spatial symmetry as the mode profile, i.e., a uniform microwave field must
be used rather than a microwave current flowing through the nanopillar.",1201.6344v1
2012-01-31,Nonreciprocal Directional Dichroism and Toroidalmagnons in Helical Magnets,"We investigate a dynamical magnetoelectric effect due to a magnetic resonance
in helical spin structures through the coupling between magnetization and
electric polarization via a spin current mechanism. We show that the magnon has
both the dynamical magnetic moment $\Delta M^\omega$ and the electric moment
$\Delta P^\omega$ ($\perp \Delta M^\omega$), i.e., a dynamical toroidal moment,
under external magnetic fields, and thus it is named the {\em toroidalmagnon}.
The toroidalmagnon exists in most conical spin structures owing to the
generality of the spin current mechanism. In the absorption of electromagnetic
waves, the toroidalmagnon excitation process generally induces a nonreciprocal
directional dichroism as a consequence of an interference of the magnetic and
electric responses.",1201.6458v1
2014-05-09,Current-induced magnetization dynamics in two magnetic insulators separated by a normal metal,"We study the dynamics of spin valves consisting of two layers of magnetic
insulators separated by a normal metal in the macrospin model. A current
through the spacer generates a spin Hall current that can actuate the
magnetization via the spin-transfer torque. We derive expressions for the
effective Gilbert damping and the critical currents for the onset of
magnetization dynamics including the effects of spin pumping that can be tested
by ferromagnetic resonance experiments. The current generates an amplitude
asymmetry between the in-phase and out-of-phase modes. We briefly discuss
superlattices of metals and magnetic insulators.",1405.2267v1
2014-06-06,Relativistic Particle and Relativistic Fluids: Magnetic Moment and Spin-Orbit Interactions,"We consider relativistic charged particle dynamics and relativistic
magnetohydrodynamics using symplectic structures and actions given in terms of
co-adjoint orbits of the Poincar\'e group. The particle case is meant to
clarify some points such as how minimal coupling (as defined in text) leads to
a gyromagnetic ratio of $2$, and to set the stage for fluid dynamics. The
general group-theoretic framework is further explained and is then used to set
up Abelian magnetohydrodynamics including spin effects. An interesting new
physical effect is precession of spin density induced by gradients in pressure
and energy density. The Euler equation (the dynamics of the velocity field) is
also modified by gradients of the spin density.",1406.1551v1
2014-06-10,Coherent spin-rotational dynamics of oxygen super rotors,"We use state- and time-resolved coherent Raman spectroscopy to study the
rotational dynamics of oxygen molecules in ultra-high rotational states. While
it is possible to reach rotational quantum numbers up to $N \approx 50$ by
increasing the gas temperature to 1500 K, low population levels and gas
densities result in correspondingly weak optical response. By spinning O$_2$
molecules with an optical centrifuge, we efficiently excite extreme rotational
states with $N\leqslant 109$ in high-density room temperature ensembles. Fast
molecular rotation results in the enhanced robustness of the created rotational
wave packets against collisions, enabling us to observe the effects of weak
spin-rotation coupling in the coherent rotational dynamics of oxygen. The decay
rate of spin-rotation coherence due to collisions is measured as a function of
the molecular angular momentum and explained in terms of the general scaling
law. We find that at high values of $N$, the rotational decoherence of oxygen
is much faster than that of the previously studied non-magnetic nitrogen
molecules. This may suggest a different mechanism of rotational relaxation in
paramagnetic gases.",1406.2668v1
2017-07-03,Role of temperature-dependent spin model parameters in ultra-fast magnetization dynamics,"In the spirit of multi-scale modelling magnetization dynamics at elevated
temperature is often simulated in terms of a spin model where the model
parameters are derived from first principles. While these parameters are mostly
assumed temperature-independent and thermal properties arise from spin
fluctuations only, other scenarios are also possible. Choosing bcc Fe as an
example, we investigate the influence of different kinds of model assumptions
on ultra-fast spin dynamics, where following a femtosecond laser pulse a sample
is demagnetized due to a sudden rise of the electron temperature. While
different model assumptions do not affect the simulational results
qualitatively, their details do depend on the nature of the modelling.",1707.00374v1
2017-07-07,Many-body kinetics of dynamic nuclear polarization by the cross effect,"Dynamic nuclear polarization (DNP) is an out-of-equilibrium method for
generating non-thermal spin polarization which provides large signal
enhancements in modern diagnostic methods based on nuclear magnetic resonance.
A particular instance is cross effect DNP, which involves the interaction of
two coupled electrons with the nuclear spin ensemble. Here we develop a theory
for this important DNP mechanism and show that the non-equilibrium nuclear
polarization build-up is effectively driven by three-body incoherent Markovian
dissipative processes involving simultaneous state changes of two electrons and
one nucleus. Our theoretical approach allows for the first time simulations of
the polarization dynamics on an individual spin level for ensembles consisting
of hundreds of nuclear spins. The insight obtained by these simulations can be
used to find optimal experimental conditions for cross effect DNP and to design
tailored radical systems that provide optimal DNP efficiency.",1707.02128v1
2017-07-11,"Aging, memory, and nonhierarchical energy landscape of spin jam","The notion of complex energy landscape underpins the intriguing dynamical
behaviors in many complex systems ranging from polymers, to brain activity, to
social networks and glass transitions. The spin glass state found in dilute
magnetic alloys has been an exceptionally convenient laboratory frame for
studying complex dynamics resulting from a hierarchical energy landscape with
rugged funnels. Here, we show, by a bulk susceptibility and Monte Carlo
simulation study, that densely populated frustrated magnets in a spin jam state
exhibit much weaker memory effects than spin glasses, and the characteristic
properties can be reproduced by a nonhierarchical landscape with a wide and
nearly flat but rough bottom. Our results illustrate that the memory effects
can be used to probe different slow dynamics of glassy materials, hence opening
a window to explore their distinct energy landscapes.",1707.03086v1
2018-01-02,The Lipkin-Meshkov-Glick model with Markovian dissipation -- A description of a collective spin on a metallic surface,"Motivated by recent prototypes of engineered atomic spin devices, we study a
fully connected system of $N$ spins $1/2$, modeled by the Lipkin-Meshkov-Glick
(LMG) model of a collective spin $s=N/2$ in the presence of Markovian
dissipation processes. We determine and classify the different phases of the
dissipative LMG model with Markovian dissipation, including the properties of
the steady-state and the dynamic behavior in the asymptotic long-time regime.
Employing variational methods and a systematic approach based on the
Holstein-Primakoff mapping, we determine the phase diagram and the spectral and
steady-state properties of the Liouvillian by studying both the infinite-$s$
limit and $1/s$ corrections. Our approach reveals the existence of different
kinds of dynamical phases and phase transitions, multi-stability and regions
where the dynamics is recurrent. We provide a classification of critical and
non-critical Liouvillians according to their spectral and steady-state
properties.",1801.00818v2
2018-09-20,Non-universal critical aging scaling in three-dimensional Heisenberg antiferromagnets,"We numerically investigate the stationary and non-equilibrium critical
dynamics in three-dimensional isotropic Heisenberg antiferromagnets. Since the
non-conserved staggered magnetization couples dynamically to the conserved
magnetization density, we employ a hybrid simulation algorithm that combines
reversible spin precession with relaxational Kawasaki spin exchange processes.
We measure the dynamic critical exponent and identify a suitable intermediate
time window to obtain the aging scaling exponents. Our results support an
earlier renormalization group prediction: While the critical aging collapse
exponent assumes a universal value, the associated temporal decay exponent in
the two-time spin autocorrelation function depends on the initial distribution
of the conserved fields; here, specifically on the width of the initial spin
orientation distribution.",1809.07799v2
2019-07-03,Spin wave excitations of magnetic metalorganic materials,"The Organic Materials Database (OMDB) is an open database hosting about
22,000 electronic band structures, density of states and other properties for
stable and previously synthesized 3-dimensional organic crystals. The web
interface of the OMDB offers various search tools for the identification of
novel functional materials such as band structure pattern matching and density
of states similarity search. In this work the OMDB is extended to include
magnetic excitation properties. For inelastic neutron scattering we focus on
the dynamical structure factor $S(\mathbf{q},\omega)$ which contains
information on the excitation modes of the material. We introduce a new dataset
containing atomic magnetic moments and Heisenberg exchange parameters for which
we calculate the spin wave spectra and dynamic structure factor with linear
spin wave theory and atomistic spin dynamics. We thus develop the materials
informatics tools to identify novel functional organic and metalorganic
magnets.",1907.01817v2
2019-09-02,Crossover from weak to strong quench in a spinor Bose-Einstein condensate,"We investigate the early-time dynamics of a quasi-two-dimensional spin-1
antiferromagnetic Bose-Einstein condensate after a sudden quench from the
easy-plane to the easy-axis polar phase. The post-quench dynamics shows a
crossover behavior as the quench strength $\tilde{q}$ is increased, where
$\tilde{q}$ is defined as the ratio of the initial excitation energy per
particle to the characteristic spin interaction energy. For a weak quench of
$\tilde{q}<1$, long-wavelength spin excitations are dominantly generated,
leading to the formation of irregular spin domains. With increasing
$\tilde{q}$, the length scale of the initial spin excitations decreases, and we
demonstrate that the long-wavelength instability is strongly suppressed for
high $\tilde{q}>2$. The observed crossover behavior is found to be consistent
with the Bogoliubov description of the dynamic instability of the initial
spinor condensate.",1909.00681v2
2019-10-11,Analytical and Numerical Methods and Test Calculations of One-Dimensional Force--Free Magnetodynamics on Arbitrary Magnetic Surfaces across Horizons of Spinning Black Holes,"Numerical simulations of the force-free magnetodynamics (FFMD) of the
electromagnetic field around a spinning black hole are useful to investigate
the dynamic electromagnetic processes around a spinning black hole, such as the
emergence of the Blandford--Znajek mechanism. To reveal the basic physics of
magnetic fields around a black hole through the dynamic process, we use
one-dimensional (1D) FFMD along the axisymmetric magnetic surface, which
provides a relatively simple, sufficiently precise, and powerful tool to
analyze the dynamic process around a spinning black hole. We review the
analytic and numerical aspects of 1D FFMD for an arbitrary magnetic surface
around a black hole. In addition, we also show some numerical simulation test
results for three types of magnetic surfaces at the equatorial plane of the
black hole.",1910.04929v1
2020-01-28,Magnetic oscillation modes in square lattice artificial spin ice,"Small amplitude dipolar oscillations are considered in artificial spin ice on
a square lattice in two dimensions. The net magnetic moment of each elongated
magnetic island in the spin ice is assumed to have Heisenberg-like dynamics.
Each island's magnetic moment is assumed to be influenced by shape anisotropies
and by the dipolar interactions with its nearest neighbors. The magnetic
dynamics is linearized around one of the ground states, leading to an $8\times
8$ matrix to be diagonalized for the magnetic spin wave modes. Analytic
solutions are found and classified as antisymmetric and symmetric with regard
to their in-plane dynamic fluctuations. Although only the leading dipolar
interactions are included, modes similar to these may be observable
experimentally.",2001.10409v1
2020-01-31,Observation of state-to-state hyperfine-changing collision in a Bose-Fermi mixture of $^6$Li and $^{41}$K atoms,"Hyperfine-changing collisions are of fundamental interest for the studying of
ultracold heteronuclear mixtures. Here, we report the state-to-state study of
the hyperfine-changing-collision dynamics in a Bose-Fermi mixture of $^6$Li and
$^{41}$K atoms. The collision products are directly observed and the
spin-changing dynamics is measured. Based on a two-body collision model, the
experimental results are simultaneously fitted from which the spin-changing
rate coefficient of $ 1.9(2)\times 10^{-12}~\rm{cm^3\cdot s^{-1}}$ is gained,
being consistent with the multi-channel quantum defect theory calculation. We
further show that the contact parameter of $^6$Li-$^{41}$K mixture can be
extracted from the measured spin-changing dynamics. The obtained results are
consistent with the first order perturbation theory in the weakly-interacting
limit. Our system offers great promise for studying spin-changing interactions
in heteronuclear mixtures.",2001.11652v1
2020-12-14,Hidden geometry and dynamics of complex networks: Spin reversal in nanoassemblies with pairwise and triangle-based interactions,"Recent studies of networks representing complex systems from the brain to
social graphs have revealed their higher-order architecture, which can be
described by aggregates of simplexes (triangles, tetrahedrons, and higher
cliques). Current research aims at quantifying these hidden geometries by the
algebraic topology methods and deep graph theory and understanding the dynamic
processes on simplicial complexes. Here, we use the recently introduced model
for geometrical self-assembly of cliques to grow nano-networks of triangles and
study the filed-driven spin reversal processes on them. With the
antiferromagnetic interactions between the Ising spins attached to the nodes,
this assembly ideally supports the geometric frustration, which is recognized
as the origin of some new phenomena in condensed matter physics. In the
dynamical model, a gradual switching from the pairwise to triangle-based
interactions is controlled by a parameter. Thus, the spin frustration effects
on each triangle give way to the mesoscopic ordering conditioned by a complex
arrangement of triangles. We show how the balance between these interactions
changes the shape of the hysteresis loop. Meanwhile, the fluctuations in the
accompanying Barkhausen noise exhibit robust indicators of self-organized
criticality, which is induced by the network geometry alone without any
magnetic disorder.",2012.07506v1
2021-01-11,Robust Dynamical Decoupling for the Manipulation of a Spin Network via a Single Spin,"High-fidelity control of quantum systems is crucial for quantum information
processing, but is often limited by perturbations from the environment and
imperfections in the applied control fields. Here, we investigate the
combination of dynamical decoupling (DD) and robust optimal control (ROC) to
address this problem. In this combination, ROC is employed to find robust
shaped pulses, wherein the directional derivatives of the controlled dynamics
with respect to control errors are reduced to a desired order. Then, we
incorporate ROC pulses into DD sequences, achieving a remarkable improvement of
robustness against multiple error channels. We demonstrate this method in the
example of manipulating nuclear spin bath via an electron spin in the NV center
system. Simulation results indicate that ROC based DD sequences outperform the
state-of-the-art robust DD sequences. Our work has implications for robust
quantum control on near-term noisy quantum devices.",2101.03976v1
2021-01-15,Magnetic properties of transition metal dimers probed by inelastic neutron scattering,"The physical characterisation and understanding of molecular magnetic
materials is one of the most important steps towards the integration of such
systems in hybrid spintronic devices. Amongst the many characterisation
techniques employed in such a task, Inelastic Neutron Scattering (INS) stands
as one of the most powerful and sensitive tools to investigate their spin
dynamics. Herein, the magnetic properties and spin dynamics of two dinuclear
complexes, namely [(M(hfacac)$_2$)$_2$(bpym)] (where M = Ni$^{2+}$, Co$^{2+}$,
abbreviated in the following as Ni$_2$, Co$_2$) are reported. These are model
systems that could constitute fundamental units of future spintronic devices.
By exploiting the highly sensitive IN5 Cold INS spectrometer, we are able to
gain a deep insight into the spin dynamics of Ni$_2$ and to fully obtain the
microscopic spin Hamiltonian parameters; while for Co$_2$, a multitude of INS
transitions are observed demonstrating the complexity of the magnetic
properties of octahedral cobalt-based systems.",2101.06225v1
2017-05-11,Spectral gap estimates in mean field spin glasses,"We show that mixing for local, reversible dynamics of mean field spin glasses
is exponentially slow in the low temperature regime. We introduce a notion of
free energy barriers for the overlap, and prove that their existence imply that
the spectral gap is exponentially small, and thus that mixing is exponentially
slow. We then exhibit sufficient conditions on the equilibrium Gibbs measure
which guarantee the existence of these barriers, using the notion of replicon
eigenvalue and 2D Guerra Talagrand bounds. We show how these sufficient
conditions cover large classes of Ising spin models for reversible
nearest-neighbor dynamics and spherical models for Langevin dynamics. Finally,
in the case of Ising spins, Panchenko's recent rigorous calculation [79] of the
free energy for a system of ""two real replica"" enables us to prove a quenched
LDP for the overlap distribution, which gives us a wider criterion for slow
mixing directly related to the Franz-Parisi-Virasoro approach [43,60]. This
condition holds in a wider range of temperatures.",1705.04243v3
2017-05-23,Coherent many-body spin dynamics in a long-range interacting Ising chain,"Coherent many-body quantum dynamics lies at the heart of quantum simulation
and quantum computation. Both require coherent evolution in the exponentially
large Hilbert space of an interacting many-body system. To date, trapped ions
have defined the state of the art in terms of achievable coherence times in
interacting spin chains. Here, we establish an alternative platform by
reporting on the observation of coherent, fully interaction-driven quantum
revivals of the magnetization in Rydberg-dressed Ising spin chains of atoms
trapped in an optical lattice. We identify partial many-body revivals at up to
about ten times the characteristic time scale set by the interactions. At the
same time, single-site-resolved correlation measurements link the magnetization
dynamics with inter-spin correlations appearing at different distances during
the evolution. These results mark an enabling step towards the implementation
of Rydberg atom based quantum annealers, quantum simulations of higher
dimensional complex magnetic Hamiltonians, and itinerant long-range interacting
quantum matter.",1705.08372v1
2017-09-11,Application of the Landau-Zener-Stueckelberg-Majorana dynamics in an electrically driven flip of a hole spin,"An idea of employing the Landau-Zener-St\""uckelberg-Majorana (LZSM) dynamics
to flip a spin of a single ground state hole is introduced and explored by a
time-dependent simulation. This configuration interaction study considers a
hole confined in a quantum molecule formed in InSb $\langle111\rangle$ quantum
wire by application of an electrostatic potential. An up-down spin-mixing
avoided crossing is formed by non-axial terms in the Kohn-Luttinger Hamiltonian
and the Dresselhaus spin-orbit one. Manipulation of the system is possible by
dynamic change of external vertical electric field, which enables the
consecutive driving of the hole through two anticrossings. Moreover, a simple
model of the power-law type noise that impedes the precise electric control of
the system is included in the form of Random Telegraph Noise to estimate the
limitations of the working conditions. We show that in principle the process is
possible, but it requires a precise control of parameters of the driving
impulse.",1709.03623v3
2017-09-13,Chaotic dynamics in a macrospin spin-torque nano-oscillator with delayed feedback,"A theoretical study of delayed feedback in spin-torque nano-oscillators is
presented. A macrospin geometry is considered, where self-sustained
oscillations are made possible by spin transfer torques associated with spin
currents flowing perpendicular to the film plane. By tuning the delay and
amplification of the self-injected signal, we identify dynamical regimes in
this system such as chaos, switching between precession modes with complex
transients, and oscillator death. Such delayed feedback schemes open up a new
field of exploration for such oscillators, where the complex transient states
might find important applications in information processing.",1709.04310v2
2017-11-13,Variational Monte Carlo study of spin dynamics in underdoped cuprates,"The hour-glass-like dispersion of spin excitations is a common feature of
underdoped cuprates. It was qualitatively explained by the random phase
approximation based on various ordered states with some phenomenological
parameters; however, its origin remains elusive. Here, we present a numerical
study of spin dynamics in the $t$-$J$ model using the variational Monte Carlo
method. This parameter-free method satisfies the no double-occupancy constraint
of the model and thus provides a better evaluation on the spin dynamics with
respect to various mean-field trial states. We conclude that the lower branch
of the hour-glass dispersion is a collective mode and the upper branch is more
likely the consequence of the stripe state than the other candidates.",1711.04479v1
2018-06-01,Dirac-Surface-State Modulated Spin Dynamics in a Ferrimagnetic Insulator at Room Temperature,"This work demonstrates dramatically modified spin dynamics of magnetic
insulator (MI) by the spin-momentum locked Dirac surface states of the adjacent
topological insulator (TI) which can be harnessed for spintronic applications.
As the Bi-concentration x is systematically tuned in 5 nm thick (BixSb1-x)2Te3
TI film, the weight of the surface relative to bulk states peaks at x = 0.32
when the chemical potential approaches the Dirac point. At this concentration,
the Gilbert damping constant of the precessing magnetization in 10 nm thick
Y3Fe5O12 MI film in the MI/TI heterostructures is enhanced by an order of
magnitude, the largest among all concentrations. In addition, the MI acquires
additional strong magnetic anisotropy that favors the in-plane orientation with
similar Bi-concentration dependence. These extraordinary effects of the Dirac
surface states distinguish TI from other materials such as heavy metals in
modulating spin dynamics of the neighboring magnetic layer.",1806.00151v1
2018-06-07,Quantum accelerated approach to the thermal state of classical spin systems with applications to pattern-retrieval in the Hopfield neural network,"We explore the question as to whether quantum effects can yield a speedup of
the non-equilibrium evolution of spin systems towards a classical thermal
state. In our approach we exploit the fact that the thermal state of a spin
system can be mapped onto a node-free quantum state whose coefficients are
given by thermal weights. This perspective permits the construction of a
dissipative -- yet quantum -- dynamics which encodes in its stationary state
the thermal state of the original problem. We show for the case of an
all-to-all connected Ising spin model that an appropriate transformation of
this dissipative dynamics allows to interpolate between a regime in which the
order parameter obeys the classical equations of motion under Glauber dynamics,
to a quantum regime with an accelerated approach to stationarity. We show that
this effect enables in principle a speedup of pattern retrieval in a Hopfield
neural network.",1806.02747v1
2018-08-27,Quantum Hydrodynamics in Spin Chains with Phase Space Methods,"Connecting short time microscopic dynamics with long time hydrodynamics in
strongly correlated quantum systems is one of the outstanding questions. In
particular, it is very difficult to determine various hydrodynamic coefficients
like the diffusion constant or viscosity starting from a microscopic model:
exact quantum simulations are limited to either small system sizes or to short
times, which are insufficient to reach asymptotic behavior. In this Letter, we
show that these difficulties, at least for a particular model, can be
circumvented by using the cluster truncated Wigner approximation (CTWA), which
maps quantum Hamiltonian dynamics into classical Hamiltonian dynamics in
auxiliary high-dimensional phase space. We apply CTWA to a XXZ
next-nearest-neighbor spin 1/2 chain and find behavior consisting of short time
spin relaxation which gradually crosses over to emergent diffusive behavior at
long times. For a random initial state we show that CTWA correctly reproduces
the whole spin spectral function. Necessary in this construction is sampling
from properly fluctuating initial conditions: the Dirac mean-field
(variational) ansatz, which neglects such fluctuations, leads to incorrect
predictions.",1808.08977v2
2018-12-05,Dynamics of spin and density fluctuations in strongly interacting few-body systems,"The decoupling of spin and density dynamics is a remarkable feature of
quantum one-dimensional many-body systems. In a few-body regime, however,
little is known about this phenomenon. To address this problem, we study the
time evolution of a small system of strongly interacting fermions after a
sudden change in the trapping geometry. We show that, even at the few-body
level, the excitation spectrum of this system presents separate signatures of
spin and density dynamics. Moreover, we describe the effect of considering
additional internal states with SU(N) symmetry, which ultimately leads to the
vanishing of spin excitations in a completely balanced system.",1812.01976v2
2019-01-29,Constructing phase space distributions with internal symmetries,"We discuss an ab initio world-line approach to constructing phase space
distributions in systems with internal symmetries. Starting from the
Schwinger-Keldysh real time path integral in quantum field theory, we derive
the most general extension of the Wigner phase space distribution to include
color and spin degrees of freedom in terms of dynamical Grassmann variables.
The corresponding Liouville distribution for colored particles, which obey
Wong's equation, has only singlet and octet components, while higher moments
are fully constrained by the Grassmann algebra. The extension of phase space
dynamics to spin is represented by a generalization of the Pauli-Lubanski
vector; its time evolution via the Bargmann-Michel-Telegdi equation also
follows from the phase space trajectories of the underlying Grassmann
coordinates. Our results for the Liouville phase space distribution in systems
with both spin and color are of interest in fields as diverse as chiral fluids,
finite temperature field theory and polarized parton distribution functions. We
also comment on the role of the chiral anomaly in the phase space dynamics of
spinning particles.",1901.10492v2
2020-03-05,The branching ratio of LIGO binary black holes,"Formation of binary black holes (BBHs) detected by gravitational-wave (GW)
observations could be broadly divided into two categories: those formed through
field binary evolution and those assembled dynamically in dense stellar
systems. The branching ratio of the BBHs refers to the contribution of each
channel. The dynamical assembly channel would predict a symmetric distribution
in the effective spins of the BBHs while field formation predicts BBHs to have
positive effective spins. By modeling these two populations based on their
effective spin distribution we show that in the 10 BBHs detected by LIGO/Virgo
the contribution of the dynamically assembled BBHs to be more than about 50\%
with 90\% confidence. This result is based on the assumption that the field
binaries are born with positive effective spins not restricted to have small
values.",2003.02764v1
2020-05-07,Ultrafast All Optical Magnetization Control for Broadband Terahertz Spin Wave Generation,"Terahertz spin waves could be generated on-demand via all-optical
manipulation of magnetization by femtosecond laser pulse. Here, we present an
energy balance model, which explains the energy transfer rates from laser pulse
to electron bath coupled with phonon, spin, and magnetization of five different
magnetic metallic thin films: Iron, Cobalt, Nickel, Gadolinium and Ni$_{2}$MnSn
Heusler alloy. Two types of transient magnetization dynamics emerge in metallic
magnetic thin films based on their Curie temperatures (T$_{C}$): type I (Fe,
Co, and Ni with T$_{C}$ > room temperature, RT) and type II films (Gd and
Ni$_{2}$MnSn with T$_{C}$ $\approx$ RT). We study the effect of laser fluence
and pulse width for single Gaussian laser pulses and the effect of metal film
thickness on magnetization dynamics. Spectral dynamics show that broadband spin
waves up to 24 THz could be generated by all-optical manipulation of
magnetization in these nanofilms.",2005.03493v1
2020-05-09,Chaotic cyclotron and Hall trajectories due to spin-orbit coupling,"We demonstrate that the synergistic effect of a gauge field, Rashba
spin-orbit coupling (SOC), and Zeeman splitting can generate chaotic cyclotron
and Hall trajectories of particles. The physical origin of the chaotic behavior
is that the SOC produces a spin-dependent (so-called anomalous) contribution to
the particle velocity and the presence of Zeeman field reduces the number of
integrals of motion. By using analytical and numerical arguments, we study the
conditions of chaos emergence and report the dynamics both in the regular and
chaotic regimes. {We observe the critical dependence of the dynamic patterns
(such as the chaotic regime onset) on small variations in the initial
conditions and problem parameters, that is the SOC and/or Zeeman constants. The
transition to chaotic regime is further verified by the analysis of phase
portraits as well as Lyapunov exponents spectrum.} The considered chaotic
behavior can occur in solid state systems, weakly-relativistic plasmas, and
cold atomic gases with synthetic gauge fields and spin-related couplings.",2005.04468v1
2020-06-16,Noisy quantum metrology enhanced by continuous nondemolition measurement,"We show that continuous quantum nondemolition (QND) measurement of an atomic
ensemble is able to improve the precision of frequency estimation even in the
presence of independent dephasing acting on each atom. We numerically simulate
the dynamics of an ensemble with up to N = 150 atoms initially prepared in a
(classical) spin coherent state, and we show that, thanks to the spin squeezing
dynamically generated by the measurement, the information obtainable from the
continuous photocurrent scales superclassically with respect to the number of
atoms N. We provide evidence that such superclassical scaling holds for
different values of dephasing and monitoring efficiency. We moreover calculate
the extra information obtainable via a final strong measurement on the
conditional states generated during the dynamics and show that the
corresponding ultimate limit is nearly achieved via a projective measurement of
the spin-squeezed collective spin operator. We also briefly discuss the
difference between our protocol and standard estimation schemes, where the
state preparation time is neglected.",2006.08974v3
2021-02-03,Spin-flip pair-density functional theory: A practical approach to treat static and dynamical correlations in large molecules,"We present a practical approach to treat static and dynamical correlation
accurately in large multi-configurational systems. The static correlation is
accounted for using the spin-flip approach which is well known for capturing
static correlation accurately at low-computational expense. Unlike previous
approaches to add dynamical correlation to spin-flip models which use
perturbation theory or coupled-cluster theory, we explore the ability to use
the on-top pair-density functional theory approaches recently developed by
Gagliardi and co-workers (JCTC, 10, 3669, 2014). External relaxations are
carried out in the spin-flip calculations though a restricted active space
framework for which a truncation scheme for the orbitals used in the external
excitation is presented. The performance of the approach is demonstrated by
computing energy gaps between ground and excited states for diradicals,
triradicals and linear polyacene chains ranging from naphthalene to dodecacene.
Accurate results are obtained using the new approach for these challenging
open-shell molecular systems.",2102.02325v1
2021-02-24,Substrate-controlled dynamics of spin qubits in low dimensional van-der-Waals materials,"We report a theoretical study of the coherence dynamics of spin qubits in
two-dimensional materials (2DMs) and van-der-Waals heterostructures, as a
function of the host thickness and the composition of the surrounding
environment. We focus on MoS$_2$ and WS$_2$, two promising systems for quantum
technology applications, and we consider the decoherence arising from the
interaction of the spin qubit with nuclear spins. We show that the Hahn-echo
coherence time is determined by a complex interplay between the source of
decoherence in the qubit host and in the environment, which in turn determines
whether the noise evolution is in a classical or quantum mechanical regime. We
suggest that the composition and thickness of van-der-Waals heterostructures
encapsulating a qubit host can be engineered to maximize coherence times.
Finally, we discuss how quantum sensors may be able to probe the dynamics of
the nuclear bath in 2DMs.",2102.12469v1
2021-05-04,Floquet Hamiltonian Engineering of an Isolated Many-Body Spin System,"Controlling interactions is the key element for quantum engineering of
many-body systems. Using time-periodic driving, a naturally given many-body
Hamiltonian of a closed quantum system can be transformed into an effective
target Hamiltonian exhibiting vastly different dynamics. We demonstrate such
Floquet engineering with a system of spins represented by Rydberg states in an
ultracold atomic gas. Applying a sequence of spin manipulations, we change the
symmetry properties of the effective Heisenberg XYZ Hamiltonian. As a
consequence, the relaxation behavior of the total spin is drastically modified.
The observed dynamics can be qualitatively captured by a semi-classical
simulation. Synthesising a wide range of Hamiltonians opens vast opportunities
for implementing quantum simulation of non-equilibrium dynamics in a single
experimental setting.",2105.01597v1
2021-05-05,Spin dynamical decoupling for generating macroscopic superpositions of a free-falling nanodiamond,"Levitated nanodiamonds containing negatively charged nitrogen-vacancy centers
(${\text{NV}}^{-}$) have been proposed as a platform to generate macroscopic
spatial superpositions. Requirements for this include having a long
${\text{NV}}^{-}$ spin coherence time, which necessitates formulating a
dynamical decoupling strategy in which the regular spin flips do not cancel the
growth of the superposition through the Stern-Gerlach effect in an
inhomogeneous magnetic field. Here, we propose a scheme to place a
$250$-nm-diameter diamond in a superposition with spatial separation of over
$250$ nm, while incorporating dynamical decoupling. We achieve this by letting
a diamond fall for $2.4$ m through a magnetic structure, including $1.13$ m in
an inhomogeneous region generated by magnetic teeth.",2105.02105v3
2021-05-31,"Dynamic polarization of electron spins in indirect band gap (In,Al)As/AlAs quantum dots in weak magnetic field: experiment and theory","A novel spin orientation mechanism - dynamic electron spin polarization has
been recently suggested in Phys. Rev. Lett. $\mathbf{125}$, 156801 (2020). It
takes place for unpolarized optical excitation in weak magnetic fields of the
order of a few millitesla. In this paper we demonstrate experimentally and
theoretically that the dynamic electron spin polarization degree changes sign
as a function of time, strength of the applied magnetic field and its
direction. The studies are performed on indirect band-gap (In,Al)As/AlAs
quantum dots and their results are explained in the framework of a theoretical
model developed for our experimental setting.",2106.00044v1
2021-07-08,Phase transition dynamics in the three-dimensional field-free $\pm J$ Ising model,"By using frustration-preserving hard-spin mean-field theory, we investigated
the phase transition dynamics in the three-dimensional field-free $\pm J$ Ising
spin glass model. As the temperature $T$ is decreased from paramagnetic phase
at high temperatures, with a rate $\omega=-dT/dt$ in time $t$, the critical
temperature depends on the cooling rate through a clear power-law $\omega^a$.
With increasing antiferromagnetic bond fraction $p$, the exponent $a$ increases
for the transition into the ferromagnetic case for $p<p_\text{c}$, and
decreases for the transition into the spin glass phase for $p>p_\text{c}$,
signaling the ferromagnetic-spin glass phase transition at
$p_\text{c}\approx0.22$. The relaxation time is also investigated, at adiabatic
case $\omega=0$, and it is found that the dynamic exponent $z\nu$ increases
with increasing $p$.",2107.03981v1
2021-07-13,PyCCE: A Python Package for Cluster Correlation Expansion Simulations of Spin Qubit Dynamic,"We present PyCCE, an open-source Python library to simulate the dynamics of
spin qubits in a spin bath, using the cluster-correlation expansion (CCE)
method. PyCCE includes modules to generate realistic spin baths, employing
coupling parameters computed from first principles with electronic structure
codes, and enables the user to run simulations with either the conventional or
generalized CCE method. We illustrate three use cases of the Python library:
the calculation of the Hahn-echo coherence time of the nitrogen vacancy in
diamond; the calculation of the coherence time of the basal divacancy in
silicon carbide at avoided crossings; and the magnetic field
orientation-dependent dynamics of a shallow donor in silicon.
  The complete documentation and installation instructions are available at
https://pycce.readthedocs.io/en/latest/.",2107.05843v1
2021-09-08,Excitonic wave-packet evolution in a two-orbital Hubbard model chain: A real-time real-space study,"Motivated by experimental developments introducing the concept of spin-orbit
separation, we study the real-space time evolution of an excitonic wave-packet
using a two-orbital Hubbard model. The exciton is created by exciting an
electron from a lower energy half-filled orbital to a higher energy empty
orbital. We carry out the real-time dynamics of the resulting excitonic
wave-packet, using the time-dependent density matrix renormalization group
method. We find clear evidence of charge-spin and spin-orbit separation in
real-space, by tracking the time evolution of local observables. We show that
the velocity of the orbiton can be tuned by varying the inter-orbital
interactions. We also present a comparative study of a hole (in one orbital)
and exciton (in two orbitals) dynamics in one-dimensional systems. Moreover, we
analyze the dynamics of an exciton with spin-flip excitation, where we observe
fractionalized spinons induced by Hund's interaction.",2109.03618v1
2021-09-20,Dynamical signatures of thermal spin-charge deconfinement in the doped Ising model,"The mechanism underlying charge transport in strongly correlated quantum
systems, such as doped antiferromagnetic Mott insulators, remains poorly
understood. Here we study the expansion dynamics of an initially localized hole
inside a two-dimensional (2D) Ising antiferromagnet at variable temperature.
Using a combination of classical Monte Carlo and a truncated basis method, we
reveal two dynamically distinct regimes: A spin-charge confined region below a
critical temperature $T^*$, characterized by slow spreading, and a spin-charge
deconfined region above $T^*$, characterized by an unbounded diffusive
expansion. The deconfinement temperature $T^*\approx 0.65 J_z$ we find is
around the N\'eel temperature $T_{\rm N} = 0.567 J_z$ of the Ising background
in 2D, but we expect $T^* < T_{\rm N}$ in higher dimensions. In both regimes we
find that the mobile hole does not thermalize with the Ising spin background on
the considered time scales, indicating weak effective coupling of spin- and
charge degrees of freedom. Our results can be qualitatively understood by an
effective parton model, and can be tested experimentally in state-of-the-art
quantum gas microscopes.",2109.09732v1
2021-09-30,Observation of the orbital Hall effect in a light metal Ti,"The orbital angular momentum is a core ingredient of orbital magnetism, spin
Hall effect, giant Rashba spin splitting, orbital Edelstein effect, and
spin-orbit torque. However, its experimental detection is tricky. In
particular, direct detection of the orbital Hall effect remains elusive despite
its importance for electrical control of magnetic nanodevices. Here we report
the direct observation of the orbital Hall effect in a light metal Ti. The Kerr
rotation by the accumulated orbital magnetic moment is measured at Ti surfaces,
whose result agrees with theoretical calculations semiquantitatively and is
supported by the orbital torque measurement in Ti-based magnetic
heterostructures. The results confirm the electron orbital angular momentum as
an essential dynamic degree of freedom, which may provide a novel mechanism for
the electric control of magnetism. The results may also deepen the
understanding of spin, valley, phonon, and magnon dynamics coupled with orbital
dynamics.",2109.14847v1
2021-10-13,Absence of superdiffusion in certain random spin models,"The dynamics of spin at finite temperature in the spin-1/2 Heisenberg chain
was found to be superdiffusive in numerous recent numerical and experimental
studies. Theoretical approaches to this problem have emphasized the role of
nonabelian SU(2) symmetry as well as integrability but the associated methods
cannot be readily applied when integrability is broken. We examine spin
transport in a spin-1/2 chain in which the exchange couplings fluctuate in
space and time around a nonzero mean $J$, a model introduced by De Nardis et
al. [Phys. Rev. Lett. 127, 057201 (2021)]. We show that operator dynamics in
the strong noise limit at infinite temperature can be analyzed using
conventional perturbation theory as an expansion in $J$. We find that regular
diffusion persists at long times, albeit with an enhanced diffusion constant.
The finite time spin dynamics is analyzed and compared with matrix product
operator simulations.",2110.06951v1
2021-10-15,Thermodynamic and Dynamical Signatures of a Quantum Spin-Hall Insulator to Superconductor Transition,"Thermodynamic and dynamical properties of a model of Dirac fermions with a
deconfined quantum critical point (DQCP) separating an interaction-generated
quantum spin-Hall insulator from an s-wave superconductor [Nature Comm.~{\bf
10}, 2658 (2019)] are studied by quantum Monte Carlo simulations. Inside the
deconfined quantum critical region bound by the single-particle gap, spinons
and spinless charge-2e skyrmions emerge. Since the model conserves total spin
and charge, and has a single length scale, these excitations lead to a
characteristic linear temperature dependence of the uniform spin and charge
susceptibilities. At the DQCP, the order parameter dynamic structure factors
show remarkable similarities that support emergent Lorentz symmetry. Above a
critical temperature, superconductivity is destroyed by the proliferation of
spin-1/2 vortices.",2110.07963v2
2022-01-07,Simulation of nonequilibrium spin dynamics in quantum dots subjected to periodic laser pulses,"Large-scale simulations of the spin dynamics in quantum dots subjected to
trains of periodic laser pulses enable us to describe and understand related
experiments. By comparing the data for different models to experimental
results, we gain an improved understanding of the relevant physical mechanisms.
Using sophisticated numerical approaches and an efficient implementation
combined with extrapolation arguments, nonequilibrium stationary states are
reached for parameter ranges close to the ones in real experiments. With the
help of high performance computing, we can tune the experimental parameters to
guide future experimental research. Importantly, our simulations reveal the
possibility of resonant spin amplification in Faraday geometry, i.e., when a
longitudinal magnetic field is applied to the quantum dots.",2201.02421v1
2022-02-07,Exceptional dynamics of interacting spin liquids,"We show that interactions in quantum spin liquids can result in non-Hermitian
phenomenology that differs qualitatively from mean-field expectations. We
demonstrate this in two prominent cases through the effects of phonons and
disorder on a Kitaev honeycomb model. Using analytic and numerical
calculations, we show the generic appearance of exceptional points and rings
depending on the symmetry of the system. Their existence is reflected in
dynamical observables including the dynamic structure function measured in
neutron scattering. The results point to new phenomenological features in
realizable spin liquids that must be incorporated into the analysis of
experimental data and also indicate that spin liquids could be generically
stable to wider classes of perturbations.",2202.03445v2
2022-02-14,Mode splitting of spin waves in magnetic nanotubes with discrete symmetries,"We investigate how geometry influences spin dynamics in polygonal magnetic
nanotubes. We find that lowering the rotational symmetry of nanotubes by
decreasing the number of planar facets, splits an increasing number of
spin-wave modes, which are doubly degenerate in cylindrical tubes. This
symmetry-governed splitting is distinct form the topological one recently
observed in cylindrical nanotubes. Doublet modes with half-integer or integer
multiple azimuthal periods of the number of facets, split to singlet pairs with
lateral standing-wave profiles of opposing mirror-plane symmetries.
Furthermore, the polygonal geometry facilitates the hybridization of modes with
different azimuthal periods but the same symmetry, manifested in avoided level
crossings. These phenomena, unimaginable in cylindrical geometry, provide new
tools to control spin dynamics on nanoscale. The presented concept can be
generalized to nano-objects of versatile geometries and order parameters,
offering new routes to engineer dynamic response in nanoscale devices.",2202.06601v1
2022-05-11,Chiral standing spin waves in skyrmion lattice,"This work studies the resonance excitations of the three-dimensional
skyrmions lattice in the finite thickness plate of an isotropic chiral magnet
using spin dynamics simulations. We found that the absorption spectra and
resonance modes differ from those predicted by the two-dimensional model and
the model of the unconfined bulk crystal. The features observed on the spectra
can be explained by the formation of chiral standing spin waves, which,
contrary to conventional standing spin waves, are characterized by the helical
profile of dynamic magnetization of fixed chirality defined by the
Dzyaloshinskii-Moriya interaction. In this case, the dynamic susceptibility
becomes a function of the plate thickness, which gives rise to an interesting
effect that manifests itself in periodical fading of the intensity of
corresponding modes and makes excitation of these modes impossible at specific
thicknesses.",2205.05466v1
2022-05-24,Understanding temperature-dependent SU($3$) spin dynamics in the $S=1$ antiferromagnet Ba$_2$FeSi$_2$O$_7$,"Quantum magnets admit more than one classical limit and $N$-level systems
with strong single-ion anisotropy are expected to be described by a classical
approximation based on SU($N$) coherent states. Here we test this hypothesis by
modeling finite temperature inelastic neutron scattering (INS) data of the
effective spin-one antiferromagnet \bfso{}. The measured dynamic structure
factor is calculated with a generalized Landau-Lifshitz dynamics for SU($3$)
spins. Unlike the traditional classical limit based on SU($2$) coherent states,
the results obtained with classical SU($3$) spins are in good agreement with
the measured temperature-dependent spectrum. The SU($3$) approach developed
here provides a general framework to understand the broad class of materials
comprising weakly coupled antiferromagnetic dimers, trimers, or tetramers, and
magnets with strong single-ion anisotropy.",2205.11770v1
2022-06-15,Driven spin dynamics enhances cryptochrome magnetoreception: Towards live quantum sensing,"The mechanism underlying magnetoreception has long eluded explanation. A
popular hypothesis attributes this sense to the quantum coherent spin dynamics
of spin-selective recombination reactions of radical pairs in the protein
cryptochrome. However, concerns about the validity of the hypothesis have been
raised as unavoidable inter-radical interactions, such as strong
electron-electron dipolar coupling, appear to suppress its sensitivity. We
demonstrate that this can be overcome by driving the spin system through a
modulation of the inter-radical distance. It is shown that this dynamical
process markedly enhances geomagnetic field sensitivity in strongly coupled
radical pairs via a Landau-Zener type transition between singlet and triplet
states. These findings suggest that a ""live"" harmonically driven
magnetoreceptor can be more sensitive than its ""dead"" static counterpart.",2206.07355v1
2022-09-06,Current-driven magnetization dynamics and their correlation with magnetization configurations in perpendicularly magnetized tunnel junctions,"We study spin-transfer-torque driven magnetization dynamics of a
perpendicular magnetic tunnel junction (MTJ) nanopillar. Based on the
combination of spin-torque ferromagnetic resonance and microwave spectroscopy
techniques, we demonstrate that the free layer (FL) and the weak pinned
reference layer (RL) exhibit distinct dynamic behaviors with opposite frequency
vs. field dispersion relations. The FL can support a single coherent spin-wave
(SW) mode for both parallel and antiparallel configurations, while the RL
exhibits spin-wave excitation only for the antiparallel state. These two SW
modes corresponding to the FL and RL coexist at an antiparallel state and
exhibit a crossover phenomenon of oscillation frequency with increasing the
external magnetic field, which could be helpful in the mutual synchronization
of auto-oscillations for SW-based neuromorphic computing.",2209.02271v1
2022-09-07,Dynamical Signatures of Symmetry Broken and Liquid Phases in an $S=1/2$ Heisenberg Antiferromagnet on the Triangular Lattice,"We present the dynamical spin structure factor of the antiferromagnetic
spin-$\frac{1}{2}$ $J_1-J_2$ Heisenberg model on a triangular lattice obtained
from large-scale matrix-product state simulations. The high frustration due to
the combination of antiferromagnetic nearest and next-to-nearest neighbour
interactions yields a rich phase diagram. We resolve the low-energy excitations
both in the $120^{\circ}$-ordered phase and in the putative spin liquid phase
at $J_2/J_1 = 0.125$. In the ordered phase, we observe an avoided decay of the
lowest magnon-branch, demonstrating the robustness of this phenomenon in the
presence of gapless excitations. Our findings in the spin-liquid phase chime
with the field-theoretical predictions for a gapless Dirac spin liquid, in
particular the picture of low-lying monopole excitations at the corners of the
Brillouin zone. We comment on possible practical difficulties of distinguishing
proximate liquid and solid phases based on the dynamical structure factor.",2209.03344v2
2022-10-13,Coherent spin dynamics of excitons in strained monolayer semiconductors,"We develop a model of the coherent exciton spin-valley dynamics in
two-dimensional transition metal dichalcogenides under elastic strain. The
strain splits the exciton radiative doublet in linearly polarized states.
Consequently, it induces an effective magnetic field acting on the exciton
pseudospin and causes its precession. As a result, under circularly polarized
excitation, the circular polarization of excitons oscillates with time, also a
time-oscillating linear polarization appears. We study competition of the
strain-induced effective magnetic field with the field caused by the exciton
longitudinal-transverse splitting. We uncover different regimes of coherent
spin dynamics of two-dimensional excitons. In particular, we show that for
sufficiently large strain-induced and longitudinal-transverse splittings two
frequencies related to these splittings appear in the exciton circular
polarization beats.",2210.07036v2
2023-03-29,Universality in relaxation of spin helices under the $XXZ$- spin chain dynamics,"We describe dynamics of transverse spin-helix state (SHS) -- a product state
with spatially rotating magnetization -- under anisotropic Heisenberg XXZ spin
chain evolution. Due to experimental relevance we especially focus on
magnetization dynamics. At long times the $U(1)$ symmetry of the Hamiltonian is
restored, leading to the decay of transverse magnetization, which can be
described as an exponential decay of a spatially harmonic profile. We show that
the dependence of the short and intermediate-time decay timescale, which in
principle depends on all different parameters, like the wavevector of the
initial helix, the anisotropy, etc., can be described well by a single scaling
function. We also briefly discuss the evolution of magnetization current.",2303.16632v2
2023-03-29,Dynamical criticality of magnetization transfer in integrable spin chains,"Recent studies have found that fluctuations of magnetization transfer in
integrable spin chains violate the central limit property. Here we revisit the
problem of anomalous counting statistics in the Landau-Lifshitz field theory by
specializing to two distinct anomalous regimes featuring a dynamical critical
point. By performing optimized numerical simulations using an integrable
space-time discretization we extract the algebraic growth exponents of
time-dependent cumulants which attain their threshold values. The distinctly
non-Gaussian statistics of magnetization transfer in the easy-axis regime is
found to converge towards the universal distribution of charged single-file
systems. At the isotropic point we infer a weakly non-Gaussian distribution,
corroborating the view that superdiffusive spin transport in integrable spin
chains does not belong to any known dynamical universality class.",2303.16691v5
2023-04-07,A two-color dual-comb system for time-resolved measurements of ultrafast magnetization dynamics using triggerless asynchronous optical sampling,"We report on an Er-doped fiber (EDF)-laser-based dual-comb system that allows
us to perform triggerless asynchronous optical sampling (ASOPS) pump-probe
measurements of ultrafast demagnetization and spin precession in magnetic
materials. Because the oscillation frequencies of the two frequency-comb light
sources are highly stabilized, the pulse-to-pulse timing jitter is sufficiently
suppressed and data accumulation without any trigger signals is possible. To
effectively induce spin precession in ferromagnetic thin films, the spectral
bandwidth of the output of one of the EDF frequency comb sources is broadened
by a highly nonlinear fiber and then amplified at a wavelength of about 1030 nm
by a Yb-doped fiber amplifier. The output of the other frequency comb source is
converted to about 775 nm by second harmonic generation. We used this system to
observe the ultrafast demagnetization and spin precession dynamics on the
picosecond and nanosecond time scales in a permalloy thin film. This
time-domain spectroscopy system is promising for the rapid characterization of
spin-wave generation and propagation dynamics in magnetic materials.",2304.03666v1
2023-04-12,High-fidelity dimer excitations using quantum hardware,"Many-body entangled quantum spin systems exhibit emergent phenomena such as
topological quantum spin liquids with distinct excitation spectra accessed in
inelastic neutron scattering (INS) experiments. Here we simulate the dynamics
of a quantum spin dimer, the basic quantum unit of emergent many-body spin
systems. While canonical Trotterization methods require deep circuits
precluding long time-scale simulations, we demonstrate 'direct'
Resource-Efficient Fast-forwarding (REFF) measurements with short-depth
circuits that can be used to capture longer time dynamics on quantum hardware.
The temporal evolution of the 2-spin correlation coefficients enabled the
calculation of the dynamical structure factor $S(\mathbf{Q},\omega)$ - the key
component of the neutron scattering cross-section. We simulate the triplet gap
and the triplet splitting of the quantum dimer with sufficient fidelity to
compare to experimental neutron data. Our results on current circuit hardware
pave an important avenue to benchmark, or even predict, the outputs of the
costly INS experiments.",2304.06146v1
2023-06-12,Continuum Limit of Spin Dynamics on Hexagonal Lattice,"Compared to their three-dimensional counterparts, two-dimensional materials
exhibit intriguing electronic and magnetic properties. Notable examples include
twisted graphene's superconducting states and chromium trichloride's meron spin
textures. Understanding nontrivial topological spin textures is crucial for
magnetization dynamics and spintronic technologies. In this study, we analyze
the full model of discrete spin dynamics on a two-dimensional hexagonal lattice
used in experiments with chromium trichloride. We prove its convergence to the
continuum Landau-Lifshitz-Gilbert equation in the weak sense, despite
difficulties arising from the absence of central symmetry when constructing
difference quotient and interpolation operators on hexagonal lattices. To
overcome these challenges, we introduce multi-step difference quotient and
interpolation operators that possess an isometric property as a generalization
of Ladysenskaya's interpolation operator. This result not only establishes a
precise connection between parameters in atomistic models and those in
continuum models but also provides necessary tools for analyzing weak
convergence in other nonlinear problems on hexagonal lattices at microscopic
and macroscopic scales seamlessly.",2306.06958v1
2023-06-12,Clocked dynamics in artificial spin ice,"Artificial spin ice (ASI) are nanomagnetic metamaterials exhibiting a wide
range of emergent properties, which have recently shown promise for
neuromorphic computing. However, the lack of efficient protocols to control the
state evolution of these metamaterials has been limiting progress. To overcome
this barrier, we introduce astroid clocking, a global field protocol offering
discrete, gradual evolution of spin states. The method exploits the intrinsic
switching astroids and dipolar interactions of the nanomagnets to selectively
address ASI spins in sequence. We demonstrate, experimentally and in
simulations, how astroid clocking of pinwheel ASI allows ferromagnetic domains
to be gradually grown or reversed at will. More complex dynamics arise when the
clock protocol allows both growth and reversal to occur simultaneously. Astroid
clocking offers unprecedented control and understanding of ASI dynamics in both
time and space, extending what is possible in nanomagnetic metamaterials.",2306.07388v2
2023-10-10,Dynamics of vacancy-induced modes in the non-Abelian Kitaev spin liquid,"We study the dynamical response of vacancy-induced quasiparticle excitations
in the site-diluted Kitaev spin liquid with a magnetic field. Due to the
flux-binding effect and the emergence of dangling Majorana fermions around each
spin vacancy, the low-energy physics is governed by a set of vacancy-induced
quasi-zero-energy modes. These localized modes result in unique characteristics
of the dynamical spin correlation functions, which intriguingly mimic the
single-quasiparticle density of states and further exhibit a
quasi-zero-frequency peak. By recognizing the potential observability of these
local correlation functions via scanning tunneling microscopy (STM), we show
how the STM response is sensitive to the local flux configuration, the magnetic
field strength, and the vacancy concentration. Constructing a simple model of
the localized modes, we also elucidate how the local correlation functions can
be interpreted in terms of the hybridization between these modes.",2310.06891v1
2023-11-01,Theory of Orbital Pumping,"We develop a theory of orbital pumping, which corresponds to the emission of
orbital currents from orbital dynamics. This phenomenon exhibits two distinct
characteristics compared to spin pumping. Firstly, while spin pumping generates
solely spin (angular momentum) currents, orbital pumping yields both orbital
angular momentum currents and orbital angular position currents. Secondly,
lattice vibrations induce orbital dynamics and associated orbital pumping as
the orbital angular position is directly coupled to the lattice. These pumped
orbital currents can be detected as transverse electric voltages via the
inverse orbital(-torsion) Hall effect, stemming from orbital textures. Our work
proposes a new avenue for generating orbital currents and provides a broader
understanding of angular momentum dynamics encompassing spin, orbital, and
phonon.",2311.00362v1
2023-11-27,Strong Spin-Motion Coupling in the Ultrafast Quantum Many-body Dynamics of Rydberg Atoms in a Mott-insulator Lattice,"Rydberg atoms in optical lattices and tweezers is now a well established
platform for simulating quantum spin systems. However, the role of the atoms'
spatial wavefunction has not been examined in detail experimentally. Here, we
show a strong spin-motion coupling emerging from the large variation of the
interaction potential over the wavefunction spread. We observe its clear
signature on the ultrafast, out-of-equilibrium, many-body dynamics of atoms
excited to a Rydberg S state from an unity-filling atomic Mott-insulator. We
also propose a novel approach to tune arbitrarily the strength of the
spin-motion coupling relative to the motional energy scale set by trapping
potentials. Our work provides a new direction for exploring the dynamics of
strongly-correlated quantum systems by adding the motional degree of freedom to
the Rydberg simulation toolbox.",2311.15575v1
2024-01-26,Efficient Control of Magnetization Dynamics Via W/CuO$_\text{x}$ Interface,"Magnetization dynamics, which determine the speed of magnetization switching
and spin information propagation, play a central role in modern spintronics.
Gaining its control will satisfy the different needs of various spintronic
devices. In this work, we demonstrate that the surface oxidized Cu
(CuO$_\text{x}$) can be employed for the tunability of magnetization dynamics
of ferromagnet (FM)/heavy metal (HM) bilayer system. The capping CuO$_\text{x}$
layer in CoFeB/W/CuO$_\text{x}$ trilayer reduces the magnetic damping value in
comparison with the CoFeB/W bilayer. The magnetic damping even becomes lower
than that of the CoFeB/CuO$_\text{x}$ by ~ 16% inferring the stabilization of
anti-damping phenomena. Further, the reduction in damping is accompanied by a
very small reduction in the spin pumping-induced output DC voltage in the
CoFeB/W/CuO$_\text{x}$ trilayer. The simultaneous observation of anti-damping
and spin-to-charge conversion can be attributed to the orbital Rashba effect
observed at the HM/CuO$_\text{x}$ interface. Our experimental findings
illustrate that the cost-effective CuO$_\text{x}$ can be employed as an
integral part of modern spintronics devices owing to its rich underneath
spin-orbital physics.",2401.14708v1
2024-03-14,Microscopic Study on Superexchange Dynamics of Composite Spin-1 Bosons,"We report on an experimental simulation of the spin-1 Heisenberg model with
composite bosons in a one-dimensional chain based on the two-component
Bose-Hubbard model. Exploiting our site-and spin-resolved quantum gas
microscope, we observed faster superexchange dynamics of the spin-1 system
compared to its spin-1/2 counterpart, which is attributed to the enhancement
effect of multi-bosons. We further probed the non-equilibrium spin dynamics
driven by the superexchange and single-ion anisotropy terms, unveiling the
linear expansion of the spin-spin correlations, which is limited by the
Lieb-Robinson bound. Based on the superexchange process, we prepared and
verified the entangled qutrits pairs with these composite spin-1 bosons,
potentially being applied in qutrit-based quantum information processing.",2403.09205v3
2013-07-06,Accuracy of gravitational waveform models for observing neutron-star--black-hole binaries in Advanced LIGO,"Gravitational waves radiated by the coalescence of compact-object binaries
containing a neutron star and a black hole are one of the most interesting
sources for the ground-based gravitational-wave observatories Advanced LIGO and
Advanced Virgo. Advanced LIGO will be sensitive to the inspiral of a $1.4\,
M_\odot$ neutron star into a $10\,M_\odot$ black hole to a maximum distance of
$\sim 900$ Mpc. Achieving this sensitivity and extracting the physics imprinted
in observed signals requires accurate modeling of the binary to construct
template waveforms. In a NSBH binary, the black hole may have significant
angular momentum (spin), which affects the phase evolution of the emitted
gravitational waves. We investigate the ability of post-Newtonian (PN)
templates to model the gravitational waves emitted during the inspiral phase of
NSBH binaries. We restrict the black hole's spin to be aligned with the orbital
angular momentum and compare several approximants. We examine restricted
amplitude waveforms that are accurate to 3.5PN order in the orbital dynamics
and complete to 2.5PN order in the spin dynamics. We also consider PN waveforms
with the recently derived 3.5PN spin-orbit and 3PN spin-orbit tail corrections.
We compare these approximants to the effective-one-body model. For all these
models, large disagreements start at low to moderate black hole spins,
particularly for binaries where the spin is anti-aligned with the orbital
angular momentum. We show that this divergence begins in the early inspiral at
$v \sim 0.2$ for $\chi_{BH} \sim 0.4$. PN spin corrections beyond those
currently known will be required for optimal detection searches and to measure
the parameters of neutron star--black hole binaries. While this complicates
searches, the strong dependence of the gravitational-wave signal on the spin
dynamics will make it possible to extract significant astrophysical
information.",1307.1757v2
2018-09-26,Phenomenological model for the gravitational-wave signal from precessing binary black holes with two-spin effects,"The properties of compact binaries, such as masses and spins, are imprinted
in the gravitational-waves they emit and can be measured using parameterised
waveform models. Accurately and efficiently describing the complicated
precessional dynamics of the various angular momenta of the system in these
waveform models is the object of active investigation. One of the key models
extensively used in the analysis of LIGO and Virgo data is the
single-precessing-spin waveform model IMRPhenomPv2. In this article we present
a new model IMRPhenomPv3 which includes the effects of two independent spins in
the precession dynamics. Whereas IMRPhenomPv2 utilizes a single-spin
frequency-dependent post-Newtonian rotation to describe precession effects, the
improved model, IMRPhenomPv3, employs a double-spin rotation that is based on
recent developments in the description of precessional dynamics. Besides
double-spin precession, the improved model benefits from a more accurate
description of precessional effects. We validate our new model against a large
set of precessing numerical-relativity simulations. We find that IMRPhenomPv3
has better agreement with the inspiral portion of precessing binary-black-hole
simulations and is more robust across a larger region of the parameter space
than IMRPhenomPv2. As a first application we analyse, for the first time, the
gravitational-wave event GW151226 with a waveform model that describes two-spin
precession. Within statistical uncertainty our results are consistent with
published results. IMRPhenomPv3 will allow studies of the measurability of
individual spins of binary black holes using GWs and can be used as a
foundation upon which to build further improvements, such as modeling
precession through merger, extending to higher multipoles, and including tidal
effects.",1809.10113v1
2021-07-07,"Deepening the knowledge of Spin Glasses: Metastate, Off-equilibrium phenomena and Temperature Chaos","This thesis pretends to be another step in the development of numerical
research in disordered systems. Specifically, we will focus on spin glasses
which have demonstrated to be a fertile field from both, experimental and
theoretical approaches. Throughout this thesis, we will discuss a variety of
interesting phenomenons and we will also open new avenues to previously
unexplored effects in the context of spin glasses. However, without a doubt,
the leitmotiv conducting this thesis is the role of numerical simulations as a
valuable tool to explore spin-glass physics.
  This thesis is organized into five different parts. The first part,
containing the Chapter 1, is focused on introducing the spin glasses to the
reader.
  The second part, containing the Chapter 2, is dedicated to discussing the
metastate.
  The third part, shaped by the Chapter 3 and Chapter 4, is devoted to studying
the off-equilibrium dynamics in spin glasses. Specifically, Chapter 3 is
focused on discussing the growth of the coherence length in spin glasses, a key
quantity that characterizes the off-equilibrium evolution of those systems. In
Chapter 4 we will discuss an interesting phenomenon: the Mpemba effect.
  The fourth part, containing the Chapter 5, Chapter 6 and Chapter 7 is devoted
to study the Temperature Chaos phenomenon in spin glasses. In Chapter 5 we
introduce the main historical results on Temperature Chaos, from its origins to
the last steps. In Chapter 6 we study equilibrated spin glasses and we
characterize the Temperature Chaos from a static and a dynamical point of view.
In Chapter 7 we tackle the problem of characterizing Temperature Chaos in
off-equilibrium dynamics.
  The fifth and last part of the main body of the thesis corresponds to the
conclusions.",2107.03276v1
1995-02-17,Full dynamical solution for a spherical spin-glass model,"We present a detailed analysis for the Langevin dynamics of a spherical
spin-glass model (the spherical Sherrington-Kirkpatrick model). All the spins
in the system are coupled by pairs via a random interaction matrix taken from
the Gaussian ensemble. One finds that for a general initial configuration the
system never reaches an equilibrium state and the theorems associated to
`equilibrium dynamics' are violated. Only very particular initial conditions
drive the system to equilibrium. The weak ergodicity breaking scenario is
demonstrated for general `non-equilibrium' initial conditions. Two-time
quantities such as the auto-correlation function explicitly depend on both
times. When the time difference is short compared to the smaller time one finds
stationary dynamics with time translation invariance and the
fluctuation-dissipation theorem satisfied. Instead, when the time difference is
of the order of the smaller time one finds non-stationary dynamics with aging
phenomena, the system {\em remembers} the time spent after the initial time
(the quench below the critical temperature). Interestingly enough the short
time-difference dynamics (FDT regime) for non-equilibrium initial conditions is
identical to the relaxation within the equilibrium states obtained for the
particular `equilibrium' initial conditions. This points to a self-similaririty
of the energy landascape. In addition we analyse the effect of temperature
variations on the behaviour of the correlation function and energy density. In
this way we are able to make some comparisons between experimentally observed
results and exact calculations for the model. Somewhat surprisingly, this
simple model captures some of the effects seen in laboratory spin-glasses.",9502075v1
2000-01-24,"Ordering Dynamics of Heisenberg Spins with Torque: Crossover, Spinwaves and Defects","We study the effect of a torque induced by the local molecular field on the
phase ordering dynamics of the Heisenberg model when the total magnetization is
conserved. The torque drives the zero-temperature ordering dynamics to a new
fixed point, characterized by exponents $z=2$ and $\lambda \approx 5$. This
`torque-driven' fixed point is approached at times such that $g^2 t\gg 1$,
where $g$ is the strength of the torque. All physical quantities, like the
domain size $L(t)$ and the equal and unequal time correlation functions obey a
crossover scaling form over the entire range of $g$. An attempt to understand
this crossover behavior from the approximate Gaussian Closure Scheme fails
completely, implying that the dynamics at late times cannot be understood from
the dynamics of defects alone. We provide convincing arguments that the spin
configurations can be decomposed in terms of defects and spin-waves which
interact with each other even at late times. In the absence of the torque term,
the spin waves decay faster, but even so we find that the Gaussian closure
scheme is inconsistent. In the latter case the inconsistency may be remedied by
including corrections to a simple gaussian distribution. For completeness we
include a discussion of the ordering dynamics at $T_c$, where the torque is
shown to be relevant, with exponents $z=4-\epsilon/2$ and $\lambda = d$ (where
$\epsilon = 6-d$). We show to all orders in perturbation theory that
$\lambda=d$ as a consequence of the conservation law.",0001340v1
2005-12-19,Dynamal (super)symmetries of monopoles and vortices,"The dynamical (super)symmetries for various monopole systems are reviewed.
For a Dirac monopole, no smooth Runge-Lenz vector can exist; there is, however,
a spectrum-generating conformal $o(2,1)$ dynamical symmetry that extends into
$osp(1/1)$ or $osp(1/2)$ for spin 1/2 particles. Self-dual 't
Hooft-Polyakov-type monopoles admit an $su(2/2)$ dynamical supersymmetry
algebra, which allows us to reduce the fluctuation equation to the spin zero
case. For large $r$ the system reduces to a Dirac monopole plus an suitable
inverse-square potential considered before by McIntosh and Cisneros, and by
Zwanziger in the spin 0 case, and to the `dyon' of D'Hoker and Vinet for spin
1/2. The asymptotic system admits a Kepler-type dynamical symmetry as well as a
`helicity-supersymmetry' analogous to the one Biedenharn found in the
relativistic Kepler problem. Similar results hold for the Kaluza-Klein monopole
of Gross-Perry-Sorkin. For the magnetic vortex, the N=2 supersymmetry of the
Pauli Hamiltonian in a static magnetic field in the plane combines with the
$o(2)\times o(2,1)$ bosonic symmetry into an $o(2)\times osp(1/2)$ dynamical
superalgebra.",0512233v2
2010-04-22,Novel ballistic to diffusive crossover in the dynamics of a one dimensional Ising model with variable range of interaction,"The idea that the dynamics of a spin is determined by the size of its
neighbouring domains was recently introduced (S. Biswas and P. Sen, Phys. Rev.
E {\bf 80}, 027101 (2009)) in a Ising spin model
  (henceforth, referred to as model I).
  A parameter $p$ is now defined to modify the dynamics such that a spin can
sense domain sizes up to $R = pL/2$ in a one dimensional system of size $L$.
For the cutoff factor $p$ \to 0$, the dynamics is Ising like and the domains
grow with time $t$ diffusively as $ t^{1/z}$ with $z=2$, while for $p=1$, the
original model I showed ballistic dynamics with $z \simeq 1$. For intermediate
values of $p$, the domain growth, magnetisation and persistence show model I
like behaviour up to a macroscopic crossover time $ t_1 \sim pL/2$. Beyond
$t_1$, characteristic power law variations of the dynamic quantities are no
longer observed. The total time to reach equilibrium is found to be $t = apL +
b(1-p)^3L^2$, from which we conclude that the later time behaviour is
diffusive. We also consider the case when a random but quenched value of $p$ is
used for each spin for which ballistic behaviour is once again obtained.",1004.3861v3
2013-06-02,Dynamical quantum correlations of Ising models on an arbitrary lattice and their resilience to decoherence,"Ising models, and the physical systems described by them, play a central role
in generating entangled states for use in quantum metrology and quantum
information. In particular, ultracold atomic gases, trapped ion systems, and
Rydberg atoms realize long-ranged Ising models, which even in the absence of a
transverse field can give rise to highly non-classical dynamics and long-range
quantum correlations. In the first part of this paper, we present a detailed
theoretical framework for studying the dynamics of such systems driven (at time
t=0) into arbitrary unentangled non-equilibrium states, thus greatly extending
and unifying the work of Ref. [1]. Specifically, we derive exact expressions
for closed-time-path ordered correlation functions, and use these to study
experimentally relevant observables, e.g. Bloch vector and spin-squeezing
dynamics. In the second part, these correlation functions are then used to
derive closed-form expressions for the dynamics of arbitrary spin-spin
correlation functions in the presence of both T_1 (spontaneous spin
relaxation/excitation) and T_2 (dephasing) type decoherence processes. Even
though the decoherence is local, our solution reveals that the competition
between Ising dynamics and T_1 decoherence gives rise to an emergent non-local
dephasing effect, thereby drastically amplifying the degradation of quantum
correlations. In addition to identifying the mechanism of this deleterious
effect, our solution points toward a scheme to eliminate it via
measurement-based coherent feedback.",1306.0172v1
2019-05-21,A generalized phase space approach for solving quantum spin dynamics,"Numerical techniques to efficiently model out-of-equilibrium dynamics in
interacting quantum many-body systems are key for advancing our capability to
harness and understand complex quantum matter. Here we propose a new numerical
approach which we refer to as GDTWA. It is based on a discrete semi-classical
phase-space sampling and allows to investigate quantum dynamics in lattice spin
systems with arbitrary $S\geq 1/2$. We show that the GDTWA can accurately
simulate dynamics of large ensembles in arbitrary dimensions. We apply it for
$S>1/2$ spin-models with dipolar long-range interactions, a scenario arising in
recent experiments with magnetic atoms. We show that the method can capture
beyond mean-field effects, not only at short times, but it also correctly
reproduces long time quantum-thermalization dynamics. We benchmark the method
with exact diagonalization in small systems, with perturbation theory for short
times, and with analytical predictions made for closed system which feature
quantum-thermalization at long times. By computing the Renyi entropy, currently
an experimentally accessible quantifier of entanglement, we reveal that large
$S$ systems can feature larger entanglement than corresponding $S=1/2$ systems.
Our analyses demonstrate that the GDTWA can be a powerful tool for modeling
complex spin dynamics in regimes where other state-of-the art numerical methods
fail.",1905.08782v2
2017-06-07,Quantum spin chains with multiple dynamics,"Many-body systems with multiple emergent time scales arise in various
contexts, including classical critical systems, correlated quantum materials,
and ultra-cold atoms. We investigate such non-trivial quantum dynamics in a new
setting: a spin-1 bilinear-biquadratic chain. It has a solvable entangled
groundstate, but a gapless excitation spectrum that is poorly understood. By
using large-scale DMRG simulations, we find that the lowest excitations have a
dynamical exponent $z$ that varies from 2 to 3.2 as we vary a coupling in the
Hamiltonian. We find an additional gapless mode with a continuously varying
exponent $2\leq z <2.7$, which establishes the presence of multiple dynamics.
In order to explain these striking properties, we construct a continuum
wavefunction for the groundstate, which correctly describes the correlations
and entanglement properties. We also give a continuum parent Hamiltonian, but
show that additional ingredients are needed to capture the excitations of the
chain. By using an exact mapping to the non-equilibrium dynamics of a classical
spin chain, we find that the large dynamical exponent is due to subdiffusive
spin motion. Finally, we discuss the connections to other spin chains and to a
family of quantum critical models in 2d.",1706.02304v2
2020-08-11,"Lattice dynamics and ultrafast energy flow between electrons, spins, and phonons in a 3d ferromagnet","The ultrafast dynamics of magnetic order in a ferromagnet are governed by the
interplay between electronic, magnetic and lattice degrees of freedom. In order
to obtain a microscopic understanding of ultrafast demagnetization, information
on the response of all three subsystems is required. A consistent description
of demagnetization and microscopic energy flow, however, is still missing.
Here, we combine a femtosecond electron diffraction study of the ultrafast
lattice response of nickel to laser excitation with ab initio calculations of
the electron-phonon interaction and energy-conserving atomistic spin dynamics
simulations. Our model is in agreement with the observed lattice dynamics and
previously reported electron and magnetization dynamics. Our approach reveals
that the spin system is the dominating heat sink in the initial few hundreds of
femtoseconds and implies a transient non-thermal state of the spins. Our
results provide a clear picture of the microscopic energy flow between
electronic, magnetic and lattice degrees of freedom on ultrafast timescales and
constitute a foundation for theoretical descriptions of demagnetization that
are consistent with the dynamics of all three subsystems.",2008.04611v2
2021-11-25,The role of q-spin singlet pairs of physical spins in the dynamical properties of the spin-1/2 Heisenberg-Ising XXZ chain,"Dynamical correlation functions contain important physical information on
correlated spin models. Here a dynamical theory suitable suitable to the
isotropic spin-1/2 Heisenberg chain in a longitudinal magnetic field is
extended to anisotropy larger than one . The aim of this paper is the study of
the line shape of the spin dynamical structure factor components +-, -+ and zz
of the spin-1/2 Heisenberg-Ising chain in a longitudinal magnetic field near
their sharp peaks. To reach that goal, the nature of the specific type of
elementary magnetic configurations both unbound and associated with real
Bethe-ansatz rapidities and bound and described by complex Bethe strings is
clarified: They are singlet q-spin pairs of physical spins 1/2. We derive
analytical expressions for the line shapes of dynamical structure factor
components +-, -+ and zz valid in the vicinity of lines of sharp peaks. Those
are mostly located at and just above lower thresholds of continua associated
with both real-rapidity states with only unbound q-spin singlet pairs and
states with real and complex rapidities populated by such unbound pairs and a
single 2-string or a single 3-string. The latter contain 2 and 3 bound q-spin
singlet pairs, respectively. Our results provide physically interesting and
important information on the microscopic processes that determine the dynamical
properties of the non-perturbative spin-1/2 Heisenberg-Ising chain in a
longitudinal magnetic field.",2111.13118v1
2021-11-26,Open quantum dynamics theory for a complex subenvironment system with a quantum thermostat: Application to a spin heat bath,"Complex environments, such as molecular matrices and biological material,
play a fundamental role in many important dynamic processes in condensed
phases. Because it is extremely difficult to conduct full quantum dynamics
simulations on such environments due to their many degrees of freedom, here we
treat in detail the environment only around the main system of interest (the
subenvironment), while the other degrees of freedom needed to maintain the
equilibrium temperature are described by a simple harmonic bath, which we call
a quantum thermostat. The noise generated by the subenvironment is spatially
non-local and non-Gaussian and cannot be characterized by the
fluctuation-dissipation theorem. We describe this model by simulating the
dynamics of a two-level system (TLS) that interacts with a subenvironment
consisting of a one-dimensional $XXZ$ spin chain. The hierarchical
Schr\""odinger equations of motion are employed to describe the quantum
thermostat, allowing time-irreversible simulations of the dynamics at arbitrary
temperature. To see the effects of a quantum phase transition of the
subenvironment, we investigate the decoherence and relaxation processes of the
TLS at zero and finite temperatures for various values of the spin anisotropy.
We observed the decoherence of the TLS at finite temperature, even when the
anisotropy of the $XXZ$ model is enormous. We also found that the population
relaxation dynamics of the TLS changed in a complex manner with the change of
the anisotropy and the ferromagnetic or antiferromagnetic orders of the spins.",2111.13277v1
2022-07-14,Attosecond magnetization dynamics in non-magnetic materials driven by intense femtosecond lasers,"Irradiating solids with ultrashort laser pulses is known to initiate
femtosecond timescale magnetization dynamics. However, sub-femtosecond spin
dynamics have not yet been observed or predicted. Here, we explore ultrafast
light-driven spin dynamics in a highly non-resonant strong-field regime.
Through state-of-the-art ab-initio calculations, we predict that a non-magnetic
material can be transiently transformed into a magnetic one via dynamical
extremely nonlinear spin-flipping processes, which occur on attosecond
timescales and are mediated by a combination of multi-photon and spin-orbit
interactions. These are non-perturbative non-resonant analogues to the inverse
Faraday effect that build up from cycle-to-cycle as electrons gain angular
momentum. Remarkably, we show that even for linearly polarized driving, where
one does not intuitively expect any magnetic response, the magnetization
transiently oscillates as the system interacts with light. This oscillating
response is enabled by transverse anomalous light-driven currents in the solid,
and typically occurs on timescales of ~500 attoseconds. We further demonstrate
that the speed of magnetization can be controlled by tuning the laser
wavelength and intensity. An experimental set-up capable of measuring these
dynamics through pump-probe transient absorption spectroscopy is outlined and
simulated. Our results pave the way for new regimes of ultrafast manipulation
of magnetism.",2207.06711v1
2023-10-30,Distinguishing Ion Dynamics from Muon diffusion in Muon Spin Relaxation,"We propose a model to describe the fluctuations in the internal magnetic
field due to ion dynamics observed in the muon spin relaxation ($\mu$SR) by an
Edwards-Anderson type autocorrelation function that separates the quasi-static
and dynamic components of the correlation by a parameter $Q$ (where $0\le
Q\le1$). Our Monte Carlo simulations for this model showed that the time
evolution of muon spin polarization deviates significantly from the Kubo-Toyabe
(KT) function. To further validate the model, the results of simulations were
compared with the $\mu$SR spectra observed in a hybrid organic-inorganic
perovskite FAPbI$_3$ [with FA referring to HC(NH$_2)_2$], where local field
fluctuations associated with the rotational motion of FA molecules and
quasi-static fields from the PbI$_3$ lattice are presumed to coexist. The
least-squares curve fitting showed reasonable agreement with the model with
$Q=0.947(3)$, and the fluctuation frequency of the dynamical component was
obtained. This result opens the door to the possibility of experimentally
distinguishing fluctuations due to dynamics of ions around muons from those due
to self-diffusion of muons. Meanwhile, it suggests the need to carefully
consider the spin relaxation function when applying $\mu$SR to the issue of ion
dynamics.",2310.19281v4
2023-11-13,Origin of reduced dynamical friction by dark matter halos with net prograde rotation,"We provide an explanation for the reduced dynamical friction on galactic bars
in spinning dark matter halos. Earlier work based on linear theory predicted an
increase in dynamical friction when dark halos have a net forward rotation,
because prograde orbits couple to bars with greater strength than retrograde
orbits. Subsequent numerical studies, however, found the opposite trend:
dynamical friction weakens with increasing spin of the halo. We revisit this
problem and demonstrate that linear theory in fact correctly predicts a reduced
torque in forward-rotating halos. We show that shifting the halo mass from
retrograde to prograde phase space generates a positive gradient in the
distribution function near the origin of the z-angular momentum (Lz=0), which
results in a resonant transfer of Lz to the bar, making the net dynamical
friction weaker. While this effect is subdominant for the major resonances,
including the corotation resonance, it leads to a significant positive torque
on the bar for the series of direct radial resonances, as these resonances are
strongest at Lz=0. The overall dynamical friction from spinning halos is shown
to decrease with the halo's spin, in agreement with the secular behavior of
N-body simulations. We validate our linear calculation by computing the
nonlinear torque from individual resonances using the angle-averaged
Hamiltonian.",2311.07640v2
1994-06-17,Replica Field Theory for Deterministic Models (II): A Non-Random Spin Glass with Glassy Behavior,"We introduce and study a model which admits a complex landscape without
containing quenched disorder. Continuing our previous investigation we
introduce a disordered model which allows us to reconstruct all the main
features of the original phase diagram, including a low $T$ spin glass phase
and a complex dynamical behavior.",9406074v1
1994-10-19,Spin Wave Frequency and Critical Dynamics of Ferromagnets Below T_C,"Employing mode-coupling theory we show that the amplitude of the spin wave
frequency scaling function for the isotropic Heisenberg Hamiltonian is
universal. Theoretical and experimental values for Fe, Ni, Co, EuO, and EuS
agree quite well. Recent measurements of the longitudinal line width in Ni are
explained quantitatively.",9410073v1
1996-12-30,Domain wall roughening in three dimensional magnets at the depinning transition,"The kinetic roughening of a driven interface between three dimensional
spin-up and spin-down domains in a model with non-conserved scalar order
parameter and quenched disorder is studied numerically within a discrete time
dynamics at zero temperature. The exponents characterizing the morphology of
the interface are obtained close to the depinning-transition",9612241v1
1997-05-14,Soliton Confinement and the Excitation Spectrum of Spin-Peierls Antiferromagnets,"The excitation spectrum of spin-Peierls antiferromagnets is discussed taking
into acount phonon dynamics but treating inter-chain elastic couplings in mean
field theory. This gives a ladder of soliton -anti-soliton boundstates, with no
soliton continuum, until soliton deconfinement takes place at a transition into
a non-dimerized phase.",9705127v1
1998-11-05,Classical frustration and quantum disorder in spin-orbital models,"The most elementary of all physical spin-orbital models is the Kugel-Khomskii
model describing a S=1/2, $e_g$ degenerate Mott-insulator. Recent theoretical
work is reviewed revealing that the classical limit is characterized by a point
of perfect dynamical frustration. It is suggested that this might give rise to
a quantum disordered ground state.",9811075v1
1999-08-22,Thermodynamic Phase Diagram of the Quantum Hall Skyrmion System,"We numerically study the interacting quantum Hall skyrmion system based on
the Chern-Simons action. By noticing that the action is invariant under global
spin rotations in the spin space with respect to the magnetic field direction,
we obtain the low-energy effective action for a many skyrmion system.
Performing extensive molecular dynamics simulations, we establish the
thermodynamic phase diagram for a many skyrmion system.",9908310v1
2002-08-08,Bose-Fermi Mixtures in One Dimension,"We analyze the phase stability and the response of a mixture of bosons and
spin-polarized fermions in one dimension (1D). Unlike in 3D, phase separation
happens for low fermion densities. The dynamics of the mixture at low energy is
independent of the spin-statistics of the components, and zero-sound-like modes
exist that are essentially undamped.",0208165v1
2002-08-21,Re-entrant spin glass and magnetoresistance in Co_{0.2}Zn_{0.8}Fe_{1.6}Ti_{0.4}O_4 spinel oxide,"We have investigated the static and dynamic response of magnetic clusters in
Co_{0.2}Zn_{0.8}Fe_{1.6}Ti_{0.4}O_4 spinel oxide, where a sequence of magnetic
phase transitions, i.e., paramagnetic (PM) to ferromagnetic at T_{C} $\leq$
270K and ferromagnetic to canted spin glass state at T_f$ $\leq$ 125K is
observed.",0208416v1
2002-12-17,Dissipative spin-boson model and Kondo effect in low dimensional quantum gases,"We show that ultracold atoms confined in a quasi-1d trap can be used to study
the dissipative spin-boson model with {\it tunable} tunneling splitting and
strength of dissipation. It is shown that with realistic parameters this system
allows to study the crossover from coherent Rabi dynamics to incoherent
tunneling.",0212413v1
2003-07-18,The Heisenberg antiferromagnet: an explicitly rotational invariant formulation,"A simple derivation of an explicitly rotational invariant Lagrangian
describing the dynamics of an antiferromagnetic spin system is presented. The
scope of the derived Lagrangian is analysed in the context of schematic models.
It is shown that the Lagrangian describes the behaviour of spin systems from
the anti-ferromagnetic to the ferromagnetic regimes.",0307461v1
2005-04-07,Fourier's Law in a Quantum Spin Chain and the Onset of Quantum Chaos,"We study heat transport in a nonequilibrium steady state of a quantum
interacting spin chain. We provide clear numerical evidence of the validity of
Fourier law. The regime of normal conductivity is shown to set in at the
transition to quantum chaos.",0504181v1
2006-11-17,How to calculate correlation functions of Heisenberg chains,"We describe a method for calculating dynamical spin-spin correlation
functions in the finite isotropic and anisotropic antiferromagnetic Heisenberg
models. Our method is able to produce results with high accuracy over the full
parameter space.",0611467v1
2007-02-05,Rabi oscillations from ultrasound in spin systems,"It is shown that ultrasound in the GHz range can generate space-time Rabi
oscillations between spin states of molecular magnets. We compute dynamics of
the magnetization generated by surface acoustic waves and discuss conditions
under which this novel quantum effect can be observed.",0702116v1
2002-08-25,Spinning particles in gravitational wave spacetime,"The dynamics of pseudo-classical spinning particles in spacetime of
gravitational plane waves of general polarization and harmonic profile is
studied. The resulting equations of motion are solved exactly and the results
are compared with those of the other approaches. The relative accelerations of
nearby particles is also calculated.",0208072v1
2002-09-26,Precession of a particle with anomalous magnetic moment in electromagnetic and gravitational pp-wave fields,"We present an exact solution of the Bargmann-Michel-Telegdi (BMT) equations
for the dynamics of a spin particle in external electromagnetic and
gravitational pp-wave fields. We demonstrate that an anomalous magnetic moment
gives rise to an additional spin rotation which is modulated both by the
electromagnetic and by the gravitational wave periodicities.",0209099v1
1996-02-23,Nuclear Modifications of Double Spin Asymmetries,"We compute nuclear spin dependent structure functions using a dynamical model
for bound nucleon densities and hence calculate nuclear modifications to
asymmetries observed in recent doubly polarised deep inelastic scattering
experiments. We conclude that while the individual densities are changed
substantially by nuclear effects, the asymmetries themselves are largely
insensitive to these changes.",9602379v1
1994-01-28,Grand-Canonical Ensemble of Random Surfaces with Four Species of Ising Spins,"The grand-canonical ensemble of dynamically triangulated surfaces coupled to
four species of Ising spins (c=2) is simulated on a computer. The effective
string susceptibility exponent for lattices with up to 1000 vertices is found
to be $\gamma = - 0.195(58)$. A specific scenario for $c > 1$ models is
conjectured.",9401143v1
2003-02-13,Integrable Markov processes and quantum spin chains,"A set of Markov processes corresponding to systems of hard-core particles
interacting along the line are shown to be solvable via a dynamic matrix
product ansatz (DMPA). We show that quantum spin Hamiltonians can be treated by
the DMPA as well, and demonstrate how the DMPA, originally formulated for
systems with open ends, works for periodic systems.",0302094v1
2007-02-14,Nonspontaneous Supersymmetry Breaking,"A new way of supersymmetry breaking involving a dynamical parameter is
introduced. It is independent of particle phenomenology and gauge groups. The
only requirement is that Lorentz invariance be valid strictly infinitesimally
(i. e. Spin(1,3) be for some values of the parameter replaced by a compact
group G locally isomorphic to Spin(1,3).",0702116v1
2002-07-24,The simplest nearest-neighbor spin system on regular graphs:Time dynamics of the mean coverage function,"We establish a characterization of the class of the simplest nearest neighbor
spin systems possesing the mean coverage function (mcf) that obeys a second
order differential equation, and derive explicit expressions for the mcf's of
the above models. Based on these expressions, the problem of ergodicity of the
models is studied and bounds for their spectral gaps are obtained.",0207217v1
2002-05-10,Long-time Behavior for the Stochastic Ising Model with Unbounded Random Couplings,"We consider the ferromagnetic Ising model with Glauber spin flip dynamics in
one dimension. The external magnetic field vanishes and the couplings are
i.i.d. random variables. If their distribution has compact support, the
disorder averaged spin auto-correlation function has an exponential decay in
time. We prove that, if the couplings are unbounded, the decay switches to
either a power law or a stretched exponential, in general.",0205014v1
2000-09-29,Semiclassical expectation values for relativistic particles with spin 1/2,"For relativistic particles with spin 1/2, which are described by the Dirac
equation, a semiclassical trace formula is introduced that incorporates
expectation values of observables in eigenstates of the Dirac-Hamiltonian.
Furthermore, the semiclassical limit of an average of expectation values is
expressed in terms of a classical average of the corresponding classical
observable.",0009052v1
1999-11-09,Quantum Spin Dynamics and Quantum Computation,"We describe a simulation method for a quantum spin model of a generic,
general purpose quantum computer. The use of this quantum computer simulator is
illustrated through several implementations of Grover's database search
algorithm. Some preliminary results on the stability of quantum algorithms are
presented.",9911038v2
2004-12-18,Non-relativistic classical mechanics for spinning particles,"We study the classical dynamics of non-relativistic particles endowed with
spin. Non-vanishing Zitterbewegung terms appear in the equation of motion also
in the small momentum limit. We derive a generalized work-energy theorem which
suggests classical interpretations for tunnel effect and quantum potential.",0412145v2
2005-05-30,Semiclassical propagation of spin coherent states,"The semiclassical propagation of spin coherent states is considered in
complex phase space. For two time-independent systems we find the appropriate
classical trajectories and show that their combined contributions are able to
describe quantum interference with great accuracy. Not only the modulus but
also the phase of the quantum propagator, both dynamical and geometric terms
combined, are accurately reproduced.",0505224v2
1996-05-03,Integrable discretizations of the spin Ruijsenaars-Schneider models,"Integrable discretizations are introduced for the rational and hyperbolic
spin Ruijsenaars--Schneider models. These discrete dynamical systems are
demonstrated to belong to the same integrable hierarchies as their
continuous--time counterparts. Explicit solutions are obtained for arbitrary
flows of the hierarchies, including the discrete time ones.",9605001v1
2007-06-01,Mean field theory of spin glasses: statics and dynamics,"In these lectures I will review some theoretical results that have been
obtained for spin glasses. I will concentrate my attention on the formulation
of the mean field approach and on its numerical and experimental verifications.
I will present the various hypothesis at the basis of the theory and I will
discuss their mathematical and physical status.",0706.0094v1
2007-10-04,Quantum-mechanical Landau-Lifshitz equation,"Quantum-mechanical analogue of Landau-Lifshitz equation has been derived. It
has been established that Landau-Lifshitz equation is fundamental physical
equation underlying the dynamics of spectroscopic transitions and transitional
phenomena. New phenomenon is predicted: electrical spin wave resonance (ESWR)
being to be electrical analogue of magnetic spin wave resonance.",0710.1058v3
2007-12-15,Local control of entanglement in a spin chain,"In a ferromagnetic spin chain, the control of the local effective magnetic
field allows to manipulate the static and dynamical properties of entanglement.
In particular, the propagation of quantum correlations can be driven to a great
extent so as to achieve an entanglement transfer on demand toward a selected
site.",0712.2509v1
2008-05-03,Neutron scattering as a probe of the Fe-pnicitide superconducting gap,"Inelastic neutron scattering provides a probe for studying the spin and
momentum structure of the superconducting gap. Here, using a two-orbital model
for the Fe-pnicitide superconductors and an RPA-BCS approximation for the
dynamic spin susceptibility, we explore the scattering response for various
gaps that have been proposed.",0805.0316v1
2008-12-10,"Supersymmetry and other beyond the Standard Model physics: Prospects for determining mass, spin and CP properties","The prospects of measuring masses, spin and CP properties within
Supersymmetry and other beyond the Standard Model extensions at the LHC are
reviewed. Emphasis is put on models with missing transverse energy due to
undetected particles, as in Supersymmetry or Universal Extra Dimensions.",0812.2045v1
2009-04-08,Variational principles for spin systems and the Kirchhoff rod,"We obtain the affine Euler-Poincar\'e equations by standard Lagrangian
reduction and deduce the associated Clebsch-constrained variational principle.
These results are illustrated in deriving the equations of motion for continuum
spin systems and Kirchhoff's rod, where they provide a unified geometric
interpretation.",0904.1428v1
2010-02-18,Spin Glass Model of Operational Risk,"We analyze operational risk in terms of a spin glass model. Several regimes
are investigated, as a functions of the parameters that characterize the
dynamics. The system is found to be robust against variations of these
parameters. We unveil the presence of limit cycles and scrutinize the features
of the asymptotic state.",1002.3560v1
2011-09-07,Planar approximation for spin transfer systems with application to tilted polarizer devices,"Planar spin-transfer devices with dominating easy-plane anisotropy can be
described by an effective one-dimensional equation for the in-plane angle. Such
a description provides an intuitive qualitative understanding of the magnetic
dynamics. We give a detailed derivation of the effective planar equation and
use it to describe magnetic switching in devices with tilted polarizer.",1109.1331v1
2011-10-20,Beyond the Heisenberg time: Semiclassical treatment of spectral correlations in chaotic systems with spin 1/2,"The two-point correlation function of chaotic systems with spin 1/2 is
evaluated using periodic orbits. The spectral form factor for all times thus
becomes accessible. Equivalence with the predictions of random matrix theory
for the Gaussian symplectic ensemble is demonstrated. A duality between the
underlying generating functions of the orthogonal and symplectic symmetry
classes is semiclassically established.",1110.4567v1
2013-06-16,"Symmetry-protected topological phases with charge and spin symmetries: response theory and dynamical gauge theory in 2D, 3D and the surface of 3D","A large class of symmetry-protected topological phases (SPT) in boson / spin
systems have been recently predicted by the group cohomology theory. In this
work, we consider SPT states at least with charge symmetry (U(1) or Z$_N$) or
spin $S^z$ rotation symmetry (U(1) or Z$_N$) in 2D, 3D, and the surface of 3D.
If both are U(1), we apply external electromagnetic field / `spin gauge field'
to study the charge / spin response. For the SPT examples we consider (i.e.
U$_c$(1)$\rtimes$Z$^T_2$, U$_s$(1)$\times$Z$^T_2$,
U$_c$(1)$\times$[U$_s$(1)$\rtimes$Z$_2$]; subscripts $c$ and $s$ are short for
charge and spin; Z$^T_2$ and Z$_2$ are time-reversal symmetry and
$\pi$-rotation about $S^y$, respectively), many variants of Witten effect in
the 3D SPT bulk and various versions of anomalous surface quantum Hall effect
are defined and systematically investigated. If charge or spin symmetry reduces
to Z$_N$ by considering charge-$N$ or spin-$N$ condensate, instead of the
linear response approach, we gauge the charge/spin symmetry, leading to a
dynamical gauge theory with some remaining global symmetry. The 3D dynamical
gauge theory describes a symmetry-enriched topological phase (SET), i.e. a
topologically ordered state with global symmetry which admits nontrivial ground
state degeneracy depending on spatial manifold topology. For the SPT examples
we consider, the corresponding SET states are described by dynamical
topological gauge theory with topological BF term and axionic $\Theta$-term in
3D bulk. And the surface of SET is described by the chiral boson theory with
quantum anomaly.",1306.3695v2
2013-11-10,A strong laser impact on spin precession of a charged particle in the semi-relativistic interaction regime,"In the present note new effects concerned the dynamics of a charged spin-1/2
particle in a strong monochromatic plane wave background are discussed beyond
the conventional dipole approximation. Namely using the semiclassical approach
in the semi-relativistic regime it is shown that the magnetic forces associated
with the laser field have been retained and alter the spin evolution
appreciably.",1311.2316v1
2015-07-16,Thomas-BMT equation generalized to electric dipole moments and field gradients,"An expression is presented for the relativistic equations of motion,
including field gradients, of a particle and its spin with electric and
magnetic dipole moments aligned along the spin axis. An electromagnetic duality
transformation is used to generalize a Thomas-BMT equation with gradient terms.
Corrections to particle dynamics in storage rings for precision $(g-2)$ and
electric dipole moment measurements are calculated, and applications to
precision particle tracking programs are considered.",1507.04440v1
2015-10-12,A gauge theory of massive spin one particles,"An Abelian gauge theory describing dynamics of massive spin one bosons is
constructed. This is achieved by appending to the Maxwell action, a gauge
invariant mass term. The theory is quantised in temporal as well as Lorentz
gauge, and the corresponding Hilbert spaces are constructed. In both the
gauges, it is found that, the theory respects Lorentz invariance, locality,
causality and unitarity.",1510.03213v1
2019-05-27,Nonequilibrium Majorana Dynamics by Quenching a Magnetic Field in Kitaev Spin Liquids,"The honeycomb Kitaev spin model provides a quantum spin liquid in the ground
state, where the spin excitations are fractionalized into itinerant and
localized Majorana fermions; the former spectrum has a broad continuum ranging
up to a high energy, while the latter has a sharp peak at a low energy. Despite
tremendous efforts, it remains elusive to clearly identify these distinct
Majorana excitations in experiments. Here we show their manifestation in the
time evolution after quenching the magnetic field, by using the time-dependent
Majorana mean-field theory for both the ferromagnetic and antiferromagnetic
Kitaev models. We find that the transient spin dynamics from the quantum spin
liquid states is qualitatively different from the conventional spin precessions
by the quench from the high-field forced-ferromagnetic state. We obtain
peculiar time evolutions with distinct time scales, i.e., short-time decay of
high-energy components associated with the itinerant Majorana excitations, and
long-lived excitations at a low energy by the localized ones. These peculiar
behaviors are caused by the energy transfer between the two Majorana
quasiparticles after the field quench. Moreover, we find that the Majorana
semimetal with the point nodes in equilibrium turns into a Majorana metal with
the transient ""Fermi surfaces"" by the energy transfer. In particular, for the
quench from the intermediate-field quantum spin liquid in the antiferromagnetic
Kitaev model, the Fermi surfaces change their topology in the time evolution,
which is regarded as a dynamical version of the Majorana ""Lifshitz transition"".
Our results unveil that the real-time dynamics provides another route to not
only the identification of the fractional Majorana excitations in candidate
materials of Kitaev magnets but also unprecedented quantum phases that cannot
be stabilized as the equilibrium states.",1905.10984v1
2013-08-12,Connection between beam polarization and systematical errors in storage ring electric-dipole-moment experiments,"Analysis of spin dynamics in storage ring electric-dipole-moment (EDM)
experiments ascertains that the use of initial vertical beam polarization
allows to cancel spin-dependent systematical errors imitating the EDM effect.
While the use of this polarization meets certain difficulties, it should be
considered as an alternative or supplementary possibility of fulfilling the EDM
experiment.",1308.2610v1
2017-04-19,Anisotropic magnetic interactions and spin dynamics in the spin-chain compound Cu(py)$_2$Br$_2$: An experimental and theoretical study,"We compare theoretical results for electron spin resonance (ESR) properties
of the Heisenberg-Ising Hamiltonian with ESR experiments on the
quasi-one-dimensional magnet Cu(py)$_2$Br$_2$ (CPB). Our measurements were
performed over a wide frequency and temperature range giving insight into spin
dynamics, spin structure, and magnetic anisotropy of this compound. By
analyzing the angular dependence of ESR parameters (resonance shift and
linewidth) at room temperature we show that the two weakly coupled inequivalent
spin chain types inside the compound are well described by Heisenberg-Ising
chains with their magnetic anisotropy axes perpendicular to the chain direction
and almost perpendicular to each other. We further determine the full
$g$-tensor from these data. In addition, the angular dependence of the
linewidth at high temperatures gives us access to the exponent of the algebraic
decay of a dynamical correlation function of the isotropic Heisenberg chain.
From the temperature dependence of static susceptibilities we extract the
strength of the exchange coupling ($J/k_B = 52.0\,\text{K}$) and the anisotropy
parameter ($\delta\approx -0.02$) of the model Hamiltonian. An independent
compatible value of $\delta$ is obtained by comparing the exact prediction for
the resonance shift at low temperatures with high-frequency ESR data recorded
at $4\,\text{K}$. The spin structure in the ordered state implied by the two
(almost) perpendicular anisotropy axes is in accordance with the propagation
vector determined from neutron scattering experiments. In addition to undoped
samples we study the impact of partial substitution of Br by Cl ions on spin
dynamics. From the dependence of the ESR linewidth on doping level we infer an
effective decoupling of the anisotropic component $J\delta$ from the isotropic
exchange $J$ in these systems.",1704.05705v2
2008-07-24,On the partial trace over collective spin-degrees of freedom,"We derive analytical properties for the degeneracy $\nu(N,j)$ occurring in
the decomposition $\bigoplus\limits_{j}^\frac{N}{2}\nu(N,j)\mathbb C^{2j+1}$ of
the state space $\mathbb C^{2\otimes N}$. We also investigate the dynamics of
two qubits coupled via Ising interactions to separate spin baths, and we study
the thermodynamic limit.",0807.3944v2
2022-09-14,Quasi-Classical Spin-Boson Models,"In this short note we study Spin-Boson Models from the Quasi-Classical
standpoint. In the Quasi-Classical limit, the field becomes macroscopic while
the particles it interacts with, they remain quantum. As a result, the field
becomes a classical environment that drives the particle system with an
explicit effective dynamics.",2209.06477v1
1997-05-07,Spin Precession and Time-Reversal Symmetry Breaking in Quantum Transport of Electrons Through Mesoscopic Rings,"We consider the motion of electrons through a mesoscopic ring in the presence
of spin-orbit interaction, Zeeman coupling, and magnetic flux. The coupling
between the spin and the orbital degrees of freedom results in the geometric
and the dynamical phases associated with a cyclic evolution of spin state.
Using a non-adiabatic Aharonov-Anandan phase approach, we obtain the exact
solution of the system and identify the geometric and the dynamical phases for
the energy eigenstates. Spin precession of electrons encircling the ring can
lead to various interference phenomena such as oscillating persistent current
and conductance. We investigate the transport properties of the ring connected
to current leads to explore the roles of the time-reversal symmetry and its
breaking therein with the spin degree of freedom being fully taken into
account. We derive an exact expression for the transmission probability through
the ring. We point out that the time-reversal symmetry breaking due to Zeeman
coupling can totally invalidate the picture that spin precession results in
effective, spin-dependent Aharonov-Bohm flux for interfering electrons.
Actually, such a picture is only valid in the Aharonov-Casher effect induced by
spin-orbit interaction only. Unfortunately, this point has not been realized in
prior works on the transmission probability in the presence of both SO
interaction and Zeeman coupling. We carry out numerical computation to
illustrate the joint effects of spin-orbit interaction, Zeeman coupling and
magnetic flux. By examining the resonant tunneling of electrons in the weak
coupling limit, we establish a connection between the observable time-reversal
symmetry breaking effects manifested by the persistent current and by the
transmission probability. For a ring formed by two-dimensional electron gas, we",9705054v1
2016-01-01,Long-Time Predictability in Disordered Spin Systems Following a Deep Quench,"We study the problem of predictability, or ""nature vs. nurture"", in several
disordered Ising spin systems evolving at zero temperature from a random
initial state: how much does the final state depend on the information
contained in the initial state, and how much depends on the detailed history of
the system? Our numerical studies of the ""dynamical order parameter"" in
Edwards-Anderson Ising spin glasses and random ferromagnets indicate that the
influence of the initial state decays as dimension increases. Similarly, this
same order parameter for the Sherrington-Kirkpatrick infinite-range spin glass
indicates that this information decays as the number of spins increases. Based
on these results, we conjecture that the influence of the initial state on the
final state decays to zero in finite-dimensional random-bond spin systems as
dimension goes to infinity, regardless of the presence of frustration. We also
study the rate at which spins ""freeze out"" to a final state as a function of
dimensionality and number of spins; here the results indicate that the number
of ""active"" spins at long times increases with dimension (for short-range
systems) or number of spins (for infinite-range systems). We provide
theoretical arguments to support these conjectures, and also study analytically
several mean-field models: the random energy model, the uniform Curie-Weiss
ferromagnet, and the disordered Curie-Weiss ferromagnet. We find that for these
models, the information contained in the initial state does not decay in the
thermodynamic limit-- in fact, it fully determines the final state. Unlike in
short-range models, the presence of frustration in mean-field models
dramatically alters the dynamical behavior with respect to the issue of
predictability.",1601.00105v2
2016-01-27,Dynamic nuclear polarization in a magnetic resonance force microscope experiment,"We report achieving enhanced nuclear magnetization in a magnetic resonance
force microscope experiment at 0.6 tesla and 4.2 kelvin using the dynamic
nuclear polarization (DNP) effect. In our experiments a microwire coplanar
waveguide delivered radiowaves to excite nuclear spins and microwaves to excite
electron spins in a 250 nm thick nitroxide-doped polystyrene sample. Both
electron and proton spin resonance were observed as a change in the mechanical
resonance frequency of a nearby cantilever having a micron-scale nickel tip.
NMR signal, not observable from Curie-law magnetization at 0.6 tesla, became
observable when microwave irradiation was applied to saturate the electron
spins. The resulting NMR signal's size, buildup time, dependence on microwave
power, and dependence on irradiation frequency was consistent with a transfer
of magnetization from electron spins to nuclear spins. Due to the presence of
an inhomogenous magnetic field introduced by the cantilever's magnetic tip, the
electron spins in the sample were saturated in a microwave-resonant slice 10's
of nm thick. The spatial distribution of the nuclear polarization enhancement
factor $\epsilon$ was mapped by varying the frequency of the applied
radiowaves. The observed enhancement factor was zero for spins in the center of
the resonant slice, was $\epsilon = +10$ to $+20$ for spins proximal to the
magnet, and was $\epsilon = -10$ to $-20$ for spins distal to the magnet. We
show that this bipolar nuclear magnetization profile is consistent with
cross-effect DNP in a $\sim \! 10^{5} \: \mathrm{T} \: \mathrm{m}^{-1}$
magnetic field gradient. Potential challenges associated with generating and
using DNP-enhanced nuclear magnetization in a nanometer-resolution magnetic
resonance imaging experiment are elucidated and discussed.",1601.07253v2
2020-12-03,New effective precession spin for modeling multimodal gravitational waveforms in the strong-field regime,"Accurately modelling the complete gravitational-wave signal from precessing
binary black holes through the late inspiral, merger and ringdown remains a
challenging problem. The lack of analytic solutions for the precession dynamics
of generic double-spin systems, and the high dimensionality of the problem,
obfuscate the incorporation of strong-field spin-precession information into
semi-analytic waveform models used in gravitational-wave data analysis.
Previously, an effective precession spin, $\chi_p$, was introduced to reduce
the number of spin degrees of freedom. Here, we show that $\chi_p$ alone does
not accurately reproduce higher-order multipolar modes, in particular the ones
that carry strong imprints due to precession such as the $(2,1)$-mode. To
improve the higher-mode content, and in particular to facilitate an accurate
incorporation of precession effects in the strong-field regime into waveform
models, we introduce a new dimensional reduction through an effective
precession spin vector, $\vec{\chi}_\perp$, which takes into account precessing
spin information from both black holes. We show that this adapted effective
precession spin (i) mimics the precession dynamics of the fully precessing
configuration remarkably well, (ii) captures the signature features of
precession in higher-order modes, and (iii) reproduces the final state of the
remnant black hole with high accuracy for the overwhelming majority of
configurations. We demonstrate the efficacy of this two-dimensional precession
spin in the strong-field regime, paving the path for meaningful calibration of
the precessing sector of semi-analytic waveform models with a faithful
representation of higher-order modes through merger and the remnant black hole
spin.",2012.02209v3
2021-04-15,Supernova Fallback as Origin of Neutron Star Spins and Spin-kick Alignment,"Natal kicks and spins are characteristic properties of neutron stars (NSs)
and black holes (BHs). Both offer valuable clues to dynamical processes during
stellar core collapse and explosion. Moreover, they influence the evolution of
stellar multiple systems and the gravitational-wave signals from their inspiral
and merger. Observational evidence of possibly generic spin-kick alignment has
been interpreted as indication that NS spins are either induced with the NS
kicks or inherited from progenitor rotation, which thus might play a
dynamically important role during stellar collapse. Current three-dimensional
supernova simulations suggest that NS kicks are transferred in the first
seconds of the explosion, mainly by anisotropic mass ejection and, on a
secondary level, anisotropic neutrino emission. In contrast, the NS spins are
only determined minutes to hours later by angular momentum associated with
fallback of matter that does not become gravitationally unbound in the
supernova. Here, we propose a novel scenario to explain spin-kick alignment as
a consequence of tangential vortex flows in the fallback matter that is
accreted mostly from the direction of the NS's motion. For this effect the
initial NS kick is crucial, because it produces a growing offset of the NS away
from the explosion center, thus promoting onesided accretion. In this new
scenario conclusions based on traditional concepts are reversed. For example,
pre-kick NS spins are not required, and rapid progenitor-core rotation can
hamper spin-kick alignment. We also discuss implications for natal BH kicks and
the possibility of tossing the BH's spin axis during its formation.",2104.07493v2
2022-06-11,Field evolution of magnetic phases and spin dynamics in the honeycomb lattice magnet Na2Co2TeO6: 23Na NMR study,"We report on the results of 23Na NMR in the honeycomb lattice magnet
Na2Co2TeO6 which has been nominated as a Kitaev material. Measurements of
magnetic shift and width of the NMR line as functions of temperature and
magnetic field show that a spin-disordered phase does not appear up to a field
of 9 T. In the antiferromagnetic phase just below the Neel temperature TN, we
find a temperature region extending down to ~TN/2 where the nuclear
spin-lattice relaxation rate 1/T1 remains enhanced and is further increased by
a magnetic field. This region crosses over to a low temperature region
characterized by the rapidly decreasing 1/T1 which is less field-sensitive.
These observations suggest incoherent spin excitations with a large spectral
weight at low energies in the intermediate temperature region transforming to
more conventional spin-wave excitations at low temperatures. The drastic change
of the low-energy spin dynamics is likely caused by strong damping of spin
waves activated only in the intermediate temperature region, which may be
realized for triple-q magnetic order possessing partially-disordered moments as
scattering centers of spin waves. In the paramagnetic phase near TN, dramatic
field suppression of 1/T1 is observed. From analysis of the temperature
dependence of 1/T1 based on the renormalized-classical description of a
two-dimensional quantum antiferromagnet, we find the field-dependent spin
stiffness constant that scales with TN as a function of magnetic field. This
implies field suppression of the energy scale characterizing both
two-dimensional spin correlations and three-dimensional long-range order, which
may be associated with an increasing effect of frustration in magnetic fields.",2206.05409v3
2022-12-14,Covariant Cubic Interacting Vertices for Massless and Massive Integer Higher Spin Fields,"We develop the BRST approach to construct the general off-shell local Lorentz
covariant cubic interaction vertices for irreducible massless and massive
higher spin fields on $d$-dimensional Minkowski space. We consider two
different cases for interacting higher spin fields: with one massive and two
massless; with two massive both with coinciding and with different masses and
one massless fields of spins $s_1, s_2, s_3$. Unlike the previous results on
cubic vertices we extend our earlier result in [arXiv:2105.12030[hep-th]] for
massless fields and employ the complete BRST operator, including the trace
constraints that is used to formulate an irreducible representation with
definite integer spin. We generalize the cubic vertices proposed for reducible
higher spin fields in [arXiv:1205.3131 [hep-th]] in the form of multiplicative
and non-multiplicative BRST-closed constituents and calculate the new
contributions to the vertex, which contain additional terms with a smaller
number space-time derivatives of the fields. We prove that without traceless
conditions for the cubic vertices in [arXiv:1205.3131 [hep-th]] it is
impossible to provide the noncontradictory Lagrangian dynamics and find
explicit traceless solution for these vertices. As the examples, we explicitly
construct the interacting Lagrangian for the massive of spin $s$ field and
massless scalars both with and without auxiliary fields. The interacting models
with different combinations of triples higher spin fields: massive of spin $s$
with massless scalar and vector fields and with two vector fields; massless of
helicity $\lambda$ with massless scalar and massive vector fields; two massive
fields of spins $s, 0$ and massless scalar are also considered.",2212.07097v7
2023-08-17,Probing Spin-Induced Quadrupole Moments in Precessing Compact Binaries,"Spin-induced quadrupole moments provide an important characterization of
compact objects, such as black holes, neutron stars and black hole mimickers
inspired by additional fields and/or modified theories of gravity. Black holes
in general relativity have a specific spin-induced quadrupole moment, with
other objects potentially having differing values. Different values of this
quadrupole moment lead to modifications of the spin precession dynamics, and
consequently modifications to the inspiral waveform. Based on the spin-dynamics
and the associated precessing waveform developed in our previous work, we
assess the prospects of measuring spin-induced moments in various black hole,
neutron star, and black-hole mimicker binaries. We focus on binaries in which
at least one of the objects is in the mass gap (similar to the $2.6 M_\odot$
object found in GW190814). We find that for generic precessing binaries, the
effect of the spin-induced quadrupole moments on the precession is sensitive to
the nature of the mass-gap object, i.e., whether it is a light black hole or a
massive neutron star. So that this is a good probe of the nature of these
objects. For precessing black-hole mimicker binaries, this waveform also
provides significantly tighter constraints on their spin-induced quadrupole
moments than the previous results obtained without incorporating the precession
effects of spin-induced quadrupole moments. We apply the waveform to sample
events in GWTC catalogs to obtain better constraints on the spin-induced
quadrupole moments, and discuss the measurement prospects for events in the
O$4$ run of the LIGO-Virgo-KAGRA Collaboration.",2308.09032v2
2023-08-27,"Quantum Field Theory, Worldline Theory, and Spin Magnitude Change in Orbital Evolution","A previous paper~\cite{Bern:2022kto} identified a puzzle stemming from the
amplitudes-based approach to spinning bodies in general relativity: additional
Wilson coefficients appear compared to current worldline approaches to
conservative dynamics of generic astrophysical objects, including neutron
stars. In this paper we clarify the nature of analogous Wilson coefficients in
the simpler theory of electrodynamics. We analyze the original field-theory
construction, identifying definite-spin states some of which have negative
norms, and relating the additional Wilson coefficients in the classical theory
to transitions between different quantum spin states. We produce a new version
of the theory which also has additional Wilson coefficients, but no
negative-norm states. We match, through $\mathcal O(\alpha^2)$ and $\mathcal
O(S^2)$, the Compton amplitudes of these field theories with those of a
modified worldline theory with extra degrees of freedom introduced by releasing
the spin supplementary condition. We build an effective two-body Hamiltonian
that matches the impulse and spin kick of the modified field theory and of the
worldline theory, displaying additional Wilson coefficients compared to
standard worldline approaches. The results are then compactly expressed in
terms of an eikonal formula. Our key conclusion is that, contrary to standard
approaches, while the magnitude of the spin tensor is still conserved, the
magnitude of the spin vector can change under conserved Hamiltonian dynamics
and this change is governed by the additional Wilson coefficients. For specific
values of Wilson coefficients the results are equivalent to those from a
definite spin obeying the spin supplementary condition, but for generic values
they are physically inequivalent. These results warrant detailed studies of the
corresponding issues in general relativity.",2308.14176v3
2024-02-27,Nuclear spin relaxation mediated by donor-bound and free electrons in wide CdTe quantum wells,"The nuclear spin systems in CdTe/(Cd,Zn)Te and CdTe/(Cd,Mg)Te quantum wells
(QW) are studied using a multistage technique combining optical pumping and
Hanle effect-based detection. The samples demonstrate drastically different
nuclear spin dynamics in zero and weak magnetic fields. In CdTe/(Cd,Zn)Te, the
nuclear spin relaxation time is found to strongly increase with the magnetic
field, growing from 3 s in zero field to tens of seconds in a field of 25 G. In
CdTe/(Cd,Mg)Te the relaxation is an order of magnitude slower, and it is
field-independent up to at least 70 G. The differences are attributed to the
nuclear spin relaxation being mediated by different kinds of resident electrons
in these QWs. In CdTe/(Cd,Mg)Te, a residual electron gas trapped in the QW
largely determines the relaxation dynamics. In CdTe/(Cd,Zn)Te, the fast
relaxation in zero field is due to interaction with localized donor-bound
electrons. Nuclear spin diffusion barriers form around neutral donors when the
external magnetic field exceeds the local nuclear field, which is about
$B_L\approx $0.4 G in CdTe. This inhibits nuclear spin diffusion towards the
donors, slowing down relaxation. These findings are supported by theoretical
modeling. In particular, we show that the formation of the diffusion barrier is
made possible by several features specific to CdTe: (i) the large donor binding
energy (about 10 meV), (ii) the low abundance of magnetic isotopes (only
$\approx$30% of nuclei have nonzero spin), and (iii) the absence of nuclear
quadrupole interactions between nuclei. The two latter properties are also
favorable to nuclear spin cooling via optical pumping followed by adiabatic
demagnetization. Under non-optimized conditions we have reached sub-microkelvin
nuclear spin temperatures in both samples, lower than all previous results
obtained in GaAs.",2402.17435v2
1995-11-03,Quantum Relaxation of Magnetisation in Magnetic Particles,"At temperatures below the magnetic anisotropy energy, monodomain magnetic
systems (small particles, nanomagnetic devices, etc.) must relax quantum
mechanically. This quantum relaxation must be mediated by the coupling to both
nuclear spins and phonons (and electrons if either particle or substrate is
conducting. We analyze the effect of each of these couplings, and then combine
them. Conducting systems can be modelled by a ""giant Kondo"" Hamiltonian, with
nuclear spins added in as well. At low temperatures, even microscopic particles
on a conducting substrate (containing only $10-50$ spins) will have their
magnetisation frozen over millenia by a combination of electronic dissipation
and the ""degeneracy blocking"" caused by nuclear spins. Raising the temperature
leads to a sudden unblocking of the spin dynamics at a well defined
temperature. Insulating systems are quite different. The relaxation is strongly
enhanced by the coupling to nuclear spins. At short times the magnetisation of
an ensemble of particles relaxes logarithmically in time, after an initial very
fast decay; this relaxation proceeds entirely via the nuclear spins. At longer
times phonons take over, but the decay rate is still governed by the
temperature-dependent nuclear bias field acting on the particles - decay may be
exponential or power-law depending on the temperature. The most surprising
feature of the results is the pivotal role played by the nuclear spins. The
results are relevant to any experiments on magnetic particles in which
interparticle dipolar interactions are unimportant. They are also relevant to
future magnetic device technology.",9511016v1
2003-05-22,Theory of spin response in underdoped cuprates as strongly fluctuating d-wave superconductors,"We study the spin dynamics in underdoped cuprates at low temperatures by
considering them as quasi two dimensional d-wave superconductors (dSC) with
strong phase fluctuations. An effective theory of spin degrees of freedom of
nodal quasiparticles coupled to vortex defects in the phase of the
superconducting order parameter is formulated. It represents the minimal
extension of the QED3 theory of the pseudogap phase into the superconducting
region. The theory predicts a single dSC-SDW transition, which may be
fluctuation induced first order, without the region of coexistence between the
two ordered phases. We compute the spin-spin correlator in the dSC, and explain
the evolution of the spin response with frequency as observed in neutron
scattering experiments on YBCO. We predict that at the frequencies much below
the resonance the (weak) spin response should become narrowly peaked at four
`diagonally' incommensurate wave vectors that span between the nodes of the
supercopnducting order parameter. These peaks represent an inherent collective
mode of the phase fluctuating dSC, the condensation of which would bring about
the SDW order in the pseudogap phase. Our interpretation of the resonance
suggests it should become more elusive in the superconductors with lower Tc, in
accord with its' conspicuous absence in LSCO.",0305512v1
2002-06-24,Nuclear spin-orbit interaction from chiral pion-nucleon dynamics,"Using the two-loop approximation of chiral perturbation theory, we calculate
the momentum and density dependent nuclear spin-orbit strength $U_{ls}(p,k_f)$.
This quantity is derived from the spin-dependent part of the interaction energy
$\Sigma_{spin} = {i\over 2} \vec \sigma \cdot (\vec q \times\vec p)
U_{ls}(p,k_f)$ of a nucleon scattering off weakly inhomogeneous isospin
symmetric nuclear matter. We find that iterated $1\pi$-exchange generates at
saturation density, $k_{f0}=272.7 $MeV, a spin-orbit strength at $p=0$ of
$U_{ls}(0,k_{f0})\simeq 35$ MeVfm$^2$ in perfect agreement with the empirical
value used in the shell model. This novel spin-orbit strength is neither of
relativistic nor of short range origin. The potential $V_{ls}$ underlying the
empirical spin-orbit strength $\widetilde U_{ls}= V_{ls} r_{ls}^2$ becomes a
rather weak one, $V_{ls}\simeq 17$ MeV, after the identification $r_{ls}=
m_\pi^{-1}$ as suggested by the present calculation. We observe however a
strong $p$-dependence of $U_{ls}(p,k_{f0})$ leading even to a sign change above
$p=200 $MeV. This and other features of the emerging spin-orbit Hamiltonian
which go beyond the usual shell model parametrization leave questions about the
ultimate relevance of the spin-orbit interaction generated by $2\pi$-exchange
for a finite nucleus. We also calculate the complex-valued isovector
single-particle potential $U_I(p,k_f)+ i W_I(p,k_f)$ in isospin asymmetric
nuclear matter proportional to $\tau_3 (N-Z)/(N+Z)$. For the real part we find
reasonable agreement with empirical values and the imaginary part vanishes at
the Fermi-surface $p=k_f$.",0206056v1
2003-01-08,Isovector nuclear spin-orbit interaction from chiral pion-nucleon dynamics,"Using the two-loop approximation of chiral perturbation theory, we calculate
the momentum and density dependent isovector nuclear spin-orbit strength
$V_{ls}(p,k_f)$. This quantity is derived from the spin-dependent part of the
interaction energy $\Sigma_{spin} = {i\over 2} \vec \sigma \cdot (\vec q
\times\vec p)[U_{ls}(p,k_f)- V_{ls}(p,k_f)\tau_3 \delta] $ of a nucleon
scattering off weakly inhomogeneous isospin-asymmetric nuclear matter. We find
that iterated $1\pi$-exchange generates at saturation density, $k_{f0}=272.7
$MeV, an isovector nuclear spin-orbit strength at $p=0$ of $V_{ls}(0,k_{f0})
\simeq 50$ MeVfm$^2$. This value is about 1.4 times the analogous isoscalar
nuclear spin-orbit strength $U_{ls}(0,k_{f0})\simeq 35$ MeVfm$^2$ generated by
the same two-pion exchange diagrams. We also calculate several relativistic
1/M-corrections to the isoscalar nuclear spin-orbit strength. In particular, we
evaluate the contributions from irreducible two-pion exchange to
$U_{ls}(p,k_f)$. The effects of the three-body diagrams constructed from the
Weinberg-Tomozawa $\pi\pi NN$-contact vertex on the isoscalar nuclear
spin-orbit strength are computed. We find that such relativistic
1/M-corrections are less than 20% of the isoscalar nuclear spin-orbit strength
generated by iterated one-pion-exchange, in accordance with the expectation
from chiral power counting.",0301019v1
2007-06-20,Kondo physics in the algebraic spin liquid,"We study Kondo physics in the algebraic spin liquid, recently proposed to
describe $ZnCu_{3}(OH)_{6}Cl_{2}$ [Phys. Rev. Lett. {\bf 98}, 117205 (2007)].
Although spin dynamics of the algebraic spin liquid is described by massless
Dirac fermions, this problem differs from the Pseudogap Kondo model, because
the bulk physics in the algebraic spin liquid is governed by an interacting
fixed point where well-defined quasiparticle excitations are not allowed.
Considering an effective bulk model characterized by an anomalous critical
exponent, we derive an effective impurity action in the slave-boson context.
Performing the large-$N_{\sigma}$ analysis with a spin index $N_{\sigma}$, we
find an impurity quantum phase transition from a decoupled local-moment state
to a Kondo-screened phase. We evaluate the impurity spin susceptibility and
specific heat coefficient at zero temperature, and find that such responses
follow power-law dependencies due to the anomalous exponent of the algebraic
spin liquid. Our main finding is that the Wilson's ratio for the magnetic
impurity depends strongly on the critical exponent in the zero temperature
limit. We propose that the Wilson's ratio for the magnetic impurity may be one
possible probe to reveal criticality of the bulk system.",0706.2943v2
2007-07-17,Quarkonium and hydrogen spectra with spin dependent relativistic wave equation,"A non-linear non-perturbative relativistic atomic theory introduces spin in
the dynamics of particle motion. The resulting energy levels of Hydrogen atom
are exactly same as the Dirac theory. The theory accounts for the energy due to
spin-orbit interaction and for the additional potential energy due to spin and
spin-orbit coupling. Spin angular momentum operator is integrated into the
equation of motion. This requires modification to classical Laplacian operator.
Consequently the Dirac matrices and the k operator of Dirac's theory are
dispensed with. The theory points out that the curvature of the orbit draws on
certain amount of kinetic and potential energies affecting the momentum of
electron and the spin-orbit interaction energy constitutes a part of this
energy. The theory is developed for spin 1/2 bound state single electron in
Coulomb potential and then further extended to quarkonium physics by
introducing the linear confining potential. The unique feature of this
quarkonium model is that the radial distance can be exactly determined and does
not have a statistical interpretation. The established radial distance is then
used to determine the wave function. The observed energy levels are used as the
input parameters and the radial distance and the string tension are predicted.
This ensures 100% conformance to all observed energy levels for the heavy
quarkonium.",0707.2431v7
2007-08-04,The Spin Density Matrix I: General Theory and Exact Master Equations,"We consider a scenario where interacting electrons confined in quantum dots
(QDs) are either too close to be resolved, or we do not wish to apply
measurements that resolve them. Then the physical observable is an electron
spin only (one cannot unambiguously ascribe a spin to a QD) and the system
state is fully described by the spin-density matrix. Accounting for the spatial
degrees of freedom, we examine to what extent a Hamiltonian description of the
spin-only degrees of freedom is valid. We show that as long as there is no
coupling between singlet and triplet states this is indeed the case, but when
there is such a coupling there are open systems effects, i.e., the dynamics is
non-unitary even without interaction with a true bath. Our primary focus is an
investigation of non-unitary effects, based on exact master equations we derive
for the spin-density matrix in the Lindblad and time-convolutionless (TCL)
forms, and the implications for quantum computation. In particular, we
demonstrate that the Heisenberg interaction does not affect the unitary part
(apart from a Lamb shift) but does affect the non-unitary contributions to time
evolution of the spin-density matrix. In a sequel paper we present a detailed
analysis of an example system of two quantum dots, including spin-orbit
effects.",0708.0644v1
2008-02-04,Thermospin Hall effect generated by thermal influence and thermoelectric effect,"In this paper, we present the theoretical predication of a thermospin Hall
effect, in which a transverse spin current can be generated in semiconductors
in the presence of spin-orbit coupling by a frequency-dependent longitudinal
temperature gradient. Because of the thermoelectric effect, there is no net
charge current but there is a heat flow from the hot side to the cold side. We
perform the theoretical calculation of dynamical thermospin Hall conductivity
in a two-dimensional Rashba spintronic system. It has been shown that the
direct interband optical transition dominates the ordering and manipulation of
spin in the generation of a transverse intrinsic spin current. In view of the
role of the thermoelectric effect, the contributions to the thermospin Hall
effect are classified as that originating from a direct contribution of thermal
electronic diffusion and that from the compensatory electron flow in balance
with the thermal diffusion. For a finite system, the analysis yields evidence
that the spin accumulation around the edges of a plate determines the
magnetization. In equilibrium, a field created by a magnetization gradient
emerges in the direction perpendicular to the temperature gradient. The
experimental observation of the thermospin Hall effect is proposed by measuring
the longitudinal temperature difference with the injection of a transverse spin
current and by analyzing the Hall angle. In addition, in order to achieve pure
spin accumulation in the spin Hall effect, an extension of the thermospin Hall
effect for exciting electron-hole pairs in semiconductors is proposed.",0802.0348v1
2008-02-08,Note on spin-orbit interactions in nuclei and hypernuclei,"A detailed comparison is made between the spin-orbit interactions in
$\Lambda$ hypernuclei and ordinary nuclei. We argue that there are three major
contributions to the spin-orbit interaction: 1) a short-range component
involving scalar and vector mean fields; 2) a ''wrong-sign'' spin-orbit term
generated by the pion exchange tensor force in second order; and 3) a
three-body term induced by two-pion exchange with excitation of virtual
$\Delta(1232)$-isobars (a la Fujita-Miyazawa). For nucleons in nuclei the
long-range pieces related to the pion-exchange dynamics tend to cancel, leaving
room dominantly for spin-orbit mechanisms of short-range origin (parametrized
e.g. in terms of relativistic scalar and vector mean fields terms). In
contrast, the absence of an analogous $2\pi$-exchange three-body contribution
for $\Lambda$ hyperons in hypernuclei leads to an almost complete cancellation
between the short-range (relativistic mean-field) component and the
''wrong-sign'' spin-orbit interaction generated by second order $\pi$-exchange
with an intermediate $\Sigma$ hyperon. These different balancing mechanisms
between short- and long-range components are able to explain simultaneously the
very strong spin-orbit interaction in ordinary nuclei and the remarkably weak
spin-orbit splitting in $\Lambda$ hypernuclei.",0802.1190v1
2008-09-26,Decoherence in Solid State Qubits,"Interaction of solid state qubits with environmental degrees of freedom
strongly affects the qubit dynamics, and leads to decoherence. In quantum
information processing with solid state qubits, decoherence significantly
limits the performances of such devices. Therefore, it is necessary to fully
understand the mechanisms that lead to decoherence. In this review we discuss
how decoherence affects two of the most successful realizations of solid state
qubits, namely, spin-qubits and superconducting qubits. In the former, the
qubit is encoded in the spin 1/2 of the electron, and it is implemented by
confining the electron spin in a semiconductor quantum dot. Superconducting
devices show quantum behavior at low temperatures, and the qubit is encoded in
the two lowest energy levels of a superconducting circuit. The electron spin in
a quantum dot has two main decoherence channels, a (Markovian) phonon-assisted
relaxation channel, due to the presence of a spin-orbit interaction, and a
(non-Markovian) spin bath constituted by the spins of the nuclei in the quantum
dot that interact with the electron spin via the hyperfine interaction. In a
superconducting qubit, decoherence takes place as a result of fluctuations in
the control parameters, such as bias currents, applied flux, and bias voltages,
and via losses in the dissipative circuit elements.",0809.4716v1
2009-05-04,$T_1$- and $T_2$-spin relaxation time limitations of phosphorous donor electrons near crystalline silicon to silicon dioxide interface defects,"A study of donor electron spins and spin--dependent electronic transitions
involving phosphorous ($^{31}$P) atoms in proximity of the (111) oriented
crystalline silicon (c-Si) to silicon dioxide (SiO$_{2}$) interface is
presented for [$^{31}$P] = 10$^{15}$ $\mathrm{cm}^{-3}$ and [$^{31}$P] =
10$^{16}$ $\mathrm{cm}^{-3}$ at about liquid $^4$He temperatures ($T = 5$
$\mathrm{K} - 15$ $\mathrm{K}$). Using pulsed electrically detected magnetic
resonance (pEDMR), spin--dependent transitions between the \Phos donor state
and two distinguishable interface states are observed, namely (i) \Pb centers
which can be identified by their characteristic anisotropy and (ii) a more
isotropic center which is attributed to E$^\prime$ defects of the \sio bulk
close to the interface. Correlation measurements of the dynamics of
spin--dependent recombination confirm that previously proposed transitions
between \Phos and the interface defects take place. The influence of these
electronic near--interface transitions on the \Phos donor spin coherence time
$T_2$ as well as the donor spin--lattice relaxation time $T_1$ is then
investigated by comparison of spin Hahn--echo decay measurements obtained from
conventional bulk sensitive pulsed electron paramagnetic resonance and surface
sensitive pEDMR, as well as surface sensitive electrically detected inversion
recovery experiments. The measurements reveal that both $T_2$ and $T_1$ of
\Phos donor electrons spins in proximity of energetically lower interface
states at $T\leq 13$ K are reduced by several orders of magnitude.",0905.0416v1
2009-05-12,Nuclear Spins in Nanostructures,"We review recent theoretical and experimental advances toward understanding
the effects of nuclear spins in confined nanostructures. These systems, which
include quantum dots, defect centers, and molecular magnets, are particularly
interesting for their importance in quantum information processing devices,
which aim to coherently manipulate single electron spins with high precision.
On one hand, interactions between confined electron spins and a nuclear-spin
environment provide a decoherence source for the electron, and on the other, a
strong effective magnetic field that can be used to execute local coherent
rotations. A great deal of effort has been directed toward understanding the
details of the relevant decoherence processes and to find new methods to
manipulate the coupled electron-nuclear system.
  A sequence of spectacular new results have provided understanding of
spin-bath decoherence, nuclear spin diffusion, and preparation of the nuclear
state through dynamic polarization and more general manipulation of the
nuclear-spin density matrix through ""state narrowing"". These results
demonstrate the richness of this physical system and promise many new mysteries
for the future.",0905.1743v2
2010-12-07,Reducing orbital eccentricity of precessing black-hole binaries,"Building initial conditions for generic binary black-hole evolutions without
initial spurious eccentricity remains a challenge for numerical-relativity
simulations. This problem can be overcome by applying an eccentricity-removal
procedure which consists in evolving the binary for a couple of orbits,
estimating the eccentricity, and then correcting the initial conditions. The
presence of spins can complicate this procedure. As predicted by post-Newtonian
theory, spin-spin interactions and precession prevent the binary from moving
along an adiabatic sequence of spherical orbits, inducing oscillations in the
radial separation and in the orbital frequency. However, spin-induced
oscillations occur at approximately twice the orbital frequency, therefore they
can be distinguished from the initial spurious eccentricity, which occurs at
approximately the orbital frequency. We develop a new removal procedure based
on the derivative of the orbital frequency and find that it is successful in
reducing the eccentricity measured in the orbital frequency to less than 0.0001
when moderate spins are present. We test this new procedure using
numerical-relativity simulations of binary black holes with mass ratios 1.5 and
3, spin magnitude 0.5 and various spin orientations. The numerical simulations
exhibit spin-induced oscillations in the dynamics at approximately twice the
orbital frequency. Oscillations of similar frequency are also visible in the
gravitational-wave phase and frequency of the dominant mode.",1012.1549v2
2013-01-28,Atomic clock transitions in silicon-based spin qubits,"A major challenge in using spins in the solid state for quantum technologies
is protecting them from sources of decoherence. This can be addressed, to
varying degrees, by improving material purity or isotopic composition for
example, or active error correction methods such as dynamic decoupling, or even
combinations of the two. However, a powerful method applied to trapped ions in
the context of frequency standards and atomic clocks, is the use of particular
spin transitions which are inherently robust to external perturbations. Here we
show that such `clock transitions' (CTs) can be observed for electron spins in
the solid state, in particular using bismuth donors in silicon. This leads to
dramatic enhancements in the electron spin coherence time, exceeding seconds.
We find that electron spin qubits based on CTs become less sensitive to the
local magnetic environment, including the presence of 29Si nuclear spins as
found in natural silicon. We expect the use of such CTs will be of additional
importance for donor spins in future devices, mitigating the effects of
magnetic or electric field noise arising from nearby interfaces.",1301.6567v1
2013-02-28,Sine-Gordon model coupled with a free scalar field emergent in the low-energy phase dynamics of a mixture of pseudospin-1/2 Bose gases with interspecies spin exchange,"Using the approach of low-energy effective field theory, the phase diagram is
studied for a mixture of two species of pseudospin-$\1/2$ Bose atoms with
interspecies spin-exchange. There are four mean-field regimes on the parameter
plane of $g_e$ and $g_z$, where $g_e$ is the interspecies spin-exchange
interaction strength, while $g_z$ is the difference between the interaction
strength of interspecies scattering without spin-exchange of equal spins and
that of unequal spins. Two regimes, with $|g_z| > |g_e|$, correspond to ground
states with the total spins of the two species parallel or antiparallel along
$z$ direction, and the low energy excitations are equivalent to those of
two-component spinless Bosons. The other two regimes, with $|g_e| > |g_z|$,
correspond to ground states with the total spins of the two species parallel or
antiparallel on $xy$ plane, and the low energy excitations are described by a
sine-Gordon model coupled with a free scalar field, where the effective fields
are combinations of the phases of the original four Boson fields. In
(1+1)-dimension, they are described by Kosterlitz-Thouless renormalization
group (RG) equations, and there are three sectors in the phase plane of a
scaling dimension and a dimensionless parameter proportional to the strength of
the cosine interaction, both depending on the densities. The gaps of these
elementary excitations are experimental probes of the underlying many-body
ground states.",1302.7214v1
2013-04-13,Detection of atomic spin labels in a lipid bi-layer using a single-spin nanodiamond probe,"Magnetic field fluctuations arising from fundamental spins are ubiquitous in
nanoscale biology, and are a rich source of information about the processes
that generate them. However, the ability to detect the few spins involved
without averaging over large ensembles has remained elusive. Here we
demonstrate the detection of gadolinium spin labels in an artificial cell
membrane under ambient conditions using a single-spin nanodiamond sensor.
Changes in the spin relaxation time of the sensor located in the lipid bilayer
were optically detected and found to be sensitive to near-individual proximal
gadolinium atomic labels. The detection of such small numbers of spins in a
model biological setting, with projected detection times of one second, opens a
new pathway for in-situ nanoscale detection of dynamical processes in biology.",1304.3789v1
2013-06-08,Observation of a Berry phase anti-damping spin-orbit torque,"Recent observations of current-induced magnetization switching at
ferromagnet/normal-conductor interfaces have important consequences for future
magnetic memory technology. In one interpretation, the switching originates
from carriers with spin-dependent scattering giving rise to a relativistic
anti-damping spin-orbit torque (SOT) in structures with broken space-inversion
symmetry. The alternative interpretation combines the relativistic spin Hall
effect (SHE), making the normal-conductor an injector of a spin-current, with
the non-relativistic spin-transfer torque (STT) in the ferromagnet. Remarkably,
the SHE in these experiments originates from the Berry phase effect in the band
structure of a clean crystal and the anti-damping STT is also based on a
disorder-independent transfer of spin from carriers to magnetization. Here we
report the observation of an anti-damping SOT stemming from an analogous Berry
phase effect to the SHE. The SOT alone can therefore induce magnetization
dynamics based on a scattering-independent principle. The ferromagnetic
semiconductor (Ga,Mn)As we use has a broken space-inversion symmetry in the
crystal. This allows us to consider a bare ferromagnetic element which
eliminates by design any SHE related contribution to the spin torque. We
provide an intuitive picture of the Berry phase origin of the anti-damping SOT
and a microscopic modeling of measured data.",1306.1893v1
2013-07-23,Resistance asymmetry of a two-dimensional electron gas caused by an effective spin injection,"We have performed conductivity measurements on a Si-MOSFET sample with a slot
in the upper gate, allowing for different electron densities n_1 and n_2 across
the slot. Dynamic longitudinal resistance was measured by a standard lock-in
technique, while maintaining a large DC current through the source-drain
channel. We find that in a parallel magnetic field, the resistance of the
sample, R(I_DC), is asymmetric with respect to the direction of the DC current.
The asymmetry becomes stronger with an increase of either the magnetic field or
the difference between n_1 and n_2. These observations are interpreted in terms
of the effective spin injection: the degree of spin polarisation is different
in the two parts of the sample, implying different magnitudes of spin current
away from the slot. The carriers thus leave the excess spin (of the appropriate
sign) in the region around the slot, leading to spin accumulation (or
depletion) and to the spin drift-diffusion phenomena. Due to the positive
magnetoresistance of the two-dimensional electron gas, this change in a local
magnetisation affects the resistivity near the slot and the measured net
resistance, giving rise to an asymmetric contribution. We further observe that
the value of R(I_DC) saturates at large I_DC; we suggest that this is due to
electron tunnelling from the two-dimensional n-type layer into the p-type
silicon (or into another ""spin reservoir"") at the slot.",1307.6260v2
2013-10-29,"Spin-orbit coupling, quantum dots, and qubits in monolayer transition metal dichalcogenides","We derive an effective Hamiltonian which describes the dynamics of electrons
in the conduction band of transition metal dichalcogenides (TMDC) in the
presence of perpendicular electric and magnetic fields. We discuss in detail
both the intrinsic and the Bychkov-Rashba spin-orbit coupling (SOC) induced by
an external electric field.
  We point out interesting differences in the spin-split conduction band
between different TMDC compounds. An important consequence of the strong
intrinsic SOC is an effective out-of-plane $g$-factor for the electrons which
differs from the free-electron g-factor $g\simeq 2$. We identify a new term in
the Hamiltonian of the Bychkov-Rashba SOC which does not exist in III-V
semiconductors. Using first-principles calculations, we give estimates of the
various parameters appearing in the theory.
  Finally, we consider quantum dots (QDs) formed in TMDC materials and derive
an effective Hamiltonian which allows us to calculate the magnetic field
dependence of the bound states in the QDs. We find that all states are both
valley and spin split, which suggests that these QDs could be used as
valley-spin filters.
  We explore the possibility of using spin and valley states in TMDCs as
quantum bits, and conclude that, due to the relatively strong intrinsic
spin-orbit splitting in the conduction band, the most realistic option appears
to be a combined spin-valley (Kramers) qubit at low magnetic fields.",1310.7720v3
2013-10-29,Recent results of high-energy spin phenomena of gluons and sea-quarks in polarized proton-proton collisions at RHIC at BNL,"The STAR experiment at the Relativistic Heavy-Ion Collider at Brookhaven
National Laboratory is carrying out a spin physics program in high-energy
polarized proton collisions at $\sqrt{s}=200\,$GeV and $\sqrt{s}=500\,$GeV to
gain a deeper insight into the spin structure and dynamics of the proton.
  One of the main objectives of the spin physics program at RHIC is the precise
determination of the polarized gluon distribution function. The STAR detector
is well suited for the reconstruction of various final states involving jets,
$\pi^{0}$, $\pi^{\pm}$, e$^{\pm}$ and $\gamma$, which allows to measure several
different processes. Recent results suggest a gluon spin contribution to the
proton spin at the same level as the quark spin contribution itself.
  The production of $W$ bosons in polarized p+p collisions at
$\sqrt{s}=500\,$GeV opens a new era in the study of the spin-flavor structure
of the proton. $W^{-(+)}$ bosons are produced in $\bar{u}+d\;(\bar{d}+u)$
collisions and can be detected through their leptonic decays,
$e^{-}+\bar{\nu}_{e}\;(e^{+}+\nu_{e})$, where only the respective charged
lepton is measured. Results of $W^{-(+)}$ production suggest a large asymmetry
between the polarization of anti-$u$ and anti-$d$ quarks.",1310.7974v1
2013-11-06,Phase diagram and exotic spin-spin correlations of anisotropic Ising model on the Sierpiński gasket,"The anisotropic antiferromagnetic Ising model on the fractal Sierpi\'{n}ski
gasket is intensively studied, and a number of exotic properties are disclosed.
The ground state phase diagram in the plane of magnetic field-interaction of
the system is obtained. The thermodynamic properties of the three plateau
phases are probed by exploring the temperature-dependence of magnetization,
specific heat, susceptibility and spin-spin correlations. No phase transitions
are observed in this model. In the absence of a magnetic field, the unusual
temperature dependence of the spin correlation length is obtained with $0
\leq$J$_b/$J$_a<1$, and an interesting crossover behavior between different
phases at J$_b/$J$_a=1$ is unveiled, whose dynamics can be described by the
J$_b/$J$_a$-dependence of the specific heat, susceptibility and spin
correlation functions. The exotic spin-spin correlation patterns that share the
same special rotational symmetry as that of the Sierpi\'{n}ski gasket are
obtained in both the $1/3$ plateau disordered phase and the $5/9$ plateau
partially ordered ferrimagnetic phase. Moreover, a quantum scheme is formulated
to study the thermodynamics of the fractal Sierpi\'{n}ski gasket with
Heisenberg interactions. We find that the unusual temperature dependence of the
correlation length remains intact in a small quantum fluctuation.",1311.1502v2
2015-10-14,Angstrom-resolution magnetic resonance imaging of single molecules via wavefunction fingerprints of nuclear spins,"Single-molecule sensitivity of nuclear magnetic resonance (NMR) and angstrom
resolution of magnetic resonance imaging (MRI) are the highest challenges in
magnetic microscopy. Recent development in dynamical-decoupling- (DD) enhanced
diamond quantum sensing has enabled single-nucleus NMR and nanoscale NMR.
Similar to conventional NMR and MRI, current DD-based quantum sensing utilizes
the frequency fingerprints of target nuclear spins. The frequency fingerprints
by their nature cannot resolve different nuclear spins that have the same noise
frequency or differentiate different types of correlations in nuclear-spin
clusters, which limit the resolution of single-molecule MRI. Here we show that
this limitation can be overcome by using wave-function fingerprints of target
nuclear spins, which is much more sensitive than the frequency fingerprints to
the weak hyperfine interaction between the targets and a sensor under resonant
DD control. We demonstrate a scheme of angstrom-resolution MRI that is capable
of counting and individually localizing single nuclear spins of the same
frequency and characterizing the correlations in nuclear-spin clusters. A
nitrogen-vacancy-center spin sensor near a diamond surface, provided that the
coherence time is improved by surface engineering in the near future, may be
employed to determine with angstrom resolution the positions and conformation
of single molecules that are isotope labeled. The scheme in this work offers an
approach to breaking the resolution limit set by the frequency gradients in
conventional MRI and to reaching the angstrom-scale resolution.",1510.04081v3
2015-11-13,Experimental observation of magnetoelectricity in spin ice Dy$_2$Ti$_2$O$_7$,"The intrinsic noncollinear spin patterns in rare-earth pyrochlore are
physically interesting, hosting many emergent properties, e.g. spin ice and
monopole-type excitation. Recently, the magnetic monopole excitation of spin
ice systems was predicted to be magnetoelectric active, while rare experimental
works have directly confirmed this scenario. In this work, we performed
systematic experimental investigation on the magnetoelectricity of
Dy$_2$Ti$_2$O$_7$ by probing the ferroelectricity, spin dynamics, and
dielectric behaviors. Two ferroelectric transitions at $T_{c1}$=25 K and
$T_{c2}$=13 K have been observed. Remarkable magnetoelectric coupling is
identified below the lower transition temperature, with a significant
suppression of the electric polarization upon applied magnetic field. It is
surprised that the lower ferroelectric transition temperature just coincides
with the Ising-spin paramagnetic transition point, below which the
quasi-particle-like monopoles are populated, indicating implicit correlation
between electric dipoles and spin moments. The possible magnetoelectric
mechanisms have also been discussed although a decent theory remains
unavailable up to date. Our results will stimulate more investigations to
explore multiferroicity in these spin ice systems and other frustrated magnets.",1511.04138v1
2016-06-24,Low-energy physics of three-orbital impurity model with Kanamori interaction,"We discuss the low-energy physics of the three-orbital Anderson impurity
model with the Coulomb interaction term of the Kanamori form which has orbital
SO(3) and spin SU(2) symmetry and describes systems with partially occupied
$t_{2g}$ shells. We focus on the case with two electrons in the impurity that
is relevant to Hund's metals. Using the Schrieffer-Wolff transformation we
derive an effective Kondo model with couplings between the bulk and impurity
electrons expressed in terms of spin, orbital, and orbital quadrupole
operators. The bare spin-spin Kondo interaction is much smaller than the
orbit-orbit and spin-orbital couplings or is even ferromagnetic. Furthermore,
the perturbative scaling equations indicate faster renormalization of the
couplings related to orbital degrees of freedom compared to spin degrees of
freedom. Both mechanisms lead to a slow screening of the local spin moment. The
model thus behaves similarly to the related quantum impurity problem with a
larger SU(3) orbital symmetry (Dworin-Narath interaction) where this was first
observed. We find that the two problems actually describe the same low-energy
physics since the SU(3) symmetry is dynamically established through the
renormalization of the splittings of coupling constants to zero. The
perturbative renormalization group results are corroborated with the
numerical-renormalization group (NRG) calculations. The dependence of spin
Kondo temperatures and orbital Kondo temperatures as a function of interaction
parameters, the hybridization, and the impurity occupancy is calculated and
discussed.",1606.07654v1
2016-07-16,Spin- and orbital-Hall effect in cyclic group symmetric metasurface,"Light possesses both spin and orbital angular momentum (AM). While spin AM is
determined by helicity of circular-polarization, orbital AM is characterized by
topological charge of vortex beam. Interaction of AM with optical beam orbit
leads to optical spin Hall or orbital Hall effect, exhibited as spin-dependent
or topological charge-dependent transverse shift of optical beam. Conservation
of AM enables spin-to-orbital AM conversion, where circular-polarized Gaussian
beam is converted to opposite-helicity circular-polarized vortex beam with
topological charge $\pm 2$, an example of controlling spatial beam profiling by
spin flip. However, the resultant vortex beam has the beam center of gravity
unchanged, the same as that of incident Gaussian beam, meaning a null
transverse shift. Here we introduce a cyclic group symmetric metasurface to
demonstrate generation of vortex beam exhibiting spin-dependent transverse
shift, namely, spin- and orbital-Hall effect, attributed to an alteration of
dynamical phase of scattered beam according to the order $n$ of cyclic group
while keeping geometric phase constant. Capability of spin-controlled spatial
beam profiling with a transverse shift via spin- and orbital-Hall effect has
important implications for spatial demultiplexing in optical communication
utilizing orbital AM mode division multiplexing as well as for optical vortex
tweezer and signal processing involving vortex beams.",1607.04806v3
2016-09-20,Low-power Spin Valve Logic using Spin-transfer Torque with Automotion of Domain Walls,"A novel scheme for non-volatile digital computation is proposed using
spin-transfer torque (STT) and automotion of magnetic domain walls (DWs). The
basic computing element is composed of a lateral spin valve (SV) with two
ferromagnetic (FM) wires served as interconnects, where DW automotion is used
to propagate the information from one device to another. The non-reciprocity of
both device and interconnect is realized by sizing different contact areas at
the input and the output as well as enhancing the local damping mechanism. The
proposed logic is suitable for scaling due to a high energy barrier provided by
a long FM wire. Compared to the scheme based on non-local spin valves (NLSVs)
in the previous proposal, the devices can be operated at lower current density
due to utilizing all injected spins for local magnetization reversals, and thus
improve both energy efficiency and resistance to electromigration. This device
concept is justified by simulating a buffer, an inverter, and a 3-input
majority gate with comprehensive numerical simulations, including spin
transport through the FM/non-magnetic (NM) interfaces as well as the NM channel
and stochastic magnetization dynamics inside FM wires. In addition to digital
computing, the proposed framework can also be used as a transducer between DWs
and spin currents for higher wiring flexibility in the interconnect network.",1609.06281v1
2019-05-06,A 10-qubit solid-state spin register with quantum memory up to one minute,"Spins associated to single defects in solids provide promising qubits for
quantum information processing and quantum networks. Recent experiments have
demonstrated long coherence times, high-fidelity operations and long-range
entanglement. However, control has so far been limited to a few qubits, with
entangled states of three spins demonstrated. Realizing larger multi-qubit
registers is challenging due to the need for quantum gates that avoid crosstalk
and protect the coherence of the complete register. In this paper, we present
novel decoherence-protected gates that combine dynamical decoupling of an
electron spin with selective phase-controlled driving of nuclear spins. We use
these gates to realize a 10-qubit quantum register consisting of the electron
spin of a nitrogen-vacancy center and 9 nuclear spins in diamond. We show that
the register is fully connected by generating entanglement between all 45
possible qubit pairs, and realize genuine multipartite entangled states with up
to 7 qubits. Finally, we investigate the register as a multi-qubit memory. We
show coherence times up to 63(2) seconds - the longest reported for a single
solid-state qubit - and demonstrate that two-qubit entangled states can be
stored for over 10 seconds. Our results enable the control of large quantum
registers with long coherence times and therefore open the door to advanced
quantum algorithms and quantum networks with solid-state spin qubits.",1905.02094v2
2020-07-16,Direct measurement of electron intervalley relaxation in a Si/SiGe quantum dot,"The presence of non-degenerate valley states in silicon can drastically
affect electron dynamics in silicon-based heterostructures, leading to electron
spin relaxation and spin-valley coupling. In the context of solid-state spin
qubits, it is important to understand the interplay between spin and valley
degrees of freedom to avoid or alleviate these decoherence mechanisms. Here we
report the observation of relaxation from the excited valley state to the
ground state in a Si/SiGe quantum dot, at zero magnetic field. Valley state
read-out is aided by a valley-dependent tunneling effect, which we attribute to
valley-orbit coupling. We find a long intervalley relaxation time of 12.0 $\pm$
0.3 ms, a value that is unmodified when a magnetic field is applied.
Furthermore, we compare our findings with the spin relaxation time and find
that the spin-valley ""hot spot"" relaxation is roughly four times slower than
intervalley relaxation, consistent with established theoretical predictions.
The precision of this technique, adapted from electron spin read-out via
energy-dependent tunneling, is an improvement over indirect valley relaxation
measurements and could be a useful probe of valley physics in spin and valley
qubit implementations.",2007.08680v1
2016-11-22,Spin and recombination dynamics of excitons and free electrons in p-type GaAs : effect of carrier density,"Carrier and spin recombination are investigated in p-type GaAs of acceptor
concentration NA = 1.5 x 10^(17) cm^(-3) using time-resolved photoluminescence
spectroscopy at 15 K. At low pho- tocarrier concentration, acceptors are mostly
neutral and photoelectrons can either recombine with holes bound to acceptors
(e-A0 line) or form excitons which are mostly trapped on neutral acceptors
forming the (A0X) complex. It is found that the spin lifetime is shorter for
electrons that recombine through the e-A0 transition due to spin relaxation
generated by the exchange scattering of free electrons with either trapped or
free holes, whereas spin flip processes are less likely to occur once the
electron forms with a free hole an exciton bound to a neutral acceptor. An
increase of exci- tation power induces a cross-over to a regime where the
bimolecular band-to-band (b-b) emission becomes more favorable due to screening
of the electron-hole Coulomb interaction and ionization of excitonic complexes
and free excitons. Then, the formation of excitons is no longer possible, the
carrier recombination lifetime increases and the spin lifetime is found to
decrease dramatically with concentration due to fast spin relaxation with free
photoholes. In this high density regime, both the electrons that recombine
through the e-A0 transition and through the b-b transition have the same spin
relaxation time.",1611.07406v1
2017-01-09,Spin-Wave versus Joule Heating in Spin-Hall-Effect/Spin-Transfer-Torque Driven Cr/Heusler/Pt Waveguides,"We present a time-resolved study of the DC-current driven magnetization
dynamics in a microstructured Cr/Heusler/Pt waveguide by means of Brillouin
light scattering. A reduction of the effective spin-wave damping via the
spin-transfer-torque effect leads to a strong increase in the magnon density.
This is accompanied by a decrease of the spin-wave frequencies. By evaluating
the time scales of these effects, the origin of this frequency shift can be
identified. However, recently, we found that the experimental setup partially
influences the decay of the spin-wave intensity after the current pulse is
switched off. Thus, further investigations on the presented effect are needed
to allow for a more detailed analysis. For this reason, we need to withdraw the
manuscript at this point and might publish an updated version later.",1701.02094v2
2018-05-22,FMR-related phenomena in spintronic devices,"Spintronic devices, such as non-volatile magnetic random access memories and
logic devices, have attracted considerable attention as potential candidates
for future high efficient data storage and computing technology. In a heavy
metal or other emerging material with strong spin-orbit coupling (SOC), the
charge currents induce spin currents or spin accumulations via SOC. The
generated spin currents can exert spin-orbit torques (SOTs) on an adjacent
ferromagnet, which opens up a new way to realize magnetization dynamics and
switching of the ferromagnetic layer for spintronic devices. In the SOT scheme,
the charge-to-spin interconversion efficiency (SOT efficiency) is an important
figure of merit for applications. For the effective characterization of this
efficiency, the ferromagnetic resonance (FMR) based methods, such as the spin
transfer torque ferromagnetic resonance (ST-FMR) and the spin pumping, are
common utilized in addition to low frequency harmonic or dc measurements. In
this review, we focus on the ST-FMR measurements for the evaluation of the SOT
efficiency. We provide a brief summary of the different ST-FMR setups and data
analysis methods. We then discuss ST-FMR and SOT studies in various materials,
including heavy metals and alloys, topological insulators, two dimensional (2D)
materials, interfaces with strong Rashba effect, antiferromagnetic materials,
two dimensional electron gas (2DEG) in oxide materials and oxidized nonmagnetic
materials.",1805.08496v1
2011-11-10,Chiral symmetry breaking and the spin content of hadrons,"From the parton distributions in the infinite momentum frame one finds that
only about 30% of the nucleon spin is carried by spins of the valence quarks,
which gave rise to the term ""spin crisis"". Similar results hold for the lowest
mesons, as it follows from the lattice simulations. We define the spin content
of a meson in the rest frame and use a complete and orthogonal $\bar q q$
chiral basis and a unitary transformation from the chiral basis to the (2S+1)LJ
basis. Then, given a mixture of different allowed chiral representations in the
meson wave function at a given resolution scale, one can obtain its spin
content at this scale. To obtain the mixture of the chiral representations in
the meson we measure in dynamical lattice simulations a ratio of couplings of
interpolarors with different chiral structure. For the rho meson we obtain
practically the 3S1 state with no trace of the spin crisis. Then a natural
question arises: which definition does reflect the spin content of a hadron?",1111.2562v1
2012-04-23,Spin decoherence in graphene quantum dots due to hyperfine interaction,"Carbon based systems are prominent candidates for a solid-state spin-qubit
due to weak spin-orbit and hyperfine interactions in combination with a low
natural abundance of spin carrying isotopes. We consider the effect of the
hyperfine interaction on the coherence of an electron-spin localized in a
graphene quantum dot. It is known, that the hyperfine interaction in these
systems is anisotropic promising interesting physics. We calculate the dynamics
of an electron spin surrounded by a bath of nuclear spins in a non-Markovian
approach using a generalized master equation. Considering a general form of the
hyperfine interaction, we are able to extend the range of validity of our
results to other systems beyond graphene. For large external magnetic fields,
we find within Born approximation that the electron spin state is conserved up
to small corrections, which oscillate with a frequency determined by the
hyperfine interaction. The amplitude of these oscillations decays with a power
law, where its initial value depends on the specific form of the anisotropy.
Analyzing this in more detail, we identify two distinct classes of anisotropy,
which can be both found in graphene depending on the orientation of the
external magnetic field with respect to the carbon layer.",1204.5112v2
2014-05-19,Approaching the Ground State of Frustrated A-site Spinels: A Combined Magnetization and Polarized Neutron Scattering Study,"We re-investigate the magnetically frustrated, {\it
diamond-lattice-antiferromagnet} spinels FeAl$_2$O$_4$ and MnAl$_2$O$_4$ using
magnetization measurements and diffuse scattering of polarized neutrons. In
FeAl$_2$O$_4$, macroscopic measurements evidence a ""cusp"" in zero field-cooled
susceptibility around 13~K. Dynamic magnetic susceptibility and {\it memory
effect} experiments provide results that do not conform with a canonical
spin-glass scenario in this material. Through polarized neutron scattering
studies, absence of long-range magnetic order down to 4~K is confirmed in
FeAl$_2$O$_4$. By modeling the powder averaged differential magnetic neutron
scattering cross-section, we estimate that the spin-spin correlations in this
compound extend up to the third nearest-neighbour shell. The estimated value of
the Land\'{e} $g$ factor points towards orbital contributions from Fe$^{2+}$.
This is also supported by a Curie-Weiss analysis of the magnetic
susceptibility. MnAl$_2$O$_4$, on the contrary, undergoes a magnetic phase
transition into a long-range ordered state below $\approx$ 40~K, which is
confirmed by macroscopic measurements and polarized neutron diffraction.
However, the polarized neutron studies reveal the existence of prominent
spin-fluctuations co-existing with long-range antiferromagnetic order. The
magnetic diffuse intensity suggests a similar short range order as in
FeAl$_2$O$_4$. Results of the present work supports the importance of spin-spin
correlations in understanding magnetic response of frustrated magnets like
$A$-site spinels which have predominant short-range spin correlations
reminiscent of the ""spin liquid"" state.",1405.4694v1
2014-06-02,Knight shift and nuclear spin relaxation in Fe/n-GaAs heterostructures,"We investigate the dynamically polarized nuclear-spin system in
Fe/\emph{n}-GaAs heterostructures using the response of the electron-spin
system to nuclear magnetic resonance (NMR) in lateral spin-valve devices. The
hyperfine interaction is known to act more strongly on donor-bound electron
states than on those in the conduction band. We provide a quantitative model of
the temperature dependence of the occupation of donor sites. With this model we
calculate the ratios of the hyperfine and quadrupolar nuclear relaxation rates
of each isotope. For all temperatures measured, quadrupolar relaxation limits
the spatial extent of nuclear spin-polarization to within a Bohr radius of the
donor sites and is directly responsible for the isotope dependence of the
measured NMR signal amplitude. The hyperfine interaction is also responsible
for the $2\text{ kHz}$ Knight shift of the nuclear resonance frequency that is
measured as a function of the electron spin accumulation. The Knight shift is
shown to provide a measurement of the electron spin-polarization that agrees
qualitatively with standard spin transport measurements.",1406.0436v2
2016-08-01,Spin-orbit coupled two-electron Fermi gases of ytterbium atoms,"We demonstrate all-optical implementation of spin-orbit coupling (SOC) in a
two-electron Fermi gas of $^{173}$Yb atoms by coupling two hyperfine ground
states with a narrow optical transition. Due to the SU($N$) symmetry of the
$^1$S$_0$ ground-state manifold which is insensitive to external magnetic
fields, an optical AC Stark effect is applied to split the ground spin states,
which exhibits a high stability compared with experiments on alkali and
lanthanide atoms, and separate out an effective spin-1/2 subspace from other
hyperfine levels for the realization of SOC. The dephasing spin dynamics when a
momentum-dependent spin-orbit gap being suddenly opened and the asymmetric
momentum distribution of the spin-orbit coupled Fermi gas are observed as a
hallmark of SOC. The realization of all-optical SOC for ytterbium fermions
should offer a new route to a long-lived spin-orbit coupled Fermi gas and
greatly expand our capability in studying novel spin-orbit physics with
alkaline-earth-like atoms.",1608.00478v3
2016-08-18,Phase diagram and spin correlations of the Kitaev-Heisenberg model: Importance of quantum effects,"We explore the phase diagram of the Kitaev-Heisenberg model with nearest
neighbor interactions on the honeycomb lattice using the exact diagonalization
of finite systems combined with the cluster mean field approximation, and
supplemented by the insights from the linear spin-wave and second--order
perturbation theories. This study confirms that by varying the balance between
the Heisenberg and Kitaev term, frustrated exchange interactions stabilize in
this model four phases with magnetic long range order: N\'eel phase,
ferromagnetic phase, and two other phases with coexisting antiferromagnetic and
ferromagnetic bonds, zigzag and stripy phases. They are separated by two
disordered quantum spin-liquid phases, and the one with ferromagnetic Kitaev
interactions has a substantially broader range of stability as the neighboring
competing ordered phases, ferromagnetic and stripy, have very weak quantum
fluctuations. Focusing on the quantum spin-liquid phases, we study spatial spin
correlations and dynamic spin structure factor of the model by the exact
diagonalization technique, and discuss the evolution of gapped low-energy spin
response across the quantum phase transitions between the disordered spin
liquid and magnetic phases with long range order.",1608.05333v1
2018-01-13,Robustness of spin coherence of the exciton bound to neutral donor states in multilayer system,"We address the temperature influence on the precessional motion of electron
spins under transverse magnetic field, studied in a GaAs/AlGaAs triple quantum
wells, using pump-probe Kerr rotation. In the presence of an applied in-plane
magnetic field the TRKR measurements show the robustness of carrier's spin
polarization against temperature which can be easily traced in an extended
range up to 250 K. By tuning the pump-probe wavelength to the exciton bound to
a neutral donor transition, we observed a remarkably long-lasting spin
coherence (with dephasing time T2* > 14 ns) limited by the spin hopping process
and exchange interaction between the donor sites as well as the ensemble spread
of g-factor. The temperature dependent spin dephasing time revealed a double
linear dependence due to the different relaxation mechanisms active at
respective temperature ranges. We observed that the increase of sample
temperature from 5 K to 250 K, leads to a strong T2* reduction by almost
98%/97% for the excitation wavelengths of 823/821 nm. Furthermore, we noticed
that the temperature increase not only causes the reduction of spin lifetime
but can also lead to the variation of electron g-factor. Additionally, the spin
dynamics was studied through the dependencies on the applied magnetic field and
optical pump power.",1801.04415v2
2018-01-24,Polarisation in Spin-Echo Experiments: Multi-point and Lock-in Measurements,"Spin-echo instruments are typically used to measure diffusive processes and
the dynamics and motion in samples on ps and ns timescales. A key aspect of the
spin-echo technique is to determine the polarisation of a particle beam. We
present two methods for measuring the spin polarisation in spin-echo
experiments. The current method in use is based on taking a number of discrete
readings. The implementation of a new method involves continuously rotating the
spin and measuring its polarisation after being scattered from the sample. A
control system running on a microcontroller is used to perform the spin
rotation and to calculate the polarisation of the scattered beam based on a
lock-in amplifier. First experimental tests of the method on a helium spin-echo
spectrometer, show that it is clearly working and that it has advantages over
the discrete approach i.e. it can track changes of the beam properties
throughout the experiment. Moreover, we show that real-time numerical
simulations can perfectly describe a complex experiment and can be easily used
to develop improved experimental methods prior to a first hardware
implementation.",1801.08168v1
2018-10-01,A New SU(2) Anomaly,"A familiar anomaly affects SU(2) gauge theory in four dimensions: a theory
with an odd number of fermion multiplets in the spin 1/2 representation of the
gauge group, and more generally in representations of spin 2r+1/2, is
inconsistent. We describe here a more subtle anomaly that can affect SU(2)
gauge theory in four dimensions under the condition that fermions transform
with half-integer spin under SU(2) and bosons with integer spin. Such a theory,
formulated in a way that requires no choice of spin structure, and with an odd
number of fermion multiplets in representations of spin 4r+3/2, is
inconsistent. The theory is consistent if one picks a spin or spin_c structure.
Under Higgsing to U(1), the new SU(2) anomaly reduces to a known anomaly of
""all-fermion electrodynamics."" Like that theory, an SU(2) theory with an odd
number of fermion multiplets in representations of spin 4r+3/2 can provide a
boundary state for a five-dimensional gapped theory whose partition function on
a closed five-manifold Y is $(-1)^{\int_Y w_2w_3}$. All statements have analogs
with SU(2) replaced by Sp(2N). There is also an analog in five dimensions.",1810.00844v4
2019-09-19,Coherent control and high-fidelity readout of chromium ions in commercial silicon carbide,"Transition metal ions provide a rich set of optically active defect spins in
wide bandgap semiconductors. Chromium (Cr4+) in silicon-carbide (SiC) produces
a spin-1 ground state with a narrow, spectrally isolated, spin-selective,
near-telecom optical interface. However, previous studies were hindered by
material quality resulting in limited coherent control. In this work, we
implant Cr into commercial 4H-SiC and show optimal defect activation after
annealing above 1600 C. We measure an ensemble optical hole linewidth of 31
MHz, an order of magnitude improvement compared to as-grown samples. An
in-depth exploration of optical and spin dynamics reveals efficient spin
polarization, coherent control, and readout with high fidelity (79%). We report
T1 times greater than 1 second at cryogenic temperatures (15 K) with a T2* =
317 nanoseconds and a T2 = 81 microseconds, where spin dephasing times are
currently limited by spin-spin interactions within the defect ensemble. Our
results demonstrate the potential of Cr4+ in SiC as an extrinsic, optically
active spin qubit.",1909.08778v1
2019-10-23,Distinguishing antiferromagnetic spin sublattices via the spin Seebeck effect,"Antiferromagnets are beneficial for future spintronic applications due to
their zero magnetic moment and ultrafast dynamics. But gaining direct access to
their antiferromagnetic order and identifying the properties of individual
magnetic sublattices, especially in thin films and small-scale devices, remains
a formidable challenge. So far, the existing read-out techniques such as
anisotropic magnetoresistance, tunneling anisotropic magnetoresistance, and
spin-Hall magnetoresistance, are even functions of sublattice magnetization and
thus allow us to detect different orientations of the N\'eel order for
antiferromagnets with multiple easy axes. In contrast direct electrical
detection of oppositely oriented spin states along the same easy axes (e.g., in
uniaxial antiferromagnets) requires sensitivity to the direction of individual
sublattices and thus is more difficult. In this study, using spin Seebeck
effect, we report the electrical detection of the two sublattices in a uniaxial
antiferromagnet Cr2O3. We find the rotational symmetry and hysteresis behavior
of the spin Seebeck signals measured at the top and bottom surface reflect the
dierction of the surface sublattice moments, but not the N\'eel order or the
net moment in the bulk. Our results demonstrate the important role of interface
spin sublattices in generating the spin Seebeck voltages, which provide a way
to access each sublattice independently, enables us to track the full rotation
of the magnetic sublattice, and distinguish different and antiparallel
antiferromagnetic states in uniaxial antiferromagnets.",1910.10340v1
2020-02-07,"Engineering Co$_2$MnAl$_x$Si$_{1-x}$ Heusler compounds as a model system to correlate spin polarization, intrinsic Gilbert damping and ultrafast demagnetization","Engineering of magnetic materials for developing better spintronic
applications relies on the control of two key parameters: the spin polarization
and the Gilbert damping responsible for the spin angular momentum dissipation.
Both of them are expected to affect the ultrafast magnetization dynamics
occurring on the femtosecond time scale. Here, we use engineered Co2MnAlxSi1-x
Heusler compounds to adjust the degree of spin polarization P from 60 to 100%
and investigate how it correlates with the damping. We demonstrate
experimentally that the damping decreases when increasing the spin polarization
from 1.1 10-3 for Co2MnAl with 63% spin polarization to an ultra-low value of
4.10-4 for the half-metal magnet Co2MnSi. This allows us investigating the
relation between these two parameters and the ultrafast demagnetization time
characterizing the loss of magnetization occurring after femtosecond laser
pulse excitation. The demagnetization time is observed to be inversely
proportional to 1-P and as a consequence to the magnetic damping, which can be
attributed to the similarity of the spin angular momentum dissipation processes
responsible for these two effects. Altogether, our high quality Heusler
compounds allow controlling the band structure and therefore the channel for
spin angular momentum dissipation.",2002.02686v1
2020-12-21,Electric fields and substrates dramatically accelerate spin relaxation in graphene,"Electrons in graphene are theoretically expected to retain spin states much
longer than most materials, making graphene a promising platform for
spintronics and quantum information technologies. Here, we use first-principles
density-matrix (FPDM) dynamics simulations to show that interaction with
electric fields and substrates strongly enhance spin relaxation through
scattering with phonons. Consequently, the relaxation time at room temperature
reduces from microseconds in free-standing graphene to nanoseconds in graphene
on hexagonal boron nitride (hBN) substrate, the order of magnitude typically
measured in experiments. Further, inversion symmetry breaking by hBN introduces
a stronger asymmetry in electron and hole spin lifetimes, than predicted by the
conventional D'yakonov-Perel' (DP) model for spin relaxation. Deviations from
the conventional DP model are stronger for in-plane spin relaxation, resulting
in out-of-plane to in-plane lifetime ratios much greater than 1/2 with a
maximum close to the Dirac point. These FPDM results, independent of
symmetry-specific assumptions or material-dependent parameters, also validate
recent modifications of the DP model to explain such deviations. Overall, our
results indicate that spin-phonon relaxation in the presence of substrates may
be more important in graphene than typically assumed, requiring consideration
for graphene-based spin technologies at room temperature.",2012.11550v3
2020-12-30,"Main Belt Asteroid Histories: Simulations of erosion, cratering, catastrophic dispersions, spins, binaries and tumblers","This is a study of the history of the asteroids in the main asteroid belt.
Collisions have been the dominant process. Every asteroid has been impacted by
others a multitude of times, with consequences of cratering, erosion, spin
increments, fragmentation, and occasional catastrophic disruption and
dispersion. Extensive information for asteroid orbits, sizes, shapes,
composition, and rotation rates of those asteroids is now available. Those are
a result of their history, but to interpret them requires understanding the
processes. That understanding can be improved by simulations of the history. A
simulation needs robust models of the dynamical and collisional events. Such
models have evolved substantially in the last few decades. Here I present
current models, a method, and a code ""SSAH"" for stochastic simulations of the
history of the main belt. That code gives a framework upon which existing and
future models can be based. The results lead to new paradigms for asteroid
histories including the distribution of spins; the irrelevance of strength spin
limits; the ""unusual"" spins of 2001 OE84; and of large slow-spinning tumbling
objects (Mathilde); the ""V-shape"" in the spin versus diameter plot; the
non-Maxwellian distribution of spins of a given diameter range; the numbers of
expected tumblers, and more. At the same time, the simulations expose gaps in
our knowledge that require further research. The SSAH code is freely available
for the use of others.",2012.15300v4
2018-03-12,Electrical initialization of electron and nuclear spins in a single quantum dot at zero magnetic field,"The emission of circularly polarized light from a single quantum dot relies
on the injection of carriers with well-defined spin polarization. Here we
demonstrate single dot electroluminescence (EL) with a circular polarization
degree up to 35% at zero applied magnetic field. The injection of spin
polarized electrons is achieved by combining ultrathin CoFeB electrodes on top
of a spin-LED device with p-type InGaAs quantum dots in the active region. We
measure an Overhauser shift of several $\mu$eV at zero magnetic field for the
positively charged exciton (trion X$^+$) EL emission, which changes sign as we
reverse the injected electron spin orientation. This is a signature of dynamic
polarization of the nuclear spins in the quantum dot induced by the hyperfine
interaction with the electrically injected electron spin. This study paves the
way for electrical control of nuclear spin polarization in a single quantum dot
without any external magnetic field.",1803.04309v1
2018-06-06,High-resolution spectroscopy of single nuclear spins via sequential weak measurements,"Quantum sensors have recently achieved to detect the magnetic moment of few
or single nuclear spins and measure their magnetic resonance (NMR) signal.
However, the spectral resolution, a key feature of NMR, has been limited by
relaxation of the sensor to a few kHz at room temperature. The spectral
resolution of NMR signals from single nuclear spins can be improved by, e.g.,
using quantum memories, however at the expense of sensitivity. Classical
signals on the other hand can be measured with exceptional spectral resolution
by using continuous measurement techniques, without compromising sensitivity.
To apply these techniques to single-spin NMR, it is critical to overcome the
impact of back action inherent of quantum measurements. Here we report
sequential weak measurements on a single $^{13}$C nuclear spin. The back-action
of repetitive weak measurements causes the spin to undergo a quantum dynamics
phase transition from coherent trapping to coherent oscillation. Single-spin
NMR at room-temperature with a spectral resolution of 3.8 Hz is achieved. These
results enable the use of measurement-correlation schemes for the detection of
very weakly coupled single spins.",1806.02181v2
2018-06-20,Teetering Stars: Resonant Excitation of Stellar Obliquities by Hot and Warm Jupiters with External Companions,"Stellar spin-orbit misalignments (obliquities) in hot Jupiter systems have
been extensively probed. Such obliquities may reveal clues about hot Jupiter
dynamical histories. Common explanations for generating obliquities include
high-eccentricity migration and primordial disk misalignment. This paper
investigates another mechanism for producing stellar spin-orbit misalignments
in systems hosting a close-in planet with an external, modestly inclined
companion. Spin-orbit misalignment may be excited due to a secular resonance,
occurring when the precession rate of the stellar spin axis (driven by the
inner planet) becomes comparable to the nodal precession rate of the inner
planet (driven by the companion). Due to the spin-down of the host star via
magnetic braking, this resonance may be achieved during the star's
main-sequence lifetime for a wide range of planet masses and orbital
architectures. Obliquity excitation is accompanied by a decrease in mutual
inclination between the inner planet and perturber, and can thus erase high
inclinations. For hot Jupiters, the stellar spin axis is strongly coupled to
the orbital axis, and obliquity excitation by a giant planet companion requires
a strong perturber, usually located within 1-2 AU. For warm Jupiters, the spin
and orbital axes are more weakly coupled, and the resonance may be achieved for
distant giant planet perturbers (at several to tens of AU). Since warm Jupiters
have a high occurrence rate of distant planetary companions with appropriate
properties for resonant obliquity excitation, stellar obliquities in warm
Jupiter systems may be common, particularly for warm Jupiters orbiting cool
stars that have undergone significant spin-down.",1806.07892v2
2018-12-21,Active Control of Mode Crossover and Mode Hopping of Spin Waves in a Ferromagnetic Antidot Lattice,"Active control of spin-wave dynamics is demonstrated using broadband
ferromagnetic resonance in two-dimensional Ni80Fe20 antidot lattices arranged
in hexagonal lattice with fixed lattice constant but varying antidot diameter.
A strong modification in the spin-wave spectra is obtained with the variation
in the antidot diameter as well as with the strength and orientation of the
bias magnetic field. A broad band of modes is observed for the lattice with
higher antidot diameter which decreases systematically as the antidot diameter
is reduced. A crossover between the higher frequency branches is achieved in
lattices with higher antidot diameter. In addition, the spin-wave modes in all
lattices show a strong six-fold anisotropic behaviour due to the variation of
internal field distribution as a function of the bias-field orientation. A mode
hopping-like behavior is observed in the angular dispersions of spin-wave
spectra for samples having intermediate hole diameters. Micromagnetic
simulations qualitatively reproduce the experimentally observed spin-wave modes
and the simulated mode profiles reveal the presence of extended and quantized
standing spin-wave modes in these lattices. These observations are significant
for large tunability and anisotropic propagation of spin waves in GHz frequency
magnetic devices.",1812.08929v1
2019-01-22,High-harmonic generation in quantum spin systems,"We theoretically study the high-harmonic generation (HHG) in one-dimensional
spin systems. While in electronic systems the driving by AC electric fields
produces radiation from the dynamics of excited charges, we consider here the
situation where spin systems excited by a magnetic field pulse generate
radiation via a time-dependent magnetization. Specifically, we study the
magnetic dipole radiation in two types of ferromagnetic spin chain models, the
Ising model with static longitudinal field and the XXZ model, and reveal the
structure of the spin HHG and its relation to spin excitations. For weak laser
amplitude, a peak structure appears which can be explained by time-dependent
perturbation theory. With increasing amplitude, plateaus with well-defined
cutoff energies emerge. In the Ising model with longitudinal field, the
thresholds of the multiple plateaus in the radiation spectra can be explained
by the annihilation of multiple magnons. In the XXZ model, which retains the
$\mathbf{Z}_{2}$ symmetry, the laser magnetic field can induce a phase
transition of the ground state when it exceeds a critical value, which results
in a drastic change of the spin excitation character. As a consequence, the
first cutoff energy in the HHG spectrum changes from a single-magnon to a
two-magnon energy at this transition. Our results demonstrate the possibility
of generating high-harmonic radiation from magnetically ordered materials and
the usefulness of high-harmonic signals for extracting information on the spin
excitation spectrum.",1901.07588v2
2019-01-27,Observation of band narrowing and mode conversion in two-dimensional binary magnonic crystal,"We introduce a new type of binary magnonic crystal, where Ni$_{80}$Fe$_{20}$
nanodots of two different sizes are diagonally connected forming a unit and
those units are arranged in a square lattice. The magnetization dynamics of the
sample is measured by using time-resolved magneto-optical Kerr effect
microscope with varying magnitude and in-plane orientation ($\phi$) of the bias
magnetic field. Interestingly, at $\phi=0^{\circ}$, the spin-wave mode profiles
show frequency selective spatial localization of spin-wave power within the
array. With the variation of $\phi$ in the range $0^{\circ}<\phi\leq
45^{\circ}$, we observe band narrowing due to localized to extended spin-wave
mode conversion. Upon further increase of $\phi$, the spin-wave modes slowly
lose the extended nature and become fully localized again at 90$^{\circ}$. We
have extensively demonstrated the role of magnetostatic stray field
distribution on the rotational symmetries obtained for the spin-wave modes.
From micromagnetic simulations, we find that the dipole-exchange coupling
between the nano-dots leads to remarkable modifications of the spin-wave mode
profiles when compared with arrays of individual small and large dots.
Numerically, we also show that the physical connection between the nano-dots
provides more control points over the spin-wave propagation in the lattice at
different orientations of bias magnetic field. This new type of binary magnonic
crystal may find potential applications in magnonic devices such as spin-wave
waveguide, filter, coupler, and other on-chip microwave communication devices.",1901.09325v1
2019-12-17,Programmable Quantum Simulations of Spin Systems with Trapped Ions,"Laser-cooled and trapped atomic ions form an ideal standard for the
simulation of interacting quantum spin models. Effective spins are represented
by appropriate internal energy levels within each ion, and the spins can be
measured with near-perfect efficiency using state-dependent fluorescence
techniques. By applying optical fields that exert optical dipole forces on the
ions, their Coulomb interaction can be modulated to produce long-range and
tunable spin-spin interactions that can be reconfigured by shaping the spectrum
and pattern of the laser fields, in a prototypical example of a quantum
simulator. Here we review the theoretical mapping of atomic ions to interacting
spin systems, the preparation of complex equilibrium states, the study of
dynamical processes in these many-body interacting quantum systems, and the use
of this platform for optimization and other tasks. The use of such quantum
simulators for studying spin models may inform our understanding of exotic
quantum materials and shed light on the behavior of interacting quantum systems
that cannot be modeled with conventional computers.",1912.07845v2
2020-03-10,Fourth post-Newtonian effective-one-body Hamiltonians with generic spins,"In a compact binary coalescence, the spins of the compact objects can have a
significant effect on the orbital motion and gravitational-wave (GW) emission.
For generic spin orientations, the orbital plane precesses, leading to
characteristic modulations of the GW signal. The observation of precession
effects is crucial to discriminate among different binary formation scenarios,
and to carry out precise tests of General Relativity. Here, we work toward an
improved description of spin effects in binary inspirals, within the
effective-one-body (EOB) formalism, which is commonly used to build waveform
models for LIGO and Virgo data analysis. We derive EOB Hamiltonians including
the complete fourth post-Newtonian (4PN) conservative dynamics, which is the
current state of the art. We place no restrictions on the spin orientations or
magnitudes, or on the type of compact object (e.g., black hole or neutron
star), and we produce the first generic-spin EOB Hamiltonians complete at 4PN
order. We consider multiple spinning EOB Hamiltonians, which are more or less
direct extensions of the varieties found in previous literature, and we suggest
another simplified variant. Finally, we compare the circular-orbit,
aligned-spin binding-energy functions derived from the EOB Hamiltonians to
numerical-relativity simulations of the late inspiral. While finding that all
proposed Hamiltonians perform reasonably well, we point out some interesting
differences, which could guide the selection of a simpler, and thus
faster-to-evolve EOB Hamiltonian to be used in future LIGO and Virgo inference
studies.",2003.04469v2
2020-06-30,Spin-orbit coupling suppression and singlet-state blocking of spin-triplet Cooper pairs,"An inhomogeneous magnetic exchange field at a superconductor/ferromagnet
interface converts spin-singlet Cooper pairs to a spin-aligned (i.e.
spin-polarized) triplet state. Although the decay envelope of such triplet
pairs within ferromagnetic materials is well studied, little is known about
their decay in non-magnetic metals and superconductors, and in particular in
the presence of spin-orbit coupling (SOC). Here we investigate devices in which
triplet supercurrents are injected into the s-wave superconductor Nb. In the
normal state of Nb, triplet supercurrents decay over a distance of 5 nm, which
is an order of magnitude smaller than the decay of spin singlet pairs due to
the SOC interacting with the spin associated with triplet pairs. In the
superconducting state of Nb, triplet supercurrents are not able to couple with
the singlet wavefunction and thus blocked by the absence of available
equilibrium states in the singlet gap. The results offer new insight into the
dynamics between s-wave singlet and s-wave triplet states.",2006.16654v3
2020-08-21,Evolution of spin excitations from bulk to monolayer FeSe,"The discovery of enhanced superconductivity (SC) in FeSe films grown on
SrTiO3 (FeSe/STO) has revitalized the field of Fe-based superconductors. In the
ultrathin limit, the superconducting transition temperature Tc is increased by
almost an order of magnitude, raising new questions on the pairing mechanism.
As in other unconventional superconductors, antiferromagnetic spin fluctuations
have been proposed as a candidate to mediate SC in this system. Thus, it is
essential to study the evolution of the spin dynamics of FeSe in the ultrathin
limit to elucidate their relationship with superconductivity. Here, we
investigate and compare the spin excitations in bulk and monolayer FeSe grown
on STO using high-resolution resonant inelastic x-ray scattering (RIXS) and
quantum Monte Carlo (QMC) calculations. Despite the absence of long-range
magnetic order, bulk FeSe displays dispersive magnetic excitations reminiscent
of other Fe-pnictides. Conversely, the spin excitations in FeSe/STO are gapped,
dispersionless, and significantly hardened relative to the bulk counterpart. By
comparing our RIXS results with simulations of a bilayer Hubbard model, we
connect the evolution of the spin excitations to the Fermiology of the two
systems. The present study reveals a remarkable reconfiguration of spin
excitations in FeSe/STO, which is essential to understand the role of spin
fluctuations in the pairing mechanism.",2008.09618v2
2020-09-22,Magnon-mediated spin currents in Tm3Fe5O12/Pt with perpendicular magnetic anisotropy,"The control of pure spin currents carried by magnons in magnetic insulator
(MI) garnet films with a robust perpendicular magnetic anisotropy (PMA) is of
great interest to spintronic technology as they can be used to carry, transport
and process information. Garnet films with PMA present labyrinth domain
magnetic structures that enrich the magnetization dynamics, and could be
employed in more efficient wave-based logic and memory computing devices. In
MI/NM bilayers, where NM being a normal metal providing a strong spin-orbit
coupling, the PMA benefits the spin-orbit torque (SOT) driven magnetization's
switching by lowering the needed current and rendering the process faster,
crucial for developing magnetic random-access memories (SOT-MRAM). In this
work, we investigated the magnetic anisotropies in thulium iron garnet (TIG)
films with PMA via ferromagnetic resonance measurements, followed by the
excitation and detection of magnon-mediated pure spin currents in TIG/Pt driven
by microwaves and heat currents. TIG films presented a Gilbert damping constant
{\alpha}~0.01, with resonance fields above 3.5 kOe and half linewidths broader
than 60 Oe, at 300 K and 9.5 GHz. The spin-to-charge current conversion through
TIG/Pt was observed as a micro-voltage generated at the edges of the Pt film.
The obtained spin Seebeck coefficient was 0.54 {\mu}V/K, confirming also the
high interfacial spin transparency.",2009.10299v1
2020-11-17,Implications of recoil kicks for black hole mergers from LIGO/Virgo catalogs,"The first and second Gravitational Wave Transient Catalogs by the LIGO/Virgo
Collaboration include $50$ confirmed merger events from the first, second, and
first half of the third observational runs. We compute the distribution of
recoil kicks imparted to the merger remnants and estimate their retention
probability within various astrophysical environments as a function of the
maximum progenitor spin ($\chi_{\rm max}$), assuming that the LIGO/Virgo binary
black hole (BBH) mergers were catalyzed by dynamical assembly in a dense star
cluster. We find that the distributions of average recoil kicks are peaked at
about $150$ km s$^{-1}$, $250$ km s$^{-1}$, $350$ km s$^{-1}$, $600$ km
s$^{-1}$, for maximum progenitor spins of $0.1$, $0.3$, $0.5$, $0.8$,
respectively. Only environments with escape speed $\gtrsim 100$ km s$^{-1}$, as
found in galactic nuclear star clusters as well as in the most massive globular
clusters and super star clusters, could efficiently retain the merger remnants
of the LIGO/Virgo BBH population even for low progenitor spins ($\chi_{\rm
max}=0.1$). In the case of high progenitor spins ($\chi_{\rm max}\gtrsim 0.5$),
only the most massive nuclear star clusters can retain the merger products. We
also show that the estimated values of the effective spin and of the remnant
spin of GW170729, GW190412, GW190519, and GW190620 can be reproduced if their
progenitors were moderately spinning ($\chi_{\rm max}\gtrsim 0.3$), while for
GW190517 if the progenitors were rapidly spinning ($\chi_{\rm max}\gtrsim
0.8$). Alternatively, some of these events could be explained if at least one
of the progenitors is already a second-generation BH, originated from a
previous merger.",2011.08935v2
2021-03-30,Isovector spin susceptibility: Isotopic evolution of collectivity in spin response,"Background: Response to spin-dependent operators has been investigated in the
magnetic dipole and Gamow-Teller transitions, which provides magnetic
properties of a nuclear system. Purpose: I investigate an isotopic dependence
of the collectivity generated by the spin-dependent interactions in the Ca and
Ni isotopes through the isovector (IV) spin-flip excitations. The responses in
the neutral $(t_z)$ and charge-exchange $(t_{\pm})$ channels are considered in
a unified way. Method: A nuclear energy-density functional approach is employed
for calculating the response functions based on the Skyrme-Kohn-Sham-Bogoliubov
method and the quasiparticle-random-phase approximation (QRPA). I adopt the
like-particle QRPA and the proton-neutron QRPA for the neutral and
charge-exchange channels, respectively. I consider the fluctuation of the
proton-neutron pair fields. Results: The collective shift due to RPA
correlations for the response in the neutral channel is explained by the
occupation probability of neutrons in the $j_>=\ell+1/2$ orbital. Many
particle-hole or two-quasiparticle excitations have a coherent contribution to
form a giant resonance in neutron-rich nuclei for the charge-exchange channel.
The IV spin susceptibility displays the isotopic evolution of the collectivity
and the underlying shell structure. Conclusions: A repulsive character of the
residual interaction in the spin-isospin channel diminishes the IV spin
susceptibility due to the collectivity, while the dynamic ${}^{3}S$ pairing
appearing in the charge-exchange channel opposes the reduction.",2103.16119v2
2021-04-12,Observation of phase synchronization and alignment during free induction decay of quantum spins with Heisenberg interactions,"Equilibration of observables in closed quantum systems that are described by
a unitary time evolution is a meanwhile well-established phenomenon apart from
a few equally well-established exceptions. Here we report the surprising
theoretical observation that integrable as well as non-integrable spin rings
with nearest-neighbor or long-range isotropic Heisenberg interaction not only
equilibrate but moreover also synchronize the directions of the expectation
values of the individual spins. We highlight that this differs from spontaneous
synchronization in quantum dissipative systems. Here, we observe mutual
synchronization of local spin directions in closed systems under unitary time
evolution. Contrary to dissipative systems, this synchronization is independent
of whether the interaction is ferro- or antiferromagnetic. In our numerical
simulations, we investigate the free induction decay (FID) of an ensemble of up
to $N = 25$ quantum spins with $s = 1/2$ each by solving the time-dependent
Schr\""odinger equation numerically exactly. Our findings are related to, but
not fully explained by conservation laws of the system. The synchronization is
very robust against for instance random fluctuations of the Heisenberg
couplings and inhomogeneous magnetic fields. Synchronization is not observed
with strong enough symmetry-breaking interactions such as the dipolar
interaction. We also compare our results to closed-system classical spin
dynamics which does not exhibit phase synchronization due to the lack of
entanglement. For classical spin systems the fixed magnitude of individual
spins effectively acts like additional $N$ conservation laws.",2104.05748v2
2021-04-26,Emergence of spin-orbit coupled ferromagnetic surface state derived from Zak phase in a nonmagnetic insulator FeSi,"A chiral compound FeSi is a nonmagnetic narrow-gap insulator, exhibiting
peculiar charge and spin dynamics beyond a simple band-structure picture. Those
unusual features have been attracting renewed attention from topological
aspects. Although a signature of surface conduction was indicated according to
size-dependent resistivity in bulk crystals, its existence and topological
properties remain elusive. Here we demonstrate an inherent surface
ferromagnetic-metal state of FeSi thin films and its strong spin-orbit-coupling
(SOC) properties through multiple characterizations of the two-dimensional (2D)
conductance, magnetization and spintronic functionality. Terminated
covalent-bonding orbitals constitute the polar surface state with
momentum-dependent spin textures due to Rashba-type spin splitting, as
corroborated by unidirectional magnetoresistance measurements and
first-principles calculations. As a consequence of the spin-momentum locking,
non-equilibrium spin accumulation causes magnetization switching. These surface
properties are closely related to the Zak phase of the bulk band topology. Our
findings propose another route to explore noble-metal-free materials for
SOC-based spin manipulation.",2104.12438v1
2021-05-19,"Determination of the spin Hall angle by the inverse spin Hall effect, device level ferromagnetic resonance, and spin torque ferromagnetic resonance: a comparison of methods","The spin torque ferromagnetic resonance (STFMR) is one of the popular methods
for measurement of the spin Hall angle (SHA). However, in order to accurately
determine SHA from STFMR measurements, the acquired data must be carefully
analyzed: The resonance linewidth should be determined to an accuracy of a
fraction of an Oe, while the dynamical interaction leading to the measured
response consists of the conventional field-induced ferromagnetic resonance
(FMR), spin-torque induced FMR, and of the inverse spin Hall effect (ISHE).
Additionally, the signal often deteriorates when DC current is passed through
the device. In this work we compare the STFMR method with two other FMR-based
methods that are used to extract SHA. The first is a device-level FMR and the
second is based on the ISHE. We identify artefacts that are caused by the noise
floor of the instrumentation that make the measurement of SHA illusive even
when the signal to noise ratio seems to be reasonable. Additionally, we
estimate a 10% error in SHA that results from neglecting the magnetic
anisotropies as in conventional measurements. Overall, we find the STFMR to be
the most robust of the three methods despite the complexity of the interaction
taking place therein. The conclusions of our work lead to a more accurate
determination of SHA and will assist in the search of novel materials for
energy efficient spin-based applications.",2105.09023v1
2021-06-18,Study of Spin-Orbit Interactions and Interlayer Ferromagnetic Coupling in Co/Pt/Co Trilayers in Wide Range of Heavy Metal Thickness,"The spin-orbit torque, a torque induced by a charge current flowing through
the heavy-metal conducting layer with strong spin-orbit interactions, provides
an efficient way to control the magnetization direction in
heavy-metal/ferromagnet nanostructures, required for applications in the
emergent magnetic technologies like random access memories, high-frequency nano
oscillators, or bio-inspired neuromorphic computations. We study the interface
properties, magnetization dynamics, magnetostatic features and spin-orbit
interactions within the multilayer system
Ti(2)/Co(1)/Pt(0-4)/Co(1)/MgO(2)/Ti(2) (thicknesses in nanometers) patterned by
optical lithography on micrometer-sized bars. In the investigated devices, Pt
is used as a source of the spin current and as a non-magnetic spacer with
variable thickness, which enables the magnitude of the interlayer ferromagnetic
exchange coupling to be effectively tuned. We also find the Pt
thickness-dependent changes in magnetic anisotropies, magnetoresistance,
effective Hall angle and, eventually, spin-orbit torque fields at interfaces.
The experimental findings are supported by the relevant interface
structure-related simulations, micromagnetic, macrospin, as well as the spin
drift-diffusion models. Finally, the contribution of the spin-orbital
Edelstein-Rashba interfacial fields is also briefly discussed in the analysis.",2106.10103v1
2021-07-30,Compton Black-Hole Scattering for $s \leq 5/2$,"Quantum scattering amplitudes for massive matter have received new attention
in connection to classical calculations relevant to gravitational-wave physics.
Amplitude methods and insights are now employed for precision computations of
observables needed for describing the gravitational dynamics of bound massive
objects such as black holes. An important direction is the inclusion of spin
effects needed to accurately describe rotating (Kerr) black holes. Higher-spin
amplitudes introduced by Arkani-Hamed, Huang and Huang at three points have by
now a firm connection to the effective description of Kerr black-hole physics.
The corresponding Compton higher-spin amplitudes remain however an elusive open
problem. Here we draw from results of the higher-spin literature and show that
physical insights can be used to uniquely fix the Compton amplitudes up to spin
5/2, by imposing a constraint on a three-point higher-spin current that is a
necessary condition for the existence of an underlying unitary theory. We give
the unique effective Lagrangians up to spin $5/2$, and show that they reproduce
the previously-known amplitudes. For the multi-graviton amplitudes analogous to
the Compton amplitude, no further corrections to our Lagrangians are expected,
and hence such amplitudes are uniquely predicted. As an essential tool, we
introduce a modified version of the massive spinor-helicity formalism which
allows us to conveniently obtain higher-spin states, propagators and compact
expressions for the amplitudes.",2107.14779v2
2021-08-01,Directional excitation of a high-density magnon gas using coherently driven spin waves,"Controlling magnon densities in magnetic materials enables driving spin
transport in magnonic devices. We demonstrate the creation of large,
out-of-equilibrium magnon densities in a thin-film magnetic insulator via
microwave excitation of coherent spin waves and subsequent multi-magnon
scattering. We image both the coherent spin waves and the resulting incoherent
magnon gas using scanning-probe magnetometry based on electron spins in
diamond. We find that the gas extends unidirectionally over hundreds of
micrometers from the excitation stripline. Surprisingly, the gas density far
exceeds that expected for a boson system following a Bose-Einstein distribution
with a maximum value of the chemical potential. We characterize the momentum
distribution of the gas by measuring the nanoscale spatial decay of the
magnetic stray fields. Our results show that driving coherent spin waves leads
to a strong out-of-equilibrium occupation of the spin-wave band, opening new
possibilities for controlling spin transport and magnetic dynamics in target
directions.",2108.00467v1
2021-08-04,Spin Seebeck coefficient and spin-thermal diffusion in the two-dimensional Hubbard model,"We investigate the spin Seebeck coefficient $S_s$ in the square lattice
Hubbard model at high temperatures of relevance to cold-atom measurements. We
solve the model with the finite-temperature Lanczos and with the dynamical
mean-field theory methods and find they give similar results in the considered
regime. $S_s$ exceeds the atomic 'Heikes' estimates and the Kelvin entropic
estimates drastically. We analyze the behavior in terms of a mapping onto the
problem of a doped attractive model and derive an approximate expression that
allows relating the enhancement of $S_s$ to distinct scattering of the
spin-majority and the spin-minority excitations. Our analysis reveals the
limitations of entropic interpretations of Seebeck coefficient even in the
high-temperature regime. Large values of $S_s$ could be observed on optical
lattices. We also calculate the full diffusion matrix. We quantify the
spin-thermal diffusion, that is, the extent of the mixing between the spin and
the thermal diffusion and discuss the results in the context of recent
measurements of the spin-diffusion constant in cold atoms.",2108.01932v4
2021-09-11,Spin-affected reflexive and stretching separation of off-center droplet collision,"Recent studies have demonstrated the significant roles of droplet self-spin
motion in affecting the head-on collision of binary droplets. In this paper, we
present a computational study by using the Volume-of-Fluid (VOF) method to
investigate the spin-affected droplet separation of off-center collisions,
which are more probable in reality and phenomenologically richer than head-on
collisions. Different separation modes are identified through a parametric
study with varying spinning speed and impact parameter. A prominent finding is
that increasing the droplet spinning speed tends to suppress the reflexive
separation and to promote the stretching separation. Physically, the reflexive
separation is suppressed because the increased rotational energy reduces the
excessive reflexive kinetic energy within the droplet, which is the cause for
the droplet reflexive separation. The stretching separation is promoted because
the increased droplet angular momentum enhances the local stretching flow
within the droplet, which tends to separate the droplet. The roles of orbital
angular momentum and spin angular momentum in affecting the droplet separation
are further substantiated by studying the collision between two spinning
droplets with either the same or opposite chirality. In addition, a theoretical
model based on conservation laws is proposed to qualitatively describe the
boundaries of coalescence-separation transition influenced by droplet self-spin
motion.",2109.05214v1
2021-10-07,Relativistic scattering of a fast spinning neutron star by a massive black hole,"The orbital dynamics of fast spinning neutron stars encountering a massive
Black Hole (BH) with unbounded orbits are investigated using the
quadratic-in-spin Mathisson-Papapetrou- Dixon (MPD) formulation. We consider
the motion of the spinning neutron stars with astrophysically relevant speed in
the gravity field of the BH. For such slow-speed scattering, the hyperbolic
orbits followed by these neutron stars all have near the e = 1 eccentricity,
and have distinct properties compared with those of e >> 1. We have found that
compared with geodesic motion, the spin-orbit and spin-spin coupling will lead
to a variation of scattering angles at spatial infinity, and this variation is
more prominent for slow-speed scattering than fast-speed scattering. Such a
variation leads to an observable difference in pulse-arrival-time within a few
hours of observation, and up to a few days or months for larger BH masses or
longer spinning periods. Such a relativistic pulsar-BH system also emits a
burst of gravitational waves (GWs) in the sensitivity band of LISA, and for
optimal settings, can be seen up to 100 Mpc away. A radio follow up of such a
GW burst with SKA or FAST will allow for measuring the orbital parameters with
high accuracy and testing the predictions of General Relativity (GR).",2110.03494v1
2022-01-11,Low-field microwave-free sensors using dipolar spin relaxation of quartet spin states in silicon carbide,"Paramagnetic defects and nuclear spins are the major sources of magnetic
field-dependent spin relaxation in point defect quantum bits. The detection of
related optical signals has led to the development of advanced relaxometry
applications with high spatial resolution. The nearly degenerate quartet ground
state of the silicon vacancy qubit in silicon carbide (SiC) is of special
interest in this respect, as it gives rise to relaxation rate extrema at
vanishing magnetic field values and emits in the first near-infra-red
transmission window of biological tissues, providing an opportunity for
developing novel sensing applications for medicine and biology. However, the
relaxation dynamics of the silicon vacancy center in SiC have not yet been
fully explored. In this paper, we present results from a comprehensive
theoretical investigation of the dipolar spin relaxation of the quartet spin
states in various local spin environments. We discuss the underlying physics
and quantify the magnetic field and spin bath dependent relaxation time $T_1$.
Using these findings we demonstrate that the silicon vacancy qubit in SiC can
implement microwave-free low magnetic field quantum sensors of great potential.",2201.03953v2
2022-01-11,Analyzing the Rydberg-based omg architecture for $^{171}$Yb nuclear spins,"Neutral alkaline earth(-like) atoms have recently been employed in atomic
arrays with individual readout, control, and high-fidelity Rydberg-mediated
entanglement. This emerging platform offers a wide range of new quantum science
applications that leverage the unique properties of such atoms: ultra-narrow
optical ""clock"" transitions and isolated nuclear spins. Specifically, these
properties offer an optical qubit (""o"") as well as ground (""g"") and metastable
(""m"") nuclear spin qubits, all within a single atom. We consider experimentally
realistic control of this ""omg"" architecture and its coupling to Rydberg states
for entanglement generation, focusing specifically on ytterbium-171
($^{171}\text{Yb}$) with nuclear spin $I = 1/2$. We analyze the $S$-series
Rydberg states of $^{171}\text{Yb}$, described by the three spin-$1/2$
constituents (two electrons and the nucleus). We confirm that the $F = 3/2$
manifold -- a unique spin configuration -- is well suited for entangling
nuclear spin qubits. Further, we analyze the $F = 1/2$ series -- described by
two overlapping spin configurations -- using a multichannel quantum defect
theory. We study the multilevel dynamics of the nuclear spin states when
driving the clock or Rydberg transition with Rabi frequency $\Omega_\text{c} =
2 \pi \times 200$ kHz or $\Omega_\text{R} = 2 \pi \times 6$ MHz, respectively,
finding that a modest magnetic field ($\approx200\,\text{G}$) and feasible
laser polarization intensity purity ($\lesssim0.99$) are sufficient for gate
fidelities exceeding 0.99.",2201.04083v3
2022-01-27,Slow spin dynamics in the hyper-honeycomb Lattice [(C2H5)3NH]2Cu2(C2O4)3 revealed by 1H NMR studies,"We report the results of magnetic susceptibility $\chi$ and $^1$H nuclear
magnetic resonance (NMR) measurements on a three-dimensional hyper-honeycomb
lattice compound [(C$_2$H$_5$)$_3$NH]$_2$Cu$_2$(C$_2$O$_4$)$_3$ (CCCO). The
average value of the antiferromagnetic (AFM) exchange coupling between the
Cu$^{2+}$ ($S$ = 1/2) spins was determined to be $J$~$\sim$~50 K from the
$\chi$ measurements. No long-range magnetic ordering has been observed down to
$T$ = 50 mK, although NMR lines become slightly broader at low temperatures
below 1 K. The broadening of the NMR spectrum observed below 1 K reveals that
the Cu spin moments remain at this temperature, suggesting a non-spin-singlet
ground state. The temperature and magnetic field dependence of 1/$T_1$ at
temperatures above 20 K is well explained by paramagnetic thermal spin
fluctuations where the fluctuation frequency of Cu$^{2+}$ spins is higher than
the NMR frequency of the order of MHz. However, a clear signature of the
slowing down of the Cu$^{2+}$ spin fluctuations was observed at low
temperatures where 1/$T_1$ shows a thermally-activated behavior. The magnetic
field dependence of the magnitude of the spin excitation gap suggests that the
magnetic behaviors of CCCO are characterized as an AFM chain at low
temperatures.",2201.11243v2
2022-01-31,Muon Spin Relaxation Study of Spin Dynamics in Quantum Spin Liquid Candidate H$_3$LiIr$_2$O$_6$,"We present detail thermodynamic and muon spin relaxation ($\mu$SR) studies of
quantum spin liquid (QSL) candidate H$_3$LiIr$_2$O$_6$. In agreement with the
low temperature thermodynamic evidence (\textit{e.g.} bulk magnetization and
heat capacity) for the absence of magnetic transition, zero-field (ZF)-$\mu$SR
measurements indicate the absence of static magnetic ordering or spin freezing
down to our lowest temperature of 80~mK. Both ZF- and longitudinal-field
(LF)-$\mu$SR measurements reveal persistent spin fluctuations at low
temperatures. These results provide well-established evidence of a QSL state in
H$_3$LiIr$_2$O$_6$. Furthermore, the observation of the time-field scaling
behavior of $\mu$SR spectra $A(t)\sim A(t/H^{0.46})$, and the low temperature
power-law specific heat coefficient $C/T \sim T^{-0.57}$, indicate the finite
density of state in the form of $N(E) \sim E^{-0.5}$, in a good agreement with
the disorder-induced states in the Kitaev spin liquid.",2201.12978v1
2022-02-07,Hole Spectral Function of a Chiral Spin Liquid in the Triangular Lattice Hubbard Model,"Quantum spin liquids are fascinating phases of matter, hosting fractionalized
spin excitations and unconventional long-range quantum entanglement. These
exotic properties, however, also render their experimental characterization
challenging, and finding ways to diagnose quantum spin liquids is therefore a
pertinent challenge. Here, we numerically compute the spectral function of a
single hole doped into the half-filled Hubbard model on the triangular lattice
using techniques based on matrix product states. At half-filling the system has
been proposed to realize a chiral spin liquid at intermediate interaction
strength, surrounded by a magnetically ordered phase at strong interactions and
a superconducting/metallic phase at weak interactions. We find that the spectra
of these phases exhibit distinct signatures. By developing appropriate parton
mean-field descriptions, we gain insight into the relevant low-energy features.
While the magnetic phase is characterized by a dressed hole moving through the
ordered spin background, we find indications of spinon dynamics in the chiral
spin liquid. Our results suggest that the hole spectral function, as measured
by angle-resolved photoemission spectroscopy, provides a useful tool to
characterize quantum spin liquids.",2202.03458v2
2022-02-20,Effective spin model in momentum space: Toward a systematic understanding of multiple-$Q$ instability by momentum-resolved anisotropic exchange interactions,"Multiple-$Q$ magnetic states, such as a skyrmion crystal, become a source of
unusual transport phenomena and dynamics. Recent theoretical and experimental
studies clarify that such multiple-$Q$ states ubiquitously appear under
different crystal structures in metals and insulators. Toward a systematic
understanding of the formation of the multiple-$Q$ states in various crystal
systems, in this theoretical study, we present a low-energy effective spin
model with anisotropic exchange interactions in momentum space. We summarize
specific six symmetry rules for nonzero symmetric and antisymmetric anisotropic
exchange interactions in momentum space, which are regarded as an extension of
Moriya's rule. According to the rules, we construct the effective spin model
for tetragonal, hexagonal, and trigonal magnets with crystal- and
momentum-dependent anisotropic exchange interactions based on magnetic
representation analysis. Furthermore, we describe the origin of the effective
anisotropic exchange interactions in itinerant magnets by perturbatively
analyzing a multi-band periodic Anderson model with the spin-orbit coupling. We
apply the effective spin model to an itinerant magnet in a $P6/mmm$ crystal and
find various multiple-$Q$ states with a spin scalar chirality in the ground
state. Our results provide a foundation of constructing effective
phenomenological spin models for any crystal systems hosting the multiple-$Q$
states, which will stimulate further exploration of exotic multiple-$Q$ states
in materials with the spin-orbit coupling.",2202.09744v1
2022-04-20,Ferrimagnet GdFeCo characterization for spin-orbitronics: large field-like and damping-like torques,"Spintronics is showing promising results in the search for new materials and
effects to reduce energy consumption in information technology. Among these
materials, ferrimagnets are of special interest, since they can produce large
spin currents that trigger the magnetization dynamics of adjacent layers or
even their own magnetization. Here, we present a study of the generation of
spin current by GdFeCo in a GdFeCo/Cu/NiFe trilayer where the FeCo sublattice
magnetization is dominant at room temperature. Magnetic properties such as the
saturation magnetization are deduced from magnetometry measurements while
damping constant is estimated from spin-torque ferromagnetic resonance
(ST-FMR). We show that the overall damping-like (DL) and field-like (FL)
effective fields as well as the associated spin Hall angles can be reliably
obtained by performing the dependence of ST-FMR by an added dc current. The sum
of the spin Hall angles for both the spin Hall effect (SHE) and the spin
anomalous Hall effect (SAHE) symmetries are: $\theta_{DL}^{SAHE} +
\theta_{DL}^{SHE}=-0.15 \pm 0.05$ and $\theta_{FL}^{SAHE} +
\theta_{FL}^{SHE}=0.026 \pm 0.005$. From the symmetry of ST-FMR signals we find
that $\theta_{DL}^{SHE}$ is positive and dominated by the negative
$\theta_{DL}^{SAHE}$. The present study paves the way for tuning the different
symmetries in spin conversion in highly efficient ferrimagnetic systems.",2204.09776v1
2022-04-25,Active orbital degree of freedom and potential spin-orbit-entangled moments in Kitaev magnet candidate BaCo$_2$(AsO$_4$)$_2$,"Candidate materials for Kitaev spin liquid phase have been intensively
studied recently because of their potential applications in fault-tolerant
quantum computing. Although most of the studies on Kitaev spin liquid have been
done in 4$d$ and 5$d$ based transition metal compounds, recently there has been
a growing research interest in Co-based quasi-two-dimensional honeycomb
magnets, such as BaCo$_2$(AsO$_4$)$_2$ because of formation of
spin-orbit-entangled $J_{\rm eff}$ = 1/2 pseudospin moments at Co$^{2+}$ sites
and potential realizations of Kitaev-like magnetism therein. Here, we obtain
high-accuracy crystal and electronic structure of BaCo$_2$(AsO$_4$)$_2$ by
employing a combined density functional and dynamical mean-field theory
calculations, which correctly capture the Mott-insulating nature of the target
system. We show that Co$^{2+}$ ions form a high spin configuration, $S=3/2$,
with an active $L_{\rm eff}=1$ orbital degree of freedom, in the absence of
spin-orbit coupling. The size of trigonal distortion within CoO$_6$ octahedra
is found to be not strong enough to completely quench the orbital degree of
freedom, so that the presence of spin-orbit coupling can give rise to the
formation of spin-orbit-entangled moments and the Kitaev exchange interaction.
Our finding supports recent studies on potential Kitaev magnetism in this
compound and other Co-based layered honeycomb systems.",2204.11465v2
2022-05-05,Tossing Black Hole Spin Axes,"The detection of double black hole (BH+BH) mergers provides a unique
possibility to understand their physical properties and origin. To date, the
LIGO-Virgo-KAGRA network of high-frequency gravitational wave observatories
have announced the detection of more than 85 BH+BH merger events (Abbott et al.
2022a). An important diagnostic feature that can be extracted from the data is
the distribution of effective inspiral spins of the BHs. This distribution is
in clear tension with theoretical expectations from both an isolated binary
star origin, which traditionally predicts close-to aligned BH component spins
(Kalogera 2000; Farr et al. 2017), and formation via dynamical interactions in
dense stellar environments that predicts a symmetric distribution of effective
inspiral spins (Mandel & O'Shaughnessy 2010; Rodriguez et al. 2016b). Here it
is demonstrated that isolated binary evolution can convincingly explain the
observed data if BHs have their spin axis tossed during their formation process
in the core collapse of a massive star, similarly to the process evidently
acting in newborn neutron stars. BH formation without spin-axis tossing,
however, has difficulties reproducing the observed data - even if alignment of
spins prior to the second core collapse is disregarded. Based on simulations
with only a minimum of assumptions, constrains from empirical data can be made
on the spin magnitudes of the first- and second-born BHs, thereby serving to
better understand massive binary star evolution prior to the formation of BHs.",2205.02541v3
2022-06-27,"Mode locking of hole spin coherences in CsPb(Cl,Br)$_3$ perovskite nanocrystals","The spin physics of perovskite nanocrystals with confined electrons or holes
is attracting increasing attention, both for fundamental studies and spintronic
applications. Here, stable CsPb(Cl$_{0.5}$Br$_{0.5}$)$_3$ lead halide
perovskite nanocrystals embedded in a fluorophosphate glass matrix are studied
by time-resolved optical spectroscopy to unravel the coherent spin dynamics of
holes and their interaction with nuclear spins of the $^{207}$Pb isotope. We
demonstrate the spin mode locking effect provided by the synchronization of the
Larmor precession of single hole spins in each nanocrystal in the ensemble that
are excited periodically by a laser in an external magnetic field. The mode
locking is enhanced by nuclei-induced frequency focusing. An ensemble spin
dephasing time $T_2^*$ of a nanosecond and a single hole spin coherence time of
$T_2=13\,$ns are measured. The developed theoretical model accounting for the
mode locking and nuclear focusing for randomly oriented nanocrystals with
perovskite band structure describes the experimental data very well.",2206.13323v1
2022-07-06,Non-trivial effect of dephasing: Enhancement of rectification of spin current in graded XX chains,"In order to reveal mechanisms to control and manipulate spin currents, we
perform a detailed investigation of the dephasing effects in the open XX model
with a Lindblad dynamics involving global dissipators and thermal baths.
Specifically, we consider dephasing noise modelled by current preserving
Lindblad dissipators acting on graded versions of these spin systems, that is,
systems in which the magnetic field and/or the spin interaction are growing
(decreasing) along the chain. In our analysis, we study the non-equilibrium
steady-state via the covariance matrix using the Jordan-Wigner approach to
compute the spin currents. We find that the interplay between dephasing and
graded systems gives rise to a non trivial behavior: when we have homogeneous
magnetic field and graded interactions we have rectification enhancement
mechanims, and when we have fully graded system we can control the spin current
in order to keep the direction of the particle/spin flow even with inverted
baths. We describe our result in detailed numerical analisys and we see that
rectification in this simple model indicates that the phenomenon may be of
general occurrence in quantum spin systems.",2207.02693v2
2022-09-05,Mass splitting and spin alignment for $φ$ mesons in a magnetic field in NJL model,"Based on the Nambu-Jona-Lasinio (NJL) model, we develop a framework for
calculating the spin alignment of vector mesons and applied it to study $\phi$
mesons in a magnetic field. We calculate mass spectra for $\phi$ mesons and
observe mass splitting between the longitudinally polarized state and
transversely polarized states. The $\phi$ meson in a thermal equilibrium system
is preferred to occupy the state with spin $\lambda=0$ than those with spin
$\lambda=\pm1$, because the former state has a smaller energy. As a
consequence, we conclude that the spin alignment will be larger than 1/3 if one
measures along the direction of the magnetic field, which is qualitatively
consistent with the recent STAR data. Around the critical temperature
$T_{C}=150$ MeV, the positive deviation from 1/3 is proportional to the square
of the magnetic field strength, which agrees with the result from the
non-relativistic coalescence model. Including the anomalous magnetic moments
for quarks will modify the dynamical masses of quarks and thus affect the mass
spectra and spin alignment of $\phi$ mesons. The discussion of spin alignment
in the NJL model may help us better understand the formation of hadron's spin
structure during the chiral phase transition.",2209.01872v2
2022-09-29,Switching Rashba spin-splitting by reversing electric-field direction,"The manipulation of the Rashba spin-splitting is crucial for the development
of nanospintronic technology. Here, it is proposed that the Rashba
spin-splitting can be turned on and off by reversing electric-field direction.
By the first-principle calculations, our proposal is illustrated by a concrete
example of Janus monolayer RbKNaBi. The designed RbKNaBi possesses dynamical,
thermal and mechanical stability, and is a large-gap quantum spin Hall
insulator (QSHI) with Rashba spin-splitting near the Fermi level. A small
built-in electric field is predicted due to very small electronegativity
difference between the bottom and top atoms, which is very key to switch Rashba
spin-splitting through the experimentally available electric field intensity.
Due to out-of-plane structural asymmetry, the Janus monolayer has distinctive
behaviors by applying external electric field $E$ with the same magnitude but
different directions ($z$ or $-z$). Our results reveal that the Rashba energy
($E_R$) and Rashba constant ($\alpha_R$) are increased by the positive $E$,
while a negative $E$ suppresses the Rashba splitting to disappear, and then
appears again. In a certain $E$ region (0.15 $\mathrm{V/\AA}$ to 0.25
$\mathrm{V/\AA}$), switching Rashba spin-splitting can be achieved by only
reversing electric-field direction. Besides, the piezoelectric strain
coefficients $d_{11}$ and $d_{31}$ (5.52 pm/V and -0.41 pm/V) are predicted,
which are higher than or compared with those of many 2D materials. By
piezoelectric effect, the strain can also be used to tune Rashba spin-splitting
of RbKNaBi. Moreover, a possible spintronic device is proposed to realize the
function of spintronic switch.",2209.14722v1
2023-02-09,Spin torques and anomalous velocity in spin textures induced by fast electron injection from topological ferromagnets: The role of gauge fields,"A new method for analysing magnetization dynamics in spin textures under the
influence of fast electron injection from topological ferromagnetic sources
such as Dirac half metals has been proposed. These electrons, traveling at a
velocity $v$ with a non-negligible value of $v/c$ (where c is the speed of
light), generate a non-equilibrium magnetization density in the spin-texture
region, which is related to an electric dipole moment via relativistic
interactions. When this resulting dipole moment interacts with gauge fields in
the spin-texture region, an effective field is created that produces spin
torques. These torques, like spin-orbit torques that occur when electrons are
injected from a heavy metal into a ferromagnet, can display both damping-like
and anti-damping-like properties. Finally, we demonstrate that such an
interaction between the dipole moment and the gauge field introduces an
anomalous velocity that can contribute to transverse electrical conductivity in
the spin texture in a way comparable to the topological Hall effect.",2302.04551v7
2023-03-06,Metaheuristic conditional neural network for harvesting skyrmionic metastable states,"We present a metaheuristic conditional neural-network-based method aimed at
identifying physically interesting metastable states in a potential energy
surface of high rugosity. To demonstrate how this method works, we identify and
analyze spin textures with topological charge $Q$ ranging from 1 to $-13$
(where antiskyrmions have $Q<0$) in the Pd/Fe/Ir(111) system, which we model
using a classical atomistic spin Hamiltonian based on parameters computed from
density functional theory. To facilitate the harvest of relevant spin textures,
we make use of the newly developed Segment Anything Model (SAM). Spin textures
with $Q$ ranging from $-3$ to $-6$ are further analyzed using
finite-temperature spin-dynamics simulations. We observe that for temperatures
up to around 20\,K, lifetimes longer than 200\,ps are predicted, and that when
these textures decay, new topological spin textures are formed. We also find
that the relative stability of the spin textures depend linearly on the
topological charge, but only when comparing the most stable antiskyrmions for
each topological charge. In general, the number of holes (i.e.,
non-self-intersecting curves that define closed domain walls in the structure)
in the spin texture is an important predictor of stability -- the more holes,
the less stable is the texture. Methods for systematic identification and
characterization of complex metastable skyrmionic textures -- such as the one
demonstrated here -- are highly relevant for advancements in the field of
topological spintronics.",2303.02876v2
2023-04-09,Dynamics for Super-Extremal Kerr Binary Systems at ${\cal O}(G^2)$,"Using the recently derived higher spin gravitational Compton amplitude from
low-energy analytically continued ($a/Gm\gg1$) solutions of the Teukolsky
equation for the scattering of a gravitational wave off the Kerr black hole,
observables for non-radiating super-extremal Kerr binary systems at second
post-Minkowskian (PM) order and up to sixth order in spin are computed. The
relevant 2PM amplitude is obtained from the triangle-leading singularity in
conjunction with a generalization of the holomorphic classical limit for
massive particles with spin oriented in generic directions. Explicit results
for the 2PM eikonal phase written for both Covariant and Canonical spin
supplementary conditions -- CovSSC and CanSSC respectively -- as well as the
2PM linear impulses and individual spin kicks in the CanSSC are presented. The
observables reported in this letter are expressed in terms of generic contact
deformations of the gravitational Compton amplitude, which can then be
specialized to Teukolsky solutions. In the latter case, the resulting 2PM
observables break the newly proposed spin-shift symmetry of the 2PM amplitude
starting at the fifth order in spin. Aligned spin checks as well as the high
energy behavior of the computed observables are discussed.",2304.04287v3
2023-06-02,A generalized effective spin-chain formalism for strongly interacting spinor gases in optical lattice,"A generalized effective spin-chain model is developed for studies of strongly
interacting spinor gases in a one-dimensional (1D) optical lattice. The spinor
gas is mapped to a system of spinless fermions and a spin-chain. A generalized
effective spin-chain Hamiltonian that acts on the mapped system is developed to
study the static and dynamic properties of the spinor gas. This provides a
computationally efficient alternative tool to study strongly interacting spinor
gases in 1D lattice systems. This formalism permits the study of spinor gases
with arbitrary spin and statistics, providing a generalized approach for 1D
strongly interacting gases. By virtue of its simplicity, it provides an easier
tool to study and gain deeper insights into the system. In combination with the
model defined previously for continuum systems, a unified framework is
developed. Studying the mapped system using this formalism recreates the
physics of spinor gas in 1D lattice. Additionally, the time evolution of a
quenched system is studied. The generalized effective spin-chain formalism has
potential applications in the study of a multitude of interesting phenomena
arising in lattice systems such as high-$T_c$ superconductivity and the
spin-coherent \& spin-incoherent Luttinger liquid regimes.",2306.01230v2
2023-08-10,Photoelectronic mapping of spin-orbit interaction of intense light fields,"The interaction between a quantum particle's spin angular momentum and its
orbital angular momentum is ubiquitous in nature. In optics, the spin-orbit
optical phenomenon is closely related with the light-matter interaction and has
been of great interest. With the development of laser technology, the
high-power and ultrafast light sources now serve as a crucial tool in revealing
the behaviour of matters under extreme conditions. The comprehensive knowledge
of the spin-orbit interaction for the intense light is of utmost importance.
Here, we achieve the in-situ modulation and visualization of the optical
orbital-to-spin conversion in strong-field regime. We show that, through
manipulating the morphology of femtosecond cylindrical vector vortex pulses by
a slit, the photons' orbital angular momentum can be controllably transformed
into spin after focusing. By employing strong-field ionization experiment, the
orbital-to-spin conversion can be imaged and measured through the photoelectron
momentum distributions. Such detection and consequent control of spin-orbit
dynamics of intense laser fields have implications on controlling the
photoelectron holography and coherent extreme ultraviolet radiation.",2308.05397v1
2024-02-07,Symplectic mechanics of relativistic spinning compact bodies II.: Canonical formalism in the Schwarzschild spacetime,"This work is the second part in a series aiming at exploiting tools from
Hamiltonian mechanics to study the motion of an extended body in general
relativity. In the first part of this work, we constructed a 10-dimensional,
covariant Hamiltonian framework that encodes all the linear-in-spin corrections
to the geodesic motion. This formulation, although non-canonical, revealed
that, at this linear-in-spin order, the integrability of Schwarzschild and Kerr
geodesics remain. Building on this formalism, in the present work, we translate
this abstract integrability result into tangible applications for
linear-in-spin dynamics of a compact object into a Schwarzschild background
spacetime. In particular, we construct a canonical system of coordinates which
exploits the spherical symmetry of the Schwarzschild spacetime. They are based
on a relativistic generalization of the classical Andoyer variables of
Newtonian rigid body motion. This canonical setup, then, allows us to derive
ready-to-use formulae for action-angle coordinates and gauge-invariant
Hamiltonian frequencies, which automatically include all linear-in-spin
effects. No external parameters or ad hoc choices are necessary, and the
framework can be used to find complete solutions by quadrature of generic,
bound, linear-in-spin orbits, including orbital inclination, precession and
eccentricity, as well as spin precession. We demonstrate the strength of the
formalism in the simple setting of circular orbits with arbitrary spin and
orbital precession, and validate them against known results in the literature.",2402.05049v1
2007-07-13,Effect of antiferromagnetic exchange interactions on the Glauber dynamics of one-dimensional Ising models,"We study the effect of antiferromagnetic interactions on the single spin-flip
Glauber dynamics of two different one-dimensional (1D) Ising models with spin
$\pm 1$. The first model is an Ising chain with antiferromagnetic exchange
interaction limited to nearest neighbors and subject to an oscillating magnetic
field. The system of master equations describing the time evolution of
sublattice magnetizations can easily be solved within a linear field
approximation and a long time limit. Resonant behavior of the magnetization as
a function of temperature (stochastic resonance) is found, at low frequency,
only when spins on opposite sublattices are uncompensated owing to different
gyromagnetic factors (i.e., in the presence of a ferrimagnetic short range
order). The second model is the axial next-nearest neighbor Ising (ANNNI)
chain, where an antiferromagnetic exchange between next-nearest neighbors (nnn)
is assumed to compete with a nearest-neighbor (nn) exchange interaction of
either sign. The long time response of the model to a weak, oscillating
magnetic field is investigated in the framework of a decoupling approximation
for three-spin correlation functions, which is required to close the system of
master equations. The calculation, within such an approximate theoretical
scheme, of the dynamic critical exponent z, defined as ${1/\tau} \approx ({1/
{\xi}})^z$ (where \tau is the longest relaxation time and \xi is the
correlation length of the chain), suggests that the T=0 single spin-flip
Glauber dynamics of the ANNNI chain is in a different universality class than
that of the unfrustrated Ising chain.",0707.1953v1
2011-04-10,Does temperature favor quantum coherence of a dissipative two-level system?,"The quantum dynamics of a two-level system coupled to an Ohmic spin- bath is
studied by means of the perturbation approach based on a unitary
transformation. A scattering function $\xi_k$ is introduced in the
transformation to take into account quantum fluctuations. By the master
equation within the Born approximation, nonequilibrium dynamics quantities are
calculated. The method works well for the coupling constant $0 < \alpha <
\alpha_c$ and a finite bare tunneling $\Delta$. It is found that (i) only at
zero temperature with small coupling or moderate one does the spin-spin-bath
model display identical behavior as the well known spin-boson-bath model; (ii)
in comparison with the known results of spin-boson-bath model, the
coherence-incoherence transition point, which occurs at
$\alpha_c={1/2}[1+\eta\Delta/\omega_c]$, is temperature independent; (iii) the
nonequilibrium correlation function $P(t)=<\tau_z(t)>$, evolves without
temperature dependence while $<\tau_x(t)>$ depends on temperature. Both $P(t)$
and $<\tau_x(t)>$ not only satisfy their initial conditions, respectively, and
also have correct long time limits. Besides, the Shiba's relation and sum rule
are exactly satisfied in the coherent regime for this method. Our results show
that increasing temperature does not help the system suppress decoherence in
the coherent regime, i.e., finite temperature does not favor the coherent
dynamics in this regime. Thus, the finite-temperature dynamics induced by two
kinds of baths spin-bath and boson-bath exhibit distinctly different physics.",1104.1751v1
2012-03-14,On the relation between kinetically constrained models of glass dynamics and the random first-order transition theory,"In this paper we revisit and extend the mapping between two apparently
different classes of models. The first class contains the prototypical models
described --at the mean-field level-- by the Random First Order Transition
(RFOT) theory of the glass transition, called either ""random XORSAT problem""
(in the information theory community) or ""diluted $p$-spin model"" (in the spin
glass community), undergoing a single-spin flip Glauber dynamics. The models in
the second class are Kinetically Constrained Models (KCM): their Hamiltonian is
that of independent spins in a constant magnetic field, hence their
thermodynamics is completely trivial, but the dynamics is such that only groups
of spin can flip together, thus implementing a kinetic constraint that induces
a non-trivial dynamical behavior. A mapping between some representatives of
these two classes has been known for long. Here we formally prove this mapping
at the level of the master equation, and we apply it to the particular case of
Bethe lattice models. This allows us to show that a RFOT model can be mapped
exactly into a KCM. However, the natural order parameter for the RFOT model,
namely the spin overlap, is mapped into a very complicated non-local function
in the KCM. Therefore, if one were to study the KCM without knowing of the
mapping onto the RFOT model, one would guess that its physics is quite
different from the RFOT one. Our results instead suggest that these two
apparently different descriptions of the glass transition are, at least in some
case, closely related.",1203.3166v2
2012-09-13,Random field Ising model swept by propagating magnetic field wave: Athermal nonequilibrium phase diagram,"The dynamical steady state behaviour of the random field
  Ising ferromagnet swept by a propagating magnetic field wave is studied at
zero temperature by Monte Carlo simulation in two dimensions. The distribution
of the random field is bimodal type. For a fixed set of values of the frequency
and wavelength of propagating magnetic field wave and the strength of the
random field, four distinct dynamical steady states or nonequilibrium phases
were identified. These four nonequilibrium phases are characterised by
different values of structure factors. State of first kind, where all spins are
parallel (up). The second one is, the propagating type, where the sharp strips
formed by parallel spins are found to move coherently. The third one is also
propagating type, where the boundary of the strips of spins is not very sharp.
The fourth kind, shows no propagation of stripes of magnetic spins, forming a
homogeneous distribution of up and down spins. This is disordered phase The
appearance of these four dynamical phases or modes depends on the value of the
amplitude of propagating magnetic field wave and the strength of random
(static) field. A phase diagram has also been drawn, in the plane formed by the
amplitude of propagating field and the strength of random field. It is checked
that, the existence of these dynamical phases is neither a finite size effect
nor a transient phenomenon.",1209.2841v2
2013-07-11,Dynamical quantum phase transitions in random spin chains,"Quantum systems can exhibit a great deal of universality at low temperature
due to the structure of ground states and the critical points separating
distinct states. On the other hand, quantum time evolution of the same systems
involves all energies and it is therefore thought to be much harder, if at all
possible, to have sharp transitions in the dynamics. In this paper we show that
phase transitions characterized by universal singularities do occur in the time
evolution of random spin chains. The sharpness of the transitions and integrity
of the phases owes to many-body localization, which prevents thermalization in
these systems. Using a renormalization group approach, we solve the time
evolution of random Ising spin chains with generic interactions starting from
initial states of arbitrary energy. As a function of the Hamiltonian
parameters, the system is tuned through a dynamical transition, similar to the
ground state critical point, at which the local spin correlations establish
true long range temporal order. In the state with dominant transverse field, a
spin that starts in an up state loses its orientation with time, while in the
""ordered"" state it never does. As in ground state quantum phase transitions,
the dynamical transition has unique signatures in the entanglement properties
of the system. When the system is initialized in a product state the
entanglement entropy grows as $log(t)$ in the two ""phases"", while at the
critical point it grows as $log^\a(t)$, with $\a$ a universal number. This
universal entanglement growth requires generic (""integrability breaking"")
interactions to be added to the pure transverse field Ising model.",1307.3256v1
2013-12-10,Real-time and real-space spin- and energy dynamics in one-dimensional spin-1/2 systems induced by local quantum quenches at finite temperatures,"We study the spin- and energy dynamics in one-dimensional spin-1/2 systems
induced by local quantum quenches at finite temperatures using a time-dependent
density matrix renormalization group method. System sizes are chosen large
enough to ensure that the time-dependent data for the accesible time scales
represents the behavior in the thermodynamic limit. As a main result, we
observe a ballistic spreading of perturbations of the energy density in the
integrable spin-1/2 XXZ chain for all temperatures and exchange anisotropies,
related to the divergent thermal conductivity in this model and the exact
conservation of the energy current. In contrast, the spin dynamics is ballistic
in the massless phase, but shows a diffusive behavior at high temperatures in
the easy-axis phase in the case of a vanishing background spin density. We
extract a quantitative estimate for the spin diffusion constant from the time
dependence of the spatial variance of the spin density, which agrees well with
values obtained from current-current correlation functions using an Einstein
relation. As an example for non-integrable models, we consider two-leg ladders,
for which we observe indications of diffusive energy and spin dynamics. The
relevance of our results for recent experiments with quantum magnets and bosons
in optical lattices is discussed.",1312.2938v3
2014-11-30,Spin and charge dynamics of a quasi-one-dimensional antiferromagnetic metal,"We use quantum Monte Carlo simulations to study a finite-temperature
dimensional-crossover-driven evolution of spin and charge dynamics in weakly
coupled Hubbard chains with a half-filled band. The low-temperature behavior of
the charge gap indicates a crossover between two distinct energy scales: a
high-energy one-dimensional (1D) Mott gap due to the umklapp process and a
low-energy gap which stems from long-range antiferromagnetic (AF) fluctuations.
Away from the 1D regime and at temperature scales above the charge gap, the
emergence of a zero-frequency Drude-like feature in the interchain optical
conductivity $\sigma_{\perp}(\omega)$ implies the onset of a higher-dimensional
metal. In this metallic phase, enhanced quasiparticle scattering off
finite-range AF fluctuations results in incoherent single-particle dynamics.
The coupling between spin and charge fluctuations is also seen in the spin
dynamical structure factor $S({\pmb q},\omega)$ displaying damped spin
excitations (paramagnons) close to the AF wave-vector ${\pmb q}=(\pi,\pi)$ and
particle-hole continua near 1D momentum transfers spanning quasiparticles at
the Fermi surface. We relate our results to the charge deconfinement in
quasi-1D organic Bechgaard-Fabre salts.",1412.0287v2
2015-03-06,Temporal decay of Neel order in the one-dimensional Fermi-Hubbard model,"Motivated by recent experiments with ultra-cold quantum gases in optical
lattices we study the decay of the staggered moment in the one-dimensional
Fermi-Hubbard model starting from a perfect Neel state using exact
diagonalization and the iTEBD method. This extends previous work in which the
same problem has been addressed for pure spin Hamiltonians. As a main result,
we show that the relaxation dynamics of the double occupancy and of the
staggered moment are different. The former is controlled by the
nearest-neighbor tunneling rate while the latter is much slower and strongly
dependent on the interaction strength, indicating that spin excitations are
important. This difference in characteristic energy scales for the fast charge
dynamics and the much slower spin dynamics is also reflected in the real-time
evolution of nearest-neighbor density and spin correlations. A very interesting
time dependence emerges in the von Neumann entropy, which at short times
increases linearly with a slope proportional to the tunneling matrix element
while the long-time growth of entanglement is controlled by spin excitations.
Our predictions for the different relaxation dynamics of the staggered moment
and the double occupancy should be observable in state-of-the art optical
lattice experiments. We further compare time averages of the double occupancy
to both the expectation values in the canonical and diagonal ensemble, which
quantitatively disagree with each other on finite systems. We relate the
question of thermalization to the eigenstate thermalization hypothesis.",1503.02010v2
2015-06-15,Coupled intertwiner dynamics: A toy model for coupling matter to spin foam models,"The universal coupling of matter and gravity is one of the most important
features of general relativity. In quantum gravity, in particular spin foams,
matter couplings have been defined in the past, yet the mutual dynamics, in
particular if matter and gravity are strongly coupled, are hardly explored,
which is related to the definition of both matter and gravitational degrees of
freedom on the discretisation. However extracting this mutual dynamics is
crucial in testing the viability of the spin foam approach and also
establishing connections to other discrete approaches such as lattice gauge
theories.
  Therefore, we introduce a simple 2D toy model for Yang--Mills coupled to spin
foams, namely an Ising model coupled to so--called intertwiner models defined
for $\text{SU}(2)_k$. The two systems are coupled by choosing the Ising
coupling constant to depend on spin labels of the background, as these are
interpreted as the edge lengths of the discretisation. We coarse grain this toy
model via tensor network renormalization and uncover an interesting dynamics:
the Ising phase transition temperature turns out to be sensitive to the
background configurations and conversely, the Ising model can induce phase
transitions in the background. Moreover, we observe a strong coupling of both
systems if close to both phase transitions.",1506.04749v3
2015-07-13,Macrospin Dynamics in Antiferromagnets Triggered by Sub-20 femtosecond Injection of Nanomagnons,"The understanding of how the sub-nanoscale exchange interaction evolves in
macroscale correlations and ordered phases of matter, such as magnetism and
superconductivity, requires to bridge the quantum and classical worlds. This
monumental challenge has so far only been achieved for systems close to their
thermodynamical equilibrium. Here we follow in real time the ultrafast dynamics
of the macroscale magnetic order parameter triggered by the impulsive optical
generation of spin excitations with the shortest possible nanometer-wavelength
and femtosecond-period. Our experiments also disclose a possibility for the
coherent control of these femtosecond nanomagnons, which are defined by the
exchange energy. These findings open up novel opportunities for fundamental
research on the role of short-wavelength spin excitations in magnetism and
high-temperature superconductivity, since they provide a macroscopic probe of
the femtosecond dynamics of sub-nanometer spin-spin correlations and,
ultimately, of the exchange energy. With this approach it becomes possible to
trace the dynamics of such short-range magnetic correlations for instance
during phase transitions. Moreover, our work suggests that nanospintronics and
nanomagnonics can employ phase-controllable spin waves with frequencies in the
20 THz domain.",1507.03377v1
2015-11-24,Dynamical magnetoelectric phenomena of multiferroic skyrmions,"Magnetic skyrmions, vortex-like swirling spin textures characterized by a
quantized topological invariant, realized in chiral-lattice magnets are
currently attracting intense research interest. In particular, their dynamics
under external fields is an issue of vital importance both for fundamental
science and for technical application. Whereas observations of magnetic
skyrmions had been limited to metallic magnets so far, their realization was
discovered also in a chiral-lattice insulating magnet Cu2OSeO3 in 2012.
Skyrmions in the insulator turned out to exhibit multiferroic nature with
spin-induced ferroelectricity. Strong magnetoelectric coupling between
noncollinear skyrmion spins and electric polarizations mediated by relativistic
spin-orbit interaction enables us to drive motion and oscillation of magnetic
skyrmions by application of electric fields instead of injection of electric
currents. Insulating materials also provide an environment suitable for
detection of pure spin dynamics through spectroscopic measurements owing to
absence of appreciable charge excitations. In this article, we review recent
theoretical and experimental studies on multiferroic properties and dynamical
magnetoelectric phenomena of magnetic skyrmions in insulators. We argue that
multiferroic skyrmions show unique coupled oscillation modes of magnetizations
and polarizations, so-called electromagnon excitations, which are both
magnetically and electrically active, and interference between the electric and
magnetic activation processes leads to peculiar magnetoelectric effects in a
microwave frequency regime.",1511.07761v1
2016-10-05,A statics-dynamics equivalence through the fluctuation-dissipation ratio provides a window into the spin-glass phase from nonequilibrium measurements,"The unifying feature of glass formers (such as polymers, supercooled liquids,
colloids, granulars, spin glasses, superconductors, ...) is a sluggish dynamics
at low temperatures. Indeed, their dynamics is so slow that thermal equilibrium
is never reached in macroscopic samples: in analogy with living beings, glasses
are said to age. Here, we show how to relate experimentally relevant quantities
with the experimentally unreachable low-temperature equilibrium phase. We have
performed a very accurate computation of the non-equilibrium
fluctuation-dissipation ratio for the three-dimensional Edwards-Anderson Ising
spin glass, by means of large-scale simulations on the special-purpose
computers Janus and Janus II. This ratio (computed for finite times on very
large, effectively infinite, systems) is compared with the equilibrium
probability distribution of the spin overlap for finite sizes. The resulting
quantitative statics-dynamics dictionary, based on observables that can be
measured with current experimental methods, could allow the experimental
exploration of important features of the spin-glass phase without
uncontrollable extrapolations to infinite times or system sizes.",1610.01418v3
2020-04-17,Many-body effects on second-order phase transitions in spinor Bose-Einstein condensates and breathing dynamics,"We unravel the correlation effects of the second-order quantum phase
transitions emerging on the ground state of a harmonically trapped spin-1 Bose
gas, upon varying the involved Zeeman terms, as well as its breathing dynamics
triggered by quenching the trapping frequency. It is found that the boundaries
of the associated magnetic phases are altered in the presence of interparticle
correlations for both ferromagnetic and anti-ferromagnetic spin-spin
interactions, an effect which becomes more prominent in the few-body scenario.
Most importantly, we unveil a correlation-induced shrinking of the
anti-ferromagnetic and broken-axisymmetry phases implying that ground states
with bosons polarized in a single spin-component are favored. Turning to the
dynamical response of the spinor gas it is shown that its breathing frequency
is independent of the system parameters while correlations lead to the
formation of filamentary patterns in the one-body density of the participating
components. The number of filaments is larger for increasing spin-independent
interaction strengths or for smaller particle numbers. Each filament maintains
its coherence and exhibits an anti-correlated behavior while distinct filaments
show significant losses of coherence and are two-body correlated.
Interestingly, we demonstrate that for an initial broken-axisymmetry phase an
enhanced spin-flip dynamics takes place which can be tuned either via the
linear Zeeman term or the quench amplitude.",2004.09303v2
2019-02-05,The Dynamics of Magnetism in Fe-Cr Alloys with Cr Clustering,"The dynamics of magnetic moments in iron-chromium alloys with different
levels of Cr clustering show unusual features resulting from the fact that even
in a perfect body-centred cubic structure, magnetic moments experience
geometric magnetic frustration resembling that of a spin glass. Due to the long
range exchange coupling and configuration randomness, magnetic moments of Cr
solutes remain non-collinear at all temperatures. To characterise magnetic
properties of Fe-Cr alloys, we explore the temperature dependence of
magnetisation, susceptibility, Curie temperature and spin-spin correlations
with spatial resolution. The static and dynamic magnetic properties are
correlated with the microstructure of Fe-Cr, where magnetisation and
susceptibility are determined by the size of Cr precipitates at nominal Cr
concentrations. The Curie temperature is always maximised when the solute
concentration of Cr in the $\alpha$ phase is close to 5 to 6 at.\%, and the
susceptibility of Fe atoms is always enhanced at the boundary between a
precipitate and solid solution. Interaction between Cr and Fe stimulates
magnetic disorder, lowering the effective Curie temperature. Dynamic simulation
of evolution of magnetic correlations shows that the spin-spin relaxation time
in Fe-Cr alloys is in the 20 to 40 ps range.",1902.01645v1
2019-08-12,"Spin beats in the photoluminescence polarization dynamics of charged excitons in InP/(In,Ga)P quantum dots in presence of nuclear quadrupole interaction","The spin dynamics of positively (X$^{+}$) and negatively (X$^{-}$) charged
excitons in InP/In$_{0.48}$Ga$_{0.52}$P quantum dots subject to a magnetic
field is studied. We find that a characteristic feature of the system under
study is the presence of nuclear quadrupole interaction, which leads to
stabilization of the nuclear and electron spins in a quantum dot in zero
external magnetic field. In detail, the nuclear quadrupole interaction leads to
pinning of the Overhauser field along the quadrupole axis, which is close to
the growth axis of the heterostructure. The nuclear effects are observed only
when resident electrons are confined in the quantum dots, i.e. for X$^{-}$
trion photoexcitation. The presence of X$^{-}$ and X$^{+}$ trion contributions
to the photoluminescence together with the quadrupole interaction significantly
affects the dynamics of optical orientation in Voigt magnetic field. In absence
of dynamic nuclear spin polarization the time evolution of the
photoluminescence polarization was fitted by a form which describes the
electron spin relaxation in ""frozen"" nuclear field fluctuations. In relatively
large external magnetic fields exceeding 60 mT good agreement between theory
and experiment is achieved.",1908.04167v1
2019-11-26,Trajectory phase transitions in non-interacting spin systems,"We show that a collection of independent Ising spins evolving stochastically
can display surprisingly large fluctuations towards ordered behaviour, as
quantified by certain types of time-integrated plaquette observables, despite
the underlying dynamics being non-interacting. In the large deviation (LD)
regime of long times and large system size, this can give rise to a phase
transition in trajectory space. As a non-interacting system we consider a
collection of spins undergoing single spin-flip dynamics at
infinite-temperature. For the dynamical observables we study, the associated
tilted generators have an exact and explicit spin-plaquette duality. Such setup
suggests the existence of a transition (in the large size limit) at the
self-dual point of the tilted generator. The nature of the LD transition
depends on the observable. We consider explicitly two situations: (i) for a
pairwise bond observable the LD transition is continuous, and equivalent to
that of the transverse field Ising model; (ii) for a higher order plaquette
observable, in contrast, the LD transition is first order. Case (i) is easy to
prove analytically, while we confirm case (ii) numerically via an efficient
trajectory sampling scheme that exploits the non-interacting nature of the
original dynamics.",1911.11739v1
2021-03-26,Temperature evolution of the phonon dynamics in the Kitaev spin liquid,"Here we present a study of the phonon dynamics in the honeycomb Kitaev spin
model at finite temperatures. We show that the fractionalized spin excitations
of the Kitaev spin liquid, the itinerant Majorana fermions and static $Z_2$
fluxes, have distinct effects on the phonon dynamics, which makes the phonon
dynamics a promising tool for exploring the Kitaev spin liquid candidate
materials. In particular, we will focus on the signature of the fractionalized
excitations in the thermodynamic behaviour of the sound attenuation and the
phonon Hall viscosity: The former describes the phonon decay into the
fractionalized excitations, and the later is the leading order time reversal
symmetry breaking effect on the acoustic phonon. We find that the angular
dependence of the attenuation coefficient and its magnitude are modified by the
thermal excitation of the $Z_2$ fluxes. The strength of this effect strongly
depends on the relative magnitude of the sound velocity and the Fermi velocity
characterizing the low-energy Majorana fermions. We also show that the Hall
viscosity is strongly suppressed by the increase of the density of the $Z_2$
fluxes at finite temperatures. All these observations reflect the effects of
the emergent disorder on the Majorana fermions introduced by the $Z_2$ fluxes.
Our analysis is based on the complementary analytical calculations in the
low-temperature zero-flux sector, and numerical calculations in the
inhomogeneous flux sectors at intermediate and high temperatures with
stratified Monte Carlo (strMC) method.",2103.14661v2
2022-08-17,The quantum dynamic range of room temperature spin imaging,"Magnetic resonance imaging of spin systems combines scientific applications
in medicine, chemistry and physics. Here, we investigate the pixel-wise
coherent quantum dynamics of spins consisting of a 40 by 40 micron sized region
of interest implanted with nitrogen vacancy centers (NV) coupled to a
nano-magnetic flake of $\mathrm{CrTe_2}$. $\mathrm{CrTe_2}$ is an in-plane van
der Waals ferromagnet, which we can probe quantitatively by the NV electron's
spin signal even at room temperature. First, we combine the nano-scale sample
shapes measured by atomic force microscope with the magnetic resonance imaging
data. We then map out the coherent dynamics of the colour centers coupled to
the van der Waals ferromagnet using pixel-wise coherent Rabi and Ramsey imaging
of the NV sensor layer. Next, we fit the pixel-wise solution of the Hamiltonian
to the quantum sensor data. Combining data and model, we can explore the
detuning range of the spin oscillation with a quantum dynamic range of over
$\left|\Delta_{max}\right|= 60 { }\mathrm{MHz} $ in the Ramsey interferometry
mode. Finally, we show the effect of the $\mathrm{CrTe_2}$ van der Waals magnet
on the coherence of the NV sensor layer and measure a 70 times increase in the
maximum frequency of the quantum oscillation going from the Rabi to the Ramsey
imaging mode.",2208.08146v1
2022-12-30,Commensurate and incommensurate magnetic order in the doped two-dimensional Hubbard model: dynamical mean-field theory analysis,"We develop a dynamical mean-field theory approach for the spiral magnetic
order, changing to a local coordinate frame with preferable spin alignment
along the $z$-axis, which can be considered with the impurity solvers treating
the spin diagonal local Green's function. We furthermore solve the
Bethe-Salpeter equations for nonuniform dynamic magnetic susceptibilities in
the local coordinate frame. We apply this approach to describe the evolution of
magnetic order with doping in the $t-t'$ Hubbard model with $t'=0.15$, which is
appropriate for the description of the doped La$_2$CuO$_4$ high-temperature
superconductor. We find that with doping the antiferromagnetic order changes to
the $(Q,\pi)$ incommensurate one, and then to the paramagnetic phase. The
spectral weight at the Fermi level is suppressed near half filling and
continuously increases with doping. The dispersion of holes in the
antiferromagnetic phase shows qualitative agreement with the results of the
$t$-$J$ model consideration. In the incommensurate phase we find two branches
of hole dispersions, one of which crosses the Fermi level. The resulting Fermi
surface forms hole pockets. We also consider the dispersion of the magnetic
excitations, obtained from the non-local dynamic magnetic susceptibilities. The
transverse spin excitations are gapless, fulfilling the Goldstone theorem; in
contrast to the mean-field approach the obtained magnetic state is found to be
stable. The longitudinal excitations are characterized by a small gap, showing
the rigidity of the spin excitations. For realistic hopping and interaction
parameters we reproduce the experimentally measured spin-wave dispersion of
La$_2$CuO$_4$.",2212.14656v2
2023-06-29,Nonequilibrium generation of charge defects in kagome spin ice under slow cooling,"Kagome spin ice is one of the canonical examples of highly frustrated
magnets. The effective magnetic degrees of freedom in kagome spin ice are Ising
spins residing on a two-dimensional network of corner-sharing triangles. Due to
strong geometrical frustration, nearest-neighbor antiferromagnetic interactions
on the kagome lattice give rise to a macroscopic number of degenerate classical
ground states characterized by ice rules. Elementary excitations at low
temperatures are defect-triangles that violate the ice rules and carry an
additional net magnetic charge relative to the background. We perform
large-scale Glauber dynamics simulations to study the nonequilibrium dynamics
of kagome ice under slow cooling. We show that the density of residual charge
defects exhibits a power law dependence on the quench rate for the class of
algebraic cooling protocols. The numerical results are well captured by the
rate equation for the charge defects based on the reaction kinetics theory. As
the relaxation time of the kagome ice phase remains finite, there is no
dynamical freezing as in the Kibble-Zurek scenario. Instead, we show that the
power-law behavior originates from a thermal excitation that decay
algebraically with time at the late stage of the cooling schedule. Similarities
and differences in quench dynamics of other spin ice systems are also
discussed.",2306.17036v2
2023-10-07,Characterizing the effect of eccentricity on the dynamics of binary black hole mergers in numerical relativity,"Many articles have partially studied the configuration of eccentric orbital
binary black hole (BBH) mergers. However, there is a scarcity of systematic and
comprehensive research on the effect of eccentricity on BBH dynamics. Thanks to
the rich and numerous numerical relativistic simulations of eccentric orbital
BBH mergers from RIT catalog, this paper aims to investigate the impact of
initial eccentricity $e_0$ on various dynamic quantities such as merger time
$T_{\text{merger}}$, peak luminosity $L_{\text{peak}}$ of gravitational waves,
recoil velocity $V_f$, mass $M_f$, and spin $\alpha_f$ of merger remnants. We
cover configurations of no spin, spin alignment, and spin precession, as well
as a broad parameter space of mass ratio ranging from 1/32 to 1 and initial
eccentricity from 0 to 1. For non-spinning BBH with an initial coordinate
separation of $11.3M$ ($M$ is the total mass of BBH), we make the first
discovery of a ubiquitous oscillation in the relationship between dynamic
quantities $L_{\text{peak}}$, $V_f$, $M_f$, $\alpha_f$, and initial
eccentricity $e_0$. Additionally, at $24.6M$, we observe the same oscillation
phenomenon in the case of mass ratio $q=1$, but do not see it in other mass
ratios, suggesting that this oscillation will be evident in numerical
simulations with sufficiently dense initial eccentricity. abbreviated",2310.04777v1
2023-10-30,Quantum to classical crossover in generalized spin systems -- the temperature-dependent spin dynamics of FeI$_2$,"Simulating quantum spin systems at finite temperatures is an open challenge
in many-body physics. This work studies the temperature-dependent spin dynamics
of a pivotal compound, FeI$_2$, to determine if universal quantum effects can
be accounted for by a phenomenological renormalization of the dynamical spin
structure factor $S(\mathbf{q}, \omega)$ measured by inelastic neutron
scattering. Renormalization schemes based on the quantum-to-classical
correspondence principle are commonly applied at low temperatures to the
harmonic oscillators describing normal modes. However, it is not clear how to
extend this renormalization to arbitrarily high temperatures. Here we introduce
a temperature-dependent normalization of the classical moments, whose magnitude
is determined by imposing the quantum sum rule, i.e. $\int d\omega d\mathbf{q}
S(\mathbf{q}, \omega) = N_S S (S+1)$ for $N_S$ dipolar magnetic moments. We
show that this simple renormalization scheme significantly improves the
agreement between the calculated and measured $S(\mathbf{q}, \omega)$ for
FeI$_{2}$ at all temperatures. Due to the coupled dynamics of dipolar and
quadrupolar moments in that material, this renormalization procedure is
extended to classical theories based on SU(3) coherent states, and by
extension, to any SU(N) coherent state representation of local multipolar
moments.",2310.19905v1
2008-04-17,"A study of the quantum classical crossover in the spin dynamics of the 2D S=5/2 antiferromagnet Rb2MnF4: neutron scattering, computer simulations, and analytic theories","We report comprehensive inelastic neutron scattering measurements of the
magnetic excitations in the 2D spin-5/2 Heisenberg antiferromagnet Rb2MnF4 as a
function of temperature from deep in the Neel ordered phase up to paramagnetic,
0.13 < kBT/4JS < 1.4. Well defined spin-waves are found for wave-vectors larger
than the inverse correlation length $\eta^{-1}$ for temperatures up to near the
Curie-Weiss temperature, $\Theta_{CW}$. For wave-vectors smaller than
$\eta^{-1}$, relaxational dynamics occurs. The observed renormalization of
spin-wave energies, and evolution of excitation line-shapes, with increasing
temperature are quantitatively compared with finite-temperature spin-wave
theory, and computer simulations for classical spins. Random phase
approximation calculations provide a good description of the low-temperature
renormalisation of spin-waves. In contrast, lifetime broadening calculated
using the first Born approximation shows, at best, modest agreement around the
zone boundary at low temperatures. Classical dynamics simulations using an
appropriate quantum-classical correspondence were found to provide a good
description of the intermediate- and high-temperature regimes over all
wave-vector and energy scales, and the crossover from quantum to classical
dynamics observed around $\Theta_{CW}/S$, where the spin S=5/2. A
characterisation of the data over the whole wave-vector/energy/temperature
parameter space is given. In this, $T^2$ behaviour is found to dominate the
wave-vector and temperature dependence of the line widths over a large
parameter range, and no evidence of hydrodynamic behaviour or dynamical scaling
behaviour found within the accuracy of the data sets.",0804.2901v2
2016-11-15,"Topology of a dissipative spin: dynamical Chern number, bath induced non-adiabaticity and a quantum dynamo effect","We analyze the topological deformations of a spin-1/2 in an effective
magnetic field induced by an ohmic quantum dissipative environment at zero
temperature. From Bethe Ansatz results and a variational approach, we confirm
that the Chern number is preserved in the delocalized phase for $\alpha<1$. We
report a divergence of the Berry curvature at the equator when $\alpha_c=1$
that appears at the localization Kosterlitz-Thouless quantum phase transition
in this model. Recent experiments in quantum circuits have engineered
non-equilibrium protocols in time to access topological properties at
equilibrium from the measure of the (quasi-)adiabatic out-of-equilibrium spin
expectation values. Applying a numerically exact stochastic Schr\""{o}dinger
equation we find that, for a fixed sweep velocity, the bath induces a crossover
from (quasi-)adiabatic to non-adiabatic dynamical behavior when the spin bath
coupling increases. We also investigate the particular regime $H/\omega_c \ll
v/H \ll 1$, where the dynamical Chern number observable built from
out-of-equilibrium spin expectation values vanishes at $\alpha=1/2$. In this
regime, the mapping to an interacting resonance level model enables us to
characterize the evolution of the dynamical Chern number in the vicinity of
$\alpha=1/2$. Then, we provide an intuitive physical explanation of the
breakdown of adiabaticity in analogy to the Faraday effect in electromagnetism.
We demonstrate that the driving of the spin leads to the production of a large
number of bosonic excitations in the bath, which in return strongly affect the
spin dynamics. Finally, we quantify the spin-bath entanglement and build an
analogy with an effective model at thermal equilibrium.",1611.05085v1
2018-12-22,Spin dynamics of $3d$ and $4d$ impurities embedded in prototypical topological insulators,"Topological insulators are insulating bulk materials hosting conducting
surface states. Their magnetic doping breaks time-reversal symmetry and
generates numerous interesting effects such as dissipationless transport.
Nonetheless, their dynamical properties are still poorly understood. Here, we
perform a systematic investigation of transverse spin excitations of $3d$ and
$4d$ single impurities embedded in two prototypical topological insulators
(Bi$_2$Te$_3$ and Bi$_2$Se$_3$). The impurity-induced states within the bulk
gap of the topological insulators are found to have a drastic impact on the
spin excitation spectra, resulting in very high lifetimes reaching up to
${microseconds}$. An intuitive picture of the spin dynamics is obtained by
mapping onto a generalized Landau-Lifshitz-Gilbert phenomenological model. The
first quantity extracted from this mapping procedure is the magnetic anisotropy
energy, which is then compared to the one provided by the magnetic force
theorem. This uncovers some difficulties encountered with the latter, which can
provide erroneous results for impurities with a high density of states at the
Fermi energy. Moreover, the Gilbert damping and nutation tensors are obtained.
The nutation effects can lead to a non-negligible shift in the spin excitation
resonance in the high-frequency regime. Finally, we study the impact of the
surface state on the spin dynamics, which may be severely altered due to the
repositioning of the impurity-induced state in comparison to the bulk case. Our
systematic investigation of this series of magnetic impurities sheds light on
their spin dynamics within topological insulators, with implications for
available and future experimental studies as, for instance, on the viability of
using such impurities for solid-state qubits.",1812.09596v1
2017-08-03,Spatial Mixing and Non-local Markov chains,"We consider spin systems with nearest-neighbor interactions on an $n$-vertex
$d$-dimensional cube of the integer lattice graph $\mathbb{Z}^d$. We study the
effects that exponential decay with distance of spin correlations, specifically
the strong spatial mixing condition (SSM), has on the rate of convergence to
equilibrium distribution of non-local Markov chains. We prove that SSM implies
$O(\log n)$ mixing of a block dynamics whose steps can be implemented
efficiently. We then develop a methodology, consisting of several new
comparison inequalities concerning various block dynamics, that allow us to
extend this result to other non-local dynamics. As a first application of our
method we prove that, if SSM holds, then the relaxation time (i.e., the inverse
spectral gap) of general block dynamics is $O(r)$, where $r$ is the number of
blocks. A second application of our technology concerns the Swendsen-Wang
dynamics for the ferromagnetic Ising and Potts models. We show that SSM implies
an $O(1)$ bound for the relaxation time. As a by-product of this implication we
observe that the relaxation time of the Swendsen-Wang dynamics in square boxes
of $\mathbb{Z}^2$ is $O(1)$ throughout the subcritical regime of the $q$-state
Potts model, for all $q \ge 2$. We also prove that for monotone spin systems
SSM implies that the mixing time of systematic scan dynamics is $O(\log n (\log
\log n)^2)$. Systematic scan dynamics are widely employed in practice but have
proved hard to analyze. Our proofs use a variety of techniques for the analysis
of Markov chains including coupling, functional analysis and linear algebra.",1708.01513v1
2016-07-29,Pulse and quench induced dynamical phase transition in a chiral multiferroic spin chain,"Quantum dynamics of magnetic order in a chiral multiferroic chain is studied.
We consider two different scenarios: Ultrashort terahertz (THz) excitations or
a sudden electric field quench. Performing analytical and numerical exact
diagonalization calculations we trace the pulse induced spin dynamics and
extract quantities that are relevant to quantum information processing. In
particular, we analyze the dynamics of the system chirality, the von Neumann
entropy, the pairwise and the many body entanglement. If the characteristic
frequencies of the generated states are non-commensurate then a partial loss of
pair concurrence occurs. Increasing the system size this effect becomes even
more pronounced. Many particle entanglement and chirality are robust and
persist in the incommensurate phase. To analyze the dynamical quantum
transitions for the quenched and pulsed dynamics we combined the Weierstrass
factorization technique for entire functions and Lanczos exact diagonalization
method. For a small system we obtained analytical results including the rate
function of Loschmidt echo. Exact numerical calculations for a system up to 40
spins confirm phase transition. Quench- induced dynamical transitions have been
extensively studied recently. Here we show that related dynamical transitions
can be achieved and controlled by appropriate electric field pulses.",1608.00030v1
2000-03-14,Role of free energy landscape in the dynamics of mean field glassy systems,"In this paper we expose the results of our recent work on the dynamical TAP
approach to mean field glassy systems. Our aim is to clarify the connection
between free energy landscape and out of equilibrium dynamics in solvable
models. Frequently qualitative explanations of glassy behaviour are based on
the ``Free Energy Landscape Paradigm''. If its relevance for equilibrium
properties is clear, the relationship between free energy landscape and out of
equilibrium dynamics is not well understood yet. In this paper we clarify this
relationship for the class of spin glass models which reproduce
phenomenologically some features of structural glasses. The method we use is a
generalisation to dynamics of the Thouless, Anderson and Palmer approach to
thermodynamics of mean field spin glasses. Within this framework we show to
what extent the dynamics can be represented as an evolution in the free energy
landscape. In particular the relationship between the long-time dynamics and
the local properties of the free energy landscape shows up explicitly using
this approach.",0003234v2
2003-11-12,Small-World Network Effect in Competing Glauber- and Kawasaki-type Dynamics,"In this article, we investigate the competing Glauber-type and Kawasaki-type
dynamics with small-world network (SWN) effect, in the framework of the
Gaussian model. The Glauber-type single-spin transition mechanism with
probability p simulates the contact of the system with a heat bath and the
Kawasaki-type dynamics with probability 1-p simulates an external energy flux.
Two different types of SWN effect are studied, one with the total number of
links increased and the other with it conserved. The competition of the
dynamics leads to an interesting self-organization process that can be
characterized by a phase diagram with two identifiable temperatures. By
studying the modification of the phase diagrams, the SWN effect on the two
dynamics is analyzed. For the Glauber-type dynamics, more important is the
altered average coordination number while the Kawasaki-type dynamics is
enhanced by the long range spin interaction and redistribution.",0311276v1
2006-12-20,Static and dynamic heterogeneities in irreversible gels and colloidal gelation,"We compare the slow dynamics of irreversible gels, colloidal gels, glasses
and spin glasses by analyzing the behavior of the so called non-linear
dynamical susceptibility, a quantity usually introduced to quantitatively
characterize the dynamical heterogeneities. In glasses this quantity typically
grows with the time, reaches a maximum and then decreases at large time, due to
the transient nature of dynamical heterogeneities and to the absence of a
diverging static correlation length. We have recently shown that in
irreversible gels the dynamical susceptibility is instead an increasing
function of the time, as in the case of spin glasses, and tends asymptotically
to the mean cluster size. On the basis of molecular dynamics simulations, we
here show that in colloidal gelation where clusters are not permanent, at very
low temperature and volume fractions, i.e. when the lifetime of the bonds is
much larger than the structural relaxation time, the non-linear susceptibility
has a behavior similar to the one of the irreversible gel, followed, at higher
volume fractions, by a crossover towards the behavior of glass forming liquids.",0612521v1
2008-12-18,Updating schemes in zero-temperature single-spin flip dynamics,"In this paper we examine the role of the so called $c$-parallel updating
schemes in relaxation from disordered states to the final ferromagnetic steady
state. We investigate two zero-temperature single-spin flip dynamics on a one
dimensional lattice of length $L$: inflow (i.e. generalized zero-temperature
Glauber dynamics) and outflow opinion dynamics. The varying $c$ allows us to
change the updating scheme from random sequential updating ($c=1/L$) to
deterministic synchronous updating (for $c=1$). We show how the mean relaxation
times depend on $c$ and scale with the system size $L$. Moreover, we
empirically find an analytical formula for the ratio between mean relaxation
times for inflow and outflow dynamics. Results obtained in this paper suggest
that in some sense the original zero-temperature Glauber dynamics is a critical
one among a broader class of inflow dynamics.",0812.3654v1
2011-07-01,Slow magnetic dynamics and hysteresis loops of a bulk ferromagnet,"Magnetic dynamics of a bulk ferromagnet, a new single crystalline compound
Co7(TeO3)4Br6, was studied by ac susceptibility and the related techniques.
Very large Arrhenius activation energy of 17.2 meV (201 K) and long attempt
time (2x10^(-4)s) span the full spectrum of magnetic dynamics inside a
convenient frequency window, offering a rare opportunity for general studies of
magnetic dynamics. Within the experimental window the ac susceptibility data
build almost ideally semicircular Cole-Cole plots. Comprehensive study of
experimental dynamic hysteresis loops of the compound is presented and
interpreted within a simple thermal-activation-assisted spin lattice relaxation
model for spin reversal. Quantitative agreement between the experimental
results and the model's prediction for dynamic coercive field is achieved by
assuming the central physical quantity, the Debye relaxation rate, to depend on
frequency, as well as on the applied field strength and sample temperature.
Cross-over between minor- to major hysteresis loops is carefully analyzed.
Low-frequency limitations of the model, relying on domain wall pinning effects,
are experimentally detected and appropriately discussed.",1107.0255v2
2012-12-01,Time evolution of autocorrelation function in dynamical replica theory,"Asynchronous dynamics given by the master equation in the
Sherrington--Kirkpatrick (SK) spin-glass model is studied based on dynamical
replica theory (DRT) with an extension to take into account the autocorrelation
function. The dynamical behaviour of the system is approximately described by
dynamical equations of the macroscopic quantities: magnetization, energy
contributed by randomness, and the autocorrelation function. The dynamical
equations under the replica symmetry assumption are derived by introducing the
subshell equipartitioning assumption and exploiting the replica method. The
obtained dynamical equations are compared with Monte Carlo (MC) simulations,
and it is demonstrated that the proposed formula describes well the time
evolution of the autocorrelation function in some parameter regions. The study
offers a reasonable description of the autocorrelation function in the SK
spin-glass system.",1212.0058v1
2016-04-20,Path integral methods for the dynamics of stochastic and disordered systems,"We review some of the techniques used to study the dynamics of disordered
systems subject to both quenched and fast (thermal) noise. Starting from the
Martin-Siggia-Rose path integral formalism for a single variable stochastic
dynamics, we provide a pedagogical survey of the perturbative, i.e.
diagrammatic, approach to dynamics and how this formalism can be used for
studying soft spin models. We review the supersymmetric formulation of the
Langevin dynamics of these models and discuss the physical implications of the
supersymmetry. We also describe the key steps involved in studying the
disorder-averaged dynamics. Finally, we discuss the path integral approach for
the case of hard Ising spins and review some recent developments in the
dynamics of such kinetic Ising models.",1604.05775v1
2017-08-27,Semiclassical dynamics of spin density waves,"We present a theoretical framework for equilibrium and nonequilibrium
dynamical simulation of quantum states with spin-density-wave (SDW) order.
Within a semiclassical adiabatic approximation that retains electron degrees of
freedom, we demonstrate that the SDW order parameter obeys a generalized
Landau-Lifshitz equation. With the aid of an enhanced kernel polynomial method,
our linear-scaling quantum Landau-Lifshitz dynamics (QLLD) method enables
dynamical SDW simulations with $N \simeq 10^5$ lattice sites. Our real-space
formulation can be used to compute dynamical responses, such as dynamical
structure factor, of complex and even inhomogeneous SDW configurations at zero
or finite temperatures. Applying the QLLD to study the relaxation of a
noncoplanar topological SDW under the excitation of a short pulse, we further
demonstrate the crucial role of spatial correlations and fluctuations in the
SDW dynamics.",1708.08050v3
2017-06-15,Chaotic dynamical ferromagnetic phase induced by non-equilibrium quantum fluctuations,"We investigate the robustness of a dynamical phase transition against quantum
fluctuations by studying the impact of a ferromagnetic nearest-neighbour spin
interaction in one spatial dimension on the non-equilibrium dynamical phase
diagram of the fully-connected quantum Ising model. In particular, we focus on
the transient dynamics after a quantum quench and study the pre-thermal state
via a combination of analytic time-dependent spin-wave theory and numerical
methods based on matrix product states. We find that, upon increasing the
strength of the quantum fluctuations, the dynamical critical point fans out
into a chaotic dynamical phase within which the asymptotic ordering is
characterised by strong sensitivity to the parameters and initial conditions.
We argue that such a phenomenon is general, as it arises from the impact of
quantum fluctuations on the mean-field out of equilibrium dynamics of any
system which exhibits a broken discrete symmetry.",1706.05062v4
2017-11-06,Interplay of charge and spin dynamics after an interaction quench in the Hubbard model,"We investigate the unitary dynamics following a sudden increase $\Delta U>0$
of repulsion in the paramagnetic sector of the half-filled Hubbard model on a
Bethe lattice, by means of a variational approach that combines a Gutzwiller
wavefunction with a partial Schrieffer-Wolff transformation, both defined
through time-dependent variational parameters. Besides recovering at $\Delta
U_c$ the known dynamical transition linked to the equilibrium Mott transition,
we find pronounced dynamical anomaly at larger $\Delta U_*>\Delta U_c$
manifested in a singular behaviour of the long-time average of double
occupancy. Although the real-time dynamics of the variational parameters at
$\Delta U_*$ strongly resembles the one at $\Delta U_c$, careful frequency
spectrum analysis suggests a dynamical crossover, instead of a dynamical
transition, separating regions of a different behaviour of the spin-exchange.",1711.01840v1
2019-11-21,Coupled spin-charge dynamics in magnetic van der Waals heterostructures,"We present a phenomenological theory for coupled spin-charge dynamics in
magnetic van der Waals heterostructures. The system studied consists of a
layered antiferromagnet inserted into a capacitive vdW heterostructure. It has
been recently demonstrated that charge doping in such layered antiferromagnets
can modulate the strength, and even the sign, of exchange coupling between the
layer magnetizations. This provides a mechanism for electrically generating
magnetization dynamics. The central result we predict here is that the
magnetization dynamics reciprocally results in inducing charge dynamics. Such
dynamics makes magnetic van der Waals heterostructures interesting candidates
for spintronics applications. To this end, we also show that these systems can
be used to convert sub-THz radiation induced magnetization dynamics into
electrical signals.",1911.09688v2
2020-06-01,Dynamical quantum phase transitions in a spin chain with deconfined quantum critical points,"We analytically and numerically study the Loschmidt echo and the dynamical
order parameters in a spin chain with a deconfined phase transition between a
dimerized state and a ferromagnetic phase. For quenches from a dimerized state
to a ferromagnetic phase, we find that the model can exhibit a dynamical
quantum phase transition characterized by an associating dimerized order
parameters. In particular, when quenching the system from the Majumdar-Ghosh
state to the ferromagnetic Ising state, we find an exact mapping into the
classical Ising chain for a quench from the paramagnetic phase to the classical
Ising phase by analytically calculating the Loschmidt echo and the dynamical
order parameters. By contrast, for quenches from a ferromagnetic state to a
dimerized state, the system relaxes very fast so that the dynamical quantum
transition may only exist in a short time scale. We reveal that the dynamical
quantum phase transition can occur in systems with two broken symmetry phases
and the quench dynamics may be independent on equilibrium phase transitions.",2006.00726v2
2023-06-23,Input-driven chaotic dynamics in vortex spin-torque oscillator,"A new research topic in spintronics relating to the operation principles of
brain-inspired computing is input-driven magnetization dynamics in nanomagnet.
In this paper, the magnetization dynamics in a vortex spin-torque oscillator
(STO) driven by a series of random magnetic field are studied through a
numerical simulation of the Thiele equation. It is found that input-driven
synchronization occurs in the weak perturbation limit, as found recently. As
well, chaotic behavior is newly found to occur in the vortex core dynamics for
a wide range of parameters, where synchronized behavior is disrupted by an
intermittency. Ordered and chaotic dynamical phases are examined by evaluating
the Lyapunov exponent. The relation between the dynamical phase and the
computational capability of physical reservoir computing is also studied.",2306.13278v1
2024-03-14,Quantum analog of Landau-Lifshitz-Gilbert dynamics,"The Landau-Lifshitz-Gilbert (LLG) and Landau-Lifshitz (LL) equations play an
essential role for describing the dynamics of magnetization in solids. While a
quantum analog of the LL dynamics has been proposed in [Phys. Rev. Lett. 110,
147201 (2013)], the corresponding quantum version of LLG remains unknown. Here,
we propose such a quantum LLG equation that inherently conserves purity of the
quantum state. We examine the quantum LLG dynamics of a dimer consisting of two
interacting spin-1/2 particles. Our analysis reveals that, in the case of
ferromagnetic coupling, the evolution of initially uncorrelated spins mirrors
the classical LLG dynamics. However, in the antiferromagnetic scenario, we
observe pronounced deviations from classical behavior, underscoring the unique
dynamics of becoming a spinless state, which is non-locally correlated.
Moreover, when considering spins that are initially correlated, our study
uncovers an unusual form of transient quantum correlation dynamics, which
differ significantly from what is typically seen in open quantum systems.",2403.09255v1
2005-08-11,"Inelastic cotunneling induced decoherence and relaxation, charge and spin currents in an interacting quantum dot under a magnetic field","We present a theoretical analysis of several aspects of nonequilibirum
cotunneling through a strong Coulomb-blockaded quantum dot (QD) subject to a
finite magnetic field in the weak coupling limit. We carry this out by
developing a generic quantum Heisenberg-Langevin equation approach leading to a
set of Bloch dynamical equations which describe the nonequilibrium cotunneling
in a convenient and compact way. These equations describe the time evolution of
the spin variables of the QD explicitly in terms of the response and
correlation functions of the free reservoir variables. This scheme not only
provides analytical expressions for the relaxation and decoherence of the
localized spin induced by cotunneling, but it also facilitates evaluations of
the nonequilibrium magnetization, the charge current, and the spin current at
arbitrary bias-voltage, magnetic field, and temperature. We find that all
cotunneling events produce decoherence, but relaxation stems only from {\em
inelastic} spin-flip cotunneling processes. Moreover, our specific calculations
show that cotunneling processes involving electron transfer (both spin-flip and
non-spin-flip) contribute to charge current, while spin-flip cotunneling
processes are required to produce a net spin current in the asymmetric coupling
case. We also point out that under the influence of a nonzero magnetic field,
spin-flip cotunneling is an energy-consuming process requiring a sufficiently
strong external bias-voltage for activation, explaining the behavior of
differential conductance at low temperature: in particular, the splitting of
the zero-bias anomaly in the charge current and a broad zero-magnitude ""window""
of differential conductance for the spin current near zero-bias-voltage.",0508278v3
2009-07-23,Spin Currents in Semiconductor Nanostructures: A Nonequilibrium Green-Function Approach,"This chapter of ""The Oxford Handbook of Nanoscience and Technology: Frontiers
and Advances"" reviews nonequilibrium Green function (NEGF) approach to modeling
spin current generation, transport, and detection in semiconductor
nanostructures containing different types of spin-orbit (SO) couplings. Its
tutorial style--with examples drawn from the field of the spin Hall effects
(SHEs) and with treatment of the Rashba, Dresselhaus and extrinsic SO
couplings--offers practical recipes to compute total spin and charge currents
flowing out of the device, as well as the nonequilibrium local spin densities
and spin fluxes within the multiterminal nanostructure. These quantities, which
are obtained from the knowledge of spin-resolved NEGFs that can describe both
ballistic and diffusive transport regimes while handling phase-coherent effects
or dephasing mechanisms relevant at room temperature, can be employed to
understand recent experiments on all-electrical detection of mesoscopic and
quantum SHE in complicated low-dimensional nanostructures, as well as to model
a multitude of ""second generation"" spintronic devices exploiting coherent spin
dynamics. The chapter also provides extensive coverage of relevant technical
and computational details, such as: (i) the construction of retarded and lesser
Green functions for SO-coupled nanostructures attached to many electrodes; (ii)
computation of self-energies introduced by different types of electrodes
attached to the central region; and (iii) accelerated algorithms for NEGF
evaluation that make possible spin transport modeling in devices of the size
comparable to the spin precession length (typically few hundreds of nanometers)
that sets the scale where mesoscopic SHE effect in ballistic SO-coupled
nanostructures is expected to reach its optimal magnitude.",0907.4122v1
2013-03-05,Quantum spin liquids in the absence of spin-rotation symmetry: application to Herbertsmithite,"It has been suggested that the nearest-neighbour (NN) antiferromagnetic
Heisenberg (HAF) model on the Kagome lattice may be a good starting point to
understand the quantum spin-liquid (QSL) behaviour discovered in
Herbertsmithite. We investigate possible QSL phases in the presence of
experimentally relevant spin-rotation symmetry-breaking perturbations such as
Dzyaloshinskii-Moriya and Ising interactions, as well as second-neighbour
antiferromagnetic Heisenberg interactions. We use the projective symmetry group
analysis within the slave-fermion framework of QSL phases and systematically
classify possible QSLs in the presence of these perturbations. The dynamical
spin-structure factor for relevant QSLs is computed and their effects are
studied. Our calculations reveal dispersive features in the spin structure
factor embedded in a generally diffuse background due to the existence of
fractionalized S=1/2 excitations called spinons. For two of the previously
proposed $Z_2$ states, the dispersive features are almost absent, and diffuse
scattering dominates over a large energy window throughout the Brillouin zone.
This resembles the structure factor observed in recent inelastic neutron
scattering experiments on singlet crystals of Herbertsmithite. Furthermore, one
of the $Z_2$ states with the spin structure factor with mostly diffuse
scattering is gapped, and it may be adiabatically connected to the gapped QSL
state observed in recent DMRG calculations for the NN HAF. The above
perturbations are found to enhance the diffuse nature of the spin structure
factor and reduce the momentum dependencies of the spin gap. We also calculate
the electron spin resonance absorption spectra that further characterize the
role of spin-rotation symmetry breaking perturbations, and can shed more light
into the nature of the ground state in Herbertsmithite.",1303.1154v3
2014-11-04,Chaotic Dynamics of Stellar Spin Driven by Planets Undergoing Lidov-Kozai Oscillations: Resonances and Origin of Chaos,"Many exoplanetary systems containing hot Jupiters are found to possess
significant misalignment between the spin axis of the host star and the
planet's orbital angular momentum axis. A possible channel for producing such
misaligned hot Jupiters involves Lidov-Kozai oscillations of the planet's
orbital eccentricity and inclination driven by a distant binary companion. In a
recent work (Storch, Anderson & Lai 2014), we have shown that a proto-hot
Jupiter undergoing Lidov-Kozai oscillations can induce complex, and often
chaotic, evolution of the spin axis of its host star. Here we explore the
origin of the chaotic spin behavior and its various features in an idealized
non-dissipative system where the secular oscillations of the planet's orbit are
strictly periodic. Using Hamiltonian perturbation theory, we identify a set of
secular spin-orbit resonances in the system, and show that overlaps of these
resonances are responsible for the onset of wide-spread chaos in the evolution
of stellar spin axis. The degree of chaos in the system depends on the
adiabaticity parameter $\epsilon$, proportional to the ratio of the Lidov-Kozai
nodal precession rate and the stellar spin precession rate, and thus depends on
the planet mass, semi-major axis and the stellar rotation rate. For systems
with zero initial spin-orbit misalignment, our theory explains the occurrence
(as a function of $\epsilon$) of ""periodic islands"" in the middle of a ""chaotic
ocean"" of spin evolution, and the occurrence of restricted chaos in middle of
regular/periodic spin evolution. Finally, we discuss a novel ""adiabatic
resonance advection"" phenomenon, in which the spin-orbit misalignment, trapped
in a resonance, gradually evolves as the adiabaticity parameter slowly changes.
This phenomenon can occur for certain parameter regimes when tidal decay of the
planetary orbit is included.",1411.0739v1
2016-03-14,Action principles for higher and fractional spin gravities,"We review various off-shell formulations for interacting higher-spin systems
in dimensions 3 and 4. Associated with higher-spin systems in spacetime
dimension 4 is a Chern-Simons action for a superconnection taking its values in
a direct product of an infinite-dimensional algebra of oscillators and a
Frobenius algebra. A crucial ingredient of the model is that it elevates the
rigid closed and central two-form of Vasiliev's theory to a dynamical 2-form
and doubles the higher-spin algebra, thereby considerably reducing the number
of possible higher spin invariants and giving a nonzero effective functional
on-shell. The two action principles we give for higher-spin systems in 3D are
based on Chern-Simons and BF models. In the first case, the theory we give
unifies higher-spin gauge fields with fractional-spin fields and an internal
sector. In particular, Newton's constant is related to the coupling constant of
the internal sector. In the second case, the BF action we review gives the
fully nonlinear Prokushkin-Vasiliev, bosonic equations for matter-coupled
higher spins in 3D. We present the truncation to a single, real matter field
relevant in the Gaberdiel-Gopakumar holographic duality. The link between the
various actions we present is the fact that they all borrow ingredients from
Topological Field Theory. It has bee conjectured that there is an underlying
and unifying 2-dimensional first-quantised description of the previous
higher-spin models in 3D and 4D, in the form of a Cattaneo-Felder-like
topological action containing fermionic fields.",1603.04454v2
2016-09-28,All-optical spin switching: A new frontier in femtomagnetism -- A short review and a simple theory,"Using an ultrafast laser pulse to manipulate the spin degree of freedom has
broad technological appeal. It allows one to control the spin dynamics on a
femtosecond time scale. The discipline, commonly called femtomagnetism, started
with the pioneering experiment by Beaurepaire and coworkers in 1996, who showed
subpicosecond demagnetization occurs in magnetic Ni thin films. This finding
has motivated extensive research worldwide. All-optical helicity-dependent spin
switching (AOS) represents a new frontier in femtomagnetism, where a single
ultrafast laser pulse can permanently switch spin without any assistance from a
magnetic field. This review summarizes some of the crucial aspects of this new
discipline: key experimental findings, leading mechanisms, controversial
issues, and possible future directions. The emphasis is on our latest
investigation. We first develop the all-optical spin switching rule that
determines how the switchability depends on the light helicity. This rule
allows one to understand microscopically how the spin is reversed and why the
circularly polarized light appears more powerful than the linearly polarized
light. Then we invoke our latest spin-orbit coupled harmonic oscillator model
to simulate single spin reversal. We consider both cw excitation and pulsed
laser excitation. The results are in a good agreement with the experimental
result. We then extend the code to include the exchange interaction among
different spin sites. We show where the ""inverse Faraday field"" comes from and
how the laser affects the spin reversal nonlinearly. Our hope is that this
review will motivate new experimental and theoretical investigations and
discussions.",1609.09139v2
2014-03-11,Spin-polaron band of heavy carriersin the heavy-fermion ferromagnetic superconductor UGe2,"In strongly correlated materials, cooperative behavior of the electrons
causes a variety of quantum ordered states that may, in some cases, coexist. It
has long been believed, however, that such coexistence among ferromagnetic
ordering, superconductivity and heavy-fermion behavior is impossible, as the
first supports parallel spin alignment while the conventional understanding of
the latter two phenomena assumes spin-singlet or anti-parallel spins. This
understanding has recently been challenged by an increasing number of
observations in uranium systems (UGe2, URhGe, UIr and UCoGe) in which
superconductivity is found within a ferromagnetic state and, more
fundamentally, both ordering phenomena are exhibited by the same set of heavy
5f electrons. Since the coexistence of superconductivity and ferromagnetism is
at odds with the standard theory of phonon-mediated spin-singlet
superconductivity, it requires an alternative pairing mechanism, in which
electrons are bound into spin-triplet pairs by spin fluctuations. Within the
heavy-fermion scenario, this alternative mechanism assumes that the magnetism
has a band character and that said band forms from heavy quasiparticles
composed of f electrons. This band is expected to be responsible for all three
phenomena although its nature and the nature of those heavy quasiparticles
still remains unclear. Here we report spectroscopic evidence for the formation
in UGe2 of subnanometer-sized spin polarons whose dynamics we follow into the
paramagnetic and ferromagnetic phases. These spin polarons behave as heavy
carriers and thus may serve as heavy quasiparticles made of 5f electrons; once
coherence is established, they form a narrow spin-polaron band which thus
provides a natural reconciliation of itinerant ferromagnetism with spin-triplet
superconductivity and heavy-fermion behavior.",1403.2597v1
2020-02-11,Direct measurement of temporal correlations above the spin-glass transition by coherent resonant magnetic x-ray spectroscopy,"In the 1970s a new paradigm was introduced that interacting quenched systems,
such as a spin-glass, have a phase transition in which long time memory of
spatial patterns is realized without spatial correlations. The principal
methods to study the spin-glass transition, besides some elaborate and elegant
theoretical constructions, have been numerical computer simulations and neutron
spin echo measurements . We show here that the dynamical correlations of the
spin-glass transition are embedded in measurements of the four-spin
correlations at very long times. This information is directly available in the
temporal correlations of the intensity, which encode the spin-orientation
memory, obtained by the technique of resonant magnetic x-ray photon correlation
spectroscopy (RM- XPCS). We have implemented this method to observe and
accurately characterize the critical slowing down of the spin orientation
fluctuations in the classic metallic spin glass alloy Cu(Mn) over time scales
of 1 to 1000 secs. Our method opens the way for studying phase transitions in
systems such as spin ices, and quantum spin liquids, as well as the structural
glass transition.",2002.04259v1
2021-12-25,Spin-tunable thermoelectric performance in monolayer chromium pnictides,"Historically, finding two-dimensional (2D) magnets is well known to be a
difficult task due to instability against thermal spin fluctuations. Metals are
also normally considered poor thermoelectric (TE) materials. Combining
intrinsic magnetism in two dimensions with conducting properties, one may
expect to get the worst for thermoelectrics. However, we will show this is not
always the case. Here, we investigate spin-dependent TE properties of monolayer
chromium pnictides (CrX, where X = P, As, Sb, and Bi) using first-principles
calculations of electrons and phonons, along with Boltzmann transport formalism
under energy-dependent relaxation time approximation. All the CrX monolayers
are dynamically stable and they also exhibit half metallicity with
ferromagnetic ordering. Using the spin-valve setup with antiparallel spin
configuration, the half metallicity and ferromagnetism in monolayer CrX enable
manipulation of spin degrees of freedom to tune the TE figure of merit (ZT). At
optimized chemical potential and operating temperature of 500 K, the maximum ZT
values (= 0.22, 0.12, and 0.09) with the antiparallel spin-valve setup in CrAs,
CrSb, and CrBi improve up to almost twice the original values (ZT = 0.12, 0.08,
and 0.05) without the spin-valve configuration. Only in CrP, which is the
lightest species and less spin-polarized among CrX, the maximum ZT (= 0.34)
without the spin-valve configuration is larger than that (= 0.19) with the
spin-valve one. We also find that, at 500 K, all the CrX monolayers possess
exceptional TE power factors of about 0.02-0.08 W/m.K2, which could be one of
the best values among 2D conductors.",2112.13229v2
2022-03-03,Spin Hall effects and the localization of massless spinning particles,"The spin Hall effects of light represent a diverse class of
polarization-dependent physical phenomena involving the dynamics of
electromagnetic wave packets. In a medium with an inhomogeneous refractive
index, wave packets can be effectively described by massless spinning particles
following polarization-dependent trajectories. Similarly, in curved spacetime
the gravitational spin Hall effect of light is represented by
polarization-dependent deviations from null geodesics. In this paper, we
analyze the equations of motion describing the gravitational spin Hall effect
of light. We show that these equations are a special case of the
Mathisson-Papapetrou equations for spinning objects in general relativity. This
allows us to use several known results for the Mathisson-Papapetrou equations,
and apply them to the study of electromagnetic wave packets. We derive
conservation laws, we discuss the limits of validity of the spin Hall
equations, and we study how the energy centroids of wave packets, effectively
described as massless spinning particles, depend on the external choice of a
timelike vector field, representing a family of observers. In flat spacetime,
the relativistic Hall effect and the Wigner(-Souriau) translations are
recovered, while our equations also provide a generalization of these effects
in arbitrary spacetimes. We construct a large class of wave packets that can be
described by the spin Hall equations, but also find its limits by giving
examples of wave packets which are more general and are not described by the
spin Hall equations. Lastly, we examine the assumption that electromagnetic
wave packets are massless. While this is approximately true in many contexts,
it is not exact. We show that failing to carefully account for the limitations
of the massless approximation results in the appearance of unphysical centroids
which are nowhere near the wave packet itself.",2203.01753v2
2022-10-13,Electron-mediated entanglement of two distant macroscopic ferromagnets within a nonequilibrium spintronic device,"Using the nascent concept of quantum spin-transfer torque [A. Zholud et al.,
Phys. Rev. Lett. {\bf 119}, 257201 (2017); M. D. Petrovi\'{c} {\em et al.},
Phys. Rev. X {\bf 11}, 021062 (2021)], we demonstrate that a current pulse can
be harnessed to entangle quantum localized spins of two spatially separated
ferromagnets (FMs) which are initially unentangled. The envisaged setup
comprises a spin-polarizer (FM$_p$) and a spin-analyzer (FM$_a$) FM layers
separated by normal metal (NM) spacer. The injection of a current pulse into
the device leads to a time-dependent superposition of many-body states
characterized by a high degree of entanglement between the spin degrees of
freedom of the two distant FM layers. The non-equilibrium dynamics are due to
the transfer of spin angular momentum from itinerant electrons to the localized
spins via a quantum spin-torque mechanism that remains active even for {\em
collinear but antiparallel} arrangements of the FM$_p$ and FM$_a$
magnetizations (a situation in which the conventional spin-torque is absent).
We quantify the mixed-state entanglement generated between the FM layers by
tracking the time-evolution of the full density matrix and analyzing the
build-up of the mutual logarithmic negativity over time. The effect of
decoherence and dissipation in the FM layers due to coupling to bosonic baths
at finite temperature, the use of multi-electron current pulses and the
dependence on the number of spins are also considered in an effort to ascertain
the robustness of our predictions under realistic conditions. Finally, we
propose a ``current-pump/X-ray-probe'' scheme, utilizing ultrafast X-ray
spectroscopy, that can witness nonequilibrium and transient entanglement of the
FM layers by extracting its time-dependent quantum Fisher information.",2210.06634v2
2003-02-18,Microstructure and velocity of field-driven Ising interfaces moving under a soft stochastic dynamic,"We present theoretical and dynamic Monte Carlo simulation results for the
mobility and microscopic structure of 1+1-dimensional Ising interfaces moving
far from equilibrium in an applied field under a single-spin-flip ``soft''
stochastic dynamic. The soft dynamic is characterized by the property that the
effects of changes in field energy and interaction energy factorize in the
transition rate, in contrast to the nonfactorizing nature of the traditional
Glauber and Metropolis rates (``hard'' dynamics). This work extends our
previous studies of the Ising model with a hard dynamic and the unrestricted
SOS model with soft and hard dynamics. [P.A. Rikvold and M. Kolesik, J. Stat.
Phys. 100, 377 (2000); J. Phys. A 35, L117 (2002); Phys. Rev. E 66, 066116
(2002).] The Ising model with soft dynamics is found to have closely similar
properties to the SOS model with the same dynamic. In particular, the local
interface width does not diverge with increasing field, as it does for hard
dynamics. The skewness of the interface at nonzero field is very weak and has
the opposite sign of that obtained with hard dynamics.",0302369v1
2004-04-28,Stochastic dynamics and the dynamic phase transition in thin ferromagnetic films,"The dynamic phase behavior of a classical Heisenberg spin system with a
bilinear exchange anisotropy in a planar thin film geometry has been
investigated by Monte Carlo simulations using different forms for the
stochastic dynamics. In simulations of the dynamic phase transition (DPT) in
films subject to a pulsed oscillatory external field with competing surface
fields, both Glauber and Metropolis dynamics show a continuous DPT. Furthermore
the field amplitude dependence of the DPT is qualitatively similar for both
Glauber and Metropolis dynamics. However, the temperature dependence of the DPT
is markedly different with the DPT being much sharper for Glauber dynamics. The
difference arises from a decoupling of the surface and bulk responses of the
film near the dynamic phase transition with Metropolis dynamics that is not
evident for Glauber dynamics.",0404686v1
2015-10-19,Dynamic Rotation and Stretch Tensors from a Dynamic Polar Decomposition,"The local rigid-body component of continuum deformation is typically
characterized by the rotation tensor, obtained from the polar decomposition of
the deformation gradient. Beyond its well-known merits, the polar rotation
tensor also has a lesser known dynamical inconsistency: it does not satisfy the
fundamental superposition principle of rigid-body rotations over adjacent time
intervals. As a consequence, the polar rotation diverts from the observed mean
material rotation of fibers in fluids, and introduces a purely kinematic memory
effect into computed material rotation. Here we derive a generalized polar
decomposition for linear processes that yields a unique, dynamically consistent
rotation component, the dynamic rotation tensor, for the deformation gradient.
The left dynamic stretch tensor is objective, and shares the principal strain
values and axes with its classic polar counterpart. Unlike its classic polar
counterpart, however, the dynamic stretch tensor evolves in time without spin.
The dynamic rotation tensor further decomposes into a spatially constant mean
rotation tensor and a dynamically consistent relative rotation tensor that is
objective for planar deformations. We also obtain simple expressions for
dynamic analogues of Cauchy's mean rotation angle that characterize a deforming
body objectively.",1510.05367v1
2021-01-21,Topological holographic quench dynamics in a synthetic dimension,"The notion of topological phases extended to dynamical systems stimulates
extensive studies, of which the characterization of non-equilibrium topological
invariants is a central issue and usually necessitates the information of
quantum dynamics in both the time and spatial dimensions. Here we combine the
recently developed concepts of the dynamical classification of topological
phases and synthetic dimension, and propose to efficiently characterize
photonic topological phases via holographic quench dynamics. A pseudo spin
model is constructed with ring resonators in a synthetic lattice formed by
frequencies of light, and the quench dynamics is induced by initializing a
trivial state which evolves under a topological Hamiltonian. Our key prediction
is that the complete topological information of the Hamiltonian is extracted
from quench dynamics solely in the time domain, manifesting holographic
features of the dynamics. In particular, two fundamental time scales emerge in
the quench dynamics, with one mimicking the Bloch momenta of the topological
band and the other characterizing the residue time evolution of the state after
quench. For this a dynamical bulk-surface correspondence is obtained in time
dimension and characterizes the topology of the spin model. This work also
shows that the photonic synthetic frequency dimension provides an efficient and
powerful way to explore the topological non-equilibrium dynamics.",2101.08606v2
2005-04-13,Environmentally induced Quantum Dynamical Phase Transition in the spin swapping operation,"Quantum Information Processing relies on coherent quantum dynamics for a
precise control of its basic operations. A swapping gate in a two-spin system
exchanges the degenerate states |+,-> and |-,+>. In NMR, this is achieved
turning on and off the spin-spin interaction b=\Delta E that splits the energy
levels and induces an oscillation with a natural frequency \Delta E/\hbar.
Interaction of strength \hbar/\tau_{SE}, with an environment of neighboring
spins, degrades this oscillation within a decoherence time scale \tau_{\phi}.
While the experimental frequency \omega and decoherence time \tau_{\phi} were
expected to be roughly proportional to b/\hbar and \tau_{SE} respectively, we
present here experiments that show drastic deviations in both \omega and
\tau_{\phi}. By solving the many spin dynamics, we prove that the swapping
regime is restricted to \Delta E \tau_{SE} > \hbar. Beyond a critical
interaction with the environment the swapping freezes and the decoherence rate
drops as 1/\tau_{\phi} \propto (b/\hbar)^2 \tau_{SE}. The transition between
quantum dynamical phases occurs when \omega \propto
\sqrt{(b/\hbar)^{2}-(k/\tau_{SE})^2} becomes imaginary, resembling an
overdamped classical oscillator. Here, 0<k^2<1 depends only on the anisotropy
of the system-environment interaction, being 0 for isotropic and 1 for XY
interactions. This critical onset of a phase dominated by the Quantum Zeno
effect opens up new opportunities for controlling quantum dynamics.",0504347v4
2013-04-19,Combining heavy quark spin and local hidden gauge symmetries in the dynamical generation of hidden charm baryons,"We present a coupled channel unitary approach to obtain states dynamically
generated from the meson baryon interaction with hidden charm, using
constraints of heavy quark spin symmetry. We use as basis of states, $\bar D
B$, $\bar D^* B$ states, with $B$ baryon charmed states belonging to the 20
representations of SU(4) with $J^P=1/2^+,~3/2^+$. In addition we also include
the $\eta_c N$ and $J/\psi N$ states. The inclusion of these coupled channels
is demanded by heavy quark spin symmetry, since in the large $m_Q$ limit the
$D$ and $D^*$ states are degenerate and are obtained from each other by means
of a spin rotation, under which QCD is invariant. The novelty in the work is
that we use dynamics from the extrapolation of the local hidden gauge model to
SU(4) and we show that this dynamics fully respects the constraints of heavy
quark spin symmetry.
  With the full space of states demanded by the heavy quark spin symmetry and
the dynamics of the local hidden gauge we look for states dynamically generated
and find four basic states which are bound, corresponding to $\bar D \Sigma_c$,
$\bar D \Sigma_c^*$, $\bar D^* \Sigma_c$ and $\bar D^* \Sigma_c^*$, decaying
mostly into $\eta_c N$ and $J/\psi N$. All the states appear in isospin $I=1/2$
and we find no bound states or resonances in $I=3/2$. The $\bar D \Sigma_c$
state appears in $J=1/2$, the $\bar D \Sigma_c^*$ in $J=3/2$, the $\bar D^*
\Sigma_c$ appears nearly degenerate in $J=1/2, ~3/2$ and the $\bar D^*
\Sigma_c^*$ appears nearly degenerate in $J=1/2, ~3/2, ~5/2$, with the
peculiarity that in $J=5/2$ the state has zero width in the space of states
chosen. All the states are bound with about 50 MeV with respect to the
corresponding $\bar D B$ thresholds and the width, except for the $J=5/2$
state, is also of the same order of magnitude.",1304.5368v1
2018-04-09,The exact dynamical Chern Simons metric for a spinning black hole possesses a fourth constant of motion: A Dynamical-Systems-Based Conjecture,"The recent gravitational wave observations by the LIGO/Virgo collaboration
have allowed the first tests of General Relativity in the extreme gravity
regime, when comparable-mass black holes and neutron stars collide. Future
space-based detectors, such as the Laser Interferometer Space Antenna, will
allow tests of Einstein's theory with gravitational waves emitted when a small
black hole falls into a supermassive one in an extreme mass-ratio inspiral. One
particular test that is tailor-made for such inspirals is the search for chaos
in extreme gravity. We here study whether chaos is present in the motion of
test particles around spinning black holes of parity-violating modified
gravity, focusing in particular on dynamical Chern-Simons gravity. We develop a
resummation strategy that restores all spin terms in the General Relativity
limit, while retaining up to fifth-order-in-spin terms in the dynamical
Chern-Simons corrections to the Kerr metric. We then calculate Poincar\'e
surfaces of section and rotation numbers of a wide family of geodesics of this
resummed metric. We find no evidence for geodesic chaos, with at most
deformations of the resonant torii that shrink as terms of higher-order in spin
are included in the dynamical Chern-Simons corrections to the Kerr metric. Our
numerical findings suggest that the geodesics of the as-of-yet unknown exact
solution for spinning black holes in this theory may be integrable, and that
there may thus exist a fourth integral of motion associated with this exact
solution. The studies presented here begin to lay the foundations for chaotic
tests of General Relativity with the observation of extreme mass ratio
inspirals with the Laser Interferometer Space Antenna.",1804.04002v2
2020-07-26,Bayesian Dynamic Mapping of an Exo-Earth from Photometric Variability,"Photometric variability of a directly imaged exo-Earth conveys spatial
information on its surface and can be used to retrieve a two-dimensional
geography and axial tilt of the planet (spin-orbit tomography). In this study,
we relax the assumption of the static geography and present a computationally
tractable framework for dynamic spin-orbit tomography applicable to the
time-varying geography. First, a Bayesian framework of static spin-orbit
tomography is revisited using analytic expressions of the Bayesian inverse
problem with a Gaussian prior. We then extend this analytic framework to a
time-varying one through a Gaussian process in time domain, and present
analytic expressions that enable efficient sampling from a full joint posterior
distribution of geography, axial tilt, spin rotation period, and
hyperparameters in the Gaussian-process priors. Consequently, it only takes 0.3
s for a laptop computer to sample one posterior dynamic map conditioned on the
other parameters with 3,072 pixels and 1,024 time grids, for a total of $\sim 3
\times 10^6$ parameters. We applied our dynamic mapping method on a toy model
and found that the time-varying geography was accurately retrieved along with
the axial-tilt and spin rotation period. In addition, we demonstrated the use
of dynamic spin-orbit tomography with a real multi-color light curve of the
Earth as observed by the Deep Space Climate Observatory. We found that the
resultant snapshots from the dominant component of a principle component
analysis roughly captured the large-scale, seasonal variations of the clear-sky
and cloudy areas on the Earth.",2007.13096v1
2017-07-14,Nonequilibrium phase transition in spin-S Ising ferromagnet driven by Propagating and Standing magnetic field wave,"The dynamical response of spin-S (S=1, 3/2, 2, 3) Ising ferromagnet to the
plane propagating wave , standing magnetic field wave and uniformly oscillating
field with constant frequency are studied separately in two dimensions by
extensive Monte Carlo simulation. Depending upon the strength of the magnetic
field and the value of the spin state of the Ising spin lattice two different
dynamical phases are observed. For a fixed value of S and the amplitude of the
propagating magnetic field wave the system undergoes a dynamical phase
transition from propagating phase to pinned phase as the temperature of the
system is cooled down. Similarly in case with standing magnetic wave the system
undergoes dynamical phase transition from high temperature phase where spins
oscillates coherently in alternate bands of half wavelength of the standing
magnetic wave to the low temperature pinned or spin frozen phase. For a fixed
value of the amplitude of magnetic field oscillation the transition temperature
is observed to decrease to a limiting value as the value of spin S is
increased. The time averaged magnetisation over a full cycle of the magnetic
field oscillation plays the role of the dynamic order parameter. A
comprehensive phase boundary is drawn in the plane of magnetic field amplitude
and dynamic transition temperature. It is found that the phase boundary shrinks
inwards for high value of spin state S. Also in the low temperature (and high
field) region the phase boundaries are closely spaced.",1707.04404v4
1992-12-09,Dynamical Properties of a Haldane Gap Antiferromagnet,"We study the dynamic spin correlation function of a spin one
antiferromagnetic chain with easy-plane single-ion anisotropy. We use exact
diagonalization by the Lancz\H os method for chains of lengths up to N=16
spins. We show that a single-mode approximation is an excellent description of
the dynamical properties. A variational calculation allows us to clarify the
nature of the excitations. The existence of a two-particle continuum near zero
wavevector is clearly seen both in finite-size effects and in the dynamical
structure factor. The recent neutron scattering experiments on the
quasi-one-dimensional antiferromagnet NENP are fully explained by our results.",9212014v1
1995-07-25,Order-Parameter Flow in the SK Spin-Glass II: Inclusion of Microscopic Memory Effects,"We develop further a recent dynamical replica theory to describe the dynamics
of the Sherrington-Kirkpatrick spin-glass in terms of closed evolution
equations for macroscopic order parameters. We show how microscopic memory
effects can be included in the formalism through the introduction of a dynamic
order parameter function: the joint spin-field distribution. The resulting
formalism describes very accurately the relaxation phenomena observed in
numerical simulations, including the typical overall slowing down of the flow
that was missed by the previous simple two-parameter theory. The advanced
dynamical replica theory is either exact or a very good approximation.",9507108v2
1999-03-08,Ultrametricity in 3D Edwards-Anderson spin glasses,"We perform an accurate test of Ultrametricity in the aging dynamics of the
three dimensional Edwards-Anderson spin glass. Our method consists in
considering the evolution in parallel of two identical systems constrained to
have fixed overlap. This turns out to be a particularly efficient way to study
the geometrical relations between configurations at distant large times. Our
findings strongly hint towards dynamical ultrametricity in spin glasses, while
this is absent in simpler aging systems with domain growth dynamics. A recently
developed theory of linear response in glassy systems allows to infer that
dynamical ultrametricity implies the same property at the level of equilibrium
states.",9903130v2
1999-09-29,Spin picture of the one-dimensional Hubbard model: Two-fluid structure and phase dynamics,"We propose a scheme for investigating the quantum dynamics of interacting
electron models by means of time-dependent variational principle and spin
coherent states of space lattice operators. We apply such a scheme to the
one-dimensional hubbard model, and solve the resulting equations in different
regimes. In particular, we find that at low densities the dynamics is mapped
into two coupled nonlinear Schroedinger equations, whereas near half-filling
the model is described by two coupled Josephson junction arrays. Focusing then
to the case in which only the phases of the spin variables are dynamically
active, we examine a number of different solutions corresponding to the
excitations of few macroscopic modes. Based on fixed point equation of the
simpler among them, we show that the standard one-band ground state phase space
is found.",9909435v1
1999-12-20,Spin dynamics simulations - a powerful method for the study of critical dynamics,"Spin-dynamics techniques can now be used to study the deterministic
time-dependent behavior of magnetic systems containing over 10^5 spins with
quite good accuracy. This approach will be introduced, including the
theoretical foundations of the methods of analysis. Then newly developed,
improved techniques based upon Suzuki-Trotter decomposition methods will be
described. The current ``state-of-the-art'' will be evaluated with specific
examples drawn from data on simple magnetic models. The examination of dynamic
critical behavior will be highlighted but the extraction of information about
excitations at low temperatures will be included.",9912375v1
2001-02-08,Mechanisms of Decoherence at Low Temperatures,"We briefly review the oscillator and spin bath models of quantum
environments, which can be used to describe the low-energy dynamics of open
quantum systems. We then use them to discuss both the mechanisms causing
decoherence at low $T$, and the dynamics of this decoherence. This is done
first for a central 2-level system coupled to these environments- the results
can be applied to the dynamics of quantum nanomagnets and superconducting
SQUIDs, where large-scale tunneling of magnetisation and flux take place.
Decoherence in these systems is caused principally by coupling to electrons and
nuclear spins, the spin bath couplings are particularly dangerous at low $T$.
  These models are also generalised to discuss quantum measurements in which
the measured system, the measuring apparatus, and the environment are treated
quantum mechanically. The results can be used to calculate the dynamics of
coupled SQUIDs and/or nanomagnets, in which one acts as a measuring apparatus
and the other exhibits large-scale quantum superpositions. The same model can
be used to describe coupled qubits.",0102156v2
2001-09-20,Spin dynamics of a one-dimensional spin-1/2 fully anisotropic Ising-like antiferromagnet in a transverse magnetic field,"We consider the one-dimensional Ising-like fully anisotropic S=1/2 Heisenberg
antiferromagnetic Hamiltonian and study the dynamics of domain wall excitations
in the presence of transverse magnetic field $h_x$. We obtain dynamical spin
correlation functions along the magnetic field $S^{xx}(q,\omega)$ and
perpendicular to it $S^{yy}(q,\omega)$. It is shown that the line shapes of
$S^{xx}(q,\omega)$ and $S^{yy}(q,\omega)$ are purely symmetric at the
zone-boundary. It is observed in $S^{yy}(q,\omega)$ for $\pi/2<q<\pi$ that the
spectral weight moves toward low energy side with the increase of $h_x$. This
model is applicable to study the spin dynamics of CsCoCl$_3$ in the presence of
weak interchain interactions.",0109364v1
2002-05-28,Dynamical structure factors of $S=1/2$ two-leg spin ladder systems,"We investigate dynamical properties of $S=1/2$ two-leg spin ladder systems.
In a strong coupling region, an isolated mode appears in the lowest excited
states, while in a weak coupling region, an isolated mode is reduced and the
lowest excited states become a lower bound of the excitation continuum. We find
in the system with equal intrachain and interchain couplings that due to a
cyclic four-spin interaction, the distribution of the weights for the dynamical
structure factor and characteristics of the lowest excited states are strongly
influenced. The dynamical properties of two systems proposed for ${\rm
SrCu_2O_3}$ are also discussed.",0205576v2
2003-04-24,Dynamical domain walls and spin-Peierls order in doped antiferromagnets: evidence from exact diagonalization of small clusters,"The hole-doped 2D t-J model is studied by exact diagonalization on a 5 x 4
cluster which, unlike the standard tilted square clusters, can in principle
accomodate an antiphase domain wall. For hole concentration 10% and J/t >= 0.5
the ground state energy/site is lower than the conventional tilted square
20-site-cluster. In the ground state two holes form a loosely bound pair pinned
to an antiphase domain wall. The dynamical density correlation function shows
sharp quasiparticle-like peaks, reminiscent of the `holons' in 1D chains, which
suggest the existence of soliton-like, propagating domain walls. The dynamical
correlation function of the bond-singlet operator has a low-energy peak
structure characteristic of columnar Spin-Peierls order, the dynamical spin
correlation function shows an intense and isolated `resonance peak' near
(pi,pi).",0304554v1
2003-06-29,Dynamical CPA approach to an itinerant fermionic spin glass model,"We study a fermionic version of the Sherrington-Kirkpatrick model including
nearest-neighbor hopping on a $\infty$-dimensional simple cubic lattices. The
problem is reduced to one of free fermions moving in a dynamical effective
random medium. By means of a CPA method we derive a set of self-consistency
equations for the spin glass order parameter and for the Fourier components of
the local spin susceptibility. In order to solve these equations numerically we
employ an approximation scheme which restricts the dynamics to a feasible
number of the leading Fourier components. From a sequence of systematically
improved dynamical approximations we estimate the location of the quantum
critical point.",0306720v2
2003-10-15,Quasiparticle Relaxation Dynamics in Two Distinct Gap Structures: La$_{0.67}$Ca$_{0.33}$MnO$_{3}$ and LaMnO$_{3}$,"The spin and quasiparticle relaxation dynamics in
La$_{0.67}$Ca$_{0.33}$MnO$_{3}$ and LaMnO$_{3}$ single crystals and thin films
is investigated as a function of temperature and magnetic field by pump-probe
spectroscopy. The unusually slow spin-lattice relaxation dynamics is governed
by the temperature- and magnetic field- dependent pseudogap in
La$_{0.67}$Ca$_{0.33}$MnO$_{3}$, and by the temperature-independent Jahn-Teller
gap in LaMnO$_{3}$. Our results show that the coupled dynamics of charge, spin
and lattice is strongly correlated with the distinct gap structures in these
manganites.",0310359v1
2005-04-13,Dynamical replica analysis of disordered Ising spin systems on finitely connected random graphs,"We study the dynamics of macroscopic observables such as the magnetization
and the energy per degree of freedom in Ising spin models on random graphs of
finite connectivity, with random bonds and/or heterogeneous degree
distributions. To do so we generalize existing implementations of dynamical
replica theory and cavity field techniques to systems with strongly disordered
and locally tree-like interactions. We illustrate our results via application
to the dynamics of e.g. $\pm J$ spin-glasses on random graphs and of the
overlap in finite connectivity Sourlas codes. All results are tested against
Monte Carlo simulations.",0504313v1
2005-05-24,Sum rules for four-spinon dynamic structure factor in XXX model,"In the context of the antiferromagnetic spin 1/2 Heisenberg quantum spin
chain (XXX model), we estimate the contribution of the exact four-spinon
dynamic structure factor $S_4$ by calculating a number of sum rules the total
dynamic structure factor $S$ is known to satisfy exactly. These sum rules are:
the static susceptibility, the integrated intensity, the total integrated
intensity, the first frequency moment and the nearest-neighbor correlation
function. We find that the contribution of $S_4$ is between 1% and 2.5%,
depending on the sum rule, whereas the contribution of the exact two-spinon
dynamic structure factor $S_2$ is between 70% and 75%. This is consistent with
the expected scattering weight of states from outside the spin-wave continuum.
The calculations are numerical and Monte Carlo based. Good statistics are
obtained.",0505594v1
2006-03-16,Direct evidence for a dynamical ground state in the highly frustrated Tb$_2$Sn$_2$O$_7$ pyrochlore,"MuSR experiments have been performed on powder sample of the ""ordered spin
ice"" Tb$_2$Sn$_2$O$_7$ pyrochlore compound. At base temperature (T=35mK) the
muon relaxation is found to be of dynamical nature which demonstrates that
strong fluctuations persist below the ferromagnetic transition (T_C=0.87K).
Hints of long range order appear as oscillations of the muon polarization when
an external field is applied and also as a hysteretic behavior below T_C. We
propose a dynamical and strongly correlated scenario where dynamics results
from fluctuation of large spin clusters with the ""ordered spin ice"" structure.",0603434v1
2006-11-20,Current Induced Order Parameter Dynamics: Microscopic Theory Applied to Co/Cu/Co spin valves,"Transport currents can alter alter order parameter dynamics and change steady
states in superconductors, in ferromagnets, and in hybrid systems. In this
article we present a scheme for fully microscopic evaluation of order parameter
dynamics that is intended for application to nanoscale systems. The approach
relies on time-dependent mean-field-theory, on an adiabatic approximation, and
on the use of non-equilibrium Greens function (NEGF) theory to calculate the
influence of a bias voltage across a system on its steady-state density matrix.
We apply this scheme to examine the spin-transfer torques which drive
magnetization dynamics in Co/Cu/Co spin-valve structures. Our microscopic
torques are peaked near Co/Cu interfaces, in agreement with most previous
pictures, but suprisingly act mainly on Co transition metal $d$-orbitals rather
than on $s$-orbitals as generally supposed.",0611534v1
2006-12-25,Dynamics of two qubits in a spin-bath of Quantum anisotropic Heisenberg XY coupling type,"The dynamics of two 1/2-spin qubits under the influence of a quantum
Heisenberg XY type spin-bath is studied. After the Holstein-Primakoff
transformation, a novel numerical polynomial scheme is used to give the
time-evolution calculation of the center qubits initially prepared in a product
state or a Bell state. Then the concurrence of the two qubits, the
$z$-component moment of either of the subsystem spins and the fidelity of the
subsystem are shown, which exhibit sensitive dependence on the anisotropic
parameter, the temperature, the coupling strength and the initial state. It is
found that (i) the larger the anisotropic parameter $\gamma$, the bigger the
probability of maintaining the initial state of the two qubits; (ii) with
increasing temperature $T$, the bath plays a more strong destroy effect on the
dynamics of the subsystem, so does the interaction $g_0$ between the subsystem
and the bath; (iii) the time evolution of the subsystem is dependent on the
initial state. The revival of the concurrence does not always means the restore
of the state. Further, the dynamical properties of the subsystem should be
judged by the combination of concurrence and fidelity.",0612619v2
1993-08-05,Dynamics of Moving and Spinning Skyrmions,"We study the intermediate- and long-range forces between moving and spinning
Skyrmions, employing two different methods. One uses a relativised product
ansatz for the Skyrme fields, the other models Skyrmions as triplets of scalar
dipoles. The methods lead to the same finite-dimensional Lagrangian dynamical
system which may be interpreted as a point-particle approximation to Skyrmion
dynamics. We discuss in detail the dynamics in the so-called attractive channel
and the interaction between well-separated and rapidly spinning Skyrmions, and
point out the resemblance between the latter and the one-pion exchange
potential in nuclear physics.",9308236v2
2005-11-13,The co-evolutionary dynamics of directed network of spin market agents,"The spin market model [S. Bornholdt, Int.J.Mod.Phys. C 12 (2001) 667] is
extended into co-evolutionary version, where strategies of interacting and
competitive traders are represented by local and global couplings between the
nodes of dynamic directed stochastic network. The co-evolutionary principles
are applied in the frame of Bak - Sneppen self-organized dynamics [P. Bak, K.
Sneppen, Phys. Rev. Letter 71 (1993) 4083] that includes the processes of
selection and extinction actuated by the local (node) fitness. The local
fitness is related to orientation of spin agent with respect to instant
magnetization. The stationary regime characterized by a fat tailed distribution
of the log-price returns with index $\alpha\simeq 3.6$ (out of the Levy range)
is identified numerically. The non-trivial consequence of the extremal dynamics
is the partially power-law decay (an effective exponent varies between -0.3 and
-0.6) of the autocorrelation function of volatility. Broad-scale network
topology with node degree distribution characterized by the exponent
$\gamma=1.8$ from the range of social networks is obtained.",0511024v1
2004-08-20,Fault-Tolerant Quantum Dynamical Decoupling,"Dynamical decoupling pulse sequences have been used to extend coherence times
in quantum systems ever since the discovery of the spin-echo effect. Here we
introduce a method of recursively concatenated dynamical decoupling pulses,
designed to overcome both decoherence and operational errors. This is important
for coherent control of quantum systems such as quantum computers. For
bounded-strength, non-Markovian environments, such as for the spin-bath that
arises in electron- and nuclear-spin based solid-state quantum computer
proposals, we show that it is strictly advantageous to use concatenated, as
opposed to standard periodic dynamical decoupling pulse sequences. Namely, the
concatenated scheme is both fault-tolerant and super-polynomially more
efficient, at equal cost. We derive a condition on the pulse noise level below
which concatenated is guaranteed to reduce decoherence.",0408128v3
2007-05-03,Planar spin-transfer device with a dynamic polarizer,"In planar nano-magnetic devices magnetization direction is kept close to a
given plane by the large easy-plane magnetic anisotropy, for example by the
shape anisotropy in a thin film. In this case magnetization shows effectively
in-plane dynamics with only one angle required for its description. Moreover,
the motion can become overdamped even for small values of Gilbert damping. We
derive the equations of effective in-plane dynamics in the presence of
spin-transfer torques. The simplifications achieved in the overdamped regime
allow to study systems with several dynamic magnetic pieces (``free layers'').
A transition from a spin-transfer device with a static polarizer to a device
with two equivalent magnets is observed. When the size difference between the
magnets is less than critical, the device does not exhibit switching, but goes
directly into the ``windmill'' precession state.",0705.0406v1
2007-07-20,Socio-economical dynamics as a solvable spin system on co-evolving networks,"We consider social systems in which agents are not only characterized by
their states but also have the freedom to choose their interaction partners to
maximize their utility. We map such systems onto an Ising model in which spins
are dynamically coupled by links in a dynamical network. In this model there
are two dynamical quantities which arrange towards a minimum energy state in
the canonical framework: the spins, s_i, and the adjacency matrix elements,
c_{ij}. The model is exactly solvable because microcanonical partition
functions reduce to products of binomial factors as a direct consequence of the
c_{ij} minimizing energy. We solve the system for finite sizes and for the two
possible thermodynamic limits and discuss the phase diagrams.",0707.3085v3
2009-07-22,Shedding light on non-equilibrium dynamics of a spin coupled to fermionic reservoir,"A single confined spin interacting with a solid-state environment has emerged
as one of the fundamental paradigms of mesoscopic physics. In contrast to
standard quantum optical systems, decoherence that stems from these
interactions can in general not be treated using the Born-Markov approximation
at low temperatures. Here we study the non-equilibrium dynamics of a
single-spin in a semiconductor quantum dot adjacent to a fermionic reservoir
and show how the dynamics can be revealed in detail in an optical absorption
experiment. We show that the highly asymmetrical optical absorption lineshape
of the resulting Kondo exciton consists of three distinct frequency domains,
corresponding to short, intermediate and long times after the initial
excitation, which are in turn described by the three fixed points of the
single-impurity Anderson Hamiltonian. The zero-temperature power-law
singularity dominating the lineshape is linked to dynamically generated Kondo
correlations in the photo-excited state. We show that this power-law
singularity is tunable with gate voltage and magnetic field, and universal.",0907.3854v1
2009-11-03,Evidence for Dynamic Phase Separation and High Energy Spin Dynamics in underdoped La$_{2-x}$Sr$_x$CuO$_4$ from Resonant Inelastic X-Ray Scattering,"We probe the collective magnetic modes of La$_2$CuO$_4$ (LCO) and underdoped
La$_{2-x}$Sr$_x$CuO$_4$ (LSCO) by momentum resolved Resonant Inelastic X-ray
Scattering (RIXS) at the Cu $L_3$ edge. In LCO the single magnon dispersion
measured by RIXS coincides with the one determined by inelastic neutron
scattering. For LSCO the spin dynamics shows a branch dispersing up to
$\sim$400 meV coexisting with a branch at lower energy. Only the latter has
been observed with neutrons so far and is considered a key signature of doped
cuprates. The presence of the high-energy branch indicates that LSCO is in a
dynamic inhomogeneous spin state.",0911.0621v1
2009-11-06,Spectral responses in granular compaction,"The slow compaction of a gently tapped granular packing is reminiscent of the
low-temperature dynamics of structural and spin glasses. Here, I probe the
dynamical spectrum of granular compaction by measuring a complex
(frequency-dependent) volumetric susceptibility $\tilde{\chi}_v$. While the
packing density $\rho$ displays glass-like slow relaxations (aging) and
history-dependence (memory) at low tapping amplitudes, the susceptibility
$\tilde{\chi}_v$ displays very weak aging effects, and its spectrum shows no
sign of a rapidly growing timescale. These features place $\tilde{\chi}_v$ in
sharp contrast to its dielectric and magnetic counterparts in structural and
spin glasses; instead, $\tilde\chi_v$ bears close similarities to the complex
specific heat of spin glasses. This, I suggest, indicates the glass-like
dynamics in granular compaction are governed by statistically rare relaxation
processes that become increasingly separated in timescale from the typical
relaxations of the system. Finally, I examine the effect of finite system size
on the spectrum of compaction dynamics. Starting from the ansatz that low
frequency processes correspond to large scale particle rearrangements, I
suggest the observed finite size effects are consistent with the suppression of
large-scale collective rearrangements in small systems.",0911.1376v1
2009-11-24,Spin Glasses on the Hypercube,"We present a mean field model for spin glasses with a natural notion of
distance built in, namely, the Edwards-Anderson model on the diluted
D-dimensional unit hypercube in the limit of large D. We show that finite D
effects are strongly dependent on the connectivity, being much smaller for a
fixed coordination number. We solve the non trivial problem of generating these
lattices. Afterwards, we numerically study the nonequilibrium dynamics of the
mean field spin glass. Our three main findings are: (i) the dynamics is ruled
by an infinite number of time-sectors, (ii) the aging dynamics consists on the
growth of coherent domains with a non vanishing surface-volume ratio, and (iii)
the propagator in Fourier space follows the p^4 law. We study as well finite D
effects in the nonequilibrium dynamics, finding that a naive finite size
scaling ansatz works surprisingly well.",0911.4667v1
2010-01-29,Manipulating and protecting entanglement by means of spin environments,"We study the dynamical behavior of two initially entangled qubits, each
locally coupled to an environment embodied by an interacting spin chain. We
consider energy-exchange qubit-environment couplings resulting in a rich and
highly non trivial entanglement dynamics. We obtain exact results for the
time-evolution of the concurrence between the two qubits and find that, by
tuning the interaction parameters, one can freeze the dynamics of entanglement,
therefore inhibiting its relaxation into the spin environments, as well as
activate a sudden-death phenomenon. We also discuss the effects of an
environmental quantum phase transition on the features of the two-qubit
entanglement dynamics.",1001.5440v2
2010-11-02,Quasistationarity in a model of classical spins with long-range interactions,"Systems with long-range interactions, while relaxing towards equilibrium,
sometimes get trapped in long-lived non-Boltzmann quasistationary states (QSS)
which have lifetimes that grow algebraically with the system size. Such states
have been observed in models of globally coupled particles that move under
Hamiltonian dynamics either on a unit circle or on a unit spherical surface.
Here, we address the ubiquity of QSS in long-range systems by considering a
different dynamical setting. Thus, we consider an anisotropic Heisenberg model
consisting of classical Heisenberg spins with mean-field interactions and
evolving under classical spin dynamics. Our analysis of the corresponding
Vlasov equation for time evolution of the phase space distribution shows that
in a certain energy interval, relaxation of a class of initial states occurs
over a timescale which grows algebraically with the system size. We support
these findings by extensive numerical simulations. This work further supports
the generality of occurrence of QSS in long-range systems evolving under
Hamiltonian dynamics.",1011.0738v2
2011-02-17,Storing entanglement of nuclear spins via Uhrig Dynamical Decoupling,"Stroboscopic spin flips have already been shown to prolong the coherence
times of quantum systems under noisy environments. Uhrig's dynamical decoupling
scheme provides an optimal sequence for a quantum system interacting with a
dephasing bath. Several experimental demonstrations have already verified the
efficiency of such dynamical decoupling schemes in preserving single qubit
coherences. In this work we describe the experimental study of Uhrig's
dynamical decoupling in preserving two-qubit entangled states using an ensemble
of spin-1/2 nuclear pairs in solution state. We find that the performance of
odd-order Uhrig sequences in preserving entanglement is superior to both
even-order Uhrig sequences and periodic spin-flip sequences. We also find that
there exists an optimal length of the Uhrig sequence at which the decoherence
time gets boosted from a few seconds to about 30 seconds.",1102.3560v3
2011-07-05,Quantum effects on one-dimensional collision dynamics of fermion clusters,"Recently, many experiments with cold atomic gases have been conducted from
interest in the non-equilibrium dynamics of correlated quantum systems. Of
these experiments, the mixing dynamics of fermion clusters motivates us to
research cluster-cluster collision dynamics in one-dimensional Fermi systems.
We adopt the one-dimensional Fermi-Hubbard model and apply the time-dependent
density matrix renormalization group method. We simulate collisions between two
fermion clusters of spin-up and spin-down, and calculate reflectance of the
clusters R changing the particle number in each cluster and the interaction
strength between two fermions with up and down spins. We also evaluate the
quasi-classical (independent collision) reflectance R^{qc} to compare it with
R. The quasi-classical picture is quantitatively valid in the limit of weak
interaction, but it is not valid when interaction is strong.",1107.0774v1
2012-03-21,"Viewpoint on the ""Theory of the superglass phase"" and a proof of principle of quantum critical jamming and related phases","A viewpoint article on the very interesting work of Biroli, Chamon, and
Zamponi on superglasses. I further suggest how additional new superglass and
""spin-superglass"" phases of matter (the latter phases contain quenched
disorder) and general characteristics may be proven as a theoretical proof of
concept in various electronic systems. The new phases include: (1) superglasses
of Cooper pairs, i.e., glassy superconductors, (2) superglass phases of quantum
spins, and (3) superglasses of the electronic orbitals. New general features
which may be derived by the same construct include (a) quantum dynamical
heterogeneities- a low temperature quantum analogue of dynamical
heterogeneities known to exist in classical glasses and spin-glasses wherein
the local dynamics and temporal correlations are spatially non-uniform. I also
discuss on a new class of quantum critical systems. In particular, I outline
(b) the derivation of the quantum analogue of the zero temperature jamming
transition that has a non-trivial dynamical exponent. We very briefly comment
on (c) quantum liquid crystals.",1203.4648v1
2013-01-25,Driven skyrmions and dynamical transitions in chiral magnets,"We study the dynamics of skyrmions in chiral magnets in the presence of a
spin polarized current. The motion of skyrmions in the ferromagnetic background
excites spin waves and contributes to additional damping. At a large current,
the spin wave spectrum becomes gapless and skyrmions are created dynamically
from the ferromagnetic state. At an even higher current, these skyrmions are
strongly deformed due to the damping and become unstable at a threshold
current, leading to a chiral liquid. We show how skyrmions can be created by
increasing the current in the magnetic spiral state. We then construct a
dynamic phase diagram for a chiral magnet with a current. The instability
transitions between different states can be observed as experimentally clear
signatures in the transport measurements, such as jumps and hysteresis.",1301.5963v2
2013-11-23,Nonunital non-Markovian dynamics induced by a spin bath and interplay of quantum Fisher information,"We explore the nonunital non-Markovian dynamics of a qubit immersed in a spin
bath. The nonunital environmental effects on the precisions of quantum
parameter estimation are investigated. The time-dependent transfer matrix and
inhomogeneity vector are obtained for the description of the open dynamical
process. The evolution of the coherent vectors for a qubit is studied so as to
geometrically demonstrate the nonunital non-Markovian effects. The revivals of
angles for the fidelity between a maximal mixed state and an arbitrary
trajectory state are presented in the nonunital non-Markovian dynamics. The
degree for the nonunitality is controllable with the changes of the local
magnetic field for a qubit and spin bath temperature. It is found out that the
increase of quantum Fisher information for composite states is connected with
the nonunital non-Markovian effects, which is helpful for the improvement of
quantum metrology.",1311.5952v1
2014-01-13,"Exit probability in inflow dynamics: nonuniversality induced by range, asymmetry and fluctuation","Probing deeper into the existing issues regarding the exit probability (EP)
in one dimensional dynamical models, we consider several models where the
states are represented by Ising spins and the information flows inwards. At
zero temperature, these systems evolve to either of two absorbing states. The
exit probability $E(x)$, which is the probability that the system ends up with
all spins up starting with $x$ fraction of up spins is found to have the
general form $E(x) = x^\alpha/\left[x^\alpha + (1-x)^\alpha\right]$. The exit
probability exponent $\alpha$ strongly depends on $r$, the range of
interaction, the symmetry of the model and the induced fluctuation. Even in a
nearest neighbour model, nonlinear form of EP can be obtained by controlling
the fluctuations and for the same range, different models give different
results for $\alpha$. Non-universal behaviour of the exit probability is thus
clearly established and the results are compared to existing studies in models
with outflow dynamics to distinguish the two dynamical scenarios.",1401.2797v2
2014-04-29,On the Spin-axis Dynamics of a Moonless Earth,"The variation of a planet's obliquity is influenced by the existence of
satellites with a high mass ratio. For instance, the Earth's obliquity is
stabilized by the Moon, and would undergo chaotic variations in the Moon's
absence. In turn, such variations can lead to large-scale changes in the
atmospheric circulation, rendering spin-axis dynamics a central issue for
understanding climate. The relevant quantity for dynamically-forced climate
change is the rate of chaotic diffusion. Accordingly, here we reexamine the
spin-axis evolution of a Moonless Earth within the context of a simplified
perturbative framework. We present analytical estimates of the characteristic
Lyapunov coefficient as well as the chaotic diffusion rate and demonstrate that
even in absence of the Moon, the stochastic change in the Earth's obliquity is
sufficiently slow to not preclude long-term habitability. Our calculations are
consistent with published numerical experiments and illustrate the putative
system's underlying dynamical structure in a simple and intuitive manner.",1404.7505v1
2014-07-16,Order and thermalized dynamics in Heisenberg-like square and Kagomé spin ices,"Thermodynamic properties of a spin ice model on a Kagom\'e lattice are
obtained from dynamic simulations and compared with properties in square
lattice spin ice. The model assumes three-component Heisenberg-like dipoles of
an array of planar magnetic islands situated on a Kagom\'e lattice. Ising
variables are avoided. The island dipoles interact via long-range dipolar
interactions and are restricted in their motion due to local shape
anisotropies. We define various order parameters and obtain them and
thermodynamic properties from the dynamics of the system via a Langevin
equation, solved by the Heun algorithm. Generally, a slow cooling from high to
low temperature does not lead to a particular state of order, even for a set of
coupling parameters that gives well thermalized states and dynamics. Some
suggestions are proposed for the alleviation of the geometric frustration
effects and for the generation of local order in the low temperature regime.",1407.4438v1
2014-10-12,Stochastic Differential Equations for Quantum Dynamics of Spin-Boson Networks,"The quantum dynamics of open many-body systems poses a challenge for
computational approaches. Here we develop a stochastic scheme based on the
positive P phase-space representation to study the nonequilibrium dynamics of
coupled spin-boson networks that are driven and dissipative. Such problems are
at the forefront of experimental research in cavity and solid state
realizations of quantum optics, as well as cold atom physics, trapped ions and
superconducting circuits. We demonstrate and test our method on a driven,
dissipative two-site system, each site involving a spin coupled to a photonic
mode, with photons hopping between the sites, where we find good agreement with
Monte Carlo Wavefunction simulations. In addition to numerically reproducing
features recently observed in an experiment [Phys. Rev. X 4, 031043 (2014)], we
also predict a novel steady state quantum dynamical phase transition for an
asymmetric configuration of drive and dissipation.",1410.3142v1
2014-11-25,Universal dynamic scaling in three-dimensional Ising spin glasses,"We use a non-equilibrium simulation method to study the spin glass transition
in three-dimensional Ising spin glasses. The transition point is repeatedly
approached at finite velocity $v$ (temperature change versus time) in Monte
Carlo simulations starting at a high temperature. The normally problematic
critical slowing-down is not hampering this kind of approach, since the system
equilibrates quickly at the initial temperature and the slowing-down is merely
reflected in the dynamic scaling of the non-equilibrium order parameter with
$v$ and the system size. The equilibrium limit does not have to be reached. For
the dynamic exponent we obtain $z = 5.85(9)$ for bimodal couplings distribution
and $z=6.00(10)$ for the Gaussian case, thus supporting universal dynamic
scaling (in contrast to recent claims of non-universal behavior).",1411.6745v1
2014-12-15,Testing statics-dynamics equivalence at the spin-glass transition in three dimensions,"The statics-dynamics correspondence in spin glasses relate non-equilibrium
results on large samples (the experimental realm) with equilibrium quantities
computed on small systems (the typical arena for theoretical computations).
Here we employ statics-dynamics equivalence to study the Ising spin-glass
critical behavior in three dimensions. By means of Monte Carlo simulation, we
follow the growth of the coherence length (the size of the glassy domains), on
lattices too large to be thermalized. Thanks to the large coherence lengths we
reach, we are able to obtain accurate results in excellent agreement with the
best available equilibrium computations. To do so, we need to clarify the
several physical meanings of the dynamic exponent close to the critical
temperature.",1412.4645v2
2015-01-22,Topologically Protected Dynamics of Spin Textures,"We study current-induced dynamics of spin textures in thin magnetic
nanowires. We derive effective equations of motion describing the dynamics of
the domain-wall soft modes associated with topological defects. Because the
magnetic domain walls are topological objects, these equations are universal
and depend only on a few parameters. We obtain spin spiral domain-wall
structure in ferromagnetic wires with Dzyaloshinskii-Moriya interaction and
critical current dependence on this interaction. We also find the most
efficient way to move the domain walls by resonant current pulses and propose a
procedure to determine their dynamics by measuring the voltage induced by a
moving domain wall. Based on translationally non-invariant nanowires, we show
how to make prospective magnetic memory nanodevices much more energy efficient.",1501.05366v1
2015-08-25,Absence of spin-orbit-coupling-induced effects on lattice dynamics in CePt3Si,"Motivated by model calculations for the heavy fermion superconductor CePt3Si
predicting phonon anomalies because of anti-symmetric spin-orbit coupling we
performed a detailed experimental study of the lattice dynamical properties of
CePt3Si. In particular, we investigated the dispersion of transverse acoustic
and low energy optic phonon branches along the [110] direction using inelastic
neutron scattering. In these branches, we found deviations from our ab-initio
lattice dynamical calculations, which overall give a good description of the
phonon dispersion in CePt3Si. However, the agreement for the [110] transverse
modes can be improved if we neglect the Ce 4f states, done in an additional
calculation. We conclude that the lattice dynamics of CePt3Si are conventional
and that the observed deviations are not related to effects of anti-symmetric
spin-orbit-coupling. More likely, ab-initio calculations overestimate the
exchange between different phonon branches, particularly in the presence of 4f
electron states. Our results imply that the ASOC plays less a role in
non-centrosymmetric superconductors than commonly believed.",1508.06048v1
2015-10-30,Identifying the Stern-Gerlach force of classical electron dynamics,"Different classical theories are commonly applied in various branches of
physics to describe the relativistic dynamics of electrons by coupled equations
for the orbital motion and spin precession. Exemplarily, we benchmark the
Frenkel model and the classical Foldy-Wouthuysen model with spin-dependent
forces (Stern-Gerlach forces) to the quantum dynamics as predicted by the Dirac
equation. Both classical theories can lead to different or even contradicting
predictions how the Stern-Gerlach forces modify the electron's orbital motion,
when the electron moves in strong electromagnetic field configurations of
emerging high-intensity laser facilities. In this way, one may evaluate the
validity and identify the limits of these classical theories via a comparison
with possible experiments to provide a proper description of spin-induced
dynamics. Our results indicate that the Foldy-Wouhuysen model is qualitatively
in better agreement with the Dirac theory than the widely used Frenkel model.",1510.09145v2
2016-01-06,RVB signatures in the spin dynamics of the square-lattice Heisenberg antiferromagnet,"We investigate the spin dynamics of the square-lattice spin-1/2 Heisenberg
antiferromagnet by means of an improved mean field Schwinger boson calculation.
By identifying both, the long range N\'eel and the RVB-like components of the
ground state, we propose an educated guess for the mean field triplet
excitation consisting on a linear combination of local and bond spin flips to
compute the dynamical structure factor. Our main result is that when this
triplet excitation is optimized in such a way that the corresponding sum rule
is fulfilled, we recover the low and high energy spectral weight features of
the experimental spectrum. In particular, the anomalous spectral weight
depletion at $(\pi,0)$ found in recent inelastic neutron scattering experiments
can be attributed to the interference of the triplet bond excitations of the
RVB component of the ground state. We conclude that the Schwinger boson theory
seems to be a good candidate to adequately interpret the dynamic properties of
the square-lattice Heisenberg antiferromagnet.",1601.01200v2
2016-01-09,Influence of the black hole spin on the chaotic particle dynamics within a dipolar halo,"We investigate the role of the spin angular momentum of astrophysical black
holes in controlling the special relativistic chaotic dynamics of test
particles moving under the influence of a post-Newtonian pseudo-Kerr black hole
potential, along with a perturbative potential created by a asymmetrically
placed (dipolar) halo. Proposing a Lyapunov-like exponent to be the effective
measure of the degree of chaos observed in the system under consideration, it
has been found that black hole spin anti-correlates with the degree of chaos
for the aforementioned dynamics. Our findings have been explained applying the
general principles of dynamical systems analysis.",1601.02100v1
2016-02-10,The inverse thermal spin-orbit torque and the relation of the Dzyaloshinskii-Moriya interaction to ground-state energy currents,"Using the Kubo linear-response formalism we derive expressions to calculate
the heat current generated by magnetization dynamics in magnets with broken
inversion symmetry and spin-orbit interaction (SOI). The effect of producing
heat currents by magnetization dynamics constitutes the Onsager reciprocal of
the thermal spin-orbit torque (TSOT), i.e., the generation of torques on the
magnetization due to temperature gradients. We find that the energy current
driven by magnetization dynamics contains a contribution from the
Dzyaloshinskii-Moriya interaction (DMI), which needs to be subtracted from the
Kubo linear response of the energy current in order to extract the heat
current. We show that the expressions of the DMI coefficient can be derived
elegantly from the DMI energy current. Guided by formal analogies between the
Berry phase theory of DMI on the one hand and the modern theory of orbital
magnetization on the other hand we are led to an interpretation of the latter
in terms of energy currents as well. Based on \textit{ab-initio} calculations
we investigate the heat current driven by magnetization dynamics in Mn/W(001)
magnetic bilayers. We predict that fast domain walls drive strong ITSOT heat
currents.",1602.03319v1
2016-07-23,A Cavity Master Equation for the continuous time dynamics of discrete spins models,"We present a new method to close the Master Equation representing the
continuous time dynamics of Ising interacting spins. The method makes use of
the the theory of Random Point Processes to derive a master equation for local
conditional probabilities. We analytically test our solution studying two known
cases, the dynamics of the mean field ferromagnet and the dynamics of the one
dimensional Ising system. We then present numerical results comparing our
predictions with Monte Carlo simulations in three different models on random
graphs with finite connectivity: the Ising ferromagnet, the Random Field Ising
model, and the Viana-Bray spin-glass model.",1607.06959v1
2016-09-27,Dynamics of polar-core spin vortices in a ferromagnetic spin-1 Bose-Einstein condensate,"A ferromagnetic spin-1 condensate supports polar-core spin vortices (PCVs) in
the easy-plane phase. We derive a model for the dynamics of these PCVs using a
variational Lagrangian approach. The PCVs behave as massive charged particles
interacting under the two dimensional Coulomb interaction, with the mass
arising from interaction effects within the vortex core. We compare this model
to numerical simulations of the spin-1 Gross-Pitaevskii equations and find
semi-quantitative agreement. In addition, the numerical results suggest that
the PCV core couples to spin waves, and this affects the PCV dynamics even far
from the core. We identify areas of further research that could extend the
model of PCV dynamics presented here.",1609.08258v2
2017-03-13,Dynamical amplification of magnetoresistances and Hall currents up to the THz regime,"Spin-orbit-related effects offer a highly promising route for reading and
writing information in magnetic units of future devices. These phenomena rely
not only on the static magnetization orientation but also on its dynamics to
achieve fast switchings that can reach the THz range. In this work, we consider
Co/Pt and Fe/W bilayers to show that accounting for the phase difference
between different processes is crucial to the correct description of the
dynamical currents. By tuning each system towards its ferromagnetic resonance,
we reveal that dynamical spin Hall angles can non-trivially change sign and be
boosted by over 500%, reaching giant values. We demonstrate that charge and
spin pumping mechanisms can greatly magnify or dwindle the currents flowing
through the system, influencing all kinds of magnetoresistive and Hall effects,
thus impacting also dc and second harmonic experimental measurements.",1703.04493v2
2017-03-23,Finite-temperature time-dependent variation with multiple Davydov states,"The Dirac-Frenkel time-dependent variational approach with Davydov Ans\""atze
is a sophisticated, yet efficient technique to obtain an acuurate solution to
many-body Schr\""odinger equations for energy and charge transfer dy- namics in
molecular aggregates and light-harvesting complexes. We extend this variational
approach to finite temperatures dynamics of the spin-boson model by adopting a
Monte Carlo importance sampling method. In or- der to demonstrate the
applicability of this approach, we compare real-time quantum dynamics of the
spin-boson model calculated with that from numerically exact iterative
quasiadiabatic propagator path integral (QUAPI) technique. The comparison shows
that our variational approach with the single Davydov Ans\""atze is in excellent
agreement with the QUAPI method at high temperatures, while the two differ at
low temperatures. Accuracy in dynamics calculations employing a multitude of
Davydov trial states is found to improve substantially over the single Davydov
Ansatz, especially at low temperatures. At a moderate computational cost, our
variational approach with the multiple Davydov Ansatz is shown to provide
accurate spin-boson dynamics over a wide range of temperatures and bath
spectral densities.",1703.08010v1
2018-11-14,Microscopic Theory of Ultrafast Out-of-Equilibrium Dynamics in Magnetic Insulators. Unraveling the Magnon-Phonon Coupling,"The interaction between lattice and spins is at the heart of an extremely
intriguing ultrafast dynamics in magnetic materials. In this work we formulate
a general non-equilibrium theory that disentangles the complex interplay
between them in a THz laser-excited antiferromagnetic insulator. The theory
provides a quantitative description of the transient energy flow between the
spin and lattice sub-systems, subject to magnon-phonon and phonon-phonon
scatterings, giving rise to finite life-times of the quasiparticles and to the
equilibration time of the system. We predict a novel kind of scattering process
where two magnons of opposite polarizations decay into a phonon, previously
omitted in the literature. The theory is combined with first-principle
calculations and then applied to simulate a realistic dynamics of NiO. The main
relaxation channels and hot spots in the reciprocal space, giving the strongest
contribution to the energy transfer between phonons and magnons are identified.
The diverse interaction strengths lead to distinct coupled dynamics of the
lattice and spin systems and subsequently to different equilibration
timescales.",1811.05841v1
2018-11-21,Metastable hard-axis polar state of a spinor Bose-Einstein condensate under a magnetic field gradient,"We investigate the stability of a hard-axis polar state in a spin-1
antiferromagnetic Bose-Einstein condensate under a magnetic field gradient,
where the easy-plane spin anisotropy is controlled by a negative quadratic
Zeeman energy $q<0$. In a uniform magnetic field, the axial polar state is
dynamically unstable and relaxes into the planar polar ground state. However,
under a field gradient $B'$, the excited spin state becomes metastable down to
a certain threshold $q_{th}$ and as $q$ decreases below $q_{th}$, its intrinsic
dynamical instability is rapidly recalled. The incipient spin excitations in
the relaxation dynamics appear with stripe structures, indicating the
rotational symmetry breaking by the field gradient. We measure the dependences
of $q_{th}$ on $B'$ and the sample size, and we find that $q_{th}$ is highly
sensitive to the field gradient in the vicinity of $B'=0$, exhibiting power-law
behavior of $|q_{th}|\propto B'^{\alpha}$ with $\alpha \sim 0.5$. Our results
demonstrate the significance of the field gradient effect in the quantum
critical dynamics of spinor condensates.",1811.08544v1
2018-11-21,The high-frequency dynamics of domain walls with strong Dzyaloshinskii-Moriya interaction,"Domain walls (DWs) in perpendicularly magnetized nanotracks (PMNTs) with
interfacial Dzyaloshinskii-Moriya interaction (DMI) have become the primary
objects of theoretical and experimental interest due to their technological
suitability in spintronic nanodevices. Chiral DWs in PMNTs can be driven
efficiently by the spin-orbit torque. However, the high-frequency dynamic
behavior of the chiral DW has not been explored. In this work, using
micromagnetic calculation, we have discovered a novel dynamic mode, the sway
mode, of DWs under an out-of-plane high-frequency alternating current (AC)
magnetic field in a PMNT with strong DMI. This dynamic phenomenon is strictly
related with DMI-related boundary effect and can be understood in terms of the
propagation of an amplitude-tuned spin wave in the DW plane. The spin wave
exhibits some characteristic frequencies due to the space-confinement of DW.
This work offers the possibility of a visual route for characterizing DMI.",1811.08590v1
2019-05-27,Coherent backaction between spins and an electronic bath: Non-Markovian dynamics and low-temperature quantum thermodynamic electron cooling,"We provide a versatile analytical framework for calculating the dynamics of a
spin system in contact with a fermionic bath beyond the Markov approximation.
The approach is based on a second order expansion of the Nakajima-Zwanzig
master equation but systematically includes all quantum coherent memory effects
leading to non-Markovian dynamics. Our results describe, for the free induction
decay, the full time range from the non-Markovian dynamics at short times, to
the well-known exponential thermal decay at long times. We provide full
analytic results for the entire time range using a bath of itinerant electrons
as an archetype for universal quantum fluctuations. Furthermore, we propose a
quantum thermodynamic scheme to employ the temperature insensitivity of the
non-Markovian decay to transport heat out of the electron system and thus, by
repeated reinitialization of a cluster of spins, to efficiently cool the
electrons at very low temperatures.",1905.11422v2
2008-07-29,Spin-Torque-Induced Rotational Dynamics of a Magnetic Vortex Dipole,"We study, both experimentally and by numerical modeling, the magnetic
dynamics that can be excited in a magnetic thin-film nanopillar device using
the spin torque from a spatially localized current injected via a
10s-of-nm-diameter aperture. The current-driven magnetic dynamics can produce
large amplitude microwave emission at zero magnetic field, with a frequency
well below that of the uniform ferromagnetic resonance mode. Micromagnetic
simulations indicate that the physical origin of this efficient microwave
nano-oscillator is the nucleation and subsequent steady-state rotational
dynamics of a magnetic vortex dipole driven by the localized spin torque. These
results show this novel implementation of a spintronic nano-oscillator is a
promising candidate for microwave technology applications.",0807.4660v2
2012-04-18,Correlation dynamics of three spin under a classical dephasing environment,"By starting from the stochastic Hamiltonian of the three correlated spins and
modeling their frequency fluctuations as caused by dephasing noisy environments
described by Ornstein-Uhlenbeck processes, we study the dynamics of quantum
correlations, including entanglement and quantum discord. We prepared initially
our open system with Greenberger-Horne-Zeilinger or W state and present the
exact solutions for evolution dynamics of entanglement and quantum discord
between three spins under both Markovian and non-Markovian regime of this
classical noise. By comparison the dynamics of entanglement with that of
quantum discord we find that entanglement can be more robust than quantum
discord against this noise. It is shown that by considering non-Markovian
extensions the survival time of correlations prolong.",1204.4011v1
2013-09-12,The theory of coherent dynamic nuclear polarization in quantum dots,"We consider the dynamic nuclear spin polarization (DNP) using two electrons
in a double quantum dot in presence of external magnetic field and spin-orbit
interaction, in various schemes of periodically repeated sweeps through the
S-T+ avoided crossing. By treating the problem semi-classically, we find that
generally the DNP have two distinct contributions - a geometrical polarization
and a dynamic polarization, which have different dependence on the control
parameters such as the sweep rates and waiting times in each period. Both terms
show non-trivial dependence on those control parameter. We find that even for
small spin-orbit term, the dynamical polarization dominates the DNP in presence
of a long waiting period near the S-T+ avoided crossing, of the order of the
nuclear Larmor precession periods. A detailed numerical analysis of a specific
control regime can explain the oscillations observed by Foletti et.~al.~in
arXiv:0801.3613.",1309.3027v1
2015-12-17,Noise in optical quantum memories based on dynamical decoupling of spin states,"Long-lived optical quantum memories are of great importance for scalable
distribution of entanglement over remote networks (e.g. quantum repeaters).
Long-lived storage generally relies on storing the optical states as spin
excitations since these often exhibit long coherence times. To extend the
storage time beyond the intrinsic spin dephasing time one can use dynamical
decoupling techniques. However, it has been shown that dynamical decoupling
introduces noise in optical quantum memories based on ensembles of atoms. In
this article a simple model is proposed to calculate the resulting
signal-to-noise ratio, based on intrinsic quantum memory parameters such as the
optical depth of the ensemble. We also characterize several dynamical
decoupling sequences that are efficient in reducing this particular noise. Our
calculations indicate that it should be feasible to reach storage times well
beyond one second under reasonable experimental conditions.",1512.05658v1
2017-07-03,Waiting time distribution revealing the internal spin dynamics in a double quantum dot,"Waiting time distribution and the zero-frequency full counting statistics of
unidirectional electron transport through a double quantum dot molecule
attached to spin-polarized leads are analyzed using the quantum master
equation. The waiting time distribution exhibits a non-trivial dependence on
the value of the exchange coupling between the dots and the gradient of the
applied magnetic field, which reveals the oscillations between the spin states
of the molecule. The zero-frequency full counting statistics, on the other
hand, is independent of the aforementioned quantities, thus giving no insight
into the internal dynamics. The fact that the waiting time distribution and the
zero-frequency full counting statistics give a non-equivalent information is
associated with two factors. Firstly, it can be explained by the sensitivity to
different timescales of the dynamics of the system. Secondly, it is associated
with the presence of the correlation between subsequent waiting times, which
makes the renewal theory, relating the full counting statistics and the waiting
time distribution, not longer applicable. The study highlights the particular
usefulness of the waiting time distribution for the analysis of the internal
dynamics of mesoscopic systems.",1707.00441v1
2017-10-17,Finite temperature dynamics of the Mott insulating Hubbard chain,"We study the dynamical response of the half-filled one-dimensional(1d)
Hubbard model for a range of interaction strengths $U$ and temperatures $T$ by
a combination of numerical and analytical techniques. Using time-dependent
density matrix renormalization group (tDMRG) computations we find that the
single-particle spectral function undergoes a crossover to a spin-incoherent
Luttinger liquid regime at temperatures $T \sim J=4t^2/U$ for sufficiently
large $U > 4t$. At smaller values of $U$ and elevated temperatures the spectral
function is found to exhibit two thermally broadened bands of excitations,
reminiscent of what is found in the Hubbard-I approximation. The dynamical
density-density response function is shown to exhibit a finite temperature
resonance at low frequencies inside the Mott gap, with a physical origin
similar to the Villain mode in gapped quantum spin chains. We complement our
numerical computations by developing an analytic strong-coupling approach to
the low-temperature dynamics in the spin-incoherent regime.",1710.06452v1
2017-12-17,Dynamical effects in the observed rate of change of the orbital and the spin periods of radio pulsars: Improvement in the method of estimation and its implications,"The observed values of the rate of change of the orbital and the spin periods
of pulsars are affected by different dynamical effects, for example, the
line-of-sight acceleration and the proper motion of the pulsar relative to the
sun. We explore these dynamical effects thoroughly and point out the drawbacks
of popular methods. We introduce a package, `GalDynPsr', that evaluates
different dynamical effects following traditional as well as improved methods
based on the model of the Galactic potential provided in a publicly available
package called `galpy'. We argue that the improved methods introduced in this
paper should be used for pulsars located 1 kpc or farther away from the solar
system, especially when precise values of the rate of change of the periods are
required, e.g., while placing limits on alternative theories of gravity,
calculating the spin-down limit of the continuous gravitational waves emitted
from a rotationally deformed neutron star, understanding pulsar `death-line',
etc. GalDynPsr is available online and open for contributions.",1712.06590v2
2019-07-17,Breaking rotational symmetry in a trapped-ion quantum tunneling rotor,"A trapped-ion quantum tunneling rotor (QTR) is in a quantum superposition of
two different Wigner crystal orientations. In a QTR system, quantum tunneling
drives the coherent transition between the two different Wigner crystal
orientations. We theoretically study the quantum dynamics of a QTR,
particularly when the spin state of one of the ions is flipped. We show that
the quantum dynamics of an $\it{N}$-ion QTR can be described by continuous-time
cyclic quantum walks. We also investigate the quantum dynamics of the QTR in a
magnetic field. Flipping the spin state breaks the rotational symmetry of the
QTR, making the quantum-tunneling-induced rotation distinguishable. This
symmetry breaking creates coupling between the spin state of the ions and the
rotational motion of the QTR, resulting in different quantum tunneling
dynamics.",1907.07404v2
2020-01-06,Quantum sensing and control of spin state dynamics in the radical pair mechanism,"Radical pairs and the dynamics they undergo are prevalent in many chemical
and biological systems. Specifically, it has been proposed that the radical
pair mechanism results from a relatively strong hyperfine interaction with its
intrinsic nuclear spin environment. While the existence of this mechanism is
undisputed, the nanoscale details remain to be experimentally shown. We analyze
here the role of a quantum sensor in detecting the spin dynamics
(non-Markovian) of individual radical pairs in the presence of a weak magnetic
field. We show how quantum control methods can be used to set apart the
dynamics of radical pair mechanism at various stages of the evolution. We
envisage these findings having far-reaching implications to the understanding
of the physical mechanism in magnetoreception and other bio-chemical processes
with a microscopic detail.",2001.01517v2
2020-01-14,Collective magnetic dynamics in artificial spin ice probed by AC susceptibility,"We report on the study of the thermal dynamics of square artificial spin ice,
probed by means of temperature and frequency dependent AC susceptibility.
Pronounced influence of the inter-island coupling strength was found on the
frequency response of the samples. Through the subsequent analysis of the
frequency- and coupling-dependent freezing temperatures, we discuss the
phenomenological parameters obtained in the framework of Vogel-Fulcher-Tammann
law in terms of the samples microscopic features. The high sensitivity and
robust signal to noise ratio of AC susceptibility validates the latter as a
promising and simple experimental technique for resolving the dynamics and
temperature driven dynamics crossovers for the case of artificial spin ice.",2001.04746v2
2021-01-08,Euclidean LQG Dynamics: An Electric Shift in Perspective,"Loop Quantum Gravity (LQG) is a non-perturbative attempt at quantization of a
classical phase space description of gravity in terms of $SU(2)$ connections
and electric fields. As emphasized recently [1], on this phase space, classical
gravitational evolution in $time$ can be understood in terms of certain gauge
covariant generalizations of Lie derivatives with respect to a $spatial$
$SU(2)$ Lie algebra valued vector field called the Electric Shift. We present a
derivation of a quantum dynamics for Euclidean LQG which is informed by this
understanding. In addition to the physically motivated nature of the action of
the Euclidean Hamiltonian constraint so derived, the derivation implies that
the spin labels of regulating holonomies are determined by corresponding labels
of the spin network state being acted upon thus eliminating the `spin
$j$-ambiguity' pointed out by Perez. By virtue of Thiemann's seminal work, the
Euclidean quantum dynamics plays a crucial role in the construction of the
Lorentzian quantum dynamics so that our considerations also have application to
Lorentzian LQG.",2101.03115v1
2000-06-09,Is dynamic ultrametricity observable in spin glasses?,"We investigate the dynamics of spin glasses from the `rheological' point of
view, in which aging is suppressed by the action of small, non-conservative
forces. The different features can be expressed in terms of the scaling of
relaxation times with the magnitude of the driving force, which plays the role
of the critical parameter. Stated in these terms, ultrametricity loses much of
its mystery and can be checked rather easily. This approach also seems a
natural starting point to investigate what would be the real-space structures
underlying the hierarchy of time scales. We study in detail the appearance of
this many-scale behavior in a mean-field model, in which dynamic ultrametricity
is clearly present. A similar analysis is performed on numerical results
obtained for a 3D spin glass: In that case, our results are compatible with
either that dynamic ultrametricity is absent or that it develops so slowly that
even in experimental time-windows it is still hardly observable.",0006161v1
2018-03-03,Dissipative dynamics of an interacting spin system with collective damping,"The competition between Hamiltonian and Lindblad dynamics in quantum systems
give rise to non-equillibrium phenomena with no counter part in conventional
condensed matter physics. In this paper, we investigate this interplay of
dynamics in infinite range Heisenberg model coupled to a non-Markovian bath and
subjected to Lindblad dynamics due to spin flipping at a given site. The spin
model is bosonized via Holstein-Primakoff transformations and is shown to be
valid for narrow range of parameters in the thermodynamic limit. Using
Schwinger-Keldysh technique, we derive mean field solution of the model and
observe that the system breaks $\mathcal{Z}_2$-symmetry at the transition
point. We calculate effective temperature that has linear dependence on the
effective system-bath coupling, and is independent of the dissipation rate and
cutoff frequency of the bath spectral density. Furthermore, we study the
fluctuations over mean field and show that the dissipative spectrum is modified
by ${\rm O}(\frac{1}{N})$ correction term which results change in various
physically measurable quantities.",1803.01167v2
2018-06-27,$z=2$ Quantum Critical Dynamics in a Spin Ladder,"By means of inelastic neutron scattering we investigate finite temperature
dynamics in the quantum spin ladder compound (C$_5$H$_{12}$N)$_2$CuBr$_4$
(BPCB) near the magnetic field induced quantum critical point with dynamical
exponent $z=2$. We observe universal finite-temperature scaling of the
transverse local dynamic structure factor in spectacular quantitative agreement
with long-standing theoretical predictions. At the same time, already at rather
low temperatures, we observe strong non-universal longitudinal fluctuations. To
separate the two, we make use of an intrinsic leg-exchange symmetry of the spin
ladder. Complementary measurements of specific heat also reveal striking
scaling behavior near the quantum critical point.",1806.10392v2
2018-08-19,Fast spin dynamics in hexagonal arrays of Fe atoms on metallic surface,"Understanding the nature of magnetic interactions in ultra-small magnetic
ensembles and their intrinsic properties is vital to uncover the dynamics
therein. In this study we reveal the spin dynamics of hexagonally arranged Fe
atoms on metallic surface that are triggered by magnetic pulse. The switching
process among various spin configurations and their relative magnetic order is
tuned by the amplitude and duration of the magnetic pulse. Even more we observe
a parity effect in the switching time as the size of the cluster varies in
which even number of Fe atoms shows faster dynamics. The changes in the
multistable magnetic states and switching times are explained by using the
relaxation of the exchange and anisotropy energies in time.",1808.06165v1
2019-03-20,Tracking the ultrafast motion of an antiferromagnetic order parameter,"The unique functionalities of antiferromagnets offer promising routes to
advance information technology. Their compensated magnetic order leads to spin
resonances in the THz-regime, which suggest the possibility to coherently
control antiferromagnetic (AFM) devices orders of magnitude faster than
traditional electronics. However, the required time resolution, complex
sublattice interations and the relative inaccessibility of the AFM order
parameter pose serious challenges to studying AFM spin dynamics. Here, we
reveal the temporal evolution of an AFM order parameter directly in the time
domain. We modulate the AFM order in hexagonal YMnO$_\mathrm{3}$ by coherent
magnon excitation and track the ensuing motion of the AFM order parameter using
time-resolved optical second-harmonic generation (SHG). The dynamic symmetry
reduction by the moving order parameter allows us to separate electron dynamics
from spin dynamics. As transient symmetry reductions are common to coherent
excitations, we have a general tool for tracking the ultrafast motion of an AFM
order parameter.",1903.08604v1
2019-04-30,Violation of single-length scaling dynamics via spin vortices in an isolated spin-1 Bose gas,"We consider the phase ordering dynamics of an isolated quasi-two-dimensional
spin-1 Bose gas quenched into an easy-plane ferromagnetic phase. Preparing the
initial system in an unmagnetized anti-ferromagnetic state the subsequent
ordering involves both polar core and Mermin-Ho spin vortices, with the ratio
between the different vortices controllable by the quench parameter.
Ferromagnetic domain growth occurs as these vortices annihilate. The distinct
dynamics of the two types of vortices means that the domain growth law is
determined by two macroscopic length scales, violating the standard dynamic
scaling hypothesis. Nevertheless we find that universality of the ordering
process manifests in the decay laws for the spin vortices.",1904.13222v1
2020-05-12,Interplay between geometric and dynamic phases in a single spin system,"We use a combination of microwave fields and free precession to drive the
spin of a nitrogen-vacancy (NV) center in diamond on different trajectories on
the Bloch sphere, and investigate the physical significance of the
frame-dependent decomposition of the total phase into geometric and dynamic
parts. The experiments are performed on a two-level subspace of the spin-1
ground state of the NV, where the Aharonov-Anandan geometric phase manifests
itself as a global phase, and we use the third level of the NV ground state
triplet to detect it. We show that while the geometric Aharonov-Anandan phase
retains its connection to the solid angle swept out by the evolving spin, it is
generally accompanied by a dynamic phase that suppresses the geometric
dependence of the system dynamics. These results offer insights into the
physical significance of frame-dependent geometric phases.",2005.05619v1
2020-06-17,Gravitational Faraday and Spin-Hall Effects of Light,"The gravitational Faraday and its dual spin-Hall effects of light arise in
space-times of non-zero angular momentum. These effects were studied in
stationary, asymptotically flat space-times. Here we study these effects in
arbitrary, non-stationary, asymptotically flat space-times. These effects arise
due to interaction between light polarisation and space-time angular momentum.
As a result of such interaction, the phase velocity of left- and right-handed
circularly polarised light becomes different, that results in the gravitational
Faraday effect. This difference implies different dynamics of these components,
that begin to propagate along different paths\textemdash the gravitational
spin-Hall effect of light. Due to this effect, the gravitational field splits a
multicomponent beam of unpolarized light and produces polarized gravitational
rainbow. The component separation is an accumulative effect observed in long
range asymptotics. To study this effect, we construct uniform eikonal expansion
and derive dynamical equation describing this effect. To analyse the dynamical
equation, we present it in the local space and time decomposition form. The
spatial part of the equation presented in the related optical metric is
analogous to the dynamical equation of a charged particle moving in magnetic
field under influence of the Coriolis force.",2006.10077v1
2021-03-03,THz Field-induced Spin Dynamics in Ferrimagnetic Iron Garnets,"THz magnetization dynamics is excited in ferrimagnetic thulium iron garnet
with a picosecond, single-cycle magnetic field pulse and seen as a
high-frequency modulation of the magneto-optical Faraday effect. Data analysis
combined with numerical modelling and evaluation of the effective Lagrangian
allow us to conclude that the dynamics corresponds to the exchange mode excited
by Zeeman interaction of the THz field with the antiferromagnetically coupled
spins. We argue that THz-pump IR-probe experiments on ferrimagnets offer a
unique tool for quantitative studies of dynamics and mechanisms to control
antiferromagnetically coupled spins.",2103.02449v1
2021-04-13,Spin dynamics of the director state in frustrated hyperkagome systems,"We present an experimental study of the magnetic structure and dynamics of
two frustrated hyperkagome compounds, Gd3Ga5O12 and Gd3Al5O12. It has
previously been shown that Gd3Ga5O12 exhibits long-range correlations of
multipolar directors, that are formed from antiferromagnetic spins on loops of
ten ions. Using neutron diffraction and Reverse Monte Carlo simulations we
prove the existence of similar magnetic correlations in Gd3Al5O12, showing the
ubiquity of these complex structures in frustrated hyperkagome materials.
  Using inelastic neutron scattering we shed further light on the director
state and the associated low lying magnetic excitations. In addition we have
measured quasielastic dynamics that show evidence of spin diffusion. Finally,
we present AC susceptibility measurements on both Gd3Ga5O12 and Gd3Al5O12,
revealing a large difference in the low frequency dynamics between the two
otherwise similar compounds.",2104.05987v2
2021-05-24,Response Dynamics of Alkali Metal-Noble Gas Hybrid Trispin System,"With numerical calculation of coupled Bloch equations, we have simulated the
spin dynamics of nuclear magnetic resonance gyroscope based on alkali
metal-noble gas hybrid trispin system. From the perspective of damping harmonic
oscillator, a thorough analysis of the response dynamics is demonstrated. The
simulation results shows a linear increasing response of gyroscope signal while
the noblge gas nuclear spin magnetization and alkali atomic spin lifetime
parameters are at the over damping condition. An upper limit of response is
imposed on the NMR gyroscope signal due to the inherent dynamics of the hybrid
trispin system. The results agrees with present available experimental results
and provide useful guidings for future experiments.",2105.11124v2
2021-09-06,Singularly perturbed dynamics of the tippedisk,"The tippedisk is a mathematical-mechanical archetype for a peculiar
friction-induced instability phenomenon leading to the inversion of an
unbalanced spinning disk, being reminiscent to (but different from) the
well-known inversion of the tippetop. A reduced model of the tippedisk, in the
form of a three-dimensional ordinary differential equation, has been derived
recently, followed by a preliminary local stability analysis of stationary
spinning solutions. In the current paper, a global analysis of the reduced
system is pursued using the framework of singular perturbation theory. It is
shown how the presence of friction leads to slow-fast dynamics and the creation
of a two-dimensional slow manifold. Furthermore, it is revealed that a
bifurcation scenario involving a homoclinic bifurcation and a Hopf bifurcation
leads to an explanation of the inversion phenomenon. In particular, a
closed-form condition for the critical spinning speed for the inversion
phenomenon is derived. Hence, the tippedisk forms an excellent
mathematical-mechanical problem for the analysis of global bifurcations in
singularly perturbed dynamics.",2109.02542v1
2021-09-06,Phases and dynamics of ultracold bosons in a tilted optical lattice,"We present a brief overview of the phases and dynamics of ultracold bosons in
an optical lattice in the presence of a tilt. We begin with a brief summary of
the possible experimental setup for generating the tilt. This is followed by a
discussion of the effective low-energy model for these systems and its
equilibrium phases. We also chart the relation of this model to the recently
studied system of ultracold Rydberg atoms. Next, we discuss the non-equilibrium
dynamics of this model for quench, ramp and periodic protocols with emphasis on
the periodic drive which can be understood in terms of an analytic, albeit
perturbative, Floquet Hamiltonian derived using Floquet perturbation theory
(FPT). Finally, taking cue from the Floquet Hamiltonian of the periodically
driven tilted boson chain, we discuss a spin model which exhibits Hilbert space
fragmentation and exact dynamical freezing for wide range of initial states.",2109.02657v2
2021-09-20,Benchmarking quantum annealing dynamics: the spin-vector Langevin model,"The classical spin-vector Monte Carlo (SVMC) model is a reference benchmark
for the performance of a quantum annealer. Yet, as a Monte Carlo method, SVMC
is unsuited for an accurate description of the annealing dynamics in
real-time.We introduce the spin-vector Langevin (SVL) model as an alternative
benchmark in which the time evolution is described by Langevin dynamics. The
SVL model is shown to provide a more stringent test than the SVMC model for the
identification of quantum signatures in the performance of quantum annealing
devices, as we illustrate by describing the Kibble-Zurek scaling associated
with the dynamics of symmetry breaking in the transverse field Ising model,
recently probed using D-Wave machines. Specifically, we show that D-Wave data
are reproduced by the SVL model.",2109.09750v3
2021-10-06,Capturing non-Markovian dynamics with the reaction coordinate method,"The reaction coordinate (RC) technique is emerging as a significant tool in
the study of quantum dissipative dynamics and quantum thermodynamics. With the
objective to further establish this tool, here we explore to what extent the
method can capture non-Markovian dynamics of open quantum systems. As a case
study, we focus on the pure decoherence model of a spin coupled to a harmonic
reservoir. We compare the spin dynamics and measures for non-Markovianity from
the exact analytical solution to simulations based on the RC method at the
level of a second order quantum master equation. We find that the RC method can
quantitatively capture non-Markovian effects at strong system-bath coupling and
for structured baths. This is rationalized by the fact that the collective RC
bath mode, which is made part of the system, maintains system-bath
correlations. Lastly, we apply our RC method and study the spin-boson model in
the non-Markovian regime.",2110.02455v2
2021-10-18,Dynamical scaling of correlations generated by short- and long-range dissipation,"We study the spatio-temporal spreading of correlations in an ensemble of
spins due to dissipation characterized by short- and long-range spatial
profiles. We consider systems initially in an uncorrelated state, and find that
correlations widen and contract in a novel pattern intimately related to both
the dissipative nature of the dynamical channel and its spatial profile.
Additionally, we make a methodological contribution by generalizing
non-equilibrium spin-wave theory to the case of dissipative systems and derive
equations of motion for any translationally invariant spin chain whose dynamics
can be described by a combination of Hamiltonian interactions and dissipative
Lindblad channels. Our work aims at extending the study of correlation dynamics
to purely dissipative quantum simulators and compare them with the established
paradigm of correlations spreading in hamiltonian systems.",2110.09547v3
2021-10-20,Simulability transitions in continuous-time dynamics of local open quantum systems,"We analyze the complexity of classically simulating continuous-time dynamics
of locally interacting quantum spin systems with a constant rate of
entanglement breaking noise. We prove that a polynomial time classical
algorithm can be used to sample from the state of the spins when the rate of
noise is higher than a threshold determined by the strength of the local
interactions. Furthermore, by encoding a 1D fault tolerant quantum computation
into the dynamics of spin systems arranged on two or higher dimensional grids,
we show that for several noise channels, the problem of weakly simulating the
output state of both purely Hamiltonian and purely dissipative dynamics is
expected to be hard in the low-noise regime.",2110.10638v2
2021-11-30,Local dynamics and thermal activation in the transverse-field Ising chain,"There has been considerable recent progress in identifying candidate
materials for the transverse-field Ising chain (TFIC), a paradigmatic model for
quantum criticality. Here, we study the local spin dynamical structure factor
of different spin components in the quantum disordered region of the TFIC. We
show that the low-frequency local dynamics of the spins in the Ising- and
transverse-field directions have strikingly distinctive temperature
dependencies. This leads to the thermal-activation gap for the secular term of
the NMR $1/T_2^{\prime}$ relaxation rate to be half of that for the $1/T_1$
relaxation rate. Our findings reveal a new surprise in the nonzero-temperature
dynamics of the venerable TFIC model and uncover a means to evince the material
realization of the TFIC universality.",2111.15107v1
2021-12-03,Quantum time dynamics of 1D-Heisenberg models employing the Yang-Baxter equation for circuit compression,"Quantum time dynamics (QTD) is considered a promising problem for quantum
supremacy on near-term quantum computers. However, QTD quantum circuits grow
with increasing time simulations. This study focuses on simulating the time
dynamics of 1-D integrable spin chains with nearest neighbor interactions. We
show how the quantum Yang-Baxter equation can be exploited to compress and
produce a shallow quantum circuit. With this compression scheme, the depth of
the quantum circuit becomes independent of step size and only depends on the
number of spins. We show that the compressed circuit scales quadratically with
system size, which allows for the simulations of time dynamics of very large
1-D spin chains. We derive the compressed circuit representations for different
special cases of the Heisenberg Hamiltonian. We compare and demonstrate the
effectiveness of this approach by performing simulations on quantum computers.",2112.01690v1
2022-02-23,Arresting classical many-body chaos by kinetic constraints,"We investigate the effect of kinetic constraints on classical many-body chaos
in a translationally-invariant Heisenberg spin chain using a classical
counterpart of the out-of-time-ordered correlator (OTOC). The strength of the
constraint drives a 'dynamical phase transition' separating a delocalised
phase, where the classical OTOC propagates ballistically, from a localised
phase, where the OTOC does not propagate at all and the entire system freezes.
This is unexpected given that all spins configurations are dynamically
connected to each other. We show that localisation arises due to the dynamical
formation of frozen islands, contiguous segments of spins immobile due to the
constraints, dominating over the melting of such islands.",2202.11726v2
2022-08-07,Algebraic-Dynamical Theory for Quantum Spin-1/2: the Two-spin limit and Implications for Lattice Models,"Recently, an {\it algebraic-dynamical theory} (ADT) for strongly interacting
many-body quantum Hamiltonians in W. Ding, arXiv: 2202.12082 (2022). By
introducing the complete operator basis set, ADT proposes a generic framework
for systematically constructing dynamical theories for interacting quantum
Hamiltonians, using quantum entanglement as the organizing principle. In this
work, we study exact ADT solutions of interacting two-spin problems which can
be used as ""free theories"" for perturbation study on relevant solvable limits.
Then we perform ADT perturbation calculations and obtain the correct ground
state under the perturbation, which shows that the ADT framework is capable of
constructing correct dynamical perturbation theories for strongly interacting
quantum spin models. We also discuss the implication for relevant lattice
models.",2208.03637v1
2022-08-18,Prethermalization in periodically-driven nonreciprocal many-body spin systems,"We analyze a new class of time-periodic nonreciprocal dynamics in interacting
chaotic classical spin systems, whose equations of motion are conservative
(phase-space-volume-preserving) yet possess no symplectic structure. As a
result, the dynamics of the system cannot be derived from any time-dependent
Hamiltonian. In the high-frequency limit, we find that the magnetization
dynamics features a long-lived metastable plateau, whose duration is controlled
by the fourth power of the drive frequency. However, due to the lack of an
effective Hamiltonian, the prethermal state the system evolves into cannot be
understood within the framework of the canonical ensemble. We propose a
Hamiltonian extension of the system using auxiliary degrees of freedom, in
which the original spins constitute an open yet nondissipative subsystem. This
allows us to perturbatively derive effective equations of motion that
manifestly display symplecticity breaking at leading order in the inverse
frequency. We thus extend the notion of prethermal dynamics, observed in the
high-frequency limit of periodically-driven systems, to nonreciprocal systems.",2208.09005v3
2022-10-19,Dynamic structure factor of one-dimensional Fermi superfluid with spin-orbit coupling,"We theoretically calculate the density dynamic structure factor of
one-dimensional Fermi superfluid with Raman-type spin-orbit coupling, and
analyze its main dynamical character during phase transition between
Bardeen-Cooper-Schrieffer superfluid and topological superfluid. Our
theoretical results display four kinds of single-particle excitations induced
by the two-branch structure of single-particle spectrum, and the cross
single-particle excitation is much easier to be seen in the spin dynamic
structure factor at a small transferred momentum. Also we find a new roton-like
collective mode emerges at a fixed transferred momentum $q \simeq 2k_F$, and it
only appears once the system enters the topological superfluid state. The
occurrence of this roton-like excitation is related to switch of global minimum
in single-particle spectrum from $k=0$ to $k \simeq 2k_F$.",2210.10407v1
2022-10-31,Dynamical fractal and anomalous noise in a clean magnetic crystal,"Fractals -- objects with non-integer dimensions -- occur in manifold settings
and length scales in nature, ranging from snowflakes and lightning strikes to
natural coastlines. Much effort has been expended to generate fractals for use
in many-body physics. Here, we identify an emergent dynamical fractal in a
disorder-free, stoichiometric three-dimensional magnetic crystal in
thermodynamic equilibrium. The phenomenon is born from constraints on the
dynamics of the magnetic monopole excitations in spin ice, which restrict them
to move on the fractal. This observation explains the anomalous exponent found
in magnetic noise experiments in the spin ice compound Dy$_2$Ti$_2$O$_7$, and
it resolves a long standing puzzle about its rapidly diverging relaxation time.
The capacity of spin ice to exhibit such striking phenomena holds promise of
further surprising discoveries in the cooperative dynamics of even simple
topological many-body systems.",2211.00051v2
2023-01-26,Generalised Jeffery's equations for rapidly spinning particles. Part 2: Helicoidal objects with chirality,"In this two-part study, we investigate the motion of rigid, active objects in
shear Stokes flow, focusing on bodies that induce rapid rotation as part of
their activity. In Part 2, we derive and analyse governing equations for
rapidly spinning complex-shaped particles - general helicoidal objects with
chirality. Using the multiscale framework we develop in Part 1
(arXiv:2301.11311), we systematically derive emergent equations of motion for
the angular and translational dynamics of these chiral spinning objects. We
show that the emergent dynamics due to rapid rotation can be described by
effective generalised Jeffery's equations, which differ from the classic
versions via the inclusion of additional terms that account for chirality and
other asymmetries. Furthermore, we use our analytic results to characterise and
quantify the explicit effect of rotation on the effective hydrodynamic shape of
the chiral objects, significantly expanding the scope of Jeffery's seminal
study.",2301.11032v3
2023-03-07,Dynamics of bistable Néel domain walls under spin-orbit torque,"N\'eel magnetic domain walls that are stabilized by achiral energy terms
instead of the usual Dzyaloshinskii-Moriya interaction will be bistable, with
the two possible chiral forms being degenerate. Here we focus on the
theoretical study of the spin-orbit torque driven dynamics of such bistable
N\'eel domain walls. We find that, for a given domain wall, two propagation
directions along a nanowire are possible, depending on its initial state. These
dynamics also exhibit complex dependence on the spin-orbit torque magnitude,
leading to important transient regimes. Finally, a few ways are proposed for
controlled or random reversal of the domain wall propagation direction. A
robust analytical model which handles all the observed behaviors of such domain
walls is developed and validated by comparing with numerical simulations. The
obtained new dynamics open the way for new uses of domain walls in information
storage and processing devices.",2303.06142v2
2023-08-23,Magnetic-order-mediated carrier and phonon dynamics in MnBi2Te4,"We investigate the quasiparticle dynamics in MnBi2Te4 single crystal using
the ultrafast optical spectroscopy. Our results show that there exist anomalous
dynamical optical responses below the antiferromagnetic (AFM) ordering
temperature TN. In specific, we reveal that both the initial carrier decay and
recombination processes can be modulated via introducing the AFM order in
sub-picosecond and picosecond timescales, respectively. We also discover a long
relaxation process emerging below TN with a timescale approaching to the
nanosecond regime, and can be attributed to the T-dependent spin-lattice
interaction. There also emerges an unusual phonon energy renormalization below
TN , which is found to arise from its coupling the spin degree via the exchange
interaction and magnetic anisotropy. Our findings provide key information for
understanding the dynamical properties of non-equilibrium carrier, spin and
lattice in MnBi2Te4.",2308.11935v1
2023-09-26,Orbital Pumping by Magnetization Dynamics in Ferromagnets,"We show that dynamics of the magnetization in ferromagnets can pump the
orbital angular momentum, which we denote by orbital pumping. This is the
reciprocal phenomenon to the orbital torque that induces magnetization dynamics
by the orbital angular momentum in non-equilibrium. The orbital pumping is
analogous to the spin pumping established in spintronics but requires the
spin-orbit coupling for the orbital angular momentum to interact with the
magnetization. We develop a formalism that describes the generation of the
orbital angular momentum by magnetization dynamics within the adiabatic
perturbation theory. Based on this, we perform first-principles calculation of
the orbital pumping in prototypical $3d$ ferromagnets, Fe, Co, and Ni. The
results show that the ratio between the orbital pumping and the spin pumping
ranges from 5 to 15 percents, being smallest in Fe and largest in Ni. This
implies that ferromagnetic Ni is a good candidate for measuring the orbital
pumping. Implications of our results on experiments are also discussed.",2309.14817v2
2023-11-30,High harmonic spin-orbit angular momentum generation in crystalline solids preserving multiscale dynamical symmetry,"Symmetries essentially provide conservation rules in nonlinear light-matter
interactions, that facilitate control and understanding of photon conversion
processes or electron dynamics. Since anisotropic solids have rich symmetries,
they are strong candidate to control both optical micro- and macroscale
structures, namely spin (circular polarization) and orbital angular momentum
(spiral wavefront), respectively. Here, we show structured high harmonic
generation linked to the anisotropic symmetry of a solid. By strategically
preserving a dynamical symmetry arising from the spin-orbit interaction of
light, we generate multiple orbital angular momentum states in high-order
harmonics. The experimental results exhibit the total angular momentum
conservation rule of light even in the extreme nonlinear region, which is
evidence that the mechanism originates from a dynamical symmetry. Our study
provides a deeper understanding of multiscale nonlinear optical phenomena and a
general guideline for using electronic structure to control structured light,
such as through Floquet engineering.",2311.18500v3
1992-09-05,Aspects of Spin Dynamics in the Cuprate Superconductors,"One of the interesting aspects of the CuO superconductors is that
superconductivity is happening so close to the antiferromagnetic state. The
nuclear magnetic resonance and the recent neutron scattering experiments
clearly indicate that magnetic correlations persist in to the heavily doped
regime. In this paper we will discuss some of the details of the coupling of
the nuclear magnetic spin to the conduction electron spins. Furthermore we will
show that a simple band structure can explain the recent neutron scattering
data in the \LaSrCuO material for the optimal concentration of $x\approx 0.15$
if the lifetime effects are included.",9209005v1
1993-12-14,Finite-Temperature Transition into a Power-Law Spin Phase with an Extensive Zero-Point Entropy,"We introduce an $xy$ generalization of the frustrated Ising model on a
triangular lattice. The presence of continuous degrees of freedom stabilizes a
{\em finite-temperature} spin state with {\em power-law} discrete spin
correlations and an extensive zero-point entropy. In this phase, the unquenched
degrees of freedom can be described by a fluctuating surface with logarithmic
height correlations. Finite-size Monte Carlo simulations have been used to
characterize the exponents of the transition and the dynamics of the
low-temperature phase.",9312057v1
1994-02-03,Exact Results for Spin and Charge Dynamics of Electrons with Supersymmetry,"Excitation spectra in the SU($\nu +1$,1) supersymmetric t-J model with
long-range exchange and transfer has quadratic dependence on spin and charge
currents for all energies. After brief review on the supersymmetry, this paper
gives a simple explanation for the spin-charge separation on the basis of a
first-quantized representation. A useful identity is derived on permutation
properties of SU($\nu$) Jastrow-type wave functions, which constitute the
ground states for a class of 1/$r^2$ interaction models.",9402009v1
1994-02-27,Thermocycling experiments with the three-dimensional Ising spin glass model,"A characteristic feature of the non--equilibrium dynamics of real spin
glasses at low temperatures are strong aging effects. These phenomena can be
manipulated by changing the external parameters in various ways: a
thermo-cycling experiment consists for instance of a short heat pulse during
the waiting time, by which the relaxation might be strongly affected. Results
of numerical experiments of this kind, performed via Monte Carlo simulations of
the three dimensional Ising spin glass model, are presented. The theoretical
implications are discussed and the scenario found is compared with the
experimental situation.",9402109v1
1994-07-26,Toulouse limit for the overscreened four-channel Kondo problem,"We show that the spin dynamics of the 4--channel Kondo model is equivalent to
the one of a model with a spin 1/2 impurity coupled to spin 1 conduction
electrons. By abelian bosonization of the latter model we find a kind of
Toulouse limit analogous to that recently discussed by Emery and Kivelson for
the 2--channel case. We analyse the model by exploiting the close analogy to
the problem of an impurity in the Luttinger liquid.",9407104v1
1995-12-29,Equation of Motion for a Spin Vortex and Geometric Force,"The Hamiltonian equation of motion is studied for a vortex occuring in
2-dimensional Heisenberg ferromagnet of anisotropic type by starting with the
effective action for the spin field formulated by the Bloch (or spin) coherent
state. The resultant equation shows the existence of a geometric force that is
analogous to the so-called Magnus force in superfluid. This specific force
plays a significant role for a quantum dynamics for a single vortex, e.g, the
determination of the bound state of the vortex trapped by a pinning force
arising from the interaction of the vortex with an impurity.",9512175v1
1996-03-02,Relaxational behavior of the infinite-range Ising spin-glass in a transverse field,"We study the zero-temperature behavior of the infinite-ranged Ising spin
glass in a transverse field. Using spin summation techniques and Monte Carlo
methods we characterize the zero-temperature quantum transition. Our results
are well compatible with a value $\nu=\frac{1}{4}$ for the correlation length
exponent, $z=4$ for the dynamical exponent and an algebraic decay $t^{-1}$ for
the imaginary-time correlation function. The zero-temperature relaxation of the
energy in the presence of the transverse field shows that the system
monotonically reaches the ground state energy due to tunneling processes and
displays strong glassy effects.",9603012v1
1996-11-13,Dramatic Switching of Magnetic Exchange in a Classic Transition Metal Oxide: Evidence for Orbital Ordering,"Spin correlations in metallic and insulating phases of $V_2O_3$ and its
derivatives are investigated using magnetic neutron scattering. Metallic
samples have incommensurate spin correlations varying little with hole doping.
Paramagnetic insulating samples have spin correlations only among near
neighbors. The transition from either of these phases into the low temperature
insulating antiferromagnetic phase is accompanied by an abrupt change of
dynamic magnetic short range order. Our results support the idea that the
transition into the antiferromagnetic insulator is also an orbital ordering
transition.",9611109v1
1996-12-02,One-dimensional spin-liquid without magnon excitations,"It is shown that a sufficiently strong four-spin interaction in the spin-1/2
spin ladder can cause dimerization. Such interaction can be generated either by
phonons or (in the doped state) by the conventional Coulomb repulsion between
the holes. The dimerized phases are thermodynamically undistinguishable from
the Haldane phase, but have dramatically different correlation functions: the
dynamical magnetic susceptibility, instead of displaying a sharp single magnon
peak near $q = \pi$, shows only a two-particle threshold separated from the
ground state by a gap.",9612014v2
1997-01-05,Numerical Simulations of Spin Glass Systems,"We discuss the status of Monte Carlo simulations of (mainly finite
dimensional) spin glass systems. After a short historical note and a brief
theoretical introduction we start by discussing the (crucial) 3D case: the warm
phase, the critical point and the cold phase, the ultrametric structure and the
out of equilibrium dynamics. With the same style we discuss the cases of 4D and
2D. In a few appendices we give some details about the definition of states and
about the tempering Monte Carlo approach.",9701016v1
1997-03-02,On the Self-Consistent Spin-Wave Theory of Two-Dimensional Magnets With Impurities,"The self-consistent spin-wave theory is applied to investigate the
magnetization distribution around the impurity in isotropic and easy-axis
two-dimensional ferro- and antiferromagents. The temperature dependences of
host magnetization disturbance and impurity magnetization are calculated. The
short-range order in the isotropic case is investigated. Importance of dynamic
and kinematic interactions of spin waves is demonstrated.",9703010v1
1997-06-09,Non-Markovian Persistence at the PC point of a 1d non-equilibrium kinetic Ising model,"One-dimensional non-equilibrium kinetic Ising models evolving under the
competing effect of spin flips at zero temperature and nearest neighbour spin
exchanges exhibiting a parity-conserving (PC) phase transition on the level of
kinks are investigated here numerically from the point of view of the
underlying spin system. The dynamical persistency exponent $\Theta$ and the
exponent $lambda$ characterising the two-time autocorrelation function of the
total magnetization under non-equilibrium conditions are reported. It is found
that the PC transition has strong effect: the process becomes non-Markovian and
the above exponents exhibit drastic changes as compared to the Glauber-Ising
case.",9706083v1
1997-10-15,Softening and Broadening of the Zone Boundary Magnons in Pr0.63Sr0.37MnO3,"We have studied the spin dynamics in Pr$_{0.63}$Sr$_{0.37}$MnO$_3$ above and
below the Curie temperature $T_C=301$ K. Three distinct new features have been
observed: a softening of the magnon dispersion at the zone boundary for
$T<T_C$, significant broadening of the zone boundary magnons as $T\to T_C$, and
no evidence for residual spin-wave like excitations just above $T_C$. The
results are inconsistent with double exchange models that have been
successfully applied to higher $T_C$ samples, indicating an evolution of the
spin system with decreasing $T_C$.",9710157v1
1997-10-22,Muon spin rotation and relaxation in magnetic materials,"A review of the muon spin rotation and relaxation ($\mu$SR) studies on
magnetic materials published from July 1993 is presented. It covers the
investigation of magnetic phase diagrams, of spin dynamics and the analysis of
the magnetic properties of superconductors. We have chosen to focus on selected
experimental works in these different topics. In addition, a list of published
works is provided.",9710235v1
1998-04-29,Anomalous diffusion in disordered media and random quantum spin chains,"Using exact expressions for the persistence probability and for the leading
eigenvalue of the Focker-Planck operator of a random walk in a random
environment we establish a fundamental relation between the statistical
properties of anomalous diffusion and the critical and off-critical behavior of
random quantum spin chains. Many new exact results are obtained from this
correspondence including the space and time correlations of surviving random
walks and the distribution of the gaps of the corresponding Focker-Planck
operator. In turn we derive analytically the dynamical exponent of the random
transverse-field Ising spin chain in the Griffiths-McCoy region.",9804316v1
1998-09-27,Magnetic Incommensurability in Doped Mott Insulator,"In this paper we explore the incommensurate spatial modulation of spin-spin
correlations as the intrinsic property of the doped Mott insulator, described
by the $t-J$ model. We show that such an incommensurability is a direct
manifestation of the phase string effect introduced by doped holes in both one-
and two-dimensional cases. The magnetic incommensurate peaks of dynamic spin
susceptibility in momentum space are in agreement with the neutron-scattering
measurement of cuprate superconductors in both position and doping dependence.
In particular, this incommensurate structure can naturally reconcile the
neutron-scattering and NMR experiments of cuprates.",9809363v1
1999-02-18,Spin Dynamical Properties of the Layered Perovskite La1.2Sr1.8Mn2O7,"Inelastic neutron-scattering measurements were performed on a single crystal
of the layered colossal magnetoresistance (CMR) material La1.2Sr1.8Mn2O7 (Tc ~
120K). We found that the spin wave dispersion is almost perfectly
two-dimensional with the in-plane spin stiffness constant D ~ 151meVA. The
value is similar to that of similarly doped La1-xSrxMnO3 though its Tc is three
times higher, indicating a large renormalization due to low dimensionality.
There exist two branches due to a coupling between layers within a
double-layer. The out-of-plane coupling is about 30% of the in-plane coupling
though the Mn-O bond lengths are similar.",9902253v1
1999-04-26,Magnon Damping by magnon-phonon coupling in Manganese Perovskites,"Inelastic neutron scattering was used to systematically investigate the
spin-wave excitations (magnons) in ferromagnetic manganese perovskites. In
spite of the large differences in the Curie temperatures ($T_C$s) of different
manganites, their low-temperature spin waves were found to have very similar
dispersions with the zone boundary magnon softening. From the wavevector
dependence of the magnon lifetime effects and its correlation with the
dispersions of the optical phonon modes, we argue that a strong magneto-elastic
coupling is responsible for the observed low temperature anomalous spin
dynamical behavior of the manganites.",9904372v1
1999-10-04,Spin Susceptibility in Underdoped $\bf YBa_2Cu_3O_{6+x}$,"We report a comprehensive polarized and unpolarized neutron scattering study
of the evolution of the dynamical spin susceptibility with temperature and
doping in three underdoped single crystals of the \YBCO{6+x} high temperature
superconductor: \YBCO{6.5} (Tc = 52 K), \YBCO{6.7} (Tc = 67 K), and \YBCO{6.85}
(T_c = 87 K). Theoretical implications of these data are discussed, and a
critique of recent attempts to relate the spin excitations to the
thermodynamics of high temperature superconductors is given.",9910041v2
1999-10-28,Dynamic Nuclear Overhauser Shifts in Larmor beats from a quantum well,"The significance of nuclear spin polarisation in time-resolved optical
studies of III-V semiconductors is addressed. Electron Larmor beats in
pump-probe reflectivity from a GaAs/AlGaAs quantum well show Overhauser shift
of 0.7 T due to accumulated nuclear polarisation <I>/I=0.065. This leads to
precision values of electron g-factor, elucidates nuclear spin pumping and
diffusion mechanisms in quantum wells and informs discussion of implications
for spin-electronics and transport.",9910475v1
2000-01-21,Theory of Diluted Magnetic Semiconductor Ferromagnetism,"We present a theory of carrier-induced ferromagnetism in diluted magnetic
semiconductors (III_{1-x} Mn_x V) which allows for arbitrary itinerant-carrier
spin polarization and dynamic correlations. Both ingredients are essential in
identifying the system's elementary excitations and describing their
properties. We find a branch of collective modes, in addition to the spin waves
and Stoner continuum which occur in metallic ferromagnets, and predict that the
low-temperature spin stiffness is independent of the strength of the exchange
coupling between magnetic ions and itinerant carriers. We discuss the
temperature dependence of the magnetization and the heat capacity.",0001320v2
2000-02-20,Impurity spin dynamics in 2D antiferromagnets and superconductors,"We discuss the universal theory of localized impurities in the paramagnetic
state of 2D antiferromagnets where the spin gap is assumed to be significantly
smaller than a typical exchange energy. We study the impurity spin
susceptibility near the host quantum transition from a gapped paramagnet to a
Neel state, and we compute the impurity-induced damping of the spin-1 mode of
the gapped antiferromagnet. Under suitable conditions our results apply also to
d-wave superconductors.",0002316v1
2000-05-23,Griffiths-McCoy singularities in random quantum spin chains: Exact results through renormalization,"The Ma-Dasgupta-Hu renormalization group (RG) scheme is used to study
singular quantities in the Griffiths phase of random quantum spin chains. For
the random transverse-field Ising spin chain we have extended Fisher's
analytical solution to the off-critical region and calculated the dynamical
exponent exactly. Concerning other random chains we argue by scaling
considerations that the RG method generally becomes asymptotically exact for
large times, both at the critical point and in the whole Griffiths phase. This
statement is checked via numerical calculations on the random Heisenberg and
quantum Potts models by the density matrix renormalization group method.",0005375v1
2000-07-04,Spin dynamics and ordering of a cuprate stripe-antiferromagnet,"In La1.48Nd0.4Sr0.12CuO4 the 139La and 63Cu NQR relaxation rates and signal
wipe-out upon lowering temperature are shown to be due to purely magnetic
fluctuations. They follow the same renormalized classical behavior as seen in
neutron data, when the electronic spins order in stripes, with a small spread
in spin stiffness (15% spread in activation energy). The La signal, which
reappears at low temperatures, is magnetically broadened and experiences
additional wipe-out due to slowing down of the Nd fluctuations.",0007057v2
2000-07-05,Memory and superposition in a spin glass,"Non-equilibrium dynamics in a Ag(Mn) spin glass are investigated by
measurements of the temperature dependence of the remanent magnetisation. Using
specific cooling protocols before recording the thermo- or isothermal remanent
magnetisations on re-heating, it is found that the measured curves effectively
disclose non-equilibrium spin glass characteristics such as ageing and memory
phenomena as well as an extended validity of the superposition principle for
the relaxation. The usefulness of this ""simple"" dc-method is discussed, as well
as its applicability to other disordered magnetic systems.",0007070v2
2000-10-03,"Continuum in the spin excitation spectrum of a Haldane chain, observed by neutron scattering in CsNiCl3","The spin excitation continuum, expected to dominate the low-energy
fluctuation spectrum in the Haldane spin chain around the Brillouin zone
center, q=0, is directly observed by inelastic magnetic neutron scattering in
the S=1 quasi-1D antiferromagnet CsNiCl3. We find that the single mode
approximation fails, and that a finite energy width appears in the dynamic
correlation function S(q,omega) for q < 0.5pi. The width increases with
decreasing q, while S(q,omega) acquires an asymmetric shape qualitatively
similar to that predicted for the 2-magnon continuum in the nonlinear
sigma-model.",0010049v1
2001-01-25,"Comment on ""Critical spin dynamics of the 2D quantum Heisenberg antiferromagnets: Sr2CuO2Cl2 and Sr2Cu3O4Cl2""","We compare the neutron measurements of Kim et al. (cond-mat/0012239) on
two-dimensional, S=1/2 antiferromagnets with the continuum quasiclassical
theory of S. Sachdev and O.A. Starykh (cond-mat/9904354). The damping of the
lowest energy spin excitations is characterized by a dimensionless number whose
temperature dependence was predicted to be determined entirely by that of the
uniform spin susceptibility. Theory and experiment are consistent with each
other.",0101394v1
2001-01-29,NMR Relaxation Rate for 1D Multicomponent Spin-Orbital Systems,"The NMR relaxation rate $1/T_{1}$ is studied for one-dimensional
multicomponent spin-orbital systems. By combining the bosonization techniques
and the exact solution of the SU($n$) model, we evaluate the power-law exponent
and the enhancement factor for $1/T_1$ at low temperatures. We discuss how the
band splitting affects the relaxation rate, and find that $1/T_{1}$ may be
enhanced around the critical value of the band splitting. The crossover
behavior in $1/T_1$ around the critical point is discussed in terms of the
low-frequency dynamical spin susceptibility. The effect of the hole-doping is
also addressed.",0101422v1
2001-01-29,Magnetic Properties for the One-Dimensional Multicomponent Spin-Gap System,"Magnetic properties for the one-dimensional multicomponent quantum spin
system with the excitation gap are studied based on the integrable spin model
introduced by Bariev {\it et al}. By exactly computing the magnetization, we
show how the characteristic structure with plateaus and cusps appears in the
magnetization process. To study low-energy dynamics of the system, we apply the
finite-size scaling analysis to the excitation spectrum, and thereby evaluate
the power-law exponent as well as the enhancement factor for the
low-temperature NMR relaxation rate $1/T_1$. We discuss the critical properties
of $1/T_1$ around plateaus and cusps in the magnetization curve.",0101423v1
2001-04-16,Enhancement of Nuclear Spin Superradiance by Electron Resonator,"Superradiance of nuclear spins is considered, when the nuclei interact via
hyperfine forces with electrons of a ferromagnet. The consideration is based on
a microscopic model. If the sample, coupled with a resonant electric circuit,
possesses electronic magnetization, then the electron subsystem plays the role
of an additional effective resonator, by enhancing the coupling between nuclear
spins and the resonant circuit. Radiation power can be increased by three
orders, while the radiation time of a superradiance burst can become three
times shorter. In the presence of dynamic nuclear polarization, the regime of
pulsing superradiance can occur.",0104276v1
2001-05-10,Spin dynamics in the $S=1/2$ weakly-coupled chains antiferromagnet BaCu$_2$Si$_2$O$_7$,"Inelastic neutron scattering is used to identify single-particle and
continuum spin excitations in the quasi-one-dimensional $S=1/2$ antiferromagnet
\ba. In the data analysis, close attention is given to resolution effects. A
gap in the continuum spectrum at $\Delta_c=4.74.8$ meV is directly observed.
The gap energy is in excellent agreement with existing theoretical predictions.
Below the gap, the spectrum is dominated by sharp accoustic spin wave
excitations.",0105223v1
2001-09-10,ESR theory for interacting 1D quantum wires,"We compute the electron spin resonance (ESR) intensity for one-dimensional
quantum wires in semiconductor heterostructures, taking into account
electron-electron interactions and spin-orbit coupling. The ESR spectrum is
shown to be very sensitive to interactions. While in the absence of
interactions, the spectrum is a flat band, characteristic threshold
singularities appear in the interacting limit. This suggests the practical use
of ESR to reveal spin dynamics in a Luttinger liquid.",0109161v1
2001-12-20,Domain growth by isothermal aging in 3d Ising and Heisenberg spin glasses,"Non-equilibrium dynamics of three dimensional model spin glasses - the Ising
system Fe$_{0.50}$Mn$_{0.50}$TiO$_3$ and the Heisenberg like system Ag(11 at%
Mn) - has been investigated by measurements of the isothermal time decay of the
low frequency ac-susceptibility after a quench from the paramagnetic to the
spin glass phase. It is found that the relaxation data measured at different
temperatures can be scaled according to predictions from the droplet scaling
model, provided that critical fluctuations are accounted for in the analyzes.",0112389v2
2002-01-14,Novel Order Parameter to Characterize Valence-Bond-Solid States,"We propose an order parameter to characterize valence-bond-solid (VBS) states
in quantum spin chains, given by the ground-state expectation value of a
unitary operator appearing in the Lieb-Schultz-Mattis argument. We show that
the order parameter changes the sign according to the configuration of the
valence bonds. This allows us to determine the phase transition point in
between different VBS states accurately. We demonstrate this theory in the
bond-alternating Heisenberg chain and in the frustrated spin ladder.",0201204v1
2002-05-21,Transition rates via Bethe ansatz for the spin-1/2 Heisenberg chain,"We use the exact determinantal representation derived by Kitanine, Maillet,
and Terras for matrix elements of local spin operators between Bethe wave
functions of the one-dimensional s=1/2 Heisenberg model to calculate and
numerically evaluate transition rates pertaining to dynamic spin structure
factors. For real solutions z_1,...,z_r of the Bethe ansatz equations, the size
of the determinants is of order r x r. We present applications to the
zero-temperature spin fluctuations parallel and perpendicular to an external
magnetic field.",0205430v1
2002-07-02,Internal localized eigenmodes on spin discrete breathers in antiferromagnetic chains with on-site easy axis anisotropy,"We investigate internal localized eigenmodes of the linearized equation
around spin discrete breathers in 1D antiferromagnets with on-site easy axis
anisotropy. The threshold of occurrence of the internal localized eigenmodes
has a typical structure in parameter space depending on the frequency of the
spin discrete breather. We also performed molecular dynamics simulation in
order to show the validity of our linear analysis.",0207053v1
2002-10-03,A comparison of extremal optimization with flat-histogram dynamics for finding spin-glass ground states,"We compare the performance of extremal optimization (EO), flat-histogram and
equal-hit algorithms for finding spin-glass ground states. The
first-passage-times to a ground state are computed. At optimal parameter of
tau=1.15, EO outperforms other methods for small system sizes, but equal-hit
algorithm is competitive to EO, particularly for large systems. Flat-histogram
and equal-hit algorithms offer additional advantage that they can be used for
equilibrium thermodynamic calculations. We also propose a method to turn EO
into a useful algorithm for equilibrium calculations.
  Keywords: extremal optimization. flat-histogram algorithm, equal-hit
algorithm, spin-glass model, ground state.",0210075v1
2002-10-31,Frustrated spin model as a hard-sphere liquid,"We show that one-dimensional topological objects (kinks) are natural degrees
of freedom for an antiferromagnetic Ising model on a triangular lattice. Its
ground states and the coexistence of spin ordering with an extensive
zero-temperature entropy can be easily understood in terms of kinks forming a
hard-sphere liquid. Using this picture we explain effects of quantum spin
dynamics on that frustrated model, which we also study numerically.",0210711v1
2002-11-05,Magnetic fluctuations and resonant peak in cuprates: a microscopic theory,"The theory for the dynamical spin susceptibility within the t-J model is
developed, as relevant for the resonant magnetic peak and normal-state magnetic
response in superconducting (SC) cuprates. The analysis is based on the
equations of motion for spins and the memory-function presentation of magnetic
response where the main damping of the low-energy spin collective mode comes
from the decay into fermionic degrees of freedom. It is shown that the damping
function at low doping is closely related to the c-axis optical conductivity.
The analysis reproduces doping-dependent features of the resonant magnetic
scattering.",0211090v1
2002-11-22,Propagating beliefs in spin glass models,"We investigate dynamics of an inference algorithm termed the belief
propagation (BP) when employed in spin glass (SG) models and show that its
macroscopic behaviors can be traced by recursive updates of certain auxiliary
field distributions whose stationary state reproduces the replica symmetric
solution offered by the equilibrium analysis. We further provide a compact
expression for the instability condition of the BP's fixed point which turns
out to be identical to that of instability for breaking the replica symmetry in
equilibrium when the number of couplings per spin is infinite. This
correspondence is extended to a SG model of finite connectivity to determine
the phase diagram, which is numerically supported.",0211500v1
2003-01-21,Hole-Doping Effects on a Two-dimensional Kondo Insulator,"We study the effects of hole doping on the two-dimensional Heisenberg-Kondo
model around the quantum critical point, where the spin liquid phase (Kondo
insulator) and the magnetically ordered phase are separated via a second-order
phase transition. By means of the self-consistent Born approximation within the
bond operator formalism as well as the standard spin wave theory, we discuss
dynamical properties of a doped hole. It is clarified that a quasi-particle
state stabilized in the spin liquid phase is gradually obscured as the system
approaches the quantum critical point. This is also the case for the
magnetically ordered phase. We argue the similarity and the difference between
these two cases.",0301401v1
2003-02-27,Off Equilibrium Study of the Fluctuation-Dissipation Relation in the Easy-Axis Heisenberg Antiferromagnet on the Kagome Lattice,"Violation of the fluctuation-dissipation theorem (FDT) in a frustrated
Heisenberg model on the Kagome lattice is investigated using Monte Carlo
simulations. The model exhibits glassy behaviour at low temperatures
accompanied by very slow dynamics. Both the spin-spin autocorrelation function
and the response to an external magnetic field are studied. Clear evidence of a
constant value of the fluctuation dissipation ratio and long range memory
effects are observed for the first time in this model. The breakdown of the FDT
in the glassy phase follows the predictions of the mean field theory for spin
glasses with one-step replica symmetry breaking.",0302594v1
2003-07-21,Nuclear Magnetic Resonance in a Ferromagnet-Semiconductor Heterostructure,"We report the observation of nuclear magnetic resonance (NMR) in a
ferromagnet-semiconductor heterostructure in the presence of a spin-polarized
current. Spin-polarized electrons injected from a metallic ferromagnet generate
a large nuclear spin population in a GaAs quantum well by dynamic polarization.
The characteristic time for the polarization process is approximately 20 sec,
and the nuclear polarization can persist for several minutes after the current
is turned off. Resonant depolarization is observed in the presence of an AC
magnetic field or when the injection current is modulated at the NMR frequency.",0307512v1
2003-08-24,Nuclear spin qubits in a pseudo-spin quantum chain,"We analyze a quantum computer (QC) design based on nuclear spin qubits in a
quasi-one-dimensional (1D) chain of non-Kramers doublet atoms. We explore the
use of spatial symmetry breaking to obtain control over the local dynamics of a
qubit. We also study the decoherence mechanisms at the single qubit level and
the interactions mediated by the magnetic media. The design can be realized in
$\textrm{PrBr}_{\textrm{3}-x}\textrm{F}_{x}$ with nuclear magnetic resonance
(NMR) techniques.",0308475v2
2003-10-12,Spin Fluctuation in Heavy Fermion CeRu_2Si_2,"Spin fluctuations of the archetypal heavy-fermion compound CeRu_2Si_2 have
been investigated by neutron scattering in an entire irreducible Brillouin
zone. The dynamical susceptibility is remarkably well described by the
self-consistent renormalization (SCR) theory of the spin fluctuation in a
phenomenological way, proving the effectiveness of the theory. The present
analysis using the SCR phenomenology has allowed us to determine fourteen
exchange constants, which show the long-range nature of the
Ruderman-Kittel-Kasuya-Yosida interaction.",0310270v3
2003-10-24,Spin-Charge Separation in Two-dimensional Frustrated Quantum Magnets,"The dynamics of a mobile hole in two-dimensional frustrated quantum magnets
is investigated by exact diagonalization techniques. Our results provide
evidence for spin-charge separation upon doping the kagome lattice, a prototype
of a spin liquid. In contrast, in the checkerboard lattice, a symmetry broken
Valence Bond Crystal, a small quasi-particle peak is seen for some crystal
momenta, a finding interpreted as a restoration of weak holon-spinon
confinement.",0310597v2
2003-12-02,Effects of dissipation on disordered quantum spin models,"We study the effects of the coupling to an Ohmic quantum reservoir on the
static and dynamical properties of a family of disordered SU(2) spin models in
a transverse magnetic field using a method of direct spin summation. The
tendency to form a glassy phase increases with the strength of the coupling of
the system to the environment. We study the influence of the environment on the
features of the phase diagram of the various models as well as the stability of
the possible phases.",0312064v1
2003-12-15,Thermodynamics of a one-dimensional S=1/2 spin-orbital model,"The thermodynamic properties of a one-dimensional model describing spin
dynamics in the presence of a twofold orbital degeneracy are studied
numerically using the transfer-matrix renormalization group (TMRG). The model
contains an integrable SU(4)-symmetric point and a gapless phase which is SU(4)
invariant up to a rescaling of the velocities for spin and orbital degrees of
freedom which allows detailed comparison of the numerical results with
conformal field theory. We pay special attention to the correlation lengths
which show an intriguing evolution with temperature. We find that the model
shows an intrinsic tendency towards dimerization at finite temperature even if
the ground state is not dimerized.",0312365v1
2004-01-07,Spin-triplet s-wave local pairing induced by Hund's rule coupling,"We show within the dynamical mean field theory that local multiplet
interactions such as Hund's rule coupling produce local pairing
superconductivity in the strongly correlated regime. Spin-triplet
superconductivity driven by the Hund's rule coupling emerges from the pairing
mediated by local fluctuations in pair exchange. In contrast to the
conventional spin-triplet theories, the local orbital degrees of freedom has
the anti-symmetric part of the exchange symmetry, leaving the spatial part as
fully gapped and symmetric s-wave.",0401104v1
2004-01-14,The spin resonance and high frequency optical properties of the cuprates,"We argue that recently observed superconductivity-induced blue shift of the
plasma frequency $\delta \omega_{pl}$ in $Bi_2Sr_2CaCu_2O_{8+\delta}$ is
related to the change in the integrated dynamical structure factor associated
with the development of the spin resonance below $T_c$. We show that the
magnitude of $\delta \omega_{pl}$ is consistent with the small integrated
spectral weight of the resonance, and its temperature dependences closely
follow that of the spin resonance peak.",0401241v1
2004-01-20,The spin excitation spectrum in striped bilayer compounds,"The spin dynamics of bilayer cuprate compounds are studied in a basic model.
The magnetic spectral properties are calculated in linear spin-wave theory for
several stripe configurations which differ by the relative location of the
stripes in the layers. We focus on the bilayer splitting of the magnon bands
near the incommensurate low energy peaks as well as near the $\pi$ resonance,
distinguishing between the odd and even channel. We find that a x-shaped
dispersion near the $\pi$ resonance is generic for stripes. By comparison of
our results to neutron scattering data for $\mathrm{YBa_2Cu_3O_{6+x}}$ we
conclude that the stripe model is consistent with characteristic features of
bilayer high-$T_c$ compounds.",0401354v1
2004-02-10,Broken Ergodicity in classically chaotic spin systems,"A one dimensional classically chaotic spin chain with asymmetric coupling and
two different inter-spin interactions, nearest neighbors and all-to-all, has
been considered. Depending on the interaction range, dynamical properties, as
ergodicity and chaoticity are strongly different. Indeed, even in presence of
chaoticity, the model displays a lack of ergodicity only in presence of all to
all interaction and below an energy threshold, that persists in the
thermodynamical limit. Energy threshold can be found analytically and results
can be generalized for a generic XY model with asymmetric coupling.",0402270v1
2004-05-15,Spin-Photon Dynamics of Quantum Dots in Two-mode Cavities,"A quantum dot interacting with two resonant cavity modes is described by a
two-mode Jaynes-Cummings model. Depending on the quantum dot energy level
scheme, the interaction of a singly doped quantum dot with a cavity photon
generates entanglement of electron spin and cavity states or allows one to
implement a SWAP gate for spin and photon states. An undoped quantum dot in the
same structure generates pairs of polarization entangled photons from an
initial photon product state. For realistic cavity loss rates, the fidelity of
these operations is of order 80%.",0405342v2
2004-07-06,The spherical $2+p$ spin glass model: an exactly solvable model for glass to spin-glass transition,"We present the full phase diagram of the spherical $2+p$ spin glass model
with $p\geq 4$. The main outcome is the presence of a new phase with both
properties of Full Replica Symmetry Breaking (FRSB) phases of discrete models,
e.g, the Sherrington-Kirkpatrick model, and those of One Replica Symmetry
Breaking (1RSB). The phase, which separates a 1RSB phase from FRSB phase, is
described by an order parameter function $q(x)$ with a continuous part (FRSB)
for $x<m$ and a discontinuous jump (1RSB) at $x=m$. This phase has a finite
complexity which leads to different dynamic and static properties.",0407129v1
2004-07-19,Scaling approach to glassy stationary states of spin-glasses under chaos effects,"Dynamics of spin-glasses subjected to slow continuous changes of working
enviroment such as slow changes of temperature or interaction bonds are studied
based on scaling arguments and numerical simulations of continuous bond
changes. Such perturbations lead to a glassy stationary state where the age or
domain size of the system are pinned to macroscopic but finite values due to
competition between relaxation and chaos effects (rejuvenation).
Flutuation-dissipation relation is also pinned to that of a finite age. The
scenario explains the anomalously weak cooling rate dependece of spin glasses.",0407459v2
2004-08-04,Two-cycles in spin systems: multi-state Ising-type ferromagnets,"Hamiltonians for general multi-state spin-glass systems with Ising symmetry
are derived for both sequential and synchronous updating of the spins. The
possibly different behaviour caused by the way of updating is studied in detail
for the (anti)-ferromagnetic version of the models, which can be solved
analytically without any approximation, both thermodynamically via a
free-energy calculation and dynamically using the generating functional
approach. Phase diagrams are discussed and the appearance of two-cycles in the
case of synchronous updating is examined. A comparative study is made for the
Q-Ising and the Blume-Emery-Griffiths ferromagnets and some interesting
physical differences are found. Numerical simulations confirm the results
obtained.",0408086v1
2004-09-25,Competing effects of interactions and spin-orbit coupling in a quantum wire,"We study the interplay of electron-electron interactions and Rashba
spin-orbit coupling in one-dimensional ballistic wires. Using the
renormalization group approach we construct the phase diagram in terms of
Rashba coupling, Tomonaga-Luttinger stiffness and backward scattering strength.
We identify the parameter regimes with a dynamically generated spin gap and
show where the Luttinger liquid prevails. We also discuss the consequences for
the operation of the Datta-Das transistor.",0409678v2
2004-11-09,Magnetization reversal in spin patterns with complex geometry,"We study field-driven dynamics of spins with antiferromagnetic interaction
along the links of a complex substrate geometry, which is modeled by graphs of
a controlled connectivity distribution. The magnetization reversal occurs in
avalanches of spin flips, which are pinned by the topological constraints of
the underlying graph. The hysteresis loop and avalanche sizes are analyzed and
classified in terms of graph's connectivity and clustering. The results are
relevant for magnets with a hierarchical spatial inhomogeneity and for design
of nanoscale magnetic devices.",0411223v1
2004-11-18,Charge and spin dynamics of interacting Fermions in a one dimensional harmonic trap,"We study an atomic Fermi gas interacting through repulsive contact forces in
a one dimensional harmonic trap. Bethe-Ansatz solutions lead to an
inhomogeneous Tomonaga-Luttinger model for the low energy excitations. The
equations of motion for charge and spin density waves are analyzed both near
the trap center and near the trap edges. While the center shows conventional
spin-charge separation the edges cause a giant increase of the separation
between these modes.",0411480v1
2004-12-06,Spin Liquid Behavior in Electronic Griffiths Phases,"We examine the interplay of the Kondo effect and the RKKY interactions in
electronic Griffiths phases using extended dynamical mean-field theory methods.
We find that sub-Ohmic dissipation is generated for sufficiently strong
disorder, leading to suppression of Kondo screening on a finite fraction of
spins, and giving rise to universal spin-liquid behavior.",0412100v2
2004-12-22,Quantum Magnets with Anisotropic Infinite Range Random Interactions,"Using exact diagonalization techniques we study the dynamical response of the
anisotropic disordered Heisenberg model for systems of S=1/2 spins with
infinite range random exchange interactions at temperature T=0. The model can
be considered as a generalization, to the quantum case, of the well known
Sherrington-Kirkpatrick classical spin-glass model. We also compute and study
the behavior of the Edwards Anderson order parameter and energy per spin as the
anisotropy evolves from the Ising to the Heisenberg limits.",0412632v1
2005-03-01,Spin-orbital physics in the optical conductivity of quarter-filled manganites,"Using finite-temperature diagonalization we investigate the optical
conductivity $\sigma(\omega)$ and spin-orbital dynamics in the CE phase of
half-doped manganites. We find $\sigma(\omega)$ characterized by a broad
spectrum with pronounced optical gap due to charge ordering induced by Coulomb
and further neighbor Jahn-Teller interactions. With increasing temperature the
conductivity shows a significant change over a wide energy range with a
characteristic shift towards lower frequencies. In the low temperature CE phase
we observe in-gap absorption due to combined orbiton-spin excitations.",0503011v1
2005-04-19,Spin-glass behavior in the random-anisotropy Heisenberg model,"We perform Monte Carlo simulations in a random anisotropy magnet at a
intermediate exchange to anisotropy ratio. We focus on the out of equilibrium
relaxation after a sudden quenching in the low temperature phase, well below
the freezing one. By analyzing both the aging dynamics and the violation of the
Fluctuation Dissipation relation we found strong evidence of a spin--glass like
behavior. In fact, our results are qualitatively similar to those
experimentally obtained recently in a Heisenberg-like real spin glass.",0504483v2
2005-06-19,Anisotropic Hubbard model on a triangular lattice -- spin dynamics in Ho Mn O_3,"The recent neutron-scattering data for spin-wave dispersion in $\rm Ho Mn
O_3$ are well described by an anisotropic Hubbard model on a triangular lattice
with a planar (XY) spin anisotropy. Best fit indicates that magnetic
excitations in $\rm Ho Mn O_3$ correspond to the strong-coupling limit $U/t >
\sim 15$, with planar exchange energy $J=4t^2/U \simeq 2.5$meV and planar
anisotropy $\Delta U \simeq 0.35$meV.",0506475v3
2005-08-08,23Na NMR Studies of Non-superconducting and Superconducting Na0.35CoO2-1.3H2O (Tc < 1.8 and ~ 4.5 K),"We report 23Na NMR studies of the polycrystalline samples of bilayer hydrated
cobalt oxides Na0.35CoO2-1.3H2O with the superconducting transition
temperatures Tc < 1.8 and ~ 4.5 K. The magnitude of the 23Na nuclear
spin-lattice relaxation rate 23(1/T1) significantly decreased from non-hydrated
Na0.7CoO2 to the bilayer hydrates. We found that the temperature dependence of
23(1/T1) of the non-superconducting bilayer hydrate is similar to that of the
non-hydrated Na0.7CoO2, the spin dynamics of which is understood by A-type
(intra-layer ferromagnetic and inter-layer antiferromagnetic) spin
fluctuations. The superconducting phase is located close to the A-type magnetic
instability.",0508197v1
2005-11-03,Electron-phonon coupling and spin-charge separation in one-dimensional Mott insulators,"We examine the single-particle excitation spectrum in the one-dimensional
Hubbard-Holstein model at half-filling by performing the dynamical density
matrix renormalization group (DDMRG) calculation. The DDMRG results are
interpreted as superposition of spectra for a spinless carrier dressed with
phonons. The superposition is a consequence of robustness of the spin-charge
separation against electron-phonon coupling. The separation is in contrast to
the coupling between phonon and spin degrees of freedom in two-dimensional
systems. We discuss implication of the results of the recent angle-resolved
photoemission spectroscopy measurements on SrCuO${}_{2}$.",0511068v1
2005-11-06,Dynamics of composite Haldane spin chains in IPA-CuCl3,"Magnetic excitations in the quasi-one-dimensional antiferromagnet IPA-CuCl3
are studied by cold neutron inelastic scattering. Strongly dispersive gap
excitations are observed. Contrary to previously proposed models, the system is
best described as an asymmetric quantum spin ladder. The observed spectrum is
interpreted in terms of ``composite'' Haldane spin chains. The key difference
from actual S=1 chains is a sharp cutoff of the single-magnon spectrum at a
certain critical wave vector.",0511143v1
2005-12-18,Spin Glasses: a Perspective,"A brief personal perspective is given of issues, questions, formulations,
methods, some answers and selected extensions posed by the spin glass problem,
showing how considerations of an apparently insignificant and practically
unimportant group of metallic alloys stimulated an explosion of new insights
and opportunities in the general area of complex many-body systems and still is
doing so",0512425v2
2006-01-08,Resonant control of spin dynamics in ultracold quantum gases by microwave dressing,"We study experimentally interaction-driven spin oscillations in optical
lattices in the presence of an off-resonant microwave field. We show that the
energy shift induced by this microwave field can be used to control the spin
oscillations by tuning the system either into resonance to achieve near-unity
contrast or far away from resonance to suppress the oscillations. Finally, we
propose a scheme based on this technique to create a flat sample with either
singly- or doubly-occupied sites, starting from an inhomogeneous Mott
insulator, where singly- and doubly-occupied sites coexist.",0601151v1
2006-02-20,Spin liquid correlations in Nd-langasite anisotropic Kagomé antiferromagnet,"Dynamical magnetic correlations in the geometrically frustrated
Nd$\_3$Ga$\_5$SiO$\_{14}$ compound were probed by inelastic neutron scattering
on a single crystal. A scattering signal with a ring shape distribution in
reciprocal space and unprecedented dispersive features was discovered.
Comparison with calculated static magnetic scattering from models of correlated
spins suggests that the observed phase is a spin liquid inherent to an
antiferromagnetic kagom\'e-like lattice of anisotropic Nd moments.",0602457v2
2006-03-23,Interferometric detection of spin-polarized transport in the depletion layer of a metal-GaAs Schottky barrier,"It is shown that the Kerr rotation of spin-polarized electrons is modulated
by the distance of the electrons from the sample surface. Time-resolved Kerr
rotation of optically-excited spin-polarized electrons in the depletion layer
of n-doped GaAs displays fast oscillations that originate from an interference
between the light reflected from the semiconductor surface and from the front
of the electron distribution moving into the semiconductor. Using this effect,
the dynamics of the photogenerated charge carriers in the depletion layer of
the biased Schottky barrier is measured.",0603630v1
2006-04-10,Quantum-dot spin qubit and hyperfine interaction,"We review our investigation of the spin dynamics for two electrons confined
to a double quantum dot under the influence of the hyperfine interaction
between the electron spins and the surrounding nuclei. Further we propose a
scheme to narrow the distribution of difference in polarization between the two
dots in order to suppress hyperfine induced decoherence.",0604252v1
2006-05-11,Power dissipation in spintronic devices out of thermodynamic equilibrium,"Quantum limits of power dissipation in spintronic computing are estimated. A
computing element composed of a single electron in a quantum dot is considered.
Dynamics of its spin due to external magnetic field and interaction with
adjacent dots is described via the Bloch equations. Spin relaxation due to
magnetic noise from various sources is described as coupling to a reservoir.
Resulting dissipation of energy is calculated and is shown to be much less than
the thermal limit, ~kT per bit, if the rate of spin relaxation is much slower
than the switching rate. Clues on how to engineer an energy efficient
spintronic device are provided.",0605298v1
2006-06-25,Quantum chaos and fluctuations in isolated nuclear spin systems,"Using numerical simulations we investigate dynamical quantum chaos in
isolated nuclear spin systems. We determine the structure of quantum states,
investigate the validity of the Curie law for magnetic susceptibility and find
the spectrum of magnetic noise. The spectrum is the same for positive and
negative temperatures. The study is motivated by recent interest in
condensed-matter experiments for searches of fundamental parity- and
time-reversal-invariance violations. In these experiments nuclear spins are
cooled down to microkelvin temperatures and are completely decoupled from their
surroundings. A limitation on statistical sensitivity of the experiments arises
from the magnetic noise.",0606635v1
2006-08-19,Spin dynamics in molecular ring nanomagnets: Significant effect of acoustic phonons and magnetic anisotropies,"The nuclear spin-lattice relaxation rate 1/T_1_ is calculated for magnetic
ring clusters by fully diagonalizing their microscopic spin Hamiltonians.
Whether the nearest-neighbor exchange interaction J is ferromagnetic or
antiferromagnetic, 1/T_1_ versus temperature T in ring nanomagnets may be
peaked at around k_B_T=|J| provided the lifetime broadening of discrete energy
levels is in proportion to T^3^. Experimental findings for ferromagnetic and
antiferromagnetic Cu^II^ rings are reproduced with crucial contributions of
magnetic anisotropies as well as acoustic phonons.",0608438v1
2006-08-31,Magnetic correlations around the Mott transition in the Kagomé lattice Hubbard model,"We study the magnetic properties around the Mott transition in the Kagom\'e
lattice Hubbard model by the cellular dynamical mean field theory combined with
quantum Monte Carlo simulations. By investigating the q-dependence of the
susceptibility, we find a dramatic change of the dominant spin fluctuations
around the Mott transition. The spin fluctuations in the insulating phase favor
down to the lowest temperature a spatial spin configuration in which
antiferromagnetic correlations are strong only in one chain direction but
almost vanishing in the others.",0608699v1
2006-09-11,Theory of Spin Susceptibility in Frustrated Layered Antiferromagnets,"The self-consistent treatment of real and imaginary renormalizations in the
dynamic spin susceptibility for the frustrated Heisenberg model reproduces for
cuprates at low doping: a spin spectrum, a saddle point for q near (pi/2,pi/2),
nearly constant q-integrated susceptibility for energy less than 150 meV and a
scaling law. Frustration increase (optimally doped case) leads to a stripe
scenario with a saddle point at q near (pi,pi/2) and $\chi_{2D}(\omega)$ peak
near 30meV. The obtained $\chi (\mathbf{q},\omega)$ describes neutron
scattering results and leads to well-known temperature transport anomalies in
doped cuprates.",0609248v1
2006-09-17,Self-Polarization and Dynamical Cooling of Nuclear Spins in Double Quantum Dots,"Spontaneous nuclear polarization is predicted in double quantum dots in the
spin-blocked electron transport regime. The polarization results from an
instability of the zero-polarization state when singlet and triplet electron
energy levels are brought into resonance by the effective hyperfine field of
the nuclei on the electrons. The nuclear spins, once polarized, serve as a cold
bath for cooling electrons below the lattice (phonon) temperature. We estimate
the relevant time scales and discuss the conditions necessary to observe these
phenomena.",0609409v2
2006-11-02,Spin-phonon coupling in ZnCr2Se4,"Spin-phonon coupling and magnetodielectric effects of ZnCr2Se4 were
investigated by means of infrared (IR) spectroscopy as a function of
temperature and magnetic field. ZnCr2Se4 is dominated by ferromagnetic exchange
but undergoes antiferromagnetic order at T = 21 K. In the magnetically ordered
phase the low-frequency IR active phonon splits, indicating strong dynamic
anisotropy via magnetic exchange interactions. Antiferromagnetic order and
concomitantly the phonon splitting is wiped out by external magnetic fields.
Hence, ZnCr2Se4 is a prominent example of a spin-driven Jahn-Teller effect
which can be fully suppressed in external magnetic fields.",0611041v1
2006-11-20,Crossover from diffusive to non-diffusive dynamics in the two-dimensional electron gas with Rashba spin-orbit coupling,"We present the calculation of the density matrix response function of the
two-dimensional electron gas with Rashba spin-orbit interaction, which is
applicable in a wide range of parameters covering the diffusive and
non-diffusive, the dirty and the clean limits. A description of the crossover
between the different regimes is thus provided as well. On the basis of the
derived microscopic expressions we study the propagating charge and
spin-polarization modes in the clean, non-diffusive regime, which is accessible
in the modern experiments.",0611523v2
2007-01-05,Spin Hall Effect For Anyons,"We explain the intrinsic spin Hall effect from generic anyon dynamics in the
presence of external electromagnetic field. The free anyon is represented as a
spinning particle with an underlying non-commutative configuration space. The
Berry curvature plays a major role in the analysis.",0701096v2
2007-01-25,Quantum Spherical Spin Glass.Supersymmetry and Annealing,"We show that the effective action of the quantum spherical spin glass is
invariant under a generalized form of the Becchi-Rouet-Stora-Tyutin(BRST)
supersymmetry. The Ward identities associated to this invariance indicate that
the spin glass order parameter must vanish, and as a result the annealed
average is exact in this model. We present new results for for the free energy,
entropy and specific heat. Due to quantum effects the entropy remains finite
and the specific het vanishes at zero temperature. results for the phase
diagram coincide with those obtained by different formalisms. At zero
temperature we derive the scaling behaviour with frequency of the dynamical
susceptibility.",0701627v1
1997-11-17,A lattice worldsheet sum for 4-d Euclidean general relativity,"A lattice model for four dimensional Euclidean quantum general relativity is
proposed for a simplicial spacetime. It is shown how this model can be
expressed in terms of a sum over worldsheets of spin networks, and an
interpretation of these worldsheets as spacetime geometries is given, based on
the geometry defined by spin networks in canonical loop quantized GR. The
spacetime geometry has a Planck scale discreteness which arises ""naturally""
from the discrete spectrum of spins of SU(2) representations (and not from the
use of a spacetime lattice).
  The lattice model of the dynamics is a formal quantization of the classical
lattice model of \cite{Rei97a}, which reproduces, in a continuum limit,
Euclidean general relativity.",9711052v1
2001-03-12,Behaviour of spin-half particles in curved space-time,"We study the behaviour of spin-half particles in curved space-time. Since
Dirac equation gives the dynamics of spin-half particles, we mainly study the
Dirac equation in Schwarzschild, Kerr, Reissner-Nordstr\""om geometry. Due to
the consideration of existence of black hole in space-time (the curved
space-time), particles are influenced and equation will be modified. As a
result the solution will be changed from that due to flat space.",0103034v1
2006-07-03,Transverse Spin Studies with STAR at RHIC,"STAR has observed sizable transverse single-spin asymmetries for inclusive
pi^0 production at forward rapidity in p+p collisions at sqrt{s}=200 GeV. These
asymmetries may arise from either the Sivers or Collins effect. Studies are
underway during the current RHIC run to elucidate the dynamics that underlie
these single-spin asymmetries. Additional measurements are underway to search
for the Sivers effect in mid-rapidity di-jet production.",0607003v1
1992-05-01,Scaling topological charge in the CP^3 spin model,"The CP^3 spin model is simulated at large correlation lengths in two
dimensions. An overrelaxation algorithm is employed which yields reduced
critical slowing down with dynamical exponents z around unity. We compare our
results with recent multigrid data on the massgap m and the spin susceptibility
and confirm the absence of asymptotic scaling. As a new result we find scaling
for the universal topological susceptibility with values extrapolating to chi_t
/ m^2 = 0.156(2) in the continuum limit.",9205001v1
1993-11-04,The SU(2) $\times$ SU(2) chiral spin model in terms of SO(3) and Z$_2$ variables: vortices and disorder,"We rewrite the two-dimensional SU(2)$\times$ SU(2) chiral spin model in terms
of SO(3) and {\bf Z}$_2$ degrees of freedom. The transformation, which is
motivated by a similar representation of the corresponding lattice gauge theory
in higher dimensions, exhibits the presence of dynamical SO(3) vortices and
associated strings. We present arguments that (pairs of) SO(3) vortices with
long strings play a crucial role in disordering the spin system at arbitrarily
low temperatures.",9311005v1
1994-07-12,Spin Effects in pp-scattering at difraction range and RHIC energies,"The spin effects in nucleon-nucleon scattering are calculated in the
framework of the dynamic model taking into account interactions at large
distances and the strong form factors; the model factorization of the $NN$
amplitude into the spin-dependent hadron-pomeron vertex and high-energy
spinless pomeron is obtained. Theoretical predictions for polarization and
$A_{nn}$ are made for the diffraction range at the RHIC energies.",9407275v1
1995-02-06,Spin Puzzle in Nucleon,"The object of this brief review is to reconcile different points of view on
how the spin of proton is made up from its constituents. On the basis of naive
quark model with flavour symmetry such as isospin or SU(3) one finds a static
description. On the contrary the local SU(3) colour symmetry gives a dynamical
view. Both these views are contrasted and the role of U(1) axial anomaly and
the ambiguity for the measurable spin content is discussed.",9502232v2
1995-03-15,THE PROTON SPIN PUZZLE AND DEPOLARIZATION IN $\bar{p}p\to\barΛΛ$,"We point out that the measurement of target spin depolarization $D_{nn}$ in
the $\bar{p}p\to\bar{\Lambda}\Lambda$ reaction may test dynamical mechanisms
invoked to explain the proton spin puzzle revealed by polarized deep--inelastic
scattering experiments. In particular, models with {\it negatively} polarized
$\bar{s}s$ pairs in the proton wave function predict $D_{nn}<0$, whereas models
with {\it positively} polarized gluons would predict $D_{nn}>0$.",9503333v1
1997-01-27,Lambda and Lambda-bar Polarization in Lepton Induced Processes,"The study of the longitudinal polarization of Lambda and Lambda-bar hyperons
produced in polarized deep inelastic scattering, neutrino scattering, and in Z0
decays allows to access the spin dynamics of the quark fragmentation process.
Different phenomenological spin transfer mechanisms are considered and
predictions for the Lambda and Lambda-bar longitudinal polarization in various
processes using unpolarized and polarized targets are made. Current and future
semi-inclusive deep inelastic scattering experiments will provide soon accurate
enough data to study these phenomena and distinguish between various models for
the spin transfer mechanisms.",9701384v2
1997-12-19,Spin content of the nucleon in a valence and sea quark mixing model,"A dynamical valence and sea quark mixing model is shown to fit the baryon
ground state properties as well as the spin content of the nucleon. The
relativistic correction and the $q^3{\leftrightarrow} q^3q\bar{q}$ transition
terms induced by the quark axial vector current
$\bar{\psi}\vec{\gamma}\gamma^5\psi$ in this model space is responsible for the
quark spin reduction.",9712448v1
2001-11-29,Hadronization mechanisms and spin effects in high energy fragmentation processes,"Spin effects in high energy fragmentation processes can provide us with
important information on hadronization mechanisms and spin structure of
hadrons. It can in particular give new tests to the hadronization models. In
this talk, we make a brief introduction to the different topics studied in this
connection and a short summary of the available data. After that, we present a
short summary of the main theoretical results we obtained in studying these
different topics. The talk was mainly based on the publications [4-8] which
have been finished in collaboration with C.Boros, Liu Chun-xiu and Xu Qing-hua.",0111403v1
2004-09-29,Nucleon spin structure and its connections to various sum rules,"Our knowledge on the nucleon spin structure has greatly improved over the
last twenty years or so, but still many fundamental questions remain unsolved.
I will try to review some of the puzzling aspects of the origin of the nucleon
spin. I will emphasize the connection with several sum rules and, when using
this tool, the relevance of some kinematic regions for testing them in the QCD
dynamics framework.",0409333v1
2005-05-20,Spin Polarization of Hyperons in the Hadron-Hadron Inclusive Collisions - Mechanisms and Dynamics -,"We discuss interplay of the scalar and vector diquarks which decide the
characteristics of the spin polarization as functions of $p_T$ and $x_F$ in the
wide kinematical range. We demonstrate a significant effect of quark masses on
the pair-creation probabilities from vacuum in $pp \to \Sigma^- X$ and $\gamma
p \to \Lambda X$ collisions, and also a remarkable correction induced by the
diquark form factor in $ \Sigma^- p \to \Lambda X $ collision.",0505179v1
1994-05-25,Derivation of the Classical Lagrangian for the Relativistic Spinning Particle,"The `classical' model for a massive spinning particle, which was recently
proposed, is derived from the isotropic rotator model. Through this derivation,
we note that the spin can be understood as the relativistic extension of the
isotropic rotator. Furthermore, the variables $t_\m$ corresponding to the
$\p^*$ of the `pseudo-classical' model, are necessary for the covariant
formulation. The dynamical term for these extra variables is naturally obtained
and the meaning of the constraint term $p^\s\L_{\s\n}+mt_\n =0$, which was
recently shown to give `quasi-supersymmetry', is clarified.",9405157v1
2003-01-29,Higher-Spin Theories and $Sp(2M)$ Invariant Space--Time,"Some methods of the ``unfolded dynamics'' machinery particularly useful for
the analysis of higher spin gauge theories are summarized. A formulation of 4d
conformal higher spin theories in Sp(8) invariant space-time with matrix
coordinates and its extension to Sp(2M) invariant space-times are discussed. A
new result on the global characterizaton of causality of physical events in the
Sp(2M) invariant space-time is announced.",0301235v1
2005-07-14,Surface charges and dynamical Killing tensors for higher spin gauge fields in constant curvature spaces,"In the context of massless higher spin gauge fields in constant curvature
spaces, we compute the surface charges which generalize the electric charge for
spin one, the color charges in Yang-Mills theories and the energy-momentum and
angular momentum for asymptotically flat gravitational fields. We show that
there is a one-to-one map from surface charges onto divergence free Killing
tensors. These Killing tensors are computed by relating them to a cohomology
group of the first quantized BRST model underlying the Fronsdal action.",0507138v2
2005-11-01,An SU(1|1)-Invariant S-Matrix with Dynamic Representations,"The spin chains originating from large-N conformal gauge theories are of a
special kind: The Hamiltonian is not invariant under the symmetry algebra, it
is rather a part of it. This leads to interesting properties within the
asymptotic Bethe ansatz. Here we study an S-matrix with u(1|1) symmetry which
arises in a long-range spin chain with fundamental spins of su(2|1).",0511013v2
2005-11-28,BRST approach to higher spin field theories,"We develop the BRST approach to Lagrangian formulation for massive bosonic
and massless fermionic higher spin fields on a flat space-time of arbitrary
dimension. General procedure of gauge invariant Lagrangian construction
describing the dynamics of the fields with any spin is given. No off-shell
constraints on the fields (like tracelessness) and the gauge parameters are
imposed. The procedure is based on construction of new representations for the
closed algebras generated by the constraints defining irreducible
representations of the Poincare group. We also construct Lagrangians describing
propagation of all massive bosonic fields and massless fermionic fields
simultaneously.",0511276v1
2006-04-24,Spin-Bits and N=4 SYM,"We briefly review the spin-bit formalism, describing the non-planar dynamics
of the $\mathcal{N}=4,d=4$ Super Yang-Mills SU(N) gauge theory. After
considering its foundations, we apply such a formalism to the $su(2)$ sector of
purely scalar operators. In particular, we report an algorithmic formulation of
a deplanarizing procedure for local operators in the planar gauge theory, used
to obtain planarly-consistent, testable conjectures for the higher-loop $su(2)$
spin-bit Hamiltonians. Finally, we outlook some possible developments and
applications.",0604174v2
2001-05-19,Integrable spin Calogero-Moser systems,"We introduce spin Calogero-Moser systems associated with root systems of
simple Lie algebras and give the associated Lax representations (with spectral
parameter) and fundamental Poisson bracket relations. The associated integrable
models (called integrable spin Calogero-Moser systems in the paper) and their
Lax pairs are then obtained via Poisson reduction and gauge transformations.
For Lie algebras of $A_{n}$-type, this new class of integrable systems includes
the usual Calogero-Moser systems as subsystems. Our method is guided by a
general framework which we develop here using dynamical Lie algebroids.",0105162v1
2006-09-19,Spin dependent point potentials in one and three dimensions,"We consider a system realized with one spinless quantum particle and an array
of $N$ spins 1/2 in dimension one and three. We characterize all the
Hamiltonians obtained as point perturbations of an assigned free dynamics in
terms of some ``generalized boundary conditions''. For every boundary condition
we give the explicit formula for the resolvent of the corresponding
Hamiltonian. We discuss the problem of locality and give two examples of spin
dependent point potentials that could be of interest as multi-component
solvable models.",0609055v2
2001-01-12,Quantum and classical ergodicity of spinning particles,"We give a formulation of quantum ergodicity for Pauli Hamiltonians with
arbitrary spin in terms of a Wigner-Weyl calculus. The corresponding classical
phase space is the direct product of the phase space of the translational
degrees of freedom and the two-sphere. On this product space we introduce a
combination of the translational motion and classical spin precession. We prove
quantum ergodicity under the condition that this product flow is ergodic.",0101022v1
2002-11-21,The Onset of Chaos in Spinning Particle Models,"The onset of chaos in one-dimensional spinning particle models derived from
pseudoclassical mechanical hamiltonians with a bosonic Duffing potential is
examined. Using the Melnikov method, we indicate the presence of homoclinic
entanglements in models with general potentials for the spins, and thus show
that chaotic motions occur in these models.",0211037v2
1996-06-04,Nucleon-Antinucleon Interaction from the Skyrme Model,"We calculate the nucleon-antinucleon static potential in the Skyrme model
using the product ansatz and including some finite $N_C$ (number of colors)
corrections. The mid and long range part of the spin-spin and tensor force are
correctly given in both iso-spin channels while the central interaction has
insufficient mid-range attraction. This is a well known problem of the product
ansatz that should be repaired with better Skyrme dynamics.",9606002v1
1998-09-22,Invariant amplitudes for coherent electromagnetic pseudoscalar production from a spin-one target,"A set of 13 linearly independent invariant amplitudes for the electromagnetic
production of a pseudoscalar particle from a spin-one particle is derived which
respect Lorentz and gauge invariance. The $T$-matrix can be represented by a
linear superposition of these amplitudes with invariant functions as
coefficients, which depend on the Mandelstam variables only. Their explicit
form is determined by the underlying dynamics. Nine of these amplitudes are
purely transverse and describe photoproduction. The remaining four appear in
electroproduction in addition, describing charge and longitudinal current
contributions. Furthermore, a reduction of these amplitudes to operators acting
in non-relativistic spin space is given.",9809067v1
1998-03-27,Semiclassical spin damping: Superradiance revisited,"A well known description of superradiance from pointlike collections of many
atoms involves the dissipative motion of a large spin. The pertinent
``superradiance master equation'' allows for a formally exact solution which we
subject to a semiclassical evaluation. The clue is a saddle-point approximation
for an inverse Laplace transform. All previous approximate treatments,
disparate as they may appear, are encompassed in our systematic formulation. A
byproduct is a hitherto unknown rigorous relation between coherences and
probabilities. Our results allow for generalizations to spin dynamics with
chaos in the classical limit.",9803041v1
2003-03-13,Interchannel coupling effects in the spin polarization of energetic photoelectrons,"Effects of the interchannel coupling on the spin polarization of energetic
photoelectrons emitted from atomic Ne valence subshells are examined. Like
previously obtained results for cross sections and angular distributions, the
photoelectron spin polarization parameters too are found considerably
influenced by the coupling. The result completes a series of studies to finally
conclude that the independent particle description is inadequate for the {\em
entire} range of photoionization dynamics over the {\em full} spectral energy
domain",0303056v1
1997-07-08,Quantum Computation in Quantum-Hall Systems,"We describe a quantum information processor (quantum computer) based on the
hyperfine interactions between the conduction electrons and nuclear spins
embedded in a two-dimensional electron system in the quantum-Hall regime.
Nuclear spins can be controlled individually by electromagnetic pulses. Their
interactions, which are of the spin-exchange type, can be possibly switched on
and off pair-wise dynamically, for nearest neighbors, by controlling
impurities. We also propose the way to feed in the initial data and explore
ideas for reading off the final results.",9707017v2
1998-02-05,Dynamics of a Quantum Control-Not Gate for an Ensemble of Four-Spin Molecules at Room Temperature,"We investigate numerically a single-pulse implementation of a quantum
Control-Not (CN) gate for an ensemble of Ising spin systems at room
temperature. For an ensemble of four-spin ``molecules'' we simulate the
time-evolution of the density matrix, for both digital and superpositional
initial conditions. Our numerical calculations confirm the feasibility of
implementation of quantum CN gate in this system at finite temperature, using
electromagnetic $\pi$-pulse.",9802016v1
1998-10-23,A rigorous path-integral formula for quantum-spin dynamics via planar Brownian motion,"Adapting ideas of Daubechies and Klauder we derive a continuum path-integral
formula for the time evolution generated by a spin Hamiltonian. For this
purpose we identify the finite-dimensional spin Hilbert space with the
ground-state eigenspace of a suitable Sch\""odinger operator on
$L^2({\mathbb{R}}^2)$, the Hilbert space of square-integrable functions on the
Euclidean plane ${\mathbb{R}}^2$, and employ the Feynman-Kac-It\^o formula.",9810069v1
1999-09-09,Simulations of Quantum Logic Operations in Quantum Computer with Large Number of Qubits,"We report the first simulations of the dynamics of quantum logic operations
with a large number of qubits (up to 1000). A nuclear spin chain in which
selective excitations of spins is provided by the gradient of the external
magnetic field is considered. The spins interact with their nearest neighbors.
We simulate the quantum control-not (CN) gate implementation for remote qubits
which provides the long-distance entanglement. Our approach can be applied to
any implementation of quantum logic gates involving a large number of qubits.",9909032v1
2002-10-07,Single-Spin Measurement and Decoherence in Magnetic Resonance Force Microscopy,"We consider a simple version of a cyclic adiabatic inversion (CAI) technique
in magnetic resonance force microscopy (MRFM). We study the problem: What
component of the spin is measured in the CAI MRFM? We show that the
non-destructive detection of the cantilever vibrations provides a measurement
of the spin component along the effective magnetic field. This result is based
on numerical simulations of the Hamiltonian dynamics (the Schrodinger equation)
and the numerical solution of the master equation.",0210043v1
2002-10-17,Ultrafast geometric manipulation of electron spin and detection of the geometric phase via Faraday rotation spectroscopy,"Time-resolved Faraday rotation spectroscopy is currently exploited as a
powerful technique to probe spin dynamics in semiconductors. We propose here an
all-optical approach to geometrically manipulate electron spin and to detect
the geometric phase by this type of extremely sensitive experiment. The global
nature of the geometric phase can make the quantum manipulation more stable,
which may find interesting application in quantum devices.",0210128v1
2003-06-16,Spin dependent observable effect for free particles using the arrival time distribution,"The mean arrival time of free particles is computed using the quantum
probability current. This is uniquely determined in the non-relativistic limit
of Dirac equation, although the Schroedinger probability current has an
inherent non-uniqueness. Since the Dirac probability current involves a
spin-dependent term, an arrival time distribution based on the probability
current shows an observable spin-dependent effect, even for free particles.
This arises essentially from relativistic quantum dynamics, but persists even
in the non-relativistic regime.",0306106v2
2004-06-11,Convergence of coined quantum walks on d-dimensional Euclidean space,"Coined quantum walks may be interpreted as the motion in position space of a
quantum particle with a spin degree of freedom; the dynamics are determined by
iterating a unitary transformation which is the product of a spin
transformation and a translation conditional on the spin state. Coined quantum
walks on the d-dimensional lattice can be treated as special cases of coined
quantum walks on d-dimensional Euclidean space. We study quantum walks on
d-dimensional Euclidean space and prove that the sequence of rescaled
probability distributions in position space associated to the unitary evolution
of the particle converges to a limit distribution.",0406072v1
2004-11-29,Characteristic parameters and dynamics of two-qubit system in self-assembled monolayers,"We suggest the application of nitronylnitroxide substituted with methyl group
and 2,2,6,6-tetramethylpiperidin organic radicals as 1/2-spin qubits for
self-assembled monolayer quantum devices. We show that the oscillating
cantilever driven adiabatic reversals technique can provide the read-out of the
spin states. We compute components of the $g$-tensor and dipole-dipole
interaction tensor for these radicals. We show that the delocalization of the
spin in the radical may significantly influence the dipole-dipole interaction
between the spins.",0411202v2
2005-06-06,Superballistic Diffusion of Entanglement in Disordered Spin Chains,"We study the dynamics of a single excitation in an infinite XXZ spin chain,
which is launched from the origin. We study the time evolution of the spread of
entanglement in the spin chain and obtain an expression for the second order
spatial moment of concurrence, about the origin, for both ordered and
disordered chains. In this way, we show that a finite central disordered region
can lead to sustained superballistic growth in the second order spatial moment
of entanglement within the chain.",0506053v2
2005-07-04,"Entanglement, chaos and atomic Wigner function of the Dicke model","We calculate the atomic (spin) Wigner function for the single mode Dicke
model in the regime of large number of two-level atoms. The dynamics of this
quasi-probability function on the Bloch sphere allows us to visualize the
consequences of the entanglement process between the boson and the spin
subsystems. Such investigation shows a distinct localization behavior of the
spin state with respect to the polar and azimuthal Bloch sphere angles. A
complete {\em breakdown of reflection symmetry} in the azimuthal angle is shown
in the non-integrable case, even at short evolution times. Also, in the
classically chaotic situation, the appearance of {\em sub-planck structures} in
the Wigner function is shown, and its evolution analyzed.",0507025v1
2005-10-19,Optimal quantum cloning via spin networks,"In this paper we present an approach to quantum cloning via free dynamical
evolution of spin networks. By properly designing the network and the couplings
between spins, we show that optimal 1->M phase covariant cloning can be
achieved without any external control. Especially, when M is an odd number, the
optimal phase-covariant cloning can be achieved without ancillas. Moreover, we
demonstrate that the same framework is capable for optimal 1->2 universal
cloning.",0510147v1
2007-02-28,Controlled Quantum State Transfer in a Spin Chain,"Control of the transfer of quantum information encoded in quantum wavepackets
moving along a spin chain is demonstrated. Specifically, based on a
relationship with control in a paradigm of quantum chaos, it is shown that
wavepackets with slow dispersion can automatically emerge from a class of
initial superposition states involving only a few spins, and that arbitrary
unspecified travelling wavepackets can be nondestructively stopped and later
relaunched with perfection. The results establish an interesting application of
quantum chaos studies in quantum information science.",0702265v1
1994-11-08,Spin Dynamics of La_2CuO_4 and the Two-Dimensional Heisenberg Model,"The spin-lattice relaxation rate $1/T_1$ and the spin echo decay rate
$1/T_{2G}$ for the 2D Heisenberg model are calculated using quantum Monte Carlo
and maximum entropy analytic continuation. The results are compared to recent
experiments on La$_2$CuO$_4$, as well as predictions based on the non-linear
$\sigma$-model.",9411002v1
2007-05-18,Optimal 1->M universal quantum cloning via spin networks,"We present a scheme that transform 1 qubit to M identical copies with optimal
fidedelity via free dynamical evolution of spin star networks. We show that the
Heisenberg XXZ coupling can fulfill the challenge. The initial state of the
copying machine and the parameters of the spin Hamiltonian are discussed in
detail. Furthermore we have proposed a feasible method to prepare the initial
state of the copying machine.",0705.2694v1
2007-07-11,Experimental application of sum rules for electron energy loss magnetic chiral dichroism,"We present a derivation of the orbital and spin sum rules for magnetic
circular dichroic spectra measured by electron energy loss spectroscopy in a
transmission electron microscope. These sum rules are obtained from the
differential cross section calculated for symmetric positions in the
diffraction pattern. Orbital and spin magnetic moments are expressed explicitly
in terms of experimental spectra and dynamical diffraction coefficients. We
estimate the ratio of spin to orbital magnetic moments and discuss first
experimental results for the Fe L_{2,3} edge.",0707.1585v1
2007-08-08,On the Newtonian origin of the spin motive force in ferromagnetic atomic wires,"We demonstrate numerically the existence of a spin-motive force acting on
spin-carriers when moving in a time and space dependent internal field. This is
the case of electrons in a one-dimensional wires with a precessing domain wall.
The effect can be explained solely by considering adiabatic dynamics and it is
shown to exist for both classical and quantum systems.",0708.1167v2
2007-08-10,Charge and spin response functions for the Tomonaga model with quadratic dispersion and different interactions,"We derive expressions for the charge and spin response function for the
Tomonaga model with quadratic dispersion and arbitrary (but finite for zero
momentum) interaction. For constant interaction these expressions are analytic
and for other types of interaction only a simple matrix has to be diagonalised.
We use a truncated expansion in particle-hole states with and without inclusion
of correlations in the ground state yielding an exact result for pure
intra-band interaction. We also discuss the possibility of power-laws in the
dynamic structure factor for the spinful and spinless model.",0708.1424v1
2007-08-21,Dynamical quantum phase transitions in the dissipative Lipkin-Meshkov-Glick model and proposed realization in optical cavity QED,"We present an optical cavity QED configuration that is described by a
dissipative version of the Lipkin-Meshkov-Glick model of an infinitely
coordinated spin system. This open quantum system exhibits both first- and
second-order non-equilibrium quantum phase transitions as a single, effective
field parameter is varied. Light emitted from the cavity offers measurable
signatures of the critical behavior, including that of the spin-spin
entanglement.",0708.2753v2
2007-08-21,Freezing distributed entanglement in spin chains,"We show how to freeze distributed entanglement that has been created from the
natural dynamics of spin chain systems. The technique that we propose simply
requires single-qubit operations and isolates the entanglement in specific
qubits at the ends of branches. Such frozen entanglement provides a useful
resource, for example for teleportation or distributed quantum processing. The
scheme can be applied to a wide range of systems -- including actual spin
systems and alternative qubit embodiments in strings of quantum dots, molecules
or atoms.",0708.2794v1
2007-10-12,Coherent Spin Manipulations of a Polarized Beam With a Localized RF Magnetic Field,"The coherent manipulation of spin observables in storage rings provides
opportunities to test the application of some fundamental dynamical principles.
In this context, it is possible to confirm, using gauge invariance and Lorentz
invariance, a conjecture framed by A. M. Kondratenko concerning the ""natural""
or ""intrinsic"" resonance strength applicable to a spin rotation from a
controlled Froissart-Stora sweep with an RF dipole magnet. The discussion
includes a brief treatment of the ""forced"" component of the resonance strength
associated with the effect of the betatron oscillations induced by the
operation of the RF diple and a discussion of the effective resonance strength
as a function of betatron tunes.",0710.2566v1
2007-12-15,Dynamic and Static Excitations of a Classical Discrete Anisotropic Heisenberg Ferromagnetic Spin Chain,"Using Jacobi elliptic function addition formulas and summation identities we
obtain several static and moving periodic soliton solutions of a classical
anisotropic, discrete Heisenberg spin chain with and without an external
magnetic field. We predict the dispersion relations of these nonlinear
excitations and contrast them with that of magnons and relate these findings to
the materials realized by a discrete spin chain. As limiting cases, we discuss
different forms of domain wall structures and their properties.",0712.2503v1
2007-12-17,Proximity effect-assisted absorption of spin currents in superconductors,"The injection of pure spin current into superconductors by the dynamics of a
ferromagnetic contact is studied theoretically. Taking into account suppression
of the order parameter at the interfaces (inverse proximity effect) and the
energy-dependence of spin-flip scattering, we determine the
temperature-dependent ferromagnetic resonance linewidth broadening. Our results
agree with recent experiments in Nb|permalloy bilayers [C. Bell et al.,
arXiv:cond-mat/0702461].",0712.2814v1
2008-02-01,Quantum plasma effects in the classical regime,"For quantum effects to be significant in plasmas it is often assumed that the
temperature over density ratio must be small. In this paper we challenge this
assumption by considering the contribution to the dynamics from the electron
spin properties. As a starting point we consider a multicomponent plasma model,
where electrons with spin up and spin down are regarded as different fluids. By
studying the propagation of Alfv\'{e}n wave solitons we demonstrate that
quantum effects can survive in a relatively high-temperature plasma. The
consequences of our results are discussed.",0802.0169v1
2008-02-21,Coherent Control of spin-orbit precession with shaped laser pulses,"Spin precession in Rubidium atoms is investigated through a pump-probe
technique. The excited wave packet corresponds to a precession of spin and
orbital angular momentum around the total angular momentum. We show that using
shaped laser pulses allows us to control this dynamics. With a Fourier
transform limited pulse, the wave packet is initially prepared in the bright
state (coupled to the initial state) whereas a pulse presenting a $\pi $ step
in the spectral phase prepares the wave packet in the dark state (uncoupled to
the initial state).",0802.2986v1
2008-04-02,Spin quantum plasmas - new aspects of collective dynamics,"Quantum plasmas is a rapidly expanding field of research, with applications
ranging from nanoelectronics, nanoscale devices and ultracold plasmas, to
inertial confinement fusion and astrophysics. Here we give a short systematic
overview of quantum plasmas. In particular, we analyze the collective effects
due to spin using fluid models. The introduction of an intrinsic magnetization
due to the plasma electron (or positron) spin properties in the
magnetohydrodynamic limit is discussed. Finally, a discussion of the theory and
examples of applications is given.",0804.0334v1
2008-04-16,Higher-spin dynamics and Chern-Simons theories,"We review the construction of consistent higher-spin theories based on
Chern-Simons actions. To this end we first introduce the required higher-spin
algebras and discuss curvature and torsion tensors in an unconstrained way.
Finally we perform a perturbative analysis of the Chern-Simons theory in D=5
for a non-maximally symmetric AdS(4) background and obtain the required
four-dimensional Fronsdal equations in the compensator formulation.",0804.2627v1
2008-08-05,Spectral functions of strongly interacting isospin-1/2 bosons in one dimension,"We study a system of one-dimensional (iso)spin-1/2 bosons in the regime of
strong repulsive interactions. We argue that the low-energy spectrum of the
system consists of acoustic density waves and the spin excitations described by
an effective ferromagnetic spin chain with a small exchange constant J. We use
this description to compute the dynamic spin structure factor and the spectral
functions of the system.",0808.0681v2
2008-09-04,Magnetic excitations in dipolar pyrochlore antiferromagnet Gd$_2$Sn$_2$O$_7$,"The spin dynamics in the geometrically frustrated pyrochlore antiferromagnet
$\rm Gd_2Sn_2O_7$ is studied by means of the electron spin resonance. In the
ordered phase ($T_N = 1$ K), we have detected three gapped resonance modes.
Their values agree well with the developed spin-wave theory which takes into
account the Heisenberg nearest-neighbor exchange, the single-ion anisotropy and
the long-range dipolar interactions. The theory also predicts a fourth
lowest-frequency gap, which lies beyond the experimental range of frequencies,
but determines the exponential decrease of the specific heat at low
temperature.",0809.0798v1
2008-09-17,Efficient Monte Carlo algorithm in quasi-one-dimensional Ising spin systems,"We have developed an efficient Monte Carlo algorithm, which accelerates slow
Monte Carlo dynamics in quasi-one-dimensional Ising spin systems. The loop
algorithm of the quantum Monte Carlo method is applied to the classical spin
models with highly anisotropic exchange interactions. Both correlation time and
real CPU time are reduced drastically. The algorithm is demonstrated in the
layered triangular-lattice antiferromagnetic Ising model. We have obtained the
relation between the transition temperature and the exchange interaction
parameters, which modifies the result of the chain-mean-field theory.",0809.2969v1
2008-12-11,Effect of a strong laser on spin precession,"The semiclassical dynamics of a charged spin-1/2 particle in an intense
electromagnetic plane wave is analyzed beyond the electric dipole approximation
and taking into account the leading relativistic corrections to the Pauli
equation. It is argued that the adiabatic spin evolution driven by a low
intensity radiation changes its character drastically as an intensity of a
laser is increasing. Particularly, it is shown that a charged particle exposes
a spin flip resonance at a certain pick value of a laser field strength, which
is determined by a particle's gyromagnetic ratio.",0812.2110v1
2008-12-14,"Magnetic resonance in the cuprates -- exciton, plasmon, or π-mode","We re-analyzed the issue whether the resonance peak observed in neutron
scattering experiments on the cuprates is an exciton, a \pi-resonance, or a
magnetic plasmon. We considered a toy model with on-cite Hubbard U and
nearest-neighbor interactions in both charge and spin channels. We found that
the resonance is predominantly an exciton, even if magnetic interaction is
absent and d-wave pairing originates from attractive density-density
interaction. Our results indicate that one cannot distinguish between spin and
charge-mediated pairing interactions by just looking at the resonance peak in
the dynamic spin susceptibility.",0812.2697v1
2008-12-23,The spin-flip amplitude in the impact-parameter representation,"The impact-parameter representation of the spin-flip amplitude of hadron
elastic scattering is examined in different unitarisation schemes, taking the
Born term of the spin-flip amplitude from the Dubna Dynamical Model (DDM). It
is shown that the basic properties of the unitarisation schemes are independent
of the functional form used for unitarisation but heavily depend on the
asymptotic value of the unitarised amplitude.",0812.4371v2
2009-01-20,"Generalized parton distributions, the hunt for quark orbital momenta","The Generalized Parton Distributions (GPDs) are the appropriate framework for
a universal description of the partonic structure of the nucleon. They
characterize the dynamics of quarks and gluons inside the nucleon and
consequently contain information about the spin of the nucleon. The current
experimental knowledge about GPDs is reviewed with the emphasis on the
determination of E^q(Q^2,x,xi,t), the least known and constrained GPD, of
particular importance in the nucleon spin puzzle. The perspectives of this
experimental program are also addressed.",0901.3016v1
2009-01-22,Kinetics of a non-glauberian Ising model: global observables and exact results,"We analyse the spin-flip dynamics in kinetic Ising chains with
Kimball-Deker-Haake (KDH) transition rates, and evaluate exactly the evolution
of global quantities like magnetisation and its fluctuations, and the two-time
susceptibilities and correlations of the global spin and the global three-spin.
Information on the ageing behaviour after a quench to zero temperature is
extracted.",0901.3428v1
2009-01-28,Electron spin dynamics in strongly correlated metals,"The temperature dependence of the electron spin life-time, T_1 and the
g-factor are anomalous in alkali fullerides (K,Rb)_3C_60, which cannot be
explained by the canonical Elliott-Yafet theory. These materials are archetypes
of strongly correlated and narrow band metals. We introduce the concept of
""complex electron spin resonance frequency shift"" to treat these measurables in
a unified manner within the Kubo formalism. The theory is applicable for metals
with nearly degenerate conduction bands and large momentum scattering even with
an anomalous temperature dependence and sizeable residual value.",0901.4453v1
2009-02-09,Incommensurability and spin excitations of diagonal stripes in cuprates,"Based on the time-dependent Gutzwiller approximation we study the possibility
that the diagonal incommensurate spin scattering in strongly underdoped
lanthanum cuprates originates from antiferromagnetic domain walls (stripes).
Calculation of the dynamic spin response for stripes in the diagonal phase
yields the characteristic hour glass dispersion with the crossing of low energy
Goldstone and high-energy branches at a characteristic energy Ecross at the
antiferromagnetic wave-vector Q_{AF}. The high energy part is close to the
parent antiferromagnet. Our results suggest that inelastic neutron scattering
experiments on strongly underdoped lanthanum cuprates can be understood as due
to a mixture of bond centered and site centered stripe configurations with
substantial disorder.",0902.1382v1
2009-05-29,Is spin-charge separation observable in a transport experiment?,"We consider a one-dimensional chain consisting of an interacting area coupled
to non-interacting leads. Within the area, interaction is mediated by a local
on-site repulsion. Using real time evolution within the Density Matrix
Renormalisation Group (DMRG) scheme, we study the dynamics of wave packets in
this two-terminal transport setup. In contrast to previous works, where
excitations were created by adding potentials to the Hamiltonian, we explicitly
create left moving single particle excitations in the right lead as the
starting condition. Our simulations show that such a transport setup allows for
a clear detection of spin-charge separation using time-resolved spin-polarised
density measurements.",0905.4743v1
2009-06-30,Quantum phase transition of the 103mRh spin-density wave,"We induce a quantum phase transition of the 103mRh excitation at the critical
density of 10^{12} cm^{-3} by bremsstrahlung pumping at 300 K. A massive 103mRh
spin-density wave carrying a spin current moves on the identical 103Rh matrix
like a quantum fluid. The collapse-and-revival spectral evolution indicates
that the collective nuclear excitation undergoes dynamic Bose-Einstein
condensation. Applying an external magnetic field, we observe the
Onsager-Feynman quantization, which gives further evidence of the superfluidic
phase.",0906.5417v1
2009-07-15,Quantum Melting of Spin Ice: Emergent Cooperative Quadrupole and Chirality,"A quantum melting of the spin ice is proposed for pyrochlore-lattice magnets
Pr$_2TM_2$O$_7$ ($TM=$Ir, Zr, and Sn). The quantum superexchange Hamiltonian
having a nontrivial magnetic anisotropy is derived in the basis of atomic
non-Kramers magnetic doublets. The ground states exhibit a cooperative
ferroquadrupole and pseudospin chirality, forming a magnetic analog of smectic
liquid crystals. Our theory accounts for dynamic spin-ice behaviors
experimentally observed in Pr$_2TM_2$O$_7$.",0907.2536v3
2009-09-09,Rapid Domain Wall Motion in Permalloy Nanowires Excited by Spin-Polarized Current Applied Perpendicular to the Nanowire,"We study domain wall (DW) dynamics in permalloy nanowires excited by
alternating spin-polarized current applied perpendicular to the nanowire. Spin
torque ferromagnetic resonance measurements reveal that DW oscillations at a
pinning site in the nanowire can be excited with velocities as high as 800 m/s
at current densities below 10$^7$ A/cm$^2$.",0909.1822v4
2009-10-08,"Comment on ""Photon energy and carrier density dependence of spin dynamics in bulk CdTe crystal at room temperature""","We comment on the conclusion by Ma et al. [Appl. Phys. Lett. {\bf 94}, 241112
(2009)] that the Elliott-Yafet mechanism is more important than the
D'yakonov-Perel' mechanism at high carrier density in intrinsic bulk CdTe at
room temperature. We point out that the spin relaxation is solely from the
D'yakonov-Perel' mechanism. The observed peak in the density dependence of spin
relaxation time is exactly what we predicted in a recent work [Phys. Rev. B
{\bf 79}, 125206 (2009)].",0910.1506v1
2009-11-12,Singlet-triplet Hamiltonian for spin excitation in the Kondo-insulator,"Within the framework of periodic asymmetric Anderson model for Kondo
isoulators an effective singlet-triplet Hamiltonian with indirect
antiferromagnetic f-f exchange interaction is introduced which allows to study
analytically the dynamic magnetic susceptibilities of f-electrons. The approach
allows to describe the three-level spin excitation spectrum with a specific
dispersion in $YbB_{12}$. Distinctive feature of the consideration is the
introduction of small radius singlet and triplet collective f-d excitations
which at movement on a lattice form low - and high-energy spin bands.",0911.2348v1
2009-11-13,From Noncommutative Sphere to Nonrelativistic Spin,"Reparametrization invariant dynamics on a sphere, being parameterized by
angular momentum coordinates, represents an example of noncommutative theory.
It can be quantized according to Berezin-Marinov prescription, replacing the
coordinates by Pauli matrices. Following the scheme, we present two
semiclassical models for description of spin without use of Grassman variables.
The first model implies Pauli equation upon the canonical quantization. The
second model produces nonrelativistic limit of the Dirac equation implying
correct value for the electron spin magnetic moment.",0911.2592v3
2010-01-27,String theory triplets and higher-spin curvatures,"Unconstrained local Lagrangians for higher-spin gauge theories are bound to
involve auxiliary fields, whose integration in the partition function generates
geometric, effective actions expressed in terms of curvatures. When applied to
the triplets, emerging from the tensionless limit of open string field theory,
the same procedure yields interesting alternative forms of geometric
Lagrangians, expressible for both bosons and fermions as squares of
field-strengths. This shows that higher-spin curvatures might play a role in
the dynamics, regardless of whether the Fronsdal-Labastida constraints are
assumed or forgone.",1001.5003v2
2010-03-07,Entropy Considerations in Spin-Selective Radical-Ion-Pair Reactions,"Radical-ion-pair reactions were recently shown to manifest a host of
non-trivial quantum effects accounted for by quantum measurement theory. An
alternative approach purporting to describe the fundamental quantum dynamics of
spin-selective radical-ion pair reactions was introduced most recently,
bringing to three the competing theories, including the one traditionally used
in spin chemistry. We here consider entropy as a fundamental concept enabling a
comparison of the predictions of these theories against what is physically
acceptable on quite general grounds.",1003.1442v3
2010-03-10,The worldsheet low-energy limit of the AdS_4 x CP^3 superstring,"We consider the AdS_4 x CP^3 IIA superstring sigma-model in the background of
the ""spinning string"" classical solution, which possesses two Noether spins. In
the limit when one of the spins is infinite there are massless excitations,
which govern the infrared worldsheet properties of the model. We obtain a
sigma-model of CP^3 with fermions, which describes the dynamics of these
massless modes.",1003.2199v1
2010-04-22,"Motion of Space Curves in Three-dimensional Minkowski Space $R_1^{3}$, SO(2,1) Spin Equation and Defocusing Nonlinear Schrödinger Equation","We consider the dynamics of moving curves in three-dimensional Minkowski
space $R_1^{3}$ and deduce the evolution equations for the curvature and
torsion of the curve. Next by mapping a continuous SO(2,1) Heisenberg spin
chain on the space curve in $R_1^{3}$, we show that the defocusing nonlinear
Schr\""odinger equation(NLSE) can be identified with the spin chain, thereby
giving a geometrical interpretation of it. The associated linear eigenvalue
problem is also obtained in a geometrical way.",1004.3856v1
2010-06-02,Identifying the multiferroic phase of doped CuFeO_2 using inelastic neutron scattering,"We report inelastic neutron scattering measurements that provide a distinct
dynamical ""fingerprint"" for the multiferroic ground state of 3.5% Ga-doped
CuFeO_2. The complex ground state is stabilized by the displacement of the
oxygen atoms, which are also responsible for the multiferroic coupling
predicted by Arima. By comparing the observed and calculated spectrum of spin
excitations, we conclude that the magnetic ground state is a distorted
screw-type spin configuration that requires a mechanism for magnetoelectric
coupling different from the generally accepted spin-current model.",1006.0414v1
2010-06-22,From extended phase space dynamics to fluid theory,"We derive a fluid theory for spin-1/2 particles starting from an extended
kinetic model based on a spin-projected density matrix formalism. The evolution
equation for the spin density is found to contain a pressure-like term. We give
an example where this term is important by looking at a linear mode previously
found in a spin kinetic model.",1006.4317v2
2010-08-24,Power-law spin correlations in a perturbed honeycomb spin model,"We consider spin-$\frac{1}{2}$ model on the honeycomb lattice~\cite{Kitaev06}
in presence of a weak magnetic field $h_{\alpha }\ll 1$. Such a perturbation
destroys exact integrability of the model in terms of gapless fermions and
\textit{static} $Z_{2}$ fluxes. We show that it results in appearance of a
long-range tail in the irreducible dynamic spin correlation function: $%
\left\langle \left\langle s^{z}(t,r)s^{z}(0,0)\right\rangle \right\rangle
\propto h_{z}^{2}f(t,r)$, where $f(t,r)\propto \lbrack \max (t,r)]^{-4}$ is
proportional to the density polarization function of fermions.",1008.4106v1
2010-10-01,Effective spin model for interband transport in a Wannier-Stark lattice system,"We show that the interband dynamics in a tilted two-band Bose-Hubbard model
can be reduced to an analytically accessible spin model in the case of resonant
interband oscillations. This allows us to predict the revival time of these
oscillations which decay and revive due to inter-particle interactions. The
presented mapping onto the spin model and the so achieved reduction of
complexity has interesting perspectives for future studies of many-body
systems.",1010.0132v1
2010-10-06,Parasitic pumping currents in an interacting quantum dot,"We analyze the charge and spin pumping in an interacting dot within the
almost adiabatic limit. By using a non-equilibrium Green's function technique
within the time-dependent slave boson approximation, we analyze the pumped
current in terms of the dynamical constraints in the infinite-U regime. The
results show the presence of parasitic pumping currents due to the additional
phases of the constraints. The behavior of the pumped current through the
quantum dot is illustrated in the spin-insensitive and in the spin-sensitive
case relevant for spintronics applications.",1010.1134v1
2010-10-11,Spin-one color superconductors: collective modes and effective Lagrangian,"We investigate the collective excitations in spin-one color superconductors.
We classify the Nambu--Goldstone modes by the pattern of spontaneous symmetry
breaking, and then use the Ginzburg--Landau theory to derive their dispersion
relations. These soft modes play an important role for the low-energy dynamics
of the system such as the transport phenomena and hence are relevant for
late-stage evolution of neutron stars. In the case of the color-spin-locking
phase, we use a functional technique to obtain the low-energy effective action
for the physical Nambu--Goldstone bosons that survive after gauging the color
symmetry.",1010.1986v1
2010-11-09,Tomography of the two-electron spin qubits in semiconductors,"We propose an approach to reconstruct two-electron spin qubit states in
semiconductor quantum dots by employing tomographic techniques. This procedure
exploits the combination of fast gate operations on electron spins trapped in
dots and dynamical nuclear polarization of the underlying Ga and As nuclei. The
presented method can be an important tool in solid state quantum computation
for complete characterization of qubit states and theirs correlations.",1011.1985v3
2010-11-23,Chimera order in spin systems,"Homogeneous populations of oscillators have recently been shown to exhibit
stable coexistence of coherent and incoherent regions. Generalizing the concept
of chimera states to the context of order-disorder transition in systems at
thermal equilibrium, we show analytically that such complex ordering can appear
in a system of Ising spins, possibly the simplest physical system exhibiting
this phenomenon. We also show numerically the existence of chimera ordering in
3-dimensional spin systems that model layered magnetic materials, suggesting
possible means of experimentally observing such states.",1011.5032v1
2011-01-05,Effects of La non-magnetic impurities on the spin resonance of CeCoIn$_{5}$,"The influence of La non magnetic impurities on the spin dynamics of
CeCoIn$_{5}$ was studied by inelastic neutron scattering. In La-substituted
systems, the spin resonance peak (observed at $\Omega_{res}=0.55 meV$ in the
pure system) is shifted to lower energies but the ratio
$\Omega_{res}/k_{B}T_{c}$ remains unchanged. The excitation broadens till it
reaches 0.3 meV equal to the value of the quasi-elastic signal in the normal
state. The evolution of La substitution is compared with the evolution of the
magnetic resonance in Ni and Zn substituted YBa$_{2}$Cu$_{3}$O$_{7}$.",1101.1018v1
2011-01-30,Spin-Charge Locking and Tunneling into a Helical Metal,"We derive a kinetic equation for the electrons moving on the surface of a
three-dimensional topological insulator. Due to the helical nature of the
excitations backward scattering is suppressed in the collision integral, and
the spin dynamics is entirely constrained by that of the charge. We further
analyze the tunneling between the helical and a conventional metal or
ferromagnet. We find that the tunnel resistance strongly depends on the angle
between the magnetization in the ferromagnet and the current in the helical
metal. A nonmagnetic layer on top of the helical metal amplifies the
current-induced spin polarization.",1101.5802v1
2011-03-16,Vanilla Technicolor at Linear Colliders,"We analyze the reach of Linear Colliders (LC)s for models of dynamical
electroweak symmetry breaking. We show that LCs can efficiently test the
compositeness scale, identified with the mass of the new spin-one resonances,
till the maximum energy in the center-of-mass of the colliding leptons. In
particular we analyze the Drell-Yan processes involving spin-one intermediate
heavy bosons decaying either leptonically or into two Standard Model (SM) gauge
bosons. We also analyze the light Higgs production in association with a SM
gauge boson stemming also from an intermediate spin-one heavy vector.",1103.3271v1
2011-03-24,Effect of nonadiabatic spin transfer torque on domain wall resonance frequency and mass,"The dynamics of a magnetic domain wall in a semi circular nanowire loop is
studied by an analytical model and micromagnetic simulations. We find a damped
sinusoidal oscillation of the domain wall for small displacement angles around
its equilibrium position under an external magnetic field in the absence of
currents. By studying the effect of current induced nonadiabatic spin transfer
torque on the magnetic domain wall resonance frequency and mass, a red shift is
found in the resonance frequency and domain wall mass increases by increasing
the ratio of nonadiabatic spin torque to adiabatic contribution above 1.",1103.4670v1
2011-04-01,Spin waves cause non-linear friction,"Energy dissipation is studied for a hard magnetic tip that scans a soft
magnetic substrate. The dynamics of the atomic moments are simulated by solving
the Landau-Lifshitz-Gilbert (LLG) equation numerically. The local energy
currents are analysed for the case of a Heisenberg spin chain taken as
substrate. This leads to an explanation for the velocity dependence of the
friction force: The non-linear contribution for high velocities can be
attributed to a spin wave front pushed by the tip along the substrate.",1104.0197v2
2011-05-16,On the line shape of the electrically detected ferromagnetic resonance,"This work reviews and examines two particular issues related with the new
technique of electrical detection of ferromagnetic resonance (FMR). This
powerful technique has been broadly applied for studying magnetization and spin
dynamics over the past few years. The first issue is the relation and
distinction between different mechanisms that give rise to a photovoltage via
FMR in composite magnetic structures, and the second is the proper analysis of
the FMR line shape, which remains the ""Achilles heel"" in interpreting
experimental results, especially for either studying the spin pumping effect or
quantifying the spin Hall angles via the electrically detected FMR.",1105.3236v1
2011-07-01,Charge pumping due to triplet vector chirality in ferromagnet/triplet superconductor junctions,"We investigate charge pumping in ferromagnet/triplet superconductor junctions
where the magnetization of the ferromagnet is inhomogeneous and dynamical. It
is shown that charge current is pumped due to the coupling of the localized
spin with triplet vector spin chirality, vector spin chirality formed by the
triplet vector of Cooper pairing. Physical mechanism of the charge pumping is
also discussed.",1107.0119v2
2011-07-04,Dissipative dynamics of a spin system with three-body interaction,"In this note we explicitly solve the Lindblad equation for a system of three
spins with a three-body interaction, coupled to the environment by bath
operators that inject or absorb spin carriers. We exemplify the properties of
this solution in the context of a simple instance of Feynman's quantum computer
in which a two-qubit program line is executed, applying the $\sqrt{NOT}$
primitive to a one-qubit register.",1107.0619v1
2011-07-28,Temperature insensitive optical alignment of the exciton in nanowire embedded GaN Quantum Dots,"We report on the exciton spin dynamics of nanowire embedded GaN/AlN Quantum
Dots (QDs) investigated by time-resolved photoluminescence spectroscopy. Under
a linearly polarized quasiresonant excitation we evidence the quenching of the
exciton spin relaxation and a temperature insensitive degree of the exciton
linear polarization, demonstrating the robustness of the optical alignment of
the exciton spin in these nanowire embedded QDs. A detailed examination of the
luminescence polarization angular dependence shows orthogonal linear exciton
eigenstates with no preferential crystallographic orientation.",1107.5644v1
2011-09-22,Molecular structure refinement by direct fitting of atomic coordinates to experimental ESR spectra,"An attempt is made to bypass spectral analysis and fit internal coordinates
of radicals directly to experimental liquid- and solid-state electron spin
resonance (ESR) spectra. We take advantage of the recently introduced
large-scale spin dynamics simulation algorithms and of the fact that the
accuracy of quantum mechanical calculations of ESR parameters has improved to
the point of quantitative correctness. Partial solutions are offered to the
local minimum problem in spectral fitting and to the problem of spin
interaction parameters (hyperfine couplings, chemical shifts, etc.) being very
sensitive to distortions in molecular geometry.",1109.4815v1
2011-09-27,Spin fluids in Bianchi-I f(R)-cosmology with torsion,"We study Weyssenhoff spin fluids in Bianchi type-I cosmological models,
within the framework of torsional f(R)-gravity; the resulting field equations
are derived and discussed in both Jordan and Einstein frames, clarifying the
role played by the spin and the non-linearity of the gravitational Lagrangian
f(R) in generating the torsional dynamical contributions. The general
conservation laws holding for f(R)-gravity with torsion are employed to provide
the conditions needed to ensure the preservation of the Hamiltonian constraint
and the consequent correct formulation of the associated initial value problem.
Examples are eventually given.",1109.5821v2
2011-12-21,Exploring spin-orbital models with dipolar fermions in zig-zag optical lattices,"Ultra-cold dipolar spinor fermions in zig-zag type optical lattices can mimic
spin-orbital models relevant in solid-state systems, as transition-metal oxides
with partially filled d-levels, with the interesting advantage of reviving the
quantum nature of orbital fluctuations. We discuss two different physical
systems in which these models may be simulated, showing that the interplay
between lattice geometry and spin-orbital quantum dynamics produces a wealth of
novel quantum phases.",1112.5082v2
2012-06-13,Frequency dependence of the spin glass freezing temperatures in icosahedral R - Mg - Zn (R = rare earth) quasicrystals,"We present ac susceptibility measurements with the frequency spanning three
orders of magnitude on single grain, icosahedral R - Mg - Zn (R = rare earth)
quasicrystals. The freezing temperature in Gd-based, Heisenberg spin glasses in
this family increases by ~ 2% with a frequency increase from 10 Hz to 10 kHz,
whereas the freezing temperature in the non-Heisenberg members of the family is
significantly more responsive to the frequency change (by 16 - 22 %),
suggesting that an additional magnetic anisotropy distribution in the
non-Heisenberg spin glasses causes changes in the low frequency magnetic
dynamics.",1206.2830v1
2012-06-26,Entanglement and Sources of Magnetic Anisotropy in Radical Pair-Based Avian Magnetoreceptors,"One of the principal models of magnetic sensing in migratory birds rests on
the quantum spin-dynamics of transient radical pairs created photochemically in
ocular cryptochrome proteins. We consider here the role of electron spin
entanglement and coherence in determining the sensitivity of a radical
pair-based geomagnetic compass and the origins of the directional response. It
emerges that the anisotropy of radical pairs formed from spin-polarized
molecular triplets could form the basis of a more sensitive compass sensor than
one founded on the conventional hyperfine-anisotropy model. This property
offers new and more flexible opportunities for the design of biologically
inspired magnetic compass sensors.",1206.5946v1
2012-09-25,Gravity with spin excludes fermionic strings,"The existence of intrinsic spin of matter requires the metric-affine
formulation of gravity, in which the affine connection is not constrained to be
symmetric and its antisymmetric part (torsion tensor) is a dynamical variable.
We show that the cyclic identity for the curvature tensor in the metric-affine
formulation forbids fermions represented by Dirac spinors to form point or
string configurations. Consequently, fermionic strings contradict the
gravitational field equations in the presence of spin. Superstring theory is
therefore incorrect.",1209.5772v1
2012-11-26,Exact out-of-equilibrium central spin dynamics from integrability,"We consider a Gaudin magnet (central spin model) with a time-dependent
exchange couplings. We explicitly show that the Schr\""odinger equation is
analytically solvable in terms of generalized hypergeometric functions for
particular choices of the time dependence of the coupling constants. Our method
establishes a new link between this system and the SU(2) Wess-Zumino-Witten
model, and sheds new light on the implications of integrability in
out-of-equilibrium quantum physics. As an application, a driven four-spin
system is studied in detail.",1211.5905v3
2013-01-03,Nonequilibrium Rashba field driven domain wall motion in ferromagnetic nanowires,"We study the effects of spin-orbit interaction (SOI) on the current-induced
motion of a magnetic (Bloch) domain wall in ultrathin ferromagnetic nanowires.
The conspiracy of spin relaxation and SOI is shown to generate a novel strong
nonequilibrium Rashba field, which is dominant even for moderate SOI. This
field causes intricate spin precession and a transition from translatory to
oscillatory wall dynamics with increasing SOI. We show that current pulses of
different lengths can efficiently be used to control the domain wall motion.",1301.0389v2
2013-02-08,Comparison of quantum and classical relaxation in spin dynamics,"The classical Landau-Lifshitz equation with damping term has been derived
from the time evolution of a quantum mechanical wave function under the
assumption of a non-hermitian Hamilton operator. Further, the trajectory of a
classical spin $\mathrm{S}$ has been compared with the expectation value of the
spin operator $\mathrm{\hat{S}}$. A good agreement between classical and
quantum mechanical trajectories can be found for Hamiltonians linear in
$\mathrm{\hat{S}}$ respectively $\mathrm{S}$. Quadratic or higher order terms
in the Hamiltonian result in a disagreement.",1302.1985v1
2013-02-11,GSE statistics without spin,"Energy levels statistics following the Gaussian Symplectic Ensemble (GSE) of
Random Matrix Theory have been predicted theoretically and observed numerically
in numerous quantum chaotic systems. However in all these systems there has
been one unifying feature: the combination of half-integer spin and
time-reversal invariance. Here we provide an alternative mechanism for
obtaining GSE statistics that is based on geometric symmetries of a quantum
system which alleviates the need for spin. As an example, we construct a
quantum graph with a particular discrete symmetry given by the quaternion group
Q8. GSE statistics is then observed within one of its subspectra.",1302.2554v1
2013-02-13,Measuring and engineering entropy and spin squeezing in weakly linked Bose-Einstein condensates,"We propose a method to infer the single-particle entropy of bosonic atoms in
an optical lattice and to study the local evolution of entropy, spin squeezing,
and entropic inequalities for entanglement detection in such systems. This
method is based on experimentally feasible measurements of
non-nearest-neighbour coherences. We study a specific example of dynamically
controlling atom tunneling between selected sites and show that this could
potentially also improve the metrologically relevant spin squeezing.",1302.3040v1
2013-02-13,Model of a disk-outflow coupled system: disk-outflow symbiosis,"Several observational evidences and deeper theoretical insights reveal that
accretion and outflow/jet are strongly correlated. We model an advective
disk-outflow coupled dynamics. We investigate the properties of the
disk-outflow surface and how is it dependent on the spin of the black hole. The
energetics of such a symbiotic system strongly depend on the mass, accretion
rate and spin of the black holes. The model clearly shows that the outflow
power extracted from the disk increases strongly with the spin of the black
hole.",1302.3443v1
2013-02-19,RX J0648.0--4418: the fastest-spinning white dwarf,"RX J0648.0-4418 is a post common-envelope X-ray binary composed of a hot
subdwarf and one of the most massive white dwarfs with a dynamical mass
measurement (1.28+/-0.05 M_sun). This white dwarf, with a spin period of 13.2
s, rotates more than twice faster than the white dwarf in the cataclysmic
variable AE Aqr. The current properties of these two binaries, as well as their
future evolution, are quite different, despite both contain a fast-spinning
white dwarf. RX J0648.0-4418 could be the progenitor of either a Type Ia
supernova or of a non-recycled millisecond pulsars.",1302.4634v1
2013-03-12,Thermally excited spin waves in a nano-structure: thermal gradient vs. constant temperature,"Using micromagnetic simulations, we have investigated spin dynamics in a
nanostructure in the presence of thermal fluctuations. In particular, we have
studied the effects of a uniform temperature and of a uniform thermal gradient.
In both cases, the stochastic field leads to an increase of the precession
angle of the magnetization, and to a mild decreas of the linewidth of the
resonance peaks. Our results indicate that the Gilbert damping parameter plays
the role of control parameter for the amplification of spin waves.",1303.2895v1
2013-03-19,Spin foams,"The spin foam framework provides a way to define the dynamics of canonical
loop quantum gravity in a spacetime covariant way, by using a path integral
over histories of quantum states which can be interpreted as `quantum
space-times'. This chapter provides a basic introduction to spin foams aimed
principally at beginning graduate students and, where possible, at broader
audiences.",1303.4636v1
2013-03-31,Semi classical modeling of isotropic Non-Heisenberg magnets for spin S=1 and linear quadrupole excitation dynamics,"In this paper, equations describing one-dimensional Non-Heisenberg model are
studied by use of generalized coherent states in real parameterization and then
dissipative spin wave equation for dipole and quadrupole branches is obtained
if there is a small linear excitation from the ground state. Finally, it is
shown that for such exchange-isotropy Hamiltonians, optical branch of spin wave
is non-dissipative.",1304.0245v1
2013-05-21,Switching of a single ferromagnetic layer driven by spin Hall effect,"The magnetization switching of a thin ferromagnetic layer placed on top of a
heavy metal (such as Pt, Ta or W) driven by an in-plane current has been
observed in recent experiments. The magnetization dynamics of these processes
is studied in a full micromagnetic framework which takes into account the
transfer-torque from spin Hall effect due to the spin-orbit coupling.
Simulations indicate that the reversal occurs via nucleation of complex
magnetization patterns. In particular, magnetic bubbles appear during the
reversal of the magnetization in the perpendicular configuration while for the
in-plane configuration, nucleation of vortexes are observed.",1305.4806v1
2013-06-07,A critique of recent theories of spin half quantum plasmas,"In this Letter certain fundamental physics issues relating to recent theories
of so-called `spin quantum plasmas' are examined. It is shown that the
derivations and some of the results obtained in these theories contradict
well-established principles of quantum mechanics, especially in their treatment
of fermions and spin. The analysis presented suggests that the aforementioned
theories do not apply for any range of temperatures at the stated densities and
furthermore fail to make any experimentally accessible and testable
predictions.",1306.1774v1
2013-06-19,A quasi-linear spin-torque nano-oscillator via enhanced negative feedback of power fluctuations,"We report an approach to improving the performance of spin torque
nano-oscillators (STNOs) that utilizes power-dependent negative feedback to
achieve a significantly enhanced dynamic damping. In combination with a
sufficiently slow variation of frequency with power this can result in a
quasi-linear STNO, with very weak non-linear coupling of power and phase
fluctuations over a range of bias current and field. An implementation of this
approach that utilizes a non-uniform spin-torque demonstrates that highly
coherent room temperature STNOs can be achieved while retaining a significant
tunability.",1306.4668v1
2013-07-29,Theoretical Study of Spin-Torque Oscillator with Perpendicularly Magnetized Free Layer,"The magnetization dynamics of spin torque oscillator (STO) consisting of a
perpendicularly magnetized free layer and an in-plane magnetized pinned layer
was studied by solving the Landau-Lifshitz-Gilbert equation. We derived the
analytical formula of the relation between the current and the oscillation
frequency of the STO by analyzing the energy balance between the work done by
the spin torque and the energy dissipation due to the damping. We also found
that the field-like torque breaks the energy balance, and change the
oscillation frequency.",1307.7427v1
2013-10-15,7Li NMR Studies of LiCrO2,"We report on 7Li NMR studies of a spin S = 3/2 triangular lattice
antiferromagnet LiCrO2 (Neel temperature TN = 62 K) in the paramagnetic state
by using the free-induction decay of 7Li nuclear magnetization. We observed
critical divergence of the 7Li nuclear spin-lattice relaxation rate 1/T1 near
TN, a narrow critical region, and a critical exponent w = 0.45 from a fit of
1/T1 $\propto$ (T/TN - 1)$^{-w}$. Although spin frustration effects have been
explored for this system, the dynamical critical phenomena suggest that LiCrO2
in the critical region is a poor low dimensional antiferromagnetic system.",1310.4119v1
2013-12-13,Extreme Harmonic Generation in Electrically Driven Spin Resonance,"We report the observation of multiple harmonic generation in electric dipole
spin resonance in an InAs nanowire double quantum dot. The harmonics display a
remarkable detuning dependence: near the interdot charge transition as many as
eight harmonics are observed, while at large detunings we only observe the
fundamental spin resonance condition. The detuning dependence indicates that
the observed harmonics may be due to Landau-Zener transition dynamics at
anticrossings in the energy level spectrum.",1312.3875v2
2013-12-15,Lagrangian approach in spin-oscillations problem,"Lagrangian of electronic liquid in magneto-inhomogeneous micro-conductor has
been constructed. A corresponding Euler-Lagrange equation has been solved. It
was shown that the described system has eigenmodes of spin polarization and
total electric current oscillations. The suggested approach permits to study
the spin dynamics in an open-circuit which contains capacitance and/or
inductivity.",1312.4138v5
2014-04-02,"On the Equivalence of Trapped Colloids, Pinned Vortices, and Spin Ice","We investigate the recently reported analogies between pinned vortices in
nano-structured superconductors or colloids in optical traps, and spin ice
materials. The frustration of the two models, one describing colloids and
vortices, the other describing spin ice, differs essentially. However, their
effective energetics is made identical by the contribution of an emergent field
associated to a topological charge. This equivalence extends to the local
low-energy dynamics of the ice manifold, yet breaks down in lattices of mixed
coordination, because of topological charge transfer between sub-latices.",1404.0451v1
2014-04-28,Quantum Landau-Lifshitz-Bloch equation and its comparison with the classical case,"The detailed derivation of the quantum Landau-Lifshitz-Bloch (qLLB) equation
for simple spin-flip scattering mechanisms based on spin-phonon and
spin-electron interactions is presented and the approximations are discussed.
The qLLB equation is written in the form, suitable for comparison with its
classical counterpart. The temperature dependence of the macroscopic relaxation
rates is discussed for both mechanisms. It is demonstrated that the
magnetization dynamics is slower in the quantum case than in the classical one.",1404.6922v4
2014-08-26,Electronic waiting-time distribution of a quantum-dot spin valve,"We discuss the electronic waiting-time distribution of a quantum-dot spin
valve, i.e. a single-level quantum dot coupled to two ferromagnetic electrodes
with magnetizations that can point in arbitrary directions. We demonstrate that
the rich transport physics of this setup such as dynamical channel blockade and
spin precession in an interaction-driven exchange field shows up in the
waiting-time distribution and analyze the conditions necessary to observe the
various effects.",1408.6092v3
2014-12-15,Nonequilibrium spin current through interacting quantum dots,"We develop a theory for charge and spin current between two canted magnetic
leads flowing through a quantum dot with an arbitrary local interaction. For a
noncollinear magnetic configuration, we calculate equilibrium and
nonequilibrium current biased by voltage or temperature difference or pumped by
magnetic dynamics. We are able to explicitly separate the equilibrium and
nonequilibrium contributions to the current, both of which can be written in
terms of the full retarded Green's function on the dot. Taking the specific
example of a single-level quantum dot with a large on-site Coulomb interaction,
we calculate the total spin current near the Kondo regime, which we find to be
generally enhanced in magnitude as compared to the noninteracting case.",1412.4663v1
2014-12-16,A uniformly moving polarizable particle in a thermal radiation field with arbitrary spin direction,"We have generalized our recent results (Arm. J. Phys., 2014) relating to the
dynamics, heating and radiation of a small rotating polarizable particle moving
in a thermal radiation field in the case of arbitrary spin orientation. General
expressions for the tangential force, heating rate and intensity of thermal and
nonthermal radiation are given. It is shown that the intensity of nonthermal
radiation does not depend on the linear velocity and spin direction of the
particle.",1412.5118v1
2014-12-22,Conserved Higher-Spin Charges in $AdS_4$,"Gauge invariant conserved conformal currents built from massless fields of
all spins in 4d Minkowski space-time and $AdS_4$ are described within the
unfolded dynamics approach. The current cohomology associated with non-zero
conserved charges is found. The resulting list of charges is shown to match the
space of parameters of the conformal higher-spin symmetry algebra in four
dimensions.",1412.7147v3
2015-01-06,Spin Wave Diffraction Control and Read-out with a Quantum Memory for Light,"A scheme for control and read-out of diffracted spins waves to propagating
light fields is presented. Diffraction is obtained via sinusoidally varying
lights shifts and ideal one-to-one mapping to light is realized using a
gradient echo quantum memory. We also show that dynamical control of the
diffracted spin waves spatial orders can be implemented to realize a quantum
pulse sequencer for temporal modes that have high time-bandwidth products. Full
numerical solutions suggest that both co-propagating and couterpropagating
light shift geometries can be used, making the proposal applicable to hot and
cold atomic vapours as well as solid state systems with two-level atoms.",1501.01194v1
2015-01-11,"Collective Motion with Anticipation: Flocking, Spinning, and Swarming","We investigate the collective dynamics of self-propelled particles able to
probe and anticipate the orientation of their neighbors. We show that a simple
anticipation strategy hinders the emergence of homogeneous flocking patterns.
Yet, anticipation promotes two other forms of self-organization: collective
spinning and swarming. In the spinning phase, all particles follow synchronous
circular orbits, while in the swarming phase, the population condensates into a
single compact swarm that cruises coherently without requiring any cohesive
interactions. We quantitatively characterize and rationalize these phases of
polar active matter and discuss potential applications to the design of
swarming robots.",1501.02468v1
2015-01-13,Spin crossover in ferropericlase from first-principles molecular dynamics,"Ferropericlase, (Mg,Fe)O, is the second-most abundant mineral of the Earth's
lower mantle. With increasing pressure, the Fe ions in the material begin to
collapse from a magnetic to non-magnetic spin state. We present a
finite-temperature first-principles phase diagram of this spin crossover,
finding a broad pressure range with coexisting magnetic and non-magnetic ions
due to favorable enthalpy of mixing of the two. Furthermore, we find the
electrical conductivity of the mineral to reach semi-metallic values inside the
Earth.",1501.02902v1
2015-02-26,A spectral method for half-integer spin fields based on spin-weighted spherical harmonics,"We present a new spectral scheme for analysing functions of half-integer
spin-weight on the $2$-sphere and demonstrate the stability and convergence
properties of our implementation. The dynamical evolution of the Dirac equation
on a manifold with spatial topology of $\mathbb{S}^2$ via pseudo-spectral
method is also demonstrated.",1502.07427v2
2015-02-27,Scaling Behavior in the Decoherence of Decoupled Multi-spin System,"We study the scaling of decoherence of decoupled electron spin qubits due to
hyperfine interaction. For a superposed state consisting of product states from
a single Zeeman manifold, both $T_2^*(n)$ and $T_2(n)$ are scale-free with
respect to $n$ and the number of basis states, $m$. For a superposed state made
up of states from different Zeeman manifolds, both $T_2(n)$ and $T_2^*(n)$ are
roughly inversely proportional to $\sqrt{n}$. Our results can be extended to
other decoherence mechanisms, including in the presence of dynamical
decoupling, which allow meaningful discussions on the scalability of spin-based
coherent solid state quantum technology.",1502.07815v1
2015-03-16,Rabi Lattice models with discrete gauge symmetry: phase diagram and implementation in trapped ion quantum simulators,"We study a spin-boson chain that exhibits a local Z2 symmetry. We investigate
the quantum phase diagram of the model by means of perturbation theory, mean
field theory and the Density Matrix Renormalization Group method. Our
calculations show the existence of a first order phase transition in the region
where the boson quantum dynamics is slow compared to the spin-spin
interactions. Our model can be implemented with trapped ion quantum simulators,
leading to a realization of minimal models showing local gauge invariance and
first order phase transitions.",1503.04614v1
2015-03-16,Detection of spin waves in permalloy using planar Hall effect,"Rectification of microwave oscillations of magnetization in a permalloy film
is realized using planar Hall effect. Two different rectified signals are
obtained: a signal from the linearly excited uniform magnetization precession
at the frequency of the external pumping and a signal from the pairs of
contra-propagating short-wavelength spin waves parametrically generated at a
half of the pumping frequency. The second, most unusual, rectified signal is
caused by the uniform component of the dynamic magnetization created due to the
interference of the phase correlated pairs of parametric spin waves.",1503.04638v1
2015-04-03,Solitons in a continuous classical Haldane-Shastry spin chain,"Motivated by Polychronakos' discovery that solitons exist in the hydrodynamic
equations of continuum version of the Calogero model, we seek solitons in the
classical dynamics of a continuum version of the Haldane-Shastry spin chain. We
have obtained analytic multi-lump solitary wave solutions for our spin-field
equation, and these solutions possess interesting topological features. We have
performed numerical collision experiments showing that these solitary waves
survive collisions, and thus suggest the existence of true multi-soliton
solutions.",1504.00873v1
2015-04-07,$Z_2$-gauge theory description of the Mott transition in infinite dimensions,"The infinite dimensional half-filled Hubbard model can be mapped exactly with
no additional constraint onto a model of free fermions coupled in a $Z_2$
gauge-invariant manner to auxiliary Ising spins in a transverse field. In this
slave-spin representation, the zero-temperature insulator-to-metal transition
translates into spontaneous breaking of the local $Z_2$ gauge symmetry, which
is not forbidden in infinite dimensions, thus endowing the Mott transition of
an order parameter that is otherwise elusive in the original fermion
representation. We demonstrate this interesting scenario by exactly solving the
effective spin-fermion model by dynamical mean-field theory both at zero and at
finite temperature.",1504.01521v1
2015-05-15,Critical current and linewidth reduction in spin-torque nano-oscillators by delayed self-injection,"Based on theoretical models, the dynamics of spin-torque nano-oscillators can
be substantially modified by re-injecting the emitted signal to the input of
the oscillator after some delay. Numerical simulations for vortex magnetic
tunnel junctions show that with reasonable parameters this approach can
decrease critical currents as much as 25 % and linewidths by a factor of 4.
Analytical calculations, which agree well with simulations, demonstrate that
these results can be generalized to any kind of spin-torque oscillator.",1505.04102v1
2015-05-21,Metal-insulator transition and local-moment collapse in FeO under pressure,"We employ a combination of the \emph{ab initio} band structure methods and
dynamical mean-field theory to determine the electronic structure and phase
stability of paramagnetic FeO at high pressure and temperature. Our results
reveal a high-spin to low-spin transition within the B1 crystal structure of
FeO upon compression of the lattice volume above 73~GPa. The spin-state
transition is accompanied by an orbital-selective Mott metal-insulator
transition (MIT). The lattice volume is found to collapse by about 8.5~\% at
the MIT, implying a complex interplay between electronic and lattice degrees of
freedom. Our results for the electronic structure and lattice properties are in
overall good agreement with experimental data.",1505.05778v1
2015-06-22,Effects on satellite orbits in the gravitational field of an axisymmetric central body with a mass monopole and arbitrary spin multipole moments,"Perturbations of satellite orbits in the gravitational field of a body with a
mass monopole and arbitrary spin multipole moments are considered for an
axisymmetric and stationary situation. Periodic and secular effects caused by
the central gravitomagnetic field are derived by a first order perturbation
theory. For a central spin-dipole field these results reduce to the well known
Lense-Thirring effects.",1506.06506v1
2015-07-23,Finite-temperature scaling of spin correlations in a partially magnetized Heisenberg $S=1/2$ chain,"Inelastic neutron scattering is employed to study transverse spin
correlations of a Heisenberg $S=1/2$ chain compound in a magnetic field of 7.5
T. The target compound is the antiferromagnetic Heisenberg $S=1/2$ chain
material 2(1,4-Dioxane)$\cdot$2(H$_2$O)$\cdot$CuCl$_2$, or CuDCl for short. The
validity and the limitations of the scaling relation for the transverse dynamic
structure factor are tested, discussed and compared to the Tomonaga-Luttinger
spin liquid theory and to Bethe-ansatz results for the Heisenberg model.",1507.06487v2
2015-10-27,Spin-$\frac{1}{2}$ particle in an absorbing environment,"The quantum dynamics of a localized spin-$\frac{1}{2} $ Particle interacting
with an absorbing environment is investigated. The quantum
Langevin-Schr\""odinger equation for spin-$\frac{1}{2} $ is obtained. The
susceptibility function of the environment is calculated in terms of the
coupling function of the spin and the environment. it is shown that the
susceptibility function satisfies the Kramers-Kronig relations. Spontaneous
emission and the shift frequency of the spin is obtained in terms of the
imaginary part of the susceptibility function in frequency domain. Some
transition probabilities between the spin states are calculated when the
absorbing environment is in the thermal state.",1510.07791v1
2015-11-29,Realized Volatility Analysis in A Spin Model of Financial Markets,"We calculate the realized volatility in the spin model of financial markets
and examine the returns standardized by the realized volatility. We find that
moments of the standardized returns agree with the theoretical values of
standard normal variables. This is the first evidence that the return dynamics
of the spin financial market is consistent with the view of the
mixture-of-distribution hypothesis that also holds in the real financial
markets.",1511.08997v1
2016-02-26,Numerical Evidence for Approximate Consistency and Markovianity of some Quantum Histories in a Class of Finite Closed Spin Systems,"Closed quantum systems obey the Schroedinger equation whereas nonequilibrium
behavior of many of systems is routinely described in terms of classical,
Markovian stochastic processes. Evidently, there are fundamental differences
between those two types of behavior. We discuss the conditions under which the
unitary dynamics may be mapped onto pertinent classical stochastic processes.
This is first principally addressed based on the notions of ""consistency"" and
""Markovianity."" Numerical data are presented that show that the above
conditions are to good approximation fulfilled for Heisenberg-type spin models
comprising 12-20 spins. The accuracy to which these conditions are met
increases with system size.",1602.08281v1
2016-03-03,Dissipative Long-Range Entanglement Generation between Electronic Spins,"We propose a scheme for deterministic generation and long-term stabilization
of entanglement between two electronic spin qubits confined in spatially
separated quantum dots. Our approach relies on an electronic quantum bus,
consisting either of quantum Hall edge channels or surface acoustic waves, that
can mediate long-range coupling between localized spins over distances of tens
of micrometers. Since the entanglement is actively stabilized by dissipative
dynamics, our scheme is inherently robust against noise and imperfections.",1603.01130v2
2016-03-07,Spin-orbit coupled correlated metal phase in Kondo lattices: an implementation with alkaline-earth atoms,"We show that an interplay between quantum effects, strong on-site
ferromagnetic exchange interaction and antiferromagnetic correlations in Kondo
lattices can give rise to an exotic spin-orbit coupled metallic state in
regimes where classical treatments predict a trivial insulating behavior. This
phenomenon can be simulated with ultracold alkaline-earth fermionic atoms
subject to a laser-induced magnetic field by observing dynamics of spin-charge
excitations in quench experiments.",1603.01946v4
2016-03-16,Local shortcut to adiabaticity for quantum many-body systems,"We study the environment assisted local transitionless dynamics in closed
spin systems driven through quantum critical points. In general shortcut to
adaiabaticity (STA) in quantum critical systems requires highly non-local
control Hamiltonians. In this work we develop an approach to achieve local
shortcuts to adiabaticity (LSTA) in spin chains, using local control fields
which scale polynomially with the system size, following universal critical
exponents. We relate the control fields to reduced fidelity susceptibility and
use transverse Ising model in one dimension to exemplify our generic results.
We also extend our analysis to achieve LSTA in central spin models.",1603.05057v2
2016-04-11,"Comment on ""Chaotic orbits for spinning particles in Schwarzschild spacetime""","The astrophysical relevance of chaos for a test particle with spin moving in
Schwarzschild spacetime was the objective of \cite{Verhaaren10}. Even if the
results of the study seem to be qualitatively in agreement with similar works,
the study presented in \cite{Verhaaren10} suffers both from theoretical and
technical issues. These issues are discussed in this comment.",1604.02955v1
2016-04-13,Spin-Exchange Pumped NMR Gyros,"We present the basic theory governing spin-exchange pumped NMR gyros. We
review the basic physics of spin-exchange collisions and relaxation as they
pertain to precision NMR. We present a simple model of operation as an NMR
oscillator and use it to analyze the dynamic response and noise properties of
the oscillator. We discuss the primary systematic errors (differential alkali
fields, quadrupole shifts, and offset drifts) that limit the bias stability,
and discuss methods to minimize them. We give with a brief overview of a
practical implementation and performance of an NMR gyro built by
Northrop-Grumman Corporation, and conclude with some comments about future
prospects.",1604.03982v1
2016-09-01,One loop graviton corrections to dynamical photons in de Sitter,"We employ a recent, general gauge computation of the one loop graviton
contribution to the vacuum polarization on de Sitter to solve for one loop
corrections to the photon mode function. The vacuum polarization takes the form
of a gauge independent, spin 2 contribution and a gauge dependent, spin 0
contribution. We show that the leading secular corrections derive entirely from
the spin 2 contribution.",1609.00386v1
2016-09-06,Generating Quantum States through Spin Chain Dynamics,"Spin chains can realise perfect quantum state transfer between the two ends
via judicious choice of coupling strengths. In this paper, we study what other
states can be created by engineering a spin chain. We conclude that, up to
local phases, all single excitation quantum states with support on every site
of the chain can be created. We pay particular attention to the generation of
W-states that are superposed over every site of the chain.",1609.01398v2
2016-09-22,Spin effects in the pion holographic light-front wavefunction,"We account for dynamical spin effects in the holographic light-front
wavefunction of the pion in order to predict its mean charge radius, decay
constant, spacelike electromagnetic form factor, twist-2 Distribution Amplitude
and the photon-to-pion transition form factor. Using a universal fundamental
AdS/QCD scale of 523 MeV and a constituent quark mass of 330 MeV, we find a
remarkable improvement in describing all observables.",1609.07024v2
2016-09-29,Phase space methods for the spin dynamics in condensed matter systems,"Using the phase-space formulation of quantum mechanics, we derive a
four-component Wigner equation for a system composed of spin-1/2 fermions
(typically, electrons) including the Zeeman effect and the spin-orbit coupling.
This Wigner equation is coupled to the appropriate Maxwell equations to form a
self-consistent mean-field model. A set of semiclassical Vlasov equations with
spin effects is obtained by expanding the full quantum model to first order in
the Planck constant. The corresponding hydrodynamic equations are derived by
taking velocity moments of the phase-space distribution function. A simple
closure relation is proposed to obtain a closed set of hydrodynamic equations.",1609.09472v1
2017-03-06,Controlling topological superconductivity by magnetization dynamics,"We study theoretically a chain of precessing classical magnetic impurities in
an $s$-wave superconductor. Utilizing a rotating wave description, we derive an
effective Hamiltonian that describes the emergent Shiba band. We find that this
Hamiltonian shows non-trivial topological properties, and we obtain the
corresponding topological phase diagrams both numerically and analytically. We
show that changing the precession frequency offers a control over topological
phase transitions and the emergence of Majorana bound states. We propose
driving the magnetic impurities or magnetic texture into precession by means of
spin-transfer torque in a spin-Hall setup, and manipulate it using spin
superfluidity in the case of planar magnetic order.",1703.01870v1
2017-03-14,Core filling and snaking instability of dark solitons in spin-imbalanced superfluid Fermi gases,"We use the time-dependent Bogoliubov de Gennes equations to study dark
solitons in three-dimensional spin-imbalanced superfluid Fermi gases. We
explore how the shape and dynamics of dark solitons are altered by the presence
of excess unpaired spins which fill their low-density core. The unpaired
particles broaden the solitons and suppress the transverse snake instability.
We discuss ways of observing these phenomena in cold atom experiments.",1703.04808v2
2017-03-28,Nonequilibrium spin noise in a quantum dot ensemble,"The spin noise in singly charged self-assembled quantum dots is studied
theoretically and experimentally under the influence of a perturbation,
provided by additional photoexcited charge carriers. The theoretical
description takes into account generation and relaxation of charge carriers in
the quantum dot system. The spin noise is measured under application of above
barrier excitation for which the data are well reproduced by the developed
model. Our analysis demonstrates a strong difference of the recharging dynamics
for holes and electrons in quantum dots.",1703.09510v1
2017-08-28,Dynamics of the Optical Spin Hall Effect,"We study the time evolution of the Optical Spin Hall Effect (OSHE), which
occurs when exciton-polaritons undergo resonant Rayleigh scattering. The
resulting spin pattern in momentum space is quantified by calculating the
degree of circular polarization of the momentum space image for each point in
time. We find the degree of circular polarization performing oscillations,
which can be described within the framework of the pseudospin model by Kavokin
et al. (Ref. 1).",1708.08433v1
2017-08-31,Spin in Compton scattering with pronounced polarization dynamics,"We theoretically investigate a scattering configuration in Compton
scattering, in which the orientation of the electron spin is reversed and
simultaneously, the photon polarization changes from linear polarization into
circular polarization. The intrinsic angular momentum of electron and photon
are computed along the coincident propagation direction of the incoming and
outgoing photon. We find that this intrinsic angular momentum is not conserved
in the considered scattering process. We also discuss the generation of
entanglement for the considered scattering setup and present an angle dependent
investigation of the corresponding differential cross section, Stokes
parameters and spin expectation.",1708.09606v3
2018-04-27,Angular Dependent Magnetization Dynamics with Mirror-symmetric Excitations in Artificial Quasicrystalline Nanomagnet Lattices,"We report angle-dependent spin-wave spectroscopy on aperiodic
quasicrystalline magnetic lattices, i.e., Ammann, Penrose P2 and P3 lattices
made of large arrays of interconnected Ni$_{80}$Fe$_{20}$ nanobars. Spin-wave
spectra obtained in the nearly saturated state contain distinct sets of
resonances with characteristic angular dependencies for applied in-plane
magnetic fields. Micromagnetic simulations allow us to attribute detected
resonances to mode profiles with specific mirror symmetries. Spectra in the
reversal regime show systematic emergence and disappearance of spin wave modes
indicating reprogrammable magnonic characteristics.",1804.10630v1
2020-07-02,An attractive spin-orbit potential from the Skyrme model,"We derive the nucleon-nucleon isoscalar spin-orbit potential from the Skyrme
model and find good agreement with the Paris potential. This solves a problem
that has been open for more than thirty years and gives a new geometric
understanding of the spin-orbit force. Our calculation is based on the dipole
approximation to skyrmion dynamics and higher order perturbation theory.",2007.01304v2
2020-07-20,Ultralong spin coherence times for rubidium atoms in solid parahydrogen via dynamical decoupling,"Coherence time is an essential parameter for quantum sensing, quantum
information, and quantum computation. In this work, we demonstrate electron
spin coherence times as long as 0.1 s for an ensemble of rubidium atoms trapped
in a solid parahydrogen matrix. We explore the underlying physics limiting the
coherence time. The properties of these matrix isolated atoms are very
promising for future applications, including quantum sensing of nuclear spins.
If combined with efficient single-atom readout, this would enable NMR and
magnetic resonance imaging of single molecules cotrapped with alkali-metal atom
quantum sensors within a parahydrogen matrix.",2007.10508v1
2013-08-01,Exchange relaxation as the mechanism of ultrafast spin reorientation in two-sublattice ferrimagnets,"In the exchange approximation, an exact solution is obtained for the
sublattice magnetizations evolution in a two-sublattice ferrimagnet. Nonlinear
regimes of spin dynamics are found that include both the longitudinal and
precessional evolution of the sublattice magnetizations, with the account taken
of the exchange relaxation. In particular, those regimes describe the spin
switching observed in the GdFeCo alloy under the influence of a femtosecond
laser pulse.",1308.0203v1
2013-08-14,Electrical Detection of Spin Wave Resonance in a Permalloy Thin Strip,"We investigated the microwave-induced DC response of spin wave resonance
(SWR) in a permalloy thin strip via electrical detection. Our experimental
results obtained by sweeping the external field reveal that: 1. the amplitude
of SWR signals depend on the direction of external field and, 2. unlike the DC
response of ferromagnetic resonance, SWR spectra are always anti-symmetrical.
The spin dynamics are discussed based on these unusual signals in resonant
condition.",1308.3069v1
2014-03-02,"Comment on ""Spin-Gradient-Driven Light Amplification in a Quantum Plasma""","A comment on the Letter by S. Braun, F. A. Asenjo and S. M. Mahajan, Phys.
Rev. Lett., 109, 175003 (2012). We show that recent arguments for light
amplification driven by inhomogeneous quantum spin fields in low temperature
electron plasmas in metals are invalid. In essence, a neglect of Pauli
`blocking' led the authors to over-estimate the effects of intrinsic spin.",1403.0228v2
2014-03-24,Skyrmionic spin Seebeck effect via dissipative thermomagnonic torques,"We derive thermomagnonic torque and its ""$\beta$-type"" dissipative correction
from the stochastic Landau-Lifshitz-Gilbert equation. The ""$\beta$-type""
dissipative correction describes viscous coupling between magnetic dynamics and
magnonic current and it stems from spin mistracking of the magnetic order. We
show that thermomagnonic torque is important for describing temperature
gradient induced motion of skyrmions in helical magnets while dissipative
correction plays an essential role in generating transverse Magnus force. We
propose to detect such skyrmionic motion by employing the transverse spin
Seebeck effect geometry.",1403.6160v2
2008-07-31,Perfect state transfer in long-range interacting spin chains,"We investigate the most general conditions under which a finite ferromagnetic
long-range inter- acting spin chain achieves unitary fidelity and the shortest
transfer time in transmitting an unknown input qubit. A deeper insight into
system dynamics, allows us to identify an ideal system involving sender and
receiver only. However, this two-spin ideal chain is unpractical due to the
rapid decrease of the coupling strength with the distance. Therefore, we
propose an optimization scheme for ap- proaching the ideal behaviour, while
keeping the interaction strength still reasonably high. The procedure is
scalable with the size of the system and straightforward to implement.",0807.5018v1
2009-12-04,A Non-Disordered Glassy Model with a Tunable Interaction Range,"We introduce a non-disordered lattice spin model, based on the principle of
minimizing spin-spin correlations up to a (tunable) distance R. The model can
be defined in any spatial dimension D, but already for D=1 and small values of
R (e.g. R=5) the model shows the properties of a glassy system: deep and well
separated energy minima, very slow relaxation dynamics, aging and non-trivial
fluctuation-dissipation ratio.",0912.0848v1
2009-12-09,Single magnetic molecule between conducting leads: Effect of mechanical rotations,"We study spin-rotation effects in a magnetic molecule bridged between two
conducting leads. Dynamics of the total angular momentum couples spin tunneling
to the mechanical rotations. Landau-Zener spin transition produced by the
time-dependent magnetic field generates a unique pattern of mechanical
oscillations that can be detected by measuring the electronic tunneling current
through the molecule.",0912.1882v1
2011-11-22,Single Spin Logic Implementation of VLSI Adders,"Some important VLSI adder circuits are implemented using quantum dots (qd)
and Spin Polarized Scanning Tunneling Microscopy (SPSTM) in Single Spin Logic
(SSL) paradigm. A simple comparison between these adder circuits shows that the
mirror adder implementation in SSL does not carry any advantage over CMOS adder
in terms of complexity and number of qds, opposite to the trend observed in
their charge-based counterparts. On the contrary, the transmission gate adder,
Static and Dynamic Manchester carry gate adders in SSL reduce the complexity
and number of qds, in harmony with the trend shown in transistor adders.",1111.5086v1
2011-11-28,Crystallized merons and inverted merons in the condensation of spin-1 Bose gases with spin-orbit coupling,"The non-equilibrium dynamics of a rapidly quenched spin-1 Bose gas with
spin-orbit coupling is studied. By solving the stochastic projected
Gross-Pitaevskii equation, we show that crystallization of merons can occur in
a spinor condensate of ^{87}Rb. Analytic form and stability of the crystal
structure are given. Likewise, inverted merons can be created in a
spin-polarized spinor condensate of ^{23}Na. Our studies provide a chance to
explore the fundamental properties of meron-like matter.",1111.6338v2
2012-04-04,Efficient spin control in high-quality-factor planar micro-cavities,"A semiconductor microcavity embedding donor impurities and excited by a laser
field is modelled. By including general decay and dephasing processes, and in
particular cavity photon leakage, detailed simulations show that control over
the spin dynamics is significally enhanced in high-quality-factor cavities, in
which case picosecond laser pulses may produce spin-flip with high-fidelity
final states.",1204.1040v2
2013-09-05,The Panic Model: Flocking with Minimal Cooperativity,"We present a 2D lattice model of self-propelled spins that can only change
direction upon collision with another spin. We show that even with ballistic
motion and minimal cooperativity, these spins display robust flocking behavior
at nearly all densities, forming long bands of stripes. The structural
transition in this system can be characterized by an order parameter, and we
demonstrate that if this parameter is studied as a dynamical variable rather
than a steady-state observable, we can extract a detailed picture of how the
flocking mechanism varies with density.",1309.1408v1
2013-09-12,High fidelity gate operations within the coupled nuclear and electron spins of a nitrogen vacancy center in diamond,"In this article we investigate the dynamics of a single negatively charged
nitrogen-vacancy center (NV-) coupled to the spin of the nucleus of a
15-nitrogen atom and show that high fidelity gate operations are possible
without the need for complicated composite pulse sequences. These operations
include both the electron and nuclear spin rotations, as well as an entangling
gate between them. These are experimentally realizable gates with current
technology of sufficiently high fidelities that they can be used to build graph
states for quantum information processing tasks.",1309.3107v1
2013-09-19,Equivariant and self-similar standing waves for a Hamiltonian hyperbolic-hyperbolic spin-field system,"In this paper we study the existence of special symmetric solutions to a
Hamiltonian hyperbolic-hyperbolic coupled spin-field system, where the spins
are maps from $\mathbb R^{2+1}$ into the sphere $\S^2$ or the pseudo-sphere
$\H^2$. This model was introduced in \cite{Martina} and it is also known as the
{\it hyperbolic-hyperbolic generalized Ishimori system}. Relying on the
hyperbolic coordinates introduced in \cite{KNZ11}, we prove the existence of
equivariant standing waves in both regular hyperbolic coordinates as well as
similarity variables, and describe their asymptotic behaviour.",1309.5066v2
2013-09-24,Motion of spin polariton bullets in semiconductor microcavities,"The dynamics of optical switching in semiconductor microcavities in the
strong coupling regime is studied using time- and spatially-resolved
spectroscopy. The switching is triggered by polarised short pulses which create
spin bullets of high polariton density. The spin packets travel with speeds of
the order of 106 m/s due to the ballistic propagation and drift of
exciton-polaritons from high to low density areas. The speed is controlled by
the angle of incidence of the excitation beams, which changes the polariton
group velocity.",1309.6344v1
2014-05-16,Spin-orbit coupled Bose-Einstein condensates in a one-dimensional optical lattice,"The realization of artificial gauge fields and spin-orbit coupling for
ultra-cold quantum gases promises new insight into paradigm solid state
systems. Here we experimentally probe the dispersion relation of a spin-orbit
coupled Bose-Einstein condensate loaded into a translating optical lattice by
observing its dynamical stability, and develop an effective band structure that
provides a theoretical understanding of the locations of the band edges. This
system presents exciting new opportunities for engineering condensed-matter
analogs using the flexible toolbox of ultra-cold quantum gases.",1405.4048v1
2014-06-25,Rogue solitons in Heisenberg spin chain,"Following the connection of the non-linear Schr\""{o}dinger equation with the
continuum Heisenberg spin chain, we find the rogue soliton equivalent in the
spin system. The breathers are also mapped to the corresponding space or time
localized oscillatory modes, through the moving curve analogy. The
spatio-temporal evolution of the curvature and torsion of the curve, underlying
these dynamical systems, are explicated to illustrate the localization property
of the rogue waves.",1406.6524v1
2014-06-26,Scaling of temporal correlations in an attractive Tomonaga-Luttinger spin liquid,"We report temperature-dependent neutron scattering measurements of the local
dynamic structure factor in the quantum spin ladder
(C$_{7}$H$_{10}$N)$_{2}$CuBr$_{4}$ in a magnetic field $H=9$~T, in its gapless
quantum-critical phase. We show that the measured quantity has a scaling form
consistent with expectations for a Tomonaga-Luttinger liquid with attraction.
The measured Luttinger parameter $K\approx1.25$ and scaling function are in
excellent agreement with density matrix renormalization group numerical
calculations for the underlying spin Hamiltonian.",1406.6876v2
2015-12-01,Discrete and Continuous Systems of Logic in Nuclear Magnetic Resonance,"We implement several non-binary logic systems using the spin dynamics of
nuclear spins in nuclear magnetic resonance (NMR). The NMR system is a suitable
test system because of its high degree of experimental control; findings from
NMR implementations are relevant for other computational platforms exploiting
particles with spin, such as electrons or photons. While we do not expect the
NMR system to become a practical computational device, it is uniquely useful to
explore strengths and weaknesses of unconventional computational approaches,
such as non-binary logic.",1512.00521v1
2015-12-29,Phonon induced two-mode squeezing of nitrogen-vacancy center ensembles,"We propose a potentially practical scheme for realization of two-mode
squeezed state with respect to two distant nitrogen-vacancy center ensembles
coupled to two interconnected mechanical modes of diamond nanoresonators. By
making use of the tunable phonon-spin interaction and the engineered
phonon-phonon tunneling, both the desired excitation transfer process and the
optimal two-mode squeezing between spin ensembles can be realized. We
investigate the dynamics of the total system under infulences from the
mechanical decay using both analytical and numerical methods, where the
realistic conditions that leads to optimized squeezing between spin ensembles
are analyzed.",1512.08605v1
2016-05-24,Solution to sign problems in models of interacting fermions and quantum spins,"We show that solutions to fermion sign problems in the CT-INT formulation can
be extended to systems involving fermions interacting with dynamical quantum
spins. While these sign problems seem unsolvable in the auxiliary field
approach, solutions emerge in the worldline representation of quantum spins.
Combining the idea with meron-cluster methods, we are able to extend the
solvable models even further. We demonstrate these novel solutions to sign
problems by considering several examples of strongly correlated systems.",1605.07420v2
2016-08-08,Efficient electrical spin readout of NV- centers in diamond,"Using pulsed photoionization the coherent spin manipulation and echo
formation of ensembles of NV- centers in diamond are detected electrically
realizing contrasts of up to 17 %. The underlying spin-dependent ionization
dynamics are investigated experimentally and compared to Monte-Carlo
simulations. This allows the identification of the conditions optimizing
contrast and sensitivity which compare favorably with respect to optical
detection.",1608.02459v1
2016-12-19,Thickness dependence study of current-driven ferromagnetic resonance in Y3Fe5O12/heavy metal bilayers,"We use ferromagnetic resonance to study the current-induced torques in
YIG/heavy metal bilayers. YIG samples with thickness varying from 14.8 nm to 80
nm, with Pt or Ta thin film on top, are measured by applying a microwave
current into the heavy metals and measuring the longitudinal DC voltage
generated by both spin rectification and spin pumping. From a symmetry analysis
of the FMR lineshape and its dependence on YIG thickness, we deduce that the
Oersted field dominates over spin-transfer torque in driving magnetization
dynamics.",1612.06111v1
2016-12-21,Critical current density of a spin-torque oscillator with an in-plane magnetized free layer and an out-of-plane magnetized polarizer,"Spin-torque induced magnetization dynamics in a spin-torque oscillator with
an in-plane (IP) magnetized free layer and an out-of-plane (OP) magnetized
polarizer under IP shape-anisotropy field ($H_{\rm k}$) and applied IP magnetic
field ($H_{\rm a}$) was theoretically studied based on the macrospin model. The
rigorous analytical expression of the critical current density ($J_{\rm c1}$)
for the OP precession was obtained. The obtained expression successfully
reproduces the experimentally obtained $H_{\rm a}$-dependence of $J_{\rm c1}$
reported in [D. Houssameddine $et$ $al$., Nat. Mater. 6, 447 (2007)].",1612.06951v1
2018-09-22,Dynamic critical properties of non-equilibrium Potts models with absorbing states,"We present extensive numerical simulations of a family of non-equilibrium
Potts models with absorbing states that allows for a variety of scenarios,
depending on the number of spin states and the range of the spin-spin
interactions. These scenarios encompass a voter critical point, a discontinuous
transition as well as the presence of both a symmetry-breaking phase transition
and an absorbing phase transition. While we also investigate standard
steady-state quantities, our emphasis is on time-dependent quantities that
provide insights into the transient properties of the models.",1809.08366v1
2019-09-10,Thermally induced spin-transfer torques in superconductor/ferromagnet bilayers,"Thermally induced magnetization dynamics is currently a flourishing field of
research due to its potential application in information technology. We study
the paradigmatic system of a magnetic domain wall in a thermal gradient which
is interacting with an adjacent superconductor. The spin-transfer torques
arising in this system due to the combined action of the giant thermoelectric
effect and the creation of equal-spin pairs in the superconductor are large
enough to give rise to high domain wall velocities $10^3$ times larger than
previously predicted.",1909.04418v2
2019-10-02,Direct Observation of Magnon Modes in Kagome Artificial Spin Ice with Topological Defects,"We investigate spin dynamics of artificial spin ice (ASI) where topological
defects confine magnon modes in Ni$_{81}$Fe$_{19}$ nanomagnets arranged on an
interconnected kagome lattice. Brillouin light scattering microscopy performed
on magnetically disordered states exhibit a series of magnon resonances which
depend on topological defect configurations detected by magnetic force
microscopy. Nanomagnets on a Dirac string and between a monopole-antimonopole
pair show pronounced modifications in magnon frequencies both in experiments
and simulations. Our work is key for the creation and annihilation of Dirac
strings via microwave assisted switching and reprogrammable magnonics based on
ASIs.",1910.00874v1
2020-01-17,Fermi Level Controlled Ultrafast Demagnetization Mechanism in Half-Metallic Heusler Alloy,"The electronic band structure-controlled ultrafast demagnetization mechanism
in Co2FexMn1-xSi Heusler alloy is underpinned by systematic variation of
composition. We find the spin-flip scattering rate controlled by spin density
of states at Fermi level is responsible for non-monotonic variation of
ultrafast demagnetization time ({\tau}M) with x with a maximum at x = 0.4.
Furthermore, Gilbert damping constant exhibits an inverse relationship with
{\tau}M due to the dominance of inter-band scattering mechanism. This
establishes a unified mechanism of ultrafast spin dynamics based on Fermi level
position.",2001.06217v1
2020-01-28,Many-particle Entanglement in Multiple Quantum NMR Spectroscopy,"We use multiple quantum (MQ) NMR dynamics of a gas of spin-carrying molecules
in nanocavities at high and low temperatures for an investigation of
many-particle entanglement. A distribution of MQ NMR intensities is obtained at
high and low temperatures in a system of 201 spins 1/2. The second moment of
the distribution, which provides a lower bound on the quantum Fisher
information, sheds light on the many-particle entanglement in the system. The
dependence of the many-particle entanglement on the temperature is
investigated. Almost all spins are entangled at low temperatures.",2001.10607v1
2020-01-31,A Baker-Campbell-Hausdorff formula for the logarithm of permutations,"The dynamics-from-permutations of classical Ising spins is studied for a
chain of four spins. We obtain the Hamiltonian operator which is equivalent to
the unitary permutation matrix that encodes assumed pairwise exchange
interactions. It is shown how this can be summarized by an exact terminating
Baker-Campbell-Hausdorff formula, which relates the Hamiltonian to a product of
exponentiated two-spin exchange permutations. We briefly comment upon physical
motivation and implications of this study.",2001.11909v1
2020-02-11,Geometric phase-control of a spin-torque oscillator,"We show that the phase of a spin-torque oscillator generically acquires a
geometric contribution upon slow and cyclic variation of the parameters that
govern its dynamics. As an example, we compute the geometric phase that results
from a cyclic excursion of the magnitude of the external field and the current.
We consider thermal phase fluctuations and conclude that the geometric phase
should be experimentally observable at room temperature with current setups. We
briefly comment on arrays of spin-torque oscillators and possible applications.",2002.04492v1
2020-04-06,Relativistic hydrodynamics for spin-polarized media,"We summarize the key ingredients of the recently proposed formalism of
relativistic perfect-fluid hydrodynamics with spin. Based on the underlying
kinetic theory definitions for the equilibrium distribution functions we obtain
the evolution equations governing the system's expansion. Employing Bjorken
symmetry we study the spin polarization dynamics of the system.",2004.02544v1
2020-04-27,Nonreciprocal directional dichroism induced by a temperature gradient as a probe for mobile spin dynamics in quantum magnets,"Novel states of matter in quantum magnets like quantum spin liquids attract
considerable interest recently. Despite the existence of a plenty of candidate
materials, there is no confirmed quantum spin liquid, largely due to the lack
of proper experimental probes. For instance, spectrosocopy experiments like
neutron scattering receive contributions from disorder-induced local modes,
while thermal transport experiments receive contributions from phonons. Here we
propose a thermo-optic experiment which directly probes the mobile magnetic
excitations in spatial-inversion symmetric and/or time-reversal symmetric Mott
insulators: the temperature-gradient-induced nonreciprocal directional
dichroism (TNDD) spectroscopy. Unlike traditional probes, TNDD directly detects
mobile magnetic excitations and decouples from phonons and local magnetic
modes.",2004.13047v1
2000-06-01,High-energy magnon dispersion and multi-magnon continuum in the two-dimensional Heisenberg antiferromagnet,"We use quantum Monte Carlo simulations and numerical analytic continuation to
study high-energy spin excitations in the two-dimensional S=1/2 Heisenberg
antiferromagnet at low temperature. We present results for both the transverse
and longitudinal dynamic spin structure factor S(q,w) at q=(pi,0) and
(pi/2,pi/2). Linear spin-wave theory predicts no dispersion on the line
connecting these momenta. Our calculations show that in fact the magnon energy
at (pi,0) is 10% lower than at (pi/2,pi/2). We also discuss the transverse and
longitudinal multi-magnon continua and their relevance to neutron scattering
experiments.",0006021v1
2000-06-23,"Issues, Concepts, and Challenges in Spintronics","We review from a theoretical perspective the emerging field of spintronics
where active control of spin transport and dynamics in electronic materials may
provide novel device application possibilities. In particular, we discuss the
quantum mechanical principles underlying spintronics applications, emphasizing
the formidable challenges involving spin decoherence and spin injection facing
any eventual device fabrication. We provide a critical assessment of the
current status of the field with special attention to possible device
applications.",0006369v1
2000-06-26,Image restoration using the Q-Ising spin glass,"We investigate static and dynamic properties of gray-scale image restoration
(GSIR) by making use of the Q-Ising spin glass model, whose ladder symmetry
allows to take in account the distance between two spins. We thus give an
explicit expression of the Hamming distance between the original and restored
images as a function of the hyper-parameters in the mean field limit. Finally,
numerical simulations for real-world pictures are carried out to prove the
efficiency of our model.",0006389v3
2012-05-08,Quantum phases of Bose-Bose mixtures on a triangular lattice,"We investigate the zero temperature quantum phases of a Bose-Bose mixture on
a triangular lattice using Bosonic Dynamical Mean Field Theory (BDMFT). We
consider the case of total filling one where geometric frustration arises for
asymmetric hopping. We map out a rich ground state phase diagram including
xy-ferromagnetic, spin-density wave, superfluid, and supersolid phases. In
particular, we identify a stripe spin-density wave phase for highly asymmetric
hopping. On top of the spin-density wave, we find that the system generically
shows weak charge (particle) density wave order.",1205.1806v2
2017-05-12,Landau-Zener transition in a continuously measured single-molecule spin transistor,"We monitor the Landau-Zener dynamics of a single-ion magnet in a
spin-transistor geometry. For increasing field-sweep rates, the spin reversal
probability shows increasing deviations from that of a closed system. In the
low-conductance limit, such deviations are shown to result from a dephasing
process. In particular, the observed behaviors are succesfully simulated by
means of an adiabatic master equation, with time averaged dephasing (Lindblad)
operators. The time average is tentatively interpeted in terms of the finite
time resolution of the continuous measurement.",1705.04512v1
2017-11-10,Chiral solitons in a non-linear model of helical molecules,"In this paper an effective integrable non-linear model describing the
electron spin dynamics in a deformable helical molecule with weak spin-orbit
coupling is presented. Non-linearity arises from the electron-lattice
interaction and it enables the formation of a variety of stable solitons such
as bright solitons, breathers and rogue waves, all of them presenting well
defined spin projection onto the molecule axis. A thorough study of the soliton
solutions is presented and discussed.",1711.03794v1
2018-08-03,A thermally driven spin-transfer-torque system far from equilibrium: enhancement of the thermoelectric current via pumping current,"We consider a small itinerant ferromagnet exposed to an external magnetic
field and strongly driven by a thermally induced spin current. For this model,
we derive the quasi-classical equations of motion for the magnetization where
the effects of a dynamical non-equilibrium distribution function are taken into
account self-consistently. We obtain the Landau-Lifshitz-Gilbert equation
supplemented by a spin-transfer torque term of Slonczewski form. We identify a
regime of persistent precessions in which we find an enhancement of the
thermoelectric current by the pumping current.",1808.01192v1
2018-08-16,{\em Zitterbewegung} in Spin-Orbit Coupled Systems and Ehrenfest's Theorem,"We use Ehrenfest's theorem to provide a particularly simple derivation of the
{\em zitterbewegung} in the dynamics of initial Gaussian wave packets in a
two-dimensional electron gas. For initial packets which are very wide in the
$y$-direction, the {\em zitterbewegung} is only in the $y$-component of the
velocity. We extend our Ehrenfest theorem based calculation to the spin-orbit
coupled spinor Bose-Einstein condensate (BEC) to predict that there can be {\em
zitterbewegung} in the $x$-component of the velocity in this situation driven
by a combination of the nonlinear interaction in the condensate and the
splitting due to the spin-orbit coupling.",1808.05397v1
2019-01-17,Secular evolution of compact binaries revolving around a spinning massive black hole,"The leading order effect of the spin of a distant supermassive black hole
(SMBH) on the orbit of compact binary revolving around it appears at the 1.5
post Newtonian (PN) expansion through coupling with the inner and outer orbital
angular momenta, and makes an oscillating characteristic contribution to the
secular evolution of the compact binary eccentricity over a long time scale
compared to the Kozai-Lidov dynamics caused by a non-spinning SMBH.",1901.05591v1
2019-03-01,"Spin Chains, Graphs and State Revival","Connections between the 1-excitation dynamics of spin lattices and quantum
walks on graphs will be surveyed. Attention will be paid to perfect state
transfer (PST) and fractional revival (FR) as well as to the role played by
orthogonal polynomials in the study of these phenomena. Included is a
discussion of the ordered Hamming scheme, its relation to multivariate
Krawtchouk polynomials of the Tratnik type, the exploration of quantum walks on
graphs of this association scheme and their projection to spin lattices with
PST and FR.",1903.00145v1
2019-03-21,Magnetic Skyrmions in Atomic Thin CrI$_3$ Monolayer,"In this letter, we report the visualization of topologically protected spin
textures, in the form of magnetic skyrmions, in recently discovered
monoatomic-thin two-dimensional CrI$_3$. By combining density functional theory
and atomistic spin dynamic simulation, we demonstrate that an application of
out-of-plane electric field to CrI$_3$ lattice favors the formation of sub-10
nm skyrmions at 0 K temperature. The spin texture arises due to a strong
correlation between magneto-crystalline anisotropy, Dzyaloshinskii-Moriya
interaction and the vertical electric field, whose shape and size could be
tuned with the magnetic field. Such finding will open new avenues for
atomic-scale quantum engineering and precision sensing.",1903.08797v1
2019-11-11,Domain wall motion in a diffusive weak ferromagnet,"We study the domain wall motion in a disordered weak ferromagnet, induced by
injecting a spin current from a strong ferromagnet. Starting from the spin
diffusion equation describing the spin accumulation in the weak ferromagnet, we
calculate the force and torque acting on the domain wall. We also study the
ensuing domain wall dynamics, and suggest a possible measurement method for
detecting the domain wall motion via measuring the additional resistance.",1911.04121v5
2019-11-24,Lindblad approximation and spin relaxation in quantum electrodynamics,"This article is concerned with the time evolution of a $\frac{1}{2}$-spin
particle in a constant external magnetic field with the quantized
electromagnetic field (photons). We derive a Lindblad (or GKLS) type
approximation of the spin dynamics together with a precise control of the error
coming from this approximation. The error term is bounded by $g^2$ where $g$ is
the coupling constant of the spin-photon interaction. The point here is the
uniformity in time $t>0$ of this error control.",1911.10481v1
2019-12-31,Spin selective scattering modes in random anisotropy optical medium,"Geometrical and dynamical phase have competing effects as far a scattering of
light form inhomogeneous anisotropic optical medium is concerned. If fine-tuned
appropriately, these effects can completely cancel each other for a chosen spin
component while having an additive effect on the orthogonal components. Here,
we show a manifestation of extraordinary spin selective modes in Fourier
spectrum of Gaussian beam transmitted through anisotropic disordered medium. We
realize the concept using a twisted nematic liquid crystal-based spatial light
modulator (SLM) with random gray level distribution for incident Gaussian beam.",1912.13235v1
2020-03-01,Spin kinetic equations in the probability representation of quantum mechanics,"We discuss the possibility to formulate the dynamics of spin states described
by the Schrodinger equation for pure states and the von Neumann equation (as
well as the GKSL equation) for mixed states in the form of quantum kinetic
equations for probability distributions. We review an approach to the
spin-state description by means of the probability distributions of dichotomic
random variables.",2003.00485v1
2020-05-19,Instability in the Hartmann--Hahn double resonance,"The Hartmann-Hahn technique allows sensitivity enhancement of magnetic
resonance imaging and spectroscopy by coupling the spins under study to another
spin species that is externally driven. Here we theoretically study the coupled
spins' dynamics, and find that for a certain region of driving parameters the
system becomes unstable. The required conditions for making this region of
instability becoming experimentally accessible are discussed.",2005.09298v3
2020-11-26,Spin polarization dynamics in the Gubser-expanding background,"Evolution of spin polarization in the Gubser-expanding conformal
perfect-fluid hydrodynamic background is studied. The analysis of the conformal
transformation properties of the conservation laws is extended to the case of
the angular momentum conservation. The explicit forms of equations of motion
for spin components are derived and analysed, and some special solutions are
found.",2011.14907v4
2021-02-09,Dynamics of spin-polarized impurity in ultracold Fermi gas,"We show that the motion of spin-polarized impurity (ferron) in ultracold
atomic gas is characterized by a certain critical velocity which can be traced
back to the amount of spin imbalance inside the impurity. We have calculated
the effective mass of ferron in two dimensions. We show that the effective mass
scales with the surface of the ferron. We discuss the impact of these findings;
in particular, we demonstrate that ferrons become unstable in the vicinity of a
vortex.",2102.04833v3
2021-03-29,Hydrodynamic model of skyrmions and vorticities in the spin-1 Bose-Einstein condensate in ferromagnetic phase at finite temperatures,"Quantum hydrodynamic of skyrmions in spinor ultracold bosons at the finite
temperature is described. The limit regime of BEC appearing at the zero
temperature is discussed either. The skyrmions are found as the solution of the
spin evolution equation for the ferromagnetic phase of spin-1 ultracold bosons.
It is demonstrated that the quantum part of the spin current gives major
contribution in the formation of the skyrmions. The interplay between the
quantum (spin) vorticity and the classic vorticity is considered for the finite
temperatures. Bosons are presented as two fluids associated with the
Bose-Einstein condensate and the normal fluid. All effects are considered for
the ferromagnetic phase.",2103.15930v1
2021-04-02,A Lieb-Robinson bound for quantum spin chains with strong on-site impurities,"We consider a quantum spin chain with nearest neighbor interactions and
sparsely distributed on-site impurities. We prove commutator bounds for its
Heisenberg dynamics which incorporate the coupling strengths of the impurities.
The impurities are assumed to satisfy a minimum spacing, and each impurity has
a non-degenerate spectrum. Our results are proven in a broadly applicable
setting, both in finite volume and in thermodynamic limit. We apply our results
to improve Lieb-Robinson bounds for the Heisenberg spin chain with a random,
sparse transverse field drawn from a heavy-tailed distribution.",2104.00968v1
2021-04-27,Field-driven dynamics of magnetic Hopfions,"We present micromagnetic simulations on resonant spin wave modes of magnetic
Hopfions up to 15 GHz driven by external magnetic fields. A sharp transition is
found around 32 mT coinciding with a transition from Hopfions to magnetic
torons. The modes exhibit characteristic amplitudes in frequency space
accompanied by unique localization patterns in real space, and are found to be
robust to damping around topological features, particularly vortex lines in
Hopfions and Bloch points in torons. The marked differences in spin wave
spectra between Hopfions, torons and target skyrmions can serve as fingerprints
in future experimental validation studies of these novel 3d topological spin
textures.",2104.13349v1
2021-05-21,OpenMP solver for rotating spin-one spin-orbit- and Rabi-coupled Bose-Einstein condensates,"We present OpenMP version of a Fortran program for solving the
Gross-Pitaevskii equation for a harmonically trapped three-component rotating
spin-1 spinor Bose-Einstein condensate (BEC) in two spatial dimensions with or
without spin-orbit (SO) and Rabi couplings. The program uses either Rashba or
Dresselhaus SO coupling. We use the split-step Crank-Nicolson discretization
scheme for imaginary- and real-time propagation to calculate stationary states
and BEC dynamics, respectively.",2105.10517v1
2021-08-07,Dynamic electron-phonon and spin-phonon interactions due to inertia,"THz radiation allows for the controlled excitation of vibrational modes in
molecules and crystals. We show that the circular motion of ions introduces
inertial effects on electrons. In analogy to the classical Coriolis and
centrifugal forces, these effects are the spin-rotation coupling, the
centrifugal field coupling, the centrifugal spin-orbit coupling, and the
centrifugal redshift. Depending on the phonon decay, these effects persist for
various picoseconds after excitation. Potential boosting of the effects would
make it a promising platform for vibration-based control of localized quantum
states or chemical reaction barriers.",2108.03473v2
2021-09-02,Causal structure in spin-foams,"The metric field of general relativity is almost fully determined by its
causal structure. Yet, in spin-foam models for quantum gravity, the role played
by the causal structure is still largely unexplored. The goal of this paper is
to clarify how causality is encoded in such models. The quest unveils the
physical meaning of the orientation of the two-complex and its role as a
dynamical variable. We propose a causal version of the EPRL spin-foam model and
discuss the role of the causal structure in the reconstruction of a
semiclassical spacetime geometry.",2109.00986v1
2021-09-21,Optical and spin-coherence properties of rubidium atoms trapped in solid neon,"In this work, we measure the properties of ensembles of rubidium atoms
trapped in solid neon that are relevant for use as quantum sensors of magnetic
fields: the spin coherence of the trapped atoms and the ability to optically
control and measure their spin state. We use the rubidium atoms as an AC
magnetometer (by employing an appropriate dynamical decoupling sequence) and
demonstrate NMR detection of Ne-21 atoms co-trapped in the neon matrix.",2109.10324v1
2021-12-13,Magnon frequency renormalization by the electronic geometrical spin torque in itinerant magnets,"We investigate non-adiabatic effects on the magnon frequency in an
interacting system of localized spins and itinerant electrons. Including the
lowest order corrections to the adiabatic dynamics in an analytically solvable
model, applicable to simple ferromagnets like Fe, Co and Ni, we find that the
magnon frequency is renormalized by a geometrical torque arising from the
electronic spin Berry curvature. Comparison to exact numerical simulations
reveals that our analytical solution captures essential low-energy features,
and provides a mechanism for the magnon frequency hardening observed in recent
first principles calculations for Fe, provided the geometrical torque is taken
into account.",2112.06547v1
2022-06-06,Quantum information spreading in random spin chains,"We study the spreading of quantum correlations and information in a
one-dimensional quantum spin chain with critical disorder as encoded in an
infinite randomness fixed point. Specifically, we focus on the dynamics after a
quantum quench of the R\'enyi entropies, of the mutual information and of the
entanglement negativity in the prototypical XXZ spin chain with random bonds
and anisotropy parameters. We provide analytic predictions in the scaling
regime based on real-space renormalization group methods. We support these
findings through numerical simulations in the non-interacting limit, where we
can access the scaling regime.",2206.02934v1
2022-07-06,Spectrum of the Hypereclectic Spin Chain and Pólya Counting,"In earlier work we proposed a generating function that encodes the Jordan
block spectrum of the integrable Hypereclectic spin chain, related to the
one-loop dilatation operator of the dynamical fishnet quantum field theory. We
significantly improve the expressions for these generating functions, rendering
them much more explicit and elegant. In particular, we treat the case of the
full spin chain without imposing any cyclicity constraints on the states, as
well as the case of cyclic states. The latter involves the P\'olya enumeration
theorem in conjunction with q-binomial coefficients.",2207.02885v1
2022-11-29,Kekule spin-orbit dimer phase and triplon dynamics,"We derive and study a spin-orbital model for ions with $d^1$ electronic
configuration on a honeycomb lattice. In this system, the directional character
of $t_{2g}$ orbital leads to extensively degenerate dimerized ground states. We
find that additional interactions from charge transfer processes completely
lift the degeneracy and stabilize the Kekule spin-orbit dimerized phase where
dimers form a kagome superlattice. For such phase, the triplon band spectrum
resembles the electronic band structure of the kagome lattice and becomes
topologically non-trivial in the presence of inter-dimer Dzyaloshinskii-Moriya
interactions. As an experimental verification of the Kekule dimerized phase, we
propose the thermal Hall experiment, which can directly uncover the topological
profile of the corresponding triplon band spectrum.",2211.16094v1
2023-01-18,Magnetic isotope effects: a potential testing ground for quantum biology,"One possible explanation for magnetosensing in biology, such as avian
magnetoreception, is based on the spin dynamics of certain chemical reactions
that involve radical pairs. Radical pairs have been suggested to also play a
role in anesthesia, hyperactivity, neurogenesis, circadian clock rhythm,
microtubule assembly, etc. It thus seems critical to probe the credibility of
such models. One way to do so is through isotope effects with different nuclear
spins. Here we briefly review the papers involving spin-related isotope effects
in biology. We suggest studying isotope effects can be an interesting avenue
for quantum biology.",2301.08554v1
2023-03-05,Many-body delocalization from planted thermal inclusion,"We numerically study quantum avalanches in 1D disordered spin systems by
attaching two XXZ spin chains. One chain has low disorder representing a rare
Griffith's region, or thermal inclusion, and the second has larger disorder,
i.e. disorder larger than the observed finite-size crossover. Comparing
dynamics of this system to identical systems with uniformly large disorder, we
find evidence for exponentially slow thermalization (in disorder) within the
MBL regime when the rare region is present. We observe a decay of the spin
imbalance in the bulk of the large disorder region that persists to long times
($\sim10^{4}$) and find a universal behavior of the spectral function.",2303.02748v1
2023-05-08,Martingale drift of Langevin dynamics and classical canonical spin statistics,"The martingale characterizes a kind of fairness or unbiased nature of the
stochastic process which is associated with another stochastic process. If
$x_t$ evolves according to the Langevin equation whose mean drift is $a_t$ as
function of $x_t,$ and that $a_t$ as induced stochastic process is martingale
in turn associated with the former process, then we show that the amplitude of
$a_t$ is the Langevin function, which is originally the canonical response of a
single classical Heisenberg spin under static field. Furthermore, the
asymptotic limit of $x_t/t$ obeys the ensemble statistics of such Heisenberg
spin.",2305.04976v2
2023-07-18,"Propagation of Coupled Acoustic, Electromagnetic and Spin Waves in Saturated Ferromagnetoelastic Solids","We study the propagation of plane waves in an unbounded body of a saturated
ferromagnetoelastic solid. The equations by Tiersten for small fields
superposed on finite initial fields in a saturated ferromagnetoelastic material
are employed, with their quasistatic magnetic field extended to dynamic
electric and magnetic fields for electromagnetic waves. Dispersion relations of
the plane waves are obtained. The cutoff frequencies and long wave
approximation of the dispersion curves are determined. Results show that
acoustic, electromagnetic and magnetic spin waves are coupled in such a
material. For YIG which is a cubic crystal without piezoelectric coupling, the
acoustic and electromagnetic waves are not directly coupled but they can still
interact indirectly through spin waves.",2307.09171v1
2024-03-18,Current-induced magnon trapping in spin torque oscillation,"Spin torque nano-oscillators realized by magnetization dynamics trapped in a
current-induced potential are reported. We fabricated Ni$_{81}$Fe$_{19}$/Pt
nanostructures and measured current-induced microwave emission from the
structures. The result shows an increase in the magnitude and spectral
narrowing of the microwave emission. We demonstrate that the current-induced
magnetic field suppresses magnon radiation loss and significantly reduces the
linewidth and the threshold current required for the spin torque oscillation.",2403.11618v1
2024-04-08,Lattice-Assisted Molecular Excitations in Frustrated Pyrochlores,"Resonance-like molecular excitations have been discovered in a series of
pyrochlore antiferromagnets, yet their origins and relationships with the
coexisting magnon excitations remain a puzzle. Here, by incorporating the
spin-lattice coupling and the consequent four-spin interactions through the
site-phonon model, we accomplish a unified description of the molecular and
magnon excitations, revealing the molecular modes as statistical approximations
of the dispersive magnon excitations. Our work demonstrates a general approach
to understand exotic spin dynamics in magnetoelastic systems.",2404.05523v1
1998-02-25,Dynamic Matrix Ansatz for Integrable Reaction-Diffusion Processes,"We show that the stochastic dynamics of a large class of one-dimensional
interacting particle systems may be presented by integrable quantum spin
Hamiltonians. Generalizing earlier work \cite{Stin95a,Stin95b} we present an
alternative description of these processes in terms of a time-dependent
operator algebra with quadratic relations. These relations generate the Bethe
ansatz equations for the spectrum and turn the calculation of time-dependent
expectation values into the problem of either finding representations of this
algebra or of solving functional equations for the initial values of the
operators. We use both strategies for the study of two specific models: (i) We
construct a two-dimensional time-dependent representation of the algebra for
the symmetric exclusion process with open boundary conditions. In this way we
obtain new results on the dynamics of this system and on the eigenvectors and
eigenvalues of the corresponding quantum spin chain, which is the isotropic
Heisenberg ferromagnet with non-diagonal, symmetry-breaking boundary fields.
(ii) We consider the non-equilibrium spin relaxation of Ising spins with
zero-temperature Glauber dynamics and an additional coupling to an
infinite-temperature heat bath with Kawasaki dynamics. We solve the functional
equations arising from the algebraic description and show non-perturbatively on
the level of all finite-order correlation functions that the coupling to the
infinite-temperature heat bath does not change the late-time behaviour of the
zero-temperature process. The associated quantum chain is a non-hermitian
anisotropic Heisenberg chain related to the seven-vertex model.",9802268v1
2014-09-01,Decoherence of Bell states by local interactions with a suddenly quenched spin environment,"We study the dynamics of disentanglement of two qubits initially prepared in
a Bell state and coupled at different sites to an Ising transverse field spin
chain (ITF) playing the role of a dynamic spin environment. The initial state
of the whole system is prepared into a tensor product state $\rho_{Bell}\otimes
\rho_{chain}$ where the state of the chain is taken to be given by the ground
state $|G(\lambda_i)\rangle$ of the ITF Hamiltonian $H_E(\lambda_i)$ with an
initial field $\lambda_i$. At time $t=0^+$, the strength of the transverse
field is suddenly quenched to a new value $\lambda_f$ and the whole system
(chain $+$ qubits) undergoes a unitary dynamics generated by the total
Hamiltonian $H_{Tot}=H_E(\lambda_f) + H_I$ where $H_I$ describes a local
interaction between the qubits and the spin chain. The resulting dynamics leads
to a disentanglement of the qubits, which is described through the Wooter's
Concurrence, due to there interaction with the non-equilibrium environment. The
concurrence is related to the Loschmidt echo which in turn is expressed in
terms of the time-dependent covariance matrix associated to the ITF. This
permits a precise numerical and analytical analysis of the disentanglement
dynamics of the qubits as a function of their distance, bath properties and
quench amplitude. In particular we emphasize the special role played by a
critical initial environment.",1409.0317v1
2012-04-19,Dynamical behavior of the Niedermayer algorithm applied to Potts models,"In this work we make a numerical study of the dynamic universality class of
the Niedermayer algorithm applied to the two-dimensional Potts model with 2, 3,
and 4 states. This algorithm updates clusters of spins and has a free
parameter, $E_0$, which controls the size of these clusters, such that $E_0=1$
is the Metropolis algorithm and $E_0=0$ regains the Wolff algorithm, for the
Potts model. For $-1<E_0<0$, only clusters of equal spins can be formed: we
show that the mean size of the clusters of (possibly) turned spins initially
grows with the linear size of the lattice, $L$, but eventually saturates at a
given lattice size $\widetilde{L}$, which depends on $E_0$. For $L \geq
\widetilde{L}$, the Niedermayer algorithm is in the same dynamic universality
class of the Metropolis one, i.e, they have the same dynamic exponent. For
$E_0>0$, spins in different states may be added to the cluster but the dynamic
behavior is less efficient than for the Wolff algorithm ($E_0=0$). Therefore,
our results show that the Wolff algorithm is the best choice for Potts models,
when compared to the Niedermayer's generalization.",1204.4353v1
2014-05-16,Role of the glassy dynamics and thermal mixing in the dynamic nuclear polarization and relaxation mechanisms of pyruvic acid,"The temperature dependence of $^1$H and $^{13}$C nuclear spin-lattice
relaxation rate $1/T_1$ has been studied in the 1.6 K - 4.2 K temperature range
in pure pyruvic acid and in pyruvic acid containing trityl radicals at a
concentration of 15 mM. The temperature dependence of $1/T_1$ is found to
follow a quadratic power law for both nuclei in the two samples. Remarkably the
same temperature dependence is displayed also by the electron spin-lattice
relaxation rate $1/T_{1e}$ in the sample containing radicals. These results are
explained by considering the effect of the structural dynamics on the
relaxation rates in pyruvic acid. Dynamic nuclear polarization experiments show
that below 4 K the $^{13}$C build up rate scales with $1/T_{\text{1e}}$, in
analogy to $^{13}$C $1/T_1$ and consistently with a thermal mixing scenario
where all the electrons are collectively involved in the dynamic nuclear
polarization process and the nuclear spin reservoir is in good thermal contact
with the electron spin system.",1405.4284v2
2014-05-25,Proton spin dynamics in polymer melts: new perspectives for experimental investigations of polymer dynamics,"Significant progress was made in recent years in the understanding of the
proton spin kinetics in polymer melts. Generally, the proton spin kinetics is
determined by intramolecular and intermolecular magnetic dipole-dipole
contributions of proton spins. During many decades it was postulated that the
main contribution is a result of intramolecular magnetic dipole-dipole
interactions of protons belonging to the same polymer segment. It appears that
this postulate is far from reality. The relative weights of intra- and
intermolecular contributions are time dependent and sensitive to details of
polymer chain dynamics. It is shown that for isotropic models of polymer
dynamics the influence of the intermolecular magnetic dipole-dipole
interactions increases faster with increasing evolution time (i.e. decreasing
frequency) than the corresponding influence of the intramolecular counterpart.
On the other hand, an inverted situation is predicted by the tube-reptation
model: here the influence of the intramolecular magnetic dipole-dipole
interactions increases faster with time than the contribution from
intermolecular interactions. The intermolecular contribution in the proton
relaxation of polymer melts can experimentally be isolated using the isotope
dilution technique and this opens a new perspective for experimental
investigations of polymer dynamics by proton NMR.",1405.6366v1
2015-12-01,Quench dynamics of a Bose-Einstein condensate under synthetic spin-orbit coupling,"We study the quench dynamics of a Bose-Einstein condensate under a
Raman-assisted synthetic spin-orbit coupling. To model the dynamical process,
we adopt a self-consistent Bogoliubov approach, which is equivalent to applying
the time-dependent Bogoliubov-de-Gennes equations. We investigate the dynamics
of the condensate fraction as well as the momentum distribution of the Bose gas
following a sudden change of system parameters. Typically, the system evolves
into a steady state in the long-time limit, which features an oscillating
momentum distribution and a stationary condensate fraction which is dependent
on the quench parameters. We investigate how different quench parameters such
as the inter- and intra-species interactions and the spin-orbit-coupling
parameters affect the condensate fraction in the steady state. Furthermore, we
find that the time average of the oscillatory momentum distribution in the
long-time limit can be described by a generalized Gibbs ensemble with two
branches of momentum-dependent Gibbs temperatures. Our study is relevant to the
experimental investigation of dynamical processes in a spin-orbit coupled
Bose-Einstein condensate.",1512.00160v3
2019-09-24,Spin-transfer dynamics in MgO-based magnetic tunnel junctions with an out-of-plane magnetized free layer and an in-plane polarizer,"Here, we present an analytical and numerical model describing the
magnetization dynamics in MgO-based spin-torque nano-oscillators with an
in-plane magnetized polarizer and an out-of-plane free layer. We introduce the
spin-transfer torque asymmetry by considering the cosine angular dependence of
the resistance between the two magnetic layers in the stack. For the analytical
solution, dynamics are determined by assuming a circular precession trajectory
around the direction perpendicular to the plane, as set by the effective field,
and calculating the energy integral over a single precession period. In a more
realistic approach, we include the bias dependence of the tunnel
magnetoresistance, which is assumed empirically to be a piecewise linear
function of the applied voltage. The dynamical states are found by solving the
stability condition for the Jacobian matrix for out-of-plane static states. We
find that the bias dependence of the tunnel magnetoresistance, which is an
inseparable effect in every tunnel junction, exhibits drastic impact on the
spin-torque nano-oscillator phase diagram, mainly by increasing the critical
current for dynamics and quenching the oscillations at high currents. The
results are in good agreement with our experimental data published elsewhere.",1909.10983v1
2020-05-25,Attosecond electron-spin dynamics in Xe 4d photoionization,"The photoionization of xenon atoms in the 70-100 eV range reveals several
fascinating physical phenomena such as a giant resonance induced by the dynamic
rearrangement of the electron cloud after photon absorption, an anomalous
branching ratio between intermediate Xe$^+$ states separated by the spin-orbit
interaction and multiple Auger decay processes. These phenomena have been
studied in the past, using in particular synchrotron radiation, but without
access to real-time dynamics. Here, we study the dynamics of Xe 4d
photoionization on its natural time scale combining attosecond interferometry
and coincidence spectroscopy. A time-frequency analysis of the involved
transitions allows us to identify two interfering ionization mechanisms: the
broad giant dipole resonance with a fast decay time less than 50 as and a
narrow resonance at threshold induced by spin-flip transitions, with much
longer decay times of several hundred as. Our results provide new insight into
the complex electron-spin dynamics of photo-induced phenomena.",2005.12008v1
2021-03-17,Quasinormal modes of slowly-rotating black holes in dynamical Chern-Simons gravity,"The detection of gravitational waves from compact binary mergers by the
LIGO/Virgo collaboration has, for the first time, allowed us to test
relativistic gravity in its strong, dynamical and nonlinear regime, thus
opening a new arena to confront general relativity (and modifications thereof)
against observations. We consider a theory which modifies general relativity by
introducing a scalar field coupled to a parity-violating curvature term known
as dynamical Chern-Simons gravity. In this theory, spinning black holes are
different from their general relativistic counterparts and can thus serve as
probes to this theory. We study linear gravito-scalar perturbations of black
holes in dynamical Chern-Simons gravity at leading-order in spin and (i) obtain
the perturbed field equations describing the evolution of the perturbed
gravitational and scalar fields, (ii) numerically solve these equations by
direct integration to calculate the quasinormal mode frequencies for the
dominant and higher multipoles and tabulate them, (iii) find strong evidence
that these rotating black holes are linearly stable, and (iv) present general
fitting functions for different multipoles for gravitational and scalar
quasinormal mode frequencies in terms of spin and Chern-Simons coupling
parameter. Our results can be used to validate the ringdown of small-spin
remnants of numerical relativity simulations of black hole binaries in
dynamical Chern-Simons gravity and pave the way towards future tests of this
theory with gravitational wave ringdown observations.",2103.09913v3
2021-04-01,"Quantum versus Classical Dynamics in Spin Models: Chains, Ladders, and Square Lattices","We present a comprehensive comparison of spin and energy dynamics in quantum
and classical spin models on different geometries, ranging from one-dimensional
chains, over quasi-one-dimensional ladders, to two-dimensional square lattices.
Focusing on dynamics at formally infinite temperature, we particularly consider
the autocorrelation functions of local densities, where the time evolution is
governed either by the linear Schr\""odinger equation in the quantum case, or
the nonlinear Hamiltonian equations of motion in the case of classical
mechanics. While, in full generality, a quantitative agreement between quantum
and classical dynamics can therefore not be expected, our large-scale numerical
results for spin-$1/2$ systems with up to $N = 36$ lattice sites in fact defy
this expectation. Specifically, we observe a remarkably good agreement for all
geometries, which is best for the nonintegrable quantum models in quasi-one or
two dimensions, but still satisfactory in the case of integrable chains, at
least if transport properties are not dominated by the extensive number of
conservation laws. Our findings indicate that classical or semi-classical
simulations provide a meaningful strategy to analyze the dynamics of quantum
many-body models, even in cases where the spin quantum number $S = 1/2$ is
small and far away from the classical limit $S \to \infty$.",2104.00472v3
2021-04-08,Flicker and random telegraph noise between gyrotropic and dynamic C-state of a vortex based spin torque nano oscillator,"Vortex based spin torque nano oscillators (STVOs) can present more complex
dynamics than the spin torque induced gyrotropic (G) motion of the vortex core.
The respective dynamic modes and the transition between them can be controlled
by experimental parameters such as the applied dc current. An interesting
behavior is the stochastic transition from the G- to a dynamic C-state
occurring for large current densities. Moreover, the C-state oscillations
exhibit a constant active magnetic volume. We present noise measurements in the
different dynamic states that allow accessing specific properties of the
stochastic transition, such as the characteristic state transition frequency.
Furthermore,we confirm, as theoretically predicted, an increase of flicker
noise with $I_{dc}^2$ when the oscillation volume remains constant with the
current. These results bring insight into the potential optimization of noise
properties sought for many potential rf applications with spin torque
oscillators. Furthermore, the investigated stochastic characteristics open up
new potentialities, for instance in the emerging field of neuromorphic
computing schemes.",2104.03647v1
2021-04-13,Collective P-Wave Orbital Dynamics of Ultracold Fermions,"We consider the non-equilibrium orbital dynamics of spin-polarized ultracold
fermions in the first excited band of an optical lattice. A specific lattice
depth and filling configuration is designed to allow the $p_x$ and $p_y$
excited orbital degrees of freedom to act as a pseudo-spin. Starting from the
full Hamiltonian for p-wave interactions in a periodic potential, we derive an
extended Hubbard-type model that describes the anisotropic lattice dynamics of
the excited orbitals at low energy. We then show how dispersion engineering can
provide a viable route to realizing collective behavior driven by p-wave
interactions. In particular, Bragg dressing and lattice depth can reduce
single-particle dispersion rates, such that a collective many-body gap is
opened with only moderate Feshbach enhancement of p-wave interactions. Physical
insight into the emergent gap-protected collective dynamics is gained by
projecting the Hamiltonian into the Dicke manifold, yielding a one-axis
twisting model for the orbital pseudo-spin that can be probed using
conventional Ramsey-style interferometry. Experimentally realistic protocols to
prepare and measure the many-body dynamics are discussed, including the effects
of band relaxation, particle loss, spin-orbit coupling, and doping.",2104.06480v3
2021-07-08,Dynamics of quantum information scrambling under decoherence effects measured via active spins clusters,"Developing quantum technologies requires the control and understanding of the
non-equilibrium dynamics of quantum information in many-body systems. Local
information propagates in the system by creating complex correlations known as
information scrambling, as this process prevents extracting the information
from local measurements. In this work, we develop a model adapted from
solid-state NMR methods, to quantify the information scrambling. The scrambling
is measured via time-reversal Loschmidt echoes (LE) and Multiple Quantum
Coherences experiments that intrinsically contain imperfections. Considering
these imperfections, we derive expressions for out-of-time-order correlators
(OTOCs) to quantify the observable information scrambling based on measuring
the number of active spins where the information was spread. Based on the OTOC
expressions, decoherence effects arise naturally by the effects of the
nonreverted terms in the LE experiment. Decoherence induces localization of the
measurable degree of information scrambling. These effects define a
localization cluster size for the observable number of active spins that
determines a dynamical equilibrium. We contrast the model's predictions with
quantum simulations performed with solid-state NMR experiments, that measure
the information scrambling with time-reversal echoes with controlled
imperfections. An excellent quantitative agreement is found with the dynamics
of quantum information scrambling and its localization effects determined from
the experimental data. The presented model and derived OTOCs set tools for
quantifying the quantum information dynamics of large quantum systems (more
than $10^{4}$ spins) consistent with experimental implementations that
intrinsically contain imperfections.",2107.03870v2
2021-07-26,Reservoir-engineering shortcuts to adiabaticity,"We propose a protocol that achieves fast adiabatic transfer between two
orthogonal states of a qubit by coupling with an ancilla. The qubit undergoes
Landau-Zener dynamics, whereas the coupling realizes a time-dependent
Hamiltonian, which is diagonal in the spin's instantaneous Landau-Zener
eigenstates. The ancilla (or meter), in turn, couples to a thermal bath, such
that the overall dynamics is incoherent. We analyse the protocol's fidelity as
a function of the strength of the coupling and of the relaxation rate of the
meter. When the meter's decay rate is the largest frequency scale of the
dynamics, the spin dynamics is encompassed by a master equation describing
dephasing of the spin in the instantaneous eigenbasis. In this regime the
fidelity of adiabatic transfer improves as the bath temperature is increased.
Surprisingly, the adiabatic transfer is significantly more efficient in the
opposite regime, where the time scale of the ancilla dynamics is comparable to
the characteristic spin time scale. Here, for low temperatures the coupling
with the ancilla tends to suppress diabatic transitions via effective cooling.
The protocol can be efficiently implemented by means of a pulsed, stroboscopic
coupling with the ancilla and is robust against moderate fluctuations of the
experimental parameters.",2107.12253v2
2021-11-23,Dynamics of ferrimagnetic skyrmionium driven by spin-orbit torque,"Magnetic skyrmionium is a skyrmion-like spin texture with nanoscale size and
high mobility. It is a topologically trivial but dynamically stable structure,
which can be used as a non-volatile information carrier for next-generation
spintronic storage and computing devices. Here, we study the dynamics of a
skyrmionium driven by the spin torque in a ferrimagnetic nanotrack. It is found
that the direction of motion is jointly determined by the internal
configuration of a skyrmionium and the spin polarization vector. Besides, the
deformation of a skyrmionium induced by the intrinsic skyrmion Hall effect
depends on both the magnitude of the driving force and the net angular
momentum. The ferrimagnetic skyrmionium is most robust at the angular momentum
compensation point, whose dynamics is quite similar to the skyrmionium in
antiferromagnet. The skyrmion Hall effect is perfectly prohibited, where it is
possible to observe the position of the skyrmionium by measuring the
magnetization. Furthermore, the current-induced dynamics of a ferrimagnetic
skyrmionium is compared with that of a ferromagnetic and antiferromagnetic
skyrmionium. We also make a comparison between the motion of a ferrimagnetic
skyrmionium and a skyrmion. Our results will open a new field of ferrimagnetic
skyrmioniums for future development of ferrimagnetic spintronics devices.",2111.11603v1
2022-02-03,Nonequilibrium dynamics of $α$-RuCl$_{3}$ -- a time-resolved magneto-optical spectroscopy study,"We present time-resolved magneto-optical spectroscopy on the magnetic
Mott-Hubbard-insulating Kitaev spin liquid candidate $\alpha$-RuCl$_3$ to
investigate the nonequilibrium dynamics of its antiferromagnetically ordered
zigzag groundstate after photoexcitation. A systematic study of the transient
magnetic linear dichroism under different experimental conditions (temperature,
external magnetic field, photoexcitation density) gives direct access to the
dynamical interplay of charge excitations with the zigzag ordered state on
ultrashort time scales. We observe a rather slow initial demagnetization (few
to 10s of ps) followed by a long-lived non-thermal antiferromagnetic
spin-disordered state (100$-$1000s of ps), which can be understood in terms of
holons and doublons disordering the antiferromagnetic background after
photoexcitation. Varying temperature and fluence in the presence of an external
magnetic field reveals two distinct photoinduced dynamics associated with the
zigzag and quantum paramagnetic disordered phases. The photo-induced
non-thermal spin-disordered state shows universal compressed-exponential
recovery dynamics related to the growth and propagation of zigzag domains on
nanosecond time scales, which is interpreted within the framework of the
Fatuzzo-Labrune model for magnetization reversal. The study of nonequilibrium
states in strongly correlated materials is a relatively unexplored topic, but
our results are expected to be extendable to a large class of Mott-Hubbard
insulator materials with strong spin-orbit coupling.",2202.01648v1
2022-02-24,Chaotic spin chains in AdS/CFT,"We consider the spectrum of anomalous dimensions in planar $\mathcal{N}=4$
supersymmetric Yang-Mills theory and its $\mathcal{N}=1$ super-conformal
Leigh-Strassler deformations. The two-loop truncation of the integrable
$\mathcal{N}=4$ dilatation operator in the SU$(2)$ sector, which is a
next-to-nearest-neighbour deformation of the XXX spin chain, is not strictly
integrable at finite coupling and we show that it indeed has Wigner-Dyson level
statistics. However, we find that it is only weakly chaotic in the sense that
the cross-over to chaotic dynamics is slower than for generic chaotic systems.
For the Leigh-Strassler deformed theory with generic parameters, we show that
the one-loop dilatation operator in the SU$(3)$ sector is chaotic, with a
spectrum that is well described by GUE Random Matrix Theory. For the
imaginary-$\beta$ deformation, the statistics are GOE and the transition from
the integrable limit is that of a generic system. This provides a weak-coupling
analogue of the chaotic dynamics seen for classical strings in the dual
background. We further study the spin chains in the semi-classical limit
described by generalised Landau-Lifshitz models, which are also known to
describe large-angular-momentum string solutions in the dual theory. We show
that for the higher-derivative theory following from the two-loop
$\mathcal{N}=4$ SU$(2)$ spin chain, the maximal Lyapunov exponent is close to
zero, consistent with the absence of chaotic dynamics. For the
imaginary-$\beta$ SU$(3)$ theory, the resulting Landau-Lifshitz model has
classically chaotic dynamics at finite values of the deformation parameter.",2202.12075v1
2022-08-05,Dynamical quantum phase transitions in Stark quantum spin chains,"We investigate the nonequilibrium dynamics of one-dimension spin models in
the presence of a uniform force. The linear potential induces
delocalization-localization transition in the free particles model which is
known as the Wannier-Stark effect. We study dynamical quantum phase transition
(DQPT) due to sudden global quenches across a quantum critical point when the
system undergoes a localization-delocalization transition. In this regard, we
consider the XX and XXZ spin chains and explore two types of quenches with and
without ramping through the delocalization-localization point. The XX model was
mapped to the free fermion particles, so both analytical and numerical results
were provided. Results unveil that the dynamical signature of
localization-delocalization transition can be characterized by the
nonanalyticities in dynamical free energy (corresponds to the zero points in
the Loschmit echo). We also explore the interaction effects considering XXZ
spin chains, using the time-dependent extension of the numerical DMRG
technique. Our results show that depending on the anisotropic parameter
$\Delta\lessgtr1.0$, if both the initial and post-quench Hamiltonian are in the
same phase or not, DQPTs may happen. Moreover, the interrelation between DQPTs
with different correlation measures such as the equilibrium order parameters or
entanglement entropy production of the system remains unclear. We provide more
analyses on the feature of DQPTs, in both types of quenches, by connecting them
to the average local magnetization, entanglement entropy production, and the
Schmidt gap.",2208.03104v1
2023-07-10,Kibble-Zurek Mechanism for Nonequilibrium Generation of Magnetic Monopoles in Spin Ices,"The proliferation of topological defects is a common out-of-equilibrium
phenomenon when a system is driven into a phase of broken symmetry. The
Kibble-Zurek mechanism (KZM) provides a theoretical framework for the critical
dynamics and generation of topological defects in such scenarios. One of the
early applications of KZM is the estimation of heavy magnetic monopoles left
behind by the cosmological phase transitions in the early universe. The
scarcity of such relic monopoles, which contradicts the prediction of KZM, is
one of the main motivations for cosmological inflationary theories. On the
other hand, magnetic monopoles as emergent quasi-particles have been observed
in spin ices, a peculiar class of frustrated magnets that remain disordered at
temperatures well below the energy scale of exchange interaction. Here we study
the annihilation dynamics of magnetic monopoles when spin ice is cooled to zero
temperature in a finite time. Through extensive Glauber dynamics simulations,
we find that the density of residual monopole follows a power law dependence on
the annealing rate. A kinetic reaction theory that precisely captures the
annihilation process from Monte Carlo simulations is developed. We further show
that the KZM can be generalized to describe the critical dynamics of spin ice,
where the exponent of the power-law behavior is determined by the dynamic
critical exponent $z$ and the cooling protocol.",2307.05267v1
2024-02-16,Live magnetic observation of parahydrogen hyperpolarization dynamics,"Nuclear spin hyperpolarization is used in physics, chemistry, and medicine to
produce strong magnetization unachievable by equilibrium polarization
techniques. Hyperpolarization enables magnetic resonance spectroscopy and
imaging with minute samples, and is used to produce MRI spin-tracers and
polarized physics targets. Although widely used, the dynamics of the
hyperpolarization process have never been studied `live' due to the extremely
low (Hz-band) frequencies involved, and/or detector saturation by the driving
fields used. Here, we use an atomic magnetometer with sub-pT sensitivity to
observe, in real time, the complex dynamics of hyperpolarization, without
disturbing or disrupting the process. We start by examining
parahydrogen-induced $^1$H and $^{13}$C magnetization build-up during adiabatic
eigenbasis transformations in the $\mu$T-field avoided state crossings at the
heart of the process; we see live hyperpolarization dynamics including coherent
oscillations, leakage mechanisms and dipolar shifts that would be challenging
or impossible to observe by post hoc measurement. We then extend the methods to
observe the chemical-exchange-driven $^{13}$C hyperpolarization of
[1-$^{13}$C]-pyruvate -- the most important spin tracer for clinical metabolic
imaging. Beyond the interests of hyperpolarization, the observation of
adiabatic transitions in real-time is a fundamentally new approach to NMR,
reveals previously hidden nuclear spin dynamics and enables quantum control and
live process optimization in a variety of chemical scenarios.",2402.10766v1
1995-02-27,Spin-Charge Separation in the $t-J$ Model: Magnetic and Transport Anomalies,"A real spin-charge separation scheme is found based on a saddle-point state
of the $t-J$ model. In the one-dimensional (1D) case, such a saddle-point
reproduces the correct asymptotic correlations at the strong-coupling
fixed-point of the model. In the two-dimensional (2D) case, the transverse
gauge field confining spinon and holon is shown to be gapped at {\em finite
doping} so that a spin-charge deconfinement is obtained for its first time in
2D. The gap in the gauge fluctuation disappears at half-filling limit, where a
long-range antiferromagnetic order is recovered at zero temperature and spinons
become confined. The most interesting features of spin dynamics and transport
are exhibited at finite doping where exotic {\em residual} couplings between
spin and charge degrees of freedom lead to systematic anomalies with regard to
a Fermi-liquid system. In spin dynamics, a commensurate antiferromagnetic
fluctuation with a small, doping-dependent energy scale is found, which is
characterized in momentum space by a Gaussian peak at ($\pi/a$, $ \pi/a$) with
a doping-dependent width ($\propto \sqrt{\delta}$, $\delta$ is the doping
concentration). This commensurate magnetic fluctuation contributes a
non-Korringa behavior for the NMR spin-lattice relaxation rate. There also
exits a characteristic temperature scale below which a pseudogap behavior
appears in the spin dynamics. Furthermore, an incommensurate magnetic
fluctuation is also obtained at a {\em finite} energy regime. In transport, a
strong short-range phase interference leads to an effective holon Lagrangian
which can give rise to a series of interesting phenomena including linear-$T$
resistivity and $T^2$ Hall-angle. We discuss the striking similarities of these
theoretical features with those found in the high-$T_c$ cuprates and give a",9502113v2
2018-10-09,Cluster spin-glass behaviour and memory effect in Cr$_{0.5}$Fe$_{0.5}$Ga,"We report the structural, static, and dynamic properties of
Cr$_{0.5}$Fe$_{0.5}$Ga by means of powder x-ray diffraction, magnetization,
heat capacity, magnetic relaxation, and magnetic memory effect measurements. DC
magnetization and AC susceptibility studies reveal a spin-glass transition at
around $T_{\rm f} \simeq 22$~K. An intermediate value of the relative shift in
freezing temperature $\delta T_{\rm f} \simeq 0.017$, obtained from the AC
susceptibility data reflects the formation of cluster spin-glass states. The
frequency dependence of $T_{\rm f}$ is also analyzed within the framework of
dynamic scaling laws. The analysis using power law yields a time constant for a
single spin flip $\tau* \simeq 1.1\times10^{-10}$~s and critical exponent
$z\nu^{\prime}=4.2\pm0.2$. On the other hand, the Vogel-Fulcher (VF) law yields
the time constant for a single spin flip $\tau_0 \simeq 6.6\times10^{-9}$~s, VF
temperature $T_{\rm 0}=21.1\pm0.1$~K, and an activation energy $E_{\rm
a}/k_{\rm B} \simeq 16$~K. The value of $\tau*$ and $\tau_0$ along with a
non-zero value of $T_{\rm 0}$ provide further evidence for the cluster
spin-glass behaviour. The magnetic field dependent $T_{\rm f}$ follows the de
Almeida-Thouless line with a non-mean-field type instability, reflecting either
a different universality class or strong anisotropy in the spin system. A
detailed non-equilibrium dynamics study via relaxation and memory effect
experiments demonstrates striking memory effects. All the above observations
render a cluster spin-glass behaviour which is triggered by magnetic
frustration due to competing antiferromagnetic and ferromagnetic interactions
and magnetic site disorder. Moreover, the asymmetric response of magnetic
relaxation with respect to the change in temperature, below $T_{\rm f}$ can be
explained by the hierarchical model.",1810.03890v1
2021-01-22,Spin dynamics in NaFeAs and NaFe$_{0.53}$Cu$_{0.47}$As probed by resonant inelastic X-ray scattering,"The parent compounds of iron-based superconductors are magnetically-ordered
bad metals, with superconductivity appearing near a putative magnetic quantum
critical point. The presence of both Hubbard repulsion and Hund's coupling
leads to rich physics in these multiorbital systems, and motivated descriptions
of magnetism in terms of itinerant electrons or localized spins. The
NaFe$_{1-x}$Cu$_x$As series consists of magnetically-ordered bad metal ($x=0$),
superconducting ($x\approx0.02$) and magnetically-ordered
semiconducing/insulating ($x\approx0.5$) phases, providing a platform to
investigate the connection between superconductivity, magnetism and electronic
correlations. Here we use X-ray absorption spectroscopy and resonant inelastic
X-ray scattering to study the valence state of Fe and spin dynamics in two
NaFe$_{1-x}$Cu$_x$As compounds ($x=0$ and 0.47). We find that magnetism in both
compounds arises from Fe$^{2+}$ atoms, and exhibits underdamped dispersive spin
waves in their respective ordered states. The dispersion of spin excitations in
NaFe$_{0.53}$Cu$_{0.47}$As is consistent with being quasi-one-dimensional.
Compared to NaFeAs, the band top of spin waves in NaFe$_{0.53}$Cu$_{0.47}$As is
slightly softened with significantly more spectral weight of the spin
excitations. Our results indicate the spin dynamics in
NaFe$_{0.53}$Cu$_{0.47}$As arise from localized magnetic moments and suggest
the iron-based superconductors are proximate to a correlated insulating state
with localized iron moments.",2101.08948v1
2020-09-10,Dependence of the dynamical properties of light-cone simulation dark matter halos on their environment,"Aims: We study the dependence of the dynamical properties of dark matter
halos on their environment in a whole-sky $\Lambda$CDM light-cone simulation
extending to $z\sim 0.65$. The properties of interest are halo shape
(parametrized by its principal axes), spin and virialisation status, the
alignment of halo spin and shape, as well as the shape-shape and spin-spin
alignments among halo neighbours. Methods: We define the halo environment using
the notion of halo isolation status determined by the distance to its nearest
neighbor. This defines a maximum spherical region around each halo devoid of
other halos, above the catalog threshold mass. We consider as 'close halo
pairs', the pairs that are separated by a distance lower than a specific
threshold. In order to decontaminate our results from the known dependence of
halo dynamical properties on mass, we use a random sampling procedure in order
to compare properties of similar halo abundance distributions. Results: (a) We
find a strong dependence of halo properties on their environment, confirming
that isolated halos are more aspherical and more prolate with lower spin
values. (b) Correlations between halo properties exist and are mostly
independent of halo environment. (c) Halo spins are aligned with the minor
axis, regardless of halo shape. (d) Close halo neighbors have their major axes
statistically aligned, while they show a slight but statistically significant
preference for anti-parallel spin directions. The latter result is enhanced for
the case of close halo pairs in low-density environments. Furthermore, we find
a preference of the spin vectors to be oriented perpendicular to the line
connecting such close halo pairs.",2009.04914v3
2022-11-07,Quantum-classical approach to spin and charge pumping and the ensuing radiation in THz spintronics: Example of ultrafast-light-driven Weyl antiferromagnet Mn$_3$Sn,"The interaction of fs light pulses with magnetic materials has been intensely
studied for more than two decades in order to understand ultrafast
demagnetization in single magnetic layers or THz emission from their bilayers
with nonmagnetic spin-orbit (SO) materials. Here we develop a multiscale
quantum-classical formalism -- where conduction electrons are described by
quantum master equation of the Lindblad type; classical dynamics of local
magnetization is described by the Landau-Lifshitz-Gilbert (LLG) equation; and
incoming light is described by classical vector potential while outgoing
electromagnetic radiation is computed using Jefimenko equations for retarded
electric and magnetic fields -- and apply it a bilayer of antiferromagnetic
Weyl semimetal Mn$_3$Sn with noncollinear local magnetization in contact with
SO-coupled nonmagnetic material. Our QME+LLG+Jefimenko scheme makes it possible
to understand how fs light pulse generates directly spin and charge pumping and
electromagnetic radiation by the latter, including both odd and even high
harmonics (of the pulse center frequency) up to order $n \le 7$. The directly
pumped spin current then exert spin torque on local magnetization whose
dynamics, in turn, pumps additional spin and charge currents radiating in the
THz range. By switching on and off LLG dynamics and SO couplings, we unravel
which microscopic mechanism contribute the most to emitted THz radiation --
charge pumping by local magnetization of Mn$_3$Sn in the presence of its
intrinsic SO coupling is far more important than standardly assumed (for other
types of magnetic layers) spin pumping and subsequent spin-to-charge conversion
within the neighboring nonmagnetic SO-coupled material.",2211.03645v3
2023-04-11,Excitation and voltage-gated modulation of single-mode dynamics in a planar nano-gap spin Hall nano-oscillator,"We experimentally study the dynamical modes excited by current-induced
spin-orbit torque and its electrostatic gating effect in a 3-terminal planar
nano-gap spin Hall nano-oscillator (SHNO) with a moderate interfacial
perpendicular magnetic anisotropy (IPMA). Both quasilinear propagating
spin-wave and localized ""bullet"" modes are achieved and controlled by varying
the applied in-plane magnetic field and driving current. The minimum linewidth
shows a linear dependence on the actual temperature of the active area,
confirming single-mode dynamics based on the nonlinear theory of spin-torque
nano-oscillation with a single mode. The observed electrostatic gating tuning
oscillation frequency arises from voltage-controlled magnetic anisotropy and
threshold current of SHNO via modification of the nonlinear damping and/or the
interfacial spin-orbit coupling of the magnetic multilayer. In contrast to
previously observed two-mode coexistence degrading the spectral purity in
Py/Pt-based SHNOs with a negligible IPMA, a single coherent spin-wave mode with
a low driven current can be achieved by selecting the ferromagnet layer with a
suitable IPMA because the nonlinear mode coupling can be diminished by bringing
in the PMA field to compensate the easy-plane shape anisotropy. Moreover, the
simulations demonstrate that the experimentally observed current and
gate-voltage modulation of auto-oscillation modes are also closely associated
with the nonlinear damping and mode coupling, which are determined by the
ellipticity of magnetization precession. The demonstrated nonlinear mode
coupling mechanism and electrical control approach of spin-wave modes could
provide the clue to facilitate the implementation of the mutual synchronization
map for neuromorphic computing applications in SHNO array networks.",2304.05026v1
1995-02-22,Ground-State Dynamical Correlation Functions: An Approach from Density Matrix Renormalization Group Method,"A numerical approach to ground-state dynamical correlation functions from
Density Matrix Renormalization Group (DMRG) is developed. Using sum rules,
moments of a dynamic correlation function can be calculated with DMRG, and with
the moments the dynamic correlation function can be obtained by the maximum
entropy method. We apply this method to one-dimensional spinless fermion
system, which can be converted to the spin 1/2 Heisenberg model in a special
case. The dynamical density-density correlation function is obtained.",9502091v1
1998-10-02,Is the broad histogram random walk dynamics correct?,"We show explicitly that the broad histogram single-spin-flip random walk
dynamics does not give correct microcanonical average even in one dimension.
The dynamics violates detailed balance condition by an amount which decreases
with system size. As a result, in distribution different configurations with
the same energy can have different probabilities. We propose a modified
dynamics which ensures detailed balance and the histogram obtained from this
dynamics is exactly flat.",9810017v1
2001-07-03,Persistence in One-dimensional Ising Models with Parallel Dynamics,"We study persistence in one-dimensional ferromagnetic and anti-ferromagnetic
nearest-neighbor Ising models with parallel dynamics. The probability P(t) that
a given spin has not flipped up to time t, when the system evolves from an
initial random configuration, decays as P(t) \sim 1/t^theta_p with theta_p
\simeq 0.75 numerically. A mapping to the dynamics of two decoupled A+A \to 0
models yields theta_p = 3/4 exactly. A finite size scaling analysis clarifies
the nature of dynamical scaling in the distribution of persistent sites
obtained under this dynamics.",0107053v1
2007-09-25,Chaotic Dynamics of Spin-Valve Oscillators,"Recent experimental and theoretical studies on the magnetization dynamics
driven by an electric current have uncovered a number of unprecedented rich
dynamic phenomena. We predict an intrinsic chaotic dynamics that has not been
previously anticipated. We explicitly show that the transition to chaotic
dynamics occurs through a series of period doubling bifurcations. In chaotic
regime, two dramatically different power spectra, one with a well-defined peak
and the other with a broadly distributed noise, are identified and explained.",0709.4045v1
2009-08-26,"""Dynamical"" interactions and gauge invariance","Appreciating the classical understanding of the elementary particle the
""dynamical"" Poincare algebra is developed. It is shown that the ""dynamical""
Poincare algebra and the equations of motion of particles with arbitrary spin
are gauge invariant and that gauge invariance and relativistic invariance stand
on equal footings. A ""dynamical"" non-minimal interaction is constructed
explicitly and the Rarita-Schwinger equation is considered in the framework of
this ""dynamical"" interaction.",0908.3761v2
2011-02-04,Current-induced dynamics of composite free layer with antiferromagnetic interlayer exchange coupling,"Current-induced dynamics in spin valves including composite free layer with
antiferromagnetic interlayer exchange coupling is studied theoretically within
the diffusive transport regime. We show that current-induced dynamics of a
synthetic antiferromagnet is significantly different from dynamics of a
synthetic ferrimagnet. From macrospin simulations we obtain conditions for
switching the composite free layer, as well as for appearance of various
self-sustained dynamical modes. Numerical simulations are compared with simple
analytical models of critical current based on linearized
Landau-Lifshitz-Gilbert equation.",1102.1028v2
2014-12-17,Revealing the role of orbital magnetism in ultrafast laser-induced demagnetization in multisublattice metallic magnets by terahertz spectroscopy,"Simultaneous detection of THz emission and transient magneto-optical response
is employed to study ultrafast laser-induced magnetization dynamics in
multisublattice magnets NdFeCo and GdFeCo amorphous alloys with in-plane
magnetic anisotropy. A satisfactory quantitative agreement between the dynamics
revealed with the help of these two techniques is obtained for GdFeCo. For
NdFeCo the THz emission reveals faster dynamics than the magneto-optical
response. This indicates that in addition to spin dynamics of Fe ultrafast
laser excitation triggers faster magnetization dynamics of Nd.",1412.5396v1
2015-04-18,Dynamic phase transitions in a ferromagnetic thin film system: A Monte Carlo simulation study,"Dynamic phase transition properties of ferromagnetic thin film system under
the influence both bias and time dependent magnetic fields have been elucidated
by means of kinetic Monte Carlo simulation with local spin update Metropolis
algorithm. The obtained results after a detailed analysis suggest that bias
field is the conjugate field to dynamic order parameter, and it also appears to
define a phase line between two antiparallel dynamic ordered states depending
on the considered system parameters. Moreover, the data presented in this study
well qualitatively reproduce the recently published experimental findings where
time dependent magnetic behavior of a uniaxial cobalt films is studied in the
neighborhood of dynamic phase transition point.",1504.04749v1
2015-10-13,Taming the dynamical sign problem in real-time evolution of quantum many-body problems,"Current nonequilibrium Monte Carlo methods suffer from a dynamical sign
problem that makes simulating real-time dynamics for long times exponentially
hard. We propose a new `Inchworm Algorithm', based on iteratively reusing
information obtained in previous steps to extend the propagation to longer
times. The algorithm largely overcomes the dynamical sign problem, changing the
scaling from exponential to quadratic. We use the method to solve the Anderson
impurity model in the Kondo and mixed valence regimes, obtaining results both
for quenches and for spin dynamics in the presence of an oscillatory magnetic
field.",1510.03534v1
2020-10-05,Cutoff Phenomenon for Cyclic Dynamics on Hypercube,"The cutoff phenomena for Markovian dynamics have been observed and rigorously
verified for a multitude of models, particularly for Glauber-type dynamics on
spin systems. However, prior studies have barely considered irreversible
chains. In this work, the cutoff phenomenon of certain cyclic dynamics are
studied on the hypercube $\Sigma_{n} = Q^{V_{n}}$, where $Q = \{1, 2, 3\}$ and
$V_{n} = \{1,...,n\}$. The main feature of these dynamics is the fact that they
are represented by an irreversible Markov chain. Based on the coupling
modifications suggested in a previous study of the cutoff phenomenon for the
Curie-Weiss-Potts model, a comprehensive proof is presented.",2010.01756v1
2022-06-25,Riemann-Cartan gravity with dynamical signature,"Model of Riemann-Cartan gravity with varying signature of metric is
considered. The basic dynamical variables of the formalism are vierbein, spin
connection, and an internal metric in the tangent space. The corresponding
action contains new terms, which depend on these fields. In general case the
signature of the metric is determined dynamically. The Minkowski signature is
preferred dynamically because the configurations with the other signatures are
dynamically suppressed. We also discuss briefly the motion of particles in the
background of the modified black hole configuration, in which inside the
horizon the signature is that of Euclidean space - time.",2206.12744v1
2022-08-22,The Hidden Phase of the Spin-Boson Model,"A quantum two-level system immersed in a sub-Ohmic bath experiences enhanced
low-frequency quantum statistical fluctuations which render the nonequilibrium
quantum dynamics highly non-Markovian. Upon using the numerically exact
time-evolving matrix product operator approach, we investigate the phase
diagram of the polarization dynamics. In addition to the known phases of damped
coherent oscillatory dynamics and overdamped decay, we identify a new third
region in the phase diagram for strong coupling showing an aperiodic behaviour.
We determine the corresponding phase boundaries. The dynamics of the quantum
two-state system herein is not coherent by itself but slaved to the oscillatory
bath dynamics.",2208.10313v2
2014-07-03,Dynamics of the radiative envelope of rapidly rotating stars: Effects of spin-down driven by mass loss,"(abridged) This paper aims at deciphering the dynamics of the envelope of a
rotating star when some angular momentum loss due to mass loss is present. We
especially wish to know when the spin-down flow forced by the mass loss
supersedes the baroclinic flows that pervade the radiative envelope of rotating
stars. We consider a Boussinesq fluid enclosed in a rigid sphere whose flows
are forced both by the baroclinic torque, the spin-down of an outer layer, and
an outward mass flux. The spin-down forcing is idealized in two ways: either by
a rigid layer that imposes its spinning down velocity at some interface or by a
turbulent layer that imposes a stress at this same interface to the interior of
the star. In the case where the layer is rigid and imposes its velocity, we
find that, as the mass-loss rate increases, the flow inside the star shows two
transitions: the meridional circulation associated with baroclinic flows is
first replaced by its spin-down counterpart, while at much stronger mass-loss
rates the baroclinic differential rotation is superseded by the spin-down
differential rotation. In fact, we find three wind regimes: weak (or no wind),
moderate, and strong. In the first case, the flow in the radiative envelope is
of baroclinic origin. In the moderate case, the circulation results from the
spin-down while the differential rotation may either be of baroclinic or of
spin-down origin, depending on the coupling between mass and angular momentum
losses. For fast rotating stars, our model says that the moderate wind regime
starts when mass loss is higher than ~1e-11 Msun/yr. In the strong wind case,
the flow in the radiative envelope is mainly driven by angular momentum
advection. This latter transition depends on the mass and the rotation rate of
the star, being around 1e-8 Msun/yr for a 3 Msun ZAMS star rotating at 200 km/s
according to our model.",1407.0946v1
2014-10-06,Hot-electron effect in spin relaxation of electrically injected electrons in intrinsic Germanium,"The hot-electron effect in the spin relaxation of electrically injected
electrons in intrinsic Germanium is investigated by the kinetic spin Bloch
equations both analytically and numerically. It is shown that in the
weak-electric-field regime with $E\lesssim 0.5$~kV/cm, our calculations has
reasonable agreement with the recent transport experiment in the spin-injection
configuration [Phys. Rev. Lett. {\bf 111}, 257204 (2013)]. We reveal that the
spin relaxation is significantly enhanced at low temperature in the presence of
weak electric field $E\lesssim 50$~V/cm, which originates from the obvious
center-of-mass drift effect due to the weak electron-phonon interaction,
whereas the hot-electron effect is demonstrated to be less important. This can
explain the discrepancy between the experimental observation and the previous
theoretical calculation [Phys. Rev. B {\bf 86}, 085202 (2012)], which deviates
from the experimental results by about two orders of magnitude at low
temperature. It is further shown that in the strong-electric-field regime with
$0.5\lesssim E \lesssim 2$~kV/cm, the spin relaxation is enhanced due to the
hot-electron effect, whereas the drift effect is demonstrated to be marginal.
Finally, we find that when $1.4 \lesssim E\lesssim 2$~kV/cm which lies in the
strong-electric-field regime, a small fraction of electrons ($\lesssim 5\%$)
can be driven from the L to $\Gamma$ valley, and the spin relaxation rates are
the same for the $\Gamma$ and L valleys in the intrinsic sample without
impurity. With the negligible influence of the spin dynamics in the $\Gamma$
valley to the whole system, the spin dynamics in the L valley can be measured
from the $\Gamma$ valley by the standard direct optical transition method.",1410.1240v3
2016-07-02,Interface-Induced Phenomena in Magnetism,"This article reviews static and dynamic interfacial effects in magnetism,
focusing on interfacially-driven magnetic effects and phenomena associated with
spin-orbit coupling and intrinsic symmetry breaking at interfaces. It provides
a historical background and literature survey, but focuses on recent progress,
identifying the most exciting new scientific results and pointing to promising
future research directions. It starts with an introduction and overview of how
basic magnetic properties are affected by interfaces, then turns to a
discussion of charge and spin transport through and near interfaces and how
these can be used to control the properties of the magnetic layer. Important
concepts include spin accumulation, spin currents, spin transfer torque, and
spin pumping. An overview is provided to the current state of knowledge and
existing review literature on interfacial effects such as exchange bias,
exchange spring magnets, spin Hall effect, oxide heterostructures, and
topological insulators. The article highlights recent discoveries of
interface-induced magnetism and non-collinear spin textures, non-linear
dynamics including spin torque transfer and magnetization reversal induced by
interfaces, and interfacial effects in ultrafast magnetization processes.",1607.00439v4
2011-11-22,Observation of spin glass state in weakly ferromagnetic Sr$_2$FeCoO$_6$ double perovskite,"We report the observation of spin glass state in the double perovskite oxide
Sr$_{2}$FeCoO$_{6}$ prepared through sol-gel technique. Initial structural
studies using x rays reveal that the compound crystallizes in tetragonal $I
4/m$ structure with lattice parameters, $a$ = 5.4609(2) \AA and $c$ = 7.7113(7)
\AA. The temperature dependent powder x ray studies reveal no structural phase
transition in the temperature range 10 -- 300 K. However, the unit cell volume
shows an anomaly coinciding with the magnetic transition temperature thereby
suggesting a close connection between lattice and magnetism. Neutron
diffraction studies and subsequent bond valence sums analysis show that in
Sr$_{2}$FeCoO$_{6}$, the $B$ site is randomly occupied by Fe and Co in the
mixed valence states of Fe$^{3+}$/Fe$^{4+}$ and Co$^{3+}$/Co$^{4+}$. The random
occupancy and mixed valence sets the stage for inhomogeneous magnetic exchange
interactions and in turn, for the spin glass like state in this double
perovskite which is observed as an irreversibility in temperature dependent dc
magnetization at $T_f\sim$ 75 K. Thermal hysteresis observed in the
magnetization profile of Sr$_{2}$FeCoO$_{6}$ is indicative of the mixed
magnetic phases present. The dynamic magnetic susceptibility displays
characteristic frequency dependence and confirms the spin glass nature of this
material. Dynamical scaling analysis of $\chi'(T)$ yields a critical
temperature $T_{ct}$ = 75.14(8) K and an exponent $z\nu$ = 6.2(2) typical for
spin glasses. The signature of presence of mixed magnetic interactions is
obtained from the thermal hysteresis in magnetization of Sr$_{2}$FeCoO$_{6}$.
Combining the neutron and magnetization results of Sr$_2$FeCoO$_6$, we deduce
the spin states of Fe to be in low spin while that of Co to be in low spin and
intermediate spin.",1111.5136v1
2021-10-04,Real-space spectral simulation of quantum spin models: Application to generalized Kitaev models,"The proliferation of quantum fluctuations and long-range entanglement
presents an outstanding challenge for the numerical simulation of interacting
spin systems with exotic ground states. Here, we present a toolset of Chebyshev
polynomial-based iterative methods that provides a unified framework to study
the thermodynamical properties, critical behavior and dynamics of frustrated
quantum spin models with controlled accuracy. Similar to previous applications
of the Chebyshev spectral methods to condensed matter systems, the algorithmic
complexity scales linearly with the Hilbert space dimension and the Chebyshev
truncation order. Using this approach, we study two paradigmatic quantum spin
models on the honeycomb lattice: the Kitaev-Heisenberg (K-H) and the
Kitaev-Ising (K-I) models. We start by applying the Chebyshev toolset to
compute nearest-neighbor spin correlations, specific heat and entropy of the
K-H model on a 24-spin cluster. Our results are benchmarked against exact
diagonalization and a popular iterative method based on thermal pure quantum
states. The transitions between a variety of magnetic phases, namely
ferromagnetic, N\'eel, zigzag and stripy antiferromagnetic and quantum spin
liquid phases are obtained accurately and efficiently. We also accurately
obtain the temperature dependence of the spin correlations, over more than
three decades in temperature, by means of a finite temperature Chebyshev
polynomial method introduced here. Finally, we report novel dynamical
signatures of the quantum phase transitions in the K-I model. Our findings
suggest that the efficiency, versatility and low-temperature stability of the
Chebyshev framework developed here could pave the way for previously
unattainable studies of quantum spin models in two dimensions.",2110.01494v3
2023-02-24,Manipulating solid-state spin concentration through charge transport,"Solid-state spin defects are attractive candidates for developing quantum
sensors and simulators. The spin and charge degrees of freedom in large defect
ensembles are a promising platform to explore complex many-body dynamics and
the emergence of quantum hydrodynamics. However, many interesting properties
can be revealed only upon changes in the density of defects, which instead is
usually fixed in material systems. Increasing the interaction strength by
creating denser defect ensembles also brings more decoherence. Ideally one
would like to control the spin concentration at will, while keeping fixed
decoherence effects. Here we show that by exploiting charge transport, we can
take some first steps in this direction, while at the same time characterizing
charge transport and its capture by defects. By exploiting the cycling process
of ionization and recombination of NV centers in diamonds, we pump electrons
from the valence band to the conduction band. These charges are then
transported to modulate the spin concentration by changing the charge state of
material defects. By developing a wide-field imaging setup integrated with a
fast single photon detector array, we achieve a direct and efficient
characterization of the charge redistribution process by measuring the complete
spectrum of the spin bath with micrometer-scale spatial resolution. We
demonstrate the concentration increase of the dominant spin defects by a factor
of 2 while keeping the $T_2$ of the NV center, which also provides a potential
experimental demonstration of the suppression of spin flip-flops via hyperfine
interactions. Our work paves the way to studying many-body dynamics with
temporally and spatially tunable interaction strengths in hybrid charge-spin
systems.",2302.12742v2
2023-06-15,Numerical signatures of ultra-local criticality in a one dimensional Kondo lattice model,"Heavy fermion criticality has been a long-standing problem in condensed
matter physics. Here we study a one-dimensional Kondo lattice model through
numerical simulation and observe signatures of local criticality. We vary the
Kondo coupling $J_K$ at fixed doping $x$. At large positive $J_K$, we confirm
the expected conventional Luttinger liquid phase with $2k_F=\frac{1+x}{2}$ (in
units of $2\pi$), an analogue of the heavy Fermi liquid (HFL) in the higher
dimension. In the $J_K \leq 0$ side, our simulation finds the existence of a
fractional Luttinger liquid (LL*) phase with $2k_F=\frac{x}{2}$, accompanied by
a gapless spin mode originating from localized spin moments, which serves as an
analogue of the fractional Fermi liquid (FL*) phase in higher dimensions. The
LL* phase becomes unstable and transitions to a spin-gapped Luther-Emery (LE)
liquid phase at small positive $J_K$. Then we mainly focus on the `critical
regime' between the LE phase and the LL phase. Approaching the critical point
from the spin-gapped LE phase, we often find that the spin gap vanishes
continuously, while the spin-spin correlation length in real space stays finite
and small. For a certain range of doping, in a point (or narrow region) of
$J_K$, the dynamical spin structure factor obtained through the time-evolving
block decimation (TEBD) simulation shows dispersion-less spin fluctuations in a
finite range of momentum space above a small energy scale (around $0.035 J$)
that is limited by the TEBD accuracy. All of these results are unexpected for a
regular gapless phase (or critical point) described by conformal field theory
(CFT). Instead, they are more consistent with exotic ultra-local criticality
with an infinite dynamical exponent $z=+\infty$. Lastly, we propose to simulate
the model in a bilayer optical lattice with a potential difference.",2306.09402v1
1997-04-28,Torque Reversal in Accretion-Powered X-ray Pulsars,"Accretion-powered X-ray pulsars 4U 1626-67, GX 1+4, and OAO 1657-415 have
recently shown puzzling torque reversals. These reversals are characterized by
short time scales, on the order of days, nearly identical spin-up and spin-down
rates, and very small changes in X-ray luminosity. We propose that this
phenomenon is the result of sudden dynamical changes in the accretion disks
triggered by a gradual variation of mass accretion rates. These sudden torque
reversals may occur at a critical accretion rate $\sim$
$10^{15}-10^{16}g~s^{-1}$ when the system makes a transition from (to) a
primarily Keplerian flow to (from) a substantially sub-Keplerian, radial
advective flow in the inner disk. For systems near spin equilibrium, the
spin-up torques in the Keplerian state are slightly larger than the spin-down
torques in the advective state, in agreement with observation. The abrupt
reversals could be a signature of pulsar systems near spin equilibrium with the
mass accretion rates modulated on a time scale of a year or longer near the
critical accretion rate. It is interesting that cataclysmic variables and black
hole soft X-ray transients change their X-ray emission properties at accretion
rates similar to the pulsars' critical rate. We speculate that the dynamical
change in pulsar systems shares a common physical origin with white dwarf and
black hole accretion disk systems.",9704269v2
2000-12-15,Nonequilibrium dynamics of random field Ising spin chains: exact results via real space RG,"Non-equilibrium dynamics of classical random Ising spin chains are studied
using asymptotically exact real space renormalization group. Specifically the
random field Ising model with and without an applied field (and the Ising spin
glass (SG) in a field), in the universal regime of a large Imry Ma length so
that coarsening of domains after a quench occurs over large scales. Two types
of domain walls diffuse in opposite Sinai random potentials and mutually
annihilate. The domain walls converge rapidly to a set of system-specific
time-dependent positions {\it independent of the initial conditions}. We obtain
the time dependent energy, magnetization and domain size distribution
(statistically independent). The equilibrium limits agree with known exact
results. We obtain exact scaling forms for two-point equal time correlation and
two-time autocorrelations. We also compute the persistence properties of a
single spin, of local magnetization, and of domains. The analogous quantities
for the spin glass are obtained. We compute the two-point two-time correlation
which can be measured by experiments on spin-glass like systems. Thermal
fluctuations are found to be dominated by rare events; all moments of truncated
correlations are computed. The response to a small field applied after waiting
time $t_w$, as measured in aging experiments, and the fluctuation-dissipation
ratio $X(t,t_w)$ are computed. For $(t-t_w) \sim t_w^{\hat{\alpha}}$,
$\hat{\alpha} <1$, it equals its equilibrium value X=1, though time
translational invariance fails. It exhibits for $t-t_w \sim t_w$ aging regime
with non-trivial $X=X(t/t_w) \neq 1$, different from mean field.",0012290v1
2001-01-26,Approach to the metal-insulator transition in La(1-x)CaxMnO3 (0<x<.2): magnetic inhomogeneity and spin wave anomaly,"We describe the evolution of the static and dynamic spin correlations of
La$_{1-x}$Ca$_x$MnO$_3$, for x=0.1, 0.125 and 0.2, where the system evolves
from the canted magnetic state towards the insulating ferromagnetic state,
approaching the metallic transition (x=0.22).
  In the x=0.1 sample, the observation of two spin wave branches typical of two
distinct types of magnetic coupling, and of a modulation in the elastic diffuse
scattering characteristic of ferromagnetic inhomogeneities, confirms the static
and dynamic inhomogeneous features previously observed at x$<$0.1. The
anisotropic q-dependence of the intensity of the low-energy spin wave suggests
a bidimensionnal character for the static inhomogeneities. At x=0.125, which
corresponds to the occurence of a ferromagnetic and insulating state, the two
spin wave branches reduce to a single one, but anisotropic. At this
concentration, an anomaly appears at {\bf q$_0$}=(1.25,1.25,0), that could be
related to an underlying periodicity, as arising from (1.5,1.5,0)
superstructures.
  At x=0.2, the spin-wave branch is isotropic. In addition to the anomaly
observed at q$_0$, extra magnetic excitations are observed at larger q, forming
an optical branch. The two dispersion curves suggest an anti-crossing behavior
at some {\bf q$_0$'} value, which could be explained by a folding due to an
underlying perodicity involving four cubic lattice spacings.",0101414v1
2002-04-21,Generalized Competing Glauber-type Dynamics and Kawasaki-type Dynamics,"In this article, we have given a systematic formulation of the new
generalized competing mechanism: the Glauber-type single-spin transition
mechanism, with probability p, simulates the contact of the system with the
heat bath, and the Kawasaki-type spin-pair redistribution mechanism, with
probability 1-p, simulates an external energy flux. These two mechanisms are
natural generalizations of Glauber's single-spin flipping mechanism and
Kawasaki's spin-pair exchange mechanism respectively. On the one hand, the new
mechanism is in principle applicable to arbitrary systems, while on the other
hand, our formulation is able to contain a mechanism that just directly
combines single-spin flipping and spin-pair exchange in their original form.
Compared with the conventional mechanism, the new mechanism does not assume the
simplified version and leads to greater influence of temperature. The fact,
order for lower temperature and disorder for higher temperature, will be
universally true. In order to exemplify this difference, we applied the
mechanism to 1D Ising model and obtained analytical results. We also applied
this mechanism to kinetic Gaussian model and found that, above the critical
point there will be only paramagnetic phase, while below the critical point,
the self-organization as a result of the energy flux will lead the system to an
interesting heterophase, instead of the initially guessed antiferromagnetic
phase. We studied this process in details.",0204453v1
2004-12-07,"Spin dynamics of heterometallic Cr7M wheels (M = Mn, Zn, Ni) probed by inelastic neutron scattering","Inelastic neutron scattering has been applied to the study of the spin
dynamics of Cr-based antiferromagnetic octanuclear rings where a finite total
spin of the ground state is obtained by substituting one Cr(III) ion (s = 3/2)
with Zn (s = 0), Mn (s = 5/2) or Ni (s = 1) di-cations. Energy and intensity
measurements for several intra-multiplet and inter-multiplet magnetic
excitations allow us to determine the spin wavefunctions of the investigated
clusters. Effects due to the mixing of different spin multiplets have been
considered. Such effects proved to be important to correctly reproduce the
energy and intensity of magnetic excitations in the neutron spectra. On the
contrary to what is observed for the parent homonuclear Cr8 ring, the symmetry
of the first excited spin states is such that anticrossing conditions with the
ground state can be realized in the presence of an external magnetic field.
Heterometallic Cr7M wheels are therefore good candidates for macroscopic
observations of quantum effects.",0412169v2
2006-09-13,Electronic transport through a double quantum dot in the spin blockade regime: Theoretical models,"We analyzed the electronic transport through a double quantum dot in the spin
blockade regime. Experiments of current rectification by Pauli exclusion
principle in double quantum dots were discussed. The electron and nuclei spin
dynamics and their interplay due to the Hyperfine interaction were
self-consistently analyzed within the framework of rate equations. Our results
show that the current leakage experimentally observed in the spin-blockade
region, is due to spin-flip processes induced by Hyperfine interaction through
Overhauser effect. We show as well how a magnetic field applied parallel to the
current allows excited states to participate in the electronic current and
removes spin blockade. Our model includes also a self-consistent description of
inelastic transitions where the energy is exchanged through interactions with
acoustic phonons in the environment. It accounts for spontaneous emission of
phonons which results in additional features in the current characteristics. We
develop a microscopical model to treat the Hyperfine interaction in each dot.
Using this model we study the dynamical nuclear polarization as a function of
the applied voltage.",0609323v4
2006-11-13,Spin Sum Rules and Polarizabilities: Results from Jefferson Lab,"The nucleon spin structure has been an active, exciting and intriguing
subject of interest for the last three decades. Recent experimental data on
nucleon spin structure at low to intermediate momentum transfers provide new
information in the confinement regime and the transition region from the
confinement regime to the asymptotic freedom regime. New insight is gained by
exploring moments of spin structure functions and their corresponding sum rules
(i.e. the generalized Gerasimov-Drell-Hearn, Burkhardt-Cottingham and Bjorken).
The Burkhardt-Cottingham sum rule is verified to good accuracy. The spin
structure moments data are compared with Chiral Perturbation Theory
calculations at low momentum transfers. It is found that chiral perturbation
calculations agree reasonably well with the first moment of the spin structure
function $g_1$ at momentum transfer of 0.05 to 0.1 GeV$^2$ but fail to
reproduce the neutron data in the case of the generalized polarizability
$\delta_{LT}$ (the $\delta_{LT}$ puzzle). New data have been taken on the
neutron ($^3$He), the proton and the deuteron at very low $Q^2$ down to 0.02
GeV$^2$. They will provide benchmark tests of Chiral dynamics in the kinematic
region where the Chiral Perturbation theory is expected to work.",0611024v2
2007-08-19,Incommensurate Spin Ordering and Fluctuations in underdoped La_{2-x}Ba_{x}CuO_{4},"Using neutron scattering techniques, we have studied incommensurate spin
ordering as well as low energy spin dynamics in single crystal underdoped \LBCO
with x$\sim$0.095 and 0.08; high temperature superconductors with T$_C \sim$ 27
K and 29 K respectively. Static two dimensional incommensurate magnetic order
appears below T$_N$=39.5 $\pm$ 0.3 K in \LBCO (x=0.095) and a similar
temperature for x=0.08 within the low temperature tetragonal phase. The spin
order is unaffected by either the onset of superconductivity or the application
of magnetic fields of up to 7 Tesla applied along the c-axis in the x=0.095
sample. Such magnetic field {\it independent} behaviour is in marked contrast
with the field induced enhancement of the staggered magnetisation observed in
the related \LSCO system, indicating this phenomenon is not a universal
property of cuprate superconductors. Surprisingly, we find that
incommensurability $\delta $ is only weakly dependent on doping relative to
\LSCO. Dispersive excitations in \LBCO (x=0.095) at the same incommensurate
wavevector persist up to at least 60 K. The dynamical spin susceptibility of
the low energy spin excitations saturates below \tc, in a similar manner to
that seen in the superconducting state of La$_2$CuO$_{4+y}$.",0708.2519v3
2008-03-31,Chern-number spin Hamiltonians for magnetic nano-clusters by DFT methods,"Combining field-theoretical methods and ab-initio calculations, we construct
an effective Hamiltonian with a single giant-spin degree of freedom, capable of
the describing the low-energy spin dynamics of ferromagnetic metal nanoclusters
consisting of up to a few tens of atoms. In our procedure, the magnetic moment
direction of the Kohn-Sham SDFT wave-function is constrained by means of a
penalty functional, allowing us to explore the entire parameter space of
directions, and to extract the magnetic anisotropy energy and Berry curvature
functionals. The average of the Berry curvature over all magnetization
directions is a Chern number - a topological invariant that can only take on
values equal to multiples of one half, representing the dimension of the
Hilbert space of the effective spin system. The spin Hamiltonian is obtained by
quantizing the classical anisotropy energy functional, after performing a
change of variables to a constant Berry curvature space. The purpose of this
article is to examine the impact of the topological effect from the Berry
curvature on the low-energy total-spin-system dynamics. To this end, we study
small transition metal clusters: Co$_{n}$ ($n=2,...,5$), Rh$_{2}$, Ni$_{2}$,
Pd$_{2}$, Mn$_{x}$N$_{y}$, Co$_{3}$Fe$_{2}$.",0803.4430v1
2008-10-02,Revisiting Static and Dynamic Spin Ice Correlations in Ho2Ti2O7,"Elastic and inelastic neutron scattering studies have been carried out on the
pyrochlore magnet Ho2Ti2O7. Measurements in zero applied magnetic field show
that the disordered spin ice ground state of Ho2Ti2O7 is characterized by a
pattern of rectangular diffuse elastic scattering within the [HHL] plane of
reciprocal space, which closely resembles the zone boundary scattering seen in
its sister compound Dy2Ti2O7. Well-defined peaks in the zone boundary
scattering develop only within the spin ice ground state below ~ 2 K. In
contrast, the overall diffuse scattering pattern evolves on a much higher
temperature scale of ~ 17 K. The diffuse scattering at small wavevectors below
[001] is found to vanish on going to Q=0, an explicit signature of expectations
for dipolar spin ice. Very high energy-resolution inelastic measurements reveal
that the spin ice ground state below ~ 2 K is also characterized by a
transition from dynamic to static spin correlations on the time scale of
10^{-9} seconds. Measurements in a magnetic field applied along the
[1${\bar1}$0] direction in zero-field cooled conditions show that the system
can be broken up into orthogonal sets of polarized alpha chains along
[1${\bar1}$0] and quasi-one-dimensional beta chains along [110]. Three
dimensional correlations between beta chains are shown to be very sensitive to
the precise alignment of the [1${\bar1}$0] externally applied magnetic field.",0810.0402v1
2009-11-03,Two-step stabilization of orbital order and the dynamical frustration of spin in the model charge-transfer insulator KCuF3,"We report a combined experimental and theoretical study of KCuF3, which
offers - because of this material's relatively simple lattice structure and
valence configuration (d9, i.e., one hole in the d-shell) - a particularly
clear view of the essential role of the orbital degree of freedom in governing
the dynamical coupling between the spin and lattice degrees of freedom. We
present Raman and x-ray scattering evidence that the phase behaviour of KCuF3
is dominated above the Neel temperature (T_N = 40 K) by coupled orbital/lattice
fluctuations that are likely associated with rotations of the CuF6 octahedra,
and we show that these orbital fluctuations are interrupted by a static
structural distortion that occurs just above T_N. A detailed model of the
orbital and magnetic phases of KCuF3 reveals that these orbital fluctuations -
and the related frustration of in-plane spin-order-are associated with the
presence of nearly degenerate low-energy spin-orbital states that are highly
susceptible to thermal fluctuations over a wide range of temperatures. A
striking implication of these results is that the ground state of KCuF3 at
ambient pressure lies near a quantum critical point associated with an
orbital/spin liquid phase that is obscured by emergent Neel ordering of the
spins; this exotic liquid phase might be accessible via pressure studies.",0911.0619v1
2009-11-16,Disk-outflow coupling: Energetics around spinning black holes,"The mechanism by which outflows and plausible jets are driven from black hole
systems, still remains observationally elusive. Notwithstanding, several
observational evidences and deeper theoretical insights reveal that accretion
and outflow/jet are strongly correlated. We model an advective disk-outflow
coupled dynamics, incorporating explicitly the vertical flux. Inter-connecting
dynamics of outflow and accretion essentially upholds the conservation laws. We
investigate the properties of the disk-outflow surface and its strong
dependence on the rotation parameter of the black hole. The energetics of the
disk-outflow strongly depend on the mass, accretion rate and spin of the black
holes. The model clearly shows that the outflow power extracted from the disk
increases strongly with the spin of the black hole, inferring that the power of
the observed astrophysical jets has a proportional correspondence with the spin
of the central object. In case of blazars (BL Lacs and Flat Spectrum Radio
Quasars), most of their emission are believed to be originated from their jets.
It is observed that BL Lacs are relatively low luminous than Flat Spectrum
Radio Quasars (FSRQs). The luminosity might be linked to the power of the jet,
which in turn reflects that the nuclear regions of the BL Lac objects have a
relatively low spinning black hole compared to that in the case of FSRQ. If the
extreme gravity is the source to power strong outflows and jets, then the spin
of the black hole, perhaps, might be the fundamental parameter to account for
the observed astrophysical processes in an accretion powered system.",0911.3049v2
2010-10-28,Magnetic structure and spin dynamics of quasi-one-dimensional spin-chain antiferromagnet BaCo2V2O8,"We report a neutron diffraction and muon spin relaxation muSR study of static
and dynamical magnetic properties of BaCo2V2O8, a quasi-one-dimensional
spin-chain system. A proposed model for the antiferromagnetic structure
includes: a propagation vector k_AF = (0, 0, 1), independent of external
magnetic fields for fields below a critical value H_c(T). The ordered moments,
of 2.18 \mu_B per Co ion, are aligned along the crystallographic c-axis. Within
the screw chains, along the c axis, the moments are arranged
antiferromagnetically. In the basal planes the spins are arranged
ferromagnetically (forming zig-zags paths) along one of the axis and
antiferromagnetically along the other. The temperature dependence of the
sub-lattice magnetization is consistent with the expectations of the 3D Ising
model. A similar behavior is observed for the internal static fields at
different muon stopping sites. Muon time spectra measured at weak longitudinal
fields and temperatures much higher than T_N can be well described using a
single muon site with an exponential muon spin relaxation that gradually
changes into an stretched exponential on approaching T_N. The
temperature-induced changes of the relaxation suggest that the Co fluctuations
dramatically slow down and the system becomes less homogeneous as it approaches
the antiferromagnetic state.",1010.5834v2
2011-04-26,Formation and dynamics of van der Waals molecules in buffer-gas traps,"We show that weakly bound He-containing van der Waals molecules can be
produced and magnetically trapped in buffer-gas cooling experiments, and
provide a general model for the formation and dynamics of these molecules. Our
analysis shows that, at typical experimental parameters, thermodynamics favors
the formation of van der Waals complexes composed of a helium atom bound to
most open-shell atoms and molecules, and that complex formation occurs quickly
enough to ensure chemical equilibrium. For molecular pairs composed of a He
atom and an S-state atom, the molecular spin is stable during formation,
dissociation, and collisions, and thus these molecules can be magnetically
trapped. Collisional spin relaxations are too slow to affect trap lifetimes.
However, helium-3-containing complexes can change spin due to adiabatic
crossings between trapped and untrapped Zeeman states, mediated by the
anisotropic hyperfine interaction, causing trap loss. We provide a detailed
model for Ag3He molecules, using ab initio calculation of Ag-He interaction
potentials and spin interactions, quantum scattering theory, and direct Monte
Carlo simulations to describe formation and spin relaxation in this system. The
calculated rate of spin-change agrees quantitatively with experimental
observations, providing indirect evidence for molecular formation in
buffer-gas-cooled magnetic traps.",1104.4973v1
2011-05-23,Signatures of Chaos in Time Series Generated by Many-Spin Systems at High Temperatures,"Extracting reliable indicators of chaos from a single experimental time
series is a challenging task, in particular, for systems with many degrees of
freedom. The techniques available for this purpose often require unachievably
long time series. In this paper, we explore a new method of discriminating
chaotic from multi-periodic integrable motion in many-particle systems. The
applicability of this method is supported by our numerical simulations of the
dynamics of classical spin lattices at high temperatures. We compared chaotic
and nonchaotic regimes of these lattices and investigated the transition
between the two. The method is based on analyzing higher-order time derivatives
of the time series of a macroscopic observable --- the total magnetization of
the spin lattice. We exploit the fact that power spectra of the magnetization
time series generated by chaotic spin lattices exhibit exponential
high-frequency tails, while, for the integrable spin lattices, the power
spectra are terminated in a non-exponential way. We have also demonstrated the
applicability limits of the above method by investigating the high-frequency
tails of the power spectra generated by quantum spin lattices and by the
classical Toda lattice.",1105.4575v2
2011-12-02,New insights into electron spin dynamics in the presence of correlated noise,"The changes of the spin depolarization length in zinc-blende semiconductors
when an external component of correlated noise is added to a static driving
electric field are analyzed for different values of field strength, noise
amplitude and correlation time. Electron dynamics is simulated by a Monte Carlo
procedure which keeps into account all the possible scattering phenomena of the
hot electrons in the medium and includes the evolution of spin polarization.
Spin depolarization is studied by examinating the decay of the initial spin
polarization of the conduction electrons through the D'yakonov-Perel process,
the only relevant relaxation mechanism in III-V crystals. Our results show
that, for electric field amplitude lower than the Gunn field, the dephasing
length shortens with the increasing of the noise intensity. Moreover, a
nonmonotonic behavior of spin depolarization length with the noise correlation
time is found, characterized by a maximum variation for values of noise
correlation time comparable with the dephasing time. Instead, in high field
conditions, we find that, critically depending on the noise correlation time,
external fluctuations can positively affect the relaxation length. The
influence of the inclusion of the electron-electron scattering mechanism is
also shown and discussed.",1112.0406v5
2012-07-04,Dimensional crossover of spin chains in a transverse staggered field: an NMR study,"Heisenberg spin-1/2 chain materials are known to substantially alter their
static and dynamic properties when experiencing an effective transverse
staggered field originating from the varying local environment of the
individual spins. We present a temperature-, angular- and field-dependent 29Si
NMR study of the model compound BaCu2Si2O7. The experimental data are
interpreted in terms of the divergent low-temperature transverse
susceptibility, predicted by theory for spin chains in coexisting longitudinal
and transverse staggered fields. Our analysis first employs a
finite-temperature ""Density Matrix Renormalization Group"" (DMRG) study of the
relevant one-dimensional Hamiltonian. Next we compare our numerical with the
presently known analytical results. With an analysis based on crystal
symmetries we show how the anisotropic contribution to the sample magnetization
is experimentally accessible even below the ordering temperature, in spite of
its competition with the collinear order parameter of the antiferromagnetic
phase. The modification of static and dynamic properties of the system due to
the presence of a local transverse staggered field (LTSF) acting on the
one-dimensional spin array are argued to cause the unusual spin reorientation
transitions observed in BaCu2Si2O7. On the basis of a Ginzburg-Landau type
analysis, we discuss aspects of competing spin structures in the presence of
magnetic order and the enhanced transverse susceptibility.",1207.1073v1
2013-04-29,"Dynamics of spin-1 bosons in an optical lattice: spin mixing, quantum phase revival spectroscopy and effective three-body interactions","We study the dynamics of spin-1 atoms in a periodic optical-lattice potential
and an external magnetic field in a quantum quench scenario where we start from
a superfluid ground state in a shallow lattice potential and suddenly raise the
lattice depth. The time evolution of the non-equilibrium state, thus created,
shows collective collapse-and-revival oscillations of matter-wave coherence as
well as oscillations in the spin populations. We show that the complex pattern
of these two types of oscillations reveals details about the superfluid and
magnetic properties of the initial many-body ground state. Furthermore, we show
that the strengths of the spin-dependent and spin-independent atom-atom
interactions can be deduced from the observations. The Hamiltonian that
describes the physics of the final deep lattice not only contains two-body
interactions but also effective multi-body interactions, which arise due to
virtual excitations to higher bands. We derive these effective spin-dependent
three-body interaction parameters for spin-1 atoms and describe how spin-mixing
is affected. Spinor atoms are unique in the sense that multi-body interactions
are directly evident in the in-situ number densities in addition to the
momentum distributions. We treat both antiferromagnetic (e.g. $^{23}$Na atoms)
and ferromagnetic (e.g. $^{87}$Rb and $^{41}$K) condensates.",1304.7565v1
2014-04-07,Coherent Radiation by Quantum Dots and Magnetic Nanoclusters,"The assemblies of either quantum dots or magnetic nanoclusters are studied.
It is shown that such assemblies can produce coherent radiation. A method is
developed for solving the systems of nonlinear equations describing the
dynamics of such assemblies. The method is shown to be general and applicable
to systems of different physical nature. Despite mathematical similarities of
dynamical equations, the physics of the processes for quantum dots and magnetic
nanoclusters is rather different. In a quantum dot assembly, coherence develops
due to the Dicke effect of dot interactions through the common radiation field.
For a system of magnetic clusters, coherence in the spin motion appears due to
the Purcell effect caused by the feedback action of a resonator. Self-organized
coherent spin radiation cannot arise without a resonator. This principal
difference is connected with the different physical nature of dipole forces
between the objects. Effective dipole interactions between the radiating
quantum dots, appearing due to photon exchange, collectivize the dot radiation.
While the dipolar spin interactions exist from the beginning, yet before
radiation, and on the contrary, they dephase spin motion, thus destroying the
coherence of moving spins. In addition, quantum dot radiation exhibits
turbulent photon filamentation that is absent for radiating spins.",1404.1739v1
2015-03-03,Charge dynamics and spin blockade in a hybrid double quantum dot in silicon,"Electron spin qubits in silicon, whether in quantum dots or in donor atoms,
have long been considered attractive qubits for the implementation of a quantum
computer due to the semiconductor vacuum character of silicon and its
compatibility with the microelectronics industry. While donor electron spins in
silicon provide extremely long coherence times and access to the nuclear spin
via the hyperfine interaction, quantum dots have the complementary advantages
of fast electrical operations, tunability and scalability. Here we present an
approach to a novel hybrid double quantum dot by coupling a donor to a
lithographically patterned artificial atom. Using gate-based rf reflectometry,
we probe the charge stability of this double quantum dot system and the
variation of quantum capacitance at the interdot charge transition. Using
microwave spectroscopy, we find a tunnel coupling of 2.7 GHz and characterise
the charge dynamics, which reveals a charge T2* of 200 ps and a relaxation time
T1 of 100 ns. Additionally, we demonstrate spin blockade at the inderdot
transition, opening up the possibility to operate this coupled system as a
singlet-triplet qubit or to transfer a coherent spin state between the quantum
dot and the donor electron and nucleus.",1503.01049v2
2015-06-01,$1/f^α$ noise and generalized diffusion in random Heisenberg spin systems,"We study the `flux noise' spectrum of random-bond quantum Heisenberg spin
systems using a real-space renormalization group (RSRG) procedure that accounts
for both the renormalization of the system Hamiltonian and of a generic probe
that measures the noise. For spin chains, we find that the dynamical structure
factor $S_q(f)$, at finite wave-vector $q$, exhibits a power-law behavior both
at high and low frequencies $f$, with exponents that are connected to one
another and to an anomalous dynamical exponent through relations that differ at
$T = 0$ and $T = \infty$. The low-frequency power-law behavior of the structure
factor is inherited by any generic probe with a finite band-width and is of the
form $1/f^\alpha$ with $0.5 < \alpha < 1$. An analytical calculation of the
structure factor, assuming a limiting distribution of the RG flow parameters
(spin size, length, bond strength) confirms numerical findings. More generally,
we demonstrate that this form of the structure factor, at high temperatures, is
a manifestation of anomalous diffusion which directly follows from a
generalized spin-diffusion propagator. We also argue that $1/f$-noise is
intimately connected to many-body-localization at finite temperatures. In two
dimensions, the RG procedure is less reliable; however, it becomes convergent
for quasi-one-dimensional geometries where we find that one-dimensional
$1/f^\alpha$ behavior is recovered at low frequencies; the latter
configurations are likely representative of paramagnetic spin networks that
produce $1/f^\alpha$ noise in SQUIDs.",1506.00643v1
2015-09-08,New insights on the spin-up of a neutron star during core-collapse,"The spin of a neutron star at birth may be impacted by the asymmetric
character of the explosion of its massive progenitor. During the first second
after bounce, the spiral mode of the Standing Accretion Shock Instability
(SASI) is able to redistribute angular momentum and spin-up a neutron star born
from a non-rotating progenitor. Our aim is to assess the robustness of this
process. We perform 2D numerical simulations of a simplified setup in
cylindrical geometry to investigate the timescale over which the dynamics is
dominated by a spiral or a sloshing mode. We observe that the spiral mode
prevails only if the ratio of the initial shock radius to the neutron star
radius exceeds a critical value. In that regime, both the degree of asymmetry
and the average expansion of the shock induced by the spiral mode increase
monotonously with this ratio, exceeding the values obtained when a sloshing
mode is artificially imposed. With a timescale of 2-3 SASI oscillations, the
dynamics of SASI takes place fast enough to affect the spin of the neutron star
before the explosion. The spin periods deduced from the simulations are
compared favorably to analytical estimates evaluated from the measured
saturation amplitude of the SASI wave. Despite the simplicity of our setup,
numerical simulations revealed unexpected stochastic variations, including a
reversal of the direction of rotation of the shock. Our results show that the
spin up of neutron stars by SASI spiral modes is a viable mechanism even though
it is not systematic.",1509.02828v2
2016-07-20,Electron dynamics in graphene with spin-orbit couplings and periodic potentials,"We use both continuum and lattice models to study the energy-momentum
dispersion and the dynamics of a wave packet for an electron moving in graphene
in the presence of spin-orbit couplings and either a single potential barrier
or a periodic array of potential barriers. Both Kane-Mele and Rashba spin-orbit
couplings are considered. A number of special things occur when the Kane-Mele
and Rashba couplings are equal in magnitude. In the absence of a potential, the
dispersion then consists of both massless Dirac and massive Dirac states. A
periodic potential is known to generate additional Dirac points; we show that
spin-orbit couplings generally open gaps at all those points, but if the two
spin-orbit couplings are equal, some of the Dirac points remain gapless. We
show that the massless and massive states respond differently to a potential
barrier; the massless states transmit perfectly through the barrier at normal
incidence while the massive states reflect from it. In the presence of a single
potential barrier, we show that there are states localized along the barrier.
Finally, we study the time evolution of a wave packet in the presence of a
periodic potential. We discover special points in momentum space where there is
almost no spreading of a wave packet; there are six such points in graphene
when the spin-orbit couplings are absent.",1607.05904v2
2016-10-14,Nonlinear Dynamics of a two-level system of a single spin driven beyond the rotating-wave approximation,"Quantum systems driven by strong oscillating fields are the source of many
interesting physical phenomena. In this work, we experimentally study the
dynamics of a two-level system of a single spin driven in the strong-driving
regime where the rotating-wave approximation is not valid. This two-level
system is a subsystem of a single Nitrogen-Vacancy center coupled to a
first-shell $^{13}$C nuclear spin in diamond at a level anti-crossing point
that occurs in the $m_{s}=\pm1$ manifold when the energy level splitting
between the $m_{s}$ = $+1$ and $-1$ spin states due to the static magnetic
field is $\approx$ 127 MHz, which is roughly equal to the spectral splitting
due to the $^{13}$C hyperfine interaction. The transition frequency of this
electron spin two-level system in a static magnetic field of 28.9 G is 1.7 MHz
and it can be driven only by the $z$-component of the RF field. Electron spin
Rabi frequencies in this system can reach tens of MHz even for moderate RF
powers. The simple sinusoidal Rabi oscillations that occur when the amplitude
of the driving field is much smaller than the transition frequency become
complex when the driving field strength is comparable or greater than the
energy level splitting. We observe that the system oscillates faster than the
amplitude of the driving field and the response of the system shows multiple
frequencies.",1610.04512v2
2016-10-31,Driven energy transfer between coupled modes in spin-torque oscillators,"The mutual interaction between the different eigenmodes of a spin-torque
oscillator can lead to a large variety of physical mechanisms from mode hopping
to multi-mode generation, that usually reduce their performances as
radio-frequency devices. To tackle this issue for the future applications, we
investigate the properties of a model spin-torque oscillator that is composed
of two coupled vortices with one vortex in each of the two magnetic layers of
the oscillator. In such double-vortex system, the remarkable properties of
energy transfer between the coupled modes, one being excited by spin transfer
torque while the second one being damped, result into an alteration of the
damping parameters. As a consequence, the oscillator nonlinear behavior is
concomitantly drastically impacted. This efficient coupling mechanism, driven
mainly by the dynamic dipolar field generated by the spin transfer torque
induced motion of the vortices, gives rise to an unexpected dynamical regime of
self-resonance excitation. These results show that mode coupling can be
leveraged for controlling the synchronization process as well as the frequency
tunability of spin-torque oscillators.",1610.10007v1
2017-03-14,Finite-Temperature Dynamics and Thermal Intraband Magnon Scattering in Haldane Spin-One Chains,"The antiferromagnetic spin-one chain is considerably one of the most
fundamental quantum many-body systems, with symmetry protected topological
order in the ground state. Here, we present results for its dynamical spin
structure factor at finite temperatures, based on a combination of exact
numerical diagonalization, matrix-product-state calculations and quantum Monte
Carlo simulations. Open finite chains exhibit a sub-gap band in the thermal
spectral functions, indicative of localized edge-states. Moreover, we observe
the thermal activation of a distinct low-energy continuum contribution to the
spin spectral function with an enhanced spectral weight at low momenta and its
upper threshold. This emerging thermal spectral feature of the Haldane spin-one
chain is shown to result from intra-band magnon scattering due to the thermal
population of the single-magnon branch, which features a large bandwidth-to-gap
ratio. These findings are discussed with respect to possible future studies on
spin-one chain compounds based on inelastic neutron scattering.",1703.04652v2
2019-05-21,Quantum Rydberg Central Spin Model,"We consider dynamics of a Rydberg impurity in a cloud of ultracold bosonic
atoms in which the Rydberg electron can undergo spin-changing collisions with
surrounding atoms. This system realizes a new type of the quantum impurity
problem that compounds essential features of the Kondo model, the Bose polaron,
and the central spin model. To capture the interplay of the Rydberg-electron
spin dynamics and the orbital motion of atoms, we employ a new variational
method that combines an impurity-decoupling transformation with a Gaussian
ansatz for the bath particles. We find several unexpected features of this
model that are not present in traditional impurity problems, including
interaction-induced renormalization of the absorption spectrum that eludes
simple explanations from molecular bound states, and long-lasting oscillations
of the Rydberg-electron spin. We discuss generalizations of our analysis to
other systems in atomic physics and quantum chemistry, where an electron
excitation of high orbital quantum number interacts with a spinful quantum
bath.",1905.08523v5
2019-05-23,Efficient variational approach to dynamics of a spatially extended bosonic Kondo model,"We develop an efficient variational approach to studying dynamics of a
localized quantum spin coupled to a bath of mobile spinful bosons. We use
parity symmetry to decouple the impurity spin from the environment via a
canonical transformation and reduce the problem to a model of the interacting
bosonic bath. We describe coherent time evolution of the latter using bosonic
Gaussian states as a variational ansatz. We provide full analytical expressions
for equations describing variational time evolution that can be applied to
study in- and out-of-equilibrium phenomena in a wide class of quantum impurity
problems. In the accompanying paper [Y. Ashida {\it et al.}, Phys. Rev. Lett.
123, 183001 (2019)], we present a concrete application of this general
formalism to the analysis of the Rydberg Central Spin Model, in which the
spin-1/2 Rydberg impurity undergoes spin-changing collisions in a dense cloud
of two-component ultracold bosons. To illustrate new features arising from
orbital motion of the bath atoms, we compare our results to the Monte Carlo
study of the model with spatially localized bosons in the bath, in which random
positions of the atoms give rise to random couplings of the standard central
spin model.",1905.09615v5
2020-07-06,"Projective symmetry group classifications of quantum spin liquids on the simple cubic, body centered cubic, and face centered cubic lattices","We perform extensive classifications of $\mathbb{Z}_2$ quantum spin liquids
on the simple cubic, body centered cubic, and face centered cubic lattices
using a spin-rotation invariant fermionic projective symmetry group approach.
Taking into account that all three lattices share the same point group $O_h$,
we apply an efficient gauge where the classification for the simple cubic
lattice can be partially carried over to the other two lattices. We identify
hundreds of projective representations for each of the three lattices, however,
when constructing short-range mean-field models for the fermionic partons
(spinons) these phases collapse to only very few relevant cases. We
self-consistently calculate the corresponding mean-field parameters for
frustrated Heisenberg models on all three lattices with up to third neighbor
spin interactions and discuss the spinon dispersions, ground state energies and
dynamical spin structure factors. Our results indicate that phases with
non-uniform spinon hopping or pairing amplitudes are energetically favored. An
unusual situation is identified for the fcc lattice where the spinon dispersion
minimizing the mean-field energy features a network of symmetry protected
line-like zero modes in reciprocal space. We further discuss characteristic
fingerprints of these phases in the dynamical spin structure factor which may
help to identify and distinguish them in future numerical or experimental
studies.",2007.02589v1
2020-07-13,Spin Wave Generation via Localized Spin-Orbit Torque in an Antiferromagnet-Topological Insulator Heterostructure,"The spin-orbit torque induced by a topological insulator (TI) is
theoretically examined for spin wave generation in a neighboring
antiferromagnetic thin film. The investigation is based on the micromagnetic
simulation of N\'{e}el vector dynamics and the analysis of transport properties
in the TI. The results clearly illustrate that propagating spin waves can be
achieved in the antiferromagnetic thin-film strip through localized excitation,
traveling over a long distance. The oscillation amplitude gradually decays due
to the non-zero damping as the N\'{e}el vector precesses around the magnetic
easy axis with a fixed frequency. The frequency is also found to be tunable via
the strength of the driving electrical current density. While both the bulk and
the surface states of the TI contribute to induce the effective torque, the
calculation indicates that the surface current plays a dominant role over the
bulk counterpart except in the heavily degenerate cases. Compared to the more
commonly applied heavy metals, the use of a TI can substantially reduce the
threshold current density to overcome the magnetic anisotropy, making it an
efficient choice for spin wave generation. The N\'{e}el vector dynamics in the
nano-oscillator geometry are examined as well.",2007.06663v1
2020-07-22,Synchronised gravitational atoms from mergers of bosonic stars,"If ultralight bosonic fields exist in Nature as dark matter, superradiance
spins down rotating black holes (BHs), dynamically endowing them with
equilibrium bosonic clouds, here dubbed synchronised gravitational atoms
(SGAs). The self-gravity of these same fields, on the other hand, can lump them
into (scalar or vector) horizonless solitons known as bosonic stars (BSs). We
show that the dynamics of BSs yields a new channel forming SGAs. We study BS
binaries that merge to form spinning BHs. After horizon formation, the BH spins
up by accreting the bosonic field, but a remnant lingers around the horizon. If
just enough angular momentum is present, the BH spin up stalls precisely as the
remnant becomes a SGA. Different initial data lead to SGAs with different
quantum numbers. Thus, SGAs may form both from superradiance-driven BH spin
down and accretion-driven BH spin up. The latter process, moreover, can result
in heavier SGAs than those obtained from the former: in one example herein,
$\sim 18\%$ of the final system's energy and $\sim 50\%$ of its angular
momentum remain in the SGA. We suggest that even higher values may occur in
systems wherein both accretion and superradiance contribute to the SGA
formation.",2007.11584v1
2020-07-27,Theoretical Description of Hyperpolarization Formation in the SABRE-relay Method,"SABRE (Signal Amplification By Reversible Exchange) has become a widely used
method for hyper-polarizing nuclear spins, thereby enhancing their Nuclear
Magnetic Resonance (NMR) signals by orders of magnitude. In SABRE experiments,
non-equilibrium spin order is transferred from parahydrogen to a substrate in a
transient organometallic complex. Applicability of SABRE is expanded by the
methodology of SABRE-relay, in which polarization can be relayed to a second
substrate either by direct chemical exchange of hyperpolarized nuclei or by
polarization transfer between two substrates in a second organometallic
complex. To understand the mechanism of the polarization transfer and study the
transfer efficiency, we propose a theoretical approach to SABRE-relay, which
can treat both spin dynamics and chemical kinetics as well as the interplay
between them. The approach is based on a set of equations for the spin density
matrices of the spin systems involved (i.e., SABRE substrates and complexes),
which can be solved numerically. Using this method, we perform a detailed study
of polarization formation and analyse in detail the dependence of attainable
polarization level on various chemical kinetic and spin dynamic parameters. We
foresee applications of the present approach for optimizing SABRE-relay
experiments with the ultimate goal of achieving maximal NMR signal enhancements
for substrates of interest.",2007.13301v1
2016-11-04,Graph spectral characterisation of the XY model on complex networks,"There is recent evidence that the $XY$ spin model on complex networks can
display three different macroscopic states in response to the topology of the
network underpinning the interactions of the spins. In this work, we present a
novel way to characterise the macroscopic states of the $XY$ spin model based
on the spectral decomposition of time series using topological information
about the underlying networks. We use three different classes of networks to
generate time series of the spins for the three possible macroscopic states. We
then use the temporal Graph Signal Transform technique to decompose the time
series of the spins on the eigenbasis of the Laplacian. From this
decomposition, we produce spatial power spectra, which summarise the activation
of structural modes by the non-linear dynamics, and thus coherent patterns of
activity of the spins. These signatures of the macroscopic states are
independent of the underlying networks and can thus be used as universal
signatures for the macroscopic states. This work opens new avenues to analyse
and characterise dynamics on complex networks using temporal Graph Signal
Analysis.",1611.01330v2
2017-01-22,Giant tunable Rashba spin splitting in two-dimensional BiSb monolayer and BiSb/AlN heterostructures,"Search of novel two-dimensional giant Rashba semiconductors is a crucial step
in the development of the forthcoming nano-spintronics technology. Using
first-principle calculations, we study a stable two-dimensional crystal phase
of BiSb having buckled honeycomb lattice geometry, which is yet unexplored. The
phonon, room temperature molecular dynamics and elastic constant calculations
verify the dynamical and mechanical stability of the monolayer at 0~K and at
room temperature. The calculated electronic bandstructure reveals the direct
bandgap semiconducting nature of BiSb monolayer with presence of highly mobile
two-dimensional electron gas (2DEG) near Fermi-level. Inclusion of spin-orbit
coupling (SOC) yields the giant Rashba spin-splitting of 2DEG near Fermi-level.
The calculated Rashba energy and Rashba splitting constant are 13 meV and 2.3
eV\AA, respectively. The strength of the Rashba splitting is amongst the
largest yet known 2D Rashba semiconductors. We demonstrate that the strength of
the Rashba spin-splitting can be significantly tuned by applying in-plane
bi-axial strain on the BiSb monolayer. Presence of the giant Rashba
spin-splitting together with the large electronic bandgap (1.6 eV) makes this
system of peculiar interest for optoelectronics applications. Furthermore, we
study the electronic properties of BiSb/AlN heterostructures having a lattice
mismatch of 1.3\% at the interface. Our results suggest that BiSb monolayer and
heterostructure systems could be potentially used to develop highly efficient
spin field-effect transistors, optoelectronics and nano-spintronics devices.
Thus, this comprehensive study of two-dimensional BiSb systems can expand the
range of possible applications in the future spintronics technology.",1701.06213v1
2017-01-27,Application of Spin-Exchange Relaxation-Free Magnetometry to the Cosmic Axion Spin Precession Experiment,"The Cosmic Axion Spin Precession Experiment (CASPEr) seeks to measure
oscillating torques on nuclear spins caused by axion or axion-like-particle
(ALP) dark matter via nuclear magnetic resonance (NMR) techniques. A sample
spin-polarized along a leading magnetic field experiences a resonance when the
Larmor frequency matches the axion/ALP Compton frequency, generating precessing
transverse nuclear magnetization. Here we demonstrate a Spin-Exchange
Relaxation-Free (SERF) magnetometer with sensitivity $\approx 1~{\rm
fT/\sqrt{Hz}}$ and an effective sensing volume of 0.1 $\rm{cm^3}$ that may be
useful for NMR detection in CASPEr. A potential drawback of
SERF-magnetometer-based NMR detection is the SERF's limited dynamic range. Use
of a magnetic flux transformer to suppress the leading magnetic field is
considered as a potential method to expand the SERF's dynamic range in order to
probe higher axion/ALP Compton frequencies.",1701.08082v5
2017-04-26,Determining the population properties of spinning black holes,"There are at least two formation scenarios consistent with the first
gravitational-wave observations of binary black hole mergers. In field models,
black hole binaries are formed from stellar binaries that may undergo common
envelope evolution. In dynamic models, black hole binaries are formed through
capture events in globular clusters. Both classes of models are subject to
significant theoretical uncertainties. Nonetheless, the conventional wisdom
holds that the distribution of spin orientations of dynamically merging black
holes is nearly isotropic while field-model black holes prefer to spin in
alignment with the orbital angular momentum. We present a framework in which
observations of black hole mergers can be used to measure ensemble properties
of black hole spin such as the typical black hole spin misalignment. We show
how to obtain constraints on population hyperparameters using minimal
assumptions so that the results are not strongly dependent on the uncertain
physics of formation models. These data-driven constraints will facilitate
tests of theoretical models and help determine the formation history of binary
black holes using information encoded in their observed spins. We demonstrate
that the ensemble properties of binary detections can be used to search for and
characterize the properties of two distinct populations of black hole mergers.",1704.08370v2
2018-04-30,Spin-fluctuation and spin-relaxation effects of single adatoms from first principles,"Single adatoms offer an exceptional playground for studying magnetism and its
associated dynamics at the atomic scale. Here we review recent results on
single adatoms deposited on metallic substrates, based on time-dependent
density functional theory. First we analyze quantum zero-point
spin-fluctuations (ZPSF) as calculated from the fluctuation-dissipation
theorem, and show how they affect the magnetic stability by modifying the
magnetic anisotropy energy. We also assess the impact of ZPSF in the limit of
small hybridization to the substrate characteristic of semi-insulating
substrates, connecting to recent experimental investigations where magnetic
stability of a single adatom was achieved for the first time. Secondly, we
inspect further the dynamics of single adatoms by considering the longitudinal
and transverse spin-relaxation processes, whose time-scales are analyzed and
related to the underlying electronic structure of both the adatom and the
substrate. Thirdly, we analyze spin-fluctuation modes of paramagnetic adatoms,
i.e., adatoms where the Stoner criterion for magnetism is almost fulfilled.
Interestingly, such modes can develop well-defined peaks in the meV range,
their main characteristics being determined by two fundamental electronic
properties, namely the Stoner parameter and the density of states at the Fermi
level. Furthermore, simulated inelastic scanning tunneling spectroscopy curves
reveal that these spin-fluctuation modes can be triggered by tunneling
electrons, opening up potential applications also for paramagnetic adatoms.
Lastly, an overview of the outstanding issues and future directions is given.",1805.00347v1
2016-05-11,"Optical orientation of hole magnetic polarons in (Cd,Mn)Te/(Cd,Mn,Mg)Te quantum wells","The optically induced spin polarization in (Cd,Mn)Te/(Cd,Mn,Mg)Te
diluted-magnetic-semiconductor quantum wells is investigated by means of
picosecond pump-probe Kerr rotation. At 1.8 K temperature, additionally to the
oscillatory signals from photoexcited electrons and Manganese spins precessing
about an external magnetic field, a surprisingly long-lived (up to 60 ns)
nonoscillating spin polarization is detected. This polarization is related to
optical orientation of equilibrium magnetic polarons involving resident holes.
The suggested mechanism for the optical orientation of the equilibrium magnetic
polarons indicates that the detected polaron dynamics originates from unexcited
magnetic polarons. The polaron spin dynamics is controlled by the anisotropic
spin structure of the heavy-hole resulting in a freezing of the polaron
magnetic moment in one of the two stable states oriented along the structure
growth axis. Spin relaxation between these states is prohibited by a potential
barrier, which depends on temperature and magnetic field. The magnetic polaron
relaxation is accelerated with increasing temperature and in magnetic field.",1605.03362v1
2016-05-29,Heisenberg Necklace Model in Magnetic Field,"Motivated by the experimental realizations of nearly one-dimensional spin-1/2
Heisenberg model found in chain cuprates SrCuO$_2$ and Sr$_2$CuO$_3$, which
remain in a quantum-critical Luttinger liquid state down to temperatures that
are much lower than in-chain exchange coupling, we consider the perturbation to
this state caused by interactions with nuclear spins on the same sites. We
study the low-energy sector of the Heisenberg Necklace model and estimate the
effect of the coupling between the nuclear and the electronic spins on the
overall spins dynamics and its dependence on the magnetic field. We find that
the Necklace model has a characteristic energy scale, $\Lambda \sim
J^{1/3}(\gamma I)^{2/3}$, at which the coupling between spins of the necklace
and the spins of the Heisenberg chain becomes strong. In the strong magnetic
field $\mu_B B > \Lambda$ the low energy spectrum is gapless, but two gapless
bosonic modes have different velocities whose ratio at strong fields approaches
a universal number, $\sqrt 2 +1$. In the case of Sr$_2$CuO$_3$ the energy scale
$\Lambda $ is sizable and comparable to the Neel ordering temperature induced
by the inter-chain coupling, and thus could noticeably modify the low
temperature magnon dynamics. We further find that the above energy scale is
insensitive to strong magnetic field, $\mu_B B \gg \Lambda \sim J^{1/3}(\gamma
I)^{2/3}$, and therefore the interaction with nuclear spins cannot lead to
unusually strong magnetic field dependence of the magnon spectrum observed by
ESR in Sr$_2$CuO$_3$, which has been attributed to the magnon interaction with
the Higgs mode.",1605.09014v2
2019-09-13,Influence of nuclear spin polarization on spin echo signal of NV center qubit,"We consider the spin echo dynamics of a nitrogen-vacancy center qubit based
the $S\!= \! 1$ ground state spin manifold, caused by a dynamically polarized
nuclear environment. We show that the echo signal acquires then a nontrivially
time-dependent phase shift. This effect should be observable for polarization
$\approx \! 0.5$ of nuclei within $\sim \! 1$ nm from the qubit, and for the NV
center initialized in a superposition of $m\! = \! 0$ and either $m\! =\! 1$ or
$m\! =\! -1$ states. This phase shift is much smaller when the NV center is
prepared in a superposition of $m\! = \! 1$ and $m\! =\! -1$ states, i.e. when
the qubit couples to the spin environment in a way analogous to that of
spin-$1/2$. For nuclear environment devoid of spins strongly coupled to the
qubit, the phase shift is well described within Gaussian approximation, which
provides an explanation for the dependence of the shift magnitude on the choice
of states on which the qubit is based, and makes it clear that its presence is
related to the linear response of the environment perturbed by an evolving
qubit. Consequently, its observation signifies the presence
environment-mediated self-interaction of the qubit, and hence, it invalidates
the notion that the nuclear environment acts as a source of external noise
driving the qubit. We also show how a careful comparison of the echo signal
from qubits based on $m\! = \! 0,1$ and $m\! =\! \pm 1$ manifolds, can
distinguish between effectively Gaussian and non-Gaussian environment.",1909.06438v3
2020-02-13,Phonon dynamics in the Kitaev spin liquid,"The search for fractionalization in quantum spin liquids largely relies on
their decoupling with the environment. However, the spin-lattice interaction is
inevitable in a real setting. While the Majorana fermion evades a strong decay
due to the gradient form of spin-lattice coupling, the study of the phonon
dynamics may serve as an indirect probe of fractionalization of spin degrees of
freedom. Here we propose that the signatures of fractionalization can be seen
in the sound attenuation and the Hall viscosity. Despite the fact that both
quantities can be related to the imaginary part of the phonon self-energy,
their origins are quite different, and the time-reversal symmetry breaking is
required for the Hall viscosity. First, we compute the sound attenuation due to
a phonon scattering off of a pair of Majorana fermions and show that it is
linear in temperature ($\sim T$). We argue that it has a particular angular
dependence providing the information about the spin-lattice coupling and the
low-energy Majorana fermion spectrum. The observable effects in the absence of
time-reversal symmetry are then analyzed. We obtain the phonon Hall viscosity
term from the microscopic Hamiltonian with time-reversal symmetry breaking
term. Importantly, the Hall viscosity term mixes the longitudinal and
transverse phonon modes and renormalize the spectrum in a unique way, which may
be probed in spectroscopy measurement.",2002.05328v2
2020-02-19,Softening of breathing elastic mode and trigonal elastic mode in disordered pyrochlore magnet NaCaCo$_2$F$_7$,"Cobalt pyrochlore fluoride NaCaCo$_2$F$_7$ is a disordered frustrated magnet
composed of Co$^{2+}$ ions with an effective spin-$\frac{1}{2}$ magnetic moment
and exhibits spin freezing below $T_f \sim$2.4 K. We perform ultrasound
velocity measurements on a single crystal of the cubic NaCaCo$_2$F$_7$. The
temperature dependence of the bulk modulus (the breathing elastic mode)
exhibits Curie-type softening upon cooling below $\sim$20 K down to $T_f$,
which is suppressed by the magnetic field. This Curie-type softening should be
a precursor to the enhancement of the strength of exchange disorder via the
spin-lattice coupling, which causes the spin freezing. In contrast to the
magnetic-field-suppressed Curie-type softening in the bulk modulus, the
trigonal shear modulus exhibits softening with a characteristic minimum upon
cooling, which is enhanced by the magnetic field at temperatures below $\sim$20
K. This magnetic-field-enhanced elastic anomaly in the trigonal shear modulus
suggests a coupling of the lattice to the dynamical spin-cluster state. For
NaCaCo$_2$F$_7$, the observed elastic anomalies reveal an occurrence of
magnetic-field-induced crossover from an isostructural lattice instability
toward the spin freezing to a trigonal lattice instability arising from the
emergent dynamical spin-cluster state.",2002.07980v2
2020-04-01,Phase transitions and spin-state of iron in FeO at the conditions of Earth's deep interior,"Iron-bearing oxides undergo a series of pressure-induced electronic, spin and
structural transitions that can cause seismic anomalies and dynamic
instabilities in Earth's mantle and outer core. We employ x-ray diffraction and
x-ray emission spectroscopy along with state-of-the-art density functional plus
dynamical mean-field theory (DFT+DMFT) to characterize the electronic structure
and spin states, and crystal-structural properties of w\""ustite (Fe$_{1-x}$O)
-- a basic oxide component of Earth's interior -- at high pressure-temperature
conditions up to 140 GPa and 2100 K. We find that FeO exhibits complex
polymorphism under pressure, with abnormal compression behavior associated with
electron-spin and crystallographic phase transitions, and resulting in a
substantial change of bulk modulus. Our results reveal the existence of a
high-pressure phase characterized by a metallic high-spin state of iron at
about the pressure-temperature conditions of Earth's core-mantle boundary. The
presence of high-spin metallic iron near the base of the mantle can
significantly influence the geophysical and geochemical properties of Earth's
deep interior.",2004.00652v2
2017-09-03,"Aspects of higher spin Hamiltonian dynamics: Conformal geometry, duality and charges","We have studied free higher spin gauge fields through an investigation of
their Hamiltonian dynamics. Over a flat space-time, their Hamiltonian
constraints were identified and solved through the introduction of
prepotentials, enjoying both linearized generalized diffeomorphism and
linearized generalized Weyl rescaling gauge invariance, motivating our study of
conformal invariants for higher spins. We built these with the Cotton tensor,
whose properties (tracelessness, symmetry, divergencelessness; completeness,
invariance) we established. With these geometric tools, a first order action
was written down in terms of the prepotentials. It is manifestly invariant
under electric-magnetic duality which, with the gauge freedom of the
prepotentials, completely fixes the action. This action is associated to
twisted self-duality conditions.
  With an interest in supersymmetric extensions, we began to extend this study
to fermions, similarly analyzing the spin $5/2$ massless free field, whose
prepotential also enjoys conformal gauge invariance. The spin $2$-spin $5/2$
supermultiplet was considered, and a rigid symmetry of its action (a
chirality-duality rotation) was built to commute with supersymmetry. We also
investigated the properties of a mixed symmetry field on a flat six-dimensional
space-time, the so-called chiral $(2,2)$-form: Hamiltonian analysis,
prepotentials, and a first order action associated to self-duality conditions.
  Finally, we studied both fermionic and bosonic higher spin surface charges
over a constantly curved background space-time. The Hamitonian constraints are
the generators of gauge transformations. Plugging into them appropriate values
of the gauge parameters (imposing a physical variation of the fields), their
finite and non-vanishing on-shell values were computed and recognized as
conserved charges of the theory. Their algebra was checked to be abelian.",1709.00719v2
2017-11-14,Magnon Splitting Induced by Charge Transfer in the Three-Orbital Hubbard Model,"Understanding spin excitations and their connection to unconventional
superconductivity have remained a central issue since the discovery of the
cuprates. Direct measurement of the dynamical spin structure factor in the
parent compounds can provide key information on important interactions relevant
in the doped regime, and variations in the magnon dispersion have been linked
closely to differences in crystal structure between families of cuprate
compounds. Here, we elucidate the relationship between spin excitations and
various controlling factors thought to be significant in high-$T_c$ materials
by systematically evaluating the dynamical spin structure factor for the
three-orbital Hubbard model, revealing differences in the spin dispersion along
the Brillouin zone axis and the diagonal. Generally, we find that the absolute
energy scale and momentum dependence of the excitations primarily are sensitive
to the effective charge-transfer energy, while changes in the on-site Coulomb
interactions have little effect on the details of the dispersion. In
particular, our result highlights the splitting between spin excitations along
the axial and diagonal directions in the Brillouin zone. This splitting
decreases with increasing charge-transfer energy and correlates with changes in
the apical oxygen position, and general structural variations, for different
cuprate families.",1711.04931v2
2018-12-13,Experimental Evidence of Non-Negligible Imaginary Part of Spin Mixing Conductance and Its Impact on Magnetization Dynamics in Heavy-Metal|Ferromagnet Bilayers,"The paper concerns experimental verification of the magnitude of imaginary
part of spin mixing conductance in bilayers comprising heavy metals. We present
results of broadband ferromagnetic resonance studies on heterostructures
consisting of Finemet thin films covered by Pt and Ta wedge layers with the aim
to observe spin pumping effects and to evaluate both the real and imaginary
parts of the spin mixing conductance. The experimental results are analyzed in
the framework of a recent microscopic theory which allows us to estimate the
value of the interfacial spin-orbit interaction and confirm its important role.
In particular, we show that the imaginary part of spin mixing conductance
cannot be regarded as negligible and we discuss its influence on magnetization
dynamics. For Finemet|Ta bilayers, the ratio
$\mathrm{Re}[g_{eff}^{\uparrow\downarrow}]/\mathrm{Im}[g_{eff}^{\uparrow\downarrow}]=$
0.38, that is, the field-like torque dominates over the damping-like torque in
such system. Consequently, relatively small enhancement of precession damping
with respect to significant total torque exerted on the magnetization in
Finemet|Ta system offers an attractive perspective for an application in the
next-generation magnetic random-access memory cells.",1812.05235v2
2019-04-05,Coexistence of magnetic order and persistent spin dynamics in a quantum kagome antiferromagnet with no intersite mixing,"One of the key questions concerning frustrated lattices that has lately
emerged is the role of disorder in inducing spin-liquid-like properties. In
this context, the quantum kagome antiferromagnets YCu$_3$(OH)$_6$Cl$_3$, which
has been recently reported as the first geometrically perfect realization of
the kagome lattice with negligible magnetic/non-magnetic intersite mixing and a
possible quantum-spin-liquid ground state, is of particular interest. However,
contrary to previous conjectures, here we show clear evidence of bulk magnetic
ordering in this compound below $T_N=15$\,K by combining bulk magnetization and
heat capacity measurements, and local-probe muon spin relaxation measurements.
The magnetic ordering in this material is rather unconventional in several
respects. Firstly, a crossover regime where the ordered state coexists with the
paramagnetic state extends down to $T_N/3$ and, secondly, the fluctuation
crossover is shifted far below $T_N$. Moreover, a reduced magnetic-entropy
release at $T_N$ and persistent spin dynamics that is observed at temperatures
as low as $T/T_N=1/300$ could be a sign of emergent excitations of correlated
spin-loops or, alternatively, a sign of fragmentation of each magnetic moment
into an ordered and a fluctuating part.",1904.02878v2
2019-11-01,Growth of resonances and chaos for a spinning test particle in the Schwarzschild background,"Inspirals of stellar mass compact objects into supermassive black holes are
known as extreme mass ratio inspirals. In the simplest approximation, the
motion of the compact object is modeled as a geodesic in the space-time of the
massive black hole with the orbit decaying due to radiated energy and angular
momentum, thus yielding a highly regular inspiral. However, once the spin of
the secondary compact body is taken into account, integrability is broken and
prolonged resonances along with chaotic motion appear.
  We numerically integrate the motion of a spinning test body in the field of a
non-spinning black hole and analyse it using various methods. We show for the
first time that resonances and chaos can be found even for astrophysical values
of spin. On the other hand, we devise a method to analyse the growth of the
resonances, and we conclude that the resonances we observe are only caused by
terms quadratic in spin and will generally stay very small in the
small-mass-ratio limit. Last but not least, we compute gravitational waveforms
by solving numerically the Teukolsky equations in the time-domain and establish
that they carry information on the motion's dynamics. In particular, we show
that the time series of the gravitational wave strain can be used to discern
regular from chaotic motion of the source.",1911.00414v1
2019-12-10,Observation of chiral solitons in the quantum spin liquid phase of LiCuVO$_4$,"Quantum spin liquids represent a magnetic ground state arising in the
presence of strong quantum fluctuations that preclude ordering down to zero
temperature and leave clear fingerprints in the excitation spectra. While
theory bears a variety of possible quantum spin liquid phases their
experimental realization is still scarce. Here, we report the first
experimental evidence of a vector-chiral quantum spin liquid state in the
$S=1/2$ spin chain compound LiCuVO$_4$ from measurements of the complex
permittivity $\varepsilon^*$ in the GHz range. In zero magnetic field our
results show short-lived thermally activated chiral fluctuations above the
multiferroic phase transition at $T_\mathrm{N}=2.4$ K with divergent life-times
when approaching $T_\mathrm{N}$. In $\varepsilon^*$ this fluctuation dynamics
are seen as the slowing down of a relaxation with a critical dynamical exponent
$\nu_\xi z \approx 1.3$ in agreement with mean-field predictions. When using a
magnetic field to suppress $T_N$ towards 0 K the influence of quantum
fluctuations is increased until they condense into the chrial spin liquid phase
below 400 mK. Within this phase we measure a nearly-gapless chiral soliton
excitation with a tiny energy gap of $E_\mathrm{SE}\approx14.1$ $\mu$eV.",1912.04705v1
2020-03-02,Non-Hermitian topology of one-dimensional spin-torque oscillator arrays,"Magnetic systems have been extensively studied both from a fundamental
physics perspective and as building blocks for a variety of applications. Their
topological properties, in particular those of excitations, remain relatively
unexplored due to their inherently dissipative nature. The recent introduction
of non-Hermitian topological classifications opens up new opportunities for
engineering topological phases in dissipative systems. Here, we propose a
magnonic realization of a non-Hermitian topological system. A crucial
ingredient of our proposal is the injection of spin current into the magnetic
system, which alters and can even change the sign of terms describing
dissipation. We show that the magnetic dynamics of an array of spin-torque
oscillators can be mapped onto a non-Hermitian Su-Schrieffer-Heeger model
exhibiting topologically protected edge states. Using exact diagonalization of
the linearized dynamics and numerical solutions of the non-linear equations of
motion, we find that a topological magnonic phase can be accessed by tuning the
spin current injected into the array. In the topologically nontrivial regime, a
single spin-torque oscillator on the edge of the array is driven into
auto-oscillation and emits a microwave signal, while the bulk oscillators
remain inactive. Our findings have practical utility for memory devices and
spintronics neural networks relying on spin-torque oscillators as constituent
units.",2003.01152v1
2020-05-07,Effect of interfacial oxidation layer in spin pumping experiments on Ni$_{80}$Fe$_{20}$/SrIrO$_3$ heterostructures,"SrIrO$_3$ with its large spin-orbit coupling and low charge conductivity has
emerged as a potential candidate for efficient spin-orbit torque magnetization
control in spintronic devices. We here report on the influence of an
interfacial oxide layer on spin pumping experiments in Ni$_{80}$Fe$_{20}$
(NiFe)/SrIrO$_3$ bilayer heterostructures. To investigate this scenario we have
carried out broadband ferromagnetic resonance (BBFMR) measurements, which
indicate the presence of an interfacial antiferromagnetic oxide layer. We
performed in-plane BBFMR experiments at cryogenic temperatures, which allowed
us to simultaneously study dynamic spin pumping properties (Gilbert damping)
and static magnetic properties (such as the effective magnetization and
magnetic anisotropy). The results for NiFe/SrIrO$_3$ bilayer thin films were
analyzed and compared to those from a NiFe/NbN/SrIrO$_3$ trilayer reference
sample, where a spin-transparent, ultra-thin NbN layer was inserted to prevent
oxidation of NiFe. At low temperatures, we observe substantial differences in
the magnetization dynamics parameters of these samples, which can be explained
by an antiferromagnetic interfacial layer in the NiFe/SrIrO$_3$ bilayers.",2005.03727v1
2020-09-01,Spin coherence on the ferromagnetic spherical surface,"Spintronics on flat surfaces has been studied over the years, and the
scenario is relatively well-known; however, there is a lack of information when
we consider non-flat surfaces. In this paper, we are concerned about the spin
dynamics of the ferromagnetic model on the spherical surface. We use the
Schwinger bosonic formalism for describing the thermodynamics of spin operators
in terms of spinon operators. Opposite to the flat two-dimensional model, which
is disordered at finite temperature, the curvature of the spherical surface
provides non-zero critical temperature for Schwinger boson condensation, which
characterizes order at finite temperature even in the absence of external
magnetic fields. The thermodynamics is then analyzed in the low-temperature
regime. In addition, we consider the presence of both static and oscillating
magnetic fields, the necessary condition for inducing the ferromagnetic
resonance, and we show systematically that the studied model is well-described
by $SU(2)$ coherent states, which provides the correct dynamics of the
magnetization. The archived results can be applied for describing a diversity
of experiments such as spin superfluidity, angular momentum injection by spin
pumping and spin-transfer torque in non-conventional junctions, magnon
dissipation, and magnetoelectronics on the spherical surface.",2009.00636v2
2021-02-25,Nuclear spin temperature reversal via continuous radio-frequency driving,"Optical spin pumping of color centers in diamond is presently attracting
broad interest as a platform for dynamic nuclear polarization at room
temperature, but the mechanisms involved in the generation and transport of
polarization within the host crystal are still partly understood. Here we
investigate the impact of continuous radio-frequency (RF) excitation on the
generation of nuclear magnetization produced by optical illumination. In the
presence of RF excitation far removed from the nuclear Larmor frequency, we
witness a magnetic-field-dependent sign reversal of the measured nuclear spin
signal when the drive is sufficiently strong, a counter-intuitive finding that
immediately points to non-trivial spin dynamics. With the help of analytical
and numerical modeling, we show our observations indicate a modified form of
'solid effect', down-converted from the microwave to the radio-frequency range
through the driving of hybrid transitions involving one (or more) nuclei and
two (or more) electron spins. Our results open intriguing opportunities for the
manipulation of many-electron spin systems by exploiting hyperfine couplings as
a means to access otherwise forbidden intra-band transitions.",2102.13171v1
2021-04-08,Spin-orbit coupling induced ultra-high harmonic generation from magnetic dynamics,"The recent boost in data transfer rates puts a daring strain on information
technology. Sustaining such a growth rate requires the development of sources,
detectors and systems working in the so-called TeraHertz (THz) gap covering the
frequency window from 0.1 to 10 THz (1 THz = 10$^{12}$~Hz). This gap represents
a challenge for conventional electronic devices due to carrier transit delays
($\sim$1-10ps), as well as for photonic devices due to thermal fluctuations
(300K$\sim$6THz). Nonetheless, designing efficient, room-temperature THz
sources would constitute a key enabler to applications spanning from
high-resolution imaging to extreme wide band wireless communication. Whereas
high-harmonic generation in solid is usually limited to less than ten
harmonics, broadband THz emission has been demonstrated using laser-induced
superdiffusive spin currents in magnetic bilayers composed of a ferromagnet
deposited on top of a noble metal. While promising, this technique presents the
major disadvantage of necessitating optical pumping and hence lacks
scalability. Here, we demonstrate that extremely high harmonic emission can be
achieved by exploiting conventional spin pumping, without the need of optical
excitation. We show that when the spin-orbit coupling strength is close to the
s-d exchange energy, a strongly non linear regime resulting from resonant spin
flip scattering occurs leading to the generation of a thousand of harmonics at
realistic antiferromagnetic precession frequencies, thereby enhancing both spin
and charge dynamics by two orders of magnitude, and allowing for an emission at
frequencies above 300 THz.",2104.04001v1
2021-08-04,"The next generation: Impact of high-order analytical information on effective one body waveform models for noncircularized, spin-aligned black hole binaries","We explore the performance of an updated effective-one-body (EOB) model for
spin-aligned coalescing black hole binaries designed to deal with any orbital
configuration. The model stems from previous work involving the \TEOBResumS{}
waveform model, but incorporates recently computed analytical information up to
fifth post-Newtonian (PN) order in the EOB potentials. The dynamics is then
informed by Numerical Relativity (NR) quasi-circular simulations (incorporating
also recently computed 4PN spin-spin and, optionally, 4.5PN spin-orbit terms).
The so-constructed model(s) are then compared to various kind of NR
simulations, covering either quasi-circular inspirals, eccentric inspirals and
scattering configurations. For quasi-circular (534 datasets) and eccentric (28
datasets) inspirals up to coalescence, the EOB/NR unfaithfulness is well below
$1\%$ except for a few outliers in the high, positive, spin corner of the
parameter space, where however it does not exceed the $3\%$ level. The EOB
values of the scattering angle are found to agree ($\lesssim 1\%$) with the NR
predictions for most configurations, with the largest disagreement of only
$\sim 4\%$ for the most relativistic one. The inclusion of some high-order
analytical information in the orbital sector is useful to improve the EOB/NR
agreement with respect to previous work, although the use of NR-informed
functions is still crucial to accurately describe the strong-field dynamics and
waveform.",2108.02043v2
2022-04-28,"Low-energy spin excitations of the frustrated ferromagnetic $J_1$-$J_2$ chain material linarite, PbCuSO$_4$(OH)$_2$, in applied magnetic fields $\mathbf{H} \parallel b$ axis","We report a study of the spin dynamics of the frustrated ferromagnetic
$J_1$-$J_2$ chain compound linarite, PbCuSO$_4$(OH)$_2$, in applied magnetic
fields up to field polarization. By means of an extreme-environment inelastic
neutron scattering experiment, we have measured the low-energy spin excitations
of linarite in fields up to 8.8 T for $\mathbf{H} \parallel b$ axis. We have
recorded the spin excitation spectra along $h$, $k$ and $l$ for the
field-induced magnetic phases IV, V and the field polarized state close to
saturation. By employing first-principles calculations, we estimate the leading
magnetic exchanges out of the $bc$ plane and model the dispersion relations
using linear spin-wave theory. In this way, we find evidence for a (very weak)
residual magnetic exchange coupling out of the $bc$ plane. Together with the
previously established dominant intrachain couplings $J_1$ and $J_2$ and the
interchain coupling $J_3$, we derive an effective set of exchange couplings for
a microscopic description of linarite. Further, we find that the peculiar
character of phase V manifests itself in the measured spin dynamics.",2204.13482v2
2022-05-12,Condensation and thermalization of an easy-plane ferromagnet in a spinor Bose gas,"The extensive control of spin makes spintronics a promising candidate for
future scalable quantum devices. For the generation of spin-superfluid systems,
a detailed understanding of the build-up of coherence and relaxation is
necessary. However, to determine the relevant parameters for robust coherence
properties and faithfully witnessing thermalization, the direct access to
space- and time-resolved spin observables is needed. Here, we study the
thermalization of an easy-plane ferromagnet employing a homogeneous
one-dimensional spinor Bose gas. Building on the pristine control of
preparation and readout we demonstrate the dynamic emergence of long-range
coherence for the spin field and verify spin-superfluidity by experimentally
testing Landau's criterion. We reveal the structure of the emergent
quasi-particles: one 'massive'(Higgs) mode, and two 'massless' (Goldstone)
modes - a consequence of explicit and spontaneous symmetry breaking,
respectively. Our experiments allow for the first time to observe the
thermalization of an easy-plane ferromagnetic Bose gas; we find agreement for
the relevant momentum-resolved observables with a thermal prediction obtained
from an underlying microscopic model within the Bogoliubov approximation. Our
methods and results pave the way towards a quantitative understanding of
condensation dynamics in large magnetic spin systems and the study of the role
of entanglement and topological excitations for its thermalization.",2205.06188v1
2022-12-05,Exploring Disordered Quantum Spin Models with a Multi-Layer Multi-Configurational Approach,"Numerical simulations of quantum spin models are crucial for a profound
understanding of many-body phenomena in a variety of research areas in physics.
An outstanding problem is the availability of methods to tackle systems that
violate area-laws of entanglement entropy. Such scenarios cover a wide range of
compelling physical situations including disordered quantum spin systems among
others. In this work, we employ a numerical technique referred to as
multi-layer multi-configuration time-dependent Hartree (ML-MCTDH) to evaluate
the ground state of several disordered spin models. ML-MCTDH has previously
been used to study problems of high-dimensional quantum dynamics in molecular
and ultracold physics but is here applied to study spin systems for the first
time. We exploit the inherent flexibility of the method to present results in
one and two spatial dimensions and treat challenging setups that incorporate
long-range interactions as well as disorder. Our results suggest that the
hierarchical multi-layering inherent to ML-MCTDH allows to tackle a wide range
of quantum many-body problems such as spin dynamics of varying dimensionality.",2212.02254v4
2022-12-07,Surfing in the phase space of spin-orbit coupling in binary asteroid systems,"For a satellite with an irregular shape, which is the common shape among
asteroids, the well-known spin-orbit resonance problem could be changed to a
spin-orbit coupling problem since a decoupled model does not accurately capture
the dynamics of the system. In this paper, having provided a definition for
close binary asteroid systems, we explore the structure of the phase space in a
classical Hamiltonian model for spin-orbit coupling in a binary system. To map
out the geography of resonances analytically and the cartography of resonances
numerically, we reformulate a fourth-order gravitational potential function, in
Poincare variables, via Stokes coefficients. For a binary system with a
near-circular orbit, isolating the Hamiltonian near each resonance yields the
pendulum model. Analysis of the results shows the geographical information,
including the location and width of resonances, is modified due to the
prominent role of the semi-major axis in the spin-orbit coupling model but not
structurally altered. However, this resulted in modified Chirikov criterion to
predict onset of large-scale chaos. For a binary system with arbitrary closed
orbit, we thoroughly surf in the phase space via cartography of resonances
created by fast Lyapunov indicator (FLI) maps. The numerical study confirms the
analytical results, provides insight into the spin-orbit coupling, and shows
some bifurcations in the secondary resonances which can occur due to material
transfer. Also, we take the (65803) Didymos binary asteroid as a case to show
analytical and numerical results.",2212.03837v1
2023-01-06,Single-point spin Chern number in a supercell framework,"We present an approach for the calculation of the $\mathbb{Z}_2$ topological
invariant in non-crystalline two-dimensional quantum spin Hall insulators.
While topological invariants were originally mathematically introduced for
crystalline periodic systems, and crucially hinge on tracking the evolution of
occupied states through the Brillouin zone, the introduction of disorder or
dynamical effects can break the translational symmetry and imply the use of
larger simulation cells, where the $\bf{k}$-point sampling is typically reduced
to the single $\Gamma$-point. Here, we introduce a single-point formula for the
spin Chern number that enables to adopt the supercell framework, where a single
Hamiltonian diagonalisation is performed. Inspired by the work of E. Prodan
[Phys. Rev. B, $\textbf{80}$, 12 (2009)], our single-point approach allows to
calculate the spin Chern number even when the spin operator $\hat{s}_z$ does
not commute with the Hamiltonian, as in the presence of Rashba spin-orbit
coupling. We validate our method on the Kane-Mele model, both pristine and in
the presence of Anderson disorder. Finally, we investigate the disorder-driven
transition from the trivial phase to the topological state known as topological
Anderson insulator. Beyond disordered systems, our approach is particularly
useful to investigate the role of defects, to study topological alloys and in
the context of ab-initio molecular dynamics simulations at finite temperature.",2301.02612v1
2023-02-01,A Brillouin light scattering study of the spin-wave magnetic field dependence in a magnetic hybrid system made of an artificial spin-ice structure and a film underlayer,"We present a combined Brillouin light scattering and micromagnetic simulation
investigation of the magnetic-field dependent spin-wave spectra in a hybrid
structure made of permalloy (NiFe) artificial spin-ice (ASI) systems, composed
of stadium-shaped nanoislands, deposited on the top of an unpatterned permalloy
film with a nonmagnetic spacer layer. The thermal spin-wave spectra were
recorded by Brillouin light scattering (BLS) as a function of the magnetic
field applied along the symmetry direction of the ASI sample. Magneto-optic
Kerr effect magnetometry was used to measure the hysteresis loops in the same
orientation as the BLS measurements. The frequency and intensity of several
spin-wave modes detected by BLS were measured as a function of the applied
magnetic field. Micromagnetic simulations enabled us to identify the modes in
terms of their frequency and spatial symmetry and to extract information about
the existence and strength of the dynamic coupling, relevant only to a few
modes of a given hybrid system. Using this approach, we suggest a way to
understand if dynamic coupling between ASI and film modes is present or not,
with interesting implications for the development of future three-dimensional
magnonic applications and devices.",2302.00483v1
2023-03-21,Solution-processed NiPS3 thin films from Liquid Exfoliated Inks with Long-Lived Spin-Entangled Excitons,"Antiferromagnets are promising materials for future opto-spintronic
applications since they show spin dynamics in the THz range and no net
magnetization. Recently, layered van der Waals (vdW) antiferromagnets have been
reported, which combine low-dimensional excitonic properties with complex
spin-structure. While various methods for the fabrication of vdW 2D crystals
exist, formation of large area and continuous thin films is challenging because
of either limited scalability, synthetic complexity, or low opto-spintronic
quality of the final material. Here, we fabricate centimeter-scale thin films
of the van der Waals 2D antiferromagnetic material NiPS3, which we prepare
using a crystal ink made from liquid phase exfoliation (LPE). We perform
statistical atomic force microscopy (AFM) and scanning electron microscopy
(SEM) to characterize and control the lateral size and number of layers through
this ink-based fabrication. Using ultrafast optical spectroscopy at cryogenic
temperatures, we resolve the dynamics of photoexcited excitons. We find
antiferromagnetic spin arrangement and spin-entangled Zhang-Rice multiplet
excitons with lifetimes in the nanosecond range, as well as ultranarrow
emission linewidths, despite the disordered nature of our films. Thus, our
findings demonstrate scalable thin-film fabrication of high-quality NiPS3,
which is crucial for translating this 2D antiferromagnetic material into
spintronic and nanoscale memory devices and further exploring its complex
spin-light coupled states.",2303.11788v1
2023-03-31,Theoretical groundwork supporting the precessing-spin two-body dynamics of the effective-one-body waveform models SEOBNRv5,"Waveform models are essential for gravitational-wave (GW) detection and
parameter estimation of coalescing compact-object binaries. More accurate
models are required for the increasing sensitivity of current and future GW
detectors. The effective-one-body (EOB) formalism combines the post-Newtonian
(PN) and small mass-ratio approximations with numerical-relativity results, and
produces highly accurate inspiral-merger-ringdown waveforms. In this paper, we
derive the analytical precessing-spin two-body dynamics for the SEOBNRv5
waveform model, which has been developed for the upcoming LIGO-Virgo-KAGRA
observing run. We obtain an EOB Hamiltonian that reduces to the exact Kerr
Hamiltonian in the test-mass limit. It includes the full 4PN precessing-spin
information, and is valid for generic compact objects (i.e., for black holes or
neutron stars). We also build an efficient and accurate EOB Hamiltonian that
includes partial precessional effects, notably orbit-averaged in-plane spin
effects for circular orbits, and derive 4PN-expanded precessing-spin equations
of motion, consistent with such an EOB Hamiltonian. The results were used to
build the computationally-efficient precessing-spin multipolar SEOBNRv5PHM
waveform model.",2303.18143v2
2023-05-04,Engineering Spin Coherence in Core-Shell Diamond Nanocrystals,"Diamond nanocrystals can harbor spin qubit sensors capable of probing the
physical properties of biological systems with nanoscale spatial resolution.
These diamond nanosensors can readily be delivered into intact cells and even
living organisms. However, applications beyond current proof-of-principle
experiments require a substantial increase in sensitivity, which is generally
limited by surface-noise-induced spin dephasing and relaxation. In this work,
we significantly reduce magnetic surface noise by engineering core-shell
structures, which in combination with dynamical decoupling result in qubit
coherence times (T2) ranging from 52us to 87us - a drastic improvement over the
1.1us to 35us seen in bare particles. This improvement in spin coherence,
combined with an overall increase in particle fluorescence, corresponds to a
two-order-of-magnitude reduction in integration time. Probing qubit dynamics at
a single particle level, furthermore, reveals that the noise characteristics
fundamentally change from a bath with spins that rearrange their spatial
configuration during the course of an experiment to a more dilute static bath.
The observed results shed light on the underlying mechanisms governing spin
dephasing in diamond nanocrystals and offer an effective noise mitigation
strategy based on engineered core-shell structures.",2305.03075v1
2023-05-22,The Spin-Orbit Misalignment of TOI-1842b: The First Measurement of the Rossiter-McLaughlin Effect for a Warm Sub-Saturn around a Massive Star,"The mechanisms responsible for generating spin-orbit misalignments in
exoplanetary systems are still not fully understood. It is unclear whether
these misalignments are related to the migration of hot Jupiters or are a
consequence of general star and planet formation processes. One promising
method to address this question is to constrain the distribution of spin-orbit
angle measurements for a broader range of planets beyond hot Jupiters. In this
work, we present the sky-projected obliquity ($\lambda=-68.1_{-14.7}^{+21.2}
\,^{\circ}$) for the warm sub-Saturn TOI-1842b, obtained through a measurement
of the Rossiter-McLaughlin effect using WIYN/NEID. Using the projected
obliquity, the stellar rotation period obtained from the TESS light curve, and
the projected rotation velocity from spectral analysis, we infer the 3D
spin-orbit angle ($\psi$) to be $\psi=73.3^{+16.3}_{-12.9} \,^{\circ}$. As the
first spin-orbit angle determination made for a sub-Saturn-mass planet around a
massive ($M_{\rm *}=1.45 \,{\rm M_\odot}$) star, our result presents an
opportunity to examine the orbital geometries for new regimes of planetary
systems. When combined with archival measurements, our observations of
TOI-1842b support the hypothesis that the previously established prevalence of
misaligned systems around hot, massive stars may be driven by planet-planet
dynamical interactions. In massive stellar systems, multiple gas giants are
more likely to form and can then dynamically interact with each other to excite
spin-orbit misalignments.",2305.13397v1
2023-06-20,Classical spin models of the windmill lattice and their relevance for PbCuTe$_2$O$_6$,"We investigate classical Heisenberg models on the distorted windmill lattice
and discuss their applicability to the spin-$1/2$ spin liquid candidate
PbCuTe$_2$O$_6$. We first consider a general Heisenberg model on this lattice
with antiferromagnetic interactions $J_n$ ($n=1,2,3,4$) up to fourth neighbors.
Setting $J_1=J_2$ (as approximately realized in PbCuTe$_2$O$_6$) we map out the
classical ground state phase diagram in the remaining parameter space and
identify a competition between $J_3$ and $J_4$ that opens up interesting
magnetic scenarios. Particularly, these couplings tune the ground states from
coplanar commensurate or non-coplanar incommensurate magnetically ordered
states to highly degenerate ground state manifolds with subextensive or
extensive degeneracies. In the latter case, we uncover an unusual classical
spin liquid defined on a lattice of corner sharing octahedra. We then focus on
the particular set of interaction parameters $J_n$ that has previously been
proposed for PbCuTe$_2$O$_6$ and investigate the system's incommensurate
magnetic ground state order and finite temperature multistage ordering
mechanism. We perform extensive finite temperature simulations of the system's
dynamical spin structure factor and compare it with published neutron
scattering data for PbCuTe$_2$O$_6$ at low temperatures. Our results
demonstrate that thermal fluctuations in the classical model can largely
explain the signal distribution in the measured spin structure factor but we
also identify distinct differences. Our investigations make use of a variety of
different analytical and numerical approaches for classical spin systems, such
as Luttinger-Tisza, classical Monte Carlo, iterative minimization, and
molecular dynamics simulations.",2306.11634v2
2023-11-14,Generation of electric current and electromotive force by an antiferromagnetic domain wall,"Dynamic magnetic textures may transfer the angular moment from the varying in
time antiferromagnetic order to spins of conduction electrons. Due to the spin
orbit coupling (SOC) these spin excitations can induce the electric current of
conduction electrons. We calculated the electric current and the electromotive
force (EMF) which are produced by a domain wall (DW) moving parallel to the
magnetically compensated interface between an antiferromagnetic insulator
(AFMI) and a two-dimensional spin orbit coupled metal. Spins of conduction
electrons interact with localized spins of a collinear AFMI through the
interface exchange interaction. The Keldysh formalism of nonequilibrium Green
functions was applied for the analysis of this system. It is shown that a Bloch
DW generates the current perpendicular to the DW motion direction. At the same
time a N\'{e}el DW creates the electric potential which builds up across the
wall. The total charge which is pumped by a Bloch DW can be expressed in terms
of a topologically invariant charge quantum. The latter does not depend on
variations of DW's velocity and shape. These effects increase dramatically when
the Fermi energy approaches the van Hove singularity of the Fermi surface. The
obtained results are important for the electrical detection and control of
dynamic magnetic textures in antiferromagnets.",2311.08067v1
2023-11-23,Two-dimensional coherent spectrum of high-spin models via a quantum computing approach,"We present and benchmark a quantum computing approach to calculate the
two-dimensional coherent spectrum (2DCS) of high-spin models. Our approach is
based on simulating their real-time dynamics in the presence of several
magnetic field pulses, which are spaced in time. We utilize the adaptive
variational quantum dynamics simulation (AVQDS) algorithm for the study due to
its compact circuits, which enables simulations over sufficiently long times to
achieve the required resolution in frequency space. Specifically, we consider
an antiferromagnetic quantum spin model that incorporates Dzyaloshinskii-Moriya
interactions and single-ion anisotropy. The obtained 2DCS spectra exhibit
distinct peaks at multiples of the magnon frequency, arising from transitions
between different eigenstates of the unperturbed Hamiltonian. By comparing the
one-dimensional coherent spectrum with 2DCS, we demonstrate that 2DCS provides
a higher resolution of the energy spectrum. We further investigate how the
quantum resources scale with the magnitude of the spin using two different
binary encodings of the high-spin operators: the standard binary encoding and
the Gray code. At low magnetic fields both encodings require comparable quantum
resources, but at larger field strengths the Gray code is advantageous. Lastly,
we compare the numerical 2DCS with experimental results on a rare-earth
orthoferrite system. The observed strength of the magnonic high-harmonic
generation signals in the 2DCS of the quantum high-spin model aligns well with
the experimental data, showing significant improvement over the corresponding
mean-field results.",2311.14035v2
2023-12-20,Strain-driven Charge Localisation and Spin Dynamics of Paramagnetic Defects in S-deficit 2H-MoS2 Nanocrystals,"A microscopic control over the origin and dynamics of localised spin centres
in lower dimensional solids turns out to be a key factor for next generation
spintronics and quantum technologies. With the help of low temperature electron
paramagnetic resonance (EPR) measurements, supported by the first-principles
calculations within density functional theory (DFT) formulation, we found the
origin of different high-spin paramagnetic intrinsic charge-centres, Mo3+(4d3)
and Mo2+(4d4) present in the nano-crystalline sulfur deficit hexagonal
molybdenum disulfide (2H-MoS_(2-x)), against the established notion of spin-1/2
, Mo5+ centres. A critical strain generated in the nano-structured 2H-MoS_(2-x)
was found to be very crucial for spin-localization in this layered material.
Indeed, computationally effective proposition of the PBE+U
exchange-correlations within DFT including D3-dispersion corrections found to
be more viable than expensive higher rung of exchange-correlation functionals,
explored earlier. It is also found that the oxygen vacancy of the reduced oxide
phase, embedded in 2H-MoS_(2-x) host lattice, has the longest relaxation times.
Moreover, the temperature dependence of spin-lattice relaxation measurements
reveals a direct process for interstitial spin centres and a Raman process for
both sulfur and oxygen vacancy sites. We expect such observation would be a
valuable pillar for better understanding of the next generation quantum
technologies and device applications.",2312.12805v2
2024-01-22,Gravitational spin-orbit coupling through the third-subleading post-Newtonian order: exploring spin-gauge flexibility,"We build upon recent work by Antonelli et al. [Phys. Rev. Lett. 125 (2020) 1,
011103] to obtain, within the effective-one-body (EOB) formalism, and for an
arbitrary choice of gauge, the third-subleading post-Newtonian (4.5PN)
corrections to the spin-orbit conservative dynamics of spin-aligned binaries.
This is then specialized to: (i) the well-known Damour-Jaranowski-Sch\""afer
($\rm DJS$) gauge, where the dependence on the angular momentum of the
gyro-gravitomagnetic functions $(G_S,G_{S_*})$ is removed and (ii) to an
alternative gauge (called anti-$\rm DJS$ gauge, $\overline{\rm DJS}$) that is
chosen so as to precisely reproduce the Hamiltonian of a spinning test-particle
at linear order in the particle spin and keep the full dependence on the radial
and angular momentum in $(G_S,G_{S_*})$. We use these results to extend by one
perturbative order, in PN sense, the analytical knowledge of the periastron
advance. After performing a suitable factorization and resummation of
$(G_S,G_{S_*})$, the $\rm DJS$ and $\overline{\rm DJS}$ performances are
compared via various gauge-invariant quantities at the EOB last stable circular
orbit. We eventually find some indications that the $\overline{\rm DJS}$ gauge
might be advantageous in the description of the inspiral dynamics of
circularized binaries.",2401.12290v1
2024-01-31,Modeling and analysis of a flexible spinning Euler-Bernoulli beam with centrifugal stiffening and softening: A Linear Fractional Representation approach with application to spinning spacecraft,"The derivation of a linear fractional representation (LFR) model for a
flexible, spinning and uniform Euler-Bernoulli beam is accomplished using the
{Lagrange} technique, fully capturing the centrifugal force generated by the
spinning motion and accounting for its dependence on the angular velocity. This
six degrees of freedom (DOF) model accounts for the behavior of deflection in
the moving body frame, encompassing the bending, traction and torsion dynamics.
The model is also designed to be compliant with the Two-Input-Two-Output Port
(TITOP) approach, which offers the possibility to model complex multibody
mechanical systems, while keeping the uncertain nature of the plant and
condensing all the possible mechanical configurations in a single LFR. To
evaluate the effectiveness of the model, various scenarios are considered and
their results are tabulated. These scenarios include uniform beams with fixed
root boundary conditions for different values of tip mass, root offset and
angular velocity. The results from the analysis of the uniform cantilever beam
are compared with solutions found in the literature and obtained from a
commercial finite element software. Ultimately, this paper presents a multibody
model for a spinning spacecraft mission scenario. A comprehensive analysis of
the system dynamics is conducted, providing insights into the behavior of the
spacecraft under spinning conditions.",2401.17519v1
2024-03-31,Charge and spin current pumping by ultrafast demagnetization dynamics,"The surprising discovery of ultrafast demagnetization -- where electric field
of femtosecond laser pulse couples to electrons of a ferromagnetic (FM) layer
causing its magnetization vector {\em to shrink while not rotating}, is also
assumed to be accompanied by generation of spin current in the direction
orthogonal to electric field. However, understanding of the microscopic origin
of such spin current and how efficiently it can be converted into charge
current, as the putative source of THz radiation, is lacking despite nearly
three decades of intense studies. Here we connect the standard pumping
phenomena driven by microwave precession of magnetization vector replacing
periodic time-dependence of magnetization precession with nonperiodic
time-dependence of demagnetization, as obtained from experiments on
ultrafast-light-driven Ni layer. Applying time-dependent nonequilibrium Green's
functions, able to evolve such setup with arbitrary time dependence, reveals
how demagnetization dynamics pumps both charge and spin currents in directions
both parallel and orthogonal to electric field of laser pulse, even in the
absence of spin-orbit coupling and thereby induced spin-to-charge conversion
mechanisms. Although pumped currents follow $dM_z/dt$ in some setups, this
becomes obscured when NM layers are disconnected and pumped currents start to
reflect from FM boundaries (as is the case of experimental setups). Finally, we
use the Jefimenko equations to compute electromagnetic radiation by charge
current pumped in disconnected setup during demagnetization, or later during
its slow recovery, unraveling that radiated electric field only in the former
time interval exhibits features in 0.1--30 THz frequency range probed
experimentally or explored for applications of spintronic THz emitters.",2404.00779v1
2020-04-23,Simulation of complex dynamics of mean-field $p$-spin models using measurement-based quantum feedback control,"We study the application of a new method for simulating nonlinear dynamics of
many-body spin systems using quantum measurement and feedback [Mu\~noz-Arias et
al., Phys. Rev. Lett. 124, 110503 (2020)] to a broad class of many-body models
known as $p$-spin Hamiltonians, which describe Ising-like models on a
completely connected graph with $p$-body interactions. The method simulates the
desired mean field dynamics in the thermodynamic limit by combining
nonprojective measurements of a component of the collective spin with a global
rotation conditioned on the measurement outcome. We apply this protocol to
simulate the dynamics of the $p$-spin Hamiltonians and demonstrate how
different aspects of criticality in the mean-field regime are readily
accessible with our protocol. We study applications including properties of
dynamical phase transitions and the emergence of spontaneous symmetry breaking
in the adiabatic dynamics of the collective spin for different values of the
parameter $p$. We also demonstrate how this method can be employed to study the
quantum-to-classical transition in the dynamics continuously as a function of
system size.",2004.11412v2
2020-05-07,Coherent dynamics in frustrated coupled parametric oscillators,"We explore the coherent dynamics in a small network of three coupled
parametric oscillators and demonstrate the effect of frustration on the
persistent beating between them. Since a single-mode parametric oscillator
represents an analog of a classical Ising spin, networks of coupled parametric
oscillators are considered as simulators of Ising spin models, aiming to
efficiently calculate the ground state of an Ising network - a computationally
hard problem. However, the coherent dynamics of coupled parametric oscillators
can be considerably richer than that of Ising spins, depending on the nature of
the coupling between them (energy preserving or dissipative), as was recently
shown for two coupled parametric oscillators. In particular, when the
energy-preserving coupling is dominant, the system displays everlasting
coherent beats, transcending the Ising description. Here, we extend these
findings to three coupled parametric oscillators, focusing in particular on the
effect of frustration of the dissipative coupling. We theoretically analyze the
dynamics using coupled nonlinear Mathieu's equations, and corroborate our
theoretical findings by a numerical simulation that closely mimics the dynamics
of the system in an actual experiment. Our main finding is that frustration
drastically modifies the dynamics. While in the absence of frustration the
system is analogous to the two-oscillator case, frustration reverses the role
of the coupling completely, and beats are found for small energy-preserving
couplings.",2005.03562v2
2020-09-13,Perfect transmission and perfect reflection of Bogoliubov quasiparticles in a dynamically unstable Bose-Einstein condensate,"The Nambu-Goldstone (NG) mode in a Bose-Einstein condensate (BEC) transmits a
potential barrier with probability 1 in the zero-energy limit, which is known
as the anomalous tunneling. In this paper, we investigate the tunneling
properties of quasiparticles in a dynamically unstable BEC. We prepare a
multi-component BEC (binary and spin-1 BEC) in a dynamically unstable state and
solve the tunneling problem of the spin-wave excitation from the condensate. We
find that the perfect transmission occurs even when the BEC is dynamically
unstable if the spin-wave is the NG mode. Here, the mode that exhibits the
perfect transmission is the dynamically unstable spin-wave mode, which is a
pure-imaginary-eigenvalue solution of the Bogoliubov-de Gennes equation. Hence,
we should take the zero-energy limit along not the real axis but the imaginary
axis. We also demonstrate the existence of the perfect reflection of a
dynamically unstable mode at the point where the imaginary part of the
eigenvalue takes its maximum. In this case, the incident and reflected waves
destructively interfere, and the amplitude of the quasiparticle wave function
is strongly suppressed. We numerically confirm that the perfect reflection is a
generic nature of dynamically unstable modes and not related to the NG mode.",2009.05998v1
2023-12-01,"From Spin States to Socially Integrated Ising Models: Proposed Applications of Graph States, Stabilizer States, Toric States to Opinion Dynamics","Recent research has developed the Ising model from physics, especially
statistical mechanics, and it plays an important role in quantum computing,
especially quantum annealing and quantum Monte Carlo methods. The model has
also been used in opinion dynamics as a powerful tool for simulating social
interactions and opinion formation processes. Individual opinions and
preferences correspond to spin states, and social pressure and communication
dynamics are modeled through interactions between spins. Quantum computing
makes it possible to efficiently simulate these interactions and analyze more
complex social networks.Recent research has incorporated concepts from quantum
information theory such as Graph State, Stabilizer State, and Surface Code (or
Toric Code) into models of opinion dynamics. The incorporation of these
concepts allows for a more detailed analysis of the process of opinion
formation and the dynamics of social networks. The concepts lie at the
intersection of graph theory and quantum theory, and the use of Graph State in
opinion dynamics can represent the interdependence of opinions and networks of
influence among individuals. It helps to represent the local stability of
opinions and the mechanisms for correcting misunderstandings within a social
network. It allows us to understand how individual opinions are subject to
social pressures and cultural influences and how they change over
time.Incorporating these quantum theory concepts into opinion dynamics allows
for a deeper understanding of social interactions and opinion formation
processes. Moreover, these concepts can provide new insights not only in the
social sciences, but also in fields as diverse as political science, economics,
marketing, and urban planning.",2312.00862v1
2024-03-06,Bath-induced interactions and transient dynamics in open quantum systems at strong coupling: Effective Hamiltonian approach,"Understanding the dynamics of dissipative quantum systems, particularly
beyond the weak coupling approximation, is central to various quantum
applications. While numerically exact methods provide accurate solutions, they
often lack the analytical insight provided by theoretical approaches. In this
study, we employ the recently-developed method dubbed the \emph{effective
Hamiltonian theory} to understand the dynamics of system-bath configurations
without resorting to a perturbative description of the system-bath coupling
energy. Through a combination of mapping steps and truncation, the effective
Hamiltonian theory offers both analytical insights into signatures of strong
couplings in open quantum systems and a straightforward path for numerical
simulations. To validate the accuracy of the method, we apply it to two
canonical models: a single spin immersed in a bosonic bath and two
noninteracting spins in a common bath. In both cases, we study the transient
regime and the steady state limit at nonzero temperature, and spanning
system-bath interactions from the weak to the strong regime. By comparing the
results of the effective Hamiltonian theory with numerically exact simulations,
we show that although the former overlooks non-Markovian features in the
transient equilibration dynamics, it correctly captures non-perturbative
bath-generated couplings between otherwise non-interacting spins as observed in
their synchronization dynamics and correlations. Altogether, the effective
Hamiltonian theory offers a powerful approach to understanding strong coupling
dynamics and thermodynamics, capturing the signatures of such interactions in
both relaxation dynamics and in the steady state limit.",2403.03386v1
2017-02-06,Loschmidt echo in many-spin systems: a quest for intrinsic decoherence and emergent irreversibility,"If a magnetic polarization excess is locally injected in a crystal of
interacting spins, this ""excitation"" would spread as consequence of spin-spin
interactions. Such an apparently irreversible process is known as spin
diffusion and it can lead the system back to ""equilibrium"". Even so, a unitary
quantum dynamics would ensure a precise memory of the non-equilibrium initial
condition. Then, if at certain time, say $t/2$, an experimental protocol
reverses the many-body dynamics, it would drive the system back to the initial
non-equilibrium state at time $t$. As a matter of fact, the reversal is always
perturbed by small experimental imperfections and/or uncontrolled internal or
environmental degrees of freedom. This limits the amount of signal $M(t)$
recovered locally at time $t$. The degradation of $M(t)$ accounts for these
perturbations, which can also be seen as the sources of decoherence. This idea
defines the Loschmidt echo (LE), which embodies the various time-reversal
procedures implemented in nuclear magnetic resonance. Here, we present an
invitation to the study of the LE following the pathway induced by the
experiments. With such a purpose, we provide a historical and conceptual
overview that briefly revisits selected phenomena that underlie the LE
dynamics, ultimately leading to the discussion of irreversibility as an
emergent phenomenon. In addition, we introduce the LE formalism by means of
spin-spin correlation functions and we present new results that could trigger
new experiments and theoretical ideas. In particular, we propose to transform
an initially localized excitation into a more complex initial state, enabling a
dynamically prepared LE. This induces a global definition of the LE in terms of
the raw overlap between many-body wave functions. Our results show that as the
complexity of the prepared state increases, it becomes more fragile towards
small perturbations.",1702.01475v1
2018-05-18,Hamiltonian formulation of general relativity and post-Newtonian dynamics of compact binaries,"Hamiltonian formalisms provide powerful tools for the computation of
approximate analytic solutions of the Einstein field equations. The
post-Newtonian computations of the explicit analytic dynamics and motion of
compact binaries are discussed within the most often applied
Arnowitt-Deser-Misner formalism. The obtention of autonomous Hamiltonians is
achieved by the transition to Routhians. Order reduction of higher derivative
Hamiltonians results in standard Hamiltonians. Tetrad representation of general
relativity is introduced for the tackling of compact binaries with spinning
components. Configurations are treated where the absolute values of the spin
vectors can be considered constant. Compact objects are modeled by use of Dirac
delta functions and their derivatives. Consistency is achieved through
transition to d-dimensional space and application of dimensional
regularization. At the fourth post-Newtonian level, tail contributions to the
binding energy show up. The conservative spin-dependent dynamics finds explicit
presentation in Hamiltonian form through next-to-next-to-leading-order
spin-orbit and spin1-spin2 couplings and to leading-order in the cubic and
quartic in spin interactions. The radiation reaction dynamics is presented
explicitly through the third-and-half post-Newtonian order for spinless
objects, and, for spinning bodies, to leading-order in the spin-orbit and
spin1-spin2 couplings. The most important historical issues get pointed out.",1805.07240v4
2018-08-03,Decoupled spin dynamics in the rare-earth orthoferrite YbFeO$_3$: Evolution of magnetic excitations through the spin-reorientation transition,"In this paper we present a comprehensive study of magnetic dynamics in the
rare-earth orthoferrite YbFeO$_3$ at temperatures below and above the
spin-reorientation (SR) transition $T_{\mathrm{SR}}=7.6$ K, in magnetic fields
applied along the $a, b$ and $c$ axes. Using single-crystal inelastic neutron
scattering, we observed that the spectrum of magnetic excitations consists of
two collective modes well separated in energy: 3D gapped magnons with a
bandwidth of $\sim$60 meV, associated with the antiferromagnetically (AFM)
ordered Fe subsystem, and quasi-1D AFM fluctuations of $\sim$1 meV within the
Yb subsystem, with no hybridization of those modes. The spin dynamics of the Fe
subsystem changes very little through the SR transition and could be well
described in the frame of semiclassical linear spin-wave theory. On the other
hand, the rotation of the net moment of the Fe subsystem at $T_{\mathrm{SR}}$
drastically changes the excitation spectrum of the Yb subsystem, inducing the
transition between two regimes with magnon and spinon-like fluctuations. At $T
< T_{\mathrm{SR}}$, the Yb spin chains have a well defined field-induced
ferromagnetic (FM) ground state, and the spectrum consists of a sharp
single-magnon mode, a two-magnon bound state, and a two-magnon continuum,
whereas at $T > T_{\mathrm{SR}}$ only a gapped broad spinon-like continuum
dominates the spectrum. In this work we show that a weak quasi-1D coupling
within the Yb subsystem $J_\text{Yb-Yb}$, mainly neglected in previous studies,
creates unusual quantum spin dynamics on the low energy scales. The results of
our work may stimulate further experimental search for similar compounds with
several magnetic subsystems and energy scales, where low-energy fluctuations
and underlying physics could be ""hidden"" by a dominating interaction.",1808.01269v2
2020-11-03,Controlling directed atomic motion and second-order tunneling of a spin-orbit-coupled atom in optical lattices,"We theoretically explore the tunneling dynamics for the tight-binding (TB)
model of a single spin-orbit-coupled atom trapped in an optical lattice
subjected to lattice shaking and to time-periodic Zeeman field. By means of
analytical and numerical methods, we demonstrate that the spin-orbit (SO)
coupling adds some new results to the tunneling dynamics in both multiphoton
resonance and far-off-resonance parameter regimes. When the driving frequency
is resonant with the static Zeeman field (multi-photon resonances), we obtain
an unexpected new dynamical localization (DL) phenomenon where the single
SO-coupled atom is restricted to making perfect two-site Rabi oscillation
accompanied by spin flipping.By using the unconventional DL phenomenon, we are
able to generate a ratchetlike effect which enables directed atomic motion
towards different directions and accompanies periodic spin-flipping under the
action of SO coupling. For the far-off-resonance case, we show that by
suppressing the usual inter-site tunneling alone, it is possible to realize a
type of spin-conserving second-order tunneling between next-nearest-neighboring
sites, which is not accessible in the conventional lattice system without SO
coupling. We also show that simultaneous controls of the usual inter-site
tunneling and the SO-coupling-related second-order-tunneling are necessary for
quasienergies flatness (collapse) and completely frozen dynamics to exist.
These results may be relevant to potential applications such as spin-based
quantum information processing and design of novel spintronics devices.",2011.01399v2
2020-11-15,Adiabaticity of spin dynamics in diamond nitrogen vacancy centers in time-dependent magnetic fields,"We study the spin dynamics of diamond nitrogen vacancy (NV) centers in an
oscillating magnetic field along the symmetry axis of the NV in the presence of
transverse magnetic fields. It is well-known that the coupling between the
otherwise degenerate Zeeman levels $|M_S=\pm1\rangle$ due to strain and
electric fields is responsible for a Landau-Zener process near the
pseudo-crossing of the adiabatic energy levels when the axial component of the
oscillating magnetic field changes sign. We derive an effective two-level
Hamiltonian for the NV system that includes coupling between the two levels via
virtual transitions into the third far-detuned level $|M_S=0\rangle$ induced by
transverse magnetic fields. This coupling adds to the coupling due to strain
and electric fields, with a phase that depends on the direction of the
transverse field in the plane perpendicular to the NV axis. Hence, the {\em
total coupling} of the Zeeman levels can be tuned to control the adiabaticity
of spin dynamics by fully or partially compensating the effect of the strain
and electric fields, or by enhancing it. Moreover, by varying the strength and
direction of the transverse magnetic fields, one can determine the strength and
direction of the local strain and electric fields at the position of the NV
center, and even the {\em external} stress and electric field. The nuclear spin
hyperfine interaction is shown to introduce a nuclear spin dependent offset of
the axial magnetic field for which the pseudo-crossing occurs, while the
adiabaticity remains unaffected by the nuclear spin. If the NV center is
coupled to the environment, modeled by a bath with a Gaussian white noise
spectrum, as appropriate for NVs near the diamond surface, then the spin
dynamics is accompanied by relaxation of the Zeeman level populations and
decoherence with a non-monotonic decrease of the purity of the system.",2011.07609v3
2021-06-25,An observable effect of spin inertia in slow magneto-dynamics: Increase of the switching error rates in nanoscale ferromagnets,"The Landau-Lifshitz-Gilbert (LLG) equation, used to model magneto-dynamics in
ferromagnets, tacitly assumes that the angular momentum associated with spin
precession can relax instantaneously when the real or effective magnetic field
causing the precession is turned off. This neglect of ""spin inertia"" is
unphysical and would violate energy conservation. Recently, the LLG equation
was modified to account for inertia effects. The consensus, however, seems to
be that such effects would be unimportant in slow magneto-dynamics that take
place over time scales much longer that the relaxation time of the angular
momentum, which is typically few fs to perhaps ~100 ps in ferromagnets. Here,
we show that there is at least one very serious and observable effect of spin
inertia even in slow magneto-dynamics. It involves the switching error
probability associated with flipping the magnetization of a nanoscale
ferromagnet with an external agent, such as a magnetic field. The switching may
take ~ns to complete when the field strength is close to the threshold value
for switching, which is much longer than the angular momentum relaxation time,
and yet the effect of spin inertia is felt in the switching error probability.
This is because the ultimate fate of a switching trajectory, i.e. whether it
results in success or failure, is influenced by what happens in the first few
ps of the switching action when nutational dynamics due to spin inertia holds
sway. Spin inertia increases the error probability, which makes the switching
more error-prone. This has vital technological significance because it relates
to the reliability of magnetic logic and memory.",2106.13766v1
2023-01-24,Spin Dynamics in van der Waals Magnetic Systems,"The discovery of atomic monolayer magnetic materials has stimulated intense
research activities in the two-dimensional (2D) van der Waals (vdW) materials
community. The field is growing rapidly and there has been a large class of 2D
vdW magnetic compounds with unique properties, which provides an ideal platform
to study magnetism in the atomically thin limit. In parallel, based on
tunneling magnetoresistance and magneto-optical effect in 2D vdW magnets and
their heterostructures, emerging concepts of spintronic and optoelectronic
applications such as spin tunnel field-effect transistors and spin-filtering
devices are explored. While the magnetic ground state has been extensively
investigated, reliable characterization and control of spin dynamics play a
crucial role in designing ultrafast spintronic devices. Ferromagnetic resonance
(FMR) allows direct measurements of magnetic excitations, which provides
insight into the key parameters of magnetic properties such as exchange
interaction, magnetic anisotropy, gyromagnetic ratio, spin-orbit coupling,
damping rate, and domain structure. In this review article, we present an
overview of the essential progress in probing spin dynamics of 2D vdW magnets
using FMR techniques. Given the dynamic nature of this field, we focus mainly
on broadband FMR, optical FMR, and spin-torque FMR, and their applications in
studying prototypical 2D vdW magnets. We conclude with the recent advances in
laboratory- and synchrotron-based FMR techniques and their opportunities to
broaden the horizon of research pathways into atomically thin magnets.",2301.09822v2
2021-04-19,"The MIT Humanoid Robot: Design, Motion Planning, and Control For Acrobatic Behaviors","Demonstrating acrobatic behavior of a humanoid robot such as flips and
spinning jumps requires systematic approaches across hardware design, motion
planning, and control. In this paper, we present a new humanoid robot design,
an actuator-aware kino-dynamic motion planner, and a landing controller as part
of a practical system design for highly dynamic motion control of the humanoid
robot. To achieve the impulsive motions, we develop two new proprioceptive
actuators and experimentally evaluate their performance using our
custom-designed dynamometer. The actuator's torque, velocity, and power limits
are reflected in our kino-dynamic motion planner by approximating the
configuration-dependent reaction force limits and in our dynamics simulator by
including actuator dynamics along with the robot's full-body dynamics. For the
landing control, we effectively integrate model-predictive control and
whole-body impulse control by connecting them in a dynamically consistent way
to accomplish both the long-time horizon optimal control and high-bandwidth
full-body dynamics-based feedback. Actuators' torque output over the entire
motion are validated based on the velocity-torque model including battery
voltage droop and back-EMF voltage. With the carefully designed hardware and
control framework, we successfully demonstrate dynamic behaviors such as back
flips, front flips, and spinning jumps in our realistic dynamics simulation.",2104.09025v1
2000-07-03,Out of Equilibrium Dynamics of the Hopfield Model in its spin-glass phase,"In this work we study numerically the out of equilibrium dynamics of the
Hopfield model for associative memory inside its spin-glass phase. Besides its
interest as a neural network model it can also be considered as a prototype of
fully connected magnetic systems with randomness and frustration. By adjusting
the ratio between the number of stored configurations $p$ and the total number
of neurons $N$ one can control the phase-space structure, whose complexity can
vary between the simple mean-field ferromagnet (when $p=1$) and that of the
Sherrington-Kirkpatrick spin-glass model (for a properly taken limit of an
infinite number of patterns). In particular, little attention has been devoted
to the spin-glass phase of this model. In this work we analyse the two-time
auto-correlation function, the decay of the magnetization and the distribution
of overlaps between states. The results show that within the spin-glass phase
of the model the dynamics exhibits ageing phenomena and presents features that
suggest a non trivial breaking of replica symmetry.",0007036v2
2001-10-18,Damping of spin waves and singularity of the longitudinal modes in the dipolar critical regime of the Heisenberg-ferromagnet EuS,"By inelastic scattering of polarized neutrons near the (200)-Bragg
reflection, the susceptibilities and linewidths of the spin waves and the
longitudinal spin fluctuations were determined separately. By aligning the
momentum transfers q perpendicular to both \delta S_sw and the spontaneous
magnetization M_s, we explored the statics and dynamics of these modes with
transverse polarizations with respect to q. In the dipolar critical regime,
where the inverse correlation length kappa_z(T) and q are smaller than the
dipolar wavenumber q_d, we observe:(i) the static susceptibility of \delta
S_sw^T(q) displays the Goldstone divergence while for \delta S_z^T(q) the
Ornstein-Zernicke shape fits the data with a possible indication of a
thermal(mass-)renormalization at the smallest q-values, i.e. we find
indications for the predicted 1/q divergence of the longitudinal
susceptibility; (ii) the spin wave dispersion as predicted by the
Holstein-Primakoff theory revealing q_d=0.23(1)\AA^{-1}in good agreement with
previous work in the paramagnetic and ferromagnetic regime of EuS; (iii) within
experimental error, the (Lorentzian) linewidths of both modes turn out to be
identical with respect to the q^2-variation, the temperature independence and
the absolute magnitude. Due to the linear dispersion of the spin waves they
remain underdamped for q<q_d. These central results differ significantly from
the well known exchange dominated critical dynamics, but are quantitatively
explained in terms of dynamical scaling and existing data for T>=T_C. The
available mode-mode coupling theory, which takes the dipolar interactions fully
into account, describes the gross features of the linewidths but not all
details of the T- and q-dependencies. PACS: 68.35.Rh, 75.40.Gb",0110371v1
2004-12-08,Glassy dynamics and domains: exact results for the East model,"A general matrix-based scheme for analyzing the long-time dynamics in
kinetically constrained models such as the East model is presented. The
treatment developed here is motivated by the expectation that slowly-relaxing
spin domains of arbitrary size govern the highly cooperative events that lead
to spin relaxation at long times. To account for the role of large spin domains
in the dynamics, a complete basis expressed in terms of domains of all sizes is
introduced. It is first demonstrated that accounting for single domains of all
possible sizes leads to a simple analytical result for the two-time single-spin
correlation function in the East model that is in excellent quantitative
agreement with simulation data for equilibrium spin up density values c greater
or equal to 0.6. It is then shown that including also two neighboring domains
leads to a closed expression that describes the slow relaxation of the system
down to c approximately 0.3. Ingredients of generalizing the method to lower
values of c are also provided, as well as to other models. The main advantage
of this approach is that it gives explicit analytical results and that it
requires neither an arbitrary closure for the memory kernel nor the
construction of an irreducible memory kernel. It also allows one to calculate
quantities that measure heterogeneity in the same framework, as is illustrated
on the neighbor-pair correlation function and the distribution of relaxation
times.",0412211v1
2009-11-22,Entanglement Dynamics and Spin Squeezing of The non-linear Tavis-Cummings model mediated by a Nonlinear Binomial Field,"We show that spin squeezing implies entanglement for quantum
tripartite-state, where the subsystem of the bipartite-state is identical. We
study the relation between spin squeezing parameters and entanglement through
the quantum entropy of a system starts initially in a pure state when the
cavity is binomial. We show that spin squeezing can be a convenient tool to
give some insight into the subsystems entanglement dynamics when the bipartite
subsystem interacts simultaneously with the cavity field subsystem, specially
when the interaction occurs off-resonantly without and with a nonlinear medium
contained in the cavity field subsystem. We illustrate that, in case of large
off-resonance interaction, spin squeezing clarifies the properties of
entanglement almost with full success. However, it is not a general rule when
the cavity is assumed to be filled with a non-linear medium. In this case, we
illustrate that the insight into entanglement dynamics becomes more clearly in
case of a weak nonlinear medium than in strong nonlinear medium. In parallel,
the role of the phase space distribution in quantifying entanglement is also
studied. The numerical results of Husimi $Q$-function show that the integer
strength of the nonlinear medium produces Schr\""{o}dinger cat states which is
necessary for quantum entanglement.",0911.4240v3
2010-10-22,Spin-Transfer Torque Induced Vortex Dynamics in Fe/Ag/Fe Nanopillars,"We report experimental and analytical work on spin-transfer torque induced
vortex dynamics in metallic nanopillars with in-plane magnetized layers. We
study nanopillars with a diameter of 150 nm, containing two Fe layers with a
thickness of 15 nm and 30 nm respectively, separated by a 6 nm Ag spacer. The
sample geometry is such that it allows for the formation of magnetic vortices
in the Fe disks. As confirmed by micromagnetic simulations, we are able to
prepare states where one magnetic layer is homogeneously magnetized while the
other contains a vortex. We experimentally show that in this configuration
spin-transfer torque can excite vortex dynamics and analyze their dependence on
a magnetic field applied in the sample plane. The center of gyration is
continuously dislocated from the disk center, and the potential changes its
shape with field strength. The latter is reflected in the field dependence of
the excitation frequency. In the second part we propose a novel mechanism for
the excitation of the gyrotropic mode in nanopillars with a perfectly
homogeneously magnetized in-plane polarizing layer. We analytically show that
in this configuration the vortex can absorb energy from the spin-polarized
electric current if the angular spin-transfer efficiency function is
asymmetric. This effect is supported by micromagnetic simulations.",1010.4791v2
2011-02-01,Real-time density matrix renormalization group dynamics of spin and charge transport in push-pull polyenes and related systems,"In this paper we investigate the effect of terminal substituents on the
dynamics of spin and charge transport in donor-acceptor substituted polyenes
($D-(CH)_{x}-A$) chains, also known as push-pull polyenes. We employ long-range
correlated model Hamiltonian for the $D-(CH)_{x}-A$ system, and time-dependent
density matrix renormalization group technique for time propagating the wave
packet obtained by injecting a hole at a terminal site, in the ground state of
the system. Our studies reveal that the end groups do not affect spin and
charge velocities in any significant way, but change the amount of charge
transported. We have compared these push-pull systems with donor-acceptor
substituted polymethine imine (PMI), $D-(CHN)_{x}-A$, systems in which besides
electron affinities, the nature of $p_{z}$ orbitals in conjugation also
alternate from site to site. We note that spin and charge dynamics in the PMIs
are very different from that observed in the case of push-pull polyenes, and
within the time scale of our studies, transport of spin and charge leads to the
formation of a ""quasi-static"" state.",1102.0130v4
2015-01-06,Exciton spin dynamics and photoluminescence polarization of CdSe/CdS dot-in-rod nanocrystals in high magnetic fields,"The exciton spin dynamics and polarization properties of the related emission
are investigated in colloidal CdSe/CdS dot-in-rod (DiR) and spherical
core/shell nanocrystal (NC) ensembles by magneto-optical photoluminescence (PL)
spectroscopy in magnetic fields up to 15 T. It is shown that the degree of
circular polarization (DCP) of the exciton emission induced by the magnetic
field is affected by the NC geometry as well as the exciton fine structure and
can provide information on nanorod orientation. A theory to describe the
circular and linear polarization properties of the NC emission in magnetic
field is developed. It takes into account phonon mediated coupling between the
exciton fine structure states as well as the dielectric enhancement effect
resulting from the anisotropic shell of DiR NCs. This theoretical approach is
used to model the experimental results and allows us to explain most of the
measured features. The spin dynamics of the dark excitons is investigated in
magnetic fields by time-resolved photoluminescence. The results highlight the
importance of confined acoustic phonons in the spin relaxation of dark
excitons. The bare core surface as well as the core/shell interface give rise
to an efficient spin relaxation channel, while the surface of core/shell NCs
seems to play only a minor role.",1501.01169v1
2016-02-29,Universal Dynamic Magnetism in Yb-Pyrochlores with Disparate Ground States,"The ytterbium pyrochlore magnets, Yb2B2O7 (B = Sn, Ti, Ge) are well described
by S_eff = 1/2 quantum spins decorating a network of corner-sharing tetrahedra
and interacting via anisotropic exchange. Structurally, only the non-magnetic
B-site cation, and hence, primarily the lattice parameter, is changing across
the series. Nonetheless, a range of magnetic behaviors are observed: the low
temperature magnetism in Yb2Ti2O7 and Yb2Sn2O7 has ferromagnetic character,
while Yb2Ge2O7 displays an antiferromagnetically ordered Neel state at low
temperatures. While the static properties of the ytterbium pyrochlores are
distinct, inelastic neutron scattering measurements reveal a common character
to their exotic spin dynamics. All three ytterbium pyrochlores show a gapless
continuum of spin excitations, resembling over-damped ferromagnetic spin waves
at low Q. Furthermore, the specific heat of the series also follows a common
form, with a broad, high-temperature anomaly followed by a sharp
low-temperature anomaly at T_C or T_N. The novel spin dynamics we report
correlate strongly with the broad specific heat anomaly only, remaining
unchanged across the sharp anomaly. This result suggests that the primary order
parameter in the ytterbium pyrochlores associated with the sharp anomaly is
""hidden"" and not simple magnetic dipole order.",1602.09011v1
2016-07-29,"A rock-salt type Li-based oxide, Li3Ni2RuO6, exhibiting a chaotic ferrimagnetism with cluster spin-glass dynamics and thermally frozen charge carriers","The area of research to discover new Li containing materials and to
understand their physical properties has been of constant interest due to
applications potential for rechargeable batteries. Here, we present the results
of magnetic investigations on a Li compound, Li3Ni2RuO6, which was believed to
be a ferrimagnet below 80K. While our neutron diffraction (ND) and isothermal
magnetization (M) data support ferrimagnetism, more detailed magnetic studies
establish that this ferrimagnetic phase exhibits some features similar to
spin-glasses. In addition, we find another broad magnetic anomaly around 40-55
K in magnetic susceptibility, attributable to cluster spin-glass phenomenon.
Gradual dominance of cluster spin-glass dynamics with a decrease of temperature
(T) and the apparent spread in freezing temperature suggest that the
ferrimagnetism of this compound is a chaotic one. The absence of a unique
freezing temperature for a crystalline material is interesting. In addition,
pyroelectric current data reveals a feature in the range 40-50 K, attributable
to thermally stimulated depolarization current. We hope this finding motivates
future work to explore whether there is any intriguing correlation of such a
feature with spin-glass dynamics. We attribute these magnetic and electric
dipole anomalies to the crystallographic disorder intrinsic to this compound.",1607.08689v1
2016-09-29,Multiscale Model Approach for Magnetization Dynamics Simulations,"Simulations of magnetization dynamics in a multiscale environment enable
rapid evaluation of the Landau-Lifshitz-Gilbert equation in a mesoscopic sample
with nanoscopic accuracy in areas where such accuracy is required. We have
developed a multiscale magnetization dynamics simulation approach that can be
applied to large systems with spin structures that vary locally on small length
scales. To implement this, the conventional micromagnetic simulation framework
has been expanded to include a multiscale solving routine. The software
selectively simulates different regions of a ferromagnetic sample according to
the spin structures located within in order to employ a suitable discretization
and use either a micromagnetic or an atomistic model. To demonstrate the
validity of the multiscale approach, we simulate the spin wave transmission
across the regions simulated with the two different models and different
discretizations. We find that the interface between the regions is fully
transparent for spin waves with frequency lower than a certain threshold set by
the coarse scale micromagnetic model with no noticeable attenuation due to the
interface between the models. As a comparison to exact analytical theory, we
show that in a system with Dzyaloshinskii-Moriya interaction leading to spin
spiral, the simulated multiscale result is in good quantitative agreement with
the analytical calculation.",1609.09295v1
2017-02-27,Current Induced Damping of Nanosized Quantum Moments in the Presence of Spin-Orbit Interaction,"Motivated by the need to understand current-induced magnetization dynamics at
the nanoscale, we have developed a formalism, within the framework of Keldysh
Green function approach, to study the current-induced dynamics of a
ferromagnetic (FM) nanoisland overlayer on a spin-orbit-coupling (SOC) Rashba
plane. In contrast to the commonly employed classical micromagnetic LLG
simulations the magnetic moments of the FM are treated {\it quantum
mechanically}. We obtain the density matrix of the whole system consisting of
conduction electrons entangled with the local magnetic moments and calculate
the effective damping rate of the FM. We investigate two opposite limiting
regimes of FM dynamics: (1) The precessional regime where the magnetic
anisotropy energy (MAE) and precessional frequency are smaller than the
exchange interactions, and (2) The local spin-flip regime where the MAE and
precessional frequency are comparable to the exchange interactions. In the
former case, we show that due to the finite size of the FM domain, the
\textquotedblleft Gilbert damping\textquotedblright does not diverge in the
ballistic electron transport regime, in sharp contrast to Kambersky's breathing
Fermi surface theory for damping in metallic FMs. In the latter case, we show
that above a critical bias the excited conduction electrons can switch the
local spin moments resulting in demagnetization and reversal of the
magnetization. Furthermore, our calculations show that the bias-induced
antidamping efficiency in the local spin-flip regime is much higher than that
in the rotational excitation regime.",1702.08408v2
2018-04-10,Spinon Fractionalization from Dynamic Structure Factor of Spin-1/2 Heisenberg Antiferromagnet on the Kagome Lattice,"We study dynamical spin structure factor (DSSF) of S = 1/2 Heisenberg model
on the kagome lattice (KAFM) by means of density-matrix renormalization group.
By comparison with the well-defined magnetic ordered state and chiral spin
liquid sitting nearby in the phase diagram, the KAFM with the nearest-neighbor
interaction shows distinct dynamical response behaviors. First of all, the DSSF
displays important spectral intensity predominantly at low frequency region
around Q = M point in momentum space, and shows a broad spectral distribution
at high frequency region for momenta along the boundary of the extended
Brillouin zone. Secondly, spinon excitation spectrum is identified from
momentum and energy resolved DSSF, which shows critical behavior with much
reduced spectrum intensity comparing to the neighboring chiral spin liquid. By
adding a weak Dzyaloshinkii-Moriya interaction, the DSSF demonstrates a strong
sensitivity to the boundary condition smore consistent with a gapless spin
liquid. These results capture the main observations in the inelastic neutron
scattering measurements of herbertsmithite, and indicate the spin liquid nature
of the ground state with fractionalized spinon excitations. By following the
DSSF crossing the quantum phase transition between the CSL and the magnetical
ordered phase, we identify the spinon condensation driving the quantum phase
transition.",1804.03333v1
2017-04-24,Spin dynamics and magnetic-field-induced polarization of excitons in ultrathin GaAs/AlAs quantum wells with indirect band gap and type-II band alignment,"The exciton spin dynamics are investigated both experimentally and
theoretically in two-monolayer-thick GaAs/AlAs quantum wells with an indirect
band gap and a type-II band alignment. The magnetic-field-induced circular
polarization of photoluminescence, $P_c$, is studied as function of the
magnetic field strength and direction as well as sample temperature. The
observed nonmonotonic behaviour of these functions is provided by the interplay
of bright and dark exciton states contributing to the emission. To interpret
the experiment, we have developed a kinetic master equation model which
accounts for the dynamics of the spin states in this exciton quartet, radiative
and nonradiative recombination processes, and redistribution of excitons
between these states as result of spin relaxation. The model offers
quantitative agreement with experiment and allows us to evaluate, for the
studied structure, the heavy-hole $g$ factor, $g_{hh}=+3.5$, and the spin
relaxation times of electron, $\tau_{se} = 33~\mu$s, and hole, $\tau_{sh} =
3~\mu$s, bound in the exciton.",1704.07277v1
2018-05-14,"The dynamics of asteroid rotation, governed by YORP effect: the kinematic ansatz","The main motivation of this research is the analytical exploration of the
dynamics of asteroid rotation when it moves in elliptic orbit through Space.
According to the results of Efroimsky, Frouard (2016), various perturbations
(collisions, close encounters, YORP effect) destabilize the rotation of a small
body (asteroid), deviating it from the initial-current spin state. This yields
evolution of the spin towards rotation about maximal-inertia axis due to the
process of nutation relaxation or to the proper spin state corresponding to
minimal energy with a fixed angular momentum. We consider in our research the
aforementioned spin state of asteroid but additionally under non-vanishing
influence of the effects of non-gravitational nature (YORP effect), which is
destabilizing the asteroid rotation during its motion far from giant planets.
Meanwhile, new solutions for asteroid rotation dynamics in case of negligible
(time-dependent) applied torques have been obtained in our development. New
method for solving Euler equations for rigid body rotation is suggested; an
elegant example for evolution of spin towards the rotation about
maximal-inertia axis is calculated.",1805.06304v2
2012-04-02,Floquet spin states in graphene under ac driven spin-orbit interaction,"We study the role of periodically driven time-dependent Rashba spin-orbit
coupling (RSOC) on a monolayer graphene sample. After recasting the originally
$4\times 4$ system of dynamical equations as two time-reversal related
two-level problems, the quasi-energy spectrum and the related dynamics are
investigated via various techniques and approximations. In the static case the
system is a gapped at the Dirac point. The rotating wave approximation (RWA)
applied to the driven system unphysically preserves this feature, while the
Magnus-Floquet approach as well as a numerically exact evaluation of the
Floquet equation show that this gap is dynamically closed. In addition, a
sizable oscillating pattern of the out-of-plane spin polarization is found in
the driven case for states which completely unpolarized in the static limit.
Evaluation of the autocorrelation function shows that the original uniform
interference pattern corresponding to time-independent RSOC gets distorted. The
resulting structure can be qualitatively explained as a consequence of the
transitions induced by the ac driving among the static eigenstates, i.e., these
transitions modulate the relative phases that add up to give the quantum
revivals of the autocorrelation function. Contrary to the static case, in the
driven scenario, quantum revivals (suppresions) are correlated to spin up
(down) phases.",1204.0404v2
2017-06-20,Dynamical characteristics of electromagnetic field under conditions of total reflection,"The dynamical characteristics of electromagnetic fields include energy,
momentum, angular momentum (spin) and helicity. We analyze their spatial
distributions near the planar interface between two transparent and
non-dispersive media, when the incident monochromatic plane wave with arbitrary
polarization is totally reflected, and an evanescent wave is formed in the
medium with lower optical density. Based on the recent arguments in favor of
the Minkowski definition of the electromagnetic momentum in a material medium
[Phys. Rev. A 83, 013823 (2011); 86, 055802 (2012); Phys. Rev. Lett. 119,
073901 (2017)], we derive the explicit expressions for the dynamical
characteristics in both media, with special attention to their behavior at the
interface. Especially, the ""extraordinary"" spin and momentum components
orthogonal to the plane of incidence are described, and the canonical (spin -
orbital) momentum decomposition is performed that contains no singular terms.
The field energy, helicity, the spin momentum and orbital momentum components
are everywhere regular but experience discontinuities at the interface; the
spin components parallel to the interface appear to be continuous, which
testifies for the consistency of the adopted Minkowski picture. The results
supply a meaningful example of the electromagnetic momentum decomposition, with
separation of spatial and polarization degrees of freedom, in inhomogeneous
media, and can be used in engineering the structured fields designed for
optical sorting, dispatching and micromanipulation.",1706.06263v4
2018-09-23,"Electronic structure and spin dynamics of ACo2As2 (A=Ba, Sr, Ca)","The electronic structures, charge and spin dynamics of the cobalt pnictide
compounds ACo2As2 (A=Ba, Sr, Ca) in the paramagnetic state are investigated by
using density functional theory combined with dynamical mean-field theory. In
contrast to their iron counterparts, these cobalt pnictide compounds have
three-dimensional electronic structures and strong ferromagnetic low-energy
spin excitations. The Co 3d eg orbitals dominate the electronic states around
the Fermi level and have stronger electronic correlation strength than the Co
3d t2g orbitals. The overall electronic correlation strength is much weaker
than that in the iron arsenides, however, the most strongly correlated Co 3d
x2-y2 orbital, especially in CaCo2As2, has electronic correlation strength
comparable to Fe 3d t2g orbitals in iron arsenides. ACo2As2 (A=Ba, Sr, Ca)
shows similar electronic structures where a conduction band of primarily Co 3d
x2-y2 orbital character is close to a Van Hove singularity around the
Brillouin-zone corner, which promotes ferromagnetic low-energy spin
excitations. Originated from its increased nearest-neighbor Co-Co distance and
significantly reduced As height from the Co plane, the strong electronic
correlation strength and close proximity to the Van Hove singularity of the Co
3d x2-y2 orbital in CaCo2As2 is responsible for its unique A-type
antiferromagnetic order observed in experiments. In comparison, despite
substantial ferromagnetic low-energy spin excitations, BaCo2As2 and SrCo2As2
remain paramagnetic down to very low temperature because the Co 3d x2-y2
orbital has weaker electronic correlation strength and is further away from the
Van Hove singularity.",1809.08550v1
2019-09-20,Impact of disorder on dynamics and ordering in the honeycomb lattice iridate Na$_2$IrO$_3$,"Kitaev's honeycomb spin-liquid model and its proposed realization in
materials such as $\alpha$-RuCl$_3$, Li$_2$IrO$_3$ and Na$_2$IrO$_3$ continue
to present open questions about how the dynamics of a spin-liquid are modified
in the presence of non-Kitaev interactions as well as the presence of
inhomogeneities. Here we use $^{23}$Na nuclear magnetic resonance to probe both
static and dynamical magnetic properties in single crystal Na$_2$IrO$_3$. We
find that the NMR shift follows the bulk susceptibility above 30 K but deviates
from it below; moreover below $T_N$ the spectra show a broad distribution of
internal magnetic fields. Both of these results provide evidence for
inequivalent magnetic sites at low temperature, suggesting inhomogeneities are
important for the magnetism. The spin-lattice relaxation rate is isotropic and
diverges at $T_N$, suggesting that the Kitaev cubic axes may control the
critical quantum spin fluctuations. In the ordered state, we observe gapless
excitations, which may arise from site substitution, emergent defects from
milder disorder, or possibly be associated with nearby quantum paramagnetic
states distinct from the Kitaev spin liquid.",1909.09356v2
2020-04-24,Persistent spin dynamics and absence of spin freezing in the $H$-$T$ phase diagram of the 2D triangular antiferromagnet YbMgGaO$_4$,"We report results of muon spin relaxation and rotation ($\mu$SR) experiments
on the spin-liquid candidate~YbMgGaO$_{4}$. No static magnetism $\gtrsim
0.003\mu_B$ per Yb ion, ordered or disordered, is observed down to 22~mK, a
factor of two lower in temperature than previous measurements. Persistent
(temperature-independent) spin dynamics are observed up to 0.20~K and at least
1~kOe, thus extending previous zero-field $\mu$SR results over a substantial
region of the $H$-$T$ phase diagram. Knight shift measurements in a 10-kOe
transverse field reveal two lines with nearly equal amplitudes. Inhomogeneous
muon depolarization in a longitudinal field, previously characterized by
stretched-exponential relaxation due to spatial inhomogeneity, is fit equally
well with two exponentials, also of equal amplitudes. We attribute these
results to two interstitial muon sites in the unit cell, rather than disorder
or other spatial distribution. Further evidence for this attribution is found
from agreement between the ratio of the two measured relaxation rates and
calculated mean-square local Yb$^{3+}$ dipolar fields at candidate muon sites.
Zero-field data can be understood as a combination of two-exponential dynamic
relaxation and quasistatic nuclear dipolar fields.",2004.11508v2
2020-12-07,Topological and dynamical features of periodically driven spin ladders,"Studies of periodically driven one-dimensional many-body systems have
advanced our understanding of complex systems and stimulated promising
developments in quantum simulation. It is hence of interest to go one step
further, by investigating the topological and dynamical aspects of periodically
driven spin ladders as clean quasi-one-dimensional systems with spin-spin
interaction in the rung direction. Specifically, we find that such systems
display subharmonic magnetization dynamics reminiscent to that of discrete time
crystals (DTCs) at finite system sizes. Through the use of generalized
Jordan-Wigner transformation, this feature can be attributed to presence of
corner Majorana $\pi$ modes (MPMs), which are of topological origin, in the
systems' equivalent Majorana lattice. Special emphasis is placed on how the
coupling in the rung direction of the ladder prevents degeneracy from occurring
between states differing by a single spin excitation, thus preserving the
MPM-induced $\pi/T$ quasienergy spacing of the Floquet eigenstates in the
presence of parameter imperfection. This feature, which is absent in their
strict one-dimensional counterparts, may yield fascinating consequences in
future studies of higher dimensional Floquet many-body systems.",2012.03443v3
2018-07-05,Thermally-robust spin correlations between two 85Rb atoms in an optical microtrap,"The complex collisional properties of atoms fundamentally limit
investigations into a range of processes in many-atom ensembles. In contrast,
the bottom-up assembly of few- and many-body systems from individual atoms
offers a controlled approach to isolating and studying such collisional
processes. Here, we use optical tweezers to individually assemble pairs of
trapped $^{85}$Rb atoms, and study the spin dynamics of the two-body system in
a thermal state. The spin-2 atoms show strong pair correlation between magnetic
sublevels on timescales exceeding one second, with measured relative number
fluctuations $11.9\pm0.3$ dB below quantum shot noise, limited only by
detection efficiency. Spin populations display relaxation dynamics consistent
with simulations and theoretical predictions for $^{85}$Rb spin interactions,
and contrary to the coherent spin waves witnessed in finite-temperature
many-body experiments and zero-temperature two-body experiments. Our
experimental approach offers a versatile platform for studying two-body quantum
dynamics and may provide a route to thermally-robust entanglement generation.",1807.01822v2
2018-08-17,Floquet states of Valley-Polarized Metal with One-way Spin or Charge Transport in Zigzag Nanoribbons,"Two-dimensional Floquet systems consisting of irradiated valley-polarized
metal are investigated. For the corresponding static systems, we consider two
graphene models of valley-polarized metal with either a staggered sublattice or
uniform intrinsic spin-orbital coupling, whose Dirac point energies are
different from the intrinsic Fermi level. If the frequency of irradiation is
appropriately designed, the largest dynamical gap (first-order dynamical gap)
opens around the intrinsic Fermi level. In the presence of the irradiation, two
types of edge state appear at the zigzag edge of semi-infinite sheet with
energy within the first-order dynamical gap: the Floquet edge states and the
strongly localized edge states. In narrow zigzag nanoribbons, the Floquet edge
states are gapped out by the finite size effect, and the strongly localized
edge states remain gapless. As a result, the conducting channels of the
nanoribbons consist of the strongly localized edge states. Under the first and
second model, the strongly localized edge states carry one-way spin polarized
and one-way charge current around the intrinsic Fermi level, respectively.
Thus, the narrow zigzag nanoribbons of the first and second model have
asymmetric spin and charge transmission rates, respectively. Quantum-transport
calculations predict sizable pumped currents of charge and spin, which could be
controlled by the Fermi level.",1808.05721v4
2018-12-31,Nonlinear Fluctuating Hydrodynamics for the Classical XXZ Spin Chain,"Using the framework of nonlinear fluctuating hydrodynamics (NFH), we examine
equilibrium spatio-temporal correlations in classical ferromagnetic spin chains
with nearest neighbor interactions. In particular, we consider the classical
XXZ-Heisenberg spin chain (also known as Lattice Landau Lifshitz or LLL model)
evolving deterministically and chaotically via Hamiltonian dynamics, for which
energy and $z$-magnetization are the only locally conserved fields. For the
easy-plane case, this system has a low-temperature regime in which the
difference between neighboring spin's angular orientations in the XY plane is
an \textit{almost conserved} field. According to the predictions of NFH, the
dynamic correlations in this regime exhibit a heat peak and propagating sound
peaks, all with anomalous broadening. We present a detailed molecular dynamics
test of these predictions and find a reasonably accurate verification. We find
that, in a suitable intermediate temperature regime, the system shows two sound
peaks with Kardar-Parisi-Zhang (KPZ) scaling and a heat peak where the expected
anomalous broadening is less clear. In high temperature regimes of both easy
plane and easy axis case of LLL, our numerics show clear diffusive spin and
energy peaks and absence of any sound modes, as one would expect. We also
simulate an integrable version of the XXZ-model, for which the ballistic
component instead moves with a broad range of speeds rather than being
concentrated in narrower peaks around the sound speed.",1901.00024v2
2019-03-05,Axial Kinetic Theory and Spin Transport for Fermions with Arbitrary Mass,"We derive the quantum kinetic theory for fermions with arbitrary mass in a
background electromagnetic field from the Wigner-function approach. Since spin
of massive fermions is a dynamical degree of freedom, the kinetic equations
with the leading-order quantum corrections describe entangled dynamics of not
only the vector- and axial-charge distributions but also of the spin
polarization. Therefore, we obtain one scalar and one axial-vector kinetic
equations with magnetization currents pertinent to the spin-orbit interaction.
We show that our results smoothly reduce to the massless limit where the spin
of massless fermions is no longer an independent dynamical degree of freedom
but is enslaved by the chirality and momentum and the accordingly kinetic
equations turn into the chiral kinetic theory for Weyl fermions. We provide a
kinetic theory covering both the massive and massless cases, and hence resolves
the problem in constructing the bridge between them. Such generalization may be
crucial for applications to various physical systems. Based on our kinetic
equations, we discuss the anomalous currents transported by massive fermions in
thermal equilibrium.",1903.01653v2
2019-04-08,Effect of orbital eccentricity on the dynamics of precessing compact binaries,"We study precession dynamics of generic binary black holes in eccentric
orbits using an effective potential based formalism derived in [M. Kesden et
al., PRL {\bf 114}, 081103 (2015)]. This effective potential is used to
classify binary black holes into three mutually exclusive spin morphologies.
During the inspiral phase, binaries make transitions from one morphology to
others. We evolve a population of binary black holes from an initial separation
of $1000\mathbf{M}$ to a final separation of $10\mathbf{M}$ using
post-Newtonian accurate evolution equations. We find that, given suitable
initial conditions, a binary's eccentricity can follow one of three distinct
evolutionary patterns: (i) eccentricity monotonically increasing until final
separation, (ii) eccentricity rising after decaying to a minimum value, and
(iii) eccentricity monotonically decreasing throughout the inspiral. The
monotonic growth or growth after reaching a certain minimum of eccentricity is
due to the effect of 2PN spin-spin coupling. Further, we investigate the
morphology transitions in eccentric binaries and find that the probability of
such binaries transiting from one to other is similar to those in circular
orbits, implying that eccentricity plays a sub-dominant role in spin morphology
evolution of a precessing binary black hole. We, hence, argue that the
morphological classification of spin precession dynamics is a robust tool to
constrain the formation channels of binaries with arbitrary eccentricity as
well.",1904.03985v2
2020-05-05,Dimensional crossover in spin Hall oscillators,"Auto-oscillations of magnetization driven by direct spin current have been
previously observed in multiple quasi-zero-dimensional (0D) ferromagnetic
systems such as nanomagnets and nanocontacts. Recently, it was shown that pure
spin Hall current can excite coherent auto-oscillatory dynamics in
quasi-one-dimensional (1D) ferromagnetic nanowires but not in
quasi-two-dimensional (2D) ferromagnetic films. Here we study the 1D to 2D
dimensional crossover of current-driven magnetization dynamics in wire-based
Pt/$\mathrm{Ni}_{80}\mathrm{Fe}_{20}$ bilayer spin Hall oscillators via varying
the wire width. We find that increasing the wire width results in an increase
of the number of excited auto-oscillatory modes accompanied by a decrease of
the amplitude and coherence of each mode. We also observe a crossover from a
hard to a soft onset of the auto-oscillations with increasing the wire width.
The amplitude of auto-oscillations rapidly decreases with increasing
temperature suggesting that interactions of the phase-coherent auto-oscillatory
modes with incoherent thermal magnons plays an important role in suppression of
the auto-oscillatory dynamics. Our measurements set the upper limit on the
dimensions of an individual spin Hall oscillator and elucidate the mechanisms
leading to suppression of coherent auto-oscillations with increasing oscillator
size.",2005.01925v2
2020-06-15,Optical computation of a spin glass dynamics with tunable complexity,"Spin Glasses (SG) are paradigmatic models for physical, computer science,
biological and social systems. The problem of studying the dynamics for SG
models is NP hard, i.e., no algorithm solves it in polynomial time. Here we
implement the optical simulation of a SG, exploiting the N segments of a
wavefront shaping device to play the role of the spin variables, combining the
interference at downstream of a scattering material to implement the random
couplings between the spins (the J ij matrix) and measuring the light intensity
on a number P of targets to retrieve the energy of the system. By implementing
a plain Metropolis algorithm, we are able to simulate the spin model dynamics,
while the degree of complexity of the potential energy landscape and the region
of phase diagram explored is user-defined acting on the ratio the P/N = \alpha.
We study experimentally, numerically and analytically this peculiar system
displaying a paramagnetic, a ferromagnetic and a SG phase, and we demonstrate
that the transition temperature T g to the glassy phase from the paramagnetic
phase grows with \alpha. With respect to standard in silico approach, in the
optical SG interaction terms are realized simultaneously when the independent
light rays interferes at the target screen, enabling inherently parallel
measurements of the energy, rather than computations scaling with N as in
purely in silico simulations.",2006.08378v2
2021-03-30,Photoinduced Transient States of Antiferromagnetic Orderings in La${}_{1/3}$Sr${}_{2/3}$FeO${}_{3}$ and SrFeO${}_{3}$ Thin Films Observed through Time-resolved Resonant Soft X-ray Scattering,"The relationship between the magnetic interaction and photoinduced dynamics
in antiferromagnetic perovskites is investigated in this study. In
La${}_{1/3}$Sr${}_{2/3}$FeO${}_{3}$ thin films, commensurate spin ordering is
accompanied by charge disproportionation, whereas SrFeO${}_{3}$ thin films show
incommensurate helical antiferromagnetic spin ordering due to increased
ferromagnetic coupling compared to La${}_{1/3}$Sr${}_{2/3}$FeO${}_{3}$. To
understand the photoinduced spin dynamics in these materials, we investigate
the spin ordering through time-resolved resonant soft X-ray scattering. In
La${}_{1/3}$Sr${}_{2/3}$FeO${}_{3}$, ultrafast quenching of the magnetic
ordering within 130 fs through a nonthermal process is observed, triggered by
charge transfer between the Fe atoms. We compare this to the photoinduced
dynamics of the helical magnetic ordering of SrFeO${}_{3}$. We find that the
change in the magnetic coupling through optically induced charge transfer can
offer an even more efficient channel for spin-order manipulation.",2103.16038v1
2021-07-23,Generalized Bloch model: a theory for pulsed magnetization transfer,"Purpose: The paper introduces a classical model to describe the dynamics of
large spin-1/2 ensembles associated with nuclei bound in large molecule
structures, commonly referred to as the semi-solid spin pool, and their
magnetization transfer (MT) to spins of nuclei in
  Theory and Methods: Like quantum-mechanical descriptions of spin dynamics and
like the original Bloch equations, but unlike existing MT models, the proposed
model is based on the algebra of angular momentum in the sense that it
explicitly models the rotations induced by radio-frequency (RF) pulses. It
generalizes the original Bloch model to non-exponential decays, which are,
e.g., observed for semi-solid spin pools. The combination of rotations with
non-exponential decays is facilitated by describing the latter as Green's
functions, comprised in an integro-differential equation.
  Results: Our model describes the data of an inversion-recovery
magnetization-transfer experiment with varying durations of the inversion pulse
substantially better than established models. We made this observation for all
measured data, but in particular for pulse durations small than 300$\mu$s.
Furthermore, we provide a linear approximation of the generalized Bloch model
that reduces the simulation time by approximately a factor 15,000, enabling
simulation of the spin dynamics caused by a rectangular RF-pulse in roughly
2$\mu$s.
  Conclusion: The proposed theory unifies the original Bloch model, Henkelman's
steady-state theory for magnetization transfer, and the commonly assumed
rotation induced by hard pulses (i.e., strong and infinitesimally short
applications of RF fields) and describes experimental data better than previous
models.",2107.11000v3
2021-09-22,Bulk and edge dynamics of a 2D Affleck-Kennedy-Lieb-Tasaki model,"We study the dynamical properties of both bulk and edge spins of a
two-dimensional Affleck-Kennedy-Lieb-Tasaki (AKLT) model mainly by using the
stochastic series expansion quantum Monte Carlo method with stochastic analytic
continuation. In the deep AKLT phase, we obtain a spin spectrum with flat band,
which is a strong evidence for a localized state. Through the spectrum
analysis, we see a clear continuous phase transition from the AKLT phase to the
N\'eel phase in the model, and the energy gap becomes closed at the
corresponding momentum point. In comparison with linear spin-wave theory, the
differences show that there are strong interactions among magnons at high
energies. With open boundary condition, the gap of edge spins in the AKLT phase
closes at both the $\Gamma$ point and the $\pi$ point interestingly to emerge
into a flat-band-like Luttinger liquid phase, which can be explained by
symmetry and perturbation approximation. This paper helps us to better
understand the completely different dynamical behaviors of bulk and edge spins
in the symmetry protected topological phase.",2109.10901v2
2021-10-12,"""Galton board"" nuclear hyperpolarization","We consider the problem of determining the spectrum of an electronic spin via
polarization transfer to coupled nuclear spins and their subsequent readout.
This suggests applications for employing dynamic nuclear polarization (DNP) for
""ESR-via-NMR"". In this paper, we describe the theoretical basis for this
process by developing a model for the evolution dynamics of the coupled
electron-nuclear system through a cascade of Landau-Zener anti-crossings
(LZ-LACs). We develop a method to map these traversals to the operation of an
equivalent ""Galton board"". Here, LZ-LAC points serve as analogues to Galton
board ""pegs"", upon interacting with which the nuclear populations redistribute.
The developed hyperpolarization then tracks the local electronic density of
states. We show that this approach yields an intuitive and analytically
tractable solution of the polarization transfer dynamics, including when DNP is
carried out at the wing of a homogeneously broadened electronic spectral line.
We apply this approach to a model system comprised of a Nitrogen Vacancy (NV)
center electron in diamond, hyperfine coupled to N neighboring 13C nuclear
spins, and discuss applications for nuclear-spin interrogated NV center
magnetometry. More broadly, the methodology of ""one-to-many""
electron-to-nuclear spectral mapping developed here suggests interesting
applications in quantum memories and sensing, as well as wider applications in
modeling DNP processes in the multiple nuclear spin limit.",2110.05742v2
2021-10-24,$^{139}$La-NMR study of spin-dynamics coupled with hole mobility in $T$*-type La$_{0.86}$Eu$_{0.86}$Sr$_{0.28}$CuO$_{4-δ}$,"In $T$*-type cuprate oxides with five oxygen coordination, little is known
about the relationship between the spin correlations and dope carriers. We
performed $^{139}$La-nuclear magnetic resonance (NMR) and electrical
resistivity measurements on an as-sintered (AS) and oxidation annealed (OA)
polycrystalline $T$*-type La$_{0.86}$Eu$_{0.86}$S$_{0.28}$CuO$_4$ (LESCO) to
investigate its magnetic and superconducting (SC) properties. Upon cooling, the
NMR spectrum of AS LESCO broadened below 3 K, at which the nuclear spin-lattice
relaxation rate $1/T_1$ against the temperature exhibited a maximum, thereby
indicating the appearance of static magnetism. The temperature dependence of
$1/T_1$ between 3 K and 20 K was similar to that of the resistivity displaying
the semiconducting behavior. Furthermore, the energy scale of the transport gap
and spin-dynamics estimated was found to be comparable. These results suggest a
close connection between the mobility of the doped carriers and low-energy
spin-dynamics, as reported for lightly doped $T$-type La$_{2-x}$Sr$_x$CuO$_4$.
In the OA SC sample, we confirmed the absence of a magnetic order and the
Korringa relation above 10 K. Therefore, in the $T$*-type LESCO with $x$ =
0.28, the magnetic state coupled with holes drastically turns to the weakly
correlated metallic state by oxidation annealing.",2110.12333v1
2021-12-25,Spin-wave-driven skyrmion dynamics in ferrimagnets: Effect of net angular momentum,"Searching for low-power-consuming and high-efficient methods for well
controllable driving of skyrmion motion is one of the most concerned issues for
future spintronic applications, raising high concern with an appreciated choice
of magnetic media and driving scenario. In this work, we propose a novel
scenario of spin wave driven skyrmion motion in a ferrimagnetic (FiM) lattice
with the net angular momentum {\delta}s. We investigate theoretically the
effect of both {\delta}s and the circular polarization of spin wave on the
skyrmion dynamics. It is revealed that the momentum onto the skyrmion imposed
by the excited spin wave can be partitioned into a ferromagnetic term plus an
antiferromagnetic term. The ratio of these two terms and consequently the Hall
angle of skyrmion motion can be formulated as the functions of {\delta}s,
demonstrating the key role of {\delta}s as an effective control-parameter for
the skyrmion motion. Moreover, the spin wave frequency dependent skyrmion
motion is discussed, predicting the frequency enhanced skyrmion Hall motion.
This work thus represents an essential contribution to understand the skyrmion
dynamics in a FiM lattice.",2112.13232v2
2022-03-22,Quantum sensing and imaging of spin-orbit-torque-driven spin dynamics in noncollinear antiferromagnet Mn3Sn,"Novel noncollinear antiferromagnets with spontaneous time-reversal symmetry
breaking, nontrivial band topology, and unconventional transport properties
have received immense research interest over the past decade due to their rich
physics and enormous promise in technological applications. One of the central
focuses in this emerging field is exploring the relationship between the
microscopic magnetic structure and exotic material properties. Here, the
nanoscale imaging of both spin-orbit-torque-induced deterministic magnetic
switching and chiral spin rotation in noncollinear antiferromagnet Mn3Sn films
using nitrogen-vacancy (NV) centers is reported. Direct evidence of the
off-resonance dipole-dipole coupling between the spin dynamics in Mn3Sn and
proximate NV centers is also demonstrated with NV relaxometry measurements.
These results demonstrate the unique capabilities of NV centers in accessing
the local information of the magnetic order and dynamics in these emergent
quantum materials and suggest new opportunities for investigating the interplay
between topology and magnetism in a broad range of topological magnets.",2203.11465v1
2022-03-25,Sensitivity of a collisional single-atom spin probe,"We study the sensitivity of a collisional single-atom probe for ultracold
gases. Inelastic spin-exchange collisions map information about the gas
temperature T or external magnetic field B onto the quantum spin-population of
single-atom probes, and previous work showed enhanced sensitivity for
short-time nonequilibrium spin dynamics [1]. Here, we numerically investigate
the steady-state sensitivity of such single-atom probes to various observables.
We find that the probe shows distinct sensitivity maxima in the (B, T )
parameter diagram, although the underlying spin-exchange rates scale
monotonically with temperature and magnetic field. In parameter space, the
probe generally has the largest sensitivity when sensing the energy ratio
between thermal energy and Zeeman energy in an externally applied magnetic
field, while the sensitivity to the absolute energy, i.e., the sum of kinetic
and Zeeman energy, is low. We identify the parameters yielding sensitivity
maxima for a given absolute energy, which we can relate to a direct comparison
of the thermal Maxwell-Boltzmann distribution with the Zeeman-energy splitting.
We compare our equilibrium results to nonequilibrium experimental results from
a single-atom quantum probe, showing that the sensitivity maxima in parameter
space qualitatively prevail also in the nonequilibrium dynamics, while a
quantitative difference remains. Our work thereby offers a microscopic
explanation for the properties and performance of this single-atom quantum
probe, connecting thermodynamic properties to microscopic interaction
mechanisms. Our results pave the way for optimization of quantum-probe
applications in (B, T ) parameter space beyond the previously shown boost by
nonequilibrium dynamics.",2203.13656v3
2022-05-20,Fermion dynamics in presence of non abelian monopoles,"In the present letter, the dynamics of a spin one-half particle with non
abelian charge, interacting with a non abelian monopole like configuration, is
studied. In the non spinning case, these equations correspond to the Wong ones
[1], and the associated dynamics has been extensively studied in [2]-[3]. The
classical limit of a spinning particle in an abelian was studied in [4], where
an interpretation of the celebrated Callan-Rubakov effect [5]-[6] was obtained
in purely classical terms. The present work studies an interpolating situation,
in which spin and non abelian charges are turned on. The corresponding
equations are obtaining by taking into account some earlier works about
spinning particles [7]-[9]. The conservation laws are studied in this context,
and it is found that energy and some generalization of angular momentum are
conserved just in particular limits. This is a reflection that the non abelian
interaction contains gauge field quartic interaction, which spoils the
symmetries leading to these conservation laws. The precession of the particle
is analyzed and compared with its abelian counterpart in this limit.",2205.10296v3
2022-06-03,Anisotropic Laser-Pulse-Induced Magnetization Dynamics in van der Waals Magnet Fe$_3$GeTe$_2$,"Femtosecond laser-pulse excitation provides an energy efficient and fast way
to control magnetization at the nanoscale, providing great potential for
ultrafast next-generation data manipulation and nonvolatile storage devices.
Ferromagnetic van der Waals materials have garnered much attention over the
past few years due to their low dimensionality, excellent magnetic properties,
and large response to external stimuli. Nonetheless, their behaviour upon fs
laser-pulse excitation remains largely unexplored. Here, we investigate the
ultrafast magnetization dynamics of a thin flake of Fe$_3$GeTe$_2$ (FGT) and
extract its intrinsic magnetic properties using a microscopic framework. We
find that our data is well described by our modelling, with FGT undergoing a
slow two-step demagnetization, and we experimentally extract the
spin-relaxation timescale as a function of temperature, magnetic field and
excitation fluence. Our observations indicate a large spin-flip probability in
agreement with a theoretically expected large spin-orbit coupling, as well as a
weak interlayer exchange coupling. The spin-flip probability is found to
increase when the magnetization is pulled away from its quantization axis,
opening doors to an external control over the spins in this material. Our
results provide a deeper understanding of the dynamics van der Waals materials
upon fs laser-pulse excitation, paving the way towards two-dimensional
materials-based ultrafast spintronics.",2206.01452v1
2022-07-15,Spin dynamics of a solid-state qubit in proximity to a superconductor,"A broad effort is underway to understand and harness the interaction between
superconductors and spin-active color centers with an eye on the realization of
hybrid quantum devices and novel imaging modalities of superconducting
materials. Most work, however, overlooks the complex interplay between either
system and the environment created by the color center host. Here we use an
all-diamond scanning probe to investigate the spin dynamics of a single
nitrogen-vacancy (NV) center proximal to a high-critical-temperature
superconducting film in the presence of a weak magnetic field. We find that the
presence of the superconductor increases the NV spin coherence lifetime, a
phenomenon we tentatively rationalize as a change in the electric noise due to
a superconductor-induced redistribution of charge carriers near the NV site. We
build on these findings to demonstrate transverse-relaxation-time-weighted
imaging of the superconductor film. These results shed light on the complex
surface dynamics governing the spin coherence of shallow NVs while
simultaneously paving the route to new forms of noise spectroscopy and imaging
of superconductors.",2207.07648v1
2022-09-28,Sensing of magnetic field effects in radical-pair reactions using a quantum sensor,"Magnetic field effects (MFE) in certain chemical reactions have been well
established in the last five decades and are attributed to the evolution of
transient radical-pairs whose spin dynamics are determined by local and
external magnetic fields. The majority of existing experimental techniques used
to probe these reactions only provide ensemble averaged reaction parameters and
spin chemistry, hindering the observation of the potential presence of quantum
coherent phenomena at the single molecule scale. Here, considering a single
nitrogen vacancy (NV) centre as quantum sensor, we investigate the prospects
and requirements for detection of MFEs on the spin dynamics of radical-pairs at
the scale of single and small ensemble of molecules. We employ elaborate and
realistic models of radical-pairs, considering its coupling to the local spin
environment and the sensor. For two model systems, we derive signals of MFE
detectable even in the weak coupling regime between radical-pair and NV quantum
sensor, and observe that the dynamics of certain populations, as well as
coherence elements, of the density matrix of the radical pair are directly
detectable. Our investigations will provide important guidelines for potential
detection of spin chemistry of bio-molecules at the single molecule scale,
required to witness the hypothesised importance of quantum coherence in
biological processes.",2209.14066v1
2023-03-04,Entanglement Entropy Growth in Disordered Spin Chains with Tunable Range Interactions,"The non-equilibrium dynamics of disordered many-body quantum systems after a
global quantum quench unveils important insights about the competition between
interactions and disorder, yielding in particular an insightful perspective on
many body localization (MBL). Still, the experimentally relevant effect of bond
randomness in long-range interacting spin chains on the quantum quench dynamics
have so far not been investigated. In this letter, we examine the entanglement
entropy growth after a global quench in a quantum spin chain with randomly
placed spins and long-range tunable interactions decaying with distance with
power $\alpha$. Using a dynamical version of the strong disorder
renormalization group (SDRG) we find for $\alpha >\alpha_c$ that the
entanglement entropy grows logarithmically with time and becomes smaller with
larger $\alpha$ as $S(t) = S_p \ln(t)/(2\alpha)$. Here, $S_p= 2 \ln2 -1$. We
use numerical exact diagonalization (ED) simulations to verify our results for
system sizes up to $ N\sim 16$ spins, yielding good agreement for sufficiently
large $\alpha > \alpha_c \approx 1.8$. For $\alpha<\alpha_c$, we find that the
entanglement entropy grows as a power-law with time, $S(t)\sim
t^{\gamma(\alpha)}$ with $0<\gamma(\alpha)<1$ a decaying function of the
interaction exponent $\alpha$.",2303.02415v1
2023-03-02,Spinning (A)dS Black Holes with Slow-Rotation Approximation in Dynamical Chern-Simons Modified Gravity,"One of the most crucial areas of gravity research, after the direct
observation of gravitational waves, is the possible modification of General
Relativity at ultraviolet and infrared scales. In particular, the possibility
of parity violation should be considered in strong field regime. The
Chern-Simons gravity takes into account parity violation in strong gravity
regime. For all conformally flat spacetimes and spacetimes with a maximally
symmetric two-dimensional subspace, Chern-Simons gravity is identical to
General Relativity. Specifically, the Anti-de Sitter (A)dS-Kerr/Kerr black hole
is not a solution for Chern-Simons gravity. The slow-rotating BH and the
quadratic order in spin solutions are some of the known solutions to quadratic
order in spin and they are rotating solutions in the frame of dynamical
Chern-Simons gravity.
  In the present study, for the (A)dS slow-rotating situation (correct to the
first order in spin), we derive the linear perturbation equations controlling
the metric and the dynamical Chern-Simons field equation corrected to the
linear order in spin and to the second order in the Chern-Simons coupling
parameter. We show that the black hole of the (A)dS-Kerr solution is stronger
(i.e. more compact and energetic) than the Kerr black hole solution and the
reason for this feature comes form contributions at Planck scales. Moreover, we
calculate the thermodynamical quantities related to this black hole. Finally,
we calculate the geodesic equation and derive the effective potential of the
black hole.",2303.03159v1
2023-04-26,Bond-dependent anisotropy and magnon decay in cobalt-based Kitaev triangular antiferromagnet,"The Kitaev model, a honeycomb network of spins with bond-dependent
anisotropic interactions, is a rare example of having a quantum spin liquid
ground state. Although most Kitaev model candidate materials eventually order
magnetically due to inevitable non-Kitaev terms, their bond-dependent
anisotropy manifests in unusual spin dynamics. It has recently been suggested
that bond-dependent anisotropy can stabilise novel magnetic phases and exotic
spin dynamics on the geometrically frustrated triangular lattice. However, few
materials have been identified with simultaneous geometric frustration and
bond-dependent anisotropy. Here, we report a frustrated triangular lattice with
bond-dependent anisotropy in the cobalt-based triangular van der Waals
antiferromagnet CoI2. Its momentum and energy-resolved spin dynamics exhibit
substantial magnon breakdown and complex level repulsion, as measured by
inelastic neutron scattering. A thorough examination of excitations in both the
paramagnetic and magnetically ordered states reveals that the bond-dependent
anisotropy is the origin of the spiral order and the magnon breakdown found in
CoI2. Our result paves the way toward a new research direction for the Kitaev
model with geometrical frustration.",2304.13236v3
2023-04-29,Dynamics and reversible control of the vortex Bloch-point vortex domain wall in short cylindrical magnetic nanowires,"Fast and efficient switching of nanomagnets is one of the main challenges in
the development of future magnetic memories. We numerically investigate the
evolution of the static and dynamic spin wave (SW) magnetization in short
(50-400 nm length and 120 nm diameter) cylindrical ferromagnetic nanowires,
where competing single vortex (SV) and vortex domain wall with a Bloch point
(BP-DW) magnetization configurations could be formed. For a limited nanowire
length range (between 150 and 300 nm) we demonstrate a reversible microwave
field induced (forward) and opposite spin currents (backwards) transitions
between the topologically different SV and BP-DW states. By tuning the nanowire
length, excitation frequency, the microwave pulse duration and the spin current
values we show that the optimum (low power) manipulation of the BP-DW could be
reached by a microwave excitation tuned to the main SW mode and for nanowire
lengths around 230-250 nm, where single vortex domain wall magnetization
reversal via nucleation and propagation of SV-DW takes place. An analytical
model for dynamics of the Bloch point provides an estimation of the gyrotropic
mode frequency close the one obtained via micromagnetic simulations. A
practical implementation of the method on a device has been proposed involving
microwave excitation and the generation of the opposite spin currents via spin
orbit torque. Our findings open a new pathway for the creation of unforeseen
topological magnetic memories.",2305.00346v1
2023-07-18,The role of spin polarization and dynamic correlation in singlet-triplet gap inversion of heptazine derivatives,"The new generation of proposed light-emitting molecules for OLEDs has raised
a considerable research interest due to its exceptional feature-a negative
singlet-triplet (ST) gap violating the Hund's multiplicity rule in the excited
S1 and T1 states. We investigate the role of spin polarization in the mechanism
of ST gap inversion. Spin polarization is associated with doubly excited
determinants of certain types, whose presence in the wavefunction expansion
favors the energy of the singlet state more than that of the triplet. Using a
perturbation theory-based model for spin polarization, we propose a simple
descriptor for prescreening of candidate molecules with negative ST gaps and
prove its usefulness for heptazine-type molecules. Numerical results show that
the quantitative effect of spin polarization is approximately
inverse-proportional to the HOMO-LUMO exchange integral. Comparison of single-
and multireference coupled- cluster predictions of ST gaps shows that the
former methods provide good accuracy by correctly balancing the effects of
doubly excited determinants and dynamic correlation. We also show that accurate
ST gaps may be obtained using a complete active space model supplemented with
dynamic correlation from multireference adiabatic connection theory.",2307.09075v1
2000-07-13,Dynamical Structure Factors of the S=1/2 Bond-Alternating Spin Chain with a Next-Nearest-Neighbor Interaction in Magnetic Fields,"The dynamical structure factor of the S=1/2 bond-alternating spin chain with
a next-nearest-neighbor interaction in magnetic field is investigated using the
continued fraction method based on the Lanczos algorithm. When the plateau
exists on the magnetization curve, the longitudinal dynamical structure factor
shows a large intensity with a periodic dispersion relation, while the
transverse one shows a large intensity with an almost dispersionless mode. The
periodicity and the amplitude of the dispersion relation in the longitudinal
dynamical structure factor are sensitive to the coupling constants. The
dynamical structure factor of the S=1/2 two-leg ladder in magnetic field is
also calculated in the strong interchain-coupling regime.
  The dynamical structure factor shows gapless or gapful behavior depending on
the wave vector along the rung.",0007219v1
2007-11-23,Static and dynamic structure factors in three-dimensional randomly diluted Ising models,"We consider the three-dimensional randomly diluted Ising model and study the
critical behavior of the static and dynamic spin-spin correlation functions
(static and dynamic structure factors) at the paramagnetic-ferromagnetic
transition in the high-temperature phase. We consider a purely relaxational
dynamics without conservation laws, the so-called model A. We present Monte
Carlo simulations and perturbative field-theoretical calculations. While the
critical behavior of the static structure factor is quite similar to that
occurring in pure Ising systems, the dynamic structure factor shows a
substantially different critical behavior. In particular, the dynamic
correlation function shows a large-time decay rate which is momentum
independent. This effect is not related to the presence of the Griffiths tail,
which is expected to be irrelevant in the critical limit, but rather to the
breaking of translational invariance, which occurs for any sample and which, at
the critical point, is not recovered even after the disorder average.",0711.3673v2
2007-12-07,Dynamical replica analysis of processes on finitely connected random graphs I: vertex covering,"We study the stochastic dynamics of Ising spin models with random bonds,
interacting on finitely connected Poissonnian random graphs. We use the
dynamical replica method to derive closed dynamical equations for the joint
spin-field probability distribution, and solve these within the replica
symmetry ansatz. Although the theory is developed in a general setting, with a
view to future applications in various other fields, in this paper we apply it
mainly to the dynamics of the Glauber algorithm (extended with cooling
schedules) when running on the so-called vertex cover optimization problem. Our
theoretical predictions are tested against both Monte Carlo simulations and
known results from equilibrium studies. In contrast to previous dynamical
analyses based on deriving closed equations for only a small numbers of scalar
order parameters, the agreement between theory and experiment in the present
study is nearly perfect.",0712.1139v1
2010-04-23,Fast-forward of quantum adiabatic dynamics in electro-magnetic field,"We show a method to accelerate quantum adiabatic dynamics of wavefunctions
under electro-magnetic field by developing the previous theory (Masuda &
Nakamura 2008 and 2010). Firstly we investigate the orbital dynamics of a
charged particle. We derive the driving field which accelerates quantum
adiabatic dynamics in order to obtain the final adiabatic states except for the
spatially uniform phase such as the adiabatic phase in any desired short time.
Fast-forward of adiabatic squeezing and transport in the electro-magnetic field
is exhibited. Secondly we investigate spin dynamics under the magnetic field,
showing the fast-forward of adiabatic spin inversion and of adiabatic dynamics
in Landau-Zener model. The connection of the present framework with
Kato-Berry's transitionless quantum driving is elucidated in Appendix.",1004.4108v1
2010-08-31,Geometry and Dynamics in Zero Temperature Statistical Mechanics Models,"We consider several models whose motivation arises from statistical
mechanics. We begin by investigating some families of distributions of
translation invariant subgraphs of some Cayley graphs, and in particular
subgraphs of the square lattice. We then discuss some properties of the
Spin-Glass model in that lattice. We continue in describing some properties of
the Spin-Glass models in some other graphs.
  The last two parts of this work are devoted to the understanding of two
dynamical processes on graphs. The first one is the well known zero-temperature
Glauber dynamics on some families of graphs.
  The second dynamics, which we call the Loop Dynamics, is a natural
generalization of the zero-temperature Glauber dynamics, which appears to have
some interesting properties. We analyzed some of its properties for planar
lattices, though the exact same techniques are applied for larger families of
graphs as well.",1008.5279v1
2011-12-12,Theory of laser-induced demagnetization at high temperatures,"Laser-induced demagnetization is theoretically studied by explicitly taking
into account interactions among electrons, spins and lattice. Assuming that the
demagnetization processes take place during the thermalization of the
sub-systems, the temperature dynamics is given by the energy transfer between
the thermalized interacting baths. These energy transfers are accounted for
explicitly through electron-magnons and electron-phonons interaction, which
govern the demagnetization time scale. By properly treating the spin system in
a self-consistent random phase approximation, we derive magnetization dynamic
equations for a broad range of temperature. The dependence of demagnetization
on the temperature and pumping laser intensity is calculated in detail. In
particular, we show several salient features for understanding magnetization
dynamics near the Curie temperature. While the critical slowdown in dynamics
occurs, we find that an external magnetic field can restore the fast dynamics.
We discuss the implication of the fast dynamics in the application of heat
assisted magnetic recording.",1112.2428v1
2011-12-19,Dynamical phases and intermittency of the dissipative quantum Ising model,"We employ the concept of a dynamical, activity order parameter to study the
Ising model in a transverse magnetic field coupled to a Markovian bath. For a
certain range of values of the spin-spin coupling, magnetic field and
dissipation rate, we identify a first order dynamical phase transition between
active and inactive {\em dynamical phases}. We demonstrate that dynamical
phase-coexistence becomes manifest in an intermittent behavior of the bath
quanta emission. Moreover, we establish the connection between the dynamical
order parameter that quantifies the activity, and the longitudinal
magnetization that serves as static order parameter. The system we consider can
be implemented in current experiments with Rydberg atoms and trapped ions.",1112.4273v2
2014-09-16,Dynamic message-passing approach for kinetic spin models with reversible dynamics,"A method to approximately close the dynamic cavity equations for synchronous
reversible dynamics on a locally tree-like topology is presented. The method
builds on $(a)$ a graph expansion to eliminate loops from the normalizations of
each step in the dynamics, and $(b)$ an assumption that a set of auxilary
probability distributions on histories of pairs of spins mainly have
dependencies that are local in time. The closure is then effectuated by
projecting these probability distributions on $n$-step Markov processes. The
method is shown in detail on the level of ordinary Markov processes ($n=1$),
and outlined for higher-order approximations ($n>1$). Numerical validations of
the technique are provided for the reconstruction of the transient and
equilibrium dynamics of the kinetic Ising model on a random graph with
arbitrary connectivity symmetry.",1409.4684v2
2012-01-30,Universal dynamical phase diagram of lattice spin models and strongly correlated ultracold atoms in optical lattices,"We study semiclassical dynamics of anisotropic Heisenberg models in two and
three dimensions. Such models describe lattice spin systems and hard core
bosons in optical lattices. We solve numerically Landau-Lifshitz type equations
on a lattice and show that in the phase diagram of magnetization and
interaction anisotropy, one can identify several distinct regimes of dynamics.
These regions can be distinguished based on the character of one dimensional
solitonic excitations, and stability of such solitons to transverse modulation.
Small amplitude and long wavelength perturbations can be analyzed analytically
using mapping of non-linear hydrodynamic equations to KdV type equations.
Numerically we find that properties of solitons and dynamics in general remain
similar to our analytical results even for large amplitude and short distance
inhomogeneities, which allows us to obtain a universal dynamical phase diagram.
As a concrete example we study dynamical evolution of the system starting from
a state with magnetization step and show that formation of oscillatory regions
and their stability to transverse modulation can be understood from the
properties of solitons. In regimes unstable to transverse modulation we observe
formation of lump type solutions with modulation in all directions. We discuss
implications of our results for experiments with ultracold atoms.",1201.6400v1
2014-06-10,Dynamic trapping near a quantum critical point,"The study of dynamics in closed quantum systems has recently been revitalized
by the emergence of experimental systems that are well-isolated from their
environment. In this paper, we consider the closed-system dynamics of an
archetypal model: spins near a second order quantum critical point, which are
traditionally described by the Kibble-Zurek mechanism. Imbuing the driving
field with Newtonian dynamics, we find that the full closed system exhibits a
robust new phenomenon -- dynamic critical trapping -- in which the system is
self-trapped near the critical point due to efficient absorption of field
kinetic energy by heating the quantum spins. We quantify limits in which this
phenomenon can be observed and generalize these results by developing a
Kibble-Zurek scaling theory that incorporates the dynamic field. Our findings
can potentially be interesting in the context of early universe physics, where
the role of the driving field is played by the inflaton or a modulus.",1406.2701v2
2019-03-05,Scaling of decoherence and energy flow in interacting quantum spin systems,"We address the quantum dynamics of a system composed of a qubit globally
coupled to a many-body system characterized by short-range interactions. We
employ a dynamic finite-size scaling framework to investigate the
out-of-equilibrium dynamics arising from the sudden variation (turning on) of
the interaction between the qubit and the many-body system, in particular when
the latter is in proximity of a quantum first-order or continuous phase
transition. Although the approach is quite general, we consider d-dimensional
quantum Ising spin models in the presence of transverse and longitudinal
fields, as paradigmatic quantum many-body systems. To characterize the
out-of-equilibrium dynamics, we focus on a number of quantum-information
oriented properties of the model. Namely, we concentrate on the decoherence
features of the qubit, the energy interchanges among the qubit and the
many-body system during the out-of-equilibrium dynamics, and the work
distribution associated with the quench. The scaling behaviors predicted by the
dynamic finite-size scaling theory are verified through extensive numerical
computations for the one-dimensional Ising model, which reveal a fast
convergence to the expected asymptotic behavior with increasing the system
size.",1903.02019v1
2019-03-24,"Synchronized, periodic, and chaotic dynamics in spin torque oscillator with two free layers","A phase diagram of the magnetization dynamics is studied by numerically
solving the Landau-Lifshitz-Gilbert (LLG) equation in a spin torque oscillator
consisting of asymmetric two free layers that are magnetized in in-plane
direction. We calculated the dynamics for a wide range of current density for
both low and high field cases, and found many dynamical phases such as
synchronization, auto-oscillation with different frequencies, and chaotic
dynamics. The observation of the synchronization indicates the presence of a
dynamical phase which has not been found experimentally by using the
conventional electrical detection method. The auto-oscillations with different
frequencies lead to an oscillation of magnetoresistance with a high frequency,
which can be measured experimentally. The chaotic and/or periodic behavior of
magnetoresistance in a high current region, on the other hand, leads to a
discontinuous change of the peak frequency in Fourier spectrum.",1903.09938v2
2020-08-26,Critical Dynamics of Anisotropic Antiferromagnets in an External Field,"We numerically investigate the non-equilibrium critical dynamics in
three-dimensional anisotropic antiferromagnets in the presence of an external
magnetic field. The phase diagram of this system exhibits two critical lines
that meet at a bicritical point. The non-conserved components of the staggered
magnetization order parameter couple dynamically to the conserved component of
the magnetization density along the direction of the external field. Employing
a hybrid computational algorithm that combines reversible spin precession with
relaxational Monte Carlo updates, we study the aging scaling dynamics for the
model C critical line, identifying the critical initial slip, autocorrelation,
and aging exponents for both the order parameter and conserved field, thus also
verifying the dynamic critical exponent. We further probe the model F critical
line by investigating the system size dependence of the characteristic spin
wave frequencies near criticality, and measure the dynamic critical exponents
for the order parameter including its aging scaling at the bicritical point.",2008.11541v2
2021-07-17,Operator growth in the transverse-field Ising spin chain with integrability-breaking longitudinal field,"We investigate the operator growth dynamics of the transverse field Ising
spin chain in one dimension as varying the strength of the longitudinal field.
An operator in the Heisenberg picture spreads in the extended Hilbert space.
Recently, it has been proposed that the spreading dynamics has a universal
feature signaling chaoticity of underlying quantum dynamics. We demonstrate
numerically that the operator growth dynamics in the presence of the
longitudinal field follows the universal scaling law for one-dimensional
chaotic systems. We also find that the operator growth dynamics satisfies a
crossover scaling law as the longitudinal field turns on. The crossover scaling
confirms that the uniform longitudinal field makes the system chaotic at any
nonzero value. We also discuss the implication of the crossover scaling on the
thermalization dynamics and the effect of a nonuniform local longitudinal
field.",2107.08287v2
2022-01-19,Non-linear dynamics of the non-Hermitian Su-Schrieffer-Heeger model,"We numerically determine the robustness of the lasing edge modes in a
spin-torque oscillator array that realizes the non-Hermitian
Su-Schrieffer-Heeger model. Previous studies found that the linearized dynamics
can enter a topological regime in which the edge mode is driven into
auto-oscillation, while the bulk dynamics are suppressed. Here we investigate
the full non-linear and finite-temperature dynamics, whose understanding is
essential for spin-torque oscillators-based applications. Our analysis shows
that the lasing edge mode dynamics persist in the non-linear domain for a broad
range of parameters and temperatures. We investigate the effects of
perturbations relevant to experimental implementations and discuss which ones
might be detrimental to the stability of the lasing edge mode. Finally, we map
our model onto a photonic model. Our analysis has the potential to shed light
onto the dynamics of a plethora of non-Hermitian systems with non-linearities.",2201.07678v2
2022-07-06,Monitored Quantum Dynamics and the Kitaev Spin Liquid,"Quantum circuit dynamics with local projective measurements can realize a
rich spectrum of entangled states of quantum matter. Motivated by the physics
of the Kitaev quantum spin liquid [1], we study quantum circuit dynamics in
(2+1)-dimensions involving local projective measurements, in which the
monitored trajectories realize (i) a phase with topological quantum order or
(ii) a ""critical"" phase with a logarithmic violation of area-law-scaling of the
entanglement entropy along with long range tripartite entanglement. A Majorana
parton description of these dynamics, which provides an out-of-equilibrium
generalization of the parton description of the Kitaev honeycomb model, permits
an analytic understanding of the universal properties of these two phases,
including the entanglement properties of the steady-state, the dynamics of the
system on the approach to equilibrium, and the phase transition between these
states. In the topologically-ordered phase, two logical qubits can be encoded
in an initial state and protected for a time which scales exponentially in the
linear dimension of the system, while no robust encoding of quantum information
persists in the critical phase. Extensive numerical simulations of these
monitored dynamics confirm our analytic predictions.",2207.02877v1
2022-08-04,Dissipative Dynamics of a Fermionic Superfluid with Two-Body Losses,"We study the dissipative dynamics of a fermionic superfluid in presence of
two-body losses. We use a variational approach for the Lindblad dynamics and
obtain dynamical equations for Anderson's pseudo-spins where dissipation enters
as a complex pairing interaction as well as effective, density-dependent,
single particle losses which break the conservation of the pseudo-spin norm. We
show that this latter has key consequences on the dynamical behavior of the
system. In the case of a sudden switching of two-body losses we show that the
superfluid order parameter decays much faster than then particle density at
short times and eventually slows-down, setting into a power-law decay at longer
time scales driven by the depletion of the system. We then consider a quench of
pairing interaction, leading to coherent oscillations in the unitary case,
followed by the switching of the dissipation. We show that losses wash away the
dynamical BCS synchronization by introducing not only damping but also a
renormalization of the frequency of coherent oscillations, which depends
non-linearly from the rate of the two-body losses.",2208.02739v3
2022-10-25,Quasi-Particle Dynamics in Quasi-Periodic Ising Model with Temporally Fluctuating Transverse Fields,"We study quasi-particle dynamics in a quasi-periodic Ising model with
temporally fluctuating transverse fields. Specifically, we calculate the
dynamical exponents of the standard deviation of a quasi-particle spreading
under a field chosen randomly from binary values $\pm h$ at every time
interval. We find that the short-time behavior of the dynamical exponents
depends on the interval of the temporally fluctuating fields. We also reveal
how the quasi-particle dynamics affects the relaxation of spin-spin correlation
functions. The dynamics can be explained via the overlap between the
eigenvectors of a Hamiltonian with $\pm h$.",2210.13814v4
2022-12-12,Dynamics of the spin-boson model: the effect of bath initial conditions,"Dynamics of the (sub-)Ohmic spin-boson model under various bath initial
conditions is investigated by employing the Dirac-Frenkel time-dependent
variational approach with the multiple Davydov $\mathrm{D_1}$ ansatz in the
interaction picture. The validity of our approach is carefully checked by
comparing results with those of the hierarchy equations of motion method. By
analyzing the features of nonequilibrium dynamics, we identify the phase
diagrams for different bath initial conditions. We find that for spectral
exponent $s<s_c$, there exists a transition from coherent to quasicoherent
dynamics with increasing the coupling strengths. For $s_c<s\leq{1}$, the
coherent to incoherent crossover occurs at a certain coupling strength, and the
quasicoherent dynamics emerges at much larger couplings. The initial
preparation of the bath has considerable influence on the dynamics.",2212.05723v1
2023-06-09,Nonlinear multi-state tunneling dynamics in a spinor Bose-Einstein condensate,"We present an experimental realization of dynamic self-trapping and
non-exponential tunneling in a multi-state system consisting of ultracold
sodium spinor gases confined in moving optical lattices. Taking advantage of
the fact that the tunneling process in the sodium spinor system is resolvable
over a broader dynamic energy scale than previously observed in rubidium scalar
gases, we demonstrate that the tunneling dynamics in the multi-state system
strongly depends on an interaction induced nonlinearity and is influenced by
the spin degree of freedom under certain conditions. We develop a rigorous
multi-state tunneling model to describe the observed dynamics. Combined with
our recent observation of spatially-manipulated spin dynamics, these results
open up prospects for alternative multi-state ramps and state transfer
protocols.",2306.05877v1
2023-08-29,Nonequilibrium glass transitions in the spherical $p$-spin model with antisymmetric interactions,"Our theoretical understanding of glassy dynamics is notoriously incomplete,
and it is even more so when the glassy systems are driven out of equilibrium.
An extreme way to drive a system out of equilibrium is to introduce
nonequilibrium dynamics at the microscopic level, e.g., through active forcing
of the constituent particles or by having nonreciprocal interactions among the
particles. While glassy dynamics under active forcing has been studied by many,
the latter nonequilibrium scenario has received little attention. Here, I study
the glassy dynamics of the spherical $p$-spin model for $p\geq 3$ with
antisymmetric interactions, which generalizes reciprocal interactions in 2-body
interactions. The spherical $p$-spin model is an integral tool in the study of
dynamical glass transition, and when antisymmetric interactions are added, I
show analytically and numerically that glassy behavior is generically
suppressed. Moreover, I obtain analytical expressions on the modified dynamical
glass transition point and the Edward-Anderson parameter (i.e., the asymptotic
plateau height value of the spin-spin correlation function) in the small
driving limit.",2308.15424v1
2023-09-22,Non-Abelian dynamical gauge field and topological superfluids in optical Raman lattice,"We propose an experimental scheme to realize non-Abelian dynamical gauge
field for ultracold fermions, which induces a novel pairing mechanism of
topological superfluidity. The dynamical gauge fields arise from nontrivial
interplay effect between the strong Zeeman splitting and Hubbard interaction in
a two-dimensional (2D) optical Raman lattice. The spin-flip transitions are
forbidden by the large Zeeman detuning, but are restored when the Zeeman
splitting is compensated by Hubbard interaction. This scheme allows to generate
a dynamical non-Abelian gauge field that leads to a Dirac type correlated 2D
spin-orbit interaction depending on local state configurations. The topological
superfluid from a novel pairing driven by 2D dynamical gauge fields is reached,
with analytic and numerical results being obtained. Our work may open up a door
to emulate non-Abelian dynamical gauge fields and correlated topological phases
with experimental feasibility.",2309.12923v2
2005-03-02,Equilibrium Kawasaki dynamics of continuous particle systems,"We construct a new equilibrium dynamics of infinite particle systems in a
Riemannian manifold $X$. This dynamics is an analog of the Kawasaki dynamics of
lattice spin systems. The Kawasaki dynamics now is a process where interacting
particles randomly hop over $X$. We establish conditions on the {\it a priori}
explicitly given symmetrizing measure and the generator of this dynamics, under
which a corresponding conservative Markov processes exists. We also outline two
types of scaling limit of the equilibrium Kawasaki dynamics: one leading to an
equilibrium Glauber dynamics in continuum (a birth-and-death process), and the
other leading to a diffusion dynamics of interacting particles (in particular,
the gradient stochastic dynamics).",0503042v2
2008-09-30,Dynamics of diluted magnetic semiconductors from atomistic spin dynamics simulations: Mn doped GaAs as a case study,"The dynamical behavior of the magnetism of diluted magnetic semiconductors
(DMS) has been investigated by means of atomistic spin dynamics simulations.
The conclusions drawn from the study are argued to be general for DMS systems
in the low concentration limit, although all simulations are done for 5%
Mn-doped GaAs with various concentrations of As antisite defects. The
magnetization curve, $M(T)$, and the Curie temperature $T_C$ have been
calculated, and are found to be in good correspondence to results from Monte
Carlo simulations and experiments. Furthermore, equilibrium and non-equilibrium
behavior of the magnetic pair correlation function have been extracted. The
dynamics of DMS systems reveals a substantial short ranged magnetic order even
at temperatures at or above the ordering temperature, with a non-vanishing pair
correlation function extending up to several atomic shells. For the high As
antisite concentrations the simulations show a short ranged anti-ferromagnetic
coupling, and a weakened long ranged ferromagnetic coupling. For sufficiently
large concentrations we do not observe any long ranged ferromagnetic
correlation. A typical dynamical response shows that starting from a random
orientation of moments, the spin-correlation develops very fast ($\sim$ 1ps)
extending up to 15 atomic shells. Above $\sim$ 10 ps in the simulations, the
pair correlation is observed to extend over some 40 atomic shells. The
autocorrelation function has been calculated and compared with ferromagnets
like bcc Fe and spin-glass materials. We find no evidence in our simulations
for a spin-glass behaviour, for any concentration of As antisites. Instead the
magnetic response is better described as slow dynamics, at least when compared
to that of a regular ferromagnet like bcc Fe.",0809.5187v1
2001-10-26,The spin evolution of nascent neutron stars,"The loss of angular momentum due to unstable r-modes in hot young neutron
stars has been proposed as a mechanism for achieving the spin rates inferred
for young pulsars. One factor that could have a significant effect on the
action of the r-mode instability is fallback of supernova remnant material. The
associated accretion torque could potentially counteract any gravitational-wave
induced spin-down, and accretion heating could affect the viscous damping rates
and hence the instability. We discuss the effects of various external agents on
the r-mode instability scenario within a simple model of supernova fallback on
to a hot young magnetized neutron star. We find that the outcome depends
strongly on the strength of the star's magnetic field. Our model is capable of
generating spin rates for young neutron stars that accord well with initial
spin rates inferred from pulsar observations. The combined action of r-mode
instability and fallback appears to cause the spin rates of neutron stars born
with very different spin rates to converge, on a timescale of about a year. The
results suggest that stars with magnetic fields $\le10^{13}$ G could emit a
detectable gravitational wave signal for perhaps several years after the
supernova event. Stars with higher fields (magnetars) are unlikely to emit a
detectable gravitational wave signal via the r-mode instability. The model also
suggests that the r-mode instability could be extremely effective in preventing
young neutron stars from going dynamically unstable to the bar-mode.",0110573v2
1994-12-06,Landau theory of quantum spin glasses of rotors and Ising spins,"We consider quantum rotors or Ising spins in a transverse field on a
$d$-dimensional lattice, with random, frustrating, short-range, exchange
interactions. The quantum dynamics are associated with a finite moment of
inertia for the rotors, and with the transverse field for the Ising spins. For
a suitable distribution of exchange constants, these models display spin glass
and quantum paramagnet phases and a zero temperature quantum transition between
them. An earlier exact solution for the critical properties of a model with
infinite-range interactions can be reproduced by minimization of a Landau
effective-action functional for the model in finite $d$ with short-range
interactions. The functional is expressed in terms of a composite spin field
which is bilocal in time. The mean-field phase diagram near the zero
temperature critical point is mapped out as a function of temperature, strength
of the quantum coupling, and applied fields. The spin glass ground state is
found to be replica symmetric, with replica symmetry breaking appearing only at
finite temperatures. Next we examine the consequences of fluctuations about
mean-field for the critical properties. Above $d=8$, and with certain
restrictions on the values of the Landau couplings, we find that the transition
is controlled by a Gaussian fixed point with mean-field critical exponents. For
couplings not attracted by the Gaussian fixed point above $d=8$, and for all
physical couplings below $d=8$, we find runaway renormalization group flows to
strong coupling. General scaling relations that should be valid even at the
strong coupling fixed point are proposed and compared with Monte Carlo
simulations.",9412032v2
1996-05-11,Rapid Suppression of the Spin Gap in Zn-doped CuGeO_3 and SrCu_2O_3,"The influence of non-magnetic impurities on the spectrum and dynamical spin
structure factor of a model for CuGeO$_3$ is studied. A simple extension to
Zn-doped ${\rm Sr Cu_2 O_3}$ is also discussed. Using Exact Diagonalization
techniques and intuitive arguments we show that Zn-doping introduces states in
the Spin-Peierls gap of CuGeO$_3$. This effect can beunderstood easily in the
large dimerization limit where doping by Zn creates ``loose'' S=1/2 spins,
which interact with each other through very weak effective antiferromagnetic
couplings. When the dimerization is small, a similar effect is observed but now
with the free S=1/2 spins being the resulting S=1/2 ground state of severed
chains with an odd number of sites. Experimental consequences of these results
are discussed. It is interesting to observe that the spin correlations along
the chains are enhanced by Zn-doping according to the numerical data presented
here. As recent numerical calculations have shown, similar arguments apply to
ladders with non-magnetic impurities simply replacing the tendency to
dimerization in CuGeO$_3$ by the tendency to form spin-singlets along the rungs
in SrCu$_2$O$_3$.",9605069v3
1997-08-06,"Spin gap in the Quasi-One-Dimensional S=1/2 Antiferromagnet: Cu2(1,4-diazacycloheptane)2Cl4","Cu_{2}(1,4-diazacycloheptane)_{2}Cl_{4} contains double chains of spin 1/2
Cu^{2+} ions. We report ac susceptibility, specific heat, and inelastic neutron
scattering measurements on this material. The magnetic susceptibility,
$\chi(T)$, shows a rounded maximum at T = 8 K indicative of a low dimensional
antiferromagnet with no zero field magnetic phase transition. We compare the
$\chi(T)$ data to exact diagonalization results for various one dimensional
spin Hamiltonians and find excellent agreement for a spin ladder with
intra-rung coupling $J_1 = 1.143(3)$ meV and two mutually frustrating
inter-rung interactions: $J_2 = 0.21(3)$ meV and $J_3 = 0.09(5)$ meV. The
specific heat in zero field is exponentially activated with an activation
energy $\Delta = 0.89(1)$ meV. A spin gap is also found through inelastic
neutron scattering on powder samples which identify a band of magnetic
excitations for $0.8 < \hbar\omega < 1.5$ meV. Using sum-rules we derive an
expression for the dynamic spin correlation function associated with
non-interacting propagating triplets in a spin ladder. The van-Hove
singularities of such a model are not observed in our scattering data
indicating that magnetic excitations in Cu_{2}(1,4-diazacycloheptane)_{2}Cl_{4}
are more complicated. For magnetic fields above $H_{c1} \simeq 7.2$ T specific
heat data versus temperature show anomalies indicating a phase transition to an
ordered state below T = 1 K.",9708053v1
2003-07-22,Electronic transport through domain walls in ferromagnetic nanowires: Co-existence of adiabatic and non-adiabatic spin dynamics,"We study the effect of a domain wall on the electronic transport in
ferromagnetic quantum wires. Due to the transverse confinement, conduction
channels arise. In the presence of a domain wall, spin up and spin down
electrons in these channels become coupled. For very short domain walls or at
high longitudinal kinetic energy, this coupling is weak, leads to very few spin
flips, and a perturbative treatment is possible. For very long domain wall
structures, the spin follows adiabatically the local magnetization orientation,
suppressing the effect of the domain wall on the total transmission, but
reversing the spin of the electrons. In the intermediate regime, we numerically
investigate the spin-dependent transport behavior for different shapes of the
domain wall. We find that the knowledge of the precise shape of the domain wall
is not crucial for determining the qualitative behavior. For parameters
appropriate for experiments, electrons with low longitudinal energy are
transmitted adiabatically while the electrons at high longitudinal energy are
essentially unaffected by the domain wall. Taking this co-existence of
different regimes into account is important for the understanding of recent
experiments.",0307531v1
2005-02-02,Analysis of NMR Spin-Lattice Relaxation Rates in Cuprates,"We investigate nuclear spin-lattice relaxation data in the normal state of
optimally doped YBaCuO_7 by analyzing the contributions to the relaxation rate
of the copper, planar oxygen and yttrium along the directions perpendicular to
the applied field. In this new picture there is no contrasting temperature
dependence of the copper and oxygen relaxation. We use the model of fluctuating
fields to express the rates in terms of hyperfine interaction energies and an
effective correlation time tau_eff characterizing the dynamics of the spin
fluid. The former contain the effects of the antiferromagnetic static spin
correlations, which cause the hyperfine field constants to be added coherently
at low temperature and incoherently at high temperature. The degree of
coherency is therefore controlled by the spin-spin correlations. The model is
used to determine the temperature-dependent correlation lengths. The
temperature-dependent effective correlation time is found to be made up of a
linear and a constant contribution that can be related to scattering and spin
fluctuations of localized moments respectively. The extrapolation of our
calculation at higher temperature fits the data also very well at those
temperatures. The underdoped compounds YBaCuO_6.63 and YBaCuO_8 are studied in
the limit of the data available with some success by modifying the effective
correlation time with a gap parameter. The copper data of the LaSrCuO series
are then discussed in terms of the interplay between the two contributions to
tau_eff.",0502075v2
2005-12-20,Theory of Spin Torque in a nanomagnet,"We present a complete theory of the spin torque phenomena in a ultrasmall
nanomagnet coupled to non-collinear ferromagnetic electrodes through tunnelling
junctions. This model system can be described by a simple microscopic model
which captures many physical effects characteristic of spintronics: tunneling
magneto resistance, intrinsic and transport induced magnetic relaxation,
current induced magnetization reversal and spin accumulation. Treating on the
same footing the magnetic and transport degrees of freedom, we arrive at a
closed equation for the time evolution of the magnetization. This equation is
very close to the Landau-Lifshitz-Gilbert equation used in spin valves
structures. We discuss how the presence of the Coulomb blockade phenomena and
the discretization of the one-body spectrum gives some additional features to
the current induced spin torque. Depending on the regime, the dynamic induced
by the coupling to electrode can be viewed either as a spin torque or as a
relaxation process. In addition to the possibility of stabilizing uniform spin
precession states, we find that the system is highly hysteretic: up to three
different magnetic states can be simultaneously stable in one region of the
parameter space (magnetic field and bias voltage).We also discuss how the
magneto-resistance can be used to provide additional information on the
non-equilibrium peaks present in the nanomagnet spectroscopy experiments.",0512508v1
2006-03-28,Renormalization of the spin-wave spectrum in three-dimentional ferromagnets with dipolar interaction,"Renormalization of the spin-wave spectrum is discussed in a cubic ferromagnet
with dipolar forces at $T_C\gg T\ge0$. First 1/S-corrections are considered in
detail to the bare spectrum $\epsilon_{\bf k} = \sqrt{Dk^2 (Dk^2 +
S\omega_0\sin^2\theta_{\bf k})}$, where $D$ is the spin-wave stiffness,
$\theta_{\bf k}$ is the angle between $\bf k$ and the magnetization and
$\omega_0$ is the characteristic dipolar energy. In accordance with previous
results we obtain the thermal renormalization of constants $D$ and $\omega_0$
in the expression for the bare spectrum. Besides, a number of previously
unknown features are revealed. We observe terms which depend on azimuthal angle
of the momentum $\bf k$. It is obtained an isotropic term proportional to $k$
which makes the spectrum linear rather than quadratic when $\sin\theta_{\bf
k}=0$ and $k \ll \omega_0/D$. In particular a spin-wave gap proportional to
$\sin\theta_{\bf k}$ is observed. Essentially, thermal contribution from the
Hartree-Fock diagram to the isotropic correction as well as to the spin-wave
gap are proportional to the demagnetizing factor in the direction of domain
magnetization. This nontrivial behavior is attributed to the long-range nature
of the dipolar interaction. It is shown that the gap screens infrared
singularities of the first 1/S-corrections to the spin-wave stiffness and
longitudinal dynamical spin susceptibility (LDSS) obtained before. We
demonstrate that higher order 1/S-corrections to these quantities are small at
$T\ll\omega_0$. However the analysis of the entire perturbation series is still
required to derive the spectrum and LDSS when $T\gg\omega_0$.",0603741v2
2006-12-19,Effect of initial spin polarization on spin dephasing and electron g factor in a high-mobility two-dimensional electron system,"We have investigated the spin dynamics of a high-mobility two-dimensional
electron system (2DES) in a GaAs--Al$_{0.3}$Ga$_{0.7}$As single quantum well by
time-resolved Faraday rotation (TRFR) in dependence on the initial degree of
spin polarization, $P$, of the 2DES. From $P\sim 0$ to $P\sim 30$ %, we observe
an increase of the spin dephasing time, $T_2^\ast$, by an order of magnitude,
from about 20 ps to 200 ps, in good agreement with theoretical predictions by
Weng and Wu [Phys. Rev. B {\bf 68}, 075312 (2003)]. Furthermore, by applying an
external magnetic field in the Voigt configuration, also the electron $g$
factor is found to decrease for increasing $P$. Fully microscopic calculations,
by numerically solving the kinetic spin Bloch equations considering the
D'yakonov-Perel' and the Bir-Aronov-Pikus mechanisms, reproduce the most
salient features of the experiments, {\em i.e}., a dramatic decrease of spin
dephasing and a moderate decrease of the electron $g$ factor with increasing
$P$. We show that both results are determined dominantly by the Hartree-Fock
contribution of the Coulomb interaction.",0612477v4
2004-11-30,Higher-Spin Fields in Braneworlds,"The dynamics of higher-spin fields in braneworlds is discussed. In
particular, we study fermionic and bosonic higher-spin fields in AdS_5 and
their localization on branes. We find that four-dimensional zero modes exist
only for spin-one fields, if there are no couplings to the boundaries. If
boundary couplings are allowed, as in the case of the bulk graviton, all bosons
acquire a zero mode irrespective of their spin. We show that there are boundary
conditions for fermions, which generate chiral zero modes in the
four-dimensional spectrum. We also propose a gauge invariant on-shell action
with cubic interactions by adding non-minimal couplings, which depend on the
Weyl tensor. In addition, consistent couplings between higher-spin fields and
matter on the brane are presented. Finally, in the AdS/CFT correspondence,
where bulk 5D theories on AdS are related to 4D CFTs, we explicitly discuss the
holographic picture of higher-spin theories in AdS_5 with and without
boundaries.",0411269v3
2007-04-23,A novel quasi-exactly solvable spin chain with nearest-neighbors interactions,"In this paper we study a novel spin chain with nearest-neighbors interactions
depending on the sites coordinates, which in some sense is intermediate between
the Heisenberg chain and the spin chains of Haldane-Shastry type. We show that
when the number of spins is sufficiently large both the density of sites and
the strength of the interaction between consecutive spins follow the Gaussian
law. We develop an extension of the standard freezing trick argument that
enables us to exactly compute a certain number of eigenvalues and their
corresponding eigenfunctions. The eigenvalues thus computed are all integers,
and in fact our numerical studies evidence that these are the only integer
eigenvalues of the chain under consideration. This fact suggests that this
chain can be regarded as a finite-dimensional analog of the class of
quasi-exactly solvable Schroedinger operators, which has been extensively
studied in the last two decades. We have applied the method of moments to study
some statistical properties of the chain's spectrum, showing in particular that
the density of eigenvalues follows a Wigner-like law. Finally, we emphasize
that, unlike the original freezing trick, the extension thereof developed in
this paper can be applied to spin chains whose associated dynamical spin model
is only quasi-exactly solvable.",0704.3046v1
2007-07-13,Dynamics of polarization buildup by spin filtering,"There has been much recent research into polarizing an antiproton beam,
instigated by the recent proposal from the PAX (Polarized Antiproton
eXperiment) project at GSI Darmstadt. It plans to polarize an antiproton beam
by repeated interaction with a polarized internal target in a storage ring. The
method of polarization by spin filtering requires many of the beam particles to
remain within the ring after scattering off the polarized internal target via
electromagnetic and hadronic interactions. We present and solve sets of
differential equations which describe the buildup of polarization by spin
filtering in many different scenarios of interest to projects planning to
produce high intensity polarized beams. These scenarios are: 1) spin filtering
of a fully stored beam, 2) spin filtering while the beam is being accumulated,
i.e. unpolarized particles are continuously being fed into the beam, 3) the
particle input rate is equal to the rate at which particles are being lost due
to scattering beyond ring acceptance angle, the beam intensity remaining
constant, 4) increasing the initial polarization of a stored beam by spin
filtering, 5) the input of particles into the beam is stopped after a certain
amount of time, but spin filtering continues. The rate of depolarization of a
stored polarized beam on passing through an electron cooler is also shown to be
negligible.",0707.2065v2
2007-09-04,"On the Bohr radius relationship to spin-orbit interaction, spin magnitude, and Thomas precession","The dynamics of the spin-orbit interaction in atomic hydrogen are studied in
a classical electrodynamics-like setting. A Rutherfordian atomic model is used
assuming a circular electron orbit, without the quantum principle as imposed
arbitrarily in the Bohr model, but with an ad hoc incorporation in the electron
of intrinsic spin and associated magnetic dipole moment. Analyzing the motions
of the electron spin and orbital angular momenta, it is found that in the
presence of Thomas precession, the total angular momentum averaged over the
orbit is not generally a constant of the motion. It is noted this differs from
the finding of Thomas in a similar assessment of 1927, and the reason for this
difference is provided. It is found that although the total orbit-averaged
angular momentum is not a constant of the motion, it precesses around a fixed
axis similarly to the precession of the total angular momentum vector seen in
spin-orbit coupling in quantum theory. The magnitude of the angular velocity of
the total orbit-averaged angular momentum is seen to vanish only when the spin
and orbital angular momenta are antiparallel and their mutual precession
frequencies equate. It is then found, there is a unique radius where the mutual
precession frequencies equate. Assuming the electron magnetic moment is the
Bohr magneton, and an electron g-factor of two, this radius corresponds to
where the orbital angular momentum is the reduced Planck's constant. The orbit
radius for stationary total angular momentum for the circular orbit model with
nonzero orbital angular momentum is thus the ground-state radius of the Bohr
model.",0709.0319v4
2007-12-18,The spin expansion for binary black hole merger: new predictions and future directions,"In a recent paper arXiv:0709.0299, we introduced a spin expansion that
provides a simple yet powerful way to understand aspects of binary black hole
(BBH) merger. This approach relies on the symmetry properties of initial and
final quantities like the black hole mass m, kick velocity {\bf k}, and spin
vector {\bf s}, rather than a detailed understanding of the merger dynamics. In
this paper, we expand on this proposal, examine how well its predictions agree
with current simulations, and discuss several future directions that would make
it an even more valuable tool. The spin expansion yields many new predictions,
including several exact results that may be useful for testing numerical codes.
Some of these predictions have already been confirmed, while others await
future simulations. We explain how a relatively small number of simulations --
10 equal-mass simulations, and 16 unequal-mass simulations -- may be used to
calibrate all of the coefficients in the spin expansion up to second order at
the minimum computational cost. For a more general set of simulations of given
covariance, we derive the minimum-variance unbiased estimators for the spin
expansion coefficients. We discuss how this calibration would be interesting
and fruitful for general relativity and astrophysics. Finally, we sketch the
extension to eccentric orbits.",0712.2819v2
2009-08-26,Long-term evolution of the spin of Mercury I. Effect of the obliquity and core-mantle friction,"The present obliquity of Mercury is very low (less than 0.1 degree), which
led previous studies to always adopt a nearly zero obliquity during the
planet's past evolution. However, the initial orientation of Mercury's rotation
axis is unknown and probably much different than today. As a consequence, we
believe that the obliquity could have been significant when the rotation rate
of the planet first encountered spin-orbit resonances. In order to compute the
capture probabilities in resonance for any evolutionary scenario, we present in
full detail the dynamical equations governing the long term evolution of the
spin, including the obliquity contribution.
  The secular spin evolution of Mercury results from tidal interactions with
the Sun, but also from viscous friction at the core-mantle boundary. Here, this
effect is also regarded with particular attention. Previous studies show that a
liquid core enhances drastically the chances of capture in spin-orbit
resonances. We confirm these results for null obliquity, but we find that the
capture probability generally decreases as the obliquity increases. We finally
show that, when core-mantle friction is combined with obliquity evolution, the
spin can evolve into some unexpected configurations as the synchronous or the
1/2 spin-orbit resonance.",0908.3912v1
2009-10-08,Side-jumps in the spin-Hall effect: construction of the Boltzmann collision integral,"We present a systematic derivation of the side-jump contribution to the
spin-Hall current in systems without band structure spin-orbit interactions,
focusing on the construction of the collision integral for the Boltzmann
equation. Starting from the quantum Liouville equation for the density operator
we derive an equation describing the dynamics of the density matrix in the
first Born approximation and to first order in the driving electric field.
Elastic scattering requires conservation of the total energy, including the
spin-orbit interaction energy with the electric field: this results in a first
correction to the customary collision integral found in the Born approximation.
A second correction is due to the change in the carrier position during
collisions. It stems from the part of the density matrix off-diagonal in wave
vector. The two corrections to the collision integral add up and are
responsible for the total side-jump contribution to the spin-Hall current. The
spin-orbit-induced correction to the velocity operator also contains terms
diagonal and off-diagonal in momentum space, which together involve the total
force acting on the system. This force is explicitly shown to vanish (on the
average) in the steady state: thus the total contribution to the spin-Hall
current due to the additional terms in the velocity operator is zero.",0910.1596v2
2010-06-03,Spin-Orbit Effects in Carbon-Nanotube Double Quantum Dots,"We study the energy spectrum of symmetric double quantum dots in narrow-gap
carbon nanotubes with one and two electrostatically confined electrons in the
presence of spin-orbit and Coulomb interactions. Compared to GaAs quantum dots,
the spectrum exhibits a much richer structure because of the spin-orbit
interaction that couples the electron's isospin to its real spin through two
independent coupling constants. In a single dot, both constants combine to
split the spectrum into two Kramers doublets, while the antisymmetric constant
solely controls the difference in the tunneling rates of the Kramers doublets
between the dots. For the two-electron regime, the detailed structure of the
spin-orbit split energy spectrum is investigated as a function of detuning
between the quantum dots in a 22-dimensional Hilbert space within the framework
of a single-longitudinal-mode model. We find a competing effect of the
tunneling and Coulomb interaction. The former favors a left-right symmetric
two-particle ground state, while in the regime where the Coulomb interaction
dominates over tunneling, a left-right antisymmetric ground state is found. As
a result, ground states on both sides of the $(11)$-$(02)$ degeneracy point may
possess opposite left-right symmetry, and the electron dynamics when tuning the
system from one side of the $(11)$-$(02)$ degeneracy point to the other is
controlled by three selection rules (in spin, isospin, and left-right
symmetry). We discuss implications for the spin-dephasing and Pauli blockade
experiments.",1006.0724v2
2010-07-23,Black hole-neutron star mergers: effects of the orientation of the black hole spin,"The spin of black holes in black hole-neutron star (BHNS) binaries can have a
strong influence on the merger dynamics and the postmerger state; a wide
variety of spin magnitudes and orientations are expected to occur in nature. In
this paper, we report the first simulations in full general relativity of BHNS
mergers with misaligned black hole spin. We vary the spin magnitude from a/m=0
to a/m=0.9 for aligned cases, and we vary the misalignment angle from 0 to 80
degrees for a/m=0.5. We restrict our study to 3:1 mass ratio systems and use a
simple Gamma-law equation of state. We find that the misalignment angle has a
strong effect on the mass of the postmerger accretion disk, but only for angles
greater than ~ 40 degrees. Although the disk mass varies significantly with
spin magnitude and misalignment angle, we find that all disks have very similar
lifetimes ~ 100ms. Their thermal and rotational profiles are also very similar.
For a misaligned merger, the disk is tilted with respect to the final black
hole's spin axis. This will cause the disk to precess, but on a timescale
longer than the accretion time. In all cases, we find promising setups for
gamma-ray burst production: the disks are hot, thick, and hyperaccreting, and a
baryon-clear region exists above the black hole.",1007.4203v2
2011-01-01,Signature effects of spin clustering and distribution of spin couplings on magnetization behaviour in Ni-Fe-Mo and Ni-Fe-W alloys,"The spontaneous magnetization as a function of temperature is investigated
for a number of disordered Ni-Fe-Mo and Ni-Fe-W alloys using superconducting
quantum interference device magnetometry, with a focus on the low-T behavior as
well as the critical exponents associated with the magnetic phase transition.
While the low-T magnetization is found to be well described by Bloch's T^{3/2}
law, an extraordinary enhancement of the spin-wave parameter B and the reduced
coefficient B_{3/2}=BT_C ^{3/2} are observed with increasing Fe dilution as
compared to conventional 3d ferromagnets, whereas the critical amplitudes are
found to decrease systematically. Recent locally self-consistent calculations
of finite-temperature spin dynamics in a generic diluted magnet provide an
understanding in terms of two distinct energy scales associated with weakly
coupled bulk spins in the FM matrix and strongly coupled cluster spins. In view
of similar behaviour observed in diluted magnetic semiconductors and other
ferromagnetic alloys, it is proposed that these distinctive features
corresponding to the three important temperature regimes provide macroscopic
indicators of signature effects of spin clustering on magnetization behaviour
in disordered ferromagnets.",1101.0343v2
2011-03-25,Unconventional temperature enhanced magnetism in iron telluride,"Highly energetic magnetic fluctuations, discovered in high-temperature
superconductors (HTSC) by inelastic neutron scattering (INS), are now widely
believed to be vital for the superconductivity. In two competing scenarios,
they either originate from local atomic spins, or are a property of cooperative
spin-density-wave (SDW) behavior of conduction electrons. Both assume clear
partition into localized electrons, giving rise to local spins, and itinerant
ones, occupying well-defined, rigid conduction bands. Here, by performing an
INS study of spin dynamics in iron telluride, a parent material of one of the
iron-based HTSC families, we have discovered that this very assumption fails,
and that conduction and localized electrons are fundamentally entangled. We
find that the real-space structure of magnetic correlations can be explained by
a simple local-spin plaquette model. However, the effective spin implicated in
such a model, appears to increase with the increasing temperature. Thus, we
observe a remarkable redistribution of magnetism between the two groups of
electrons, which occurs in the temperature range relevant for the
superconductivity. The analysis of magnetic spectral weight shows that the
effective spin per Fe at T \approx 10 K, in the antiferromagnetic phase,
corresponds to S \approx 1, consistent with the recent analyses that emphasize
importance of Hund's intra-atomic exchange. However, it grows to S \approx 3/2
in the disordered phase, a result that profoundly challenges the picture of
rigid bands, broadly accepted for HTSC.",1103.5073v1
2011-04-07,The magnetic phase diagram of an extended J1-J2 model on a modulated square lattice and its implications for the antiferromagnetic phase of KyFexSe2,"Motivated by the experimentally observed $\sqrt{5} \times \sqrt{5}$ iron
vacancy order and a block spin antiferromagnetic phase with large magnetic
moment in $\mathrm{K}_{0.8}\mathrm{Fe}_{1.6}\mathrm{Se}_2$, we study the
magnetic phase diagram of an extended $J_1-J_2$ model on a 1/5-depleted square
lattice with $\sqrt{5} \times \sqrt{5}$ vacancy order, using a classical Monte
Carlo analysis. The magnetic phase diagram involves various
antiferromagnetically ordered phases, and most of them have higher order
commensuration. We find that the experimentally relevant block-spin state
occupies a significant portion of the phase diagram, and we discuss the spin
dynamics of this phase using a linear spin-wave analysis. Based on our spin
wave calculations in different parameter regimes corresponding to the block
spin antiferromagnetic phase, we show how spin-wave degeneracy along the high
symmetry directions of the magnetic Brillouin zone can provide information
regarding the underlying exchange couplings. We have also analyzed the magnetic
phase diagram of a $J_1-J_2$ model on two different modulated square lattices
relevant for $\mathrm{K}_y\mathrm{Fe}_{1.5}\mathrm{Se}_2$, which respectively
exhibit 1/4-depleted $2\times2$ and $4\times2$ vacancy ordering.",1104.1445v2
2011-09-19,Anisotropic spin-fluctuations in SmCoPO revealed by 31^P NMR measurement,"31^P NMR spectral features in polycrystalline SmCoPO reveal an axially
symmetric local magnetic field. At low temperature, the anisotropy of the
internal magnetic field increases rapidly, with K_ab increasing faster than
that of K_c. The dominant contribution to this anisotropy arises from Sm-4f
electron contribution over that of Co-3d. The intrinsic width 2*(Beta) deviates
from linearity with respect to bulk susceptibility below 170 K due to the
enhancement of (1/T_2)dynamic, which along with the continuous increase of
anisotropy in the internal magnetic field is responsible for the wipe out
effect of the NMR signal, well above T_C. 1/T_1 shows large anisotropy
confirming a significant contribution of Sm-4f electron spin fluctuations to
1/T_1, arising from indirect RKKY type exchange interaction indicating a
non-negligible hybridization between Sm-4f orbitals and the conduction band,
over the itinerant character of the Co-3d spins. This anisotropy in originates
from the orientation dependence of chi""(q,omega). The 3d-spin fluctuations in
the ab plane is 2D FM in nature, while along the c-axis, a signature of a weak
2D AFM spin fluctuations superimposed on weak FM spin-fluctuations even in a
field of 7 T and far above T_N is observed. The enhancement of this AFM
fluctuations of the Co-3d spins along c-axis, at further low temperature is
responsible to drive the system to an AFM ordered state.",1109.3955v3
2012-07-31,Spin excitations in a single La$_2$CuO$_4$ layer,"The dynamics of S=1/2 quantum spins on a 2D square lattice lie at the heart
of the mystery of the cuprates
\cite{Hayden2004,Vignolle2007,Li2010,LeTacon2011,Coldea2001,Headings2010,Braicovich2010}.
In bulk cuprates such as \LCO{}, the presence of a weak interlayer coupling
stabilizes 3D N\'{e}el order up to high temperatures. In a truly 2D system
however, thermal spin fluctuations melt long range order at any finite
temperature \cite{Mermin1966}. Further, quantum spin fluctuations transfer
magnetic spectral weight out of a well-defined magnon excitation into a
magnetic continuum, the nature of which remains controversial
\cite{Sandvik2001,Ho2001,Christensen2007,Headings2010}. Here, we measure the
spin response of \emph{isolated one-unit-cell thick layers} of \LCO{}. We show
that coherent magnons persist even in a single layer of \LCO{} despite the loss
of magnetic order, with no evidence for resonating valence bond (RVB)-like spin
correlations \cite{Anderson1987,Hsu1990,Christensen2007}. Thus these
excitations are well described by linear spin wave theory (LSWT). We also
observe a high-energy magnetic continuum in the isotropic magnetic response.
This high-energy continuum is not well described by 2 magnon LSWT, or indeed
any existing theories.",1208.0018v1
2012-11-06,Optical Signatures of the Tunable Band Gap and Valley-Spin Coupling in Silicene,"We investigate the optical response of the silicene and similar materials,
such as germanene, in the presence of an electrically tunable band gap for
variable doping. The interplay of spin orbit coupling, due to the buckled
structure of these materials, and a perpendicular electric field gives rise to
a rich variety of phases: a topological or quantum spin Hall insulator, a
valley-spin-polarized metal and a band insulator. We show that the dynamical
conductivity should reveal signatures of these different phases which would
allow for their identification along with the determination of parameters such
as the spin orbit energy gap. We find an interesting feature where the electric
field tuning of the band gap might be used to switch on and off the Drude
intraband response. Furthermore, in the presence of spin-valley coupling, the
response to circularly polarized light as a function of frequency and electric
field tuning of the band gap is examined. Using right- and left-handed circular
polarization it is possible to select a particular combination of spin and
valley index. The frequency for this effect can be varied by tuning the band
gap.",1211.1336v1
2012-11-26,"Universality, maximum radiation and absorption in high-energy collisions of black holes with spin","We explore the impact of black hole spins on the dynamics of high-energy
black hole collisions. We report results from numerical simulations with
gamma-factors up to 2.49 and dimensionless spin parameter +0.85, +0.6, 0, -0.6,
-0.85. We find that the scattering threshold becomes independent of spin at
large center-of-mass energies, confirming previous conjectures that structure
does not matter in ultrarelativistic collisions. It has further been argued
that in this limit all of the kinetic energy of the system may be radiated by
fine tuning the impact parameter to threshold. On the contrary, we find that
only about 60% of the kinetic energy is radiated for gamma=2.49. By monitoring
apparent horizons before and after scattering events we show that the ""missing
energy"" is absorbed by the individual black holes in the encounter, and
moreover the individual black-hole spins change significantly. We support this
conclusion with perturbative calculations. An extrapolation of our results to
the limit gamma->infinity suggests that about half of the center-of-mass energy
of the system can be emitted in gravitational radiation, while the rest must be
converted into rest-mass and spin energy.",1211.6114v2
2013-05-13,Landau-Zener and Rabi oscillations in the spin-dependent conductance,"We describe the spin-dependent quantum conductance in a wire where a magnetic
field is spatially modulated. The change in direction and intensity of the
magnetic field acts as a perturbation that mixes spin projections. This is
exemplified by a ferromagnetic nanowire. There the local field varies smoothly
its direction generating a domain wall (DW) as described by the well-known
Cabrera-Falicov model. Here, we generalize this model to include also a
strength modulation. We identify two striking diabatic regimes that appear when
such magnetic inhogeneity occurs. 1) If the field strength at the DW is weak
enough, the local Zeeman energies result in an avoided crossing. Thus, the
spin-flip probability follows the Landau-Zener formula. 2) For strong fields,
the spin-dependent conductance shows oscillations as a function of the DW
width. We interpret them in terms of Rabi oscillations. Time and length scales
obtained from this simplified view show an excellent agreement with the exact
dynamical solution of the spin-dependent transport. These results remain valid
for other situations involving modulated magnetic structures and thus they open
new prospects for the use of quantum interferences in spin-based devices.
  This paper is dedicated to the memory of the lifelong collaborator Patricia
Rebeca Levstein.",1305.2887v3
2013-11-11,Three-dimensional light-matter interface for collective spin squeezing in atomic ensembles,"We study the three-dimensional nature of the quantum interface between an
ensemble of cold, trapped atomic spins and a paraxial laser beam, coupled
through a dispersive interaction. To achieve strong entanglement between the
collective atomic spin and the photons, one must match the spatial mode of the
collective radiation of the ensemble with the mode of the laser beam while
minimizing the effects of decoherence due to optical pumping. For ensembles
coupling to a probe field that varies over the extent of the cloud, the set of
atoms that indistinguishably radiates into a desired mode of the field defines
an inhomogeneous spin wave. Strong coupling of a spin wave to the probe mode is
not characterized by a single parameter, the optical density, but by a
collection of different effective atom numbers that characterize the coherence
and decoherence of the system. To model the dynamics of the system, we develop
a full stochastic master equation, including coherent collective scattering
into paraxial modes, decoherence by local inhomogeneous diffuse scattering, and
backaction due to continuous measurement of the light entangled with the spin
waves. This formalism is used to study the squeezing of a spin wave via
continuous quantum nondemolition (QND) measurement. We find that the greatest
squeezing occurs in parameter regimes where spatial inhomogeneities are
significant, far from the limit in which the interface is well approximated by
a one-dimensional, homogeneous model.",1311.2328v2
2014-02-13,"Fractionalization, entanglement, and separation: understanding the collective excitations in a spin-orbital chain","Using a combined analytical and numerical approach, we study the collective
spin and orbital excitations in a spin-orbital chain under a crystal field.
Irrespective of the crystal field strength, these excitations can be
universally described by fractionalized fermions. The fractionalization
phenomenon persists and contrasts strikingly with the case of a spin chain,
where fractionalized spinons cannot be individually observed but confined to
form magnons in a strong magnetic field. In the spin-orbital chain, each of the
fractional quasiparticles carries both spin and orbital quantum numbers, and
the two variables are always entangled in the collective excitations. Our
result further shows that the recently reported separation phenomenon occurs
when crystal fields fully polarize the orbital degrees of freedom. In this
case, however, the spinon and orbiton dynamics are decoupled solely because of
a redefinition of the spin and orbital quantum numbers.",1402.3255v4
2014-04-15,Muon spin rotation and relaxation in Pr$_{1-x}$Nd$_x$Os$_4$Sb$_{12}$: Magnetic and superconducting ground states,"Muon spin rotation and relaxation ($\mu$SR) experiments have been carried out
to characterize magnetic and superconducting ground states in the
Pr$_{1-x}$Nd$_x$Os$_4$Sb$_{12}$ alloy series. In the ferromagnetic end compound
NdOs$_4$Sb$_{12}$ the spontaneous local field at positive-muon ($\mu^+$) sites
below the ordering temperature $T_C$ is greater than expected from dipolar
coupling to ferromagnetically aligned Nd$^{3+}$ moments, indicating an
additional indirect RKKY-like transferred hyperfine mechanism. For 0.45 $\le x
\le$ 0.75, $\mu^+$ spin relaxation rates in zero and weak longitudinal applied
fields indicate that static fields at $\mu^+$ sites below $T_C$ are reduced and
strongly disordered. We argue this is unlikely to be due to reduction of
Nd$^{3+}$ moments, and speculate that the Nd$^{3+}$-$\mu^+$ interaction is
suppressed and disordered by Pr doping. In an $x$ = 0.25 sample, which is
superconducting below $T_c$ = 1.3 K, there is no sign of ""spin freezing""
(static Nd$^{3+}$ magnetism), ordered or disordered, down to 25 mK. Dynamic
$\mu^+$ spin relaxation is strong, indicating significant Nd-moment
fluctuations. The $\mu^+$ diamagnetic frequency shift and spin relaxation in
the superconducting vortex-lattice phase decrease slowly below $T_c$,
suggesting pair breaking and/or possible modification of Fermi-liquid
renormalization by Nd spin fluctuations. For 0.25 $\le x \le$ 0.75, the $\mu$SR
data provide evidence against phase separation; superconductivity and Nd$^{3+}$
magnetism coexist on the atomic scale.",1404.4090v1
2014-09-25,Spin glass like ground state and observation of exchange bias in Mn_{0.8}Fe_{0.2}NiGe alloy,"The ground-state magnetic properties of hexagonal equiatomic alloy of nominal
composition Mn_{0.8}Fe_{0.2}NiGe were investigated through dc magnetization and
heat capacity measurements. The alloy undergoes first order martensitic
transition below 140 K with simultaneous development of long range
ferromagnetic ordering from the high temperature paramagnetic phase. The
undoped compound MnNiGe has an antiferromagnetic ground state and it shows
martensitic like structural instability well above room temperature. Fe doping
at the Mn site not only brings down the martensitic transition temperature, it
also induces ferromagnetism in the sample. Our study brings out two important
aspects regarding the sample, namley (i) the observation of exchange bias at
low temperature, and (ii) spin glass like ground state which prevails below the
martensitic and magnetic transition points. In addition to the observed usual
relaxation behavior the spin glass state is confirmed by zero field cooled
memory experiment, thereby indicating cooperative freezing of spin and/or spin
clusters rather than uncorrelated dynamics of superparamagnetic like spin
clusters. We believe that doping disorder can give rise to some islands of
antiferromagnetic clusters in the otherwise ferromagnetic background which can
produce interfacial frustration and exchange pinning responsible for spin glass
and exchange bias effect. A comparison is made with doped rare-earth manganites
where similar phase separation can lead to glassy ground state.",1409.7221v1
2014-11-24,Manipulating Femtosecond Spin--Orbit Torques with Laser Pulse Sequences to Control Magnetic Memory States and Ringing,"Femtosecond (fs) coherent control of collective order parameters is important
for non--equilibrium phase dynamics in correlated materials. Here we propose a
possible scheme for fs control of a ferromagnetic order parameter based on
non--adiabatic optical manipulation of electron--hole ($e$--$h$)
photoexcitations between spin--orbit--coupled bands that are exchange--split by
magnetic interaction with local spins. We photoexcite fs carrier spin--pulses
with controllable direction and time profile without using
circularly--polarized light, via time--reversal symmetry--breaking by
non--perturbative interplay between spin--orbit and magnetic exchange coupling
of coherent photocarriers. We manipulate photoexcited {\em fs spin--orbit
torques} to control complex switching pathways of the magnetization between
multiple magnetic memory states. We calculate the photoinduced fs magnetic
anisotropy in the time domain by using density matrix equations of motion
rather than the quasi--equilibrium free energy. By comparing to pump--probe
experiments, we identify a ""sudden"" magnetization canting induced by laser
excitation, which displays magnetic hysteresis absent in static
magneto--optical measurements and agrees with switchings measured by Hall
magnetoresistivity. The fs magnetization canting switches direction with
magnetic state and laser frequency, which distinguishes it from nonlinear
optical and demagnetization longitudinal effects. By shaping two--color
laser--pulse sequences analogous to multi--dimensional Nuclear Magnetic
Resonance (NMR) spectroscopy, we show that sequences of clockwise or
counter--clockwise fs spin--orbit torques can enhance or suppress magnetic
ringing and switching rotation at any desired time. We propose protocols that
can provide controlled access to four magnetic states via consequative 90$^{o}$
switchings.",1411.6662v1
2015-10-14,Spin dynamics near a putative antiferromagnetic quantum critical point in Cu substituted BaFe$_2$As$_2$ and its relation to high-temperature superconductivity,"We present the results of elastic and inelastic neutron scattering
measurements on non-superconducting
Ba(Fe${_{0.957}}$Cu${_{0.043}}$)${_2}$As${_2}$, a composition close to a
quantum critical point between AFM ordered and paramagnetic phases. By
comparing these results with the spin fluctuations in the low Cu composition as
well as the parent compound BaFe$_2$As$_2$ and superconducting
Ba(Fe$_{1-x}$Ni$_x$)$_2$As$_2$ compounds, we demonstrate that paramagnon-like
spin fluctuations are evident in the antiferromagnetically ordered state of
Ba(Fe$_{0.957}$Cu$_{0.043}$)$_2$As$_2$, which is distinct from the AFM-like
spin fluctuations in the superconducting compounds. Our observations suggest
that Cu substitution decouples the interaction between quasiparticles and the
spin fluctuations. We also show that the spin-spin correlation length,
${\xi(T)}$, increases rapidly as the temperature is lowered and find
${\omega/T}$ scaling behavior, the hallmark of quantum criticality, at an
antiferromagnetic quantum critical point.",1510.04167v1
2015-11-09,Optically controlled spin-polarization memory effect on Mn delta-doped heterostrucutres,"We investigated the dynamics of the interaction between spin-polarized
photo-created carriers and Mn ions on InGaAs/GaAs:Mn structures. The carriers
are confined in an InGaAs quantum well and the Mn ions come from a Mn
delta-layer grown at the GaAs barrier close to the well. Even though the
carriers and the Mn ions are spatially separated, the interaction between them
is demonstrated by time-resolved spin-polarized photoluminescence measurements.
Using a pre-pulse laser excitation with an opposite circular-polarization
clearly reduces the polarization degree of the quantum-well emission for
samples where a strong magnetic interaction is observed. The results
demonstrate that the Mn ions act as a spin-memory that can be optically
controlled by the polarization of the photocreated carriers. On the other hand,
the spin-polarized Mn ions also affect the spin-polarization of the
subsequently created carriers as observed by their spin relaxation time. These
effects fade away with increasing time delays between the pulses as well as
with increasing temperatures.",1511.02881v2
2016-02-10,Imaging Spin Dynamics in Monolayer WS2 by Time-Resolved Kerr Rotation Microscopy,"Monolayer transition metal dichalcogenides (TMD) have immense potential for
future spintronic and valleytronic applications due to their two-dimensional
nature and long spin/valley lifetimes. We investigate the origin of these
long-lived states in n-type WS2 using time-resolved Kerr rotation microscopy
and photoluminescence microscopy with ~1 micron spatial resolution. Comparing
the spatial dependence of the Kerr rotation signal and the photoluminescence
reveals a correlation with neutral exciton emission, which is likely due to the
transfer of angular momentum to resident conduction electrons with long
spin/valley lifetimes. In addition, we observe an unexpected anticorrelation
between the Kerr rotation and trion emission, which provides evidence for the
presence of long-lived spin/valley-polarized dark trions. We also find that the
spin/valley polarization in WS2 is robust to magnetic fields up to 700 mT,
indicative of spins and valleys that are stabilized with strong spin-orbit
fields.",1602.03568v2
2016-04-29,Spin Seebeck effect through antiferromagnetic NiO,"We report temperature-dependent spin-Seebeck measurements on Pt/YIG bilayers
and Pt/NiO/YIG trilayers, where YIG (Yttrium iron garnet, Y$_3$Fe$_5$O$_{12}$)
is an insulating ferrimagnet and NiO is an antiferromagnet at low temperatures.
The thickness of the NiO layer is varied from 0 to 10 nm. In the Pt/YIG
bilayers, the temperature gradient applied to the YIG stimulates dynamic spin
injection into the Pt, which generates an inverse spin Hall voltage in the Pt.
The presence of a NiO layer dampens the spin injection exponentially with a
decay length of $2 \pm 0.6$ nm at 180 K. The decay length increases with
temperature and shows a maximum of $5.5 \pm 0.8$ nm at 360 K. The temperature
dependence of the amplitude of the spin-Seebeck signal without NiO shows a
broad maximum of $6.5 \pm 0.5$ $\mu$V/K at 20 K. In the presence of NiO, the
maximum shifts sharply to higher temperatures, likely correlated to the
increase in decay length. This implies that NiO is most transparent to magnon
propagation near the paramagnet-antiferromagnet transition. We do not see the
enhancement in spin current driven into Pt reported in other papers when 1-2 nm
NiO layers are sandwiched between Pt and YIG.",1604.08659v2
2016-06-02,Orbital selective spin excitations and their impact on superconductivity of LiFe1-xCoxAs,"We use neutron scattering to study spin excitations in single crystals of
LiFe$_{0.88}$Co$_{0.12}$As, which is located near the boundary of the
superconducting phase of LiFe$_{1-x}$Co$_{x}$As and exhibits non-Fermi-liquid
behavior indicative of a quantum critical point. By comparing spin excitations
of LiFe$_{0.88}$Co$_{0.12}$As with a combined density functional theory (DFT)
and dynamical mean field theory (DMFT) calculation, we conclude that
wave-vector correlated low energy spin excitations are mostly from the $d_{xy}$
orbitals, while high-energy spin excitations arise from the $d_{yz}$ and
$d_{xz}$ orbitals. Unlike most iron pnictides, the strong orbital selective
spin excitations in LiFeAs family cannot be described by anisotropic Heisenberg
Hamiltonian. While the evolution of low-energy spin excitations of
LiFe$_{1-x}$Co$_x$As are consistent with electron-hole Fermi surface nesting
condition for the $d_{xy}$ orbital, the reduced superconductivity in
LiFe$_{0.88}$Co$_{0.12}$As suggests that Fermi surface nesting conditions for
the $d_{yz}$ and $d_{xz}$ orbitals are also important for superconductivity in
iron pnictides.",1606.00727v1
2016-10-17,Momentum and doping dependence of spin excitations in electron-doped cuprate superconductors,"Superconductivity in copper oxides emerges on doping holes or electrons into
their Mott insulating parent compounds. The spin excitations are thought to be
the mediating glue for the pairing in superconductivity. Here the momentum and
doping dependence of the dynamical spin response in the electron-doped cuprate
superconductors is studied based on the kinetic-energy-driven superconducting
mechanism. It is shown that the dispersion of the low-energy spin excitations
changes strongly upon electron doping, however, the hour-glass-shaped
dispersion of the low-energy spin excitations appeared in the hole-doped side
is absent in the electron-doped case due to the electron-hole asymmetry. In
particular, the commensurate resonance appears in the superconducting-state
with the resonance energy that correlates with the dome-shaped doping
dependence of the superconducting gap. Moreover, the spectral weight and
dispersion of the high-energy spin excitations in the superconducting-state are
comparable with those in the corresponding normal-state, indicating that the
high-energy spin excitations do not play an important part in the pair
formation.",1610.05041v2
2017-02-07,Resonant spin transfer torque nano-oscillators,"Spin transfer torque nano-oscillators are potential candidates for replacing
the traditional inductor based voltage controlled oscillators in modern
communication devices. Typical oscillator designs are based on trilayer
magnetic tunnel junctions which are disadvantaged by low power outputs and poor
conversion efficiencies. In this letter, we theoretically propose to use
resonant spin filtering in pentalayer magnetic tunnel junctions as a possible
route to alleviate these issues and present device designs geared toward a high
microwave output power and an efficient conversion of the d.c. input power. We
attribute these robust qualities to the resulting non-trivial spin current
profiles and the ultra high tunnel magnetoresistance, both arising from
resonant spin filtering. The device designs are based on the nonequilibrium
Green's function spin transport formalism self-consistently coupled with the
stochastic Landau-Lifshitz-Gilbert-Slonczewski's equation and the Poisson's
equation. We demonstrate that the proposed structures facilitate oscillator
designs featuring a large enhancement in microwave power of around $775\%$ and
an efficiency enhancement of over $1300\%$ in comparison with typical trilayer
designs. We also rationalize the optimum operating regions via an analysis of
the dynamic and static device resistances. This work sets stage for pentalyer
spin transfer torque nano-oscillator device designs that extenuate most of the
issues faced by the typical trilayer designs.",1702.01869v1
2017-02-14,Quantum magnetic resonance microscopy,"Magnetic resonance spectroscopy is universally regarded as one of the most
important tools in chemical and bio-medical research. However, sensitivity
limitations typically restrict imaging resolution to length scales greater than
10 \mu m. Here we bring quantum control to the detection of chemical systems to
demonstrate high resolution electron spin imaging using the quantum properties
of an array of nitrogen-vacancy (NV) centres in diamond. Our quantum magnetic
resonance microscope selectively images electronic spin species by precisely
tuning a magnetic field to bring the quantum probes into resonance with the
external target spins. This provides diffraction limited spatial resolution of
the target spin species over a field of view of ~50x50 \mu m^2. We demonstrate
imaging and spectroscopy on aqueous Cu2+ ions over microscopic volumes (0.025
\mu m^3), with detection sensitivity at resonance of 104 spins/voxel, ~100
zeptomol (10^-19 mol). The ability to image, perform spectroscopy and
dynamically monitor spin-dependent redox reactions and transition metal
biochemistry at these scales opens up a new realm of nanoscopic electron spin
resonance and zepto-chemistry in the physical and life sciences.",1702.04418v1
2017-08-30,Pulsar spin-down: the glitch-dominated rotation of PSR J0537-6910,"The young, fast-spinning, X-ray pulsar J0537-6910 displays an extreme glitch
activity, with large spin-ups interrupting its decelerating rotation every ~100
days. We present nearly 13 years of timing data from this pulsar, obtained with
the {\it Rossi X-ray Timing Explorer}. We discovered 22 new glitches and
performed a consistent analysis of all 45 glitches detected in the complete
data span. Our results corroborate the previously reported strong correlation
between glitch spin-up size and the time to the next glitch, a relation that
has not been observed so far in any other pulsar. The spin evolution is
dominated by the glitches, which occur at a rate ~3.5 per year, and the
post-glitch recoveries, which prevail the entire inter-glitch intervals. This
distinctive behaviour provides invaluable insights into the physics of
glitches. The observations can be explained with a multi-component model which
accounts for the dynamics of the neutron superfluid present in the crust and
core of neutron stars. We place limits on the moment of inertia of the
component responsible for the spin-up and, ignoring differential rotation, the
velocity difference it can sustain with the crust. Contrary to its rapid
decrease between glitches, the spin-down rate increased over the 13 years, and
we find the long-term braking index $n_{\rm l}=-1.22(4)$, the only negative
braking index seen in a young pulsar. We briefly discuss the plausible
interpretations of this result, which is in stark contrast to the predictions
of standard models of pulsar spin-down.",1708.09459v2
2018-02-01,Phase separation and hidden vortices induced by spin-orbit coupling in spin-1 Bose-Einstein condensates,"We investigate phase separation and hidden vortices in spin-orbit coupled
ferromagnetic BoseEinstein condensates with rotation and Rabi coupling. The
hidden vortices are invisible in density distribution but are visible in phase
distribution, which can carry angular momentum like the ordinary quantized
vortices. In the absence of the rotation, we observe the phase separation
induced by the spin-orbit coupling and determine the entire phase diagram of
the existence of phase separation. For the rotation case, in addition to the
phase separation, we demonstrate particularly that the spin-orbit coupling can
result in the hidden vortices and hidden vortex-antivortex pairs. The
corresponding entire phase diagrams are determined, depending on the interplay
of the spin-orbit coupling strength, the rotation frequency, and Rabi
frequency, which reveals the critical condition of the occurrence of the hidden
vortices and vortex-antivortex pairs. The hidden vortices here are proved to be
long-lived in the time scale of experiment by the dynamic analysis. These
findings not only provide a clear illustration of the phase separation in
spin-orbit coupled spinor Bose-Einstein condensates, but also open a new
direction for investigating the hidden vortices in high-spin quantum system.",1802.00138v1
2018-02-13,Electric control of emergent magnonic spin current and dynamic multiferroicity in magnetic insulators at finite temperatures,"Conversion of thermal energy into magnonic spin currents and/or effective
electric polarization promises new device functionalities. A versatile approach
is presented here for generating and controlling open circuit magnonic spin
currents and an effective multiferroicity at a uniform temperature with the aid
of spatially inhomogeneous, external, static electric fields. This field
applied to a ferromagnetic insulator with a Dzyaloshinskii-Moriya type coupling
changes locally the magnon dispersion and modifies the density of thermally
excited magnons in a region of the scale of the field inhomogeneity. The
resulting gradient in the magnon density can be viewed as a gradient in the
effective magnon temperature. This effective thermal gradient together with
local magnon dispersion result in an open-circuit, electric field controlled
magnonic spin current. In fact, for a moderate variation in the external
electric field the predicted magnonic spin current is on the scale of the spin
(Seebeck) current generated by a comparable external temperature gradient.
Analytical methods supported by full-fledge numerics confirm that both, a
finite temperature and an inhomogeneous electric field are necessary for this
emergent non-equilibrium phenomena. The proposal can be integrated in magnonic
and multiferroic circuits, for instance to convert heat into electrically
controlled pure spin current using for example nanopatterning, without the need
to generate large thermal gradients on the nanoscale.",1802.04614v1
2019-05-16,Signatures for spinons in the quantum spin liquid candidate Ca$_{10}$Cr$_7$O$_{28}$,"We present new experimental low-temperature heat capacity and detailed
dynamical spin-structure factor data for the quantum spin liquid candidate
material Ca$_{10}$Cr$_7$O$_{28}$. The measured heat capacity shows an almost
perfect linear temperature dependence in the range $0.1$ K $\lesssim
T\lesssim0.5$ K, reminiscent of fermionic spinon degrees of freedom. The spin
structure factor exhibits two energy regimes of strong signal which display
rather different but solely diffuse scattering features. We theoretically
describe these findings by an effective spinon hopping model which crucially
relies on the existence of strong ferromagnetically coupled triangles in the
system. Our spinon theory is shown to naturally reproduce the overall weight
distribution of the measured spin structure factor. Particularly, we argue that
various different observed characteristic properties of the spin structure
factor and the heat capacity consistently indicate the existence of a spinon
Fermi surface. A closer analysis of the heat capacity at the lowest accessible
temperatures hints towards the presence of weak $f$-wave spinon pairing terms
inducing a small partial gap along the Fermi surface (except for discrete nodal
Dirac points) and suggesting an overall $\mathbb{Z}_2$ quantum spin liquid
scenario for Ca$_{10}$Cr$_7$O$_{28}$.",1905.06761v1
2020-07-13,Molecule Oxygen Induced Ferromagnetism and Half-metallicity in α-BaNaO4: A First Principles Study,"Molecule oxygen resembles 3d and 4f metals in exhibiting long-range spin
ordering and electron strong correlated behaviors in compounds. The
ferromagnetic spin ordering and half-metallicity, however, are quite elusive
and have not been well acknowl-edged. In this article, we address this issue to
study how spins will interact each other if the oxygen dimers are arranged in a
dif-ferent way from that in the known super- and per-oxides by first principles
calculations. Based on the results of structure search, thermodynamic study and
lattice dynamics, we show that tetragonal {\alpha}-BaNaO4 is a stable
half-metal with a Curie temperature at 120 K, a first example in this class of
compounds. Like 3d and 4f metals, the O2 dimer carries a local magnetic moment
0.5 {\mu}B due to the unpaired electrons in its {\pi}* orbitals. This compound
can be regarded as forming from the O2 dimer layers stacking in a head to head
way. Different from that in AO2 (A=K, Rb, Cs), the spins are both
ferromagnetically coupled within and between the layers. Spin polarization
occurs in {\pi}* orbitals with spin-up electrons fully occupying the valence
band and spin-down electrons partially the conduction band, forming the
semiconducting and metallic channels, respectively. Our results highlight the
im-portance of geometric arrangement of O2 dimers in inducing ferromagnetism
and other novel properties in O2 dimer containing compounds.",2007.06433v1
2020-07-16,Theory of the Inverse Faraday Effect due to the Rashba Spin-Oribt Interactions: Roles of Band Dispersions and Fermi Surfaces,"We theoretically study the inverse Faraday effect, i.e., the optical
induction of spin polarization with circularly polarized light, by particularly
focusing on effects of band dispersions and Fermi surfaces in crystal systems
with the spin-orbit interaction (SOI). By numerically solving the
time-dependent Schr\""odinger equation of a tight-binding model with the
Rashba-type SOI, we reproduce the light-induced spin polarization proportional
to $E_0^2/\omega^3$ where $E_0$ and $\omega$ are the electric-field amplitude
and the angular frequency of light, respectively. This optical spin induction
is attributed to dynamical magnetoelectric coupling between the light electric
field and the electron spins mediated by the SOI. We elucidate that the
magnitude and sign of the induced spin polarization sensitively depend on the
electron filling. To understand these results, we construct an analytical
theory based on the Floquet theorem. The theory successfully explains the
dependencies on $E_0$ and $\omega$ and ascribes the electron-filling dependence
to a momentum-dependent effective magnetic field governed by the Fermi-surface
geometry. Several candidate materials and experimental conditions relevant to
our theory and model parameters are also discussed. Our findings will enable us
to engineer the magneto-optical responses of matters via tuning the material
parameters.",2007.08072v1
2016-10-31,"Kinetic analysis of spin current contribution to spectrum of electromagnetic waves in spin-1/2 plasma, Part II: Dispersion dependencies","The dielectric permeability tensor for spin polarized plasmas derived in
terms of the spin-1/2 quantum kinetic model in six-dimensional phase space in
Part I of this work is applied for study of spectra of high-frequency
transverse and transverse-longitudinal waves propagating perpendicular to the
external magnetic field. Cyclotron waves are studied at consideration of waves
with electric field directed parallel to the external magnetic field. It is
found that the separate spin evolution modifies the spectrum of cyclotron
waves. These modifications increase with the increase of the spin polarization
and the number of the cyclotron resonance. Spin dynamics with no account of the
anomalous magnetic moment gives a considerable modification of spectra either.
The account of anomalous magnetic moment leads to a fine structure of each
cyclotron resonance. So, each cyclotron resonance splits on three waves.
Details of this spectrum and its changes with the change of spin polarization
are studied for the first and second cyclotron waves. A cyclotron resonance
existing at $\omega\approx0.001\mid\Omega_{e}\mid$ due to the anomalous
magnetic moment is also described, where $\mid\Omega_{e}\mid$ is the cyclotron
frequency. The ordinary waves does not have any considerable modification. The
electrostatic and electromagnetic Berstein modes are studied during the
analysis of waves propagating perpendicular to the external magnetic field with
the electric field perturbation directed perpendicular to the external field. A
modification of the oscillatory structure caused by the equilibrium spin
polarization is found in both regimes. Similar modification is found for the
extraordinary wave spectrum.",1611.00046v1
2018-05-03,Post-Newtonian spin-tidal couplings for compact binaries,"We compute the spin-tidal couplings that affect the dynamics of two orbiting
bodies at the leading order in the post-Newtonian (PN) framework and to linear
order in the spin. These corrections belong to two classes: (i) terms arising
from the coupling between the ordinary tidal terms and the point-particle
terms, which depend on the standard tidal Love numbers of order $l$ and affect
the gravitational-wave (GW) phase at $(2l+5/2)$PN order and (ii) terms
depending on the rotational tidal Love numbers, recently introduced in previous
work, that affect the GW phase at $(2l+1/2+\delta_{2l})$PN order. For circular
orbits and spins orthogonal to the orbital plane, all leading-order spin-tidal
terms enter the GW phase at $1.5$PN order relative to the standard,
quadrupolar, tidal deformability term (and, thus, before the standard octupolar
tidal deformability terms). We present the GW phase that includes all tidal
terms up to $6.5$PN order and to linear order in the spin. We comment on a
conceptual issue related to the inclusion of the rotational tidal Love numbers
in a Lagrangian formulation and on the relevance of spin-tidal couplings for
parameter estimation in coalescing neutron-star binaries and for tests of
gravity.",1805.01487v3
2018-05-16,Direct observation of intravalley spin relaxation in single-layer WS$_2$,"In monolayer Transition Metal Dichalcogenides (TMDs) the valence and
conduction bands are spin split because of the strong spin-orbit interaction.
In tungsten-based TMDs the spin-ordering of the conduction band is such that
the so-called dark exciton, consisting of an electron and a hole with opposite
spin orientation, has lower energy than the A exciton. A possible mechanism
leading to the transition from bright to dark excitons involves the scattering
of the electrons from the upper to the lower conduction band state in K. Here
we exploit the valley selective optical selection rules and use two-color
helicity-resolved pump-probe spectroscopy to directly measure the intravalley
spin-flip relaxation dynamics of electrons in the conduction band of
single-layer WS$_2$. This process occurs on a sub-ps time scale and it is
significantly dependent on the temperature, indicative of a phonon-assisted
relaxation. These experimental results are supported by time-dependent
ab-initio calculations which show that the intra-valley spin-flip scattering
occurs on significantly longer time scales only exactly at the K point. In a
realistic situation the occupation of states away from the minimum of the
conduction band leads to a dramatic reduction of the scattering time.",1805.06259v1
2013-09-25,Critical behavior of spin and chiral degrees of freedom in three-dimensional disordered XY models studied by the nonequilibrium aging method,"The critical behavior of the gauge-glass and the XY spin-glass models in
three dimensions is studied by analyzing their nonequilibrium aging dynamics. A
new numerical method, which relies on the calculation of the two-time
correlation and integrated response functions, is used to determine both the
critical temperature and the nonequilibrium scaling exponents, both for spin
and chiral degrees of freedom. First, the ferromagnetic XY model is studied to
validate this nonequilibirum aging method (NAM), since for this nondisordered
system we can compare with known results obtained with standard equilibrium and
nonequilibrium techniques. When applied to the case of the gauge-glass model,
we show that the NAM allows us to obtain precise and reliable values of its
critical quantities, improving previous estimates. The XY spin-glass model with
both Gaussian and bimodal bond distributions, is analyzed in more detail. The
spin and the chiral two-time correlation and integrated response functions are
calculated in our simulations. The results obtained mainly for Gaussian and, to
a lesser extent, for bimodal interactions, support the existence of a
spin-chiral decoupling scenario, where the chiral order occurs at a finite
temperature while the spin degrees of freedom order at very low or zero
temperature.",1309.6438v2
2016-12-21,Nuclear magnetic resonance and nuclear spin relaxation in AlAs quantum well probed by ESR,"The study of nuclear magnetic resonance and nuclear spin-lattice relaxation
was conducted in an asymmetrically doped to $n\sim1.8\times10^{11}$ cm$^{-2}$
16 nm AlAs quantum well grown in the $[001]$-direction. Dynamic polarization of
nuclear spins due to the hyperfine interaction resulted in the so-called
Overhauser shift of the two-dimensional conduction electron spin resonance. The
maximum shifts achieved in the experiments are several orders of magnitude
smaller than in GaAs-based heterostructures indicating that hyperfine
interaction is weak. The nuclear spin-lattice relaxation time extracted from
the decay of Overhauser shift over time turned out to depend on the filling
factor of the two-dimensional electron system. This observation indicates that
nuclear spin-lattice relaxation is mostly due to the interaction between
electron and nuclear spins. Overhauser shift diminishes resonantly when the
RF-radiation of certain frequencies was applied to the sample. This effect
served as an indirect, yet powerful method for nuclear magnetic resonance
detection: NMR quadrupole splitting of $^{75}$As nuclei was clearly resolved.
Theoretical calculations performed describe well these experimental findings.",1612.07302v1
2017-07-12,TMDs of Spin-one Targets: Formalism and Covariant Calculations,"We present a covariant formulation and model calculations of transverse
momentum-dependent quark distribution functions (TMDs) for spin-one hadrons.
Emphasis is placed on a description of these 3-dimensional distribution
functions which is independent of any constraints on the spin quantization
axis. We apply our covariant spin description to all nine leading-twist
time-reversal even $\rho$ meson TMDs in the framework provided by the
Nambu--Jona-Lasinio model, incorporating important aspects of quark confinement
via the infrared cut-off in the proper-time regularization scheme. In
particular, the behavior of the 3-dimensional TMDs in a tensor polarized
spin-one hadron are illustrated. Sum rules and positivity constraints are
discussed in detail. Results of particular interest include the finding that
the tensor polarized TMDs -- associated with spin-one hadrons -- are very
sensitive to quark orbital angular momentum, and that the TMDs associated with
the quark operator $\gamma^+\boldsymbol{\gamma}_T\gamma_5$ would vanish were it
not for dynamical chiral symmetry breaking. In addition, we find that 44% of
the $\rho$ meson's spin is carried by the orbital angular momentum of the
quarks, and that the magnitude of the tensor polarized quark distribution
function is about 30% of the unpolarized quark distribution. A qualitative
comparison between our results for the tensor structure of a quark-antiquark
bound state is made to previous experimental and theoretical results for the
two-nucleon (deuteron) bound state.",1707.03787v2
2019-06-07,Tuning the exchange bias on a single atom from 1 mT to 10 T,"Shrinking spintronic devices to the nanoscale ultimately requires localized
control of individual atomic magnetic moments. At these length scales, the
exchange interaction plays important roles, such as in the stabilization of
spin-quantization axes, the production of spin frustration, and creation of
magnetic ordering. Here, we demonstrate the precise control of the exchange
bias experienced by a single atom on a surface, covering an energy range of
four orders of magnitude. The exchange interaction is continuously tunable from
milli-eV to micro-eV by adjusting the separation between a spin-1/2 atom on a
surface and the magnetic tip of a scanning tunneling microscope (STM). We
seamlessly combine inelastic electron tunneling spectroscopy (IETS) and
electron spin resonance (ESR) to map out the different energy scales. This
control of exchange bias over a wide span of energies provides versatile
control of spin states, with applications ranging from precise tuning of
quantum state properties, to strong exchange bias for local spin doping. In
addition we show that a time-varying exchange interaction generates a localized
AC magnetic field that resonantly drives the surface spin. The static and
dynamic control of the exchange interaction at the atomic-scale provides a new
tool to tune the quantum states of coupled-spin systems.",1906.03213v1
2019-06-26,Measurement of back-action from electron spins in a gate defined GaAs double quantum dot coupled to a mesoscopic nuclear spin bath,"Decoherence of a quantum system arising from its interaction with an
environment is a key concept for understanding the transition between the
quantum and classical world as well as performance limitations in quantum
technology applications. The effects of large, weakly coupled environments are
often described as a classical, fluctuating field whose dynamics is unaffected
by the qubit, whereas a fully quantum description still implies some
back-action from the qubit on the environment. Here we show direct experimental
evidence for such a back-action for an electron-spin-qubit in a GaAs quantum
dot coupled to a mesoscopic environment of order $10^6$ nuclear spins. By means
of a correlation measurement technique, we detect the back-action of a single
qubit-environment interaction whose duration is comparable to the qubit's
coherence time, even in such a large system. We repeatedly let the qubit
interact with the spin bath and measure its state. Between such cycles, the
qubit is reinitialized to different states. The correlations of the measurement
outcomes are strongly affected by the intermediate qubit state, which reveals
the action of a single electron spin on the nuclear spins.",1906.11264v2
2019-07-29,Non-linear dynamics of spinning bosonic stars: formation and stability,"We perform numerical evolutions of the fully non-linear Einstein-(complex,
massive)Klein-Gordon and Einstein-(complex)Proca systems, to assess the
formation and stability of spinning bosonic stars. In the scalar/vector case
these are known as boson/Proca stars. Firstly, we consider the formation
scenario. Starting with constraint-obeying initial data, describing a dilute,
axisymmetric cloud of spinning scalar/Proca field, gravitational collapse
towards a spinning star occurs, via gravitational cooling. In the scalar case
the formation is transient, even for a non-perturbed initial cloud; a
non-axisymmetric instability always develops ejecting all the angular momentum
from the scalar star. In the Proca case, by contrast, no instability is
observed and the evolutions are compatible with the formation of a spinning
Proca star. Secondly, we address the stability of an existing star, a
stationary solution of the field equations. In the scalar case, a
non-axisymmetric perturbation develops collapsing the star to a spinning black
hole. No such instability is found in the Proca case, where the star survives
large amplitude perturbations; moreover, some excited Proca stars decay to, and
remain as, fundamental states. Our analysis suggests bosonic stars have
different stability properties in the scalar/vector case, which we tentatively
relate to their toroidal/spheroidal morphology. A parallelism with
instabilities of spinning fluid stars is briefly discussed.",1907.12565v1
2019-10-30,Global phase diagram of a spin-orbital Kondo impurity model and the suppression of Fermi-liquid scale,"Many correlated metallic materials are described by Landau Fermi-liquid
theory at low energies, but for Hund metals the Fermi-liquid coherence scale
$T_{\text{FL}}$ is found to be surprisingly small. In this Letter, we study the
simplest impurity model relevant for Hund metals, the three-channel
spin-orbital Kondo model, using the numerical renormalization group (NRG)
method and compute its global phase diagram. In this framework, $T_{\text{FL}}$
becomes arbitrarily small close to two new quantum critical points (QCPs) which
we identify by tuning the spin or spin-orbital Kondo couplings into the
ferromagnetic regimes. We find quantum phase transitions to a singular
Fermi-liquid or a novel non-Fermi-liquid phase. The new non-Fermi-liquid phase
shows frustrated behavior involving alternating overscreenings in spin and
orbital sectors, with universal power laws in the spin ($\omega^{-1/5}$),
orbital ($\omega^{1/5}$) and spin-orbital ($\omega^1$) dynamical
susceptibilities. These power laws, and the NRG eigenlevel spectra, can be
fully understood using conformal field theory arguments, which also clarify the
nature of the non-Fermi-liquid phase.",1910.13643v2
2020-02-26,Local spin polarizations in relativistic heavy ion collisions,"Based on a generalized side-jump formalism for massless chiral fermions,
which naturally takes into account the spin-orbit coupling in the scattering of
two chiral fermions and the chiral vortical effect in a rotating chiral fermion
matter, we have developed a covariant and total angular momentum conserved
chiral transport model to study both the global and local polarizations of this
matter. For a system of massless quarks of random spin orientations and finite
vorticity in a box, we have demonstrated that the model can exactly conserve
the total angular momentum of the system and dynamically generate the quark
spin polarization expected from a thermally equilibrated quark matter. Using
this model to study the spin polarization in relativistic heavy-ion collision,
we have found that the local quark spin polarizations depend strongly on the
reference frame where they are evaluated as a result of the nontrivial axial
charge distribution caused by the chiral vortical effect. We have further shown
that because of the anomalous orbital or side-jump contribution to the quark
spin polarization, the local quark polarizations calculated in the medium rest
frame are qualitatively consistent with the local polarizations of Lambda
hyperons measured in experiments.",2002.11752v1
2021-01-15,Enhanced spin coherence while displacing electron in a 2D array of quantum dots,"The ability to shuttle coherently individual electron spins in arrays of
quantum dots is a key procedure for the development of scalable quantum
information platforms. It allows the use of sparsely populated electron spin
arrays, envisioned to efficiently tackle the one- and two-qubit gate
challenges. When the electrons are displaced in an array, they are submitted to
site-dependent environment interactions such as hyperfine coupling with
substrate nuclear spins. Here, we demonstrate that the electron
multi-directional displacement in a $3\times 3$ array of tunnel coupled quantum
dots enhances the spin coherence time via the motional narrowing phenomenon.
More specifically, up to 10 configurations are explored by the electrons to
study the impact of the displacement on spin dynamics. An increase of the
coherence time by a factor up to 10 is observed in case of fast and repetitive
displacement. The physical mechanism responsible for the loss of coherence
induced by displacement is quantitatively captured by a simple model and its
implications on spin coherence properties during the electron displacement are
discussed in the context of large-scale quantum circuits.",2101.05968v1
2017-09-22,Homogenization of Doppler broadening in spin noise spectroscopy,"The spin noise of cesium atoms vapor with admixture of buffer gas is
experimentally investigated by measuring the spin induced Faraday rotation
fluctuations in the vicinity of D 2 line. The line, under these conditions, is
known to be strongly inhomogeneously broadened due to the Doppler effect.
Despite that, optical spectrum of the spin noise power, as we have found, has
the characteristic shape of the homogeneously broadened line with the dip at
the line center. This fact is in stark contrast with the results of previous
studies of inhomogeneous quantum dot ensembles. In addition, the two-color
experiments, where correlations of the Faraday rotation fluctuations for two
probe wavelengths were measured, have shown, in a highly spectacular way, that
these fluctuations are either correlated, or anticorrelated depending on
whether the two wavelengths lie on the same side, or on different sides of the
resonance. The experimental data are explained within the developed theoretical
model which takes into account both kinetics and spin dynamics of Cs atoms. It
is shown that the unexpected behavior of the optical Faraday rotation noise
spectra and effective homogenization of the optical transition in the
spin-noise measurements are related to smallness of the momentum relaxation
time of the atoms as compared with their spin relaxation time.",1709.07959v2
2018-07-17,"Field-induced intermediate phase in $α$-RuCl$_3$: Non-coplanar order, phase diagram, and proximate spin liquid","Frustrated magnets with strong spin-orbit coupling promise to host
topological states of matter, with fractionalized excitations and emergent
gauge fields. Kitaev's proposal for a honeycomb-lattice Majorana spin liquid
has triggered an intense search for experimental realizations, with
bond-dependent Ising interaction being the essential building block. A prime
candidate is $\alpha$-RuCl$_3$ whose phase diagram in a magnetic field is,
however, not understood to date. Here we present conclusive experimental
evidence for a novel field-induced ordered phase in $\alpha$-RuCl$_3$,
sandwiched between the zigzag and quantum disordered phases at low and high
fields, respectively. We provide a detailed theoretical study of the relevant
effective spin model which we show to display a field-induced intermediate
phase as well. We fully characterize the intermediate phase within this model,
including its complex spin structure, and pinpoint the parameters relevant to
$\alpha$-RuCl$_3$ based on the experimentally observed critical fields. Most
importantly, our study connects the physics of $\alpha$-RuCl$_3$ to that of the
Kitaev-$\Gamma$ model, which displays a quantum spin liquid phase in zero
field, and hence reveals the spin liquid whose signatures have been detected in
a variety of dynamical probes of $\alpha$-RuCl$_3$.",1807.06192v2
2018-08-15,Chirality and intrinsic dissipation of spin modes in two-dimensional electron liquids,"We review recent theoretical and experimental developments concerning
collective spin excitations in two-dimensional electron liquid (2DEL) systems,
with particular emphasis on the interplay between many-body and spin-orbit
effects, as well as the intrinsic dissipation due to the spin-Coulomb drag.
Historically, the experimental realization of 2DELs in silicon inversion layers
in the 60s and 70s created unprecedented opportunities to probe subtle quantum
effects, culminating in the discovery of the quantum Hall effect. In the
following years, high quality 2DELs were obtained in doped quantum wells made
in typical semiconductors like GaAs or CdTe. These systems became important
test beds for quantum many-body effects due to Coulomb interaction, spin
dynamics, spin-orbit coupling, effects of applied magnetic fields, as well as
dissipation mechanisms. Here we focus on the recent results involving chiral
effects and intrinsic dissipation of collective spin modes: these are not only
of fundamental interest but also important towards demonstrating new concepts
in spintronics. Moreover, new realizations of 2DELs are emerging beyond
traditional semiconductors, for instance in multilayer graphene, oxide
interfaces, dichalcogenide monolayers, and many more. The concepts discussed in
this review will be relevant also for these emerging systems.",1808.05266v2
2018-08-29,An exact solution of the partition function for mean-field quantum spin systems without the static approximation,"Suzuki-Trotter decomposition is a well-known technique used to calculate the
partition function of quantum spin systems, in which the imaginary-time
dependence of the partition function occurs inevitably. Since it is very
difficult to explicitly treat the imaginary-time dependence of the partition
function, we usually neglect the imaginary-time dynamical effect, which is
called the static approximation. Although the static approximation is the first
approach, it is not even clear when the static approximation is justified for
mean-field quantum spin systems, that is, mean-field quantum spin systems have
not been solved exactly so far. In this study, we solve exactly the partition
function for a particular class of mean-field quantum spin systems including
randomness without the static approximation. The partition function can be
regarded as a result of time evolution in the imaginary-time Schr\""odinger
equation, and solving the exact solution of the partition function is
equivalent to solving the optimal control problem in the imaginary-time
Schr\""odinger equation. As the result, the solution of the optimal control
problem coincides exactly with the static approximate solution of the partition
function and, therefore, the static approximation is exact for the particular
class of mean-field quantum spin systems including randomness in general.
Furthermore, we prove that the analysis of the previous study in quantum
annealing is exact where the non-stoquastic interaction and the inhomogeneous
transverse field accelerate the computational time exponentially for mean-field
quantum spin systems.",1808.09707v1
2018-12-24,Non-Reciprocal Spin Pumping in Asymmetric Magnetic Trilayers,"In magnetic trilayer systems, spin pumping is generally addressed as a
reciprocal mechanism characterized by one unique spin mixing conductance common
to both interfaces. However, this assumption is questionable in cases where
different types of interfaces are present in the material. Here, we present a
general theory for analyzing spin pumping in cases with more than one unique
interface. The theory is applied to analyze layer-resolved ferromagnetic
resonance experiments on the trilayer system
Ni$_{20}$Fe$_{80}$/Ru/Fe$_{49}$Co$_{49}$V$_2$ where the Ru spacer thickness is
varied to tune the indirect exchange coupling. The results show that the spin
pumping in trilayer systems with dissimilar magnetic layers is non-reciprocal,
with a surprisingly large difference between spin-pumping induced damping of
different interfaces. Our findings have importance on dynamics of spintronic
devices based on magnetic multilayer materials.",1812.09978v1
2019-04-22,Spontaneously scalarised Kerr black holes,"We construct asymptotically flat, spinning, regular on and outside an event
horizon, scalarised black holes (SBHs) in extended scalar-tensor-Gauss-Bonnet
models. They reduce to Kerr BHs when the scalar field vanishes. For an
illustrative choice of non-minimal coupling, we scan the domain of existence.
For each value of spin, SBHs exist in an interval between two critical masses,
with the lowest one vanishing in the static limit. Non-uniqueness with Kerr BHs
of equal global charges is observed; the SBHs are entropically favoured. This
suggests SBHs form dynamically from the spontaneous scalarisation of Kerr BHs,
which are prone to a scalar-triggered tachyonic instability, below the largest
critical mass. Phenomenologically, the introduction of BH spin damps the
maximal observable difference between comparable scalarised and vacuum BHs. In
the static limit, (perturbatively stable) SBHs can store over 20% of the
spacetime energy outside the event horizon; in comparison with Schwarzschild
BHs, their geodesic frequency at the ISCO can differ by a factor of 2.5 and
deviations in the shadow areal radius may top 40%. As the BH spin grows, low
mass SBHs are excluded, and the maximal relative differences decrease, becoming
of order $\sim$ few % for dimensionless spin $j\gtrsim 0.5$. This reveals a
spin selection effect: non-GR effects are only significant for low spin. We
discuss if and how the recently measured shadow size of the M87 supermassive
BH, constrains the length scale of the Gauss-Bonnet coupling.",1904.09997v1
2019-08-07,Reconfigurable sub-micron spin-wave majority gate with electrical transducers,"Spin waves are excitations in ferromagnetic media that have been proposed as
information carriers in hybrid spintronic devices with much lower operation
power than conventional charge-based electronics. Their wave nature can be
exploited in majority gates by using interference for computation. However, a
scalable spin-wave majority gate that can be co-integrated alongside
conventional electronics is still lacking. Here, we demonstrate a sub-micron
inline spin-wave majority gate with fan-out. Time-resolved imaging of the
magnetization dynamics by scanning transmission x-ray microscopy illustrates
the device operation. All-electrical spin-wave spectroscopy further
demonstrates majority gates with sub-micron dimensions, reconfigurable input
and output ports, and frequency-division multiplexing. Challenges for hybrid
spintronic computing systems based on spin-wave majority gates are discussed.",1908.02546v3
2019-12-20,Slow-wave based magnonic diode,"Spin waves, the collective excitations of the magnetic order parameter, and
magnons, the associated quasiparticles, are envisioned as possible data
carriers in future wave-based computing architectures. On the road towards
spin-wave computing, the development of a diode-like device capable of
transmitting spin waves in only one direction, thus allowing controlled signal
routing, is an essential step. Here, we report on the design and experimental
realization of a microstructured magnonic diode in a ferromagnetic bilayer
system. Effective unidirectional propagation of spin waves is achieved by
taking advantage of nonreciprocities produced by dynamic dipolar interactions
in transversally magnetized media, which lack symmetry about their horizontal
midplane. More specifically, dipolar-induced nonreciprocities are used to
engineer the spin-wave dispersion relation of the bilayer system so that the
group velocity is reduced to very low values for one direction of propagation,
and not for the other, thus producing unidirectional slow spin waves. Brillouin
light scattering and propagating spin-wave spectroscopy are used to demonstrate
the diode-like behavior of the device, the composition of which was previously
optimized through micromagnetic simulations. simulations.",1912.09735v1
2020-05-01,Spin-Lasers: Spintronics Beyond Magnetoresistance,"Introducing spin-polarized carriers in semiconductor lasers reveals an
alternative path to realize room-temperature spintronic applications, beyond
the usual magnetoresistive effects. Through carrier recombination, the angular
momentum of the spin-polarized carriers is transferred to photons, thus leading
to the circularly polarized emitted light. The intuition for the operation of
such spin-lasers can be obtained from simple bucket and harmonic oscillator
models, elucidating their steady-state and dynamic response, respectively.
These lasers extend the functionalities of spintronic devices and exceed the
performance of conventional (spin-unpolarized) lasers, including an order of
magnitude faster modulation frequency. Surprisingly, this ultrafast operation
relies on a short carrier spin relaxation time and a large anisotropy of the
refractive index, both viewed as detrimental in spintronics and conventional
lasers. Spin-lasers provide a platform to test novel concepts in spin devices
and offer progress connected to the advances in more traditional areas of
spintronics.",2005.00591v1
2020-06-30,Spin and density self-ordering in dynamic polarization gradients fields,"We study the zero-temperature quantum phase diagram for a two-component
Bose-Einstein condensate in an optical cavity. The two atomic spin states are
Raman coupled by two transverse orthogonally-polarized, blue detuned plane-wave
lasers inducing a repulsive cavity potential. For weak pump the lasers favor a
state with homogeneous density and predefined uniform spin direction. When one
pump laser is polarized parallel to the cavity mode polarization, the photons
coherently scattered into the resonator induce a polarization gradient along
the cavity axis, which mediates long-range density-density, spin-density, and
spin-spin interactions. We show that the coupled atom-cavity system implements
central aspects of the $t$-$J$-$V$-$W$ model with a rich phase diagram. At the
mean-field limit we identify at least four qualitatively distinct density- and
spin-ordered phases including ferro- and anti-ferromagnetic order along the
cavity axis, which can be controlled via the pump strength and detuning. A real
time observation of amplitude and phase of the emitted fields bears strong
signatures of the realized phase and allows for real-time determination of
phase transition lines. Together with measurements of the population imbalance
most properties of the phase diagram can be reconstructed.",2006.16582v2
2020-11-20,Exchange interactions and magnetic force theorem,"We critically reexamine the problem of interatomic exchange interactions,
which describe the total energy change caused by infinitesimal rotations of
spins near some equilibrium state. For the small variations, such interactions
can be always related to the response function. However, the form of this
relation can depend on additional approximations. Particularly, the commonly
used magnetic force theorem (MFT) prescribes the linear relation between the
exchange interactions and the response function, while the exact theory
requires this dependence to be inverse. We explore the origin and consequences
of these differences in the definition for the wide class of materials:
ferromagnetic Ni, antiferromagnetic NiO, half-metallic CrO2, multiferroic
HoMnO3, and layered magnets CrCl3 and CrI3. While in most of these cases, MFT
produces quite reasonable results and can be rigorously justifies in the long
wavelength and strong-coupling limits, the exact formulation appears to be more
consistent, especially in dealing with two important issues, which typically
arise in the theory of exchange interactions: (i) the treatment of the ligand
states, and (ii) the choice of the suitable variable for the description of
infinitesimal rotations of spins. Both issues can be efficiently resolved by
employing the ideas of adiabatic spin dynamics supplemented with the exact
expression for the exchange interactions. Particularly, we propose a simple
""downfolding"" procedure for the elimination of the ligand spins by transferring
their effect to the interaction parameters between the localized spins.
Furthermore, we argue that the rotations of spin moments are more suitable for
the description of low-energy excitations, while the rotations of the whole
magnetization matrix cause much stronger perturbation in the system of spins.",2011.10204v1
2020-11-21,Effect of phase string on single-hole dynamics in the two-leg Hubbard ladder,"Optical measurements in doped Mott insulators have discovered the emergence
of spectral weights at mid-infrared (MIR) upon chemical doping and photodoping.
MIR weights may have a relation to string-type excitation of spins, which is
induced by a doped hole generating misarranged spins with respect to their
sublattice. There are two types of string effects: one is an $S^z$ string that
is repairable by quantum spin flips and the other is a phase string irreparable
by the spin flips. We investigate the effect of $S^{z}$ and phase strings on
MIR weights. Calculating the optical conductivity of the single-hole Hubbard
model in the strong-coupling regime and the $t$-$J$ model on two-leg ladders by
using time-dependent Lanczos and density-matrix renormalization group, we find
that phase strings make a crucial effect on the emergence of MIR weights as
compared with $S^{z}$ strings. Our findings indicate that a mutual Chern-Simons
gauge field acting between spin and charge degrees of freedom, which is the
origin of phase strings, is significant for obtaining MIR weights. Conversely,
if we remove this gauge field, no phase is picked up by a doped hole. As a
result, a spin-polaron accompanied by a local spin distortion emerges and a
quasiparticle with a cosine-like energy dispersion is formed in single-particle
spectral function. Furthermore, we suggest a Floquet engineering to examine the
phase-string effect in cold atoms.",2011.10686v2
2021-05-10,Three-body spin mixing in spin-1 Bose-Einstein condensates,"We study zero-energy collisions between three identical bosons with spin $f =
1$ interacting via pairwise potentials. We quantify the corresponding
three-body scattering hypervolumes, which parametrize the effective three-body
interaction strengths in a many-body description of spin-1 Bose-Einstein
condensates. Our results demonstrate universal behavior of the scattering
hypervolumes for strong $s$- and $p$-wave two-body interactions. At weak
interactions we find that the real parts of the scattering hypervolumes are
predominantly determined by hard-hyperspherelike collisions which we
characterize by a simple formula. With this universal result we estimate that
spin mixing via three-body collisions starts to dominate over two-body spin
mixing at a typical particle density of $10^{17}~\mathrm{cm}^{-3}$ for
${}^{23}$Na and ${}^{41}$K spinor condensates. This density can be reduced by
tuning the two-body interactions to an $s$- or $p$-wave dimer resonance or to a
point where two-body spin mixing effectively vanishes. Another possibility to
observe effects of three-body spin mixing involves the application of weak
magnetic fields to cancel out the effective two-body interaction strength in
the characteristic timescale describing the spin dynamics.",2105.04497v2
2021-07-08,"Magnetism, symmetry and spin transport in van der Waals layered systems","The discovery of an ever increasing family of atomic layered magnetic
materials, together with the already established vast catalogue of strong
spin-orbit coupling (SOC) and topological systems, calls for some guiding
principles to tailor and optimize novel spin transport and optical properties
at their interfaces. Here we focus on the latest developments in both fields
that have brought them closer together and make them ripe for future fruitful
synergy. After outlining fundamentals on van der Waals (vdW) magnetism and SOC
effects, we discuss how their coexistence, manipulation and competition could
ultimately establish new ways to engineer robust spin textures and drive the
generation and dynamics of spin current and magnetization switching in 2D
materials-based vdW heterostructures. Grounding our analysis on existing
experimental results and theoretical considerations, we draw a prospective
analysis about how intertwined magnetism and spin-orbit torque (SOT) phenomena
combine at interfaces with well-defined symmetries, and how this dictates the
nature and figures-of-merit of SOT and angular momentum transfer. This will
serve as a guiding role in designing future non-volatile memory devices that
utilize the unique properties of 2D materials with the spin degree of freedom.",2107.03763v2
2021-10-04,Five-second coherence of a single spin with single-shot readout in silicon carbide,"An outstanding hurdle for defect spin qubits in silicon carbide (SiC) is
single-shot readout - a deterministic measurement of the quantum state. Here,
we demonstrate single-shot readout of single defects in SiC via spin-to-charge
conversion, whereby the defect's spin state is mapped onto a long-lived charge
state. With this technique, we achieve over 80% readout fidelity without pre-
or post-selection, resulting in a high signal-to-noise ratio (SNR) that enables
us to measure long spin coherence times. Combined with pulsed dynamical
decoupling sequences in an isotopically purified host material, we report
single spin T2 > 5s, over two orders of magnitude greater than previously
reported in this system. The mapping of these coherent spin states onto single
charges unlocks both single-shot readout for scalable quantum nodes and
opportunities for electrical readout via integration with semiconductor
devices.",2110.01590v2
2021-10-21,Angular harmonic Hall voltage and magnetoresistance measurements of Pt/FeCoB and Pt-Ti/FeCoB bilayers for spin Hall conductivity determination,"Materials with significant spin-orbit coupling enable efficient
spin-to-charge interconversion, which can be utilized in novel spin electronic
devices. A number of elements, mainly heavy-metals (HM) have been identified to
produce a sizable spin current ($j_\mathrm{s}$), while supplied with a charge
current ($j$), detected mainly in the neighbouring ferromagnetic (FM) layer.
Apart from the spin Hall angle $\theta_\mathrm{SH}$ = $j_\mathrm{s}$/$j$, spin
Hall conductivity ($\sigma_\mathrm{SH}$) is an important parameter, which takes
also the resistivity of the material into account. In this work, we present a
measurement protocol of the HM/FM bilayers, which enables for a precise
$\sigma_\mathrm{SH}$ determination. Static transport measurements, including
resistivity and magnetization measurements are accompanied by the angular
harmonic Hall voltage analysis in a dedicated low-noise rotating probe station.
Dynamic characterization includes effective magnetization and magnetization
damping measurement, which enable HM/FM interface absorption calculation. We
validate the measurement protocol in Pt and Pt-Ti underlayers in contact with
FeCoB and present the $\sigma_\mathrm{SH}$ of up to 3.3$\times$10$^5$ S/m,
which exceeds the values typically measured in other HM, such as W or Ta.",2110.11483v1
2021-11-15,Observation of spin-dependent dual ferromagnetism in perovskite ruthenates,"We performed in-situ angle-resolved photoemission spectroscopy (ARPES) and
spin-resolved ARPES (SARPES) experiments to investigate the relationship
between electronic band structures and ferromagnetism in SrRuO$_3$ (SRO) thin
films. Our high-quality ARPES and SARPES results show clear spin-lifted band
structures. The spin polarization is strongly dependent on momentum around the
Fermi level, whereas it becomes less dependent at high-binding energies. This
experimental observation matches our dynamical mean-field theory (DMFT) results
very well. As temperature increases from low to the Curie temperature,
spin-splitting gap decreases and band dispersions become incoherent. Based on
the ARPES study and theoretical calculation results, we found that SRO
possesses spin-dependent electron correlations in which majority and minority
spins are localized and itinerant, respectively. Our finding explains how
ferromagnetism and electronic structure are connected, which has been under
debate for decades in SRO.",2111.07750v2
2021-12-03,Long Spin Coherence Times of Nitrogen Vacancy Centres in Milled Nanodiamonds,"Nanodiamonds containing negatively charged nitrogen vacancy centres
(${\text{NV}}^{-}$) have applications as localized sensors in biological
material and have been proposed as a platform to probe the macroscopic limits
of spatial superposition and the quantum nature of gravity. A key requirement
for these applications is to obtain nanodiamonds containing ${\text{NV}}^{-}$
with long spin coherence times. Using milling to fabricate nanodiamonds
processes the full 3D volume of the bulk material at once, unlike etching, but
has, up to now, limited ${\text{NV}}^{-}$ spin coherence times. Here, we use
natural isotopic abundance nanodiamonds produced by
${\text{Si}}_{3}{\text{N}}_{4}$ ball milling of bulk diamond grown by chemical
vapour deposition with an average single substitutional nitrogen concentration
of $121 ~\text{ppb}$. We show that the electron spin coherence times of
${\text{NV}}^{-}$ centres in these nanodiamonds can exceed $400 ~\mu\text{s}$
at room temperature with dynamical decoupling. Scanning electron microscopy
provides images of the specific nanodiamonds containing ${\text{NV}}^{-}$ for
which a spin coherence time was measured.",2112.01899v2
2021-12-07,Estimating the spin of the black hole candidate MAXI J1659-152 with the X-ray continuum-fitting method,"As a transient X-ray binary, MAXI J1659-152 contains a black hole candidate
as its compact star. MAXI J1659-152 was discovered on 2010 September 25 during
its only known outburst. Previously-published studies of this outburst indicate
that MAXI J1659-152 may have an extreme retrograde spin, which, if confirmed,
would provide an important clue as to the origin of black hole spin. In this
paper, utilizing updated dynamical binary-system parameters (i.e. the black
hole mass, the orbital inclination and the source distance) provided by
\cite{Torres2021}, we analyze 65 spectra of MAXI J1659-152 from
\emph{RXTE}/PCA, in order to assess the spin parameter. With a final selection
of 9 spectra matching our $f_{\mathrm{sc}} \lesssim 25 \%$, soft-state
criteria, we apply a relativistic thin disk spectroscopic model
\texttt{kerrbb2} over 3.0-45.0 keV. We find that inclination angle correlates
inversely with spin, and, considering the possible values for inclination
angle, we constrain spin to be $-1 < a_{*} \lesssim 0.44$ at 90\% confidence
interval via X-ray continuum-fitting. We can only rule out an extreme prograde
(positive) spin. We confirm that an extreme retrograde solution is possible and
is not ruled out by considering accretion torques given the young age of the
system.",2112.03479v1
2021-12-07,Influence of low-energy magnons on magnon Hanle experiments in easy-plane antiferromagnets,"Antiferromagnetic materials host pairs of spin-up and spin-down magnons which
can be described in terms of a magnonic pseudospin. The close analogy between
this magnonic pseudospin systems and that of electronic charge carriers led to
the prediction of fascinating phenomena in antiferromagnets. Recently, the
associated dynamics of antiferromagnetic pseudospin has been experimentally
demonstrated and, in particular, the first observation of the magnon Hanle
effect has been reported. We here expand the magnonic spin transport
description by explicitly taking into account contributions of finite-spin
low-energy magnons. In our experiments we realize the spin injection and
detection process by two Platinum strips and investigate the influence of the
Pt-strips on the generation and diffusive transport of magnons in films of the
antiferromagnetic insulator hematite. For both a 15 nm and a 100 nm thick film,
we find a distinct signal caused by the magnon Hanle effect. However, the
magnonic spin signal exhibits clear differences in both films. In contrast to
the thin film, for the thicker one, we observe an oscillating behavior in the
high magnetic field range as well as an additional offset signal in the low
magnetic field regime. We attribute this offset signal to the presence of
finite-spin low-energy magnons.",2112.03820v1
2021-12-13,Fluctuating magnetic droplets immersed in a sea of quantum spin liquid,"The search of quantum spin liquid (QSL), an exotic magnetic state with
strongly-fluctuating and highly-entangled spins down to zero temperature, is a
main theme in current condensed matter physics. However, there is no
smoking-gun evidence for deconfined spinons in any QSL candidate so far. The
disorders and competing exchange interactions may prevent the formation of an
ideal QSL state on frustrated spin lattices. Here we report comprehensive and
systematic measurements of the magnetic susceptibility, ultra-low temperature
specific heat, muon spin relaxation (muSR), nuclear magnetic resonance (NMR),
and thermal conductivity for NaYbSe2 single crystals, in which Yb3+ ions with
effective spin-1/2 form a perfect triangular lattice. All these complementary
techniques find no evidence of long-range magnetic order down to their
respective base temperatures. Instead, specific heat, muSR and NMR measurements
suggest the coexistence of quasi-static and dynamic spins in NaYbSe2. The
scattering from these quasi-static spins may cause the absence of magnetic
thermal conductivity. Thus, we propose a scenario of fluctuating ferrimagnetic
droplets immersed in a sea of QSL. This may be quite common on the way pursuing
an ideal QSL, and provides a brand-new platform to study how a QSL state
survives impurities and coexists with other magnetically ordered states.",2112.06523v1
2022-03-09,Relativistic second-order dissipative spin hydrodynamics from the method of moments,"We derive relativistic second-order dissipative fluid-dynamical equations of
motion for massive spin-1/2 particles from kinetic theory using the method of
moments. Besides the usual conservation laws for charge, energy, and momentum,
such a theory of relativistic dissipative spin hydrodynamics features an
equation of motion for the rank-3 spin tensor, which follows from the
conservation of total angular momentum. Extending the conventional method of
moments for spin-0 particles, we expand the spin-dependent distribution
function near local equilibrium in terms of moments of the momentum and spin
variables. We work to next-to-leading order in the Planck constant $\hbar$. As
shown in previous work, at this order in $\hbar$ the Boltzmann equation for
spin-1/2 particles features a nonlocal collision term. From the Boltzmann
equation, we then obtain an infinite set of equations of motion for the
irreducible moments of the deviation of the single-particle distribution
function from local equilibrium. In order to close this system of moment
equations, a truncation procedure is needed. We employ the ""14+24-moment
approximation"", where ""14"" corresponds to the components of the charge current
and the energy-momentum tensor and ""24"" to the components of the spin tensor,
which completes the derivation of the equations of motion of second-order
dissipative spin hydrodynamics. For applications to heavy-ion phenomenology, we
also determine dissipative corrections to the Pauli-Lubanski vector.",2203.04766v2
2022-03-13,Fast high-fidelity single-shot readout of spins in silicon using a single-electron box,"Three key metrics for readout systems in quantum processors are measurement
speed, fidelity and footprint. Fast high-fidelity readout enables mid-circuit
measurements, a necessary feature for many dynamic algorithms and quantum error
correction, while a small footprint facilitates the design of scalable,
highly-connected architectures with the associated increase in computing
performance. Here, we present two complementary demonstrations of fast
high-fidelity single-shot readout of spins in silicon quantum dots using a
compact, dispersive charge sensor: a radio-frequency single-electron box. The
sensor, despite requiring fewer electrodes than conventional detectors,
performs at the state-of-the-art achieving spin read-out fidelity of 99.2% in
less than 6 $\mu$s. We demonstrate that low-loss high-impedance resonators,
highly coupled to the sensing dot, in conjunction with Josephson parametric
amplification are instrumental in achieving optimal performance. We quantify
the benefit of Pauli spin blockade over spin-dependent tunneling to a
reservoir, as the spin-to-charge conversion mechanism in these readout schemes.
Our results place dispersive charge sensing at the forefront of readout
methodologies for scalable semiconductor spin-based quantum processors.",2203.06608v1
2022-05-19,Energy-efficient quantum non-demolition measurement with a spin-photon interface,"Spin-photon interfaces (SPIs) are key devices of quantum technologies, aimed
at coherently transferring quantum information between spin qubits and
propagating pulses of polarized light. We study the potential of a SPI for
quantum non demolition (QND) measurements of a spin state. After being
initialized and scattered by the SPI, the state of a light pulse depends on the
spin state. It thus plays the role of a pointer state, information being
encoded in the light's temporal and polarization degrees of freedom. Building
on the fully Hamiltonian resolution of the spin-light dynamics, we show that
quantum superpositions of zero and single photon states outperform coherent
pulses of light, producing pointer states which are more distinguishable with
the same photon budget. The energetic advantage provided by quantum pulses over
coherent ones is maintained when information on the spin state is extracted at
the classical level by performing projective measurements on the light pulses.
The proposed schemes are robust against imperfections in state of the art
semi-conducting devices.",2205.09623v4
2022-06-02,Ideal refocusing of an optically active spin qubit under strong hyperfine interactions,"Combining highly coherent spin control with efficient light-matter coupling
offers great opportunities for quantum communication and networks, as well as
quantum computing. Optically active semiconductor quantum dots have
unparalleled photonic properties, but also modest spin coherence limited by
their resident nuclei. Here, we demonstrate that eliminating strain
inhomogeneity using lattice-matched GaAs-AlGaAs quantum dot devices prolongs
the electron spin coherence by nearly two orders of magnitude, beyond 0.113(3)
ms. To do this, we leverage the 99.30(5)% fidelity of our optical pi-pulse
gates to implement dynamical decoupling. We vary the number of decoupling
pulses up to N = 81 and find a coherence time scaling of N^{0.75(2)}. This
scaling manifests an ideal refocusing of strong interactions between the
electron and the nuclear-spin ensemble, holding the promise of lifetime-limited
spin coherence. Our findings demonstrate that the most punishing material
science challenge for such quantum-dot devices has a remedy, and constitute the
basis for highly coherent spin-photon interfaces.",2206.01223v1
2022-06-12,Kagome lattice promotes chiral spin fluctuations,"Magnetic materials with tilted electron spins often exhibit conducting
behavior that cannot be explained from semiclassical theories without invoking
fictitious (emergent) electromagnetic fields. Quantum-mechanical models
explaining such phenomena are rooted in the concept of a moving quasiparticle's
Berry phase, driven by a chiral (left- or right-handed) spin-habit. Dynamical
and nearly random spin fluctuations, with a slight bent towards left- or
right-handed chirality, represent a promising route to realizing Berry-phase
phenomena at elevated temperatures, but little is known about the effect of
crystal lattice geometry on the resulting macroscopic observables. Here, we
report thermoelectric and electric transport experiments on two metals with
large magnetic moments on a triangular and on a slightly distorted kagom\'e
lattice, respectively. We show that the impact of chiral spin fluctuations is
strongly enhanced for the kagom\'e lattice. Both these spiral magnets have
similar magnetic phase diagrams including a periodic array of magnetic
skyrmions. However, our modelling shows that the geometry of the kagom\'e
lattice, with corner-sharing spin-trimers, helps to avoid cancellation of
Berry-phase contributions; spin fluctuations are endowed with a net chiral
habit already in the thermally disordered (paramagnetic) state. Hence, our
observations for the kagom\,e material contrast with theoretical models
treating magnetization as a continuous field, and emphasize the role of lattice
geometry on emergent electrodynamic phenomena.",2206.05756v2
2022-07-02,Spin excitations in the quantum dipolar magnet Yb(BaBO$_3$)$_3$,"We report results of magnetization, specific-heat and muon-spin relaxation
measurements on single crystals of disorder-free Yb$^{3+}$ triangular lattice
Yb(BaBO$_3$)$_3$. The magnetization experiments show anisotropic magnetic
properties with Curie-Weiss temperatures $\theta_{\perp}=-1.40$~K ($H \perp c$)
and $\theta_{\parallel}=-1.16$~K ($H \parallel c$) determined from low
temperature data. The absence of both long-range antiferromagnetic order and
spin freezing is confirmed down to 0.27 K at zero field. A two-level Schottky
anomaly due to the opening of the ground-state Kramers doublet is observed from
the low-temperature specific-heat measurements when the applied magnetic fields
$\mu_0H >0.7$~T. At zero field, the increase of both $C_{\rm mag}/T$ and the
muon spin relaxation rate $\lambda$ below 1~K is due to the electronic spin
excitations, which often exist in quantum magnets where dipole-dipole
interaction creates an anisotropy of magnetic properties. The spin excitation
is also supported by the unusual maximum of field dependence of $\lambda$ due
to the field-induced increase of the density of excitations. We argue that
dipolar interaction is dominant and induces the spin dynamics in the quantum
magnet Yb(BaBO$_3$)$_3$.",2207.00702v1
2022-07-13,Probing the dynamics and coherence of a semiconductor hole spin via acoustic phonon-assisted excitation,"Spins in semiconductor quantum dots are promising local quantum memories to
generate polarization-encoded photonic cluster states, as proposed in the
pioneering Rudolph-Lindner scheme [1]. However, harnessing the polarization
degree of freedom of the optical transitions is hindered by resonant excitation
schemes that are widely used to obtain high photon indistinguishability. Here
we show that acoustic phonon-assisted excitation, a scheme that preserves high
indistinguishability, also allows to fully exploit the polarization selective
optical transitions to initialise and measure single spin states. We access the
coherence of hole spin systems in a low transverse magnetic field and directly
monitor the spin Larmor precession both during the radiative emission process
of an excited state or in the quantum dot ground state. We report a spin state
detection fidelity of $94.7 \pm 0.2 \%$ granted by the optical selection rules
and a $20\pm5$~ns hole spin coherence time, demonstrating the potential of this
scheme and system to generate linear cluster states with a dozen of photons",2207.05981v1
2022-08-05,Scattering of gravitational waves off spinning compact objects with an effective worldline theory,"We study the process, within classical general relativity, in which an
incident gravitational plane wave, of weak amplitude and long wavelength,
scatters off a massive spinning compact object, such as a black hole or neutron
star. The amplitude of the asymptotic scattered wave, considered here at linear
order in Newton's constant $G$ while at higher orders in the object's multipole
expansion, is a valuable characterization of the response of the object to
external gravitational fields. This amplitude coincides with a classical
($\hbar\to0$) limit of a quantum 4-point (object and graviton in, object and
graviton out) gravitational Compton amplitude, at the tree (linear-in-$G$)
level. Such tree-level Compton amplitudes are key building blocks in
generalized-unitary-based approaches to the post-Minkowskian dynamics of
binaries of spinning compact objects. In this paper, we compute the classical
amplitude using an effective worldline theory to describe the compact object,
determined by an action functional for translational and rotational degrees of
freedom, including couplings of spin-induced higher multipole moments to
spacetime curvature. We work here up to the levels of quadratic-in-spin
quadrupole and cubic-in-spin octupole couplings, respectively involving Wilson
coefficients $C_2$ and $C_3$. For the special case $C_2=C_3=1$ corresponding to
a black hole, we find agreement through cubic-in-spin order between our
classical amplitude and previous conjectures arising from considerations of
quantum scattering amplitudes. We also present new results for general $C_2$
and $C_3$, anticipating instructive comparisons with results from effective
quantum theories.",2208.03170v2
2022-08-28,Spin Josephson effects of spin-orbit-coupled Bose-Einstein condensates in a non-Hermitian double well,"In this paper, we investigate the spin and tunneling dynamics of a
spin-orbit-coupled noninteracting Bose-Einstein condensate in a periodically
driven non-Hermitian double-well potential. Under high-frequency driving, we
obtain the effective time-averaged Hamiltonian by using the standard
time-averaging method, and analytically calculate the Floquet quasienergies,
revealing that the parity-time (PT)-breaking phase transition appears even for
arbitrarily small non-Hermitian parameters when the spin-orbit coupling
strength takes half-integer value, irrespective of the values of other
parameters used. When the system is PT-symmetric with balanced gain and loss,
we find numerically and analytically that in the broken PT-symmetric regions,
there will exist the net spin current together with a vanishing atomic current,
if we drop the contribution of the exponential growth of the norm to the
current behaviors. When the system is non-PT-symmetric, though the
quasienergies are partial complex, a stable net spin current can be generated
by controlling the periodic driving field, which is accompanied by a spatial
localization of the condensate in the well with gain. The results deepen the
understanding of non-Hermitian physics and could be useful for engineering a
variety of devices for spintronics.",2208.13198v1
2022-09-23,Gravitational recoil from binary black hole mergers in scalar field clouds,"In vacuum, the gravitational recoil of the final black hole from the merger
of two black holes depends exclusively on the mass ratio and spins of the
coalescing black holes, and on the eccentricity of the binary. If matter is
present, accretion by the merging black holes may modify significantly their
masses and spins, altering both the dynamics of the binary and the
gravitational recoil of the remnant black hole. This paper considers such
scenario. We investigate the effects on the kick of the final black hole from
immersing the binary in a scalar field cloud. We consider two types of
configurations: one with non-spinning and unequal-mass black holes, and a
second with equal mass and spinning holes. For both types, we investigate how
the gravitational recoil of the final black hole changes as we vary the energy
density of the scalar field. We find that the accretion of scalar field by the
merging black holes could have a profound effect. For the non-spinning,
unequal-mass binary black holes, the kicks are in general larger than in the
vacuum case, with speeds of approximately 1,200 km/s for binaries with mass
ratio 2:1, one order of magnitude larger than in vacuum. For equal mass,
binaries with black holes with spins aligned with the orbital angular momentum,
kicks larger than in vacuum are also found. For systems with spins in the
super-kick configuration, the scalar field triggers a similar dependence of the
kicks with the entrance angle at merger as in the vacuum case but in this case
depending on the strength of the scalar field.",2209.11814v1
2022-10-06,Direct probing of a large spin-orbit coupling in the FeSe superconducting monolayer on STO: Evidence for nontrivial topological states,"In condensed-matter physics spin-orbit coupling (SOC) is a fundamental
physical interaction, which describes how the electrons' spin couples to their
orbital motion. It is the source of a vast variety of fascinating phenomena in
solids such as topological phases of matter, quantum spin Hall states, and many
other exotic quantum states. Although in most theoretical descriptions of the
phenomenon of high-temperature superconductivity SOC has been neglected,
including this interaction can, in principle, revise the microscopic picture of
superconductivity in these compounds. Not only the interaction leading to
Cooper pairing but also the symmetry of the order parameter and the topological
character of the involved states can be determined by SOC. Here by preforming
energy-, momentum-, and spin-resolved spectroscopy experiments with an
unprecedented resolution we demonstrate that while probing the dynamic charge
response of the FeSe monolayer on strontium titanate, a prototype two
dimensional high-temperature superconductor using slow electrons, the
scattering cross-section shows a considerable spin asymmetry. We unravel the
origin of the observed spin asymmetry by developing a model in which SOC is
taken into consideration. Our analysis indicates that SOC in this two
dimensional superconductor is rather strong. We anticipate that such a strong
SOC can have several serious consequences on the electronic structures and can
lead to the formation of topological states. Moreover, a sizable SOC can
compete with other pairing scenarios and is crucial for the mechanism of
high-temperature superconductivity.",2210.02810v1
2022-10-10,Continuous transition from a Landau quasiparticle to a neutral spinon,"We examine a wavefunction ansatz in which a doped hole can experience a
quantum transition from a charge $+e$ Landau quasiparticle to a neutral spinon
as a function of the underlying spin-spin correlation. As shown variationally,
such a wavefunction accurately captures all the essential features revealed by
exact diagonalization and density matrix renormalization group simulations in a
two-leg $t$-$J$ ladder. Hence its analytic form can provide an explicit
understanding of the mechanism for the unconventional ground state. The
transition in the phase diagram is accompanied by a change of the hole
composite from a tight charge-spin binding to a loosely-bound hole-spin pair.
In the latter, the hole carries a \emph{finite} spin current but with vanishing
charge current in the degenerate ground states. We show that the charge of the
hole composite here is dynamically diminished due to an internal relative
hole-spin motion, which is fundamentally distinct from a simple charge-spin
separation in a one-dimensional case. We further show that the same effect is
also responsible for a strong pairing between two doped holes in such a
non-Landau quasiparticle regime.",2210.04918v2
2022-10-14,Optimization of nuclear polarization in an alkali-noble gas comagnetometer,"Self-compensated comagnetometers, employing overlapping samples of
spin-polarized alkali and noble gases (for example K-$^3$He) are promising
sensors for exotic beyond-the-standard-model fields and high-precision
metrology such as rotation sensing. When the comagnetometer operates in the
so-called self-compensated regime, the effective field, originating from
contact interactions between the alkali valence electrons and the noble-gas
nuclei, is compensated with an applied magnetic field. When the comagnetometer
begins operation in a given magnetic field, spin-exchange optical pumping
establishes equilibrium between the alkali electron-spin polarization and the
nuclear-spin polarization. Subsequently, when the magnetic field is tuned to
the compensation point, the spin polarization is brought out of the equilibrium
conditions. This causes a practical issue for long measurement times. We report
on a novel method for closed-loop control of the compensation field. This
method allows optimization of the operating parameters, especially magnetic
field gradients, in spite of the inherently slow (hours to days) dynamics of
the system. With the optimization, higher stable nuclear polarization, longer
relaxation times and stronger electron-nuclear coupling are achieved which is
useful for nuclear-spin-based quantum memory, spin amplifiers and gyroscopes.
The optimized sensor demonstrates a sensitivity comparable to the best previous
comagnetometer but with four times lower noble gas density. This paves the way
for applications in both fundamental and applied science.",2210.07687v4
2023-02-05,Spin-Flip Raman Scattering on Electrons and Holes in Two-Dimensional (PEA)$_2$PbI$_4$ Perovskites,"The class of Ruddlesden-Popper type (PEA)$_2$PbI$_4$ perovskites comprises
two-dimensional (2D) structures whose optical properties are determined by
excitons with a large binding energy of about 260 meV. It complements the
family of other 2D semiconductor materials by having the band structure typical
for lead halide perovskites, that can be considered as inverted compared to
conventional III-V and II-VI semiconductors. Accordingly, novel spin phenomena
can be expected for them. Spin-flip Raman scattering is used here to measure
the Zeeman splitting of electrons and holes in a magnetic field up to 10 T.
From the recorded data, the electron and hole Land\'e factors ($g$-factors) are
evaluated, their signs are determined, and their anisotropies are measured. The
electron $g$-factor value changes from $+2.11$ out-of-plane to $+2.50$
in-plane, while the hole $g$-factor ranges between $-0.13$ and $-0.51$. The
spin flips of the resident carriers are arranged via their interaction with
photogenerated excitons. Also the double spin-flip process, where a resident
electron and a resident hole interact with the same exciton, is observed
showing a cumulative Raman shift. Dynamic nuclear spin polarization induced by
spin-polarized holes is detected in corresponding changes of the hole Zeeman
splitting. An Overhauser field of the polarized nuclei acting on the holes as
large as $0.6$ T can be achieved.",2302.02349v1
2023-03-09,Electrical manipulation of a single electron spin in CMOS with micromagnet and spin-valley coupling,"For semiconductor spin qubits, complementary-metal-oxide-semiconductor (CMOS)
technology is the ideal candidate for reliable and scalable fabrication. Making
the direct leap from academic fabrication to qubits fabricated fully by
industrial CMOS standards is difficult without intermediate solutions. With a
flexible back-end-of-line (BEOL) new functionalities such as micromagnets or
superconducting circuits can be added in a post-CMOS process to study the
physics of these devices or achieve proof of concepts. Once the process is
established it can be incorporated in the foundry-compatible process flow.
Here, we study a single electron spin qubit in a CMOS device with a micromagnet
integrated in the flexible BEOL. We exploit the synthetic spin orbit coupling
(SOC) to control the qubit via electric field and we investigate the
spin-valley physics in the presence of SOC where we show an enhancement of the
Rabi frequency at the spin-valley hotspot. Finally, we probe the high frequency
noise in the system using dynamical decoupling pulse sequences and demonstrate
that charge noise dominates the qubit decoherence in this range.",2303.04960v1
2023-05-22,Ultralong 100 ns Spin Relaxation Time in Graphite at Room Temperature,"Graphite has been intensively studied, yet its electron spins dynamics
remains an unresolved problem even 70 years after the first experiments. The
central quantities, the longitudinal ($T_1$) and transverse ($T_2$) relaxation
times were postulated to be equal, mirroring standard metals, but $T_1$ has
never been measured for graphite. Here, based on a detailed band structure
calculation including spin-orbit coupling, we predict an unexpected behavior of
the relaxation times. We find, based on saturation ESR measurements, that $T_1$
is markedly different from $T_2$. Spins injected with perpendicular
polarization with respect to the graphene plane have an extraordinarily long
lifetime of $100$ ns at room temperature. This is ten times more than in the
best graphene samples. The spin diffusion length across graphite planes is thus
expected to be ultralong, on the scale of $\sim 70~\mu$m, suggesting that thin
films of graphite -- or multilayer AB graphene stacks -- can be excellent
platforms for spintronics applications compatible with 2D van der Waals
technologies. Finally, we provide a qualitative account of the observed spin
relaxation based on the anisotropic spin admixture of the Bloch states in
graphite obtained from density functional theory calculations.",2305.15433v1
2023-07-12,Isotope engineering for spin defects in van der Waals materials,"Spin defects in van der Waals materials offer a promising platform for
advancing quantum technologies. Here, we propose and demonstrate a powerful
technique based on isotope engineering of host materials to significantly
enhance the coherence properties of embedded spin defects. Focusing on the
recently-discovered negatively charged boron vacancy center
($\mathrm{V}_{\mathrm{B}}^-$) in hexagonal boron nitride (hBN), we grow
isotopically purified $\mathrm{h}{}^{10}\mathrm{B}{}^{15}\mathrm{N}$ crystals.
Compared to $\mathrm{V}_{\mathrm{B}}^-$ in hBN with the natural distribution of
isotopes, we observe substantially narrower and less crowded
$\mathrm{V}_{\mathrm{B}}^-$ spin transitions as well as extended coherence time
$T_2$ and relaxation time $T_1$. For quantum sensing,
$\mathrm{V}_{\mathrm{B}}^-$ centers in our
$\mathrm{h}{}^{10}\mathrm{B}{}^{15}\mathrm{N}$ samples exhibit a factor of $4$
($2$) enhancement in DC (AC) magnetic field sensitivity. For additional quantum
resources, the individual addressability of the $\mathrm{V}_{\mathrm{B}}^-$
hyperfine levels enables the dynamical polarization and coherent control of the
three nearest-neighbor ${}^{15}\mathrm{N}$ nuclear spins. Our results
demonstrate the power of isotope engineering for enhancing the properties of
quantum spin defects in hBN, and can be readily extended to improving spin
qubits in a broad family of van der Waals materials.",2307.06441v2
2023-07-19,A spin-rotation mechanism of Einstein-de Haas effect based on a ferromagnetic disk,"Spin-rotation coupling (SRC) is a fundamental phenomenon that connects
electronic spins with the rotational motion of a medium. We elucidate the
Einstein-de Haas (EdH) effect and its inverse with SRC as the microscopic
mechanism using the dynamic spin-lattice equations derived by elasticity theory
and Lagrangian formalism. By applying the coupling equations to an iron disk in
a magnetic field, we exhibit the transfer of angular momentum and energy
between spins and lattice, with or without damping. The timescale of the
angular momentum transfer from spins to the entire lattice is estimated by our
theory to be on the order of 0.01 ns, for the disk with a radius of 100 nm.
Moreover, we discover a linear relationship between the magnetic field strength
and the rotation frequency, which is also enhanced by a higher ratio of Young's
modulus to Poisson's coefficient. In the presence of damping, we notice that
the spin-lattice relaxation time is nearly inversely proportional to the
magnetic field. Our explorations will contribute to a better understanding of
the EdH effect and provide valuable insights for magneto-mechanical
manufacturing.",2307.10390v2
2023-08-11,Design of Sn-doped cadmium chalcogenide based monolayers for valleytronics properties,"Valleytronics, that uses the valley index or valley pseudospin to encode
information, has emerged as an interesting field of research in two-dimensional
(2D) systems with promising device applications. Spin-orbit coupling (SOC) and
inversion symmetry breaking leads to spin-splitting of bands near the energy
extrema (valleys). In order to find a new 2D material useful for valleytronics,
we have designed hexagonal planar monolayers of cadmium chalcogenides (CdX, X =
S, Se, Te) from the (111) surface of bulk CdX zinc blende structure. Band
structure study reveals valence band local maxima at symmetry point K and its
time reversal conjugate point K$\textquotesingle$. Application of SOC initiates
spin-splitting in the valleys that lifts the energy degeneracy and shows strong
valley-spin coupling character. We have substituted two Cd atoms in the planar
monolayers by Sn atoms which increases the spin-splitting significantly. The
structural, dynamic, mechanical and thermal stability of all the monolayers has
been confirmed. Values of formation energies indicate that it may be feasible
to synthesize the Sn-doped CdSe and CdTe monolayers using bottom-up approach.
Zeeman-type spin-splitting is observed in the valley region and Rashba
spin-splitting is observed at the $\Gamma$ point for Sn-doped CdSe and CdTe
monolayers. Berry curvature values are more in all the Sn-doped monolayers than
the pristine monolayers. These newly designed monolayers are thus found to be
suitable for valleytronics applications. Sn-doped monolayers show band
inversion deep in the valence and conduction bands between Sn~$s$ and $p$ and
X~$p$ states but lack topological properties.",2308.06011v1
2023-09-11,"GRMHD simulations of accretion flows onto unequal-mass, precessing massive binary black hole mergers","In this work, we use general relativistic magnetohydrodynamics simulations to
explore the effect of spin orientation on the dynamics of gas in the vicinity
of merging black holes. We present a suite of eight simulations of
unequal-mass, spinning black hole binaries embedded in magnetized clouds of
matter. Each binary evolution covers approximately 15 orbits before the
coalescence. The geometry of the accretion flows in the vicinity of the black
holes is significantly altered by the orientation of the individual spins with
respect to the orbital angular momentum, with the primary black hole dominating
the mass accretion rate $\dot{M}$. We observe quasiperiodic modulations of
$\dot{M}$ in most of the configurations, whose amplitude is dependent on the
orientation of the black hole spins. We find the presence of a relation between
the average amplitude of $\dot{M}$ and the spin precession parameter
$\chi_{\mathrm{p}}$ showing that spin misalignment systematically leads to
stronger modulation, whereas configurations with spins aligned to the orbital
angular momentum damp out the quasiperiodicity. This finding suggests a
possible signature imprinted in the accretion luminosity of precessing binaries
approaching merger and has possible consequences on future multimessenger
observations of massive binary black hole systems.",2309.05738v1
2023-10-24,"Mergers of double neutron stars with one high-spin component: brighter kilonovae and fallback accretion, weaker gravitational waves","Neutron star (NS) mergers where both stars have negligible spins are commonly
considered as the most likely ``standard'' case. In globular clusters, however,
the majority of NSs have been spun up to millisecond (ms) periods and, based on
observed systems, we estimate that a non-negligible fraction of all double NS
mergers ($\sim 4\pm2\;\%$) contains one component with a spin of a (few) ms. We
use the Lagrangian numerical relativity code \SpB to simulate mergers where one
star has no spin and the other has a dimensionless spin parameter of
$\chi=0.5$. Such mergers exhibit several distinct signatures compared to
irrotational cases. They form only one, very pronounced spiral arm and they
dynamically eject an order of magnitude more mass of unshocked material at the
original, very low electron fraction. One can therefore expect particularly
bright, red kilonovae. Overall, the spinning case collisions are substantially
less violent and they eject smaller amounts of shock-generated
semi-relativistic material. Therefore, the ejecta produce a weaker blue/UV
kilonova {\em precursor} signal, but -- since the total amount is larger --
brighter kilonova {\em afterglows} months after the merger. The spinning cases
also have significantly more fallback accretion and thus could power late-time
X-ray flares. Since the post-merger remnant loses energy and angular momentum
significantly less efficiently to gravitational waves, such systems can delay a
potential collapse to a black hole and are therefore candidates for
merger-triggered gamma-ray bursts with longer emission time scales.",2310.15920v2
2024-02-12,Gravitational Magnus effect from scalar dark matter,"In fluid dynamics, the Magnus effect is the force perpendicular to the motion
of a spinning object as it moves through a medium. In general relativity, an
analogous effect exists for a spinning compact object moving through matter,
purely as a result of gravitational interactions. In this work we consider a
Kerr black hole moving at relativistic velocities through scalar dark matter
that is at rest. We simulate the system numerically and extract the total
spin-curvature force on the black hole perpendicular to its motion. We confirm
that the force scales linearly with the dimensionless spin parameter $a/M$ of
the black hole up to $a/M = 0.99$, and measure its dependence on the speed $v$
of the black hole in the range $0.1 \le v \le 0.55$ for a fixed spin. Compared
to previous analytic work applicable at small $v$, higher-order corrections in
the velocity are found to be important: the total force is nonzero, and the
dependence is not linear in $v$. We find that in all cases the total force is
in the opposite direction to the hydrodynamical analogue, although at low
speeds it appears to approach the expectation that the Weyl and Magnus
components cancel. Spin-curvature effects may leave an imprint on gravitational
wave signals from extreme mass-ratio inspirals, where the secondary black hole
has a nonnegligible spin and moves in the presence of a dark matter cloud. We
hope that our simulations can be used to support and extend the limits of
analytic results, which are necessary to better quantify such effects in the
relativistic regime.",2402.07977v1
2024-04-08,Optical spin orientation of localized electrons and holes interacting with nuclei in an FA0.9Cs0.1PbI2.8Br0.2 perovskite crystal,"Optical orientation of carrier spins by circularly polarized light is the
basic concept and tool of spin physics in semiconductors. We study the optical
orientation of electrons and holes in a crystal of the
FA$_{0.9}$Cs$_{0.1}$PbI$_{2.8}$Br$_{0.2}$ lead halide perovskite by means of
polarized photoluminescence, time-resolved differential reflectivity, and
time-resolved Kerr rotation. At the cryogenic temperature of 1.6 K the optical
orientation degree measured for continuous-wave excitaton reaches 6\% for
localized electrons and 2\% for localized holes. Their contributions are
distinguished from each other and from exciton optical orientation through the
pronounced Hanle effect in transverse magnetic fields and the polarization
recovery effect in longitudinal magnetic fields. The optical orientation degree
is highly stable against detuning of the laser photon energy from the band gap
by up to 0.25 eV, showing then a gradual decrease for detunings up to 0.9 eV.
This evidences the inefficiency of spin relaxation mechanisms for free carriers
during their energy relaxation. Spin relaxation for localized electrons and
holes is provided by the hyperfine interaction with the nuclear spins. Dynamic
polarization of nuclear spins is demonstrated by the Overhauser field reaching
4 mT acting on the electrons and $-76$ mT acting on the holes. This confirms
the specifics of lead halide perovskite semiconductors, where the hole
hyperfine interaction with the nuclei considerably exceeds that of the
electron.",2404.05369v1
1994-07-06,"Exact spectra, spin susceptibilities and order parameter of the quantum Heisenberg antiferromagnet on the triangular lattice","Exact spectra of periodic samples are computed up to $ N=36 $.
  Evidence of an extensive set of low lying levels, lower than the softest
magnons, is exhibited.
  These low lying quantum states are degenerated in the thermodynamic limit;
their symmetries and dynamics as well as their finite-size scaling are strong
arguments in favor of N\'eel order.
  It is shown that the N\'eel order parameter agrees with first-order spin-wave
calculations. A simple explanation of the low energy dynamics is given as well
as the numerical determinations of the energies, order parameter and spin
susceptibilities of the studied samples. It is shown how suitable boundary
conditions, which do not frustrate N\'eel order, allow the study of samples
with $ N=3p+1 $ spins.
  A thorough study of these situations is done in parallel with the more
conventional case $ N=3p $.",9407028v1
1994-09-23,Spin and charge dynamics of the t-J model at intermediate electron densities: absence of spin-charge separation,"We present an exact diagonalization study of the dynamical spin and density
correlation functions in small clusters of 2D t-J model for intermediate and
low electron densities, rho<0.7. Both correlation functions agree remarkably
well with the convolution of the single-particle spectral function, i.e. the
simplest estimate within the Fermi liquid picture. Deviations from the
convolution are shown to originate from symmetry-related selection rules, which
are unaccounted for in the convolution estimate. Comparing the momentum
distribution in the final states of the low lying spin and charge excitations
to that of the ground state we establish that for all fillings under
consideration the low energy peaks in both correlation functions originate from
particle-hole excitations, as expected in a Fermi liquid.",9409102v1
1995-01-05,Anomalous Spin and Charge Dynamics of the 2D t-J Model at low doping,"We present an exact diagonalization study of the dynamical spin and density
correlation function of the 2D t-J model for hole doping < 25%. Both
correlation functions show a remarkably regular, but completely different
scaling behaviour with both hole concentration and parameter values: the
density correlation function is consistent with that of bosons corresponding to
the doped holes and condensed into the lowest state of the noninteracting band
of width 8t, the spin correlation function is consistent with Fermions in a
band of width J. We show that the spin bag picture gives a natural explanation
for this unusual behaviour.",9501009v1
1996-11-30,Slow antiferromagnetic dynamics in the low temperature tetragonal phase of La_{2-x}Sr_xCuO_4 as revealed by ESR of Gd spin probes,"Measuring the ESR of Gd spin probes we have studied the magnetic properties
of the copper oxide planes in the low temperature tetragonal (LTT) phase of Eu
doped La_{2-x}Sr_xCuO_4. The data give evidence that at particular levels of Sr
and Eu doping the frequency of the antiferromagnetic fluctuations in the LTT
phase dramatically decreases at low temperatures by almost three orders of
magnitude. However, no static magnetic order has been found for T>8K in
contrast to the observation by neutron scattering of stripe ordering of spins
below 50K in a Nd doped La_{2-x}Sr_xCuO_4 single crystal. To our opinion static
order in the Nd doped compound is induced due to the interaction between the Cu
spins with the rare earth magnetic moments. Therefore, a really characteristic
property of the magnetism in the LTT structural phase may be not static
magnetic order at elevated temperatures but rather extremely slow
antiferromagnetic dynamics.",9612011v1
1997-04-17,Quantum Critical Dynamics of the Random Transverse Field Ising Spin Chain,"Dynamical correlations of the spin and the energy density are investigated in
the critical region of the random transverse-field Ising chain by numerically
exact calculations in large finite systems (L<=128). The spin-spin
autocorrelation function is found to decay proportional to (log t)^{-2x_m} and
(log t)^{-2x_m^s} in the bulk and on the surface, respectively, with x_m and
x_m^s the bulk and surface magnetization exponents, respectively. On the other
hand the critical energy-energy autocorrelation functions have a power law
decay, which are characterized by novel critical exponents eta_e~2.2 in the
bulk and eta_e^s~2.5 at the surface, respectively. The numerical results are
compared with the predictions of a scaling theory.",9704152v1
1997-12-17,Dynamics of a Pair of Interacting Spins Coupled to an Environmental Sea,"We solve for the dynamics of a pair of spins, coupled to each other and also
to an environmental sea of oscillators. The environment mediates an indirect
interaction between the spins, causing both mutual coherence effects and
dissipation. This model describes a wide variety of physical systems, ranging
from 2 coupled microscopic systems (eg., magnetic impurities, bromophores,
etc), to 2 coupled macroscopic quantum systems. We obtain analytic results for
3 regimes, viz., (i) The locked regime, where the 2 spins lock together; (ii)
The correlated relaxation regime (mutually correlated incoherent relaxation);
and (iii) The mutual coherence regime, with correlated damped oscillations.
These results cover most of the parameter space of the system.",9712215v1
1998-03-02,Dynamic Spin Correlation Function of the Alternating Spin-1/2 Antiferromagnetic Chain with Competing Interactions,"Dynamic spin correlation function of the $S=1/2$ antiferromagnetic spin chain
with alternating nearest neighbor and competing next nearest neighbor
interactions is studied using the numerical diagonalization method. We find
characteristics of the correlation function, which are the consequence of the
dimer order in the ground state: (1) A typical singlet-triplet gap is observed
and such a lowest-energy triplet state is found to form a bound state, showing
strong peaks below a continuum band with weak but distinct upper and lower
boundaries. (2) The intensity of the bound state shows a quite different
wavevector-dependence from that of the corresponding intensity at the lower
boundary in the usual antiferromagnet. These features are examined by the
variational calculation and are favorably discussed in connection with recent
experimental results of neutron inelastic scattering in the inorganic
spin-Peierls system, CuGeO$_3$.",9803009v2
1998-05-11,Spin Dynamics of the Magnetoresistive Pyrochlore Tl_2Mn_2O_7,"Neutron scattering has been used to study the magnetic order and spin
dynamics of the colossal magnetoresistive pyrochlore Tl_2Mn_2O_7. On cooling
from the paramagnetic state, magnetic correlations develop and appear to
diverge at T_C (123 K). In the ferromagnetic phase well defined spin waves are
observed, with a gapless ($\Delta <0.04$ meV) dispersion relation E=Dq^{2} as
expected for an ideal isotropic ferromagnet. As T approaches T_C from low T,
the spin waves renormalize, but no significant central diffusive component to
the fluctuation spectrum is observed in stark contrast to the
La$_{1-x}$(Ca,Ba,Sr)$_x$MnO$_3$ system. These results argue strongly that the
mechanism responsible for the magnetoresistive effect has a different origin in
these two classes of materials.",9805131v1
1998-08-07,"Scaling relations in charge and spin excitations for (La,Sr)MnO3","Scaling relations in the charge and spin excitations of (La,Sr)MnO3 are
studied from both theoretical and experimental points of view. In the
ferromagnetic metal phase, we investigate optical conductivity and neutron
inelastic scattering, and compare with a theoretical calculation based on the
dynamical mean-field theory of the double-exchange hamiltonian. Spin and charge
dynamics of (La,Sr)MnO3 exhibit typical behaviors of half metals. In these
manganite compounds with high Curie temperature, various behaviors in spin and
charge properties are explained by the double-exchange hamiltonian alone.
Magnetoresistance of these compounds as well as other compounds with lower
Curie temperature are also discussed.",9808076v1
1998-08-27,Single hole dynamics in dimerized spin liquids,"The dynamics of a single hole in quantum antiferromagnets is influenced by
magnetic fluctuations. In the present work we consider two situations. The
first one corresponds to a single hole in the two leg t-J spin ladder. In this
case the wave function renormalization is relatively small and the
quasiparticle residue of the S=1/2 state remains close to unity. However at
large t/J there are higher spin (S=3/2,5/2,..) bound states of the hole with
the magnetic excitations, and therefore there is a crossover from
quasiparticles with S=1/2 to quasiparticles with higher spin.
  The second situation corresponds to a single hole in two coupled
antiferromagnetic planes very close to the point of antiferromagnetic
instability. In this case the hole wave function renormalization is very strong
and the quasiparticle residue vanishes at the point of instability.",9808302v1
1999-03-31,Spin dynamics in hole-doped two-dimensional S=1/2 Heisenberg antiferromagnets: ^{63}Cu NQR relaxation in La_{2-x}Sr_xCuO_4 for $x\leq 0.04$,"The effects on the correlated Cu^{2+} S = 1/2 spin dynamics in the
paramagnetic phase of La_{2-x}Sr_xCuO_4 (for $x \lesssim 0.04$) due to the
injection of holes are studied by means of ^{63}Cu NQR spin-lattice relaxation
time T_1 measurements. The results are discussed in the framework of the
connection between T_1 and the in-plane magnetic correlation length
$\xi_{2D}(x,T)$. It is found that at high temperatures the system remains in
the renormalized classical regime, with a spin stiffness constant $\rho_s(x)$
reduced by small doping to an extent larger than the one due to Zn doping. For
$x\gtrsim 0.02$ the effect of doping on $\rho_s(x)$ appears to level off. The
values for $\rho_s(x)$ derived from T_1 for $T\gtrsim 500$ K are much larger
than the ones estimated from the temperature behavior of sublattice
magnetization in the ordered phase ($T\leq T_N$). It is argued that these
features are consistent with the hypothesis of formation of stripes of
microsegregated holes.",9903449v1
1999-04-06,Non-Fermi-liquid behavior in the Kondo lattices induced by peculiarities of magnetic ordering and spin dynamics,"A scaling consideration of the Kondo lattices is performed with account of
singularities in the spin excitation spectral function. It is shown that a
non-Fermi-liquid (NFL) behavior between two critical values of the bare $s-f$
coupling constant occurs naturally for complicated magnetic structures with
several magnon branches. This may explain the fact that a NFL behavior takes
place often in the heavy-fermion systems with peculiar spin dynamics. Another
kind of a NFL-like state (with different critical exponents) can occur for
simple antiferromagnets with account of magnon damping, and for paramagnets,
especially with two-dimensional character of spin fluctuations. The mechanisms
proposed lead to some predictions about behavior of specific heat, resistivity,
magnetic susceptibility, and anisotropy parameter, which can be verified
experimentally.",9904072v3
2001-06-18,Low-frequency dynamics of disordered XY spin chains and pinned density waves: from localized spin waves to soliton tunneling,"A long-standing problem of the low-energy dynamics of a disordered XY spin
chain is re-examined. The case of a rigid chain is studied where the quantum
effects can be treated quasiclassically. It is shown that as the frequency
decreases, the relevant excitations change from localized spin waves to
two-level systems to soliton-antisoliton pairs. The linear-response correlation
functions are calculated. The results apply to other periodic glassy systems
such as pinned density waves, planar vortex lattices, stripes, and disordered
Luttinger liquids.",0106350v3
2001-09-29,Fractionalization in an Easy-axis Kagome Antiferromagnet,"We study an antiferromagnetic spin-1/2 model with up to third
nearest-neighbor couplings on the Kagome lattice in the easy-axis limit, and
show that its low-energy dynamics are governed by a four site XY ring exchange
Hamiltonian. Simple ``vortex pairing'' arguments suggest that the model
sustains a novel fractionalized phase, which we confirm by exactly solving a
modification of the Hamiltonian including a further four-site interaction. In
this limit, the system is a featureless ``spin liquid'', with gaps to all
excitations, in particular: deconfined S^z=1/2 bosonic ``spinons'' and Ising
vortices or ``visons''. We use an Ising duality transformation to express vison
correlators as non-local strings in terms of the spin operators, and calculate
the string correlators using the ground state wavefunction of the modified
Hamiltonian. Remarkably, this wavefunction is exactly given by a kind of
Gutzwiller projection of an XY ferromagnet. Finally, we show that the
deconfined spin liquid state persists over a finite range as the additional
four-spin interaction is reduced, and study the effect of this reduction on the
dynamics of spinons and visons.",0110005v1
2001-12-12,Systematic (63)Cu NQR and (89)Y NMR Study of Spin Dynamics in Y(1-z)Ca(z)Ba(2)Cu(3)O(y) Across Superconductor-Insulator Boundary,"We demonstrate that the spin dynamics in underdoped Y(1-z)Ca(z)Ba(2)Cu(3)O(y)
for y=~6.0 exhibit qualitatively the same behavior to underdoped
La(2-x)Sr(x)CuO(4) for an equal amount of hole concentration p=z/2=x<0.11.
However,a spin-gap appears as more holes are doped into the CuO(2) plane by
increasing the oxygen concentration to y=~6.5 for a fixed value of Ca
concentration z. Our results also suggest that Ca doping causes disorder
effects that enhance the low frequency spin fluctuations.",0112234v4
2002-06-15,Spin and charge dynamics of stripes in doped Mott insulators,"We study spin and charge dynamics of stripes in doped Mott insulators by
considering a two-dimensional Hubbard model with N fermion flavors. For N =2 we
recover the normal one-band model while for N -> infty a spin density wave
mean-field solution. For all band fillings, lattice topologies and N= 4 n the
model may be solved by means of Monte Carlo methods without encountering the
sign problem. At N=4 and in the vicinity of the Mott insulator, the single
particle density of states shows a gap. Within this gap and on rectangular
topologies of sizes up to 30 X 12 we find gapless spin collective modes
centered around q = (\pi \pm \epsilon_x,\pi \pm \epsilon_y) as well as charge
modes centered around q = (\pm 2 \epsilon_x, \pm 2 \epsilon_y), q = (\pm
\epsilon_x, \pm \epsilon_y) and q = (0,0). \epsilon_{x,y} depends on the
lattice topology and doping.",0206287v2
2002-07-01,Spin fluctuations in a metallic antiferromagnet,"The magnon energy and amplitude renormalization due to intraband
particle-hole excitations are studied in a metallic antiferromagnet. The change
in sign of the intraband contribution with $\omega$ results in significant
differences between static and dynamical behaviours. For electron doping, while
the coherent magnon peak looses spectral weight and is shifted to higher energy
with doping, the low-energy incoherent part becomes increasingly prominent as
it narrows in width and shifts to lower energy. Implications for spin dynamics
in the electron-doped cuprate $\rm Nd_{2-x} Ce_x Cu O_4$ are discussed. Due to
an exact cancellation of two logarithmically divergent spin-fluctuation
processes, the AF order parameter is unaffected to leading order. For hole
doping, short wavelength transverse perturbations ($q > q^* \sim \sqrt{x}$) are
found to be stable, implying short-range AF order with a spin correlation
length $\xi/a \sim 1/\sqrt{x}$.",0207032v1
2002-07-30,Spin-polarized muons in condensed matter physics,"A positive muon is a spin-1/2 particle. Beams of muons with all their spins
polarized can be prepared and subsequently implanted in various types of
condensed matter. The subsequent precession and relaxation of their spins can
then be used to investigate a variety of static and dynamic effects in a sample
and hence to deduce properties concerning magnetism, superconductivity and
molecular dynamics. Though strictly a lepton, and behaving essentially like a
heavy electron, it is convenient to think of a muon as a light proton, and it
is often found with a captured electron in a hydrogen-like atom known as
muonium. This article outlines the principles of various experimental
techniques which involve implanted muons and describes some recent
applications. The use of muons in condensed matter physics has shed new light
on subjects as diverse as passivation in semiconductors, frustrated spin
systems, vortex lattice melting, and quantum diffusion of light particles.",0207699v1
2003-06-11,Microwave Oscillations of a Nanomagnet Driven by a Spin-Polarized Current,"We describe direct electrical measurements of microwave-frequency dynamics in
individual nanomagnets that are driven by spin transfer from a DC
spin-polarized current. We map out the dynamical stability diagram as a
function of current and magnetic field, and we show that spin transfer can
produce several different types of magnetic excitations, including small-angle
precession, a more complicated large-angle motion, and a high-current state
that generates little microwave signal. The large-angle mode can produce a
significant emission of microwave energy, as large as 40 times the
Johnson-noise background.",0306259v1
2003-07-17,Dynamical Coulomb blockade and spin-entangled electrons,"We consider the production of mobile and nonlocal pairwise spin-entangled
electrons from tunneling of a BCS-superconductor (SC) to two normal Fermi
liquid leads. The necessary mechanism to separate the two electrons coming from
the same Cooper pair (spin-singlet) is achieved by coupling the SC to leads
with a finite resistance. The resulting dynamical Coulomb blockade effect,
which we describe phenomenologically in terms of an electromagnetic
environment, is shown to be enhanced for tunneling of two spin-entangled
electrons into the same lead compared to the process where the pair splits and
each electron tunnels into a different lead. On the other hand in the
pair-split process, the spatial correlation of a Cooper pair leads to a current
suppression as a function of distance between the two tunnel junctions which is
weaker for effectively lower dimensional SCs.",0307444v1
2003-07-25,Field-Shift Aging Protocol on the 3D Ising Spin-Glass Model: Dynamical Crossover between the Spin-Glass and Paramagnetic States,"Spin-glass (SG) states of the 3-dimensional Ising Edwards-Anderson model
under a static magnetic field $h$ are examined by means of the standard Monte
Carlo simulation on the field-shift aging protocol at temperature $T$. For each
process with $(T; \tw, h)$, $\tw$ being the waiting time before the field is
switched on, we extract the dynamical crossover time, $\tcr(T; \tw, h)$. We
have found a nice scaling relation between the two characteristic length scales
which are properly determined from $\tcr$ and $\tw$ and then are normalized by
the static field crossover length introduced in the SG droplet theory. This
scaling behavior implies the instability of the SG phase in the equilibrium
limit even under an infinitesimal $h$. In comparison with this numerical result
the field effect on real spin glasses is also discussed.",0307641v2
2003-08-14,The magnetic reversal in dot arrays recognized by the self-organized adaptive neural network,"The remagnetization dynamics of monolayer dot array superlattice XY 2-D spin
model with dipole-dipole interactions is simulated. Within the proposed model
of array, the square dots are described by the spatially modulated
exchange-couplings. The dipole-dipole interactions are approximated by the
hierarchical sums and spin dynamics is considered in regime of the
Landau-Lifshitz equation. The simulation of reversal for $40 000$ spins
exhibits formation of nonuniform intra-dot configurations with nonlinear
wave/anti-wave pairs developed at intra-dot and inter-dot scales. Several
geometric and parametric dependences are calculated and compared with
oversimplified four-spin model of reversal. The role of initial conditions and
the occurrence of coherent rotation mode is also investigated. The emphasis is
on the classification of intra-dot or inter-dot (interfacial) magnetic
configurations done by adaptive neural network with varying number of neurons.",0308287v1
2003-10-15,Constrained spin dynamics description of random walks on hierarchical scale-free networks,"We study a random walk problem on the hierarchical network which is a
scale-free network grown deterministically. The random walk problem is mapped
onto a dynamical Ising spin chain system in one dimension with a nonlocal spin
update rule, which allows an analytic approach. We show analytically that the
characteristic relaxation time scale grows algebraically with the total number
of nodes $N$ as $T \sim N^z$. From a scaling argument, we also show the
power-law decay of the autocorrelation function $C_{\bfsigma}(t)\sim
t^{-\alpha}$, which is the probability to find the Ising spins in the initial
state ${\bfsigma}$ after $t$ time steps, with the state-dependent non-universal
exponent $\alpha$. It turns out that the power-law scaling behavior has its
origin in an quasi-ultrametric structure of the configuration space.",0310344v2
2003-10-21,Return to return point memory,"We describe a new class of systems exhibiting return point memory (RPM) that
are different from those discussed before in the context of ferromagnets. We
show numerically that one dimensional random Ising antiferromagnets have RPM,
when configurations evolve from a large field. However, RPM is violated when
started from some stable configurations at finite field unlike in the
ferromagnetic case. This implies that the standard approach to understanding
ferromagnetic RPM systems will fail for this case. We also demonstrate RPM with
a set of variables that keep track of spin flips at each site. Conventional RPM
for the spin configuration is a projection of this result, suggesting that spin
flip variables might be a more fundamental representation of the dynamics. We
also present a mapping that embeds the antiferromagnetic chain in a two
dimensional ferromagnetic model, and prove RPM for spin exchange dynamics in
the interior of the chain with this mapping.",0310484v1
2003-12-19,Field-Induced Disorder Point in Non-Collinear Ising Spin Chains,"We perform a theoretical study of a non-collinear Ising ferrimagnetic spin
chain inspired by the compound Co(hfac)2NITPhOMe. The basic building block of
its structure contains one Cobalt ion and one organic radical each with a spin
1/2. The exchange interaction is strongly anisotropic and the corresponding
axes of anisotropy have a period three helical structure. We introduce and
solve a model Hamiltonian for this spin chain. We show that the present
compound is very close to a so-called disorder point at which there is a
massive ground state degeneracy. We predict the equilibrium magnetization
process and discuss the impact of the degeneracy on the dynamical properties by
using arguments based on the Glauber dynamics.",0312528v1
2004-02-10,Magnetism in semiconductors: A dynamical mean field study of ferromagnetism in Ga_{1-x}Mn_xAs,"We employ the dynamical mean field approximation to perform a systematic
study of magnetism in Ga_{1-x}Mn_xAs. Our model incorporates the effects of the
strong spin-orbit coupling on the J=3/2 GaAs valence bands and of the exchange
interaction between the randomly distributed magnetic ions and the itinerant
holes. The ferromagnetic phase transition temperature T_c is obtained for
different values of the impurity-hole coupling J_c and of the hole
concentration n_h at the Mn doping of x=0.05. We also investigate the
temperature dependence of the local magnetization and spin polarization of the
holes. By comparing our results with those for a single band Hamiltonian in
which the spin-orbit coupling is switched off, we conclude that the spin-orbit
coupling in Ga_{1-x}Mn_xAs gives rise to frustration in the ferromagnetic
order, strengthening recent findings by Zarand and Janko (Phys. Rev. Lett. 89,
047201 (2002)).",0402289v1
2004-03-10,Role of Correlation and Exchange for Quasi-particle Spectra of Magnetic and Diluted Magnetic Semiconductors,"Theoretical foundation and application of the generalized spin-fermion (sp-d)
exchange lattice model to magnetic and diluted magnetic semiconductors are
discussed. The capabilities of the model to describe spin quasi-particle
spectra are investigated. The main emphasis is made on the dynamic behavior of
two interacting subsystems, the localized spins and spin density of itinerant
carriers. A nonperturbative many-body approach, the Irreducible Green Functions
(IGF) method, is used to describe the quasi-particle dynamics. Scattering
states are investigated and three branches of magnetic excitations are
calculated in the regime, characteristic of a magnetic semiconductor. For a
simplified version of the model (Kondo lattice model) we study the spectra of
quasi-particle excitations with special attention given to diluted magnetic
semiconductors. For this, to include the effects of disorder, modified mean
fields are determined self-consistently. The role of the Coulomb correlation
and exchange is clarified by comparing of both the cases.",0403266v1
2004-03-16,Quantum dynamics under coherent and incoherent effects of a spin bath in the Keldysh formalism: application to a spin swapping operation,"We develop the Keldysh formalism for the polarization dynamics of an open
spin system. We apply it to the swapping between two qubit states in a model
describing an NMR cross-polarization experiment. The environment is a set of
interacting spins. For fast fluctuations in the environment, the analytical
solution shows effects missed by the secular approximation of the Quantum
Master Equation for the density matrix: a frequency decrease depending on the
system-environment escape rate and the quantum quadratic short time behavior.
Considering full memory of the bath correlations yields a progressive change of
the swapping frequency.",0403399v3
2004-04-05,"Large-angle, gigahertz-rate random telegraph switching induced by spin-momentum transfer","We show that spin-polarized dc current passing through a small magnetic
element induces two-state, random telegraph switching of the magnetization via
the spin-momentum transfer effect. The resistances of the states differ by up
to 50% of the change due to complete magnetization reversal. Fluctuations are
seen for a wide range of currents and magnetic fields, with rates that can
exceed 2 GHz, and involve collective motion of a large volume (10^4 nm^3) of
spins. Switching rate trends with field and current indicate that increasing
temperature alone cannot explain the dynamics. The rates approach a stochastic
regime wherein dynamics are governed by both precessional motion and thermal
perturbations.",0404109v1
2004-05-02,Spin Dynamics and Multiple Reflections in Ferromagnetic Film in Contact with Normal Metal Layers,"Spin dynamics of a metallic ferromagnetic film imbedded between normal metal
layers is studied using the spin-pumping theory of Tserkovnyak et al. [Phys.
Rev. Lett. 88, 117601 (2002)]. The scattering matrix for this structure is
obtained using a spin-dependent potential with quantum well in the
ferromagnetic region. Owing to multiple reflections in the well, the excess
Gilbert damping and the gyromagnetic ratio exhibit quantum oscillations as a
function of the thickness of the ferromagnetic film. The wavelength of the
oscillations is given by the depth of the quantum well. For iron film imbedded
between gold layers, the amplitude of the oscillations of the Gilbert damping
is in an order of magnitude agreement with the damping observed by Urban et al.
[Phys. Rev. Lett. 87, 217204 (2001)]. The results are compared with the linear
response theory of Mills [Phys. Rev. B 68, 0144419 (2003)].",0405020v1
2004-08-10,Majority Rule Dynamics in Finite Dimensions,"We investigate the long-time behavior of a majority rule opinion dynamics
model in finite spatial dimensions. Each site of the system is endowed with a
two-state spin variable that evolves by majority rule. In a single update
event, a group of spins with a fixed (odd) size is specified and all members of
the group adopt the local majority state. Repeated application of this update
step leads to a coarsening mosaic of spin domains and ultimate consensus in a
finite system. The approach to consensus is governed by two disparate time
scales, with the longer time scale arising from realizations in which spins
organize into coherent single-opinion bands. The consequences of this
geometrical organization on the long-time kinetics are explored.",0408219v2
2004-10-07,Quantum Fluctuations and Excitations in Antiferromagnetic Quasicrystals,"We study the effects of quantum fluctuations and the excitation spectrum for
the antiferromagnetic Heisenberg model on a two-dimensional quasicrystal, by
numerically solving linear spin-wave theory on finite approximants of the
octagonal tiling. Previous quantum Monte Carlo results for the distribution of
local staggered magnetic moments and the static spin structure factor are
reproduced well within this approximate scheme. Furthermore, the magnetic
excitation spectrum consists of magnon-like low-energy modes, as well as
dispersionless high-energy states of multifractal nature. The dynamical spin
structure factor, accessible to inelastic neutron scattering, exhibits
linear-soft modes at low energies, self-similar structures with bifurcations
emerging at intermediate energies, and flat bands in high-energy regions. We
find that the distribution of local staggered moments stemming from the
inhomogeneity of the quasiperiodic structure leads to a characteristic energy
spread in the local dynamical spin susceptibility, implying distinct nuclear
magnetic resonance spectra, specific for different local environments.",0410180v1
2005-05-19,Coherent collisional spin dynamics in optical lattices,"We report on the observation of coherent, purely collisionally driven spin
dynamics of neutral atoms in an optical lattice. For high lattice depths, atom
pairs confined to the same lattice site show weakly damped Rabi-type
oscillations between two-particle Zeeman states of equal magnetization, induced
by spin changing collisions. This paves the way towards the efficient creation
of robust entangled atom pairs in an optical lattice. Moreover, measurement of
the oscillation frequency allows for precise determination of the spin-changing
collisional coupling strengths, which are directly related to fundamental
scattering lengths describing interatomic collisions at ultracold temperatures.",0505492v2
2005-06-06,Spin dynamics and violation of the fluctuation dissipation theorem in a non-equilibrium ohmic spin boson model,"We present results for the dynamics of an impurity spin coupled to a magnetic
field and to two ohmic baths which are out-of equilibrium due to the
application of a bias voltage. Both the non-equilibrium steady state and the
rate constants describing the approach to steady state are found to depend
sensitively on the relative strengths of a magnetic field and a voltage
dependent decoherence rate. Computation of physical quantities including the
frequency dependent ratio of response to correlation functions and the
probabilities of the two spin states allows the extraction of voltage dependent
effective temperatures. The temperatures extracted from different quantities
differ from one another in magnitude and their dependence on parameters, and in
general are non-monotonic.",0506154v2
2005-07-30,Metamagnetic Quantum Criticality Revealed by 17O-NMR in the Itinerant Metamagnet Sr3Ru2O7,"We have investigated the spin dynamics in the bilayered perovskite Sr3Ru2O7
as a function of magnetic field and temperature using 17O-NMR. This system sits
close to a metamagnetic quantum critical point (MMQCP) for the field
perpendicular to the ruthenium oxide planes. We confirm Fermi-liquid behavior
at low temperatures except for a narrow field region close to the MMQCP. The
nuclear spin-lattice relaxation rate divided by temperature 1/T1T is enhanced
on approaching the metamagnetic critical field of 7.9 T and at the critical
field 1/T1T continues to increase and does not show Fermi- liquid behavior down
to 0.3 K. The temperature dependence of T1T in this region suggests the
critical temperature Theta to be 0 K, which is a strong evidence that the spin
dynamics possesses a quantum critical character. Comparison between uniform
susceptibility and 1/T1T reveals that antiferromagnetic fluctuations instead of
two-dimensional ferromagnetic fluctuations dominate the spin fluctuation
spectrum at the critical field, which is unexpected for itinerant
metamagnetism.",0508012v1
2005-11-08,"Anomalous spin dynamics in charge ordered, 'two-electron' doped manganite Ca_0.9Ce_0.1MnO_3 : consequence of a spin-liquid phase?","The 'two-electron' doped rare earth mangnites Ca_1-x Ce_x MnO_3 (x = 0.1,0.2)
are probed using resistivity, ac susceptibility and electron paramagnetic
resonance (EPR) measurements across their respective charge ordering (CO)
temperatures T_CO = 173 K and 250 K. The EPR 'g' factor and intensity as well
as the transport and magnetic behaviours of the two compositions are
qualitatively similar and are as expected for CO systems. However, the EPR
linewidth, reflective of the spin dynamics, for x = 0.1, shows a strongly
anomalous temperature dependence, decreasing with decreasing temperature below
T_CO in contrast with the sample with x = 0.2 and other CO systems. Keeping in
view the evidence for magnetic frustration in the system, we propose that the
anomalous temperature dependence of the linewidth is the signature of the
occurrence of a disorder driven spin liquid phase, present along with charge
ordering.",0511184v1
2005-12-12,Coherent spin dynamics of an interwell excitons gas in GaAs/AlGaAs coupled quantum wells,"The spin dynamics of an interwell excitons gas has been investigated in n-i-n
GaAs/AlGaAs coupled quantum wells (CQWs). In these heterostructures the
electron and the hole are spatially separated in neighboring quantum wells by a
narrow AlAs barrier, when an electric field is applied. The time evolution
kinetics of the interwell exciton photoluminescence has been measured under
resonant excitation of the 1sHH intrawell exciton, using a pulsed tunable
laser. The formation of a collective exciton phase in time and the temperature
dependence of its spin relaxation rate have been studied. The spin relaxation
rate of the interwell excitons is strongly reduced in the collective phase.
This observation provides evidence for the coherence of the indirect excitons
collective phase at temperatures below a critical $T_c$.",0512221v1
2005-12-23,Cavity Enhanced Faraday Rotation of Semiconductor Quantum Dots,"A dielectric vertical cavity is used to study the spin dynamics of
molecularly self-assembled colloidal CdSe quantum dots (QDs). Using this
structure, a nearly 30-fold enhancement of Faraday rotation is observed, which
scales with the quality factor of the cavity. In this classical nonperturbative
regime, the amplified rotation is attributed to optically excited spins
interacting with multiple passes of the probe photons in the cavity. By
applying this general planar cavity motif to Faraday rotation, dynamical
measurements are accessible at extremely low powers on relatively small numbers
of quantum confined spins. In CdSe QDs, low power measurements reveal that
contributions from exciton and electron spin precession are largely dependent
upon the power of excitation. We demonstrate that this scheme is amenable to
both soft and hard systems as a means to increase detection sensitivity.",0512625v1
2005-12-25,Exchange and spin Jahn-Teller distortions for a triangular cluster of spin-1/2,"We study the effects of magnetoelastic coupling on the degenerate ground
state of the spin-1/2 antiferromagnetic Heisenberg model for the regular
triangular spin cluster. Static displacement of spins spontaneously lifts the
degeneracy of the ground state through the distance dependence of exchange
coupling, i.e., a spin Jahn-Teller mechanism takes place. On the other hand,
dynamical displacement does not lift the degeneracy, though the cluster
distorts spontaneously. The energy decrease obtained by dynamical theory is
twice as large as that obtained by static theory because of quantum
fluctuation.",0512642v3
2006-03-20,How spin-orbit interaction can cause electronic shot noise,"The shot noise in the electrical current through a ballistic chaotic quantum
dot with N-channel point contacts is suppressed for N --> infinity, because of
the transition from stochastic scattering of quantum wave packets to
deterministic dynamics of classical trajectories. The dynamics of the electron
spin remains quantum mechanical in this transition, and can affect the
electrical current via spin-orbit interaction. We explain how the role of the
channel number N in determining the shot noise is taken over by the ratio
l_{so}/lambda_F of spin precession length l_{so} and Fermi wave length
lambda_F, and present computer simulations in a two-dimensional billiard
geometry (Lyapunov exponent alpha, mean dwell time tau_{dwell}, point contact
width W) to demonstrate the scaling (lambda_F/l_{so})^{1/alpha tau_{dwell}} of
the shot noise in the regime lambda_F << l_{so} << W.",0603524v1
2006-04-21,Decoherence and Dephasing in Kondo Tunneling through Double Quantum Dots,"We describe the mechanism of charge-spin transformation in a double quantum
dot (DQD) with even occupation, where a time dependent gate voltage v(t) is
applied to one of its two valleys, whereas the other one is coupled to the
source and drain electrodes. The Kondo tunneling regime under strong Coulomb
blockade may be realized when the spin spectrum of the DQD is formed by the
ground state spin triplet and two singlet excitations. Charge fluctuations
induced by v(t) result in transitions within the spin multiplet characterized
by the SO(5) dynamical symmetry group. In a weakly non-adiabatic regime the
decoherence, dephasing and relaxation processes affect Kondo tunneling. Each of
these processes is caused by a special type of dynamical gauge fluctuations, so
that one may discriminate between the decoherence in the ground state of a DQD
and dephasing at finite temperatures.",0604518v1
2006-04-27,Restoring Coherence Lost to a Slow Interacting Mesoscopic Bath,"For a two-state quantum object interacting with a slow mesoscopic interacting
spin bath, we show that a many-body solution of the bath dynamics conditioned
on the quantum-object state leads to an efficient control scheme to recover the
lost quantum-object coherence through disentanglement. We demonstrate the
theory with the realistic problem of one electron spin in a bath of many
interacting nuclear spins in a semiconductor quantum dot. The spin language is
easily generalized to a quantum object in contact with a bath of interacting
multi-level quantum units with the caveat that it is mesoscopic and its
dynamics is slow compared with the quantum object.",0604634v3
2006-10-27,Charge and spin dynamics in a two dimensional electron gas,"A number of time resolved optical experiments probing and controlling the
spin and charge dynamics of the high mobility two-dimensional electron gas in a
GaAs/AlGaAs heterojunction are discussed. These include time resolved
reflectivity, luminescence, transient grating, magneto-optical Kerr effect, and
electro-optical Kerr effect experiments. The optical experiments provide
information on the carrier lifetimes and spin dephasing times, as well as on
the carrier diffusion coefficient which directly gives the charge mobility. A
combination of the two types of Kerr experiments, shows to be useful in
extracting both the carrier lifetimes and spin dephasing times in a single
experiment.",0610783v1
2006-11-29,Irregular Spin Tunnelling for Spin-1 Bose-Einstein Condensates in a Sweeping Magnetic Field,"We investigate the spin tunnelling of spin-1 Bose-Einstein condensates in a
linearly sweeping magnetic field with a mean-field treatment. We focus on the
two typical alkali Bose atoms $^{87}Rb$ and $^{23}Na$ condensates and study
their tunnelling dynamics according to different sweeping rates of external
magnetic fields. In the adiabatic (i.e., slowly sweeping) and sudden (i.e.,
fast sweeping) limits, no tunnelling is observed. For the case of moderate
sweeping rates, the tunnelling dynamics is found to be very sensitive on the
sweeping rates with showing a chaotic-like tunnelling regime. With magnifying
the regime, however, we find interestedly that the plottings become resolvable
under a resolution of $10^{-4}$ G/s where the tunnelling probability with
respect to the sweeping rate shows a regular periodic-like pattern. Moreover, a
conserved quantity standing for the magnetization in experiments is found can
dramatically affect the above picture of the spin tunnelling. Theoretically we
have given a reasonable interpretation to the above findings and hope our
studies would bring more attention to spin tunnelling experimentally.",0611734v1
2006-12-05,Multi-component gap solitons in spinor Bose-Einstein condensates,"We model the nonlinear behaviour of spin-1 Bose-Einstein condensates (BECs)
with repulsive spin-independent interactions and either ferromagnetic or
anti-ferromagnetic (polar) spin-dependent interactions, loaded into a
one-dimensional optical lattice potential. We show that both types of BECs
exhibit dynamical instabilities and may form spatially localized
multi-component structures. The localized states of the spinor matter waves
take the form of vector gap solitons and self-trapped waves that exist only
within gaps of the linear Bloch-wave band-gap spectrum. Of special interest are
the nonlinear localized states that do not exhibit a common spatial density
profile shared by all condensate components, and consequently cannot be
described by the single mode approximation (SMA), frequently employed within
the framework of the mean-field treatment. We show that the non-SMA states can
exhibits Josephson-like internal oscillations and self-magnetisation, i.e.
intrinsic precession of the local spin. Finally, we demonstrate that
non-stationary states of a spinor BEC in a lattice exhibit coherent undamped
spin-mixing dynamics, and that their controlled conversion into a stationary
state can be achieved by the application of an external magnetic field.",0612104v1
2007-03-13,Ettingshausen Effect around Landau Level Filling Factor nu=3 Studied by Dynamic Nuclear Polarization,"Spin current perpendicular to the electric current is investigated around
Landau level filling factor $\nu=3$ in a GaAs/AlGaAs two-dimensional electron
system. Measurements of dynamic nuclear polarization in the vicinity of the
edge of a specially designed Hall bar sample indicate that the direction of the
spin current with respect to the Hall electric field reverses its polarity at
$\nu=3$, where the dissipative current carried by holes in the spin up Landau
level is replaced with that by electrons in the spin down Landau level.",0703325v5
1997-05-29,The Spectrum from Lattice NRQCD,"I review recent results for heavy-heavy spectroscopy using Lattice NRQCD. The
NRQCD collaboration reports that spin-independent splittings for the $\Upsilon$
are scaling for a sensible range of $\beta$ values in the quenched
approximation. Spin-dependent splittings are not, if the scale is set by
spin-independent splittings. Results which include higher order spin-dependent
relativistic and discretisation corrections show differences from previous
(NRQCD collaboration) results without these. As expected, the differences are
small for $\Upsilon$ but rather large for charmonium. New results from the
SESAM collaboration for $\Upsilon$ spectroscopy on configurations with Wilson
dynamical fermions show good agreement with previous results on HEMCGC
configurations with staggered dynamical fermions.",9705039v1
2001-05-15,"O(n) Spin Systems- Some General Properties: A Generalized Mermin-Wagner-Coleman Theorem, Ground States, Peierls Bounds, and Dynamics","Here we examine O(n) systems with arbitrary two spin interactions (of
unspecified range) within a general framework. We shall focus on
translationally invariant interactions. In the this case, we determine the
ground states of the $O(n \ge 2)$ systems. We further illustrate how one may
establish Peierls bounds for many Ising systems with long range interactions.
We study the effect of thermal fluctuations on the ground states and derive the
corresponding fluctuation integrals. The study of the thermal fluctuation
spectra will lead us to discover a very interesting odd-even $n$
(coupling-decoupling) effect. We will prove a generalized Mermin-Wagner-Coleman
(integral divergence) theorem for all translationally invariant interactions in
two dimensions with an analytic kernel in momentum space. We will show that
many three dimensional systems have smectic like thermodynamics. We will
examine the topology of the ground state manifolds for both translationally
invariant and spin glass systems. We conclude with a discussion of O(n) spin
dynamics in the general case.",0105143v2
1991-10-07,Classical Scattering in 2+1 Gravity with N Spinning Sources,"The classical dynamics of N spinning point sources in 2+1 Einstein-Cartan
gravity is considered. It corresponds to the ISO(2,1) Chern-Simons theory, in
which the torsion source is restricted to its intrinsic spin part. A class of
explicit solutions is found for the dreibein and the spin connection, which are
torsionless in the spinless limit. By using the residual local Poincare'
invariance of the solutions, we fix the gauge so that the metric is smooth
outside the particles and satisfies proper asymptotic conditions at space and
time infinity. We recover previous results for test bodies and find new ones
for the scattering of two dynamical particles in the massless limit.",9110020v1
1994-02-23,Dynamically Triangulated Ising Spins in Flat Space,"A model describing Ising spins with short range interactions moving randomly
in a plane is considered. In the presence of a hard core repulsion, which
prevents the Ising spins from overlapping, the model is analogous to a
dynamically triangulated Ising model with spins constrained to move on a flat
surface. It is found that as a function of coupling strength and hard core
repulsion the model exhibits multicritical behavior, with first and second
order transition lines terminating at a tricritical point. The thermal and
magnetic exponents computed at the tricritical point are consistent with the
exact two-matrix model solution of the random Ising model, introduced
previously to describe the effects of fluctuating geometries.",9402131v1
2001-05-15,"O(n) Spin Systems- Some General Properties: A Generalized Mermin-Wagner-Coleman Theorem, Ground States, Peierls Bounds, and Dynamics","Here we examine O(n) systems with arbitrary two spin interactions (of
unspecified range) within a general framework. We shall focus on
translationally invariant interactions. In the this case, we determine the
ground states of the $O(n \ge 2)$ systems. We further illustrate how one may
establish Peierls bounds for many Ising systems with long range interactions.
We study the effect of thermal fluctuations on the ground states and derive the
corresponding fluctuation integrals. The study of the thermal fluctuation
spectra will lead us to discover a very interesting odd-even $n$
(coupling-decoupling) effect. We will prove a generalized Mermin-Wagner-Coleman
theorem for all two dimensional systems (of arbitrary range) with analytic
kernels in $k$ space. We will show that many three dimensional systems have
smectic like thermodynamics. We will examine the topology of the ground state
manifolds for both translationally invariant and spin glass systems. We
conclude with a discussion of O(n) spin dynamics in the general case.",0105147v4
2005-03-12,Generalized Number Theoretic Spin Chain-Connections to Dynamical Systems and Expectation Values,"We generalize the number theoretic spin chain, a one-dimensional statistical
model based on the Farey fractions, by introducing a new parameter x>=0. This
allows us to write recursion relations in the length of the chain. These
relations are closely related to the Lewis three-term equation, which is useful
in the study of the Selberg \zeta-function. We then make use of these relations
and spin orientation transformations. We find a simple connection with the
transfer operator of a model of intermittency in dynamical systems. In
addition, we are able to calculate certain spin expectation values explicitly
in terms of the free energy or correlation length. Some of these expectation
values appear to be directly connected with the mechanism of the phase
transition.",0503030v1
2005-06-10,"Poisson involutions, spin Calogero-Moser systems associated with symmetric Lie subalgebras and the symmetric space spin Ruijsenaars-Schneider models","We develop a general scheme to construct integrable systems starting from
realizations in symmetric coboundary dynamical Lie algebroids and symmetric
coboundary Poisson groupoids. The method is based on the successive use of
Dirac reduction and Poisson reduction. Then we show that certain spin
Calogero-Moser systems associated with symmetric Lie subalgebras can be studied
in this fashion. We also consider some spin-generalized Ruisjenaars- Schneider
equations which correspond to the $N$-soliton solutions of $A^{(1)}_n$ affine
Toda field theory. In this case, we show how the equations are obtained from
the Dirac reduction of some Hamiltonian system on a symmetric coboundary
dynamical Poisson groupoid.",0506025v1
2002-07-17,Torus quantization for spinning particles,"We derive semiclassical quantization conditions for systems with spin. To
this end one has to define the notion of integrability for the corresponding
classical system which is given by a combination of the translational motion
and classical spin precession. We determine the geometry of the invariant
manifolds of this product dynamics which support semiclassical solutions of the
wave equation. The semiclassical quantization conditions contain a new term,
which is of the same order as the Maslov correction. This term is identified as
a rotation angle for a classical spin vector. Applied to the relativistic
Kepler problem the procedure sheds some light on the amazing success of
Sommerfeld's theory of fine structure [Ann. Phys. (Leipzig) 51 (1916) 1-94].",0207095v1
2005-01-03,Spin Chains as Perfect Quantum State Mirrors,"Quantum information transfer is an important part of quantum information
processing. Several proposals for quantum information transfer along linear
arrays of nearest-neighbor coupled qubits or spins were made recently. Perfect
transfer was shown to exist in two models with specifically designed strongly
inhomogeneous couplings. We show that perfect transfer occurs in an entire
class of chains, including systems whose nearest-neighbor couplings vary only
weakly along the chain. The key to these observations is the Jordan-Wigner
mapping of spins to noninteracting lattice fermions which display perfectly
periodic dynamics if the single-particle energy spectrum is appropriate. After
a half-period of that dynamics any state is transformed into its mirror image
with respect to the center of the chain. The absence of fermion interactions
preserves these features at arbitrary temperature and allows for the transfer
of nontrivially entangled states of several spins or qubits.",0501007v3
2006-02-15,Entanglement dynamics of electron-electron scattering in low-dimensional semiconductor systems,"We perform the quantitative evaluation of the entanglement dynamics in
scattering events between two insistinguishable electrons interacting via
Coulomb potential in 1D and 2D semiconductor nanostructures. We apply a
criterion based on the von Neumann entropy and the Schmidt decomposition of the
global state vector suitable for systems of identical particles. From the
timedependent numerical solution of the two-particle wavefunction of the
scattering carriers we compute their entanglement evolution for different spin
configurations: two electrons with the same spin, with different spin, singlet,
and triplet spin state. The procedure allows to evaluate the mechanisms that
govern entanglement creation and their connection with the characteristic
physical parameters and initial conditions of the system. The cases in which
the evolution of entanglement is similar to the one obtained for
distinguishable particles are discussed.",0602127v1
2007-05-24,Nonequilibrium Dynamics of Anisotropic Large Spins in the Kondo Regime: Time-Dependent Numerical Renormalization Group Analysis,"We investigate the time-dependent Kondo effect in a single-molecule magnet
(SMM) strongly coupled to metallic electrodes. Describing the SMM by a Kondo
model with large spin S > 1/2, we analyze the underscreening of the local
moment and the effect of anisotropy terms on the relaxation dynamics of the
magnetization. Underscreening by single-channel Kondo processes leads to a
logarithmically slow relaxation, while finite uniaxial anisotropy causes a
saturation of the SMM's magnetization. Additional transverse anisotropy terms
induce quantum spin tunneling and a pseudospin-1/2 Kondo effect sensitive to
the spin parity.",0705.3654v2
2007-06-14,Viscous spin exchange torque on precessional magnetization in $(\mathrm{LaMnO}_3)_{2n}/(\mathrm{SrMnO}_3)_{n}$ superlattices,"Photoinduced magnetization dynamics is investigated in chemically ordered
$(\mathrm{LaMnO}_3)_{2n}/(\mathrm{SrMnO}_3)_n$ superlattices using the
time-resolved magneto-optic Kerr effect. A monotonic frequency-field dependence
is observed for the $n=1$ superlattice, indicating a single spin population
consistent with a homogeneous hole distribution. In contrast, for $n\geq2$
superlattices, a large precession frequency is observed at low fields
indicating the presence of an exchange torque in the dynamic regime. We propose
a model that ascribes the emergence of exchange torque to the coupling between
two spin populations -- viscous and fast spins.",0706.2157v1
2007-06-25,Electron Spin Dynamics of the Superconductor CaC6 probed by ESR,"Conduction Electron Spin Resonance (CESR) was measured on a thick slab of
CaC6 in the normal and superconducting state. A surprising increase of the CESR
intensity below Tc can not be explained by the theoretically predicted change
in spin susceptibility. It is interpreted as a vortex enhanced increase of the
effective skin depth. Non-linear microwave absorption measurements in the
superconducting state describe CaC6 as an anisotropic BCS superconductor. The
study of the spin dynamics in the superconducting state and the discovery of
the vortex enhanced increase of the skin depth poses a challenge to theory to
provide a comprehensive description of the observed phenomena. CESR data in the
normal state characterize CaC6 as a three-dimensional (3D) metal. The analysis
suggests that the scattering of conduction electrons is dominated by impurities
and supports the description of superconductivity in the dirty limit.",0706.3609v2
2007-08-06,Dynamical magnetic susceptibility in the lamellar cobaltate superconductor Na_xCoO_2$\cdot y$H_2O,"We systematically analyze the influence of the superconducting gap symmetry
and the electronic structure on the dynamical spin susceptibility in
superconducting Na_xCoO_2$\cdot y$H_2O within a three different models: the
single a_{1g}-band model with nearest-neighbor hoppings, the realistic
three-band t_{2g}-model with, and without e'_g pockets present at the Fermi
surface. We show that the magnetic response in the normal state is dominated by
the incommensurate antiferromagnetic spin density wave fluctuations at large
momenta in agreement with experimental temperature dependence of the
spin-lattice relaxation rate. Also, we demonstrate that the presence or the
absence of the e'_g-pockets at the Fermi surface does not affect significantly
this conclusion. In the superconducting state our results for d_{x^2-y^2}- or
d_{xy}-wave symmetries of the superconducting order parameter are consistent
with experimental data and exclude nodeless $d_{x^2-y^2} + id_{xy}$-wave
symmetry. We further point out that the spin-resonance peak proposed earlier is
improbable for the realistic band structure of Na_xCoO_2$\cdot y$H_2O.
Moreover, even if present the resonance peak is confined to the
antiferromagnetic wave vector and disappears away from it.",0708.0807v2
2007-09-05,Muon spin rotation studies of spin dynamics at avoided level crossings in LiY0.998Ho0.002F4,"We have studied the Ho3+ spin dynamics for LiY0.998Ho0.002F4 through the
positive muon (mu+) transverse field depolarization rate lambda_TF as a
function of temperature and magnetic field. We find sharp reductions in
lambda_TF(H) at fields of 23, 46 and 69 mT, for which the Ho3+ ion system has
field-induced (avoided) level crossings. The reduction scales with calculated
level repulsions, suggesting that mu+ depolarization by slow fluctuations of
non-resonant Ho3+ spin states is partially suppressed when resonant tunneling
opens new fluctuation channels at frequencies much greater than the muon
precession frequency.",0709.0684v1
2008-04-09,Dynamics of spin and orbital phase transitions in YVO3,"YVO3 exhibits a well separated sequence of orbital and spin order transitions
at 200 K and 116 K, followed by a combined spin-orbital reorientation at 77 K.
It is shown that the spin order can be destroyed by a sufficiently strong
optical pulse within less than 4 ps. In contrast, the orbital reordering
transition from C-type to G-type orbital order is slower than 100 ps and goes
via an intermediate nonthermal phase. We propose that the dynamics of phase
transitions is subjected to symmetry relations between the associated phases.",0804.1472v1
2008-05-19,Collective processes of an ensemble of spin-1/2 particles,"When the dynamics of a spin ensemble are expressible solely in terms of
symmetric processes and collective spin operators, the symmetric collective
states of the ensemble are preserved. These many-body states, which are
invariant under particle relabeling, can be efficiently simulated since they
span a subspace whose dimension is linear in the number of spins. However, many
open system dynamics break this symmetry, most notably when ensemble members
undergo identical, but local, decoherence. In this paper, we extend the
definition of symmetric collective states of an ensemble of spin-1/2 particles
in order to efficiently describe these more general collective processes. The
corresponding collective states span a subspace which grows quadratically with
the number of spins. We also derive explicit formulae for expressing arbitrary
identical, local decoherence in terms of these states.",0805.2911v1
2008-05-28,Dynamic nuclear polarization with simultaneous excitation of electronic and nuclear transitions,"Dynamic nuclear polarization transfers spin polarization from electrons to
nuclei. We have achieved this by a new method, simultaneously exciting
transitions of electronic and nuclear spins. The efficiency of this technique
improves with increasing magnetic field. Experimental results are shown for
N@C60 with continuous-wave microwaves, which can be expected to produce even
higher polarization than the corresponding pulsed techniques for electron spins
greater than 1/2. The degree of nuclear polarization in this case can be easily
monitored through the intensities of the well resolved hyperfine components in
the EPR spectrum. The nuclear spin-lattice relaxation time is orders of
magnitude longer than that of the electrons.",0805.4357v1
2008-05-30,Induced Entanglement Enhanced by Quantum Criticality,"Two qubit entanglement can be induced by a quantum data bus interacting with
them. In this paper, with the quantum spin chain in the transverse field as an
illustration of quantum data bus, we show that such induced entanglement can be
enhanced by the quantum phase transition (QPT) of the quantum data bus. We
consider two external spins simultaneously coupled to a transverse field Ising
chain. By adiabatically eliminating the degrees of the chain, the effective
coupling between these two spins are obtained. The matrix elements of the
effective Hamiltonian are expressed in terms of dynamical structure factor
(DSF) of the chain. The DSF is the Fourier transformation of the Green function
of Ising chain and can be calculated numerically by a method introduced in [O.
Derzhko, T. Krokhmalskii, Phys. Rev. B \textbf{56}, 11659 (1997)]. Since all
characteristics of QPT are embodied in the DSF, the dynamical evolution of the
two external spins displays singularity in the vicinity of the critical point.",0805.4659v1
2008-06-27,Exploiting Quench Dynamics in Spin Chains for Distant Entanglement and Quantum Communication,"We suggest a method of entangling significantly the distant ends of a spin
chain using minimal control. This entanglement between distant individual spins
is brought about solely by exploiting the dynamics of an initial mixed state
with Neel order if the lattice features nearest-neighbor XXZ interaction. There
is no need to control single spins or to have engineered couplings or to pulse
globally. The method only requires an initial nonadiabatic switch (a quench)
between two Hamiltonians followed by an evolution under the second Hamiltonian.
The scheme is robust to randomness of the couplings as well as the finiteness
of an appropriate quench and could potentially be implemented in various
experimental setups, ranging from atoms in optical lattices to
Josephson-junction arrays.",0806.4568v3
2008-06-28,Theory of spin magnetohydrodynamics,"We develop a phenomenological hydrodynamic theory of coherent magnetic
precession coupled to electric currents. Exchange interaction between electron
spin and collective magnetic texture produces two reciprocal effects:
spin-transfer torque on the magnetic order parameter and the Berry-phase gauge
field experienced by the itinerant electrons. The dissipative processes are
governed by three coefficients: the ohmic resistance, Gilbert damping of the
magnetization, and the ""beta coefficient"" describing viscous coupling between
magnetic dynamics and electric current, which stems from spin mistracking of
the magnetic order. We develop general magnetohydrodynamic equations and
discuss the net dissipation produced by the coupled dynamics. The latter in
particular allows us to determine a lower bound on the magnetic-texture
resistivity.",0806.4656v2
2008-10-03,Dilution effects in Ho$_{2-x}$Y$_x$Sn$_2$O$_7$: from the Spin Ice to the single-ion magnet,"A study of the modifications of the magnetic properties of
Ho$_{2-x}$Y$_x$Sn$_2$O$_7$ upon varying the concentration of diamagnetic
Y$^{3+}$ ions is presented. Magnetization and specific heat measurements show
that the Spin Ice ground-state is only weakly affected by doping for $x\leq
0.3$, even if non-negligible changes in the crystal field at Ho$^{3+}$ occur.
In this low doping range $\mu$SR relaxation measurements evidence a
modification in the low-temperature dynamics with respect to the one observed
in the pure Spin Ice. For $x\to 2$, or at high temperature, the dynamics
involve fluctuations among Ho$^{3+}$ crystal field levels which give rise to a
characteristic peak in $^{119}$Sn nuclear spin-lattice relaxation rate. In this
doping limit also the changes in Ho$^{3+}$ magnetic moment suggest a variation
of the crystal field parameters.",0810.0608v1
2008-10-16,Pressure-Driven Metal-Insulator Transition in Hematite from Dynamical Mean-Field Theory,"The Local Density Approximation combined with Dynamical Mean-Field Theory
(LDA+DMFT method) is applied to the study of the paramagnetic and magnetically
ordered phases of hematite Fe$_2$O$_3$ as a function of volume. As the volume
is decreased, a simultaneous 1st order insulator-metal and high-spin to
low-spin transition occurs close to the experimental value of the critical
volume. The high-spin insulating phase is destroyed by a progressive reduction
of the charge gap with increasing pressure, upon closing of which the high spin
phase becomes unstable. We conclude that the transition in Fe$_2$O$_3$ at
$\approx$50 GPa can be described as an electronically driven volume collapse.",0810.2864v1
2008-10-31,Injected Power Fluctuations in 1D dissipative systems : role of ballistic transport,"This paper is a generalization of the models considered in [J. Stat. Phys.
128,1365 (2007)]. Using an analogy with free fermions, we compute exactly the
large deviation function (ldf) of the energy injected up to time $t$ in a
one-dimensional dissipative system of classical spins, where a drift is
allowed. The dynamics are T=0 asymmetric Glauber dynamics driven out of rest by
an injection mechanism, namely a Poissonian flipping of one spin. The drift
induces anisotropy in the system, making the model more comparable to
experimental systems with dissipative structures. We discuss the physical
content of the results, specifically the influence of the rate of the Poisson
injection process and the magnitude of the drift on the properties of the ldf.
We also compare the results of this spin model to simple phenomenological
models of energy injection (Poisson or Bernoulli processes of domain wall
injection). We show that many qualitative results of the spin model can be
understood within this simplified framework.",0810.5699v1
2008-11-17,Kondo Cloud Mediated Long Range Entanglement After Local Quench in a Spin Chain,"We show that, in the gapless Kondo Regime, a single local quench at one end
of a Kondo spin chain induces a fast and long lived oscillatory dynamics. This
quickly establishes a high quality entanglement between the spins at the
opposite ends of the chain. This entanglement is mediated by the Kondo Cloud,
attains a constant high value independent of the length for large chains, and
shows thermal robustness. In contrast, when the Kondo cloud is absent, e.g. in
the gapped dimer regime, only finite size end to end effects can create some
entanglement on a much longer time-scale for rather short chains. By decoupling
one end of the chain during the dynamics one can distinguish between this
end-end effect which vanishes, and the global Kondo cloud mediated
entanglement, which persists. This quench approach paves the way to detect the
elusive Kondo cloud through the entanglement between two individual spins. Our
results show that non-perturbative cooperative phenomena from condensed matter
may be exploited for quantum information.",0811.2677v3
2008-11-25,Electronic theory of ultrafast spin dynamics,"NiO is a good candidate for ultrafast magnetic switching because of its large
spin density, antiferromagnetic order, and clearly separated intragap states.
In order to detect and monitor the switching dynamics, we develop a systematic
approach to study optical second harmonic generation (SHG) in NiO, both at the
(001) surface and in the bulk. In our calculations NiO is modeled as a doubly
embedded cluster. All intragap \emph{d}-states of the bulk and the (001)
surface are obtained with highly-correlational quantum chemistry and propagated
in time under the influence of a static magnetic field and a laser pulse. We
find that demagnetization and switching can be best achieved in a subpicosecond
regime with linearly rather than circularly polarized light. We also show the
importance of including an external magnetic field in order to distinguish
spin-up and spin-down states and the necessity of including magnetic-dipole
transitions in order to realize the $\Lambda$-process in the centrosymmetric
bulk. Having already shown the effects of phonons in the SHG for the bulk NiO
within the frozen-phonon approximation, and following the same trail of
thoughts, we discuss the role of phonons in a fully quantized picture as a
symmetry-lowering mechanism in the switching scenario and investigate the
electronic and lattice temperature effects.",0811.4042v1
2009-03-03,Dynamical stability of entanglement between spin ensembles,"We study the dynamical stability of the entanglement between the two spin
ensembles in the presence of an environment. For a comparative study, we
consider the two cases: a single spin ensemble, and two ensembles linearly
coupled to a bath, respectively. In both circumstances, we assume the validity
of the Markovian approximation for the bath. We examine the robustness of the
state by means of the growth of the linear entropy which gives a measure of the
purity of the system. We find out macroscopic entangled states of two spin
ensembles can stably exist in a common bath. This result may be very useful to
generate and detect macroscopic entanglement in a common noisy environment and
even a stable macroscopic memory.",0903.0639v1
2009-04-05,Static and Dynamic Magnetism in Underdoped Superconductor BaFe$_{1.92}$Co$_{0.08}$As$_2$,"We report neutron scattering measurements on single crystals of
BaFe$_{1.92}$Co$_{0.08}$As$_2$. The magnetic Bragg peak intensity is reduced by
6 % upon cooling through T$_C$. The spin dynamics exhibit a gap of 8 meV with
anisotropic three-dimensional (3d) interactions. Below T$_C$ additional
intensity appears at an energy of $\sim$4.5(0.5) meV similar to previous
observations of a spin resonance in other Fe-based superconductors. No further
gapping of the spin excitations is observed below T$_C$ for energies down to 2
meV. These observations suggest the redistribution of spectral weight from the
magnetic Bragg position to a spin resonance demonstrating the direct
competition between static magnetic order and superconductivity.",0904.0767v1
2009-06-04,Thermoelectric spin transfer in textured magnets,"We study charge and energy transport in a quasi-1D magnetic wire in the
presence of magnetic textures. The energy flows can be expressed in a fashion
similar to charge currents, leading to new energy-current induced spin torques.
In analogy to charge currents, we can identify two reciprocal effects:
spin-transfer torque on the magnetic order parameter induced by energy current
and the Berry-phase gauge field induced energy flow. In addition, we
phenomenologically introduce new $\beta-$like viscous coupling between magnetic
dynamics and energy current into the LLG equation, which originates from spin
mistracking of the magnetic order. We conclude that the new viscous term should
be important for the thermally induced domain wall motion. We study the
interplay between charge and energy currents and find that many of the effects
of texture motion on the charge currents can be replicated with respect to
energy currents. For example, the moving texture can lead to energy flows which
is an analogue of the electromotive force in case of charge currents. We
suggest a realization of cooling effect by magnetic texture dynamics.",0906.1002v2
2009-07-22,Contrasting Spin Dynamics Between Underdoped and Overdoped Ba(Fe[1-x]Co[x])2As2,"We report the first NMR investigation of spin dynamics in the overdoped
non-superconducting regime of Ba(Fe[1-x]Co[x])2As2 up to x =0.26. We
demonstrate that the absence of inter-band transitions with large momentum
transfer Q(AF) ~ (pi, 0) between the hole and electron Fermi surfaces results
in complete suppression of antiferromagnetic spin fluctuations for x > 0.15.
Our experimental results provide direct evidence for a correlation between Tc
and the strength of Q(AF) antiferromagnetic spin fluctuations.",0907.3875v3
2009-10-01,Relaxation vs decoherence: Spin and current dynamics in the anisotropic Kondo model at finite bias and magnetic field,"Using a nonequilibrium renormalization group method we study the real-time
evolution of spin and current in the anisotropic Kondo model (both
antiferromagnetic and ferromagnetic) at finite magnetic field $h_0$ and bias
voltage $V$. We derive analytic expressions for all times in the weak-coupling
regime $\max\{V,h_0,1/t\}\gg T_c$ ($T_c=$ strong coupling scale). We find that
all observables decay both with the spin relaxation and decoherence rates
$\Gamma_{1/2}$. Various $V$-dependent logarithmic, oscillatory, and power-law
contributions are predicted. The low-energy cutoff of logarithmic terms is
generically identified by the difference of transport decay rates. For small
times $t\ll \max\{V,h_0\}^{-1}$, we obtain universal dynamics for spin and
current.",0910.0119v2
2009-10-17,Spin waves in a spin-1 Bose gas,"We present a theory of spin waves in a non-condensed gas of spin-1 bosons:
providing both analytic calculations of the linear theory, and full numerical
simulations of the nonlinear response. We highlight the role of spin-dependent
contact interactions in the dynamics of a thermal gas. Although these
interactions are small compared to the thermal energy, they set the scale for
low energy long wavelength spin waves. In particular, we find that the polar
state of Rb-87 is unstable to collisional mixing of magnetic sublevels even in
the normal state. We augment our analytic calculations by providing full
numerical simulations of a trapped gas, explicitly demonstrating this
instability. Further we show that for strong enough anti-ferromagnetic
interactions, the polar gas is unstable. Finally we explore coherent population
dynamics in a collisionless transversely polarized gas.",0910.3268v1
2009-10-23,Intrinsic effects of the boundary condition on switching processes in spin-crossover solids,"We investigated domain growth in switching processes between the low-spin and
high-spin phases in thermally induced hysteresis loops of spin-crossover (SC)
solids. Elastic interactions among the molecules induce effective long-range
interactions, and thus the boundary condition plays a significant role in the
dynamics. In contrast to SC systems with periodic boundary conditions, where
uniform configurations are maintained during the switching process, we found
that domain structures appear with open boundary conditions. Unlike Ising-like
models with short-range interactions, domains always grow from the corners of
the system. The present clustering mechanism provides an insight into the
switching dynamics of SC solids, in particular, in nano-scale systems.",0910.4519v2
2009-11-24,Origin of adiabatic and non-adiabatic spin transfer torques in current-driven magnetic domain wall motion,"A consistent theory to describe the correlated dynamics of quantum mechanical
itinerant spins and semiclassical local magnetization is given. We consider the
itinerant spins as quantum mechanical operators, whereas local moments are
considered within classical Lagrangian formalism. By appropriately treating
fluctuation space spanned by basis functions, including a zero-mode wave
function, we construct coupled equations of motion for the collective
coordinate of the center-of-mass motion and the localized zero-mode coordinate
perpendicular to the domain wall plane. By solving them, we demonstrate that
the correlated dynamics is understood through a hierarchy of two time scales:
Boltzmann relaxation time when a non-adiabatic part of the spin-transfer torque
appears, and Gilbert damping time when adiabatic part comes up.",0911.4628v1
2010-04-13,Incommensurate magnetic order and dynamics induced by spinless impurities in YBa$_2$Cu$_3$O$_{6.6}$,"We report an inelastic-neutron-scattering and muon-spin-relaxation study of
the effect of 2% spinless (Zn) impurities on the magnetic order and dynamics of
YBa$_2$Cu$_3$O$_{6.6}$, an underdoped high-temperature superconductor that
exhibits a prominent spin-pseudogap in its normal state. Zn substitution
induces static magnetic order at low temperatures and triggers a large-scale
spectral-weight redistribution from the magnetic resonant mode at 38 meV into
uniaxial, incommensurate spin excitations with energies well below the
spin-pseudogap. These observations indicate a competition between
incommensurate magnetic order and superconductivity close to a quantum critical
point. Comparison to prior data on La$_{2-x}$Sr$_x$CuO$_{4}$ suggests that this
behavior is universal for the layered copper oxides and analogous to
impurity-induced magnetic order in one-dimensional quantum magnets.",1004.2139v1
2010-04-16,Edge Dynamics in a Quantum Spin Hall State: Effects from Rashba Spin-Orbit Interaction,"We analyze the dynamics of the helical edge modes of a quantum spin Hall
state in the presence of a spatially non-uniform Rashba spin-orbit (SO)
interaction. A randomly fluctuating Rashba SO coupling is found to open a
scattering channel which causes localization of the edge modes for a weakly
screened electron-electron (e-e) interaction. A periodic modulation of the SO
coupling, with a wave number commensurate with the Fermi momentum, makes the
edge insulating already at intermediate strengths of the e-e interaction. We
discuss implications for experiments on edge state transport in a HgTe quantum
well.",1004.2777v2
2010-04-21,Effects of Spin Fluctuations and Anomalous Thermal Expansion of delta-Plutonium,"We suggest a model for the magnetic dynamics of - plutonium and its alloys in
order to show that the dynamical fluctuations of the magnetization density, or
spin fluctuations, may be responsible for the anomalies of their observed
thermal expansion. We show that due to strong magneto-elastic coupling, spin
fluctuations may essentially contribute to the volume strain by giving a
negative magneto-volume contribution that is proportional to the squared local
magnetic moment and the magnetic Gruneisen constant which is negative in -
plutonium. In the presented model, the local magnetic moment increases as the
temperature rises, resulting in the interplay between the positive
contributions to the volume strain from the lattice and the negative
contribution from spin fluctuations, and finally leads to the Invar anomaly or
to the negative coefficient of thermal expansion. Our results agree closely
with the measured thermal expansion data for Pu-Ga alloys.",1004.3658v1
2010-04-29,Theory of charged impurities in correlated electron materials: Application to muon spectroscopy of high-Tc superconductors,"Single-site and cluster dynamical mean-field methods are used to estimate the
response of a doped Mott insulator to a charged impurity. The effect of
correlations on the Thomas-Fermi screening properties is determined. The charge
density, the on-site and near-neighbor spin-spin correlations in the vicinity
of the impurity are compared to those far from it. The theory is used to
address the question of the effect of the density perturbation induced by the
muon charge on the local response functions of a high-temperature
superconductor. For reasonable values of the background dielectric constant and
basic correlation strength, a muon is shown to lead to an observable
perturbation of the local spin dynamics, raising questions about the
interpretation of muon-spin-rotation experiments in metallic high-temperature
superconductors.",1004.5369v2
2010-06-18,Influence of spin fluctuations near the Mott transition: a DMFT study,"Dynamics of magnetic moments near the Mott metal-insulator transition is
investigated by a combined slave-rotor and Dynamical Mean-Field Theory solution
of the Hubbard model with additional fully-frustrated random Heisenberg
couplings. In the paramagnetic Mott state, the spinon decomposition allows to
generate a Sachdev-Ye spin liquid in place of the collection of independent
local moments that typically occurs in the absence of magnetic correlations.
Cooling down into the spin-liquid phase, the onset of deviations from pure
Curie behavior in the spin susceptibility is found to be correlated to the
temperature scale at which the Mott transition lines experience a marked
bending. We also demonstrate a weakening of the effective exchange energy upon
approaching the Mott boundary from the Heisenberg limit, due to quantum
fluctuations associated to zero and doubly occupied sites.",1006.3620v3
2010-06-30,Microscopic energy flows in disordered Ising spin systems,"An efficient microcanonical dynamics has been recently introduced for Ising
spin models embedded in a generic connected graph even in the presence of
disorder i.e. with the spin couplings chosen from a random distribution. Such a
dynamics allows a coherent definition of local temperatures also when open
boundaries are coupled to thermostats, imposing an energy flow. Within this
framework, here we introduce a consistent definition for local energy currents
and we study their dependence on the disorder. In the linear response regime,
when the global gradient between thermostats is small, we also define local
conductivities following a Fourier dicretized picture. Then, we work out a
linearized ""mean-field approximation"", where local conductivities are supposed
to depend on local couplings and temperatures only. We compare the approximated
currents with the exact results of the nonlinear system, showing the
reliability range of the mean-field approach, which proves very good at high
temperatures and not so efficient in the critical region. In the numerical
studies we focus on the disordered cylinder but our results could be extended
to an arbitrary, disordered spin model on a generic discrete structures.",1006.5905v1
2010-07-22,Theory of the power spectrum of spin-torque nanocontact vortex oscillators,"Spin-transfer torques in magnetic nanocontacts can lead to self-sustained
magnetization oscillations that involve large-amplitude gyrotropic vortex
motion. This dynamics consists of a steady state orbit around the nanocontact,
which is made possible because the intrinsic magnetic damping is compensated by
spin torques. In this article, we present an analytical theory of the power
spectrum of these oscillations based on a rigid-vortex model. The appearance of
vortex oscillations in nanocontacts is not associated with a Hopf bifurcation:
there is no critical current and the only precondition for steady-state
oscillations at finite currents is the existence of a vortex in the system, in
contrast with conventional spin-torque oscillators that involve large-angle
magnetization precession. The oscillation frequency is found to depend linearly
on the applied current and inversely proportional to the orbital radius. By
solving the associated Langevin problem for the vortex dynamics, the lineshape
and linewidth for the power spectrum are also obtained. Under typical
experimental conditions, a Lorentzian lineshape with a current-independent
linewidth is predicted. Good quantitative agreement between the theory and
recent experiments is shown.",1007.3859v1
2010-08-11,Dynamical Decoupling of a single electron spin at room temperature,"Here we report the increase of the coherence time T$_2$ of a single electron
spin at room temperature by using dynamical decoupling. We show that the
Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence can prolong the T$_2$ of a
single Nitrogen-Vacancy center in diamond up to 2.44 ms compared to the Hahn
echo measurement where T$_2 = 390 \mu$s. Moreover, by performing spin locking
experiments we demonstrate that with CPMG the maximum possible $T_2$ is
reached. On the other hand, we do not observe strong increase of the coherence
time in nanodiamonds, possibly due to the short spin lattice relaxation time
$T_1=100 \mu$s (compared to T$_1$ = 5.93 ms in bulk). An application for
detecting low magnetic field is demonstrated, where we show that the
sensitivity using the CPMG method is improved by about a factor of two compared
to the Hahn echo method.",1008.1953v2
2010-09-11,Qubit Entanglement Dephasing Dynamics Driven by a Bath of Spins,"We study the entanglement dynamics for a two-spin system coupled to a spin
environment of different configurations by z-x type interaction. The models
considered in this paper are solved both analytically and numerically giving
rise to some concise analytical expressions when certain approximations are
properly made. Our purpose is to find how the initial states of the environment
with different numbers of spins affect the decay or revival of the entanglement
between central qubits. In Particular, it is found that the block-entangled
environment could speed up the decay and revival of the qubit entanglement. Our
results exhibit some interesting features that have not been found for a boson
bath.",1009.2128v2
2010-10-11,Parity Broken Chiral Spin Dynamics in Ba$_3$NbFe$_3$Si$_2$O$_{14}$,"The spin wave excitations emerging from the chiral helically modulated
120$^{\circ}$ magnetic order in a langasite Ba$_3$NbFe$_3$Si$_2$O$_{14}$
enantiopure crystal were investigated by unpolarized and polarized inelastic
neutron scattering. A dynamical fingerprint of the chiral ground state is
obtained, singularized by (i) spectral weight asymmetries answerable to the
structural chirality and (ii) a full chirality of the spin correlations
observed over the whole energy spectrum. The intrinsic chiral nature of the
spin waves elementary excitations is shown in absence of macroscopic time
reversal symmetry breaking.",1010.2008v2
2010-12-10,Artifacts of opinion dynamics at one dimension,"The dynamics of a one dimensional Ising spin system is investigated using
three families of local update rules, the Galam majority rules, Glauber inflow
influences and Sznadj outflow drives. Given an initial density p of up spins
the probability to reach a final state with all spins up is calculated exactly
for each choice. The various formulas are compared to a series of previous
calculations obtained analytically using the Kirkwood approximation. They turn
out to be identical. The apparent discrepancy with the Galam unifying frame is
addressed. The difference in the results seems to stem directly from the
implementation of the local update rule used to perform the associated
numerical simulations. The findings lead to view the non stepwise exit
probability as an artifact of the one dimensional finite size system with fixed
spins. The suitability and the significance to perform numerical simulations to
model social behavior without solid constraints is discussed and the question
of what it means to have a mean field result in this context is addressed.",1012.2283v1
2011-03-10,Suppression of Standing Spin Waves in Low-Dimensional Ferromagnets,"We examine the experimental absence of standing spin wave modes in thin
magnetic films, by means of atomistic spin dynamics simulations. Using Co on
Cu(001) as a model system, we demonstrate that by increasing the number of
layers, the ""optical"" branches predicted from adiabatic first-principles
calculations are strongly suppressed, in agreement with spin-polarized electron
energy loss spectroscopy measurements reported in the literature. Our results
suggest that a dynamical analysis of the Heisenberg model is sufficient in
order to capture the strong damping of the standing modes.",1103.1997v2
2011-04-15,Digital Quantum Simulation with Rydberg Atoms,"We discuss in detail the implementation of an open-system quantum simulator
with Rydberg states of neutral atoms held in an optical lattice. Our scheme
allows one to realize both coherent as well as dissipative dynamics of complex
spin models involving many-body interactions and constraints. The central
building block of the simulation scheme is constituted by a mesoscopic Rydberg
gate that permits the entanglement of several atoms in an efficient, robust and
quick protocol. In addition, optical pumping on ancillary atoms provides the
dissipative ingredient for engineering the coupling between the system and a
tailored environment. As an illustration, we discuss how the simulator enables
the simulation of coherent evolution of quantum spin models such as the
two-dimensional Heisenberg model and Kitaev's toric code, which involves
four-body spin interactions. We moreover show that in principle also the
simulation of lattice fermions can be achieved. As an example for controlled
dissipative dynamics, we discuss ground state cooling of frustration-free spin
Hamiltonians.",1104.3081v2
2011-04-19,On the accuracy of the state space restriction approximation for spin dynamics simulations,"We present an algebraic foundation for the state space restriction
approximation in spin dynamics simulations and derive applicability criteria as
well as minimal basis set requirements for practically encountered simulation
tasks. The results are illustrated with NMR, ESR, DNP and Spin Chemistry
simulations. It is demonstrated that state space restriction yields accurate
results in systems where the time scale of spin relaxation processes
approximately matches the time scale of the experiment. Rigorous error bounds
and basis set requirements are derived.",1104.3866v2
2011-06-21,Quantum phase transition in the delocalized regime of the spin-boson model,"The existence of the delocalized-localized quantum phase transition (QPT) in
the ohmic spin-boson model has been commonly recognized. While the physics in
the localized regime is relatively simple, the delocalized regime shows many
interesting behaviors. Here we reveal that in this regime there exists a novel
QPT: namely, from a phase without a bound state to a phase with a bound state,
which leads to completely different dynamical behaviors in these two phases. If
the reservoir is initially in the displaced vacuum state (i.e., the coherent
state), the spin dynamics exhibits lossless oscillation when the bound state
exists; otherwise, the oscillation will decay completely. This result is
compatible with the coherence-incoherence transition occurring in the
small-tunneling limit. Our work indicates that the QPT physics in the
spin-boson model needs further exploration.",1106.4173v2
2011-08-25,Driving Force of Ultrafast Magnetization Dynamics,"Irradiating a ferromagnetic material with an ultrashort laser pulse leads to
demagnetization on a femtosecond timescale. We implement Elliott-Yafet type
spin-flip scattering, mediated by electron-electron and electron-phonon
collisions, into the framework of a spin-resolved Boltzmann equation.
Considering three mutually coupled reservoirs, (i) spin-up electrons, (ii)
spin-down electrons and (iii) phonons, we trace non-equilibrium electron
distributions during and after laser excitation. We identify the driving force
for ultrafast magnetization dynamics as the equilibration of temperatures and
chemical potentials between the electronic subsystems. This principle can be
used to easily predict the maximum quenching of magnetization upon ultrashort
laser irradiation in any material, as we show for the example of
3d-ferromagnetic nickel.",1108.5170v1
2011-10-02,Metastable magnetic domain wall dynamics,"The dynamics of metastable magnetic domain walls in straight ferromagnetic
nanowires under spin waves, external magnetic fields, and current induced spin
transfer torque are studied by micromagnetic simulations. It is found that in
contrast to a stable wall, it is possible to displace a metastable domain wall
in the absence of any external excitation. In addition, independent of the
domain wall excitation method, the velocity of a metastable wall is much
smaller than a stable wall and their displacement direction could be different
from the stable wall depending on the structure of metastable walls. Under the
current induced spin transfer torque excitation, the direction of domain wall
displacement is directly related to the intensity of nonadiabatic spin transfer
torque. In a rough nanowire, it is found that the displacement of a metastable
wall could happen much below the critical excitation of a stable wall.
Furthermore, we show that it is possible to have either a forward or backward
displacement of a metastable domain wall by changing the pulse width of the
excitation.",1110.0175v1
2011-10-07,Short-time Spin Dynamics in Strongly Correlated Few-fermion Systems,"The non-equilibrium spin dynamics of a one-dimensional system of repulsively
interacting fermions is studied by means of density-matrix
renormalization-group simulations. We focus on the short-time decay of the
oscillation amplitudes of the centers of mass of spin-up and spin-down
fermions. Due to many-body effects, the decay is found to evolve from quadratic
to linear in time, and eventually back to quadratic as the strength of the
interaction increases. The characteristic rate of the decay increases linearly
with the strength of repulsion in the weak-coupling regime, while it is
inversely proportional to it in the strong-coupling regime. Our predictions can
be tested in experiments on tunable ultra-cold few-fermion systems in
one-dimensional traps.",1110.1568v3
2011-10-07,Nonlinear Dynamics in a Magnetic Josephson Junction,"We theoretically consider a Josephson junction formed by a ferromagnetic
spacer with a strong spin-orbit interaction or a magnetic spin valve, i.e., a
bilayer with one static and one free layer. Electron spin transport facilitates
a nonlinear dynamical coupling between the magnetic moment and charge current,
which consists of normal and superfluid components. By phenomenologically
adding reactive and dissipative interactions (guided by structural and Onsager
symmetries), we construct magnetic torques and charge pumping, whose
microscopic origins are also discussed. A stability analysis of our coupled
nonlinear systems generates a rich phase diagram with fixed points, limit
cycles, and quasiperiodic states. Our findings reduce to the known phase
diagrams for current-biased nonmagnetic Josephson junctions, on the one hand,
and spin-torque driven magnetic films, on the other, in the absence of coupling
between the magnetic and superconducting order parameters.",1110.1680v1
2011-10-17,Dynamics of nano-magnetic oscillators,"We explore how non-equilibrium noise affects spin-torque switching elements
and oscillators. To do so we first discuss the deterministic dynamics of
magnetic tunnel junctions, introducing a convenient set of slow and fast
degrees of freedom. We then derive effective Langevin equation for the slowly
varying energy of precessional orbit and introduce the corresponding energy
noise and energy diffusion coefficient. This allows for the formulation of a
Fokker-Planck equation for the energy density distribution. We use it to
analyse switching time distribution as well as the shape of the optimal
spin-current pulse, which minimizes Joule losses of a switch. Finally we derive
a generic expression for the linewidth of a spin-torque oscillator and discuss
its dependence on temperature, spin-current amplitude and other parameters.",1110.3750v1
2011-10-18,Observation of Topologically Stable 2D Skyrmions in an Antiferromagnetic Spinor Bose-Einstein Condensate,"We present the creation and time evolution of two-dimensional Skyrmion
excitations in an antiferromagnetic spinor Bose-Einstein condensate. Using a
spin rotation method, the Skyrmion spin textures were imprinted on a sodium
condensate in a polar phase, where the two-dimensional Skyrmion is
topologically protected. The Skyrmion was observed to be stable on a short time
scale of a few tens of ms but to have dynamical instability to deform its shape
and eventually decay to a uniform spin texture. The deformed spin textures
reveal that the decay dynamics involves breaking the polar phase inside the
condensate without having topological charge density flow through the boundary
of the finite-sized sample. We discuss the possible formation of half-quantum
vortices in the deformation process.",1110.3858v2
2011-10-25,Dynamic nuclear spin polarization in resonant laser spectroscopy of a quantum dot,"Resonant optical excitation of lowest-energy excitonic transitions in
self-assembled quantum dots lead to nuclear spin polarization that is
qualitatively different from the well known optical orientation phenomena. By
carrying out a comprehensive set of experiments, we demonstrate that nuclear
spin polarization manifests itself in quantum dots subjected to finite external
magnetic field as locking of the higher energy Zeeman transition to the driving
laser field, as well as the avoidance of the resonance condition for the lower
energy Zeeman branch. We interpret our findings on the basis of dynamic nuclear
spin polarization originating from non-collinear hyperfine interaction and find
an excellent agreement between the experimental results and the theoretical
model.",1110.5524v1
2011-12-13,Binary mixture of pseudospin-1/2 Bose gases with interspecies spin exchange: from classical fixed points and ground states to quantum ground states,"We consider the effective spin Hamiltonian describing a mixture of two
species of pseudo-spin-1/2 Bose gases with interspecies spin exchange. First we
analyze the stability of the fixed points of the corresponding classical
dynamics, of which the signature is found in quantum dynamics with a
disentangled initial state. Focusing on the case without an external potential,
we find all the ground states by taking into account quantum fluctuations
around the classical ground state in each parameter regime. The nature of
entanglement and its relation with classical bifurcation is investigated. When
the total spins of the two species are unequal, the maximal entanglement at the
parameter point of classical bifurcation is possessed by the excited state
corresponding to the classical fixed point which bifurcates, rather than by the
ground state.",1112.2852v1
2012-02-15,Current-induced motion of a transverse magnetic domain wall in the presence of spin Hall effect,"We theoretically study the current-induced dynamics of a transverse magnetic
domain wall in bi-layer nanowires consisting of a ferromagnet on top of a
nonmagnet having strong spin-orbit coupling. Domain wall dynamics is
characterized by two threshold current densities, $J_{th}^{WB}$ and
$J_{th}^{REV}$, where $J_{th}^{WB}$ is a threshold for the chirality switching
of the domain wall and $J_{th}^{REV}$ is another threshold for the reversed
domain wall motion caused by spin Hall effect. Domain walls with a certain
chirality may move opposite to the electron-flow direction with high speed in
the current range $J_{th}^{REV} < J < J_{th}^{WB}$ for the system designed to
satisfy the conditions $J_{th}^{WB} > J_{th}^{REV}$ and \alpha > \beta, where
\alpha is the Gilbert damping constant and \beta is the nonadiabaticity of spin
torque. Micromagnetic simulations confirm the validity of analytical results.",1202.3450v1
2012-03-05,Frequency generation by a magnetic vortex-antivortex dipole in spin-polarized current,"A vortex-antivortex (VA) dipole may be generated due to a spin-polarized
current flowing through a nano-aperture in a magnetic element. We study the
vortex dipole dynamics using the Landau-Lifshitz equation in the presence of an
in-plane applied magnetic field and a Slonczewski spin-torque term with
in-plane polarization. We establish that the vortex dipole is set in steady
state rotational motion. The frequency of rotation is due to two independent
forces: the interaction between the two vortices and the external magnetic
field. The nonzero skyrmion number of the dipole is responsible for both forces
giving rise to rotational dynamics. The spin-torque acts to stabilize the
vortex dipole motion at a definite vortex-antivortex separation distance. We
give analytical and numerical results for the angular frequency of rotation and
VA dipole features as functions of the parameters.",1203.0880v1
2012-06-04,Quantitative cw Overhauser DNP Analysis of Hydration Dynamics,"Liquid state Overhauser Effect Dynamic Nuclear Polarization (ODNP) has
experienced a recent resurgence of interest. In particular, a new manifestation
of the ODNP measurement measures the translational mobility of water within
5-10 \AA\ of an ESR-active spin probe (i.e. the local translational diffusivity
D_{local} near an electron spin resonance active molecule). Such spin probes,
typically stable nitroxide radicals, have been attached to the surface or
interior of macromolecules, including proteins, polymers, and membrane
vesicles. Despite the unique specificity of this measurement, it requires only
a standard X-band (~10 GHz) continuous wave (cw) electron spin resonance (ESR)
spectrometer, coupled with a standard nuclear magnetic resonance (NMR)
spectrometer. Here, we present a set of developments and corrections that allow
us to improve the accuracy of quantitative ODNP and apply it to samples more
than two orders of magnitude lower than were previously feasible.",1206.0510v1
2012-06-19,Spin hydrodynamics in the S = 1/2 anisotropic Heisenberg chain,"We study the finite-temperature dynamical spin susceptibility of the
one-dimensional (generalized) anisotropic Heisenberg model within the
hydrodynamic regime of small wave vectors and frequencies. Numerical results
are analyzed using the memory function formalism with the central quantity
being the spin-current decay rate gamma(q,omega). It is shown that in a generic
nonintegrable model the decay rate is finite in the hydrodynamic limit,
consistent with normal spin diffusion modes. On the other hand, in the gapless
integrable model within the XY regime of anisotropy Delta < 1 the behavior is
anomalous with vanishing gamma(q,omega=0) proportional to |q|, in agreement
with dissipationless uniform transport. Furthermore, in the integrable system
the finite-temperature q = 0 dynamical conductivity sigma(q=0,omega) reveals
besides the dissipationless component a regular part with vanishing
sigma_{reg}(q=0,omega to 0) to 0.",1206.4248v2
2012-08-08,Spin coherence lifetime extension in Tm$^{3+}$:YAG through dynamical decoupling,"We report on spin coherence lifetime extension on Tm$^{3+}$:YAG obtained
through dynamically decoupling the thulium spins from their magnetic
environment. The coherence lifetime reached with a Carr-Purcell-Meiboom-Gill
sequence revealed a 450-fold extension [$\sim$$(230 \pm 30)$ ms] with respect
to previously measured values. Comparison to a simple theoretical model allowed
us to estimate the correlation time of the fluctuations of the ground level
transition frequency to $(172 \pm 30)$ $\mu$s at 1.7 K. For attaining efficient
decoupling sequences, we developed a strategy inspired by the
\emph{zero-first-order Zeeman} effect to minimize the large inhomogeneous
broadening of the ground level spin transition.",1208.1622v2
2012-08-28,NMR Search for the Spin Nematic State in LaFeAsO Single Crystal,"We report a 75-As single crystal NMR investigation of LaFeAsO, the parent
phase of a pnictide high Tc superconductor. We demonstrate that spin dynamics
develop a strong two-fold anisotropy within each orthorhombic domain below the
tetragonal-orthorhombic structural phase transition at T[TO]~156 K. This
intermediate state with a dynamical breaking of the rotational symmetry freezes
progressively into a spin density wave (SDW) below T[SDW]~142 K. Our findings
are consistent with the presence of a spin nematic state below T[TO] with an
incipient magnetic order.",1208.5652v2
2012-09-05,Charm and Strangeness with Heavy-Quark Spin Symmetry,"We study charmed and strange baryon resonances that are generated dynamically
within a unitary meson-baryon coupled-channel model which incorporates
heavy-quark spin symmetry. This is accomplished by extending the SU(3)
Weinberg-Tomozawa chiral Lagrangian to SU(8) spin-flavor symmetry and
implementing a strong flavor symmetry breaking. The model generates dynamically
resonances with negative parity in all the isospin, spin, and strange and charm
sectors that one can form from an s-wave interaction between pseudoscalar and
vector meson multiplets with $1/2^+$ and $3/2^+$ baryons. Our results are
compared with experimental data from several facilities as well as with other
theoretical models. Moreover, we obtain the properties of charmed pseudoscalar
and vector mesons in dense matter within this coupled-channel unitary effective
model by taking into account Pauli-blocking effects and meson self-energies in
a self-consistent manner. We obtain the open-charm meson spectral functions in
this dense nuclear environment, and discuss their implications on the formation
of $D$-mesic nuclei at FAIR energies.",1209.0907v1
2012-09-19,Dynamic stabilization of a quantum many-body spin system,"We demonstrate dynamic stabilization of an unstable strongly interacting
quantum many-body system by periodic manipulation of the phase of the
collective states. The experiment employs a spin-1 atomic Bose condensate
initialized to an unstable (hyperbolic) fixed point of the spin-nematic phase
space, where subsequent free evolution gives rise to squeezing and quantum spin
mixing. To stabilize the system, periodic microwave pulses are applied that
manipulate the spin-nematic many-body fluctuations and limit their growth. The
range of pulse periods and phase shifts for which the condensate can be
stabilized is measured and the resulting stability diagram compares well with a
linear stability analysis of the problem.",1209.4363v2
2012-10-09,Polarized Neutron Laue Diffraction on a Crystal Containing Dynamically Polarized Proton Spins,"We report on a polarized-neutron Laue diffraction experiment on a single
crystal of neodynium doped lanthanum magnesium nitrate hydrate containing
polarized proton spins. By using dynamic nuclear polarization to polarize the
proton spins, we demonstrate that the intensities of the Bragg peaks can be
enhanced or diminished significantly, whilst the incoherent background, due to
proton spin disorder, is reduced. It follows that the method offers unique
possibilities to tune continuously the contrast of the Bragg reflections and
thereby represents a new tool for increasing substantially the signal-to-noise
ratio in neutron diffraction patterns of hydrogenous matter.",1210.2606v1
2012-11-26,Low temperature dynamic freezing and the fragility of ordering in Tb2Sn2O7,"We have probed the low temperature magnetic behavior of the ordered spin ice
material Tb2Sn2O7 through ac magnetic susceptibility measurements of both the
pure material and samples with small percentages of Ti substituted on the Sn
sublattice. We observe a clear signature for the previously reported ordering
transition at TC = 850 mK, as well as evidence for dynamic freezing at
temperatures well below TC, confirming the persistence of significant magnetic
fluctuations deep in the spin-ordered regime. The long range ordering
transition was completely suppressed with as little as 5% Ti for Sn
substitution, and 10% Ti substitution resulted in a spin-glass-like spin
freezing transition near 250 mK. The results demonstrate that the long range
magnetic ordering is surprisingly fragile in this system.",1211.6047v1
2012-12-27,A quantum many-body spin system in an optical lattice clock,"Strongly interacting quantum many-body systems are fundamentally compelling
and ubiquitous in science. However, their complexity generally prevents exact
solutions of their dynamics. Precisely engineered ultracold atomic gases are
emerging as a powerful tool to unravel these challenging physical problems.
Here we present a new laboratory for the study of many-body effects: strongly
interacting two-level systems formed by the clock states in ${}^{87}$Sr, which
are used to realize a neutral atom optical clock that performs at the highest
level of optical-atomic coherence and with precision near the limit set by
quantum fluctuations. Our measurements of the collective spin evolution reveal
signatures of many-body dynamics, including beyond-mean-field effects. We
derive a many-body Hamiltonian that describes the experimental observation of
severely distorted lineshapes, atomic spin coherence decay, density-dependent
frequency shifts, and correlated quantum spin noise. These investigations open
the door to exploring quantum many-body effects and entanglement in quantum
systems with optical energy splittings, using highly coherent and precisely
controlled optical lattice clocks.",1212.6291v1
2013-01-19,"Molecular Dynamics of Spin Crossover: the (P,T) phase diagram of [Fe(PM-BIA)2(NCS)2]","The spin crossover properties and the domains of existence of the different
phases for the [Fe(PM-BIA)2(NCS)2] complex are obtained from combining DFT and
classical molecular dynamics (MD). The potential energy surfaces expressed in
the Morse form for Fe-N interactions are deduced from molecular DFT
calculations and they allow producing Infra Red and Raman frequencies. These
Fe-N potentials inserted in a classical force field lead from MD calculations
to the relative energies of the high spin and low spin configurations of the
orthorhombic structure. The MD investigations have also allowed assessing the
experimental (P, T) phase diagram by showing the monoclinic polymorph in its
two spin- states, and generating two triple points.",1301.4568v1
2013-01-31,Absence of spin liquid in non-frustrated correlated systems,"The question of the existence of a spin liquid state in the half-filled
Hubbard model on the honeycomb (aka graphene) lattice is revisited. The
Variational Cluster Approximation (VCA), the Cluster Dynamical Mean Field
Theory (CDMFT) and the Cluster Dynamical Impurity Approximation (CDIA) are
applied to various cluster systems. Assuming that the spin liquid phase
coincides with the Mott insulating phase in this non-frustrated system, we find
that the Mott transition is pre-empted by a magnetic transition occuring at a
lower value of the interaction $U$, and therefore the spin liquid phase does
not occur. This conclusion is obtained using clusters with two bath orbitals
connected to each boundary cluster site. We argue that using a single bath
orbital per boundary site is insufficient and leads to the erroneous conclusion
that the system is gapped for all nonzero values of $U$.",1301.7672v1
2013-04-03,Silicon spin chains at finite temperature: dynamics of Si(553)-Au,"When gold is deposited on Si(553), the surface self-assembles to form a
periodic array of steps with nearly perfect structural order. In scanning
tunneling microscopy these steps resemble quasi-one-dimensional atomic chains.
At temperatures below ~50 K the chains develop tripled periodicity. We recently
predicted, on the basis of density-functional theory calculations at T=0, that
this tripled periodicity arises from the complete polarization of the electron
spin on every third silicon atom along the step; in the ground state these
linear chains of silicon spins are antiferromagnetically ordered. Here we
explore, using ab-initio molecular dynamics and kinetic Monte Carlo
simulations, the behavior of silicon spin chains on Si(553)-Au at finite
temperature. Thermodynamic phase transitions at T>0 in one-dimensional systems
are prohibited by the Mermin-Wagner theorem. Nevertheless we find that a
surprisingly sharp onset occurs upon cooling---at about 30 K for perfect
surfaces and at higher temperature for surfaces with defects---to a
well-ordered phase with tripled periodicity, in good agreement with experiment.",1304.1024v1
2013-06-26,Spin dynamics in p-doped semiconductor nanostructures subject to a magnetic field tilted from the Voigt geometry,"We develop a theoretical description of the spin dynamics of resident holes
in a p-doped semiconductor quantum well (QW) subject to a magnetic field tilted
from the Voigt geometry. We find the expressions for the signals measured in
time-resolved Faraday rotation (TRFR) and resonant spin amplification (RSA)
experiments and study their behavior for a range of system parameters. We find
that an inversion of the RSA peaks can occur for long hole spin dephasing times
and tilted magnetic fields. We verify the validity of our theoretical findings
by performing a series of TRFR and RSA experiments on a p-modulation doped
GaAs/Al_{0.3}Ga_{0.7}As single QW and showing that our model can reproduce
experimentally observed signals.",1306.6363v2
2013-10-11,Ultrafast supercontinuum fiber-laser based pump-probe scanning MOKE microscope for the investigation of electron spin dynamics in semiconductors at cryogenic temperatures with picosecond time and micrometer spatial resolution,"We describe a two-color pump-probe scanning magneto-optical Kerr effect
(MOKE) microscope which we have developed to investigate electron spin
phenomena in semiconductors at cryogenic temperatures with picosecond time and
micrometer spatial resolution. The key innovation of our microscope is the
usage of an ultrafast `white light' supercontinuum fiber-laser source which
provides access to the whole visible and near-infrared spectral range. Our Kerr
microscope allows for the independent selection of the excitation and detection
energy while avoiding the necessity to synchronize the pulse trains of two
separate picosecond laser systems. The ability to independently tune the pump
and probe wavelength enables the investigation of the influence of excitation
energy on the optically induced electron spin dynamics in semiconductors. We
demonstrate picosecond real-space imaging of the diffusive expansion of
optically excited electron spin packets in a (110) GaAs quantum well sample to
illustrate the capabilities of the instrument.",1310.3027v1
2013-10-25,Mode coupling in spin torque oscillators,"A number of recent experimental works have shown that the dynamics of a
single spin torque oscillator can exhibit complex behavior that stems from
interactions between two or more modes of the oscillator. Examples are observed
mode-hopping or mode coexistence. There has been some intial work indicating
how the theory for a single-mode (macro-spin) spin torque oscillator should be
generalized to include several modes and the interactions between them. In the
present work, we derive such a theory starting with the Landau-Lifshitz-Gilbert
equation for magnetization dynamics. We compare our results with the
single-mode theory, and show how it is a natural extension of that theory to
include mode interactions.",1310.6791v2
2013-11-29,Generation linewidth of mode-hopping spin torque oscillators,"Experiments on spin torque oscillators commonly observe multi-mode signals.
Recent theoretical works have ascribed the multi-mode signal generation to
coupling between energy-separated spin wave modes. Here, we analyze in detail
the dynamics generated by such mode coupling. We show analytically that the
mode-hopping dynamics broaden the generation linewidth and makes it generally
well described by a Voigt lineshape. Furthermore, we show that the mode-hopping
contribution to the linewidth can dominate in which case it provides a direct
measure of the mode-hopping rate. Due to the thermal drive of mode-hopping
events, the mode-hopping rate also provides information on the energy barrier
separating modes and temperature-dependent linewidth broadening. Our results
are in good agreement with experiments, revealing the physical mechanism behind
the linewidth broadening in multi-mode spin torque oscillators.",1311.7660v1
2014-01-31,Far from equilibrium monopole dynamics in spin ice,"Condensed matter in the low temperature limit reveals much exotic physics
associated with unusual orders and excitations, examples ranging from helium
superfluidity to magnetic monopoles in spin ice. The far-from-equilibrium
physics of such low temperature states may be even more exotic, yet to access
it in the laboratory remains a challenge. Here we demonstrate a simple and
robust technique, the 'magnetothermal avalanche quench', and its use in the
controlled creation of nonequilibrium populations of magnetic monopoles in spin
ice at millikelvin temperatures. These populations are found to exhibit
spontaneous dynamical effects that typify far-from-equilibrium systems, yet are
captured by simple models. Our method thus opens the door to the study of
far-from-equilibrium states in spin ice and other exotic magnets.",1401.8194v1
2014-02-08,High-field spectroscopy of singlet-triplet transitions in the spin-dimer systems Sr3Cr2O8 and Ba3Cr2O8,"Magnetic excitations in the isostructural spin-dimer systems Sr3Cr2O8 and
Ba3Cr2O8 are probed by means of high-field electron spin resonance at
sub-terahertz frequencies. Three types of magnetic modes were observed. One
mode is gapless and corresponds to transitions within excited states, while two
other sets of modes are gapped and correspond to transitions from the ground to
the first excited states. The selection rules of the gapped modes are analyzed
in terms of a dynamical Dzyaloshinskii-Moriya interaction, suggesting the
presence of phonon-assisted effects in the low-temperature spin dynamics of
Sr3Cr2O8 and Ba3Cr2O8",1402.1877v1
2014-02-24,Spin-dependent recombination involving oxygen-vacancy complexes in silicon,"Spin-dependent relaxation and recombination processes in $\gamma$-irradiated
$n$-type Czochralski-grown silicon are studied using continuous wave (cw) and
pulsed electrically detected magnetic resonance (EDMR). Two processes involving
the SL1 center, the neutral excited triplet state of the oxygen-vacancy
complex, are observed which can be separated by their different dynamics. One
of the processes is the relaxation of the excited SL1 state to the ground state
of the oxygen-vacancy complex, the other a charge transfer between $^{31}$P
donors and SL1 centers forming close pairs, as indicated by electrically
detected electron double resonance. For both processes, the recombination
dynamics are studied with pulsed EDMR techniques. We demonstrate the
feasibility of true zero-field cw and pulsed EDMR for spin 1 systems and use
this to measure the lifetimes of the different spin states of SL1 also at
vanishing external magnetic field.",1402.5957v2
2014-04-29,Spin dynamics in a two dimensional quantum gas,"We have investigated spin dynamics in a 2D quantum gas. Through spin-changing
collisions, two clouds with opposite spin orientations are spontaneously
created in a Bose-Einstein condensate. After ballistic expansion, both clouds
acquire ring-shaped density distributions with superimposed angular density
modulations. The density distributions depend on the applied magnetic field and
are well explained by a simple Bogoliubov model. We show that the two clouds
are anti-correlated in momentum space. The observed momentum correlations pave
the way towards the creation of an atom source with non-local
Einstein-Podolsky-Rosen entanglement.",1404.7385v2
2014-07-17,Ultrafast and reversible control of the exchange interaction in Mott insulators,"The strongest interaction between microscopic spins in magnetic materials is
the exchange interaction $J_\text{ex}$. Therefore, ultrafast control of
$J_\text{ex}$ holds the promise to control spins on ultimately fast timescales.
We demonstrate that time-periodic modulation of the electronic structure by
electric fields can be used to reversibly control $J_\text{ex}$ on ultrafast
timescales in extended antiferromagnetic Mott insulators. In the regime of weak
driving strength, we find that $J_\text{ex}$ can be enhanced and reduced for
frequencies below and above the Mott gap, respectively. Moreover, for strong
driving strength, even the sign of $J_\text{ex}$ can be reversed and we show
that this causes time reversal of the associated quantum spin dynamics. These
results suggest wide applications, not only to control magnetism in condensed
matter systems, for example, via the excitation of spin resonances, but also to
assess fundamental questions concerning the reversibility of the quantum
many-body dynamics in cold atom systems.",1407.4761v2
2014-08-14,Engineering the Dynamics of Effective Spin-Chain Models for Strongly Interacting Atomic Gases,"We consider a one-dimensional gas of cold atoms with strong contact
interactions and construct an effective spin-chain Hamiltonian for a
two-component system. The resulting Heisenberg spin model can be engineered by
manipulating the shape of the external confining potential of the atomic gas.
We find that bosonic atoms offer more flexibility for tuning independently the
parameters of the spin Hamiltonian through interatomic (intra-species)
interaction which is absent for fermions due to the Pauli exclusion principle.
Our formalism can have important implications for control and manipulation of
the dynamics of few- and many-body quantum systems; as an illustrative example
relevant to quantum computation and communication, we consider state transfer
in the simplest non-trivial system of four particles representing
exchange-coupled qubits.",1408.3414v2
2014-08-22,Dynamics of quadrupolar bodies in a Schwarzschild spacetime,"The dynamics of extended bodies endowed with multipolar structure up to the
mass quadrupole moment is investigated in the Schwarzschild background
according to the Dixon's model, extending previous works. The whole set of
evolution equations is numerically integrated under the simplifying assumptions
of constant frame components of the quadrupole tensor and that the motion of
the center of mass be confined on the equatorial plane, the spin vector being
orthogonal to it. The equations of motion are also solved analytically in the
limit of small values of the characteristic length scales associated with the
spin and quadrupole with respect to the background curvature characteristic
length. The results are qualitatively and quantitatively different from
previous analyses involving only spin structures. In particular, the presence
of the quadrupole turns out to be responsible for the onset of a non-zero spin
angular momentum, even if initially absent.",1408.5261v1
2014-11-13,Exact solitons and manifold mixing dynamics in the spin-orbit-coupled spinor condensates,"We derive exact static as well as moving solitonic solutions to the
one-dimensional spin-orbit-coupled F=1 Bose-Einstein condensates. The static
polar soliton is shown to be the ground state by the imaginary-time evolution
method. It shows a helical modulation of the order parameter due to the
spin-orbit coupling. In particular, the moving soliton exhibits a periodic
oscillation among the particle numbers of the hyperfine states. We further
explore the temporal evolution of the static polar soliton and find that the
spin-polarization exhibits dynamical oscillations. This disappearance and
re-emergence of the ferromagnetic state indicates the mixing of the
ferromagnetic and the antiferromagnetic manifolds.",1411.3420v1
2014-11-14,Lifetimes of Magnons in Two-Dimensional Diluted Ferromagnetic Systems,"Spin dynamics in low dimensional magnetic systems has been of fundamental
importance for a long time and has currently received an impetus owing to the
emerging field of nanoelectronics. Knowledge of the spin wave lifetimes, in
particular, can be favorable for future potential applications. We investigate
the low-temperature spin wave excitations in two-dimensional disordered
ferromagnetic systems, with a particular focus on the long wavelength magnon
lifetimes. A semi-analytical Green's functions based approach is used to
determine the dynamical spectral functions, for different magnetic impurity
concentrations, from which the intrinsic linewidth is extracted. We obtain an
unambiguous $q^4$ scaling of the magnon linewidth which is ascribed to the
disorder induced damping of the spin waves, thereby settling a longstanding
unresolved issue on the wave-vector dependence. Our findings are also in good
agreement with previous theoretical studies on Heisenberg ferromagnets.
Additionally, we demonstrate the futility of using the low moments associated
with the spectral densities to evaluate the magnon dispersions and lifetimes.",1411.3876v2
2015-01-01,Phenomenological modelling for Time-Resolved Electron Paramagnetic Resonance in radical-triplet system,"The spin dynamics of radical-triplet system (RTS) has been calculated by
using the Lindblad formalism within the theory of open quantum system. The
single-radical-triplet system (SRTS) is considered here for single-qubit
quantum gate operations while double-radical-triplet system (DRTS) for
two-qubit operations. The environment effects taken into account include the
spin-lattice relaxation of the triplet exciton and radical spin-$\frac{1}{2}$,
the inter-system crossing process that induces the transition from singlet
excited state to the triplet ground state, and the rather slow relaxation
process from the triplet ground state back down to the singlet ground state.
These calculations shown that the line shape broadening is strongly related to
the exchange interaction between triplet and exciton, which can be understood
as a spontaneous magnetic field created by the triplet renormalises the
original spin-$\frac{1}{2}$ electron spin resonance spectra. This work will
provide key information about the spin dynamics for building
optically-controlled molecular quantum gate out of radical-bearing molecules.
Moreover, this has generated the further theoretical question on how the
mixture of fermion and boson behaves.",1501.00316v1
2015-03-04,Coherent spin mixing dynamics in thermal $^{87}$Rb spin-1 and spin-2 gases,"We study the non-equilibrium coherent spin mixing dynamics in ferromagnetic
spin-1 and antiferromagnetic spin-2 thermal gases of ultracold $^{87}$Rb atoms.
Long lasting spin population oscillations with magnetic field dependent
resonances are observed in both cases. Our observations are well reproduced by
Boltzmann equations of the Wigner distribution function. Compared to the
equation of motion of spinor Bose-Einstein condensates, the only difference
here is a factor of two increase in the spin-dependent interaction, which is
confirmed directly in the spin-2 case by measuring the relation between the
oscillation amplitude and the sample's density.",1503.01171v1
2015-03-06,NMR evidence for inhomogeneous glassy behavior driven by nematic fluctuations in iron arsenide superconductors,"We present $^{75}$As nuclear magnetic resonance spin-lattice and spin-spin
relaxation rate data in Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ and
Ba(Fe$_{1-x}$Cu$_x$)$_2$As$_2$ as a function of temperature, doping and
magnetic field. The relaxation curves exhibit a broad distribution of
relaxation rates, consistent with inhomogeneous glassy behavior up to 100 K.
The doping and temperature response of the width of the dynamical heterogeneity
is similar to that of the nematic susceptibility measured by elastoresistance
measurements. We argue that quenched random fields which couple to the nematic
order give rise to a nematic glass that is reflected in the spin dynamics.",1503.01844v2
2015-03-10,Microwave-induced dynamic switching of magnetic skyrmion cores in nanodots,"The nonlinear dynamic behavior of a magnetic skyrmion in circular nanodots
was studied numerically by solving the Landau-Lifshitz-Gilbert equation with a
classical spin model. We show that a skyrmion core reversal can be achieved
within nanoseconds using a perpendicular oscillating magnetic field. Two
symmetric switching processes that correspond to excitations of the breathing
mode and the mixed mode (combination of the breathing mode and a radial
spin-wave mode) are identified. For excitation of the breathing mode, the
skyrmion core switches through nucleation of a new core from a transient
uniform state. In the mixed mode, the skyrmion core reverses with the help of
spins excited both at the edge and core regions. Unlike the magnetic vortex
core reversal, the excitation of radial spin waves does not dominate the
skyrmion core reversal process.",1503.02869v1
2015-03-31,Real-time monitoring of Lévy flights in a single quantum system,"L\'evy flights are random walks where the dynamics is dominated by rare
events. Even though they have been studied in vastly different physical
systems, their observation in a single quantum system has remained elusive.
Here we analyze a periodically driven open central spin system and demonstrate
theoretically that the dynamics of the spin environment exhibits L\'evy
flights. For the particular realization in a single-electron charged quantum
dot driven by periodic resonant laser pulses, we use Monte Carlo simulations to
confirm that the long waiting times between successive nuclear spin flip events
are governed by a power-law distribution; the corresponding exponent $\eta
=-3/2$ can be directly measured in real-time by observing the waiting time
distribution of successive photon emission events. Remarkably, the dominant
intrinsic limitation of the scheme arising from nuclear quadrupole coupling can
be minimized by adjusting the magnetic field or by implementing spin echo.",1503.09017v1
2015-04-11,Spin-charge separated quasiparticles in one dimensional quantum fluids,"We revisit the problem of dynamical response in spin-charge separated one
dimensional quantum fluids. In the framework of Luttinger liquid theory, the
dynamical response is formulated in terms of noninteracting bosonic collective
excitations carrying either charge or spin. We argue that, as a result of
spectral nonlinearity, long-lived excitations are best understood in terms of
generally strongly interacting fermionic holons and spinons. This has far
reaching ramifications for the construction of mobile impurity models used to
determine threshold singularities in response functions. We formulate and solve
the appropriate mobile impurity model describing the spinon threshold in the
single-particle Green's function. Our formulation further raises the question
whether it is possible to realize a model of noninteracting fermionic holons
and spinons in microscopic lattice models of interacting spinful fermions. We
investigate this issue in some detail by means of density matrix
renormalization group (DMRG) computations.",1504.02894v1
2015-05-01,Density functional versus spin-density functional and the choice of correlated subspace in multi-variable effective action theories of electronic structure,"Modern extensions of density functional theory such as the density functional
theory plus U and the density functional theory plus dynamical mean-field
theory require choices, including selection of variable (charge vs spin
density) for the density functional and specification of the correlated
subspace. This paper examines these issues in the context of the ""plus U""
extensions of density functional theory, in which additional correlations on
specified correlated orbitals are treated using a Hartree-Fock approximation.
Differences between using charge-only or spin-density-dependent
exchange-correlation functionals and between Wannier and projector-based
definitions of the correlated orbitals are considered on the formal level and
in the context of the structural energetics of the rare earth nickelates. It is
demonstrated that theories based on spin-dependent exchange-correlation
functionals can lead to large and in some cases unphysical effective on-site
exchange couplings. Wannier and projector-based definitions of the correlated
orbitals lead to similar behavior near ambient pressure, but substantial
differences are observed at large pressures. Implications for other beyond
density functional methods such as the combination of density functional and
dynamical mean field theory are discussed.",1505.00227v1
2015-08-13,On the dynamics of the Meissner effect,"The question of how a metal becoming superconducting expels a magnetic field
is addressed. It is argued that the conventional theory of superconductivity
has not answered this question despite its obvious importance. We argue that
the growth of the superconducting into the normal region and associated
expulsion of magnetic field from the superconducting region can only be
understood if it is accompanied by motion of charge from the superconducting
into the normal region. From a microscopic point of view it is shown that the
perfect diamagnetism of superconductors requires that superconducting electrons
reside in orbits of spatial extent $2\lambda_L$, with $\lambda_L$ the London
penetration depth. Associated with this physics, the spin-orbit interaction of
the electron magnetic moment and the positively charged ionic background gives
rise to a ""Spin Meissner"" effect, the generation of a macroscopic spin current
near the surface of superconductors. We point out that both the Meissner and
the Spin Meissner effect can be understood dynamically under the assumption
that the superfluid condensate wavefunction $\Psi(\vec{r})$ does not screen
itself, just like the $\Psi(\vec{r})$ for an electron in a hydrogen atom. We
argue that the conventional theory of superconductivity cannot explain the
Meissner effect because it does not contain the physical elements discussed
here.",1508.03307v1
2015-08-19,Skyrmion dynamics in chiral ferromagnets under spin-transfer torque,"We study the dynamics of skyrmions under spin-transfer torque in
Dzyaloshinskii-Moriya materials with easy-axis anisotropy. In particular, we
study the motion of a topological skyrmion with skyrmion number $Q=1$ and a
non-topological skyrmionium with $Q=0$ using their linear momentum, virial
relations, and numerical simulations. The non-topological $Q=0$ skyrmionium is
accelerated in the direction of the current flow and it either reaches a steady
state with constant velocity, or it is elongated to infinity. The steady-state
velocity is given by a balance between current and dissipation and has an upper
limit. In contrast, the topological $Q=1$ skyrmion converges to a steady-state
with constant velocity at an angle to the current flow. When the spin current
stops the $Q=1$ skyrmion is spontaneously pinned whereas the $Q=0$ skyrmionium
continues propagation. Exact solutions for the propagating skyrmionium are
identified as solutions of equations given numerically in a previous work.
Further exact results for propagating skyrmions are given in the case of the
pure exchange model. The traveling solutions provide arguments that a
spin-polarized current will cause rigid motion of a skyrmion or a skyrmionium.",1508.04821v1
2015-09-07,ESR modes in a Strong-Leg Ladder in the Tomonaga-Luttinger Liquid Phase,"Magnetic excitations in the strong-leg quantum spin ladder compound
(C$_7$H$_{10}$N)$_2$CuBr$_4$ (known as DIMPY) in the field-induced
Tomonaga-Luttinger spin liquid phase are studied by means of high-field
electron spin resonance (ESR) spectroscopy. The presence of a gapped ESR mode
with unusual non-linear frequency-field dependence is revealed experimentally.
Using a combination of analytic and exact diagonalization methods, we compute
the dynamical structure factor and identify this mode with longitudinal
excitations in the antisymmetric channel. We argue that these excitations
constitute a fingerprint of the spin dynamics in a strong-leg spin-1/2
Heisenberg antiferromagnetic ladder and owe its ESR observability to the
uniform Dzyaloshinskii-Moriya interaction.",1509.02056v2
2015-09-14,Spectral characteristics of time resolved magnonic spin Seebeck effect,"Spin Seebeck effect (SSE) holds promise for new spintronic devices with
low-energy consumption. The underlying physics, essential for a further
progress, is yet to be fully clarified. This study of the time resolved
longitudinal SSE in the magnetic insulator yttrium iron garnet (YIG) concludes
that a substantial contribution to the spin current stems from small
wave-vector subthermal exchange magnons. Our finding is in line with the recent
experiment by S. R. Boona and J. P. Heremans, Phys. Rev. B 90, 064421 (2014).
Technically, the spin-current dynamics is treated based on the
Landau-Lifshitz-Gilbert (LLG) equation also including magnons back-action on
thermal bath, while the formation of the time dependent thermal gradient is
described self-consistently via the heat equation coupled to the magnetization
dynamics",1509.04018v1
2015-09-30,Terahertz Antiferromagnetic Spin Hall Nano-Oscillator,"We consider the current-induced dynamics of insulating antiferromagnets in a
spin Hall geometry. Sufficiently large in-plane currents perpendicular to the
N\'{e}el order trigger spontaneous oscillations at frequencies between the
acoustic and the optical eigenmodes. The direction of the driving current
determines the chirality of the excitation. When the current exceeds a
threshold, the combined effect of spin pumping and current-induced torques
introduces a dynamic feedback that sustains steady-state oscillations with
amplitudes controllable via the applied current. The ac voltage output is
calculated numerically as a function of the dc current input for different
feedback strengths. Our findings open a route towards terahertz
antiferromagnetic spin-torque oscillators.",1509.09229v3
2015-10-05,Relativistic ponderomotive Hamiltonian of a Dirac particle in a vacuum laser field,"We report a point-particle ponderomotive model of a Dirac electron
oscillating in a high-frequency field. Starting from the Dirac Lagrangian
density, we derive a reduced phase-space Lagrangian that describes the
relativistic time-averaged dynamics of such a particle in a geometrical-optics
laser pulse propagating in vacuum. The pulse is allowed to have an arbitrarily
large amplitude (provided radiation damping and pair production are negligible)
and a wavelength comparable to the particle de Broglie wavelength. The model
captures the Bargmann-Michel-Telegdi (BMT) spin dynamics, the Stern-Gerlach
spin-orbital coupling, the conventional ponderomotive forces, and the
interaction with large-scale background fields. Agreement with the BMT spin
precesison equation is shown numerically. The commonly known theory in which
ponderomotive effects are incorporated in the particle effective mass is
reproduced as a special case when the spin-orbital coupling is negligible. This
model could be useful for studying laser-plasma interactions in relativistic
spin-$1/2$ plasmas.",1510.01268v2
2016-01-14,Theory of triplon dynamics in the quantum magnet BiCu$_2$PO$_6$,"We provide a theory of triplon dynamics in the valence bond solid ground
state of the coupled spin-ladders modelled for BiCu$_2$PO$_6$. Utilizing the
recent high quality neutron scattering data [Nature Physics (2015), DOI:
10.1038/NPHYS3566] as guides and a theory of interacting triplons via the bond
operator formulation, we determine a minimal spin Hamiltonian for this system.
It is shown that the splitting of the low energy triplon modes and the peculiar
magnetic field dependence of the triplon dispersions can be explained by
including substantial Dzyaloshinskii-Moriya and symmetric anisotropic spin
interactions. Taking into account the interactions between triplons and the
decay of the triplons to the two-triplon continuum via anisotropic spin
interactions, we provide a theoretical picture that can be used to understand
the main features of the recent neutron scattering experimental data.",1601.03747v3
2016-01-18,Anti-symmetry consideration on the preservation of Entanglement of spin system,"In this work we offer an approach to protect the entanglement based on the
anti-symmetric property of the hamiltonian. Our main objective is to protect
the entanglement of a given initial three-qubit state which is governed by
hamiltonian of a three-spin Ising chain in site-dependent transverse fields. We
show that according to anti-symmetric property of the hamiltonian with respect
to some operators mimicking the time reversal operator, the dynamics of the
system can be effectively reversed. It equips us to control the dynamics of the
system. The control procedure is implemented as a sequence of cyclic evolution;
accordingly the entanglement of the system is protected for any given initial
state with any desired accuracy an long-time. Using this approach we could
control not only the multiparty entanglement but also the pairwise
entanglement. It is also notable that in this paper although we restrict
ourselves mostly within a three-spin Ising chain in site-dependent transverse
fields, our approach could be applicable to any n-qubit spin system models.",1601.04442v1
2016-02-15,Half-Skyrmion Spin Textures In Polariton Microcavities,"We study the polarization dynamics of a spatially expanding polariton
condensate under nonresonant linearly polarized optical excitation. The
spatially and temporally resolved polariton emission reveals the formation of
non-trivial spin textures in the form of a quadruplet polarization pattern both
in the linear and circular Stokes parameters, and an octuplet in the diagonal
Stokes parameter. The continuous rotation of the polariton pseudospin vector
through the condensate due to TE-TM splitting exhibits an ordered pattern of
half-skyrmions associated with a half-integer topological number. A theoretical
model based on a driven-dissipative Gross-Pitaevskii equation coupled with an
exciton reservoir describes the dynamics of the nontrivial spin textures
through the optical spin-Hall effect.",1602.04711v2
2016-02-25,Study of the ultrafast dynamics of ferromagnetic materials with a Quantum Monte Carlo atomistic model,"We study of the ultrafast dynamics of the atomic angular momentum in
ferrimagnets irradiated by laser pulses. My apply a quantum atomistic spin
approach based on the Monte Carlo technique. Our model describes the coherent
transfer of angular momentum between the spin and the orbital momentum as well
as the quenching of the orbital momentum induced by the lattice field. The
Elliott-Yafet collision mechanism is also included. We focus on elementary
mechanisms that lead to the dissipation of the total angular momentum in a rare
earth-transition metal (RE-TM) alloy in which the two sublattices have opposite
spin orientation. Our model shows that the observed ultrafast quenching of the
magnetization can be explained microscopically by the transfer of spin between
the sublattices and by the quenching of the localized orbital angular momentum.",1602.07950v1
2016-03-29,Evidences of spin-temperature in Dynamic Nuclear Polarization: an exact computation of the EPR spectrum,"In dynamic nuclear polarization (DNP) experiments, the compound is driven
out-of-equilibrium by microwave (MW) irradiation of the radical electron spins.
Their stationary state has been recently probed via electron double resonance
(ELDOR) techniques showing, at low temperature, a broad depolarization of the
electron paramagnetic resonance (EPR) spectrum under microwave irradiation. In
this theoretical manuscript, we develop a numerical method to compute exactly
the EPR spectrum in presence of dipolar interactions. Our results reproduce the
observed broad depolarisation and provide a microscopic justification for
spectral diffusion mechanism. We show the validity of the spin-temperature
approach for typical radical concentration used in dissolution DNP protocols.
In particular once the interactions are properly taken into account, the
spin-temperature is consistent with the non-monotonic behavior of the EPR
spectrum with a wide minimum around the irradiated frequency.",1603.08620v2
2016-06-15,Spin dynamics in Kapitza-Dirac scattering of electrons from bichromatic laser fields,"Kapitza-Dirac scattering of nonrelativistic electrons from counterpropagating
bichromatic laser waves of linear polarization is studied. The focus lies on
the electronic spin dynamics in the Bragg regime when the laser fields possess
a frequency ratio of two. To this end, the time-dependent Pauli equation is
solved numerically, both in coordinate space and momentum space. Our numerical
results are corroborated by analytical derivations. We demonstrate that, for
certain incident electron momenta, the scattering crucially relies on the
electron spin which undergoes characteristic Rabi-like oscillations. A
parameter regime is identified where the Rabi oscillations reach maximum
amplitude. We also briefly discuss spin-dependent Kapitza-Dirac scattering of
protons.",1606.04813v2
2016-10-01,Microscopic Observation of the Light-Cone-Like Thermal Correlations in Cracking Excitations,"Many seemingly intractable systems can be reduced to a system of interacting
spins. Here, we introduce a system of artificial acoustic spins which are
manipulated with ultrasound excitations associated with micro-cracking sources
in thin sheets of crystals. Our spin-like system shows a peculiar relaxation
mechanism after inducing an impulsive stress-ramp akin to splitting, or
rupturing, of the system. Using real-time construction of correlations between
spins states, we observe a clear emergence of the light cone effect. It has
been proposed that equilibration horizon occurs on a local scale in systems
where correlations between distant sites are established at a finite speed. The
observed equilibration horizon in our observations defines a region where
elements of the material are in elastic communication through excited
elementary excitations. These results yield important insights into dynamic
communication between failing elements in brittle materials during processes
such as brittle fragmentation and dynamic stress triggering of
earthquake-generating faults.",1610.00165v1
2016-10-04,Effect of temperature on spin-transfer torque induced magnetic solitons,"Spin-transfer torques in a nanocontact to an extended magnetic film can
create spin waves that condense to form dissipative droplet solitons. Here we
report an experimental study of the temperature dependence of the current and
applied field thresholds for droplet soliton formation, as well as the
nanocontact's electrical characteristics associated with droplet dynamics.
Nucleation of droplet solitons requires higher current densities at higher
temperatures, in contrast to typical spin-transfer torque induced switching
between static magnetic states. Magnetoresistance and electrical noise
measurements show that soliton instabilities become more pronounced with
increasing temperature. These results are of fundamental interest in
understanding the influence of thermal noise on droplet solitons, and in
controlling their dynamics.",1610.00931v1
2016-10-11,Self-Consistent Field Theory studies of the thermodynamics and quantum spin dynamics of magnetic Skyrmions,"A self-consistent field theory is introduced and used to investigate the
thermodynamics and spin dynamics of an $S = 1$ quantum spin system with a
magnetic Skyrmion. The temperature dependence of the Skyrmion profile as well
as the phase diagram are calculated. It is shown that the Skyrmion carries a
phase transition to the ferromagnetic phase of first order with increasing
temperature, while the magnetization of the surrounding ferromagnet undergoes a
phase transition of second order when changing to the paramagnetic phase.
Furthermore, the electric field driven annihilation process of the Skyrmion is
described quantum mechanical by solving the time dependent Schr\""odinger
equation. The results are compared with the trajectories of the semi-classical
description of the spin expectation values using a differential equation
similar to the classical Landau-Lifshitz-Gilbert equation.",1610.03191v2
2016-10-21,Spin-torque switching in large size nano-magnet with perpendicular magnetic fields,"DC current induced magnetization reversal and magnetization oscillation was
observed in 500 nm large size Co90Fe10/Cu/Ni80Fe20 pillars. A perpendicular
external field enhanced the coercive field separation between the reference
layer (Co90Fe10) and free layer (Ni80Fe20) in the pseudo spin valve, allowing a
large window of external magnetic field for exploring the free-layer reversal.
The magnetization precession was manifested in terms of the multiple peaks on
the differential resistance curves. Depending on the bias current and applied
field, the regions of magnetic switching and magnetization precession on a
dynamical stability diagram has been discussed in details. Micromagnetic
simulations are shown to be in good agreement with experimental results and
provide insight for synchronization of inhomogenieties in large sized device.
The ability to manipulate spin-dynamics on large size devices could prove
useful for increasing the output power of the spin-transfer nano-oscillators
(STNOs).",1610.06959v1
2017-02-20,Simulating quantum light propagation through atomic ensembles using matrix product states,"A powerful method to interface quantum light with matter is to propagate the
light through an ensemble of atoms. Recently, a number of such interfaces have
emerged, most prominently Rydberg ensembles, that enable strong nonlinear
interactions between propagating photons. A largely open problem is whether
these systems produce exotic many-body states of light and developing new tools
to study propagation in the large photon number limit is highly desirable.
Here, we provide a method based on a ""spin model"" that maps quasi
one-dimensional (1D) light propagation to the dynamics of an open 1D
interacting spin system, where all photon correlations are obtained from those
of the spins. The spin dynamics in turn are numerically solved using the
toolbox of matrix product states. We apply this formalism to investigate vacuum
induced transparency, wherein the different photon number components of a pulse
propagate with number-dependent group velocity and separate at output.",1702.05954v3
2017-03-02,Dynamical Correlation Functions of the Quadratic Coupling Spin-Boson Model,"The spin-boson model with quadratic coupling is studied using the bosonic
numerical renormalization group method. We focus on the dynamical
auto-correlation functions $C_{O}(\omega)$, with the operator $\hat{O}$ taken
as $\hat{\sigma}_x$, $\hat{\sigma}_z$, and $\hat{X}$, respectively. In the
weak-coupling regime $\alpha < \alpha_c$, these functions show power law
$\omega$-dependence in the small frequency limit, with the powers $1+2s$,
$1+2s$, and $s$, respectively. At the critical point $\alpha = \alpha_c$ of the
boson-unstable quantum phase transition, the critical exponents $y_{O}$ of
these correlation functions are obtained as $y_{\sigma_x} = y_{\sigma_z} =
1-2s$ and $y_{X}=-s$, respectively. Here $s$ is the bath index and $X$ is the
boson displacement operator. Close to the spin flip point, the high frequency
peak of $C_{\sigma_{x}}(\omega)$ is broadened significantly and the line shape
changes qualitatively, showing enhanced dephasing at the spin flip point.",1703.00618v1
2017-08-02,Optically-pumped dynamic nuclear hyperpolarization in $^{13}$C enriched diamond,"We investigate nuclear spin hyperpolarization from nitrogen vacancy centers
in isotopically enriched diamonds with $^{13}$C concentrations up to 100%.
$^{13}$C enrichment leads to hyperfine structure of the nitrogen vacancy
electron spin resonance spectrum and as a result the spectrum of dynamic
nuclear polarization. We show that strongly-coupled $^{13}$C spins in the first
shell surrounding a nitrogen vacancy center generate resolved hyperfine
splittings, but do not act as an intermediary in the transfer of
hyperpolarization of bulk nuclear spins. High levels of $^{13}$C enrichment are
desirable to increase the efficiency of hyperpolarizaiton for magnetic
resonance signal enhancement, imaging contrast agents, and as a platform for
quantum sensing and many-body physics.",1708.00561v1
2017-08-02,Flocking from a quantum analogy: Spin-orbit coupling in an active fluid,"Systems composed of strongly interacting self-propelled particles can form a
spontaneously flowing polar active fluid. The study of the connection between
the microscopic dynamics of a single such particle and the macroscopic dynamics
of the fluid can yield insights into experimentally realizable active flows,
but this connection is well understood in only a few select cases. We introduce
a model of self-propelled particles based on an analogy with the motion of
electrons that have strong spin-orbit coupling. We find that, within our model,
self-propelled particles are subject to an analog of the Heisenberg uncertainty
principle that relates translational and rotational noise. Furthermore, by
coarse-graining this microscopic model, we establish expressions for the
coefficients of the Toner-Tu equations---the hydrodynamic equations that
describe an active fluid composed of these ""active spins."" The connection
between self-propelled particles and quantum spins may help realize exotic
phases of matter using active fluids via analogies with systems composed of
strongly correlated electrons.",1708.00937v1
2017-08-10,Many-body localization phase in a spin-driven chiral multiferroic chain,"Many-body localization (MBL) is an emergent phase in correlated quantum
systems with promis- ing applications, particularly in quantum information.
Here, we unveil the existence and analyse this phase in a chiral multiferroic
model system. Conventionally, MBL occurrence is traced via level statistics by
implementing a standard finite-size scaling procedure. Here, we present an
approach based on the full distribution of the ratio of adjacent energy
spacings. We find a strong broadening of the histograms of counts of these
level spacings directly at the transition point from MBL to the ergodic phase.
The broadening signals reliably the transition point without relying on an
averaging procedure. The fast convergence of the histograms even for relatively
small systems allows moni- toring the MBL dynamics with much less computational
effort. Numerical results are presented for a chiral spin chain with a
dynamical Dzyaloshinskii Moriya (DM) interaction, an established model to
describe the spin excitations in a single phase spin-driven multiferroic
system. The multiferroic MBL phase is uncovered and it is shown how to steer it
via electric fields.",1708.03169v1
2018-02-01,Theory of spin and lattice wave dynamics excited by focused laser pulses,"We develop a theory of the spin wave dynamics excited by ultrafast focused
laser pulses in a magnetic film. We take into account both volume and surface
spin wave modes in the presence of applied, dipolar and magnetic anisotropy
fields and include the dependence on laser spot exposure size and magnetic
damping. We show that the sound waves generated by local heating by an
ultrafast focused laser pulse can excite a wide spectrum of spin waves (on top
of a dominant magnon-phonon contribution). Good agreement with recent
experiments supports the validity of the model.",1802.00178v2
2018-02-12,Easy-Plane Magnetic Strip as a Long Josephson Junction,"Spin-torque-biased magnetic dynamics in an easy-plane ferromagnet (EPF) is
theoretically studied in the presence of a weak in-plane anisotropy. While this
anisotropy spoils U(1) symmetry thereby quenching the conventional spin
superfluidity, we show that the system instead realizes a close analog of a
long Josephson junction (LJJ) model. The traditional magnetic-field and
electric-current controls of the latter map respectively onto the symmetric and
antisymmetric combinations of the out-of-plane spin torques applied at the ends
of the magnetic strip. This suggests an alternative route towards realizations
of superfluid-like transport phenomena in insulating magnetic systems. We study
spin-torque-biased phase diagram, providing an analytical solution for static
multidomain phases in the EPF. We adapt an existing self-consistency method for
the LJJ to develop an approximate solution for the EPF dynamics. The LJJ-EPF
mapping allows us to envision superconducting circuit functionality at elevated
temperatures. The results apply equally to antiferromagnets with suitable
effective free energy in terms of the N\'{e}el order instead of magnetization.",1802.04229v1
2018-04-02,Longitudinal relaxation of a nitrogen-vacancy center in a spin bath by generalized cluster-correlation expansion method,"We theoretically study the longitudinal relaxation of a nitrogen-vacancy (NV)
center surrounded by a 13C nuclear spin bath in diamond. By incorporating
electron spin in the cluster, we generalize the cluster-correlation expansion
(CCE) to theoretically simulate the population dynamics of electron spin of NV
center. By means of the generalized CCE, we numerically demonstrate the decay
process of electronic state induced by cross relaxation at the ambient
temperature. It is shown that the CCE method is not only capable of describing
pure-dephasing effect at large-detuning regime, but it can also simulate the
quantum dynamics of populations in the nearly-resonant regime.",1804.01008v2
2018-04-23,Asymptotic Floquet states of a periodically driven spin-boson system in the nonperturbative coupling regime,"As a paradigmatic model of open quantum system, the spin-boson model is
widely used in theoretical and experimental investigations. Beyond the weak
coupling limit, the spin dynamics can be described by a time-nonlocal
generalized master equation with a memory kernel accounting for the dissipative
effects induced by the bosonic environment. When the spin is additionally
modulated by an external time-periodic electromagnetic field, the interplay
between dissipation and modulations yields a spectrum of nontrivial asymptotic
states, especially in the regime of nonlinear response. Here we implement a
method for the evaluation of Floquet dynamics in non-Markovian systems [L.
Magazz\`u et al., Phys. Rev. A 96, 042103 (2017)] to find these strongly
non-equilibrium states.",1804.08764v1
2019-05-20,Quantum Transport of Rydberg Excitons with Synthetic Spin-Exchange Interactions,"We present a scheme for engineering quantum transport dynamics of spin
excitations in a chain of laser-dressed Rydberg atoms, mediated by synthetic
spin-exchange arising from diagonal van der Waals interaction. The dynamic
tunability and long-range interaction feature of our scheme allows for the
exploration of transport physics unattainable in conventional spin systems. As
two concrete examples, we first demonstrate a topological exciton pumping
protocol that facilitates quantized entanglement transfer, and secondly we
discuss a highly nonlocal correlated transport phenomenon which persists even
in the presence of dephasing. Unlike previous schemes, our proposal requires
neither resonant dipole-dipole interaction nor off-diagonal van der Waals
interaction. It can be readily implemented in existing experimental systems.",1905.08280v2
2020-07-07,Accessing long timescales in the relaxation dynamics of spins coupled to a conduction-electron system using absorbing boundary conditions,"The relaxation time of a classical spin interacting with a large
conduction-electron system is computed for a weak magnetic field, which
initially drives the spin out of equilibrium. We trace the spin and the
conduction-electron dynamics on a time scale, which exceeds the characteristic
electronic scale that is set by the inverse nearest-neighbor hopping by more
than five orders of magnitude. This is achieved with a novel construction of
absorbing boundary conditions, which employs a generalized Lindblad
master-equation approach to couple the edge sites of the conduction-electron
tight-binding model to an external bath. The failure of the standard Lindblad
approach to absorbing boundaries is traced back to artificial excitations
initially generated due to the coupling to the bath. This can be cured by
introducing Lindblad parameter matrices and by fixing those matrices to
perfectly suppress initial-state artifacts as well as reflections of physical
excitations propagating to the system boundaries. Numerical results are
presented and discussed for generic one-dimensional models of the electronic
structure.",2007.03655v2
2020-07-09,Dynamic Spin Fluctuations in the Frustrated A-site Spinel CuAl2O4,"We performed nuclear magnetic resonance (NMR) and muon spin relaxation
({\mu}SR) experiments to identify the magnetic ground state of the frustrated
quantum A-site spinel, CuAl2O4. Our results verify that the ground state does
not exhibit a long-range magnetic ordering, but a glass-like transition
manifests at T*=2.3 K. However, the Gaussian shape and the weak longitudinal
field dependence of {\mu}SR spectra below T* show that the ground state has
dynamic spin fluctuations, distinct from those of conventional spin-glasses.",2007.04761v1
2010-05-04,Disorder-induced freezing of dynamical spin fluctuations in underdoped cuprates,"We study the dynamical spin susceptibility of a correlated d-wave
superconductor (dSC) in the presence of disorder, using an unrestricted
Hartree-Fock approach. This model provides a concrete realization of the notion
that disorder slows down spin fluctuations, which eventually ""freeze out"". The
evolution of disorder-induced spectral weight transfer agrees qualitatively
with experimental observations on underdoped cuprate superconductors. For
sufficiently large disorder concentrations, static spin density wave (SDW)
order is created when droplets of magnetism nucleated by impurities overlap. We
also study the disordered stripe state coexisting with a dSC and compare its
magnetic fluctuation spectrum to that of the disorder-generated SDW phase.",1005.0520v2
2010-05-27,Renormalized parameters and perturbation theory for an n-channel Anderson model with Hund's rule coupling,"We extend the renormalized perturbation theory for the single impurity
Anderson model to the n-channel model with a Hund's rule coupling, and show
that the exact results for the spin, orbital and charge susceptibilities, as
well as the leading low temperature dependence for the resistivity, are
obtained by working to second order in the renormalized couplings. A universal
relation is obtained between the renormalized parameters, independent of n, in
the Kondo regime. An expression for the dynamic spin susceptibility is also
derived by taking into account repeated quasiparticle scattering, which is
asymptotically exact in the low frequency regime and satisfies the
Korringa-Shiba relation. The renormalized parameters, including the
renormalized Hund's rule coupling, are deduced from numerical renormalization
group calculations for the model for the case n=2. The results confirm
explicitly the universal relations between the parameters in the Kondo regime.
Using these results we evaluate the spin, orbital and charge susceptibilities,
temperature dependence of the low temperature resistivity and dynamic spin
susceptibility for the particle-hole symmetric n=2 model.",1005.5113v1
2013-08-20,Dynamics of a two-dimensional quantum spin liquid: signatures of emergent Majorana fermions and fluxes,"Topological states of matter present a wide variety of striking new
phenomena. Prominent among these is the fractionalisation of electrons into
unusual particles: Majorana fermions [1], Laughlin quasiparticles [2] or
magnetic monopoles [3]. Their detection, however, is fundamentally complicated
by the lack of any local order, such as, for example, the magnetisation in a
ferromagnet. While there are now several instances of candidate topological
spin liquids [4], their identification remains challenging [5]. Here, we
provide a complete and exact theoretical study of the dynamical structure
factor of a two-dimensional quantum spin liquid in gapless and gapped phases.
We show that there are direct signatures - qualitative and quantitative - of
the Majorana fermions and gauge fluxes emerging in Kitaev's honeycomb model.
These include counterintuitive manifestations of quantum number
fractionalisation, such as a neutron scattering response with a gap even in the
presence of gapless excitations, and a sharp component despite the
fractionalisation of electron spin. Our analysis identifies new varieties of
the venerable X-ray edge problem and explores connections to the physics of
quantum quenches.",1308.4336v1
2016-11-23,Dynamics of extended bodies with spin-induced quadrupole in Kerr spacetime: generic orbits,"We discuss motions of extended bodies in Kerr spacetime by using
Mathisson-Papapetrou-Dixon equations. We firstly solve the conditions for
circular orbits, and calculate the orbital frequency shift due to the mass
quadrupoles. The results show that we need not consider the spin-induced
quadrupoles in extreme-mass-ratio inspirals for spatial gravitational wave
detectors. We quantitatively investigate the temporal variation of rotational
velocity of the extended body due to the coupling of quadrupole and background
gravitational field. For generic orbits, we numerically integrate the
Mathisson-Papapetrou-Dixon equations for evolving the motion of an extended
body orbiting a Kerr black hole. By comparing with the monopole-dipole
approximation, we reveal the influences of quadrupole moments of extended
bodies on the orbital motion and chaotic dynamics of extreme-mass-ratio
systems. We do not find any chaotic orbits for the extended bodies with
physical spins and spin-induced quadrupoles. Possible implications for
gravitational wave detection and pulsar timing observation are outlined.",1611.07602v1
2016-11-23,Simultaneous measurement of two non-commuting quantum variables: Solution of a dynamical model,"The possibility of performing simultaneous measurements in quantum mechanics
is investigated in the context of the Curie-Weiss model for a projective
measurement. Concretely, we consider a spin-$\frac{1}{2}$ system simultaneously
interacting with two magnets, which act as measuring apparatuses of two
different spin components. We work out the dynamics of this process and
determine the final state of the measuring apparatuses, from which we can find
the probabilities of the four possible outcomes of the measurements. The
measurement is found to be non-ideal, as (i) the joint statistics do not
coincide with the one obtained by separately measuring each spin component, and
(ii) the density matrix of the spin does not collapse in either of the measured
observables. However, we give an operational interpretation of the process as a
generalised quantum measurement, and show that it is fully informative: The
expected value of the measured spin components can be found with arbitrary
precision for sufficiently many runs of the experiment.",1611.07937v3
2017-01-10,Attenuation of the NMR signal in a field gradient due to stochastic dynamics with memory,"The attenuation function S(t) for an ensemble of spins in a magnetic-field
gradient is calculated by accumulation of the phase shifts in the rotating
frame resulting from the displacements of spin-bearing particles. The found
S(t), expressed through the particle mean square displacement, is applicable
for any kind of stationary stochastic motion of spins, including their
non-markovian dynamics with memory. The known expressions valid for normal and
anomalous diffusion are obtained as special cases in the long time
approximation. The method is also applicable to the NMR pulse sequences based
on the refocusing principle. This is demonstrated by describing the Hahn spin
echo experiment. The attenuation of the NMR signal is also evaluated providing
that the random motion of particle is modeled by the generalized Langevin
equation with the memory kernel exponentially decaying in time.",1701.02486v1
2017-01-17,Dynamics of the Kitaev-Heisenberg Model,"We introduce a matrix-product state based method to efficiently obtain
dynamical response functions for two-dimensional microscopic Hamiltonians,
which we apply to different phases of the Kitaev-Heisenberg model. We find
significant broad high energy features beyond spin-wave theory even in the
ordered phases proximate to spin liquids. This includes the phase with zig-zag
order of the type observed in $\alpha$-RuCl$_3$, where we find high energy
features like those seen in inelastic neutron scattering experiments. Our
results provide an example of a natural path for proximate spin liquid features
to arise at high energies above a conventionally ordered state, as the diffuse
remnants of spin-wave bands intersect to yield a broad peak at the Brillouin
zone center.",1701.04678v1
2017-04-03,Spin dynamics and spin-dependent recombination of a polaron pair under a strong ac drive,"We study theoretically the recombination within a pair of two polarons in
magnetic field subject to a strong linearly polarized ac drive. Strong drive
implies that the Zeeman frequencies of the pair-partners are much smaller than
the Rabi frequency, so that the rotating wave approximation does not apply.
What makes the recombination dynamics nontrivial, is that the partners
recombine only when they form a singlet, S. By admixing singlet to triplets,
the drive induces the triplet recombination as well. We calculate the effective
decay rate of all four spin modes. Our main finding is that, under the strong
drive, the major contribution to the decay of the modes comes from short time
intervals when the driving field passes through zero. When the recombination
time in the absence of drive is short, fast recombination from S leads to
anomalously slow recombination from the other spin states of the pair. We show
that, with strong drive, this recombination becomes even slower. The
corresponding decay rate falls off as a power law with the amplitude of the
drive.",1704.00392v1
2017-04-18,Gate controlled spin-valley locking of resident carriers in WSe2 monolayers,"Using time-resolved Kerr rotation, we measure the spin/valley dynamics of
resident electrons and holes in single charge-tunable monolayers of the
archetypal transition-metal dichalcogenide (TMD) semiconductor WSe2. In the
n-type regime, we observe long (70 ns) polarization relaxation of electrons
that is sensitive to in-plane magnetic fields $B_y$, indicating spin
relaxation. In marked contrast, extraordinarily long (2 microsecond)
polarization relaxation of holes is revealed in the p-type regime, that is
unaffected by $B_y$, directly confirming long-standing expectations of strong
spin-valley locking of holes in the valence band of monolayer TMDs. Supported
by continuous-wave Kerr spectroscopy and Hanle measurements, these studies
provide a unified picture of carrier polarization dynamics in monolayer TMDs,
which can guide design principles for future valleytronic devices.",1704.05448v1
2013-08-31,Zeros of the partition function and dynamical singularities in spin-glass systems,"We study spin-glass systems characterized by continuous occurrence of
singularities. The theory of Lee-Yang zeros is used to find the singularities.
By using the replica method in mean-field systems, we show that two-dimensional
distributions of zeros of the partition function in a complex parameter plane
are characteristic feature of random systems. The results of several models
indicate that the concept of chaos in the spin-glass state is different from
that of the replica symmetry breaking. We discuss that a chaotic phase at
imaginary temperature is different from the spin-glass phase and is accessible
by quantum dynamics in a quenching protocol.",1309.0076v1
2014-05-10,"All-optical implementation of a dynamic-decoupling protocol for hole spins in (In,Ga)As quantum dots","We demonstrate the potential of a periodic laser-pulse protocol for dynamic
decoupling of hole spins in (In,Ga)As quantum dots from surrounding baths. When
doubling the repetition rate of inversionlaser pulses between two reference
pulses for orienting the spins, we find that the spin coherence time is
increased by a factor of two.",1405.2396v4
2015-12-11,Quantum spin dynamics and entanglement generation with hundreds of trapped ions,"Quantum simulation of spin models can provide insight into complex problems
that are difficult or impossible to study with classical computers. Trapped
ions are an established platform for quantum simulation, but only systems with
fewer than 20 ions have demonstrated quantum correlations. Here we study
non-equilibrium, quantum spin dynamics arising from an engineered, homogeneous
Ising interaction in a two-dimensional array of $^9$Be$^+$ ions in a Penning
trap. We verify entanglement in the form of spin-squeezed states for up to 219
ions, directly observing 4.0$\pm$0.9 dB of spectroscopic enhancement. We also
observe evidence of non-Gaussian, over-squeezed states in the full counting
statistics. We find good agreement with ab-initio theory that includes
competition between entanglement and decoherence, laying the groundwork for
simulations of the transverse-field Ising model with variable-range
interactions, for which numerical solutions are, in general, classically
intractable.",1512.03756v2
2016-08-19,Depolarization dynamics in a strongly interacting solid-state spin ensemble,"We study the depolarization dynamics of a dense ensemble of dipolar
interacting spins, associated with nitrogen-vacancy centers in diamond. We
observe anomalously fast, density-dependent, and non-exponential spin
relaxation. To explain these observations, we propose a microscopic model where
an interplay of long-range interactions, disorder, and dissipation leads to
predictions that are in quantitative agreement with both current and prior
experimental results. Our results pave the way for controlled many-body
experiments with long-lived and strongly interacting ensembles of solid-state
spins.",1608.05471v2
2016-08-21,Directly probing spin dynamics in insulating antiferromagnets using ultrashort terahertz pulses,"We investigate spin dynamics in the antiferromagnetic (AFM) multiferroic
TbMnO3 using optical- pump, terahertz (THz)-probe spectroscopy. Photoexcitation
results in a broadband THz transmission change, with an onset time of 25 ps at
6 K that becomes faster at higher temperatures. We attribute this time constant
to spin-lattice thermalization. The excellent agreement between our
measurements and previous ultrafast resonant x-ray diffraction measurements on
the same material confirms that our THz pulse directly probes spin order. We
suggest that this could be the case in general for insulating AFM materials, if
the origin of the static absorption in the THz spectral range is magnetic.",1608.05991v1
2016-08-29,Impurity effects on spin dynamics in magnetic and superconducting iron pnictides and chalcogenides,"In this paper we summarize the effects of magnetic and nonmagnetic impurities
on the spin dynamics in Febased superconductors and their parent compounds. The
effects of chemical substitution, vacancies, and disorder on the suppression or
stabilization of superconductivity and spin-density-wave phases are reviewed in
the context of recent neutron-spectroscopy measurements of spin excitations. We
also present new results on the structure of magnetic fluctuations in BaFe2As2
single crystals doped with Mn local moments and discuss them in relationship to
the previously reported (pi, pi) branch of checkerboard magnetic excitations.",1608.08123v4
2016-12-14,Measurement of the excited-state transverse hyperfine coupling in NV centers via dynamic nuclear polarization,"Precise knowledge of a quantum system's Hamiltonian is a critical
pre-requisite for its use in many quantum information technologies. Here, we
report a method for the precise characterization of the non-secular part of the
excited-state Hamiltonian of an electronic-nuclear spin system in diamond. The
method relies on the investigation of the dynamic nuclear polarization mediated
by the electronic spin, which is currently exploited as a primary tool for
initializing nuclear qubits and performing enhanced nuclear magnetic resonance.
By measuring the temporal evolution of the population of the ground-state
hyperfine levels of a nitrogen-vacancy center, we obtain the first direct
estimation of the excited-state transverse hyperfine coupling between its
electronic and nitrogen nuclear spin. Our method could also be applied to other
electron-nuclear spin systems, such as those related to defects in silicon
carbide.",1612.04783v2
2017-06-17,\emph{Ab initio} calculation of spin-orbit coupling for NV center in diamond exhibiting dynamic Jahn-Teller effect,"Point defects in solids may realize solid state quantum bits. The spin-orbit
coupling in these point defects plays a key role in the magneto-optical
properties that determine the conditions of quantum bit operation. However,
experimental data and methods do not directly yield this highly important data,
particularly, for such complex systems where dynamic Jahn-Teller (DJT) effect
damps the spin-orbit interaction. Here, we show for an exemplary quantum bit,
nitrogen-vacancy (NV) center in diamond, that \emph{ab initio} supercell
density functional theory provide quantitative prediction for the spin-orbit
coupling damped by DJT. We show that DJT is responsible for the multiple
intersystem crossing rates of NV center at cryogenic temperatures. Our results
pave the way toward optimizing solid state quantum bits for quantum information
processing and metrology applications.",1706.05523v2
2017-07-24,Magnetic order and spin dynamics in the helical magnetic system Fe$_3$PO$_4$O$_3$,"The 3$d$-electronic spin dynamics and the magnetic order in Fe$_3$PO$_4$O$_3$
were investigated by muon spin rotation and relaxation ($\mu$SR) and $^{57}$Fe
M\""ossbauer spectroscopy. Zero-field (ZF)-$\mu$SR and $^{57}$Fe M\""ossbauer
studies confirm static long range magnetic ordering below $T_{\mathrm{N}}$
$\approx$ 164\,K. Both transverse-field (TF) and ZF-$\mu$SR results evidence
100\% magnetic volume fraction in the ordered state. The ZF-$\mu$SR time
spectra can be best described by a Bessel function, which is consistent with
the helical magnetic structure proposed by neutron scattering experiments. The
M\""ossbauer spectra are described in detail by considering the specific angular
distribution of the local hyperfine field $B_{\mathrm{hyp}}$ with respect to
the local electric field gradient. The $\mu$SR spin-lattice relaxation rate
exhibits two peaks: One at the magnetic ordering temperature related to
critical magnetic fluctuations and another peak at 35\,K signaling the presence
of a secondary low energy scale in Fe$_3$PO$_4$O$_3$.",1707.07433v1
2017-07-29,Statistical mechanics of coevolving spin system,"We propose a statistical mechanics approach to a coevolving spin system with
an adaptive network of interactions. The dynamics of node states and network
connections is driven by both spin configuration and network topology. We
consider a Hamiltonian that merges the classical Ising model and the
statistical theory of correlated random networks. As a result, we obtain rich
phase diagrams with different phase transitions both in the state of nodes and
in the graph topology. We argue that the coupling between the spin dynamics and
the structure of the network is crucial in understanding the complex behavior
of real-world systems and omitting one of the approaches renders the
description incomplete.",1707.09495v3
2017-10-28,High frequency dynamics modulated by collective magnetization reversal in artificial spin ice,"Spin-torque ferromagnetic resonance (ST-FMR) arises in heavy
metal/ferromagnet heterostructures when an alternating charge current is passed
through the bilayer stack. The methodology to detect the resonance is based on
the anisotropic magnetoresistance, which is the change in the electrical
resistance due to different orientations of the magnetization. In connected
networks of ferromagnetic nanowires, known as artificial spin ice, the
magnetoresistance is rather complex owing to the underlying collective behavior
of the geometrically frustrated magnetic domain structure. Here, we demonstrate
ST-FMR investigations in a square artificial spin-ice system and correlate our
observations to magnetotransport measurements. The experimental findings are
described using a simulation approach that highlights the importance of the
correlated dynamics response of the magnetic system. Our results open the
possibility of designing reconfigurable microwave oscillators and
magnetoresistive devices based on connected networks of nanomagnets.",1710.10534v1
2017-12-14,Muon spin relaxation and inelastic neutron scattering investigations of all-in/all-out antiferromagnet Nd2Hf2O7,"Nd2Hf2O7, belonging to the family of geometrically frustrated cubic rare
earth pyrochlore oxides, was recently identified to order antiferromagnetically
below T_N = 0.55 K with an all-in/all-out arrangement of Nd3+ moments, however
with a much reduced ordered state moment. Herein we investigate the spin
dynamics and crystal field states of Nd2Hf2O7 using muon spin relaxation (muSR)
and inelastic neutron scattering (INS) measurements. Our muSR study confirms
the long range magnetic ordering and shows evidence for coexisting persistent
dynamic spin fluctuations deep inside the ordered state down to 42 mK. The INS
data show the crytal electric field (CEF) excitations due to the transitions
both within the ground state multiplet and to the first excited state
multiplet. The INS data are analyzed by a model based on CEF and crystal field
states are determined. Strong Ising-type anisotropy is inferred from the ground
state wavefunction. The CEF parameters indicate the CEF-split Kramers doublet
ground state of Nd3+ to be consistent with the dipolar-octupolar character.",1712.05201v1
2017-12-18,Dipole-like dynamical nuclear spin polarization around a quantum point contact,"We theoretically investigate the dynamical nuclear spin polarization in a
quantum point contact (QPC) at finite magnetic field. We find that when the QPC
is tuned to be spin selective, at the conductance of e^2/h, a finite bias
induces a dipole-like (spatially anti-symmetric) nuclear polarization: at the
QPC center the polarization is zero, while, for GaAs parameters, the nuclear
spins down (up) are induced on the source (drain) side. We predict that the
dipole-like polarization pattern can be distinguished from a uniform
polarization due to a qualitatively different response of the QPC conductance
to the NMR field.",1712.06280v2
2018-01-23,Cooperation between coherent control and noises in quantum metrology,"In this paper we study the cooperation between coherent control and noises in
open spin systems, aiming to demonstrate that such cooperation can provide new
possibilities for parametrization in quantum metrology. The cooperative scheme
proposed here outperforms the standard scheme, with higher precision achieved.
More specifically, we illustrate the effect of cooperative interaction between
coherent control and noises in conventional single-spin systems described by
Lindblad master equations, with the magnitude of a magnetic field taken as the
parameter to be estimated and encoded in the noisy dynamics besides the
Hamiltonian. The scenarios of both spontaneous emission and dephasing noise
have been analyzed, where the associated quantum Fisher information has been
given. Furthermore, it has been demonstrated that in the realm where quantum
metrology is mostly applied in practice, the precision limit under the
cooperative scheme in the presence of noises can surpass the ultimate precision
limit under the unitary dynamics. On the other hand, multiple-spin systems have
also been considered. We show that the coupling between different spins can
help realize non-local parametrization under the cooperative scheme, with the
ground state made entangled. This thus leads to the improvement of precision
limit, which has been proved and visualized in our paper.",1801.07563v2
2018-10-26,Correlated Quantum Tunnelling of Monopoles in Spin Ice,"The spin ice materials Ho$_{2}$Ti$_{2}$O$_{7}$ and Dy$_{2}$Ti$_{2}$O$_{7}$
are by now perhaps the best-studied classical frustrated magnets. A crucial
step towards the understanding of their low temperature behaviour -- both
regarding their unusual dynamical properties and the possibility of observing
their quantum coherent time evolution -- is a quantitative understanding of the
spin-flip processes which underpin the hopping of magnetic monopoles. We attack
this problem in the framework of a quantum treatment of a single-ion subject to
the crystal, exchange and dipolar fields from neighbouring ions. By studying
the fundamental quantum mechanical mechanisms, we discover a bimodal
distribution of hopping rates which depends on the local spin configuration, in
broad agreement with rates extracted from experiment. Applying the same
analysis to Pr$_{2}$Sn$_{2}$O$_{7}$ and Pr$_{2}$Zr$_{2}$O$_{7}$, we find an
even more pronounced separation of timescales signalling the likelihood of
coherent many-body dynamics.",1810.11469v3
2018-10-31,Dynamical Charge Structure Factor of a One-Dimensional Ionic Hubbard Model in the Low-Energy Region,"We present a numerical study of the charge dynamical structure factor
N(k,omega) of a one-dimensional (1D) ionic Hubbard model in the Mott insulator
phase. We show that the low-energy spectrum of N(k,omega) is expressed in terms
of the spin operators for the spin degrees of freedom. Numerical results of
N(k,omega) for the spin degrees of freedom, obtained by the Lanczos
diagonalization method, well reproduce the low-energy spectrum of N(k,omega) of
the 1D ionic Hubbard model. In addition, we show that these spectral peaks
probe the dispersion of the spin-singlet excitations of the system and are
observed in the wide parameter region of the MI phase.",1810.13106v4
2019-06-12,Dynamic nuclear spin polarization induced by Edelstein effect at Bi(111) surfaces,"Nuclear spin polarization induced by hyperfine interaction and the Edelstein
effect due to strong spin-orbit interaction is investigated by quantum
transport in Bi(111) thin film samples. The Bi(111) films are deposited on mica
by van der Waals epitaxial growth. The Bi(111) films show micrometer-sized
triangular islands with 0.39 nm step height, corresponding to the Bi(111)
bilayer height. At low temperatures a high current density is applied to
generate a non-equilibrium carrier spin polarization by the Edelstein effect at
the Bi(111) surface, which then induces dynamic nuclear polarization by
hyperfine interaction. Comparative quantum magnetotransport antilocalization
measurements indicate a suppression of antilocalization by the in-plane
Overhauser field from the nuclear polarization and allow a quantification of
the Overhauser field. Hence nuclear polarization was both achieved and
quantified by a purely electronic transport-based approach.",1906.05408v2
2019-07-17,Inhomogeneous domain walls in spintronic nanowires,"In case of a spin-polarized current, the magnetization dynamics in nanowires
are governed by the classical Landau-Lifschitz equation with Gilbert damping
term, augmented by a typically non-variational Slonczewski term. Taking axial
symmetry into account, we study the existence of domain wall type coherent
structure solutions, with focus on one space dimension and spin-polarization,
but our results also apply to vanishing spin-torque term. Using methods from
bifurcation theory for arbitrary constant applied fields, we prove the
existence of domain walls with non-trivial azimuthal profile, referred to as
inhomogeneous. We present an apparently new type of domain wall, referred to as
non-flat, whose approach of the axial magnetization has a certain oscillatory
character. Additionally, we present the leading order mechanism for the
parameter selection of flat and non-flat inhomogeneous domain walls for an
applied field below a threshold, which depends on anisotropy, damping, and
spin-transfer. Moreover, numerical continuation results of all these domain
wall solutions are presented.",1907.07470v2
2019-07-23,Controlling decoherence via $\mathcal{PT}$-symmetric non-Hermitian open quantum systems,"We have studied the effect of a non-Hermitian Bosonic bath on the dynamics of
a two-level spin system. The non-Hermitian Hamiltonian of the bath is chosen
such that it converges to the harmonic oscillator Hamiltonian when the
non-Hermiticity is switched off. We calculate the dynamics of the spin system
and found that the non-Hermiticity can have positive as well as negative
effects on the coherence of the system. However, the decoherence can be
completely eliminated by choosing the non-Hermiticity parameter and the phase
of the system bath interaction appropriately. We have also studied the effect
of this bath on the entanglement of a two-spin system when the bath is acting
only on one spin.",1907.11088v1
2020-01-22,Resonant Precession Modulation Based Magnetic Field Receivers,"Antenna technology provides the crucial interface between electronic devices
and electromagnetic waves required for wireless communications. This technology
has operated under largely the same general principles for over a century,
resulting in stagnation of advancements in modern times and fundamentally
limiting the extent to which potential applications of wireless communications
may be realized. Herein we propose a novel concept for antenna operation
employing the nonlinear precession dynamics of subatomic spins. An
electromagnetic wave incident on a precessing spin will serve to modulate the
spin frequency of precession. Antennas operating based on a detection of these
spin dynamics are then able to fully characterize the incident wave while
achieving substantial amplifications, higher sensitivities, and smaller form
factors as compared to conventional antennas. A preliminary experimental
implementation of the proposed concept establishes its feasibility and is
already able to demonstrate significant amplification and size benefits.",2001.08059v1
2020-01-25,Theory of field-modulated spin-valley-orbital pseudospin physics,"Pioneering studies in transition metal dichalcogenides have demonstrated
convincingly the co-existence of multiple angular momentum degrees of freedom
-- of spin (1/2 $s_z = \pm 1/2$), valley ($\tau = K, K'$ or $\pm 1$), and
atomic orbital ($l_z = \pm 2$) origins -- in the valence band with strong
interlocking among them, which results in noise-resilient pseudospin states
ideal for spintronic type applications. With field modulation a powerful,
universal means in physics studies and applications, this work develops, from
bare models in the context of complicated band structure, a general effective
theory of field-modulated spin-valley-orbital pseudospin physics that is able
to describe both intra- and inter- valley dynamics. Based on the theory, it
predicts and discusses the linear response of a pseudospin to external fields
of arbitrary orientations. Paradigm field configurations are identified for
pseudospin control including pseudospin flipping. For a nontrivial example, it
presents a spin-valley-orbital quantum computing proposal, where the theory is
applied to address all-electrical, simultaneous control of $s_z$, $\tau$, and
$l_z$ for qubit manipulation. It demonstrates the viability of such control
with static field effects and an additional dynamic electric field. An
optimized qubit manipulation time ~ O(ns) is given.",2001.09255v1
2020-02-03,Theory of Spin-Dependent Electron Transfer Dynamics at Ar/Co(0001) and Ar/Fe(110) Interfaces,"Recent core-hole-clock experiments [Phys. Rev. Lett. $\textbf{112}$, 086801
(2014)] showed that the spin dependence of electron injection times at
Ar/Co(0001) and Ar/Fe(110) interfaces is at variance with the expectations
based on previous calculations for related systems. Here we reconcile theory
and experiment, and demonstrate that the observed dependence is rooted in the
details of the spin-split surface band structures. Our ab initio calculations
back that minority electrons are injected significantly faster than majority
electrons in line with the experimentally reported ultrashort injection times.
The dynamics is particularly sensitive to the size (in reciprocal-space) of the
projected band gaps around $\overline{\Gamma}$ for both substrates at the
resonance energies. A simple tunneling model incorporating the spin-dependent
gap sizes further supports these findings.",2002.01042v1
2020-04-02,Simulation of XXZ Spin Models using Sideband Transitions in Trapped Bosonic Gases,"We theoretically propose and experimentally demonstrate the use of motional
sidebands in a trapped ensemble of $^{87}$Rb atoms to engineer tunable
long-range XXZ spin models. We benchmark our simulator by probing a
ferromagnetic to paramagnetic dynamical phase transition in the
Lipkin-Meshkov-Glick (LMG) model, a collective XXZ model plus additional
transverse and longitudinal fields, via Rabi spectroscopy. We experimentally
reconstruct the boundary between the dynamical phases, which is in good
agreement with mean-field theoretical predictions. Our work introduces new
possibilities in quantum simulation of anisotropic spin-spin interactions and
quantum metrology enhanced by many-body entanglement.",2004.01282v2
2020-04-06,Interplay of spin mode locking and nuclei-induced frequency focusing in quantum dots,"We study the influence of nuclei-induced frequency focusing on the mode
locking of spin coherence in quantum dots subjected to a periodic train of
optical pulses. In particular, we address the question whether or not
nuclei-induced frequency focusing always enhances the effect of spin mode
locking. We combine two advanced semiclassical approaches and extend the
resulting model by including the full dynamics of the optically excited trion
state. In order to reduce the discrepancy to a full quantum model, we establish
a nondeterministic pulse description by interpreting each pump pulse as a
measurement. Both extensions lead to significant qualitative changes of the
physics. Their combination improves the description of the corresponding
experiments. Importantly, we observe the emergence of dynamic nuclear
polarization, i.e., the formation of a nonzero average polarization of the
nuclear spin bath, leading to a certain increase of the coherence time.",2004.02623v3
2020-04-22,Dynamic Rashba-Dresselhaus Effect,"The Rashba-Dresselhaus effect is the splitting of doubly degenerate band
extrema in semiconductors, accompanied by the emergence of counter-rotating
spin textures and spin-momentum locking. Here we investigate how this effect is
modified by lattice vibrations. We show that, in centrosymmetric non-magnetic
crystals, for which a bulk Rashba-Dresselhaus effect is symmetry-forbidden,
electron-phonon interactions can induce a phonon-assisted, dynamic
Rashba-Dresselhaus spin splitting in the presence of an out-of-equilibrium
phonon population. In particular, we show how Rashba, Dresselhaus, or Weyl spin
textures can selectively be established by driving coherent infrared-active
phonons, and we perform ab initio calculations to quantify this effect for
halide perovskites.",2004.10477v2
2020-12-01,Nanocontact vortex oscillators based on Co$_2$MnGe pseudo-spin valves,"We present an experimental study of vortex dynamics in magnetic nanocontacts
based on pseudo spin valves comprising the Co$_2$MnGe Heusler compound. The
films were grown by molecular beam epitaxy, where precise stoichiometry control
and tailored stacking order allowed us to define the bottom ferromagnetic layer
as the reference layer, with minimal coupling between the free and reference
layers. 20-nm diameter nanocontacts were fabricated using a nano-indentation
technique, leading to self-sustained gyration of the vortex generated by
spin-transfer torques above a certain current threshold. By combining
frequency- and time-domain measurements, we show that different types of
spin-transfer induced dynamics related to different modes associated to the
magnetic vortex configuration can be observed, such as mode hopping, mode
coexistence and mode extinction appear in addition to the usual gyration mode.",2012.00522v3
2020-12-07,Where does the spin angular momentum go in laser induced demagnetisation?,"The dynamics of ultrafast demagnetisation in 3$d$ magnets is complicated by
the presence of both spin ${\v S}$ and orbital ${\v L}$ angular momentum, with
the microscopic mechanism by which the magnetic moment is redistributed to the
lattice, and at what time scales, yet to be resolved. Employing
state-of-the-art time dependent density function theory we disentangle the
dynamics of these two momenta. Utilising ultra short (5~fs) pulses that
separate spin-orbit (SO) and direct optical excitation time scales, we
demonstrate a two-step microscopic mechanism: (i) an initial loss of ${\v L}$
due to laser excitation, followed post pulse by (ii) an increase of ${\v L}$ as
${\v S}$ transfers to ${\v L}$ during subsequent ($> 15$~fs) SO induced
spin-flip demagnetisation. We also show that to see an unambiguous transfer of
${\v S}$ to ${\v L}$ a short pulse is required.",2012.03657v1
2020-12-16,Observation of spin-exchange dynamics between itinerant and localized $^{171}\mathrm{Yb}$ atoms,"We report on the observation of the spin-exchange dynamics of
$^{171}\mathrm{Yb}$ atoms in the ground state $^1\mathrm{S}_0$ and in the
metastable state $^3\mathrm{P}_0$. We implement the mixed-dimensional
two-orbital system using a near-resonant and magic-wavelength optical lattices,
where the $^1\mathrm{S}_0$ and $^3\mathrm{P}_0$ atoms are itinerant in a
one-dimensional tube and localized in three dimensions, respectively. By
exploiting an optical Stern-Gerlach method, we observe the spin depolarization
of the $^1\mathrm{S}_0$ atoms induced by the spin-exchange interaction with the
$^3\mathrm{P}_0$ atom. Our work could open the way to the quantum simulation of
the Kondo effect.",2012.08708v2
2021-01-03,Magnon-polaron formation in XXZ quantum Heisenberg chains,"We study the formation of magnon-polaron excitations and the consequences of
different time scales between the magnon and lattice dynamics. The spin-spin
interactions along the 1D lattice are ruled by a Heisenberg Hamiltonian in the
anisotropic form XXZ, in which each spin exhibits a vibrational degree of
freedom around its equilibrium position. By considering a magnetoelastic
coupling as a linear function of the relative displacement between
nearest-neighbor spins, results provide an original framework for achieving a
hybridized state of magnon-polaron. Such state is characterized by high
cooperation between the underlying excitations, where the traveling or
stationary formation of magnon-polaron depends on the effective magnetoelastic
coupling. A systematic investigation reveals the critical amount of the
magnon-lattice interaction ($\chi_c$) necessary to emergence of the stationary
magnon-polaron quasi-particle. Different characteristic time scales of the
magnon and the vibrational dynamics unveiled the threshold between the two
regimes, as well as a limiting value of critical magnetoelastic interaction,
above which the magnon velocity no longer interferes at the critical
magnetoelastic coupling capable of inducing the stationary regime.",2101.00673v1
2021-01-15,Linear and Nonlinear Optical Responses in Kitaev Spin Liquids,"We theoretically study THz-light-driven high-harmonic generation (HHG) in the
spin-liquid states of the Kitaev honeycomb model with a magnetostriction
coupling between spin and electric polarization. To compute the HHG spectra, we
numerically solve the Lindblad equation, taking account of the dissipation
effect. We find that isotropic Kitaev models possess a dynamical symmetry,
which is broken by a static electric field, analogous to HHG in electron
systems. We show that the HHG spectra exhibit characteristic continua of
Majorana fermion excitations, and their broad peaks can be controlled by
applying static electric or magnetic fields. In particular, the magnetic-field
dependence of the HHG spectra drastically differs from those of usual ordered
magnets. These results indicate that an intense THz laser provides a powerful
tool to observe dynamic features of quantum spin liquids.",2101.06081v2
2021-01-23,Non-Markovian effects in the spin-boson model at zero temperature,"We investigate memory effects in the spin-boson model using a recently
proposed measure for non-Markovian behavior based on the information exchange
between an open system and its environment. Employing the numerical exact
multilayer multiconfguration time-dependent Hartree approach, we simulate the
dynamics of the spin-boson model at zero temperature for a broad range of
parameters. For a fast bath, i.e. in the scaling limit, we find non-Markovian
dynamics for a coherently decaying spin at weak system-bath coupling, whereas
memory effects are absent for stronger coupling in the regimes of incoherent
decay and localization. If the time scales of system and bath are comparable, a
complex, non-monotonic dependence of non-Markovianity on the system-bath
coupling strength is observed.",2101.09463v1
2021-01-29,Hierarchical excitations from correlated spin tetrahedra on the breathing pyrochlore lattice,"The hierarchy of the coupling strengths in a physical system often engenders
an effective model at low energies where the decoupled high-energy modes are
integrated out. Here, using neutron scattering, we show that the spin
excitations in the breathing pyrochlore lattice compound CuInCr$_4$S$_8$ are
hierarchical and can be approximated by an effective model of correlated
tetrahedra at low energies. At higher energies, intra-tetrahedron excitations
together with strong magnon-phonon couplings are observed, which suggests the
possible role of the lattice degree of freedom in stabilizing the spin
tetrahedra. Our work illustrates the spin dynamics in CuInCr$_4$S$_8$ and
demonstrates a general effective-cluster approach to understand the dynamics on
the breathing-type lattices.",2101.12363v1
2000-06-07,Independent freezing of charge and spin dynamics in La1.5Sr0.5CoO4,"We present elastic and quasielastic neutron scattering measurements
characterizing peculiar short-range charge-orbital and spin order in the
layered perovskite material La1.5Sr0.5CoO4. We find that below Tc~750 K holes
introduced by Sr doping lose mobility and enter a statically ordered {\it
charge glass} phase with loosely correlated checkerboard arrangement of empty
and occupied d{3z2-r2} orbitals (Co3+ and Co2+). The dynamics of the resultant
mixed spin system is governed by the anisotropic nature of the crystal-field
Hamiltonian and the peculiar exchange pattern produced by the orbital order. It
undergoes a {\it spin freezing} transition at much a lower temperature, Ts~30
K.",0006115v1
2012-05-21,Tuning non-Markovianity by spin-dynamics control,"We study the interplay between forgetful and memory-keeping evolution
enforced on a two-level system by a multi-spin environment whose elements are
coupled to local bosonic baths. Contrarily to the expectation that any
non-Markovian effect would be buried by the forgetful mechanism induced by the
spin-bath coupling, one can actually induce a full Markovian-to-non-Markovian
transition of the two-level system's dynamics, controllable by parameters such
as the mismatch between the energy of the two-level system and of the spin
environment. For a symmetric coupling, the amount of non-Markovianity
surprisingly grows with the number of decoherence channels.",1205.4535v2
2017-11-15,Spin-orbit coupled bosons in one dimension: emergent gauge field and Lifshitz transition,"In the presence of strong spin-independent interactions and spin-orbit
coupling, we show that the spinor Bose liquid confined to one spatial dimension
undergoes an interaction- or density-tuned quantum phase transition similar to
one theoretically proposed for itinerant magnetic solid-state systems. The
order parameter describes broken $Z_2$ inversion symmetry, with the ordered
phase accompanied by non-vanishing momentum which is generated by fluctuations
of an emergent dynamical gauge field at the phase transition. This quantum
phase transition has dynamical critical exponent $z \simeq 2$, typical of a
Lifshitz transition, but is described by a nontrivial interacting fixed point.
From direct numerical simulation of the microscopic model, we extract
previously unknown critical exponents for this fixed point. Our model describes
a realistic situation of 1D ultracold atoms with Raman-induced spin-orbit
coupling, establishing this system as a platform for studying exotic critical
behavior of the Hertz-Millis type.",1711.05794v2
2017-11-29,Continuous-spin mixed-symmetry fields in AdS(5),"Free mixed-symmetry continuous-spin fields propagating in AdS(5) space and
flat R(4,1) space are studied. In the framework of a light-cone gauge
formulation of relativistic dynamics, we build simple actions for such fields.
Realization of relativistic symmetries on space of light-cone gauge
mixed-symmetry continuous-spin fields is also found. Interrelations between
constant parameters entering the light-cone gauge actions and eigenvalues of
the Casimir operators of space-time symmetry algebras are obtained. Using these
interrelations and requiring that the field dynamics in AdS(5) be irreducible
and classically unitary, we derive restrictions on the constant parameters and
eigenvalues of the 2nd-order Casimir operator of the so(4,2) algebra.",1711.11007v2
2018-03-13,Fast electron spin flips via strong subcycle electric excitation,"An important goal in quantum information processing is to reduce the duration
of quantum-logical operations. Motivated by this, we provide a theoretical
analysis of electrically induced fast dynamics of a single-electron spin-orbit
qubit. We study the example of a one-dimensional quantum dot with Rashba
spin-orbit interaction and harmonic driving, and focus on the case of strong
driving, when the real-space oscillation amplitude of the driven electron is
comparable to the width of its wave function. We provide simple approximate
analytical relations between the qubit Larmor frequency, the shortest
achievable qubit-flip time, and the driving amplitude required for the shortest
achievable qubit flip. We find that these relations compare well with results
obtained from numerical simulations of the qubit dynamics. Based on our
results, we discuss practical guidelines to maximize speed and quality of
electric single-qubit operations on spin-orbit qubits.",1803.04677v1
2018-03-19,Quenched dynamics and spin-charge separation in an interacting topological lattice,"We analyze the static and dynamical properties of a one-dimensional
topological lattice, the fermionic Su-Schrieffer-Heeger model, in the presence
of on-site interactions. Based on a study of charge and spin correlation
functions, we elucidate the nature of the topological edge modes, which
depending on the sign of the interactions, either display particles of opposite
spin on opposite edges, or a pair and a holon. This study of correlation
functions also highlights the strong entanglement that exists between the
opposite edges of the system. This last feature has remarkable consequences
upon subjecting the system to a quench, where an instantaneous edge-to-edge
signal appears in the correlation functions characterizing the edge modes.
Besides, other correlation functions are shown to propagate in the bulk
according to the light-cone imposed by the Lieb-Robinson bound. Our study
reveals how one-dimensional lattices exhibiting entangled topological edge
modes allow for a non-trivial correlation spreading, while providing an
accessible platform to detect spin-charge separation using state-of-the-art
experimental techniques.",1803.06957v2
2018-06-18,Non-perturbative spinning black holes in dynamical Chern-Simons gravity,"Spinning black holes in dynamical Einstein-Chern-Simons gravity are
constructed by directly solving the field equations, without resorting to any
perturbative expansion. This model is obtained by adding to the
Einstein-Hilbert action a particular higher-curvature correction: the
Pontryagin density, linearly coupled to a scalar field. The spinning black
holes are stationary, axi-symmetric, asymptotically flat generalisations of the
Kerr solution of Einstein's gravity, but they possess a non-trivial
(odd-parity) scalar field. They are regular on and outside the horizon and
satisfy a generalized Smarr relation. We discuss the deviations from Kerr at
the level of the spin and mass distribution, the horizon angular velocity, the
ergo-region and some basic properties of geodesic motion. For sufficiently
small values of the Chern-Simons coupling our results match those previously
obtained using a perturbative approach.",1806.06700v2
2018-07-06,Spin-torque-induced magnetization dynamics in ferrimagnets based on Landau-Lifshitz-Bloch Equation,"A theoretical model based on the Landau-Lifshitz-Bloch equation is developed
to study the spin-torque effect in ferrimagnets. Experimental findings, such as
the temperature dependence, the peak in spin torque, and the angular-momentum
compensation, can be well captured. In contrast to the ferromagnet system, the
switching trajectory in ferrimagnets is found to be precession free. The two
sublattices are not always collinear, which produces large exchange field
affecting the magnetization dynamics. The study of material composition shows
the existence of an oscillation region at intermediate current density, induced
by the nondeterministic switching. Compared to the Landau-Lifshitz-Gilbert
model, our developed model based on the Landau-Lifshitz-Bloch equation enables
the systematic study of spin-torque effect and the evaluation of
ferrimagnet-based devices.",1807.02445v1
2018-07-12,Particle-in-cell simulation of ultrafast hot-carrier transport in Fe/Au-heterostructures,"We describe a theoretical approach for spin-polarized hot-electron transport,
as it occurs after excitation by ultrafast optical pulses in heterostructures
formed by ferromagnetic and normal metals. We formulate a spin-dependent
particle-in-cell model that solves the Boltzmann equation for excited
electrons. It includes lifetimes and transmission coefficients as parameters,
which can be taken from ab-initio calculations or experiment, and can be easily
extended to multilayer systems. This approach is capable of describing electron
transport in the ballistic, super-diffusive and diffusive regime including
secondary-carrier generation. We apply the model to optically excited carriers
in Fe/Au bilayers and Fe/Au/Fe spin-valve structures. We gain microscopic
insight into the hot-electron transport dynamics probed in recent experiments
on spin-valves. We find contributions to the demagnetization dynamics induced
in Fe/Au/Fe trilayers regardless of the parallel or antiparallel magnetic
alignment of the Fe layers.",1807.04733v2
2018-07-13,Dynamic imaging of an antiferromagnetic domain wall via quantum-impurity relaxometry,"While spin textures in materials exhibiting zero net magnetization, such as
antiferromagnetic domain walls (DWs), have attracted much interest lately due
to their robustness against external magnetic noise, their generic detection
via conventional magnetometry remains a challenging task. Here, we propose
quantum relaxometry as a new route to image spin textures by probing the
collective spin modes harbored by them. We investigate the Goldstone modes
hosted by an antiferromagnetic domain wall and assess the relaxation rate of a
quantum-spin sensor interacting with them. We show that such modes can be
detected via relaxometry in some common antiferromagnets. Moreover, based on
symmetry considerations, we propose a simple protocol to probe the individual
dynamics of each mode.",1807.05114v1
2018-07-17,Black hole spin from wobbling and rotation of the M87 jet and a sign of a magnetically arrested disc,"New long-term Very Long Baseline Array observations of the well-known jet in
the M87 radio galaxy at 43 GHz show that the jet experiences a sideways shift
with an approximately 8-10 yr quasi-periodicity. Such jet wobbling can be
indicative of a relativistic Lense-Thirring precession resulting from a tilted
accretion disc. The wobbling period together with up-to-date kinematic data on
jet rotation opens up the possibility for estimating angular momentum of the
central supermassive black hole. In the case of a test-particle precession, the
specific angular momentum is $J/Mc=(2.7\pm1.5)\times10^{14}$ cm, implying
moderate dimensionless spin parameters $a=0.5\pm0.3$ and $0.31\pm0.17$ for
controversial gas-dynamic and stellar-dynamic black hole masses. However, in
the case of a solid-body-like precession, the spin parameter is much smaller
for both masses, $0.15\pm0.05$. Rejecting this value on the basis of other
independent spin estimations requires the existence of a magnetically arrested
disc in M87.",1807.06296v1
2018-08-15,Difference in charge and spin dynamics in a quantum dot-lead coupled system,"We analyze time evolution of charge and spin states in a quantum dot coupled
to an electric reservoir. Utilizing high-speed single-electron detection, we
focus on dynamics induced by the first-order tunneling. We find that there is a
difference between the spin and the charge relaxation: the former appears
slower than the latter. The difference depends on the Fermi occupation factor
and the spin relaxation becomes slower when the energy level of the quantum dot
is lowered. We explain this behavior by a theory which includes the first-order
tunneling processes. We conduct detailed comparison of the experiment and the
theory with changing the energy of the quantum dot levels, and the theory can
reproduce the experimental results.",1808.05303v1
2018-08-17,Distinct Nature of Orbital Selective Mott Phases Dominated by the Low-energy Local Spin Fluctuations,"Quantum orbital selective Mott (OSM) transitions are investigated within
dynamical mean-field theory based on a two-orbital Hubbard model with different
bandwidth at half filling. We find two distinct OSM phases both showing
coexistence of itinerant electrons and localized spins, dependent on whether
the Hund's coupling is full or of Ising type. The critical values and the
nature of the OSM transitions are efficiently determined by entanglement
entropy. We reveal that vanishing of the Kondo energy scale evidenced by
absence of local spin fluctuations at low frequency in local dynamical spin
susceptibility is responsible for the appearance of non-Fermi-liquid OSM phase
in Ising Hund's coupling case. We argue that this scenario can also be applied
to account for emergent quantum non-Fermi liquid in one-band Hubbard model when
short-range antiferromagnetic order is considered.",1808.05786v1
2018-08-22,On the Equivalence between Spin and Charge Dynamics of the Fermi Hubbard Model,"Utilizing the Fermi gas microscope, recently the MIT group has measured the
spin transport of the Fermi Hubbard model starting from a spin-density-wave
state, and the Princeton group has measured the charge transport of the Fermi
Hubbard model starting from a charge-density-wave state. Motivated by these two
experiments, we prove a theorem that shows under certain conditions, the spin
and charge transports can be equivalent to each other. The proof makes use of
the particle-hole transformation of the Fermi Hubbard model and a recently
discovered symmetry protected dynamical symmetry. Our results can be directly
verified in future cold atom experiment with the Fermi gas microscope.",1808.07225v2
2018-12-03,Spinning-black-hole scattering and the test-black-hole limit at second post-Minkowskian order,"Recently, the gravitational scattering of two black holes (BHs) treated at
the leading order in the weak-field, or post-Minkowskian (PM), approximation to
General Relativity has been shown to map bijectively onto a simpler effectively
one-body process: the scattering of a test BH in a stationary BH spacetime.
Here, for BH spins aligned with the orbital angular momentum, we propose a
simple extension of that mapping to 2PM order. We provide evidence for the
validity and utility of this 2PM mapping by demonstrating its compatibility
with all known analytical results for the conservative local-in-time dynamics
of binary BHs in the post-Newtonian (weak-field and slow-motion) approximation
and, separately, in the test-BH limit. Our result could be employed in the
construction of improved effective-one-body models for the conservative
dynamics of inspiraling spinning binary BHs.",1812.00956v2
2018-12-14,Non-ergodic extended phase of the Quantum Random Energy model,"The concept of non-ergodicity in quantum many body systems can be discussed
in the context of the wave functions of the many body system or as a property
of the dynamical observables, such as time-dependent spin correlators. In the
former approach the non-ergodic delocalized states is defined as the one in
which the wave functions occupy a volume that scales as a non-trivial power of
the full phase space. In this work we study the simplest spin glass model and
find that in the delocalized non-ergodic regime the spin-spin correlators decay
with the characteristic time that scales as non-trivial power of the full
Hilbert space volume. The long time limit of this correlator also scales as a
power of the full Hilbert space volume. We identify this phase with the glass
phase whilst the many body localized phase corresponds to a 'hyperglass' in
which dynamics is practically absent. We discuss the implications of these
finding to quantum information problems.",1812.06016v2
2018-12-30,Spin chains for two-qubit teleportation,"Generating high-quality multi-particle entanglement between communicating
parties is the primary resource in quantum teleportation protocols. To this
aim, we show that the natural dynamics of a single spin chain is able to
sustain the generation of two pairs of Bell states - possibly shared between a
sender and a distant receiver - which can in turn enable two-qubit
teleportation. In particular, we address a spin-1/2 chain with XX interactions,
connecting two pairs of spins located at its boundaries, playing the roles of
sender and receiver. In the regime where both end pairs are weakly coupled to
the spin chain, it is possible to generate at predefinite times a state that
has vanishing infidelity with the product state of two Bell pairs, thereby
providing nearly unit fidelity of teleportation. We also derive an effective
Hamiltonian via a second-order perturbation approach that faithfully reproduces
the dynamics of the full system.",1812.11609v1
2019-01-05,Canonical Quantization of Noncompact Spin System,"We consider spin system defined on the coadjoint orbit with noncompact
symmetry and investigate the quantization. Classical spin with noncompact
SU(N,1) symmetry is first formulated as a dynamical system and the constraint
analysis is performed to reduce the system from the group space to the
coadjoint orbit which is a symplectic manifold with Kahler structure. We
achieve this by solving the constraint directly. It is shown that the dynamical
variables describing the noncompact spins can be written as functions of
canonically conjugate variables and canonical quantization is possible on the
reduced phase space. With the quantum mechanical Hamiltonian acting on the
holomorphic coherent state in Hilbert space, we obtain the exact propagator by
solving the time-dependent Schrodinger equation.",1901.02524v1
2019-01-25,Domain wall dynamics in the Landau--Lifshitz magnet and the classical-quantum correspondence for spin transport,"We investigate the dynamics of spin in the axially anisotropic
Landau--Lifshitz field theory with a magnetic domain wall initial condition.
Employing the analytic scattering technique, we obtain the exact scattering
data and reconstruct the time-evolved profile. We identify three qualitatively
distinct regimes of spin transport, ranging from ballistic expansion in the
easy-plane regime, absence of transport in the easy-axis regime and
log-modified diffusion for the isotropic interaction. Our results are in
perfect qualitative agreement with those found in the anisotropic quantum
Heisenberg spin-$1/2$ chain, indicating a remarkable classical-quantum
correspondence for macroscopic spin transport.",1901.08944v2
2019-03-01,Nanoscale X-Ray Imaging of Spin Dynamics in Yttrium Iron Garnet,"Time-resolved scanning transmission x-ray microscopy (TR-STXM) has been used
for the direct imaging of spin wave dynamics in thin film yttrium iron garnet
(YIG) with spatial resolution in the sub 100 nm range. Application of this
x-ray transmission technique to single crystalline garnet films was achieved by
extracting a lamella (13x5x0.185 $\mathrm{\mu m^3}$) of liquid phase epitaxy
grown YIG thin film out of a gadolinium gallium garnet substrate. Spin waves in
the sample were measured along the Damon-Eshbach and backward volume directions
of propagation at gigahertz frequencies and with wavelengths in a range between
100~nm and 10~$\mathrm{\mu}$m. The results were compared to theoretical models.
Here, the widely used approximate dispersion equation for dipole-exchange spin
waves proved to be insufficient for describing the observed Damon-Eshbach type
modes. For achieving an accurate description, we made use of the full
analytical theory taking mode-hybridization effects into account.",1903.00498v1
2019-03-13,Quantum synchronization in a collision model,"We reveal the emergence of environment-induced spontaneous synchronization
between two spin-1/2 quantum objects in a collision model setting. In
particular, we determine the conditions for the dynamical establishment of
synchronous evolution between local spin observables of a pair of spins
undergoing open-system dynamics in the absence of an external drive. Exploiting
the versatility of the collision model framework, we show that the formation of
quantum or classical correlations between the principal spin pair are of no
significant relevance to the manifestation of spontaneous quantum
synchronization between them. Furthermore, we discuss the consequences of
thermal effects on the environmental spins for the emergence of quantum
synchronization.",1903.05545v2
2019-03-20,Turing-like patterns in an asymmetric dynamic Ising model,"To investigate novel aspects of pattern formation in spin systems, we use a
mapping between reactive concentrations in a reaction-diffusion system and spin
orientations in a dynamic multiple-spin Ising model. While pattern formation in
Ising models always rely on infinite-range interactions, this mapping allows us
to design an finite-range interactions Ising model that can produce patterns
observed in reaction diffusion systems including Turing patterns with a tunable
typical length scale. This model has asymmetric interactions and several spin
types coexisting at a site. While we use the example of genetic regulation
during embryo-genesis to build our model, it can be used to study the behavior
of other complex systems of interacting agents.",1903.08506v2
2019-04-01,Quantum bath control with nuclear spin state selectivity via pulse-adjusted dynamical decoupling,"Dynamical decoupling (DD) is a powerful method for controlling arbitrary open
quantum systems. In quantum spin control, DD generally involves a sequence of
timed spin flips ($\pi$ rotations) arranged to average out or selectively
enhance coupling to the environment. Experimentally, errors in the spin flips
are inevitably introduced, motivating efforts to optimise error-robust DD. Here
we invert this paradigm: by introducing particular control ""errors"" in standard
DD, namely a small constant deviation from perfect $\pi$ rotations (pulse
adjustments), we show we obtain protocols that retain the advantages of DD
while introducing the capabilities of quantum state readout and polarisation
transfer. We exploit this nuclear quantum state selectivity on an ensemble of
nitrogen-vacancy centres in diamond to efficiently polarise the $^{13}$C
quantum bath. The underlying physical mechanism is generic and paves the way to
systematic engineering of pulse-adjusted protocols with nuclear state
selectivity for quantum control applications.",1904.00893v1
2019-04-11,Single-shot determination of spin-polarization for ultrarelativistic electron beams via nonlinear Compton scattering,"Impacts of spin-polarization of an ultrarelativistic electron beam head-on
colliding with a strong laser pulse on emitted photon spectra and electron
dynamics have been investigated in the quantum radiation regime. We simulate
photon emissions quantum mechanically and electron dynamics semiclassically via
taking spin-resolved radiation probabilities in the local constant field
approximation. A small ellipticity of the laser field brings about an asymmetry
in angle-resolved photon spectrum, which sensitively relies on the polarization
of the electron beam. The asymmetry is particularly significant in high-energy
photon spectra, and is employed for the polarization detection of a high-energy
electron beam with extraordinary precision, e.g., better than 0.3\% for a
few-GeV electron beam at a density of the scale of $10^{16}$ cm$^{-3}$ with
currently available strong laser fields. This method demonstrates for the first
time a way of single-shot determination of polarization for ultrarelativistic
electron beams via nonlinear Compton scattering. A similar method based on the
asymmetry in the electron momentum distribution after the interaction due to
spin-dependent radiation reaction is proposed as well.",1904.05910v1
2019-04-19,Sub-terahertz ferrimagnetic spin-transfer torque oscillator,"A theory of magnetization dynamics in ferrimagnetic materials with
antiparallel aligned spin sub-lattices under action of spin-transfer torques
(STT) is developed. We consider magnetization dynamics in GdFeCo layers in two
cases of magnetic anisotropy: easy plane and easy axis. We demonstrate that,
(i) for the easy plane anisotropy the precession of the N\'{e}el vector is
conical and the cone angle depends on the STT strength and the value of spin
non-compensation, while the frequency of precession can reach sub-THz
frequencies; (ii) for the easy axis anisotropy two regimes are possible:
deterministic switching of the net magnetization and a conical sub-THz
precession depending on the STT strength.",1904.09341v1
2019-04-26,Terahertz spin dynamics driven by a field-derivative torque,"Efficient manipulation of magnetization at ultrashort time scales is of
particular interest for future technology. Here, we numerically investigate the
influence of the so-called field-derivative torque, which was derived earlier
based on relativistic Dirac theory [Mondal et al., Phys. Rev. B 94, 144419
(2016)], on the spin dynamics triggered by ultrashort laser pulses. We find
that only considering the THz Zeeman field can underestimate the spin
excitation in antiferromagnetic oxide systems as, e.g., NiO and CoO. However,
accounting for both, the THz Zeeman torque and the field-derivative torque, the
amplitude of the spin excitation increases significantly. Studying the damping
dependence of field-derivative torque we observe larger effects for materials
having larger damping constants.",1904.11768v2
2019-04-29,Exact real-time dynamics of single-impurity Anderson model from a single-spin hybridization-expansion,"In this work we introduce a modified real-time continuous-time
hybridization-expansion quantum Monte Carlo solver for a time-dependent
single-orbital Anderson impurity model: CT-1/2-HYB-QMC. In the proposed method
the diagrammatic expansion is performed only for one out of the two spin
channels, while the resulting effective single-particle problem for the other
spin is solved semi-analytically for each expansion diagram. CT-1/2-HYB-QMC
alleviates the dynamical sign problem by reducing the order of sampled diagrams
and makes it possible to reach twice as long time scales in comparison to the
standard CT-HYB method. We illustrate the new solver by calculating an electric
current through impurity in paramagnetic and spin-polarized cases.",1904.12582v2
2019-10-31,Peering into the darkness: vison-generated photon mass in quantum spin ice,"Describing experimental signatures of quantum spin ice has been the focus of
many theoretical efforts, as definitive experimental verification of this
candidate quantum spin liquid is yet to be achieved. Gapped excitations known
as visons have largely eluded those efforts. We provide a theoretical
framework, which captures their dynamics and predicts new signatures in the
magnetic response. We achieve this by studying the ring-exchange Hamiltonian of
quantum spin ice in the large-$s$ approximation, taking into account the
compact nature of the emergent $U(1)$ gauge theory. We find the stationary
solutions of the action -- the instantons -- which correspond to visons
tunneling between lattice sites. By integrating out the instantons, we
calculate the effective vison Hamiltonian, including their mass. We show that
in the ground state virtual vison pairs simply renormalise the speed of light.
At low temperatures, however, thermally activated visons form a Debye plasma
and introduce a mass gap in the photon spectrum, equal to the plasma frequency,
which we calculate as a function of temperature. We demonstrate that this
dynamical mass gap should be visible in energy-resolved neutron scattering
spectra but not in the energy-integrated ones. We also show that it does not
lead to confinement of static spinons.",1911.00097v1
2019-11-11,Asymmetric environment induces protein-like relaxation in spin chain,"Proteins are aminoacid chains that diffusively fold or unfold depending on
the thermal and chemical environmental conditions. While sophisticated models
account for detailed aspects of real proteins, finding traits that unify
protein dynamics to general open chains relaxation is still challenging. The
principle of minimal frustration represents a key step towards this goal,
revealing a fundamental link between proteins and spin glasses. Here, we search
for the emergence of protein-like relaxation in open spin chains by going
beyond the validity domain of the minimal frustration principle as to focus on
the role of system-environment interactions rather than on frustration in the
system's Hamiltonian. We find that strong asymmetries between the couplings of
each spin to its immediate surroundings imply close similarities to protein
folding and unfolding dynamics. Namely, an asymmetric bath can (i) block the
system from finding its minimum energy state, even in the complete absence of
energetic frustration in the system's Hamiltonian, and (ii) excite the system
resembling the well-known distinction between thermal and chemical
denaturations.",1911.04433v1
2019-11-13,Oscillatory behavior in a model of non-Markovian mean field interacting spins,"We analyze a non-Markovian mean field interacting spin system, related to the
Curie--Weiss model. We relax the Markovianity assumption by replacing the
memoryless distribution of the waiting times of a classical spin-flip dynamics
with a distribution with memory. The resulting stochastic evolution for a
single particle is a spin-valued renewal process, an example of two-state
semi-Markov process. We associate to the individual dynamics an equivalent
Markovian description, which is the subject of our analysis. We study a
corresponding interacting particle system, where a mean field interaction is
introduced as a time scaling, depending on the overall magnetization of the
system, on the waiting times between two successive particle's jumps. Via
linearization arguments on the Fokker-Planck mean field limit equation, we give
evidence of emerging periodic behavior. Specifically, numerical analysis on the
discrete spectrum of the linearized operator, characterized by the zeros of an
explicit holomorphic function, suggests the presence of a Hopf bifurcation for
a critical value of the temperature, which is in accordance with the one
obtained by simulating the N-particle system.",1911.05373v1
2019-11-27,Experimental quantum kernel machine learning with nuclear spins in a solid,"We employ so-called quantum kernel estimation to exploit complex quantum
dynamics of solid-state nuclear magnetic resonance for machine learning. We
propose to map an input to a feature space by input-dependent Hamiltonian
evolution, and the kernel is estimated by the interference of the evolution.
Simple machine learning tasks, namely one-dimensional regression tasks and
two-dimensional classification tasks, are performed using proton spins which
exhibit correlation over 10 spins. We also performed numerical simulations to
evaluate the performance without the noise inevitable in the actual
experiments. The performance of the trained model tends to increase with the
longer evolution time, or equivalently, with a larger number of spins involved
in the dynamics for certain tasks. This work presents a quantum machine
learning experiment using one of the largest quantum systems to date.",1911.12021v1
2020-03-03,Sub-picosecond exchange-relaxation in the compensated ferrimagnet Mn$_2$Ru$_x$Ga,"We study the demagnetization dynamics of the fully compensated half-metallic
ferrimagnet Mn$_2$Ru$_x$Ga. While the two antiferromagnetically coupled
sublattices are both composed of manganese, they exhibit different temperature
dependencies due to their differing local environments. The sublattice
magnetization dynamics triggered by femtosecond laser pulses are studied to
reveal the roles played by the spin and intersublattice exchange. We find a
two-step demagnetization process, similar to the well-established case of
Gd(FeCo)$_3$, where the two Mn-sublattices have different demagnetization
rates. The behaviour is analysed using a four-temperature model, assigning
different temperatures to the two manganese spin baths. Even in this strongly
exchange-coupled system, the two spin reservoirs have considerably different
behaviour. The half-metallic nature and strong exchange coupling of
Mn$_2$Ru$_x$Ga lead to spin angular momentum conservation at much shorter time
scales than found for Gd(FeCo)$_3$ which suggests that low-power,
sub-picosecond switching of the net moment of Mn$_2$Ru$_x$Ga is possible.",2003.01420v1
2020-03-25,Magnon Trap by Chiral Spin Pumping,"Chiral spin pumping is the generation of a unidirectional spin current in
half of ferromagnetic films or conductors by dynamic dipolar stray fields from
close-by nanomagnets. We formulate a general theory of long-range chiral
interactions between magnets mediated by unidirectional traveling waves, e.g.,
spin waves in a magnetic film or microwaves in a waveguide. The traveling waves
emitted by an excited magnet can be perfectly trapped by a second, initially
passive, magnet by a dynamical interference effect. When both magnets are
excited by a uniform microwave, the chiral interaction between them creates a
large imbalance in their magnon numbers.",2003.11581v2
2020-03-27,Phonon dispersions throughout the iron spin crossover in ferropericlase,"Ferropericlase (Fp), (Mg$_\mathrm{1-x}$Fe$_\mathrm{x}$)O, is the second most
abundant phase in the Earths lower mantle. At relevant pressure-temperature
conditions, iron in Fp undergoes a high spin (HS), S=2, to low spin (LS), S=0,
state change. The nature of this phenomenon is quite well understood now, but
there are still basic questions regarding the structural stability and the
existence of soft phonon modes during this iron state change. General theories
exist to explain the volume reduction, the significant thermo-elastic
anomalies, and the broad nature of this HS-LS crossover. These theories make
extensive use of the quasi-harmonic approximation (QHA). Therefore, dynamical
and structural stability is essential to their validity. Here, we investigate
the vibrational spectrum of Fp throughout this spin-crossover using $\textit{ab
initio}$ DFT+Usc calculations. We address vibrational modes associated with
isolated and (2nd) nearest neighbor iron ions undergoing the HS-LS state
change. As expected, acoustic modes of this solid solution are resilient while
optical modes are the most affected. We show that there are no soft phonon
modes across this HS-LS crossover, and Fp is dynamically stable at all relevant
pressures.",2003.12348v1
2020-06-14,Resonant-amplified and invisible Bragg scattering based on spin coalescing modes,"Unlike a real magnetic field, which separates the energy levels of particle
with opposite spin polarization, a complex field can lead to a special kind of
spectral degeneracy, known as exceptional point (EP), at which two spin
eigenmodes coalesce. It allows an EP impurity to be an invisible scattering
center for a fermion with the resonant spin polarization, but an amplifying
emitter for opposite polarization. We show that a pair of conjugate EP modes
supports resonant mutual stimulation, acting as a resonant amplifier based on
the underlying mechanism of positive-feedback loop. Together with other
Hermitian eigenmodes, a fermion with EP polarization exhibits some exclusive
dynamics, referred to as EP dynamics. We construct several typical
superlattices, which are built up by embedding EP-impurity arrays in a
Hermitian two-dimensional square lattice. Numerical simulations are performed
to demonstrate resonant amplification and invisibility of Bragg scattering.",2006.07875v2
2020-08-19,Dynamical Fermionization in One Dimensional Spinor Gases,"Dynamical fermionization refers to the phenomenon in Tonks-Girardeau (TG)
gases where, upon release from harmonic confinement, the gas's momentum density
profile evolves asymptotically to that of an ideal Fermi gas in the initial
trap. This phenomenon has been demonstrated theoretically in hardcore and
anyonic TG gases, and recently experimentally observed in a strongly
interacting Bose gas. We extend this study to a one dimensional (1D) spinor gas
of arbitrary spin in the strongly interacting regime, and analytically prove
that the total momentum distribution after the harmonic trap is turned off
approaches that of a spinless ideal Fermi gas, while the asymptotic momentum
distribution of each spin component takes the same shape of the initial real
space density profile of that spin component. Our work demonstrates the rich
physics arising from the interplay between the spin and the charge degrees of
freedom in a spinor system.",2008.08383v1
2020-08-28,Signatures of nonlinear magnetoelectricity in second harmonic spectra of SU(2) symmetry broken quantum many-body systems,"Quantum mechanical perturbative expressions for second order dynamical
magnetoelectric (ME) susceptibilities have been derived and calculated for a
small molecular system using the Hubbard Hamiltonian with SU(2) symmetry
breaking in the form of spin-orbit coupling (SOC) or spin-phonon coupling.
These susceptibilities will have signatures in second harmonic generation
spectra. We show that SU(2) symmetry breaking is the key to generate these
susceptibilities. We have calculated these ME coefficients by solving the
Hamiltonian for low lying excited states using Lanczos method. Varying the
Hubbard term along with SOC strength, we find spin and charge and both
spin-charge dominated spectra of dynamical ME coefficients. We have shown that
intensities of the peaks in the spectra are highest when the magnitudes of
Hubbard term and SOC coupling term are in similar range.",2008.12521v1
2020-09-09,Micromagnetic instabilities in spin-transfer switching of perpendicular magnetic tunnel junctions,"Micromagnetic instabilities and non-uniform magnetization states play a
significant role in spin transfer induced switching of nanometer scale magnetic
elements. Here we model domain wall mediated switching dynamics in
perpendicularly magnetized magnetic tunnel junction nanopillars. We show that
domain wall surface tension always leads to magnetization oscillations and
instabilities associated with the disk shape of the junction. A collective
coordinate model is developed that captures aspects of these instabilities and
illustrates their physical origin. Model results are compared to those of
micromagnetic simulations. The switching dynamics is found to be very sensitive
to the domain wall position and phase, which characterizes the angle of the
magnetization in the disk plane. This sensitivity is reduced in the presence of
spin torques and the spin current needed to displace a domain wall can be far
less than the threshold current for switching from a uniformly magnetized
state. A prediction of this model is conductance oscillations of increasing
frequency during the switching process.",2009.04376v1
2020-09-21,Critically-enhanced spin-nematic squeezing and entanglement in dipolar spinor condensates,"We study the quantum critical effect enhanced spin-nematic squeezing and
quantum Fisher information (QFI) in the spin-1 dipolar atomic Bose-Einstein
condensate. We show that the quantum phase transitions can improve the
squeezing and QFI in the nearby regime of critical point, and the
Heisenberg-limited high-precision metrology can be obtained. The different
properties of the ground squeezing and entanglement under even and odd number
of atoms are further analyzed, by calculating the exact analytical
expressions.We also demonstrate the squeezing and entanglement generated by the
spin-mixing dynamics around the phase transition point. It is shown that the
steady squeezing and entanglement can be obtained, and the Bogoliubov
approximation can well describe the dynamics of spin-nematic squeezed vacuum
state.",2009.09728v1
2020-10-05,Finite temperature spin dynamics of a two-dimensional Bose-Bose atomic mixture,"We examine the role of thermal fluctuations in uniform two-dimensional binary
Bose mixtures of dilute ultracold atomic gases. We use a mean-field
Hartree-Fock theory to derive analytical predictions for the
miscible-immiscible transition. A nontrivial result of this theory is that a
fully miscible phase at $T=0$ may become unstable at $T\neq0$, as a consequence
of a divergent behaviour in the spin susceptibility. We test this prediction by
performing numerical simulations with the Stochastic (Projected)
Gross-Pitaevskii equation, which includes beyond mean-field effects. We
calculate the equilibrium configurations at different temperatures and
interaction strengths and we simulate spin oscillations produced by a weak
external perturbation. Despite some qualitative agreement, the comparison
between the two theories shows that the mean-field approximation is not able to
properly describe the behavior of the two-dimensional mixture near the
miscible-immiscible transition, as thermal fluctuations smoothen all sharp
features both in the phase diagram and in spin dynamics, except for temperature
well below the critical temperature for superfluidity.",2010.01933v2
2020-10-21,Electric activity at magnetic moment fragmentation in spin ice,"Spin ice systems display a variety of very nontrivial properties, the most
striking being the existence in them of magnetic monopoles. Such monopole
states can also have nontrivial electric properties: there exist electric
dipoles attached to each monopole. A novel situation is encountered in the
moment fragmentation (MF) state, in which monopoles and antimonopoles are
perfectly ordered, whereas spins themselves remain disordered. We show that
such partial ordering strongly modifies the electric activity of such systems:
the electric dipoles, which are usually random and dynamic, become paired in
the MF state in (d,-d) pairs, thus strongly reducing their electric activity.
The electric currents existing in systems with noncoplanar spins are also
strongly influenced by MF. We also consider modifications in dipole and current
patterns in magnetic textures (domain walls, local defects) and at excitations
with nontrivial dynamics in a MF state, which show very rich behaviour and
which could in principle allow to control them by electric field.",2010.11149v2
2020-11-03,Driving spin chirality by electron dynamics in laser-excited antiferromagnets,"Optical generation of complex spin textures is one of the most exciting
challenges of modern spintronics. Here, we uncover a distinct physical
mechanism for imprinting spin chirality into collinear magnets with short laser
pulses. By simultaneously treating the laser-ignited evolution of electronic
structure and magnetic order, we show that their intertwined dynamics can
result in an emergence of quasi-stable chiral states. We find that laser-driven
chirality does not require any auxiliary external fields or intrinsic
spin-orbit interaction to exist, and it can survive on the time scale of
nanoseconds even in the presence of thermal fluctuations, which makes the
uncovered mechanism relevant for understanding various optical experiments on
magnetic materials. Our findings open a new perspective at the interaction of
complex chiral magnetism with light.",2011.01670v3
2020-11-03,Tunable-spin-model generation with spin-orbit-coupled fermions in optical lattices,"We study the dynamical behaviour of ultracold fermionic atoms loaded into an
optical lattice under the presence of an effective magnetic flux, induced by
spin-orbit coupled laser driving. At half filling, the resulting system can
emulate a variety of iconic spin-1/2 models such as an Ising model, an XY
model, a generic XXZ model with arbitrary anisotropy, or a collective one-axis
twisting model. The validity of these different spin models is examined across
the parameter space of flux and driving strength. In addition, there is a
parameter regime where the system exhibits chiral, persistent features in the
long-time dynamics. We explore these properties and discuss the role played by
the system's symmetries. We also discuss experimentally-viable implementations.",2011.01842v3
2020-11-17,Spinning and tumbling of long fibers in isotropic turbulence,"We simultaneously measure both spinning and tumbling components of rotation
for long near-neutrally buoyant fibers in homogeneous and isotropic turbulence.
The lengths and diameters of the measured fibers extend to several orders of
the Kolmogorov length of the surrounding turbulent flow. Our measurements show
that the variance of the spinning rate follows a -4/3 power law scaling with
the fiber diameter ($d$) and is always larger than the variance of the tumbling
rate. This behavior surprisingly resembles that observed previously for
sub-Kolmogorov fibers. The general picture that emerges from this study is that
long fibers preferentially align with vortex filaments that can be as long as
the integral length of turbulence. We compute the Lagrangian time scale and the
distribution of both tumbling and spinning that supports this outlook. Our
measurements also allow us to quantify the importance of the Coriolis term on
the rotational dynamics of fibers in turbulent flows.",2011.08546v2
2020-11-17,Single-shot dynamics of spin-orbit torque and spin transfer torque switching in three-terminal magnetic tunnel junctions,"Current-induced spin-transfer torques (STT) and spin-orbit torques (SOT)
enable the electrical switching of magnetic tunnel junctions (MTJs) in
nonvolatile magnetic random access memories. In order to develop faster memory
devices, an improvement of the timescales underlying the current driven
magnetization dynamics is required. Here we report all-electrical time-resolved
measurements of magnetization reversal driven by SOT in a three-terminal MTJ
device. Single-shot measurements of the MTJ resistance during current injection
reveal that SOT switching involves a stochastic two-step process consisting of
a domain nucleation time and propagation time, which have different genesis,
timescales, and statistical distributions compared to STT switching. We further
show that the combination of SOT, STT, and voltage control of magnetic
anisotropy (VCMA) leads to reproducible sub-ns switching with a spread of the
cumulative switching time smaller than 0.2 ns. Our measurements unravel the
combined impact of SOT, STT, and VCMA in determining the switching speed and
efficiency of MTJ devices.",2011.08709v1
2021-03-01,Spin drag and fast response in a quantum mixture of atomic gases,"By applying a sudden perturbation to one of the components of a mixture of
two quantum fluids, we explore the effect on the motion of the second component
on a short time scale. By implementing perturbation theory, we prove that for
short times the response of the second component is fixed by the energy
weighted moment of the crossed dynamic structure factor (crossed f-sum rule).
We also show that by properly monitoring the time duration of the perturbation
it is possible to identify peculiar fast spin drag regimes, which are sensitive
to the interaction effects in the Hamiltonian. Special focus is given to the
case of coherently coupled Bose-Einstein condensates, interacting Bose mixtures
exhibiting the Andreev-Bashkin effect, normal Fermi liquids and the polaron
problem. The relevant excitations of the system contributing to the spin drag
effect are identified and the contribution of the low frequency gapless
excitations to the f-sum rule in the density and spin channels is explicitly
calculated employing the proper macroscopic dynamic theories. Both spatially
periodic and Galilean boost perturbations are considered.",2103.00918v2
2021-03-09,Coherence Protection of Electron Spin in Earth-field Range by All-optical Dynamic Decoupling,"In recent years, unshielded atomic systems have been attracting researchers'
attention, in which decoherence is one of the major problems, especially for
high precision measurements. The nonlinear Zeeman effect and magnetic field
gradient are the main decoherence sources of atomic electron spin in
Earth-field range. Here, we propose a method to cancel out the two dominant
broadening effects simultaneously by an all-optical dynamic decoupling approach
based on Raman scattering in the 87Rb Zeeman sublevels. By adjusting the
parameters of the Raman lasers, we realize spin control along an arbitrary
direction. We analyze the state evolution of atomic spin under the Raman light
control sequence in detail. The results show that both the nonlinear Zeeman
effect and magnetic field gradient can be significantly suppressed.",2103.05169v1
2021-03-14,Transverse spin dynamics in the anisotropic Heisenberg model realized with ultracold atoms,"In Heisenberg models with exchange anisotropy, transverse spin components are
not conserved and can decay not only by transport, but also by dephasing. Here
we utilize ultracold atoms to simulate the dynamics of 1D Heisenberg spin
chains, and observe fast, local spin decay controlled by the anisotropy.
Additionally, we directly observe an effective magnetic field created by
superexchange which causes an inhomogeneous decay mechanism due to variations
of lattice depth between chains, as well as dephasing within each chain due to
the twofold reduction of the effective magnetic field at the edges of the
chains and due to fluctuations of the effective magnetic field in the presence
of mobile holes. The latter is a new coupling mechanism between holes and
magnons. All these dephasing mechanisms, corroborated by extensive numerical
simulations, have not been observed before with ultracold atoms and illustrate
basic properties of the underlying Hubbard model.",2103.07866v1
2021-04-08,Probing the interplay between lattice dynamics and short-range magnetic correlations in CuGeO3 with femtosecond RIXS,"Investigations of magnetically ordered phases on the femtosecond timescale
have provided significant insights into the influence of charge and lattice
degrees of freedom on the magnetic sub-system. However, short-range magnetic
correlations occurring in the absence of long-range order, for example in
spin-frustrated systems, are inaccessible to many ultrafast techniques. Here,
we show how time-resolved resonant inelastic X-ray scattering (trRIXS) is
capable of probing such short-ranged magnetic dynamics in a charge-transfer
insulator through the detection of a Zhang-Rice singlet exciton. Utilizing
trRIXS measurements at the O K-edge, and in combination with model
calculations, we probe the short-range spin-correlations in the frustrated spin
chain material CuGeO3 following photo-excitation, revealing a strong coupling
between the local lattice and spin sub-systems.",2104.03557v1
2021-04-23,Nematicity Liquid in a Trimerized-Kagome Antiferromagnet,"We theoretically study low-temperature properties of the antiferromagnetic
Heisenberg model with half-integer spin $S$ on the Kagome lattice with large
trimerization. We have derived a low-energy effective model for general $S$ in
terms of spin and nematicity operators in triangular units, and studied their
low-temperature correlations for S=3/2 by classical Monte Carlo simulations.
The previous study for the S=1/2 case [M. Ferrero et al., Phys. Rev. B 68,
214431 (2003)] reported a spin liquid state at low temperatures driven by a
glassy behavior of isolated dimers and trimers of nematicities. The results for
S=3/2 show that nematicity dimers and trimers are connected by weak links to
form a defective planar network. At very low temperatures, nematicities show
glassy slow dynamics, and cluster spins continue to fluctuate in a
nonperiodically frozen background of nematicities. The characteristic time of
glassy dynamics scales with temperature following a power law.",2104.11363v2
2021-04-23,Exact solution for the Lindbladian dynamics for the open XX spin chain with boundary dissipation,"We obtain exact formulas for the time-dependence of a few physical
observables for the open XX spin chain with Lindbladian dynamics. Our analysis
is based on the fact that the Lindblad equation for an arbitrary open quadratic
system of $N$ fermions is explicitly solved in terms of diagonalization of a
$4N\times4N$ matrix called structure matrix by following the scheme of the
third quantization. We mainly focus on the time-dependence of magnetization and
spin current. As a short-time behavior at a given site, we observe the plateau
regime except near the center of the chain. Basic features of this are
explained by the light-cone structure created by propagations of boundary
effects from the initial time, but we can explain their more detailed
properties analytically using our exact formulas. On the other hand, after the
plateau regime, the magnetization and spin current exhibit a slow decay to the
steady state values described by the Liouvillian gap. We analytically establish
its $O(N^{-3})$ scaling and also determine its coefficient.",2104.11479v2
2021-05-11,Helicity current generation by distorted Rashba coupling,"We theoretically study spin transport in two-or three-dimensional Rashba
systems dynamically distorted by surface acoustic waves. The spin currents in
the linear response to lattice distortion dynamics are calculated on the basis
of a microscopic theory combined with local coordinate transformations. As a
result, we find a mechanism of direct spin-current generation from lattice
distortion not associated with a charge current or spin accumulation. Moreover,
the in-plane helicity currents are generated by shear surface acoustic waves
via the present mechanism. The generated helicity currents are not parallel to
the vorticity of the lattice, and cannot be created with the conventional
methods. Thus, our findings offer an alternative functionality of the
conventional Rashba systems in the field of spintronics.",2105.04804v1
2021-05-13,Collective dynamics of domain walls: an antiferromagnetic spin texture in an optical cavity,"Spin canting and complex spin textures in antiferromagnetic materials can
often be described in terms of Dzyaloshinskii-Moriya interactions (DMI). Values
for DMI parameters are not easily measurable directly, and often inferred from
other quantities. In this work, we examine how domain wall dynamics in an
antiferromagnetic optomagnonic system can display unique features directly
related to the existence of DMI. Our results indicate that the presence of DMI
enables spin interactions with cavity photons in a geometry which otherwise
allows no magneto-optical coupling, and on the other hand modulates frequencies
in a geometry where coupling is already realized in the absence of DMI. This
result may be used to measure the DMI constant in optomagnonic experiments by
comparing resonances obtained with different polarisations of the exciting
field.",2105.06430v1
2021-05-24,A non-perturbative study of bulk photovoltaic effect enhanced by an optically induced phase transition,"Solid systems with strong correlations and interactions under light
illumination have the potential for exhibiting interesting bulk photovoltaic
behavior in the non-perturbative regime, which has remained largely unexplored
in the past theoretical studies. We investigate the bulk photovoltaic response
of a perovskite manganite with strongly coupled electron-spin-lattice dynamics,
using real-time simulations performed with a tight-binding model. The transient
changes in the band structure and the photoinduced phase transitions, emerging
from spin and phonon dynamics, result in a nonlinear current versus intensity
behavior beyond the perturbative limit. The current rises sharply across a
photoinduced magnetic phase transition, which later saturates at higher light
intensities due to excited phonon and spin modes. The predicted peak
photoresponsivity is orders of magnitude higher than other known ferroelectric
oxides such as BiFeO$_3$. We disentangle phonon-and spin-assisted components to
the ballistic photocurrent, showing that they are comparable in magnitude. Our
results illustrate a promising alternative way for controlling and optimizing
the bulk photovoltaic response through the photoinduced phase transitions in
strongly-correlated systems.",2105.11310v1
2021-05-26,Crystal-field excitations and vibronic modes in triangular-lattice spin-liquid candidate TbInO$_3$,"We study the ground state properties, the electronic excitations and lattice
dynamics in spin-liquid candidate TbInO$_3$. By employing polarization resolved
Raman spectroscopy we define the inter- and intra-multiplet excitations, and
establish the low-energy crystal-field (CF) level scheme. In particular, we
demonstrate that the ground state of the Tb$^{3+}$ ions is a non-Kramers
doublet, and relate the enhanced linewidth of the CF modes to the magnetic
fluctuations near the spin-liquid ground state. We identify all 38 allowed
Raman-active phonon modes at low temperature. Moreover, we observe hybrid
vibronic excitations involving coupled CF and low-lying phonon modes,
suggesting strong spin-lattice dynamics. We develop a model for vibronic states
and obtain the parameters of the bare responses and coupling strength. We
further demonstrate that the obtained CF level scheme is consistent with
specific heat data.",2105.12656v1
2021-05-31,Far-from-equilibrium universality in the two-dimensional Heisenberg model,"We characterize the universal far-from-equilibrium dynamics of the
two-dimensional quantum Heisenberg magnet isolated from its environment. For a
broad range of initial conditions, we find a long-lived universal prethermal
regime characterized by self-similar behavior of spin-spin correlations. We
analytically derive the spatial-temporal scaling exponents and find excellent
agreement with numerics using phase space methods. The scaling exponents are
insensitive to the choice of initial conditions, which include coherent and
incoherent spin states with values of total magnetization and energy in a wide
range. Compared to previously-studied self-similar dynamics in non-equilibrium
$O(n)$ field theories and Bose gases, we find qualitatively distinct scaling
behavior originating from the presence of spin modes which remain gapless at
long times and which are protected by the global SU(2) symmetry. Our
predictions, which suggest a new non-equilibrium universality class, are
readily testable in ultra-cold atoms simulators of Heisenberg magnets.",2106.00023v2
2021-06-02,Spin-Valley Qubit Dynamics In Exchange Coupled Silicon Quantum Dots,"The presence of valley states is a significant obstacle to realizing quantum
information technologies in Silicon quantum dots, as leakage into alternate
valley states can introduce errors into the computation. We use a perturbative
analytical approach to study the dynamics of exchange-coupled quantum dots with
valley degrees of freedom. We show that if the valley splitting is large and
electrons are not properly initialized to valley eigenstates, then time
evolution of the system will lead to spin-valley entanglement. Spin-valley
entanglement will also occur if the valley splitting is small and electrons are
not initialized to the same valley state. Additionally, we show that for small
valley splitting, spin-valley entanglement does not affect measurement
probabilities of two-qubit systems; however, systems with more qubits will be
affected. This means that two-qubit gate fidelities measured in two-qubit
systems may miss the effects of valley degrees of freedom. Our work shows how
the existence of valleys may adversely affect multiqubit fidelities even when
the system temperature is very low.",2106.01391v1
2021-06-02,Spontaneous emergence of a spin state for an emitter in a time-varying medium,"Time varying media can dramatically modify the emission of embedded sources
by producing time reversed waves refocusing on the source. Here we show that
such a back action can create an angular momentum by setting the source in a
spontaneous spin state. We experimentally implement this coupling using
self-propelled bouncing droplets sources coupled to the surface waves they emit
on a parametrically excited bath. The spin state dynamics result from a
self-organized interplay between the source motion and the time reversed waves.
The discrete stability analysis agrees with the experimental observations. In
addition, we show that these spin states provide a unique opportunity for an
experimental access to parameters enabling comparison and calibration of the
various existing models.",2106.01448v3
2021-06-15,Experimental confirmation of the delayed Ni demagnetization in FeNi alloy,"Element-selective techniques are central for the understanding of ultrafast
spin dynamics in multi-element materials like magnetic alloys. Recently,
though, it turned out that the commonly used technique of transverse
magneto-optical Kerr effect (T-MOKE) in the EUV range may have linearity issues
including unwanted cross talk between different elemental signals. This problem
can be sizeable, which puts recent observations of ultrafast spin transfer from
Fe to Ni sites in FeNi alloys into question. In this study, we investigate the
Fe-to-Ni spin transfer in a cross-talk-free time-resolved X-ray magnetic
circular dichroism (XMCD) experiment with a reliable time reference. We find a
very similar Fe and Ni dynamics with XMCD as with T-MOKE from identical
samples. Considering the non-linearities of the T-MOKE response, the agreement
with our findings appears fortuitous. We discuss possible reasons why T-MOKE
seems to give accurate results in this case. Our data provide the ongoing
discussion about ultrafast spin-transfer mechanisms in FeNi systems with a
sound experimental basis.",2106.07956v1
2021-06-16,Random iron-nickel alloys: From first principles to dynamic spin fluctuation theory,"We provide a systematic analysis of finite-temperature magnetic properties of
random alloys Fe$_x$Ni$_{1-x}$ with the face-centered-cubic structure over a
broad concentration range $x$. By means of the spin-polarized relativistic
Korringa-Kohn-Rostoker method we calculate the electronic structure of
disordered iron-nickel alloys and discuss how a composition change affects
magnetic moments of Fe and Ni and the density of states. We investigate how the
Curie temperature depends on Fe concentration using conventional approaches,
such as mean-field approximation or Monte Carlo simulations, and dynamic
spin-fluctuation theory. Being devised to account for spin fluctuations
explicitly, the latter method shows the best fit to experimental results.",2106.08765v2
2021-07-18,Statistical correlation between quantum entanglement and spin-orbit coupling in crossed beam molecular dynamics,"Non-classical features like interference is already being harnessed to
control the output of chemical reactions. However quantum entanglement which is
an equally enigmatic many-body quantum correlation can also be used as a
powerful resource yet have eluded explicit attention. In this report, we
propose an experimental scheme under the crossed beam molecular dynamical
setup, with the F+HD reaction, aiming to study the possible influence of
entanglement within reactant pairs on the angular features of the product
distribution. The aforesaid reaction has garnered interest recently as an
unusual horseshoe shape pattern in the product (HF) distribution was observed,
which has been attributed to the coupling of spin and orbital degrees of
freedom. We propose an experimental scheme aiming to study the possible
influence of entanglement on the necessity for the inclusion of such spin-orbit
characteristics, under circumstances wherein the existence of entanglement and
spin-orbit interaction is simultaneously detectable. We further numerically
simulate the attainable results highlighting specific patterns corresponding to
various possibilities. Such studies if extended can provide unforeseen
mechanistic insight in analogous reactions too from the lens of quantum
information.",2107.08483v1
2021-09-12,Relativistic spin dynamics conditioned by dark matter axions,"The relativistic spin dynamics defined by the pseudoscalar field of dark
matter axions is rigorously determined. The relativistic Hamiltonian in the
Foldy-Wouthuysen representation is derived. It agrees with the previously
obtained nonrelativistic Hamiltonians and the relativistic classical estimation
of the axion wind effect. In the relativistic Hamiltonian, the biggest term
describes the extraordinary (three orders of magnitude) enhancement of the
axion wind effect in storage ring experiments as compared with experiments with
immobile particles. This term defines the spin rotation about the longitudinal
axis. The effects caused by the axion-induced oscillating EDM and the axion
wind consist in the spin rotations about the different horizontal axes and
phases of stimulating oscillations differ by $\pi/2$. Experiments in a search
for dark matter axions has been discussed. The two experimental designs for
axion search experiments in storage rings have been elaborated.",2109.05576v2
2021-10-09,Field induced spin freezing and low temperature heat capacity of disordered pyrochlore oxide Ho$_{2}$Zr$_{2}$O$_{7}$,"Spin ice materials are the model systems that have a zero-point entropy as
\textit{T} $\rightarrow$ 0 K, owing to the frozen disordered states. Here, we
chemically alter the well-known spin ice Ho$_{2}$Ti$_{2}$O$_{7}$ by replacing
Ti sites with isovalent but larger Zr ion. Unlike the Ho$_{2}$Ti$_{2}$O$_{7}$
which is a pyrochlore material, Ho$_{2}$Zr$_{2}$O$_{7}$ crystallizes in
disordered pyrochlore structure. We have performed detailed structural, ac
magnetic susceptibility and heat capacity studies on Ho$_{2}$Zr$_{2}$O$_{7}$ to
investigate the interplay of structural disorder and frustrated interactions.
The zero-field ground state exhibits large magnetic susceptibility and remains
dynamic down to 30 mK without showing Pauling's residual entropy. The dynamic
state is suppressed continuously with the magnetic field and freezing
transition evolves ($\sim$ 10 K) at a field of $\sim$ 10 kOe. These results
suggest that the alteration of chemical order and local strain in
Ho$_{2}$Ti$_{2}$O$_{7}$ prevents the development of spin ice state and provides
a new material to study the geometrical frustration based on the structure.",2110.04555v1
2021-11-24,A generalized model of magnon kinetics and subgap magnetic noise,"Magnetic noise spectroscopy provides a noninvasive probe of spin dynamics in
magnetic materials. We consider two-dimensional magnetically ordered insulators
with magnon excitations, especially those supporting long-distance magnon
transport, where nitrogen-vacancy (NV) centers enable the access to (nearly)
ballistic transport regime of magnons. We develop a generalized theory to
describe the magnon transport across a wide range of length scales. The
longitudinal dynamic spin susceptibility is derived from the Boltzmann equation
and extended to a Lindhard form, which is modified by both the spin-conserving
magnon collisions and spin relaxation. Our result is consistent with the
diffusive (ballistic) model for the length scale much larger (smaller) than the
magnon mean free path, and provides a description for the intermediate regime.
We also give a prediction for the NV transition rate in different magnon
transport regimes.",2111.12613v2
2021-12-15,Efficient Simulation of Dynamics in Two-Dimensional Quantum Spin Systems with Isometric Tensor Networks,"We investigate the computational power of the recently introduced class of
isometric tensor network states (isoTNSs), which generalizes the isometric
conditions of the canonical form of one-dimensional matrix-product states to
tensor networks in higher dimensions. We discuss several technical details
regarding the implementation of isoTNSs-based algorithms and compare different
disentanglers -- which are essential for an efficient handling of isoTNSs. We
then revisit the time evolving block decimation for isoTNSs ($\text{TEBD}^2$)
and explore its power for real time evolution of two-dimensional (2D) lattice
systems. Moreover, we introduce a density matrix renormalization group
algorithm for isoTNSs ($\text{DMRG}^2$) that allows to variationally find
ground states of 2D lattice systems. As a demonstration and benchmark, we
compute the dynamical spin structure factor of 2D quantum spin systems for two
paradigmatic models: First, we compare our results for the transverse field
Ising model on a square lattice with the prediction of the spin-wave theory.
Second, we consider the Kitaev model on the honeycomb lattice and compare it to
the result from the exact solution.",2112.08394v2
2021-12-21,Nonreciprocal spin-wave dynamics in Pt/Co/W/Co/Pt multilayers,"We present a detailed study of the spin-wave dynamics in single Pt/Co/W and
double Pt/Co/W/Co/Pt ferromagnetic layer systems. The dispersion of spin waves
was measured by wavevector-resolved Brillouin light scattering spectroscopy
while the in-plane and out-of-plane magnetization curves were measured by
alternating gradient field magnetometry. The interfacial Dzyaloshinskii-Moriya
interaction induced nonreciprocal dispersion relation was demonstrated for both
single and double ferromagnetic layers and explicated by numerical simulations
and theoretical formulas. The results indicate the crucial role of the order of
layers deposition on the magnetic parameters. A significant difference between
the perpendicular magnetic anisotropy constant in double ferromagnetic layer
systems conduces to the decline of the interlayer interactions and different
dispersion relations for the spin-wave modes. Our study provides a significant
contribution to the realization of the multifunctional nonreciprocal magnonic
devices based on ultrathin ferromagnetic/heavy-metal layer systems.",2112.11206v1
2021-12-29,Excitation and detection of coherent sub-terahertz magnons in ferromagnetic and antiferromagnetic heterostructures,"Excitation of coherent high-frequency magnons (quanta of spin waves) is
critical to the development of high-speed magnonic devices. Here we
computationally demonstrate the excitation of coherent sub-terahertz (THz)
magnons in ferromagnetic (FM) and antiferromagnetic (AFM) thin films by a
photoinduced picosecond acoustic pulse. Analytical calculations are also
performed to reveal the magnon excitation mechanism. Through spin pumping and
spin-charge conversion, these magnons can inject sub-THz charge current into an
adjacent heavy-metal film which in turn emits electromagnetic (EM) waves. Using
a dynamical phase-field model that considers the coupled dynamics of acoustic
waves, spin waves, and EM waves, we show that the emitted EM wave retains the
spectral information of all the sub-THz magnon modes and has a sufficiently
large amplitude for near-field detection. These predictions indicate that the
excitation and detection of sub-THz magnons can be realized in rationally
designed FM or AFM thin-film heterostructures via ultrafast optical-pump
THz-emission-probe spectroscopy.",2112.14749v2
2022-01-13,Anomalously field-susceptible spin soft-matter emerging in an electric-dipole liquid candidate,"Mutual interactions in many-body systems bring about a variety of exotic
phases, among which liquid-like states failing to order due to frustration are
of keen interest. Recently, an organic system with an anisotropic triangular
lattice of molecular dimers has been suggested to host a dipole liquid arising
from intradimer charge-imbalance instability, possibly offering an
unprecedented stage for the spin degrees of freedom. Here we show that an
extraordinary unordered(unfrozen) spin state having soft-matter-like
spatiotemporal characteristics is substantiated in this system. $^1$H NMR
spectra and magnetization measurements indicate that gigantic, staggered
moments are non-linearly and inhomogeneously induced by magnetic field whereas
the moments vanish in the zero-field limit. The analysis of the NMR relaxation
rate signifies that the moments fluctuate at a characteristic frequency slowing
down to below MHz at low temperatures. The inhomogeneity, local correlation,
and slow dynamics indicative of middle-scale dynamical correlation length
suggest a novel frustration-driven spin clusterization.",2201.04857v1
2022-06-09,Power-law dynamics in the spin-liquid kagome lattices SrCr8Ga4O19 and ZnCu3(OH)6Cl2,"We consider the polarization function P^{exp}_Z(t) measured by the muon-spin
relaxation (muSR) technique for the SrCr8Ga4O19 and ZnCu3(OH)6Cl2 spin-liquid
systems. We show the functional form of P^{exp}_Z(t) to imply that, in the
temperature range of order 0.1 K, the spectral-weight function F(\omega) of the
magnetic correlations scales with 1/|\omega|^{1 -x} (0 < x < 1) in the energy
range of one microelectronvolt, i.e. \hbar \omega ~ 1 \mu eV. We derive the
parameters involved in F(\omega) from fits to available experimental data.
Inelastic neutron scattering data probing F(\omega) in the millielectronvolt
energy range are consistent with a more conventional behavior. These
differences could be due to a variety of spin-dynamics mechanisms, i.e.
intrinsic to the kagome layer or related to the magnetic defects that have been
evidenced in these compounds, acting at different energies. New muSR
measurements are proposed and theoretical developments are suggested to
pinpoint the mechanisms at play.",2206.04352v1
2022-07-07,Experimental Demonstration of High-Performance Physical Reservoir Computing with Nonlinear Interfered Spin Wave Multi-Detection,"Physical reservoir computing, which is a promising method for the
implementation of highly efficient artificial intelligence devices, requires a
physical system with nonlinearity, fading memory, and the ability to map in
high dimensions. Although it is expected that spin wave interference can
perform as highly efficient reservoir computing in some micromagnetic
simulations, there has been no experimental verification to date. Herein, we
demonstrate reservoir computing that utilizes multidetected nonlinear spin wave
interference in an yttrium iron garnet single crystal. The subject computing
system achieved excellent performance when used for hand-written digit
recognition, second-order nonlinear dynamical tasks, and nonlinear
autoregressive moving average (NARMA). It is of particular note that normalized
mean square errors (NMSEs) for NARMA2 and second-order nonlinear dynamical
tasks were 1.81x10-2 and 8.37x10-5, respectively, which are the lowest figures
for any experimental physical reservoir so far reported. Said high performance
was achieved with higher nonlinearity and the large memory capacity of
interfered spin wave multi-detection.",2207.03216v1
2022-08-03,Magnetic field driven dynamics in twisted bilayer artificial spin ice at superlattice angles,"Geometrical designs of interacting nanomagnets have been studied extensively
in the form of two dimensional arrays called artificial spin ice. These systems
are usually designed to create geometrical frustration and are of interest for
the unusual and often surprising phenomena that can emerge. Advanced
lithographic and element growth techniques have enabled the realization of
complex designs that can involve elements arranged in three dimensions. Using
numerical simulations employing the dumbbell approximation, we examine possible
magnetic behaviours for bilayer artificial spin ice (BASI) in which the
individual layers are rotated with respect to one another. The goal is to
understand how magnetization dynamics are affected by long-range dipolar
coupling that can be modified by varying the layer separation and layer
alignment through rotation. We consider bilayers where the layers are both
either square or pinwheel arrangements of islands. Magnetic reversal processes
are studied and discussed in terms of domain and domain wall configurations of
the magnetic islands. Unusual magnetic ordering is predicted for special angles
which define lateral spin superlattices for the bilayer systems.",2208.02243v1
2022-08-22,Ultrafast Spin Dynamics and Photoinduced Insulator-to-Metal Transition in $α$-$RuCl_3$,"Laser-induced ultrafast demagnetization is a phenomenon of utmost interest
and attracts significant attention because it enables potential applications in
ultrafast optoelectronics and spintronics. As a spin-orbit coupling assisted
magnetic insulator, $\alpha$-$RuCl_3$ provides an attractive platform to
explore the physics of electronic correlations and related unconventional
magnetism. Using time-dependent density functional theory, we explore the
ultrafast laser-induced dynamics of the electronic and magnetic structures in
$\alpha$-$RuCl_3$. Our study unveils that laser pulses can introduce ultrafast
demagnetizations in $\alpha$-$RuCl_3$, accompanied by an out-of-equilibrium
insulator-to-metal transition in a few tens of femtoseconds. The spin response
significantly depends on the laser wavelength and polarization on account of
the electron correlations, band renormalizations and charge redistributions.
These findings provide physical insights into the coupling between the
electronic and magnetic degrees of freedom in $\alpha$-$RuCl_3$ and shed light
on suppressing the long-range magnetic orders and reaching a proximate spin
liquid phase for two-dimensional magnets on an ultrafast timescale.",2208.10222v1
2022-08-25,Evidence of Kardar-Parisi-Zhang scaling on a digital quantum simulator,"Understanding how hydrodynamic behaviour emerges from the unitary evolution
of the many-particle Schr\""odinger equation is a central goal of
non-equilibrium statistical mechanics. In this work we implement a digital
simulation of the discrete time quantum dynamics of a spin-$\frac{1}{2}$ XXZ
spin chain on a noisy near-term quantum device, and we extract the high
temperature transport exponent at the isotropic point. We simulate the temporal
decay of the relevant spin correlation function at high temperature using a
pseudo-random state generated by a random circuit that is specifically tailored
to the ibmq-montreal $27$ qubit device. The resulting output is a spin
excitation on a highly inhomogeneous background. From the subsequent discrete
time dynamics on the device we are able to extract an anomalous super-diffusive
exponent consistent with the conjectured Kardar-Parisi-Zhang (KPZ) scaling at
the isotropic point. Furthermore we simulate the restoration of spin diffusion
with the application of an integrability breaking potential.",2208.12243v3
2022-11-15,Interacting triplons in frustrated spin ladders: Binding and decay in BiCu$_2$PO$_6$,"Establishing a comprehensive model of the rich spin dynamics in
BiCu$_2$PO$_6$ has been a challenge over the last decade. Inelastic neutron
scattering experiments revealed that its elementary triplons are non-degenerate
showing the existence of significant anisotropic spin couplings. Evidence for
triplon decay into two triplons has been found, but two prominent downturns in
the dispersions eluded an explanation. Level repulsion due to hybridization of
single triplons with the continuum of two-triplon scattering states has been
proposed as explanation. We show that this concept may explain the weak
downturn at higher energies, but fails for the most pronounced downturn at
lower energy. In turn, we provide evidence that this downturn is the signature
of a two-triplon bound state of essentially singlet character pointing to
triplon-triplon interaction as the second crucial ingredient of the spin
dynamics in this exemplary system.",2211.08204v1
2022-11-16,Spin structure and dynamics of the topological semimetal Co$_{3}$Sn$_{2-x}$In$_{x}$S$_{2}$,"The anomalous Hall effect (AHE), typically observed in ferromagnetic (FM)
metals with broken time-reversal symmetry, depends on electronic and magnetic
properties. In Co$_{3}$Sn$_{2-x}$In$_{x}$S$_{2}$, a giant AHE has been
attributed to Berry curvature associated with the FM Weyl semimetal phase, yet
recent studies report complicated magnetism. We use neutron scattering to
determine the spin dynamics and structures as a function of $x$ and provide a
microscopic understanding of the AHE and magnetism interplay. Spin gap and
stiffness indicate a contribution from Weyl fermions consistent with the AHE.
The magnetic structure evolves from $c$-axis ferromagnetism at $x$ = 0 to a
canted antiferromagnetic (AFM) structure with reduced $c$-axis moment and
in-plane AFM order at $x$ = 0.12 and further reduced $c$-axis FM moment at $x$
= 0.3. Since noncollinear spins can induce non-zero Berry curvature in real
space acting as a fictitious magnetic field, our results revealed another AHE
contribution, establishing the impact of magnetism on transport.",2211.08660v1
2022-12-12,Kerr Black Holes From Massive Higher-Spin Gauge Symmetry,"We propose that the dynamics of Kerr black holes is strongly constrained by
the principle of gauge symmetry. We initiate the construction of EFTs for Kerr
black holes of any integer quantum spin s using Stueckelberg fields, and show
that the known three-point Kerr amplitudes are uniquely predicted using massive
higher-spin gauge symmetry. This symmetry is argued to be connected to an
enhanced range of validity for the Kerr EFTs. We consider the closely related
root-Kerr electromagnetic solution in parallel, for which the dynamical
interactions with photons are also constrained by massive higher-spin gauge
symmetry. Finally, the spin-s Compton amplitudes are analyzed, and we discuss
contact-term constraints at s=2 from Ward identities.",2212.06120v2
2023-01-16,Real-time polarimetry of hyperpolarized $^{13}$C nuclear spins using an atomic magnetometer,"We introduce a method for non-destructive quantification of nuclear spin
polarization, of relevance to hyperpolarized spin tracers widely used in
magnetic resonance from spectroscopy to in vivo imaging. In a bias field of
around 30 nT we use a high-sensitivity miniaturized $^{87}$Rb vapor
magnetometer to measure the field generated by the sample, as it is driven by a
windowed dynamical decoupling pulse sequence that both maximizes the nuclear
spin lifetime and modulates the polarization for easy detection. We demonstrate
the procedure applied to a 0.08 M hyperpolarized [1--$^{13}$C]-pyruvate
solution produced by dissolution dynamic nuclear polarization, measuring
polarization repeatedly during natural decay at Earth's field. Application to
real-time quality monitoring of hyperpolarized substances is discussed.",2301.06607v2
2023-01-30,Dynamical nuclear polarization for dissipation-induced entanglement in NV centers,"We propose a practical implementation of a two-qubit entanglement engine
which denotes a scheme to generate quantum correlations through purely
dissipative processes. On a diamond platform, the electron spin transitions of
two Nitrogen-Vacancy (NV) centers play the role of artificial atoms (qubits),
interacting through a dipole-dipole Hamiltonian. The surrounding Carbon-13
nuclear spins act as spin baths playing the role of thermal reservoirs at
well-defined temperatures and exchanging heat through the NV center qubits. In
our scheme, a key challenge is therefore to create a temperature gradient
between two spin baths surrounding each NV center, for which we propose the
exploit the recent progresses in dynamical nuclear polarization, combined with
microscopy superresolution methods. We discuss how these techniques should
allow us to initialize such a long lasting out-of-equilibrium polarization
situation between them, effectively leading to suitable conditions to run the
entanglement engine successfully. Within a quantum master equation approach, we
make theoretical predictions using state-of-the-art values for experimental
parameters. We obtain promising values for the concurrence, reaching
theoretical maxima.",2301.13085v2
2023-02-23,Ultrafast laser-induced spin-lattice dynamics in the van der Waals antiferromagnet CoPS3,"CoPS3 stands out in the family of the van der Waals antiferromagnets XPS3
(X=Mn, Ni, Fe, Co) due to the unquenched orbital momentum of the magnetic Co2+
ions which is known to facilitate the coupling of spins to both electromagnetic
waves and lattice vibrations. Here, using a time-resolved magneto-optical
pump-probe technique we experimentally study the ultrafast laser-induced
dynamics of mutually correlated spins and lattice. It is shown that a
femtosecond laser pulse acts as an ultrafast heater and thus results in the
melting of the antiferromagnetic order. At the same time, the resonant pumping
of the 4T1g - 4T2g electronic transition in Co2+ ions effectively changes their
orbital momentum, giving rise to a mechanical force that moves the ions in the
direction parallel to the orientation of their spins, thus generating a
coherent Bg phonon mode at the frequency of about 4.7 THz.",2302.12104v1
2023-03-06,Larmor precession in strongly correlated itinerant electron systems,"Many-electron systems undergo a collective Larmor precession in the presence
of a magnetic field. In a paramagnetic metal, the resulting spin wave provides
insight into the correlation effects generated by the electron-electron
interaction. Here, we use dynamical mean-field theory to investigate the
collective Larmor precession in the strongly correlated regime, where dynamical
correlation effects such as quasiparticle lifetimes and non-quasiparticle
states are essential. We study the spin excitation spectrum, which includes a
dispersive Larmor mode as well as electron-hole excitations that lead to Stoner
damping. We also extract the momentum-resolved damping of slow spin waves. The
accurate theoretical description of these phenomena relies on the Ward
identity, which guarantees a precise cancellation of self-energy and vertex
corrections at long wavelengths. Our findings pave the way towards a better
understanding of spin wave damping in correlated materials.",2303.03468v2
2023-04-26,Quantum many-body scars in spin models with multibody interactions,"We introduce and study several classes of quantum spin models with multi-body
interactions that exhibit quantum many-body scars. The models are constructed
by two different methods: one exploiting boundary states in integrable spin
chains and the other based on a variant of existing methods such as restricted
spectrum generating algebras. The first method allows us to construct
deformations of the Majumdar-Ghosh and Affleck-Kennedy-Lieb-Tasaki models --
prototypes of frustration-free systems. With the second method, we construct a
large class of spin-$1$ models involving scalar spin chirality in both one and
two dimensions. Interestingly, in some cases, the models so constructed have
towers of scar states of different character. For each example, we show that
the scar states behave differently from thermal states by comparing their
spectral and dynamical properties with those of other states. We also show that
a superposition of the scar states constructed by the second method exhibits
perfectly periodic revivals in the dynamics.",2304.13624v3
2023-06-03,Machine learning enabled experimental design and parameter estimation for ultrafast spin dynamics,"Advanced experimental measurements are crucial for driving theoretical
developments and unveiling novel phenomena in condensed matter and material
physics, which often suffer from the scarcity of facility resources and
increasing complexities. To address the limitations, we introduce a methodology
that combines machine learning with Bayesian optimal experimental design
(BOED), exemplified with x-ray photon fluctuation spectroscopy (XPFS)
measurements for spin fluctuations. Our method employs a neural network model
for large-scale spin dynamics simulations for precise distribution and utility
calculations in BOED. The capability of automatic differentiation from the
neural network model is further leveraged for more robust and accurate
parameter estimation. Our numerical benchmarks demonstrate the superior
performance of our method in guiding XPFS experiments, predicting model
parameters, and yielding more informative measurements within limited
experimental time. Although focusing on XPFS and spin fluctuations, our method
can be adapted to other experiments, facilitating more efficient data
collection and accelerating scientific discoveries.",2306.02015v1
2023-06-12,Exact Solution for the Transverse Field Sherrington-Kirkpatrick Spin Glass Model with Continuous-Time Quantum Monte Carlo Method,"We construct the first complete exact numerical solution of a mean field
quantum spin glass model, the transverse field Sherrington-Kirkpatrick model,
by implementing a continuous-time quantum Monte Carlo method in the presence of
full replica symmetry breaking. We extract the full numerically exact phase
diagram, displaying a glassy phase with continuous replica symmetry breaking at
small transverse fields and low temperatures. A paramagnetic phase emerges once
thermal and quantum fluctuations melt the spin glass. We characterize both
phases by extracting the order parameter, as well as the static and dynamical
local spin susceptibilities. The static susceptibility shows a plateau in the
glassy phase, but remains smooth across the phase boundary, while the shape of
dynamical susceptibility varies upon crossing the glass transition by reducing
quantum fluctuations. We qualitatively compare these results to a.c.
susceptibility measurements on dipole-coupled Ising magnets in a transverse
magnetic field. Our work provides a general framework for the exact numerical
solution of mean field quantum glass models, constituting an important step
towards understanding glassiness in realistic systems.",2306.07337v1
2023-06-26,The dynamical structure factor of the SU(4) algebraic spin liquid on the honeycomb lattice,"We compute the momentum resolved dynamical spin structure factor
$S(k,\omega)$ of the SU(4) Heisenberg model on the honeycomb lattice assuming
the $\pi$-flux Dirac spin liquid ground state by two methods: (i) variationally
using Gutzwiller projected particle-hole excitations of the $\pi$-flux Fermi
sea and (ii) in the non-interacting parton mean-field picture. The two
approaches produce qualitatively similar results. Based on this analogy, we
argue that the energy spectrum of the projected excitations is a gapless
continuum of fractional excitations. Quantitatively, the Gutzwiller projection
shifts the weight from higher to lower energies, thus emphasizing the lower
edge of the continuum. In the mean-field approach, we obtained the
$1/\text{distance}^4$ decay of the spin correlation function, and the local
correlations show $S^{33}_{\text{MF}}(\omega)\propto \omega^3$ behavior.",2306.16242v2
2023-08-28,Coherent Spin-Phonon Coupling in the Layered Ferrimagnet Mn3Si2Te6,"We utilize ultrafast photoexcitation to drive coherent lattice oscillations
in the layered ferrimagnetic crystal Mn3Si2Te6, which significantly stiffen
below the magnetic ordering temperature. We suggest that this is due to an
exchange-mediated contraction of the lattice, stemming from strong
magneto-structural coupling in this material. Additionally, simulations of the
transient incoherent dynamics reveal the importance of spin relaxation channels
mediated by optical and acoustic phonon scattering. Our findings highlight the
importance of spin-lattice coupling in van der Waals magnets and a promising
route for their dynamic optical control through their intertwined electronic,
lattice, and spin degrees of freedom.",2308.14931v1
2023-10-02,SpinPSO: An agent-based optimization workflow for identifying global noncollinear magnetic ground-states from first-principles,"We propose and implement a novel hybrid meta-heuristic optimization algorithm
for the identification of non-collinear global ground-states in magnetic
systems. The inputs to this optimization scheme are directly from non-collinear
density functional theory (DFT), and the workflow is implemented in the atomate
code framework, making it suitable to run on high-performance computing
architectures. The hybrid algorithm provides a seamless theoretical extension
of particle swarm optimization (PSO) algorithms to continuous $\mathcal S^2$
spins, giving it the name SpinPSO. The hybrid nature of the algorithm stems
from setting the dynamics of individual spins to be governed by physically
motivated atomistic spin dynamics. Using this algorithm, we are able to achieve
convergence to experimentally resolved magnetic ground-states for a set of
diverse test case materials that exhibit exotic spin textures.",2310.01383v1
2023-12-04,Emergent electric field induced by current-driven domain wall motion in a room-temperature antiferromagnet FeSn2,"Antiferromagnets have attracted extensive interest as platforms for nanoscale
spintronic devices owing to ultrafast spin dynamics and lack of a stray field.
One of the crucial missing pieces in antiferromagnets is a quantum-mechanical
electric field known as an emergent electric field, which has been observed for
the motion of ferromagnetic spin texture. Since this phenomenon allows for the
development of novel spintronic devices such as quantum inductors, its
identification in antiferromagnets is vital for developing nanoscale spintronic
devices. Here, we demonstrate that the motion of antiferromagnetic spin
textures generates an emergent electric field. In a room-temperature
antiferromagnet FeSn2, we observed large current-nonlinear responses in the
imaginary part of the complex impedance at and well above room temperature.
This signal is attributed to an emergent electric field resulting from the
nonadiabatic electron spin dynamics during the current-induced motion of
antiferromagnetic domain walls. Notably, the observed electric response is
strongly enhanced as the sample size decreases and robust against magnetic
fields. Our finding may pave the way for novel nanoscale quantum spintronic
devices.",2312.01553v1
2023-12-07,Hole Flying Qubits in Quantum Dot Arrays,"Quantum information transfer is fundamental for scalable quantum computing in
any potential platform and architecture. Hole spin qubits, owing to their
intrinsic spin-orbit interaction (SOI), promise fast quantum operations which
are fundamental for the implementation of quantum gates. Yet, the influence of
SOI in quantum transfer protocols remains an open question. Here, we
investigate hole flying qubits using shortcuts to adiabaticity protocols, i.e.,
the long-range transfer of hole spin states and the quantum distribution of
entangled pairs in semiconductor quantum dot arrays. We show that electric
field manipulation allows dynamical control of the SOI, enabling simultaneously
the implementation of quantum gates during the transfer, with the potential to
significantly accelerate quantum algorithms. By harnessing the ability to
perform quantum gates in parallel with the transfer, we employ dynamical
decoupling schemes to focus and preserve the spin state, leading to higher
transfer fidelity.",2312.04631v3
2023-12-22,Dynamical structures associated with high-order and secondary resonances in the spin-orbit problem,"In our Solar system, spin-orbit resonances are common under Sun--planet,
planet--satellite and binary asteroid configurations. In this work, high-order
and secondary spin-orbit resonances are investigated by taking numerical and
analytical approaches. Poincar\'e sections as well as two types of dynamical
maps are produced, showing that there are complicated structures in the phase
space. To understand numerical structures, we adopt the theory of perturbative
treatments to formulate resonant Hamiltonian for describing spin-orbit
resonances. Results show that there is an excellent agreement between
analytical and numerical structures. It is concluded that the main V-shape
structure arising in the parameter space $(\dot\theta,\alpha)$ is sculpted by
the synchronous primary resonance, those minute structures inside the V-shape
region are dominated by secondary resonances and those structures outside the
V-shape region are governed by high-order resonances. At last, the analytical
approach is applied to binary asteroid systems (65803) Didymos and (4383)
Suruga to reveal their phase-space structures.",2312.14413v1
2023-12-29,Understanding the magnetic interactions of the zig-zag honeycomb lattice: Application to $α$-RuCl$_3$,"This investigation covers the effects of variable exchange interactions on
the spin dynamics of the zig-zag honeycomb lattice. Using a Holstein-Primakoff
expansion of the Heisenberg Hamiltonian with easy-axis anisotropy, we
characterize the effects of multiple nearest-neighbor and next-nearest-neighbor
interactions with asymmetry within the context of a frustrated and
non-frustrated zig-zag magnetic configuration. Furthermore, we compare to the
known inelastic neutron scattering data for the proximate quantum spin liquid
$\alpha$-RuCl$_3$, and we provide insight into the evolution of the spin
dynamics, showing that the Heisenberg interaction dominates the majority of the
spin excitation behavior. By analyzing the frustrated system with multiple
interactions, direction-dependent Dirac nodes present themselves, and we can
demonstrate that a standard Heisenberg model can accurately describe the
observed magnon spectra.",2312.17433v1
2024-01-25,Universal collective Larmor-Silin mode emerging in magnetized correlated Dirac fermions,"Employing large-scale quantum Monte Carlo simulations, we find in magnetized
interacting Dirac fermion model, there emerges a new and universal collective
Larmor-Silin spin wave mode in the transverse dynamical spin susceptibility.
Such mode purely originates from the interaction among Dirac fermions and
distinguishes itself from the usual particle-hole continuum with finite
lifetime and clear dispersion, both at small and large momenta in a large
portion of the Brillouin zone. Our unbiased numerical results offer the dynamic
signature of this new collective excitations in interacting Dirac fermion
systems, and provide experimental guidance for inelastic neutron scattering,
electron spin resonance and other spectroscopic approaches in the investigation
of such universal collective modes in quantum Moire materials, topological
insulators and quantum spin liquid materials under magnetic field, with
quintessential interaction nature beyond the commonly assumed noninteracting
Dirac fermion or spinon approximations.",2401.14358v2
2024-02-07,Macroscopic Magnetic Dynamics,"Ferromagnetic metals and spin-polarized $^{3}$He are spin 1/2 systems with
the same macroscopic symmetry, and thus should have macroscopic magnetic
dynamics with the same structure. Using Onsager's irreversible thermodynamics,
we develop a theory for these systems that contains two relaxation times (one
for the magnetization $\vec{M}$ and the other for the spin current
$\vec{J}_{i}$), a magnetic compressibility, and a mean-field parameter.
Currently spintronics data on metallic ferromagnets are analyzed using a
complex decay length from a theory employing a diffusion constant, a lifetime,
and a mean-field parameter. The present theory leads to a complex decay length
with the same structure. On neglecting decay of $\vec{M}$, the present theory
applies to liquids and gases. For macroscopic equations the particle statistics
is not relevant, so the theory also applies to bosons. The theory predicts a
longitudinal spin wave whose velocity we estimate for liquid $^{3}$He and for
paramagnetic metals; but such a wave should also occur for ferromagnets and for
gases.",2402.04639v1
2024-02-12,Simulating the spin-boson model with a controllable reservoir in an ion trap,"The spin-boson model is a prototypical model for open quantum dynamics. Here
we simulate the spin-boson model using a chain of trapped ions where a spin is
coupled to a structured reservoir of bosonic modes. We engineer the spectral
density of the reservoir by adjusting the ion number, the target ion location,
the laser detuning to the phonon sidebands, and the number of frequency
components in the laser, and we observe their effects on the collapse and
revival of the initially encoded information. Our work demonstrates the ion
trap as a powerful platform for simulating open quantum dynamics with
complicated reservoir structures.",2402.07461v1
2024-02-21,Time-reversal in a dipolar quantum many-body spin system,"Time reversal in a macroscopic system is contradicting daily experience. It
is practically impossible to restore a shattered cup to its original state by
just time reversing the microscopic dynamics that led to its breakage. Yet,
with the precise control capabilities provided by modern quantum technology,
the unitary evolution of a quantum system can be reversed in time. Here, we
implement a time-reversal protocol in a dipolar interacting, isolated many-body
spin system represented by Rydberg states in an atomic gas. By changing the
states encoding the spin, we flip the sign of the interaction Hamiltonian, and
demonstrate the reversal of the relaxation dynamics of the magnetization by
letting a demagnetized many-body state evolve back-in-time into a magnetized
state. We elucidate the role of atomic motion using the concept of a Loschmidt
echo. Finally, by combining the approach with Floquet engineering, we
demonstrate time reversal for a large family of spin models with different
symmetries. Our method of state transfer is applicable across a wide range of
quantum simulation platforms and has applications far beyond quantum many-body
physics, reaching from quantum-enhanced sensing to quantum information
scrambling.",2402.13873v1
2024-02-21,Quantum state preparation of topological chiral spin liquids via Floquet engineering,"In condensed matter, Chiral Spin Liquids (CSL) are quantum spin analogs of
electronic Fractional Quantum Hall states (in the continuum) or Fractional
Chern Insulators (on the lattice). As the latter, CSL are remarquable states of
matter, exhibiting topological order and chiral edge modes. Preparing CSL on
quantum simulators like cold atom platforms is still an open challenge. Here we
propose a simple setup on a finite cluster of spin-1/2 located at the sites of
a square lattice. Using a Resonating Valence Bond (RVB) non-chiral spin liquid
as initial state on which fast time-modulations of strong nearest-neighbor
Heisenberg couplings are applied, following different protocols
(out-of-equilibrium quench or semi-adiabatic ramping of the drive), we show the
slow emergence of such a CSL phase. An effective Floquet dynamics, obtained
from a high-frequency Magnus expansion of the drive Hamiltonian, provides a
very accurate and simple framework fully capturing the out-of-equilibrium
dynamics. An analysis of the resulting prepared states in term of Projected
Entangled Pair states gives further insights on the topological nature of the
chiral phase. Finally, we discuss possible applications to quantum computing.",2402.14141v2
2024-03-28,Modeling local decoherence of a spin ensemble using a generalized Holstein-Primakoff mapping to a bosonic mode,"We show how the decoherence that occurs in an entangling atomic spin-light
interface can be simply modeled as the dynamics of a bosonic mode. Although one
seeks to control the collective spin of the atomic system in the
permutationally invariant (symmetric) subspace, diffuse scattering and optical
pumping are local, making an exact description of the many-body state
intractable. To overcome this issue we develop a generalized Holstein-Primakoff
approximation for collective states which is valid when decoherence is uniform
across a large atomic ensemble. In different applications the dynamics is
conveniently treated as a Wigner function evolving according to a thermalizing
diffusion equation, or by a Fokker-Planck equation for a bosonic mode decaying
in a zero temperature reservoir. We use our formalism to study the combined
effect of Hamiltonian evolution, local and collective decoherence, and
measurement backaction in preparing nonclassical spin states for application in
quantum metrology.",2403.19801v1
1995-08-04,Thermally-driven Neutron Star Glitches,"We examine the thermal and dynamical response of a neutron star to a sudden
perturbation of the inner crust temperature. During the star's evolution,
starquakes and other processes may deposit $\gap 10^{42}$ ergs, causing
significant internal heating and increased frictional coupling between the
crust and the more rapidly rotating neutron superfluid the star is expected to
contain. Through numerical simulation we study the propagation of the thermal
wave created by the energy deposition, the induced motion of the interior
superfluid, and the resulting spin evolution of the crust. We find that energy
depositions of $\sim 10^{40}$ ergs produce gradual spin-ups above the timing
noise level, while larger energy depositions produce sudden spin jumps
resembling pulsar glitches. For a star with a temperature in the observed range
of the Vela pulsar, an energy deposition of $\sim 10^{42}$ ergs produces a
large spin-up taking place over minutes, similar to the Vela ``Christmas''
glitch. Comparable energy deposition in a younger and hotter ``Crab-like'' star
produces a smaller spin-up taking place over $\sim 1$ day, similar to that seen
during the partially time-resolved Crab glitch of 1989.",9508021v1
1992-12-21,Gapless Spin-Fluid Ground State in a Random Quantum Heisenberg Magnet,"We examine the spin-$S$ quantum Heisenberg magnet with Gaussian-random,
infinite-range exchange interactions. The quantum-disordered phase is accessed
by generalizing to $SU(M)$ symmetry and studying the large $M$ limit. For large
$S$ the ground state is a spin-glass, while quantum fluctuations produce a
spin-fluid state for small $S$. The spin-fluid phase is found to be generically
gapless - the average, zero temperature, local dynamic spin-susceptibility
obeys $\bar{\chi} (\omega ) \sim \log(1/|\omega|) + i (\pi/2) \mbox{sgn}
(\omega)$ at low frequencies. This form is identical to the phenomenological
`marginal' spectrum proposed by Varma {\em et. al.\/} for the doped cuprates.",9212030v1
1993-03-09,Quantum Antiferromagnets in Two Dimensions,"These are lectures presented at the summer course on ``Low Dimensional
Quantum Field Theories for Condensed Matter Physicists'', 24 Aug. to 4 Sep.
1992, Trieste, Italy. I review recent work, performed in collaboration
primarily with N. Read and Jinwu Ye, on the properties of quantum
antiferromagnets in two dimensions. The emphasis is on the properties of the
antiferromagnet in states which do not have any long-range magnetic order. The
universal spin dynamics in the quantum critical region of number of frustrated
and random antiferromagnets is studied; implications for neutron scattering
experiments in the lightly-doped cuprates are noted. The nature of the
quantum-disordered phase of non-random frustrated antiferromagnets is examined
in some detail: the states found have ({\em i\/}) collinear spin correlations,
spin-Peierls or valence-bond-solid order, and confined spinons, order and
confined spinons or ({\em ii\/}) coplanar spin correlations, no spin-Peierls
order and deconfined bosonic spinons.",9303014v1
1995-04-11,Quantum field theory of metallic spin glasses,"We introduce an effective field theory for the vicinity of a zero temperature
quantum transition between a metallic spin glass (``spin density glass'') and a
metallic quantum paramagnet. Following a mean field analysis, we perform a
perturbative renormalization-group study and find that the critical properties
are dominated by static disorder-induced fluctuations, and that dynamic
quantum-mechanical effects are dangerously irrelevant. A Gaussian fixed point
is stable for a finite range of couplings for spatial dimensionality $d > 8$,
but disorder effects always lead to runaway flows to strong coupling for $d
\leq 8$. Scaling hypotheses for a {\em static\/} strong-coupling critical field
theory are proposed. The non-linear susceptibility has an anomalously weak
singularity at such a critical point. Although motivated by a perturbative
study of metallic spin glasses, the scaling hypotheses are more general, and
could apply to other quantum spin glass to paramagnet transitions.",9504036v2
1996-02-19,Overscreened Single Channel Kondo Problem,"We consider the single channel Kondo problem with the Kondo coupling between
a spin $S$ impurity and conduction electrons with spin $j$. These problems
arise as multicritical points in the parameter spaces of two- and higher-level
tunneling systems, and some impurity models of heavy fermion compounds. In
contrast to the previous Bethe-anstaz conjectures, it turns out that the
dynamics of the spin sector is the same as that of a spin $S$ impurity coupled
to $k(j)$ channels of spin $1/2$ electrons with $k(j) = 2j(j+1)(2j+1)/3$. As a
result, for $2S < k(j)$, the system shows non-Fermi liquid behavior with the
same exponents for the thermodynamic quantities as those of $k(j)$ channel
Kondo problem. However, both the finite-size spectrum and the operator content
are different due to the presence of the other sectors and can be obtained by
conformal field theory techniques.",9602100v3
1997-07-30,Spin in a Fluctuating Field: The Bose (+Fermi) Kondo models,"I consider models with an impurity spin coupled to a fluctuating gaussian
field with or without additional Kondo coupling of the conventional sort. In
the case of isotropic fluctuations, the renormalisation group flows for these
models have controlled fixed points when the autocorrelation of the gaussian
field $h(t)$, $<T h(t) h(0)> \sim {1\over t^{2-\epsilon}}$ with small positive
$\epsilon$. In absence of any additional Kondo coupling, I get powerlaw decay
of spin correlators, $<T S(t) S(0)> \sim {1\over t^{\epsilon}}$ . For negative
$\epsilon$, the spin autocorrelation is constant in long time limit. The
results agree with calculations in Schwinger Boson mean field theory. In
presence of a Kondo coupling to itinerant electrons, the model shows a phase
transition from a Kondo phase to a field fluctuation dominated phase. These
models are good starting points for understanding behaviour of impurities in a
system near a zero-temperature magnetic transition. They are also useful for
understanding the dynamical local mean field theory of Kondo lattice with
Heisenberg (spin-glass type) magnetic interactions.",9707316v1
1997-10-13,Violation of the Fluctuation Dissipation Theorem in Finite Dimensional Spin Glasses,"We study the violation of the fluctuation-dissipation theorem in the three
and four dimensional Gaussian Ising spin glasses using on and off equilibrium
simulations. We have characterized numerically the function X(C) that determine
the violation and we have studied its scaling properties. Moreover we have
computed the function x(C) which characterize the breaking of the replica
symmetry directly from equilibrium simulations. The two functions are
numerically equal and in this way we have established that the conjectured
connection between the violation of fluctuation dissipation theorem in the
off-equilibrium dynamics and the replica symmetry breaking at equilibrium holds
for finite dimensional spin glasses. These results point to a spin glass phase
with spontaneously broken replica symmetry in finite dimensional spin glasses.",9710120v1
1998-06-19,Spin-filter effect of the europium chalcogenides: An exactly solved many-body model,"A model Hamiltonian is introduced which considers the main features of the
experimental spin filter situation as s-f interaction, planar geometry and the
strong external electric field. The proposed many-body model can be solved
analytically and exactly using Green functions.
  The spin polarization of the field-emitted electrons is expressed in terms of
spin-flip probabilities, which on their part are put down to the exactly known
dynamic quantities of the system.
  The calculated electron spin polarization shows remarkable dependencies on
the electron velocity perpendicular to the emitting plane and the strength of
s-f coupling. Experimentally observed polarization values of about 90% are well
understood within the framework of the proposed model.",9806234v1
1998-08-03,Coupled quantum dots as quantum gates,"We consider a new quantum gate mechanism based on electron spins in coupled
semiconductor quantum dots. Such gates provide a general source of spin
entanglement and can be used for quantum computers. We determine the exchange
coupling J in the effective Heisenberg model as a function of magnetic (B) and
electric fields, and of the inter-dot distance (a) within the Heitler-London
approximation of molecular physics. This result is refined by using
sp-hybridization, and by the Hund-Mulliken molecular-orbit approach which leads
to an extended Hubbard description for the two-dot system that shows a
remarkable dependence on B and a due to the long-range Coulomb interaction. We
find that the exchange J changes sign at a finite field (leading to a
pronounced jump in the magnetization) and then decays exponentially. The
magnetization and the spin susceptibilities of the coupled dots are calculated.
We show that the dephasing due to nuclear spins in GaAs can be strongly
suppressed by dynamical nuclear spin polarization and/or by magnetic fields.",9808026v2
1999-07-13,Nonlinear Spin Dynamics in Ferromagnets with Electron-Nuclear Coupling,"Nonlinear spin motion in ferromagnets is considered with nonlinearity due to
three factors: (i) the sample is prepared in a strongly nonequilibrium state,
so that evolution equations cannot be linearized as would be admissible for
spin motion not too far from equilibrium, (ii) the system considered consists
of interacting electron and nuclear spins coupled with each other via hyperfine
forces, and (iii) the sample is inserted into a coil of a resonant electric
circuit producing a resonator feedback field. Due to these nonlinearities,
coherent motion of spins can develop, resulting in their ultrafast relaxation.
A complete analysis of mechanisms triggering such a coherent motion is
presented. This type of ultrafast coherent relaxation can be used for studying
intrinsic properties of magnetic materials.",9907188v1
1999-08-27,Spin relaxation in low-dimensional systems,"We review some of the newest findings on the spin dynamics of carriers and
excitons in GaAs/GaAlAs quantum wells. In intrinsic wells, where the optical
properties are dominated by excitonic effects, we show that exciton-exciton
interaction produces a breaking of the spin degeneracy in two-dimensional
semiconductors. In doped wells, the two spin components of an optically created
two-dimensional electron gas are well described by Fermi-Dirac distributions
with a common temperature but different chemical potentials. The rate of the
spin depolarization of the electron gas is found to be independent of the mean
electron kinetic energy but accelerated by thermal spreading of the carriers.",9908416v1
1999-10-05,"Observation of two time scales in the ferromagnetic manganite La(1-x)Ca(x)MnO(3), x = 0.3","We report new zero-field muon spin relaxation and neutron spin echo
measurements in ferromagnetic (FM) (La,Ca)MnO3 which taken together suggest two
spatially separated regions in close proximity possessing very different Mn-ion
spin dynamics. One region corresponds to an extended cluster which displays
'critical slowing down' near Tc and an increasing volume fraction below Tc. The
second region possesses more slowly fluctuating spins and a decreasing volume
fraction below Tc. These data are discussed in terms of the growth of small
polarons into overlapping regions of correlated spins below Tc, resulting in a
microscopically inhomogeneous FM transition.",9910064v1
2000-02-13,Magnetic impurities in the one-dimensional spin-orbital model,"Using one-dimensional spin-orbital model as a typical example of quantum spin
systems with richer symmetries, we study the effect of an isolated impurity on
its low energy dynamics in the gapless phase through bosonization and
renormalization group methods. In the case of internal impurities, depending on
the symmetry, the boundary fixed points can be either an open chain with a
residual spin or (and) orbital triplet left behind, or a periodic chain.
However, these two fixed points are indistinguishable in the sense that in both
cases, the lead-correction-to-scaling boundary operators (LCBO) only show
Fermi-liquid like corrections to thermodynamical quantities. (Except the
possible Curie-like contributions from the residual moments in the latter
cases.) In the case of external (Kondo) impurities, the boundary fixed points,
depending on the sign of orbital couplings, can be either an open chain with an
isolated orbital doublet due to Kondo screening or it will flow to an
intermediate fixed point with the same LCBO as that of the two-channel Kondo
problem. Comparison with the Kondo effect in one-dimensional (1D) Heisenberg
spin chain and multi-band Hubbard models is also made.",0002184v1
2000-04-10,Quantum Impurity in a Nearly Critical Two Dimensional Antiferromagnet,"We describe the spin dynamics of an arbitrary localized impurity in an
insulating two dimensional antiferromagnet, across the host transition from a
paramagnet with a spin gap to a Neel state. The impurity spin susceptibility
has a Curie-like divergence at the quantum-critical coupling, but with a
universal, effective spin which is neither an integer nor a half-odd-integer.
In the Neel state, the transverse impurity susceptibility is a universal number
divided by the host spin stiffness (which determines the energy cost to slow
twists in the orientation of the Neel order). These, and numerous other results
for the thermodynamics, Knight shift, and magnon damping have significant
applications to experiments on layered transition metal oxides.",0004156v1
2000-09-06,Mixing of magnetic and phononic excitations in incommensurate Spin-Peierls systems,"We analyze the excitation spectra of a spin-phonon coupled chain in the
presence of a soliton. This is taken as a microscopic model of a Spin-Peierls
material placed in a high magnetic field. We show, by using a semiclassical
approximation in the bosonized representation of the spins that a trapped
magnetic state obtained in the adiabatic approximation is destroyed by
dynamical phonons. Low energy states are phonons trapped by the soliton. When
the magnetic gap is smaller than the phonon frequencies the only low energy
state is a mixed magneto-phonon state with the energy of the gap. We emphasize
that our results are relevant for the Raman spectra of the inorganic
Spin-Peierls material CuGeO$_3$.",0009091v1
2001-02-21,Spin correlation and Discrete symmetry in Spinor Bose-Einstein Condensates,"We study spin correlations in Bose-Einstein condensates of spin 1 bosons with
scatterings dominated by a total spin equal 2 channel. We show the low energy
spin dynamics in the system can be mapped into an $o(n)$ nonlinear sigma
model(NL$\sigma$M). $n=3$ at the zero magnetic field limit and $n=2$ in the
presence of weak magnetic fields. In an ordered phase, the ground state has a
hidden $Z_2$ symmetry and is degenerate under the group $[U(1)\times
S^{n-1}]/Z_2$. We explore consequences of the hidden symmetry and propose some
measurements to probe it.",0102372v4
2001-05-03,Probing Spin-Charge Separation in Tunnel-Coupled Parallel Quantum Wires,"Interactions in one-dimensional (1D) electron systems are expected to cause a
dynamical separation of electronic spin and charge degrees of freedom. A
promising system for experimental observation of this non-Fermi-liquid effect
consists of two quantum wires coupled via tunneling through an extended uniform
barrier. Here we consider the minimal model of an interacting 1D electron
system exhibiting spin-charge separation and calculate the differential
tunneling conductance as well as the density-density response function. Both
quantities exhibit distinct strong features arising from spin-charge
separation. Our analysis of these features within the minimal model neglects
interactions between electrons of opposite chirality and applies therefore
directly to chiral 1D electron systems realized, e.g., at the edge of integer
quantum-Hall systems. Physical insight gained from our results is useful for
interpreting current experiment in quantum wires as our main conclusions still
apply with nonchiral interactions present. In particular, we discuss the effect
of charging due to applied voltages, and the possibility to observe spin-charge
separation in a time-resolved experiment.",0105066v3
2001-05-15,Haldane Gapped Spin Chains: Exact Low Temperature Expansions of Correlation Functions,"We study both the static and dynamic properties of gapped, one-dimensional,
Heisenberg, anti-ferromagnetic, spin chains at finite temperature through an
analysis of the O(3) non-linear sigma model. Exploiting the integrability of
this theory, we are able to compute an exact low temperature expansion of the
finite temperature correlators. We do so using a truncated `form-factor'
expansion and so provide evidence that this technique can be successfully
extended to finite temperature. As a direct test, we compute the static
zero-field susceptibility and obtain an exact match to the susceptibility
derived from the low temperature expansion of the exact free energy. We also
study transport properties, computing both the spin conductance and the
NMR-relaxation rate, 1/T_1. We find these quantities to show ballistic
behaviour. In particular, the computed spin conductance exhibits a non-zero
Drude weight at finite temperature and zero applied field. The physics thus
described differs from the spin diffusion reported by Takigawa et al. from
experiments on the Haldane gap material, AgVP_2S_6.",0105284v1
2001-06-04,Haldane-Gapped Spin Chains as Luttinger Liquids: Correlation Functions at Finite Field,"We study the behavior of Heisenberg, antiferromagnetic, integer-spin chains
in the presence of a magnetic field exceeding the attendant spin gap. For
temperatures much smaller than the gap, the spin chains exhibit Luttinger
liquid behavior. We compute exactly both the corresponding Luttinger parameter
and the Fermi velocity as a function of magnetic field. This enables the
computation of a number of correlators from which we derive the spin
conductance, the expected form of the dynamic structure factor relevant to
inelastic neutron scattering experiments, and NMR relaxation rates. We also
comment upon the robustness of the magnetically induced gapless phase both to
finite temperature and finite couplings between neighbouring chains.",0106037v2
2002-01-07,"Quantum and classical localisation, the spin quantum Hall effect and generalisations","We consider network models for localisation problems belonging to symmetry
class C. This symmetry class arises in a description of the dynamics of
quasiparticles for disordered spin-singlet superconductors which have a
Bogoliubov - de Gennes Hamiltonian that is invariant under spin rotations but
not under time-reversal. Our models include but also generalise the one studied
previously in the context of the spin quantum Hall effect. For these systems we
express the disorder-averaged conductance and density of states in terms of
sums over certain classical random walks, which are self-avoiding and have
attractive interactions. A transition between localised and extended phases of
the quantum system maps in this way to a similar transition for the classical
walks. In the case of the spin quantum Hall effect, the classical walks are the
hulls of percolation clusters, and our approach provides an alternative
derivation of a mapping first established by Gruzberg, Read and Ludwig, Phys.
Rev. Lett. 82, 4254 (1999).",0201080v1
2002-04-10,Dynamical Critical Phenomena in three-dimensional Heisenberg Spin Glasses,"Spin-glass (SG) and chiral-glass (CG) orderings in three dimensional (3D)
Heisenberg spin glass with and without magnetic anisotropy are studied by using
large-scale off-equilibrium Monte Carlo simulations. A characteristic time of
relaxation, which diverges at a transition temperature in the thermodynamic
limit, is obtained as a function of the temperature and the system size. Based
on the finite-size scaling analysis for the relaxation time, it is found that
in the isotropic Heisenberg spin glass, the CG phase transition occurs at a
finite temperature, while the SG transition occurs at a lower temperature,
which is compatible with zero. Our results of the anisotropic case support the
chirality scenario for the phase transitions in the 3D Heisenberg spin glasses.",0204225v2
2002-06-27,Spin dynamics in stripe-ordered La5/3Sr1/3NiO4,"Polarized and unpolarized neutron inelastic scattering has been used to
measure the spin excitations in the spin-charge-ordered stripe phase of
La5/3Sr1/3NiO4. At high energies, sharp magnetic modes are observed
characteristic of a static stripe lattice. The energy spectrum is described
well by a linear spin wave model with intra- and inter-stripe exchange
interactions between neighbouring Ni spins given by J = 15 +/- 1.5 meV and J' =
7.5 +/- 1.5 meV respectively. A pronounced broadening of the magnetic
fluctuations in a band between 10 meV and 25 meV is suggestive of coupling to
collective motions of the stripe domain walls.",0206536v1
2002-09-25,Spin Glass Behavior in RuSr2Gd1.5Ce0.5Cu2O10,"The dynamics of the magnetic properties of polycrystalline
RuSr2Gd1.5Ce0.5Cu2O10 (Ru-1222) have been studied by ac susceptibility and dc
magnetization measurements, including relaxation and ageing studies. Ru-1222 is
a reported magneto-superconductor with Ru spins magnetic ordering at
temperatures near 100 K and superconductivity in Cu-O2 planes below Tc ~ 40 K.
The exact nature of Ru spins magnetic ordering is still debated and no
conclusion has been reached yet. In this work, a frequency-dependent cusp was
observed in ac susceptibility vs. T measurements, which is interpreted as a
spin glass transition. The change in the cusp position with frequency follows
the Vogel-Fulcher law, which is commonly accepted to describe a spin glass with
magnetically interacting clusters. Such interpretation is supported by
themoremanaent magnetization (TRM) measurements at T = 60 K. TRM relaxations
are well described by a stretched exponential relation, and present significant
ageing effects.",0209593v1
2002-10-04,Jordan-Wigner approach to dynamic correlations in spin-ladders,"We present a method for studying the excitations of low-dimensional quantum
spin systems based on the Jordan-Wigner transformation. Using an extended
RPA-scheme we calculate the correlation function of neighboring spin flips
which well approximates the optical conductivity of ${\rm Sr_2CuO_3}$. We
extend this approach to the two-leg $S=1/2$--ladder by numbering the spin
operators in a meander-like sequence. We obtain good agreement with the optical
conductivity of the spin ladder compound (La,Ca)$_{14}$Cu$_{24}$O$_{41}$ for
polarization along the rungs. For polarization along the legs higher order
correlations are important to explain the weight of high-energy continuum
excitations and we estimate the contribution of 4-- and 6--fermion processes.",0210103v1
2002-11-19,Theory of phase fluctuating d-wave superconductors and the spin response in underdoped cuprates,"The minimal theory of spin of gapless quasiparticles coupled to fluctuating
vortex defects in the phase of the d-wave superconducting order parameter at
T=0 is studied. With the proliferation of the vortex loops the theory reduces
to the previuosly studied QED3, with its concomitant spin-density-wave (chiral)
instability. We find a single superconductor-insulator phase transition, which
may be fluctuation induced first-order, at which vortices condense and the
chiral symmetry for fermions dynamically breaks. We compute the spin-spin
correlation function deep in the fluctuating superconducting state, and discuss
some prominent trends in the neutron scattering data on underdoped cuprates in
light of our results.",0211418v4
2003-01-08,Spin relaxation in (110) and (001) InAs/GaSb superlattices,"We report an enhancement of the electron spin relaxation time (T1) in a (110)
InAs/GaSb superlattice by more than an order of magnitude (25 times) relative
to the corresponding (001) structure. The spin dynamics were measured using
polarization sensitive pump probe techniques and a mid-infrared, subpicosecond
PPLN OPO. Longer T1 times in (110) superlattices are attributed to the
suppression of the native interface asymmetry and bulk inversion asymmetry
contributions to the precessional D'yakonov Perel spin relaxation process.
Calculations using a nonperturbative 14-band nanostructure model give good
agreement with experiment and indicate that possible structural inversion
asymmetry contributions to T1 associated with compositional mixing at the
superlattice interfaces may limit the observed spin lifetime in (110)
superlattices. Our findings have implications for potential spintronics
applications using InAs/GaSb heterostructures.",0301080v1
2003-04-04,Kinetic Theory of a Spin-1/2 Bose-Condensed Gas,"We derive a kinetic theory for a spin-1/2 Bose-condensed gas of two-level
atoms at finite temperatures. The condensate dynamics is described by a
generalized Gross-Pitaevskii equation for the two-component spinor order
parameter, which includes the interaction with the uncondensed fraction. The
noncondensate atoms are described by a quantum kinetic equation, which is a
generalization of the spin kinetic equation for spin-polarized quantum gases to
include couplings to the condensate degree of freedom. The kinetic equation is
used to derive hydrodynamic equations for the noncondensate spin density. The
condensate and noncondensate spins are coupled directly through the exchange
mean field. Collisions between the condensate and noncondensate atoms give rise
to an additional contribution to the spin diffusion relaxation rate. In
addition, they give rise to mutual relaxation of the condensate and
noncondensate due to lack of local equilibrium between the two components.",0304095v3
2003-06-16,Gate control of spin dynamics in III-V semiconductor quantum dots,"We show that the g-factor and the spin-flip time T_{1} of a heterojunction
quantum dot is very sensitive to the band-bending interface electric field even
in the absence of wave function penetration into the barrier. When this
electric field is of the order of 10^{5} V/cm, g and T_{1} show high
sensitivity to dot radius and magnetic field arising from the interplay between
Rashba and Dresselhaus spin-orbit interactions. This result opens new
possibilities for the design of a quantum dot spin quantum computer where
g-factor and T_{1} can be engineered by manipulating the spin-orbit coupling
through external gates.",0306417v2
2003-09-06,Observation of spinor dynamics in optically trapped 87Rb Bose-Einstein Condensates,"We measure spin mixing of F=1 and F=2 spinor condensates of 87Rb atoms
confined in an optical trap. We determine the spin mixing time to be typically
less than 600 ms and observe spin population oscillations. The equilibrium spin
configuration in the F=1 manifold is measured for different magnetic fields and
found to show ferromagnetic behavior for low field gradients. An F=2 condensate
is created by microwave excitation from F=1 manifold, and this spin-2
condensate is observed to decay exponentially with time constant 250 ms.
Despite the short lifetime in the F=2 manifold, spin mixing of the condensate
is observed within 50 ms.",0309164v2
2003-09-08,Hidden glassy behaviors in an ideal Heisenberg Kagomé antiferromagnet,"Dynamics of classical Heisenberg spins, ${\bf S}_i=({\bf s}_i,S_{iz})$, on
the Kagom\'{e} lattice has been studied. An ideal Heisenberg Kagom\'{e}
antiferromagnet is known to remain disordered down to T=0 due to the
macroscopic degeneracy of the ground state. Through the study, however, we find
that ${\bf S}_i$ and their planar components ${\bf s}_i$ behave in a
qualitatively different way and especially planar spins (${\bf s}_i$) show the
exotic glass-like transition in the very low temperature $T\sim 0.003J$ ($J$:
spin exchange). The glassy behaviors of ${\bf s}_i$ would be found to be driven
by the spin-nematic fluctuations, different from ordinary spin glasses by
disorders or anisotropies.",0309200v1
2003-10-14,Unusual interplay between copper-spin and vortex dynamics in slightly overdoped La{1.83}Sr{0.17}CuO{4},"Our inelastic neutron scattering experiments of the spin excitations in the
slightly overdoped La{1.83}Sr{0.17}CuO{4} compound show that, under the
application of a magnetic field of 5 Tesla, the low-temperature susceptibility
undergoes a weight redistribution centered at the spin-gap energy. Furthermore,
by comparing the temperature dependence of the neutron data with
ac-susceptibility and magnetization measurements, we conclude that the filling
in of the spin gap tracks the irreversibility/melting temperature rather than
Tc2, which indicates an unusual interplay between the magnetic vortices and the
spin excitations even in the slightly overdoped regime of high-temperature
superconductors.",0310298v1
2003-12-31,Spinons in the strongly correlated copper oxide chains in SrCuO2,"We have investigated the spin dynamics in the strongly correlated chain
copper oxide SrCuO$_2$ for energies up to $\gtrsim 0.6$ eV using inelastic
neutron scattering. We observe an acoustic band of magnetic excitations which
is well described by the ""Muller-ansatz"" for the two-spinon continuum in the
S=1/2 antiferromagnetic Heisenberg spin chain. The lower boundary of the
continuum extends up to $\approx 360$ meV, which corresponds to an exchange
constant $J = 226(12)$ meV. Our finding that an effective Heisenberg spin
Hamlitonian adequately describes the spin sector of this 1D electron system,
even though its energy scale is comparable to that of charge excitations,
provides compelling experimental evidence for spin-charge separation.",0312724v2
2004-04-06,"Disorder, inhomogeneity and spin dynamics in f-electron non-Fermi liquid systems","Muon spin rotation and relaxation ($\mu$SR) experiments have yielded evidence
that structural disorder is an important factor in many f-electron-based
non-Fermi-liquid (NFL) systems. Disorder-driven mechanisms for NFL behaviour
are suggested by the observed broad and strongly temperature-dependent $\mu$SR
(and NMR) linewidths in several NFL compounds and alloys. Local disorder-driven
theories (Kondo disorder, Griffiths-McCoy singularity) are, however, not
capable of describing the time-field scaling seen in muon spin relaxation
experiments, which suggest cooperative and critical spin fluctuations rather
than a distribution of local fluctuation rates. A strong empirical correlation
is established between electronic disorder and slow spin fluctuations in NFL
materials",0404118v1
2004-06-18,Spin pumping and magnetization dynamics in ferromagnet-Luttinger liquid junctions,"We study spin transport between a ferromagnet with time-dependent
magnetization and a conducting carbon nanotube or quantum wire, modeled as a
Luttinger liquid. The precession of the magnetization vector of the ferromagnet
due for instance to an outside applied magnetic field causes spin pumping into
an adjacent conductor. Conversely, the spin injection causes increased
magnetization damping in the ferromagnet. We find that, if the conductor
adjacent to the ferromagnet is a Luttinger liquid, spin pumping/damping is
suppressed by interactions, and the suppression has clear Luttinger liquid
power law temperature dependence. We apply our result to a few particular
setups. First we study the effective Landau-Lifshitz-Gilbert (LLG) coupled
equations for the magnetization vectors of the two ferromagnets in a FM-LL-FM
junction. Also, we compute the Gilbert damping for a FM-LL and a FM-LL-metal
junction.",0406437v1
2004-12-15,"Absence of the impurity-induced magnetic order in the electron-doped high-T_c_ cuprates Pr_0.86_LaCe_0.14_Cu_1-y_(Zn, Ni)_y_O_4_","Zero-field muon-spin-relaxation measurements have been carried out in order
to investigate the Zn- and Ni-substitution effects on the Cu-spin dynamics in
the electron-doped Pr_0.86_LaCe_0.14_Cu_1-y_(Zn, Ni)_y_O_4+\alpa-\delta_ with y
= 0, 0.01, 0.02, 0.05 and different values of the reduced oxygen content
\delta(\delta \le 0.09). For the samples with y = 0 and very small \delta
values of \delta < 0.01, a muon-spin precession due to the formation of a
long-range antiferromagnetic order has been observed at low temperatures below
\~ 5 K. For the moderately oxygen-reduced samples of 0.01 \le \delta \le 0.09,
on the contrary, no muon-spin precession has been observed and the temperature
dependence of the spectra is similar to one another regardless of the y value.
That is, no impurity-induced slowing down of the Cu-spin fluctuations has been
detected, which is very different from the results of the hole-doped high-T_c_
cuprates. The reason is discussed.",0412398v2
2005-01-20,Magnetically Stabilized Order. II: Critical states and algebraically ordered nematic spin liquids in one-dimensional optical lattices,"We investigate the Zeeman-field-driven quantum phase transitions between
singlet spin liquids and algebraically ordered O(2) nematic spin liquids of
spin-one bosons in one-dimensional optical lattices. We find that the critical
behavior is characterized by condensation of hardcore bosons instead of ideal
magnons in high dimensional lattices. Critical exponents are strongly
renormalized by hardcore interactions and critical states are equivalent to the
free Fermion model up to the Friedal oscillations. We also find that the
algebraically ordered nematic spin liquids close to critical points are fully
characterized by the Luttinger liquid dynamics with Luttinger liquid parameters
magnetically tunable. The Bethe Ansatz solution has been applied to determine
the critical magnetization and nematic correlations.",0501490v2
2005-02-08,Determining Energy Barriers by Iterated Optimization: The Two-Dimensional Ising Spin Glass,"Energy barriers determine the dynamics in many physical systems like
structural glasses, disordered spin systems or proteins. Here we present an
approach, which is based on subdividing the configuration space in a
hierarchical manner, leading to upper and lower bounds for the energy barrier
separating two configurations. The fundamental operation is to perform a
constrained energy optimization, where the degree of constraintness increases
with the level in the hierarchy. As application, we consider Ising spin
glasses, where the energy barrier which needs to be surmounted in order to flip
a compact region of spins of linear dimension $L$ are expected to scale as
$L^{\psi}$. The exponent $\psi$ is very hard to estimate from experimental and
simulation studies. By using the new approach, applying efficient combinatorial
matching algorithms, we are able to give the first non-trivial numerical bounds
$0.25 < \psi < 0.54$ for the two-dimensional Ising spin glass.",0502201v1
2005-03-07,Neutron scattering studies of the spin ices Ho2Ti2O7 and Dy2Ti2O7 in applied magnetic field,"Neutron diffraction has been used to investigate the magnetic correlations in
single crystals of the spin ice materials Ho2Ti2O7 and Dy2Ti2O7 in an external
magnetic field applied along either the [001] or [1-10] crystallographic
directions. With the field applied along [001] a long range ordered groundstate
is selected from the spin ice manifold. With the field applied along [1-10] the
experiments show that the spin system is separated into parallel (alpha) and
perpendicular (beta) chains with respect to the field. This leads to partial
ordering and the appearance of quasi-one-dimensional magnetic structures. In
both field orientations this frustrated spin system is defined by the
appearance of metastable states, magnetization plateaux and unusually slow,
field regulated dynamics.",0503160v1
2005-04-14,Optical pumping of the electron spin polarization in bulk CuCl,"In CuCl bulk crystal negatively charged excitons (trions $X^-$) can be
induced by the resonant optical excitation of extra electrons in conduction
band minimum. In the case of light polarization and due to the top valence band
structure of CuCl only the electrons with spin antiparallel to the direction of
the light propagation contribute to the formation of $X^-$, while the emerging
$X^-$ can recombine into both possible electron states, with spin parallel and
antiparallel to the direction of light propagation. We propose to use this
mechanism for optical electronic spin pumping. We describe the dynamics of
pumping in terms of density matrix formalism. The coherent pumping laser pulse
propagating through the sample is described by Maxwell wave equation coupled to
the density matrix evolution equations. The results of our approximate simple
model calculations suggest that spin polarization close to 100% can be achieved
in time shorter than 100ps.",0504368v2
2005-05-20,The lower bound of barrier-energy in spin glasses: a calculation of the exponent on hierarchical lattice,"We argue that the lower bound to the barrier energy to flip an up/down spin
domain embedded in a down/up spin environment for Ising spin glass is
independent of the size of the system. The argument shows the existence of at
least one dynamical way through which it is possible to bypass local maxima in
the phase space. For an arbitrary case where one flips any cluster of spin of
size $l$, we have numerically calculated a lower bound to the exponent $\psi$
characterizing the barrier one has to overcome. In this case $\psi$
corresponding to the lower bound calculated on hierarchical lattice comes out
to be equal to $\theta $ the exponent characterizing the domain wall energy in
ground state.",0505516v1
2005-07-12,Symplectic integrators for classical spin systems,"We suggest a numerical integration procedure for solving the equations of
motion of certain classical spin systems which preserves the underlying
symplectic structure of the phase space. Such symplectic integrators have been
successfully utilized for other Hamiltonian systems, e. g. for molecular
dynamics or non-linear wave equations. Our procedure rests on a decomposition
of the spin Hamiltonian into a sum of two completely integrable Hamiltonians
and on the corresponding Lie-Trotter decomposition of the time evolution
operator. In order to make this method widely applicable we provide a large
class of integrable spin systems whose time evolution consists of a sequence of
rotations about fixed axes. We test the proposed symplectic integrator for
small spin systems, including the model of a recently synthesized magnetic
molecule, and compare the results for variants of different order.",0507262v1
2005-07-22,Neutron Scattering Study of Quantum Phase Transitions in Integral Spin Chains,"Quite a few low-dimensional magnets are quantum-disordered ``spin liquids''
with a characteristic gap in the magnetic excitation spectrum. Among these are
antiferromagnetic chains of integer quantum spins. Their generic feature are
long-lived massive (gapped) excitations (magnons) that are subject to Zeeman
splitting in external magnetic fields. The gap in one of the magnon branches
decreases with field, driving a soft-mode quantum phase transition. The system
then enters a qualitatively new high-field phase. The actual properties at high
fields, particularly the spin dynamics, critically depend on the system under
consideration. Recent neutron scattering studies of organometallic polymer
crystals NDMAP (Haldane spin chains with anisotropy) and NTENP (dimerized S=1
chains) revealed rich and unique physics.",0507534v1
2005-07-27,"Electronic interactions in strongly correlated systems: what is the ""glue"" for high temperature superconductivity?","Recent observation of a ""kink"" in single-particle dispersion in photoemission
experiments on cuprate superconductors has initiated a heated debate over the
issue of a boson that mediates the pairing in cuprates. If the ""kink"" is indeed
caused by interaction with a bosonic excitation, then there are two possible
candidates: phonons and spin fluctuations. Here, the role of anti-ferromagnetic
spin fluctuations in shaping the phase diagram of cuprate superconductors will
be discussed. By using the local (momentum-integrated) dynamic spin
susceptibility, recently measured in neutron scattering experiments to high
energies, the electronic self-energies are calculated that agree in many
aspects with those measured directly in angle-resolved photoemission (ARPES)
and optical spectroscopies. The spin fluctuations therefore seem to play a role
typically played by phonons in renormalizing single particles. The key question
emerging from this picture is whether the coupling detected in ARPES reflects
the mediating boson, i.e. whether the spin fluctuations may be responsible for
superconducting pairing.",0507653v1
2005-10-13,Statics and dynamics of an incommensurate spin order in a geometrically frustrated antiferromagnet CdCr$_2$O$_4$,"Using elastic and inelastic neutron scattering we show that a cubic spinel,
CdCr$_2$O$_4$, undergoes an elongation along the c-axis ($c > a = b$) at its
spin-Peierls-like phase transition at $T_N$ = 7.8 K. The N\'{e}el phase ($T <
T_N$) has an incommesurate spin structure with a characteristic wave vector
\textbf{Q}$_M$ = (0,$\delta$,1) with $\delta \sim$ 0.09 and with spins lying on
the $ac$-plane. This is in stark contrast to another well-known Cr-based
spinel, ZnCr$_2$O$_4$, that undergoes a c-axis contraction and a commensurate
spin order. The magnetic excitations of the incommensurate N\'{e}el state has a
weak anisotropy gap of 0.6 meV and it consists of at least three bands
extending up to 5 meV.",0510363v1
2005-12-16,Rashba billiards,"We study the energy levels of non-interacting electrons confined to move in
two-dimensional billiard regions and having a spin-dependent dynamics due to a
finite Rashba spin splitting. The Green's function for such Rashba billiards is
constructed analytically and used to find the area and perimeter contributions
to the density of states, as well as the smooth counting function. We show
that, in contrast to systems with spin-rotational invariance, Rashba billiards
always possess a negative energy spectrum. A semi-classical analysis is
presented to interpret the singular behavior of the density of states at
certain negative energies. Our detailed analysis of the spin structure of
Rashba billiards reveals a finite out-of-plane spin projection for electron
eigenstates.",0512397v2
2006-01-17,Electron Correlations and the Minority-Spin Band Gap in Half-Metallic Heusler Alloys,"Electron-electron correlations affect the band gap of half-metallic
ferromagnets by introducing non-quasiparticle states just above the Fermi
level. In contrast to the spin-orbit coupling, a large asymmetric
non-quasiparticle spectral weight is present in the minority-spin channel,
leading to a peculiar finite-temperature spin depolarization effects. Using
recently developed first-principle dynamical mean field theory, we investigate
these effects for the half-metallic ferrimagnetic Heusler compound FeMnSb. We
discuss depolarization effects in terms of strength of local Coulomb
interaction $U$ and temperature in FeMnSb. We propose Ni$_{1-x}$Fe$_{x}$MnSb
alloys as a perspective materials to be used in spin-valve structures and for
experimental search of non-quasiparticle states in half-metallic materials.",0601376v1
2006-04-28,Emergence of inhomogeneous moments from spin liquid in the triangular-lattice Mott insulator $κ$-(ET)$_2$Cu$_2$(CN)$_3$,"The static and dynamic local spin susceptibility of the organic Mott
insulator $\kappa$-(ET)$_2$Cu$_2$(CN)$_3$, a model material of the spin- 1/2
triangular lattice, is studied by $^{13}$C NMR spectroscopy from room
temperature down to 20 mK. We observe an anomalous field-dependent spectral
broadening with the continuous and bipolar shift distribution, appearing
without the critical spin fluctuations. It is attributable to spatially
nonuniform magnetizations induced in the spin liquid under magnetic fields. The
amplitude of the magnetization levels off below 1 K, while the low-lying spin
fluctuations survive toward the ground state, as indicated by the temperature
profile of the relaxation rates.",0604650v2
2006-05-15,Solution of the problem of catastrophic relaxation of homogeneous spin precession in superfluid $^3$He-B,"The quantitative analysis of the ""catastrophic relaxation"" of the coherent
spin precession in $^3$He-B is presented. This phenomenon has been observed
below the temperature about 0.5 T$_c$ as an abrupt shortening of the induction
signal decay. It is explained in terms of the decay instability of homogeneous
transverse NMR mode into spin waves of the longitudinal NMR. Recently the cross
interaction amplitude between the two modes has been calculated by Sourovtsev
and Fomin \cite{SF} for the so-called Brinkman-Smith configuration, i.e. for
the orientation of the orbital momentum of Cooper pairs along the magnetic
field, ${\bf L}\parallel {\bf H}$. In their treatment, the interaction is
caused by the anisotropy of the speed of the spin waves. We found that in the
more general case of the non-parallel orientation of ${\bf L}$ corresponding to
the typical conditions of experiment, the spin-orbital interaction provides the
additional interaction between the modes. By analyzing experimental data we are
able to distinguish which contribution is dominating in different regimes.",0605386v1
2006-05-23,Dynamics of a trapped domain wall in a current perpendicular to the plane spin valve nano-structure,"A study of transverse tail-to-tail magnetic domain walls (DW) in novel
current perpendicular to the plane (CPP) spin valves (SV) of various dimensions
is presented. For films with dimensions larger than the DW width, we find that
DW motion can give rise to a substantial low frequency noise. For dimensions
comparable to the DW width, we show that the DW can be controlled by an
external field or by a spin momentum torque as opposed to the case of CPP-SV
with uniform magnetization. It is shown that in a single domain biased CPP-SV,
the spin torque can give rise to 1/f-type noise. The dipolar field, the spin
torque and the Oersted field are all accounted for in this work. Our proposed
SV requires low current densities to move DW and can simulate devices for
logical operation or magnetic sensing without having to switch the
magnetization in the free layer.",0605586v1
2006-06-27,Destruction of Neel order and local spin spirals in insulating La_{2-x}Sr_xCuO_4,"Starting from the t-J model, we derive an effective field theory describing
the spin dynamics in the insulating phase of La_{2-x}Sr_xCuO_4, x < 0.055, at
low temperature. Using Monte Carlo simulations, we show that the destruction of
Neel order is driven by the single-hole localization length kappa. A phase
transition at 2% doping is consistent with the value of kappa known from the
variable range hopping conductivity. The static spin structure factor obtained
in our calculations is in perfect agreement with neutron scattering data over
the whole range of doping. We also demonstrate that topological defects (spin
vortex-antivortex pairs) are an intrinsic property of the spin-glass ground
state.",0606679v1
2006-07-28,Spin-polaron excitations in a doped Shastry-Sutherland model,"Using variational algorithm on an infinite Shastry-Sutherland (SS) lattice we
show that the introduction of a static nonmagnetic impurity into a dimerized
ground state leads to a formation of a small, localized spin polaron
surrounding the impurity site. Due to a particular symmetry of the SS lattice,
the polaron is extremely anisotropic with a short spatial extent. The presence
of nonmagnetic impurities leads to a formation of pronounced in-gap peaks in
the dynamical spin structure factor, which we attribute to the spin-doublet
excitations of a single unpaired spin $S=1/2$ surrounded by triplet
fluctuations. Our results are relevant for the description of
SrCu$_2$(BO$_3$)$_{2}$ compound when doped with nonmagnetic atoms at Cu sites.",0607753v1
2006-09-11,Effects of a strict site-occupation constraint in the description of quantum spin systems at finite temperature,"We study quantum spin systems described by Heisenberg-like models at finite
temperature with a strict site-occupation constraint imposed by a procedure
originally proposed by V. N. Popov and S. A. Fedotov \cite{Popov-88}. We show
that the strict site-occupation constraint modifies quantitatively the
behaviour of physical quantities when compared to the case for which this
constraint is fixed in the average by means of a Lagrange multiplier method.
The relevance of the N\'eel state with the strict site-occupation contraint of
the spin lattice is studied. With an exact site-occupation the transition
temperature of the antiferromagnetic N\'eel and spin liquid order parameters
are twice as large as the critical temperature one gets with an average
Lagrange multiplier method. We consider also a mapping of the low-energy spin
Hamiltonian into a $QED_3$ Lagrangian of spinons. In this framework we compare
the dynamically generated mass to the one obtained by means of an average
site-occupation constraint.",0609239v1
2007-02-07,Anomalous magnetic phase in an undistorted pyrochlore oxide Cd2Os2O7 induced by geometrical frustration,"We report on the muon spin rotation/relaxation study of a pyrochlore oxide,
Cd2Os2O7, which exhibits a metal-insulator (MI) transition at T_{MI}~225 K
without structural phase transition. It reveals strong spin fluctuation
(>10^8/s) below the MI transition, suggesting a predominant role of geometrical
spin frustration amongst Os^{5+} ions. Meanwhile, upon further cooling, a
static spin density wave discontinuously develops below T_{SDW}~150 K. These
observations strongly suggest the occurrence of an anomalous magnetic
transition and associated change in the local spin dynamics in undistorted
pyrochlore antiferromagnet.",0702164v2
2007-03-08,Quantum Rings with Rashba spin orbit coupling: a path integral approach,"We employ a path integral real time approach to compute the DC conductance
and spin polarization for electrons transported across a ballistic Quantum Ring
with Rashba spin-orbit interaction. We use a piecewise semiclassical
approximation for the particle orbital motion and solve the spin dynamics
exactly, by accounting for both Zeeman coupling and spin-orbit interaction at
the same time. Within our approach, we are able to study how the interplay
between Berry phase, Ahronov Casher phase, Zeeman interaction and weak
localization corrections influences the quantum interference in the conductance
within a wide range of externally applied fields. Our results are helpful in
inerpreting recent measurements on interferometric rings.",0703216v2
2004-02-25,Three dimensional loop quantum gravity: physical scalar product and spin foam models,"In this paper, we address the problem of the dynamics in three dimensional
loop quantum gravity with zero cosmological constant. We construct a rigorous
definition of Rovelli's generalized projection operator from the kinematical
Hilbert space--corresponding to the quantization of the infinite dimensional
kinematical configuration space of the theory--to the physical Hilbert space.
In particular, we provide the definition of the physical scalar product which
can be represented in terms of a sum over (finite) spin-foam amplitudes.
Therefore, we establish a clear-cut connection between the canonical
quantization of three dimensional gravity and spin-foam models. We emphasize
two main properties of the result: first that no cut-off in the kinematical
degrees of freedom of the theory is introduced (in contrast to standard
`lattice' methods), and second that no ill-defined sum over spins (`bubble'
divergences) are present in the spin foam representation.",0402110v3
2006-04-04,Spinning-black-hole binaries: The orbital hang up,"We present the first fully-nonlinear numerical study of the dynamics of
highly spinning black-hole binaries. We evolve binaries from quasicircular
orbits (as inferred from Post-Newtonian theory), and find that the last stages
of the orbital motion of black-hole binaries are profoundly affected by their
individual spins. In order to cleanly display its effects, we consider two
equal mass holes with individual spin parameters S/m^2=0.757, both aligned and
anti-aligned with the orbital angular momentum (and compare with the spinless
case), and with an initial orbital period of 125M. We find that the aligned
case completes three orbits and merges significantly after the anti-aligned
case, which completes less than one orbit. The total energy radiated for the
former case is ~7% while for the latter it is only ~2%. The final Kerr hole
remnants have rotation parameters a/M=0.89 and a/M=0.44 respectively, showing
the unlikeliness of creating a maximally rotating black hole out of the merger
of two spinning holes.",0604012v2
1997-05-07,"Mass Gap, Abelian Dominance and Vortex Dynamics in SU(2) Spin Model","We discuss a new approach to the investigation of the nature of the mass gap
in spin systems with continuous global symmetries which is much analogous to
the method of abelian projection in the gauge theories. We suggest that the
abelian degrees of freedom, in particular, abelian vortices are responsible for
the mass gap generation phenomena in the non-abelian spin systems. To check our
hypothesis we study numerically the three-dimensional SU(2) spin model in the
Maximal Abelian projection. We find that the abelian mass gap in the projected
theory coincides with the full non-abelian mass gap within numerical errors.
The study of the percolation properties of the abelian vortex trajectories
shows that the phase transition and the mass gap generation in the 3D SU(2)
spin model are driven by the abelian vortex condensation.",9705010v2
2004-02-26,"Polarization observables in the processes $p+p\to Θ^+ +Σ^+$ and $n+p\to Θ^+ +Λ^0$, for any spin and parity of the $Θ^+$-hyperon in the threshold region","Using the symmetry properties of the strong interaction, such as the Pauli
principle, the P-invariance, the conservation of the total angular momentum and
isotopic invariance, we establish the spin structure of the threshold matrix
elements for the processes $p+p\to \Theta^+ +\Sigma^+$ and $n+p\to \Theta^+
+\Lambda^0$, in a model independent way, which applies to any spin and parity
of the $\Theta^+$-hyperon in the near threshold region. We predict the double
spin observables for these processes, such as the dependence of the
differential cross section on the polarizations of the colliding nucleons, and
the coefficients of polarization transfer from a nucleon beam or target to the
produced $\Sigma^+$ or $\Lambda^0$ hyperon. We prove that these observables are
sensitive to the P-parity of the $\Theta^+$ baryon, for any value of its spin.
As an example of dynamical considerations, we analyzed these reactions in the
framework of K-meson exchange.",0402277v1
1994-07-25,Random Ising Spins in Two Dimensions - A Flat Space Realization of the KPZ Exponents,"A model describing Ising spins with short range interactions moving randomly
in a plane is considered. In the presence of a hard core repulsion, which
prevents the Ising spins from overlapping, the model is analogous to a
dynamically triangulated Ising model with spins constrained to move on a flat
surface. As a function of coupling strength and hard core repulsion the model
exhibits multicritical behavior, with first and second order transition lines
terminating at a tricritical point. The thermal and magnetic exponents computed
at the tricritical point are consistent with the KPZ values associated with
Ising spins, and with the exact two-matrix model solution of the random Ising
model, introduced previously to describe the effects of fluctuating geometries.",9407166v2
1999-03-02,Higher Spin N=8 Supergravity in AdS_4,"We review the basic structure of the higher spin extension of D=4, N=8 AdS
supergravity. The theory is obtained by gauging the higher spin superalgebra
shs^E(8|4) by a procedure pioneered by Vasiliev. The algebra shs^E(8|4) is a
subalgebra of the enveloping algebra of OSp(8|4). The physical states of the
theory are in one to one correspondence with the symmetric product of two
OSp(8|4) singletons. This singleton theory, which may be viewed in a certain
limit as the supermembrane theory on AdS_4 x S^7, is expected to describe the
dynamics of the higher spin theory. Thus, the higher spin N=8 supergravity on
AdS_4 is conjectured to describe the field theory limit of M-theory on AdS_4 x
S^7.",9903020v1
1999-12-30,Coordinate-Free Action for AdS3 Higher-Spin-Matter Systems,"A coordinate-free action principle for the N=2 supersymmetric model of spin 0
and spin 1/2 matter fields interacting via Chern-Simons higher spin gauge
fields in AdS3 is formulated in terms of star-product algebra of two
oscillators. Although describing proper relativistic dynamics the action does
not contain space-time coordinates. It is given by a supertrace of a
forth-order polynomial in the 3d higher spin superalgebra. The theory admits a
free parameter characterizing the inequivalent vacua associated with the
parameter of mass m of the matter fields. For the case of the massless matter,
the model has a form of the noncommutative 2d Yang-Mills theory with some
infinite-dimensional gauge group. The limit m\to\infty corresponds to the
SU(\infty) 2d Yang-Mills theory.",9912280v2
2004-04-08,Spin bit models from non-planar N=4 SYM,"We study spin models underlying the non-planar dynamics of ${\cal N}=4$ SYM
gauge theory. In particular, we derive the non-local spin chain Hamiltonian
generating dilatations in the gauge theory at leading order in $g_{\rm YM}^2 N$
but exact in ${1\over N}$.
  States in the spin chain are characterized by a spin-configuration and a
linking variable describing how sites in the chain are connected. Joining and
splitting of string/traces are mimicked by a twist operator acting on the
linking variable. The results are applied to a systematic study of non-planar
anomalous dimensions and operator mixing in ${\cal N}=4$ SYM. Intriguingly, we
identify a sequence of SYM operators for which corrections to the one-loop
anomalous dimensions stop at the first ${1\over N}$ non-planar order.",0404066v2
2005-12-29,Cubic interaction vertices for massive and massless higher spin fields,"Using the light-cone formulation of relativistic dynamics, we develop various
methods for constructing cubic interaction vertices and apply these methods to
the study of higher spin fields propagating in flat space of dimension greater
than or equal to four. Generating functions of parity invariant cubic
interaction vertices for massive and massless higher spin fields of arbitrary
symmetry are obtained. We derive restrictions on the allowed values of spins
and the number of derivatives, which provide a classification of cubic
interaction vertices for totally symmetric fields. As an example of application
of the light-cone formalism, we obtain simple expressions for the minimal
Yang-Mills and gravitational interactions of massive totally symmetric
arbitrary spin fields. We give the complete list of parity invariant and parity
violating cubic interaction vertices that can be constructed for massless
fields in five and six-dimensional spaces.",0512342v3
2006-08-01,Gauge invariant Lagrangian formulation of higher spin massive bosonic field theory in AdS space,"We develop the BRST approach to Lagrangian construction for the massive
integer higher spin fields in an arbitrary dimensional AdS space. The theory is
formulated in terms of auxiliary Fock space. Closed nonlinear symmetry algebra
of higher spin bosonic theory in AdS space is found and method of deriving the
BRST operator for such an algebra is proposed. General procedure of Lagrangian
construction describing the dynamics of bosonic field with any spin is given on
the base of the BRST operator. No off-shell constraints on the fields and the
gauge parameters are used from the very beginning. As an example of general
procedure, we derive the Lagrangians for massive bosonic fields with spin 0, 1
and 2 containing total set of auxiliary fields and gauge symmetries.",0608005v3
2007-03-06,BRST approach to Lagrangian construction for fermionic higher spin fields in AdS space,"We develop a general gauge invariant Lagrangian construction for half-integer
higher spin fields in the AdS space of any dimension. Starting with formulation
in terms of auxiliary Fock space we derive the closed nonlinear symmetry
algebras of higher spin fermionic fields in the AdS space and find the
corresponding BRST operator. A universal procedure of constructing the gauge
invariant Lagrangians describing the dynamics of fermionic fields of any spin
is developed. No off-shell constraints for the fields and gauge parameters are
imposed from the very beginning. It is shown that all the constraints
determining the irreducible representation of the AdS group arise as a
consequence of the equations of motion and gauge transformations. As an example
of the general procedure, we derive the gauge invariant Lagrangians for massive
fermionic fields of spin 1/2 and 3/2 containing the total set of auxiliary
fields and gauge symmetries.",0703049v4
2001-04-10,The Gutzwiller Trace Formula for Quantum Systems with Spin,"The Gutzwiller trace formula provides a semiclassical approximation for the
density of states of a quantum system in terms of classical periodic orbits. In
its original form Gutzwiller derived the trace formula for quantum systems
without spin. We will discuss the modifications that arise for quantum systems
with both translational and spin degrees of freedom and which are either
described by Pauli- or Dirac-Hamiltonians. In addition, spectral densities
weighted by expectation values of observables will be considered. It turns out
that in all cases the semiclassical approximation yields sums over periodic
orbits of the translational motion. Spin contributes via weight factors that
take a spin precession along the translational orbits into account.",0104028v1
2002-07-23,Classical Mechanics of a Three Spin Cluster,"A cluster of three spins coupled by single-axis anisotropic exchange exhibits
classical behaviors ranging from regular motion at low and high energies, to
chaotic motion at intermediate energies. A change of variable, taking advantage
of the conserved z-angular momentum, combined with a 3-d graphical presentation
(described in the Appendix), produce Poincare sections that manifest all
symmetries of the system and clearly illustrate the transition to chaos as
energy is increased.
  The three-spin system has four families of periodic orbits. Linearization
around stationary points predicts orbit periods in the low energy
(antiferromagnetic) and high energy (ferromagnetic) limits and also determines
the stability properties of certain orbits at a special intermediate energy.
The energy surface undergoes interesting changes of topology as energy is
varied. We describe the similiarities of our three spin system with the
Anisotropic Kepler Problem and the Henon-Heiles Hamiltonian. An appendix
discusses numerical integration techniques for spin systems.",0207040v1
2005-11-05,The spectral form factor for quantum graphs,"We consider quantum graphs with spin-orbit couplings at the vertices.
Time-reversal invariance implies that the bond S-matrix is in the orthogonal or
symplectic symmetry class, depending on spin quantum number s being integer or
half-integer, respectively. The periodic-orbit expansion of the spectral form
factor is shown to acquire additional weights from spin rotations along orbits.
We determine the spin contribution to the coefficients in an expansion of the
form factor from properties of the representation of the group of spin
transformations on the graph. Consistency with the Circular Orthogonal and
Circular Symplectic Ensemble, respectively, of random matrices is obtained.",0511011v1
1996-05-24,Test of Parity-Conserving Time-Reversal Invariance Using Polarized Neutrons and Nuclear Spin Aligned Holmium,"A test of parity-conserving, time-reversal non-invariance (PC TRNI) has been
performed in 5.9 MeV polarized neutron transmission through nuclear spin
aligned holmium. The experiment searches for the T-violating five-fold
correlation via a double modulation technique - flipping the neutron spin while
rotating the alignment axis of the holmium. Relative cross sections for spin-up
and spin-down neutrons are found to be equal to within $1.2 \times 10^{-5}$
(80\% confidence). This is a two order of magnitude improvement compared to
traditional detailed balance studies of time reversal, and represents the most
precise test of PC TRNI in a dynamical process.",9605005v1
2006-09-06,Coherent Spin Dynamics into Space Quantization,"We propose a mechanism to describe how a physical quantity, which initially
can take continuous values, is restricted within some discrete values after a
measurement. As an example of the present theory, in which interplay between
coherence of motion and fluctuation from disturbance plays an important role,
we investigate motion of a spin state in a magnetic field. First, we point out
that discrete eigenstates are formed from continuous states as a result of
coherence of precession motion of a spin. Next, by assuming disturbance from
environmental electromagnetic fields, we investigate temporal change of
direction of a spin state by applying the first order perturbation theory and
the Monte Carlo technique. Results of simulations show that the spins, whose
directions are randomly distributed at the initial time, are reoriented toward
only two directions due to fluctuation guided by coherence.",0609039v1
2007-05-02,Geodesics for Efficient Creation and Propagation of Order along Ising Spin Chains,"Experiments in coherent nuclear and electron magnetic resonance, and optical
spectroscopy correspond to control of quantum mechanical ensembles, guiding
them from initial to final target states by unitary transformations. The
control inputs (pulse sequences) that accomplish these unitary transformations
should take as little time as possible so as to minimize the effects of
relaxation and decoherence and to optimize the sensitivity of the experiments.
Here we give efficient syntheses of various unitary transformations on Ising
spin chains of arbitrary length. The efficient realization of the unitary
transformations presented here is obtained by computing geodesics on a sphere
under a special metric. We show that contrary to the conventional belief, it is
possible to propagate a spin order along an Ising spin chain with coupling
strength J (in units of Hz), significantly faster than 1/(2J) per step. The
methods presented here are expected to be useful for immediate and future
applications involving control of spin dynamics in coherent spectroscopy and
quantum information processing.",0705.0378v1
2007-05-11,Magnetic focusing of charge carriers from spin-split bands: Semiclassics of a Zitterbewegung effect,"We present a theoretical study of the interplay between cyclotron motion and
spin splitting of charge carriers in solids. While many of our results apply
more generally, we focus especially on discussing the Rashba model describing
electrons in the conduction band of asymmetric semiconductor heterostructures.
Appropriate semiclassical limits are distinguished that describe various
situations of experimental interest. Our analytical fomulae, which take full
account of Zeeman splitting, are used to analyse recent magnetic-focusing data.
Surprisingly, it turns out that the Rashba effect can dominate the splitting of
cyclotron orbits even when the Rashba and Zeeman spin-splitting energies are of
the same order. We also find that the origin of spin-dependent cyclotron motion
can be traced back to Zitterbewegung-like oscillatory dynamics of charge
carriers from spin-split bands. The relation between the two phenomena is
discussed, and we estimate the effect of Zitterbewegung-related corrections to
the charge carriers' canonical position.",0705.1741v2
2007-06-02,Long-range frustration in T=0 first-step replica-symmetry-broken solutions of finite-connectivity spin glasses,"In a finite-connectivity spin-glass at the zero-temperature limit, long-range
correlations exist among the unfrozen vertices (whose spin values being
non-fixed). Such long-range frustrations are partially removed through the
first-step replica-symmetry-broken (1RSB) cavity theory, but residual
long-range frustrations may still persist in this mean-field solution. By way
of population dynamics, here we perform a perturbation-percolation analysis to
calculate the magnitude of long-range frustrations in the 1RSB solution of a
given spin-glass system. We study two well-studied model systems, the minimal
vertex-cover problem and the maximal 2-satisfiability problem. This work points
to a possible way of improving the zero-temperature 1RSB mean-field theory of
spin-glasses.",0706.0259v1
2007-06-13,Interplay and optimization of decoherence mechanisms in the optical control of spin quantum bits implemented on a semiconductor quantum dot,"We study the influence of the environment on an optically induced rotation of
a single electron spin in a charged semiconductor quantum dot. We analyze the
decoherence mechanisms resulting from the dynamical lattice response to the
charge evolution induced in a trion-based optical spin control scheme.
Moreover, we study the effect of the finite trion lifetime and of the
imperfections of the unitary evolution such as off-resonant excitations and the
nonadiabaticity of the driving. We calculate the total error of the operation
on a spin-based qubit in an InAs/GaAs quantum dot system and discuss possible
optimization against the different contributions. We indicate the parameters
which allow for coherent control of the spin with a single qubit gate error as
low as $10^{-4}$.",0706.1989v2
2007-06-21,Quantum and thermal fluctuations in a two-dimensional correlated band ferromagnet -- Goldstone-mode preserving investigation with self-energy and vertex corrections,"Ferromagnetism in the t-t' Hubbard model is investigated on a square lattice.
Correlation effects in the form of self-energy and vertex corrections are
systematically incorporated within a spin-rotationally-symmetric scheme which
explicitly preserves the Goldstone mode and is therefore in accord with the
Mermin-Wagner theorem. Interplay of band dispersion and correlation effects on
ferromagnetic-state stability are highlighted with respect to both long- and
short-wavelength fluctuations, which are shown to have substantially different
behaviour. Our approach provides a novel understanding of the enhancement of
ferromagnetism near van Hove filling for t'~0.5 in terms of strongly suppressed
saddle-point contribution to the destabilizing exchange part of spin stiffness.
Finite-temperature electron spin dynamics is investigated directly in terms of
spectral-weight transfer across the Fermi energy due to electron-magnon
coupling. Relevant in the context of recent magnetization measurements on
ultrathin films, the role of strong thermal spin fluctuations in low dimensions
is highlighted, in the anisotropy-stabilized ordered state, by determining the
thermal decay of magnetization and T_c within a renormalized spin-fluctuation
theory.",0706.3088v1
2007-07-24,Pauli-Spin-Blockade Transport through a Silicon Double Quantum Dot,"We present measurements of resonant tunneling through discrete energy levels
of a silicon double quantum dot formed in a thin silicon-on-insulator layer. In
the absence of piezoelectric phonon coupling, spontaneous phonon emission with
deformation-potential coupling accounts for inelastic tunneling through the
ground states of the two dots. Such transport measurements enable us to observe
a Pauli spin blockade due to effective two-electron spin-triplet correlations,
evident in a distinct bias-polarity dependence of resonant tunneling through
the ground states. The blockade is lifted by the excited-state resonance by
virtue of efficient phonon emission between the ground states. Our experiment
demonstrates considerable potential for investigating silicon-based spin
dynamics and spin-based quantum information processing.",0707.3513v2
2007-09-06,Dynamic Nuclear Polarization with Single Electron Spins,"We polarize nuclear spins in a GaAs double quantum dot by controlling
two-electron spin states near the anti-crossing of the singlet (S) and m_S=+1
triplet (T+) using pulsed gates. An initialized S state is cyclically brought
into resonance with the T+ state, where hyperfine fields drive rapid rotations
between S and T+, 'flipping' an electron spin and 'flopping' a nuclear spin.
The resulting Overhauser field approaches 80 mT, in agreement with a simple
rate-equation model. A self-limiting pulse sequence is developed that allows
the steady-state nuclear polarization to be set using a gate voltage.",0709.0920v2
2007-09-27,Spin-liquid dynamics of pyrochlore magnets Gd2Ti2O7 and Gd2Sn2O7,"The spin-liquid phase of two highly frustrated pyrochlore magnets Gd2Ti2O7
and Gd2Sn2O7 is probed using electron spin resonance in the temperature range
1.3 - 30 K. The deviation of the absorption line from the paramagnetic position
\nu =\gamma H observed in both compounds below the Curie-Weiss temperature
\Theta_CW ~ 10 K, suggests an opening up of a gap in the excitation spectra. On
cooling to 1.3 K (which is above the ordering transition T_N ~ 1.0 K) the
resonance spectrum is transformed into a wide band of excitations with the gap
amounting to \Delta ~ 26 GHz (1.2 K) in Gd2Ti2O7 and 18 GHz (0.8 K) in
Gd2Sn2O7. The gaps increase linearly with the external magnetic field. For
Gd2Ti2O7 this branch co-exists with an additional nearly paramagnetic line
absent in Gd2Sn2O7. These low lying excitations with gaps, which are preformed
in the spin-liquid state, may be interpreted as collective spin modes split by
the single-ion anisotropy.",0709.4379v1
2007-11-06,"Four-dimensional CP$^1+$ U(1) lattice gauge theory for 3D antiferromagnets: Phase structure, gauge bosons and spin liquid","In this paper we study the lattice CP$^1$ model in (3+1) dimensions coupled
with a dynamical compact U(1) gauge field. This model is an effective field
theory of the $s={1 \over 2}$ antiferromagnetic Heisenberg spin model in three
spatial dimensions. By means of Monte Carlo simulations, we investigate its
phase structure. There exist the Higgs, Coulomb and confinement phases, and the
parameter regions of these phases are clarified. We also measure magnetization
of O(3) spins, energy gap of spin excitations, and mass of gauge boson. Then we
discuss the relationship between these three phases and magnetic properties of
the high-$T_{\rm c}$ cuprates, in particular the possibility of
deconfined-spinon phase. Effect of dimer-like spin exchange coupling and
ring-exchange coupling is also studied.",0711.0818v1
2007-11-09,A Digital Switch and Femto-Tesla Magnetic Field Sensor Based on Fano Resonance in a Spin Field Effect Transistor,"We show that a Spin Field Effect Transistor, realized with a semiconductor
quantum wire channel sandwiched between half-metallic ferromagnetic contacts,
can have Fano resonances in the transmission spectrum. These resonances appear
because the ferromagnets are half-metallic, so that the Fermi level can be
placed above the majority but below the minority spin band. In that case, the
majority spins will be propagating, but the minority spins will be evanescent.
At low temperatures, the Fano resonances can be exploited to implement a
digital binary switch that can be turned on or off with a very small gate
voltage swing of few tens of microvolts, leading to extremely small dynamic
power dissipation during switching. An array of 500,000 x 500,000 such
transistors can detect ultrasmall changes in a magnetic field with a
sensitivity of 1 femto-Tesla/sqrt{Hz}, if each transistor is biased near a Fano
resonance.",0711.1475v1
2008-05-21,"Manifestations of the hyperfine interaction between electron and nuclear spins in singly-charged (In,Ga)As/GaAs quantum dots","The nuclear spin fluctuations (NSF) as well as the dynamic nuclear
polarization (DNP) and their effects on the electron spins in negatively
charged (In,Ga)As/GaAs quantum dots have been studied by polarized pump-probe
and photoluminescence spectroscopy techniques. The effective magnetic field of
the NSF is about 30 mT at low excitation power. The NSF distribution becomes
highly anisotropic at strong optical excitation by circularly polarized light
with periodically alternating helicity. This phenomenon is attributed to a
decrease of the nuclear spin entropy due to the hyperfine interaction with
polarized electron spins. The DNP is limited to small values for intense, but
short photoexcitation.",0805.3247v1
2008-06-03,Dynamical suppression of the spin-orbit interaction in hadrons,"Spin-dependent interaction in hadrons is considered in the approach of the
QCD string. The string moment of inertia, which ensures the correct (inverse)
Regge slope 2*pi*sigma, is found to suppress the spin-orbit interaction. For
light quarks and moderate angular momenta the suppression constitutes around
25% whereas for large angular momenta the spin-orbit interaction is suppressed
by the factor L^(-2/5). For heavy quarks the effect manifests itself as a
string correction for the spin-dependent potential.",0806.0502v2
2008-06-04,Spin Hall Effect in Noncommutative Coordinates,"A semiclassical constrained Hamiltonian system which was established to study
dynamical systems of matrix valued non-Abelian gauge fields is employed to
formulate spin Hall effect in noncommuting coordinates at the first order in
the constant noncommutativity parameter theta . The method is first illustrated
by studying the Hall effect on the noncommutative plane in a gauge independent
fashion. Then, the Drude model type and the Hall effect type formulations of
spin Hall effect are considered in noncommuting coordinates and \theta deformed
spin Hall conductivities which they provide are acquired. It is shown that by
adjusting \theta different formulations of spin Hall conductivity are
accomplished. Hence, the noncommutative theory can be envisaged as an effective
theory which unifies different approaches to similar physical phenomena.",0806.0707v2
2008-06-05,Theory of spin current in chiral helimagnet,"We give detailed description of the transport spin current in the chiral
helimagnet. Under the static magnetic field applied perpendicular to the
helical axis, the magnetic kink crystal (chiral soliton lattice) is formed.
Once the kink crystal begins to move under the Galilean boost, the spin-density
accumulation occurs inside each kink and there emerges periodic arrays of the
induced magnetic dipoles carrying the transport spin current. The coherent
motion of the kink crystal dynamically generates the spontaneous
demagnetization field. This mechanism is analogous to the
D\""{o}ring-Becker-Kittel mechanism of the domain wall motion in ferromagnets.
To describe the kink crystal motion, we took account of not only the tangential
$\phi$-fluctuations but the longitudinal $\theta$-fluctuations around the
helimagnetic configuration. Based on the collective coordinate method and the
Dirac's canonical formulation for the singular Lagrangian system, we derived
the closed formulae for the mass, spin current and induced magnetic dipole
moment accompanied with the kink crystal motion. To materialize the theoretical
model presented here, symmetry-adapted material synthesis would be required,
where the interplay of crystallographic and magnetic chirality plays a key role
there.",0806.0968v2
2008-06-14,High domain wall velocities due to spin currents perpendicular to the plane,"We consider long and narrow spin valves composed of a first magnetic layer
with a single domain wall (DW), a normal metal spacer and a second magnetic
layer that is a planar or a perpendicular polarizer. For these structures, we
study numerically DW dynamics taking into account the spin torques due to the
perpendicular spin currents. We obtain high DW velocities: 50 m/s for planar
polarizer and 640 m/s for perpendicular polarizer for J = 5*10^6 A/cm^2. These
values are much larger than those predicted and observed for DW motion due to
the in-plane spin currents. The ratio of the magnitudes of the torques, which
generate the DW motion in the respective cases, is responsible for these large
differences.",0806.2369v1
2008-08-22,Perturbation Method for Classical Spinning Particle Motion: II. Vaidya Space-Time,"This paper describes an application of the Mathisson-Papapetrou-Dixon (MPD)
equations in analytic perturbation form to the case of circular motion around a
radially accreting or radiating black hole described by the Vaidya metric.
Based on the formalism presented earlier, this paper explores the effects of
mass accretion or loss of the central body on the overall dynamics of the
orbiting spinning particle. This includes changes to its squared mass and spin
magnitude due to the classical analog of radiative corrections from
spin-curvature coupling. Various quantitative consequences are explored when
considering orbital motion near the black hole's event horizon. An analysis on
the orbital stability properties due to spin-curvature interactions is examined
briefly, with conclusions in general agreement with previous work performed for
the case of circular motion around a Kerr black hole.",0808.3006v3
2008-08-27,Entanglement control in one-dimensional $s=1/2$ random XY spin chain,"The entanglement in one-dimensional random XY spin systems where the
impurities of exchange couplings and the external magnetic fields are
considered as random variables is investigated by solving the different
spin-spin correlation functions and the average magnetization per spin. The
entanglement dynamics near particular locations of the system is also studied
when the exchange couplings (or the external magnetic fields) satisfy three
different distributions(the Gaussian distribution, double-Gaussian
distribution, and bimodal distribution). We find that the entanglement can be
controlled by varying the strength of external magnetic field and the different
distributions of impurities. Moreover, the entanglement of some
nearest-neighboring qubits can be increased for certain parameter values of the
three different distributions.",0808.3678v1
2008-08-27,Entanglement and quantum phase transition in alternating XY spin chain with next-nearest neighbour interactions,"By using the method of density-matrix renormalization-group to solve the
different spin-spin correlation functions, the nearest-neighbouring
entanglement(NNE) and next-nearest-neighbouring entanglement(NNNE) of
one-dimensional alternating Heisenberg XY spin chain is investigated in the
presence of alternating nearest neighbour interactions of exchange couplings,
external magnetic fields and next-nearest neighbouring interactions. For
dimerized ferromagnetic spin chain, NNNE appears only above the critical
dimerized interaction, meanwhile, the dimerized interaction effects quantum
phase transition point and improves NNNE to a large value. We also study the
effect of ferromagnetic or antiferromagnetic next-nearest neighboring (NNN)
interactions on the dynamics of NNE and NNNE. The ferromagnetic NNN interaction
increases and shrinks NNE below and above critical frustrated interaction
respectively, while the antiferromagnetic NNN interaction always decreases NNE.
The antiferromagnetic NNN interaction results to a larger value of NNNE in
comparison to the case when the NNN interaction is ferromagnetic.",0808.3686v1
2008-08-29,Effect of Induced Spin-Orbit Coupling for Atoms via Laser Fields,"We propose an experimental scheme to study spin-orbit coupling effects in a
of two-dimensional (2D) Fermi atomic gas cloud by coupling its internal
electronic states (pseudospins) to radiation in a delta configuration. The
induced spin-orbit coupling can be of the Dresselhaus and Rashba type with and
without a Zeeman term. We show that the optically induced spin-orbit coupling
can lead to a spin-dependent effective mass under appropriate condition, with
one of them able to be tuned between positive and negative effective mass. As a
direct observable we show that in the expansion dynamics of the atomic cloud
the initial atomic cloud splits into two clouds for the positive effective mass
case regime, and into four clouds for the negative effective mass regime.",0808.4137v2
2008-09-04,Readout of a single electron spin in a double quantum dot using a quantum point contact,"We study the dynamics of a single electron spin in a double quantum dot (DQD)
and its readout via a quantum point contact (QPC). We model the system
microscopically and derive rate equations for the reduced electron density
matrix of the DQD. Two cases with one and two electrons in the DQD are studied.
In the one-electron case, with different Zeeman splittings in the two dots, the
electron spin states are distinctly characterized by a constant and an
oscillatory current through the QPC. In the two-electron case, the readout of
the spin state of the electron in one of the dots called the qubit dot is
essentially similar after considering hyperfine interactions between the
electrons and the nuclear spins of the host materials and a uniform magnetic
field applied to the DQD. Moreover, to ensure that an electron is properly
injected into the qubit dot, we propose to determine the success of the
electron injection from the variations of the QPC current after applying an
oscillating magnetic field to the qubit dot.",0809.0807v1
2009-03-18,Magnetic field resonantly enhanced free spins in underdoped YBa$_{2}$Cu$_{3}$O$_{6+x}$,"Using neutron scattering, we investigate the effect of a magnetic field on
the static and dynamic spin response in heavily underdoped superconducting
YBa$_{2}$Cu$_{3}$O$_{6+x}$ (YBCO$_{6+x}$) with x=0.33 (T$_{c}$=8 K) and 0.35
(T$_{c}$=18 K). In contrast to the heavily doped and superconducting monolayer
cuprates, the elastic central peak characterizing static spin correlations does
not respond observably to a magnetic field which suppresses superconductivity.
Instead, we find a magnetic field induced resonant enhancement of the spin
fluctuations. The energy scale of the enhanced fluctuations matches the Zeeman
energy within both the normal and vortex phases while the momentum dependence
is the same as the zero field bilayer response. The magnitude of the
enhancement is very similar in both phases with a fractional intensity change
of $(I/I_{0}-1) \sim 0.1$. We suggest that the enhancement is not directly
correlated with superconductivity but is the result of almost free spins
located near hole rich regions.",0903.3172v2
2009-04-09,Origin of the Canonical Ensemble: Thermalization with Decoherence,"We solve the time-dependent Schrodinger equation for the combination of a
spin system interacting with a spin bath environment. In particular, we focus
on the time development of the reduced density matrix of the spin system. Under
normal circumstances we show that the environment drives the reduced density
matrix to a fully decoherent state, and furthermore the diagonal elements of
the reduced density matrix approach those expected for the system in the
canonical ensemble. We show one exception to the normal case is if the spin
system cannot exchange energy with the spin bath. Our demonstration does not
rely on time-averaging of observables nor does it assume that the coupling
between system and bath is weak. Our findings show that the canonical ensemble
is a state that may result from pure quantum dynamics, suggesting that quantum
mechanics may be regarded as the foundation of quantum statistical mechanics.",0904.1501v2
2009-04-22,Nonstationary theory of magnetic field induced current for molecular spin nanojunction,"For the study of molecular spin junctions, we take into account two types of
couplings between the molecule and the metal leads: (i) electron transfer that
gives rise to net current in the biased junction and (ii) energy transfer
between the molecule and the leads. Using a rotating wave approximation in the
Heisenberg representation, we derive a set of differential equations for the
expectation values of relevant variables: electron and phonon populations and
molecular polarization. A magnetic field control method to enhance the charge
transfer at spin nanojunctions, which characterizes the molecule feature, is
discussed. An approximate analytical solution of the resulting dynamical
equation is supported by numerical solution. The magnetic control by charge
transfer is described by transient pseudo-fermions of electrons interacting
with spins. The rapid adiabatic passage of the energy between the molecule and
the leads is taken into account. The current for molecular spin nanojunctions
is derived.",0904.3461v1
2009-04-29,Quadrupolar correlations and spin freezing in S = 1 triangular lattice antiferromagnets,"Motivated by experiments on NiGa2S4, we discuss characteristic (finite
temperature) properties of spin S = 1 quantum antiferromagnets on the
triangular lattice. Several recent theoretical studies have suggested the
possibility of quadrupolar (spin-nematic) ground states in the presence of
sufficient biquadratic exchange. We argue that quadrupolar correlations are
substantially more robust than the spin-nematic ground state, and give rise to
a two peak structure of the specific heat. We characterize this behavior by a
novel T > 0 semiclassical approximation, which is amenable to efficient Monte
Carlo simulations. Turning to low temperatures, we consider the effects of weak
disorder on incommensurate magnetic order, which is present when interactions
beyond nearest neighbor exchange are substantial. We show that non-magnetic
impurities act as random fields on a component of the order parameter, leading
to the disruption of long-range magnetic order even when the defects are
arbitrarily weak. Instead, a gradual freezing phenomena is expected on lowering
the temperature, with no sharp transition but a rapid slowing of dynamics and
the development of substantial spin-glass-like correlations. We discuss these
observations in relation to measurements of NiGa2S4.",0904.4683v2
2009-04-30,Confluence of resonant laser excitation and bi-directional quantum dot nuclear spin polarization,"Resonant laser scattering along with photon correlation measurements have
established the atom-like character of quantum dots. Here, we present
measurements which challenge this identification for a wide range of
experimental parameters: the absorption lineshapes that we measure at magnetic
fields exceeding 1 Tesla indicate that the nuclear spins polarize by an amount
that ensures locking of the quantum dot resonances to the incident laser
frequency. In contrast to earlier experiments, this nuclear spin polarization
is bi-directional, allowing the electron+nuclear spin system to track the
changes in laser frequency dynamically on both sides of the quantum dot
resonance. Our measurements reveal that the confluence of the laser excitation
and nuclear spin polarization suppresses the fluctuations in the resonant
absorption signal. A master equation analysis shows narrowing of the nuclear
Overhauser field variance, pointing to potential applications in quantum
information processing.",0904.4767v1
2009-05-22,Spin and Orbital Rotation of Electrons and Photons via Spin-Orbit Interaction,"We show that when an electron or photon propagates in a cylindrically
symmetric waveguide, its spin angular momentum (SAM) and its orbital angular
momentum (OAM) interact. Remarkably, we find that the dynamics resulting from
this spin-orbit interaction are quantitatively described by a single expression
applying to both electrons and photons. This leads to the prediction of several
novel rotational effects: the spatial or time evolution of either particle's
spin/polarization vector is controlled by the sign of its OAM quantum number,
or conversely, its spatial wavefunction is controlled by its SAM. We show that
the common origin of these effects in electrons and photons is a universal
geometric phase. We demonstrate how these phenomena can be used to reversibly
transfer entanglement between the SAM and OAM degrees of freedom of
two-particle states.",0905.3778v2
2009-06-11,Optimized pulses for the perturbative decoupling of spin and decoherence bath,"In the framework of nuclear magnetic resonance, we consider the general
problem of the coherent control of a spin coupled to a bath by means of
composite or continuous pulses of duration $\tau_\mathrm{p}$. We show explicity
that it is possible to design the pulse in order to achieve a decoupling of the
spin from the bath up to the third order in $\tau_\mathrm{p}$. The evolution of
the system is separated in the evolution of the spin under the action of the
pulse and of the bath times correction terms. We derive the correction terms
for a general time dependent axis of rotation and for a general coupling
between the spin and the environment. The resulting corrections can be made
vanish by an appropriate design of the pulse. For $\pi$ and $\pi/2$ pulses, we
demonstrate explicitly that pulses exist which annihilate the first and the
second order corrections even if the bath is fully quantum mechanical, i.e., it
displays internal dynamics. Such pulses will also be useful for quantum
information processing.",0906.2070v2
2009-06-30,Cooling a magnetic resonance force microscope via the dynamical back-action of nuclear spins,"We analyze the back-action influence of nuclear spins on the motion of the
cantilever of a magnetic force resonance microscope. We calculate the
contribution of nuclear spins to the damping and frequency shift of the
cantilever. We show that, at the Rabi frequency, the energy exchange between
the cantilever and the spin system cools or heats the cantilever depending on
the sign of the high-frequency detuning. We also show that the spin noise leads
to a significant damping of the cantilever motion.",0906.5420v2
2009-08-11,Spontaneous Vortex Lattices in Quasi 2D Dipolar Spinor Condensates,"Motivated by recent experiments\cite{BA}\cite{BB}, we study quasi 2D
ferromagnetic condensates with various aspect ratios. We find that in zero
magnetic field, dipolar energy generates a local energy minimum with all the
spins lie in the 2D plane forming a row of {\em circular} spin textures with
{\em alternating} orientation, corresponding to a packing of vortices of {\em
identical} vorticity in different spin components. In a large magnetic field,
the system can fall into a long lived dynamical state consisting of an array of
elliptic and hyperbolic Mermin-Ho spin textures, while the true equilibrium is
an uniaxial spin density wave with a single wave-vector along the magnetic
field, and a wavelength similar to the characteristic length of the long lived
vortex array state.",0908.1593v1
2009-09-11,Magnetism of one-dimensional strongly repulsive spin-1 bosons with antiferromagnetic spin exchange interaction,"We investigate magnetism and quantum phase transitions in a one-dimensional
system of integrable spin-1 bosons with strongly repulsive density-density
interaction and antiferromagnetic spin exchange interaction via the
thermodynamic Bethe ansatz method. At zero temperature, the system exhibits
three quantum phases: (i) a singlet phase of boson pairs when the external
magnetic field $H$ is less than the lower critical field $H_{c1}$; (ii) a
ferromagnetic phase of atoms in the hyperfine state $|F=1, m_{F}=1>$ when the
external magnetic field exceeds the upper critical field $H_{c2}$; and (iii) a
mixed phase of singlet pairs and unpaired atoms in the intermediate region
$H_{c1}<H<H_{c2}$. At finite temperatures, the spin fluctuations affect the
thermodynamics of the model through coupling the spin bound states to the
dressed energy for the unpaired $m_{F}=1$ bosons. However, such spin dynamics
is suppressed by a sufficiently strong external field at low temperatures. Thus
the singlet pairs and unpaired bosons may form a two-component Luttinger liquid
in the strong coupling regime.",0909.2097v1
2009-10-27,Spin transport theory in ferromagnet/semiconductor systems with non-collinear magnetization configurations,"We present a comprehensive theory of spin transport in a non-degenerate
semiconductor that is in contact with multiple ferromagnetic terminals. The
spin dynamics in the semiconductor is studied during a perturbation of a
general, non-collinear magnetization configuration and a method is shown to
identify the various configurations from current signals. The conventional
Landauer-B\""{u}ttiker description for spin transport across Schottky contacts
is generalized by the use of a non-linearized I-V relation, and it is extended
by taking into account non-coherent transport mechanisms. The theory is used to
analyze a three terminal lateral structure where a significant difference in
the spin accumulation profile is found when comparing the results of this model
with the conventional model.",0910.5012v1
2009-11-05,Optical Polarization of $^{13}$C Nuclei in Diamond through Nitrogen-Vacancy Centers,"We determine the polarization of the bulk $^{13}$C nuclear spin system in
diamond produced by interaction with optically oriented nitrogen-vacancy (NV-)
defect centers. $^{13}$C nuclei are polarized into the higher energy Zeeman
state with a bulk-average polarization up to 5.2%, although local polarization
may be higher. The kinetics of polarization are temperature independent, and
occur within 5 minutes. Fluctuations in the dipolar field of the NV- center
spin bath are identified as the mechanism by which nuclear spin transitions are
induced near defect centers. Polarization is then transported to the bulk
material via spin diffusion, which accounts for the observed kinetics of
polarization. These results indicate control over the nuclear spin bath, a
methodology to study dynamics of an NV- center ensemble, and application to
sensitivity-enhanced NMR.",0911.1098v3
2010-02-27,Spin current through an ESR quantum dot: A real-time study,"The spin transport in a strongly interacting spin-pump nano-device is studied
using the time-dependent variational-matrix-product-state (VMPS) approach. The
precession magnetic field generates a dissipationless spin current through the
quantum dot. We compute the real time spin current away from the equilibrium
condition. Both transient and stationary states are reached in the simulation.
The essentially exact results are compared with those from the Hartree-Fock
approximation (HFA). It is found that correlation effect on the physical
quantities at quasi-steady state are captured well by the HFA for small
interaction strength. However the HFA misses many features in the real time
dynamics. Results reported here may shed light on the understanding of the
ultra-fast processes as well as the interplay of the non-equilibrium and
strongly correlated effect in the transport properties.",1003.0069v1
2010-03-08,Real Time Dynamics of Hole Propagation in Strongly Correlated Conjugated Molecular Chains: A time-dependent DMRG Study,"In this paper, we address the role of electron-electron interactions on the
velocities of spin and charge transport in one-dimensional systems typified by
conjugated polymers. We employ the Hubbard model to model electron-electron
interactions. The recently developed technique of time dependent Density Matrix
Renormalization Group (tdDMRG) is used to follow the spin and charge evolution
in an initial wavepacket described by a hole doped in the ground state of the
neutral system. We find that the charge and spin velocities are different in
the presence of correlations and are in accordance with results from earlier
studies; the charge and spin move together in the noninteracting picture while
interaction slows down only the spin velocity. We also note that dimerization
of the chain only weakly affects these velocities.",1003.1581v1
2010-03-12,Spin dynamics in electron-doped pnictide superconductors,"The doping dependence of spin excitations in
Ba(Fe$_{1-x}$Co$_{x}$)$_{2}$As$_{2}$ is studied based on a two-orbital model
under RPA approximation. The interplay between the spin-density-wave (SDW) and
superconductivity (SC) is considered in our calculation. Our results for the
spin susceptibility are in good agreement with neutron scattering (NS)
experiments in various doping ranges at temperatures (T) above and below the
superconducting transition temperature T$_{c}$. For the overdoped sample where
one of the two hole pockets around $\Gamma$ point disappears according to
ARPES, we show that the imaginary part of the spin susceptibility in both SC
and normal phases exhibits a gap-like behavior. This feature is consistent with
the ""pseudogap"" as observed by recent NMR and NS experiments.",1003.2609v1
2010-03-29,Chaotic Transport in the Symmetry Crossover Regime with a Spin-orbit Interaction,"We study a chaotic quantum transport in the presence of a weak spin-orbit
interaction. Our theory covers the whole symmetry crossover regime between
time-reversal invariant systems with and without a spin-orbit interaction. This
situation is experimentally realizable when the spin-orbit interaction is
controlled in a conductor by applying an electric field. We utilize a
semiclassical approach which has recently been developed. In this approach, the
non-Abelian nature of the spin diffusion along a classical trajectory plays a
crucial role. New analytical expressions with one crossover parameter are
semiclassically derived for the average conductance, conductance variance and
shot noise. Moreover numerical results on a random matrix model describing the
crossover from the GOE (Gaussian Orthogonal Ensemble) to the GSE (Gaussian
Symplectic Ensemble) are compared with the semiclassical expressions.",1003.5537v2
2010-03-30,Large effects of boundaries on spin amplification in spin chains,"We investigate the effect of boundary conditions on spin amplification in
spin chains. We show that the boundaries play a crucial role for the dynamics:
A single additional coupling between the first and last spins can
macroscopically modify the physical behavior compared to the open chain, even
in the limit of infinitely long chains. We show that this effect can be
understood in terms of a ""bifurcation"" in Hilbert space that can give access to
different parts of Hilbert space with macroscopically different physical
properties of the basis functions, depending on the boundary conditions. On the
technical side, we introduce semiclassical methods whose precision increase
with increasing chain length and allow us to analytically demonstrate the
effects of the boundaries in the thermodynamic limit.",1003.5863v2
2010-04-06,Spin and pseudospin symmetries in the antinucleon spectrum of nuclei,"Spin and pseudospin symmetries in the spectra of nucleons and antinucleons
are studied in a relativistic mean-field theory with scalar and vector
Woods-Saxon potentials, in which the strength of the latter is allowed to
change. We observe that, for nucleons and antinucleons, the spin symmetry is of
perturbative nature and it is almost an exact symmetry in the physical region
for antinucleons. The opposite situation is found in the pseudospin symmetry
case, which is better realized for nucleons than for antinucleons, but is of
dynamical nature and cannot be viewed in a perturbative way both for nucleons
and antinucleons. This is shown by computing the spin-orbit and
pseudospin-orbit couplings for selected spin and pseudospin partners in both
spectra.",1004.0823v1
2010-07-02,How higher-spin gravity surpasses the spin two barrier: no-go theorems versus yes-go examples,"Aiming at non-experts, we explain the key mechanisms of higher-spin
extensions of ordinary gravity. We first overview various no-go theorems for
low-energy scattering of massless particles in flat spacetime. In doing so we
dress a dictionary between the S-matrix and the Lagrangian approaches,
exhibiting their relative advantages and weaknesses, after which we high-light
potential loop-holes for non-trivial massless dynamics. We then review positive
yes-go results for non-abelian cubic higher-derivative vertices in constantly
curved backgrounds. Finally we outline how higher-spin symmetry can be
reconciled with the equivalence principle in the presence of a cosmological
constant leading to the Fradkin--Vasiliev vertices and Vasiliev's higher-spin
gravity with its double perturbative expansion (in terms of numbers of fields
and derivatives).",1007.0435v3
2010-07-06,Electromagnetically Induced Transparency with an Ensemble of Donor-Bound Electron Spins in a Semiconductor,"We present measurements of electromagnetically induced transparency with an
ensemble of donor- bound electrons in low-doped n-GaAs. We used optical
transitions from the Zeeman-split electron spin states to a bound trion state
in samples with optical densities of 0.3 and 1.0. The electron spin dephasing
time T* \approx 2 ns was limited by hyperfine coupling to fluctuating nuclear
spins. We also observe signatures of dynamical nuclear polarization, but find
these effects to be much weaker than in experiments that use electron spin
resonance and related experiments with quantum dots.",1007.1010v2
2010-07-14,Coupled Spin-Phonon Excitations in Helical Multiferroics,"Both the Dzyaloshiskii-Moriya interaction and the exchange-striction are
shown to affect dynamically the magnetoelectric excitations in the perovskite
multiferroic RMnO3. The exchange-striction results in a biquadratic interaction
between the spins and the transverse phonons, giving rise to quantum
fluctuations of the ferroelectric polarization P. This leads to low-lying
phonon modes that are perpendicular to P and to the helical spins at small wave
vector but are parallel to P at a wave vector close to the magnetic modulation
vector. For spin-1/2 helimagnet, the local polarization can be completely
reversed by the spin fluctuation, and so does the direction of the on-site spin
chirality, which allows for a finite differential scattering intensity of
polarized neutrons from a cycloidal magnet.",1007.2273v1
2010-08-04,Study of electron spin dynamics in grain aligned LaCoPO: an itinerant ferromagnet,"139La NMR study was performed in grain aligned (c|| H0) sample of LaCoPO and
polycrystalline LaFePO. Knight shift is isotropic and temperature independent
in LaFePO. It is strongly temperature dependent and anisotropic in LaCoPO. The
spin-lattice relaxation rate in LaCoPO clearly reveals the existence of 3D spin
fluctuations both in the paramagnetic and ferromagnetic state over and above
the dominant 2D spin fluctuations in the paramagnetic state, observed earlier
from 31P NMR measurements in the same oriented sample. The spin fluctuation
parameters in LaCoPO determined from 139La NMR relaxation and magnetization
data, using the self consistent renormalization (SCR) theory, are in close
agreement and follow the universal Rhodes-Wohlfarth curve.",1008.0749v1
2010-10-09,Spinning branes in Riemann-Cartan spacetime,"We use the conservation law of the stress-energy and spin tensors to study
the motion of massive brane-like objects in Riemann-Cartan geometry. The
world-sheet equations and boundary conditions are obtained in a manifestly
covariant form. In the particle case, the resultant world-line equations turn
out to exhibit a novel spin-curvature coupling. In particular, the spin of a
zero-size particle does not couple to the background curvature. In the string
case, the world-sheet dynamics is studied for some special choices of spin and
torsion. As a result, the known coupling to the Kalb-Ramond antisymmetric
external field is obtained. Geometrically, the Kalb-Ramond field has been
recognized as a part of the torsion itself, rather than the torsion potential.",1010.1861v1
2010-10-26,Partial annealing of a coupled mean-field spin-glass model with an embedded pattern,"A partially annealed mean-field spin-glass model with a locally embedded
pattern is studied. The model consists of two dynamical variables, spins and
interactions, that are in contact with thermal baths at temperatures T_S and
T_J, respectively. Unlike the quenched system, characteristic correlations
among the interactions are induced by the partial annealing. The model exhibits
three phases, which are paramagnetic, ferromagnetic and spin-glass phases. In
the ferromagnetic phase, the embedded pattern is stably realized. The phase
diagram depends significantly on the ratio of two temperatures n=T_J/T_S. In
particular, a reentrant transition from the embedded ferromagnetic to the
spin-glass phases with T_S decreasing is found only below at a certain value of
n. This indicates that above the critical value n_c the embedded pattern is
supported by local field from a non-embedded region. Some equilibrium
properties of the interactions in the partial annealing are also discussed in
terms of frustration.",1010.5346v2
2010-11-01,Repulsively-bound exciton-biexciton states in high-spin fermions in optical lattices,"We show that the interplay between spin-changing collisions and quadratic
Zeeman coupling provides a novel mechanism for the formation of repulsively
bound composites in high-spin fermions, which we illustrate by considering spin
flips in an initially polarized hard-core 1D Mott insulator of spin-3/2
fermions. We show that after the flips the dynamics is characterized by the
creation of two types of exciton-biexciton composites. We analyze the
conditions for the existence of these bound states, and discuss their
intriguing properties. In particular we show that the effective mass and
stability of the composites depends non-trivially on spin-changing collisions,
on the quadratic Zeeman effect and on the initial exciton localization.
Finally, we show that the composites may remain stable against inelastic
collisions, opening the possibility of novel quantum composite phases.",1011.0388v3
2010-11-03,Existence of vertical spin stiffness in Landau-Lifshitz-Gilbert equation in ferromagnetic semiconductors,"We calculate the magnetization torque due to the spin polarization of the
itinerant electrons by deriving the kinetic spin Bloch equations based on the
$s$-$d$ model. We find that the first-order gradient of the magnetization
inhomogeneity gives rise to the current-induced torques, which are consistent
to the previous works. At the second-order gradient, we find an effective
magnetic field perpendicular to the spin stiffness filed. This field is
proportional to the nonadiabatic parameter $\beta$. We show that this vertical
spin stiffness term can significantly modify the domain-wall structure in
ferromagnetic semiconductors and hence should be included in the
Landau-Lifshitz-Gilbert equation in studying the magnetization dynamics.",1011.0871v1
2010-11-04,Higher Spin Scattering in Superstring Theory,"We compute scattering amplitudes of leading Regge trajectory states in open
superstring theories. Highest spin states at mass level n with spin s=n+1 for
bosons and s=n+1/2 for fermions are generated by particularly simple vertex
operators. Hence, the cubic couplings of bosons and fermions on the leading
Regge trajectory are given for arbitrary n. The same can be achieved for higher
point amplitudes, and this article focuses on four point level with one heavy
maximum spin state and three massless states in any bose-fermi combination,
putting particular emphasis on manifest cyclic symmetry. Except for the four
fermion coupling, all our results remain valid in any D<10 dimensional
compactification scenario, so they might become relevant at LHC in case of an
experimentally accessible low string scale. But even if not directly
observable, superstring amplitudes provide important clues on higher spin
dynamics and their consistent interactions in field theory.",1011.1235v3
2010-11-08,Rapidly fluctuating orbital occupancy above the orbital ordering transition in spin-gap compounds,"Several spin systems with low dimensionality develop a spin-dimer phase
within a molecular orbital below TS, competing with long-range
antiferromagnetic order. Very often, preferential orbital occupancy and
ordering are the actual driving force for dimerization, as in the so-called
orbitally-driven spin-Peierls compounds (MgTi2O4, CuIr2S4, La4Ru2O10,
NaTiSi2O6, etc.). Through a microscopic analysis of the thermal conductivity k
(T) in La4Ru2O10, we show that the orbital occupancy fluctuates rapidly above
TS, resulting in an orbital-liquid state. The strong orbital-lattice coupling
introduces dynamic bond-length fluctuations that scatter the phonons to produce
a k (T) proportional to T (i.e. glass-like) above TS. This phonon-glass to
phonon-crystal transition is shown to occur in other spin-dimer systems, like
NaTiSi2O6, pointing to a general phenomenon.",1011.1860v1
2010-12-14,Superconducting pairing of interacting electrons: implications from the two-impurity Anderson model,"We study the non-local superconducting pairing of two interacting Anderson
impurities, which has an instability near the quantum critical point from the
competition between the Kondo effect and an antiferromagnetic inter-impurity
spin exchange interaction. As revealed by the dynamics over the whole energy
range, the superconducting pairing fluctuations acquire considerable strength
from an energy scale much higher than the characteristic spin fluctuation scale
while the low energy behaviors follow those of the staggered spin
susceptibility. We argue that the glue to the superconducting pairing is not
the spin fluctuations, but rather the effective Coulomb interaction. On the
other hand, critical spin fluctuations in the vicinity of quantum criticality
are also crucial to a superconducting pairing instability, by preventing a
Fermi liquid fixed point being reached to keep the superconducting pairing
fluctuations finite at low energies. A superconducting order, to reduce the
accumulated entropy carried by the critical degrees of freedom, may arise
favorably from this instability.",1012.3161v3
2010-12-16,Spin Transfer Torques in MnSi at Ultra-low Current Densities,"Spin manipulation using electric currents is one of the most promising
directions in the field of spintronics. We used neutron scattering to observe
the influence of an electric current on the magnetic structure in a bulk
material. In the skyrmion lattice of MnSi, where the spins form a lattice of
magnetic vortices similar to the vortex lattice in type II superconductors, we
observe the rotation of the diffraction pattern in response to currents which
are over five orders of magnitude smaller than those typically applied in
experimental studies on current-driven magnetization dynamics in
nanostructures. We attribute our observations to an extremely efficient
coupling of inhomogeneous spin currents to topologically stable knots in spin
structures.",1012.3496v1
2011-02-03,"Absence of halfmetallicity in defect-free Cr, Mn-delta-doped Digital Magnetic Heterostructures","We present results of a combined density functional and many-body
calculations for the electronic and magnetic properties of the defect-free
digital ferromagnetic heterostructures obtained by doping GaAs with Cr and Mn.
While local density approximation/(+U) predicts half-metallicity in these
defect-free delta-doped heterostructures, we demonstrate that local many-body
correlations captured by Dynamical Mean Field Theory induce within the minority
spin channel non-quasiparticle states just above $E_F$. As a consequence of the
existence of these many-body states the half-metallic gap is closed and the
carriers spin polarization is significantly reduced. Below the Fermi level the
minority spin highest valence states are found to localize more on the GaAs
layers being independent of the type of electronic correlations considered.
Thus, our results confirm the confinement of carriers in these delta-doped
heterostructures, having a spin-polarization that follow a different
temperature dependence than magnetization. We suggest that polarized
hot-electron photoluminescence experiments might bring evidence for the
existence of many-body states within the minority spin channel and their finite
temperature behavior.",1102.0646v1
2011-02-11,Entanglement dynamics via geometric phases in quantum spin chains,"We introduce a connection between entanglement induced by interaction and
geometric phases acquired by a composite quantum spin system. We begin by
analyzing the evaluation of cyclic (Aharonov-Anandan) and non-cyclic
(Mukunda-Simon) geometric phases for general spin chains evolving in the
presence of time-independent magnetic fields. Then, by considering Heisenberg
chains, we show that the interaction geometric phase, namely, the total
geometric phase with subtraction of free spin contributions, is directly
related to the global (Meyer-Wallach) entanglement exhibited by an initially
separable state during its evolution in Hilbert space. This is analytically
shown for N=2 spins and numerically illustrated for larger chains. This
relationship promotes the interaction geometric phase to an indicator of global
entanglement in the system, which may constitute a useful tool for quantum
tasks based on entanglement as a resource to their performance.",1102.2415v2
2011-03-07,Similarity between Ni and Zn impurity effects on the superconductivity and Cu-spin correlation in La2-xSrxCu1-yNiyO4 high-Tc cuprates: A comparison based on the hole trapping by Ni,"Ni-substitution effects on the superconductivity and Cu-spin correlation have
been investigated in La2-xSrxCu1-yNiyO4 from the electrical resistivity and
muon spin relaxation measurements, taking into account the hole trapping by Ni
recently suggested. It has been found that the Ni-substitution suppresses the
superconductivity, induces the localization of holes and develops the Cu-spin
correlation to the same degree as the Zn substitution. These suggest that Ni
with a trapped hole tends to give rise to potential scattering of holes in the
CuO2 plane to the same degree as Zn, being discussed in relation to the
so-called dynamical stripe correlations of spins and holes.",1103.1265v2
2011-03-07,Polariton spin Faraday rotation dynamics in a GaAs microcavity,"Polariton spin carries the combination of the exciton and the photon spin,
which is manifested in the circularly polarized emission degree in a III-V
quantum wells microcavity system. Relaxation process of such spin system is a
complex subject since it involve upper or lower polariton branch, resonant or
non resonant polariton excitation process and if the particles are in strong or
weak coupling regime. We present here experimental polariton spin Faraday
rotation time measurement in GaAs single quantum well microcavity, using time
resolved polariton photoluminescence by resonant excitation process in a
pump-probe system.",1103.1337v2
2011-04-14,Approaching the ground states of the random maximum two-satisfiability problem by a greedy single-spin flipping process,"In this brief report we explore the energy landscapes of two spin glass
models using a greedy single-spin flipping process, {\tt Gmax}. The
ground-state energy density of the random maximum two-satisfiability problem is
efficiently approached by {\tt Gmax}. The achieved energy density $e(t)$
decreases with the evolution time $t$ as $e(t)-e(\infty)=h (\log_{10} t)^{-z}$
with a small prefactor $h$ and a scaling coefficient $z > 1$, indicating an
energy landscape with deep and rugged funnel-shape regions. For the $\pm J$
Viana-Bray spin glass model, however, the greedy single-spin dynamics quickly
gets trapped to a local minimal region of the energy landscape.",1104.2656v1
2011-06-07,Classical Skyrmions -- Static Solutions and Dynamics,"Skyrmions with a realistic value of the pion mass parameter are expected to
be quite compact structures, but beyond baryon number B=8 only a few examples
are known. The largest of these is the cubically symmetric B=32 Skyrmion which
is a truncated piece of the Skyrme crystal. Here it is proposed that many more
such Skyrmions could be found, without any restriction on the baryon number, as
pieces of the Skyrme crystal. Particular attention is given to the possibility
of reducing B by 1 by chopping a corner off a cubic crystal chunk.
  Nuclei are modelled by Skyrmions with quantised spin and isospin. Here it is
argued that these quantised states can be approximated by classically spinning
Skyrmions. The orientations of the spinning Skyrmions corresponding to
polarised protons, neutrons and deuterons are identified. Nuclear collisions
and the nuclear spin-orbit force are discussed in terms of classically spinning
Skyrmions. Going beyond the rigid collective motions of Skyrmions, there are
spatially modulated collective motions, which are oscillatory in time. They are
argued to describe not just vibrational excitations of nuclei, but also giant
resonance states.
  A speculative proposal for identifying quarks inside Skyrmions is briefly
discussed.",1106.1298v1
2011-06-14,All Spin Logic device with inbuilt Non-Reciprocity,"The need for low power alternatives to digital electronic circuits has led to
increasing interest in logic devices where information is stored in
nanomagnets. This includes both nanomagnetic logic (NML) where information is
communicated through magnetic fields of nanomagnets and all-spin logic (ASL)
where information is communicated through spin currents. A key feature needed
for logic implementation is non-reciprocity, whereby the output is switched
according to the input but not the other way around, thus providing directed
information transfer. The objective of this paper is to draw attention to
possible ASL-based schemes that utilize the physics of spin-torque to build in
non-reciprocity similar to transistors that could allow logic implementation
without the need for special clocking schemes. We use an experimentally
benchmarked coupled spin-transport/ magnetization-dynamics model to show that a
suitably engineered single ASL unit indeed switches in a non-reciprocal manner.
We then present heuristic arguments explaining the origin of this directed
information transfer. Finally we present simulations showing that individual
ASL devices with inbuilt directionality can be cascaded to construct circuits.",1106.2789v1
2011-07-14,The dimerized ferromagnetic Heisenberg chain,"Ferromagnetic, in contrast to antiferromagnetic, Heisenberg chains can
undergo a Spin-Peierls dimerization only at finite temperatures. They show
reentrant behavior as a function of temperature, which might play a role for
systems with small effective elastic constants as, for example, monatomic
chains on surfaces. We investigate the physical properties of the dimerized
ferromagnetic Heisenberg chain using a modified spin-wave theory. We calculate
the exponentially decaying spin and dimer correlation functions, analyze the
temperature dependence of the corresponding coherence lengths, the
susceptibility, as well as the static and dynamic spin structure factor. By
comparing with numerical data obtained by the density-matrix renormalization
group applied to transfer matrices, we find that the modified spin wave theory
yields excellent results for all these quantities for a wide range of
dimerizations and temperatures.",1107.2772v1
2011-07-28,Full Electrical Control of the Electron Spin Relaxation in GaAs Quantum Wells,"The electron spin dynamics in (111)-oriented GaAs/AlGaAs quantum wells is
studied by timeresolved photoluminescence spectroscopy. By applying an external
field of 50 kV/cm a two-order of magnitude increase of the spin relaxation time
can be observed reaching values larger than 30 ns; this is a consequence of the
electric field tuning of the spin-orbit conduction band splitting which can
almost vanish when the Rashba term compensates exactly the Dresselhaus one. The
measurements under transverse magnetic field demonstrate that the electron spin
relaxation time for the three space directions can be tuned simultaneously with
the applied electric field.",1107.5642v1
2011-08-03,Transverse Spin Results From PHENIX,"The PHENIX experiment at the Relativistic Heavy Ion Collider explores the
spin structure of the proton in polarized p+p collisions at center-of-mass
energies up to 500 GeV. Tremendous experimental and theoretical progress has
been made toward understanding the physics involved with transversely polarized
beams or targets in recent years. Not only nucleon structure and parton
distribution functions but also QCD dynamics have been studied in various
physics processes in high-energy polarized DIS and p+p collisions. In the 2006
and 2008 RHIC runs, the PHENIX experiment took a significant amount of
transversely polarized p+p collision data at 200 GeV center-of-mass energy,
with an integrated luminosity of 8 $pb^{-1}$ and beam polarizations up to 50%.
Single spin asymmetries of different probes have been measured in mid- and
forward-rapidities. In this report, we present the latest transverse spin
results from the PHENIX experiment and discuss briefly the prospects of future
transverse spin physics with the PHENIX detectors upgrades.",1108.0911v1
2011-09-02,Measurement of statistical nuclear spin polarization in a nanoscale GaAs sample,"We measure the statistical polarization of quadrupolar nuclear spins in a
sub-micrometer (0.6 um^3) particle of GaAs using magnetic resonance force
microscopy. The crystalline sample is cut out of a GaAs wafer and attached to a
micro-mechanical cantilever force sensor using a focused ion beam technique.
Nuclear magnetic resonance is demonstrated on ensembles containing less than 5
x 10^8 nuclear spins and occupying a volume of around (300 nm)^3 in GaAs with
reduced volumes possible in future experiments. We discuss how the further
reduction of this detection volume will bring the spin ensemble into a regime
where random spin fluctuations, rather than Boltzmann polarization, dominate
its dynamics. The detection of statistical polarization in GaAs therefore
represents an important first step toward 3D magnetic resonance imaging of
III-V materials on the nanometer-scale.",1109.0411v2
2011-09-08,Electrically Controlled Pumping of Spin Currents in Topological Insulators,"Pure spin currents are shown to be generated by an electrically controlled
quantum pump applied at the edges of a topological insulator. The electric
rather than the more conventional magnetic control offers several advantages
and avoids, in particular, the necessity of delicate control of magnetization
dynamics over tiny regions. The pump is implemented by pinching the sample at
two quantum point contacts and phase modulating two external gate voltages
between them. The spin current is generated for the full range of parameters.
On the other hand, pumping via amplitude modulation of the inter-boundary
couplings generates both charge and spin currents, with a pure charge current
appearing only for special values of the parameters for which the Bohm-Aharonov
flux takes integer values. Our setup can therefore serve to fingerprint the
helical nature of the edges states with the zeros of the pumped spin and charge
currents occurring at distinct universal locations where the Fabry-Perot or the
Aharonov-Bohm phases take integer values.",1109.1711v1
2011-10-04,Negative magnetization of Li2Ni2Mo3O12 having a spin system composed of distorted honeycomb lattices and linear chains,"We study themagnetism of a spin-1 substance Li2Ni2Mo3O12. The spin system
consists of distorted honeycomb lattices and linear chains of Ni2+ spins. Li+
ions enter about 25% and 50% of the honeycomb and chain Ni sites, respectively,
creating disorder in both spin subsystems. A magnetic phase transition occurs
at Tc = 8.0 K in the zero magnetic field. In low magnetic fields, the
magnetization increases rapidly below Tc, decreases below 7 K, and finally
becomes negative at low temperatures. We determine the magnetic structure using
neutron powder diffraction results. The honeycomb lattices and linear chains
show antiferromagnetic and ferromagnetic long-range order, respectively. We
investigate static and dynamic magnetic properties using the local probe
technique of muon spin relaxation. We discuss the origin of the negative
magnetization.",1110.0587v1
2011-12-04,Spin relaxation in Kondo lattices,"A model of spin relaxation in Kondo lattices is proposed to explain the
presence of an electron spin resonance (ESR) signal in the heavy fermion
compounds YbRh2Si2 and YbIr2Si2. Coupled equations for dynamical
susceptibilities of Kondo ions and conduction electrons are derived by means of
the functional derivative method. The perturbational scaling approach reveals
the collective spin motion of Yb ions with conduction electrons in the
bottleneck regime. A common energy scale due to the Kondo effect regulates the
temperature dependence of the different kinetic coefficients and results in a
mutual cancelation of all divergent parts in a collective spin mode. The
angular dependence of the ESR linewidth is shown to be in a qualitative
agreement with experimental data on YbRh2Si2 and YbIr2Si2. Linewidth
contributions other than the Kondo interaction are also discussed.",1112.0785v2
2012-02-22,Temperature dependence of the resonance and low energy spin excitations in superconducting FeTe$_{0.6}$Se$_{0.4}$,"We use inelastic neutron scattering to study the temperature dependence of
the low-energy spin excitations in single crystals of superconducting
FeTe$_{0.6}$Se$_{0.4}$ ($T_c=14$ K). In the low-temperature superconducting
state, the imaginary part of the dynamic susceptibility at the electron and
hole Fermi surfaces nesting wave vector $Q=(0.5,0.5)$,
$\chi^{\prime\prime}(Q,\omega)$, has a small spin gap, a two-dimensional
neutron spin resonance above the spin gap, and increases linearly with
increasing $\hbar\omega$ for energies above the resonance. While the intensity
of the resonance decreases like an order parameter with increasing temperature
and disappears at temperature slightly above $T_c$, the energy of the mode is
weakly temperature dependent and vanishes concurrently above $T_c$. This
suggests that in spite of its similarities with the resonance in electron-doped
superconducting BaFe$_{2-x}$(Co,Ni)$_x$As$_2$, the mode in
FeTe$_{0.6}$Se$_{0.4}$ is not directly associated with the superconducting
electronic gap.",1202.5015v1
2012-03-06,Persistent dynamics in the S=1/2 quasi-one-dimensional chain compound Rb4Cu(MoO4)3 probed with muon-spin relaxation,"We report the results of muon-spin relaxation measurements on the
low-dimensional antiferromagnet Rb4Cu(MoO4)3. No long-range magnetic order is
observed down to 50 mK implying a ratio T_N/J<0.005 (where J is the principal
exchange strength along the spin chains) and an effective ratio of interchain
to intrachain exchange of |J_perp/J|<2 x 10^-3, making the material an
excellent realization of a one-dimensional quantum Heisenberg antiferromagnet.
We probe the persistent spin excitations at low temperatures and find that
ballistic spin transport dominates the excitations detected below 0.3 K.",1203.1161v1
2012-03-20,Is the Yb2Ti2O7 pyrochlore a quantum spin ice?,"We use numerical linked cluster (NLC) expansions to compute the specific
heat, C(T), and entropy, S(T), of a quantum spin ice model of Yb2Ti2O7 using
anisotropic exchange interactions recently determined from inelastic neutron
scattering measurements and find good agreement with experimental calorimetric
data. In the perturbative weak quantum regime, this model has a ferrimagnetic
ordered ground state, with two peaks in C(T): a Schottky anomaly signalling the
paramagnetic to spin ice crossover followed at lower temperature by a sharp
peak accompanying a first order phase transition to the ferrimagnetic state. We
suggest that the two C(T) features observed in Yb2Ti2O7 are associated with the
same physics. Spin excitations in this regime consist of weakly confined
spinon-antispinon pairs. We suggest that conventional ground state with exotic
quantum dynamics will prove a prevalent characteristic of many real quantum
spin ice materials.",1203.4569v1
2012-06-27,Discrete antiferromagnetic spin-wave excitations in the giant ferric wheel Fe18,"The low-temperature elementary spin excitations in the AFM molecular wheel
Fe18 were studied experimentally by inelastic neutron scattering and
theoretically by modern numerical methods, such as dynamical density matrix
renormalization group or quantum Monte Carlo techniques, and analytical
spin-wave theory calculations. Fe18 involves eighteen spin-5/2 Fe(III) ions
with a Hilbert space dimension of 10^14, constituting a physical system that is
situated in a region between microscopic and macroscopic. The combined
experimental and theoretical approach allowed us to characterize and discuss
the magnetic properties of Fe18 in great detail. It is demonstrated that
physical concepts such as the rotational-band or L&E-band concepts developed
for smaller rings are still applicable. In particular, the higher-lying
low-temperature elementary spin excitations in Fe18 or AFM wheels in general
are of discrete antiferromagnetic spin-wave character.",1206.6203v1
2012-07-02,Dynamics of a Dirac Fermion in the presence of spin noncommutativity,"Recently, it has been proposed a spacetime noncommutativity that involves
spin degrees of freedom, here called ""spin noncommutativity"". One of the
motivations for such a construction is that it preserves Lorentz invariance,
which is deformed or simply broken in other approaches to spacetime
noncommutativity. In this work, we gain further insight in the physical aspects
of the spin noncommutativity. The noncommutative Dirac equation is derived from
an action principle, and it is found to lead to the conservation of a modified
current, which involves the background electromagnetic field. Finally, we study
the Landau problem in the presence of spin noncommutativity. For this scenario
of a constant magnetic field, we are able to derive a simple Hermitean
non-commutative correction to the Hamiltonian operator, and show that the
degeneracy of the excited states is lifted by the noncommutativity at the
second order or perturbation theory.",1207.0412v1
2012-07-25,L-valley Electron Spin Dynamics in GaAs,"Optical orientation experiments have been performed in GaAs epilayers with
photoexcitation energies in the 3 eV region yielding the photogeneration of
spin-polarized electrons in the satellite L valley. We demonstrate that a
significant fraction of the electron spin memory can be conserved when the
electron is scattered from the L to the $\Gamma$ valley following an energy
relaxation of several hundreds of meV. Combining these high energy
photo-excitation experiments with time-resolved photoluminescence spectroscopy
of $\Gamma$ valley spin-polarized photogenerated electrons allows us to deduce
a typical L valley electron spin relaxation time of 200 fs, in agreement with
theoretical calculations.",1207.5978v1
2012-07-31,Random matrix ensemble with random two-body interactions in presence of a mean-field for spin one boson systems,"For $m$ number of bosons, carrying spin ($S$=1) degree of freedom, in
$\Omega$ number of single particle orbitals, each triply degenerate, we
introduce and analyze embedded Gaussian orthogonal ensemble of random matrices
generated by random two-body interactions that are spin (S) scalar
[BEGOE(2)-$S1$]. The embedding algebra is $U(3) \supset G \supset G1 \otimes
SO(3)$ with SO(3) generating spin $S$. A method for constructing the ensembles
in fixed-($m$, $S$) space has been developed. Numerical calculations show that
the form of the fixed-($m$, $S$) density of states is close to Gaussian and
level fluctuations follow GOE. Propagation formulas for the fixed-($m$, $S$)
space energy centroids and spectral variances are derived for a general one
plus two-body Hamiltonian preserving spin. In addition to these, we also
introduce two different pairing symmetry algebras in the space defined by
BEGOE(2)-$S1$ and the structure of ground states is studied for each paring
symmetry.",1207.7225v1
2012-08-06,Spin-state Crossover Model for the Magnetism of Iron Pnictides,"We propose a minimal model describing magnetic behavior of Fe-based
superconductors. The key ingredient of the model is a dynamical mixing of
quasi-degenerate spin states of Fe2+ ion by intersite electron hoppings,
resulting in an effective local spin Seff. The moments Seff tend to form
singlet pairs, and may condense into a spin nematic phase due to the emergent
biquadratic exchange couplings. The long-range ordered part m of Seff varies
widely, 0<=m<=Seff, but magnon spectra are universal and scale with Seff,
resolving the puzzle of large but fluctuating Fe-moments. Unusual temperature
dependences of a local moment and spin susceptibility are also explained.",1208.1197v3
2012-08-14,Field induced spin exciton doublet splitting in d_{x^2-y^2}-wave 115-heavy electron superconductors,"We investigate the spin-exciton modes in the superconducting d_{x^2-y^2}
state of CeMIn_5 heavy fermion compounds found at the antiferromagnetic wave
vector by inelastic neutron scattering. We present a theoretical model that
explains the field dependence for both field directions. We show that the
recently observed splitting of the spin exciton doublet in CeCoIn_5 into two
non-degenerate modes for in-plane field appears naturally in this model. This
is due to the spin anisotropy of g- factors and quasiparticle interactions
which lead to different resonant conditions for the dynamic susceptibility
components. We predict that the splitting of the spin resonance doublet becomes
strongly nonlinear for larger fields when the energy of both split components
decreases. For field along the tetragonal axis no splitting but only a
broadening of the resonance is found in agreement with experiment.",1208.2897v1
2012-08-17,Quantum simulation via filtered Hamiltonian engineering: application to perfect quantum transport in spin networks,"We propose a method for Hamiltonian engineering in quantum information
processing architectures that requires no local control, but only relies on
collective qubit rotations and field gradients. The technique achieves a
spatial modulation of the coupling strengths via a dynamical construction of a
weighting function combined with a Bragg grating. As an example, we demonstrate
how to generate the ideal Hamiltonian for perfect quantum information transport
between two separated nodes of a large spin network. We engineer a spin chain
with optimal couplings from a large spin network, such as naturally occurring
in crystals, while decoupling all unwanted interactions. For realistic
experimental parameters, our method can be used to drive perfect quantum
information transport at room-temperature. The Hamiltonian engineering method
can be made more robust under coherence and coupling disorder by a novel
apodization scheme. Thus the method is quite general and can be used engineer
the Hamiltonian of many complex spin lattices with different topologies and
interactions.",1208.3656v2
2012-08-25,Spin dynamics of possible density wave states in the pseudogap phase of the high temperature superconductors,"In a recent inelastic neutron scattering experiment in the pseudogap state of
the high temperature superconductor $\mathrm{YBa_{2}Cu_{3}O_{6.6}}$ an unusual
`vertical' dispersion of the spin excitations with a large in-plane anisotropy
was observed. In this paper we discuss in detail the spin susceptibility of the
singlet $d$-density wave, the triplet $d$-density wave, as well as the more
common spin density wave orders with hopping anisotropies. From numerical
calculations within the framework of random phase approximation, we find nearly
vertical dispersion relations for spin excitations with anisotropic
incommensurability at low energy $\omega \le 90 meV$, which are reminiscent of
the experiments. At very high energy $\omega \ge 165 meV$, we also find
energy-dependent incommensurability. Although there are some important
difference between the three cases, unpolarized neutron measurements cannot
discriminate between these alternate possibilities; the vertical dispersion,
however, is a distinct feature of all three density wave states in contrast to
the superconducting state, which shows an hour-glass shape dispersion.",1208.5108v1
2012-10-25,Practicality of spin chain 'wiring' in diamond quantum technologies,"Coupled spin chains are promising candidates for 'wiring up' qubits in
solid-state quantum computing (QC). In particular, two nitrogen-vacancy centers
in diamond can be connected by a chain of implanted nitrogen impurities; when
driven by a suitable global fields the chain can potentially enable quantum
state transfer at room temperature. However, our detailed analysis of error
effects suggests that foreseeable systems may fall far short of the fidelities
required for QC. Fortunately the chain can function in the more modest role as
a mediator of noisy entanglement, enabling QC provided that we use subsequent
purification. For instance, a chain of 5 spins with inter-spin distances of 10
nm has finite entangling power as long as the T2 time of the spins exceeds 0.55
ms. Moreover we show that re-purposing the chain this way can remove the
restriction to nearest-neighbor interactions, so eliminating the need for
complicated dynamical decoupling sequences.",1210.6886v3
2012-11-13,Longitudinal and spin/valley Hall optical conductivity in single layer $MoS_{2}$,"A monolayer of $MoS_{2}$ has a non-centrosymmetric crystal structure, with
spin polarized bands. It is a two valley semiconductor with direct gap falling
in the visible range of the electromagnetic spectrum. Its optical properties
are of particular interest in relation to valleytronics and possible device
applications. We study the longitudinal and the transverse Hall dynamical
conductivity which is decomposed into charge, spin and valley contributions.
Circular polarized light associated with each of the two valleys separately is
considered and results are filtered according to spin polarization. Temperature
can greatly change the spin admixture seen in the frequency window where they
are not closely in balance.",1211.3094v2
2012-11-30,Sensitive Magnetic Control of Ensemble Nuclear Spin Hyperpolarisation in Diamond,"Dynamic nuclear polarisation, which transfers the spin polarisation of
electrons to nuclei, is routinely applied to enhance the sensitivity of nuclear
magnetic resonance; it is also critical in spintronics, particularly when spin
hyperpolarisation can be produced and controlled optically or electrically.
Here we show the complete polarisation of nuclei located near the
optically-polarised nitrogen-vacancy (NV) centre in diamond. When approaching
the ground-state level anti-crossing condition of the NV electron spins, 13C
nuclei in the first-shell are polarised in a pattern that depends sensitively
and sharply upon the magnetic field. Based on the anisotropy of the hyperfine
coupling and of the optical polarisation mechanism, we predict and observe a
complete reversal of the nuclear spin polarisation with a few-mT change in the
magnetic field. The demonstrated sensitive magnetic control of nuclear
polarisation at room temperature will be useful for sensitivity-enhanced NMR,
nuclear-based spintronics, and quantum computation in diamond.",1212.0035v1
2013-01-18,Current induced torques and interfacial spin-orbit coupling: Semiclassical Modeling,"In bilayer nanowires consisting of a ferromagnetic layer and a non-magnetic
layer with strong spin-orbit coupling, currents create torques on the
magnetization beyond those found in simple ferromagnetic nanowires. The
resulting magnetic dynamics appear to require torques that can be separated
into two terms, damping-like and field-like. The damping-like torque is
typically derived from models describing the bulk spin Hall effect and the spin
transfer torque, and the field-like torque is typically derived from a Rashba
model describing interfacial spin-orbit coupling. We derive a model based on
the Boltzmann equation that unifies these approaches. We also consider an
approximation to the Boltzmann equation, the drift-diffusion model, that
qualitatively reproduces the behavior, but quantitatively fails to reproduce
the results. We show that the Boltzmann equation with physically reasonable
parameters can match the torques for any particular sample, but in some cases,
it fails to describe the experimentally observed thickness dependences.",1301.4513v1
2013-02-12,Collapse and Revival and Cat States with an N Spin System,"We discuss collapse and revival of Rabi oscillations in a system comprising a
qubit and a ""big spin"" (made of N qubits, or spin-1/2 particles). We
demonstrate a regime of behaviour analogous to conventional collapse and
revival for a qubit-field system, employing spin coherent states for the
initial state of the big spin. These dynamics can be used to create a
""Schrodinger cat"" state of the big spin. Even for relatively small values of N,
states with significant potential for quantum metrology applications can
result, giving sensitivity approaching the Heisenberg limit.",1302.2806v2
2013-03-02,Nuclear-spin-dependent coherent population trapping of single nitrogen vacancy centers in diamond,"Coherent population trapping (CPT) provides a highly sensitive means for
probing the energy level structure of an atomic system. For a nitrogen vacancy
center in diamond, the CPT offers an alternative to the standard
optically-detected magnetic resonance method for measuring the hyperfine
structure of the electronic ground states. We show that the nuclear spin
dependent CPT measures directly the hyperfine splitting of these states due to
the 14N nuclear spin. The CPT spectral response obtained in the presence of a
strong microwave field, resonant or nearly resonant with a ground state spin
transition, maps out the dynamic Stark splitting induced by the coherent spin
excitation.",1303.0421v1
2013-03-06,Li$_2$RhO$_3$: A spin-glassy relativistic Mott insulator,"Motivated by the rich interplay among electronic correlation, spin-orbit
coupling (SOC), crystal-field splitting, and geometric frustrations in the
honeycomb-like lattice, we systematically investigated the electronic and
magnetic properties of Li$_2$RhO$_3$. The material is semiconducting with a
narrow band gap of $\Delta\sim$78 meV, and its temperature dependence of
resistivity conforms to 3D variable range hopping mechanism. No long-range
magnetic ordering was found down to 0.5 K, due to the geometric frustrations.
Instead, single atomic spin-glass behavior below the spin-freezing temperature
($\sim$6 K) was observed and its spin dynamics obeys the universal critical
slowing down scaling law. First principle calculations suggested it to be a
relativistic Mott insulator mediated by both electronic correlation and SOC.
With moderate strength of electronic correlation and SOC, our results shed new
light to the research of Heisenberg-Kitaev model in realistic materials.",1303.1235v2
2013-03-21,Relaxation of flying spin qubits in quantum wires by hyperfine interaction,"We consider the relaxation of a spin qubit in a quantum dot propagating as a
whole in a one-dimensional semiconductor with hyperfine coupling. We show that
this motion leads to qualitatively new features in this process compared to
static quantum dots. For a fast straightforward motion, the initial spin
density decreases to zero with the relaxation rate independent of the spatial
spread of the electron wave function and inversely proportional to the electron
speed. However, for the oscillatory motion, the qubit acquires memory, and the
dephasing becomes Gaussian rather than exponential. After some time, one third
of the initial spin polarization is restored, as it happens for static qubits.
This revival can occur either through periodic peaks or through a monotonous
increase in the polarization, after a minimum, until a plateau has been
reached. Our results can be useful for the understanding of the spin dynamics
and decoherence in quantum wires.",1303.5273v1
2013-04-17,Derivation of a linear collision operator for the spinorial Wigner equation and its semiclassical limit,"We systematically derive a linear quantum collision operator for the
spinorial Wigner transport equation from the dynamics of a composite quantum
system. For suitable two particle interaction potentials, the particular matrix
form of the collision operator describes spin decoherence or even spin
depolarization as well as relaxation towards a certain momentum distribution in
the long time limit. It is demonstrated that in the semiclassical limit the
spinorial Wigner equation gives rise to several semiclassical spin-transport
models. As an example, we derive the Bloch equations as well as the spinorial
Boltzmann equation, which in turn gives rise to spin drift-diffusion models
which are increasingly used to describe spin-polarized transport in spintronic
devices. The presented derivation allows to systematically incorporate
Born-Markov as well as quantum corrections into these models.",1304.4772v1
2013-04-22,Magnetic anisotropic energy gap and low energy spin wave excitation in antiferromagnetic block phase of K2Fe4Se5,"Neutron scattering experiments were performed to investigate magnetic order
and magnetic excitations in ternary iron chalcogenide K2Fe4Se5. The formation
of a superlattice structure below 580 K together with the decoupling between
the Fe-vacancy order-disorder transition and the antiferromagnetic order
transition appears to be a common feature in the A2Fe4Se5 family. The study of
spin dynamics of K2Fe4Se5 reveals two distinct energy gaps at the magnetic
Brillouin zone center, which indicates the presence of magnetic anisotropy and
the decrease of local symmetry due to electronic and orbital anisotropy. The
low-energy spin wave excitations of K2Fe4Se5 can be properly described by
linear spin wave theory within a Heisenberg model. Compared to iron pnictides,
K2Fe4Se5 exhibits a more two-dimensional magnetism as characterized by large
differences not only between out-of-plane and in-plane spin wave velocities,
but also between out-of-plane and in-plane exchange interactions.",1304.5950v1
2013-05-09,Low-temperature muon spin rotation studies of the monopole charges and currents in Y doped Ho2Ti2O7,"In the ground state of Ho2Ti2O7 spin ice, the disorder of the magnetic
moments follows the same rules as the proton disorder in water ice. Excitations
take the form of magnetic monopoles that interact via a magnetic Coulomb
interaction. Muon spin rotation has been used to probe the low-temperature
magnetic behaviour in single crystal Ho2-xYxTi2O7 (x=0, 0.1, 1, 1.6 and 2). At
very low temperatures, a linear field dependence for the relaxation rate of the
muon precession lambda(B), that in some previous experiments on Dy2Ti2O7 spin
ice has been associated with monopole currents, is observed in samples with
x=0, and 0.1. A signal from the magnetic fields penetrating into the silver
sample plate due to the magnetization of the crystals is observed for all the
samples containing Ho allowing us to study the unusual magnetic dynamics of Y
doped spin ice.",1305.2048v1
2013-05-13,Normal state spin dynamics in the iron-pnictide superconductors BaFe2(As1-xPx)2 and Ba(Fe1-xCox)2As2 probed with NMR measurements,"The NMR results in iron pnictides BaFe2(As1-xPx)2 and Ba(Fe1-xCox)2As2 are
analyzed based on the self-consistent renormalization (SCR) spin fluctuation
theory. The temperature dependence of the NMR relaxation rate (T_1)^{-1} as
well as the electrical resistivity is well reproduced by a SCR model where
two-dimensional antiferromagnetic (AF) spin fluctuations are dominant. The
successful description of the crossover feature from non-Fermi liquid to Fermi
liquid behavior strongly suggests that low-lying spin fluctuations in
BaFe2(As1-xPx)2 and Ba(Fe1-xCox)2As2 possess an itinerant AF nature, and that
chemical substitution in the two compounds tunes the distance of these systems
to an AF quantum critical point. The close relationship between spin
fluctuations and superconductivity is discussed compared with the other
unconventional superconductors, cuprate and heavy fermion superconductors. In
addition, it is suggested that magnetism and lattice instability in these
pnictides are strongly linked via orbital degrees of freedom.",1305.2656v1
2013-06-12,Atomic spin-orbit coupling synthesized with magnetic-field-gradient pulses,"We discuss a general scheme for creating atomic spin-orbit coupling (SOC)
such as the Rashba or Dresselhaus types using magnetic-field-gradient pulses.
In contrast to conventional schemes based on adiabatic center-of-mass motion
with atomic internal states restricted to a dressed-state subspace, our scheme
works for the complete subspace of a hyperfine-spin manifold by utilizing the
coupling between the atomic magnetic moment and external magnetic fields. A
spatially dependent pulsed magnetic field acts as an internal-state-dependent
impulse, thereby coupling the atomic internal spin with its orbital
center-of-mass motion, as in the Einstein-de Haas effect. This effective
coupling can be dynamically manipulated to synthesize SOC of any type (Rashba,
Dresselhaus, or any linear combination thereof). Our scheme can be realized
with most experimental setups of ultracold atoms and is especially suited for
atoms with zero nuclear spins.",1306.2829v1
2013-07-11,Progressive slowing down of spin fluctuations in underdoped LaFeAsO$_{1-x}$F$_x$,"The evolution of low-energy spin dynamics in the iron-based superconductor
LaFeAsO$_{1-x}$F$_x$ was studied over a broad doping, temperature, and magnetic
field range (x = 0 - 0.15, T up to 480K, H up to 30T) by means of As nuclear
magnetic resonance (NMR). An enhanced spin-lattice relaxation rate divided by
temperature, 1/T1T, in underdoped superconducting samples (x = 0.045, 0.05 and
0.075) suggests the presence of antiferromagnetic spin fluctuations, which are
strongly reduced in optimally-doped (x = 0.10) and completely absent in
overdoped (x = 0.15) samples. In contrast to previous analysis, Curie-Weiss
fits are shown to be insufficient to describe the data over the whole
temperature range. Instead, a BPP-type model is used to describe the occurrence
of a peak in 1/T1T clearly above the superconducting transition, reflecting a
progressive slowing down of the spin fluctuations down to the superconducting
phase transition.",1307.3138v1
2013-07-21,Spatiotemporal buildup of the Kondo screening cloud,"We investigate how the Kondo screening cloud builds up as a function of space
and time. Starting from an impurity spin decoupled from the conduction band,
the Kondo coupling is switched on at time t=0. We work at the Toulouse point
where one can obtain exact analytical results for the ensuing spin dynamics at
both zero and nonzero temperature T. For t>0 the Kondo screening cloud starts
building up in the wake of the impurity spin being transported to infinity. In
this buildup process the impurity spin--conduction band spin susceptibility
shows a sharp light cone due to causality, while the corresponding correlation
function has a tail outside the light cone. At T=0 this tail has a power law
decay as a function of distance from the impurity, which we interpret as due to
initial entanglement in the Fermi sea.",1307.5488v1
2013-10-01,Higher Order Spin Noise Statistics,"The optical spin noise spectroscopy (SNS) is a minimally invasive route
towards obtaining dynamical information about electrons and atomic gases by
measuring mesoscopic time-dependent spin fluctuations. Recent improvements of
the sensitivity of SNS should make it possible to observe higher order spin
correlators at thermodynamic equilibrium. We develop theoretical methods to
explore higher order (3rd and 4th) cumulants of the spin noise in the frequency
domain. We make predictions for the possible functional form of these
correlators in single quantum dot experiments and then apply the method of the
stochastic path integral to estimate effects of many-body interactions.",1310.0478v2
2013-10-03,Observing bulk diamond spin coherence in high-purity nanodiamonds,"Nitrogen-vacancy centres (NVs) in diamond are attractive for research
straddling quantum information science and nanoscale magnetometry and
thermometry. While ultrapure bulk diamond NVs sustain the longest spin
coherence times among optically accessible spins, nanodiamond NVs display
persistently poor spin coherence. Here we introduce high-purity nanodiamonds
accommodating record-long NV coherence times, >60 us, observed via universal
dynamical decoupling. We show that the main contribution to decoherence comes
from nearby nitrogen impurities rather than surface states. We protect the NV
spin free precession, essential to DC magnetometry, by driving solely these
impurities into the motional narrowing regime. This extends the NV free
induction decay time from 440 ns, longer than that in type Ib bulk diamond, to
1.27 us, which is comparable to that in type IIa (impurity-free) diamond. These
properties allow the simultaneous exploitation of both high sensitivity and
nanometre resolution in diamond-based emergent quantum technologies.",1310.1133v1
2013-10-14,Asteroid spin-axis longitudes from the Lowell Observatory database,"By analyzing brightness variation with ecliptic longitude and using the
Lowell Observatory photometric database, we estimate spin-axis longitudes for
more than 350 000 asteroids. Hitherto, spin-axis longitude estimates have been
made for fewer than 200 asteroids. We investigate longitude distributions in
different dynamical groups and asteroid families. We show that asteroid
spin-axis longitudes are not isotropically distributed as previously
considered. We find that the spin-axis longitude distribution for main-belt
asteroids is clearly non-random, with an excess of longitudes from the interval
30{\deg}-110{\deg} and a paucity between 120{\deg}-180{\deg}. The explanation
of the non-isotropic distribution is unknown at this point. Further studies
have to be conducted to determine if the shape of the distribution can be
explained by observational bias, selection effects, a real physical process or
other mechanism.",1310.3617v1
2013-11-23,Finite-temperature decoherence of spin states in a $\texttt{\{}\emph{Cu}_3\texttt{\}}$ single molecular magnet,"We investigate the quantum evolution of spin states of a single molecular
magnet in a local electric field. The decoherence of a
$\texttt{\{}\emph{Cu}_3\texttt{\}}$ single molecular magnet weakly coupled to a
thermal bosonic environment can be analyzed by the spin-boson model. Using the
finite-temperature time-convolutionless quantum master equation, we obtain the
analytical expression of the reduced density matrix of the system in the
secular approximation. The suppressed and revived dynamical behavior of the
spin states are presented by the oscillation of the chirality spin polarization
on the time scale of the correlation time of the environment. The quantum
decoherence can be effectively restrained with the help of the manipulation of
local electric field and the environment spectral density function. Under the
influence of the dissipation, the pointer states measured by the von Neumann
entropy are calculated to manifest the entanglement property of the
system-environment model.",1311.5953v1
2013-11-26,Lattice and orbital fluctuations in TiPO4,"In the s = 1/2 antiferromagnetic spin chain material TiPO4 the formation of a
spin gap takes place in a two step process with two characteristic
temperatures, T*=111 K and TSP=74 K. We observe an unusual lattice dynamics
over a large temperature regime as well as evidence for an orbital instability
preceding the spin-Peierls transition. We relate different intrachain exchange
interactions of the high temperature compared to the spin-Peierls phase to a
modification of the orbital ordering pattern. In particular, our observation of
a high energy excitation of mixed electronic and lattice origin suggests an
exotic dimerization process different from other spin-Peierls materials.",1311.6538v1
2013-12-15,Spin-Orbit Effects in Atomic High-Harmonic Generation,"Spin-orbit interactions lead to small energy gaps between the outer-most
$p_{1/2}$ and $p_{3/2}$ shells of noble gas atoms. Strong-field pulses
tunnel-ionize an electron out of either shell resulting in spin-orbit-driven
hole motion. These hole dynamics affect the HHG yield. However, the spectral
shape as well as the angular distribution of the HHG emission is not influenced
by spin-orbit coupling. We demonstrate the spin-orbit effect on atomic krypton
by solving the multi-electron Schr\""odinger equation with the time-dependent
configuration-interaction singles (TDCIS) approach. We also provide pulse
parameters where this effect can be identified in experiments through an
enhancement in the HHG yield as the wavelength of the strong-field pulse
increases.",1312.4151v1
2013-12-19,Gravitational waves from spinning compact object binaries: New post-Newtonian results,"We report on recent results obtained in the post-Newtonian framework for the
modelling of the gravitational waves emitted by binary systems of spinning
compact objects (black holes and/or neutron stars). These new results are
obtained at the spin-orbit (linear-in-spin) level and solving Einstein's field
equations iteratively in harmonic coordinates as well as the multipolar
post-Newtonian formalism. The dynamics of the binary was tackled at the
next-to-next-to-leading order, corresponding to the 3.5 post-Newtonian (PN)
order for maximally spinning objects, and the result is found to be consistent
with a previously obtained reduced Hamiltonian in the ADM approach. The
corresponding contribution to the energy flux emitted by the binary was
obtained at the 3.5PN order, as well as the next-to-leading 4PN tail
contribution to this flux, an imprint of the non-linearity in the propagation
of the wave. These new terms can be used to build more accurate PN templates
for the next generation of gravitational wave detectors. We give an
illustrative estimate of the quantitative relevance of the new terms in the
orbital phasing of the binary.",1312.5375v1
2013-12-26,Structural determination and electronic properties of 4d perovskite SrPdO3,"The structure and ground state electronic structure of the recently
synthesized SrPdO$_3$ perovskite [A. Galal {\em et al.}, J. Power Sources, {\bf
195}, 3806 (2010)] have been studied by means of screened hybrid functional and
the GW approximation with the inclusion of electron-hole interaction within the
test-charge/test-charge scheme. By conducting a structural search based on
lattice dynamics and group theoretical method we identify the orthorhombic
phase with $P_{nma}$ space group as the most stable crystal structure. The
phase transition from the ideal cubic perovskite structure to the $P_{nma}$ one
is explained in terms of the simultaneous stabilization of the
antiferrodistortive phonon modes $R_4^+$ and $M_3^+$. Our results indicate that
SrPdO$_3$ exhibits an insulating ground state, substantiated by a GW$_0$ gap of
about 1.1 eV. Spin polarized calculations suggests that SrPdO$_3$ adopts a low
spin state
($t_{2g}^{\uparrow\downarrow\uparrow\downarrow\uparrow\downarrow}e_g^0$), and
is expected to exhibit spin excitations and spin state crossovers at finite
temperature, analogous to the case of 3$d$ isoelectronic LaCoO$_3$. This would
provide a new playground for the study of spin state transitions in 4$d$ oxides
and new opportunity to design multifunctional materials based on 4$d$ $P_{nma}$
building block.",1312.7121v1
2013-12-27,Exact Nonadiabatic Holonomic Transformations of Spin-Orbit Qubits,"An exact analytical solution is derived for the wavefunction of an electron
in a one-dimensional moving quantum dot in a nanowire, in the presence of
time-dependent spin-orbit coupling. For cyclic evolutions we show that the spin
of the electron is rotated by an angle proportional to the area of a closed
loop in the parameter space of the time-dependent quantum dot position and the
amplitude of a fictitious classical oscillator driven by the time-dependent
spin-orbit coupling. By appropriate choice of parameters, we show that
arbitrary spin rotations may be performed on the Bloch sphere. Exact
expressions for dynamical and geometrical phases are also derived.",1312.7254v3
2014-01-08,Diluted Mean-Field Spin-Glass Models at Criticality,"We present a method derived by cavity arguments to compute the spin-glass and
higher-order susceptibilities in diluted mean-field spin-glass models. The
divergence of the spin-glass susceptibility is associated to the existence of a
non-zero solution of a homogeneous linear integral equation. Higher order
susceptibilities, relevant for critical dynamics through the parameter exponent
$\lambda$, can be expressed at criticality as integrals involving the critical
eigenvector. The numerical evaluation of the corresponding analytic expressions
is discussed. The method is illustrated in the context of the de
Almeida-Thouless line for a spin-glass on a Bethe lattice but can be
generalized straightforwardly to more complex situations.",1401.1729v3
2014-02-06,Conservation laws protect dynamic spin correlations from decay: Limited role of integrability in the central spin model,"Mazur's inequality renders statements about persistent correlations possible.
We generalize it in a convenient form applicable to any set of linearly
independent constants of motion. This approach is used to show rigorously that
a fraction of the initial spin correlations persists indefinitely in the
isotropic central spin model unless the average coupling vanishes. The central
spin model describes a major mechanism of decoherence in a large class of
potential realizations of quantum bits. Thus the derived results contribute
significantly to the understanding of the preservation of coherence. We will
show that persisting quantum correlations are not linked to the integrability
of the model, but caused by a finite operator overlap with a finite set of
constants of motion.",1402.1277v3
2014-02-13,Unusual spin fluctuations and magnetic frustration in olivine and non-olivine LiCoPO$_4$ detected by $^{31}$P and $^7$Li nuclear magnetic resonance,"We report $^{31}$P and $^{7}$Li nuclear magnetic resonance (NMR) studies in
new non-olivine LiZnPO$_4$-type LiCoPO$_4^\text{tetra}$ microcrystals, where
the Co$^{2+}$ ions are tetrahedrally coordinated. Olivine LiCoPO$_4$, which was
directly transformed from LiCoPO$_4^\text{tetra}$ by an annealing process, was
also studied and compared. The uniform bulk magnetic susceptibility and the
$^{31}$P Knight shift obey the Curie-Weiss law for both materials with a high
spin Co$^{2+}$ ($3d^7$, $S=3/2$), but the Weiss temperature $\Theta$ and the
effective magnetic moment $\mu_\text{eff}$ are considerably smaller in
LiCoPO$_4^\text{tetra}$. The spin-lattice relaxation rate $T_1^{-1}$ reveals a
quite different nature of the spin dynamics in the paramagnetic state of both
materials. Our NMR results imply that strong geometrical spin frustration
occurs in tetrahedrally coordinated LiCoPO$_4$, which may lead to the
incommensurate magnetic ordering.",1402.3082v2
2014-02-21,Probing surface noise with depth-calibrated spins in diamond,"Sensitive nanoscale magnetic resonance imaging (MRI) of target spins using
nitrogen-vacancy (NV) centers in diamond will require a quantitative
understanding of dominant noise at the surface. We probe this noise by applying
dynamical decoupling to shallow NVs at calibrated depths. Results support a
model of NV dephasing by a surface bath of electronic spins having a
correlation rate of 200 kHz, much faster than that of the bulk N spin bath. Our
method of combining nitrogen delta-doping growth and nanoscale depth imaging
paves a way for studying spin noise present in diverse material surfaces.",1402.5392v1
2014-02-25,Coherent Transmutation of Electrons into Fractionalized Anyons,"Electrons have three quantized properties -- charge, spin, and Fermi
statistics -- that are directly responsible for a vast array of phenomena. Here
we show how these properties can be coherently and dynamically stripped from
the electron as it enters certain exotic states of matter known as a quantum
spin liquid (QSL). In a QSL, electron spins collectively form a highly
entangled quantum state that gives rise to emergent gauge forces and
fractionalization of spin, charge, and statistics. We show that certain QSLs
host distinct, topologically robust boundary types, some of which allow the
electron to coherently enter the QSL as a fractionalized quasiparticle, leaving
its spin, charge, or statistics behind. We use these ideas to propose a number
of universal, conclusive experimental signatures that would establish
fractionalization in QSLs.",1402.6321v2
2014-04-08,Integrable Motion of Curves in Self-Consistent Potentials : Relation to Spin Systems and Soliton Equations,"Motion of curves and surfaces in $\R^3$ lead to nonlinear evolution equations
which are often integrable. They are also intimately connected to the dynamics
of spin chains in the continuum limit and integrable soliton systems through
geometric and gauge symmetric connections/equivalence. Here we point out the
fact that a more general situation in which the curves evolve in the presence
of additional self consistent vector potentials can lead to interesting
generalized spin systems with self consistent potentials or soliton equations
with self consistent potentials. We obtain the general form of the evolution
equations of underlying curves and report specific examples of generalized spin
chains and soliton equations. These include principal chiral model and various
Myrzakulov spin equations in (1+1) dimensions and their geometrically
equivalent generalized nonlinear Schr\""odinger (NLS) family of equations,
including Hirota-Maxwell-Bloch equations, all in the presence of self
consistent potential fields. The associated gauge equivalent Lax pairs are also
presented to confirm their integrability.",1404.2088v1
2014-04-15,Localization of a spin-orbit coupled Bose-Einstein condensate in a bichromatic optical lattice,"We study the localization of a noninteracting and weakly interacting
Bose-Einstein condensate with spin-orbit coupling loaded in a quasiperiodic
bichromatic optical lattice potential using the numerical solution and
variational approximation of a binary mean-field Gross-Pitaevskii equation with
two pseudo-spin components. We confirm the existence of the stationary
localized states in the presence of the spin-orbit and Rabi couplings for an
equal distribution of atoms in the two components. We find that the interaction
between the spin-orbit and Rabi couplings favors the localization or
delocalization of the BEC depending on the the phase difference between the
components. We also studied the oscillation dynamics of the localized states
for an initial population imbalance between the two components.",1404.4017v2
2014-04-16,Protecting a Spin Ensemble against Decoherence in the Strong-Coupling Regime of Cavity QED,"Hybrid quantum systems based on spin ensembles coupled to superconducting
microwave cavities are promising candidates for robust experiments in cavity
quantum electrodynamics (QED) and for future technologies employing quantum
mechanical effects. Currently the main source of decoherence in these systems
is inho- mogeneous spin broadening, which limits their performance for the
coherent transfer and storage of quantum information. Here we study the
dynamics of a superconducting cavity strongly coupled to an ensemble of
nitrogen-vacancy centers in diamond. We experimentally observe for the first
time, how decoherence induced by a non-Lorentzian spin distribution can be
suppressed in the strong-coupling regime - a phenomenon known as ""cavity
protection"". To demonstrate the potential of this effect for coherent control
schemes, we show how appropriately chosen microwave pulses can increase the
amplitude of coherent oscillations between cavity and spin ensemble by two
orders of magnitude.",1404.4169v1
2014-04-17,Anisotropic nuclear-spin diffusion in double quantum wells,"Nuclear-spin diffusion in double quantum wells (QWs) is examined by using
dynamic nuclear polarization (DNP) at a Landau level filling factor $\nu=2/3$
spin phase transition (SPT). The longitudinal resistance increases during the
DNP of one of the two QW (the polarization QW) by means of a large applied
current and starts to decrease just after the termination of the DNP. On the
other hand, the longitudinal resistance of the other QW (the detection QW)
continuously increases for approximately 2h after the termination of the DNP of
the polarization QW. It is therefore concluded that the nuclear spins diffuse
from the polarization QW to the detection QW. The time evolution of the
longitudinal resistance of the polarization QW is explained mainly by the
nuclear-spin diffusion in the in-plane direction. In contrast, that of the
detection QW manifests much slower nuclear diffusion in the perpendicular
direction through the AlGaAs barrier.",1404.4423v2
2014-06-30,Spin foam models as energetic causal sets,"Energetic causal sets are causal sets endowed by a flow of energy-momentum
between causally related events. These incorporate a novel mechanism for the
emergence of space-time from causal relations. Here we construct a spin foam
model which is also an energetic causal set model. This model is closely
related to the model introduced in parallel by Wolfgang Wieland in
arXiv:1407.0025, and this construction makes use of results used there. What
makes a spin foam model also an energetic causal set is Wieland's
identification of new momenta, conserved at events (or four-simplices), whose
norms are not mass, but the volume of tetrahedra. This realizes the torsion
constraints, which are missing in previous spin foam models, and are needed to
relate the connection dynamics to those of the metric, as in general
relativity. This identification makes it possible to apply the new mechanism
for the emergence of space-time to a spin foam model.",1407.0032v2
2014-06-30,Spin-dependent polaron formation dynamics in Eu$_{0.75}$Y$_{0.25}$MnO$_3$ probed by femtosecond pump-probe spectroscopy,"We present a femtosecond optical pump-probe study of the multiferroic
manganite Eu$_{0.75}$Y$_{0.25}$MnO$_3$. The optical response of the material at
pump energies of 1.55 and 3.1 eV is dominated by the $d$-$d$ and $p$-$d$
transitions of the Mn$^{3+}$ ions. The relaxation of photoexcited electrons
includes the relaxation of the Jahn-Teller distortion and polaron trapping at
Mn$^{2+}$ and Mn$^{4+}$ sites. Ultrafast switching of superexchange
interactions due to modulated $e_g$ orbital occupancy creates a localized spin
excitation, which then decays on a time scale of tens of picoseconds at low
temperatures. The localized spin state decay appears as a tremendous increase
in the amplitude of the photoinduced reflectance, due to the strong coupling of
optical transitions to the spin-spin correlations in the crystalline $a$-$b$
plane.",1407.0073v1
2014-08-05,A one-dimensional liquid of fermions with tunable spin,"Correlations in systems with spin degree of freedom are at the heart of
fundamental phenomena, ranging from magnetism to superconductivity. The effects
of correlations depend strongly on dimensionality, a striking example being
one-dimensional (1D) electronic systems, extensively studied theoretically over
the past fifty years. However, the experimental investigation of the role of
spin multiplicity in 1D fermions - and especially for more than two spin
components - is still lacking. Here we report on the realization of 1D,
strongly-correlated liquids of ultracold fermions interacting repulsively
within SU(N) symmetry, with a tunable number N of spin components. We observe
that static and dynamic properties of the system deviate from those of ideal
fermions and, for N>2, from those of a spin-1/2 Luttinger liquid. In the
large-N limit, the system exhibits properties of a bosonic spinless liquid. Our
results provide a testing ground for many-body theories and may lead to the
observation of fundamental 1D effects.",1408.0928v1
2014-08-08,CdSe/ZnSe quantum dot with a single Mn$^{2+}$ ion - a new system for a single spin manipulation,"We present a magneto-optical study of individual self-assembled CdSe/ZnSe
quantum dots doped with single Mn$^{2+}$ ions. Properties of the studied dots
are analyzed analogously to more explored system of Mn-doped CdTe/ZnTe dots.
Characteristic sixfold splitting of the neutral exciton emission line as well
as its evolution in the magnetic field are described using a spin Hamiltonian
model. Dynamics of both exciton recombination and Mn$^{2+}$ spin relaxation are
extracted from a series of time-resolved experiments. Presence of a single
dopant is shown not to affect the average excitonic lifetime measured for a
number of nonmagnetic and Mn-doped dots. On the other hand, non-resonant
pumping is demonstrated to depolarize the Mn$^{2+}$ spin in a quantum dot
placed in external magnetic field. This effect is utilized to determine the ion
spin relaxation time in the dark.",1408.1981v1
2014-08-21,Spin-geodesic deviations in the Kerr spacetime,"The dynamics of extended spinning bodies in the Kerr spacetime is
investigated in the pole-dipole particle approximation and under the assumption
that the spin-curvature force only slightly deviates the particle from a
geodesic path. The spin parameter is thus assumed to be very small and the back
reaction on the spacetime geometry neglected. This approach naturally leads to
solve the Mathisson-Papapetrou-Dixon equations linearized in the spin variables
as well as in the deviation vector, with the same initial conditions as for
geodesic motion. General deviations from generic geodesic motion are studied,
generalizing previous results limited to the very special case of an equatorial
circular geodesic as the reference path.",1408.4952v1
2014-08-29,Spinning Particle in Gravitational Field of Black Hole Involving Global Monopole,"In this paper we study the dynamics of trajectory of a spinning particle in a
Schwarzschild spacetime involving a global monopole. We set up the equations of
motion and find three types of trajectories. We study the conditions that a
spinning particle, originally moving in the innermost stable circular orbit
around the black hole involving a global monopole, will escape to infinity
after it is kicked by another particle or photon. Three types of trajectories
of a spinning particle in a Schwarzschild spacetime involving a global monopole
are simulated in detail and the escaping energy and velocity of the spinning
particle is also obtained in the present paper.",1408.6901v1
2014-09-23,Microscopic control of $^{29}$Si nuclear spins near phosphorus donors in silicon,"We demonstrate an efficient control of $^{29}$Si nuclear spin orientation for
specific lattice sites near $^{31}$P donors in silicon crystals at temperatures
below 1 K and in high magnetic field of 4.6 T. Excitation of the forbidden
electron-nuclear transitions leads to a pattern of narrow holes and peaks in
the ESR lines of $^{31}$P. The pattern originates from dynamic polarization the
$^{29}$Si nuclear spins near the donors via the solid effect. This method can
be used for initialization of qubits based on $^{29}$Si nuclear spins in the
all-silicon quantum computer. In comparison, polarization of $^{29}$Si
performed by pumping the allowed ESR transitions, did not create any patterns.
Instead, a single narrow spectral hole was burnt in the ESR line. The
difference is explained by a rapid spin diffusion during the microwave pumping
of the allowed transitions.",1409.6462v3
2014-10-13,Spin-polarized dynamic transport in tubular two-dimensional electron gases,"The ac conductance of a finite tubular two-dimensional electron gas is
studied in the presence of the Rashba spin-orbit interaction. When the tube is
coupled to two reservoirs, that interaction splits the steps in the dc current,
introducing energy ranges with spin-polarized currents. For this setup, we
calculate the current-current correlations (the noise spectrum) and show that
the existence of these dc spin-polarized currents can be deduced from the shot
noise. We also find that the Wigner-Smith time delay is almost unaffected by
the spin-orbit interaction. When the tube is coupled to a single reservoir, we
calculate the quantum capacitance and the charge-relaxation resistance, and
find that they exhibit singularities near the openings of new channels.",1410.3262v1
2014-10-21,Bose-Einstein condensation with spin-orbit coupling,"The recent realization of synthetic spin-orbit coupling represents an
outstanding achievement in the physics of ultracold quantum gases. In this
review we explore the properties of a spin-orbit-coupled Bose-Einstein
condensate with equal Rashba and Dresselhaus strengths. This system presents a
rich phase diagram, which exhibits a tricritical point separating a
zero-momentum phase, a spin-polarized plane-wave phase, and a stripe phase. In
the stripe phase translational invariance is spontaneously broken, in analogy
with supersolids. Spin-orbit coupling also strongly affects the dynamics of the
system. In particular, the excitation spectrum exhibits intriguing features,
including the suppression of the sound velocity, the emergence of a roton
minimum in the plane-wave phase, and the appearance of a double gapless band
structure in the stripe phase. Finally, we discuss a combined procedure to make
the stripes visible and stable, thus allowing for a direct experimental
detection.",1410.5526v2
2014-10-24,"The remains of a spinning, hyperbolic encounter","We review a recently proposed approach to construct gravitational wave (GW)
polarization states of unbound spinning compact binaries. Through this rather
simple method, we are able to include corrections due to the dominant order
spin-orbit interactions, in the quadrupolar approximation and in a
semi-analytic way. We invoke the 1.5 post-Newtonian (PN) accurate
quasi-Keplerian parametrization for the radial part of the dynamics and impose
its temporal evolution in the PN accurate polarization states equations.
Further, we compute 1PN accurate amplitude corrections for the polarization
states of non-spinning compact binaries on hyperbolic orbits. As an interesting
application, we perform comparisons with previously available results for both
the GW signals in the case of non-spinning binaries and the theoretical
prediction for the amplitude of the memory effect on the metric after the
hyperbolic passage.",1410.6606v1
2014-10-24,Rectification of radio frequency current in giant magnetoresistance spin valve,"We report on a highly efficient spin diode effect in an exchange-biased
spin-valve giant magnetoresistance (GMR) strips. In such multilayer structures,
symmetry of the current distribution along the vertical direction is broken
and, as a result, a non-compensated Oersted field acting on the magnetic free
layer appears. This field, in turn, is a driving force of magnetization
precessions. Due to the GMR effect, resistance of the strip oscillates
following the magnetization dynamics. This leads to rectification of the
applied radio frequency current and induces a direct current voltage $V_{DC}$.
We present a theoretical description of this phenomenon and calculate the spin
diode signal, $V_{DC}$, as a function of frequency, external magnetic field,
and angle at which the external field is applied. A satisfactory quantitative
agreement between theoretical predictions and experimental data has been
achieved. Finally, we show that the spin diode signal in GMR devices is
significantly stronger than in the anisotropic magnetoresistance
permalloy-based devices.",1410.6672v1
2014-11-07,Effect of cosmic string on spin dynamics,"In the present paper, we have investigated the role of cosmic string on spin
current and Hall electric field. Due to the background cosmic string, the
modified electric field of the system generates renormalized spin orbit
coupling, which induces a modified non-Abelian gauge field. The defect causes a
change in the AB and AC phases appearing due to the modified electromagnetic
field. In addition, for a time varying electric field we perform explicit
analytic calculations to derive the exact form of spin electric field and spin
current, which is defect parameter dependent and of oscillating type.
Furthermore, in an asymmetric crystal within the Drude model approach we
investigate the dependence of the cosmic string parameters on cosmic string
induced Hall electric field.",1411.1818v1
2014-11-28,Topological Charge Analysis of Ultrafast Single Skyrmion Creation,"Magnetic skyrmions are topologically non-trivial spin textures of potential
interest for future information storage applications, and for such purposes,
the control and understanding of single skyrmion creation is required. A scheme
is analyzed to create single N\'{e}el-type and Bloch-type skyrmions in
helimagnetic thin films utilizing the dynamical excitations induced by the
Oersted field and the spin transfer torque given by a vertically injected
spin-polarized current. A topological charge analysis using a lattice version
of the topological charge provides insight into the locally triggered
transition from a trivial to a non-trivial topological spin texture of the
N\'{e}el or Bloch type skyrmion. The topological protection of the magnetic
skyrmion is determined by the symmetric Heisenberg exchange energy. The
critical switching current density is $\sim10^{7}\thinspace\textrm{A/cm}^{2}$,
which decreases with the easy-plane type uniaxial anisotropy and thermal
fluctuations. In-plane spin polarization of the injected current performs
better than out-of-plane polarization, and it provides ultrafast switching
times (within 100 ps) and reliable switching outcomes.",1411.7762v2
2014-12-17,Recursive polarization of nuclear spins in diamond at arbitrary magnetic fields,"We introduce an alternate route to dynamically polarize the nuclear spin host
of nitrogen-vacancy (NV) centers in diamond. Our approach articulates optical,
microwave and radio-frequency pulses to recursively transfer spin polarization
from the NV electronic spin. Using two complementary variants of the same
underlying principle, we demonstrate nitrogen nuclear spin initialization
approaching 80% at room temperature both in ensemble and single NV centers.
Unlike existing schemes, our approach does not rely on level anti-crossings and
is thus applicable at arbitrary magnetic fields. This versatility should prove
useful in applications ranging from nanoscale metrology to sensitivity-enhanced
NMR.",1412.5441v1
2014-12-21,Asymptotic symmetries of three-dimensional higher-spin gravity: the metric approach,"The asymptotic structure of three-dimensional higher-spin anti-de Sitter
gravity is analyzed in the metric approach, in which the fields are described
by completely symmetric tensors and the dynamics is determined by the standard
Einstein-Fronsdal action improved by higher order terms that secure gauge
invariance. Precise boundary conditions are given on the fields. The asymptotic
symmetries are computed and shown to form a non-linear W-algebra, in complete
agreement with what was found in the Chern-Simons formulation. The W-symmetry
generators are two-dimensional traceless and divergenceless rank-s symmetric
tensor densities of weight s (s = 2, 3, ...), while asymptotic symmetries
emerge at infinity through the conformal Killing vector and conformal Killing
tensor equations on the two-dimensional boundary, the solution space of which
is infinite-dimensional. For definiteness, only the spin 3 and spin 4 cases are
considered, but these illustrate the features of the general case: emergence of
the W-extended conformal structure, importance of the improvement terms in the
action that maintain gauge invariance, necessity of the higher spin gauge
transformations of the metric, role of field redefinitions.",1412.6774v2
2015-01-14,Correlation-driven charge and spin fluctuations in LaCoO$_3$,"The spin transition in LaCoO$_3$ has been investigated within the
density-functional theory + dynamical mean-field theory formalism using
continuous time quantum Monte Carlo. Calculations on the experimental
rhombohedral atomic structure with two Co sites per unit cell show that an
independent treatment of the Co atoms results in a ground state with strong
charge fluctuations induced by electronic correlations. Each atom shows a
contribution from either a $d^5$ or a $d^7$ state in addition to the main $d^6$
state. These states play a relevant role in the spin transition which can be
understood as a low spin-high spin (LS-HS) transition with significant
contributions ($\sim$ $10$ %) to the LS and HS states of $d^5$ and $d^7$ states
respectively. A thermodynamic analysis reveals a significant kinetic energy
gain through introduction of charge fluctuations, which in addition to the
potential energy reduction lowers the total energy of the system.",1501.03294v1
2015-01-22,A Generalized Model for the Classical Relativistic Spinning Particle,"Following the Poincare algebra for a free spinning particle and using the
Casimirs of the algebra in the Hamiltonian approach, we construct
systematically a set of Lagrangians for the relativistic spinning particle
which includes the Lagrangian given in the literature. Then we analyze the
dynamics of this generalized system in the Lagrangian formulation and show that
the equations of motion support an oscillatory solution corresponding to the
spinning nature of the system. Next we analyze the canonical structure of the
system and present the correct gauge suitable for the spinning motion of the
system.",1501.05512v5
2015-01-22,Efficient Cluster Algorithm for Spin Glasses in Any Space Dimension,"Spin systems with frustration and disorder are notoriously difficult to study
both analytically and numerically. While the simulation of ferromagnetic
statistical mechanical models benefits greatly from cluster algorithms, these
accelerated dynamics methods remain elusive for generic spin-glass-like
systems. Here we present a cluster algorithm for Ising spin glasses that works
in any space dimension and speeds up thermalization by at least one order of
magnitude at temperatures where thermalization is typically difficult. Our
isoenergetic cluster moves are based on the Houdayer cluster algorithm for
two-dimensional spin glasses and lead to a speedup over conventional
state-of-the-art methods that increases with the system size. We illustrate the
benefits of the isoenergetic cluster moves in two and three space dimensions,
as well as the nonplanar chimera topology found in the D-Wave Inc.~quantum
annealing machine.",1501.05630v2
2015-02-02,Electron-phonon correlations on spin texture of gapped helical Dirac Fermions,"The metallic surface states of a topological insulator support helical Dirac
fermions protected by topology with their spin locked perpendicular to their
momentum. They can acquire mass through magnetic doping or through
hybridization of states on opposite faces of a thin sample. In this case there
can be a component of electron spin oriented perpendicular to the surface
plane. The electron-phonon interaction renormalizes the dynamics of the charge
carriers through their spectral density. It also modifies the gap channel and a
second spectral function enters which, not only determines the out of plane
spin component, but also comes into in-plane properties. While the out of plane
spin component is decreased below the Fermi momentum ($k_F$), the in plane
component increases. There are also correlation tails extending well beyond
$k_F$. The angular resolved photo-emission line shapes aquire Holstein side
bands. The effective gap in the density of states is reduced and the optical
conductivity aquires distinct measurable phonon structure even for modest value
of the electron-phonon coupling.",1502.00372v2
2015-02-02,A model for massless higher spin field interacting with a geometrical background,"We study a very general four dimensional Field Theory model describing the
dynamics of a massless higher spin $N$ symmetric tensor field particle
interacting with a geometrical background.This model is invariant under the
action of an extended linear diffeomorphism. We investigate the consistency of
the equations of motion, and the highest spin degrees of freedom are extracted
by means of a set of covariant constraints. Moreover the the highest spin
equations of motions (and in general all the highest spin field 1-PI
irreducible Green functions) are invariant under a chain of transformations
induced by a set of $N-2$ Ward operators, while the auxiliary fields equations
of motion spoil this symmetry. The first steps to a quantum extension of the
model are discussed on the basis of the Algebraic Field Theory.Technical
aspects are reported in Appendices; in particular one of them is devoted to
illustrate the spin-$2$ case.",1502.00452v2
2015-02-22,Excitation and detection of propagating spin waves at the single magnon level,"Ferro- and ferrimagnets play host to small-signal, microwave-frequency
magnetic excitations called spin waves, the quanta of which are known as
magnons. Over the last decade, the field of spin-wave dynamics has contributed
much to our understanding of fundamental magnetism. To date, experiments have
focussed overwhelmingly on the study of room-temperature systems within
classical limits. Here we demonstrate, for the first time, the excitation and
detection of propagating spin waves at the single magnon level. Our results
allow us to project that coupling of propagating spin-wave excitations to
quantum circuits is achievable, enabling fundamental quantum-level studies of
magnon systems and potentially opening doors to novel hybrid quantum
measurement and information processing devices.",1502.06263v1
2015-02-26,Magnetic phase diagram of an Fe monolayer on W(110) and Ta(110) surfaces based on ab initio calculations,"We present detailed investigations of the magnetic properties of an Fe
monolayer on W and Ta (110) surfaces based on the ab initio screened
Korringa-Kohn-Rostoker method. By calculating tensorial exchange coupling
coefficients, the ground states of the systems are determined using atomistic
spin dynamics simulations. Different types of ground states are found in the
systems as a function of relaxation of the Fe layer. In case of W(110)
substrate this is reflected in a reorientation of the easy axis from in-plane
to out-of-plane. For Ta(110) a switching appears from the ferromagnetic state
to a cycloidal spin spiral state, then to another spin spiral state with a
larger wave vector and, for large relaxations, a rotation of the normal vector
of the spin spiral is found. Classical Monte Carlo simulations indicate
temperature-induced transitions between the different magnetic phases observed
in the Fe/Ta(110) system. These phase transitions are analyzed both
quantitatively and qualitatively by finite-temperature spin wave theory.",1502.07510v2
2015-03-06,Separation of ultrafast spin currents and spin-flip scattering in Co/Cu(001) driven by femtosecond laser excitation via the complex MOKE,"Ultrafast magnetization dynamics in metallic heterostructures consists of a
combination of local demagnetization in the ferromagnetic constituent and
spin-dependent transport contributions within and in between the constituents.
Separation of these local and non-local contributions is essential to obtain
microscopic understanding and for potential applications of the underlying
microscopic processes. By comparing the ultrafast changes of the polarization
rotation and ellipticity in the magneto-optical Kerr effect (MOKE) we observe a
time-dependent magnetization profile M(z,t) in Co/Cu(001) films by exploiting
the effective depth sensitivity of the method. By analyzing the spatio-temporal
correlation of these profiles we find that on time scales before hot electron
thermalization (<100 fs) the transient magnetization of Co films is governed by
spin-dependent transport effects, while after hot electron thermalization (>200
fs) local spin-flip processes dominate.",1503.01979v2
2015-03-10,Ripples in hexagonal lattices of atoms coupled to Glauber spins,"A system of atoms connected by harmonic springs to their nearest neighbors on
a lattice is coupled to Ising spins that are in contact with a thermal bath and
evolve under Glauber dynamics. Assuming a nearest-neighbor antiferromagnetic
interaction between spins, we calculate analytically the equilibrium state. On
a one-dimensional attice, the system exhibits first and second order phase
transitions. The order parameters are the total magnetization and the number of
spin pairs in an antiferromagnetic configuration. On a hexagonal two
dimensional lattice, spins interact with their nearest-neighbors and
next-nearest-neighbors. Together with the coupling to atoms, these interactions
produce a complex behavior that is displayed on a phase diagram. There are:
ordered phases associated to ripples with atomic wavelength and
antiferromagnetic order, ordered phases associated to ripples with nanometer
wavelengths and ferromagnetic order, disordered glassy phases, and other phases
presenting stripes formed by different domains. These static phases are
discussed in relation to existing experiments and results for other models
found in the literature.",1503.03112v1
2015-03-12,Emergence of Quantum Nonmagnetic Insulating Phase in Spin-Orbit Coupled Square Lattices,"We investigate the metal-insulator transition (MIT) and phase diagram of the
half-filled Fermi Hubbard model with Rashba-type spin-orbit coupling (SOC) on a
square optical lattice. The interplay between the atomic interactions and SOC
results in distinctive features of the MIT. Significantly, in addition to the
diverse spin ordered phases, a nonmagnetic insulating phase emerges in a
considerably large regime of parameters near the Mott transition. This phase
has a finite single-particle gap but vanishing magnetization and spin
correlation exhibits a power-law scaling, suggesting a potential algebraic
spin-liquid ground state. These results are confirmed by the non-perturbative
cluster dynamical mean-field theory.",1503.03545v1
2015-04-01,Direct observation and imaging of a spin-wave soliton with $p-$like symmetry,"The prediction and realization of magnetic excitations driven by electrical
currents via the spin transfer torque effect, enables novel magnetic
nano-devices where spin-waves can be used to process and store information. The
functional control of such devices relies on understanding the properties of
non-linear spin-wave excitations. It has been demonstrated that spin waves can
show both an itinerant character, but also appear as localized solitons. So
far, it was assumed that localized solitons have essentially cylindrical,
$s-$like symmetry. Using a newly developed high-sensitivity time-resolved
magnetic x-ray microscopy, we instead observe the emergence of a novel
localized soliton excitation with a nodal line, i.e. with $p-$like symmetry.
Micromagnetic simulations identify the physical mechanism that controls the
transition from $s-$ to $p-$like solitons. Our results suggest a potential new
pathway to design artificial atoms with tunable dynamical states using
nanoscale magnetic devices.",1504.00144v1
2015-06-24,Spin and thermal conductivity in classical disordered spin chain,"Transport quantities of the classical spin chain with the quenched disorder
in the antiferromagnetic coupling $J_i$ are evaluated using the dynamical
simulation at finite temperatures $T>0$ . Since the classical model is
nonintegrable, spin and thermal conductivities remain finite even in the pure
case. On the other hand, the role of disorder becomes crucial at low $T $
leading to a vanishing transport due to the Anderson localization within the
linearized regime. The crossover from the insulator to the conductor appears
both for the spin and thermal transport at quite low $T^* \ll J$. Still the
many-body localization regime at $T>0$ evidenced by extremely short mean free
paths can be strongly enhanced by introducing into the model an additional
staggered field.",1506.07284v2
2015-06-30,Anomalous Spin Response and Virtual-Carrier-Mediated Magnetism in a Topological Insulator,"We present a comprehensive theoretical study of the static spin response in
HgTe quantum wells, revealing distinctive behavior for the topologically
nontrivial inverted structure. Most strikingly, the q=0 (long-wave-length) spin
susceptibility of the undoped topological-insulator system is constant and
equal to the value found for the gapless Dirac-like structure, whereas the same
quantity shows the typical decrease with increasing band gap in the
normal-insulator regime. We discuss ramifications for the ordering of localized
magnetic moments present in the quantum well, both in the insulating and
electron-doped situations. The spin response of edge states is also considered,
and we extract effective Lande g-factors for the bulk and edge electrons. The
variety of counter-intuitive spin-response properties revealed in our study
arises from the system's versatility in accessing situations where the
charge-carrier dynamics can be governed by ordinary Schrodinger-type physics,
mimics the behavior of chiral Dirac fermions, or reflects the material's
symmetry-protected topological order.",1506.08913v2
2015-07-31,Strongly polarizing weakly coupled $^{13}$C nuclear spins with optically pumped nitrogen-vacancy center,"Enhancing the polarization of nuclear spins surrounding the nitrogen-vacancy
(NV) center in diamond has attracted widespread attention recently due to its
various applications. Here we present an analytical theory and comprehensive
understanding on how to optimize the dynamic nuclear polarization by an
optically pumped NV center near the ground state level anticrossing. Our
results not only provide a parameter-free explanation and a clearly physics
picture for the recently observed polarization dependence on the magnetic field
for strongly coupled $^{13}$C nuclei [H. J. Wang \textit{et al}., Nat. Commun.
4, 1 (2013)], but also demonstrate the possibility to strongly polarize weakly
coupled $^{13}$C nuclei under weak optical pumping and suitably chosen magnetic
field. This allows sensitive magnetic control of the $^{13}$C nuclear spin
polarization for NMR applications and significant suppression of the $^{13}$C
nuclear spin noise to prolong the NV spin coherence time.",1507.08775v1
2015-09-01,Driving spin excitations by hydrostatic pressure in BiFeO3,"Optical spectroscopy has been combined with computational and theoretical
techniques to show how the spin dynamics in the model multiferroic BiFeO3
responds to the application of hydrostatic pressure and its corresponding
series of structural phase transitions from R3c to the Pnma phases. As pressure
increases, multiple spin excitations associated with non-collinear cycloidal
magnetism collapse into two excitations, which show jump discontinuities at
some of the ensuing crystal phase transitions. Effective Hamiltonian approach
provides information on the electrical polarization and structural changes of
the oxygen octahedra through the successive structural phases. The extracted
parameters are then used in a Ginzburg-Landau model to reproduce the evolution
with pressure of the spin waves excitations observed at low energy and we
demonstrate that the structural phases and the magnetic anisotropy drive and
control the spin excitations.",1509.00284v1
2015-09-03,Spin-mediated dissipation and frequency shifts of a cantilever at milliKelvin temperatures,"We measure the dissipation and frequency shift of a magnetically coupled
cantilever in the vicinity of a silicon chip, down to $25$ mK. The dissipation
and frequency shift originates from the interaction with the unpaired
electrons, associated with the dangling bonds in the native oxide layer of the
silicon, which form a two dimensional system of electron spins. We approach the
sample with a $3.43$ $\mu$m-diameter magnetic particle attached to an ultrasoft
cantilever, and measure the frequency shift and quality factor as a function of
temperature and the distance. Using a recent theoretical analysis [J. M. de
Voogd et al., arXiv:1508.07972 (2015)] of the dynamics of a system consisting
of a spin and a magnetic resonator, we are able to fit the data and extract the
relaxation time $T_1=0.39\pm0.08$ ms and spin density $\sigma=0.14\pm0.01$
spins per nm$^2$. Our analysis shows that at temperatures $\leq500$ mK magnetic
dissipation is an important source of non-contact friction.",1509.01251v2
2015-09-18,Self-injection locking of a vortex spin torque oscillator by delayed feedback,"The self-synchronization of spin torque oscillators is investigated
experimentally by re-injecting its radiofrequency (rf) current after a certain
delay time. We demonstrate that the emission power and the spectral linewidth
are improved for optimal delay times. Moreover by varying the phase difference
between the emitted power and the re-injected one, we find a clear oscillatory
dependence with a 2\pi\ periodicity of the frequency of the oscillator as well
as its power and linewidth. Such periodical behavior within the self-injection
regime is well described by the general model of nonlinear auto-oscillators
including not only a delayed rf current but also all spin torque forces
responsible for the self-synchronization. Our results reveal new approaches for
controlling the non-autonomous dynamics of spin torque oscillators, a key issue
for rf spintronics applications as well as for the development of
neuro-inspired spin-torque oscillators based devices.",1509.05583v1
2015-11-18,Anomalous Microwave Emission from Spinning Dust and its Polarization Spectrum,"Nearly twenty years after the discovery of anomalous microwave emission (AME)
that contaminates to the cosmic microwave background (CMB) radiation, its
origin remains inconclusive. Observational results from numerous experiments
have revealed that AME is most consistent with spinning dust emission from
rapidly spinning ultrasmall interstellar grains. In this paper, I will first
review our improved model of spinning dust, which treats realistic dynamics of
wobbling non-spherical grains, impulsive interactions of grains with ions in
the ambient plasma, and some other important effects. I will then discuss
recent progress in quantifying the polarization of spinning dust emission from
polycyclic aromatic hydrocarbons. I will finish with a brief discussion on
remaining issues about the origins of AME.",1511.05997v1
2015-11-23,The Sagnac Effect in Optical Lattices with Laser-Assisted Tunneling,"We propose a scheme to realize the rotation sensing using optical lattices
with laser-assisted tunneling. We demonstrate that the competition between the
rotation and the spin-orbit coupling governs the spin-dependent response of the
cyclotron dynamics of the spin-orbit coupled bosons. The Sagnac-type cumulative
phase can be read out from the envelop of a beat-frequency particle current in
the spin-balanced system and enhanced by the cyclotron motion. We also
theoretically show that the sensitivity limit of the spin-orbit-coupled system
to the rotational motion can reach 7*10^-8 rad s^-1 Hz^1/2.",1511.07197v3
2016-02-02,Iterating free-field AdS/CFT: higher spin partition function relations,"We find a simple relation between a free higher spin field partition function
on thermal quotient of AdS(d+1) and the partition function of the associated
d-dimensional conformal higher spin field on thermal quotient of AdS(d).
Starting with a conformal higher spin field defined on AdS(d) one may also
associate to it another conformal field in d-1 dimensions, thus ""iterating""
AdS/CFT. We observe that in the case of d=4 this iteration leads to a ""trivial""
3d higher spin conformal theory with parity-even non-local action: it describes
zero total number of dynamical degrees of freedom and the corresponding
partition function on thermal AdS(3) is equal to 1.",1602.00948v2
2016-02-14,Ultra-sensitive nanoscale magnetic field sensors based on resonant spin filtering,"Solid state magnetic field sensors based on magneto-resistance modulation
find direct applications in communication devices, specifically in proximity
detection, rotational reference detection and current sensing. In this work, we
propose sensor structures based on the magneto-resistance physics of resonant
spin-filtering and present device designs catered toward exceptional magnetic
field sensing capabilities. Using the non-equilibrium Green's function spin
transport formalism self consistently coupled to the Poisson's equation, we
present highly-tunable pentalayer magnetic tunnel junction structures that are
capable of exhibiting an ultra-high peak tunnel magneto resistance $(\approx
2500 \%$). We show how this translates to device designs featuring an
ultra-high current sensitivity enhancement of over 300\% in comparison with
typical trilayer MTJ sensors, and a wider tunable range of field sensitivity.
We also demonstrate that a dynamic variation in sensor functionalities with the
structural landscape enables a superior design flexibility over typical
trilayer sensors. An optimal design exhibiting close to a 700\% sensitivity
increase as a result of angle dependent spin filtering is then presented.This
work sets a stage to engineer spintronic building blocks via the design of
functional structures tailored to exhibit ultra-sensitive spin filtering.",1602.04438v1
2016-02-18,Observation of Four-body Ring-exchange Interactions and Anyonic Fractional Statistics,"Ring exchange is an elementary interaction for modeling unconventional
topological matters which hold promise for efficient quantum information
processing. We report the observation of four-body ring-exchange interactions
and the topological properties of anyonic excitations within an ultracold atom
system. A minimum toric code Hamiltonian in which the ring exchange is the
dominant term, was implemented by engineering a Hubbard Hamiltonian that
describes atomic spins in disconnected plaquette arrays formed by two
orthogonal superlattices. The ring-exchange interactions were resolved from the
dynamical evolutions in the spin orders, matching well with the predicted
energy gaps between two anyonic excitations of the spin system. A braiding
operation was applied to the spins in the plaquettes and an induced phase
$1.00(3)\pi$ in the four-spin state was observed, confirming
$\frac{1}{2}$-anynoic statistics. This work represents an essential step
towards studying topological matters with many-body systems and the
applications in quantum computation and simulation.",1602.05709v1
2016-03-10,Spin and quadrupolar orders in the spin-1 bilinear-biquadratic model for iron-based superconductors,"Motivated by recent experimental and theoretical progresses of the magnetic
properties of iron-based superconductors, we provide a comprehensive analysis
of the spin-1 bilinear-biquadratic (BBQ) model on the square lattice. Using
variational approach in the mean-field level, we identify the existence of
various magnetic phases, including conventional spin dipolar orderings (ferro-
or antiferromagnet), novel quadrupolar (spin nematic) orderings and mixed
dipolar-quadrupolar orderings. In contrast to the usual Heisenberg model, the
elementary excitations of the spin-1 BBQ model are described by the flavor-wave
theory within the SU(3) representation. By fitting the experimental spin-wave
dispersion, we determine the refined exchange couplings corresponding to the
collinear antiferromagnetic iron pnictides. We also present the dynamic
structure factors of both spin dipolar and quadrupolar components with
connections to the future experiments.",1603.03273v2
2016-03-21,Statics and dynamics of the highly correlated spin ice Ho2Ge2O7,"The pyrochlore Ho2Ge2O7 is a new highly correlated spin ice material.
Physical property measurements including x-ray diffraction, dc susceptibility
and ac susceptibility, confirm that it shares the distinctive characteristics
of other known spin ices. Polarized neutron scattering measurements on a powder
sample, combined with reverse Monte Carlo (RMC) refinements, give unique
information about the spin ice state in Ho2Ge2O7. RMC refinements are used to
fit the powder magnetic diffuse scattering and predict the single crystal
magnetic scattering of Ho2Ge2O7, demonstrating consistency with spin ice
behavior.",1603.06319v1
2016-03-25,Large spin pumping effect in antisymmetric precession of Ni$_{79}$Fe$_{21}$/Ru/Ni$_{79}$Fe$_{21}$,"In magnetic trilayer structures, a contribution to the Gilbert damping of
ferromagnetic resonance arises from spin currents pumped from one layer to
another. This contribution has been demonstrated for layers with weakly
coupled, separated resonances, where magnetization dynamics are excited
predominantly in one layer and the other layer acts as a spin sink. Here we
show that trilayer structures in which magnetizations are excited
simultaneously, antisymmetrically, show a spin-pumping effect roughly twice as
large. The antisymmetric (optical) mode of antiferromagnetically coupled
Ni$_{79}$Fe$_{21}$(8nm)/Ru/Ni$_{79}$Fe$_{21}$(8nm) trilayers shows a Gilbert
damping constant greater than that of the symmetric (acoustic) mode by an
amount as large as the intrinsic damping of Py ($\Delta
\alpha\simeq\textrm{0.006}$). The effect is shown equally in field-normal and
field-parallel to film plane geometries over 3-25 GHz. The results confirm a
prediction of the spin pumping model and have implications for the use of
synthetic antiferromagnets (SAF)-structures in GHz devices.",1603.07977v1
2016-04-07,Magnon-mediated spin current noise in ferromagnet$|$non-magnetic conductor hybrids,"The quantum excitations of the collective magnetization dynamics in a
ferromagnet (F) - magnons - enable spin transport without an associated charge
current. This pure spin current can be transferred to electrons in an adjacent
non-magnetic conductor (N). We evaluate the finite temperature noise of the
magnon-mediated spin current injected into N by an adjacent F driven by a
coherent microwave field. We find that the dipolar interaction leads to
squeezing of the magnon modes giving them wavevector dependent non-integral
spin, which directly manifests itself in the shot noise. For temperatures
higher than the magnon gap, the thermal noise is dominated by large wavevector
magnons which exhibit negligible squeezing. The noise spectrum is white up to
the frequency corresponding to the maximum of the temperature or the magnon
gap. At larger frequencies, the noise is dominated by vacuum fluctuations. The
shot noise is found to be much larger than its thermal counterpart over a broad
temperature range, making the former easier to be measured experimentally.",1604.02079v2
2016-04-13,Charge and spin diffusion on the metallic side of the metal-insulator transition: a self-consistent approach,"We develop a self-consistent theory describing the spin and spatial electron
diffusion in the impurity band of doped semiconductors under the effect of a
weak spin-orbit coupling. The resulting low-temperature spin-relaxation time
and diffusion coefficient are calculated within different schemes of the
self-consistent framework. The simplest of these schemes qualitatively
reproduces previous phenomenological developments, while more elaborate
calculations provide corrections that approach the values obtained in numerical
simulations. The results are universal for zinc-blende semiconductors with
electron conductance in the impurity band, and thus they are able to account
for the measured spin-relaxation times of materials with very different
physical parameters. From a general point of view, our theory opens a new
perspective for describing the hopping dynamics in random quantum networks.",1604.03917v2
2016-04-14,Quantum walks accompanied by spin flipping in one-dimensional optical lattices,"We investigate continuous-time quantum walks of two fermionic atoms loaded in
one-dimensional optical lattices with on-site interaction and subjected to a
Zeeman field. The quantum walks are accompanied by spin-flipping processes. We
calculate the time-dependent density distributions of the two fermions with
opposite spins which are initially positioned on the center site by means of
exact numerical method. Besides the usual fast linear expansion behavior, we
find an interesting spin-flipping induced localization in the time-evolution of
density distributions. We show that the fast linear expansion behavior could be
restored by simply ramping on the Zeeman field or further increasing the
spin-flipping strength. The intrinsic origin of this exotic phenomenon is
attributed to the emergence of a flat band in the single particle spectrum of
the system. Furthermore, we investigate the effect of on-site interaction on
the dynamics of the quantum walkers. The two-particle correlations are
calculated and signal of localization is also shown therein. A simple potential
experimental application of this interesting phenomenon is proposed.",1604.04011v1
2016-04-20,Robust Picosecond writing of a Layered Antiferromagnet by Staggered Spin-Orbit-Fields,"Ultrafast electrical switching by current-induced staggered spin-orbit
fields, with minimal risk of overshoot, is shown in layered easy-plane
antiferromagnets with basal-plane biaxial anisotropy. The reliable switching is
due to the field-like torque, relaxing stringent requirements with respect to
precision in the time-duration of the excitation pulse. We investigate the
switching characteristics as a function of the spin-orbit field strength, pulse
duration, pulse rise and fall time and damping by atomistic spin dynamics
simulations and an effective equation of motion for the antiferromagnetic
order-parameter. The condition, determining the critical spin-orbit field
strength for switching is determined and we go on to show that robust
picosecond writing is possible at feasible current magnitudes.",1604.05918v1
2016-06-06,Spin-Wave and Electromagnon Dispersions in Multiferroic MnWO4 as Observed by Neutron Spectroscopy: Isotropic Heisenberg Exchange versus Anisotropic Dzyaloshinskii-Moriya Interaction,"High resolution inelastic neutron scattering reveals that the elementary
magnetic excitations in multiferroic MnWO4 consist of low energy dispersive
electromagnons in addition to the well-known spin-wave excitations. The latter
can well be modeled by a Heisenberg Hamiltonian with magnetic exchange coupling
extending to the 12th nearest neighbor. They exhibit a spin-wave gap of 0.61(1)
meV. Two electromagnon branches appear at lower energies of 0.07(1) meV and
0.45(1) meV at the zone center. They reflect the dynamic magnetoelectric
coupling and persist in both, the collinear magnetic and paraelectric AF1
phase, and the spin spiral ferroelectric AF2 phase. These excitations are
associated with the Dzyaloshinskii-Moriya exchange interaction, which is
significant due to the rather large spin-orbit coupling.",1606.01954v1
2016-06-14,Antiferromagnetic spintronics,"Antiferromagnetic materials could represent the future of spintronic
applications thanks to the numerous interesting features they combine: they are
robust against perturbation due to magnetic fields, produce no stray fields,
display ultrafast dynamics and are capable of generating large
magneto-transport effects. Intense research efforts over the past decade have
been invested in unraveling spin transport properties in antiferromagnetic
materials. Whether spin transport can be used to drive the antiferromagnetic
order and how subsequent variations can be detected are some of the thrilling
challenges currently being addressed. Antiferromagnetic spintronics started out
with studies on spin transfer, and has undergone a definite revival in the last
few years with the publication of pioneering articles on the use of spin-orbit
interactions in antiferromagnets. This paradigm shift offers possibilities for
radically new concepts for spin manipulation in electronics. Central to these
endeavors are the need for predictive models, relevant disruptive materials and
new experimental designs. This paper reviews the most prominent spintronic
effects described based on theoretical and experimental analysis of
antiferromagnetic materials. It also details some of the remaining bottlenecks
and suggests possible avenues for future research.",1606.04284v2
2016-06-27,Robust Spin Squeezing Preservation in Photonic Crystal Cavities,"We show that the robust spin squeezing preservation can be achieved by
utilizing detuning modification for an ensemble of N separate two-level atoms
embedded in photonic crystal cavities (PCC). In particular, we explore the
different dynamical behaviors of spin squeezing between isotropic and
anisotropic PCC cases when the atomic frequency is inside the band gap. In both
cases, it is shown that the robust preservation of spin squeezing is completely
determined by the formation of bound states. Intriguingly, we find that unlike
the isotropic case where steady-state spin squeezing varies smoothly when the
atomic frequency moves from the inside to the outside band edge, a sudden
transition occurs for the anisotropic case. The present results may be of
direct importance for, e.g., quantum metrology in open quantum systems.",1606.08236v1
2016-07-14,Simultaneous Measurement of Resistively and Optically Detected Nuclear Magnetic Resonance in the $ν=2/3$ Fractional Quantum Hall Regime,"We observe nuclear magnetic resonance (NMR) in the fractional quantum Hall
regime at Landau level filling factor $\nu=2/3$ from simultaneous measurement
of longitudinal resistance and photoluminescence (PL). The dynamic nuclear spin
polarization is induced by applying a huge electronic current at the spin phase
transition point of $\nu=2/3$. The NMR spectra obtained from changes in
resistance and PL intensity are qualitatively the same; that is, the Knight
shift (spin polarized region) and zero-shift (spin unpolarized region)
resonances are observed in both. The observed change in PL intensity is
interpreted as a consequence of the trion scattering induced by polarized
nuclear spins. We conclude that both detection methods probe almost the same
local phenomena.",1607.04094v1
2016-09-05,Role of coherence in transport through engineered atomic spin devices,"We give a further step in the quantum mechanical description of engineered
atomic spin structures by deriving a master equation of the Redfield type that
governs the dynamics of the atomic spin density matrix. By generalizing this
approach to charge-specific density matrices, we are able to describe magnetic
transport quantities, such as the average inelastic current and the shot noise,
accessible by tunneling spectroscopy. Our method suitably describes moderate
lead-atom coupling regimes where quantum coherence effects cannot be
disregarded. We contrast our approach with the existing descriptions in terms
of rate equations and show examples where coherence effects are crucial to
understand the physics of spin-polarized tunnel current through spin
structures.",1609.01318v2
2016-09-06,Spin supplementary conditions for spinning compact binaries,"We consider different spin supplementary conditions (SSC) for a spinning
compact binary with the leading-order spin-orbit (SO) interaction. The
Lagrangian of the binary system can be constructed but it is
acceleration-dependent in two cases of SSC. We rewrite the generalized
Hamiltonian formalism proposed by Ostrogradsky and compute the conserved
quantities and the dissipative part of relative motion during the gravitational
radiation of each SSC. We give the orbital elements and observed quantities of
the SO dynamics, for instance the energy and the orbital angular momentum
losses and waveforms and discuss their SSC dependence.",1609.01536v2
2016-09-20,Static and Dynamic Magnetic Response of Fragmented Haldane-like Spin Chains in Layered Li3Cu2SbO6,"The structure and the magnetic properties of layered Li3Cu2SbO6 are
investigated by powder X-ray diffraction, static susceptibility, and electron
spin resonance studies up to 330 GHz. The XRD data experimentally verify the
space group C2/m with halved unit cell volume in contrast to previously
reported C2/c. In addition, the data show significant Li/Cu-intersite exchange.
Static magnetic susceptibility and ESR measurements show two magnetic
contributions, i.e. quasi-free spins at low-temperature and a spin-gapped
magnetic subsystem, with about half of the spins being associated to each
subsystem. The data suggest ferromagnetic-antiferromagnetic alternating chains
with JFM = -285 K and JAFM = 160 K with a significant amount of Li-defects in
the chains. The results are discussed in the scenario of fragmented 1D S = 1
AFM chains with a rather high defect concentration of about 17% and associated
S = 1/2 edge states of the resulting finite Haldane chains.",1609.06091v1
2016-09-25,Effects of Spin-Orbit Coupling on Jaynes-Cummings and Tavis-Cummings Models,"We consider ultracold atoms inside a ring optical cavity that supports a
single plane-wave mode. The cavity field, together with an external coherent
laser field, drives a two-photon Raman transition between two internal
pseudo-spin states of the atom. This gives rise to an effective coupling
between atom's pseudo-spin and external center-of-mass (COM) motion. For the
case of a single atom inside the cavity, We show how the spin-orbit coupling
modifies the static and dynamic properties of the Jaynes-Cummings (JC) model.
In the case of many atoms in thermodynamic limit, we show that the spin-orbit
coupling modifies the Dicke superradiance phase transition boundary and the
non-superradiant normal phase may become reentrant in some regimes.",1609.07815v2
2016-09-27,Spin-wave dynamics in FeGe helimagnet: studied by small-angle neutron scattering,"We have studied the spin-wave stiffness of the Dzyaloshinskii-Moriya
helimagnet FeGe in a temperature range from 225~K up to $T_C \approx$~278.7~K
by small-angle neutron scattering. The method we have used is based on [S. V.
Grigoriev et al. Phys. Rev. B \textbf{92} 220415(R) (2015)] and was extended
here for the application in polycrystalline samples. We confirm the validity of
the anisotropic spin-wave dispersion for FeGe caused by the
Dzyaloshinskii-Moriya interaction. We have shown that the spin-wave stiffness
$A$ for FeGe helimagnet decreases with a temperature as $A(T) =
194(1-0.7(T/T_C)^{4.2})$ meV\AA$^2$. The finite value of the spin-wave
stiffness $A = 58$ meV\AA$^2$ at $T_C$ classifies the order-disorder phase
transition in FeGe as being the first order one.",1609.08358v1
2016-10-01,Pancharatnam-Berry phase induced spin-selective transmission in herringbone dielectric metamaterials,"Manipulating the polarisation of light is crucial for sensing and imaging
applications. One such aspect in particular is selective transmission of one
circular polarisation (spin) when light is transmitted through a medium or a
device. However, most present methods of achieving this have relatively low
efficiency and selectivity, whilst high selectivity examples rely on lossy and
complex three-dimensional helical or multilayer structures. Here, we propose a
dielectric metamaterial approach for achieving spin-selective transmission of
electromagnetic waves, utilizing spin-controlled constructive or destructive
interference between two Pancharatnam-Berry (PB) phases in conjunction with
propagative dynamic phase. The dielectric metamaterial, consisting of
monolithic silicon herringbone structures, exhibits a broadband operation in
the terahertz regime whilst obtaining a spin-selective efficiency upwards of
60%. Such a device is robust and is not easily degraded by errors in
fabrication.",1610.00196v1
2016-10-10,"Spin-Wave Spectrum in Magnetic Nanodot with Continuous Transition between Vortex, Bloch-type Skyrmion and Néel-type Skyrmion States","We study spin-wave excitations in a circular ferromagnetic nanodot in
different inhomogeneous, topologically non-trivial magnetization states,
specifically, vortex and skyrmion states. Gradual change in the strength of the
out-of-plane magnetic anisotropy and the Dzyaloshinskii-Moriya exchange
interaction leads to continuous phase transitions between different stable
magnetic configurations and allows for mapping of dynamic spin modes in and
between the vortex, Bloch-type skyrmion and N\'eel-type skyrmion states. Our
study elucidates the connections between gyrotropic modes, azimuthal spin waves
and breathing modes in various stable magnetization states and helps to
understand the rich spin excitation spectrum on the skyrmion background.",1610.02859v1
2016-10-15,Bloch Oscillations in Optical and Zeeman Lattices in the Presence of Spin-Orbit Coupling,"We address Bloch oscillations of a spin-orbit coupled atom in periodic
potentials of two types: Optical and Zeeman lattices. We show that in optical
lattices the spin-orbit coupling allows controlling the direction of atomic
motion and may lead to complete suppression of the oscillations at specific
values of the coupling strength. In Zeeman lattices the energy bands are found
to cross each other at the boundaries of the Brillouin zone, resulting in
period-doubling of the oscillations. In all cases, the oscillations are
accompanied by rotation of the pseudo-spin, with a dynamics that is determined
by the strength of the spin-orbit coupling. The predicted effects are discussed
also in terms of a Wannier-Stark ladder, which in optical lattices consist of
two mutually-shifted equidistant sub-ladders.",1610.04716v2
2016-10-27,Spin transfer driven resonant expulsion of a magnetic vortex core for efficient rf detector,"Spin transfer magnetization dynamics have led to considerable advances in
Spintronics, including opportunities for new nanoscale radiofrequency devices.
Among the new functionalities is the radiofrequency(rf) detection using the
spin diode rectification effect in spin torque nano-oscillators (STNOs). In
this study, we focus on a new phenomenon, the resonant expulsion of a magnetic
vortex in STNOs. This effect is observed when the excitation vortex radius, due
to spin torques associated to rf currents, becomes larger than the actual
radius of the STNO. This vortex expulsion is leading to a sharp variation of
the voltage at the resonant frequency. Here we show that the detected frequency
can be tuned by different parameters; furthermore, a simultaneous detection of
different rf signals can be achieved by real time measurements with several
STNOs having different diameters. This result constitutes a first
proof-of-principle towards the development of a new kind of nanoscale rf
threshold detector.",1610.08660v1
2017-02-02,A majority gate with chiral magnetic solitons,"In magnetic materials nontrivial spin textures may emerge owing to the
competition among different types of magnetic interactions. Among such spin
textures, chiral magnetic solitons represent topologically protected spin
configurations with particle-like properties. Based on atomistic spin dynamics
simulations, we demonstrate that these chiral magnetic solitons are ideal to
use for logical operations, and we demonstrate the functionality of a
three-input majority gate, in which the input states can be controlled by
applying an external electromagnetic field or spin-polarized currents. One of
the main advantages of the proposed device is that the input and output signals
are encoded in the chirality of solitons, that may be moved, allowing to
perform logical operations using only minute electric currents. As an example
we illustrate how the three input majority gate can be used to perform logical
relations, such as Boolean AND and OR.",1702.00579v1
2017-02-15,Phonon-mediated spin-flipping mechanism in the spin ices Dy$_2$Ti$_2$O$_7$ and Ho$_2$Ti$_2$O$_7$,"To understand emergent magnetic monopole dynamics in the spin ices
Ho$_2$Ti$_2$O$_7$ and Dy$_2$Ti$_2$O$_7$, it is necessary to investigate the
mechanisms by which spins flip in these materials. Presently there are thought
to be two processes: quantum tunneling at low and intermediate temperatures and
thermally activated at high temperatures. We identify possible couplings
between crystal field and optical phonon excitations and construct a strictly
constrained model of phonon-mediated spin flipping that quantitatively
describes the high-temperature processes in both compounds, as measured by
quasielastic neutron scattering. We support the model with direct experimental
evidence of the coupling between crystal field states and optical phonons in
Ho$_2$Ti$_2$O$_7$.",1702.04612v1
2017-02-16,Robust antiferromagnetic spin waves across the metal-insulator transition in hole-doped BaMn$_{2}$As$_{2}$,"BaMn$_{2}$As$_{2}$ is an antiferromagnetic insulator where a metal-insulator
transition occurs with hole doping via the substitution of Ba with K. The
metal-insulator transition causes only a small suppression of the N\'eel
temperature ($T_\mathrm{N}$) and the ordered moment, suggesting that doped
holes interact weakly with the Mn spin system. Powder inelastic neutron
scattering measurements were performed on three different powder samples of
Ba$_{1-x}$K$_{x}$Mn$_{2}$As$_{2}$ with $x=$0, 0.125 and 0.25 to study the
effect of hole doping and metallization on the spin dynamics of these
compounds. We compare the neutron intensities to a linear spin wave theory
approximation to the $J_{1}-J_{2}-J_{c}$ Heisenberg model. Hole doping is found
to introduce only minor modifications to the exchange energies and spin gap.
The changes observed in the exchange constants are consistent with the small
drop of $T_\mathrm{N}$ with doping.",1702.05082v1
2017-03-08,A Nonequilibrium quantum phase transition in strongly coupled spin chains,"We study spin transport in a boundary driven XXZ spin chain. Driving at the
chain boundaries is modeled by two additional spin chains prepared in
oppositely polarized states. Emergent behavior, both in the transient dynamics
and in the long-time quasi-steady state, is demonstrated. Time-dependent
matrix-product-state simulations of the system-bath state show ballistic spin
transport below the Heisenberg isotropic point. Indications of exponentially
vanishing transport are found above the Heisenberg point for low energy initial
states while the current decays asymptotically as a power law for high energy
states. Precisely at the critical point, non-ballistic transport is observed.
Finally, it is found that the sensitivity of the quasi-stationary state on the
initial state of the chain is a good witness of the different transport phases.",1703.02934v6
2017-03-24,Spin excitations and thermodynamics of the antiferromagnetic Heisenberg model on the layered honeycomb lattice,"We present a spin-rotation-invariant Green-function theory for the dynamic
spin susceptibility in the spin-1/2 antiferromagnetic Heisenberg model on a
stacked honeycomb lattice. Employing a generalized mean-field approximation for
arbitrary temperatures, the thermodynamic quantities (two-spin correlation
functions, internal energy, magnetic susceptibility, staggered magnetization,
N'eel temperature, correlation length) and the spin-excitation spectrum are
calculated by solving a coupled system of self-consistency equations for the
correlation functions. The temperature dependence of the magnetic (uniform
static) susceptibility is ascribed to antiferromagnetic short-range order. The
N\'{e}el temperature is calculated for arbitrary interlayer couplings. Our
results are in a good agreement with numerical computations for finite clusters
and with available experimental data on the \beta-Cu2V2O2 compound.",1703.08391v1
2017-08-01,Longitudinal and transverse spin relaxation times of magnetic single adatoms: an ab initio analysis,"We present a systematic ab initio investigation of the longitudinal and
transverse spin relaxation times of magnetic single adatoms deposited on
metallic substrates. Our analysis based on time-dependent density functional
theory shows that the longitudinal time, $T_{\parallel}$, is of order
femtosecond while the transverse time, $T_{\perp}$, is of order picosecond,
i.e. $T_{\perp}\gg T_{\parallel}$. This comes as a consequence of the different
energy scales of the corresponding processes: $T_{\parallel}$ involves
spin-density excitations of order eV, while $T_{\perp}$ is governed by atomic
spin-excitations of order meV. Comparison to available inelastic scanning
tunneling spectroscopy $\mathrm{d}I/\mathrm{d}V$ experimental curves shows that
the order of magnitude of $T_{\perp}$ agrees well with our results. Regarding
$T_{\parallel}$, the time scale calculated here is several orders of magnitude
faster than what has been measured up to now; we therefore propose that an
ultrafast laser pulse measuring technique is required in order to access the
ultrafast spin-dynamics described in this work.",1708.00280v1
2017-08-07,Pauli blockade microscopy of quantum dots,"We propose a spin-sensitive scanning probe microscopy experiment on double
quantum dots in Pauli blockade conditions. Electric spin resonance is induced
by an AC voltage applied to the scanning gate which induces lifting of the
Pauli blockade of the current. The stationary Hamiltonian eigenstates are used
as a basis for description of the spin dynamics with the AC potential of the
probe. For the two-electron system we evaluate the transitions rates from
triplet $\mathrm{T}_+$ state to singlet $\mathrm{S}$ or triplet $\mathrm{T}_0$
states, i.e. to conditions in which the Pauli blockade of the current is
lifted. The rates of the spin-flip transitions are consistent with the
transition matrix elements and strongly dependent on the tip position. Probing
the spin densities and identification of the final transition state are
discussed.",1708.02007v1
2017-08-13,Observation of Spin Superfluidity in a Bose Gas Mixture,"The spin dynamics of a harmonically trapped Bose-Einstein condensed binary
mixture of sodium atoms is experimentally investigated at finite temperature.
In the collisional regime the motion of the thermal component is shown to be
damped because of spin drag, while the two condensates exhibit a counter flow
oscillation without friction, thereby providing direct evidence for spin
superfluidity. Results are also reported in the collisionless regime where the
spin components of both the condensate and thermal part oscillate without
damping, their relative motion being driven by a mean field effect. We also
measure the static polarizability of the condensed and thermal parts and we
find a large increase of the condensate polarizability with respect to the T=0
value, in agreement with the predictions of theory.",1708.03923v2
2017-08-20,Signatures of spin-orbital states of ${t_{2g}}^{2}$ system in the optical conductivity : The case of $R$VO$_{3}$ ($R$=Y and La),"We investigate signatures of spin and orbital states of $R$VO$_{3}$ ($R$=Y
and La) in the optical conductivity using density functional theory plus
dynamical mean-field theory (DFT+DMFT). From the assignment of multiplet states
to optical transitions, DFT+DMFT reproduces experimental temperature dependent
evolutions of optical conductivity for both YVO$_{3}$ and LaVO$_{3}$. We also
show that the optical conductivity is a useful quantity to probe the evolution
of the orbital state even in the absence of spin order. The result provides a
reference to investigate spin and orbital states of ${t_{2g}}^{2}$ vanadate
systems which is an important issue for both fundamental physics on spin and
orbital states and applications of vanadates by means of orbital state control.",1708.05923v2
2017-08-29,Antiferromagnetic resonance excited by oscillating electric currents,"In antiferromagnetic materials the order parameter exhibits resonant modes at
frequencies that can be in the terahertz range, making them interesting
components for spintronic devices. Here, it is shown that antiferromagnetic
resonance can be excited using the inverse spin-Hall effect in a system
consisting of an antiferromagnetic insulator coupled to a normal-metal
waveguide. The time-dependent interplay between spin-torque, ac
spin-accumulation and magnetic degrees of freedom is studied. It is found that
the dynamics of the antiferromagnet effects the frequency-dependent
conductivity of the normal metal. Further, it is shown that in
antiferromagnetic insulators, the resonant excitation by ac spin-currents can
be orders of magnitude more efficient than excitation by the current-induced
Oersted field.",1708.08965v2
2018-02-01,Spin-Imbalanced Pairing and Fermi Surface Deformation in Flat Bands,"We study the attractive Hubbard model with spin imbalance on two lattices
featuring a flat band: the Lieb and kagome lattices. We present mean-field
phase diagrams featuring exotic superfluid phases, similar to the
Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state, whose stability is confirmed by
dynamical mean-field theory (DMFT). The nature of the pairing is found to be
richer than just the Fermi surface shift responsible for the usual FFLO state.
The presence of a flat band allows for changes in the particle momentum
distributions at null energy cost. This facilitates formation of nontrivial
superfluid phases via multiband Cooper pair formation: the momentum
distribution of the spin component in the flat band deforms to mimic the Fermi
surface of the other spin component residing in a dispersive band. The Fermi
surface of the unpaired particles that are typical for gapless superfluids
becomes deformed as well. The results highlight the profound effect of flat
dispersions on Fermi surface instabilities, and provide a potential route for
observing spin-imbalanced superfluidity and superconductivity.",1802.00274v2
2018-11-07,Spin torque nano-oscillators based on antiferromagnetic skyrmions,"Skyrmion-based spin torque nano-oscillators are potential next-generation
microwave signal generators. However, ferromagnetic skyrmion-based spin torque
nano-oscillators cannot reach high oscillation frequencies. In this work, we
propose to use the circular motion of an antiferromagnetic skyrmion to create
the oscillation signal in order to overcome this obstacle. Micromagnetic
simulations demonstrate that the antiferromagnetic skyrmion-based spin torque
nano-oscillators can produce high frequencies (tens of GHz). Furthermore, the
speed of the circular motion for an antiferromagnetic skyrmion in a nanodisk is
analytically derived, which agrees well with the results of numerical
simulations. Our findings are useful for the understanding of the inertial
dynamics of an antiferromagnetic skyrmion and the development of future
skyrmion-based spin torque nano-oscillators.",1811.02869v1
2018-11-13,Enhanced domain wall velocity near a ferromagnetic instability,"Assuming a Fermi liquid behavior for $s$-conduction electrons, we rewrite the
extended Landau-Lifshitz-Gilbert (LLG) equation renormalized by interactions
through the Landau parameters $F^{a}_{l}$ ($l=0,1,2 \cdots$) in an explicit
form to describe the dynamic of a domain wall (DW) due to spin transfer torque
phenomenon. The interaction between spins of the \textit{s}-conduction
electrons explains qualitatively the DW velocity experimental observations in
$\mathrm{Ni_{81}}\mathrm{Fe_{19}}$ (Permalloy) recalculated by us without
defects or impurity hypothesis. Close to Stoner ferromagnetic instability point
where $F^{a}_{0} \approx -0.99$, the DW velocity becomes high
($v^{*}_{DW}\approx 600$ $ms^{-1}$) and critical spin current density becomes
reduced ($j^{*}_{c}\approx1\times10^{12}$ $Am^{-2}$) when compared to that
calculated by nonadiabatic approach. At the critical point, the DW velocity
diverges while critical spin current density at the same point goes to zero.
Our theory also provides a prediction to looking for materials in which is
possible applies a smallest critical spin current density and observes higher
DW velocity.",1811.05380v4
2019-05-24,Quantum Kinetic Theory of Spin Polarization of Massive Quarks in Perturbative QCD: Leading Log,"We present the quantum kinetic equation for spin polarization of massive
quarks in leading log order of perturbative QCD, which describes time evolution
of the spin density matrix in momentum space of a massive quark interacting
with a background QCD plasma. We find that the time evolution operator of the
spin density matrix, or the quantum kinetic collision terms, are universally of
order $\alpha_s^2\log(1/\alpha_s)$ in terms of the QCD coupling constant
$\alpha_s=g^2/(4\pi)$. Our quantum kinetic equation is valid for an arbitrary
quark mass $m\gg m_D\sim gT$, where $m_D$ is the Debye mass, and can be used to
study relaxation dynamics of spin polarization of massive quarks in
perturbative QCD regime.",1905.10463v1
2019-05-31,Time-Resolved Observation of Spin-Charge Deconfinement in Fermionic Hubbard Chains,"Elementary particles such as the electron carry several quantum numbers, for
example, charge and spin. However, in an ensemble of strongly interacting
particles, the emerging degrees of freedom can fundamentally differ from those
of the individual constituents. Paradigmatic examples of this phenomenon are
one-dimensional systems described by independent quasiparticles carrying either
spin (spinon) or charge (holon). Here we report on the dynamical deconfinement
of spin and charge excitations in real space following the removal of a
particle in Fermi-Hubbard chains of ultracold atoms. Using space- and
time-resolved quantum gas microscopy, we track the evolution of the excitations
through their signatures in spin and charge correlations. By evaluating
multi-point correlators, we quantify the spatial separation of the excitations
in the context of fractionalization into single spinons and holons at finite
temperatures.",1905.13638v1
2020-07-02,Coarse graining spin foam quantum gravity -- a review,"In quantum gravity, we envision renormalization as the key tool for bridging
the gap between microscopic models and observable scales. For spin foam quantum
gravity, which is defined on a discretisation akin to lattice gauge theories,
the goal is to derive an effective theory on a coarser discretisation from the
dynamics on the finer one, coarse graining the system in the process and thus
relating physics at different scales. In this review I will discuss the
motivation for studying renormalization in spin foam quantum gravity, e.g. to
restore diffeomorphism symmetry, and explain how to define renormalization in a
background independent setting by formulating it in terms of boundary data. I
will motivate the importance of the boundary data by studying coarse graining
of a concrete example and extending this to the spin foam setting. This will
naturally lead me to the methods currently used for renormalizing spin foam
quantum gravity, such as tensor network renormalization, and a discussion of
recent results. I will conclude with an overview of future prospects and
research directions.",2007.01315v1
2020-07-06,Thermodynamics and screening in the Ising-Kondo model,"We introduce and study a simplification of the symmetric single-impurity
Kondo model. In the Ising-Kondo model, host electrons scatter off a single
magnetic impurity at the origin whose spin orientation is dynamically
conserved. This reduces the problem to potential scattering of spinless
fermions that can be solved exactly using the equation-of-motion technique. The
Ising-Kondo model provides an example for static screening. At low
temperatures, the thermodynamics at finite magnetic fields resembles that of a
free spin-1/2 in a reduced external field. Alternatively, the Curie law can be
interpreted in terms of an antiferromagnetically screened effective spin. The
spin correlations decay algebraically to zero in the ground state and display
commensurate Friedel oscillations. In contrast to the symmetric Kondo model,
the impurity spin is not completely screened, i.e., the screening cloud
contains less than a spin-1/2 electron. At finite temperatures and weak
interactions, the spin correlations decay to zero exponentially with
correlation length $\xi(T)=1/(2\pi T)$.",2007.02664v1
2020-07-15,Janus Monolayers of Magnetic Transition Metal Dichalcogenides as an All-in-One Platform for Spin-Orbit Torque,"We theoretically predict that vanadium-based Janus dichalcogenide monolayers
constitute an ideal platform for spin-orbit-torque memories. Using first
principles calculations, we demonstrate that magnetic exchange and magnetic
anisotropy energies are higher for heavier chalcogen atoms, while the broken
inversion symmetry in the Janus form leads to the emergence of Rashba-like
spin-orbit coupling. The spin-orbit torque efficiency is evaluated using
optimized quantum transport methodology and found to be comparable to heavy
nonmagnetic metals. The coexistence of magnetism and spin-orbit coupling in
such materials with tunable Fermi-level opens new possibilities for monitoring
magnetization dynamics in the perspective of non-volatile magnetic random
access memories.",2007.07579v1
2020-07-24,Can the dynamics of test particles around charged stringy black holes mimic the spin of Kerr black holes?,"We study the motion of electrically charged particles, magnetic monopoles,
and magnetic dipoles around electrically and magnetically charged stringy black
holes. From the analysis of the radius of the innermost stable circular orbit
(ISCO) of electrically charged particles, we show that the electric charge $Q$
of stringy black holes can mimic well the spin of Kerr black holes; the black
hole magnetic charge $Q_m$ can mimic spins up to $a_* \simeq 0.85$ for magnetic
dipoles; the magnetic charge parameter $g$ of a magnetic monopole can mimic
spins up to $a_* \simeq 0.8$. This is due to the destructive character of the
magnetic field and such a result excludes the existence of an appreciable black
hole magnetic charge in astrophysical black holes from the observation of
rapidly rotating objects with dimensionless spin up to $a_* \simeq 0.99$. We
then consider the magnetar SGR (PSR) J1745-2900 as a magnetic dipole orbiting
the supermassive black hole Sagittarius A* (Sgr A*). We show that Sgr A* may be
interpreted as a stringy black hole with magnetic charge $Q_{\rm m}/M \leq
0.4118$.",2007.12462v1
2020-07-28,Electron correlation effects on exchange interactions and spin excitations in 2D van der Waals materials,"Despite serious effort, the nature of the magnetic interactions and the role
of electron-correlation effects in magnetic two-dimensional (2D) van der Waals
materials remain elusive. Using CrI$_3$ as a model system, we show that the
calculated electronic structure including nonlocal electron correlations yields
spin excitations consistent with inelastic neutron scattering measurements.
Remarkably, this approach identifies an unreported correlation-enhanced
interlayer super-superexchange, which rotates the magnon Dirac lines off, and
introduces a gap along, the high-symmetry $\Gamma$-$K$-$M$ path. This discovery
provides a different perspective on the gap opening mechanism observed in
CrI$_3$, which was previously associated with spin-orbit coupling through the
Dzyaloshinskii-Moriya interaction or Kitaev interaction. Our observation
elucidates the critical role of electron correlations on the spin ordering and
spin dynamics in magnetic van der Waals materials and demonstrates the
necessity of explicit treatment of electron correlations in the broad family of
2D magnetic materials.",2007.14518v2
2013-08-01,Dynamics and decoherence in the central spin model in the low-field limit,"We present a combination of analytic calculations and a powerful numerical
method for large spin baths in the low-field limit. The hyperfine interaction
between the central spin and the bath is fully captured by the density matrix
renormalization group. The adoption of the density matrix renormalization group
for the central spin model is presented and a proper method for calculating the
real-time evolution at infinite temperature is identified. In addition, we
study to which extent a semiclassical model, where a quantum spin-1/2 interacts
with a bath of classical Gaussian fluctuations, can capture the physics of the
central spin model. The model is treated by average Hamiltonian theory and by
numerical simulation.",1308.0242v2
2014-03-11,Overcoming damping in spin wave propagation: A continuous excitation approach to determine time-dependent dispersion diagrams in 2D magnonic crystals,"We propose an alternative micromagnetic approach to determine the spin wave
dispersion relations in magnonic structures. Characteristic of the method is
that a limited area of the system is continuously excited with a spatially
uniform oscillating field, tuned at a given frequency. After a transitory time,
the regime magnetization dynamics is collected and a spatial Fourier analysis
on it determines the frequency vs wave vector relation. Combining several
simulations in any predetermined range of frequencies, at any resolution, we
investigate the dispersion relations for different kinds of magnonic crystals:
a dot array, an antidot array, and a bicomponent film. Especially compared to
traditional pulse-excitation methods this technique has many advantages. First,
the excitation power is concentrated at a single frequency, allowing the
corresponding spin waves to propagate with very low attenuation, resulting in a
higher k-space resolution. Second, the model allows to include very large wave
vector components, necessary to describe the high-frequency response of
non-quantized spin waves in quasi-continuous systems. Finally, we address some
possible experimental opportunities with respect to excitation/detection
techniques over large distances and the observation of the odd/even symmetry of
spin waves using Brillouin light scattering.",1403.2549v1
2014-03-31,Degenerate Quantum Gases with Spin-Orbit Coupling,"This review focuses on recent developments on studying synthetic spin-orbit
(SO) coupling in ultracold atomic gases. Two types of SO coupling are
discussed. One is Raman process induced coupling between spin and motion along
one of the spatial directions, and the other is Rashba SO coupling. We
emphasize their common features in both single-particle and two-body physics
and their consequences in many-body physics. For instance, single particle
ground state degeneracy leads to novel features of superfluidity and richer
phase diagram; increased low-energy density-of-state enhances interaction
effects; the absence of Galilean invariance and spin-momentum locking give rise
to intriguing behaviors of superfluid critical velocity and novel quantum
dynamics; and mixing of two-body singlet and triplet states yields novel
fermion pairing structure and topological superfluids. With these examples, we
show that investigating SO coupling in cold atom systems can enrich our
understanding of basic phenomena such as superfluidity, provide a good platform
for simulating condensed matter states such as topological superfluids, and
more importantly, result in novel quantum systems such as SO coupled unitary
Fermi gas or high spin quantum gases. Finally we also point out major
challenges and possible future directions.",1403.8021v2
2016-11-02,Experimental Studies of Artificial Spin Ice,"Artificial spin ices were originally introduced as analogs of the pyrochlore
spin ices, but have since become a much richer field . The original attraction
of building nanotechnological analogs of the pyrochlores were threefold: to
allow room temperature studies of geometrical frustration; to provide model
statistical mechanical systems where all the relevant parameters in an
experiment can be tuned by design; and to be able to examine the exact
microstate of those systems using advanced magnetic microscopy methods. From
this beginning the field has grown to encompass studies of the effects of
quenched disorder, thermally activated dynamics, microwave frequency responses,
magnetotransport properties, and the development of lattice geometries--with
related emergent physics---that have no analog in naturally-occurring
crystalline systems. The field also offers the prospect of contributing to
novel magnetic logic devices, since the arrays of nanoislands that form
artificial spin ices are similar in many respects to those that are used in the
development of magnetic quantum cellular automata. In this chapter, I review
the experimental aspects of this story, complementing the theoretical chapter
by Gia-Wei Chern.",1611.00744v1
2016-11-04,A photonic Carnot engine powered by a quantum spin-star network,"We propose a spin-star network, where a central spin-$1/2$ is coupled with
XXZ interaction to $N$ outer spin-$1/2$ particles, as a quantum fuel. If the
network is in thermal equilibrium with a cold bath, the central spin can have
an effective temperature larger than the bath one and scaling nonlinearly with
$N$. The nonlinearity can be tuned to $N^2, N^3$ or $N^4$ with the anisotropy
parameter of the coupling. Using a stream of central-spin particles to pump a
micromaser cavity, we calculate the dynamics of the cavity field using a
coarse-grained master equation. Our study reveals that the central-spin beam
effectively acts as a hot reservoir to the cavity field and brings the field to
a thermal steady-state whose temperature benefits from the same nonlinear
enhancement with $N$, and results in a highly efficient photonic Carnot engine.
The validity of our conclusions is tested against the presence of atomic and
cavity damping using a microscopic master equation method for typical microwave
cavity-QED parameters. An alternative equivalent scheme where the spin-$1/2$ is
coupled to a macroscopic spin-$(N/2)$ particle is also discussed.",1611.01475v1
2016-11-20,"The influence of Coulomb Correlations and Spin-Orbit Coupling in the electronic structure of double perovskites Sr$_2$XOsO$_6$ (X$=$Sc, Mg)","We investigate the antiferromagnetic insulating state of the recently
discovered double perovskites Sr$_2$XOsO$_6$ (X$=$Sc, Mg) by using ab-initio
calculations (based on Density Functional Theory and Dynamical Mean-Field
Theory) to elucidate the interplay between electronic correlations and
spin-orbit coupling. The structural details of Sr$_2$XOsO$_6$ (X$=$Sc, Mg)
induce band narrowing effects which enhance local electronic correlations. The
half-filled $5d^3$ orbitals of Os in Sr$_2$ScOsO$_6$ fall into a magnetically
ordered correlated regime, which is slightly affected and reduced by the
spin-orbit coupling. The electronic configuration $5d^2$ of Os in
Sr$_2$MgOsO$_6$ responses differently to electronic correlations promoting a
less localized state than Sr$_2$ScOsO$_6$ at the same strength of electronic
interactions. We find that the inclusion of spin-orbit coupling drives
Sr$_2$MgOsO$_6$ toward insulating behaviour and promotes a large tendency in
formation of orbital magnetization antiparallel to the spin moment. The
formation of the AFM state is linked to the evidence of correlated Hubbard
bands in the paramagnetic solution of Sr$_2$XOsO$_6$ (X$=$Sc, Mg).",1611.06482v1
2017-04-03,Spin-orbit-coupling induced localization in the expansion of an interacting Bose-Einstein condensate,"By developing a hydrodynamic formalism, we investigate the expansion dynamics
of the single-minimum phase of a binary spin-orbit coupled Bose-Einstein
condensate, after releasing from an external harmonic trap. We find that the
expansion of the condensate along the direction of the spin-orbit coupling is
dramatically slowed down near the transition between the single-minimum phase
and the plane-wave phase. Such a slow expansion, resembling a form of an
effective localization, is due to the quenching of the superfluid motion which
results in a strong increase of the effective mass. In the single-minimum phase
the anisotropic expansion of the Bose gas, which is spin balanced at
equilibrium, is accompanied by the emergence of a local spin polarization. Our
analytic scaling solutions emerging from hydrodynamic picture are compared with
a full numerical simulation based on the coupled Gross-Pitaevskii equations.",1704.00677v1
2017-04-09,"Spin-based single-photon transistor, dynamic random access memory, diodes and routers in semiconductors","The realization of quantum computers and quantum Internet requires not only
quantum gates and quantum memories, but also transistors at single-photon
levels to control the flow of information encoded on single photons.
Single-photon transistor (SPT) is an optical transistor in the quantum limit,
which uses a single photon to open or block a photonic channel. In sharp
contrast to all previous SPT proposals which are based on single-photon
nonlinearities, here I present a novel design for a high-gain and high-speed
(up to THz) SPT based on a linear optical effect - giant circular birefringence
(GCB) induced by a single spin in a double-sided optical microcavity. A gate
photon sets the spin state via projective measurement and controls the light
propagation in the optical channel. This spin-cavity transistor can be directly
configured as diodes, routers, DRAM units, switches, modulators, etc. Due to
the duality as quantum gate and transistor, the spin-cavity unit provides a
solid-state platform ideal for future Internet - a mixture of all-optical
Internet with quantum Internet.",1704.02610v1
2017-04-12,Fracton Topological Order from Nearest-Neighbor Two-Spin Interactions and Dualities,"Fracton topological order describes a remarkable phase of matter which can be
characterized by fracton excitations with constrained dynamics and a ground
state degeneracy that increases exponentially with the length of the system on
a three-dimensional torus. However, previous models exhibiting this order
require many-spin interactions which may be very difficult to realize in a real
material or cold atom system. In this work, we present a more physically
realistic model which has the so-called X-cube fracton topological order but
only requires nearest-neighbor two-spin interactions. The model lives on a
three-dimensional honeycomb-based lattice with one to two spin-1/2 degrees of
freedom on each site and a unit cell of 6 sites. The model is constructed from
two orthogonal stacks of $Z_2$ topologically ordered Kitaev honeycomb layers,
which are coupled together by a two-spin interaction. It is also shown that a
four-spin interaction can be included to instead stabilize 3+1D $Z_2$
topological order. We also find dual descriptions of four quantum phase
transitions in our model, all of which appear to be discontinuous first order
transitions.",1704.03870v2
2018-05-07,Phase dynamics of oscillating magnetizations coupled via spin pumping,"A theoretical formalism is developed to simultaneously solve equation of
motion of the magnetizations in two ferromagnets and the spin-pumping induced
spin transport equation. Based on the formalism, a coupled motion of the
magnetizations in a self-oscillation state is studied. The spin pumping is
found to induce an in-phase synchronization of the magnetizations for the
oscillation around the easy axis. For an out-of-plane self-oscillation around
the hard axis, on the other hand, the spin pumping leads to an in-phase
synchronization in a small current region, whereas an antiphase synchronization
is excited in a large current region. An analytical theory based on the phase
equation reveals that the phase difference between the magnetizations in a
steady state depends on the oscillation direction, clockwise or
counterclockwise, of the magnetizations.",1805.02766v1
2018-05-25,Parity-time symmetry breaking in spin chains,"We investigate nonequilibrium phase transitions in classical Heisenberg spin
chains associated with spontaneous breaking of parity-time ($\mathcal{PT}$)
symmetry of the system under the action of Slonczewski spin-transfer torque
(STT) modeled by an applied \textit{imaginary} magnetic field. We reveal the
STT-driven $\mathcal{PT}$ symmetry-breaking phase transition between the
regimes of precessional and exponentially damped spin dynamics and show that
its several properties can be derived from the distribution of zeros of the
system's partition function, the approach first introduced by Yang and Lee for
studying equilibrium phase transitions in Ising spin chains. The physical
interpretation of imaginary magnetic field as describing the action of
non-conservative forces opens the possibility of direct observations of
Lee-Yang zeros in nonequilibrium physical systems.",1805.10346v1
2009-12-18,Spin correlations in rare-earth paramagnetic systems; neutron linewidths and muSR spin-lattice relaxation rates,"We consider the spin correlation functions for rare-earth compounds in their
paramagnetic state with the aim to understand the temperature dependence of the
quasi-elastic and crystal-field linewidths and the spin-lattice relaxation
rates measured by the muon-spin-relaxation technique. Both the conduction
electron and phonon relaxation mechanisms are treated. First the single-ion
dynamics is described using an iterative method introduced by P. M. Richards.
Then the case of a regular lattice of rare-earth ions is studied using the
random-phase approximation (RPA). Applications to simple crystal-field level
schemes are given with particular emphasis on the phonon relaxation mechanism.
This allows us to investigate the domain of validity of our results. In order
to account for data recorded on insulators, a phenomelogical modification is
suggested.",0912.3739v1
2009-12-30,Pulsed Nuclear Pumping and Spin Diffusion in a Single Charged Quantum Dot,"We report the observation of a feedback process between the nuclear spins in
a single charged quantum dot and its trion transition, driven by a periodic
sequence of optical pulses. The pulse sequence intersperses off-resonant
ultrafast pulses for coherent electron-spin rotation and resonant narrow-band
optical pumping. The feedback manifests as a hysteretic triangle-like pattern
in the free-induction-decay of the single spin. We present a simple,
quasi-analytic numerical model to describe this observation, indicating that
the feedback process results from the countering effects of optical nuclear
pumping and nuclear spin-diffusion inside the quantum dot. This effect allows
dynamic tuning of the electron Larmor frequency to a value determined by the
pulse timing, potentially allowing more complex coherent control operations.",0912.5401v1
2011-11-04,Diffusive spin dynamics in ferromagnetic thin films with a Rashba interaction,"In a ferromagnetic metal layer, the coupled charge and spin diffusion
equations are obtained in the presence of both Rashba spin-orbit interaction
and magnetism. The mis-alignment between the magnetization and the
non-equilibrium spin density induced by the Rashba field gives rise to Rashba
spin torque acting on the ferromagnetic order parameter. In a general form, we
find that the Rashba torque consists of both in-plane and out-of-plane
components, ie $\bm{T}=T_{\bot}\hat{\bm{y}}\times{\hat{\bm
m}}+T_{\parallel}{\hat{\bm m}}\times({\hat{\bm y}}\times{\hat{\bm m}})$.
Numerical simulations on a two dimensional nano-wire discuss the impact of
diffusion on the Rashba torque, which reveals a large enhancement to the ratio
$T_{\parallel}/T_{\bot}$ for thin wires. Our theory provides an explanation to
the mechanism that drives the magnetization switching in a single ferromagnet
as observed in the recent experiments.",1111.1216v2
2011-11-28,Quantum criticality of the sub-ohmic spin-boson model,"We revisit the critical behavior of the sub-ohmic spin-boson model. Analysis
of both the leading and subleading terms in the temperature dependence of the
inverse static local spin susceptibility at the quantum critical point,
calculated using a numerical renormalization-group method, provides evidence
that the quantum critical point is interacting in cases where the
quantum-to-classical mapping would predict mean-field behavior. The subleading
term is shown to be consistent with an w/T scaling of the local dynamical
susceptibility, as is the leading term. The frequency and temperature
dependences of the local spin susceptibility in the strong-coupling
(delocalized) regime are also presented. We attribute the violation of the
quantum-to-classical mapping to a Berry-phase term in a continuum path-integral
representation of the model. This effect connects the behavior discussed here
with its counterparts in models with continuous spin symmetry.",1111.6623v1
2012-01-21,Measurement and Control of Single Nitrogen-Vacancy Center Spins above 600 K,"We study the spin and orbital dynamics of single nitrogen-vacancy (NV)
centers in diamond between room temperature and 700 K. We find that the ability
to optically address and coherently control single spins above room temperature
is limited by nonradiative processes that quench the NV center's
fluorescence-based spin readout between 550 and 700 K. Combined with electronic
structure calculations, our measurements indicate that the energy difference
between the 3E and 1A1 electronic states is approximately 0.8 eV. We also
demonstrate that the inhomogeneous spin lifetime (T2*) is temperature
independent up to at least 625 K, suggesting that single NV centers could be
applied as nanoscale thermometers over a broad temperature range.",1201.4420v2
2012-04-09,Microscopic phase separation in triangular-lattice quantum spin magnet kappa-(BEDT-TTF)2Cu2(CN)3 probed by muon spin relaxation,"The ground state of the quantum spin system kappa-(BEDT-TTF)2Cu2(CN)3 in
which antiferromagnetically-interacting S=1/2 spins are located on a nearly
equilateral triangular lattice attracts considerable interest both from
experimental and theoretical aspects, because a simple antiferromagnetic order
may be inhibited because of the geometrical frustration and hence an exotic
ground state is expected. Furthermore, recent two reports on the ground state
of this system have made it further intriguing by showing completely
controversial results; one indicates the gapless state and the other gapped. By
utilizing microscopic probe of muSR, we have investigated its spin dynamics
below 0.1 K, unveiling its microscopically phase separated ground state at zero
field.",1204.1785v2
2012-04-12,Evidence for an exotic magnetic transition in the triangular spin system FeGa2S4,"We report positive muon spin relaxation measurements on the triangular
lattice magnetic system FeGa2S4. A magnetic transition not previously detected
by specific heat and magnetic susceptibility measurements is found in zero
field at T^* \simeq 30 K. It is observed through the temperature dependencies
of the signal amplitude and the spin-lattice relaxation rate. This transition
is therefore not a conventional magnetic phase transition. Since persistent
spin dynamics is observed down to 0.1 K, the ground state cannot be of the
canonical spin-glass type, which could be suggested from hysteresis effects in
the bulk susceptibility below T_f \simeq 16 K. These results are compared to
those found for the isomorph NiGa2S4. It is argued that the fate of the
transition, which has been interpreted in terms of the Z_2 topological
transition in this latter system, is probably different in FeGa2S4.",1204.2739v1
2013-09-12,Interplay of spin gap and nanoscopic quantum fluctuations in intermetallic CeCu2Ge2,"Neutron scattering measurements are used to elucidate interplay of the
field-induced spin gap and the quantum fluctuations in archetypal heavy
electron system CeCu$_{2}$Ge$_{2}$. A spin gap of $\Delta$ = 0.56 meV is found
to develop near the field-induced quantum critical state at $H$$_{c}$$\simeq$ 8
T, driven by fluctuations of the long range antiferromagnetic order parameter.
The superconducting transition temperature in many magnetic superconductors is
found to exhibit one-to-one correspondence with the spin gap. In this regard,
the demonstration of an interplay of the spin gap with the nanoscopic dynamic
correlation provides new arena to explore direct relation between the quantum
critical behavior and the unconventional superconductivity, especially in heavy
electrons systems.",1309.3331v1
2013-09-19,Wave packet dynamics in the one-dimensional extended Hubbard model,"Using time-dependent density-matrix renormalization group, we study the time
evolution of electronic wave packets in the one-dimensional extended Hubbard
model with on-site and nearest neighbor repulsion, U and V, respectively. As
expected, the wave packets separate into spin-only and charge-only excitations
(spin-charge separation). Charge and spin velocities exhibit non-monotonic
dependence on V. For small and intermediate values of V, both velocities
increase with V. However, the charge velocity exhibits a stronger dependence
than that of the spin, leading to a more pronounced spin-charge separation.
Charge fractionalization, on the other hand, is weakly affected by V. The
results are explained in terms of Luttinger liquid theory in the weak-coupling
limit, and an effective model in the strong-coupling regime.",1309.5119v1
2013-09-19,Analytic solutions to the central spin problem for Nitrogen Vacancy centres in diamond,"Due to interest in both solid state based quantum computing architectures and
the application of quantum mechanical systems to nanomagnetometry, there has
been considerable recent attention focused on understanding the microscopic
dynamics of solid state spin baths and their effects on the coherence of a
controllable, coupled central electronic spin. Many analytic approaches are
based on simplified phenomenological models in which it is difficult to capture
much of the complex physics associated with this system. Conversely, numerical
approaches reproduce this complex behaviour, but are limited in the amount of
theoretical insight they can provide. Using a systematic approach based on the
spatial statistics of spin bath constituents, we develop a purely analytic
theory for the central spin decoherence problem of Nitrogen Vacancy centres in
diamond that reproduces the experimental and numerical results found in the
literature, whilst correcting a number of limitations and inaccuracies
associated with existing analytical approaches.",1309.5921v1
2013-09-29,Spin nutation effects in molecular nanomagnet$-$superconductor tunnel junctions,"We study the spin nutation effects of the molecular nanomagnet on the
Josephson current through a superconductor$|$molecular
nanomagnet$|$superconductor tunnel junction. We explicitly demonstrate that due
to the spin nutation of the molecular nanomagnet two oscillatory terms emerge
in the $ac$ Josephson current in addition to the conventional $ac$ Josephson
current. Some resonances occur in the junction due to the interactions of the
transported quasiparticles with the bias voltage and molecular nanomagnet spin
dynamics. The appearance of them indicate that the energy exchanged during
these interactions is in the range of the superconducting energy gap. We also
show that the spin nutation is able to convert the $ac$ Josephson current to a
$dc$ one which is interesting for applications.",1309.7585v1
2014-06-02,"Berry Phase, Lorentz Covariance, and Anomalous Velocity for Dirac and Weyl Particles","We consider the relation between spin and the Berry-phase contribution to the
anomalous velocity of massive and massless Dirac particles. We extend the Berry
connection that depends only on the spatial components of the particle momentum
to one that depends on the the space and time components in a covariant manner.
We show that this covariant Berry connection captures the Thomas-precession
part of the Bargmann-Michel-Telegdi spin evolution, and contrast it with the
traditional (unitary, but not naturally covariant) Berry connection that
describes spin-orbit coupling. We then consider how the covariant connection
enters the classical relativistic dynamics of spinning particles due to
Mathisson, Papapetrou and Dixon. We discuss the problems that arise with
Lorentz covariance in the massless case, and trace them mathematically to a
failure of the Wigner-translation part of the massless-particle little group to
be an exact gauge symmetry in the presence of interactions, and physically to
the fact that the measured position of a massless spinning particle is
necessarily observer dependent.",1406.0354v2
2015-12-01,Imaging nuclear spins weakly coupled to a probe paramagnetic center,"Optically-detected paramagnetic centers in wide-bandgap semiconductors are
emerging as a promising platform for nanoscale metrology at room temperature.
Of particular interest are applications where the center is used as a probe to
interrogate other spins that cannot be observed directly. Using the
nitrogen-vacancy center in diamond as a model system, we propose a new strategy
to determining the spatial coordinates of weakly coupled nuclear spins. The
central idea is to label the target nucleus with a spin polarization that
depends on its spatial location, which is subsequently revealed by making this
polarization flow back to the NV for readout. Using extensive analytical and
numerical modeling, we show that the technique can attain high spatial
resolution depending on the NV lifetime and target spin location. No external
magnetic field gradient is required, which circumvents complications resulting
from changes in the direction of the applied magnetic field, and considerably
simplifies the required instrumentation. Extensions of the present technique
may be adapted to pinpoint the locations of other paramagnetic centers in the
NV vicinity or to yield information on dynamical processes in molecules on the
diamond surface.",1512.00499v1
2015-12-09,Entanglement between Lowly and Highly Lying Atomic Spin Waves,"Establishing a quantum interface between different physical systems is of
special importance for developing the practical versatile quantum networks.
Entanglement between low- and high-lying atomic spin waves is essential for
building up Rydberg-based quantum information engineering, otherwhile be more
helpful to study the dynamics behavior of entanglement under external pertur-
bations. Here, we report on the successful storage of a single photon as a
high-lying atomic spin wave in quantum regime. Via storing a K-vector
entanglement between single photon and lowly lying spin wave, we thereby
experimentally realize the entanglement between low- and high-lying atomic spin
waves in two separated atomic systems. This makes our experiment the primary
demonstration of Rydberg quantum memory of entanglement, making a primary step
toward the construction of a hybrid quantum interface.",1512.02772v3
2015-12-21,Spin effects on the dynamics of compact binaries,"Compact binaries are the most promising source for the advanced gravitational
wave detectors, which will start operating this year. The influence of spin on
the binary evolution is an important consequence of general relativity and can
be large. It is argued that the spin supplementary condition, which is related
to the observer dependence of the center, gives rise to a gauge symmetry in the
action principle of spinning point-particles. These spinning point-particles
serve as an analytic model for extended bodies. The internal structure can be
modelled by augmenting the point-particle with higher-order multipole moments.
Consequences of the recently discovered universal (equation of state
independent) relations between the multipole moments of neutron stars are
discussed.",1512.06768v2
2016-08-13,Quantitative measure for the spin-charge separation in two dimensional Hubbard model,"We introduce a qauantitative measure of spin-charge separation, $\zeta (t)$
which is based on the difference between the fluctuations with respect to
background of the spin and charge profiles at any time t and is suitable for
studying the non-equilibrium dynamics of excitations in strongly correlated
systems. This quantity is not only a direct measure of the spin-charge
separation in strongly correlated systems, but its long time behaviour can
further serve as a possible order parameter for the interaction induced (Mott)
insulating state. Within the nu- merically exact diagonzalization we calculate
this quantity for the two dimensional Hubbard model away from Half filling. Our
quantitative measure in chain, ladder and two-dimensional geometries gives the
same order of magnitude for the quantity of spin-charge separation. Furthermore
from the temporal behaviour of $\zeta (t)$ a threshold time can be identified
that provides clues onto the breakdown of underlying Mott insulating phase.",1608.03948v1
2016-12-03,Attosecond control of spin polarization in electron-ion recollision driven by intense tailored fields,"We show that electrons recolliding with the ionic core upon tunnel ionization
of noble gas atoms driven by a strong circularly polarized laser field in
combination with a counter-rotating second harmonic are spin polarized and that
their degree of polarization depends strongly on the recollision time. Spin
polarization arises as a consequence of (1) entanglement between the
recolliding electron and the ion, and (2) sensitivity of ionization to the
sense of electron rotation in the initial state. We demonstrate that one can
engineer the degree of spin polarization as a function of time by tuning the
relative intensities of the counter-rotating fields, opening the door for
attosecond control of spin-resolved dynamics.",1612.01021v2
2016-12-09,The Fermi surface of Sr2RuO4: spin-orbit and anisotropic Coulomb interaction effects,"The topology of the Fermi surface of Sr2RuO4 is well described by
local-density approximation calculations with spin-orbit interaction, but the
relative size of its different sheets is not. By accounting for many-body
effects via dynamical mean-field theory, we show that the standard isotropic
Coulomb interaction alone worsens or does not correct this discrepancy. In
order to reproduce experiments, it is essential to account for the Coulomb
anisotropy. The latter is small but has strong effects; it competes with the
Coulomb-enhanced spin-orbit coupling and the isotropic Coulomb term in
determining the Fermi surface shape. Its effects are likely sizable in other
correlated multi-orbital systems. In addition, we find that the low-energy
self-energy matrix -- responsible for the reshaping of the Fermi surface --
sizably differ from the static Hartree-Fock limit. Finally, we find a strong
spin-orbital {entanglement}; this supports the view that the conventional
description of Cooper pairs via factorized spin and orbital part might not
apply to Sr2RuO4.",1612.03060v1
2016-12-16,Ultrafast demagnetization in bulk vs thin films: an ab-initio study,"We report on {\it ab-initio} simulations of the quantum dynamics of
electronic charge and spin when subjected to intense laser pulses. By
performing separate calculations for a Ni thin film and bulk Ni, we conclude
that surface effects have a dramatic influence on amplifying the laser induced
demagnetization. We show that the reason for this amplification is due to
increased spin-currents on the surface of the thin film. This enhancement is a
direct consequence of the broken symmetry originating from the surface
formation. We find that the underlying physics of demagnetization, during the
early femtoseconds, for both bulk and thin film is dominated by spin-flips
induced by spin-orbit coupling. After the first $\sim 40$ fs this changes in
that the dominant cause of demagnetization is the flow of spin-currents, which
leads to stronger demagnetization in the film compared to that of the bulk.",1612.05663v2
2016-12-22,New Hamiltonians for loop quantum cosmology with arbitrary spin representations,"In loop quantum cosmology, one has to make a choice of SU(2) irreducible
representation in which to compute holonomies and regularize the curvature of
the connection. The systematic choice made in the literature is to work in the
fundamental representation, and very little is known about the physics
associated with higher spin labels. This constitutes an ambiguity whose
understanding, we believe, is fundamental for connecting loop quantum cosmology
to full theories of quantum gravity like loop quantum gravity, its spin foam
formulation, or cosmological group field theory. We take a step in this
direction by providing here a new closed formula for the Hamiltonian of flat
FLRW models regularized in a representation of arbitrary spin. This expression
is furthermore polynomial in the basic variables which correspond to
well-defined operators in the quantum theory, takes into account the so-called
inverse-volume corrections, and treats in a unified way two different
regularization schemes for the curvature. After studying the effective
classical dynamics corresponding to single and multiple spin Hamiltonians, we
study the behavior of the critical density when the number of representations
is increased, and the stability of the difference equations in the quantum
theory.",1612.07615v1
2016-12-27,Magnetic phase transition in coupled spin-lattice systems: A replica-exchange Wang-Landau study,"Coupled, dynamical spin-lattice models provide a unique test ground for
simulations investigating the finite-temperature magnetic properties of
materials under the direct influence of the lattice vibrations. These models
are constructed by combining a coordinate-dependent interatomic potential with
a Heisenberg-like spin Hamiltonian, facilitating the treatment of both the
atomic coordinates and spins as explicit phase variables. Using a model
parameterized for bcc iron, we study the magnetic phase transition in these
complex systems via the recently introduced, massively parallel
replica-exchange Wang-Landau Monte Carlo method. Comparison with the results
obtained from rigid lattice (spin only) simulations show that the transition
temperature as well as the amplitude of the peak in the specific heat curve is
marginally affected by the lattice vibrations. Moreover, the results were found
to be sensitive to the particular choice of the interatomic potential.",1612.08464v1
2017-06-01,Doping-induced spin-orbit splitting in Bi-doped ZnO nanowires,"Our predictions, based on density-functional calculations, reveal that
surface doping of ZnO nanowires with Bi leads to a linear-in-$k$ splitting of
the conduction-band states, through spin-orbit interaction, due to the lowering
of the symmetry in the presence of the dopant. This finding implies that spin
polarization of the conduction electrons in Bi-doped ZnO nanowires could be
controlled with applied electric (as opposed to magnetic) fields, making them
candidate materials for spin-orbitronic applications. Our findings also show
that the degree of spin splitting could be tuned by adjusting the dopant
concentration. Defect calculations and ab initio molecular dynamics simulations
indicate that stable doping configurations exhibiting the foregoing
linear-in-$k$ splitting could be realized under reasonable thermodynamic
conditions.",1706.00249v1
2017-06-06,Observation of spin superfluidity: YIG magnetic films and beyond,"From topology of the order parameter of the magnon condensate observed in
yttrium-iron-garnet (YIG) magnetic films one must not expect energetic barriers
making spin supercurrents metastable. But we show that some barriers of
dynamical origin are possible nevertheless until the gradient of the phase
(angle of spin precession) does not exceed the critical value (analog of the
Landau critical velocity in superfluids). On the other hand, recently published
claims of experimental detection of spin superfluidity in YIG films and
antiferromagnets are not justified, and spin superfluidity in magnetically
ordered solids has not yet been experimentally confirmed.",1706.01932v2
2017-06-26,Tunable RKKY interaction in a double quantum dot nanoelectromechanical device,"We propose a realization of mechanically tunable
Ruderman-Kittel-Kasuya-Yosida interaction in a double quantum dot
nanoelectromechanical device. The coupling between spins of two quantum dots
suspended above a metallic plate is mediated by conduction electrons. We show
that the spin-mechanical interaction can be driven by a slow modulation of
charge density in the metallic plate. We propose to use Stuckelberg
oscillations as a sensitive tool for detection of the spin and charge states of
the coupled quantum dots. Theory of mechanical back action induced by a
dynamical spin-spin interaction is discussed.",1706.08389v4
2017-06-29,Quantum spin liquid signatures in Kitaev-like frustrated magnets,"Motivated by recent experiments on $\alpha$-RuCl$_3$, we investigate a
possible quantum spin liquid ground state of the honeycomb-lattice spin model
with bond-dependent interactions. We consider the $K-\Gamma$ model, where $K$
and $\Gamma$ represent the Kitaev and symmetric-anisotropic interactions
between spin-1/2 moments on the honeycomb lattice. Using the infinite density
matrix renormalization group (iDMRG), we provide compelling evidence for the
existence of quantum spin liquid phases in an extended region of the phase
diagram. In particular, we use transfer matrix spectra to show the evolution of
two-particle excitations with well-defined two-dimensional dispersion, which is
a strong signature of quantum spin liquid. These results are compared with
predictions from Majorana mean-field theory and used to infer the quasiparticle
excitation spectra. Further, we compute the dynamical structure factor using
finite size cluster computations and show that the results resemble the
scattering continuum seen in neutron scattering experiments on
$\alpha$-RuCl$_3$. We discuss these results in light of recent and future
experiments.",1706.09908v2
2017-07-04,Entanglement Dynamics for Two Spins in an Optical Cavity---Field Interaction Induced Decoherence and Coherence Revival,"We in this paper study quantum correlations for two neutral spin-particles
coupled with a single-mode optical cavity through the usual magnetic
interaction. Two-spin entangled states for both antiparallel and parallel
spin-polarizations are generated under the photon coherent-state assumption.
Based on the quantum master equation we derive the time-dependent quantum
correlation of Clauser-Horne-Shimony-Holt (CHSH) type explicitly in comparison
with the well known entanglement-measure concurrence. In the two-spin singlet
state, which is recognized as one eigenstate of the system, the CHSH
correlation and concurrence remain in their maximum values invariant with time
and independent of the average photon-numbers either. The correlation varies
periodically with time in the general entangled-states for the low average
photon-numbers. When the photon number increases to a certain value the
oscillation becomes random and the correlations are suppressed below the Bell
bound indicating the decoherence of the entangled states. In the high
photon-number limit the coherence revivals periodically such that the CHSH
correlation approaches the upper bound value at particular time points
associated with the cavity-field period",1707.00851v1
2017-07-23,Investigating different $Λ$ and $\barΛ$ polarizations in relativistic heavy-ion collisions,"Based on the chiral kinetic equations of motion, spin polarizations of
various quarks, due to the magnetic field induced by spectator protons as well
as the quark-antiquark vector interaction, are studied within a partonic
transport approach. Although the magnetic field in QGP enhances the splitting
of the spin polarizations of partons compared to the results under the magnetic
field in vacuum, the spin polarizations of $s$ and $\bar s$ quarks are also
sensitive to the quark-antiquark vector interaction, challenging that the
different $\Lambda$ and $\bar \Lambda$ spin polarization is a good measure of
the magnetic field in relativistic heavy-ion collisions. It is also found that
there is no way to obtain the large splitting of the spin polarization between
$\Lambda$ and $\bar \Lambda$ at $\sqrt{s_{NN}}=7.7$ GeV with partonic dynamics.",1707.07262v3
2017-07-25,Non-equilibrium nuclear spin distribution function in quantum dots subject to periodic pulses,"Electron spin dephasing in a singly charged semiconductor quantum dot can
partially be suppressed by periodic laser pulsing. We propose a semi-classical
approach describing the decoherence of the electron spin polarization governed
by the hyperfine interaction with the nuclear spins as well as the
probabilistic nature of the photon absorption. We use the steady-state Floquet
condition to analytically derive two subclasses of resonance conditions
excellently predicting the peak locations in the part of the Overhauser field
distribution which is projected in the direction of the external magnetic
field. As a consequence of the periodic pulsing, a non-equilibrium distribution
develops as a function of time. The numerical simulation of the coupled
dynamics reveals the influence of the hyperfine coupling constant distribution
onto the evolution of the electron spin polarisation before the next laser
pulse. Experimental indications are provided for both subclasses of resonance
conditions.",1707.07841v1
2017-10-15,Tunable multi-electron Pancharatnam phase in intensity interferometry,"Pancharatnam phase was discovered in the context of polarization optics in
nineteen fifties. However, its full realization in quantum many-body systems
still eludes us. This is primarily due to the fact that electron spin is not
easily tunable. In the present proposal, we suggest that edge states of quantum
spin Hall effect (QSHE) in conjunction with spin polarized electrodes (SPE)
provide us with a unique opportunity to explore the Pancharatnam phase. We
demonstrate the possibility of generating and detecting the multi-electron
version of this phase that can as well be interpreted as multi-particle
Aharonov-Bohm (A-B) effect in spin space arising solely due to spin dynamics.
We further show that our proposed set-up leads to a robust interference pattern
which survives orbital dephasing.",1710.05266v1
2017-12-07,Spin waves in coupled YIG/Co heterostructures,"We investigate yttrium iron garnet (YIG)/cobalt (Co) heterostructures using
broadband ferromagnetic resonance (FMR). We observe an efficient excitation of
perpendicular standing spin waves (PSSWs) in the YIG layer when the resonance
frequencies of the YIG PSSWs and the Co FMR line coincide. Avoided crossings of
YIG PSSWs and the Co FMR line are found and modeled using mutual spin pumping
and exchange torques. The excitation of PSSWs is suppressed by a thin aluminum
oxide (AlOx) interlayer but persists with a copper (Cu) interlayer, in
agreement with the proposed model.",1712.02561v1
2017-12-21,"Electron spin polarization in realistic trajectories around the magnetic node of two counter-propagating, circularly polarized, ultra-intense lasers","It has recently been suggested that two counter-propagating, circularly
polarized, ultra-intense lasers can induce a strong electron spin polarization
at the magnetic node of the electromagnetic field that they setup. We confirm
these results by considering a more sophisticated description that integrates
over realistic trajectories. The electron dynamics is weakly affected by the
variation of power radiated due to the spin polarization. The degree of spin
polarization differs by approximately 5\% if considering electrons initially at
rest or already in a circular orbit. The instability of trajectories at the
magnetic node induces a spin precession associated with the electron migration
that establishes an upper temporal limit to the polarization of the electron
population of about one laser period.",1712.08118v2
2018-01-02,Spin Glass in the Bond-Diluted J1-J2 Ising Model on the Square Lattice,"We use Monte Carlo (MC) methods to simulate a two-dimensional (2D)
bond-diluted Ising model on the square lattice which has frustration between
the nearest-neighbor interaction J1 and the next-nearest-neighbor interaction
J2. In this paper, we use the parallel tempering algorithm to study the
thermodynamics for different diluted ratio x and give the phase diagram. The
presence of both frustration and disorder results in a spin-glass phase, which
exists between the stripe antiferromagnetic phase and the Neel phase. We
present the ground-state energy of T -> 0 and the size-dependence of
Edwards-Anderson (EA) order parameter for the spin glass phase. By scaling the
mean energy and the EA order parameter from the simulated annealing with the
Kibble-Zurek (KZ) mechanism, we obtain two different dynamic exponents z_E and
z_q for the spin glass phase. Experimentally, this model has close implication
with the FeAs plane of the iron-based superconductor BaFe2(As(1-x)P(x))2, where
a spin-glass like phase was found.",1801.00659v1
2018-01-11,Aspects of the decoherence in high spin environments: Breakdown of the mean-field approximation,"The study of the decoherence of qubits in spin systems is almost restricted
to environments whose constituents are spin-$\frac{1}{2}$ particles. In this
paper we consider environments that are composed of particles of higher spin,
and we investigate the consequences on the dynamics of a qubit coupled to such
baths via Heisenberg $XY$ and Ising interactions. It is shown that while the
short time decay in both cases gets faster as the magnitude of the spin
increases, the asymptotic behavior exhibits an improvement of the suppression
of the decoherence when the coupling is through Heisenberg $XY$ interactions.
In the case of a transverse Ising model, we find that the mean field
approximation breaks down for high values of the spin.",1801.03750v2
2018-09-05,Poisson-Lie analogues of spin Sutherland models,"We present generalizations of the well-known trigonometric spin Sutherland
models, which were derived by Hamiltonian reduction of `free motion' on
cotangent bundles of compact simple Lie groups based on the conjugation action.
Our models result by reducing the corresponding Heisenberg doubles with the aid
of a Poisson-Lie analogue of the conjugation action. We describe the reduced
symplectic structure and show that the `reduced main Hamiltonians' reproduce
the spin Sutherland model by keeping only their leading terms. The solutions of
the equations of motion emerge from geodesics on the compact Lie group via the
standard projection method and possess many first integrals. Similar hyperbolic
spin Ruijsenaars--Schneider type models were obtained previously by L.-C. Li
using a different method, based on coboundary dynamical Poisson groupoids, but
their relation with spin Sutherland models was not discussed.",1809.01529v3
2018-10-13,Spin-torque resonance due to diffusive dynamics at a surface of topological insulator,"We investigate spin-orbit torques on magnetization in an insulating
ferromagnetic (FM) layer that is brought into a close proximity to a
topological insulator (TI). In addition to the well-known field-like spin-orbit
torque, we identify an anisotropic anti-damping-like spin-orbit torque that
originates in a diffusive motion of conduction electrons. This diffusive torque
is vanishing in the limit of zero momentum (i. e. for spatially homogeneous
electric field or current), but may, nevertheless, have a strong effect on
spin-torque resonance at finite frequency provided external field is neither
parallel nor perpendicular to the TI surface. The required electric field
configuration can be created by a grated top gate.",1810.05828v3
2018-10-18,A novel chiral spin texture: Antiferromagnetic Skyrmionium,"Exotic spin textures viz. chiral domain wall, vortices, skyrmion,
skyrmionium, etc. have recently emerged as active field of research because of
their potential applications in high density data storage technology and logic
gate computing. Magnetic skyrmionium is a skyrmion like soliton, which carries
zero topological quantum number. Skyrmioniums are superior to conventional
skyrmions in ferromagnets due to their negligible skyrmion hall effect and
higher velocity. The physical properties of both skyrmion and skyrmionium have
been investigated rigorously in ferromagnetic systems. Recent observations hint
that such chiral spin structures in antiferromagnetic (AFM) systems are more
promising in comparison to the ferromagnetic ones because of their robustness
towards external perturbation, absence of Skyrmion hall effect, etc. However
skyrmionium in AFM materials are not reported in literature so far. In this
work, we demonstrate that skyrmionium can be created and stabilized in AFM
materials by application of spin polarized current in an experimentally
feasible geometry. We have further studied the dynamics of AFM skyrmionium by
applying spin polarized current.",1810.08262v2
2018-10-19,Preparing the spin-singlet state of a spinor gas in an optical cavity,"We propose a method to prepare the spin singlet in an ensemble of
integer-spin atoms confined within a high-finesse optical cavity. Using a
cavity-assisted Raman transition to produce an effective Tavis-Cummings model,
we show that a high fidelity spin singlet can be produced probabilistically,
although with low efficiency, heralded by the \emph{absence} of photons
escaping the cavity. In a different limit, a similar configuration of laser and
cavity fields can be used to engineer a model that emulates spinor collisional
dynamics. Borrowing from techniques used in spinor Bose-Einstein condensates,
we show that adiabatic transformation of the system Hamiltonian (via a
time-dependent, effective quadratic Zeeman shift) can be used to produce a low
fidelity spin singlet. Then, by following this method with the aforementioned
heralding technique, we show that it is possible to prepare the singlet state
with both high fidelity and good efficiency for a large ensemble.",1810.08353v2
2018-10-23,Sharp reversals of steady-state nuclear polarisation as a tool for quantum sensing,"The polarisation dynamics of nuclear spins weakly coupled to an NV center is
highly sensitive to the parameters of the microwave control and the nuclear
Larmor frequency. What is commonly regarded as a challenge, we propose here as
a resource for quantum sensing. By varying a single experimental parameter in a
suitable set-up, i.e., the Rabi frequency of a continual microwave driving or
the nuclear Larmor frequency, we predict periodic reversals of the steady-state
polarisation of the nuclear spin. Crucially, interference between the
transverse and longitudinal dipolar interaction of electron and nuclear spins
results in remarkably sharp steady-state polarisation reversals of nuclear
spins within only a few tens of Hz change in the nuclear Larmor frequency. Our
method is particularly robust against imperfections such as decoherence of the
electron spin and the frequency resolution of the sensor is not limited by the
coherence time $T_2$ of the electron sensor.",1810.09709v1
2019-06-01,Polarized inelastic neutron scattering of non-reciprocal spin waves in MnSi,"We report spin-polarized inelastic neutron scattering of the dynamical
structure factor of the conical magnetic helix in the cubic chiral magnet MnSi.
We find that the spectral weight of spin-flip scattering processes is
concentrated on single branches for wavevector transfer parallel to the helix
axis as inferred from well-defined peaks in the neutron spectra. In contrast,
for wavevector transfers perpendicular to the helix the spectral weight is
distributed among different branches of the magnon band structure as reflected
in broader features of the spectra. Taking into account the effects of
instrumental resolution, our experimental results are in excellent quantitative
agreement with parameter-free theoretical predictions. Whereas the dispersion
of the spin waves in MnSi appears to be approximately reciprocal at low
energies and small applied fields, the associated spin-resolved spectral weight
displays a pronounced non-reciprocity that implies a distinct non-reciprocal
response in the limit of vanishing uniform magnetization at zero magnetic
field.",1906.00221v3
2019-06-06,Kardar-Parisi-Zhang Scaling for an Integrable Lattice Landau-Lifshitz Spin Chain,"Recent studies report on anomalous spin transport for the integrable
Heisenberg spin chain at its isotropic point. Anomalous scaling is also
observed in the time-evolution of non-equilibrium initial conditions, the decay
of current-current correlations, and non-equilibrium steady state averages.
These studies indicate a space-time scaling with $x \sim t^{2/3}$ behavior at
the isotropic point, in sharp contrast to the ballistic form $x \sim t$
generically expected for integrable systems. In our contribution we study the
scaling behavior for the integrable lattice Landau-Lifshitz spin chain. We
report on equilibrium spatio-temporal correlations and dynamics with step
initial conditions. Remarkably, for the case with zero mean magnetization, we
find strong evidence that the scaling function is identical to the one obtained
from the stationary stochastic Burgers equation, alias Kardar-Parisi-Zhang
equation. In addition, we present results for the easy-plane and easy-axis
regimes for which, respectively, ballistic and diffusive spin transport is
observed, whereas the energy remains ballistic over the entire parameter
regime.",1906.02760v2
2019-07-18,Understanding the Linewidth of the ESR Spectrum Detected by a Single NV Center in Diamond,"Spectral analysis of electron spin resonance (ESR) is a powerful technique
for various investigations including characterization of spin systems,
measurements of spin concentration, and probing spin dynamics. The
nitrogen-vacancy (NV) center in diamond is a promising magnetic sensor enabling
improvement of ESR sensitivity to the level of a single spin. Therefore,
understanding the nature of NV-detected ESR (NV-ESR) spectrum is critical for
applications to nanoscale ESR. Within this work we investigate the linewidth of
NV-ESR from single substitutional nitrogen centers (called P1 centers). NV-ESR
is detected by a double electron-electron resonance (DEER) technique. By
studying the dependence of the DEER excitation bandwidth on NV-ESR linewidth,
we find that the spectral resolution is improved significantly and eventually
limited by inhomogeneous broadening of the detected P1 ESR. Moreover, we show
that the NV-ESR linewidth can be as narrow as 0.3 MHz.",1907.08156v1
2019-07-23,Optical quantum nondemolition measurement of a solid-state spin without a cycling transition,"Optically-interfaced spins in the solid state are a promising platform for
quantum technologies. A crucial component of these systems is high-fidelity,
projective measurement of the spin state. In previous work with laser-cooled
atoms and ions, and solid-state defects, this has been accomplished using
fluorescence on an optical cycling transition; however, cycling transitions are
not ubiquitous. In this work, we demonstrate that modifying the electromagnetic
environment using an optical cavity can induce a cycling transition in a
solid-state atomic defect. By coupling a single Erbium ion defect to a
telecom-wavelength silicon nanophotonic device, we enhance the cyclicity of its
optical transition by a factor of more than 100, which enables single-shot
quantum nondemolition readout of the ion's spin with 94.6% fidelity. We use
this readout to probe coherent dynamics and relaxation of the spin. This
approach will enable quantum technologies based on a much broader range of
atomic defects.",1907.09992v1
2019-07-28,Dirac Wire,"The interplay of photon spin and orbital angular momentum (OAM) in the
optical fiber (1D waveguide) has recently risen to the forefront of quantum
nanophotonics. Here, we introduce the fermionic dual of the optical fiber, the
Dirac wire, which exhibits unique electronic spin and OAM properties arising
from confined solutions of the Dirac equation. The Dirac wires analyzed here
represent cylindrical generalizations of the Jackiw-Rebbi domain wall and the
minimal topological insulator, which are of significant interest in
spintronics. We show the unique longitudinal spin arising from electrons
confined to propagation in a wire, an effect which is fundamentally prohibited
in planar geometries. Our work sheds light on the universal spatial dynamics of
electron spin in confined geometries and the duality between electronic and
photonic spin.",1907.12151v1
2019-09-27,Thermally driven two-magnet nano-oscillator with large spin-charge conversion,"Next-generation spintronic applications require material properties that can
be hardly met by one material candidate. Here we demonstrate that by combining
insulating and metallic magnets, enhanced spin-charge conversion and
energy-efficient thermal spin currents can be realized. We develop a nanowire
device consisting of an yttrium iron garnet and permalloy bi-layer. An
interfacial temperature gradient drives the nanowire magnetization into
auto-oscillations at gigahertz frequencies. Interfacial spin coupling and
magnetoresistance of the permalloy layer translate spin dynamics into sizable
microwave signals. The results show prospect for energy-efficient spintronic
devices and present an experimental realization of magnon condensation in a
heterogeneous magnetic system.",1909.12445v1
2019-10-14,Generation of atomic spin orientation with a linearly polarised beam in room-temperature alkali-metal vapour,"Traditionally, atomic spin orientation is achieved by the transfer of angular
momentum from polarised light to an atomic system. We demonstrate the mechanism
of orientation generation in room-temperature caesium vapours that combines
three elements: optical pumping, non-linear spin dynamics and spin-exchange
collisions. Through the variation of the spin-exchange relaxation rate, the
transition between an aligned and an oriented atomic sample is presented. The
observation is performed by monitoring the atomic radio-frequency spectra. The
measurement configuration discussed, paves the way to simple and robust
radio-frequency atomic magnetometers that are based on a single low power laser
diode that approach the performance of multi-laser pump-probe systems.",1910.06131v2
2020-01-15,Doping and temperature evolution of pseudogap and spin-spin correlations in the two-dimensional Hubbard model,"Cluster perturbation theory is applied to the two-dimensional Hubbard
$t-t'-t''-U$ model to obtain doping and temperature dependent electronic
spectral function with $4 \times 4$ and 12-site clusters. It is shown that
evolution of the pseudogap and electronic dispersion with doping and
temperature is similar and in both cases it is significantly influenced by
spin-spin short-range correlations. When short-range magnetic order is weakened
by doping or temperature and Hubbard-I like electronic dispersion becomes more
pronounced, the Fermi arc turns into large Fermi surface and the pseudogap
closes. It is demonstrated how static spin correlations impact the overall
dispersion's shape and how accounting for dynamic contributions leads to
momentum-dependent spectral weight at the Fermi surface and broadening effects.",2001.05143v2
2020-01-27,Acoustic ferromagnetic resonance and spin pumping induced by surface acoustic waves,"Voltage induced magnetization dynamics of magnetic thin films is a valuable
tool to study anisotropic fields, exchange couplings, magnetization damping and
spin pumping mechanism. A particularly well established technique is the
ferromagnetic resonance (FMR) generated by the coupling of microwave photons
and magnetization eigenmodes in the GHz range. Here we review the basic
concepts of the so-called acoustic ferromagnetic resonance technique (a-FMR)
induced by the coupling of surface acoustic waves (SAW) and magnetization of
thin films. Interestingly, additional to the benefits of the microwave excited
FMR technique, the coupling between SAW and magnetization also offers fertile
ground to study magnon-phonon and spin rotation couplings. We describe the
in-plane magnetic field angle dependence of the a-FMR by measuring the
absorption / transmission of SAW and the attenuation of SAW in the presence of
rotational motion of the lattice, and show the consequent generation of spin
current by acoustic spin pumping.",2001.09581v1
2020-02-10,Relativistic dissipative spin dynamics in the relaxation time approximation,"The concept of the Wigner function is used to construct a semi-classical
kinetic theory describing the evolution of the axial-current phase-space
density of spin-1/2 particles in the relaxation time approximation. The
resulting approach can be used to study spin-polarization effects in
relativistic matter, in particular, in heavy-ion collisions. An expression for
the axial current based on the classical treatment of spin is also introduced
and we show that it is consistent with earlier calculations using Wigner
functions. Finally, we derive non-equilibrium corrections to the spin tensor,
which are used to define, for the first time, the structure of spin transport
coefficients in relativistic matter.",2002.03937v2
2020-02-26,Quantum Entangled Fractional Topology and Curvatures,"We propose a two-spin quantum-mechanical model with applied magnetic fields
acting on the Poincar\'e-Bloch sphere, to reveal a new class of topological
energy bands with Chern number one half for each spin-1/2. The mechanism behind
this fractional topology is a two-spin product state at the north pole and a
maximally entangled state close to the south pole. The fractional Chern number
of each spin can be measured through the magnetizations at the poles. We study
a precise protocol where the spin dynamics in time reflects the Landau-Zener
physics associated with energy band crossing effects. We show a correspondence
between the two-spin system and topological bilayer models on a honeycomb
lattice. These models describe semimetals with a nodal ring surrounding the
region of entanglement.",2002.11823v5
2020-04-15,Effective Spin Foam Models for Four-Dimensional Quantum Gravity,"A number of approaches to four-dimensional quantum gravity, such as loop
quantum gravity and holography, situate areas as their fundamental variables.
However, this choice of kinematics can easily lead to gravitational dynamics
peaked on flat spacetimes. We show that this is due to how regions are glued in
the gravitational path integral via a discrete spin foam model. We introduce a
family of `effective' spin foam models that incorporate a quantum area
spectrum, impose gluing constraints as strongly as possible, and leverage the
discrete general relativity action to specify amplitudes. These effective spin
foam models avoid flatness in a restricted regime of the parameter space. The
simpler effective spin foam models will be useful for numerical studies and in
the investigation of coarse graining and renormalization.",2004.07013v2
2020-04-21,Ultrafast antiferromagnetic switching in NiO induced by spin transfer torques,"NiO is a prototypical antiferromagnet with a characteristic resonance
frequency in the THz range. From atomistic spin dynamics simulations that take
into account the crystallographic structure of NiO, and in particular a
magnetic anisotropy respecting its symmetry, we describe antiferromagnetic
switching at THz frequency by a spin transfer torque mechanism. Sub-picosecond
S-state switching between the six allowed stable spin directions is found for
reasonably achievable spin currents, like those generated by laser induced
ultrafast demagnetization. A simple procedure for picosecond writing of a
six-state memory is described, thus opening the possibility to speed up current
logic of electronic devices by several orders of magnitude.",2004.09822v3
2020-04-24,The Colored Noise of Magnetic Monopoles: Subdiffusion in a Coevolving Vacuum and Spin Ice Exponents,"We relate the anomalous noise found experimentally in spin ice to the
subdiffusion of magnetic monopoles. Because monopoles are emergent particles,
they do not move in a structureless vacuum. Rather, the underlying spin
ensemble filters the thermal white noise, leading to non-trivial coevolution.
Thus, monopoles can be considered as random walkers under the effect of
stochastic forces only as long as those are not trivially white, but instead
subsume the evolution of the spin vacuum. Via this conceptualization, we
conjecture relations between the color of the noise and other observables, such
as relaxation time, monopole density, the dynamic exponent, and the order of
the annihilation reaction, which lead us to introduce spin ice specific
critical exponents in a neighborhood of the ice manifold.",2004.11965v3
2020-04-27,Emergence and disruption of spin-charge separation in one-dimensional repulsive fermions,"At low temperature, collective excitations of one-dimensional (1D)
interacting fermions exhibit spin-charge separation, a unique feature predicted
by the Tomonaga-Luttinger liquid (TLL) theory, but a rigorous understanding
remains challenging. Using the thermodynamic Bethe Ansatz (TBA) formalism, we
analytically derive universal properties of a 1D repulsive spin-1/2 Fermi gas
with arbitrary interaction strength. We show how spin-charge separation emerges
from the exact TBA formalism, and how it is disrupted by the interplay between
the two degrees of freedom which brings us beyond the TLL paradigm. Based on
the exact low-lying excitation spectra, we further evaluate the spin and charge
dynamical structure factors (DSFs). The peaks of the DSFs exhibit
distinguishable propagating velocities of spin and charge as functions of
interaction strength, which can be observed by Bragg spectroscopy with
ultracold atoms.",2004.12637v3
2020-04-27,Numerical analysis of spin foam dynamics and the flatness problem,"In this paper, we apply a recently proposed numerical algorithm for finding
stationary phase points in spin foam amplitudes. We study a spin foam amplitude
with three vertices and a bulk face in 4d BF theory. We fix the boundary
coherent states to three possible triangulations, one with zero deficit angle
on the bulk face and two with non-zero deficit angle. We compute the amplitude
numerically and we find a stationary phase point already at low spins in all
the three cases. We comment on how this result contrasts with the claims of
flatness problem in spin foam theories. We point out where these arguments may
be misleading and we propose further computations to definitively answer the
question.",2004.12911v3
2020-12-04,"Growth, strain and spin orbit torques in epitaxial NiMnSb films sputtered on GaAs","We report current-induced spin torques in epitaxial NiMnSb films on a
commercially available epi-ready GaAs substrate. The NiMnSb was grown by
co-sputtering from three targets using optimised parameter. The films were
processed into micro-scale bars to perform current-induced spin-torque
measurements. Magnetic dynamics were excited by microwave currents and electric
voltages along the bars were measured to analyse the symmetry of the
current-induced torques. We found that the extracted symmetry of the spin
torques matches those expected from spin-orbit interaction in a tetragonally
distorted half-Heusler crystal. Both field-like and damping-like torques are
observed in all the samples characterised, and the efficiency of the
current-induced torques is comparable to that of ferromagnetic metal/heavy
metal bilayers.",2012.02568v4
2020-12-25,Asymptotic boundary KZB operators and quantum Calogero-Moser spin chains,"Asymptotic boundary KZB equations describe the consistency conditions of
degenerations of correlation functions for boundary Wess-Zumino-Witten-Novikov
conformal field theory on a cylinder. In the first part of the paper we define
asymptotic boundary KZB operators for connected real semisimple Lie groups G
with finite center. We prove their main properties algebraically using
coordinate versions of Harish-Chandra's radial component map. We show that
their commutativity is governed by a system of equations involving coupled
versions of classical dynamical Yang-Baxter equations and reflection equations.
We use the coordinate radial components maps to introduce a new class of
quantum superintegrable systems, called quantum Calogero-Moser spin chains. A
quantum Calogero-Moser spin chain is a mixture of a quantum spin Calogero-Moser
system associated to the restricted root system of G and an one-dimensional
spin chain with two-sided reflecting boundaries. The asymptotic boundary KZB
operators provide explicit expressions for its first order quantum
Hamiltonians. We also explicitly describe the Schr\""odinger operator.",2012.13497v1
2021-01-19,Equal-time kinetic equations in a rotational field,"We investigate quantum kinetic theory for a massive fermion system under a
rotational field. From the Dirac equation in curved space we derive the
complete set of kinetic equations for the spin components of the covariant and
equal-time Wigner functions. While the particles are no longer on a mass shell
in general case due to the rotation-spin coupling, there are always only two
independent components, which can be taken as the number and spin densities.
With the help from the off-shell constraint we obtain the closed transport
equations for the two independent components in classical limit and at quantum
level. The classical rotation-orbital coupling controls the dynamical evolution
of the number density, but the quantum rotation-spin coupling explicitly
changes the spin density.",2101.07596v1
2021-01-21,Spin-Conserved and Spin-Flip Optical Excitations From the Bethe-Salpeter Equation Formalism,"Like adiabatic time-dependent density-functional theory (TD-DFT), the
Bethe-Salpeter equation (BSE) formalism of many-body perturbation theory, in
its static approximation, is ""blind"" to double (and higher) excitations, which
are ubiquitous, for example, in conjugated molecules like polyenes. Here, we
apply the spin-flip \textit{ansatz} (which considers the lowest triplet state
as the reference configuration instead of the singlet ground state) to the BSE
formalism in order to access, in particular, double excitations. The present
scheme is based on a spin-unrestricted version of the $GW$ approximation
employed to compute the charged excitations and screened Coulomb potential
required for the BSE calculations. Dynamical corrections to the static BSE
optical excitations are taken into account via an unrestricted generalization
of our recently developed (renormalized) perturbative treatment. The
performance of the present spin-flip BSE formalism is illustrated by computing
excited-state energies of the beryllium atom, the hydrogen molecule at various
bond lengths, and cyclobutadiene in its rectangular and square-planar
geometries.",2101.08680v2
2000-06-20,Microscopic Theory of Dipole-Exchange Spin Waves in Ferromagnetic Films: Linear and Nonlinear Processes,"The linear and nonlinear processes in ferromagnetic films at low temperatures
T<< Tc are studied in a microscopic theory. Both the long-range magnetic
dipole-dipole and the Heisenberg exchange interactions to nearest and
next-nearest neighbors are included. The results obtained for the linearized
spin-wave spectrum are compared with previous macroscopic theories. For
ultrathin films (or for large wave vectors) the microscopic theory provides
important corrections. The nonlinear dynamics of the spin waves are studied
through a finite-temperature perturbation theory based on Feynman diagrams. We
obtain explicit results for the energy shift and damping (or reciprocal
lifetime) of the dipole-exchange spin waves due to all possible three-magnon
and four-magnon processes involving combinations of the surface and quantized
bulk spin waves at low temperatures. To investigate different dipole
interaction strengths (relative to the exchange) numerical results are
presented using parameters for Fe, EuO, and GdCl3.",0006308v1
2000-06-22,Quantum and classical dynamics in complex one-dimensional antiferromagnets,"Of great recent interest in condensed matter physics are phenomena of
coexistence of quantum and classical properties in the same material. Such
duality occurs in certain mixed-spin antiferromagnets composed of quantum spin
chains interacting through ``auxiliary'' magnetic ions. In this category are
linear-chain rare earth nickelates that exhibit a seemingly paradoxical
co-existence of long-range magnetic order and one-dimensional gapped quantum
spin excitations at low temperatures. In the present paper we propose a unified
physical description of these compounds, supported by recent neutron
diffraction and inelastic scattering studies. Our basic concept is the
effective separation between low-frequency classical and high-frequency quantum
spin correlations. This interpretation enables experimental measurements of
some previously inaccessible fundamental properties of quantum spin chains, and
predicts new exotic magnetic excitations and mechanisms of long-range ordering
in complex quantum magnets.",0006350v1
2017-05-09,Local optical control of the resonant dipole-dipole interaction between Rydberg atoms,"We report on the local control of the transition frequency of a spin-$1/2$
encoded in two Rydberg levels of an individual atom by applying a
state-selective light shift using an addressing beam. With this tool, we first
study the spectrum of an elementary system of two spins, tuning it from a
non-resonant to a resonant regime, where ""bright"" (superradiant) and ""dark""
(subradiant) states emerge. We observe the collective enhancement of the
microwave coupling to the bright state. We then show that after preparing an
initial single spin excitation and letting it hop due to the spin-exchange
interaction, we can freeze the dynamics at will with the addressing laser,
while preserving the coherence of the system. In the context of quantum
simulation, this scheme opens exciting prospects for engineering inhomogeneous
XY spin Hamiltonians or preparing spin-imbalanced initial states.",1705.03293v1
2017-05-24,Bound states of fractionalized excitations in a modulated Kitaev spin liquid,"Fractionalization is a hallmark of spin-liquid behavior; it typically leads
to response functions consisting of continua instead of sharp modes. However,
microscopic processes can enable the formation of short-distance bound states
of fractionalized excitations, despite asymptotic deconfinement. Here we study
such bound-state formation for the $Z_2$ spin liquid realized in Kitaev's
honeycomb compass model, supplemented by a kekule distortion of the lattice.
Bound states between flux pairs and Majorana fermions form in the Majorana band
gaps. We calculate the dynamic spin susceptibility and show that bound states
lead to sharp modes in the magnetic response of the spin liquid, with the
momentum dependence of the corresponding spectral weight encoding internal
symmetry of the bound state. As a byproduct, we also show that isolated fluxes
may produce Majorana bound states at exactly zero energy. Generalizations and
implications of the results are discussed.",1705.08913v1
2017-09-01,Algebraic Charge Dynamics of Quantum Spin Liquid b'-EtMe3Sb[Pd(dmit)2]2,"Nuclear spin-lattice (1/T1) and spin-spin (1/T2) relaxation rates of the
cation sites of a quantum spin-liquid candidate b'-EtMe3Sb[Pd(dmit)2]2 and its
deuterated sample are presented. The enhanced 1/T1 of 1H and 2D are well
analyzed considering the rotations of methyl- and ethyl-groups of the cation
with the activation energies of 200K and 1200K respectively. The 1/T1 and 1/T2
at the Sb site that is located on the 2-fold rotation axis remain active down
to the lowest temperature with an algebraic temperature dependence of the
correlation time as has been observed in the ac response of the dielectric
constants.",1709.00156v2
2017-09-05,Newton's second law in spin-orbit torque,"Spin-orbit torque (SOT) refers to the excitation of magnetization dynamics
via spin-orbit coupling under the application of a charged current. In this
work, we introduce a simple and intuitive description of the SOT in terms of
spin force. In Rashba spin-orbit coupling system, the damping-like SOT can be
expressed as ${\mathbf T}^\mathrm{so}={\mathbf R}_c\times {\mathbf F}^{{\mathrm
{so}}}$, in analogy to the classical torque-force relation, where $R_c$ is the
effective radius characterizing the Rashba splitting in the momentum space. As
a consequence, the magnetic energy is transferred to the conduction electrons,
which dissipates through Joule heating at a rate of $({\mathbf j}_e\cdot
{\mathbf F}^{\mathrm {so}})$, with $j_e$ being the applied current. Finally, we
propose an experimental verification of our findings via measurement of the
anisotropic magnetoresistance effect.",1709.01302v2
2017-09-27,Dynamic transport in a quantum wire driven by spin-orbit interaction,"We consider a gated one-dimensional (1D) quantum wire disturbed in a
contactless manner by an alternating electric field produced by a tip of a
scanning probe microscope. In this schematic 1D electrons are driven not by a
pulling electric field but rather by a non-stationary spin-orbit interaction
(SOI) created by the tip. We show that a charge current appears in the wire in
the presence of the Rashba SOI produced by the gate net charge and image
charges of 1D electrons induced on the gate (iSOI). The iSOI contributes to the
charge susceptibility by breaking the spin-charge separation between the
charge- and spin collective excitations, generated by the probe. The velocity
of the excitations is strongly renormalized by SOI, which opens a way to
fine-tune the charge and spin response of 1D electrons by changing the gate
potential. One of the modes softens upon increasing the gate potential to
enhance the current response as well as the power dissipated in the system.",1709.09530v3
2017-11-03,Dipolarly-Coupled Chaotic Quantum Spin Systems,"We numerically study quantum chaos properties of long-range XXZ dipolar
Hamiltonian spin systems. Two geometries are considered: (i) an open chain with
19 spins, (ii) a face-centered cubic lattice with 14 spins. Energy
level-spacing distribution indicates that the three-dimensional geometry is
highly chaotic, while the one-dimensional system is mildly chaotic for small
chains, but has increasing chaoticity for larger chains. We also look at
statistical properties of energy eigenvectors, and of one- and two-body local
observables. Finally, we present some preliminary results on time-evolution,
local spin dynamics and thermalization. Quantum chaos may have important
implications for ""scrambling"" of quantum information, in both condensed matter
systems and in astrophysical applications such as black holes.",1711.01948v1
2017-11-06,Quantum gap and spin-wave excitations in the Kitaev model on a triangular lattice,"We study the effects of quantum fluctuations on the dynamical generation of a
gap and on the evolution of the spin-wave spectra of a frustrated magnet on a
triangular lattice with bond-dependent Ising couplings, analog of the Kitaev
honeycomb model. The quantum fluctuations lift the subextensive degeneracy of
the classical ground-state manifold by a quantum order-by-disorder mechanism.
Nearest-neighbor chains remain decoupled and the surviving discrete degeneracy
of the ground state is protected by a hidden model symmetry. We show how the
four-spin interaction, emergent from the fluctuations, generates a spin gap
shifting the nodal lines of the linear spin-wave spectrum to finite energies.",1711.02016v1
2017-11-08,Collinear Spin-density-wave Order and Anisotropic Spin Fluctuations in the Frustrated $J_1$--$J_2$ Chain Magnet NaCuMoO$_4$(OH),"The phase diagram of the quasi-one-dimensional magnet NaCuMoO$_4$(OH) is
established through single-crystal NMR and heat-capacity measurements. The
$^{23}$Na and $^1$H NMR experiments indicate a spiral and a collinear
spin-density-wave (SDW) order below and above $B_c$ = 1.5-1.8 T, respectively.
Moreover, in the paramagnetic state above the SDW transition temperature, the
nuclear spin-lattice relaxation rate $1/T_1$ indicates anisotropic spin
fluctuations that have gapped excitations in the transverse spectrum but
gapless ones in the longitudinal spectrum. These static and dynamic properties
are well described by a theoretical model assuming quasi-one-dimensional chains
with competing ferromagnetic nearest-neighbor interactions $J_1$ and
antiferromagnetic next-nearest-neighbor interactions $J_2$ ($J_1$-$J_2$
chains). Because of the excellent crystal quality and good one dimensionality,
NaCuMoO$_4$(OH) is a promising compound to elucidate the unique physics of the
frustrated $J_1$-$J_2$ chain.",1711.03175v1
2017-11-24,Quantum mechanical treatment of large spin baths,"The electronic spin in quantum dots can be described by central spin models
(CSMs) with a very large number $N_\mathrm{eff} \approx 10^4$ to $10^6$ of bath
spins posing a tremendous challenge to theoretical simulations. Here, a fully
quantum mechanical theory is developed for the limit $N_\mathrm{eff} \to
\infty$ by means of iterated equations of motion (iEoM). We find that the CSM
can be mapped to a four-dimensional impurity coupled to a non-interacting
bosonic bath in this limit. Remarkably, even for infinite bath the CSM does not
become completely classical. The data obtained by the proposed iEoM approach is
tested successfully against data from other, established approaches. Thus, the
iEoM mapping extends the set of theoretical tools which can be used to
understand the spin dynamics in large CSMs.",1711.08919v2
2018-03-07,Spin excitations and thermodynamics of the t-J model on the honeycomb lattice,"We present a spin-rotation-invariant Green-function theory for the dynamic
spin susceptibility in the spin-1/2 antiferromagnetic t-J Heisenberg model on
the honeycomb lattice. Employing a generalized mean-field approximation for
arbitrary temperatures and hole dopings, the electronic spectrum of
excitations, the spin-excitation spectrum and thermodynamic quantities
(two-spin correlation functions, staggered magnetization, magnetic
susceptibility, correlation length) are calculated by solving a coupled system
of self-consistency equations for the correlation functions. The temperature
and doping dependence of the magnetic (uniform static) susceptibility is
ascribed to antiferromagnetic short-range order. Our results on the doping
dependencies of the magnetization and susceptibility are analyzed in comparison
with previous results for the t_J model on the square lattice.",1803.03140v1
2018-03-19,Spin-orbital-lattice entangled states in cubic $d^1$ double perovskites,"Interplay of spin-orbit coupling and vibronic coupling on heavy $d^1$ site of
cubic double perovskites is investigated by ab initio calculations. The
stabilization energy of spin-orbital-lattice entangled states is found
comparable to or larger than the exchange interactions, suggesting the presence
of Jahn-Teller dynamics in the systems. In Ba$_2$YMoO$_6$, the pseudo JT
coupling enhances the mixing of the ground and excited spin-orbit multiplet
states, which results in strong temperature dependence of effective magnetic
moments. The entanglement of the spin and lattice degrees of freedom induces a
strong magneto-elastic response. This multiferroic effect is at the origin of
the recently reported breaking of local point symmetry accompanying the
development of magnetic ordering in Ba$_2$NaOsO$_6$.",1803.06945v3
2018-03-19,Valence and Spin fluctuations in Mn-doped ferroelectric BaTiO3,"We study Mn substitution for Ti in BaTiO3 with and without compensating
oxygen vacancies using density functional theory (DFT) in combination with
dynamical mean field theory (DMFT). We find strong charge and spin
fluctuations. Without compensating oxygen vacancies, the ground state is found
to be a quantum superposition of two distinct atomic valences, 3d4 and 3d5.
Introducing a compensating oxygen vacancy at a neighboring site reduces both
charge and spin fluctuations due to the reduction of electron hopping from Mn
to its ligands. As a consequence, valence fluctuations are reduced, and is
closely fixed to the high spin 3d5 state. Here we show that inclusion of charge
and spin fluctuations is necessary to obtain an accurate ground state of
transition metal doped ferroelectrics.",1803.07134v3
2018-06-11,Quantum Spin Fragmentation in Kagome Ice Ho3Mg2Sb3O14,"A promising route to realize entangled magnetic states combines geometrical
frustration with quantum-tunneling effects. Spin-ice materials are canonical
examples of frustration, and Ising spins in a transverse magnetic field are the
simplest many-body model of quantum tunneling. Here, we show that the tripod
kagome lattice material Ho3Mg2Sb3O14 unites an ice-like magnetic degeneracy
with quantum-tunneling terms generated by an intrinsic splitting of the Ho3+
ground-state doublet, realizing a frustrated transverse Ising model. Using
neutron scattering and thermodynamic experiments, we observe a
symmetry-breaking transition at T*~0.32 K to a remarkable quantum state with
three peculiarities: a continuous magnetic excitation spectrum down to T~0.12K;
a macroscopic degeneracy of ice-like states; and a fragmentation of the spin
into periodic and aperiodic components strongly affected by quantum
fluctuations. Our results establish that Ho3Mg2Sb3O14 realizes a
spin-fragmented state on the kagome lattice, with intrinsic quantum dynamics
generated by a homogeneous transverse field.",1806.04081v1
2018-06-21,Spin transfer torque induced paramagnetic resonance,"We show how the spin-transfer torque generated by an ac voltage may be used
to excite a paramagnetic resonance of an atomic spin deposited on a metallic
surface. This mechanism is independent of the environment of the atom and may
explain the ubiquity of the paramagnetic resonance reported by Baumann
$\textit{et al.}$ [$\href{http://dx.doi.org/10.1126/science.aac8703}{Science
\textbf{350}, 417 (2015)}$]. The current and spin dynamics are modeled by a
time-dependent Redfield master equation generalized to account for the periodic
driven voltage. Our approach shows that the resonance effect is a consequence
of the nonlinearity of the coupling between the magnetic moment and the
spin-polarized current which generates a large second-harmonic amplitude that
can be measured in the current signal.",1806.08260v2
2018-06-25,Quench dynamics of quantum spin models with flat bands of excitations,"We investigate the unitary evolution following a quantum quench in quantum
spin models possessing a (nearly) flat band in the linear excitation spectrum.
Inspired by the perspective offered by ensembles of individually trapped
Rydberg atoms, we focus on the paradigmatic trasverse-field Ising model on two
dimensional lattices featuring a flat band as a result of destructive
interference effects (Lieb and Kagom\'e lattice); or a nearly flat band due to
a strong energy mismatch among sublattices (triangular lattice). Making use of
linear spin-wave theory, we show that quantum quenches, equipped with
single-spin imaging, can directly reveal the spatially localized nature of the
dispersionless excitations, and their slow propagation or lack of propagation
altogether. Moreover we show that Fourier analysis applied to the post-quench
time evolution of wavevector-dependent quantities allows for the spectroscopic
reconstruction of the flat bands. Our results pave the way for future
experiments with Rydberg quantum simulators, which can extend our linear
spin-wave study to the fully nonlinear regime, characterized by the appearance
of dense, strongly interacting gases of dispersionless excitations.",1806.09722v1
2018-07-04,Spin Waves in Detwinned BaFe$_2$As$_2$,"Understanding magnetic interactions in the parent compounds of
high-temperature superconductors forms the basis for determining their role for
the mechanism of superconductivity. For parent compounds of iron pnictide
superconductors such as $A$Fe$_2$As$_2$ ($A=$ Ba, Ca, Sr), although spin
excitations have been mapped out throughout the entire Brillouin zone (BZ),
measurements were carried out on twinned samples and did not allow for a
conclusive determination of the spin dynamics. Here we use inelastic neutron
scattering to completely map out spin excitations of $\sim$100\% detwinned
BaFe$_2$As$_2$. By comparing observed spectra with theoretical calculations, we
conclude that the spin excitations can be well described by an itinerant model
with important contributions from electronic correlations.",1807.01471v1
2018-07-13,Spin-orbit coupling and correlations in three-orbital systems,"We investigate the influence of spin-orbit coupling $\lambda$ in
strongly-correlated multiorbital systems that we describe by a three-orbital
Hubbard-Kanamori model on a Bethe lattice. We solve the problem at all integer
fillings $N$ with the dynamical mean-field theory using the continuous-time
hybridization expansion Monte Carlo solver. We investigate how the
quasiparticle renormalization $Z$ varies with the strength of spin-orbit
coupling. The behavior can be understood for all fillings except $N=2$ in terms
of the atomic Hamiltonian (the atomic charge gap) and the polarization in the
$j$-basis due to spin-orbit induced changes of orbital degeneracies and the
associated kinetic energy. At $N=2$, $\lambda$ increases $Z$ at small $U$ but
suppresses it at large $U$, thus eliminating the characteristic Hund's metal
tail in $Z(U)$. We also compare the effects of the spin-orbit coupling to the
effects of a tetragonal crystal field. Although this crystal field also lifts
the orbital degeneracy, its effects are different, which can be understood in
terms of the different form of the interaction Hamiltonian expressed in the
respective diagonal single-particle basis.",1807.05106v2
2018-07-18,Rapid filling of the spin gap with temperature in the Schwinger-boson mean-field theory of the antiferromagnetic Heisenberg kagome model,"Using Schwinger-boson mean-field theory, we calculate the dynamic spin
structure factor at low temperatures $0<T\ll J$ for the spin-$1/2$
antiferromagnetic Heisenberg kagome model, within the gapped $\mathbb{Z}_2$
spin liquid phase Ansatz. We find that the spectral gap rapidly fills with
temperature, with robust low-energy spectral weight developing by a temperature
of $\Delta/3$, where the spin gap is $2\Delta$ (i.e., $\Delta$ is the spinon
gap), before any appreciable rise in spinon density or change in
zero-temperature mean-field parameters. This is due to deconfinement of spinons
which leads to terms suppressed only by $\exp(-\Delta/T)$. At still higher
temperatures, the spinon density increases rapidly leading to a breakdown of
the Schwinger-boson mean-field approach. We suggest that if the impurity-free
spectral functions can be obtained through neutron scattering experiments on
kagome herbertsmithites, temperature dependence of the subgap weight can
provide distinct signatures of a $\mathbb{Z}_2$ quantum spin liquid.",1807.07071v2
2018-07-19,Anomalous direction for skyrmion bubble motion,"Magnetic skyrmions are localized topological excitations that behave as
particles and can be mobile, with great potential for novel data storage
devices. In this work, the current-induced dynamics of large skyrmion bubbles
is studied. When skyrmion motion in the direction opposite to the electron flow
is observed, this is usually interpreted as a perpendicular spin current
generated by the spin Hall effect exerting a torque on the chiral N\'{e}el
skyrmion. By designing samples in which the direction of the net generated spin
current can be carefully controlled, we surprisingly show that skyrmion motion
is always against the electron flow, irrespective of the net vertical
spin-current direction. We find that a negative bulk spin-transfer torque is
the most plausible explanation for the observed results, which is qualitatively
justified by a simple model that captures the essential behaviour. These
findings demonstrate that claims about the skyrmion chirality based on their
current-induced motion should be taken with great caution.",1807.07365v1
2018-08-01,The generalized gradient approximation kernel in time-dependent density functional theory,"A complete understanding of a material requires both knowledge of the excited
states as well as of the ground state. In particular, the low energy
excitations are of utmost importance while studying the electronic, magnetic,
dynamical, and thermodynamical properties of the material. Time-Dependent
Density Functional Theory (TDDFT), within the linear regime, is a successful
\textit{ab-initio} method to access the electronic charge and spin excitations.
However, it requires an approximation to the exchange-correlation (XC) kernel
which encapsulates the effect of electron-electron interactions in the
many-body system. In this work we derive and implement the spin-polarized XC
kernel for semi-local approximations such as the adiabatic Generalized Gradient
Approximation (AGGA). This kernel has a quadratic dependence on the wavevector,
{\bf q}, of the perturbation, however the impact of this on the electron energy
loss spectra (EELS) is small. Although the GGA functional is good in predicting
structural properties, it generality overestimates the exchange spin-splitting.
This leads to higher magnon energies, as compared to both ALDA and experiment.
In addition, interaction with the Stoner spin-flip continuum is enhanced by
AGGA, which strongly suppresses the intensity of spin-waves.",1808.00215v1
2018-08-02,Quantum kinetic theory of spin-transfer torque and magnon-assisted transport in nanostructures,"We theoretically investigate the role of spin fluctuations in charge
transport through a magnetic junction. Motivated by recent experiments that
measure a nonlinear dependence of the current on electrical bias, we develop a
systematic understanding of the interplay of charge and spin dynamics in
nanoscale magnetic junctions. Our model captures two distinct features arising
from these fluctuations: magnon-assisted transport and the effect of
spin-transfer torque on the magnetoconductance. The latter stems from magnetic
misalignment in the junction induced by spin-current fluctuations. As the
temperature is lowered, inelastic quantum scattering takes over thermal
fluctuations, exhibiting signatures that make it readily distinguishable from
magnon-assisted transport.",1808.00777v2
2018-08-03,Winding up quantum spin helices: How avoided level crossings exile classical topological protection,"A magnetic helix can be wound into a classical Heisenberg chain by fixing one
end while rotating the other one. We show that in quantum Heisenberg chains
\new{of finite length}, the magnetization slips back to the trivial state
beyond a finite turning angle. Avoided level crossings thus undermine classical
topological protection. Yet, for special values of the axial Heisenberg
anisotropy, stable spin helices form again, which are non-locally entangled.
Away from these sweet spots, spin helices can be stabilized dynamically or by
dissipation. For half-integer spin chains of odd length, a spin slippage state
and its Kramers partner define a qubit with a non-trivial Berry connection.",1808.01283v2
2018-12-05,Spin-imbalance-induced transverse magnetization in the Hofstadter-Hubbard model,"The fermionic, time-reversal invariant Hofstadter-Hubbard model with a
population difference between the two spin states is investigated. In the
strongly interacting regime, where the system can be described by an effective
spin model, we find an exotic spin structure by means of classical Monte-Carlo
calculations. Remarkably, this spin structure exhibits a transverse net
magnetization perpendicular to the magnetization induced by the population
imbalance. It is thus inherently different from canted antiferromagnetism. We
further investigate effects of quantum fluctuations within the dynamical
mean-field approximation and obtain a rich phase diagram including
ferromagnetic, anti-ferromagnetic, ferrimagnetic, and transverse magnetization
phases.",1812.02001v2
2018-12-20,Spin-Energy Correlation in Degenerate Weakly-Interacting Fermi Gases,"Weakly interacting Fermi gases exhibit rich collective dynamics in
spin-dependent potentials, arising from correlations between spin degrees of
freedom and conserved single atom energies, offering broad prospects for
simulating many-body quantum systems by engineering energy-space ""lattices,""
with controlled energy landscapes and site to site interactions. Using quantum
degenerate clouds of $^6$Li, confined in a spin-dependent harmonic potential,
we measure complex, time-dependent spin-density profiles, varying on length
scales much smaller than the cloud size. We show that a one-dimensional mean
field model, without additional simplifying approximations, quantitatively
predicts the observed fine structure. We measure the magnetic fields where the
scattering lengths vanish for three different hyperfine state mixtures to
provide new constraints on the collisional (Feshbach) resonance parameters.",1812.08832v4
2019-01-25,Observation of spin-orbit-dependent electron scattering using long-range Rydberg molecules,"We present experimental evidence for spin-orbit interaction of an electron as
it scatters from a neutral atom. The scattering process takes place within a
Rb$_2$ ultralong-range Rydberg molecule, consisting of a Rydberg atomic core, a
Rydberg electron, and a ground state atom. The spin-orbit interaction leads to
characteristic level splittings of vibrational molecular lines which we
directly observe via photoassociation spectroscopy. We benefit from the fact
that molecular states dominated by resonant $p$-wave interaction are
particularly sensitive to the spin-orbit interaction. Our work paves the way
for studying novel spin dynamics in ultralong-range Rydberg molecules.
Furthermore, it shows that the molecular setup can serve as a microlaboratory
to perform precise scattering experiments in the low-energy regime of a few
meV.",1901.08792v4
2019-02-08,Magnetization beyond the Ising limit of Ho$_2$Ti$_2$O$_7$,"We report that the local Ising anisotropy in pyrochlore oxides - the crucial
requirement for realizing the spin-ice state - can be broken by means of high
magnetic fields. For the case of the well-established classical spin-ice
compound Ho$_2$Ti$_2$O$_7$ the magnetization exceeds the angle-dependent
saturation value of the Ising limit using ultra-high fields up to 120 T.
However, even under such extreme magnetic fields full saturation cannot be
achieved. Crystal-electric-field calculations reveal that a level crossing for
two of the four ion positions leads to magnetization steps at 55 and 100 T. In
addition, we show that by using a field sweep rate in the range of the
spin-relaxation time the dynamics of the spin system can be probed. Exclusively
at 25 ns/T a new peak of the susceptibility appears around 2 T. We argue, this
signals the cross-over between spin-ice and polarized correlations.",1902.02990v1
2019-02-24,Evidence of a cluster spin-glass state in the B-site disordered perovskite SrTi0.5Mn0.5O3,"SrTi0.5Mn0.5O3 (STMO) is a chemically disordered perovskite having random
distribution of Ti and Mn over 1b site. Striking discrepancies about the
structural and magnetic properties of STMO demands detailed analysis which is
addressed. To explore the magnetic ground state of STMO, static and dynamic
magnetic properties were studied over a broad temperature range (2-300 K). The
dc, ac magnetization show a cusp like peak at Tf ~ 14 K, which exhibits field
and frequency dependence. The thermoremanent magnetization is characterized by
using stretched exponential function and characteristic time suggests the
existence of spin clusters. Also the other features observed in magnetic memory
effect, muon spin resonance/rotation and neutron powder diffraction confirm the
existence of cluster spin glass state in STMO, rather than the long range
ordered ground state. Intriguingly, the observed spin relaxation can be
attributed to the dilute magnetism due to non-magnetic doping at Mn-site and
competing antiferromagnetic and ferromagnetic interactions resulting from the
site disorder.",1902.08961v1
2019-04-01,Inelastic spin-wave scattering by Bloch domain wall flexure oscillations,"The calculations of the inelastic spin wave scattering by flexure vibrations
of the Bloch domain wall (Winters magnons) in thin magnetic films are
presented. The approach is based on the interaction of the propagating spin
waves with the dynamical emergent electromagnetic field generated by the moving
inhomogeneous magnetization texture (domain wall). The probability of the spin
wave scattering for the Winters magnon emission and absorption processes
essentially rises with the spin wave scattering angle increase up to 900. The
angular dependence of the scattering probability is essentially stronger for
the magnon absorption processes that allow distinguishing these elementary
emission/absorption processes experimentally.",1904.00596v1
2019-08-14,Spin-orbital glass transition in a model of a frustrated pyrochlore magnet without quenched disorder,"We show theoretically that spin and orbital degrees of freedom in the
pyrochlore oxide Y2Mo2O7, which is free of quenched disorder, can exhibit a
simultaneous glass transition, working as dynamical randomness to each other.
The interplay of spins and orbitals is mediated by the Jahn-Teller lattice
distortion that selects the choice of orbitals, which then generates variant
spin exchange interactions ranging from ferromagnetic to antiferromagnetic
ones. Our Monte Carlo simulations detect the power-law divergence of the
relaxation times and the negative divergence of both the magnetic and
dielectric non-linear susceptibilities, resolving the long-standing puzzle on
the origin of the disorder-free spin glass.",1908.05070v3
2019-11-07,Quantum Oscillations of Gilbert Damping in Ferromagnetic/Graphene Bilayer Systems,"We study the spin dynamics of a ferromagnetic insulator on which graphene is
placed. We show that the Gilbert damping is enhanced by the proximity exchange
coupling at the interface. The modulation of the Gilbert damping constant is
proportional to the product of the spin-up and spin-down densities of states of
graphene. Consequently, the Gilbert damping constant in a strong magnetic field
oscillates as a function of the external magnetic field that originates from
the Landau level structure of graphene. We find that a measurement of the
oscillation period enables the strength of the exchange coupling constant to be
determined. The results demonstrate in theory that the ferromagnetic resonance
measurements may be used to detect the spin resolved electronic structure of
the adjacent materials, which is critically important for future spin device
evaluations.",1911.02775v2
2019-11-08,Giant anisotropy of Gilbert damping in a Rashba honeycomb antiferromagnet,"Giant Gilbert damping anisotropy is identified as a signature of strong
Rashba spin-orbit coupling in a two-dimensional antiferromagnet on a honeycomb
lattice. The phenomenon originates in spin-orbit induced splitting of
conduction electron subbands that strongly suppresses certain spin-flip
processes. As a result, the spin-orbit interaction is shown to support an
undamped non-equilibrium dynamical mode that corresponds to an ultrafast
in-plane N\'eel vector precession and a constant perpendicular-to-the-plane
magnetization. The phenomenon is illustrated on the basis of a two dimensional
$s$-$d$ like model. Spin-orbit torques and conductivity are also computed
microscopically for this model. Unlike Gilbert damping these quantities are
shown to reveal only a weak anisotropy that is limited to the semiconductor
regime corresponding to the Fermi energy staying in a close vicinity of
antiferromagnetic gap.",1911.03408v1
2019-11-14,Correlation holes and slow dynamics induced by fractional statistics in gapped quantum spin liquids,"Realistic model Hamiltonians for quantum spin liquids frequently exhibit a
large separation of energy scales between their elementary excitations. At
intermediate, experimentally relevant temperatures, some excitations are sparse
and hop coherently, whereas others are thermally incoherent and dense. Here we
study the interplay of two such species of quasiparticle, dubbed spinons and
visons, which are subject to nontrivial mutual statistics -- one of the
hallmarks of quantum spin liquid behaviour. Our results for $\mathbb{Z}_2$
quantum spin liquids show an intriguing feedback mechanism, akin to the Nagaoka
effect, whereby spinons become localised on temperature-dependent patches of
expelled visons. This phenomenon has important consequences for the
thermodynamic and transport properties of the system, as well as for its
response to quenches in temperature. We argue that these effects can be
measured in experiments and may provide viable avenues for obtaining signatures
of quantum spin liquid behaviour.",1911.06331v2
2019-11-18,Spin transport in disordered long-range interacting spin chain,"Using a numerically exact technique we study spin transport and the evolution
of spin-density excitation profiles in a disordered spin-chain with long-range
interactions, decaying as a power-law, $r^{-\alpha}$ with distance and
$\alpha<2$. Our study confirms the prediction of recent theories that the
system is delocalized in this parameters regime. Moreover we find that for
$\alpha>3/2$ the underlying transport is diffusive with a transient
super-diffusive tail, similarly to the situation in clean long-range systems.
We generalize the Griffiths picture to long-range systems and show that it
captures the essential properties of the exact dynamics.",1911.07857v2
2019-11-21,Comprehensive Control of Metamagnetic Transition of Antiferromagnetic Mott Insulator Sr2IrO4 by in-situ Anisotropic Strain,"Metamagnetism in antiferromagnets exhibits distinct critical behaviors and
dynamics when invoking spin reversal and rotation. Here we show a 0.05%
anisotropic strain suffices to in-situ modulate the metamagnetic critical field
of the Mott insulator Sr2IrO4 by over 50%, enabling electrical switching of the
transition. Resonant x-ray scattering and model simulation reveal that the
transition is completely tuned from the spin-flop to spin-flip type as the
strain introduces C4-symmetry-breaking magnetic anisotropy. Simultaneous
transport study indicates the metamagnetic responses are reflected in the large
elasto- and magnetoconductance, highlighting the active charge degree of
freedom in the spin-orbit-coupled Mott state and its potential for
spin-electronics.",1911.09504v2
2019-11-25,Snell's law for spin waves at a 90-degree domain wall,"We report experimental observation of the refraction and re ection of
propagating magnetostatic spin waves crossing a 90-degree domain wall (DW) in
terms of time-resolved magneto-optical imaging. Due to the magnetization
rotation across the 90-degree DW, the dispersion relation of magnetostatic spin
waves rotates by 90 degrees, which results in the change in the propagation
dynamics of spin waves in both sides of the DW. We observe the refraction and
re ection of magnetosatatc spin waves at the 90-degree DW, and reveal their
characteristics, such as negative refraction. The incident-angle dependence of
the refraction angle is explained by the wavenumber conservation along the DW,
same as the case of Snell's law for light.",1911.10659v1
2019-12-06,Implications of spin symmetry for XYZ states,"Numerous exotic candidates containing a heavy quark and anti-quark (the
so-called $XYZ$ states) have been reported since the observation of the
$X(3872)$ in 2003. For these systems a study of the implications of the heavy
quark spin symmetry and its breaking is expected to provide useful guidance
towards a better understanding of their nature. For instance, since the
formation of the complete spin multiplets is described with the same parameter
sets, in some cases the currently available experimental data on the $XYZ$
states allows us to predict properties of spin partner states. To illustrate
this point we extract the parameters of the two $Z_b$ states by analyzing the
most recent experimental data within an effective-field theory approach which
treats both short-ranged contact interactions and the long-ranged
one-pion/one-eta Goldstone boson exchanges (OPE/OEE) dynamically. The line
shapes and pole positions of their spin partners are then predicted in a
parameter-free way and await to be tested by future experimental data.",1912.02944v1
2020-03-04,On the open Dicke-type model generated by an infinite-component vector spin,"We consider an open Dicke model comprising a single infinite-component vector
spin and a single-mode harmonic oscillator which are connected by
Jaynes--Cummings-type interaction between them. This open quantum model is
referred to as the OISD (Open Infinite-component Spin Dicke) model. The
algebraic structure of the OISD Liouvillian is studied in terms of
superoperators acting on the space of density matrices. An explicit invertible
superoperator (precisely, a completely positive trace-preserving map) is
obtained that transforms the OISD Liouvillian into a sum of two independent
Liouvillians, one generated by a dressed spin only, the other generated by a
dressed harmonic oscillator only. The time evolution generated by the OISD
Liouvillian is shown to be asymptotically equivalent to that generated by an
adjusted decoupled Liouvillian with some synchronized frequencies of the spin
and the harmonic oscillator. This asymptotic equivalence implies that the time
evolution of the OISD model dissipates completely in the presence of any (tiny)
dissipation.",2003.02262v3
2020-03-25,Two-photon driven magnon-pair resonance as a signature of spin-nematic order,"We theoretically study the nonlinear magnetic resonance driven by intense
laser or electromagnetic wave in a fully polarized frustrated magnet near a
less-visible spin-nematic ordered phase. In general, both magnons and magnon
pairs (two-magnon bound state) appear as the low-energy excitation in the
saturated state of spin-nematic magnets. Their excitation energies are usually
in terahertz (THz) or gigahertz range. Magnon pairs with angular momentum
2$\hbar$ can be excited by the simultaneous absorption of two photons, and such
multi-photon processes occur if the applied THz laser is strong enough. We
compute laser-driven magnetic dynamics of a frustrated four-spin system with
both magnon ($\hbar$) and magnon-pair (2$\hbar$) like excitations which is
analogous to a macroscopic frustrated magnet with a spin nematic phase. We
estimate the required strength of magnetic field of laser for the realization
of two photon absorption, taking into account dissipation effects with the
Lindblad equation. We show that intense THz laser with ac magnetic field of
0.1-1.0 Tesla is enough to observe magnon-pair resonance.",2003.11240v2
2020-03-28,Detweiler's redshift invariant for extended bodies orbiting a Schwarzschild black hole,"We compute the first-order self-force contribution to Detweiler's redshift
invariant for extended bodies endowed with both dipolar and quadrupolar
structure (with spin-induced quadrupole moment) moving along circular orbits on
a Schwarzschild background. Our analysis includes effects which are second
order in spin, generalizing previous results for purely spinning particles. The
perturbing body is assumed to move on the equatorial plane, the associated spin
vector being orthogonal to it. The metric perturbations are obtained by using a
standard gravitational self-force approach in a radiation gauge. Our results
are accurate through the 6.5 post-Newtonian order, and are shown to reproduce
the corresponding post-Newtonian expression for the same quantity computed by
using the available Hamiltonian from an effective field theory approach for the
dynamics of spinning binaries.",2003.12887v1
2020-05-02,The $\mathfrak{su}(2)$ spin $s$ representations via $\mathbb{C}P^{2s}$ sigma models,"We establish and analyze a new relationship between the matrices describing
an arbitrary component of a spin $s$, where $2s\in \mathbb{Z}^+$, and the
matrices of $\mathbb{C}P^{2s}$ two-dimensional Euclidean sigma models. The spin
matrices are constructed from the rank-1 Hermitian projectors of the sigma
models or from the antihermitian immersion functions of their soliton surfaces
in the $\mathfrak{su}(2s+1)$ algebra. For the spin matrices which can be
represented as a linear combination of the generalized Pauli matrices, we find
the dynamics equation satisfied by its coefficients. The equation proves to be
identical to the stationary equation of a two-dimensional Heisenberg model. We
show that the same holds for the matrices congruent to the generalized Pauli
ones by any coordinate-independent unitary linear transformation. These
properties open the possibility for new interpretations of the spins and also
for application of the methods known from the theory of sigma models to the
situations described by the Heisenberg model, from statistical mechanics to
quantum computing.",2005.00843v1
2020-05-15,Planetary Spin and Obliquity from Mergers,"In planetary systems with sufficiently small inter-planet spacing, close
encounters can lead to planetary collisions/mergers or ejections. We study the
spin property of the merger products of two giant planets in a statistical
manner using numerical simulations and analytical modeling. Planetary
collisions lead to rapidly rotating objects and a broad range of obliquities.
We find that, under typical conditions for two-planet scatterings, the
distributions of spin magnitude $S$ and obliquity $\Theta_{\rm SL}$ of the
merger products have simple analytical forms: $f_{S} \propto S$ and
$f_{\cos\Theta_{\rm SL}} \propto (1-\cos^2\Theta_{\rm SL})^{-1/2}$. Though
parameter studies, we determine the regime of validity for the analytical
distributions of spin and obliquity. Since planetary mergers is a major outcome
of planet-planet scatterings, observational search for the spin/obliquity
signatures of exoplanets would provide important constraints on the dynamical
history of planetary systems.",2005.07718v1
2020-05-21,Effect of Dzyaloshinskii-Moriya interaction on magnetic vortex switching driven by radial spin waves,"We theoretically investigate the radial-spin-wave induced magnetic vortex
switching in the presence of Dzyaloshinskii-Moriya interaction (DMI). From
micromagnetic simulations, we observe a circular-to-radial vortex phase
transition by increasing the DMI strength. The radial spin-wave excitation
spectrum for each magnetization configuration is analyzed, showing that the
frequency of spin-wave mode with a given radial node number monotonically
increases (decreases) with the DMI parameter of the radial (circular) vortex.
Interestingly, we find that the DMI can significantly facilitate the polarity
switching of the circular vortex driven by radial spin waves. Our work provides
a new insight into the DMI effect on the vortex dynamics and is helpful for
designing fast all-magnonic memory devices.",2005.10440v1
2020-06-03,Nonthermal excitonic condensation near a spin-state transition,"We consider a two-orbital Hubbard model with Hund coupling and crystal-field
splitting and show that in the vicinity of the high-spin/low-spin transition,
crystal-field quenches can induce an excitonic condensation at initial
temperatures above the highest ordering temperature in equilibrium. This
condensation is the effect of an increase in the spin entropy and an associated
cooling of the effective electronic temperature. We identify a dynamical phase
transition and show that such quenches can result in long-lived nonthermal
excitonic condensates which have no analogue in the equilibrium phase diagram.
The results are interpreted by means of an effective pseudo-spin model.",2006.02096v2
2020-06-26,Anisotropy-induced soliton excitation in magnetized strong-rung spin ladders,"We report low temperature electron spin resonance experimental and
theoretical studies of an archetype $S=1/2$ strong-rung spin ladder material
(C$_{5}$H$_{12}$N)$_{2}$CuBr$_{4}$. Unexpected dynamics is detected deep in the
Tomonaga-Luttinger spin liquid regime. Close to the point where the system is
half-magnetized (and believed to be equivalent to a gapless easy plane chain in
zero field) we observed orientation-dependent spin gap and anomalous $g$-factor
values. Field theoretical analysis demonstrates that the observed low-energy
excitation modes in magnetized (C$_{5}$H$_{12}$N)$_{2}$CuBr$_{4}$ are solitonic
excitations caused by Dzyaloshinskii-Moriya interaction presence.",2006.14899v2
2020-08-05,NMR study of the spin correlations in the $S=1$ armchair chain Ni$_2$NbBO$_6$,"We report our nuclear magnetic resonance (NMR) study on the structurally spin
chain compound Ni$_2$NbBO$_6$ with complex magnetic coupling. The
antiferromagnetic transition is monitored by the line splitting resulting from
the staggered internal hyperfine field. The magnetic coupling configuration
proposed by the first-principle density functional theory (DFT) is supported by
our NMR spectral analysis. For the spin dynamics, a prominent peak at $T\sim35$
K well above the N\'{e}el temperature ($T_N\sim20$ K at $\mu_0H=10$ T) is
observed from the spin-lattice relaxation data. As compared with the
dc-susceptibility, this behavior indicates a antiferromagnetic coupling with
the typical energy scale of $\sim3$ meV. Thus, the Ni$_2$NbBO$_6$ compound can
be viewed as strongly ferromagnetically coupled armchair spin chains along the
crystalline $b$-axis. These facts place strong constraints to the theoretical
model for this compound.",2008.01949v1
2020-08-19,From Chiral Kinetic Theory To Relativistic Viscous Spin Hydrodynamics,"In this work, we start with chiral kinetic theory and construct the spin
hydrodynamic framework for a chiral spinor system. Using the 14-moment
expansion formalism, we obtain the equations of motion of second-order
dissipative relativistic fluid dynamics with non-trivial spin polarization
density. In a chiral spinor system, the spin alignment effect could be treated
in the same framework as the Chiral Vortical Effect (CVE). However, the quantum
corrections due to fluid vorticity induce not only CVE terms in the
vector/axial charge currents but also corrections to the stress tensor. In this
framework, viscous corrections to the hadron spin polarization are
self-consistently obtained, which will be important for the precise prediction
of the polarization rate for the observed hadrons, e.g. $\Lambda$-hyperon.",2008.08618v2
2020-08-21,Quantum sensing of a coherent single spin excitation in a nuclear ensemble,"The measurement of single quanta in a collection of coherently interacting
objects is transformative in the investigations of emergent quantum phenomena.
An isolated nuclear-spin ensemble is a remarkable platform owing to its
coherence, but detecting its single spin excitations has remained elusive.
Here, we use an electron spin qubit in a semiconductor quantum dot to sense a
single nuclear-spin excitation (a nuclear magnon) with 1.9-ppm precision via
the 200-kHz hyperfine shift on the 28-GHz qubit frequency. We demonstrate this
single-magnon precision across multiple modes identified by nuclear species and
polarity. Finally, we monitor the coherent dynamics of a nuclear magnon and the
emergence of quantum correlations competing against decoherence. A direct
extension of this work is to probe engineered quantum states of the ensemble
including long-lived memory states.",2008.09541v1
2020-09-06,Spin and Entanglement in General Relativity,"In a previous paper, we have shown that the classical and quantum
relativistic dynamics of the Stueckelberg-Horwitz-Piron [SHP] theory can be
embedded in general relativity (GR). We briefly review the SHP theory here,
and, in particular, the formulation of the theory of spin in the framework of
relativistic quantum theory. We show here how the quantum theory of
relativistic spin can be embedded, using a theorem of Abraham, Marsden and
Ratiu, and also explicit derivation, into the framework of GR by constructing a
local induced representation. The relation to the work of Fock and Ivanenko is
also discussed. We show that in a gravitational field there is s highly complex
structure for the spin distribution in the support of the wave function. We
then discuss entanglement for the spins of a two body system.",2009.02744v3
2020-09-07,Field-theory spin and momentum in water waves,"Spin is a fundamental yet nontrivial intrinsic angular-momentum property of
quantum particles or fields, which appears within relativistic field theory.
The spin density in wave fields is described by the theoretical
Belinfante-Rosenfeld construction based on the difference between the canonical
and kinetic momentum densities. These quantities are usually considered as
abstract and non-observable per se. Here, we demonstrate, both theoretically
and experimentally, that the Belinfante-Rosenfeld construction naturally arises
in gravity (water surface) waves. There, the canonical momentum is associated
with the generalized Stokes-drift phenomenon, while the spin is generated by
subwavelength circular motion of water particles. Thus, we directly observe
these fundamental field-theory properties as microscopic mechanical properties
of a classical wave system. Our findings shed light onto the nature of spin and
momentum in wave fields, demonstrate the universality of relativistic
field-theory concepts, and offer a new platform for their studies.",2009.03245v4
2020-09-24,Turbulent relaxation after a quench in the Heisenberg model,"We predict the emergence of turbulent scaling in the quench dynamics of the
two-dimensional Heisenberg model for a wide range of initial conditions and
model parameters. In the isotropic Heisenberg model, we find that the spin-spin
correlation function exhibits universal scaling consistent with a turbulent
energy cascade. When the spin rotational symmetry is broken by an easy-plane
exchange anisotropy, we find a dual cascade of energy and an emergent conserved
charge associated to transverse magnetization fluctuations. The scaling
exponents are estimated analytically and agree with numerical simulations using
phase space methods. We also define the space of initial conditions (as a
function of energy, magnetization, and spin number $S$) that lead to a
turbulent cascade. The universal character of the cascade, insensitive to
microscopic details or initial conditions, suggests that turbulence in spin
systems can be broadly realized in cold atom and solid-state experiments.",2009.11883v2
2020-10-14,Spin torque gate magnetic field sensor,"Spin-orbit torque provides an efficient pathway to manipulate the magnetic
state and magnetization dynamics of magnetic materials, which is crucial for
energy-efficient operation of a variety of spintronic devices such as magnetic
memory, logic, oscillator, and neuromorphic computing. Here, we describe and
experimentally demonstrate a strategy for the realization of a spin torque gate
magnetic field sensor with extremely simple structure by exploiting the
longitudinal field dependence of the spin torque driven magnetization
switching. Unlike most magnetoresistance sensors which require a delicate
magnetic bias to achieve a linear response to the external field, the spin
torque gate sensor can achieve the same without any magnetic bias, which
greatly simplifies the sensor structure. Furthermore, by driving the sensor
using an ac current, the dc offset is automatically suppressed, which
eliminates the need for a bridge or compensation circuit. We verify the concept
using the newly developed WTe2/Ti/CoFeB trilayer and demonstrate that the
sensor can work linearly in the range of 3-10 Oe with negligible dc offset.",2010.07158v1
2020-10-30,Time-domain anyon interferometry in Kitaev honeycomb spin liquids and beyond,"Motivated by recent experiments on the Kitaev honeycomb magnet
$\alpha\text{-RuCl}_3$, we introduce time-domain probes of the edge and
quasiparticle content of non-Abelian spin liquids. Our scheme exploits
ancillary quantum spins that communicate via time-dependent tunneling of energy
into and out of the spin liquid's chiral Majorana edge state. We show that the
ancillary-spin dynamics reveals the edge-state velocity and, in suitable
geometries, detects individual non-Abelian anyons and emergent fermions via a
time-domain counterpart of quantum-Hall anyon interferometry. We anticipate
applications to a wide variety of topological phases in solid-state and
cold-atoms settings.",2011.00015v1
2020-11-05,Magnetoacoustic Resonance to Probe Quadrupole-Strain Coupling in a Diamond Nitrogen-Vacancy Center as a Spin-Triplet System,"A theory of magnetoacoustic resonance is proposed to measure
quadrupole-strain couplings in a spin-triplet state with the $C_{3v}$ point
group symmetry, considering the spin-strain interaction in a diamond
nitrogen-vacancy (NV) center. Based on the Floquet theory, we demonstrate how
the single- and two-phonon transition probabilities depend on the change in the
longitudinal and transverse quadrupole couplings, which can be controlled by
rotating an applied magnetic field, around the threefold axis. The obtained
quadrupole dynamics results are useful for realizing mechanical or ac
strain-control of the NV spin as an alternative to the conventional magnetic
control by spin resonance.",2011.02703v1
2020-11-13,Transverse instability and universal decay of spin spiral order in the Heisenberg model,"We analyze the stability of spin spiral states in the two-dimensional
Heisenberg model. Our analysis reveals that the SU(2) symmetric point hosts a
dynamic instability that is enabled by the existence of energetically favorable
transverse deformations---both in real and spin space---of the spiral order.
The instability is universal in the sense that it applies to systems with any
spin number, spiral wavevector, and spiral amplitude. Unlike the Landau or
modulational instabilities which require impurities or periodic potential
modulation of an optical lattice, quantum fluctuations alone are sufficient to
trigger the transverse instability. We analytically find the most unstable mode
and its growth rate, and compare our analysis with phase space methods. By
adding an easy plane exchange coupling that reduces the Hamiltonian symmetry
from SU(2) to U(1), the stability boundary is shown to continuously interpolate
between the modulational instability and the transverse instability. This
suggests that the transverse instability is an important mechanism that hinders
the formation of a spin superfluid, even in the presence of strong exchange
anisotropy.",2011.07058v1
2021-02-16,Magnetic phase diagram of rare-earth orthorhombic perovskite oxides,"Spin reorientation and magnetisation reversal are two important features of
the rare-earth orthorhombic provskites ($RM$O$_{3}$'s) that have attracted a
lot of attention, though their exact microscopic origin has eluded researchers.
Here, using density functional theory and classical atomistic spin dynamics we
build a general Heisenberg magnetic model that allows to explore the whole
phase diagram of the chromite and ferrite compounds and to scrutinize the
microscopic mechanism responsible for spin reorientations and magnetisation
reversals. We show that the occurrence of a magnetization reversal transition
depends on the relative strength and sign of two interactions between
rare-earth and transition-metal atoms: superexchange and Dzyaloshinsky-Moriya.
We also conclude that the presence of a smooth spin reorientation transition
between the so-called $\Gamma_4$ and the $\Gamma_2$ phases through a coexisting
region, and the temperature range in which it occurs, depends on subtle balance
of metal--metal (superexchange and Dzyaloshinsky-Moriya) and metal--rare-earth
(Dzyaloshinsky-Moriya) couplings. In particular, we show that the intermediate
coexistence region occurs because the spin sublattices rotate at different
rates.",2102.08152v1
2021-02-16,Spin-glass behavior in Shastry-Sutherland lattice of Tm$_\textbf{2}$Cu$_\textbf{2}$In,"The spin-glass behavior in the ferromagnetic phase of $\mathrm{Tm_2Cu_2In}$
was investigated by dc-, ac-magnetization, and non-equilibrium dynamics
characterizations. Arc-melted polycrystalline compound of $\mathrm{Tm_2Cu_2In}$
crystallizes in $\mathrm{Mo_2FeB_2}$-type tetragonal structure (space group
$P_4/mbm$). The temperature variation dc-magnetization exhibits a ferromagnetic
behavior with Curie temperature $T_C$ = 32.5 K. The zero-field cooled (ZFC) and
field cooled (FC) magnetic curves show a thermomagnetic irreversible behavior
below $T_C$. The field dependence of irreversible temperature follows
Almeida-Thouless line. The frequency and ac-driven field-dependent anomalies in
ac-susceptibility results indicate the existence of spin-glass state in
$\mathrm{Tm_2Cu_2In}$. The time dependence of magnetization further supports
the spin-glass behavior observed in $\mathrm{Tm_2Cu_2In}$. The frequency
dependence of the freezing temperature in the real part of ac-susceptibility
has been analyzed on the basis power-law divergence and Vogel-Fulcher law. The
obtained results revealed that $\mathrm{Tm_2Cu_2In}$ belongs to a ferromagnetic
canonical spin-glass class of compounds.",2102.08230v2
2021-02-19,Critical Energy Dissipation in a Binary Superfluid Gas by a Moving Magnetic Obstacle,"We study the critical energy dissipation in an atomic superfluid gas with two
symmetric spin components by an oscillating magnetic obstacle. Above a certain
critical oscillation frequency, spin-wave excitations are generated by the
magnetic obstacle, demonstrating the spin superfluid behavior of the system.
When the obstacle is strong enough to cause density perturbations via local
saturation of spin polarization, half-quantum vortices (HQVs) are created for
higher oscillation frequencies, which reveals the characteristic evolution of
critical dissipative dynamics from spin-wave emission to HQV shedding. Critical
HQV shedding is further investigated using a pulsed linear motion of the
obstacle, and we identify two critical velocities to create HQVs with different
core magnetization.",2102.09826v2
2021-02-19,Exact steady state of the open XX-spin chain: entanglement and transport properties,"We study the reduced dynamics of open quantum spin chains of arbitrary length
$N$ with nearest neighbour $XX$ interactions, immersed within an external
constant magnetic field along the $z$ direction, whose end spins are weakly
coupled to heat baths at different temperatures, via energy preserving
couplings. We find the analytic expression of the unique stationary state of
the master equation obtained in the so-called global approach based on the
spectralization of the full chain Hamiltonian. Hinging upon the explicit
stationary state, we reveal the presence of sink and source terms in the
spin-flow continuity equation and compare their behaviour with that of the
stationary heat flow. Moreover, we also obtain analytic expressions for the
steady state two-spin reduced density matrices and for their concurrence. We
then set up an algorithm suited to compute the stationary bipartite
entanglement along the chain and to study its dependence on the Hamiltonian
parameters and on the bath temperatures.",2102.10036v1
2021-03-05,Local heat emission due to unidirectional spin-wave heat conveyer effect observed by lock-in thermography,"Lock-in thermography measurements were performed to reveal heat source
distribution induced by the unidirectional spin-wave heat conveyer effect
(USHCE) of magnetostatic surface spin waves. When the magnetostatic surface
spin waves are excited in an yttrium iron garnet slab, the lock-in thermography
images show spatially biased sharp and complicated heating patterns, indicating
the importance of edge spin-wave dynamics for USHCE. The accessibility to the
local heat emission properties allows us to clarify a capability of remote
heating realized by USHCE; it can transfer energy for heating even through a
macro-scale air gap between two magnetic materials owing to the long-range
dipole-dipole coupling.",2103.03694v1
2021-03-12,Elliptic solutions to matrix KP hierarchy and spin generalization of elliptic Calogero-Moser model,"We consider solutions of the matrix KP hierarchy that are elliptic functions
of the first hierarchical time $t_1=x$. It is known that poles $x_i$ and matrix
residues at the poles $\rho_i^{\alpha \beta}=a_i^{\alpha}b_i^{\beta}$ of such
solutions as functions of the time $t_2$ move as particles of spin
generalization of the elliptic Calogero-Moser model (elliptic Gibbons-Hermsen
model). In this paper we establish the correspondence with the spin elliptic
Calogero-Moser model for the whole matrix KP hierarchy. Namely, we show that
the dynamics of poles and matrix residues of the solutions with respect to the
$k$-th hierarchical time of the matrix KP hierarchy is Hamiltonian with the
Hamiltonian $H_k$ obtained via an expansion of the spectral curve near the
marked points. The Hamiltonians are identified with the Hamiltonians of the
elliptic spin Calogero-Moser system with coordinates $x_i$ and spin degrees of
freedom $a_i^{\alpha}, \, b_i^{\beta}$.",2103.07357v1
2021-03-15,"Controlled coherent dynamics of [VO(TPP)], a prototype molecular nuclear qudit with an electronic ancilla","We show that [VO(TPP)] (vanadyl tetraphenylporphyrinate) is a promising
system suitable to implement quantum computation algorithms based on encoding
information in multi-level (qudit) units. Indeed, it embeds an electronic spin
1/2 coupled through hyperfine interaction to a nuclear spin 7/2, both
characterized by remarkable coherence. We demonstrate this by an extensive
broadband nuclear magnetic resonance study, which allow us to characterize the
nuclear spin-Hamiltonian and to measure the spin dephasing time as a function
of the magnetic field. In addition, we combine targeted measurements and
numerical simulations to show that nuclear spin transitions conditioned by the
state of the electronic qubit can be individually addressed and coherently
manipulated by resonant radio-frequency pulses, thanks to the remarkably long
coherence times and the effective quadrupolar coupling induced by the strong
hyperfine coupling. This approach may open new perspectives for developing new
molecular qubit-qudit systems.",2103.08730v1
2021-03-19,Spin-orbit torque characterization in a nutshell,"Spin current and spin torque generation through the spin-orbit interactions
in solids, of bulk or interfacial origin, is at the heart of spintronics
research. The realization of spin-orbit torque (SOT) driven magnetic dynamics
and switching in diverse magnetic heterostructures also pave the way for
developing SOT magnetoresistive random access memory and other novel SOT memory
and logic devices. Of scientific and technological importance are accurate and
efficient SOT quantification techniques, which have been abundantly developed
in the last decade. In this article, we summarize popular techniques to
experimentally quantify SOTs in magnetic heterostructures at micro- and
nano-scale. For each technique, we give an overview of its principle,
variations, strengths, shortcomings, error sources, and any cautions in usage.
Finally, we discuss the remaining challenges in understanding and quantifying
the SOTs in heterostructures.",2103.10634v1
2021-03-30,Zeno crossovers in the entanglement speed of spin chains with noisy impurities,"We use a noisy signal with finite correlation time to drive a spin
(dissipative impurity) in the quantum XY spin chain and calculate the dynamics
of entanglement entropy of a bipartition of spins, for a stochastic quantum
trajectory. We compute the noise averaged entanglement entropy of a bipartition
of spins and observe that its speed of spreading decreases at strong
dissipation, as a result of the Zeno effect. We recover the Zeno crossover and
show that noise averaged entanglement entropy can be used as a proxy for the
heating and Zeno regimes. Upon increasing the correlation time of the noise,
the location of the Zeno crossover shifts at stronger dissipation, extending
the heating regime.",2103.16172v4
2021-04-09,Non-thermal breaking of magnetic order via photo-generated spin defects,"In Mott insulators the evolution of antiferromagnetic order to
superconducting or charge-density-wave-like states upon chemical doping
underpins the control of quantum phases. Photo-doping can induce similar
transitions on the ultrafast timescale, however the response of the spin system
has remained elusive. Here, we use 4D-ultrafast optical spectroscopy to extract
quantitative magnetic dynamics in the spin-orbit coupled Mott insulator
Sr3Ir2O7. We demonstrate that light can non-thermally melt long-range spin
order. At low fluences magnetic order recovers within 1 ps despite
demagnetization of roughly 50%. However, high fluences induce a crossover to a
long-lived demagnetized state without increasing the lattice temperature. We
show that the generation of photo-induced spin defects enables a mechanism that
stabilizes the demagnetized state which could help expose new transient phases.",2104.04294v2
2021-05-19,Phenomenology of spectral functions in disordered spin chains at infinite temperature,"Studies of disordered spin chains have recently experienced a renewed
interest, inspired by the question to which extent the exact numerical
calculations comply with the existence of a many-body localization phase
transition. For the paradigmatic random field Heisenberg spin chains, many
intriguing features were observed when the disorder is considerable compared to
the spin interaction strength. Here, we introduce a phenomenological theory
that may explain some of those features. The theory is based on the proximity
to the noninteracting limit, in which the system is an Anderson insulator.
Taking the spin imbalance as an exemplary observable, we demonstrate that the
proximity to the local integrals of motion of the Anderson insulator determines
the dynamics of the observable at infinite temperature. In finite interacting
systems our theory quantitatively describes its integrated spectral function
for a wide range of disorders.",2105.09336v2
2021-05-24,Cavity magnomechanics with surface acoustic waves,"Magnons, namely spin waves, are collective spin excitations in ferromagnets,
and their control through coupling with other excitations is a key technology
for future hybrid spintronic devices. Although strong coupling has been
demonstrated with microwave photonic structures, an alternative approach
permitting high density integration and minimized electromagnetic crosstalk is
required. Here we report a planar cavity magnomechanical system, where the
cavity of surface acoustic waves enhances the spatial and spectral power
density to thus implement magnon-phonon coupling at room temperature.
Excitation of spin-wave resonance involves significant acoustic power
absorption, whereas the collective spin motion reversely exerts a back-action
force on the cavity dynamics. The cavity frequency and quality-factor are
significantly modified by the back-action effect, and the resultant
cooperativity exceeds unity, suggesting coherent interaction between magnons
and phonons. The demonstration of a chip-scale magnomechanical system paves the
way to the development of novel spin-acoustic technologies for classical and
quantum applications.",2105.11127v1
2021-06-08,Spectral-fingerprinting: Microstate readout via remanence ferromagnetic resonance in artificial spin systems,"Artificial spin ices are magnetic metamaterials comprising
geometrically-tiled interacting nanomagnets. There is significant interest in
these systems for reconfigurable magnonics due to their vast microstate
landscape. Studies to-date have focused on the in-field GHz spin-wave response,
convoluting effects from applied field, nanofabrication-imperfections
('quenched disorder') and microstate-dependent dipolar field landscapes. Here,
we study artificial spin ices in pure and disordered microstates and evaluate
their zero-field spectra. Removing the applied field allows us to deconvolute
contributions to reversal dynamics and spin-wave spectra, directly measuring
the dipolar field landscape and quenched disorder. Mode-amplitude provides
population readout of nanomagnet magnetisation direction, and hence net
magnetisation as well as local vertex populations. We demonstrate
microstate-fingerprinting via distinct spectral-readout of three microstates
with identical (zero) magnetisation, supported by simulation. These results
establish remanence 'spectral-fingerprinting' as a rapid, scalable on-chip
readout of both magnetic state and nanoscale dipolar field texture, a critical
step in realising next-generation functional magnonic devices.",2106.04406v2
2021-06-09,Long-Range Order and Quantum Criticality in a Dissipative Spin Chain,"Environmental interaction is a fundamental consideration in any controlled
quantum system. While interaction with a dissipative bath can lead to
decoherence, it can also provide desirable emergent effects including induced
spin-spin correlations. In this paper we show that under quite general
conditions, a dissipative bosonic bath can induce a long-range ordered phase,
without the inclusion of any additional direct spin-spin couplings. Through a
quantum-to-classical mapping and classical Monte Carlo simulation, we
investigate the $T=0$ quantum phase transition of an Ising chain embedded in a
bosonic bath with Ohmic dissipation. We show that the quantum critical point is
continuous, Lorentz invariant with a dynamical critical exponent $z=1.07(9)$,
has correlation length exponent $\nu=0.80(5)$, and anomalous exponent
$\eta=1.02(6)$, thus the universality class distinct from the previously
studied limiting cases. The implications of our results on experiments in
ultracold atomic mixtures and qubit chains in dissipative environments are
discussed.",2106.05371v1
2021-06-30,Quantum gas microscopy of Kardar-Parisi-Zhang superdiffusion,"The Kardar-Parisi-Zhang (KPZ) universality class describes the coarse-grained
behavior of a wealth of classical stochastic models. Surprisingly, it was
recently conjectured to also describe spin transport in the one-dimensional
quantum Heisenberg model. We test this conjecture by experimentally probing
transport in a cold-atom quantum simulator via the relaxation of domain walls
in spin chains of up to 50 spins. We find that domain-wall relaxation is indeed
governed by the KPZ dynamical exponent $z = 3/2$, and that the occurrence of
KPZ scaling requires both integrability and a non-abelian SU(2) symmetry.
Finally, we leverage the single-spin-sensitive detection enabled by the
quantum-gas microscope to measure a novel observable based on spin-transport
statistics, which yields a clear signature of the non-linearity that is a
hallmark of KPZ universality.",2107.00038v1
2021-07-01,Radiative polarization dynamics of relativistic electrons in an intense electromagnetic field,"We propose a self-consistent model which utilizes the polarization vector to
theoretically describe the evolution of spin polarization of relativistic
electrons in an intense electromagnetic field. The variation of radiative
polarization due to instantaneous no photon emission is introduced into our
model, which extends the applicability of the polarization vector model derived
from the nonlinear Compton scattering under local constant crossed-field
approximation to the complex electromagnetic environment in laser plasma
interaction. According to this model, we develop a Monte Carlo method to
simulate the electron spin under the influence of radiation and precession
simultaneously. Our model is consistent with the quantum physical picture that
spin can only be described by a probability distribution before measurement,
and it contains the entire information on the spin. The correctness of our
model is confirmed by the successful reproduction of the Sokolov-Ternov effect
and the comparison of the simulation results with other models in the
literature. The results show the superiority in accuracy, applicability, and
computational efficiency of our model, and we believe that our model is a
better choice to deal with the electron spin in particle-in-cell simulation for
laser plasma interaction.",2107.00597v1
2021-07-13,Supersolid phase of a spin-orbit-coupled Bose-Einstein condensate: a perturbation approach,"The phase diagram of a Bose-Einstein condensate with Raman-induced spin-orbit
coupling includes a stripe phase with supersolid features. In this work we
develop a perturbation approach to study the ground state and the Bogoliubov
modes of this phase, holding for small values of the Raman coupling. We obtain
analytical predictions for the most relevant observables (including the
periodicity of stripes, sound velocities, compressibility, and magnetic
susceptibility) which are in excellent agreement with the exact (non
perturbative) numerical results, obtained for significantly large values of the
coupling. We further unveil the nature of the two gapless Bogoliubov modes in
the long-wavelength limit. We find that the spin branch of the spectrum,
corresponding in this limit to the dynamics of the relative phase between the
two spin components, describes a translation of the fringes of the equilibrium
density profile, thereby providing the crystal Goldstone mode typical of a
supersolid configuration. Finally, using sum-rule arguments, we show that the
superfluid density can be experimentally accessed by measuring the ratio of the
sound velocities parallel and perpendicular to the direction of the spin-orbit
coupling.",2107.06425v2
2021-07-27,Measurement of Bell-type inequalities and quantum entanglement from $Λ$-hyperon spin correlations at high energy colliders,"Spin correlations of $\Lambda$-hyperons embedded in the QCD strings formed in
high energy collider experiments provide unique insight into their locality and
entanglement features. We show from general considerations that while the
Clauser-Horne-Shimony-Holt inequality is less stringent for such states, they
provide a benchmark for quantum-to-classical transitions induced by varying i)
the associated hadron multiplicity, ii) the spin of nucleons, iii) the
separation in rapidity between pairs, and iv) the kinematic regimes accessed.
These studies also enable the extraction of quantitative measures of quantum
entanglement. We first explore such questions within a simple model of a QCD
string composed of singlets of two partial distinguishable fermion flavors and
compare analytical results to those obtained on quantum hardware. We further
discuss a class of spin Hamiltonians that model the dynamics of $\Lambda$ spin
correlations. Prospects for extracting quantum features of QCD strings from
hyperon measurements at current and future colliders are outlined.",2107.13007v3
2021-09-02,Terahertz Nonlinear Optics in Two-dimensional Semi-Hydrogenated SiB,"Phase transition and current of planar clusters with loops of Josephson $\pi$
junction is of great importance for application in the adiabatic quantum
computation devices (AQC). Each $\pi$-ring possesses an orbital moment with a
current. The orientation of these orbital moments is altered by
self-interactions and controlled with a bias current. In the current research,
we construct the phase diagram of semi-hydrogenated SiB (H-SiB) semiconductor
using a two-dimensional (2D) Ising model with considering nearest-neighbor and
diagonal interactions of spin planes on the on the hexagonal lattice. Our
findings reveal that by decreasing temperature, two phase transitions of order
and disorder occur and at low temperatures a glassy state appears, where this
model maps to spin qubit. We theoretically study the magnetostriction effect by
considering of laser electromagnetic field coupled to the spin planes of
electric polarization of magnetic insulator for both unstrained and strained
H-SiB monolayers. The dynamic of laser-spin coupling and spin current shows
nonlinear optical effects and high-harmonic generation (HHG) under both
terahertz (THz) and gigahertz (GHz) electromagnetic waves. The findings of this
research open an avenue for experimentalists how to detect HHG in the
topological insulators, Dirac systems, Mott insulators, and superconducting
memories.",2109.00858v1
2021-09-05,Metastable spin-phase diagrams in antiferromagnetic Bose-Einstein condensates,"Spinor Bose-Einstein condensates under external magnetic fields exhibit
well-characterized spin domains of its ground state due to spin-dependent
interactions. At low temperatures, collision-induced spin-mixing instabilities
may promote the condensate to dwell into metastable states occurring near the
phase boundaries. In this work, we study theoretically the metastable
spin-phase diagram of a spin-1 antiferromagnetic Bose-Einstein condensate at
zero and finite temperatures. The approach makes use of Hartree-Fock theory and
exploits the symmetry of the Hamiltonian and of the order parameters yielding a
closed system of transcendental equations for the free energy, fully avoiding
the use of selfconsistency. Our results are consistent with recent experiments
and allow us to explain qualitatively the different types of observed quench
dynamics. In addition, we found that similar phenomena should occur in
antiferromagnetic spinor condensates with a sudden change in the temperature.
It is shown also that the increase of temperature induces a traceable shift of
the Ferromagnetic-Polar transition boundary, behavior previously not noticed by
selfconsistent mean-field calculations.",2109.01986v1
2021-09-14,Stability and molecular pathways to the formation of spin defects in silicon carbide,"Spin defects in wide-bandgap semiconductors provide a promising platform to
create qubits for quantum technologies. Their synthesis, however, presents
considerable challenges, and the mechanisms responsible for their generation or
annihilation are poorly understood. Here, we elucidate spin defect formation
processes in a binary crystal for a key qubit candidate--the divacancy complex
(VV) in silicon carbide (SiC). Using atomistic models, enhanced sampling
simulations, and density functional theory calculations, we find that VV
formation is a thermally activated process that competes with the conversion of
silicon ($V_{Si}$) to carbon monovacancies ($V_{C}$), and that VV reorientation
can occur without dissociation. We also find that increasing the concentration
of $V_{Si}$ relative to $V_{C}$ favors the formation of divacancies. Moreover,
we identify pathways to create spin defects consisting of antisite-double
vacancy complexes and determine their electronic properties. The detailed view
of the mechanisms that underpin the formation and dynamics of spin defects
presented here may facilitate the realization of qubits in an industrially
relevant material.",2109.06420v2
2021-10-14,Collisional losses of ultracold molecules due to intermediate complex formation,"Understanding the sources of losses and chemical reactions of ultracold
alkali-metal molecules is among the critical elements needed for their
application in precision measurements and quantum technologies. Recent
experiments with nonreactive systems have reported unexpectedly large loss
rates, posing a challenge for theoretical explanation. Here, we examine the
dynamics of intermediate four-atom complexes formed in bimolecular collisions.
We calculate the nuclear spin--rotation, spin--spin, and quadrupole coupling
constants for bialkali tetramers using ab intio quantum-chemical methods. We
show that the nuclear spin--spin and quadrupole couplings are strong enough to
couple different rotational manifolds to increase the density of states and
lifetimes of the collision complexes, which is consistent with experimental
results. We propose further experiments to confirm our predictions.",2110.07501v2
2021-12-03,Magnetic field-induced deformation of the spin-density wave microphases in Ca$_3$Co$_2$O$_6$,"The frustrated triangular Ising magnet Ca$_3$Co$_2$O$_6$ has long been known
for an intriguing combination of extremely slow spin dynamics and peculiar
magnetic orders, such as the evenly-spaced non-equilibrium metamagnetic
magnetization steps and the long-wavelength spin density wave (SDW) order, the
latter of which is essentially an emergent crystal of solitons. Recently, an
elaborate field-cooling protocol to bypass the low-field SDW phase was proposed
to overcome the extraordinarily long timescale of spin relaxation that impeded
previous experimental studies in equilibrium, which may point to a deep
connection between the low-temperature slow relaxation and the cooling process
passing through the low-field SDW phase. As the first step to elucidate the
conjectured connection, we investigate the magnetic field-induced deformation
of the SDW state and incommensurate-commensurate transitions, thereby mapping
out the equilibrium in-field phase diagram for a realistic three-dimensional
lattice spin model by using Monte Carlo simulations. We also discuss
Ginzburg-Landau theory that includes several Umklapp terms as well as an
effective sine-Gordon model, which can qualitatively explain the observed
magnetic field-induced deformation of the SDW microphases.",2112.01701v2
2021-12-29,Evolution of $Λ$ polarization in the hadronic phase of heavy-ion collisions,"Using the AMPT + MUSIC+UrQMD hybrid model, we study the global and local spin
polarizations of $\Lambda$ hyperons as functions of the freeze-out temperature
of the spin degree of freedom in the hadronic phase of Au+Au collisions at
$\sqrt{s_{NN}}=19.6$ GeV. Including contributions from both the thermal
vorticity and thermal shear of the hadronic matter, we find that, with the spin
freeze-out temperature dropping from the hadronization temperature of 160 MeV
to 110 MeV at the kinetic freeze-out, both the global and local spin
polarizations of $\Lambda$ hyperons due to the thermal vorticity decrease by a
factor of two, while those due to the thermal shear decrease quickly and become
negligibly small at 140 MeV. Our results suggest the importance of
understanding the dynamical evolution of the spin degree of freedom in the
hadronic stage in relativistic heavy-ion collisions.",2112.14410v2
2021-12-31,Freezing of the Lattice in the Kagome Lattice Heisenberg Antiferromagnet Zn-barlowite ZnCu$_3$(OD)$_6$FBr,"We use $^{79}$Br nuclear quadrupole resonance (NQR) to demonstrate that ultra
slow lattice dynamics set in below the temperature scale set by the Cu-Cu
super-exchange interaction $J$~($\simeq160$~K) in the kagome lattice Heisenberg
antiferromagnet Zn-barlowite. The lattice completely freezes below 50~K, and
$^{79}$Br NQR lineshapes become twice broader due to increased lattice
distortions. Moreover, the frozen lattice exhibits an oscillatory component in
the transverse spin echo decay, a typical signature of pairing of nuclear spins
by indirect nuclear spin-spin interaction. This indicates that some Br sites
form structural dimers via a pair of kagome Cu sites prior to the gradual
emergence of spin singlets below $\sim30$~K. Our findings underscore the
significant roles played by subtle structural distortions in determining the
nature of the disordered magnetic ground state of the kagome lattice.",2112.15582v3
2022-01-25,Hydrodynamics of interacting spinons in the magnetized spin-$1/2$ chain with the uniform Dzyaloshinskii-Moriya interaction,"We use a hydrodynamic approach to investigate dynamic spin susceptibility of
the antiferromagnetic spin-$1/2$ Heisenberg chain with a uniform
Dzyaloshinskii-Moriya (DM) interaction in the presence of an external magnetic
field. We find that transverse (with respect to the magnetic field) spin
susceptibility harbors two (respectively, three) spin excitation modes when the
magnetic field is parallel (respectively, orthogonal) to the DM axis. In all
cases, the marginally irrelevant backscattering interaction between the spinons
creates a finite energy splitting between optical branches of excitations at $k
= 0$. Additionally, for the orthogonal geometry, the two lower spin branches
exhibit avoided crossing at finite momentum which is determined by the total
magnetic field (the sum of the external and internal molecular fields) acting
on spinons. Our approximate analytical calculations compare well with numerical
results obtained using matrix-product-state (MPS) techniques. Physical
consequences of our findings for the electron spin resonance experiments are
discussed in detail.",2201.10570v2
2022-01-31,Searching for mass-spin correlations in the population of gravitational-wave events: the GWTC-3 case study,"One fundamental goal of the newly born gravitational wave astronomy is
discovering the origin of the observed binary black hole mergers. Towards this
end, identifying features in the growing wealth of data may help in
distinguishing different formation pathways. While large uncertainties still
affect the binary formation models, spin-mass relations remain characteristic
features of specific classes of channels. By focusing on the effective inspiral
spin $\chi_\text{eff}$, the best reconstructed spin-related merger parameter,
we show that current GWTC-3 data support the hypothesis that a fraction of
events may display mass-spin correlations similar to one expected by dynamical
formation channels of either astrophysical or primordial nature. We quantify
the Bayesian evidence in favour of those models, which are substantially
preferred when compared to the Gaussian phenomenological model adopted to
describe the distribution of $\chi_\text{eff}$ in the recent LIGO/Virgo/KAGRA
population analyses.",2201.13098v2
2022-02-14,Violation of the fluctuation-dissipation theorem and effective temperatures in spin ice,"We present numerical tests of the fluctuation-dissipation theorem (FDT) in
the dumbbell model of spin ice with parameters suitable for dysprosium
titanate. The tests are made for local spin variables, magnetic monopole
density, and energy. We are able to achieve local equilibrium in which the FDT
is satisfied down to $T=0.4$ K below which the system completely freezes.
Non-equilibrium dynamics, together with violation of the FDT, are nonetheless
observed following a thermal quench into the non-contractable monopole pair
regime. Despite FDT violation, an approximate linear response regime allows for
the identification of effective non-equilibrium temperatures which are
different for each variable. The spin variable appears hotter than the heat
reservoir, the monopole concentration responds with a lower effective
temperature while the energy has a negative effective temperature. Results are
discussed in the context of the monopole picture of spin ice and compared to
the structure of FDT violations in other glassy materials. Prospectives for
future experiments are reviewed.",2202.06815v2
2022-02-23,Probing spin dynamics of 2D excitons with twisted light,"We propose a mechanism of intravalley spin-flip scattering in spin-valley
coupled two dimensional systems by transferring momentum of light into exciton
center of mass using optical vortex (OV) beams. By varying the dispersion of
light using the topological charge of OV beam, we demonstrate a unique approach
to control the intra-valley spin-flip scattering rate of excitons. From our
photoluminescence measurements, we demonstrate that the intra-valley scattering
rate in W-based TMDs can be tuned externally by OV beams. Variation of
photoluminescence intensity with topological charges shows a crossover
temperature (> 150 K), indicating competitions among time scales involving
radiative recombination, spin-flip scattering, and thermal relaxations. Our
proposed technique utilizing a structured light beam can open up a new approach
to explore the physics of excitons in 2D systems.",2202.11603v2
2022-03-04,Non-Markovian Quantum State Diffusion for Spin Environments,"We introduce an exact open system method to describe the dynamics of quantum
systems that are strongly coupled to specific types of environments comprising
of spins, such as central spin systems. Our theory is similar to the
established non-Markovian quantum state diffusion (NMQSD) theory, but for a
spin bath instead of a Gaussian bath. The method allows us to represent the
time-evolved reduced state of the system as an ensemble average of
stochastically evolving pure states. We present a comprehensive theory for
arbitrary linear spin environments at both zero and finite temperatures.
Furthermore, we introduce a hierarchical expansion method that enables the
numerical computation of the time evolution of the stochastic pure states,
facilitating a numerical solution of the open system problem in relevant strong
coupling regimes.",2203.02417v3
2022-03-31,Chaos enhancement in large-spin chains,"We study the chaotic properties of a large-spin XXZ chain with onsite
disorder and a small number of excitations above the fully polarized state. We
show that while the classical limit, which is reached for large spins, is
chaotic, enlarging the spin suppresses quantum chaos features. We attribute
this suppression to the occurrence of large and slow clusters of onsite
excitations, and propose a way to facilitate their fragmentation by introducing
additional decay channels. We numerically verify that the introduction of such
relaxation channels restores chaoticity for large spins, so that only three
excitations are required to achieve strong level repulsion and ergodic
eigenstates.",2204.00018v1
2022-04-16,Homonuclear J-Coupling Spectroscopy using J-Synchronized Echo Detection,"In the strong coupling regime with J-coupling much larger than chemical shift
differences, J-coupling spectroscopy enables spectral identification of
molecules even when conventional NMR fails. While this classically required the
presence of a heteronucleus, we recently showed that J-coupling spectra can be
acquired in many homonuclear systems using spin-lock induced crossing (SLIC).
Here, we present an alternative method using a spin echo train in lieu of a
spin-locking SLIC pulse, which has a number of advantages. In particular, spin
echo acquisition within the pulse train enables simultaneous collection of time
and frequency data. The resulting 2D spectrum can be used to study dynamic spin
evolution, and the time domain data can be averaged to create a 1D J-coupling
spectrum with increased signal-to-noise ratio.",2204.07686v1
2022-05-15,Conservative Binary Dynamics with a Spinning Black Hole at $\mathcal{O}(G^3)$ from Scattering Amplitudes,"We compute the conservative two-body Hamiltonian of a compact binary system
with a spinning black hole through $\mathcal{O}(G^3)$ to all orders in
velocity, including linear and quadratic spin terms. To obtain our results we
calculate the classical limit of the two-loop amplitude for the scattering of a
massive scalar particle with a massive spin-1 particle minimally coupled to
gravity. We employ modern scattering amplitude and loop integration techniques,
in particular numerical unitarity, integration-by-parts identities, and the
method of regions. The conservative potential in terms of rest-frame spin
vectors is extracted by matching to a non-relativistic effective field theory.
We also apply the Kosower-Maybee-O'Connell (KMOC) formalism to calculate the
impulse in the covariant spin formalism directly from the amplitude. We work
systematically in conventional dimensional regularization and explicitly
evaluate all divergent integrals that appear in full- and effective-theory
amplitudes, as well as in the phase-space integrals that arise in the KMOC
formalism.",2205.07357v2
2022-05-27,Nonlinear $σ$-model for disordered systems with intrinsic spin-orbit coupling,"We derive the nonlinear $\sigma$-model to describe diffusive transport in
normal metals and superconductors with intrinsic spin-orbit coupling (SOC). The
SOC is described via an SU(2) gauge field, and we expand the model to the
fourth order in gradients to find the leading non-Abelian field-strength
contribution. This contribution generates the spin-charge coupling that is
responsible for the spin-Hall effect. We discuss how its symmetry differs from
the leading quasiclassical higher-order gradient terms. We also derive the
corresponding Usadel equation describing the diffusive spin-charge dynamics in
superconducting systems. As an example, we apply the obtained equations to
describe the anomalous supercurrent in dirty Rashba superconductors at
arbitrary temperatures.",2205.14075v1
2022-07-26,Spinful topological phases in acoustic crystals with projective PT symmetry,"For the classification of topological phases of matter, an important
consideration is whether a system is spinless or spinful, as these two classes
have distinct symmetry algebra that gives rise to fundamentally different
topological phases. However, only recently has it been realized theoretically
that in the presence of gauge symmetry, the algebraic structure of symmetries
can be projectively represented, which possibly enables the switch between
spinless and spinful topological phases. Here, we report the first experimental
demonstration of this idea by realizing spinful topological phases in
""spinless"" acoustic crystals with projective space-time inversion symmetry. In
particular, we realize a DIII-class one-dimensional topologically gapped phase
characterized by a 2Z winding number, which features Kramers degenerate bands
and Kramers pair of topological boundary modes. Our work thus overcomes a
fundamental constraint on topological phases by spin classes.",2207.13000v1
2022-07-29,Spin alignment from turbulent color fields,"We study the important, yet widely overlooked, role of gluons for spin
transport with a connection to local parity violation in quark gluon plasmas.
We extend the newly developed quantum kinetic theory for relativistic fermions
to the case coupled with non-Abelian chromo-electromagnetic fields and employ
this formalism to investigate the spin polarization of quarks under dynamically
generated color fields in near-equilibrium quark gluon plasmas. It is found
that the spin polarization could be induced by parity-odd correlators of color
fields, which may dominate over collisional effects at weak coupling. Our
result provides with a possible explanation for the spin alignment of vector
mesons measured in high-energy nuclear collisions and alludes to the connection
with local parity violation.",2207.14504v1
2022-08-10,Spin and valley effects on the quantum phase transition in two dimensions,"Using several independent methods, we find that the metal-insulator
transition occurs in the strongly-interacting two-valley two-dimensional
electron system in ultra-high mobility SiGe/Si/SiGe quantum wells in zero
magnetic field. The transition survives in this system in parallel magnetic
fields strong enough to completely polarize the electrons' spins, thus making
the electron system ""spinless"". In both cases, the resistivity on the metallic
side near the transition increases with decreasing temperature, reaches a
maximum at a temperature $T_{\text{max}}$, and then decreases. The decrease
reaches more than an order of magnitude in zero magnetic field. The value of
$T_{\text{max}}$ in zero magnetic field is found to be close to the
renormalized Fermi temperature. However, rather than increasing along with the
Fermi temperature, the value $T_{\text{max}}$ decreases appreciably for
spinless electrons in spin-polarizing magnetic fields. The observed behavior of
$T_{\text{max}}$ cannot be described by existing theories. The results indicate
the spin-related origin of the effect. At the same time, the low-temperature
resistivity drop in both spin-unpolarized and spinless electron systems is
described quantitatively by the dynamical mean-field theory.",2208.05356v1
2022-09-19,Exploiting disorder to probe spin and energy hydrodynamics,"An outstanding challenge in large-scale quantum platforms is to
simultaneously achieve strong interactions, giving rise to the most interesting
behaviors, and local addressing -that can probe them. In the context of
correlated phases, local addressing enables one to directly probe the nature of
the system's order. Meanwhile, for out-ofequilibrium dynamics, such addressing
allows the study of quantum information spreading and operator growth. Here, we
introduce a novel technique that enables the measurement of local correlation
functions, down to single-site resolution, despite access to only global
controls. Our approach leverages the intrinsic disorder present in a
solid-state spin ensemble to dephase the nonlocal components of the correlation
function. Utilizing this toolset, we measure both the spin and energy transport
in nuclear spin chains. By tuning the interaction Hamiltonian via Floquet
engineering, we investigate the cross-over between ballistic and diffusive
hydrodynamics. Interestingly, when the system is both interacting and
(nearly-)integrable, we observe the coexistence of diffusive spin transport
with ballistic energy transport.",2209.09322v2
2022-09-26,Scanning tunneling spectroscopy of Majorana zero modes in a Kitaev spin liquid,"We describe scanning tunneling spectroscopic signatures of Majorana zero
modes (MZMs) in Kitaev spin liquids. The tunnel conductance is determined by
the dynamical spin correlations of the spin liquid, which we compute exactly,
and by spin-anisotropic cotunneling form factors. Near a $\mathbb{Z}_2$ vortex,
the tunnel conductance has a staircase voltage dependence, where conductance
steps arise from MZMs and (at higher voltages) from additional vortex
configurations. By scanning the probe tip position, one can detect the vortex
locations. Our analysis suggests that topological magnon bound states near
defects or magnetic impurities generate spectroscopic signatures that are
qualitatively different from those of MZMs.",2209.12930v2
2022-09-26,"Sufficient condition for gapless spin-boson Lindbladians, and its connection to dissipative time-crystals","We discuss a sufficient condition for gapless excitations in the Lindbladian
master equation for collective spin-boson systems and permutationally invariant
systems. The condition relates a nonzero macroscopic cumulant correlation in
the steady state to the presence of gapless modes in the Lindbladian. In phases
arising from competing coherent and dissipative Lindbladian terms, we argue
that such gapless modes, concomitant with angular momentum conservation, can
lead to persistent dynamics in the spin observables with the possible formation
of dissipative time-crystals. We study different models within this
perspective, from Lindbladians with Hermitian jump operators, to non-Hermitian
ones composed by collective spins and Floquet spin-boson systems. We also
provide a simple analytical proof for the exactness of mean-field semiclassical
approach in such systems based on a cumulant expansion.",2209.12949v3
2022-10-24,Effects of spin-orbit coupling and in-plane Zeeman fields on the critical current in two-dimensional hole gas SNS junctions,"Superconductor--semiconductor hybrid devices are currently attracting much
attention, fueled by the fact that strong spin--orbit interaction in
combination with induced superconductivity can lead to exotic physics with
potential applications in fault-tolerant quantum computation. The detailed
nature of the spin dynamics in such systems is, however, often strongly
dependent on device details and hard to access in experiment. In this paper we
theoretically investigate a superconductor--normal--superconductor junction
based on a two-dimensional hole gas with additional Rashba spin
orbit--coupling, and we focus on the dependence of the critical current on the
direction and magnitude of an applied in-plane magnetic field. We present a
simple model, which allows us to systematically investigate different parameter
regimes and obtain both numerical results and analytical expressions for all
limiting cases. Our results could serve as a tool for extracting more
information about the detailed spin physics in a two-dimensional hole gas based
on a measured pattern of critical currents.",2210.13266v2
2022-11-02,Continuous Symmetry Breaking in a Trapped-Ion Spin Chain,"One-dimensional systems exhibiting a continuous symmetry can host quantum
phases of matter with true long-range order only in the presence of
sufficiently long-range interactions. In most physical systems, however, the
interactions are short-ranged, hindering the emergence of such phases in one
dimension. Here we use a one-dimensional trapped-ion quantum simulator to
prepare states with long-range spin order that extends over the system size of
up to $23$ spins and is characteristic of the continuous symmetry-breaking
phase of matter. Our preparation relies on simultaneous control over an array
of tightly focused individual-addressing laser beams, generating long-range
spin-spin interactions. We also observe a disordered phase with frustrated
correlations. We further study the phases at different ranges of interaction
and the out-of-equilibrium response to symmetry-breaking perturbations. This
work opens an avenue to study new quantum phases and out-of-equilibrium
dynamics in low-dimensional systems.",2211.01275v1
2022-12-08,Semiclassical analysis of Dirac fields on curved spacetime,"We present a semiclassical analysis for Dirac fields on an arbitrary
spacetime background and in the presence of a fixed electromagnetic field. Our
approach is based on a Wentzel-Kramers-Brillouin approximation, and the results
are analyzed at leading and next-to-leading order in the small expansion
parameter $\hbar$. Taking into account the spin-orbit coupling between the
internal and external degrees of freedom of wave packets, we derive effective
ray equations with spin-dependent terms. These equations describe the
gravitational spin Hall effect of localized Dirac wave packets. We treat both
massive and massless Dirac fields and show how a covariantly defined Berry
connection and the associated Berry curvature govern the semiclassical
dynamics. The gravitational spin Hall equations are shown to be particular
cases of the Mathisson-Papapetrou equations for spinning objects.",2212.04414v2
2022-12-12,Magnon-Plasmon Hybridization Mediated by Spin-Orbit Interaction in Magnetic Materials,"We propose a mechanism for magnon-plasmon coupling and hybridization in
ferromagnetic (FM) and antiferromagnetic (AFM) systems. The electric field
associated with plasmon oscillations creates a non-equilibrium spin density via
the inverse spin galvanic effect. This plasmon-induced spin density couples to
magnons by an exchange interaction. The strength of magnon-plasmon coupling
depends on the magneto-electric susceptibility of the system and the wavevector
at which the level repulsion is happened. This wavevector may be tuned by an
applied magnetic field. In AFM systems, the degeneracy of two chiral magnons is
broken in the presence of a magnetic field, and we find two separate hybrid
modes for left-handed and right-handed AFM magnons. Furthermore, we show that
magnon-plasmon coupling in AFM systems is enhanced because of strong
intra-sublattice spin dynamics. We argue that the recently discovered
two-dimensional magnetic systems are ideal platforms to investigate proposed
magnon-plasmon hybrid modes.",2212.06105v1
2023-01-05,Ultrafast spontaneous spin switching in an antiferromagnet,"Owing to their high magnon frequencies, antiferromagnets are key materials
for future high-speed spintronics. Picosecond switching of antiferromagnetic
order has been viewed a milestone for decades and pursued only by using
ultrafast external perturbations. Here, we show that picosecond spin switching
occurs spontaneously due to thermal fluctuations in the antiferromagnetic
orthoferrite Sm0.7Er0.3FeO3. By analysing the correlation between the
pulse-to-pulse polarisation fluctuations of two femtosecond optical probes, we
extract the autocorrelation of incoherent magnon fluctuations. We observe a
strong enhancement of the magnon fluctuation amplitude and the coherence time
around the critical temperature of the spin reorientation transition. The
spectrum shows two distinct modes, one corresponding to the quasi-ferromagnetic
mode and another one which has not been previously reported in pump-probe
experiments. Comparison to a stochastic spin dynamics simulation reveals this
new mode as smoking gun of ultrafast spontaneous spin switching within the
double-well anisotropy potential.",2301.02006v1
2023-01-12,Spectroscopic signatures of fractionalization in octupolar quantum spin ice,"Recent investigations on the dipolar-octupolar compounds Ce$_2$Zr$_2$O$_7$
and Ce$_2$Sn$_2$O$_7$ suggest that they may stabilize so-called $\pi$-flux
octupolar quantum spin ice ($\pi$-O-QSI), a novel three-dimensional quantum
spin liquid hosting emergent photons. Confirmation of such an exotic phase
would require the prediction of a distinctive signature and its subsequent
experimental observation. So far, however, theoretical predictions for any such
sharp smoking-gun signatures are lacking. In this Letter, we thoroughly
investigate O-QSI using an extension of gauge mean-field theory. This framework
produces a phase diagram consistent with previous studies and an
energy-integrated neutron scattering signal with intensity-modulated rod
motifs, as reported in experiments and numerical studies. We predict that the
dynamical spin structure factor of $\pi$-O-QSI is characterized by a broad
continuum with three distinctive peaks as a consequence of the two mostly flat
spinon bands. These three peaks should be measurable by high-resolution
inelastic neutron scattering. Such spectroscopic signatures would be clear
evidence for the realization of $\pi$-flux quantum spin ice.",2301.05240v3
2023-01-27,A semi-analytical model to simulate the spin-diode effect and accelerate its use in neuromorphic computing,"The spin-diode effect is studied both experimentally and with our original
semi-analytical method. The latter is based on an improved version of the
Thiele equation approach (TEA) that we combine to micromagnetic simulation data
to accurately model the non-linear dynamics of spin-torque vortex oscillator
(STVO). This original method, called data-driven Thiele equation approach
(DD-TEA), absorbs the difference between the analytical model and micromagnetic
simulations to provide a both ultra-fast and quantitative model. The DD-TEA
model predictions also agree very well with the experimental data. The reversal
of the spin-diode effect with the chirality of the vortex, the impact of the
input current and the origin of a variation at half of the STVO frequency are
presented as well as the ability of the model to reproduce the experimental
behavior. Finally, the spin-diode effect and its simulation using the DD-TEA
model are discussed as a promising perspective in the framework of neuromorphic
computing.",2301.11980v1
2023-03-15,Instability of magnetic skyrmion strings induced by longitudinal spin currents,"It is well established that spin-transfer torques exerted by in-plane spin
currents give rise to a motion of magnetic skyrmions resulting in a skyrmion
Hall effect. In films of finite thickness or in three-dimensional bulk samples
the skyrmions extend in the third direction forming a string. We demonstrate
that a spin current flowing longitudinally along the skyrmion string instead
induces a Goldstone spin wave instability. Our analytical results are confirmed
by micromagnetic simulations of both a single string as well as string lattices
suggesting that the instability eventually breaks the strings. A longitudinal
current is thus able to melt the skyrmion string lattice via a dynamical phase
transition. For films of finite thickness or in the presence of disorder a
threshold current will be required, and we estimate the latter assuming weak
collective pinning.",2303.08532v1
2023-03-27,Static and dynamical magnetic properties of the extended Kitaev-Heisenberg model with spin vacancies,"Motivated by the potential to suppress the antiferromagnetic long-range order
in favor of the long-sought-after Kitaev quantum spin liquid state, we study
the effect of spin vacancies in the extended Kitaev-Heisenberg model. In
particular, we focus on a realistic model obtained from fitting inelastic
neutron scattering on $\alpha$-RuCl$_3$. We observe that the long-range zigzag
magnetic ordered state only survives when the doping concentration is smaller
than 5\%. Upon further increasing the spin vacancy concentration, the ground
state becomes a short-range ordered state at low temperatures. Compared with
experiments, our classical solution over-stabilizes the zigzag correlation in
the presence of spin vacancies. Our theoretical results provide guidance toward
interpreting inelastic neutron scattering experiments on magnetically diluted
Kitaev candidate materials.",2303.15526v1
2023-04-11,Squeezed superradiance enables robust entanglement-enhanced metrology even with highly imperfect readout,"Quantum metrology protocols using entangled states of large spin ensembles
attempt to achieve measurement sensitivities surpassing the standard quantum
limit (SQL), but in many cases they are severely limited by even small amounts
of technical noise associated with imperfect sensor readout. Amplification
strategies based on time-reversed coherent spin-squeezing dynamics have been
devised to mitigate this issue, but are unfortunately very sensitive to
dissipation, requiring a large single-spin cooperativity to be effective. Here,
we propose a new dissipative protocol that combines amplification and squeezed
fluctuations. It enables the use of entangled spin states for sensing well
beyond the SQL even in the presence of significant readout noise. Further, it
has a strong resilience against undesired single-spin dissipation, requiring
only a large collective cooperativity to be effective.",2304.05471v2
2023-05-15,Intra-atomic Hund's exchange interaction determines spin states and energetics of Li-rich layered sulfides for battery applications,"Motivated by experimental suggestions of anionic redox processes helping to
design higher energy lithium ion-battery cathode materials, we investigate this
effect using first-principles electronic structure calculations for Li-rich
layered sulfides. We identify the determination of the energetic contribution
of intra-atomic Hund's exchange coupling as a major obstacle to a reliable
theoretical description. We overcome this challenge by developing a
particularly efficient flavor of charge-self-consistent combined density
functional + dynamical mean-field theory (DFT+DMFT) calculations. Our scheme
allows us to describe the spin ground states of the transition metal d shell,
the electronic structure of the materials, and its energetics. As a result of
the high-spin to low-spin transition the average intercalation voltage shows
intriguing non-monotonic behavior. We rationalize these findings by an analysis
of the fluctuations of spin and charge degrees of freedom. Our work
demonstrates the relevance of most recent insights into correlated electron
materials for the physics of functional materials such as Li-ion battery
compounds.",2305.08526v1
2023-05-15,Long-time relaxation of a finite spin bath linearly coupled to a qubit,"We discuss the long-time relaxation of a qubit linearly coupled to a finite
bath of $N$ spins (two-level systems, TLSs), with the interaction Hamiltonian
in rotating wave approximation. We focus on the regime $N\gg 1$, assuming that
the qubit-bath coupling is weak, that the range of spin frequencies is
sufficiently broad, and that all the spins are initialized in the ground state.
Despite the model being perfectly integrable, we make two interesting
observations about the effective system relaxation. First, as one would expect,
the qubit relaxes exponentially towards its zero-temperature state at a well
characterized rate. Second, the bath spins, even when mutually coupled, do not
relax towards a thermal distribution, but rather form a Lorentzian distribution
peaked at the frequency of the initially excited qubit. This behavior is
captured by an analytical approximation that makes use of the property $N\gg 1$
to treat the TLS frequencies as a continuum and is confirmed by our numerical
simulations.",2305.08692v2
2023-05-26,Anisotropic signatures in the spin-boson model,"Thermal equilibrium properties of nanoscale systems deviate from standard
macroscopic predictions due to a non-negligible coupling to the environment.
For anisotropic three-dimensional materials, we derive the mean force
corrections to the equilibrium state of a classical spin vector. The result is
valid at arbitrary coupling strength. Specifically, we consider cubic,
orthorhombic, and monoclinic symmetries, and compare their spin expectation
values as a function of temperature. We underpin the correctness of the mean
force state by evidencing its match with the steady state of the simulated
non-Markovian spin dynamics. The results show an explicit dependence on the
symmetry of the confining material. In addition, some coupling symmetries show
a spin alignment transition at zero temperature. Finally, we quantify the work
extraction potential of the mean force-generated inhomogeneities in the energy
shells. Such inhomogeneities constitute a classical equivalent to quantum
coherences.",2305.16964v1
2023-06-20,Kardar-Parisi-Zhang scaling in the Hubbard model,"We explore the Kardar-Parisi-Zhang (KPZ) scaling in the one-dimensional
Hubbard model, which exhibits global $SU_c(2)\otimes SU_s(2)$ symmetry at
half-filling, for the pseudo-charge and the total spin. We analyze dynamical
scaling properties of high temperature charge and spin correlations and
transport. At half-filling, we observe a clear KPZ scaling in both charge and
spin sectors. Away from half-filling, the $SU_c(2)$ charge symmetry is reduced
to $U_c(1)$, while the $SU_s(2)$ symmetry for the total spin is retained.
Consequently, transport in the charge sector becomes ballistic, while KPZ
scaling is preserved in the spin sector. These findings confirm the link
between non-abelian symmetries and KPZ scaling in the presence of
integrability. We study two settings of the model: one involving a quench from
a bi-partitioned state asymptotically close to the $T=\infty$ equilibrium state
of the system, and another where the system is coupled to two markovian
reservoirs at the two edges of the chain.",2306.11540v1
2023-06-29,Quantum sensing via magnetic-noise-protected states in an electronic spin dyad,"Extending the coherence lifetime of a qubit is central to the implementation
and deployment of quantum technologies, particularly in the solid-state where
various noise sources intrinsic to the material host play a limiting role.
Here, we theoretically investigate the coherent spin dynamics of a hetero-spin
system formed by a spin S=1 featuring a non-zero crystal field and in proximity
to a paramagnetic center S'=1/2. We capitalize on the singular energy level
structure of the dyad to identify pairs of levels associated to
magnetic-field-insensitive transition frequencies, and theoretically show that
the zero-quantum coherences we create between them can be remarkably
long-lived. Further, we find these coherences are selectively sensitive to
'local' - as opposed to 'global' - field fluctuations, suggesting these spin
dyads could be exploited as nanoscale gradiometers for precision magnetometry
or as probes for magnetic-noise-free electrometry and thermal sensing.",2306.17273v1
2023-07-01,Quantum non-demolition measurement of an electron spin qubit through its low-energy many-body spin environment,"The measurement problem dates back to the dawn of quantum mechanics. Here, we
measure a quantum dot electron spin qubit through off-resonant coupling with
thousands of redundant nuclear spin ancillae. We show that the link from
quantum to classical can be made without any ""wavefunction collapse"", in
agreement with the Quantum Darwinism concept. Large ancilla redundancy allows
for single-shot readout with high fidelity $\approx99.85\%$. Repeated
measurements enable heralded initialization of the qubit and probing of the
equilibrium electron spin dynamics. Quantum jumps are observed and attributed
to burst-like fluctuations in a thermally populated phonon bath.",2307.00308v1
2023-07-11,Microscopic Entanglement Wedges,"We study the holographic duality between the free $O(N)$ vector model and
higher spin gravity. Conserved spinning primary currents of the conformal field
theory (CFT) are dual to spinning gauge fields in the gravity. Reducing to
independent components of the conserved CFT currents one finds two components
at each spin. After gauge fixing the gravity and then reducing to independent
components, one finds two components of the gauge field at each spin.
Collective field theory provides a systematic way to map between these two sets
of degrees of freedom, providing a complete and explicit identification between
the dynamical degrees of freedom of the CFT and the dual gravity. The resulting
map exhibits many features expected of holographic duality: it provides a valid
bulk reconstruction, it reproduces insights expected from the holography of
information and it provides a microscopic derivation of entanglement wedge
reconstruction.",2307.05032v2
2023-07-23,Polarization of spin-1/2 particles with effective spacetime dependent masses,"Semiclassical expansion of the Wigner function for spin-1/2 fermions having
an effective spacetime-dependent mass is used to analyze spin-polarization
effects. The existing framework is reformulated to obtain a differential
equation directly connecting the particle spin tensor with the effective mass.
It reflects the conservation of the total angular momentum in a system. In
general, we find that the gradients of mass act as a source of the spin
polarization. Although this effect is absent for simple boost-invariant
dynamics, an extension to non-boost-invariant systems displays a non-trivial
dependence of the spin density on the mass indicating that the spin
polarization effects may be intertwined with the phenomenon of chiral
restoration.",2307.12436v2
2023-07-26,Ultrafast Control of Magnetic Correlations in a Heisenberg Spin Ladder,"We study the time-dependent response of a Heisenberg spin ladder subjected to
a time-dependent square form variation of its rung spin exchange coupling. To
do so, we employ a field theoretic representation of the Heisenberg spin ladder
consisting of a singlet and a triplet of Majorana fermions. Because this
underlying description is free fermionic, we are able to develop closed form
analytic expressions for dynamical quantities, both one-body measures of local
spin correlations as well as two-time correlation functions. These expressions
involve both the gaps to triplet and singlet excitations. We analyze these
expressions obtaining both the time scales for their transients and long-time
athermal steady state behaviors. We show that variations in the rung coupling
are directly tied to changes in the local antiferromagnetic correlations. We
further discuss the application of these results to pump-probe experiments on
material realizations of low-dimensional magnetic systems.",2307.13914v3
2023-08-04,Coherent spin qubit shuttling through germanium quantum dots,"Quantum links can interconnect qubit registers and are therefore essential in
networked quantum computing. Semiconductor quantum dot qubits have seen
significant progress in the high-fidelity operation of small qubit registers
but establishing a compelling quantum link remains a challenge. Here, we show
that a spin qubit can be shuttled through multiple quantum dots while
preserving its quantum information. Remarkably, we achieve these results using
hole spin qubits in germanium, despite the presence of strong spin-orbit
interaction. We accomplish the shuttling of spin basis states over effective
lengths beyond 300 $\mu$m and demonstrate the coherent shuttling of
superposition states over effective lengths corresponding to 9 $\mu$m, which we
can extend to 49 $\mu$m by incorporating dynamical decoupling. These findings
indicate qubit shuttling as an effective approach to route qubits within
registers and to establish quantum links between registers.",2308.02406v1
2023-08-05,Analytical results for a spin-orbit coupled atom held in a non-Hermitian double well under synchronous combined modulation,"We propose a simple method of synchronous combined modulations to generate
the exact analytic solutions for a spin-orbit (SO) coupled ultracold atom held
in a non-Hermitian double-well potential. Based on the obtained analytical
solutions, we mainly study the parity-time ($\mathcal{PT}$) symmetry of this
system and the system stability for both balanced and unbalanced gain-loss
between two wells. Under balanced gain and loss, the effect of the proportional
constants between synchronous combined modulations and the SO-coupling strength
on the $\mathcal{PT}$-symmetry breaking is revealed analytically. Surprisingly,
we find when the Zeeman field is present, the stable spin-flipping tunneling
between two wells can not occur in the non-Hermitian SO-coupled ultracold
atomic system, but the stable spin-conserving tunneling can be performed. Under
unbalanced gain and loss, the unique set of parameter conditions that can cause
the system to stabilize is found. The results may provide a possibility for the
exact control of $\mathcal{PT}$-symmetry breaking and quantum spin dynamics in
a non-Hermitian SO-coupled system.",2308.02848v1
2023-08-23,Toward experimental determination of spin entanglement of nucleon pairs,"Nuclear entanglement is a flagship in the interdisciplinary direction of
nuclear physics and quantum information science. Spin entanglement, a special
kind of nuclear entanglement, is ubiquitous in nuclear structures and dynamics.
Based on the idea of quantum state tomography, the problem of experimental
determination of spin entanglement of two-nucleon pure states is studied
directly within the scope of nuclear physics. It is shown that the amount of
spin entanglement can be obtained by measuring three spin polarizations of one
nucleon in polarization experiments. The errors from imperfect preparation of
nucleon pairs are also analyzed. This work not only complements the existing
literature of nuclear entanglement but also provides new opportunities for
nuclear physics with polarized particles.",2308.12327v2
2023-08-30,Approximate Bound State Solutions of the Fractional Schrödinger Equation under the Spin-Spin-Dependent Cornell Potential,"In this work, the approximate bound state solutions of the fractional
Schr\""odinger equation under a spin-spin-dependent Cornell potential are
obtained via the convectional Nikiforov-Uvarov approach. The energy spectra are
applied to obtain the mass spectra of the heavy mesons such as bottomonium,
charmonium and bottom-charm. The masses for the singlet and triplet spin
numbers increase as the quantum numbers increase. The fractional Schr\""odinger
equation improves the mass spectra compared to the masses obtained in the
existing literature. The bottomonium masses agree with the experimental data of
the Particle Data Group where percentage errors for fractional parameters of
\b{eta}=1,{\alpha}=0.97 and \b{eta}=1,{\alpha}=0.50 were found to be 0.67% and
0.49% respectively. The respective percentage errors of 1.97% and 1.62% for
fractional parameters of \b{eta}=1,{\alpha}=0.97 and \b{eta}=1,{\alpha}=0.50
were obtained for charmonium meson. The results indicate that the potential
curves coupled with the fractional parameters account for the short-range gluon
exchange between the quark-antiquark interactions and the linear confinement
phenomena which is associated with the quantum chromo-dynamic and
phenomenological potential models in particle and high-energy physics",2308.15843v1
2023-09-12,Dynamical Spin Limit Shape of Young Diagram and Spin Jucys-Murphy Elements for Symmetric Groups,"The branching rule for spin irreducible representations of symmetric groups
gives rise to a Markov chain on the spin dual
$(\widetilde{\mathfrak{S}}_n)^\wedge_{spin}$ of symmetric group
$\mathfrak{S}_n$. This further produces a continuous time random walk
$(X_s^{(n)})_{s\geqq 0}$ on $(\widetilde{\mathfrak{S}}_n)^\wedge_{spin}$ by
introducing an appropriate pausing time. Taking diffusive scaling limit for
these random walks under $s=tn$ and $1/\sqrt{n}$ reduction as $n\to\infty$, we
consider a concentration phenomenon at each macroscopic time $t$. Since an
element of $(\widetilde{\mathfrak{S}}_n)^\wedge_{spin}$ is regarded as a strict
partition of $n$ with $\pm 1$ indices, the limit shapes of profiles of strict
partitions appear. In this paper, we give a framework in which initial
concentration at $t=0$ is propagated to concentration at any $t>0$. We thus
meet the limit shape $\omega_t$ depending on macroscopic time $t$, and describe
the time evolution by using devices in free probability theory. A spin version
of the Jucys--Murphy element plays an important role in our analysis.",2309.06059v1
2023-10-26,Spin wave behavior of a novel hopfion-like chiral state in Co/Pt nanodiscs,"This work discusses the rich phase diagram of non-trivial chiral spin
textures in confined ferromagnetic/heavy-metal (FM/HM) bilayer nanomagnets of
circular cross-section. These spin textures are realized as a minimum-energy
ground state during an external bias field sweep for a range of nanomagnet's
diameter (d). Our study, based on micromagnetic simulations, has revealed a
novel Hopfion-like state which can be stabilized for a wide range of diameters
and external magnetic fields. We explored the dynamical characteristics of this
novel Hopfion-like state under a transient magnetic field applied along the
plane's perpendicular direction. Simulation results have demonstrated the
excitation of nonreciprocal spin wave (SW) modes for this novel chiral state,
in contrast to other stabilized chiral states. These modes are characterized as
breathing and quantized radial modes, which also exhibit hybridization with
azimuthal modes. The resonant SW modes have been used to demonstrate the
switching from a Hopfion-like state to a skyrmion within a few nanoseconds of
SW excitation. Furthermore, we establish a correlation between the behavior of
excited SW modes as a function of external magnetic field strength and
underlying chiral spin texture states.",2310.17460v1
2023-11-17,Superradiance in the Kerr-Taub-NUT spacetime,"Superradiance is the effect of field waves being amplified during reflection
from a charged or rotating black hole. In this paper, we study the low-energy
dynamics of super-radiant scattering of massive scalar and massless higher spin
field perturbations in a generic axisymmetric stationary Kerr-Taub-NUT
(Newman-Unti-Tamburino) spacetime, which represents sources with both
gravitomagnetic monopole moment (magnetic mass) and gravitomagnetic dipole
moment (angular momentum). We obtain a generalized Teukolsky master equation
for all spin perturbation fields. The equations are separated into their
angular and radial parts. The angular equations lead to spin-weighted
spheroidal harmonic functions that generalize those in Kerr spacetime. We
identify an effective spin as a coupling between frequency (or energy) and the
NUT parameter. The behaviors of the radial wave function near the horizon and
at the infinite boundary are studied. We provide analytical expressions for
low-energy observables such as emission rates and cross sections of all
massless fields with spin, including scalar, neutrino, electromagnetic,
Rarita-Schwinger, and gravitational waves.",2311.10559v1
2023-11-27,Near-resonant nuclear spin detection with high-frequency mechanical resonators,"Mechanical resonators operating in the high-frequency regime have become a
versatile platform for fundamental and applied quantum research. Their
exceptional properties, such as low mass and high quality factor, make them
also very appealing for force sensing experiments. In this Letter, we propose a
method for detecting and ultimately controlling nuclear spins by directly
coupling them to high-frequency resonators via a magnetic field gradient.
Dynamical backaction between the sensor and an ensemble of nuclear spins
produces a shift in the sensor's resonance frequency, which can be measured to
probe the spin ensemble. Based on analytical as well as numerical results, we
predict that the method will allow nanoscale magnetic resonance imaging with a
range of realistic devices. At the same time, this interaction paves the way
for new manipulation techniques, similar to those employed in cavity
optomechanics, enriching both the sensor's and the spin ensemble's features.",2311.16273v1
2023-12-01,Incommensurate Spiral Spin Order in CaMn$_2$Bi$_2$ observed via High Pressure Neutron Diffraction,"High pressure neutron diffraction is employed to investigate the magnetic
behavior of CaMn$_2$Bi$_2$ in extreme conditions. In contrast to
antiferromagnetic ordering on Mn atoms reported at ambient pressure, our
results reveal that at high pressure, incommensurate spiral spin order emerges
due to the interplay between magnetism on the Mn atoms and strong spin-orbit
coupling on the Bi atoms: sinusoidal spin order is observed at pressures as
high as 7.4 GPa. Competing antiferromagnetic order is observed at different
temperatures in the partially frustrated lattice. This research provides a
unique toolbox for conducting experimental magnetic and spin dynamics studies
on magnetic quantum materials via high pressure neutron diffraction.",2312.00397v1
2023-12-12,Tailoring the overlap distribution in driven mean-field spin models,"In a statistical physics context, inverse problems consists in determining
microscopic interactions such that a system reaches a predefined collective
state. A complex collective state may be prescribed by specifying the overlap
distribution between microscopic configurations, a notion originally introduced
in the context of disordered systems like spin-glasses. We show that in spite
of the absence of disorder, nonequilibrium spin models exhibiting spontaneous
magnetization oscillations provide a benchmark to prescribe a non-trivial
overlap distribution with continuous support, qualitatively analogous to the
ones found in disordered systems with full replica symmetry breaking. The
overlap distribution can be explicitly tailored to take a broad range of
predefined shapes by monitoring the spin dynamics. The presence of a
non-trivial overlap distribution is traced back to an average over infinitely
many pure states, a feature shared with spin-glasses.",2312.07453v1
2023-12-15,Mutual synchronization in spin torque and spin Hall nano-oscillators,"This chapter reviews the state of the art in mutually synchronized
spin-torque and spin Hall nano-oscillator (STNO and SHNO) arrays. After briefly
introducing the underlying physics, we discuss different nano-oscillator
implementations and their functional properties with respect to frequency
range, output power, phase noise, and modulation rates. We then introduce the
concepts and the theory of mutual synchronization and discuss the possible
coupling mechanisms in spintronic nano-oscillators, such as dipolar,
electrical, and spin-wave coupling. We review the experimental literature on
mutually synchronized STNOs and SHNOs in one- and two-dimensional arrays and
discuss ways to increase the number of mutually synchronized nano-oscillators.
Finally, the potential for applications ranging from microwave signal
sources/detectors and ultrafast spectrum analyzers to neuromorphic computing
elements and Ising machines is discussed together with the specific electronic
circuitry that has been designed so far to harness this potential.",2312.09656v1
2023-12-17,Spin control with triplet and doublet excitons in organic semiconductors,"Spin triplet exciton formation sets limits on technologies using organic
semiconductors that are confined to singlet-triplet photophysics. In contrast,
excitations in the spin doublet manifold in organic radical semiconductors can
show efficient luminescence. Here we explore the dynamics of the spin allowed
process of intermolecular energy transfer from triplet to doublet excitons. We
employ a carbene-metal-amide (CMA-CF3) as a model triplet donor host, since
following photoexcitation it undergoes extremely fast intersystem crossing to
set up a population of triplet excitons within 4 ps. This enables a
foundational study for tracking energy transfer from triplets to a model
radical semiconductor, TTM-3PCz. Over 90% of all radical luminescence
originates from the triplet channel in this system under photoexcitation. We
find that intermolecular triplet-to-doublet energy transfer can occur directly
and rapidly, with 12% of triplet excitons transferring already on sub-ns
timescales. This enhanced triplet harvesting mechanism is utilised in efficient
near-infrared organic light-emitting diodes, which can be extended to other
opto-electronic and -spintronic technologies by radical-based spin control in
molecular semiconductors.",2312.10595v1
2023-12-20,Heisenberg spin chain with random-sign couplings,"We study the 1D quantum Heisenberg chain with randomly ferromagnetic or
antiferromagnetic couplings (a model previously studied by approximate
strong-disorder renormalization group). We find that, at least for sufficiently
large spin $S$, the ground state has ""spin glass"" order. The spin waves on top
of this state have the dynamical exponent ${z=3/2}$, intermediate between the
values $z=1$ of the antiferromagnet and ${z=2}$ of the ferromagnet. DMRG
simulations are in good agreement with the analytical results for spins ${S=1}$
and ${S=3/2}$. The case ${S=1/2}$ shows large finite size effects: we suggest
that this case is also ordered, but with a small ordered moment.",2312.13452v1
2024-01-29,Prepare Non-classical Collective Spin State by Reinforcement Learning,"We propose a scheme leveraging reinforcement learning to engineer control
fields for generating non-classical states. It is exemplified by the
application to prepare spin squeezed state for an open collective spin model
where a linear control term is designed to govern the dynamics. The
reinforcement learning agent determines the temporal sequence of control
pulses, commencing from coherent spin state in an environment characterized by
dissipation and dephasing. When compared to constant control scenarios, this
approach provides various control sequences maintaining collective spin
squeezing and entanglement. It is observed that denser application of the
control pulses enhances the performance of the outcomes. Furthermore, there is
a minor enhancement in the performance by adding control actions. The proposed
strategy demonstrates increased effectiveness for larger systems. And thermal
excitations of the reservoir are detrimental to the control outcomes. It should
be confirmed that this is an open-loop strategy by closed-loop simulation,
circumventing collapse of quantum state induced by measurements. Thanks to the
flexible replaceability of the optimization modules and the controlled system,
this research paves the way for its application in manipulating other quantum
systems.",2401.16320v1
2024-02-02,THz spin-wave excitations in the transverse conical phase of BiFeO$_3$,"Although BiFeO$_3$ is one of the most studied multiferroic materials, recent
magnetization and neutron scattering studies have revealed a new magnetic phase
in this compound - the transverse conical phase. To study the collective spin
excitations of this phase, we performed THz spectroscopy in magnetic fields up
to 17 T at and above room temperature. We observed five spin-wave branches in
the magnetic phase with long wavelength conical modulation. Using a numerical
spin dynamics model we found two kinds of excitations with magnetic moments
oscillating either along or perpendicular to the static fields. Remarkably, we
detected strong directional dichroism, an optical manifestation of the
magnetoelectric effect, for two spin-wave modes of the conical phase. According
to our experiments, the stability of the conical state is sensitive to the
magnetic field history and it can become (meta)stable at or close to zero
magnetic field, which may allow exploiting its magnetoelectric properties at
room temperature.",2402.01417v1
2024-02-07,Are magnetic monopoles at the origin of magneto-electricity in spin ices?,"The possibilities of combining several degrees of freedom inside a unique
material have recently been highlighted in their dynamics and proposed as
information carriers in quantum devices where their cross-manipulation by
external parameters such as electric and magnetic fields could enhance their
functionalities. An emblematic example is that of electromagnons, spin-waves
dressed with electric dipoles, that are fingerprints of multiferroics.
Point-like objects have also been identified, which may take the form of
excited quasiparticles. This is the case for magnetic monopoles, the exotic
excitations of spin ices, that have been recently proposed to carry an electric
dipole although experimental evidences remain elusive. Presently, we
investigate the electrical signature of a classical spin ice and a related
compound that supports quantum fluctuations. Our in-depth study clearly
attributes magnetoelectricity to the correlated spin ice phase distinguishing
it from extrinsic and single-ion effects. Our calculations show that the
proposed model conferring magnetoelectricity to monopoles is not sufficient,
calling for higher order contributions.",2402.05260v2
2024-02-23,Searching for Exotic Spin-Dependent Interactions with Diamond-Based Vector Magnetometer,"We propose a new method to search for exotic spin-spin interactions between
electrons and nucleons using a diamond-based vector magnetometer. The vector
magnetometer can be constructed from ensembles of nitrogen-vacancy centers
along different axes in a diamond. The $^{14}\mathrm{N} $ nuclear spins of
nitrogen-vacancy centers in the same diamond can be polarized through the
dynamic nuclear polarization method to serve as spin sources. With the vector
magnetometer, the sought-after exotic interactions can be distinguished from
the magnetic dipole-dipole interaction. For the axion-mediated interaction $
V_{PP} $, new upper bounds of the coupling $ |g_{P}^{e} g_{P}^{N}| $ are
expected within the force range from 10 nm to 100 $ \mu $m. For the $ Z'
$-mediated interaction $ V_{AA} $, new upper bounds of the coupling $
|g_{A}^{e} g_{A}^{N}| $ are expected within the force range from 10 nm to 1 cm.
The new upper bounds for $ V_{PP} $ and $ V_{AA} $ are both expected to be more
than 5 orders of magnitude more stringent than existing constraints at the
force range of 1 $ \mu $m with the total measurement time of one day.",2402.15042v1
2024-03-13,Phase diagram of the $J_1$-$J_2$ quantum Heisenberg model for arbitrary spin,"We use the spin functional renormalization group to investigate the
$J_1$-$J_2$ quantum Heisenberg model on a square lattice. By incorporating sum
rules associated with the fixed length of the spin operators as well as the
nontrivial quantum dynamics implied by the spin algebra, we are able to compute
the ground state phase diagram for arbitrary spin $S$, including the quantum
paramagnetic phase at strong frustration. Our prediction for the extent of this
paramagnetic region for $ S = 1/2 $ agrees well with other approaches that are
computationally more expensive. We find that the quantum paramagnetic phase
disappears for $ S \gtrsim 5 $ due to the suppression of quantum fluctuations
with increasing $S$.",2403.08713v1
2024-03-24,Covariant Lagrangian Cubic Interaction Vertices For Irreducible Higher Spin Fields in Minkowski Backgrounds,"We review the application of BRST and BRST-BV approaches to construct the
generic off-shell local Lorentz covariant cubic interaction vertices for
irreducible massless and massive higher integer spin fields (as the candidates
for massive particles in the Dark Matter problem) on $d$-dimensional Minkowski
spaces. It is shown that equivalence among two Lagrangian dynamics for the same
cubically interacting fields with given masses and spins obtained by means of
the approach with complete BRST, $Q$, operator and of one with incomplete BRST,
$Q_c$, operator in presence of consistent off-shell holonomic (traceless)
constraints can be uplifted from the equivalence of the Lagrangians for free
higher spin fields. We found that to get non-contradictory Lagrangians for
irreducible interacting higher-spin fields within approach with $Q_c$ operator,
together with off-shell algebraic constraints in addition to necessary
condition of superconmmuting of $Q_c$ with appropriate holonomic constraints on
the field and gauge parameter vectors, these constraints should form Abelian
superalgebra both with BRST operator above and with operators of cubic
vertices.",2403.16164v1
2024-04-08,Candidate quantum spin liquids on the maple-leaf lattice,"Motivated by recent numerical studies reporting putative quantum paramagnetic
behavior in spin-$1/2$ Heisenberg models on the maple-leaf lattice, we classify
Abrikosov fermion mean-field Ans\""atze of fully symmetric $U(1)$ and
$\mathbb{Z}_{2}$ quantum spin liquids within the framework of projective
symmetry groups. We obtain a total of $17$ $U(1)$ and $12$ $\mathbb{Z}_{2}$
algebraic PSGs, and, upon restricting their realization via mean-field
Ans\""atze with nearest-neighbor amplitudes (relevant to the studied models),
only 12 $U(1)$ and 8 $\mathbb{Z}_{2}$ distinct phases are obtained. We present
both singlet and triplet fields for all Ans\""atze up to third nearest-neighbor
bonds and discuss their spinon dispersions as well as their dynamical spin
structure factors. We further assess the effects of Gutzwiller projection on
the equal-time spin structure factors, and identify a $U(1)$ Fermi surface spin
liquid whose structure factor most closely reproduces the one obtained from
pseudo-fermion functional renormalization group calculations.",2404.05617v1
2023-06-05,Non-equilibrium dynamics of spin-lattice coupling,"Interactions between the different degrees of freedom form the basis of many
manifestations of intriguing physics in condensed matter. In this respect,
quantifying the dynamics of normal modes that themselves arise from these
interactions and how they interact with other excitations is of central
importance. Of the different types of coupling that are often important,
spin-lattice coupling is relevant to several sub-fields of condensed matter
physics; examples include spintronics, high-TC superconductivity, and
topological materials. While theories of materials where spin-lattice coupling
is relevant can sometimes be used to infer the magnitude and character of this
interaction, experimental approaches that can directly measure it are rare and
incomplete. Here we use time-resolved X-ray diffraction to directly access the
spin-lattice coupling by measuring both ultrafast atomic motion and the
associated spin dynamics following the excitation of a coherent electromagnon
by an intense THz pulse in a multiferroic hexaferrite. Comparing the dynamics
of the two different components, one striking outcome is the different phase
shifts relative to the driving field. This phase shift provides insight into
the excitation process of such a coupled mode. This direct observation of
combined lattice and magnetization dynamics paves the way to access the
mode-selective spin-lattice coupling strength, which remains a missing
fundamental parameter for ultrafast control of magnetism and is relevant to a
wide variety of correlated electron physics.",2306.02676v1
2012-06-04,Electron doping evolution of the anisotropic spin excitations in BaFe2-xNixAs2,"We use inelastic neutron scattering to systematically investigate the
Ni-doping evolution of the low-energy spin excitations in BaFe2-xNixAs2
spanning from underdoped antiferromagnet to overdoped superconductor (0.03< x <
0.18). In the undoped state, the low-energy (<80 meV) spin waves of BaFe2As2
form transversely elongated ellipses in the [H, K] plane of the reciprocal
space. Upon Ni-doping, the c-axis magnetic exchange coupling is rapidly
suppressed and the momentum distribution of spin excitations in the [H, K]
plane is enlarged in both the transverse and longitudinal directions with
respect to the in-plane AF ordering wave vector of the parent compound. As a
function of increasing Ni-doping x, the spin excitation widths increase
linearly but with a larger rate along the transverse direction. These results
are in general agreement with calculations of dynamic susceptibility based on
the random phase approximation (RPA) in an itinerant electron picture. For
samples near optimal superconductivity at x= 0.1, a neutron spin resonance
appears in the superconducting state. Upon further increasing the
electron-doping to decrease the superconducting transition temperature Tc, the
intensity of the low-energy magnetic scattering decreases and vanishes
concurrently with vanishing superconductivity in the overdoped side of the
superconducting dome. Comparing with the low-energy spin excitations centered
at commensurate AF positions for underdoped and optimally doped materials
(x<0.1), spin excitations in the over-doped side (x=0.15) form transversely
incommensurate spin excitations, consistent with the RPA calculation.
Therefore, the itinerant electron approach provides a reasonable description to
the low-energy AF spin excitations in BaFe2-xNixAs2.",1206.0653v2
2015-08-25,Controlling spin relaxation with a cavity,"Spontaneous emission of radiation is one of the fundamental mechanisms by
which an excited quantum system returns to equilibrium. For spins, however,
spontaneous emission is generally negligible compared to other non-radiative
relaxation processes because of the weak coupling between the magnetic dipole
and the electromagnetic field. In 1946, Purcell realized that the spontaneous
emission rate can be strongly enhanced by placing the quantum system in a
resonant cavity -an effect which has since been used extensively to control the
lifetime of atoms and semiconducting heterostructures coupled to microwave or
optical cavities, underpinning single-photon sources. Here we report the first
application of these ideas to spins in solids. By coupling donor spins in
silicon to a superconducting microwave cavity of high quality factor and small
mode volume, we reach for the first time the regime where spontaneous emission
constitutes the dominant spin relaxation mechanism. The relaxation rate is
increased by three orders of magnitude when the spins are tuned to the cavity
resonance, showing that energy relaxation can be engineered and controlled
on-demand. Our results provide a novel and general way to initialise spin
systems into their ground state, with applications in magnetic resonance and
quantum information processing. They also demonstrate that, contrary to popular
belief, the coupling between the magnetic dipole of a spin and the
electromagnetic field can be enhanced up to the point where quantum
fluctuations have a dramatic effect on the spin dynamics; as such our work
represents an important step towards the coherent magnetic coupling of
individual spins to microwave photons.",1508.06148v2
2018-08-07,Spin orientations of merging black holes formed from the evolution of stellar binaries,"We study the expected spin misalignments of merging binary black holes (BHs)
formed in isolation by combining state-of-the-art population-synthesis models
with efficient post-Newtonian evolutions, thus tracking sources from stellar
formation to gravitational-wave detection. We present extensive predictions of
the properties of sources detectable by both current and future
interferometers. We account for the fact that detectors are more sensitive to
spinning BH binaries with suitable spin orientations and find that this
significantly impacts the population of sources detectable by LIGO, while this
is not the case for 3rd-generation detectors. We find that three formation
pathways, differentiated by the order of core collapse and common-envelope
phases, dominate the observed population, and that their relative importance
critically depends on the recoils imparted to BHs at birth. Our models suggest
that measurements of the ""effective-spin"" parameter $\chi_{\rm eff}$ will allow
for powerful constraints. For instance, we find that the role of spin
magnitudes and spin directions in $\chi_{\rm eff}$ can be largely disentangled,
and that the symmetry of the effective-spin distribution is a robust indicator
of the binary's formation history. Our predictions for individual spin
directions and their precessional morphologies confirm and extend early toy
models, while exploring substantially more realistic and broader sets of
initial conditions. Our main conclusion is that specific subpopulations of BH
binaries will exhibit distinctive precessional dynamics: these classes include
(but are not limited to) sources where stellar tidal interactions act on
sufficiently short timescales, and massive binaries produced in pulsational
pair-instability supernovae. Measurements of BH spin orientations have enormous
potential to constrain specific evolutionary processes in the lives of massive
binary stars.",1808.02491v2
2020-08-21,"One dimensional nexus objects, network of Kibble-Lazarides-Shafi string walls, and their spin dynamic response in polar distorted B-phase of $^3$He","The Kibble-Lazarides-Shafi (KLS) domain wall problem in the axion solution of
CP violation in QCD has condensed-matter based analogy in the nafen-distorted
superfluid $^3$He. Recent experiment in rotating superfluid $^3$He produced the
network of KLS string walls in human controllable system. In this system, KLS
string wall appears in two-step symmetry break transition from normal phase to
polar-distorted B phase and turn out to be the descendants of HQVs of polar
phase. Here we show the KLS string wall smoothly connects to spin solitons when
the spin orbital coupling is taken into account. This means HQVs are 1D nexus
which connects the spin solitons and the KLS domain walls. This is because the
subgroup $G=\pi_{1}(S_{S}^{1},\tilde{R}_{2})$ of relative homotopy group
describing the spin solitons is isomorphic to the group describing the half
spin vortices -- the spin textures KLS string wall. In the nafen-distorted
$^3$He system, 1D nexus objects and the spin solitons with topological
invariant $2/4$ form two different types of network, which are named as
pseudo-random lattices of inseparable and separable spin solitons. These two
types lattices correspond to two different representations of $G$. We discuss
the condition under which pseudo-random lattices model works. The equilibrium
configuration and surface densities of free energies are calculated by numeric
minimization. Based on the equilibrium spin textures of different pseudo-random
lattices, we calculated their transverse NMR spectrum, the resulted frequency
shifts and $\sqrt{\Omega}$-scaling of ratio intensity exactly coincide with the
experimental measurements. We also discussed the mirror symmetry in the
presence of KLS domain wall and the influence of the explicitly break of this
discrete symmetry. Our discussions and considerations can be applied to the
composite defects in other condensed matter and cosmological system.",2008.09286v5
2022-01-18,Magnetic correlation between two local spins in a quantum spin Hall insulator,"Two spins located at the edge of a quantum spin Hall insulator may interact
with each other via indirect spin-exchange interaction mediated by the helical
edge states, namely the RKKY interaction, which can be measured by the magnetic
correlation between the two spins. By means of the newly developed natural
orbitals renormalization group (NORG) method, we investigated the magnetic
correlation between two Kondo impurities interacting with the helical edge
states, based on the Kane-Mele model defined in a finite zigzag graphene
nanoribbon with spin-orbital coupling (SOC). We find that the SOC effect breaks
the symmetry in spatial distribution of the magnetic correlation, leading to
anisotropy in the RKKY interaction. Specifically, the total correlation is
always ferromagnetic (FM) when the two impurities are located at the same
sublattice, while it is always antiferromagnetic (AFM) when at the different
sublattices. Meanwhile, the behavior of the in-plane correlation is consistent
with that of the total correlation. However, the out-of-plane correlation can
be tuned from FM to AFM by manipulating either the Kondo coupling or the
interimpurity distance. Furthermore, the magnetic correlation is tunable by the
SOC, especially that the out-of-plane correlation can be adjusted from FM to
AFM by increasing the strength of SOC. Dynamic properties of the system,
represented by the spin-staggered excitation spectrum and the spin-staggered
susceptibility at the two impurity sites, are finally explored. It is shown
that the spin-staggered susceptibility is larger when the two impurities are
located at the different sublattices than at the same sublattice, which is
consistent with the behavior of the out-of-plane correlation. On the other
hand, our study further demonstrates that the NORG is an effective numerical
method for studying the quantum impurity systems.",2201.06790v1
2022-02-09,First-principles theory of extending the spin qubit coherence time in hexagonal boron nitride,"Negatively charged boron vacancies (VB-) in hexagonal boron nitride (h-BN)
are a rapidly developing qubit platform in two-dimensional materials for
solid-state quantum applications. However, their spin coherence time (T2) is
very short, limited to a few microseconds owing to the inherently dense nuclear
spin bath of the h-BN host. As the coherence time is one of the most
fundamental properties of spin qubits, the short T2 time of VB- could
significantly limit its potential as a promising spin qubit candidate. In this
study, we theoretically proposed two materials engineering methods, which can
substantially extend the T2 time of the VB- spin by four times more than its
intrinsic T2. We performed quantum many-body computations by combining density
functional theory and cluster correlation expansion and showed that replacing
all the boron atoms in h-BN with the 10B isotope leads to the coherence
enhancement of the VB- spin by a factor of three. In addition, the T2 time of
the VB- can be enhanced by a factor of 1.3 by inducing a curvature around VB-.
Herein, we elucidate that the curvature-induced inhomogeneous strain creates
spatially varying quadrupole nuclear interactions, which effectively suppress
the nuclear spin flip-flop dynamics in the bath. Importantly, we find that the
combination of isotopic enrichment and strain engineering can maximize the VB-
T2, yielding 207.2 and 161.9 {\mu}s for single- and multi-layer h-10BN,
respectively. Furthermore, our results can be applied to any spin qubit in
h-BN, strengthening their potential as material platforms to realize
high-precision quantum sensors, quantum spin registers, and atomically thin
quantum magnets.",2202.04346v2
2022-06-23,The curious case of GW200129: interplay between spin-precession inference and data-quality issues,"Measurement of spin-precession in black hole binary mergers observed with
gravitational waves is an exciting milestone as it relates to both general
relativistic dynamics and astrophysical binary formation scenarios. In this
study, we revisit the evidence for spin-precession in GW200129 and localize its
origin to data in LIGO Livingston in the 20--50\,Hz frequency range where the
signal amplitude is lower than expected from a non-precessing binary given all
the other data. These data are subject to known data quality issues as a glitch
was subtracted from the detector's strain data. The lack of evidence for
spin-precession in LIGO Hanford leads to a noticeable inconsistency between the
inferred binary mass ratio and precessing spin in the two LIGO detectors,
something not expected from solely different Gaussian noise realizations. We
revisit the LIGO Livingston glitch mitigation and show that the difference
between a spin-precessing and a non-precessing interpretation for GW200129 is
smaller than the statistical and systematic uncertainty of the glitch
subtraction, finding that the support for spin-precession depends sensitively
on the glitch modeling. We also investigate the signal-to-noise ratio $\sim7$
trigger in the less sensitive Virgo detector. Though not influencing the
spin-precession studies, the Virgo trigger is grossly inconsistent with the
ones in LIGO Hanford and LIGO Livingston as it points to a much heavier system.
We interpret the Virgo data in the context of further data quality issues.
While our results do not disprove the presence of spin-precession in GW200129,
we argue that any such inference is contingent upon the statistical and
systematic uncertainty of the glitch mitigation. Our study highlights the role
of data quality investigations when inferring subtle effects such as
spin-precession for short signals such as the ones produced by high-mass
systems.",2206.11932v2
2022-08-01,Terahertz spin-to-charge current conversion in stacks of ferromagnets and the transition-metal dichalcogenide NbSe$_2$,"Transition-metal dichalcogenides (TMDCs) are an aspiring class of materials
with unique electronic and optical properties and potential applications in
spin-based electronics. Here, we use terahertz emission spectroscopy to study
spin-to-charge current conversion (S2C) in the TMDC NbSe$_2$ in
ultra-high-vacuum-grown F|NbSe$_2$ thin-film stacks, where F is a layer of
ferromagnetic Fe or Ni. Ultrafast laser excitation triggers an ultrafast spin
current that is converted into an in-plane charge current and, thus, a
measurable THz electromagnetic pulse. The THz signal amplitude as a function of
the NbSe$_2$ thickness shows that the measured signals are fully consistent
with an ultrafast optically driven injection of an in-plane-polarized spin
current into NbSe$_2$. Modeling of the spin-current dynamics reveals that a
sizable fraction of the total S2C originates from the bulk of NbSe$_2$ with the
same, negative, sign as the spin Hall angle of pure Nb. By quantitative
comparison of the emitted THz radiation from F|NbSe$_2$ to F|Pt reference
samples and the results of ab-initio calculations, we estimate that the spin
Hall angle of NbSe$_2$ for an in-plane polarized spin current lies between
-0.2% and -1.1%, while the THz spin-current relaxation length is of the order
of a few nanometers.",2208.00846v1
2023-06-20,Dynamical nuclear spin polarization in a quantum dot with an electron spin driven by electric dipole spin resonance,"We analyze the polarization of nuclear spins in a quantum dot induced by a
single-electron spin that is electrically driven to perform coherent Rabi
oscillations. We derive the associated nuclear-spin polarization rate and
analyze its dependence on the accessible control parameters, especially the
detuning of the driving frequency from the electron Larmor frequency. The
arising nuclear-spin polarization is related to the Hartmann-Hahn effect known
from the NMR literature with two important differences. First, in quantum dots
one typically uses a micro magnet, leading to a small deflection of the
quantization axes of the electron and nuclear spins. Second, the electric
driving wiggles the electron with respect to the atomic lattice. The two
effects, absent in the traditional Hartmann-Hahn scenario, give rise to two
mechanisms of nuclear-spin polarization in gated quantum dots. The arising
nuclear-spin polarization is a resonance phenomenon, achieving maximal
efficiency at the resonance of the electron Rabi and nuclear Larmor frequency
(typically a few or a few tens of MHz). As a function of the driving frequency,
the polarization rate can develop sharp peaks and reach large values at them.
Since the nuclear polarization is experimentally detected as changes of the
electron Larmor frequency, we often convert the former to the latter in our
formulas and figures. In these units, the polarization can reach hundreds of
MHz/s in GaAs quantum dots and at least tens of kHz/s in Si quantum dots. We
analyze possibilities to exploit the resonant polarization effects for
achieving large nuclear polarization and for stabilizing the Overhauser field
through feedback.",2306.11253v2
2023-10-11,Anomalously large spin-dependent electron correlation in nearly half-metallic ferromagnet CoS$_2$,"The spin-dependent band structure of CoS$_2$ which is a candidate for a
half-metallic ferromagnet was investigated by both spin- and angle-resolved
photoemission spectroscopy and theoretical calculations, in order to reappraise
the half-metallicity and electronic correlations. We determined the
three-dimensional Fermi surface and the spin-dependent band structure. As a
result, we found that a part of the minority spin bands is on the occupied side
in the vicinity of the Fermi level, providing spectroscopic evidence that
CoS$_2$ is not but very close to a half-metal. Band calculations using density
functional theory with generalized gradient approximation showed a good
agreement with the observed majority spin $e_g$ bands, while it could not
explain the observed band width of the minority-spin eg bands. On the other
hand, theoretical calculations using dynamical mean field theory could better
reproduce the strong mass renormalization in the minority-spin $e_g$ bands. All
those results strongly suggest the presence of anomalously enhanced
spin-dependent electron correlation effects on the electronic structure in the
vicinity of the half-metallic state. We also report the temperature dependence
of the electronic structure across the Curie temperature and discuss the
mechanism of the thermal demagnetization. Our discovery of the anomalously
large spin-dependent electronic correlations not only demonstrates a key factor
in understanding the electronic structure of half-metals but also provides a
motivation to improve theoretical calculations on spin-polarized strongly
correlated systems.",2310.07274v1
1998-05-22,WKB for a damped spin,"The master equation for a damped spin well known from the theory of
superradiance, is written as a finite-difference equation and solved by a
WKB-like method. The propagator thus obtained looks like the van Vleck
propagator of a certain classical Hamiltonian system with one degree of
freedom. A new interpretation is provided of the temporal broadening of
initially sharp probability distributions as the analogue of the spreading of
the quantum mechanical wave packet.",9805018v1
1999-11-12,Classical statistical mechanics of a few-body interacting spin model,"We study the emergence of Boltzmann's law for the ""single particle energy
distribution"" in a closed system of interacting classical spins. It is shown
that for a large number of particles Boltzmann's law may occur, even if the
interaction is very strong. Specific attention is paid to classical analogs of
the average shape of quantum eigenstates and ""local density of states"", which
are very important in quantum chaology. Analytical predictions are then
compared with numerical data.",9911018v1
1993-03-20,Analytical Solution of the Off-Equilibrium Dynamics of a Long Range Spin-Glass Model,"We study the non-equilibrium relaxation of the spherical spin-glass model
with p-spin interactions in the $N \rightarrow \infty$ limit. We analytically
solve the asymptotics of the magnetization and the correlation and response
functions for long but finite times. Even in the thermodynamic limit the system
exhibits `weak' (as well as `true') ergodicity breaking and aging effects. We
determine a functional Parisi-like order parameter $P_d(q)$ which plays a
similar role for the dynamics to that played by the usual function for the
statics.",9303036v1
1993-03-26,Nonequilibrium Dynamics and Aging in the Three--Dimensional Ising Spin Glass Model,"The low temperature dynamics of the three dimensional Ising spin glass in
zero field with a discrete bond distribution is investigated via MC
simulations. The thermoremanent magnetization is found to decay algebraically
and the temperature dependent exponents agree very well with the experimentally
determined values. The nonequilibrium autocorrelation function $C(t,t_w)$ shows
a crossover at the waiting (or {\em aging}) time $t_w$ from algebraic {\em
quasi-equilibrium} decay for times $t$$\ll$$t_w$ to another, faster algebraic
decay for $t$$\gg$$t_w$ with an exponent similar to one for the remanent
magnetization.",9303048v1
1994-04-28,Dynamics of N-spins Quantum Ferromagnet with Uniform Exchange: Exact Solution,"The transverse spin autocorrelation function at an arbitrary temperature are
calculated rigorously for the system of $N$ uniformly exchanged quantum spins.
At large $N$ the correlator in the para-phase is found to have a Gaussian bump
at small times and a non vanishing tail at large times. A possible application
of those exact results as forming a starting dynamical mean-field approximation
for long-range quantum magnets and an accompanied physical picture are
discussed.",9404093v1
1994-08-19,Escape from Metastability via Aging: Non-Equilibrium Dynamics in a One- Dimensional Ising Model,"The non-equilibrium dynamics of a one-dimensional Ising model with uniform,
short-ranged three-spin interactions is investigated. It is shown that this
model possesses an exponentially large number of metastable configurations that
are stable against single spin flips. This glass-like situation results in a
complete freezing of the system at low temperatures for times smaller than an
intrinsic time-scale, which diverges exponentially with inverse temperature.
Via thermal activation the system eventually escapes from this frozen state,
which is signals the onset of aging by domain growth.",9408060v1
1995-03-31,Recipes for metastable states in Spin Glasses,"In this paper we develop a method introduced by one of us to study metastable
states in spin glasses. We consider a `potential function' defined as the free
energy of a system at a given temperature $T$ constrained to have a fixed
overlap with a reference configuration of equilibrium at temperature $T'$. We
apply the method to the spherical p-spin glass and to some generalization of
this model in the range of temperatures between the dynamic and the static
transition. The analysis suggests a correspondence among local minima of the
potential and metastable states. This correspondence is confirmed studying the
relaxation dynamics at temperature $T$ of a system starting from an initial
configuration equilibrated at a different temperature $T'$.",9503167v1
1996-03-10,Macros and Multiscale Dynamics in Spin Glasses,"We study the spacial and temporal multiscale properties of complex systems.
We present accelerated algorithms for dilute spin glasses and display
explicitly their relation to the effective dynamics of specific collective
degrees of freedom (macros).
  We discuss the difficulties in applying multiscale-cluster algorithms(MCA) to
general frustrated systems: MCA does not succeed to break the system into
clusters. We relate these difficulties to rigorous negative results in systems
with an ultrametric space of ground states: the tunneling between vacua cannot
be expressed into an algorithm acting upon independent macros.",9603056v1
1996-04-17,Cluster Dynamics for Randomly Frustrated Systems with Finite Connectivity,"In simulations of some infinite range spin glass systems with finite
connectivity, it is found that for any resonable computational time, the
saturatedenergy per spin that is achieved by a cluster algorithm is lowered in
comparison to that achieved by Metropolis dynamics.The gap between the average
energies obtained from these two dynamics is robust with respect to variations
of the annealing schedule. For some probability distribution of the
interactions the ground state energy is calculated analytically within the
replica symmetry assumptionand is found to be saturated by a cluster algorithm.",9604112v1
1996-12-25,Aging Relation for Ising Spin Glasses,"We derive a rigorous dynamical relation on aging phenomena -- the aging
relation -- for Ising spin glasses using the method of gauge transformation.
The waiting-time dependence of the auto-correlation function in the
zero-field-cooling process is equivalent with that in the field-quenching
process. There is no aging on the Nishimori line; this reveals arguments for
dynamical properties of the Griffiths phase and the mixed phase. The present
method can be applied to other gauge-symmetric models such as the XY gauge
glass.",9612225v1
1997-01-06,"Directed polymer in random media, in two dimensions: numerical study of the aging dynamics","Following a recent work by Yoshino, we study the aging dynamics of a directed
polymer in random media, in 1+1 dimensions. Through temperature quench, and
temperature cycling numerical experiments similar to the experiments on real
spin glasses, we show that the observed behaviour is comparable to the one of a
well known mean field spin glass model. The observation of various quantities
(correlation function, ``clonation'' overlap function) leads to an analysis of
the phase space landscape.",9701021v1
1997-08-01,Double exchange magnets: Spin-dynamics in the paramagnetic phase,"The electronic structure of perovskite manganese oxides is investigated in
terms of a Kondo lattice model with ferromagnetic Hund coupling and
antiferromagnetic exchange between $t_{2g}$-spins using a finite temperature
diagonalization technique. Results for the dynamic structure factor are
consistent with recent neutron scattering experiments for the bilayer manganite
La$_{1.2}$Sr$_{1.8}$Mn$_2$O$_7$ . The susceptibility shows Curie-Weiss
behaviour and is used to derive a phase diagram. In the paramagnetic phase
carriers are characterized as ferromagnetic polarons in an antiferromagnetic
spin liquid.",9708007v1
1997-09-25,Dynamical fluctuations in an exactly solvable model of spin glasses,"In this work we calculate the dynamical fluctuations at O(1/N) in the low
temperature phase of the $p=2$ spherical spin glass model. We study the
large-times asymptotic regimes and we find, in a short time-differences regime,
a fluctuation dissipation relation for the four-point correlation functions.
This relation can be extended to the out of equilibrium regimes introducing a
function $X_{t}$ which, for large time $t$, we find scales as $t^{-1/2}$ as in
the case of the two-point functions.",9709279v1
1997-10-15,A projection method for statics and dynamics of lattice spin systems,"A method based on Monte Carlo sampling of the probability flows projected
onto the subspace of one or more slow variables is proposed for investigation
of dynamic and static properties of lattice spin systems. We illustrate the
method by applying it, with projection onto the order-parameter subspace, to
the three-dimensional 3-state Potts model in equilibrium and to metastable
decay in a three-dimensional 3-state kinetic Potts model.",9710153v2
1998-02-10,Dynamics of the Ising Spin-Glass Model in a Transverse Field,"We use quantum Monte Carlo methods and various analytic approximations to
solve the Ising spin-glass model in a transverse field in the disordered phase.
We focus on the behavior of the frequency dependent susceptibility of the
system above and below the critical field . We establish the existence of an
exact equivalence between this problem and the single-impurity Kondo model at
the quantum critical point. Our predictions for the long-time dynamics of the
model are in good agreement with experimental results on
$LiHo_{0.167}Y_{0.833}F_4$.",9802106v2
1998-05-05,The phase space structure of supercooled liquids: Evidence of a dynamical critical temperature,"We calculate local potential energy minima (inherent structures) for a simple
model of orthoterphenyl (OTP), from computer simulations over a wide
temperature range. We show that the results are very sensitive to the system
size. We locate, from the temperature and size dependence of inherent structure
energies, a well defined cross-over temperature that corresponds to the
dynamical critical temperature predicted by mode coupling theory and in mean
field spin glass models. Comparing the known phase space structure of mean
field $p$-spin models and the present results for the OTP model, we find
evidence supporting the proposed similarity between glass-forming liquids and a
class of spin glass models.",9805040v1
1999-06-08,Arrested States formed on Quenching Spin Chains with Competing Interactions and Conserved Dynamics,"We study the effects of rapidly cooling to T = 0 a spin chain with conserved
dynamics and competing interactions. Depending on the degree of competition,
the system is found to get arrested in different kinds of metastable states.
The most interesting of these has an inhomogeneous mixture of interspersed
active and quiescent regions. In this state, the steady-state autocorrelation
function decays as a stretched exponential $\sim
\exp(-{(t/\tau_{o})}^{{1}\over{3}})$, and there is a two-step relaxation to
equilibrium when the temperature is raised slightly.",9906117v1
1999-08-03,Semiclassical mechanics of a non-integrable spin cluster,"We study detailed classical-quantum correspondence for a cluster system of
three spins with single-axis anisotropic exchange coupling. With autoregressive
spectral estimation, we find oscillating terms in the quantum density of states
caused by classical periodic orbits: in the slowly varying part of the density
of states we see signs of nontrivial topology changes happening to the energy
surface as the energy is varied. Also, we can explain the hierarchy of quantum
energy levels near the ferromagnetic and antiferromagnetic states with EKB
quantization to explain large structures and tunneling to explain small
structures.",9908055v1
1999-08-13,Single-Particle Pseudogap in Two-Dimensional Electron Systems,"We investigate pseudogap phenomena in the 2D electron system.
  Based on the mode-mode coupling theory of antiferromagnetic (AFM) and
$d_{x^2-y^2}$-wave superconducting ($d$SC) fluctuations, single-particle
dynamics is analyzed. For the parameter values of underdoped cuprates,
pseudogap structure grows in the single-particle spectral weight $A(k,\omega)$
around the wave vector $(\pi,0)$ and $(0,\pi)$ below the pseudo-spin-gap
temperature $\TPG$ signaled by the reduction of dynamical spin correlations in
qualitative agreement with the experimental data. The calculated results for
the overdoped cuprates also reproduce the absence of the pseudogap in the
experiments. We also discuss limitations of our weak-coupling approach.",9908195v1
1999-09-08,Non-equilibrium dynamics in an interacting nanoparticle system,"Non-equilibrium dynamics in an interacting Fe-C nanoparticle sample,
exhibiting a low temperature spin glass like phase, has been studied by low
frequency ac-susceptibility and magnetic relaxation experiments. The
non-equilibrium behavior shows characteristic spin glass features, but some
qualitative differences exist. The nature of these differences is discussed.",9909123v2
1999-09-27,Condensation energy in the spin-fermion model for cuprates,"We use the Scalapino-White relation between the condensation energy and the
difference between the dynamical structure factor in the normal and the
superconducting states to compute the condensation energy in the spin-fermion
model. We show that at strong coupling, the extra low-frequency spectral weight
associated with the resonance peak in the dynamical structure factor in a
superconductor is compensated only at energies $\sim J$ which are much larger
than the superconducting gap $\Delta$. We argue that in this situation, the
condensation energy is large and well accounts for the data for cuprates.",9909385v1
1999-09-29,Evidence for Anisotropic Kondo Behavior in Ce0.8La0.2Al3,"We have performed an inelastic neutron scattering study of the low energy
spin dynamics of the heavy fermion compound Ce0.8La0.2Al3 as a function of
temperature and external pressure up to 5 kbar. At temperatures below 3 K, the
magnetic response transforms from a quasi-elastic form, common to many heavy
fermion systems, to a single well-defined inelastic peak, which is extremely
sensitive to external pressure. The scaling of the spin dynamics and the
thermodynamic properties are in agreement with the predictions of the
anisotropic Kondo model.",9909438v1
1999-11-22,Parallel dynamics of the asymmetric extremely diluted Ashkin-Teller neural network,"The parallel dynamics of the asymmetric extremely diluted Ashkin-Teller
neural network is studied using signal-to-noise analysis techniques. Evolution
equations for the order parameters are derived, both at zero and finite
temperature. The retrieval properties of the network are discussed in terms of
the four-spin coupling strength and the temperature. It is shown that the
presence of a four-spin coupling enhances the retrieval quality.",9911349v1
1999-12-21,Anderson impurity in a correlated conduction band,"We investigate the physics of a magnetic impurity with spin 1/2 in a
correlated metallic host. Describing the band by a Hubbard Hamiltonian, the
problem is analyzed using dynamical mean-field-theory in combination with
Wilson's nonperturbative numerical renormalization group. We present results
for the single-particle density of states and the dynamical spin susceptibility
at zero temperature. New spectral features (side peaks) are found which should
be observable experimentally. In addition, we find a general enhancement of the
Kondo scale due to correlations. Nevertheless, in the metallic phase, the Kondo
scale always vanishes exponentially in the limit of small hybridization.",9912396v2
2000-03-17,The role of Berry phase in the spectrum of order parameter dynamics: a new perspective on Haldane's conjecture on antiferromagnetic spin chains,"We formulate the dynamics of local order parameters by extending the recently
developed adiabatic spinwave theory involving the Berry curvature, and derive a
formula showing explicitly the role of the Berry phase in determining the
spectral form of the low-lying collective modes. For antiferromagnetic spin
chains, the Berry phase becomes a topological invariant known as the Chern
number. Our theory predicts the existence of the Haldane gap for a
topologically trivial ground state, and a linear dispersion of low-lying
excitations for a non-trivial ground state.",0003293v1
2000-11-02,Real-Time-RG Analysis of the Dynamics of the Spin-Boson Model,"Using a real-time renormalization group method we determine the complete
dynamics of the spin-boson model with ohmic dissipation for coupling strengths
$\alpha\lesssim 0.1-0.2$. We calculate the relaxation and dephasing time, the
static susceptibility and correlation functions. Our results are consistent
with quantum Monte Carlo simulations and the Shiba relation. We present for the
first time reliable results for finite cutoff and finite bias in a regime where
perturbation theory in $\alpha$ or in tunneling breaks down. Furthermore, an
unambigious comparism to results from the Kondo model is achieved.",0011051v1
2001-01-04,Dynamical mean-field theory for pairing and spin gap in the attractive Hubbard model,"We solve the attractive Hubbard model for arbitrary interaction strengths
within dynamical mean-field theory. We compute the transition temperature for
superconductivity and analyze electron pairing in the normal phase. The normal
state is a Fermi liquid at weak coupling and a non-Fermi liquid state with a
spin gap at strong coupling. Away from half-filling, the quasi-particle weight
vanishes discontinuously at the transition between the two normal states.",0101047v1
2001-07-24,Fast relaxation time in a spin model with glassy behavior,"We consider a frustrated spin model with a glassy dynamics characterized by a
slow component and a fast component in the relaxation process. The slow process
involves variables with critical behavior at finite temperature T_p and has a
global character like the (structural) alpha-relaxation of glasses. The fast
process has a more local character and can be associated to the beta-relaxation
of glasses. At temperature T>T_p the fast relaxation follows the non-Arrhenius
behavior of the slow variables. At T ~< T_p the fast variables have an
Arrhenius behavior, resembling the alpha-beta bifurcation of fragile glasses.
The model allows us to analyze the relation between the dynamics and the
thermodynamics.",0107491v1
2001-08-04,Magnetic Field Pinning of a Dynamic Electron-Spin-Resonance Line in a GaAs/AlGaAs Heterostructure,"Electrically detected electron spin resonance (ESR) is used to study the
hyperfine interaction of the two-dimensional electrons and the nuclei of the
host lattice in a GaAs/AlGaAs heterostructure. Under the microwave and radio-
frequency double excitations, we have observed that the ESR line can be pinned
in a very narrow range of magnetic field - in the vicinity of the nuclear
magnetic resonance (NMR) of the nuclei of the GaAs crystal. Our observations
suggest that this pinning effect is the result of a competition process between
the ESR induced dynamic nuclear polarization and the NMR induced
depolarization.",0108080v1
2001-09-19,Dynamical mean-field theory for the normal phase of the attractive Hubbard model,"We analyze the normal phase of the attractive Hubbard model within dynamical
mean-field-theory. We present results for the pair-density, the
spin-susceptibility, the specific heat, the momentum distribution, and for the
quasiparticle weight. At weak coupling the low-temperature behavior of all
quantities is consistent with Fermi liquid theory. At strong coupling all
electrons are bound pairs, which leads to a spin gap and removes fermionic
quasi-particle excitations. The transition between the Fermi liquid phase and
the pair phase takes place at a critical coupling of the order of the
band-width and is generally discontinuous at sufficiently low temperatures.",0109343v1
2001-10-01,Metastable states in the Blume-Emery-Griffiths spin glass model,"We study the Blume-Emery-Griffiths spin glass model in presence of an
attractive coupling between real replicas, and evaluate the effective potential
as a function of the density overlap. We find that there is a region, above the
first order transition of the model, where metastable states with a large
density overlap exist. The line where these metastable states appear should
correspond to a purely dynamical transition, with a breaking of ergodicity.
Differently from what happens in p-spin glasses, in this model the dynamical
transition would not be the precursor of a 1-step RSB transition, but
(probably) of a full RSB transition.",0110029v1
2001-11-02,Critical dynamics of singlet and triplet excitations in strongly frustrated spin systems,"New data for the two-dimensional J1-J2 model shows that the critical points
for singlet and triplet excitations near J2/J1=0.38 are very close together, or
coincident. We propose that this is a more general result: in strongly
frustrated spin systems the critical dynamics of singlet and triplet
excitations are closely related. An effective field theory for such a critical
point, or points, is developed, and its implications discussed. The analysis
suggests the existance of gapless or almost gapless singlet excitations in the
magnetically disordered phase.",0111025v1
2002-07-10,Dynamics of price and trading volume in a spin model of stock markets with heterogeneous agents,"The dynamics of a stock market with heterogeneous agents is discussed in the
framework of a recently proposed spin model for the emergence of bubbles and
crashes. We relate the log returns of stock prices to magnetization in the
model and find that it is closely related to trading volume as observed in real
markets. The cumulative distribution of log returns exhibits scaling with
exponents steeper than 2 and scaling is observed in the distribution of
transition times between bull and bear markets.",0207253v1
2003-03-06,A real space renormalization group approach to spin glass dynamics,"The slow non-equilibrium dynamics of the Edwards-Anderson spin glass model on
a hierarchical lattice is studied by means of a coarse-grained description
based on renormalization concepts. We evaluate the isothermal aging properties
and show how the occurrence of temperature chaos is connected to a gradual loss
of memory when approaching the overlap length. This leads to rejuvenation
effects in temperature shift protocols and to rejuvenation--memory effects in
temperature cycling procedures with a pattern of behavior parallel to
experimental observations.",0303116v1
2003-05-19,"Raman scattering studies of spin, charge, and lattice dynamics in Ca_{2-x}Sr_{x}RuO_{4} (0 =< x < 0.2)","We use Raman scattering to study spin, charge, and lattice dynamics in
various phases of Ca_{2-x}Sr_{x}RuO_{4}. With increasing substitution of Ca by
Sr in the range 0 =< x < 0.2, we observe (1) evidence for an increase of the
electron-phonon interaction strength, (2) an increased temperature-dependence
of the two-magnon energy and linewidth in the antiferromagnetic insulating
phase, and (3) evidence for charge gap development, and hysteresis associated
with the structural phase change, both of which are indicative of a first-order
metal-insulator transition (T_{MI}) and a coexistence of metallic and
insulating components for T < T_{MI}.",0305427v1
2003-05-22,Dissipative dynamics of an extended magnetic nanostructure: Spin necklace in a metallic environment,"We study theoretically the dynamics of an ``xxz'' spin necklace coupled to a
conduction electron sea, a model system for a nanostructure in a dissipative
environment. We extract the long-time behavior via a mapping to a multichannel
Coulomb gas problem followed by a scaling analysis. The strong quantum
fluctuations of the necklace cause a nontrivial dependence of couplings on
system size which we extract via an analysis involving the ``boundary condition
changing operator'', and confirm via a detailed numerical evaluation of one
case.",0305534v1
2003-06-13,Scaling of the magnetic response in doped antiferromagnets,"A theory of the anomalous $\omega/T$ scaling of the dynamic magnetic response
in cuprates at low doping is presented. It is based on the memory function
representation of the dynamical spin suceptibility in a doped antiferromagnet
where the damping of the collective mode is constant and large, whereas the
equal-time spin correlations saturate at low $T$. Exact diagonalization results
within the t-J model are shown to support assumptions. Consequences, both for
the scaling function and the normalization amplitude, are well in agreement
with neutron scattering results.",0306366v2
2003-07-16,"The quantum dynamics of atomic magnets, co-tunneling and dipolar-biased tunneling","Multi-spins tunneling cross-relaxations in an ensemble of weakly-coupled
Ho$^{3+}$ ions, mediated by weak anisotropic dipolar interactions, can be
evidenced by ac-susceptibility measurements in a high temperature regime. Based
on a four-body representation, including the rare-earth nuclear spin, two-ions
tunneling mechanisms can be attributed to both dipolar-biased tunneling and
co-tunneling processes. The co-reversal involving entangled pairs of magnetic
moments is discussed with a particular emphasis, giving new evidences to
elucidate the many-body quantum dynamics.",0307405v1
2003-10-14,Hole Dynamics in the Orthogonal-Dimer Spin System,"The dynamics of a doped hole in the orthogonal-dimer spin system is
investigated systematically in one, two and three dimensions. By combining the
bond-operator method with the self-consistent
  Born approximation, we argue that a dispersive quasi-particle state in the
dimer phase is well defined even for quasi-two-dimensional systems. On the
other hand, a doped hole in the plaquette-singlet phase hardly itinerates,
forming an almost localized mode. We further clarify that although the
quasi-particle weight in the dimer phase is decreased in the presence of the
interchain coupling, it is not suppressed but even enhanced upon the
introduction of the interlayer coupling.",0310320v1
2003-11-14,Magnetization reversal and spin dynamics exchange in biased F/AF bilayers probed with complex permeability spectra,"The spin dynamics of the ferromagnetic pinned layer of
ferro-antiferromagnetic coupled NiFe/MnNi bilayers is investigated in a broad
frequency range (30 MHz-6 GHz). A phenomenological model based on the
Landau-Lifshitz equation for the complex permeability of the F/AF bilayer is
proposed. The experimental results are compared to theoretical predictions. We
show that the resonance frequencies, measured during the magnetization, are
likewise hysteretic.",0311338v1
2003-11-14,Spin dynamics in exchange-biased F/AF bilayers,"The spin dynamics of the ferromagnetic pinned layer of
ferro-antiferromagnetic coupled NiFe/MnNi bilayers is investigated in a broad
frequency range (30 MHz-6 GHz). A phenomenological model based on the
Landau-Lifshitz equation for the complex permeability of the F/AF bilayer is
proposed. The experimental results are compared to theoretical predictions.",0311342v1
2003-11-19,Theory of indirect resonant inelastic X-ray scattering,"We express the cross section for indirect resonant inelastic X-ray scattering
in terms of an intrinsic dynamic correlation function of the system that is
studied with this technique. The cross section is a linear combination of the
charge response function and the dynamic longitudinal spin density correlation
function. This result is asymptotically exact for both strong and weak local
core-hole potentials. We show that one can change the relative charge and spin
contribution to the inelastic spectral weight by varying the incident photon
energy.",0311446v1
2004-12-24,"""Glassy Dynamics"" in Ising Spin Glasses -- Experiment and Simulation","The field-cooled magnetization (FCM) processes of Ising spin glasses under
relatively small fields are investigated by experiment on
Fe_{0.55}Mn_{0.45}TiO_3 and by numerical simulation on the three-dimensional
Edwards-Anderson model. Both results are explained in a unified manner by means
of the droplet picture. In particular, the cusp-like behavior of the FCM is
interpreted as evidence, not for an equilibrium phase transition under a finite
magnetic field, but for a dynamical (`blocking') transition frequently observed
in glassy systems.",0412674v2
2005-01-10,The mean field infinite range p=3 spin glass: equilibrium landscape and correlation time scales,"We investigate numerically the dynamical behavior of the mean field 3-spin
spin glass model: we study equilibrium dynamics, and compute equilibrium time
scales as a function of the system size V. We find that for increasing volumes
the time scales $\tau$ increase like $\ln \tau \propto V$. We also present an
accurate study of the equilibrium static properties of the system.",0501198v2
2005-06-24,Dynamics of Dipolar Spinor Condensates,"We study the semiclassical dynamics of a spinor condensate with the magnetic
dipole-dipole interaction included. The time evolution of the population
imbalance and the relative phase among different spin components depends
greatly on the relative strength of interactions as well as on the initial
conditions. The interplay of spin exchange and dipole-dipole interaction makes
it possible to manipulate the atomic population on different components,
leading to the phenomena of spontaneous magnetization and Macroscopic Quantum
Self Trapping. Simple estimate demonstrates that these effects are accessible
and controllable by modifying the geometry of the trapping potential.",0506630v1
2005-07-26,Butterfly hysteresis curve is a signature of adiabatic Landau-Zener transition,"We stress that the so-called butterfly hysteresis curves observed in
dynamical magnetization measurements on systems of low-spin magnetic molecules
such as V-15 and V-6 are a signature of adiabatic Landau-Zener transitions
rather than that of a phonon bottleneck. We investigate the magnetization
dynamics analytically with the help of a simple relaxation theory in the basis
of the adabatic energy levels of the spin 1/2, to a qualitative accordance with
experimental observations. In particular, reversible behavior is found near
zero field, the corresponding susceptibility being bounded by the equilibrium
and adiabatic susceptibilities from below and above, respectively.",0507618v1
2005-08-11,Quantum Dynamics of Spins Coupled by Electrons in 1D Channel,"We develop a unified theoretical description of the induced interaction and
quantum noise in a system of two spins (qubits) coupled via a
quasi-one-dimensional electron gas in the Luttinger liquid regime. Our results
allow evaluation of the degree of coherence in quantum dynamics driven by the
induced indirect exchange interaction of localized magnetic moments due to
conduction electrons, in channel geometries recently experimentally studied for
qubit control and measurement.",0508297v1
2005-09-09,Quantum trajectory analysis for electrical detection of single-electron spin resonance,"A Monte Carlo simulation on the basis of quantum trajectory approach is
carried out for the measurement dynamics of a single electron spin resonance.
The measured electron, which is confined in either a quantum dot or a defect
trap, is tunnel-coupled to a side reservoir and continuously monitored by a
mesoscopic detector. The simulation not only recovers the observed telegraphic
signal of detector current, but also predicts unique features in the output
power spectrum which are associated with electron dynamics in different
regimes.",0509228v2
2005-10-31,The Topological Non-connectivity Threshold and magnetic phase transitions in classical anisotropic long-range interacting spin system,"We analyze from the dynamical point of view the classical characteristics of
the Topological Non-connectivity Threshold (TNT), recently introduced in
F.Borgonovi, G.L.Celardo, M.Maianti, E.Pedersoli, J.Stat.Phys.,116,516(2004).
This shows interesting connections among Topology, Dynamics, and
Thermo-Statistics of ferro/paramagnetic phase transition in classical spin
systems, due to the combined effect of anisotropy and long-range interactions.",0510835v1
2005-11-11,Coherent-incoherent transition in the sub-Ohmic spin-boson model,"We study the spin-boson model with a sub-Ohmic bath using a variational
method. The transition from coherent dynamics to incoherent tunneling is found
to be abrupt as a function of the coupling strength $\alpha$ and to exist for
any power $0 < s< 1$, where the bath coupling is described by $J(\omega) \sim
\alpha \omega^{s}$. We find non-monotonic temperature dependence of the
two-level gap $\tilde{K}$ and a re-entrance regime close to the transition due
to non-adiabatic low-frequency bath modes. Differences between thermodynamic
and dynamic conditions for the transition as well as the limitations of the
simplified bath description are discussed.",0511285v1
2006-01-17,Electric field control of magnetization dynamics in ZnMnSe/ZnBeSe diluted-magnetic-semiconductor heterostructures,"We show that the magnetization dynamics in diluted magnetic semiconductors
can be controlled separately from the static magnetization by means of an
electric field. The spin-lattice relaxation (SLR) time of magnetic Mn2+ ions
was tuned by two orders of magnitude by a gate voltage applied to n-type
modulation-doped (Zn,Mn)Se/(Zn,Be)Se quantum wells. The effect is based on
providing an additional channel for SLR by a two-dimensional electron gas
(2DEG). The static magnetization responsible for the giant Zeeman spin
splitting of excitons was not influenced by the 2DEG density.",0601383v1
2006-02-21,Strict site-occupation constraint in 2d Heisenberg models and dynamical mass generation in $QED_3$ at finite temperature,"We study the effect of site occupation in 2d quantum spin systems at finite
temperature in a $\pi$-flux state description at the mean-field level. We
impose each lattice site to be occupied by a single SU(2) spin. This is
realized by means of a specific prescription. We consider the low-energy
Hamiltonian which is mapped into a $QED_3$ Lagrangian of spinons. We compare
the dynamically generated mass to the one obtained by means of an average site
occupation constraint.",0602487v1
2006-03-08,Quantum Dynamics of Atomic Coherence in a Spin-1 Condensate: Mean-Field versus Many-Body Simulation,"We analyse and numerically simulate the full many-body quantum dynamics of a
spin-1 condensate in the single spatial mode approximation. Initially, the
condensate is in a ``ferromagnetic'' state with all spins aligned along the $y$
axis and the magnetic field pointing along the z axis. In the course of
evolution the spinor condensate undergoes a characteristic change of symmetry,
which in a real experiment could be a signature of spin-mixing many-body
interactions. The results of our simulations are conveniently visualised within
the picture of irreducible tensor operators.",0603204v1
2006-03-22,Mott transition in Kagomé lattice Hubbard model,"We investigate the Mott transition in the Kagom\'e lattice Hubbard model
using a cluster extension of dynamical mean field theory. The calculation of
the double occupancy, the density of states, the static and dynamical spin
correlation functions demonstrates that the system undergoes the first-order
Mott transition at the Hubbard interaction $U/W \sim 1.4$ ($W$:bandwidth). In
the metallic phase close to the Mott transition, we find the strong
renormalization of three distinct bands, giving rise to the formation of heavy
quasiparticles with strong frustration. It is elucidated that the quasiparticle
states exhibit anomalous behavior in the temperature-dependent spin correlation
functions.",0603596v1
2006-04-25,Spin Precession and Avalanches,"In many magnetic materials, spin dynamics at short times are dominated by
precessional motion as damping is relatively small. In the limit of no damping
and no thermal noise, we show that for a large enough initial instability, an
avalanche can transition to an ergodic phase where the state is equivalent to
one at finite temperature, often above that for ferromagnetic ordering. This
dynamical nucleation phenomenon is analyzed theoretically. For small finite
damping the high temperature growth front becomes spread out over a large
region. The implications for real materials are discussed.",0604563v1
2006-09-22,Theory of magnetoresistance based on variable-range hopping in the presence of Hubbard interaction and spin-dynamics,"We develop a theory of magnetoresistance based on variable-range hopping. An
exponentially large, low-field and necessarily positive magnetoresistance
effect is predicted in the presence of Hubbard interaction and spin-dynamics
under certain conditions. The theory was developed with the recently discovered
organic magnetoresistance in mind. To account for the experimental observation
that the organic magnetoresistance effect can also be negative, we tentatively
amend the theory with a mechanism of bipolaron formation.",0609592v2
2006-10-04,Dynamic nuclear polarization induced by hot electrons,"A new method for local dynamic nuclear polarization is demonstrated in a
GaAs/AlGaAs heterostructure at the Landau level filling factor $\nu=3$. Using a
narrow channel sample, where the width varies stepwise along the electron flow,
we find that electron cooling (heating) causes the polarization of nuclear
spins against (toward) the external magnetic field at liquid helium
temperatures. The longitudinal nuclear spin relaxation rate varies
exponentially with inverse temperature.",0610102v1
2006-10-17,Quantum Dissipative Dynamics of Entanglement in the Spin-Boson Model,"We study quantum dissipative dynamics of entanglement in the spin-boson
model, described by the generalized master equation. We consider the two
opposite limits of pure-dephasing and relaxation models, measuring the degree
of entanglement with the concurrence. When the Markovian approximation is
employed, entanglement is shown to decay exponentially in both cases. On the
other hand, non-Markovian contributions alter the analytic structure of the
master equation, resulting in logarithmic decay in the pure dephasing model.",0610449v1
2006-10-21,Dynamical nuclear spin polarization and the Zamboni effect in gated double quantum dots,"A dynamical nuclear polarization scheme is studied in gated double dots. We
demonstrate that a small polarization ($\sim 0.5%$) is sufficient to enhance
the singlet decay time by two orders of magnitude. This enhancement is
attributed to an equilibration process between the nuclear reservoirs in the
two dots accompanied by reduced fluctuations in the Overhauser fields, that are
mediated by the electron-nuclear spin hyperfine interaction.",0610585v2
2006-11-01,Scaling of dynamic spin correlations in BaCu2SiGeO7,"The magnetic dynamic structure factor of the one-dimensional S = 1/2 chain
system BaCu2(Si0.5Ge0.5)2O7 is studied in a wide range of energy transfers and
temperatures. Contrary to previous erroneous reports [T. Masuda et al., Phys.
Rev. Lett. 93, 077206 (2004)], the scaling properties observed in the range
0.5-25 meV are found to be fully consistent with expectations for a Luttinger
spin liquid. At higher energies, a breakdown of scaling laws is observed and
attributed to lattice effects. The results are complementary to those found in
literature for other S = 1/2-chain compounds, such as KCuF3 and Cu-benzoate.",0611030v1
2006-12-04,Non-linear susceptibilities of spherical models,"The static and dynamic susceptibilities for a general class of mean field
random orthogonal spherical spin glass models are studied. We show how the
static and dynamical properties of the linear and nonlinear susceptibilities
depend on the behaviour of the density of states of the two body interaction
matrix in the neighbourhood of the largest eigenvalue. Our results are compared
with experimental results and also with those of the droplet theory of spin
glasses.",0612086v1
2006-12-21,Photoinduced charge and spin dynamics in strongly correlated electron systems,"Motivated by photoinduced phase transition in manganese oxides, charge and
spin dynamics induced by photoirradiation are examined. We calculate the
transient optical absorption spectra of the extended double-exchange model by
the density matrix renormalization group (DMRG) method. A charge-ordered
insulating (COI) state becomes metallic just after photoirradiation, and the
system tends to recover the initial COI state. The recovery is accompanied with
remarkable suppression of an antiferromagnetic correlation in the COI state.
The DMRG results are consistent with recent pump-probe spectroscopy data.",0612540v1
2007-02-11,Non-Markovian coherence dynamics of driven spin boson model: damped quantum beat or large amplitude coherence oscillation,"The dynamics of driven spin boson model is studied analytically by means of
the perturbation approach based on a unitary transformation. We gave the
analytical expression for the population difference and coherence of the two
level system. The results show that in the weak driven case, the population
difference present damped coherent oscillation (single or double frequency) and
the frequencies depend on the initial state. The coherence exhibit damped
oscillation with Rabi frequency. When driven field is strong enough, the
population difference exhibit undamped large-amplitude coherent oscillation.
The results easily return to the two extreme cases without dissipation or
without periodic driven.",0702268v1
2007-03-05,Non--Heisenberg Spin Dynamics of Double-Exchange Ferromagnets with Coulomb Repulsion,"With a variational three--body calculation we study the role of the interplay
between the onsite Coulomb, Hund's rule, and superexchange interactions on the
spinwave excitation spectrum of itinerant ferromagnets. We show that
correlations between a Fermi sea electron--hole pair and a magnon result in a
very pronounced zone boundary softening and strong deviations from the
Heisenberg spinwave dispersion. We show that this spin dynamics depends
sensitively on the Coulomb and exchange interactions and discuss its possible
relevance to experiments in the manganites.",0703099v2
2007-03-16,Injected Power Fluctuations in 1D Dissipative Systems,"Using fermionic techniques, we compute exactly the large deviation function
(ldf) of the time-integrated injected power in several one-dimensional
dissipative systems of classical spins. The dynamics are T=0 Glauber dynamics
supplemented by an injection mechanism, which is taken as a Poissonian flipping
of one particular spin. We discuss the physical content of the results,
specifically the influence of the rate of the Poisson process on the properties
of the ldf.",0703430v1
2002-05-09,Continuum spin foam model for 3d gravity,"An example illustrating a continuum spin foam framework is presented. This
covariant framework induces the kinematics of canonical loop quantization, and
its dynamics is generated by a {\em renormalized} sum over colored polyhedra.
  Physically the example corresponds to 3d gravity with cosmological constant.
Starting from a kinematical structure that accommodates local degrees of
freedom and does not involve the choice of any background structure (e. g.
triangulation), the dynamics reduces the field theory to have only global
degrees of freedom. The result is {\em projectively} equivalent to the
Turaev-Viro model.",0205037v1
2004-02-25,Dynamics of loop quantum gravity and spin foam models in three dimensions,"We present a rigorous regularization of Rovellis's generalized projection
operator in canonical 2+1 gravity. This work establishes a clear-cut connection
between loop quantum gravity and the spin foam approach in this simplified
setting. The point of view adopted here provides a new perspective to tackle
the problem of dynamics in the physically relevant
  3+1 case.",0402112v2
1993-03-26,Nonequilibrium Dynamics and Aging in the Three--Dimensional Ising Spin Glass Model,"The low temperature dynamics of the three dimensional Ising spin glass in
zero field with a discrete bond distribution is investigated via MC
simulations. The thermoremanent magnetization is found to decay algebraically
and the temperature dependent exponents agree very well with the experimentally
determined values. The nonequilibrium autocorrelation function $C(t,t_w)$ shows
a crossover at the waiting (or {\em aging}) time $t_w$ from algebraic {\em
quasi-equilibrium} decay for times $t$$\ll$$t_w$ to another, faster algebraic
decay for $t$$\gg$$t_w$ with an exponent similar to one for the remanent
magnetization.",9303013v1
1997-10-23,Filtering glueball from $q\bar{q}$ production in proton proton or double tagged $e^+e^- \to e^+e^-R$ and implications for the spin structure of the Pomeron,"The production of $J^{PC} = 1^{++},0^{-+}$ and $2^{-+}$ mesons in double
tagged $e^+e^- \to e^+e^-R$ is calculated and found to have the same
polarisation and dynamical characteristics as observed in $pp \to ppR$.
Implications for the spin structure of the Pomeron are considered. Production
of $0^{++},2^{++}$ mesons in these two processes may enable the dynamical
nature of these mesons to be determined.",9710450v2
2002-06-05,Production and decay of spinning black holes at colliders and tests of black hole dynamics,"We analyse the angular momentum distribution of black holes produced in high
energy collisions in space-times with extra spatial dimensions. We show that
the black hole spin significantly affects the energy and angular spectra of
Hawking radiation. Our results show the experimental sensitivity to the angular
momentum distribution and provide tests of black hole production dynamics.",0206055v1
1993-11-17,Vortex Dynamics in Selfdual Maxwell-Higgs Systems with Uniform Background Electric Charge Density,"We introduce selfdual Maxwell-Higgs systems with uniform background electric
charge density and show that the selfdual equations satisfied by topological
vortices can be reduced to the original Bogomol'nyi equations without any
background. These vortices are shown to carry no spin but to feel the Magnus
force due to the shielding charge carried by the Higgs field. We also study the
dynamics of slowly moving vortices and show that the spin-statistics theorem
holds to our vortices.",9311100v1
1994-07-13,The Multisite Antiferromagnetic Ising Spin Model and Universality of Feigenbaum Constants,"The Feigenbaum constants $\alpha$ and $\delta$ for the three-site
antiferromagnetic Ising spin model on Husimi tree are calculated. It is shown
that the numerical values of these constants for this real physical system
coincide with the famous universal Feigenbaum constants with high accuracy. The
quantitative description from ordering to chaos is also obtained.",9407073v1
1995-08-27,The trigonometric counterpart of the Haldane Shastry Model,"The hierarchy of Integrable Spin Chain Hamiltonians, which are trigonometric
analogs of the Haldane Shastry Model and of the associated higher conserved
charges, is derived by a reduction from the trigonometric Dynamical Models of
Bernard-Gaudin-Haldane-Pasquier. The Spin Chain Hamiltonians have the property
of $U_q(\hat{gl}_2)$-invariance. The spectrum of the Hamiltonians and the
$U_q(\hat{gl}_2)$-representation content of their eigenspaces are found by a
descent from the Dynamical Models.",9508145v2
2001-03-06,"Free conical dynamics: charge-monopole as a particle with spin, anyon and nonlinear fermion-monopole supersymmetry","We discuss the origin of the effectively free dynamics of the charge in the
magnetic monopole field to apply it for finding the alternative treatment of
the charge-monopole as a particle with spin, for tracing out the relation of
the charge-monopole to the free relativistic anyon and for clarifying the
nature of the non-standard nonlinear supersymmetry of the fermion-monopole
system.",0103040v2
2002-06-26,Spin-isospin rotation dynamics,"The equations for the solitons arbitrarily rotating in the ordinary and
isotopic space are obtained. The wave functions of the corresponding dynamic
states in the quantum case are found. The generalized matrix of the moments of
inertia is degenerate for the O(2)-invariant configurations characteristic for
the nucleon and delta-isobar. The equation for such configurations is
established. It is shown that the spin-isospin rotation prevents the collapse
of the soliton states in the SU(2) sigma-model. The entire consideration is
based on the variational approach to the method of collective variables.",0206230v3
2005-06-30,"4D, N =1 Higher Spin Gauge Superfields and Quantized Twistors","For the gauge massless higher spin 4D, N = 1 off-shell supermultiplets
previously developed, we provide evidence of a twistor-like oscillator
realization that is intrinsically related to the superfield structure of the
dynamical variables and gauge transformations. Gauge invariant field strengths
and linearized Bianchi identities for these multiplets are worked out. It is
further argued, inspired by earlier non- supersymmetric constructions due to
Klishevich and Zinoviev, that a massive superspin-$s$ multiplet can be
described as a gauge-invariant dynamical system involving massless multiplets
of superspins s, s-1/2, ..., 0. A gauge-invariant formulation for the massive
gravitino multiplet is discussed in some detail.",0506255v1
2003-04-24,Aging and spin-glass dynamics,"We survey the recent mathematical results about aging in certain simple
disordered models. We start by the Bouchaud trap model. We then survey the
results obtained for simple models of spin-glass dynamics, like the REM (the
Random Energy Model, which is well approximated by the Bouchaud model on the
complete graph), then the spherical Sherrington-Kirkpatrick model. We will
insist on the differences in phenomenology for different types of aging in
different time scales and different models. This talk is based on joint works
with A.Bovier, J.Cerny, A.Dembo, V.Gayrard, A.Guionnet, as well as works by
C.Newman, R.Fontes, M.Isopi, D.Stein.",0304364v1
2002-09-21,Selected Topics in Near Threshold Pion Photoproduction and Compton Scattering off Nucleons,"Some open topics in the field of low energy photon-nucleon interactions are
discussed--which in my opinion are of interest both for obtaining new
information on nucleon structure as well as for precision tests of our
theoretical understanding of chiral dynamics. In particular, I discuss p-wave
multipoles in charged pion photoproduction off protons as well as the role of
spin-dependent effects in (unpolarized) Compton scattering off nucleons. There
the concept of dynamical spin polarizabilities is found to be essential for the
understanding of differential Compton cross sections above 120 MeV cms photon
energy.",0209067v1
1999-03-18,Hamiltonian Methods for the Study of Polarized Proton Beam Dynamics in Accelerators and Storage Rings,"The equations of classical spin-orbit motion can be extended to a Hamiltonian
system in 9-dimensional phase space by introducing a coupled spin-orbit Poisson
bracket and a Hamiltonian function. After this extension and by establishing
connections between initial and extended systems it becomes possible to apply
the methods of the theory of Hamiltonian systems to the study of polarized
particle beam dynamics in circular accelerators and storage rings. Some of
those methods have been implemented in the computer code FORGET-ME-NOT.",9903032v1
1999-02-05,Pattern formation in quantum Turing machines,"We investigate the iteration of a sequence of local and pair unitary
transformations, which can be interpreted to result from a Turing-head
(pseudo-spin $S$) rotating along a closed Turing-tape ($M$ additional
pseudo-spins). The dynamical evolution of the Bloch-vector of $S$, which can be
decomposed into $2^{M}$ primitive pure state Turing-head trajectories, gives
rise to fascinating geometrical patterns reflecting the entanglement between
head and tape. These machines thus provide intuitive examples for quantum
parallelism and, at the same time, means for local testing of quantum network
dynamics.",9902020v1
1999-11-17,The stochastic limit of quantum spin systems,"The stochastic limit for the system of spins interacting with a boson field
is investigated. In the finite volume an application of the stochastic golden
rule shows that in the limit the dynamics of a quantum system is described by a
quantum white noise equation that after taking of normal order is equivalent to
quantum stochastic differential equation (QSDE). For the quantum Langevin
equation the dynamics is well defined and is a quantum flow on the infinite
lattice system.",9911077v1
2000-04-20,Special collision dynamics of massless fermions leading to confinement,"This is a theory for the fundamental structure of nature based on spinors as
unique building blocks. Confinement of the spinors in particles is due uniquely
to the dynamics of the collisions between them. The interaction operator
contains only spin and momentum operators. The eigenfunctions of the
interaction operator have negative as well as positive eigenvalues, limited in
magnitude to the Planck energy. Interactions in one-center particles between
spinors with eigenvalues of different sign tend to bring the energy of the
particle closer to zero.
  At the origin of the energy reduction through interaction is the spin
precession, taking place when two spinors of different type come together. The
model can explain the existence of stable particles and all the known forces,
including gravitation.",0004082v1
2001-11-28,Local Realistic Model for the Dynamics of Bulk-Ensemble NMR Information Processing,"We construct a local realistic hidden-variable model that describes the
states and dynamics of bulk-ensemble NMR information processing up to about 12
nuclear spins. The existence of such a model rules out violation of any Bell
inequality, temporal or otherwise, in present high-temperature, liquid-state
NMR experiments. The model does not provide an efficient description in that
the number of hidden variables grows exponentially with the number of nuclear
spins.",0111152v1
2002-12-13,Semiclassical quantisation rules for the Dirac and Pauli equations,"We derive explicit semiclassical quantisation conditions for the Dirac and
Pauli equations. We show that the spin degree of freedom yields a contribution
which is of the same order of magnitude as the Maslov correction in
Einstein-Brillouin-Keller quantisation. In order to obtain this result a
generalisation of the notion of integrability for a certain skew product flow
of classical translational dynamics and classical spin precession has to be
derived. Among the examples discussed is the relativistic Kepler problem with
Thomas precession, whose treatment sheds some light on the amazing success of
Sommerfeld's theory of fine structure [Ann. Phys. (Leipzig) 51 (1916) 1--91].",0212082v1
2003-08-09,Exact quantum jump approach to open systems in Bosonic and spin baths,"A general method is developed which enables the exact treatment of the
non-Markovian quantum dynamics of open systems through a Monte Carlo simulation
technique. The method is based on a stochastic formulation of the von Neumann
equation of the composite system and employs a pair of product states following
a Markovian random jump process. The performance of the method is illustrated
by means of stochastic simulations of the dynamics of open systems interacting
with a Bosonic reservoir at zero temperature and with a spin bath in the strong
coupling regime.",0308052v1
2003-12-17,Quantum dynamics in single spin measurement,"We study the quantum dynamics of a model for the single-spin measurement in
magnetic-resonance force microscopy. We consider an oscillating driven
cantilever coupled with the magnetic moment of the sample. Then, the cantilever
is damped through an external bath and its readout is provided by a radiation
field. Conditions for reliable measurements will be discussed.",0312147v2
2006-02-13,Entanglement and dynamics of spin-chains in periodically-pulsed magnetic fields: accelerator modes,"We study the dynamics of a single excitation in a Heisenberg spin-chain
subjected to a sequence of periodic pulses from an external, parabolic,
magnetic field. We show that, for experimentally reasonable parameters, a pair
of counter-propagating coherent states are ejected from the centre of the
chain. We find an illuminating correspondence with the quantum time evolution
of the well-known paradigm of quantum chaos, the Quantum Kicked Rotor (QKR).
  From this we can analyse the entanglement production and interpret the
ejected coherent states as a manifestation of so-called `accelerator modes' of
a classically chaotic system.",0602106v2
2007-07-03,Efficient dynamical nuclear polarization in quantum dots: Temperature dependence,"We investigate in micro-photoluminescence experiments the dynamical nuclear
polarization in individual InGaAs quantum dots. Experiments carried out in an
applied magnetic field of 2T show that the nuclear polarization achieved
through the optical pumping of electron spins is increasing with the sample
temperature between 2K and 55K, reaching a maximum of about 50%. Analysing the
dependence of the Overhauser shift on the spin polarization of the optically
injected electron as a function of temperature enables us to identify the main
reasons for this increase.",0707.0370v1
2007-11-07,Paraelectric-to-ferroelectric crossover and electron dynamics from time-dependent Hartree-Fock calculations,"In recent years, researchers have discovered various excited states of
electrons having an excited domain with a structural order different from the
original one. We examine a dynamics of electron system and phonon system by
using the time-dependent Hartree-Fock approximation. We examine time evolution
with spin degree of freedom. We found a thermally excited
paraelectric-to-ferroelectric crossover. The metastable state is spin pierls
state. We also examine the Landau expansion of electron system at
quarter-filled.",0711.1021v1
2007-12-12,Universality of REM-like aging in mean field spin glasses,"Aging has become the paradigm to describe dynamical behavior of glassy
systems, and in particular spin glasses. Trap models have been introduced as
simple caricatures of effective dynamics of such systems. In this Letter we
show that in a wide class of mean field models and on a wide range of time
scales, aging occurs precisely as predicted by the REM-like trap model of
Bouchaud and Dean. This is the first rigorous result about aging in mean field
models except for the REM and the spherical model.",0712.1914v1
2008-05-14,Quantum Billiards in Optical Lattices,"We study finite two dimensional spin lattices with definite geometry (spin
billiards) demonstrating the display of collective integrable or chaotic
dynamics depending on their shape. We show that such systems can be quantum
simulated by ultra-cold atoms in optical lattices and discuss how to identify
their dynamical features in a realistic experimental setup. Possible
applications are the simulation of quantum information tasks in mesoscopic
devices.",0805.2120v1
2008-05-26,Frustration-induced valence bond crystal and its melting in Mo3Sb7,"121/123Sb nuclear quadrupole resonance and muon spin relaxation experiments
of Mo3Sb7 revealed symmetry breakdown to a nonmagnetic state below the
transition recently found at TS=50 K. The transition is characterized by a
distinct lattice dynamics suggested from narrowing of nuclear fields. We point
out that the Mo sublatice is a unique three-dimensional frustrated lattice
where nearest-neighbor and next-nearest-neighbor antiferromagnetic interactions
compete, and propose that tetragonal distortion to release the frustration
stabilizes long-range order of spin-singlet dimers, i.e., valence bond crystal,
which is thermally excited to the dynamic state with cubic symmetry.",0805.3892v1
2008-05-30,Collective excitations in one-dimensional ultracold Fermi gases: a comparative study,"Time-dependent density-functional theory (TDDFT) is a powerful tool to study
the non-equilibrium dynamics of inhomogeneous interacting many-body systems.
Here we show that the simple adiabatic local-spin-density approximation for the
time-dependent exchange-correlation potential is surprisingly accurate in
describing collective density and spin dynamics in strongly correlated
one-dimensional ultracold Fermi gases. Our conclusions are based on extensive
comparisons between our TDDFT results and accurate results based on the
adaptive time-dependent density-matrix renormalization-group method.",0805.4743v1
2008-06-29,Dynamical Regimes Induced by Spin Transfer in Magnetic Nanopillars,"We demonstrate the predicted out-of-plane precession induced by spin transfer
in magnetic nanostructures with in-plane magnetic field. We show that other
magnetic excitations have a significant effect on the stability of the out-of
plane precession, making it extremely sensitive to the orientation of the
applied magnetic field. The data are supported with micromagnetic simulations.
Our results elucidate the relation between the excitation spectrum and the
specific dynamical behaviors of nanoscale magnets.",0806.4731v2
2008-06-29,The Magnetic Eden Model,"In the magnetic Eden model (MEM), particles have a spin and grow in contact
with a thermal bath. Although Ising-like interactions affect the growth
dynamics, deposited spins are frozen and not allowed to flip. This review
article focuses on recent developments and future prospects, such as
spontaneous switching phenomena, critical behavior associated with fractal,
wetting, and order-disorder phase transitions, the equilibrium/nonequilibrium
correspondence conjecture, as well as dynamical and critical features of the
MEM defined on complex network substrates.",0806.4767v1
2008-08-04,Dynamics of a one-dimensional spinor Bose liquid: a phenomenological approach,"The ground state of a spinor Bose liquid is ferromagnetic, while the softest
excitation above the ground state is the magnon mode. The dispersion relation
of the magnon in a one-dimensional liquid is periodic in the wavenumber q with
the period 2\pi n, determined by the density n of the liquid. Dynamic
correlation functions, such as e.g. spin-spin correlation function, exhibit
power-law singularities at the magnon spectrum, $\omega\to\omega_m(q,n)$.
Without using any specific model of the inter-particle interactions, we relate
the corresponding exponents to independently measurable quantities
$\partial\omega_m/\partial q$ and $\partial\omega_m/\partial n$.",0808.0479v2
2008-12-02,Experimental Test of Analytic Theory of Spin Torque Oscillator Dynamics,"We make measurements of power spectral density of the microwave voltage
emitted by a spin torque nano-oscillator (STNO) and compare our experimental
results to predictions of an analytic theory of a single-mode STNO dynamics by
V. S. Tiberkevich, A. N. Slavin, J. V. Kim,[Phys. Rev. B 78, 092401 (2008)]. We
find that a complete set of the oscillator spectral properties: power,
frequency, spectral line width and line shape as functions of current are
self-consistently described by the analytic theory for moderate amplitudes of
oscillations (< 70 degrees).",0812.0541v2
2009-01-20,Phase-imprint induced domain formations and spin dynamics in spinor condensates,"We demonstrate that certain domain structures can be created both in ferro-
and antiferro-magnetic spinor condensates if the initial phase is spatially
modulated. Meanwhile, spin dynamics of the condensate with modulated phases
exhibits exotic features in comparison with those of a condensate with a
uniform phase. We expect that these phenomena could be observed experimentally
using a phase-imprinting method.",0901.3152v1
2009-01-23,Non-equilibrium reversible dynamics of work production in four-spin system in a magnetic field,"A closed system of the equations for the local Bloch vectors and spin
correlation functions is obtained by decomplexification of the Liouville-von
Neumann equation for 4 magnetic particles with the exchange interaction that
takes place in an arbitrary time-dependent external magnetic field. The
analytical and numerical analysis of the quantum thermodynamic variables is
carried out depending on separable mixed initial state and the magnetic field
modulation. Under unitary evolution, non-equilibrium reversible dynamics of
power production in the finite environment is investigated.",0901.3637v3
2009-03-27,Quantum transport through a Tonks-Girardeau gas,"We investigate the propagation of spin impurity atoms through a strongly
interacting one-dimensional Bose gas. The initially well localized impurities
are accelerated by a constant force, very much analogous to electrons subject
to a bias voltage, and propagate as a one-dimensional impurity spin wave
packet. We follow the motion of the impurities in situ and characterize the
interaction induced dynamics. We observe a very complex non-equilibrium
dynamics, including the emergence of large density fluctuations in the
remaining Bose gas, and multiple scattering events leading to dissipation of
the impurity's motion.",0903.4823v2
2009-05-05,Edge exponent in the dynamic spin structure factor of the Yang-Gaudin model,"The dynamic spin structure factor $\mathcal{S}(k,\omega)$ of a system of
spin-1/2 bosons is investigated at arbitrary strength of interparticle
repulsion. As a function of $\omega$ it is shown to exhibit a power-law
singularity at the threshold frequency defined by the energy of a magnon at
given $k.$ The power-law exponent is found exactly using a combination of the
Bethe Ansatz solution and an effective field theory approach.",0905.0598v1
2009-06-14,Non-Equilibrium Thermal Entanglement Dynamics of Heisenberg Systems,"The effects of initial conditions and system parameters on entanglement
dynamics and asymptotic entanglement for a two-qubit anisotropic XY Heisenberg
system in the presence of an inhomogeneous magnetic field and spin-orbit
interaction are investigated. We suppose that each qubit interacts with a
separate thermal reservoir which is held in its own temperature. The effects of
the parameters of the system and environment like spin-orbit interaction and
temperature difference of reservoirs are also discussed.",0906.2534v1
2009-10-06,Metastable states and space-time phase transitions in a spin-glass model,"We study large deviations of the dynamical activity in the random orthogonal
model (ROM). This is a fully connected spin-glass model with one-step replica
symmetry breaking behaviour, consistent with the random first-order transition
scenario for structural glasses. We show that this model displays dynamical
(space-time) phase-transitions between active and inactive phases, as
demonstrated by singularities in large deviation functions. We argue that such
transitions are generic in systems with long-lived metastable states.",0910.1111v1
2009-11-08,Nonequilibrium dynamical ferromagnetism of interacting Single-Molecule Magnets,"We propose a nonequilibrium Monte Carlo (MC) approach to explore
nonequilibrium dynamical ferromagnetism of interacting single molecule magnets
(SMMs). Both quantum spin tunneling and thermally activated spin reversal are
successfully implemented in the same MC simulation framework. Applied to a
typical example, this simulation method satisfactorily reproduces experimental
magnetization curves with experimental parameters. Our results show that both
quantum and classical effects are essential to determine the hysteresis
behaviors. This method is effective and reliable to gain deep insights into
SMMs.",0911.1539v1
2010-03-19,Dynamics of magnetization on the topological surface,"We investigate theoretically the dynamics of magnetization coupled to the
surface Dirac fermions of a three dimensional topological insulator, by
deriving the Landau-Lifshitz-Gilbert (LLG) equation in the presence of charge
current. Both the inverse spin-Galvanic effect and the Gilbert damping
coefficient $\alpha$ are related to the two-dimensional diagonal conductivity
$\sigma_{xx}$ of the Dirac fermion, while the Berry phase of the ferromagnetic
moment to the Hall conductivity $\sigma_{xy}$. The spin transfer torque and the
so-called $\beta$-terms are shown to be negligibly small. Anomalous behaviors
in various phenomena including the ferromagnetic resonance are predicted in
terms of this LLG equation.",1003.3769v1
2010-04-16,Correlation induced spin freezing transition in FeSe: a dynamical mean field study,"The effect of local Coulomb interactions on the electronic properties of FeSe
is explored within dynamical mean field theory combined with finite-temperature
exact diagonalization. The low-energy scattering rate is shown to exhibit
non-Fermi-liquid behavior caused by the formation of local moments.
Fermi-liquid properties are restored at large electron doping. In contrast,
FeAsLaO is shown to be located on the Fermi-liquid side of this spin freezing
transition.",1004.2851v1
2010-07-27,Universality in three-dimensional Ising spin glasses: Nonequilibrium dynamics from Monte Carlo simulations,"The non-equilibrium dynamics of the three-dimensional Edwards-Anderson
spin-glass model with different bond distributions is investigated by means of
Monte Carlo simulation. A numerical method is used to determine the critical
temperature and the scaling exponents of the correlation and the integrated
response functions. The results obtained agree with those calculated in
equilibrium simulations and suggest that the universality class does not depend
on the exact form of the bond distribution.",1007.4780v2
2010-10-12,Coherent spin-current oscillations in transverse magnetic fields,"We address the coherence of the dynamics of spin-currents with components
transverse to an external magnetic field for the spin-1/2 Heisenberg chain. We
study current autocorrelations at finite temperatures and the real-time
dynamics of currents at zero temperature. Besides a coherent Larmor
oscillation, we find an additional collective oscillation at higher
frequencies, emerging as a coherent many-magnon effect at low temperatures.
Using numerical and analytical methods, we analyze the oscillation frequency
and decay time of this coherent current-mode versus temperature and magnetic
field.",1010.2351v2
2010-11-16,Dynamic susceptibility of a spin ice near the critical point,"We consider spin ice magnets (primarily, $\mathrm{Dy_2Ti_2O_7}$) in the
vicinity of their critical point on the $(H,T)$ plane. We find that the
longitudinal susceptibility diverges at the critical point, leading to the
behaviour qualitatively similar to the one which would result from non-zero
conductance of magnetic charges. We show that dynamics of critical fluctuations
belongs to the universality class of easy-axis ferroelectric and calculate
logarithmic corrections (within two-loop approximation) to the mean-field
critical behavior.",1011.3659v2
2011-02-01,Collision of one dimensional (1D) spin polarized Fermi gases in an optical lattice,"In this work we analyze the dynamical behavior of the collision between two
clouds of fermionic atoms with opposite spin polarization. By means of the
time-evolving block decimation (TEBD) numerical method, we simulate the
collision of two one-dimensional clouds in a lattice. There is a symmetry in
the collision behaviour between the attractive and repulsive interactions. We
analyze the pair formation dynamics in the collision region, providing a
quantitative analysis of the pair formation mechanism in terms of a simple
two-site model.",1102.0133v1
2011-02-12,Dynamic Symmetries and Entropic Inequalities in the Probability Representation of Quantum Mechanics,"The probability representation of quantum and classical statistical mechanics
is discussed. Symplectic tomography, center-of-mass tomography, and spin
tomography are studied. The connection of tomographic probabilities with
dynamic symmetries like symplectic group is considered. Entropic uncertainty
relations and inequalities for spin tomograms are reviewed.",1102.2497v1
2011-02-26,Dynamics of Skyrmion Crystals in Metallic Thin Films,"We study the collective dynamics of the Skyrmion crystal (SkX) in thin films
of ferromagnetic metals resulting from the nontrivial Skyrmion topology. We
show that the current-driven motion of the crystal reduces the topological Hall
effect and the Skyrmion trajectories bend away from the direction of the
electric current (the Skyrmion Hall effect). We find a new dissipation
mechanism in non-collinear spin textures that can lead to a much faster spin
relaxation than Gilbert damping, calculate the dispersion of phonons in the
SkX, and discuss effects of impurity pinning of Skyrmions.",1102.5384v2
2011-05-11,Dynamic fields in the partial magnetization plateau of Ca3Co2O6,"Fluctuation dynamics in magnetization plateaux are a relatively poorly
explored area in frustrated magnetism. Here we use muon spin relaxation to
determine the fluctuation timescale and associated field distribution width in
the partial magnetization plateau of Ca3Co2O6. The muon spin relaxation rate
has a simple and characteristic field dependence which we model and by fitting
to the data at 15 K extract a fluctuation timescale tau = 880(30) ps and a
field distribution width Delta = 40.6(3) mT. Comparison with previous results
on Ca3Co2O6 suggests that this fluctuation timescale can be associated with
short-range, slowly fluctuating magnetic order.",1105.2200v1
2011-07-18,Molecular-spin dynamics study of electromagnons in multiferroic RMn$_2$O$_5$,"We investigate the electromagnon in magnetoferroelectrics RMn$_2$O$_5$ using
combined molecular-spin dynamics simulations. We identify the origin of the
electromagnon modes observed in the optical spectra and reproduce the most
salient features of the electromagnon in these compounds. We find that the
electromagnon frequencies are very sensitive to the magnetic wave vector along
the $a$ direction. We further investigate the electromagnon in magnetic field.
Although the modes frequencies change significant under magnetic field, the
static dielectric constant electromagnon does not change much in the magnetic
field.",1107.3349v1
2011-07-28,Multiple quantum NMR dynamics in a gas of spin-carrying molecules in fluctuating nanopores,"The effect of Gaussian fluctuations of nanopores filled with a gas of
spin-carrying molecules ($s=1/2$) on the multiple quantum (MQ) NMR dynamics is
investigated at different variances and correlation times of the fluctuations.
We show that the fluctuations smooth out the evolution of MQ NMR coherence
intensities which rapidly oscillate as functions of time in the absence of
fluctuations. The growth and decay of the MQ coherence clusters in the
fluctuating nanopore are also investigated.",1107.5716v2
2011-10-18,Momentum dependent ultrafast electron dynamics in antiferromagnetic EuFe2As2,"Employing the momentum-sensitivity of time- and angle-resolved photoemission
spectroscopy we demonstrate the analysis of ultrafast single- and many-particle
dynamics in antiferromagnetic EuFe2As2. Their separation is based on a
temperature-dependent difference of photo-excited hole and electron relaxation
times probing the single particle band and the spin density wave gap,
respectively. Reformation of the magnetic order occurs at 800 fs, which is four
times slower compared to electron-phonon equilibration due to a smaller
spin-dependent relaxation phase space.",1110.3938v2
2011-12-14,Dynamics of Thermal Effects in the Spin-Wave Theory of Quantum Antiferromagnets,"We derive a master equation that allows us to study non-equilibrium dynamics
of a quantum antiferromagnet. By resorting to spin-wave theory, we obtain a
closed analytic form for the magnon decay rates. These turn out to be closely
related to form factors, which are experimentally accessible by means of
neutron and Raman scattering. Furthermore, we compute the time evolution of the
staggered magnetization showing that, for moderate temperatures, the magnetic
order is not spoiled even if the coupling is fully isotropic.",1112.3158v3
2012-06-21,Relaxation Dynamics of Disordered Spin Chains: Localization and the Existence of a Stationary State,"We study the unitary relaxation dynamics of disordered spin chains following
a sudden quench of the Hamiltonian. We give analytical arguments, corroborated
by specific numerical examples, to show that the existence of a stationary
state depends crucially on the spectral and localization properties of the
final Hamiltonian, and not on the initial state. We test these ideas on
integrable one-dimensional models of the Ising or XY class, but argue more
generally on their validity for more complex (nonintegrable) models.",1206.4787v3
2012-06-22,Radical-free dynamic nuclear polarization using electronic defects in silicon,"Direct dynamic nuclear polarization of 1H nuclei in frozen water and
water-ethanol mixtures is demonstrated using silicon nanoparticles as the
polarizing agent. Electron spins at dangling-bond sites near the silicon
surface are identified as the source of the nuclear hyperpolarization. This
novel polarization method open new avenues for the fabrication of surface
engineered nanostructures to create high nuclear-spin polarized solutions
without introducing contaminating radicals, and for the study of molecules
adsorbed onto surfaces.",1206.5125v1
2012-11-26,Quantum corrections to phi^4 model solutions and applications to Heisenberg chain dynamics,"The Heisenberg spin chain is considered in phi^4 model approximation. Quantum
corrections to classical solutions of the one-dimensional phi^4 model within
the correspondent physics are evaluated with account of rest $d-1$ dimensions
of a d-dimensional theory. A quantization of the models is considered in terms
of space-time functional integral. The generalized zeta-function formalism is
used to renormalize and evaluate the functional integral and quantum
corrections to energy in quasiclassical approximation. The results are applied
to appropriate conditions of the spin chain models and its dynamics, which
elementary solutions, energy and the quantum corrections are calculated.",1211.5956v1
2013-01-07,Quantum simulation of many-body spin interactions with ultracold polar molecules,"We present an architecture for the quantum simulation of many-body spin
interactions based on ultracold polar molecules trapped in optical lattices.
Our approach employs digital quantum simulation, i.e., the dynamics of the
simulated system is reproduced by the quantum simulator in a stroboscopic
pattern, and allows to simulate both coherent and dissipative dynamics. We
discuss the realization of Kitaev's toric code Hamiltonian, a paradigmatic
model involving four-body interactions, and we analyze the requirements for an
experimental implementation.",1301.1342v2
2013-01-18,Field-Free Synthetic-Ferromagnet Spin Torque Oscillator,"We study the magnetization dynamics of spin valve structures with a free
composite synthetic ferromagnet (SyF) that consists of two ferromagnetic layers
coupled through a normal metal spacer. A ferromagnetically coupled SyF can be
excited into dynamical precessional states by an applied current without
external magnetic fields. We analytically determine the stability of these
states in the space spanned by the current density and SyF interlayer exchange
coupling. Numerical simulations confirm our analytical results.",1301.4294v1
2013-01-30,Disconnected glass-glass transitions and swallowtail bifurcations in microscopic spin models with facilitated dynamics,"It has been recently established that heterogeneous bootstrap percolation and
related dynamic facilitation models exhibit a complex hierarchy of continuous
and discontinuous transitions depending on lattice connectivity and kinetic
constraints. Here the range of the previously observed phase diagram topologies
and higher-order singularities is extended to disconnected glass-glass
transitions and to cusp and swallowtail bifurcations (which can be generic and
degenerate). The phase diagram and the order parameter for two different types
of spin mixtures are analytically determined and an experimental realization of
the new predictions emerging in our approach is suggested.",1301.7296v2
2013-02-20,Parity Violating Deep Inelastic Electron-Deuteron Scattering: Higher Twist and Parton Angular Momentum,"We study the effect of parton angular momentum on the twist-four correction
to the left-right asymmetry in the electron-deuteron parity-violating deep
inelastic scattering (PVDIS). We show that this higher-twist correction is
transparent to the dynamics of parton angular momentum needed to account for
the Sivers and Boer-Mulders functions and spin-independent parton distribution
functions. A sufficiently precise measurement of the PVDIS asymmetry may, thus,
provide additional information about the parton dynamics responsible for
nucleon spin.",1302.5047v2
2013-04-20,Dynamics of Entanglement in one and two-dimensional spin systems,"We present a review of dynamics of entanglement in one and two dimensional
systems under the effect of external magnetic field and different degrees of
anisotropy at zero and finite temperatures. Different techniques for treating
the spin systems with large Hilbert space dimensions are discussed such as
trace minimization algorithm, time-evolution matrix transformation and step by
step projection technique.",1304.5569v1
2013-06-17,Robust synchronization of spin-torque oscillators with an LCR load,"We study dynamics of a serial array of spin-torque-oscillators with a
parallel inductor-capacitor-resistor (LCR) load. In a large range of parameters
the fully synchronous regime, where all the oscillators have the same state and
the output field is maximal, is shown to be stable. However, not always such a
robust complete synchronization develops from the random initial state, in many
cases nontrivial clustering is observed, with a partial synchronization
resulting in a quasiperiodic or chaotic mean field dynamics.",1306.3803v1
2013-11-06,Competing interaction in magnets: the root of ordered disorder or only frustration?,"What does the equilibrium atomic, molecular or spin configuration of a glass
phase look like? Is there only one unique equilibrium configuration or are
there infinitely many configurations of equal energy? The processes and
mechanisms governing the path towards equilibrium, i.e. the dynamics of glassy
systems, provide insights to these questions. Here we discuss the intrinsic
dynamics of different glassy magnets: of spin-glasses, frustrated ferromagnets,
superspin-glasses and other nanostructured systems with competing ferro- and
antiferromagnetic interactions and randomness in their spatial distribution.
This paper is intended as a brief update on some unsolved problems and the
current empirical status in the field of disordered and frustrated magnetism.",1311.1350v1
2013-11-07,Topological lattice field theories from intertwiner dynamics,"We introduce a class of 2D lattice models that describe the dynamics of
intertwiners, or, in a condensed matter interpretation, the fusion and
splitting of anyons. We identify different families and instances of
triangulation invariant, that is, topological, models inside this class. These
models give examples for symmetry protected topologically ordered 1D quantum
phases with quantum group symmetries. Furthermore the models provide
realizations for anyon condensation into a new effective vacuum. We explain the
relevance of our findings for the problem of identifying the continuum limit of
spin foam and spin net models.",1311.1798v1
2013-12-13,"Quantum states, symmetry and dynamics in degenerate spin s=1 magnets","The article deals with spin s=1 magnets. The symmetry conditions for normal
and degenerate equilibrium states are defined and types of magnetic ordering
found out. For each type of symmetry breaking the structure of source in the
Gibbs statistical operator has been obtained and additional thermodynamic
parameters introduced. The algebra of Poisson bracket for magnetic degrees of
freedom has been established and nonlinear dynamic equations have been derived.
Using the models of the exchange interaction, we have calculated the spectra of
collective excitations for two degenerate states whose order parameters have
digerent signature under the time reversal transformation.",1312.3799v2
2014-01-29,Quantum magnetism of ultracold atoms with a dynamical pseudospin degree of freedom,"We consider bosons in a Hubbard lattice with an SU($\cal N$) pseudospin
degree of freedom which is made dynamical via a coherent transfer term. It is
shown that, in the basis which diagonalizes the pseudospin coupling, a generic
hopping process affects the spin state, similar to a spin-orbit coupling. This
results, for the system in the Mott phase, in a ferromagnetic phase with
variable quantization axis. In extreme cases, it can even give rise to
antiferromagnetic order.",1401.7608v1
2014-04-29,Growth-induced breaking and unbreaking of ergodicity in fully-connected spin systems,"Two canonical models of statistical mechanics, the fully-connected voter and
Glauber-Ising models, are modified to incorporate growth via the addition or
replication of spins. The resulting behaviour is examined in a regime where the
timescale of expansion cannot be separated from that of the internal dynamics.
Depending on the model specification, growth radically alters the long-time
dynamical behaviour by breaking or unbreaking ergodicity.",1404.7317v2
2014-08-08,Short cycle pulse sequence for dynamical decoupling of local fields and dipole-dipole interactions,"We propose a new pulse sequence for dynamical averaging of the dipole-dipole
interactions and inhomogeneities of the magnetic fields in the nuclear spin
system. The sequence contains a short cycle of the periodic resonant pulse
excitation that offers new possibilities for implementing the long-lived
multi-qubit quantum memory on the condensed spin ensembles that are so
important for construction of universal quantum computer and long-distance
quantum communications.",1408.1916v3
2014-08-17,Phase Locked Loop of the Spin-Torque Nanooscillator,"We have studied the dynamics of a spin-torque nanooscillator's (STNO) phase
locked loop (PLL) generating microwave oscillations in a broad range of
frequencies under the effect of direct current and external magnetic field.
Bifurcations in the system caused by a change in the frequency detuning of
synchronized oscillations are considered. Bands of phase locking and
synchronism are determined. The existence of a phase locking band in the
filterless PLL of STNOs basically distinguishes these oscillators from other
types of microwave generators.",1408.3868v1
2014-08-31,Continuous quantum measurement in spin environments,"We derive a formalism of stochastic master equations (SME) which describes
the decoherence dynamics of a system in spin environments conditioned on the
measurement record. Markovian and non-Markovian nature of environment can be
revealed by a spectroscopy method based on weak quantum measurement (weak
spectroscopy). On account of that correlated environments can lead to a
nonlocal open system which exhibits strong non-Markovian effects although the
local dynamics are Markovian, the spectroscopy method can be used to
demonstrate that there is correlation between two environments.",1409.0191v1
2014-09-24,Entanglement and spin squeezing in non-Hermitian phase transitions,"We show that non-Hermitian dynamics generate substantial entanglement in
many-body systems. We consider the non-Hermitian Lipkin-Meshkov-Glick model and
show that its phase transition occurs with maximum multiparticle entanglement:
there is full N-particle entanglement at the transition, in contrast to the
Hermitian case. The non-Hermitian model also exhibits more spin squeezing than
the Hermitian model, showing that non-Hermitian dynamics are useful for quantum
metrology. Experimental implementations with trapped ions and cavity QED are
discussed.",1409.7067v2
2014-10-03,Dynamics of a vortex dipole across a magnetic phase boundary in a spinor Bose-Einstein condensate,"Dynamics of a vortex dipole in a spin-1 Bose-Einstein condensate in which
magnetic phases are spatially distributed is investigated. When a vortex dipole
travels from the ferromagnetic phase to the polar phase, or vice versa, it
penetrates the phase boundary and transforms into one of the various spin
vortex dipoles, such as a leapfrogging ferromagnetic-core vortex dipole and a
half-quantum vortex dipole. Topological connections of spin wave functions
across the phase boundary are discussed.",1410.0743v1
2014-10-08,Low temperature dynamics of nonlinear Luttinger liquids,"We generalize nonlinear Luttinger liquid theory to describe the dynamics of
one-dimensional quantum critical systems at low temperatures. Analyzing
density-matrix renormalization group results for the spin autocorrelation
function in the XXZ chain we provide, in particular, direct evidence for spin
diffusion in sharp contrast to the exponential decay in time predicted by
conventional Luttinger liquid theory. Furthermore, we discuss how the
frequencies and exponents of the oscillatory contributions from the band edges
are renormalized by irrelevant interactions and obtain excellent agreement
between our finite temperature nonlinear Luttinger liquid theory and the
numerical data.",1410.2226v1
2014-10-15,Ultra-fast photo-carrier relaxation in Mott insulators with short-range spin correlations,"We compute the time-resolved photoemission spectrum after photo-doping in a
two-dimensional Mott-Hubbard insulator. We find that the relaxation rate of
high-energy photo-doped electrons in the paramagnetic phase scales with the
strength of the nearest-neighbor spin correlations, which implies a pronounced
increase of the relaxation times with temperature and excitation density.
Finite doping, in contrast, opens additional scattering channels and leads to a
faster relaxation. To obtain our results we have implemented a nonequilibrium
version of the dynamical cluster approximation (DCA), which, in contrast to
single-site dynamical mean-field theory, captures the effect of short-range
correlations.",1410.3956v1
2014-10-21,Magnetic switching dynamics in a ferrimagnetic two sub-lattice model including ultrafast exchange scattering,"We study the heat-induced magnetization dynamics in a toy model of a
ferrimagnetic alloy, which includes localized spins antiferromagnetically
coupled to an itinerant carrier system with a Stoner gap. We determine the
one-particle spin-density matrix including exchange scattering between
localized and itinerant bands as well as scattering with phonons. While a
transient ferromagnetic-like state can always be achieved by a sufficiently
strong excitation, this transient ferromagnetic-like state only leads to
magnetization switching for model parameters that also yield a compensation
point in the equilibrium M(T) curve.",1410.5745v2
2015-03-07,Collisionless spin dynamics in a magnetic field gradient,"We study the collisionless spin dynamics of a harmonically trapped Fermi gas
in a magnetic field gradient. In the absence of interactions, the system
evolution is periodic: the magnetization develops twists, which evolve into a
longitudinal polarization. Recurrences follow. For weak interaction, the
exchange interactions lead to beats in these oscillations. We present an array
of analytic and numerical techniques for studying this physics.",1503.02131v2
2015-03-29,Bulk from Bi-locals in Thermo Field CFT,"We study the Large $N$ dynamics of the $O(N)$ field theory in the Thermo
field dynamics approach. The question of recovering the high temperature phase
and the corresponding $O(N)$ gauging is clarified. Through the associated
bi-local representation we discuss the emergent bulk space-time and
construction of (Higher spin) fields. We note the presence of `evanescent'
modes in this construction and also the mixing of spins at finite temperature.",1503.08484v3
2015-07-10,Dissipative quantum control of a spin chain,"A protocol is discussed for preparing a spin chain in a generic many-body
state in the asymptotic limit of tailored non-unitary dynamics. The dynamics
require the spectral resolution of the target state, optimized coherent pulses,
engineered dissipation, and feedback. As an example, we discuss the preparation
of an entangled antiferromagnetic state, and argue that the procedure can be
applied to chains of trapped ions or Rydberg atoms.",1507.02997v1
2015-08-21,Local factorisation of the dynamics of quantum spin systems,"Motivated by the study of area laws for the entanglement entropy of gapped
ground states of quantum spin systems and their stability, we prove that the
unitary cocycle generated by a local time-dependent Hamiltonian can be
approximated, for any finite set $X$, by a tensor product of the corresponding
unitaries in $X$ and its complement, multiplied by a dynamics strictly
supported in the neighbourhood of the surface $\partial X$. The error decays
almost exponentially in the size of the neighbourhood and grows with the square
of the area~$\vert \partial X\vert^2$.",1508.05254v2
2015-09-11,Non-Markovian Effects in the Spin Transfer Dynamics in Diluted Magnetic Semiconductors due to Excitation in Proximity to the Band Edge,"The non-Markovian effects in the spin dynamics in diluted magnetic
semiconductors found in quantum kinetic calculations can be reproduced very
well by a much simpler effective single electron theory, if a finite memory is
accounted for. The resulting integro-differential equation can be solved by a
differential transform method, yielding the Taylor series of the solution. From
the comparison of both theories it can be concluded that the non-Markovian
effects are due to the spectral proximity of the excited electrons to the band
edge.",1509.03487v1
2015-10-11,A Current of the Cheshire Cat's Smile: Dynamical Analysis of Weak Values,"Recently it was demonstrated, both theoretically and experimentally, how to
separate a particle from its spin, or any other property, a phenomenon known as
the ""Quantum Cheshire Cat"". We present two novel gedanken experiments, based on
the quantum Zeno effect, suggesting a dynamical process thorough which this
curious phenomenon occurs. We analyze, for the first time, a quantum current
consisting of spin without mass. Thus, the quantum variables of pre- and
post-selected particles are understood to be involved in various interactions,
even in the absence of their owners. This current is shown to provide a local
explanation for seemingly nonlocal interactions.",1510.03087v1
2015-10-29,An effective field theory approach to tidal dynamics of spinning astrophysical systems,"We develop a description of tidal effects in astrophysical systems using
effective field theory techniques. While our approach is equally capable of
describing objects in the Newtonian regime (e.g. moons, rocky planets, main
sequence stars, etc.) as well as relativistic objects (e.g. neutron stars and
black holes), in this paper we focus special attention on the Newtonian regime.
In this limit, we recover the dynamical equations for the ""weak friction model""
with additional corrections due to tidal and rotational deformations.",1510.08889v2
2016-09-07,Dynamic Control of Topological Defects in Artificial Colloidal Ice,"We demonstrate the use of an external field to stabilize and control defect
lines connecting topological monopoles in spin ice. For definiteness we perform
Brownian dynamics simulations with realistic units mimicking experimentally
realized artificial colloidal spin ice systems, and show how defect lines can
grow, shrink or move under the action of direct and alternating fields.
Asymmetric alternating biasing fields can cause the defect line to ratchet in
either direction, making it possible to precisely position the line at a
desired location. Such manipulation could be employed to achieve fast, dense,
and mobile information storage in these metamaterials.",1609.02129v1
2017-03-06,Spin-orbit interactions in optically active materials,"We investigate the inherent influence of light polarization on the intensity
distribution in anisotropic media undergoing a local inhomogeneous rotation of
the principal axes. Whereas in general such configuration implies a complicated
interaction between geometric and dynamic phase, we show that, in a medium
showing an inhomogeneous circular birefringence, the geometric phase vanishes.
Due to the spin-orbit interaction, the two circular polarizations perceive
reversed spatial distribution of the dynamic phase. Based upon this effect,
polarization-selective lens, waveguides and beam deflectors are proposed.",1703.01823v1
2018-02-26,Dynamics and Instabilities of the Shastry-Sutherland Model,"We study the excitation spectrum in the dimer phase of the Shastry-Sutherland
model by using an unbiased variational method that works in the thermodynamic
limit. The method outputs dynamical correlation functions in all possible
channels. This output is exploited to identify the order parameters with the
highest susceptibility (single or multitriplon condensation in a specific
channel) upon approaching a quantum phase transition in the magnetic field
versus the $J'/J$ phase diagram. We find four different instabilities:
antiferro spin nematic, plaquette spin nematic, stripe magnetic order, and
plaquette order, two of which have been reported in previous studies.",1802.09428v2
2018-11-13,Quench Dynamics in a Trapped Bose-Einstein Condensate with Spin-Orbit Coupling,"We consider the phase transition dynamics of a trapped Bose-Einstein
condensate subject to Raman-type spin-orbit coupling (SOC). By tuning the
coupling strength the condensate is taken through a second order phase
transition into an immiscible phase. We observe the domain wall defects
produced by a finite speed quench is described by the Kibble-Zurek mechanism
(KZM), and quantify a power law behavior for the scaling of domain number and
formation time with the quench speed.",1811.05327v2
2019-05-10,Lagrangian formulation for emergent elastic waves in magnetic emergent crystals,"Magnetic emergent crystals are periodic alignment of ""particle-like"" spin
textures that emerge in magnets. Instead of focusing on an individual spin or a
macroscopic magnetization field, we analyze the dynamical behaviors of these
novel states by taking a solid-state point of view. Based on variational
principles, the basic equations for lattice dynamics of any emergent
crystalline states appearing in magnetic materials is established. For small
amplitude emergent elastic waves propagating in emergent crystals, the basic
equations reduce to an eigenvalue problem, from which the dispersion relation
and vibrational patterns for all emergent phonons are determined at the long
wavelength limit.",1905.03991v1
2010-05-04,Subleading Spin-Orbit Correction to the Newtonian Potential in Effective Field Theory Formalism,"We study the gravitational dynamics in the early inspiral phase of coalescing
compact binaries using Non-Relativistic General Relativity (NRGR) - an
effective field theory formalism based on the post-newtonian expansion, but
which provides a consistent lagrangian framework and a systematic way in which
to study binary dynamics and gravitational wave emission. We calculate in this
framework the spin-orbit correction to the newtonian potential at 2.5 PN.",1005.0634v2
2014-03-06,Ultrafast separation of photo-doped carriers in Mott antiferromagnets,"We use inhomogeneous nonequilibrium dynamical mean-field theory to
investigate the spreading of photo-excited carriers in Mott insulating
heterostructures with strong internal fields. Antiferromagnetic correlations
are found to affect the carrier dynamics in a crucial manner: An
antiferromagnetic spin background can absorb energy from photo-excited carriers
on an ultrafast timescale, thus enabling fast transport between different
layers and the separation of electron and hole-like carriers, whereas in the
paramagnetic state, carriers become localized in strong fields. This interplay
between charge and spin degrees of freedom can be exploited to control the
functionality of devices based on Mott insulating heterostructures with polar
layers, e.g., for photovoltaic applications.",1403.1461v1
2016-11-02,High temperature dynamics in quantum compass models,"We analyze the high temperature spin dynamics of compass models using a
moment expansion. We point out that the evaluation of moments maps to the
enumeration of paths in a branching process on the lattice. This mapping to a
statistical mechanics combinatorics problem provides an elegant visualization
of the analysis. We present results for the time dependent spin correlation
function (which is of relevance to NMR experiments) for two compass models: the
Kitaev honeycomb model and two-dimensional compass model.",1611.00637v2
2017-04-05,Dynamical spin effects in the pion,"We take into account dynamical spin effects in the holographic light-front
pion wavefunction in order to predict the pion radius, decay constant, the pion
electromagnetic and photon-to-pion transition form factors. We report a
striking improvement in the description of all data.",1704.01228v1
2008-07-28,High Field ESR in the Two-Dimensional Triangular Lattice Antiferromagnet NiGa2S4,"In this Letter, we report the results of ESR measurements in high magnetic
fields up to about 53 T on single crystals of NiGa2S4 to clarify the spin
dynamics in more detail. We have found that the dynamics of Z2 vortices affects
the temperature dependence of the ESR absorption linewidth and the frequency
dependence of the ESR resonance fields at 1.3 K is well explained by a
conventional spin wave theory. These results suggest an occurrence of Z2
vortex-induced topological transition.",0807.4438v2
2011-11-21,Magnetic Compton profiles of Fe and Ni corrected by dynamical electron correlations,"Magnetic Compton profiles (MCPs) of Ni and Fe along [111] direction have been
calculated using a combined Density Functional and many-body theory approach.
At the level of the local spin density approximation the theoretical MCPs does
not describe correctly the experimental results around the zero momentum
transfer. In this work we demonstrate that inclusion of electronic correlations
as captured by Dynamical Mean Field Theory (DMFT) improves significantly the
agreement between the theoretical and the experimental MCPs. In particular, an
energy decomposition of Ni MCPs gives indication of spin polarization and
intrinsic nature of Ni 6 eV satellite, a genuine many-body feature.",1111.4848v1
2012-01-11,Frequency domain studies of current-induced magnetization dynamics in single magnetic-layer nanopillars,"Spin transfer torque-induced high-frequency dynamics of single thin
cobalt-layer nanopillars of circular and elliptical shape have been observed
directly. Two types of precessional modes can be identified as a function of
magnetic field perpendicular to the layer plane, excited for negative current
polarity only. They are assigned to vortex-core and transverse spin-wave
excitations, which corroborate recent model predictions. The observed narrow
linewidth of 4 MHz at room temperature indicates the high coherence of the
magnetic excitations.",1201.2268v1
2012-04-23,Tensor network techniques for the computation of dynamical observables in 1D quantum spin systems,"We analyze the recently developed folding algorithm [Phys. Rev. Lett. 102,
240603 (2009)] to simulate the dynamics of infinite quantum spin chains, and
relate its performance to the kind of entanglement produced under the evolution
of product states. We benchmark the accomplishments of this technique with
respect to alternative strategies using Ising Hamiltonians with transverse and
parallel fields, as well as XY models. Additionally, we evaluate its ability to
find ground and thermal equilibrium states.",1204.5080v1
2013-09-03,Interaction effects on dynamic correlations in non-condensed Bose gases,"We consider dynamic, i.e., frequency-dependent, correlations in non-condensed
ultracold atomic Bose gases. In particular, we consider the single-particle
correlation function and its power spectrum. We compute this power spectrum for
a one-component Bose gas, and show how it depends on the interatomic
interactions that lead to a finite single-particle relaxation time. As another
example, we consider the power spectrum of spin-current fluctuations for a
two-component Bose gas and show how it is determined by the spin-transport
relaxation time.",1309.0667v1
2016-08-09,Charges and currents in quantum spin chains: late-time dynamics and spontaneous currents,"We review the structure of the conservation laws in noninteracting spin
chains and unveil a formal expression for the corresponding currents. We
briefly discuss how interactions affect the picture. In the second part, we
explore the effects of a localized defect. We show that the emergence of
spontaneous currents near the defect undermines any description of the
late-time dynamics by means of a stationary state in a finite chain. In
particular, the diagonal ensemble does not work. Finally, we provide numerical
evidence that simple generic localized defects are not sufficient to induce
thermalization.",1608.02869v2
2016-08-29,Spin measurements in strangeness production at the LHC,"We briefly recollect the problem of significant hyperon polarization
emphasizing the role of spin in dynamics of hadron interactions. We provide
also some model predictions based on chiral dynamics and the impact parameter
picture for illustration. The old, but yet unsolved problem of hyperon
polarization, can obtain a new insight from the measurements at the LHC
energies and, in combination with other measurements, can be used for tagging
QGP formation in $pp$--collisions.",1608.07940v2
2017-11-30,The pion holographic wavefunction with dynamical spin effects,"We report that the inclusion of dynamical spin effects in the pion
holographic light-front wavefunction leads to a remarkable improvement in
describing pion observables (pion mean charge radius, decay constant, spacelike
electromagnetic form factor) without the need to invoke higher Fock state
contributions and/or a special AdS/QCD mass scale for the pion.",1712.00051v1
2020-01-25,Field-induced freezing in the unfrustrated Ising antiferromagnet,"We study instantaneous quenches from infinite temperature to well below $T_c$
in the two-dimensional square lattice Ising antiferromagnet in the presence of
a longitudinal external magnetic field. Under single-spin-flip Metropolis
algorithm Monte Carlo dynamics, this protocol produces a pair of magnetization
plateaus that prevent the system from reaching the equilibrium ground state
except for some special values of the field. We explain the plateaus in terms
of local spin configurations that are stable under the dynamics.",2001.09268v2
2020-01-29,Qubit exchange interactions from permutations of classical bits,"In order to prepare for the introduction of dynamical many-body and,
eventually, field theoretical models, we show here that quantum mechanical
exchange interactions in a three-spin chain can emerge from the deterministic
dynamics of three classical Ising spins. States of the latter form an
ontological basis, which will be discussed with reference to the ontology
proposed in the Cellular Automaton Interpretation of Quantum Mechanics by 't
Hooft. Our result illustrates a new Baker-Campbell-Hausdorff formula with
terminating series expansion.",2001.10907v1
2000-06-06,A critical examination of the spin dynamics in high-$T_C$ cuprates,"A critical examination of the spin dynamics in high-$T_C$ cuprates is made on
the light of inelastic neutron scattering results obtained by different groups.
Recent neutron data show that incommensurate magnetic peaks in YBCO belong to
the same excitation as the resonance peak observed at $(\pi/a,\pi/a)$. Being
only observed in the superconducting state, the incommensurability is then
rather difficult to reconcile with a stripe picture. We also discuss the link
between the resonance peak spectral weight and the superconducting condensation
energy.",0006085v2
2000-06-29,Statistics of energy levels and zero temperature dynamics for deterministic spin models with glassy behaviour,"We consider the zero-temperature dynamics for the infinite-range, non
translation invariant one-dimensional spin model introduced by Marinari, Parisi
and Ritort to generate glassy behaviour out of a deterministic interaction. It
is shown that there can be a large number of metatastable (i.e., one-flip
stable) states with very small overlap with the ground state but very close in
energy to it, and that their total number increases exponentially with the size
of the system.",0006476v1
2018-03-22,Transient dynamics of strongly coupled spin vortex pairs: effects of anharmonicity and resonant excitation on inertial switching,"Spin vortices in magnetic nanopillars are used as GHz oscillators, with
frequency however essentially fixed in fabrication. We demonstrate a model
system of a two-vortex nanopillar, in which the resonance frequency can be
changed by an order of magnitude, without using high dc magnetic fields. The
effect is due to switching between the two stable states of the vortex pair,
which we show can be done with low-amplitude fields of sub-ns duration. We
detail the relevant vortex-core dynamics and explain how field anharmonicity
and phase control can be used to enhance the performance.",1803.08413v1
2018-07-27,Thick Permalloy films for the imaging of spin texture dynamics in perpendicularly magnetized systems,"We demonstrated that thick Permalloy films exhibiting a weak growth-induced
perpendicular magnetic anisotropy can be employed as an ideal test system for
the investigation of gyration dynamics in topologically trivial and non-trivial
magnetic states ranging from an isolated magnetic skyrmion to more complex
n$\pi$ spin configurations.",1807.10654v1
2019-01-23,Accelerated relaxation and suppressed dynamic heterogeneity in a kinetically constrained (East) model with swaps,"We introduce a kinetically constrained spin model with a local softness
parameter, such that spin flips can violate the kinetic constraint with an
(annealed) site-dependent rate. We show that adding MC swap moves to this model
can dramatically accelerate structural relaxation. We discuss the connection of
this observation with the fact that swap moves are also able to accelerate
relaxation in structural glasses. We analyse the rates of relaxation in the
model. We also show that the extent of dynamical heterogeneity is strongly
suppressed by the swap moves.",1901.07797v2
2019-02-04,Correction to: Effect of the rotation and tidal dissipation history of stars on the evolution of close-in planets,"This is an erratum for the publication Bolmont & Mathis 2016 (Celestial
Mechanics and Dynamical Astronomy, 126, 275-296,
https://doi.org/10.1007/s10569-016-9690-3). There was a small mistake for the
spin integration of our code which we corrected and we take advantage of this
erratum to investigate a bit further the influence of a planet on the spin of
its host star.",1902.01283v1
2019-03-01,Recurrence analysis of spinning particles in the Schwarzschild background,"In this work the dynamics of a spinning particle moving in the Schwarzschild
background is studied. In particular, the methods of Poincar\'{e} section and
recurrence analysis are employed to discern chaos from order. It is shown that
the chaotic or regular nature of the orbital motion is reflected on the
gravitational waves.",1903.00360v1
2020-09-02,Skyrmion-antiskyrmion droplets in a chiral ferromagnet,"We find numerically skyrmionic textures with skyrmion number Q=0 in
ferromagnets with the Dzyaloshinskii-Moriya interaction and perpendicular
anisotropy. These have the form of a skyrmion-antiskyrmion pair and may be
called chiral droplets. They are stable in an infinite film as well as in
disc-shaped magnetic elements. Droplets are found for values of the parameters
close to the transition from the ferromagnetic to the spiral phase. We study
their motion under spin-transfer torque. They move in the direction of the spin
flow and, thus, their dynamics are drastically different than the Hall dynamics
of the standard Q=0 skyrmion.",2009.00890v1
2020-10-01,Dissipative dynamics in isolated quantum spin chains after a local quench,"We provide numerical evidence that after a local quench in an isolated
infinite quantum spin chain, the quantum state locally relaxes to the ground
state of the post-quenched Hamiltonian, i.e. dissipates. This is a consequence
of the unitary quantum dynamics. A mechanism similar to the eigenstate
thermalization hypothesis is shown to be responsible for the dissipation
observed. We also demonstrate that integrability obstructs dissipation. The
numerical simulations are done directly in the thermodynamic limit with a
time-evolution algorithm based on matrix product states. The area law of
entanglement entropy is observed to hold after the local quench. As a result,
the simulations can be performed for long times with small bond dimensions.
Various local quenches on the Ising chain and the three-state Potts chain are
studied.",2010.00700v1
2020-10-03,"Hydrodynamic limit of the Kawasaki dynamics on the 1D-lattice with strong, finite-range interaction","We derive the hydrodynamic limit of the Kawasaki dynamics for the
one-dimensional conservative system of unbounded real-valued spins with
arbitrary strong, quadratic and finite-range interactions. This extends prior
results for non-interacting spin systems. The result is obtained by adapting
two scale approach of Grunewald, Otto, Villani and Westdickenberg combined with
the authors' recent approach on conservative systems with strong interactions.",2010.01266v2
2020-11-16,Time-Evolving Weiss Fields in the Stochastic Approach to Quantum Spins,"We investigate non-equilibrium quantum spin systems via an exact mapping to
stochastic differential equations. This description is invariant under a shift
in the mean of the Gaussian noise. We show that one can extend the simulation
time for real-time dynamics in one and two dimensions by a judicious choice of
this shift. This can be updated dynamically in order to reduce the impact of
stochastic fluctuations. We discuss the connection to drift gauges in the
gauge-P literature.",2011.07924v3
2021-06-03,Ultrafast Electron Dynamics in Magnetic Thin Films,"In past decades, ultrafast spin dynamics in magnetic systems have been
associated with heat deposition from high energy laser pulses, limiting the
selective access to spin order. Here we use a long wavelength terahertz pump
optical probe setup to measure structural features in the ultrafast time scale.
We find that complete demagnetisation is possible with <6 THz pulses. This
occurs concurrently with longitudinal acoustic phonons and an electronic
response, followed by the magnetic response. The required fluence for full
demagnetisation is low, ruling out the necessity of a high power light source.",2106.01828v1
2021-09-19,Theory of the Magnon Parametron,"The 'magnon parametron' is a ferromagnetic particle that is parametrically
excited by microwaves in a cavity. Above a certain threshold of the microwave
power, a bistable steady state emerges that forms an effective Ising spin. We
calculate the dynamics of the magnon parametron as a function of microwave
power, applied magnetic field and temperature for the interacting magnon
system, taking into account thermal and quantum fluctuations. We predict three
dynamical phases, viz. a stable Ising spin, telegraph noise of thermally
activated switching, and an intermediate regime that at lower temperatures is
quantum correlated with significant distillible magnon entanglement. These
three regimes of operation are attractive for alternative computing schemes.",2109.09117v1
2021-11-24,Hysteresis and return point memory in the random field Blume Capel model,"We study the zero temperature steady state of the random field Blume Capel
model with spin-flip Glauber dynamics on a random regular graph. The
magnetization m as a function of the external field H is observed to have
double hysteresis loops with a return point memory. We also solve the model on
a Bethe lattice in the approximation that the spin relaxation dynamics is
abelian and find good agreement between simulations on random regular graphs
and Bethe lattice calculations for negative values of H.",2111.12302v2
2022-03-04,Dissipation in spin chains using quantized nonequilibrium thermodynamics,"We investigate the open dynamics of a chain of interacting spins using the
quantized version of the GENERIC equation from classical out-of-equilibrium
thermodynamics. We focus on both equilibrium and nonequilibrium scenarios for
chains of different sizes. While in the equilibrium case we demonstrate thermal
equilibration to the correct many-body Gibbs density matrix, in the
nonequilibrium dynamics we show a ballistic-to-diffusive transition in the
steady-state energy current and a scaling that is consistent with Fourier's law
of heat transfer.",2203.02174v2
2022-03-11,Self-interfering dynamics in Bose-Einstein condensates with engineered dispersions,"Optical lattice and spin-orbit coupling are typical experimental approaches
to engineer dispersion. We reveal a self-interfering dynamics in a
noninteracting Bose-Einstein condensate with the engineered dispersion by
optical lattice or spin-orbit coupling. The self-interference results from the
co-occupation of positive and negative effect mass regimes in the engineered
dispersion. The physical origination of the self-interference is explained by
the Wigner distribution function of the self-interfering wave-packet. We
characterize detail features of the self-interference pattern.",2203.05722v1
2022-04-05,Numerical calculation of Green's function and momentum distribution for spin-polarized fermions by path integral molecular dynamics,"Most recently, path integral molecular dynamics (PIMD) has been successfully
applied to perform simulations of identical bosons and fermions by B. Hirshberg
et al.. In this work, we demonstrate that PIMD can be developed to calculate
Green's function and extract momentum distribution for spin-polarized fermions.
In particular, we show that the momentum distribution calculated by PIMD has
potential application to numerous quantum systems, such as cold atom simulation
of Mott insulator in Fermi-Hubbard model.",2204.02401v1
2022-04-06,Intertwiner Entanglement Excitation and Holonomy Operator,"In the loop quantum gravity framework, spin network states carry entanglement
between quantum excitations of the geometry at different space points. This
intertwiner entanglement is gauge-invariant and comes from quantum
superposition of spins and intertwiners. Bipartite entanglement can be
interpreted as a witness of distance, while multipartite entanglement reflects
the curvature of the quantum geometry. The present work investigates how the
bipartite and multipartite intertwiner entanglement changes under the action of
the holonomy operator, which is the basic building block of loop quantum
gravity's dynamics. We reveal the relation between entanglement excitation and
the dispersion of the holonomy operator. This leads to a new interesting
connection between bulk geometry and boundary observables via the dynamics of
entanglement.",2204.03093v1
2022-06-07,A HC model with countable set of spin values: uncountable set of Gibbs measures,"We consider a hard core (HC) model with a countable set $\mathbb{Z}$ of spin
values on the Cayley tree. This model is defined by a countable set of
parameters $\lambda_{i}>0, i \in \mathbb{Z}\setminus\{0\}$. For all possible
values of parameters, we give limit points of the dynamical system generated by
a function which describes the consistency condition for finite-dimensional
measures. Also, we prove that every periodic Gibbs measure for the given model
is either translation-invariant or periodic with period two. Moreover, we
construct uncountable set of Gibbs measures for this HC model.",2206.06333v1
2022-09-18,Nucleon spin decomposition with one dynamical gluon,"We solve for the light-front wave functions of the nucleon from a light-front
quantum chromodynamics (QCD) effective Hamiltonian with three-dimensional
confinement. We obtain solutions using constituent three quarks combined with
three quarks and one gluon Fock components. The resulting light-front wave
functions provide a good quality description of the nucleon's quark
distribution functions following QCD scale evolution. We present the effects
from incorporating a dynamical gluon on the nucleon's gluon densities, helicity
distribution and orbital angular momentum that constitutes the nucleon spin sum
rule.",2209.08584v1
2023-01-21,First post-Newtonian $N$-body problem in Einstein-Cartan theory with the Weyssenhoff fluid: Lagrangian and first integrals,"The rotational dynamics of an $N$-body system at the first post-Newtonian
order in Einstein-Cartan theory is derived. This result is achieved by
performing the point-particle limit of the equations of motion of the
Weyssenhoff fluid, which models the quantum spin effects residing inside the
bodies. For the special case of binary systems, we determine the Lagrangian
function and the resulting first integrals underlying the translational
dynamics and the spin precession.",2301.08954v2
2023-08-28,Laser-enhanced magnetism in SmFeO$_3$,"To coherently enhance inherent weak magnetic interactions in rare-earth
orthoferrite SmFeO$_3$ as a functional material for spintronic applications, we
simulate the dissipative spin dynamics that are linearly and quadratically
coupled to laser-driven infrared-active phonons. When linear coupling
dominates, we discover a magnetophononic dynamical first-order phase transition
in the nonequilibrium steady state which can inhibit strong enhancement of
magnetic interactions. By contrast, when quadratic spin-phonon coupling
dominates, no phase transition exists at experimentally relevant parameters. By
utilizing a chirp protocol, the phase transition can be engineered, enabling
stronger magnetic interactions. We also discuss the route for experimental
observation of our results.",2308.14939v2
2023-11-18,Small and simple systems that favor the arrow of time,"The 2nd law of thermodynamics yields an irreversible increase in entropy
until thermal equilibrium is achieved. This irreversible increase is often
assumed to require large and complex systems to emerge from the reversible
microscopic laws of physics. We test this assumption using simulations and
theory of a 1D ring of N Ising spins coupled to an explicit heat bath of N
Einstein oscillators. The exact entropy of the spins and bath can be calculated
for any N, with dynamics that is readily altered from reversible to
irreversible. We find thermal equilibrium behavior in the thermodynamic limit,
and in systems as small as N=2, but only if the microscopic dynamics is
intrinsically irreversible.",2311.11149v1
2004-09-22,On the Rotational Dynamics of Magnetically Threaded Disks around Neutron Stars,"We investigate the rotational dynamics of disk accretion around a strongly
magnetized neutron star with an aligned dipole field. The magnetospheric field
is assumed to thread the disk plasma both inside and outside the corotation
radius. As a result of disk-star interaction, the magnetic torque on the disk
affects the structure of accretion flow to yield the observed spin-up or
spin-down rates for a source of given fastness, magnetic field strength, and
mass accretion rate. Within the model we obtain a prescription for the
dynamical viscosity of such magnetically modified solutions for a Keplerian
disk. We then use this prescription to find a model solution for the rotation
rate profile throughout the entire disk including the non-Keplerian inner disk.
We find that the non-Keplerian angular velocity transition region is not
necessarily narrow for a source of given spin state. The boundary layer
approximation, as in the standard magnetically threaded disk model, holds only
in the case of dynamical viscosity decreasing all the way to the innermost edge
of the disk. These results are applied to several observed disk-fed X-ray
pulsars that have exhibited quasi-periodic oscillations (QPOs). The QPO
frequencies provide a constraint on the fastness parameter and enable one to
determine uniquely the width of the angular velocity transition zone for each
source within model assumptions. We discuss the implications of these results
on the value of the critical fastness parameter for a magnetized star in spin
equilibrium. Applications of our model are also made with relevant parameters
from recent numerical simulations of quasi-stationary disk-magnetized star
interactions.",0409545v1
1997-01-28,Dynamical Properties of an Antiferromagnet near the Quantum Critical Point: Application to LaCuO_2.5,"For a system of two-chain spin ladders, the ground state for weak interladder
coupling is the spin-liquid state of the isolated ladder, but is an ordered
antiferromagnet (AF) for sufficiently large interactions. We generalize the
bond-operator mean-field theory to describe both regimes, and to focus on the
transition between them. In the AF phase near the quantum critical point (QCP)
we find both spin waves and a low-lying but massive amplitude mode which is
absent in a conventional AF. The static susceptibility has the form $\chi(T) =
\chi_0 + a T^2$, with $\chi_0$ small for a system near criticality. We consider
the dynamical properties to examine novel features due to the presence of the
amplitude mode, and compute the dynamic structure factor. LaCuO$_{2.5}$ is
thought to be such an unconventional AF, whose ordered phase is located very
close to the QCP of the transition to the spin liquid. From the N\'eel
temperature we deduce the interladder coupling, the small ordered moment and
the gap in the amplitude mode. The dynamical properties unique to near-critical
AFs are expected to be observable in LaCuO$_{2.5}$.",9701202v1
1999-11-16,Long-Time Relaxation on Spin Lattice as Manifestation of Chaotic Dynamics,"The long-time behavior of the infinite temperature spin correlation functions
describing the free induction decay in nuclear magnetic resonance and
intermediate structure factors in inelastic neutron scattering is considered.
These correlation functions are defined for one-, two- and three-dimensional
infinite lattices of interacting spins both classical and quantum. It is shown
that, even though the characteristic timescale of the long-time decay of the
correlation functions considered is non-Markovian, the generic functional form
of this decay is either simple exponential or exponential multiplied by cosine.
This work contains (i) summary of the existing experimental and numerical
evidence of the above asymptotic behavior; (ii) theoretical explanation of this
behavior; and (iii) semi-empirical analysis of various factors discriminating
between the monotonic and the oscillatory long-time decays. The theory is based
on a fairly strong conjecture that, as a result of chaos generated by the spin
dynamics, a Brownian-like Markovian description can be applied to the long-time
properties of ensemble average quantities on a non-Markovian timescale. The
formalism resulting from that conjecture can be described as ``correlated
diffusion in finite volumes.''",9911230v2
2001-10-14,Bornholdt's spin model of a market dynamics in high dimensions,"We present results of an extension of the market model introduced by
Bornholdt to high dimensions. Three and four dimensions are shown to behave
similar to two, for suitable parameters.",0110279v1
2005-04-09,Critical Dynamics of Three-Dimensional Spin Systems with Long-Range Interactions,"A field-theoretic description of critical behavior of Ising systems with
long-range interactions is obtained in the two-loop approximation directly in
the three-dimensional space. It is shown that long-range interactions affect
the relaxation time of the system.",0504219v1
1999-01-23,Acceleration and Storage of Polarized Electron Beams,"I review recent developments in spin dynamics in electron storage rings and
accelerators.",9901040v1
1999-04-15,The Dynamic Effect of Quantum Decoherence,"An effective force induced by spatially depending decoherence is predicted.
The phenomenon is illustrated by a simple model of a 1/2-spin particle
subjected to distributed unselective measurement of noncommuting spin
components.",9904061v1
2001-04-10,A Hamiltonian for the description of a non-relativistic spin-1/2 free particle,"We propose a Hamiltonian for a nonrelativistic spin 1/2 \QTR{it}{free}
particle (e.g. an electron) and find that it contains information of its
internal degrees of freedom in the rest coordinate system. We comment on the
dynamical symmetry associated with the electron \QTR{it}{Zitterbewegung}.",0104051v1
2006-06-21,On non-completely positive quantum dynamical maps on spin chains,"The new arguments based on Majorana fermions indicating that non-completely
positive maps can describe open quantum evolution are presented.",0606176v2
2008-06-13,Coherent control of nanomagnet dynamics via ultrafast spin torque pulses,"The magnetization orientation of a nanoscale ferromagnet can be manipulated
using an electric current via the spin transfer effect. Time domain
measurements of nanopillar devices at low temperatures have directly shown that
magnetization dynamics and reversal occur coherently over a timescale of
nanoseconds. By adjusting the shape of a spin torque waveform over a timescale
comparable to the free precession period (100-400 ps), control of the
magnetization dynamics in nanopillar devices should be possible. Here we report
coherent control of the free layer magnetization in nanopillar devices using a
pair of current pulses as narrow as 30 ps with adjustable amplitudes and delay.
We show that the switching probability can be tuned over a broad range by
timing the current pulses with the underlying free-precession orbits, and that
the magnetization evolution remains coherent for more than 1 ns even at room
temperature. Furthermore, we can selectively induce transitions along
free-precession orbits and thereby manipulate the free magnetic moment motion.
We expect this technique will be adopted for further elucidating the dynamics
and dissipation processes in nanomagnets, and will provide an alternative for
spin torque driven spintronic devices, such as resonantly pumping microwave
oscillators, and ultimately, for efficient reversal of memory bits in magnetic
random access memory (MRAM).",0806.2297v1
2011-06-21,Symmetry and the macroscopic dynamics of antiferromagnetic materials in the presence of spin-polarized current,"Antiferromagnetic (AFM) materials with zero or vanishingly small macroscopic
magnetization are nowadays the constituent elements of spintronic devices.
However, possibility to use them as active elements that show nontrivial
controllable magnetic dynamics is still discussible. In the present paper we
extend the theory [A.F.Andreev, V.I.Marchenko, Sov. Phys. --- Uspekhi, 23
(1980), 21] of macroscopic dynamics in AFMs for the cases typical for
spin-valve devices. In particular, we consider the solid-like magnetic dynamics
of AFMs with strong exchange coupling in the presence of spin-polarized current
and give an expression for the current-induced Rayleigh dissipation function in
terms of the rotation vector for different types %generalized potential of
AFMs. Basing on the analysis of linearized equations of motion we predict the
current-induced reorientation and AFM resonance, and found the values of
critical currents in terms of AFMR frequencies and damping constants. We show
the possibility of current-induced spin-diode effect and second-harmonic
generation in AF layer. The proposed approach is generalized for the
description of current-related phenomena in inhomogeneous AFMs.",1106.4231v3
2012-10-29,Spin-Transfer Torque Magnetization Reversal in Uniaxial Nanomagnets with Thermal Noise,"We consider the general Landau-Lifshitz-Gilbert (LLG) dynamical theory
underlying the magnetization switching rates of a thin film uniaxial magnet
subject to spin-torque effects and thermal fluctuations (thermal noise). After
discussing the various dynamical regimes governing the switching phenomena, we
present analytical results for the mean switching time behavior. Our approach,
based on explicitly solving the first passage time problem, allows for a
straightforward analysis of the thermally assisted, low spin-torque, switching
asymptotics of thin film magnets. To verify our theory, we have developed an
efficient GPU-based micromagnetic code to simulate the stochastic LLG dynamics
out to millisecond timescales. We explore the effects of geometrical tilts
between the spin-current and uniaxial anisotropy axes on the thermally assisted
dynamics. We find that even in the absence of axial symmetry, the switching
times can be functionally described in a form virtually identical to the
collinear case. We further verify that asymptotic behavior is reached fairly
slowly, thus quantifying the role of thermal noise in the crossover regime
linking deterministic to thermally assisted magnetization reversal.",1210.7675v3
2012-12-31,Preparation of Non-equilibrium Nuclear Spin States in Double Quantum Dots,"We theoretically study the dynamic polarization of lattice nuclear spins in
GaAs double quantum dots containing two electrons. In our prior work [Phys.
Rev. Lett. 104, 226807 (2010)] we identified three regimes of long-term
dynamics, including the build up of a large difference in the Overhauser fields
across the dots, the saturation of the nuclear polarization process associated
with formation of so-called ""dark states,"" and the elimination of the
difference field. In particular, when the dots are different sizes we found
that the Overhauser field becomes larger in the smaller dot. Here we present a
detailed theoretical analysis of these problems including a model of the
polarization dynamics and the development of a new numerical method to
efficiently simulate semiclassical central-spin problems. When nuclear spin
noise is included, the results agree with our prior work indicating that large
difference fields and dark states are stable configurations, while the
elimination of the difference field is unstable; however, in the absence of
noise we find all three steady states are achieved depending on parameters.
These results are in good agreement with dynamic nuclear polarization
experiments in double quantum dots.",1212.6953v3
2014-08-16,Information Transfer Fidelity in Spin Networks and Ring-based Quantum Routers,"Spin networks are endowed with an Information Transfer Fidelity (ITF), which
defines an absolute upper bound on the probability of transmission of an
excitation from one spin to another. The ITF is easily computable but the bound
can be reached asymptotically in time only under certain conditions. General
conditions for attainability of the bound are established and the process of
achiev-ing the maximum transfer probability is given a dynamical model, the
translation on the torus. The time to reach the maximum probability is
estimated using the simultaneous Diophantine approximation, implemented using a
variant of the Lenstra-Lenstra-Lovasz (LLL) algorithm. For a ring with uniform
couplings, the network can be made a metric space by defining a distance
(satisfying the triangle inequality) that quantifies the lack of transmission
fidelity between two nodes. It is shown that transfer fidelities and transfer
times can be improved significantly by means of simple controls taking the form
of non-dynamic, spatially localized bias fields, opening up the possibility for
intelligent design of spin networks and dynamic routing of information encoded
in them, while being more flexible than engineering fixed couplings to favor
some transfers, and less demanding than control schemes requiring fast dynamic
controls.",1408.3765v3
2014-09-12,The dynamics of a doped hole in cuprates is not controlled by spin fluctuations,"Twenty seven years after the discovery of high-temperature superconductivity
\cite{BedMu}, consensus on its theoretical explanation is still absent. To a
good extent, this is due to the difficulty of studying strongly correlated
systems near half-filling, needed to understand the behaviour of one or few
holes doped into a CuO$_2$ layer. To simplify this task it is customary to
replace three-band models \cite{Emery} describing the doping holes as entering
the O $2p$ orbitals of these charge-transfer insulators \cite{ZSA} with much
simpler one-band Hubbard or $tJ$ models \cite{rev1,rev2}. Here we challenge
this approach, showing that not only is the dynamics of a doped hole easier to
understand in models that explicitly include the O orbitals, but also that our
solution contradicts the long-held belief that the quantum spin fluctuations of
the antiferromagnetic (AFM) background play a key role in determining this
dynamics. Indeed, we show that the correct, experimentally observed dispersion
is generically obtained for a hole moving on the O sublattice, and coupled to a
N\'eel lattice of spins without spin fluctuations. This marks a significant
conceptual change in our understanding of the relevant phenomenology and opens
the way to studying few-holes dynamics without finite-size effect issues
\cite{BayoB}, to understand the actual strength of the ""magnetic glue"".",1409.3647v1
2015-04-15,Spin and valley dynamics of excitons in transition metal dichalcogenides monolayers,"Monolayers of transition metal dichalcogenides, namely, molybdenum and
tungsten disulfides and diselenides demonstrate unusual optical properties
related to the spin-valley locking effect. Particularly, excitation of
monolayers by circularly polarized light selectively creates electron-hole
pairs or excitons in non-equivalent valleys in momentum space, depending on the
light helicity. This allows studying the inter-valley dynamics of charge
carriers and Coulomb complexes by means of optical spectroscopy. Here we
present a concise review of the neutral exciton fine structure and its spin and
valley dynamics in monolayers of transition metal dichalcogenides. It is
demonstrated that the long-range exchange interaction between an electron and a
hole in the exciton is an efficient mechanism for rapid mixing between bright
excitons made of electron-hole pairs in different valleys. We discuss the
physical origin of the long-range exchange interaction and outline its
derivation in both the electrodynamical and $\mathbf k \cdot \mathbf p$
approaches. We further present a model of bright exciton spin dynamics driven
by an interplay between the long-range exchange interaction and scattering.
Finally, we discuss the application of the model to describe recent
experimental data obtained by time-resolved photoluminescence and Kerr rotation
techniques.",1504.03911v2
2015-05-25,Quantum Dynamical Phase Transition in a Spin-Orbit Coupled Bose Condensate,"Spin-orbit coupled bosons can exhibit rich equilibrium phases at low
temperature and in the presence of particle-particle interactions. In the case
with a 1D synthetic spin-orbit interaction, it has been observed that the
ground state of a Bose gas can be a normal phase, stripe phase, or magnetized
phase in different experimentally controllable parameter regimes. The
magnetized states are doubly degenerate and consist of a many-particle
two-state system. In this work, we investigate the nonequilibrium quantum
dynamics by switching on an external perturbation to induce resonant couplings
between the magnetized phases, and predict the novel quantum spin dynamics
which cannot be obtained in the single-particle systems. In particular, due to
particle-particle interactions, the transition of the Bose condensate from one
magnetized phase to the other is forbidden when the strength of external
perturbation is less than a critical value, and a full transition can occur
only when the perturbation exceeds such critical strength. This phenomenon
manifests itself a quantum dynamical phase transition, with the critical point
behavior being exactly solvable. From the numerical simulations and exact
analytic studies we show that the predicted many-body effects can be well
observed with the current experiments.",1505.06687v1
2016-01-08,Spin-glass like dynamics of ferromagnetic clusters in La$_{0.75}$Ba$_{0.25}$CoO$_3$,"We report the magnetization study of the compound
La$_{0.75}$Ba$_{0.25}$CoO$_3$ where Ba$^{2+}$ doping is just above the critical
limit for percolation of ferromagnetic clusters. The field cooled (FC) and zero
field cooled (ZFC) magnetization exhibit a thermomagnetic irreversibility and
the ac susceptibility show a frequency dependent peak at the ferromagnetic
ordering temperature (T$_C$$\approx$203~K) of the clusters. These features
indicate about the presence of a non-equilibrium state below T$_C$. In the
non-equilibrium state, the dynamic scaling of the imaginary part of ac
susceptibility and the static scaling of the nonlinear susceptibility clearly
establish a spin-glass like cooperative freezing of ferromagnetic clusters at
200.9(2)~K. The existence of spin-glass like freezing of ferromagnetic clusters
is further substantiated by the ZFC aging and memory experiments. We also
observe certain dynamical features which are not present in a typical
spin-glass, such as, initial magnetization after ZFC aging first increases and
then decreases with the wait time and an imperfect recovery of relaxation in
negative temperature cycling experiments. This imperfect recovery transforms to
perfect recovery on concurrent field cycling. Our analysis suggests that these
additional dynamical features have their origin in inter-cluster exchange
interaction and cluster size distribution. The inter-cluster exchange
interaction above the magnetic percolation gives a superferromagnetic state in
some granular thin films but our results show the absence of typical
superferromagnetic like state in La$_{0.75}$Ba$_{0.25}$CoO$_3$.",1601.02009v1
2016-09-23,Reply to the Comment on 'Unraveling Photoinduced Spin Dynamics in the Topological Insulator Bi2Se3',"Reply to the Comment [arXiv:1609.04476] on a recent work in PRL [Phys. Rev.
Lett. 116, 036601 (2016), arXiv:1511.02994v2].",1609.07286v2
2016-10-12,Exact master equation for a spin interacting with a spin bath: Non-Markovianity and negative entropy production rate,"An exact canonical master equation of the Lindblad form is derived for a
central spin interacting uniformly with a sea of completely unpolarized spins.
The Kraus operators for the dynamical map are also derived. The
non-Markovianity of the dynamics in terms of the divisibility breaking of the
dynamical map and increase of the trace distance fidelity between quantum
states is shown. Moreover, it is observed that the irreversible entropy
production rate is always negative (for a fixed initial state) whenever the
dynamics exhibits non-Markovian behavior. In continuation with the study of
witnessing non-Markovianity, it is shown that the positive rate of change of
the purity of the central qubit is a faithful indicator of the non-Markovian
information back flow. Given the experimental feasibility of measuring the
purity of a quantum state, a possibility of experimental demonstration of
non-Markovianity and the negative irreversible entropy production rate is
addressed. This gives the present work considerable practical importance for
detecting the non-Markovianity and the negative irreversible entropy production
rate.",1610.03895v2
2017-02-24,Magnetic order and spin dynamics across a ferromagnetic quantum critical point: $μ$SR investigations of YbNi$_4$(P$_{1-x}$As$_x$)$_2$,"In the quasi-1D heavy-fermion system YbNi$_4$(P$_{1-x}$As$_x$)$_2$ the
presence of a ferromagnetic (FM) quantum critical point (QCP) at $x_c$ $\approx
0.1$ with unconventional quantum critical exponents in the thermodynamic
properties has been recently reported. Here, we present muon-spin relaxation
($\mu$SR) experiments on polycrystals of this series to study the magnetic
order and the low energy 4$f$-electronic spin dynamics across the FM QCP. The
zero field $\mu$SR measurements on pure YbNi$_4$(P$_{2}$ proved static long
range magnetic order and suggested a strongly reduced ordered Yb moment of
about 0.04$\mu_B$. With increasing As substitution the ordered moment is
reduced by half at $x = 0.04$ and to less than 0.005 $\mu_B$ at $x=0.08$. The
dynamic behavior in the $\mu$SR response show that magnetism remains
homogeneous upon As substitution, without evidence for disorder effect. In the
paramagnetic state across the FM QCP the dynamic muon-spin relaxation rate
follows 1/$T_{1}T\propto T^{-n}$ with $1.01 \pm 0.04 \leq n \leq 1.13 \pm
0.06$. The critical fluctuations are very slow and are even becoming slower
when approaching the QCP.",1702.07504v2
2018-02-20,Ultrafast magnetization dynamics in pure and doped Heusler and inverse Heusler alloys,"By using a multiscale approach based on first-principles density functional
theory combined with atomistic spin dynamics, we investigate the electronic
structure and magnetization dynamics of an inverse Heusler and a Heusler
compound and their alloys, i. e. Mn$_{2-x}Z_x$CoAl and Mn$_{2-x}Z_x$VAl, where
$Z$ = Mo, W, Os and Ru, respectively. A signature of the ferrimagnetic ordering
of Mn$_{2}$CoAl and Mn$_{2}$VAl Heusler alloys is reflected in the calculated
Heisenberg exchange constants. They decay very rapidly with the interatomic
distance and have short range, which is a consequence of the existence of the
finite gap in the minority spin band. The calculated Gilbert damping parameter
of both Mn$_2$CoAl and Mn$_2$VAl is high compared to other half-metals, but
interestingly in the particular case of the inverse Mn$_{2}$CoAl alloys and due
to the spin-gapless semiconducting property, the damping parameters decrease
with the doping concentration in clear contradiction to the general trend.
Atomistic spin dynamics simulations predict ultrafast magnetisation switching
in Mn$_{2}$CoAl and Mn$_{2}$VAl under the influence of an external magnetic
field, starting from a threshold field of $2\text{T}$. Our overall finding
extends with Heusler and inverse Heusler alloys, the class of materials that
exhibits laser induced magnetic switching.",1802.07195v1
2019-05-16,Quench dynamics of two component dipolar fermions subject to a quasiperiodic potential,"Motivated by recent experiments in fermionic polar gases, we study the
non-equilibrium dynamics of two-component dipolar fermions subject to a
quasiperiodic potential. We investigate the localization of charge and spin
degrees of freedom time evolving with a long-range spin-SU(2) symmetric
fermionic Hamiltonian, by calculating experimentally accessible dynamical
observables. To study the non-equilibrium dynamics, we start the time evolution
with two initial states at half-filling: (i) product state with doublons
$|\uparrow \downarrow 0 \uparrow \downarrow 0 \uparrow \downarrow 0 \uparrow
\downarrow 0 \uparrow \downarrow \rangle$ and (ii) product state with singlons
$|\uparrow \ \downarrow \ \uparrow \ \downarrow \ \uparrow \ \downarrow \
\uparrow \ \downarrow \ \uparrow \ \downarrow \ \rangle$. We carried out the
real-time evolution via the fermionic Hamiltonian using exact
diagonalization(ED) and the time-dependent variational principle (TDVP) for
finite Matrix product states(MPSs), within experimentally relevant time scales.
For the product state with doublons, we observe a delocalized to localized
phase transition varying disorder strengths, by monitoring the decay of charge
imbalance with time. For the long-range interacting Hamiltonian of our focus,
and in the presence of strong enough disorder, starting the time evolution with
singlons we find a strong reduction in the spin delocalization, contrary to
results of previous studies using the disordered short-range (on-site) Hubbard
model with SU(2) symmetry. Our predictions for localization of both charge and
spin should be observable in ultra-cold experiments with fermionic dipolar
atoms subject to a quasiperiodic potential.",1905.06677v3
2009-12-24,"Charge, Lattice, and Spin Dynamics in Photoinduced Phase Transitions from Charge-Order-Insulator to Metal in Quasi-Two-Dimensional Organic Conductors","To elucidate different photoinduced melting dynamics of charge orders
observed in quasi-two-dimensional organic conductors $ \theta
$-(BEDT-TTF)$_2$RbZn(SCN)$_4$ and $ \alpha $-(BEDT-TTF)$_2$I$_3$
[BEDT-TTF=bis(ethylenedithio)tetrathiafulvalene], we theoretically study
photoinduced time evolution of charge and spin correlation functions on the
basis of exact many-electron wave functions coupled with classical phonons in
extended Peierls-Hubbard models on anisotropic triangular lattices. In both
salts, the so-called horizontal-stripe charge order is stabilized by
nearest-neighbor repulsive interactions and by electron-lattice interactions.
In $ \theta $-(BEDT-TTF)$_2$RbZn(SCN)$_4$ (abbreviated as $ \theta $-RbZn), the
stabilization energy due to lattice distortion is larger, so that larger
quantity of energy needs to be absorbed for the melting of the charge and
lattice orders. The photoinduced charge dynamics shows a complex behavior owing
to a substantial number of nearly degenerate eigenstates involved. This is
related to the high structural symmetry when the lattice is undistorted. In $
\alpha $-(BEDT-TTF)$_2$I$_3$ (abbreviated as $ \alpha $-I$_3$), the lattice
stabilization energy is smaller, and smaller quantity of energy is sufficient
to melt the charge and lattice orders leading to a metallic phase. The
photoinduced charge dynamics shows a sinusoidal oscillation. In $ \alpha
$-I$_3$, the low structural symmetry ensures nearly spin-singlet bonds between
hole-rich sites, where the spin correlation survives even after
photoexcitation.",0912.4850v2
2014-06-15,Dynamical topological phases in quenched spin-orbit coupled degenerate Fermi gas,"The spin-orbit coupled degenerate Fermi gas provides a totally new platform
to realize topological superfluids and related topological excitations.
Previous studies have mainly focused on the properties of the ground state.
Here we consider a two-dimensional Fermi gas with Rashba spin-orbit coupling
subject to a perpendicular Zeeman field. For this system, we have found that
its ground state topological structure is captured by the spin texture, which
is readily measurable in experiments. We show that, when the Zeeman field is
suddenly quenched, dynamical topological phases can be realized. More
specifically, three post-quench dynamical phases can be identified according to
the asymptotic behavior of the order parameter. In the undamped phase, a
persistent oscillation of the order parameter may support a topological Floquet
state with multiple edge states. In the Landau damped phase, the magnitude of
the order parameter approaches a constant via a power-law decay, and this
system can support a dynamical topological phase with a pair of edge states at
the boundary. In the over-damped phase, the order parameter decays to zero
exponentially although the condensate fraction remains finite. These
predictions can be observed in the strong coupling regime of ultracold Fermi
gas.",1406.3821v2
2015-12-14,Random SU(2)-symmetric spin-$S$ chains,"We study the low-energy physics of a broad class of time-reversal invariant
and SU(2)-symmetric one-dimensional spin-S systems in the presence of quenched
disorder via a strong-disorder renormalization-group technique. We show that,
in general, there is an antiferromagnetic phase with an emergent SU(2S+1)
symmetry. The ground state of this phase is a random singlet state in which the
singlets are formed by pairs of spins. For integer spins, there is an
additional antiferromagnetic phase which does not exhibit any emergent symmetry
(except for S=1). The corresponding ground state is a random singlet one but
the singlets are formed mostly by trios of spins. In each case the
corresponding low-energy dynamics is activated, i.e., with a formally infinite
dynamical exponent, and related to distinct infinite-randomness fixed points.
The phase diagram has two other phases with ferromagnetic tendencies: a
disordered ferromagnetic phase and a large spin phase in which the effective
disorder is asymptotically finite. In the latter case, the dynamical scaling is
governed by a conventional power law with a finite dynamical exponent.",1512.04542v3
2017-12-20,Optical Manipulation of Magnetic Vortex Visualized in situ by 4D Electron Microscopy,"Understanding the fundamental dynamics of topological vortex and antivortex
naturally formed in micro/nanoscale ferromagnetic building blocks under
external perturbations is crucial to magnetic vortex based information
processing and spintronic devices. All previous studies have focused on
magnetic vortex-core switching via external magnetic fields, spin-polarized
currents, or spin waves, which have largely prohibited the investigation of
novel spin configurations that could emerge from the ground states in
ferromagnetic disks and their underlying dynamics. Here, we report in situ
visualization of femtosecond laser quenching induced magnetic vortex change in
various symmetric ferromagnetic Permalloy disks by Lorentz phase imaging using
4D electron microscopy. Besides the switching of magnetic vortex chirality and
polarity, we observed with distinct occurrence frequencies a plenitude of
complex magnetic structures that have never been observed by magnetic field or
current assisted switching. These complex magnetic structures consist of a
number of newly created topological magnetic defects (vortex and antivortex)
strictly conserving the topological winding number, demonstrating the direct
impact of topological invariant on the magnetization dynamics in ferromagnetic
disks. Their spin configurations show mirror or rotation symmetry due to the
geometrical confinement of the disks. Combined micromagnetic simulations with
the experimental observations reveal the underlying magnetization dynamics and
formation mechanism of the optical quenching induced complex magnetic
structures. Their distinct occurrence rates are pertinent to their
formation-growth energetics and pinning effects at the disk edge. Based on
these findings, we propose a paradigm of optical-quenching-assisted fast
switching of vortex cores for the control of magnetic vortex based information
recording and spintronic devices.",1712.07280v1
2012-05-11,Nonequilibrium quantum dynamics of the magnetic Anderson model,"We study the non-equilibrium dynamics of a spinful single-orbital quantum dot
with an incorporated quantum mechanical spin-1/2 magnetic impurity. Due to the
spin degeneracy, double occupancy is allowed, and Coulomb interaction together
with the exchange coupling of the magnetic impurity influence the dynamics. By
extending the iterative summation of real-time path integrals (ISPI) to this
coupled system, we monitor the time-dependent non-equilibrium current and the
impurity spin polarization to determine features of the time-dependent
non-equilibrium dynamics. We particulary focus on the deep quantum regime,
where all time and energy scales are of the same order of magnitude and no
small parameter is available. We observe a significant influence of the
non-equilibrium decay of the impurity spin polarization both in the presence
and in the absence of Coulomb interaction. The exponential relaxation is faster
for larger bias voltages, electron-impurity interactions and temperatures. We
show that the exact relaxation rate deviates from the corresponding
perturbative result. In addition, we study in detail the impurity's back action
on the charge current and find a reduction of the stationary current for
increasing coupling to the impurity. Moreover, our approach allows us to
systematically distinguish mean-field Coulomb and impurity effects from the
influence of quantum fluctuations and flip-flop scattering, respectively. In
fact, we find a local maximum of the current for a finite Coulomb interaction
due to the presence of the impurity.",1205.2462v2
2018-07-30,Comparison of dynamical and equilibrium surface spin-reorientations: Inferences on the nature of the phase transitions in the presence of dipole interactions,"The influence of long-range dipole interactions on two dimensional magnetism
has been studied extensively in the spin-reorientation transition of
ferromagnetic ultrathin films. Although there is a great deal of experimental
information on the perpendicular domain phase that is stabilized by dipole
interactions, the transitions to or from the domain phase are subtle and
difficult to characterize experimentally. Magnetic susceptibility measurements
show no divergence in the vicinity of the spin-reorientation transition as a
function of thickness -- a null result that is difficult to interpret with
confidence. This article reports separate dynamical and equilibrium versions of
the reorientation transition in Fe/2ML Ni/W(110) films, using measurements of
the magnetic susceptibility as the films are grown. The dynamical version
occurs when increasing the film thickness causes the domain walls to depin, and
the system moves from a configuration that minimizes local energetics to one
that minimizes global energetics. The dynamical transition \textit{is} marked
by a divergent magnetic susceptibility measured with a field applied along the
in-plane W[001] direction. A comparative study of the two versions of the same
spin-reorientation transition aids in the experimental characterization of the
effects of dipole interactions on the phase transitions. This comparison
confirms the original null result found in magnetic susceptibility measurements
of the equilibrium transition; despite its name, the spin-reorientation
transition in ferromagnetic ultrathin films has no critical phase transition in
either the magnetization or its orientation.",1807.11434v2
2019-02-18,Dynamics of frequency-swept nuclear spin optical pumping in powdered diamond at low magnetic fields,"A broad effort is underway to improve the sensitivity of nuclear magnetic
resonance through the use of dynamic nuclear polarization. Nitrogen-vacancy
(NV) centers in diamond offer an appealing platform because these paramagnetic
defects can be optically polarized efficiently at room temperature. However,
work thus far has been mainly limited to single crystals because most
polarization transfer protocols are sensitive to misalignment between the NV
and magnetic field axes. Here we study the spin dynamics of NV-13C pairs in the
simultaneous presence of optical excitation and microwave frequency sweeps at
low magnetic fields. We show that a subtle interplay between illumination
intensity, frequency sweep rate, and hyperfine coupling strength leads to
efficient, sweep-direction-dependent 13C spin polarization over a broad range
of orientations of the magnetic field. In particular, our results strongly
suggest that finely-tuned, moderately coupled nuclear spins are key to the
hyperpolarization process, which makes this mechanism distinct from other known
dynamic polarization channels. These findings pave the route to applications
where powders are intrinsically advantageous, including the hyper-polarization
of target fluids in contact with the diamond surface or the use of
hyperpolarized particles as contrast agents for in-vivo imaging.",1902.06805v1
2020-05-25,Dynamics of ferromagnetic bimerons driven by spin currents and magnetic fields,"Magnetic bimeron composed of two merons is a topological counterpart of
magnetic skyrmion in in-plane magnets, which can be used as the nonvolatile
information carrier in spintronic devices. Here we analytically and numerically
study the dynamics of ferromagnetic bimerons driven by spin currents and
magnetic fields. Numerical simulations demonstrate that two bimerons with
opposite signs of topological numbers can be created simultaneously in a
ferromagnetic thin film via current-induced spin torques. The current-induced
spin torques can also drive the bimeron and its speed is analytically derived,
which agrees with the numerical results. Since the bimerons with opposite
topological numbers can coexist and have opposite drift directions, two-lane
racetracks can be built in order to accurately encode the data bits. In
addition, the dynamics of bimerons induced by magnetic field gradients and
alternating magnetic fields are investigated. It is found that the bimeron
driven by alternating magnetic fields can propagate along a certain direction.
Moreover, combining a suitable magnetic field gradient, the
Magnus-force-induced transverse motion can be completely suppressed, which
implies that there is no skyrmion Hall effect. Our results are useful for
understanding of the bimeron dynamics and may provide guidelines for building
future bimeron-based spintronic devices.",2005.11924v2
2021-07-14,On The Spin Dynamics of Elongated Minor Bodies with Applications to a Possible Solar System Analogue Composition for `Oumuamua,"The first interstellar object, 1I/2017 U1 (`Oumuamua), exhibited several
unique properties, including an extreme aspect ratio, a lack of typical
cometary volatiles, and a deviation from a Keplerian trajectory. Several
authors have hypothesized that the non-gravitational acceleration was caused by
either cometary outgassing or radiation pressure. Here, we investigate the spin
dynamics of `Oumuamua under the action of high surface area fractional activity
and radiation pressure. We demonstrate that a series of transient jets that
migrate across the illuminated surface will not produce a secular increase in
the spin rate. We produce 3D tumbling simulations that approximate the dynamics
of a surface covering jet, and show that the resulting synthetic light curve
and periodogram are reasonably consistent with the observations. Moreover, we
demonstrate that radiation pressure also produces a steady spin-state. While
carbon monoxide (CO) has been dismissed as a possible accelerant because of its
non-detection in emission by $\textit{Spitzer}$, we show that outgassing from a
surface characterized by a modest covering fraction of CO ice can satisfy the
non-ballistic dynamics for a plausible range of assumed bulk densities and
surface albedos. $\textit{Spitzer}$ upper limits on CO emission are, however,
inconsistent with the CO production necessary to provide the acceleration.
Nonetheless, an ad hoc but physically plausible explanation is that the
activity level varied greatly during the time that the trajectory was
monitored. We reproduce the astrometric analysis presented in Micheli et al.
(2018), and verify that the non-gravitational acceleration was consistent with
stochastic changes in outgassing.",2107.06834v1
2021-11-17,Probing the magnetic polaron state in the ferromagnetic semiconductor HgCr$_2$Se$_4$ with resistance fluctuation and muon-spin spectroscopy measurements,"Combined resistance noise and muon-spin relaxation ($\mu$SR) measurements of
the ferromagnetic semiconductor HgCr$_2$Se$_4$ suggest a degree of
magnetoelectric coupling and provide evidence for the existence of isolated
magnetic polarons. These form at elevated temperatures and undergo a
percolation transition with a drastic enhancement of the low-frequency
1/$f$-type charge fluctuations at the insulator-to-metal transition at $\sim 95
- 98$ K in the vicinity of the magnetic ordering temperature $T_C \sim 105 -
107$ K. Upon approaching the percolation threshold from above, the strikingly
unusual dynamics of a distinct two-level fluctuator superimposed on the $1/f$
noise can be described by a slowing down of the dynamics of a nanoscale
magnetic cluster, a magnetic polaron, when taking into account an effective
radius of the polaron depending on the spin correlation length. Coinciding
temperature scales found in $\mu$SR and noise measurements suggest changes in
the magnetic dynamics over a wide range of frequencies and are consistent with
the existence of large polarized and domain-wall-like regions at low
temperatures, that result from the freezing of spin dynamics at the magnetic
polaron percolation transition.",2111.08990v1
2021-11-22,"Disentangling Electronic, Lattice and Spin Dynamics in the Chiral Helimagnet Cr1/3NbS2","We investigate the static and ultrafast magneto-optical response of the
hexagonal chiral helimagnet $Cr_{1/3}NbS_{2}$ above and below the helimagnetic
ordering temperature. The presence of a magnetic easy plane contained within
the crystallographic ab-plane is confirmed, while degenerate optical pump-probe
experiments reveal significant differences in the dynamic between the parent,
$NbS_{2}$, and Cr-intercalated compounds. Time resolved magneto-optical Kerr
effect measurements show a two-step demagnetization process, where an initial,
sub-ps relaxation and subsequent buildup ($\tau > 50$ ps) in the
demagnetization dynamic scale similarly with increasing pump fluence. Despite
theoretical evidence for partial gapping of the minority spin channel,
suggestive of possible half metallicity in $Cr_{1/3}NbS_{2}$, such a long
demagnetization dynamic likely results from spin lattice-relaxation as opposed
to minority state blocking. However, comparison of the two-step demagnetization
process in $Cr_{1/3}NbS_{2}$ with other 3d intercalated transition metal
dichalcogenides reveals a behavior that is unexpected from conventional
spin-lattice relaxation, and may be attributed to the complicated interaction
of local moments with itinerant electrons in this material system.",2111.11465v1
2021-12-11,Optical excitation of electromagnons in hexaferrite,"Understanding ultrafast magnetization dynamics on the microscopic level is of
strong current interest due to the potential for applications in information
storage. In recent years, the spin-lattice coupling has been recognized to be
essential for ultrafast magnetization dynamics. Magnetoelectric multiferroics
of type II possess intrinsic correlations among magnetic sublattices and
electric polarization (P) through spin-lattice coupling, enabling fundamentally
coupled dynamics between spins and lattice. Here we report on ultrafast
magnetization dynamics in a room-temperature multiferroic hexaferrite
possessing ferrimagnetic and antiferromagnetic sublattices, revealed by
time-resolved resonant x-ray diffraction. A femtosecond above-bandgap
excitation triggers a coherent magnon in which the two magnetic sublattices
entangle and give rise to a transient modulation of P. A novel microscopic
mechanism for triggering the coherent magnon in this ferrimagnetic insulator
based on the spin-lattice coupling is proposed. Our finding opens up a novel
but general pathway for ultrafast control of magnetism.",2112.05961v1
2022-01-28,Spin Excitation Spectra of Anisotropic Spin-$1/2$ Triangular Lattice Heisenberg Antiferromagnets,"Investigation of dynamical excitations is difficult but crucial to the
understanding of many exotic quantum phenomena discovered in quantum materials.
This is particularly true for highly frustrated quantum antiferromagnets whose
dynamical properties deviate strongly from theoretical predictions made based
on the spin-wave or other approximations. Here we present a large-scale
numerical calculation on the dynamical correlation functions of spin-$1/2$
triangular Heisenberg model using a state-of-the-art tensor network
renormalization group method. The calculated results allow us to gain for the
first time a comprehensive picture on the nature of spin excitation spectra in
this highly frustrated quantum system. It provides a quantitative account for
all the key features of the dynamical spectra disclosed by inelastic neutron
scattering measurements for $\rm Ba_3CoSb_2O_9$, revealing the importance of
the interplay between low- and high-energy excitations and its renormalization
effect to the low-energy magnon bands and high-energy continuums. We identify
the longitudinal Higgs modes in the intermediate-energy scale and predict the
energy and momentum dependence of spectral functions along the three principal
axes that can be verified by polarized neutron scattering experiments.
Furthermore, we find that the spin excitation spectra weakly depend on the
anisotropic ratio of the antiferromagnetic interaction.",2201.12121v2
2022-08-18,Dynamics of quantum soliton in Lee-Huang-Yang spin-orbit coupled Bose-Einstein condensates,"We present the numerical results of the structure and dynamics of the
self-bound ground state arising solely because of the presence of beyond mean
field quantum fluctuation in spin-orbit coupled binary Bose-Einstein
condensates in one dimension. Depending upon spin-obit (SO) and Rabi couplings,
we observe that the ground state exhibits either quantum-bright (plane) or
quantum-stripe soliton nature. We find an analytical soliton solution for
non-zero SO coupling that matches quite well with the numerical results.
Further, we investigate the dynamical stability of these solitons by adopting
three protocols, such as (i) adding initial velocity to each component, (ii)
quenching the SO and Rabi coupling parameters at initial and finite time, and
(iii) allowing collision between the two spin-components by giving equal and
opposite direction velocity to them. Many interesting dynamical features of the
solitons, like, multi-fragmented, repelling, and breathing in time and
space-time, are observed. For given Rabi coupling frequency, the breathing
frequency of the soliton increases upon the increase in SO coupling, attaining
a maximum at the critical SO coupling where the phase transition from the
bright to stripe soliton occurs. We observe that the maximum breathing
frequency exhibits power law dependence on the Rabi coupling frequency with an
exponent $\sim 0.16$.",2208.08777v2
2022-10-20,Coherent dynamics of strongly interacting electronic spin defects in hexagonal boron nitride,"Optically active spin defects in van der Waals materials are promising
platforms for modern quantum technologies. Here we investigate the coherent
dynamics of strongly interacting ensembles of negatively charged boron-vacancy
($\mathrm{V}_{\mathrm{B}}^-$) centers in hexagonal boron nitride (hBN) with
varying defect density. By employing advanced dynamical decoupling sequences to
selectively isolate different dephasing sources, we observe more than 5-fold
improvement in the measured coherence times across all hBN samples. Crucially,
we identify that the many-body interaction within the
$\mathrm{V}_{\mathrm{B}}^-$ ensemble plays a substantial role in the coherent
dynamics, which is then used to directly estimate the concentration of
$\mathrm{V}_{\mathrm{B}}^-$. We find that at high ion implantation dosage, only
a small portion of the created boron vacancy defects are in the desired
negatively charged state. Finally, we investigate the spin response of
$\mathrm{V}_{\mathrm{B}}^-$ to the local charged defects induced electric field
signals, and estimate its ground state transverse electric field
susceptibility. Our results provide new insights on the spin and charge
properties of $\mathrm{V}_{\mathrm{B}}^-$, which are important for future use
of defects in hBN as quantum sensors and simulators.",2210.11485v3
2022-11-09,Time-resolved measurement of spin excitations in Cu$_2$OSeO$_3$,"Magnetic diffraction in combination with x-ray detected ferromagnetic
resonance (DFMR) is a powerful technique for performing time-resolved
measurements on individual spin textures. Here, we study the ferromagnetic
resonance (FMR) modes of both the conical and field-polarized phases in the
chiral magnet Cu$_2$OSeO$_3$. Following the identification of the FMR modes at
different temperatures using broadband vector network analyzer FMR, we use DFMR
on the crystalline (001) Bragg peak to reveal the time-dependent spin
configurations of the selected FMR modes. By being able to measure both the
amplitude and phase response of the spin system across the resonance, a
continuous phase advance (of 180$^\circ$) in the conical mode, and a phase lag
(of 180$^\circ$) in the field-polarized mode is found. By performing dynamic
measurements in the conical phase as a function of the linear polarization
angle of the x-rays, i.e., successively probing the dynamics of the moments, we
find an inversion of the dynamics along the conical axis upon inverting the
applied field direction. By allowing for time-resolved measurements of the
phase and amplitude of individual magnetic phases, DFMR opens up new
opportunities for obtaining a deeper understanding of the complex dynamics of
chiral magnets.",2211.05195v1
2022-12-05,On detailed balance in nonadiabatic dynamics: From spin spheres to equilibrium ellipsoids,"Trajectory-based methods that propagate classical nuclei on multiple quantum
electronic states are often used to simulate nonadiabatic processes in the
condensed phase. A long-standing problem of these methods is their lack of
detailed balance, meaning that they do not conserve the equilibrium
distribution. In this article, we investigate ideas for how to restore detailed
balance in mixed quantum--classical systems by tailoring the previously
proposed spin-mapping approach to thermal equilibrium. We find that adapting
the spin magnitude can recover the correct long-time populations but is
insufficient to conserve the full equilibrium distribution. The latter can
however be achieved by a more flexible mapping of the spin onto an ellipsoid,
which is constructed to fulfill detailed balance for arbitrary potentials. This
ellipsoid approach solves the problem of negative populations that has plagued
previous mapping approaches and can therefore be applied also to strongly
asymmetric and anharmonic systems. Because it conserves the thermal
distribution, the method can also exploit efficient sampling schemes used in
standard molecular dynamics, which drastically reduces the number of
trajectories needed for convergence. The dynamics does however still have
mean-field character, as is observed most clearly by evaluating reaction rates
in the golden-rule limit. This implies that although the ellipsoid mapping
provides a rigorous framework, further work is required to find an accurate
classical-trajectory approximation that captures more properties of the true
quantum dynamics.",2212.02382v1
2023-03-10,Field-driven collapsing dynamics of skyrmions in magnetic multilayers,"Magnetic skyrmions are fascinating topological particle-like textures
promoted by a trade-off among interfacial properties (perpendicular anisotropy
and Dzyaloshinskii-Moriya interaction (DMI)) and dipolar interactions.
Depending on the dominant interaction, complex spin textures, including pure
N\'eel and hybrid skyrmions have been observed in multilayer heterostructures.
A quantification of these different spin textures typically requires a
depth-reoslved magnetic imaging or scattering techniques. In the present work,
we will show qualitatively different collapsing dynamics for pure N\'eel and
hybrid skyrmions induced by a perpendicular magnetic field in two
representative systems, [Pt/Co/Ir]15 and [Ta/CoFeB/MgO]15 multilayers.
Skyrmions in the former stack undergo two morphological transitions, upon
reversing the perpendicular field direction. Skyrmions in [Ta/CoFeB/MgO]15
multilayers exhibit a continuous transition, which is mainly linked to a
reversible change of the skyrmion size. A full micromagnetic phase diagram is
presented to identify these two collapsing mechanisms as a function of material
parameters. Since the two distinct collapsing dynamics rely on the detailed
layer-dependent spin structures of skyrmions, they could be used as potential
fingerprints for identifying the skyrmion type in magnetic multilayers. Our
work suggests the employment of pure and hybrid skyrmions for specific
applications, due to the strong correlation between the skyrmion dynamics and
3-dimentional spin profiles.",2303.05988v1
2024-02-05,Circular motion of non-collinear spin textures in Corbino disks: Dynamics of Néel- versus Bloch-type skyrmions and skyrmioniums,"Magnetic skyrmions are nano-scale magnetic whirls that can be driven by
currents via spin torques. They are promising candidates for spintronic devices
such as the racetrack memory, where a motion along the uniform current is
typically desired. However, in Corbino disks, the goal is to achieve a circular
motion, perpendicular to the radially applied current. As we show, based on
analytical calculations and micromagnetic simulations, Bloch skyrmions engage
in a circular motion with frequencies in the MHz range when driven by
spin-orbit torques. In contrast, N\'eel skyrmions get stuck at the edges of the
disk. Our analysis reveals that the antagonistic dynamics between Bloch- and
N\'eel-type magnetic textures arise from their helicity. Furthermore, we find
that skyrmioniums, which are topologically trivial variations of skyrmions,
move even faster and allow an increase in the current density without being
pushed toward the edges of the disk. When driven by spin-transfer torques
instead, Bloch and N\'eel skyrmions no longer exhibit different dynamics.
Instead, they move along a circular trajectory due to the skyrmion Hall effect
caused by their topological charge. Consequently, the topologically trivial
skyrmioniums inevitably become trapped at the disk edge in this scenario. To
provide a comprehensive understanding, our study also examines currents applied
tangentially, further enriching our insights into skyrmion dynamics and
appropriate current injection methods for skyrmion-based devices.",2402.03023v1
2024-02-17,Spin dynamics and dark particle in a weak-coupled quantum Ising ladder with $\mathcal{D}_8^{(1)}$ spectrum,"Emergent Ising$_h^2$ integrability is anticipated in a quantum Ising ladder
composed of two weakly coupled, critical transverse field Ising chains. This
integrable system is remarkable for including eight types of massive
relativistic particles, with their scattering matrix and spectrum characterized
by the $\mathcal{D}_8^{(1)}$ Lie algebra. In this article we delve into the
zero-temperature spin dynamics of this integrable quantum Ising ladder. By
computing the dynamical structure factors from analytical form factor approach,
we clearly identify dispersive single-particle excitations of (anti-) soliton
and breathers as well as their multi-particle continua in the spin dynamical
spectrum. We show that the selection rule to the form factor, which is inherent
in the intrinsic charge-parity $\mathcal{C}$ of the Ising$_h^2$ particles as
well as the local spin operators, causes a significant result that
$\mathcal{C}$-odd particles, termed as dark particles, cannot be directly
excited from the ground state through any local or quasi-local operations.
Furthermore, the lightest dark particle is proposed to be generated and
controlled through resonant absorption-resonant emission processes. The long
lifetime of dark particle suggests its potential as a stable qubit for
advancing quantum information technology.",2402.11229v1
2024-03-19,Beyond Point Masses. III. Detecting Haumea's Nonspherical Gravitational Field,"The dwarf planet Haumea is one of the most compelling transneptunian objects
(TNOs) to study, hosting two small, dynamically interacting satellites, a
family of nearby spectrally unique objects, and a ring system. Haumea itself is
extremely oblate due to its 3.9 hour rotation period. Understanding the orbits
of Haumea's satellites, named Hi'iaka and Namaka, requires detailed modeling of
both satellite-satellite gravitational interactions and satellite interactions
with Haumea's nonspherical gravitational field (parameterized here as $J_2$).
Understanding both of these effects allows for a detailed probe of the
satellites' masses and Haumea's $J_2$ and spin pole. Measuring Haumea's $J_2$
provides information about Haumea's interior, possibly determining the extent
of past differentation. In an effort to understand the Haumea system, we have
performed detailed non-Keplerian orbit fitting of Haumea's satellites using a
decade of new ultra-precise observations. Our fits detect Haumea's $J_2$ and
spin pole at $\gtrsim2.5\sigma$ confidence. Degeneracies present in the
dynamics prevent us from precisely measuring Haumea's $J_2$ with the current
data, but future observations should enable a precise measurement. Our
dynamically determined spin pole shows excellent agreement with past results,
illustrating the strength of non-Keplerian orbit fitting. We also explore the
spin-orbit dynamics of Haumea and its satellites, showing that axial precession
of Hi'iaka may be detectable over decadal timescales. Finally, we present an
ephemeris of the Haumea system over the coming decade, enabling high-quality
observations of Haumea and its satellites for years to come.",2403.12782v1
2018-02-27,Dynamical classification of topological quantum phases,"Topological phase of matter is now a mainstream of research in condensed
matter physics, of which the classification, synthesis, and detection of
topological states have brought excitements over the recent decade while remain
incomplete with ongoing challenges in both theory and experiment. Here we
propose to establish a universal dynamical characterization of the topological
quantum phases classified by integers, and further propose the high-precision
dynamical schemes to detect such states. The framework of {the dynamical
classification theory} consists of basic theorems. First, we uncover that
classifying a $d$-dimensional ($d$D) gapped topological phase {of generic
multibands} can reduce to a ($d-1$)D invariant defined on so-called band
inversion surfaces (BISs), rendering a {\it bulk-surface duality} which
simplifies the topological characterization. Further, we show in quenching
across phase boundary the (pseudo)spin dynamics to exhibit unique topological
patterns on BISs, which are attributed to the post-quench bulk topology and
manifest a {\it dynamical bulk-surface correspondence}. For this the
topological phase is classified by a dynamical topological invariant measured
from dynamical spin-texture field on the BISs. Applications to quenching
experiments on feasible models are proposed and studied, demonstrating the new
experimental strategies to detect topological phases with high feasibility.
This work opens a broad new direction to classify and detect topological phases
by quantum dynamics.",1802.10061v3
2019-05-16,Observing topological charges and dynamical bulk-surface correspondence with ultracold atoms,"In quenching a topological phase across phase transition, the dynamical
bulk-surface correspondence emerges that the bulk topology of $d$-dimensional
($d$D) phase relates to the nontrivial pattern of quench dynamics emerging on
$(d-1)$D subspace, called band inversion surfaces (BISs) in momentum space.
Here we report the first experimental observation of the dynamical bulk-surface
correspondence through measuring the topological charges in a 2D quantum
anomalous Hall model realized in an optical Raman lattice. The system can be
quenched with respect to every spin axis by suddenly varying the two-photon
detuning or phases of the Raman couplings, in which the topological charges and
BISs are measured dynamically by the time-averaged spin textures. We observe
that the total charges in the region enclosed by BISs define a dynamical
topological invariant, which equals the Chern index of the post-quench band.
The topological charges relate to an emergent dynamical field which exhibits
nontrivial topology on BIS, rendering the dynamical bulk-surface
correspondence. This study opens a new avenue to explore topological phases
dynamically.",1905.06478v1
2021-06-18,Engineered dissipation induced entanglement transition in quantum spin chains: from logarithmic growth to area law,"Recent theoretical work has shown that the competition between coherent
unitary dynamics and stochastic measurements, performed by the environment,
along wavefunction trajectories can give rise to transitions in the
entanglement scaling. In this work, complementary to these previous studies, we
analyze a situation where the role of Hamiltonian and dissipative dynamics is
reversed. We consider an engineered dissipation, which stabilizes an entangled
phase of a quantum spin$-1/2$ chain, while competing single-particle or
interacting Hamiltonian dynamics induce a disentangled phase. Focusing on the
single-particle unitary dynamics, we find that the system undergoes an
entanglement transition from a logarithmic growth to an area law when the
competition ratio between the unitary evolution and the non-unitary dynamics
increases. We evidence that the transition manifests itself in state-dependent
observables at a finite competition ratio for Hamiltonian and measurement
dynamics. On the other hand, it is absent in trajectory-averaged steady-state
dynamics, governed by a Lindblad master equation: although purely dissipative
dynamics stabilizes an entangled state, for any non-vanishing Hamiltonian
contribution the system ends up irremediably in a disordered phase. In
addition, a single trajectory analysis reveals that the distribution of the
entanglement entropy constitutes an efficient indicator of the transition.
Complementarily, we explore the competition of the dissipation with coherent
dynamics generated by an interacting Hamiltonian, and demonstrate that the
entanglement transition also occurs in this second model. Our results suggest
that this type of transition takes place for a broader class of Hamiltonians,
underlining its robustness in monitored open quantum many-body systems.",2106.10092v1
2021-10-01,Intrinsic energy flow in laser-excited 3$d$ ferromagnets,"Ultrafast magnetization dynamics are governed by energy flow between
electronic, magnetic, and lattice degrees of freedom. A quantitative
understanding of these dynamics must be based on a model that agrees with
experimental results for all three subsystems. However, ultrafast dynamics of
the lattice remain largely unexplored experimentally. Here, we combine
femtosecond electron diffraction experiments of the lattice dynamics with
energy-conserving atomistic spin dynamics (ASD) simulations and ab-initio
calculations to study the intrinsic energy flow in the 3d ferromagnets cobalt
(Co) and iron (Fe). The simulations yield a good description of experimental
data, in particular an excellent description of our experimental results for
the lattice dynamics. We find that the lattice dynamics are influenced
significantly by the magnetization dynamics due to the energy cost of
demagnetization. Our results highlight the role of the spin system as the
dominant heat sink in the first hundreds of femtoseconds. Together with
previous findings for nickel [Zahn et al., Phys. Rev. Research 3, 023032
(2021)], our work demonstrates that energy-conserving ASD simulations provide a
general and consistent description of the laser-induced dynamics in all three
elemental 3d ferromagnets.",2110.00525v2
2022-12-23,NMR investigations of Dynamical Tunneling in Spin Systems,"In the usual quantum tunneling, a low-energy quantum particle penetrates
across a physical barrier of higher potential energy, by traversing a
classically forbidden region, and finally escapes into another region. In an
analogous scenario, a classical particle inside a closed regular region in the
phase space is dynamically bound from escaping to other regions of the phase
space. Here, the physical potential barrier is replaced by dynamical barriers
which separate different regions of the phase space. However, in the quantum
regime, the system can overcome such dynamical barriers and escape through
them, giving rise to dynamical tunneling. In chaotic Hamiltonian systems,
dynamical tunneling refers to quantum tunneling between states whose classical
limit correspond to symmetry-related regular regions separated by a chaotic
zone between which any classical transport is prohibited. Here, an experimental
realization of dynamical tunneling in spin systems is reported using nuclear
magnetic resonance (NMR) architecture. In particular, dynamical tunneling in
quantum kicked tops of spin-1 and spin-3/2 systems using two- and three-qubit
NMR registers is investigated. By extracting time-dependent expectation values
of the angular momentum operator components, size-dependent tunneling behaviour
for various initial states is systematically investigated. Further, by
monitoring the adverse effects of dephasing noise on the tunneling
oscillations, we assert the importance of quantum coherence in enabling
dynamical tunneling.",2212.12350v2
2024-04-09,Fundamental interactions in self-organized critical dynamics on higher-order networks,"In functionally complex systems, higher-order connectivity is often revealed
in the underlying geometry of networked units. Furthermore, such systems often
show signatures of self-organized criticality, a specific type of
non-equilibrium collective behaviour associated with an attractor of internal
dynamics with long-range correlations and scale invariance, which ensures the
robust functioning of complex systems, such as the brain. Here, we highlight
the intertwining of features of higher-order geometry and self-organized
critical dynamics as a plausible mechanism for the emergence of new properties
on a larger scale, representing the central paradigm of the physical notion of
complexity. Considering the time scale of the structural evolution with the
known separation of the time scale in self-organized criticality, i.e.,
internal dynamics and external driving, we distinguish three classes of
geometries that can shape the self-organized dynamics on them differently. We
provide an overview of current trends in the study of collective dynamics
phenomena, such as the synchronization of phase oscillators and discrete spin
dynamics with higher-order couplings embedded in the faces of simplicial
complexes. For a representative example of self-organized critical behaviour
induced by higher-order structures, we present a more detailed analysis of the
dynamics of field-driven spin reversal on the hysteresis loops in simplicial
complexes composed of triangles. These numerical results suggest that two
fundamental interactions representing the edge-embedded and triangle-embedded
couplings must be taken into account in theoretical models to describe the
influence of higher-order geometry on critical dynamics.",2404.06175v1
1998-07-09,Real-time non-equilibrium dynamics of quantum glassy systems,"We develop a systematic analytic approach to aging effects in quantum
disordered systems in contact with an environment. Within the closed-time
path-integral formalism we include dissipation by coupling the system to a set
of independent harmonic oscillators that mimic a quantum thermal bath. After
integrating over the bath variables and averaging over disorder we obtain an
effective action that determines the real-time dynamics of the system. The
classical limit yields the Martin-Siggia-Rose generating functional associated
to a colored noise. We apply this general formalism to a prototype model
related to the $p$ spin-glass. We show that the model has a dynamic phase
transition separating the paramagnetic from the spin-glass phase and that
quantum fluctuations depress the transition temperature until a quantum
critical point is reached. We show that the dynamics in the paramagnetic phase
is stationary but presents an interesting crossover from a region controlled by
the classical critical point to another one controlled by the quantum critical
point. The most characteristic property of the dynamics in a glassy phase,
namely aging, survives the quantum fluctuations. In the sub-critical region the
quantum fluctuation-dissipation theorem is modified in a way that is consistent
with the notion of effective temperatures introduced for the classical case. We
discuss these results in connection with recent experiments in dipolar quantum
spin-glasses and the relevance of the effective temperatures with respect to
the understanding of the low temperature dynamics.",9807138v1
2008-03-27,Doping variation of anisotropic charge and orbital dynamics in Y1-xCaxVO3 : Comparison with La1-xSrxVO3,"The doping variation of charge and orbital dynamics in perovskite-type
Y1-xCaxVO3 (0<x<0.1) is investigated by measurements of the optical
conductivity and Raman scattering spectra in comparison with the
larger-bandwidth system La1-xSrxVO3. We also take into consideration the
magnitude of the GdFeO3-type orthorhombic lattice distortion, which is large
and small in Y1-xCaxVO3 and La1-xSrxVO3, respectively, and discuss its effect
on the evolution of charge dynamics. The optical conductivity spectra show that
the doped hole is well localized and forms the small polaron like state. The
hole dynamics in Y1-xCaxVO3 is nearly isotropic up to the doping level of the
orbital order-disorder transition, while that in La1-xSrxVO3 is anisotropic in
the lightly doped region due to the one-dimensional orbital exchange
interaction. The possible origin of the difference in the hole dynamics is
discussed in terms of the local lattice distortion, which is induced by the
formation of the small polaron like state and becomes more significant for the
reduced one-electron bandwidth. In addition, the optical Mott-gap excitation in
the nominally C-type spin and $G$-type orbital ordered phase is distinct from
that for La1-xSrxVO3 in its intensity and spectral shape. This suggests that
the orthorhombic lattice distortion enhances the modification of the spin and
orbital ordering from the pure C-type and G-type, respectively. The systematic
study of Raman scattering spectra has shown that the dynamic G-type spin and
C-type orbital correlation subsists at low temperatures in the doping induced
phase of the nominally C-type SO and G-type OO.",0803.3862v1
2017-03-27,Anomalous dynamical phase in quantum spin chains with long-range interactions,"The existence or absence of non-analytic cusps in the Loschmidt-echo return
rate is traditionally employed to distinguish between a regular dynamical phase
(regular cusps) and a trivial phase (no cusps) in quantum spin chains after a
global quench. However, numerical evidence in a recent study [J. C. Halimeh and
V. Zauner-Stauber, arXiv:1610.02019] suggests that instead of the trivial phase
a distinct anomalous dynamical phase characterized by a novel type of
non-analytic cusps occurs in the one-dimensional transverse-field Ising model
when interactions are sufficiently long-range. Using an analytic semiclassical
approach and exact diagonalization, we show that this anomalous phase also
arises in the fully-connected case of infinite-range interactions, and we
discuss its defining signature. Our results show that the transition from the
regular to the anomalous dynamical phase coincides with Z2-symmetry breaking in
the infinite-time limit, thereby showing a connection between two different
concepts of dynamical criticality. Our work further expands the dynamical phase
diagram of long-range interacting quantum spin chains, and can be tested
experimentally in ion-trap setups and ultracold atoms in optical cavities,
where interactions are inherently long-range.",1703.09195v2
2017-08-22,Synchronization transition in dipole-coupled two-level systems with positional disorder,"We study the decoherence dynamics of dipole-coupled two-level quantum systems
in Ramsey-type experiments. We focus on large networks of two-level systems,
confined to two spatial dimensions and with positional disorder giving rise to
disordered dipolar couplings. This setting is relevant for modeling the
decoherence dynamics of the rotational excitations of polar molecules confined
to deep optical lattices, where disorder arises from the random filling of
lattice sites with occupation probability $p$. We show that the decoherence
dynamics exhibits a phase transition at a critical filling $p_c\simeq 0.15$.
For $p<p_c$ the dynamics is disorder-dominated and the Ramsey interference
signal decays on a timescale $T_2 \propto p^{-3/2}$. For $p>p_c$ the dipolar
interactions dominate the disorder, and the system behaves as a collective
spin-ordered phase, representing synchronization of the two-level systems and
persistent Ramsey oscillations with divergent $T_2$ for large systems. For a
finite number of two-level systems, $N$, the spin-ordered phase at $p> p_c$
undergoes a crossover to a collective spin-squeezed state on a timescale
$\tau_{\rm sq} \propto \sqrt{N}$. We develop a self-consistent mean-field
theory that is capable of capturing the synchronization transition at $p_c$,
and provide an intuitive theoretical picture that describes the phase
transition in the long-time dynamics. We also show that the decoherence
dynamics appear to be ergodic in the vicinity of $p_c$, the long-time behaviour
being well described by the predictions of equilibrium thermodynamics. The
results are supported by the results of exact diagonalization studies of small
systems.",1708.06676v1
2018-11-14,Opening the Doors to Dynamic Camouflaging: Harnessing the Power of Polymorphic Devices,"The era of widespread globalization has led to the emergence of
hardware-centric security threats throughout the IC supply chain. Prior
defenses like logic locking, layout camouflaging, and split manufacturing have
been researched extensively to protect against intellectual property (IP)
piracy at different stages. In this work, we present dynamic camouflaging as a
new technique to thwart IP reverse engineering at all stages in the supply
chain, viz., the foundry, the test facility, and the end-user. Toward this end,
we exploit the multi-functionality, post-fabrication reconfigurability, and
run-time polymorphism of spin-based devices, specifically the magneto-electric
spin-orbit (MESO) device. Leveraging these unique properties, dynamic
camouflaging is shown to be resilient against state-of-the-art analytical
SAT-based attacks and test-data mining attacks. Such dynamic reconfigurability
is not afforded in CMOS owing to fundamental differences in operation. For such
MESO-based camouflaging, we also anticipate massive savings in power,
performance, and area over other spin-based camouflaging schemes, due to the
energy-efficient electric-field driven reversal of the MESO device. Based on
thorough experimentation, we outline the promises of dynamic camouflaging in
securing the supply chain end-to-end along with a case study, demonstrating the
efficacy of dynamic camouflaging in securing error-tolerant image processing
IP.",1811.06012v2
2020-03-20,Probing the Possibilities of Ergodicity in the 1D Spin-1/2 XY Chain with Quench Dynamics,"Ergodicity sits at the heart of the connection between statistical mechanics
and dynamics of a physical system. By fixing the initial state of the system
into the ground state of the Hamiltonian at zero temperature and tuning a
control parameter, we consider the occurrence of the ergodicity with quench
dynamics in the one-dimensional (1D) spin-1/2 XY model in a transverse magnetic
field. The ground-state phase diagram consists of two ferromagnetic and
paramagnetic phases. It is known the magnetization in this spin system is
non-ergodic. We set up two different experiments as we call them single and
double quenches and test the dynamics of the magnetization along the $Z$-axis
and the spin-spin correlation function along the $X$-axis which are the order
parameters of the zero-temperature phases . Our exact results reveal that for
single quenches at zero-temperature, the ergodicity depends on the initial
state and the order parameter. Interestingly on the other setup, a double
quench on a cyclic path, ergodicity is completely broken for starting from the
phase corresponding to the order parameter. Otherwise, it depends on the first
quenched point, and the quench time $T$ when the model spent before a second
quench in the way back which gives an ability to controlling the ergodicity in
the system. Therefore, and contrary to expectations, in the mentioned model the
ergodicity can be observed with probing quench dynamics at zero-temperature.
Our results provide further insight into the zero-temperature dynamical
behavior of quantum systems and their connections to the ergodicity phenomenon.",2003.09462v2
2021-12-23,"Duality symmetry conjugates of the quantum Rabi model : effective bosonic, fermionic and coupling-only dynamical properties","Symmetry transformations have proved useful in determining the algebraic
structure and internal dynamical properties of physical systems. In the quantum
Rabi model, invariance under parity symmetry transformation has been used to
obtain exact solutions of the eigenvalue equation and very good approximations
of the internal dynamics of the interacting atom-light system. In this article,
two symmetry operators, characterized as ""duality"" symmetry operators, have
been introduced which transform the quantum Rabi Hamiltonian into duality
conjugates. The parity and duality symmetry operators constitute an
algebraically closed set of symmetry transformation operators of the quantum
Rabi model. The closed $SU(2)$ Lie algebra provides the standard eigenvalues
and eigenstates of the parity symmetry operator. It is established that
Jaynes-Cummings and anti-Jaynes-Cummings operators are duality symmetry
conjugates. Symmetric or antisymmetric linear combinations of the Rabi
Hamiltonian and a corresponding duality conjugate yield the familiar
spin-dependent force driven bosonic , coupling-only or quantized light mode
quadrature-driven fermionic Hamiltonian. It is established that the effective
bosonic, fermionic and coupling-only Hamiltonians are exact, not approximate
forms of the quantum Rabi Hamiltonian as they have generally been interpreted.
The effective bosonic form generates the dynamics of the light mode driven by
the atomic spin-dependent force, while the fermionic form generates the
dynamics of the atomic spin driven by the quantized light mode
quadrature-dependent force, thus providing a complete picture of the quantum
Rabi dynamics.",2112.12514v2
2022-06-22,Resonant Islands of Effective-One-Body Dynamics,"We study the chaotic signatures of the geodesic dynamics of a non-spinning
test particle in the effective-one-body (EOB) formalism for the inspiral
process of spinning binary black holes. We first show that the second order
post-Newtonian (2PN) EOB dynamics is non-integrable by demonstrating that the
EOB metric does not satisfy the criterion for the existence of Carter constant.
We then employ the numerical study to find the plateaus of the rotation curve,
which are associated with the existence of Birkhoff islands in the Poincar\'e
surface of section, signifying the chaotic dynamics in the system. Our results
show the signatures of chaos for the EOB dynamics, especially in the regime of
interest for which the Kerr bounds of the component black holes hold. We also
find that chaotic behavior is more obvious as the spin parameter $a$ of the
deformed EOB background metric increases. Our results can help to uncover the
implications of dynamical chaos in gravitational wave astronomy. Finally, we
also present some preliminary results due to corrections at 3PN order.",2206.10966v2
2022-08-22,Skin effect and dynamical delocalization in non-Hermitian quasicrystals with spin-orbit interaction,"The investigations of the spectral and dynamical delocalization-localization
(DL) transition have revealed intriguing features in a wide range of
non-Hermitian systems. The present study aims at exploring the spectral and
dynamical properties in a non-Hermitian quasiperiodic system with asymmetric
hopping in the presence of Rashba Spin-Orbit (RSO) interaction. In particular,
in such systems, we have identified that the DL transition is associated with a
concurrent change in the energy spectrum, where the eigenstates always break
the time-reversal symmetry for all strenghts of the quasiperiodic potential,
contrary to the systems without RSO interaction. Remarkably, we find that the
reality of energy spectrum under the open boundary condition that is frequently
symbolised as a hallmark of the skin-effect, is a system-size dependent
phenomena, and appears even when the associated energies are indeed complex. In
addition, it is demonstrated that the spin-flip term in the RSO interaction in
fact possesses a tendency to diminish the directionality of the skin-effect. On
scrutinizing the dynamical attributes in our non-Hermitian system, we unveil
that in spite of the fact that the spectral DL transition accords with the
dynamical phase transition, interestingly, the system comes across
hyper-diffusive and negative diffusion dynamical regimes depending upon the
strength of the RSO interaction, in the spectrally localized regime.",2208.10359v1
2024-01-08,Chiral Dynamics of Ultracold Atoms under a Tunable SU(2) Synthetic Gauge Field,"Surface currents emerge in superconductors exposed to magnetic fields, and
are a key signature of the Meissner effect. Analogously, chiral dynamics were
observed in quantum simulators under synthetic Abelian gauge fields. The
flexible control of these simulators also facilitates the engineering of
non-Abelian gauge fields, but their impact on the chiral dynamics remains
elusive. Here, by employing the cutting-edge momentum-lattice technique, we
implement a synthetic SU(2) gauge field in a spinful 1D ladder and study the
rich chiral dynamics therein. We confirm the non-Abelian nature of the
synthetic potential by observing the non-Abelian Aharonov-Bohm effect on a
single plaquette. More importantly, the chiral current along the two legs of
the ladder is observed to be spin-dependent and highly tunable through the
parameters of the gauge potential. We experimentally map out different dynamic
regimes of the chiral current, and reveal the underlying competition between
overlaying flux ladders with distinct spin compositions. Our experiment
demonstrates the dramatic impact of non-Abelian gauge fields on the system
dynamics, paving the way for future studies of exotic synthetic gauge fields on
the versatile platform of momentum lattices.",2401.03612v1
2024-03-29,Theory of the inverse Faraday effect in dissipative Rashba electron systems: Floquet engineering perspective,"We theoretically study the inverse Faraday effect (IFE), i.e., photo-induced
magnetization, in two-dimensional Rashba spin-orbit coupled electron systems
irradiated by a circularly polarized light. Quantum master (GKSL) equation
enables us to accurately compute the laser driven dynamics, taking inevitable
dissipation effects into account. To find the universal features of
laser-driven magnetization and its dynamics, we investigate (i) the
nonequilibrium steady state (NESS) driven by a continuous wave (CW) and (ii)
ultrafast spin dynamics driven by short laser pulses. In the NESS (i), the
laser-induced magnetization and its dependence of several parameters (laser
frequency, laser field strength, temperature, dissipation strength, etc.) are
shown to be in good agreement with the predictions from Floquet theory for
dissipative systems in the high-frequency regime. In the case (ii), we focus on
ferromagnetic metal states by introducing an effective magnetic field to the
Rashba model as the mean field of electron-electron interaction. We find that a
precession of the magnetic moment occurs due to the pulse-driven instantaneous
magnetic field and the initial phase of the precession is controlled by
changing the sign of light polarization. This is well consistent with the spin
dynamics observed in experiments of laser-pulse-driven IFE. We discuss how the
pulse-driven dynamics are captured by the Floquet theory. Our results provides
a microscopic method to compute ultrafast dynamics in many electron systems
irradiated by intense light.",2403.20110v1
2016-10-04,Gravitomagnetic dynamical friction,"A supermassive black hole moving through a field of stars will
gravitationally scatter the stars, inducing a backreaction force on the black
hole known as dynamical friction. In Newtonian gravity, the axisymmetry of the
system about the black hole's velocity $\mathbf{v}$ implies that the dynamical
friction must be anti-parallel to $\mathbf{v}$. However, in general relativity
the black hole's spin $\mathbf{S}$ need not be parallel to $\mathbf{v}$,
breaking the axisymmetry of the system and generating a new component of
dynamical friction similar to the Lorentz force $\mathbf{F} = q\mathbf{v}
\times \mathbf{B}$ experienced by a particle with charge $q$ moving in a
magnetic field $\mathbf{B}$. We call this new force gravitomagnetic dynamical
friction and calculate its magnitude for a spinning black hole moving through a
field of stars with Maxwellian velocity dispersion $\sigma$, assuming that both
$v$ and $\sigma$ are much less than the speed of light $c$. We use
post-Newtonian equations of motion accurate to $\mathcal{O}(v^3/c^3)$ needed to
capture the effect of spin-orbit coupling and also include direct stellar
capture by the black hole's event horizon. Gravitomagnetic dynamical friction
will cause a black hole with uniform speed to spiral about the direction of its
spin, similar to a charged particle spiraling about a magnetic field line, and
will exert a torque on a supermassive black hole orbiting a galactic center,
causing the angular momentum of this orbit to slowly precess about the
black-hole spin. As this effect is suppressed by a factor $(\sigma/c)^2$ in
nonrelativistic systems, we expect it to be negligible in most astrophysical
contexts but provide this calculation for its theoretical interest and
potential application to relativistic systems.",1610.01590v2
2006-09-28,Dynamical decoupling induced renormalization of the non-Markovian dynamics,"In this work we develop a numerical framework to investigate the
renormalization of the non-Markovian dynamics of an open quantum system to
which dynamical decoupling is applied. We utilize a non-Markovian master
equation which is derived from the non-Markovian quantum trajectories
formalism. It contains incoherent Markovian dynamics and coherent Schr\""odinger
dynamics as its limiting cases and is capable of capture the transition between
them. We have performed comprehensive simulations for the cases in which the
system is either driven by the Ornstein-Uhlenbeck noise or or is described by
the spin-boson model. The renormalized dynamics under bang-bang control and
continuous dynamical decoupling are simulated. Our results indicate that the
renormalization of the non-Markovian dynamics depends crucially on the spectral
density of the environment and the envelop of the decoupling pulses. The
framework developed in this work hence provides an unified approach to
investigate the efficiency of realistic decoupling pulses. This work also opens
a way to further optimize the decoupling via pulse shaping.",0609222v1
2016-07-04,Spin-1/2 sub-dynamics nested in the quantum dynamics of two coupled qutrits,"In this paper we investigate the quantum dynamics of two spin-1 systems,
$\vec{\textbf{S}}_1$ and $\vec{\textbf{S}}_2$, adopting a generalized
$(\vec{\textbf{S}}_1+\vec{\textbf{S}}_2)^2$-nonconserving Heisenberg model. We
show that, due to its symmetry property, the nine-dimensional dynamics of the
two qutrits exactly decouples into the direct sum of two sub-dynamics living in
two orthogonal four- and five-dimensional subspaces. Such a reduction is
further strengthened by our central result consisting in the fact that in the
four-dimensional dynamically invariant subspace, the two qutrits quantum
dynamics, with no approximations, is equivalent to that of two non interacting
spin 1/2's. The interpretative advantages stemming from such a remarkable and
non-intuitive nesting are systematically exploited and various intriguing
features consequently emerging in the dynamics of the two qutrits are deeply
scrutinised. The possibility of exploiting the dynamical reduction brought to
light in this paper for exactly treating as well time-dependent versions of our
Hamiltonian model is briefly discussed.",1607.00799v2
2002-11-11,Statics and dynamics of the ten-state nearest-neighbor Potts glass on the simple-cubic lattice,"We present the results of Monte Carlo simulations of two different Potts
glass models with short range random interactions. In the first model a \pm
J-distribution of the bonds is chosen, in the second model a Gaussian
distribution. In both cases the first two moments of the distribution are
chosen to be J_0=-1, Delta J=+1, so that no ferromagnetic ordering of the Potts
spins can occur. We find that for all temperatures investigated the spin glass
susceptibility remains finite, the spin glass order parameter remains zero, and
that the specific heat has only a smooth Schottky-like peak. These results can
be understood quantitatively by considering small but independent clusters of
spins. Hence we have evidence that there is no static phase transition at any
nonzero temperature. Consistent with these findings, only very minor size
effects are observed, which implies that all correlation lengths of the models
remain very short. We also compute for both models the time auto-correlation
function C(t) of the Potts spins. While in the Gaussian model C(t) shows a
smooth uniform decay, the correlator for the \pm J model has several distinct
steps. These steps correspond to the breaking of bonds in small clusters of
ferromagnetically coupled spins (dimers, trimers, etc.). The relaxation times
follow simple Arrhenius laws, with activation energies that are readily
interpreted within the cluster picture, giving evidence that the system does
not have a dynamic transition at a finite temperature. Hence we find that for
the present models all the transitions known for the mean-field version of the
model are completely wiped out. Finally we also determine the time
auto-correlation functions of individual spins, and show that the system is
dynamically very heterogeneous.",0211195v1
2013-01-17,Critical exponents and irreversibility lines of La$_{0.9}$Sr$_{0.1}$CoO$_3$ single crystal,"We have studied the dynamic and static critical behavior of spin glass
transition in insulating La$_{0.9}$Sr$_{0.1}$CoO$_3$ single crystal by ac
susceptibility and dc magnetization measurements in the vicinity of its
freezing temperature ($T_f$). The dynamic scaling analysis of the frequency
dependence of ac susceptibility data yields the characteristic time constant
$\tau_{0}$=1.6(9)$\times10^{-12}$ s, the dynamic critical exponent
$z\nu$=9.5(2), and a frequency dependence factor
$K$=$\Delta$$T_{f}/T_{f}$($\Delta$$log$$f$)=0.017, indicating that the sample
enters into a canonical spin-glass phase below $T_{f}$=34.8(2) K. The scaling
analysis of non-linear magnetization in the vicinity of $T_{f}$ through the
static scaling hypothesis yields critical exponents $\beta$=0.89(1) and
$\gamma$=2.9(1), which match well with that observed for well known
three-dimensional (3D) Heisenberg spin glasses. From the longitudinal component
of zero-field-cooled and field-cooled magnetization measurement we have
constructed the $H-T$ phase diagram which represents the field evolution of two
characteristic temperatures: the upper one, $T_{w}(H)$, indicates the onset of
spin freezing in a uniform external field $H$, while the lower one, $T_{s}(H)$,
marks the onset of strong irreversibility of the frozen state. The low field
$T_{s}(H)$ follows the critical line suggested by d'Almeida-Thouless model for
canonical spin glass, whereas the $T_{w}(H)$ exhibits a reentrant behavior with
a maximum in the $T_{w}(H)$ at a nonzero field above which it follows the
Gabay-Toulouse (GT) critical line which is a characteristic of Heisenberg spin
glass. The re-entrant behavior of the GT line resembles that predicted
theoretically for $n$-component vector spin glasses in the presence of a
uniaxial anisotropy field.",1301.4120v1
2014-11-23,Dynamics of entanglement of two electron spins interacting with nuclear spin baths in quantum dots,"We study the dynamics of entanglement of two electron spins in two quantum
dots, in which each electron is interacting with its nuclear spin environment.
Focusing on the case of uncoupled dots, and starting from either Bell or Werner
states of two qubits, we calculate the decay of entanglement due to the
hyperfine interaction with the nuclei. We mostly focus on the regime of
magnetic fields in which the bath-induced electron spin flips play a role, for
example their presence leads to the appearance of entanglement sudden death at
finite time for two qubits initialized in a Bell state. For these fields the
intrabath dipolar interactions and spatial inhomogeneity of hyperfine couplings
are irrelevant on the time scale of coherence (and entanglement) decay, and
most of the presented calculations are performed using the uniform-coupling
approximation to the exact hyperfine Hamiltonian. We provide a comprehensive
overview of entanglement decay in this regime, considering both free evolution
of the qubits, and an echo protocol with simultaneous application of $\pi$
pulses to the two spins. All the currently relevant for experiments bath states
are considered: the thermal state, narrowed states (characterized by diminished
uncertainty of one of the components of the Overhauser field) of two
uncorrelated baths, and a correlated narrowed state with a well-defined value
of the $z$ component of the Overhauser field interdot gradient. While we mostly
use concurrence to quantify the amount of entanglement in a mixed state of the
two electron spins, we also show that their entanglement dynamics can be
reconstructed from measurements of the currently relevant for experiments
entanglement witnesses, and the fidelity of quantum teleportation performed
using a partially disentangled state as a resource.",1411.6269v2
2016-01-14,Immense magnetic response of exciplex light emission due to correlated spin-charge dynamics,"As carriers slowly move through a disordered energy landscape in organic
semiconductors, tiny spatial variations in spin dynamics relieve spin blocking
at transport bottlenecks or in the electron-hole recombination process that
produces light. Large room-temperature magnetic-field effects (MFE) ensue in
the conductivity and luminescence. Sources of variable spin dynamics generate
much larger MFE if their spatial structure is correlated on the nanoscale with
the energetic sites governing conductivity or luminescence such as in
co-evaporated organic blends within which the electron resides on one molecule
and the hole on the other (an exciplex). Here we show that exciplex
recombination in blends exhibiting thermally-activated delayed fluorescence
(TADF) produces MFE in excess of 60% at room temperature. In addition, effects
greater than 4000% can be achieved by tuning the device's current-voltage
response curve by device conditioning. These immense MFEs are both the largest
reported values for their device type at room temperature. Our theory traces
this MFE and its unusual temperature dependence to changes in spin mixing
between triplet exciplexes and light-emitting singlet exciplexes. In contrast,
spin mixing of excitons is energetically suppressed, and thus spin mixing
produces comparatively weaker MFE in materials emitting light from excitons by
affecting the precursor pairs. Demonstration of immense MFE in common organic
blends provides a flexible and inexpensive pathway towards magnetic
functionality and field sensitivity in current organic devices without
patterning the constituent materials on the nanoscale. Magnetic fields increase
the power efficiency of unconditioned devices by 30% at room temperature, also
showing that magnetic fields may increase the efficiency of the TADF process.",1601.03621v1
2016-10-20,Magnetic excitations in quasi-one dimensional helimagnets: Magnon decays and in uence of the inter-chain interactions,"We present a comprehensive study of the magnetic properties of the long-range
ordered quasi-one dimensional $J_{1}$-$J_{2}$ systems with a newly developed
torque equilibrium spin-wave expansion approach, which can describe the spin
Casimir and magnon decay effects in a unified framework. While the framework
does not lose the generality, our discussion will be restricted to two
representative types of inter-chain coupling systems: $J_{3}$- or
$J_{4}$-system respectively. In spite of the long-range spiral order, the
dynamical properties of these systems turn out to be highly nontrivial due to
the incommensurate noncollinear spin configuration and the strong quantum
fluctuation effects enhanced by the frustration and low-dimensionality. Both
the systems show prominent spin Casimir effects induced by the vacuum
fluctuation of the spin waves and related modification of the ordering vector,
Lifshitz point's position and sublattice magnetization. Significant and
spontaneous magnon decay effects are manifested in the quantum corrections to
the excitation spectrum. By adjusting the strength of magnetic anisotropy and
varying the approximation scheme, it is revealed that these striking distinct
features are quite robust and have deep connection with both the spin Casimir
and the magnon decay effects. Thus these special consequences of the
inter-chain coupling on the spin wave dynamics may be served as a set of probes
for different types of inter-chain couplings in experiments. At last, to guide
experimental measurements such as inelastic neutron scattering in realistic
materials and complement our theoretical framework, we develop the analytical
theory of the dynamical structure factor within the torque equilibrium
formulism and provide the explicit results of the quasi-one dimensional
$J_{1}$-$J_{2}$ systems.",1610.06365v2
2018-02-27,Dynamic magnetism in the disordered hexagonal double perovskite BaTi$_{1/2}$Mn$_{1/2}$O$_{3}$,"Magnetic frustration and disorder are key ingredients to prevent the onset of
magnetic order. In the disordered hexagonal double perovskite
BaTi$_{1/2}$Mn$_{1/2}$O$_{3}$, Mn$^{4+}$ cations, with $S=3/2$ spins, can
either form highly correlated states of magnetic trimers or dimers or remain as
weakly interacting orphan spins. At low temperature ($T$), the dimer response
is negligible, and magnetism is dominated by the trimers and orphans. To
explore the role of magnetic frustration, disorder and possibly of quantum
fluctuations, the low-$T$ magnetic properties of the remaining magnetic degrees
of freedom of BaTi$_{1/2}$Mn$_{1/2}$O$_{3}$ are investigated. Heat-capacity
data and magnetic susceptibility display no evidence for a phase transition to
a magnetically ordered phase but indicate the formation of a correlated spin
state. The low-temperature spin dynamics of this state is then explored by
$\mu$SR experiments. The zero field $\mu^{+}$ relaxation rate data show no
static magnetism down to $T=19$ mK and longitudinal field experiments support
as well that dynamic magnetism persists at low $T$. Our results are interpreted
in terms of a spin glass state which stems from a disordered lattice of orphans
spins and trimers. A spin liquid state in BaTi$_{1/2}$Mn$_{1/2}$O$_{3}$,
however, is not excluded and is also discussed.",1802.09950v2
2017-01-24,Influence of interlayer coupling on the spin torque driven excitations in a spin torque oscillator,"The influence of dynamic interlayer interactions on the spin torque driven
and damped excitations are illustrated for a three layer macrospin model system
that corresponds to a standard spin-torque oscillator. The free layer and a
synthetic antiferromagnetic (SyF) pinned layer of the spin-torque oscillator
are in-plane magnetized. In order to understand experimental results, numerical
simulations have been performed considering three types of interlayer
interactions: exchange interaction between the two magnetic layers of the SyF,
mutual spin torque between the top layer of the SyF and the free layer and
dipolar interaction between all three magnetic layers. It will be shown that
the dynamic dipolar coupling plays a predominant role. First, it leads to a
hybridization of the free layer and the SyF linear modes and through this gives
rise to a strong field dependence of the critical current. In particular, there
is a field range of enhanced damping in which much higher current is required
to drive the modes into steady state. This results in a gap in the excitation
spectrum. Second, the dynamic dipolar interaction is also responsible for the
non-linear interaction between the current driven steady state mode and the
damped modes of the system. Here one can distinguish: (i) a resonant
interaction that leads to a kink in the frequency-field and frequency-current
dispersions accompanied by a small hysteresis and a reduction of the linewidth
of the steady state mode and (ii) a non-resonant interaction that leads to a
strong frequency redshift of the damped mode. The results underline the strong
impact of interlayer coupling on the excitation spectra of spin-torque
oscillators and illustrate in a simple three mode model system how in the
non-linear regime the steady state and damped modes influence each other.",1701.06787v1
2020-10-21,Probing the coherence of solid-state qubits at avoided crossings,"Optically addressable paramagnetic defects in wide-band-gap semiconductors
are promising platforms for quantum communications and sensing. The presence of
avoided crossings between the electronic levels of these defects can
substantially alter their quantum dynamics and be both detrimental and
beneficial for quantum information applications. Avoided crossings give rise to
clock transitions, which can significantly improve protection from magnetic
noise and favorably increase coherence time. However, the reduced coupling
between electronic and nuclear spins at an avoided crossing may be detrimental
to applications where nuclear spins act as quantum memories. Here we present a
combined theoretical and experimental study of the quantum dynamics of
paramagnetic defects interacting with a nuclear spin bath at avoided crossings.
We develop a computational approach based on a generalization of the cluster
expansion technique, which can account for processes beyond pure dephasing and
describe the dynamics of any solid-state spin-qubits near avoided crossings.
Using this approach and experimental validation, we determine the change in
nature and source of noise at avoided crossings for divacancies in SiC. We find
that we can condition the clock transition of the divacancies in SiC on
multiple adjacent nuclear spins states. In our experiments, we demonstrate that
one can suppress the effects of fluctuating charge impurities with depletion
techniques, leading to an increased coherence time at clock transition, limited
purely by magnetic noise. Combined with ab-initio predictions of spin
Hamiltonian parameters, the proposed theoretical approach paves the way to
designing the coherence properties of spin qubits from first principles.",2010.11077v1
2023-02-11,Generation of genuine all-way entanglement in defect-nuclear spin systems through dynamical decoupling sequences,"Multipartite entangled states are an essential resource for sensing, quantum
error correction, and cryptography. Color centers in solids are one of the
leading platforms for quantum networking due to the availability of a nuclear
spin memory that can be entangled with the optically active electronic spin
through dynamical decoupling sequences. Creating electron-nuclear entangled
states in these systems is a difficult task as the always-on hyperfine
interactions prohibit complete isolation of the target dynamics from the
unwanted spin bath. While this emergent cross-talk can be alleviated by
prolonging the entanglement generation, the gate durations quickly exceed
coherence times. Here we show how to prepare high-quality GHZ$_M$-like states
with minimal cross-talk. We introduce the $M$-tangling power of an evolution
operator, which allows us to verify genuine all-way correlations. Using
experimentally measured hyperfine parameters of an NV center spin in diamond
coupled to carbon-13 lattice spins, we show how to use sequential or
single-shot entangling operations to prepare GHZ$_M$-like states of up to
$M=10$ qubits within time constraints that saturate bounds on $M$-way
correlations. We study the entanglement of mixed electron-nuclear states and
develop a non-unitary $M$-tangling power which additionally captures
correlations arising from all unwanted nuclear spins. We further derive a
non-unitary $M$-tangling power which incorporates the impact of electronic
dephasing errors on the $M$-way correlations. Finally, we inspect the
performance of our protocols in the presence of experimentally reported pulse
errors, finding that XY decoupling sequences can lead to high-fidelity GHZ
state preparation.",2302.05580v3
2024-01-14,Introduction to Loop Quantum Gravity. The Holst's action and the covariant formalism,"We review Holst formalism and we discuss dynamical equivalence with standard
GR (in dimension 4). Holst formalism is written for a spin coframe field
$e^I_\mu$ and a $Spin(3,1)$-connection $\omega^{IJ}_\mu$ on spacetime $M$ and
it depends on the Holst parameter $\gamma\in \mathbb{R}-\{0\}$.
  We show the model is dynamically equivalent to standard GR, in the sense that
up to a pointwise $Spin(3,1)$-gauge transformation acting on frame indices,
solutions of the two models are in one-to-one correspondence. Hence the two
models are classically equivalent.
  One can also introduce new variables by splitting the spin connection into a
pair of a $Spin(3)$-connection $A^i_\mu$ and a $Spin(3)$-valued 1-form
$k^i_\mu$. The construction of these new variables relies on a particular
algebraic structure, called a reductive splitting. A reductive splitting is a
weaker structure than requiring that the gauge group splits as the products of
two sub-groups, as it happens in Euclidean signature in the selfdual
formulation originally introduced in this context by Ashtekar, and it still
allows to deal with the Lorentzian signature without resorting to
complexifications.
  The reductive splitting of $SL(2, \mathbb{C})$ is not unique and it is
parameterized by a real parameter $\beta$, called the Immirzi parameter. The
splitting is here done on spacetime, not on space, to obtain a
$Spin(3)$-connection $A^i_\mu$, which is called the Barbero-Immirzi connection
on spacetime. One obtains a covariant model depending on the fields $(e^I_\mu,
A^i_\mu, k^i_\mu)$ which is again dynamically equivalent to standard GR (as
well as the Holst action).
  Usually, in the literature one sets $\beta=\gamma$ for the sake of
simplicity. Here we keep the Holst and Immirzi parameters distinct to show that
eventually, only $\beta$ will survive in boundary field equations.",2401.07307v1
2024-03-29,Theory of Electron Spin Resonance in Scanning Tunneling Microscopy,"Electron spin resonance (ESR) spectroscopy in scanning tunneling microscopy
(STM) has enabled probing the electronic structure of single magnetic atoms and
molecules on surfaces with unprecedented energy resolution, as well as
demonstrating coherent manipulation of single spins. Despite this remarkable
success, the field could still be greatly advanced by a more quantitative
understanding of the ESR-STM physical mechanisms. Here, we present a theory of
ESR-STM which quantitatively models not only the ESR signal itself, but also
the full background tunneling current, from which the ESR signal is derived.
Our theory is based on a combination of Green's function techniques to describe
the electron tunneling and a quantum master equation for the dynamics of the
spin system along with microwave radiation interacting with both the tunneling
current and the spin system. We show that this theory is able to quantitatively
reproduce the experimental results for a spin-1/2 system (TiH molecules on MgO)
across many orders of magnitude in tunneling current, providing access to the
relaxation and decoherence rates that govern the spin dynamics due to intrinsic
mechanisms and to the applied bias voltage. More importantly, our work
establishes that: (i) sizable ESR signals, which are a measure of
microwave-induced changes in the junction magnetoresistance, require
surprisingly high tip spin polarizations, (ii) the coupling of the
magnetization dynamics to the microwave field gives rise to the asymmetric ESR
spectra often observed in this spectroscopy. Additionally, our theory provides
very specific predictions for the dependence of the relaxation and decoherence
times on the bias voltage and the tip-sample distance. Finally, with the help
of electromagnetic simulations, we find that the transitions in our ESR-STM
experiments can be driven by the ac magnetic field at the junction.",2403.20247v1
2004-09-09,Magnetically Driven Accretion Flows in the Kerr Metric IV: Dynamical Properties of the Inner Disk,"This paper continues the analysis of a set of general relativistic 3D MHD
simulations of accreting tori in the Kerr metric with different black hole
spins. We focus on bound matter inside the initial pressure maximum, where the
time-averaged motion of gas is inward and an accretion disk forms. We use the
flows of mass, angular momentum, and energy in order to understand dynamics in
this region. The sharp reduction in accretion rate with increasing black hole
spin reported in Paper I of this series is explained by a strongly
spin-dependent outward flux of angular momentum conveyed electromagnetically;
when a/M > 0.9, this flux can be comparable to the inward angular momentum flux
carried by the matter. In all cases, there is outward electromagnetic angular
momentum flux throughout the flow; in other words, contrary to the assertions
of traditional accretion disk theory, there is in general no ""stress edge"", no
surface within which the stress is zero. The retardation of accretion in the
inner disk by electromagnetic torques also alters the radial distribution of
surface density, an effect that may have consequences for observable properties
such as Compton reflection. The net accreted angular momentum is sufficiently
depressed by electromagnetic effects that in the most rapidly-spinning black
holes mass growth can lead to spindown. Spinning black holes also lose energy
by Poynting flux; this rate is also a strongly increasing function of black
hole spin, rising to 10% or more of the rest-mass accretion rate at very high
spin. As the black hole spins faster, the path of the Poynting flux changes
from being predominantly within the accretion disk to predominantly within the
funnel outflow.",0409231v1
2001-12-19,Competing orders in a magnetic field: spin and charge order in the cuprate superconductors,"We describe two-dimensional quantum spin fluctuations in a superconducting
Abrikosov flux lattice induced by a magnetic field applied to a doped Mott
insulator. Complete numerical solutions of a self-consistent large N theory
provide detailed information on the phase diagram and on the spatial structure
of the dynamic spin spectrum. Our results apply to phases with and without
long-range spin density wave order and to the magnetic quantum critical point
separating these phases. We discuss the relationship of our results to a number
of recent neutron scattering measurements on the cuprate superconductors in the
presence of an applied field. We compute the pinning of static charge order by
the vortex cores in the `spin gap' phase where the spin order remains
dynamically fluctuating, and argue that these results apply to recent scanning
tunnelling microscopy (STM) measurements. We show that with a single typical
set of values for the coupling constants, our model describes the field
dependence of the elastic neutron scattering intensities, the absence of
satellite Bragg peaks associated with the vortex lattice in existing neutron
scattering observations, and the spatial extent of charge order in STM
observations. We mention implications of our theory for NMR experiments. We
also present a theoretical discussion of more exotic states that can be built
out of the spin and charge order parameters, including spin nematics and phases
with `exciton fractionalization'.",0112343v4
2006-09-07,$^{1}$H-NMR spin-echo measurements of the static and dynamic spin properties in $λ$-(BETS)$_{2}$FeCl$_{4}$,"$^{1}$H-NMR spin-echo measurements of the spin-echo decay $M(2\tau)$ with a
decay rate 1/$T_{2}$ and the frequency shift $\Delta\nu/\nu_{0}$ under applied
magnetic field $\mathbf{B}$$_{0}$ = 9 T along the a-axis over a temperature
range 2.0$-$180 K are reported for a single crystal of the organic conductor
$\lambda$-(BETS)$_{2}$FeCl$_{4}$. It provides the spin dynamic and static
properties in the paramagnetic metal (PM) and antiferromagnetic insulator (AFI)
states as well as across the PM$-$AFI phase transition. A large slow beat
structure in the spin-echo decay is observed with a typical beat frequency of
$f$ $\sim$ 7 kHz and it varies across the spectrum. Its origin is attributed to
the $^{1}$H$-$$^{1}$H dipole interactions rather than to the much larger
dipolar field contribution from the Fe$^{3+}$ electrons (spin $S$ = 5/2). A
simple phenomenological model provides an excellent fit to the data. The
dominant $^{1}$H-NMR frequency shift comes from the dipolar field from the 3d
Fe$^{3+}$ ions, and the Fe$^{3+}$ $-$ Fe$^{3+}$ exchange interactions ($J_{0}$)
($J_{0} $ includes the d$-$d exchange interactions through the $\pi-$electrons)
have a substantial effect to the local field at the proton sites expecially at
low temperatures. A good fit is obtained with $J_{0}$ = - 1.7 K. The data of
the spin-echo decay rate 1/$T_{2}$ indicates that there is a significant change
in the slow fluctuations of the local magnetic field at the $^{1}$H-sites on
traversing the PM to AFI phase. This evidence supports earlier reports that the
PM$-$AFI phase transition in $\lambda$-(BETS)$_{2}% $FeCl$_{4} $ is driven
magnetically and first order.",0609151v2
2012-07-02,Spacetime dynamics of spinning particles - exact electromagnetic analogies,"We compare the rigorous equations describing the motion of spinning test
particles in gravitational and electromagnetic fields, and show that if the
Mathisson-Pirani spin condition holds then exact gravito-electromagnetic
analogies emerge. These analogies provide a familiar formalism to treat
gravitational problems, as well as a means for comparing the two interactions.
Fundamental differences are manifest in the symmetries and time projections of
the electromagnetic and gravitational tidal tensors. The physical consequences
of the symmetries of the tidal tensors are explored comparing the following
analogous setups: magnetic dipoles in the field of non-spinning/spinning
charges, and gyroscopes in the Schwarzschild, Kerr, and Kerr-de Sitter
spacetimes. The implications of the time projections of the tidal tensors are
illustrated by the work done on the particle in various frames; in particular,
a reciprocity is found to exist: in a frame comoving with the particle, the
electromagnetic (but not the gravitational) field does work on it, causing a
variation of its proper mass; conversely, for ""static observers,"" a stationary
gravitomagnetic (but not a magnetic) field does work on the particle, and the
associated potential energy is seen to embody the Hawking-Wald spin-spin
interaction energy. The issue of hidden momentum, and its counterintuitive
dynamical implications, is also analyzed. Finally, a number of issues regarding
the electromagnetic interaction and the physical meaning of Dixon's equations
are clarified.",1207.0470v3
2012-10-10,Bodily tides near the 1:1 spin-orbit resonance. Correction to Goldreich's dynamical model,"Spin-orbit coupling is often described in the ""MacDonald torque"" approach
which has become the textbook standard. Within this method, a concise
expression for the additional tidal potential, derived by MacDonald (1964; Rev.
Geophys. 2, 467), is combined with an assumption that the Q factor is
frequency-independent (i.e., that the geometric lag angle is constant in time).
This makes the approach unphysical because MacDonald's derivation of the said
formula was implicitly based on keeping the time lag frequency-independent,
which is equivalent to setting Q to scale as the inverse tidal frequency. The
contradiction requires the MacDonald treatment of both non-resonant and
resonant rotation to be rewritten.
  The non-resonant case was reconsidered by Efroimsky & Williams (2009; CMDA
104, 257), in application to spin modes distant from the major
commensurabilities. We continue this work by introducing the necessary
alterations into the MacDonald-torque-based model of falling into a 1:1
resonance. (For the original version of the model, see Goldreich 1966; AJ 71,
1.)
  We also study the effect of the triaxiality on both circulating and librating
rotation near the synchronous state. Circulating rotation may evolve toward the
libration region or toward a spin rate larger than synchronous
(pseudosynchronous spin). Which behaviour depends on the eccentricity, the
triaxiality of the primary, and the mass ratio of the secondary and primary
bodies. The spin evolution will always stall for the oblate case. For
small-amplitude librations, expressions are derived for the libration
frequency, damping rate, and average orientation.
  However, the stability of pseudosynchronous spin hinges upon the dissipation
model. Makarov and Efroimsky (2012; arXiv:1209.1616) have found that a more
realistic dissipation model than the corrected MacDonald torque makes
pseudosynchronous spin unstable.",1210.2923v3
2015-06-26,Modeling and Simulation of Spin Transfer Torque Generated at Topological Insulator/Ferromagnetic Heterostructure,"Topological Insulator (TI) has recently emerged as an attractive candidate
for possible application to spintronic circuits because of its strong spin
orbit coupling. TIs are unique materials that have an insulating bulk but
conducting surface states due to band inversion and these surface states are
protected by time reversal symmetry. In this paper, we propose a physics-based
spin dynamics simulation framework for TI/Ferromagnet (TI/FM) bilayer
heterostructures that is able to capture the electronic band structure of a TI
while calculating the electron and spin transport properties. Our model differs
from TI/FM models proposed in the literature in that it is able to account for
the 3D band structure of TIs and the effect of exchange coupling and external
magnetic field on the band structure. Our proposed approach uses 2D surface
Hamiltonian for TIs that includes all necessary features for spin transport
calculations so as to properly model the characteristics of a TI/FM
heterostructure. Using this Hamiltonian and appropriate parameters, we show
that the effect of quantum confinement and exchange coupling are successfully
captured in the calculated surface band structure compared with the quantum
well band diagram of a 3D TI, and matches well with experimental data reported
in the literature. We then show how this calibrated Hamiltonian is used with
the self-consistent non equilibrium Green's functions (NEGF) formalism to
determine the charge and spin transport in TI/FM bilayer heterostructures. Our
calculations agree well with experimental data and capture the unique features
of a TI/FM heterostructure such as high spin Hall angle, high spin conductivity
etc. Finally, we show how the results obtained from NEGF calculations may be
incorporated into the Landau-Lifshitz-Gilbert-Slonczewski (LLGS) formulation to
simulate the magnetization dynamics of an FM layer sitting on top of a TI.",1506.07932v2
2015-11-03,Relativistic Simulations of Eccentric Binary Neutron Star Mergers: One-arm Spiral Instability and Effects of Neutron Star Spin,"We perform general-relativistic hydrodynamical simulations of dynamical
capture binary neutron star mergers, emphasizing the role played by the neutron
star spin. Dynamical capture mergers may take place in globular clusters, as
well as other dense stellar systems, where most neutron stars have large spins.
We find significant variability in the merger outcome as a function of initial
neutron star spin. For cases where the spin is aligned with the orbital angular
momentum, the additional centrifugal support in the remnant hypermassive
neutron star can prevent the prompt collapse to a black hole, while for
antialigned cases the decreased total angular momentum can facilitate the
collapse to a black hole. We show that even moderate spins can significantly
increase the amount of ejected material, including the amount unbound with
velocities greater than half the speed of light, leading to brighter
electromagnetic signatures associated with kilonovae and interaction of the
ejecta with the interstellar medium. Furthermore, we find that the initial
neutron star spin can strongly affect the already rich phenomenology in the
postmerger gravitational wave signatures that arise from the oscillation modes
of the hypermassive neutron star. In several of our simulations, the resulting
hypermassive neutron star develops the one-arm ($m=1$) spiral instability, the
most pronounced cases being those with small but non-negligible neutron star
spins. For long-lived hypermassive neutron stars, the presence of this
instability leads to improved prospects for detecting these events through
gravitational waves, and thus may give information about the neutron star
equation of state.",1511.01093v2
2016-09-08,Coarse graining flow of spin foam intertwiners,"Simplicity constraints play a crucial role in the construction of spin foam
models, yet their effective behaviour on larger scales is scarcely explored. In
this article we introduce intertwiner and spin net models for the quantum group
$\text{SU}(2)_k \times \text{SU}(2)_k$, which implement the simplicity
constraints analogous to 4D Euclidean spin foam models, namely the
Barrett-Crane (BC) and the Engle-Pereira-Rovelli-Livine/Freidel-Krasnov
(EPRL/FK) model. These models are numerically coarse grained via tensor network
renormalization, allowing us to trace the flow of simplicity constraints to
larger scales. In order to perform these simulations we have substantially
adapted tensor network algorithms, which we discuss in detail.
  The BC and the EPRL/FK model behave very differently under coarse graining:
While the unique BC intertwiner model is a fixed point and therefore
constitutes a 2D topological phase, BC spin net models flow away from the
initial simplicity constraints and converge to several different topological
phases. Most of these phases correspond to decoupling spin foam vertices,
however we find also a new phase in which this is not the case, and in which a
non-trivial version of the simplicity constraints holds. The coarse graining
flow of the BC spin net models indicates furthermore that the phase transitions
are not of second order. The EPRL/FK model by contrast reveals a far more
intricate and complex dynamics. We observe an immediate flow away from the
original simplicity constraints, however, with the truncation employed here,
the models generically do not converge to a fixed point.
  The results show that the imposition of simplicity constraints can indeed
lead to interesting and complex dynamics. Thus we will need to further develop
coarse graining tools to efficiently study the large scale behaviour of spin
foam models, in particular for the EPRL/FK model.",1609.02429v2
2018-10-23,"B-site spin-state and anti-site disorder driven multiple-magnetic phases: Griffiths phase, re-entrant cluster glass and exchange bias in double perovskite Pr$_2$CoFeO$_6$","We report the comprehensive experimental results identifying the magnetic
spin ordering and the magnetization dynamics of a double perovskite Pr2CoFeO6
by employing the (dc and ac) magnetization, powder neutron diffraction (NPD)
and X-ray magnetic circular dichroism (XMCD) techniques. X-ray diffraction and
neutron diffraction studies revealed that Pr2CoFeO6 adopts a B-site disordered
orthorhombic structure with space group Pnma. Additionally, ab initio band
structure calculations performed on this system suggested an insulating
anti-ferromagnetic (Fe-Fe) ground state. Magnetometry study showed the system
to possess a spectrum of interesting magnetic phases including long range
antiferromagnetic (canted) spin ordering (TN ~269 K), Griffiths phase,
re-entrant cluster glass (RCG) (TG~ 34 K) and exchange bias. However, the NPD
study divulged the exhibition of a long range G-type (below TN ~269 K) of spin
ordering by Fe spins. Spin dynamics study by ac susceptibility technique
confirmed the system possessing long range ordering at higher
temperatureundergoes a RCG transition at ~34 K. Existence of Griffiths phase
was confirmed by non-analytic field variation of magnetization and Heisenberg
type temporal spin relaxation above long range ordering temperature TN ~269 K.
The anti-site disorder related to the B-sites (Co/Fe) is found to be the main
driving force forthe observed multiple magnetic phases. Furthermore, the
electronic structure probed by the X-ray absorption spectroscopy (XAS) study
suggested a nominal valance state of +3 for both of the B-site ions (Co/Fe)
which in turn triggered the anti-site disorder in the system. Magnetic, XRD,
NPD and XAS analysis yielded a low spin state (LS) for the Co3+ ions. The
random non-magnetic dilution of magnetic Fe3+ (HS) ions by Co3+ (LS) ions
essentially played a crucial role in manifesting the magnetic properties of the
system.",1810.09788v1
2020-01-17,Temporal and spectral fingerprints of ultrafast all-coherent spin switching,"Future information technology demands ultimately fast, low-loss quantum
control. Intense light fields have facilitated important milestones, such as
inducing novel states of matter, accelerating electrons ballistically, or
coherently flipping the valley pseudospin. These dynamics leave unique
signatures, such as characteristic bandgaps or high-order harmonic radiation.
The fastest and least dissipative way of switching the technologically most
important quantum attribute - the spin - between two states separated by a
potential barrier is to trigger an all-coherent precession. Pioneering
experiments and theory with picosecond electric and magnetic fields have
suggested this possibility, yet observing the actual dynamics has remained out
of reach. Here, we show that terahertz (1 THz = 10$^{12}$ Hz) electromagnetic
pulses allow coherent navigation of spins over a potential barrier and we
reveal the corresponding temporal and spectral fingerprints. This goal is
achieved by coupling spins in antiferromagnetic TmFeO$_{3}$ with the locally
enhanced THz electric field of custom-tailored antennas. Within their duration
of 1 ps, the intense THz pulses abruptly change the magnetic anisotropy and
trigger a large-amplitude ballistic spin motion. A characteristic phase flip,
an asymmetric splitting of the magnon resonance, and a long-lived offset of the
Faraday signal are hallmarks of coherent spin switching into adjacent potential
minima, in agreement with a numerical simulation. The switchable spin states
can be selected by an external magnetic bias. The low dissipation and the
antenna's sub-wavelength spatial definition could facilitate scalable spin
devices operating at THz rates.",2001.06255v1
2020-12-02,Synthesis and Characterization of Sodium Iron Antimonate Na2FeSbO5 One-Dimensional Antiferromagnetic Chain Compound with a Spin Glass Ground State,"A new oxide, sodium iron antimonate, Na2FeSbO5, was synthesized and
structurally characterized, and its static and dynamic magnetic properties were
comprehensively studied both experimentally by dc and ac magnetic
susceptibility, magnetization, specific heat, electron spin resonance (ESR) and
Moessbauer measurements, and theoretically by density functional calculations.
The resulting single-crystal structure (a = 15.6991(9) A; b = 5.3323 (4) A; c =
10.8875(6) A; S.G. Pbna) consists of edge-shared SbO6 octahedral chains, which
alternate with vertex-linked, magnetically active FeO4 tetrahedral chains. The
57Fe Moessbauer spectra confirmed the presence of high-spin Fe3+ (3d5) ions in
a distorted tetrahedral oxygen coordination. The magnetic susceptibility and
specific heat data show the absence of a long-range magnetic ordering in
Na2FeSbO5 down to 2 K, but ac magnetic susceptibility unambigously demonstrates
spin-glass-type behavior with a unique two-step freezing at Tf1 about 80 K and
Tf2 about 35 K. Magnetic hyperfine splitting of 57Fe Moessbauer spectra was
observed below T* about 104 K (Tf1 < T*). The spectra just below T* (Tf1 < T <
T*) exhibit a relaxation behavior caused by critical spin fluctuations,
indicating the existence of short-range correlations. The stochastic model of
ionic spin relaxation was used to account for the shape of the Moessbauer
spectra below the freezing temperature. A complex slow dynamics is further
supported by ESR data revealing two different absorption modes presumably
related to ordered and disordered segments of spin chains. The data imply a
spin-cluster ground state for Na2FeSbO5.",2012.01106v1
2022-06-08,Toward matter dynamics in spin foam quantum gravity,"Any approach to pure quantum gravity must eventually face the question of
coupling quantum matter to the theory. In the past, several ways of coupling
matter to spin foam quantum gravity have been proposed, but the dynamics of the
coupled matter-gravity system is challenging to explore. To take first steps
towards uncovering the influence quantum matter has on spin foam models, we
couple free, massive scalar lattice field theory to a restricted,
semi-classical 4d spin foam model, called quantum cuboids. This model can be
understood as a superposition of hypercuboidal (and thus irregular) lattices.
Both theories are coupled by defining scalar lattice field theory on irregular
lattices via discrete exterior calculus and then superimposing these theories
by summing over spin foam configurations. We compute expectation values of
geometric and matter observables using Markov Chain Monte Carlo techniques.
From the observables, we identify a regime in parameter space, in which the
spin foam possesses a finite total volume and looks on average like a regular
lattice with an emergent lattice spacing dependent on the mass of the scalar
field. We also measure the 2-point correlation function and correlation length
of the scalar field in relation to the geodesic distance encoded in the spin
foam. Our results are consistent with the correlation function of ordinary
scalar lattice field theory defined on a fixed regular lattice with the
emergent lattice spacing and the same mass. We conclude that in this regime of
the model, the scalar field is not sensitive to the fluctuations of the spin
foam and effectively behaves as if it is defined on a fixed regular lattice.",2206.04076v2
2022-08-05,Quantum critical spin-liquid-like behavior in S = 1/2 quasikagome lattice CeRh1-xPdxSn investigated using muon spin relaxation and neutron scattering,"We present the results of muon spin relaxation ($\mu$SR) and neutron
scattering on the Ce-based quasikagome lattice CeRh$_{1-x}$Pd$_{x}$Sn ($x=0.1$
to 0.75). Our ZF-$\mu$SR results reveal the absence of static long-range
magnetic order down to 0.05~K in $x = 0.1$ single crystals. The weak
temperature-dependent plateaus of the dynamic spin fluctuations below 0.2~K in
ZF-$\mu$SR together with its longitudinal-field (LF) dependence between 0 and
3~kG indicate the presence of dynamic spin fluctuations persisting even at $T$
= 0.05~K without static magnetic order. On the other hand, $C_{\text{4f}}$/$T$
increases as --log $T$ on cooling below 0.9~K, passes through a broad maximum
at 0.13~K and slightly decreases on further cooling. The ac-susceptibility also
exhibits a frequency independent broad peak at 0.16~K, which is prominent with
an applied field $H$ along $c$-direction. We, therefore, argue that such a
behavior for $x=0.1$ (namely, a plateau in spin relaxation rate ($\lambda$)
below 0.2~K and a linear $T$ dependence in $C_{\text{4f}}$ below 0.13~K) can be
attributed to a metallic spin-liquid (SL) ground state near the quantum
critical point in the frustrated Kondo lattice. The LF-$\mu$SR study suggests
that the out of kagome plane spin fluctuations are responsible for the SL
behavior. Low energy inelastic neutron scattering (INS) of $x$ = 0.1 reveals
gapless magnetic excitations, which are also supported by the behavior of
$C_{\text{4f}}$ proportional to $T^{1.1}$ down to 0.06~K.",2208.03148v1
2022-12-23,Collective topological spin dynamics in a correlated spin glass,"The interplay between spin-orbit interaction (SOI) and magnetic order is
currently one of the most active research fields in condensed matter physics
and leading the search for materials with novel and tunable magnetic and spin
properties. Here we report on a variety of unexpected and unique observations
in thin multiferroic \Ge$_{1-x}$Mn$_x$Te films. The ferrimagnetic order in this
ferroelectric semiconductor is found to reverse with current pulses six orders
of magnitude lower as for typical spin-orbit torque systems. Upon a switching
event, the magnetic order spreads coherently and collectively over macroscopic
distances through a correlated spin-glass state. Lastly, we present a novel
methodology to controllably harness this stochastic magnetization dynamics,
allowing us to detect spatiotemporal nucleation of topological spin textures we
term ``skyrmiverres''.",2212.12262v1
2023-10-30,Dynamical renormalisation of a spin Hamiltonian via high-order nonlinear magnonics,"The macroscopic magnetic order in the ground state of solids is determined by
the spin-dependent Hamiltonian of the system. In the absence of external
magnetic fields, this Hamiltonian contains the exchange interaction, which is
of electrostatic origin, and the spin-orbit coupling, whose magnitude depends
on the atomic charge. Spin-wave theory provides a representation of the entire
spectrum of collective magnetic excitations, called magnons, assuming the
interactions to be constant and the number of magnons in the system negligible.
However, the electric field component of light is able to perturb electrostatic
interactions, charge distributions and, at the same time, can create a magnon
population. A fundamental open question therefore concerns the possibility to
optically renormalise the spin Hamiltonian. Here, we test this hypothesis by
using femtosecond laser pulses to resonantly pump electric-dipole-active pairs
of high-energy magnons near the edges of the Brillouin zone. The transient spin
dynamics reveals the activation and a surprising amplification of coherent
low-energy zone-centre magnons, which are not directly driven. Strikingly, the
spectrum of these low-energy magnons differs from the one observed in thermal
equilibrium, the latter being consistent with spin-wave theory. The light-spin
interaction thus results in a room-temperature renormalisation of the magnetic
Hamiltonian, with an estimated modification of the magnetic interactions by 10%
of their ground-state values. We rationalise the observation in terms of a
novel resonant scattering mechanism, in which zone-edge magnons couple
nonlinearly to the zone-centre modes. In a quantum mechanical model, we
analytically derive the corrections to the spectrum due to the photo-induced
magnon population, which are consistent with our experiments. Our results
present a milestone for an all-optical engineering of Hamiltonians.",2310.19667v1
2023-11-04,Evidence for Low-Level Dynamical Excitation in Near-Resonant Exoplanet Systems,"The geometries of near-resonant planetary systems offer a relatively pristine
window into the initial conditions of exoplanet systems. Given that
near-resonant systems have likely experienced minimal dynamical disruptions,
the spin-orbit orientations of these systems inform the typical outcomes of
quiescent planet formation, as well as the primordial stellar obliquity
distribution. However, few measurements have been made to constrain the
spin-orbit orientations of near-resonant systems. We present a
Rossiter-McLaughlin measurement of the near-resonant warm Jupiter TOI-2202 b,
obtained using the Carnegie Planet Finder Spectrograph (PFS) on the 6.5m
Magellan Clay Telescope. This is the eighth result from the Stellar Obliquities
in Long-period Exoplanet Systems (SOLES) survey. We derive a sky-projected 2D
spin-orbit angle $\lambda=26^{+12}_{-15}$ $^{\circ}$ and a 3D spin-orbit angle
$\psi=31^{+13}_{-11}$ $^{\circ}$, finding that TOI-2202 b - the most massive
near-resonant exoplanet with a 3D spin-orbit constraint to date - likely
deviates from exact alignment with the host star's equator. Incorporating the
full census of spin-orbit measurements for near-resonant systems, we
demonstrate that the current set of near-resonant systems with period ratios
$P_2/P_1\lesssim4$ is generally consistent with a quiescent formation pathway,
with some room for low-level ($\lesssim20^{\circ}$) protoplanetary disk
misalignments or post-disk-dispersal spin-orbit excitation. Our result
constitutes the first population-wide analysis of spin-orbit geometries for
near-resonant planetary systems.",2311.02478v1
1999-07-18,Stability of Dynamically Collapsing Gas Sphere,"We discuss stability of dynamically collapsing gas spheres. We use a
similarity solution for a dynamically collapsing sphere as the unperturbed
state. In the similarity solution the gas pressure is approximated by a
polytrope of $ P = K \rho ^\gamma $. We examine three types of perturbations:
bar ($ \ell = 2$) mode, spin-up mode, and Ori-Piran mode. When $ \gamma < 1.097
$, it is unstable against bar-mode. It is unstable against spin-up mode for any
$ \gamma $. When $ \gamma < 0.961 $, the similarity solution is unstable
against Ori-Piran mode. The unstable mode grows in proportion to $ | t - t_0 |
^{-\sigma} $ while the central density increases in proportion to $ \rho_c
\propto (t - t_0) ^{-2} $ in the similarity solution. The growth rate, $ \sigma
$ is obtained numerically as a function of $ \gamma $ for bar mode and
Ori-Piran mode. The growth rate of the bar mode is larger for a smaller $
\gamma $. The spin-up mode has the growth rate of $ \sigma = 1/3 $ for any $
\gamma $.",9907242v1
1997-08-01,Determination of the universality class of Gadolinium,"We resolve a longstanding puzzle for the static and dynamic critical behavior
of Gadolinium by a combined theoretical and experimental investigation. It is
shown that the spin dynamics of a three dimensional ferromagnet with hcp
lattice structure and a spin-spin interaction given by both exchange and
dipole-dipole interaction belongs to a new dynamic universality class, model
J$^*$. Comparing results from mode coupling theory with results from three
different hyperfine interaction probes we find quantitative agreement. The
crossover scenario for the wavevector dependence of the hyperfine relaxation
rate is determined by a subtle interplay between three length scales: the
correlation length, the dipolar and the uniaxial wave vector.",9708008v1
1998-07-28,Dynamical spin correlations in Heisenberg ladder under magnetic field and correlation functions in SO(5) ladder,"The zero-temperature dynamical spin-spin correlation functions are calculated
for the spin-1/2 two-leg Heisenberg ladder in a magnetic field above the lower
critical field Hc1. The dynamical structure factors are calculated which
exhibit both massless and massive excitations. These modes appear in different
sectors characterized by the parity in the rung direction and by the momentum
in the direction of the chains. The structure factors have power-law
singularities at the lower edges of their support. The results are also
applicable to spin-1 Heisenberg chain. The implications are briefly discussed
for various correlation functions and the pi-resonance in the SO(5) symmetric
ladder model.",9807375v3
1998-11-05,Zero Temperature Phase Transition in Spin-ladders: Phase Diagram and Dynamical studies of Cu(Hp)Cl,"In a magnetic field, spin-ladders undergo two zero-temperature phase
transitions at the critical fields Hc1 and Hc2. An experimental review of
static and dynamical properties of spin-ladders close to these critical points
is presented. The scaling functions, universal to all quantum critical points
in one-dimension, are extracted from (a) the thermodynamic quantities
(magnetization) and (b) the dynamical functions (NMR relaxation). A simple
mapping of strongly coupled spin ladders in a magnetic field on the exactly
solvable XXZ model enables to make detailed fits and gives an overall
understanding of a broad class of quantum magnets in their gapless phase
(between Hc1 and Hc2). In this phase, the low temperature divergence of the NMR
relaxation demonstrates its Luttinger liquid nature as well as the novel
quantum critical regime at higher temperature. The general behaviour close
these quantum critical points can be tied to known models of quantum magnetism.",9811068v2
1999-04-05,"Energy landscapes, supergraphs, and ""folding funnels"" in spin systems","Dynamical connectivity graphs, which describe dynamical transition rates
between local energy minima of a system, can be displayed against the
background of a disconnectivity graph which represents the energy landscape of
the system. The resulting supergraph describes both dynamics and statics of the
system in a unified coarse-grained sense. We give examples of the supergraphs
for several two dimensional spin and protein-related systems. We demonstrate
that disordered ferromagnets have supergraphs akin to those of model proteins
whereas spin glasses behave like random sequences of aminoacids which fold
badly.",9904060v2
1999-11-16,Universal Long-Time Relaxation on the Lattices of Classical Spins: Markovian Behavior on non-Markovian Timescales,"The long-time behavior of certain fast-decaying infinite temperature
correlation functions on one-, two- and three-dimensional lattices of classical
spins with various kinds of nearest-neighbor interactions is studied
numerically, and evidence is presented that the functional form of this
behavior is either simple exponential or exponential multiplied by cosine. Due
to the fast characteristic timescale of the long-time decay, such a
universality cannot be explained on the basis of conventional Markovian
assumptions. It is suggested that this behavior is related to the chaotic
properties of the spin dynamics.",9911229v2
2000-03-30,Magnetic dilution in the geometrically frustrated SrCr$_{9p}$Ga$_{12-9p}$O$_{19}$ and the role of local dynamics: a $μ$SR study,"We investigate the spin dynamics of SrCr$_{9p}$Ga$_{12-9p}$O$_{19}$ for p
below and above the percolation threshold p_c using muon spin relaxation. Our
major findings are: (I) At T->0 the relaxation rate is T independent and
proportional to p^3, (II) the slowing down of spin fluctuation is activated
with an energy U which is also a linear function of p^3 and lim_{p-> 0}U = 8 K;
this energy scale could stem only from a single ion anisotropy, and (III) the p
dependence of the dynamical properties is identical below and above p_c,
indicating that they are controlled by local excitation.",0003489v1
2000-05-24,Dynamical Linked Cluster Expansions for Spin Glasses,"Dynamical linked cluster expansions are linked cluster expansions with
hopping parameter terms endowed with their own dynamics. This amounts to a
generalization from 2-point to point-link-point interactions. An associated
graph theory with a generalized notion of connectivity is reviewed. We discuss
physical applications to disordered systems, in particular to spin glasses,
such as the bond-diluted Ising model and the Sherrington-Kirkpatrick spin
glass. We derive the rules and identify the full set of graphs that contribute
to the series in the quenched case. This way it becomes possible to avoid the
vague extrapolation from positive integer n to n=0, that usually goes along
with an application of the replica trick.",0005412v1
2000-12-11,Molecular dynamics simulations of spin and pure liquids with preserving all the conservation laws,"A new methodology is developed to integrate numerically the equations of
motion for classical many-body systems in molecular dynamics simulations. Its
distinguishable feature is the possibility to preserve, independently on the
size of the time step, all the conservation laws inherent in the description
without breaking the time reversibility. As a result, an implicit second-order
algorithm is derived and applied to pure as well as spin liquids for which the
dynamics is characterized by the conservation of total energy, linear and
angular momenta as well as magnetization and individual spin lengths. It is
demonstrated on the basis of Lennard-Jones and Heisenberg fluid models that
when such quantities as energy and magnetization must be conserved perfectly,
the new algorithm turns out to be more efficient than popular decomposition
integrators and standard predictor-corrector schemes.",0012182v1
2001-09-11,Spin dynamics and coherent tunnelling in the molecular magnetic rings Fe_6 and Fe_8,"We present detailed calculations of low-energy spin dynamics in the ``ferric
wheel'' systems Na:Fe_6 and Cs:Fe_8 in a magnetic field. We compute by exact
diagonalisation the low-energy spectra and matrix elements for total-spin and
N'eel-vector components, and thus the time-dependent correlation functions of
these operators. Comparison of our results with the semiclassical theory of
coherent quantum tunnelling of the N'eel vector demonstrates the validity of a
two-state description for the low-energy dynamics of ferric wheels. We discuss
the implications of our results for mesoscopic quantum coherent phenomena, and
for the experimental techniques to observe them, in molecular magnetic rings.",0109201v2
2002-07-17,"A microscopic description of the aging dynamics: fluctuation-dissipation relations, effective temperature and heterogeneities","We consider the dynamics of a diluted mean-field spin glass model in the
aging regime. The model presents a particularly rich heterogeneous behavior. In
order to catch this behavior, we perform a **spin-by-spin analysis** for a
**given disorder realization**. The results compare well with the outcome of a
static calculation which uses the ``survey propagation'' algorithm of Mezard,
Parisi, and Zecchina [Sciencexpress 10.1126/science.1073287 (2002)]. We thus
confirm the connection between statics and dynamics at the level of single
degrees of freedom. Moreover, working with single-site quantities, we can
introduce a new response-vs-correlation plot, which clearly shows how
heterogeneous degrees of freedom undergo coherent structural rearrangements.
Finally we discuss the general scenario which emerges from our work and
(possibly) applies to more realistic glassy models. Interestingly enough, some
features of this scenario can be understood recurring to thermometric
considerations.",0207416v1
2003-01-14,Dynamics of a Complex Quantum Magnet,"We have computed the low energy quantum states and low frequency dynamical
susceptibility of complex quantum spin systems in the limit of strong
interactions, obtaining exact results for system sizes enormously larger than
accessible previously. The ground state is a complex superposition of a
substantial fraction of all the classical ground states, and yet the dynamical
susceptibility exhibits sharp resonances reminiscent of the behavior of single
spins. These results show that strongly interacting quantum systems can
organize to generate coherent excitations and shed light on recent experiments
demonstrating that coherent excitations are present in a disordered spin
liquid. The dependence of the energy spectra on system size differs
qualitatively from that of the energy spectra of random undirected bipartite
graphs with similar statistics, implying that strong interactions are giving
rise to these unusual spectral properties.",0301251v1
2003-06-03,The spin glass-like dynamics of gelatin gels,"We show that there are several striking parallels between the dynamics of
gelatin gels and spin glasses. In general, glassy systems retain a memory of
their past history. A key characteristic differentiating spin glasses from most
other glassy systems is that on cooling they appear to ""forget"" what happened
just below the glass transition temperature, but the memory is recovered on
heating. We show that gelatin gels also behave in this way. Both systems show
critical scaling of the kinetics with temperature and undergo physical aging,
that is they never reach equilibrium, but continue to harden indefinitely at a
rate which is linear in log(time). The parallels between the dynamics of these
two completely different kinds of condensed matter strongly suggest that they
share an underlying theory.",0306056v1
2003-07-24,Novel dynamic scaling regime in hole-doped La2CuO4,"Only 3% hole doping by Li is sufficient to suppress the long-range
3-dimensional (3D) antiferromagnetic order in La2CuO4.
  The spin dynamics of such a 2D spin liquid state at T << J was investigated
with measurements of the dynamic magnetic structure factor S(omega,q), using
cold neutron spectroscopy, for single crystalline La2Cu0.94Li0.06O4.
  S(omega,q) peaks sharply at (pi,pi) and crosses over around 50K from omega/T
scaling to a novel low temperature regime characterized by a constant energy
scale. The possible connection to a crossover from the quantum critical to the
quantum disordered regime of the 2D antiferromagnetic spin liquid is discussed.",0307605v1
2003-10-06,"Aging in Spin Glasses in three, four and infinite dimensions","The SUE machine is used to extend by a factor of 1000 the time-scale of
previous studies of the aging, out-of-equilibrium dynamics of the
Edwards-Anderson model with binary couplings, on large lattices (L=60). The
correlation function, $C(t+t_w,t_w)$, $t_w$ being the time elapsed under a
quench from high-temperature, follows nicely a slightly-modified power law for
$t>t_w$. Very tiny (logarithmic), yet clearly detectable deviations from the
full-aging $t/t_w$ scaling can be observed. Furthermore, the $t<t_w$ data shows
clear indications of the presence of more than one time-sector in the aging
dynamics. Similar results are found in four-dimensions, but a rather different
behaviour is obtained in the infinite-dimensional $z=6$ Viana-Bray model. Most
surprisingly, our results in infinite dimensions seem incompatible with
dynamical ultrametricity. A detailed study of the link correlation function is
presented, suggesting that its aging-properties are the same as for the spin
correlation-function.",0310087v2
2004-02-09,Critical behavior and driven Monte Carlo dynamics of the XY spin glass in the phase representation,"A driven Monte Carlo dynamics is introduced to study resistivity scaling in
XY-type models in the phase representation. The method is used to study the
phase transition of the three-dimensional XY spin glass with a Gaussian
coupling distribution. We find a phase-coherence transition at finite
temperature in good agreement with recent equilibrium Monte Carlo simulations
which shows a single (spin and chiral) glass transition. Estimates of the
static and dynamic critical exponents indicate that the critical behavior is in
the same universality class as the the model with a bimodal coupling
distribution. Relevance of these results for $\pi$-junction superconductors is
also discussed.",0402264v1
2004-04-23,Exact Analysis of Soliton Dynamics in Spinor Bose-Einstein Condensates,"We propose an integrable model of a multicomponent spinor Bose-Einstein
condensate in one dimension, which allows an exact description of the dynamics
of bright solitons with spin degrees of freedom. We consider specifically an
atomic condensate in the F=1 hyperfine state confined by an optical dipole
trap. When the mean-field interaction is attractive (c_0 < 0) and the
spin-exchange interaction of a spinor condensate is ferromagnetic (c_2 < 0), we
prove that the system possesses a completely integrable point leading to the
existence of multiple bright solitons. By applying results from the inverse
scattering method, we analyze a collision law for two-soliton solutions and
find that the dynamics can be explained in terms of the spin precession.",0404569v2
2004-06-15,Ma-Dasgupta renormalization studies of various disordered systems,"The Ma-Dasgupta real-space renormalization methods allow to study disordered
systems which are governed by strong disorder fixed points. After a general
introduction to the qualitative ideas and to the quantitative renormalization
rules, we describe the explicit exact results that can be obtained in various
one-dimensional models, either classical or quantum, either for dynamics or
statics. The main part of this dissertation is devoted to statistical physics
models, with special attention to (i) the off-equilibrium dynamics of a
particle diffusing in a Brownian potential or in a trap landscape, (ii) the
coarsening dynamics and the equilibrium of classical disordered spin chains,
(iii) the delocalization transition of a random polymer at an interface. The
last part of the dissertation deals with two disordered quantum spin chains
which exhibit a zero-temperature phase transition as the disorder varies,
namely (a) the random antiferromagnetic S=1 spin chain, (b) the random
transverse field Ising chain.",0406334v1
2004-07-20,Off-equilibrium generalization of the fluctuation dissipation theorem for Ising spins and measurement of the linear response function,"We derive for Ising spins an off-equilibrium generalization of the
fluctuation dissipation theorem, which is formally identical to the one
previously obtained for soft spins with Langevin dynamics [L.F.Cugliandolo,
J.Kurchan and G.Parisi, J.Phys.I France \textbf{4}, 1641 (1994)]. The result is
quite general and holds both for dynamics with conserved and non conserved
order parameter. On the basis of this fluctuation dissipation relation, we
construct an efficient numerical algorithm for the computation of the linear
response function without imposing the perturbing field, which is alternative
to those of Chatelain [J.Phys. A \textbf{36}, 10739 (2003)] and Ricci-Tersenghi
[Phys.Rev.E {\bf 68}, 065104(R) (2003)]. As applications of the new algorithm,
we present very accurate data for the linear response function of the Ising
chain, with conserved and non conserved order parameter dynamics, finding that
in both cases the structure is the same with a very simple physical
interpretation. We also compute the integrated response function of the two
dimensional Ising model, confirming that it obeys scaling $\chi (t,t_w)\simeq
t_w^{-a}f(t/t_w)$, with $a =0.26\pm 0.01$, as previously found with a different
method.",0407523v2
2004-10-05,Singular Dynamics of Underscreened Magnetic Impurity Models,"We give a comprehensive analysis of the singular dynamics and of the
low-energy fixed point of one-channel impurity s-d models with ferromagnetic
and underscreened antiferromagnetic couplings. We use the numerical
renormalization group (NRG) to perform calculations at T=0. The spectral
densities of the one-electron Green's functions and t-matrices are found to
have very sharp cusps at the Fermi level (w=0), but do not diverge. The
approach of the Fermi level is governed by terms proportional to 1/ln^2(w/T_0)
as w -> 0. The scaled NRG energy levels show a slow convergence as 1/(N+C) to
their fixed point values, where N is the iteration number and C is a constant
dependent on the coupling J from which the low energy scale T_0 can be deduced.
We calculate also the dynamical spin susceptibility, and the elastic and
inelastic scattering cross-sections as a function of w. The inelastic
scattering goes to zero as w-> 0, as expected for a Fermi liquid, but
anomalously slowly compared to the fully screened case. We obtain the
asymptotic forms for the phase shifts for elastic scattering of the
quasiparticles in the high-spin and low-spin channels.",0410127v1
2004-12-21,Dynamics of two interacting electrons in a one-dimensional crystal with impurities,"We investigated the role that the electron-electron interaction plays on the
propagating properties of wave packets in a one-dimensional crystal with
impurities. We considered two interacting particles with opposite spins in a
band, where we treated their interaction along the Hubbard model. We have
obtained the density of states of the crystal for different values of the
interaction term, as well as solved the dynamical Schr\""{o}dinger equation by
varying the initial conditions. We have introduced a method through which we
were able to follow the time evolution of the wave packets for both spins
showed in three-dimensional plots, and have evaluated, for each particle, the
corresponding $MSD^{\prime}s $ and the centroids as function of time . These
measurements allow us to determine the influence of the interaction on
dynamical properties. We discussed the combined effect that the extension of
the initial wave packets and the interaction strength have on propagating
properties. Under certain conditions we obtained an entanglement of the two
packets associated with both spins that takes place in a small region of the
lattice.",0412596v1
2005-07-22,Dynamics of F=1 87Rb condensates at finite temperatures,"We investigate the dynamics of a F=1 spinor Bose-Einstein condensate of 87Rb
atoms confined in a quasi-one-dimensional trap both at zero and at finite
temperature. At zero temperature, we observe coherent oscillations between
populations of the various spin components and the formation of multiple
domains in the condensate. We study also finite temperature effects in the spin
dynamics taking into account the phase fluctuations in the Bogoliubov-de Gennes
framework. At finite T, despite complex multidomain formation in the
condensate, population equipartition occurs. The length scale of these spin
domains seems to be determined intrinsically by nonlinear interactions.",0507521v3
2005-10-08,Full Counting Statistics of Non-Commuting Variables: the Case of Spin Counts,"We discuss the Full Counting Statistics of non-commuting variables with the
measurement of successive spin counts in non-collinear directions taken as an
example. We show that owing to an irreducible detector back-action, the FCS in
this case may be sensitive to the dynamics of the detectors, and may differ
from the predictions obtained with using a naive version of the Projection
Postulate. We present here a general model of detector dynamics and
path-integral approach to the evaluation of FCS. We concentrate further on a
simple ""diffusive"" model of the detector dynamics where the FCS can be
evaluated with transfer-matrix method. The resulting probability distribution
of spin counts is characterized by anomalously large higher cumulants and
substantially deviates from Gaussian Statistics.",0510215v1
2005-12-14,Measurement of Magnetization Dynamics in Single-Molecule Magnets Induced by Pulsed Millimeter-Wave Radiation,"We describe an experiment aimed at measuring the spin dynamics of the Fe8
single-molecule magnet in the presence of pulsed microwave radiation. In
earlier work, heating was observed after a 0.2-ms pulse of intense radiation,
indicating that the spin system and the lattice were out of thermal equilibrium
at millisecond time scale [Bal et al., Europhys. Lett. 71, 110 (2005)]. In the
current work, an inductive pick-up loop is used to probe the photon-induced
magnetization dynamics between only two levels of the spin system at much
shorter time scales (from ns to us). The relaxation time for the magnetization,
induced by a pulse of radiation, is found to be on the order of 10 us.",0512289v1
2006-01-10,Quantum beat phenomenon presence in coherent spin dynamics of spin-2 $^{87}$Rb atoms in a deep optical lattice,"Motivated by the recent experimental work (A. Widera, \textit{et al}, Phys.
Rev. Lett. 95, 19045), we study the collisional spin dynamics of two spin-2 $%
^{87}$Rb atoms confined in a deep optical lattice. When the system is
initialized as $|0,0>$, three different two-particle Zeeman states are involved
in the time evolution due to the conservation of magnetization. For a large
magnetic field $B>0.8$ Guass, the spin coherent dynamics reduces to a Rabi-like
oscillation between the states $|0,0>$ and $% |1,-1>$. However, under a small
magnetic field, a general three-level coherent oscillation displays. In
particular, around a critical magnetic field $B_{c}\simeq 0.48$ Guass, the
probability in the Zeeman states $% |2,-2> $ exhibits a novel quantum beat
phenomenon, ready to be confirmed in future experiments.",0601188v1
2006-01-18,Mechanism for the failure of the Edwards hypothesis in the SK spin glass,"The dynamics of the SK model at T=0 starting from random spin configurations
is considered. The metastable states reached by such dynamics are atypical of
such states as a whole, in that the probability density of site energies,
$p(\lambda)$, is small at $\lambda=0$. Since virtually all metastable states
have a much larger $p(0)$, this behavior demonstrates a qualitative failure of
the Edwards hypothesis. We look for its origins by modelling the changes in the
site energies during the dynamics as a Markov process. We show how the small
$p(0)$ arises from features of the Markov process that have a clear physical
basis in the spin-glass, and hence explain the failure of the Edwards
hypothesis.",0601402v2
2006-09-01,Oscillatory multiband dynamics of free particles: The ubiquity of zitterbewegung effects,"In the Dirac theory for the motion of free relativistic electrons, highly
oscillatory components appear in the time evolution of physical observables
such as position, velocity, and spin angular momentum. This effect is known as
zitterbewegung. We present a theoretical analysis of rather different
Hamiltonians with gapped and/or spin-split energy spectrum (including the
Rashba, Luttinger, and Kane Hamiltonians) that exhibit analogs of
zitterbewegung as a common feature. We find that the amplitude of oscillations
of the Heisenberg velocity operator v(t) generally equals the uncertainty for a
simultaneous measurement of two linearly independent components of v. It is
also shown that many features of zitterbewegung are shared by the simple and
well-known Landau Hamiltonian describing the dynamics of two-dimensional (2D)
electron systems in the presence of a magnetic field perpendicular to the
plane. Finally, we also discuss the oscillatory dynamics of 2D electrons
arising from the interplay of Rashba spin splitting and a perpendicular
magnetic field.",0609005v2
2006-11-06,Dynamic $0-π$ transition induced by pumping mechanism,"Using Nambu$\otimes $spin space Keldysh Green's function approach, we present
a nonequilibrium charge and spin pumping theory of a quantum dot in the
mico-cavity coupled to two superconducting leads. It is found that the charge
currents include two parts: The dissipationless supercurrent standing for the
transfer of coherent Cooper pairs and the pumped quasi-particle current. The
supercurrent exhibits a dynamic $0-\pi $ transition induced by the frequency
and strength of the $\sigma_{-}$ polarized laser field. This dynamic transition
is not affected by the strong Coulomb interaction. Especially, the spin current
appears and is an even function of the phase difference between two
superconductors when the frequency of the polarized laser field is larger than
two times superconducting energy gap. Our theory serves as an extension to
non-superconducting spintronics.",0611134v2
2007-03-29,Dynamical structure factor of random antiferromagnetic Heisenberg spin chains,"Combining quantum Monte Carlo simulations with the maximum entropy method, we
study the dynamical structure factor $S(k,\omega)$ of spin-1/2
antiferromagnetic Heisenberg chains with various random bond distributions. We
emphasize the crossover behavior in the dynamical properties from pure chain to
disorder-dominated random singlet phase due to bond randomness. For the
distribution corresponding to the infinite randomness fixed point,
$S(k,\omega)$ develops broad non-spinon excitations as well as the
random-singlet peak near $(k, \omega) = (\pi, 0)$, consistent with the known
results obtained by the real-space renormalization group method. For weak
disorder, however, we find clear signature of spinon excitations, reminiscent
of pure spin chains, blurred by disorder. We discuss the implication for
experiments on random-bond antiferromagnetic spin chains, realizable, e.g., in
BaCu$_2$(Si$_x$Ge$_{1-x}$)$_2$O$_7$.",0703772v2
1998-10-15,Einstein-Cartan-Heisenberg Theory of Gravity with Dynamical Torsion,"On the basis of an algebraic relation between torsion and a classical spinor
field a new interpretation of Einstein-Cartan gravity interacting with
classical spinor field is proposed. In this approach the spinor field becomes
an auxiliary field and the dynamical equation for this field (the Heisenberg
equation) is a dynamical, gravitational equation for torsion. The simplest
version of this theory is examined where the metric degrees of freedom are
frozen and only torsion plays a role. A spherically symmetric solution of this
theory is examined. This solution can be interpreted, in the spirit of
Wheeler's ideas of ``charge without charge'' and ``mass without mass'', as a
geometrical model for an uncharged and massless particle with spin (``spin
without spin'').",9810050v2
2001-10-04,Relating Covariant and Canonical Approaches to Triangulated Models of Quantum Gravity,"In this paper explore the relation between covariant and canonical approaches
to quantum gravity and $BF$ theory. We will focus on the dynamical
triangulation and spin-foam models, which have in common that they can be
defined in terms of sums over space-time triangulations. Our aim is to show how
we can recover these covariant models from a canonical framework by providing
two regularisations of the projector onto the kernel of the Hamiltonian
constraint. This link is important for the understanding of the dynamics of
quantum gravity. In particular, we will see how in the simplest dynamical
triangulations model we can recover the Hamiltonian constraint via our
definition of the projector. Our discussion of spin-foam models will show how
the elementary spin-network moves in loop quantum gravity, which were
originally assumed to describe the Hamiltonian constraint action, are in fact
related to the time-evolution generated by the constraint. We also show that
the Immirzi parameter is important for the understanding of a continuum limit
of the theory.",0110026v1
2006-04-11,Effect of Electric and Magnetic Fields on Spin Dynamics in the Resonant Electric Dipole Moment Experiment,"A buildup of the vertical polarization in the resonant electric dipole moment
(EDM) experiment [Y. F. Orlov, W. M. Morse, and Y. K. Semertzidis, Phys. Rev.
Lett. 96, 214802 (2006)] is affected by a horizontal electric field in the
particle rest frame oscillating at a resonant frequency. This field is defined
by the Lorentz transformation of an oscillating longitudinal electric field and
a uniform vertical magnetic one. The effect of a longitudinal electric field is
significant, while the contribution from a magnetic field caused by forced
coherent longitudinal oscillations of particles is dominant. The effect of
electric field on the spin dynamics was not taken into account in previous
calculations. This effect is considerable and leads to decreasing the EDM
effect for the deuteron and increasing it for the proton. The formula for
resonance strengths in the EDM experiment has been derived. The spin dynamics
has been calculated.",0604095v2
2002-04-19,Higher Spin Conserved Currents in $Sp(2M)$ Symmetric Spacetime,"Infinite set of higher spin conserved charges is found for the $sp(2M)$
symmetric dynamical systems in $\f{1}{2} M (M+1)$-dimensional generalized
spacetime $\M_M$. Since the dynamics in $\M_M$ is equivalent to the conformal
dynamics of infinite towers of fields in $d$-dimensional Minkowski spacetime
with $d=3,4,6,10,...$ for $M=2,4,8,16, ...$, respectively, the constructed
currents in $\M_M$ generate infinite towers of (mostly new) higher spin
conformal currents in Minkowski spacetime. The charges have a form of integrals
of $M$-forms which are bilinear in the field variables and are closed as a
consequence of the field equations. Conservation implies independence of a
value of charge of a local variation of a $M$-dimensional integration surface
$\Sigma \subset \M_M$ analogous to Cauchy surface in the usual spacetime. The
scalar conserved charge provides an invariant bilinear form on the space of
solutions of the field equations that gives rise to a positive definite norm on
the space of quantum states.",0204167v1
2006-11-02,Integrable Vortex Dynamics in Anisotropic Planar Spin Liquid Model,"The problem of magnetic vortex dynamics in an anisotropic spin liquid model
is considered. For incompressible flow the model admits reduction to saturating
Bogomolny inequality analytic projections of spin variables, subject the linear
holomorphic Schr\""odinger equation. It allows us to construct N vortex
configurations in terms of the complex Hermite polynomials. Using complex
Galilean boost transformations, the interaction of the vortices and the vortex
chain lattices (vortex crystals) are studied. By the complexified Cole-Hopf
transformation, integrable N vortex dynamics is described by the holomorphic
Burgers equation. Mapping of the point vortex problem to N-particle problem,
the complexified Calogero-Moser system, showing its integrability and the
Hamiltonian structure, is given.",0611002v1
2005-06-20,Spin-glass-like Dynamics of Social Networks,"In this work we study spin-glass (SG) like behavior in the dynamics of
multiple agents in a social or economic context using interactions which are
similar to the physical case. The different preferences shown by individual
agents are represented by orientations of spin-like variables. Because of
limited resources, each agent tries to maximize her total utility function,
giving a prescription for the dynamics of the system similar to the evolution
resulting from the optimization of the interaction of a SG. The coupling
between agents for different attributes may be positive or negative, as in a
physical SG system, forming ""frustrations"" from the ensuing conflicts, with the
system trying to find an overall equilibrium, but in vain, so that we observe
oscillations. The couplings are provided by matrices corresponding to each
attribute and each agent, which are allowed to have some fixed bias, indicating
the unchangeable component of the make up of the agents from genetic factors or
lasting environmental influences, and also contain a random part from
environmental noise, i.e. the cumulative stochastic effect of lumped factors
not explicitly accounted for in the model.",0506161v1
2005-07-05,Stiff spinning torus of electromagnetic two-body motion,"We study an orbit of the electromagnetic two-body problem that involves a
fast (stiff) spinning motion about a circular orbit. We give a multiscale
method of solution that solves for the fast timescale first. The solvability
condition of the asymptotic expansion demands resonances for the fast dynamics.
The stiff resonant tori are found precisely in the atomic magnitude and agree
with many features of the Bohr atom in quantitative and qualitative detail; We
calculate every first emission line of the first 13 observable spectroscopic
series of hydrogen within a few percent deviation. The resonant orbits have
angular momenta that are approximate multiples of Planck's constant and the
emitted frequencies are given by a difference of two linear eigenvalues. This
Lorentz-invariant two-body dynamics exhibts the phenomenon of resonant
dissipation, i.e., the metastable dynamics radiates the center-of-mass energy
while the particles perform fast spinning oscillations of small amplitude about
a circular orbit, a collective radiative recoil.",0507033v3
1997-06-01,How to Probe for Dynamical Structure in the Collapse of Entangled States Using Nuclear Magnetic Resonance,"The spin state of two magnetically inequivalent protons in contiguous atoms
of a molecule becomes entangeled by the indirect spin-spin interaction
(j-coupling). The degree of entanglement oscillates at the beat frequency
resulting from the splitting of a degeneracy. This beating is manifest in NMR
spectroscopy as an envelope of the transverse magnetization and should be
visible in the free induction decay signal. The period (approximately 1 sec) is
long enough for interference between the linear dynamics and collapse of the
wave-function induced by a Stern-Gerlach inhomogeneity to significantly alter
the shape of that envelope. Various dynamical collapse theories can be
distinguished by their observably different predictions with respect to this
alteration. Adverse effects of detuning due to the Stern-Gerlach inhomogeneity
can be reduced to an acceptable level by having a sufficiently thin sample or a
strong rf field.",9706002v2
1999-06-28,Influence of Non-Resonant Effects on the Dynamics of Quantum Logic Gates at Room Temperature,"We study numerically the influence of non-resonant effects on the dynamics of
a single $\pi$-pulse quantum CONTROL-NOT (CN) gate in a macroscopic ensemble of
fo ur-spin molecules at room temperature. The four nuclear spins in each
molecule r epresent a four-qubit register. The qubits are ``labeled'' by the
characteristic frequencies, $\omega_k$, ($k=0$ to 3) due to the Zeeman
interaction of the nuclear spins with the magnetic field. The qubits interact
with each other through an Ising interaction of strength $J$. T he paper
examines the feasibility of implementing a single-pulse quantum CN gate in an
ensemble of quantum molecules at room temperature. We determine a paramet er
region, $\omega_k$ and $J$, in which a single-pulse quantum CN gate can be i
mplemented at room temperature. We also show that there exist characteristic
cri tical values of parameters,
$\Delta\omega_{cr}\equiv|\omega_{k^\prime}-\omega_k|_{cr}$ and $J_{cr}$, such
that for $J<J_{cr}$ and
$\Delta\omega_k\equiv|\omega_{k^\prime}-\omega_k|<\Delta\omega_{cr}$,
non-resonant effects are sufficient to d estroy the dynamics required for
quantum logic operations.",9906109v1
2004-05-31,Decoherence by a chaotic many-spin bath,"We numerically investigate decoherence of a two-spin system (central system)
by a bath of many spins 1/2. By carefully adjusting parameters, the dynamical
regime of the bath has been varied from quantum chaos to regular, while all
other dynamical characteristics have been kept practically intact. We
explicitly demonstrate that for a many-body quantum bath, the onset of quantum
chaos leads to significantly faster and stronger decoherence compared to an
equivalent non-chaotic bath. Moreover, the non-diagonal elements of the
system's density matrix decay differently for chaotic and non-chaotic baths.
Therefore, knowledge of the basic parameters of the bath (strength of the
system-bath interaction, bath's spectral density of states) is not always
sufficient, and much finer details of the bath's dynamics can strongly affect
the decoherence process.",0406001v1
2007-05-23,Controllable dynamics of two separate qubits in Bell states,"The dynamics of entanglement and fidelity for a subsystem of two separate
spin-1/2 qubits prepared in Bell states is investigated. One of the subsystem
qubit labelled $A$ is under the influence of a Heisenberg XY spin-bath, while
another one labelled $B$ is uncoupled with that. We discuss two cases: (i) the
number of bath spins $N\to\infty$; (ii) $N$ is finite: N=40. In both cases, the
bath is initially prepared in a thermal equilibrium state. It is shown that the
time dependence of the concurrence and the fidelity of the two subsystem qubits
can be controlled by tuning the parameters of the spin-bath, such as the
anisotropic parameter, the temperature and the coupling strength with qubit
$A$. It is interesting to find the dynamics of the concurrence is independent
of four different initial Bell states and that of the fidelity is divided into
two groups.",0705.3276v2
2007-06-15,Weyssenhoff fluid dynamics in general relativity using a 1+3 covariant approach,"The Weyssenhoff fluid is a perfect fluid with spin where the spin of the
matter fields is the source of torsion in an Einstein-Cartan framework. Obukhov
and Korotky showed that this fluid can be described as an effective fluid with
spin in general relativity. A dynamical analysis of such a fluid is performed
in a gauge invariant manner using the 1+3 covariant approach. This yields the
propagation and constraint equations for the set of dynamical variables. A
verification of these equations is performed for the special case of
irrotational flow with zero peculiar acceleration by evolving the constraints.",0706.2367v2
2007-07-13,Non-Markovian dynamics of a qubit coupled to an Ising spin bath,"We study the analytically solvable Ising model of a single qubit system
coupled to a spin bath. The purpose of this study is to analyze and elucidate
the performance of Markovian and non-Markovian master equations describing the
dynamics of the system qubit, in comparison to the exact solution. We find that
the time-convolutionless master equation performs particularly well up to
fourth order in the system-bath coupling constant, in comparison to the
Nakajima-Zwanzig master equation. Markovian approaches fare poorly due to the
infinite bath correlation time in this model. A recently proposed
post-Markovian master equation performs comparably to the time-convolutionless
master equation for a properly chosen memory kernel, and outperforms all the
approximation methods considered here at long times. Our findings shed light on
the applicability of master equations to the description of reduced system
dynamics in the presence of spin-baths.",0707.2096v1
2007-09-10,Decoherence induced by an interacting spin environment in the transition from integrability to chaos,"We investigate the decoherence properties of a central system composed of two
spins 1/2 in contact with a spin bath. The dynamical regime of the bath ranges
from a fully integrable integrable limit to complete chaoticity. We show that
the dynamical regime of the bath determines the efficiency of the decoherence
process. For perturbative regimes, the integrable limit provides stronger
decoherence, while in the strong coupling regime the chaotic limit becomes more
efficient. We also show that the decoherence time behaves in a similar way. On
the contrary, the rate of decay of magnitudes like linear entropy or fidelity
does not depend on the dynamical regime of the bath. We interpret the latter
results as due to a comparable complexity of the Hamiltonian for both the
integrable and the fully chaotic limits.",0709.1383v1
2007-09-18,Dynamics of the Distorted Diamond Chain,"We present results on the dynamics of the distorted diamond chain, S=1/2
dimers alternating with single spins 1/2 and exchange couplings $J_1$ and $J_3$
in between. The dynamics in the spin fluid (SF) and tetramer-dimer (TD) phases
is investigated numerically by exact diagonalisation for up to 24 spins.
Representative excitation spectra are presented, both for zero magnetic field
and in the 1/3 plateau phase and the relevant parameters are determined across
the phase diagram. The behavior across the SF-TD phase transition line is
discussed for the specific heat and for excitation spectra. The relevance of
the distorted diamond chain model for the material Cu$_3$(CO$_3$)$_2$(OH)$_2$
(azurite) is discussed with particular emphasis on inelastic neutron scattering
experiments, a recent suggestion of one possibly ferromagnetic coupling
constant is not confirmed.",0709.2863v1
2007-12-29,Time reparametrization symmetry in spin glass models,"We study the long-time aging dynamics of spin-glass models with two-spin
interactions by performing a Renormalization Group transformation on the time
variable in the non-equilibrium dynamical generating functional. We obtain the
RG equations and find that the flow converges to an exact fixed point. We show
that this fixed point is invariant under reparametrizations of the time
variable. This continuous symmetry is broken, as evidenced by the fact that the
observed correlations and responses are not invariant under it. We argue that
this gives rise to the presence of Goldstone modes, and that those Goldstone
modes shape the behavior of fluctuations in the nonequilibrium dynamics.",0801.0014v2
2008-01-22,A Dynamical Quantum Cluster Approach to Two-Particle Correlation Functions in the Hubbard Model,"We investigate the charge- and spin dynamical structure factors for the 2D
one-band Hubbard model in the strong coupling regime within an extension of the
Dynamical Cluster Approximation (DCA) to two-particle response functions. The
full irreducible two-particle vertex with three momenta and frequencies is
approximated by an effective vertex dependent on the momentum and frequency of
the spin/charge excitation. In the spirit of the DCA, the effective vertex is
calculated with quantum Monte Carlo methods on a finite cluster. On the basis
of a comparison with high temperature auxiliary field quantum Monte Carlo data
we show that near and beyond optimal doping, our results provide a consistent
overall picture of the interplay between charge, spin and single-particle
excitations.",0801.3377v1
2008-02-21,Antiferromagnetic Order of Strongly Interacting Fermions in a Trap: Real-Space Dynamical Mean-Field Analysis,"We apply Dynamical Mean-Field Theory to strongly interacting fermions in an
inhomogeneous environment. With the help of this Real-Space Dynamical
Mean-Field Theory (R-DMFT) we investigate antiferromagnetic states of
repulsively interacting fermions with spin 1/2 in a harmonic potential. Within
R-DMFT, antiferromagnetic order is found to be stable in spatial regions with
total particle density close to one, but persists also in parts of the system
where the local density significantly deviates from half filling. In systems
with spin imbalance, we find that antiferromagnetism is gradually suppressed
and phase separation emerges beyond a critical value of the spin imbalance.",0802.3211v2
2008-03-26,Effects of rf Current on Spin Transfer Torque Induced Dynamics,"The impact of radiofrequency (rf) currents on the direct current (dc) driven
switching dynamics in current-perpendicular-to-plane nanoscale spin valves is
demonstrated. The rf currents dramatically alter the dc driven free layer
magnetization reversal dynamics as well as the dc switching level. This occurs
when the frequency of the rf current is tuned to a frequency range around the
dc driven magnetization precession frequencies. For these frequencies,
interactions between the dc driven precession and the injected rf induce
frequency locking and frequency pulling effects that lead to a measurable
dependence of the critical switching current on the frequency of the injected
rf. Based on macrospin simulations, including dc as well as rf spin torque
currents, we explain the origin of the observed effects.",0803.3791v2
2008-05-21,Non-equilibrium thermodynamic study of magnetization dynamics in the presence of spin-transfer torque,"The dynamics of magnetization in the presence of spin-transfer torque was
studied. We derived the equation for the motion of magnetization in the
presence of a spin current by using the local equilibrium assumption in
non-equilibrium thermodynamics. We show that, in the resultant equation, the
ratio of the Gilbert damping constant, $\alpha$, and the coefficient, $\beta$,
of the current-induced torque, called non-adiabatic torque, depends on the
relaxation time of the fluctuating field $\tau_{c}$. The equality
$\alpha=\beta$ holds when $\tau_c$ is very short compared to the time scale of
magnetization dynamics. We apply our theory to current-induced magnetization
reversal in magnetic multilayers and show that the switching time is a
decreasing function of $\tau_{c}$.",0805.3306v1
2008-06-24,Non-Markovian dynamics and von Neumann entropy evolution of a qubit in a spin environment,"The dynamics of a central spin-1/2 in presence of a local magnetic field and
a bath of N spin-1/2 particles is studied in the thermodynamic limit. The
interaction between the spins is Heisenberg XY type and the bath is considered
to be a perfect thermal reservoir. In this case, the evolution of the
populations of the reduced density matrix are obtained for different
temperatures. A Born approximation is made but not a Markov approximation
resulting a non-Markovian dynamics. The measure of the way that the system
mixes is obtained by means of the von Neumann entropy. For low temperatures,
results show that there are oscillations of populations and of the von Neumann
entropy, indicating that the central spin becomes a pure state with
characteristic time periods in which it is possible to extract or recuperate
information. In the regime of high temperatures, the evolution shows a final
maximum mixed state with entropy S=ln 2 as it is expected for a two level
system.",0806.3786v2
2008-10-08,Systems with two symmetric absorbing states: relating the microscopic dynamics with the macroscopic behavior,"We propose a general approach to study spin models with two symmetric
absorbing states. Starting from the microscopic dynamics on a square lattice,
we derive a Langevin equation for the time evolution of the magnetization
field, that successfully explains coarsening properties of a wide range of
nonlinear voter models and systems with intermediate states. We find that the
macroscopic behavior only depends on the first derivatives of the spin-flip
probabilities. Moreover, an analysis of the mean-field term reveals the three
types of transitions commonly observed in these systems -generalized voter,
Ising and directed percolation-. Monte Carlo simulations of the spin dynamics
qualitatively agree with theoretical predictions.",0810.1436v1
2009-06-12,Using neutron spin-echo to investigate proton dynamics in proton-conducting perovskites,"We demonstrate the applicability of studying the proton dynamics in
proton-conducting perovskites using neutron spin-echo spectroscopy, a powerful
method hitherto neglected for studies of the proton dynamics in ceramic proton
conductors. By combining our neutron spin-echo results of hydrated
BaZr0.90Y0.10O2.95 with results obtained from kinetic modeling based on
first-principles calculations we show that already over a length-scale as short
as 2 nm the long-range proton self-diffusion is observed, and the likely effect
of dopant atoms acting as trapping centers has averaged out.",0906.2346v1
2009-10-26,"Turbulence - ""motion of multitude"": a multi-agent spin model for complex flows","We propose a new paradigm for emergence of macroscopic flows. The latter are
considered as a collective phenomenon created by many agents that exchange
abstract information. The information exchange causes agents to change their
relative positions which results in a flow. This paradigm, aimed at the study
of the nature of turbulence, appeals to the original meaning of the word:
""turbulence"" siginifies ""disordered motions of crowds"". We give a preliminary
discussion on a model of multi-agent dynamics that realizes the paradigm. This
dynamics is reminiscent of spin glasses and neural networks. The model is
relational, i. e. it assumes no spatio-temporal background and may serve as a
basis for an approach to quantum gravity via spin models.",0910.4923v1
2009-11-11,Real-time dynamics of particle-hole excitations in Mott insulator-metal junctions,"Charge excitations in Mott insulators (MIs) are distinct from their
band-insulator counterparts and they can provide a mechanism for energy
harvesting in solar cells based on strongly correlated electronic materials. In
this paper, we study the real-time dynamics of holon-doublon pairs in a MI
connected to metallic leads using the time-dependent density matrix
renormalization group method. The transfer of charge across the MI-metal
interface is controlled by both the electron-electron interaction strength
within the MI and the voltage difference between the leads. We find an overall
enhancement of the charge transfer as compared to the case of a
(noninteracting) band insulator-metal interface with a similar band gap.
Moreover, the propagation of holon-doublon excitations within the MI
dynamically changes the spin-spin correlations, introducing time-dependent
phase shifts in the spin structure factor.",0911.2141v2
2009-11-30,Organization and Complexity in a Nested Hierarchical Spin-Glass like Social Space,"In this paper, we mathematically formulate the interaction and dynamics of a
hierarchical complex social system where each agent is seen as an array of many
variables. The formation of identities and modifications can be studied by
using interaction physics in an energy landscape. The spin glass Hamiltonian is
modified to suit our needs in light of complexity. The expression of variables
subject to weights and topology is considered. Interactions within the same
hierarchy level as well as the effect of one hierarchy level on another are
studied. The effect of having many variables associated with a single agent
brings about interesting dynamics. The persistence of the identity units
subject to stiffness, continuous changes and also sudden reorganizations is
discussed.",0911.5570v2
2010-01-08,Exciton spin dynamics in spherical CdS quantum dots,"Exciton spin dynamics in quasi-spherical CdS quantum dots is studied in
detail experimentally and theoretically. Exciton states are calculated using
the 6-band k.p Hamiltonian. It is shown that for various sets of Luttinger
parameters, when the wurtzite lattice crystal field splitting and Coulomb
interaction between the electron-hole pair are taken into account exactly, both
the electron and hole wavefunction in the lowest exciton state are of S-type.
This rules out the spatial-symmetry-induced origin of the dark exciton in CdS
quantum dots. The exciton bleaching dynamics is studied using time- and
polarization-resolved transient absorption technique of ultrafast laser
spectroscopy. Several samples with a different mean size of CdS quantum dots in
different glass matrices were investigated. This enabled the separation of
effects that are typical for one particular sample from those that are general
for this type of material. The experimentally determined dependence of the
electron spin relaxation rate on the radius of quantum dots agrees well with
that computed theoretically.",1001.1318v1
2010-04-28,Toward the excited meson spectrum of dynamical QCD,"We present a detailed description of the extraction of the highly excited
isovector meson spectrum on dynamical anisotropic lattices using a new
quark-field construction algorithm and a large variational basis of operators.
With careful operator construction, the combination of these techniques is used
to identify the continuum spin of extracted states reliably, overcoming the
reduced rotational symmetry of the cubic lattice. Excited states, states with
exotic quantum numbers (0+-, 1-+ and 2+-) and states of high spin are resolved,
including, for the first time in a lattice QCD calculation, spin-four states.
The determinations of the spectrum of isovector mesons and kaons are performed
on dynamical lattices with two volumes and with pion masses down to ~ 400 MeV,
with statistical precision typically at or below 1% even for highly excited
states.",1004.4930v1
2010-07-27,Solution of the problem of uniqueness and hermiticity of hamiltonians for Dirac particles in gravitational fields,"The authors prove that the dynamics of spin 1/2 particles in stationary
gravitational fields can be described using an approach, which builds upon the
formalism of pseudo-Hermitian Hamiltonians. The proof consists in the analysis
of three expressions for Hamiltonians, which are derived from the Dirac
equation and describe the dynamics of spin 1/2 particles in the gravitational
field of the Kerr solution. The Hamiltonians correspond to different choices of
tetrad vectors and differ from each other. The differences between the
Hamiltonians confirm the conclusion known from many studies that the
Hamiltonians derived from the Dirac equation are non-unique. Application of
standard pseudo-Hermitian quantum mechanics rules to each of these Hamiltonians
produces the same Hermitian Hamiltonian. The eigenvalue spectrum of the
resulting Hamiltonian is the same as that of the Hamiltonians derived from the
Dirac equation with any chosen system of tetrad vectors. For description of the
dynamics of spin 1/2 particles in stationary gravitational fields can be used
not only the formalism of pseudo-Hermitian Hamiltonians, but also an
alternative approach, which employs the Parker scalar product. The authors show
that the alternative approach is equivalent to the formalism of
pseudo-Hermitian Hamiltonians.",1007.4631v1
2011-01-05,The Fascinating World of Landau-Lifshitz-Gilbert Equation: An Overview,"The Landau-Lifshitz-Gilbert (LLG) equation is a fascinating nonlinear
evolution equation both from mathematical and physical points of view. It is
related to the dynamics of several important physical systems such as
ferromagnets, vortex filaments, moving space curves, etc. and has intimate
connections with many of the well known integrable soliton equations, including
nonlinear Schr\""odinger and sine-Gordon equations. It can admit very many
dynamical structures including spin waves, elliptic function waves, solitons,
dromions, vortices, spatio-temporal patterns, chaos, etc. depending on the
physical and spin dimensions and the nature of interactions. An exciting recent
development is that the spin torque effect in nanoferromagnets is described by
a generalization of the LLG equation which forms a basic dynamical equation in
the field of spintronics. This article will briefly review these developments
as a tribute to Robin Bullough who was a great admirer of the LLG equation.",1101.1005v1
2011-02-04,"Topological phases, Majorana modes and quench dynamics in a spin ladder system","We explore the salient features of the `Kitaev ladder', a two-legged ladder
version of the spin-1/2 Kitaev model on a honeycomb lattice, by mapping it to a
one-dimensional fermionic p-wave superconducting system. We examine the
connections between spin phases and topologically non-trivial phases of
non-interacting fermionic systems, demonstrating the equivalence between the
spontaneous breaking of global Z2 symmetry in spin systems and the existence of
isolated Majorana modes. In the Kitaev ladder, we investigate topological
properties of the system in different sectors characterized by the presence or
absence of a vortex in each plaquette of the ladder. We show that vortex
patterns can yield a rich parameter space for tuning into topologically
non-trivial phases. We introduce a new topological invariant which explicitly
determines the presence of zero energy Majorana modes at the boundaries of such
phases. Finally, we discuss dynamic quenching between topologically non-trivial
phases in the Kitaev ladder, and in particular, the post-quench dynamics
governed by tuning through a quantum critical point.",1102.0824v1
2011-03-23,Zero-temperature spin-glass freezing in self-organized arrays of Co nanoparticles,"We study, by means of magnetic susceptibility and magnetic aging experiments,
the nature of the glassy magnetic dynamics in arrays of Co nanoparticles,
self-organized in N layers from N=1 (two-dimensional limit) up to N=20
(three-dimensional limit). We find no qualitative differences between the
magnetic responses measured in these two limits, in spite of the fact that no
spin-glass phase is expected above T=0 in two dimensions. More specifically,
all the phenomena (critical slowing down, flattening of the field-cooled
magnetization below the blocking temperature and the magnetic memory induced by
aging) that are usually associated with this phase look qualitatively the same
for two-dimensional and three-dimensional arrays. The activated scaling law
that is typical of systems undergoing a phase transition at zero temperature
accounts well for the critical slowing down of the dc and ac susceptibilities
of all samples. Our data show also that dynamical magnetic correlations
achieved by aging a nanoparticle array below its superparamagnetic blocking
temperature extend mainly to nearest neighbors. Our experiments suggest that
the glassy magnetic dynamics of these nanoparticle arrays is associated with a
zero-temperature spin-glass transition.",1103.4492v1
2011-04-28,Measurement back-action on the quantum spin-mixing dynamics of a spin-1 Bose-Einstein condensate,"We consider a small F=1 spinor condensate inside an optical cavity driven by
an optical probe field, and subject the output of the probe to a homodyne
detection, with the goal of investigating the effect of measurement back-action
on the spin dynamics of the condensate. Using the stochastic master equation
approach, we show that the effect of back-action is sensitive to not only the
measurement strength but also the quantum fluctuation of the spinor condensate.
The same method is also used to estimate the atom numbers below which the
effect of back-action becomes so prominent that extracting spin dynamics from
this cavity-based detection scheme is no longer practical.",1104.5301v1
2011-07-26,Studying Spin-Orbit Dynamics using Measurements of the Proton's Polarized Gluon Asymmetry,"Measurements involving the gluon spin density, Delta G=G++ - G+-, can play an
important role in the quantitative understanding of proton structure. To
demonstrate this, we show that the shape of the gluon asymmetry, A(x,t)=Delta
G(x,t)/G(x,t), contains significant dynamical information about
non-perturbative spin-orbit effects. It is instructive to use a separation
A(x,t)=A_0^epsilon(x)+epsilon(x,t), where A_0^epsilon(x) is an approximately
scale-invariant form that can be calculated within a given factorization
prescription from the measured distributions Delta q(x,t), q(x,t) and G(x,t).
Applying this separation with the J_z=1/2 sum rule provides a convenient way to
determine the total amount of orbital angular momentum generated by mechanisms
associated with confinement and chiral dynamics. The results are consistent
with alternate non-perturbative approaches to the determination of orbital
angular momentum in the proton. Our studies help to specify the accuracy that
future measurements should achieve to constrain theoretical models for nucleon
structure.",1107.5292v1
2011-08-22,Electron-phonon-scattering dynamics in ferromagnetic metals and its influence on ultrafast demagnetization processes,"We theoretically investigate spin-dependent carrier dynamics due to the
electron-phonon interaction after ultrafast optical excitation in ferromagnetic
metals. We calculate the electron-phonon matrix elements including the
spin-orbit interaction in the electronic wave functions and the interaction
potential. Using the matrix elements in Boltzmann scattering integrals, the
momentum-resolved carrier distributions are obtained by solving their equation
of motion numerically. We find that the optical excitation with realistic laser
intensities alone leads to a negligible magnetization change, and that the
demagnetization due to electron-phonon interaction is mostly due to hole
scattering. Importantly, the calculated demagnetization quenching due to this
Elliot-Yafet type depolarization mechanism is not large enough to explain the
experimentally observed result. We argue that the ultrafast demagnetization of
ferromagnets does not occur exclusively via an Elliott-Yafet type process,
i.e., scattering in the presence of the spin-orbit interaction, but is
influenced to a large degree by a dynamical change of the band structure, i.e.,
the exchange splitting.",1108.4454v1
2011-09-10,Entanglement Evolution via Quantum Resonances,"We consider two qubits interacting with local and collective thermal
reservoirs. Each spin-reservoir interaction consists of an energy exchange and
an energy conserving channel. We prove a resonance representation of the
reduced dynamics of the spins, valid for all times t>=0, with errors (small
interaction) estimated rigorously, uniformly in time. Subspaces associated to
non-interacting energy differences evolve independently, partitioning the
reduced density matrix into dynamically decoupled clusters of jointly evolving
matrix elements. Within each subspace the dynamics is markovian with a
generator determined entirely by the resonance data of the full Hamiltonian.
Based on the resonance representation we examine the evolution of entanglement
(concurrence). We show that, whenever thermalization takes place, entanglement
of any initial state dies out in a finite time and will not return. For a
concrete class of initially entangled spin states we find explicit bounds on
entanglement survival and death times in terms of the initial state and the
resonance data.",1109.2235v1
2011-10-15,Atomistic spin dynamic method with both damping and moment of inertia effects included from first principles,"We consider spin dynamics for implementation in an atomistic framework and we
address the feasibility of capturing processes in the femtosecond regime by
inclusion of moment of inertia. In the spirit of an {\it s-d} -like interaction
between the magnetization and electron spin, we derive a generalized equation
of motion for the magnetization dynamics in the semi-classical limit, which is
non-local in both space and time. Using this result we retain a generalized
Landau-Lifshitz-Gilbert equation, also including the moment of inertia, and
demonstrate how the exchange interaction, damping, and moment of inertia, all
can be calculated from first principles.",1110.3387v2
2011-12-16,Domain dynamics and fluctuations in artificial square ice at finite temperatures,"The thermally-driven formation and evolution of vertex domains is studied for
square artificial spin ice. A self consistent mean field theory is used to show
how domains of ground state ordering form spontaneously, and how these evolve
in the presence of disorder. The role of fluctuations is studied, using Monte
Carlo simulations and analytical modelling. Domain wall dynamics are shown to
be driven by a biasing of random fluctuations towards processes that shrink
closed domains, and fluctuations within domains are shown to generate isolated
small excitations, which may stabilise as the effective temperature is lowered.
Domain dynamics and fluctuations are determined by interaction strengths, which
are controlled by inter-element spacing. The role of interaction strength is
studied via experiments and Monte Carlo simulations. Our mean field model is
applicable to ferroelectric `spin' ice, and we show that features similar to
that of magnetic spin ice can be expected, but with different characteristic
temperatures and rates.",1112.3817v1
2012-02-08,High-Frequency QPOs as a Product of Inner Disk Dynamics around Neutron Stars,"The kHz QPOs observed in a neutron star low mass X-ray binary are likely to
be produced in the innermost regions of accretion disk around the neutron star.
The rotational dynamics of the inner disk can be characterized by the presence
of either sub-Keplerian or super-Keplerian accretion flow depending on the
relative fastness of the neutron spin as compared to the Keplerian frequency at
the inner disk radius. Within the magnetosphere-disk interaction model, the
frequency difference between the two kHz QPOs observed in a given source can be
estimated to be slightly higher than or nearly around the neutron star spin
frequency if the neutron star is a slow rotator and less than the stellar spin
frequency if the neutron star is a fast rotator.",1202.1681v1
2012-07-18,Universal and non-universal features of the generalized voter class for ordering dynamics,"By considering three different spin models belonging to the generalized voter
class for ordering dynamics in two dimensions [I. Dornic, \textit{et al.} Phys.
Rev. Lett. \textbf{87}, 045701 (2001)], we show that they behave differently
from the linear voter model when the initial configuration is an unbalanced
mixture up and down spins. In particular we show that for nonlinear voter
models the exit probability (probability to end with all spins up when starting
with an initial fraction $x$ of them) assumes a nontrivial shape. The change is
traced back to the strong nonconservation of the average magnetization during
the early stages of dynamics. Also the time needed to reach the final consensus
state $T_N(x)$ has an anomalous nonuniversal dependence on $x$.",1207.4333v2
2012-08-08,Indivisible quantum evolution of a driven open spin-$S$ system,"Using a recently proposed measure for divisibility of a dynamical map, we
study the non-Markovian character of a quantum evolution of a driven spin-$S$
system weakly coupled to a bosonic bath. The complete tomographic knowledge
about the dynamics of the open system is obtained by the time-convolutionless
master equation in the secular approximation. The derived equation can be
applied to a wide range of spin-boson models with the Hermitian or
non-Hermitian coupling operator in the system-environment interaction
Hamiltonian. Besides the influence of the environmental spectral densities, the
tunneling energy of the system Hamiltonian can affect the measure of quantum
non-Markovianity. It is found that the non-Markovian feature of a dynamical map
of a high-dimension spin system is noticeable in contrast to that of a
low-dimension spin system.",1208.1546v1
2012-10-06,Coarsening Dynamics of Nonequilibrium Chiral Ising Models,"We investigate a nonequilibrium coarsening dynamics of a one-dimensional
Ising spin system with chirality. Only spins at domain boundaries are updated
so that the model undergoes a coarsening to either of equivalent absorbing
states with all spins + or -. Chirality is imposed by assigning different
transition rates to events at down (+-) kinks and up (-+) kinks. The coarsening
is characterized by power-law scalings of the kink density $\rho \sim
t^{-\delta}$ and the characteristic length scale $\xi \sim t^{1/z}$ with time
$t$. Surprisingly the scaling exponents vary continuously with model
parameters, which is not the case for systems without chirality. These results
are obtained from extensive Monte Carlo simulations and spectral analyses of
the time evolution operator. Our study uncovers the novel universality class of
the coarsening dynamics with chirality.",1210.1961v1
2012-10-23,Correlations between the dynamics of parallel tempering and the free-energy landscape in spin glasses,"We present the results of a large-scale numerical study of the equilibrium
three-dimensional Edwards-Anderson Ising spin glass with Gaussian disorder.
Using parallel tempering (replica exchange) Monte Carlo we measure various
static, as well as dynamical quantities, such as the autocorrelation times and
round-trip times for the parallel tempering Monte Carlo method. The correlation
between static and dynamic observables for 5000 disorder realizations and up to
1000 spins down to temperatures at 20% of the critical temperature is examined.
Our results show that autocorrelation times are directly correlated with the
roughness of the free-energy landscape.",1210.6290v2
2012-11-05,Adiabatic Electron Dynamics in Antiferromagnetic Texture,"Adiabatic dynamics of conduction electrons in antiferromagnetic (AFM)
materials with slowly varying spin texture is developed. Quite different from
the ferromagnetic (FM) case, adiabaticity in AFM texture does not imply perfect
alignment of conduction electron spins with background profile, instead, it
introduces an internal dynamics between degenerate bands. As a result, the
orbital motion of conduction electrons becomes spin-dependent and is affected
by two emergent gauge fields: one of them is the non-Abelian version of what
has been discovered in FM systems; the other leads to an anomalous velocity
that has no FM counterpart. Two examples with experimental predictions are
provided.",1211.0782v2
2012-12-15,Non-equilibrium magnetic interactions in strongly correlated systems,"We formulate a low-energy theory for the magnetic interactions between
electrons in the multi-band Hubbard model under non-equilibrium conditions
determined by an external time-dependent electric field which simulates
laser-induced spin dynamics. We derive expressions for dynamical exchange
parameters in terms of non-equilibrium electronic Green functions and
self-energies, which can be computed, e.g., with the methods of time-dependent
dynamical mean-field theory. Moreover, we find that a correct description of
the system requires, in addition to exchange, a new kind of magnetic
interaction, that we name ""twist exchange"", which formally resembles
Dzyaloshinskii-Moriya coupling, but is not due to spin-orbit, and is actually
due to an effective three-spin interaction. Our theory allows the evaluation of
the related time-dependent parameters as well.",1212.3671v1
2013-06-19,Organic magnetoresistance under resonant ac drive,"We study the spin dynamics of an electron-hole pair in a random hyperfine
magnetic field and an external field, B0, under a resonant drive with frequency
omega0 = gamma B0. The fact that the pair decays by recombination exclusively
from a singlet configuration, S, in which the spins of the pair-partners are
entangled, makes this dynamics highly nontivial. Namely, as the amplitude, B1,
of the driving field grows, mixing all of the triplet components, the
long-living modes do not disappear, but evolve from T+, T- into (T+ +/- sqrt(2)
T0 + T-)/2. Upon further increase of B1, the lifetime of the S-mode is cut in
half, while the T0-mode transforms into an antisymmetric combination (T- -
T-)/sqrt(2) and acquires a long lifetime, in full analogy to the superradiant
and subradiant modes in the Dicke effect. Peculiar spin dynamics translates
into a peculiar dependence on B1. In particular, at small B1, the
radiation-induced correction to the current is linear in B1.",1306.4436v1
2013-07-31,Femtosecond dynamics of magnetic excitations from resonant inelastic x-ray scattering in CaCu2O3,"Taking spinon excitations in the quantum antiferromagnet CaCu2O3 as an
example, we demonstrate that femtosecond dynamics of magnetic excitations can
be probed by direct resonant inelastic x-ray scattering (RIXS). To this end, we
isolate the contributions of single and double spin-flip excitations in
experimental RIXS spectra, identify the physical mechanisms that cause them and
determine their respective timescales. By comparing theory and experiment, we
find that double spin flips need a finite amount of time to be generated,
rendering them sensitive to the core-hole lifetime, whereas single spin flips
are to a very good approximation independent of it. This shows that RIXS can
grant access to time-domain dynamics of excitations and illustrates how RIXS
experiments can distinguish between excitations in correlated electron systems
based on their different time dependence.",1307.8393v1
2014-01-17,Computation of dynamical correlation functions of the spin-1 Babujan-Takhtajan chain,"The dynamical structure factor of the Babujan-Takhtajan antiferromagnetic
spin-1 chain is computed numerically at zero temperature and zero magnetic
field, using the higher-spin generalization of an Algebraic Bethe Ansatz-based
method previously used for spin-1/2 integrable chains. This method, which
consists in the explicit construction of eigenstates and the summation of the
Lehmann representation of the correlator, is here particularly challenging to
implement in view of the presence of strongly deviated string solutions to the
Bethe equations. We show that a careful treatment of these deviations makes it
possible to obtain perfect saturation of sum rules for small system sizes, and
extremely good saturation for large system sizes where the dynamical structure
factor is computed by including all two-spinon and four-spinon contributions.
The real-space spin-spin correlation, obtained by Fourier transforming our
results, displays asymptotics fitting predictions from conformal field theory.",1401.4450v1
2014-04-04,Evolution of magnetic dynamics in an artificially frustrated Fe nanoparticle system,"Frustrated lattices1-3, characterized by minor breakdown in local order in an
otherwise periodic lattice, lead to simultaneous possibilities of several
ground states which can trigger unique physical properties, in condensed matter
systems. In magnetic materials with atomic spins, frustration takes another
shape with added possibilities to construct various topological arrangements of
spins, whereby magnetic order is disturbed2,4. We have achieved a new approach
to introduce positional atomic disorder inside a Fe nanoparticle lattice,
forming domains without boundaries to study magnetic dynamics of the
constituent spins. This magnetism overrides the exchange bias derived magnetic
enhancement, appears only at temperatures around 200 K and is characterized by
a dynamic polarity, p = +/-1 (positive or negative) with a precise frequency.
The material otherwise behaves like a superparamagnet with characteristic
magnetization behaviour at room temperature and 2 K.",1404.1163v1
2014-07-04,Dissipative quantum dynamics of fermions in optical lattices: a slave-spin approach,"We investigate the influence of a Markovian environment on the dynamics of
interacting spinful fermionic atoms in a lattice. In order to explore the
physical phenomena occurring at short times, we develop a method based on a
slave-spin representation of fermions which is amenable to the investigation of
the dynamics of dissipative systems. We apply this approach to two different
dissipative couplings which can occur in current experiments: a coupling via
the local density and a coupling via the local double occupancy. We complement
our study based on this novel method with results obtained using the adiabatic
elimination technique and with an exact study of a two-site model. We uncover
that the decoherence is slowed down by increasing either the interaction
strength or the dissipative coupling (the Zeno effect). We also find, for the
coupling to the local double occupancy, that the final steady state can sustain
single-particle coherence.",1407.1098v1
2014-11-18,Dynamical spin structure factor of one-dimensional interacting fermions,"We revisit the dynamic spin susceptibility, $\chi(q,\omega)$, of
one-dimensional interacting fermions. To second order in the interaction,
backscattering results in a logarithmic correction to $\chi(q,\omega)$ at $q\ll
k_F$, even if the single-particle spectrum is linearized near the Fermi points.
Consequently, the dynamic spin structure factor, $\mathrm{Im}\chi(q,\omega)$,
is non-zero at frequencies above the single-particle continuum. In the boson
language, this effect results from the marginally irrelevant backscattering
operator of the sine-Gordon model. Away from the threshold, the high-frequency
tail of $\mathrm{Im}\chi(q,\omega)$ due to backscattering is larger than that
due to finite mass by a factor of $k_F/q$. We derive the renormalization group
equations for the coupling constants of the $g$-ology model at finite $\omega$
and $q$ and find the corresponding expression for $\chi(q,\omega)$, valid to
all orders in the interaction but not in the immediate vicinity of the
continuum boundary, where the finite-mass effects become dominant.",1411.4993v1
2014-11-28,Hydrodynamic Regimes of Spinning Black D3-Branes,"We present the long-wavelength effective description of non-extremal spinning
black D3-branes in flat space. Our setup is motivated by recent explorations of
low energy dynamics on black brane world-volumes within the blackfold approach
and its connections to the fluid/gravity correspondence. The spinning D3-branes
with a rigid radial Dirichlet cut-off give rise to an effective field theory.
This theory describes a charged plasma which is driven by external forces,
given by one vector and two scalar operators. Furthermore, the flavour charge
of this plasma is anomalous, allowing us to examine features of anomaly-induced
transport in the blackfold context. We calculate the hydrodynamic transport
coefficients to first order and show that in the near-horizon limit, they
reproduce the conformal charged fluid dynamics of ${\cal N}=4$ Super Yang-Mills
theory. More generally the system interpolates smoothly between the blackfold,
fluid/gravity, and Rindler fluid dynamics.",1412.0020v1
2015-01-14,A spin-wave logic gate based on a width-modulated dynamic magnonic crystal,"An electric current controlled spin-wave logic gate based on a
width-modulated dynamic magnonic crystal is realized. The device utilizes a
spin-wave waveguide fabricated from a single-crystal Yttrium Iron Garnet film
and two conducting wires attached to the film surface. Application of electric
currents to the wires provides a means for dynamic control of the effective
geometry of the waveguide and results in a suppression of the magnonic band
gap. The performance of the magnonic crystal as an AND logic gate is
demonstrated.",1501.03486v2
2015-02-05,Comparing Post-Newtonian and Numerical-Relativity Precession Dynamics,"Binary black-hole systems are expected to be important sources of
gravitational waves for upcoming gravitational-wave detectors. If the spins are
not colinear with each other or with the orbital angular momentum, these
systems exhibit complicated precession dynamics that are imprinted on the
gravitational waveform. We develop a new procedure to match the precession
dynamics computed by post-Newtonian (PN) theory to those of numerical binary
black-hole simulations in full general relativity. For numerical relativity NR)
simulations lasting approximately two precession cycles, we find that the PN
and NR predictions for the directions of the orbital angular momentum and the
spins agree to better than $\sim 1^{\circ}$ with NR during the inspiral,
increasing to $5^{\circ}$ near merger. Nutation of the orbital plane on the
orbital time-scale agrees well between NR and PN, whereas nutation of the spin
direction shows qualitatively different behavior in PN and NR. We also examine
how the PN equations for precession and orbital-phase evolution converge with
PN order, and we quantify the impact of various choices for handling partially
known PN terms.",1502.01747v1
2015-05-17,Differences in the quasiparticle dynamics for one-band and three-band cuprate models,"We study the quasiparticles of the one-band $t$-$J$ and $t$-$t'$-$t""$-$J$
models using a variational approximation that includes spin fluctuations in the
vicinity of the hole. We explain why the spin fluctuations and the longer range
hopping have complementary contributions to the quasiparticle dynamics, and
thus why both are essential to obtain a dispersion in agreement with that
measured experimentally. This is very different from the three-band Emery model
in the strongly-correlated limit, where the same variational approximation
shows that spin fluctuations have a minor effect on the quasiparticle dynamics.
This difference proves that these one-band and three-band models describe
qualitatively different quasiparticles, and therefore they they cannot both be
suitable to describe the physics of underdoped cuprates.",1505.04405v1
2015-07-08,Simulating open quantum dynamics with time-dependent variational matrix product states: Towards microscopic correlation of environment dynamics and reduced system evolution,"Many-body approaches to open quantum systems have recently become powerful
tools for investigating the detailed role of dissipative environments in
diverse non-equilibrium molecular and condensed matter processes. Here, we
report the development of an efficient algorithm that utilises a time-dependent
variational principle for matrix product states to evolve large
system-environment states. By thus capturing all system-environment
correlations, we reproduce the highly non-perturbative, quantum-critical
dynamics of the zero temperature spin-boson model, and then exploit the
many-body information to output a complete time-frequency spectrum of the
environmental excitations. We highlight how theoretical 'environmental spectra'
could yield valuable insights into a wide range of complex dissipative
processes, by showing that correlated motion of modes entangled with the spin
can appear with persistent vibrational coherence, in spite of incoherent spin
relaxation.",1507.02202v2
2015-07-22,Dynamical properties of the honeycomb-lattice Iridates ${\rm Na_2IrO_3}$,"We investigate the dynamical properties of ${\rm Na_2IrO_3}$. For five
effective models proposed for ${\rm Na_2IrO_3}$, we numerically calculate
dynamical structure factors (DSFs) with an exact diagonalization method. An
effective model obtained from $ab$ $initio$ calculations explains inelastic
neutron scattering experiments adequately. We further calculate excitation
modes based on linearized spin-wave theory. The spin-wave excitation of the
effective models obtained by $ab$ $initio$ calculations disagrees with the
low-lying excitation of DSFs. We attribute this discrepancy to the location of
${\rm Na_2IrO_3}$ in a parameter space close to the phase boundary with the
Kitaev spin-liquid phase.",1507.06044v2
2015-11-28,Accessing Rydberg-dressed interactions using many-body Ramsey dynamics,"We demonstrate that Ramsey spectroscopy can be used to observe
Rydberg-dressed interactions. In contrast to many prior proposals, our scheme
operates comfortably within experimentally measured lifetimes, and accesses a
regime where quantum superpositions are crucial. The key idea is to build a
spin-1/2 from one level that is Rydberg-dressed and another that is not. These
levels may be hyperfine or long-lived electronic states. An Ising spin model
governs the Ramsey dynamics, for which we derive an exact solution. Due to the
structure of Rydberg interactions, the dynamics differs significantly from that
in other spin systems. As one example, spin echo can increase the rate at which
coherence decays. The results also apply to bare (undressed) Rydberg states as
a special case, for which we quantitatively reproduce recent ultrafast
experiments without fitting.",1511.08856v2
2016-02-02,Time-resolved spin-torque switching in MgO-based perpendicularly magnetized tunnel junctions,"We study ns scale spin-torque-induced switching in perpendicularly magnetized
tunnel junctions (pMTJ). Although the switching voltages match with the
macrospin instability threshold, the electrical signatures of the reversal
indicate the presence of domain walls in junctions of various sizes. In the
antiparallel (AP) to parallel (P) switching, a nucleation phase is followed by
an irreversible flow of a wall through the sample at an average velocity of 40
m/s with back and forth oscillation movements indicating a Walker propagation
regime. A model with a single-wall locally responding to the spin-torque
reproduces the essential dynamical signatures of the reversal. The P to AP
transition has a complex dynamics with dynamical back-hopping whose probability
increases with voltage. We attribute this back-hopping to the instability of
the nominally fixed layers.",1602.00894v1
2016-03-02,Electric-Field-Induced Spin Resonance in Antiferromagnetic Insulators: Inverse Process of the Dynamical Chiral Magnetic Effect,"We propose a realization of the electric-field-induced antiferromagnetic
resonance. We consider three-dimensional antiferromagnetic insulators with
spin-orbit coupling characterized by the existence of a topological term called
the $\theta$ term. By solving the Landau-Lifshitz-Gilbert equation in the
presence of the $\theta$ term, we show that, in contrast to conventional
methods using ac magnetic fields, the antiferromagnetic resonance state is
realized by ac electric fields along with static magnetic fields. This
mechanism can be understood as the inverse process of the dynamical chiral
magnetic effect, an alternating current generation by magnetic fields. In other
words, we propose a way to electrically induce the dynamical axion field in
condensed matter. We discuss a possible experiment to observe our proposal,
which utilizes the spin pumping from the antiferromagnetic insulator into a
heavy metal contact.",1603.00614v3
2016-04-27,Spin dynamics of large-spin (spinor) fermions in a harmonic trap,"Understanding the collective dynamics in a many-body system has been a
central task in condensed matter physics. To achieve this task, we develop a
Hartree-Fock theory to study the collective oscillations of spinor Fermi
system, motivated by recent experiment on spin-9/2 fermions. We observe an
oscillation period shoulder for small rotation angles. Different from previous
studies, where the shoulder is found connected to the resonance from periodic
to running phase, here the system is always in a running phase in the two-body
phase space. This shoulder survives even in the many-body oscillations, which
could be tested in the experiments. We also show how these collective
oscillations evolve from two- to many-body. Our theory provides an alternative
way to understand the collective dynamics in large-spin Fermi systems.",1604.07933v3
2016-06-21,Torsion Effects and LLG Equation,"Based on the non-relativistic regime of the Dirac equation coupled to a
torsion pseudo-vector, we study the dynamics of magnetization and how it is
affected by the presence of torsion. We consider that torsion interacting terms
in Dirac equation appear in two ways one of these is thhrough the covariant
derivative considering the spin connection and gauge magnetic field and the
other is through a non-minimal spin torsion coupling. We show within this
framework, that it is possible to obtain the most general Landau, Lifshitz and
Gilbert (LLG) equation including the torsion effects, where we refer to torsion
as a geometric field playing an important role in the spin coupling process. We
show that the torsion terms can give us two important landscapes in the
magnetization dynamics: one of them related with damping and the other related
with the screw dislocation that give us a global effect like a helix damping
sharped. These terms are responsible for changes in the magnetization
precession dynamics.",1606.06610v1
2016-10-10,QuSpin: a Python Package for Dynamics and Exact Diagonalisation of Quantum Many Body Systems part I: spin chains,"We present a new open-source Python package for exact diagonalization and
quantum dynamics of spin(-photon) chains, called QuSpin, supporting the use of
various symmetries in 1-dimension and (imaginary) time evolution for chains up
to 32 sites in length. The package is well-suited to study, among others,
quantum quenches at finite and infinite times, the Eigenstate Thermalisation
hypothesis, many-body localisation and other dynamical phase transitions,
periodically-driven (Floquet) systems, adiabatic and counter-diabatic ramps,
and spin-photon interactions. Moreover, QuSpin's user-friendly interface can
easily be used in combination with other Python packages which makes it
amenable to a high-level customisation. We explain how to use QuSpin using four
detailed examples: (i) Standard exact diagonalisation of XXZ chain (ii)
adiabatic ramping of parameters in the many-body localised XXZ model, (iii)
heating in the periodically-driven transverse-field Ising model in a parallel
field, and (iv) quantised light-atom interactions: recovering the
periodically-driven atom in the semi-classical limit of a static Hamiltonian.",1610.03042v4
2016-10-18,Neural Network for Quantum Brain Dynamics: 4D CP$^1$+U(1) Gauge Theory on Lattice and its Phase Structure,"We consider a system of two-level quantum quasi-spins and gauge bosons put on
a 3+1D lattice. As a model of neural network of the brain functions, these
spins describe neurons quantum-mechanically, and the gauge bosons describes
weights of synaptic connections. It is a generalization of the Hopfield model
to a quantum network with dynamical synaptic weights. At the microscopic level,
this system becomes a model of quantum brain dynamics proposed by Umezawa et
al., where spins and gauge field describe water molecules and photons,
respectively. We calculate the phase diagram of this system under quantum and
thermal fluctuations, and find that there are three phases; confinement,
Coulomb, and Higgs phases. Each phase is classified according to the ability to
learn patterns and recall them. By comparing the phase diagram with that of
classical networks, we discuss the effect of quantum fluctuations and thermal
fluctuations (noises in signal propagations) on the brain functions.",1610.05443v1
2017-03-28,A general method to describe intersystem crossing dynamics in trajectory surface hopping,"Intersystem crossing is a radiationless process that can take place in a
molecule irradiated by UV-Vis light, thereby playing an important role in many
environmental, biological and technological processes. This paper reviews
different methods to describe intersystem crossing dynamics, paying attention
to semiclassical trajectory theories, which are especially interesting because
they can be applied to large systems with many degrees of freedom. In
particular, a general trajectory surface hopping methodology recently developed
by the authors, which is able to include non-adiabatic and spin-orbit couplings
in excited-state dynamics simulations, is explained in detail. This method,
termed SHARC, can in principle include any arbitrary coupling, what makes it
generally applicable to photophysical and photochemical problems, also those
including explicit laser fields. A step-by-step derivation of the main
equations of motion employed in surface hopping based on the fewest-switches
method of Tully, adapted for the inclusion of spin-orbit interactions, is
provided. Special emphasis is put on describing the different possible choices
of the electronic bases in which spin-orbit can be included in surface hopping,
highlighting the advantages and inconsistencies of the different approaches.",1703.09456v1
2017-08-02,Logarithmically Slow Relaxation in Quasi-Periodically Driven Random Spin Chains,"We simulate the dynamics of a disordered interacting spin chain subject to a
quasi-periodic time-dependent drive, corresponding to a stroboscopic Fibonacci
sequence of two distinct Hamiltonians. Exploiting the recursive drive
structure, we can efficiently simulate exponentially long times. After an
initial transient, the system exhibits a long-lived glassy regime characterized
by a logarithmically slow growth of entanglement and decay of correlations
analogous to the dynamics at the many-body delocalization transition.
Ultimately, at long time-scales, which diverge exponentially for weak or rapid
drives, the system thermalizes to infinite temperature. The slow relaxation
enables metastable dynamical phases, exemplified by a ""time quasi-crystal"" in
which spins exhibit persistent oscillations with a distinct quasi-periodic
pattern from that of the drive. We show that in contrast with Floquet systems,
a high-frequency expansion strictly breaks down above fourth order, and fails
to produce an effective static Hamiltonian that would capture the pre-thermal
glassy relaxation.",1708.00865v2
2018-02-02,Stochastic model for quantum spin dynamics in magnetic nanostructures,"We develop a numerical model that reproduces the thermal equilibrium and the
spin transfer mechanisms in magnetic nanomaterials. We analyze the coherent
two-particle spin exchange interaction and the electron-electron collisions.
Our study is based on a quantum atomistic approach and the particle dynamics is
performed by using a Monte Carlo technique. The coherent quantum evolution of
the atoms is interrupted by instantaneous collisions with itinerant electrons.
The collision processes are associated to the quantum collapse of the local
atomic wave function. We show that particle-particle interactions beyond the
molecular field approximation can be included in this framework. Our model is
able to reproduce the thermal equilibrium and strongly out-of-equilibrium
phenomena such as the ultrafast dynamics of the magnetization in nanomatrials.",1802.00663v1
2020-07-15,Magnetic Charge Propagation upon a 3D Artificial Spin-ice,"Magnetic charge propagation in bulk frustrated materials has yielded a
paradigm-shift in science, allowing the symmetry between electricity and
magnetism to be studied. Recent work is now suggesting magnetic charge dynamics
upon the spin-ice surface may have important implications in determining the
ordering and associated phase space. Here we detail a 3D artificial spin-ice, a
3D nanostructured array of magnetic islands which captures the exact geometry
of bulk systems, allowing field-driven dynamics of magnetic charge to be
directly visualized upon the surface. Using magnetic microscopy, we observe
vastly different magnetic charge dynamics along two principle directions. These
striking differences are found to be due to the surface-termination and
associated coordination which yields different energetics and interaction
strengths for magnetic charges upon the surface.",2007.07618v2
2020-07-28,Dynamical Zeeman resonance in spin-orbit-coupled spin-1 Bose gases,"We predict a dynamical resonant effect, which is driven by externally applied
linear and quadratic Zeeman fields, in a spin-orbit-coupled spin-1
Bose-Einstein condensate. The Bose-Einstein condensate is assumed to be
initialized in some superposed state of Zeeman sublevels and subject to a
sudden shift of the trapping potential. It is shown that the time-averaged
center-of-mass oscillation and the spin polarizations of the Bose-Einstein
condensate exhibit remarkable resonant peaks when the Zeeman fields are tuned
to certain strengths. The underlying physics behind this resonance can be
traced back to the out-of-phase interference of the dynamical phases carried by
different spinorbit states. By analyzing the single particle spectrum, the
resonant condition is summarized as a simple algebraic relation, connecting the
strengths of the linear and quadratic Zeeman fields. This property is
potentially applicable in quantum information and quantum precision
measurement.",2007.14131v1
2010-05-03,Dynamics of two coupled vortices in a spin valve nanopillar excited by spin transfer torque,"We investigate the dynamics of two coupled vortices driven by spin transfer.
We are able to independently control with current and perpendicular field, and
to detect, the respective chiralities and polarities of the two vortices. For
current densities above $J=5.7*10^7 A/cm^2$, a highly coherent signal
(linewidth down to 46 kHz) can be observed, with a strong dependence on the
relative polarities of the vortices. It demonstrates the interest of using
coupled dynamics in order to increase the coherence of the microwave signal.
Emissions exhibit a linear frequency evolution with perpendicular field, with
coherence conserved even at zero magnetic field.",1005.0290v2
2016-11-15,Dynamical and Reversible Control of Topological Spin Textures,"Recent observations of topological spin textures brought spintronics one step
closer to new magnetic memories. Nevertheless, the existence of Skyrmions, as
well as their stabilization, require very specific intrinsic magnetic
properties which are usually fixed in magnets. Here we address the possibility
to dynamically control their intrinsic magnetic interactions by varying the
strength of a high-frequency laser field. It is shown that drastic changes can
be induced in the antiferromagnetic exchange interactions and the latter can
even be reversed to become ferromagnetic, provided the direct exchange is
already non-negligible in equilibrium as predicted, for example, in Si doped
with C, Sn, or Pb adatoms. In the presence of Dzyaloshinskii-Moriya
interactions, this enables us to tune features of ferromagnetic Skyrmions such
as their radius, making them easier to stabilize. Alternatively, such
topological spin textures can occur in frustrated triangular lattices. Then, we
demonstrate that a high-frequency laser field can induce dynamical frustration
in antiferromagnets, where the degree of frustration can subsequently be tuned
suitably to drive the material toward a Skyrmionic phase.",1611.05075v2
2017-04-08,Dynamical Stochastic Higher Spin Vertex Models,"We introduce a new family of integrable stochastic processes, called
\textit{dynamical stochastic higher spin vertex models}, arising from fused
representations of Felder's elliptic quantum group $E_{\tau, \eta}
(\mathfrak{sl}_2)$. These models simultaneously generalize the stochastic
higher spin vertex models, studied by Corwin-Petrov and Borodin-Petrov, and are
dynamical in the sense of Borodin's recent stochastic interaction round-a-face
models.
  We provide explicit contour integral identities for observables of these
models (when run under specific types of initial data) that characterize the
distributions of their currents. Through asymptotic analysis of these
identities in a special case, we evaluate the scaling limit for the current of
a dynamical version of a discrete-time partial exclusion process. In
particular, we show that its scaling exponent is $1 / 4$ and that its one-point
marginal converges (in a sense of moments) to that of a non-trivial random
variable, which we determine explicitly.",1704.02499v1
2008-07-10,Study of the Hubbard model on the triangular lattice using dynamical cluster approximation and dual fermion methods,"We investigate the Hubbard model on the triangular lattice at half-filling
using the dynamical cluster approximation (DCA) and dual fermion (DF) methods
in combination with continuous-time quantum Monte carlo (CT QMC) and
semiclassical approximation (SCA) methods. We study the one-particle properties
and nearest-neighbor spin correlations using the DCA method. We calculate the
spectral functions using the CT QMC and SCA methods. The spectral function in
the SCA and obtained by analytic continuation of the Pade approximation in CT
QMC are in good agreement. We determine the metal-insulator transition (MIT)
and the hysteresis associated with a first-order transition in the double
occupancy and nearest-neighbor spin correlation functions as a function of
temperature. As a further check, we employ the DF method and discuss the
advantages and limitation of the dynamical mean field theory (DMFT), DCA and
recently developed DF methods by comparing Green's functions. We find an
enhancement of antiferromagnetic (AF) correlations and provide evidence for
magnetically ordered phases by calculating the spin susceptibility.",0807.1683v1
2008-07-16,Classical big-bounce cosmology: dynamical analysis of a homogeneous and irrotational Weyssenhoff fluid,"A dynamical analysis of an effective homogeneous and irrotational Weyssenhoff
fluid in general relativity is performed using the 1+3 covariant approach that
enables the dynamics of the fluid to be determined without assuming any
particular form for the space-time metric. The spin contributions to the field
equations produce a bounce that averts an initial singularity, provided that
the spin density exceeds the rate of shear. At later times, when the spin
contribution can be neglected, a Weyssenhoff fluid reduces to a standard
cosmological fluid in general relativity. Numerical solutions for the time
evolution of the generalised scale factor in spatially-curved models are
presented, some of which exhibit eternal oscillatory behaviour without any
singularities. In spatially-flat models, analytical solutions for particular
values of the equation-of-state parameter are derived. Although the scale
factor of a Weyssenhoff fluid generically has a positive temporal curvature
near a bounce, it requires unreasonable fine tuning of the equation-of-state
parameter to produce a sufficiently extended period of inflation to fit the
current observational data.",0807.2523v2
2011-11-10,Magnetic friction: From Stokes to Coulomb behavior,"We demonstrate that in a ferromagnetic substrate, which is continuously
driven out of equilibrium by a field moving with constant velocity $v$, at
least two types of friction may occur when $v$ goes to zero: The substrate may
feel a friction force proportional to $v$ (Stokes friction), if the field
changes on a time scale which is longer than the intrinsic relaxation time. On
the other hand, the friction force may become independent of $v$ in the
opposite case (Coulomb friction). These observations are analogous to e.g.
solid friction. The effect is demonstrated in both, the Ising (one spin
dimension) and the Heisenberg model (three spin dimensions), irrespective which
kind of dynamics (Metropolis spin-flip dynamics or Landau-Lifshitz-Gilbert
precessional dynamics) is used. For both models the limiting case of Coulomb
friction can be treated analytically. Furthermore we present an empiric
expression reflecting the correct Stokes behavior and therefore yielding the
correct cross-over velocity and dissipation.",1111.2494v1
2012-01-30,Non-contact Friction and Relaxational Dynamics of Surface Defects,"Motion of cantilever near sample surfaces exhibits additional friction even
before two bodies come into mechanical contact. Called non-contact friction
(NCF), this friction is of great practical importance to the ultrasensitive
force detection measurements. Observed large NCF of a micron-scale cantilever
found anomalously large damping that exceeds theoretical predictions by 8-11
orders of magnitude. This finding points to contribution beyond fluctuating
electromagnetic fields within van der Waals approach. Recent experiments
reported by Saitoh et al. (Phys. Rev. Lett. 105, 236103 (2010)) also found
nontrivial distance dependence of NCF. Motivated by these observations, we
propose a mechanism based on the coupling of cantilever to the relaxation
dynamics of surface defects. We assume that the surface defects couple to the
cantilever tip via spin-spin coupling and their spin relaxation dynamics gives
rise to the backaction terms and modifies both the friction coefficient and the
spring constant. We explain the magnitude, as well as the distance dependence
of the friction due to these backaction terms. Reasonable agreement is found
with the experiments.",1201.6378v1
2013-09-21,Implementation of dynamically corrected gates for single-spin qubits,"Precise control of an open quantum system is critical to quantum information
processing, but is challenging due to inevitable interactions between the
quantum system and the environment. We demonstrated experimentally at room
temperature a type of dynamically corrected gates on the nitrogen-vacancy
centers in diamond. The infidelity of quantum gates caused by environment
nuclear spin bath is reduced from being the second-order to the sixth-order of
the noise to control field ratio, which offers greater efficiency in reducing
the infidelity by reducing the noise level. The decay time of the coherent
oscillation driven by dynamically corrected gates is shown to be two orders of
magnitude longer than the dephasing time, and is essentially limited by
spin-lattice relaxation. The infidelity of DCG, which is actually constrained
by the decay time, reaches $4\times 10^{-3}$ at room temperature and is further
reducible by 2-3 orders of magnitudes via lowering temperature. The greatly
reduced noise dependence of infidelity and the uttermost extension of the
coherent time mark an important step towards fault-tolerant quantum computation
in realistic systems.",1309.5424v1
2016-08-12,Ultrafast inhomogeneous magnetization dynamics analyzed by interface-sensitive nonlinear magneto-optics,"We analyze laser-induced ultrafast, spatially inhomogeneous magnetization
dynamics of epitaxial Co/Cu(001) films in a 0.4-10 nm thickness range with
time-resolved magnetization-induced second harmonic generation, which probes
femtosecond spin dynamics at the vacuum/Co and Co/Cu interfaces. The
interference of these two contributions makes the overall signal particularly
sensitive to differences in the transient magnetization redistribution between
the two interfaces, i.e. ultrafast magnetization profiles in the ferromagnetic
film. We find in films of up to 3 nm thickness a stronger demagnetization at
the surface, because the film thickness is smaller than the effective mean free
path of the spin current mediating the demagnetization, i.e. the difference
between the mean free paths of the majority and minority carriers. For film
thicknesses larger than 3 nm, the magnetization profile reverses, since
majority spins can escape into the conducting substrate only from the
interface-near region.",1608.03842v1
2016-12-19,Geometric representation of spin correlations and applications to ultracold systems,"We provide a one-to-one map between the spin correlations and certain
three-dimensional shapes, analogous to the map between single spins and Bloch
vectors, and demonstrate its utility. Much as one can reason geometrically
about dynamics using a Bloch vector -- e.g. a magnetic field causes it to
precess and dissipation causes it to shrink -- one can reason similarly about
the shapes we use to visualize correlations. This visualization demonstrates
its usefulness by unveiling the hidden structure in the correlations. For
example, seemingly complex correlation dynamics can be described as simple
motions of the shapes. We demonstrate the simplicity of the dynamics, which is
obscured in conventional analyses, by analyzing several physical systems of
relevance to cold atoms.",1612.06459v2
2017-06-19,Magnetic Excitations and Continuum of a Field-Induced Quantum Spin Liquid in $α$-RuCl$_3$,"We report on terahertz spectroscopy of quantum spin dynamics in
$\alpha$-RuCl$_3$, a system proximate to the Kitaev honeycomb model, as a
function of temperature and magnetic field. An extended magnetic continuum
develops below the structural phase transition at $T_{s2}=62$K. With the onset
of a long-range magnetic order at $T_N=6.5$K, spectral weight is transferred to
a well-defined magnetic excitation at $\hbar \omega_1 = 2.48$meV, which is
accompanied by a higher-energy band at $\hbar \omega_2 = 6.48$meV. Both
excitations soften in magnetic field, signaling a quantum phase transition at
$B_c=7$T where we find a broad continuum dominating the dynamical response.
Above $B_c$, the long-range order is suppressed, and on top of the continuum,
various emergent magnetic excitations evolve. These excitations follow clear
selection rules and exhibit distinct field dependencies, characterizing the
dynamical properties of the field-induced quantum spin liquid.",1706.06157v1
2017-07-20,Quantum dynamics in transverse-field Ising models from classical networks,"The efficient representation of quantum many-body states with classical
resources is a key challenge in quantum many-body theory. In this work we
analytically construct classical networks for the description of the quantum
dynamics in transverse-field Ising models that can be solved efficiently using
Monte Carlo techniques. Our perturbative construction encodes time-evolved
quantum states of spin-1/2 systems in a network of classical spins with local
couplings and can be directly generalized to other spin systems and higher
spins. Using this construction we compute the transient dynamics in one, two,
and three dimensions including local observables, entanglement production, and
Loschmidt amplitudes using Monte Carlo algorithms and demonstrate the accuracy
of this approach by comparisons to exact results. We include a mapping to
equivalent artificial neural networks, which were recently introduced to
provide a universal structure for classical network wave functions.",1707.06656v4
2017-12-07,Dynamical properties of dissipative XYZ Heisenberg lattices,"We study dynamical properties of dissipative XYZ Heisenberg lattices where
anisotropic spin-spin coupling competes with local incoherent spin flip
processes. In particular, we explore a region of the parameter space where
dissipative magnetic phase transitions for the steady state have been recently
predicted by mean-field theories and exact numerical methods. We investigate
the asymptotic decay rate towards the steady state both in 1D (up to the
thermodynamical limit) and in finite-size 2D lattices, showing that critical
dynamics does not occur in 1D, but it can emerge in 2D. We also analyze the
behavior of individual homodyne quantum trajectories, which well reveal the
nature of the transition.",1712.02716v2
2019-07-04,Resonant Acoustic Wave Assisted Spin-Transfer-Torque Switching of Nanomagnets,"We report the possibility of achieving an order of magnitude reduction in the
energy dissipation needed to write bits in perpendicular magnetic tunnel
junctions (p-MTJs) by simulating the magnetization dynamics under a combination
of resonant surface acoustic waves (r-SAW) and spin-transfer-torque (STT). The
magnetization dynamics were simulated using the Landau-Lifshitz-Gilbert
equation under macrospin assumption with the inclusion of thermal noise. The
resonant magnetization dynamics in the magnetostrictive nanomagnet build over
few 10s of cycles of SAW application that drives the magnetization to precess
in a cone with a deflection of ~45 degrees from the perpendicular direction.
This reduces the STT current density required to switch the magnetization
direction without increasing the STT application time or degrading the
switching probability in the presence of room temperature thermal noise. This
could lead to a pathway to achieve energy efficient switching of spin transfer
torque random access memory (STTRAM) whose lateral dimensions can be scaled
aggressively despite using materials with low magnetostriction by employing
resonant excitation.",1907.02255v1
2019-07-04,Different types of torsion and their effect on the dynamics of fields,"One of the formalisms that introduces torsion conveniently in gravity is the
vierbein-Einstein-Palatini (VEP) formalism. The independent variables are the
vierbein (tetrads) and the components of the spin connection. The latter can be
eliminated in favor of the tetrads using the equations of motion in the absence
of fermions; otherwise there is an effect of torsion on the dynamics of fields.
We find that the conformal transformation of off-shell spin connection is not
uniquely determined unless additional assumptions are made. One possibility
gives rise to Nieh-Yan theory, another one to conformally invariant torsion; a
one-parameter family of conformal transformations interpolates between the two.
We also find that for dynamically generated torsion the spin connection does
not have well defined conformal properties. In particular, it affects fermions
and the non-minimally coupled conformal scalar field.",1907.02341v1
2019-07-05,Spinning drop dynamics in miscible and immiscible environments,"We report on the extensional dynamics of spinning drops in miscible and
immiscible background fluids following a rotation speed jump. Two radically
different behaviours are observed. Drops in immiscible environments relax
exponentially to their equilibrium shape, with a relaxation time that does not
depend on the centrifugal forcing. We find an excellent quantitative agreement
with the relaxation time predicted for quasi-spherical drops by Stone and Bush
(Q. Appl. Math. 54, 551 (1996)), while other models proposed in the literature
fail to capture our data. By contrast, drops immersed in a miscible background
fluid do not relax to a steady shape: they elongate indefinitely, their length
following a power-law $l(t)\sim t^{\frac{2}{5}}$ in very good agreement with
the dynamics predicted by Lister and Stone (J. Fluid Mech. 317, 275 (1996)) for
inviscid drops. Our results strongly suggest that low compositional gradients
in miscible fluids do not give rise to an effective interfacial tension
measurable by spinning drop tensiometry.",1907.02802v1
2019-10-23,Gauging Defects in Quantum Spin Systems,"The goal of this work is to build a dynamical theory of defects for quantum
spin systems. A kinematic theory for an indefinite number of defects is first
introduced exploiting distinguishable Fock space. Dynamics are then
incorporated by allowing the defects to become mobile via a microscopic
Hamiltonian. This construction is extended to topologically ordered systems by
restricting to the ground state eigenspace of Hamiltonians generalizing the
golden chain. We illustrate the construction with the example of a spin chain
with $\mathbf{Vec}(\mathbb{Z}/2\mathbb{Z})$ fusion rules, employing generalized
tube algebra techniques to model the defects in the chain. The resulting
dynamical defect model is equivalent to the critical transverse Ising model.",1910.10619v1
2019-10-31,Quantum critical nematic fluctuations and spin excitation anisotropy in iron pnictides,"Quantum criticality in iron pnictides involves both the nematic and
antiferromagnetic degrees of freedom, but the relationship between the two
types of fluctuations has yet to be clarified. Here we study this problem in
the presence of a small external uniaxial potential, which breaks the
$C_4$-symmetry in the B$_{1g}$ sector. We establish an identity that connects
the spin excitation anisotropy, which is the difference of the dynamical spin
susceptibilities at $\vec{Q}_1=\left(\pi,0\right)$ and
$\vec{Q}_2=\left(0,\pi\right)$, with the dynamical magnetic susceptibility and
static nematic susceptibility. Using this identity, we introduce a scaling
procedure to determine the dynamical nematic susceptibility in the quantum
critical regime, and illustrate the procedure for the case of the optimally
Ni-doped BaFe$_2$As$_2$[Y. Song \textit{et al.}, Phys. Rev. B 92, 180504
(2015)]. The implications of our results for the overall physics of the
iron-based superconductors are discussed.",1910.14597v4
2020-02-26,Control of spin dynamics in artificial honeycomb spin-ice-based nanodisks,"We report the experimental and theoretical characterization of the
angular-dependent spin dynamics in arrays of ferromagnetic nanodisks arranged
on a honeycomb lattice. The magnetic field and microwave frequency dependence,
measured by broadband ferromagnetic resonance, reveal a rich spectrum of modes
that is strongly affected by the microstate of the network. Based on symmetry
arguments with respect to the external field, we show that certain parts of the
ferromagnetic network contribute to the detected signal. A comparison of the
experimental data with micromagnetic simulations reveals that different
subsections of the lattice predominantly contribute to the high-frequency
response of the array. This is confirmed by optical characterizations using
microfocused Brillouin light scattering. Furthermore, we find indications that
nucleation and annihilation of vortex-like magnetization configurations in the
low-field range affect the dynamics, which is different from clusters of
ferromagnetic nanoellipses. Our work opens up new perspectives for designing
magnonic devices that combine geometric frustration in gyrotropic vortex
crystals at low frequencies with magnonic crystals at high frequencies.",2002.11694v1
2020-04-08,Hybrid Quantum Annealing via Molecular Dynamics,"A novel quantum-classical hybrid scheme is proposed to efficiently solve
large-scale combinatorial optimization problems. The key concept is to
introduce a Hamiltonian dynamics of the classical flux variables associated
with the quantum spins of the transverse-field Ising model. Molecular dynamics
of the classical fluxes can be used as a powerful preconditioner to sort out
the frozen and ambivalent spins for quantum annealers. The performance and
accuracy of our smooth hybridization in comparison to the standard classical
algorithms (the tabu search and the simulated annealing) are demonstrated by
employing the MAX-CUT and Ising spin-glass problems.",2004.03972v2
2020-12-04,Nutation in antiferromagnetic resonance,"The effect of inertial spin dynamics is compared between ferromagnetic,
antiferromagnetic and ferrimagnetic systems. The linear response to an
oscillating external magnetic field is calculated within the framework of the
inertial Landau--Lifshitz--Gilbert equation using analytical theory and
computer simulations. Precession and nutation resonance peaks are identified,
and it is demonstrated that the precession frequencies are reduced by the spin
inertia, while the lifetime of the excitations is enhanced. The interplay
between precession and nutation is found to be the most prominent in
antiferromagnets, where the timescale of the exchange-driven sublattice
dynamics is comparable to inertial relaxation times. Consequently,
antiferromagnetic resonance techniques should be better suited for the search
for intrinsical inertial spin dynamics on ultrafast timescales than
ferromagnetic resonance.",2012.02790v3
2020-12-18,Superradiant phase transition with cavity assisted dynamical spin-orbit coupling,"Superradiant phase transition represents an important quantum phenomenon that
shows the collective excitations based on the coupling between atoms and cavity
modes. The spin-orbit coupling is another quantum effect which induced from the
interaction of the atom internal degrees of freedom and momentum of
center-of-mass. In this work, we consider the cavity assisted dynamical
spin-orbit coupling which comes from the combination of these two effects. It
can induce a series of interesting quantum phenomena, such as the flat spectrum
and the singularity of the excitation energy spectrum around the critical point
of quantum phase transition. We further discuss the influence of atom decay and
nonlinear coupling to the phase diagram. The atom decay suppresses the
singularity of the phase diagram and the nonlinear coupling can break the
symmetric properties of the phase transition. Our work provide the theoretical
methods to research the rich quantum phenomena in this dynamic many-body
systems.",2012.10098v1
2020-12-21,Explicit volume-preserving numerical schemes for relativistic trajectories and spin dynamics,"A class of explicit numerical schemes is developed to solve for the
relativistic dynamics and spin of particles in electromagnetic fields, using
the Lorentz-BMT equation formulated in the Clifford algebra representation of
Baylis. It is demonstrated that these numerical methods, reminiscent of the
leapfrog and Verlet methods, share a number of important properties: they are
energy-conserving, volume-conserving and second order convergent. These
properties are analysed empirically by benchmarking against known analytical
solutions in constant uniform electrodynamic fields. It is demonstrated that
the numerical error in a constant magnetic field remains bounded for long time
simulations in contrast to the Boris pusher, whose angular error increases
linearly with time. Finally, the intricate spin dynamics of a particle is
investigated in a plane wave field configuration.",2012.11652v1
2012-05-10,Dipolar broadening of nuclear spin resonance under dynamical pumping,"We study the polarisation dependence of the homogeneously broadened nuclear
spin resonance in a crystal. We employ a combinatorial method to restrict the
nuclear states to a fixed polarisation and show that the centre of the
resonance is shifted linearly with the nuclear polarisation by up to the zero
polarisation line width. The width shrinks from its maximum value at zero
polarisation to zero at full polarisation. This suggests to use the line shape
as a direct measure of nuclear polarisation reached under dynamical pumping. In
the limit of single quantum of excitation above the fully ferromagnetic state,
we provide an explicit solution to the problem of nuclear spin dynamics which
links a bound on the fastest decay rate to the observable width of the
resonance line.",1205.2189v1
2012-05-18,Decoherence in an infinite range Heisenberg model,"We study decoherence in an infinite range Heisenberg model (IRHM) in the two
situations where the system is coupled to a bath of either local optical
phonons or global optical phonons. Using a non-perturbative treatment, we
derive an effective Hamiltonian that is valid in the regime of strong
spin-phonon coupling under non-adiabatic conditions. It is shown that the
effective Hamiltonian commutes with the IRHM and thus has the same eigenstates
as the IRHM. By analyzing the dynamics of the system using a quantum master
equation approach, we show that the quantum states of the IRHM system do not
decohere under Markovian dynamics when the spins interact with local phonons.
For interactions with global phonons, the off-diagonal matrix elements of the
system's reduced density matrix, obtained for non-Markovian dynamics, do not
indicate decoherence only when states with the same $S^z_T$ (i.e., eigenvalue
for the z-component of the total spin) are considered.",1205.4093v3
2017-05-31,Valley Dynamics of Excitons in Monolayer Dichalcogenides,"Monolayer transition-metal dichalcogenides (TMDCs) have recently emerged as
possible candidates for valleytronic applications, as the spin and valley
pseudospin are directly coupled and stabilized by a large spin splitting. In
these semiconducting materials, optically excited electron-hole pairs form
tightly Coulomb-bound excitons with large binding energies. The selection rules
for excitonic transitions allow for direct optical generation of a
valley-polarized exciton population using resonant excitation. Here, we
investigate the exciton valley dynamics in monolayers of three different TMDCs
by means of time-resolved Kerr rotation at low temperatures. We observe
pronounced differences in the valley dynamics of tungsten- and molybdenum-based
TMDCs, which are directly related to the opposite order of the conduction-band
spin splitting in these materials.",1705.10988v2
2017-11-11,Fast forward of adiabatic spin dynamics of entangled states,"We develop a scheme of fast forward of adiabatic spin dynamics of quantum
entangled states. We settle the quasi-adiabatic dynamics by adding the
regularization terms to the original Hamiltonian and then accelerate it with
use of a large time-scaling factor. Assuming the experimentally-realizable
candidate Hamiltonian consisting of the exchange interactions and magnetic
field, we solved the regularization terms. These terms multiplied by the
velocity function give rise to the state-dependent counter-diabatic terms. The
scheme needs neither knowledge of full spectral properties of the system nor
solving the initial and boundary value problem. Our fast forward Hamiltonian
generates a variety of state-dependent counter-diabatic terms for each of
adiabatic states, which can include the state-independent one. We highlight
this fact by using minimum (two-spin) models for a simple transverse Ising
model, quantum annealing and generation of entanglement.",1711.04074v2
2018-06-16,Ultrafast dissipative spin-state dynamics triggered by X-ray pulse trains,"Frontiers of attosecond science are constantly shifting, thus addressing more
and more intricate effects with increasing resolution. Ultrashort pulses offer
a practical way to prepare complex superpositions of quantum states, follow,
and steer their dynamics. In this contribution, an ultrafast spin-flip process
triggered by sub-femtosecond (fs) excitation and strong spin-orbit coupling
between 2p core-excited states of a transition metal complex is investigated
using density matrix-based time-dependent restricted active space configuration
interaction theory. The effect of the nuclear vibrations is incorporated making
use of an electronic system plus vibrational bath partitioning. The differences
between isolated sub-fs pulses and pulse trains as well as influence of various
pulse characteristics on the initiated dynamics are discussed. The effect under
study can be potentially used for ultrafast clocking in sub-few fs experiments.",1806.06262v1
2018-08-02,Bounding flows for spherical spin glass dynamics,"We introduce a new approach to studying spherical spin glass dynamics based
on differential inequalities for one-time observables. Using this approach, we
obtain an approximate phase diagram for the evolution of the energy $H$ and its
gradient under Langevin dynamics for spherical $p$-spin models. We then derive
several consequences of this phase diagram. For example, at any temperature,
uniformly over all starting points, the process must reach and remain in an
absorbing region of large negative values of $H$ and large (in norm) gradients
in order 1 time. Furthermore, if the process starts in a neighborhood of a
critical point of $H$ with negative energy, then both the gradient and energy
must increase macroscopically under this evolution, even if this critical point
is a saddle with index of order $N$. As a key technical tool, we estimate
Sobolev norms of spin glass Hamiltonians, which are of independent interest.",1808.00929v2
2018-12-04,Ultra-slow dynamics in a translationally invariant spin model for multiplication and factorization,"We construct a model of short-range interacting Ising spins on a
translationally invariant two-dimensional lattice that mimics a reversible
circuit that multiplies or factorizes integers, depending on the choice of
boundary conditions. We prove that, for open boundary conditions, the model
exhibits no finite-temperature phase transition. Yet we find that it displays
glassy dynamics with astronomically slow relaxation times, numerically
consistent with a double exponential dependence on the inverse temperature. The
slowness of the dynamics arises due to errors that occur during thermal
annealing that cost little energy but flip an extensive number of spins. We
argue that the energy barrier that needs to be overcome in order to heal such
defects scales linearly with the correlation length, which diverges
exponentially with inverse temperature, thus yielding the double exponential
behavior of the relaxation time.",1812.01621v1
2018-12-05,Open system approach to non-equilibrium dynamical theory of quantum dot systems,"We theoretically investigate the non-equilibrium quantum dynamical theory of
a quantum dot system coupled to fermionic reservoirs using the recently
developed stochastic fermionic quantum state diffusion (FQSD) equation. The
exact or approximate dynamical equations associated with the FQSD equation can
describe the non-equilibrium quantum transport processes beyond the long-time
limit leading to a steady state. We study in details the electron transport of
a quantum-dot system coupled to two fermionic environments with different
chemical potentials. We report the onset of Coulomb blockade in quantum dots in
two distinctive cases: one involving a spin degeneracy one-quantum dot model,
and the other a specific spin non-degeneracy two-quantum dot model. While the
spin degeneracy case shows that the current in the quantum dot may be blockaded
non-monotonically with respect to Coulomb energy, the non-degeneracy case
exhibits significant non-Markovian effects, and it enables us to study the
relations between initial conditions of the dots and the steady state currents.",1812.02231v1
2018-12-06,Selective measurement of charge dynamics in an ensemble of nitrogen-vacancy centers in nano- and bulk diamonds,"Nitrogen-vacancy (NV) centers in diamond have attracted considerable interest
in sensing of weak magnetic fields, such as those created by biological
systems. Detecting such feeble signals requires near-surface NV centers, to
reduce the distance between NVs and sources. Moreover, dense ensembles of NVs
are highly desirable to reduce measurement time. However, robust charge state
switching is often observed in these systems, resulting in a complex interplay
between charge and spin dynamics that can reduce the attainable level of spin
polarization, and consequently, sensitivity. Understanding the mechanisms
behind charge state switching is, therefore, crucial to developing NV based
sensors. Here, we demonstrate a novel method to selectively measure charge
dynamics in an ensemble of NVs by quenching the spin polarization using an
off-axis magnetic field. Utilizing this technique, we show that, in
nanodiamonds, charge state instability increases with increasing NV density. In
the case of bulk single crystal diamond, we show that NV centers located near
the surface are more stable in the neutral (NV$^{0}$) charge state, while the
negatively charged (NV$^{-}$) form is more stable in bulk.",1812.02702v1
2018-12-20,Nonlinear dynamics of a spin-orbit-coupled Bose-Einstein condensate,"Single-particle dynamics of a spin-orbit-coupled Bose-Einstein condensate has
recently been investigated in experiments that explore the physics of
Landau-Zener tunneling and of the Zitterbewegung. In this paper, we study the
influence of a nonlinearity due to interactions on these dynamics and show that
the dispersion relation develops interesting loop strucures. The atoms can move
along the nonlinear dispersion curve in the presence of a weak acceleration
force and we show that the loops lead to straightforward nonlinear Landau-Zener
tunneling. However, we find that for the Zitterbewegung, induced by a sudden
quench in the spin-orbit coupling parameters, the nonlinear dispersion is
irrelevant.",1812.08303v2
2019-02-04,Domain dynamics in LiCuVO$_4$: Evidence for polarized nanoregions,"LiCuVO$_4$ is a model system of a 1D spin-1/2 chain that enters a planar
spin-spiral ground state below its N\'eel temperature of 2.4 K due to competing
nearest and next nearest neighbor interactions. The spin-spiral state is
multiferroic with an electric polarization along the a axis which has been
proposed to be caused purely by the spin supercurrent mechanism. With external
magnetic fields in c direction T$_N$ can be suppressed down to 0 K at 7.4 T.
Here we report dynamical measurements of the polarization from P(E)-hysteresis
loops, magnetic field dependent pyro-current and non-linear dielectric
spectroscopy as well as thermal expansion and magnetostriction measurements at
very low temperatures. The multiferroic transition is accompanied by strong
anomalies in the thermal expansion and magnetostriction coefficients and we
find slow switching times of electric domain reversal. Both observations
suggest a sizable magnetoelastic coupling in LiCuVO$_4$. By analyzing the
non-linear polarization dynamics we derive domain sizes in the nm range that
are probably caused by Li defects.",1902.01135v1
2019-02-21,Stochastic ejection of nanocontact droplet solitons via drift instability,"The magnetic droplet soliton is a large amplitude, coherently precessing wave
state that exists in ferromagnetic thin films with perpendicular magnetic
anisotropy. To effectively sustain a droplet, magnetic damping can be locally
compensated in a nanocontact region that imparts spin-transfer torque; this has
been successfully deployed in experiment to directly image the droplet and
probe its dynamics electrically. However, theory predicts and experiments
indicate the existence of a drift instability whereby the droplet is ejected
from the spin-transfer-torque-active region and subsequently decays, an effect
that may be enhanced or possibly induced by thermal fluctuations. Using soliton
perturbation theory and large deviation theory, this work determines the
soliton ejection rate and the most likely path an ejected soliton tracks in the
presence of thermal fields. These results lead to an effective lower bound on
the stability of magnetic droplet solitons in spin-transfer torque nanocontact
devices operating at finite temperature and point to ways in which droplets can
be made more robust.",1902.09310v1
2019-02-28,Dynamical scaling of charge and spin responses at a Kondo destruction quantum critical point,"Quantum critical points often arise in metals perched at the border of an
antiferromagnetic order. The recent observation of singular and dynamically
scaling charge conductivity in an antiferromagnetic quantum critical heavy
fermion metal implicates beyond-Landau quantum criticality. Here we study the
charge and spin dynamics of a Kondo destruction quantum critical point (QCP),
as realized in an SU(2)-symmetric Bose-Fermi Kondo model. We find that the
critical exponents and scaling functions of the spin and single-particle
responses of the QCP in the SU(2) case are essentially the same as those of the
large-N limit, showing that $1/N$ corrections are subleading. Building on this
insight, we demonstrate that the charge responses at the Kondo destruction QCP
are singular and obey $\omega/T$ scaling. This property persists at the Kondo
destruction QCP of the SU(2)-symmetric Kondo lattice model.",1902.11293v2
2019-03-07,Interplay between intra- and inter-nanowires dynamic dipolar interactions in the spin wave band structure of Py/Cu/Py nanowires,"We have studied both experimentally and theoretically the reprogrammable spin
wave band structure in Permalloy(10nm)/Cu(5nm)/Permalloy(30nm) nanowire arrays
of width w=280 nm and inter-wire separation in the range from 80 to 280 nm. We
found that, depending on the inter-wire separation, the anti-parallel
configuration, where the magnetizations of the two Permalloy layers point in
opposite directions, is stabilized over specific magnetic field ranges thus
enabling us to directly compare the band structure with that of the parallel
alignment. We show that collective spin waves of the Bloch type propagate
through the arrays with different magnonic bandwidths as a consequence of the
interplay between the intra- and inter-nanowire dynamic dipolar interactions. A
detailed understanding, e.g. whether they have a stationary or propagating
character, is achieved by considering the phase relation (in-phase or
out-of-phase) between the dynamic magnetizations in the two ferromagnetic
layers and their average value. This work opens the path to magnetic
field-controlled reconfigurable layered magnonic crystals that can be used for
future nanoscale magnon spintronic devices.",1903.02935v1
2019-03-30,Dynamical sign reversal of magnetic correlations in dissipative Hubbard models,"In quantum magnetism, the virtual exchange of particles mediates an
interaction between spins. Here, we show that an inelastic Hubbard interaction
fundamentally alters the magnetism of the Hubbard model due to dissipation in
spin-exchange processes, leading to sign reversal of magnetic correlations in
dissipative quantum dynamics. This mechanism is applicable to both fermionic
and bosonic Mott insulators, and can naturally be realized with ultracold atoms
undergoing two-body inelastic collisions. The dynamical reversal of magnetic
correlations can be detected by using a double-well optical lattice or
quantum-gas microscopy, the latter of which facilitates the detection of the
magnetic correlations in one-dimensional systems because of spin-charge
separation. Our results open a new avenue toward controlling quantum magnetism
by dissipation.",1904.00154v3
2019-04-01,Kitaev honeycomb models in magnetic fields: Dynamical response and hidden symmetries,"Motivated by recent reports of a field-induced intermediate phase (IP) in the
antiferromagnetic honeycomb Kitaev model that may be a spin liquid whose nature
is distinct from the Kitaev Z2 phase, we present a detailed numerical study on
the nature and dynamical response (such as dynamical spin-structure factors and
resonant inelastic x-ray scattering intensities) of this field-induced IP and
neighboring phases in a family of Kitaev-based models related by hidden
symmetries and duality transformations. We further show that the same
field-induced IP can appear in models relevant for $\alpha$-RuCl${_3}$, which
exhibit a ferromagnetic Kitaev coupling and additional interactions. In
$\alpha$-RuCl${_3}$, the IP represents a new phase, that is likely independent
from the putative field-induced (spin-liquid) phase recently reported from
thermal Hall conductivity measurements.",1904.01025v1
2019-08-05,Parallel simulation of two--dimensional Ising models using Probabilistic Cellular Automata,"We perform a numerical investigation of the \emph{shaken dynamics}, a
parallel Markovian dynamics for spin systems with local interaction and whose
transition probabilities depend on two parameters, $q$ and $J$, that tune the
geometry of the underlying lattice. We determine a phase transition curve, in
the $(q, J)$ plane, separating the disordered phase from the ordered one, study
the mixing time of the Markov chain and evaluate the spin-spin correlations as
$q$ and $J$ vary. Further, we investigate the relation between the equilibrium
measure of the shaken dynamics and the Gibbs measure for the Ising model. Two
different approaches are considered for the implementation of the dynamics: a
multicore CPU approach, with code written in Julia and a GPU approach with code
written in CUDA.",1908.07341v1
2019-11-07,Electric field effect on spin waves and magnetization dynamics: role of magnetic moment current,"We show that a static electric field $E_x$ gives rise to a shift of the spin
wave dispersion relation $\omega(q_y-q_E)$ in the direction of the wavenumber
$q_y$ of the quantity $q_E=-\gamma_LE_x/c^2$. This effect is caused by the
magnetic moment current carried by the spin wave itself that generates an
additional phase proportional to the electric field, as in the Aharonov-Casher
effect. This effect is independent from the possibly present magneto-electric
effects of insulating ferromagnets and superimposes to them. By extending this
picture to arbitrary magnetization dynamics, we find that the electric field
gives rise to a dynamic interaction term which has the same chiral from of the
Dzyaloshinskii-Moriya interaction but is fully tunable with the applied
electric field.",1911.02902v1
2019-11-21,Single-Particle Decoherence Can Improve Spin-Squeezing Generated In Collective Dynamics,"We study the generation of spin-squeezing in arrays of long-lived dipoles
subject to collective emission, coherent drive, elastic interactions, and
spontaneous emission. Counter-intuitively, it is found that the introduction of
spontaneous emission leads to an enhancement of the achievable spin-squeezing,
relative to that which emerges in the steady-state of the purely collective
dynamics for the same model parameters. This behavior is connected to the
dynamical self-tuning of the system through a dissipative phase transition that
is present in the collective system alone. Our findings will be applicable to
next-generation quantum sensors harnessing correlated quantum matter, including
cavity-QED and trapped ion systems.",1911.09617v2
2020-03-16,Dynamical spin excitations of topological Haldane gapped phase in the $S=1$ Heisenberg antiferromagnetic chain with single-ion anisotropy,"We study the dynamical spin excitations of the one-dimensional $S=1$
Heisenberg antiferromagnetic chain with single-ion anisotropy by using quantum
Monte Carlo simulations and stochastic analytic continuation of imaginary-time
correlation function. Using the transverse dynamic spin structure factor, we
observe the quantum phase transition with a critical point between the
topological Haldane gapped phase and the trivial phase. At the quantum critical
point, we find a broad continuum characterized by the Tomonaga-Luttinger liquid
similar to a $S=1/2$ Heisenberg antiferromagnetic chain. We further identify
that the elementary excitations are fractionalized spinons.",2003.07857v1
2020-05-15,Multiple magnon modes in spin-1/2 Heisenberg antiferromagnet on simple square lattice in strong magnetic field,"We discuss spin-$\frac12$ Heisenberg antiferromagnet on simple square lattice
in magnetic field $H$ using recently proposed bond-operator technique. It is
well known that magnetically ordered phases of quantum magnets are well
described at least qualitatively by the conventional spin-wave theory that only
introduces quantum corrections into the classical solution of the problem. We
observe that quantum fluctuations change drastically dynamical properties of
the considered model at $H$ close to its saturation value: the dynamical
structure factor shows anomalies corresponding to Green's function poles which
have no counterparts in the spin-wave theory. That is, quantum fluctuations
produce multiple short-wavelength magnon modes not changing qualitatively the
long-wavelength spin dynamics. Our results are in agreement with previous
quantum Monte-Carlo simulations and exact diagonalization of finite clusters.",2005.07537v3
2020-06-04,Dynamical pairwise entanglement and two-point correlations in the three-ligand spin-star structure,"We consider the three-ligand spin-star structure through homogeneous
Heisenberg interactions (XXX-3LSSS) in the framework of dynamical pairwise
entanglement. It is shown that the time evolution of the central qubit
""one-particle"" state (COPS) results in the generation of quantum W states at
periodical time instants. On the contrary, W states cannot be generated from
the time evolution of a ligand ""one-particle"" state (LOPS). We also investigate
the dynamical behavior of two-point quantum correlations as well as the
expectation values of the different spin-components for each element in the
XXX-3LSSS. It is found that when a W state is generated, the same value of
concurrence among all qubits arises from xx and yy two-point quantum
correlations. On the opposite, zz quantum correlation between any two qubits
vanishes at these time instants.",2006.02738v1
2020-09-07,Breaking of Coulomb blockade by macrospin-assisted tunneling,"A magnet with precessing magnetization pumps a spin current into adjacent
leads. As a special case of this spin pumping, a precessing macrospin
(magnetization) can assist electrons in tunneling. In small systems, however,
the Coulomb blockade effect can block the transport of electrons. Here, we
investigate the competition between macrospin-assisted tunneling and Coulomb
blockade for the simplest system where both effects meet; namely, for a single
tunnel junction between a normal metal and a metallic ferromagnet with
precessing magnetization. By combining Fermi's golden rule with magnetization
dynamics and charging effects, we show that the macrospin-assisted tunneling
can soften or even break the Coulomb blockade. The details of these effects --
softening and breaking of Coulomb blockade -- depend on the macrospin dynamics.
This allows, for example, to measure the macrospin dynamics via a system's
current-voltage characteristics. It also allows to control a spin current
electrically. From a general perspective, our results provide a platform for
the interplay between spintronics and electronics on the mesoscopic scale. We
expect our work to provide a basis for the study of Coulomb blockade in more
complicated spintronic systems.",2009.03373v3
2020-09-20,Floquet dynamical phase transition and entanglement spectrum,"We explore both pure and mixed states Floquet dynamical quantum phase
transitions (FDQFTs) in the one-dimensional p-wave superconductor with a
time-driven pairing phase. In the Fourier space, the model is recast to the
non-interacting quasi-spins subjected to a time-dependent effective magnetic
field. We show that FDQFTs occur within a range of driving frequency without
resorting to any quenches. Moreover, FDQFTs appear in the region where
quasi-spins are in the resonance regime. In the resonance regime, the
population completely cycles the population between the spin down and up
states. Additionally, we study the conditions for the appearance of FDQFTs
using the entanglement spectrum and purity entanglement measure. Our results
imply that the entanglement spectrum can truly capture the resonance regime
where FDQFTs occur. Particularly, the dynamical topological region results in
the degeneracy of the entanglement spectrum. It is shown that the boundary of
the driven frequency range, over which the system reveals FDQFTs, signaled by
the purity entanglement measure.",2009.09484v2
2020-10-31,Spin-orbit interaction induces charge beatings in a lightwave-STM single molecule junction,"Recent lightwave-STM experiments have shown space and time resolution of
single molecule vibrations directly on their intrinsic length and time scales.
We address here theoretically the electronic dynamics of a
copper-phthalocynanine in a lightwave-STM, explored within a pump-probe cycle
scheme. The spin-orbit interaction in the metallic center induces beatings of
the electric charge flowing through the molecule as a function of the delay
time between the pump and the probe pulses. Interference between the
quasi-degenerate anionic states of the molecule and the intertwined dynamics of
the associated spin and pseudospin degrees of freedom are the key aspects of
such phenomenon. We study the dynamics directly in the time domain within a
generalized master equation approach.",2011.00281v2
2021-02-02,Dynamic Cooper Pair Splitter,"Cooper pair splitters are promising candidates for generating spin-entangled
electrons. However, the splitting of Cooper pairs is a random and noisy
process, which hinders further synchronized operations on the entangled
electrons. To circumvent this problem, we here propose and analyze a dynamic
Cooper pair splitter that produces a noiseless and regular flow of
spin-entangled electrons. The Cooper pair splitter is based on a superconductor
coupled to quantum dots, whose energy levels are tuned in and out of resonance
to control the splitting process. We identify the optimal operating conditions
for which exactly one Cooper pair is split per period of the external drive and
the flow of entangled electrons becomes noiseless. To characterize the
regularity of the Cooper pair splitter in the time domain, we analyze the
$g^{(2)}$-function of the output currents and the distribution of waiting times
between split Cooper pairs. Our proposal is feasible using current technology,
and it paves the way for dynamic quantum information processing with
spin-entangled electrons.",2102.01406v2
2021-02-12,Manipulation of magnetic domain wall by ferroelectric switching: Dynamic magnetoelectricity at the nanoscale,"Controlling magnetism using voltage is highly desired for applications, but
remains challenging due to fundamental contradiction between polarity and
magnetism. Here we propose a mechanism to manipulate magnetic domain walls in
ferrimagnetic or ferromagnetic multiferroics using electric field. Different
from those studies based on static domain-level couplings, here the
magnetoelectric coupling relies on the collaborative spin dynamics around
domain walls. Accompanying the reversal of spin chirality driven by
polarization switching, a ""rolling-downhill""-like motion of domain wall is
achieved at the nanoscale, which tunes the magnetization locally. Our mechanism
opens an alternative route to pursuit practical and fast converse
magnetoelectric functions via spin dynamics.",2102.06471v2
2021-02-20,Observation of mode splitting in artificial spin ice,"We report the dependence of the magnetization dynamics in a square artificial
spin-ice lattice on the in-plane magnetic field angle. Using two complementary
measurement techniques - broadband ferromagnetic resonance and micro-focused
Brillouin light scattering spectroscopy - we systematically study the evolution
of the lattice dynamics, both for a coherent radiofrequency excitation and an
incoherent thermal excitation of spin dynamics. We observe a splitting of modes
facilitated by inter-element interactions that can be controlled by the
external field angle and magnitude. Detailed time-dependent micromagnetic
simulations reveal that the split modes are localized in different regions of
the square network. This observation suggests that it is possible to
disentangle modes with different spatial profiles by tuning the external field
configuration.",2102.10415v1
2021-03-09,Nonlinear superfluidity and time-delay based chaotic spin-down in pulsars,"We investigate the chaotic spin-down behavior seen from some pulsars in terms
of the nonlinear superfluid dynamics. To this end, we numerically solve the set
of equations for the superfluid-normal matter system whose coupling is mediated
by creep of the vortex lines. We show that glitch perturbations which introduce
a time-delay to the steady-state dynamics leave behind a remnant in the third
time derivative of the rotational phase. This time-delay induces a
hyper-chaotic spin-down for pulsars. We find that glitch-induced changes in the
rotational parameters lead to non-closing cyclic patterns in the time-delayed
phase difference diagram. We observe that the number of cycles, $N$, in the
diagram results from $N+1$ glitches occurred in total observation time.",2103.05421v1
2021-03-30,Importance Sampling Scheme for the Stochastic Simulation of Quantum Spin Dynamics,"The numerical simulation of dynamical phenomena in interacting quantum
systems is a notoriously hard problem. Although a number of promising numerical
methods exist, they often have limited applicability due to the growth of
entanglement or the presence of the so-called sign problem. In this work, we
develop an importance sampling scheme for the simulation of quantum spin
dynamics, building on a recent approach mapping quantum spin systems to
classical stochastic processes. The importance sampling scheme is based on
identifying the classical trajectory that yields the largest contribution to a
given quantum observable. An exact transformation is then carried out to
preferentially sample trajectories that are close to the dominant one. We
demonstrate that this approach is capable of reducing the temporal growth of
fluctuations in the stochastic quantities, thus extending the range of
accessible times and system sizes compared to direct sampling. We discuss
advantages and limitations of the proposed approach, outlining directions for
further developments.",2103.16468v2
2021-04-01,Glassy quantum dynamics of disordered Ising spins,"We study the out-of-equilibrium dynamics in the quantum Ising model with
power-law interactions and positional disorder. For arbitrary dimension $d$ and
interaction range $\alpha \geq d$ we analytically find a stretched exponential
decay of the global magnetization and ensemble-averaged single-spin purity with
a stretch-power $\beta = d/\alpha$ in the thermodynamic limit. Numerically, we
confirm that glassy behavior persists for finite system sizes and sufficiently
strong disorder. We identify dephasing between disordered coherent pairs as the
main mechanism leading to a relaxation of global magnetization, whereas genuine
many-body interactions lead to a loss of single-spin purity which signifies the
build-up of entanglement. The emergence of glassy dynamics in the quantum Ising
model extends prior findings in classical and open quantum systems, where the
stretched exponential law is explained by a scale-invariant distribution of
time scales, to both integrable and non-integrable quantum systems.",2104.00349v2
2021-05-10,Quasi-static strain governing ultrafast spin dynamics,"The quasi-static strain (QSS) is the product generated by the lattice thermal
expansion after ultrafast photo-excitation and the effects of thermal and QSS
are inextricable. Nevertheless, the two phenomena with the same relaxation
timescale should be treated separately because of their different fundamental
actions to the ultrafast spin dynamics. By employing ultrafast Sagnac
interferometry and magneto-optical Kerr effect, we quantitatively prove the
existence of QSS, which has been disregarded, and decouple two effects
counter-acting each other. Through the magnetoelastic energy analysis, rather
we show that QSS in ferromagnets plays a governing role on ultrafast spin
dynamics, which is opposite to what have been known on the basis of thermal
effect. Our demonstration provides an essential way of analysis on ultrafast
photo-induced phenomena.",2105.04168v1
2021-05-17,Dynamics and thermodynamics of a topological transition in spin ice materials under strain,"We study single crystals of Dy$_2$Ti$_2$O$_7$ and Ho$_2$Ti$_2$O$_7$ under
magnetic field and stress applied along their [001] direction. We find that
many of the features that the emergent gauge field of spin ice confers to the
macroscopic magnetic properties are preserved in spite of the finite
temperature. The magnetisation vs. field shows an upward convexity within a
broad range of fields, while the static and dynamic susceptibilities present a
peculiar peak. Following this feature for both compounds, we determine a single
experimental transition curve: that for the Kasteleyn transition in three
dimensions, proposed more than a decade ago. Additionally, we observe that
compression up to $-0.8\%$ along [001] does not significantly change the
thermodynamics. However, the dynamical response of Ho$_2$Ti$_2$O$_7$ is quite
sensitive to changes introduced in the ${\rm Ho}^{3+}$ environment. Uniaxial
compression can thus open up experimental access to equilibrium properties of
spin ice at low temperatures.",2105.07977v1
2021-05-25,Dynamics of a spin qubit in an optical dipole trap,"We present a theoretical investigation of coherent dynamics of a spin qubit
encoded in hyperfine sublevels of an alkali-metal atom in a far off-resonant
optical dipole trap. The qubit is prepared in the ""clock transition"" utilizing
the Zeeman states with zero projection of the spin angular momentum. We focus
on various dephasing processes such as the residual motion of the atom,
fluctuations of the trapping field and its incoherent scattering and their
effects on the qubit dynamics. We implement the most general fully-quantum
treatment of the atomic motion, so our results remain valid in the limit of
close-to-ground-state cooling with low number of vibrational excitations. We
support our results by comparison with an experiment showing reasonable
correspondence with no fitting parameters.",2105.11833v1
2021-07-04,Dynamics of rotating spin-orbit-coupled Bose-Einstein condensates in a quasicrystalline optical lattice,"We investigate the dynamics of rotating pseudo-spin-1/2 Bose-Einstein
condensates (BECs) with Rashba spin-orbit coupling (SOC) in a quasicrystalline
optical lattice (QOL). For given parameters, the system evolves from an initial
heliciform-stripe phase into a final visible vortex necklace with a giant
vortex and a hidden vortex necklace. Simultaneously, the corresponding spin
texture undergoes a transition from a meron-antimeron pair to a
half-antiskyrmion necklace. During the dynamic evolution process, the angular
momentum increases gradually, and then approaches to a convergent value.
Furthermore, typical quantum phases of rotating two-component BECs with SOC in
different external potentials are summarized.",2107.01564v1
2021-07-21,Transverse Single-Spin Asymmetries of Midrapidity Direct Photons and Neutral Mesons at PHENIX,"Results are presented for the transverse single-spin asymmetries of direct
photons, neutral pions, and eta mesons for $|\eta|<0.35$ from $p^\uparrow + p$
collisions with $\sqrt{s} = 200$ GeV at PHENIX. As hadrons, $\pi^0$ and $\eta$
mesons are sensitive to both initial- and final-state effects and at
midrapidity probe the dynamics of gluons along with a mix of quark flavors.
Because direct photon production does not include hadronization, the direct
photon TSSA is only sensitive to initial-state effects and at midrapidity
provides a clean probe of the gluon dynamics in transversely polarized protons.
All three of these results will help constrain the collinear twist-3 trigluon
correlation function as well as the gluon Sivers function, improving our
knowledge of spin-dependent gluon dynamics in QCD.",2107.10079v2
2021-08-16,Lattice-driven femtosecond magnon dynamics in $α$-MnTe,"The light-induced femtosecond dynamics of the sublattice magnetizations in
the antiferromagnetically ordered phase of the semiconductor $\alpha$-MnTe is
investigated theoretically as function of an external driving field. The
electromagnetic field is coupled to optical modes and the concomitant atomic
displacements modulate the Heisenberg exchange couplings. We derive the
equations of motion for the time-dependent sublattice magnetization in spin
wave theory and analyze the contributions from the driven magnon modes. The
antiferromagnetic order parameter exhibits coherent longitudinal oscillations
determined by the external driving frequency which decay due to dephasing.
Including a phenomenological dissipative term to mimic spin-lattice relaxation
processes leads to relaxation back to thermal equilibrium. We provide
approximate analytic solutions of the resulting differential equations which
allow us to understand the effect of the driving light pulse on the amplitude,
frequency, and lifetime of the coherent spin dynamics.",2108.07079v2
2021-08-20,Semi-Classical Discretization and Long-Time Evolution of Variable Spin Systems,"We apply the semi-classical limit of the generalized $SO(3)$ map for
representation of variable-spin systems in a four-dimensional symplectic
manifold and approximate their evolution terms of effective classical dynamics
on $T^{\ast }\mathcal{S}_{2}$. Using the asymptotic form of the star-product,
we manage to ""quantize"" one of the classical dynamic variables and introduce a
discretized version of the Truncated Wigner Approximation (TWA). Two emblematic
examples of quantum dynamics (rotor in an external field and two coupled spins)
are analyzed, and the results of exact, continuous, and discretized versions of
TWA are compared.",2108.09324v1
2021-09-01,Dynamical properties of the Haldane chain with bond disorder,"By using Lanczos exact diagonalization and quantum Monte Carlo combined with
stochastic analytic continuation, we study the dynamical properties of the
$S=1$ antiferromagnetic Heisenberg chain with different strengths of bond
disorder. In the weak disorder region, we find weakly coupled bonds which can
induce additional low-energy excitation below the one-magnon mode. As the
disorder increases, the average Haldane gap closes at $\delta_{\Delta}\sim 0.5$
with more and more low-energy excitations coming out. After the critical
disorder strength $\delta_c\sim 1$, the system reaches a random-singlet phase
with prominent sharp peak at $\omega=0$ and broad continuum at $\omega>0$ of
the dynamic spin structure factor. In addition, we analyze the distribution of
random spin domains and numerically find three kinds of domains hosting
effective spin-1/2 quanta or spin-1 sites in between. These ""spins"" can form
the weakly coupled long-range singlets due to quantum fluctuation which
contribute to the sharp peak at $\omega=0$.",2109.00552v1
2021-09-06,Relaxation of the Ising spin system coupled to a bosonic bath and the time dependent mean field equation,"The Ising model doesn't have a strictly defined dynamics, only a spectrum.
There are different ways to equip it with a time dependence e.g. the Glauber or
the Kawasaki dynamics, which are both stochastic, but it means there is a
master equation which can also describes their dynamics. We present a
Gluber-type master equation derived from the Redfield equation, where the spin
system is coupled to a bosonic bath. We derive a time dependent mean field
equation which describes the relaxation of the spin system at finite
temperature. Using the fully connected, uniform Ising model the relaxation time
will be studied, and the critical behaviour around the critical temperature.
The master equation shows the finite size effects, and the mean field equation
the thermodynamic limit.",2109.02341v1
2021-10-07,Experimental Realization of the Rabi-Hubbard Model with Trapped Ions,"Quantum simulation provides important tools in studying strongly correlated
many-body systems with controllable parameters. As a hybrid of two fundamental
models in quantum optics and in condensed matter physics, the Rabi-Hubbard
model demonstrates rich physics through the competition between local
spin-boson interactions and long-range boson hopping. Here we report an
experimental realization of the Rabi-Hubbard model using up to $16$ trapped
ions and present a controlled study of its equilibrium properties and quantum
dynamics. We observe the ground-state quantum phase transition by slowly
quenching the coupling strength, and measure the quantum dynamical evolution in
various parameter regimes. With the magnetization and the spin-spin correlation
as probes, we verify the prediction of the model Hamiltonian by comparing
theoretical results in small system sizes with experimental observations. For
larger-size systems of $16$ ions and $16$ phonon modes, the effective Hilbert
space dimension exceeds $2^{57}$, whose dynamics is intractable for classical
supercomputers.",2110.03227v3
2021-11-11,Spin dynamics in the Van der Waals magnet CrCl$_3$,"The magnetic nature of low dimensional compound, CrCl$_3$, was investigated
by muon spin rotation, relaxation and resonance ($\mu^+$SR). The $\mu^+$SR
measurements revealed three distinct phases as a function of temperature: an
antiferromagnetic state (AF) for $T\leq T_{\rm N}=14.32(6)$~K, a ferromagnetic
short range ordered state (FM-SRO) for $T_{\rm N}<T<\sim18$~K and a
paramagnetic phase (PM) above $\sim18$~K. Moreover, the AF state exhibits
appreciable spin dynamics, which increases with decreasing temperature below
$T_{\rm N}$. These dynamics originate from out of plane fluctuations, which
seem to settle for $9.5$~K$\leq T\leq T_{\rm N}$, evidenced from measurements
in ZF and complementary local field calculations. Moreover, the presented muon
Knight shift measurements just above $T_{\rm N}$ represent a clear microscopic
evidence for the absence of the previously speculated long range quasi-2D FM
order.",2111.06246v1
2021-12-04,Quantum map approach to entanglement transfer and generation in spin chains,"Quantum information processing protocols are efficiently implemented on
spin-$\frac{1}{2}$ networks. A quantum communication protocol generally
involves a certain number of parties having local access to a subset of a
larger system, whose intrinsic dynamics are exploited in order to perform a
specific task. In this chapter, we address such a scenario with the quantum
dynamical map formalism, where the dynamics of the larger system is expressed
as a quantum map acting on the parties' access to their respective subsets of
spins. We reformulate widely investigated protocols, such as one-qubit quantum
state transfer and two-qubit entanglement distribution, with the quantum map
formalism and demonstrate its usefulness in exploring less investigated
protocols such as multi-qubit entanglement generation.",2112.02348v3
2021-12-21,Giant dynamical electron-magnon coupling in metal-metal-ferromagnetic insulator heterostructure,"Magnon-mediated spin transport across nonmagnetic metal (NM) and
ferromagnetic insulator (FI) interface depends critically on electron-magnon
coupling. We propose a novel route to enhance electron-magnon coupling
dynamically from transport viewpoint. Using non-equilibrium Green's function a
theoretical formalism for magnon-mediated spin current is developed. In the
language of transport, the effective electron-magnon coupling at NM/FI
interface is determined by self-energy of FI lead, which is proportional to
density of states (DOS) at NM/FI interface due to nonlinear process of
electron-magnon conversion. By modifying interfacial DOS, the spin conductance
of 2D and 3D NM/FI systems can be increased by almost three orders of
magnitude, setting up a new platform of manipulating dynamical electron-magnon
coupling.",2112.11021v1
2022-01-05,Non-Hermitian skin effect in a spin-orbit-coupled Bose-Einstein condensate,"We study a Bose-Einstein condensate of ultracold atoms subject to a
non-Hermitian spin-orbit coupling, where the system acquires non-Hermitian skin
effect under the interplay of spin-orbit coupling and laser-induced atom loss.
The presence of the non-Hermitian skin effect is confirmed through its key
signatures in term of the spectral winding under the periodic boundary
condition, the accumulation of eigen wavefunctions at boundaries under an open
boundary condition, as well as bulk dynamics signaled by a directional flow. We
show that the bulk dynamics in particular serves as a convenient signal for
experimental detection. The impact of interaction and trapping potentials are
also discussed based on non-Hermitian Gross-Pitaevskii equations. Our work
demonstrates that the non-Hermitian skin effect and its rich implications in
topology, dynamics and beyond are well within reach of current cold-atom
experiments.",2201.01580v2
2022-01-31,Dynamical Mean-Field Theory for spin-dependent electron transport in spin-valve devices,"We present the combination of Density Functional Theory (DFT) and Dynamical
Mean Field Theory (DMFT) for computing the electron transmission through
two-terminals nanoscale devices. The method is then applied to metallic
junctions presenting alternating Cu and Co layers, which exhibit spin-dependent
charge transport and giant magnetoresistance (GMR) effect. The calculations
show that the coherent transmission through the $3d$ states is greatly
suppressed by electron correlations. This is mainly due to the finite lifetime
induced by the electron-electron interaction and is directly related to the
imaginary part of the computed many-body DMFT self-energy. At the Fermi energy,
where in accordance with the Fermi-liquid behavior the imaginary part of the
self-energy vanishes, the suppression of the transmission is entirely due to
the shifts of the energy spectrum induced by electron correlations. Based our
results, we finally suggest that the GMR measured in Cu/Co heterostructures for
electrons with energies about 1 eV above the Fermi energy is a clear
manifestation of dynamical correlation effects.",2201.13118v2
2022-02-06,Magnetic monopole relaxation effects probed by modulation calorimetry in small spin-ice samples,"We use modulation calorimetry to study the heat capacity of small samples (30
nano gram-10 micro gram) of the classical spin-ice compounds Dy2Ti2O7 and
Ho2Ti2O7 at low temperature (0.5-3 K). Using modulation frequencies of 0.1-200
Hz we find a strong frequency dependence in the measured heat capacity and are
able to study thermal relaxation effects on the corresponding timescales.
Performing dynamic Monte Carlo simulations we verify that the specific heat
frequency response has its origin in the slow magnetic monopole dynamics
indigenous to spin ice. We find a timescale of 20ms per Monte Carlo step at 4K
in contrast to 2.5ms mentioned in previous studies by other 1 techniques. Our
study establishes modulation calorimetry as a versatile experimental probe of
dynamic processes in frustrated magnetic materials.",2202.02801v1
2022-02-23,Spin canting in nonlinear terahertz magnon dynamics revealed by magnetorefractive probing in orthoferrite,"We excite the spin precession in rare-earth orthoferrite YFeO3 by the
magnetic field of intense terahertz pulse and probe its dynamics by transient
absorption change in the near infrared. The observed waveforms contain
quasi-ferromagnetic-mode magnon oscillation and its second harmonics with a
comparably strong amplitude. The result can be explained by dielectric function
derived from magnetorefractive Hamiltonian. We reveal that the strong second
harmonic signal microscopically originates from novel dynamics of the
quasi-ferromagnetic mode magnon at nonlinear regime, wherein spin canting angle
periodically oscillates.",2202.11365v1
2022-03-07,Ultrafast optical observation of spin-pumping induced dynamic exchange coupling in ferromagnetic semiconductor/metal bilayer,"Spin angular momentum transfer in magnetic bilayers offers the possibility of
ultrafast and low-loss operation for next-generation spintronic devices. We
report the field- and temperature- dependent measurements on the magnetization
precessions in Co$_2$FeAl/(Ga,Mn)As by time-resolved magneto-optical Kerr
effect (TRMOKE). Analysis of the effective Gilbert damping and phase shift
indicates a clear signature of an enhanced dynamic exchange coupling between
the two ferromagnetic (FM) layers due to the reinforced spin pumping at
resonance. The temperature dependence of the dynamic exchange-coupling reveals
a primary contribution from the ferromagnetism in (Ga,Mn)As.",2203.03225v2
2022-03-14,Noncollinear antiferromagnetic textures driven high harmonic generation from magnetic dynamics in the absence of spin-orbit coupling,"We demonstrate the generation of high order harmonics in carrier pumping from
precessing ferromagnetic or antiferromagnetic orders, excited via magnetic
resonance, in the presence of topological antiferromagnetic textures. This
results in an enhancement of the carrier dynamics by orders of magnitude.
Interestingly, the generation process occurs in an intrinsic manner, and is
solely governed by the interplay between the s-d exchange coupling underlying
the noncollinear antiferromagnetic order and the dynamical s-d exchange
parameter of the magnetic drive. Therefore, the relativistic spin-orbit
interaction is not required for the emergence of high harmonics in the pumped
currents. Accordingly, the noncollinear topological antiferromagnetic order is
presented as an alternative to spin-orbit interaction for the purpose of
harnessing high harmonic emission in carrier pumping. Our proposal initiates a
tantalizing perspective for the exploitation of topological magnetic textures
in the context of the highly active domain of ultrafast spintronics.",2203.07310v2
2022-04-06,Ultrafast spin dynamics: complementing theoretical analyses by quantum-information measures,"Theoretical analyses of ultrafast spin dynamics commonly address and discuss
simulated phenomena by means of observables, whereas in quantum information
theory one often utilizes measures of quantum states. In this Paper we report
on possible benefits of quantum information measures in simulations of
ultrafast spin dynamics. For Co/Cu heterostructures illuminated by femtosecond
laser pulses, we discuss the general behaviour of quantum information measures,
in particular distances in Hilbert space and degrees of mixing in the density
matrix. The measures are in particular sensitive to variations of the
polarization of a laser pulse and the sample composition. Moreover, they are
closely related to magnetization and number of excited electrons.",2204.02771v1
2022-04-12,Dynamical hadron formation in long-range interacting quantum spin chains,"The study of confinement in quantum spin chains has seen a large surge of
interest in recent years. It is not only important for understanding a range of
effective one-dimensional condensed matter realizations, but also shares some
of the non-perturbative physics with quantum chromodynamics (QCD) which makes
it a prime target for current quantum simulation efforts. In analogy with QCD,
the confinement-induced two-particle boundstates that appear in these models
are dubbed mesons. Here, we study scattering events due to meson collisions in
a quantum spin chain with long-range interactions such that two mesons have an
extended interaction. We show how novel hadronic boundstates, e.g. with four
constituent particles akin to tetraquarks, may form dynamically in fusion
events. In a natural collision their signal is weak as elastic meson scattering
dominates. However, we propose two controllable protocols which allow for a
clear observation of dynamical hadron formation. We discuss how this physics
can be simulated in trapped ion or Rydberg atom set-ups.",2204.05641v2
2022-05-05,Universal Kardar-Parisi-Zhang dynamics in integrable quantum systems,"Although the Bethe ansatz solution of the spin-1/2 Heisenberg model dates
back nearly a century, the anomalous nature of its high-temperature transport
dynamics has only recently been uncovered. Indeed, numerical and experimental
observations have demonstrated that spin transport in this paradigmatic model
falls into the Kardar-Parisi-Zhang (KPZ) universality class. This has inspired
the significantly stronger conjecture that KPZ dynamics, in fact, occur in all
integrable spin chains with non-Abelian symmetry. Here, we provide extensive
numerical evidence affirming this conjecture. Moreover, we observe that KPZ
transport is even more generic, arising in both supersymmetric and
periodically-driven models. Motivated by recent advances in the realization of
SU(N)-symmetric spin models in alkaline-earth-based optical lattice
experiments, we propose and analyze a protocol to directly investigate the KPZ
scaling function in such systems.",2205.02853v1
2022-05-27,Quantum Simulation of the Two-Dimensional Weyl Equation in a Magnetic Field,"Quantum simulation of 1D relativistic quantum mechanics has been achieved in
well-controlled systems like trapped ions, but properties like spin dynamics
and response to external magnetic fields that appear only in higher dimensions
remain unexplored. Here we simulate the dynamics of a 2D Weyl particle. We show
the linear dispersion relation of the free particle and the discrete Landau
levels in a magnetic field, and we explicitly measure the spatial and spin
dynamics from which the conservation of helicity and properties of
antiparticles can be verified. Our work extends the application of an ion trap
quantum simulator in particle physics with the additional spatial and spin
degrees of freedom.",2205.14038v1
2022-06-14,A dynamical theory for one-dimensional fermions with strong two-body losses: universal non-Hermitian Zeno physics and spin-charge separation,"We study an interacting one-dimensional gas of spin-1/2 fermions with
two-body losses. The dynamical phase diagram that characterises the approach to
the stationary state displays a wide quantum-Zeno region, identified by a
peculiar behaviour of the lowest eigenvalues of the associated non-Hermitian
Hamiltonian. We characterise the universal dynamics of this Zeno regime using
an approximation scheme based on a effective decoupling of charge and spin
degrees of freedom, where the latter effectively evolve in a non-Markovian way
according to a non-Hermitian Heisenberg Hamiltonian. We present detailed
results for the time evolution from initial states with one particle per site
with either incoherent and antiferromagnetic spin order, showing how the two
non-equilibrium evolutions build up drastically different charge correlations.",2206.06837v3
2022-06-27,Data-driven Thiele equation approach for solving the full nonlinear spin-torque vortex oscillator dynamics,"The dynamics of vortex based spin-torque nano-oscillators is investigated
theoretically. Starting from a fully analytical model based on the Thiele
equation approach, fine-tuned data-driven corrections are carried out to the
gyrotropic and damping terms. These adjustments, based on micromagnetic
simulation results, allow to quantitatively model the response of such
oscillators to any dc current within the range of the vortex stability. Both,
the transient and the steady-state regimes are accurately predicted under the
proposed data-driven Thiele equation approach. Furthermore, the computation
time required to solve the dynamics of such system is reduced by about six
orders of magnitude compared to the most powerful micromagnetic simulations.
This major breakthrough opens the path for unprecedented high-throughput
simulations of spin-torque vortex oscillators submitted to long-duration input
signals, for example in neuromorphic computing applications.",2206.13596v1
2022-08-02,Entanglement dynamics and phase transitions of the Floquet cluster spin chain,"Cluster states were introduced in the context of measurement based quantum
computing. In one dimension, the cluster Hamiltonian possesses topologically
protected states. We investigate the Floquet dynamics of the cluster spin chain
in an external field, interacting with a particle. We explore the entanglement
properties of the topological and magnetic phases, first in the integrable spin
lattice case, and then in the interacting quantum walk case. We find, in
addition to thermalization, dynamical phase transitions separating low- and
high-entanglement nonthermal states, reminiscent of the ones present in the
integrable case, but differing in their magnetic properties. The nonergodic
phases are characterized by the emergence of magnetic order, persistent at long
times.",2208.01706v2
2022-10-13,Influence of Ferromagnetic Interlayer Exchange Coupling on Current-induced Magnetization Switching and Dzyaloshinskii-Moriya Interaction in Co/Pt/Co Multilayer System,"This paper investigates the relationship among interlayer exchange coupling
(IEC), Dzyaloshinskii-Moriya interaction (DMI), and multilevel magnetization
switching within a Co/Pt/Co heterostructure, where varying Pt thicknesses
enable control over the coupling strength. Employing Brillouin Light Scattering
to quantify the effective DMI, we explore its potential role in magnetization
dynamics and multilevel magnetization switching. Experimental findings show
four distinct resistance states under an external magnetic field and spin Hall
effect related spin current. We explain this phenomenon based on the asymmetry
between Pt/Co and Co/Pt interfaces and the interlayer coupling, which, in turn,
influences DMI and subsequently impacts the magnetization dynamics. Numerical
simulations, including macrospin, 1D domain wall, and simple spin wave models,
further support the experimental observations of multilevel switching and help
uncover the underlying mechanisms. Our proposed explanation, supported by
magnetic domain observation using polar-magnetooptical Kerr microscopy, offers
insights into both the spatial distribution of magnetization and its dynamics
for different IECs, thereby shedding light on its interplay with DMI, which may
lead to potential applications in storage devices.",2210.07357v2
2022-10-21,Emergent many-body composite excitations of interacting spin-1/2 trimers,"Understanding exotic forms of magnetism in quantum spin systems is an
emergent topic of modern condensed matter physics. Quantum dynamics can be
described by particle-like carriers of information, known-as quasiparticles
that appear from the collective behaviour of the underlying system. Spinon
excitations, governing the excitations of quantum spin-systems, have been
accurately calculated and precisely verified experimentally for the
antiferromagnetic chain model. However, identification and characterization of
novel quasiparticles emerging from the topological excitations of the spin
system having periodic exchange interactions are yet to be obtained. Here, we
report the identification of emergent composite excitations of the novel
quasiparticles doublons and quartons in spin-1/2 trimer-chain antiferromagnet
Na2Cu3Ge4O12 (having periodic intrachain exchange interactions J1-J1-J2) and
its topologically protected quantum 1/3 magnetization-plateau state. The
characteristic energies, dispersion relations, and dynamical structure factor
of neutron scattering as well as macroscopic quantum 1/3 magnetization-plateau
state are in good agreement with the state-of-the-art dynamical density matrix
renormalization group calculations.",2210.11765v1
2022-11-16,Temperature-Dependent Dynamic Disproportionation in LiNiO$_2$,"The layered oxide LiNiO$_2$ is the model system for high-performance Ni-rich
cathodes for lithium-ion batteries. Here we investigate computationally the
local electronic and spin structure and dynamics of nickels in LiNiO$_2$. Ab
initio molecular dynamics simulations suggest that disproportionation of
spin-half ($S = 1/2$) nickels to $S = 0$ and $S = 1$ is favored towards
cryogenic temperatures. Upon heating, the spin states of the nickels
interconvert between $0$, $1/2$, and $1$ on a sub-picosecond timescale. We
propose that the transitions between differing states of the Ni correspond to
the heat-activated electronic conduction in LiNiO$_2$. The $S = 1$ nickels are
also found to stabilize antisite nickel defects via antiferromagnetic
interactions. Finally, we suggest avenues for the experimental verification of
our hypothesis.",2211.09047v2
2022-12-01,Distinct spin and orbital dynamics in Sr$_{2}$RuO$_{4}$,"The unconventional superconductor Sr$_2$RuO$_4$ has long served as a
benchmark for theories of correlated-electron materials. The determination of
the superconducting pairing mechanism requires detailed experimental
information on collective bosonic excitations as potential mediators of Cooper
pairing. We have used Ru $L_3$-edge resonant inelastic x-ray scattering to
obtain comprehensive maps of the electronic excitations of Sr$_2$RuO$_4$ over
the entire Brillouin zone. We observe multiple branches of dispersive spin and
orbital excitations associated with distinctly different energy scales. The
spin and orbital dynamical response functions calculated within the dynamical
mean-field theory are in excellent agreement with the experimental data. Our
results highlight the Hund metal nature of Sr$_{2}$RuO$_{4}$ and provide key
information for the understanding of its unconventional superconductivity.",2212.00245v1
2023-01-05,Emergence of anyonic correlations from spin and charge dynamics in one dimension,"We propose a transformation for spin and charge degrees of freedom in
one-dimensional lattice systems, constrained to have no doubly occupied sites,
that allows direct access to the dynamical correlations of the system. The
transformation delivers particle creation and annihilation operators in a form
of a spinless particle and a non-local operator acting on the space of states
of a spin-$1/2$ chain. This permits a decomposition of dynamical correlation
functions as a convolution of those for impenetrable anyons together with those
of a spin chain. Further analysis can be done by methods tailored for each part
of the convolution, greatly increasing the impact and flexibility of the
approach.",2301.02164v2
2023-01-18,The role of initial system-environment correlations with a spin environment,"Open quantum systems are a subject of immense interest as their understanding
is crucial in the implementation of modern quantum technologies. In the study
of their dynamics, the role of the initial system-environment correlations is
commonly ignored. In this work, to gain insights into the role of these
correlations, we solve an exactly solvable model of a single two-level system
interacting with a spin environment, with the initial system state prepared by
a suitable unitary operation. By solving the dynamics exactly for arbitrary
system-environment coupling strength while taking into account the initial
system-environment correlations, we show that the effect of the initial
correlations is, in general, very significant and non-trivial. To further
highlight the importance of the initial system-environment correlations, we
also extend our study to investigate the dynamics of the entanglement between
two two-level systems interacting with a common spin environment.",2301.07332v1
2023-02-06,Observation of Coherently Coupled Cation Spin Dynamics in an Insulating Ferrimagnetic Oxide,"Many technologically useful magnetic oxides are ferrimagnetic insulators,
which consist of chemically distinct cations. Here, we examine the spin
dynamics of different magnetic cations in ferrimagnetic NiZnAl-ferrite
(Ni$_{0.65}$Zn$_{0.35}$Al$_{0.8}$Fe$_{1.2}$O$_4$) under continuous microwave
excitation. Specifically, we employ time-resolved x-ray ferromagnetic resonance
to separately probe Fe$^{2+/3+}$ and Ni$^{2+}$ cations on different sublattice
sites. Our results show that the precessing cation moments retain a rigid,
collinear configuration to within $\approx$2$^\circ$. Moreover, the effective
spin relaxation is identical to within $<$10% for all magnetic cations in the
ferrite. We thus validate the oft-assumed ``ferromagnetic-like'' dynamics in
resonantly driven ferrimagnetic oxides, where the magnetic moments from
different cations precess as a coherent, collective magnetization.",2302.03100v1
2023-03-15,The Dynamical Stripes in Spin-Orbit Coupled Bose-Einstein Condensates with Josephson Junctions,"The Josephson dynamics of the Bose-Einstein condensation with Raman-induced
spin-orbit coupling is investigated. A quasi-1D trap is divided into two
reservoirs by an optical barrier. Before the tunneling between the reservoirs
is turned on, the system stays in its equilibrium ground state. For different
spin-orbit coupling parameters and interaction strengthes, the ground state
displays a rich phase diagram. In this work we focus on the plane wave phase
and the stripe phase. Our calculation shows that, when the tunneling is turned
on, the plane wave phase evolves into a dynamical stripe phase, that is, the
density of the particle changes from uniform to periodically modulated.
Basically, this stripe is described by a sine function and the wave length, the
amplitude and the initial phase of the function are all varying with time. If
the system stays in stripe phase initially, the stripes become ``sliding"" when
the tunneling is turned on, which reflects the running of one of the phases of
the wave function.",2303.08585v1
2023-04-24,Half-quantum vortex generation in a two-component Bose-Einstein condensate by an oscillatory magnetic obstacle,"We numerically investigate the dynamics of vortex generation in a
two-dimensional, twocomponent Bose-Einstein condensate subjected to an
oscillatory magnetic obstacle. The obstacle creates both repulsive and
attractive Gaussian potentials for the two symmetric spin-$\uparrow$ and
$\downarrow$ components, respectively. We demonstrate that, as the oscillating
frequency f increases, two distinct critical dynamics arise in the generation
of half-quantum vortices (HQVs) with different spin circulations.
Spin-$\uparrow$ vortices are nucleated directly from the moving obstacle at low
f, while spin-$\downarrow$ vortices are created at high f by breaking a spin
wave pulse in front of the obstacle. We find that vortex generation is
suppressed for sufficiently weak obstacles, in agreement with recent
experimental results by Kim et al. [Phys. Rev. Lett. 127, 095302 (2021)]. This
suppression is caused by the finite sweeping distance of the oscillating
obstacle and the reduction in friction in a supersonic regime. Finally, we show
that the characteristic length scale of the HQV generation dynamics is
determined by the spin healing length of the system.",2304.11786v1
2023-05-05,Equivariant Neural Networks for Spin Dynamics Simulations of Itinerant Magnets,"I present a novel equivariant neural network architecture for the large-scale
spin dynamics simulation of the Kondo lattice model. This neural network mainly
consists of tensor-product-based convolution layers and ensures two
equivariances: translations of the lattice and rotations of the spins. I
implement equivariant neural networks for two Kondo lattice models on
two-dimensional square and triangular lattices, and perform training and
validation. In the equivariant model for the square lattice, the validation
error (based on root mean squared error) is reduced to less than one-third
compared to a model using invariant descriptors as inputs. Furthermore, I
demonstrate the ability to reproduce phase transitions of skyrmion crystals in
the triangular lattice, by performing dynamics simulations using the trained
model.",2305.03804v1
2023-06-21,Acoustic Kerr Metric in Analogue Gravity,"The present paper is based on a previous work (involving two of the present
authors) where a generalized fluid dynamical model was proposed. The underlying
symplectic structure of the Lagrangian discrete degrees of freedom obeyed a
Non-Commutative algebra, generated by Berry curvature correction. In an Euler
(or Hamiltonian) framework, this is manifested as an extended algebra between
the fluid variables, leading to the extended fluid model. Here we study the
dynamics of sonic fluctuations that live in this effective analogue gravity
spacetime. Interestingly enough, the effective metric resembles that of a
spinning Black Hole; the spin is induced by the underlying Non-Commutative
structure. The effective mass and spin parameters of the Black Hole, in terms
of fluid parameters, are also identified. The connection of our model with
anomalous Hall systems may lead to observable signatures of the analogue black
hole in physical systems.",2306.12201v1
2023-07-25,Simulating quantum transport via collisional models on a digital quantum computer,"Digital quantum computers have the potential to study the dynamics of complex
quantum systems. Nonequilibrium open quantum systems are, however, less
straightforward to be implemented. Here we consider a collisional model
representation of the nonequilibrium open dynamics for a boundary-driven XXZ
spin chain, with a particular focus on its steady states. More specifically, we
study the interplay between the accuracy of the result versus the depth of the
circuit by comparing the results generated by the corresponding master
equations. We study the simulation of a boundary-driven spin chain in regimes
of weak and strong interactions, which would lead in large systems to diffusive
and ballistic dynamics, considering also possible errors in the implementation
of the protocol. Last, we analyze the effectiveness of digital simulation via
the collisional model of current rectification when the XXZ spin chains are
subject to non-uniform magnetic fields.",2307.13576v2
2023-07-29,Single-spin spectroscopy of spontaneous and phase-locked spin torque oscillator dynamics,"We employ N-$V$ magnetometry to measure the stray field dynamics of a
ferromagnetic permalloy nanowire driven by spin-orbit torques. Specifically, we
observe the optically detected magnetic resonance (ODMR) signatures of both
spontaneous DC-driven magnetic oscillations and phase-locking to a second
harmonic drive, developing a simple macrospin model that captures the salient
features. We also observe signatures of dynamics beyond the macrospin model,
including an additional ODMR feature (associated with a second SW mode) and one
mode sapping power from another. Our results provide additional insight into
N-$V$-spin wave coupling mechanisms, and represent a new modality for
sub-wavelength N-$V$ scanned probe microscopy of nanoscale magnetic
oscillators.",2307.16049v1
2023-08-18,Spin-wave dispersion and magnon chirality in multiferroic TbMnO3,"Inelastic neutron scattering experiments combining time-of-flight and
polarized techniques yield a comprehensive picture of the magnon dispersion in
multiferroic TbMnO3 including the dynamic chirality. Taking into account only
Mn3+ moments, spin-wave calculations including nearest-neighbor interactions,
frustrating next-nearest neighbor exchange as well as single-ion anisotropy and
antisymmetric terms describe the energy dispersion and the distribution of
neutron scattering intensity in the multiferroic state very well. Polarized
neutron scattering reveals strong dynamic chirality of both signs that may be
controlled by external electric fields in the multiferroic phase. Also above
the onset of long-range multiferroic order in zero electric field, a small
inelastic chiral component can be inverted by an electric field. The
microscopic spin-wave calculations fully explain also the dynamic chirality of
magnetic excitations, which is imprinted by the static chirality of the
multiferroic phase. The ordering of Tb3+ moments at lower temperature reduces
the broadening of magnons but also renders the magnon dispersion more complex.",2308.09407v1
2023-10-09,Exact quench dynamics of the Floquet quantum East model at the deterministic point,"We study the non-equilibrium dynamics of the Floquet quantum East model (a
Trotterized version of the kinetically constrained quantum East spin chain) at
its ""deterministic point"", where evolution is defined in terms of CNOT
permutation gates. We solve exactly the thermalization dynamics for a broad
class of initial product states by means of ""space evolution"". We prove: (i)
the entanglement of a block of spins grows at most at one-half the maximal
speed allowed by locality (i.e., half the speed of dual-unitary circuits); (ii)
if the block of spins is initially prepared in a classical configuration, speed
of entanglement is a quarter of the maximum; (iii) thermalization to the
infinite temperature state is reached exactly in a finite time that scales with
the system size.",2310.06128v1
2023-11-07,"Magnetism in AV3Sb5 (A = Cs, Rb, K): Complex Landscape of the Dynamical Magnetic Textures","We have investigated the dynamical magnetic properties of the V-based kagome
stibnite compounds by combining the ab-initio calculated magnetic parameters of
a spin Hamiltonian like inter-site exchange parameters, magnetocrystalline
anisotropy and site projected magnetic moments, with full-fledged simulations
of atomistic spin-dynamics. Our calculations reveal that in addition to a
ferromagnetic order along the [001] direction, the system hosts a complex
landscape of magnetic configurations comprised of commensurate and
incommensurate spin-spirals along the [010] direction. The presence of such
chiral magnetic textures may be the key to solve the mystery about the origin
of the experimentally observed inherent breaking of the C6 rotational symmetry-
and the time-reversal symmetry.",2311.04099v1
2023-12-12,Local dynamics and detection of topology in spin-1 chains,"Antiferromagnetic spin-1 chains host the celebrated symmetry protected
topological Haldane phase, whose spin-1/2 edge states were evidenced in bulk
by, e.g., Electron Spin Resonance (ESR). Recent success in assembling effective
spin-1 antiferromagnetic chains from nanographene and porphyrin molecules opens
the possibility of local, site-by-site, characterization. The nascent technique
of combined ESR-STM is able to measure the spin dynamics with atomic real-space
resolution, and could fully reveal and manipulate the spin-1/2 degree of
freedom. In this work, we combine exact diagonalization and DMRG to investigate
the local dynamic spin structure factor of the different phases of the
bilinear-biquadratic Hamiltonian with single-ion anisotropy in presence of an
external magnetic field. We find that the signature of the Haldane phase is a
low-energy peak created by singlet-triplet transitions in the edge-state
manifold. We predict that the signature peak is experimentally observable,
although for chains of length above N = 30 its energy should be first tuned by
application of external magnetic field. We fully characterize the peak in
real-space and energy, and further show its robustness to weak anisotropy and a
relevant range of temperatures.",2312.07147v1
2023-12-27,Emergent hydrodynamics in a non-reciprocal classical isotropic magnet,"The Hamiltonian nature of the precessional dynamics of the classical
Heisenberg model leads to reciprocal interactions amongst the spins. Heisenberg
spins are reciprocal in nature. In this work, we study the dynamics of a
nonequilibrium classical spin chain in which the neighbours interact through a
purely non-reciprocal exchange coupling [EPL 60, 418 (2002)] which preserves
rotational symmetry. The resultant dynamics conserves neither magnetization nor
energy. We uncover other local conservation laws in their place in the extreme
case of a strictly antisymmetric coupling. We show numerically that the model
undergoes an analogue of thermalization. We present results on the presence of
conserved quantities, their diffusive spreading and a hydrodynamic picture, and
the nature of the decorrelation front upon adding an initial perturbation to
the system.",2312.16500v1
2024-01-04,Truncated string-state-space approach and its application to non-integrable spin 1/2 Heisenberg chain,"By circumventing the difficulty of obtaining exact string state solutions to
Bethe ansatz equations, we devise a truncated string-state-space approach for
investigating spin dynamics in non-integrable spin-1/2 Heisenberg chain
subjected to staggered field at various magnetization. The obtained dynamical
spectra reveal a series of elastic peaks at integer multiples of the ordering
wavevector $Q$, indicating the presence of multi-$Q$ Bethe string states within
the ground state. The spectrum exhibits a separation between different string
continua as the strength of the staggered field increases at low
magnetization,reflecting the confinement of the Bethe strings. The approach has
successfully provided a unified string-state-based picture for understanding
spin dynamics observed in various phases of quasi-1D antiferromagnet $\rm
YbAlO_3$ \cite{Yang_CBS_2023}, and also paves a way for investigating
low-dimensional non-integrable systems.",2401.02018v1
2024-01-19,Coupling Dynamics and Linear Polarization Phenomena in Codirectional Polariton Waveguide Couplers,"In this work, we explore the potential of spin-based integrated devices using
polariton waveguides that form codirectional couplers. For suitable coupler
parameters, a transfer of condensates between the arms of the coupler, occurs
leading to the observation of Josephson-like oscillations. The ability to tune
the periodicity of these oscillations opens the way to the design of
polaritonic circuits in which the directionality of the signal towards the
output terminals can be controlled. We also investigate the response of the
devices to linearly polarized excitation, delving into the dynamics of linear
polarization at the output terminals of long couplers, providing valuable
insights into the potential applications of spin-based polariton devices,
including polariton switches and logic gates with efficient operation. Our
results are supported by numerical simulations based on generalized
Gross-Pitaevskii equation describing the dynamics of coherent polaritons in
spatially non-uniform system. We show, how the coupling and the controllable
spin degree of freedom in polariton couplers opens avenues for innovative
optical architectures and functionalities.",2401.10742v1
2024-02-26,Large-Enhancement Nanoscale Dynamic Nuclear Polarization Near a Silicon Nanowire Surface,"Dynamic nuclear polarization (DNP) has revolutionized the field of NMR
spectroscopy, expanding its reach and capabilities to investigate diverse
materials, biomolecules, and complex dynamic processes. Bringing
high-efficiency DNP to the nanometer scale would open new avenues for studying
nanoscale nuclear spin ensembles, such as single biomolecules, virus particles,
and condensed matter systems. Combining pulsed DNP with nanoscale
force-detected magnetic resonance measurements, we demonstrated a 100-fold
enhancement in the Boltzmann polarization of proton spins in nanoscale sugar
droplets at 6 K and 0.33 T. Crucially, this enhancement corresponds to a factor
of 200 reduction in the averaging time compared to measurements that rely on
the detection of statistical fluctuations in nanoscale nuclear spin ensembles.
These results significantly advance the capabilities of force-detected magnetic
resonance detection as a practical tool for nanoscale imaging.",2402.16283v1
2024-04-08,Many-body quantum dynamics of spin-orbit coupled Andreev states in a Zeeman field,"We provide a theoretical framework to describe the quantum many-body dynamics
of Andreev states in Josephson junctions with spin-orbit coupling and a
magnetic Zeeman field. In such cases, employing a doubled Nambu spinor
description is technically advantageous but one then has to be careful to avoid
double-counting problems. By deriving the Lindblad master equation in the
socalled excitation picture, we show that a physically consistent many-body
theory free from doublecounting problems follows. We apply our formalism to a
study of dynamical parity stabilization of the Andreev sector at intermediate
times after an initial microwave pulse, in particular addressing the combined
effects of spin-orbit coupling and Zeeman field.",2404.05485v1
1996-08-07,Dynamics of the 1D Heisenberg model and optical absorption of spinons in cuprate antiferromagnetic chains,"We use numerical and analytical results to construct a simple ansatz for the
energy dynamical correlation function of the 1D antiferromagnetic Heisenberg
model. This is applied to compute the phonon assisted absorption spectra of
magnetic excitations (spinons) in quasi-one dimensional spin 1/2 insulators and
show to reproduce very well recent infrared measurements in Sr$_2$CuO$_3$.",9608035v1
1998-06-17,Exact Result on Hole Dynamics of One-Dimensional Supersymmetric t-J Model with Long Range Interaction,"We obtain an exact result on single hole dynamics in one-dimensional
Mott-insulators through the study on the supersymmetric t-J model with long
range interaction at half-filling. We calculate the expression G_{1s1h}(x,t)
for one spinon one holon contribution to the hole propagator. We find that
G_{1s1h}(x=0,t=0)=3/8, which amounts to 75% of the spin-fixed mean particle
density 1/2.",9806202v1
1999-07-09,Barriers in the p-spin interacting spin-glass model. The dynamical approach,"We investigate the barriers separating metastable states in the spherical
p-spin glass model using the instanton method. We show that the problem of
finding the barrier heights can be reduced to the causal two-real-replica
dynamics. We find the probability for the system to escape one of the highest
energy metastable states and the energy barrier corresponding to this process.",9907135v1
2000-04-26,Glassy dynamics near zero temperature,"We numerically study finite-dimensional spin glasses at low and zero
temperature, finding evidences for (i) strong time/space heterogeneities, (ii)
spontaneous time scale separation and (iii) power law distributions of flipping
times. Using zero temperature dynamics we study blocking, clustering and
persistence phenomena.",0004438v2
2000-09-25,Spin dynamics in Cuprates and its relation to superconductivity,"The relevance of magnetism for the mechanism responsible for high-temperature
superconductivity remains an open and still interesting issue. The observation
by inelastic neutron scattering of strong antiferromagnetic dynamical
correlations in superconducting cuprates is discussed in relation to the
unusual physical properties of the cuprates as well as in relation to the
superconducting pairing.",0009373v1
2001-10-19,Very low-frequency excitations in frustrated two-dimensional $S=1/2$ Heisenberg antiferromagnets,"muSR and 7Li NMR relaxation measurements in frustrated two-dimensional S=1/2
Heisenberg antiferromagnets on a square lattice are presented. It is found that
both in Li2VOSiO4 and Li2VOGeO4, spin dynamics at frequencies well below the
Heisenberg exchange frequency are present. These dynamics are associated with
the motions of walls separating coexisting collinear domains with a magnetic
wave vector rotated by 90 degrees.",0110398v1
2005-03-03,Quantum dynamics of a nanomagnet in a rotating field,"Quantum dynamics of a two-state spin system in a rotating magnetic field has
been studied. Analytical and numerical results for the transition probability
have been obtained along the lines of the Landau-Zener-Stueckelberg theory. The
effect of various kinds of noise on the evolution of the system has been
analyzed.",0503085v1
1996-07-29,A Renormalization Group for Dynamical Triangulations in Arbitrary Dimensions,"A block spin renormalization group approach is proposed for the dynamical
triangulation formulation of quantum gravity in arbitrary dimensions.
Renormalization group flow diagrams are presented for the three-dimensional and
four-dimensional theories near their respective transitions.",9607074v1
1997-11-05,Two-Dimensional Dynamical Triangulation using the Grand-canonical Ensemble,"The string susceptibility exponents of dynamically triangulated two
dimensional surfaces with sphere and torus topology were calculated using the
grand-canonical Monte Carlo method. We also simulated the model coupled to
d-Ising spins (d=1,2,3,5).",9711008v1
2003-08-27,Spinodal Decomposition and the Deconfining Phase Transition,"We study the Glauber dynamics of simple spin systems to identify dynamical
scenarios which may be of relevance for the deconfining phase transition in
heavy ion collisions.",0308032v1
1996-10-14,Signatures of Dynamical Symmetry Breaking at Tevatron Upgrade and LHC,"We study the phenomenology of a strongly interacting electroweak symmetry
breaking sector in which the physics is dominated by spin one resonances.
Specifically we will consider an effective description of dynamical symmetry
breaking based on a particular model which passes all the low-energy precision
tests and gives clear signals at LHC but also at Tevatron Upgrade.",9610356v1
2003-03-21,Loop quantum gravity induced modifications to particle dynamics,"The construction of effective Hamiltonians arising from Loop Quantum Gravity
and incorporating Planck scale corrections to the dynamics of photons and spin
1/2 particles is summarized. The imposition of strict bounds upon some
parameters of the model using already existing experimental data is also
reviewed.",0303189v1
2004-02-10,"Isospin Squeezed States, Disoriented Chiral condensates and Pion Production: A Dynamic Group Theoretical Approach","We make a complete dynamical study of Isotopic spin conservation effects on
the multiplicity distributions of both hard and soft pions emitted in a quark
gluon plasma undergoing a non-equilibrium phase transition.",0402101v1
1993-10-27,A Note on the Relation between Different Forms of Superparticle Dynamics',"A formulation of $D\is 10$ superparticle dynamics is given that contain
space-time and twistor variables. The set of constraints is entirely first
class, and gauge conditions may be imposed that reduces the system to a
Casalbuoni-Brink-Schwarz superparticle, a spinning particle or a twistor
particle.",9310177v1
2006-04-19,Chemically Induced Dynamic Nuclear Polarization of 19F Nuclei,"This study explores, both theoretically and experimentally, the
photochemically induced dynamic nuclear polarization (photo-CIDNP) of 19F
nuclei, the associated spin relaxation, cross-relaxation and cross-correlation
effects, as well as potential applications of 19F CIDNP to protein structure
and folding problems. Keywords: CIDNP, relaxation, fluorine, NMR, NOE,
TR-CIDNP, tc5b, Trp-cage, GFP",0604156v2
1997-12-04,Dynamical systems related to the Cremmer-Gervais R-matrix,"The generalized Cremmer-Gervais R-matrix being a twist of the standard
R-matrix of $SL_q(3)$, depends on two extra parameters. Properties of this
R-matrix are discussed and two dynamical systems, the quantum group covariant
$q$-oscillator and an integrable spin chain with a non-hermitian Hamiltonian,
are constructed.",9712016v1
2001-01-15,Prospects for a Quantum Dynamic Random Access Memory (Q-DRAM),"Compared to quantum logic gates, quantum memory has received far less
attention. Here, we explore the prognosis for a solid-state, scalable quantum
dynamic random access memory (Q-DRAM), where the qubits are encoded by the spin
orientations of single quantons in exchange-decoupled quantum dots. We address,
in particular, various possibilities for implementing refresh cycles.",0101058v2
2007-10-12,Dynamical instability of the XY spiral state of ferromagnetic condensates,"We calculate the spectrum of collective excitations of the XY spiral state
prepared adiabatically or suddenly from a uniform ferromagnetic F=1 condensate.
For spiral wavevectors past a critical value, spin wave excitation energies
become imaginary indicating a dynamical instability. We construct phase
diagrams as functions of spiral wavevector and quadratic Zeeman energy.",0710.2499v1
2008-06-24,Magnetic Susceptibility of Quark Matter,"Magnetic properties of quark matter is discussed by evaluating the spin
susceptibility within Fermi-liquid theory. We take into account the dynamical
and static screening effects. At finite temperature, an anomalous T^2 ln T term
for susceptibity is shown as a non-Fermi-liquid effect due to the dynamical
screening of transverse gluons.",0806.3882v1
2008-08-19,Density-matrix renormalization group methods for momentum- and frequency-resolved dynamical correlation functions,"Several density-matrix renormalization group methods have been proposed to
compute the momentum- and frequency-resolved dynamical correlation functions of
low-dimensional strongly correlated systems. The most relevant approaches are
discussed in this contribution. Their applications in various studies of
quasi-one-dimensional strongly correlated systems (spin chains, itinerant
electron systems, electron-phonon systems) are reviewed.",0808.2620v1
2009-04-22,Dynamic equations for three different qudits in a magnetic field,"A closed system of equations for the local Bloch vectors and spin correlation
functions of three magnetic qudits, which are in an arbitrary, time-dependent,
external magnetic field, is obtained using decomplexification of the
Liouville-von Neumann equation. The algorithm of the derivation of the dynamic
equations is presented. In the basis convenient for the important physical
applications structure constants of algebra su(2S+1) are calculated.",0904.3533v1
2011-04-21,Partial Dynamical Symmetry in the f7/2 and g9/2 shell,"We discuss partial dynamical symmetries which occur in single j shell
calculations mostly for high spin states for systems of three or four particles
(holes). The relevant nuclei are 43Ti,43Sc, 44Ti, 52Fe,53Fe, 53Co,96Cd,97Cd,
and 97In.",1104.4329v4
2012-08-07,Vortex dynamics and skyrmions in four to six dimensions: Coherence vortices in Bose-Einstein condensates,"I point out how coherence vortices, i.e., topological defects in a
correlation function, could help explore new physics if they are created in
matter waves. Vortex dynamics could be studied in up to six dimensions, and
spin topological defects unseen in lower dimensions could be created. A
rudimentary proof-of-principle experiment is sketched and simulated, in which
three Bose-Einstein condensates are used to create and detect coherence
vortices.",1208.1489v1
2014-02-14,Extremely high-resolution measurements of microwave magnetisation dynamics in magnetic thin films and nanostructures,"In this work we discuss the use of interferometric measurement technique to
study microwave magnetization dynamics on ferromagnetic nanostructures. We
demonstrate that in this way one can resolve features which are impossible to
resolve with broadband ferromagnetic resonance and traveling spin wave
spectroscopy otherwise.",1402.3459v1
2013-08-19,An Electronically Non-Adiabatic Generalization of Ring Polymer Molecular Dynamics,"In this thesis I generalize Ring Polymer Molecular Dynamics (RPMD) rate
theory to electronically non-adiabatic systems, followed by application to two
one-dimensional curve crossing models and a multidimensional spin-boson model.",1308.3950v1
2012-01-20,Macrodimension - an invariant of local dynamics,"We define a Markov process on the set of countable graphs with spins.
Transitions are local substitutions in the graph. It is proved that the scaling
macrodimension is an invariant of such dynamics.",1201.4295v1
2017-09-04,The pion in holographic light-front QCD,"We report that the pion radius, decay constant, EM and transition form
factors can simultaneously and accurately be predicted in light-front
holographic QCD with a universal AdS/QCD mass scale, provided dynamical spin
effects are taken into account.",1709.01125v1
2019-04-06,Phenomenological description of the dynamics of bipartite antiferromagnets in the limit of strong exchange,"The equation of motion of the staggered order parameter is derived in a
step-by-step manner from the coupled Landau-Lifshitz-Gilbert dynamics of
bipartite spin moments in the limit of strong antiferromagnetic exchange
coupling.",1904.03529v4
2021-09-20,Gravity with dynamical torsion,"We propose four simple Lagrangians for gravity models with dynamical torsion
which are free from ghosts and tachyons. The torsion propagates two massive or
massless particles of spin 1^\pm and 0^\pm besides the massless graviton 2^+
propagated by metric.",2109.09546v1
2022-08-26,Mechanics of a ferromagnetic domain wall,"This paper gives a pedagogical introduction to the mechanics of ferromagnetic
solitons. We start with the dynamics of a single spin and develop all the tools
required for the description of the dynamics of solitons in a ferromagnet.",2208.12799v3
2022-09-06,Dynamical Heterogeneity in Glass-Forming Liquids,"We review the phenomena of dynamical heterogeneity in glass-forming systems
and its description within replica and mean-field theories of the glass
transition.",2209.02825v1
2022-12-23,Dynamics of $\vartheta$-solitons in the HPD state of superfluid $^3$He-B,"In this note we present numerical study of spin dynamics of
$\vartheta$-soliton in Homogeneously precessing domain (HPD) in superfluid
$^3$He-B. The soliton consists of a small heavy core and long tails, in 1D
simulation we observe their mutual motion. We also discuss mass density and
tension of the soliton membrane and its 3D oscillations in a cylindrical cell.",2212.12232v1
2023-09-07,Non-perturbative localization for quasi-periodic Jacobi block matrices,"We prove non-perturbative Anderson localization for quasi-periodic Jacobi
block matrix operators assuming non-vanishing of all Lyapunov exponents. The
base dynamics on tori $\mathbb{T}^b$ is assumed to be a Diophantine rotation.
Results on arithmetic localization are obtained for $b=1$, and applications to
the skew shift, stacked graphene, XY spin chains, and coupled Harper models are
discussed.",2309.03423v1
1994-11-09,Low-temperature dynamical simulation of spin-boson systems,"The dynamics of spin-boson systems at very low temperatures has been studied
using a real-time path-integral simulation technique which combines a
stochastic Monte Carlo sampling over the quantum fluctuations with an exact
treatment of the quasiclassical degrees of freedoms. To a large degree, this
special technique circumvents the dynamical sign problem and allows the
dynamics to be studied directly up to long real times in a numerically exact
manner. This method has been applied to two important problems: (1) crossover
from nonadiabatic to adiabatic behavior in electron transfer reactions, (2) the
zero-temperature dynamics in the antiferromagnetic Kondo region 1/2<K<1 where K
is Kondo's parameter.",9411006v1
1995-01-09,Dynamic fluctuations in a Short-Range Spin Glass model,"We study the dynamic fluctuations of the soft-spin version of the
Edwards-Anderson model in the critical region for $T\rightarrow T_{c}^{+}$.
First we solve the infinite-range limit of the model using the random matrix
method. We define the static and dynamic 2-point and 4-point correlation
functions at the order $O(1/N)$ and we verify that the static limit obtained
from the dynamic expressions is correct. In a second part we use the functional
integral formalism to define an effective short-range Lagrangian $L$ for the
fields $\delta Q^{\alpha\beta}_{i}(t_{1},t_{2})$ up to the cubic order in the
series expansion around the dynamic Mean-Field value
$\overline{{Q}^{\alpha\beta}}(t_{1},t_{2})$. We find the more general
expression for the time depending non-local fluctuations, the propagators
$[\langle\delta Q^{\alpha\beta}_{i}(t_{1},t_{2}) \delta
Q^{\alpha\beta}_{j}(t_{3},t_{4})\rangle_{\xi}]_{J}$, in the quadratic
approximation. Finally we compare the long-range limit of the correlations,
derived in this formalism, with the correlations of the infinite-range model
studied with the previous approach (random matrices).",9501027v2
1999-03-15,Monte Carlo algorithms based on the number of potential moves,"We discuss Monte Carlo dynamics based on <N(sigma, Delta E)>_E, the
(microcanonical) average number of potential moves which increase the energy by
Delta E in a single spin flip. The microcanonical average can be sampled using
Monte Carlo dynamics of a single spin flip with a transition rate min(1,
<N(sigma', E-E')>_E' / <N(sigma, E'-E) >_E) from energy E to E'. A cumulative
average (over Monte Carlo steps) can be used as a first approximation to the
exact microcanonical average in the flip rate. The associated histogram is a
constant independent of the energy. The canonical distribution of energy can be
obtained from the transition matrix Monte Carlo dynamics. This second dynamics
has fast relaxation time - at the critical temperature the relaxation time is
proportional to specific heat. The dynamics are useful in connection with
reweighting methods for computing thermodynamic quantities.",9903224v1
1999-07-15,Dynamical Properties of the One-Dimensional Supersymmetric t-J Model: A View from Elementary Excitations,"Dynamical properties, such as dynamical spin and charge structure factors and
single-particle spectral functions, are studied for the one-dimensional
supersymmetric t-J model with inverse-square interaction. Exact diagonalization
and the recursion method are used for finite systems up to 16 sites. A simple
rule is proposed to understand the supermultiplet structure in the excitation
spectrum. Numerical calculations show that the dynamical spin structure factor
is independent of the electron density in the region where only two spinons
contribute. In the electron removal spectrum from half-filling, close
correspondence is found between the dominant contribution from three-spinon
plus one-holon states in the t-J model and the two-spinon excitations in the
Haldane-Shastry model. Comparison is made with dynamics of the nearest-neighbor
supersymmetric t-J model.",9907215v1
2000-07-24,Glassiness and constrained dynamics of a short-range non-disordered spin model,"We study the low temperature dynamics of a two dimensional short-range spin
system with uniform ferromagnetic interactions, which displays glassiness at
low temperatures despite the absence of disorder or frustration. The model has
a dual description in terms of free defects subject to dynamical constraints,
and is an explicit realization of the ``hierarchically constrained dynamics''
scenario for glassy systems. We give a number of exact results for the statics
of the model, and study in detail the dynamical behaviour of one-time and
two-time quantities. We also consider the role played by the configurational
entropy, which can be computed exactly, in the relation between fluctuations
and response.",0007372v2
2002-07-03,Aging dynamics of +-J Edwards-Anderson spin glasses,"We analyze by means of extensive computer simulations the out of equilibrium
dynamics of Edwards-Anderson spin glasses in d=4 and d=6 dimensions with +-J
interactions. In particular, we focus our analysis on the scaling properties of
the two-time autocorrelation function in a range of temperatures from T=0.07
T_c to T=0.75 T_c in both systems. We observe that the aging dynamics of the
+-J models is different from that observed in the corresponding Gaussian
models. In both the 4d and 6d models at very low temperatures we study the
effects of discretization of energy levels. Strong interrupted aging behaviors
are found. We argue that this is because in the times accessible to our
simulations the systems are only able to probe activated dynamics through the
lowest discrete energy levels and remain trapped around nearly flat regions of
the energy landscape. For temperatures T >= 0.5 T_c in 4d we find logarithmic
scalings that are compatible with dynamical ultrametricity, while in 6d the
relaxation can also be described by super-aging scalings.",0207105v1
2004-09-15,"Facilitated spin models on Bethe lattice: bootstrap percolation, mode-coupling transition and glassy dynamics","We show that facilitated spin models of cooperative dynamics introduced by
Fredrickson and Andersen display on Bethe lattices a glassy behaviour similar
to the one predicted by the mode-coupling theory of supercooled liquids and the
dynamical theory of mean-field disordered systems. At low temperature such
cooperative models show a two-step relaxation and their equilibration time
diverges at a finite temperature according to a power-law. The geometric nature
of the dynamical arrest corresponds to a bootstrap percolation process which
leads to a phase space organization similar to the one of mean-field disordered
systems. The relaxation dynamics after a subcritical quench exhibits aging and
converges asymptotically to the threshold states that appear at the bootstrap
percolation transition.",0409393v3
2004-09-18,Unifying Local Dynamics in Two-State Spin Systems,"We present a new two-state {+-} opinion dynamics model which defines a
general frame to include all local dynamics in two-state spin systems. Agents
evolve by probabilistic local rules. In each update, groups of various sizes k
are formed according to some probability distribution {a_k}. Given a specific
group with an initial (j) agents sharing opinion {+} and (k-j) agents opinion
{-}, all k members adopt opinion {+} with a probability m_{k,j} and opinion {-}
with (1-m_{k,j}). A very rich and new spectrum of dynamics is obtained. The
final opinion is a polarization along the initial majority, along the initial
minority or a perfect consensus with an equality of opinions as function of the
parameters {a_k, m_{k,j}}. In last case, two regimes exist, monotonic and
dampened oscillatory. The transition from polarization to consensus dynamics
occurs for values of the parameters which reproduce exactly the Voter model. A
scheme is presented to express any local update in terms of a specific set
{a_k, m_{k,j}}. Most existing opinion models are exhibited at particular
limits.",0409484v1
1998-11-12,A semiclassical approach to the Dirac equation,"We derive a semiclassical time evolution kernel and a trace formula for the
Dirac equation. The classical trajectories that enter the expressions are
determined by the dynamics of relativistic point particles. We carefully
investigate the transport of the spin degrees of freedom along the trajectories
which can be understood geometrically as parallel transport in a vector bundle
with SU(2) holonomy. Furthermore, we give an interpretation in terms of a
classical spin vector that is transported along the trajectories and whose
dynamics, dictated by the equation of Thomas precession, gives rise to
dynamical and geometric phases every orbit is weighted by. We also present an
analogous approach to the Pauli equation which we analyse in two different
limits.",9811025v1
2001-11-30,The quantum dynamics of two coupled qubits,"We investigate the difference between classical and quantum dynamics of
coupled magnetic dipoles. We prove that in general the dynamics of the
classical interaction Hamiltonian differs from the corresponding quantum model,
regardless of the initial state. The difference appears as non
positive-definite diffusion terms in the quantum evolution equation of an
appropriate positive phase-space probability density. Thus, it is not possible
to express the dynamics in terms of a convolution of a positive transition
probability function and the initial condition as can be done in the classical
case. We conclude that the dynamics is a quantum element of NMR quantum
information processing. There are two limits where our quantum evolution
coincide with the classical one: the short time limit before spin-spin
interaction sets in and the long time limit when phase diffusion is
incorporated.",0112001v1
2005-05-02,Dynamical phase transitions and temperature induced quantum correlations in an infinite spin chain,"We study the dynamics of entanglement in the infinite asymmetric XY spin
chain, in an applied transverse field. The system is prepared in a thermal
equilibrium state (ground state at zero temperature) at the initial instant,
and it starts evolving after the transverse field is completely turned off. We
investigate the evolved state of the chain at a given fixed time, and show that
the nearest neighbor entanglement in the chain exhibits a critical behavior
(which we call a dynamical phase transition), controlled by the initial value
of the transverse field. The character of the dynamical phase transition is
qualitatively different for short and long evolution times. We also find a
nonmonotonic behavior of entanglement with respect to the temperature of the
initial equilibrium state. Interestingly, the region of the initial field for
which we obtain a nonmonotonicity of entanglement (with respect to temperature)
is directly related to the position and character of the dynamical phase
transition in the model.",0505006v2
2008-06-05,Dissipative dynamics of a two - level system resonantly coupled to a harmonic mode,"We propose an approximation scheme to describe the dynamics of the spin-boson
model when the spectral density of the environment shows a peak at a
characteristic frequency $\Omega$ which can be very close (or even equal) to
the spin Zeeman frequency $\Delta$. Mapping the problem onto a two-state system
(TSS) coupled to a harmonic oscillator (HO) with frequency $\omega_0$ we show
that the representation of displaced HO states provides an appropriate basis to
truncate the Hilbert space of the TSS-HO system and therefore a better picture
of the system dynamics. We derive an effective Hamiltonian for the TSS-HO
system, and show it furnishes a very good approximation for the system dynamics
even when its two subsystems are moderately coupled. Finally, assuming the
regime of weak HO-bath coupling and low temperatures, we are able to
analytically evaluate the dissipative TSS dynamics.",0806.0992v2
2008-10-01,Fractal geometry of Ising magnetic patterns: signatures of criticality and diffusive dynamics,"We investigate the geometric properties displayed by the magnetic patterns
developing on a two-dimensional Ising system, when a diffusive thermal dynamics
is adopted. Such a dynamics is generated by a random walker which diffuses
throughout the sites of the lattice, updating the relevant spins. Since the
walker is biased towards borders between clusters, the border-sites are more
likely to be updated with respect to a non-diffusive dynamics and therefore, we
expect the spin configurations to be affected. In particular, by means of the
box-counting technique, we measure the fractal dimension of magnetic patterns
emerging on the lattice, as the temperature is varied. Interestingly, our
results provide a geometric signature of the phase transition and they also
highlight some non-trivial, quantitative differences between the behaviors
pertaining to the diffusive and non-diffusive dynamics.",0810.0216v1
2008-10-20,A resonance theory for open quantum systems with time-dependent dynamics,"We develop a resonance theory to describe the evolution of open systems with
time-dependent dynamics. Our approach is based on piecewise constant
Hamiltonians: we represent the evolution on each constant bit using a recently
developed dynamical resonance theory, and we piece them together to obtain the
total evolution. The initial state corresponding to one time-interval with
constant Hamiltonian is the final state of the system corresponding to the
interval before. This results in a non-markovian dynamics. We find a
representation of the dynamics in terms of resonance energies and resonance
states associated to the Hamiltonians, valid for all times $t\geq 0$ and for
small (but fixed) interaction strengths. The representation has the form of a
path integral over resonances. We present applications to a spin-fermion
system, where the energy levels of the spin may undergo rather arbitrary
crossings in the course of time. In particular, we find the probability for
transition between ground- and excited state at all times.",0810.3540v1
2008-11-23,Unitarity in Technicolor,"We investigate the longitudinal $WW$ scattering in models of dynamical
electroweak symmetry breaking featuring a spin one axial and vector state and a
composite Higgs. We also investigate the effects of a composite spin two state
which has the same properties of a massive graviton. Any model of dynamical
electroweak symmetry breaking will feature, depending on the dynamics, some or
all these basic resonances as part of the low energy spectrum. We suggest how
to take limits in the effective Lagrangian parameter space to reproduce the
dynamics of different types of underlying gauge theories, from the traditional
Technicolor models to the newest ones featuring nearly conformal dynamics. We
study the direct effects of a light composite Higgs and the indirect ones
stemming from the presence of a light axial resonance on the longitudinal $WW$
scattering.",0811.3719v2
2009-01-07,Dynamical replica analysis of processes on finitely connected random graphs II: Dynamics in the Griffiths phase of the diluted Ising ferromagnet,"We study the Glauber dynamics of Ising spin models with random bonds, on
finitely connected random graphs. We generalize a recent dynamical replica
theory with which to predict the evolution of the joint spin-field
distribution, to include random graphs with arbitrary degree distributions. The
theory is applied to Ising ferromagnets on randomly diluted Bethe lattices,
where we study the evolution of the magnetization and the internal energy. It
predicts a prominent slowing down of the flow in the Griffiths phase, it
suggests a further dynamical transition at lower temperatures within the
Griffiths phase, and it is verified quantitatively by the results of Monte
Carlo simulations.",0901.0788v1
2009-11-23,Spatial pattern formation and polarization dynamics of a nonequilibrium spinor polariton condensate,"Quasiparticles in semiconductors -- such as microcavity polaritons -- can
form condensates in which the steady-state density profile is set by the
balance of pumping and decay. By taking account of the polarization degree of
freedom for a polariton condensate, and considering the effects of an applied
magnetic field, we theoretically discuss the interplay between polarization
dynamics, and the spatial structure of the pumped decaying condensate. If
spatial structure is neglected, this dynamics has attractors that are linearly
polarized condensates (fixed points), and desynchronized solutions (limit
cycles), with a range of bistability. Considering spatial fluctuations about
the fixed point, the collective spin modes can either be diffusive, linearly
dispersing, or gapped. Including spatial structure, interactions between the
spin components can influence the dynamics of vortices; produce stable
complexes of vortices and rarefaction pulses with both co- and counter-rotating
polarizations; and increase the range of possible limit cycles for the
polarization dynamics, with different attractors displaying different spatial
structures.",0911.4468v1
2010-01-14,Interaction quench dynamics in the Kondo model in presence of a local magnetic field,"In this work we investigate the quench dynamics in the Kondo model on the
Toulouse line in presence of a local magnetic field. It is shown that this
setup can be realized by either applying the local magnetic field directly or
by preparing the system in a macroscopically spin-polarized initial state. In
the latter case, the magnetic field results from a subtlety in applying the
bosonization technique where terms that are usually referred to as finite-size
corrections become important in the present non-equilibrium setting. The
transient dynamics is studied by analyzing exact analytical results for the
local spin dynamics. The time scale for the relaxation of the local dynamical
quantities turns out to be exclusively determined by the Kondo scale. In the
transient regime, one observes damped oscillations in the local correlation
functions with a frequency set by the magnetic field.",1001.2418v2
2010-02-15,Nonequilibrium dynamic-correlation-length scaling method,"The finite-size scaling method in the equilibrium Monte Carlo(MC) simulations
and the finite-time scaling method in the nonequilibrium-relaxation simulations
are compromised. MC time data of various physical quantities are scaled by the
MC time data of the dynamic correlation length, which corresponds to changing
the system size in the finite-size scaling method. This scaling method is
tested in the three-dimensional ferromagnetic Ising spin model and in the three
dimensional $\pm J$ Ising spin-glass model. The transition temperature and the
critical exponents, $\eta$ and $\nu$, are obtained by the nonequilibrium
relaxation data of the susceptibility and the dynamic correlation length apart
from the dynamic exponent. We also comment on the definition of the dynamic
correlation length in the nonequilibrium relaxation process. The
Ornstein-Zernike formula is not always appropriate.",1002.2817v1
2010-10-05,Coevolution of Glauber-like Ising dynamics on typical networks,"We consider coevolution of site status and link structures from two different
initial networks: a one dimensional Ising chain and a scale free network. The
dynamics is governed by a preassigned stability parameter $S$, and a rewiring
factor $\phi$, that determines whether the Ising spin at the chosen site flips
or whether the node gets rewired to another node in the system. This dynamics
has also been studied with Ising spins distributed randomly among nodes which
lie on a network with preferential attachment. We have observed the steady
state average stability and magnetisation for both kinds of systems to have an
idea about the effect of initial network topology. Although the average
stability shows almost similar behaviour, the magnetisation depends on the
initial condition we start from. Apart from the local dynamics, the global
effect on the dynamics has also been studied. These parameters show interesting
variations for different values of $S$ and $\phi$, which helps in determining
the steady-state condition for a given substrate.",1010.0863v1
2011-12-21,Linear Ramps of Interaction in the Fermionic Hubbard Model,"We study the out of equilibrium dynamics of the Fermionic Hubbard Model
induced by a linear ramp of the repulsive interaction $U$ from the metallic
state through the Mott transition. To this extent we use a time dependent
Gutzwiller variational method and complement this analysis with the inclusion
of quantum fluctuations at the leading order, in the framework of a $Z_2$ slave
spin theory. We discuss the dynamics during the ramp and the issue of
adiabaticity through the scaling of the excitation energy with the ramp
duration $\tau$. In addition, we study the dynamics for times scales longer
than the ramp time, when the system is again isolated and the total energy
conserved. We establish the existence of a dynamical phase transition analogous
to the one present in the sudden quench case and discuss its properties as a
function of final interaction and ramp duration. Finally we discuss the role of
quantum fluctuations on the mean field dynamics for both long ramps, where spin
wave theory is sufficient, and for very short ramps, where a self consistent
treatment of quantum fluctuations is required in order to obtain relaxation.",1112.5063v2
2012-06-27,"Evaluation of the importance of spin-orbit couplings in the nonadiabatic quantum dynamics with quantum fidelity and with its efficient ""on-the-fly"" ab initio semiclassical approximation","We propose to measure the importance of spin-orbit couplings (SOCs) in the
nonadiabatic molecular quantum dynamics rigorously with quantum fidelity. To
make the criterion practical, quantum fidelity is estimated efficiently with
the multiple-surface dephasing representation (MSDR). The MSDR is a
semiclassical method that includes nuclear quantum effects through interference
of mixed quantum-classical trajectories without the need for the Hessian of
potential energy surfaces. Two variants of the MSDR are studied, in which the
nuclei are propagated either with the fewest-switches surface hopping or with
the locally mean field dynamics. The fidelity criterion and MSDR are first
tested on one-dimensional model systems amenable to numerically exact quantum
dynamics. Then, the MSDR is combined with ""on-the-fly"" computed electronic
structure to measure the importance of SOCs and nonadiabatic couplings (NACs)
in the photoisomerization dynamics of CH2NH2+ considering 20 electronic states
and in the collision of F + H2 considering six electronic states.",1206.6299v1
2014-01-09,Dynamics of the two-dimensional directed Ising model in the paramagnetic phase,"We consider the non-conserved dynamics of the Ising model on the
two-dimensional square lattice, where each spin is influenced preferentially by
its East and North neighbours. The single-spin flip rates are such that the
stationary state is Gibbsian with respect to the usual ferromagnetic Ising
Hamiltonian. We show the existence, in the paramagnetic phase, of a dynamical
transition between two regimes of violation of the fluctuation-dissipation
theorem in the nonequilibrium stationary state: a regime of weak violation
where the stationary fluctuation-dissipation ratio is finite, when the
asymmetry parameter is less than a threshold value, and a regime of strong
violation where this ratio vanishes asymptotically above the threshold. The
present study suggests that this novel kind of dynamical transition in
nonequilibrium stationary states, already found for the directed Ising chain
and the spherical model with asymmetric dynamics, might be quite general. In
contrast with the later models, the equal-time correlation function for the
two-dimensional directed Ising model depends on the asymmetry.",1401.1988v1
2014-04-12,Dynamical magnetic skyrmions,"Spin transfer torque (STT) affords magnetic nanodevices the potential to act
as memory, computing, and microwave elements operating at ultra-low currents
and at a low energy cost. Spin transfer torque is not only effective in
manipulating well-known magnetic structures, such as domain walls and vortices,
but can also nucleate previously unattainable nano-magnetic objects, such as
magnetic droplets and skyrmions. While the droplet and the skyrmion are both
solitons, the former is inherently dynamic and non-topological, whereas the
latter is static but topologically protected. Here we show that it is possible
to combine these properties into a novel topologically protected dynamical
skyrmion, which adds additional degrees of freedom, and functionality, to both
droplet and skyrmion based applications. Unlike static skyrmions, the dynamical
skyrmion can be nucleated and sustained without Dzyaloshinskii-Moriya
interaction (DMI) or dipole-dipole interaction (DDI), and is a generic soliton
solution independent of STT and damping once nucleated. In the presence of
large DMI, the dynamical skyrmion experiences strong breathing with particular
promise for skyrmion-based memory and microwave applications.",1404.3281v2
2014-04-17,Rényi Information flow in the Ising model with single-spin dynamics,"The $n$-index R\'enyi mutual information and transfer entropy for the
two-dimensional kinetic Ising model with arbitrary single-spin dynamics in the
thermodynamic limit are derived as functions of thermodynamic quantities. By
means of Monte Carlo simulations with the Wolff algorithm, we calculate the
information flows in the Ising model with the Metropolis dynamics and the
Glauber dynamics. We find that, not only the global R\'enyi transfer entropy,
but also the pairwise R\'enyi transfer entropy peaks in the disorder phase.
Therefore, the R\'enyi information flows may be used as better tools than the
Shannon counterparts in the study of phase transitions in complex dynamical
systems.",1404.4567v2
2014-10-10,Collective dynamics in a binary mixture of hydrodynamically coupled micro-rotors,"We study, numerically, the collective dynamics of self-rotating nonaligning
particles by considering a monolayer of spheres driven by constant clockwise or
counterclockwise torques. We show that hydrodynamic interactions alter the
emergence of large-scale dynamical patterns compared to those observed in dry
systems. In dilute suspensions, the flow stirred by the rotors induces
clustering of opposite-spin rotors, while at higher densities same-spin rotors
phase separate. Above a critical rotor density, dynamic hexagonal crystals
form. Our findings underscore the importance of inclusion of the many-body,
long-range hydrodynamic interactions in predicting the phase behavior of active
particles.",1410.2878v2
2016-04-15,Direct observation of magnetization dynamics generated by nano-contact spin-torque vortex oscillators,"Time-resolved scanning Kerr microscopy has been used to directly image the
magnetization dynamics of nano-contact (NC) spin-torque vortex oscillators
(STVOs) when phase-locked to an injected microwave (RF) current. The Kerr
images reveal free layer magnetization dynamics that extend outside the NC
footprint, where they cannot be detected electrically, but which are crucial to
phase-lock STVOs that share common magnetic layers. For a single NC, dynamics
were observed not only when the STVO frequency was fully locked to that of the
RF current, but also for a partially locked state characterized by periodic
changes in the core trajectory at the RF frequency. For a pair of NCs, images
reveal the spatial character of dynamics that electrical measurements show to
have enhanced amplitude and reduced linewidth. Insight gained from these images
may improve understanding of the conditions required for mutual phase-locking
of multiple STVOs, and hence enhanced microwave power emission.",1604.04455v1
2016-04-20,Nonlinear Dynamics of Dipoles in Microtubules: Pseudo-Spin Model,"We perform a theoretical study of the dynamics of the electric field
excitations in a microtubule by taking into consideration the realistic
cylindrical geometry, dipole-dipole interactions of the tubulin-based protein
heterodimers, the radial electric field produced by the solvent, and a possible
degeneracy of energy states of individual heterodimers. The consideration is
done in the frames of the classical pseudo-spin model. We derive the system of
nonlinear dynamical ordinary differential equations of motion for interacting
dipoles, and the continuum version of these equations. We obtain the solutions
of these equations in the form of snoidal waves, solitons, kinks, and localized
spikes. Our results will help to a better understanding of the functional
properties of microtubules including the motor protein dynamics and the
information transfer processes. Our considerations are based on classical
dynamics. Some speculations on the role of possible quantum effects are also
made.",1604.05971v1
2016-10-06,Dynamical phase diagram of spin chains with long-range interactions,"Using an infinite Matrix Product State (iMPS) technique based on the
time-dependent variational principle (TDVP), we study two major types of
dynamical phase transitions (DPT) in the one-dimensional transverse-field Ising
model (TFIM) with long-range power-law ($\propto1/r^{\alpha}$ with $r$
inter-spin distance) interactions out of equilibrium in the thermodynamic limit
-- \textit{DPT-I}: based on an order parameter in a (quasi-)steady state, and
\textit{DPT-II}: based on non-analyticities (cusps) in the Loschmidt-echo
return rate. We construct the corresponding rich dynamical phase diagram,
whilst considering different quench initial conditions. We find a nontrivial
connection between both types of DPT based on their critical lines. Moreover,
and very interestingly, we detect a new DPT-II dynamical phase in a certain
range of interaction exponent $\alpha$, characterized by what we call
\textit{anomalous cusps} that are distinct from the \textit{regular cusps}
usually associated with DPT-II. Our results provide the characterization of
experimentally accessible signatures of the dynamical phases studied in this
work.",1610.02019v2
2017-02-17,Complex semiclassical analysis of the Loschmidt amplitude and dynamical quantum phase transitions,"We propose a new computational method of the Loschmidt amplitude in a generic
spin system on the basis of the complex semiclassical analysis on the
spin-coherent state path integral. We demonstrate how the dynamical transitions
emerge in the time evolution of the Loschmidt amplitude for the infinite-range
transverse Ising model with a longitudinal field, exposed by a quantum quench
of the transverse field $\Gamma$ from $\infty$ or $0$. For both initial
conditions, we obtain the dynamical phase diagrams that show the presence or
absence of the dynamical transition in the plane of transverse field after a
quantum quench and the longitudinal field. The results of semiclassical
analysis are verified by numerical experiments. Experimental observation of our
findings on the dynamical transition is also discussed.",1702.05396v2
2017-03-10,Kinetic Ising models with various single-spin flip dynamics on quenched and annealed random regular graphs,"We investigate a kinetic Ising model with several single-spin flip dynamics
(including Metropolis and heat-bath) on quenched and annealed random regular
graphs. As expected, on the quenched structures all proposed algorithms
reproduce the same results since the conditions for the detailed balance and
the Boltzmann distribution in an equilibrium are satisfied. However, on the
annealed graphs situation is far less clear -- the network annealing disturbs
the equilibrium moving the system away from it. Consequently, distinct dynamics
lead to different steady states. We show that some algorithms are more
resistant to the annealed disorder, which causes only small quantitative
changes in the model behavior. On the other hand, there are dynamics for which
the influence of annealing on the system is significant, and qualitative
changes arise like switching the type of phase transition from continuous to
discontinuous one. We try to identify features of the proposed dynamics which
are responsible for the above phenomenon.",1703.03602v1
2018-11-07,"Magnetization and energy dynamics in spin ladders: Evidence of diffusion in time, frequency, position, and momentum","The dynamics of magnetization and energy densities are studied in the two-leg
spin-1/2 ladder. Using an efficient pure-state approach based on the concept of
typicality, we calculate spatio-temporal correlation functions for large
systems with up to 40 lattice sites. In addition, two subsequent Fourier
transforms from real to momentum space as well as from time to frequency domain
yield the respective dynamic structure factors. Summarizing our main results,
we unveil the existence of genuine diffusion both for spin and energy. In
particular, this finding is based on four distinct signatures which can all be
equally well detected: (i) Gaussian density profiles, (ii) time-independent
diffusion coefficients, (iii) exponentially decaying density modes, and (iv)
Lorentzian line shapes of the dynamic structure factor. The combination of (i)
- (iv) provides a comprehensive picture of high-temperature dynamics in
thisarchetypal nonintegrable quantum model.",1811.02806v2
2018-11-13,Phase locking of a pair of nano ferromagnetic oscillators on a topological insulator,"We investigate the magnetization dynamics of a pair of ferromagnetic
insulators (FMIs) deposited on the surface of a topological insulator (TI). Due
to the nonlinear nature of the underlying physics and intrinsic dynamics, the
FMIs can exhibit oscillatory behaviors even under a constant applied voltage.
The motion of the surface electrons of the TI, which obeys relativistic quantum
mechanics, provides a mechanism of direct coupling between the FMIs. In
particular, the spin polarized current of the TI surface electrons can affect
the magnetization of the two FMIs, which in turn modulates the electron
transport, giving rise to a hybrid relativistic quantum/classical nonlinear
dynamical system. We find robust phase and anti-phase locking between the
magnetization dynamics. As driving the surface electrons of a TI only requires
extremely low power, our finding suggests that nano FMIs coupled by a spin
polarized current on the surface of TI have the potential to serve as the
fundamental building blocks of unconventional, low-power computing paradigms.",1811.05551v1
2017-04-04,Nematic ordering dynamics of an anti-ferromagnetic spin-1 condensate,"We consider the formation of order in a quasi-two-dimensional (quasi-2D)
anti-ferromagnetic spin-1 condensate quenched from an easy-axis (EA) to an
easy-plane (EP) nematic phase. We define the relevant order parameter to
quantify the spin-nematic degrees of freedom and study the evolution of the
spin-nematic and superfluid order during the coarsening dynamics using
numerical simulations. We observe dynamical scaling in the late time dynamics
with both types of order extending across the system with a diffusive growth
law. We identify half-quantum vortices (HQVs) as the relevant topological
defects of the ordering dynamics, and demonstrate that the growth of both types
of order is determined by the mutual annihilation of these vortices.",1704.00871v1
2017-04-13,Efficient Real-Time Path Integrals for Non-Markovian Spin-Boson Models,"Strong coupling between a system and its environment leads to the emergence
of non-Markovian dynamics, which cannot be described by a time-local master
equation. One way to capture such dynamics is to use numerical real-time path
integrals, where assuming a finite bath memory time enables manageable
simulation scaling. However, by comparing to the exactly soluble independent
boson model, we show that the presence of transient negative decay rates in the
exact dynamics can result in simulations with unphysical exponential growth of
density matrix elements when the finite memory approximation is used. We
therefore reformulate this approximation in such a way that the exact dynamics
are reproduced identically and then apply our new method to the spin-boson
model with superohmic environmental coupling, commonly used to model phonon
environments, but which cannot be solved exactly. Our new method allows us to
easily access parameter regimes where we find revivals in population dynamics
which are due to non-Markovian backflow of information from the bath to the
system.",1704.04099v2
2017-04-24,A hybrid memory kernel approach for condensed phase non-adiabatic dynamics,"The spin-boson model is a simplified Hamiltonian often used to study
non-adiabatic dynamics in large condensed phase systems, even though it has not
been solved in a fully analytic fashion. Herein, we present an exact analytic
expression for the dynamics of the spin-boson model in the infinitely slow bath
limit and generalize it to approximate dynamics for faster baths. We achieve
the latter by developing a hybrid approach that combines the exact slow-bath
result with the popular NIBA method to generate a memory kernel that is
formally exact to second order in the diabatic coupling but also contains
higher-order contributions approximated from the second order term alone. This
kernel has the same computational complexity as NIBA, but is found to yield
dramatically superior dynamics in regimes where NIBA breaks down---such as
systems with large diabatic coupling or energy bias. This indicates that this
hybrid approach could be used to cheaply incorporate higher order effects into
second order methods, and could potentially be generalized to develop alternate
kernel resummation schemes.",1704.07477v2
2018-01-09,Observation of entanglement sudden death and rebirth by controlling solid-state spin bath,"Quantum entanglement, the essential resource for quantum information
processing, has rich dynamics under different environments. Probing different
entanglement dynamics typically requires exquisite control of complicated
system-environment coupling in real experimental systems. Here, by a simple
control of the effective solid-state spin bath in a diamond sample, we observe
rich entanglement dynamics, including the conventional asymptotic decay as well
as the entanglement sudden death, a term coined for the phenomenon of complete
disappearance of entanglement after a short finite time interval. Furthermore,
we observe counter-intuitive entanglement rebirth after its sudden death in the
same diamond sample by tuning an experimental parameter, demonstrating that we
can conveniently control the non-Markovianity of the system-environment
coupling through a natural experimental knob. Further tuning of this
experimental knob can make the entanglement dynamics completely coherent under
the same environmental coupling. Probing of entanglement dynamics, apart from
its fundamental interest, may find applications in quantum information
processing through control of the environmental coupling.",1801.02729v1
2018-10-08,Generating Macroscopic Superpositions with Interacting Bose-Einstein Condensates: Multi-Mode Speed-Ups and Speed Limits,"We theoretically investigate the effect of multi-mode dynamics on the
creation of macroscopic superposition states (spin-cat states) in Bose-Einstein
condensates via one-axis twisting. A two-component Bose-Einstein condensate
naturally realises an effective one-axis twisting interaction, under which an
initially separable state will evolve toward a spin-cat state. However, the
large evolution times necessary to realise these states is beyond the scope of
current experiments. This evolution time is proportional to the degree of
asymmetry in the relative scattering lengths of the system, which results in
the following trade-off; faster evolution times are associated with an increase
in multi-mode dynamics, and we find that generally multi-mode dynamics reduce
the degree of entanglement present in the final state. However, we find that
highly entangled cat-like states are still possible in the presence of
significant multi-mode dynamics, and that these dynamics impose a speed-limit
on the evolution such states.",1810.03236v2
2019-07-29,Simulating nonlinear dynamics of collective spins via quantum measurement and feedback,"We study a method to simulate quantum many-body dynamics of spin ensembles
using measurement-based feedback. By performing a weak collective measurement
on a large ensemble of two-level quantum systems and applying global rotations
conditioned on the measurement outcome, one can simulate the dynamics of a
mean-field quantum kicked top, a standard paradigm of quantum chaos. We
analytically show that there exists a regime in which individual quantum
trajectories adequately recover the classical limit, and show the transition
between noisy quantum dynamics to full deterministic chaos described by
classical Lyapunov exponents. We also analyze the effects of decoherence, and
show that the proposed scheme represents a robust method to explore the
emergence of chaos from complex quantum dynamics in a realistic experimental
platform based on an atom-light interface.",1907.12606v2
2019-10-02,Quantum criticality of loops with topologically constrained dynamics,"Quantum fluctuating loops in 2+1 dimensions give gapless many-body states
that are beyond current field theory techniques. Microscopically, these loops
can be domain walls between up and down spins, or chains of flipped spins
similar to those in the toric code. The key feature of their dynamics is that
the reconnection of a pair of strands is forbidden. This happens at
previously-studied multi-critical points between topologically nontrivial
phases. We show that this topologically constrained dynamics leads to
universality classes with unusual scaling properties. For example, scaling
operators at these fixed points are classified by topology, and not only by
symmetry. We introduce the concept of the topological operator classification,
provide universal scaling forms for correlation functions, and analytical and
numerical results for critical exponents. We use an exact correspondence
between the imaginary-time dynamics of the 2+1D quantum models and a classical
Markovian dynamics for 2D classical loop models with a nonlocal Boltzmann
weight (for which we also provide scaling results). We comment on open
questions and generalizations of the models discussed for both quantum
criticality and classical Markov processes.",1910.01136v1
2020-01-15,Entanglement generation via power-of-SWAP operations between dynamic electron-spin qubits,"Surface acoustic waves (SAWs) can create moving quantum dots in piezoelectric
materials. Here we show how electron-spin qubits located on dynamic quantum
dots can be entangled. Previous theoretical and numerical models of quantum-dot
entanglement generation have been insufficient to study quantum dynamics in
realistic experimental devices. We utilize state-of-the-art graphics processing
units to simulate the wave function dynamics of two electrons carried by a SAW
through a 2D semiconductor heterostructure. We build a methodology to implement
a power-of-SWAP gate via the Coulomb interaction. A benefit of the SAW
architecture is that it provides a coherent way of transporting the qubits
through an electrostatic potential. This architecture allows us to avoid
problems associated with fast control pulses and guarantees operation
consistency, providing an advantage over static qubits. For inter-dot barrier
heights where the double occupation energy is sufficiently greater than the
double-dot hopping energy, we find that parameters based on experiments in
GaAs/AlGaAs heterostructures can produce a high-fidelity root-of-SWAP
operation. Our results provide a methodology for a crucial component of
dynamic-qubit quantum computing.",2001.05502v1
2018-03-13,Spin-glass--like aging in colloidal and granular glasses,"Motivated by the mean field prediction of a Gardner phase transition between
a ""normal glass"" and a ""marginally stable glass"", we investigate the
off-equilibrium dynamics of three-dimensional polydisperse hard spheres, used
as a model for colloidal or granular glasses. Deep inside the glass phase, we
find that a sharp crossover pressure $P_{\rm G}$ separates two distinct
dynamical regimes. For pressure $P < P_{\rm G}$, the glass behaves as a normal
solid, displaying fast dynamics that quickly equilibrates within the glass free
energy basin. For $P>P_{\rm G}$, instead, the dynamics becomes strongly
anomalous, displaying very large equilibration time scales, aging, and a
constantly increasing dynamical susceptibility. The crossover at $P_{\rm G}$ is
strongly reminiscent of the one observed in three-dimensional spin-glasses in
an external field, suggesting that the two systems could be in the same
universality class, consistently with theoretical expectations.",1803.05031v3
2018-05-31,Scrambling and entanglement spreading in long-range spin chains,"We study scrambling in connection to multipartite entanglement dynamics in
regular and chaotic long-range spin chains, characterized by a well defined
semi-classical limit. For regular dynamics, scrambling and entanglement
dynamics are found to be very different: up to the Ehrenfest time they rise
side by side departing only afterwards. Entanglement saturates and becomes
extensively multipartite, while scrambling continues its growth up to the
recurrence time. Remarkably, the exponential behaviour of scrambling emerges
not only in the chaotic case, but also in the regular one, when the dynamics
occurs at a dynamical critical point.",1806.00022v2
2019-08-25,Spin-reorientation critical dynamics in the two-dimensional XY model with a domain wall,"In recent years, static and dynamic properties of non-$180^\circ$ domain
walls in magnetic materials have attracted a great deal of interest. In this
paper, spin-reorientation critical dynamics in the two-dimensional XY model is
investigated with Monte Carlo simulations and theoretical analyses based on the
Langevin equation. At the Kosterlitz-Thouless phase transition, dynamic scaling
behaviors of the magnetization and the two-time correlation function are
carefully analyzed, and critical exponents are accurately determined. When the
initial value of the angle between adjacent domains is slightly lower than
$\pi$, a critical exponent is introduced to characterize the abnormal power-law
increase of the magnetization in the horizontal direction inside the domain
interface, which is measured to be $\psi=0.0568(8)$. Besides, the relation
$\psi=\eta/2z$ is analytically deduced from the Langevin dynamics in the
long-wavelength approximation, well consistent with numerical results.",1908.09247v1
2020-09-25,Coherent Dynamics of the Off-Diagonal Spin-Boson Model in the Ultra-Strong Coupling Regime,"Quantum mechanics describes the unitary time evolution of closed systems. In
practice, every quantum system interacts with the environment leading to an
irreversible loss of coherence. The Spin-Boson model (SBM) is central to the
understanding of the fundamental process of decoherence of a two-state quantum
system interacting with a bosonic heat bath but the nature of transient
dynamics in the presence of hybrid diagonal and off-diagonal system-bath
interactions remains largely unexplored. Here, we investigate how the hybrid
system-bath interactions of an Ohmic environment induce localization in the
bias-free SBM. For strong coupling to the environment, localization is strongly
affected by a dynamically generated bias via the renormalization of the
tunneling amplitude. We find that counteractive effects of Hamiltonian
parameters on non-exponential short-time dynamics and long-time population
equilibration can lead to a separation of timescales and non-equilibrium
quantum coherent dynamics that can persist even for ultra-strong system-bath
interaction. The findings offer novel opportunities to exploit coherence as a
resource in quantum devices operating in the ultra-strong coupling regime.",2009.12296v1
2020-10-03,Dynamical Crystallites of Active Chiral Particles,"One of the intrinsic characteristics of far-from-equilibrium systems is the
nonrelaxational nature of the system dynamics, which leads to novel properties
that cannot be understood and described by conventional pathways based on
thermodynamic potentials. Of particular interest are the formation and
evolution of ordered patterns composed of active particles that exhibit
collective behavior. Here we examine such a type of nonpotential active system,
focusing on effects of coupling and competition between chiral particle
self-propulsion and self-spinning. It leads to the transition between three
bulk dynamical regimes dominated by collective translative motion,
spinning-induced structural arrest, and dynamical frustration. In addition, a
persistently dynamical state of self-rotating crystallites is identified as a
result of a localized-delocalized transition induced by the crystal-melt
interface. The mechanism for the breaking of localized bulk states can also be
utilized to achieve self-shearing or self-flow of active crystalline layers.",2010.01252v1
2020-10-28,Recent progress in antiferromagnetic dynamics,"Spintronics, since its inception, has mainly focused on ferromagnetic
materials for manipulating the spin degree of freedom in addition to the charge
degree of freedom, whereas much less attention has been paid to
antiferromagnetic materials. Thanks to the advances of micro-nano-fabrication
techniques and the electrical control of the N\'eel order parameter,
antiferromagnetic spintronics is booming as a result of abundant room
temperature materials, robustness against external fields and dipolar coupling,
and rapid dynamics in the terahertz regime. For the purpose of applications of
antiferromagnets, it is essential to have a comprehensive understanding of the
antiferromagnetic dynamics at the microscopic level. Here, we first review the
general form of equations that govern both antiferromagnetic and ferrimagnetic
dynamics. This general form unifies the previous theories in the literature. We
also provide a survey for the recent progress related to antiferromagnetic
dynamics, including the motion of antiferromagnetic domain walls and skyrmions,
the spin pumping and quantum antiferromagnetic spintronics. In particular, open
problems in several topics are outlined. Furthermore, we discuss the
development of antiferromagnetic quantum magnonics and its potential
integration with modern information science and technology.",2010.14940v1
2020-11-13,Slow dynamics of the Fredkin spin chain,"The dynamical behavior of a quantum many-particle system is characterized by
the lifetime of its excitations. When the system is perturbed, observables of
any non-conserved quantity decay exponentially, but those of a conserved
quantity relax to equilibrium with a power law. Such processes are associated
with a dynamical exponent $z$ that relates the spread of correlations in space
and time. We present numerical results for the Fredkin model, a quantum spin
chain with a three-body interaction term, which exhibits an unusually large
dynamical exponent. We discuss our efforts to produce a reliable estimate
$z$=3.16(1) through direct simulation of the quantum evolution and to explain
the slow dynamics in terms of an excited bond that executes a constrained
random walk in Monte Carlo time.",2011.07110v2
2021-12-08,"Couplings of ${\cal N}=4$, $d=1$ mirror supermultiplets","We construct models of coupled semi-dynamical (spin) and dynamical mirror
multiplets of ${\cal N}=4$ supersymmetric mechanics in $d=1$ harmonic
superspace. Specifically, we consider a semi-dynamical mirror multiplet ${\bf
(3,4,1)}$ coupled to dynamical mirror multiplets ${\bf (1, 4, 3)}$ and ${\bf
(2, 4, 2)}$. Coupling of the multiplets ${\bf (3, 4, 1)}$ and ${\bf (1, 4, 3)}$
yields a mirror counterpart of the earlier constructed model implying the Nahm
equations for the spin variables with the bosonic component of the multiplet
${\bf (1, 4, 3)}$ as an evolution parameter. We also couple the mirror
multiplet ${\bf (2,4,2)}$ to the mirror semi-dynamical multiplet ${\bf (3, 4,
1)}$ using chiral ${\cal N}=4$ superspace. The models constructed admit a
generalization to the SU$(2|1)$ deformation of ${\cal N}=4$, $d=1$ Poincar\'e
supersymmetry.",2112.04420v3
2021-12-13,Extreme many-body scarring in a quantum spin chain via weak dynamical constraints,"It has recently been established that quantum many-body scarring can prevent
the thermalisation of some isolated quantum systems, starting from certain
initial states. One of the first models to show this was the so-called PXP
Hamiltonian, which was used to theoretically model an experiment on a chain of
strongly interacting Rydberg atoms. A defining feature of the PXP Hamiltonian
is a set of dynamical constraints that make certain states inaccessible to the
dynamics. In this paper we construct a class of spin chain models that are
parameterised by a discrete variable $\ell$ that controls the ""strength"" of a
dynamical constraint. We show that by increasing $\ell$ the constraint becomes
weaker, in the sense that fewer states are excluded from the dynamics. The PXP
Hamiltonian is special case for $\ell = 2$. By weakening the constraint to
$\ell \geq 4$, however, we find a more extreme version of quantum scarring than
in the PXP Hamiltonian, with the number of scar states growing exponentially in
the system size.",2112.06573v1
2021-12-27,Skyrmion based energy efficient straintronic physical reservoir computing,"Physical Reservoir Computing (PRC) is an unconventional computing paradigm,
which exploits nonlinear dynamics of reservoir blocks to perform recognition
and classification tasks. Here we show with simulations that patterned thin
films hosting several skyrmions, particularly one, two, four and nine
skyrmions, can implement energy efficient reservoir computing. This reservoir
computing (RC) block is based on nonlinear breathing dynamics of skyrmions,
which are coupled to each other through dipole interaction and spin waves, in
response to a voltage generated strain. This nonlinear and coupled
magnetization dynamics is exploited to perform temporal pattern recognition.
Two performance metrics, namely Short-Term Memory (STM) and Parity Check (PC)
capacity are studied to demonstrate the potential of such skyrmion based PRC in
addition to showing it can classify sine and square waves with 100% accuracy.
Furthermore, our study demonstrates that nonlinear magnetization dynamics and
interaction through spin waves and dipole coupling have a strong influence on
STM and PC capacity, thus explaining the role of physical interactions in a
dynamical system on its ability to perform Reservoir Computing (RC).",2112.13527v2
2022-02-11,Dynamical quantum phase transitions in strongly correlated two-dimensional spin lattices following a quench,"Dynamical quantum phase transitions are at the forefront of current efforts
to understand quantum matter out of equilibrium. Except for a few exactly
solvable models, predictions of these critical phenomena typically rely on
advanced numerical methods. However, those approaches are mostly restricted to
one dimension, making investigations of two-dimensional systems highly
challenging. Here, we present evidence of dynamical quantum phase transitions
in strongly correlated spin lattices in two dimensions. To this end, we apply
our recently developed cumulant method [Phys. Rev. X 11, 041018 (2021)] to
determine the zeros of the Loschmidt amplitude in the complex plane of time and
predict the crossing points of the thermodynamic lines of zeros with the
real-time axis, where dynamical quantum phase transitions occur. We find the
critical times of a two-dimensional quantum Ising lattice and the XYZ model
with ferromagnetic or antiferromagnetic couplings. We also show how dynamical
quantum phase transitions can be predicted by measuring the initial energy
fluctuations, for example, in quantum simulators or other engineered quantum
systems.",2202.05519v2
2022-02-28,A Phase-Space Semiclassical Approach for Modeling Nonadiabatic Nuclear Dynamics with Electronic Spin,"Chemical relaxation phenomena, including photochemistry and electron transfer
processes, form a vigorous area of research in which nonadiabatic dynamics
plays a fundamental role. Here, we show that for nonadiabatic dynamics with two
electronic states and a complex-valued Hamiltonian that does not obey
time-reversal symmetry, the optimal semiclassical approach is to run surface
hopping dynamics on a set of phase-space adiabatic surfaces. In order to
generate such phase-adiabats, one must isolate a proper set of diabats and
apply a phase gauge transformation, before eventually diagonalizing the total
Hamiltonian (which is now parameterized by both R and P). The resulting
algorithm is valid in both the adiabatic and nonadiabatic limits, incorporates
all Berry curvature effects, and allows for the study of semiclassical
nonadiabatic dynamics in the presence of spin-orbit coupling and/or external
magnetic fields.",2202.13973v1
2022-03-02,A.C. susceptibility as a probe of low-frequency magnetic dynamics,"The experimental technique of a.c. susceptibility can be used as a probe of
magnetic dynamics in a wide variety of systems. Its use is restricted to the
low-frequency regime and thus is sensitive to relatively slow processes. Rather
than measuring the dynamics of single spins, a.c. susceptibility can be used to
probe the dynamics of collective objects, such as domain walls in ferromagnets
or vortex matter in superconductors. In some frustrated systems, such as spin
glasses, the complex interactions lead to substantial spectral weight of
fluctuations in the low-frequency regime, and thus a.c. susceptibility can play
a unique role. We review the theory underlying the technique and magnetic
dynamics more generally and give applications of a.c. susceptibility to a wide
variety of experimental situations.",2203.00989v1
2022-11-15,Low temperature dynamics for confined $p=2$ soft spin in the quenched regime,"This paper aims to address the low-temperature dynamics issue for the $p=2$
spin dynamics with confining potential, focusing especially on quartic and
sextic cases. The dynamics are described by a Langevin equation for a real
vector $q_i$ of size $N$, where disorder is materialized by a Wigner matrix and
we especially investigate the self consistent evolution equation for effective
potential arising from self averaging of the square length $a(t)\equiv \sum_i
q_i^2(t)/N$ for large $N$. We first focus on the static case, assuming the
system reached some equilibrium point, and we then investigate the way the
system reach this point dynamically. This allows to identify a critical
temperature, above which the relaxation toward equilibrium follows an
exponential law but below which it has infinite time life and corresponds to a
power law decay.",2211.07809v3
2022-12-01,"Quantum dynamic and geometric phases in harmonic oscillator, spin 1/2 and two-level thermal engines systems","Dynamical phases are obtained for a quantum thermal engine, whose working
medium is a single harmonic oscillator. The dynamics of this engine is obtained
by using four steps where in two steps the time dependent frequency is
changing. In the other two steps, the thermal engine is coupled alternatively
to hot and cold heat baths. Similar dynamical phases are obtained in a quantum
thermal engine whose working medium is spin 1/2 system. The role of times
durations of such steps in the quantum engines for getting maximal efficiency
is analyzed. The dynamic of charge pumping in a quantum dot coupled to two
reservoirs is studied. The effects of many modulation parameters including
their fluctuations for getting geometric phases are analyzed. Since the
separate steps in thermal engines describe non-cyclic circuits, we propose to
use a special method for measuring geometric phases in thermal engines for
non-cyclic circuits which is gauge invariant.",2212.02970v1
2023-05-09,Muonium state exchange dynamics in n-type Gallium Arsenide,"Muonium (Mu), a pseudo-isotope atom of hydrogen with a positively charged
muon at the place of the proton, can form in a wide range of semiconductor
materials. They can appear in different states, depending on their charge state
and microscopic site within a crystal lattice. After the Mu formation, they
undergo interactions with free charge carriers, electronic spins, and other Mu
sites, and form a dynamic network of state exchange. We identified the model of
Mu dynamics in n-type Gallium Arsenide using the density matrix simulation and
photoexcited muon spin spectroscopy technique. Fitting to the dark and
illuminated $\mu$SR data provided transition rates between Mu states, which in
turn showed the underlying mechanism of the $\mu$SR time spectra. Deduced
capture/scattering cross sections of the Mu states reflected the microscopic
dynamics of Mu. Illumination studies enable us to measure interactions between
Mu and generated minority carriers, which are unavailable in dark measurements.
The methodology we developed in this study can be applied to other
semiconductor systems for a deeper microscopic understanding of the Mu state
exchange dynamics.",2305.05513v1
2023-05-28,"Orthogonal Dualities and Asymptotics of Dynamic Stochastic Higher Spin Vertex Models, using the Drinfeld Twister","We introduce a new, algebraic method to construct duality functions for
integrable dynamic models. This method will be implemented on dynamic
stochastic higher spin vertex models, where we prove the duality functions are
the $ _3 \varphi_2$ functions. A degeneration of these duality functions are
orthogonal polynomial dualities of Groenevelt--Wagener arXiv:2306.12318. The
method involves using the universal twister of
$\mathcal{U}_q(\mathfrak{sl}_2)$, viewed as a quasi--triangular,
quasi--$^*$--Hopf algebra. The algebraic method is presented very generally and
is expected to produce duality functions for other dynamic integrable models.
As an application of the duality, we prove that the asymptotic fluctuations of
the dynamic stochastic six vertex model with step initial conditions are
governed by the Tracy--Widom distribution.",2305.17602v2
2023-12-19,Dynamically selected steady states and criticality in non-reciprocal networks,"Diverse equilibrium systems with heterogeneous interactions lie at the edge
of stability. Such marginally stable states are dynamically selected as the
most abundant ones or as those with the largest basins of attraction. On the
other hand, systems with non-reciprocal (or asymmetric) interactions are
inherently out of equilibrium, and exhibit a rich variety of steady states,
including fixed points, limit cycles and chaotic trajectories. How are steady
states dynamically selected away from equilibrium? We address this question in
a simple neural network model, with a tunable level of non-reciprocity. Our
study reveals different types of ordered phases and it shows how
non-equilibrium steady states are selected in each phase. In the spin-glass
region, the system exhibits marginally stable behaviour for reciprocal (or
symmetric) interactions and it smoothly transitions to chaotic dynamics, as the
non-reciprocity (or asymmetry) in the couplings increases. Such region, on the
other hand, shrinks and eventually disappears when couplings become
anti-symmetric. Our results are relevant to advance the knowledge of disordered
systems beyond the paradigm of reciprocal couplings, and to develop an
interface between statistical physics of equilibrium spin-glasses and dynamical
systems theory.",2312.12039v1
2011-04-21,Dynamical Response of Single Bi-layer Spin Model : A Theoretical Analysis,"The spin dynamics of a single bi-layer ferromagnetic model, as proposed for a
manganite system $La_{1.2}Sr_{1.8}Mn_{2}O_{7}$ as an approximate minimal model,
is studied both below and above the bulk magnetic transition temperature using
the semi-classical Monte Carlo-molecular dynamics technique. The quantities
studied are:- (i) the static spin configurations, (ii) the spin
auto-correlation function (SAF) $C(t)$ and (iii) the dynamical structure
function (DSF) $S(\bf q, \omega)$. The major aim is to probe the nature of
collective modes and in particular to ascertain whether the propagating modes
can exist above the ordering temperature. We find that the typical spin
configurations contain a high degree of mis-aligned spins, particularly in the
high temperature phase. Nevertheless, in the low temperature phase a long range
ferromagnetic ordering can be seen. The shape of the curves corresponding to
$S(\bf q, \omega)$ vs. $\omega$ in the constant $\bf q$-scan are found in
general to be quite complex viz. containing peaks, cusps and broad plateau.
Moreover, in a large regime of $(\bf q, \omega)$ space, $S(\bf q ,\omega)$ is
found to be negative, signalling a total breakdown of the semi-classical
approximation in the presence of the enormous thermodynamic and quantum
fluctuations. Considering the physically allowed regime only, we can
theoretically extract an effective $\omega$ vs. $q$ dispersion curve for the
collective excitations, which exhibits a slope opposite to that expected for a
full three-dimensional system and disagrees with the results of inelastic
neutron scattering experiments in the nature of the dispersion curve along the
$<100>$ direction in the ordered phase. The theoretical results also exhibit
the existence of propagating modes even in the high temperature (disordered)
phase from our calculations based on a minimal single bi-layer ferromagnetic
model.",1104.4197v1
2013-11-19,Dynamical evolution and spin-orbit resonances of potentially habitable exoplanets. The case of GJ 667C,"We investigate the dynamical evolution of the potentially habitable
super-earth GJ 667Cc in the multiple system of at least two exoplanets orbiting
a nearby M dwarf, paying special attention to its spin-orbital state. The
published radial velocities for this star are re-analyzed and evidence is found
for additional periodic signals, which could be taken for two additional
planets on eccentric orbits. Such systems are not dynamically viable and break
up quickly in numerical integrations. Limiting the scope to the two originally
detected planets, we assess the dynamical stability of the system and find no
evidence for bounded chaos in the orbital motion. The orbital eccentricity of
the planets b and c is found to change cyclicly in the range 0.06 - 0.28 and
0.05 - 0.25, respectively, with a period of approximately 0.46 yr. Taking the
eccentricity variation into account, numerical integrations are performed of
the differential equations modeling the spin-orbit interaction of the planet GJ
667Cc with its host star assuming a terrestrial composition of its mantle.
Depending on the interior temperature of the planet, it is likely to be
entrapped in the 3:2 (probability 0.51) or even higher spin-orbit resonance. It
is less likely to reach the 1:1 resonance (probability 0.24). The estimated
characteristic spin-down times are quite short for the two planets, i.e.,
within 1 Myr for planet c and even shorter for planet b. Both planet arrived at
their current and, most likely, ultimate spin-orbit states a long time ago. The
rate of tidal dissipation of energy is formidably high in the planets of GJ
667, estimated at $10^{23.7}$ and $10^{26.7}$ J yr$^{-1}$ for c and b,
respectively. This raises a question of how such relatively massive, close
super-Earths could survive overheating and destruction.",1311.4831v1
2020-07-04,Time-domain imaging of curling modes in a confined magnetic vortex and a micromagnetic study exploring the role of spiral spin waves emitted by the core,"The curling spin wave modes of a ferromagnetic vortex confined to a
microscale disc have been directly imaged in response to a microwave field
excitation using time-resolved scanning Kerr microscopy. Micromagnetic
simulations have been used to explore the interaction of gyrotropic vortex core
dynamics with the curling modes observed in the region of circulating in-plane
magnetization. Hybridization of the fundamental gyrotropic mode with the
degenerate, lowest-frequency, azimuthal modes has previously been reported to
lead to their splitting and counter propagating motion, as we observe in our
spectra and measured images. The curling nature of the modes can be ascribed to
asymmetry in the static and dynamic magnetization across the disc thickness,
but here we also present evidence that spiral spin waves emitted by the core
can influence the spatial character of higher frequency curling modes for which
hybridization is only permitted with gyrotropic modes of the same sense of
azimuthal motion. While it is challenging to identify if such modes are truly
hybridized from the mode dispersion in a confined disc, our simulations reveal
that spiral spin waves from the core may act as mediators of the interaction
between the core dynamics and azimuthal modes. At higher frequency, modes with
radial character only do not exhibit marked curling, but instead show evidence
of interaction with spin waves generated at the edge of the disc. The measured
spatio-temporal character of the observed curling modes is accurately
reproduced by our simulations, which reveal the emission of propagating
short-wavelength spiral spin waves from both core and edge regions of the disc.
Our simulations suggest that the propagating modes are not inconsequential, but
may play a role in the dynamic overlap required for hybridization of modes of
the core and in-plane magnetised regions.",2007.02043v2
2016-11-17,Dynamic localization in optical and Zeeman lattices in the presence of spin-orbit coupling,"The dynamic localization of a two-level atom in a periodic potential under
the action of spin-orbit coupling and a weak harmonically-varying linear force
is studied. We consider optical and Zeeman potentials that are either in-phase
or out-of-phase in two spinor components, respectively. The expectation value
for the position of the atom after one oscillation period of the linear force
is recovered in authentic resonances or in pseudo-resonances. The frequencies
of the linear force corresponding to authentic resonances are determined by the
band structure of the periodic potential and are affected by the spin-orbit
coupling. The width/dispersion of the wavepacket in authentic resonances is
usually minimal. The frequencies corresponding to pseudo-resonances do not
depend on the type of potential and on the strength of the spin-orbit coupling,
while the evolution of excitations at the corresponding frequencies is usually
accompanied by significant dispersion. Pseudo-resonances are determined by the
initial phase of the linear force and by the quasi-momentum of the wavepacket.
Due to the spinor nature of the system, the motion of the atom is accompanied
by periodic, but not harmonic, spin oscillations. Under the action of
spin-orbit coupling the oscillations of the wavepacket can be nearly completely
suppressed in optical lattices. Dynamic localization in Zeeman lattices is
characterized by doubling of the resonant oscillation periods due to band
crossing at the boundary of the Brillouin zone. We also show that higher
harmonics in the Fourier expansion of the energy band lead to effective
dispersion, which can be strong enough to prevent dynamic localization of the
Bloch wavepacket.",1611.05745v1
2020-08-10,"Transverse Single-Spin Asymmetries of Midrapidity Direct Photons, Neutral Pions, and Eta Mesons in 200 GeV Polarized Proton-Proton Collisions at PHENIX","Experimental observations of strikingly large transverse single-spin
asymmetries (TSSAs) opened a window into quark and gluon dynamics present in
hadronic collisions, revealing large spin-momentum correlations within nucleons
and in the process of forming hadrons. Though originally measured in lower
energy fixed target experiments, they have been found to persist in collisions
with momentum transfer well into the perturbative regime of quantum
chromodynamics (QCD) and yet their origin remains poorly understood. TSSA
measurements have allowed for the development of both transverse momentum
dependent and collinear twist-3 descriptions of nonperturbative spin-momentum
correlations for both initial- and final-state effects. Results are presented
for the TSSAs of direct photons, neutral pions, and eta mesons in the
pseudorapidity range $|\eta|<0.35$ from $p^\uparrow+p$ collisions with
$\sqrt{s} = 200$ GeV at PHENIX. As hadrons, $\pi^0$ and $\eta$ mesons are
sensitive to both initial- and final-state effects. At midrapidity, $\pi^0$ and
$\eta$ measurements are sensitive to the dynamics of gluons along with a mix of
quark flavors. These results are a factor of three increase in statistical
precision and extend to higher transverse momentum when compared with previous
PHENIX measurements in this kinematic region. Because direct photon production
does not include hadronization, the direct photon TSSA is only sensitive to
spin-momentum correlations in the proton. The kinematics of this result in
particular make the direct photon TSSA a clean probe of gluon dynamics in the
transversely polarized proton. All three of these asymmetries will help
constrain the twist-3 trigluon collinear correlation function as well as the
gluon Sivers function, improving our knowledge of spin-dependent gluon dynamics
in QCD.",2008.04283v2
2020-11-17,Black hole-neutron star coalescence: effects of the neutron star spin on jet launching and dynamical ejecta mass,"Black hole-neutron star (BHNS) mergers are thought to be sources of
gravitational waves (GWs) with coincident electromagnetic (EM) counterparts. To
further probe whether these systems are viable progenitors of short gamma-ray
bursts (sGRBs) and kilonovae, and how one may use (the lack of) EM counterparts
associated with LIGO/Virgo candidate BHNS GW events to sharpen parameter
estimation, we study the impact of neutron star spin in BHNS mergers. Using
dynamical spacetime magnetohydrodynamic simulations of BHNSs initially on a
quasicircular orbit, we survey configurations that differ in the BH spin
($a_{\rm BH}/M_{\rm BH}=0$ and $0.75$), the NS spin ($a_{\rm NS}/M_{\rm
NS}=-0.17,\,0,\,0.23$ and $0.33$), and the binary mass ratio ($q\equiv M_{\rm
BH}:M_{\rm NS}=3:1$ and $5:1$). The general trend we find is that increasing
the NS prograde spin increases both the rest mass of the accretion disk onto
the remnant black hole, and the rest mass of dynamically ejected matter. By a
time~$\Delta t\sim 3500-5500M\sim 88-138(M_{\rm NS}/1.4M_\odot)\,\rm ms$ after
the peak gravitational wave amplitude, a magnetically--driven jet is launched
only for $q=3:1$ regardless of the initial NS spin. The lifetime of the jets
[$\Delta t\sim 0.5-0.8(M_{\rm NS}/1.4 M_\odot)\,\rm s$] and their outgoing
Poynting luminosity [$L_{\rm Poyn}\sim 10^{51.5\pm 0.5}\,\rm erg/s$] are
consistent with typical sGRBs luminosities and expectations from the
Blandford-Znajek mechanism. By the time we terminate our simulations, we do not
observe either an outflow or a large-scale magnetic field collimation for the
other systems we considered. The mass range of dynamically ejected matter is
$10^{-4.5}-10^{-2}~(M_{\rm NS}/1.4M_\odot)M_\odot$, which can power kilonovae
with peak bolometric luminosities $L_{\rm knova}\sim 10^{40}-10^{41.4}$ erg/s
with rise times $\lesssim 6.5\,\rm h$ and potentially detectable by the LSST.",2011.08863v2
2022-04-11,Curvilinear spin-wave dynamics beyond the thin-shell approximation: Magnetic nanotubes as a case study,"Surface curvature of magnetic systems can lead to many static and dynamic
effects which are not present in flat systems of the same material. These
emergent magnetochiral effects can lead to frequency nonreciprocity of spin
waves, which has been shown to be a bulk effect of dipolar origin and is
related to a curvature-induced symmetry breaking in the magnetic volume
charges. So far, such effects have been investigated theoretically mostly for
thin shells, where the spatial profiles of the spin waves can be assumed to be
homogeneous along the thickness. Here, using a finite-element dynamic-matrix
approach, we investigate the transition of the spin-wave spectrum from thin to
thick curvilinear shells, at the example of magnetic nanotubes in the vortex
state. With increasing thickness, we observe the appearance of higher-order
radial modes which are strongly hybridized and resemble the
perpendicular-standing-waves (PSSWs) in flat films. Along with an increasing
dispersion asymmetry, we uncover the curvature-induced non-reciprocity of the
mode profiles. This is explained in a very simple picture general for thick
curvilinear shells, considering the inhomogeneity of the emergent geometric
volume charges along the thickness of the shell. Such curvature-induced
mode-profile asymmetry also leads to non-reciprocal hybridization which can
facilitate unidirectional spin-wave propagation. With that, we also show how
curvature allows for nonlinear three-wave splitting of a higher-order radial
mode into secondary modes which can also propagate unidirectionally. We believe
that our study provides a significant contribution to the understanding of the
spin-wave dynamics in curvilinear magnetic systems, but also advertises these
for novel magnonic applications.",2204.05065v1
2023-03-30,Fate of entanglement in magnetism under Lindbladian or non-Markovian dynamics and conditions for their transition to Landau-Lifshitz-Gilbert classical dynamics,"It is commonly assumed in spintronics and magnonics that localized spins
within antiferromagnets are in the N\'{e}el ground state (GS), as well as that
such state evolves, when pushed out of equilibrium by current or external
fields, according to the Landau-Lifshitz-Gilbert (LLG) equation viewing
localized spins as classical vectors of fixed length. On the other hand, the
true GS of antiferromagnets is highly entangled, as confirmed by very recent
neutron scattering experiments witnessing their entanglement. Although GS of
ferromagnets is always unentangled, their magnonic low-energy excitation are
superpositions of many-body spin states and, therefore, entangled. In this
study, we initialize quantum Heisenberg ferro- or antiferromagnetic chains
hosing localized spins $S=1/2$, $S=1$ or $S=5/2$ into unentangled pure state
and then evolve them by quantum master equations (QMEs) of Lindblad or
non-Markovian type, derived by coupling localized spins to a bosonic bath (such
as due to phonons) or by using additional ``reaction coordinate'' in the latter
case. The time evolution is initiated by applying an external magnetic field,
and entanglement of time-evolving {\em mixed} quantum states is monitored by
computing its logarithmic negativity. We find that non-Markovian dynamics
maintains some degree of entanglement, which shrinks the length of the vector
of spin expectation values, thereby making the LLG equation inapplicable.
Conversely, Lindbladian (i.e., Markovian) dynamics ensures that entanglement
goes to zero, thereby enabling quantum-to-classical (i.e., to LLG) transition
in all cases -- $S=1/2$, $S=1$ and $S=5/2$ ferromagnet or $S=5/2$
antiferromagnet -- {\em except} for $S=1/2$ and $S=1$ antiferromagnet. We also
investigate the stability of entangled antiferromagnetic GS upon suddenly
coupling it to the bosonic bath.",2303.17596v3
2020-05-05,Stability of dynamical topology against dynamical noise in quantum quenches,"Equilibrium topological phases are robust against weak static disorder but
may break down in the strong disorder regime. Here we explore the stability of
the quench-induced emergent dynamical topology in the presence of dynamical
noise. We develop an analytic theory and show that for weak noise, the quantum
dynamics induced by quenching an initial trivial phase to Chern insulating
regime exhibits robust emergent topology on certain momentum subspaces called
band inversion surfaces (BISs). The dynamical topology is protected by the
minimal oscillation frequency over the BISs, mimicking a bulk gap of the
dynamical phase. Singularities emerge in the quench dynamics, with the minimal
oscillation frequency vanishing on the BISs if increasing noise to critical
strength, manifesting a dynamical topological transition, beyond which the
emergent topology breaks down. Two types of dynamical transitions are
predicted. Interestingly, we predict a sweet spot in the critical transition
when noise couples to all three spin components in the same strength, in which
case the dynamical topology survives at arbitrarily strong noise regime. This
work unveils novel features of the dynamical topology under dynamical noise,
which can be probed with control in experiment.",2005.02345v1
1995-06-01,Chaotic Dynamics of Binary Systems,"We propose a theory of chaos for discrete systems, based on their
representation in a space of ``binary histories'', $ {\cal B^{\infty}} $. We
show that $ {\cal B^{\infty}} $ is a metrizable Cantor set which embeds the
attractor $\Lambda$, itself also a Cantor set.",9505015v2
1997-03-26,Stochastic Resonance in Chaotic Spin-Wave Dynamics,"We report the first experimental observation of noise-free stochastic
resonance by utilizing the intrinsic chaotic dynamics of the system. To this
end we have investigated the effect of an external periodic modulation on
intermittent signals observed by high power ferromagnetic resonance in yttrium
iron garnet spheres. Both the signal-to-noise ratio and the residence time
distributions show the characteristic features of stochastic resonance. The
phenomena can be explained by means of a one-dimensional intermittent map. We
present analytical results as well as computer simulations.",9703018v1
1997-11-03,Chaos and Thermalization in a Dynamical Model of Two Interacting Particles,"A quantum dynamical model of two interacting spins, with chaotic and regular
components, is investigated using a finite two-particles symmetrized basis.
Chaotic eigenstates give rise to an equilibrium occupation number distribution
in close agreement with the Bose-Einstein distribution despite the small number
of particles ($n=2$). However, the corresponding temperature differs from that
derived from the standard Canonical Ensemble. On the other side, an acceptable
agreement with the latter is restored by artificially randomizing the model.
Different definitions of temperature are then discussed and compared .",9711005v1
1994-06-13,Off equilibrium dynamics and aging in unfrustrated systems,"We analyse the Langevin dynamics of the random walk, the scalar field, the
X-Y model and the spinoidal decomposition. We study the deviations from the
equilibrium dynamics theorems (FDT and homogeneity), the asymptotic behaviour
of the systems and the aging phenomena. We compare the results with the
dynamical behaviour of (random) spin-glass mean-field models.",9406053v2
1996-07-05,Dynamical Magnetic Susceptibility for the $t$-$J$ Model,"We present results for the {\em dynamical}\/ magnetic susceptibility of the
$t$-$J$ model, calculated with the dynamical mean field theory. For $J=0$ we
find enhanced ferromagnetic correlations but an otherwise relatively
$\vec{q}$-independent dynamical magnetic susceptibility. For $J>0$ the explicit
antiferromagnetic exchange leads to a dynamic spin structure factor with the
expected peak at the antiferromagnetic Bragg point.",9607034v1
1998-09-12,Transition Matrix Monte Carlo Reweighting and Dynamics,"We study an induced dynamics in the space of energy of single-spin-flip Monte
Carlo algorithm. The method gives an efficient reweighting technique. This
dynamics is shown to have relaxation times proportional to the specific heat.
Thus, it is plausible for a logarithmic factor in the correlation time of the
standard 2D Ising local dynamics.",9809181v1
1999-01-08,Scaling for domain growth in the Ising model with competing dynamics,"We study the domain growth of the one-dimensional kinetic Ising model under
the competing influence of Glauber dynamics at temperature T and Kawasaki
dynamics with a configuration-independent rate. The scaling of the structure
factor is shown to have the form for nonconserved dynamics with the corrections
arising from the spin-exchange process, i.e., $S(k,t)=Lg_0(kL,t/\tau
)+g_1(kL,t/\tau)+... $, and the corresponding scaling functions are calculated
analytically. A correction to the Porod law at zero temperature is also given.",9901060v1
2001-04-19,The High Temperature Dynamics of a mean field Potts glass,"We use Monte Carlo simulations to investigate the dynamical properties of the
infinite range 10 states Potts glass. By analyzing the spin autocorrelation
function for system sizes up to N=2560, we show that strong finite size effects
are present around the predicted dynamical transition temperature. The
autocorrelation function shows strong self-averaging at high temperatures,
whereas close to the dynamical transition they show the lack of self-averaging.",0104355v1
2001-09-10,Relieving the fermionic and the dynamical sign problem: Multilevel Blocking Monte Carlo simulations,"This article gives an introduction to the multilevel blocking (MLB) approach
to both the fermion and the dynamical sign problem in path-integral Monte Carlo
simulations. MLB is able to substantially relieve the sign problem in many
situations. Besides an exposition of the method, its accuracy and several
potential pitfalls are discussed, providing guidelines for the proper choice of
certain MLB parameters. Simulation results are shown for strongly interacting
electrons in a 2D parabolic quantum dot, the real-time dynamics of several
simple model systems, and the dissipative two-state dynamics (spin-boson
problem).",0109173v1
2002-05-13,Pseudogap effects on the charge dynamics in the underdoped copper oxide materials,"Within the t-J model, the charge dynamics of copper oxide materials in the
underdoped regime is studied based on the fermion-spin theory. It is shown that
both in-plane charge dynamics and c-axis charge dynamics are mainly governed by
the scattering from the in-plane fluctuation, which would be suppressed when
the holon pseudogap opens at low temperatures, leading to the temperature
linear to the nonlinear range in the in-plane resistivity and crossovers to the
semiconducting-like range in the c-axis resistivity.",0205248v1
2002-11-15,Relationship between dynamical heterogeneities and stretched exponential relaxation,"We identify the dynamical heterogeneities as an essential prerequisite for
stretched exponential relaxation in dynamically frustrated systems. This
heterogeneity takes the form of ordered domains of finite but diverging
lifetime for particles in atomic or molecular systems, or spin states in
magnetic materials. At the onset of the dynamical heterogeneity, the
distribution of time intervals spent in such domains or traps becomes stretched
exponential at long time. We rigorously show that once this is the case, the
autocorrelation function of the renewal process formed by these time intervals
is also stretched exponential at long time.",0211322v3
2003-02-20,Dynamic critical behavior of the classical anisotropic BCC Heisenberg antiferromagnet,"Using a recently implemented integration method [Krech et. al.] based on an
iterative second-order Suzuki-Trotter decomposition scheme, we have performed
spin dynamics simulations to study the critical dynamics of the BCC Heisenberg
antiferromagnet with uniaxial anisotropy. This technique allowed us to probe
the narrow asymptotic critical region of the model and estimate the dynamic
critical exponent $z=2.25 \pm 0.08$. Comparisons with competing theories and
experimental results are presented.",0302396v1
2003-09-01,Direct-Current Induced Dynamics in Co90Fe10/Ni80Fe20 Point Contacts,"We have directly measured coherent high-frequency magnetization dynamics in
ferromagnet films induced by a spin-polarized DC current. The precession
frequency can be tuned over a range of several gigahertz, by varying the
applied current. The frequencies of excitation also vary with applied field,
resulting in a microwave oscillator that can be tuned from below 5 GHz to above
40 GHz. This novel method of inducing high-frequency dynamics yields
oscillations having quality factors from 200 to 800. We compare our results
with those from single-domain simulations of current-induced dynamics.",0309042v1
2005-05-19,Chaotic properties of systems with Markov dynamics,"We present a general approach for computing the dynamic partition function of
a continuous-time Markov process. The Ruelle topological pressure is identified
with the large deviation function of a physical observable. We construct for
the first time a corresponding finite Kolmogorov-Sinai entropy for these
processes. Then, as an example, the latter is computed for a symmetric
exclusion process. We further present the first exact calculation of the
topological pressure for an N-body stochastic interacting system, namely an
infinite-range Ising model endowed with spin-flip dynamics. Expressions for the
Kolmogorov-Sinai and the topological entropies follow.",0505483v1
2004-08-26,Control Theoretical Approach to Quantum Control,"We derive the quantum stochastic master equation for bosonic systems without
measurement theory but control theory. It is shown that the quantum effect of
the measurement can be represented as the correlation between dynamical and
measurement noise. The transfer function representation allows us to analyze a
dynamical uncertainty relation which imposes strong constraints on the dynamics
of the linear quantum systems. In particular, quantum systems preserving the
minimum uncertainty are uniquely determined. For large spin systems, it is
shown that local dynamics are equivalent to bosonic systems. Considering global
behavior, we find quantum effects to which there is no classical counterparts.
A control problem of producing maximal entanglement is discussed as the
stabilization of a filtering process.",0408160v1
2007-08-05,Persistence and Memory in Patchwork Dynamics for Glassy Models,"Slow dynamics in disordered materials prohibits direct simulation of their
rich nonequilibrium behavior at large scales. ""Patchwork dynamics"" is
introduced to mimic relaxation over a very broad range of time scales by
equilibrating or optimizing directly on successive length scales. This dynamics
is used to study coarsening and to replicate memory effects for spin glasses
and random ferromagnets. It is also used to find, with high confidence, exact
ground states in large or toroidal samples.",0708.0683v2
2009-02-27,Population Dynamics of a Spin-1 Bose Gas Above the Bose-Einstein Transition Temperature,"We study population dynamics of a trapped spin-1 Bose gas above the
Bose-Einstein transition temperature. Starting from the semiclassical kinetic
equation for a spin-1 gas, we derive a coupled rate equations for the
populations of internal states. Solving the rate equations, we discuss the
dynamical evolution of spin populations. We also estimate the characteristic
timescale in which the system reaches equilibrium. Finally, we briefly discuss
how the presence of the condensate will affect the population dynamics.",0902.4792v1
2011-03-24,Can anything from Noether's theorem be salvaged for discrete dynamical systems?,"The dynamics of a physical system is linked to its phase-space geometry by
Noether's theorem, which holds under standard hypotheses including continuity.
Does an analogous theorem hold for discrete systems? As a testbed, we take the
Ising spin model with both ferromagnetic and antiferromagnetic bonds. We show
that---and why---energy not only acts as a generator of the dynamics for this
family of systems, but is also conserved when the dynamics is time-invariant.",1103.4785v2
2011-04-03,Dynamical magnetoelectric effects in multiferroic oxides,"Multiferroics with coexistent ferroelectric and magnetic orders can provide
an interesting laboratory to test unprecedented magnetoelectric responses and
their possible applications. One such example is the dynamical and/or resonant
coupling between magnetic and electric dipoles in a solid. As the examples of
such dynamical magnetoelectric effects, (1) the multiferroic domain wall
dynamics and (2) the electric-dipole active magnetic responses are discussed
with the overview of recent experimental observations.",1104.0357v1
2011-06-27,The role of environmental correlations in the non-Markovian dynamics of a spin system,"We put forward a framework to study the dynamics of a chain of interacting
quantum particles affected by individual or collective multi-mode environment,
focussing on the role played by the environmental quantum correlations over the
evolution of the chain. The presence of entanglement in the state of the
environmental system magnifies the non-Markovian nature of the chain's
dynamics, giving rise to structures in figures of merit such as entanglement
and purity that are not observed under a separable multi-mode environment. Our
analysis can be relevant to problems tackling the open-system dynamics of
biological complexes of strong current interest.",1106.5447v1
2012-08-14,Dynamical Singularities of Glassy Systems in a Quantum Quench,"We present a prototype of behavior of glassy systems driven by quantum
dynamics in a quenching protocol by analyzing the random energy model in a
transverse field. We calculate several types of dynamical quantum amplitude and
find a freezing transition at some critical time. The behavior is understood by
the partition-function zeros in the complex temperature plane. We discuss the
properties of the freezing phase as a dynamical chaotic phase, which are
contrasted to those of the spin-glass phase in the static system.",1208.2800v2
2015-04-24,Universal coarsening dynamics of a quenched ferromagnetic spin-1 condensate,"We demonstrate that a quasi-two-dimensional spin-1 condensate quenched to a
ferromagnetic phase undergoes universal coarsening in its late time dynamics.
The quench can be implemented by a sudden change in the applied magnetic field
and, depending on the final value, the ferromagnetic phase has easy-axis
(Ising) or easy-plane (XY) symmetry, with different dynamical critical
exponents. Our results for the easy-plane phase reveal a fractal domain
structure and the crucial role of polar-core spin vortices in the coarsening
dynamics.",1504.06404v2
2015-08-17,Degenerated ground-states in a class of 1D Ising-like models: a characterization by symbolic dynamics,"In this note we study a class of one-dimensional Ising chain having a highly
degenerated set of ground-state configurations. The model consists of spin
chain having infinite-range pair interactions with a given structure. We show
that the set of ground-state configurations of such a model can be fully
characterized by means of symbolic dynamics. Particularly we found that the set
ground- state configurations defines what in symbolic dynamics is called sofic
shift space. Finally we prove that this system has a non-vanishing residual
entropy (the topological entropy of the shift space), which can be exactly
calculated.",1508.04041v1
2016-01-18,Metastable and scaling regimes of a one-dimensional Kawasaki dynamics,"We investigate the large-time scaling regimes arising from a variety of
metastable structures in a chain of Ising spins with both first- and
second-neighbor couplings while subject to a Kawasaki dynamics. Depending on
the ratio and sign of these former, different dynamic exponents are suggested
by finite-size scaling analyses of relaxation times. At low but
nonzero-temperatures these are calculated via exact diagonalizations of the
evolution operator in finite chains under several activation barriers. In the
absence of metastability the dynamics is always diffusive.",1601.04375v2
2016-06-28,Anomalous diffusion in convergence to effective ergodicity,"Power-law exponents in the convergence to effective ergodicity is quantified
for Ising-Lenz model in one dimension. Modified Thirumalai-Mountain (TM) metric
for magnetisation is computed for the range of temperature values under
strongly correlated dynamics. In producing evolution of TM metric over time,
time-averaged dynamics is generated by using Metropolis and Glauber
single-spin-flip dynamics, and ensemble-averaged dynamics with an exact
solution. Superdiffusive behaviour is numerically identified in the parameter
regimes studied, i.e., power-law exponents, $\alpha > 1.0$.",1606.08693v1
2013-09-24,Dynamics of the modified Kibble-Żurek mechanism in antiferromagnetic spin-1 condensates,"We investigate the dynamics and outcome of a quantum phase transition from an
antiferromagnetic to phase separated ground state in a spin-1 Bose-Einstein
condensate of ultracold atoms. We explicitly demonstrate double universality in
dynamics within experiments with various quench time. Furthermore, we show that
spin domains created in the nonequilibrium transition constitute a set of
mutually incoherent quasicondensates. The quasicondensates appear to be
positioned in a semi-regular fashion, which is a result of the conservation of
local magnetization during the post-selection dynamics.",1309.6107v1
2016-05-24,Systematics of dynamic moment of inertia in super-deformed bands in Mass ~150 region,"An empirical semi-classical model have been proposed to investigate the
nature of dynamic moment-of-inertia , of the super-deformed (SD) bands in
nuclei of mass 150 region. The model incorporates an additional frequency
dependent distortion, to the dynamic moment-of-inertia term akin to a
vibrational component to explain the extreme spin structure of these bands.
Using this model two separate components to the dynamic moment of inertia,
$\Im^{(2)}$ have been identified for the SD band structure for the mass 150
region. Three distinct nature of the moment-of-inertia, also have been
identified using the two parameter model.",1605.07295v2
2019-06-03,Dynamical Phase Diagram of a Quantum Ising Chain with Long Range Interactions,"We investigate the effect of short-range correlations on the dynamical phase
diagram of quantum many-body systems with long-range interactions. Focusing on
Ising spin chains with power-law decaying interactions and accounting for
short-range correlations by a cluster mean field theory we show that
short-range correlations are responsible for the emergence of a chaotic
dynamical region. Analyzing the fine details of the phase diagram, we show that
the resulting chaotic dynamics bears close analogies with that of a tossed
coin.",1906.00691v1
2019-10-08,Understanding nonequilibrium scaling laws governing collapse of a polymer,"Recent emerging interest in experiments of single-polymer dynamics urge
computational physicists to revive their understandings, particularly in the
nonequilibrium context. Here we briefly discuss the currently evolving
approaches of investigating the evolution dynamics of homopolymer collapse in
computer simulations. Primary focus of these approaches is to understand
various dynamic scaling laws related to coarsening and aging during the
collapse in space dimension $d=3$, using tools popular in nonequilibrium
coarsening dynamics of particle or spin systems. In addition to providing an
overview of those results, we also present new preliminary data for $d=2$.",1910.03394v1
2017-11-03,Colloidal particle electrorotation in a non-uniform electric field,"A model to study the dynamics of colloidal particles in nonuniform electric
fields is proposed. For an isolated sphere, the conditions and threshold for
sustained (Quincke) rotation in a linear direct current (dc) field are
determined. Particle dynamics becomes more complex with increasing electric
field strength, changing from steady spinning around the particle center to
time-dependent orbiting motion around the minimum field location. Pairs of
particles exhibit intricate trajectories, which are combination of translation,
due to dielectrophoresis, and rotation, due to the Quincke effect. Our model
provides a basis to study the collective dynamics of many particles in a
general electric field.",1711.01331v1
2019-11-12,Coding closed and open quantum systems in MATLAB: applications in quantum optics and condensed matter,"We develop a package of numerical simulations implemented in MATLAB to solve
complex many-body quantum systems. We focus on widely used examples that
include the calculation of the magnetization dynamics for the closed and open
Ising model, dynamical quantum phase transition in cavity QED arrays, Markovian
dynamics for interacting two-level systems, and the non-Markovian dynamics of
the pure-dephasing spin-boson model. These examples will be useful for
undergraduate and graduate students with a medium or high background in MATLAB,
and also for researches interested in numerical studies applied to quantum
optics and condensed matter systems.",1911.04906v2
2022-06-15,Constrained Dynamics and Directed Percolation,"In a recent work [A. Deger et al., Phys. Rev. Lett. 129, 160601 (2022)] we
have shown that kinetic constraints can completely arrest many-body chaos in
the dynamics of a classical, deterministic, translationally-invariant spin
system with the strength of the constraint driving a dynamical phase
transition. Using extensive numerical simulations and scaling analyses we
demonstrate here that this constraint-induced phase transition lies in the
directed percolation universality class in both one and two spatial dimensions.",2206.07724v2
2022-10-03,Probing domain wall dynamics in magnetic Weyl semimetals via the non-linear anomalous Hall effect,"The magnetic textures of Weyl semimetals are embedded into their topological
structure and interact dynamically with it. Here, we examine electric
field-induced structural phase transitions in domain walls mediated by the spin
transfer torque, and their footprint in charge transport. Remarkably, domain
wall dynamics lead to a transient, local, non-linear anomalous Hall effect and
non-linear anomalous drift current, which serve as direct probes of the
magnetization dynamics and of the domain wall location. We discuss experimental
observation in state-of-the-art samples.",2210.01150v1
2023-09-02,Learning conservation laws in unknown quantum dynamics,"We present a learning algorithm for discovering conservation laws given as
sums of geometrically local observables in quantum dynamics. This includes
conserved quantities that arise from local and global symmetries in closed and
open quantum many-body systems. The algorithm combines the classical shadow
formalism for estimating expectation values of observable and data analysis
techniques based on singular value decompositions and robust polynomial
interpolation to discover all such conservation laws in unknown quantum
dynamics with rigorous performance guarantees. Our method can be directly
realized in quantum experiments, which we illustrate with numerical
simulations, using closed and open quantum system dynamics in a
$\mathbb{Z}_2$-gauge theory and in many-body localized spin-chains.",2309.00774v1
2000-07-18,Pulsar Jets: Implications for Neutron Star Kicks and Initial Spins,"We study implications for the apparent alignment of the spin axes,
proper-motions, and polarization vectors of the Crab and Vela pulsars. The spin
axes are deduced from recent Chandra X-ray Observatory images that reveal jets
and nebular structure having definite symmetry axes. The alignments indicate
these pulsars were born either in isolation or with negligible velocity
contributions from binary motions. We examine the effects of rotation and the
conditions under which spin-kick alignment is produced for various models of
neutron star kicks. If the kick is generated when the neutron star first forms
by asymmetric mass ejection or/and neutrino emission, then the alignment
requires that the protoneutron star possesses an original spin with period
$P_s$ much less than the kick timescale, thus spin-averaging the kick forces.
The kick timescale ranges from 100 ms to 10 s depending on whether the kick is
hydrodynamically driven or neutrino-magnetic field driven. For hydrodynamical
models, spin-kick alignment further requires the rotation period of an
asymmetry pattern at the radius near shock breakout (>100 km) to be much less
than ~100 ms; this is difficult to satisfy unless rotation plays a dynamically
important role in the core collapse and explosion ($P_s\lo 1$ ms). Aligned kick
and spin vectors are inherent to the slow process of asymmetric electromagnetic
radiation from an off-centered magnetic dipole. We reassess the viability of
this effect, correcting a factor of 4 error in Harrison and Tademaru's
calculation that increases the size of the effect. To produce a kick velocity
of order a few hundred km/s requires that the neutron star be born with an
initial spin close to 1 ms and that spindown due to r-mode driven gravitational
radiation be inefficient compared to standard magnetic braking.",0007272v2
2010-02-25,Wannier-function approach to spin excitations in solids,"We present a computational scheme to study spin excitations in magnetic
materials from first principles. The central quantity is the transverse spin
susceptibility, from which the complete excitation spectrum, including
single-particle spin-flip Stoner excitations and collective spin-wave modes,
can be obtained. The susceptibility is derived from many-body perturbation
theory and includes dynamic correlation through a summation over ladder
diagrams that describe the coupling of electrons and holes with opposite spins.
In contrast to earlier studies, we do not use a model potential with adjustable
parameters for the electron-hole interaction but employ the random-phase
approximation. To reduce the numerical cost for the calculation of the
four-point scattering matrix we perform a projection onto maximally localized
Wannier functions, which allows us to truncate the matrix efficiently by
exploiting the short spatial range of electronic correlation in the partially
filled d or f orbitals. Our implementation is based on the FLAPW method.
Starting from a ground-state calculation within the LSDA, we first analyze the
matrix elements of the screened Coulomb potential in the Wannier basis for the
3d transition-metal series. In particular, we discuss the differences between a
constrained nonmagnetic and a proper spin-polarized treatment for the
ferromagnets Fe, Co, and Ni. The spectrum of single-particle and collective
spin excitations in fcc Ni is then studied in detail. The calculated spin-wave
dispersion is in good overall agreement with experimental data and contains
both an acoustic and an optical branch for intermediate wave vectors along the
[100] direction. In addition, we find evidence for a similar double-peak
structure in the spectral function along the [111] direction.",1002.4897v1
2010-09-16,Evolution of Spin Direction of Accreting Magnetic Protostars and Spin-Orbit Misalignment in Exoplanetary Systems: II. Warped Discs,"Magnetic interactions between a protostar and its accretion disc tend to
induce warping in the disc and produce secular changes in the stellar spin
direction, so that the spin axis may not always be perpendicular to the disc.
This may help explain the recently observed spin-orbit misalignment in a number
of exoplanetary systems. We study the dynamics of warped protoplanetary discs
under the combined effects of magnetic warping/precession torques and internal
stresses in the disc, including viscous damping of warps and propagation of
bending waves. We show that when the outer disc axis is misaligned with the
stellar spin axis, the disc evolves towards a warped steady-state on a
timescale that depends on the disc viscosity or the bending wave propagation
speed, but in all cases is much shorter than the timescale for the spin
evolution (of order of a million years). Moreover, for the most likely physical
parameters characterizing magnetic protostars, circumstellar discs and their
interactions, the steady-state disc has a rather small warp, such that the
whole disc lies approximately in a single plane determined by the outer disc
boundary conditions, although more extreme parameters may give rise to larger
disc warps. In agreement with our recent analysis (Lai et al. 2010) based on
flat discs, we find that the back-reaction magnetic torques of the slightly
warped disc on the star can either align the stellar spin axis with the disc
axis or push it towards misalignment, depending on the parameters of the
star-disc system. This implies that newly formed planetary systems may have a
range of inclination angles between the stellar spin axis and the symmetry axis
of the planetary orbits.",1009.3233v2
2011-08-04,Gravitational waves from spinning black hole-neutron star binaries: dependence on black hole spins and on neutron star equations of state,"We study the merger of black hole (BH)-neutron star (NS) binaries with a
variety of BH spins aligned or anti-aligned with the orbital angular momentum,
and with the mass ratio in the range MBH/MNS = 2--5, where MBH and MNS are the
mass of the BH and NS, respectively. We model NS matter by systematically
parametrized piecewise polytropic equations of state. The initial condition is
computed in the puncture framework adopting an isolated horizon framework to
estimate the BH spin and assuming an irrotational velocity field for the fluid
inside the NS. Dynamical simulations are performed in full general relativity
by an adaptive mesh refinement code, SACRA. The treatment of hydrodynamic
equations and estimation of the disk mass are improved. We find that the NS is
tidally disrupted irrespective of the mass ratio when the BH has a moderately
large prograde spin, whereas only binaries with low mass ratios, MBH/MNS <~ 3
or small compactnesses of the NSs, bring the tidal disruption when the BH spin
is zero or retrograde. The mass of the remnant disk is accordingly large as >~
0.1 Msun, which is required by central engines of short gamma-ray bursts, if
the BH spin is prograde. Information of the tidal disruption is reflected in a
clear relation between the compactness of the NS and an appropriately defined
""cutoff frequency"" in the gravitational-wave spectrum, above which the spectrum
damps exponentially. We find that the tidal disruption of the NS and excitation
of the quasinormal mode of the remnant BH occur in a compatible manner in high
mass-ratio binaries with the prograde BH spin. The correlation between the
compactness and the cutoff frequency still holds for such cases. It is also
suggested by extrapolation that the merger of an extremely spinning BH and an
irrotational NS binary does not lead to formation of an overspinning BH.",1108.1189v2
2012-08-08,Spin-charge conversion in multiterminal Aharonov-Casher ring coupled to precessing ferromagnets: A charge conserving Floquet-nonequilibrium Green function approach,"We derive a non-perturbative solution to the Floquet-nonequilibrium Green
function (Floquet-NEGF) describing open quantum systems periodically driven by
an external field of arbitrary strength of frequency. By adopting the
reduced-zone scheme, we obtain expressions rendering conserved charge currents
for any given maximum number of photons, distinguishable from other existed
Floquet-NEGF-based expressions where, less feasible, infinite number of photons
needed to be taken into account to ensure the conservation. To justify our
derived formalism and to investigate spin-charge conversions by spin-orbit
coupling (SOC), we consider the spin-driven setups as reciprocal to the
electric-driven setups in S. Souma et. al., Phys. Rev. B 70, 195346 (2004) and
Phys. Rev. Lett. 94, 106602 (2005). In our setups, pure spin currents are
driven by the magnetization dynamics of a precessing ferromagnetic (FM) island
and then are pumped into the adjacent two- or four-terminal mesoscopic
Aharonov-Casher (AC) ring of Rashba SOC where spin-charge conversions take
place. Our spin-driven results show reciprocal features that excellently agree
with the findings in the electric-driven setups mentioned above. We propose two
types of symmetry operations, under which the AC ring Hamiltonian is invariant,
to argue the relations of the pumped/converted currents in the leads within the
same or between different pumping configurations. The symmetry arguments are
independent of the ring width and the number of open channels in the leads,
terminals, and precessing FM islands, In particular, net pure in-plane spin
currents and pure spin currents can be generated in the leads for certain
setups of two terminals and two precessing FM islands with the current
magnitude and polarization direction tunable by the pumping configuration, gate
voltage covering the two-terminal AC ring in between the FM islands.",1208.2275v1
2013-01-21,Low-temperature spin dynamics of a valence bond glass in Ba2YMoO6,"We carried out AC magnetic susceptibility measurements and muon spin
relaxation spectroscopy on the cubic double perovskite Ba2YMoO6, down to 50 mK.
Below ~1 K the muon relaxation is typical of a magnetic insulator with a
spin-liquid type ground state, i.e. without broken symmetries or frozen
moments. However, the AC susceptibility revealed a dilute-spin-glass like
transition below ~ 1 K. Antiferromagnetically coupled Mo5+ 4d1 electrons in
triply degenerate t2g orbitals are in this material arranged in a geometrically
frustrated fcc lattice. Bulk magnetic susceptibility data has previously been
interpreted in terms of a freezing to a heterogeneous state with non-magnetic
sites where 4d^1 electrons have paired in spin-singlets dimers, and residual
unpaired Mo5+ 4d1 electrons. Based on the magnetic heat capacity data it has
been suggested that this heterogeneity is the result of kinetic constraints
intrinsic to the physics of the pure system (possibly due to topological
overprotection), leading to a self-induced glass of valence bonds between
neighbouring 4d1 electrons. The muSR relaxation unambiguously points to a
static heterogeneous state with a static arrangement of unpaired electrons
isolated by spin-singlet (valence bond) dimers between the majority of Mo5+ 4d
electrons. The AC susceptibility data indicate that the residual magnetic
moments freeze into a dilute-spin-glass-like state. This is in apparent
contradiction with the muon-spin decoupling at 50 mK in fields up to 200 mT,
which indicates that, remarkably, the time scale of the field fluctuations from
the residual moments is ~ 5 ns. Comparable behaviour has been observed in other
geometrically frustrated magnets with spin-liquid-like behaviour and the
implications of our observations on Ba2YMoO6 are discussed in this context.",1301.4982v3
2013-02-20,Multiplet effects in orbital and spin ordering phenomena: A hybridization-expansion quantum impurity solver study,"Orbital and spin ordering phenomena in strongly correlated systems are
commonly studied using the local-density approximation + dynamical mean-field
theory approach. Typically, however, such simulations are restricted to
simplified models (density-density Coulomb interactions, high symmetry
couplings and few-band models). In this work we implement an efficient general
hybridization-expansion continuous-time quantum Monte Carlo impurity solver
(Krylov approach) which allows us to investigate orbital and spin ordering in a
more realistic setting, including interactions that are often neglected (e.g.,
spin-flip and pair-hopping terms), enlarged basis sets (full d versus eg),
low-symmetry distortions, and reaching the very low-temperature (experimental)
regime. We use this solver to study ordering phenomena in a selection of
exemplary low-symmetry transition-metal oxides: LaMnO3 and rare-earth
manganites as well as the perovskites CaVO3 and YTiO3. We show that spin-flip
and pair hopping terms do not affect the Kugel-Khomskii orbital-order melting
transition in rare-earth manganites, or the suppression of orbital fluctuations
driven by crystal field and Coulomb repulsion. For the Mott insulator YTiO3 we
find a ferromagnetic transition temperature 50 K, in remarkably good agreement
with experiments. For LaMnO3 we show that the classical t2g-spin approximation,
commonly adopted for studying manganites, yields indeed an occupied eg orbital
in very good agreement with that obtained for the full d 5-orbital Hubbard
model, while the spin-spin e_g-t_{2g} correlation function calculated from the
full d model is 0.74, very close to the value expected for aligned eg and t2g
spins; the eg spectral function matrix is also well reproduced. Finally, we
show that the t2g screening reduces the eg-eg Coulomb repulsion by about 10%",1302.5068v1
2013-06-02,Competing 4f-electron dynamics in Ce(Ru1-xFex)2Al10 (x=0 to 1): magnetic ordering emerging from the Kondo semiconducting state,"We have carried out muon spin relaxation (muSR), neutron diffraction and
inelastic neutron scattering (INS) investigations on polycrystalline samples of
Ce(Ru1-xFex)2Al10 (x=0, 0.3, 0.5, 0.8 and 1) to investigate the nature of the
ground state (magnetic ordered versus paramagnetic) and the origin of the spin
gap formation as evident from the bulk measurements in the end members. Our
zero-field muSR spectra clearly reveal coherent two-frequency oscillations at
low temperature in x=0, 0.3 and 0.5 samples, which confirms the long-range
magnetic ordering of the Ce-moment with TN=27, 26 and 21 K respectively. On the
other hand the muSR spectra of x=0.8 and x=1 down to 1.4 K and 0.045 K,
respectively exhibit a temperature independent Kubo-Toyabe term confirming a
paramagnetic ground state. The long-range magnetic ordering in x=0.5 below 21 K
has been confirmed through the neutron diffraction study. INS measurements of
x=0 clearly reveal the presence of a sharp inelastic excitation near 8 meV
between 5 K and 26 K, due to an opening of a gap in the spin excitation
spectrum, which transforms into a broad response at and above 30 K.
Interestingly, at 4.5 K the spin gap excitation broadens in x=0.3 and exhibits
two clear peaks at 8.4(3) and 12.0(5) meV in x=0.5. In the x=0.8 sample, which
remains paramagnetic down to 1.2 K, there is a clear signature of a spin gap of
10-12 meV at 7 K, with a strong Q-dependent intensity. Evidence of a spin gap
of 12.5(5) meV has also been found in x=1. The observation of a spin gap in the
paramagnetic samples (x=0.8 and 1) is an interesting finding in this study and
it challenges our understanding of the origin of the semiconducting gap in
CeT2Al10 (T=Ru and Os) compounds in terms of hybridization gap opening only a
small part of the Fermi surface, gapped spin waves, or a spin-dimer gap.",1306.0223v1
2015-06-27,Theory of the nonlinear Rashba-Edelstein effect,"It is well known that a current driven through a two-dimensional electron gas
with Rashba spin-orbit coupling induces a spin polarization in the
perpendicular direction (Edelstein effect). This phenomenon has been
extensively studied in the linear response regime, i.e., when the average drift
velocity of the electrons is a small fraction of the Fermi velocity. Here we
investigate the phenomenon in the nonlinear regime, meaning that the average
drift velocity is comparable to, or exceeds the Fermi velocity. This regime is
realized when the electric field is very large, or when electron-impurity
scattering is very weak. The quantum kinetic equation for the density matrix of
noninteracting electrons is exactly and analytically solvable, reducing to a
problem of spin dynamics for ""unpaired"" electrons near the Fermi surface. The
crucial parameter is $\gamma=eEL_s/E_F$, where $E$ is the electric field, $e$
is the absolute value of the electron charge, $E_F$ is the Fermi energy, and
$L_s = \hbar/(2m\alpha)$ is the spin-precession length in the Rashba spin-orbit
field with coupling strength $\alpha$. If $\gamma\ll1$ the evolution of the
spin is adiabatic, resulting in a spin polarization that grows monotonically in
time and eventually saturates at the maximum value $n(\alpha/v_F)$, where $n$
is the electron density and $v_F$ is the Fermi velocity. If $\gamma \gg 1$ the
evolution of the spin becomes strongly non-adiabatic and the spin polarization
is progressively reduced, and eventually suppressed for $\gamma\to \infty$. We
also predict an inverse nonlinear Edelstein effect, in which an electric
current is driven by a magnetic field that grows linearly in time. The
""conductivities"" for the direct and the inverse effect satisfy generalized
Onsager reciprocity relations, which reduce to the standard ones in the linear
response regime.",1506.08330v1
2020-07-09,Magnetic resonance of collective paramagnets with gapped excitations spectrum,"Some magnets due to particular geometry of the exchange bonds do not undergo
transition to the conventional magnetically ordered state despite of the
presence of significant exchange couplings. Instead, a collective paramagnetic
state is formed. The later state can remain stable down to $T=0$ if the ground
state of this magnet turns out to be nonmagnetic singlet separated from the
excited triplet states by an energy gap. Low-temperature spin dynamics of the
collective paramagnets with gapped excitations spectrum (or spin-gap magnets)
can be described in terms of a dilute gas of the triplet excitations. Applied
magnetic field can suppress the energy gap, resulting in the formation of the
gapless spin-liquid state or even leading to the unusual phenomenon of
field-induced antiferromagnetic order. Introduction of defects in the
crystallographic structure of the spin-gap magnet can result either in the
formation of multi-spin paramagnetic center or in the formation of randomly
distributed modified exchange bonds in the crystal. This review includes
results of electron spin resonance (ESR) spectroscopy study of several
representative quantum paramagnets with gapped excitations spectrum:
quasy-two-dimensional magnet \phcc{}, quasy-one-dimensional magnets of
""spin-tube"" type \sul{} and ""spin-ladder"" type \dimpy{}. We will demonstrate
that ESR absorption spectra reveal common features of these systems: ESR
spectroscopy allows to observe and characterize fine structure if the triplet
energy levels, to identify many-particles relaxation processes in the gas of
triplet excitations and to observe collective spin-wave oscillations in the
field induced antiferromagnetically ordered state, as well as to observe some
individual features of the studied systems.",2007.04885v1
2018-12-26,"Hydrodynamic description of long-distance spin transport through noncollinear magnetization states: the role of dispersion, nonlinearity, and damping","Nonlocal compensation of magnetic damping by spin injection has been
theoretically shown to establish dynamic, noncollinear magnetization states
that carry spin currents over micrometer distances. Such states can be
generically referred to as dissipative exchange flows (DEFs) because spatially
diffusing spin currents are established by the mutual exchange torque exerted
by neighboring spins. Analytical studies to date have been limited to the weak
spin injection assumption whereby the equation of motion for the magnetization
is mapped to hydrodynamic equations describing spin flow and then linearized.
Here, we analytically and numerically study easy-plane ferromagnetic channels
subject to spin injection of arbitrary strength at one extremum under a unified
hydrodynamic framework. We find that DEFs generally exhibit a nonlinear profile
along the channel accompanied by a nonlinear frequency tuneability. At large
injection strengths, we fully characterize a novel magnetization state we call
a contact-soliton DEF (CS-DEF) composed of a stationary soliton at the
injection site, which smoothly transitions into a DEF and exhibits a negative
frequency tuneability. The transition between a DEF and a CS-DEF occurs at the
maximum precessional frequency and coincides with the Landau criterion: a
subsonic to supersonic flow transition. Leveraging the hydraulic-electrical
analogy, the current-voltage characteristics of a nonlinear DEF circuit are
presented. Micromagnetic simulations of nanowires that include
magnetocrystalline anisotropy and non-local dipole fields are in qualitative
agreement with the analytical results. The magnetization states found here
along with their characteristic profile and spectral features provide
quantitative guidelines to pursue an experimental demonstration of DEFs in
ferromagnetic materials and establishes a unified description for long-distance
spin transport.",1812.10438v3
2019-04-16,Engineering spin squeezing in a 3D optical lattice with interacting spin-orbit-coupled fermions,"One of the most important tasks in modern quantum science is to coherently
control and entangle many-body systems, and to subsequently use these systems
to realize powerful quantum technologies such as quantum-enhanced sensors.
However, many-body entangled states are difficult to prepare and preserve since
internal dynamics and external noise rapidly degrade any useful entanglement.
Here, we introduce a protocol that counterintuitively exploits inhomogeneities,
a typical source of dephasing in a many-body system, in combination with
interactions to generate metrologically useful and robust many-body entangled
states. Motivated by current limitations in state-of-the-art three-dimensional
(3D) optical lattice clocks (OLCs) operating at quantum degeneracy, we use
local interactions in a Hubbard model with spin-orbit coupling to achieve a
spin-locking effect. In addition to prolonging inter-particle spin coherence,
spin-locking transforms the dephasing effect of spin-orbit coupling into a
collective spin-squeezing process that can be further enhanced by applying a
modulated drive. Our protocol is fully compatible with state-of-the-art 3D OLC
interrogation schemes and may be used to improve their sensitivity, which is
currently limited by the intrinsic quantum noise of independent atoms. We
demonstrate that even with realistic experimental imperfections, our protocol
may generate $\sim10$--$14$ dB of spin squeezing in $\sim1$ second with
$\sim10^2$--$10^4$ atoms. This capability allows OLCs to enter a new era of
quantum enhanced sensing using correlated quantum states of driven
non-equilibrium systems.",1904.07866v2
2020-11-26,Direct high resolution resonant Raman scattering measurements of InAs quantum dot dynamic nuclear spin polarization states,"We report on the direct measurement of the electron spin splitting and the
accompanying nuclear Overhauser (OH) field, and thus the underlying nuclear
spin polarization (NSP) and fluctuation bandwidth, in a single InAs quantum dot
under resonant excitation conditions with unprecedented spectral resolution.
The electron spin splitting is measured directly via resonant spin-flip single
photon Raman scattering detected by superconducting nanowires to generate
excitation-emission energy maps. The observed two-dimensional maps reveal an OH
field that has a non-linear dependence on excitation frequency. This study
provides new insight into earlier reports of so-called avoidance and tracking,
showing two distinct NSP responses directly by the addition of a emission
energy axis. The data show that the polarization processes depend on which
electron spin state is optically driven, with surprising differences in the
polarization fluctuations for each case: in one case, a stabilized field
characterized by a single-peaked distribution shifts monotonically with the
laser excitation frequency resulting in a nearly constant optical interaction
strength across a wide detuning range, while in the other case the previously
reported avoidance behavior is actually the result of a nonlinear dependence on
the laser excitation frequency near zero detuning leading to switching between
two distinct mesoscopic nuclear spin states. The magnitude of the field, which
is as large as 400 mT, is measured with sub-100 nuclear spin sensitivity.
Stable/unstable points of the OH field distribution are observed, resulting
from the non-linear feedback loop in the electron-trion-nuclear system. Nuclear
spin polarization state switching occurs between fields differing by 160 mT at
least as fast as 25 ms. Control experiments indicate that the strain-induced
quadrupolar interaction may explain the measured OH fields.",2011.13249v1
2022-01-29,"The mean flow, velocity dispersion, energy transfer and evolution of rotating and growing dark matter halos","By decomposing velocity dispersion into non-spin and spin-induced, mean flow
and dispersion are analytically solved for axisymmetric rotating and growing
halos. The polar flow can be neglected and azimuthal flow is directly related
to dispersion. The fictitious (""Reynolds"") stress acts on mean flow to enable
energy transfer from mean flow to random motion and maximize system entropy.
For large halos (high peak height $\nu$ at early stage of halo life) with
constant concentration, there exists a self-similar radial flow (outward in
core and inward in outer region). Halo mass, size and specific angular momentum
increase linearly with time via fast mass accretion. Halo core spins faster
than outer region. Large halos rotate with an angular velocity proportional to
Hubble parameter and spin-induced dispersion is dominant. All specific energies
(radial/rotational/kinetic/potential) are time-invariant. Both halo spin
($\sim$0.031) and anisotropic parameters can be analytically derived. For
""small"" halos with stable core and slow mass accretion (low peak height $\nu$
at late stage of halo life), radial flow vanishes. Small halos rotate with
constant angular velocity and non-spin axial dispersion is dominant. Small
halos are spherical in shape, incompressible, and isotropic. Radial and
azimuthal dispersion are comparable and greater than polar dispersion. Due to
finite spin, kinetic energy is not equipartitioned with the greatest energy
along azimuthal direction. Different from normal matter, small halos are hotter
with faster spin. Halo relaxation from early to late stage involves variation
of shape, density, mean flow, momentum, and energy. During relaxation, halo
isotopically ""stretches"" with conserved specific rotational kinetic energy,
increasing concentration and momentum of inertial. Halo ""stretching"" leads to
decreasing angular velocity, increasing angular momentum and spin parameter.",2201.12665v2
2022-10-19,Heat current magnification in Classical and Quantum spin networks,"We investigate heat current magnification due to asymmetry in the number of
spins in two-branched classical and quantum spin systems. We begin by studying
the classical Ising like spin models using Q2R and CCA dynamics and show that
just the difference in the number of spins is not enough and some other source
of asymmetry is required to observe heat current magnification. Unequal
spin--spin interaction strength in the upper and lower branch is employed as a
source of this asymmetry and it proves adequate for generating current
magnification in both the models. Suitable physical motivation is then provided
for current magnification in these systems, along with ways to control and
manipulate magnification through various system parameters. We also study a
five spin Quantum system with modified Heisenberg XXZ interaction and preserved
magnetisation using the Redfield master equation. We show that it is possible
to generate current magnification in this model by the asymmetry in the number
of spins only. Our results indicate that the onset of current magnification is
accompanied by a dip in the total current flowing through the system. On
analysis it is revealed that this dip might occur because of the intersection
of two non-degenerate energy levels for certain values of the asymmetry
parameter in the modified XXZ model. We deduce that the additional degeneracy
and the ergodic constraint due to fixed magnetisation in the system are the
main reasons for current magnification and other atypical behaviors observed.
We then use the concept of `ergotropy' to support these findings. Finally, for
both the classical and quantum models, we see that current magnification is
only observed when temperature gradient and intra-system interaction strength
have similar order of energy.",2210.10511v3
2023-08-05,Modulating Spin Current Induced Effective Damping in $β-W/Py$ Heterostructures by a Systematic Variation in Resistivity of the Sputtered Deposited $β-W$ films,"Utilizing the spin-induced pumping from a ferromagnet (FM) into a heavy metal
(HM) under the ferromagnetic resonance (FMR) condition, we report an
enhancement in effective damping in $\beta$- W/Py bilayers by systematically
varying resistivity ($\rho_{W}$) of $\beta$-W films. Different resistivity
ranging from 100 $\mu\Omega$-cm to 1400 $\mu\Omega$-cm with a thickness of 8 nm
can be achieved by varying the argon pressure ($P_{Ar}$) during the growth by
the method of sputtering. The coefficient of effective damping $\alpha_{eff}$
is observed to increase from 0.010 to 0.025 with $\rho_{W}$, which can be
modulated by $P_{Ar}$. We observe a modest dependence of $\alpha_{eff}$ on the
sputtering power ($p_{S}$) while keeping the $P_{Ar}$ constant. $\alpha_{eff}$
dependence on both $P_{Ar}$ and $p_{S}$ suggests that there exists a strong
correlation between $\alpha_{eff}$ and $\rho_{W}$. It is thus possible to
utilize $\rho_{W}$ as a tuning parameter to regulate the $\alpha_{eff}$, which
can be advantageous for faster magnetization dynamics switching. The thickness
dependence study of Py in the aforementioned bilayers manifests a higher spin
mixing conductance ($g^{\uparrow\downarrow}_{eff}$) which suggests a strong
spin pumping from Py into the $\beta$-W layer. The effective spin current
($J_{S(eff)}$) is also evaluated by considering the spin-back flow in this
process. Intrinsic spin mixing conductance ($g^{\uparrow\downarrow}_{W}$) and
spin diffusion length ($\lambda_{SD}$) of $\beta$-W are additionally
investigated using thickness variations in $\beta$-W. Furthermore, the
low-temperature study in $\beta$-W/Py reveals an intriguing temperature
dependence in $\alpha_{eff}$ which is quite different from $\alpha_{b}$ of
single Py layer and the enhancement in $\alpha_{eff}$ at low temperature can be
attributed to the spin-induced pumping from Py layer into $\beta$-W.",2308.02939v1
2024-02-10,The SAMI Galaxy Survey: galaxy spin is more strongly correlated with stellar population age than mass or environment,"We use the SAMI Galaxy Survey to examine the drivers of galaxy spin,
$\lambda_{R_e}$, in a multi-dimensional parameter space including stellar mass,
stellar population age (or specific star formation rate) and various
environmental metrics (local density, halo mass, satellite vs. central). Using
a partial correlation analysis we consistently find that age or specific star
formation rate is the primary parameter correlating with spin. Light-weighted
age and specific star formation rate are more strongly correlated with spin
than mass-weighted age. In fact, across our sample, once the relation between
light-weighted age and spin is accounted for, there is no significant residual
correlation between spin and mass, or spin and environment. This result is
strongly suggestive that present-day environment only indirectly influences
spin, via the removal of gas and star formation quenching. That is, environment
affects age, then age affects spin. Older galaxies then have lower spin, either
due to stars being born dynamically hotter at high redshift, or due to secular
heating. Our results appear to rule out environmentally dependent dynamical
heating (e.g. galaxy-galaxy interactions) being important, at least within
$1R_e$ where our kinematic measurements are made. The picture is more complex
when we only consider high-mass galaxies ($M_*\gtrsim 10^{11}$M$_{\odot}$).
While the age-spin relation is still strong for these high-mass galaxies, there
is a residual environmental trend with central galaxies preferentially having
lower spin, compared to satellites of the same age and mass. We argue that this
trend is likely due to central galaxies being a preferred location for mergers.",2402.06877v1
2002-01-11,"Towards a Resolution of the Galactic Spin Crisis: Mergers, Feedback, and Spin Segregation","We model in simple terms the angular-momentum problems of galaxy formation in
CDM cosmologies, and identify the key elements of a scenario that may solve
them. The buildup of angular momentum is modeled via dynamical friction and
tidal stripping in a sequence of mergers. We demonstrate how over-cooling in
incoming halos leads to a transfer of angular momentum from the baryons to the
dark matter, in conflict with observations. By incorporating a simple recipe of
supernova feedback, we are able to solve the problems of angular momentum in
disk formation. Gas removal from the numerous small incoming halos, which merge
to become the low specific angular momentum (j) component of the product,
eliminates the low-j baryons. Heating and puffing-up of the gas in larger
incoming halos, combined with efficient tidal stripping, reduces the angular
momentum loss of baryons due to dynamical friction. Dependence of the feedback
effects on the progenitor halo mass implies that the spin of baryons is
typically higher for lower mass halos. The observed low baryonic fraction in
dwarf galaxies is used to calibrate the characteristic velocity associated with
supernova feedback, yielding ~100 km/s, within the range of theoretical
expectations. We then find that the model naturally produces the observed
distribution of the spin parameter among dwarf and bright disk galaxies, as
well as the j profile inside these galaxies. This suggests that the model
indeed captures the main features of a full scenario for resolving the spin
crisis.",0201187v1
2003-07-17,Mercury's spin-orbit model and signature of its dynamical parameters,"The 3:2 spin-orbit resonance between the rotational and orbital motions of
Mercury results from a functional dependance on a tidal friction adding to a
non-zero eccentricity with a permanent asymmetry in the equatorial plane of the
planet. The upcoming space missions, MESSENGER and BepiColombo with onboard
instrumentation capable of measuring the Mercury's rotational parameters,
stimulate the objective to attempt to an accurate theory of the planet's
rotation. We have used our BJV relativistic model of solar system integration
including the spin-orbit motion of the Moon. This model had been previously
built in accordance with the requirements of the Lunar Laser Ranging
observational accuracy. We extended this model to the spin-orbit couplings of
the terrestrial planets including Mercury; the updated model is called SONYR
(acronym of Spin-Orbit N-BodY Relativistic model). An accurate rotation of
Mercury has been then obtained. Moreover, the conception of the SONYR model is
suitable for analyzing the different families of hermean rotational librations.
We accurately identify the non-linear relations between the rotation of Mercury
and its dynamical figure (\cmr2, $C_{20}$, and $C_{22}$). Notably, for a
variation of 1% on the \cmr2 value, signatures in the $\phi$ hermean libration
in longitude as well as in the $\eta$ obliquity of the planet are respectively
0.45 arcseconds (as) and 2.4 milliarcseconds (mas). These determinations
provide new constraints on the internal structure of Mercury to be discussed
with the expected accuracy forecasted in the BepiColombo mission (respectively
3.2 and 3.7 as according to Milani et al 2001).",0307328v1
1995-11-10,Contrasting Dynamic Spin Susceptibility Models and their Relation to High Temperature Superconductivity,"We compare the normal-state resistivities $\rho$ and the critical
temperatures $T_c$ for superconducting $d_{x^2-y^2}$ pairing due to
antiferromagnetic (AF) spin fluctuation exchange in the context of the two
phenomenological dynamical spin susceptibility models, recently proposed by
Millis, Monien, and Pines (MMP) and Monthoux and Pines (MP) and, respectively,
by Radtke, Ullah, Levin, and Norman (RULN), for the cuprate high-$T_c$
materials. Assuming comparable electronic bandwidths and resistiviies in both
models, we show that the RULN model gives a much lower d-wave $T_c$
($\lsim20$K) than the MMP model (with $T_c\sim100$K). We demonstrate that these
profound differences in the $T_c$'s arise from fundamental differences in the
spectral weight distributions of the two model susceptibilities and are
{\it{not}} primarily caused by differences in the calculational techniques
employed by MP and RULN. The MMP model, claimed to fit NMR data in YBCO,
exhibits substantial amounts of spin fluctuation spectral weight up to an
imposed cut-off of 400meV, whereas, in the RULN model, claimed to fit YBCO
neutron scattering data, the weight is narrowly peaked and effectively cut-off
by 100meV. Further neutron scattering experiments, to explore the spectral
weight distribution at all wavevectors over a sufficiently large excitation
energy range, will thus be of crucial importance to resolve the question
whether AF spin fluctuation exchange provides a viable mechanism to account for
high-$T_c$ superconductivity. The large high-frequency boson spectral weight,
needed to generate both a high d-wave $T_c$ and a low normal-state resistivity,
also implies large values, of order unity, for the Migdal smallness parameter,
thus casting serious doubt on the validity of the very",9511051v1
1996-01-18,Universality of Charge and Spin Response in Doped Antiferromagnets,"Recent results for the finite-temperature static and dynamical properties of
the planar $t-J$ model, obtained by a novel numerical method for small
correlated systems, are reviewed. Of particular interest are $T>0$ charge and
spin response functions: optical conductivity $\sigma(\omega)$ and spin
susceptibility $\chi(\vec q,\omega)$, which show very universal features at
intermediate doping. In spin dynamics the universality is best seen in the
local spin correlation function, which appears to be $T$-independent and only
weakly doping dependent. Results apply directly to the inelastic neutron
scattering and to the NMR relaxation experiments in cuprates. Analysing
$\sigma(\omega)$ we find that the current correlation function $C(\omega)$ is
nearly $T$- and moreover $\omega$-independent in the regime $T <J$, leading to
the $\sigma(\omega)$ behavior, very close to the marginal Fermi liquid concept
and experiments. These properties are interpreted in connection with the large
entropy, related to the large degeneracy of the low-lying states and quantum
frustration in the doped antiferromagnets. On the other hand, results for the
uniform susceptibility $\chi_0(T)$, as well as for the $\sigma(\omega)$, reveal
qualitative changes on entering the underdoped regime.",9601073v1
1998-03-19,Parisi-Symmetry of the Many-Body Quantum Theory of randomly interacting fermionic systems,"We show that fermion systems with random interactions lead to strong coupling
of glassy order and fermionic correlations, which culminates in the
implementation of Parisi replica permutation symmetry breaking (RPSB) in their
T=0 quantum field theories. Precursor effects below fermionic AT-lines become
stronger as the temperature decreases and play a crucial role within the entire
low T regime. The Parisi ultrametric structure is shown to determine low energy
excitations and the dynamic behaviour of fermionic correlations for large
times, which is predicted to affect transport properties in metallic (and
superconducting) spin glasses. Thus we reveal quantum dynamical fingerprints of
the Parisi scheme. These effects, being strongest as T->0, are contrasted with
quantum spin glass transitions at T=0 displaying only small RPSB corrections at
low T. RPSB-effects moreover appear to influence the loci of the ground state
transitions at O(T^0) and hence the phase diagrams. We derive a new
representation of the T=0 Green's function which leads to a map of the
fermionic (insulating) spin glass solution to the local limit solution of a
Hubbard model with a random repulsive interaction. We obtain the distribution
of the Hubbard interaction fluctuation and its dependence on the order of RPSB.
A generalized mapping between metallic spin glass and random U Hubbard model is
conjectured. The new representation of the Green's function at T=0 is suggested
to be useful for generalizations to superconductors with spin glass phases.",9803239v1
1998-11-03,Dynamical Transition from Triplets to Spinon Excitations: A Series Expansion Study of the $J_1-J_2-δ$ spin-half chain,"We study the spin-half Heisenberg chain with alternating nearest neighbor
interactions $J_1(1+\delta)$ and $J_1(1-\delta)$ and a uniform second neighbor
interaction $J_2=y (1-\delta)$ by series expansions around the limit of
decoupled dimers ($\delta=1$). By extrapolating to $\delta=0$ and tuning $y$,
we study the critical point separating the power-law and spontaneously
dimerized phases of the spin-half antiferromagnet. We then focus on the
disorder line $y=0.5$, $0\le \delta\le 1$, where the ground states are known
exactly. We calculate the triplet excitation spectrum, their spectral weights
and wavevector dependent static susceptibility along this line. It is well
known that as $\delta \to 0$, the spin-gap is still non-zero but the triplets
are replaced by spinons as the elementary excitations. We study this dynamical
transition by analyzing the series for the spectral weight and the static
susceptibility. In particular, we show that the spectral weight for the
triplets vanishes and the static spin-susceptibility changes from a simple pole
at imaginary wavevectors to a branch cut at the transition.",9811028v2
1999-12-27,Quantum dynamics of charged and neutral magnetic solitons: Spin-charge separation in the one-dimensional Hubbard model,"We demonstrate that the Configuration Interaction (CI) Approximation
recaptures essential features of the exact (Bethe Ansatz) solution to the 1D
Hubbard model. As such, it provides valuable route for describing effects which
go beyond mean-field theory for strongly correlated electron systems in higher
dimensions. The CI method systematically describes fluctuation and quantum
tunneling corrections to the Hartree-Fock Approximation (HFA). HFA predicts
that doping a half-filled Hubbard chain leads to the appearance of charged
spin-polarons or charged domain-wall solitons in the antiferromagnetic (AFM)
background. The CI method, on the other hand, describes the quantum dynamics of
these charged magnetic solitons and quantum tunneling effects between various
mean-field configurations. In this paper, we test the accuracy of the CI method
against the exact solution of the one-dimensional Hubbard model. We find
remarkable agreement between the energy of the mobile charged bosonic
domain-wall (as given by the CI method) and the exact energy of the doping hole
(as given by the Bethe Ansatz) for the entire $U/t$ range. The CI method also
leads to a clear demonstration of the spin-charge separation in 1D. Addition of
one doping hole to the half-filled antiferromagnetic chain results in the
appearance of two different carriers: a charged bosonic domain-wall (which
carries the charge but no spin) and a neutral spin-1/2 domain wall (which
carries the spin but no charge).",9912460v1
2000-10-25,Spin and charge dynamics of the ferromagnetic and antiferromagnetic two-dimensional half-filled Kondo lattice model,"We present a detailed numerical study of spin and charge dynamics of the
two-dimensional Kondo lattice model with hopping t and exchange J. At T=0 and J
> 0, the competition between the RKKY interaction and Kondo effect triggers a
quantum phase transition between magnetically ordered and disordered
insulators: J_c/t = 1.45(5). The quasiparticle gap scales as |J|. S(q,\omega),
evolves smoothly from its strong coupling form with spin gap at q = (\pi,\pi)
to a spin wave form. At J>0, A(\vec{k},\omega) shows a dispersion relation
following that of hybridized bands. For J < J_c this feature is supplemented by
shadows thus pointing to a coexistence of Kondo screening and magnetism. For J
< 0 A(\vec{k},\omega) is similar to that of non-interacting electrons in a
staggered magnetic field. Spin, T_S, and charge, T_C, scales are defined. For
weak to intermediate couplings, T_S marks the onset of antiferromagnetic
fluctuations and follows a J^2 law. At strong couplings T_S scales as J. T_C
scales as J both at weak and strong couplings. At and slightly below T_C we
observe i) a rise in the resistivity as a function of decreasing temperature,
ii) a dip in the integrated density of states at the Fermi energy and iii) the
occurrence of hybridized bands in A(k,\omega). It is shown that in the weak
coupling limit, the charge gap of order J is of magnetic origin. The specific
heat shows a two peak structure, the low temperature peak being of magnetic
origin. Our results are compared to various mean-field theories.",0010393v1
2004-05-19,Auxiliary-Fermion Approach to Critical Fluctuations in the 2D Quantum AF Heisenberg Model,"The nearest-neighbor quantum-antiferromagnetic (AF) Heisenberg model for spin
1/2 on a two-dimensional square lattice is studied in the auxiliary-fermion
representation. Expressing spin operators by canonical fermionic particles
requires a constraint on the fermion charge Q=1 on each lattice site, which is
imposed approximately through the thermal average. The resulting interacting
fermion system is first treated in mean-field theory (MFT), which yields an AF
ordered ground state and spin waves in quantitative agreement with conventional
spin-wave theory. At finite temperature a self-consistent approximation beyond
mean field is required in order to fulfill the Mermin-Wagner theorem. We first
discuss a fully self-consistent approximation, where fermions are renormalized
due to fluctuations of their spin density, in close analogy to FLEX. While
static properties like the correlation length come out correctly, the dynamical
response lacks the magnon-like peaks which would reflect the appearance of
short-range order at low T. This drawback, which is caused by overdamping, is
overcome in a `minimal self-consistent approximation' (MSCA), which we derive
from the equations of motion. The MSCA features dynamical scaling at small
energy and temperature and is qualitatively correct both in the regime of
order-parameter relaxation at long wavelengths and in the short-range-order
regime. We also discuss the impact of vertex corrections and the problem of
pseudo-gap formation in the single-particle density of states due to long-range
fluctuations. Finally we show that the (short-range) magnetic order in MFT and
MSCA helps to fulfill the constraint on the local fermion occupancy.",0405438v2
2005-08-18,Probing spin dynamics and quantum relaxation in LiY0.998Ho0.002F4 via 19F NMR,"We report measurements of 19F nuclear spin-lattice relaxation 1/T1 as a
function of temperature and external magnetic field in LiY0.998Ho0.002F4 single
crystal, a single-ion magnet exhibiting interesting quantum effects. The 19F
1/T1 is found to depend on the coupling with the diluted rare-earth (RE)
moments. Depending on the temperature range, a fast spin diffusion regime or a
diffusion limited regime is encountered. In both cases we find it possible to
use the 19F nucleus as a probe of the rare-earth spin dynamics. The results for
1/T1 show a behavior similar to that observed in molecular nanomagnets, a
result which we attribute to the discreteness of the energy levels in both
cases. At intermediate temperatures the lifetime broadening of the crystal
field split RE magnetic levels follows a T3 power law. At low temperature the
field dependence of 1/T1 shows peaks in correspondence to the critical magnetic
fields for energy level crossings (LC). The results can be explained by
inelastic scattering between the fluorine nuclear spins and the RE magnetic
levels. A key result of this study is that the broadening of the levels at LC
is found to be become extremely small at low temperatures, about 1.7 mT, a
value which is comparable to the weak dipolar fields at the RE lattice
positions. Thus, unlike the molecular magnets, decoherence effects are strongly
suppressed, and it may be possible to measure directly the level repulsions at
avoided level crossings.",0508406v1
2006-03-28,Relaxation times of kinetically constrained spin models with glassy dynamics,"We analyze the density and size dependence of the relaxation time $\tau$ for
kinetically constrained spin systems. These have been proposed as models for
strong or fragile glasses and for systems undergoing jamming transitions. For
the one (FA1f) or two (FA2f) spin facilitated Fredrickson-Andersen model at any
density $\rho<1$ and for the Knight model below the critical density at which
the glass transition occurs, we show that the persistence and the spin-spin
time auto-correlation functions decay exponentially. This excludes the
stretched exponential relaxation which was derived by numerical simulations.
For FA2f in $d\geq 2$, we also prove a super-Arrhenius scaling of the form
$\exp(1/(1-\rho))\leq \tau\leq\exp(1/(1-\rho)^2)$. For FA1f in $d$=$1,2$ we
rigorously prove the power law scalings recently derived in \cite{JMS} while in
$d\geq 3$ we obtain upper and lower bounds consistent with findings therein.
Our results are based on a novel multi-scale approach which allows to analyze
$\tau$ in presence of kinetic constraints and to connect time-scales and
dynamical heterogeneities. The techniques are flexible enough to allow a
variety of constraints and can also be applied to conservative stochastic
lattice gases in presence of kinetic constraints.",0603745v1
2006-12-01,Chaos and Order in Models of Black Hole Pairs,"Chaos in the orbits of black hole pairs has by now been confirmed by several
independent groups. While the chaotic behavior of binary black hole orbits is
no longer argued, it remains difficult to quantify the importance of chaos to
the evolutionary dynamics of a pair of comparable mass black holes. None of our
existing approximations are robust enough to offer convincing quantitative
conclusions in the most highly nonlinear regime. It is intriguing to note that
in three different approximations to a black hole pair built of a spinning
black hole and a non-spinning companion, two approximations exhibit chaos and
one approximation does not. The fully relativistic scenario of a spinning
test-mass around a Schwarzschild black hole shows chaos, as does the
Post-Newtonian Lagrangian approximation. However, the approximately equivalent
Post-Newtonian Hamiltonian approximation does not show chaos when only one body
spins. It is well known in dynamical systems theory that one system can be
regular while an approximately related system is chaotic, so there is no formal
conflict. However,the physical question remains, Is there chaos for comparable
mass binaries when only one object spins? We are unable to answer this question
given the poor convergence of the Post-Newtonian approximation to the fully
relativistic system. A resolution awaits better approximations that can be
trusted in the highly nonlinear regime.",0612003v1
2004-07-02,Universal Dynamics of Spontaneous Lorentz Violation and a New Spin-Dependent Inverse-Square Law Force,"We study the universal low-energy dynamics associated with the spontaneous
breaking of Lorentz invariance down to spatial rotations. The effective
Lagrangian for the associated Goldstone field can be uniquely determined by the
non-linear realization of a broken time diffeomorphism symmetry, up to some
overall mass scales. It has previously been shown that this symmetry breaking
pattern gives rise to a Higgs phase of gravity, in which gravity is modified in
the infrared. In this paper, we study the effects of direct couplings between
the Goldstone boson and standard model fermions, which necessarily accompany
Lorentz-violating terms in the theory. The leading interaction is the coupling
to the axial vector current, which reduces to spin in the non-relativistic
limit. A spin moving relative to the ""ether"" rest frame will emit Goldstone
Cerenkov radiation. The Goldstone also induces a long-range inverse-square law
force between spin sources with a striking angular dependence, reflecting the
underlying Goldstone shockwaves and providing a smoking gun for this theory. We
discuss the regime of validity of the effective theory describing these
phenomena, and the possibility of probing Lorentz violations through Goldstone
boson signals in a way that is complementary to direct tests in some regions of
parameter space.",0407034v3
2007-05-14,Spin Effects in Quantum Chromodynamics and Recurrence Lattices with Multi-Site Exchanges,"In this thesis, we consider some spin effects in QCD and recurrence lattices
with multi-site exchanges. Main topic of our manuscript are critical phenomena
in spin systems defined on the recurrence lattices. Main tool of our approach
is the method of recursive (hierarchical) lattices. We apply the method of
dynamical mapping (or recursive lattices) for investigation of magnetic
properties of the fluid and solid $^3$He, phase transitions in crystals and
macromolecules. First, we analyze the helix-coil phase transition for
polypeptides and proteins, and describe an quasi unfolding transition (like the
cold denaturation process) for the degree of helicity (the order parameter for
macromolecules). Next we consider the recurrent models of $^3$He defined on the
square, Husimi and hexagon lattices. Using the method of dynamical mapping, the
magnetization curves with plateaus, bifurcation point and one period doubling
are obtained. Then we investigate the model with cubic symmetry defined on the
Bethe lattice and containing both linear and quadratic spin-spin interactions.
The magnetization of the system is calculated, and a complex structure of the
phase transitions between the disordered, partially ordered and completely
ordered states is observed. In the framework of QCD, we consider the azimuthal
asymmetries in heavy flavor production in the lepton-nucleon deep inelastic
scattering (DIS). We calculate the azimuthal (or $\phi$-) dependence of the
next-to-leading order heavy-quark-initiated contributions to DIS. It is shown
that, contrary to the basic gluon-initiated component, the photon-quark
scattering mechanism is practically $\cos2\phi$-independent. We investigate the
possibility of measuring both nonperturbative (intrinsic) and perturbative
(CTEQ, MRST) charm distributions using the $\cos2\phi$ asymmetry.",0705.1932v1
2008-02-01,Spin observables and spin structure functions: inequalities and dynamics,"Model-independent identities and inequalities relating the various spin
observables of a reaction are reviewed in a unified formalism, together with
their implications for dynamical models, their physical interpretation, and the
quantum aspects of the information carried by spins, in particular
entanglement. These constraints between observables can be obtained from the
explicit expression of the observables in terms of a set of amplitudes, a
non-trivial algebraic exercise which can be preceded by numerical simulation
with randomly chosen amplitudes, from anticommutation relations, or from the
requirement that any polarisation vector is less than unity. The most powerful
tool is the positivity of the density matrices describing the reaction or its
crossed channels, with a projection to single out correlations between two or
three observables. For the exclusive reactions, the cases of the
strangeness-exchange proton-antiproton scattering and the photoproduction of
pseudoscalar mesons are treated in some detail: all triples of observables are
constrained, and new results are presented for the allowed domains. The
positivity constraints for total cross-sections and single-particle inclusive
reactions are reviewed, with application to spin-dependent structure functions
and parton distributions. The corresponding inequalities are shown to be
preserved by the evolution equations of QCD.",0802.0164v2
2008-09-01,Spin Fluctuation Dynamics and Multiband Superconductivity in Iron Pnictides,"Multiband superconductivity, involving resonant pair scattering between
different bands, has emerged as a possible explanation of some of the main
characteristics of the recently discovered iron pnictides. A key feature of
such interband pairing mechanism is that it can generate or enhance
superconducting pairing irrespective of whether it is attractive or repulsive.
The latter case typically leads to the superconducting gap switching its sign
among different sections of the Fermi surface. In iron pnictides, the natural
scenario is that the gap changes sign between the hole and the electron Fermi
surfaces. However, the macroscopic symmetry of such an extended s'-wave state
still belongs to the general s-wave category, raising the question of how to
distinguish it from an ordinary s-wave. In such a quest, it is essential to use
experimental techniques that have a momentum space resolution and can probe
momenta of order M, the wavevector that separates the hole and the electron
Fermi surfaces in the Brillouin zone. Here we study experimental signatures in
the spin fluctuation dynamics of the fully-gapped s- and s'-wave
superconducting states, as well as those of the nodal d- and p-wave. The
coupling between spin fluctuations of the incipient nearly-nested spin
density-wave (SDW) and the Bogoliubov-deGennes quasiparticles of the
superconducting state leads to the Landau-type damping of the former. The
intrinsic structure of the superconducting gap leaves a distinctive signature
in the form of this damping, allowing it to be used to diagnose the nature of
iron-based superconductivity in neutron scattering and other experiments
sensitive to spin fluctuations in momentum space. We also discuss the
coexistence between superconductivity and SDW order.",0809.0014v1
2009-02-04,Spin dynamics of frustrated easy-axis triangular antiferromagnet 2H-AgNiO2 explored by inelastic neutron scattering,"We report inelastic neutron scattering measurements of the spin dynamics in
the layered hexagonal magnet 2H-AgNiO2 which has stacked triangular layers of
antiferromagnetically-coupled Ni2+ spins (S=1) ordered in a collinear
alternating stripe pattern. We observe a broad band of magnetic excitations
above a small gap of 1.8 meV and extending up to 7.5 meV, indicating strongly
dispersive excitations. The measured dispersions of the boundaries of the
powder-averaged spectrum can be quantitatively explained by a linear spin-wave
dispersion for triangular layers with antiferromagnetic nearest- and weak
next-nearest neighbor couplings, a strong easy-axis anisotropy and additional
weak inter-layer couplings. The resulting dispersion relation has global minima
not at magnetic Bragg wavevectors but at symmetry-related soft points and we
attribute this anomalous feature to the strong competition between the
easy-axis anisotropy and the frustrated antiferromagnetic couplings. We have
also calculated the quantum corrections to the dispersion relation to order 1/S
in spin-wave theory by extending the work of Chubukov and Jolicoeur [Phys. Rev.
B v46, 11137 (1992)] and find that the presence of easy-axis anisotropy
significantly reduces the quantum renormalizations predicted for the isotropic
model.",0902.0676v1
2010-04-27,Recent STAR results in high-energy polarized proton-proton collisions at RHIC,"The STAR experiment at the Relativistic Heavy-Ion Collider at Brookhaven
National Laboratory is carrying out a spin physics program in high-energy
polarized $\vec{p}+\vec{p}$ collisions at $\sqrt{s}=200-500\,$GeV to gain a
deeper insight into the spin structure and dynamics of the proton.
  One of the main objectives of the spin physics program at RHIC is the
extraction of the polarized gluon distribution function based on measurements
of gluon initiated processes, such as hadron and jet production. The STAR
detector is well suited for the reconstruction of various final states
involving jets, $\pi^{0}$, $\pi^{\pm}$, e$^{\pm}$ and $\gamma$, which allows to
measure several different processes. Recent results will be shown on the
measurement of jet production and hadron production at $\sqrt{s}=200\,$GeV. The
RHIC spin physics program has recently completed the first data taking period
in 2009 of polarized $\vec{p}+\vec{p}$ collisions at $\sqrt{s}=500\,$GeV. This
opens a new era in the study of the spin-flavor structure of the proton based
on the production of $W^{-(+)}$ bosons. Recent STAR results on the first
measurement of $W$ boson production in polarized $\vec{p}+\vec{p}$ collisions
will be shown.",1004.4884v1
2011-01-13,"Entanglement, decoherence and thermal relaxation in exactly solvable models","Exactly solvable models provide an opportunity to study different aspects of
reduced quantum dynamics in detail. We consider the reduced dynamics of a
single spin in finite XX and XY spin 1/2 chains. First we introduce a general
expression describing the evolution of the reduced density matrix. This
expression proves to be tractable when the combined closed system (i.e. open
system plus environment) is integrable. Then we focus on comparing decoherence
and thermalization timescales in the XX chain. We find that for a single spin
these timescales are comparable, in contrast to what should be expected for a
macroscopic body. This indicates that the process of quantum relaxation of a
system with few accessible states can not be separated in two distinct stages -
decoherence and thermalization. Finally, we turn to finite-size effects in the
time evolution of a single spin in the XY chain. We observe three consecutive
stages of the evolution: regular evolution, partial revivals, irregular
(apparently chaotic) evolution. The duration of the regular stage is
proportional to the number of spins in the chain. We observe a ""quiet and cold
period"" in the end of the regular stage, which breaks up abruptly at some
threshold time.",1101.2535v1
2011-10-07,On the Mass Difference between pion and rho meson using a Relativistic Two-Body Model,"The big mass difference between the pion and rho meson possibly originates
from the spin-dependent nature of the interactions in the two states since
these two states are similar except for spin. Both pi and rho are
quark-antiquark systems which can be treated using the two-body Dirac equations
(TBDE) of constraint dynamics. This relativistic approach for two-body system
has the advantage over the non-relativistic treatment in the sense that the
spin-dependent nature is automatically coming out from the formalism. We
employed Dirac's relativistic constraint dynamics to describe quark-antiquark
systems. Within this formalism, the 16-component Dirac equation is reduced to
the 4-component 2nd-order differential equation and the radial part of this
equation is simply a Schroedinger-type equation with various terms calculated
from the basic radial potential. We used a modified Richardson potential for
quark-antiquark systems which satisfies the conditions of confinement and
asymptotic freedom. We obtained the wave functions for these two mesons which
are not singular at short distances. We also found that the cancellation
between the Darwin and spin-spin interaction terms occurs in the pi mass but
not in the rho mass and this is the main source of the big difference in the
two meson masses.",1110.1598v1
2013-05-31,Relevance of electron spin dissipative processes to dynamic nuclear polarization via thermal mixing,"The available theoretical approaches aiming at describing Dynamic Nuclear
spin Polarization (DNP) in solutions containing molecules of biomedical
interest and paramagnetic centers are not able to model the behaviour observed
upon varying the concentration of trityl radicals or the polarization
enhancement caused by moderate addition of gadolinium complexes. In this
manuscript, we first show experimentally that the nuclear steady state
polarization reached in solutions of pyruvic acid with 15 mM trityl radicals is
substantially independent from the average internuclear distance. This
evidences a leading role of electron (over nuclear) spin relaxation processes
in determining the ultimate performances of DNP. Accordingly, we have devised a
variant of the Thermal Mixing model for inhomogenously broadened electron
resonance lines which includes a relaxation term describing the exchange of
magnetic anisotropy energy of the electron spin system with the lattice. Thanks
to this additional term, the dependence of the nuclear polarization on the
electron concentration can be properly accounted for. Moreover, the model
predicts a strong increase of the final polarization on shortening the electron
spin-lattice relaxation time, providing a possible explanation for the effect
of gadolinium doping.",1305.7324v3
2013-10-07,Tunable Landau-Zener transitions in a spin-orbit coupled Bose-Einstein condensate,"The Landau-Zener (LZ) transition is one of the most fundamental phenomena in
quantum dynamics. It describes nonadiabatic transitions between quantum states
near an avoided crossing that can occur in diverse physical systems. Here we
report experimental measurements and tuning of LZ transitions between the
dressed eigenlevels of a Bose-Einstein condensate (BEC) that is synthetically
spin-orbit (SO) coupled. We measure the transition probability as the BEC is
accelerated through the SO avoided crossing and study its dependence on the
coupling between the diabatic (bare) states, eigenlevel slope, and eigenstate
velocity--the three parameters of the LZ model that are independently
controlled in our experiments. Furthermore, we performed time-resolved
measurements to demonstrate the breaking down of the spin-momentum locking of
the spin-orbit-coupled BEC in the nonadiabatic regime, and we determined the
diabatic switching time of the LZ transitions. Our observations show
quantitative agreement with the LZ model and numerical simulations of the
quantum dynamics in the quasimomentum space. The tunable LZ transition may be
exploited to enable a spin-dependent atomtronic transistor.",1310.1818v2
2013-10-29,Wave packet dynamics and zitterbewegung of heavy holes in a quantizing magnetic field,"In this work we study wave packet dynamics and $zitterbewegung$, an
oscillatory quantum motion, of heavy holes in III-V semiconductor quantum wells
in presence of a quantizing magnetic field. It is revealed that a Gaussian
wave-packet describing a heavy hole diffuses asymmetrically along the circular
orbit while performing cyclotron motion. The wave packet splits into two peaks
with unequal amplitudes after a certain time depending on spin-orbit coupling
constant. This unequal splitting of the wave packet is attributed to the cubic
Rashba interaction for heavy holes. The difference in the peak amplitudes
disappears with time. At a certain time the two peaks diffuse almost along the
entire cyclotron orbit. Then tail and head of the diffused wave packet
interfere and as a result a completely randomized pattern of the wave packet is
observed. The diffusion rate of the wave packet increases with increase of the
spin-orbit interaction strength. Also strong spin-orbit coupling expedite the
splitting and the randomization of the wave packet. We also study the
$zitterbewegung$ in various physical observables such as position, charge
current and spin angular momentum of the heavy hole. The $zitterbewegung$
oscillations are very much sensitive to the initial wave vector of the Gaussian
wave packet and the strength of the Rashba spin-orbit coupling.",1310.7749v2
2014-07-22,Stability analysis for new theories of massive spin-two particle and black hole entropy of new bigravity,"In Phys.\ Rev.\ D 90 043006 (2014), we proposed a new ghost-free massive
spin-two model in flat spacetime. Furthermore, as some extension, we couple the
new model with a non-dynamical curved background in Phys.\ Rev.\ D 90 123013
(2014) and constructed new interaction terms without appearance of an extra
mode. The characteristic property of the new model is the existence of
nonlinear potential terms which give the nontrivial vacua. The presence of the
nontrivial vacua, however, does not mean that the particle can be defined
around all vacua. Therefore, in this paper, we discuss the condition for the
new model to have stable vacua in flat spacetime and curved spacetime. Then, we
couple this spin-two theory with a dynamical background and obtain the
solutions. Moreover, we investigate the effect of this new spin-two model to
the Einstein gravity by calculating the black hole entropy since the gravity
coupled massive spin-two theory admits a black hole solution in addition to
(anti-) de Sitter space solution.",1407.5765v3
2014-08-08,Towards models of gravitational waveforms from generic binaries II: Modelling precession effects with a single effective precession parameter,"Gravitational waves (GWs) emitted by generic black-hole binaries show a rich
structure that directly reflects the complex dynamics introduced by the
precession of the orbital plane, which poses a real challenge to the
development of generic waveform models. Recent progress in modelling these
signals relies on an approximate decoupling between the non-precessing secular
inspiral and a precession-induced rotation. However, the latter depends in
general on all physical parameters of the binary which makes modelling efforts
as well as understanding parameter-estimation prospects prohibitively complex.
Here we show that the dominant precession effects can be captured by a reduced
set of spin parameters. Specifically, we introduce a single \emph{effective
precession spin} parameter, $\chi_p$, which is defined from the spin components
that lie in the orbital plane at some (arbitrary) instant during the inspiral.
We test the efficacy of this parameter by considering binary inspiral
configurations specified by the physical parameters of a corresponding
non-precessing-binary configuration (total mass, mass ratio, and spin
components (anti-)parallel to the orbital angular momentum), plus the effective
precession spin applied to the larger black hole. We show that for an
overwhelming majority of random precessing configurations, the precession
dynamics during the inspiral are well approximated by our equivalent
configurations. Our results suggest that in the comparable-mass regime waveform
models with only three spin parameters faithfully represent generic waveforms,
which has practical implications for the prospects of GW searches, parameter
estimation and the numerical exploration of the precessing-binary parameter
space.",1408.1810v2
2015-11-09,Free Nano-Object Ramsey Interferometry for Large Quantum Superpositions,"We propose an interferometric scheme based on an untrapped nano-object
subjected to gravity. The motion of the center of mass (c.m.) of the free
object is coupled to its internal spin system magnetically, and a free flight
scheme is developed based on coherent spin control. The wavepacket of the test
object, under a spin-dependent force, may then be delocalized to a macroscopic
scale. A gravity induced dynamical phase (accrued solely on the spin state, and
measured through a Ramsey scheme) is used to reveal the above spatially
delocalised superposition of the spin-nano-object composite system that arises
during our scheme. We find a remarkable immunity to the motional noise in the
c.m. (initially in a thermal state with moderate cooling), and also a dynamical
decoupling nature of the scheme itself. Together they secure a high visibility
of the resulting Ramsey fringes. The mass independence of our scheme makes it
viable for a nano-object selected from an ensemble with a high mass
variability. Given these advantages, a quantum superposition with $100$ nm
spatial separation for a massive object of $10^9$ amu is achievable
experimentally, providing a route to test postulated modifications of quantum
theory such as continuous spontaneous localisation.",1511.02738v2
2016-07-14,Dynamics of a coupled spin vortex pair in dipolar spinor Bose-Einstein condensates,"The collisional and magnetic field quench dynamics of a coupled spin-vortex
pair in dipolar spinor Bose-Einstein condensates in a double well potential are
numerically investigated in the mean field theory. Upon a sudden release of the
potential barrier the two layers of condensates collide with each other in the
trap center with the chirality of the vortex pair exchanged after each
collision, showing the typical signature of in-phase collision for the parallel
spin vortex phase, and out-of-phase collision for the antiparallel phase. When
quenching the transverse magnetic field, the vortex center in the
single-layered condensate starts to make a helical motion with oval-shaped
trajectories and the displacement of the center position is found to exhibit a
damped simple harmonic oscillation with an intrinsic frequency and damping
rate. The oscillation mode of the spin vortex pair may be tuned by the initial
magnetic field and the height of the Gaussian barrier, e.g. the gyrotropic
motions for parallel spin vortex pair are out of sync with each other in the
two layers, while those for the antiparallel pair exhibit a
double-helix-structure with the vortex centers moving opposite to each other
with the same amplitude.",1607.03983v1
2016-09-01,The role of the internal demagnetizing field in a surface-modulated magnonic crystal,"Magnonic crystals with locally alternating properties and specific
periodicities exhibit interesting effects, such as a multitude of different
spin-wave states and large band gaps. This work aims for demonstrating and
understanding the key role of local demagnetizing fields in such systems. To
achieve this, hybrid structures are investigated consisting of a continuous
thin film with a stripe modulation on top favorable due to the adjustability of
the magnonic effects with the modulation size. For a direct access to the spin
dynamics, a magnonic crystal was reconstructed from `bottom-up', i.e., the
structural shape as well as the internal field landscape of the structure were
experimentally obtained on the nanoscale using electron holography.
Subsequently, both properties were utilized to perform dynamic response
calculations. The simulations yield the frequency-field dependence as well as
the angular dependence of spin waves in a magnonic crystal and reveal the
governing role of the internal field landscape around the backward-volume
geometry. The complex angle-dependent spin-wave behavior is described for a 360
degree in-plane rotation of an external field by connecting the internal field
landscape with the individual spin-wave localization.",1609.00342v3
2016-09-03,Multiscale simulation of polymer melt spinning by using the dumbbell model,"We investigated the spinning process of a polymeric material by using a
multiscale simulation method which connects the macroscopic and microscopic
states through the stress and strain-rate tensor fields, by using Lagrangian
particles (filled with polymer chains) along the spinning line. We introduce a
large number of Lagrangian fluid particles into the fluid, each containing
Np-Hookean-dumbbells to mimic the polymer chains (Np=$10^4$), which is
equivalent to the upper convected Maxwell fluid in the limit that
Np$\rightarrow \infty$. Depending on the Reynolds number Re, we studied the
dynamical behaviors of fibers for the (a) Re =0 and (b) finite Re cases, for
different draw ratios Dr, ranging from 10 to 30, and two typical Deborah
numbers De=$10^{-3}$ and De=$10^{-2}$. In the limit Re$\rightarrow$ 0 (a), as
the Deborah number De increases, the elastic effect makes the system stable. At
finite Re (b), we found that inertial effects play an important role in
determining the dynamical behavior of the spinning process, and for
Dr=$10^{-2}$ the system is quite stable, at least up to a draw ratio of Dr=30.
We also found that the fiber velocity and cross section area are determined
solely by the draw ratio. By comparing the velocity and cross section area
profiles with the end-point distribution for the dumbbell connective vectors,
for dumbbells located in Lagrangian particles along typical places along the
spinning line, we show that our multiscale simulation method successfully
bridges the microscopic state of the system with its simultaneous macroscopic
flow behavior. It is also confirmed that the present schemes gives good
agreements with the results obtained by the Maxwell constitutive equation.",1609.00793v1
2016-09-30,Dynamic nuclear polarization and relaxation of H and D atoms in solid mixtures of hydrogen isotopes,"We report on a study of Dynamic Nuclear Polarization and electron and nuclear
spin relaxation of atomic hydrogen and deuterium in solid molecular matrices of
H$_{2}$, D$_{2}$, and HD mixtures. The electron and nuclear spin relaxation
times ($T_{1e}$ and $T_{1N}$) were measured within the temperature range
0.15-2.5$\,$K in a magnetic field of 4.6 T, conditions which ensure a high
polarization of electron spins. We found that $T_{1e}$ is nearly temperature
independent in this temperature range, while $T_{1N}$ decreased by 2 orders of
magnitude. Such strong temperature dependence is typical for the nuclear Orbach
mechanism of relaxation via the electron spins. We found that the nuclear spins
of H atoms in solid D$_{2}$ and D$_{2}:$HD can be efficiently polarized by the
Overhauser effect. Pumping the forbidden transitions of H atoms also leads to
DNP, with the efficiency strongly dependent on the concentration of D atoms.
This behaviour indicates the Cross effect mechanism of the DNP and nuclear
relaxation, which turns out to be well resolved in the conditions of our
experiments. Efficient DNP of H atoms was also observed when pumping the middle
D line located in center of the ESR spectrum. This phenomenon can be explained
in terms of clusters or pairs of H atoms with strong exchange interaction.
These clusters have partially allowed transitions in the center of the ESR
spectrum and DNP may be created via the resolved Cross effect.",1609.09772v1
2017-08-09,Dynamics of interacting fermions under spin-orbit coupling in an optical lattice clock,"Quantum statistics and symmetrization dictate that identical fermions do not
interact via s-wave collisions. However, in the presence of spin-orbit coupling
(SOC), fermions prepared in identical internal states with distinct momenta
become distinguishable. The resulting strongly interacting system can exhibit
exotic topological and pairing behaviors, many of which are yet to be observed
in condensed matter systems. Ultracold atomic gases offer a promising pathway
for simulating these rich phenomena. Two recent experiments reported the
observation of single atom SOC in optical lattice clocks (OLCs) based on
alkaline-earth atoms. In these works encoding the effective spin degree of
freedom in the long-lived electronic clock states significantly reduced the
detrimental effects of spontaneous emission and heating that have thus far
hindered the study of interacting SOC with alkali atoms. Beyond first studies
of interacting SOC with alkali atoms in a bulk gas and with two particles in a
lattice, here we enter a new regime of many-body interacting SOC in an OLC.
Using clock spectroscopy, we observe the precession of the collective
magnetization and the emergence of spin locking effects arising from an
interplay between p-wave and SOC-induced exchange interactions. The many-body
dynamics are well captured by a collective XXZ spin model, which describes a
broad class of condensed matter systems ranging from superconductors to quantum
magnets. Furthermore, our work will aid in the design of next-generation OLCs
by offering a route for avoiding the observed large density shifts caused by
SOC-induced exchange interactions.",1708.02704v2
2018-04-19,Loschmidt echo driven by hyperfine and electric-quadrupole interactions in nanoscale nuclear spin baths,"The nuclear spin bath (NSB) dynamics and its quantum control are of
importance for the storage and processing of quantum information within a
semiconductor environment. In the presence of a carrier spin, primarily it is
the hyperfine interaction that rules the high frequency NSB characteristics.
Here, we first study the overall coherence decay and rephasings in a
hyperfine-driven NSB through the temporal and spectral behaviors of the
so-called Loschmidt echo (LE). Its dependence on the NSB size, initial
polarization, and coupling inhomogeneity are separately investigated, which
leads to a simple phenomenological expression that can accommodate all of these
attributes. Unlike the prevailing emphasis on spin 1/2, the NSBs with larger
spin quantum numbers are equally considered. For this case, additionally the
effect of nuclear electric quadrupole interaction is taken into account where
its biaxiality term is influential on the decoherence. The insights gained from
model systems are then put to use for two generic realistic semiconductor
systems, namely, a donor center and a quantum dot that represent small and
large nanoscale NSB examples, respectively. The spectrum of LE for large
quantum dots can reach the 100~MHz range, whereas, for donor centers, it
reduces to a few MHz, making them readily amenable for dynamical decoupling
techniques. The effect of quadrupole interaction on LE is seen to be negligible
for large quantum dots, while it becomes significant for donor centers, most
notably in the form of depolarizing a polarized NSB.",1804.07219v2
2018-11-01,Competition between static and dynamic magnetism in the Kitaev spin liquid material Cu2IrO3,"Anyonic excitations emerging from a Kitaev spin liquid can form a basis for
quantum computers. Searching for such excitations motivated intense research on
the honeycomb iridate materials. However, access to a spin liquid ground state
has been hindered by magnetic ordering. Cu2IrO3 is a new honeycomb iridate
without thermodynamic signatures of a long-range order. Here, we use muon spin
relaxation to uncover the magnetic ground state of Cu2IrO3. We find a
two-component depolarization with slow and fast relaxation rates corresponding
to distinct regions with dynamic and static magnetism, respectively. X-ray
absorption spectroscopy and first principles calculations identify a mixed
copper valence as the origin of this behavior. Our results suggest that a
minority of Cu2+ ions nucleate regions of static magnetism whereas the majority
of Cu+/Ir4+ on the honeycomb lattice give rise to a Kitaev spin liquid.",1811.00565v1
2018-05-09,Dynamic spin-lattice coupling and nematic fluctuations in NaFeAs,"We use inelastic neutron scattering to study acoustic phonons and spin
excitations in single crystals of NaFeAs, a parent compound of iron pnictide
superconductors. NaFeAs exhibits a tetragonal-to-orthorhombic structural
transition at $T_s\approx 58$ K and a collinear antiferromagnetic (AF) order at
$T_N\approx 45$ K. While longitudinal and out-of-plane transverse acoustic
phonons behave as expected, the in-plane transverse acoustic phonons reveal
considerable softening on cooling to $T_s$, and then harden on approaching
$T_N$ before saturating below $T_N$. In addition, we find that spin-spin
correlation lengths of low-energy magnetic excitations within the FeAs layer
and along the $c$-axis increase dramatically below $T_s$, and show weak anomaly
across $T_N$. These results suggest that the electronic nematic phase present
in the paramagnetic tetragonal phase is closely associated with dynamic
spin-lattice coupling, possibly arising from the one-phonon-two-magnon
mechanism.",1805.03493v1
2012-01-29,Collective Dipole Oscillation of a Spin-Orbit Coupled Bose-Einstein Condensate,"We present an experimental study of the collective dipole oscillation of a
spin-orbit coupled Bose-Einstein condensate in a harmonic trap. Dynamics of the
center-of-mass dipole oscillation is studied in a broad parameter region, as a
function of spin-orbit coupling parameters as well as oscillation amplitude.
Anharmonic properties beyond effective-mass approximation are revealed, such as
amplitude-dependent frequency and finite oscillation frequency at place with
divergent effective mass. These anharmonic behaviors agree quantitatively with
variational wave-function calculations. Moreover, we experimentally demonstrate
a unique feature of spin-orbit coupled system predicted by a sum-rule approach,
stating that spin polarization susceptibility--a static physical quantity--can
be measured via dynamics of dipole oscillation. The divergence of polarization
susceptibility is observed at the quantum phase transition that separates
magnetic nonzero-momentum condensate from nonmagnetic zero-momentum phase. The
good agreement between the experimental and theoretical results provides a
bench mark for recently developed theoretical approaches.",1201.6018v2
2013-09-23,Polaron dynamics and decoherence in an interacting two-spin system coupled to optical phonon environment,"We study two anisotropically interacting spins coupled to optical phonons; we
restrict our analysis to the regime of strong coupling to the environment, to
the antiadiabatic region, and to the subspace with zero value for $S^z_T$ (the
z-component of the total spin). In the case where each spin is coupled to a
different phonon bath, we assume that the system and the environment are
initially uncorrelated (and form a simply separable state) in the polaronic
frame of reference. By analyzing the {polaron} dynamics through non-Markovian
quantum master equation, we find that the system manifests a small amount of
decoherence that decreases both with increasing non-adiabaticity and with
enhancing strength of coupling; whereas, under the Markovian approximation, the
polaronic system exhibits a decoherence free behavior. For the situation where
both spins are coupled to the same phonon bath, we also show that the system is
decoherence free in the subspace where $S^z_T$ is fixed. To suppress
decoherence through quantum control, we employ a train of pi pulses and
demonstrate that unitary evolution of the system can be retained. We propose
realization of a weakly decohering charge qubit from an electron in an
oxide-based (tunnel-coupled) double quantum dot system.",1309.5824v3
2014-06-30,Recent results of gluon and sea quark polarization measurements in polarized proton-proton collisions at STAR,"The STAR experiment at RHIC is carrying out a comprehensive high-energy spin
physics program to understand the internal structure and dynamics of the proton
in polarized proton-proton collisions at $\sqrt{s} = 200$ GeV and $\sqrt{s} =
500/510$ GeV. STAR has the capability, with nearly full azimuthal coverage, to
reconstruct leptons, hadrons and jets in the mid-rapidity region ($|\eta|<1$).
The results for inclusive jet longitudinal double spin asymmetries taken during
the 2009 RHIC run indicate the first non-zero gluon contribution ($\Delta
g(x,Q^{2}) / g(x,Q^{2})$) to the proton spin for $0.05<x<1$ (Bjorken-x:
momentum fraction of partons). Recent longitudinal single-spin asymmetry
measurements of $W^{+/-}$ bosons at $\sqrt{s} = 500/510$ GeV in polarized
proton-proton collisions provide a direct probe of the polarized anti-u and
anti-d quark distributions ($\Delta \bar{u}(x,Q^{2})$, $\Delta
\bar{d}(x,Q^{2})$). These results better constrain the polarized gluon and sea
quark distributions of the proton in the RHIC sensitive kinematic region.
Future measurements with continuing high energy polarized proton-proton run at
RHIC and detector upgrade will explore the gluonic contribution to the proton
spin in extended range.",1406.7774v1
2015-12-15,Coupling spin to velocity: collective motion of Hamiltonian polar particles,"We propose a conservative two-dimensional particle model in which particles
carry a continuous and classical spin. The model includes standard
ferromagnetic interactions between spins of two different particles, and a
nonstandard coupling between spin and velocity of the same particle inspired by
the coupling observed in self-propelled hard discs. Because of this coupling
Galilean invariance is broken and the conserved linear momentum associated to
translation invariance is not proportional to the velocity of the center of
mass. Also, the dynamics is not invariant under a global rotation of the spins
alone. This, in principle, leaves room for collective motion and thus raises
the question whether collective motion can arise in Hamiltonian systems. We
study the statistical mechanics of such a system, and show that, in the fully
connected (or mean-field) case, a transition to collective motion does exist in
spite of momentum conservation. Interestingly, the velocity of the center of
mass, which in the absence of Galilean invariance, is a relevant variable, also
feeds back on the magnetization properties, as it acts as an external magnetic
field that smoothens the transition. Molecular dynamics simulations of finite
size systems indeed reveal a rich phase diagram, with a transition from a
disordered to a homogeneous polar phase, but also more complex inhomogeneous
phases with local order interrupted by topological defects.",1512.04884v2
2016-05-27,The Many-agent limit of the Extreme Introvert-Extrovert model,"We consider a toy model of interacting extrovert and introvert agents
introduced earlier by Liu et al [Europhys. Lett. {\bf 100} (2012) 66007]. The
number of extroverts, and introverts is $N$ each. At each time step, we select
an agent at random, and allow her to modify her state. If an extrovert is
selected, she adds a link at random to an unconnected introvert. If an
introvert is selected, she removes one of her links. The set of $N^2$ links
evolves in time, and may be considered as a set of Ising spins on an $N \times
N$ square-grid with single-spin-flip dynamics. This dynamics satisfies detailed
balance condition, and the probability of different spin configurations in the
steady state can be determined exactly. The effective hamiltonian has
long-range multi-spin couplings that depend on the row and column sums of
spins. If the relative bias of choosing an extrovert over an introvert is
varied, this system undergoes a phase transition from a state with very few
links to one in which most links are occupied. We show that the behavior of the
system can be determined exactly in the limit of large $N$. The behavior of
large fluctuations in the total numer of links near the phase transition is
determined. We also discuss two variations, called egalitarian and elitist
agents, when the agents preferentially add or delete links to their least/
most-connected neighbor. These shows interesting cooperative behavior.",1605.08517v2
2016-08-11,Minority spin dynamics in non-homogeneous Ising model: diverging timescales and exponents,"We investigate the dynamical behaviour of the Ising model under a zero
temperature quench with the initial fraction of up spins $0\leq x\leq 1$. In
one dimension, the known results for persistence probability are verified; it
shows algebraic decay for both up and down spins asymptotically with different
exponents. It is found that the conventional finite size scaling is valid here.
In two dimensions however, the persistence probabilities are no longer
algebraic; in particular for $x\leq 0.5$, persistence for the up (minority)
spins shows the behaviour $P_{min}(t) \sim t^{-\gamma}\exp(-(t/\tau)^{\delta})$
with time $t$, while for the down (majority) spins, $P_{maj}(t)$ approaches a
finite value. We find that the timescale $\tau$ diverges as $(x_c-x)^{-
\lambda}$, where $x_c=0.5$ and $\lambda\simeq2.31$. The exponent $\gamma$
varies as $\theta_{2d}+c_0(x_c-x)^{\beta}$ where $\theta_{2d}\simeq0.215$ is
very close to the persistence exponent in two dimensions; $\beta\simeq1$. The
results in two dimensions can be understood qualitatively by studying the exit
probability, which for different system size is found to have the form $E(x) =
f\big[(\frac{x-x_c}{x_c})L^{1/\nu}\big]$, with $\nu \approx 1.47$. This result
suggests that $\tau \sim L^{\tilde{z}}$, where $\tilde{z} = \frac{\lambda}{\nu}
= 1.57 \pm 0.11$ is an exponent not explored earlier.",1608.03399v3
2017-06-14,The sensitivity of a radical pair compass magnetoreceptor can be significantly amplified by radical scavengers,"Birds have a remarkable ability to obtain navigational information from the
Earth's magnetic field. The primary detection mechanism of this compass sense
is uncertain but appears to involve the quantum spin dynamics of radical pairs
formed transiently in cryptochrome proteins. We propose here a new version of
the current model in which spin-selective recombination of the radical pair is
not essential. One of the two radicals is imagined to react with a paramagnetic
scavenger via spin-selective electron transfer. By means of simulations of the
spin dynamics of cryptochrome-inspired radical pairs, we show that the new
scheme offers two clear and important benefits. The sensitivity to a 50 {\mu}T
magnetic field is greatly enhanced and, unlike the current model, the radicals
can be more than 2 nm apart in the magnetoreceptor protein. The latter means
that animal cryptochromes that have a tetrad (rather than a triad) of
tryptophan electron donors can still be expected to be viable as magnetic
compass sensors. Lifting the restriction on the rate of the spin-selective
recombination reaction also means that the detrimental effects of inter-radical
exchange and dipolar interactions can be minimised by placing the radicals much
further apart than in the current model.",1706.04564v3
2017-07-05,Numerically exploring the 1D-2D dimensional crossover on spin dynamics in the doped Hubbard model,"Using determinant quantum Monte Carlo (DQMC) simulations, we systematically
study the doping dependence of the crossover from one to two dimensions and its
impact on the magnetic properties of the Hubbard model. A square lattice of
chains is used, in which the dimensionality can be tuned by varying the
interchain coupling $t_\perp$. The dynamical spin structure factor and static
quantities, such as the static spin susceptibility and nearest-neighbor spin
correlation function, are characterized in the one- and two-dimensional limits
as a benchmark. When the dimensionality is tuned between these limits, the
magnetic properties, while evolving smoothly from one to two dimensions,
drastically change regardless of the doping level. This suggests that the spin
excitations in the two-dimensional Hubbard model, even in the heavily doped
case, cannot be explained using the spinon picture known from one dimension.
The DQMC calculations are complemented by cluster perturbation theory studies
to form a more complete picture of how the crossover occurs as a function of
doping and how doped holes impact magnetic order.",1707.01562v1
2017-10-03,"Long-range dynamical magnetic order and spin tunneling in the cooperative paramagnetic states of the pyrochlore analogous spinel antiferromagnets CdYb2X4 (X = S, Se)","Magnetic systems with spins sitting on a lattice of corner sharing regular
tetrahedra have been particularly prolific for the discovery of new magnetic
states for the last two decades. The pyrochlore compounds have offered the
playground for these studies, while little attention has been comparatively
devoted to other compounds where the rare earth R occupies the same
sub-lattice, e.g. the spinel chalcogenides CdR2X4 (X = S, Se). Here we report
measurements performed on powder samples of this series with R = Yb using
specific heat, magnetic susceptibility, neutron diffraction and
muon-spin-relaxation measurements. The two compounds are found to be
magnetically similar. They long-range order into structures described by the
\Gamma_5 irreducible representation. The magnitude of the magnetic moment at
low temperature is 0.77 (1) and 0.62 (1) mu_B for X = S and Se, respectively.
Persistent spin dynamics is present in the ordered states. The spontaneous
field at the muon site is anomalously small, suggesting magnetic moment
fragmentation. A double spin-flip tunneling relaxation mechanism is suggested
in the cooperative paramagnetic state up to 10 K. The magnetic space groups
into which magnetic moments of systems of corner-sharing regular tetrahedra
order are provided for a number of insulating compounds characterized by null
propagation wavevectors.",1710.01062v1
2017-10-06,Optimal control of universal quantum gates in a double quantum dot,"We theoretically investigate electron spin operations driven by applied
electric fields in a semiconductor double quantum dot (DQD). Our model
describes a DQD formed in semiconductor nanowire with longitudinal potential
modulated by local gating. The eigenstates for two electron occupation,
including spin-orbit interaction, are calculated and then used to construct a
model for the charge transport cycle in the DQD taking into account the spatial
dependence and spin mixing of states. The dynamics of the system is simulated
aiming at implementing protocols for qubit operations, that is, controlled
transitions between the singlet and triplet states. In order to obtain fast
spin manipulation, the dynamics is carried out taking advantage of the
anticrossings of energy levels introduced by the spin-orbit and interdot
couplings. The theory of optimal quantum control is invoked to find the
specific electric-field driving that performs qubit logical operations. We
demonstrate that it is possible to perform within high efficiency a universal
set of quantum gates $\{$CNOT, H$\otimes$I, I$\otimes$H, T$\otimes$I, and
T$\otimes$I$\}$, where H is the Hadamard gate, T is the $\pi/8$ gate, and I is
the identity, even in the presence of a fast charge transport cycle and charge
noise effects.",1710.02499v1
2018-01-29,Spin dynamics and exchange interactions in CuO measured by neutron scattering,"The magnetic properties of CuO encompass several contemporary themes in
condensed matter physics, including quantum magnetism, magnetic frustration,
magnetically-induced ferroelectricity and orbital currents. Here we report
polarized and unpolarized neutron inelastic scattering measurements which
provide a comprehensive map of the cooperative spin dynamics in the low
temperature antiferromagnetic (AFM) phase of CuO throughout much of the
Brillouin zone. At high energies ($E \gtrsim 100$\,meV) the spectrum displays
continuum features consistent with the des Cloizeax--Pearson dispersion for an
ideal $S=\frac{1}{2}$ Heisenberg AFM chain. At lower energies the spectrum
becomes more three-dimensional, and we find that a linear spin-wave model for a
Heisenberg AFM provides a very good description of the data, allowing for an
accurate determination of the relevant exchange constants in an effective spin
Hamiltonian for CuO. In the high temperature helicoidal phase, there are
features in the measured low-energy spectrum that we could not reproduce with a
spin-only model. We discuss how these might be associated with the
magnetically-induced multiferroic behavior observed in this phase.",1801.09473v2
2018-09-21,Tailored single-atom collisions at ultra-low energies,"We employ collisions of individual atomic cesium (Cs) impurities with an
ultracold rubidium (Rb) gas to probe atomic interaction with hyperfine- and
Zeeman-state sensitivity. Controlling the Rb bath's internal state yields
access to novel phenomena observed in inter-atomic spin-exchange. These can be
tailored at ultra-low energies, owing to the excellent experimental control
over all relevant energy scales. First, detecting spin-exchange dynamics in the
Cs hyperfine state manifold, we resolve a series of previously unreported
Feshbach resonances at magnetic fields below 300 mG, separated by energies as
low as $h\times 15$ kHz. The series originates from a coupling to molecular
states with binding energies below $h\times 1$ kHz and wave function extensions
in the micrometer range. Second, at magnetic fields below $\approx 100\,$mG, we
observe the emergence of a new reaction path for alkali atoms, where in a
single, direct collision between two atoms two quanta of angular momentum can
be transferred. This path originates from the hyperfine-analogue of dipolar
spin-spin relaxation. Our work yields control of subtle ultra-low-energy
features of atomic collision dynamics, opening new routes for advanced
state-to-state chemistry, for controlling spin-exchange in quantum many-body
systems for solid state simulations, or for determination of high-precision
molecular potentials.",1809.08165v2
2018-10-04,Chaos and relaxation oscillations in spin-torque windmill neurons,"Spintronic neurons which emit sharp voltage spikes are required for the
realization of hardware neural networks enabling fast data processing with
low-power consumption. In many neuroscience and computer science models,
neurons are abstracted as non-linear oscillators. Magnetic nano-oscillators
called spin-torque nano-oscillators are interesting candidates for imitating
neurons at nanoscale. These oscillators, however, emit sinusoidal waveforms
without spiking while biological neurons are relaxation oscillators that emit
sharp voltage spikes. Here we propose a simple way to imitate neuron spiking in
high-magnetoresistance nanoscale spin valves where both magnetic layers are
free and thin enough to be switched by spin torque. Our numerical-simulation
results show that the windmill motion induced by spin torque in the proposed
spintronic neurons gives rise to spikes whose shape and frequency, set by the
charging and discharging times, can be tuned through the amplitude of injected
dc current. We also found that these devices can exhibit chaotic oscillations.
Chaotic-like neuron dynamics has been observed in the brain, and it is
desirable in some neuromorphic computing applications whereas it should be
avoided in others. We demonstrate that the degree of chaos can be tuned in a
wide range by engineering the magnetic stack and anisotropies and by changing
the dc current. The proposed spintronic neuron is a promising building block
for hardware neuromorphic chips leveraging non-linear dynamics for computing.",1810.02073v1
2018-10-09,Scrambling dynamics and many-body chaos in a random dipolar spin model,"Is there a quantum many-body system that scrambles information as fast as a
black hole? The Sachev-Ye-Kitaev model can saturate the conjectured bound for
chaos, but it requires random all-to-all couplings of Majorana fermions that
are hard to realize in experiments. Here we examine a quantum spin model of
randomly oriented dipoles where the spin exchange is governed by dipole-dipole
interactions. The model is inspired by recent experiments on dipolar spin
systems of magnetic atoms, dipolar molecules, and nitrogen-vacancy centers. We
map out the phase diagram of this model by computing the energy level
statistics, spectral form factor, and out-of-time-order correlation (OTOC)
functions. We find a broad regime of many-body chaos where the energy levels
obey Wigner-Dyson statistics and the OTOC shows distinctive behaviors at
different times: Its early-time dynamics is characterized by an exponential
growth, while the approach to its saturated value at late times obeys a power
law. The temperature scaling of the Lyapunov exponent $\lambda_L$ shows that
while it is well below the conjectured bound $2\pi T$ at high temperatures,
$\lambda_L$ approaches the bound at low temperatures and for large number of
spins.",1810.03815v2
2018-10-11,Accretion in a dynamical spacetime and spinning up of the black hole in the gamma ray burst central engine,"We compute the evolution of a quasi-spherical, slowly rotating accretion flow
around a black hole, whose mass and spin evolve adequately to the mass-energy
transfer through the horizon. Our model is relevant for the central engine
driving a long gamma ray burst, that originates from the collapse of a massive
star. The computations of a GRB engine in a dynamically evolving spacetime
metric are important specifically due to the transient nature of the event, in
which a huge amount of mass is accreted and changes the fundamental black hole
parameters, its mass and spin, during the process. We discuss the results in
the context of angular momentum magnitude of the collapsing star. We also study
the possible formation and evolution of shocks in the envelope, which may
temporarily affect accretion. Our results are important for the limitations on
the mass and spin range of black holes detected independently by
electromagnetic observations of GRBs and gravitational waves. We speculate on
the possible constraints for the final masses and spins of these astrophysical
black holes. It is shown that the most massive BHs were rahter not formed in a
powerful GRB explosion, if the cores of their progenitors were only weakly
rotating.",1810.05261v1
2019-06-24,High-Harmonic generation from spin-polarised defects in solids,"Generation of high-order harmonics in gases enabled to probe the attosecond
electron dynamics in atoms and molecules with unprecedented resolution.
Extending the techniques developed originally for atomic and molecular gases to
solid state materials requires a fundamental understanding of the physics that
has been partially addressed theoretically. Here we employ time-dependent
density-functional theory to investigate how the electron dynamics resulting in
high-harmonic emission in monolayer hexagonal boron nitride is affected by the
presence of vacancies. We show how these realistic spin-polarised defects
modify the harmonic emission, and demonstrate that important differences exist
between harmonics from a pristine solid and a defected-solid. In particular, we
found that the different spin channels are affected differently because of the
presence of the spin-polarized point defect, and that localisation of the
wavefunction, the geometry of the defect and the electron-electron interaction
are all important ingredients to describe high-harmonic generation in
defected-solids. We show that different vacancies lead to qualitatively
different effects, thus opening the door to the high-harmonic imaging of
spin-polarised defects in solids.",1906.10224v3
2019-09-04,"Lattice dynamics, phonon chirality and spin-phonon coupling in 2D itinerant ferromagnet Fe3GeTe2","Fe3GeTe2 has emerged as one of the most fascinating van der Waals crystals
due to its two-dimensional (2D) itinerant ferromagnetism, topological nodal
lines and Kondo lattice behavior. However, lattice dynamics, chirality of
phonons and spin-phonon coupling in this material, which set the foundation for
these exotic phenomena, have remained unexplored. Here we report the first
experimental investigation of the phonons and mutual interactions between spin
and lattice degrees of freedom in few-layer Fe3GeTe2. Our results elucidate
three prominent Raman modes at room temperature: two A1g({\Gamma}) and one
E2g({\Gamma}) phonons. The doubly degenerate E2g({\Gamma}) mode reverses the
helicity of incident photon, indicating the pseudo-angular momentum and
chirality. Through analysis of temperature-dependent phonon energies and
lifetimes, which strongly diverge from the anharmonic model below Curie
temperature, we determine the spin-phonon coupling in Fe3GeTe2. Such
interaction between lattice oscillations and spin significantly enhances the
Raman susceptibility, allowing us to observe two additional Raman modes at the
cryogenic temperature range. In addition, we reveal laser radiation induced
degradation of Fe3GeTe2 in ambient conditions and the corresponding Raman
fingerprint. Our results provide the first experimental analysis of phonons in
this novel 2D itinerant ferromagnet and their applicability for further
fundamental studies and application development.",1909.01598v1
2020-01-24,Dynamics of Spiral Spin Waves in Magnetic Nano-patches: Influence of Thickness and Shape,"We explore the dynamics of spiral spin waves in Permalloy nano-elements with
variable aspect ratio of geometric dimensions, and their potential use as
improved spin wave emitters with no or little biasing field required. Numerical
results show that above a certain thickness, propagating spiral waves can be
obtained in circular and square shaped elements in a flux closure state.
VNA-FMR experiments on 20 nm (thin) and 80 nm (thick) samples confirm two type
of spectra corresponding to different dispersions for thinner and thicker
elements. We show that, for the thicker films, the vortex core region acts as a
source of large amplitude spiral spin waves, which dominate over other modes.
In case of the thinner elements, these modes are critically damped. For
different shapes of the patch, we show that a rich collection of confined
propagating modes can also be excited, modifying the final wave front and
enriching the potential of the nano-dot as a spin wave emitter. We give an
explanation for the intense spiral modes from the perspective of a balance of
dipolar and exchange energies in the sample.",2001.09053v1
2020-01-29,Theoretical and Computational Framework for the Analysis of the Relaxation Properties of Arbitrary Spin Systems. Application to High-Resolution Relaxometry,"A wide variety of nuclear magnetic resonance experiments rely on the
prediction and analysis of relaxation processes. Recently, innovative
approaches have been introduced where the sample travels through a broad range
of magnetic fields in the course of the experiment, such as dissolution dynamic
nuclear polarization or high-resolution relaxometry. Understanding the
relaxation properties of nuclear spin systems over orders of magnitude of
magnetic fields is essential to rationalize the results of these experiments.
For example, during a high-resolution relaxometry experiment, the absence of
control of nuclear spin relaxation pathways during the sample transfers and
relaxation delays leads to systematic deviations of polarization decays from an
ideal mono-exponential decay with the pure longitudinal relaxation rate. These
deviations have to be taken into account to describe quantitatively the
dynamics of the system. Here, we present computational tools to (1) calculate
analytical expressions of relaxation rates for a broad variety of spin systems
and (2) use these analytical expressions to correct the deviations arising in
high-resolution relaxometry experiments. These tools lead to a better
understanding of nuclear spin relaxation, which is required to improve the
sensitivity of many pulse sequences, and to better characterize motions in
macromolecules.",2001.10775v2
2018-07-06,Spin wave modes in a cylindrical nanowire in crossover dipolar-exchange regime,"Nanoscale magnetic systems have been studied extensively in various
geometries, such as wires of different cross-sections, arrays of wires, dots,
rings, etc. Such systems have interesting physical properties and promising
applications in advanced magnetic devices. Uniform magnetic nanowires are the
basic structures which were broadly investigated. However, some of their
dynamical properties, like: (anti)crossing between the spin wave modes and
impact of the magnetic field on spin wave spectrum, still need to be exploited.
We continue this research by investigation of the spin wave dynamics in solid
Ni nanowire of the circular cross-section. We use two approaches:
semi-analytical calculations and numerical computations based on finite element
method. We solve coupled Landau-Lifshitz and Maxwell equations and consider
both magnetostatic and exchange interactions. We identify the dispersion
brunches and its (anti)crossing by plotting the spatial profiles of spin wave
amplitudes and magnetostatic potential. We also check how we can tune the
spectrum of the modes by application of the external magnetic field and how it
affects the modes and their dominating type of interaction.",1807.02580v3
2018-08-31,Wide dynamic range magnetic field cycler: Harnessing quantum control at low and high fields,"We describe the construction of a fast field cycling device capable of
sweeping a 4-order-of-magnitude range of magnetic fields, from ~1mT to 7T, in
under 700ms. Central to this system is a high-speed sample shuttling mechanism
between a superconducting magnet and a magnetic shield, with the capability to
access arbitrary fields in between with high resolution. Our instrument serves
as a versatile platform to harness the inherent dichotomy of spin dynamics on
offer at low and high fields - in particular, the low anisotropy, fast spin
manipulation, and rapid entanglement growth at low field as well as the long
spin lifetimes, spin specific control, and efficient inductive measurement
possible at high fields. Exploiting these complementary capabilities in a
single device open up applications in a host of problems in quantum control,
sensing, and information storage, besides in nuclear hypepolarization,
relaxometry and imaging. In particular, in this paper, we focus on the ability
of the device to enable low-field hyperpolarization of 13C nuclei in diamond
via optically pumped electronic spins associated with Nitrogen Vacancy (NV)
defect centers.",1808.10579v1
2019-01-26,Thermodynamics of the pyrochlore-lattice quantum Heisenberg antiferromagnet,"We use the rotation-invariant Green's function method (RGM) and the
high-temperature expansion (HTE) to study the thermodynamic properties of the
Heisenberg antiferromagnet on the pyrochlore lattice. We discuss the excitation
spectra as well as various thermodynamic quantities, such as spin correlations,
uniform susceptibility, specific heat and static and dynamical structure
factors. For the ground state we present RGM data for arbitrary spin quantum
numbers $S$. At finite temperatures we focus on the extreme quantum cases
$S=1/2$ and $S=1$. We do not find indications for magnetic long-range order for
any value of $S$. We discuss the width of the pinch point in the static
structure factor in dependence on temperature and spin quantum number. We
compare our data with experimental results for the pyrochlore compound
NaCaNi$_2$F$_7$ ($S=1$). Thus, our results for the dynamical structure factor
agree well with the experimentally observed features at 3 \ldots 8~meV for
NaCaNi$_2$F$_7$. We analyze the static structure factor ${S}_{\bf q}$ to find
regions of maximal ${S}_{\bf q}$. The high-temperature series of the ${S}_{\bf
q}$ provide a fingerprint of weak {\it order by disorder} selection of a
collinear spin structure, where (classically) the total spin vanishes on each
tetrahedron and neighboring tetrahedra are dephased by $\pi$.",1901.09194v1
2019-03-07,Spin-orbit Torque and Spin Hall Effect-based Cellular Level Therapeutic Neuromodulators: Modulating Neuron Activities through Spintronic Nanodevices,"Artificial modulation of a neuronal subset through ion channels activation
can initiate firing patterns of an entire neural circuit in vivo. As nanovalves
in the cell membrane, voltage-gated ion channels can be artificially controlled
by the electric field gradient that caused by externally applied time varying
magnetic fields. Herein, we theoretically investigate the feasibility of
modulating neural activities by using magnetic spintronic nanostructures. An
antiferromagnet/ferromagnet (AFM/FM) structure is explored as neuromodulator.
For FM layer with perpendicular magnetization, stable bidirectional
magnetization switching can be achieved by applying in-plane currents through
AFM layer to induce the spin-orbit torque (SOT) due to the spin Hall effect
(SHE). This Spin-orbit Torque Neurostimulator (SOTNS) utilizes in-plane charge
current pulses to switch the magnetization in FM layer. The time changing
magnetic stray field induces electric field that modulates the surrounding
neurons. The Object Oriented Micromagnetic Framework (OOMMF) is used to
calculate space and time dependent magnetic dynamics of SOTNS structure. The
current driven magnetization dynamics in SOTNS has no mechanically moving
parts. Furthermore, the size of SOTNS can be down to tens of nanometers, thus,
arrays of SOTNSs could be fabricated, integrated together and patterned on a
flexible substrate, which gives us much more flexible control of the
neuromodulation with cellular resolution.",1903.02726v1
2019-03-27,"Charge-stripe order, antiferromagnetism, and spin dynamics in the cuprate-analog nickelate La$_4$Ni$_3$O$_8$","We report a muon spin rotation ($\mu$SR) study of the cuprate-analog
nickelate La$_4$Ni$_3$O$_8$, which undergoes a transition at 105 K to a
low-temperature phase with charge-stripe and antiferromagnetic (AFM) order on
square planar NiO$_2$ layers. Zero-field $\mu$SR shows that this transition is
abrupt and that the AFM configuration is commensurate. Comparison of observed
muon precession frequencies with Ni dipolar field calculations yields Ni
moments $\lesssim 0.5\mu_B$. Dynamic muon spin relaxation above 105 K suggests
critical slowing of Ni spin fluctuations, but is inconsistent with
corresponding $^{139}$La NMR results. Critical slowing and an abrupt transition
are also observed in the planar cuprate AFM La$_2$CuO$_{4+\delta}$, where they
are evidence for weakly interplanar-coupled two-dimensional AFM spin
fluctuations, but our $\mu$SR data do not agree quantitatively with theoretical
predictions for this scenario.",1903.11706v2
2019-08-25,Electric field manipulation enhanced by strong spin-orbit coupling: promoting rare-earth ions as qubits,"Quantum information processing based on magnetic ions are considered
potential candidates for applications because they can be modified and scaled
up by a variety of chemical methods. For these systems to achieve individual
spin addressability and high energy efficiency, we exploited the electric field
as a tool to manipulate their quantum behaviours, functioning via spin-orbit
coupling. A Ce:YAG single crystal was employed due to that rare-earth ions have
strong spin-orbit coupling and with considerations regarding the dynamics and
the symmetry requirements. The Stark effect of the Ce3+ ion was observed and
measured. When demonstrated as a quantum phase gate, the electric field
manipulation exhibited high efficiency which allowed up to 57 {\pi}/2
operations before decoherence with optimized field directions. It was also
utilized to carry out quantum bang-bang control, as a method of dynamic
decoupling, and the refined Deutsch-Jozsa algorithm. Our experiments
highlighted rare-earth ions as potentially applicable qubits since they offer
enhanced spin-electric coupling which enables high-efficiency quantum
manipulation.",1908.09274v2
2019-11-01,Precessional spin-torque dynamics in biaxial antiferromagnets,"The N\'eel order of an antiferromagnet subject to a spin torque can undergo
precession in a circular orbit about any chosen axis. To orient and stabilize
the motion against the effects of magnetic anisotropy, the spin polarization
should have components in-plane and normal to the plane of the orbit, where the
latter must exceed a threshold. For biaxial antiferromagnets, the precessional
motion is described by the equation for a damped-driven pendulum, which has
hysteresis a function of the spin current with a critical value where the
period diverges. The fundamental frequency of the motion varies inversely with
the damping, and as $(x^p-1)^{1/p}$ with the drive-to-criticality ratio $x$ and
the parameter $p>2$. An approximate closed-form result for the threshold spin
current is presented, which depends on the minimum cutoff frequency the orbit
can support. Precession about the hard axis has zero cutoff frequency and the
lowest threshold, while the easy axis has the highest cutoff. A device setup is
proposed for electrical control and detection of the dynamics, which is
promising to demonstrate a tunable terahertz nano-oscillator.",1911.00445v4
2019-11-26,Dynamic nuclear polarization and ESR hole burning in As doped silicon,"We present an experimental study of the Dynamic Nuclear Polarization (DNP) of
\si{} nuclei in silicon crystals of natural abundance doped with As in the
temperature range 0.1-1 K and in strong magnetic field of 4.6 T. This ensures
very high degree of electron spin polarization, extremely slow nuclear
relaxation and optimal conditions for realization of Overhauser and resolved
solid effects. We found that the solid effect DNP leads to an appearance of a
pattern of holes and peaks in the ESR line, separated by the super-hyperfine
interaction between the donor electron and \si{} nuclei closest to the donor.
On the contrary, the Overhauser effect DNP mainly affects the remote \si{}
nuclei having the weakest interaction with the donor electron. This leads to an
appearance of a very narrow ($\approx$ 3 mG wide) hole in the ESR line. We
studied relaxation of the holes after burning, which is caused by the nuclear
spin diffusion. Analyzing the spin diffusion data with a simple one-dimensional
spectral diffusion model leads to a value of the spectral diffusion coefficient
$D=8(3)\times 10^{-3}$ mG$^2$/s. Our data indicate that the spin diffusion is
not completely prevented even in the frozen core near the donors. The emergence
of the narrow hole after the Overhauser DNP may be explained by a partial
""softening"" of the frozen core caused by Rabi oscillations of the electron
spin.",1911.11654v2
2020-06-18,Spin-orbit alignment of the $β$ Pictoris planetary system,"A crucial diagnostic that can tell us about processes involved in the
formation and dynamical evolutionof planetary systems is the angle between the
rotation axis of a star and a planet's orbital angular momentum vector
(""spin-orbit"" alignment or ""obliquity""). Here we present the first spin-orbit
alignment measurement for a wide-separation exoplanetary system, namely on the
directly-imaged planet $\beta$ Pictoris b. We use VLTI/GRAVITY
spectro-interferometry with an astrometric accuracy of 1 $\mu$as
(microarcsecond) in the Br$\gamma$ photospheric absorption line to measure the
photocenter displacement associated with the stellar rotation. Taking
inclination constraints from astroseismology into account, we constrain the
3-dimensional orientation of the stellar spin axis and find that $\beta$ Pic b
orbits its host star on a prograde orbit. The angular momentum vectors of the
stellar photosphere, the planet, and the outer debris disk are well-aligned
with mutual inclinations $<3\pm5^{\circ}$, which indicates that $\beta$ Pic b
formed in a system without significant primordial misalignments. Our results
demonstrate the potential of infrared interferometry to measure the spin-orbit
alignment for wide-separation planetary systems, probing a highly complementary
regime to the parameter space accessible with the Rossiter-McLaughlin effect.
If the low obliquity is confirmed by measurements on a larger sample of
wide-separation planets, it would lend support to theories that explain the
obliquity in Hot Jupiter systems with dynamical scattering and the Kozai-Lidov
mechanism.",2006.10784v1
2020-09-07,Spin pumping in d-wave superconductor/ferromagnet hybrids,"Spin-pumping across ferromagnet/superconductor (F/S) interfaces has attracted
much attention lately. Yet the focus has been mainly on s-wave
superconductors-based systems whereas (high-temperature) d-wave superconductors
such as YBa2Cu3O7-d (YBCO) have received scarce attention despite their
fundamental and technological interest. Here we use wideband ferromagnetic
resonance to study spin-pumping effects in bilayers that combine a soft
metallic Ni80Fe20 (Py) ferromagnet and YBCO. We evaluate the spin conductance
in YBCO by analyzing the magnetization dynamics in Py. We find that the Gilbert
damping exhibits a drastic drop as the heterostructures are cooled across the
normal-superconducting transition and then, depending on the S/F interface
morphology, either stays constant or shows a strong upturn. This unique
behavior is explained considering quasiparticle density of states at the YBCO
surface, and is a direct consequence of zero-gap nodes for particular
directions in the momentum space. Besides showing the fingerprint of d-wave
superconductivity in spin-pumping, our results demonstrate the potential of
high-temperature superconductors for fine tuning of the magnetization dynamics
in ferromagnets using k-space degrees of freedom of d-wave/F interfaces.",2009.03196v3
2020-10-10,Coherent Helicity-Dependent Spin-Phonon Oscillations in the Ferromagnetic van der Waals Crystal CrI3,"The discovery of two-dimensional (2D) systems hosting intrinsic long-range
magnetic order represents a seminal addition to the rich physical landscape of
van der Waals (vdW) materials. CrI3 has emerged as perhaps the most salient
example, as the interdependence of crystalline structure and magnetic order,
along with strong light-matter interactions provides a promising platform to
explore the optical control of magnetic, vibrational, and charge degrees of
freedom at the 2D limit. However, the fundamental question of how this
relationship between structure and magnetism manifests on their intrinsic
timescales has rarely been explored. Here, we use ultrafast optical
spectroscopy to probe magnetic and vibrational dynamics in CrI3, revealing
demagnetization dynamics governed by spin-flip scattering and remarkably, a
strong transient exchange-mediated interaction between lattice vibrations and
spin oscillations. The latter yields a coherent spin-coupled phonon mode that
is highly sensitive to the helicity of the driving pulse in the magnetically
ordered phase. Our results shed light on the nature of spin-lattice coupling in
vdW magnets on ultrafast timescales and highlight their potential for
applications requiring non-thermal, high-speed control of magnetism at the
nanoscale.",2010.04915v1
2020-10-17,Tuning spin excitations in magnetic films by confinement,"Spin excitations of magnetic thin films are the founding element for novel
transport concepts in spintronics, magnonics, and magnetic devices in general.
While spin dynamics have been extensively studied in bulk materials, their
behaviour in mesoscopic films is less known due to experimental limitations.
Here, we employ Resonant Inelastic X-Ray Scattering to investigate the spin
excitation spectrum in mesoscopic Fe films, from bulk-like down to 3 unit cells
thick. In bulk-like samples, we find isotropic, dispersive ferromagnons
consistent with the dispersion observed by neutron scattering in bulk single
crystals. As the thickness is reduced, these ferromagnons survive and evolve
anisotropically: renormalising to lower energies along the out-of-plane
direction while retaining their dispersion in the in-plane direction. This
thickness dependence is captured by simple Heisenberg model calculations
accounting for the confinement in the out-of-plane direction through the loss
of Fe bonds. Our findings highlight the effects of mesoscopic scaling on spin
dynamics and identify thickness as a knob for fine-tuning and controlling
magnetic properties in films.",2010.08745v1
2021-02-12,"Minidisk dynamics in accreting, spinning black hole binaries: Simulations in full general relativity","We perform magnetohydrodynamic simulations of accreting, equal-mass binary
black holes in full general relativity focusing on the impact of black hole
spin on the dynamical formation and evolution of minidisks. We find that during
the late inspiral the sizes of minidisks are primarily determined by the
interplay between the tidal field and the effective innermost stable orbit
around each black hole. Our calculations support that a minidisk forms when the
Hill sphere around each black hole is significantly larger than the black
hole's effective innermost stable orbit. As the binary inspirals, the radius of
the Hill sphere decreases, and minidisk sconsequently shrink in size. As a
result, electromagnetic signatures associated with minidisks may be expected to
gradually disappear prior to merger when there are no more stable orbits within
the Hill sphere. In particular, a gradual disappearance of a hard
electromagnetic component in the spectrum of such systems could provide a
characteristic signature of merging black hole binaries. For a binary of given
total mass, the timescale to minidisk ""evaporation"" should therefore depend on
the black hole spins and the mass ratio. We also demonstrate that accreting
binary black holes with spin have a higher efficiency for converting accretion
power to jet luminosity. These results could provide new ways to estimate black
hole spins in the future.",2102.06712v3
2021-02-16,Spin excitations coupled with lattice and charge dynamics in La$_{2-x}$Sr$_{x}$CuO$_4$,"Spin excitations of layered copper oxide show various characteristic
features, depending on the carrier concentration. In this study, we conducted
inelastic neutron scattering (INS) measurements on La$_{2-x}$Sr$_{x}$CuO$_4$
(LSCO), with $x$ = 0, 0.075, 0.18, and 0.30 and La$_{2-x}$Sr$_{x}$NiO$_4$
(LSNO) with 1/3, to clarify the origin of the intensity enhancement in the
excitation spectrum of LSCO at the energy ($\omega$) of 16--19 meV [Phys. Rev.
B {\bf 91}, 224404 (2015), {\it ibid}. {\bf 93}, 094416 (2016)]. We confirmed
the presence of a peak-structure in the $\omega$-dependence of the local spin
susceptibility $\chi''(\omega)$ of superconducting (SC) LSCO with a peak energy
of 16--19 meV, where the spin excitations intersect optical phonon branches. A
comparable peak-structure is not observed in the insulating La$_2$CuO$_4$,
LSNO, and heavily overdoped LSCO with $x$ = 0.30. A dome-shaped $x$-dependence
of the integrated intensity around the peak energies is revealed for SC phase
by summarizing the present and previously reported results. Furthermore, our
phonon calculation on LCO shows the existence of two optical branches at
$\sim$19 meV that could stabilize stripe-alignment of carriers due to
out-of-plane vibrations of Cu or O of the CuO$_2$ planes. These results
indicate the interplay among spin, charge, and lattice dynamics and suggest
that the intensity enhancement is associated with their composite excitations.",2102.07971v1
2021-04-13,Asymptotic optimality of twist-untwist protocols for Heisenberg scaling in atomic interferometry,"Twist-untwist protocols for quantum metrology consist of a serial application
of: 1. unitary nonlinear dynamics (e.g., spin squeezing or Kerr nonlinearity),
2. parameterized dynamics $U(\phi)$ (e.g., a collective rotation or phase space
displacement), 3. time reversed application of step 1. Such protocols are known
to produce states that allow Heisenberg scaling for experimentally accessible
estimators of $\phi$ even when the nonlinearities are applied for times much
shorter than required to produce Schr\""{o}dinger cat states. In this work, we
prove that twist-untwist protocols provide the lowest estimation error among
quantum metrology protocols that utilize two calls to a weakly nonlinear
evolution and a readout involving only measurement of a spin operator
$\vec{n}\cdot \vec{J}$, asymptotically in the number of particles. We consider
the following physical settings: all-to-all interactions generated by one-axis
twisting $J_{z}^{2}$ (e.g., interacting Bose gases), constant finite range
spin-spin interactions of distinguishable or bosonic atoms (e.g., trapped ions
or Rydberg atoms, or lattice bosons). In these settings, we further show that
the optimal twist-untwist protocols asymptotically achieve $85\%$ and $92\%$ of
the respective quantum Cram\'{e}r-Rao bounds. We show that the error of a
twist-untwist protocol can be decreased by a factor of $L$ without an increase
in the noise of the spin measurement if the twist-untwist protocol can be
noiselessly iterated as an $L$ layer quantum alternating operator ansatz.",2104.06532v2
2021-04-14,Finite-element dynamic-matrix approach for spin-wave dispersions in magnonic waveguides with arbitrary cross section,"We present a numerical approach to efficiently calculate spin-wave
dispersions and spatial mode profiles in magnetic waveguides of arbitrarily
shaped cross section with any non-collinear equilibrium magnetization which is
translationally invariant along the waveguide. Our method is based on the
propagating-wave dynamic-matrix approach by Henry et al. and extends it to
arbitrary cross sections using a finite-element method. We solve the linearized
equation of motion of the magnetization only in a single waveguide cross
section which drastically reduces computational effort compared to common
three-dimensional micromagnetic simulations. In order to numerically obtain the
dipolar potential of individual spin-wave modes, we present a plane-wave
version of the hybrid finite-element/boundary-element method by Frekdin and
Koehler which, for the first time, we extend to a modified version of the
Poisson equation. Our method is applied to several important examples of
magnonic waveguides including systems with surface curvature, such as magnetic
nanotubes, where the curvature leads to an asymmetric spin-wave dispersion. In
all cases, the validity of our approach is confirmed by other methods. Our
method is of particular interest for the study of curvature-induced or
magnetochiral effects on spin-wave transport but also serves as an efficient
tool to investigate standard magnonic problems.",2104.06943v1
2021-06-10,Probing the rotational spin-Hall effect in higher order Gaussian beams,"Spin-to-orbit conversion of light is a dynamical optical phenomenon in
non-paraxial fields leading to various manifestations of the spin and orbital
Hall effect. However, effects of spin-orbit interaction (SOI) have not been
explored extensively for higher order Gaussian beams carrying no intrinsic
orbital angular momentum. Indeed, the SOI effects on such structured beams can
be directly visualized due to azimuthal rotation of their transverse intensity
profiles - a phenomenon we call the rotational Hall effect. In this paper, we
show that for an input circularly polarized (right/left) $HG_{10}$ mode, SOI
leads to a significant azimuthal rotation of the transverse intensity
distribution of both the orthogonal circularly polarized (left/right)
component, and the transverse component of the longitudinal field intensity
with respect to the input intensity profile. We validate our theoretical and
numerically simulated results experimentally by tightly focusing a circularly
polarized $HG_{10}$ beam in an optical tweezers configuration, and projecting
out the opposite circular polarization component and the transverse component
of the longitudinal field intensity at the output of the tweezers. We also
measure the rotational shift as a function of the refractive index contrast in
the path of the tightly focused light, and in general observe a proportional
increase. The enhanced spin-orbit conversion in these cases may lead to
interesting applications in inducing complex dynamics in optically trapped
birefringent particles using higher order Gaussian beams with no intrinsic
orbital angular momentum.",2106.05880v1
2021-08-03,Magneto Optical Sensing beyond the Shot Noise Limit,"Magneto-optical sensors including spin noise spectroscopies and
magneto-optical Kerr effect microscopies are now ubiquitous tools for materials
characterization that can provide new understanding of spin dynamics, hyperfine
interactions, spin-orbit interactions, and charge-carrier g-factors. Both
interferometric and intensity-difference measurements can provide photon
shot-noise limited sensitivity, but further improvements in sensitivity with
classical resources require either increased laser power that can induce
unwanted heating and electronic perturbations or increased measurement times
that can obscure out-of-equilibrium dynamics and radically slow experimental
throughput. Proof-of-principle measurements have already demonstrated quantum
enhanced spin noise measurements with a squeezed readout field that are likely
to be critical to the non-perturbative characterization of spin excitations in
quantum materials that emerge at low temperatures. Here, we propose a truncated
nonlinear interferometric readout for low-temperature magneto-optical Kerr
effect measurements that is accessible with today's quantum optical resources.
We show that 10 $\text{nrad}/\sqrt{\text{Hz}}$ sensitivity is achievable with
optical power as small as 1 $\mu$W such that a realistic $T$ = 83 mK can be
maintained in commercially available dilution refrigerators. The quantum
advantage for the proposed measurements persists even in the limit of large
loss and small squeezing parameters.",2108.01242v1
2021-09-10,Thermally-induced magnetic order from glassiness in elemental neodymium,"Temperature in thermodynamics is synonymous with disorder, and responsible
for ultimately destroying ordered phases. Here, we show an unusual magnetic
transition where, with increasing the temperature of elemental neodymium,
long-range multi-Q magnetic order emerges from a self-induced spin glass. Using
temperature-dependent spin-polarized scanning tunneling microscopy, we
characterize the local Q order in the spin-Q glass phase and quantify the
emergence of long-range multi-Q order with increasing temperature. We develop
two distinct analysis tools, which enable the quantification of the glass
transition temperature, based on measured spatially-dependent magnetization. We
compare these observations with atomic spin dynamics simulations, which
reproduce the qualitative observation of a phase transition from a
low-temperature spin glass phase to an intermediate ordered multi-Q phase.
These simulations trace the origin of the unexpected high temperature order in
weakened frustration driven by temperature-dependent sublattice correlations.
These findings constitute an example of order from disorder and provide a rich
platform to study magnetization dynamics in a self-induced spin glass.",2109.04815v1
2021-09-22,Intermediate spin state and the B1-B2 transition in ferropericlase at tera-Pascal pressures,"Ferropericlase (fp), (Mg$_{1-x}$Fe$_x$)O, the second most abundant mineral in
the Earth's lower mantle, is expected to be an essential component of
super-Earths' mantles. Here we present an ab initio investigation of the
structure and magnetic ground state of fp up to $\sim$ 3 TPa with iron
concentrations (x$_{Fe}$) varying from 0.03 to 0.12. Calculations were
performed using LDA+U$_{sc}$ and PBE exchange-correlation functionals to
elucidate the pressure range for which the Hubbard U (U$_{sc}$) is required.
Similar to the end-members FeO and MgO, fp also undergoes a B1 to B2 phase
transition that should be essential for modeling the structure and dynamics of
super-Earths' mantles. This structural transition involves a simultaneous
change in magnetic state from a low spin (LS) B1 phase with iron total spin S=0
to an intermediate spin (IS) B2 phase with S=1. This is a rare form of
pressure/strain-induced magnetism produced by local cation coordination
changes. Phonon calculations confirm the dynamical stability of the iron B2-IS
state. Free energy calculations are then carried out including vibrational
effects and electronic and magnetic entropy contributions. The phase diagram is
then obtained for low concentration fp using a quasi-ideal solid solution
model. For x$_{Fe}$ > 0.12 this approach is no longer valid. At ultra-high
pressures, there is an IS to LS spin state change in Fe in the B2 phase, but
the transition pressure depends sensitively on thermal electronic excitations
and on x$_{Fe}$.",2109.11008v2
2021-12-03,Global Natural Orbital Functional: Towards the Complete Description of the Electron Correlation,"The current work presents a natural orbital functional (NOF) for electronic
systems with any spin value independent of the external potential being
considered, that is, a global NOF (GNOF). It is based on a new two-index
reconstruction of the two-particle reduced density matrix for spin multiplets.
The emergent functional describes the complete intrapair electron correlation,
and the correlation between orbitals that make up both the pairs and the
individual electrons. The interorbital correlation is composed of static and
dynamic terms. The concept of dynamic part of the occupation numbers is
introduced. To evaluate the accuracy achieved with GNOF, calculation of a
variety of properties is presented. They include the total energies and energy
differences between the ground state and the lowest-lying excited state with
different spin of atoms from H to Ne, ionization potentials of the first-row
transition-metal atoms (Sc-Zn), and the total energies of a selected set of 55
molecular systems in different spin states. GNOF is also applied to the
homolytic dissociation of selected diatomic molecules in different spin states
and to the rotation barrier of ethylene, both paradigmatic cases of systems
with significant multi-configurational character. The values obtained agree
with those reported at high level of theory and experimental data.",2112.02119v1
2021-12-25,Lattice and magnetic dynamics in YVO$_{3}$ Mott insulator studied by neutron scattering and first-principles calculations,"The Mott insulator YVO$_{3}$ with $T_{N}$ = 118 K is revisited to explore the
role of spin, lattice and orbital correlations across the multiple structural
and magnetic transitions observed as a function of temperature. Upon cooling,
the crystal structure changes from orthorhombic to monoclinic at 200 K, and
back to orthorhombic at 77 K, followed by magnetic transitions. From the
paramagnetic high temperature phase, C-type ordering is first observed at 118
K, followed by a G-type spin re-orientation transition at 77 K. The dynamics of
the transitions were investigated via inelastic neutron scattering and first
principles calculations. An overall good agreement between the neutron data and
calculated spectra was observed. From the magnon density of states, the
magnetic exchange constants were deduced to be $J_{ab}$ = $J_{c}$ = -5.8 meV in
the G-type spin phase, and $J_{ab}$ = -3.8 meV, $J_{c}$ = 7.6 meV at 80 K and
$J_{ab}$ = -3.0 meV, $J_{c}$ = 6.0 meV at 100 K in the C-type spin phase.
Paramagnetic scattering was observed in the spin ordered phases, well below the
C-type transition temperature, that continuously increased above the
transition. Fluctuations in the temperature dependence of the phonon density of
states were observed between 50 and 80 K as well, coinciding with the G-type to
C-type transition. These fluctuations are attributed to optical oxygen modes
above 40 meV, from first principles calculations. In contrast, little change in
the phonon spectra is observed across $T_{N}$.",2112.13172v1
2021-12-29,Quantum kinetic theory for spin transport of quarks with background chromo-electromagnetic fields,"We derive the quantum kinetic equations for massive and massless quarks
coupled with the background chromo-electromagnetic fields from the
Wigner-function approach with the $\hbar$ expansion and effective
power-counting scheme. For each case, one obtains coupled color-singlet and
color-octet kinetic equations, which also involve the scalar and axial-vector
components for the charge and spin transport. These kinetic equations delineate
entangled evolution of the corresponding distribution functions decomposed in
color space. At weak coupling, we derive the close form of the color-singlet
kinetic equations for spin transport, which incorporates the diffusion term and
the source term that triggers dynamical spin polarization led by correlation
functions of color fields. Also, the non-dynamical source term is found in the
axial Wigner function. The induced spin polarization and axial charge currents
by these source terms are discussed under physical assumptions for color-field
correlators in near-equilibrium quark gluon plasmas. In the constant-field
limit, we further obtain non-vanishing axial Ward identities, from which we
extract the pseudo-scalar condensate for massive quarks at finite temperature.",2112.14392v2
2022-03-04,Reservoir Computing with Spin Waves in Skyrmion Crystal,"Magnetic skyrmions are nanometric spin textures characterized by a quantized
topological invariant in magnets and often emerge in a crystallized form called
skyrmion crystal in an external magnetic field. We propose that magnets hosting
a skyrmion crystal possess high potential for application to reservoir
computing, which is one of the most successful information processing
techniques inspired by functions of human brains. Our skyrmion-based reservoir
exploits precession dynamics of magnetizations, i.e., spin waves, propagating
in the skyrmion crystal. Because of complex interferences and slow relaxations
of the spin-wave dynamics, the skyrmion spin-wave reservoir attains several
important characteristics required for reservoir computing, e.g., the
generalization ability, the nonlinearity, and the short-term memory. We
investigate these properties by imposing three standard tasks to test the
performances of reservoir, i.e., the duration-estimation task, the short-term
memory task, and the parity-check task. Through these investigations, we
demonstrate that magnetic skyrmion crystals are promising materials for
spintronics reservoir devices. Because magnetic skyrmions emerge spontaneously
in magnets via self-organization process under application of a static magnetic
field, the proposed skyrmion reservoir requires neither advanced
nanofabrication nor complicated manufacturing for production in contrast to
other previously proposed magnetic reservoirs constructed with fabricated
spintronics devices. Our proposal is expected to realize a breakthrough in the
research of spintronics reservoirs of high performance.",2203.02160v1
2022-07-24,Wigner-molecularization-enabled dynamic nuclear field programming,"Multielectron semiconductor quantum dots (QDs) provide a novel platform to
study the role of Coulomb correlations in finite quantum systems and their
impact on many-body energy spectra. An example is the formation of
interaction-driven, spatially localized electron states of Wigner molecules
(WMs). Although Wigner molecularization has been confirmed by real-space
imaging and coherent spectroscopy, the open system dynamics of the
strongly-correlated states with the environment are not yet well understood.
Here, we demonstrate efficient control of spin transfer between an artificial
three-electron WM and the nuclear environment in a GaAs double QD. A
Landau-Zener sweep-based polarization sequence and low-lying anti-crossings of
spin multiplet states enabled by Wigner molecularization are utilized. An
efficient polarization rate of 2.58 $h \cdotp kHz \cdotp (g^* \cdotp
\mu_B)^{-1}$ per electron spin flip and, consequently, programmable nuclear
polarization by controlled single-electron tunneling are achieved. Combined
with coherent control of spin states, we achieve control of magnitude,
polarity, and site dependence of the nuclear field. It is demonstrated that the
same level of control cannot be achieved in the non-interacting regime. Thus,
we confirm the multiplet spin structure of a WM, paving the way for active
control of newly emerging correlated electron states for application in
mesoscopic environment engineering.",2207.11655v1
2022-07-28,Emergent pair localization in a many-body quantum spin system,"Understanding how closed quantum systems dynamically approach thermal
equilibrium presents a major unresolved problem in statistical physics.
Generically, non-integrable quantum systems are expected to thermalize as they
comply with the Eigenstate Thermalization Hypothesis. However, in the presence
of strong disorder, the dynamics can possibly slow down to a degree that
systems fail to thermalize on experimentally accessible timescales, as in spin
glasses or many-body localized systems. In general, particularly in long-range
interacting quantum systems, the specific nature of the disorder necessary for
the emergence of a prethermal, metastable state--distinctly separating the
timescales of initial relaxation and subsequent slow thermalization--remains an
open question. We study an ensemble of Heisenberg spins with a tunable
distribution of random coupling strengths realized by a Rydberg quantum
simulator. We observe a drastic change in the late-time magnetization when
increasing disorder strength. The data is well described by models based on
pairs of strongly interacting spins, which are treated as thermal for weak
disorder and isolated for strong disorder. Our results indicate a crossover
into a pair-localized prethermal regime in a closed quantum system of thousands
of spins in the critical case where the exponent of the power law interaction
matches the spatial dimension.",2207.14216v2
2022-09-12,Holes and magnetic polarons in a triangular lattice antiferromagnet,"The intricate interplay between charge motion and magnetic order in
geometrically frustrated lattices is central for the properties of many
two-dimensional quantum materials. The triangular lattice antiferromagnet is a
canonical example of a frustrated system, and here we analyse the dynamics of a
hole in such a lattice focusing on observables that have become accessible in a
new generation of experiments. Using the $t$-$J$ model, we solve the problem
exactly within linear spin wave theory in the limit of strong magnetic
interactions, showing that the ground state is described by a coherent state of
spin waves. The derivation highlights the crucial role played by the
interaction between a static hole and the neighboring spins, which originates
in the geometric frustration and has often been omitted in earlier works.
Furthermore, we show that the non-equilibrium dynamics after a hole has
abruptly been inserted at a lattice site is given exactly by a coherent state
with time-dependent oscillatory coefficients. Physically, this describes a
burst of magnetic frustration propagating through only two-thirds of the
lattice sites, since a destructive interference of spin waves leaves spins
parallel to that removed by the hole unperturbed. After the wave has propagated
through the lattice, the magnetization relaxes to that of the ground state. We
then use our analytical solution to benchmark the widely used self-consistent
Born approximation (SCBA), showing that it is very accurate also for a
triangular lattice. The magnetic polaron spectrum is analysed for general
magnetic interactions using the SCBA, and we compare our results with those for
a square lattice.",2209.05131v1
2022-09-21,Performance enhancement of a spin-wave-based reservoir computing system utilizing different physical conditions,"The authors have numerically studied how to enhance reservoir computing
performance by thoroughly extracting their spin-wave device potential for
higher-dimensional information generation. The reservoir device has a 1-input
exciter and 120-output detectors on the top of a continuous magnetic garnet
film for spin-wave transmission. For various nonlinear and fading-memory
dynamic phenomena distributing in the film space, small in-plane magnetic
fields were used to prepare stripe domain structures and various damping
constants at the film sides and bottom were explored. The ferromagnetic
resonant frequency and relaxation time of spin precession clearly characterized
the change in spin dynamics with the magnetic field and damping constant. The
common input signal for reservoir computing was a 1 GHz cosine wave with random
6-valued amplitude modulation. A basic 120-dimensional reservoir output vector
was obtained from time-series signals at the 120 output detectors under each of
the three magnetic field conditions. Then, 240- and 360-dimensional reservoir
output vectors were also constructed by concatenating two and three basic ones,
respectively. In nonlinear autoregressive moving average (NARMA) prediction
tasks, the computational performance was enhanced as the dimension of the
reservoir output vector becomes higher and a significantly low prediction error
was achieved for the 10th-order NARMA using the 360-dimensional vector and
optimum damping constant. The results are clear evidence that the collection of
diverse output signals efficiently increases the dimensionality effective for
reservoir computing, i.e., reservoir-state richness. This paper demonstrates
that performance enhancement through various configuration settings is a
practical approach for on-chip reservoir computing devices with small numbers
of real output nodes.",2209.10123v1
2022-10-31,"The Bardeen-Petterson effect, disk breaking, and the spin orientations of supermassive black-hole binaries","Supermassive black-hole binaries are driven to merger by dynamical friction,
loss-cone scattering of individual stars, disk migration, and
gravitational-wave emission. Two main formation scenarios are expected.
Binaries that form in gas-poor galactic environments do not experience disk
migration and likely enter the gravitational-wave dominated phase with roughly
isotropic spin orientations. Comparatively, binaries that evolve in gas-rich
galactic environments might experience prominent phases of disk accretion,
where the Bardeen-Petterson effect acts to align the spins of the black holes
with the orbital angular momentum of the disk. However, if the accretion disk
breaks alignment is expected to be strongly suppressed -- a phenomenon that was
recently shown to occur in a large portion of the parameter space. In this
paper, we develop a semi-analytic model of joint gas-driven migration and spin
alignment of supermassive black-hole binaries taking into account the impact of
disk breaking for the first time. Our model predicts the occurrence of distinct
subpopulations of binaries depending on the efficiency of spin alignment. This
implies that future gravitational-wave observations of merging black holes
could potentially be used to (i) discriminate between gas-rich and gas-poor
hosts and (ii) constrain the dynamics of warped accretion disks.",2211.00044v2
2023-03-08,"Photocurrents, inverse Faraday effect and photospin Hall effect in Mn$_2$Au","Among antiferromagnetic materials, Mn$_2$Au is one of the most intensively
studied, and it serves as a very popular platform for testing various ideas
related to antiferromagnetic magnetotransport and dynamics. Since recently,
this material has also attracted considerable interest in the context of
optical properties and optically-driven antiferromagnetic switching. In this
work, we use first principles methods to explore the physics of charge
photocurrents, spin photocurrents and inverse Faraday effect in
antiferromagnetic Mn$_2$Au. We predict the symmetry and magnitude of these
effects, and speculate that they can be used for tracking the dynamics of
staggered moments during switching. Our calculations reveal the emergence of
large photocurrents of spin in collinear Mn$_2$Au, whose properties can be
understood as a result of a non-linear optical version of spin Hall effect $-$
which we refer to as the $\textit{photospin Hall effect}$ encoded into the
relation between the driving charge and resulting spin photocurrents. Moreover,
we suggest that even a very small canting in Mn$_2$Au can give rise to colossal
spin photocurrents which are $\textit{chiral}$ in flavor. We conclude that the
combination of staggered magnetization with the structural and electronic
properties of this material results in a unique blend of prominent
photocurrents, which makes Mn$_2$Au a unique platform for advanced
optospintronics applications.",2303.04578v1
2023-03-24,Dynamics of rapidly spinning blob-filaments: fluid theory with a parallel kinetic extension,"Blob-filaments (or simply 'blobs') are coherent structures formed by
turbulence and sustained by nonlinear processes in the edge and scrape-off
layer (SOL) of tokamaks and other magnetically confined plasmas. The dynamics
of these blob-filaments, in particular their radial motion, can influence the
scrape-off layer width and plasma interactions with both the divertor target
and with the main chamber walls. Motivated by recent results from the XGC1
gyrokinetic simulation code reported on elsewhere [J. Cheng et al. submitted to
Nucl. Fusion and available at arXiv:2302.02877v1], a theory of rapidly spinning
blob-filaments has been developed. The theory treats blob filaments in the
closed flux surface region or the region that is disconnected from sheaths in
the SOL. It extends previous work by treating blob spin, arising from partially
or fully adiabatic electrons, as the leading order effect and retaining
inertial (ion charge polarization) physics in next order. Spin helps to
maintain blob coherency and affects the blob's propagation speed. Dipole charge
polarization, treated perturbatively, gives rise to blob-filaments with
relatively slow radial velocity, comparable to that observed in the
simulations. The theory also treats the interaction of rapidly spinning blob
filaments with a zonal flow layer. It is shown analytically that the flow layer
can act like a transport barrier for these structures. Finally parallel
electron kinetic effects are incorporated into the theory. Various asymptotic
parameter regimes are discussed and asymptotic expressions for the radial and
poloidal motion of the blob-filaments are obtained.",2303.14273v2
2023-04-05,Modeling temperature-dependent population dynamics in the excited state of the nitrogen-vacancy center in diamond,"The nitrogen-vacancy (NV) center in diamond is well known in quantum
metrology and quantum information for its favorable spin and optical
properties, which span a wide temperature range from near zero to over 600 K.
Despite its prominence, the NV center's photo-physics is incompletely
understood, especially at intermediate temperatures between 10-100 K where
phonons become activated. In this work, we present a rate model able to
describe the cross-over from the low-temperature to the high-temperature
regime. Key to the model is a phonon-driven hopping between the two orbital
branches in the excited state (ES), which accelerates spin relaxation via an
interplay with the ES spin precession. We extend our model to include magnetic
and electric fields as well as crystal strain, allowing us to simulate the
population dynamics over a wide range of experimental conditions. Our model
recovers existing descriptions for the low- and high-temperature limits, and
successfully explains various sets of literature data. Further, the model
allows us to predict experimental observables, in particular the
photoluminescence (PL) emission rate, spin contrast, and spin initialization
fidelity relevant for quantum applications. Lastly, our model allows probing
the electron-phonon interaction of the NV center and reveals a gap between the
current understanding and recent experimental findings.",2304.02521v2
2023-04-10,Efficient multi-timescale dynamics of precessing black-hole binaries,"We present analytical and numerical progress on black-hole binary spin
precession at second post-Newtonian order using multi-timescale methods. In
addition to the commonly used effective spin which acts as a constant of
motion, we exploit the weighted spin difference and show that such
reparametrization cures the coordinate singularity that affected the previous
formulation for the case of equal-mass binaries. The dynamics on the precession
timescale is written down in closed form in both coprecessing and inertial
frames. Radiation reaction can then be introduced in a quasi-adiabatic fashion
such that, at least for binaries on quasi-circular orbits, gravitational
inspirals reduce to solving a single ordinary differential equation. We provide
a broad review of the resulting phenomenology and rewrite the relevant physics
in terms of the newly adopted parametrization. This includes the spin-orbit
resonances, the up-down instability, spin propagation at past time infinity,
and new precession estimators to be used in gravitational-wave astronomy. Our
findings are implemented in version 2 of the public Python module PRECESSION.
Performing a precession-averaged post-Newtonian evolution from/to arbitrarily
large separation takes $\lesssim 0.1$ s on a single off-the-shelf processor - a
50x speedup compared to our previous implementation. This allows for a wide
variety of applications including propagating gravitational-wave posterior
samples as well as population-synthesis predictions of astrophysical nature.",2304.04801v2
2023-05-01,DREAM II. The spin-orbit angle distribution of close-in exoplanets under the lens of tides,"The spin-orbit angle, or obliquity, is a powerful observational marker that
allows us to access the dynamical history of exoplanetary systems. Here, we
have examined the distribution of spin-orbit angles for close-in exoplanets and
put it in a statistical context of tidal interactions between planets and their
stars. We confirm the observed trends between the obliquity and physical
quantities directly connected to tides, namely the stellar effective
temperature, the planet-to-star mass ratio, and the scaled orbital distance. We
further devised a tidal efficiency factor combining critical parameters that
control the strength of tidal effects and used it to corroborate the strong
link between the spin-orbit angle distribution and tidal interactions. In
particular, we developed a readily usable formula to estimate the probability
that a system is misaligned, which will prove useful in global population
studies. By building a robust statistical framework, we reconstructed the
distribution of the three-dimensional spin-orbit angles, allowing for a sample
of nearly 200 true obliquities to be analyzed for the first time. This
realistic distribution maintains the sky-projected trends, and additionally
hints toward a striking pileup of truly aligned systems. The comparison between
the full population and a pristine subsample unaffected by tidal interactions
suggests that perpendicular architectures are resilient toward tidal
realignment, providing evidence that orbital misalignments are sculpted by
disruptive dynamical processes that preferentially lead to polar orbits. On the
other hand, star-planet interactions seem to efficiently realign or quench the
formation of any tilted configuration other than for polar orbits, and in
particular for antialigned orbits.",2305.00829v1
2023-07-11,Conventional and unconventional Dicke models: Multistabilities and nonequilibrium dynamics,"The Dicke model describes the collective behavior of a sub-wavelength--size
ensemble of two-level atoms (i.e., spin-1/2) interacting identically with a
single quantized radiation field of a cavity. Across a critical coupling
strength it exhibits a zero-temperature phase transition from the normal state
to the superradiant phase where the field is populated and the collective spin
acquires a nonzero $x$-component, which can be imagined as ferromagnetic
ordering of the atomic spins along $x$. Here we introduce a variant of this
model where two sub-wavelength--size ensembles of spins interact with a single
quantized radiation field with different strengths. Subsequently, we restrict
ourselves to a special case where the coupling strengths are opposite (which is
unitarily equivalent to equal-coupling strengths). Due to the conservation of
the total spin in each ensemble individually, the system supports two distinct
superradiant states with $x$-ferromagnetic and $x$-ferrimagnetic spin ordering,
coexisting with each other in a large parameter regime. The stability and
dynamics of the system in the thermodynamic limit are examined using a
semiclassical approach, which predicts non-stationary behaviors due to the
multistabilities. At the end, we also perform small-scale full
quantum-mechanical calculations, with results consistent with the semiclassical
ones.",2307.05686v3
2023-11-02,"Spin-orbit-lattice entangled state in A$_2$MgReO$_6$ (A = Ca, Sr, Ba) revealed by resonant inelastic X-ray scattering","The $5d^1$ ordered double perovskites present an exotic playground for
studying novel multi-polar physics due to large spin-orbit coupling. We present
Re L3 edge resonant inelastic X-ray scattering (RIXS) results that reveal the
presence of the dynamic Jahn-Teller effect in the A$_2$MgReO$_6$ (A = Ca, Sr,
Ba) family of $5d^1$ double perovskites. The spin-orbit excitations in these
materials show a strongly asymmetric lineshape and exhibit substantial
temperature dependence, indicating that they are dressed with lattice
vibrations. Our experimental results are explained quantitatively through a
RIXS calculation based on a spin-orbit-lattice entangled electronic ground
state with the dynamic Jahn-Teller effect taken into consideration. We find
that the spin-orbit-lattice entangled state is robust against magnetic and
structural phase transitions as well as against significant static Jahn-Teller
distortions. Our results illustrate the importance of including vibronic
coupling for a complete description of the ground state physics of $5d^1$
double perovskites. Usage: Secondary publications and information retrieval
purposes.",2311.01621v1
2023-12-24,Room temperature relaxometry of single nitrogen-vacancy centers in proximity to $α$-RuCl$_3$ nanoflakes,"Investigating spin and charge noise in strongly correlated electron systems
is a valuable way to analyze their physical properties and unlock new phases of
matter. In this context, nitrogen-vacancy (NV) center-based magnetometry has
been proven to be a versatile sensor for various classes of magnetic materials
in broad temperature and frequency ranges. Here, we use longitudinal relaxation
time $T_1$ of single NV centers to investigate the spin dynamics of
nanometers-thin flakes of $\alpha$-RuCl$_3$ at room temperature. We observe a
significant reduction in the $T_1$ in the presence of $\alpha$-RuCl$_3$ in
proximity to our NVs, which we attribute to paramagnetic spin noise confined in
the 2D hexagonal plane. Furthermore, the $T_1$ time exhibits an almost linear
increase with an applied external magnetic field. We associate this trend with
the alteration of spin and charge noise in $\alpha$-RuCl$_3$ under an external
magnetic field. These findings suggest that the influence of the
room-temperature spin dynamics of $\alpha$-RuCl$_3$ on the longitudinal
relaxation time of the NV center can be used to gain information on the
material itself and the technique to be used on other 2D materials.",2312.15541v1
2024-01-19,Exploration of magnon-magnon coupling in an antidot lattice: The role of non-uniform magnetization texture,"We numerically study the spin wave dynamics in an antidot lattice based on a
Co/Pd multilayer structure with reduced perpendicular magnetic anisotropy at
the edges of the antidots. This structure forms a magnonic crystal with a
periodic antidot pattern and a periodic magnetization configuration consisting
of out-of-plane magnetized bulk and in-plane magnetized rims. Our results show
the different behavior of spin waves in the bulk and in the rims under varying
out-of-plane external magnetic field strength, revealing complex spin-wave
spectra and hybridizations between the modes of these two subsystems. A
particularly strong magnon-magnon coupling, due to exchange interactions, is
found between the fundamental bulk spin-wave mode and the second-order radial
rim modes. However, the dynamical coupling between the spin-wave modes at low
frequencies, involving the first-order radial rim modes, is masked by the
changes in the static magnetization at the bulk-rim interface with magnetic
field changes. The study expands the horizons of magnonic-crystal research by
combining periodic structural patterning and non-collinear magnetization
texture to achieve strong magnon-magnon coupling, highlighting the significant
role of exchange interactions in the coupling.",2401.10540v2
2024-02-03,Spintronic devices and applications using noncollinear anti-chiral antiferromagnets,"Antiferromagnetic materials have a vanishingly small net magnetization, which
generates weak dipolar fields and makes them robust against external magnetic
perturbation and rapid magnetization dynamics, as dictated by the geometric
mean of their exchange and anisotropy energies. However, experimental and
theoretical techniques to detect and manipulate the antiferromagnetic order in
a fully electrical manner must be developed to enable advanced spintronic
devices with antiferromagnets (AFMs) as their active spin-dependent elements.
Among the various AFMs, conducting AFMs offer high electrical and thermal
conductivities and strong electron-spin-phonon interactions. Noncollinear
metallic AFMs with negative chirality, including Mn3Sn, Mn3Ge, and Mn3GaN,
offer rich physics that arises from their topology. In this review article, we
introduce the crystal structure and the physical phenomena observed in negative
chirality AFMs. Experimental and theoretical advances related to
current-induced dynamics on the spin structure of Mn3Sn are discussed. We then
present a potential AFM spintronic device that can serve as a non-volatile
memory, high-frequency signal generator, neuron emulator, and even a
probabilistic bit, depending on the design parameters and the input stimuli,
i.e., amplitude and pulse width of the injected spin current and the external
magnetic field. In this device, spin-orbit torques can be used to manipulate
the order parameter, while the device state can be read via tunneling
magnetoresistance. We also present analytic models that relate the performance
characteristics of the device with its design parameters, thus enabling a rapid
technology-device assessment. Effects of Joule heating and thermal noise on the
device characteristics are briefly discussed. We close the paper by summarizing
the status of research and present our outlook in this rapidly evolving
research field.",2402.01977v1
2024-03-18,Coarsening of chiral domains in itinerant electron magnets: A machine learning force field approach,"Frustrated itinerant magnets often exhibit complex noncollinear or
noncoplanar magnetic orders which support topological electronic structures. A
canonical example is the anomalous quantum Hall state with a chiral spin order
stabilized by electron-spin interactions on a triangular lattice. While a
long-range magnetic order cannot survive thermal fluctuations in two
dimensions, the chiral order which results from the breaking of a discrete
Ising symmetry persists even at finite temperatures. We present a scalable
machine learning (ML) framework to model the complex electron-mediated
spin-spin interactions that stabilize the chiral magnetic domains in a
triangular lattice. Large-scale dynamical simulations, enabled by the ML
force-field models, are performed to investigate the coarsening of chiral
domains after a thermal quench. While the chiral phase is described by a broken
$Z_2$ Ising-type symmetry, we find that the characteristic size of chiral
domains increases linearly with time, in stark contrast to the expected
Allen-Cahn domain growth law for a non-conserved Ising order parameter field.
The linear growth of the chiral domains is attributed to the orientational
anisotropy of domain boundaries. Our work also demonstrates the promising
potential of ML models for large-scale spin dynamics of itinerant magnets.",2403.11705v1
2009-03-13,Spin-torque driven magnetization dynamics in a nanocontact setup for low external fields: numerical simulation study,"We present numerical simulation studies of the steady-state magnetization
dynamics driven by a spin-polarized current in a point contact geometry for the
case of a relatively large contact diameter (D = 80 nm) and small external
field (H = 30 Oe). We show, that under these conditions the magnetization
dynamics is qualitatively different from the dynamics observed for small
contacts in large external fields. In particular, the 'bullet' mode with a
homogeneous mode core, which was the dominating localized mode for small
contacts, is not found here. Instead, all localized oscillation modes observed
in simulations correspond to different motion kinds of vortex-antivortex (V-AV)
pairs. These kinds include rotational and translational motion of pairs with
the V-AV distance d ~ D and creation/annihilation of much smaller (satellite)
V-AV pairs. We also show that for the geometry studied here the Oersted field
has a qualitative effect on the magnetization dynamics of a 'free' layer. This
effect offers a possibility to control magnetization dynamics by a suitable
electric contact setup, optimized to produce a desired Oersted field. Finally,
we demonstrate that when the magnetization dynamics of the 'fixed' layer
(induced only by the stray field interaction with the 'free' layer) is taken
into account, the threshold current for the oscillation onset is drastically
reduced and new types of localized modes appear. In conclusion, we show that
our simulations reproduce semiquantitatively several important features of the
magnetization dynamics in a point contact system for low external fields
reported experimentally.",0903.2416v1
2017-03-08,Non-Markovianity of qubit evolution under the action of spin environment,"The question, whether an open system dynamics is Markovian or non-Markovian
can be answered by studying the direction of the information flow in the
dynamics. In Markovian dynamics, information must always flow from the system
to the environment. If the environment is interacting with only one of the
subsystems of a bipartite system, the dynamics of the entanglement in the
bipartite system can be used to identify the direction of information flow.
Here we study the dynamics of a two-level system interacting with an
environment, which is also a heat bath, and consists of a large number of
two-level quantum systems. Our model can be seen as a close approximation to
the `spin bath' model at low temperatures. We analyze the Markovian nature of
the dynamics, as we change the coupling between the system and the environment.
We find the Kraus operators of the dynamics for certain classes of couplings.
We show that any form of time-independent or time-polynomial coupling gives
rise to non-Markovianity. Also, we witness non-Markovianity for certain
parameter values of time-exponential coupling. Moreover, we study the
transition from non-Markovian to Markovian dynamics as we change the value of
coupling strength.",1703.02749v2
2022-10-25,Crafting the dynamical structure of synchronization by harnessing bosonic multilevel cavity QED,"Many-body cavity QED experiments are established platforms to tailor and
control the collective responses of ensembles of atoms, interacting through one
or more common photonic modes. The rich diversity of dynamical phases they can
host, calls for a unified framework. Here we commence this program by showing
that a cavity QED simulator assembled from $N$-levels bosonic atoms, can
reproduce and extend the possible dynamical responses of collective observables
occurring after a quench. Specifically, by initializing the atoms in classical
or quantum states, or by leveraging intra-levels quantum correlations, we craft
on demand the entire synchronization/desynchronization dynamical crossover of
an exchange model for $SU(N)$ spins. We quantitatively predict the onset of
different dynamical responses by combining the Liouville-Arnold theorem on
classical integrability with an ansatz for reducing the collective evolution to
an effective few-body dynamics. Among them, we discover a synchronized chaotic
phase induced by quantum correlations and associated to a first order
non-equilibrium transition in the Lyapunov exponent of collective atomic
dynamics. Our outreach includes extensions to other spin-exchange quantum
simulators and a universal conjecture for the dynamical reduction of
non-integrable all-to-all interacting systems.",2210.14224v4
2000-11-01,Spin Profile of Galactic Halos and Disk Formation,"We summarize recent developments in the study of the origin of halo spin
profiles and preliminary implications on disk formation. The specific
angular-momentum distributions within halos in N-body simulations match a
universal shape, M(<j) \propto j/(j_0+j). It is characterized by a power law
over most of the mass, and one shape parameter in addition to the spin
parameter \lambda. The angular momentum tends to be aligned throughout the halo
and of cylindrical symmetry. Even if angular momentum is conserved during
baryonic infall, the resultant disk density profile is predicted to deviate
from exponential, with a denser core and an extended tail. A slightly corrected
version of the scaling relation due to linear tidal-torque theory is used to
explain the origin of a typical power-law profile in shells, j(M) \propto M^s
with s \gsim 1. While linear theory crudely predicts the amplitudes of halo
spins, it is not a good predictor of their directions. Independently, mergers
of halos are found to produce a similar profile due to j transfer from the
orbit to the product halo via dynamical friction and tidal stripping. The halo
spin is correlated with having a recent major merger, though this correlation
is weakened by mass loss. These two effects are due to a correlation between
the spins of neighboring halos and their orbit, leading to prograde mergers.",0011002v1
2003-07-07,Quasi-periodic X-ray brightness fluctuations in an accreting millisecond pulsar,"The relativistic plasma flows onto neutron stars that are accreting material
from stellar companions can be used to probe strong-field gravity as well as
the physical conditions in the supranuclear-density interiors of neutron stars.
Plasma inhomogeneities orbiting a few kilometres above the stars are observable
as X-ray brightness fluctuations on the millisecond dynamical timescale of the
flows. Two frequencies in the kilohertz range dominate these fluctuations: the
twin kilohertz quasi-periodic oscillations (kHz QPOs). Competing models for the
origins of these oscillations (based on orbital motions) all predict that they
should be related to the stellar spin frequency, but tests have been difficult
because the spins were not unambiguously known. Here we report the detection of
kHz QPOs from a pulsar whose spin frequency is known. Our measurements
establish a clear link between kHz QPOs and stellar spin, but one not predicted
by any current model. A new approach to understanding kHz QPOs is now required.
We suggest that a resonance between the spin and general relativistic orbital
and epicyclic frequencies could provide the observed relation between QPOs and
spin.",0307123v1
1996-01-05,NMR and Neutron Scattering Experiments on the Cuprate Superconductors: A Critical Re-Examination,"We show that it is possible to reconcile NMR and neutron scattering
experiments on both LSCO and YBCO, by making use of the Millis-Monien-Pines
mean field phenomenological expression for the dynamic spin-spin response
function, and reexamining the standard Shastry-Mila-Rice hyperfine Hamiltonian
for NMR experiments. The recent neutron scattering results of Aeppli et al on
LSCO (x=14%) are shown to agree quantitatively with the NMR measurements of
$^{63}T_1$ and the magnetic scaling behavior proposed by Barzykin and Pines.
The reconciliation of the $^{17}T_1$ relaxation rates with the degree of
incommensuration in the spin fluctuation spectrum seen in neutron experiments
is achieved by introducing a new transferred hyperfine coupling $C'$ between
oxygen nuclei and their next nearest neighbor $Cu^{2+}$ spins; this leads to a
near-perfect cancellation of the influence of the incommensurate spin
fluctuation peaks on the oxygen relaxation rates of LSCO. The inclusion of the
new $C'$ term also leads to a natural explanation, within the one-component
model, the different temperature dependence of the anisotropic oxygen
relaxation rates for different field orientations, recently observed by
Martindale $et~al$. The measured significant decrease with doping of the
anisotropy ratio, $R= ^{63}T_{1ab}/^{63}T_{1c}$ in LSCO system, from $R =3.9$
for ${\rm La_2CuO_4}$ to $R ~ 3.0$ for LSCO (x=15%) is made compatible with the
doping dependence of the shift in the incommensurate spin fluctuation peaks
measured in neutron experiments, by suitable choices of the direct and
transferred hyperfine coupling constants $A_{\beta}$ and B.",9601016v1
1996-04-29,"Kondo lattice model: Unitary transformations, spin dynamics, strongly correlated charged modes, and vacuum instability","Using unitary transformations, we express the Kondo lattice Hamiltonian in
terms of fermionic operators that annihilate the ground state of the
interacting system and that represent the best possible approximations to the
actual charged excitations. In this way, we obtain an effective Hamiltonian
which, for small couplings, consists in a kinetic term for conduction electrons
and holes, an RKKY-like term, and a renormalized Kondo interaction. The
physical picture of the system implied by this formalism is that of a vacuum
state consisting in a background of RKKY-induced spin correlations, where two
kinds of elementary modes can be excited: Soft neutral modes associated with
deformations of the spin liquid, which lead to very large low-temperature
values of the heat capacity and magnetic susceptibility, and charged modes
corresponding to the excitation of electrons and holes in the system. Using the
translational and spin rotational symmetries, we construct a simple ansatz to
determine the charged excitations neglecting the effects of the spin
correlations. Apart from the `normal', uncorrelated states, we find strongly
correlated charged modes involving soft electrons (or holes) and spin
fluctuations, which strongly renormalize the low-energy charged spectrum, and
whose energy becomes negative beyond a critical coupling, signaling a vacuum
instability and a transition to a new phase.",9604168v1
1997-09-03,The Ferromagnetic Kondo Model for Manganites: Phase Diagram and Charge Segregation Effects,"The phase diagram of the ferromagnetic Kondo model for manganites is
investigated using computational techniques. In clusters of dimensions 1 and 2,
Monte Carlo simulations in the limit where the localized spins are classical
show a rich low temperature phase diagram with three dominant regions: (i) a
ferromagnetic phase, (ii) phase separation between hole-poor antiferromagnetic
and hole-rich ferromagnetic domains, and (iii) a phase with incommensurate spin
correlations. Possible experimental consequences of the regime of phase
separation are discussed. Studies using the Lanczos algorithm and the Density
Matrix Renormalization Group method applied to chains with localized spin 1/2
(with and without Coulombic repulsion for the mobile electrons) and spin 3/2
degrees of freedom give results in excellent agreement with those in the spin
localized classical limit. The Dynamical Mean Field ($D=\infty$) approximation
was also applied to the same model. At large Hund coupling phase separation and
ferromagnetism were identified, again in good agreement with results in low
dimensions. In addition, a Monte Carlo study of spin correlations allowed us to
estimate the critical temperature for ferromagnetism $T_c^{FM}$ in 3
dimensional clusters. It is concluded that $T_c^{FM}$ is compatible with
current experimental results.",9709029v1
1997-09-14,"Damage spreading for one-dimensional, non-equilibrium models with parity conserving phase transitions","The damage spreading (DS) transitions of two one-dimensional stochastic
cellular automata suggested by Grassberger (A and B) and the kinetic Ising
model of Menyh\'ard (NEKIM) have been investigated on the level of kinks and
spins. On the level of spins the parity conservation is not satisfied and
therefore studying these models provides a convenient tool to understand the
dependence of DS properties on symmetries. For the model B the critical point
and the DS transition point is well separated and directed percolation damage
spreading transition universality was found for spin damage as well as for kink
damage in spite of the conservation of damage variables modulo 2 in the latter
case. For the A stochastic cellular automaton, and the NEKIM model the two
transition points coincide with drastic effects on the damage of spin and kink
variables showing different time dependent behaviours. While the kink DS
transition is continuous and shows regular PC class universality, the spin
damage exhibits a discontinuous phase transition with compact clusters and PC
like dynamical scaling ($\eta^,$), ($\delta_s$) and ($z_s$) exponents whereas
the static exponents determined by FSS are consistent with that of the spins of
the NEKIM model at the PC transition point. The generalised hyper-scaling law
is satisfied.",9709154v2
1997-09-29,Canted antiferromagnetic and spin singlet quantum Hall states in double-layer systems,"We present details of earlier studies (Zheng et al, Phys. Rev. Lett. 78, 310
(1997) and Das Sarma et al, ibid 79, 917 (1997)) and additional new results on
double-layer quantum Hall systems at a total filling \nu = 2 \nu_1, where a
single layer at filling \nu_1 forms a ferromagnetic, fully spin-polarized,
gapped incompressible quantum Hall state. For the case \nu_1 = 1, a detailed
Hartree-Fock analysis is carried out on a realistic, microscopic Hamiltonian.
Apart from the state continuously connected to the ground state of two well
separated layers, we find two double-layer quantum Hall phases: one with a
finite interlayer antiferromagnetic spin ordering in the plane orthogonal to
the applied field (the `canted' state), and the other a spin singlet. The
quantum transitions between the various quantum Hall states are continuous, and
are signaled by the softening of collective intersubband spin density
excitations. For the case of general \nu_1, closely related results are
obtained by a semi-phenomenological continuum quantum field theory description
of the low-lying spin excitations using a non-linear sigma model. Because of
its broken symmetry, the canted phase supports a linearly dispersing Goldstone
mode and has a finite temperature Kosterlitz-Thouless transition. We present
results on the form of the phase diagram, the magnitude of the canted order
parameter, the collective excitation dispersions, the specific heat, the form
of the dynamic light scattering spectrum at finite temperature, and the
Kosterlitz-Thouless critical temperature. Our findings are consistent with
recent experimental results.",9709315v2
1999-02-17,Quantum Monte Carlo Study of Weakly Coupled Spin Ladders,"We report a quantum Monte Carlo study of the thermodynamic properties of
arrays of spin ladders with various widths ($n$), coupled via a weak
inter-ladder exchange coupling $\alpha J$, where $J$ is the intra-ladder
coupling both along and between the chains. This coupled ladder system serves
as a simplified model for the magnetism of presumed ordered spin and charge
stripes in the two-dimensional CuO$_2$ planes of hole-doped copper oxides. Our
results for $n=3$ with weak inter-ladder coupling $\alpha=0.05$, estimated from
the $t-t'-t''-J$ model, show good agreement with the ordering temperature of
the recently observed spin density wave condensation in La$_2$CuO$_{4+y}$. We
show that there exists a quantum critical point at $\alpha_c \simeq 0.07$ for
$n=4$, and determine the phase diagram. Our data at this quantum critical point
agree quantitatively with the universal scaling predicted by the quantum
nonlinear $\sigma$ model. We also report results on random mixtures of $n=2$
and $n=3$ ladders, which correspond to the doping region near but above 1/8.
Our study on the magnetic static structure factor reveals a saturation of the
incommensurability of the spin correlations around 1/8, while the
incommensurability of the charge stripes grows linearly with hole
concentration. The implications of this result for the interpretation of
neutron scattering experiments on the dynamic spin fluctuations in
La$_{2-x}$Sr$_x$CuO$_4$ are discussed.",9902248v1
2000-07-20,Spin glasses without time-reversal symmetry and the absence of a genuine structural glass transition,"We study the three-spin model and the Ising spin glass in a field using
Migdal-Kadanoff approximation. The flows of the couplings and fields indicate
no phase transition, but they show even for the three-spin model a slow
crossover to the asymptotic high-temperature behaviour for strong values of the
couplings. We also evaluated a quantity that is a measure of the degree of
non-self-averaging, and we found that it can become large for certain ranges of
the parameters and the system sizes. For the spin glass in a field the maximum
of non-self-averaging follows for given system size a line that resembles the
de Almeida-Thouless line. We conclude that non-self-averaging found in
Monte-Carlo simulations cannot be taken as evidence for the existence of a
low-temperature phase with replica-symmetry breaking. Models similar to the
three-spin model have been extensively discussed in order to provide a
description of structural glasses. Their theory at mean-field level resembles
the mode-coupling theory of real glasses. At that level the one-step replica
symmetry approach breaking predicts two transitions, the first transition being
dynamical and the second thermodynamical. Our results suggest that in real
finite dimensional glasses there will be no genuine transitions at all, but
that some features of mean-field theory could still provide some useful
insights.",0007315v1
2000-11-01,Evolution of the resonance and incommensurate spin fluctuations in superconducting YBa$_2$Cu$_3$O$_{6+x}$,"Polarized and unpolarized neutron triple-axis spectrometry was used to study
the dynamical magnetic susceptibility $\chi^{\prime\prime}({\bf q},\omega)$ as
a function of energy ($\hbar\omega$) and wave vector (${\bf q}$) in a wide
temperature range for the bilayer superconductor YBa$_2$Cu$_3$O$_{6+x}$ with
oxygen concentrations, $x$, of 0.45, 0.5, 0.6, 0.7, 0.8, 0.93, and 0.95. The
most prominent features in the magnetic spectra include a spin gap in the
superconducting state, a pseudogap in the normal state, the much-discussed
resonance, and incommensurate spin fluctuations below the resonance. We
establish the doping dependence of the spin gap in the superconducting state,
the resonance energy, and the incommensurability of the spin fluctuations. We
discuss in detail the procedure used for separating the magnetic scattering
from phonon and other spurious effects. In the comparison of our experimental
results with various microscopic theoretical models, particular emphasis was
made to address the similarities and differences in the spin fluctuations of
YBa$_2$Cu$_3$O$_{6+x}$ and La$_{2-x}$Sr$_x$CuO$_4$.",0011019v1
2004-04-20,Spin Susceptibility of Ga-Stabilized delta-Pu Probed by {69}^Ga NMR,"Spin susceptibility of stabilized \delta phase in the Pu-Ga alloy is studied
by measuring {69,71}^Ga NMR spectra and nuclear spin-lattice relaxation rate
{69}T_{1}^{-1} in the temperature range 5 - 350 K. The shift ({69}^K) of the
{69,71}^Ga NMR line and {69}^T_{1}^{-1} are controlled correspondingly by the
static and the fluctuating in time parts of local magnetic field arisen at
nonmagnetic gallium due to transferred hyperfine coupling with the nearest f
electron environment of the more magnetic Pu. The nonmonotonic with a maximum
around 150 K behavior of {69}^K(T) \chi_{s,5f}(T) is attributed to the
peculiarities in temperature dependence of the f electron spin susceptibility
\chi_{s,5f}(T) in \delta phase of plutonium. The temperature reversibility
being observed in {69}^K(T) data provides strong evidence for an electronic
instability developed with T in f electron bands near the Fermi energy and
accompanied with a pseudogap-like decrease of \chi_{s,5f}(T) at T<150 K. The
NMR data at high temperature are in favor of the mainly localized character of
5f electrons in \delta phase of the alloy with characteristic spin-fluctuation
energy \Gamma(T) T^{0.35(5)}, which is close to $\Gamma(T) T^{0.5} predicted by
Cox et al. [J. Appl. Phys. 57, 3166 (1985)] for 3D Kondo-system above T_Kondo}.
The dynamic spin correlations of 5f electrons become essential to consider for
{69}^T_{1}^{-1}(T) only at T<100 K. However, no NMR evidences favoring
formation of the static magnetic order in \delta-Pu were revealed down to 5K .",0404460v1
2005-04-14,Fast Flat-Histogram Method for Generalized Spin Models,"We present a Monte Carlo method that efficiently computes the density of
states for spin models having any number of interaction per spin. By combining
a random-walk in the energy space with collective updates controlled by the
microcanonical temperature, our method yields dynamic exponents close to their
ideal random-walk values, reduced equilibrium times, and very low statistical
error on the density of states. The method can host any density of states
estimation scheme, including the Wang-Landau algorithm and the transition
matrix method. Our approach proves remarkably powerful in the numerical study
of models governed by long-range interactions, where it is shown to reduce the
algorithm complexity to that of a short-range model with the same number of
spins. We apply the method to the $q$-state Potts chains $(3\leq q \leq 12)$
with power-law decaying interactions in their first-order regime; we find that
conventional local-update algorithms are outperformed already for sizes above a
few hundred spins. By considering chains containing up to $2^{16}$ spins, which
we simulated in fairly reasonable time, we obtain estimates of transition
temperatures correct to five-figure accuracy. Finally, we propose several
efficient schemes aimed at estimating the microcanonical temperature.",0504367v2
2005-05-03,Central mode and spin confinement near the boundary of the superconducting phase in YBa2Cu3O6.353 (Tc=18 K),"We have mapped the neutron scattering spin spectrum at low-energies in
YBa2Cu3O6.353 (Tc=18 K) where the doping ~0.06 is near the critical value
(pc=0.055) for superconductivity. No coexistence with long range ordered
antiferromagnetism is found. The spins fluctuate on two energy scales, one a
damped spin response with a ~2 meV relaxation rate and the other a central mode
with a relaxation rate that slows to less than 0.08 meV below Tc. The spectrum
mirrors that of a soft mode driving a central mode. Extremely short correlation
lengths, 42+-5 Angstrom in-plane and 8+-2 Angstrom along the c direction, and
isotropic spin orientations for the central mode indicate that the correlations
are subcritical with respect to any second order transition to Neel order. The
dynamics follows a model where damped spin fluctuations are coupled to the slow
fluctuations of regions with correlations shortened by the hole doping.",0505083v2
2006-09-21,Magnetocaloric Study of Spin Relaxation in `Frozen' Dipolar Spin Ice Dy2Ti2O7,"The magnetocaloric effect of polycrystalline samples of pure and Y-doped
dipolar spin ice Dy2Ti2O7 was investigated at temperatures from nominally 0.3 K
to 6 K and in magnetic fields of up to 2 T. As well as being of intrinsic
interest, it is proposed that the magnetocaloric effect may be used as an
appropriate tool for the qualitative study of slow relaxation processes in the
spin ice regime. In the high temperature regime the temperature change on
adiabatic demagnetization was found to be consistent with previously published
entropy versus temperature curves. At low temperatures (T < 0.4 K) cooling by
adiabatic demagnetization was followed by an irreversible rise in temperature
that persisted after the removal of the applied field. The relaxation time
derived from this temperature rise was found to increase rapidly down to 0.3 K.
The data near to 0.3 K indicated a transition into a metastable state with much
slower relaxation, supporting recent neutron scattering results. In addition,
magnetic dilution of 50 % concentration was found to significantly prolong the
dynamical response in the milikelvin temperature range, in contrast with
results reported for higher temperatures at which the spin correlations are
suppressed. These observations are discussed in terms of defects and loop
correlations in the spin ice state.",0609537v1
2006-10-18,Magnetic Properties and Metastable States in Spin-Crossover Transition of Co-Fe Prussian Blue Analogues,"The combination of spin transitions and magnetic ordering provides an
interesting structure of phase transitions in Prussian blue analogues (PBAs).
To understand the structure of stable and metastable states of Co-Fe PBA, it is
necessary to clarify free energy as a function of magnetization and the
fraction of the high-temperature component. Including the magnetic interaction
between high-temperature states, we study the magnetic phase transition of
Co-Fe PBA in addition to spin transitions. Here, we take into account the
degeneracy changes due to charge transfer between Co and Fe atoms accompanying
the spin transition. In this study, the charge transfer between Co and Fe atoms
is explicitly taken into account and also the ferrimagnetic structure of Co-Fe
PBAs is expressed in the proper way. First, we found systematic changes in the
structures of stable and metastable states as functions of system parameters
using mean field theory. In particular, the existence of a metastable
magnetic-ordered high-temperature state is confirmed at temperatures lower than
that of the hysteresis region of spin transitions. Second, we found that the
magnetic interaction causes complex ordering processes of a spin transition and
a magnetic phase transition. The effect of a magnetic field on the phase
structure is also investigated and we found metamagnetic magnetization
processes. Finally, the dynamical properties of this metastable state are
studied by Monte Carlo method.",0610500v2
1998-08-02,Theory of higher spin tensor currents and central charges,"We study higher spin tensor currents in quantum field theory. Scalar, spinor
and vector fields admit unique ""improved"" currents of arbitrary spin, traceless
and conserved. Off-criticality as well as at interacting fixed points
conservation is violated and the dimension of the current is anomalous. In
particular, currents J^(s,I) with spin s between 0 and 5 (and a second label I)
appear in the operator product expansion of the stress tensor. The TT OPE is
worked out in detail for free fields; projectors and invariants encoding the
space-time structure are classified. The result is used to write and discuss
the most general OPE for interacting conformal field theories and
off-criticality. Higher spin central charges c_(s,I) with arbitrary s are
defined by higher spin channels of the many-point T-correlators and central
functions interpolating between the UV and IR limits are constructed. We
compute the one-loop values of all c_(s,I) and investigate the RG trajectories
of quantum field theories in the conformal window following our approach. In
particular, we discuss certain phenomena (perturbative and nonperturbative)
that appear to be of interest, like the dynamical removal of the I-degeneracy.
Finally, we address the problem of formulating an action principle for the RG
trajectory connecting pairs of CFT's as a way to go beyond perturbation theory.",9808004v4
2005-07-14,Spinning strings and integrable spin chains in the AdS/CFT correspondence,"In this introductory review we discuss dynamical tests of the AdS_5 x S^5
string/N=4 super Yang-Mills duality. After a brief introduction to AdS/CFT we
argue that semiclassical string energies yield information on the quantum
spectrum of the string in the limit of large angular momenta on the S^5. The
energies of the folded and circular spinning string solutions rotating on a S^3
within the S^5 are derived, which yield all loop predictions for the dual gauge
theory scaling dimensions. These follow from the eigenvalues of the dilatation
operator of N=4 super Yang-Mills in a minimal SU(2) subsector and we display
its reformulation in terms of a Heisenberg s=1/2 spin chain along with the
coordinate Bethe ansatz for its explicit diagonalization. In order to make
contact to the spinning string energies we then study the thermodynamic limit
of the one-loop gauge theory Bethe equations and demonstrate the matching with
the folded and closed string result at this loop order. Finally the known gauge
theory results at higher-loop orders are reviewed and the associated long-range
spin chain Bethe ansatz is introduced, leading to an asymptotic all-loop
conjecture for the gauge theory Bethe equations. This uncovers discrepancies at
the three-loop order between gauge theory scaling dimensions and string theory
energies and the implications of this are discussed. Along the way we comment
on further developments and generalizations of the subject and point to the
relevant literature.",0507136v2
2001-07-06,Perturbation Theory and Numerical Modeling of Quantum Logic Operations with a Large Number of Qubits,"The perturbation theory is developed based on small parameters which
naturally appear in solid state quantum computation. We report the simulations
of the dynamics of quantum logic operations with a large number of qubits (up
to 1000). A nuclear spin chain is considered in which selective excitations of
spins are provided by having a uniform gradient of the external magnetic field.
Quantum logic operations are utilized by applying resonant electromagnetic
pulses. The spins interact with their nearest neighbors. We simulate the
creation of the long-distance entanglement between remote qubits in the spin
chain. Our method enables us to minimize unwanted non-resonant effects in a
controlled way. The method we use cannot simulate complicated quantum logic (a
quantum computer is required to do this), but it can be useful to test the
experimental performance of simple quantum logic operations. We show that: (a)
the probability distribution of unwanted states has a ``band'' structure, (b)
the directions of spins in typical unwanted states are highly correlated, and
(c) many of the unwanted states are high-energy states of a quantum computer (a
spin chain). Our approach can be applied to simple quantum logic gates and
fragments of quantum algorithms involving a large number of qubits.",0107038v1
2006-11-23,Decoherence induced by interacting quantum spin baths,"We study decoherence induced on a two-level system coupled to a
one-dimensional quantum spin chain. We consider the cases where the dynamics of
the chain is determined by the Ising, XY, or Heisenberg exchange Hamiltonian.
This model of quantum baths can be of fundamental importance for the
understanding of decoherence in open quantum systems, since it can be
experimentally engineered by using atoms in optical lattices. As an example,
here we show how to implement a pure dephasing model for a qubit system coupled
to an interacting spin bath. We provide results that go beyond the case of a
central spin coupled uniformly to all the spins of the bath, in particular
showing what happens when the bath enters different phases, or becomes
critical; we also study the dependence of the coherence loss on the number of
bath spins to which the system is coupled and we describe a
coupling-independent regime in which decoherence exhibits universal features,
irrespective of the system-environment coupling strength. Finally, we establish
a relation between decoherence and entanglement inside the bath. For the Ising
and the XY models we are able to give an exact expression for the decay of
coherences, while for the Heisenberg bath we resort to the numerical
time-dependent Density Matrix Renormalization Group.",0611242v1
2007-09-07,On the oscillations in Mercury's obliquity,"One major objective of MESSENGER and BepiColombo spatial missions is to
accurately measure Mercury's rotation and its obliquity in order to obtain
constraints on internal structure of the planet. Which is the obliquity's
dynamical behavior deriving from a complete spin-orbit motion of Mercury
simultaneously integrated with planetary interactions? We have used our SONYR
model integrating the spin-orbit N-body problem applied to the solar System
(Sun and planets). For lack of current accurate observations or ephemerides of
Mercury's rotation, and therefore for lack of valid initial conditions for a
numerical integration, we have built an original method for finding the
libration center of the spin-orbit system and, as a consequence, for avoiding
arbitrary amplitudes in librations of the spin-orbit motion as well as in
Mercury's obliquity. The method has been carried out in two cases: (1) the
spin-orbit motion of Mercury in the 2-body problem case (Sun-Mercury) where an
uniform precession of the Keplerian orbital plane is kinematically added at a
fixed inclination (S2K case), (2) the spin-orbit motion of Mercury in the
N-body problem case (Sun and planets) (Sn case). We find that the remaining
amplitude of the oscillations in the Sn case is one order of magnitude larger
than in the S2K case, namely 4 versus 0.4 arcseconds (peak-to-peak). The mean
obliquity is also larger, namely 1.98 versus 1.80 arcminutes, for a difference
of 10.8 arcseconds. These theoretical results are in a good agreement with
recent radar observations but it is not excluded that it should be possible to
push farther the convergence process by drawing nearer still more precisely to
the libration center.",0709.1111v1
2008-05-29,Supermassive binary black hole mergers,"When galaxies collide, dynamical friction drives their central supermassive
black holes close enought to each other such that gravitational radiation
becomes the leading dissipative effect. Gravitational radiation takes away
energy, momentum and angular momentum from the compact binary, such that the
black holes finally merge. In the process, the spin of the dominant black hole
is reoriented. On observational level, the spins are directly related to the
jets, which can be seen at radio frequencies. Images of the X-shaped radio
galaxies together with evidence on the age of the jets illustrate that the jets
are reoriented, a phenomenon known as spin-flip. Based on the galaxy luminosity
statistics we argue here that the typical galaxy encounters involve mass ratios
between 1:3 to 1:30 for the central black holes. Based on the spin-orbit
precession and gravitational radiation we also argue that for this typical mass
ratio in the inspiral phase of the merger the initially dominant orbital
angular momentum will become smaller than the spin, which will be reoriented.
We prove here that the spin-flip phenomenon typically occurs already in the
inspiral phase, and as such is describable by post-Newtonian techniques.",0805.4582v1
2009-01-29,Supersymmetric vacua and Bethe ansatz,"An announcement of some results of a longer paper where the supersymmetric
vacua of two dimensional N=2 susy gauge theories with matter are shown to be in
one-to-one correspondence with the eigenstates of integrable spin chain
Hamiltonians. The Heisenberg spin chain is mapped to the two dimensional U(N)
theory with fundamental hypermultiplets, the XXZ spin chain is mapped to the
analogous three dimensional super-Yang-Mills theory compactified on a circle,
the XYZ spin chain and eight-vertex model are related to the four dimensional
theory compactified on a torus. The correspondence extends to any spin group,
representations, boundary conditions, and inhomogeneity, it includes
Sinh-Gordon and non-linear Schroedinger models as well as the dynamical spin
chains such as the Hubbard model. Compactifications of four dimensional N=2
theories on a two-sphere lead to the instanton-corrected Bethe equations. We
propose a completely novel way for the Yangian, quantum affine, and elliptic
algebras to act as a symmetry of a union of quantum field theories.
  This paper accompanies arXiv:0901.4748",0901.4744v2
2009-03-02,"Ferromagnetic properties of p-(Cd,Mn)Te quantum wells: Interpretation of magneto-optical measurements by Monte Carlo simulations","In order to single out dominant phenomena that account for carrier-controlled
magnetism in p-(Cd,Mn)Te quantum wells we have carried out magneto-optical
measurements and Monte Carlo simulations of time dependent magnetization. The
experimental results show that magnetization relaxation is faster than 20 ns in
the paramagnetic state. Decreasing temperature below the Curie temperature Tc
results in an increase of the relaxation time but to less than 10 micro
seconds. This fast relaxation may explain why the spontaneous spin splitting of
electronic states is not accompanied by the presence of non-zero macroscopic
magnetization below Tc. Our Monte Carlo results reproduce the relative change
of the relaxation time on decreasing temperature. At the same time, the
numerical calculations demonstrate that antiferromagnetic spin-spin
interactions, which compete with the hole-mediated long-range ferromagnetic
coupling, play an important role in magnetization relaxation of the system. We
find, in particular, that magnetization dynamics is largely accelerated by the
presence of antiferromagnetic couplings to the Mn spins located outside the
region, where the holes reside. This suggests that macroscopic spontaneous
magnetization should be observable if the thickness of the layer containing
localized spins will be smaller than the extension of the hole wave function.
Furthermore, we study how a spin-independent part of the Mn potential affects
Tc. Our findings show that the alloy disorder potential tends to reduce Tc, the
effect being particularly strong for the attractive potential that leads to
hole localization.",0903.0406v1
2009-03-10,Interfacing nuclear spins in quantum dots to cavity or traveling-wave fields,"We show how to realize a quantum interface between optical fields and the
polarized nuclear spins in a singly charged quantum dot, which is strongly
coupled to a high-finesse optical cavity. An effective direct coupling between
cavity and nuclear spins is obtained by adiabatically eliminating the (far
detuned) excitonic and electronic states. The requirements needed to map qubit
and continuous variable states of cavity or traveling-wave fields to the
collective nuclear spin are investigated: For cavity fields, we consider
adiabatic passage processes to transfer the states. It is seen that a
significant improvement in cavity lifetimes beyond present-day technology would
be required for a quantum interface. We then turn to a scheme which couples the
nuclei to the output field of the cavity and can tolerate significantly shorter
cavity lifetimes. We show that the lifetimes reported in the literature and the
recently achieved nuclear polarization of ~90% allow both high-fidelity
read-out and write-in of quantum information between the nuclear spins and the
output field. We discuss the performance of the scheme and provide a convenient
description of the dipolar dynamics of the nuclei for highly polarized spins,
demonstrating that this process does not affect the performance of our
protocol.",0903.1727v2
2009-03-13,Unified Description of the Intrinsic Spin-Hall Effects,"The intrinsic spin-Hall effects (SHE) in $p$-doped semiconductors [S.
Murakami et al., Science 301, 1348 (2003)] and two-dimensional electron gases
with Rashba spin-orbit coupling [J. Sinova et al., Phys. Rev. Lett. 92, 126603
(2004)] have been the subject of many theoretical studies, but their driving
mechanisms have yet to be described in a unified manner. The former effect
arises from the adiabatic topological curvature of momentum space, from which
holes acquire a spin-dependent anomalous velocity. The SHE in the Rashba
system, on the other hand, results from the momentum-dependent spin dynamics in
the presence of an external electric field. The two effects clearly appear to
originate from distinct mechanisms. Our motivation for this article is to
address this apparent disparity and, in particular, to seek a unifying
description of the effects. In this endeavor, we consider the explicit
time-dependence of SHE systems starting with a general spin-orbit model. We
find that by performing a gauge transformation of the general model with
respect to time, a well-defined gauge field appears in time space which has the
physical significance of an effective magnetic field. This magnetic field is
shown to precisely account for the SHE in the Rashba system in the adiabatic
limit. Remarkably, by carefully analyzing the equation of motion of the general
model, this field component is also found to be the origin of the anomalous
velocity due to the momentum space curvature. Our study therefore unifies the
two seemingly disparate intrinsic SHEs under a common adiabatic framework.",0903.2305v2
2009-04-21,Tensor damping in metallic magnetic multilayers,"The mechanism of spin-pumping, described by Tserkovnyak et al., is formally
analyzed in the general case of a magnetic multilayer consisting of two or more
metallic ferromagnetic (FM) films separated by normal metal (NM) layers. It is
shown that the spin-pumping-induced dynamic coupling between FM layers modifies
the linearized Gilbert equations in a way that replaces the scalar Gilbert
damping constant with a nonlocal matrix of Cartesian damping tensors. The
latter are shown to be methodically calculable from a matrix algebra solution
of the Valet-Fert transport equations. As an example, explicit analytical
results are obtained for a 5-layer (spin-valve) of form NM/FM/NM'/FM/NM.
Comparisons with earlier well known results of Tserkovnyak et al. for the
related 3-layer FM/NM/FM indicate that the latter inadvertently hid the tensor
character of the damping, and instead singled out the diagonal element of the
local damping tensor along the axis normal to the plane of the two
magnetization vectors. For spin-valve devices of technological interest, the
influence of the tensor components of the damping on thermal noise or
spin-torque critical currents are strongly weighted by the relative magnitude
of the elements of the nonlocal, anisotropic stiffness-field tensor-matrix, and
for in-plane magnetized spin-valves are generally more sensitive to the
in-plane element of the damping tensor.",0904.3150v2
2009-09-21,Spin Waves and Switching: The Dynamics of Exchange - Biased Co Core - CoO Shell Nanoparticles,"The utility of nanoscaled ferromagnetic particles requires both stabilized
moments and maximized switching speeds. During reversal, the spatial modulation
of the nanoparticle magnetization evolves in time, and the energy differences
between each new configuration are accomodated by the absorption or emission
spin waves with different wavelengths and energy profiles. The switching speed
is limited by how quickly this spin wave energy is dissipated. We present here
the first observation of dispersing spin waves in a nanoscaled system, using
neutron scattering to detect spin waves in the CoO shells of exchange biased Co
core- CoO shell nanoparticles. Their dispersion is little affected by finite
size effects, but the spectral weight shifts to energies and wave vectors which
increase with decreasing system size. Core-shell coupling leads to a
substantial enhancement of the CoO spin wave population above its conventional
thermal level, suggesting a new mechanism for dissipating core switching
energy.",0909.3833v1
2010-02-24,Quantum Quenches in an XXZ Spin Chain from a Spatially Inhomogeneous Initial State,"Results are presented for the nonequilibrium dynamics of a quantum $XXZ$-spin
chain whose spins are initially arranged in a domain wall profile via the
application of a magnetic field in the $z$-direction which is spatially varying
along the chain. The system is driven out of equilibrium in two ways: a). by
rapidly turning off the magnetic field, b). by rapidly quenching the
interactions at the same time as the magnetic field is turned off. The
time-evolution of the domain wall profile as well as various two-point spin
correlation functions is studied by the exact solution of the fermionic problem
for the $XX$ chain and via a bosonization approach and a mean-field approach
for the $XXZ$ chain. At long times the magnetization is found to equilibrate
(reach the ground state value), while the two-point correlation functions in
general do not. In particular, for quenches within the gapless $XX$ phase, the
transverse spin correlation functions acquire a spatially inhomogeneous
structure at long times whose details depend on the initial domain wall
profile. The spatial inhomogeneity is also recovered for the case of classical
spins initially arranged in a domain wall profile and shows that the
inhomogeneities arise due to the dephasing of transverse spin components as the
domain wall broadens. A generalized Gibbs ensemble approach is found to be
inadequate in capturing this spatially inhomogeneous state.",1002.4446v3
2010-04-12,Magnetism in Fe-based superconductors,"In this review, we present a summary of experimental studies of magnetism in
Fe-based superconductors. The doping dependent phase diagram shows strong
similarities to the generic phase diagram of the cuprates. Parent compounds
exhibit magnetic order together with a structural phase transition both of
which are progressively suppressed with doping allowing superconductivity to
emerge. The stripe-like spin arrangement of Fe moments in the magnetically
ordered state shows the identical in-plane structure for the RFeAsO (R=rare
earth) and AFe2As2 (A=Sr, Ca, Ba, Eu and K) parent compounds, notably different
than the spin configuration of the cuprates. Interestingly, Fe1+yTe orders with
a different spin order despite very similar Fermi surface topology. Studies of
the spin dynamics in the parent compounds shows that the interactions are best
characterized as anisotropic three-dimensional (3D) interactions. Despite the
room temperature tetragonal structure, analysis of the low temperature spin
waves under the assumption of a Heisenberg Hamiltonian indicates strong
in-plane anisotropy with a significant next-near neighbor interaction. In the
superconducting state, a resonance, localized in both wavevector and energy is
observed in the spin excitation spectrum as in the cuprates. This resonance is
observed at a wavevector compatible with a Fermi surface nesting instability
independent of the magnetic ordering of the relevant parent compound. The
resonance energy (Er) scales with superconducting transition temperature (TC)
as Er ~4.9 kBTC consistent with the canonical value of ~5 kBTC observed in the
cuprates. Moreover, the relationship between the resonance energy and the
superconducting gap, \Delta, is similar to that observed in many unconventional
superconductors (Er/2\Delta ~ 0.64).",1004.1969v1
2010-04-28,Scalable quantum register based on coupled electron spins in a room temperature solid,"Realization of devices based on quantum laws might lead to building
processors that outperform their classical analogues and establishing
unconditionally secure communication protocols. Solids do usually present a
serious challenge to quantum coherence. However, owing to their spin-free
lattice and low spin orbit coupling, carbon materials and particularly diamond
are suitable for hosting robust solid state quantum registers. We show that
scalable quantum logic elements can be realized by exploring long range
magnetic dipolar coupling between individually addressable single electron
spins associated with separate color centers in diamond. Strong distance
dependence of coupling was used to characterize the separation of single qubits
98 A with unprecedented accuracy (3 A) close to a crystal lattice spacing. Our
demonstration of coherent control over both electron spins, conditional
dynamics, selective readout as well as switchable interaction, opens the way
towards a room temperature solid state scalable quantum register. Since both
electron spins are optically addressable, this solid state quantum device
operating at ambient conditions provides a degree of control that is currently
available only for atomic systems.",1004.5090v1
2010-06-24,Nucleon Spin-Polarisabilities from Polarisation Observables in Low-Energy Deuteron Compton Scattering,"We investigate the dependence of polarisation observables in elastic deuteron
Compton scattering below the pion production threshold on the spin-independent
and spin-dependent iso-scalar dipole polarisabilities of the nucleon. The
calculation uses Chiral Effective Field Theory with dynamical Delta(1232)
degrees of freedom in the Small Scale Expansion at next-to-leading order.
Resummation of the NN intermediate rescattering states and including the Delta
induces sizeable effects. The analysis considers cross-sections and the
analysing power of linearly polarised photons on an unpolarised target, and
cross-section differences and asymmetries of linearly and circularly polarised
beams on a vector-polarised deuteron. An intuitive argument helps one to
identify kinematics in which one or several polarisabilities do not contribute.
Some double-polarised observables are only sensitive to linear combinations of
two of the spin-polarisabilities, simplifying a multipole-analysis of the data.
Spin-polarisabilities can be extracted at photon energies \gtrsim 100 MeV,
after measurements at lower energies of \lesssim 70 MeV provide high-accuracy
determinations of the spin-independent ones. An interactive Mathematica 7.0
notebook of our findings is available from hgrie@gwu.edu.",1006.4849v2
2010-10-13,Simulating merging binary black holes with nearly extremal spins,"Astrophysically realistic black holes may have spins that are nearly extremal
(i.e., close to 1 in dimensionless units). Numerical simulations of binary
black holes are important tools both for calibrating analytical templates for
gravitational-wave detection and for exploring the nonlinear dynamics of curved
spacetime. However, all previous simulations of binary-black-hole inspiral,
merger, and ringdown have been limited by an apparently insurmountable barrier:
the merging holes' spins could not exceed 0.93, which is still a long way from
the maximum possible value in terms of the physical effects of the spin. In
this paper, we surpass this limit for the first time, opening the way to
explore numerically the behavior of merging, nearly extremal black holes.
Specifically, using an improved initial-data method suitable for binary black
holes with nearly extremal spins, we simulate the inspiral (through 12.5
orbits), merger and ringdown of two equal-mass black holes with equal spins of
magnitude 0.95 antialigned with the orbital angular momentum.",1010.2777v3
2011-02-02,Phase relationship between the long-time beats of free induction decays and spin echoes in solids,"Recent theoretical work on the role of microscopic chaos in the dynamics and
relaxation of many-body quantum systems has made several experimentally
confirmed predictions about the systems of interacting nuclear spins in solids,
focusing, in particular, on the shapes of spin echo responses measured by
nuclear magnetic resonance (NMR). These predictions were based on the idea that
the transverse nuclear spin decays evolve in a manner governed at long times by
the slowest decaying eigenmode of the quantum system, analogous to a chaotic
resonance in a classical system. The present paper extends the above
investigations both theoretically and experimentally. On the theoretical side,
the notion of chaotic eigenmodes is used to make predictions about the
relationships between the long-time oscillation phase of the nuclear free
induction decay (FID) and the amplitudes and phases of spin echoes. On the
experimental side, the above predictions are tested for the nuclear spin decays
of F-19 in CaF2 crystals and Xe-129 in frozen xenon. Good agreement between the
theory and the experiment is found.",1102.0527v2
2011-03-07,Density of defects and the scaling law of the entanglement entropy in quantum phase transition of one dimensional spin systems induced by a quench,"We have studied quantum phase transition induced by a quench in different one
dimensional spin systems. Our analysis is based on the dynamical mechanism
which envisages nonadiabaticity in the vicinity of the critical point. This
causes spin fluctuation which leads to the random fluctuation of the Berry
phase factor acquired by a spin state when the ground state of the system
evolves in a closed path. The two-point correlation of this phase factor is
associated with the probability of the formation of defects. In this framework,
we have estimated the density of defects produced in several one dimensional
spin chains. At the critical region, the entanglement entropy of a block of $L$
spins with the rest of the system is also estimated which is found to increase
logarithmically with $L$. The dependence on the quench time puts a constraint
on the block size $L$. It is also pointed out that the Lipkin-Meshkov-Glick
model in point-splitting regularized form appears as a combination of the XXX
model and Ising model with magnetic field in the negative z-axis. This unveils
the underlying conformal symmetry at criticality which is lost in the sharp
point limit. Our analysis shows that the density of defects as well as the
scaling behavior of the entanglement entropy follows a universal behavior in
all these systems.",1103.1212v1
2011-03-18,The galactic spin of AGN galaxies,"Using an extensive sample of galaxies selected from the Sloan Digital Sky
Survey Data Release 5, we compare the angular momentum distribution of active
galactic nucleus (AGN) with non-AGN hosting late-type galaxies. To this end we
characterize galactic spin through the dimensionless angular momentum parameter
$\lambda$, which we estimate approximately through simple dynamical
considerations. Using a volume limited sample, we find a considerable
difference when comparing the empirical distributions of $\lambda$ for AGNs and
non-AGN galaxies, the AGNs showing typically low $\lambda$ values and
associated dispersions, while non-AGNs present higher $\lambda$ values and a
broader distribution. A more striking difference is found when looking at
$\lambda$ distributions in thin $M_{r}$ cuts, while the spin of non-AGN
galaxies presents an anti-correlation with $M_{r}$, with bright (massive)
galaxies having low spins, AGN host galaxies present uniform values of
$\lambda$ at all magnitudes, a behavior probably imposed by the fact that most
late-type AGN galaxies present a narrow range in color, with a typical constant
$\lambda$ value. We also find that the fraction of AGN hosting galaxies in our
sample strongly depends on galactic spin, increasing dramatically for
decreasing $\lambda$. For AGN host galaxies we compute the mass of their
supermassive black holes and find that this value tends to be higher for low
spin galaxies, even at fixed luminosity, a result that could account, to a
certain extent, for the spread on the luminosity black-hole mass relation.",1103.3542v3
2013-09-30,Synthesis of thin silicon dioxide layers with high E' center densities and investigation of the E' center spin relaxation dynamics for single spin readout applications,"Methods for the creation of thin amorphous silicon dioxide (aSiO2) layers on
crystalline silicon substrates with very high densities of silicon dangling
bonds (so called E' centers) have been explored and volume densities of [E']>
5x10^18 cm-3 throughout a 60nm thick film have been demonstrated by exposure of
a thermal oxide layer to a low pressure Argon radio frequency plasma. While the
generated high E' center densities can be annealed completely at 300C, they are
comparatively stable at room temperature with a half life of about one month.
Spin relaxation time measurements of these states between T = 5K and T = 70K
show that the phase relaxation time T2 does not strongly depend on temperature
and compared to SiO2 films of lower E' density, is significantly shortened. The
longitudinal relaxation time T1 ~195(5)us at room temperature is in agreement
with low-density SiO2. In contrast, T1 ~625(51)us at T = 5K is much shorter
than in films of lower E' density. These results are discussed in the context
of E' centers being used as probe spins for spin-selection rules based single
spin-readout.",1310.0094v1
2013-11-29,Optical signatures of antiferromagnetic ordering of fermionic atoms in an optical lattice,"We show how off-resonant light scattering can provide quantitative
information on antiferromagnetic ordering of a two-species fermionic atomic gas
in a tightly-confined two-dimensional optical lattice. We analyze the emerging
magnetic ordering of atoms in the mean-field and in random phase approximations
and show how the many-body static and dynamic correlations, evaluated in the
standard Feynman-Dyson perturbation series, can be detected in the scattered
light signal. The staggered magnetization reveals itself in the magnetic Bragg
peaks of the individual spin components. These magnetic peaks, however, can be
considerably suppressed in the absence of a true long-range antiferromagnetic
order. The light scattered outside the diffraction orders can be collected by a
lens a with highly improved signal-to-shot-noise ratio when the diffraction
maxima are blocked. The collective and single-particle excitations are
identified in the spectrum of the scattered light. We find that the
spin-conserving and spin-exchanging atomic transitions convey information on
density, longitudinal spin, and transverse spin correlations. The different
correlations and scattering processes exhibit characteristic angular
distribution profiles for the scattered light and, e.g., the diagnostic signal
of transverse spin correlations could be separated from the signal by the
scattering direction, frequency, or polarization. We also analyze the detection
accuracy by estimating the number of required measurements, constrained by the
heating rate that is determined by inelastic light scattering events. The
imaging technique could be extended to the two-species fermionic states in
other regions of the phase diagram where the ground state properties are still
not fully understood.",1311.7605v1
2014-07-10,Two-color spin noise spectroscopy: Using spin fluctuation correlations to reveal homogeneous linewidths within quantum dot ensembles,"""Spin noise spectroscopy"" (SNS) is a powerful optical technique for probing
electron and hole spin dynamics that is based on detecting their intrinsic and
random fluctuations while in thermal equilibrium, an approach guaranteed by the
fluctuation-dissipation theorem. Because SNS measures fluctuation properties
rather than conventional response functions, we show that fluctuation
\emph{correlations} can be exploited in multi-probe noise studies to reveal
information that in general cannot be accessed by conventional linear optical
spectroscopy, such as the underlying homogeneous linewidths of individual
constituents within inhomogeneously-broadened systems. This is demonstrated in
an ensemble of singly-charged (In,Ga)As quantum dots using two weak probe
lasers: When the two lasers have the same wavelength, they are sensitive to the
same QDs in the ensemble and their spin fluctuation signals are correlated. In
contrast, two probe lasers that are widely detuned from each other measure
different subsets of QDs, leading to uncorrelated fluctuations. Measuring the
noise correlation versus laser detuning directly reveals the QD homogeneous
linewidth even in the presence of a strong inhomogeneous broadening. Such
noise-based correlation techniques are not limited to semiconductor spin
systems, but can be widely applied to any system in which intrinsic
fluctuations are measurable.",1407.2962v1
2014-12-29,Structural properties and spin-phonon coupling in orthorhombic Y-substituted GdMnO$_{3}$,"We present a systematic study of the structure and lattice dynamics at room
temperature, and the phonon behavior at low temperatures in orthorhombic
Gd$_{1-x}$Y$_{x}$MnO$_{3}$ manganites, with 0 $\leq$ x $\leq$ 0.4, using powder
x-ray diffraction and Raman scattering. A thorough analysis towards the
correlation between both structural and Raman modes parameters was undertaken.
The data obtained at room temperature reveal structural distortions arising
from the Jahn-Teller distortion and octahedra tilting. The Jahn-Teller
distortion is apparently x-independent, while an increase of Mn-O1-Mn bond
angle of about 0.5{\deg} could be ascertain when x changes from 0 to 0.4.
Spin-phonon coupling was evidenced from the Raman results. The temperature
dependence of the B1g in-plane O2 stretching mode of the MnO6 octahedron has
revealed either a positive or negative shift regarding the pure anharmonic
temperature dependence of the phonon frequency, which strongly depends on the
Y-concentration. The frequency renormalization is explained in terms of a
competition between ferro and antiferromagnetic interactions. The ratio between
the spin-phonon coupling constant and the effective magnetic exchange integral
per spin was determined from the renormalized wave number of the in-plane O2
stretching mode, associated with the spin-spin correlation function.",1412.8350v2
2015-01-13,Room-Temperature in situ Nuclear Spin Hyperpolarization from Optically-Pumped Nitrogen Vacancy Centers in Diamond,"We report bulk, room-temperature hyperpolarization of 13C nuclear spins
observed via high-field nuclear magnetic resonance (NMR). The hyperpolarization
is achieved by optical pumping (OP) of nitrogen vacancy defect centers in
diamond accompanied by dynamic nuclear polarization (DNP). The technique
harnesses the large optically-induced spin polarization of NV- centers at room
temperature, which is many orders of magnitude greater than thermal equilibrium
polarization and typically achievable only at sub-Kelvin temperatures. Transfer
of the spin polarization to the 13C nuclear spins is accomplished via a
combination of OP and microwave irradiation. The OP/DNP is performed at 420 mT,
where inductive detection of NMR is feasible, in contrast to the typically
exploited level anticrossing regimes at 100 mT and 50 mT. Here, we report a
bulk nuclear spin polarization of 6%. This polarization was generated in situ
and detected with a standard, inductive NMR probe without the need for sample
shuttling or precise crystal orientation. Hyperpolarization via OP/DNP should
operate at arbitrary magnetic fields, enabling orders of magnitude sensitivity
enhancement for NMR of solids and liquids at ambient conditions.",1501.02897v1
2015-02-24,"Quantum sweeps, synchronization, and Kibble-Zurek physics in dissipative quantum spin systems","We address dissipation effects on the non-equilibrium quantum dynamics of an
ensemble of spins-1/2 coupled via an Ising interaction. Dissipation is modeled
by a (ohmic) bath of harmonic oscillators at zero temperature and correspond
either to the sound modes of a one-dimensional Bose-Einstein (quasi-)condensate
or to the zero-point fluctuations of a long transmission line. We consider the
dimer comprising two spins and the quantum Ising chain with long-range
interactions, and develop a (mathematically and numerically) exact stochastic
approach to address non-equilibrium protocols in the presence of an
environment. For the two spin case, we first investigate the dissipative
quantum phase transition induced by the environment through quantum quenches,
and study the effect of the environment on the synchronization properties.
Then, we address Landau-Zener-Stueckelberg-Majorana protocols for two spins,
and for the spin array. In this latter case, we adopt a stochastic mean-field
point of view and present a Kibble-Zurek type argument to account for
interaction effects in the lattice. Such dissipative quantum spin arrays can be
realized in ultra-cold atoms, trapped ions, mesoscopic systems, and are related
to Kondo lattice models.",1502.06863v4
2015-02-26,"Strong Interplay between Stripe Spin Fluctuations, Nematicity and Superconductivity in FeSe","Elucidating the microscopic origin of nematic order in iron-based
superconducting materials is important because the interactions that drive
nematic order may also mediate the Cooper pairing. Nematic order breaks
fourfold rotational symmetry in the iron plane, which is believed to be driven
by either orbital or spin degrees of freedom. However, as the nematic phase
often develops at a temperature just above or coincides with a stripe magnetic
phase transition, experimentally determining the dominant driving force of
nematic order is difficult. Here, we use neutron scattering to study
structurally the simplest iron-based superconductor FeSe, which displays a
nematic (orthorhombic) phase transition at $T_s=90$ K, but does not order
antiferromagnetically. Our data reveal substantial stripe spin fluctuations,
which are coupled with orthorhombicity and are enhanced abruptly on cooling to
below $T_s$. Moreover, a sharp spin resonance develops in the superconducting
state, whose energy (~4 meV) is consistent with an electron boson coupling mode
revealed by scanning tunneling spectroscopy, thereby suggesting a spin
fluctuation-mediated sign-changing pairing symmetry. By normalizing the dynamic
susceptibility into absolute units, we show that the magnetic spectral weight
in FeSe is comparable to that of the iron arsenides. Our findings support
recent theoretical proposals that both nematicity and superconductivity are
driven by spin fluctuations.",1502.07544v1
2015-08-27,Coherent population trapping of a single nuclear spin under ambient conditions,"Coherent control of quantum systems has far-reaching implications in quantum
engineering. In this context, coherent population trapping (CPT) involving dark
resonances has played a prominent role, leading to a wealth of major
applications including laser cooling of atoms and molecules, optical
magnetometry, light storage and highly precise atomic clocks. Extending CPT
methods to individual solid-state quantum systems has been only achieved in
cryogenic environments for electron spin impurities and superconducting
circuits. Here, we demonstrate efficient CPT of a single nuclear spin in a room
temperature solid. To this end, we make use of a three-level system with a
$\Lambda$-configuration in the microwave domain, which consists of nuclear spin
states addressed through their hyperfine coupling to the electron spin of a
single nitrogen-vacancy defect in diamond. Dark state pumping requires a
relaxation mechanism which, in atomic systems, is simply provided by
spontaneous emission. In this work, the relaxation process is externally
controlled through incoherent optical pumping and separated in time from
consecutive coherent microwave excitations of the nuclear spin
$\Lambda$-system. Such a pumping scheme with controlled relaxation allows us
(i) to monitor the sequential accumulation of population into the dark state
and (ii) to reach a new regime of CPT dynamics for which periodic arrays of
dark resonances can be observed, owing to multiple constructive interferences.
This work offers new prospects for quantum state preparation, information
storage in hybrid quantum systems and metrology.",1508.06914v2
2015-09-17,Ising Spin Network States for Loop Quantum Gravity: a Toy Model for Phase Transitions,"Non-perturbative approaches to quantum gravity call for a deep understanding
of the emergence of geometry and locality from the quantum state of the
gravitational field. Without background geometry, the notion of distance should
entirely emerge from the correlations between the gravity fluctuations. In the
context of loop quantum gravity, quantum states of geometry are defined as spin
networks. These are graphs decorated with spin and intertwiners, which
represent quantized excitations of areas and volumes of the space geometry.
Here, we develop the condensed matter point of view on extracting the physical
and geometrical information out of spin network states: we introduce new Ising
spin network states, both in 2d on a square lattice and in 3d on a hexagonal
lattice, whose correlations map onto the usual Ising model in statistical
physics. We construct these states from the basic holonomy operators of loop
gravity and derive a set of local Hamiltonian constraints which entirely
characterize our states. We discuss their phase diagram and show how the
distance can be reconstructed from the correlations in the various phases.
Finally, we propose generalizations of these Ising states, which open the
perspective to study the coarse graining and dynamics of spin network states
using well-known condensed matter techniques and results.",1509.05297v1
2016-01-05,Quantum revivals and magnetization tunneling in effective spin systems,"Quantum mechanical objects or nanoobjects have been proposed as bits for
information storage. While time-averaged properties of magnetic,
quantum-mechanical particles have been extensively studied experimentally and
theoretically, experimental investigations of the real time evolution of
magnetization in the quantum regime were not possible until recent developments
in pump-probe techniques. Here we investigate the quantum dynamics of effective
spin systems by means of analytical and numerical treatments. Particular
attention is paid to the quantum revival time and its relation to the
magnetization tunneling. The quantum revival time has been initially defined as
the recurrence time of a total wave-function. Here we show that the quantum
revivals of wave-functions and expectation values in spin systems may be quite
different which gives rise to a more sophisticated definition of the quantum
revival within the realm of experimental research. Particularly, the revival
times for integer spins coincide which is not the case for half-integer spins.
Furthermore, the quantum revival is found to be shortest for integer ratios
between the on-site anisotropy and an external magnetic field paving the way to
novel methods of anisotropy measurements. We show that the quantum tunneling of
magnetization at avoided level crossing is coherent to the quantum revival time
of expectation values, leading to a connection between these two fundamental
properties of quantum mechanical spins.",1601.00803v1
2016-01-25,Notch filtering the nuclear environment of a spin qubit,"Electron spins in gate-defined quantum dots provide a promising platform for
quantum computation. In particular, spin-based quantum computing in gallium
arsenide takes advantage of the high quality of semiconducting materials,
reliability in fabricating arrays of quantum dots, and accurate qubit
operations. However, the effective magnetic noise arising from the hyperfine
interaction with uncontrolled nuclear spins in the host lattice constitutes a
major source of decoherence. Low frequency nuclear noise, responsible for fast
(10 ns) inhomogeneous dephasing, can be removed by echo techniques. High
frequency nuclear noise, recently studied via echo revivals, occurs in narrow
frequency bands related to differences in Larmor precession of the three
isotopes $\mathbf{^{69}Ga}$, $\mathbf{^{71}Ga}$, and $\mathbf{^{75}As}$. Here
we show that both low and high frequency nuclear noise can be filtered by
appropriate dynamical decoupling sequences, resulting in a substantial
enhancement of spin qubit coherence times. Using nuclear notch filtering, we
demonstrate a spin coherence time ($\mathbf{T_{2}}$) of 0.87 ms, five orders of
magnitude longer than typical exchange gate times, and exceeding the longest
coherence times reported to date in Si/SiGe gate-defined quantum dots.",1601.06677v3
2016-03-22,Nonlinear tides in a homogeneous rotating planet or star: global simulations of the elliptical instability,"I present results from the first global hydrodynamical simulations of the
elliptical instability in a tidally deformed gaseous planet (or star) with a
free surface. The elliptical instability is potentially important for tidal
evolution of the shortest-period hot Jupiters. I model the planet as a
spin-orbit aligned or anti-aligned, and non-synchronously rotating, tidally
deformed, homogeneous fluid body. A companion paper presented an analysis of
the global modes and instabilities of such a planet. Here I focus on the
nonlinear evolution of the elliptical instability. This is observed to produce
bursts of turbulence that drive the planet towards synchronism with its orbit
in an erratic manner. If the planetary spin is initially anti-aligned, the
elliptical instability also drives spin-orbit alignment on a similar timescale
as the spin synchronisation. The instability generates differential rotation
inside the planet in the form of zonal flows, which play an important role in
the saturation of the instability, and in producing the observed burstiness.
These results are broadly consistent with the picture obtained using a local
Cartesian model (where columnar vortices played the role of zonal flows). I
also simulate the instability in a container that is rigid (but stress-free)
rather than free, finding broad quantitative agreement. The dissipation
resulting from the elliptical instability could explain why the shortest-period
hot Jupiters tend to have circular orbits inside about 2-3 days, and predicts
spin-synchronisation (and spin-orbit alignment) out to about 10-15 days.
However, other mechanisms must be invoked to explain tidal circularisation for
longer orbital periods.",1603.06840v1
2016-04-08,Coherent transfer of electron spin correlations assisted by dephasing noise,"Quantum coherence of superposed states, especially of entangled states, is
indispensable for many quantum technologies. However, it is vulnerable to
environmental noises, posing a fundamental challenge in solid-state systems
including spin qubits. Here we show a scheme of entanglement engineering where
pure dephasing assists the generation of quantum entanglement at distant sites
in a chain of electron spins confined in semiconductor quantum dots. One party
of an entangled spin pair, prepared at a single site, is transferred to the
next site and then adiabatically swapped with a third spin using a transition
across a multi-level avoided crossing. This process is accelerated by the
noise-induced dephasing through a variant of the quantum Zeno effect, without
sacrificing the coherence of the entangled state. Our finding brings insight
into the spin dynamics in open quantum systems coupled to noisy environments,
opening an avenue to quantum state manipulation utilizing decoherence effects.",1604.02232v2
2016-06-15,Coupling a single electron spin to a microwave resonator: Controlling transverse and longitudinal couplings,"Microwave-frequency superconducting resonators are ideally suited to perform
dispersive qubit readout, to mediate two-qubit gates, and to shuttle states
between distant quantum systems. A prerequisite for these applications is a
strong qubit-resonator coupling. Strong coupling between an electron-spin qubit
and a microwave resonator can be achieved by correlating spin- and orbital
degrees of freedom. This correlation can be achieved through the Zeeman
coupling of a single electron in a double quantum dot to a spatially
inhomogeneous magnetic field generated by a nearby nanomagnet. In this paper,
we consider such a device and estimate spin-resonator couplings of order ~ 1
MHz with realistic parameters. Further, through realistic simulations, we show
that precise placement of the double dot relative to the nanomagnet allows to
select between a purely longitudinal coupling (commuting with the bare spin
Hamiltonian) and a purely transverse (spin non-conserving) coupling.
Additionally, we suggest methods to mitigate dephasing and relaxation channels
that are introduced in this coupling scheme. This analysis gives a clear route
toward the realization of coherent state transfer between a microwave resonator
and a single electron spin in a GaAs double quantum dot with a fidelity above
90%. Improved dynamical decoupling sequences, low-noise environments, and
longer-lived microwave cavity modes may lead to substantially higher fidelities
in the near future.",1606.04736v3
2016-06-28,Perspective: Ultrafast magnetism and THz spintronics,"This year the discovery of femtosecond demagnetization by laser pulses is 20
years old. For the first time this milestone work by Bigot and coworkers gave
insight in a very direct way into the time scales of microscopic interactions
that connect the spin and electron system. While intense discussions in the
field were fueled by the complexity of the processes in the past, it now became
evident that it is a puzzle of many different parts. Rather than giving an
overview that has been presented in previous reviews on ultrafast processes in
ferromagnets, this perspective will show that with our current depth of
knowledge the first real applications are on their way: THz spintronics and
all-optical spin manipulation are becoming more and more feasible. The aim of
this perspective is to point out where we can connect the different puzzle
pieces of understanding gathered over 20 years to develop novel applications.
based on many observations in a large number of experiments. Differences in the
theoretical models arise from the localized and delocalized nature of
ferromagnetism. Transport effects are intrinsically non-local in spintronic
devices and at interfaces. We review the need for multiscale modeling to
address processes starting from electronic excitation of the spin system on the
picometer length scale and sub-femtosecond time scale, to spin wave generation,
and towards the modeling of ultrafast phase transitions that altogether
determine the response time of the ferromagnetic system. Today, our current
understanding gives rise to the first real applications of ultrafast spin
physics for ultrafast magnetism control: THz spintronic devices. This makes the
field of ultrafast spin-dynamics an emerging topic open for many researchers
right now.",1606.08725v1
2016-09-01,Topical Review: Spins and mechanics in diamond,"There has been rapidly growing interest in hybrid quantum devices involving a
solid-state spin and a macroscopic mechanical oscillator. Such hybrid devices
create exciting opportunities to mediate interactions between disparate qubits
and to explore the quantum regime of macroscopic mechanical objects. In
particular, a system consisting of the nitrogen-vacancy defect center in
diamond coupled to a high quality factor mechanical oscillator is an appealing
candidate for such a hybrid quantum device, as it utilizes the highly coherent
and versatile spin properties of the defect center. In this paper, we will
review recent experimental progress on diamond-based hybrid quantum devices in
which the spin and orbital dynamics of single defects are driven by the motion
of a mechanical oscillator. In addition, we discuss prospective applications
for this device, including long range, phonon-mediated spin-spin interactions,
and phonon cooling in the quantum regime. We conclude the review by evaluating
the experimental limitations of current devices and identifying alternative
device architectures that may reach the strong coupling regime.",1609.00418v2
2017-02-08,A magnetic phase-transition graphene transistor with tunable spin polarization,"Graphene nanoribbons (GNRs) have been proposed as potential building blocks
for field effect transistor (FET) devices due to their quantum confinement
bandgap. Here, we propose a novel GNR device concept, enabling the control of
both charge and spin signals, integrated within the simplest three-terminal
device configuration. In a conventional FET device, a gate electrode is
employed to tune the Fermi level of the system in and out of a static bandgap.
By contrast, in the switching mechanism proposed here, the applied gate voltage
can dynamically open and close an interaction gap, with only a minor shift of
the Fermi level. Furthermore, the strong interplay of the band structure and
edge spin configuration in zigzag ribbons enables such transistors to carry
spin polarized current without employing an external magnetic field or
ferromagnetic contacts. Using an experimentally validated theoretical model, we
show that such transistors can switch at low voltages and high speed, and the
spin polarization of the current can be tuned from 0% to 50% by using the same
back gate electrode. Furthermore, such devices are expected to be robust
against edge irregularities and can operate at room temperature. Controlling
both charge and spin signal within the simplest FET device configuration could
open up new routes in data processing with graphene based devices.",1702.02458v1
2017-02-17,Enhanced concentrations of nitrogen-vacancy centers in diamond through TEM irradiation,"The studies of many-body dynamics of interacting spin ensembles, as well as
quantum sensing in solid state systems, are often limited by the need for high
spin concentrations, along with efficient decoupling of the spin ensemble of
interest from its spin-bath environment. In particular, for an ensemble of
nitrogen-vacancy (NV) centers in diamond, high conversion efficiencies between
nitrogen (P1) defects and NV centers are essential, while maintaining long
coherence times of an NV ensemble. In this work, we study the effect of
electron irradiation on the conversion efficiency and the coherence time of
various types of diamond samples with different initial nitrogen
concentrations. The samples were irradiated using a 200 keV transmission
electron microscope (TEM). Our study reveals that the efficiency of NV creation
strongly depends on the initial conversion efficiency as well as on the initial
nitrogen concentration. We observe an order of magnitude improvement in the NV
concentration (up to $\sim 10^{11}$ NV/cm^2), without any degradation in their
coherence times of $\sim 180$ \mu m. We address the potential of this technique
to pave the way toward the study of many-body physics of ensembles of NV spins,
and contribute to the creation of non-classical spin states for quantum
sensing.",1702.05332v3
2017-03-21,Sensitive detection of level anti-crossing spectra of nitrogen-vacancy centers in diamond,"We report a study of the magnetic field dependence of photoluminescence of
NV$^-$ centers (negatively charged nitrogen-vacancy centers) in diamond single
crystals. In such a magnetic field dependence characteristic sharp features are
observed, which are coming from Level Anti-Crossings (LACs) in a coupled
electron-nuclear spin system. For sensitive detection of such LAC-lines we use
lock-in detection to measure the photoluminescence intensity. This experimental
technique allows us to obtain new LAC lines. Additionally, a remarkably strong
dependence of the LAC-lines on the modulation frequency is found. Specifically,
upon decrease of the modulation frequency from 12 kHz to 17 Hz the amplitude of
the LAC-lines increases by approximately two orders of magnitude. To take a
quantitative account for such effects, we present a theoretical model, which
describes the spin dynamics in a coupled electron-nuclear spin system under the
action of an oscillating external magnetic field. Good agreement between
experiments and theory allows us to conclude that the observed effects are
originating from coherent spin polarization exchange in a coupled spin system
comprising the spin-polarized NV$^-$ center. Our results are of great practical
importance allowing one to optimize the experimental conditions for probing
LAC-derived lines in diamond crystals comprising NV$^-$ centers and for
indirect detection and identification of other paramagnetic defect centers.",1703.07101v1
2017-08-19,Coarsening model on $\mathbb{Z}^d$ with biased zero-energy flips and an exponential large deviation bound for ASEP,"We study the coarsening model (zero-temperature Ising Glauber dynamics) on
$\mathbb{Z}^d$ (for $d \geq 2$) with an asymmetric tie-breaking rule. This is a
Markov process on the state space $\{-1,+1\}^{\mathbb{Z}^d}$ of ""spin
configurations"" in which each vertex updates its spin to agree with a majority
of its neighbors at the arrival times of a Poisson process. If a vertex has
equally many $+1$ and $-1$ neighbors, then it updates its spin value to $+1$
with probability $q \in [0,1]$ and to $-1$ with probability $1-q$. The initial
state of this Markov chain is distributed according to a product measure with
probability $p$ for a spin to be $+1$. In this paper, we show that for any
given $p>0$, there exist $q$ close enough to 1 such that a.s. every spin has a
limit of $+1$. This is of particular interest for small values of $p$, for
which it is known that if $q=1/2$, a.s. all spins have a limit of $-1$. For
dimension $d=2$, we also obtain near-exponential convergence rates for $q$
sufficiently large, and for general $d$, we obtain stretched exponential rates
independent of $d$. Two important ingredients in our proofs are refinements of
block arguments of Fontes-Schonmann-Sidoravicius and a novel exponential large
deviation bound for the Asymmetric Simple Exclusion Process.",1708.05806v2
2017-08-29,Spin wave damping arising from phase coexistence below $T_c$ in colossal magnetoresistive La$_{0.7}$Ca$_{0.3}$MnO$_3$,"While the spin dynamics of La$_{0.7}$Ca$_{0.3}$MnO$_3$ in the ferromagnetic
phase are known to be unconventional, previous measurements have yielded
contradictory results regarding the damping of spin wave excitations. Neutron
spectroscopy measurements on a sample with a transition temperature of
$T_c$=257 K, higher than most single crystals, unambiguously reveal an
anomalous increase in spin wave damping for excitations approaching the
Brillouin zone boundary along the [$100$] direction that cannot be explained as
an artifact due to a noninteracting phonon branch. Spin waves throughout the
($HK0$) plane display a common trend where the spin wave damping is dependent
upon the excitation energy, increasing for energies above roughly 15 meV and
reaching a full width at half maximum of at least 20 meV. The results are
consistent with a model of intrinsic spatial inhomogeneity with phase separated
regions approximately 18 {\AA} in size persisting over a large range of
temperatures below $T_c$.",1708.08960v2
2018-02-13,Spin-liquid-like state in a spin-1/2 square-lattice antiferromagnet perovskite induced by $d^{10}$-$d^0$ cation mixing,"A quantum spin liquid state has long been predicted to arise in spin-1/2
Heisenberg square-lattice antiferromagnets at the boundary region between
N\'eel (nearest-neighbor interaction dominates) and columnar
(next-nearest-neighbor dominates) antiferromagnetic order. However, there are
no known compounds in this region. Here we use $d^{10}$-$d^0$ cation mixing to
tune the magnetic interactions on the square lattice while simultaneously
introducing disorder. We find spin-liquid-like behavior in the double
perovskite Sr$_2$Cu(Te$_{0.5}$W$_{0.5}$)O$_6$, where the isostructural end
phases Sr$_2$CuTeO$_6$ and Sr$_2$CuWO$_6$ are N\'eel and columnar type
antiferromagnets, respectively. We show that magnetism in
Sr$_2$Cu(Te$_{0.5}$W$_{0.5}$)O$_6$ is entirely dynamic down to 19 mK.
Additionally, we observe at low temperatures for
Sr$_2$Cu(Te$_{0.5}$W$_{0.5}$)O$_6$, similar to several spin liquid candidates,
a plateau in muon spin relaxation rate and a strong $T$-linear dependence in
specific heat. Our observations for Sr$_2$Cu(Te$_{0.5}$W$_{0.5}$)O$_6$
highlight the role of disorder in addition to magnetic frustration in spin
liquid physics.",1802.04805v1
2018-04-19,3D dynamics and morphology of bow-shock Pulsar Wind Nebulae,"Bow-shock pulsar wind nebulae (PWNe) show a variety of morphological shapes.
We attribute this diversity to the geometrical factors: relative orientations
of the pulsar rotation axis, proper velocity, and the line of sight (magnetic
inclination angle may also have a certain influence on the morphology). We
identify three basic types of bow-shock nebulae: (i) a ""Rifle Bullet"" (pulsar
spin axis and proper velocity are aligned); (ii) a ""Frisbee"" (pulsar spin axis
and proper velocity are orthogonal with the spin axis lying in the plane of the
sky), and (iii) a Cart Wheel"" (like frisbee but the spin axis is perpendicular
to the plane of the sky). Using 3D RMHD simulations, as well as analytical
calculations, we reproduce the key morphological features of the bow-shock
PWNe, as well as variations, are seen across different systems. magnetic
stresses within the shocked pulsar wind affect the overall structure strongly,
producing ""whiskers"", ""tails"", ""filled-in"" and ""mushroom"" shapes, as well as
non-symmetric morphologies. On the other hand, the interstellar medium
inhomogeneities and the anisotropy of the energy flux in the pulsar wind have
only a mild impact of the PWN morphology. In a few cases, when we clearly
identify specific morphological structures, our results do not favor alignment
of the pulsar spin axis and proper velocity. Our calculations of the underlying
emission processes explain the low synchrotron X-ray efficiency (in terms of
the spin-down luminosity) and imply an energetical subdominant contribution of
the inverse Compton process.",1804.07327v2
2018-04-24,"Einstein-Podolsky-Rosen steering, depth of steering and planar spin squeezing in two-mode Bose-Einstein condensates","We show how one can prepare and detect entanglement and
Einstein-Podolsky-Rosen (EPR) steering between two distinguishable groups
(modes) of atoms in a Bose-Einstein condensate (BEC) atom interferometer. Our
paper extends previous work that developed criteria for two-mode entanglement
and EPR steering based on the reduced variances of two spins defined in a
plane. Observation of planar spin squeezing will imply entanglement, and
sufficient planar spin squeezing implies EPR steering, between the two groups
of atoms. By using a two-mode dynamical model to describe BEC interferometry
experiments, we show that the two-mode entanglement and EPR steering criteria
are predicted to be satisfied for realistic parameters. The reported
observation of spin squeezing in these parameter regimes suggests it is very
likely that the criteria can be used to infer an EPR steering between
mesoscopic groups of atoms, provided the total atom number can be determined to
sub-Poissonian uncertainty. The criteria also apply to a photonic Mach-Zehnder
interferometer. Finally, we give a method based on the amount of planar spin
squeezing to determine a lower bound on the number of particles that are
genuinely comprise the two-mode EPR steerable state - the so-called two-mode
EPR steering depth.",1804.09126v2
2019-05-20,Orbitally Dominated Rashba-Edelstein Effect in Noncentrosymmetric Antiferromagnets,"Efficient manipulation of magnetic order with electric current pulses is
desirable for achieving fast spintronic devices. The Rashba-Edelstein effect,
wherein a spin polarization is electrically induced in noncentrosymmetric
systems, provides a mean to achieve current-induced staggered spin-orbit
torques. Initially predicted for spin, the orbital counterpart of this effect
has been disregarded up to now. Here, we present a generalized Rashba-Edelstein
effect, which generates not only spin polarization but also orbital
polarization, which we find to be far from being negligible and could play a
crucial role in the magnetization dynamics. We show that the orbital
Rashba-Edelstein effect does not require spin-orbit coupling to exist. We
present first-principles calculations of the frequency-dependent spin and
orbital Rashba-Edelstein susceptibility tensors for the noncentrosymmetric
antiferromagnets CuMnAs and Mn2Au. We show that the electrically induced local
magnetization has both staggered in-plane components and non-staggered
out-of-plane components, and can exhibit Rashba-like or Dresselhaus-like
symmetries, depending on the magnetic configuration. Furthermore, there is an
induced local magnetization on the nonmagnetic atoms as well, that is smaller
in Mn2Au than in CuMnAs. We compute sizable induced magnetizations at optical
frequencies, which suggest that electric-field driven switching could be
achieved at much higher frequencies.",1905.08279v1
2019-05-25,Large-$S$ limit of the large-$N$ theory for the triangular antiferromagnet,"Large-$S$ and large-$N$ theories (spin value $S$ and spinor component number
$N$) are complementary, and sometimes conflicting, approaches to quantum
magnetism. While large-$S$ spin-wave theory captures the correct semiclassical
behavior, large-$N$ theories, on the other hand, emphasize the quantumness of
spin fluctuations. In order to evaluate the possibility of the non-trivial
recovery of the semiclassical magnetic excitations within a large-$N$ approach,
we compute the large-$S$ limit of the dynamic spin structure of the triangular
lattice Heisenberg antiferromagnet within a Schwinger boson spin
representation. We demonstrate that, only after the incorporation of Gaussian
($1/N$) corrections to the saddle-point ($N=\infty$) approximation, we are able
to exactly reproduce the linear spin wave theory results in the large-$S$
limit. The key observation is that the effect of $1/N$ corrections is to cancel
out exactly the main contribution of the saddle-point solution; while the
collective modes (magnons) consist of two spinon bound states arising from the
poles of the RPA propagator. This result implies that it is essential to
consider the interaction of the spinons with the emergent gauge fields and that
the magnon dispersion relation should not be identified with that of the
saddle-point spinons.",1905.10689v3
2020-07-29,The Bloch equation for spin dynamics in electron storage rings: computational and theoretical aspects,"In this paper we describe our work on spin polarization in high-energy
electron storage rings which we base on the Bloch equation for the polarization
density and which aims towards the e-/e+ option of the proposed Future Circular
Collider (FCC-ee) and the proposed Circular Electron Positron Collider (CEPC).
The Bloch equation takes into account non spin-flip and spin-flip effects due
to synchrotron radiation including the spin-diffusion effects and the
Sokolov-Ternov effect with its Baier-Katkov generalization as well as the
kinetic-polarization effect. This mathematical model is an alternative to the
standard mathematical model based on the Derbenev-Kondratenko formulas. For our
numerical and analytical studies of the Bloch equation we develop an
approximation to the latter to obtain an effective Bloch equation. This is
accomplished by finding a third mathematical model based on a system of
stochastic differential equations underlying the Bloch equation and by
approximating that system via the method of averaging from perturbative ODE
theory. We also give an overview of our algorithm for numerically integrating
the effective Bloch equation. This discretizes the phase space using spectral
methods and discretizes time via the additive Runge-Kutta method which is a
high-order semi-implicit method. We also discuss the relevance of the third
mathematical model for spin tracking.",2007.14613v1
2013-08-15,Hole propagation in the Kitaev-Heisenberg model: From quasiparticles in quantum Neel states to non-Fermi liquid in the Kitaev phase,"We explore with exact diagonalization the propagation of a single hole in
four magnetic phases of the t-J-like Kitaev-Heisenberg model on a honeycomb
lattice: the Neel antiferromagnetic, stripe, zigzag and Kitaev spin-liquid
phase. We find coherent propagation of spin-polaron quasiparticles in the
antiferromagnetic phase by a similar mechanism as in the $t$-$J$ model for
high-$T_c$ cuprates. In the stripe and zigzag phases clear quasiparticles
features appear in spectral functions of those propagators where holes are
created and annihilated on one sublattice, while they remain largely {\it
hidden} in those spectral functions that correspond to photoemission
experiments. As the most surprising result, we find a totally incoherent
spectral weight distribution for the spectral function of a hole moving in the
Kitaev spin-liquid phase in the strong coupling regime relevant for iridates.
At intermediate coupling the finite systems calculation reveals a well defined
quasiparticle at the $\Gamma$ point, however, we find that the gapless spin
excitations wipe out quasiparticles at finite momenta. Also for this more
subtle case we conclude that in the thermodynamic limit the lightly doped
Kitaev liquid phase does not support quasiparticle states in the neighborhood
of $\Gamma$, and therefore yields a {\it non-Fermi liquid}, contrary to earlier
suggestions based on slave-boson studies. These observations are supported by
the presented study of the dynamic spin-structure factor for the Kitaev spin
liquid regime.",1308.3373v3
2016-11-21,Relativistic orbits around spinning supermassive black holes. Secular evolution to 4.5 post-Newtonian order,"We derive the secular evolution of the orbital elements of a stellar-mass
object orbiting a spinning massive black hole. We use the post-Newtonian
approximation in harmonic coordinates, with test-body equations of motion for
the conservative dynamics that are valid through 3PN order, including
spin-orbit, quadrupole and (spin)$^2$ effects, and with radiation-reaction
contributions linear in the mass of the body that are valid through 4.5PN
order, including the 4PN damping effects of spin-orbit coupling. The evolution
equations for the osculating orbit elements are iterated to high PN orders
using a two-timescale approach and averaging over orbital timescales. We derive
a criterion for terminating the orbit when its Carter constant drops below a
critical value, whereupon the body plunges across the event horizon at the next
closest approach. The results are valid for arbitrary eccentricities and
arbitrary inclinations. We then analyze numerically the orbits of objects
injected into high-eccentricity orbits via interactions within a surrounding
star cluster, obtaining the number of orbits and the elapsed time between
injection and plunge, and the residual orbital eccentricity at plunge as a
function of inclination. We derive an analytic approximation for the time to
plunge in terms of initial orbital variables. We show that, if the black hole
is spinning rapidly, the flux of gravitational radiation during the final orbit
before plunge may be suppressed by as much as three orders of magnitude if the
orbit is retrograde on the equatorial plane compared to its prograde
counterpart.",1611.06931v1
2017-01-24,Tailoring spin defects in diamond,"Atomic-size spin defects in solids are unique quantum systems. Most
applications require nanometer positioning accuracy, which is typically
achieved by low energy ion implantation. So far, a drawback of this technique
is the significant residual implantation-induced damage to the lattice, which
strongly degrades the performance of spins in quantum applications. In this
letter we show that the charge state of implantation-induced defects
drastically influences the formation of lattice defects during thermal
annealing. We demonstrate that charging of vacancies localized at e.g.
individual nitrogen implantation sites suppresses the formation of vacancy
complexes, resulting in a tenfold-improved spin coherence time of single
nitrogen-vacancy (NV) centers in diamond. This has been achieved by confining
implantation defects into the space charge layer of free carriers generated by
a nanometer-thin boron-doped diamond structure. Besides, a twofold-improved
yield of formation of NV centers is observed. By combining these results with
numerical calculations, we arrive at a quantitative understanding of the
formation and dynamics of the implanted spin defects. The presented results
pave the way for improved engineering of diamond spin defect quantum devices
and other solid-state quantum systems.",1701.07055v1
2017-04-20,Orbital and spin ordering physics of the Mn$_3$O$_4$ spinel,"Motivated by recent experiments, we present a comprehensive theoretical study
of the geometrically frustrated strongly correlated magnetic insulator
Mn$_3$O$_4$ spinel oxide based on a microscopic Hamiltonian involving lattice,
spin and orbital degrees of freedom. Possessing the physics of degenerate e$_g$
orbitals, this system shows a strong Jahn-Teller effect at high temperatures.
Further, careful attention is paid to the special nature of the superexchange
physics arising from the 90$^o$ Mn-O-Mn bonding angle. The Jahn-Teller and
superexchange-based orbital-spin Hamiltonians are then analysed in order to
track the dynamics of orbital and spin ordering. We find that a
high-temperature structural transition results in orbital ordering whose nature
is mixed with respect to the two originally degenerate $e_{g}$ orbitals. This
ordering of orbitals is shown to relieve the intrinsic geometric frustration of
the spins on the spinel lattice, leading to ferrimagnetic Yafet-Kittel ordering
at low-temperatures. Finally, we develop a model for a magnetoelastic coupling
in Mn$_3$O$_4$, enabling a systematic understanding of the experimentally
observed complexity in the low-temperature structural and magnetic
phenomenology of this spinel. Our analysis predicts that a quantum
fluctuation-driven orbital-spin liquid phase may be stabilised at low
temperatures upon the application of pressure.",1704.06026v1
2018-05-01,Tracking the spin axes orbital alignment in selected binary systems - Torun Rossiter-McLaughlin effect survey,"We have obtained high-resolution spectra of four eclipsing binary systems (FM
Leo, NN Del, V963 Cen and AI Phe) with the view to gaining insight into the
relative orientation of their stellar spin axes and orbital axes. The so called
Rossiter-McLaughlin (RM) effect, i.e. the fact that the broadening and the
amount of blue- or redshift in the spectra during an eclipse depend on the tilt
of the spin axis of the background star, has the potential of reconciling
observations and theoretical models if such a tilt is found. We analyse the RM
effect by disentangling the spectra, removing the front component and measuring
the remaining, distorted lines with a broadening function (BF) obtained from
single value decomposition (SVD), weighting by the intensity centre of the BF
in the eclipse. All but one of our objects show no significant misalignment,
suggesting that aligned systems are dominant. We provide stellar as well as
orbital parameters for our systems. With five measured spin-orbit angles we
significantly increase (from 9 to 14) the number of stars for which it has been
measured. The spin-orbit angle $\beta$ calculated for AI Phe's secondary
component shows a misalignment of 87$\pm$17 degrees. NN Del, with a large
separation of components and a long dynamical timescale for circularisation and
synchronisation, is an example of a close to primordial spin-orbit angle
measurement.",1805.00520v1
2018-05-05,Theory of Radiative Electron Polarization in Strong Laser Fields,"Radiative polarization of electrons and positrons through the Sokolov-Ternov
effect is important for applications in high-energy physics. Radiative
spin-polarization is a manifestation of quantum radiation reaction affecting
the spin-dynamics of electrons. We recently proposed that an analogue of the
Sokolov-Ternov effect could occur in the strong electromagnetic fields of
ultra-high-intensity lasers, which would result in a build-up of
spin-polarization in femtoseconds. In this paper we develop a density matrix
formalism for describing beam polarization in strong electromagnetic fields. We
start by using the density matrix formalism to study spin-flips in non-linear
Compton scattering and its dependence on the initial polarization state of the
electrons. Numerical calculations show a radial polarization of the scattered
electron beam in a circularly polarized laser, and we find azimuthal
asymmetries in the polarization patterns for ultra-short laser pulses. A degree
of polarization approaching 9 % is achieved after emitting just a single
photon. We develop the theory by deriving a local constant crossed field
approximation (LCFA) for the polarization density matrix, which is a
generalization of the well known LCFA scattering rates. We find spin-dependent
expressions that may be included in electromagnetic charged-particle simulation
codes, such as particle-in-cell plasma simulation codes, using Monte-Carlo
modules. In particular, these expressions include the spin-flip rates for
arbitrary initial polarization of the electrons. The validity of the LCFA is
confirmed by explicit comparison with an exact QED calculation of electron
polarization in an ultrashort laser pulse.",1805.02027v2
2018-05-10,"Angular momenta, helicity, and other properties of dielectric-fiber and metallic-wire modes","Spin and orbital angular momenta (AM) of light are well studied for
free-space electromagnetic fields, even nonparaxial. One of the important
applications of these concepts is the information transfer using AM modes,
often via optical fibers and other guiding systems. However, the
self-consistent description of the spin and orbital AM of light in optical
media (including dispersive and metallic cases) was provided only recently
[K.Y. Bliokh et al., Phys. Rev. Lett. 119, 073901 (2017)]. Here we present the
first accurate calculations, both analytical and numerical, of the spin and
orbital AM, as well as the helicity and other properties, for the full-vector
eigenmodes of cylindrical dielectric and metallic (nanowire) waveguides. We
find remarkable fundamental relations, such as the quantization of the
canonical total AM of cylindrical guided modes in the general nonparaxial case.
This quantization, as well as the noninteger values of the spin and orbital AM,
are determined by the generalized geometric and dynamical phases in the mode
fields. Moreover, we show that the spin AM of metallic-wire modes is
determined, in the geometrical-optics approximation, by the transverse spin of
surface plasmon-polaritons propagating along helical trajectories on the wire
surface. Our work provides a solid platform for future studies and applications
of the AM and helicity properties of guided optical and plasmonic waves.",1805.03820v2
2018-05-22,"Single beam detection of optically driven spin dynamics in CdTe/(Cd,Mg)Te quantum wells","We study optical pumping of resident electron spins under resonant excitation
of trions in n-type CdTe/(Cd,Mg)Te quantum wells subject to a transverse
magnetic field. In contrast to the comprehensively used time-resolved
pump-probe techniques with polarimetric detection, we exploit here a single
beam configuration in which the time-integrated intensity of the excitation
laser light transmitted through the quantum wells is detected. The transmitted
intensity reflects the bleaching of light absorption due to optical pumping of
the resident electron spins and can be used to evaluate the Larmor precession
frequency of the optically oriented carriers and their spin relaxation time.
Application of the magnetic field leads to depolarization of the electron spin
ensemble so that the Hanle effect is observed. Excitation with a periodic
sequence of laser pulses leads to optical pumping in the rotating frame if the
Larmor precession frequency is synchronized with the pulse repetition rate.
This is manifested by the appearance of Hanle curves every 3.36 or 44.2 mT for
pulse repetition rates of 75.8 or 999 MHz, respectively. From the experimental
data we evaluate the g factor of |g|=1.61 and the spin relaxation time of 14 ns
for the optically pumped resident electrons, in agreement with previous
time-resolved pump-probe studies.",1805.08871v1
2008-07-09,An exactly solvable supersymmetric spin chain of BC_N type,"We construct a new exactly solvable supersymmetric spin chain related to the
BC_N extended root system, which includes as a particular case the BC_N version
of the Polychronakos-Frahm spin chain. We also introduce a supersymmetric spin
dynamical model of Calogero type which yields the new chain in the large
coupling limit. This connection is exploited to derive two different
closed-form expressions for the chain's partition function by means of
Polychronakos's freezing trick. We establish a boson-fermion duality relation
for the new chain's spectrum, which is in fact valid for a large class of (not
necessarily integrable) spin chains of BC_N type. The exact expressions for the
partition function are also used to study the chain's spectrum as a whole,
showing that the level density is normally distributed even for a moderately
large number of particles. We also determine a simple analytic approximation to
the distribution of normalized spacings between consecutive levels which fits
the numerical data with remarkable accuracy. Our results provide further
evidence that spin chains of Haldane-Shastry type are exceptional integrable
models, in the sense that their spacings distribution is not Poissonian, as
posited by the Berry-Tabor conjecture for ""generic'' quantum integrable
systems.",0807.1495v1
2014-06-16,Early Excitation of Spin-Orbit Misalignments in Close-in Planetary Systems,"Continued observational characterization of transiting planets that reside in
close proximity to their host stars has shown that a substantial fraction of
such objects posses orbits that are inclined with respect to the spin axes of
their stars. Mounting evidence for the wide-spread nature of this phenomenon
has challenged the conventional notion that large-scale orbital transport
occurs during the early epochs of planet formation and is accomplished via
planet-disk interactions. However, recent work has shown that the excitation of
spin-orbit misalignment between protoplanetary nebulae and their host stars can
naturally arise from gravitational perturbations in multi-stellar systems as
well as magnetic disk-star coupling. In this work, we examine these processes
in tandem. We begin with a thorough exploration of the
gravitationally-facilitated acquisition of spin-orbit misalignment and
analytically show that the entire possible range of misalignments can be
trivially reproduced. Moreover, we demonstrate that the observable spin-orbit
misalignment only depends on the primordial disk-binary orbit inclination.
Subsequently, we augment our treatment by accounting for magnetic torques and
show that more exotic dynamical evolution is possible, provided favorable
conditions for magnetic tilting. Cumulatively, our results suggest that
observed spin-orbit misalignments are fully consistent with disk-driven
migration as a dominant mechanism for the origin of close-in planets.",1406.4183v1
2014-06-20,Spin-orbit density wave: A new phase of matter applicable to the hidden order state of URu2Si2,"We provide a brief review and detailed analysis of the spin-orbit density
wave (SODW), proposed as a possible explanation to the `hidden order' phase of
URu2Si2. Due to the interplay between inter-orbital Coulomb interaction and
spin-orbit coupling (SOC) in this compound, the SODW is shown to arise from
Fermi surface nesting instability between two spin-orbit split bands. An
effective low-energy Hamiltonian including single-particle SOC and two-particle
SODW is derived, while numerical results are calculated by using
density-functional theory (DFT) based band structure input. Computed gapped
quasiparticle spectrum, entropy loss and spin-excitation spectrum are in
detailed agreement with experiments. Interestingly, despite the fact that SODW
governs dynamical spin-excitations, the static magnetic moment is calculated to
be zero, owing to the time-reversal invariance imposed by SOC. As a
consequence, SODW can be destroyed by finite magnetic field even at zero
temperature. Our estimation of the location of the quantum critical point is
close to the experimental value of Bc ~ 35 T. Finally, we extend the idea of
SODW to other SOC systems including iridium oxides (iridates) and
two-dimensional electronic systems such as BiAg2 surface and LaAlO3/SrTiO3
interface. We show hints of quasiparticle gapping, reduction of preexisting
magnetic moment, large magneto-resistance etc. in these systems which can be
explained consistently within the SODW theory.",1406.5271v2
2015-12-15,Local Magnetism and Spin Dynamics of the Frustrated Honeycomb Rhodate Li2RhO3,"We report magnetization, heat capacity, 7Li - nuclear magnetic resonance
(NMR), and muSR (muon spin roration) measurements on the honeycomb 4d5 spin
liquid candidate Li2RhO3. The magnetization in small magnetic fields provides
evidence of the partial spin-freezing of a small fraction of Rh4+ -moments at 6
K, whereas the Curie-Weiss behavior above 100 K suggests a pseudo-spin-1/2
paramagnet with a moment of about 2.2 muB. The magnetic specific heat (Cm)
exhibits no field dependence and demonstrates the absence of long range
magnetic order down to 0.35 K. Cm/T passes through a broad maximum at about 10
K and Cm=T^2 at low temperatures. Measurements of the spin-lattice relaxation
rate (1/T1) reveal a gapless slowing down of spin fluctuations upon cooling
with 1/T1=T^2.2. The results from NMR and muSR are consistent with a scenario
in which a minority of Rh4+ moments are in a ahort-range correlated frozen
state and coexist with a majority of moments in a liquid-like state that
continue to fluctuate at low temperatures.",1512.04904v4
2015-12-16,Path large deviations for interacting diffusions with local mean-field interactions in random environment,"We consider a system of $N^{d}$ spins in random environment with a random
local mean field type interaction. Each spin has a fixed spatial position on
the torus $\mathbb{T}^{d}$, an attached random environment and a spin value in
$\mathbb{R}$ that evolves according to a space and environment dependent
Langevin dynamic. The interaction between two spins depends on the spin values,
on the spatial distance and the random environment of both spins. We prove the
path large deviation principle from the hydrodynamic (or local mean field
McKean-Vlasov) limit and derive different expressions of the rate function for
the empirical process and for the empirical measure of the paths. To this end,
we generalize an approach of Dawson and G\""artner. By the space and random
environment dependency, this requires new ingredients compared to mean field
type interactions. Moreover, we prove the large deviation principle by using a
second approach. This requires a generalisation of Varadhan's lemma to nowhere
continuous functions.",1512.05323v3
2016-05-02,Emergent Cosmos in Einstein-Cartan Theory,"Based on the Padmanabhan's proposal, the accelerated expansion of the
universe can be driven by the difference between the surface and bulk degrees
of freedom in a region of space, described by the relation
$dV/dt=N_{sur}-N_{bulk}$ where $N_{sur}$ and $N_{bulk}=-N_{em}+N_{de}$ are the
degrees of freedom assigned to the surface area and the matter-energy content
inside the bulk such that the indexes $""em""$ and $""de""$ represent
energy-momentum and dark energy, respectively. In the present work, the
dynamical effect of the Weyssenhoff perfect fluid with intrinsic spin and its
corresponding spin degrees of freedom in the framework of Einstein-Cartan (EC)
theory are investigated. Based on the modification of Friedmann equations due
to the spin-spin interactions, a correction term for the Padmanabhan's original
relation $dV/dt=N_{sur}+N_{em}-N_{de}$ including the number of degrees of
freedom related to this spin interactions is obtained through the modification
in $N_{bulk}$ term as $N_{bulk}=-N_{em}+N_{spin}+N_{de}$ leading to $dV /d
t=N_{sur}+N_{em}-N_{spin} -N_{de}$ in which $N_{spin}$ is the corresponding
degrees of freedom related to the intrinsic spin of the matter content of the
universe. Moreover, the validity of the unified first law and the generalized
second law of thermodynamics for the Einstein-Cartan cosmos are investigated.
Finally, by considering the covariant entropy conjecture and the bound
resulting from the emergent scenario, a total entropy bound is obtained. Using
this bound, it is shown that the for the universe as an expanding
thermodynamical system, the total effective Komar energy never exceeds the
square of the expansion rate with a factor of $\frac{3}{4\pi}$.",1605.00552v2
2016-05-12,On turbulence driven by axial precession and tidal evolution of the spin-orbit angle of close-in giant planets,"The spin axis of a rotationally deformed planet is forced to precess about
its orbital angular momentum vector, due to the tidal gravity of its host star,
if these directions are misaligned. This induces internal fluid motions inside
the planet that are subject to a hydrodynamic instability. We study the
turbulent damping of precessional fluid motions, as a result of this
instability, in the simplest local computational model of a giant planet (or
star), with and without a weak internal magnetic field. Our aim is to determine
the outcome of this instability, and its importance in driving tidal evolution
of the spin-orbit angle in precessing planets (and stars). We find that this
instability produces turbulent dissipation that is sufficiently strong that it
could drive significant tidal evolution of the spin-orbit angle for hot
Jupiters with orbital periods shorter than about 10-18 days. If this mechanism
acts in isolation, this evolution would be towards alignment or anti-alignment,
depending on the initial angle, but the ultimate evolution (if other tidal
mechanisms also contribute) is expected to be towards alignment. The turbulent
dissipation is proportional to the cube of the precession frequency, so it
leads to much slower damping of stellar spin-orbit angles, implying that this
instability is unlikely to drive evolution of the spin-orbit angle in stars
(either in planetary or close binary systems). We also find that the
instability-driven flow can act as a system-scale dynamo, which may play a role
in producing magnetic fields in short-period planets.",1605.03867v1
2017-06-19,Spin order and dynamics in the diamond-lattice Heisenberg antiferromagnets CuRh2O4 and CoRh2O4,"Antiferromagnetic insulators on the diamond lattice are candidate materials
to host exotic magnetic phenomena ranging from spin-orbital entanglement to
degenerate spiral ground-states and topological paramagnetism. Compared to
other three-dimensional networks of magnetic ions, such as the geometrically
frustrated pyrochlore lattice, the investigation of diamond-lattice magnetism
in real materials is less mature. In this work, we characterize the magnetic
properties of model A-site spinels CoRh2O4 (cobalt rhodite) and CuRh2O4 (copper
rhodite) by means of thermo-magnetic and neutron scattering measurements and
perform group theory analysis, Rietveld refinement, mean-field theory, and spin
wave theory calculations to analyze the experimental results. Our investigation
reveals that cubic CoRh2O4 is a canonical S=3/2 diamond-lattice Heisenberg
antiferromagnet with a nearest neighbor exchange J = 0.63 meV and a Neel
ordered ground-state below a temperature of 25 K. In tetragonally distorted
CuRh2O4, competiting exchange interactions between up to third nearest-neighbor
spins lead to the development of an incommensurate spin helix at 24 K with a
magnetic propagation vector k = (0,0,0.79). Strong reduction of the ordered
moment is observed for the S=1/2 spins in CuRh2O4 and captured by our 1/S
corrections to the staggered magnetization. Our work identifies CoRh2O4 and
CuRh2O4 as reference materials to guide future work searching for exotic
quantum behavior in diamond-lattice antiferromagnets.",1706.05881v1
2017-10-30,Spin-dependent charge recombination along para-phenylene molecular wires,"We have used an efficient new quantum mechanical method for radical pair
recombination reactions to study the spin-dependent charge recombination along
PTZ$^{\bullet+}$--Ph$_n$--PDI$^{\bullet-}$ molecular wires. By comparing our
results to the experimental data of E. Weiss {\em et al.} [J. Am. Chem. Soc.
{\bf 126}, 5577 (2004)], we are able to extract the spin-dependent (singlet and
triplet) charge recombination rate constants for wires with $n=2-5$. These
spin-dependent rate constants have not been extracted previously from the
experimental data because they require fitting its magnetic field-dependence to
the results of quantum spin dynamics simulations. We find that the triplet
recombination rate constant decreases exponentially with the length of the
wire, consistent with the superexchange mechanism of charge recombination.
However, the singlet recombination rate constant is nearly independent of the
length of the wire, suggesting that the singlet pathway is dominated by an
incoherent hopping mechanism. A simple qualitative explanation for the
different behaviours of the two spin-selective charge recombination pathways is
provided in terms of Marcus theory. We also find evidence for a magnetic
field-independent background contribution to the triplet yield of the charge
recombination reaction, and suggest several possible explanations for it. Since
none of these explanations is especially compelling given the available
experimental evidence, and since the result appears to apply more generally to
other molecular wires, we hope that this aspect of our study will stimulate
further experimental work.",1710.11106v1
2017-12-17,"Low temperature ferromagnetic properties, magnetic field induced spin order and random spin freezing effect in Ni1.5Fe1.5O4 ferrite; prepared at different pH values and annealing temperatures","We present the low temperature magnetic properties in Ni1.5Fe1.5O4 ferrite as
the function of pH at which the material was prepared by chemical route and
post annealing temperature. The material is a ferri or ferromagnet, but showed
magnetic blocking and random spin freezing process on lowering the measurement
temperature down to 5 K. The sample prepared at pH =12 and annealed at 800 ^C
showed a sharp magnetization peak at 105 K, the superparamagnetic blocking
temperature of the particles. The magnetization peak remained incomplete within
measurement temperature up to 350 K for rest of the samples, although peak
temperature was brought down by increasing applied dc field. The fitting of
temperature dependence of coercivity data according to Kneller law suggested
random orientation of ferromagnetic particles. The fitting of saturation
magnetization according to Bloch law provided the exponent that largely
deviated from 1.5, a typical value for long ranged ferromagnet. An abrupt
increase of saturation magnetization below 50 K suggested the active role of
frozen surface spins in low temperature magnetic properties. AC susceptibility
data elucidated the low temperature spin freezing dynamics and exhibited the
characters of cluster spin glass in the samples depending on pH value and
annealing temperature.",1712.06114v1
2017-12-21,Exchange-torque-induced excitation of perpendicular standing spin waves in nanometer-thick YIG films,"Spin waves in ferrimagnetic yttrium iron garnet (YIG) films with ultralow
magnetic damping are relevant for magnon-based spintronics and low-power
wave-like computing. The excitation frequency of spin waves in YIG is rather
low in weak external magnetic fields because of its small saturation
magnetization, which limits the potential of YIG films for high-frequency
applications. Here, we demonstrate how exchange-coupling to a CoFeB film
enables efficient excitation of high-frequency perpendicular standing spin
waves (PSSWs) in nanometer-thick (80 nm and 295 nm) YIG films using uniform
microwave magnetic fields. In the 295-nm-thick YIG film, we measure intense
PSSW modes up to 10th order. Strong hybridization between the PSSW modes and
the ferromagnetic resonance mode of CoFeB leads to characteristic anti-crossing
behavior in broadband spin-wave spectra. A dynamic exchange torque at the
YIG/CoFeB interface explains the excitation of PSSWs. The localized torque
originates from exchange coupling between two dissimilar magnetization
precessions in the YIG and CoFeB layers. As a consequence, spin waves are
emitted from the YIG/CoFeB interface and PSSWs form when their wave vector
matches the perpendicular confinement condition. PSSWs are not excited when the
exchange coupling between YIG and CoFeB is suppressed by a Ta spacer layer.
Micromagnetic simulations confirm the exchange-torque mechanism.",1712.08204v1
2018-01-27,The LArase Satellites Spin mOdel Solutions (LASSOS): a comprehensive model for the spin evolution of the LAGEOS and LARES satellites,"The two LAGEOS and LARES are laser-ranged satellites tracked with the best
accuracy ever achieved. Using their range measurements many geophysical
parameters were calculated and some General Relativity effects were directly
observed. To obtain precise and refined measurements of the effects due to the
predictions of General Relativity on the orbit of these satellites, it is
mandatory to model with high precision and accuracy all other forces, reducing
the free parameters introduced in the orbit determination. A main category of
non-gravitational forces to be considered are those of thermal origin, whose
fine modeling strongly depends on the knowledge of the evolution of the spin
vector. We present a complete model, named LASSOS, to describe the evolution of
the spin of the LAGEOS and LARES satellites. In particular, we solved Euler
equations of motion considering not-averaged torques. This is the most general
case, and the predictions of the model well fit the available observations of
the satellites spin. We also present the predictions of our model in the
fast-spin limit, based on the application of averaged equations. The results
are in good agreement with those already published, but with our approach we
have been able to highlight small errors within these previous works. LASSOS
was developed within the LARASE research program. LARASE aims to improve the
dynamical model of the two LAGEOS and LARES satellites to provide very precise
and accurate measurements of relativistic effects on their orbit, and also to
bring benefits to geophysics and space geodesy.",1801.09098v1
2018-09-21,Constant circulation sequences of binary neutron stars and their spin characterization,"For isentropic fluids, dynamical evolution of a binary system conserves the
baryonic mass and circulation; therefore, sequences of constant rest mass and
constant circulation are of particular importance. In this work, we present the
extension of our Compact Object CALculator (\cocal{}) code to compute such
quasiequilibria and compare them with the well-known corotating and
irrotational sequences, the latter being the simplest, zero-circulation case.
The circulation as a measure of the spin for a neutron star in a binary system
has the advantage of being exactly calculable since it is a local quantity. To
assess the different measures of spin, such as the angular velocity of the
star, the quasilocal, dimensionless spin parameter $J/M^2$, or the circulation
$\mathcal{C}$, we first compute sequences of single, uniformly rotating stars
and describe how the different spin diagnostics are related to each other. The
connection to spinning binary systems is accomplished through the concept of
circulation and the use of the constant rotational velocity formulation.
Finally, we explore a modification of the latter formulation that naturally
leads to differentially rotating binary systems.",1809.08237v2
2018-10-16,Spin-wave-induced lateral temperature gradient in a YIG thin film/GGG system excited in an ESR cavity,"Lateral thermal gradient of an yttrium iron garnet (YIG) film under the
microwave application in the cavity of the electron spin resonance system (ESR)
was measured at room temperature by fabricating a Cu/Sb thermocouple onto it.
To date, thermal transport in YIG films caused by the Damon-Eshbach mode (DEM)
- the unidirectional spin-wave heat conveyer effect - was demonstrated only by
the excitation using coplanar waveguides. Here we show that effect exists even
under YIG excitation using the ESR cavity - tool often employed to realize spin
pumping. The temperature difference observed around the ferromagnetic resonance
(FMR) field under the 4 mW microwave power peaked at 13 mK. The observed
thermoelectric signal indicates the imbalance of the population between the
DEMs that propagate near the top and bottom surfaces of the YIG film. We
attribute the DEM population imbalance to the different magnetic damping near
the top and bottom YIG surfaces. Additionally, the spin wave dynamics of the
system were investigated using the micromagnetic simulations. The micromagnetic
simulations confirmed the existence of the DEM imbalance in the system with the
increased Gilbert damping at one of the YIG interfaces. The reported results
are indispensable for the quantitative estimation of the electromotive force in
the spin-charge conversion experiments using ESR cavities.",1810.06875v1
2019-10-04,Spin-wave directional anisotropies in antiferromagnetic Ba$_{3}$NbFe$_{3}$Si$_{2}$O$_{14}$,"Ba$_{3}$NbFe$_{3}$Si$_{2}$O$_{14}$ (langasite) is structurally and
magnetically single domain chiral with the magnetic helicity induced through
competing symmetric exchange interactions. Using neutron scattering, we show
that the spin-waves in antiferromagnetic langasite display directional
anisotropy. On applying a time reversal symmetry breaking magnetic field along
the $c$-axis, the spin wave energies differ when the sign is reversed for
either the momentum transfer $\pm$ $\vec{Q}$ or applied magnetic field $\pm$
$\mu_{0}$H. When the field is applied within the crystallographic $ab$-plane,
the spin wave dispersion is directionally \textit{isotropic} and symmetric in
$\pm$ $\mu_{0}$H. However, a directional anisotropy is observed in the spin
wave intensity. We discuss this directional anisotropy in the dispersion in
langasite in terms of a field induced precession of the dynamic unit cell
staggered magnetization. Directional anisotropy, or often referred to as non
reciprocal responses, can occur in antiferromagnetic phases in the absence of
the Dzyaloshinskii-Moriya interaction or other effects resulting from
spin-orbit coupling.",1910.01977v2
2020-02-12,Hyperfine and quadrupole interactions for Dy isotopes in DyPc$_2$ molecules,"Nuclear spin levels play an important role in understanding magnetization
dynamics and implementation and control of quantum bits in lanthanide-based
single-molecule magnets. We investigate the hyperfine and nuclear quadrupole
interactions for $^{161}$Dy and $^{163}$Dy nucleus in anionic DyPc$_2$
(Pc=phthalocyanine) single-molecule magnets, using multiconfigurational
ab-initio methods (beyond density-functional theory) including spin-orbit
interaction. The two isotopes of Dy are chosen because the others have zero
nuclear spin. Both isotopes have the nuclear spin $I=5/2$, although the
magnitude and sign of the nuclear magnetic moment differ from each other. The
large energy gap between the electronic ground and first-excited Kramers
doublets, allows us to map the microscopic hyperfine and quadrupole interaction
Hamiltonian onto an effective Hamiltonian with an electronic pseudo-spin
$S_{\rm eff}=1/2$ that corresponds to the ground Kramers doublet. Our ab-initio
calculations show that the coupling between the nuclear spin and electronic
orbital angular momentum contributes the most to the hyperfine interaction and
that both the hyperfine and nuclear quadrupole interactions for $^{161}$Dy and
$^{163}$Dy nucleus are much smaller than those for $^{159}$Tb nucleus in
TbPc$_2$ single-molecule magnets. The calculated separations of the
electronic-nuclear levels are comparable to experimental data reported for
$^{163}$DyPc$_2$. We demonstrate that hyperfine interaction for Dy Kramers ion
leads to tunnel splitting (or quantum tunneling of magnetization) at zero
field. This effect does not occur for TbPc$_2$ single-molecule magnets. The
magnetic field values of the avoided level crossings for $^{161}$DyPc$_2$ and
$^{163}$DyPc$_2$ are found to be noticeably different, which can be observed
from experiment.",2002.05134v1
2020-12-15,Fracton excitations in classical frustrated kagome spin models,"Fractons are topological quasiparticles with limited mobility. While there
exists a variety of models hosting these excitations, typical fracton systems
require rather complicated many-particle interactions. Here, we discuss fracton
behavior in the more common physical setting of classical kagome spin models
with frustrated two-body interactions only. We investigate systems with
different types of elementary spin degrees of freedom (three-state Potts, XY,
and Heisenberg spins) which all exhibit characteristic subsystem symmetries and
fracton-like excitations. The mobility constraints of isolated fractons and
bound fracton pairs in the three-state Potts model are, however, strikingly
different compared to the known type-I or type-II fracton models. One may still
explain these properties in terms of type-I fracton behavior and construct an
effective low-energy tensor gauge theory when considering the system as a 2D
cut of a 3D cubic lattice model. Our extensive classical Monte-Carlo
simulations further indicate a crossover into a low temperature glassy phase
where the system gets trapped in metastable fracton states. Moving on to XY
spins, we find that in addition to fractons the system hosts fractional vortex
excitations. As a result of the restricted mobility of both types of defects,
our classical Monte-Carlo simulations do not indicate a Kosterlitz-Thouless
transition but again show a crossover into a glassy low-temperature regime.
Finally, the energy barriers associated with fractons vanish in the case of
Heisenberg spins, such that defect states may continuously decay into a ground
state. These decays, however, exhibit a power-law relaxation behavior which
leads to slow equilibration dynamics at low temperatures.",2012.08167v1
2021-01-21,Spin liquid behavior of a three-dimensional magnetic system Ba$_3$NiIr$_2$O$_9$ with $S$ = 1,"The quantum spin liquid (QSL) is an exotic phase of magnetic materials where
the spins continue to fluctuate without any symmetry breaking down to zero
temperature. Among the handful reports of QSL with spin $S\ge$1, examples with
magnetic ions on a three-dimensional magnetic lattice are extremely rare since
both larger spin and higher dimension tend to suppress quantum fluctuations. In
this work, we offer a new strategy to achieve 3-D QSL with high spin by
utilizing two types of transition metal ions, both are magnetically active but
located at crystallographically inequivalent positions. We design a 3-D
magnetic system Ba$_3$NiIr$_2$O$_9$ consisting of interconnected corner shared
NiO$_6$ octahedra and face shared Ir$_2$O$_9$ dimer, both having triangular
arrangements in \textit{a-b} plane. X-ray absorption spectroscopy measurements
confirm the presence of Ni$^{2+}$ ($S$=1). Our detailed thermodynamic and
magnetic measurements reveal that this compound is a realization of gapless QSL
state down to at least 100 mK. Ab-initio calculations find a strong magnetic
exchange between Ir and Ni sublattices and in-plane antiferromagnetic coupling
between the dimers, resulting in dynamically fluctuating magnetic moments on
both the Ir and Ni sublattice.",2101.08445v1
2012-05-26,Laser-assisted spin-polarized transport in graphene tunnel junctions,"Keldysh nonequilibrium Green's function method is utilized to study
theoretically the spin polarized transport through a graphene spin valve
irradiated by a monochromatic laser field. It is found that the bias dependence
of the differential conductance exhibits successive peaks corresponding to the
resonant tunneling through the photon-assisted sidebands. The multi photon
processes originate from the combined effects of the radiation field and the
graphene tunneling properties, and are shown to be substantially suppressed in
a graphene spin valve which results in a decrease of the differential
conductance for a high bias voltage. We also discussed the appearance of a
dynamical gap around zero bias due to the radiation field. The gap width can be
tuned by changing the radiation electric field strength and the frequency. This
leads to a shift of the resonant peaks in the differential conductance. We also
demonstrate numerically the dependencies of the radiation and spin valve
effects on the parameters of the external fields and those of the electrodes.
We find that the combined effects of the radiation field, the graphene, and the
spin valve properties bring about an oscillatory behavior in the tunnel
magnetoresistance (TMR), and this oscillatory amplitude can be changed by
scanning the radiation field strength and/or the frequency.",1205.5864v2
2017-09-03,Determinant representations of spin-operator matrix elements in the XX spin chain and their applications,"For the one-dimensional spin-1/2 XX model with either periodic or open
boundary conditions, it is shown by using a fermionic approach that the matrix
element of the spin operator $S^-_j$ ($S^-_{j}S^+_{j'}$) between two
eigenstates with numbers of excitations $n$ and $n+1$ ($n$ and $n$) can be
expressed as the determinant of an appropriate $(n+1)\times (n+1)$ matrix whose
entries involve the coefficients of the canonical transformations diagonalizing
the model. In the special case of a homogeneous periodic XX chain, the matrix
element of $S^-_j$ reduces to a variant of the Cauchy determinant that can be
evaluated analytically to yield a factorized expression. The obtained compact
representations of these matrix elements are then applied to two physical
scenarios: (i) Nonlinear optical response of molecular aggregates, for which
the determinant representation of the transition dipole matrix elements between
eigenstates provides a convenient way to calculate the third-order nonlinear
responses for aggregates from small to large sizes compared with the optical
wavelength, and (ii) real-time dynamics of an interacting Dicke model
consisting of a single bosonic mode coupled to a one-dimensional XX spin bath.
In this setup, full quantum calculation up to $N\leq 16$ spins for vanishing
intrabath coupling shows that the decay of the reduced bosonic occupation
number approaches a finite plateau value (in the long-time limit) that depends
on the ratio between the number of excitations and the total number of spins.
Our results can find useful applications in various ""system-bath"" systems, with
the system part inhomogeneously coupled to an interacting XX chain.",1709.00682v2
2017-11-09,Fabrication of magnetic tunnel junctions connected through a continuous free layer to enable spin logic devices,"Magnetic tunnel junctions (MTJs) interconnected via a continuous
ferromagnetic free layer were fabricated for Spin Torque Majority Gate (STMG)
logic. The MTJs are biased independently and show magnetoelectric response
under spin transfer torque. The electrical control of these devices paves the
way to future spin logic devices based on domain wall (DW) motion. In
particular, it is a significant step toward the realization of a majority gate,
even though further downscaling may be required. To our knowledge, this is the
first fabrication of a cross-shaped free layer shared by several perpendicular
MTJs. The fabrication process can be generalized to any geometry and any number
of MTJs. Thus, this framework can be applied to other spin logic concepts based
on magnetic interconnect. Moreover, it allows exploration of spin dynamics for
logic applications",1711.03609v2
2018-08-01,Raman fingerprint of two terahertz spin wave branches in a two-dimensional honeycomb Ising ferromagnet,"Two-dimensional (2D) magnetism has been long sought-after and only very
recently realized in atomic crystals of magnetic van der Waals materials. So
far, a comprehensive understanding of the magnetic excitations in such 2D
magnets remains missing. Here we report polarized micro-Raman spectroscopy
studies on a 2D honeycomb ferromagnet CrI3. We show the definitive evidence of
two sets of zero-momentum spin waves at frequencies of 2.28 terahertz (THz) and
3.75 THz, respectively, that are three orders of magnitude higher than those of
conventional ferromagnets. By tracking the thickness dependence of both spin
waves, we reveal that both are surface spin waves with lifetimes an order of
magnitude longer than their temporal periods. Our results of two branches of
high-frequency, long-lived surface spin waves in 2D CrI3 demonstrate intriguing
spin dynamics and intricate interplay with fluctuations in the 2D limit, thus
opening up opportunities for ultrafast spintronics incorporating 2D magnets.",1808.00168v3
2018-08-17,Spin-mediated particle transport in the disordered Hubbard model,"Motivated by the recent experiments that reported signatures of many-body
localization of ultracold atoms in optical lattices [M. Schreiber {\it et al.},
Science {\bf 349}, 842 (2015)], we study dynamics of highly excited states in
the strongly disordered Hubbard model in one dimension. Owing to the $SU(2)$
spin symmetry, spin degrees of freedom form a delocalized thermal bath with a
narrow bandwidth. The spin bath mediates slow particle transport, eventually
leading to delocalization of particles. The particle hopping rate is
exponentially small in $t/W$ ($t$, $W$ being hopping and disorder scales) owing
to the narrow bandwidth of the spin bath. We find the optimal lenghtscale for
particle hopping, and show that the particle transport rate depends strongly on
the density of singly occupied sites in the initial state. The delocalization
rate is zero for initial states with only doubly occupied or empty sites,
suggesting that such states are truly many-body localized, and therefore the
Hubbard model may host both localized and delocalized states. Full many-body
localization can be induced by breaking spin rotational symmetry.",1808.05764v2
2018-08-30,Metallic glasses for spintronics: anomalous temperature dependence and giant enhancement of inverse spin Hall effect,"Spin-charge conversion via inverse spin Hall effect (ISHE) is essential for
enabling various applications of spintronics. The spin Hall response usually
follows a universal scaling relation with longitudinal electric resistivity and
has mild temperature dependence because elementary excitations play only a
minor role in resistivity and hence ISHE. Here we report that the ISHE of
metallic glasses shows nearly two orders of magnitude enhancements with
temperature increase from a threshold of 80-100 K to glass transition points.
As electric resistivity changes only marginally in the temperature range, the
anomalous temperature dependence is in defiance of the prevailing scaling law.
Such a giant temperature enhancement can be well described by a two-level
thermal excitation model of glasses and disappears after crystallization,
suggesting a new mechanism which involves unique thermal excitations of
glasses. This finding may pave new ways to achieve high spin-charge conversion
efficiency at room and higher temperatures for spintronic devices and to detect
structure and dynamics of glasses using spin currents.",1808.10371v1
2018-12-03,Tidal Disruptions of Stars by Binary Black Holes: Modifying the Spin Magnitudes and Directions of LIGO Sources in Dense Stellar Environments,"Binary black holes (BBHs) appear to be widespread and are able to merge
through the emission of gravitational waves, as recently illustrated by LIGO.
The spin of the BBHs is one of the parameters that LIGO can infer from the
gravitational wave signal and can be used to constrain their production site.
If BBHs are assembled in stellar clusters they are likely to interact with
stars, which could occasionally lead to a tidal disruption event (TDE). When a
BBH tidally disrupts a star it can accrete a significant fraction of the
debris, effectively altering the spins of the BHs. Therefore, although
dynamically formed BBHs are expected to have random spin orientations, tidal
stellar interactions can significantly alter their birth spins both in
direction and magnitude. Here we investigate how TDEs by BBHs can affect the
properties of the BH members as well as exploring the characteristics of the
resulting electromagnetic signatures. We conduct hydrodynamic simulations with
a Lagrangian Smoothed Particle Hydrodynamics code of a wide range of
representative tidal interactions. We find that both spin magnitude and
orientation can be altered and temporarily aligned or anti-aligned through
accretion of stellar debris, with a significant dependence on the mass ratio of
the disrupted star and the BBH members. These tidal interactions feed material
to the BBH at very high accretion rates, with the potential to launch a
relativistic jet. The corresponding beamed emission is a beacon to an otherwise
quiescent BBH.",1812.01118v1
2019-01-26,All optical detection of picosecond spin-wave dynamics in two-dimensional annular antidot lattice,"Novel magnetic structures with precisely controlled dimensions and shapes at
the nanoscale have potential applications in spin logic, spintronics and other
spin-based communication devices. We report the fabrication of two-dimensional
bi-structure magnonic crystal in the form of embedded nanodots in a periodic
Ni80Fe20 antidot lattice structure (annular antidot) by focused ion-beam
lithography. The spin-wave spectra of the annular antidot sample,studied for
the first time by a time-resolved magneto-optic Kerr effect microscopy show a
remarkable variation with bias field, which is important for the above device
applications. The optically induced spin-wave spectra show multiple modes in
the frequency range 14.7 GHz to 3.5 GHz due to collective interactions between
the dots and antidots as well as the annular elements within the whole array.
Numerical simulations qualitatively reproduce the experimental results, and
simulated mode profiles reveal the spatial distribution of the spin wave modes
and internal magnetic fields responsible for these observations. It is observed
that the internal field strength increases by about 200 Oe inside each dot
embedded within the hole of annular antidot lattice as compared to pure antidot
lattice and pure dot lattice. The stray field for the annular antidot lattice
is found to be significant (0.8kOe) as opposed to the negligible values of the
same for the pure dot lattice and pure antidot lattice. Our findings open up
new possibilities for development of novel artificial crystals.",1901.09152v1
2019-03-04,Charge and spin-specific local integrals of motion in a disordered Hubbard model,"While many-body localization has primarily been studied in systems with a
single local degree of freedom, experimental studies of many-body localization
in cold atom systems motivate exploration of the disordered Hubbard model. With
two coupled local degrees of freedom it is natural to ask how localization in
spin relates to disorder in charge and vice versa. Most prior work has
addressed disorder in only one of these sectors and often has not used measures
of localization which distinguish between charge and spin. Here we explore
localization in the Hubbard model with a wide range of independent values of
charge and spin disorder, using measures of localization based on charge and
spin-specific integrals of motion. Our results demonstrate symmetry between the
response of the spin to charge disorder and vice versa, and we find very weak
disorder in one channel, so long as the disorder in the other channel is
sufficiently strong, results in localization in both channels. The strength of
disorder required in the less disordered channel declines as the system size
increases. Further, the weaker the disorder in the less-disordered channel, the
longer the time scale at which localization appears in the dynamics of this
degree of freedom.",1903.01049v2
2019-03-08,Spin-transfer torques for domain walls in antiferromagnetically coupled ferrimagnets,"Antiferromagnetic materials are outstanding candidates for next generation
spintronic applications, because their ultrafast spin dynamics makes it
possible to realize several orders of magnitude higher-speed devices than
conventional ferromagnetic materials1. Though spin-transfer torque (STT) is a
key for electrical control of spins as successfully demonstrated in
ferromagnetic spintronics, experimental understanding of STT in
antiferromagnets has been still lacking despite a number of pertinent
theoretical studies2-5. Here, we report experimental results on the effects of
STT on domain-wall (DW) motion in antiferromagnetically-coupled ferrimagnets.
We find that non-adiabatic STT acts like a staggered magnetic field and thus
can drive DWs effectively. Moreover, the non-adiabaticity parameter {\beta} of
STT is found to be significantly larger than the Gilbert damping parameter
{\alpha}, challenging our conventional understanding of the non-adiabatic STT
based on ferromagnets as well as leading to fast current-induced
antiferromagnetic DW motion. Our study will lead to further vigorous
exploration of STT for antiferromagnetic spin textures for fundamental physics
on spin-charge interaction as wells for efficient electrical control of
antiferromagnetic devices.",1903.03251v1
2019-11-14,Long-lived coherence in driven spin systems: from two to infinite spatial dimensions,"Long-lived coherences, emerging under periodic pulse driving in the
disordered ensembles of strongly interacting spins, offer immense advantages
for future quantum technologies, but the physical origin and the key properties
of this phenomenon remain poorly understood. We theoretically investigate this
effect in ensembles of different dimensionality, and predict existence of the
long-lived coherences in two-dimensional and infinite-dimensional (where every
spin is coupled to all others) systems, which are of particular importance for
quantum sensing and quantum information processing. We explore the transition
from two to infinite dimensions, and show that the long-time coherence dynamics
in all dimensionalities is qualitatively similar, although the short-time
behavior is drastically different, exhibiting dimensionality-dependent
singularity. Our study establishes the common physical origin of the long-lived
coherences in different dimensionalities, and suggests that this effect is a
generic feature of the strongly coupled spin systems with positional disorder.
Our results lay out foundation for utilizing the long-lived coherences in a
range of application, from quantum sensing with two-dimensional spin ensembles,
to quantum information processing with the infinitely-dimensional spin systems
in the cavity-QED settings.",1911.06272v3
2019-11-21,Gapless ground state in the archetypal quantum kagome antiferromagnet ZnCu$_3$(OH)$_6$Cl$_2$,"Spin liquids are exotic phases of quantum matter challenging Landau's
paradigm of symmetry-breaking phase transitions. Despite strong exchange
interactions, spins do not order or freeze down to zero temperature. While
well-established for 1D quantum antiferromagnets, in higher dimension where
quantum fluctuations are less acute, realizing and understanding such states
represent major issues, both theoretical and experimental. In this respect the
simplest nearest-neighbor Heisenberg antiferromagnet Hamiltonian on the highly
frustrated kagome lattice has proven to be a fascinating and inspiring model.
The exact nature of its ground state remains elusive and the existence of a
spin-gap is the first key-issue to be addressed to discriminate between the
various classes of proposed spin liquids. Here, through low-temperature Nuclear
Magnetic Resonance (NMR) contrast experiments on high quality single crystals,
we single out the kagome susceptibility and the corresponding dynamics in the
kagome archetype, the mineral herbertsmithite, ZnCu$_3$(OH)$_6$Cl$_2$. We
firmly conclude that this material does not harbor any spin-gap, which restores
a convergence with recent numerical results promoting a gapless Dirac spin
liquid as the ground state of the Heisenberg kagome antiferromagnet.",1911.09552v1
2019-11-30,Quadrupole Effects on Nuclear Magnetic Resonance Gyroscopes,"Nuclear magnetic resonance gyroscopes that detect rotation as a shift in the
precession frequency of nuclear spins, have attracted a lot of attentions.
Under a feedback-generated drive, the precession frequency is supposed to be
dependent only on the angular momentum and an applied magnetic field. However,
nuclei with spins larger than 1/2, experience electric quadrupole interaction
with electric field gradients at the cell walls. This quadrupole interaction
shifts the precession frequencies of the nuclear spins, which brings inaccuracy
to the rotation measurement as the quadrupole interaction constant $C_q$ is
difficult to precisely measure. In this work, the effects of quadrupole
interaction on nuclear magnetic resonance gyroscopes is theoretically studied.
We find that, when the constant $C_q$ is small compared to the characteristic
decay rate of the system, as the strength of the feedback-driving field
increases, the quadrupole shift monotonically decreases, regardless of the sign
of $C_q$. In large $C_q$ regime, more than one precession frequency exists, and
the nuclear spins may precess with a single frequency or multi-frequencies
depending on initial conditions. In this regime, with large driving amplitudes,
the nuclear spin can restore the single-frequency-precession. These results are
obtained by solving an effective master equation of the nuclear spins in a
rotating frame, from which both the steady-state solutions and dynamics of the
system are shown.",1912.00216v1
2020-03-02,Spin-caloritronic transport in hexagonal graphene nanoflakes,"We investigate the spin-dependent thermoelectric effect of graphene flakes
with magnetic edges in the ballistic regime. Employing static, respectively,
dynamic mean-field theory we first show that magnetism appears at the zigzag
edges for a window of Coulomb interactions that increases significantly with
increasing flake size. We then use the Landauer formalism in the framework of
the non-equilibrium Green's function method to calculate the spin and charge
currents in magnetic hexagonal graphene flakes by varying the temperature of
the junction for different flake sizes. While in non-magnetic gated graphene
the temperature gradient drives a charge current, we observe a significant spin
current for hexagonal graphene flakes with magnetic zigzag edges. Specifically,
we show that in the ""meta"" configuration of a hexagonal flake subject to weak
Coulomb interactions, a pure spin current can be driven just by a temperature
gradient in a temperature range that is promising for device applications.
Bigger flakes are found to yield a bigger window of Coulomb interactions where
such spin currents are induced by the magnetic zigzag edges, and larger values
of the current.",2003.01139v2
2020-03-25,Stochasticity in radiative polarization of ultrarelativistic electrons in an ultrastrong laser pulse,"Stochasticity effects in the spin (de)polarization of an ultrarelativistic
electron beam during photon emissions in a counterpropoagating ultrastrong
focused laser pulse in the quantum radiation reaction regime are investigated.
We employ a Monte Carlo method to describe the electron dynamics
semiclassically, and photon emissions as well as the electron radiative
polarization quantum mechanically. While in the latter the photon emission is
inherently stochastic, we were able to identify its imprints in comparison with
the new developed semiclassical stochasticity-free method of radiative
polarization applicable in the quantum regime. With an initially spin-polarized
electron beam, the stochastic spin effects are seen in the dependence of the
depolarization degree on the electron scattering angle and the electron final
energy (spin stochastic diffusion). With an initially unpolarized electron
beam, the spin stochasticity is exhibited in enhancing the known effect of
splitting of the electron beam along the propagation direction into two
oppositely polarized parts by an elliptically polarized laser pulse. The
considered stochasticity effects for the spin are observable with currently
achievable laser and electron beam parameters.",2003.11200v1
2020-06-23,Imaging non-collinear antiferromagnetic textures via single spin relaxometry,"Antiferromagnetic materials are promising platforms for next-generation
spintronics owing to their fast dynamics and high robustness against parasitic
magnetic fields. However, nanoscale imaging of the magnetic order in such
materials with zero net magnetization remains a major experimental challenge.
Here we show that non-collinear antiferromagnetic spin textures can be imaged
by probing the magnetic noise they locally produce via thermal populations of
magnons. To this end, we perform nanoscale, all-optical relaxometry with a
scanning quantum sensor based on a single nitrogen-vacancy (NV) defect in
diamond. Magnetic noise is detected through an increase of the spin relaxation
rate of the NV defect, which results in an overall reduction of its
photoluminescence signal under continuous laser illumination. As a
proof-of-concept, the efficiency of the method is demonstrated by imaging
various spin textures in synthetic antiferromagnets, including domain walls,
spin spirals and antiferromagnetic skyrmions. This imaging procedure could be
extended to a large class of intrinsic antiferromagnets and opens up new
opportunities for studying the physics of localized spin wave modes for
magnonics.",2006.13130v1
2020-09-23,Magnetodielectric coupling and multi-blocking effect in the Ising-chain magnet Sr2Ca2CoMn2O9,"We have demonstrated magnetodielectric (MD) coupling in an Ising-chain magnet
Sr2Ca2CoMn2O9, via detailed investigation of ac susceptibility and dielectric
constant as a function of temperature, magnetic field and frequency.
Sr2Ca2CoMn2O9 consists of spin-chains, made of the regular stacking of one CoO6
trigonal prism with two MnO6 octahedra. The (Co2+ Mn4+ Mn4+) unit stabilizes a
(up-down-up) spin-state along the chains which are distributed on a triangular
lattice. This compound undergoes a partially disordered antiferromagnetic
transition at TN ~ 28 K. The dielectric constant exhibits a clear peak at TN
only in presence of an external magnetic field (above 5 kOe), evidencing the
presence of MD coupling, which is further confirmed by field-dependent
dielectric measurements. We argue that spatial inversion symmetry can be broken
as a result of exchange-striction along each spin chain, inducing uncompensated
local dipoles. At low temperatures, a dipolar relaxation phenomenon is
observed, bearing strong similarities with the blocking effect typical of the
spin dynamics in this compound. Such a spin-dipole relationship is referred to
as a multi-blocking effect, in relation with the concept of magnetodielectric
multiglass previously introduced for related materials.",2009.10969v2
2020-10-17,Time-Energy Uncertainty Limit for spin-related wavepacket evolution,"In this report we study the quantum transport of charge carriers for low
dimensional systems with spin-orbit coupling by means of Heisenberg's
inequalities. To develop our analysis, an accurate \emph{gendanken} experiment
was carefully put together, mainly based on the spin-field effect transistor
phenomenology and taking into account several wide accepted approaches on
quantum mechanical limited determinism. While verifying the applicability of
time-energy uncertainty relation (TEUR) during electronic wavepacket's
evolution through a semiconductor quantum wire, some qualitative information
related the dynamic behavior of the system is found. The problem is also
approached in the framework of the stationary phase method to guarantee robust
coherence for wavepacket's evolution, which lately implies certain restrictions
on the incident energy values for the envisioned cases. Tailoring different
input parameters such as: incoming particles spin polarization, barrier
thickness and Rashba's spin-orbit interaction (R-SOI) strength, we have
observed appealing effects while the packet evolves through a quasi-1D
heterostructure. Hopefully some of them could be of help in spintronics device
designing. We have obtained most of the numerical simulation results, within
the so-called conservation zone. However, for certain barrier thicknesses, some
values drop into the forbidden area regarding the clear theoretical limit
imposed by the TEUR. As an expected bonus throughout our theoretical validation
of the TEUR, spin splitting due to finite values of R-SOI was nicely noticed.",2010.08803v3
2020-11-02,Signatures of magnetostriction and spin-phonon coupling in magnetoelectric hexagonal 15R-BaMnO3,"Spin-phonon coupling, the interaction of spins with surrounding lattice is a
key parameter to understand the underlying physics of multiferroics and
engineer their magnetization dynamics. Elementary excitations in multiferroic
materials are strongly influenced by spin-phonon interaction, making Raman
spectroscopy a unique tool to probe these coupling(s). Recently, it has been
suggested that the dielectric and magnetic properties of 15R-type hexagonal
BaMnO3 are correlated through the spin-lattice coupling. Here, we report the
observation of an extensive renormalization of the Raman spectrum of 15R-BaMnO3
at 230 K, 280 K, and 330 K. Magnetic measurements reveal the presence of a
long-range and a short-range magnetic ordering in 15R-BaMnO3 at 230 K and 330
K, respectively. The Raman spectrum shows the appearance of new Raman modes in
the magnetically ordered phases. Furthermore, an additional Raman phonon
appears below ~ 280 K, possibly arising from a local lattice-distortion due to
the displacement of Mn-ions, that exhibits anomalous shift with temperature.
The origin of the observed renormalization and phonon anomalies in Raman
spectra are discussed based on the evidences from temperature- and
magnetic-field-dependent Raman spectra, temperature-dependent x-ray
diffraction, magnetization, and specific heat measurements. Our results
indicate the presence of magnetostriction and spin-phonon coupling in
15R-BaMnO3 thus suggesting that the optical phonons are strongly correlated to
its magnetoelectric properties.",2011.00757v1
2021-02-02,Spin misalignment of black hole binaries from young star clusters: implications for the origin of gravitational waves events,"Recent studies indicate that the progenitors of merging black hole (BH)
binaries from young star clusters can undergo a common envelope phase just like
isolated binaries. If the stars emerge from the common envelope as naked cores,
tidal interactions can efficiently synchronize their spins before they collapse
into BHs. Contrary to the isolated case, these binary BHs can also undergo
dynamical interactions with other BHs in the cluster before merging. The
interactions can tilt the binary orbital plane, leading to spin-orbit
misalignment. We estimate the spin properties of merging binary BHs undergoing
this scenario by combining up-to-date binary population synthesis and accurate
few-body simulations. We show that post-common envelope binary BHs are likely
to undergo only a single encounter, due to the high binary recoil velocity and
short coalescence times. Adopting conservative limits on the binary-single
encounter rates, we obtain a local BH merger rate density of ~6.6 yr^-1 Gpc^-3.
Assuming low (<0.2) natal BH spins, this scenario reproduces the trends in the
distributions of effective spin Xeff and precession parameters Xp inferred from
GWTC-2, including the peaks at (Xeff, Xp) ~ (0.1, 0.2) and the tail at negative
Xeff values.",2102.01689v2
2021-02-17,Spectroscopic analysis of vibronic relaxation pathways in molecular spin qubit $[$Ho(W$_5$O$_{18}$)$_2]^{9-}$: sparse spectra are key,"Molecular vibrations play a key role in magnetic relaxation processes of
molecular spin qubits as they couple to spin states, leading to the loss of
quantum information. Direct experimental determination of vibronic coupling is
crucial to understand and control the spin dynamics of these nano-objects,
which represent the limit of miniaturization for quantum devices. Herein, we
measure the vibrational properties of the molecular spin qubit
$[$Ho(W$_5$O$_{18}$)$_2]^{9-}$ by means of magneto-infrared spectroscopy. Our
results allow us to unravel the vibrational decoherence pathways in combination
with $ab$ $initio$ calculations including vibronic coupling. We observe
field-induced spectral changes near 63 and 370 cm$^{-1}$ that are modeled in
terms of $f$-manifold crystal field excitations activated by odd-symmetry
vibrations. The overall extent of vibronic coupling in this system is limited
by a transparency window in the phonon density of states that acts to keep the
intramolecular vibrations and $M_J$ levels apart. These findings advance the
understanding of vibronic coupling in molecular magnets, place significant
constraints on the pattern of crystal field levels in these systems, and
provide a strategy for designing molecular spin qubits with improved coherence
lifetimes.",2102.08713v1
2021-04-15,Emergent hydrodynamics in a strongly interacting dipolar spin ensemble,"Conventional wisdom holds that macroscopic classical phenomena naturally
emerge from microscopic quantum laws. However, despite this mantra, building
direct connections between these two descriptions has remained an enduring
scientific challenge. In particular, it is difficult to quantitatively predict
the emergent ""classical"" properties of a system (e.g. diffusivity, viscosity,
compressibility) from a generic microscopic quantum Hamiltonian. Here, we
introduce a hybrid solid-state spin platform, where the underlying disordered,
dipolar quantum Hamiltonian gives rise to the emergence of unconventional spin
diffusion at nanometer length scales. In particular, the combination of
positional disorder and on-site random fields leads to diffusive dynamics that
are Fickian yet non-Gaussian. Finally, by tuning the underlying parameters
within the spin Hamiltonian via a combination of static and driven fields, we
demonstrate direct control over the emergent spin diffusion coefficient. Our
work opens the door to investigating hydrodynamics in many-body quantum spin
systems.",2104.07678v1
2021-04-25,Temperature dependence of divacancy spin coherence in implanted silicon carbide,"Spin defects in silicon carbide (SiC) have attracted increasing interest due
to their excellent optical and spin properties, which are useful in quantum
information processing. In this paper, we systematically investigate the
temperature dependence of the spin properties of divacancy defects in implanted
4\emph{H}-SiC. The zero-field splitting parameter $D$, the inhomogeneous
dephasing time $T_2^{*}$, the coherence time $T_2$, and the depolarization time
$T_1$ are extensively explored in a temperature range from 5 to 300 K. Two
samples implanted with different nitrogen molecule ion fluences ($\rm
{N_2}^{+}$, $1\times 10^{14}/\rm cm^{2}$ and $1\times 10^{13}/\rm cm^{2}$) are
investigated, whose spin properties are shown to have similar
temperature-dependent behaviors. Still, the sample implanted with a lower ion
fluence has longer $T_{2}$ and $T_{1}$. We provide possible theoretical
explanations for the observed temperature-dependent dynamics. Our work promotes
the understanding of the temperature dependence of spin properties in
solid-state systems, which can be helpful for constructing wide
temperature-range thermometers based on the mature semiconductor material.",2104.12089v3
2021-05-03,Relaxation of a single defect spin by the low-frequency gyrotropic mode of a magnetic vortex,"We excite the gyrotropic mode of a magnetic vortex and observe the resulting
effect on the spin state of a nearby nitrogen-vacancy (NV) defect in diamond.
Thin permalloy disks fabricated on a diamond sample are magnetized in a vortex
state in which the magnetization curls around a central core. The magnetization
dynamics of this configuration are described by a discrete spectrum of confined
magnon modes, as well as a low-frequency gyrotropic mode in which the vortex
core precesses about its equilibrium position. Despite the spin transition
frequencies being far-detuned from the modes of the ferromagnet, we observe
enhanced relaxation of the NV spin when driving the gyrotropic mode. Moreover,
we map the spatial dependence of the interaction between the vortex and the
spin by translating the vortex core within the disk with an applied magnetic
field, resulting in steplike motion as the vortex is pinned and de-pinned. The
strong spin relaxation is observed when the vortex core is within approximately
250 nm of the NV center defect. We attribute this effect to the higher
frequencies in the spectrum of the magnetic fringe field arising from the
soliton-like nature of the gyrotropic mode when driven with sufficiently large
amplitude.",2105.00927v1
2021-06-08,Identification of Magnetic Interactions and High-field Quantum Spin Liquid in $α$-RuCl$_3$,"The frustrated magnet $\alpha$-RuCl$_3$ constitutes a fascinating quantum
material platform that harbors the intriguing Kitaev physics. However, a
consensus on its intricate spin interactions and field-induced quantum phases
has not been reached yet. Here we exploit multiple state-of-the-art many-body
methods and determine the microscopic spin model that quantitatively explains
major observations in $\alpha$-RuCl$_3$, including the zigzag order,
double-peak specific heat, magnetic anisotropy, and the characteristic M-star
dynamical spin structure, etc. According to our model simulations, the in-plane
field drives the system into the polarized phase at about 7 T and a thermal
fractionalization occurs at finite temperature, reconciling observations in
different experiments. Under out-of-plane fields, the zigzag order is
suppressed at 35 T, above which, and below a polarization field of 100 T level,
there emerges a field-induced quantum spin liquid. The fractional entropy and
algebraic low-temperature specific heat unveil the nature of a gapless spin
liquid, which can be explored in high-field measurements on $\alpha$-RuCl$_3$.",2106.04557v1
2021-06-20,Temperature and Pressure-driven Spin transitions and Piezochromism in a Mn-based Hybrid Perovskite,"Hybrid perovskites have been at the forefront of condensed matter research
particularly in context of device applications primarily in relation to
applications in the field of solar cells. In this article, we demonstrate that
several new functionalities may be added to the arsenal of hybrid perovskites,
in terms of external stimuli driven spin transitions as well as piezochromism.
As an example, we study Dimethylammonium Manganese Formate (DMAMnF), a hybrid
perovskite investigated quite extensively experimentally. We show by employing
first principles DFT+U calculations with the aid of ab initio molecular
dynamics calculations that DMAMnF shows temperature and pressure driven spin
transitions, from a low spin $S=1/2$ to a high spin $S=5/2$ state. This
transition is accompanied by a hysteresis, and we find that this hysteresis and
the transition temperature are quite close to room temperature, which is
desirable for device applications particularly in memory, display, and
switching devices. The operating pressure is a few GPa, which is accessible in
standard laboratory settings. We find that the cooperative behaviour showing up
as hysteresis accompanying the transition is driven primarily by elastic
interactions, assisted by magnetic superexchange between Mn atoms. Last but not
least we demonstrate that the spin transition is associated with piezochromism
which could also be important for applications.",2106.10675v2
2021-06-23,Field-Induced Spin Excitations in the Spin-1/2 Triangular-Lattice Antiferromagnet CsYbSe$_2$,"A layered triangular lattice with spin-1/2 ions is an ideal platform to
explore highly entangled exotic states like quantum spin liquid (QSL). Here, we
report a systematic in-field neutron scattering study on a perfect
two-dimensional triangular-lattice antiferromagnet, CsYbSe$_2$, a member of the
large QSL candidate family rare-earth chalcogenides. The elastic neutron
scattering measured down to 70 mK shows that there is a short-range
120$^{\circ}$ magnetic order at zero field. In the field-induced ordered
states, the spin-spin correlation lengths along the $c$ axis are relatively
short, although the heat capacity results indicate long-range magnetic orders
at 3 T $-$ 5 T. The inelastic neutron scattering spectra evolve from highly
damped continuum-like excitations at zero field to relatively sharp spin wave
modes at the plateau phase. Our extensive large-cluster density-matrix
renormalization group calculations with a Heisenberg triangular-lattice
nearest-neighbor antiferromagnetic model reproduce the essential features of
the experimental spectra, including continuum-like excitations at zero field,
series of sharp magnons at the plateau phase as well as two-magnon excitations
at high energy. This work presents comprehensive experimental and theoretical
overview of the unconventional field-induced spin dynamics in
triangular-lattice Heisenberg antiferromagnet and thus provides valuable
insight into quantum many-body phenomena.",2106.12451v2
2021-07-01,Charge disproportionation and Hund's insulating behavior in a five-orbital Hubbard model applicable to $d^4$ perovskites,"We explore the transition to a charge-disproportionated insulating phase in a
five-orbital cubic tight-binding model applicable to transition-metal
perovskites with a formal $d^4$ occupation of the transition-metal cation, such
as ferrates or manganites. We use dynamical mean-field theory to obtain the
phase diagram as a function of the average local Coulomb repulsion $U$ and the
Hund's coupling $J$. The main structure of the phase diagram follows from the
zero band-width (atomic) limit and represents the competition between high-spin
and low-spin homogeneous and an inhomogeneous charge-disproportionated state.
This results in two distinct insulating phases: the standard homogeneous Mott
insulator and the inhomogeneous charge-disproportionated insulator, recently
also termed Hund's insulator. We characterize the unconventional nature of this
Hund's insulating state. Our results are consistent with previous studies of
two- and three-orbital models applicable to isolated $t_{2g}$ and $e_g$
subshells, respectively, with the added complexity of the low-spin/high-spin
transition. We also test the applicability of an effective two-orbital
($e_g$-only) model with disordered $S=3/2$ $t_{2g}$ core spins. Our results
show that the overall features of the phase diagram in the high-spin region are
well described by this simplified two-orbital model but also that the spectral
features exhibit pronounced differences compared to the full five-orbital
description.",2107.00348v2
2021-07-07,Locking of skyrmion cores on a centrosymmetric discrete lattice: onsite versus offsite,"A magnetic skyrmion crystal (SkX) with a swirling spin configuration, which
is one of topological spin crystals as a consequence of an interference between
multiple spin density waves, shows a variety of noncoplanar spin patterns
depending on a way of superposing the waves. By focusing on a phase degree of
freedom among the constituent waves in the SkX, we theoretically investigate a
position of the skyrmion core on a discrete lattice, which is relevant with the
symmetry of the SkX. The results are obtained for the double exchange
(classical Kondo lattice) model on a discrete triangular lattice by the
variational calculations. We find that the skyrmion cores in both two SkXs with
the skyrmion number of one and two are locked at the interstitial site on the
triangular lattice, while it is located at the onsite by introducing a
relatively large easy-axis single-ion anisotropy. The variational parameters
and the resultant Fermi surfaces in each SkX spin texture are also discussed.
The different symmetry of the Fermi surfaces depending on the core position is
obtained when the skyrmion crystal is commensurate with the lattice. The
different Fermi-surface topology is directly distinguished by an electric probe
of angle-resolved photoemission spectroscopy. Furthermore, we show that the
SkXs obtained by the variational calculations are also confirmed by numerical
simulations on the basis of the kernel polynomial method and the Langevin
dynamics for the double exchange model and the simulated annealing for an
effective spin model.",2107.03500v2
2021-07-19,The final twist: A model of gravitational waves from precessing black-hole binaries through merger and ringdown,"We present PhenomPNR, a frequency-domain phenomenological model of the
gravitational-wave (GW) signal from binary-black-hole mergers that is tuned to
numerical relativity (NR) simulations of precessing binaries. In many current
waveform models, e.g., the ""Phenom"" and ""EOBNR"" families that have been used
extensively to analyse LIGO-Virgo GW observations, analytic approximations are
used to add precession effects to models of non-precessing (aligned-spin)
binaries, and it is only the aligned-spin models that are fully tuned to NR
results. In PhenomPNR we incorporate precessing-binary NR results in two ways:
(i) we produce the first NR-tuned model of the signal-based precession dynamics
through merger and ringdown, and (ii) we extend a previous aligned-spin model,
PhenomD, to include the effects of misaligned spins on the signal in the
co-precessing frame. The NR calibration has been performed on 40 simulations of
binaries with mass ratios between 1:1 and 1:8, where the larger black hole has
a dimensionless spin magnitude of 0.4 or 0.8, and we choose five angles of spin
misalignment with the orbital angular momentum. PhenomPNR has a typical
mismatch accuracy within 0.1% up to mass-ratio 1:4, and within 1% up to
mass-ratio 1:8.",2107.08876v1
2021-08-18,Harmonic dual dressing of spin one-half systems,"Controlled modifications of the quantum magnetic response are produced in
dressed systems by a high frequency, strong and not-resonant electromagnetic
field. This quantum control is greatly enhanced and enriched by the harmonic,
commensurable and orthogonally oriented dual dressing theoretically discussed
here. The secondary field enables a fine tuning of the qubit response, with
control parameters amplitude, harmonic content, spatial orientation and phase
relation. Our analysis is based on a perturbative approach and includes few
numerical solutions. The long-time dynamics is described in terms of an
anisotropic effective static magnetic field representing the handle for the
system full engineering. Through a low-order harmonic mixing the bichromatic
driving generates a rectified static field acting on the spin. The Zeeman
response becomes anisotropic in a triaxial geometry and includes a quadratic
contribution. Our dressing increases the two-level energy splitting, improving
the spin detection sensitivity. On the low field direction it compensates the
static fields applied in different geometries. A resonant spin exchange between
two species having very different magnetic response as electron and nucleus is
allowed by the dressing. The spin temporal evolution includes a micromotion at
harmonics of the driving frequency whose role in the spin detection is examined
and can be exploited in quantum information. The results presented here lay a
foundation for additional applications to be harnessed in quantum simulations.",2108.08174v2
2021-09-12,Zero-field magnetometry using hyperfine-biased nitrogen-vacancy centers near diamond surfaces,"Shallow nitrogen-vacancy (NV) centers in diamond are promising for
nano-magnetometry for they can be placed proximate to targets. To study the
intrinsic magnetic properties, zero-field magnetometry is desirable. However,
for shallow NV centers under zero field, the strain near diamond surfaces would
cause level anti-crossing between the spin states, leading to clock transitions
whose frequencies are insensitive to magnetic signals. Furthermore, the charge
noises from the surfaces would induce extra spin decoherence and hence reduce
the magnetic sensitivity. Here we demonstrate that the relatively strong
hyperfine coupling (130 MHz) from a first-shell 13C nuclear spin can provide an
effective bias field to an NV center spin so that the clock-transition
condition is broken and the charge noises are suppressed. The hyperfine bias
enhances the dc magnetic sensitivity by a factor of 22 in our setup. With the
charge noises suppressed by the strong hyperfine field, the ac magnetometry
under zero field also reaches the limit set by decoherence due to the nuclear
spin bath. In addition, the 130 MHz splitting of the NV center spin transitions
allows relaxometry of magnetic noises simultaneously at two well-separated
frequencies (~2.870 +/- 0.065 GHz), providing (low-resolution) spectral
information of high-frequency noises under zero field. The hyperfine-bias
enhanced zero-field magnetometry can be combined with dynamical decoupling to
enhance single-molecule magnetic resonance spectroscopy and to improve the
frequency resolution in nanoscale magnetic resonance imaging.",2109.05445v1
2021-09-16,Disappearance of spin glass behavior in ThCr2Si2-type intermetallic PrAu2Si2,"It is unexpected that a spin-glass transition, which generally occurs only in
the system with some form of disorder, was observed in the ThCr2Si2-type
compound PrAu2Si2 at a temperature of ~3 K. This puzzling phenomenon was later
explained based on a novel dynamic frustration model that does not involve
static disorder. We present the results of re-verification of the reported
spin-glass behaviors by measuring the physical properties of three
polycrystalline PrAu2Si2 samples annealed under different conditions. Indeed,
in the sample annealed at 827 C for one week, a spin-glass transition does
occur at a temperature of Tf=2.8 K as that reported previously in the
literature. However, it is newly found that the spin-glass effect is actually
more pronounced in the as-cast sample, and almost completely disappears in the
well-annealed (at 850 C for 4 weeks) sample. The apparent sample dependence of
the magnetic characteristics of PrAu2Si2 is discussed by comparing it with
similar phenomena observed in the isomorphic compounds URh2Ge2 and CeAu2Si2.
Our experimental results strongly suggest that the spin-glass behavior observed
in the as cast and insufficient annealed samples is most likely due to the
presence of small amount of crystalline impurities and/or partial site disorder
on the Au and Si sublattices, and thus is not the inherent characteristic of
ideal ThCr2Si2-type PrAu2Si2. The perfectly ordered PrAu2Si2 should be regarded
as a paramagnetic system with obvious crystal-field effects.",2109.07641v1
2021-09-30,Selection rules and dynamic magnetoelectric effect of the spin waves in multiferroic BiFeO$_3$,"We report the magnetic field dependence of the THz absorption and
non-reciprocal directional dichroism spectra of BiFeO$_3$ measured on the three
principal crystal cuts for fields applied along the three principal directions
of each cut. From the systematic study of the light polarization dependence we
deduced the optical selection rules of the spin-wave excitations. Our THz data,
combined with small-angle neutron scattering results showed that i) an in-plane
magnetic field rotates the $\mathbf{q}$ vectors of the cycloids perpendicular
to the magnetic field, and ii) the selection rules are mostly determined by the
orientation of the $\mathbf{q}$ vector with respect to the electromagnetic
fields. We observed a magnetic field history dependent change in the strength
and the frequency of the spin-wave modes, which we attributed to the change of
the orientation and the length of the cycloidal $\mathbf{q}$ vector,
respectively. Finally, we compared our experimental data with the results of
linear spin-wave theory that reproduces the magnetic field dependence of the
spin-wave frequencies and most of the selection rules, from which we identified
the spin-polarization coupling terms relevant for the optical magnetoelectric
effect.",2109.14990v1
2021-11-05,Quadrupolar magnetic excitations in an isotropic spin-1 antiferromagnet,"The microscopic origins of emergent behaviours in condensed matter systems
are encoded in their excitations. In ordinary magnetic materials, single
spin-flips give rise to collective dipolar magnetic excitations called magnons.
Likewise, multiple spin-flips can give rise to multipolar magnetic excitations
in magnetic materials with spin $\mathbf{S} \boldsymbol{\ge} \mathbf{1}$.
Unfortunately, since most experimental probes are governed by dipolar selection
rules, collective multipolar excitations have generally remained elusive. For
instance, only dipolar magnetic excitations have been observed in isotropic
$\mathbf{S}\boldsymbol{=}\mathbf{1}$ Haldane spin systems. Here, we unveil a
hidden quadrupolar constituent of the spin dynamics in antiferromagnetic
$\mathbf{S}\boldsymbol{=}\mathbf{1}$ Haldane chain material
Y$_\mathbf{2}$BaNiO$_\mathbf{5}$ using Ni $\mathbf{L_3}$-edge resonant
inelastic x-ray scattering. Our results demonstrate that pure quadrupolar
magnetic excitations can be probed without direct interactions with dipolar
excitations or anisotropic perturbations. Originating from on-site double
spin-flip processes, the quadrupolar magnetic excitations in
Y$_\mathbf{2}$BaNiO$_\mathbf{5}$ show a remarkable dual nature of collective
dispersion. While one component propagates as non-interacting entities, the
other behaves as a bound quadrupolar magnetic wave. This result highlights the
rich and largely unexplored physics of higher-order magnetic excitations.",2111.03625v1
2021-11-30,Competing $U(1)$ and $\mathbb{Z}_2$ dipolar-octupolar quantum spin liquids on the pyrochlore lattice: application to Ce$_2$Zr$_2$O$_7$,"Recent experiments on the dipolar-octupolar pyrochlore compound
Ce$_2$Zr$_2$O$_7$ indicate that it may realize a three-dimensional quantum spin
liquid (QSL). In particular, the analyses of available data suggest that the
system is in a region of parameter space, where the so-called $\pi$-flux $U(1)$
octupolar quantum spin ice (QSI) with an emergent photon could be realized. On
the other hand, because the system is far from the perturbative classical spin
ice regime, it is unclear whether the quantum ground state is primarily a
coherent superposition of 2-in-2-out configurations as in the canonical QSI
phases. In this work, we explore other possible competing quantum spin liquid
states beyond QSI using the Schwinger boson parton construction of the
dipolar-octupolar pseudospin-1/2 model. After classifying all symmetric $U(1)$
and $\mathbb{Z}_2$ QSLs using the projective symmetry group (PSG), we construct
a mean-field phase diagram that possesses a number of important features
observed in an earlier exact diagonalization study. In the experimentally
relevant frustrated region of the phase diagram, we find two closely competing
gapped $\mathbb{Z}_2$ QSLs with a narrow spinon dispersion. The equal-time and
dynamical spin structure factors of these states show key features similar to
what was reported in neutron scattering experiments. Hence, these QSLs are
closely competing ground states in addition to the $\pi$-flux $U(1)$ QSI, and
they should be taken into account on equal footing for the interpretation of
experiments on Ce$_2$Zr$_2$O$_7$.",2112.00014v1
2021-12-02,Entanglement and scattering in quantum electrodynamics: S-matrix information from an entangled spectator particle,"We consider a general quantum field relativistic scattering involving two
half spin fermions, $A$ and $B$, which are initially entangled with another
fermion $C$ that does not participate in the scattering dynamics. We construct
general expressions for the reduced spin matrices for the out-state considering
a general tripartite spin-entangled state. In particular we study an inelastic
QED process at tree-level, namely $e^-e^+\rightarrow \mu^- \mu^+$ and a half
spin fermion $C$ as an spectator particle which can be entangled to the $AB$
system in the following ways: W state, GHZ state, $|\text{A}^\alpha \rangle
\otimes |\Psi^{\pm} \rangle_{\text{BC}}$ and $|\text{A}^\alpha \rangle \otimes
|\Phi^{\pm} \rangle_{\text{BC}}$, where $\{|\Psi^{\pm} \rangle,|\Phi^{\pm}
\rangle\}$ are the Bell basis states and $|\text{A}^\alpha \rangle$ is a spin
superposition state of system $A$. We calculate the von-Neumann entropy
variation before and after the scattering for the particle $C$ and show that
spin measurements in $C$ contain numerical information about the total cross
section of the process. We compare the initial states W and GHZ as well as
study the role played by the parameter $\alpha$ in the evaluation of the
entropy variations and the cross section encoded in the spectator particle.",2112.01300v2
2022-01-10,Impact of extreme spins and mass ratios on the post-merger observables of high-mass binary neutron stars,"The gravitational-wave events GW170817 and GW190425 have led to a number of
important insights on the equation of state of dense matter and the properties
of neutron stars, such as their radii and the maximum mass. Some of these
conclusions have been drawn on the basis of numerical-relativity simulations of
binary neutron-star mergers with vanishing initial spins. While this may be a
reasonable assumption in equal-mass systems, it may be violated in the presence
of large mass asymmetries accompanied by the presence of high spins. To
quantify the impact of high spins on multi-messenger gravitational-wave events,
we have carried out a series of high-mass binary neutron-star mergers with a
highly spinning primary star and large mass asymmetries that have been modelled
self-consistently using two temperature-dependent equations of state. We show
that, when compared with equal-mass, irrotational binaries, these systems can
lead to significant differences in the remnant lifetime, in the dynamical
ejecta, in the remnant disc masses, in the secular ejecta, and on the bulk
kilonova properties. These differences could be exploited to remove the
degeneracy between low- and high-spin priors in the detection of gravitational
waves from binary neutron-star mergers.",2201.03632v2
2022-01-11,Resonant Precession of Magnetization and Precession -- Induced DC voltages in FeGaB Thin Films,"Measurements of frequency dependent ferromagnetic resonance (FMR) and spin
pumping driven dc voltage (V_{dc}) are reported for amorphous films of
Fe_{78}Ga_{13}B_{9} (FeGaB) alloy to address the phenomenon of self-induced
inverse spin Hall effect (ISHE) in plain films of metallic ferromagnets. The
V_{dc} signal, which is antisymmetric on field reversal, comprises of symmetric
and asymmetric Lorentzians centered around the resonance field. Dominant role
of thin film size effects is seen in setting the magnitude of static
magnetization, V_{dc} and dynamics of magnetization precession in thinner films
(\leq 8 nm). The film thickness dependence of magnetization parameters
indicates the presence of a magnetically disordered region at the
film-substrate interface, which may promote preferential flow of spins
generated by the precessing magnetization towards the substrate. However, the
V_{dc} signal also draws contributions from rectification effects of a \approx
0.4 \% anisotropic magnetoresistance and a large (\approx 54 n\Omega.m)
anomalous Hall resistivity (AHR) of these films which ride over the effect of
spin-orbit coupling driven spin-to-charge conversion near the film-substrate
interface. We have addressed these data in the framework of the existing
theories of electrodynamics of a ferromagnetic film subjected to
radio-frequency field in a coplanar waveguide geometry. Our estimation of the
self-induced ISHE for the sample with 54 n\Omega.m AHR shows that it may
contribute significantly (\approx 90\%) to the measured symmetric voltage. This
study is expected to be very useful for fully understanding the spin pumping
induced dc voltages in metallic ferromagnets with disordered interfaces and
large anomalous Hall effect.",2201.03739v1
2022-01-26,SOiCI and iCISO: Combining iterative configuration interaction with spin-orbit coupling in two ways,"The near-exact iCIPT2 approach for strongly correlated systems of electrons,
which stems from the combination of iterative configuration interaction (iCI,
an exact solver of full CI) with configuration selection for static correlation
and second-order perturbation theory (PT2) for dynamic correlation, is extended
to the relativistic domain. In the spirit of spin separation, relativistic
effects are treated in two steps: scalar relativity is treated by the
infinite-order, spin-free part of the exact two-component (X2C) relativistic
Hamiltonian, whereas spin-orbit coupling (SOC) is treated by the first-order,
Douglas-Kroll-Hess-like SOC operator derived from the same X2C Hamiltonian. Two
possible combinations of iCIPT2 with SOC are considered, i.e., SOiCI and iCISO.
The former treats SOC and electron correlation on an equal footing, whereas the
latter treats SOC in the spirit of state interaction, by constructing and
diagonalizing an effective spin-orbit Hamiltonian matrix in a small number of
correlated scalar states. Both double group and time reversal symmetries are
incorporated to simplify the computation. Pilot applications reveal that SOiCI
is very accurate for the spin-orbit splitting (SOS) of heavy atoms, whereas the
computationally very cheap iCISO can safely be applied to the SOS of light
atoms and even of systems containing heavy atoms when SOC is largely quenched
by ligand fields.",2201.10783v1
2022-02-11,Disorder-induced broadening of the spin waves in a triangular-lattice quantum-spin-liquid candidate YbZnGaO$_4$,"Disorder is important in the study of quantum spin liquids, but its role on
the spin dynamics remains elusive. Here, we explore the disorder effect by
investigating the magnetic-field dependence of the low-energy magnetic
excitations in a triangular-lattice frustrated magnet YbZnGaO$_4$ with
inelastic neutron scattering. With an intermediate field of 2.5 T applied along
the $c$-axis, the broad continuum at zero field becomes more smeared both in
energy and momentum. With a field up to 10 T, which fully polarizes the
magnetic moments, we observe clear spin-wave excitations with a gap of
$\sim$1.4 meV comparable to the bandwidth. However, the spectra are
significantly broadened. The excitation spectra both at zero and high fields
can be reproduced by performing classical Monte Carlo simulations which take
into account the disorder effect arising from the random site mixing of
nonmagnetic Zn$^{2+}$ and Ga$^{3+}$ ions. These results elucidate the critical
role of disorder in broadening the magnetic excitation spectra and mimicking
the spin-liquid features in frustrated quantum magnets.",2202.05462v1
2022-03-11,Binary Dynamics Through the Fifth Power of Spin at $\mathcal{O}(G^2)$,"We use a previously developed scattering-amplitudes-based framework for
determining two-body Hamiltonians for generic binary systems with arbitrary
spin $S$. By construction this formalism bypasses difficulties with unphysical
singularities or higher-time derivatives. This framework has been previously
used to obtain the exact velocity dependence of the $\mathcal O(G^2)$
quadratic-in-spin two-body Hamiltonian. We first evaluate the $S^3$ scattering
angle and two-body Hamiltonian at this order in $G$, including not only all
operators corresponding to the usual worldline operators, but also an
additional set due to an interesting subtlety. We then evaluate $S^4$ and $S^5$
contributions at $\mathcal O(G^2)$ which we confirm by comparing against
aligned-spin results. We conjecture that a certain shift symmetry together with
a constraint on the high-energy growth of the scattering amplitude specify the
Wilson coefficients for the Kerr black hole to all orders in the spin and
confirm that they reproduce the previously-obtained results through $S^4$.",2203.06202v3
2022-04-08,Manipulating the transverse spin angular momentum and Belinfante momentum of spin-polarized light by a tilted stratified medium in optical tweezers,"In the recent past, optical tweezers incorporating a stratified medium have
been exploited to generate complex translational and rotational dynamics in
mesoscopic particles due to the coupling between the spin and orbital angular
momentum of the light, generated as a consequence of the tight focusing of
light by a high numerical aperture objective lens into the stratified medium.
Here, we consider an optical tweezers system with a tilted stratified medium
(direction of stratification at an angle with the axis of the incident beam),
and show that for input circularly polarized Gaussian beams, the resulting
spin-orbit interaction deeply influences the generation of transverse spin
angular momentum (TSAM) and Belinfante momentum of light, and allows additional
control on their magnitude. Importantly, the TSAM generated in our system
consists of both the orthogonal components, which is in sharp contrast to the
case of evanescent waves and surface plasmons, where only one of the TSAM
components are generated. The broken symmetry due to the tilt ensures that,
depending upon the helicity of the input beam, the magnitude of the mutually
orthogonal components of the TSAM depend entirely on the tilt angle. This may
prove to be an effective handle in exotic spin-controlled manipulation of
particles in experiments.",2204.04316v2
2022-06-13,Charge and spin correlations in insulating and incoherent metal states of twisted bilayer graphene,"We study electronic, charge, and magnetic properties of twisted bilayer
graphene with fillings $2\leq n\leq 6$ per moire unit cell within the recently
introduced formulation of extended dynamical mean-field theory (E-DMFT) for
two-sublattice systems. We use previously obtained hopping parameters between
the states, described by Wannier functions, centered at the lattice spots of AB
and BA stacking, and the long-range Coulomb interaction, obtained within cRPA
analysis. We show that account of spin exchange between AB and BA nearest
neighbour spots is crucial to introduce charge and spin correlations between
these spots. Account of this exchange yields preferable concentration of
electrons in the same valley, with the tendency of parallel spin alignment of
electrons in AB and BA spots, in agreement with earlier results of the strong
coupling analysis, suggested SU(2)$\times$SU(2) emergent spin-valley symmetry.
The local spectral functions show almost gapped state at the fillings
$n=2,4,6$, and incoherent metal state for the other fillings. We find that in
both cases the local states of electrons have rather long lifetime. At the same
time, the non-local charge- and spin susceptibilities, obtained within the
ladder approximation, are peaked at incommensurate wave vectors, which implies
that the above discussed ordering tendencies are characterised by an
incommensurate pattern.",2206.06231v3
2022-06-27,Optical readout of singlet fission biexcitons with photoluminescence detected magnetic resonance,"Molecular spin systems based on photoexcited triplet pairs formed via singlet
fission (SF) are attractive as carriers of quantum information because of their
potentially pure and controllable spin polarization, but developing systems
that offer optical routes to readout as well as initialization is challenging.
Herein, we characterize the electron spin magnetic resonance change in
photoluminescence intensity for a tailored organic molecular crystal while
sweeping a microwave drive up to 10 GHz in a broadband loop structure. We
observe resonant transitions for both triplet and quintet spin sublevel
populations showing their optical sensitivity, and revealing zero-field
parameters for each. We map the evolution of these spectra in both microwave
frequency and magnetic field, producing a pattern of optically-detected
magnetic resonance (ODMR) peaks. Fits to this data using a suitable model
suggest significant spin polarization in this system with orientation
selectivity. Unusual excitation intensity dependence is also observed, which
inverts the sign of the ODMR signal for triplet features, but not for quintet.
These observations demonstrate optical detection of the spin sublevel
population dictated by SF and intermolecular geometry, and provide unique
insight into the dynamics of triplet pairs.",2206.13636v1
2022-09-20,Theoretical discrepancies in the nucleon spin structure and the hyperfine splitting of muonic hydrogen,"Two groups, ours (Mainz) and Bochum, have recently been re-evaluating the
spin polarizabilities and spin structure functions at low $Q$, using the baryon
chiral perturbation theory (B$\chi$PT), the manifestly-covariant counterpart of
the heavy-baryon chiral perturbation theory (HB$\chi$PT). Whilst the two groups
agree that the B$\chi$PT framework works better than HB$\chi$PT in this sector,
their quantitative results disagree in some of the quantities; most notably,
the proton spin polarizabilities $\gamma_0$ and $\delta_{LT}$. These
discrepancies are especially intriguing in light of new experimental data
coming from the Jefferson Lab ""Spin Physics Program"". The preliminary data on
the proton are reported by Karl Slifer in a plenary session of this workshop.
  Another theoretical discrepancy is emerging in the proton-polarizability
contribution to the hyperfine splitting (hfs) in hydrogen and muonic hydrogen.
Our B$\chi$PT calculation shows a significantly smaller effect than the
state-of-the-art data-driven evaluations based on empirical spin structure
functions. The smaller polarizability contribution leads to a smaller Zemach
radius of the proton. This discrepancy could be relevant for the planned
first-ever measurement of the ground-state hfs in muonic hydrogen.",2209.09995v1
2022-10-12,Effective dark energy through spin-gravity coupling,"We investigate cosmological scenarios with spin-gravity coupling. In
particular, due to the spin of the baryonic and dark matter particles and its
coupling to gravity, they probe an effective spin-dependent metric, which can
be calculated semi-classically in the Mathisson-Papapetrou-Tulczyjew-Dixon
formalism. Hence, the usual field equations give rise to modified Friedmann
equations, in which the extra terms can be identified as an effective
dark-energy sector. Additionally, we obtain an effective interaction between
the matter and dark-energy sectors. In the case where the spin-gravity coupling
switches off, we recover standard $\Lambda$CDM cosmology. We perform a
dynamical system analysis and we find a matter-dominated point that can
describe the matter era, and a stable late-time solution corresponding to
acceleration and dark-energy domination. For small values of the spin coupling
parameter, deviations from $\Lambda$CDM concordance scenario are small, however
for larger values they can be brought to the desired amount, leading to
different dark-energy equation-of-state parameter behavior, as well as to
different transition redshift from acceleration to deceleration. Finally, we
confront the model predictions with Hubble function data.",2210.06598v2
2022-11-01,Trimer quantum spin liquid in a honeycomb array of Rydberg atoms,"Quantum spin liquids are elusive but paradigmatic examples of strongly
correlated quantum states that are characterized by long-range quantum
entanglement. Recently, the direct signatures of a gapped topological
$\mathbb{Z}_2$ spin liquid have been observed in a system of Rydberg atoms
arrayed on the ruby lattice. Here, we illustrate the concrete realization of a
fundamentally different class of spin liquids in a honeycomb array of Rydberg
atoms. Exploring the quantum phase diagram of this system using both
density-matrix renormalization group and exact diagonalization simulations,
several density-wave-ordered phases are characterized and their origins
explained. More interestingly, in the regime where third-nearest-neighbor atoms
lie within the Rydberg blockade radius, we find a novel ground state -- with an
emergent $\mathrm{U}(1)\times \mathrm{U}(1)$ local symmetry -- formed from
superpositions of classical {\it trimer} configurations on the dual triangular
lattice. The fidelity of this trimer spin liquid state can be enhanced via
dynamical preparation, which we explain by a Rydberg-blockade-based projection
mechanism associated with the smooth turnoff of the laser drive. Finally, we
discuss the robustness of the trimer spin liquid phase under realistic
experimental parameters and demonstrate that our proposal can be readily
implemented in current Rydberg atom quantum simulators.",2211.00653v1
2022-11-11,Simulating Spin-Orbit Coupling With Quasidegenerate N-Electron Valence Perturbation Theory,"We present the first implementation of spin-orbit coupling effects in fully
internally contracted second-order quasidegenerate N-electron valence
perturbation theory (SO-QDNEVPT2). The SO-QDNEVPT2 approach enables the
computations of ground- and excited-state energies and oscillator strengths
combining the description of static electron correlation with an efficient
treatment of dynamic correlation and spin-orbit coupling. In addition to
SO-QDNEVPT2 with the full description of one- and two-body spin-orbit
interactions at the level of two-component Breit-Pauli Hamiltonian, our
implementation also features a simplified approach that takes advantage of
spin-orbit mean-field approximation (SOMF-QDNEVPT2). The accuracy of these
methods is tested for the group 14 and 16 hydrides, 3d and 4d transition metal
ions, and two actinide dioxides (neptunyl and plutonyl dications). The
zero-field splittings of group 14 and 16 molecules computed using SO-QDNEVPT2
and SOMF-QDNEVPT2 are in a good agreement with the available experimental data.
For the 3d transition metal ions, the SO-QDNEVPT2 method is significantly more
accurate than SOMF-QDNEVPT2, while no substantial difference in the performance
of two methods is observed for the 4d ions. Finally, we demonstrate that for
the actinide dioxides the results of SO-QDNEVPT2 and SOMF-QDNEVPT2 are in a
good agreement with the data from previous theoretical studies of these
systems. Overall, our results demonstrate that SO-QDNEVPT2 and SOMF-QDNEVPT2
are promising multireference methods for treating spin-orbit coupling with a
relatively low computational cost.",2211.06466v3
2022-11-18,Quantum-classical correspondence of strongly chaotic many-body spin models,"We study the quantum-classical correspondence for systems with interacting
spin-particles that are strongly chaotic in the classical limit. This is done
in the presence of constants of motion associated with the fixed angular
momenta of individual spins. Our analysis of the Lyapunov spectra reveals that
the largest Lyapunov exponent agrees with the Lyapunov exponent that determines
the local instability of each individual spin moving under the influence of all
other spins. Within this picture, we introduce a rigorous and simple test of
ergodicity for the spin motion, and use it to identify when classical chaos is
both strong and global in phase space. In the quantum domain, our analysis of
the Hamiltonian matrix in a proper representation allows us to obtain the
conditions for the onset of quantum chaos as a function of the model
parameters. From the comparison between the quantum and classical domains, we
demonstrate that quantum quantities, such as the local density of states (LDOS)
and the shape of the chaotic eigenfunctions written in the non-interacting
many-body basis, have well-defined classical counterparts. Another central
finding is the relationship between the Kolmogorov-Sinai entropy and the width
of the LDOS, which is useful for studies of many-body dynamics.",2211.10451v1
2022-11-21,General time-reversal equivariant neural network potential for magnetic materials,"This study introduces time-reversal E(3)-equivariant neural network and
SpinGNN++ framework for constructing a comprehensive interatomic potential for
magnetic systems, encompassing spin-orbit coupling and noncollinear magnetic
moments. SpinGNN++ integrates multitask spin equivariant neural network with
explicit spin-lattice terms, including Heisenberg, Dzyaloshinskii-Moriya,
Kitaev, single-ion anisotropy, and biquadratic interactions, and employs
time-reversal equivariant neural network to learn high-order spin-lattice
interactions using time-reversal E(3)-equivariant convolutions. To validate
SpinGNN++, a complex magnetic model dataset is introduced as a benchmark and
employed to demonstrate its capabilities. SpinGNN++ provides accurate
descriptions of the complex spin-lattice coupling in monolayer CrI$_3$ and
CrTe$_2$, achieving sub-meV errors. Importantly, it facilitates large-scale
parallel spin-lattice dynamics, thereby enabling the exploration of associated
properties, including the magnetic ground state and phase transition.
Remarkably, SpinGNN++ identifies a new ferrimagnetic state as the ground
magnetic state for monolayer CrTe2, thereby enriching its phase diagram and
providing deeper insights into the distinct magnetic signals observed in
various experiments.",2211.11403v3
2022-11-22,Magnetic resonance study of rare-earth titanates,"We present a nuclear magnetic resonance (NMR) and electron spin resonance
(ESR) study of rare-earth titanates derived from the spin-1/2 Mott insulator
YTiO$_3$. Measurements of single-crystalline samples of (Y,Ca,La)TiO$_3$ in a
wide range of isovalent substitution (La) and hole doping (Ca) reveal several
unusual features in the paramagnetic state of these materials. $^{89}$Y NMR
demonstrates a clear discrepancy between the static and dynamic local magnetic
susceptibilities, with deviations from Curie-Weiss behavior far above the Curie
temperature $T_C$. No significant changes are observed close to $T_C$, but a
suppression of fluctuations is detected in the NMR spin-lattice relaxation time
at temperatures of about $3\times T_C$. Additionally, the nuclear spin-spin
relaxation rate shows an unusual peak in dependence on temperature for all
samples. ESR of the unpaired Ti electron shows broad resonance lines at all
temperatures and substitution/doping levels, which we find to be caused by
short electronic spin-lattice relaxation times. We model the relaxation as an
Orbach process that involves a low-lying electronic excited state, which
enables the determination of the excited-state gap from the temperature
dependence of the ESR linewidths. We ascribe the small gap to Jahn-Teller
splitting of the two lower Ti $t_{2g}$ orbitals. The value of the gap closely
follows $T_C$ and is consistent with the temperatures at which deviations from
Curie-Weiss fluctuations are observed in NMR. These results provide insight
into the interplay between orbital and spin degrees of freedom in rare-earth
titanates and indicate that full orbital degeneracy lifting is associated with
ferromagnetic order.",2211.12387v2
2022-12-23,Spin-lattice interaction parameters from first principles: theory and implementation,"A scheme is presented to calculate on a first-principles level
  the spin-lattice coupling (SLC) parameters needed to perform
  combined molecular-spin dynamics (MSD) simulations. By treating changes to
the spin configuration and atomic positions on the same level, closed
expressions for the atomic SLC parameters could be derived in a coherent way up
to any order. The properties of the SLC parameters are discussed considering
separately the symmetric and antisymmetric parts of the SLC tensor. The changes
due to atomic displacements of the spin-spin exchange coupling (SSC) parameters
estimated using the SLC parameters are compared with the SSC parameters
calculated for an embedded cluster with the central atom displaced,
demonstrating good agreement of these results. Moreover, this allows to study
the impact of different SLC contributions, linear and quadratic with respect to
displacements, on the properties of the modified SSC parameters. In addition,
we represent an approach to calculate the site-diagonal SLC parameters
characterizing local magnetic anisotropy induced by a lattice distortion, which
is a counterpart of the approach based on magnetic torque used for the
investigations of magneto-crystalline anisotropy (MCA) as well as for
calculations of the MCA constants. In particular, the dependence of the induced
magnetic torque on different types of atomic displacements is analyzed.",2212.12430v1
2022-12-24,Extending the coherence time of spin defects in hBN enables advanced qubit control and quantum sensing,"Spin defects in hexagonal Boron Nitride (hBN) attract increasing interest for
quantum technology since they represent optically-addressable qubits in a van
der Waals material. In particular, negatively-charged boron vacancy centers
(${V_B}^-$) in hBN have shown promise as sensors of temperature, pressure, and
static magnetic fields. However, the short spin coherence time of this defect
currently limits its scope for quantum technology. Here, we apply dynamical
decoupling techniques to suppress magnetic noise and extend the spin coherence
time by nearly two orders of magnitude, approaching the fundamental $T_1$
relaxation limit. Based on this improvement, we demonstrate advanced spin
control and a set of quantum sensing protocols to detect electromagnetic
signals in the MHz range with sub-Hz resolution. This work lays the foundation
for nanoscale sensing using spin defects in an exfoliable material and opens a
promising path to quantum sensors and quantum networks integrated into
ultra-thin structures.",2212.12826v1
2023-01-10,Magnetic anisotropy and low-energy spin dynamics in the van der Waals compounds Mn$_{2}$P$_{2}$S$_{6}$ and MnNiP$_{2}$S$_{6}$,"We report the detailed high-field and high-frequency electron spin resonance
(HF-ESR) spectroscopic study of the single-crystalline van der Waals compounds
Mn$_{2}$P$_{2}$S$_{6}$ and MnNiP$_{2}$S$_{6}$. Analysis of magnetic excitations
shows that in comparison to Mn$_{2}$P$_{2}$S$_{6}$ increasing the Ni content
yields a larger magnon gap in the ordered state and a larger g-factor value and
its anisotropy in the paramagnetic state. The studied compounds are found to be
strongly anisotropic having each the unique ground state and type of magnetic
order. Stronger deviation of the g-factor from the free electron value in the
samples containing Ni suggests that the anisotropy of the exchange is an
important contributor to the stabilization of a certain type of magnetic order
with particular anisotropy. At temperatures above the magnetic order, we have
analyzed the spin-spin correlations resulting in a development of slowly
fluctuating short-range order. They are much stronger pronounced in
MnNiP$_{2}$S$_{6}$ compared to Mn$_{2}$P$_{2}$S$_{6}$. The enhanced spin
fluctuations in MnNiP$_{2}$S$_{6}$ are attributed to the competition of
different types of magnetic order. Finally, the analysis of the temperature
dependent critical behavior of the magnon gaps below the ordering temperature
in Mn$_{2}$P$_{2}$S$_{6}$ suggests that the character of the spin wave
excitations in this compound undergoes a field induced crossover from a 3D-like
towards 2D XY regime.",2301.04239v2
2023-02-15,Momentum-independent magnetic excitation continuum in the honeycomb iridate H$_3$LiIr$_2$O$_6$,"In the search for realizations of Quantum Spin Liquids (QSL), it is essential
to understand the interplay between inherent disorder and the correlated
fluctuating spin ground state. H$_3$LiIr$_2$O$_6$ is regarded as a spin liquid
proximate to the Kitaev-limit (KQSL) in which H zero-point motion and stacking
faults are known to be present. Bond disorder has been invoked to account for
the existence of unexpected low-energy spin excitations. Controversy remains
about the nature of the underlying correlated state and if any KQSL physics
survives. Here, we use resonant X-ray spectroscopies to map the collective
excitations in H$_3$LiIr$_2$O$_6$ and characterize its magnetic state. We
uncover a broad bandwidth and momentum-independent continuum of magnetic
excitations at low temperatures that are distinct from the paramagnetic state.
The center energy and high-energy tail of the continuum are consistent with
expectations for dominant ferromagnetic Kitaev interactions between dynamically
fluctuating spins. The absence of a momentum dependence to these excitations
indicates a broken translational invariance. Our data support an interpretation
of H$_3$LiIr$_2$O$_6$ as a disordered topological spin liquid in close
proximity to bond-disordered versions of the KQSL. Our results shed light on
how random disorder affects topological magnetic states and have implications
for future experimental and theoretical works toward realizing the Kitaev model
in condensed matter systems",2302.07907v1
2023-02-28,Symmetries and spectral statistics in chaotic conformal field theories,"We discuss spectral correlations in coarse-grained chaotic two-dimensional
CFTs with large central charge. We study a partition function describing the
dense part of the spectrum of primary states in a way that disentangles the
chaotic properties of the spectrum from those which are a consequence of
Virasoro symmetry and modular invariance. We argue that random matrix
universality in the near-extremal limit is an independent feature of each spin
sector separately; this is a non-trivial statement because the exact spectrum
is fully determined by only the spectrum of spin zero primaries and those of a
single non-zero spin (""spectral determinacy""). We then describe an argument
analogous to the one leading to Cardy's formula for the averaged density of
states, but in our case applying it to spectral correlations: assuming
statistical universalities in the near-extremal spectrum in all spin sectors,
we find similar random matrix universality in a large spin regime far from
extremality.",2302.14482v4
2023-03-03,Detecting spin bath polarization with quantum quench phase shifts of single spins in diamond,"Single-qubit sensing protocols can be used to measure qubit-bath coupling
parameters. However, for sufficiently large coupling, the sensing protocol
itself perturbs the bath, which is predicted to result in a characteristic
response in the sensing measurements. Here, we observe this bath perturbation,
also known as a quantum quench, by preparing the nuclear spin bath of a
nitrogen-vacancy (NV) center in polarized initial states and performing
phase-resolved spin echo measurements on the NV electron spin. These
measurements reveal a time-dependent phase determined by the initial state of
the bath. We derive the relationship between sensor phase and Gaussian spin
bath polarization, and apply it to reconstruct both the axial and transverse
polarization components. Using this insight, we optimize the transfer
efficiency of our dynamic nuclear polarization sequence. This technique for
directly measuring bath polarization may assist in preparing high-fidelity
quantum memory states, improving nanoscale NMR methods, and investigating
non-Gaussian quantum baths.",2303.02233v1
2023-03-09,Formations and dynamics of two-dimensional spinning asymmetric quantum droplets controlled by a PT-symmetric potential,"In this paper, vortex solitons are produced for a variety of 2D spinning
quantum droplets (QDs) in a PT-symmetric potential, modeled by the amended
Gross-Pitaevskii equation with Lee-Huang-Yang corrections. In particular, exact
QD states are obtained under certain parameter constraints, providing a guide
to finding the respective generic family. In a parameter region of the unbroken
PT symmetry, different families of QDs originating from the linear modes are
obtained in the form of multipolar and vortex droplets at low and high values
of the norm, respectively, and their stability is investigated. In the spinning
regime, QDs become asymmetric above a critical rotation frequency, most of them
being stable. The effect of the PT -symmetric potential on the spinning and
nonspinning QDs is explored by varying the strength of the gain-loss
distribution. Generally, spinning QDs trapped in the PT -symmetric potential
exhibit asymmetry due to the energy flow affected by the interplay of the
gain-loss distribution and rotation. Finally, interactions between spinning or
nonspinning QDs are explored, exhibiting elastic collisions under certain
conditions.",2303.05210v1
2023-04-10,"Spin-phonon interactions and magnetoelectric coupling in Co$_4$$B_2$O$_9$ ($B$ = Nb, Ta)","In order to explore the consequences of spin-orbit coupling on spin-phonon
interactions in a set of chemically-similar mixed metal oxides, we measured the
infrared vibrational properties of Co$_4B_2$O$_9$ ($B$ = Nb, Ta) as a function
of temperature and compared our findings with lattice dynamics calculations and
several different models of spin-phonon coupling. Frequency vs. temperature
trends for the Co$^{2+}$ shearing mode near 150 cm$^{-1}$ reveal significant
shifts across the magnetic ordering temperature that are especially large in
relative terms. Bringing these results together and accounting for
noncollinearity, we obtain spin-phonon coupling constants of -3.4 and -4.3
cm$^{-1}$ for Co$_4$Nb$_2$O$_9$ and the Ta analog, respectively. Analysis
reveals that these coupling constants derive from interlayer (rather than
intralayer) exchange interactions and that the interlayer interactions contain
competing antiferromagnetic and ferromagnetic contributions. At the same time,
beyond-Heisenberg terms are minimized due to fortuitous symmetry
considerations, different than most other 4$d$- and 5$d$-containing oxides.
Comparison with other contemporary oxides shows that spin-phonon coupling in
this family of materials is among the strongest ever reported, suggesting an
origin for magnetoelectric coupling.",2304.04865v1
2023-06-09,Static and dynamical properties of the spin-5/2 nearly ideal triangular lattice antiferromagnet Ba3MnSb2O9,"We study the ground state and spin excitations in Ba3MnSb2O9, an easy-plane S
= 5/2 triangular lattice antiferromagnet. By combining single-crystal neutron
scattering, electric spin resonance (ESR), and spin wave calculations, we
determine the frustrated quasi-two-dimensional spin Hamiltonian parameters
describing the material. While the material has a slight monoclinic structural
distortion, which could allow for isosceles-triangular exchanges and biaxial
anisotropy by symmetry, we observe no deviation from the behavior expected for
spin waves in the in-plane 120o state. Even the easy-plane anisotropy is so
small that it can only be detected by ESR in our study. In conjunction with the
quasi-two-dimensionality, our study establishes that Ba3MnSb2O9 is a nearly
ideal triangular lattice antiferromagnet with the quasi-classical spin S = 5/2,
which suggests that it has the potential for an experimental study of Z- or
Z2-vortex excitations.",2306.05802v2
2023-06-20,The spin axes of globular clusters and correlations with gamma-ray emission,"A growing number of Milky Way globular clusters have been identified to
possess a noticeable degree of solid-body rotation. For several clusters, the
combination of stellar proper motions and radial velocities allows for
3-dimensional spin axes to be extracted. In this paper we consider the
orientations of these spin axes, and ask whether they are correlated with any
other properties of the clusters -- either global properties to do with their
orbits and origin, or internal properties related to the cluster composition.
We discuss the possibility of alignments between the spin axes of globular
clusters, chemodynamical groupings, and their orbital poles. We also point out
a previously unidentified negative correlation between the measured gamma-ray
emissivities and the inclination of the globular cluster spins with respect to
the line of sight. Given that this correlation is not present in other
wavelengths, we cannot conclusively attribute it solely to sampling bias. If
the correlation holds up to scrutiny with more data, it may be indicative of
sources of anisotropic gamma-ray emission in globular clusters. We discuss the
plausibility of such an anisotropy arising from a population of dynamically
formed millisecond pulsars with some degree of spin-orbit alignment.",2306.11276v1
2023-06-27,Pressure-tuned quantum criticality in the large-$D$ antiferromagnet DTN,"Strongly correlated spin systems can be driven to quantum critical points via
various routes. In particular, gapped quantum antiferromagnets can undergo
phase transitions into a magnetically ordered state with applied pressure or
magnetic field, acting as tuning parameters. These transitions are
characterized by $z=1$ or $z=2$ dynamical critical exponents, determined by the
linear and quadratic low-energy dispersion of spin excitations, respectively.
Employing high-frequency susceptibility and ultrasound techniques, we
demonstrate that the tetragonal easy-plane quantum antiferromagnet
NiCl$_{2}\cdot$4SC(NH$_2$)$_2$ (aka DTN) undergoes a spin-gap closure
transition at about $4.2$ kbar, resulting in a pressure-induced magnetic
ordering. The studies are complemented by high-pressure-electron spin-resonance
measurements confirming the proposed scenario. Powder neutron diffraction
measurements revealed that no lattice distortion occurs at this pressure and
the high spin symmetry is preserved, establishing DTN as a perfect platform to
investigate $z=1$ quantum critical phenomena. The experimental observations are
supported by DMRG calculations, allowing us to quantitatively describe the
pressure-driven evolution of critical fields and spin-Hamiltonian parameters in
DTN.",2306.15450v2
2023-10-24,Evolution of MHD Torus and Mass Outflow Around Spinning AGN,"We perform axisymmetric, two-dimensional magnetohydrodynamic (MHD)
simulations to investigate accretion flows around spinning AGN. To mimic the
space-time geometry of spinning black holes, we consider effective Kerr
potential, and the mass of the black holes is $10^8 M_{\odot}$. We initialize
the accretion disc with a magnetized torus by adopting the toroidal component
of the magnetic vector potential. The initial magnetic field strength is set by
using the plasma beta parameter ($\beta_0$). We observe self-consistent
turbulence generated by magneto rotational instability (MRI) in the disc. The
MRI turbulence transports angular momentum in the disc, resulting in an angular
momentum distribution that approaches a Keplerian distribution. We investigate
the effect of the magnetic field on the dynamics of the torus and associated
mass outflow from the disc around a maximally spinning black hole $(a_k =
0.99)$. For the purpose of our analysis, we investigate the magnetic state of
our simulation model. The model $\beta_0 = 10$ indicates the behaviour similar
to the ""magnetically arrested disk (MAD)'' state, and all the other low
magnetic model remains in the SANE state. We observe that mass outflow rates
are significantly enhanced with the increased magnetic field in the disc. We
find a positive correlation between the magnetic field and mass outflow rates.
We also investigate the effect of black hole spin on the magnetized torus
evolution. However, we have not found any significant effect of black hole spin
on mass outflows in our model. Finally, we discuss the possible astrophysical
applications of our simulation results.",2310.15501v1
2023-11-09,Electrically induced angular momentum flow between separated ferromagnets,"Converting angular momentum between different degrees of freedom within a
magnetic material results from a dynamic interplay between electrons, magnons
and phonons. This interplay is pivotal to implementing spintronic device
concepts that rely on spin angular momentum transport. We establish a new
concept for long-range angular momentum transport that further allows to
address and isolate the magnonic contribution to angular momentum transport in
a nanostructured metallic ferromagnet. To this end, we electrically excite and
detect spin transport between two parallel and electrically insulated
ferromagnetic metal strips on top of a diamagnetic substrate. Charge-to-spin
current conversion within the ferromagnetic strip generates electronic spin
angular momentum that is transferred to magnons via electron-magnon coupling.
We observe a finite angular momentum flow to the second ferromagnetic strip
across a diamagnetic substrate over micron distances, which is electrically
detected in the second strip by the inverse charge-to-spin current conversion
process. We discuss phononic and dipolar interactions as the likely cause to
transfer angular momentum between the two strips. Moreover, our work provides
the experimental basis to separate the electronic and magnonic spin transport
and thereby paves the way towards magnonic device concepts that do not rely on
magnetic insulators.",2311.05290v1
2023-11-30,Dynamical Implications of the Kerr Multipole Moments for Spinning Black Holes,"Previously the linearized stress tensor of a stationary Kerr black hole has
been used to determine some of the values of gravitational couplings for a
spinning black hole to linear order in the Riemann tensor in the action
(worldline or quantum field theory). In particular, the couplings on operators
containing derivative structures of the form $(S\cdot\nabla)^n$ acting on the
Riemann tensor were fixed, with $S^\mu$ the spin vector of the black hole. In
this paper we find that the Kerr solution determines all of the multipole
moments in the sense of Dixon of a stationary spinning black hole and that
these multipole moments determine all linear in $R$ couplings. For example,
additional couplings beyond the previously mentioned are fixed on operators
containing derivative structures of the form $S^{2n}(p\cdot\nabla)^{2n}$ acting
on the Riemann tensor with $p^\mu$ the momentum vector of the black hole. These
additional operators do not contribute to the three-point amplitude, and so do
no contribute to the linearized stress tensor for a stationary black hole.
However, we find that they do contribute to the Compton amplitude.
Additionally, we derive formal expressions for the electromagnetic and
gravitational Compton amplitudes of generic spinning bodies to all orders in
spin in the worldline formalism and evaluated expressions for these amplitudes
to order $S^3$ in electromagnetism and order $S^5$ in gravity.",2311.18421v2
2023-12-03,Femtosecond spin-state switching dynamics of spin-crossover molecules condensed in thin films,"The photoinduced switching of Fe(II)-based spin-crossover complexes from
singlet to quintet takes place at ultrafast time scales. This a priori
spin-forbidden transition triggered numerous time-resolved experiments of
solvated samples to elucidate the mechanism at play. The involved intermediate
states remain uncertain. We apply ultrafast x-ray spectroscopy in molecular
films as a method sensitive to spin, electronic, and nuclear degrees of
freedom. Combining the progress in molecule synthesis and film growth with the
opportunities at x-ray free-electron lasers, we analyze the transient evolution
of the Fe L3 fine structure at room temperature. Our measurements and
calculations indicate the involvement of an Fe triplet intermediate state. The
high-spin state saturates at half of the available molecules, limited by
molecule-molecule interaction within the film.",2312.01483v1
2023-12-09,Spin noise spectroscopy of an alignment-based atomic magnetometer,"Optically pumped magnetometers (OPMs) are revolutionising the task of
magnetic-field sensing due to their extremely high sensitivity combined with
technological improvements in miniaturisation which have led to compact and
portable devices. OPMs can be based on spin-oriented or spin-aligned atomic
ensembles which are spin-polarized through optical pumping with circular or
linear polarized light, respectively. Characterisation of OPMs and the
dynamical properties of their noise is important for applications in real-time
sensing tasks. In our work, we experimentally perform spin noise spectroscopy
of an alignment-based magnetometer. Moreover, we propose a stochastic model
that predicts the noise power spectra exhibited by the device when, apart from
the strong magnetic field responsible for the Larmor precession of the spin,
white noise is applied in the perpendicular direction aligned with the
pumping-probing beam. By varying the strength of the noise applied as well as
the linear-polarisation angle of incoming light, we verify the model to
accurately predict the heights of the Larmor-induced spectral peaks and their
corresponding line-widths. Our work paves the way for alignment-based
magnetometers to become operational in real-time sensing tasks.",2312.05577v1
2024-02-08,The non-collinear phase of the antiferromagnetic sawtooth chain,"The antiferromagnetic sawtooth chain is a prototypical example of a
frustrated spin system with vertex-sharing triangles, giving rise to complex
quantum states. Depending on the interaction parameters, this system has three
phases, of which the gapless non-collinear phase (for strongly coupled basal
spins and loosely attached apical spins) has received little theoretical
attention so far. In this work, we comprehensively investigate the properties
of the non-collinear phase using large-scale tensor network computations which
exploit the full SU(2) symmetry of the underlying Heisenberg model. We study
the ground state both for finite systems using the density-matrix
renormalization group (DMRG) as well as for infinite chains via the variational
uniform matrix-product state (VUMPS) formalism. Finite temperatures and
correlation functions are tackled via imaginary- or real time evolutions, which
we implement using the time-dependent variational principle (TDVP). We find
that the non-collinear phase is characterized by a double-Q structure for the
apex-apex correlations. Deep into the phase, two peaks merge into a single one
indicating a 90-degree spiral. The apical spins are soft and highly susceptible
to external perturbations; they form a large number of gapless magnetic states
that are polarized by weak fields and cause a long low-temperature tail in the
specific heat. The dynamic spin-structure factor exhibits additive
contributions from a two-spinon continuum (excitations of the basal chain) and
a gapless peak at $k=\pi/2$ (excitations of the apical spins). Small
temperatures excite the gapless states and smear the spectral weight of the
$k=\pi/2$ peak out into a homogeneous flat-band structure. Our results are
relevant, e.g., for the material atacamite Cu$_2$Cl(OH)$_3$ in high magnetic
fields.",2402.05759v1
2006-08-02,Magnetocatalytic Adiabatic Spin Torque Orbital Transformations for Novel Chemical and Catalytic Reaction Dynamics: The Little Effect,"In this manuscript the theory and phenomena associated with the Little Effect
are introduced as the spin induced orbital dynamics of confined fermions under
strong magnetic and thermal environments. This Little Effect is considered in
details for the electron transfer reactions associated with redox processes of
Cu-Ag alloy within deionized water and for the orbital dynamics during the iron
catalyzed covalent bond rearrangements associated with amorphous carbon
conversion to diamond. Furthermore, prolong extreme conditions of 74,000 amps,
403 V, strong Lorentz compression, and thermal stresses upon this Cu-Ag- H2O
system on the basis of the Little Effect of high spin, thermally induced
orbital dynamics are predicted and demonstrated to cause the magnetically
organized reverse beta, electron capture, proton capture and neutron capture
processes for various infrequent pycnonuclear transmutations within the Cu-Ag
coil. The general experimental verification and the broad implications of this
Little Effect on chemistry are demonstrated within these two ideal systems: an
ionic case and a molecular case. The Little Effect is contrasted with the
Hedvall Effect as a dynamical phenomenon causing the kinematics of the Hedvall
Effect. The compatibility of the Little Effect with the Woodward-Hoffmann Rule
is demonstrated. The Little Effect provides greater understanding of order in
systems far from equilibrium. The implications of the Little Effect for other
interesting phenomena such as ferromagnetism, unconventional magnetism,
superparamagnetism, superconductivity, and pycnonuclear effects are concluded.",0608071v1
2009-11-20,Magnetisation dynamics in exchange coupled spring systems with perpendicular anisotropy,"Magnetisation dynamics in exchange spring magnets have been studied using
simulations of the FePt/Fe bilayer system. The FePt hard layer exhibits strong
perpendicular magnetocrystalline anisotropy, while the soft (Fe) layer has
negligible magnetocrystalline anisotropy. The variation of the local spin
orientation in the Fe layer is determined by the competition of the exchange
coupling interaction with the hard layer and the magnetostatic energy which
favours in-plane magnetisation. Dynamics were studied by monitoring the
response of the Fe layer magnetisation after the abrupt application of a
magnetic field which causes the systems to realign via precessional motion.
This precessional motion allows us to obtain the frequency spectrum and hence
examine the dynamical magnetisation motion. Since the rotation of the spins in
the soft layer does not have a well defined magnetic anisotropy, the system
does not present the usual frequency field characteristics for a thin film.
Additionally we obtain multi-peaked resonance spectra for the application of
magnetic fields perpendicular to the film plane, though we discount the
existence of spin wave modes and propose that this arises due to variations in
the local effective field across the Fe layer. The dynamic response is only
considered in the Fe layer, with the FePt layer held fixed in the perpendicular
orientation.",0911.4137v2
2010-04-14,Nonadiabatic geometric rotation of electron spin in a quantum dot by 2Pi hyperbolic secant pulses,"In this paper, the geometric and dynamic phase components of overall phase
induced by 2{\pi} hyperbolic secant pulses in a quantum dot is analyzed. The
dependence of two phase components on the ratio of the Rabi frequency to the
detuning is investigated. Numerical results indicate that only for one resonant
pulse the induced overall phase is purely the geometric phase. With other
values of the ratio the overall phase consists of a nonzero dynamic part. The
effect of spin precession to decrease the dynamic phase is characterized and
discussed by analytical and numerical techniques. Utilizing the symmetry
relations of the phases, a scheme to eliminate the dynamic phase by multipulse
control is proposed. By choosing the proper parameter for each pulse, the
dynamic phases induced by different pulses cancel out. The total pure geometric
phase varies from -{\pi} to {\pi}, which realizes the arbitrary geometric
rotation of spin. Average fidelity is calculated and the effects of magnetic
field and decay of the trion state are compared and discussed. The results show
the crucial role of weak magnetic field for high fidelity (above 99.3%).",1004.2317v3
2010-04-23,Time domain study of frequency-power correlation in spin-torque oscillators,"This paper describes a numerical experiment, based on full micromagnetic
simulations of current-driven magnetization dynamics in nanoscale spin valves,
to identify the origins of spectral linewidth broadening in spin torque
oscillators. Our numerical results show two qualitatively different regimes of
magnetization dynamics at zero temperature: regular (single-mode precessional
dynamics) and chaotic. In the regular regime, the dependence of the oscillator
integrated power on frequency is linear, and consequently the dynamics is well
described by the analytical theory of current-driven magnetization dynamics for
moderate amplitudes of oscillations. We observe that for higher oscillator
amplitudes, the functional dependence of the oscillator integrated power as a
function of frequency is not a single-valued function and can be described
numerically via introduction of nonlinear oscillator power. For a range of
currents in the regular regime, the oscillator spectral linewidth is a linear
function of temperature. In the chaotic regime found at large current values,
the linewidth is not described by the analytical theory. In this regime we
observe the oscillator linewidth broadening, which originates from sudden jumps
of frequency of the oscillator arising from random domain wall nucleation and
propagation through the sample. This intermittent behavior is revealed through
a wavelet analysis that gives superior description of the frequency jumps
compared to several other techniques.",1004.4184v1
2012-09-17,Ultrafast quasiparticle dynamics in superconducting iron pnictide CaFe1.89Co0.11As2,"Nonequilibrium quasiparticle relaxation dynamics is reported in
superconducting CaFe1.89Co0.11As2 single crystal using femtosecond
time-resolved pump-probe spectroscopy. The carrier dynamics reflects a
three-channel decay of laser deposited energy with characteristic time scales
varying from few hundreds of femtoseconds to order of few nanoseconds where the
amplitudes and time-constants of the individual electronic relaxation
components show significant changes in the vicinity of the spin density wave
(T_SDW ~ 85 K) and superconducting (T_SC ~ 20 K) phase transition temperatures.
The quasiparticles dynamics in the superconducting state reveals a charge gap
with reduced gap value of 2$\Delta$_0/k_BT_SC ~ 1.8. We have determined the
electron-phonon coupling constant $\lemda$ to be ~ 0.14 from the temperature
dependent relaxation time in the normal state, a value close to those reported
for other types of pnictides. From the peculiar temperature-dependence of the
carrier dynamics in the intermediate temperature region between the
superconducting and spin density wave phase transitions, we infer a temperature
scale where the charge gap associated with the spin ordered phase is maximum
and closes on either side while approaching the two phase transition
temperatures.",1209.3551v2
2013-11-19,Influence of spin dependent carrier dynamics on the properties of a dual-frequency vertical-external-cavity surface-emitting laser (VECSEL),"The properties of a dual-frequency vertical external cavity surface emitting
laser (VECSEL), in which two linear orthogonal polarization modes are
oscillating simultaneously, are theoretically investigated. We derive a model
based on the ideas introduced by San Miguel et al. [San Miguel, Feng, and
Moloney, Phys. Rev. A \textbf{52}, 1728 (1995)], taking into account the spin
dynamics of the carriers inside the quantum well (QW) based gain medium of the
dual-frequency VECSEL. This model is shown to succeed in describing quite a few
properties of the dual-frequency VECSEL, such as the behavior of nonlinear
coupling strength between the modes, the spectral behavior of intensity noises
of the modes, and also the correlation between these intensity noises. A good
agreement is found with experimental data. The variables associated with the
spin dependent carrier dynamics can be adiabatically eliminated due to the
class-A dynamical behavior of the considered laser which is based on a cm-long
external cavity. This leads to a simple analytical description of the dynamics
of the dual-frequency VECSEL providing a better understanding of the physics
involved",1311.4657v4
2013-12-17,Dynamical resonance locking in tidally interacting binary systems,"We examine the dynamics of resonance locking in detached, tidally interacting
binary systems. In a resonance lock, a given stellar or planetary mode is
trapped in a highly resonant state for an extended period of time, during which
the spin and orbital frequencies vary in concert to maintain the resonance.
This phenomenon is qualitatively similar to resonance capture in planetary
dynamics. We show that resonance locks can accelerate the course of tidal
evolution in eccentric systems and also efficiently couple spin and orbital
evolution in circular binaries. Previous analyses of resonance locking have not
treated the mode amplitude as a fully dynamical variable, but rather assumed
the adiabatic (i.e. Lorentzian) approximation valid only in the limit of
relatively strong mode damping. We relax this approximation, analytically
derive conditions under which the fixed point associated with resonance locking
is stable, and further check these analytic results using numerical
integrations of the coupled mode, spin, and orbital evolution equations. These
show that resonance locking can sometimes take the form of complex limit cycles
or even chaotic trajectories. We provide simple analytic formulae that define
the binary and mode parameter regimes in which resonance locks of some kind
occur (stable, limit cycle, or chaotic). We briefly discuss the astrophysical
implications of our results for white dwarf and neutron star binaries as well
as eccentric stellar binaries.",1312.4966v2
2013-12-26,Synchronization and chaos in spin-transfer-torque nano-oscillators coupled via a high speed Op Amp,"We propose a system of two coupled spin-torque nano-oscillators (STNOs), one
driver and another response, and demonstrate {using numerical studies} the
synchronization of the response system to the frequency of the driver system.
To this end we use a high speed operational amplifier in the form of a voltage
follower which essentially isolates the drive system from the response system.
We find the occurrence of 1:1 as w ell as 2:1 synchronization in the system,
wherein the oscillators show limit cycle dynamics. An increase in power output
is noticed when the two oscillators are locked in 1:1 synchronization. Moreover
in the cro ssover region between these two synchronization dynamics we show the
existence of chaotic dynamics in the slave system. The coupled dynamics under
periodic forcing, using a small ac input current in addition to that of the dc
part, is also studied. The slave oscillator is seen to retain its qualitative
identity in the parameter space in spite of being fed in, at times, a chaotic
signal. Such electrically coupled STNOs will be highly useful in fabricating
commercial spin-valve oscillators with high power output, when integrated with
other spintronic devices.",1312.7092v1
2014-07-22,Ground states and dynamics of spin-orbit-coupled Bose-Einstein condensates,"We study analytically and asymptotically as well as numerically ground states
and dynamics of two-component spin-orbit-coupled Bose-Einstein condensates
(BECs) modeled by the coupled Gross-Pitaevskii equations (CGPEs). In fact, due
to the appearance of the spin-orbit (SO) coupling in the two-component BEC with
a Raman coupling, the ground state structures and dynamical properties become
very rich and complicated. For the ground states, we establish the existence
and non-existence results under different parameter regimes, and obtain their
limiting behaviors and/or structures with different combinations of the SO and
Raman coupling strengths. For the dynamics, we show that the motion of the
center-of-mass is either non-periodic or with different frequency to the
trapping frequency when the external trapping potential is taken as harmonic
and the initial data is chosen as a stationary state (e.g. ground state) with a
shift, which is completely different from the case of a two-component BEC
without the SO coupling, and obtain the semiclassical limit of the CGPEs in the
linear case via the Wigner transform method. Efficient and accurate numerical
methods are proposed for computing the ground states and dynamics, especially
for the case of box potentials. Numerical results are reported to demonstrate
the efficiency and accuracy of the numerical methods and show the rich
phenomenon in the SO-coupled BECs.",1407.5815v1
2018-11-27,Hybrid magneto-dynamical modes in a single magnetostrictive nanomagnet on a piezoelectric substrate arising from magneto-elastic modulation of precessional dynamics,"Magneto-elastic (or ""straintronic"") switching has emerged as an extremely
energy-efficient mechanism for switching the magnetization of magnetostrictive
nanomagnets in magnetic memory, logic and non-Boolean circuits. Here, we
investigate the ultrafast magneto-dynamics associated with straintronic
switching in a single quasi-elliptical magnetostrictive Co nanomagnet deposited
on a piezoelectric PMN-PT substrate using time-resolved magneto-optical Kerr
effect (TR-MOKE) measurements. The pulsed laser pump beam in the TR-MOKE plays
a dual role: it causes precession of the nanomagnet's magnetization about an
applied bias magnetic field and it also generates surface acoustic waves (SAWs)
in the piezoelectric substrate that produce periodic strains in the
magnetostrictive nanomagnet and modulate the precessional dynamics. This
modulation gives rise to intriguing hybrid magneto-dynamical modes in the
nanomagnet, with rich spin wave texture. The characteristic frequencies of
these modes are 5-15 GHz, indicating that strain can affect magnetization in a
magnetostrictive nanomagnet in time scales much smaller than 1 ns (~100 ps).
This can enable ~10 GHz-range magneto-elastic nano-oscillators that are
actuated by strain instead of a spin-polarized current, as well as ultrafast
magneto-electric generation of spin waves for magnonic logic circuits,
holograms, etc.",1811.11297v1
2017-04-26,Anomalous lattice dynamics in a sigma-Fe60V40 alloy: Mossbauer spectroscopic study,"Lattice dynamics in a sigma-Fe60V40 compound, which shows a re-entrant
magnetism and orders ferromagnetic ally at ca. 170K, was investigated with the
Mossbauer spectroscopy in the temperature interval of 5-300 K. Two relevant
spectral parameters viz. the average center shift, <CS>, and the relative
recoil-free fraction, f/fo, were explored. The former yielded the Debye
temperature, T_D1, and the mean-square velocity of vibration, <v^2>, while the
latter T_D2 and the mean-square amplitude of vibrations, <x^2>. Significant
differences in the lattice-dynamical behaviors in the magnetic and paramagnetic
phases were revealed. In particular, the values of T_D were notably lower and
those of f/fo greatly higher in the former. This anomalous result has likely
its origin in a remarkably high inharmonic contribution to the vibrations found
for the ground magnetic state (spin-glass). Especially anomalous behavior vs.
temperature exhibits <x^2> where four well defined ranges could have been
identified and ascribed to the paramagnetic, ferromagnetic and two spin-glass
phases. Linear correlations between <v^2>-<x^2> were found within each of the
four ranges. They enabled determination of force constants, hence a change of
the potential energy, Ep, in each of the ranges. The total change of Ep=30 meV
while the corresponding one of the kinetic energy, determined from the
knowledge of <v^2>, was Ek=21 meV. The lack of balance between Ep and Ek
follows from the anharmonic lattice-dynamical behavior observed in the
spin-glass state. The results give a strong evidence that magnetism can
significantly affect the lattice dynamics.",1704.08054v1
2020-02-13,Semiclassical dynamics of a disordered two-dimensional Hubbard model with long-range interactions,"Quench dynamics in a two-dimensional system of interacting fermions is
analyzed within the semiclassical truncated Wigner approximation (TWA). The
models with short-range and long-range interactions are considered. We show
that in the latter case, the TWA is very accurate, becoming asymptotically
exact in the infinite-range limit, provided that the semiclassical Hamiltonian
is correctly identified. Within the TWA, different dynamical timescales of
charges and spins can be clearly distinguished. Interestingly, for a weak and
moderate disorder strength, we observe subdiffusive behavior of charges, while
spins exhibit diffusive dynamics. At strong disorder, the quantum Fisher
information shows logarithmic growth in time with a slower increase for charges
than for spins. It is shown that in contrast to the short-range model, strong
inhomogeneities such as domain walls in the initial state can significantly
slow down thermalization dynamics, especially at weak disorder. This behavior
can put additional challenges in designing cold-atom experimental protocols
aimed to analyze possible many-body localization in such systems. While within
this approach we cannot make any definite statements about the existence of a
many-body localized phase, we see a very fast crossover as a function of
disorder strength from rapidly thermalizing to a slow glassy like regime both
for the short-range and long-range models.",2002.05549v2
2021-01-12,Localization dynamics in a centrally coupled system,"In systems where interactions couple a central degree of freedom and a bath,
one would expect signatures of the bath's phase to be reflected in the dynamics
of the central degree of freedom. This has been recently explored in connection
with many-body localized baths coupled with a central qubit or a single cavity
mode -- systems with growing experimental relevance in various platforms. Such
models also have an interesting connection with Floquet many-body localization
via quantizing the external drive, although this has been relatively
unexplored. Here we adapt the multilayer multiconfigurational time-dependent
Hartree (ML-MCTDH) method, a well-known tree tensor network algorithm, to
numerically simulate the dynamics of a central degree of freedom, represented
by a $d$-level system (qudit), coupled to a disordered interacting 1D spin
bath. ML-MCTDH allows us to reach $\approx 10^2$ lattice sites, a far larger
system size than what is feasible with exact diagonalization or kernel
polynomial methods. From the intermediate time dynamics, we find a well-defined
thermodynamic limit for the qudit dynamics upon appropriate rescaling of the
system-bath coupling. The spin system shows similar scaling collapse in the
Edward-Anderson spin glass order parameter or entanglement entropy at
relatively short times. At longer time scales, we see slow growth of the
entanglement, which may arise from dephasing mechanisms in the localized system
or long-range interactions mediated by the central degree of freedom. Similar
signs of localization are shown to appear as well with unscaled system-bath
coupling.",2101.04674v2
2017-05-18,Exploring quantum signatures of chaos on a Floquet synthetic lattice,"Ergodicity and chaos play an integral role in the dynamical behavior of
many-particle systems and are crucial to the formulation of statistical
mechanics. Still, a general understanding of how randomness and chaos emerge in
the dynamical evolution of closed quantum systems remains elusive. Here, we
develop an experimental platform for the realization of canonical quantum
chaotic Hamiltonians based on quantum simulation with synthetic lattices. We
map the angular momentum projection states of an effective quantum spin onto
the linear momentum states of a $^{87}$Rb Bose-Einstein condensate, which can
alternatively be viewed as lattice sites in a synthetic dimension. This
synthetic lattice, with local and dynamical control of tight-binding lattice
parameters, enables new capabilities related to the experimental study of
quantum chaos. In particular, the capabilities of our system let us tune the
effective size of our spin, allowing us to illustrate how classical chaos can
emerge from a discrete quantum system. Moreover, spectroscopic control over our
synthetic lattice allows us to explore unique aspects of our spin's dynamics by
measuring the out-of-time-ordered correlation function, and enables future
investigations into entirely new classes of chaotic systems.",1705.06714v1
2018-07-22,Quantum spin chain dissipative mean-field dynamics,"We study the emergent dynamics resulting from the infinite volume limit of
the mean-field dissipative dynamics of quantum spin chains with clustering, but
not time-invariant states. We focus upon three algebras of spin operators: the
commutative algebra of mean-field operators, the quasi-local algebra of
microscopic, local operators and the collective algebra of fluctuation
operators. In the infinite volume limit, mean-field operators behave as
time-dependent, commuting scalar macroscopic averages while quasi-local
operators, despite the dissipative underlying dynamics, evolve unitarily in a
typical non-Markovian fashion. Instead, the algebra of collective fluctuations,
which is of bosonic type with time-dependent canonical commutation relations,
undergoes a time-evolution that retains the dissipative character of the
underlying microscopic dynamics and exhibits non-linear features. These latter
disappear by extending the time-evolution to a larger algebra where it is
represented by a continuous one-parameter semigroup of completely positive
maps. The corresponding generator is not of Lindblad form and displays mixed
quantum-classical features, thus indicating that peculiar hybrid systems may
naturally emerge at the level of quantum fluctuations in many-body quantum
systems endowed with non time-invariant states.",1807.08323v1
2019-12-13,Dynamical structure factor of a fermionic supersolid on an optical lattice,"Interfacing unbiased quantum Monte Carlo simulations with state-of-art
analytic continuation techniques, we obtain exact numerical results for
dynamical density and spin correlations in the attractive Hubbard model,
describing a spin-balanced two-dimensional cold Fermi gas on an optical
lattice. We focus on half-filling, where on average one fermion occupies each
lattice site, and the system displays an intriguing supersolid phase: a
superfluid with a checkerboard density modulation. The coexistence of $U(1)$
broken symmetry and the density modulations makes this regime very challenging
and interesting for the calculation of dynamical properties. We compare our
unbiased results with state-of-the-art Generalized Random Phase Approximation
calculations: both approaches agree on a well-defined low-energy
Nambu-Goldstone collective mode in the density correlations, while the higher
energy structures appear to differ significantly. We also observe an
interesting high-energy spin mode. We argue that our results provide a robust
benchmark for Generalized Random Phase Approximation techniques, which are
widely considered to be the method of choice for dynamical correlations in
Fermi gases. Also, our calculations yield new physical insight in the
high-energy behavior of the dynamical structure factor of the attractive
Hubbard model, which is a well known prototype lattice model for
superconductors and is a fertile field to target the observation of collective
modes in strongly correlated systems.",1912.06272v5
2020-05-28,Spintronics meets nonadiabatic molecular dynamics: Geometric spin torque and damping on noncollinear classical magnetism due to electronic open quantum system,"We analyze a quantum-classical hybrid system of steadily precessing slow
classical localized magnetic moments, forming a head-to-head domain wall,
embedded into an open quantum system of fast nonequilibrium electrons. The
electrons reside within a metallic wire connected to macroscopic reservoirs.
The model captures the essence of dynamical noncollinear and noncoplanar
magnetic textures in spintronics, while making it possible to obtain the exact
time-dependent nonequilibrium density matrix of electronic system and split it
into four contributions. The Fermi surface contribution generates dissipative
(or damping-like in spintronics terminology) spin torque on the moments, and
one of the two Fermi sea contributions generates geometric torque dominating in
the adiabatic regime. When the coupling to the reservoirs is reduced, the
geometric torque is the only nonzero contribution. Locally it has both
nondissipative (or field-like in spintronics terminology) and damping-like
components, but with the sum of latter being zero, which act as the
counterparts of geometric magnetism force and electronic friction in
nonadiabatic molecular dynamics. Such current-independent geometric torque is
absent from widely used micromagnetics or atomistic spin dynamics modeling of
magnetization dynamics based on the Landau-Lifshitz-Gilbert equation, where
previous analysis of Fermi surface-type torque has severely underestimated its
magnitude.",2005.14153v2
2020-09-28,Detection of Kardar-Parisi-Zhang hydrodynamics in a quantum Heisenberg spin-$1/2$ chain,"Classical hydrodynamics is a remarkably versatile description of the
coarse-grained behavior of many-particle systems once local equilibrium has
been established. The form of the hydrodynamical equations is determined
primarily by the conserved quantities present in a system. Some quantum spin
chains are known to possess, even in the simplest cases, a greatly expanded set
of conservation laws, and recent work suggests that these laws strongly modify
collective spin dynamics even at high temperature. Here, by probing the
dynamical exponent of the one-dimensional Heisenberg antiferromagnet KCuF$_3$
with neutron scattering, we find evidence that the spin dynamics are well
described by the dynamical exponent $z=3/2$, which is consistent with the
recent theoretical conjecture that the dynamics of this quantum system are
described by the Kardar-Parisi-Zhang universality class. This observation shows
that low-energy inelastic neutron scattering at moderate temperatures can
reveal the details of emergent quantum fluid properties like those arising in
non-Fermi liquids in higher dimensions.",2009.13535v2
2021-12-06,Timescale of local moment screening across and above the Mott transition,"A material's phase diagram typically indicates the types of realized
long-range orders, corresponding to instabilities in static response functions.
In correlated systems, however, key phenomena crucially depend on dynamical
processes, too: In a Mott insulator, the electrons' spin moment fluctuates in
time, while it is dynamically screened in Kondo systems. Here, we introduce a
timescale $t_m$ characteristic for the screening of the local spin moment and
demonstrate that it fully characterizes the dynamical mean-field phase diagram
of the Hubbard model: The retarded magnetic response delineates the Mott
transition and provides a new perspective on its signatures in the
supercritical region above. We show that $t_m$ has knowledge of the Widom line
and that it can be used to demarcate the Fermi liquid from the bad metal
regime. Additionally, it reveals new structures inside the Fermi liquid phase:
First, we identify a region with preformed local moments that we suggest to
have a thermodynamic signature. Second, approaching the Mott transition from
weak coupling, we discover a regime in which the spin dynamics becomes
adiabatic, in the sense that it is much slower than valence fluctuations. Our
findings provide resolution limits for magnetic measurements and may build a
bridge to the relaxation dynamics of non-equilibrium states.",2112.02881v1
2022-04-09,Bifurcation analysis of strongly nonlinear injection locked spin torque oscillators,"We investigate the dynamics of an injection locked in-plane uniform spin
torque oscillator for several forcing configurations at large driving
amplitudes. For the analysis, the spin wave amplitude equation is used to
reduce the dynamics to a general oscillator equation in which the forcing is a
complex valued function $F(p,{\psi})\propto{\epsilon}_1
(p)cos({\psi})+i{\epsilon}_2 (p)sin({\psi})$. Assuming that the oscillator is
strongly nonisochronous and/or forced by a power forcing
$(|{\nu}{\epsilon}_1/{\epsilon}_2 |\gg 1)$, we show that the parameters
${\epsilon}_{1,2} (p)$ govern the main bifurcation features of the Arnold
tongue diagram : (i) the locking range asymmetry is mainly controlled by
$d{\epsilon}_1 (p)/dp$, (ii) the Taken-Bogdanov bifurcation occurs for a power
threshold depending on ${\epsilon}_{1,2} (p)$ and (iii) the frequency
hysteretic range is related to the transient regime through the resonant
frequency at zero mismatch frequency. Then, the model is compared with the
macrospin simulation for driving amplitudes as large as $10^0-10^3 A/m$ for the
magnetic field and $10^{10}-10^{12} A/m^2$ for the current density. As
predicted by the model, the forcing configuration (nature of the driving
signal, applied direction, the harmonic orders) affects substantially the
oscillator dynamic. However, some discrepancies are observed. In particular,
the prediction of the frequency and power locking range boundaries may be
misestimated if the hysteretic boundaries are of same magnitude order.
Moreover, the misestimation can be of two different types according if the
bifurcation is Saddle node or Taken Bogdanov. These effects are a further
manifestation of the complexity of the dynamics in nonisochronous
auto-oscillators.",2204.04454v1
2022-05-20,A feasibility analysis towards the simulation of hysteresis with spin-lattice dynamics,"We use spin-lattice dynamics simulations to study the possibility of modeling
the magnetic hysteresis behavior of a ferromagnetic material. The temporal
evolution of the magnetic and mechanical degrees of freedom is obtained through
a set of two coupled Langevin equations. Hysteresis loops are calculated for
different angles between the external field and the magnetocrystalline
anisotropy axes. The influence of several relevant parameters is studied,
including the field frequency, magnetic damping, magnetic anisotropy (magnitude
and type), magnetic exchange, and system size. The role played by a moving
lattice is also discussed. For a perfect bulk ferromagnetic system we find
that, at low temperatures, the exchange and lattice dynamics barely affect the
loops, while the field frequency and magnetic damping have a large effect on
it. The influence of the anisotropy magnitude and symmetry are found to follow
the expected behavior. We show that a careful choice of simulation parameters
allows for an excellent agreement between the spin-lattice dynamics
measurements and the paradigmatic Stoner-Wohlfarth model. Furthermore, we
extend this analysis to intermediate and high temperatures for the perfect bulk
system and for spherical nanoparticles, with and without defects, reaching
values close to the Curie temperature. In this temperature range, we find that
lattice dynamics has a greater role on the magnetic behavior, especially in the
evolution of the defective samples. The present study opens the possibility for
more accurate inclusion of lattice defects and thermal effects in hysteresis
simulations",2205.10418v3
2022-10-24,Averaged Solar Torque Rotational Dynamics for Defunct Satellites,"Spin state predictions for defunct satellites in geosynchronous earth orbit
(GEO) are valuable for active debris removal and servicing missions as well as
material shedding studies and attitude-dependent solar radiation pressure (SRP)
modeling. Previous studies have shown that solar radiation torques can explain
the observed spin state evolution of some GEO objects via the
Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect. These studies have focused
primarily on uniform rotation. Nevertheless, many objects are in non-principal
axis rotation (i.e. tumbling). Recent exploration of the tumbling regime for
the family of retired GOES 8-12 satellites has shown intriguing YORP-driven
behavior including spin-orbit coupling, tumbling cycles, and tumbling period
resonances. To better explore and understand the tumbling regime, we develop a
semi-analytical tumbling-averaged rotational dynamics model. The derivation
requires analytically averaging over the satellite's torque-free rotation,
defined by Jacobi elliptic functions. Averaging is facilitated by a second
order Fourier series approximation of the facet illumination function. The
averaged model is found to capture and explain the general long-term behavior
of the full dynamics while reducing computation time by roughly three orders of
magnitude. This improved computation efficiency promises to enable rapid
exploration of general long-term rotational dynamics for defunct satellites and
rocket bodies.",2210.13380v2
2022-11-07,Non-adiabatic Ring Polymer Molecular Dynamics in the Phase Space of the SU(N) Lie Group,"We derive the non-adiabatic ring polymer molecular dynamics (RPMD) approach
in the phase space of the SU(N) Lie Group. This method, which we refer to as
the spin mapping non-adiabatic RPMD (SM-NRPMD), is based on the spin-mapping
formalism for the electronic degrees of freedom (DOFs) and ring polymer
path-integral description for the nuclear DOFs. Using the Stratonovich-Weyl
transform for the electronic DOFs, and the Wigner transform for the nuclear
DOFs, we derived an exact expression of the Kubo-transformed time-correlation
function (TCF). We further derive the spin mapping non-adiabatic Matsubara
dynamics using the Matsubara approximation that removes the high frequency
nuclear normal modes in the TCF and derive the SM-NRPMD approach from the
non-adiabatic Matsubara dynamics by discarding the imaginary part of the
Liouvillian. The SM-NRPMD method has numerical advantages compared to the
original NRPMD method based on the MMST mapping formalism, due to a more
natural mapping using the SU(N) Lie Group that preserves the symmetry of the
original system. We numerically compute the Kubo-transformed position
auto-correlation function and electronic population correlation function for
three-state model systems. The numerical results demonstrate the accuracy of
the SM-NRPMD method, which outperforms the original MMST-based NRPMD. We
envision that the SM-NRPMD method will be a powerful approach to simulate
electronic non-adiabatic dynamics and nuclear quantum effects accurately.",2211.04330v1
2022-12-29,Probability transport on the Fock space of a disordered quantum spin chain,"Within the broad theme of understanding the dynamics of disordered quantum
many-body systems, one of the simplest questions one can ask is: given an
initial state, how does it evolve in time on the associated Fock-space graph,
in terms of the distribution of probabilities thereon? A detailed quantitative
description of the temporal evolution of out-of-equilibrium disordered quantum
states and probability transport on the Fock space, is our central aim here. We
investigate it in the context of a disordered quantum spin chain which hosts a
disorder-driven many-body localisation transition. Real-time
dynamics/probability transport is shown to exhibit a rich phenomenology, which
is markedly different between the ergodic and many-body localised phases. The
dynamics is for example found to be strongly inhomogeneous at intermediate
times in both phases, but while it gives way to homogeneity at long times in
the ergodic phase, the dynamics remain inhomogeneous and multifractal in nature
for arbitrarily long times in the localised phase. Similarly, we show that an
appropriately defined dynamical lengthscale on the Fock-space graph is directly
related to the local spin-autocorrelation, and as such sheds light on the
(anomalous) decay of the autocorrelation in the ergodic phase, and lack of it
in the localised phase.",2212.14333v1
2023-02-23,Slow Dynamics and Kohlrausch Relaxation in Isolated Disordered Many-Body Systems,"The Kohlrausch(-Williams-Watts) law of stretched exponential relaxation has
been observed for more than a century and a half in diverse complex classical
systems. Here we show that this law describes relaxation quite generically in
closed (executing Schr\""{o}dinger dynamics), interacting disordered many-body
systems across a range of system sizes using interaction range and disorder
strength as primary tuning parameters. This we observe for both
time-independent and periodically driven (Floquet) systems. Finite-size
analysis indicates the persistence of this non-thermal relaxation regime in the
thermodynamic limit thus defining a distinct dynamical regime. This regime
exhibits a peak in the time-scale of the perceptible relaxation, upon crossing
over from weak to strong disorder. We provide a simple picture of this
behavior, which naturally accounts for its general occurrence. Formation of
spin-glass -- one of the possible mechanisms for stretched relaxation appears
incidental to the occurrence of Kohlrausch law in our context. Finally, we
provide a simple non-Hermitian Hamiltonian formulation for the dynamics of a
single spin embedded in the disordered chain. This provides an analytical
formula that captures not only the Kohlrausch relaxation of the disorder
averaged auto-correlation but also captures the largely diverse dynamics of an
arbitrary target spin in the system. Our work hence also provides a concrete
quantification of the ``pre-thermal slowness"" in many-body disordered system.",2302.12275v1
2023-05-15,Order parameter dynamics in Mn$_3$Sn driven by DC and pulsed spin-orbit torques,"We numerically investigate and develop analytic models for both the DC and
pulsed spin-orbit-torque (SOT)-driven response of order parameter in
single-domain Mn$_3$Sn, which is a metallic antiferromagnet with an anti-chiral
120$^\circ$ spin structure. We show that DC currents above a critical threshold
can excite oscillatory dynamics of the order parameter in the gigahertz to
terahertz frequency spectrum. Detailed models of the oscillation frequency
versus input current are developed and found to be in excellent agreement with
the numerical simulations of the dynamics. In the case of pulsed excitation,
the magnetization can be switched from one stable state to any of the other
five stable states in the Kagome plane by tuning the duration or the amplitude
of the current pulse. Precise functional forms of the final switched state
versus the input current are derived, offering crucial insights into the
switching dynamics of Mn$_3$Sn. The readout of the magnetic state can be
carried out via either the anomalous Hall effect, or the recently demonstrated
tunneling magnetoresistance in an all-Mn$_3$Sn junction. We also discuss
possible disturbance of the magnetic order due to heating that may occur if the
sample is subject to large currents. Operating the device in pulsed mode or
using low DC currents reduces the peak temperature rise in the sample due to
Joule heating. Our predictive modeling and simulation results can be used by
both theorists and experimentalists to explore the interplay of SOT and the
order dynamics in Mn$_3$Sn, and to further benchmark the device performance.",2305.08728v2
2022-03-12,"Magnetic excitations, non-classicality and quantum wake spin dynamics in the Hubbard chain","Recent work has demonstrated that quantum Fisher information (QFI), a witness
of multipartite entanglement, and magnetic Van Hove correlations $G(r,t)$, a
probe of local real-space real-time spin dynamics, can be successfully
extracted from inelastic neutron scattering on spin systems through accurate
measurements of the dynamical spin structure factor $S(k,\omega)$. Here we
apply theoretically these ideas to the half-filled Hubbard chain with
nearest-neighbor hopping, away from the strong-coupling limit. This model has
nontrivial redistribution of spectral weight in $S(k,\omega)$ going from the
non-interacting limit ($U=0$) to strong coupling ($U\rightarrow \infty$), where
it reduces to the Heisenberg quantum spin chain. We use the density matrix
renormalization group (DMRG) to find $S(k,\omega)$, from which QFI is then
calculated. We find that QFI grows with $U$. With realistic energy resolution
it becomes capable of witnessing bipartite entanglement above $U=2.5$ (in units
of the hopping), where it also changes slope. This point is also proximate to
slope changes of the bandwidth $W(U)$ and the half-chain von Neumann
entanglement entropy. We compute $G(r,t)$ by Fourier-transforming
$S(k,\omega)$. The results indicate a crossover in the short-time
short-distance dynamics at low $U$ characterized by ferromagnetic lightcone
wavefronts, to a Heisenberg-like behavior at large $U$ featuring
antiferromagnetic lightcones and spatially period-doubled antiferromagnetism.
We find this crossover has largely been completed by $U=3$. Our results thus
provide evidence that, in several aspects, the strong-coupling limit of the
Hubbard chain is reached qualitatively already at a relatively modest
interaction strength. We discuss experimental candidates for observing the
$G(r,t)$ dynamics found at low $U$.",2203.06332v4
2023-01-03,Gaussian-state Ansatz for the non-equilibrium dynamics of quantum spin lattices,"The study of non-equilibrium dynamics is one of the most important challenges
of modern quantum many-body physics, in relationship with fundamental questions
in quantum statistical mechanics, as well as with the fields of quantum
simulation and computing. In this work we propose a Gaussian Ansatz for the
study of the nonequilibrium dynamics of quantum spin systems. Within our
approach, the quantum spins are mapped onto Holstein-Primakoff bosons, such
that a coherent spin state -- chosen as the initial state of the dynamics --
represents the bosonic vacuum. The state of the system is then postulated to
remain a bosonic Gaussian state at all times, an assumption which is exact when
the bosonic Hamiltonian is quadratic; and which is justified in the case of a
nonlinear Hamiltonian if the boson density remains moderate. We test the
accuracy of such an Ansatz in the paradigmatic case of the $S=1/2$
transverse-field Ising model, in one and two dimensions, initialized in a state
aligned with the applied field. We show that the Gaussian Ansatz, when applied
to the bosonic Hamiltonian with nonlinearities truncated to quartic order, is
able to reproduce faithfully the evolution of the state, including its
relaxation to the equilibrium regime, for fields larger than the critical field
for the paramagnetic-ferromagnetic transition in the ground state. In
particular the spatio-temporal pattern of correlations reconstructed via the
Gaussian Ansatz reveals the dispersion relation of quasiparticle excitations,
exhibiting the softening of the excitation gap upon approaching the critical
field. Our results suggest that the Gaussian Ansatz correctly captures the
essential effects of nonlinearities in quantum spin dynamics; and that it can
be applied to the study of fundamental phenomena such as quantum thermalization
and its breakdown.",2301.01363v2
2003-12-01,Glassy Dynamics and Aging in Disordered Systems,"This lecture deals with glassy dynamics and aging in disordered systems.
Special emphasis is put on dynamic mean field theory. In the first part I
present some of the systems of interest, in particular spin-glasses,
supercooled liquids and glasses, drift, creep and pinning of a particle in a
random potential, neural networks, graph partitioning as an example of
combinatorial optimisation, the K-sat problem and the minority game as a model
for the behaviour of agents on markets. The second part deals with the dynamics
of the spherical p-spin-glass with long ranged interactions. This model is a
prototype for glassy dynamics. The equations of motion for correlation- and
response-functions are derived and solutions above and below the freezing
temperature are investigated. At the end I discuss the so called crossover
region and aging in glasses. The commonly used mode coupling theory results in
equations of motion identical to those of the $p$-spin model above the
dynamical transition temperature. The p-spin model is extended introducing the
random interactions as slow dynamical variables as well. This takes changes in
the configuration of cages into account. This is an activated process.
Depending on the waiting time, equilibrium or aging is found.",0312039v1
2010-06-12,"Glassy dynamics as a melting process (On melting dynamics and the glass transition, Part II)","There are deep analogies between the melting dynamics in systems with a first
order phase transition and the dynamics from equilibrium in super-cooled
liquids. For a class of Ising spin models undergoing a first order transition -
namely p-spin models on the so-called Nishimori line - it can be shown that the
melting dynamics can be exactly mapped to the equilibrium dynamics. In this
mapping the dynamical -or mode-coupling- glass transition corresponds to the
spinodal point, while the Kauzmann transition corresponds to the first order
phase transition itself. Both in mean field and finite dimensional models this
mapping provides an exact realization of the random first order theory scenario
for the glass transition. The corresponding glassy phenomenology can then be
understood in the framework of a standard first order phase transition.",1006.2479v2
2012-06-18,Quasi-equilibrium in glassy dynamics: an algebraic view,"We study a chain of identical glassy systems in a constrained equilibrium
where each bond of the chain is forced to remain at a preassigned distance to
the previous one. We apply this description to Mean Field Glassy systems in the
limit of long chain where each bond is close to the previous one. We show that
in specific conditions this pseudo-dynamic process can formally describe real
relaxational dynamics the long time. In particular, in mean field spin glass
models we can recover in this way the equations of Langevin dynamics in the
long time limit at the dynamical transition temperature and below. We interpret
the formal identity as an evidence that in these situations the configuration
space is explored in a quasi-equilibrium fashion. Our general formalism, that
relates dynamics to equilibrium puts slow dynamics in a new perspective and
opens the way to the computation of new dynamical quantities in glassy systems.",1206.4067v2
2022-06-21,Dynamical Triplet Unravelling: A quantum Monte Carlo algorithm for reversible dynamics,"We introduce a quantum Monte Carlo method to simulate the reversible dynamics
of correlated many-body systems. Our method is based on the Laplace transform
of the time-evolution operator which, as opposed to most quantum Monte Carlo
methods, makes it possible to access the dynamics at longer times. The Monte
Carlo trajectories are realised through a piece-wise stochastic-deterministic
reversible evolution where free dynamics is interspersed with two-process
quantum jumps. The dynamical sign problem is bypassed via the so-called
deadweight approximation, which stabilizes the many-body phases at longer
times. We benchmark our method by simulating spin excitation propagation in the
XXZ model and dynamical confinement in the quantum Ising chain, and show how to
extract dynamical information from the Laplace representation.",2206.10283v1
2022-08-06,Generalized Glauber dynamics for inference in biology,"Large interacting systems in biology often exhibit emergent dynamics, such as
coexistence of multiple time scales, manifested by fat tails in the
distribution of waiting times. While existing tools in statistical inference,
such as maximum entropy models, reproduce the empirical steady state
distributions, it remains challenging to learn dynamical models. We present a
novel inference method, called generalized Glauber dynamics. Constructed
through a non-Markovian fluctuation dissipation theorem, generalized Glauber
dynamics tunes the dynamics of an interacting system, while keeping the steady
state distribution fixed. We motivate the need for the method on real data from
Eco-HAB, an automated habitat for testing behavior in groups of mice under
semi-naturalistic conditions, and present it on simple Ising spin systems. We
show its applicability for experimental data, by inferring dynamical models of
social interactions in a group of mice that reproduce both its collective
behavior and the long tails observed in individual dynamics.",2208.03483v2
2022-11-12,Learning dynamical systems: an example from open quantum system dynamics,"Machine learning algorithms designed to learn dynamical systems from data can
be used to forecast, control and interpret the observed dynamics. In this work
we exemplify the use of one of such algorithms, namely Koopman operator
learning, in the context of open quantum system dynamics. We will study the
dynamics of a small spin chain coupled with dephasing gates and show how
Koopman operator learning is an approach to efficiently learn not only the
evolution of the density matrix, but also of every physical observable
associated to the system. Finally, leveraging the spectral decomposition of the
learned Koopman operator, we show how symmetries obeyed by the underlying
dynamics can be inferred directly from data.",2211.06678v2
2023-03-31,Dephasing and pseudo-coherent quantum dynamics in super-Ohmic environments,"Dephasing in quantum systems is typically the result of its interaction with
environmental degrees of freedom. We investigate within a spin-boson model the
influence of a super-Ohmic environment on the dynamics of a quantum two-state
system. A super-Ohmic enviroment, thereby, models typical bulk phonons which
are a common disturbance for solid state quantum systems as, for example, NV
centers. By applying the numerically exact quasi-adiabatic path integral
approach we show that for strong system-bath coupling, pseudo-coherent dynamics
emerges, i.e., oscillatory dynamics at short times due to slaving of the
quantum system to the bath dynamics. We extend the phase diagram known for
sub-Ohmic and Ohmic environments into the super-Ohmic regime and observe a
pronounced non-monotonous behaviour. Super-Ohmic purely dephasing fluctuations
strongly suppress the amplitude of coherent dynamics at very short times with
no subsequent further decay at later times. Nevertheless, they render the
dynamics overdamped. The according phase separation line shows also a
non-monotonous behaviour, very similar to the pseudo-coherent dynamics.",2303.18213v1
1997-05-21,Spin Dynamics of the One-Dimensional J-J' Model and Spin-Peierls Transition in CuGeO_3,"Spin dynamics as well as static properties of the one-dimensional J-J' model
(S=1/2, J>0 and 0\le \alpha=J'/J\le 0.5) are studied by the exact
diagonalization and the recursion method of finite systems up to 26 sites.
Especially, the dynamical structure factor S(q,\omega) is investigated
carefully for various values of \alpha. As \alpha increases beyond the
gapless-gapful critical value \alpha_c=0.2411, there appear features definitely
different from the Heisenberg model but the same with the Majumdar-Ghosh model.
Some of these features depend only on the value of \alpha and not on \delta: a
parameter introduced for the coupling alternation. By comparing these results
with a recent inelastic neutron scattering spectrum of an inorganic
spin-Peierls compound CuGeO_3 [M. Arai et al.: Phys. Rev. Lett. 77 (1996)
3649], it is found that the frustration by J' in CuGeO_3 is unexpectedly strong
(\alpha=0.4-0.45), and at least \alpha must be larger than \alpha_c to some
extent. The value of J is evaluated at \sim 180K consistent with other
estimations. The coupling alternation is extremely small. This large
frustration is a primary origin of the various anomalous properties CuGeO_3
possesses. For comparison we refer also to \alpha'-NaV_2O_5.",9705207v2
2003-08-13,Nonlinear magnetic susceptibility and aging phenomena in reentrant ferromagnet: Cu$_{0.2}$Co$_{0.8}$Cl$_{2}$-FeCl$_{3}$ graphite bi-intercalation compound,"Linear and nonlinear dynamic properties of a reentrant ferromagnet
Cu$_{0.2}$Co$_{0.8}$Cl$_{2}$-FeCl$_{3}$ graphite bi-intercalation compound are
studied using AC and DC magnetic susceptibility. This compound undergoes
successive phase transitions at the transition temperatures $T_{h}$ (= 16 K),
$T_{c}$ (= 9.7 K), and $T_{RSG}$ (= 3.5 K). The static and dynamic behaviors of
the reentrant spin glass phase below $T_{RSG}$ are characterized by those of
normal spin glass phase with critical exponent $\beta$ = 0.57 $\pm$ 0.10, a
dynamic critical exponent $x$ = 8.5 $\pm$ 1.8, and an exponent $p$ (= 1.55
$\pm$ 0.13) for the de Almeida -Thouless line. A prominent nonlinear
susceptibility is observed between $T_{RSG}$ and $T_{c}$ and around $T_{h}$,
suggesting a chaotic nature of the ferromagnetic phase ($T_{RSG} \leq T \leq
T_{c}$) and the helical spin ordered phase ($T_{c} \leq T \leq T_{h}$). The
aging phenomena are observed both in the RSG and FM phases, with the same
qualitative features as in normal spin glasses. The aging of zero-field cooled
magnetization indicates a drastic change of relaxation mechanism below and
above $T_{RSG}$. The time dependence of the absorption $\chi^{\prime \prime}$
is described by a power law form ($\approx t^{-b^{\prime \prime}}$) in the
ferromagnetic phase, where $b^{\prime \prime} \approx 0.074 \pm 0.016$ at $f$ =
0.05 Hz and $T$ = 7 K. No $\omega t$-scaling law for $\chi^{\prime \prime}$
[$\approx (\omega t)^{-b^{\prime \prime}}$] is observed.",0308247v1
2006-08-28,Evolution of the low energy spin dynamics in electron-doped high-transition temperature superconductor Pr0.88LaCe0.12CuO4-d,"We use inelastic neutron scattering to explore the evolution of the low
energy spin dynamics in the electron-doped cuprate Pr0.88LaCe0.12CuO4-d (PLCCO)
as the system is tuned from its nonsuperconducting, as-grown antiferromagnetic
(AF) state into an optimally-doped superconductor (Tc~24 K) without static AF
order. The low temperature, low energy response of the spin excitations in
under-doped samples is coupled to the presence of the AF phase, whereas the
low-energy magnetic response for samples near optimal Tc exhibits spin
fluctuations surprisingly insensitive to the sample temperature. This evolution
of the low energy excitations is consistent with the influence of a quantum
critical point in the phase diagram of PLCCO associated with the suppression of
the static AF order. We carried out scaling analysis of the data and discuss
the influence of quantum critical dynamics in the observed excitation spectrum.",0608610v2
2002-04-08,The Dynamics of Test Particles and Pointlike Gyroscopes in the Brane World and Other 5D Models,"We study the dynamics of test particles and pointlike gyroscopes in 5D
manifolds like those used in the Randall-Sundrum brane world and non-compact
Kaluza-Klein models. Our analysis is based on a covariant foliation of the
manifold using 3+1 dimensional spacetime slices orthogonal to the extra
dimension, and is hence similar to the ADM 3+1 split in ordinary general
relativity. We derive gauge invariant equations of motion for freely-falling
test particles in the 5D and 4D affine parameterizations and contrast these
results with previous work concerning the so-called ``fifth force''. Motivated
by the conjectured localization of matter fields on a 3-brane, we derive the
form of the classical non-gravitational force required to confine particles to
a 4D hypersurface and show that the resulting trajectories are geometrically
identical to the spacetime geodesics of Einstein's theory. We then discuss the
issue of determining the 5D dynamics of a torque-free spinning body in the
point-dipole approximation, and then perform a covariant (3+1)+1 decomposition
of the relevant formulae (i.e. the 5D Fermi-Walker transport equation) for the
cases of freely-falling and hypersurface-confined point gyroscopes. In both
cases, the 4D spin tensor is seen to be subject to an anomalous torque. We
solve the spin equations for a gyroscope confined to a single spacetime section
in a simple 5D cosmological model and observe a cosmological variation of the
magnitude and orientation of the 4D spin.",0204032v1
1995-05-31,A Local Deterministic Model of Quantum Spin Measurement,"The conventional view, that Einstein was wrong to believe that quantum
physics is local and deterministic, is challenged. A parametrised model, Q, for
the state vector evolution of spin 1/2 particles during measurement is
developed. Q draws on recent work on so-called riddled basins in dynamical
systems theory, and is local, deterministic, nonlinear and time asymmetric.
Moreover the evolution of the state vector to one of two chaotic attractors
(taken to represent observed spin states) is effectively uncomputable.
Motivation for this model arises from Penrose's speculations about the nature
and role of quantum gravity. Although the evolution of Q's state vector is
uncomputable, the probability that the system will evolve to one of the two
attractors is computable. These probabilities correspond quantitatively to the
statistics of spin 1/2 particles. In an ensemble sense the evolution of the
state vector towards an attractor can be described by a diffusive random walk.
Bell's theorem and a version of the Bell-Kochen_specker quantum entanglement
paradox are discussed. It is shown that proving an inconsistency with locality
demands the existence of definite truth values to certain counterfactual
propositions. In Q these deterministic propositions are physically uncomputable
and no non-algorithmic solution is either known or suspected. Adapting the
mathematical formalist approach, the non-existence of definite truth values to
such counterfactual propositions is posited. No inconsistency with experiment
is found. Hence Q is not necessarily constrained by Bell's inequality.",9505025v1
2000-05-15,Dynamics of multiply charged ions in intense laser fields,"We numerically investigate the dynamics of multiply charged hydrogenic ions
in near-optical linearly polarized laser fields with intensities of order 10^16
to 10^17 W/cm^2. Depending on the charge state Z of the ion the relation of
strength between laser field and ionic core changes. We find around Z=12
typical multiphoton dynamics and for Z=3 tunneling behaviour, however with
clear relativistic signatures. In first order in v/c the magnetic field
component of the laser field induces a Z-dependent drift in the laser
propagation direction and a substantial Z-dependent angular momentum with
repect to the ionic core. While spin oscillations occur already in first order
in v/c as described by the Pauli equation, spin induced forces via spin orbit
coupling only appear in the parameter regime where (v/c)^2 corrections are
significant. In this regime for Z=12 ions we show strong splittings of resonant
spectral lines due to spin-orbit coupling and substantial corrections to the
conventional Stark shift due to the relativistic mass shift while those to the
Darwin term are shown to be small. For smaller charges or higher laser
intensities, parts of the electronic wavepacket may tunnel through the
potential barrier of the ionic core, and when recombining are shown to give
rise to keV harmonics in the radiation spectrum. Some parts of the wavepacket
do not recombine after ionisation and we find very energetic electrons in the
weakly relativistic regime of above threshold ionization.",0005053v1
2007-12-12,Facilitated spin models: recent and new results,"Facilitated or kinetically constrained spin models (KCSM) are a class of
interacting particle systems reversible w.r.t. to a simple product measure.
Each dynamical variable (spin) is re-sampled from its equilibrium distribution
only if the surrounding configuration fulfills a simple local constraint which
\emph{does not involve} the chosen variable itself. Such simple models are
quite popular in the glass community since they display some of the peculiar
features of glassy dynamics, in particular they can undergo a dynamical arrest
reminiscent of the liquid/glass transitiom. Due to the fact that the jumps
rates of the Markov process can be zero, the whole analysis of the long time
behavior becomes quite delicate and, until recently, KCSM have escaped a
rigorous analysis with the notable exception of the East model. In these notes
we will mainly review several recent mathematical results which, besides being
applicable to a wide class of KCSM, have contributed to settle some debated
questions arising in numerical simulations made by physicists. We will also
provide some interesting new extensions. In particular we will show how to deal
with interacting models reversible w.r.t. to a high temperature Gibbs measure
and we will provide a detailed analysis of the so called one spin facilitated
model on a general connected graph.",0712.1934v1
2009-10-09,Optical probing of spin dynamics of two-dimensional and bulk electrons in a GaAs/AlGaAs heterojunction system,"We present time-resolved Kerr rotation measurements of electron spin dynamics
in a GaAs/AlGaAs heterojunction system that contains a high-mobility
two-dimensional electron gas (2DEG). Due to the complex layer structure of this
material the Kerr rotation signals contain information from electron spins in
three different layers: the 2DEG layer, a GaAs epilayer in the heterostructure,
and the underlying GaAs substrate. The 2DEG electrons can be observed at low
pump intensities, using that they have a less negative g-factor than electrons
in bulk GaAs regions. At high pump intensities, the Kerr signals from the GaAs
epilayer and the substrate can be distinguished when using a barrier between
the two layers that blocks intermixing of the two electron populations. This
allows for stronger pumping of the epilayer, which results in a shift of the
effective g-factor. Thus, three populations can be distinguished using
differences in g-factor. We support this interpretation by studying how the
spin dynamics of each population has its unique dependence on temperature, and
how they correlate with time-resolved reflectance signals.",0910.1714v1
2009-11-20,Nonequilibrium Stationary States and Phase Transitions in Directed Ising Models,"We study the nonequilibrium properties of directed Ising models with non
conserved dynamics, in which each spin is influenced by only a subset of its
nearest neighbours. We treat the following models: (i) the one-dimensional
chain; (ii) the two-dimensional square lattice; (iii) the two-dimensional
triangular lattice; (iv) the three-dimensional cubic lattice. We raise and
answer the question: (a) Under what conditions is the stationary state
described by the equilibrium Boltzmann-Gibbs distribution? We show that for
models (i), (ii), and (iii), in which each spin ""sees"" only half of its
neighbours, there is a unique set of transition rates, namely with exponential
dependence in the local field, for which this is the case. For model (iv), we
find that any rates satisfying the constraints required for the stationary
measure to be Gibbsian should satisfy detailed balance, ruling out the
possibility of directed dynamics. We finally show that directed models on
lattices of coordination number $z\ge8$ with exponential rates cannot
accommodate a Gibbsian stationary state. We conjecture that this property
extends to any form of the rates. We are thus led to the conclusion that
directed models with Gibbsian stationary states only exist in dimension one and
two. We then raise the question: (b) Do directed Ising models, augmented by
Glauber dynamics, exhibit a phase transition to a ferromagnetic state? For the
models considered above, the answers are open problems, to the exception of the
simple cases (i) and (ii). For Cayley trees, where each spin sees only the
spins further from the root, we show that there is a phase transition provided
the branching ratio, $q$, satisfies $q \ge 3$.",0911.4011v1
2010-06-04,Cold Fermi-gas with long range interaction in a harmonic trap,"We study equilibrium density and spin density profiles for a model of cold
one-dimensional spin 1/2 fermions interacting via inverse square interaction
and exchange in an external harmonic trap. This model is the well-known
spin-Calogero model (sCM) and its fully nonlinear collective field theory
description is known. We extend the field theory description to the presence of
an external harmonic trap and obtain analytic results for statics and dynamics
of the system. For instance, we find how the equilibrium density profile
changes upon tuning the interaction strength. The results we obtain for
equilibrium configurations are very similar to the ones obtained recently by Ma
and Yang [1] for a model of fermions with short ranged interactions. Our main
approximation is the neglect of the terms of higher order in spatial
derivatives in equations of motion - gradientless approximation [2]. Within
this approximation the hydrodynamic equations of motion can be written as a set
of decoupled forced Riemann-Hopf equations for the dressed Fermi momenta of the
model. This enables us to write analytical solutions for the dynamics of spin
and charge. We describe the time evolution of the charge density when an
initial non-equilibrium profile is created by cooling the gas with an
additional potential in place and then suddenly removing the potential. We
present our results as a simple ""single-particle"" evolution in the phase-space
reminiscing a similar description of the dynamics of non-interacting
one-dimensional fermions.",1006.0966v2
2010-08-27,Spin-transfer-torque resonant switching and injection locking in presence of a weak external microwave field for spin valves with perpendicular materials,"The effects of a weak microwave field in the magnetization dynamics driven by
spin-transfer-torque in spin-valves with perpendicular materials have been
systematically studied by means of full micromagnetic simulations. In the
system we studied, depending on the working point (bias field and current) in
the dynamical stability diagram, we observe either resonant switching and
injection locking. The resonant switching, observed in the switching region,
occurs when the field frequency is approaching the frequency of the main
pre-switching mode giving rise to an asymmetric power distribution of that mode
in the sectional area of the free layer. At the resonant frequency, the
switching time is weakly dependent on the relative phase between the instant
when the current pulse is applied and the microwave field. The injection
locking, observed in the dynamical region, is characterized by the following
properties: (i) a locking bandwidth which is linearly dependent on the force
locking, and (ii) a locking for integer harmonics of the self-oscillation
frequency. We compare our numerical results with analytical theory for
non-autonomous non-linear system obtaining a good agreement in the current
region where the oscillation frequency and output power are characterized from
a linear relationship.",1008.4746v1
2013-12-03,Beyond the Spin Model Approximation for Ramsey Spectroscopy,"Ramsey spectroscopy has become a powerful technique for probing
non-equilibrium dynamics of internal (pseudospin) degrees of freedom of
interacting systems. In many theoretical treatments, the key to understanding
the dynamics has been to assume the external (motional) degrees of freedom are
decoupled from the pseudospin degrees of freedom. Determining the validity of
this approximation -- known as the spin model approximation -- is complicated,
and has not been addressed in detail. Here we shed light in this direction by
calculating Ramsey dynamics exactly for two interacting spin-1/2 particles in a
harmonic trap. We focus on $s$-wave-interacting fermions in quasi-one and
two-dimensional geometries. We find that in 1D the spin model assumption works
well over a wide range of experimentally-relevant conditions, but can fail at
time scales longer than those set by the mean interaction energy. Surprisingly,
in 2D a modified version of the spin model is exact to first order in the
interaction strength. This analysis is important for a correct interpretation
of Ramsey spectroscopy and has broad applications ranging from precision
measurements to quantum information and to fundamental probes of many-body
systems.",1312.0887v3
2013-12-20,Exciton spin dynamics of colloidal CdTe nanocrystals in magnetic field,"The recombination and spin dynamics of excitons in colloidal CdTe
nanocrystals (NCs) are studied by time-resolved photoluminescence in high
magnetic fields up to 15 T and at cryogenic temperatures. The recombination
decay shows a nonexponential temporal behavior, with the longest component
corresponding to the dark excitons having 260 ns decay time at zero magnetic
field and 4.2 K temperature. This long component shortens to 150 ns at 15 T due
to the magnetic-field-induced mixing of the bright and dark exciton states. The
spin dynamics, assessed through the evolution of the magnetic-field-induced
circular polarization degree of the photoluminescence, has a fast component
shorter than 1 ns related to the bright excitons and a slow component of 5-10
ns associated with the dark excitons. The latter shortens with increasing
magnetic field, which is characteristic for a phonon-assisted spin relaxation
mechanism. The relatively low saturation level of the associated
magnetic-field-induced circular polarization degree of -30 % is explained by a
model that suggests the CdTe NCs to constitute an ensemble of prolate and
oblate NCs, both having a structural quantization axis. The exciton g-factor of
2.4-2.9 evaluated from fitting the experimental data in the frame of the
suggested approach is in good agreement with the expected value for the dark
excitons in CdTe NCs.",1312.5929v1
2014-07-31,Maximizing the purity of a qubit evolving in an anisotropic environment,"We provide a general method to calculate and maximize the purity of a qubit
interacting with an anisotropic non-Markovian environment. Counter to
intuition, we find that the purity is often maximized by preparing and storing
the qubit in a superposition of non-interacting eigenstates. For a model
relevant to decoherence of a heavy-hole spin qubit in a quantum dot or for a
singlet-triplet qubit for two electrons in a double quantum dot, we show that
preparation of the qubit in its non-interacting ground state can actually be
the worst choice to maximize purity. We further give analytical results for
spin-echo envelope modulations of arbitrary spin components of a hole spin in a
quantum dot, going beyond a standard secular approximation. We account for
general dynamics in the presence of a pure-dephasing process and identify a
crossover timescale at which it is again advantageous to initialize the qubit
in the non-interacting ground state. Finally, we consider a general two-axis
dynamical decoupling sequence and determine initial conditions that maximize
purity, minimizing leakage to the environment.",1407.8340v2
2014-10-08,Multi-qubit gates protected by adiabaticity and dynamical decoupling applicable to donor qubits in silicon,"We present a strategy for producing multi-qubit gates that promise high
fidelity with minimal tuning requirements. Our strategy combines gap protection
from the adiabatic theorem with dynamical decoupling in a complementary manner.
To avoid degenerate states and maximize the benefit of the gap protection, the
scheme is best suited when there are two different kinds of qubits (not
mutually resonant). Furthermore, we require a robust operating point in control
space where the qubits interact with little sensitivity to noise. This allows
us to circumvent a No-Go theorem that prevents block-box dynamically corrected
gates [Phys. Rev. A 80, 032314 (2009)]. We show how to apply our strategy to an
architecture in Si with P donors where we assume we can shuttle electrons
between different donors. Electron spins act as mobile ancillary qubits and P
nuclear spins act as long-lived data qubits. This system can have a very robust
operating point where the electron spin is bound to a donor in the quadratic
Stark shift regime. High fidelity single qubit gates may be performed using
well-established global magnetic resonance pulse sequences. Single electron
spin preparation and measurement has also been demonstrated. Putting this all
together, we present a robust universal gate set for quantum computation.",1410.2245v3
2015-02-27,Dynamical decoupling based quantum sensing: Floquet spectroscopy,"Sensing the internal dynamics of individual nuclear spins or clusters of
nuclear spins has recently become possible by observing the coherence decay of
a nearby electronic spin: the weak magnetic noise is amplified by a periodic,
multi-pulse decoupling sequence. However, it remains challenging to robustly
infer underlying atomic-scale structure from decoherence traces in all but the
simplest cases. We introduce Floquet spectroscopy as a versatile paradigm for
analysis of these experiments, and argue it offers a number of general
advantages. In particular, this technique generalises to more complex
situations, offering physical insight in regimes of many-body dynamics, strong
coupling and pulses of finite duration. As there is no requirement for resonant
driving, the proposed spectroscopic approach permits physical interpretation of
striking, but overlooked, coherence decay features in terms of the form of the
avoided crossings of the underlying quasienergy eigenspectrum. This is
exemplified by a set of ""diamond"" shaped features arising for transverse-field
scans in the case of single-spin sensing by NV-centers in diamond. We
investigate also applications for donors in silicon showing that the resulting
tunable interaction strengths offer highly promising future sensors.",1502.07960v4
2015-06-11,Static and dynamical spin correlations of the S=1/2 random-bond antiferromagnetic Heisenberg model on the triangular and the kagome lattices,"Inspired by the recent theoretical suggestion that the random-bond $S=1/2$
antiferromagnetic Heisenberg model on the triangular and the kagome lattices
might exhibit a randomness-induced quantum spin liquid (QSL) behavior when the
strength of the randomness exceeds a critical value, and that this
""random-singlet state"" might be relevant to the QSL behaviors experimentally
observed in triangular organic salts $\kappa {\rm -(ET)_2 Cu_2 (CN)_3}$and
${\rm EtMe_3 Sb[Pd(dmit)_2]_2}$ and in kagome herbertsmithite ${\rm
CuZn_3(OH)_6Cl_2}$, we further investigate the nature of the static and the
dynamical spin correlations of these models. We compute the static and the
dynamical spin structure factors, $S({\bf q})$ and $S({\bf q},\omega)$, by
means of an exact diagonalization method. In both triangular and kagome models,
the computed $S({\bf q},\omega)$ in the random-singlet state depends on the
wavevector ${\bf q}$ only weakly, robustly exhibiting gapless behaviors
accompnied by the broad distribution extending to higher energy $\omega$.
Especially in the strongly random kagome model, $S({\bf q},\omega)$ hardly
depends on ${\bf q}$, and exhibits an almost flat distribution for a wide range
of $\omega$, together with a $\omega=0$ peak. These features agree
semi-quantitatively with the recent neutron-scattering data on a single-crystal
herbertsmithite, suggesting that the QSL state observed in herbersmithite might
indeed be the randomness-induced QSL state, {\it i.e.\/}, the random-singlet
state.",1506.03576v2
2015-11-24,Dynamical properties of the sine-Gordon quantum spin magnet Cu-PM at zero and finite temperature,"The material copper pyrimidine dinitrate (Cu-PM) is a quasi-one-dimensional
spin system described by the spin-1/2 XXZ Heisenberg antiferromagnet with
Dzyaloshinskii-Moriya interactions. Based on numerical results obtained by the
density-matrix renormalization group, exact diagonalization, and accompanying
electron spin resonance (ESR) experiments we revisit the spin dynamics of this
compound in an applied magnetic field. Our calculations for momentum and
frequency-resolved dynamical quantities give direct access to the intensity of
the elementary excitations at both zero and finite temperature. This allows us
to study the system beyond the low-energy description by the quantum
sine-Gordon model. We find a deviation from the Lorentz invariant dispersion
for the single-soliton resonance. Furthermore, our calculations only confirm
the presence of the strongest boundary bound state previously derived from a
boundary sine-Gordon field theory, while composite boundary-bulk excitations
have too low intensities to be observable. Upon increasing the temperature, we
find a temperature-induced crossover of the soliton and the emergence of new
features, such as interbreather transitions. The latter observation is
confirmed by our ESR experiments on Cu-PM over a wide range of the applied
field.",1511.07880v2
2016-01-21,Real-space renormalization for the finite temperature statics and dynamics of the Dyson Long-Ranged Ferromagnetic and Spin-Glass models,"The finite temperature dynamics of the Dyson hierarchical classical spins
models is studied via real-space renormalization rules concerning the couplings
and the relaxation times. For the ferromagnetic model involving Long-Ranged
coupling $J(r) \propto r^{-1-\sigma}$ in the region $1/2<\sigma<1$ where there
exists a non-mean-field-like thermal Ferromagnetic-Paramagnetic transition, the
RG flows are explicitly solved: the characteristic relaxation time $\tau(L)$
follows the critical power-law $\tau(L)\propto L^{z_c(\sigma)} $ at the phase
transition and the activated law $\ln \tau(L)\propto L^{\psi} $ with
$\psi=1-\sigma$ in the ferromagnetic phase. For the Spin-Glass model involving
random Long-Ranged couplings of variance $\overline{J^2(r)} \propto
r^{-2\sigma}$ in the region $2/3<\sigma<1$ where there exists a
non-mean-field-like thermal SpinGlass-Paramagnetic transition, the coupled RG
flows of the couplings and of the relaxation times are studied numerically :
the relaxation time $\tau(L)$ follows some power-law $\tau(L)\propto
L^{z_c(\sigma)} $ at criticality and the activated law $\ln \tau(L)\propto
L^{\psi} $ in the Spin-Glass phase with the dynamical exponent
$\psi=1-\sigma=\theta$ coinciding with the droplet exponent governing the flow
of the couplings $J(L) \propto L^{\theta} $.",1601.05643v2
2016-10-02,Non-linear charge and energy dynamics of an adiabatically driven interacting quantum dot,"We formulate a general theory to study the time-dependent charge and energy
transport of an adiabatically driven interacting quantum dot in contact to a
reservoir for arbitrary amplitudes of the driving potential. We study within
this framework the Anderson impurity model with a local ac gate voltage. We
show that the exact adiabatic quantum dynamics of this system is fully
determined by the behavior of the charge susceptibility of the frozen problem.
At $T=0$, we evaluate the dynamic response functions with the numerical
renormalization group (NRG). The time-resolved heat production exhibits a
pronounced feature described by an instantaneous Joule law characterized by an
universal resistance quantum $R_0=h/(2 e^2)$ for each spin channel. We show
that this law holds in non-interacting as well as in the interacting system and
also when the system is spin-polarized. In addition, in the presence of a
static magnetic field, the interplay between many-body interactions and spin
polarization leads to a non-trivial energy exchange between electrons with
different spin components.",1610.00308v5
2017-03-13,Quantum kinetic equations for the ultrafast spin dynamics of excitons in diluted magnetic semiconductor quantum wells after optical excitation,"Quantum kinetic equations of motion for the description of the exciton spin
dynamics in II-VI diluted magnetic semiconductor quantum wells with laser
driving are derived. The model includes the magnetic as well as the nonmagnetic
carrier-impurity interaction, the Coulomb interaction, Zeeman terms, and the
light-matter coupling, allowing for an explicit treatment of arbitrary
excitation pulses. Based on a dynamics-controlled truncation scheme,
contributions to the equations of motion up to second order in the generating
laser field are taken into account. The correlations between the carrier and
the impurity subsystems are treated within the framework of a correlation
expansion. For vanishing magnetic field, the Markov limit of the quantum
kinetic equations formulated in the exciton basis agrees with existing theories
based on Fermi's golden rule. For narrow quantum wells excited at the $1s$
exciton resonance, numerical quantum kinetic simulations reveal pronounced
deviations from the Markovian behavior. In particular, the spin decays
initially with approximately half the Markovian rate and a non-monotonic decay
in the form of an overshoot of up to $10\,\%$ of the initial spin polarization
is predicted.",1703.04435v3
2019-05-12,On the dynamics of non-rigid asteroid rotation,"We have presented in this communication a new solving procedure for the
dynamics of non-rigid asteroid rotation, considering the final spin state of
rotation for a small celestial body (asteroid). The last condition means the
ultimate absence of the applied external torques (including short-term effect
from torques during collisions, long-term YORP effect, etc.). Fundamental law
of angular momentum conservation has been used for the aforementioned solving
procedure. The system of Euler equations for dynamics of non-rigid asteroid
rotation has been explored with regard to the existence of an analytic way of
presentation of the approximated solution. Despite of various perturbations
(such as collisions, YORP effect) which destabilize the rotation of asteroid
via deviating from the current spin state, the inelastic (mainly, tidal)
dissipation reduces kinetic energy of asteroid. So, evolution of the spinning
asteroid should be resulting by the rotation about maximal-inertia axis with
the proper spin state corresponding to minimal energy with a fixed angular
momentum. Basing on the aforesaid assumption (component K_1 is supposed to be
fluctuating near the given appropriate constant of the fixed angular momentum),
we have obtained that 2-nd component K_2 is the solution of appropriate Riccati
ordinary differential equation of 1-st order, whereas component K_3 should be
determined via expression for K_2.",1905.06842v4
2019-05-17,Testing the multipole structure and conservative dynamics of compact binaries using gravitational wave observations: The spinning case,"In an earlier work [S. Kastha et al., PRD {\bf 98}, 124033 (2018)], we
developed the {\it parametrized multipolar gravitational wave phasing formula}
to test general relativity, for the non-spinning compact binaries in
quasi-circular orbit. In this paper, we extend the method and include the
important effect of spins in the inspiral dynamics. Furthermore, we consider
parametric scaling of PN coefficients of the conserved energy for the compact
binary, resulting in the parametrized phasing formula for non-precessing
spinning compact binaries in quasi-circular orbit. We also compute the
projected accuracies with which the second and third generation ground-based
gravitational wave detector networks as well as the planned space-based
detector LISA will be able to measure the multipole deformation parameters and
the binding energy parameters. Based on different source configurations, we
find that a network of third-generation detectors would have comparable ability
to that of LISA in constraining the conservative and dissipative dynamics of
the compact binary systems. This parametrized multipolar waveform would be
extremely useful not only in deriving the first upper limits on any deviations
of the multipole and the binding energy coefficients from general relativity
using the gravitational wave detections, but also for science case studies of
next generation gravitational wave detectors.",1905.07277v1
2020-07-20,Emergent topology under slow non-adiabatic quantum dynamics,"Characterization of equilibrium topological quantum phases by non-equilibrium
quench dynamics provides a novel and efficient scheme in detecting topological
invariants defined in equilibrium. Nevertheless, most of the previous studies
have focused on the ideal sudden quench regime. Here we provide a generic
non-adiabatic protocol of slowly quenching the system Hamiltonian, and
investigate the non-adiabatic dynamical characterization scheme of topological
phase. The {\it slow} quench protocol is realized by introducing a Coulomb-like
Landau-Zener problem, and it can describe, in a unified way, the crossover from
sudden quench regime (deep non-adiabatic limit) to adiabatic regime. By
analytically obtaining the final state vector after non-adiabatic evolution, we
can calculate the time-averaged spin polarization and the corresponding
topological spin texture. We find that the topological invariants of the
post-quench Hamiltonian are characterized directly by the values of spin
texture on the band inversion surfaces. Compared to the sudden quench regime,
where one has to take an additional step to calculate the {\it gradients} of
spin polarization, this non-adiabatic characterization provides a {\it minimal}
scheme in detecting the topological invariants. Our findings are not restricted
to 1D and 2D topological phases under Coulomb-like quench protocol, but are
also valid for higher dimensional system or different quench protocol.",2007.09842v1
2010-05-11,"Spin dynamics, short range order and spin freezing in Y0.5Ca0.5BaCo4O7","Y0.5Ca0.5BaCo4O7 was recently introduced as a possible candidate for
capturing some of the predicted classical spin kagome ground state features.
Stimulated by this conjecture we have taken up a more complete study of the
spin correlations in this compound with neutron scattering methods on a powder
sample characterized with high-resolution neutron diffraction and the
temperature dependence of magnetic susceptibility and specific heat. We have
found that the frustrated near neighbor magnetic correlations involve not only
the kagome planes but concern the full Co sub-lattice as evidenced by the
analysis of the wavevector-dependence of the short range order. We conclude
from our results that the magnetic moments are located on the Co sub-lattice as
a whole and that correlations extend beyond the two-dimensional kagome planes.
We identify intriguing dynamical properties, observing high-frequency
fluctuations with a lorentzian line-width {\Gamma} <= 20 meV at ambient
temperature. On cooling a low-frequency (~ 1 meV) dynamical component develops
alongside the high-frequency fluctuations, which eventually becomes static at
temperatures below T ~ 50 K. The high-frequency response with an overall
line-width of ~ 10 meV prevails at T <= 2 K coincident with a fully elastic
short-range ordered contribution.",1005.1883v3
2017-01-13,Spin dynamics of quadrupole nuclei in InGaAs quantum dots,"Photoluminescence polarization is experimentally studied for samples with
(In,Ga)As/GaAs selfassembled quantum dots in transverse magnetic field (Hanle
effect) under slow modulation of the excitation light polarization from
fractions of Hz to tens of kHz. The polarization reflects the evolution of
strongly coupled electron-nuclear spin system in the quantum dots. Strong
modification of the Hanle curves under variation of the modulation period is
attributed to the peculiarities of the spin dynamics of quadrupole nuclei,
which states are split due to deformation of the crystal lattice in the quantum
dots. Analysis of the Hanle curves is fulfilled in the framework of a
phenomenological model considering a separate dynamics of a nuclear field BNd
determined by the +/- 12 nuclear spin states and of a nuclear field BNq
determined by the split-off states +/- 3/2, +/- 5/2, etc. It is found that the
characteristic relaxation time for the nuclear field BNd is of order of 0.5 s,
while the relaxation of the field BNq is faster by three orders of magnitude.",1701.03591v1
2016-05-03,PRECESSION: Dynamics of spinning black-hole binaries with python,"We present the numerical code PRECESSION: a new open-source python module to
study the dynamics of precessing black-hole binaries in the post-Newtonian
regime. The code provides a comprehensive toolbox to (i) study the evolution of
the black-hole spins along their precession cycles, (ii) perform
gravitational-wave driven binary inspirals using both orbit-averaged and
precession-averaged integrations, and (iii) predict the properties of the
merger remnant through fitting formulae obtained from numerical-relativity
simulations. PRECESSION is a ready-to-use tool to add the black-hole spin
dynamics to larger-scale numerical studies such as gravitational-wave parameter
estimation codes, population synthesis models to predict gravitational-wave
event rates, galaxy merger trees and cosmological simulations of structure
formation. PRECESSION provides fast and reliable integration methods to
propagate statistical samples of black-hole binaries from/to large separations
where they form to/from small separations where they become detectable, thus
linking gravitational-wave observations of spinning black-hole binaries to
their astrophysical formation history. The code is also a useful tool to
compute initial parameters for numerical-relativity simulations targeting
specific precessing systems. PRECESSION can be installed from the Python
Package Index and it is freely distributed under version control on Github,
where further documentation is provided.",1605.01067v3
2016-08-11,Secular and tidal evolution of circumbinary systems,"We investigate the secular dynamics of three-body circumbinary systems under
the effect of tides. We use the octupolar non-restricted approximation for the
orbital interactions, general relativity corrections, the quadrupolar
approximation for the spins, and the viscous linear model for tides. We derive
the averaged equations of motion in a simplified vectorial formalism, which is
suitable to model the long-term evolution of a wide variety of circumbinary
systems in very eccentric and inclined orbits. In particular, this vectorial
approach can be used to derive constraints for tidal migration, capture in
Cassini states, and stellar spin-orbit misalignment. We show that circumbinary
planets with initial arbitrary orbital inclination can become coplanar through
a secular resonance between the precession of the orbit and the precession of
the spin of one of the stars. We also show that circumbinary systems for which
the pericenter of the inner orbit is initially in libration present chaotic
motion for the spins and for the eccentricity of the outer orbit. Because our
model is valid for the non-restricted problem, it can also be applied to any
three-body hierarchical system such as star-planet-satellite systems and triple
stellar systems.",1608.03484v1
2016-08-16,Incommensurate spiral magnetic order on anisotropic triangular lattice: Dynamical mean field study in a spin-rotating frame,"We study the ground-state magnetism of the half-filled Hubbard model on the
anisotropic triangular lattice, where two out of three bonds have hopping $t$
and the third one has $t^\prime$ in a unit triangle. Working in a spin-rotating
frame and using the density matrix renormalization group method as an impurity
solver, we provide a proper description of incommensurate magnetizations at
zero temperature in the framework of the dynamical mean-field theory (DMFT). It
is shown that the incommensurate spiral magnetic order for $t^\prime/t\gtrsim
0.7$ survives the dynamical fluctuations of itinerant electrons in the Hubbard
interaction range from the strong-coupling (localized-spin) limit down to the
insulator-to-metal transition. We also find that the magnetic moment reduction
from the localized-spin limit is pronounced in the vicinity of the transition
between the commensurate N\'eel and incommensurate spiral phases at
$t^\prime/t\sim 0.7$. When the anisotropy parameter $t^\prime/t$ increases from
the N\'eel-to-spiral transition, the magnitude of the magnetic moment
immediately reaches a maximum and then rapidly decreases in the range of larger
$t^\prime/t$ including the isotropic triangular lattice point $t^\prime/t=1$.
This work gives a solid foundation for further extension of the study including
nonlocal correlation effects neglected at the standard DMFT level.",1608.04490v1
2017-06-17,Dynamic scaling in the 2D Ising spin glass with Gaussian couplings,"We carry out simulated annealing and employ a generalized Kibble-Zurek
scaling hypothesis to study the 2D Ising spin glass with normal-distributed
couplings. The system has an equilibrium glass transition at temperature $T=0$.
From a scaling analysis when $T\rightarrow 0$ at different annealing
velocities, we extract the dynamic critical exponent $z$, i.e., the exponent
relating the relaxation time $\tau$ to the system length $L$; $\tau\sim L^z$.
We find $z=13.6 \pm 0.4$ for both the Edwards-Anderson spin-glass order
parameter and the excess energy. This is different from a previous study of the
system with bimodal couplings [S. J. Rubin, N. Xu, and A. W. Sandvik, Phys.
Rev. E {\bf 95}, 052133 (2017)] where the dynamics is faster and the above two
quantities relax with different exponents (and that of the energy is larger).
We here argue that the different behaviors arise as a consequence of the
different low-energy landscapes---for normal-distributed couplings the ground
state is unique (up to a spin reflection) while the system with bimodal
couplings is massively degenerate. Our results reinforce the conclusion of
anomalous entropy-driven relaxation behavior in the bimodal Ising glass. In the
case of a continuous coupling distribution, our results presented here indicate
that, although Kibble-Zurek scaling holds, the perturbative behavior normally
applying in the slow limit breaks down, likely due to quasi-degenerate states,
and the scaling function takes a different form.",1706.05472v2
2017-12-29,Coupled charge and spin dynamics in high-density ensembles of nitrogen-vacancy centers in diamond,"We studied the spin depolarization of ensembles of nitrogen-vacancy (NV)
centers in nitrogen-rich single crystal diamonds. We found a strong dependence
of the evolution of the polarized state in the dark on the concentration of NV
centers. At low excitation power, we observed a simple exponential decay
profile in the low-density regime and a paradoxical inverted exponential
profile in the high-density regime. At higher excitation power, we observed
complex behavior, with an initial sharp rise in luminescence signal after the
preparation pulse followed by a slower exponential decay. Magnetic field and
excitation laser power-dependent measurements suggest that the rapid initial
increase of the luminescence signal is related to recharging of the
nitrogen-vacancy centers (from neutral to negatively charged) in the dark. The
slow relaxing component corresponds to the longitudinal spin relaxation of the
NV ensemble. The shape of the decay profile reflects the interplay between two
mechanisms: the NV charge state conversion in the dark and the longitudinal
spin relaxation. These mechanisms, in turn, are influenced by ionization,
recharging and polarization dynamics during excitation. Interestingly, we found
that charge dynamics are dominant in NV-dense samples even at very feeble
excitation power. These observations may be important for the use of ensembles
of NV centers in precession magnetometry and sensing applications.",1801.00047v1
2019-06-20,Numerical binary black hole collisions in dynamical Chern-Simons gravity,"We produce the first numerical relativity binary black hole gravitational
waveforms in a higher-curvature theory beyond general relativity. In
particular, we study head-on collisions of binary black holes in order-reduced
dynamical Chern-Simons gravity. This is a precursor to producing
beyond-general-relativity waveforms for inspiraling binary black hole systems
that are useful for gravitational wave detection. Head-on collisions are
interesting in their own right, however, as they cleanly probe the quasi-normal
mode spectrum of the final black hole. We thus compute the leading-order
dynamical Chern-Simons modifications to the complex frequencies of the
post-merger gravitational radiation. We consider equal-mass systems, with equal
spins oriented along the axis of collision, resulting in remnant black holes
with spin. We find modifications to the complex frequencies of the quasi-normal
mode spectrum that behave as a power law with the spin of the remnant, and that
are not degenerate with the frequencies associated with a Kerr black hole of
any mass and spin. We discuss these results in the context of testing general
relativity with gravitational wave observations.",1906.08789v2
2020-02-20,Quantum Paraelectricity in the Kitaev Quantum-Spin-Liquid Candidates H$_{3}$LiIr$_{2}$O$_{6}$ and D$_{3}$LiIr$_{2}$O$_{6}$,"H3LiIr2O6 is the first honeycomb-lattice system without any signs of
long-range magnetic order down to the lowest temperatures, raising the hope for
the realization of an ideal Kitaev quantum spin liquid. Its honeycomb layers
are coupled by interlayer hydrogen bonds. Static or dynamic disorder of these
hydrogen bonds was proposed to strongly affect the magnetic exchange and to
make Kitaev-type interactions dominant. Using dielectric spectroscopy, here we
provide experimental evidence for dipolar relaxations in H3LiIr2O6 and
deuterated D3LiIr2O6, which mirror the dynamics of protons and deuterons within
the double-well potentials of the hydrogen bonds. The detected hydrogen
dynamics reveals glassy freezing, characterized by a strong slowing down under
cooling, with a crossover from thermally-activated hopping to
quantum-mechanical tunneling towards low temperatures. Thus, besides being
Kitaev quantum-spin-liquid candidates, these materials also are quantum
paraelectrics. However, the small relaxation rates in the mHz range, found at
low temperatures, practically realize quasi-static hydrogen disorder, as
assumed in recent theoretical works to explain the quantum-spin-liquid ground
state of both compounds.",2002.09016v1
2020-04-08,Spin dynamics and a nearly continuous magnetic phase transition in an entropy-stabilized oxide antiferromagnet,"The magnetic order and the spin dynamics in the antiferromagnetic
entropy-stabilized oxide (Mg$_{0.2}$Co$_{0.2}$Ni$_{0.2}$Cu$_{0.2}$Zn$_{0.2}$)O
(MgO-ESO) have been studied using muon spin relaxation ($\mu$SR) and inelastic
neutron scattering. We find that antiferromagnetic order develops gradually in
the sample volume as it is cooled below 140 K, becoming fully ordered around
100 K. The spin dynamics show a critical slowing down in the vicinity of the
transition, and the magnetic order parameter grows continuously in the ordered
state. These results indicate that the antiferromagnetic transition is
continuous but proceeds with a Gaussian distribution of ordering temperatures.
The magnetic contribution to the specific heat determined from inelastic
neutron scattering likewise shows a broad feature centered around 120 K.
High-resolution inelastic neutron scattering further reveals an initially
gapped spectrum at low temperature which sees an increase in a quasielastic
contribution upon heating until the ordering temperature.",2004.04218v2
2018-07-25,Algorithmic simulation of far-from-equilibrium dynamics using quantum computer,"We point out that superconducting quantum computers are prospective for the
simulation of the dynamics of spin models far from equilibrium, including
nonadiabatic phenomena and quenches. The important advantage of these machines
is that they are programmable, so that different spin models can be simulated
in the same chip, as well as various initial states can be encoded into it in a
controllable way. This opens an opportunity to use superconducting quantum
computers in studies of fundamental problems of statistical physics such as the
absence or presence of thermalization in the free evolution of a closed quantum
system depending on the choice of the initial state as well as on the
integrability of the model. In the present paper, we performed
proof-of-principle digital simulations of two spin models, which are the
central spin model and the transverse-field Ising model, using 5- and 16-qubit
superconducting quantum computers of the IBM Quantum Experience. We found that
these devices are able to reproduce some important consequences of the symmetry
of the initial state for the system's subsequent dynamics, such as the
excitation blockade. However, lengths of algorithms are currently limited due
to quantum gate errors. We also discuss some heuristic methods which can be
used to extract valuable information from the imperfect experimental data.",1807.10149v1
2018-08-22,Environment Overwhelms both Nature and Nurture in a Model Spin Glass,"The microscopic dependence of glassy equilibration on sample history, both
the initial configuration and the specific sequence of random noise, is
examined. The temporal evolution of spin configurations in a two-dimensional
Ising spin glass is simulated using patchwork dynamics, a coarse-grained
heuristic for glassy dynamics, allowing simulations over a wide range of length
scales. Most of the nearest-neighbor spin correlations are independent of the
details of evolution, due to the formation of rigid domains. The correlations
on a fractal set of domain walls are found to be variable and to depend
distinctly on the noise history and the initial state. Correlations in samples
with independent initial configurations are found to persistently differ when
subject to identical noise histories, for coarsening scales of up to hundreds
of lattice units. However, samples with identical initial configurations and
subject to independent noise histories have correlations that converge to each
other as a power law in scale. The initial ""nature"" of the state is retained in
the domain walls during coarsening under distinct noises (""nurture""), while the
location of the domain walls at each scale is determined by the frozen disorder
(""environment""), independent of initial state or noise history. We also provide
evidence that coarsening with local dynamics at finite temperature gives
persistence of overlaps roughly consistent with coarsening at zero temperature.",1808.07236v1
2018-12-18,Petahertz Spintronics,"The enigmatic coupling between electronic and magnetic phenomena was one of
the riddles propelling the development of modern electromagnetism. Today, the
fully controlled electric field evolution of ultrashort laser pulses permits
the direct and ultrafast control of electronic properties of matter and is the
cornerstone of light-wave electronics. In sharp contrast, because there is no
first order interaction between light and spins, the magnetic properties of
matter can only be affected indirectly on the much slower tens-of-femtosecond
timescale in a sequence of optical excitation followed by the rearrangement of
the spin structure. Here we record an orders of magnitude faster magnetic
switching with sub-femtosecond response time by initiating optical excitations
with near-single-cycle laser pulses in a ferromagnetic layer stack. The
unfolding dynamics are tracked in real-time by a novel attosecond time-resolved
magnetic circular dichroism (atto-MCD) detection scheme revealing optically
induced spin and orbital momentum transfer (OISTR) in synchrony with light
field driven charge relocation. In tandem with ab-initio quantum dynamical
modelling, we show how this mechanism provides simultaneous control over
electronic and magnetic properties that are at the heart of spintronic
functionality. This first incarnation of attomagnetism observes light field
coherent control of spin-dynamics in the initial non-dissipative temporal
regime and paves the way towards coherent spintronic applications with
Petahertz clock rates.",1812.07420v1
2019-02-21,Effects of the removal of Ta capping layer on the magnetization dynamics of Permalloy thin films,"We have investigated the spin wave dynamics of Permalloy (Py) thin films with
and without a Ta capping layer for varying Py thickness (15 nm, 20 nm and 30
nm) using all optical time-resolved magneto-optical Kerr effect measurements.
XPS measurements confirm the oxidation of the originally-prepared samples and
also that the removal of the Ta capping layer is achievable by a few sputtering
cycles. The magnetic field strength dependencies of the spin wave modes with
the variation of the Py film thickness for the samples are studied. We observe
that the presence of the Ta capping layer reduces the precessional frequencies
of the samples while the samples without a Ta capping layer enhance the role of
Py thickness. We also observe that the decay time of spin waves is highly
dependent on the top layer of the samples. The decay time increases with
increasing Py thicknesses for Ta/Py/Ta samples implying that the enhancement of
decay time is caused by the Ta/Py/Ta interfaces. Whereas, for Ta/Py samples the
decay time decreases with increasing Py thickness. The results of this work
extend the knowledge on the magnetization dynamics of Py thin films giving
information on how to resume and even enhance the spin mobility after a
deleterious oxidation process. This can open new scenarios on the building
process and on the maintenance of fast magnetic switching devices.",1902.07832v1
2019-11-08,Phase-separation of vector solitons in spin-orbit coupled spin-1 condensates,"We study the phase-separation in three-component bright vector solitons in a
quasi-one-dimensional spin-orbit-coupled hyper-fine spin $F=1$ ferromagnetic
Bose-Einstein condensate upon an increase of the strength of spin-orbit (SO)
coupling $p_x \Sigma_z$ above a critical value, where $p_x$ is the linear
momentum and $\Sigma_z$ is the $z$-component of the spin-1 matrix. The bright
vector solitons are demonstrated to be mobile and dynamically stable. The
collision between two such vector solitons is found to be elastic at all
velocities with the conservation of density of each vector soliton. The two
colliding vector solitons repel at small separation and at very small colliding
velocity, they come close and bounce back with the same velocity without ever
encountering each other. This repulsion produced by SO coupling is responsible
for the phase separation in a vector soliton for large strengths of SO
coupling. { The collision dynamics is found to be completely insensitive to the
relative phase of the colliding solitons.} However, in the absence of SO
coupling, at very small velocity, the two colliding vector solitons attract
each other and form a vector soliton molecule and the collision dynamics is
sensitive to the relative phase as in scalar solitons. The present
investigation is carried out through a numerical solution and an analytic
variational approximation of the underlying mean-field Gross-Pitaevskii
equation.",1911.03498v1
2020-05-06,Holographic quantum algorithms for simulating correlated spin systems,"We present a suite of ""holographic"" quantum algorithms for efficient
ground-state preparation and dynamical evolution of correlated spin-systems,
which require far-fewer qubits than the number of spins being simulated. The
algorithms exploit the equivalence between matrix-product states (MPS) and
quantum channels, along with partial measurement and qubit re-use, in order to
simulate a $D$-dimensional spin system using only a ($D$-1)-dimensional subset
of qubits along with an ancillary qubit register whose size scales
logarithmically in the amount of entanglement present in the simulated state.
Ground states can either be directly prepared from a known MPS representation,
or obtained via a holographic variational quantum eigensolver (holoVQE).
Dynamics of MPS under local Hamiltonians for time $t$ can also be simulated
with an additional (multiplicative) ${\rm poly}(t)$ overhead in qubit
resources. These techniques open the door to efficient quantum simulation of
MPS with exponentially large bond-dimension, including ground-states of 2D and
3D systems, or thermalizing dynamics with rapid entanglement growth. As a
demonstration of the potential resource savings, we implement a holoVQE
simulation of the antiferromagnetic Heisenberg chain on a trapped-ion quantum
computer, achieving within $10(3)\%$ of the exact ground-state energy of an
infinite chain using only a pair of qubits.",2005.03023v1
2020-05-26,"From magnetic order to quantum disorder: a $μ$SR study of the Zn-barlowite series of $S={\frac{1}{2}}$ kagomé antiferromagnets, Zn$_{x}$Cu$_{4-x}$(OH)$_{6}$FBr","We report a comprehensive muon spectroscopy study of the Zn-barlowite series
of $S={\frac{1}{2}}$ kagom\'e antiferromagnets, Zn$_x$Cu$_{4-x}$(OH)$_{6}$FBr,
for $x=0.00$ to $0.99(1)$. By combining muon spin relaxation and rotation
measurements with state-of-the-art density-functional theory muon-site
calculations, we observe the formation of both $\mu$--F and $\mu$--OH complexes
in Zn-barlowite. From these stopping sites, implanted muon spins reveal the
suppression of long-range magnetic order into a possible quantum spin liquid
state upon increasing concentration of Zn-substitution. In the parent compound
($x=0$), static long-range magnetic order below $T_{\mathsf{N}}=15$ K manifests
itself in the form of spontaneous oscillations in the time-dependent muon
asymmetry signal consistent with the dipolar fields expected from the
calculated muon stopping sites and the previously determined magnetic structure
of barlowite. Meanwhile, in the $x=1.0$ end-member of the series---in which
antiferromagnetic kagom\'e layers of Cu$^{2+}$ $S={\frac{1}{2}}$ moments are
decoupled by diamagnetic Zn$^{2+}$ ions---we observe that dynamic magnetic
moment fluctuations persist down to at least 50 mK, indicative of a quantum
disordered ground state. We demonstrate that this crossover from a static to
dynamic magnetic ground state occurs for compositions of Zn-barlowite with
$x>0.5$, which bears resemblance to dynamical behaviour of the widely studied
Zn-paratacamite series that contains the quantum spin liquid candidate
herbertsmithite.",2005.12615v1
2020-09-09,Disorder-free localization in quantum walks,"The phenomenon of localization usually happens due to the existence of
disorder in a medium. Nevertheless, certain quantum systems allow dynamical
localization solely due to the nature of internal interactions. We study a
discrete time quantum walker which exhibits disorder free localization. The
quantum walker moves on a one-dimensional lattice and interacts with on-site
spins by coherently rotating them around a given axis at each step. Since the
spins do not have dynamics of their own, the system poses the local spin
components along the rotation axis as an extensive number of conserved moments.
When the interaction is weak, the spread of the walker shows subdiffusive
behaviour having downscaled ballistic tails in the evolving probability
distribution at intermediate time scales. However, as the interaction gets
stronger the walker gets exponentially localized in the complete absence of
disorder in both lattice and initial state. Using a matrix-product-state
ansatz, we investigate the relaxation and entanglement dynamics of the on-site
spins due to their coupling with the quantum walker. Surprisingly, we find that
even in the delocalized regime, entanglement growth and relaxation occur slowly
unlike marjority of the other models displaying a localization transition.",2009.04571v2
2021-03-31,Integrable systems and the boundary dynamics of (higher spin) gravity on AdS$_3$,"This thesis extends a previously found relation between the integrable KdV
hierarchy and the boundary dynamics of pure gravity on AdS$_3$ described in the
highest weight gauge, to a more general class of integrable systems associated
to three-dimensional gravity on AdS$_3$ and higher spin gravity with gauge
group $SL(N,\mathbb{R})\times SL(N,\mathbb{R})$ in the diagonal gauge. We
present new sets of boundary conditions for the (higher spin) gravitational
theories on AdS$_3$, where the dynamics of the boundary degrees of freedom is
described by two independent left and right members of a hierarchy of
integrable equations. For the pure gravity case, the associated hierarchy
corresponds to the Gardner hierarchy, also known as the ""mixed KdV-mKdV"" one,
while for the case of higher spin gravity, they are identified with the
""modified Gelfand-Dickey"" hierarchies. The complete integrable structure of the
hierarchies, i.e., the phase space, the Poisson brackets and the infinite
number of commuting conserved charges, are directly obtained from the
asymptotic structure and the conserved surface integrals in the gravitational
theories. Consequently, the corresponding Miura transformation is recovered
from a purely geometric construction in the bulk. Black hole solutions that fit
within our boundary conditions, the Hamiltonian reduction at the boundary and
more general thermodynamic ensembles called ""Generalized Gibbs Ensemble"" are
also discussed.",2104.00068v1
2021-04-13,Spin-triplet proton-neutron pair in spin-dipole excitations,"Background: Spin-triplet ($S=1$) proton-neutron (pn) pairing in nuclei has
been under debate. It is well known that the dynamical pairing affects the
nuclear matrix element of the Gamow-Teller (GT) transition and the double beta
decay. Purpose: We investigate the effect of the pn-pair interaction in the
$T=0, S=1$ channel on the low-lying spin-dipole (SD) transition. We then aim at
clarifying the distinction of the role in between the SD and GT transitions.
Method: We perform a three-body model calculation for the transition
${}^{80}\mathrm{Ni}\to{}^{80}\mathrm{Cu}$, where ${}^{78}\mathrm{Ni}$ is taken
as a core. The strength of the pair interaction is varied to see the effect on
the SD transition-strength distribution. To fortify the finding obtained by the
three-body model, we employ the nuclear energy-density functional method for
the SD transitions in several nuclei, where one can expect a strong effect.
Results: The effect of the $S=1$ pn-pair interaction depends on the spatial
overlap of the pn pair and the angular momentum of the valence nucleons; the
higher the angular momentum of the orbitals, the more significant the effect.
Conclusions: The dynamical $S=1$ pairing is effective even for SD states
although the spatial overlap of the pn pair can be smaller than GT states. The
SD transition involving high-$\ell$ orbitals with the same principal quantum
number is strongly affected by the dynamical $S=1$ pairing.",2104.06049v2
2021-06-09,Spin dynamics slowdown near the antiferromagnetic critical point in atomically thin FePS3,"Two-dimensional (2D) magnetic materials have attracted much recent interest
with unique properties emerging at the few-layer limit. Beyond the reported
impacts on the static magnetic properties, the effects of reducing the
dimensionality on the magnetization dynamics are also of fundamental interest
and importance for 2D device development. In this report, we investigate the
spin dynamics in atomically-thin antiferromagnetic FePS3 of varying layer
numbers using ultrafast pump-probe spectroscopy. Following the absorption of an
optical pump pulse, the time evolution of the antiferromagnetic order parameter
is probed by magnetic linear birefringence. We observe a strong divergence in
the demagnetization time near the N\'eel temperature. The divergence can be
characterized by a power-law dependence on the reduced temperature, with an
exponent decreasing with sample thickness. We compare our results to
expectations from critical slowing down and a two-temperature model involving
spins and phonons, and discuss the possible relevance of spin-substrate phonon
interactions.",2106.05159v1
2021-06-23,The dynamical exponent of a quantum critical itinerant ferromagnet: a Monte Carlo study,"We consider the effect of the coupling between 2D quantum rotors near an XY
ferromagnetic quantum critical point and spins of itinerant fermions. We
analyze how this coupling affects the dynamics of rotors and the self-energy of
fermions.A common belief is that near a $q=0$ ferromagnetic transition,
fermions induce an $\Omega/q$ Landau damping of rotors (i.e., the dynamical
critical exponent is $z=3$) and Landau overdamped rotors give rise to non-Fermi
liquid fermionic self-energy $\Sigma\propto \omega^{2/3}$. This behavior has
been confirmed in previous quantum Monte Carlo (QMC) studies.Here we show that
for the XY case the behavior is different.We report the results of large scale
quantum Monte Carlo simulations,which show that at small frequencies $z=2$ and
$\Sigma\propto \omega^{1/2}$. We argue that the new behavior is associated with
the fact that a fermionic spin is by itself not a conserved quantity due to
spin-spin coupling to rotors, and a combination of self-energy and vertex
corrections replaces $1/q$ in the Landau damping by a constant. We discuss the
implication of these results to experiments.",2106.12601v3
2021-08-03,Dynamic transformation between a skyrmion string and a bimeron string in a layered frustrated system,"Frustrated topological spin textures have unique properties that may enable
novel spintronic applications, such as helicity-based information storage and
computing. Here, we report the statics and current-induced dynamics of
two-dimensional (2D) pancake skyrmions in a stack of weakly coupled frustrated
magnetic monolayers, which form a three-dimensional (3D) skyrmion string. The
Bloch-type skyrmion string is energetically more stable than its N\'eel-type
counterpart. It can be driven into translational motion by the dampinglike
spin-orbit torque and shows the damping-dependent skyrmion Hall effect. Most
notably, the skyrmion string can be transformed to a dynamically stable bimeron
string by the dampinglike spin-orbit torque. The current-induced bimeron string
rotates stably with respect to its center, which can spontaneously transform
back to a skyrmion string when the current is switched off. Our results reveal
unusual physical properties of 3D frustrated spin textures, and may open up
different possibilities for spintronic applications based on skyrmion and
bimeron strings.",2108.01365v2
2021-10-14,Ab-initio study of ultrafast spin dynamics in Gdx(FeCo){1-x} alloys,"Using an ultrashort laser pulse we explore {\it ab-initio} the spin dynamics
of Gd$_x$(FeCo)$_{1-x}$ at femtosecond time scales. Optical excitations are
found to drive charge from Fe majority $d$-states to the unoccupied Gd
$f$-minority states, with $f$-electron character excited occupation lagging
behind that of the $d$-electron character, leading to substantial
demagnetisation of both species while leaving the global moment almost
unchanged. For $x > 0.33$ this results in the creation of an ultrafast
ferromagnetic (FM) transient by the end of the laser pulse, with the Gd
demagnetization rate slower than that of Fe. For all concentrations the Gd
moments begin to rotate from their ground state orientations developing
in-plane moments of between 0.2-0.5~$\mu_B$. Thus, the ultrafast spin dynamics
of the material captures three important ingredients of the all optical
switching that occurs at much later (picosecond) times: (i) the development of
a FM transient, (ii) the different rates of demagnetisation of Fe and Gd and,
(iii), the breaking of the colinear symmetry of the ground state. Furthermore,
several predictions are made about the behaviour of Fe-Gd alloys that can be
experimentally tested and can lead to a spin-filtering device.",2110.07180v1
2021-11-11,All-optical scalable spatial coherent Ising machine,"Networks of optical oscillators simulating coupled Ising spins have been
recently proposed as a heuristic platform to solve hard optimization problems.
These networks, called coherent Ising machines (CIMs), exploit the fact that
the collective nonlinear dynamics of coupled oscillators can drive the system
close to the global minimum of the classical Ising Hamiltonian, encoded in the
coupling matrix of the network. To date, realizations of large-scale CIMs have
been demonstrated using hybrid optical-electronic setups, where optical
oscillators simulating different spins are subject to electronic feedback
mechanisms emulating their mutual interaction. While the optical evolution
ensures an ultrafast computation, the electronic coupling represents a
bottleneck that causes the computational time to severely depend on the system
size. Here, we propose an all-optical scalable CIM with fully-programmable
coupling. Our setup consists of an optical parametric amplifier with a spatial
light modulator (SLM) within the parametric cavity. The spin variables are
encoded in the binary phases of the optical wavefront of the signal beam at
different spatial points, defined by the pixels of the SLM. We first discuss
how different coupling topologies can be achieved by different configurations
of the SLM, and then benchmark our setup with a numerical simulation that
mimics the dynamics of the proposed machine. In our proposal, both the spin
dynamics and the coupling are fully performed in parallel, paving the way
towards the realization of size-independent ultrafast optical hardware for
large-scale computation purposes.",2111.06737v1
2022-02-20,Spinor matterwave control with nanosecond spin-dependent kicks,"Significant aspects of advanced quantum technology today rely on rapid
control of atomic matterwaves with hyperfine Raman transitions. Unfortunately,
efficient Raman excitations are usually accompanied by uncompensated dynamic
phases and coherent spin-leakages, preventing accurate and repetitive transfer
of recoil momentum to large samples. We provide systematic study to demonstrate
that the limitations can be substantially overcame by dynamically programming
an adiabatic pulse sequence. Experimentally, counter-propagating
frequency-chirped pulses are programmed on an optical delay line to parallelly
drive five $\Delta m=0$ hyperfine Raman transitions of $^{85}$Rb atoms for
spin-dependent kick (SDK) within $\tau=40$~nanoseconds, with an $f_{\rm
SDK}\approx 97.6\%$ inferred fidelity. Aided by numerical modeling, we
demonstrate that by alternating the chirps of successive pulses in a balanced
fashion, accumulation of non-adiabatic errors including the spin-leakages can
be managed, while the dynamic phases can be robustly cancelled. Operating on a
phase-stable delay line, the method supports precise, fast, and flexible
control of spinor matterwave with efficient Raman excitations.",2202.09709v4
2022-07-17,Rapid quantitative magnetization transfer imaging: utilizing the hybrid state and the generalized Bloch model,"Purpose: To explore efficient encoding schemes for quantitative magnetization
transfer (qMT) imaging with few constraints on model
  Theory and Methods: We combine two recently proposed models in a
Bloch-McConnell equation: the dynamics of the free spin pool are confined to
the hybrid state, and the dynamics of the semi-solid spin pool are described by
the generalized Bloch model. We numerically optimize the flip angles and
durations of a train of radio frequency pulses to enhance the encoding of three
qMT parameters while accounting for all 8 parameters of the 2-pool model. We
sparsely sample each time frame along this spin dynamics with a 3D radial
koosh-ball trajectory, reconstruct the data with subspace modeling, and fit the
qMT model with a neural network for computational efficiency.
  Results: We extracted qMT parameter maps of the whole brain with an effective
resolution of 1.24mm from a 12.6-minute scan. In lesions of multiple sclerosis
subjects, we observe a decreased size of the semi-solid spin pool and longer
relaxation times, consistent with previous
  Conclusion: The encoding power of the hybrid state, combined with regularized
image reconstruction, and the accuracy of the generalized Bloch model provide
an excellent basis for efficient quantitative magnetization transfer imaging
with few constraints on model parameters.",2207.08259v6
2022-08-17,"Characteristic, dynamic, and near saturation regions of Out-of-time-order correlation in Floquet Ising models","We study characteristic, dynamic, and saturation regimes of the
out-of-time-order correlation (OTOC) in the constant field Floquet system with
and without longitudinal field. In the calculation of OTOC, we take local spins
in longitudinal and transverse directions as observables which are local and
non-local in terms of Jordan-Wigner fermions, respectively. We use the exact
analytical solution of OTOC for the integrable model (without longitudinal
field term) with transverse direction spins as observables and numerical
solutions for other integrable and nonintegrable cases. OTOCs generated in both
cases depart from unity at a kick equal to the separation between the
observables when the local spins in the transverse direction and one additional
kick is required when the local spins in the longitudinal direction. The number
of kicks required to depart from unity depends on the separation between the
observables and is independent of the Floquet period and system size. In the
dynamic region, OTOCs show power-law growth in both models, the integrable
(without longitudinal field) as well as the nonintegrable (with longitudinal
field). The exponent of the power-law increases with increasing separation
between the observables. Near the saturation region, OTOCs grow linearly with a
very small rate.",2208.08283v1
2022-11-20,Quench dynamics in the one-dimensional mass-imbalanced ionic Hubbard model,"Using the time-dependent Lanczos method, we study the non-equilibrium
dynamics of the one-dimensional ionic-mass imbalanced Hubbard chain driven by a
quantum quench of the on-site Coulomb interaction, where the system is prepared
in the ground state of the Hamiltonian with a different Hubbard interaction. A
full exact diagonalization is adopted to study the zero temperature phase
diagram in equilibrium, which is shown to be in good agreement with previous
studies using density matrix renormalization group (DMRG). We then study the
non-equilibrium quench dynamics of the spin and charge order parameters by
fixing the initial and final Coulomb interaction while changing the quenching
time protocols. The Lanczos method allows us to reach longer times following
the quench than DMRG. Our study shows that the time evolution of the charge and
spin order parameters strongly depend on the quenching time protocols. In
particular, the effective temperature of the system will decrease monotonically
as the quenching time is increased. Finally, by taking the final Coulomb
interaction strength to be in the strong coupling regime, we find that the
oscillation frequency of the charge order parameter increases monotonically
with the Coulomb interaction. By contrast, the frequency of the spin order
parameter decreases monotonically with increasing Coulomb interaction. We
explain this result using an effective spin model in the strong coupling limit.
Our study suggests strategies to engineer the relaxation behavior of
interacting quantum many-particle systems.",2211.10868v1
2023-01-19,Current-driven dynamics and ratchet effect of skyrmion bubbles in a ferrimagnetic insulator,"Magnetic skyrmions are compact chiral spin textures that exhibit a rich
variety of topological phenomena and hold potential for developing high-density
memory devices and novel computing schemes driven by spin currents. Here, we
demonstrate room temperature interfacial stabilization and current-driven
control of skyrmion bubbles in the ferrimagnetic insulator Tm3Fe5O12 (TmIG)
coupled to Pt. We track the current-induced motion of individual skyrmion
bubbles. The ferrimagnetic order of the crystal together with the interplay of
spin-orbit torques and pinning determine the skyrmion dynamics in TmIG and
result in a strong skyrmion Hall effect characterized by a negative deflection
angle and hopping motion. Further, we show that the velocity and depinning
threshold of the skyrmion bubbles can be modified by exchange coupling TmIG to
an in-plane magnetized Y3Fe5O12 layer, which distorts the spin texture of the
skyrmions and leads to a directional-dependent rectification of their dynamics.
This effect, which is equivalent to a magnetic ratchet, is exploited to control
the skyrmion flow in a racetrack-like device.",2301.08183v1
2023-03-29,Quasi-equilibrium and quantum correlation in an open spin-pair system,"Quasi-equilibrium states that can be prepared in solids through Nuclear
Magnetic Resonance (NMR) techniques are out-of-equilibrium states that slowly
relax towards thermodynamic equilibrium with the lattice. In this work, we use
the quantum discord dynamics as a witness of the quantum correlation in this
kind of state. The studied system is a dipole interacting spin pair whose
initial state is prepared with the NMR Jeener-Broekaert pulse sequence,
starting from equilibrium at high temperature and high external magnetic field.
It then evolves as an open quantum system within two different dynamic
scenarios: adiabatic decoherence driven by the coupling of the pairs to a
common phonon field, described within a non-markovian approach; and
spin-lattice relaxation represented by a markovian master equation, and driven
by thermal fluctuations. In this way, the studied model is endowed with the
dynamics of a realistic solid sample. The quantum discord rapidly increases
during the preparation of the initial state, escalating several orders of
magnitude compared with thermal equilibrium at room temperature. Despite the
vanishing of coherences during decoherence, the quantum discord oscillates
around this high value and undergoes a minor attenuation, holding the same
order of magnitude as the initial state. Finally, the quantum discord
dissipates within a time scale shorter than but comparable to spin-lattice
relaxation.",2303.16451v2
2023-04-21,Surprises in the Deep Hilbert Space of all-to-all systems: From super-exponential scrambling to slow entanglement growth,"The quantum dynamics of spin systems with uniform all-to-all interaction are
often studied in the totally symmetric space (TSS) of maximal total spin.
However the TSS states are atypical in the full many-body Hilbert space. In
this work, we explore several aspects of the all-to-all quantum dynamics away
from the TSS, and reveal surprising features of the ""deep Hilbert space"" (DHS).
We study the out-of-time order correlator (OTOC) in the infinite-temperature
ensemble of the full Hilbert space. We derive a phase-space representation of
the DHS OTOC and show that the OTOC can grow super-exponentially in the large
$N$ limit, due to the fast dynamics in an unbounded phase space (in finite
systems, we observe numerically that the super-exponential growth ends
precociously and gives way to a power-law one until saturation). By a similar
mechanism, the Krylov complexity grows explosively. We also study the
entanglement growth in a quantum quench from a DHS product state, i.e., one of
non-aligned spins that resemble the DHS infinite-temperature ensemble with
respect to the statistics of the collective spins. Using a field-theoretical
method, We exactly calculate the entanglement entropy in the large $N$ limit.
We show that, in the DHS, fast OTOC growth does not imply fast entanglement
growth, in contrast to the Zurek-Paz relation derived in the TSS.",2304.11138v2
2023-07-11,Adiabatic dynamics of coupled spins and phonons in magnetic insulators,"In conventional \textit{ab initio} methodologies, phonons are calculated by
solving equations of motion involving static interatomic force constants and
atomic masses. The Born-Oppenheimer approximation, where all electronic degrees
of freedom are assumed to adiabatically follow the nuclear dynamics, is also
adopted. This approach does not fully account for the effects of broken
time-reversal symmetry in systems with magnetic order. Recent attempts to
rectify this involve the inclusion of the velocity dependence of the
interatomic forces in the equations of motion, which accounts for time-reversal
symmetry breaking, and can result in chiral phonon modes with non-zero angular
momentum even at the zone center. However, since the energy ranges of phonons
and magnons typically overlap, the spins cannot be treated as adiabatically
following the lattice degrees of freedom. Instead, phonon and spins must be
treated on a similar footing. Focusing on zone-center modes, we propose a
method involving Hessian matrices and Berry curvature tensors in terms of both
phonon and spin degrees of freedom, and describe a first-principles methodology
for calculating these. We then solve Lagrange's equations of motion to
determine the energies and characters of the mixed excitations, allowing us to
quantify, for example, the energy splittings between chiral pairs of phonons in
some cases, and the degree of magnetically induced mixing between infrared and
Raman modes in others. The approach is general, and can be applied to determine
the adiabatic dynamics of any mixed set of slow variables.",2307.05668v2
2023-09-15,Geometric landscape annealing as an optimization principle underlying the coherent Ising machine,"Given the fundamental importance of combinatorial optimization across many
diverse application domains, there has been widespread interest in the
development of unconventional physical computing architectures that can deliver
better solutions with lower resource costs. These architectures embed discrete
optimization problems into the annealed, analog evolution of nonlinear
dynamical systems. However, a theoretical understanding of their performance
remains elusive, unlike the cases of simulated or quantum annealing. We develop
such understanding for the coherent Ising machine (CIM), a network of optical
parametric oscillators that can be applied to any quadratic unconstrained
binary optimization problem. Here we focus on how the CIM finds low-energy
solutions of the Sherrington-Kirkpatrick spin glass. As the laser gain is
annealed, the CIM interpolates between gradient descent on the soft-spin energy
landscape, to optimization on coupled binary spins. By exploiting spin-glass
theory, we develop a detailed understanding of the evolving geometry of the
high-dimensional CIM energy landscape as the laser gain increases, finding
several phase transitions, from flat, to rough, to rigid. Additionally, we
develop a cavity method that provides a precise geometric interpretation of
supersymmetry breaking in terms of the response of a rough landscape to
specific perturbations. We confirm our theory with numerical experiments, and
find detailed information about critical points of the landscape. Our extensive
analysis of phase transitions provides theoretically motivated optimal
annealing schedules that can reliably find near-ground states. This analysis
reveals geometric landscape annealing as a powerful optimization principle and
suggests many further avenues for exploring other optimization problems, as
well as other types of annealed dynamics, including chaotic, oscillatory or
quantum dynamics.",2309.08119v1
2023-10-27,Effect of interfacial Dzyaloshinskii-Moriya interaction in spin dynamics of an Antiferromagnet coupled Ferromagnetic double-barrier Magnetic Tunnel Junction,"In this work, we have studied the spin dynamics of a synthethic
Antiferromagnet (SAFM)$|$Heavy Metal (HM)$|$Ferromagnet (FM) double barrier
magnetic tunnel junction (MTJ) in presence of Ruderman-Kittel-Kasuya-Yoside
interaction (RKKYI), interfacial Dzyaloshinskii-Moriya interaction (iDMI),
N\'eel field and Spin-Orbit Coupling (SOC) with different Spin Transfer Torque
(STT). We employ Landau-Lifshitz-Gilbert-Slonczewski (LLGS) equation to
investigate the AFM dynamics of the proposed system. We found that the system
exhibits a transition from regular to damped oscillations with the increase in
strength of STT for systems with weaker iDMI than RKKYI while display sustained
oscillatons for system having same order of iDMI and RKKYI. On the other hand
the iDMI dominating system exhibits self-similar but aperiodic patterns in
absence of N\'eel field. In the presence of N\'eel field, the RKKYI dominating
systems exhibit chaotic oscillations for low STT but display sustained
oscillation under moderate STT. Our results suggest that the decay time of
oscillations can be controlled via SOC. The system can works as an oscillator
for low SOC but display nonlinear characteristics with the rise in SOC for
systems having weaker iDMI than RKKYI while an opposite characteristic are
noticed for iDMI dominating systems. We found periodic oscillations under low
external magnetic field in RKKYI dominating systems while moderate field are
necessary for sustained oscillation in iDMI dominating systems. Moreover, the
system exhibits saddle-node bifurcation and chaos under moderate N\'eel field
and SOC with suitable iDMI and RKKYI. In addition, our results indicate that
the magnon lifetime can be enhanced by increasing the strength of iDMI for both
optical and acoustic modes.",2310.18175v1
2023-11-16,Future Prospects for Constraining Black-Hole Spacetime: Horizon-scale Variability of Astrophysical Jet,"The Event Horizon Telescope (EHT) Collaboration has recently published the
first horizon-scale images of the supermassive black holes M87* and Sgr A* and
provided some first information on the physical conditions in their vicinity.
The comparison between the observations and the three-dimensional
general-relativistic magnetohydrodynamic (GRMHD) simulations has enabled the
EHT to set initial constraints on the properties of these black-hole
spacetimes. However, accurately distinguishing the properties of the accretion
flow from those of the spacetime, most notably, the black-hole mass and spin,
remains challenging because of the degeneracies the emitted radiation suffers
when varying the properties of the plasma and those of the spacetime. The
next-generation EHT (ngEHT) observations are expected to remove some of these
degeneracies by exploring the complex interplay between the disk-jet dynamics,
which represents one of the most promising tools for extracting information on
the black-hole spin. By using GRMHD simulations of magnetically arrested disks
(MADs) and general-relativistic radiative-transfer (GRRT) calculations of the
emitted radiation, we have studied the properties of the jet and the
accretion-disk dynamics on spatial scales that are comparable with the horizon.
In this way, we are able to highlight that the radial and azimuthal dynamics of
the jet are well correlated with the black-hole spin. Based on the resolution
and image reconstruction capabilities of the ngEHT observations of M87*, we can
assess the detectability and associated uncertainty of this correlation.
Overall, our results serve to assess what are the prospects for constraining
the black-hole spin with future EHT observations.",2311.10141v1
2023-11-29,Spin Dynamics of Planets in Resonant Chains,"About a dozen exoplanetary systems have been discovered with three or more
planets participating in a sequence of mean-motion resonances. The unique and
complex architectures of these so-called ""resonant chains"" motivate efforts to
characterize their planets holistically. In this work, we perform a
comprehensive exploration of the spin-axis dynamics of planets in resonant
chains. Planetary spin states are closely linked with atmospheric dynamics and
habitability and are thus especially relevant to resonant chains like
TRAPPIST-1, which hosts several temperate planets. Considering a set of
observed resonant chains, we calculate the equilibrium states of the planetary
axial tilts (""obliquities""). We show that high obliquity states exist for
$\sim60\%$ of planets in our sample, and many of these states can be stable in
the presence of tidal dissipation. Using case studies of two observed systems
(Kepler-223 and TOI-1136), we demonstrate how these high obliquity states could
have been attained during the initial epoch of disk-driven orbital migration
that established the resonant orbital architectures. We show that the
TRAPPIST-1 planets most likely have zero obliquities, with the possible
exception of planet d. Overall, our results highlight that both the orbital and
spin states of resonant chains are valuable relics of the early stages of
planet formation and evolution.",2311.17908v1
2023-12-06,Dynamics of spin-momentum entanglement from superradiant phase transitions,"Exploring operational regimes of many-body cavity QED with multi-level atoms
remains an exciting research frontier for their enhanced storage capabilities
of intra-level quantum correlations. In this work, we propose an extension of a
prototypical many-body cavity QED experiment from a two to a four-level
description by optically addressing a combination of momentum and spin states
of the ultracold atoms in the cavity. The resulting model comprises a pair of
Dicke Hamiltonians constructed from pseudo-spin operators, effectively
capturing two intertwined superradiant phase transitions. The phase diagram
reveals regions featuring weak and strong entangled states of spin and momentum
atomic degrees of freedom. These states exhibit different dynamical responses,
ranging from slow to fast relaxation, with the added option of persistent
entanglement temporal oscillations. We discuss the role of cavity losses in
steering the system dynamics into such entangled states and propose a readout
scheme that leverages different light polarizations within the cavity. Our work
paves the way to connect the rich variety of non-equilibrium phase transitions
that occur in many-body cavity QED to the buildup of quantum correlations in
systems with multi-level atom descriptions.",2312.03827v1
2023-12-06,"Integrability, multifractality, and two-photon dynamics in disordered Tavis-Cummings models","The Tavis-Cummings model is a paradigmatic central-mode model where a set of
two-level quantum emitters (spins) are coupled to a collective cavity mode.
Here we study the eigenstate spectrum, its localization properties and the
effect on dynamics, focusing on the two-excitation sector relevant for
nonlinear photonics. These models admit two sources of disorder: in the
coupling between the spins and the cavity and in the energy shifts of the
individual spins. While this model was known to be exactly solvable in the
limit of a homogeneous coupling and inhomogeneous energy shifts, we here
establish the solvability in the opposite limit of a homogeneous energy shift
and inhomogeneous coupling, presenting the exact solution and corresponding
conserved quantities. We identify three different classes of eigenstates,
exhibiting different degrees of multifractality and semilocalization closely
tied to the integrable points, and study their stability to perturbations away
from these solvable points. The dynamics of the cavity occupation number away
from equilibrium, exhibiting boson bunching and a two-photon blockade, is
explicitly related to the localization properties of the eigenstates and
illustrates how these models support a collective spin description despite the
presence of disorder.",2312.03833v1
2024-03-17,Merons and magnetoelectric switching in centrosymmetric spiral magnets,"Spiral multiferroics exhibit a strong coupling between magnetic and
ferroelectric orders, allowing cross-control. Since the seminal work of Kimura
et al. in 2003, these materials have attracted great interest galvanized by the
prospect of new high-efficiency memory devices, where magnetic (electric) bits
are switched via an external electric (magnetic) field. Nevertheless, the
mechanism underlying such a switching process - the electric field-driven
dynamics of domain walls (DWs) - is still poorly understood. We address this
problem for meron DWs, which represent one of the main DW types in spiral
multiferroics and consist of an array of meron (half-skyrmion) strings. Minimum
energy walls feature merons with alternating topological charges and move as
relativistic massive particles, with the limiting velocity set by magnon speed.
Low-energy defects in this alternating charge sequence, which appear during
domain nucleation, can lead to DWs with net topological charge. This induces a
peculiar non-local dynamics where all the spins in the system rotate, merons
translate within the wall, and the DW mobility is suppressed. The topological
charge of the wall and the meron helicity can be easily modified via an
external magnetic and electric field, respectively, offering fine control over
DW dynamics. Defects within the meron strings, analogous to Bloch points, have
hedgehog-like spin texture and are strongly pinned to the lattice. The
fascinating interplay between domain wall motion, translation of merons within
the wall, and precession of spins in the entire domains opens a new playground
for the electric manipulation of topological spin textures.",2403.11195v1
2016-12-05,Spatial Mixing and Systematic Scan Markov chains,"We consider spin systems on the integer lattice graph $\mathbb{Z}^d$ with
nearest-neighbor interactions. We develop a combinatorial framework for
establishing that exponential decay with distance of spin correlations,
specifically the strong spatial mixing condition (SSM), implies rapid mixing of
a large class of Markov chains. As a first application of our method we prove
that SSM implies $O(\log n)$ mixing of systematic scan dynamics (under mild
conditions) on an $n$-vertex $d$-dimensional cube of the integer lattice graph
$\mathbb{Z}^d$. Systematic scan dynamics are widely employed in practice but
have proved hard to analyze. A second application of our technology concerns
the Swendsen-Wang dynamics for the ferromagnetic Ising and Potts models. We
show that SSM implies an $O(1)$ bound for the relaxation time (i.e., the
inverse spectral gap). As a by-product of this implication we observe that the
relaxation time of the Swendsen-Wang dynamics in square boxes of $\mathbb{Z}^2$
is $O(1)$ throughout the subcritical regime of the $q$-state Potts model, for
all $q \ge 2$. We also use our combinatorial framework to give a simple
coupling proof of the classical result that SSM entails optimal mixing time of
the Glauber dynamics. Although our results in the paper focus on
$d$-dimensional cubes in $\mathbb{Z}^d$, they generalize straightforwardly to
arbitrary regions of $\mathbb{Z}^d$ and to graphs with subexponential growth.",1612.01576v3
2005-07-28,Motion of the Tippe Top : Gyroscopic Balance Condition and Stability,"We reexamine a very classical problem, the spinning behavior of the tippe top
on a horizontal table. The analysis is made for an eccentric sphere version of
the tippe top, assuming a modified Coulomb law for the sliding friction, which
is a continuous function of the slip velocity $\vec v_P$ at the point of
contact and vanishes at $\vec v_P=0$. We study the relevance of the gyroscopic
balance condition (GBC), which was discovered to hold for a rapidly spinning
hard-boiled egg by Moffatt and Shimomura, to the inversion phenomenon of the
tippe top. We introduce a variable $\xi$ so that $\xi=0$ corresponds to the GBC
and analyze the behavior of $\xi$. Contrary to the case of the spinning egg,
the GBC for the tippe top is not fulfilled initially. But we find from
simulation that for those tippe tops which will turn over, the GBC will soon be
satisfied approximately. It is shown that the GBC and the geometry lead to the
classification of tippe tops into three groups: The tippe tops of Group I never
flip over however large a spin they are given. Those of Group II show a
complete inversion and the tippe tops of Group III tend to turn over up to a
certain inclination angle $\theta_f$ such that $\theta_f<\pi$, when they are
spun sufficiently rapidly. There exist three steady states for the spinning
motion of the tippe top. Giving a new criterion for stability, we examine the
stability of these states in terms of the initial spin velocity $n_0$. And we
obtain a critical value $n_c$ of the initial spin which is required for the
tippe top of Group II to flip over up to the completely inverted position.",0507198v1
2014-10-28,Spin dynamics and disorder effects in the S=1/2 kagome Heisenberg spin liquid phase of kapellasite,"We report $^{35}$Cl NMR, ESR, $\mu$SR and specific heat measurements on the
$S=1/2$ frustrated kagom\'e magnet kapellasite,
$\alpha-$Cu$_3$Zn(OH)$_6$Cl$_2$, where a gapless spin liquid phase is
stabilized by a set of competing exchange interactions. Our measurements
confirm the ferromagnetic character of the nearest-neighbour exchange
interaction $J_1$ and give an energy scale for the competing interactions $|J|
\sim 10$ K. The study of the temperature-dependent ESR lineshift reveals a
moderate symmetric exchange anisotropy term $D$, with $|D/J|\sim 3$%. These
findings validate a posteriori the use of the $J_1 - J_2 - J_d$ Heisenberg
model to describe the magnetic properties of kapellasite [Bernu et al., Phys.
Rev. B 87, 155107 (2013)]. We further confirm that the main deviation from this
model is the severe random depletion of the magnetic kagom\'e lattice by 27%,
due to Cu/Zn site mixing, and specifically address the effect of this disorder
by $^{35}$Cl NMR, performed on an oriented polycrystalline sample.
Surprisingly, while being very sensitive to local structural deformations, our
NMR measurements demonstrate that the system remains homogeneous with a unique
spin susceptibility at high temperature, despite a variety of magnetic
environments. Unconventional spin dynamics is further revealed by NMR and
$\mu$SR in the low-$T$, correlated, spin liquid regime, where a broad
distribution of spin-lattice relaxation times is observed. We ascribe this to
the presence of local low-energy modes.",1410.7688v1
2015-02-03,Static and Dynamic Properties of Interacting Spin-1 Bosons in an Optical Lattice,"We study the physics of interacting spin-$1$ bosons in an optical lattice
using a variational Gutzwiller technique. We compute the mean-field ground
state wave-function and discuss the evolution of the condensate, spin, nematic,
and singlet order parameters across the superfluid-Mott transition. We then
extend the Gutzwiller method to derive the equations governing the dynamics of
low energy excitations in the lattice. Linearizing these equations, we compute
the excitation spectra in the superfluid and Mott phases for both ferromagnetic
and antiferromagnetic spin-spin interactions. In the superfluid phase, we
recover the known excitation spectrum obtained from Bogoliubov theory. In the
nematic Mott phase, we obtain gapped, quadratically dispersing particle and
hole-like collective modes, whereas in the singlet Mott phase, we obtain a
non-dispersive gapped mode, corresponding to the breaking of a singlet pair.
For the ferromagnetic Mott insulator, the Gutzwiller mean-field theory only
yields particle-hole like modes but no Goldstone mode associated with long
range spin order. To overcome this limitation, we supplement the Gutzwiller
theory with a Schwinger boson mean-field theory which captures super-exchange
driven fluctuations. In addition to the gapped particle-hole-like modes, we
obtain a gapless quadratically dispersing ferromagnetic spin-wave Goldstone
mode. We discuss the evolution of the singlet gap, particle-hole gap, and the
effective mass of the ferromagnetic Goldstone mode as the superfluid-Mott phase
boundary is approached from the insulating side. We discuss the relevance and
validity of Gutzwiller mean-field theories to spinful systems, and potential
extensions of this framework to include more exotic physics which appears in
the presence of spin-orbit coupling or artificial gauge fields.",1502.01041v1
2018-04-20,Theory of Ultrafast Spin--Charge Quantum Dynamics in Strongly Correlated Systems Controlled by Femtosecond Photoexcitation: an Application to Insulating Antiferromagnetic Manganites,"We use a non-equilibrium many-body theory that engages the elements of
transient coherence, correlation, and nonlinearity to describe changes in the
magnetic and electronic phases of strongly correlated systems induced by
femtosecond nonlinear photoexcitation. Using a generalized tight--binding mean
field approach based on Hubbard operators and including the coupling of the
laser field, we describe a mechanism for simultaneous insulator--to--metal and
anti-- to ferro--magnetic transition to a transient state triggered by
non-thermal ultrafast spin and charge coupled excitations. We demontrate, in
particular, that photoexcitation of composite fermion quasiparticles induces
quasi-instantaneous spin canting that quenches the energy gap of the
antiferromagnetic insulator and acts as a nonadiabatic ""initial condition"" that
triggers non-thermal lattice dynamics leading to an insulator to metal and
antiferromagnetic (AFM) to ferromagnetic (FM) transitions. Our theoretical
predictions are consistent with recent ultrafast pump-probe spectroscopy
experiments that revealed a magnetic phase transition during 100fs laser pulse
photoexcitation of the CE--type AFM insulating phase of colossal
magnetoresistive manganites. In particular, experiment observes two distinct
charge relaxation components, fs and ps, with nonlinear threshold dependence at
a pump fluence threshold that coincides with that for femtosecond magnetization
photo excitation. Our theory attributes the correlation between femtosecond
spin and charge nonlinearity leading to transition in the magnetic and
electronic state to spin/charge/lattice coupling and laser-induced quantum spin
canting that accompanies the driven population inversion between two
quasi--particle bands with different properties: a mostly occupied polaronic
band and a mostly empty metallic band, whose dispersion is determined by
quantum spin canting.",1804.07811v1
2019-05-01,Black Hole and Neutron Star Binary Mergers in Triple Systems: II. Merger Eccentricity and Spin-Orbit Misalignment,"We study the dynamical signatures of black hole (BH) and neutron star (NS)
binary mergers via Lidov-Kozai oscillations induced by tertiary companions in
hierarchical triple systems. For each type of binaries (BH-BH and BH-NS), we
explore a wide range of binary/triple parameters that lead to binary mergers,
and determine the distributions of eccentricity ($e_\mathrm{m}$) and spin-orbit
misalignment angle ($\theta_\rm {sl}^\rm f$) when the binary enters the
LIGO/VIRGO band. We use the double-averaged (over both orbits) and
single-averaged (over the inner orbit) secular equations, as well as N-body
integration, to evolve systems with different hierarchy levels, including the
leading-order post-Newtonian effect, spin-orbit coupling and gravitational
radiation. We find that for merging BH-BH binaries with comparable masses,
about $7\%$ have $e_\mathrm{m}>0.1$ and $0.7\%$ have $e_{\rm m}>0.9$. The
majority of the mergers have significant eccentricities in the LISA band. The
BH spin evolution and $\theta_\rm {sl}^\rm f$ are correlated with the orbital
evolution and $e_{\rm m}$. Mergers with $e_{\rm m} \lesssim 10^{-3}$ have a
distribution of $\theta_\rm {sl}^\rm f$ that peaks around $90^\circ$ (and thus
favoring a projected binary spin parameter $\chi_{\rm eff}\sim 0$), while
mergers with larger $e_{\rm m}$ have a more isotropic spin-orbit misalignments.
For typical BH-NS binaries, strong octuple effects lead to more mergers with
non-negligible $e_\mathrm{m}$ (with $\sim 18\%$ having $e_\mathrm{m}>0.1$ and
$2.5\%$ having $e_\mathrm{m}>0.9$), and the final BH spin axis tends to be
randomly orientated. Measurements or constraints on eccentric mergers and
$\theta_\rm {sl}^\rm f$ from LIGO/VIRGO and LISA would provide useful
diagnostics on the dynamical formation of merging BH or NS binaries in triples.",1905.00427v2
2018-07-15,LiZn$_{2}$V$_{3}$O$_{8}$: A new geometrically frustrated cluster spin-glass,"We have investigated the structural and magnetic properties of a new cubic
spinel LiZn$_{2}$V$_{3}$O$_{8}$ (LZVO) through x-ray diffraction, dc and ac
susceptibility, magnetic relaxation, aging, memory effect, heat capacity and
$^{7}$Li nuclear magnetic resonance (NMR) measurements. A Curie-Weiss fit of
the dc susceptibility $\chi_{\mathrm{dc}}$($\mathit{T}$) yields a Curie-Weiss
temperature $\mathrm{\theta}_{\mathrm{CW}}$ = -185 K. This suggests strong
antiferromagnetic (AFM) interactions among the magnetic vanadium ions. The dc
and ac susceptibility data indicate the spin-glass behavior below a freezing
temperature $T_{f}$ $\simeq$ 3 K. The frequency dependence of the $T_{f}$ is
characterized by the Vogel-Fulcher law and critical dynamic scaling behavior or
power law. From both fitting, we obtained the value of the characteristic
angular frequency $\omega_{0}$ $\approx$ 3.56$\times$10$^{6}$ Hz, the dynamic
exponent $\mathit{zv}$ $\approx$ 2.65, and the critical time constant
$\tau_{0}$ $\approx$ 1.82$\times$10$^{-6}$ s, which falls in the conventional
range for typical cluster spin-glass (CSG) systems. The value of relative shift
in freezing temperature $\delta T_{f}$ $\simeq$ 0.039 supports a CSG ground
states. We also found aging phenomena and memory effects in LZVO. The
asymmetric response of the magnetic relaxation below $T_{f}$ supports the
hierarchical model. Heat capacity data show no long-range or short-range
ordering down to 2 K. Only about 25% magnetic entropy change $(\Delta
S_{\mathrm{m}})$ signifies the presence of strong frustration in the system.
The $^{7}$Li NMR spectra show a shift and broadening with decreasing
temperature. The spin-lattice and spin-spin relaxation rates show anomalies due
to spin freezing around 3 K as the bulk magnetization.",1807.05612v3
2021-04-15,Quantum many-body states and Green functions of nonequilibrium electron-magnon systems: Localized spin operators vs. their mapping to Holstein-Primakoff bosons,"The operators of localized spins within a magnetic material commute at
different sites of its lattice and anticommute on the same site, so they are
neither fermionic nor bosonic operators. Thus, to construct diagrammatic
many-body perturbation theory, the spin operators are usually mapped to the
bosonic ones with Holstein-Primakoff (HP) transformation being the most widely
used in magnonics and spintronics literature. However, to make calculations
tractable, the square root of operators in the HP transformation is expanded
into a Taylor series truncated to some low order. This poses a question on the
range of validity of truncated HP transformation when describing nonequilibrium
dynamics of localized spins interacting with each other or with conduction
electron spins. Here we apply exact diagonalization techniques to Hamiltonian
of fermions (i.e., electrons) interacting with HP bosons vs. Hamiltonian of
fermions interacting with the original localized spin operators in order to
compare their many-body states and one-particle equilibrium or nonequilibrium
Green functions. The Hamiltonian of fermions interacting with HP bosons gives
incorrect ground state and electronic spectral function, unless large number of
terms are retained in truncated HP transformation. Furthermore, tracking
nonequilibrium dynamics of localized spins over longer time intervals requires
progressively larger number of terms in truncated HP transformation. Finally,
we show that recently proposed [M. Vogl et al., Phys. Rev. Research 2, 043243
(2020); J. K\""{o}nig et al., SciPost Phys. 10, 007 (2021)] resummed HP
transformation resolves the trouble with truncated HP transformation, while
allowing us to derive an exact (manifestly Hermitian) Hamiltonian consisting of
finite and fixed number of boson-boson and electron-boson interacting terms.",2104.07657v2
2022-03-08,"$^{139}$La NMR investigation of the interplay between the lattice, charge, and spin dynamics in charge ordered high $T_c$ cuprate La$_{1.875}$Ba$_{0.125}$CuO$_{4}$","We investigate the interplay between the lattice, charge, and spin dynamics
in charge ordered high $T_c$ cuprate La$_{1.875}$Ba$_{0.125}$CuO$_{4}$ ($T_{c}
=4$~K) based on the inverse Laplace transform (ILT) analysis of the $^{139}$La
nuclear spin-lattice relaxation rate $1/T_1$ (dubbed ILTT$_{1}$ analysis here
after). A major thrust of the ILTT$_{1}$ analysis is that one can deduce the
probability density function $P(1/T_1)$ of distributed $1/T_1$. We demonstrate
that $1/T_{1}^{lm}$, defined as the log-mean (i.e. the center of gravity on a
logarithmic scale) of $P(1/T_1)$, can be well approximated by $1/T_{1}^{str}$
deduced from the phenomenological stretched fit, however, $P(1/T_1)$ can
provide much richer insight into how the lattice, charge, and spin fluctuations
and their distribution develop near and below the long range charge order at
$T_{charge} \sim 54$~K. Upon entering the charge ordered state, a divergent
increase of $1/T_{1}^{lm}$ toward the spin ordering at $T_{spin}^{\mu SR}
\simeq 35$~K is accompanied by an asymmetric broadening of $P(1/T_1)$. Even
deep inside the charge ordered state, $1/T_{1}$ at a gradually diminishing
fraction of $^{139}$La sites continues to slow down as temperature is lowered,
as expected for canonical superconducting CuO$_2$ planes without enhanced spin
fluctuations. The fraction of such canonical $^{139}$La sites almost disappears
by $\simeq 40$~K. In contrast, nearly a half of the $^{139}$La sites in
La$_{1.885}$Sr$_{0.115}$CuO$_{4}$ ($T_{charge} \simeq 80$~K) still exhibits the
canonical behavior without enhanced spin fluctuations even near its $T_{c} =
31$~K. These contrasting behaviors explain why superconductivity in
La$_{1.875}$Ba$_{0.125}$CuO$_{4}$ is more strongly suppressed than in
La$_{1.885}$Sr$_{0.115}$CuO$_{4}$ despite the lower onset temperature of the
charge order.",2203.04265v1
2022-09-27,Quantum and classical correlations in open quantum-spin lattices via truncated-cumulant trajectories,"The study of quantum many-body physics in Liouvillian open quantum systems
becomes increasingly important with the recent progress in experimental control
on dissipative systems and their technological exploitation . A central
question in open quantum systems concerns the fate of quantum correlations, and
the possibility of controlling them by engineering the competition between the
Hamiltonian dynamics and the coupling to a bath. Such a question is challenging
from a theoretical point of view, as numerical methods faithfully accounting
for quantum correlations are either relying on exact diagonalization, limiting
drastically the sizes that can be treated; or on approximations on the range or
strength of quantum correlations, associated to the choice of a specific Ansatz
for the density matrix. In this work we propose a new method to treat open
quantum-spin lattices, based on stochastic quantum trajectories for the
solution of the open-system dynamics. Along each trajectory, the hierarchy of
equations of motion for many-point spin-spin correlators is truncated to a
given finite order, assuming that multivariate $k$-th order cumulants vanish
for $k$ exceeding a cutoff $k_c$. This allows tracking the evolution of quantum
spin-spin correlations up to order $k_c$ for all length scales. We validate
this approach in the paradigmatic case of the phase transitions of the
dissipative 2D XYZ lattice, subject to spontaneous decay. We convincingly
assess the existence of steady-state phase transitions from paramagnetic to
ferromagnetic, and back to paramagnetic, upon increasing one of the Hamiltonian
couplings; as well as their classical Ising nature. Moreover, the approach
allows us to show the presence of significant quantum correlations in the
vicinity of the dissipative critical point, and to unveil the presence of spin
squeezing, a tight lower bound to the quantum Fisher information.",2209.13377v4
2022-10-17,Non-equilibrium Ising Model on a 2D Additive Small-World Network,"In this work, we have studied the Ising model with one- and two-spin flip
competing dynamics on a two-dimensional additive small-world network (A-SWN).
The system model consists of a $L\times L$ square lattice where each site of
the lattice is occupied by a spin variable that interacts with the nearest
neighbor spins and it has a certain probability $p$ of being additionally
connected at random to one of its farther neighbors. The dynamics present in
the system can be defined by the probability $q$ of being in contact with a
heat bath at a given temperature $T$ and, at the same time, with a probability
of $1-q$ the system is subjected to an external flux of energy into the system.
The contact with the heat bath is simulated by one-spin flip according to the
Metropolis prescription, while the input of energy is mimicked by the two-spin
flip process, involving a simultaneous flipping of a pair of neighboring spins.
We have employed Monte Carlo simulations to obtain the thermodynamic quantities
of the system, such as, the total $\textrm{m}_{\textrm{L}}^{\textrm{F}}$ and
staggered $\textrm{m}_{\textrm{L}}^{\textrm{AF}}$ magnetizations per spin, the
susceptibility $\chi_{\textrm{L}}$, and the reduced fourth-order Binder
cumulant $\textrm{U}_{\textrm{L}}$. We have built the phase diagram for the
stationary states of the model in the plane $T$ versus $q$, showing the
existence of two continuous transition lines for each value of $p$: one line
between the ferromagnetic $F$ and paramagnetic $P$ phases, and the other line
between the $P$ and antiferromagnetic $AF$ phases. Therefore, we have shown
that the phase diagram topology changes when $p$ increases. Using the
finite-size scaling analysis, we also obtained the critical exponents for the
system, where varying the parameter $p$, we have observed a different
universality class from the Ising model in the regular square lattice to the
A-SWN.",2210.09174v1
2023-03-01,Rotor/spin-wave theory for quantum spin models with U(1) symmetry,"The static and dynamics properties of finite-size lattice quantum spin models
which spontaneously break a continuous $U(1)$ symmetry in the thermodynamic
limit are of central importance for a wide variety of physical systems, from
condensed matter to quantum simulation. Such systems are characterized by a
Goldstone excitation branch, terminating in a zero mode whose theoretical
treatment within a linearized approach leads to divergencies on finite-size
systems, revealing that the assumption of symmetry breaking is ill-defined away
from the thermodynamic limit. In this work we show that, once all its
non-linearities are taken into account, the zero mode corresponds exactly to a
U(1) quantum rotor, related to the Anderson tower of states expected in systems
showing symmetry breaking in the thermodynamic limit. The finite-momentum
modes, when weakly populated, can be instead safely linearized (namely treated
within spin-wave theory) and effectively decoupled from the zero mode. This
picture leads to an approximate separation of variables between rotor and
spin-wave ones, which allows for a correct description of the ground-state and
low-energy physics. Most importantly, it offers a quantitative treatment of the
finite-size non-equilibrium dynamics -- following a quantum quench -- dominated
by the zero mode, for which a linearized approach fails. Focusing on the 2$d$
XX model with power-law decaying interactions, we compare our equilibrium
predictions with unbiased quantum Monte Carlo results and exact
diagonalization; and our non-equilibrium results with time-dependent
variational Monte Carlo. The agreement is remarkable for all interaction
ranges, and it improves the longer the range. Our rotor/spin-wave theory
defines a successful strategy for the application of spin-wave theory and its
extensions to finite-size systems at equilibrium or away from it.",2303.00380v2
2023-10-31,Coherent manipulation of nuclear spins in the strong driving regime,"Spin-based quantum information processing makes extensive use of spin-state
manipulation. This ranges from dynamical decoupling of nuclear spins in quantum
sensing experiments to applying logical gates on qubits in a quantum processor.
Here we present an antenna for strong driving in quantum sensing experiments
and theoretically address challenges of the strong driving regime. First, we
designed and implemented a micron-scale planar spiral RF antenna capable of
delivering intense fields to a sample. The planar antenna is tailored for
quantum sensing experiments using the diamond's nitrogen-vacancy (NV) center
and should be applicable to other solid-state defects. The antenna has a broad
bandwidth of 22 MHz, is compatible with scanning probes, and is suitable for
cryogenic and ultrahigh vacuum conditions. We measure the magnetic field
induced by the antenna and estimate a field-to-current ratio of $113\pm 16$
G/A, representing a x6 increase in efficiency compared to the state-of-the-art.
We demonstrate the antenna by driving Rabi oscillations in $^1$H spins of an
organic sample on the diamond surface and measure $^1$H Rabi frequencies of
over 500 kHz, i.e., $\mathrm{\pi}$-pulses shorter than 1 $\mu s$ - faster than
previously reported in NV-based nuclear magnetic resonance (NMR). Finally, we
discuss the implications of driving spins with a field tilted from the
transverse plane in a regime where the driving amplitude is comparable to the
spin-state splitting, such that the rotating wave approximation does not
describe the dynamics well. We present a recipe to optimize pulse fidelity in
this regime based on a phase and offset-shifted sine drive, that may be
optimized without numerical optimization procedures or precise modeling of the
experiment. We consider this approach in a range of driving amplitudes and show
that it is particularly efficient in the case of a tilted driving field.",2310.20667v1
2004-03-15,The relative influences of disorder and of frustration on the glassy dynamics in magnetic systems,"The magnetisation relaxations of three different types of geometrically
frustrated magnetic systems have been studied with the same experimental
procedures as previously used in spin glasses. The materials investigated are
Y$_2$Mo$_2$O$_7$ (pyrochlore system), SrCr$_{8.6}$Ga$_{3.4}$O$_{19}$ (piled
pairs of Kagom\'e layers) and (H$_3$O)Fe$_3$(SO$_4$)$_2$(OH)$_6$ (jarosite
compound). Despite a very small amount of disorder, all the samples exhibit
many characteristic features of spin glass dynamics below a freezing
temperature $T_g$, much smaller than their Curie-Weiss temperature $\theta$.
The ageing properties of their thermoremanent magnetization can be well
accounted for by the same scaling law as in spin glasses, and the values of the
scaling exponents are very close. The effects of temperature variations during
ageing have been specifically investigated. In the pyrochlore and the
bi-Kagom\'e compounds, a decrease of temperature after some waiting period at a
certain temperature $T_p$ re-initializes ageing and the evolution at the new
temperature is the same as if the system were just quenched from above $T_g$.
However, as the temperature is raised back to $T_p$, the sample recovers the
state it had previously reached at that temperature. These features are known
in spin glasses as rejuvenation and memory effects. They are clear signatures
of the spin glass dynamics. In the Kagom\'e compound, there is also some
rejuvenation and memory, but much larger temperature changes are needed to
observe the effects. In that sense, the behaviour of this compound is
quantitatively different from that of spin glasses.",0403356v1
2015-04-06,Vortex Dynamics in a Spin-Orbit Coupled Bose-Einstein Condensate,"Vortices in a one-component dilute atomic ultracold Bose-Einstein condensate
(BEC) usually arise as a response to externally driven rotation. Apart from a
few special situations, these vortices are singly quantized with unit
circulation. Recently, the NIST group has constructed a two-component BEC with
a spin-orbit coupled Hamiltonian involving Pauli matrices, and I here study the
dynamics of a two-component vortex in such a spin-orbit coupled condensate.
These spin-orbit coupled BECs use an applied magnetic field to split the
hyperfine levels. Hence they rely on a focused laser beam to trap the atoms. In
addition, two Raman laser beams create an effective (or synthetic) gauge
potential. The resulting spin-orbit Hamiltonian is discussed in some detail.
The various laser beams are fixed in the laboratory, so that it is not feasible
to nucleate a vortex by an applied rotation that would need to rotate all the
laser beams and the magnetic field. In a one-component BEC, a vortex can also
be created by a thermal quench, starting from the normal state and suddenly
cooling deep into the condensed state. I propose that a similar method would
work for a vortex in a spin-orbit coupled BEC. Such a vortex has two
components, and each has its own circulation quantum number. If both components
have the same circulation, I find that the composite vortex should execute
uniform precession, like that observed in a single-component BEC. In contrast,
if one component has unit circulation and the other has zero circulation, then
some fraction of the dynamical vortex trajectories should eventually leave the
condensate, providing clear experimental evidence for this unusual vortex
structure. In the context of exciton-polariton condensates, such a vortex is
known as a ""half-quantum vortex"".",1504.01314v1
2021-01-04,Spin-glass dynamics in the presence of a magnetic field: exploration of microscopic properties,"The synergy between experiment, theory, and simulations enables a microscopic
analysis of spin-glass dynamics in a magnetic field in the vicinity of and
below the spin-glass transition temperature $T_\mathrm{g}$. The spin-glass
correlation length, $\xi(t,t_\mathrm{w};T)$, is analysed both in experiments
and in simulations in terms of the waiting time $t_\mathrm{w}$ after the spin
glass has been cooled down to a stabilised measuring temperature
$T<T_\mathrm{g}$ and of the time $t$ after the magnetic field is changed. This
correlation length is extracted experimentally for a CuMn 6 at. % single
crystal, as well as for simulations on the Janus II special-purpose
supercomputer, the latter with time and length scales comparable to experiment.
The non-linear magnetic susceptibility is reported from experiment and
simulations, using $\xi(t,t_\mathrm{w};T)$ as the scaling variable. Previous
experiments are reanalysed, and disagreements about the nature of the Zeeman
energy are resolved. The growth of the spin-glass magnetisation in zero-field
magnetisation experiments, $M_\mathrm{ZFC}(t,t_\mathrm{w};T)$, is measured from
simulations, verifying the scaling relationships in the dynamical or
non-equilibrium regime. Our preliminary search for the de Almeida-Thouless line
in $D=3$ is discussed.",2101.00821v3
2019-03-04,Effective theories for quantum spin clusters: Geometric phases and state selection by singularity,"Magnetic systems with frustration often have large classical degeneracy. We
show that their low-energy physics can be understood as dynamics within the
space of classical ground states. We demonstrate this mapping in a family of
quantum spin clusters where every pair of spins is connected by an $XY$
antiferromagnetic bond. The dimer with two spin-$S$ spins provides the simplest
example, it maps to a quantum particle on a ring ($S^1$). The trimer is more
complex, equivalent to a particle that lives on two disjoint rings ($S^1\otimes
\mathbb{Z}_2$). It has an additional subtlety for half-integer $S$ values,
wherein both rings must be threaded by $\pi$-fluxes to obtain a satisfactory
mapping. This is a consequence of the geometric phase incurred by spins. For
both the dimer and the trimer, the effective theory can be seen from a
path-integral-based derivation. This approach cannot be extended to the
quadrumer which has a non-manifold ground state space, consisting of three tori
that touch pairwise along lines. In order to understand the dynamics of a
particle in this space, we develop a tight-binding model with this
connectivity. Remarkably, this successfully reproduces the low-energy spectrum
of the quadrumer. For half-integer spins, a geometric phase emerges which can
be mapped to two $\pi$-flux tubes that reside in the space between the tori.
The non-manifold character of the space leads to a remarkable effect - the
dynamics at low energies is not ergodic as the particle is localized around
singular lines of the ground state space. The low-energy spectrum consists of
an extensive number of bound states formed around singularities. Physically,
this manifests as an order-by-disorder-like preference for collinear ground
states. However, unlike order-by-disorder, this `order by singularity' persists
even in the classical limit. We discuss consequences for field theoretic
studies of magnets.",1903.01499v2
2021-03-28,Magnetic field-induced softening of spin waves and hard-axis order in Kondo-lattice ferromagnet CeAgSb$_{2}$,"A significant number of Kondo-lattice ferromagnets order perpendicular to the
easy magnetization axis dictated by the crystalline electric field. The nature
of this phenomenon has attracted considerable attention, but remains poorly
understood. In the present paper we use inelastic neutron scattering supported
by magnetization and specific heat measurements to study the spin dynamics in
the hard-axis ferromagnet CeAgSb2. In the zero field state we observed two
sharp magnon modes, which are associated with Ce ordering and extended up to
$\approx 3 meV with a considerable spin gap of 0.6 meV. Application of a
magnetic field perpendicular to the moment direction reduces the spectral
intensity and suppresses the gap and significantly enhances the low-temperature
specific heat at a critical field of Bc ~ 2.8 T via a mean-field-like
transition. Above the transition, in the field polarized state, the gap
eventually reopens due to the Zeeman effect. We modeled the observed dispersion
using linear spin-wave theory (LSWT) taking into account the ground state Gamma
6 doublet and exchange anisotropy. Our model correctly captures the essential
features of the spin dynamics including magnetic dispersion, distribution of
the spectral intensity as well as the field-induced behavior, although several
minor features remain obscure. The observed spectra do not show significant
broadening due to the finite lifetime of the quasiparticles. Along with a
moderate electronic specific heat coefficient gamma = 46 mJ/mol K2 this
indicates that the Kondo coupling is relatively weak and the Ce moments are
well localized. Altogether, our results provide profound insight into the spin
dynamics of the hard-axis ferromagnet CeAgSb2 and can be used as solid ground
for studying magnetic interactions in isostructural compounds including
CeAuSb2, which exhibits nematicity and unusual mesoscale magnetic textures.",2103.15137v2
1995-05-09,SPIN-ORBIT INTERACTION IN NEUTRON STAR/MAIN SEQUENCE BINARIES AND IMPLICATIONS FOR PULSAR TIMING,"The spin-induced quadrupole moment of a rapidly rotating star changes the
orbital dynamics in a binary system, giving rise to advance (or regression) of
periastron and precession of the orbital plane. We show that these effects are
important in the recently discovered radio pulsar/main sequence star binary
system PSR J0045$-$7319, and can reliably account for the observed peculiar
timing residuals. Precise measurements of the apsidal motion and orbital plane
precession can yield valuable information on the internal structure and
rotation of the star. The detection of orbital precession implies that the spin
of the companion star is not aligned with the orbital angular momentum, and
suggests that the supernova gave the pulsar a kick out of the original orbital
plane. Tidal excitation of g-mode oscillations in the PSR J0045$-$7319 system
induces an orbital period change of order $|\Delta P_{\rm orb}/P_{\rm orb}|\sim
10^{-6}$ at each periastron passage, but the secular trend depends on the
radiative damping time of the g-modes. We also discuss the spin-orbit coupling
effects for the accreting X-ray pulsars and the other known radio pulsar/main
sequence binary, PSR B1259$-$63.",9505042v1
2005-08-14,Estimating the Spin of Stellar-Mass Black Holes via Spectral Fitting of the X-ray Continuum,"We fit X-ray spectral data in the thermal dominant or high soft state of two
dynamically confirmed black holes, GRO J1655-40 and 4U 1543-47, and estimate
the dimensionless spin parameters a* = a/M of the two holes. For GRO J1655-40,
using a spectral hardening factor computed for a non-LTE relativistic accretion
disk, we estimate a* ~ 0.75 and ~ 0.65-0.75, respectively, from ASCA and RXTE
data. For 4U 1543-47, we estimate a* ~ 0.75-0.85 from RXTE data. Thus, neither
black hole has a spin approaching the theoretical maximum a* = 1.",0508302v2
2006-10-03,The effect of Semi-Collisional Accretion on Planetary Spins,"Planetesimal accretion during planet formation is usually treated as
collisionless. Such accretion from a uniform and dynamically cold disk predicts
protoplanets with slow retrograde rotation. However, if the building blocks of
protoplanets, planetesimals, are small, of order of a meter in size, then they
are likely to collide within the protoplanet's sphere of gravitational
influence, creating a prograde accretion disk around the protoplanet. The
accretion of such a disk results in the formation of protoplanets spinning in
the prograde sense with the maximal spin rate allowed before centrifugal forces
break them apart. As a result of semi-collisional accretion, the final spin of
a planet after giant impacts is not completely random but is biased toward
prograde rotation. The eventual accretion of the remaining planetesimals in the
post giant-impact phase might again be in the semi-collisional regime and
delivers a significant amount of additional prograde angular momentum to the
terrestrial planets. We suggest that in our Solar System, semi-collisional
accretion gave rise to the preference for prograde rotation observed in the
terrestrial planets and perhaps the largest asteroids.",0610093v1
1995-04-04,Ground state properties and dynamics of the bilayer t-J model,"We present an exact diagonalization study of bilayer clusters of t-J model.
Our results indicate a crossover between two markedly different regimes which
occurs when the ratio J_perp/J between inter-layer and intra-layer exchange
constants increases: for small J_perp/J the data suggest the development of 3D
antiferromagnetic correlations without appreciable degradation of the
intra-layer spin order and the d_(x2-y2) hole pairs within the planes persist.
For larger values of J_perp/J local singlets along the inter-layer bonds
dominate, leading to an almost complete suppression of the intra-layer spin
correlation and the breaking of the intra-layer pairs. The ground state with
two holes in this regime has s-like symmetry. The data suggest that the
crossover may occur for values of J_perp/J as small as 0.2. We present data for
static spin correlations, spin gap, and electron momentum distribution and
spectral function of the `inter-layer RVB state' realized for large J_perp/J.
The latter deviates from the single layer ground state, making it an
implausible candidate for modelling high-temperature superconductors.",9504013v1
1995-08-14,Antiferromagnetic spin ladders: crossover between spin S = 1/2 and S = 1 chains,"We study a model of two weakly coupled isotropic spin-1/2 Heisenberg chains
with an antiferromagnetic coupling along the chains. It is shown that the
system always has a spectral gap. For the case of identical chains the model in
the continuous limit is equivalent to 4 decoupled noncritical Ising models. For
this case we obtain the exact expressions for the asymptotics of spin-spin
correlation functions. When the chains have different exchange integrals the
spectrum at low energies is well described by the O(3) nonlinear sigma model.
We discuss the topological order parameter related to the gap formation and
give a detailed description of the dynamical magnetic susceptibility.",9508047v2
1996-05-22,High-Frequency Spin Waves in YBa2Cu3O6.15,"Pulsed neutron spectroscopy is used to make absolute measurements of the
dynamic magnetic susceptibility of insulating YBa2Cu3O6.15. Acoustic and
optical modes, derived from in- and out-of-phase oscillation of spins in
adjacent CuO2 planes, dominate the spectra and are observed up to 250 meV. The
optical modes appear first at 74 meV. Linear-spin-wave theory gives an
excellent description of the data and yields intra- and inter-layer exchange
constants of J_parallel =125 meV and J_perp = 11 meV respectively and a
spin-wave intensity renormalization Z_chi = 0.4.",9605139v2
1996-06-30,Stable Spin Precession at one Half of Equilibrium Magnetization in Superfluid 3He-B,"New stable modes of spin precession have been observed in superfluid 3He-B.
These dynamical order parameter states include precession with a magnetization
S=pS_{eq} which is different from the equilibrium value S_{eq}. We have
identified modes with p=1, 1/2 and \approx 0. The p=1/2 mode is the second
member of phase correlated states of a spin superfluid. The new states can be
excited in the temperature range 1-T/T_c \lesssim 0.02 where the energy
barriers between the different local minima of the spin-orbit energy are small.
They are stable in CW NMR due to low dissipation close to T_c.",9606221v1
1996-07-12,Phase transitions and critical behaviour in one-dimensional non-equilibrium kinetic Ising models with branching annihilating random walk of kinks,"One-dimensional non-equilibrium kinetic Ising models evolving under the
competing effect of spin flips at zero temperature and nearest-neighbour spin
exchanges exhibiting directed percolation-like parity conserving(PC) phase
transition on the level of kinks are now further investigated, numerically,
from the point of view of the underlying spin system. Critical exponents
characterising its statics and dynamics are reported. It is found that the
influence of the PC transition on the critical exponents of the spins is strong
and the origin of drastic changes as compared to the Glauber-Ising case can be
traced back to the hyperscaling law stemming from directed percolation(DP).
Effect of an external magnetic field, leading to DP-type critical behaviour on
the level of kinks, is also studied, mainly through the generalised mean field
approximation.",9607089v2
1997-08-21,Single Hole Green's Functions in Insulating Copper Oxides at Nonzero Temperature,"We consider the single hole dynamics in a modified $t-J$ model at finite
temperature. The modified model includes a next nearest ($t'$) and next-next
nearest ($t''$) hopping. The model has been considered before in the zero
temperature limit to explain angle resolved photo-emission measurements. We
extend this consideration to the case of finite temperature where long-range
anti-ferromagnetic order is destroyed, using the self-consistent Born
approximation. The Dyson equation which relates the single hole Green's
functions for a fixed pseudo-spin and for fixed spin is derived. The Green's
function with fixed pseudo-spin is infrared stable but the Green's function
with fixed spin is close to an infrared divergency. We demonstrate how to
renormalize this Green's function in order to assure numerical convergence. At
non-zero temperature the quasi-particle peaks are found to shift down in energy
and to be broadened.",9708159v1
1997-10-08,Spin susceptibility and the pi-excitation in underdoped cuprates,"The dynamical spin susceptibility chi'' at wave vector (pi, pi) and the
spectrum pi'' of the spin-triplet particle--particle excitation with center of
mass momentum (pi, pi) (pi-excitation) are considered in the slave-boson
formulation of the t--J-model. Propagators are calculated in a diagrammatic
t-matrix approximation in the d-wave superconducting state for a wide doping
range. The resulting spectra chi'' and pi'' both show a resonance at a doping
dependent energy, in qualitative agreement with recent numerical cluster
calculations. In underdoped systems, the peak position is comparable to that
found in neutron scattering experiments. The peak in chi'' as well as pi'' is
at low doping entirely caused by spin fluctuations, whereas the triplet
particle--particle channel does not contribute as a collective mode.",9710065v1
1997-11-14,Charge and Spin Dynamics of an Ordered Stripe Phase in La_(1 2/3)Sr_(1/3)NiO_4 by Raman Spectroscopy,"For La_(1 2/3)Sr_(1/3)NiO_4 -- a commensurately doped Mott-Hubbard system --
charge- and spin-ordering in a stripe phase has been investigated by phononic
and magnetic Raman scattering. Formation of a superlattice and an opening of a
pseudo-gap in the electron-hole excitation spectra as well as two types of
double-spin excitations -- within the antiferromagnetic domain and across the
domain wall -- are observed below the charge-ordering transition. The
temperature dependence suggests that the spin ordering is driven by charge
ordering and that fluctuating stripes persist above the ordering transition.",9711139v1
1998-05-28,Slow Coarsening in an Ising Chain with Competing Interactions,"We investigate the zero-temperature coarsening dynamics of a chain of Ising
spins with a nearest-neighbor ferromagnetic and an nth-neighbor
antiferromagnetic interactions. For sufficiently large antiferromagnetic
interaction, the ground state consists of $n$ consecutive up spins followed by
n down spins, etc. We show that the asymptotic coarsening into this ground
state is governed by a multispecies reactive gas of elementary excitations. The
basic elementary excitations are identified and each decays at a different
power-law rate in time. The dominant excitations are domains of n+1 spins which
diffuse freely and disappear through processes which are effectively governed
by (n+1)-particle annihilation. This implies that the ground state is
approached slowly with time, as t^{-1/n}.",9805385v1
1998-08-31,New quantum Monte Carlo study of quantum critical phenomena with Trotter-number-dependent finite-size scaling and non-equilibrium relaxation,"We propose a new efficient scheme for the quantum Monte Carlo study of
quantum critical phenomena in quantum spin systems. Rieger and Young's
Trotter-number-dependent finite-size scaling in quantum spin systems and Ito
{\it et al.}'s evaluation of the transition point with the non-equilibrium
relaxation in classical spin systems are combined and generalized. That is,
only one Trotter number and one inverse temperature proportional to system
sizes are taken for each system size, and the transition point of the
transformed classical spin model is estimated as the point at which the order
parameter shows power-law decay. The present scheme is confirmed by the
determination of the critical phenomenon of the one-dimensional $S=1/2$
asymmetric XY model in the ground state. The estimates of the transition point
and the critical exponents $\beta$, $\gamma$ and $\nu$ are in good agreement
with the exact solutions. The dynamical critical exponent is also estimated as
${\mit \Delta}=2.14(I4(Jpm 0.06$, which is consistent with that of the
two-dimensional Ising model.",9808337v1
1998-09-01,Exactly solvable Kondo problem in the open $t-J$ chains,"We study the problem of a boundary magnetic impurity coupled with the
solvable $t-J$ chains. Our model provides a good start point to understand the
Kondo problem in a Luttinger liquid as well as in a strongly correlated host.
The Kondo coupling constant $J$ can take arbitrary values, which allows us to
study the ferromagnetic and antiferromagnetic Kondo problems simultaneously. It
is shown that both the Kondo coupling and the scalar potential effectively
reconcile the spin dynamics at low temperatures. Generally, the impurity spin
is split into two ghost spins via coupling effect. The residual entropy, which
can be exactly derived for the present model, is strongly
interaction-dependent. This hints the local spin configuration is very
complicated and very different from that in the conventional Kondo problem. An
unscreening phenomenon in the antiferromagnetic regime is found, which reveals
the impurity potential plays an important role for the Kondo problem in a
strongly correlated host. The low temperature specific heat is calculated in
the framework of local Landau-Luttinger liquid theory.",9809008v1
1999-04-10,Numerical Study on Aging Dynamics in the 3D Ising Spin-Glass Model. I. Energy Relaxation and Domain Coarsening,"Using Monte Carlo simulations, we have studied the relaxation of energy of
the three-dimensional Ising spin-glass model in aging process. Our
finite-size-scaling analysis on the isothermal energy decay after the quench
suggests strongly that the energy relaxes by coarsening of domain walls in
agreement with the droplet theory. We have also evaluated relaxation times
required for spin configurations in small systems, which are regarded as
isolated droplets, to flip globally. The results support the fundamental
assumption of the droplet theory that coarsening of domain walls, in case of
spin glasses, is driven by successive nucleation of thermally activated
droplets.",9904143v1
1999-05-20,Impurity spin relaxation in S=1/2 XX chains,"Dynamic autocorrelations $<S_i^{\alpha}(t) S_i^{\alpha}>$ (\alpha=x,z) of an
isolated impurity spin in a S=1/2 XX chain are calculated. The impurity spin,
defined by a local change in the nearest-neighbor coupling, is either in the
bulk or at the boundary of the open-ended chain. The exact numerical
calculation of the correlations employs the Jordan-Wigner mapping from spin
operators to Fermi operators; effects of finite system size can be eliminated.
Two distinct temperature regimes are observed in the long-time asymptotic
behavior. At T=0 only power laws are present. At high T the x correlation
decays exponentially (except at short times) while the z correlation still
shows an asymptotic power law (different from the one at T=0) after an
intermediate exponential phase. The boundary impurity correlations follow power
laws at all T. The power laws for the z correlation and the boundary
correlations can be deduced from the impurity-induced changes in the properties
of the Jordan-Wigner fermion states.",9905293v2
1999-06-17,High Magnetic Field ESR in the Haldane Spin Chains NENP and NINO,"We present electron spin resonance experiments in the one-dimensional
antiferromagnetic S=1 spin chains NENP and NINO in pulsed magnetic fields up to
50T. The measured field dependence of the quantum energy gap for B||b is
analyzed using the exact diagonalization method and the density matrix
renormalization group method (DMRG). A staggered anisotropy term (-1)^i d(S_i^x
S_i^z + S_i^z S_i^x) was considered for the first time in addition to a
staggered field term (-1)^i S_i^x B_st. We show that the spin dynamics in high
magnetic fields strongly depends on the orthorhombic anisotropy E.",9906273v1
1999-07-19,Ultraslow Electron Spin Dynamics in GaAs Quantum Wells Probed by Optically Pumped NMR,"Optically pumped nuclear magnetic resonance (OPNMR) measurements were
performed in two different electron-doped multiple quantum well samples near
the fractional quantum Hall effect ground state nu=1/3. Below 0.5K, the spectra
provide evidence that spin-reversed charged excitations of the nu=1/3 ground
state are localized over the NMR time scale of ~40 microseconds. Furthermore,
by varying NMR pulse parameters, the electron spin temperature (as measured by
the Knight shift) could be driven above the lattice temperature, which shows
that the value of the electron spin-lattice relaxation time lies between 100
microseconds and 500 milliseconds at nu=1/3.",9907279v2
1999-08-02,Aging phenomena in spin glass and ferromagnetic phases: domain growth and wall dynamics,"We compare aging in a disordered ferromagnet and in a spin glass, by studying
the different phases of a reentrant system. We have measured the relaxation of
the low-frequency ac susceptibility, in both the ferromagnetic and spin-glass
phases of a CdCr_{1.9}In_{0.1}S_4 sample. A restart of aging processes when the
temperature is lowered (`chaos-like' effect) is observed in both phases. The
memory of previous aging at a higher temperature can be retrieved upon
re-heating, but in the ferromagnetic phase it can rapidly be erased by the
growth of ferromagnetic domains. We interpret the behaviour observed in the
ferromagnetic phase in terms of a combination of domain growth and pinned wall
reconformations, and suggest that aging in spin glasses is dominated by such
wall reconformation processes.",9908030v2
1999-08-05,Numerical Study on Aging Dynamics in the 3D Ising Spin-Glass Model. II. Quasi-Equilibrium Regime of Spin Auto-Correlation Function,"Using Monte Carlo simulations, we have studied isothermal aging of
three-dimensional Ising spin-glass model focusing on quasi-equilibrium behavior
of the spin auto-correlation function. Weak violation of the time translational
invariance in the quasi-equilibrium regime is analyzed in terms of {\it
effective stiffness} for droplet excitations in the presence of domain walls.
Within the range of computational time window, we have confirmed that the
effective stiffness follows the expected scaling behavior with respect to the
characteristic length scales associated with droplet excitations and domain
walls, whose growth law has been extracted from our simulated data. Implication
of the results are discussed in relation to experimental works on ac
susceptibilities.",9908078v2
1999-09-04,Suppression of Ground-State Magnetization in Finite-Sized Systems Due to Off-Diagonal Interaction Fluctuations,"We study a generic model of interacting fermions in a finite-sized disordered
system. We show that the off-diagonal interaction matrix elements induce
density of states fluctuations which generically favor a minimum spin ground
state at large interaction amplitude, $U$. This effect competes with the
exchange effect which favors large magnetization at large $U$, and it
suppresses this exchange magnetization in a large parameter range. When
off-diagonal fluctuations dominate, the model predicts a spin gap which is
larger for odd-spin ground states as for even-spin, suggesting a simple
experimental signature of this off-diagonal effect in Coulomb blockade
transport measurements.",9909067v3
1999-09-16,Numerical Study on Aging Dynamics in the 3D Ising Spin-Glass Model --- Quasi-Equilibrium Behaviour of Spin Auto-Correlation Functions,"Using Monte Carlo simulations, we have studied aging phenomena in
three-dimensional Gaussian Ising spin-glass model focusing on quasi-equilibrium
behavior of the spin auto-correlation functions. Weak violation of the time
translational invariance in the quasi-equilibrium regime is analyzed in terms
of effective stiffness for droplet excitations in the presence of domain walls.
The simulated results in not only isothermal but also $T$-shift aging processes
exhibit the expected scaling behavior with respect to the characteristic length
scales associated with droplet excitations and domain walls in spite of the
fact that the growth law for these length scales still shows a pre-asymptotic
behavior compared with the asymptotic form proposed by the droplet theory.
Implications of our simulational results are also discussed in relation to
experimental observations.",9909228v1
1999-11-27,Spin correlation functions and susceptibilities in the easy-plane XXZ chain,"We present a Green's-function theory of magnetic short-range order in the
$S=1/2$ easy-plane XXZ chain based on the projection method for the dynamic
spin susceptibility and a decoupling of three-spin operator products
introducing vertex parameters. The longitudinal and transverse static
susceptibilities and two-point correlation functions of arbitrary range are
calculated self-consistently for all wavenumbers, temperatures, and anisotropy
parameters $ -1\leq \Delta \leq 1$. In the easy-plane ferromagnetic region
$(\Delta < 0)$, the longitudinal correlators of spins at distance $n$ change
sign at a finite temperature $T_0(n,\Delta)$, in reasonable agreement with
recent data obtained by finite-chain diagonalizations. The temperature
dependence of the uniform static susceptibilities exhibits a maximum which is
explained as an effect of magnetic short-range order which decreases with
increasing temperature.",9911447v2
2000-01-24,Aging in a topological spin glass,"We have examined the nonconventional spin glass phase of the 2-dimensional
kagome antiferromagnet (H_3 O) Fe_3 (SO_4)_2 (OH)_6 by means of ac and dc
magnetic measurements. The frequency dependence of the ac susceptibility peak
is characteristic of a critical slowing down at Tg ~ 18K. At fixed temperature
below Tg, aging effects are found which obey the same scaling law as in spin
glasses or polymers. However, in clear contrast with conventional spin glasses,
aging is remarkably insensitive to temperature changes. This particular type of
dynamics is discussed in relation with theoretical predictions for highly
frustrated non-disordered systems.",0001344v2
2000-02-29,Static magnetization induced by time-periodic fields with zero mean,"We consider a single spin in a constant magnetic field or an anisotropy
field. We show that additional external time-periodic fields with zero mean may
generate nonzero time-averaged spin components which are vanishing for the
time-averaged Hamiltonian. The reason is a lowering of the dynamical symmetry
of the system. A harmonic signal with proper orientation is enough to display
the effect. We analyze the problem both with and without dissipation, both for
quantum spins (s=1/2,1) and classical spins. The results are of importance for
controlling the system's state using high or low frequency fields and for using
new resonance techniques which probe internal system parameters, to name a few.",0002463v1
2000-03-29,Static and dynamic spin correlations in the spin-glass phase of slightly-doped La_{2-x}Sr_xCuO_4,"Neutron scattering experiments reveal that a diagonal spin modulation, which
is a one-dimensional modulation rotated away by 45$^\circ$ from that in the
superconducting phase, occurs universally across the insulating spin-glass
phase in La$_{2-x}$Sr$_x$CuO$_4$ (0.02$\le x\le$0.055). This establishes an
intimate relation between the magnetism and the transport properties in the
high-temperature copper oxide superconductors. Furthermore, it is found that
the charge density per unit length estimated using a charge stripe model is
almost constant throughout the phase diagram, even when the modulation rotates
away by 45$^\circ$ at the superconducting boundary. However, at the lowest
values for $x$ the density changes approaching 1 hole/Cu as in
La$_{2-x}$Sr$_x$NiO$_4$. Magnetic excitation spectra suggest that magnetic
correlations change from incommensurate to commensurate at $\omega\sim$7 meV
and $T\sim$70 K, indicating a characteristic energy for the incommensurate
structure of 6-7 meV.",0003466v2
2000-10-04,The Resonance Peak in Sr$_2$RuO$_4$: Signature of Spin Triplet Pairing,"We study the dynamical spin susceptibility, $\chi({\bf q}, \omega)$, in the
normal and superconducting state of Sr$_2$RuO$_4$. In the normal state, we find
a peak in the vicinity of ${\bf Q}_i\simeq (0.72\pi,0.72\pi)$ in agreement with
recent inelastic neutron scattering (INS) experiments. We predict that for spin
triplet pairing in the superconducting state a {\it resonance peak} appears in
the out-of-plane component of $\chi$, but is absent in the in-plane component.
In contrast, no resonance peak is expected for spin singlet pairing.",0010067v2
2000-12-22,The magnetic ordering in the mixed valence compound beta-Na0.33V2O5,"The low-temperature electron spin resonance (ESR) spectra and the static
magnetization data obtained for the stoichiometric single crystals of
$\beta$-Na$_{0.33}$V$_2$O$_5$ indicate that this quasi-one-dimensional mixed
valence (V4+/V5+) compound demonstrates at $T_N=22$ K the phase transition into
the canted antiferromagnetically ordered state. The spontaneous magnetization
of $3.4\times 10^{-3}$ $\mu_B$ per V$^{4+}$ ion was found to be oriented along
the two-fold $b$ axis of the monoclinic structure, the vector of
antiferromagnetism is aligned with the $a$ axis and the Dzyaloshinsky vector is
parallel to the $c$-axis. The experimental data were successfully described in
the frame of the macroscopic spin dynamics and the following values for the
macroscopic parameters of the spin system were obtained: the Dzyaloshinsky
field $H_D=6$ kOe, the energy gaps of two branches of the spin wave spectrum
$\Delta_1=48$ GHz and $\Delta_2=24$ GHz.",0012434v1
2001-04-18,Memory and chaos in an Ising spin glass,"The non-equilibrium dynamics of the model 3d-Ising spin glass
  - Fe$_{0.55}$Mn$_{0.45}$TiO$_3$ - has been investigated from the temperature
and time dependence of the zero field cooled magnetization recorded under
certain thermal protocols. The results manifest chaos, rejuvenation and memory
features of the equilibrating spin configuration that are very similar to those
observed in corresponding studies of the archetypal RKKY spin glass Ag(Mn). The
sample is rapidly cooled in zero magnetic field, and the magnetization recorded
on re-heating. When a stop at constant temperature $T_s$ is made during the
cooling, the system evolves toward its equilibrium state at this temperature.
The equilibrated state established during the stop becomes frozen in on further
cooling and is retrieved on re-heating. The memory of the aging at $T_s$ is not
affected by a second stop at a lower temperature
  $T'_s$. Reciprocally, the first equilibration at $T_s$ has no influence on
the relaxation at $T'_s$, as expected within the droplet model for domain
growth in a chaotic landscape.",0104333v1
2001-05-03,A new approach to strongly correlated fermion systems: the spin-particle-hole coherent-state path integral,"We describe a new path integral approach to strongly correlated fermion
systems, considering the Hubbard model as a specific example. Our approach is
based on the introduction of spin-particle-hole coherent states which
generalize the spin-1/2 coherent states by allowing the creation of a hole or
an additional particle. The action of the fermion system
$S[\gamma^*,\gamma;{\bf\Omega}]$ can be expressed as a function of two
Grassmann variables ($\gamma_\uparrow$,$\gamma_\downarrow$) describing
particles propagating in the lower and upper Hubbard bands, and a unit vector
field ${\bf\Omega}$ whose dynamics arises from spin fluctuations. In the strong
correlation limit, $S[\gamma^*,\gamma;{\bf\Omega}]$ can be truncated to quartic
order in the fermionic fields and used as the starting point of a
strong-coupling diagrammatic expansion in $t/U$ ($t$ being the intersite
hopping amplitude and $U$ the on-site Coulomb repulsion). We discuss possible
applications of this formalism and its connection to the t-J model and the
spin-fermion model.",0105062v1
2001-05-31,Dynamic Oscillations of Magnetization in High Spin Magnetic Clusters,"We have studied the time evolution of magnetization of a high spin magnetic
cluster in the ground state, in the presence of a sinusoidal axial magnetic
field and a static transverse field by explicitly solving time dependent
schr\""odinger equation. We observe oscillations of magnetization in the plateau
region which has all the characteristics reminiscent of the oscillation of
probability of occupation of a state in a two level lattice in the presence of
an oscillating electric field. The high spin of the ground state leads to a
large but finite two-level pseudo-lattice. The oscillations in magnetization
occur at amplitude of magnetic fields achievable in a laboratory and they also
persist for a wide range of spin-dipolar interactions.
  Thus, our study provides a magnetic analog of the optical two-level lattice.",0105616v1
2001-08-15,Spin and charge order in Mott insulators and d-wave superconductors,"We argue that aspects of the anomalous, low temperature, spin and charge
dynamics of the high temperature superconductors can be understood by studying
the corresponding physics of undoped Mott insulators. Such insulators display a
quantum transition from a magnetically ordered Neel state to a confining
paramagnet with a spin gap; the latter state has bond-centered charge order, a
low energy S=1 spin exciton, confinement of S=1/2 spinons, and a free S=1/2
moment near non-magnetic impurities. We discuss how these characteristics, and
the quantum phase transitions, evolve upon doping the insulator into a d-wave
superconductor. This theoretical framework was used to make a number of
predictions for STM measurements and for the phase diagram of the doped Mott
insulator in an applied magnetic field.",0108238v4
2001-09-04,Continuum spin excitations in S=1 one-dimensional antiferromagnet,"We present detailed measurement of the non-hydrodynamic part of the spin
excitation spectrum in the model quasi-1D S=1 antiferromagnet CsNiCl3 by
inelastic magnetic neutron scattering. In the better part of the Brillouin zone
the effect of the inter-chain coupling is negligible, and spin dynamics
reflects that of a single Haldane chain. We find that at q ~< 0.6pi this
quantum spin system ceases to support coherent propagating excitation, which
gradually turns into a continuum band of states, whose width grows with
decreasing q. This finding is consistently verified under different resolution
conditions, obtained with two different high-luminosity experimental setups.",0109065v1
2001-10-03,Grassmannian Fields and Doubly Enhanced Skyrmions in Bilayer Quantum Hall system at $ν=2$,"At the filling factor $\nu=2$ the bilayer quantum Hall system has three
phases, the ferromagnetic phase (spin phase), the spin singlet phase (ppin
phase) and the canted antiferromagnetic phase. We analyze soft waves and
quasiparticle excitations in the spin and ppin phases. It is shown that the
dynamic field is the Grassmannian G$_{4,2}$ field carrying four complex degrees
of freedom. In each phase there are four complex soft waves (pseudo-Goldstone
modes) and one kind of skyrmion excitations (G$_{4,2}$ skyrmions) flipping
either spins or pseudospins coherently. An intriguing property is that a
quasiparticle is a G$_{4,2}$ skyrmion essentially consisting of two CP$^{3}$
skyrmions and thus possesses charge $2e$.",0110072v3
2001-12-29,From Linear to Nonlinear Response in Spin Glasses: Importance of Mean-Field-Theory Predictions,"Deviations from spin-glass linear response in a single crystal Cu:Mn 1.5 at %
are studied for a wide range of changes in magnetic field, $\Delta H$. Three
quantities, the difference $TRM-(MFC-ZFC)$, the effective waiting time,
$t_{w}^{eff}$, and the difference $TRM(t_{w})-TRM(t_{w}=0)$ are examined in our
analysis. Three regimes of spin-glass behavior are observed as $\Delta H$
increases. Lines in the $(T,\Delta H)$ plane, corresponding to ``weak'' and
``strong'' violations of linear response under a change in magnetic field, are
shown to have the same functional form as the de Almeida-Thouless critical
line. Our results demonstrate the existence of a fundamental link between
static and dynamic properties of spin glasses, predicted by the mean-field
theory of aging phenomena.",0112489v2
2002-01-02,Anisotropies of the Hamiltonian and the Wave Function: Inversion Phenomena in Quantum Spin Chains,"We investigate the inversion phenomenon between the XXZ anisotropies of the
Hamiltonian and the wave function in quantum spin chains, mainly focusing on
the S=1/2 trimerized XXZ model with the next-nearest-neighbor interactions. We
have obtained the ground-state phase diagram by use of the degenerate
perturbation theory and the level spectroscopy analysis of the numerical data
calculated by the Lanczos method. In some parameter regions, the spin-fluid is
realized for the Ising-like anisotropy, and the Neel state for the XY-like
anisotropy, against the ordinary situation.",0201014v1
2002-03-22,Cyclic Spin Exchange in Cuprate Spin Ladders,"We investigate the influence of a cyclic spin exchange J_{cyc} on the one-
and two-triplet excitations of an undoped two-leg S=1/2 ladder, using the
density matrix renormalization group (DMRG). The dispersion of the S=0
two-triplet bound state is dramatically reduced by J_{cyc} due to a repulsion
between triplets on neighboring rungs. In (La,Ca)_{14}Cu_{24}O_{41} a
consistent description of both the spin gap and the S=0 bound state requires
$J_{cyc}/J_\perp \approx 0.20-0.27$ and $J/J_{\perp} \approx 1.25-1.35$. With
these coupling ratios the recently developed dynamical DMRG yields an excellent
description of the entire S=0 excitation spectrum observed in the optical
conductivity, including the continuum contribution.",0203472v1
2002-05-14,Gibbsian Hypothesis in Turbulence,"We show that Kolmogorov multipliers in turbulence cannot be statistically
independent of others at adjacent scales (or even a finite range apart) by
numerical simulation of a shell model and by theory. As the simplest
generalization of independent distributions, we suppose that the steady-state
statistics of multipliers in the shell model are given by a
translation-invariant Gibbs measure with a short-range potential, when
expressed in terms of suitable ``spin'' variables: real-valued spins that are
logarithms of multipliers and XY-spins defined by local dynamical phases.
Numerical evidence is presented in favor of the hypothesis for the shell model,
in particular novel scaling laws and derivative relations predicted by the
existence of a thermodynamic limit. The Gibbs measure appears to be in a
high-temperature, unique-phase regime with ``paramagnetic'' spin order.",0205286v2
2002-07-08,Coherence peak in the spin susceptibility from nesting in spin-triplet superconductors; A probe for line nodes in Sr$_2$RuO$_4$,"We study the dynamical spin susceptibility $\chi ({\bf q},\omega)$ for
spin-triplet superconductivity. We show that a large peak at $\omega = 2
\Delta$ appears in $\textrm{Im} \chi_{zz}({\mathbf{Q}}, \omega)$, where $z$ is
the direction of the $\mathbf{d}$ vector for triplet pairing, if Fermi surface
has a nested part with the nesting vector $\mathbf{Q}$ and the order parameter
is $+\Delta$ and $-\Delta$ in this part of the Fermi surface. If there are line
nodes in the nested part of the Fermi surface, a peak appears in either
$\textrm{Im} \chi_{zz}(\mathbf{Q}, \omega)$ or
  $\textrm{Im} \chi_{+-}(\mathbf{Q}, \omega)$, or both, depending on the
perpendicular component of the nesting vector. The comparison with inelastic
neutron scattering experiments can determine the position of the line nodes in
triplet superconductor Sr$_2$RuO$_4$.",0207193v2
2002-08-16,Spin collective mode and quasiparticle contributions to STM spectra of d-wave superconductors with pinning,"We present additional details of the scanning tunneling microscopy (STM)
spectra predicted by the model of pinning of dynamic spin collective modes in
d-wave superconductor proposed by Polkovnikov et al. (cond-mat/0203176). Along
with modulations at the twice the wavevector of the spin collective mode, the
local density of states (LDOS) displays features linked to the spectrum of the
Bogoliubov quasiparticles. The former is expected to depend more strongly on an
applied magnetic field or the doping concentration. The spin collective mode
and the quasiparticles are distinct, co-existing, low energy excitations of the
d-wave superconductor (strongly coupled only in some sectors of the Brillouin
zone), and should not be viewed as mutually exclusive sources of LDOS
modulation.",0208334v5
2002-10-15,Competition between dynamic and thermal relaxation in non-equilibrium spin systems above the critical point,"We study the long-time behaviour and the spatial correlations of a simple
ferromagnetic spin system whose kinetics is governed by a thermal bath with a
time-dependent temperature which is characterized by a given external
relaxation time tau. Exact results are obtained in the framework of the
spherical model in d dimensions. In the paramagnetic phase, the long-time
kinetics is shown to depend crucially on the ratio between tau and the internal
equilibration time tau_eq.
  If tau is less than tau_eq, the model relaxes rapidly towards an equilibrium
state but there appear transient and spatially oscillating contributions in the
spin-spin correlation function. On the other hand, if tau is much greater than
tau_eq the system is clamped and its time evolution is delayed with respect to
the one of the heat bath. For waiting times s such that tau << s << tau_eq, a
quasi-stationary state is found where the fluctuation-dissipation theorem does
not hold.",0210330v3
2002-10-28,Spectral Function Analysis on Spin Dynamics in Double-Exchange Systems with Randomness,"Spin excitation spectrum is studied in the double-exchange model with
randomness. Applying the spin wave approximation and the spectral function
analysis, we examine excitation energy and linewidth using analytical as well
as numerical methods. For small wave number $q \sim 0$, the excitation energy
is cosine-like and the linewidth shows a $q$-linear behavior. This indicates
that the spin excitation becomes incoherent or localized near $q = 0$.
Crossover takes place to marginally-coherent regime where both the excitation
energy and the linewidth are proportional to $q^2$. The incoherence is due to
local fluctuations of the kinetic energy of electrons. Comparison with
experimental results in colossal magnetoresistance manganites suggests that
spatially-correlated or mesoscopic-scale fluctuations are more important in
real compounds than local or atomic-scale ones.",0210606v1
2002-12-12,Observation of the spin-charge thermal isolation of ferromagnetic Ga_{0.94}Mn_{0.06}As by time-resolved magneto-optical measurement,"The dynamics of magnetization under femtosecond optical excitation is studied
in a ferromagnetic semiconductor Ga_{0.94}Mn_{0.06}As with a time-resolved
magneto-optical Kerr effect measurement with two color probe beams. The
transient reflectivity change indicates the rapid rise of the carrier
temperature and relaxation to a quasi-thermal equilibrium within 1 ps, while a
very slow rise of the spin temperature of the order of 500ps is observed. This
anomalous behavior originates from the thermal isolation between the charge and
spin systems due to the spin polarization of carriers (holes) contributing to
ferromagnetism. This constitutes experimental proof of the half-metallic nature
of ferromagnetic Ga_{0.94}Mn_{0.06}As arising from double exchange type
mechanism originates from the d-band character of holes.",0212276v2
2003-02-17,Thermally assisted magnetization reversal in the presence of a spin-transfer torque,"We propose a generalized stochastic Landau-Lifshitz equation and its
corresponding Fokker-Planck equation for the magnetization dynamics in the
presence of spin transfer torques. Since the spin transfer torque can pump a
magnetic energy into the magnetic system, the equilibrium temperature of the
magnetic system is ill-defined. We introduce an effective temperature based on
a stationary solution of the Fokker-Planck equation. In the limit of high
energy barriers, the law of thermal agitation is derived. We find that the
N\'{e}el-Brown relaxation formula remains valid as long as we replace the
temperature by an effective one that is linearly dependent of the spin torque.
We carry out the numerical integration of the stochastic Landau-Lifshitz
equation to support our theory. Our results agree with existing experimental
data.",0302339v2
2003-03-11,Theory of the [111] magnetization plateau in spin ice,"The application of a magnetic field along the [111] direction in the spin ice
compounds leads to two magnetization plateaux, in the first of which the ground
state entropy is reduced but still remains extensive. We observe that under
reasonable assumptions, the remaining degrees of freedom in the low field
plateau live on decoupled kagome planes, and can be mapped to hard core dimers
on a honeycomb lattice. The resulting two dimensional state is critical, and we
have obtained its residual entropy -- in good agreement with a recent
experiments -- the equal time spin correlations as well as a theory for the
dynamical spin correlations. Small tilts of the field are predicted to lead a
vanishing of the entropy and the termination of the critical phase by a
Kasteleyn transition characterized by highly anisotropic scaling. We discuss
the thermally excited defects that terminate the plateau either end, among them
an exotic string defect which restores three dimensionality.",0303210v1
2003-04-01,Voltage control of nuclear spin in ferromagnetic Schottky diodes,"We employ optical pump-probe spectroscopy to investigate the voltage
dependence of spontaneous electron and nuclear spin polarizations in hybrid
MnAs/n-GaAs and Fe/n-GaAs Schottky diodes. Through the hyperfine interaction,
nuclear spin polarization that is imprinted by the ferromagnet acts on
conduction electron spins as an effective magnetic field. We demonstrate tuning
of this nuclear field from <0.05 to 2.4 kG by varying a small bias voltage
across the MnAs device. In addition, a connection is observed between the diode
turn-on and the onset of imprinted nuclear polarization, while traditional
dynamic nuclear polarization exhibits relatively little voltage dependence.",0304030v1
2003-08-27,Positive cross-correlations in a three-terminal quantum dot with ferromagnetic contacts,"We study current fluctuations in an interacting three-terminal quantum dot
with ferromagnetic leads. For appropriately polarized contacts, the transport
through the dot is governed by a novel dynamical spin blockade, i.e., a
spin-dependent bunching of tunneling events not present in the paramagnetic
case. This leads for instance to positive zero-frequency cross-correlations of
the currents in the output leads even in the absence of spin accumulation on
the dot. We include the influence of spin-flip scattering and identify
favorable conditions for the experimental observation of this effect with
respect to polarization of the contacts and tunneling rates.",0308564v2
2003-09-17,Fermi-Bose mapping and N-particle ground state of spin-polarized fermions in tight atom waveguides,"A K-matrix for waveguide confined spin-polarized fermionic atoms recently
computed by Granger and Blume is identified, in the low-energy domain, with a
contact condition for one-dimensional (1D) spinless fermions. Difficulties in
consistently formulating the contact conditions in terms of interaction
potentials are discussed and a rigorous alternative variational reformulation
is constructed. A duality between 1D fermions and bosons with zero-range
interactions suggested by Cheon and Shigehara is shown to hold for the
effective 1D dynamics of a spin-polarized Fermi gas with 3D p-wave interactions
and that of a Bose gas with 3D s-wave interactions in a tight waveguide. This
generalizes the mapping from impenetrable bosons (TG gas) to free fermions and
is used to derive the equation of state of an ultracold spin-polarized
fermionic vapor in a tight waveguide. Near a 1D confinement-induced resonance
one has a ""fermionic TG gas"" which maps to an ideal Bose gas.",0309396v1
2003-12-26,Direct relation between the low-energy spin excitations and superconductivity of overdoped high-$T_c$ superconductors,"The dynamic spin susceptibility, $\chi''(\omega)$, has been measured over the
energy range of $2 \leq \omega \leq 10$ meV for overdoped
La$_{2-x}$Sr$_{x}$CuO$_{4}$. Incommensurate (IC) spin excitations are observed
at 8 K for all superconducting samples for $0.25 \leq x \leq 0.28$ with
$\chi''$ peaking at $\sim 6$ meV. The IC peaks at 6 meV become smaller in
intensity with increasing $x$ and, finally, become unobservable for a sample
with $x=0.30$ which has no bulk superconductivity. The maximum $\chi''$
decreases linearly with $T_c$(onset) in the overdoped region, implying a direct
cooperative relation between the spin fluctuations and the superconductivity.",0312648v2
2004-01-26,Spin dynamics in lightly doped La$_{2-x}$Sr$_x$CuO$_4$: Relaxation function within the $t - J$ model,"The relaxation function theory of doped two-dimensional $S=1/2$ Heisenberg
antiferromagnetic (AF) system in the paramagnetic state is presented taking
into account the hole subsystem as well as both the electron and AF
correlations. The expression for fourth frequency moment of relaxation shape
function is derived within the $t-J$ model. The presentation obeys rotational
symmetry of the spin correlation functions and is valid for all wave vectors
through the Brillouin zone. The spin diffusion contribution to relaxation rates
is evaluated and is shown to play a significant role in carrier free and doped
antiferromagnet in agreement with exact diagonalization calculations. At low
temperatures the main contribution to the nuclear spin-lattice relaxation rate,
$^{63}(1/T_1)$, of plane $^{63}$Cu arises from the AF fluctuations, and
$^{17}(1/T_1)$, of plane $^{17}$O, has the contributions from the wavevectors
in the vicinity of $(\pi,\pi)$ and small $q \sim 0$. It is shown that the
theory is able to explain the main features of experimental data on temperature
and doping dependence of $^{63}(1/T_1)$ in the paramagnetic state of both
carrier free La$_2$CuO$_4$ and doped La$_{2-x}$Sr$_x$CuO$_4$ compounds.",0401514v1
2004-05-13,Absence of rejuvenation in a Superspin Glass,"Effects of temperature changes on the nonequilibrium spin-glass dynamics of a
strongly interacting ferromagnetic nanoparticle system (superspin glass) are
studied. In contrary to atomic spin glasses, strong cooling rate effects are
observed, and no evidence for temperature-chaos is found. The flip time of a
magnetic moment is much longer than that of an atomic spin and hence much
shorter time scales are probed within the experimental time window for a
superspin glass than for an atomic spin glass. Within a real space picture the
cumulative aging observed for the superspin glass can be explained considering
that all investigated length scales are shorter than the temperature-chaos
overlap length. The transient relaxation, observed in experiments after
temperature changes, can be understood as the adjustment of thermally active
droplets, which is mutatis mutandis the Kovacs effect observed in most glassy
systems.",0405276v1
2004-08-01,Spin Gap in Chains with Hidden Symmetries,"We investigate the formation of spin gap in one-dimensional models
characterized by the groups with hidden dynamical symmetries. A family of
two-parametric models of isotropic and anisotropic Spin-Rotator Chains
characterized by SU(2)x SU(2) and SO(2)x SO(2)x Z_2 x Z_2 symmetries is
introduced to describe the transition from SU(2) to SO(4) antiferromagnetic
Heisenberg chain. The excitation spectrum is studied with the use of the
Jordan-Wigner transformation generalized for o_4 algebra and by means of
bosonization approach. Hidden discrete symmetries associated with invariance
under various particle-hole transformations are discussed. We show that the
spin gap in SRC Hamiltonians is characterized by the scaling dimension 2/3 in
contrast to dimension 1 in conventional Haldane problem.",0408016v1
2004-08-09,"Role of Disorder in Mn:GaAs, Cr:GaAs, and Cr:GaN","We present calculations of magnetic exchange interactions and critical
temperature T_c in Mn:GaAs, Cr:GaAs and Cr:GaN. The local spin density
approximation is combined with a linear-response technique to map the magnetic
energy onto a Heisenberg hamiltonion, but no significant further approximations
are made. Special quasi-random structures in large unit cells are used to
accurately model the disorder. T_c is computed using both a spin-dynamics
approach and the cluster variation method developed for the classical
Heisenberg model.
  We show the following: (i) configurational disorder results in large
dispersions in the pairwise exchange interactions; (ii) the disorder strongly
reduces T_c; (iii) clustering in the magnetic atoms, whose tendency is
predicted from total-energy considerations, further reduces T_c. Additionally
the exchange interactions J(R) are found to decay exponentially with distance
R^3 on average; and the mean-field approximation is found to be a very poor
predictor of T_c, particularly when J(R) decays rapidly. Finally the effect of
spin-orbit coupling on T_c is considered. With all these factors taken into
account, T_c is reasonably predicted by the local spin-density approximation in
MnGaAs without the need to invoke compensation by donor impurities.",0408185v1
2004-08-13,The quantum measurement process in an exactly solvable model,"An exactly solvable model for a quantum measurement is discussed which is
governed by hamiltonian quantum dynamics. The $z$-component $\hat s_z$ of a
spin-1/2 is measured with an apparatus, which itself consists of magnet coupled
to a bath. The initial state of the magnet is a metastable paramagnet, while
the bath starts in a thermal, gibbsian state. Conditions are such that the act
of measurement drives the magnet in the up or down ferromagnetic state
according to the sign of $s_z$ of the tested spin. The quantum measurement goes
in two steps. On a timescale $1/\sqrt{N}$ the off-diagonal elements of the
spin's density matrix vanish due to a unitary evolution of the tested spin and
the $N$ apparatus spins; on a larger but still short timescale this is made
definite by the bath. Then the system is in a `classical' state, having a
diagonal density matrix. The registration of that state is a quantum process
which can already be understood from classical statistical mechanics. The von
Neumann collapse and the Born rule are derived rather than postulated.",0408316v1
2004-10-28,Inelastic neutron scattering study of single crystal heavy fermion YbAgGe,"Single crystals of the heavy-fermion compound YbAgGe have been studied by
neutron scattering. The magnetic ordering occurring below T1=0.5 K is
characterized by a commensurate propagation vector k=(1/3,0,1/3) and the
moments in the basal plane of the hexagonal structure. The dynamic magnetic
susceptibility is dominated by quasielastic spin fluctuations with a
characteristic energy Gamma of the order of 1 meV. The spins fluctuate
predominantly in the basal plane. No spin-wave excitations are observed in the
magnetically ordered phase. Below the Kondo temperature, TK=20 K, Gamma shows a
strong q dependence for wave vectors along the c* direction, but is
q-independent in the basal plane. Gamma shows initially a rapid increase with
temperature T at the antiferromagnetic zone center, but follows a standard
sqrt(T) law for other q values and for T>TK in general. These observations
classify YbAgGe as a well-behaved heavy-fermion compound with a particular
q-dependence of the antiferromagnetic spin fluctuations, possibly related to
the geometrical frustration of the Yb3+ ions.",0410736v1
2004-11-09,Entanglement transfer from electron spins to photons in spin light-emitting diodes containing quantum dots,"We show that electron recombination using positively charged excitons in
single quantum dots provides an efficient method to transfer entanglement from
electron spins onto photon polarizations. We propose a scheme for the
production of entangled four-photon states of GHZ type. From the GHZ state, two
fully entangled photons can be obtained by a measurement of two photons in the
linear polarization basis, even for quantum dots with observable fine structure
splitting for neutral excitons and significant exciton spin decoherence.
Because of the interplay of quantum mechanical selection rules and
interference, maximally entangled electron pairs are converted into maximally
entangled photon pairs with unity fidelity for a continuous set of observation
directions. We describe the dynamics of the conversion process using a
master-equation approach and show that the implementation of our scheme is
feasible with current experimental techniques.",0411235v3
2004-11-13,Spin transfer switching of spin valve nanopillars using nanosecond pulsed currents,"Spin valve nanopillars are reversed via the mechanism of spin momentum
transfer using current pulses applied perpendicular to the film plane of the
device. The applied pulses were varied in amplitude from 1.8 mA to 7.8 mA, and
varied in duration within the range of 100 ps to 200 ns. The probability of
device reversal is measured as a function of the pulse duration for each pulse
amplitude. The reciprocal pulse duration required for 95% reversal probability
is linearly related to the pulse current amplitude for currents exceeding 1.9
mA. For this device, 1.9 mA marks the crossover between dynamic reversal at
larger currents and reversal by thermal activation for smaller currents.",0411363v1
2004-12-13,Field-tuned quantum critical point of antiferromagnetic metals,"A magnetic field applied to a three-dimensional antiferromagnetic metal can
destroy the long-range order and thereby induce a quantum critical point. Such
field-induced quantum critical behavior is the focus of many recent
experiments. We investigate theoretically the quantum critical behavior of
clean antiferromagnetic metals subject to a static, spatially uniform external
magnetic field. The external field does not only suppress (or induce in some
systems) antiferromagnetism but also influences the dynamics of the order
parameter by inducing spin precession. This leads to an exactly marginal
correction to spin-fluctuation theory. We investigate how the interplay of
precession and damping determines the specific heat, magnetization,
magnetocaloric effect, susceptibility and scattering rates. We point out that
the precession can change the sign of the leading \sqrt{T} correction to the
specific heat coefficient c(T)/T and can induce a characteristic maximum in
c(T)/T for certain parameters. We argue that the susceptibility \chi =\partial
M/\partial B is the thermodynamic quantity which shows the most significant
change upon approaching the quantum critical point and which gives experimental
access to the (dangerously irrelevant) spin-spin interactions.",0412284v1
2005-01-18,Incommensurate spin dynamics in underdoped cuprate perovskites,"The incommensurate magnetic response observed in normal-state cuprate
perovskites is interpreted based on the projection operator formalism and the
t-J model of Cu-O planes. In agreement with experiment the calculated
dispersion of maxima in the susceptibility has the shape of two parabolas with
upward and downward branches which converge at the antiferromagnetic wave
vector. The maxima are located at the momenta $({1/2},{1/2}\pm\delta)$,
$({1/2}\pm\delta,{1/2})$ and at $({1/2}\pm\delta,{1/2}\pm\delta)$,
$({1/2}\pm\delta,{1/2}\mp\delta)$ in the lower and upper parabolas,
respectively. The upper parabola reflects the dispersion of magnetic
excitations of the localized Cu spins, while the lower parabola arises due to a
dip in the spin-excitation damping at the antiferromagnetic wave vector. For
moderate doping this dip stems from the weakness of the interaction between the
spin excitations and holes near the hot spots. The frequency dependence of the
susceptibility is shown to depend strongly on the hole bandwidth and damping
and varies from the shape observed in YBa$_2$Cu$_3$O$_{7-y}$ to that inherent
in La$_{2-x}$Sr$_x$CuO$_4$.",0501418v1
2005-02-09,Coulomb Promotion of Spin-Dependent Tunnelling,"We study transport of spin-polarized electrons through a magnetic
single-electron transistor (SET) in the presence of an external magnetic field.
Assuming the SET to have a nanometer size central island with a single electron
level we find that the interplay on the island between coherent spin-flip
dynamics and Coulomb interactions can make the Coulomb correlations promote
rather than suppress the current through the device. We find the criteria for
this new phenomenon -- Coulomb promotion of spin-dependent tunnelling -- to
occur.",0502243v2
2005-06-28,Spin-fluctuation mechanism of superconductivity,"Normal and superconducting state spectral properties of cuprates are
theoretically described within the extended t-J model. The method is based on
the equations of motion for projected fermionic operators and the mode-coupling
approximation for the self-energy matrix. The dynamical spin susceptibility at
various doping is considered as an input, extracted from experiments. The
analysis shows that the onset of superconductivity is dominated by the
spin-fluctuation contribution. The coupling to spin fluctuations directly
involves the next-nearest-neighbor hopping t', hence Tc shows a pronounced
dependence on t'. The latter can offer an explanation for the variation of Tc
among different families of hole-doped cuprates. A formula for maximum Tc is
given and it is shown that optimum doping, where maximum Tc is reached, is with
increasing -t' progresively increased.",0506726v1
2005-08-04,Electron and Spin Correlations in Semiconductor Heterostructures: Quantum Singwi-Tosi-Land-Sjolander Theory,"We apply the quantum Singwi-Tosi-Land-Sjolander (QSTLS) theory for a study of
many-body effects in the quasi-two-dimensional (Q2D) electron liquid (EL) in
GaAs/AlxGa1-xAs heterojunctions. The effect of the layer thickness is included
through a variational approach. We have calculated the density, spin-density
static structure factors, spin-dependent pair distribution functions (PDF) and
compared our results with those of two-dimensional (2D) EL given in earlier
papers. Using the static structure factors (SSF) we have calculated various
dynamic correlation functions such as spin-dependent local-field factors (LFF)
and effective potentials of the Q2D EL. We have also calculated the inverse
static dielectric function of the 2D and Q2D EL using different approximations.
We find that the effect of finite thickness on the dielectric function is
remarkable and at the intermediate values of wave number q there is a
significant difference between the QSTLS and STLS results.",0508121v1
2005-08-22,Algebraic vortex liquid in spin-1/2 triangular antiferromagnets: Scenario for Cs_2CuCl_4,"Motivated by inelastic neutron scattering data on Cs_2CuCl_4, we explore
spin-1/2 triangular lattice antiferromagnets with both spatial and easy-plane
exchange anisotropies, the latter due to an observed Dzyaloshinskii-Moriya
interaction. Exploiting a duality mapping followed by a fermionization of the
dual vortex degrees of freedom, we find a novel ""critical"" spin-liquid phase
described in terms of Dirac fermions with an emergent global SU(4) symmetry
minimally coupled to a non-compact U(1) gauge field. This ``algebraic vortex
liquid"" supports gapless spin excitations and universal power-law correlations
in the dynamical spin structure factor which are consistent with those observed
in Cs_2CuCl_4. We suggest future neutron scattering experiments that should
help distinguish between the algebraic vortex liquid and other spin liquids and
quantum critical points previously proposed in the context of Cs_2CuCl_4.",0508536v2
2005-08-30,Observation and theoretical description of the pure Fano-effect in the valence-band photo-emission of ferromagnets,"The pure Fano-effect in angle-integrated valence-band photo-emission of
ferromagnets has been observed for the first time. A contribution of the
intrinsic spin polarization to the spin polarization of the photo-electrons has
been avoided by an appropriate choice of the experimental parameters. The
theoretical description of the resulting spectra reveals a complete analogy to
the Fano-effect observed before for paramagnetic transition metals. While the
theoretical photo-current and spin difference spectra are found in good
quantitative agreement with experiment in the case of Fe and Co only a
qualitative agreement could be achieved in the case of Ni by calculations on
the basis of plain local spin density approximation (LSDA). Agreement with
experimental data could be improved in this case in a very substantial way by a
treatment of correlation effects on the basis of dynamical mean field theory
(DMFT).",0508724v1
2005-09-13,Synchronization of spin-transfer oscillators driven by stimulated microwave currents,"We have simulated the non-linear dynamics of networks of spin-transfer
oscillators. The oscillators are magnetically uncoupled but electrically
connected in series. We use a modified Landau-Lifschitz- Gilbert equation to
describe the motion of each oscillator in the presence of the oscillations of
all the others. We show that the oscillators of the network can be synchronized
not only in frequency but also in phase. The coupling is due to the microwave
components of the current induced in each oscillator by the oscillations in all
the other oscillators. Our results show how the emitted microwave power of
spin-transfer oscillators can be considerably enhanced by current-induced
synchronization in an electrically connected network. We also discuss the
possible application of our synchronization mechanism to the interpretation of
the surprisingly narrow microwave spectrum in some isolated spin-transfer
oscillators.",0509326v2
2005-09-14,Critical exponents and the correlation length in the charge exchange manganite spin glass Eu_{0.5}Ba_{0.5}MnO_{3},"The critical regime of the charge exchange (CE) manganite spin glass
Eu_{0.5}Ba_{0.5}MnO_{3} is investigated using linear and non linear magnetic
susceptibility and the divergence of the third ordered susceptibility (chi{_3})
signifying the onset of a conventional freezing transition is experimentally
demonstrated. The divergence in chi{_3}, dynamical scaling of the linear
susceptibility and relevant scaling equations are used to determine the
critical exponents associated with this freezing transition, the values of
which match well with the 3D Ising universality class. Magnetic field
dependence of the spin glass response function is used to estimate the spin
correlation length which is seen to be larger than the charge/orbital
correlation length reported in this system.",0509360v1
2005-09-14,Vanishing spin-Hall current in a diffusive Rashba two-dimensional electron system: A quantum Boltzmann equation approach,"We present a quantum Boltzmann equation analysis of the spin-Hall effect in a
diffusive Rashba two-dimensional electron system. Within the framework of the
self-consistent Born approximation, we consider the roles of disorder-induced
quasiclassical relaxation, collisional broadening of the quasiparticles, and
the intracollisional field effect in regard to spin-Hall dynamics. We present
an analytical proof that the spin-Hall current vanishes, independently of the
coupling strength, of the quasiparticle broadening, of temperature and of the
specific form of the isotropic scattering potential. A sum relation of the
collision terms in a helicity basis is also examined.",0509365v2
2005-09-28,Spin-dynamics of the low-dimensional magnet (CH3)2NH2CuCl3,"Dimethylammonium copper (II) chloride (also known as DMACuCl3 or MCCL) is a
low dimensional S=1/2 quantum spin system proposed to be an alternating
ferro-antiferromagnetic chain with similar magnitude ferromagnetic (FM) and
antiferromagnetic (AFM) exchange interactions. Subsequently, it was shown that
the existing bulk measurements could be adequately modeled by considering
DMACuCl3 as independent AFM and FM dimer spin pairs. We present here new
inelastic neutron scattering measurements of the spin-excitations in single
crystals of DMACuCl3. These results show significant quasi-one-dimensional
coupling, however the magnetic excitations do not propagate along the expected
direction. We observe a band of excitations with a gap of 0.95 meV and a
bandwidth of 0.82 meV.",0509745v1
2005-10-07,Nuclear spin state narrowing via gate--controlled Rabi oscillations in a double quantum dot,"We study spin dynamics for two electrons confined to a double quantum dot
under the influence of an oscillating exchange interaction. This leads to
driven Rabi oscillations between the $\ket{\uparrow\downarrow}$--state and the
$\ket{\downarrow\uparrow}$--state of the two--electron system. The width of the
Rabi resonance is proportional to the amplitude of the oscillating exchange. A
measurement of the Rabi resonance allows one to narrow the distribution of
nuclear spin states and thereby to prolong the spin decoherence time. Further,
we study decoherence of the two-electron states due to the hyperfine
interaction and give requirements on the parameters of the system in order to
initialize in the $\ket{\uparrow\downarrow}$--state and to perform a
$\sqrt{\mathrm{SWAP}}$ operation with unit fidelity.",0510177v2
2005-10-07,NMR Evidence for Gapped Spin Excitations in Metallic Carbon Nanotubes,"We report on the spin dynamics of 13C isotope enriched inner-walls in
double-wall carbon nanotubes (DWCNT) using 13C nuclear magnetic resonance
(NMR). Contrary to expectations, we find that our data set implies that the
spin-lattice relaxation time (T1) has the same temperature (T) and magnetic
field (H) dependence for most of the innerwall nanotubes detected by NMR. In
the high temperature regime (T > 150 K), we find that the T and H dependence of
1/T1T is consistent with a 1D metallic chain. For T < 150 K, we find a
significant increase in 1/T1T with decreasing T, followed by a sharp drop below
20 K. The data clearly indicates the formation of a gap in the spin excitation
spectrum, where the gap value 2 Delta = 40 K (= 3.7 meV) is H independent.",0510195v1
2005-11-04,Magnetic excitations and phonons in the spin-chain compound NaCu2O2,"We report an inelastic light scattering study of single-crystalline
NaCu$_2$O$_2$, a spin-chain compound known to exhibit a phase with helical
magnetic order at low temperatures. Phonon excitations were studied as a
function of temperature and light polarization, and the phonon frequencies are
compared to the results of ab-initio lattice dynamical calculations, which are
also reported here. The good agreement between the observed and calculated
modes allows an assignment of the phonon eigenvectors. Two distinct high-energy
two-magnon features as well as a sharp low-energy one-magnon peak were also
observed. These features are discussed in terms of the magnon modes expected in
a helically ordered state. Their polarization dependence provides evidence of
substantial exchange interactions between two closely spaced spin chains within
a unit cell. At high temperatures, the spectral features attributable to
magnetic excitations are replaced by a broad, quasielastic mode due to
overdamped spin excitations.",0511116v1
2005-11-29,Coherent Interaction of Spins Induced by Thermal Bosonic Environment,"We obtain and analyze the indirect exchange interaction between two two-state
systems, e.g., spins, in a formulation that also incorporates the quantum noise
that they experience, due to a bosonic environment, for instance, phonons. We
utilize a perturbative approach to obtain a quantum evolution equation for the
two-spin dynamics. A non-perturbative approach is used to study the onset of
the induced interaction, which is calculated exactly. We predict that for low
enough temperatures the interaction is coherent over time scales sufficient to
create entanglement, dominated by the zero-point quantum fluctuations of the
environment. We identify the time scales for which the spins develop
entanglement for various spatial separations.",0511680v3
2006-01-06,Magnetic Excitations of Stripes Near a Quantum Critical Point,"We calculate the dynamical spin structure factor of spin waves for weakly
coupled stripes. At low energy, the spin wave cone intensity is strongly peaked
on the inner branches. As energy is increased, there is a saddlepoint followed
by a square-shaped continuum rotated 45 degree from the low energy peaks. This
is reminiscent of recent high energy neutron scattering data on the cuprates.
The similarity at high energy between this semiclassical treatment and quantum
fluctuations in spin ladders may be attributed to the proximity of a quantum
critical point with a small critical exponent $\eta$.",0601128v3
2006-01-17,Frequency-Dependent Current Noise through Quantum-Dot Spin Valves,"We study frequency-dependent current noise through a single-level quantum dot
connected to ferromagnetic leads with non-collinear magnetization. We propose
to use the frequency-dependent Fano factor as a tool to detect single-spin
dynamics in the quantum dot. Spin precession due to an external magnetic and/or
a many-body exchange field affects the Fano factor of the system in two ways.
First, the tendency towards spin-selective bunching of the transmitted
electrons is suppressed, which gives rise to a reduction of the low-frequency
noise. Second, the noise spectrum displays a resonance at the Larmor frequency,
whose lineshape depends on the relative angle of the leads' magnetizations.",0601366v1
2006-01-26,Spin dynamics characterization in magnetic dots,"The spin structure in a magnetic dot, which is an example of a quantum
few-body system, is studied as a function of exchange coupling strength and dot
size with in the semiclassical approximation on a discrete lattice. As the
exchange coupli ng is decreased or the size is increased, the ground state
undergoes a phase cha nge from a single domain ferromagnet to a spin vortex.
The line separating these two phases has been calculated numerically for small
system sizes. %, and analytically for larger dots. The dipolar interaction has
been fully included in our calculations. Magnon frequencies in such a dot have
also been calculated in both phases by the linearized equation of motion
method. These results have also been reproduced f rom the Fourier transform of
the spin autocorrelation function. From the magnon Density Of States (DOS), it
is possible to identify the magnetic phase of the dot. Furthermore, the magnon
modes have been characterized for both the ferromagnetic and the vortex phase,
and the magnon instability mechanism leading to the vortex-ferro transition has
also been identified. The results can also be used to compute finite
temperature magnetization or vort icity of magnetic dots.",0601624v1
2006-02-01,Screening properties of the two-dimensional electron gas with spin-orbit coupling,"We study screening properties of the two-dimensional electron gas with Rashba
spin-orbit coupling. Calculating the dielectric function within the random
phase approximation, we describe the new features of screening induced by
spin-orbit coupling, which are the extension of the region of particle-hole
excitations and the spin-orbit-induced suppression of collective modes. The
required polarization operator is calculated in an analytic form without any
approximations. Carefully deriving its static limit, we prove the absence of a
small-$q$ anomaly at zero frequency. On the basis of our results at finite
frequencies we establish the new boundaries of the particle-hole continuum and
calculate the SO-induced lifetime of collective modes such as plasmons and
longitudinal optical phonons. According to our estimates, these effects can be
resolved in inelastic Raman scattering. We evaluate the experimentally
measurable dynamic structure factor and establish the range of parameters where
the described phenomena are mostly pronounced.",0602029v2
2006-04-03,Precision measurement of spin-dependent interaction strengths for spin-1 and spin-2 87Rb atoms,"We report on precision measurements of spin-dependent interaction-strengths
in the 87Rb spin-1 and spin-2 hyperfine ground states. Our method is based on
the recent observation of coherence in the collisionally driven spin-dynamics
of ultracold atom pairs trapped in optical lattices. Analysis of the Rabi-type
oscillations between two spin states of an atom pair allows a direct
determination of the coupling parameters in the interaction hamiltonian. We
deduce differences in scattering lengths from our data that can directly be
compared to theoretical predictions in order to test interatomic potentials.
Our measurements agree with the predictions within 20%. The knowledge of these
coupling parameters allows one to determine the nature of the magnetic ground
state. Our data imply a ferromagnetic ground state for 87Rb in the f=1
manifold, in agreement with earlier experiments performed without the optical
lattice. For 87Rb in the f=2 manifold the data points towards an
antiferromagnetic ground state, however our error bars do not exclude a
possible cyclic phase.",0604038v1
2006-04-04,A General Theorem Relating the Bulk Topological Number to Edge States in Two-dimensional Insulators,"We prove a general theorem on the relation between the bulk topological
quantum number and the edge states in two dimensional insulators. It is shown
that whenever there is a topological order in bulk, characterized by a
non-vanishing Chern number, even if it is defined for a non-conserved quantity
such as spin in the case of the spin Hall effect, one can always infer the
existence of gapless edge states under certain twisted boundary conditions that
allow tunneling between edges. This relation is robust against disorder and
interactions, and it provides a unified topological classification of both the
quantum (charge) Hall effect and the quantum spin Hall effect. In addition, it
reconciles the apparent conflict between the stability of bulk topological
order and the instability of gapless edge states in systems with open
boundaries (as known happening in the spin Hall case). The consequences of time
reversal invariance for bulk topological order and edge state dynamics are
further studied in the present framework.",0604071v2
2006-04-19,High Energy Spin Excitations in Electron-Doped Superconducting Pr$_{0.88}$LaCe$_{0.12}$CuO$_{4-δ}$ with $T_c=21$ K,"We use high-resolution inelastic neutron scattering to study the
low-temperature magnetic excitations of electron-doped superconducting
Pr$_{0.88}$LaCe$_{0.12}$CuO$_{4-\delta}$ ($T_c=21\pm 1$ K) over a wide energy
range (4 meV$\le\hbar\omega\le 330$ meV). The effect of electron-doping is to
cause a wave vector ($Q$) broadening in the low-energy ($\hbar\omega\le 80$
meV) commensurate spin fluctuations at ($\pi$,$\pi$) and to suppress the
intensity of spin-wave-like excitations at high energies ($\hbar\omega\ge 100$
meV). This leads to a substantial redistribution in the spectrum of the local
dynamical spin susceptibility $\chi^{\prime\prime}(\omega)$, and reveals a new
energy scale similar to that of the lightly hole-doped YB$_2$Cu$_3$O$_{6.353}$
($T_c=18$ K).",0604449v1
2006-05-02,Boundary Green's Function for Spin-Incoherent Interacting Electrons in One Dimension,"The spin-incoherent regime of one-dimensional electrons has recently been
explored using the Bethe ansatz and a bosonized path integral approach,
revealing that the spin incoherence dramatically influences the correlations of
charge excitations. We here introduce a bosonization scheme for strongly
interacting electrons, allowing us to generalize the description to account for
the presence of an open boundary. By calculating the single-electron Green's
function we find that the charge sector power-law scaling is highly sensitive
to the boundary. Our result allows for a detailed description of the crossover
between boundary and bulk regimes. We predict that scanning tunneling
microscopy on a spin-incoherent system will pick up oscillations in the
differential tunneling conductance as a function of the applied voltage $V$ at
""intermediate"" distances $x$ from a real or a dynamically generated boundary.
The wavelength of the oscillations, $\pi v_c/x$, probes the speed $v_c$ of the
charge excitations, and therefore the strength of the electron-electron
interaction.",0605062v3
2006-05-10,Entanglement and Quantum Noise Due to a Thermal Bosonic Field,"We analyze the indirect exchange interaction between two two-state systems,
e.g., spins 1/2, subject to a common finite-temperature environment modeled by
bosonic modes. The environmental modes, e.g., phonons or cavity photons, are
also a source of quantum noise. We analyze the coherent vs noise-induced
features of the two-spin dynamics and predict that for low enough temperatures
the induced interaction is coherent over time scales sufficient to create
entanglement. A nonperturbative approach is utilized to obtain an exact
solution for the onset of the induced interaction, whereas for large times, a
Markovian scheme is used. We identify the time scales for which the spins
develop entanglement for various spatial separations. For large enough times,
the initially created entanglement is erased by quantum noise. Estimates for
the interaction and the level of quantum noise for localized impurity electron
spins in Si-Ge type semiconductors are given.",0605278v2
2006-06-19,"Giant current-driven domain wall mobility in (Ga,Mn)As","We study theoretically hole current-driven domain wall dynamics in (Ga,Mn)As.
We show that the spin-orbit coupling causes significant hole reflection at the
domain wall, even in the adiabatic limit when the wall is much thicker than the
Fermi wavelength, resulting in spin accumulation and mistracking between
current-carrying spins and the domain wall magnetization. This increases the
out-of-plane non-adiabatic spin transfer torque and consequently the
current-driven domain wall mobility by three to four orders of magnitude.
Trends and magnitude of the calculated domain wall current mobilities agree
with experimental findings.",0606498v3
2006-06-30,"Measurement, control, and decay of quantum-dot spins","In this review we discuss a recent proposal to perform partial Bell-state
(parity) measurements on two-electron spin states for electrons confined to
quantum dots. The realization of this proposal would allow for a physical
implementation of measurement-based quantum computing. In addition, we consider
the primary sources of energy relaxation and decoherence which provide the
ultimate limit to all proposals for quantum information processing using
electron spins in quantum dots. We give an account of the Hamiltonians used for
the most important interactions (spin-orbit and hyperfine) and survey some of
the recent work done to understand dynamics, control, and decoherence under the
action of these Hamiltonians. We conclude the review with a table of important
decay times found in experiment, and relate these time scales to the potential
viability of measurement-based quantum computing.",0606782v2
2006-07-26,Room temperature electron spin coherence in telecom-wavelength quaternary quantum wells,"Time-resolved Kerr rotation spectroscopy is used to monitor the room
temperature electron spin dynamics of optical telecommunication wavelength
AlInGaAs multiple quantum wells lattice-matched to InP. We found that electron
spin coherence times and effective g-factors vary as a function of aluminum
concentration. The measured electron spin coherence times of these multiple
quantum wells, with wavelengths ranging from 1.26 microns to 1.53 microns,
reach approximately 100 ps at room temperature, and the measured electron
effective g-factors are in the range from -2.3 to -1.1.",0607702v1
2006-09-07,Magnetic Ordering of CoCl_{2}-GIC: a Spin Ceramic -Hierarchical Successive Transitions and the Intermediate Glassy Phase-,"Stage-2 CoCl$_{2}$-GIC is a spin ceramic and shows hierarchical successive
transitions at $T_{cu}$ (= 8.9 K) and $T_{cl}$ (= 7.0 K) from the paramagnetic
phase into an intra-cluster (two-dimensional ferromagnetic) order with
inter-cluster disorder and then to an inter-cluster (three-dimensional
antiferromagnetic like) order over the whole system. The nature of the
inter-cluster disorder was suggested to be of spin glass by nonlinear magnetic
response analyses around $T_{cu}$ and by studies on dynamical aspects of
ordering between $T_{cu}$ and $T_{cl}$. Here, we present a further extensive
examination of a series of time dependence of zero-field cooled magnetization
$M_{ZFC}$ after the aging protocol below $T_{cu}$. The time dependence of the
relaxation rates $S_{ZFC}(t) = (1/H)dM_{ZFC}(t)/d\ln t$ dramatically changes
from the curves of simple spin glass aging effect below $T_{cl}$ to those of
two peaks above $T_{cl}$. The characteristic relaxation behavior apparently
indicates that there coexist two different kinds of glassy correlated regions
below $T_{cu}$.",0609174v1
2006-09-15,Nuclear Spin Switch in Semiconductor Quantum Dots,"We show that by illuminating an InGaAs/GaAs self-assembled quantum dot with
circularly polarized light, the nuclei of atoms constituting the dot can be
driven into a bistable regime, in which either a threshold-like enhancement or
reduction of the local nuclear field by up to 3 Tesla can be generated by
varying the intensity of light. The excitation power threshold for such a
nuclear spin ""switch"" is found to depend on both external magnetic and electric
fields. The switch is shown to arise from the strong feedback of the nuclear
spin polarization on the dynamics of spin transfer from electrons to the nuclei
of the dot.",0609371v1
2006-09-29,Integral and fractional Quantum Hall Ising ferromagnets,"We compare quantum Hall systems at filling factor 2 to those at filling
factors 2/3 and 2/5, corresponding to the exact filling of two lowest electron
or composite fermion (CF) Landau levels. The two fractional states are examples
of CF liquids with spin dynamics. There is a close analogy between the
ferromagnetic (spin polarization P=1) and paramagnetic (P=0) incompressible
ground states that occur in all three systems in the limits of large and small
Zeeman spin splitting. However, the excitation spectra are different. At
filling factor 2, we find spin domains at half-polarization (P=1/2), while
antiferromagnetic order seems most favorable in the CF systems. The transition
between P=0 and 1, as seen when e.g. the magnetic field is tilted, is also
studied by exact diagonalization in toroidal and spherical geometries. The
essential role of an effective CF-CF interaction is discussed, and the
experimentally observed incompresible half-polarized state is found in some
models.",0609756v1
2006-10-03,Effective Field and the Bloch-Siegert Shift at Bihromatic Excitation of Multiphoton EPR,"The dynamics of multiphoton transitions in a two-level spin system excited by
transverse microwave and longitudinal RF fields with the frequencies w_{mw} and
w_{rf}, respectively, is analyzed. The effective time-independent Hamiltonian
describing the ""dressed"" spin states of the ""spin + bichromatic field"" system
is obtained by using the Krylov-Bogoliubov-Mitropolsky averaging method. The
direct detection of the time behavior of the spin system by the method of
nonstationary nutations makes it possible to identify the multiphoton
transitions for resonances w_{0} = w_{mw} + rw_{rf} (w_{0} is the central
frequency of the EPR line, r = 1, 2), to measure the amplitudes of the
effective fields of these transitions, and to determine the features generated
by the inhomogeneous broadening of the EPR line. It is shown that the
Bloch-Siegert shifts for multiphoton resonances at the inhomogeneous broadening
of spectral lines reduce only the nutation amplitude but do not change their
frequencies.",0610063v1
2006-10-31,Spin-transfer torque in magnetic multilayer nanopillars,"We consider a quasi one-dimensional configuration consisting of two small
pieces of ferromagnetic material separated by a metallic one and contacted by
two metallic leads. A spin-polarized current is injected from one lead. Our
goal is to investigate the correlation induced between the magnetizations of
the two ferromagnets by spin-transfer torque. This torque results from the
interaction between the magnetizations and the spin polarization of the
current. We discuss the dynamics of a single ferromagnet, the extension to the
case of two ferromagnets, and give some estimates for the parameters based on
experiments.",0610878v1
2006-11-22,Magnetization damping in a local-density approximation,"The linear response of itinerant transition metal ferromagnets to transverse
magnetic fields is studied in a self-consistent adiabatic local-density
approximation. The susceptibility is calculated from a microscopic Hamiltonian,
including spin-conserving impurities, impurity induced spin-orbit interaction
and magnetic impurities using the Keldysh formalism. The Gilbert damping
constant in the Landau-Lifshitz-Gilbert equation is identified, parametrized by
an effective transverse spin dephasing rate, and is found to be inversely
proportional to the exchange splitting. Our result justify the phenomenological
treatment of transverse spin dephasing in the study of current-induced
magnetization dynamics in weak, itinerant ferromagnets by Tserkovnyak
\textit{et al.}. We show that neglect of gradient corrections in the
quasiclassical transport equations leads to incorrect results when the exchange
potential becomes of the order of the Fermi energy.",0611588v1
2007-01-09,Twenty years of magnon Bose condensation and spin current superfluidity in 3He-B,"20 years ago a new quantum state of matter was discovered and identified. The
observed dynamic quantum state of spin precession in superfluid 3He-B bears the
properties of spin current superfluidity, Bose condensation of spin waves --
magnons, off-diagonal long-range order and related phenomena of quantum
coherence",0701180v13
2007-02-01,Quantum Magnetism and Superconductivity,"The spin of the neutron allows neutron scattering to reveal the magnetic
structure and dynamics of materials over nanometre length scales and picosecond
timescales. Neutron scattering is particularly in demand in order to understand
high-temperature superconductors, which lie close to magnetically ordered
phases, and highly correlated metals with giant effective fermion masses, which
lie close to magnetic order or pass through a mysterious phase of hidden order
before becoming superconducting. Neutron scattering also is the probe of choice
for revealing new phases of matter and new particles, as seen in the surprising
behaviour of quantum spin chains and ladders where mass gaps and excited
triplons replace conventional spin waves. Examples are given of quantum
phenomena where neutron scattering has played a defining role that challenges
current understanding of condensed matter.",0702024v1
1997-09-21,Background Geometry in Gauge Gravitation Theory,"Dirac fermion fields are responsible for spontaneous symmetry breaking in
gauge gravitation theory because the spin structure associated with a tetrad
field is not preserved under general covariant transformations. Two solutions
of this problem can be suggested. (i) There exists the universal spin structure
$S\to X$ such that any spin structure $S^h\to X$ associated with a tetrad field
$h$ is a subbundle of the bundle $S\to X$. In this model, gravitational fields
correspond to different tetrad (or metric) fields. (ii) A background tetrad
field $h$ and the associated spin structure $S^h$ are fixed, while
gravitational fields are identified with additional tensor fields $q^\la{}_\m$
describing deviations $\wt h^\la_a=q^\la{}_\m h^\m_a$ of $h$. One can think of
$\wt h$ as being effective tetrad fields. We show that there exist gauge
transformations which keep the background tetrad field $h$ and act on the
effective fields by the general covariant transformation law. We come to
Logunov's Relativistic Theory of Gravity generalized to dynamic connections and
fermion fields.",9709054v1
2002-10-18,Implementing causality in the spin foam quantum geometry,"We analyse the classical and quantum geometry of the Barrett-Crane spin foam
model for four dimensional quantum gravity, explaining why it has to be
considering as a covariant realization of the projector operator onto physical
quantum gravity states. We discuss how causality requirements can be
consistently implemented in this framework, and construct causal transiton
amplitudes between quantum gravity states, i.e. realising in the spin foam
context the Feynman propagator between states. The resulting causal spin foam
model can be seen as a path integral quantization of Lorentzian first order
Regge calculus, and represents a link between several approaches to quantum
gravity as canonical loop quantum gravity, sum-over-histories formulations,
dynamical triangulations and causal sets. In particular, we show how the
resulting model can be rephrased within the framework of quantum causal sets
(or histories).",0210064v3
2005-09-02,Parametric derivation of the observable relativistic periastron advance for binary pulsars,"We compute the dimensionless relativistic periastron advance parameter $k$,
which is measurable from the timing of relativistic binary pulsars. We employ
for the computation the recently derived Keplerian-type parametric solution to
the post-Newtonian (PN) accurate conservative dynamics of spinning compact
binaries moving in eccentric orbits. The parametric solution and hence the
parameter $k$ are applicable for the cases of \emph{simple precession}, namely,
case (i), the binary consists of equal mass compact objects, having two
arbitrary spins, and case (ii), the binary consists of compact objects of
arbitrary mass, where only one of them is spinning with an arbitrary spin. Our
expression, for the cases considered, is in agreement with a more general
formula for the 2PN accurate $k$, relevant for the relativistic double pulsar
PSR J0737--3039, derived by Damour and Sch\""afer many years ago, using a
different procedure.",0509012v1
2006-02-06,Some partial solutions of Mathisson-Papapetrou equations in a Schwarzschild field,"The analytical and numerical solutions of the Mathisson-Papapetrou equations
under the Mathisson-Pirani supplementary condition describing highly
relativistic (ultrarelativistic) motions of a spinning particle in a
Schwarzschild field are investigated. The known condition S/mr<<1, which is
necessary for a test particle, holds on all these solutions. The explicit
expressions for the non-equatorial circular orbits, in particular for the space
boundaries of the region of existence of these orbits, are obtained. The
dynamics of the deviation of a spinning particle from the equatorial
ultrarelativistic circular orbit with r=3M caused by the non-zero initial value
of the radial particle's velocity is studied. It is shown in the concrete cases
that spin can considerable influence the shape of an ultrarelativistic
trajectory, as compared to the corresponding geodesic trajectory, for the short
time, less than the time of one or two revolutions of a spinning particle
around a Schwarzschild mass.",0602020v2
2006-03-20,The conformal factor in the parameter-free construction of spin-gauge variables for gravity,"The newly found conformal decomposition in canonical general relativity is
applied to drastically simplify the recently formulated parameter-free
construction of spin-gauge variables for gravity. The resulting framework
preserves many of the main structures of the existing canonical framework for
loop quantum gravity related to the spin network and Thiemann's regularization.
However, the Barbero-Immirzi parameter is now converted into the conformal
factor as a canonical variable. It behaves like a scalar field but is somehow
non-dynamical since the effective Hamiltonian constraint does not depend on its
momentum. The essential steps of the mathematical derivation of this
parameter-free framework for the spin-gauge variables of gravity are spelled
out. The implications for the loop quantum gravity programme are briefly
discussed.",0603077v1
2000-08-04,Spin Observables in Antilambda-Lambda Production from Antiproton-Proton Annihilation with a Transverse Inital State Polarization,"The formalism describing the scattering of two spin-1/2 objects is reviewed
for the case of antilambda-lambda production from antiproton-proton
annihilation. It is shown that an experiment utilizing a transverse target
polarization can, in principle, completely determine the spin structure of the
reaction. Additional measurements, even those using both beam and target
polarizations, would not be sensitive to any additional spin dynamics. Thus,
the transverse target polarization allows access to the complete set of spin
observables, not just the subset upon which the literature has previously
focused. This discussion is especially relevant in light of the data collected
by PS185/3 at LEAR.",0008008v1
2006-12-29,Transverse spin structure of the nucleon from lattice QCD simulations,"We present the first calculation in lattice QCD of the lowest two moments of
transverse spin densities of quarks in the nucleon. They encode correlations
between quark spin and orbital angular momentum. Our dynamical simulations are
based on two flavors of clover-improved Wilson fermions and Wilson gluons. We
find significant contributions from certain quark helicity flip generalized
parton distributions, leading to strongly distorted densities of transversely
polarized quarks in the nucleon. In particular, based on our results and recent
arguments by Burkardt [Phys. Rev. D 72 (2005) 094020], we predict that the
Boer-Mulders-function $h_1^\perp$, describing correlations of transverse quark
spin and intrinsic transverse momentum of quarks, is large and negative for
both up and down quarks.",0612032v1
1997-08-01,Proton-Proton Spin Correlations at Charm Threshold and Quarkonium Bound to Nuclei,"The anomalous behavior of the spin-spin correlation at large momentum
transfer in pp elastic scattering is described in terms of the degrees of
freedom associated with the onset of the charm threshold. A non-perturbative
analysis based on the symmetries of QCD is used to extract the relevant
dynamics of the charmonium-proton interaction. The enhancement to pp amplitudes
and their phase follow from analyticity and unitarity, giving a plausible
explanation of the spin anomaly. The interaction between charmonium and light
quarks in nuclei may form a distinct kind of nuclear matter, nuclear bound
quarkonium.",9708202v2
1999-08-12,Pseudo-spin of time-like lepton and the solar neutrino problem,"Based on the dual principle in super-luminous Lorentz transformation this
work shows that pseudo-spin of a time-like bradyon appears to space-like
observers as iso-spin of a corresponding tachyon. Due to the weak interaction,
lepton-tachyon appears as neutrino with hidden imaginary transcendent mass,
suppressed by a factor of $\rho\sim G_F m^2_0$ compared to the rest mass $m_0$
of a corresponding space-like lepton. Assuming a coexistance of tachyon dark
matter in the solar system, we show that the solar neutrino deficit might be
explained by depolarisation of time-like electrons due to elastic scattering in
time-like plasma and the maximal deficit would reach 0.5. Neither day-night nor
seasonal effects are expected due to dynamic balance of fluxes with opposite
pseudo-spin polarisation.",9908344v1
2001-02-27,Spin correlations and consequences of quantum-mechanical coherence,"The difference in the properties of the spin correlation tensor for
factorizable and nonfactorizable two-particle states is analyzed. The
inequalities for linear combinations of the components of this tensor are
obtained for the case of incoherent mixtures of factorizable two-particle spin
states. They include the well known Bell inequalities and can be violated for
coherent superpositions of two-particle spin states. The possibility to verify
the consequences of the quantum-mechanical coherence is discussed using the
angular correlations in the asymmetric (parity violating) decays of the pairs
of spin-1/2 particles (muons, top-quarks or lambda-hyperons), the coherence
arising either from the production dynamics or due to the effect of quantum
statistics.",0102333v1
2001-09-12,Nonrelativistic spin 1/2 particle in an arbitrary non-Abelian magnetic field in two spatial dimensions,"The (group and spin space) matrix Hamiltonian describing the dynamics of a
nonrelativistic spin 1/2 particle moving in a static, but spatially dependent,
non-Abelian magnetic field in two spatial dimensions is shown to take the form
of an anticommutator of a nilpotent operator and its hermitian conjugate.
Consequently, the (group space) matrix Hamiltonians for the two different spin
projections form partners of a supersymmetric quantum mechanical system. The
resulting supersymmetry algebra is exploited to explicitly construct the exact
zero energy ground state wavefunction(s) for the system. The remaining
eigenstates and eigenvalues of the two partner Hamiltonians form positive
energy degenerate pairs.",0109107v1
2003-08-15,Single-Spin Beam Asymmetry in Semi-Exclusive Deep-Inelastic Electroproduction,"Recent measurements from Jefferson Lab show significant beam single spin
asymmetries in deep inelastic scattering. The asymmetry is due to interference
of longitudinal and transverse photoabsorption amplitudes which have different
phases induced by the final-state interaction between the struck quark and the
target spectators. We developed a dynamical model for a single-spin beam
asymmetry in deep-inelastic scattering. Our results are consistent with the
experimentally observed magnitude of this effect. We conclude that similar
mechanisms involving quark orbital angular momentum (`Sivers effect') are
responsible for both target and beam single-spin asymmetries.",0308163v1
1994-03-29,A Field Theory Approach to the $t$-$J$ Model and the Spin-Charge Separation,"We analyze the $t$-$J$ model using the ${\rm CP}^1$ representation for the
slave operators (holons and spinons) which is particularly suited to study the
phenomenon of the spin-charge separation in strongly correlated electron
systems. In particular, we show that for the one-dimensional $t$-$J$ model
below half-filling the low energy effective dynamics of the spin and charge
degrees of freedom is represented in the continuum limit by a ${\rm CP}^1$
model with a topological term, minimally coupled to a massless Dirac field with
a four-fermion interaction. The bosonic term of this action describes the spin
waves produced by the spinons, while the fermionic term represents the low
energy charge excitations. This theory exhibits explicitly a local abelian
gauge invariance.",9403176v1
1996-03-26,A Universal Model of D=4 Spinning Particle,"A universal model for D=4 spinning particle is constructed with the
configuration space chosen as ${\bf R}^{3,1}\times S^2$, where the sphere
corresponds to the spinning degrees of freedom. The Lagrangian includes all the
possible world--line first order invariants of the manifold. Each combination
of the four constant parameters entering the Lagrangian gives the model, which
describes the proper irreducible Poincar\'e dynamics both at the classical and
quantum levels, and thereby the construction uniformly embodies the massive,
massless and continuous helicity cases depending upon the special choice of the
parameters. For the massive case, the connection with the Souriau approach to
elementary systems is established. Constrained Hamiltonian formulation is built
and Dirac canonical quantization is performed for the model in the covariant
form. An explicit realization is given for the physical wave functions in terms
of smooth tensor fields on ${\bf R}^{3,1}\times S^2$. One-parametric family of
consistent interactions with general electromagnetic and gravitational fields
is introduced in the massive case. The spin tensor is shown to satisfy the
Frenkel-Nyborg equation with arbitrary fixed gyromagnetic ratio in a limit of
weakly varying electromagnetic field.",9603174v1
2001-06-21,Cubic Interactions of Bosonic Higher Spin Gauge Fields in $AdS_5$,"The dynamics of totally symmetric free massless higher spin fields in $AdS_d$
is reformulated in terms of the compensator formalism for AdS gravity. The
$AdS_5$ higher spin algebra is identified with the star product algebra with
the $su(2,2)$ vector (i.e., $o(4,2)$ spinor) generating elements. Cubic
interactions of the totally symmetric bosonic higher spin gauge fields in
$AdS_5$, including the interaction with gravity, are formulated at the action
level.",0106200v4
2001-12-19,Inconsistencies of Massive Charged Gravitating Higher Spins,"We examine the causality and degrees of freedom (DoF) problems encountered by
charged, gravitating, massive higher spin fields. For spin s=3/2, making the
metric dynamical yields improved causality bounds. These involve only the mass,
the product eM_P of the charge and Planck mass and the cosmological constant
\Lambda. The bounds are themselves related to a gauge invariance of the
timelike component of the field equation at the onset of acausality. While
propagation is causal in arbitrary E/M backgrounds, the allowed mass ranges of
parameters are of Planck order. Generically, interacting spins s>3/2 are
subject to DoF violations as well as to acausality; the former must be overcome
before analysis of the latter can even begin. Here we review both difficulties
for charged s=2 and show that while a g-factor of 1/2 solves the DoF problem,
acausality persists for any g. Separately we establish that no s=2 theory --DoF
preserving or otherwise -- can be tree unitary.",0112182v1
2003-01-10,Higher Spins from Tensorial Charges and OSp(N|2n) Symmetry,"It is shown that the quantization of a superparticle propagating in an N=1,
D=4 superspace extended with tensorial coordinates results in an infinite tower
of massless spin states satisfying the Vasiliev unfolded equations for free
higher spin fields in flat and AdS_4 N=1 superspace. The tensorial extension of
the AdS_4 superspace is proved to be a supergroup manifold OSp(1|4). The model
is manifestly invariant under an OSp(N|8) (N=1,2) superconformal symmetry. As a
byproduct, we find that the Cartan forms of arbitrary Sp(2n) and OSp(1|2n)
groups are GL(2n) flat, i.e. they are equivalent to flat Cartan forms up to a
GL(2n) rotation. This property is crucial for carrying out the quantization of
the particle model on OSp(1|4) and getting the higher spin field dynamics in
super AdS_4, which can be performed in a way analogous to the flat case.",0301067v2
2003-08-07,Instability of Ultra-Spinning Black Holes,"It has long been known that, in higher-dimensional general relativity, there
are black hole solutions with an arbitrarily large angular momentum for a fixed
mass. We examine the geometry of the event horizon of such ultra-spinning black
holes and argue that these solutions become unstable at large enough rotation.
Hence we find that higher-dimensional general relativity imposes an effective
`Kerr-bound' on spinning black holes through a dynamical decay mechanism. Our
results also give indications of the existence of new stationary black holes
with `rippled' horizons of spherical topology. We consider various scenarios
for the possible decay of ultra-spinning black holes, and finally discuss the
implications of our results for black holes in braneworld scenarios.",0308056v2
2005-05-11,Gauge invariant Lagrangian construction for massive bosonic higher spin fields in D dimentions,"We develop the BRST approach to Lagrangian formulation for massive higher
integer spin fields on a flat space-time of arbitrary dimension. General
procedure of gauge invariant Lagrangian construction describing the dynamics of
massive bosonic field with any spin is given. No off-shell constraints on the
fields (like tracelessness) and the gauge parameters are imposed. The procedure
is based on construction of new representation for the closed algebra generated
by the constraints defining an irreducible massive bosonic representation of
the Poincare group. We also construct Lagrangian describing propagation of all
massive bosonic fields simultaneously. As an example of the general procedure,
we derive the Lagrangians for spin-1, spin-2 and spin-3 fields containing total
set of auxiliary fields and gauge symmetries of free massive bosonic higher
spin field theory.",0505092v3
2006-07-04,Multispin Giant Magnons,"We investigate giant magnons from classical rotating strings in two different
backgrounds. First we generalize the solution of Hofman and Maldacena and
investigate new magnon excitations of a spin chain which are dual to a string
on $R\times S^5$ with two non-vanishing angular momenta. Alowing string
dynamics along the third angle in the five sphere, we find a dispersion
relation that reproduces the Hofman and Maldacena and the one found by Dorey
for the two spin case. In the second part of the paper we generalize the two
""spin"" giant magnon to the case of $\b$-deformed $\axs$ background. We find
agreement between the dispersion relation of the rotating string and the
proposed dispersion relation of the magnon bound state on the spin chain.",0607018v3
2001-02-28,A spin-statistics theorem for quantum fields on curved spacetime manifolds in a generally covariant framework,"A model-independent, locally generally covariant formulation of quantum field
theory over four-dimensional, globally hyperbolic spacetimes will be given
which generalizes similar, previous approaches. Here, a generally covariant
quantum field theory is an assignment of quantum fields to globally hyperbolic
spacetimes with spin-structure where each quantum field propagates on the
spacetime to which it is assigned. Imposing very natural conditions such as
local general covariance, existence of a causal dynamical law, fixed spinor- or
tensor-type for all quantum fields of the theory, and that the quantum field on
Minkowski spacetime satisfies the usual conditions, it will be shown that a
spin-statistics theorem hols: If for some spacetimes the corresponding quantum
field obeys the ""wrong"" connection between spin and statistics, then all
quantum fields of the theory, on each spacetime, are trivial.",0102035v2
2002-05-29,Asymptotics and functional form of correlators in the XX - spin chain of finite length,"We verify the functional form of the asymptotics of the spin - spin equal -
time correlation function for the XX-chain, predicted by the hypothesis of
conformal invariance at large distances and by the bosonization procedure. We
point out that bosonization also predicts the functional form of the
correlators for the chains of finite length. We found the exact expression for
the spin- spin equal- time correlator on finite lattice. We find the excellent
agreement of the exact correlator with the prediction given by the leading
asymptotics result up to the very small distances. We also establish the
correspondence between the value of the constant before the asymptotics for the
XX- chain with the expression for this constant proposed by Lukyanov and
Zamolodchikov. We also evaluate the constant corresponding to the subleading
term in the asymptotics in a way which is different from the previous studies.",0205045v3
2002-05-15,"Quantum relativistic Toda chain at root of unity: isospectrality, modified Q-operator and functional Bethe ansatz","We investigate an N-state spin model called quantum relativistic Toda chain
and based on the unitary finite dimensional representations of the Weyl algebra
with q being N-th primitive root of unity. Parameters of the finite dimensional
representation of the local Weyl algebra form the classical discrete integrable
system. Nontrivial dynamics of the classical counterpart corresponds to
isospectral transformations of the spin system. Similarity operators are
constructed with the help of modified Baxter's Q-operators. The classical
counterpart of the modified Q-operator for the initial homogeneous spin chain
is a Baecklund transformation. This transformation creates an extra Hirota-type
soliton in a parameterization of the chain structure. Special choice of values
of solitonic amplitudes yields a degeneration of spin eigenstates, leading to
the quantum separation of variables, or the functional Bethe ansatz. A
projector to the separated eigenstates is constructed explicitly as a product
of modified Q-operators.",0205037v1
2005-04-25,Evaluation of excitation energy and spin from light charged particles multiplicities in heavy-ion collisions,"A simple procedure for evaluating the excitation energy and the spin transfer
in heavy-ion dissipative collisions is proposed. It is based on a prediction of
the GEMINI evaporation code : for a nucleus with a given excitation energy, the
average number of emitted protons decreases with increasing spin, whereas the
average number of alpha particles increases. Using that procedure for the
reaction 107Ag+58Ni at 52 MeV/nucleon, the excitation energy and spin of
quasi-projectiles have been evaluated. The results obtained in this way have
been compared with the predictions of a model describing the primary dynamic
stage of heavy-ion collisions.",0504025v1
2007-03-07,Spin distribution of nuclear levels using static path approximation with random-phase approximation,"We present a thermal and quantum-mechanical treatment of nuclear rotation
using the formalism of static path approximation (SPA) plus random-phase
approximation (RPA). Naive perturbation theory fails because of the presence of
zero-frequency modes due to dynamical symmetry breaking. Such modes lead to
infrared divergences. We show that composite zero-frequency excitations are
properly treated within the collective coordinate method. The resulting
perturbation theory is free from infrared divergences. Without the assumption
of individual random spin vectors, we derive microscopically the spin
distribution of the level density. The moment of inertia is thereby related to
the spin-cutoff parameter in the usual way. Explicit calculations are performed
for 56^Fe; various thermal properties are discussed. In particular, we
demonstrate that the increase of the moment of inertia with increasing
temperature is correlated with the suppression of pairing correlations.",0703016v1
1999-03-22,The Dirac Oscillator. A relativistic version of the Jaynes--Cummings model,"The dynamics of wave packets in a relativistic Dirac oscillator is compared
to that of the Jaynes-Cummings model. The strong spin-orbit coupling of the
Dirac oscillator produces the entanglement of the spin with the orbital motion
similar to what is observed in the model of quantum optics. The collapses and
revivals of the spin which result extend to a relativistic theory our previous
findings on nonrelativistic oscillator where they were known under the name of
`spin-orbit pendulum'. There are important relativistic effects (lack of
periodicity, zitterbewegung, negative energy states). Many of them disappear
after a Foldy-Wouthuysen transformation.",9903073v1
2005-08-24,Decoherence from spin environments,"We examine two exactly solvable models of decoherence -- a central
spin-system, (i) with and (ii) without a self--Hamiltonian, interacting with a
collection of environment spins. In the absence of a self--Hamiltonian we show
that in this model (introduced some time ago to illustrate environment--induced
superselection) generic assumptions about the coupling strengths can lead to a
universal (Gaussian) suppression of coherence between pointer states. On the
other hand, we show that when the dynamics of the central spin is dominant a
different regime emerges, which is characterized by a non--Gaussian decay and a
dramatically different set of pointer states. We explore the regimes of
validity of the Gaussian--decay and discuss its relation to the spectral
features of the environment and to the Loschmidt echo (or fidelity).",0508184v1
2005-09-01,Limits on entanglement in rotationally-invariant scattering of spin systems,"This paper investigates the dynamical generation of entanglement in
scattering systems, in particular two spin systems that interact via
rotationally-invariant scattering. The spin degrees of freedom of the in-states
are assumed to be in unentangled, pure states, as defined by the entropy of
entanglement. Because of the restriction of rotationally-symmetric
interactions, perfectly-entangling S-matrices, i.e. those that lead to a
maximally entangled out-state, only exist for a certain class of separable
in-states. Using Clebsch-Gordan coefficients for the rotation group, the
scattering phases that determine the S-matrix are determined for the case of
spin systems with $\sigma = 1/2$, 1, and 3/2.",0509013v3
2005-09-30,Macroscopic quantum information channel via the polarization-sensitive interaction between the light and spin subsystems,"We discuss the quantum information channel, which is based on coherent and
polarization sensitive interaction of light and atomic spin waves. We show that
the joint Heisenberg dynamics of the polarization Stokes components of light
and of the angular momenta of atoms has a wave nature and can be properly
described in terms of the macroscopic polariton-type spin wave created in the
sample. The principles of the quantum memory and readout protocols via the wave
coupling of the output time modes in the light subsystem and the output spatial
modes in the spin subsystem are demonstrated.",0509220v1
2006-11-28,Suppression of decoherence by bath ordering,"The dynamics of two coupled spins-1/2 coupled to a spin-bath is studied as an
extended model of the Tessieri-Wilkie Hamiltonian \cite{TWmodel}. The pair of
spins served as an open subsystem were prepared in one of the Bell states and
the bath consisted of some spins-1/2 is in a thermal equilibrium state from the
very beginning. It is found that with the increasing the coupling strength of
the bath spins, the bath forms a resonant antiferromagnetic order. The
polarization correlation between the two spins of the subsystem and the
concurrence are recovered in some extent to the isolated subsystem. This
suppression of the subsystem decoherence may be used to control the quantum
devices in practical applications.",0611267v1
2007-04-03,Shaped angular dependence of the spin transfer torque and microwave generation without magnetic field,"The generation of oscillations in the microwave frequency range is one of the
most important applications expected from spintronics devices exploiting the
spin transfer phenomenon. We report transport and microwave power measurements
on specially designed nanopillars for which a non-standard angular dependence
of the spin transfer torque (wavy variation) is predicted by theoretical
models. We observe a new kind of current-induced dynamics that is characterized
by large angle precessions in the absence of any applied field, as this is also
predicted by simulation with such a wavy angular dependence of the torque. This
type of non-standard nanopillars can represent an interesting way for the
implementation of spin transfer oscillators since they are able to generate
microwave oscillations without applied magnetic field. We also emphasize the
theoretical implications of our results on the angular dependence of the
torque.",0704.0370v1
2007-04-06,Spinor Dynamics in an Antiferromagnetic Spin-1 Condensate,"We observe coherent spin oscillations in an antiferromagnetic spin-1
Bose-Einstein condensate of sodium. The variation of the spin oscillations with
magnetic field shows a clear signature of nonlinearity, in agreement with
theory, which also predicts anharmonic oscillations near a critical magnetic
field. Measurements of the magnetic phase diagram agree with predictions made
in the approximation of a single spatial mode. The oscillation period yields
the best measurement to date of the sodium spin-dependent interaction
coefficient, determining that the difference between the sodium spin-dependent
s-wave scattering lengths $a_{f=2}-a_{f=0}$ is $2.47\pm0.27$ Bohr radii.",0704.0925v2
2007-05-08,Topological spin liquid on the hyper-kagome lattice of Na_4Ir_3O_8,"Recent experiments on the ""hyper-kagome"" lattice system Na$_4$Ir$_3$O$_8$
have demonstrated that it is a rare example of a three dimensional spin-1/2
frustrated antiferromagnet. We investigate the role of quantum fluctuations as
the primary mechanism lifting the macroscopic degeneracy inherited by classical
spins on this lattice. In the semi-classical limit we predict, based on large-N
calculations, that an unusual $\vec q=0$ coplaner magnetically ordered ground
state is stabilized with no local ""weather vane"" modes. This phase melts in the
quantum limit and a gapped topological Z$_2$ spin liquid phase emerges. In the
vicinity of this quantum phase transition, we study the dynamic spin structure
factor and comment on the relevance of our results for future neutron
scattering experiments.",0705.0990v3
2007-05-24,Electrical coherent control of nuclear spins in a breakdown regime of quantum Hall effect,"Using a conventional Hall-bar geometry with a micro-metal strip on top of the
surface, we demonstrate an electrical coherent control of nuclear spins in an
AlGaAs/GaAs semiconductor heterostructure. A breakdown of integer quantum Hall
(QH) effect is utilized to dynamically polarize nuclear spins. By applying a
pulse rf magnetic field with the metal strip, the quantum state of the nuclear
spins shows Rabi oscillations, which is detected by measuring longitudinal
voltage of the QH conductor.",0705.3547v3
2007-06-20,Matching Kasteleyn Cities for Spin Glass Ground States,"As spin glass materials have extremely slow dynamics, devious numerical
methods are needed to study low-temperature states. A simple and fast
optimization version of the classical Kasteleyn treatment of the Ising model is
described and applied to two-dimensional Ising spin glasses. The algorithm
combines the Pfaffian and matching approaches to directly strip droplet
excitations from an excited state. Extended ground states in Ising spin glasses
on a torus, which are optimized over all boundary conditions, are used to
compute precise values for ground state energy densities.",0706.2866v4
2007-07-13,Network of inherent structures in spin glasses: scaling and scale-free distributions,"The local minima (inherent structures) of a system and their associated
transition links give rise to a network. Here we consider the topological and
distance properties of such a network in the context of spin glasses. We use
steepest descent dynamics, determining for each disorder sample the transition
links appearing within a given barrier height. We find that differences between
linked inherent structures are typically associated with local clusters of
spins; we interpret this within a framework based on droplets in which the
characteristic ``length scale'' grows with the barrier height. We also consider
the network connectivity and the degrees of its nodes. Interestingly, for spin
glasses based on random graphs, the degree distribution of the network of
inherent structures exhibits a non-trivial scale-free tail.",0707.1965v2
2007-07-16,Semiclassical Approach to Parametric Spectral Correlation with Spin 1/2,"The spectral correlation of a chaotic system with spin 1/2 is universally
described by the GSE (Gaussian Symplectic Ensemble) of random matrices in the
semiclassical limit. In semiclassical theory, the spectral form factor is
expressed in terms of the periodic orbits and the spin state is simulated by
the uniform distribution on a sphere. In this paper, instead of the uniform
distribution, we introduce Brownian motion on a sphere to yield the parametric
motion of the energy levels. As a result, the small time expansion of the form
factor is obtained and found to be in agreement with the prediction of
parametric random matrices in the transition within the GSE universality class.
Moreover, by starting the Brownian motion from a point distribution on the
sphere, we gradually increase the effect of the spin and calculate the form
factor describing the transition from the GOE (Gaussian Orthogonal Ensemble)
class to the GSE class.",0707.2276v1
2007-09-23,Quantum dynamics and entanglement of spins on a square lattice,"Bulk magnetism in solids is fundamentally quantum mechanical in nature. Yet
in many situations, including our everyday encounters with magnetic materials,
quantum effects are masked, and it often suffices to think of magnetism in
terms of the interaction between classical dipole moments. Whereas this
intuition generally holds for ferromagnets, even as the size of the magnetic
moment is reduced to that of a single electron spin (the quantum limit), it
breaks down spectacularly for antiferromagnets, particularly in low dimensions.
Considerable theoretical and experimental progress has been made in
understanding quantum effects in one-dimensional quantum antiferromagnets, but
a complete experimental description of even simple two-dimensional
antiferromagnets is lacking. Here we describe a comprehensive set of neutron
scattering measurements that reveal a non-spin-wave continuum and strong
quantum effects, suggesting entanglement of spins at short distances in the
simplest of all two-dimensional quantum antiferromagnets, the square lattice
Heisenberg system.",0709.3632v1
2007-10-04,Spin Meissner Effect in Superconductors and the Origin of the Meissner Effect,"We propose a dynamical explanation of the Meissner effect in superconductors
and predict the existence of a spin Meissner effect: that a macroscopic spin
current flows within a London penetration depth $\lambda_L$ of the surface of
superconductors in the absence of applied external fields, with carrier density
= the superfluid density and carrier speed $v=\hbar/(4m_e\lambda_L$)
($m_e=$bare electron mass). The two members of a Cooper pair circulate in
orbits of radius $2\lambda_L$ in opposite direction and the spin current in a
Cooper pair has orbital angular momentum $\hbar$. Our description also provides
a 'geometric' interpretation of the difference between type I and type II
superconductors.",0710.0876v2
2007-10-09,Long wavelength spin dynamics of ferromagnetic condensates,"We obtain the equations of motion for a ferromagnetic Bose condensate of
arbitrary spin in the long wavelength limit. We find that the magnetization of
the condensate is described by a non-trivial modification of the
Landau-Lifshitz equation, in which the magnetization is advected by the
superfluid velocity. This hydrodynamic description, valid when the condensate
wavefunction varies on scales much longer than either the density or spin
healing lengths, is physically more transparent than the corresponding
time-dependent Gross-Pitaevskii equation. We discuss the conservation laws of
the theory and its application to the analysis of the stability of magnetic
helices and Larmor precession. Precessional instabilities in particular provide
a novel physical signature of dipolar forces. Finally, we discuss the
anisotropic spin wave instability observed in the recent experiment of
Vengalattore et. al. (Phys. Rev. Lett. 100, 170403, (2008)).",0710.1848v2
2007-11-14,$Σ$-nuclear spin-orbit coupling from two-pion exchange,"Using SU(3) chiral perturbation theory we calculate the density-dependent
complex-valued spin-orbit coupling strength $U_{\Sigma ls}(k_f)+ i W_{\Sigma
ls}(k_f)$ of a $\Sigma$ hyperon in the nuclear medium. The leading long-range
$\Sigma N$ interaction arises from iterated one-pion exchange with a $\Lambda$
or a $\Sigma$ hyperon in the intermediate state. We find from this unique
long-range dynamics a sizeable ``wrong-sign'' spin-orbit coupling strength of
$U_{\Sigma ls}(k_{f0}) \simeq -20$ MeVfm$^2$ at normal nuclear matter density
$\rho_0 = 0.16 $fm$^{-3}$. The strong $\Sigma N\to \Lambda N$ conversion
process contributes at the same time an imaginary part of $W_{\Sigma
ls}(k_{f0}) \simeq -12$ MeVfm$^2$. When combined with estimates of the
short-range contribution the total $\Sigma$-nuclear spin-orbit coupling becomes
rather weak.",0711.2237v1
2007-11-15,Finite-temperature lineshapes in gapped quantum spin chains,"We consider the finite-temperature dynamical structure factor (DSF) of gapped
quantum spin chains such as the spin one Heisenberg model and the transverse
field Ising model in the disordered phase. At zero temperature the DSF in these
models is dominated by a delta-function line arising from the coherent
propagation of single particle modes. Using methods of integrable quantum field
theory we determine the evolution of the lineshape at low temperatures. We show
that the line shape is in general asymmetric in energy and becomes Lorentzian
only at temperatures far below the gap. We discuss the relevance of our results
for the analysis of inelastic neutron scattering experiments on gapped spin
chain systems such as CsNiCl_3 and YBaNiO_5.",0711.2524v2
2007-12-20,Cubic interaction vertices for fermionic and bosonic arbitrary spin fields,"Using the light-cone gauge approach to relativistic field dynamics, we study
arbitrary spin fermionic and bosonic fields propagating in flat space of
dimension greater than or equal to four. Generating functions of parity
invariant cubic interaction vertices for totally symmetric and mixed-symmetry
massive and massless fields are obtained. For the case of totally symmetric
fields, we derive restrictions on the allowed values of spins and the number of
derivatives. These restrictions provide a complete classification of parity
invariant cubic interaction vertices for totally symmetric fermionic and
bosonic fields. As an example of application of the light-cone formalism, we
obtain simple expressions for the Yang-Mills and gravitational interactions of
massive arbitrary spin fermionic fields. For some particular cases, using our
light-cone cubic vertices, we discuss the corresponding manifestly Lorentz
invariant and on-shell gauge invariant cubic vertices.",0712.3526v2
2008-01-03,Exact Haldane mapping for all $S$ and super universality in spin chains,"The low energy dynamics of the anti-ferromagnetic Heisenberg spin $S$ chain
in the semiclassical limit $S\to\infty$ is known to map onto the O(3) nonlinear
$\sigma$ model with a $\theta$ term in 1+1 dimension. Guided by the underlying
dual symmetry of the spin chain, as well as the recently established
topological significance of ""dangling edge spins,"" we report an {\em exact}
mapping onto the O(3) model that avoids the conventional large $S$
approximation altogether. Our new methodology demonstrates all the super
universal features of the $\theta$ angle concept that previously arose in the
theory of the quantum Hall effect. It explains why Haldane's original ideas
remarkably yield the correct answer in spite of the fundamental complications
that generally exist in the idea of semiclassical expansions.",0801.0511v1
2008-01-30,Time-Resolved X-ray Microscopy of Spin-Torque-Induced Magnetic Vortex Gyration,"Time-resolved X-ray microscopy is used to image the influence of alternating
high-density currents on the magnetization dynamics of ferromagnetic vortices.
Spin-torque induced vortex gyration is observed in micrometer-sized permalloy
squares. The phases of the gyration in structures with different chirality are
compared to an analytical model and micromagnetic simulations, considering both
alternating spinpolarized currents and the current's Oersted field. In our case
the driving force due to spin-transfer torque is about 70% of the total
excitation while the remainder originates from the current's Oersted field.
This finding has implications to magnetic storage devices using spin-torque
driven magnetization switching and domain-wall motion.",0801.4719v1
2008-02-04,Reproducing spin lattice models in strongly coupled atom-cavity systems,"In an array of coupled cavities where the cavities are doped with an atomic
V-system, and the two excited levels couple to cavity photons of different
polarizations, we show how to construct various spin models employed in
characterizing phenomena in condensed matter physics, such as the spin-1/2
Ising, XX, Heisenberg, and XXZ models. The ability to construct networks of
arbitrary geometry also allows for the simulation of topological effects. By
tuning the number of excitations present, the dimension of the spin to be
simulated can be controlled, and mixtures of different spin types produced. The
facility of single-site addressing, the use of only the natural hopping photon
dynamics without external fields, and the recent experimental advances towards
strong coupling, makes the prospect of using these arrays as efficient quantum
simulators promising.",0802.0488v4
2008-02-12,Controlling soliton excitations in Heisenberg spin chain through magic angle,"We study the nonlinear dynamics of collective excitation in a $N$-site $XXZ$
quantum spin chain, which is manipulated by an oblique magnetic field. We show
that, when the tilted field is applied along the magic angle $\theta_{0}
=\pm\arccos \sqrt{1/3}$, the anisotropic Heisenberg spin chain becomes
isotropic and thus an free propagating spin wave is stimulated. And in the
regime of the tilted angle larger and smaller then the magic angle, two types
of nonlinear excitations appear, which are bright soliton and dark soliton.",0802.1610v4
2008-03-14,Magnetoresistance and spin-transfer torque in magnetic tunnel junctions,"We comment on both recent progress and lingering puzzles related to research
on magnetic tunnel junctions (MTJs). MTJs are already being used in
applications such as magnetic-field sensors in the read heads of disk drives,
and they may also be the first device geometry in which spin-torque effects are
applied to manipulate magnetic dynamics, in order to make nonvolatile magnetic
random access memory. However, there remain many unanswered questions about
such basic properties as the magnetoresistance of MTJs, how their properties
change as a function of tunnel-barrier thickness and applied bias, and what are
the magnitude and direction of the spin-transfer-torque vector induced by a
tunnel current.",0803.2254v1
2008-04-04,Modification of the thermal spin-wave spectrum in a Ni81Fe19 stripe by a domain wall,"The thermal spin-wave distribution in a Ni81Fe19 stripe with an asymmetric
transverse domain wall has been investigated using Brillouin light scattering
microscopy. Clear evidence has been found that the existence of the domain wall
influences the spin-wave distribution of the thermal modes. The thermal
spin-wave modes are quantized due to the confinement in radial direction. They
vanish near the domain wall and a new mode evolves inside this complex domain
wall structure. This effect is attributed to a change of the effective internal
field in the domain wall region. The experimental results agree well with
static and dynamic micromagnetic simulations.",0804.0734v2
2008-04-09,High-temperature spin relaxation process in Dy$_2$Ti$_2$O$_7$ probed by $^{47}$Ti-NQR,"We have performed nuclear quadrupole resonance (NQR) experiments on $^{47}$Ti
nuclei in Dy$_2$Ti$_2$O$_7$ in the temperature range 70 -- 300 K in order to
investigate the dynamics of $4f$ electrons with strong Ising anisotropy. A
significant change of the NQR frequency with temperature was attributed to the
variation of the quadrupole moment of Dy $4f$ electrons. A quantitative account
was given by the mean field analysis of the quadrupole-quadrupole (Q-Q)
interaction in the presence of the crystalline-electric-field splitting. The
magnitude and the temperature dependence of the nuclear spin-lattice relaxation
rate was analyzed, including both the spin-spin and the Q-Q interactions. The
results indicate that these two types of interaction contribute almost equally
to the fluctuation of Dy magnetic moments.",0804.1413v2
2008-04-17,Effect of electron-electron scattering on spin dephasing in a high-mobility low-density twodimensional electron gas,"Utilizing time-resolved Kerr rotation techniques, we have investigated the
spin dynamics of a high mobility, low density two dimensional electron gas in a
GaAs/Al0:35Ga0:65As heterostructure in dependence on temperature from 1.5 K to
30 K. It is found that the spin relaxation/dephasing time under a magnetic
field of 0.5 T exhibits a maximum of 3.12 ns around 14 K, superimposed on an
increasing background with rising temperature. The appearance of the maximum is
ascribed to that at the temperature where the crossover from the degenerate to
the nondegenerate regime takes place, electron-electron Coulomb scattering
becomes strongest, and thus inhomogeneous precession broadening due to
D'yakonov-Perel'(DP) mechanism becomes weakest. These results agree with the
recent theoretical predictions [Zhou et al., PRB 75, 045305 (2007)], verifying
the importance of electron-electron Coulomb scattering to electron spin
relaxation/dephasing.",0804.2840v1
2008-04-18,Hidden quantum spin gap state in the static stripe phase of La$_{2-x}$Sr$_{x}$CuO$_{4}$,"Low energy spin excitations were investigated in the static stripe phase of
La_{2-x}Sr_xCuO_4 using elastic and inelastic neutron scattering on single
crystals. For x = 1/8 in which long-range static stripe order exists, an energy
gap of E_g = 4 meV exists in the excitation spectrum in addition to strong
quasi-elastic, incommensurate spin fluctuations associated with the static
stripes. When x increases, the spectral weight of the spin fluctuations shifts
from the quasi-elastic continuum to the excitation spectrum above E_g. The
dynamic correlation length as a function of energy and the temperature
evolution of the energy spectrum suggest a phase separation of two distinct
magnetic phases in real space.",0804.3041v3
2008-05-13,Universal Long-time Behavior of Nuclear Spin Decays in a Solid,"Magnetic resonance studies of nuclear spins in solids are exceptionally well
suited to probe the limits of statistical physics. We report experimental
results indicating that isolated macroscopic systems of interacting nuclear
spins possess the following fundamental property: spin decays that start from
different initial configurations quickly evolve towards the same long-time
behavior. This long-time behavior is characterized by the shortest ballistic
microscopic timescale of the system and therefore falls outside of the validity
range for conventional approximations of statistical physics. We find that the
nuclear free induction decay and different solid echoes in hyperpolarized solid
xenon all exhibit sinusoidally modulated exponential long-time behavior
characterized by identical time constants. This universality was previously
predicted on the basis of analogy with resonances in classical chaotic systems.",0805.1751v1
2008-06-05,State Tomography of a Chain of Qubits Embedded in a Spin Field-Effect Transistor via Repeated Spin-Blockade Measurements on the Edge Qubit,"As a possible physical realization of a quantum information processor, a
system with stacked self-assembled InAs quantum dots buried in GaAs in adjacent
to the channel of a spin field-effect transistor has been proposed. In this
system, only one of the stacked qubits, i.e. the edge qubit (the qubit closest
to the channel), is measurable via ""spin-blockade measurement."" It is shown
that the state tomography of the whole chain of the qubits is still possible
even under such a restricted accessibility. The idea is to make use of the
entangling dynamics of the qubits. A recipe for the two-qubit system is
explicitly constructed and the effect of an imperfect fidelity of the
measurement is clarified. A general scheme for multiple qubits based on
repeated measurements is also presented.",0806.1032v2
2008-06-18,Selective Heating Mechanism of Magnetic Metal Oxides by Alternating Magnetic Field in Microwave Sintering Process,"The mechanism of rapid and selective heating of magnetic metal oxides under
the magnetic field of microwaves which continues beyond the Curie temperature $
T_{c} $ is identified by using the Heisenberg model. Monte Carlo calculations
based on the energy principle show that such heating is caused by non-resonant
response of electron spins in the unfilled 3d shell to the wave magnetic field.
Small spin reorientation thus generated leads to a large internal energy change
through the exchange interactions between spins, which becomes maximal around $
T_{c} $ for magnetite $ {\rm Fe}_{3}{\rm O}_{4} $. The dissipative spin
dynamics simulation yields the imaginary part of the magnetic susceptibility,
which becomes largest around $ T_{c} $ and for the microwave frequency around 2
GHz. Hematite $ {\rm Fe}_{2}{\rm O}_{3} $ with weak spontaneous magnetization
responds much less to microwaves as observed in experiments. The heating of
titanium oxide by microwave magnetic field only when oxygen defects are present
is also explained by our theory in terms of the absence of spontaneous
magnetization.",0806.3055v3
2008-06-27,Observation of Spin Fluctuations in a High-Tc Parent Compound Using Resonant Inelastic X-ray Scattering,"We report the first observation of soft-x-ray scattering from spin
fluctuations in a high-Tc parent compound. An antiferromagnetic charge transfer
insulator, CaCuO2, was irradiated by Cu M-edge soft x-rays. Ultra-high
resolution measurements of scattered intensity revealed magnon-magnon
excitations, due to spin exchange scattering, as low-energy loss features. The
process is analogous to optical Raman scattering. The spectra provide the first
measurement of the two-magnon excitation energy and the antiferromagnetic
exchange parameter in infinite-layer CaCuO2. The results reveal resonant
inelastic soft x-ray scattering as a novel probe of the spin dynamics in
cuprates.",0806.4432v1
2008-09-03,Dynamics and transport of the Z_2 spin liquid: application to kappa-(ET)2Cu2(CN)3,"We describe neutron scattering, NMR relaxation, and thermal transport
properties of Z_2 spin liquids in two dimensions. Comparison to recent
experiments on the spin S=1/2 triangular lattice antiferromagnet in
kappa-(ET)2Cu2(CN)3 shows that this compound may realize a Z_2 spin liquid. We
argue that the topological `vison' excitations dominate thermal transport, and
that recent thermal conductivity experiments by M. Yamashita et al. have
observed the vison gap.",0809.0694v4
2008-09-16,Derivation of Green's Function of Spin Calogero-Sutherland Model by Uglov's Method,"Hole propagator of spin 1/2 Calogero-Sutherland model is derived using
Uglov's method, which maps the exact eigenfunctions of the model, called
Yangian Gelfand-Zetlin basis, to a limit of Macdonald polynomials (gl_2-Jack
polynomials). To apply this mapping method to the calculation of 1-particle
Green's function, we confirm that the sum of the field annihilation operator on
Yangian Gelfand-Zetlin basis is transformed to the field annihilation operator
on gl_2-Jack polynomials by the mapping. The resultant expression for hole
propagator for finite-size system is written in terms of renormalized momenta
and spin of quasi-holes and the expression in the thermodynamic limit coincides
with the earlier result derived by another method. We also discuss the
singularity of the spectral function for a specific coupling parameter where
the hole propagator of spin Calogero-Sutherland model becomes equivalent to
dynamical colour correlation function of SU(3) Haldane-Shastry model.",0809.2673v1
2008-10-14,Coherent spin rotation in the presence of a phonon-bottleneck effect,"A characteristic of spin reversal in the presence of phonon-bottleneck is the
deviation of the magnetization cycle from a reversible function into an opened
hysterezis cycle. In recent experiments on molecular magnets (e.g. V$_{15}$ and
Ru$_2$), the zero-field level repulsion was sufficiently large to ensure an
otherwise adiabatic passage through zero-field and the magnetization curves can
be described by using only a phonon-bottleneck model. Here, we generalize the
phonon-bottleneck model into a model able to blend the non-adiabatic dynamics
of spins with the presence of a non-equilibrium phonon bath. In this simple
phenomenological model, Bloch equations are written in the eigenbasis of the
effective spin Hamiltonian, considered to be a two-level system at low
temperatures. The relaxation term is given by the phonon-bottleneck mechanism.
To the expense of calculus time, the method can be generalized to multi-level
systems, where the notion of Bloch sphere does not apply but the density matrix
formalism is still applicable.",0810.2502v4
2008-10-27,Density and spin response function of a normal Fermi gas at unitarity,"Using Landau theory of Fermi liquids we calculate the dynamic response of
both a polarized and unpolarized normal Fermi gas at zero temperature in the
strongly interacting regime of large scattering length. We show that at small
excitation energies the {\it in phase} (density) response is enhanced with
respect to the ideal gas prediction due to the increased compressibility.
Viceversa, the {\it out of phase} (spin) response is quenched as a consequence
of the tendency of the system to pair opposite spins. The long wavelength
behavior of the static structure factor is explicitly calculated. The results
are compared with the predictions in the collisional and superfluid regimes.
The emergence of a spin zero sound solution in the unpolarized normal phase is
explicitly discussed.",0810.4880v1
2008-12-08,Vortex splitting and phase separating instabilities of coreless vortices in F=1 spinor Bose-Einstein condensates,"The low lying excitations of coreless vortex states in F = 1 spinor
Bose-Einstein condensates (BECs) are theoretically investigated using the
Gross-Pitaevskii and Bogoliubov-de Gennes equations. The spectra of the
elementary excitations are calculated for different spin-spin interaction
parameters and ratios of the number of particles in each sublevel. There exist
dynamical instabilities of the vortex state which are suppressed by
ferromagnetic interactions, and conversely, enhanced by antiferromagnetic
interactions. In both of the spin-spin interaction regimes, we find vortex
splitting instabilities in analogy with scalar BECs. In addition, a phase
separating instability is found in the antiferromagnetic regime.",0812.1439v1
2008-12-16,Stationary and transient leakage current in the Pauli spin blockade,"We study the effects of cotunneling and a non-uniform Zeeman splitting on the
stationary and transient leakage current through a double quantum dot in the
Pauli spin blockade regime. We find that the stationary current due to
cotunneling vanishes at low temperature and large applied magnetic field,
allowing for the dynamical preparation of a pure spin ground state, even at
large voltage bias. Additionally, we analyze current that flows between
blocking events, characterized, in general, by a fractional effective charge
$e^*$. This charge can be used as a sensitive probe of spin relaxation
mechanisms and can be used to determine the visibility of Rabi oscillations.",0812.2957v2
2008-12-21,Suppression of antiferromagnetic spin fluctuations in the collapsed tetragonal phase of CaFe2As2,"Inelastic neutron scattering measurements of CaFe2As2 under applied
hydrostatic pressure show that the antiferromagnetic spin fluctuations observed
in the ambient pressure, paramagnetic, tetragonal (T) phase are strongly
suppressed, if not absent, in the collapsed tetragonal (cT) phase. These
results are consistent with a quenched Fe moment in the cT phase and the strong
decrease in resistivity observed upon crossing the boundary from the T to cT
phase. The suppression or absence of static antiferromagnetic order and dynamic
spin fluctuations in the non-superconducting cT phase supports the notion of a
coupling between spin fluctuations and superconductivity in the iron arsenides.",0812.4056v1
2008-12-26,Test membranes in Riemann-Cartan spacetimes,"The dynamics of brane-like extended objects in spacetimes with torsion is
derived from the conservation equations of stress-energy and spin tensors. Thus
obtained world-sheet equations are applied to macroscopic test membranes made
of spinning matter. Specifically, we consider membranes with maximally
symmetric distribution of stress-energy and spin. These are characterized by
two constants only: the tension and spin magnitude. By solving the world-sheet
equations, we discover a similarity between such membranes in Riemann-Cartan
backgrounds, and string theory membranes in low-energy string backgrounds. In
the second part of the paper, we apply this result to cylindrical membranes
wrapped around the extra compact dimension of a $(D+1)$-dimensional spacetime.
In the narrow membrane limit, we discover how effective macroscopic strings
couple to torsion. An observed similarity with the string sigma model is noted.",0812.4694v2
2009-01-15,Suppression of nuclear spin diffusion at a GaAs/AlGaAs interface measured with a single quantum dot nano-probe,"Nuclear spin polarization dynamics are measured in optically pumped
individual GaAs/AlGaAs interface quantum dots by detecting the time-dependence
of the Overhauser shift in photoluminescence (PL) spectra. Long nuclear
polarization decay times of ~ 1 minute have been found indicating inefficient
nuclear spin diffusion from the GaAs dot into the surrounding AlGaAs matrix in
externally applied magnetic field. A spin diffusion coefficient two orders
lower than that previously found in bulk GaAs is deduced.",0901.2281v1
2009-03-04,"Vitrification, relaxation and free volume in glycerol-water binary liquid mixture: Spin probe ESR studies","Glass transition and relaxation of the glycerol-water binary mixture system
are studied over the glycerol concentration range of 5 - 85 mol% using the
highly sensitive technique of spin probe ESR. For the water rich mixture the
glass transition, sensed by the spin probe, arises from the vitrified
mesoscopic portion of the binary system. The concentration dependence of the
glass transition temperature manifests a closely related molecular level
cooperativity in the system. A drastic change in the mesoscopic structure of
the system at the critical concentration of 40 mol% is confirmed by an
estimation of the spin probe effective volume in a temperature range where the
tracer reorientation is strongly coupled to the system dynamics.",0903.0828v2
2009-06-13,Degradation of superconductivity and spin fluctuations by electron over-doping in LaFeAsO$_{1-x}$F$_{x}$,"Low energy spin fluctuations are studied for the electron-doped Fe-based
superconductor LaFeAsO(1-x)F(x) by inelastic neutron scattering up to the
energy transfer of w = 15 meV using polycrystalline samples. Superconducting
samples (x=0.057, Tc=25 K and x=0.082, Tc=29 K) show dynamical spin
susceptibility chi""(w) almost comparable with the parent sample's. However
chi""(w) is almost vanished in the x=0.158 sample where the superconductivity is
highly suppressed. These results are compatible with the theoretical
suggestions that the spin fluctuation plays an important role for the
superconductivity.",0906.2453v3
2009-06-18,Spin-charge interplay in electronic liquid crystals: fluctuating spin stripe driven by charge nematic,"We study the interplay between charge and spin ordering in electronic liquid
crystalline states with a particular emphasis on fluctuating spin stripe
phenomena observed in recent neutron scattering experiments\cite{Hinkov2008,
Haug2009}. Based on a phenomenological model, we propose that charge nematic
ordering is indeed behind the formation of temperature dependent incommensurate
inelastic peaks near wavevector $(\pi,\pi)$ in the dynamic structure factor of
YBa$_2$Cu$_3$O$_{6+y}$. We strengthen this claim by providing a compelling fit
to the experimental data which cannot be reproduced by a number of other
ordering possibilities.",0906.3460v2
2009-06-22,Nuclear spin coherence in a quantum wire,"We have observed millisecond-long coherent evolution of nuclear spins in a
quantum wire at 1.2 K. Local, all-electrical manipulation of nuclear spins is
achieved by dynamic nuclear polarization in the breakdown regime of the Integer
Quantum Hall Effect combined with pulsed Nuclear Magnetic Resonance. The
excitation thresholds for the breakdown are significantly smaller than what
would be expected for our sample and the direction of the nuclear polarization
can be controlled by the voltage bias. As a four-level spin system, the device
is equivalent to two qubits.",0906.3970v2
2009-06-26,"Magnetic anomalies in nanocrystalline Ca3CoRhO6, a geometrically frustrated spin-chain compound,","We have investigated the magnetic behavior of the nano crystals, synthesized
by high-energy ball-milling, for a well-known geometrically frustrated
spin-chain system, Ca3CoRhO6, and compared its magnetic characteristics with
those of the bulk form by measuring ac and dc magnetization. The features
attributable to the onset of 'partially disordered antiferromagnetism'
(characterizing the bulk form) are not seen in the magnetization data of the
nano particles; the magnetic moment at high fields in the very low temperature
range in the magnetically ordered state gets relatively enhanced in the nano
particles. It appears that the ferromagnetic intrachain interaction, judged by
the sign of the paramagnetic Curie temperature, is preserved in the nano
particles. These trends are opposite to those seen in Ca3Co2O6. However, the
complex spin-dynamics as evidenced by large frequency dependence of ac
susceptibility is retained in the nano particles as well. Thus, there are some
similarities and dissimilarities between the properties of the nano particles
and those of the bulk. We believe that these findings would be useful to
understand correlation lengths deciding various properties of geometrical
frustration and/or spin-chain phenomena.",0906.4886v1
2009-07-02,Coexistence of the antiferromagnetic and superconducting order and its effect on spin dynamics in electron-doped high-$T_{c}$ cuprates,"In the framework of the slave-boson approach to the $t-t'-t''-J$ model, it is
found that for electron-doped high-$T_c$ cuprates, the staggered
antiferromagnetic (AF) order coexists with superconducting (SC) order in a wide
doping level ranged from underdoped to nearly optimal doping at the mean-field
level. In the coexisting phase, it is revealed that the spin response is
commensurate in a substantial frequency range below a crossover frequency
$\omega_{c}$ for all dopings considered, and it switches to the incommensurate
structure when the frequency is higher than $\omega_{c}$. This result is in
agreement with the experimental measurements. Comparison of the spin response
between the coexisting phase and the pure SC phase with a
$d_{x^{2}-y^{2}}$-wave pairing plus a higher harmonics term (DP+HH) suggests
that the inclusion of the two-band effect is important to consistently account
for both the dispersion of the spin response and the non-monotonic gap behavior
in the electron-doped cuprates.",0907.0357v1
2009-08-20,Repeating head-on collisions in an optical trap and the evaluation of spin-dependent interactions among neutral particles,"A dynamic process of repeating collisions of a pair of trapped neutral
particles with weak spin-dependent interaction is designed and studied. Related
theoretical derivation and numerical calculation have been performed to study
the inherent coordinate-spin and momentum-spin correlation. Due to the
repeating collisions the effect of the weak interaction can be accumulated and
enlarged, and therefore can be eventually detected. Numerical results suggest
that the Cr-Cr interaction, which has not yet been completely clear, could be
thereby determined. The design can be in general used to determine various
interactions among neutral atoms and molecules, in particular for the
determination of very weak forces.",0908.2929v2
2009-08-21,High precision beam momentum determination in a synchrotron using a spin resonance method,"In order to measure the mass of the eta meson with high accuracy using the
d+p -> 3He+eta reaction, the momentum of the circulating deuteron beam in the
Cooler Synchrotron COSY of the Forschungszentrum Juelich has to be determined
with unprecedented precision. This has been achieved by studying the spin
dynamics of the polarized deuteron beam. By depolarizing the beam through the
use of an artificially induced spin resonance, it was possible to evaluate its
momentum p with a precision of dp/p < 10-4 for a momentum of roughly 3 GeV/c.
Different possible sources of error in the application of the spin resonance
method are discussed in detail and its possible use during a standard
experiment is considered.",0908.3103v2
2009-09-19,Phenomenology of ESR in heavy fermion systems: Fermi liquid and non-Fermi liquid regime,"We extend and apply a recent theory of the dynamical spin response of
Anderson lattice systems to interpret ESR data on YbRh2Si2. Starting within a
semiphenomenological Fermi liquid description at low temperatures T < Tx (a
crossover temperature) and low magnetic fields B << Bx, we extend the
description to the non-Fermi liquid regime by adopting a quasiparticle picture
with effective mass and spin susceptibility varying logarithmically with
energy/temperature, as observed in experiment. We find a sharp ESR resonance
line slightly shifted from the local f-level resonance and broadened by
quasiparticle scattering (taking unequal g-factors of conduction and f
electrons) and by spin-lattice relaxation, both significantly reduced by the
effect of ferromagnetic fluctuations. A detailed comparison of our theory with
the data shows excellent agreement in the Fermi liquid regime. In the non-Fermi
liquid regime we find a close relation of the T-dependence of the specific
heat/spin susceptibility with the observed T-dependence of line shift and
linewidth.",0909.3552v1
2009-10-02,Signatures of nonadiabatic O2 dissociation at Al(111): First-principles fewest-switches study,"Recently, spin selection rules have been invoked to explain the discrepancy
between measured and calculated adsorption probabilities of molecular oxygen
reacting with Al(111). In this work, we inspect the impact of nonadiabatic spin
transitions on the dynamics of this system from first principles. For this
purpose the motion on two distinct potential-energy surfaces associated to
different spin configurations and possible transitions between them are
inspected by means of the Fewest Switches algorithm. Within this framework we
especially focus on the influence of such spin transitions on observables
accessible to molecular beam experiments. On this basis we suggest experimental
setups that can validate the occurrence of such transitions and discuss their
feasibility.",0910.0336v1
2009-11-21,Free-induction decay and envelope modulations in a narrowed nuclear spin bath,"We evaluate free-induction decay for the transverse components of a localized
electron spin coupled to a bath of nuclear spins via the Fermi contact
hyperfine interaction. Our perturbative treatment is valid for special
(narrowed) bath initial conditions and when the Zeeman energy of the electron
$b$ exceeds the total hyperfine coupling constant $A$: $b>A$. Using one unified
and systematic method, we recover previous results reported at short and long
times using different techniques. We find a new and unexpected modulation of
the free-induction-decay envelope, which is present even for a purely isotropic
hyperfine interaction without spin echoes and for a single nuclear species. We
give sub-leading corrections to the decoherence rate, and show that, in
general, the decoherence rate has a non-monotonic dependence on electron Zeeman
splitting, leading to a pronounced maximum. These results illustrate the
limitations of methods that make use of leading-order effective Hamiltonians
and re-exponentiation of short-time expansions for a strongly-interacting
system with non-Markovian (history-dependent) dynamics.",0911.4149v1
2009-11-23,Non-Hermitian spin chains with inhomogeneous coupling,"An open U_q(sl_2)-invariant spin chain of spin S and length N with
inhomogeneous coupling is investigated as an example of a non-Hermitian
(quasi-Hermitian) model. For several particular cases of such a chain, the
ranges of the deformation parameter gamma are determined for which the spectrum
of the model is real. For a certain range of gamma, a universal metric operator
is constructed and thus the quasi-Hermiticity of the model is established. The
constructed metric operator is non-dynamical, its structure is determined only
by the symmetry of the model. The results apply, in particular, to all known
homogeneous U_q(sl_2)-invariant integrable spin chains with nearest-neighbour
interaction. In addition, the most general form of a metric operator for a
quasi-Hermitian operator in finite dimensional space is discussed.",0911.4476v3
2009-12-31,Dielectric properties and spin-phonon coupling in multiferroic double perovskite Bi$_2$CoMnO$_6$,"First-principles electronic structure calculations have been performed for
the double perovskite Bi$_2$CoMnO$_6$ in its non-centrosymmetric polar state
using generalized gradient approximation plus Hubbard U approach. We find that
while Co is in a high spin state, Mn is in an intermediate spin state. The
calculated dynamical charge tensors are anisotropic reflecting a low-symmetry
structure of the compound. Magnetic structure dependent phonon frequencies
indicate the presence of spin-phonon coupling. Using Berry phase method, we
obtain a spontaneous electronic polarization of 5.88 ${\mu}C/cm^2$ which is
close to the experimental value observed for a similar compound,
Bi$_2$NiMnO$_6$.",1001.0128v2
2010-01-20,Precise probing spin wave mode frequencies in the vortex state of circular magnetic dots,"We report on detailed broadband ferromagnetic resonance measurements of
azimuthal and radial spin wave excitations in circular Permalloy dots in the
vortex ground state. Dots with aspect ratio (Beta =height over radius) varied
from 0.03 to 0.1 were explored. We found that for Beta exceeding approximately
0.05, variation of the spin wave eigenfrequencies with Beta deviates from the
predicted dependence. The frequency splitting of two lowest azimuthal modes was
observed. The experimentally observed dependence of the frequency splitting on
beta was reasonably well described by dynamic splitting model accounting the
spin-waves and, vortex gyrotropic mode interaction.",1001.3605v1
2010-02-19,Chirality-spin separation in the Hubbard model on the kagome lattice,"Effect of geometrical frustration in strongly-correlated metallic region is
studied for the Hubbard model on the kagome lattice at half filling by a
cluster extension of the dynamical mean-field theory combined with a
continuous-time auxiliary-field quantum Monte Carlo method. We find that the
electron correlation enhances the spin chirality in both vector and scalar
channels. The chirality grows as decreasing temperature and exhibits a peak at
a low temperature, indicating a new energy scale under strong correlation. The
peak temperature is considerably lower than that for the local spin moment,
namely, the characteristic temperatures for the chirality and the local moment
are well separated. This is a signature of separation between spin and chiral
degrees of freedom in the correlated metallic regime under geometrical
frustration.",1002.3692v1
2010-03-04,Quantum spin metal state on a decorated honeycomb lattice,"We present a modification of exactly solvable spin-(1/2) Kitaev model on the
decorated honeycomb lattice, with a ground state of ""spin metal"" type. The
model is diagonalized in terms of Majorana fermions; the latter form a 2D
gapless state with a Fermi-circle those size depends on the ratio of exchange
couplings. Low-temperature heat capacity C(T) and dynamic spin susceptibility
\chi(\omega,T) are calculated in the case of small Fermi-circle. Whereas
C(T)\sim T at low temperatures as it is expected for a Fermi-liquid, spin
excitations are gapful and \chi(\omega,T) demonstrate unusual behaviour with a
power-law peak near the resonance frequency. The corresponding exponent as well
as the peak shape are calculated.",1003.0992v1
2010-03-23,Investigation of the spin-glass regime between the antiferromagnetic and superconducting phases in Fe$_{1+y}$Se$_x$Te$_{1-x}$,"Using bulk magnetization along with elastic and inelastic neutron scattering
techniques, we have investigated the phase diagram of
Fe$_{1+y}$Se$_{x}$Te$_{1-x}$ and the nature of magnetic correlations in three
nonsuperconducting samples of Fe$_{1.01}$Se$_{0.1}$Te$_{0.9}$,
Fe$_{1.01}$Se$_{0.15}$Te$_{0.85}$ and Fe$_{1.02}$Se$_{0.3}$Te$_{0.7}$. A cusp
and hysteresis in the temperature dependence of the magnetization for the
$x=0.15$ and 0.3 samples indicates spin-glass (SG) ordering below $T_{\rm sg} =
23$K. Neutron scattering measurements indicate that the spin-glass behavior is
associated with short-range spin density wave (SDW) ordering characterized by a
static component and a low-energy dynamic component with a characteristic
incommensurate wave vector of ${\bf Q}_m = (0.46, 0, 0.50)$ and an anisotropy
gap of $\sim$ 2.5 meV. Our high ${\bf Q}$-resolution data also show that the
systems undergo a glassy structural distortion that coincides with the
short-range SDW order.",1003.4525v1
2010-06-04,The effect of spin-orbit interaction and attractive Coulomb potential on the magnetic properties of Ga$_{1-x}$Mn$_{x}$As,"We employ the dynamical mean-field approximation to study the magnetic
properties of a model relevant for the dilute magnetic semiconductors. Our
model includes the spin-orbit coupling on the hole bands, the exchange
interaction, and the attractive Coulomb potential between the negatively
charged magnetic ions and the itinerant holes. The inclusion of the Coulomb
potential significantly renormalizes the exchange coupling and enhances the
ferromagnetic transition temperature for a wide range of couplings. We also
explore the effect of the spin-orbit interaction by using two different values
of the ratio of the effective masses of the heavy and light holes. We show that
in the regime of small $J_{c}$-$V$ the spin-orbit interaction enhances $T_{c}$,
while for large enough values of $J_{c}$-$V$ magnetic frustration reduces $T_c$
to values comparable to the previously calculated strong coupling limit.",1006.0998v2
2010-06-08,Simulating spin-charge separation with light,"In this work we show that stationary light-matter excitations generated
inside a hollow one-dimensional waveguide filled with atoms, can be made to
generate a photonic two-component Lieb Liniger model. We explain how to prepare
and drive the atomic system to a strongly interacting regime where spin-charge
separation could be possible. We then proceed by explaining how to measure the
corresponding effective spin and charge densities and velocities through
standard optical methods based in measuring dynamically the emitted photon
intensities or by analyzing the photon spectrum. The relevant interactions
exhibit the necessary tunability both to generate and efficiently observe spin
charge separation with current technology.",1006.1644v1
2010-06-29,Quenching of magnetic excitations in single adsorbates at surfaces: Mn on CuN/Cu(100),"The lifetimes of spin excitations of Mn adsorbates on CuN/Cu(100) are
computed from first-principles. The theory is based on a strong-coupling
T-matrix approach that evaluates the decay of a spin excitation due to
electron-hole pair creation. Using a previously developed theory [Phys. Rev.
Lett. {\bf 103}, 176601 (2009) and Phys. Rev. B {\bf 81}, 165423 (2010)], we
compute the excitation rates by a tunneling current for all the Mn spin states.
A rate equation approach permits us to simulate the experimental results by
Loth and co-workers [Nat. Phys. {\bf 6}, 340 (2010)] for large tunnelling
currents, taking into account the finite population of excited states. Our
simulations give us insight into the spin dynamics, in particular in the way
polarized electrons can reveal the existence of an excited state population. In
addition, it reveals that the excitation process occurs in a way very different
from the deexcitation one. Indeed, while excitation by tunnelling electrons
proceeds via the s and p electrons of the adsorbate, deexcitation mainly
involves the d electrons.",1006.5605v1
2010-07-02,External field control of collective spin excitations in an optical lattice of $^2Σ$ molecules,"We show that an ensemble of $^2\Sigma$ molecules in the rotationally ground
state trapped on an optical lattice exhibits collective spin excitations that
can be controlled by applying superimposed electric and magnetic fields. In
particular, we show that the lowest energy excitation of the molecular ensemble
at certain combinations of electric and magnetic fields leads to the formation
of a magnetic Frenkel exciton. The exciton bandwidth can be tuned by varying
the electric or magnetic fields. We show that the exciton states can be
localized by creating vacancies in the optical lattice. The localization
patterns of the magnetic exciton states are sensitive to the number and
distribution of vacancies, which can be exploited for engineering many-body
entangled spin states. We consider the dynamics of magnetic exciton wavepackets
and show that the spin excitation transfer between molecules in an optical
lattice can be accelerated or slowed down by tuning an external magnetic or
electric field.",1007.0458v1
2010-07-13,Weak coupling study of decoherence of a qubit in disordered magnetic environments,"We study the decoherence of a qubit weakly coupled to frustrated spin baths.
We focus on spin-baths described by the classical Ising spin glass and the
quantum random transverse Ising model which are known to have complex
thermodynamic phase diagrams as a function of an external magnetic field and
temperature. Using a combination of numerical and analytical methods, we show
that for baths initally in thermal equilibrium, the resulting decoherence is
highly sensitive to the nature of the coupling to the environment and is
qualitatively different in different parts of the phase diagram. We find an
unexpected strong non-Markovian decay of the coherence when the random
transverse Ising model bath is prepared in an initial state characterized by a
finite temperature paramagnet. This is contrary to the usual case of
exponential decay (Markovian) expected for spin baths in finite temperature
paramagnetic phases, thereby illustrating the importance of the underlying
non-trivial dynamics of interacting quantum spinbaths.",1007.2105v1
2010-07-14,"Spin dynamics in S = 1/2 antiferromagnetic chain compounds delta-(EDT-TTF-CONMe_2)_2X (X=AsF_6, Br): a multi-frequency Electron Spin Resonance study","We present a multi-frequency Electron Spin Resonance (ESR) study in the range
of 4 GHz to 420 GHz of the quasi-one-dimensional, non-dimerized, quarter-filled
Mott insulators, delta-(EDT-TTF-CONMe_2)_2X (X=AsF_6, Br). In the high
temperature orthorhombic phase above T~190 K, the magnitude and the temperature
dependence of the high temperature spin susceptibility are described by a S =
1/2 Heisenberg antiferromagnetic chain with J_AsF6=298 K and J_Br=474 K
coupling constants for X=AsF_6 and Br respectively. We estimate from the
temperature dependence of the line width an exchange anisotropy, J'/J of ~2 *
10^{-3}. The frequency dependence of the line width and the g-shift have an
unusual quadratic dependence in all crystallographic orientations that we
attribute to an antisymmetric exchange (Dzyaloshinskii--Moriya) interaction.",1007.2251v1
2010-07-14,The Interplay of Charge and Spin in Quantum Dots: The Ising Case,"The physics of quantum dots is succinctly depicted by the {\it Universal
Hamiltonian}, where only zero mode interactions are included. In the case where
the latter involve charging and isotropic spin-exchange terms, this would lead
to a non-Abelian action. Here we address an Ising spin-exchange interaction,
which leads to an Abelian action. The analysis of this simplified yet
non-trivial model shed some light on a more general case of charge and spin
entanglement. We present a calculation of the tunneling density of states and
of the dynamic magnetic susceptibility. Our results are amenable to
experimental study and may allow for an experimental determination of the
exchange interaction strength.",1007.2436v1
2010-09-28,The magnonic limit of domain wall propagation in ferromagnetic nanotubes,"We report a study on the field-driven propagation of vortex-like domain walls
in ferromagnetic nanotubes. This particular geometry gives rise to a special
feature of the static wall configuration, which significantly influences its
dynamics. Unlike domain walls in flat strips, the left-right symmetry of domain
wall propagation is broken. Furthermore, the domain wall velocity is not
limited by the Walker breakdown. Under sufficiently large magnetic fields, the
domain wall velocity reaches the velocity of spin waves (about 1000 m/s) and is
thereafter connected with a direct emission of spin waves. The moving domain
wall maintains its main structure but has characteristic spin-wave tails
attached. The spatial profile of this topological soliton is determined by the
spin-wave dispersion.",1009.5552v1
2010-10-25,Plasmon mass and Drude weight in strongly spin-orbit-coupled 2D electron gases,"Spin-orbit-coupled two-dimensional electron gases (2DEGs) are a textbook
example of helical Fermi liquids, i.e. quantum liquids in which spin (or
pseudospin) and momentum degrees-of-freedom at the Fermi surface have a
well-defined correlation. Here we study the long-wavelength plasmon dispersion
and the Drude weight of archetypical spin-orbit-coupled 2DEGs. We first show
that these measurable quantities are sensitive to electron-electron
interactions due to broken Galileian invariance and then discuss in detail why
the popular random phase approximation is not capable of describing the
collective dynamics of these systems even at very long wavelengths. This work
is focussed on presenting approximate microscopic calculations of these
quantities based on the minimal theoretical scheme that captures the basic
physics correctly, i.e. the time-dependent Hartree-Fock approximation. We find
that interactions enhance the ""plasmon mass"" and suppress the Drude weight. Our
findings can be tested by inelastic light scattering, electron energy loss, and
far-infrared optical-absorption measurements.",1010.5169v1
2010-11-26,Modes of magnetic resonance of S=1 dimer chain compound NTENP,"The spin dynamics of a quasi one dimensional $S=1$ bond alternating spin-gap
antiferromagnet Ni(C$_9$H$_{24}$N$_4$)NO$_2$(ClO$_4$) (abbreviated as NTENP) is
studied by means of electron spin resonance (ESR) technique. Five modes of ESR
transitions are observed and identified: transitions between singlet ground
state and excited triplet states, three modes of transitions between spin
sublevels of collective triplet states and antiferromagnetic resonance
absorption in the field-induced antiferromagnetically ordered phase.
Singlet-triplet and intra-triplet modes demonstrate a doublet structure which
is due to two maxima in the density of magnon states in the low-frequency
range. A joint analysis of the observed spectra and other experimental results
allows to test the applicability of the fermionic and bosonic models. We
conclude that the fermionic approach is more appropriate for the particular
case of NTENP.",1011.5742v1
2010-12-06,Magnetic polaron formation and exciton spin relaxation in single CdMnTe quantum dots,"We study the formation dynamics of a spontaneous ferromagnetic order in
single self-assembled CdMnTe quantum dots. By measuring time-resolved
photoluminescence, we determine the formation times for QDs with Mn ion
contents x varying from 0.01 to 0.2. At low x these times are orders of
magnitude longer than exciton spin relaxation times evaluated from the decay of
photoluminescence circular polarization. This allows us to conclude that the
direction of the spontaneous magnetization is determined by a momentary Mn spin
fluctuation rather than resulting from an optical orientation. At higher x, the
formation times are of the same order of magnitude as found in previous studies
on higher dimensional systems. We also find that the exciton spin relaxation
accelerates with increasing Mn concentration.",1012.1179v1
2011-02-01,Low Temperature Dynamics of Magnons in a Spin-1/2 Ladder Compound,"We have used a combination of neutron resonant spin-echo and triple-axis
spectroscopies to determine the energy, fine structure, and linewidth of the
magnon resonance in the model spin-1/2 ladder antiferromagnet IPA-CuCl_3 at
temperatures T << Delta_0 /k_B, where Delta_0 is the spin gap at T=0. In this
low-temperature regime we find that the results deviate substantially from the
predictions of the non-linear sigma model proposed as a description of magnon
excitations in one-dimensional quantum magnets and attribute these deviations
to real-space and spin-space anisotropies in the spin Hamiltonian as well as
scattering of magnon excitations from a dilute density of impurities. These
effects are generic to experimental realizations of one-dimensional quantum
magnets.",1102.0214v1
2011-02-12,Electrical control of ferromagnetism in Mn-doped semiconductor heterostructures,"The interplay of tunneling transport and carrier-mediated ferromagnetism in
narrow semiconductor multi-quantum well structures containing layers of GaMnAs
is investigated within a self-consistent Green's function approach, accounting
for disorder in the Mn--doped regions and unwanted spin-flips at
heterointerfaces on phenomenological ground. We find that the magnetization in
GaMnAs layers can be controlled by an external electric bias. The underlying
mechanism is identified as spin-selective hole tunneling in and out of the
Mn-doped quantum wells, whereby the applied bias determines both hole
population and spin polarization in these layers. In particular we predict
that, near resonance, ferromagnetic order in the Mn doped quantum wells is
destroyed. The interplay of both magnetic and transport properties combined
with structural design potentially leads to several interrelated physical
phenomena, such as dynamic spin filtering, electrical control of magnetization
in individual magnetic layers, and, under specific bias conditions, to
self-sustained current and magnetization oscillations
(magneticmulti-stability). Relevance to recent experimental results is
discussed.",1102.2507v2
2011-03-03,The role of excitons and trions on electron spin polarization in quantum wells,"We have studied the time evolution of the electron spin polarization under
continuous photoexcitation in remotely n-doped semiconductor quantum wells. The
doped region allows us to get the necessary excess of free electrons to form
trions. We have considered electron resonant photoexcitation at free, exciton
and trion electron energy levels. Also, we have studied the relative effect of
photoexcitation energy density and doping concentration. In order to obtain the
two-dimensional density evolution of the different species, we have performed
dynamic calculations through the matrix density formalism. Our results indicate
that photoexcitation of free electron level leads to a higher spin
polarization. Also, we have found that increasing the photoexcitation energy or
diminishing the doping enhances spin polarization.",1103.0756v1
2011-03-18,Cotunneling theory of inelastic STM spin spectroscopy,"We propose cotunneling as the microscopic mechanism that makes possible
inelastic electron spectroscopy of magnetic atoms in surfaces for a wide range
of systems, including single magnetic adatoms, molecules and molecular stacks.
We describe electronic transport between the scanning tip and the conducting
surface through the magnetic system (MS) with a generalized Anderson model,
without making use of effective spin models. Transport and spin dynamics are
described with an effective cotunneling Hamiltonian in which the correlations
in the magnetic system are calculated exactly and the coupling to the
electrodes is included up to second order in the tip-MS and MS-substrate. In
the adequate limit our approach is equivalent to the phenomenological Kondo
exchange model that successfully describe the experiments . We apply our method
to study in detail inelastic transport in two systems, stacks of Cobalt
Phthalocyanines and a single Mn atom on Cu$_2$N. Our method accounts both, for
the large contribution of the inelastic spin exchange events to the conductance
and the observed conductance asymmetry.",1103.3676v1
2011-04-20,Observation of a level crossing in a molecular nanomagnet using implanted muons,"We have observed an electronic energy level crossing in a molecular
nanomagnet (MNM) using muon-spin relaxation. This effect, not observed
previously despite several muon studies of MNM systems, provides further
evidence that the spin relaxation of the implanted muon is sensistive to the
dynamics of the electronic spin. Our measurements on a broken ring MNM
[H_{2}N^{t}Bu^{is}Pr][Cr_{8}CdF_{9}(O_{2}CC(CH_{3})_{3})_{18}] (hereafter
Cr_{8}Cd), which contains eight Cr ions, show clear evidence for the S=0 to S=1
transition that takes place at B_{c}=2.3 T. The crossing is observed as a
resonance-like dip in the average positron asymmetry and also in the muon-spin
relaxation rate, which shows a sharp increase in magnitude at the transition
and a peak centred within the S=1 regime.",1104.4027v1
2011-04-27,Coupled spin models for magnetic variation of planets and stars,"Geomagnetism is characterized by intermittent polarity reversals and rapid
fluctuations. We have recently proposed a coupled macro-spin model to describe
these dynamics based on the idea that the whole dynamo mechanism is described
by the coherent interactions of many small dynamo elements. In this paper, we
further develop this idea and construct a minimal model for magnetic
variations. This simple model naturally yields many of the observed features of
geomagnetism: its time evolution, the power spectrum, the frequency
distribution of stable polarity periods, etc. This model has coexistent two
phases; i.e. the cluster phase which determines the global dipole magnetic
moment and the expanded phase which gives random perpetual perturbations that
yield intermittent polarity flip of the dipole moment. This model can also
describe the synchronization of the spin oscillation. This corresponds to the
case of sun and the model well describes the quasi-regular cycles of the solar
magnetism. Furthermore, by analyzing the relevant terms of MHD equation based
on our model, we have obtained a scaling relation for the magnetism for
planets, satellites, sun, and stars. Comparing it with various observations, we
can estimate the scale of the macro-spins.",1104.5093v1
2011-04-29,Doping dependence of magnetic excitations of 1D cuprates as probed by Resonant Inelastic x-ray Scattering,"We study the dynamical, momentum dependent two- and four-spin response
functions in doped and undoped 1D cuprates, as probed by resonant inelastic
x-ray scattering, using an exact numerical diagonalization procedure. In the
undoped $t-J$ system the four-spin response vanishes at $\pi$, whereas the
two-spin correlator is peaked around $\pi/2$, with generally larger spectral
weight. Upon doping spectra tend to soften and broaden, with a transfer of
spectral weight towards higher energy. However, the total spectral weight and
average peak position of either response are only weakly affected by doping up
to a concentration of 1/8. Only the two-spin response at $\pi$ changes
strongly, with a large reduction of spectral weight and enhancement of
excitation energy. At other momenta the higher-energy, generic features of the
magnetic response are robust against doping. It signals the presence of strong
short-range antiferromagnetic correlations, even after doping mobile holes into
the system. We expect this to hold also in higher dimensions.",1104.5588v1
2011-05-12,Quasi-One-Dimensional Spin Dynamics in $d$-Electron Heavy-Fermion Metal Y$_{1-x}$Sc$_x$Mn$_2$,"Slow spin fluctuations ($\nu < 10^{12}$ s$^-1$) observed by the muon spin
relaxation technique in Y$_{1-x}$Sc$_x$Mn$_2$ exhibits a power law dependence
on temperature ($\nu \propto T^\alpha$), where the power converges
asymptotically to unity ($\alpha\rightarrow 1$) as the system moves away from
spin-glass instability with increasing Sc content $x$. This linear $T$
dependence, which is common to that observed in LiV$_2$O$_4$, is in line with
the prediction of the ""intersecting Hubbard chains"" model for a metallic
pyrochlore lattice, suggesting that the geometrical constraints to t2g bands
specific to the pyrochlore structure serve as a basis of the $d$-electron
heavy-fermion state.",1105.2360v1
2011-05-23,Heavy quark spin structure in Z_b resonances,"We discuss the heavy quark spin structure of the recently observed `twin'
resonances $Z_b(10610)$ and $Z_b(10650)$ assuming that these are mostly of a
`molecular' type, i.e. that their internal dynamics is dominated by the
coupling to meson pairs $B^* \bar B - B {\bar B}^*$ and $B^* {\bar B}^*$. We
find that the state of the $b \bar b$ pair within the $Z_b(10610)$ and
$Z_b(10650)$ resonances is a mixture of a spin-triplet and a spin-singlet of
equal amplitude and with the phase orthogonal between the two resonances. Such
a structure gives rise to specific relations between observable amplitudes that
are in agreement with the data obtained recently by Belle. We also briefly
discuss possible properties of the isotopically singlet counterparts of the
newly found resonances, and also of their $C$ ($G$) parity opposites that
likely exist in the same mass range near the open $B$ flavor threshold.",1105.4473v2
2011-06-01,Remarkable paramagnetic features of Fermi-Dirac plasmas,"In this paper by using the relativistic magnetic susceptibility of a
Fermi-Dirac (relativistically degenerate) plasma, quantum magnetohydrodynamics
(QMHD) model is used to investigate the propagation of spin-induced (SI)
magnetosonic nonlinear excitations in a normally and relativistically
degenerate dense electron-ion plasma in the presence of the spin magnetization
effect. Based on the conventional pseudopotential method the matching criterion
for the evolution of SI solitary structures is evaluated. It is found that, the
plasma mass density and strength of the magnetic field have significant effects
on excitation and evolution of magnetosonic nonlinear structures in Fermi-Dirac
plasmas. Only rarefactive SI magnetosonic solitary structures are found to
excite in such plasmas. Furthermore, fundamental differences are shown to exist
in magnetosonic soliton dynamics in the two distinct plasma degeneracy regimes,
which is due to interplay between the negative spin paramagnetism pressure-like
and positive relativistic degeneracy pressure of electrons. Current
investigation can help better understand the electron spin effects on nonlinear
wave propagations in strongly magnetized dense astrophysical objects such as
white dwarfs and pulsar magnetospheres.",1106.0226v1
2011-06-14,Quantum phase transition in the spin boson model,"In this paper we give a general introduction to quantum critical phenomena,
which we practically illustrate by a detailed study of the low energy
properties of the spin boson model (SBM), describing the dynamics of a spin 1/2
impurity (or more generically a two-level system) coupled to a bath of
independent harmonic oscillators. We show that the behavior of the model is
very sensitive to the bath spectrum, in particular how the properties of the
quantum critical point in the SBM are affected by the functional form of the
bath Density of States (DoS). To this effect, we review the renormalization
group (RG) treatment of the SBM for various bath DoS, based on an
unconventional Majorana representation of the spin 1/2 degree of freedom. We
also discuss the derivation of Shiba's relation for the sub-ohmic SBM, and
explicitely derive an effective action vindicating the quantum to classical
mapping.",1106.2654v1
2011-07-02,Rotating states in driven clock- and XY-models,"We consider 3D active plane rotators, where the interaction between the spins
is of XY-type and where each spin is driven to rotate. For the clock-model,
when the spins take N\gg1 possible values, we conjecture that there are two
low-temperature regimes. At very low temperatures and for small enough drift
the phase diagram is a small perturbation of the equilibrium case. At larger
temperatures the massless modes appear and the spins start to rotate
synchronously for arbitrary small drift. For the driven XY-model we prove that
there is essentially a unique translation-invariant and stationary distribution
despite the fact that the dynamics is not ergodic.",1107.0370v1
2011-08-16,Magnetic rogue wave in a perpendicular anisotropic ferromagnetic nanowire with spin-transfer torque,"We present the current controlled motion of dynamic soliton embedded in spin
wave background in ferromagnetic nanowire. With the stronger breather character
we get the novel magnetic rogue wave and clarify its formation mechanism. The
generation of magnetic rogue wave is mainly arose from the accumulation of
energy and magnons toward to its central part. We also observe that the
spin-polarized current can control the exchange rate of magnons between
envelope soliton and background, and the critical current condition is obtained
analytically. Even more interesting is that the spin-transfer torque plays the
completely opposite role for the cases of below and above the critical value.",1108.3252v2
2011-09-07,"Spin wave theory study of neutron intensity, magnetic field, and anisotropy of Type IIA FCC antiferromagnet","We study the spin dynamics in a 3D quantum antiferromagnet on a face-centered
cubic (FCC) lattice. The effects of magnetic field, single-ion anisotropy, and
biquadratic interactions are investigated using linear spin wave theory with
spins in a canted basis about the Type IIA FCC antiferromagnetic ground state
structure which is known to be stable. We calculate the expected finite
frequency neutron scattering intensity and give qualitative criteria for
typical FCC materials MnO and CoO. The magnetization reduction due to quantum
zero point fluctuations is also analyzed.",1109.1350v3
2011-09-26,Deterministic preparation of Dicke states of donor nuclear spins in silicon by cooperative pumping,"For donor nuclear spins in silicon, we show how to deterministically prepare
various symmetric and asymmetric Dicke states which span a complete basis of
the many-body Hilbert space. The state preparation is realized by cooperative
pumping of nuclear spins by coupled donor electrons, and the required controls
are in situ to the prototype Kane proposal for quantum computation. This scheme
only requires a sub-gigahertz donor exchange coupling which can be readily
achieved without atomically precise donor placement, hence it offers a
practical way to prepare multipartite entanglement of spins in silicon with
current technology. All desired Dicke states appear as the steady state under
various pumping scenarios and therefore the preparation is robust and does not
require accurate temporal controls. Numerical simulations with realistic
parameters show that Dicke states of 10-20 qubits can be prepared with high
fidelity in presence of decoherence and unwanted dynamics.",1109.5495v2
2011-10-05,Spin and orbital hybridization at specifically nested Fermi surfaces in URu$_2$Si$_2$,"The Fermi surface (FS) nesting properties of URu$_2$Si$_2$ are analyzed with
particular focus on their implication for the mysterious hidden order phase. We
show that there exist two Fermi surfaces that exhibit a strong nesting at the
antiferromagnetic wavevector, $\boldsymbol{Q}_0$=(0,\,0,\,1). The corresponding
energy dispersions fulfill the relation $\epsilon_{1}(\boldsymbol{k})$=$-
\epsilon_{2} (\boldsymbol{k}\pm \boldsymbol{Q}_0)$ at eight FS hotspot lines.
The spin-orbital characters of the involved $5f$ states are {\it distinct}
($j_z$=$\pm$5/2 {\it vs.} $\pm$3/2) and hence the degenerate Dirac crossings
are symmetry protected in the nonmagnetic normal state. Dynamical symmetry
breaking through an Ising-like spin and orbital excitation mode with $\Delta
j_z$=$\pm$1 induces a hybridization of the two states, causing substantial FS
gapping. Concomitant spin and orbital currents in the uranium planes give rise
to a rotational symmetry breaking.",1110.0981v1
2011-10-10,Magnetic order and transitions in the spin-web compound Cu3TeO6,"The spin-web compound Cu3TeO6, belongs to an intriguing group of materials
where magnetism is governed by 3d9 copper Cu2+ ions. This compound has been
sparsely experimentally studied and we here present the first investigation of
its local magnetic properties using muon-spin relaxation/rotation ({\mu}+SR).
Our results show a clear long-range 3D magnetic order below TN as indicated by
clear zero-field (ZF) muon-precessions. At TN = 61.7 K a very sharp transition
is observed in the weak transverse-field (wTF) as well as ZF data. Contrary to
suggestions by susceptibility measurements and inelastic neutron scattering, we
find no evidence for either static or dynamic (on the time-scale of {\mu}+SR)
spin-correlations above TN.",1110.2073v1
2011-10-10,Elimination of the spin supplementary condition in the effective field theory approach to the post-Newtonian approximation,"The present paper addresses open questions regarding the handling of the spin
supplementary condition within the effective field theory approach to the
post-Newtonian approximation. In particular it is shown how the covariant spin
supplementary condition can be eliminated at the level of the potential (which
is subtle in various respects) and how the dynamics can be cast into a fully
reduced Hamiltonian form. Two different methods are used and compared, one
based on the well-known Dirac bracket and the other based on an action
principle. It is discussed how the latter approach can be used to improve the
Feynman rules by formulating them in terms of reduced canonical spin variables.",1110.2094v3
2011-10-16,Role of Spin Diffusion in Current-Induced Domain Wall Motion,"Current-induced spin torque and magnetization dynamics in the presence of
spin diffusion in magnetic textures is studied theoretically. We uncover an
additional torque on the form \sim{\bm\nabla}^2[{\bf M}x({\bf u}\cdot{\bm
\nabla}){\bf M}], where {\bf M} is the local magnetization and {\bf u} is the
direction of injected current. This torque is inversely proportional to the
square of the domain wall width (\approx\frac{1}{W^2}) and strongly depends on
the domain wall structure. Whereas its influence remains moderate for
transverse domain walls, it can significantly increase the transverse velocity
of vortex cores. Consequently, the spin diffusion can dramatically enhance the
non-adiabaticity of vortex walls.",1110.3487v1
2011-12-04,Zn-induced spin dynamics in overdoped La$_{2-x}$Sr$_x$Cu$_{1-y}$Zn$_y$O$_4$,"Spin fluctuations and the local spin susceptibility in isovalently
Zn-substituted La$_{2-x}$Sr$_{x}$Cu$_{1-y}$Zn$_y$O$_4$ ($x=0.25$,
$y\approx0.01$) are measured via inelastic neutron scattering techniques. As
Zn$^{2+}$ is substituted onto the Cu$^{2+}$-sites, an anomalous enhancement of
the local spin susceptibility $\chi^{\prime\prime}(\omega)$ appears due to the
emergence of a commensurate antiferromagnetic excitation centered at wave
vector \textbf{Q}$=(\pi, \pi, 0)$ that coexists with the known incommensurate
SDW excitations at \textbf{Q}$_{HK}=(\pi\pm\delta,\pi), (\pi,\pi\pm\delta)$.
Our results support a picture of Zn-induced antiferromagnetic (AF) fluctuations
appearing through a local staggered polarization of Cu$^{2+}$-spins, and the
simultaneous suppression of T$_c$ as AF fluctuations are slowed in proximity to
Zn-impurities suggests the continued importance of high energy AF fluctuations
at the far overdoped edge of superconductivity in the cuprates.",1112.0775v2
2011-12-05,Magnetic anisotropy of elongated thin ferromagnetic nano-islands for artifical spin ice arrays,"The energetics of thin elongated ferromagnetic nano-islands is considered for
some different shapes, aspect ratios, and applied magnetic field directions.
These nano-island particles are important for artificial spin-ice materials.
For low temperature, the magnetic internal energy of an individual particle is
evaluated numerically as a function of the direction of a particle's net
magnetization. This leads to estimations of effective anisotropy constants for
(1) the easy axis along the particle's long direction, and (2) the hard axis
along the particle's thin direction. A spin relaxation algorithm together with
fast Fourier transform for the demagnetization field is used to solve the
micromagnetics problem for a thin system. The magnetic hysteresis is also
found. The results indicate some possibilities for controlling the equilibrium
and dynamics in spin-ice materials by using different island geometries.",1112.0913v2
2011-12-16,"Spin Ice, Fractionalization and Topological Order","The spin ice compounds {\dys} and {\holm} are highly unusual magnets which
epitomize a set of concepts of great interest in modern condensed matter
physics: their low-energy physics exhibits an emergent gauge field and their
excitations are magnetic monopoles which arise from the fractionalization of
the microscopic magnetic spin degrees of freedom. In this review, we provide an
elementary introduction to these concepts and we survey the thermodynamics,
statics and dynamics---in and out of equilibrium---of spin ice from these
vantage points. Along the way, we touch on topics such as emergent Coulomb
plasmas, observable ""Dirac strings"", and irrational charges. We close with the
outlook for these unique materials.",1112.3793v1
2012-02-02,Paramagnetic Spin Correlations in Colossal Magnetoresistive La0.7Ca0.3MnO3,"Neutron spectroscopy measurements reveal dynamic spin correlations throughout
the Brillouin zone in the colossal magnetoresistive material La0.7Ca0.3MnO3 at
265 K (approximately 1.03 Tc). The long-wavelength behavior is consistent with
spin diffusion, yet an additional and unexpected component of the scattering is
also observed in low-energy constant-E measurements, which takes the form of
ridges of strong quasielastic scattering running along (H 0 0) and equivalent
directions. Well-defined Q-space correlations are observed in constant-E scans
at energies up to at least 28 meV, suggesting robust short-range spin
correlations in the paramagnetic phase.",1202.0487v2
2012-02-14,"Polaron, molecule and pairing in one-dimensional spin-1/2 Fermi gas with an attractive Delta-function interaction","Using solutions of the discrete Bethe ansatz equations, we study in detail
the quantum impurity problem of a spin-down fermion immersed into a fully
ploarized spin-up Fermi sea with weak attraction. We prove that this impurity
fermion in the one-dimensional (1D) fermionic medium behaves like a polaron for
weak attraction. However, as the attraction grows, the spin-down fermion binds
with one spin-up fermion from the fully-polarized medium to form a tightly bond
molecule. Thus it is seen that the system undergos a cross-over from a mean
field polaron-like nature into a mixture of excess fermions and a bosonic
molecule as the attraction changes from weak attraction into strong attraction.
This polaron-molecule cross-over is universal in 1D many-body systems of
interacting fermions. In thermodynamic limit, we further study the relationship
between the Fredholm equations for the 1D spin-1/2 Fermi gas with weakly
repulsive and attractive delta-function interactions.",1202.2941v1
2012-03-09,Two-dimensional Heisenberg behavior of Jeff = 1/2 isospins in the paramagnetic state of spin-orbital Mott insulator Sr2IrO4,"Dynamical correlations of Jeff = 1/2 isospins in the paramagnetic state of
spin-orbital Mott insu- lator Sr2IrO4 was revealed by resonant magnetic x-ray
diffuse scattering. We found two-dimensional antiferromagnetic fluctuation with
a large in-plane correlation length exceeding 100 lattice spacings at even 20 K
above the mangnetic ordering temperature. In marked contrast to the naive
expecta- tion of strong magnetic anisotropy associated with an enhanced
spin-orbit coupling, we discovered isotropic isospin correlation that is well
described by the two-dimensional S = 1/2 quantum Heisen- berg model. The
estimated antiferromagnetic coupling constant as large as J ~ 0.1 eV that is
comparable to the small Mott gap (< 0.5 eV) points the weak and marginal Mott
character of this spin-orbital entangled system.",1203.1983v1
2012-03-17,Effect of strain on hyperfine-induced hole-spin decoherence in quantum dots,"We theoretically consider the effect of strain on the spin dynamics of a
single heavy-hole (HH) confined to a self-assembled quantum dot and interacting
with the surrounding nuclei via hyperfine interaction. Confinement and strain
hybridize the HH states, which show an exponential decay for a narrowed nuclear
spin bath. For different strain configurations within the dot, the dependence
of the spin decoherence time $T_2$ on external parameters is shifted and the
non-monotonic dependence of the peak is altered. Application of external strain
yields considerable shifts in the dependence of $T_2$ on external parameters.
We find that external strain affects mostly the effective hyperfine coupling
strength of the conduction band (CB), indicating that the CB admixture of the
hybridized HH states plays a crucial role in the sensitivity of $T_2$ on
strain.",1203.3876v2
2012-06-01,Deep Spin-Glass Hysteresis Area Collapse and Scaling in the $d=3$ $\pm J$ Ising Model,"We investigate the dissipative loss in the $\pm J$ Ising spin glass in three
dimensions through the scaling of the hysteresis area, for a maximum magnetic
field that is equal to the saturation field. We perform a systematic analysis
for the whole range of the bond randomness as a function of the sweep rate, by
means of frustration-preserving hard-spin mean field theory. Data collapse
within the entirety of the spin-glass phase driven adiabatically (i.e.,
infinitely-slow field variation) is found, revealing a power-law scaling of the
hysteresis area as a function of the antiferromagnetic bond fraction and the
temperature. Two dynamic regimes separated by a threshold frequency $\omega_c$
characterize the dependence on the sweep rate of the oscillating field. For
$\omega < \omega_c$, the hysteresis area is equal to its value in the adiabatic
limit $\omega = 0$, while for $\omega > \omega_c$ it increases with the
frequency through another randomness-dependent power law.",1206.0230v2
2012-06-20,Optical and dc conductivities of cuprates: Spin-fluctuation scattering in the t-J model,"A microscopic theory of the electrical conductivity $\sigma(\omega)$ within
the t-J model is developed. An exact representation for $\sigma(\omega)$ is
obtained using the memory-function technique for the relaxation function in
terms of the Hubbard operators, and the generalized Drude law is derived. The
relaxation rate due to the decay of charge excitations into particle-hole pairs
assisted by antiferromagnetic spin fluctuations is calculated in the
mode-coupling approximation. Using results for the spectral function of spin
excitations calculated previously, the relaxation rate and the optical and dc
conductivities are calculated in a broad region of doping and temperatures. The
reasonable agreement of the theory with experimental data for cuprates proves
the important role of spin-fluctuation scattering in the charge dynamics.",1206.4474v2
2012-06-26,The coexistence of superconductivity and ferromagnetism in nano-scale metallic grains,"A nano-scale metallic grain in which the single-particle dynamics are chaotic
is described by the so-called universal Hamiltonian. This Hamiltonian includes
a superconducting pairing term and a ferromagnetic exchange term that compete
with each other: pairing correlations favor minimal ground-state spin, while
the exchange interaction favors maximal spin polarization. Of particular
interest is the fluctuation-dominated regime where the bulk pairing gap is
comparable to or smaller than the single-particle mean level spacing and the
Bardeen-Cooper-Schrieffer theory of superconductivity breaks down.
Superconductivity and ferromagnetism can coexist in this regime. We identify
signatures of the competition between superconductivity and ferromagnetism in a
number of quantities: ground-state spin, conductance fluctuations when the
grain is weakly coupled to external leads and the thermodynamic properties of
the grain, such as heat capacity and spin susceptibility.",1206.6059v2
2012-07-24,Perfect quantum transport in arbitrary spin networks,"Spin chains have been proposed as wires to transport information between
distributed registers in a quantum information processor. Unfortunately, the
challenges in manufacturing linear chains with engineered couplings has
hindered experimental implementations. Here we present strategies to achieve
perfect quantum information transport in arbitrary spin networks. Our proposal
is based on the weak coupling limit for pure state transport, where information
is transferred between two end-spins that are only weakly coupled to the rest
of the network. This regime allows disregarding the complex, internal dynamics
of the bulk network and relying on virtual transitions or on the coupling to a
single bulk eigenmode. We further introduce control methods capable of tuning
the transport process and achieve perfect fidelity with limited resources,
involving only manipulation of the end-qubits. These strategies could be thus
applied not only to engineered systems with relaxed fabrication precision, but
also to naturally occurring networks; specifically, we discuss the practical
implementation of quantum state transfer between two separated nitrogen vacancy
(NV) centers through a network of nitrogen substitutional impurities.",1207.5580v1
2012-07-24,Dissipative spin chains: Implementation with cold atoms and steady-state properties,"We propose a quantum optical implementation of a class of dissipative spin
systems, including the XXZ and Ising model, with ultra-cold atoms in optical
lattices. Employing the motional degree of freedom of the atoms and detuned
Raman transitions we show how to obtain engineerable dissipation and a tunable
transversal magnetic field, enabling the study of the dynamics and
steady-states of dissipative spin models. As an example of effects made
accessible this way, we consider small spin chains and weak dissipation and
show by numerical simulation that steady-state expectation values display
pronounced peaks at certain critical system parameters. We show that this
effect is related to degeneracies in the Hamiltonian and derive a sufficient
condition for its occurrence.",1207.5768v2
2012-08-02,Geometric Phase Gates with Adiabatic Control in Electron Spin Resonance,"High-fidelity quantum operations are a key requirement for fault-tolerant
quantum information processing. In electron spin resonance, manipulation of the
quantum spin is usually achieved with time-dependent microwave fields. In
contrast to the conventional dynamic approach, adiabatic geometric phase
operations are expected to be less sensitive to certain kinds of noise and
field inhomogeneities. Here, we investigate such phase gates applied to
electron spins both through simulations and experiments, showing that the
adiabatic geometric phase gate is indeed inherently robust against
inhomogeneity in the applied microwave field strength. While only little
advantage is offered over error-correcting composite pulses for modest
inhomogeneities <=10%, the adiabatic approach reveals its potential for
situations where field inhomogeneities are unavoidably large.",1208.0555v3
2012-08-16,"Note on lattice spin in graphene and ""spin from isospin"" phenomenon","It is well-known that the dynamics of low energy electron in graphene
honeycomb lattice near the K/K' points can be described, in tight-binding
approximation, by 2+1 massless Dirac equation. Graphene's spin equivalent,
""pseudospin"", arises from the degeneracy introduced by the honeycomb lattice's
two inequivalent atomic sites per unit cell. Mecklenburg and Regan (Phys. Rev.
Lett. 106 (2011), 116803) have shown that, contrary to the common view, the
pseudospin has all attributes of real angular momentum. In some circumstances,
the internal symmetries can produce an important contribution to angular
momentum. This phenomenon has been known for many years in particle physics and
called ""spin from isospin"". We show that similar mechanism works in the case of
lattice pseudospin.",1208.3451v1
2012-08-21,Augmenting the spin properties of shallow implanted NV-centers by CVD-overgrowth,"The controlled scaling of diamond defect center based quantum registers
relies on the ability to position NVs with high spatial resolution. Using ion
implantation, shallow (< 10 nm) NVs can be placed with accuracy below 20nm, but
generally show reduced spin properties compared to bulk NVs. We demonstrate the
augmentation of spin properties for shallow implanted NV centers using an
overgrowth technique. An increase of the coherence times up to an order of
magnitude (T_2 = 250 \mu s) was achieved. Dynamic decoupling of defects spins
achieves ms decoherence times. The study marks a further step towards achieving
strong coupling among defects positioned with nm precision.",1208.4216v1
2012-08-31,"Asymptotically Matched Spacetime Metric for Non-Precessing, Spinning Black Hole Binaries","We construct a closed-form, fully analytical 4-metric that approximately
represents the spacetime evolution of non-precessing, spinning black hole
binaries from infinite separations up to a few orbits prior to merger. We
employ the technique of asymptotic matching to join a perturbed Kerr metric in
the neighborhood of each spinning black hole to a near-zone, post-Newtonian
metric farther out. The latter is already naturally matched to a far-zone,
post-Minkowskian metric that accounts for full temporal retardation. The result
is a 4-metric that is approximately valid everywhere in space and in a small
bundle of spatial hypersurfaces. We here restrict our attention to quasi-
circular orbits, but the method is valid for any orbital motion or physical
scenario, provided an overlapping region of validity or buffer zone exists. A
simple extension of such a metric will allow for future studies of the
accretion disk and jet dynamics around spinning back hole binaries.",1208.6489v1
2012-10-08,Inelastic magnetic scattering effect on LDOS of topological insulators,"Magnetic ions such as Fe, Mn and Co with localized spins may be adsorbed on
the surface of topological insulators like \Bi. They form scattering centers
for the helical surface states which have a Dirac cone dispersion as long as
the local spins are disordered. However, the local density of states (LDOS) may
be severely modified by the formation of bound states. Commonly only elastic
scattering due to normal and exchange potentials of the adatom is assumed.
Magnetization measurements show, however, that considerable magnetic single ion
anisotropies exist which lead to a splitting of the local impurity spin states
resulting in a singlet ground state. Therefore inelastic scattering processes
of helical Dirac electrons become possible as described by a dynamical local
self energy of second order in the exchange interaction. The self energy
influences bound state formation and leads to significant new anomalies in the
LDOS at low energies and low temperatures which we calculate within T-matrix
approach. We propose that they may be used for spectroscopy of local impurity
spin states by appropriate tuning of chemical potential and magnetic field.",1210.2222v2
2012-10-29,Thermally-Assisted Spin-Transfer Torque Magnetization Reversal of Uniaxial Nanomagnets in Energy Space,"The asymptotic behavior of switching time as a function of current for a
uniaxial macrospin under the effects of both spin-torque and thermal noise is
explored analytically by focusing on its diffusive energy space dynamics. The
scaling dependence ($I\rightarrow 0$, $<\tau\propto\exp(-\xi(1-I)^2)$) is shown
to confirm recent literature results. The analysis shows the mean switching
time to be functionally independent of the angle between the spin current and
magnet's uniaxial axes. These results have important implications for modeling
the energetics of thermally assisted magnetization reversal of spin transfer
magnetic random access memory bit cells.",1210.7682v2
2012-10-30,Quantum Tunneling in Half-Integer-Spin Kagome-Lattice Langasites,"Employing the muon spin relaxation technique we evidence temperature
independent magnetic fluctuations persisting down to the lowest temperatures in
the samarium-based ($J=5/2$) kagome-lattice Langasite. A detailed
bulk-magnetization characterization and comparison to the neodymium-based
($J=9/2$) compound allow us to assign the persistent spin dynamics to a quantum
tunneling process. This is facilitated by pairwise anisotropic magnetic
interactions, leading to a universal scaling of the muon relaxation. Our study
reveals a remarkable analogy between weakly interacting half-integer-spin
rare-earth magnets and molecular nanomagnets.",1210.8187v1
2012-11-13,Gate control of Berry phase in III-V semiconductor quantum dots,"Berry phase in semiconductor quantum dots (QDs) can be induced by moving the
dots adiabatically in a closed loop with the application of the distortion
potential in the lateral direction. We show that the Berry phase is highly
sensitive to the electric fields arising from the interplay between the Rashba
and the Dresselhaus spin-orbit couplings. We report that the accumulated Berry
phase can be induced from other available quantum state that are only differed
by one quantum number of the same spin state. The sign change in the g-factor
due to the penetration of the Bloch wavefunctions into the barrier material can
be reflected in the Berry phase. We solve the time dependent
Schr$\mathrm{\ddot{o}}$dinger equation and investigate the evolution of the
spin dynamics during the adiabatic movement of the QDs in the 2D plane. Our
results might open the possibilities of building a topological quantum dot
quantum computer where the Berry phase can be engineered and can be manipulated
with the application of the spin-orbit couplings through gate controlled
electric fields.",1211.2936v2
2012-11-14,Spin analyzing power for polarized top decays with jets,"We perform perturbative QCD factorization of infrared radiations associated
with an energetic $b$ quark from a polarized top quark decay, taking the
semi-leptonic channel as an example. The resultant formula is expressed as a
convolution of an infrared-finite heavy-quark kernel with a $b$-quark jet
function. Evaluating the heavy-quark kernel up to leading order in the coupling
constant and adopting the jet function from QCD resummation, we predict the
dependence of the spin analyzing power for a polarized top quark on the
invariant mass of the $b$-quark jet. It is observed that the spin analyzing
power could be enhanced by a factor 2 compared to the inclusive case with the
jet mass being integrated over. It is worthwhile to test experimentally the
enhancement of the spin analyzing power due to the inclusion of jet dynamics.",1211.3260v2
2012-11-15,A partonic description of the transverse target single-spin asymmetry in inclusive DIS,"The single-spin asymmetry of unpolarized leptons scattering
deep-inelastically off transversely polarized nucleons is studied in a partonic
picture within a collinear twist-3 framework. Since this observable is
generated by multi-photon exchanges between lepton and nucleon a partonic
description of the asymmetry contains essential elements of a full
next-to-leading order calculation for single-spin asymmetries in perturbative
Quantum Chromodynamics. In particular it is shown how nontrivial cancellations
between kinematical and dynamical twist-3 contributions lead to a well-behaved
and finite formula. This final result can be expressed in terms of
multipartonic quark-gluon and quark-photon correlation functions. Hence, a
measurement of the transverse target single-spin asymmetry may provide new
constraints on these multipartonic correlations.",1211.3579v1
2012-11-30,Spin splitting of relativistic particles in 3D,"The behavior of relativistic particles in an electric and/or magnetic field
is considered in the general case when the direction of propagation may differ
from the direction of the field. A special attention is paid to the spin
splitting and the ensuing Larmor precession frequency of both neutral and
charged particles. For both neutral and charged particles, the Larmor frequency
shows a longitudinal motional red shift. For a neutral particle, there is a
dynamical upper bound, which depends on both the mass and the transverse
momentum of the particle; moreover, the transverse motion leads to a blue shift
of the Larmor frequency. For a charged particle, the longitudinal motional
decrease of the spin splitting is determined by the formation of Landau levels
and it has no upper limit. Unlike the nonrelativistic limit, the relativistic
spin splitting depends on the Landau levels and decreases for higher Landau
levels, thereby signalling the presence of a Landau ladder red shift effect.",1211.7214v1
2012-12-17,Heavy-quark spin symmetry for charmed and strange baryon resonances,"We study charmed and strange baryon resonances that are generated dynamically
by a unitary baryon-meson coupled-channels model which incorporates heavy-quark
spin symmetry. This is accomplished by extending the SU(3) Weinberg-Tomozawa
chiral Lagrangian to SU(8) spin-flavor symmetry plus a suitable symmetry
breaking. The model generates resonances with negative parity from the s-wave
interaction of pseudoscalar and vector mesons with 1/2+ and 3/2+ baryons in all
the isospin, spin, and strange sectors with one, two, and three charm units.
Some of our results can be identified with experimental data from several
facilities, such as the CLEO, Belle, or BaBar Collaborations, as well as with
other theoretical models, whereas others do not have a straightforward
identification and require the compilation of more data and also a refinement
of the model.",1212.3943v2
2013-01-15,Thermal spin fluctuations in spinor Bose-Einstein condensates,"We study the thermal activation of spin fluctuations in dynamically-stable
spinor Bose-Einstein condensates. We analyze the specific cases of a
non-dipolar spin-1 condensate in m = 0, where thermal activation results from
spin-changing collisions, and of a Chromium condensate in the maximally
stretched state m = -3, where thermal spin fluctuations are due to
dipole-induced spin- relaxation. In both cases, we show that the low energy
associated to the spinor physics may be employed for thermometry purposes down
to extremely low temperatures, typically impossible to measure in BECs with
usual thermometric techniques. Moreover, the peculiar dependence of the
system's entropy with the applied Zeeman energy opens a possible route for
adiabatic cooling.",1301.3406v1
2013-01-24,Topological phase in a two-dimensional metallic heavy-fermion system,"We report on a topological insulating state in a heavy-fermion system away
from half-filling, which is hidden within a ferromagnetic metallic phase. In
this phase, the cooperation of the RKKY interaction and the Kondo effect,
together with the spin-orbit coupling, induces a spin-selective gap, bringing
about topologically non-trivial properties. This topological phase is robust
against a change in the chemical potential in a much wider range than the gap
size. We analyze these remarkable properties by using dynamical mean field
theory and the numerical renormalization group. Its topological properties
support a gapless chiral edge mode, which exhibits a non-Tomonaga-Luttinger
liquid behavior due to the coupling with bulk ferromagnetic spin fluctuations.
We also propose that the effects of the spin fluctuations on the edge mode can
be detected via the NMR relaxation time measurement.",1301.5688v2
2013-01-28,Evidence for Dimer Crystal Melting in the Frustrated Spin-Ladder BiCu2PO6,"In the spin ladder compound BiCu$_2$PO$_6$ there exists a decisive dynamics
of spin excitations that we classify and characterize using inelastic light
scattering. We observe low-energy singlets and a broad triplon continuum
extending from 36 cm$^{-1}$ to 700 cm$^{-1}$ in ($aa$), ($bb$), and ($cc$)
light scattering polarizations. Though isolated spin ladder physics can roughly
account for the observed excitations at high energies, frustration and
interladder interactions need to be considered to fully describe the spectral
distribution and scattering selection rules at low and intermediate energies.
More significantly, an interladder singlet bound mode at 24 cm$^{-1}$, lying
below the continuum, shows its largest scattering intensity in interladder
($ab$) polarization. In contrast, two intraladder bound states at 62 cm$^{-1}$
and 108 cm$^{-1}$ with energies comparable to the continuum are observed with
light polarization along the leg ($bb$) and the rung ($cc$). We attribute the
rich spectrum of singlet bound modes to a melting of a dimer crystal. Our study
provides evidence for a Z$_2$ quantum phase transition from a dimer to a
resonating valence bond state driven by singlet fluctuations.",1301.6769v1
2013-02-14,Thermodynamic properties of correlated fermions in lattices with spin-dependent disorder,"Motivated by the rapidly growing possibilities for experiments with ultracold
atoms in optical lattices we investigate the thermodynamic properties of
correlated lattice fermions in the presence of an external spin-dependent
random potential. The corresponding model, a Hubbard model with spin-dependent
local random potentials, is solved within dynamical mean-field theory. This
allows us to present a comprehensive picture of the thermodynamic properties of
this system. In particular, we show that for a fixed total number of fermions
spin-dependent disorder induces a magnetic polarization. The magnetic response
of the polarized system differs from that of a system with conventional
disorder.",1302.3395v2
2013-03-07,Theory of atomistic simulation of spin-transfer torque in nanomagnets,"In spin-transfer torque (STT) for technological applications, the
miniaturization of the magnet may reach the stage of requiring a fully
quantum-mechanical treatment. We present an STT theory which uses the quantum
macrospin ground and excited (magnon) states of the nanomagnet. This allows for
energy and angular momentum exchanges between the current electron and the
nano-magnet. We develop a method of magnetization dynamics simulation which
captures the heating effect on the magnet by the spin-polarized current and the
temperature-dependence in STT. We also discuss the magnetostatics effect on
magnon scattering for ferromagnetic relaxation in a thin film. Our work
demonstrates a realistic step towards simulation of quantum spin-transfer
torque physics in nano-scale magnets.",1303.1775v1
2013-03-15,Inducing spin-correlations and entanglement in a double quantum dot through non-equilibrium transport,"For a double quantum dot system in a parallel geometry, we demonstrate that
by combining the effects of a flux and driving an electrical current through
the structure, the spin correlations between electrons localized in the dots
can be controlled at will. In particular, a current can induce spin
correlations even if the spins are uncorrelated in the initial equilibrium
state. Therefore, we are able to engineer an entangled state in this double-dot
structure. We take many-body correlations fully into account by simulating the
real-time dynamics using the time-dependent density matrix renormalization
group method. Using a canonical transformation, we provide an intuitive
explanation for our results, related to Ruderman-Kittel-Kasuya-Yoshida physics
driven by the bias.",1303.3860v2
2013-03-15,Strong coupling theory of heavy fermion criticality,"We present a theory of the scaling behavior of the thermodynamic, transport
and dynamical properties of a three-dimensional metal at an antiferromagnetic
critical point. We show how the critical spin fluctuations at the AFM
wavevector q=Q induce energy fluctuations at small q, giving rise to a
diverging quasiparticle effective mass over the whole Fermi surface. The
coupling of the fermionic and bosonic degrees of freedom leads to a
self-consistent relation for the effective mass, which has a strong coupling
solution in addition to the well-known weak-coupling, spin-density-wave
solution. We thereby use the recently-introduced concept of critical
quasiparticles, employing a scale-dependent effective mass ratio m*/m and
quasiparticle weight factor Z. As a consequence of the diverging effective mass
the Landau Fermi liquid interaction is found to diverge in all channels except
the critical one, causing important vertex corrections. The ensuing spin
fluctuation spectrum obeys omega/T scaling. Our results are in good agreement
with experimental data on the heavy fermion compounds YbRh2Si2$ and
CeCu(6-x)Au(x) assuming 3D and 2D spin fluctuations, respectively.",1303.3926v2
2013-03-18,Non-Markovian spin transfer dynamics in magnetic semiconductors despite short memory times,"A quantum kinetic theory of the spin transfer between carriers and Mn atoms
in a Mn doped diluted magnetic semiconductor is presented. It turns out that
the typical memory time associated with these processes is orders of magnitude
shorter than the time scale of the spin transfer. Nevertheless, Markovian rate
equations, which are obtained by neglecting the memory, work well only for bulk
systems. For quantum wells and wires the quantum kinetic results qualitatively
deviate from the Markovian limit under certain conditions. Instead of a
monotonic decay of an initially prepared excess electron spin, an overshoot or
even coherent oscillations are found. It is demonstrated that these features
are caused by energetic redistributions of the carriers due to the energy-time
uncertainty.",1303.4322v1
2013-03-23,Dissipative versus Conditional Generation of Gaussian Entanglement and Spin Squeezing,"Spin squeezing of collective atomic spins can be achieved conditionally via
probing with light and subsequent homodyne detection, as is done in a Quantum
Nondemolition measurement. Recently it has been shown that squeezing can also
be created unconditionally by a properly designed dissipative dynamics. We
compare the two approaches in a Gaussian description, and optimize over all
Gaussian light-matter interactions. We find that in the optimal unconditional
scheme based on dissipation the level of squeezing scales as $d^{-1/2}$. In
contrast, the optimal conditional scheme based on measurement of light -- which
in fact is not a Quantum Nondemolition measurement -- can provide squeezing
which scales as $d^{-1}$ in the most relevant regime of moderate optical
depths. Our results apply directly also to the creation of entanglement in the
form of non-local spin squeezing of two atomic ensembles.",1303.5888v3
2013-04-03,Synchronization of an array of spin torque nano oscillators in periodic applied external magnetic field,"Considering an array of spin torque transfer nano oscillators (STNOs), we
have investigated the synchronization property of the system under the action
of a common periodically driven applied external magnetic field by numerically
analyzing the underlying system of Landau-Lifshitz-Gilbert-Slonczewski (LLGS)
equations for the macro-spin variables. We find the novel result that the
applied external magnetic field can act as a medium to induce synchronization
of periodic oscillations, both in-phase and anti-phase, even without coupling
through spin current, thereby leading to the exciting possibility of
enhancement of microwave power in a straightforward way.",1304.0875v1
2013-04-03,Higher Spin Contributions to Holographic Fluid Dynamics in $AdS_5/CFT_4$,"We calculate the graviton's $\beta$-function in $AdS$ string-theoretic
sigma-model, perturbed by vertex operators for Vasiliev's higher spin gauge
fields in $AdS_5$. The result is given by $\beta_{mn}=R_{mn}+4T_{mn}(g,u)$
(with the AdS radius set to 1 and the graviton polarized along the $AdS_5$
boundary), with the matter stress-energy tensor given by that of conformal
holographic fluid in $d=4$, evaluated at the temperature given by
$T={1\over{\pi}}$. The stress-energy tensor is given by
$T_{mn}={g_{mn}}+4u_mu_n+\sum_{N}T^{(N)}_{mn}$ where $u$ is the vector
excitation satisfying $u^2=-1$ and $N$ is the order of the gradient expansion
in the dissipative part of the tensor. We calculate the contributions up to
N=2. The higher spin excitations contribute to the $\beta$-function, ensuring
the overall Weyl covariance of the matter stress tensor. We conjecture that the
structure of gradient expansion in $d=4$ conformal hydrodynamics at higher
orders is controlled by the higher spin operator algebra in $AdS_5$.",1304.0898v1
2013-05-17,Spin and energy relaxation in germanium studied by spin-polarized direct-gap photoluminescence,"Spin orientation of photoexcited carriers and their energy relaxation is
investigated in bulk Ge by studying spin-polarized recombination across the
direct band gap. The control over parameters such as doping and lattice
temperature is shown to yield high polarization degree, namely larger than 40%,
as well as a fine-tuning of the angular momentum of the emitted light with a
complete reversal between right- and left-handed circular polarization. By
combining the measurement of the optical polarization state of band-edge
luminescence and Monte Carlo simulations of carrier dynamics, we show that
these very rich and complex phenomena are the result of the electron
thermalization and cooling in the multi-valley conduction band of Ge. The
circular polarization of the direct-gap radiative recombination is indeed
affected by energy relaxation of hot electrons via the X valleys and the
Coulomb interaction with extrinsic carriers. Finally, thermal activation of
unpolarized L valley electrons accounts for the luminescence depolarization in
the high temperature regime.",1305.4024v1
2013-05-21,Effect of Hole Shape on Spin-Wave Band Structure in One-Dimensional Magnonic Antidot Waveguide,"We present the possibility of tuning the spin-wave band structure,
particularly the bandgaps in a nanoscale magnonic antidot waveguide by varying
the shape of the antidots. The effects of changing the shape of the antidots on
the spin-wave dispersion relation in a waveguide have been carefully monitored.
We interpret the observed variations by analysing the equilibrium magnetic
configuration and the magnonic power and phase distribution profiles during
spin-wave dynamics. The inhomogeneity in the exchange fields at the antidot
boundaries within the waveguide is found to play a crucial role in controlling
the band structure at the discussed length scales. The observations recorded
here will be important for future developments of magnetic antidot based
magnonic crystals and waveguides.",1305.4812v2
2013-06-06,Voltage control of electron-nuclear spin correlation time in a single quantum dot,"We demonstrate bias control of the hyperfine coupling between a single
electron in an InAs quantum dot and the surrounding nuclear spins monitored
through the positively charged exciton X+ emission. In applied longitudinal
magnetic fields we vary simultaneously the correlation time of the hyperfine
interaction and the nuclear spin relaxation time and thereby the amplitude of
the achieved dynamic nuclear polarization under optical pumping conditions. In
applied transverse magnetic fields a change in the applied bias allows to
switch from the anomalous Hanle effect to the standard electron spin
depolarization curves.",1306.1415v1
2013-06-17,Magnetic excitations in the spin-1/2 triangular-lattice antiferromagnet Cs$_2$CuBr$_4$,"We report on high-field electron spin resonance (ESR) studies of magnetic
excitations in the spin-1/2 triangular-lattice antiferromagnet Cs$_2$CuBr$_4$.
Frequency-field diagrams of ESR excitations are measured for different
orientations of magnetic fields up to 25 T. We show that the substantial
zero-field energy gap, $\Delta\approx9.5$ K, observed in the low-temperature
excitation spectrum of Cs$_2$CuBr$_4$ [Zvyagin $et~al.$, Phys. Rev. Lett. 112,
077206 (2014)], is present well above $T_N$. Noticeably, the transition into
the long-range magnetically ordered phase does not significantly affect the
size of the gap, suggesting that even below $T_N$ the high-energy spin dynamics
in Cs$_2$CuBr$_4$ is determined by short-range-order spin correlations. The
experimental data are compared with results of model spin-wave-theory
calculations for spin-1/2 triangle-lattice antiferromagnet.",1306.3887v3
2013-06-21,Magnetic properties of a family of quinternary oxalates,"We report on the magnetic properties of four isomorphous compounds of a
family of quinternary oxalates down to 60 mK. In all these materials, the
magnetic FeII ions with a strong magneto-crystalline anisotropy form a
distorted kagome lattice, topologically equivalent to a perfect kagome one if
nearest-neighbor interactions only are considered. All the compounds order at
low temperature in an antiferromagnetic arrangement with magnetic moments at
120{\deg}. A remarkable magnetic behavior emerges below the N\'eel temperature
in three compounds (with inter-kagome-layer Zr, Sn, Fe but not with Al): the
spin anisotropy combined with a low exchange path network connectivity lead to
domain walls intersecting the kagome planes through strings of free spins.
These produce an unfamiliar slow spin dynamics in the ordered phase observed by
AC susceptibility, evolving from exchange-released spin-flips towards a
cooperative behavior on decreasing the temperature.",1306.5188v1
2013-06-29,First-principles calculations of current-induced spin-transfer torques in magnetic domain walls,"Current-induced spin-transfer torques (STTs) have been studied in Fe, Co and
Ni domain walls (DWs) by the method based on the first-principles noncollinear
calculations of scattering wave functions expanded in the tight-binding
linearized muffin-tin orbital (TB-LMTO) basis. The results show that the
out-of-plane component of nonadiabatic STT in Fe DW has localized form, which
is in contrast to the typical nonlocal oscillating nonadiabatic torques
obtained in Co and Ni DWs. Meanwhile, the degree of nonadiabaticity in STT is
also much greater for Fe DW. Further, our results demonstrate that compared to
the well-known first-order nonadiabatic STT, the torque in the third-order
spatial derivative of local spin can better describe the distribution of
localized nonadiabatic STT in Fe DW. The dynamics of local spin driven by this
third-order torques in Fe DW have been investigated by the
Landau-Lifshitz-Gilbert (LLG) equation. The calculated results show that with
the same amplitude of STTs the DW velocity induced by this third-order term is
about half of the wall speed for the case of the first-order nonadiabatic STT.",1307.0062v1
2013-07-01,Local spin relaxation within the random Heisenberg chain,"Finite-temperature local spin dynamics within the random spin-1/2
antiferromagnetic Heisenberg chain is studied numerically. The aim is to
explain measured NMR spin-lattice relaxation times in
BaCu_{2}(Si_{0.5}Ge_{0.5})_{2}O_{7}, which is the realization of a random spin
chain. In agreement with experiments we find that the distribution of
relaxation times within the model shows a very large span similar to the
stretched-exponential form. The distribution is strongly reduced with
increasing T but stays finite also in the high-T limit. Our results reveal the
crucial role of the anisotropy (interaction), since the behavior is essentially
contrast with the ones for XX model (equivalent to noninteracting fermions),
where we do not find any significant T dependence of the distribution.",1307.0370v2
2013-07-04,Proposal for an on-demand source of polarized electrons into the edges of a topological insulator,"We propose a device that allows for the emission of pairs of spin-polarized
electrons into the edge-states of a two dimensional topological insulator.
Charge and spin emission is achieved using a periodically driven quantum dot
weakly coupled to the edge states of the host topological insulator. We present
calculations of the emitted time-dependent charge and spin currents of such a
dynamical scatterer using the Floquet scattering matrix approach. Experimental
signatures of spin-polarized two-particle emission can be found in noise
measurements. Here a new form of noise suppression, named
$\mathbb{Z}_2$--antibunching, is introduced. Additionally, we propose a set-up
in which entanglement of the emitted electrons is generated. This entanglement
is based on a post-selection procedure and becomes manifest in a violation of a
Clauser-Horne-Shimony-Holt inequality.",1307.1198v4
2013-07-04,Magnetic transition and spin dynamics in the triangular Heisenberg antiferromagnet $α$-KCrO$_{2}$,"We present the results of muon-spin relaxation measurements on the triangular
lattice Heisenberg antiferromagnet $\alpha$-KCrO$_{2}$. We observe sharp
changes in behaviour at an ordering temperature of $T_{\mathrm{c}}=23$ K, with
an additional broad feature in the muon-spin relaxation rate evident at T=13 K,
both of which correspond to features in the magnetic contribution to the heat
capacity. This behaviour is distinct from both the Li- and Na- containing
members of the series. These data may be qualitatively described with the
established theoretical predictions for the underlying spin system.",1307.1377v1
2013-07-12,Noise to lubricate qubit transfer in a spin network,"We consider quantum state transfer in a fully connected spin network, in
which the results indicate that it is impossible to achieve high fidelity by
free dynamics. However, the addition of certain kinds of noise can be helpful
for this purpose. In fact, we introduce a model of Gaussian white noise
affecting the spin-spin couplings (edges), except those linked to the input and
output node, and prove that it enhances the fidelity of state transfer. The
observed noise benefit is scale free as it applies to a quantum network of any
size. The amount of the fidelity enhancement, depending on the noise strength
as well as on the number of edges to which it is applied, can be so high as to
take the fidelity close to one.",1307.3465v2
2013-07-16,Effect of Transverse Gluons on Chiral Restoration in Excited Mesons,"The effect of transverse gluons on the chiral symmetry patterns of excited
mesons is studied in a Coulomb gauge QCD model. The linear rising static
quark-antiquark potential and the transverse gluon propagator known from
lattice studies are input into the model. The non-perturbative quark
propagator, which enters the meson bound state equations, is derived from the
Dyson--Schwinger equations and a complete set of mesons for general spin
quantum number is presented. From analyzing the bound state equations for large
spins it is demonstrated, that chiral and axial symmetry are restored. In this
limit a complete degeneracy of all multiplets with given spin is observed. The
effect of the transverse gluon interaction is shown to vanish rapidly as the
spin quantum number is increased. For vanishing dynamical quark mass the
expected meson degeneracies are recovered.",1307.4224v1
2013-10-11,Analytical theory of modulated magnetic solitons,"Droplet solitons are coherently precessing solitary waves that have been
recently realized in thin ferromagnets with perpendicular anisotropy.In the
strongly nonlinear regime, droplets can be well approximated by a slowly
precessing, circular domain wall with a hyperbolic tangent form. Utilizing this
representation, this work develops a general droplet modulation theory and
applies it to study the long range effects of the magnetostatic field and a
nanocontact spin torque oscillator (NC-STO) where spin polarized currents act
as a gain source to counteract magnetic damping. An analysis of the dynamical
equations for the droplet's center, frequency and phase demonstrates a negative
processional frequency shift due to long range dipolar interactions, dependent
on film thickness. Further analysis also demonstrates the onset of a
saddle-node bifurcation at the minimum sustaining current for the NC-STO. The
basin of attraction associated with the stable node demonstrates that spin
torque enacts a restoring force to excursions of the droplet from the
nanocontact center, observed previously in numerical simulations. Large
excursions lead to the droplet's eventual decay into spin waves.",1310.3118v1
2013-11-02,Charge-cluster glass in an organic conductor,"Geometrically frustrated spin systems often do not exhibit long-range
ordering, resulting in either quantum-mechanically disordered states, such as
quantum spin liquids, or classically disordered states, such as spin ices or
spin glasses. Geometric frustration may play a similar role in charge ordering,
potentially leading to unconventional electronic states without long-range
order; however, there are no previous experimental demonstrations of this
phenomenon. Here, we show that a charge-cluster glass evolves upon cooling in
the absence of long-range charge ordering for an organic conductor with a
triangular lattice, theta-(BEDT-TTF)2RbZn(SCN)4. A combination of time-resolved
transport measurements and x-ray diffraction reveal that the charge-liquid
phase has charge clusters that fluctuate extremely slowly (<10-100 Hz) and
heterogeneously. Upon further cooling, the cluster dynamics freeze, and a
charge-cluster glass is formed. Surprisingly, these observations correspond to
recent ideas regarding the structural glass formation of supercooled liquids,
indicating that a glass-forming charge liquid relates correlated-electron
physics to glass physics in soft matter.",1311.0344v2
2013-11-04,Spin-Resolved Self-Doping Tunes the Intrinsic Half-Metallicity of AlN Nanoribbons,"We present a first-principles theoretical study of electric field-and
strain-controlled intrinsic half-metallic properties of zigzagged aluminium
nitride (AlN) nanoribbons. We show that the half-metallic property of AlN
ribbons can undergo a transition into fully-metallic or semiconducting behavior
with application of an electric field or uniaxial strain. An external
transverse electric field induces a full charge screening that renders the
material semiconducting. In contrast, as uniaxial strain varies from
compressive to tensile, a spin-resolved selective self-doping increases the
half-metallic character of the ribbons. The relevant strain-induced changes in
electronic properties arise from band structure modifications at the Fermi
level as a consequence of a spin-polarized charge transfer between pi-orbitals
of the N and Al edge atoms in a spin-resolved self-doping process. This band
structure tunability indicates the possibility ofdesigning magnetic nanoribbons
with tunable electronic structure by deriving edge states from elements with
sufficiently different localization properties. Finite temperature molecular
dynamics reveal a thermally stable half-metallic nanoribbon up to room
temperature.",1311.0895v1
2013-11-18,N and $Δ$ hidden-charm resonances with heavy-quark spin symmetry,"We study N and $\Delta$ hidden-charm baryon resonances that are generated
dynamically from the s-wave interaction of pseudoscalar and vector mesons with
$1/2^+$ and $3/2^+$ baryons. We use a unitary coupled-channels model that
fulfills heavy-quark spin symmetry and respects spin-flavor symmetry in the
light sector. We predict seven N-like and five $\Delta$-like states with masses
around 4 GeV, most of them as bound states. Some of these states form
heavy-quark spin multiplets, which are almost degenerate in mass.",1311.4427v1
2013-12-03,Gravitational self-torque and spin precession in compact binaries,"We calculate the effect of self-interaction on the ""geodetic"" spin precession
of a compact body in a strong-field orbit around a black hole. Specifically, we
consider the spin precession angle $\psi$ per radian of orbital revolution for
a particle carrying mass $\mu$ and spin $s \ll (G/c) \mu^2$ in a circular orbit
around a Schwarzschild black hole of mass $M \gg \mu$. We compute $\psi$
through $O(\mu/M)$ in perturbation theory, i.e, including the correction
$\delta\psi$ (obtained numerically) due to the torque exerted by the
conservative piece of the gravitational self-field. Comparison with a
post-Newtonian (PN) expression for $\delta\psi$, derived here through 3PN
order, shows good agreement but also reveals strong-field features which are
not captured by the latter approximation. Our results can inform
semi-analytical models of the strong-field dynamics in astrophysical binaries,
important for ongoing and future gravitational-wave searches.",1312.0775v2
2013-12-11,Black hole spin measurements through the relativistic precession model: XTE J1550-564,"We present a systematic analysis of the complete set of observations of the
black hole (BH) binary XTE J1550-564 obtained by the Rossi X-ray Timing
Explorer. We study the fast time variability properties of the source and
determine the spin of the black hole through the relativistic precession model.
Similarly to what is observed in the BH binary GRO J1655-40, the frequencies of
the QPOs and broad band noise components match the general relativistic
frequencies of particle motion close to the compact object predicted by the
relativistic precession model. The combination of two simultaneously observed
quasi-periodic oscillation (QPO) frequencies together with the dynamical BH
mass from optical/infrared observations yields a spin equal to a = 0.34 +/-
0.01, consistent with previous determinations from X-ray spectroscopy. Based on
the derived BH parameters, the low frequency QPO emission radii vary from about
30 gravitational radii to the innermost stable orbit for this spin (about 5
gravitational radii), where they sharply disappear as observed for the case of
GRO J1655-40.",1312.3114v1
2013-12-18,Spin-current autocorrelations from single pure-state propagation,"We demonstrate that the concept of quantum typicality allows for significant
progress in the study of real-time spin dynamics and transport in quantum
magnets. To this end, we present a numerical analysis of the spin-current
autocorrelation function of the antiferromagnetic and anisotropic spin-1/2
Heisenberg chain as inferred from propagating only a single pure state,
randomly chosen as a ""typical"" representative of the statistical ensemble.
Comparing with existing time-dependent density-matrix renormalization group
(tDMRG) data, we show that typicality is fulfilled extremely well, consistent
with an error of our approach, which is perfectly under control and vanishes in
the thermodynamic limit. In the long-time limit, our results provide for a new
benchmark for the enigmatic spin Drude weight, which we obtain from chains as
long as L=33 sites, i.e., from Hilbert spaces of dimensions almost O(10^4)
larger than in existing exact-diagonalization studies.",1312.5319v2
2013-12-25,Dynamic Lattice Supersymmetry in gl(n|m) Spin Chains,"Supersymmetry operators that change a spin chain's length have appeared in
numerous contexts, ranging from the AdS/CFT correspondence to statistical
mechanics models. In this article, we present, via an analysis of the Bethe
equations, all homogeneous, rational and trigonometric, integrable gl(n|m) spin
chains for which length-changing supersymmetry can be present. Furthermore, we
write down the supercharges explicitly for the simplest new models, namely the
sl(n|1) spin chains with the (n-1)-fold antisymmetric tensor product of the
fundamental representation at each site and check their compatibility with
integrability.",1312.7021v2
2014-01-03,"Spin-Transfer-Torque Driven Magneto-Logic OR, AND and NOT Gates","We show that current induced magneto-logic gates like AND, OR and NOT can be
designed with the simple architecture involving a single nano spin-valve
pillar, as an extension of our recent work on spin-torque-driven magneto-logic
universal gates, NAND and NOR. Here the logical operation is induced by
spin-polarized currents which also form the logical inputs. The operation is
facilitated by the simultaneous presence of a constant controlling magnetic
field, in the absence of which the same element operates as a magnetoresistive
memory element. We construct the relevant phase space diagrams for the free
layer magnetization dynamics in the monodomain approximation and show the
rationale and functioning of the proposed gates. The flipping time for the
logical states of these non-universal gates is estimated to be within nano
seconds, just like their universal counter parts.",1401.0627v1
2014-02-05,Theoretical probing of inelastic spin-excitations in adatoms on surfaces,"We review our recent work on the simulation, description and prediction of
spin-excitations in adatoms and dimers deposited on metallic surfaces. This
work done together with Douglas L. Mills, is an extension of his seminal
contribution (with Pascal Lederer) published 50 years ago on the spin-dynamics
of transition metal impurities embedded in transition metal hosts [P. Lederer,
D.L. Mills, Phys. Rev. {\bf 160}, 590 (1967)]. The main predictions of his
model were verified experimentally with state of the art inelastic scanning
tunneling spectroscopy on adatoms. Our formalism, presented in this review, is
based on time-dependent density functional theory, combined with the
Korringa-Kohn-Rostoker Green function method. Comparison to experiments is
shown and discussed in detail. Our scheme enables the description and
prediction of the main characteristics of these excitations, \emph{i.e.} their
resonance frequency, their lifetime and their behavior upon application of
external perturbations such as a magnetic field.",1402.1113v1
2014-02-09,Site specific spin dynamics in BaFe2As2: tuning the ground state by orbital differentiation,"The role of orbital differentiation on the emergence of superconductivity in
the Fe-based superconductors remains an open question to the scientific
community. In this investigation, we employ a suitable microscopic spin probe
technique, namely Electron Spin Resonance (ESR), to investigate this issue on
selected chemically substituted BaFe$_{2}$As$_{2}$ single crystals. As the
spin-density wave (SDW) phase is suppressed, we observe a clear increase of the
Fe 3$d$ bands anisotropy along with their localization at the FeAs plane. Such
an increase of the planar orbital content interestingly occurs independently on
the chemical substitution responsible for suppressing the SDW phase. As a
consequence, the magnetic fluctuations combined with the resultant particular
symmetry of the Fe 3$d$ bands are propitious ingredients to the emergence of
superconductivity in this class of materials.",1402.2001v1
2014-04-03,Bose-Bose Mixtures with Synthetic Spin-Orbit Coupling in Optical Lattices,"We investigate the ground state properties of Bose-Bose mixtures with
Rashba-type spin-orbit (SO) coupling in a square lattice. The system displays
rich physics from the deep Mott-insulator (MI) all the way to the superfluid
(SF) regime. In the deep MI regime, novel spin-ordered phases arise due to the
effective Dzyaloshinskii-Moriya type super-exchange interactions. By employing
the non-perturbative Bosonic Dynamical Mean-Field-Theory (BDMFT), we
numerically study and establish the stability of these magnetic phases against
increasing hopping amplitude. We show that as hopping is increased across the
MI to SF transition, exotic superfluid phases with magnetic textures emerge. In
particular, we identify a new spin-spiral magnetic texture with spatial period
3 in the superfluid close to the MI-SF transition.",1404.0970v2
2014-04-08,Resonant Spin Wave Excitation by Terahertz Magnetic Near-field Enhanced with Split Ring Resonator,"Excitation of antiferromagnetic spin waves in HoFeO$_{3}$ crystal combined
with a split ring resonator (SRR) is studied using terahertz (THz)
electromagnetic pulses. The magnetic field in the vicinity of the SRR induced
by the incident THz electric field component excites and the Faraday rotation
of the polarization of a near-infrared probe pulse directly measures
oscillations that correspond to the antiferromagnetic spin resonance mode. The
good agreement of the temperature-dependent magnetization dynamics with the
calculation using the two-lattice Landau-Lifshitz-Gilbert equation confirms
that the spin wave is resonantly excited by the THz magnetic near-field
enhanced at the LC resonance frequency of the SRR, which is 20 times stronger
than the incident magnetic field.",1404.2179v1
2014-04-23,Effect of spin orbit coupling and Hubbard $U$ on the electronic structure of IrO$_2$,"We have studied in detail the electronic structure of IrO$_2$ including
spin-orbit coupling (SOC) and electron-electron interaction, both within the
GGA+U and GGA+DMFT approximations. Our calculations reveal that the Ir t$_{2g}$
states at the Fermi level largely retain the J$_{\rm eff}$ = $\frac{1}{2}$
character, suggesting that this complex spin-orbit entangled state may be
robust even in metallic IrO$_2$. We have calculated the phase diagram for the
ground state of IrO$_2$ as a function of $U$ and find a metal insulator
transition that coincides with a magnetic phase change, where the effect of SOC
is only to reduce the critical values of $U$ necessary for the transition. We
also find that dynamic correlations, as given by the GGA+DMFT calculations,
tend to suppress the spin-splitting, yielding a Pauli paramagnetic metal for
moderate values of the Hubbard $U$. Our calculated optical spectra and
photoemission spectra including SOC are in good agreement with experiment
demonstrating the importance of SOC in IrO$_2$.",1404.5991v1
2014-04-24,Large-amplitude spin oscillations triggered by nonequilibrium strongly correlated $t_{2g}$ electrons,"Laser-induced ultrafast (fs) magnetization experiments in antiferromagnets
have recently attracted large attention, paving the road for inherently fast
spin dynamics in the THz regime without invoking stray fields. The technical
importance is emphasized by the rising new research field of antiferromagnetic
(AFM) spintronics, where superexchange-dominated strongly correlated compounds
provide an interesting materials playground. An intriguing question is whether
the Coulomb interaction may be a key to control AFM order on ultrafast time
scales. Therefore, we study (de)magnetization processes in a time-dependent
multiorbital Hubbard model, focusing on $t_{2g}$ electrons in a wider doping
range. Depending on filling, we reveal large-amplitude spin oscillations via
interaction quenches from the antiferromagnetic or paramagnetic state.
Nonequilibrium ultrafast spin-orientation effects in prominent correlated
transition-metal oxides are therefrom predicted.",1404.6118v4
2014-04-24,Strong driving of a single spin using arbitrarily polarized fields,"The strong driving regime occurs when a quantum two-level system is driven
with an external field whose amplitude is greater or equal to the energy
splitting between the system's states, and is typically identified with the
breaking of the rotating wave approximation (RWA). We report an experimental
study, in which the spin of a single nitrogen-vacancy (NV) center in diamond is
strongly driven with microwave (MW) fields of arbitrary polarization. We
measure the NV center spin dynamics beyond the RWA, and characterize the
limitations of this technique for generating high-fidelity quantum gates. Using
circularly polarized MW fields, the NV spin can be harmonically driven in its
rotating frame regardless of the field amplitude, thus allowing rotations
around arbitrary axes. Our approach can effectively remove the RWA limit in
quantum-sensing schemes, and assist in increasing the number of operations in
QIP protocols.",1404.6282v1
2014-07-25,Far-from-equilibrium spin transport in Heisenberg quantum magnets,"We study experimentally the far-from-equilibrium dynamics in ferromagnetic
Heisenberg quantum magnets realized with ultracold atoms in an optical lattice.
After controlled imprinting of a spin spiral pattern with adjustable wave
vector, we measure the decay of the initial spin correlations through
single-site resolved detection. On the experimentally accessible timescale of
several exchange times we find a profound dependence of the decay rate on the
wave vector. In one-dimensional systems we observe diffusion-like spin
transport with a dimensionless diffusion coefficient of 0.22(1). We show how
this behavior emerges from the microscopic properties of the closed quantum
system. In contrast to the one-dimensional case, our transport measurements for
two-dimensional Heisenberg systems indicate anomalous super-diffusion.",1407.6934v2
2014-09-10,Realizing Exactly Solvable SU(N) Magnets with Thermal Atoms,"We show that $n$ thermal fermionic alkaline-earth atoms in a flat-bottom trap
allow one to robustly implement a spin model displaying two symmetries: the
$S_n$ symmetry that permutes atoms occupying different vibrational levels of
the trap and the SU($N$) symmetry associated with $N$ nuclear spin states. The
high symmetry makes the model exactly solvable, which, in turn, enables the
analytic study of dynamical processes such as spin diffusion in this SU($N$)
system. We also show how to use this system to generate entangled states that
allow for Heisenberg-limited metrology. This highly symmetric spin model should
be experimentally realizable even when the vibrational levels are occupied
according to a high-temperature thermal or an arbitrary non-thermal
distribution.",1409.3234v2
2014-09-13,A spin-boson theory for charge photogeneration in organic molecules: Role of quantum coherence,"The charge photogeneration process in organic molecules is investigated by a
quantum heat engine model, in which two molecules are modeled by a two-spin
system sandwiched between two bosonic baths at their own temperatures. The two
baths represent the photon emission source and the phonon environment,
respectively. We utilize the time-dependent density matrix renormalization
group algorithm to investigate the ultrafast quantum thermodynamical processes
of the model. We find that the transient energy flow through the two spins
behaves a two-stage effect: The first stage shows a coherent dynamics which
represents the ultrafast delocalization and dissociation of the charge-transfer
state, and in the second stage a steady current is establish. The
photo-to-charge conversion is highly efficient with the maximum efficiency
being $93\%$ with optimized model parameters. The survival entanglement between
the two spins is found to be mostly responsible for the hyper efficiency.",1409.3916v1
2014-09-14,Landslides and Mass Shedding on Spinning Spheroidal Asteroids,"Conditions for regolith landslides to occur on spinning, gravitating
spheroidal asteroids and their aftermath are studied. These conditions are
developed by application of classical granular mechanics stability analysis to
the asteroid environment. As part of our study we determine how slopes evolve
across the surface of these bodies as a function of spin rate, the dynamical
fate of material that exceeds the angle of repose, and an analysis of how the
shape of the body may be modified based on these results. We find specific
characteristics for body surfaces and shapes when spun near the surface
disruption limit and develop what their observable implications are. The small,
oblate and rapidly spinning asteroids such as 1999 KW4 Alpha and 2008 EV5
exhibit some of these observable traits. The detailed mechanisms outlined here
can also provide insight and constraints on the recently observed active
asteroids such as P/2013 P5, and the creation of asteroidal meteor streams.",1409.4015v1
2014-09-18,Decoherence imaging of spin ensembles using a scanning single-electron spin in diamond,"The nitrogen-vacancy (NV) defect center in diamond has demonstrated great
capability for nanoscale magnetic sensing and imaging for both static and
periodically modulated target fields. However, it remains a challenge to detect
and image randomly fluctuating magnetic fields. Recent theoretical and
numerical works have outlined detection schemes that exploit changes in
decoherence of the detector spin as a sensitive measure for fluctuating fields.
Here we experimentally monitor the decoherence of a scanning NV center in order
to image the fluctuating magnetic fields from paramagnetic impurities on an
underlying diamond surface. We detect a signal corresponding to roughly 800
${\mu}_B$ in 2 s of integration time, without any control on the target spins,
and obtain magnetic-field spectral information using dynamical decoupling
techniques. The extracted spatial and temporal properties of the surface
paramagnetic impurities provide insight to prolonging the coherence of
near-surface qubits for quantum information and metrology applications.",1409.5418v1
2014-09-26,"Two-laser dynamic nuclear polarization with semiconductor electrons: feedback, suppressed fluctuations, and bistability near two-photon resonance","We present how optical coherent population trapping (CPT) of the spin of
localized semiconductor electrons stabilizes the surrounding nuclear spin bath
via the hyperfine interaction, resulting in a state which is more ordered than
the thermal equilibrium state. We find distinct control regimes for different
signs of laser detuning and examine the transition from an unpolarized,
narrowed state to a polarized state possessing a bistability. The narrowing of
the state yields slower electron spin dephasing and self-improving CPT. Our
analysis is relevant for a variety of solid state systems where
hyperfine-induced dephasing is a limitation for using electron spin coherence.",1409.7576v2
2014-10-02,Simultaneous detection of the spin-Hall magnetoresistance and the spin-Seebeck effect in Platinum and Tantalum on Yttrium Iron Garnet,"The spin-Seebeck effect (SSE) in platinum (Pt) and tantalum (Ta) on yttrium
iron garnet (YIG) has been investigated by both externally heating the sample
(using an on-chip Pt heater on top of the device) as well as by current-induced
heating. For SSE measurements, external heating is the most common method to
obtain clear signals. Here we show that also by current-induced heating it is
possible to directly observe the SSE, separate from the also present spin-Hall
magnetoresistance (SMR) signal, by using a lock-in detection technique. Using
this measurement technique, the presence of additional 2nd order signals at low
applied magnetic fields and high heating currents is revealed. These signals
are caused by current-induced magnetic fields (Oersted fields) generated by the
used AC-current, resulting in dynamic SMR signals.",1410.0551v2
2014-10-07,Hydrodynamics of Turning Flocks,"We present a hydrodynamic model of flocking that generalizes the familiar
Toner-Tu equations to incorporate turning inertia of well-polarized flocks. The
continuum equations controlled by only two dimensionless parameters,
orientational inertia and alignment strength, are derived by coarse graining
the inertial spin model recently proposed by Cavagna et al. The interplay
between orientational inertia and bend elasticity of the flock yields
anisotropic spin waves that mediate the propagation of turning information
throughout the flock. The coupling between spin current density to the local
vorticity field through a nonlinear friction gives rise to a hydrodynamic mode
with angular-dependent propagation speed at long wavelength. This mode goes
unstable as a result of the growth of bend and splay deformations augmented by
the spin wave, signaling the transition to complex spatio-temporal patterns of
continuously turning and swirling flocks.",1410.1827v4
2014-10-24,Non-linear spin-wave excitation at low bias fields,"Non-linear magnetization dynamics is essential for the operation of many
spintronics devices. For microwave assisted switching of magnetic elements the
low field regime is of particular interest. In addition a large number of
experiments uses high amplitude FMR in order to generate d.c. currents via spin
pumping mechanism. Here we use time resolved X-ray magnetic circular dichroism
experiments to determine the number density of excited magnons in magnetically
soft Ni_80Fe_20 thin films at small bias fields and large rf-excitation
amplitudes. Our data shows that the common model of non-linear ferromagnetic
resonance is not suitable to describe the low bias field limit. Here we derive
a new model of parametric spin-wave excitation which correctly predicts
threshold amplitudes and decay rates also at low bias fields. In fact a new
series of critical modes with amplitude phase oscillations is found,
generalizing the theory of parametric spin-wave excitation.",1410.6693v1
2014-10-26,Short-range correlations in the magnetic ground state of Na4Ir3O8,"The magnetic ground state of the hyper-kagome lattice in Na4Ir3O8 is explored
via combined bulk magnetization, muon spin relaxation, and neutron scattering
measurements. A short-range, frozen, state comprised of quasi-static moments
develops below a characteristic temperature of T_F=6 K, revealing an
inhomogeneous distribution of spins occupying the entirety of the sample
volume. Quasi-static, short-range, spin correlations persist until at least 20
mK and differ substantially from the nominally dynamic response of a quantum
spin liquid. Our data demonstrate that an inhomogeneous magnetic ground state
arises in Na4Ir3O8 driven either by disorder inherent to the creation of the
hyper-kagome lattice itself or stabilized via quantum fluctuations.",1410.7072v1
2014-10-27,Quasi Many-body Localization in Translation Invariant Systems,"It is typically assumed that disorder is essential to realize Anderson
localization. Recently, a number of proposals have suggested that an
interacting, translation invariant system can also exhibit localization. We
examine these claims in the context of a one-dimensional spin ladder. At
intermediate time scales, we find slow growth of entanglement entropy
consistent with the phenomenology of many-body localization. However, at longer
times, all finite wavelength spin polarizations decay in a finite time,
independent of system size. We identify a single length scale which
parametrically controls both the eventual spin transport times and the
divergence of the susceptibility to spin glass ordering. We dub this long
pre-thermal dynamical behavior, intermediate between full localization and
diffusion, quasi-many body localization.",1410.7407v1
2014-10-28,Generalized analysis of thermally activated domain-wall motion in Co/Pt multilayers,"Thermally activated domain-wall (DW) motion driven by magnetic field and
electric current is investigated experimentally in out-of-plane magnetized
Pt(Co/Pt)$_3$ multilayers. We directly extract the thermal activation energy
barrier for DW motion and observe the dynamic regimes of creep, depinning, and
viscous flow. Further analysis reveals that the activation energy must be
corrected with a factor dependent on the Curie temperature, and we derive a
generalized Arrhenius-like equation governing thermally activated motion. By
using this generalized equation, we quantify the efficiency of current-induced
spin torque in assisting DW motion. Current produces no effect aside from Joule
heating in the multilayer with 7-\AA\ thick Co layers, whereas it generates a
finite spin torque on DWs in the multilayer with atomically thin 3-\AA\ Co
layers. These findings suggest that conventional spin-transfer torques from
in-plane spin-polarized current do not drive DWs in ultrathin Co/Pt
multilayers.",1410.7685v1
2014-10-30,Intrinsic synchronization of an array of spin-torque oscillators driven by the spin-Hall effect,"This paper micromagnetically studies the magnetization dynamics driven by the
spin-Hall effect in a Platinum/Permalloy bi-layer. For a certain field and
current range, the excitation of a uniform mode, characterized by a power with
a spatial distribution in the whole ferromagnetic cross section, is observed.
We suggest to use the ferromagnet of the bi-layer as basis for the realization
of an array of spin-torque oscillators (STOs): the Permalloy ferromagnet will
act as shared free layer, whereas the spacers and the polarizers are built on
top of it. Following this strategy, the frequency of the uniform mode will be
the same for the whole device, creating an intrinsic synchronization. The
synchronization of an array of parallely connected STOs will allow to increase
the output power, as necessary for technological applications.",1410.8342v1
2014-11-07,Entanglement dynamics of electrons and photons,"Entanglement is a fundamental feature of quantum theory as well as a key
resource for quantum computing and quantum communication, but the entanglement
mechanism has not been found at present. We think when the two subsystems exist
interaction directly or indirectly, they can be in entanglement state. such as,
in the Jaynes-Cummings model, the entanglement between an atom and light field
comes from their interaction. In this paper, we have studied the entanglement
mechanism of electron-electron and photon-photon, which are from the spin-spin
interaction. We found their total entanglement states are relevant both space
state and spin state. When two electrons or two photons are far away, their
entanglement states should be disappeared even if their spin state is
entangled.",1411.1814v2
2014-11-12,Electric-Field Control over Spin-Wave and Current Induced Domain Wall Motion and Magnonic Torques in Multiferroics,"We discover that the way spin-waves exert magnetic torques in multiferroic
materials can cause not only domain wall motion, but also magnetization
dynamics for homogeneous magnetization textures. Interestingly, the domain wall
motion can be controlled via purely electrical means with the spin-waves being
generated by an ac electric field $E$ while the direction of the wall motion
also is sensitive to an applied dc $E$ field. Moreover, we determine the
interaction between spin-transfer torque from an electric current and a
magnetic domain wall in multiferroics and show that the Walker breakdown
threshold scales with the magnitude of a perpendicular electric field, offering
a way to control the properties of domain wall propagation via electric gating.",1411.3327v2
2014-11-18,Density-matrix renormalization group study of third harmonic generation in one-dimensional Mott insulator coupled with phonon,"We examine the third-order non-linear optical response of a one-dimensional
Mott insulator coupled with phonons. The Mott insulator is described by an
extended Hubbard-Holstein model. The third harmonic generation (THG) of the
model is calculated by dynamical density-matrix renormalization group. We find
that the electron-phonon interaction enhances the intensity of THG if the
on-site Coulomb interaction is comparable to the band width, but the
enhancement is small for a realistic parameter value of a typical Mott
insulator Sr$_2$CuO$_3$. The low-energy spin excitation does not contribute to
the optical response if the electron-phonon coupling is neglected. We find that
the THG spectrum can detect the spin excitations even for no electron-phonon
coupling. The introduction of the electron-phonon coupling leads to a slight
increase of low-energy weight in THG without peak structure through
phonon-assisted spin excitation. To fully understand the phonon-assisted spin
excitation, we additionally calculate the linear susceptibility of a doped
Hubbard-Holstein model, showing a spectral distribution different from that at
half filling.",1411.4767v1
2014-11-26,Bose-Einstein condensates with localized spin-orbit coupling: soliton complexes and spinor dynamics,"Spin-orbit (SO) coupling can be introduced in a Bose--Einstein condensate
(BEC) as a gauge potential acting only in a localized spatial domain. Effect of
such a SO ""defect"" can be understood by transforming the system to the
integrable vector model. The properties of the SO-BEC change drastically if the
SO defect is accompanied by the Zeeman splitting. In such a non-integrable
system, the SO defect qualitatively changes the character of soliton
interactions and allows for formation of stable nearly scalar soliton complexes
with almost all atoms concentrated in only one dark state. These solitons exist
only if the number of particles exceeds a threshold value. We also report on
the possibility of transmission and reflection of a soliton upon its scattering
on the SO defect. Scattering strongly affects the pseudo-spin polarization and
can induce pseudo-spin precession. The scattering can also result in almost
complete atomic transfer between the dark states.",1411.7322v1
2014-11-26,Feasibility of a metamagnetic transition in correlated systems,"The long-standing issue of the competition between the magnetic field and the
Kondo effect, favoring, respectively, triplet and singlet ground states is
addressed using a cluster slave-rotor mean field theory for the Hubbard model
and its spin-correlated, spin-frustrated extensions in 2 dimension. The
metamagnetic jump is established and compared with earlier results of dynamical
mean-field theory. The present approach also reproduces the emergent
super-exchange energy scale in the insulating side. A scaling is found for the
critical Zeeman field in terms of the intrinsic coherence scale just below the
metal-insulator transition where the critical spin fluctuations are soft. The
conditions for metamagnetism to appear at a reasonable field are also
underlined. The Gutzwiller analysis on the 2D Hubbard model and a quantum Monte
Carlo calculation on the Heisenberg spin system are performed to check the
limiting cases of the cluster slave-rotor results for the Hubbard model.
Low-field scaling features for magnetization are discussed.",1411.7335v2
2014-12-16,State-selective intersystem crossing in nitrogen-vacancy centers,"The intersystem crossing (ISC) is an important process in many solid-state
atomlike impurities. For example, it allows the electronic spin state of the
nitrogen-vacancy (NV) center in diamond to be initialized and read out using
optical fields at ambient temperatures. This capability has enabled a wide
array of applications in metrology and quantum information science. Here, we
develop a microscopic model of the state-selective ISC from the optical excited
state manifold of the NV center. By correlating the electron-phonon
interactions that mediate the ISC with those that induce population dynamics
within the NV center's excited state manifold and those that produce the phonon
sidebands of its optical transitions, we quantitatively demonstrate that our
model is consistent with recent ISC measurements. Furthermore, our model
constrains the unknown energy spacings between the center's spin-singlet and
spin-triplet levels. Finally, we discuss prospects to engineer the ISC in order
to improve the spin initialization and readout fidelities of NV centers.",1412.4865v2
2014-12-22,Locally gauge-invariant spin response of $^3$He-$B$ films with Majorana surface states,"A locally gauge-invariant theory of the spin response of a thin film of
$^3$He-$B$ film is given that describes fluctuation effects arising from the
coupled dynamics of the superconducting order parameter (the collective mode)
and in-gap Majorana surface states. In contrast to a mean-field calculation of
the spin response, which predicts a nonzero imaginary longitudinal spin
susceptibility at frequencies inside the bulk gap due to absorption from the
Majorana states, our gauge-invariant theory shows that this response is
strongly suppressed above the collective mode frequency and vanishes if
dipole-dipole interactions are neglected. In the presence of dipole-dipole
interactions, in sufficiently thin films, and at ultra-low temperatures, the
Majorana states lead to a distinctive magnetic-field- and temperature-dependent
damping of the collective mode, a feature that may be observable in
longitudinal NMR experiments.",1412.7153v2
2014-12-24,Effect of an arbitrary spin orientation on the quadrupolar structure of an extended body in a Schwarzschild spacetime,"The influence of an arbitrary spin orientation on the quadrupolar structure
of an extended body moving in a Schwarzschild spacetime is investigated. The
body dynamics is described by the Mathisson-Papapetrou-Dixon model, without any
restriction on the motion or simplifying assumption on the associated spin
vector and quadrupole tensor, generalizing previous works. The equations of
motion are solved analytically in the limit of small values of the
characteristic length scales associated with the spin and quadrupole variables
with respect to the characteristic length of the background curvature. The
solution provides all corrections to the circular geodesic on the equatorial
plane taken as the reference trajectory due to both dipolar and quadrupolar
structure of the body as well as the conditions which the nonvanishing
components of the quadrupole tensor must fulfill in order that the problem be
self-consistent.",1412.7643v2
2015-01-08,Long-Distance Entanglement of Soliton Spin Qubits in Gated Nanowires,"We investigate numerically charge, spin, and entanglement dynamics of two
electrons confined in a gated semiconductor nanowire. The electrostatic
coupling between electrons in the nanowire and the charges in the metal gates
leads to a self-trapping of the electrons which results in soliton-like
properties. We show that the interplay of an all-electrically controlled
coherent transport of the electron solitons and of the exchange interaction can
be used to realize ultrafast SWAP and entangling $\sqrt{\text{SWAP}}$ gates for
distant spin qubits. We demonstrate that the latter gate can be used to
generate a maximally entangled spin state of spatially separated electrons. The
results are obtained by quantum mechanical time-dependent calculations with
exact inclusion of electron-electron correlations.",1501.01932v1
2015-01-08,Complete All-Optical Quantum Control of Electron Spins in InAs/GaAs Quantum Dot Molecule,"The spin states of electrons and holes confined in InAs quantum dot molecules
have recently come to fore as a promising system for the storage or
manipulation of quantum information. We describe here a feasible scheme for
complete quantum optical control of two electron spin qubits in two
vertically-stacked singly-charged InAs quantum dots coupled by coherent
electron tunneling. With an applied magnetic field transverse to the growth
direction, we construct a universal set of gates that corresponds to the
possible Raman transitions between the spin states. We detail the procedure to
decompose a given two-qubit unitary operation, so as to realize it with a
successive application of up to 8 of these gates. We give the pulse shapes for
the laser pulses used to implement this universal set of gates and demonstrate
the realization of the two-qubit quantum Fourier transform with fidelity of
0.881 and duration of 414 ps. Our proposal therefore offers an accessible path
to universal computation in quantum dot molecules and points to the advantages
of using pulse shaping incoherent manipulation of optically active quantum dots
to mitigate the negative effects of unintended dynamics and spontaneous
emission.",1501.01952v1
2015-01-09,Giant spin-phonon-electronic coupling in a 5d oxide,"Enhanced coupling of material properties offers new fundamental insights and
routes to multifunctional devices. In this context 5d oxides provide new
paradigms of cooperative interactions driving novel emergent behavior. This is
exemplified in 5d osmates that host a metal-insulator transition (MIT) driven
by magnetic order. Here we consider the most robust case, the 5d perovskite
NaOsO3, and reveal a giant coupling between spin and phonon through a frequency
shift of {\Delta}{\omega}=40 cm-1, the largest measured in any material. We
identify the dominant octahedral breathing mode and show isosymmetry with spin
ordering which induces dynamic charge disproportionation that sheds new light
on the MIT. The occurrence of the dramatic spin-phonon-electronic coupling in
NaOsO3 is due to a property common to all 5d materials: the large spatial
extent of the 5d ion. This allows magnetism to couple to phonons on an
unprecedented scale and consequently offers multiple new routes to enhanced
coupled phenomena.",1501.02290v1
2015-01-10,Group manifold approach to higher spin theory,"We consider the group manifold approach to higher spin theory. The deformed
local higher spin transformation is realized as the diffeomorphism
transformation in the group manifold $\textbf{M}$. With the suitable rheonomy
condition and the torsion constraint imposed, the unfolded equation can be
obtained from the Bianchi identity, by solving which, fields in $\textbf{M}$
are determined by the multiplet at one point, or equivalently, by
$(W^{[a(s-1),b(0)]}_{\mu},H)$ in $AdS_{4}\subset \textbf{M}$. Although the
space is extended to $\textbf{M}$ to get the geometrical formulation, the
dynamical degrees of freedom are still in $AdS_{4}$. The $4d$ equations of
motion for $(W^{[a(s-1),b(0)]}_{\mu},H)$ are obtained by plugging the rheonomy
condition into the Bianchi identity. The proper rheonomy condition allowing for
the maximum on-shell degrees of freedom is given by Vasiliev equation. We also
discuss the theory with the global higher spin symmetry, which is in parallel
with the WZ model in supersymmetry.",1501.02322v3
2015-01-12,Magnetic correlations beyond the Heisenberg model in an Fe monolayer on Rh(001),"Motivated by a recent experimental observation of a complex magnetic
structure [Takada et al. 2013 J. Magn. Magn. Mater. 329 95] we present a
theoretical study of the magnetic structure of an Fe monolayer deposited on
Rh(001). We use a classical spin Hamiltonian with parameters obtained from ab
initio calculations and go beyond the usual anisotropic Heisenberg model by
including isotropic biquadratic interactions. Zero-temperature
Landau--Lifshitz--Gilbert spin dynamics simulations lead to a complex collinear
spin configuration that, however, contradicts experimental finding. We thus
conclude that higher order multi-spin interactions are likely needed to account
for the magnetic ordering of the system.",1501.02657v1
2015-01-15,Evolution of the inhomogeneously-broadened spin noise spectrum with ac drive,"In the presence of random hyperfine fields, the noise spectrum, \delta
s_{\omega}^2, of a spin ensemble represents a narrow peak centered at \omega =0
and a broad ""wing"" reflecting the distribution of the hyperfine fields. In the
presence of an ac drive, the dynamics of a single spin acquires additional
harmonics at frequencies determined by both, the drive frequency and the local
field. These harmonics are reflected as additional peaks in the noise spectrum.
We study how the ensemble-averaged \delta s_{\omega}^2 evolves with the drive
amplitude, \omega_dr (in the frequency units). Our main finding is that
additional peaks in the spectrum, caused by the drive, remain sharp even when
\omega_dr is much smaller than the typical hyperfine field. The reason is that
the drive affects only the spins for which the local Larmour frequency is close
to the drive frequency. The shape of the low-frequency ""Rabi""-peak in \delta
s_{\omega}^2 is universal with both, the position and the width, being of the
order of \omega_dr. When the drive amplitude exceeds the width of the hyperfine
field distribution, the noise spectrum transforms into a set of sharp peaks
centered at harmonics of the drive frequency.",1501.03560v1
2015-01-22,Anatomy of Dzyaloshinskii-Moriya Interaction at Co/Pt Interfaces,"The Dzyaloshinskii-Moriya Interaction (DMI) between spins is induced by
spin-orbit coupling in magnetic materials lacking inversion symmetry. DMI is
recognized to play a crucial role at the interface between ferromagnetic (FM)
and heavy nonmagnetic (NM) metals to create topological textures called
magnetic skyrmions which are very attractive for ultra-dense information
storage and spintronic devices. DMI also plays an essential role for fast
domain wall (DW) dynamics driven by spin-orbit torques. Here, we present first
principles calculations which clarify the main features and microscopic
mechanisms of DMI in Co/Pt bilayers. DMI is found to be predominantly located
at the interfacial Co layer, originating from spin-orbit energy provided by the
adjacent NM layer. Furthermore, no direct correlation is found between DMI and
proximity induced magnetism in Pt. These results clarify underlying mechanisms
of DMI at FM/NM bilayers and should help optimizing material combinations for
skyrmion- and DW-based storage and memory devices.",1501.05511v1
2015-01-27,Non-equilibrium evolution of window overlaps in spin glasses,"We investigate numerically the time dependence of ""window"" overlaps in a
three-dimensional Ising spin glass below its transition temperature after a
rapid quench. Using an efficient GPU implementation, we are able to study large
systems up to lateral length $L=128$ and up to long times of $t=10^8$ sweeps.
We find that the data scales according to the ratio of the window size $W$ to
the non-equilibrium coherence length $\xi(t)$. We also show a substantial
change in behavior if the system is run for long enough that it globally
equilibrates, i.e. $\xi(t) \approx L/2$, where $L$ is the lattice size. This
indicates that the local behavior of a spin glass depends on the spin
configurations (and presumably also the bonds) far away. We compare with
similar simulations for the Ising ferromagnet. Based on these results, we
speculate on a connection between the non-equilibrium dynamics discussed here
and averages computed theoretically using the ""metastate"".",1501.06760v2
2015-02-04,"Linear optics, Raman scattering, and spin noise spectroscopy","Spin noise spectroscopy (SNS) is a new method for studying magnetic resonance
and spin dynamics based on measuring the Faraday rotation noise. In strong
contrast with methods of nonlinear optics, the spectroscopy of spin noise is
considered to be essentially nonperturbative. Presently, however, it became
clear that the SNS, as an optical technique, demonstrates properties lying far
beyond the bounds of conventional linear optics. Specifically, the SNS shows
dependence of the signal on the light power density, makes it possible to
penetrate inside an inhomogeneously broadened absorption band and to determine
its homogeneous width, allows one to realize an effective pump-probe
spectroscopy without any optical nonlinearity, etc. This may seem especially
puzzling when taken into account that SNS can be considered just as a version
of Raman spectroscopy, which is known to be deprived of such abilities. In this
paper, we clarify this apparent inconsistency.",1502.01155v1
2015-02-21,Spin liquid polymorphism in a correlated electron system on the threshold of superconductivity,"We report neutron scattering measurements, which reveal spin-liquid
polymorphism in a '11' iron chalcogenide superconductor, a poorly-metallic
magnetic FeTe tuned towards superconductivity by substitution of a small amount
of Tellurium with iso-electronic Sulphur. We observe liquid-like magnetic
dynamics, which is described by a competition of two phases with different
local structure, whose relative abundance depends on temperature. One is the
ferromagnetic (FM) plaquette phase observed in the non-superconducting FeTe,
which preserves the C$_4$ symmetry of the underlying square lattice and is
favored at high temperatures. The other is the antiferromagnetic plaquette
phase with broken C$_4$ symmetry, which emerges with doping and is predominant
at low temperatures. These findings suggest a first-order liquid-liquid phase
transition in the electronic spin system of FeTe$_{1-x}$(S,Se)$_x$. We thus
discover remarkable new physics of competing spin liquid polymorphs in a
correlated electron system approaching superconductivity. Our results
facilitate an understanding of large swaths of recent experimental data in
unconventional superconductors.",1502.06051v1
2015-02-23,Spin fluctuations in iron pnictides and chalcogenides: From antiferromagnetism to superconductivity,"The present article reviews recent experimental investigations of spin
dynamics in iron-based superconductors and their parent compounds by means of
inelastic neutron scattering. It mainly focuses on the most contemporary
developments in this field, pertaining to the observations of magnetic resonant
modes in new superconductors, spin anisotropy of low-energy magnetic
fluctuations that has now been observed in a wide range of chemical
compositions and doping levels, as well as their momentum-space anisotropy
incurred by the spin-nematic order. The implications of these new findings for
our understanding of the superconducting state, along with the remaining
unsettled challenges for neutron spectroscopy, are discussed.",1502.06570v1
2015-02-28,Interaction of Strain and Nuclear Spins in Silicon: Quadrupolar Effects on Ionized Donors,"The nuclear spins of ionized donors in silicon have become an interesting
quantum resource due to their very long coherence times. Their perfect
isolation, however, comes at a price, since the absence of the donor electron
makes the nuclear spin difficult to control. We demonstrate that the
quadrupolar interaction allows us to effectively tune the nuclear magnetic
resonance of ionized arsenic donors in silicon via strain and determine the two
nonzero elements of the S tensor linking strain and electric field gradients in
this material to $S_{11}=1.5\times10^{22}$ V/m$^2$ and $S_{44}=6\times 10^{22}$
V/m$^2$. We find a stronger benefit of dynamical decoupling on the coherence
properties of transitions subject to first-order quadrupole shifts than on
those subject to only second-order shifts and discuss applications of
quadrupole physics including mechanical driving of magnetic resonance, cooling
of mechanical resonators, and strain-mediated spin coupling.",1503.00133v2
2015-03-13,Controllable spin entanglement production in a quantum spin Hall ring,"We study the entanglement production in a quantum spin Hall ring geometry
where electrons of opposite spins are emitted in pairs from a source and
collected in two different detectors. Postselection of coincidence detector
events gives rise to entanglement in the system, measurable through
correlations between the outcomes in the detectors. We have chosen a geometry
such that the entanglement depends on the dynamical phases picked up by the
edge states as they move around the ring. In turn, the dependence of the phases
on gate potential and Rashba interaction allows for a precise electrical
control of the entanglement production in the ring.",1503.03985v2
2015-03-22,DMFT+NRG study of spin-orbital separation in a three-band Hund's metal,"We show that the numerical renormalization group (NRG) is a viable multi-band
impurity solver for Dynamical Mean Field Theory (DMFT), offering unprecedent
real-frequency spectral resolution at arbitrarily low energies and
temperatures. We use it to obtain a numerically exact DMFT solution to the
Hund's metal problem for a three-orbital model with filling factor $n_d=2$. The
ground state is a Fermi liquid. The one-particle spectral function has a strong
particle-hole asymmetry, with a clear apparent power law for positive
frequencies only. With increasing temperature it shows a coherence-incoherence
crossover with spectral weight transfered from low to high energies and evolves
qualitatively differently from a doped Mott insulator. The spin and orbital
spectral functions show ""spin-orbital separation"": spin screening occurs at
much lower energies than orbital screening. The renormalization group flows
clearly reveal the relevant physics at all energy scales.",1503.06467v1
2015-03-24,Eccentric mergers of black holes with spinning neutron stars,"We study dynamical capture binary black hole-neutron star (BH-NS) mergers
focusing on the effects of the neutron star spin. These events may arise in
dense stellar regions, such as globular clusters, where the majority of neutron
stars are expected to be rapidly rotating. We initialize the BH-NS systems with
positions and velocities corresponding to marginally unbound Newtonian orbits,
and evolve them using general-relativistic hydrodynamical simulations. We find
that even moderate spins can significantly increase the amount of mass in
unbound material. In some of the more extreme cases, there can be up to a third
of a solar mass in unbound matter. Similarly, large amounts of tidally stripped
material can remain bound and eventually accrete onto the BH---as much as a
tenth of a solar mass in some cases. These simulations demonstrate that it is
important to treat neutron star spin in order to make reliable predictions of
the gravitational wave and electromagnetic transient signals accompanying these
sources.",1503.07171v3
2015-03-26,Lagrangian geometrical optics of nonadiabatic vector waves and spin particles,"Linear vector waves, both quantum and classical, experience
polarization-driven bending of ray trajectories and polarization dynamics that
can be interpreted as the precession of the ""wave spin"". Both phenomena are
governed by an effective gauge Hamiltonian, which vanishes in leading-order
geometrical optics. This gauge Hamiltonian can be recognized as a
generalization of the Stern-Gerlach Hamiltonian that is commonly known for
spin-1/2 quantum particles. The corresponding reduced Lagrangians for
continuous nondissipative waves and their geometrical-optics rays are derived
from the fundamental wave Lagrangian. The resulting Euler-Lagrange equations
can describe simultaneous interactions of $N$ resonant modes, where $N$ is
arbitrary, and lead to equations for the wave spin, which happens to be a
$(N^2-1)$-dimensional spin vector. As a special case, classical equations for a
Dirac particle $(N=2)$ are deduced formally, without introducing additional
postulates or interpretations, from the Dirac quantum Lagrangian with the Pauli
term. The model reproduces the Bargmann-Michel-Telegdi equations with added
Stern-Gerlach force.",1503.07829v1
2015-04-06,Spin Pumping in Electrodynamically Coupled Magnon-Photon Systems,"We use electrical detection, in combination with microwave transmission, to
investigate both resonant and non-resonant magnon-photon coupling at room
temperature. Spin pumping in a dynamically coupled magnon-photon system is
found to be distinctly different from previous experiments. Characteristic
coupling features such as modes anti-crossing, line width evolution, peculiar
line shape, and resonance broadening are systematically measured and
consistently analyzed by a theoretical model set on the foundation of classical
electrodynamic coupling. Our experimental and theoretical approach pave the way
for pursuing microwave coherent manipulation of pure spin current via the
combination of spin pumping and magnon-photon coupling.",1504.01335v1
2015-04-14,Filter design for hybrid spin gates,"The impact of control sequences on the environmental coupling of a quantum
system can be described in terms of a filter. Here we analyze how the coherent
evolution of two interacting spins subject to periodic control pulses, at the
example of a nitrogen vacancy center coupled to a nuclear spin, can be
described in the filter framework in both the weak and the strong coupling
limit. A universal functional dependence around the filter resonances then
allows for tuning the coupling type and strength. Originally limited to small
rotation angles, we show how the validity range of the filter description can
be extended to the long time limit by time-sliced evolution sequences. Based on
that insight, the construction of tunable, noise decoupled, conditional gates
composed of alternating pulse sequences is proposed. In particular such an
approach can lead to a significant improvement in fidelity as compared to a
strictly periodic control sequence. Moreover we analyze the decoherence impact,
the relation to the filter for classical noise known from dynamical decoupling
sequences, and we outline how an alternating sequence can improve spin sensing
protocols.",1504.03575v2
2015-04-23,Optical Spin Polarization Dynamics in GaSe Nanoslabs,"We report nearly complete preservation of ""spin memory"" between optical
absorption and photoluminescence (PL) in nanometer slabs of GaSe pumped with up
to 0.2 eV excess energy. At cryogenic temperatures, the initial degree of
circular polarization ($\rho_0$) of PL approaches unity, with the major
fraction of the spin polarization decaying with a time constant $>$500 ps in
sub-100-nm GaSe nanoslabs. Even at room temperature, $\rho_0$ as large as 0.7
is observed, while pumping 1 eV above the band edge yields $\rho_0$ = 0.15.
Angular momentum preservation for both electrons and holes is due to the
separation of the non-degenerate conduction and valence bands from other bands.
In contrast to valley polarization in atomically thin transition metal
dichalcogenides, here optical spin polarization is preserved in nanoslabs of
100 layers or more of GaSe.",1504.06220v1
2015-05-05,Three-dimensional Character of the Magnetization Dynamics in Magnetic Vortex Structures - Hybridization of Flexure Gyromodes with Spin Waves,"Three-dimensional linear spin-wave eigenmodes of a Permalloy disk having
finite thickness are studied by micromagnetic simulations based on the
Landau-Lifshitz-Gilbert equation. The eigenmodes found in the simulations are
interpreted as linear superpositions (hybridizations) of 'approximate'
three-dimensional eigenmodes, which are the fundamental gyromode $G_0$, the
spin-wave modes and the higher-order gyromodes $G_N$ (flexure modes), the
thickness dependence of which is represented by perpendicular standing spin
waves. This hybridization leads to new and surprising dependencies of the mode
frequencies on the disk thickness. The three-dimensional character of the
eigenmodes is essential to explain the recent experimental results on
vortex-core reversal observed in relatively thick Permalloy disks.",1505.01148v2
2015-06-01,Numerical evidence of the double-Griffiths phase of the random quantum Ashkin-Teller chain,"The random quantum Ashkin-Teller chain is studied numerically by means of
time-dependent Density-Matrix Renormalization Group. The critical lines are
estimated as the location of the peaks of the integrated autocorrelation times,
computed from spin-spin and polarization-polarization autocorrelation
functions. Disorder fluctuations of magnetization and polarization are observed
to be maximum on these critical lines. Entanglement entropy leads to the same
phase diagram, though with larger Finite-Size effects. The decay of spin-spin
and polarization-polarization autocorrelation functions provides numerical
evidence of the existence of a double Griffiths phase when taking into account
finite-size effects. The two associated dynamical exponents z increase rapidly
as the critical lines are approached, in agreement with the recent conjecture
of a divergence at the two transitions in the thermodynamic limit.",1506.00416v2
2015-06-04,The role of spin fluctuations in the conductivity of CrO$_2$,"We present a time-resolved terahertz spectroscopic study of the half-metallic
ferromagnet CrO$_2$. The ultrafast conductivity dynamics excited by an optical
pump displays a very short (several picoseconds) and a very long (several
hundred picoseconds) characteristic time scales. We attribute the former to the
electron-phonon relaxation and the latter to the spin-lattice relaxation. We
use this distinction to quantify the relative contribution of the scattering by
spin fluctuations to the resistivity of CrO$_2$: we find that they contribute
less than one half of all scattering events below room temperature. This
contribution rises to $\sim70$ % as the temperature approaches $T_C$=390 K. The
small effect of spin fluctuations on the resistivity is unexpected in the light
of the proposed double-exchange nature of the electronic and magnetic
properties of CrO$_2$.",1506.01745v2
2015-06-12,Criticality at the Haldane-insulator charge-density-wave quantum phase transition,"Exploiting the entanglement concept within a matrix-product-state based
infinite density-matrix renormalization group approach, we show that the
spin-density-wave and bond-order-wave ground states of the one-dimensional
half-filled extended Hubbard model give way to a symmetry-protected topological
Haldane state in case an additional alternating ferromagnetic spin interaction
is added. In the Haldane insulator the lowest entanglement level features a
characteristic twofold degeneracy. Increasing the ratio between
nearest-neighbor and local Coulomb interaction $V/U$, the enhancement of the
entanglement entropy, the variation of the charge, spin and neutral gaps, and
the dynamical spin/density response signal a quantum phase transition to a
charge-ordered state. Below a critical point, which belongs to the universality
class of the tricritical Ising model with central charge 7/10, the model is
critical with $c=1/2$ along the transition line. Above this point, the
transition between the Haldane insulator and charge-density-wave phases becomes
first order.",1506.04003v2
2015-07-14,Quartic interaction vertex in the massive integer higher spin field theory in a constant electromagnetic field,"We consider the massive integer higher spin fields coupled to an external
constant electromagnetic field in flat space of arbitrary dimension and find a
gauge invariant quartic interaction vertex which is quadratic in dynamical
higher spin field and quadratic in external field. Construction of the vertex
is based on the BRST approach to higher spin filed theory where no off-shell
constraints on the fields and on the gauge parameters are imposed from the very
beginning (unconstrained formulation).",1507.03723v3
2015-09-03,Landau levels of Majorana fermions in a spin liquid,"Majorana fermions were originally proposed as elementary particles acting as
their own antiparticles. In recent years, it has become clear that Majorana
fermions can instead be realized in condensed-matter systems as emergent
quasiparticles, a situation often accompanied by topological order. Here we
propose a physical system which realizes Landau levels - highly degenerate
single-particle states usually resulting from an orbital magnetic field acting
on charged particles - for Majorana fermions. This is achieved in a variant of
a quantum spin system due to Kitaev which is distorted by triaxial strain. This
strained Kitaev model displays a spin-liquid phase with charge-neutral
Majorana-fermion excitations whose spectrum corresponds to that of Landau
levels, here arising from a tailored pseudo-magnetic field. We show that
measuring the dynamic spin susceptibility reveals the Landau-level structure by
a remarkable mechanism of probe-induced bound-state formation.",1509.01246v2
2015-09-06,Proposal for a Domain Wall Nano-Oscillator driven by Non-uniform Spin Currents,"We propose a new mechanism and a related device concept for a robust,
magnetic field tunable radio-frequency (rf) oscillator using the self
oscillation of a magnetic domain wall subject to a uniform static magnetic
field and a spatially non-uniform vertical dc spin current. The self
oscillation of the domain wall is created as it translates periodically between
two unstable positions, one being in the region where both the dc spin current
and the magnetic field are present, and the other, being where only the
magnetic field is present. The vertical dc spin current pushes it away from one
unstable position while the magnetic field pushes it away from the other. We
show that such oscillations are stable under noise and can exhibit a quality
factor of over 1000. A domain wall under dynamic translation, not only being a
source for rich physics, is also a promising candidate for advancements in
nanoelectronics with the actively researched racetrack memory architecture,
digital and analog switching paradigms as candidate examples. Devising a stable
rf oscillator using a domain wall is hence another step towards the realization
of an all domain wall logic scheme.",1509.01791v1
2015-09-07,Influence of spin dynamics of defects on weak localization in paramagnetic 2D metals,"Spin-flip scattering of charge carriers in metals with magnetic defects leads
to the low-temperature saturation of the decoherence time, $\tau_\varphi$, of
electrons at the value comparable to their spin relaxation time, $\tau_s$. In
two-dimensional (2D) conductors such a saturation can be lifted by an in-plane
magnetic field, $B_\parallel$, which polarizes spins of scatterers without
affecting orbital motion of free carriers. Here, we show that in 2D conductors
with substantially different values of the g-factors of electrons ($g_e$) and
magnetic defects ($g_i$), the decoherence time $\tau_\varphi(B_\parallel)$
(reflected by the curvature of magnetoconductance) displays an anomaly: it
first gets shorter, decaying on the scale $B_\parallel\sim \hbar/|g_i-g_e|\mu_B
\tau_s$, before becoming longer at higher values of $B_\parallel$.",1509.01955v2
2015-10-05,Continuous dynamical decoupling of a single diamond nitrogen-vacancy center spin with a mechanical resonator,"Inhomogeneous dephasing from uncontrolled environmental noise can limit the
coherence of a quantum sensor or qubit. For solid state spin qubits such as the
nitrogen-vacancy (NV) center in diamond, a dominant source of environmental
noise is magnetic field fluctuations due to nearby paramagnetic impurities and
instabilities in a magnetic bias field. In this work, we use ac stress
generated by a diamond mechanical resonator to engineer a dressed spin basis in
which a single NV center qubit is less sensitive to its magnetic environment.
For a qubit in the thermally isolated subspace of this protected basis, we
prolong the dephasing time $T_2^*$ from $2.7\pm0.1$ $\mu$s to $15\pm1$ $\mu$s
by dressing with a $\Omega=581\pm2$ kHz mechanical Rabi field. Furthermore, we
develop a model that quantitatively predicts the relationship between $\Omega$
and $T_2^*$ in the dressed basis. Our model suggests that a combination of
magnetic field fluctuations and hyperfine coupling to nearby nuclear spins
limits the protected coherence time over the range of $\Omega$ accessed here.
We show that amplitude noise in $\Omega$ will dominate the dephasing for larger
driving fields.",1510.01194v1
2015-10-05,Universality in antiferromagnetic strange metals,"We propose a theory of metals at the spin-density wave quantum critical point
in spatial dimension $d=2$. We provide a first estimate of the full set of
critical exponents (dynamical exponent $z=2.13$, correlation length $\nu
=1.02$, spin susceptibility $\gamma = 0.96$, electronic non-Fermi liquid
$\eta^f_\tau = 0.53$, spin-wave Landau damping $\eta^b_\tau = 1.06$), which
determine the universal power-laws in thermodynamics and response functions in
the quantum-critical regime relevant for experiments in heavy-fermion systems
and iron pnictides. We present approximate numerical and analytical solutions
of Polchinski-Wetterich type flow equations with soft frequency regulators for
an effective action of electrons coupled to spin-wave bosons. Performing the
renormalization group in frequency -instead of momentum- space allows to track
changes of the Fermi surface shape and to capture Landau damping during the
flow. The technique is easily generalizable from models retaining only patches
of the Fermi surface to full, compact Fermi surfaces.",1510.01331v3
2015-10-30,Anatomy of a Spin: The Information-Theoretic Structure of Classical Spin Systems,"Collective organization in matter plays a significant role in its expressed
physical properties. Typically, it is detected via an order parameter,
appropriately defined for each given system's observed emergent patterns.
Recent developments in information theory, however, suggest quantifying
collective organization in a system- and phenomenon-agnostic way: decompose the
system's thermodynamic entropy density into a localized entropy, that solely
contained in the dynamics at a single location, and a bound entropy, that
stored in space as domains, clusters, excitations, or other emergent
structures. We compute this decomposition and related quantities explicitly for
the nearest-neighbor Ising model on the 1D chain, the Bethe lattice with
coordination number k=3, and the 2D square lattice, illustrating its generality
and the functional insights it gives near and away from phase transitions. In
particular, we consider the roles that different spin motifs play (in cluster
bulk, cluster edges, and the like) and how these affect the dependencies
between spins.",1510.08954v2
2015-11-11,Single spin asymmetries from a single Wilson loop,"We study the leading-power gluon transverse momentum dependent distributions
(TMDs) of relevance to the study of asymmetries in the scattering off
transversely polarized hadrons. Next-to-leading-order perturbative calculations
of these TMDs show that at large transverse momentum they have common dynamical
origins, but that in the limit of small longitudinal momentum fraction $x$ only
one origin remains. We find that in this limit only the dipole-type gluon TMDs
survive and become identical to each other. At small $x$ they are all given by
the expectation value of a single Wilson loop inside the transversely polarized
hadron, the so-called spin-dependent odderon. This universal origin of
transverse spin asymmetries at small $x$ is of importance to current and future
experimental studies, paving the way to a better understanding of the role of
gluons in the three-dimensional structure of spin-polarized protons.",1511.03485v2
2016-01-29,Switching of chiral magnetic skyrmions by picosecond magnetic field pulses via transient topological states,"Magnetic chiral skyrmions are vortex like spin structures that appear as
stable or meta-stable states in magnetic materials due to the interplay between
the symmetric and antisymmetric exchange interactions, applied magnetic field
and/or uniaxial anisotropy. Their small size and internal stability make them
prospective objects for data storage but for this, the controlled switching
between skyrmion states of opposite polarity and topological charge is
essential. Here we present a study of magnetic skyrmion switching by an applied
magnetic field pulse based on a discrete model of classical spins and atomistic
spin dynamics. We found a finite range of coupling parameters corresponding to
the coexistence of two degenerate isolated skyrmions characterized by mutually
inverted spin structures with opposite polarity and topological charge. We
demonstrate how for a wide range of material parameters a short inclined
magnetic field pulse can initiate the reliable switching between these states
at GHz rates. Detailed analysis of the switching mechanism revealed the complex
path of the system accompanied with the excitation of a chiral-achiral meron
pair and the formation of an achiral skyrmion.",1601.08212v1
2016-02-02,Engineering of frustration in colloidal artificial ices realized on microfeatured grooved lattices,"Artificial spin ice systems, namely lattices of interacting single domain
ferromagnetic islands, have been used to date as microscopic models of
frustration induced by lattice topology, allowing for the direct visualization
of spin arrangements and textures. However, the engineering of frustrated ice
states in which individual spins can be manipulated in situ and the real-time
observation of their collective dynamics remain both challenging tasks.
Inspired by recent theoretical advances, here we realize a colloidal version of
an artificial spin ice system using interacting polarizable particles confined
to lattices of bistable gravitational traps. We show quantitatively that
ice-selection rules emerge in this frustrated soft matter system by tuning the
strength of the pair interactions between the microscopic units. Via
independent control of particle positioning and dipolar coupling, we introduce
monopole-like defects and strings and use loops with defined chirality as an
elementary unit to store binary information.",1602.00990v1
2016-02-12,Spin dynamics in the high-field phases of volborthite,"We report single-crystal 51V NMR studies on volborthite Cu3V2O7(OH)2 2H2O,
which is regarded as a quasi-two-dimensional frustrated magnet with competing
ferromagnetic and antiferromagnetic interactions. In the 1/3 magnetization
plateau above 28 T, the nuclear spin-lattice relaxation rate 1/T1 indicates an
excitation gap with a large effective g factor in the range of 4.6-5.9,
pointing to magnon bound states. Below 26 T where the gap has closed, the NMR
spectra indicate small internal fields with a Gaussian-like distribution,
whereas 1/T1 shows a power-law-like temperature dependence in the paramagnetic
state, which resembles a slowing down of spin fluctuations associated with
magnetic order. We discuss the possibility of an exotic spin state caused by
the condensation of magnon bound states below the magnetization plateau.",1602.04028v2
2016-02-22,Staggering antiferromagnetic domain wall velocity in a staggered spin-orbit field,"We demonstrate the possibility to drive an antiferromagnet domain-wall at
high velocities by field-like N\'{e}el spin-orbit torques. Such torques arise
from current-induced local fields that alternate their orientation on each
sub-lattice of the antiferromagnet and whose orientation depend primarily on
the current direction, giving them their field-like character. The domain-wall
velocities that can be achieved by this mechanism are two orders of magnitude
greater than the ones in ferromagnets. This arises from the efficiency of the
staggered spin-orbit fields to couple to the order parameter and from the
exchange-enhanced phenomena in antiferromagnetic texture dynamics, which leads
to a low domain-wall effective mass and the absence of a Walker break-down
limit. In addition, because of its nature, the staggered spin-orbit field can
lift the degeneracy between two 180$^\circ$ rotated states in a collinear
antiferromagnet and provides a force that can move such walls and control the
switching of the states.",1602.06766v2
2016-04-01,Dynamic Symmetries and Quantum Nonadiabatic Transitions,"Kramers degeneracy theorem is one of the basic results in quantum mechanics.
According to it, the time-reversal symmetry makes each energy level of a
half-integer spin system at least doubly degenerate, meaning the absence of
transitions or scatterings between degenerate states if the Hamiltonian does
not depend on time explicitly. We generalize this result to the case of
explicitly time-dependent spin Hamiltonians. We prove that for a spin system
with the total spin being a half integer, if its Hamiltonian and the evolution
time interval are symmetric under a specifically defined time reversal
operation, the scattering amplitude between an arbitrary initial state and its
time reversed counterpart is exactly zero. We also discuss applications of this
result to the multistate Landau-Zener (LZ) theory.",1604.00106v1
2016-04-06,Pressure-Tuned Exchange Coupling of a Quantum Spin Liquid in the Molecular Triangular Lattice $κ$-(ET)$_2$Ag$_2$(CN)$_3$,"The effects of pressure on a quantum spin liquid are investigated in an
organic Mott insulator $\kappa$-(ET)$_2$Ag$_2$(CN)$_3$ with a spin-1/2
triangular lattice. The application of negative chemical pressure to
$\kappa$-(ET)$_2$Cu$_2$(CN)$_3$, which is a well-known sister Mott insulator,
allows for extensive tuning of antiferromagnetic exchange coupling, with
$J/k_{\rm B} = 175 - 310$ K, under hydrostatic pressure. Based on $^{13}$C
nuclear magnetic resonance measurements under pressure, we uncover universal
scaling in the static and dynamic spin susceptibilities down to low
temperatures $\sim 0.1k_{\rm B}T/J$. The persistent fluctuations and residual
specific heat coefficient are consistent with the presence of gapless low-lying
excitations. Our results thus demonstrate fundamental finite-temperature
properties of quantum spin liquid in a wide parameter range.",1604.01460v2
2016-06-08,Skyrmions with attractive interactions in an ultrathin magnetic film,"We determined the parameters of a classical spin Hamiltonian describing an Fe
monolayer on Pd(111) surface with a Pt_{1-x}Ir_{x} alloy overlayer from ab
initio calculations. While the ground state of the system is ferromagnetic for
x=0.00, it becomes a spin spiral state as Ir is intermixed into the overlayer.
Although the Dzyaloshinsky-Moriya interaction is present in the system, we will
demonstrate that the frustrated isotropic exchange interactions play a
prominent role in creating the spin spiral state, and these frustrated
couplings lead to an attractive interaction between skyrmions at short
distances. Using spin dynamics simulations, we show that under these conditions
the individual skyrmions form clusters, and that these clusters remain stable
at finite temperature.",1606.02464v2
2016-06-09,Hybrid quantum device with nitrogen-vacancy centers in diamond coupled to carbon nanotubes,"We show that nitrogen-vacancy (NV) centers in diamond interfaced with a
suspended carbon nanotube carrying a dc current can facilitate a
spin-nanomechanical hybrid device. We demonstrate that strong magnetomechanical
interactions between a single NV spin and the vibrational mode of the suspended
nanotube can be engineered and dynamically tuned by external control over the
system parameters. This spin-nanomechanical setup with strong, \emph{intrinsic}
and \emph{tunable} magnetomechanical couplings allows for the construction of
hybrid quantum devices with NV centers and carbon-based nanostructures, as well
as phonon-mediated quantum information processing with spin qubits.",1606.02998v2
2016-06-27,The Turbulent Origin of Outflow and Spin Misalignment in Multiple Star Systems,"The protostellar outflows of wide-separation forming binaries frequently
appear misaligned. We use magneto-hydrodynamic simulations to investigate the
alignment of protostellar spin and molecular outflows for forming binary pairs.
We show that the protostellar pairs, which form from turbulent fragmentation
within a single parent core, have randomly oriented angular momenta. Although
the pairs migrate to closer separations, their spins remain partially
misaligned. We produce $^{12}$CO(2-1) synthetic observations of the simulations
and characterize the outflow orientation in the emission maps. The
CO-identified outflows exhibit a similar random distribution and are also
statistically consistent with the observed distribution of molecular outflows.
We conclude that observed misalignment provides a clear signature of binary
formation via turbulent fragmentation. The persistence of misaligned outflows
and stellar spins following dynamical evolution may provide a signature of
binary origins for more evolved multiple star systems.",1606.08445v1
2016-06-27,Topological spin ordering via Chern-Simons superconductivity,"We use the Chern-Simons (CS) fermion representation of s =1/2 spin operators
to construct topological, long-range magnetically ordered states of interacting
two-dimensional (2D) quantum spin models. We show that the fermion-fermion
interactions mediated by the dynamic CS flux attachment may give rise to Cooper
pairing of the fermions. Specifically, in an XY model on the honeycomb lattice,
this construction leads to a ""CS superconductor,"" which belongs to a
topologically non-trivial in 2D symmetry class DIII, with particle-hole and
time-reversal symmetries. It is shown that in the original spin language, this
state corresponds to a symmetry protected topological state, which coexists
with a magnetic long-range order. We discuss physical manifestations of the
topological character of the corresponding state and requirements for models
that could host it.",1606.08473v1
2016-07-01,Spin and localization of relativistic fermions and uncertainty relations,"We discuss relations between several relativistic spin observables and derive
a Lorentz-invariant characteristic of a reduced spin density matrix.A
relativistic position operator that satisfies all the properties of its
nonrelativistic analog does not exist. Instead we propose two
causality-preserving positive operator-valued measures (POVMs) that are based
on projections onto one-particle and antiparticle spaces, and on the normalized
energy density. They predict identical expectation values for position. The
variances differ by less than a quarter of the squared de Broglie wavelength
and coincide in the nonrelativistic limit. Since the resulting statistical
moment operators are not canonical conjugates of momentum, the Heisenberg
uncertainty relations need not hold. Indeed, the energy density POVM leads to a
lower uncertainty. We reformulate the standard equations of the spin dynamics
by explicitly considering the charge-independent acceleration, allowing a
consistent treatment of backreaction and inclusion of a weak gravitational
field.",1607.00123v2
2016-07-12,Minimum-Time Selective Control of Homonuclear Spins,"In NMR (Nuclear Magnetic Resonance) quantum computation, the selective
control of multiple homonuclear spins is usually slow because their resonance
frequencies are very close to each other. To quickly implement controls against
decoherence effects, this paper presents an efficient numerical algorithm
fordesigning minimum-time local transformations in two homonuclear spins. We
obtain an accurate minimum-time estimation via geometric analysis on the
two-timescale decomposition of the dynamics. Such estimation narrows down the
range of search for the minimum-time control with a gradient-type optimization
algorithm. Numerical simulations show that this method can remarkably reduce
the search efforts, especially when the frequency difference is very small and
the control field is high. Its effectiveness is further demonstrated by NMR
experiments with two homunuclear carbon spins in a trichloroethylene (C2H1Cl3)
sample system.",1607.03213v1
2016-07-18,J-freezing and Hund's rules in spin-orbit-coupled multiorbital Hubbard models,"We investigate the phase diagram of the spin-orbit-coupled three orbital
Hubbard model at arbitrary filling by means of dynamical mean-field theory
combined with continuous-time quantum Monte Carlo. We find that the
spin-freezing crossover occurring in the metallic phase of the non-relativistic
multiorbital Hubbard model can be generalized to a $\mathbf{J}$-freezing
crossover, with $\mathbf{J}=\mathbf{L}+\mathbf{S}$, in the spin-orbit-coupled
case. In the $\mathbf{J}$-frozen regime the correlated electrons exhibit a
non-trivial flavor selectivity and energy dependence. Furthermore, in the
regions near $n=2$ and $n=4$ the metallic states are qualitatively different
from each other, which reflects the atomic Hund's third rule. Finally, we
explore the appearance of magnetic order from exciton condensation at $n=4$ and
discuss the relevance of our results for real materials.",1607.05196v2
2016-07-18,Investigations into Light-front Quartic Interactions for Massless Fields (I): Non-constructibility of Higher Spin Quartic Amplitudes,"The dynamical commutators of the light-front Poincar\'e algebra yield first
order differential equations in the $p^+$ momenta for the interaction vertex
operators. The homogeneous solution to the equation for the quartic vertex is
studied. Consequences as regards the constructibility assumption of quartic
higher spin amplitudes from cubic amplitudes are discussed. The existence of
quartic contact interactions unrelated to cubic interactions by Poincar\'e
symmetry indicates that the higher spin S-matrix is not constructible. Thus
quartic amplitude based no-go results derived by BCFW recursion for Minkowski
higher spin massless fields may be circumvented.",1607.06659v3
2016-09-06,Tailoring Spin Chain Dynamics for Fractional Revivals,"The production of quantum states required for use in quantum protocols &
technologies is studied by developing the tools to re-engineer a perfect state
transfer spin chain so that a separable input excitation is output over
multiple sites. We concentrate in particular on cases where the excitation is
superposed over a small subset of the qubits on the spin chain, known as
fractional revivals, demonstrating that spin chains are capable of producing a
far greater range of fractional revivals than previously known, at high speed.
We also provide a numerical technique for generating chains that produce
arbitrary single-excitation states, such as the W state.",1609.01397v5
2016-09-21,Level anti-crossing spectra of nitrogen-vacancy centers in diamond detected by using modulation of the external magnetic field,"We report a study of the magnetic field dependence of the photo-luminescence
of NV$^-$ centers (negatively charged nitrogen-vacancy centers) in diamond
single crystals. In such a magnetic field dependence characteristic lines are
observed, which are coming from Level Anti-Crossings (LACs) in the coupled
electron-nuclear spin system. For enhancing the sensitivity, we used lock-in
detection to measure the photo-luminescence intensity and observed a remarkably
strong dependence of the LAC-derived lines on the modulation frequency. Upon
decreasing of the modulation frequency from 12 kHz to 17 Hz the amplitude of
the lines increases by approximately two orders of magnitude. To take a
quantitative account for such effects, we developed a theoretical model, which
describes the spin dynamics in the coupled electron-nuclear spin system under
the action of an oscillating external magnetic field. Good agreement between
experiments and theory allows us to conclude that the observed effects are
originating from coherent spin polarization exchange in the NV$^-$ center. Our
results are of great practical importance allowing one to optimize the
experimental conditions for probing LAC-derived lines in diamond defect
centers.",1609.06661v1
2016-09-22,Strength and scales of itinerant spin fluctuations in 3d paramagnetic metals,"The full spin density fluctuations (SDF) spectra in 3d paramagnetic metals
are analyzed from first principles using the linear response technique. Using
the calculated complete wavevector and energy dependence of the dynamic spin
susceptibility, we obtain the most important, but elusive, characteristic of
SDF in solids: on-site spin correlator (SC). We demonstrate that the SDF have a
mixed character consisting of interacting collective and single-particle
excitations of similar strength spreading continuously over the entire
Brillouin zone and a wide energy range up to femtosecond time scales. These
excitations cannot be adiabatically separated and their intrinsically
multiscale nature should be always taken into account for a proper description
of metallic systems. Overall, in all studied systems, despite the lack of local
moment, we found a very large SC resulting in an effective fluctuating moment
of the order of several Bohr magnetons.",1609.07023v1
2016-09-29,The gap of Fredkin quantum spin chain is polynomially small,"We prove a new result on the spectral gap and mixing time of a Markov chain
with Glauber dynamics on the space of Dyck paths (i.e., Catalan paths) and
their generalization, which we call colored Dyck paths. The proof uses the
comparison theorem of Diaconis and Saloff-Coste and our previous results.
  Let $2n$ be the number of spins. We prove that the gap of the Fredkin quantum
spin chain Hamiltonian [6, 20], is $\Theta(n^{-c})$ with $c\ge2$. Our results
on the spectral gap of the Markov chain are used to prove a lower bound of
$O(n^{-15/2})$ on the energy of first excited state above the ground state of
the Fredkin quantum spin chain. We prove an upper bound of $O(n^{-2})$ using
the universality of Brownian motion and convergence of Dyck random walks to
Brownian excursions. Lastly, the 'unbalanced' ground state energies are proved
to be polynomially small in $n$ by mapping the Hamiltonian to an effective
hopping Hamiltonian with next nearest neighbor interactions and analytically
solving its ground state.",1609.09160v2
2017-02-03,Significant reduction of critical currents in MRAM designs using dual free layer with perpendicular and in-plane anisotropy,"One essential feature in MRAM cells is the spin torque efficiency, which
describes the ratio of the critical switching current to the energy barrier.
Within this paper it is reported that the spin torque efficiency can be
improved by a factor of 3.2 by the use a of dual free layer device, which
consists of one layer with perpendicular crystalline anisotropy and a second
layer with in-plane crystalline anisotropy. Detailed simulations solving the
spin transport equations simultaneously with the micromagnetics equation were
performed in order to understand the origin of the switching current reduction
by a factor of 4 for the dual layer structure compared to a single layer
structure. The main reason could be attributed to an increased spin
accumulation within the free layer due to the dynamical tilting of the
magnetization within the in-plane region of the dual free layer.",1702.00996v2
2017-02-10,Phase space curvature in spin-orbit coupled ultracold atom systems,"We consider a system with spin-orbit coupling and derive equations of motion
which include the effects of Berry curvatures. We apply these equations to
investigate the dynamics of particles with equal Rashba-Dresselhaus spin-orbit
coupling in one dimension. In our derivation, the adiabatic transformation is
performed first and leads to quantum Heisenberg equations of motion for
momentum and position operators. These equations explicitly contain
position-space, momentum-space, and phase-space Berry curvature terms.
Subsequently, we perform the semiclassical approximation, and obtain the
semiclassical equations of motion. Taking the low-Berry-curvature limit results
in equations that can be directly compared to previous results for the motion
of wavepackets. Finally, we show that in the semiclassical regime, the
effective mass of the equal Rashba-Dresselhaus spin-orbit coupled system can be
viewed as a direct effect of the phase-space Berry curvature.",1702.03298v2
2017-02-10,Gyrotropic elastic response of skyrmion crystals to current-induced tensions,"We theoretically study the dynamics of skyrmion crystals in
electrically-insulating chiral magnets subjected to current-induced spin
torques by adjacent metallic layers. We develop an elasticity theory that
accounts for the gyrotropic force engendered by the non-trivial topology of the
spin texture, tensions at the boundaries due to the exchange of linear and spin
angular momentum with the metallic reservoirs, and dissipation in the bulk of
the film. A steady translation of the skyrmion crystal is triggered by the
current-induced tensions and subsequently sustained by dissipative forces,
generating an electromotive force on itinerant spins in the metals. This
phenomenon should be revealed as a negative drag in an open two-terminal
geometry, or equivalently, as a positive magnetoresistance when the terminals
are connected in parallel. We propose non-local transport measurements with
these salient features as a tool to characterize the phase diagram of
insulating chiral magnets.",1702.03347v2
2017-02-21,Human brain ferritin studied by muon Spin Rotation: a pilot study,"Muon Spin Rotation is employed to investigate the spin dynamics of ferritin
proteins isolated from the brain of an Alzheimer's disease (AD) patient and of
a healthy control, using a sample of horse-spleen ferritin as a reference. A
model based on the N\'eel theory of superparamagnetism is developed in order to
interpret the spin relaxation rate of the muons stopped by the core of the
protein. Using this model, our preliminary observations show that ferritins
from the healthy control are filled with a mineral compatible with
ferrihydrite, while ferritins from the AD patient contain a crystalline phase
with a larger magnetocrystalline anisotropy, possibly compatible with magnetite
or maghemite.",1702.07222v2
2017-03-03,Transverse spin relaxation and magnetic correlation in $Pr_{1-x}Ca_{x}MnO_{3}$ : influence of particle size variation and chemical doping,"The short ranged magnetic correlations and dynamics of hole doped
$Pr_{1-x}Ca_{x}MnO_{3}$ (0.33 < x < 0.5) of different crystallite sizes have
been investigated using electron spin resonance spectroscopy (ESR). The major
contribution to the temperature dependence of paramagnetic line-width is
attributed to the spin-lattice relaxation dominated by thermally activated
hopping of small polarons with typical activation energy of 20-50 meV.
Irrespective of the crystallite size and dopant concentration, the transverse
spin relaxation time ($t_{2}$) follows a universal scaling behaviour of the
type $t_{2}$~($T/T_{0})^n$ in the paramagnetic regime, where $T_0$ and n are
scaling parameters. Using the temperature dependence of $t_{2}$, we construct a
phase diagram which shows that near half-doping, the magnetic correlations
associated with charge ordering not just survives even down to the crystallite
size of 22 nm, but is actually enhanced. We conclude that the eventual
suppression of charge ordering with reduction in particle size is possibly more
to do with greater influence of chemical disorder than any intrinsic effect.",1703.01111v1
2017-03-06,"Spindynamics in the antiferromagnetic phases of the Dirac metals $A$MnBi$_2$ ($A=$ Sr, Ca)","The square Bi layers in $A$MnBi$_2$ ($A =$ Sr, Ca) host Dirac fermions which
coexist with antiferromagnetic order on the Mn sublattice below $T_\mathrm{N} =
290\,$K (Sr) and $270\,$K (Ca). We have measured the spin-wave dispersion in
these materials by triple-axis neutron spectroscopy. The spectra show
pronounced spin gaps of 10.2(2)$\,$meV (Sr) and 8.3(8)$\,$meV (Ca) and extend
to a maximum energy transfer of 61 - 63$\,$meV. The observed spectra can be
accurately reproduced by linear spin-wave theory from an Heisenberg effective
spin Hamiltonian. Detailed global fits of the full magnon dispersion are used
to determine the in-plane and inter-layer exchange parameters as well as on the
magnetocrystalline anisotropy constant. To within experimental error we find no
evidence that the magnetic dynamics are influenced by the Dirac fermions.",1703.01849v1
2017-03-08,Spin dynamics of antiferromagnets in the presence of a homogeneous magnetization,"We use general hydrodynamic equations to determine the long-wavelength spin
excitations in isotropic antiferromagnets in the presence of a homogeneous
magnetization. The latter may be induced, such as in antiferromagnets in an
external magnetic field, or spontaneous, such as in ferrimagnetic or canted
phases that are characterized by the coexistence of antiferromagnetic and
ferromagnetic order. Depending on the physical situation, we find propagating
spin waves that are gapped in some cases and gapless in others, diffusive
modes, or relaxational modes. The excitation spectra turn out to be
qualitatively different depending on whether or not the homogeneous
magnetization is a conserved quantity. The results lay the foundation for a
description of a variety of quantum phase transitions, including the transition
from a ferromagnetic metal to an antiferromagnetic one, and the spin-flop
transitions that are observed in some antiferromagnets. They also are crucial
for incorporating weak-localization and Altshuler-Aronov effects into the
descriptions of quantum phases in both clean and disordered magnetic metals.",1703.03009v1
2017-03-10,Ultrafast and Energy-Efficient Quenching of Spin Order: Antiferromagnetism Beats Ferromagnetism,"By comparing femtosecond laser pulse induced ferro- and antiferromagnetic
dynamics in one and the same material - metallic dysprosium - we show both to
behave fundamentally different. Antiferromagnetic order is considerably faster
and much more efficiently manipulated by optical excitation than its
ferromagnetic counterpart. We assign the fast and extremely efficient process
in the antiferromagnet to an interatomic transfer of angular momentum within
the spin system. Our findings do not only reveal this angular momentum transfer
channel effective in antiferromagnets and other magnetic structures with
non-parallel spin alignment, they also point out a possible route towards
energy-efficient spin manipulation for magnetic devices.",1703.03689v3
2017-03-10,Fingerprints of quantum spin ice in Raman scattering,"We develop a theory of the dynamical response of a minimal model of quantum
spin ice (QSI) by means of inelastic light scattering. In particular, we are
interested in the Raman response of the fractionalized U(1) spin liquid
realized in the XXZ QSI. We show that the low-energy Raman intensity is
dominated by spinon and gauge fluctuations. We find that the Raman response in
the QSI state of that model appears only in the $T_{2g}$ polarization channel.
We show that the Raman intensity profile displays a broad continuum from the
spinons and coupled spinon and gauge fluctuations, and a low-energy peak
arising entirely from gauge fluctuations. Both features originate from the
exotic interaction between photon and the fractionalized excitations of QSI.
Our theoretical results suggest that inelastic Raman scattering can in
principle serve as a promising experimental probe of the nature of a U(1) spin
liquid in QSI.",1703.03836v1
2017-03-23,Nonlinear tidal flows in short-period planets,"I discuss two related nonlinear mechanisms of tidal dissipation that require
finite tidal deformations for their operation: the elliptical instability and
the precessional instability. Both are likely to be important for the tidal
evolution of short-period extrasolar planets. The elliptical instability is a
fluid instability of elliptical streamlines, such as in tidally deformed
non-synchronously rotating or non-circularly orbiting planets. I summarise the
results of local and global simulations that indicate this mechanism to be
important for tidal spin synchronisation, planetary spin-orbit alignment and
orbital circularisation for the shortest period hot Jupiters. The precessional
instability is a fluid instability that occurs in planets undergoing axial
precession, such as those with spin-orbit misalignments (non-zero obliquities).
I summarise the outcome of local MHD simulations designed to study the
turbulent damping of axial precession, which suggest this mechanism to be
important in driving tidal evolution of the spin-orbit angle for hot Jupiters.
Avenues for future work are also discussed.",1703.08003v1
2017-08-27,Electronic and spin dynamics in the insulating iron pnictide NaFe$_{0.5}$Cu$_{0.5}$As,"NaFe$_{0.5}$Cu$_{0.5}$As represents a rare exception in the metallic iron
pnictide family, in which a small insulating gap is opened. Based on
first-principles study, we provide a comprehensive theoretical characterization
of this insulating compound. The Fe$^{3+} $spin degree of freedom is quantified
as a quasi-1D $S=\frac{5}{2}$ Heisenberg model. The itinerant As hole state is
downfolded to a $p_{xy}$-orbital hopping model on a square lattice. A unique
orbital-dependent Hund's coupling between the spin and the hole is revealed.
Several important material properties are analyzed, including (a) factors
affecting the small $p-d$ charge-transfer gap; (b) role of the extra interchain
Fe; and (c) the quasi-1D spin excitation in the Fe chains. The experimental
manifestations of these properties are discussed.",1708.08065v1
2018-02-15,Tunneling magnetoresistance enhancement by symmetrization in spin-orbit torque magnetic tunnel junction,"Heavy metals with strong spin-orbit coupling (SOC) have been employed to
generate spin current to control the magnetization dynamics by spin-orbit
torque (SOT). Magnetic tunnel junction based on SOT (SOT-MTJ) is a promising
application with efficient writing operation. Unfortunately, SOT-MTJ faces the
low tunneling magnetoresistance (TMR) problem. In this work, we present an ab
initio calculation on the TMR in SOT-MTJ. It is demonstrated that TMR would be
enhanced by SOT-MTJ symmetry structure. The symmetrization induces interfacial
resonant states (IRSs). When IRSs match identical resonances at the opposite
barrier interface, resonant tunneling occurs in SOT-MTJ, which significantly
contributes to the conductance in parallel configuration and improves TMR. We
demonstrate the occurrence of resonant tunneling by transmission spectra,
density of scattering states and differential density of states. We also point
out that the thickness of heavy metal has limited influence on TMR. This work
would benefit the TMR optimization in SOT-MTJ, as well as the SOT spintronics
device.",1802.05787v2
2018-02-20,Cross-over between collective and independent-particle excitations in quasi-2D electron gas with one filled miniband,"While it has been recently demonstrated that, for quasi-2D electron gas
(Q2DEG) with one filled miniband, the dynamic exchange $f_x$ and Hartree $f_H$
kernels cancel each other in the low-density regime $r_s\rightarrow \infty$ (by
half and completely, for the spin-neutral and fully spin-polarized cases,
respectively), here we analytically show that the same happens at arbitrary
densities at short distances. This motivates us to study the confinement
dependence of the excitations in Q2DEG. Our calculations unambiguously confirm
that, at strong confinements, the time-dependent exact exchange excitation
energies approach the single-particle Kohn-Sham ones for the spin-polarized
case, while the same, but less pronounced, tendency is observed for
spin-neutral Q2DEG.",1802.07004v1
2018-04-18,Spin dynamics from time-dependent density functional perturbation theory,"We present a new method to model spin-wave excitations in magnetic solids,
based on the Liouville-Lanczos approach to time-dependent density functional
perturbation theory. This method avoids computationally expensive sums over
empty states and naturally deals with the coupling between spin and charge
fluctuations, without ever explicitly computing charge-density
susceptibilities. Spin-wave excitations are obtained with one Lanczos chain per
magnon wave-number and polarization, avoiding the solution of the
linear-response problem for every individual value of frequency, as other
state-of-the-art approaches do. Our method is validated by computing magnon
dispersions in bulk Fe and Ni, resulting in agreement with previous theoretical
studies in both cases, and with experiment in the case of Fe. The disagreement
in the case of Ni is also comparable with that of previous computations.",1804.06573v2
2018-11-05,Localization in spin chains with facilitation constraints and disordered interactions,"Quantum many-body systems with kinetic constraints exhibit intriguing
relaxation dynamics. Recent experimental progress in the field of cold atomic
gases offers a handle for probing collective behavior of such systems, in
particular for understanding the interplay between constraints and disorder.
Here we explore a spin chain with facilitation constraints --- a feature which
is often used to model classical glass formers --- together with disorder that
originates from spin-spin interactions. The specific model we study, which is
realized in a natural fashion in Rydberg quantum simulators, maps onto an
XX-chain with non-local disorder. Our study shows that the combination of
constraints and seemingly unconventional disorder may lead to interesting
non-equilibrium behaviour in experimentally relevant setups.",1811.01667v1
2018-11-08,Numerical study of barriers and valleys in the free-energy landscape of spin glasses,"We study the problem of glassy relaxations in the presence of an external
field in the highly controlled context of a spin-glass simulation. We consider
a small spin glass in three dimensions (specifically, a lattice of size L=8,
small enough to be equilibrated through a Parallel Tempering simulations at low
temperatures, deep in the spin glass phase). After equilibrating the sample, an
external field is switched on, and the subsequent dynamics is studied. The
field turns out to reduce the relaxation time, but huge statistical
fluctuations are found when different samples are compared. After taking care
of these fluctuations we find that the expected linear regime is very narrow.
Nevertheless, when regarded as a purely numerical method, we find that the
external field is extremely effective in reducing the relaxation times.",1811.03414v2
2018-11-18,Quantum Twist-Deformed D=4 Phase Spaces with Spin Sector and Hopf Algebroid Structures,"We consider the generalized (10+10)-dimensional D=4 quantum phase spaces
containing translational and Lorentz spin sectors associated with the dual pair
of twist-quantized Poincare Hopf algebra $\mathbb{H}$ and quantum Poincare Hopf
group $\widehat{\mathbb{G}}$. Two Hopf algebroid structures of generalized
phase spaces with spin sector will be investigated: first one $%
\mathcal{H}^{(10,10)}$ describing dynamics on quantum group algebra $%
\widehat{\mathbb{G}}$ provided by the Heisenberg double algebra $\mathcal{HD=%
}\mathbb{H}\rtimes \widehat{\mathbb{G}}$, and second, denoted by $\mathcal{%
\tilde{H}}^{(10,10)}$, describing twisted Hopf algebroid with base space
containing twisted noncommutative Minkowski space $\hat{x}_{\mu }$. We obtain
the first explicit example of Hopf algebroid structure of relativistic quantum
phase space which contains quantum-deformed Lorentz spin sector.",1811.07365v1
2018-11-20,A novel derivation of the Marchenko-Pastur law through analog bipartite spin-glasses,"In this work we consider the {\em analog bipartite spin-glass} (or {\em
real-valued restricted Boltzmann machine} in a neural network jargon), whose
variables (those quenched as well as those dynamical) share standard Gaussian
distributions. First, via Guerra's interpolation technique, we express its
quenched free energy in terms of the natural order parameters of the theory
(namely the self- and two-replica overlaps), then, we re-obtain the same result
by using the replica-trick: a mandatory tribute, given the special occasion.
Next, we show that the quenched free energy of this model is the functional
generator of the moments of the correlation matrix among the weights connecting
the two layers of the spin-glass (i.e., the Wishart matrix in random matrix
theory or the Hebbian coupling in neural networks): as weights are quenched
stochastic variables, this plays as a novel tool to inspect random matrices. In
particular, we find that the Stieltjes transform of the spectral density of the
correlation matrix is determined by the (replica-symmetric) quenched free
energy of the bipartite spin-glass model. In this setup, we re-obtain the
Marchenko-Pastur law in a very simple way.",1811.08298v1
2020-07-01,Circumventing spin glass traps by microcanonical spontaneous symmetry breaking,"The planted p-spin interaction model is a paradigm of random-graph systems
possessing both a ferromagnetic phase and a disordered phase with the latter
splitting into many spin glass states at low temperatures. Conventional
simulated annealing dynamics is easily blocked by these low-energy spin glass
states. Here we demonstrate that, actually this planted system is exponentially
dominated by a microcanonical polarized phase at intermediate energy densities.
There is a discontinuous microcanonical spontaneous symmetry breaking
transition from the paramagnetic phase to the microcanonical polarized phase.
This transition can serve as a mechanism to avoid all the spin glass traps, and
it is accelerated by the restart strategy of microcanonical random walk. We
also propose an unsupervised learning problem on microcanonically sampled
configurations for inferring the planted ground state.",2007.00303v4
2020-07-12,Density Dependent Spin-Orbit Coupling in Degenerate Quantum Gases,"In this letter we propose a method to realize a kind of spin-orbit coupling
in ultracold Bose and Fermi gases whose format and strength depend on density
of atoms. Our method combines two-photon Raman transition and periodical
modulation of spin-dependent interaction, which gives rise to the direct Raman
process and the interaction assisted Raman process, and the latter depends on
density of atoms. These two processes have opposite effects in term of
spin-momentum locking and compete with each other. As the interaction
modulation increases, the system undergoes a crossover from the direct Raman
process dominated regime to the interaction assisted Raman process dominated
regime. For this crossover, we show that for bosons, both the condensate
momentum and the chirality of condensate wave function change sign, and for
fermions, the Fermi surface distortion is inverted. We highlight that there
exists an emergent spatial reflection symmetry in the crossover regime, which
can manifest itself universally in both Bose and Fermi gases. Our method paves
a way to novel phenomena in a non-abelian gauge field with intrinsic dynamics.",2007.05999v2
2020-07-14,"Large spin gaps in half metals MN4 (M=Mn, Fe, Co) with N2 dimers","We predict that cubic MN4 (M=Mn, Fe, Co) are all half metals with the largest
spin gap up to ~ 5 eV. They possess robust ferromagnetic ground states with the
highest Curie temperature up to ~ 103 K. Our calculations indicate these
compounds are energetically favored, dynamically and mechanically stable. It is
proposed that self-doping of these 3d transition metals occurs in MN4 due to
the reduction in electronegativity of N2 dimers. This model can well explain
the calculated integer magnetic moments, large spin gaps of MN4 and
semiconducting behavior for NiN4 as well. Our results highlight the difference
in electronegativity between transition metal ions and non-metal entities in
forming half metals and the role of N2 dimer in enlarging the spin gaps for
nitride half metals.",2007.07119v1
2020-07-14,Feedback Induced Magnetic Phases in Binary Bose-Einstein Condensates,"Weak measurement in tandem with real-time feedback control is a new route
toward engineering novel non-equilibrium quantum matter. Here we develop a
theoretical toolbox for quantum feedback control of multicomponent
Bose-Einstein condensates (BECs) using backaction-limited weak measurements in
conjunction with spatially resolved feedback. Feedback in the form of a
single-particle potential can introduce effective interactions that enter into
the stochastic equation governing system dynamics. The effective interactions
are tunable and can be made analogous to Feshbach resonances --
spin-independent and spin-dependent -- but without changing atomic scattering
parameters. Feedback cooling prevents runaway heating due to measurement
backaction and we present an analytical model to explain its effectiveness. We
showcase our toolbox by studying a two-component BEC using a stochastic
mean-field theory, where feedback induces a phase transition between easy-axis
ferromagnet and spin-disordered paramagnet phases. We present the steady-state
phase diagram as a function of intrinsic and effective spin-dependent
interaction strengths. Our result demonstrates that closed-loop quantum control
of Bose-Einstein condensates is a powerful new tool for quantum engineering in
cold-atom systems.",2007.07266v1
2020-07-15,Local Probes for Charge-Neutral Edge States in Two-Dimensional Quantum Magnets,"The bulk-boundary correspondence is a defining feature of topological states
of matter. However, for quantum magnets such as spin liquids or topological
magnon insulators a direct observation of topological surface states has proven
challenging because of the charge-neutral character of the excitations. Here we
propose spin-polarized scanning tunneling microscopy as a spin-sensitive local
probe to provide direct information about charge neutral topological edge
states. We show how their signatures, imprinted in the local structure factor,
can be extracted by specifically employing the strengths of existing
technologies. As our main example, we determine the dynamical spin correlations
of the Kitaev honeycomb model with open boundaries. We show that by contrasting
conductance measurements of bulk and edge locations, one can extract direct
signatures of the existence of fractionalized excitations and non-trivial
topology. The broad applicability of this approach is corroborated by a second
example of a kagome topological magnon insulator.",2007.07912v1
2020-07-25,"Structure, phase stability, half-metallicity, and fully spin-polarized Weyl states in compound NaV2O4: a new example for topological spintronic material","Here, we systematically investigate the structure, phase stability,
half-metallicity, and topological electronic structure for a new topological
spintronic material NaV2O4. The material has a tetragonal structure with
excellent dynamical and thermal stabilities. It shows a half-metallic ground
state, where only the spin-up bands present near the Fermi level. These bands
form a Weyl nodal line close to the Fermi level, locating in the kz = 0 plane.
The nodal line is robust against SOC, under the protection of the mirror
symmetry. The nodal line band structure is very clean, thus the drumhead
surface states can be clearly identified. Remarkably, the nodal line and
drumhead surface states have the 100% spin polarization, which are highly
desirable for spintronics applications. In addition, by shifting the magnetic
field in-plane, we find that the Weyl nodal line can transform into single pair
of Weyl nodes. The Weyl-line and Weyl-node fermions in the bulk, as well as the
drumhead fermions on the surface are all fully spin-polarized, which may
generate new physical properties and promising applications.",2007.12844v1
2020-07-26,Dynamical Tidal Locking Theory: A new source of the Spin of Dark Matter Halos,"We revisit the question of what mechanism is responsible for the spins of
halos of dark matter. The answer to this question is of high importance for
modeling galaxy intrinsic alignment, which can potentially contaminate current
and future lensing data. In particular, we show that when the dark matter halos
pass nearly by each other in dense environments-- namely halo assemblies-- they
swing and spin each other via exerting mutual tidal torques. We show that this
has a significant contribution to the spin of dark matter halos comparable to
that of calculated by the so-called tidal torque theory (TTT). We use the
results of state-of-the-art simulation of Illutris to check the prediction of
this theory against the simulation data.",2007.13148v1
2010-05-05,Quasiparticle dynamics in ferromagnetic compounds of the Co-Fe and Ni-Fe systems,"We report a theoretical study of the quasiparticle lifetime and the
quasiparticle mean free path caused by inelastic electron-electron scattering
in ferromagnetic compounds of the Co-Fe and Ni-Fe systems. The study is based
on spin-polarized calculations, which are performed within the $GW$
approximation for equiatomic and Co- and Ni-rich compounds, as well as for
their constituents. We mainly focus on the spin asymmetry of the quasiparticle
properties, which leads to the spin-filtering effect experimentally observed in
spin-dependent transport of hot electrons and holes in the systems under study.
By comparing with available experimental data on the attenuation length, we
estimate the contribution of the inelastic mean free path to the latter.",1005.0679v2
2013-08-01,Inverse Spin Hall Effect in nanometer-thick YIG/Pt system,"High quality nanometer-thick (20 nm, 7 nm and 4 nm) epitaxial YIG films have
been grown on GGG substrates using pulsed laser deposition. The Gilbert damping
coefficient for the 20 nm thick films is 2.3 x 10-4 which is the lowest value
reported for sub-micrometric thick films. We demonstrate Inverse spin Hall
effect (ISHE) detection of propagating spin waves using Pt. The amplitude and
the lineshape of the ISHE voltage correlate well to the increase of the Gilbert
damping when decreasing thickness of YIG. Spin Hall effect based
loss-compensation experiments have been conducted but no change in the
magnetization dynamics could be detected.",1308.0192v1
2013-08-09,"The Hour-Glass Magnetic Spectrum Arising from a Striped, Cluster Spin Glass Ground State in La1.75Sr0.25CoO4","We report inelastic neutron scattering results that reveal an hour-glass
magnetic excitation spectrum in La1.75Sr0.25CoO4. The magnetic spectrum is
similar to that observed previously in La1.67Sr0.33CoO4, but the spectral
features are broader. We show that the spectrum of La1.75Sr0.25CoO4 can be
modeled by the spin dynamics of a system with a disordered cluster spin glass
ground state. Bulk magnetization measurements are presented which support the
proposed glassy ground state. The observations reiterate the importance of
quasi-one-dimensional magnetic correlations and disorder for the hour-glass
spectrum, and suggest that disordered spin and charge stripes exist at lower
doping in La2-xSrxCoO4 than previously thought.",1308.2141v1
2013-08-20,Laplace-Runge-Lenz vector for arbitrary spin,"A countable set of superintegrable quantum mechanical systems is presented
which admit the dynamical symmetry with respect to algebra so(4). This algebra
is generated by the Laplace-Runge-Lenz vector generalized to the case of
arbitrary spin. The presented systems describe neutral particles with
non-trivial multipole momenta. Their spectra can be found algebraically like in
the case of Hydrogen atom. Solutions for the systems with spins 1/2 and 1 are
presented explicitly, solutions for spin 3/2 are expressed via solutions of an
ordinary differential equation of first order..",1308.4279v3
2013-08-21,Spin in an arbitrary gravitational field,"We study the quantum mechanics of a Dirac fermion on a curved spacetime
manifold. The metric of the spacetime is completely arbitrary, allowing for the
discussion of all possible inertial and gravitational field configurations. In
this framework, we find the Hermitian Dirac Hamiltonian for an arbitrary
classical external field (including the gravitational and electromagnetic
ones). In order to discuss the physical content of the quantum-mechanical
model, we further apply the Foldy-Wouthuysen transformation, and derive the
quantum equations of motion for the spin and position operators. We analyse the
semiclassical limit of these equations and compare the results with the
dynamics of a classical particle with spin in the framework of the standard
Mathisson-Papapetrou theory and in the classical canonical theory. The
comparison of the quantum mechanical and classical equations of motion of a
spinning particle in an arbitrary gravitational field shows their complete
agreement.",1308.4552v1
2014-03-12,Spectroscopic observation of SU(N)-symmetric interactions in Sr orbital magnetism,"SU(N) symmetry can emerge in a quantum system with N single-particle spin
states when spin is decoupled from inter-particle interactions. So far, only
indirect evidence for this symmetry exists, and the scattering parameters
remain largely unknown. Here we report the first spectroscopic observation of
SU(N=10) symmetry in Sr-87 using the state-of-the-art measurement precision
offered by an ultra-stable laser. By encoding the electronic orbital degree of
freedom in two clock states, while keeping the system open to 10 nuclear spin
sublevels, we probe the non-equilibrium two-orbital SU(N) magnetism via Ramsey
spectroscopy of atoms confined in an array of two-dimensional optical traps. We
study the spin-orbital quantum dynamics and determine all relevant interaction
parameters. This work prepares for using alkaline-earth atoms as test-beds for
iconic orbital models.",1403.2964v2
2016-11-09,Effect of nanostructure layout on spin pumping phenomena in antiferromagnet/ nonmagnetic metal/ ferromagnet multilayered stacks,"In this work we focus on magnetic relaxation in Mn$_{80}$Ir$_{20}$(12 nm)/
Cu(6 nm)/ Py($d_\mathrm{F}$) antiferromagnet/Cu/ferromagnet (AFM/Cu/FM)
multilayers with different thickness of the ferromagnetic permalloy layer. An
effective FM-AFM interaction mediated via the conduction electrons in the
nonmagnetic Cu spacer -- the spin-pumping effect -- is detected as an increase
in the linewidth of the ferromagnetic resonance (FMR) spectra and a shift of
the resonant magnetic field. We further find experimentally that the
spin-pumping-induced contribution to the linewidth is inversely proportional to
the thickness of the Py layer. We show that this thickness dependence likely
originates from the dissipative dynamics of the free and localized spins in the
AFM layer. The results obtained could be used for tailoring the dissipative
properties of spintronic devices incorporating antiferromagnetic layers.",1611.02865v1
2017-01-07,Torsion effects on Condensed Matter: like a magnetic field but not so much,"In this work, we study the effects of torsion due to a uniform distribution
of topological defects (screw dislocations) on free spin/carrier dynamics in
elastic solids. When a particle moves in such a medium, the effect of the
torsion associated to the defect distribution is analogous to that of an
applied magnetic field but with subtle differences. Analogue Landau levels are
present in this system but they cannot be confined to two dimensions. In the
case of spinless carriers, zero modes, which do not appear in the magnetic
Landau levels, show up for quantized values of the linear momentum projected on
the defects axis. Particles with spin are subjected to a Zeeman-like coupling
between spin and torsion, which is insensitive to charge. This suggests the
possibility of spin resonance experiments without a magnetic field for charged
carriers or quasiparticles without electrical charge, like triplet excitons,
for instance.",1701.01829v1
2017-01-20,Two-magnon excitations in resonant inelastic x-ray scattering studied by spin-density-wave formalism,"We study two-magnon excitations in resonant inelastic x-ray scattering (RIXS)
at the transition-metal $K$-edge. Instead of working with effective Heisenberg
spin models, we work with a Hubbard-type model ($d$-$p$ model) for a typical
insulating cuprate La$_2$CuO$_4$. For the antiferromagnetic ground state within
the spin-density-wave (SDW) mean-field formalism, we calculate the dynamical
correlation function within the random-phase approximation (RPA), and then
obtain two-magnon excitation spectra by calculating the convolution of it.
Coupling between the $K$-shell hole and the magnons in the intermediate state
is calculated by means of diagrammatic perturbation expansion in the Coulomb
interaction. Calculated momentum dependence of RIXS spectra agrees well with
that of experiments. A notable difference from previous calculations based on
the Heisenberg spin models is that RIXS spectra have a large two-magnon weight
near the zone center, which may be confirmed by further careful high-resolution
experiments.",1701.05684v2
2017-04-05,Collective excitation of a trapped Bose-Einstein condensate with spin-orbit coupling,"We investigate the collective excitations of a Raman-induced spin-orbit
coupled Bose-Einstein condensate confined in a quasi one-dimension harmonic
trap using the Bogoliubov method. By tuning the Raman coupling strength, three
phases of the system can be identified. By calculating the transition strength,
we are able to classify various excitation modes that are experimentally
relevant. We show that the three quantum phases possess distinct features in
their collective excitation properties. In particular, the spin dipole and the
spin breathing modes can be used to clearly map out the phase boundaries. We
confirm these predictions by direct numerical simulations of the quench
dynamics that excites the relevant collective modes.",1704.01242v1
2017-04-12,Towards a Cosmological subsector of Spin Foam Quantum Gravity,"We examine the four dimensional path integral for Euclidean quantum gravity
in the context of the EPRL-FK spin foam model. The state sum is restricted to
certain symmetric configurations which resembles the geometry of a flat
homogeneous and isotropic universe. The vertex structure is specially chosen so
that a basic concept of expansion and contraction of the lattice universe is
allowed.
  We compute the asymptotic form of the spin foam state sum in the symmetry
restricted setting, and recover a Regge-type action, as well as an explicit
form of the Hessian matrix, which captures quantum corrections. We investigate
the action in the three cases of vacuum, a cosmological constant, and coupled
to dust, and find that in all cases, the corresponding FRW dynamics is
recovered in the limit of large lattices. While this work demonstrates a large
intersection with computations done in the context of cosmological modelling
with Regge Calculus, it is ultimately a setup for treating curved geometries in
the renormalization of the EPRL-FK spin foam model.",1704.03691v1
2017-04-19,"Dynamical reduction of the dimensionality of exchange interactions and the ""spin-liquid"" phase of $κ$-(BEDT-TTF)$_2X$","We show that the anisotropy of the effective spin model for the dimer Mott
insulator phase of $\kappa$-(BEDT-TTF)$_2X$ salts is dramatically different
from that of the underlying tight-binding model. Intra-dimer quantum
interference results in a model of coupled spin chains, where frustrated
interchain interactions suppress long-range magnetic order. Thus, we argue, the
""spin liquid"" phase observed in some of these materials is a remnant of the
Tomonaga-Luttinger physics of a single chain. This is consistent with previous
experiments and resolves some outstanding puzzles. An erratum [Phys. Rev. Lett.
120, 199901 (2018).] is added as an appendix.",1704.05688v3
2017-04-21,Distribution of eigenstate populations and dissipative beating dynamics in uniaxial single-spin magnets,"Numerical simulations of magnetization reversal of a quantum uniaxial magnet
under a swept magnetic field [Hatomura, \textit{et al}., \textit{Quantum
Stoner-Wohlfarth Model}, Phys. Rev. Lett. \textbf{116}, 037203 (2016)] are
extended. In particular, how the ""wave packet"" describing the time-evolution of
the system is scattered in the successive avoided level crossings is
investigated from the viewpoint of the distribution of the eigenstate
populations. It is found that the peak of the distribution as a function of the
magnetic field does not depend on spin-size $S$, which indicates that the delay
of magnetization reversal due to the finite sweeping rate is the same in both
the quantum and classical cases. The peculiar synchronized oscillations of all
the spin components result in the beating of the spin-length. Here, dissipative
effects on this beating are studied by making use of the generalized
Lindblad-type master equation. The corresponding experimental situations are
also discussed in order to find conditions for experimental observations.",1704.06466v1
2017-04-25,Unified description of dynamics of a repulsive two-component Fermi gas,"We study a binary spin-mixture of a zero-temperature repulsively interacting
$^6$Li atoms using both the atomic-orbital and the density functional
approaches. The gas is initially prepared in a configuration of two magnetic
domains and we determine the frequency of the spin-dipole oscillations which
are emerging after the repulsive barrier, initially separating the domains, is
removed. We find, in agreement with recent experiment (G. Valtolina et al.,
arXiv:1605.07850 (2016)), the occurrence of a ferromagnetic instability in an
atomic gas while the interaction strength between different spin states is
increased, after which the system becomes ferromagnetic. The ferromagnetic
instability is preceded by the softening of the spin-dipole mode.",1704.07707v2
2018-05-14,Universal Spin Transport and Quantum Bounds for Unitary Fermions,"We review recent advances in experimental and theoretical understanding of
spin transport in strongly interacting Fermi gases. The central new phenomenon
is the observation of a lower bound on the (bare) spin diffusivity in the
strongly interacting regime. Transport bounds are of broad interest for the
condensed matter community, with a conceptual similarity to observed bounds in
shear viscosity and charge conductivity. We discuss the formalism of spin
hydrodynamics, how dynamics are parameterized by transport coefficients, the
effect of confinement, the role of scale invariance, the quasi-particle
picture, and quantum critical transport. We conclude by highlighting open
questions, such as precise theoretical bounds, relevance to other phases of
matter, and extensions to lattice systems.",1805.05354v1
2018-05-15,Magnetosphere of a spinning black hole and the role of the current sheet,"We revisit the problem of a spinning black hole immersed in a uniformly
magnetized plasma within the context of force-free electrodynamics. Such
configurations have been found to relax to stationary jetlike solutions that
are powered by the rotational energy of the black hole. We write down an
analytic description for the jet solutions in the low black hole spin limit,
and demonstrate that it provides a good approximation to the configurations
found dynamically. For characterizing the magnetospheres of rapidly spinning
black holes, we find that the current sheet which forms in the black hole
ergosphere plays an essential role. We study the properties of the current
sheet, and its importance in determining the jet solution and the rate at which
energy is extracted from the black hole.",1805.05952v2
2008-07-08,Semiclassical spin liquid state of easy axis Kagome antiferromagnets,"Motivated by recent experiments on Nd-langasite, we consider the effect of
strong easy axis single-ion anisotropy $D$ on $S > 3/2$ spins interacting with
antiferromagnetic exchange $J$ on the Kagome lattice. When $T \ll DS^2$, the
collinear low energy states selected by the anisotropy map on to configurations
of the classical Kagome lattice Ising antiferromagnet. However, the low
temperature limit is quite different from the cooperative Ising paramagnet that
obtains classically for $T \ll JS^2$. We find that sub-leading ${\mathcal
O}(J^3S/D^2)$ multi-spin interactions arising from the transverse quantum
dynamics result in a crossover from an intermediate temperature classical
cooperative Ising paramagnet to a semiclassical spin liquid with distinct
short-ranged correlations for $T \ll J^3S/D^2$.",0807.1163v1
2009-12-14,"Optical control of electron spin coherence in CdTe/(Cd,Mg)Te quantum wells","Optical control of the spin coherence of quantum well electrons by short
laser pulses with circular or linear polarization is studied experimentally and
theoretically. For that purpose the coherent electron spin dynamics in a
n-doped CdTe/(Cd,Mg)Te quantum well structure was measured by time-resolved
pump-probe Kerr rotation, using resonant excitation of the negatively charged
exciton (trion) state. The amplitude and phase shifts of the electron spin beat
signal in an external magnetic field, that are induced by laser control pulses,
depend on the pump-control delay and polarization of the control relative to
the pump pulse. Additive and non-additive contributions to pump-induced signal
due to the control are isolated experimentally. These contributions can be well
described in the framework of a two-level model for the optical excitation of
the resident electron to the trion.",0912.2589v1
2009-12-15,Dimer mean-field model for the Ising spin glass,"A dimer mean-field model for the Ising spin-glass is presented. Despite its
simplicity it captures some of the essential features of the spin-glass
physics. The distribution of the single-spin magnetization is determined from a
self-consistent integral equation. By solving the self-consistency condition
numerically, we find that there are two temperature scales characterizing the
glass transition. At the first, higher temperature, the glass order parameter
becomes non-vanishing, and at the second, freezing temperature, it saturates to
its maximal value. The effect of magnetic field and the existence of the
Almeida-Thouless line are discussed. Finally, it is shown that the information
compressibility, defined as the derivative of entropy with respect to energy,
diverges at the freezing temperature. This indicates a zero internal
temperature and true glassy dynamics with diverging relaxation times.",0912.2959v1
2009-12-30,Spin torque and critical currents for magnetic vortex nano-oscillator in nanopillars,"We calculated the main dynamic parameters of the spin polarized current
induced magnetic vortex oscillations in nanopillars, such as the range of
current density, where a vortex steady oscillations exist, the oscillation
frequency and orbit radius. We accounted for both the non-linear vortex
frequency and non-linear vortex damping. To describe the vortex excitations by
the spin polarized current we used a generalized Thiele approach to motion of
the vortex core as a collective coordinate. All the calculation results are
represented via the free layer sizes, saturation magnetization, Gilbert damping
and the degree of the spin polarization of the fixed layer. Predictions of the
developed model can be checked experimentally.",0912.5521v1
2012-01-04,Non-Kondo mechanism for resistivity minimum in spin ice conduction systems,"We present a mechanism of resistivity minimum in conduction electron systems
coupled with localized moments, which is distinguished from the Kondo effect.
Instead of the spin-flip process in the Kondo effect, electrons are elastically
scattered by local spin correlations which evolve in a particular way under
geometrical frustration as decreasing temperature. This is demonstrated by the
cellular dynamical mean-field theory for a spin-ice type Kondo lattice model on
a pyrochlore lattice. Peculiar temperature dependences of the resistivity,
specific heat, and magnetic susceptibility in the non-Kondo mechanism are
compared with the experimental data in metallic Ir pyrochlore oxides.",1201.0929v2
2012-01-08,Mapping between quantum dot and quantum well lasers: From conventional to spin lasers,"We explore similarities between the quantum wells and quantum dots used as
optical gain media in semiconductor lasers. We formulate a mapping procedure
which allows a simpler, often analytical, description of quantum well lasers to
study more complex lasers based on quantum dots. The key observation in
relating the two classes of laser is that the influence of a finite capture
time on the operation of quantum dot lasers can be approximated well by a
suitable choice of the gain compression factor in quantum well lasers. Our
findings are applied to the rate equations for both conventional
(spin-unpolarized) and spin lasers in which spin-polarized carriers are
injected optically or electrically. We distinguish two types of mapping that
pertain to the steady-state and dynamical operation respectively and elucidate
their limitations.",1201.1644v1
2012-01-10,A spin-foam vertex amplitude with the correct semiclassical limit,"Spin-foam models are hoped to provide a dynamics for loop quantum gravity.
These start from the Plebanski formulation of gravity, in which gravity is
obtained from a topological field theory, BF theory, through constraints,
which, however, select more than one gravitational sector, as well as an
unphysical degenerate sector. We show this is why terms beyond the needed
Feynman-prescribed one appear in the semiclassical limit of the EPRL spin-foam
amplitude. By quantum mechanically isolating a single gravitational sector, we
modify this amplitude, yielding a spin-foam amplitude for loop quantum gravity
with the correct semiclassical limit.",1201.2187v2
2012-01-25,Shot Noise Induced by Electron-nuclear Spin-flip Scattering in a Nonequilibrium Quantum Wire,"We study the shot noise (nonequilibrium current fluctuation) associated with
dynamic nuclear polarization in a nonequilibrium quantum wire (QW) fabricated
in a two-dimensional electron gas. We observe that the spin-polarized
conductance quantization of the QW in the integer quantum Hall regime collapses
when the QW is voltage biased to be driven to nonequilibrium. By measuring the
shot noise, we prove that the spin polarization of electrons in the QW is
reduced to $\sim 0.7$ instead of unity as a result of electron-nuclear
spin-flip scattering. The result is supported by Knight shift measurements of
the QW using resistively detected NMR.",1201.5191v1
2012-04-05,The Jefferson Lab Frozen Spin Target,"A frozen spin polarized target, constructed at Jefferson Lab for use inside a
large acceptance spectrometer, is described. The target has been utilized for
photoproduction measurements with polarized tagged photons of both longitudinal
and circular polarization. Protons in TEMPO-doped butanol were dynamically
polarized to approximately 90% outside the spectrometer at 5 T and 200--300 mK.
Photoproduction data were acquired with the target inside the spectrometer at a
frozen-spin temperature of approximately 30 mK with the polarization maintained
by a thin, superconducting coil installed inside the target cryostat. A 0.56 T
solenoid was used for longitudinal target polarization and a 0.50 T dipole for
transverse polarization. Spin-lattice relaxation times as high as 4000 hours
were observed. We also report polarization results for deuterated propanediol
doped with the trityl radical OX063.",1204.1250v1
2012-04-10,Observation of spin-glass behavior in nickel adsorbed few layer graphene,"Nickel-adsorbed graphene was prepared by first synthesizing graphite oxide
(GO) by modified Hummers' method and then reducing a solution containing both
GO and $Ni^{2+}$. EDX analysis showed 31 atomic percent nickel was present.
Magnetization measurements under both dc and ac magnetic fields were carried
out in the temperature range 2 K to 300 K. The zero field cooled and field
cooled magnetization data showed a pronounced irreversibility at a temperature
around 20 K. The analysis of the ac susceptibility data were carried out by
both Vogel-Fulcher as well as power law. From dynamic scaling analysis the
microscopic flipping time $\tau_{0}\sim 10^{-13} s$ and critical exponent
$z\nu=5.9\pm0.1$ were found, indicating presence of conventional spin glass in
the system. The spin glass transition temperature was estimated as 19.5 K.
  Decay of thermoremanent magnetization (TRM) was explained by stretched
exponential function with a value of the exponent as 0.6 .
  From the results it is concluded that nickel adsorbed graphene behaves like a
spin-glass.",1204.2123v2
2012-04-23,Interaction Induced Hall Response in a Spin-Orbit Coupled Bose-Einstein Condensate,"In this letter we consider the dynamic behaviors of spin-orbit coupled Bose
condensates realized in recent experiments. We show that there exists an
interaction induced ac Hall response which is absent in a non-interacting
system. This condensate has two distinct equilibrium phases known as the plane
wave phase and the stripe phase. In the plane wave phase, we show that an ac
longitudinal current will induce an ac radial current in the transverse
direction, and vice versa, as a cooperation effect of spin-velocity locking and
spin-dependent interaction. In the stripe phase, we show that the dominant
longitudinal response to a transverse radial current is sliding of the density
stripe, because it is the low-lying excitation mode originated from spontaneous
spatial translational symmetry breaking in this phase.",1204.5121v1
2012-04-27,Quantum correlations of Two-Qubit XXZ Heisenberg Chain with Dzyaloshinsky-Moriya interaction coupled to bath spin as non-Markovian environment,"We consider the quantum correlations (entanglement and quantum discord)
dynamics of two coupled spin qubits with Dzyaloshinsky-Moriya interaction
influenced by a locally external magnetic field along $z$-direction and coupled
to bath spin-1/2 particles as independent non-Markovian environment. We find
that with increasing $D_{z}$ and decreasing $J_{z}$, the value of entanglement
and quantum discord increase for both antiferromagnetic and ferromagnetic
materials. Not that, this growth is more for the ferromagnetic materials. In
addition, we perceive that entanglement and quantum discord decrease with
increased temperature and increased coupling constants between reduced system
and bath. But, strong quantum correlations within the spins of bath reduce
decoherence effects. We discuss about type of the constituent material of the
central spins that it can speedup the quantum information processing and as a
result, we perceive that one can improve and control the quantum information
processing with correct selection of the properties of the reduced system ($J$,
$J_{z}$, $D_{z}$).",1204.6124v2
2012-04-27,Prediction of polaron-like vortices and dissociation depinning transition in magnetic superconductors: The example of ErNi2B2C,"In borocarbide ErNi$_2$B$_2$C the phase transition to the commensurate spin
density wave at 2.3 K leaves 1/20 part of Ising-like Er spins practically free.
Vortices polarize these spins nonuniformly and repolarize them when moving. At
a low spin relaxation rate and at low bias currents vortices carrying magnetic
polarization clouds become polaron-like and their velocities are determined by
the effective drag coefficient which is significantly bigger than the
Bardeen-Stephen (BS) one. As current increases, at a critical current $J_c$
vortices release polarization clouds and the velocity as well as the voltage in
the I-V characteristics jump to values corresponding to the BS drag
coefficient. The nonuniform components of the magnetic field and magnetization
drop as velocity increases resulting in weaker polarization and discontinuous
dynamic dissociation depinning transition. As current decreases, on the way
back, vortices are retrapped by polarization clouds at the current $J_r<J_c$.",1204.6348v2
2013-09-09,Scaling of the largest dynamical barrier in the one-dimensional long-range Ising spin-glass,"The long-range one-dimensional Ising spin-glass with random couplings
decaying as $J(r) \propto r^{-\sigma}$ presents a spin-glass phase
$T_c(\sigma)>0$ for $0 \leq \sigma<1$ (the limit $\sigma=0$ corresponds to the
mean-field SK-model). We use the eigenvalue method introduced in our previous
work [C. Monthus and T. Garel, J. Stat. Mech. P12017 (2009)] to measure the
equilibrium time $t_{eq}(N)$ at temperature $T=T_c(\sigma)/2$ as a function of
the number $N$ of spins. We find the activated scaling $\ln t_{eq}(N) \sim
N^{\psi}$ with the same barrier exponent $\psi \simeq 0.33$ in the whole region
$0\leq\sigma <1$.",1309.2154v3
2013-09-20,"Ground state and Spin-Wave dynamics in Brownmillerite SrCoO2.5, A combined Hybrid Functional and LSDAU study","We theoretically investigate the ground state magnetic properties of the
brownmillerite phase of SrCoO2.5. Strong correlations within Co d electrons are
treated within the local spin density approximations of Density Functional
theory (DFT) with Hubbard U corrections (LSDAU) and results are compared with
the Heyd Scuzeria Ernzerhof (HSE) functional. The parameters computed with a U
value of 7.5 eV are found to match closely to those computed within the HSE
functional. A G type antiferromagnetic structure is found to be the most stable
one, consistent with experimental observation. By mapping the total energies of
different magnetic configurations onto a Heisenberg Hamiltonian we compute the
magnetic exchange interaction parameters, J, between the nearest neighbor Co
atoms. The J s obtained are then used to compute the spin wave frequencies and
inelastic neutron scattering intensities. Among four spin wave branches, the
lowest energy mode was found to have the largest scattering intensity at the
magnetic zone center, while the other modes becomes dominant at different
momenta. These predictions can be tested by experimentally.",1309.5287v1
2013-09-24,Noncompact dynamical symmetry of a spin-orbit coupled oscillator,"We explain the finite as well as infinite degeneracy in the spectrum of a
particular system of spin-1/2 fermions with spin-orbit coupling in three
spatial dimensions. Starting from a generalized Runge-Lenz vector, we
explicitly construct a complete set of symmetry operators, which span a
noncompact SO(3,2) algebra. The degeneracy of the physical spectrum only
involves a particular, infinite, so called singleton representation. In the
branch where orbital and spin angular momentum are aligned the full
representation appears, constituting a 3D analogue of Landau levels.
Anti-aligning the spin leads to a finite degeneracy due to a truncation of the
singleton representation. We conclude the paper by constructing the spectrum
generating algebra of the problem.",1309.6128v2
2014-05-13,Higher order exchange interactions leading to metamagnetism in FeRh,"The origin of the metamagnetic antiferromagnetic-ferromagnetic phase
transition of FeRh is a subject of much debate. Competing explanations invoke
magnetovolume effects and purely ther- modynamic transitions within the spin
system. It is experimentally difficult to observe the changes in the magnetic
system and the lattice simultaneously, leading to differing conclusions over
which mechanism is responsible for the phase transition. A non-collinear
electronic structure study by Mryasov [O.N. Mryasov, Phase Transitions 78, 197
(2005)] showed that non-linear behavior of the Rh moment leads to higher order
exchange terms in FeRh. Using atomistic spin dynamics (ASD) we demonstrate that
the phase transition can occur due to the competition between bilinear and the
higher order four spin exchange terms in an effective spin Hamiltonian. The
phase transition we see is of first order and shows thermal hysteresis in
agreement with experimental observations. Simulating sub-picosecond laser
heating we show an agreement with pump-probe experiments with a ferromagnetic
response on a picosecond timescale.",1405.3043v1
2014-05-13,Quantum impurity in a Tomonaga-Luttinger liquid: continuous-time quantum Monte Carlo approach,"We develop a continuous-time quantum Monte Carlo (CTQMC) method for quantum
impurities coupled to interacting quantum wires described by a
Tomonaga-Luttinger liquid. The method is negative-sign free for any values of
the Tomonaga-Luttinger parameter, which is rigorously proved, and thus,
efficient low-temperature calculations are possible. Duality between electrons
and bosons in one dimensional systems allows us to construct a simple formula
for the CTQMC algorithm in these systems. We show that the CTQMC for
Tomonaga-Luttinger liquids can be implemented with only minor modifications of
previous CTQMC codes developed for impurities coupled to non-interacting
fermions. We apply this method to the Kane-Fisher model of a potential
scatterer in a spin-less quantum wire and to a single spin coupled with the
edge state of a two-dimensional topological insulator assuming an anisotropic
XXZ coupling. Various dynamical response functions such as the electron Green's
function and spin-spin correlation functions are calculated numerically and
their scaling properties are discussed.",1405.3300v3
2014-05-18,Ultracold Spin-Orbit Coupled Bose-Einstein Condensate in a Cavity: Route to Magnetic Phases Through Cavity Transmission,"We study the spin orbit coupled ultra cold Bose-Einstein condensate placed in
a single mode Fabry-P\'erot cavity. The cavity introduces a quantum optical
lattice potential which dynamically couples with the atomic degrees of freedom
and realizes a generalized extended Bose Hubbard model whose zero temperature
phase diagram can be controlled by tuning the cavity parameters. In the
non-interacting limit, where the atom-atom interaction is set to zero, the
resulting atomic dispersion shows interesting features such as bosonic analogue
of Dirac points, cavity controlled Hofstadter spectrum which bears the hallmark
of pseudo-spin-1/2 bosons in presence of Abelian and non-Abelian gauge field
(the later due to spin-orbit coupling) in a cavity induced optical lattice
potential. In the presence of atom-atom interaction, using a mapping to a
generalized Bose Hubbard model of spin-orbit coupled bosons in classical
optical lattice, we show that the system realizes a host of quantum magnetic
phases whose magnetic order can be be detected from the cavity transmission.
This provides an alternative approach for detecting quantum magnetism in ultra
cold atoms. We discuss the effect of cavity induced optical bistability on this
phases and their experimental consequences.",1405.4500v1
2014-05-21,Spin Glass Behavior in the Dy3-xYxTaO7 System,"Several x-compositions of the polycrystalline Dy3-xYxTaO7 system,
crystallizing in the weberite-type structure, were synthesized and structurally
characterized using Rietveld refinements based on X-ray diffraction data. In
previous magnetic characterization of Dy3TaO7 (x = 0), with the same crystal
structure, an antiferromagnetic transition at T = 2.3 K has been assigned to
this compound. On the basis of DC and AC magnetic susceptibilities analyses, we
show in this work that all compounds in the x range of 0-1.0 exhibit a spin
glass behavior. The nature of the spin glass behavior in Dy3-xYxTaO7, can be
attributed to the highly frustrated antiferromagnetic interaction of the Dy3+
sublattice and to the Dy3+-Dy3+ distorted tetrahedra array in the weberite-type
structure of this system. By fitting AC susceptibility data, using dynamical
scaling theory equations, we conclude that a cluster spin glass is present in
Dy3-xYxTaO7 in the low temperature range. Depending on the x-composition, Tg ~
2.2 - 3.2 K. In the range 15-300 K the system obeys a Curie-Weiss magnetic
behavior.",1405.5269v1
2014-06-22,Coherent manipulation of dipolar coupled spins in an anisotropic environment,"We study coherent dynamics in a system of dipolar coupled spin qubits diluted
in solid and subjected to a driving microwave field. In the case of rare earth
ions, anisotropic crystal background results in anisotropic g tensor and thus
modifies the dipolar coupling. We develop a microscopic theory of spin
relaxation in transient regime for the frequently encountered case of axially
symmetric crystal field. The calculated decoherence rate is nonlinear in Rabi
frequency. We show that the direction of static magnetic field that corresponds
to the highest spin g-factor is preferable in order to obtain higher number of
coherent qubit operations. The results of calculations are in excellent
agreement with our experimental data on Rabi oscillations recorded for a series
of CaWO4 crystals with different concentrations of Nd3+ ions.",1406.5740v2
2014-06-30,Interplay of magnetism and superconductivity in EuFe$_{2}$(As$_{1-x}$P$_{x}$)$_{2}$ single crystals probed by muon spin rotation and ${}^{57}$Fe Mössbauer spectroscopy,"We present our results of a local probe study on
EuFe$_{2}$(As$_{1-x}$P$_{x}$)$_{2}$ single crystals with $x$=0.13, 0.19 and
0.28 by means of muon spin rotation and ${}^{57}$Fe M\""ossbauer spectroscopy.
We focus our discussion on the sample with $x$=0.19 viz. at the optimal
substitution level, where bulk superconductivity ($T_{\text{SC}}=28$ K) sets in
above static europium order ($T^{\text{Eu}}=20$K) but well below the onset of
the iron antiferromagnetic (AFM) transition ($\sim$100 K). We find enhanced
spin dynamics in the Fe sublattice closely above $T_{\text{SC}}$ and propose
that these are related to enhanced Eu fluctuations due to the evident coupling
of both sublattices observed in our experiments.",1406.7715v1
2015-12-02,Dynamics of Fe atoms in Fe-gluconate as seen by Mössbauer spectroscopy,"Fe-gluconate was studied by means of the M\""ossbauer spectroscopy in the
temperature interval of 80-305K. The measured spectra were analyzed in terms of
two subspectra and, alternatively, two distributions of the quadrupole
splitting. The major component (ca.85%) was identified as due to high-spin Fe2+
ions while the identification of the minor component (ca.15%) was not unique:
some characteristics are in favour of the high-spin Fe3+ state while other ones
are consistent with the low-spin Fe2+ state. Values of the Debye temperature
were determined for both phases from a temperature dependence of the center
shift as well as from that of the spectral area. The force constant for the
high-spin ferrous atoms was evaluated to be equal to 44 N/m (243 cm-1).",1512.00654v1
2015-12-02,Optically tunable spin transport on the surface of a topological insulator,"The emerging field of spinoptronics has a potential to supersede the
functionality of modern electronics, while a proper description of strong
light-matter coupling pose the most intriguing questions from both fundamental
scientific and technological perspectives. In this paper we address a highly
relevant issue for such a development. We theoretically explore spin dynamics
on the surface of a 3D topological insulator (TI) irradiated with an
off-resonant high-frequency electromagnetic wave. The strong coupling between
electrons and the electromagnetic wave drastically modifies the spin properties
of TI. The effects of irradiation are shown to result in anisotropy of electron
energy spectrum near the Dirac point and suppression of spin current and are
investigated in detail in this work.",1512.00798v2
2015-12-04,Polarization dependence of nonlinear wave mixing of spinor polaritons in semiconductor microcavities,"The pseudo-spin dynamics of propagating exciton-polaritons in semiconductor
microcavities are known to be strongly influenced by TE-TM splitting. As a
vivid consequence, in the Rayleigh scattering regime, the TE-TM splitting gives
rise to the optical spin Hall effect (OSHE). Much less is known about its role
in the nonlinear optical regime in which four-wave mixing for example allows
the formation of spatial patterns in the polariton density, such that hexagons
and two-spot patterns are observable in the far field. Here we present a
detailed analysis of spin-dependent four-wave mixing processes, by combining
the (linear) physics of TE-TM splitting with spin-dependent nonlinear
processes, i.e., exciton-exciton interaction and fermionic phase-space filling.
Our combined theoretical and experimental study elucidates the complex physics
of the four-wave mixing processes that govern polarization and orientation of
off-axis modes.",1512.01378v1
2015-12-22,Observation of Unusual Magnetoelastic Effects in a Quasi-1D Spiral Magnet,"We present a systematic study of spin and lattice dynamics in the
quasi-one-dimensional spiral magnet CuBr2, using Raman scattering in
conjunction with infrared and neutron spectroscopy. Along with the development
of spin correlations upon cooling, we observe a rich set of broad Raman bands
at energies that correspond to phonon-dispersion energies near the
one-dimensional magnetic wave vector. The low-energy bands further exhibit a
distinct intensity maximum at the spiral magnetic ordering temperature. We
attribute these unusual observations to two possible underlying mechanisms: (1)
formation of hybrid spin-lattice excitations, and/or (2) ""quadrumerization"" of
the lattice caused by spin-singlet entanglement in competition with the spiral
magnetism.",1512.07120v2
2016-05-05,Enhanced spin lifetimes in a two dimensional electron gas in a gate-controlled GaAs quantum well,"Exciton, trion and electron spin dynamics in a 20 nm wide modulation-doped
GaAs single quantum well are investigated using resonant ultrafast two-color
Kerr rotation spectroscopy. Excitons and trions are selectively detected by
resonant probe pulses while their relative spectral weight is controlled by
adjusting the gate voltage which tunes the carrier density. Tuning the carrier
density markedly influences the spin decay time of the two dimensional electron
gas. The spin decay time can be enhanced by a factor of 3 at an intermediate
carrier concentration in the quantum well, where excitons and trions coexist in
the system. In addition, we explore the capability to tune the g-factor of the
electron gas via the carrier density.",1605.01771v1
2016-05-11,Doublon-holon binding as origin of Mott transition and fractionalized spin liquid -- Asymptotic solution of the Hubbard model in the limit of large coordination,"An analytical solution of the Mott transition is obtained for the Hubbard
model on the Bethe lattice in the large coordination number ($z$) limit. The
excitonic binding of doublons (doubly occupied sites) and holons (empty sites)
is shown to be the origin of a continuous Mott transition between a metal and
an emergent quantum spin liquid insulator. The doublon-holon binding theory
enables a different large-$z$ limit and a different phase structure than the
dynamical meanfield theory by allowing intersite spinon correlations to lift
the $2^N$-fold degeneracy of the local moments in the insulating phase. We show
that the spinons are coupled to doublons/holons by a dissipative compact U(1)
gauge field that is in the deconfined phase, stabilizing the spin-charge
separated gapless spin liquid Mott insulator.",1605.03597v2
2016-05-26,Topological defect formation in 1D and 2D spin chains realized by network of optical parametric oscillators,"A network of optical parametric oscillators is used to simulate classical
Ising and XY spin chains. The collective nonlinear dynamics of this network,
driven by quantum noise rather than thermal fluctuations, seeks out the Ising /
XY ground state as the system transitions from below to above the lasing
threshold. We study the behavior of this ""Ising machine"" for three canonical
problems: a 1D ferromagnetic spin chain, a 2D square lattice, and problems
where next-nearest-neighbor couplings give rise to frustration. If the pump
turn-on time is finite, topological defects form (domain walls for the Ising
model, winding number and vortices for XY) and their density can be predicted
from a numerical model involving a linear ""growth stage"" and a nonlinear
""saturation stage"". These predictions are compared against recent data for a
10,000-spin 1D Ising machine.",1605.08121v1
2017-06-05,Asymmetry Observables for Measuring Spin Correlations in Top-Quark Pair Production,"Spin correlations between top-quark and anti-top-quark in pair production are
sensitive to physics beyond the standard model. A complete set of observables,
that can be used to measure all independent parameters of the production spin
density matrix, is necessary to search for anomalous interactions in the
production dynamics. In this letter, we provide a set of asymmetry observables
for measuring all the density matrix elements. These observables are defined
regardless of the production mechanism, and can be specified in any desired
reference frame, particularly the laboratory frame in which the first evidence
of spin correlation was observed experimentally. Our method can be used to find
an optimal Lorentz frame in which the sensitivity to the density matrices is
high for given production process and experimental environment, or to test
possible correlations among the matrix elements.",1706.01492v4
2017-06-06,Nature vs. Nurture in Discrete Spin Dynamics,"The problem of predictability, or ""nature vs. nurture"", in both ordered and
disordered Ising systems following a deep quench from infinite to zero
temperature is reviewed. Two questions are addressed. The first deals with the
nature of the final state: for an infinite system, does every spin flip
infinitely often, or does every spin flip only finitely many times, or do some
spins flip infinitely often and others finitely often? Once this question is
determined, the evolution of the system from its initial state can be studied
with attention to the issue of how much information contained in the final
state depends on that contained in the initial state, and how much depends on
the detailed history of the system. This problem has been addressed both
analytically and numerically in several papers, and their main methods,
results, and conclusions will be reviewed. The discussion closes with some open
problems that remain to be addressed.",1706.01914v1
2017-06-26,Optically and electrically controllable adatom spin-orbital dynamics in transition metal dichalcogenides,"We analyze the interplay of spin-valley coupling, orbital physics and
magnetic anisotropy taking place at single magnetic atoms adsorbed on
semiconducting transition-metal dichalcogenides, MX$_2$ (M = Mo, W; X = S, Se).
Orbital selection rules turn out to govern the kinetic exchange coupling
between the adatom and charge carriers in the MX$_2$ and lead to highly
orbitally dependent spin-flip scattering rates, as we illustrate for the
example of transition metal adatoms with $d^9$ configuration. Our ab initio
calculations suggest that $d^9$ configurations are realizable by single Co, Rh,
or Ir adatoms on MoS$_2$, which additionally exhibit a sizable magnetic
anisotropy. We find that the interaction of the adatom with carriers in the
MX$_2$ allows to tune its behavior from a quantum regime with full Kondo
screening to a regime of ""Ising spintronics"" where its spin-orbital moment acts
as classical bit, which can be erased and written electronically and optically.",1706.08365v1
2017-06-27,"Intrinsic 2D ferromagnetism, quantum anomalous Hall conductivity, and fully-spin-polarized edge states of FeBr3 monolayer","It is of great interest to explore intrinsic two-dimensional ferromagnetism
and seek better two-dimensional quantum anomalous Hall insulator materials.
Here, we show that the FeBr$_3$ monolayer is an intrinsic two-dimensional
ferromagnetic material whose Curie temperature is 140 K thanks to its strong
spin exchange interaction and giant uniaxial magnetic anisotropy. Our phonon
spectra and mechanical analysis indicate that the FeBr$_3$ monolayer is
dynamically and mechanically stable. Our electronic structure calculation shows
that there is one Dirac cone at K point in the Brillouin zone and the
spin-orbit coupling opens a semiconductor gap of 33.5 meV. Further
tight-binding analysis reveals that the Chern number is equivalent to 1 and
there is a quantum anomalous Hall conductivity $\sigma _{xy} = e^2/h$, and the
chiral edge states are fully spin-polarized when an edge is created.
Furthermore, it is shown that the main results are not affected by electron
correlation effects and biaxial strain. Therefore, this FeBr$_3$ monolayer as
2D material would be useful for spintronic applications.",1706.08943v2
2017-10-05,Magnetic Skyrmionic Polarons,"We study a two-dimensional electron gas exchanged-coupled to a system of
classical magnetic ions. For large Rashba spin-orbit coupling a single electron
can become self-trapped in a skyrmion spin texture self-induced in the magnetic
ions system. This new quasiparticle carries electrical and topological charge
as well as a large spin, and we named it as magnetic skyrmionic polaron. We
study the range of parameters; temperature, exchange coupling, Rashba coupling
and magnetic field, for which the magnetic skyrmionic polaron is the
fundamental state in the system. The dynamics of this quasiparticle is studied
using the collective coordinate approximation, and we obtain that in presence
of an electric field the new quasiparticle shows, because the chirality of the
skyrmion, a Hall effect. Finally we argue that the magnetic skyrmionic polarons
can be found in large Rashba spin-orbit coupling semiconductors as GeMnTe.",1710.02182v1
2017-10-06,Tunneling statistics for analysis of spin-readout fidelity,"We investigate spin and charge dynamics of a quantum dot of phosphorus atoms
coupled to a radio-frequency single-electron transistor (rf-SET) using full
counting statistics. We show how the magnetic field plays a role in determining
the bunching or anti-bunching tunnelling statistics of the donor dot and SET
system. Using the counting statistics we show how to determine the lowest
magnetic field where spin-readout is possible. We then show how such a
measurement can be used to investigate and optimise single electron
spin-readout fidelity.",1710.02243v1
2017-10-21,Finite temperature dynamical correlations for the dimerized spin-1/2 chain,"We use the density matrix renormalization group method (DMRG) to compute the
frequency and momentum resolved spin-spin correlation functions of a dimerized
spin-1/2 chain under a magnetic field at finite temperature. The spectral
features strongly depend on the regime of the magnetic field. For increasing
magnetic fields, the transitions from a gapped spin liquid phase to a
Tomonaga-Luttinger liquid, and then to a totally polarized phase, can be
identified in the spectra. Compared to the zero temperature case, the finite
temperature excitations give rise to additional spectral features that we
compute numerically and identify analytically as transitions from thermally
excited states. We compute quantitatively the broadening of the dispersion of a
single spin-flip excitation due to the temperature and find a strong asymmetric
broadening. We discuss the consequences of these findings for neutron
experiments on dimerized one dimensional quantum chains.",1710.07811v2
2017-10-25,Co- and contra-directional vertical coupling between ferromagnetic layers with grating for short-wavelength spin wave generation,"The possibility to generate short spin waves is of great interest in the
field of magnonics nowadays. We present an effective and technically affordable
way of conversion of long spin waves, which may be generated by conventional
microwave antenna, to the short, sub-micrometer waves. It is achieved by
grating-assisted resonant dynamic dipolar interaction between two ferromagnetic
layers separated by some distance. We analyze criteria for the optimal
conversion giving a semi-analytical approach for the coupling coefficient. We
show by the numerical calculations the efficient energy transfer between layers
which may be either of co-directional or contra-directional type. Such a system
may operate either as a short spin wave generator or a frequency filter, moving
foreward possible application of magnonics.",1710.09138v1
2017-10-25,Collective spin waves in arrays of Permalloy nanowires with single-side periodically modulated width,"We have experimentally and numerically investigated the dispersion of
collective spin waves prop-agating through arrays of longitudinally magnetized
nanowires with periodically modulated width. Two nanowire arrays with
single-side modulation and different periodicity of modulation were studied and
compared to the nanowires with homogeneous width. The spin-wave dispersion,
meas-ured up to the third Brillouin zone of the reciprocal space, revealed the
presence of two dispersive modes for the width-modulated NWs, whose amplitude
of magnonic band depends on the modula-tion periodicity, and a set of
nondispersive modes at higher frequency. These findings are different from
those observed in homogeneous width NWs where only the lowest mode exhibits
sizeable dis-persion. The measured spin-wave dispersion has been satisfactorily
reproduced by means of dynam-ical matrix method. Results presented in this work
are important in view of the possible realization of frequency tunable magnonic
device.",1710.09163v1
2017-10-30,Protecting quantum spin coherence of nanodiamonds in living cells,"Due to its superior coherent and optical properties at room temperature, the
nitrogen-vacancy (N-V ) center in diamond has become a promising quantum probe
for nanoscale quantum sensing. However, the application of N-V containing
nanodiamonds to quantum sensing suffers from their relatively poor spin
coherence times. Here we demonstrate energy efficient protection of N-V spin
coherence in nanodiamonds using concatenated continuous dynamical decoupling,
which exhibits excellent performance with less stringent microwave power
requirement. When applied to nanodiamonds in living cells we are able to extend
the spin coherence time by an order of magnitude to the $T_1$-limit of up to
$30\mu$s. Further analysis demonstrates concomitant improvements of sensing
performance which shows that our results provide an important step towards in
vivo quantum sensing using N-V centers in nanodiamond.",1710.10744v3
2017-10-30,How do External Companions Affect Spin-Orbit Misalignment of Hot Jupiters?,"Consider a planet with its orbital angular momentum axis aligned with the
spin axis of its host star. To what extent does an inclined distant companion
(giant planet or binary star) affect this alignment? We provide an analytic,
quantitative answer and apply it to hot Jupiter systems, for which
misalignments between the orbital axis and the stellar spin axis have been
detected. We also show how similar consideration can be applied to multi-planet
systems with distant companions (such as Kepler-56). The result of this paper
provides a simple method to assess the dynamical role played by external
companions on spin-orbit misalignments in exoplanetary systems.",1710.11140v1
2017-12-05,Surface plasmon-mediated nanoscale localization of laser-driven sub-THz spin dynamics in magnetic dielectrics,"Ultrafast all-optical control of spins with femtosecond laser pulses is one
of the hot topics at the crossroads of photonics and magnetism with a direct
impact on future magnetic recording. Unveiling light-assisted recording
mechanisms for an increase of the bit density beyond the diffraction limit
without excessive heating of the recording medium is an open challenge. Here we
show that surface plasmon-polaritons in hybrid metal-dielectric structures can
provide spatial confinement of the inverse Faraday effect, mediating the
excitation of localized coherent spin precession with 0.41 THz frequency. We
demonstrate a two orders of magnitude enhancement of the excitation efficiency
at the surface plasmon resonance within the 100 nm layer in dielectric garnet.
Our findings broaden the horizons of ultrafast spin-plasmonics and open
pathways towards non-thermal opto-magnetic recording at the nano-scale.",1712.01617v1
2017-10-31,Macro-spin Modeling and Experimental Study of Spin-orbit Torque Biased Magnetic Sensors,"We reported a systematic study of spin-orbit torque biased magnetic sensors
based on NiFe/Pt bilayers through both macro-spin modeling and experiments. The
simulation results show that it is possible to achieve a linear sensor with a
dynamic range of 0.1 - 10 Oe, power consumption of 1uW - 1 mW, and sensitivity
of 0.1-0.5 Ohm/Oe. These characteristics can be controlled by varying the
sensor dimension and current density in the Pt layer. The latter is in the
range of 1 x 10^5 - 10^7 A/cm^2. Experimental results of fabricated sensors
with selected sizes agree well with the simulation results. For a Wheatstone
bridge sensor comprising of four sensing elements, a sensitivity up to 0.548
Ohm/Oe, linearity error below 6%, and detectivity of about 2.8 nT/Sqrt(Hz) were
obtained. The simple structure and ultrathin thickness greatly facilitate the
integration of these sensors for on-chip applications. As a proof-of-concept
experiment, we demonstrate its application in detection of current flowing in
an on-chip Cu wire.",1712.02384v1
2017-12-21,Eigenstate versus Zeeman-based approaches to the solid-effect,"The solid effect is one of the simplest and most effective mechanisms for
Dynamic Nuclear Polarization. It involves the exchange of polarization between
one electron and one nuclear spin coupled via the hyperfine interaction. Even
for such a small spin system, the theoretical understanding is complicated by
the contact with the lattice and the microwave irradiation. Both being weak,
they can be treated within perturbation theory. In this work, we analyze the
two most popular perturbation schemes: the Zeeman and the eigenstate-based
approaches which differ in the way the hyperfine interaction is treated. For
both schemes, we derive from first principles an effective Liouville equation
which describes the density matrix of the spin system; we then study
numerically the behavior of the nuclear polarization for several values of the
hyperfine coupling. In general, we obtain that the Zeeman-based approach
underestimates the value of the nuclear polarization. By performing a
projection onto the diagonal part of the spin-system density matrix, we are
able to understand the origin of the discrepancy, which is due to the presence
of parasite leakage transitions appearing whenever the Zeeman basis is
employed.",1712.07895v2
2017-12-27,Understanding the properties of $Ξ(1690)$ and $Ξ(2120)$,"In this manuscript we discuss the results of our recent study on $\Xi$
resonances. We have studied meson-baryon interaction with strangeness $-2$ by
solving scattering equations in a coupled channel approach and found that the
dynamics gives rise to the development of two poles in the complex plane close
to the real axis. The corresponding narrow states have isospin half and spin
half in one case and spin 3/2 in the other case. We find that the properties of
the isospin and spin 1/2 state are strikingly similar to $\Xi(1690)$, while the
state with spin 3/2 can be related to $\Xi(2120)$. We find that our results on
$\Xi(1690)$ are in good agreement with the data available from the BELLE and
BABAR Collaborations. Our formalism consists of treating pseudoscalar-baryon
and vector-baryon channels on an equal footing. Since the thresholds of such
channels are distributed over a relatively larger energy range, we obtain all
interaction kernels needed to solve the Bethe-Salpeter equation without
resorting to any nonrelativistic approximation even though the amplitudes are
calculated at low energies.",1712.09465v1
2017-12-29,Symmetry Preservation and Critical Fluctuations in a Pseudospin Crossover Perovskite LaCoO$_3$,"Spin-state crossover beyond a conventional ligand-field theory has been a
fundamental issue in condensed matter physics. Here, we report microscopic
observations of spin states and low-energy dynamics through orbital-resolved
NMR spectroscopy in the prototype compound LaCoO$_3$. The $^{59}$Co NMR
spectrum shows the preserved crystal symmetry across the crossover,
inconsistent with $d$ orbital ordering due to the Jahn-Teller distortion. The
orbital degeneracy results in a pseudospin ($\tilde{J} = 1$) excited state with
an orbital moment observed as $^{59}$Co hyperfine coupling tensors. We found
that the population of the excited state evolves above the heart crossover
temperature. The crossover involves critical spin-state fluctuations emerging
under the magnetic field. These results suggest that the spin-state crossover
can be mapped into a statistical problem, analogous to the supercritical liquid
in liquid-gas transition.",1712.10137v1
2018-01-10,Quantum state transfer in spin chains via shortcuts to adiabaticity,"Based on shortcuts to adiabaticity and quantum Zeno dynamics, we present a
protocol to implement quantum state transfer (QST) in a quantum spin-1/2 chain.
In the protocol, the complex Hamiltonian of an $N$-site system is simplified,
and a simple effective Hamiltonian is present. It is shown that only the
control of the coupling strengths between the boundary spins and the bulk spins
are required for QST. Numerical simulations demonstrate that the protocol
possesses high efficiency and is robust against the decay and the fluctuations
of the control fields. The protocol might provide an alternative choice for
transferring quantum states via spin chain systems.",1801.03330v1
2018-01-22,Enhanced pairing susceptibility in a photo-doped two-orbital Hubbard model,"Local spin fluctuations provide the glue for orbital-singlet spin-triplet
pairing in the doped Mott insulating regime of multi-orbital Hubbard models. At
large Hubbard repulsion $U$, the pairing susceptibility is nevertheless very
low, because the pairing interaction cannot overcome the suppression of charge
fluctuations. Using nonequilibrium dynamical mean field simulations of the
two-orbital Hubbard model, we show that out of equilibrium the pairing
susceptibility in this large-$U$ regime can be strongly enhanced by creating a
photo-induced population of the relevant charge states, and that this
susceptibility correlates with the local spin susceptibility. Since a strong
enhancement of the pairing requires a low kinetic energy of the charge
carriers, the phenomenon is supported by the ultra-fast cooling of the
photo-doped carriers through the creation of local spin excitations.",1801.07053v1
2018-01-30,Bi-scalar integrable CFT at any dimension,"We propose a $D$-dimensional generalization of $4D$ bi-scalar conformal
quantum field theory recently introduced by G\""{u}rdogan and one of the authors
as a strong-twist double scaling limit of $\gamma$-deformed $\mathcal{N}=4$ SYM
theory. Similarly to the $4D$ case, this D-dimensional CFT is also dominated by
""fishnet"" Feynman graphs and is integrable in the planar limit. The dynamics of
these graphs is described by the integrable conformal $SO(D+1,1)$ spin chain.
In $2D$ it is the analogue of L. Lipatov's $SL(2,\mathbb{C})$ spin chain for
the Regge limit of $QCD$, but with the spins $s=1/4$ instead of $s=0$.
Generalizing recent $4D$ results of Grabner, Gromov, Korchemsky and one of the
authors to any $D$ we compute exactly, at any coupling, a four point
correlation function, dominated by the simplest fishnet graphs of cylindric
topology, and extract from it exact dimensions of R-charge 2 operators with any
spin and some of their OPE structure constants.",1801.09844v3
2018-01-31,Ultra-High Resolution Neutron Spectroscopy of Low-Energy Spin Dynamics in UGe$_2$,"Studying the prototypical ferromagnetic superconductor UGe$_2$ we demonstrate
the potential of the Modulated IntEnsity by Zero Effort (MIEZE) technique---a
novel neutron spectroscopy method with ultra-high energy resolution of at least
1~$\mu$eV---for the study of quantum matter. We reveal purely longitudinal spin
fluctuations in UGe$_2$ with a dual nature arising from $5f$ electrons that are
hybridized with the conduction electrons. Local spin fluctuations are perfectly
described by the Ising universality class in three dimensions, whereas
itinerant spin fluctuations occur over length scales comparable to the
superconducting coherence length, showing that MIEZE is able to
spectroscopically disentangle the complex low-energy behavior characteristic of
quantum materials.",1801.10278v2
2018-09-07,Gravitational self-force corrections to gyroscope precession along circular orbits in the Kerr spacetime,"We generalize to Kerr spacetime previous gravitational self-force results on
gyroscope precession along circular orbits in the Schwarzschild spacetime. In
particular we present high order post- Newtonian expansions for the gauge
invariant precession function along circular geodesics valid for arbitrary Kerr
spin parameter and show agreement between these results and those derived from
the full post-Newtonian conservative dynamics. Finally we present strong field
numerical data for a range of the Kerr spin parameter, showing agreement with
the GSF-PN results, and the expected lightring divergent behaviour. These
results provide useful testing benchmarks for self- force calculations in Kerr
spacetime, and provide an avenue for translating self-force data into the
spin-spin coupling in effective-one-body models.",1809.02516v1
2018-09-26,Echo trains in pulsed electron spin resonance of a strongly coupled spin ensemble,"We report on a novel dynamical phenomenon in electron spin resonance
experiments of phosphorus donors. When strongly coupling the paramagnetic
ensemble to a superconducting lumped element resonator, the coherent exchange
between these two subsystems leads to a train of periodic, self-stimulated
echos after a conventional Hahn echo pulse sequence. The presence of these
multi-echo signatures is explained using a simple model based on spins rotating
on the Bloch sphere, backed up by numerical calculations using the
inhomogeneous Tavis-Cummings Hamiltonian.",1809.10116v3
2019-07-01,DC spinmotive force from microwave-active resonant dynamics of skyrmion crystal under a tilted magnetic field,"We theoretically show that a temporally oscillating spin-driven electromotive
force or voltage with a large DC component can be generated by exciting
microwave-active spin-wave modes of a skyrmion crystal confined in a quasi
two-dimensional magnet under a tilted magnetic field. The DC component and the
AC amplitude of the oscillating electric voltage is significantly enhanced when
the microwave frequency is tuned to an eigenfrequency of the peculiar spin-wave
modes of the skyrmion crystal called ``rotation modes"" and ``breathing mode"",
whereas the sign of the DC component depends on the microwave polarization and
on the spin-wave mode. These results provide an efficient means to convert
microwaves to a DC electric voltage by using skyrmion-hosting magnets and to
switch the sign of the voltage via tuning the microwave frequency, which are
important capabilities for spintronic devices.",1907.00621v1
2019-07-02,Bias-free reconfigurable magnonic phase shifter based on a spin-current controlled ferromagnetic resonator,"Controllable phase modulation plays a pivotal role in the researches of
magnonic logic gates. Here we propose a reconfigurable spin-current controlled
magnonic phase shifter based on a ferromagnetic resonator. The proposed phase
shifter requires no magnetic bias field during operation. The device is
directly configured over the waveguide while keeping the original structure of
the waveguide unaffected. Numerical micromagnetic simulations show that the
phase shifter could yield either a {\pi}-phase or no shift depending on the
magnetization status of the resonator, which can be controlled by a current
pulse. Moreover, the phase-shifting operation could be affected by spin
current. At different input current density, the device could be either used as
a dynamic controlled phase shifter or a spin-wave valve. Finally, a XNOR
magnonic logic gate is demonstrated using the proposed phase shifter. Our work
can be a beneficial step to enhance the functionality and compatibility of the
magnonic logic circuits.",1907.01303v1
2019-07-05,Topological Nematic Spin Liquid on the Square-Kagome Lattice,"The ground state of the spin$-1/2$ kagome antiferromagnet remains uncertain
despite decades of active research. Here we step aside from this debated
question to address the ground-state nature of a related, and potentially just
as rich, system made of corner-sharing triangles: the square-kagome lattice
(SKL). Our work is motivated by the recent synthesis of a distorted SKL
compound mentioned in [Morita & Tohyama, J. Phys. Soc. Japan 87, 043704
(2018)]. We have studied its spin$-1/2$ $J_{1}$-$J_{2}$ phase diagram with an
unrestricted Schwinger boson mean-field theory (SBMFT). We show that, in
addition of agreeing with previous studies, three original phases appear: two
incommensurate orders and a topological quantum spin liquid with weak
nematicity. The topological order is characterized by fluxes on specific
gauge-invariant quantities and the phase is stable under anisotropic
perturbations relevant for experiments. Finally, we provide dynamical structure
factors of the reported phases that could be observed in inelastic neutron
scattering.",1907.02883v2
2019-07-24,Relaxation Time for Strange Quark Spin in Rotating Quark-Gluon Plasma,"Experiments at the Relativistic Heavy Ion Collider (RHIC) have measured the
net polarization of $\Lambda$ and $\bar{\Lambda}$ hyperons and attributed it to
a coupling between their spin and the vorticity of the fluid created in heavy
ion collisions. Equipartition of energy is generally assumed, but the dynamical
mechanism which polarizes them has yet to be determined. We consider two such
mechanisms: vorticity fluctuations and helicity flip in scatterings between
strange quarks and light quarks and gluons. With reasonable parameters both
mechanisms lead to equilibration times orders of magnitude too large to be
relevant to heavy ion collisions. Our conclusion is that strange quark spin or
helicity is unchanged from the time they are created to the time they
hadronize. A corollary is that vorticity fluctuations do not affect the hyperon
spin either.",1907.10750v1
2019-09-01,Magnetic field-dependent low-energy magnon dynamics in $α$-RuCl3,"Revealing the spin excitations of complex quantum magnets is key to
developing a minimal model that explains the underlying magnetic correlations
in the ground state. We investigate the low-energy magnons in $\alpha$-RuCl$_3$
by combining time-domain terahertz spectroscopy under an external magnetic
field and model Hamiltonian calculations. We observe two absorption peaks
around 2.0 and 2.4 meV, which we attribute to zone-center spin waves. Using
linear spin-wave theory with only nearest-neighbor terms of the exchange
couplings, we calculate the antiferromagnetic resonance frequencies and reveal
their dependence on an external field applied parallel to the nearest-neighbor
Ru-Ru bonds. We find that the magnon behavior in an applied magnetic field can
be understood only by including an off-diagonal $\Gamma$ exchange term to the
minimal Heisenberg-Kitaev model. Such an anisotropic exchange interaction that
manifests itself as a result of strong spin-orbit coupling can naturally
account for the observed mixing of the modes at higher fields strengths.",1909.00462v1
2019-09-05,Strongly correlated materials from a numerical renormalization group perspective: How the Fermi-liquid state of Sr$_2$RuO$_4$ emerges,"The crossover from fluctuating atomic constituents to a collective state as
one lowers temperature or energy is at the heart of the dynamical mean-field
theory description of the solid state. We demonstrate that the numerical
renormalization group is a viable tool to monitor this crossover in a
real-materials setting. The renormalization group flow from high to arbitrarily
small energy scales clearly reveals the emergence of the Fermi-liquid state of
Sr$_2$RuO$_4$. We find a two-stage screening process, where orbital
fluctuations are screened at much higher energies than spin fluctuations, and
Fermi-liquid behavior, concomitant with spin coherence, below a temperature of
25 K. By computing real-frequency correlation functions, we directly observe
this spin--orbital scale separation and show that the van Hove singularity
drives strong orbital differentiation. We extract quasiparticle interaction
parameters from the low-energy spectrum and find an effective attraction in the
spin-triplet sector.",1909.02389v2
2019-10-22,Controlled nonlinear magnetic damping in spin-Hall nano-devices,"Large-amplitude magnetization dynamics is substantially more complex compared
to the low-amplitude linear regime, due to the inevitable emergence of
nonlinearities. One of the fundamental nonlinear phenomena is the nonlinear
damping enhancement, which imposes strict limitations on the operation and
efficiency of magnetic nanodevices. In particular, nonlinear damping prevents
excitation of coherent magnetization auto-oscillations driven by the injection
of spin current into spatially extended magnetic regions. Here, we propose and
experimentally demonstrate that nonlinear damping can be controlled by the
ellipticity of magnetization precession. By balancing different contributions
to anisotropy, we minimize the ellipticity and achieve coherent magnetization
oscillations driven by spatially extended spin current injection into a
microscopic magnetic disk. Our results provide a novel route for the
implementation of efficient active spintronic and magnonic devices driven by
spin current.",1910.09801v1
2019-10-30,"Emergence of Griffiths phase, re-entrant cluster glass,metamagnetic transition and field induced unusual spin dynamics in Tb2CoMnO6","The structural and magnetic properties of double perovskiteTb2CoMnO6 have
been investigated. Electronic structure analysis by XPS study reveals the
presence of mixed oxidation state (Mn4+/Mn3+ and Co2+/Co3+) of B-site ions. The
dc and ac magnetization measurements reveal different interesting phases such
as Griffith phase, re-entrant spin glass, metamagnetic steps, Hopkinson like
peak and also unusual slow relaxation. The M-H curve indicates the presence of
competing AFM/FM interactions. The disorder in Tb2CoMnO6 leads to spin
frustration at low temperature giving rise to the re-entrant spin glass.
Moreover, the field-dependent ac susceptibility studies unraveled the presence
of Hopkinson like peak associated with the domain wall motion and the large
anisotropy field. The further study yielded that the relaxation associated with
this peak is unusually slow.",1910.13734v1
2019-10-30,Understanding Thermal Annealing of Artificial Spin Ice,"We have performed a detailed study of thermal annealing of the moment
configuration in artificial spin ice. Permalloy (Ni$_{80}$Fe$_{20}$) artificial
spin ice samples were examined in the prototypical square ice geometry,
studying annealing as a function of island thickness, island shape, and
annealing temperature and duration. We also measured the Curie temperature as a
function of film thickness, finding that thickness has a strong effect on the
Curie temperature in regimes of relevance to many studies of the dynamics of
artificial spin ice systems. Increasing the interaction energy between island
moments and reducing the energy barrier to flipping the island moments allows
the system to more closely approach the collective low energy state of the
moments upon annealing, suggesting new channels for understanding the
thermalization processes in these important model systems.",1910.14158v1
2020-01-10,Switching time of spin-torque-driven magnetization in biaxial ferromagnets,"We analytically model the magnetization switching time of a biaxial
ferromagnet driven by an antidamping-like spin torque. The macrospin
magnetization dynamics is mapped to an energy-flow equation, wherein a
rational-function approximation of the elliptic integrals for moderate spin
current and small damping results in a closed-form expression of the switching
time. Randomness in the initial angle of magnetization gives the distribution
function of the switching time. The analytic model conforms to the results
obtained from Monte Carlo simulation for a broad range of material parameters.
Our results can ameliorate design and benchmarking of in-plane spin torque
magnetic memory by obviating expensive numerical computation.",2001.03300v2
2020-01-20,Magnetisms of spinor alkali and alkaline-earth atoms in optical lattices,"We theoretically investigate zero-temperature magnetic ordering of mixtures
of spin-1 (alkali atoms) and spin-0 (alkaline-earth atoms) bosons in a
three-dimensional optical lattice. With the single-mode approximation for the
spin-1 bosons, we obtain an effective Bose-Hubbard model for describing the
heteronuclear mixtures in optical lattices. By controlling the interspecies
interactions between alkali and alkaline-earth atoms, we map out complete phase
diagrams of the system with both positive and negative spin-dependent
interactions for spin-1 atoms, based on bosonic dynamical mean-field theory. We
find that the spin-1 components feature ferromagnetic and nematic insulating
phases, in addition to the superfluid, depending on spin-dependent
interactions. Take the spin-1 alkali bosons as spin $\uparrow$, and spin-0
alkaline-earth bosons as spin $\downarrow$, we observe that the system favors
ferromagnetic insulator at filling $n=1$, and unorder insulator at $n=2$.
Interestingly, we observe a two-step Mott-insulating-superfluid phase
transition, as a result of mass imbalance between alkali and alkaline-earth
atoms.",2001.06991v2
2020-01-20,Spin current generation and control in carbon nanotubes by combining rotation and magnetic field,"We study the quantum dynamics of ballistic electrons in rotating carbon
nanotubes in the presence of a uniform magnetic field. When the field is
parallel to the nanotube axis, the rotation-induced electric field brings about
the spin-orbit interaction which, together with the kinetic, inertial, and
Zeeman terms, compose the Schr\""odinger-Pauli Hamiltonian of the system. Full
diagonalization of this Hamiltonian yields the eigenstates and eigenenergies
leading to the calculation of the charge and spin currents. Our main result is
the demonstration that, by suitably combining the applied magnetic field
intensity and rotation speed, one can tune one of the currents to zero while
keeping the other one finite, giving rise to a spin current generator.",2001.07024v1
2020-01-30,Neutron inelastic scattering study of rare-earth orthoferrite HoFeO$_3$,"By the single crystal inelastic neutron scattering the orthoferrite HoFeO3
was studied. We show that the spin dynamics of the Fe subsystem does not change
through the spin-reorientation transitions. The observed spectrum of magnetic
excitations was analyzed in the frames of linear spin-wave theory. Within this
approach the antiferromagnetic exchange interactions of nearest neighbors and
next nearest neighbors were obtained for Fe subsystem. Parameters of
Dzyaloshinskii-Moriya interactions at Fe subsystem were refined. The
temperature dependence of the gap in Fe spin-wave spectrum indicates the
temperature evolution of the anisotropy parameters. The estimations for the
values of Fe-Ho and Ho-Ho exchange interaction were made as well.",2001.11313v3
2020-02-10,Resistivity minimum in diluted metallic magnets,"Resistivity minima are commonly seen in itinerant magnets and they are often
attributed to the Kondo effect. However, recent experiments are revealing an
increasing number of materials showing resistivity minima in the absence of
indications of Kondo singlet formation. In a previous work [Z. Wang, K. Barros,
G.-W. Chern, D. L. Maslov, and C. D. Batista, Phys. Rev. Lett. 117, 206601
(2016)], we demonstrated that the Ruderman-Kittel-Kasuya-Yosida (RKKY)
interaction can produce a classical spin liquid state at finite temperature,
whose resistivity increases with decreasing temperature. The classical spin
liquid exists over a relatively large temperature window because of the
frustrated nature of the RKKY interaction produced by a 2D electron gas. In
this work, we investigate the robustness of the RKKY-induced resistivity upturn
against site dilution, which provides an alternative, and more robust, way of
stabilizing the classical spin liquid state down to T=0. By using series
expansions and stochastic Landau-Lifshitz dynamics simulation, we show that
site dilution competes with thermal fluctuations and further stabilizes the
resistivity upturn, which is accompanied by a negative magnetoresistivity due
to suppression of the electron-spin scattering.",2002.03858v2
2020-02-14,Influence of Lorentz Invariation Violation on Arbitrarily Spin Fermions Tunneling Radiation in the Vaidya-Bonner Spacetime,"In the spacetime of non-stationary spherical symmetry Vaidya-Bonner black
hole, an accurate modification of Hawking tunneling radiation for fermions with
arbitrarily spin is researched. Considering a light dispersion relationship
derived from string theory, quantum gravitational theory and Rarita-Schwinger
Equation in the non-stationary spherical symmetry spacetime, we derive an
accurately modified dynamic equation for fermions with arbitrarily spin. By
solving the equation, modified tunneling rate of fermions with arbitrarily
spin, Hawking temperature and entropy at the event horizon of Vaidya-Bonner
black hole are presented. We find the Hawking temperature will increase, but
the the entropy will decrease comparing with the case without Lorentz
Invariation Violation modification.",2002.05946v1
2020-02-14,All-electrical spectroscopy of topological phases in semiconductor-superconductor heterostructures,"Semiconductors in the proximity of superconductors have been proposed to
support phases hosting Majorana bound states. When the systems undergo a
topological phase transition towards the Majorana phase, the spectral gap
closes, then reopens, and the quasiparticle band spin polarization is inverted.
We focus on two paradigmatic semiconductor-superconductor heterostructures and
propose an all-electrical spectroscopic probe sensitive to the spin inversion
at the topological transition. Our proposal relies on the indirect coupling of
a time-dependent electric field to the electronic spin due to the strong Rashba
spin-orbit coupling in the semiconductor. We analyze within linear response
theory the dynamical correlation functions and demonstrate that some components
of the susceptibility can be used to detect the nontrivial topological phases.",2002.06092v2
2020-04-02,Spin-Dependent Charge-Carrier Recombination Processes in Tris(8-Hydroxyquinolinato) Aluminum,"We have studied the nature and dynamics of spin-dependent charge carrier
recombination in Tris(8-hydroxyquinolinato) aluminum (Alq$_3$) films in light
emitting diodes at room temperature using continuous wave and pulsed
electrically detected magnetic resonance (EDMR) spectroscopy. We found that the
EDMR signal is dominated by an electron-hole recombination process, and
another, weaker EDMR signal whose fundamental nature was investigated. From the
pulsed EDMR measurements we obtained a carrier spin relaxation time, $T_2 =
45\pm 25$ ns which is much shorter than $T_2$ in conjugated polymers, but
relatively long for a molecule containing elements with high atomic number.
Using multi-frequency continuous wave EDMR spectroscopy, we obtained the local
hyperfine field distributions for electrons and holes, as well as their
respective spin-orbit coupling induced g-factor and g-strain values.",2004.00765v1
2020-04-02,Stable solitons in a nearly PT-symmetric ferromagnet with spin-transfer torque,"We consider the Landau-Lifshitz equation for the spin torque oscillator - a
uniaxial ferromagnet in an external magnetic field with polarised spin current
driven through it. In the absence of the Gilbert damping, the equation turns
out to be PT-symmetric. We interpret the PT-symmetry as a balance between gain
and loss - and identify the gaining and losing modes. In the vicinity of the
bifurcation point of a uniform static state of magnetisation, the PT-symmetric
Landau-Lifshitz equation with a small dissipative perturbation reduces to a
nonlinear Schr\""odinger equation with a quadratic nonlinearity. The analysis of
the Schr\""odinger dynamics demonstrates that the spin torque oscillator
supports stable magnetic solitons. The PT near-symmetry is crucial for the
soliton stability: the addition of a finite dissipative term to the
Landau-Lifshitz equation destabilises all solitons that we have found.",2004.01245v2
2020-04-20,The three body first post-Newtonian effects on the secular dynamics of a compact binary near a spinning supermassive black hole,"The binary black holes (BBHs) formed near the supermassive black holes
(SMBHs) in the galactic nuclei would undergo eccentricity excitation due to the
gravitational perturbations from the SMBH and therefore merger more
efficiently. In this paper, we study the coupling of the three body 1st
post-Newtonian (PN) effects with the spin effects from the SMBH in the
hierarchical triple system. We extend previous work by including the coupling
between the de Sitter precession and the Lense-Thirring precession from the
SMBH spin. This coupling includes both the precessions of the inner orbit
angular momentum and the Runge-Lenz vector around the outer orbit angular
momentum in a general reference frame. We find the change of the (maximal)
eccentricity in the neighboring Kozai-Lidov cycles due to spin effects is
detectable by LISA in the future. Our general argument on the coupling of the
three body 1PN effects in three body systems could be extended to any other
situation as long as the outer orbital plane evolves.",2004.09390v2
2020-12-07,Electric current noise in mesoscopic organic semiconductors,"We demonstrate that nuclear spin fluctuations lead to the electric current
noise in the mesoscopic samples of organic semiconductors showing the
pronounced magnetoresistance in weak fields. For the bipolaron and
electron-hole mechanisms of organic magnetoresistance, the current noise
spectrum consists of the high frequency peak related to the nuclear spin
precession in the Knight field of the charge carriers and the low frequency
peak related to the nuclear spin relaxation. The shape of the spectrum depends
on the external magnetic and radiofrequency fields, which allows one to prove
the role of nuclei in magnetoresistance experimentally.",2012.03870v1
2020-12-11,Slow Spin Relaxation in Single Endohedral Fullerene Molecules,"Well-protected magnetization, tunable quantum states and long coherence time
are desired for the use of magnetic molecules in spintronics and quantum
information technologies. In this work, endohedral fullerene molecules M@C28
with different transition metal cores were explored through systematic
first-principles calculations and spin dynamics analyses. Many of them have
stable magnetization, giant magnetic anisotropy energy and bias-tunable
structure. In particular, some of them may have coherence time up to several
milliseconds for their quantum spin states at high temperature (~10K) after
full consideration of spin-vibration couplings. These results suggest that
these M@C28 provide a rich pool for the development of single-molecule magnets,
magnetic molecular junctions, and molecular qubits.",2012.06141v2
2020-12-17,Intrinsic decoherence and recurrences in a large ferromagnetic $F = 1$ spinor Bose-Einstein condensate,"Decoherence with recurrences appear in the dynamics of the one-body density
matrix of an $F = 1$ spinor Bose-Einstein condensate, initially prepared in
coherent states, in the presence of an external uniform magnetic field and
within the single mode approximation. The phenomenon emerges as a many-body
effect of the interplay of the quadratic Zeeman effect, that breaks the
rotational symmetry, and the spin-spin interactions. By performing full quantum
diagonalizations very accurate time evolution of large condensates are
analyzed, leading to heuristic analytic expressions for the time dependence of
the one-body density matrix, in the weak and strong interacting regimes, for
initial coherent states. We are able to find accurate analytical expressions
for both the decoherence and the recurrence times, in terms of the number of
atoms and strength parameters, that show remarkable differences depending on
the strength of the spin-spin interactions. The features of the stationary
states in both regimes is also investigated. We discuss the nature of these
limits in the light of the thermodynamic limit.",2012.09891v1
2012-05-04,On Spin-Statistics and Bogoliubov Transformations in Flat Spacetime With Acceleration Conditions,"A single real scalar field of spin zero obeying the Klein-Gordon equation in
flat space-time under external conditions is considered in the context of the
spin-statistics connection. An imposed accelerated boundary on the field is
made to become, in the far future, (1) asymptotically inertial and (2)
asymptotically non-inertial (with an infinite acceleration). The constant
acceleration Unruh effect is also considered. The systems involving non-trivial
Bogoliubov transformations contain dynamics which point to commutation
relations. Particles described by in-modes obey the same statistics as
particles described by out-modes. It is found in the non-trivial systems that
the spin-statistics connection can be manifest from the acceleration. The
equation of motion for the boundary which forever emits thermal radiation is
revealed.",1205.0881v2
2012-05-21,Impact cratering on Mercury: consequences for the spin evolution,"Impact basins identified by Mariner 10 and Messenger flyby images provide us
a fossilized record of the impactor flux of asteroids on Mercury during the
last stages of the early Solar System. The distribution of these basins is not
uniform across the surface, and is consistent with a primordial synchronous
rotation (Wieczorek et al. 2012). By analyzing the size of the impacts, we show
that the distribution for asteroid diameters D < 110 km is compatible with an
index power law of 1.2, a value that matches the predicted primordial
distribution of the main-belt. We then derive a simple collisional model
coherent with the observations, and when combining it with the secular
evolution of the spin of Mercury, we are able to reproduce the present 3/2
spin-orbit resonance (about 50% of chances), as well as a primordial
synchronous rotation. This result is robust with respect to variations in the
dissipation and collisional models, or in the initial spin state of the planet.",1205.4615v1
2017-05-09,Low spin wave damping in the insulating chiral magnet Cu$_{2}$OSeO$_{3}$,"Chiral magnets with topologically nontrivial spin order such as Skyrmions
have generated enormous interest in both fundamental and applied sciences. We
report broadband microwave spectroscopy performed on the insulating chiral
ferrimagnet Cu$_{2}$OSeO$_{3}$. For the damping of magnetization dynamics we
find a remarkably small Gilbert damping parameter of about $1\times10^{-4}$ at
5 K. This value is only a factor of 4 larger than the one reported for the best
insulating ferrimagnet yttrium iron garnet. We detect a series of sharp
resonances and attribute them to confined spin waves in the mm-sized samples.
Considering the small damping, insulating chiral magnets turn out to be
promising candidates when exploring non-collinear spin structures for high
frequency applications.",1705.03416v1
2017-05-10,Boltzmann sampling for an XY model using a non-degenerate optical parametric oscillator network,"We present an experimental scheme of implementing multiple spins in a
classical XY model using a non-degenerate optical parametric oscillator (NOPO)
network. We built an NOPO network to simulate a one-dimensional XY Hamiltonian
with 5000 spins and externally controllable effective temperatures. The XY spin
variables in our scheme are mapped onto the phases of multiple NOPO pulses in a
single ring cavity and interactions between XY spins are implemented by mutual
injections between NOPOs. We show the steady-state distribution of optical
phases of such NOPO pulses is equivalent to the Boltzmann distribution of the
corresponding XY model. Estimated effective temperatures converged to the
setting values, and the estimated temperatures and the mean energy exhibited
good agreement with the numerical simulations of the Langevin dynamics of NOPO
phases.",1705.03611v1
2017-05-18,Classical Emergence of Intrinsic Spin-Orbit Interaction of Light at the Nanoscale,"Traditionally, in macroscopic geometrical optics intrinsic polarization and
spatial degrees of freedom of light can be treated independently. However, at
the subwavelength scale these properties appear to be coupled together, giving
rise to the spin-orbit interaction (SOI) of light. In this work we address
theoretically the classical emergence of the optical SOI at the nanoscale. By
means of a full-vector analysis involving spherical vector waves we show that
the spin-orbit factorizability condition, accounting the mutual influence
between the amplitude (spin) and phase (orbit), is fulfilled only in the
far-field limit. On the other side, in the near-field region, an additional
relative phase introduces an extra term that hinders the factorization and
reveals an intricate dynamical behavior according to the SOI regime. As a
result, we find a suitable theoretical framework able to capture analytically
the main features of intrinsic SOI of light. Besides allowing for a better
understanding into the mechanism leading to its classical emergence at the
nanoscale, our approach may be useful in order to design experimental setups
that enhance the response of SOI-based effects.",1705.06501v3
2017-05-26,"Low-energy spin dynamics of orthoferrites AFeO$_3$ (A = Y, La, Bi)","YFeO$_3$ and LaFeO$_3$ are members of the rare-earth orthoferrites family
with \textit{Pbnm} space group. Using inelastic neutron scattering, the
low-energy spin excitations have been measured around magnetic Brillouin zone
center. Splitting of magnon branches and non-zero magnon gap is observed for
both compounds, which is similar to the behavior observed in multiferroic
BiFeO$_3$. Spin wave calculations which include both Dzyaloshinsky-Moriya
interactions and single-ion anisotropy in the spin-Hamiltonian comprehensively
accounts for all the experimentally observed features. Our results offer
insight into the unifying physics underlying the Fe$^{3+}$-based perovskites as
well as their distinguishing characteristics.",1705.09441v3
2017-09-18,Low-energy spin dynamics and critical hole concentrations in La$_{2-x}$Sr$_x$CuO$_4$ ($0.07\leq x \leq 0.2$) revealed by $^{139}$La and $^{63}$Cu nuclear magnetic resonance,"We report a comprehensive $^{139}$La and $^{63}$Cu nuclear magnetic resonance
study on La$_{2-x}$Sr$_x$CuO$_4$ ($0.07\leq x \leq 0.2$) single crystals. The
$^{139}$La spin-lattice relaxation rate $^{139}T_1^{-1}$ is drastically
influenced by Sr doping $x$ at low temperatures. A detailed field dependence of
$^{139}T_1^{-1}$ at $x=1/8$ suggests that charge ordering induces the critical
slowing down of spin fluctuations toward glassy spin order and competes with
superconductivity. On the other hand, the $^{63}$Cu relaxation rate
$^{63}T_1^{-1}$ is well described by a Curie-Weiss law at high temperatures,
yielding the Curie-Weiss temperature $\Theta$ as a function of doping. $\Theta$
changes sharply through a critical hole concentration $x_c\sim 0.09$. $x_c$
appears to correspond to the delocalization limit of doped holes, above which
the bulk nature of superconductivity is established.",1709.06148v1
2017-09-26,Frustrated spin order and stripe fluctuations in FeSe,"The charge and spin dynamics of the structurally simplest iron-based
superconductor, FeSe, may hold the key to understanding the physics of high
temperature superconductors in general. Unlike the iron pnictides, FeSe lacks
long range magnetic order in spite of a similar structural transition around
90\,K. Here, we report results of Raman scattering experiments as a function of
temperature and polarization and simulations based on exact diagonalization of
a frustrated spin model. Both experiment and theory find a persistent low
energy peak close to 500cm$^{-1}$ in $B_{1g}$ symmetry, which softens slightly
around 100\,K, that we assign to spin excitations. By comparing with results
from neutron scattering, this study provides evidence for nearly frustrated
stripe order in FeSe.",1709.08998v3
2018-03-03,Stable spin domains in a non-degenerate ultra-cold gas,"We study the stability of two-domain spin structures in an ultra-cold gas of
magnetically trapped $^{87}$Rb atoms above quantum degeneracy. Adding a small
effective magnetic field gradient stabilizes the domains via coherent
collective spin rotation effects, despite negligibly perturbing the potential
energy relative to the thermal energy. We demonstrate that domain stabilization
is accomplished through decoupling the dynamics of longitudinal magnetization,
which remains in time-independent domains, from transverse magnetization, which
undergoes a purely transverse spin wave trapped within the domain wall. We
explore the effect of temperature and density on the steady-state domains, and
compare our results to a hydrodynamic solution to a quantum Boltzmann equation.",1803.01096v1
2018-03-05,Formation of a spin texture in a quantum gas coupled to a cavity,"We observe cavity mediated spin-dependent interactions in an off-resonantly
driven multi-level atomic Bose-Einstein condensate that is strongly coupled to
an optical cavity. Applying a driving field with adjustable polarization, we
identify the roles of the scalar and the vectorial components of the atomic
polarizability tensor for single and multi-component condensates. Beyond a
critical strength of the vectorial coupling, we observe a spin texture in a
condensate of two internal states, providing perspectives for global dynamic
gauge fields and self-consistently spin-orbit coupled gases.",1803.01803v4
2018-03-12,Energy spectra in $p$-shell $Λ$ hypernuclei and $^{19}_Λ\textrm{F}$ and spin-dependent $ΛN$ interactions,"Energy spectra of $0s$-orbit $\Lambda$ states in $p$-shell $\Lambda$
hypernuclei ($^{A}_\Lambda Z$) and those in $^{19}_{\Lambda}\textrm{F}$ are
studied with the microscopic cluster model and antisymmetrized molecular
dynamics using the $G$-matrix effective $\Lambda N$ ($\Lambda NG$)
interactions. Spin-dependent terms of the ESC08a version of the $\Lambda NG$
interactions are tested and phenomenologically tuned to reproduce observed
energy spectra in $p$-shell $^{A}_\Lambda Z$. Spin-dependent contributions of
the $\Lambda N$ interactions to spin-doublet splitting and excitation energies
are discussed. Energy spectra for unobserved excited states in $p$-shell
$^{A}_\Lambda Z$ and $^{19}_{\Lambda}\textrm{F}$ are predicted with the
modified $\Lambda NG$ interactions.",1803.04089v1
2018-03-29,Giant resonant nonlinear damping in nanoscale ferromagnets,"Magnetic damping is a key metric for emerging technologies based on magnetic
nanoparticles, such as spin torque memory and high-resolution biomagnetic
imaging. Despite its importance, understanding of magnetic dissipation in
nanoscale ferromagnets remains elusive, and the damping is often treated as a
phenomenological constant. Here we report the discovery of a giant
frequency-dependent nonlinear damping that strongly alters the response of a
nanoscale ferromagnet to spin torque and microwave magnetic field. This novel
damping mechanism originates from three-magnon scattering that is strongly
enhanced by geometric confinement of magnons in the nanomagnet. We show that
the giant nonlinear damping can invert the effect of spin torque on a
nanomagnet leading to a surprising current-induced enhancement of damping by an
antidamping torque. Our work advances understanding of magnetic dynamics in
nanoscale ferromagnets and spin torque devices.",1803.10925v1
2018-06-07,Irreversible Work Reduction by Disorder in Many-Body Quantum Systems,"We study the effect of disorder on work exchange associated to quantum
Hamiltonian processes by considering an Ising spin chain in which the strength
of coupling between spins are randomly drawn from either Normal or Gamma
distributions. The chain is subjected to a quench of the external transverse
field which induces this exchange of work. In particular, we study the
irreversible work incurred by a quench as a function of the initial
temperature, field strength and magnitude of the disorder. While presence of
weak disorder generally increases the irreversible work generated, disorder of
sufficient strength can instead reduce it, giving rise to a disorder induced
lubrication effect. This reduction of irreversible work depends on the nature
of the distribution considered, and can either arise from acquiring the
behavior of an effectively smaller quench for the Normal-distributed spin
couplings, or that of effectively single spin dynamics in the case of Gamma
distributed couplings.",1806.02555v2
2018-06-07,Magnetic domain walls as broadband spin wave and elastic magnetisation wave emitters,"We report on the direct observation of spin wave and elastic wave emission
from magnetic domain walls in ferromagnetic thin films. Driven by alternating
homogeneous magnetic fields the magnetic domain walls act as coherent
magnetisation wave sources. Directional and low damped elastic waves below and
above the ferromagnetic resonance are excited. The wave vector of the
magnetoelastically induced acoustic shear waves is linearly tuned by varying
the excitation frequency. Domain wall emitted magnetostatic surface spin waves
occur at higher frequencies, which characteristics are confirmed by
micromagnetic simulations. The distinct modes of magnetisation wave excitation
from micromagnetic objects are a general physical phenomenon relevant for
dynamic magnetisation processes in structured magnetic films. Magnetic domain
walls can act as reconfigurable antennas for spin wave and elastic wave
generation with control of the wave orientation.",1806.02646v1
2018-06-08,Super-diffusion in one-dimensional quantum lattice models,"We identify a class of one-dimensional spin and fermionic lattice models
which display diverging spin and charge diffusion constants, including several
paradigmatic models of exactly solvable strongly correlated many-body dynamics
such as the isotropic Heisenberg spin chains, the Fermi-Hubbard model, and the
t-J model at the integrable point. Using the hydrodynamic transport theory, we
derive an analytic lower bound on the spin and charge diffusion constants by
calculating the curvature of the corresponding Drude weights at half filling,
and demonstrate that for certain lattice models with isotropic interactions
some of the Noether charges exhibit super-diffusive transport at finite
temperature and half filling.",1806.03288v3
2018-06-13,Enhanced Spin-Orbit Torques and Magnetization Switching through Interface Engineering,"The origin of spin-orbit torques generated from the conversion of
charge-to-spin currents is of considerable debate. Solid understanding of the
physics behind is key to the development of current and voltage controlled
switching dynamics in ultrathin heterostuctures. The field free switching
observed recently (Phys. Rev. Lett. 120, 117703 (2018)) in a Pt/W/CoFeB
structure has intensified such a debate. Here we derive a formula to evaluate a
perpendicular effective field generated when the current flows through the
heterostructure, considering the large resistivity difference between the two
normal metal layers and the chemical potential gradient created at the
interface. Together with recent X-ray photoelectron spectroscopy findings at
the interface of a Pd/CoFeB structure, we conclude that a new torque generated
may play a key role in the field free switching. The model and mechanism
proposed agrees with previous reports on spin current injection and field free
switching using different interface engineering methods.",1806.05163v1
2018-06-20,Magneto-optic Kerr effect in a spin-polarized zero-moment ferrimagnet,"The magneto-optical Kerr effect (MOKE) is often assumed to be proportional to
the magnetisation of a magnetically ordered metallic sample; in metallic
ferrimagnets with chemically distinct sublattices, such as rare-earth
transition-metal alloys, it depends on the difference between the sublattice
contributions. Here we show that in a highly spin polarized, fully compensated
ferrimagnet, where the sublattices are chemically similar, MOKE is observed
even when the net moment is strictly zero. We analyse the spectral ellipsometry
and MOKE of Mn 2 Ru x Ga, and show that this behaviour is due to a highly
spin-polarized conduction band dominated by one of the two manganese
sublattices which creates helicity-dependent reflectivity determined by a broad
Drude tail. Our findings open new prospects for studying spin dynamics in the
infra-red.",1806.07719v2
2018-06-29,Global optimization of spin Hamiltonians with gain-dissipative systems,"Recently, several platforms were proposed and demonstrated a
proof-of-principle for finding the global minimum of the spin Hamiltonians such
as the Ising and XY models using gain-dissipative quantum and classical
systems. The implementation of dynamical adjustment of the gain and coupling
strengths has been established as a vital feedback mechanism for analog
Hamiltonian physical systems that aim to simulate spin Hamiltonians. Based on
the principle of operation of such simulators we develop a novel class of
gain-dissipative algorithms for global optimisation of NP-hard problems and
show its performance in comparison with the classical global optimisation
algorithms. These systems can be used to study the ground state and statistical
properties of spin systems and as a direct benchmark for the performance
testing of the gain-dissipative physical simulators. The estimates of the time
operation of the physical implementation of the gain-dissipative simulators for
large matrices show a possible speed-up of the several orders of magnitude in
comparison with classical computations.",1807.00699v1
2018-07-06,Hydrodynamic Diffusion in Integrable Systems,"We show that hydrodynamic diffusion is generically present in many-body
interacting integrable models. We extend the recently developed generalised
hydrodynamic (GHD) to include terms of Navier-Stokes type which lead to
positive entropy production and diffusive relaxation mechanisms. These terms
provide the subleading diffusive corrections to Euler-scale GHD for the
large-scale non-equilibrium dynamics of integrable systems, and arise due to
two-body scatterings among quasiparticles. We give exact expressions for the
diffusion coefficients. Our results apply to a large class of integrable
models, including quantum and classical, Galilean and relativistic field
theories, chains and gases in one dimension, such as the Lieb-Liniger model
describing cold atom gases and the Heisenberg quantum spin chain. We provide
numerical evaluations in the Heisenberg spin chain, both for the spin diffusion
constant, and for the diffusive effects during the melting of a small domain
wall of spins, finding excellent agreement with tDMRG numerical simulations.",1807.02414v2
2018-07-11,Dynamical coupling of dilute magnetic impurities with quantum spin liquid state in the S = 3/2 dimer compound Ba3ZnRu2O9,"We have investigated the dilute magnetic impurity effect on the magnetic
properties of a quantum spin liquid candidate Ba3ZnRu2O9 and a spin gapped
compound Ba3CaRu2O9. The magnetic ground state of each compound stands against
2% substitution of magnetic impurities for Zn or Ca. We have found that the
magnetic response of these impurities, which behave as paramagnetic spins,
depends on the host materials and the difference of the two manifests itself in
the Weiss temperature, which can hardly be explained by the dilute magnetic
impurities alone in the case of Ba3ZnRu2O9. We consider a contribution from the
Ru5+ ions which would appear only in the substituted Ba3ZnRu2O9 and discuss a
possible physical meaning of the observed Weiss temperature.",1807.04076v1
2018-07-16,Quantum state tomography of a single electron spin in diamond with Wigner reconstruction,"We present the experimental reconstruction of the Wigner function of an
individual electronic spin qubit associated with a nitrogen-vacancy (NV) center
in diamond at room temperature. This spherical Wigner function contains the
same information as the density matrix for arbitrary spin systems. As an
example, we exactly characterize the quantum state of a single qubit undergoing
a nearly pure dephasing process by Wigner function. The fidelities and purities
during this process are extracted from the experimental reconstructed Wigner
functions, whose dynamics agree with the theoretical prediction. Our method can
be applied to multi-qubit systems for measuring the Wigner function of their
collective spin state.",1807.05682v1
2018-08-03,Exact open dynamics of a generalized class of dephasing-type spin-boson models,"We discuss a generalization of the dephasing-type spin-boson model in which N
qubits are connected to K bosonic modes in an arbitrary way. The model can be
solved exactly for any initial state and coupling type. We found that this
leads to two important effects, which are specific of the multipartite nature
of the problem. First, the bosons can mediate an effective interaction among
the spins, which corresponds to a type of time-dependent Lamb-shift. By tuning
the types of couplings, this interaction can also be varied at will. Second,
the dephasing rate of the qubits is found to depend on the order of the
coherence, with superpositions that have drastically different magnetizations
being exponentially more affected. The relative strength of the Lamb-shift and
dephasing can also be tuned by changing the spin-boson couplings.",1808.01224v3
2018-08-08,High throughput screening for spin-gapless semiconductors in quaternary Heusler compounds,"Based on high throughput density functional theory calculations, we performed
systematic screening for spin-gapless semiconductors (SGSs) in quaternary
Heusler alloys XX 0 YZ (X, X 0 , and Y are transition metal elements without
Tc, and Z is one of B, Al, Ga, In, Si, Ge, Sn, Pb, P, As, Sb, and Bi).
Following the empirical rule, we focused on compounds with 21, 26, or 28
valence electrons, resulting in 12, 000 possible chemical compositions. After
systematically evaluating the thermodynamic, mechanical, and dynamical
stabilities, we successfully identified 70 stable SGSs, confirmed by explicit
electronic structure calculations with proper magnetic ground states. It is
demonstrated that all four types of SGSs can be realized, defined based on the
spin characters of the bands around the Fermi energy, and the type-II SGSs show
promising transport properties for spintronic applications. The effect of
spin-orbit coupling is investigated, resulting in large anisotropic
magnetoresistance and anomalous Nernst effects.",1808.02684v1
2018-08-22,Temperature dependence of nuclear spin-isospin response and beta decay in hot astrophysical environments,"A microscopic approach to the proton-neutron nuclear response is formulated
in the finite-temperature relativistic nuclear field theory framework. The
approach is based on the meson-nucleon Lagrangian of quantum hadrodynamics and
advances the relativistic field theory for spin-isospin response beyond the
finite-temperature random phase approximation. The dynamical contribution to
the in-medium proton-neutron interaction amplitude is described in a
parameter-free way by the coupling between the single nucleons and
strongly-correlated particle-hole excitations (phonons) within the newly
developed finite-temperature formalism. In this framework we investigate
temperature dependence of the Gamow-Teller and spin dipole resonances in the
closed-shell nuclei $^{48}$Ca, $^{78}$Ni, and $^{132}$Sn. Broader impacts of
their temperature dependence are illustrated for the associated beta decay
rates and lifetimes of $^{78}$Ni and $^{132}$Sn in hot astrophysical
environments. We found a remarkable sensitivity of the beta decay rates to the
enhanced low-energy spin-isospin strength at finite temperature, in particular,
to the contribution of the first-forbidden transitions.",1808.07223v3
2018-08-23,First harmonic measurements of the spin Seebeck effect,"We present measurements of the spin Seebeck effect (SSE) by a technique that
combines alternating currents (AC) and direct currents (DC). The method is
applied to a ferrimagnetic insulator/heavy metal bilayer,
Y$_3$Fe$_5$O$_{12}$(YIG)/Pt. Typically, SSE measurements use an AC current to
produce an alternating temperature gradient and measure the voltage generated
by the inverse spin-Hall effect in the heavy metal at twice the AC frequency.
Here we show that when Joule heating is associated with AC and DC bias
currents, the SSE response occurs at the frequency of the AC current drive and
can be larger than the second harmonic SSE response. We compare the first and
second harmonic responses and show that they are consistent with the SSE. The
field dependence of the voltage response is used to characterize the
damping-like and field-like torques. This method can be used to explore
nonlinear thermoelectric effects and spin dynamics induced by temperature
gradients.",1808.07813v1
2018-12-05,Fractionalization of long-range ordered states in a Falicov-Kimball model,"A Falicov-Kimball model which thermodynamically reduces the local Coulomb
interaction of particles to attraction or repulsion is studied within the
dynamical mean-field theory. In the strong interaction regime a
fractionalization of particles into charge and spin objects, the physical
properties of which are different from the whole particles, is observed in both
high- and low-temperature phases. At high temperature and strong interaction
the single-particle density of states opens an excitation gap, but the charge
compressibility and the spin susceptibility exhibit the features of gapless
excitations. The low-temperature phase has a long-range order, and the
single-particle spectra are always gapped, while the charge and spin
excitations are gapless in the strong interaction regime. In the fractionalized
long-range ordered phase both the charge compressibility and the spin
susceptibility are universal scaling functions of temperature.",1812.01795v3
2018-12-13,Spinning constraints on chaotic large $c$ CFTs,"We study out-of-time ordered four-point functions in two dimensional
conformal field theories by suitably analytically continuing the Euclidean
correlator. For large central charge theories with a sparse spectrum, chaotic
dynamics is revealed in an exponential decay; this is seen directly in the
contribution of the vacuum block to the correlation function. However,
contributions from individual non-vacuum blocks with large spin and small twist
dominate over the vacuum block. We argue, based on holographic intuition, that
suitable summations over such intermediate states in the block decomposition of
the correlator should be sub-dominant, and attempt to use this criterion to
constrain the OPE data with partial success. Along the way we also discuss the
relation between the spinning Virasoro blocks and the on-shell worldline action
of spinning particles in an asymptotically AdS spacetime.",1812.05585v3
2018-12-14,The Higgs Mode of Planar Coupled Spin-Ladders and its Observation in C$_9$H$_{18}$N$_2$CuBr$_4$,"Polarized inelastic neutron scattering experiments recently identified the
amplitude (Higgs) mode in C$_9$H$_{18}$N$_2$CuBr$_4$, a two-dimensional
near-quantum-critical spin-1/2 two-leg ladder compound, which exhibits a weak
easy-axis exchange anisotropy. Here, we theoretically examine the dynamic spin
structure factor of such planar coupled spin-ladder systems using large-scale
quantum Monte Carlo simulations. This allows us to provide a quantitative
account of the experimental neutron scattering data within a consistent quantum
spin model. Moreover, we trance the details of the continuous evolution of the
amplitude mode from a two-particle bound state of coupled ladders in the
classical Ising limit all the way to the quantum spin-1/2 Heisenberg limit with
fully restored SU(2) symmetry, where it gets overdamped by the two-magnon
continuum in neutron scattering.",1812.05853v1
2019-01-11,Transport through a magnetic impurity: a slave-spin approach,"We study transport across a magnetic impurity by means of a recently
developed slave-spin technique that does not require any constraint. Within a
conserving mean-field approximation we find a conductance that displays both
the known zero-bias anomaly but also the expected peak at bias of order U. We
extend the slave-spin mean-field approximation to study the out of equilibrium
transient evolution of a quantum dot. We apply the method to investigate the
time-evolution of a quantum dot induced by a time-dependent electrochemical
potential applied to the contacts. Similarly to the time-dependent Gutzwiller
approximation, the mean-field slave-spin dynamics is able to capture
dissipation in the leads, so that a steady-state is reached after a
characteristic relaxation time.",1901.03636v2
2019-01-17,"Influences of interfacial oxidization on surface magnetic energy, magnetic damping and spin-orbit-torques in Pt / ferromagnet / capping structures","We investigate the effect of capping layer (CAP) on the interfacial magnetic
anisotropy energy density (K_S), magnetic damping ({\alpha}), and spin-orbit
torques (SOTs) in heavy-metal (Pt) / ferromagnet (Co or Py) / CAP (MgO/Ta,
HfOx, or TaN). At room temperature (RT) the CAP materials influence the
effective magnitude of K_S, which is associated with a formation of interfacial
magnetic oxides. The dynamical dissipation parameters of Co are considerably
influenced by the CAP (especially MgO) while those of Py are not. This is
possibly due to an extra magnetic damping via spin-pumping process across the
Co/CoO interface and incoherent magnon generation (spin fluctuation) in the
interfacial CoO. It is also observed that both anti-damping and field-like SOT
efficiencies vary marginally with the CAP in the thickness ranges we examined.
Our results reveal the crucial role of interfacial oxides on the perpendicular
magnetic anisotropy, magnetic damping, and SOTs.",1901.05777v1
2019-01-23,Gapless spin-liquid state in the structurally disorder-free triangular antiferromagnet NaYbO$_2$,"We present the structural characterization and low-temperature magnetism of
the triangular-lattice delafossite NaYbO$_2$. Synchrotron x-ray diffraction and
neutron scattering exclude both structural disorder and crystal-electric-field
randomness, whereas heat-capacity measurements and muon spectroscopy reveal the
absence of magnetic order and persistent spin dynamics down to at least 70\,mK.
Continuous magnetic excitations with the low-energy spectral weight
accumulating at the $K$-point of the Brillouin zone indicate the formation of a
novel spin-liquid phase in a triangular antiferromagnet. This phase is gapless
and shows a non-trivial evolution of the low-temperature specific heat. Our
work demonstrates that NaYbO$_2$ practically gives the most direct experimental
access to the spin-liquid physics of triangular antiferromagnets.",1901.07810v1
2019-02-01,Ground state and low-energy excitations of the Kitaev-Heisenberg ladder,"We study the ground state and low-lying excited states of the
Kitaev-Heisenberg model on a ladder geometry using the density matrix
renormalization group and Lanczos exact diagonalization methods. The Kitaev and
Heisenberg interactions are parametrized as $K=\sin\phi$ and $J=\cos\phi$ with
an angle parameter $\phi$. Based on the results for several types of order
parameters, excitation gaps, and entanglement spectra, the $\phi$-dependent
ground-state phase diagram is determined. Remarkably, the phase diagram is
quite similar to that of the Kitaev-Heisenberg model on a honeycomb lattice,
exhibiting the same long-range ordered states, namely rung-singlet (analog to
N\'eel in 3D), zigzag, ferromagnetic, and stripy; and the presence of Kitaev
spin liquids around the exactly solvable Kitaev points $\phi=\pm\pi/2$. We also
calculate the expectation value of a plaquette operator corresponding to a
$\pi$-flux state in order to establish how the Kitaev spin liquid extends away
from the $\phi=\pm\pi/2$. Furthermore, we determine the dynamical spin
structure factor and discuss the effect of the Kitaev interaction on the
spin-triplet dispersion.",1902.00466v1
2019-02-07,Triplet excitations in the frustrated spin ladder Li$_2$Cu$_2$O(SO$_4$)$_2$,"Magnetic excitations of the recently discovered frustrated spin-1/2 two-leg
ladder system Li$_2$Cu$_2$O(SO$_4$)$_2$ are investigated using inelastic
neutron scattering, magnetic susceptibility and infrared absorption
measurements. Despite the presence of a magnetic dimerization concomitant with
the tetragonal-to-triclinic structural distortion occurring below 125 K,
neutron scattering experiments reveal the presence of dispersive triplet
excitations above a spin gap of $\Delta = 10.6$ meV at 1.5 K, a value
consistent with the estimates extracted from magnetic susceptibility. The
likely detection of these spin excitations in infrared spectroscopy is
explained by invoking a dynamic Dzyaloshinskii-Moriya mechanism in which light
is coupled to the dimer singlet-to-triplet transition through an optical
phonon. These results are qualitatively explained by exact diagonalization and
higher-order perturbation calculations carried out on the basis of the
dimerized spin Hamiltonian derived from first-principles.",1902.02798v1
2019-02-13,Interacting non-Hermitian ultracold atoms in a harmonic trap: Two-body exact solution and high-order exceptional point,"We study interacting ultracold atoms in a three-dimensional (3D) harmonic
trap with spin-selective dissipations, which can be effectively described by
non-Hermitian parity-time ($\mathcal{PT}$) symmetric Hamiltonians. By solving
the non-Hermitian two-body problem of spin-1/2 (spin-1) bosons in a 3D harmonic
trap exactly, we find that the system can exhibit third-order (fifth-order)
exceptional point (EP) with ultra-sensitive cube-root (fifth-root) spectral
response due to interaction anisotropies in spin channels. We also present the
general principle for the creation of high-order EPs and their spectral
sensitivities with arbitrary particle number $N$ and arbitrary spin $s$.
Generally, with spin-independent interactions, the EP order of bosons can be as
high as $2Ns+1$, and the spectral response around EP can be as sensitive as
$\sim \epsilon^{1/(2ks+1)}$ under a $k$-body interaction anisotropy. Moreover,
we propose to detect the ultra-sensitive spectral response through the
probability dynamics of certain state. These results suggest a convenient route
towards more powerful sensor devices in spinor cold atomic systems.",1902.04769v3
2019-02-19,"Spinning extensions of $D(2,1;α)$ superconformal mechanics","As is known, any realization of SU(2) in the phase space of a dynamical
system can be generalized to accommodate the exceptional supergroup
$D(2,1;\alpha)$, which is the most general $\mathcal{N}{=}\,4$ supersymmetric
extension of the conformal group in one spatial dimension. We construct novel
spinning extensions of $D(2,1;\alpha)$ superconformal mechanics by adjusting
the SU(2) generators associated with the relativistic spinning particle coupled
to a spherically symmetric Einstein-Maxwell background. The angular sector of
the full superconformal system corresponds to the orbital motion of a particle
coupled to a symmetric Euler top, which represents the spin degrees of freedom.
This particle moves either on the two-sphere, optionally in the external field
of a Dirac monopole, or in the SU(2) group manifold. Each case is proven to be
superintegrable, and explicit solutions are given.",1902.06851v1
2019-02-27,Propagating spin excitations along skyrmion strings,"Magnetic skyrmions, topological solitons characterized by a two-dimensional
swirling spin texture, have recently attracted attention as stable
particle-like objects. In a three-dimensional system, a skyrmion can extend in
the third dimension forming a robust and flexible string structure, whose
unique topology and symmetry are anticipated to host nontrivial functional
responses. Here, we experimentally demonstrate the coherent propagation of spin
excitations along skyrmion strings for the chiral-lattice magnet Cu2OSeO3. We
find that this propagation is directionally non-reciprocal, and the degree of
non-reciprocity, as well as the associated group velocity and decay length, are
strongly dependent on the character of the excitation modes. Our theoretical
calculation establishes the corresponding dispersion relationship, which well
reproduces the experimentally observed features. Notably, these spin
excitations can propagate over a distance exceeding 10^3 times the skyrmion
diameter, demonstrating the excellent long-range nature of the excitation
propagation on the skyrmion strings. Our combined experimental and theoretical
results offer a comprehensive account of the propagation dynamics of
skyrmion-string excitations, and suggest the possibility of unidirectional
information transfer along such topologically-protected strings.",1902.10302v1
2019-03-01,Anomalous Knight shift and low-energy spin dynamics in the nematic state of FeSe$_{\rm 1-x}$S$_{\rm x}$,"The interplay between the nematic order and magnetism in FeSe is not yet well
understood. There is a controversy concerning the relationship between orbital
and spin degrees of freedom in FeSe and their relevance for superconductivity.
Here we investigate the effect of S substitution on the nematic transition
temperature ($T_{\rm n}$) and the low-energy spin fluctuations (SF) in FeSe
single crystals. We show that the low-energy SF emerge below the nematic
transition. The difference between the onset temperature for the critical SF
($T_{\rm SF}$) and $T_{\rm n}$ is small for FeSe but significantly increases
with S substitution. Below $T_{\rm SF}$ the Korringa relation is violated and
the effective muon hyperfine coupling constant changes a sign. Our results
exclude a direct coupling of the low-energy SF to the electronic nematic order
indicating a presence of multiple spin degrees of freedom in FeSe$_{\rm
1-x}$S$_{\rm x}$.",1903.00530v1
2019-03-06,Isolated zero field sub-10 nm skyrmions in ultrathin Co films,"Due to their exceptional topological and dynamical properties magnetic
skyrmions - localized stable spin structures on the nanometre scale - show
great promise for future spintronic applications. To become technologically
competitive, isolated skyrmions with diameters below 10 nm that are stable at
zero magnetic field and room temperature are desired. Despite finding skyrmions
in a wide spectrum of materials, the quest for a material with these envisioned
properties is still ongoing. Here we report zero field isolated skyrmions with
diameters smaller than 5 nm coexisting with 1 nm thin domain walls in Rh/Co
atomic bilayers on the Ir(111) surface. These spin structures are characterized
by spin-polarized scanning tunnelling microscopy and can also be detected using
non-spin-polarized tips due to a large non-collinear magnetoresistance. We
demonstrate that sub-10 nm skyrmions are stabilised in these ferromagnetic Co
films at zero field due to strong frustration of exchange interaction, together
with Dzyaloshinskii-Moriya interaction and a large magnetocrystalline
anisotropy.",1903.02258v1
2019-03-06,Anomalous Magnetic Behavior in Ba2CoO4 with Isolated CoO4 Tetrahedra,"The dimensionality of the electronic and magnetic structure of a given
material is generally predetermined by its crystal structure. Here, using
elastic and inelastic neutron scattering combined with magnetization
measurements, we find unusual magnetic behavior in three-dimensional (3D)
Ba2CoO4. In spite of isolated CoO4 tetrahedra, the system exhibits a 3D
noncollinear antiferromagnetic order in the ground state with an anomalously
large Curie-Weiss temperature of 110 K compared to TN = 26 K. More
unexpectedly, spin dynamics displays quasi-2D spin wave dispersion with an
unusually large spin gap, and 1D magnetoelastic coupling. Our results indicate
that Ba2CoO4 is a unique system for exploring the interplay between isolated
polyhedra, low-dimensional magnetism, and novel spin states in oxides.",1903.02490v1
2019-03-12,Antiferromagnetic Piezospintronics,"Antiferromagnets naturally exhibit three obvious advantages over ferromagnets
for memory device applications: insensitivity to external magnetic fields, much
faster spin dynamics (~THz) and higher packing density due to the absence of
any stray field. Recently, antiferromagnetic spintronics emerges as a
cutting-edge field in the magnetic community. The key mission of this rapidly
rising field is to steer the spins or spin axes of antiferromagnets via
external stimuli and then realize advanced devices based on their physical
property changes. Herein, the state of the art of antiferromagnetic spintronics
is presented. Subsequently, the history of ferromagnetic/ferroelectric
multiferroic composites is briefly revisited. Finally, we introduce an
ultralow-power, long-range, and magnetic-field-insensitive approach for
harnessing antiferromagnetic spins based on our recent experimental progress,
i.e., piezoelectric strain control. Relevant theoretical and experimental
studies have formed an attractive new branch in antiferromagnetic spintronics,
which we coin as antiferromagnetic piezospintronics.",1903.04782v1
2019-03-13,Experimental studies at low $Q^2$ of the spin structure of the nucleon at Jefferson Lab,"We summarize the experimental program of Jefferson Lab that studies the
nucleon spin structure at low $Q^2$. This program completes the precise
experimental mapping of the nucleon spin structure functions $g_1(\nu, Q^2)$
and $g_2(\nu, Q^2)$ and their moments started at SLAC, CERN and DESY at high
$Q^2$, and continued at Jefferson Lab at intermediate $Q^2$. The results
presented cover the domain where Chiral Effective Field Theory ($\chi$EFT)
should describe the strong interaction. They provide a comprehensive set of
benchmark measurements for $\chi$EFT. The preliminary conclusion is that
nucleon spin structure data are still challenging for $\chi$EFT in spite of the
notable improvements in these calculations.",1903.05661v2
2019-03-25,State transfer in an inhomogeneous spin chain,"We present an analytical study of state transfer in a spin chain in the
presence of an inhomogeneous set of exchange coefficients. We initially
consider the homogeneous case and describe a method to obtain the energy
spectrum of the system. Under certain conditions, the state transfer time can
be predicted by taking into account the energy gap between the two lowest
energy eigenstates. We then generalize our approach to the inhomogeneous case
and show that including a barrier in the chain can lead to a reduction of the
state transfer time. We additionally extend our analysis to the case of
multiple barriers. These advances may contribute to the understanding of spin
transfer dynamics in long chains where connections between neighboring spins
can be manipulated.",1903.10538v2
2019-04-01,Theoretical study of the spin and charge dynamics of two-leg ladders as probed by resonant inelastic x-ray scattering,"Resonant inelastic x-ray scattering (RIXS) has become an important tool for
studying elementary excitations in correlated materials. Here, we present a
systematic theoretical investigation of the Cu L-edge RIXS spectra of undoped
and doped cuprate two-leg spin-ladders in both the non-spin-conserving (NSC)
and spin-conserving (SC) channels. The spectra are rich and host many exotic
excitations. In the NSC-channel of the undoped case, we identify one-triplon
and bound $\textit{triplet}$ two-triplon excitations in the strong-rung
coupling limit, as well as confined spinons in the weak-rung coupling limit. In
the doped case, we observe a quasiparticle excitation formed from a bound
charge and spin-$\frac{1}{2}$ in the strong-rung coupling limit. In the
SC-channel, we also identify several new features, including bound
$\textit{singlet}$ two-triplon excitations and confined spinons in the undoped
ladders in the strong- and weak-rung coupling limits, respectively. Conversely,
in the doped case, the SC channel primarily probes both gapless and gapped
charge excitations. Finally, we revisit the available data for the ladder
compound Sr$_{14}$Cu$_{24}$O$_{41}$ in the context of our results.",1904.00530v1
2019-04-12,Magnetic excitations in hole-doped Sr2IrO4: A comparison with electron-doped cuprates,"We have studied the evolution of magnetic and orbital excitations as a
function of hole-doping in single crystal samples of Sr2Ir(1-x)Rh(x)O4 (0.07 <
x < 0.42) using high resolution Ir L3-edge resonant inelastic x-ray scattering
(RIXS). Within the antiferromagnetically ordered region of the phase diagram (x
< 0.17) we observe highly dispersive magnon and spin-orbit exciton modes.
Interestingly, both the magnon gap energy and the magnon bandwidth appear to
increase as a function of doping, resulting in a hardening of the magnon mode
with increasing hole doping. As a result, the observed spin dynamics of
hole-doped iridates more closely resemble those of the electron-doped, rather
than hole-doped, cuprates. Within the paramagnetic region of the phase diagram
(0.17 < x < 0.42) the low-lying magnon mode disappears, and we find no evidence
of spin fluctuations in this regime. In addition, we observe that the orbital
excitations become essentially dispersionless in the paramagnetic phase,
indicating that magnetic order plays a crucial role in the propagation of the
spin-orbit exciton.",1904.06402v1
2019-08-02,Theoretical prediction of a highly responsive material: Spin fluctuations and superconductivity in FeNiB2 system,"By analyzing Fe-Ni-B compositional diagram we predict an energetically and
dynamically stable FeNiB2 compound. This system belongs to the class of highly
responsive state of material, as it is very sensitive to the external
perturbations. This state is also characterized by a high level of spin
fluctuations which strongly influence possible magnetic long- and short-range
orders. Furthermore, we demonstrate that these antiferromagnetically dominating
fluctuations could lead to the appearance of spin mediated superconductivity.
The obtained results suggest a promising avenue for the search of strong spin
fluctuation systems and related superconductors.",1908.01025v2
2019-11-17,Theory of two-dimensional nonlinear spectroscopy for the Kitaev spin liquid,"Unambiguous identification of fractionalized excitations in quantum spin
liquids has been a long-standing issue in correlated topological phases.
Conventional spectroscopic probes, such as the dynamical spin structure factor,
can only detect composites of fractionalized excitations, leading to a broad
continuum in energy. Lacking a clear signature in conventional probes has been
the biggest obstacle in the field. In this work, we theoretically investigate
what kinds of distinctive signatures of fractionalized excitations can be
probed in two-dimensional nonlinear spectroscopy by considering the exactly
solvable Kitaev spin liquids. We demonstrate the existence of a number of
salient features of the Majorana fermions and fluxes in two-dimensional
nonlinear spectroscopy, which provide crucial information about such
excitations.",1911.07138v3
2019-11-29,Scaling theory of magnetism in frustrated Kondo lattices,"A scaling theory of the Kondo lattices with frustrated exchange interactions
is developed, criterium of antiferromagnetic ordering and quantum-disordered
state being investigated. The calculations taking into account magnon and
incoherent spin dynamics are performed. Depending on the bare model parameters,
one or two quantum phase transitions into non-magnetic spin-liquid and Kondo
Fermi-liquid ground states can occur with increasing the bare coupling
constant. Whereas the renormalization of the magnetic moment in the ordered
phase can reach orders of magnitude, spin fluctuation frequency and coupling
constant are moderately renormalized in the spin-liquid phase. This justifies
application of the scaling approach. Possibility of a non-Fermi-liquid behavior
is treated.",1911.13083v1
2019-12-05,Damping of spinful excitons in LaCoO$_3$ by thermal fluctuations: Theory and experiment,"We present Co $L_3$-edge resonant inelastic x-ray scattering (RIXS) of bulk
LaCoO$_3$ across the thermally-induced spin-state crossover around 100~K. Owing
to a high energy resolution of 25~meV, we observe unambiguously the dispersion
of the intermediate-spin (IS) excitations in the low temperature regime.
Approaching the intermediate temperature regime, the IS excitations are damped
and the bandwidth is reduced. The observed behavior can be well described by a
model of mobile IS excitons with strong attractive interaction, which we solve
using dynamical mean-field theory for hard-core bosons. Our results provide a
detailed mechanism of how high-spin (HS) and IS excitations interact to
establish the physical properties of cobaltite perovskites.",1912.02564v3
2019-12-08,Generalizing the Sokolov-Ternov effect for radiative polarization in intense laser fields,"A consistent description of the radiative polarization for relativistic
electrons in intense laser fields is derived by generalizing the Sokolov-Ternov
effect in general field structure. The new form together with the
spin-dependent radiation-reaction force provides a complete set of dynamical
equations for electron momentum and spin in strong fields. When applied to
varying intense fields, e.g. the laser fields, the generalized Sokolov-Ternov
effect allows electrons to gain or lose polarization in any directions other
than along the magnetic field in the rest frame of the electron. The
generalized theory is applied to the collision process between initially
polarized/unpolarized high energy electrons with linearly polarized
ultra-intense laser pulse, showing results that eliminate the dependence on
specific choices of a quantization axis and spin initialization existing in
spin-projection models.",1912.03625v2
2019-12-08,Magnetic excitations in magnetization plateaux of a frustrated spin ladder,"Magnetization plateaux emerging in quantum spin systems due to spontaneously
breaking of translational symmetry have been reported both theoretically and
experimentally. The broken symmetry can induce reconstruction of elementary
excitations such as Goldstone and Higgs modes, whereas its microscopic
mechanism and reconstructed quasi-particle in magnetization-plateau phases have
remained unclear so far. Here we theoretically study magnetic excitations in
the magnetization-plateau phases of a frustrated spin ladder by using dynamical
density-matrix renormalization-group method. Additionally, analytical
approaches with perturbation theory are performed to obtain intuitive view of
magnetic excitations. Comparison between numerical and analytical results
indicates the presence of a reconstructed quasi-particle originating from
spontaneously broken translational symmetry, which is realized as a collective
mode of spin trimer called trimeron.",1912.03693v2
2019-12-12,Weak-coupling Mean-field Theory of Magnetic Properties of NiGa$_2$S$_4$,"We report a mean-field theoretical study of a triangular lattice magnet
NiGa$_2$S$_4$. Specifically, spiral mean-field theory is applied to a 17-band
$d$-$p$ model constructed from the maximally localized Wannier functions. Our
itinerant-model approach shows that the most stable spiral magnetic state has
an ordering vector near ${\bf Q}=(0.15,0.15,0)$, consistent with neutron
scattering experiments, when we assume the Ni-site Coulomb interaction is not
so strong ($U \approx 2$ eV). To map onto a classical Heisenberg spin model, we
estimate spin exchange interactions from the mean-field results, and find that
the nearest-neighbor exchange is ferromagnetic and the largest (larger than the
third nearest-neighbor exchange, in contrast to early studies). We also
calculate the dynamical spin correlation function $S({\bf q}, \omega)$, using
the same model within the random-phase approximation (RPA). Calculated $S({\bf
q}, \omega)$ has a spectral structure quite different from that of conventional
spin-wave excitations.",1912.05720v2
2019-12-17,Probing Electron-Electron Interactions with a Quantum Antidot,"In the integer quantum Hall (IQH) regime, an antidot provides a finite,
controllable `edge' of quantum Hall fluid that is an ideal laboratory for
investigating the collective dynamics of large numbers of interacting
electrons. Transport measurements of single antidots probe the excitation
spectra of the antidot edge, and gate-defined antidot devices offer the
flexibility to vary both the antidot's dimensions and its couplings to extended
IQH edge modes which serve as leads. We also use the spin-selectivity of the
IQH edge modes to perform spin-resolved transport measurements, from which we
can infer the antidot spin-structure. This thesis describes a combination of
such transport experiments and related computational models designed to
investigate the effects of electron-electron interactions in quantum antidots,
with general implications for the physics of spin and charge in IQH systems.",1912.08006v1
2019-12-18,Relaxation dynamics of spin 3/2 silicon vacancies in 4H-Silicon carbide,"Room temperature optically detected magnetic resonance experiments on spin
3/2 Silicon vacancies in 4H-SiC are reported. The $m_s=+1/2\leftrightarrow
-1/2$ transition is accessed using a two microwave frequency excitation
protocol. The ratio of the Rabi frequencies of the $+3/2 \leftrightarrow +1/2$
and $+1/2\leftrightarrow -1/2$ transitions is measured to be $(0.901\pm
0.013)$. The deviation from $\sqrt{3}/2$ is attributed to small difference in
g-factor for different magnetic dipole transitions. Whereas a spin-1/2 system
is characterized by a single spin lifetime $T_1$, we experimentally demonstrate
that the spin 3/2 system has three distinct relaxation modes that can be
preferentially excited and detected. The measured relaxation times are
$(0.41\pm 0.02) T_{slow}=T_d= (3.3\pm 0.5)T_{fast} $. This differs from the
values of $ T_p/3 =T_d= 2T_f $ expected for pure dipole ($T_p$), quadrupole
($T_d$), and octupole ($T_f$) relaxation modes, respectively, and implies
admixing of the slow dipole and fast octupole relaxation modes.",1912.08513v2
2019-12-19,A Hahn-Ramsey Scheme for Dynamical Decoupling and DC Magnetometry with Single Solid-State Qubits,"Spin systems in solid state materials are promising qubit candidates for
quantum information or quantum sensing. A major prerequisite here is the
coherence of spin phase oscillations. In this work, we show a control sequence
which, by applying RF pulses of variable detuning, allows to increase the spin
phase oscillation visibility and to perform DC magnetometry as well. We
experimentally demonstrate the scheme on single NV centers in diamond and
analytically describe how the NV electron spin phase oscillations behave in the
presence of classical noise models. We hereby introduce detuning as the
enabling factor that modulates the filter function of the sequence, in order to
achieve a visibility of the Ramsey fringes comparable to or longer than the
Hahn-echo $T_2$ time and an improved sensitivity to DC magnetic fields in
various experimental settings.",1912.09245v3
2020-05-13,Magneto-optics of excitons interacting with magnetic ions in CdSe/CdMnS colloidal nanoplatelets,"Excitons in diluted magnetic semiconductors represent excellent probes for
studying the magnetic properties of these materials. Various magneto-optical
effects, which depend sensitively on the exchange interaction of the excitons
with the localized spins of the magnetic ions can be used for probing. Here, we
study core/shell CdSe/(Cd,Mn)S colloidal nanoplatelets hosting diluted magnetic
semiconductor layers. The inclusion of the magnetic Mn$^{2+}$ ions is evidenced
by three magneto-optical techniques using high magnetic fields up to 15 T:
polarized photoluminescence, optically detected magnetic resonance, and
spin-flip Raman scattering. In particular, information on the Mn$^{2+}$
concentration in the CdS shell layers can be obtained from the spin-lattice
relaxation dynamics of the Mn$^{2+}$ spin system.",2005.06548v1
2020-05-17,Spin-orbital liquid in Ba$_3$CuSb$_2$O$_9$ stabilized by oxygen holes,"Both the Jahn-Teller distortion of Cu$^{2+}$O$_6$ octahedra and magnetic
ordering are absent in hexagonal Ba$_3$CuSb$_2$O$_9$ suggesting a Cu 3$d$
spin-orbital liquid state. Here, by means of resonant x-ray scattering and
absorption experiment, we show that oxygen 2$p$ holes play crucial role in
stabilizing this spin-orbital liquid state. These oxygen holes appear due to
the ""reaction"" Sb$^{5+}$$\rightarrow$Sb$^{3+}$ $+$ two oxygen holes, with these
holes being able to attach to Cu ions. The hexagonal phase with oxygen 2$p$
holes exhibits also a novel charge-orbital dynamics which is absent in the
orthorhombic phase of Ba$_3$CuSb$_2$O$_9$ with Jahn-Teller distortion and Cu
3$d$ orbital order. The present work opens up a new avenue towards
spin-charge-orbital entangled liquid state in transition-metal oxides with
small or negative charge transfer energy.",2005.08200v1
2020-05-27,Effects of the Zhang-Li Torque on Spin Torque nano Oscillators,"Spin-torque nano-oscillators (STNO) are microwave auto-oscillators based on
magnetic resonances having a nonlinear response with the oscillating amplitude,
which provides them with a large frequency tunability including the possibility
of mutual synchronization. The magnetization dynamics in STNO are induced by
spin transfer torque (STT) from spin currents and can be detected by changes in
electrical resistance due to giant magnetoresistance or tunneling
magnetoresistance. The STT effect is usually treated as a damping-like term
that reduces magnetic dissipation and promotes excitation of magnetic modes.
However, an additional term, known as Zhang-Li term has an effect on
magnetization gradients such as domain walls, and could have an effect on
localized magnetic modes in STNO. Here we study the effect of Zhang-Li torques
in magnetic excitations produced in STNO with a nanocontact geometry. Using
micromagnetic simulations we find that Zhang-Li torque modify threshold
currents of magnetic modes and their effective sizes. Additionally we show that
effects can be controlled by changing the ratio between nanocontact size and
layer thickness.",2005.13364v1
2020-09-30,Breathing kagome XY quantum magnet with four-site ring exchange,"We study the impact of trimerization (breathing) of the nearest-neighbor (NN)
exchange on the planar XY spin-1/2 ferromagnet on the kagome lattice, including
additional four-site ring exchange. For uniform NN exchange, this model has
previously been shown to transit from a long-range ordered ferromagnet into a
Z2 quantum spin liquid by virtue of the ring exchange. Using quantum
Monte-Carlo calculations, based on the stochastic series expansion, we present
results for the spin stiffness, the quantum phase diagram, the longitudinal
static, as well as the transverse dynamic structure factor. Our results
corroborate 3D XY universality also at finite trimerization and suggest a
simple continuation of the quantum critical point of the uniform case into a
line in terms of rescaled exchange parameters. Moreover, at any trimerization
and in the ordered phase the elementary excitations can be understood very well
in terms of linear spin wave theory, while beyond the critical line, in the
spin liquid phase we find signatures of spinon continua.",2010.00014v2
2020-11-02,Spin wave propagation in corrugated waveguides,"Curvature-induced effects allow us to tailor the static and dynamic response
of a magnetic system with a high degree of freedom. We study corrugated
magnonic waveguides deposited on a sinusoidally modulated substrate prepared by
focused electron beam deposition. The surface curvature in films with
thicknesses comparable to the amplitude of modulation locally modifies the
contributions of dipolar and exchange energies and results in an effective
anisotropy term which can be tuned on-demand based on the exact geometry. We
show, by Brillouin light scattering microscopy, that without the presence of an
external magnetic field, spin waves propagate over a distance 10$\times$larger
in the corrugated waveguide than in the planar waveguide. Further, we analyze
the influence of the modulation amplitude on spin-wave propagation and conclude
that for moderate modulation amplitudes, the spin-wave decay length is not
affected. For larger amplitudes, the decay length decreases linearly with
increasing modulation.",2011.01274v1
2020-11-03,Delta-Davidson method for interior eigenproblem in many-spin systems,"Many numerical methods, such as tensor network approaches including density
matrix renormalization group calculations, have been developed to calculate the
extreme/ground states of quantum many-body systems. However, little attention
has been paid to the central states, which are exponentially close to each
other in terms of system size. We propose a Delta-Davidson (DELDAV) method to
effciently find such interior (including the central) states in many-spin
systems. The DELDAV method utilizes Delta filter in Chebyshev polynomial
expansion combined with subspace diagonalization to overcome the nearly
degenerate problem. Numerical experiments on Ising spin chain and spin glass
shards show the correctness, effciency, and robustness of the proposed method
in finding the interior states as well as the ground states. The sought
interior states may be employed to identify many-body localization phase,
quantum chaos, and extremely long-time dynamical structure.",2011.01554v1
2020-11-08,Quantum teleportation by utilizing helical spin chains for sharing entanglement,"We develop a new protocol for sharing entanglement (one ebit) between two
parties using the natural dynamics of helical multiferroic spin chains. We
introduce a novel kicking scheme of the electric field for enhancing the
teleportation fidelity in our protocol that works in the presence of an
appropriate choice of parameters. We also investigate the effect of a common
spin environment causing decoherence in the entanglement sharing channel. We
compare the results to that of XXZ and XX models subject to a similar
entanglement sharing protocol and find that the helical multiferroic chain with
the kicking scheme provides a better singlet fraction. We show that the kicking
scheme in conjugation with the optimized parameters enhances the fidelity of
teleportation even in the presence of impurities and/or decoherence. The
advantage of the kicking scheme shown in the impurity cases is an important
result to be useful in a realizable setup of helical multiferroic spin chain.",2011.03873v1
2020-11-10,Wavefunction-Based Analysis of Dynamics Versus Yield of Free Triplets in Intramolecular Singlet Fission,"Experiments in several intramolecular singlet fission materials have
indicated that the triplet-triplet spin biexciton has a much longer lifetime
than believed until recently, opening up loss mechanisms that can annihilate
the biexciton prior to its dissociation to free triplets. We have performed
many-body calculations of excited state wavefunctions of hypothetical
phenylene-linked anthracene molecules to better understand linker-dependent
behavior of dimers of larger acenes being investigated as potential singlet
fission candidates. The calculations reveal unanticipated features that we show
carry over to the real covalently-linked pentacene dimers. Dissociation of the
correlated triplet-triplet spin biexciton and free triplet generation may be
difficult in acene dimers where the formation of the triplet-triplet spin
biexciton is truly ultrafast. Conversely, relatively slower biexciton formation
may indicate smaller spin biexciton binding energy and greater yield of free
triplets. Currently available experimental results appear to support this
conclusion. Whether or not the two distinct behaviors are consequences of
distinct mechanisms of triplet-triplet generation from the optical singlet is
an interesting theoretical question.",2011.05434v1
2020-11-23,Asymmetric spin wave dispersion due to a saturation magnetization gradient,"We demonstrate using micromagnetic simulations and a theoretical model that a
gradient in the saturation magnetization ($M_s$) of a perpendicularly
magnetized ferromagnetic film induces a non-reciprocal spin wave propagation
and, consequently an asymmetric dispersion relation. The $M_s$ gradient adds a
linear potential to the spin wave equation of motion consistent with the
presence of a force. We consider a transformation from an inertial reference
frame in which the $M_s$ is constant to an accelerated reference frame where
the resulting inertial force corresponds to the force from the $M_s$ gradient.
As in the Doppler effect, the frequency shift leads to an asymmetric dispersion
relation. Additionally, we show that under certain circumstances,
unidirectional propagation of spin waves can be achieved which is essential for
the design of magnonic circuits. Our results become more relevant in light of
recent experimental works in which a suitable thermal landscape is used to
dynamically modulate the saturation magnetization.",2011.11148v2
2020-11-25,Antiferromagnetic magnon pseudospin: Dynamics and diffusive transport,"We formulate a theoretical description of antiferromagnetic magnons and their
transport in terms of an associated pseudospin. The need and strength of this
formulation emerges from the antiferromagnetic eigenmodes being formed from
superpositions of spin-up and -down magnons, depending on the material
anisotropies. Consequently, a description analogous to that of spin-1/2
electrons is demonstrated while accounting for the bosonic nature of the
antiferromagnetic eigenmodes. Introducing the concepts of a pseudospin chemical
potential together with a pseudofield and relating magnon spin to pseudospin
allows a consistent description of diffusive spin transport in
antiferromagnetic insulators with any given anisotropies and interactions.
Employing the formalism developed, we elucidate the general features of recent
non-local spin transport experiments in antiferromagnetic insulators hosting
magnons with different polarisations. The pseudospin formalism developed herein
is valid for any pair of coupled bosons and is likely to be useful in other
systems comprising interacting bosonic modes.",2011.12927v1
2021-04-01,Multiparameter quantum metrology using strongly interacting spin systems,"Interacting quantum systems are attracting increasing interest for developing
precise metrology. In particular, the realisation that quantum-correlated
states and the dynamics of interacting systems can lead to entirely new and
unexpected phenomena have initiated an intense research effort to explore
interaction-based metrology both theoretically and experimentally. However, the
current framework of interaction-based metrology mainly focuses on
single-parameter estimations, a demonstration of multiparameter metrology using
interactions as a resource was heretofore lacking. Here we demonstrate an
interaction-based multiparameter metrology with strongly interacting nuclear
spins. We show that the interacting spins become intrinsically sensitive to all
components of a multidimensional field when their interactions are
significantly larger than their Larmor frequencies. Using liquid-state
molecules containing strongly interacting nuclear spins, we demonstrate the
proof-of-principle estimation of all three components of an unknown magnetic
field and inertial rotation. In contrast to existing approaches, the present
interaction-based multiparameter sensing does not require external reference
fields and opens a path to develop an entirely new class of multiparameter
quantum sensors.",2104.00211v1
2021-04-08,Out-of-plane magnetization oscillation in spin Hall device assisted by field-like torque,"An excitation of a large-amplitude out-of-plane magnetization oscillation in
a ferromagnet by the spin Hall effect is of great interest for practical
applications such as microwave generator and neuromorphic computing. However,
both experimental and theoretical works have revealed that only small-amplitude
oscillation around an in-plane easy axis can be excited via the spin Hall
effect. Here, we propose that an out-of-plane oscillation can be excited due to
an assistance of field-like torque. We focus on an in-plane magnetized
ferromagnet with an easy axis parallel to current direction. We notice that the
field-like torque with an appropriate sign provides an additional field
modifying the dynamic trajectory of the magnetization and drives the
auto-oscillation. The condition on the sign of the field-like torque is
satisfied for typical nonmagnet used in spin Hall devices such as tungsten.",2104.04057v1
2021-04-17,Critical dynamics and phase transition of a strongly interacting warm spin-gas,"Phase transitions are emergent phenomena where microscopic interactions drive
a disordered system into a collectively ordered phase. Near the boundary
between two phases, the system can exhibit critical, scale-invariant behavior.
Here, we report on a second-order phase transition accompanied by critical
behavior in a system of warm cesium spins driven by linearly-polarized light.
The ordered phase exhibits macroscopic magnetization when the interactions
between the spins become dominant. We measure the phase diagram of the system
and observe the collective behavior near the phase boundaries, including
power-law dependence of the magnetization and divergence of the susceptibility.
Out of equilibrium, we observe a critical slow-down of the spin response time
by two orders of magnitude, exceeding five seconds near the phase boundary.
This work establishes a controlled platform for investigating equilibrium and
nonequilibrium properties of magnetic phases.",2104.08622v2
2021-04-19,Photoionization of negatively charged NV centers in diamond: theory and ab initio calculations,"We present ab-initio calculations of photoionization thresholds and cross
sections of the negatively charged nitrogen-vacancy (NV) center in diamond from
the ground $^{3}\!A_2$ and the excited $^{3}\!E$ states. We show that after the
ionization from the $^{3}\!E$ level the NV center transitions into the
metastable $^{4}\!A_2$ electronic state of the neutral defect. We reveal how
spin polarization of $\mathrm{NV}^{-}$ gives rise to spin polarization of the
$^{4}\!A_2$ state, providing an explanation of electron spin resonance
experiments. We obtain smooth photoionization cross sections by employing dense
$k$-point meshes for the Brillouin zone integration together with the band
unfolding technique to rectify the distortions of the band structure induced by
artificial periodicity of the supercell approach. Our calculations provide a
comprehensive picture of photoionization mechanisms of $\mathrm{NV}^{-}$. They
will be useful in interpreting and designing experiments on charge-state
dynamics at NV centers. In particular, we offer a consistent explanation of
recent results of spin-to-charge conversion of NV centers.",2104.09144v2
2015-08-01,Spin-Orbit Larmor Clock for Ionisation Times in One-Photon and Strong-Field Regimes,"Photoionisation is a process where absorption of one or several photons
liberates an electron and creates a hole in a quantum system, such as an atom
or a molecule. Is it faster to remove an electron using one or many photons,
and how to define this time? Here we introduce a clock that allows us to define
ionisation time for both one-photon and many-photon ionisation regimes. The
clock uses the interaction of the electron or hole spin with the magnetic field
created by their orbital motion, known as the spin-orbit interaction. The angle
of spin precession in the magnetic field records time. We use the combination
of analytical theory and ab-initio calculations to show how ionisation delay
depends on the number of absorbed photons, how it appears in the experiment and
what electron dynamics it signifies. In particular, we apply our method to
calculate the derived time delays in tunnelling regime of strong-field
ionisation.",1508.00112v3
2015-07-31,Spin Glass Models of Syntax and Language Evolution,"Using the SSWL database of syntactic parameters of world languages, and the
MIT Media Lab data on language interactions, we construct a spin glass model of
language evolution. We treat binary syntactic parameters as spin states, with
languages as vertices of a graph, and assigned interaction energies along the
edges. We study a rough model of syntax evolution, under the assumption that a
strong interaction energy tends to cause parameters to align, as in the case of
ferromagnetic materials. We also study how the spin glass model needs to be
modified to account for entailment relations between syntactic parameters. This
modification leads naturally to a generalization of Potts models with external
magnetic field, which consists of a coupling at the vertices of an Ising model
and a Potts model with q=3, that have the same edge interactions. We describe
the results of simulations of the dynamics of these models, in different
temperature and energy regimes. We discuss the linguistic interpretation of the
parameters of the physical model.",1508.00504v1
2015-08-04,Acoustic signatures of the phases and phase transitions in Yb$_2$Ti$_2$O$_7$,"We report on measurements of the sound velocity and attenuation in a single
crystal of the candidate quantum- spin-ice material Yb$_2$Ti$_2$O$_7$ as a
function of temperature and magnetic field. The acoustic modes couple to the
spins magneto-elastically and, hence, carry information about the spin
correlations that sheds light on the intricate magnetic phase diagram of
Yb$_2$Ti$_2$O$_7$ and the nature of spin dynamics in the material.
Particularly, we find a pronounced thermal hysteresis in the acoustic data with
a concomitant peak in the specific heat indicating a possible first-order phase
transition at about $0.17$ K. At low temperatures, the acoustic response to
magnetic field saturates hinting at the development of magnetic order.
Furthermore, mean-field calculations suggest that Yb$_2$Ti$_2$O$_7$ undergoes a
first-order phase transition from a cooperative paramagnetic phase to a
ferromagnet below $T\approx 0.17$ K.",1508.00925v1
2015-08-14,Spin correlations and entanglement in partially magnetised ensembles of fermions,"We show that the singlet fraction $p_s$ and total magnetisation (or
polarisation) $m$ can bound the minimum concurrence in an ensemble of spins. We
identify $p_s > (1-m^2)/2$ as a sufficient and tight condition for bipartite
entanglement. Our proof makes no assumptions about the state of the system or
symmetry of the particles, and can therefore be used as a witness for spin
entanglement between fermions. We discuss the implications for recent
experiments in which spin correlations were observed, and the prospect to study
entanglement dynamics in the demagnetisation of a cold Fermi gas.",1508.03570v2
2015-08-26,On the theory of proton solid echo in polymer melts,"Based on a modified Anderson-Weiss approximation (N. Fatkullin, A.
Gubaidullin, C. Mattea, S.Stapf, J. Chem. Phys. 137 (2012), 224907) an improved
theory of proton spin solid echo in polymer melts is formulated, taking into
account contribution from intermolecular magnetic dipole-dipole interactions.
The solid echo build-up function defined by the relation , where , and are the
respective signals arising from ( ),( ) and ( ) spin echo experiments, where is
an operator rotating the spin system on the angle relatively axis , is
investigated. It is shown that the intermolecular part of this function at
short times , where is a characteristic time for flip-flop transitions between
proton spins, contains information about the relative mean squared
displacements of polymer segments at different macromolecules, opening up a new
opportunity for obtaining information about polymer dynamics in the millisecond
regime.",1508.06487v1
2016-03-03,Cloaking the magnons,"We propose two approaches to cloak the spin waves (magnons) by investigating
magnetization dynamics. One approach is based on a spatially inhomogeneous
anisotropic magnetic moment tensor. The other mechanism is using a spatially
inhomogeneous anisotropic gyromagnetic factor tensor and an inhomogeneous
external magnetic field. For both approaches, the damping tensor is also
inhomogeneous and anisotropic. The magnetic characteristic functions of the
magnetic materials have been theoretically derived for both mechanisms. A
non-magnetic core, which prevents magnons from entering and consequently
distorts the spin wave propagation, can be cloaked by a structured magnetic
shell to redirect the spin wave around the core using the above design
mechanisms. We discuss the feasibility of the proposed mechanisms in an
ensemble of quantum dot molecules and magnetic semiconductors. The proposed
approaches shed light on transformation magnonics, and can be utilized for
future spin-wave lenses, concentrators, low back-scattering waveguides, and
ultimately quantum computing.",1603.01000v1
2016-03-04,Stochastic Boltzmann Equation for Magnetic Relaxation in High-Spin Molecules,"We introduce the stochastic Boltzmann equation (SBE) as an approach for
exploring the spin dynamics of magnetic molecules coupled to a stochastic
environment. The SBE is a time-evolution equation for the probability density
of the spin density matrix of the system. This probability density is relevant
to experiments which take measurements on single molecules, in which
probabilities of observing particular spin states (rather than ensemble
averages) are of interest. By analogy with standard treatments of the regular
Boltzmann equation, we propose a relaxation-time approximation for the SBE, and
show that solutions to the SBE under the relaxation-time approximation can be
obtained by performing simple trajectory simulations for the case of a boson
gas environment. Cases where the relaxation-time approximation are satisfied
can therefore be investigated by careful choice of the parameters for the boson
gas environment, even if the actual environment is quite different from a boson
gas. The application of the SBE approach is demonstrated through an
illustrative example.",1603.01320v1
2016-03-10,Quantum Zeno subspaces by repeated multi-spin projections,"Repeated observations inhibit the coherent evolution of quantum states
through the quantum Zeno effect. In multi-qubit systems this effect provides
new opportunities to control complex quantum states. Here, we experimentally
demonstrate that repeatedly projecting joint observables of multiple spins
creates coherent quantum Zeno subspaces and simultaneously suppresses dephasing
caused by the environment. We encode up to two logical qubits in these
subspaces and show that the enhancement of the dephasing time with increasing
number of projections follows a scaling law that is independent of the number
of spins involved. These results provide new insights into the interplay
between frequent multi-spin measurements and non-Markovian noise and pave the
way for tailoring the dynamics of multi-qubit systems through repeated
projections.",1603.03368v1
2016-03-14,Merging droplets in double nano-contact spin torque oscillators,"We demonstrate how magnetic droplet soliton pairs, nucleated by two separated
nano-contact (NC) spin torque oscillators, can merge into a single droplet
soliton. A detailed description of the magnetization dynamics of this merger
process is obtained by micromagnetic simulations: A droplet pair with a
steady-state in-phase spin precession is generated through the spin-transfer
torque effect underneath two separate NCs, followed by a gradual expansion of
the droplets volume and the out phase of magnetization on the inner side of the
two droplets, resulting in the droplets merging into a larger droplet. This
merger occurs only when the NC separation is smaller than a critical value. A
transient breathing mode is observed before the merged droplet stabilizes into
a steady precession state. The precession frequency of the merged droplet is
lower than that of the droplet pair, consistent with its larger size. Merged
droplets can again break up into droplet pairs at high enough magnetic field
with a strong hysteretic response.",1603.04133v1
2016-03-24,Voltage induced switching dynamics of a coupled spin pair in a molecular junction,"Molecular spintronics is made possible by the coupling between electronic
configuration and magnetic po- larization of the molecules. For control and
application of the individual molecular states it is necessary to both read and
write their spin states. Conventionally, this is achieved by means of external
magnetic fields or ferromagnetic contacts, which may change the intentional
spin state and may present additional challenges when downsizing devices. Here,
we predict that coupling magnetic molecules together opens up possibilities for
all electrical control of both the molecular spin states as well as the current
flow through the system. Tuning between the regimes of ferromagnetic and
anti-ferromagnetic exchange interaction, the current can be, at least, an order
of magnitude enhanced or reduced. The effect is susceptible to the tunnel
coupling and molecular level alignment which can be used to achieve current
rectification.",1603.07652v1
2015-07-24,First-principles approach to the dynamic magnetoelectric couplings in BiFeO$_3$,"Despite its great technological importance, the magnetoelectric (ME)
couplings in \BF are barely understood. By using a first-principles approach,
we uncover the {\it dynamic} ME couplings of the long-range spin-cycloid in
BiFeO$_3$. Based on a microscopic Hamiltonian, our first-principles approach
disentangles the hidden ME couplings due to spin-current and
exchange-striction. Beyond the spin-current polarization governed by the
inverse Dzyaloshinskii-Moriya interaction \cite{iDM}, various spin-current
polarizations derived from both ferroelectric and antiferrodistortive
distortions cooperatively produce the strong non-reciprocal directional
dichroism or the asymmetry in the absorption of counter-propagating light in
BiFeO$_3$. Our systematic approach can be generally applied to any multiferroic
material, laying the foundation for revealing hidden ME couplings on an atomic
scale and for exploiting optical ME effects in the next generation of
technological devices such as optical diodes.",1603.09576v1
2016-10-03,Linear dynamics of classical spin as Möbius transformation,"Although the overwhelming majority of natural processes occurs far from the
equilibrium, general theoretical approaches to non-equilibrium phase
transitions remain scarce. Recent breakthroughs introducing description of open
dissipative systems in terms of non-Hermitian quantum mechanics allowed to
identify a class of non-equilibrium phase transitions associated with the loss
of combined parity (reflection) and time-reversal symmetries. Here we report
that time evolution of a single classical spin (e.g. monodomain ferromagnet)
governed by the Landau-Lifshitz-Gilbert-Slonczewski equation in absence of
higher-order anisotropy terms is described by a M\""{o}bius transformation in
complex stereographic coordinates. We identify the \textit{parity-time}
symmetry-breaking phase transition occurring in spin-transfer torque-driven
linear spin systems as a transition between hyperbolic and loxodromic classes
of M\""{o}bius transformations, with the critical point of the transition
corresponding to the parabolic transformation. This establishes the
understanding of non-equilibrium phase transitions as topological transitions
in configuration space.",1610.00762v1
2016-10-14,Electric-field tunable spin waves in PMN-PT/NiFe heterostructure: experiment and micromagnetic simulations,"We present a comprehensive theoretical and experimental study of
voltage-controlled standing spin waves resonance (SSWR) in PMN-PT/NiFe
multiferroic heterostructures patterned into microstrips. A spin-diode
technique was used to observe ferromagnetic resonance (FMR) mode and SSWR in
NiFe strip mechanically coupled with a piezoelectric substrate. Application of
an electric field to a PMNPT creates a strain in permalloy and thus shifts the
FMR and SSWR fields due to the magnetostriction effect. The experimental
results are compared with micromagnetic simulations and a good agreement
between them is found for dynamics of FMR and SSWR with and without electric
field. Moreover, micromagnetic simulations enable us to discuss the amplitude
and phase spatial distributions of FMR and SSWR modes, which are not directly
observable by means of spin diode detection technique.",1610.04500v1
2016-10-28,Spin-Orbit Torque Efficiency in Compensated Ferrimagnetic Cobalt-Terbium Alloys,"Despite the potential advantages of information storage in
antiferromagnetically coupled materials, it remains unclear whether one can
control the magnetic moment orientation efficiently because of the cancelled
magnetic moment. Here, we report spin-orbit torque induced magnetization
switching of ferrimagnetic Co1-xTbx films with perpendicular magnetic
anisotropy. Current induced switching is demonstrated in all of the studied
film compositions, including those near the magnetization compensation point.
The spin-orbit torque induced effective field is further quantified in the
domain wall motion regime. A divergent behavior that scales with the inverse of
magnetic moment is confirmed close to the compensation point, which is
consistent with angular momentum conservation. Moreover, we also quantify the
Dzyaloshinskii-Moriya interaction energy in the Ta/Co1-xTbx system and we find
that the energy density increases as a function of the Tb concentration. The
demonstrated spin-orbit torque switching, in combination with the fast magnetic
dynamics and minimal net magnetization of ferrimagnetic alloys, promises
spintronic devices that are faster and with higher density than traditional
ferromagnetic systems.",1610.09200v1
2016-12-06,Nuclear spin relaxation in n-GaAs: from insulating to metallic regime,"Nuclear spin relaxation is studied in n-GaAs thick layers and microcavity
samples with different electron densities. We reveal that both in metallic
samples where electrons are free and mobile, and in insulating samples, where
electrons are localized, nuclear spin relaxation is strongly enhanced at low
magnetic field. The origin of this effect could reside in the quadrupole
interaction between nuclei and fluctuating electron charges, that has been
proposed to drive nuclear spin dynamics at low magnetic fields in the
insulating samples. The characteristic values of these magnetic fields are
given by dipole-dipole interaction between nuclei in bulk samples, and are
greatly enhanced in microcavities, presumably due to additional strain,
inherent to micro and nanostructures.",1612.01699v2
2016-12-15,Exploring Localization in Nuclear Spin Chains,"Characterizing out-of-equilibrium many-body dynamics is a complex but crucial
task for quantum applications and the understanding of fundamental phenomena. A
central question is the role of localization in quenching quantum
thermalization, and whether localization survives in the presence of
interactions. The localized phase of interacting systems (many-body
localization, MBL) exhibits a long-time logarithmic growth in entanglement
entropy that distinguishes it from the noninteracting Anderson localization
(AL), but entanglement is difficult to measure experimentally. Here, we present
a novel correlation metric, capable of distinguishing MBL from AL in
high-temperature spin systems. We demonstrate the use of this metric to detect
localization in a natural solidstate spin system using nuclear magnetic
resonance (NMR). We engineer the natural Hamiltonian to controllably introduce
disorder and interactions and observe the emergence of localization. In
particular, while our correlation metric saturates for AL, it keeps increasing
logarithmically for MBL, a behavior reminiscent of entanglement entropy, as we
confirm by simulations. Our results show that our NMR techniques, akin to
measuring out-of-time correlations, are well suited for studying localization
in spin systems.",1612.05249v1
2017-07-05,Thermodynamics of the pyrochlore Heisenberg ferromagnet with arbitrary spin $S$,"We use the rotation-invariant Green's function method (RGM) and the
high-temperature expansion (HTE) to study the thermodynamic properties of the
spin-$S$ Heisenberg ferromagnet on the pyrochlore lattice. We examine the
excitation spectra as well as various thermodynamic quantities, such as the
order parameter (magnetization), the uniform static susceptibility, the
correlation length, the spin-spin correlations, and the specific heat, as well
as the static and dynamic structure factors. We discuss the influence of the
spin quantum number $S$ on the temperature dependence of these quantities. We
compare our results for the pyrochlore ferromagnet with the corresponding ones
for the simple-cubic lattice both having the same coordination number $z=6$. We
find a significant suppression of magnetic ordering for the pyrochlore lattice
due to its geometry with corner-sharing tetrahedra.",1707.01529v1
2017-07-08,Spin-Orbit Coupling and Electronic Correlations in Sr2RuO4,"We investigate the interplay of spin-orbit coupling (SOC) and electronic
correlations in Sr2RuO4 using dynamical mean-field theory. We find that SOC
does not affect the correlation-induced renormalizations, which validates the
Hund's metal picture of ruthenates even in the presence of the sizable SOC
relevant to these materials. Nonetheless, SOC found to change significantly the
electronic structure at k-points where a degeneracy applies in its absence. We
explain why these two observations are consistent with one another and
calculate effects of SOC on the correlated electronic structure. The magnitude
of these effects is found to depend on the energy of the quasiparticle state
under consideration, leading us to introduce the notion of an ""energy-dependent
quasiparticle spin-orbit coupling"". This notion is generally applicable to all
materials in which both the spin-orbit coupling and electronic correlations are
sizable.",1707.02462v2
2017-07-11,Spin switching via quantum dot spin valves,"We develop a theory for spin transport and magnetization dynamics in a
quantum-dot spin valve, i.e., two magnetic reservoirs coupled to a quantum dot.
Our theory is able to take into account effects of strong correlations. We
demonstrate that, as a result of these strong correlations, the dot gate
voltage enables control over the current-induced torques on the magnets, and,
in particular, enables voltage-controlled magnetic switching. The electrical
resistance of the structure can be used to read out the magnetic state. Our
model may be realized by a number of experimental systems, including magnetic
scanning-tunneling microscope tips and artificial quantum dot systems.",1707.03373v4
2017-07-18,Quasi-continuous transition from a Fermi liquid to a spin liquid,"The Mott metal-insulator transition-a drastic manifestations of Coulomb
interactions among electrons-is the first-order transition of clear
discontinuity, as shown by various experiments and the celebrated dynamical
mean-field theory. Recent theoretical works, however, suggest that the
transition is continuous if the Mott insulator carries an exotic spin liquid
with a spinon Fermi surface. Here, we demonstrate the case of a
quasi-continuous Mott transition from a Fermi liquid to a spin liquid in an
organic triangular-lattice system k-(ET)2Cu2(CN)3. Transport experiments
performed under fine pressure tuning find that, as the Mott transition is
approached, the Fermi-liquid coherence temperature continuously falls to the
scale of kelvins with divergent quasi-particle decay rate in the metal side and
the charge gap gradually closes in the insulator side. The Clausius-Clapeyron
analysis of the pressure-temperature phase diagram provides thermodynamic
evidence for the extremely weak first-order nature of the Mott transition.
These results suggest that the spin liquid hosts a spinon Fermi surface, which
turns into an electron Fermi surface when charges are Mott delocalized.",1707.05586v1
2017-11-01,Proposal for the Detection of Magnetic Monopoles in Spin Ice via Nanoscale Magnetometry,"We present a proposal for applying nanoscale magnetometry to the search for
magnetic monopoles in the spin ice materials holmium and dysprosium titanate.
Employing Monte Carlo simulations of the dipolar spin ice model, we find that
when cooled to below $1.5\,$K these materials exhibit a sufficiently low
monopole density to enable the direct observation of magnetic fields from
individual monopoles. At these temperatures we demonstrate that noise
spectroscopy can capture the intrinsic fluctuations associated with monopole
dynamics, allowing one to isolate the qualitative effects associated with both
the Coulomb interaction between monopoles and the topological constraints
implied by Dirac strings. We describe in detail three different nanoscale
magnetometry platforms (muon spin rotation, nitrogen vacancy defects, and
nanoSQUID arrays) that can be used to detect monopoles in these experiments,
and analyze the advantages of each.",1711.00408v1
2017-11-13,"Active SU(1,1) atom interferometry","Active interferometers use amplifying elements for beam splitting and
recombination. We experimentally implement such a device by using spin exchange
in a Bose-Einstein condensate. The two interferometry modes are initially empty
spin states that get spontaneously populated in the process of parametric
amplification. This nonlinear mechanism scatters atoms into both modes in a
pairwise fashion and generates a nonclassical state. Finally, a matched second
period of spin exchange is performed that nonlinearly amplifies the output
signal and maps the phase onto readily detectable first moments. Depending on
the accumulated phase this nonlinear readout can reverse the initial dynamics
and deamplify the entangled state back to empty spin states. This sequence is
described in the framework of SU(1,1) mode transformations and compared to the
SU(2) angular momentum description of passive interferometers.",1711.04552v1
2017-11-16,A Microscopic Explanation of Microwave Spin Pumping,"We contend that Microwave Spin Pumping was first predicted and observed -
albeit using a different and more sensitive detection mechanism than Inverse
Spin Hall Effect - in the 1950's. This discovery was the founding step in the
widely used analytical tool that is now known as Dynamic Nuclear Polarisation.
Recognising this hitherto unsung connection between 20th Century Magnetic
Resonance and 21st Century Spintronics not only helps to explain and unify
contemporary metallic spin pumping observations: it is also the key to
unlocking the immense and very sophisticated toolbox of Magnetic Resonance and
placing it at the disposal of the future of Spintronics.",1711.06048v3
2017-11-18,Topological edge states and pumping in a chain of coupled superconducting qubits,"Topological insulators have inspired the study with various quantum
simulators. Exploiting the tunability of the qubit frequency and qubit-qubit
coupling, we show that a superconducting qubit chain can simulate various
topological band models. When the system is restricted to the single-spin
excitation subspace, the Su-Schrieffer-Heeger (SSH) model can be equivalently
simulated by alternating the coupling strength between neighboring qubits. The
existence of topological edge states in this qubit chain is demonstrated in the
quench dynamics after the first qubit is excited. This excitation propagates
along the chain where the qubit-qubit coupling is homogeneous. In contrast, in
our qubit chain, the spin-up state localizes at the first qubit and the rest
qubits remain in the spin-down state. We further show that the spin-up state
can be transported along the chain by modulating the coupling strengths and the
qubit frequencies. This demonstrates adiabatic pumping based on the Rice-Mele
model. Moreover, we also discuss possible ways to construct other topological
models with different topological phenomena within the current technology of
superconducting qubits.",1711.06829v1
2017-11-29,Complete many-body localization in the t-J model caused by random magnetic field,"The many body localization (MBL) of spin-1/2 fermions poses a challenging
problem. It is known that the disorder in the charge sector may be insufficient
to cause full MBL. Here, we study dynamics of a single hole in one dimensional
t-J model subject to a random magnetic field. We show that strong disorder that
couples only to the spin sector localizes both spin and charge degrees of
freedom. Charge localization is confirmed also for a finite concentration of
holes. While we cannot precisely pinpoint the threshold disorder, we conjecture
that there are two distinct transitions. Weaker disorder first causes
localization in the spin sector. Carriers become localized for somewhat
stronger disorder, when the spin localization length is of the order of a
single lattice spacing.",1711.10956v1
2018-10-02,Microwave preparation of two-dimensional fermionic spin mixtures,"We present a method for preparing a single two-dimensional sample of a
two-spin mixture of fermionic potassium in a single antinode of an optical
lattice, in a quantum-gas microscope apparatus. Our technique relies on
spatially-selective microwave transitions in a magnetic field gradient.
Adiabatic transfer pulses were optimized for high efficiency and minimal atom
loss and heating due to spin-changing collisions. We have measured the dynamics
of those loss processes, which are more pronounced in the presence of a spin
mixture. As the efficient preparation of atoms in a single antinode requires a
homogeneous transverse magnetic field, we developed a method to image and
minimize the magnetic field gradients in the focal plane of the microscope.",1810.01434v2
2018-10-05,Asymptotic Freedom and Large Spin Antiferromagnetic Chains,"Building on the mapping of large-$S$ spin chains onto the O($3$) nonlinear
$\sigma$ model with coupling constant $2/S$, and on general properties of that
model (asymptotic freedom, implying that perturbation theory is valid at high
energy, and Elitzur's conjecture that rotationally invariant quantities are
infrared finite in perturbation theory), we use the Holstein-Primakoff
representation to derive analytic expressions for the equal-time and dynamical
spin-spin correlations valid at distances smaller than $S^{-1} \exp(\pi S)$ or
at energies larger than $J S^2 \exp(-\pi S)$, where $J$ is the Heisenberg
exchange coupling. This is supported by comparing the static correlations with
quantum Monte Carlo simulations for $S = 5/2$.",1810.02626v2
2018-10-09,Non-uniform spin wave softening in 2D magnonic crystals as a tool for opening omnidirectional magnonic band gaps,"By means of the plane wave method we study spin wave dynamics in
two-dimensional bi-component magnonic crystals based on a squeezed hexagonal
lattice and consist of a permalloy thin film with cobalt inclusions. We explore
the dependence of a spin wave frequency on the external magnetic field,
especially in weak fields where the mode softening takes place. For considered
structures, the mode softening proves to be highly non-uniform on both the mode
number and the wave vector. We found this effect to be responsible for the
omnidirectional band gap opening. Moreover, we show that the enhancement of the
demagnetizing field caused by the squeezing of the structure is of crucial
importance for the non-uniform mode softening. This allows us to employ this
mechanism to design magnonic gaps with different sensitivity for the tiny
change of the external field. The effects we have found should be useful in
designing and optimization of spin wave filters highly tunable by a small
external magnetic field.",1810.04005v3
2018-10-19,Quantum simulation of multiphoton and nonlinear dissipative spin-boson models,"We present a framework for the realization of dissipative evolutions of
spin-boson models, including multiphoton exchange dynamics, as well as
nonlinear transition rates. Our approach is based on the implementation of a
generalized version of a dissipative linear quantum Rabi model. The latter
comprises a linearly coupled spin-boson term, spin rotations, and standard
dissipators. We provide numerical simulations of illustrative cases supporting
the good performance of our method. Our work allows for the simulation of a
large class of fundamentally different quantum models where the effect of
distinct dissipative processes can be easily investigated.",1810.08465v3
2018-10-25,Scattering amplitudes as multi-particle higher-spin charges in the correspondence space,"Following the proposal of arXiv:1312.6673, multi-particle scattering
amplitudes are represented as conserved higher-spin charges. The advantage of
such reformulation is that multi-particle amplitudes acquire the form of an
integral of a closed form in the correspondence unifying usual space-time with
the twistor-like spinor space. This allows one to identify seemingly different
formulae for amplitudes in terms of twistor and space-time integrals. Example
of tree MHV amplitudes of Yang-Mills theory is considered in detail. Our
results are derived using unfolded dynamics formulation of massless fields. In
these terms all information on the amplitude is contained in a single function
$\eta$ that, even for lower spin amplitudes, can be interpreted as a
higher-spin symmetry parameter. The proposed technique can be useful to relate
different approaches to amplitude calculations.",1810.11140v1
2019-05-02,Probing quantum criticality and symmetry breaking at the microscopic level,"We report on an experimental study of the Lipkin-Meshkov-Glick model of
quantum spins interacting at infinite range in a transverse magnetic field,
which exhibits a ferromagnetic phase transition in the thermodynamic limit. We
use Dysprosium atoms of electronic spin $J=8$, subjected to a quadratic Zeeman
light shift, to simulate $2J=16$ interacting spins $1/2$. We probe the system
microscopically using single magnetic sublevel resolution, giving access to the
spin projection parity, which is the collective observable characterizing the
underlying $\mathbb{Z}_2$ symmetry. We measure the thermodynamic properties and
dynamical response of the system, and study the quantum critical behavior
around the transition point. In the ferromagnetic phase, we achieve coherent
tunneling between symmetry-broken states, and test the link between symmetry
breaking and the appearance of a finite order parameter.",1905.00807v1
2019-05-23,Cluster integrable systems and spin chains,"We discuss relation between the cluster integrable systems and spin chains in
the context of their correspondence with 5d supersymmetric gauge theories. It
is shown that $\mathfrak{gl}_N$ XXZ-type spin chain on $M$ sites is isomorphic
to a cluster integrable system with $N \times M$ rectangular Newton polygon and
$N \times M$ fundamental domain of a 'fence net' bipartite graph. The Casimir
functions of the Poisson bracket, labeled by the zig-zag paths on the graph,
correspond to the inhomogeneities, on-site Casimirs and twists of the chain,
supplemented by total spin. The symmetricity of cluster formulation implies
natural spectral duality, relating $\mathfrak{gl}_N$-chain on $M$ sites with
the $\mathfrak{gl}_M$-chain on $N$ sites. For these systems we construct
explicitly a subgroup of the cluster mapping class group
$\mathcal{G}_\mathcal{Q}$ and show that it acts by permutations of zig-zags
and, as a consequence, by permutations of twists and inhomogeneities. Finally,
we derive Hirota bilinear equations, describing dynamics of the tau-functions
or A-cluster variables under the action of some generators of
$\mathcal{G}_\mathcal{Q}$.",1905.09921v1
2019-05-27,Particle motion near high-spin black holes,"General relativity predicts that the Kerr black hole develops qualitatively
new and surprising features in the limit of maximal spin. Most strikingly, the
region of spacetime near the event horizon stretches into an infinitely long
throat and displays an emergent conformal symmetry. Understanding dynamics in
this NHEK (Near-Horizon Extreme Kerr) geometry is necessary for connecting
theory to upcoming astronomical observations of high-spin black holes. We
review essential properties of NHEK and its relationship to the rapidly
rotating Kerr black hole. We then completely solve the geodesic equation in the
NHEK region and describe how the resulting trajectories transform under the
action of its enhanced symmetries. In the process, we derive explicit
expressions for the angular integrals appearing in the Kerr geodesic equation
and obtain a useful formula, valid at arbitrary spin, for a particle's polar
angle in terms of its radial motion. These results will aid in the analytic
computation of astrophysical observables relevant to ongoing and future
experiments.",1905.11406v2
2019-05-29,Experimental Hamiltonian Learning of An 11-qubit Solid-State Quantum Spin Register,"Learning Hamiltonian of a quantum system is indispensable for prediction of
the system dynamics and realization of high fidelity quantum gates. However, it
is a significant challenge to efficiently characterize the Hamiltonian when its
Hilbert space dimension grows exponentially with the system size. Here, we
experimentally demonstrate an adaptive method to learn the effective
Hamiltonian of an 11-qubit quantum system consisting of one electron spin and
ten nuclear spins associated with a single Nitrogen-Vacancy center in a
diamond. We validate the estimated Hamiltonian by designing universal quantum
gates based on the learnt Hamiltonian parameters and demonstrate high-fidelity
gates in experiment. Our experimental demonstration shows a well-characterized
11-qubit quantum spin register with the ability to test quantum algorithms and
to act as a multi-qubit single node in a quantum network.",1905.12248v1
2019-06-03,Dynamics and field-induced order in the layered spin $S=1/2$ dimer system (C$_5$H$_6$N$_2$F)$_2$CuCl$_4$,"The quasi-two-dimensional Heisenberg spin $S=1/2$ dimer system
bis(2-amino-5-fluoro-pyridinium) tetrachlorocuprate(II) is studied by means of
inelastic neutron scattering, calorimetry and nuclear magnetic resonance (NMR)
experiments. In the absence of an applied magnetic field we find dispersive
triplet excitations with a spin gap of $\Delta=1.112(15)$ meV and a bandwidth
of $0.715(15)$ meV within the layers and $0.116(15)$ meV between the layers,
respectively. In an applied magnetic field of $\mu_0H_c\approx 8.5$ T the spin
gap is closed and we find a field induced antiferromagnetically ordered phase.",1906.00602v2
2019-06-04,125Te-NMR Study on a Single Crystal of Heavy Fermion Superconductor UTe2,"We report 125Te-NMR studies on a newly discovered heavy fermion
superconductor UTe2. Using a single crystal, we have measured the 125Te-NMR
Knight shift K and spin-lattice relaxation rate 1/T1 for fields along the three
orthorhombic crystal axes. The data confirm a moderate Ising anisotropy for
both the static (K) and dynamical susceptibilities (1/T1) in the paramagnetic
state above about 20 K. Around 20 K, however, we have observed a sudden loss of
NMR spin-echo signal due to sudden enhancement of the NMR spin-spin relaxation
rate 1/T2, when the field is applied along the easy axis of magnetization (=a
axis). This behavior suggests the development of longitudinal magnetic
fluctuations along the a axis at very low frequencies below 20 K.",1906.01303v1
2019-06-06,Hyperbolic spin Ruijsenaars-Schneider model from Poisson reduction,"We derive a Hamiltonian structure for the $N$-particle hyperbolic spin
Ruijsenaars-Schneider model by means of Poisson reduction of a suitable initial
phase space. This phase space is realised as the direct product of the
Heisenberg double of a factorisable Lie group with another symplectic manifold
that is a certain deformation of the standard canonical relations for $N\ell$
conjugate pairs of dynamical variables. We show that the model enjoys the
Poisson-Lie symmetry of the spin group ${\rm GL}_{\ell}({\mathbb C})$ which
explains its superintegrability. Our results are obtained in the formalism of
the classical $r$-matrix and they are compatible with the recent findings on
the different Hamiltonian structure of the model established in the framework
of the quasi-Hamiltonian reduction applied to a quasi-Poisson manifold.",1906.02619v2
2019-06-11,Discovery of ST1 centers in natural diamond,"The ST1 center is a point defect in diamond with bright fluorescence and a
mechanism for optical spin initialization and readout. The center has
impressive potential for applications in diamond quantum computing as a quantum
bus to a register of nuclear spins. This is because it has an exceptionally
high readout contrast and, unlike the well-known nitrogen-vacancy center, it
does not have a ground state electronic spin that decoheres the nuclear spins.
However, its chemical structure is unknown and there are large gaps in our
understanding of its properties. We present the discovery of ST1 centers in
natural diamond. Our experiments identify interesting power dependence of the
center's optical dynamics and reveal new electronic structure. We also present
a theory of its electron-phonon interactions, which we combine with previous
experiments, to shortlist likely candidates for its chemical structure.",1906.04385v2
2019-06-19,Edge localization of spin waves in antidot multilayers with perpendicular magnetic anisotropy,"We study the spin-wave dynamics in nanoscale antidot lattices based on Co/Pd
multilayers with perpendicular magnetic anisotropy. Using time-resolved
magneto-optical Kerr effect measurements we demonstrate that the variation of
the antidot shape introduces significant change in the spin-wave spectra,
especially in the lower frequency range. By employing micromagnetic simulations
we show that additional peaks observed in the measured spectra are related to
narrow shell regions around the antidots, where the magnetic anisotropy is
reduced due to the Ga+ ion irradiation during the focused ion beam milling
process of the antidot fabrication. The results point at new possibilities for
exploitation of localized spin waves in out-of-plane magnetized thin films,
which are easily tunable and suitable for magnonics applications.",1906.08109v2
2020-02-28,Purcell enhancement of a single silicon carbide color center with coherent spin control,"Silicon carbide has recently been developed as a platform for optically
addressable spin defects. In particular, the neutral divacancy in the 4H
polytype displays an optically addressable spin-1 ground state and
near-infrared optical emission. Here, we present the Purcell enhancement of a
single neutral divacancy coupled to a photonic crystal cavity. We utilize a
combination of nanolithographic techniques and a dopant-selective
photoelectrochemical etch to produce suspended cavities with quality factors
exceeding 5,000. Subsequent coupling to a single divacancy leads to a Purcell
factor of ~50, which manifests as increased photoluminescence into the
zero-phonon line and a shortened excited-state lifetime. Additionally, we
measure coherent control of the divacancy ground state spin inside the cavity
nanostructure and demonstrate extended coherence through dynamical decoupling.
This spin-cavity system represents an advance towards scalable long-distance
entanglement protocols using silicon carbide that require the interference of
indistinguishable photons from spatially separated single qubits.",2003.00042v1
2020-03-24,A spiking neuron constructed by the skyrmion-based spin torque nano-oscillator,"Magnetic skyrmions are particle-like topological spin configurations, which
can carry binary information and thus are promising building blocks for future
spintronic devices. In this work, we investigate the relationship between the
skyrmion dynamics and the characteristics of injected current in a
skyrmion-based spin torque nano-oscillator, where the excitation source is
introduced from a point nano-contact at the center of the nanodisk. It is found
that the skyrmion will move away from the center of the nanodisk if it is
driven by a spin-polarized current; however, it will return to the initial
position in the absence of stimulus. Therefore, we propose a skyrmion-based
artificial spiking neuron, which can effectively implement the
leaky-integrate-fire operation. We study the feasibility of the skyrmion-based
spiking neuron by using micromagnetic simulations. Our results may provide
useful guidelines for building future magnetic neural networks with ultra-high
density and ultra-low energy consumption.",2003.10651v1
2020-06-01,Spin squeezing with short-range spin-exchange interactions,"We investigate many-body spin squeezing dynamics in an XXZ model with
interactions that fall off with distance $r$ as $1/r^\alpha$ in $D=2$ and $3$
spatial dimensions. In stark contrast to the Ising model, we find a broad
parameter regime where spin squeezing comparable to the infinite-range
$\alpha=0$ limit is achievable even when interactions are short-ranged,
$\alpha>D$. A region of ""collective"" behavior in which optimal squeezing grows
with system size extends all the way to the $\alpha\to\infty$ limit of
nearest-neighbor interactions. Our predictions, made using the discrete
truncated Wigner approximation (DTWA), are testable in a variety of
experimental cold atomic, molecular, and optical platforms.",2006.00723v3
2020-06-12,Real-time modelling of Optical orientation in GaAs: generation and decay of the degree of spin polarization,"We present a real-time abinitio description of optical orientation in bulk
GaAs due to the coupling with an ultrashort circular polarized laser source.
The injection of spin polarized electrons in the conduction band is correctly
reproduced, and a non vanishing spin polarization ($\mathbf{P}$) parallel to
the direction of propagation of the laser ($z$) emerges. A detailed analysis of
the generation and the evolution of $\mathbf{P}(t)$ is discussed. The single
$\mathbf{k}$-point dynamics is a motion of precession around a fixed axis with
constant $|\mathbf{P}|$ and fixed frequency. Instead, the
$\mathbf{k}$-integrated signal shows only a time dependent $P_z(t)$ and decays
few pico seconds after the end of the laser pump due to decoherence.
Decoherence emerges since the individual contributions activated by the pump
give rise to destructive interference. We interpret the results in terms of the
\emph{free induction decay} mechanism proposed some years ago. For the first
time we are able to reproduce such effect in a full abinitio fashion, giving a
quantitative estimate of the associated decay time. Our result also shows a
possible explanation to the time decay of spin magnetization observed in many
real-time abinitio simulations.",2006.07241v1
2020-06-14,Hypersonic heat-induced flows of magnons induced by femtosecond laser pulses,"In this work, we present evidence for the existence of a magnonic current on
the sub-picosecond time-scale in a ferrimagnetic bilayer and its effect on
ultrafast spin dynamics. The ferrimagnet, GdFeCo, is a material known to
undergo ultrafast switching within 1-2ps after excitation with femtosecond
laser pulses. Here, we show that the strong thermal gradients induced by
applying femtosecond laser pulses and the presence of chemical inhomogeneities
lead to local imbalances in the effective temperatures of the spins that
produces a rapid transfer of spin angular momentum, which we interpret as an
ultrafast spin Seebeck effect. We have quantified the typical magnon
propagation in such a system. The results show ballistic magnon propagation
with 30nm/ps velocities. The characteristic time scale of such magnon
propagation indicates that this magnon transport can play an important role in
switching, a crucial piece of understanding towards realising next generation
data processing devices that operate at much higher frequencies.",2006.07935v1
2020-09-03,Realization of a Bosonic Antiferromagnet,"Quantum antiferromagnets are of broad interest in condensed matter physics as
they provide a platform for studying exotic many-body states including spin
liquids and high-temperature superconductors. Here, we report on the creation
of a one-dimensional Heisenberg antiferromagnet with ultracold bosons. In a
two-component Bose-Hubbard system, we switch the sign of the spin-exchange
interaction and realize the isotropic antiferromagnetic Heisenberg model in an
extended 70-site chain. Starting from a low-entropy N\'eel-ordered state, we
use optimized adiabatic passage to approach the bosonic antiferromagnet. We
demonstrate the establishment of antiferromagnetism by probing the evolution of
the staggered magnetization and spin correlations of the system. Compared with
condensed matter systems, ultracold gases in optical lattices can be
microscopically engineered and measured, offering significant advantages for
exploring bosonic magnetism and spin dynamics.",2009.01426v2
2020-09-06,Intersystem Crossing and Exciton-Defect Coupling of Spin Defects in Hexagonal Boron Nitride,"Despite the recognition of two-dimensional (2D) systems as emerging and
scalable host materials of single photon emitters or spin qubits, uncontrolled
and undetermined chemical nature of these quantum defects has been a roadblock
to further development. Leveraging the design of extrinsic defects can
circumvent these persistent issues and provide an ultimate solution. Here we
established a complete theoretical framework to accurately and systematically
design quantum defects in wide-bandgap 2D systems. With this approach,
essential static and dynamical properties are equally considered for spin qubit
discovery. In particular, many-body interactions such as defect-exciton
couplings are vital for describing excited state properties of defects in
ultrathin 2D systems. Meanwhile, nonradiative processes such as phonon-assisted
decay and intersystem crossing rates require careful evaluation, which compete
together with radiative processes. From a thorough screening of defects based
on first-principles calculations, we identify promising single photon emitters
such as SiVV and spin qubits such as TiVV and MoVV in hexagonal boron nitride.
This work provided a complete first-principles theoretical framework for defect
design in 2D materials.",2009.02830v2
2020-09-28,Spin-orbit coupling and linear crossings of dipolar magnons in van der Waals antiferromagnets,"A magnon spin-orbit coupling, induced by the dipole-dipole interaction, is
derived in monoclinic-stacked bilayer honeycomb spin lattice with perpendicular
magnetic anisotropy and antiferromagnetic interlayer coupling. Linear crossings
are predicted in the magnon spectrum around the band minimum in G valley, as
well as in the high frequency range around the zone boundary. The linear
crossings in K and K' valleys, which connect the acoustic and optical bands,
can be gapped when the intralayer dipole-dipole or Kitaev interactions exceed
the interlayer dipole-dipole interaction, resulting in a phase transition from
semimetal to insulator. Our results are useful for analyzing the magnon spin
dynamics and transport properties in van der Waals antiferromagnet.",2009.13660v1
2020-09-30,Spin-diffusion model for micromagnetics in the limit of long times,"In this paper, we consider spin-diffusion Landau-Lifshitz-Gilbert equations
(SDLLG), which consist of the time-dependent Landau-Lifshitz-Gilbert (LLG)
equation coupled with a time-dependent diffusion equation for the electron spin
accumulation. The model takes into account the diffusion process of the spin
accumulation in the magnetization dynamics of ferromagnetic multilayers. We
prove that in the limit of long times, the system reduces to simpler equations
in which the LLG equation is coupled to a nonlinear and nonlocal steady-state
equation, referred to as SLLG. As a by-product, the existence of global weak
solutions to the SLLG equation is obtained. Moreover, we prove weak-strong
uniqueness of solutions of SLLG, i.e., all weak solutions coincide with the
(unique) strong solution as long as the latter exists in time. The results
provide a solid mathematical ground to the qualitative behavior originally
predicted by Zhang, Levy, and Fert in [Physical Review Letters 88 (2002)] in
ferromagnetic multilayers.",2009.14534v1
2021-01-25,Antiferromagnetic State in $κ$-type Molecular Conductors: Spin Splitting and Mott Gap,"We numerically investigate the dynamical properties of $\kappa$-type
molecular conductors in their antiferromagnetic Mott insulating state. By
treating the extended Hubbard model on the two-dimensional $\kappa$-type
lattice within the Lanzcos exact diagonalization method, we calculate the
one-particle spectral function $A(\boldsymbol{k}, \omega)$ and the optical
absorption spectra taking advantage of twisted boundary conditions. We find
spin splitting in $A(\boldsymbol{k}, \omega)$ predicted by a previous
Hartree-Fock study [M. Naka et al., Nat. Commun. 10, 4305 (2019)]; namely,
their up- and down-spin components become different in the general
$\boldsymbol{k}$-points of the Brillouin zone, even without the spin-orbit
coupling. Furthermore, we demonstrate the variation in the optical properties
near the Mott gap by the presence or absence of the antiferromagnetic order,
tuned by a small staggered magnetic field.",2101.09883v2
2021-02-02,Vector currents of integer-spin Majorana particles,"A general and comprehensive analysis for the vector currents of two massive
particles, $X_2$ and $X_1$, with arbitrary integer-spin values is given. Our
special focus is on the case when two particles are charge self-conjugate, i.e.
Majorana bosons. The general structure of their couplings to an on-shell or
off-shell vector boson $V$ is described in a manifestly covariant way and then
the constraints on the triple vertex due to discrete CP symmetry and the
Majorana condition of two particles being Majorana are worked out. The validity
of our full analytic investigation is checked by studying the two-body decay,
$X_2\to V X_1$, with an on-shell or off-shell $V$ boson in the helicity
formalism complementary to the covariant formulation. Threshold effects of the
two-lepton invariant-mass and polar-angle correlations in the two sequential
two-body decays, $X_2\to V X_1$ and $V\to \ell^-\ell^+$ with $\ell=e$ or $\mu$,
are derived analytically in a compact form by use of the Wick helicity rotation
and they are investigated numerically in a few specific spin-combination
scenarios for probing the spin and dynamical structure of the $X_2X_1V$ vertex.",2102.01317v1
2021-02-12,The Teukolsky--Starobinsky constants: facts and fictions,"The Teukolsky Master Equation describes the dynamics of massless fields with
spin on a Kerr black hole. Under separation of variables, spin-reversal for
this equation is accomplished through the so-called Teukolsky--Starobinsky
identities. These identities are associated to the so-called
Teukolsky--Starobinsky constants, which are spin-dependent.
  We collect some properties of the Teukolsky--Starobinsky constants and dispel
some myths present in the literature. We show that, contrary to popular belief,
these constants can be negative for spin larger than 2. Such fields thus
exhibit a novel form of energy amplification which occurs for non-superradiant
frequencies.",2102.06734v1
2021-02-23,Site-resolved imaging of ultracold fermions in a triangular-lattice quantum gas microscope,"Quantum gas microscopes have expanded the capabilities of quantum simulation
of Hubbard models by enabling the study of spatial spin and density
correlations in square lattices. However, quantum gas microscopes have not been
realized for fermionic atoms in frustrated geometries. Here, we demonstrate the
single-atom resolved imaging of ultracold fermionic $^{6}$Li atoms in a
triangular optical lattice with a lattice constant of 1003 nm. The optical
lattice is formed by a recycled narrow-linewidth, high-power laser combined
with a light sheet to allow for Raman sideband cooling on the $D_1$ line. We
optically resolve single atoms on individual lattice sites using a
high-resolution objective to collect scattered photons while cooling them close
to the two-dimensional ground vibrational level in each lattice site. By
reconstructing the lattice occupation, we measure an imaging fidelity of ~98%.
Our new triangular lattice microscope platform for fermions clears the path for
studying spin-spin correlations, entanglement and dynamics of geometrically
frustrated Hubbard systems which are expected to exhibit exotic emergent
phenomena including spin liquids and kinetic frustration.",2102.11862v1
2021-03-07,Phonon Hall Viscosity in Magnetic Insulators,"The Phonon Hall Viscosity is the leading term evincing time-reversal symmetry
breaking in the low energy description of lattice phonons. It may generate
phonon Berry curvature, and can be observed experimentally through the acoustic
Faraday effect and thermal Hall transport. We present a systematic procedure to
obtain the phonon Hall viscosity induced by phonon-magnon interactions in
magnetic insulators under an external magnetic field. We obtain a general
symmetry criterion that leads to non-zero Faraday rotation and Hall
conductivity, and clarify the interplay between lattice symmetry,
spin-orbit-coupling, external magnetic field and magnetic ordering. The
symmetry analysis is verified through a microscopic calculation. By
constructing the general symmetry-allowed effective action that describes the
spin dynamics and spin-lattice coupling, and then integrating out the spin
fluctuations, the leading order time-reversal breaking term in the phonon
effective action, i.e. the phonon Hall viscosity, can be obtained. The analysis
of the square lattice antiferromagnet for a cuprate Mott insulator,
Sr$_2$CuO$_2$Cl$_2$, is presented explicitly, and the procedure described here
can be readily generalized to other magnetic insulators.",2103.04223v1
2021-03-15,Quantum-enhanced sensing of displacements and electric fields with large trapped-ion crystals,"Developing the isolation and control of ultracold atomic systems to the level
of single quanta has led to significant advances in quantum sensing, yet
demonstrating a quantum advantage in real world applications by harnessing
entanglement remains a core task. Here, we realize a many-body quantum-enhanced
sensor to detect weak displacements and electric fields using a large crystal
of $\sim 150$ trapped ions. The center of mass vibrational mode of the crystal
serves as high-Q mechanical oscillator and the collective electronic spin as
the measurement device. By entangling the oscillator and the collective spin
before the displacement is applied and by controlling the coherent dynamics via
a many-body echo we are able to utilize the delicate spin-motion entanglement
to map the displacement into a spin rotation such that we avoid quantum
back-action and cancel detrimental thermal noise. We report quantum enhanced
sensitivity to displacements of $8.8 \pm 0.4~$dB below the standard quantum
limit and a sensitivity for measuring electric fields of
$240\pm10~\mathrm{nV}\mathrm{m}^{-1}$ in $1$ second
($240~\mathrm{nV}\mathrm{m}^{-1}/\sqrt{\mathrm{Hz}}$).",2103.08690v1
2021-03-23,GRIT: a package for structure-preserving simulations of gravitationally interacting rigid-bodies,"Spin-orbit coupling of planetary systems plays an important role in the
dynamics and habitability of planets. However, symplectic integrators that can
accurately simulate not only how orbit affects spin but also how spin affects
orbit have not been constructed for general systems. Thus, we develop
symplectic Lie-group integrators to simulate systems consisting gravitationally
interacting rigid bodies. A user friendly package (GRIT
\url{https://github.com/GRIT-RBSim/GRIT}) is provided and external forcings
such as tidal interactions are also included. As a demonstration, this package
is applied to Trappist-I. It shows that the differences in transit timing
variations due to spin-orbit coupling could reach a few min in ten year
measurements, and strong planetary perturbations can push Trappist-I f, g and h
out of the synchronized states.",2103.12767v2
2021-03-25,Ground State Microwave-Stimulated Raman Transitions and Adiabatic Spin Transfer in the $^{15}$Nitrogen-Vacancy Center,"Microwave pulse sequences are the basis of coherent manipulation of the
electronic spin ground state in nitrogen-vacancy (NV) centers. In this work we
demonstrate stimulated Raman transitions (SRT) and stimulated Raman adiabatic
passage (STIRAP), two ways to drive the dipole-forbidden transition between two
spin sublevels in the electronic triplet ground state of the NV center. This is
achieved by a multitone Raman microwave pulse which simultaneously drives two
detuned transitions via a virtual level for SRT or via two adiabatic and
partially overlapping resonant microwave pulses for STIRAP. We lay the
theoretical framework of SRT and STIRAP dynamics and verify experimentally the
theoretical predictions of population inversion by observing the
dipole-forbidden transition in the ground state of a single NV center. A
comparison of the two schemes showed a better robustness and success of the
spin swap for STIRAP as compared to SRT.",2103.13788v1
2021-05-05,Probing the Spins of Supermassive Black Holes with Gravitational Waves from Surrounding Compact Binaries,"Merging compact black-hole (BH) binaries are likely to exist in the nuclear
star clusters around supermassive BHs (SMBHs), such as Sgr A$^\ast$. They may
also form in the accretion disks of active galactic nuclei. Such compact
binaries can emit gravitational waves (GWs) in the low-frequency band (0.001-1
Hz) that are detectable by several planned space-borne GW observatories. We
show that the orbital axis of the compact binary may experience significant
variation due to the frame-dragging effect associated with the spin of the
SMBH. The dynamical behavior of the orbital axis can be understood analytically
as a resonance phenomenon. We show that rate of change of the binary orbital
axis encodes the information on the spin of the SMBH. Therefore detecting GWs
from compact binaries around SMBHs, particularly the modulation of the waveform
associated with the variation of the binary orbital axis, can provide a new
probe on the spins of SMBHs.",2105.02230v2
2021-05-11,Spin/Valley pumping of resident electrons in WSe2 and WS2 monolayers,"Monolayers of transition metal dichalcogenides are ideal materials to control
both spin and valley degrees of freedom either electrically or optically.
Nevertheless, optical excitation mostly generates excitons species with
inherently short lifetime and spin/valley relaxation time. Here we demonstrate
a very efficient spin/valley optical pumping of resident electrons in n-doped
WSe2 and WS2 monolayers. We observe that, using a continuous wave laser and
appropriate doping and excitation densities, negative trion doublet lines
exhibit circular polarization of opposite sign and the photoluminescence
intensity of the triplet trion is more than four times larger with circular
excitation than with linear excitation. We interpret our results as a
consequence of a large dynamic polarization of resident electrons using
circular light.",2105.04861v1
2021-05-31,Optical lattice with spin-dependent sub-wavelength barriers,"We analyze a tripod atom light coupling scheme characterized by two dark
states playing the role of quasi-spin states. It is demonstrated that by
properly configuring the coupling laser fields, one can create a lattice with
spin-dependent sub-wavelength barriers. This allows to flexibly alter the
atomic motion ranging from atomic dynamics in the effective brick-wall type
lattice to free motion of atoms in one dark state and a tight binding lattice
with a twice smaller periodicity for atoms in the other dark state. Between the
two regimes, the spectrum undergoes significant changes controlled by the laser
fields. The tripod lattice can be produced using current experimental
techniques. The use of the tripod scheme to create a lattice of degenerate dark
states opens new possibilities for spin ordering and symmetry breaking.",2105.15148v2
2021-06-02,Effective exchange interaction for terahertz spin waves in iron layers,"The exchange stiffness is a central material parameter of all ferromagnetic
materials. Its value controls the Curie temperature as well as the dynamic
properties of spin waves to a large extend. Using ultrashort spin current
pulses we excite perpendicular standing spin waves (PSSW) in ultrathin
epitaxial iron layers at frequencies of up to 2.4 THz. Our analysis shows that
for the PSSWs the observed exchange stiffness of iron is about 20% smaller
compared to the established iron bulk value. In addition, we find an
interface-related reduction of the effective exchange stiffness for layers with
the thickness below 10 nm. To understand and discuss the possible mechanisms of
the exchange stiffness reduction we develop an analytical 1D-model. In doing so
we find that the interface induced reduction of the exchange stiffness is
mode-dependent.",2106.01066v1
2021-06-23,Minimal spin deflection of Kerr-Newman and Supersymmetric black hole,"Recent studies have shown that minimal couplings for massive spinning
particles, which in the classical limit reproduce the leading PM Kerr black
hole dynamics, leads to an Eikonal S-matrix exhibiting spin-entanglement
suppression. In this paper we trace this phenomenon to the suppression of
spin-flipping components in the S-matrix, known to be the hallmark of minimal
coupling in the ultra-relativistic limit. We further generalize the
consideration to charged and $\mathcal{N}=4$ black holes, demonstrating that in
both cases maximal suppression occurs at the extremal limit.",2106.12518v2
2021-06-29,Extraction of autonomous quantum coherences,"Quantum coherence is an essential resource to gain advantage over classical
physics and technology. Recently, it has been proposed that a low-temperature
environment can induce quantum coherence of a spin without an external coherent
pump. We address a critical question if such coherence is extractable by a weak
coupling to an output system dynamically affecting back the spin-environment
coupling. Describing the entire mechanism, we prove that such extraction is
generically possible for output spins (also oscillators or fields) and, as
well, in a fermionic analogue of such a process. We compare the internal spin
coherence and output coherence over temperature and characteristic frequencies.
The proposed optimal coherence extraction opens paths for the upcoming
experimental tests with atomic and solid-state systems.",2106.15721v3
2021-07-28,Transport theory and spin-transfer physics for frustrated magnets,"We study the electron dynamics in magnetic conductors with frustrated
interactions dominated by isotropic exchange. We present a transport theory for
itinerant carriers built upon the (single-band) doped Hubbard model and the
slave-boson formalism, which incorporates the spin-exchange with the
magnetically frustrated background into the representation of electron
operators in a clear and controllable way. We also formulate hydrodynamic
equations for the itinerant charge and spin degrees of freedom, whose currents
contain new contributions that depend on the spatiotemporal variations of the
order parameter of the frustrated magnet, which are described by Yang-Mills
fields. Furthermore, we elucidate the transfer of angular momentum from the
itinerant charge fluid to the magnet (i.e., the spin-transfer torque) via
reciprocity arguments. A detailed microscopic derivation of our effective
theory is also provided for one of the simplest models of frustrated magnetism,
namely the Heisenberg antiferromagnet on a triangular lattice. Our findings
point towards the possibility of previously unanticipated Hall physics in these
frustrated platforms.",2107.13330v2
2021-07-29,Spin and velocity correlations in a confined two-dimensional fluid of disk-shaped active rotors,"We study the velocity autocorrelations in an experimental configuration of
confined two-dimensional active rotors (disks). We report persistent small
scale oscillations in both rotational and translational velocity
autocorrelations, with their characteristic frequency increasing as rotational
activity increases. While these small oscillations are qualitatively similar in
all experiments, we found that, at strong particle rotational activity, the
large scale particle spin fluctuations tend to vanish, with the small
oscillations around zero persisting in this case, and spins remain
predominantly and strongly anti-correlated at longer times. For weaker
rotational activity, however, spin fluctuations become increasingly larger and
angular velocities remain de-correlated at longer times. We discuss in detail
how the autocorrelation oscillations are related to the rotational activity and
why this feature is generically a signal of the emergence of chirality in the
dynamics of a particulate system.",2107.14186v2
2021-08-03,Squeezed-light enhancement and backaction evasion in a high sensitivity optically pumped magnetometer,"We study the effect of optical polarization squeezing on the performance of a
sensitive, quantum-noise-limited optically pumped magnetometer. We use
Bell-Bloom (BB) optical pumping to excite a $^{87}$Rb vapor containing $8.2
\cdot 10^{12} \mathrm{atoms/cm^3}$ and Faraday rotation to detect spin
precession. The sub-$\mathrm{pT}/\sqrt{\mathrm{Hz}}$ sensitivity is limited by
spin projection noise (photon shot noise) at low (high) frequencies. Probe
polarization squeezing both improves high-frequency sensitivity and increases
measurement bandwidth, with no loss of sensitivity at any frequency, a direct
demonstration of the evasion of measurement backaction noise. We provide a
model for the quantum noise dynamics of the BB magnetometer, including spin
projection noise, probe polarization noise, and measurement backaction effects.
The theory shows how polarization squeezing reduces optical noise, while
measurement backaction due to the accompanying ellipticity anti-squeezing is
shunted into the unmeasured spin component. The method is compatible with
high-density and multi-pass techniques that reach extreme sensitivity.",2108.01519v2
2021-08-17,Generation of Spin Cat States in an Engineered Dicke Model,"We study trajectories of collective spin states of an ensemble of spinors.
The spinors considered here are either trapped ions in free space or atoms
confined in a cavity, both systems of which are engineered through their
interactions with light fields to obey an effective Dicke model. In an
appropriate limit of the Dicke model, one obtains one-axis twisting dynamics of
the collective spin and evolution after a finite time to a spin cat state, or,
in the long-time limit, the Dicke state $|S,0\rangle_x$, conditioned upon there
being no photon emissions from the system (i.e., no quantum jumps). If there is
a jump, however, the system evolves probabilistically into one of a finite
number of entangled-state cycles, where the system then undergoes a persistent
sequence of jumps between two Dicke state superpositions in a rotated basis.
The different cycles can be distinguished by the frequency at which jumps
occur.",2108.07415v1
2021-08-30,Engineering local strain for single-atom nuclear acoustic resonance in silicon,"Mechanical strain plays a key role in the physics and operation of nanoscale
semiconductor systems, including quantum dots and single-dopant devices. Here
we describe the design of a nanoelectronic device where a single nuclear spin
is coherently controlled via nuclear acoustic resonance (NAR) through the local
application of dynamical strain. The strain drives spin transitions by
modulating the nuclear quadrupole interaction. We adopt an AlN piezoelectric
actuator compatible with standard silicon metal-oxide-semiconductor processing,
and optimize the device layout to maximize the NAR drive. We predict NAR Rabi
frequencies of order 200 Hz for a single $^{123}$Sb nucleus in a wide region of
the device. Spin transitions driven directly by electric fields are suppressed
in the center of the device, allowing the observation of pure NAR. Using
electric field gradient-elastic tensors calculated by density-functional
theory, we extend our predictions to other high-spin group-V donors in silicon,
and to the isoelectronic $^{73}$Ge atom.",2108.13234v1
2021-09-02,Enhanced magnon spin current using the bosonic Klein paradox,"Efficient manipulation of magnons for information processing is a central
topic in spintronics and magnonics. An outstanding challenge for long-distance
spin transport with minimal dissipation is to overcome the relaxation of
magnons and to amplify the spin current they carry. Here, we propose to amplify
magnon currents based on the realization of the bosonic Klein paradox in
magnetic nanostructures. This paradox involves the magnon's antiparticle, the
antimagnon, of which the existence is usually precluded by magnetic
instabilities as it is an excitation at negative energy. We show that, by
appropriately tuning the effective dissipation through spin-orbit torques, both
magnons and antimagnons are dynamically stabilized. As a result, we find that
the reflection coefficient of incident magnons at an interface between two
coupled magnets can become larger than one, thereby amplifying the reflected
magnon current. Our findings can lead to magnon amplifier devices for
spintronic applications. Furthermore, our findings yield a solid-state platform
to study the relativistic behavior of bosonic particles, which is an
outstanding challenge with fundamental particles.",2109.00865v3
2021-10-21,Physics-Based Models for Magneto-Electric Spin-Orbit Logic Circuits,"Spintronic devices are a promising beyond-CMOS device option thanks to their
energy efficiency and compatibility with CMOS. To accurately capture their
multi-physics dynamics, a rigorous treatment of both spin and charge and their
inter-conversion is required. Here we present physics-based device models based
on 4x4 matrices for the spin-orbit coupling part of the magneto-electric
spin-orbit (MESO) device. Also, a more rigorous physics model of ferroelectric
and magnetoelectric switching of ferromagnets, based on Landau-Lifshitz-Gilbert
(LLG) and Landau-Khalatnikov (LK) equations, is presented. With the combined
model implemented in a SPICE circuit simulator environment, simulation results
were obtained which show feasibility of MESO implementation and functional
operation of buffers, oscillators, and majority gates.",2110.10890v1
2021-10-29,Anomalous spin polarization from turbulent color fields,"We study the important, yet widely overlooked, role of gluons for spin
transport with a connection to local parity violation in quark gluon plasmas.
We employ the formalism of quantum kinetic theory to quarks in weakly coupled
quantum chromodynamics to derive the source terms for quark spin polarization.
These source terms involve parity-odd correlators of dynamically generated
color fields in near-equilibrium quark gluon plasmas and give rise to locally
fluctuating axial charge currents. Our results provide a possible explanation
for the spin alignment of vector mesons measured in high-energy nuclear
collisions.",2110.15630v3
2021-11-29,Thermal Conductivity of Square Ice,"We investigate thermal transport in square ice, a two-dimensional analogue of
spin ice, exploring the role played by emergent magnetic monopoles in
transporting energy. Using kinetic Monte Carlo simulations based on energy
preserving extensions of single-spin-flip dynamics, we explicitly compute the
(longitudinal) thermal conductivity, $\kappa$, over a broad range of
temperatures. We use two methods to determine $\kappa$: a measurement of the
energy current between thermal baths at the boundaries, and the Green-Kubo
formula, yielding quantitatively consistent values for the thermal
conductivity. We interpret these results in terms of transport of energy by
diffusion of magnetic monopoles. We relate the thermal diffusivity, $\kappa/C$
where $C$ is the heat capacity, to the diffusion constant of an isolated
monopole, showing that the subdiffusive monopole implies $\kappa/C$ vanishes at
zero temperature. Finally, we discuss the implications of these results for
thermal transport in three-dimensional spin ice, in spin ice materials such as
Dy$_2$Ti$_2$O$_7$ and Ho$_2$Ti$_2$O$_7$, and outline some open questions for
thermal transport in highly frustrated magnets.",2111.14872v1
2021-12-06,"Spin, Statistics, Spacetime and Quantum Gravity","We explore the possibility that the connection between spin and statistics in
quantum physics is of dynamical origin. We suggest that the gravitational field
could provide a fully local mechanism for the phase that arises when fermionic
and bosonic particles are exchanged. Our results hold even if the symmetry of
space and time is Galilean, thus establishing that special relativity is not
needed to explain the existence of spin (although it does motivate the
introduction of creation and annihilation of particles, but this is a separate
issue). We provide a model for the coupling between a particle of general spin
and the gravitational field and discuss it within the context of both the
equivalence principle and the Sagnac effect. This leads us to present a new
experiment for testing the quantum nature of the gravitational field.",2112.03392v1
2021-12-13,Excited-state optically detected magnetic resonance of spin defects in hexagonal boron nitride,"Negatively charged boron vacancy (VB-) centers in hexagonal boron nitride
(hBN) are promising spin defects in a van der Waals crystal. Understanding the
spin properties of the excited state (ES) is critical for realizing dynamic
nuclear polarization. Here, we report zero-field splitting in the ES of DES =
2160 MHz and an optically detected magnetic resonance (ODMR) contrast of 12% at
cryogenic temperature. The ES has a g-factor similar to the ground state. The
ES photodynamics is further elucidated by measuring the level anti-crossing of
the VB- defects under varying external magnetic fields. In contrast to nitrogen
vacancy (NV-) centers in diamond, the emission change caused by excited-state
level anti-crossing (ESLAC) is more prominent at cryo-temperature than at room
temperature. Our results provide important information for utilizing the spin
defects of hBN in quantum technology.",2112.06420v2
2021-12-19,Engineering spin wave spectra in thick Ni$_{80}$Fe$_{20}$ rings by using competition between exchange and dipolar fields,"Control of the spin wave dynamics in nanomagnetic elements is very important
for the realization of a broad range of novel magnonic devices. Here we study
experimentally the spin wave resonance in thick ferromagnetic rings (100 nm)
using perpendicular ferromagnetic resonance spectroscopy. Different from what
was observed for the continuous film of the same thickness, or from ring with
similar lateral dimensions but with lower thicknesses, the spectra of thick
patterned rings show a non-monotonic dependence of the mode intensity on the
resonance field for a fixed frequency. To explain this effect, the theoretical
approach by considering the dependence of the mode profiles on both the radial
and axial coordinates was developed. It was demonstrated that such unusual
behavior is a result of the competition between exchange and dipolar fields
acting at the spin excitations in the structure under study. The calculations
are in a good agreement with the experimental results.",2112.13657v1
2021-12-29,Dzyaloshinskii-Moriya Induced Spin-Transfer Torques in Kagome Antiferromagnets,"In recent years antiferromagnets (AFMs) have become very promising for
nanoscale spintronic applications due to their unique properties such as THz
dynamics and absence of stray fields. Manipulating antiferromagnetic textures
is currently, however, limited to very few exceptional material symmetry
classes allowing for staggered torques on the magnetic sublattices. In this
work, we predict for kagome AFMs with broken mirror symmetry a new coupling
mechanism between antiferromagnetic domain walls (DWs) and spin currents,
produced by the relativistic Dzyaloshinskii-Moriya interaction (DMI). We
microscopically derive the DMI's free energy contribution for the kagome AFMs.
Unlike ferromagnets and collinear AFMs, the DMI does not lead to terms linear
in the spatial derivatives but instead renormalizes the spin-wave stiffness and
anisotropy energies. Importantly, we show that the DMI induces a highly
nontrivial twisted DW profile that is controllable via two linearly independent
components of the spin accumulation. This texture manipulation mechanism goes
beyond the concept of staggered torques and implies a higher degree of
tunability for the current-driven DW motion compared to conventional
ferromagnets and collinear AFMs.",2112.14504v2
2022-01-20,Motional decoherence in ultracold Rydberg atom quantum simulators of spin models,"Ultracold Rydberg atom arrays are an emerging platform for quantum simulation
and computing. However, decoherence in these systems remains incompletely
understood. Recent experiments [Guardado-Sanchez et al. Phys. Rev. X 8, 021069
(2018)] observed strong decoherence in the quench and longitudinal-field-sweep
dynamics of two-dimensional Ising models realized with Lithium-6 Rydberg atoms
in optical lattices. This decoherence was conjectured to arise from spin-motion
coupling. Here we show that spin-motion coupling indeed leads to decoherence in
qualitative, and often quantitative, agreement with the experimental data,
treating the difficult spin-motion coupled problem using the discrete truncated
Wigner approximation method. We also show that this decoherence will be an
important factor to account for in future experiments with Rydberg atoms in
optical lattices and microtrap arrays, and discuss methods to mitigate the
effect of motion, such as using heavier atoms or deeper traps.",2201.08463v4
2022-02-15,Electron Transfer and Spin-Orbit Coupling: How Strong are Berry Force Effects In and Out of Equilibrium in the Presence of Nuclear Friction?,"We investigate a spin-boson inspired model of electron transfer, where the
diabatic coupling is given by a position-dependent phase, exp(iWx). We consider
both equilibrium and nonequilibrium initial conditions. We show that, for this
model, all equilibrium results are completely invariant to the sign of W(to
infinite order). However, the nonequilibrium results do depend on the sign of
W, suggesting that photo-induced electron transfer dynamics are meaningfully
affected by Berry forces even in the presence of nuclear friction; furthermore,
whenever there is spin-orbit coupling, electronic spin polarization can emerge
(at least for some time).",2202.07204v1
2022-02-18,Nematicity and fractional magnetization plateaus induced by spin-lattice coupling in the classical kagome-lattice Heisenberg antiferromagnet,"We investigate the effect of spin-lattice coupling (SLC) on the magnetic
properties of the classical kagome-lattice Heisenberg antiferromagnet (KHAF)
using improved Monte Carlo updates. The lattice modes are represented by
Einstein site phonons, which introduce effective further-neighbor spin
interactions in addition to the nearest-neighbor biquadratic interactions. In
the weak SLC, the macroscopically degenerate coplanar ground state remains at
zero field, while a $\sqrt{3} \times \sqrt{3}$ ordered phase accompanied by a
1/3-magnetization plateau appears in external magnetic fields. In the strong
SLC, we find a nematic order at zero field and a 1/9-magnetization plateau
associated with a $3 \times 3$ collinear order. Near the phase transition
between the 1/9- and 1/3-plateau states, the ergodicity in the single spin flip
is practically broken, and slow dynamics appear. We propose that relevant KHAFs
with strong SLC would be realized in spinel-based materials.",2202.09077v3
2022-02-21,Results on spin sum rules and polarizabilities at low $Q^2$,"We report on recently published experimental results on spin sum rules, and
particularly on the generalized spin polarizabilities $\gamma_0(Q^2)$ (for both
the proton and neutron) and $\delta_\mathrm{LT}(Q^2)$ (for the neutron). The
data were taken at Jefferson Lab in Hall A by experiment E97110 (neutron) and
in Hall B by experiments E03006 and E05111 (proton and deuteron, respectively).
The experiments covered the very low $Q^2$ domain, down to $Q^2 \simeq 0.02$
GeV$^2$. This is well into the domain where Chiral Effective Field Theory
($\chi$EFT) predictions should be valid. Some measured observables agree with
the state-of-the-art $\chi$EFT predictions but others are in tension, including
$\delta_\mathrm{LT}^n(Q^2)$ which $\chi$EFT prediction was expected to be
robust. This suggests that $\chi$EFT does not yet consistently describe nucleon
spin observables, even at the very low $Q^2$ covered by the experiments.",2202.10511v1
2022-03-11,Strategy to Extract Kitaev Interaction using Symmetry in Honeycomb Mott Insulators,"The Kitaev spin liquid, a ground state of the bond-dependent Kitaev model in
a honeycomb lattice has been a centre of attraction, since a microscopic theory
to realize such an interaction in solid-state materials was discovered. A
challenge in real materials though is the presence of the Heisenberg and
another bond-dependent Gamma interactions detrimental to the Kitaev spin
liquid, and there have been many debates on their relative strengths. Here we
offer a strategy to extract the Kitaev interaction out of a full microscopic
model by utilizing the symmetries of the Hamiltonian. Two tilted magnetic field
directions related by a two-fold rotational symmetry generate distinct spin
excitations originating from a specific combination of the Kitaev and Gamma
interactions. Together with the in- and out-of-plane magnetic anisotropy, one
can determine the Kitaev and Gamma interactions separately. Dynamic spin
structure factors are presented to motivate future experiments. The proposed
setups will advance the search for Kitaev materials.",2203.06193v3
2022-03-21,A Unified Description for Polarization-Transfer Mechanisms in Magnetic Resonance in Static Solids: Cross Polarization and DNP,"Polarization transfers are crucial building blocks in magnetic resonance
experiments, i.e., they can be used to polarize insensitive nuclei and
correlate nuclear spins in multidimensional NMR spectroscopy. The polarization
can be transferred either across different nuclear spin species or from
electron spins to the relatively low-polarized nuclear spins. The former route
occurring in solid-state NMR (ssNMR) can be performed via cross polarization
(CP), while the latter route is known as dynamic nuclear polarization (DNP).
Despite having different operating conditions, we opinionate that both
mechanisms are theoretically similar processes in ideal conditions, i.e., the
electron is merely another spin-1/2 particle with a much higher gyromagnetic
ratio. Here, we show that the CP and DNP processes can be described using a
unified theory based on average Hamiltonian theory (AHT) combined with
fictitious operators. The intuitive and unified approach has allowed new
insights on the cross effect (CE) DNP mechanism, leading to better design of
DNP polarizing agents and extending the applications beyond just
hyperpolarization. We explore the possibility of exploiting theoretically
predicted DNP transients for electron-nucleus distance measurements--like
routine dipolar-recoupling experiments in solid-state NMR.",2203.11339v1
2022-04-11,Chiral spin symmetry and the QCD phase diagram,"Lattice QCD simulations with chirally symmetric quarks have recently
established approximate $SU(2)_{CS}$ and $SU(2N_F)$ symmetries of the quantum
effective action in a temperature range above the chiral crossover
$T_\mathrm{ch}$, in which color-electric interactions between quarks dominate
the dynamics. We show that such an intermediate temperature range between the
chirally broken and plasma regimes is fully consistent with published screening
mass spectra, which demonstrate the breakdown of thermal perturbation theory at
the crossover between the partonic and the chiral spin symmetric regime at
$T_s\sim (2-3)T_\mathrm{ch}$. From the known behavior of screening masses with
baryon chemical potential, we deduce qualitatively how this chiral spin
symmetric band extends into the QCD phase diagram. In the cold and dense
region, we propose parity doubled baryons as possible candidates for chiral
spin symmetric matter. This represents a special case of quarkyonic matter with
confinement and restored chiral symmetry, and can smoothly transform to quark
matter at sufficiently high densities. Finally, we discuss the potential of
dilepton spectra to identify such matter forms.",2204.05083v2
2022-04-29,Rydberg Atomic Antenna in Strongly Driven Multi-Electron Atoms,"We study the role of intermediate excitations of Rydberg states as an example
of Kuchiev's ""atomic antenna"" in above-threshold ionization of xenon, in
particular their effect on the coherence between the spin-orbit-split states of
the ion. We focus on the case of a laser frequency close to resonant with the
spin-orbit splitting, where a symmetry (parity) argument would preclude any
coherence being directly generated by strong-field ionization. Using ab initio
simulations of coupled multielectron spin-orbit dynamics in strong laser
fields, we show how field-driven rescattering of the trapped Rydberg electrons
introduces efficient coupling between the spin-orbit-split channels, leading to
substantial coherences, exceeding 10 % for some photon energies.",2204.14082v2
2022-05-10,Non-hermitian off-diagonal magnetic response of Dirac fermions,"We perform a comparative study for the magnetization dynamics within linear
response theory of one and two dimensional massive Dirac electrons, after
switching on either a real (hermitian) or an imaginary (non-hermitian) magnetic
field. While hermitian dc magnetic fields polarize the spins in the direction
of the external magnetic field, non-hermitian magnetic fields induce only off
diagonal response. An imaginary dc magnetic field perpendicular to the mass
term induces finite magnetization in the third direction only according to the
right hand rule. This can be understood by analyzing the non-hermitian equation
of motion of the spin, which becomes analogous to a classical particle in
crossed electric and magnetic fields. Therein, the spin expectation value, the
mass term and imaginary magnetic field play the role of the classical momentum,
magnetic and electric field, respectively. The latter two create a drift
velocity perpendicular to them, which gives rise to the off-diagonal component
of the dc spin susceptibility, similarly to how the Hall effect develops in the
classical description.",2205.04795v2
2022-05-10,Exact solutions for the time-evolution of quantum spin systems under arbitrary waveforms using algebraic graph theory,"A general approach is presented that offers exact analytical solutions for
the time-evolution of quantum spin systems during parametric waveforms of
arbitrary functions of time. The proposed method utilises the \emph{path-sum}
method that relies on the algebraic and combinatorial properties of walks on
graphs. A full mathematical treatment of the proposed formalism is presented,
accompanied by an implementation in \textsc{Matlab}. Using computation of the
spin dynamics of monopartite, bipartite, and tripartite quantum spin systems
under chirped pulses as exemplar parametric waveforms, it is demonstrated that
the proposed method consistently outperforms conventional numerical methods,
including ODE integrators and piecewise-constant propagator approximations.",2205.05195v1
2022-05-17,Gyrohydrodynamics: Relativistic spinful fluid with strong vorticity,"We develop a relativistic (quasi-)hydrodynamic framework, dubbed the
gyrohydrodynamics, to describe fluid dynamics of many-body systems with spin
under strong vorticity based on entropy-current analysis. This framework
generalizes the recently-developed spin hydrodynamics to the regime where the
spin density is at the leading order in derivatives but suppressed by another
small parameter, the Planck constant $\hbar$, due to its quantum nature. Our
analysis shows that the complete first-order constitutive relations of
gyrohydrodynamics involve seventeen transport coefficients and are highly
anisotropic.",2205.08051v2
2022-05-25,Gauge-theoretic origin of Rydberg quantum spin liquids,"Recent atomic physics experiments and numerical works have reported
complementary signatures of the emergence of a topological quantum spin liquid
in models with blockade interactions. However, the specific mechanism
stabilizing such a phase remains unclear. Here, we introduce an exact relation
between an Ising-Higgs lattice gauge theory on the kagome lattice and blockaded
models on Ruby lattices. This relation elucidates the origin of previously
observed topological spin liquids by directly linking the latter to a
deconfined phase of a solvable gauge theory. By means of exact diagonalization
and unbiased quantum Monte Carlo simulations, we show that the deconfined
phases extend in a broad region of the parameter space; these states are
characterized by a large ground state overlap with resonating valence bond
wavefunctions. These blockaded models include both creation/annihilation and
hopping dynamics, and can be experimentally realized with Rydberg-dressed
atoms, offering novel and controllable platforms for the engineering and
characterisation of spin liquid states.",2205.13000v2
2022-06-06,Fermi spin polaron and dissipative Fermi-polaron Rabi dynamics,"We consider a spin impurity with multiple energy levels moving in a
non-interacting Fermi sea, and theoretically solve this Fermi spin polaron
problem at nonzero temperature by using a non-self-consistent many-body
$T$-matrix theory. We focus on the simplest case with spin half, where the two
energy states of the impurity are coupled by a Rabi flip term. At small Rabi
coupling, the impurity exhibits damped Rabi oscillations, where the decoherence
is caused by the interaction with the Fermi sea, as recently reported in Fermi
polaron experiments with ultracold atoms. We investigate the dependence of Rabi
oscillations on the Rabi coupling strength and examine the additional nonlinear
damping due to large Rabi coupling. At finite temperature and at nonzero
impurity concentration, the impurity can acquire a pronounced momentum
distribution. We show that the momentum/thermal average can sizably reduce the
visibility of Rabi oscillations. We compare our theoretical predictions to the
recent experimental data and find a good agreement without any adjustable
parameter.",2206.02317v4
2022-06-15,Giant Rashba electrical control of magnetism in band models,"It is of considerable technological importance to achieve an electrical
control of magnetism of sufficient magnitude. To overcome the in-plane shape
anisotropy, needed is the electrical control of a perpendicular magnetic
anisotropy (PMA). It is known, within a free electron model, the Rashba
spin-orbit coupling provides such a control. Surprisingly, this same Rashba PMA
is enhanced by two to three orders of magnitude when a periodic potential is
added. Usually spin Berry phase physics reflects time dependent magnetic
fields. Here it is shown, within a time independent model, such physics arises
because the Rashba effective magnetic field has texture within the unit cell.
Predicted are electrical controllable band-structure gaps, linear in the
applied electric field $E$, that can result in a truly giant linear PMA. Also
possible is a Peierls mechanism, in which the magnetisation tilts from the
vertical, shifting these gaps to the Fermi level. As a consequence there are
low dissipation electric field driven dynamics, an alternative to the more
dissipative spin torque transfer (STT) effect. The theory requires the
introduction of an intrinsic spin Berry connection $\vec A_s$, an effective
vector potential, and is incompatible with current density functional theories
(DFT).",2206.07399v1
2022-07-06,Nonadiabatic quantum control of quantum dot arrays with fixed exchange using Cartan decomposition,"In semiconductor spin qubits which typically interact through short-range
exchange coupling, shuttling of spin is a practical way to generate quantum
operations between distant qubits. Although the exchange is often tunable
through voltages applied to gate electrodes, its minimal value can be
significantly large, which hinders the applicability of existing shuttling
protocols to such devices, requiring a different approach. In this work, we
extend our previous results for double- and triple-dot systems, and describe a
method for implementing spin shuttling in long chains of quantum dots in a
nonadiabatic manner. We make use of Cartan decomposition to break down the
interacting problem into simpler problems in a systematic way, and use
dynamical invariants to design smooth nonadiabatic pulses that can be
implemented in devices with modest control bandwidth. Finally, we discuss the
extensibility of our results to directed shuttling of spin states on
two-dimensional lattices of quantum dots with fixed coupling.",2207.02381v2
2022-07-08,Light-induced magnetization driven by interorbital charge motion in a spin-orbit assisted Mott insulator alpha-RuCl3,"In a honeycomb-lattice spin-orbit assisted Mott insulator {\alpha}-RuCl3, an
ultrafast magnetization is induced by circularly polarized excitation below the
Mott gap. Photo-carriers play an important role, which are generated by turning
down the synergy of the on-site Coulomb interaction and the spin-orbit
interaction realizing the insulator state. An ultrafast 6- fs measurement of
photo-carrier dynamics and a quantum mechanical analysis clarify the mechanism,
according to which the magnetization emerges from a coherent charge motion
between different t2g orbitals (dyz-dxz-dxy) of Ru3+ ions. This ultrafast
magnetization is weakened in the antiferromagnetic (AF) phase, which is
opposite to the general tendency that the inverse Faraday effect is larger in
AF compounds than in paramagnetic ones. This temperature dependence indicates
that the interorbital charge motion is affected by pseudo-spin rotational
symmetry breaking in the AF phase.",2207.03877v2
2022-08-03,Relativistic dissipative spin hydrodynamics from kinetic theory with a nonlocal collision term,"We derive relativistic dissipative spin hydrodynamics from kinetic theory
featuring a nonlocal collision term using the method of moments. In this
framework, the components of the spin tensor are dynamical variables which obey
relaxation-type equations. We find that the corresponding relaxation times are
determined by the local part of the collision term, while the nonlocal part
contributes to the Navier-Stokes terms in these equations of motion. The spin
relaxation time scales are comparable to those of the usual dissipative
currents. Finally, the Navier-Stokes limit of the Pauli-Lubanski vector
receives contributions proportional to the shear tensor of the fluid, which
implies that the polarization of hadrons observed in heavy-ion collisions is
influenced by dissipative effects.",2208.01955v2
2022-08-16,Tunable planar Josephson junctions driven by time-dependent spin-orbit coupling,"Integrating conventional superconductors with common III-V semiconductors
provides a versatile platform to implement tunable Josephson junctions (JJs)
and their applications. We propose that with gate-controlled time-dependent
spin-orbit coupling, it is possible to strongly modify the current-phase
relations and Josephson energy and provide a mechanism to drive the JJ
dynamics, even in the absence of any bias current. We show that the transition
between stable phases is realized with a simple linear change in the strength
of the spin-orbit coupling, while the transition rate can exceed the
gate-induced electric field GHz changes by an order of magnitude. The resulting
interplay between the constant effective magnetic field and changing spin-orbit
coupling has direct implications for superconducting spintronics, controlling
Majorana bound states, and emerging qubits. We argue that topological
superconductivity, sought for fault-tolerant quantum computing, offers simpler
applications in superconducting electronics and spintronics.",2208.07512v2
2022-08-16,Charge dynamics in spintronic THz emitters,"We show that to correctly describe the ultrafast currents in spintronic THz
emitters it is necessary to take charge equilibration into account. The charge
current which is locally induced by a fs laser pulse and the inverse spin-Hall
effect (ISHE) leads to ultrafast charging phenomena at the edge of the
illuminated area. Subsequent discharging leads to a current backflow with a
delay and a time constant that mainly depends on the conductivity of the
emitter. On the one hand, only this delayed charge equilibration allows the
detection of the primary current pulse via THz emission because an
instantaneous backflow would cancel any far field emission. On the other hand,
especially for longer light pulses the backflow can significantly change the
emitted spectrum compared to the initial spin-current pulse by suppressing low
frequency components. For the analysis of spin physics based on the charge
current profile it is important to understand that the timing of the spin
current cannot be inferred from the charge current unless the contribution by
the ISHE and the backflow can be deconvoluted.",2208.07616v1
2022-08-24,Dissipative time crystals with long-range Lindbladians,"Dissipative time crystals can appear in spin systems, when the $Z_2$ symmetry
of the Hamiltonian is broken by the environment, and the square of total spin
operator $S^2$ is conserved. In this manuscript, we relax the latter condition
and show that time-translation-symmetry breaking collective oscillations
persist, in the thermodynamic limit, even in the absence of spin symmetry. We
engineer an \textit{ad hoc} Lindbladian using power-law decaying spin operators
and show that time-translation symmetry breaking appears when the decay
exponent obeys $0<\eta\leq 1$. This model shows a surprisingly rich phase
diagram, including the time-crystal phase as well as first-order, second-order,
and continuous transitions of the fixed points. We study the phase diagram and
the magnetization dynamics in the mean-field approximation. We prove that this
approximation is quantitatively accurate, when $0<\eta\leq1$ and the
thermodynamic limit is taken, because the system does not develop sizable
quantum fluctuations, if the Gaussian approximation is considered.",2208.11659v3
2022-08-25,Ultrashort spin-orbit torque generated by femtosecond laser pulses,"To realize the very objective of spintronics, namely the development of
ultra-high frequency and energy-efficient electronic devices, an ultrafast and
scalable approach to switch magnetic bits is required. Magnetization switching
with spin currents generated by the spin-orbit interaction at
ferromagnetic/non-magnetic interfaces is one of such scalable approaches, where
the ultimate switching speed is limited by the Larmor precession frequency.
Understanding the magnetization precession dynamics induced by spin-orbit
torques (SOTs) is therefore of great importance. Here we demonstrate generation
of ultrashort SOT pulses that excite Larmor precession at an epitaxial Fe/GaAs
interface by converting femtosecond laser pulses into high-amplitude current
pulses in an electrically biased p-i-n photodiode. We control the polarity,
amplitude, and duration of the current pulses and, most importantly, also their
propagation direction with respect to the crystal orientation. The SOT origin
of the excited Larmor precession was revealed by a detailed analysis of the
precession phase and amplitude at different experimental conditions.",2208.11974v1
2022-08-27,Quantum Langevin Equation of a spin in a magnetic field : an analysis,"We derive a quantum Langevin equation for a quantum spin in the presence of a
magnetic field and study its dynamics in the Markovian limit using the Ohmic
bath model. We extend our analysis to the Drude bath with a finite memory. We
study the time evolution of the expectation values of the magnetic moments. The
spin auto-correlation functions exhibit a damped oscillatory behaviour with the
randomization time being determined by the damping rate and also the memory
time for the Drude bath model. We also analyse the spin response function of
the system for the Ohmic bath model. Our results are consistent with findings
in cold atom experiments. In addition we make predictions which can be tested
in future ultra cold atom experiments.",2208.12989v1
2022-09-23,Phonon Induced Spin Dephasing Time of Nitrogen Vacancy Centers in Diamond from First Principles,"Spin qubits with long dephasing times are an essential requirement for the
development of new quantum technologies and have many potential applications
ranging from quantum information processing to quantum memories and quantum
networking. Here we report a theoretical study and the calculation of the spin
dephasing time of defect color centers for the negatively charged nitrogen
vacancy center in diamond. We employ ab initio density functional theory to
compute the electronic structure, and extract the dephasing time using a
cumulant expansion approach. We find that phonon-induced dephasing is a
limiting factor for T2 at low temperatures, in agreement with recent
experiments that use dynamical decoupling techniques. This approach can be
generalized to other spin defects in semiconductors, molecular systems, and
other band gapped materials.",2209.11412v1
2022-10-12,Quantum amplification of spin currents in cavity magnonics by a parametric drive induced long-lived mode,"Cavity-mediated magnon-magnon coupling can lead to a transfer of spin-wave
excitations between two spatially separated magnetic samples. We enunciate how
the application of a two-photon parametric drive to the cavity can lead to
stark amplification in this transfer efficiency. The recurrent multiphoton
absorption by the cavity opens up an infinite ladder of accessible energy
levels, which can induce higher-order transitions within the magnon Fock space.
This is reflected in a heightened spin-current response from one of the
magnetic samples when the neighboring sample is coherently pumped. The
enhancement induced by the parametric drive can be considerably high within the
stable dynamical region. Specifically, near the periphery of the stability
boundary, the spin current is amplified by several orders of magnitude. Such
striking enhancement factors are attributed to the emergence of parametrically
induced strong coherences precipitated by a long-lived mode. While
contextualized in magnonics, the generality of the principle would allow
applications to energy transfer between systems contained in parametric
cavities.",2210.05898v1
2022-10-12,Thermal disruption of a Luttinger liquid,"The Tomonaga-Luttinger liquid (TLL) theory describes the low-energy
excitations of strongly correlated one-dimensional (1D) fermions. In the past
years, a number of studies have provided a detailed understanding of this
universality class. More recently, theoretical investigations that go beyond
the standard low-temperature, linear-response, TLL regime have been developed.
While these provide a basis for understanding the dynamics of the
spin-incoherent Luttinger liquid, there are few experimental investigations in
this regime. Here we report the observation of a thermally-induced,
spin-incoherent Luttinger liquid in a $^6$Li atomic Fermi gas confined to 1D.
We use Bragg spectroscopy to measure the suppression of spin-charge separation
and the decay of correlations as the temperature is increased. Our results
probe the crossover between the coherent and incoherent regimes of the
Luttinger liquid, and elucidate the roles of the charge and the spin degrees of
freedom in this regime.",2210.06306v2
2022-11-02,Disordered structures in ultracold spin-imbalanced Fermi gas,"We investigate properties of spin-imbalanced ultracold Fermi gas in a large
range of spin polarizations at low temperatures. We present results of
microscopic calculations based on mean-field and density functional theory
approaches, with no symmetry constraints. At low polarization values we predict
the structure of the system as consisting of several spin-polarized droplets.
As the polarization increases, the system self-organizes into a disordered
structures similar to liquid crystals, and energetically they can compete with
ordered structures such as grid-like domain walls. At higher polarizations the
system starts to develop regularities that, in principle, can be called
supersolid, where periodic density modulation and pairing correlations coexist.
The robustness of the results has been checked with respect to temperature
effects, dimensionality, and the presence of a trapping potential. Dynamical
stability has also been investigated.",2211.01055v2
2022-11-07,Hydrodynamic relaxation of spin helices,"Motivated by recent cold atom experiments, we study the relaxation of spin
helices in quantum XXZ spin chains. The experimentally observed relaxation of
spin helices follows scaling laws that are qualitatively different from
linear-response transport. We construct a theory of the relaxation of helices,
combining generalized hydrodynamics (GHD) with diffusive corrections and the
local density approximation. Although helices are far from local equilibrium
(so GHD need not apply a priori), our theory reproduces the experimentally
observed relaxational dynamics of helices. In particular, our theory explains
the existence of temporal regimes with apparent anomalous diffusion, as well as
the asymmetry between positive and negative anisotropy regimes.",2211.03725v2
2022-11-15,Nonequilibrium Phase Transition To Temporal Oscillations In Mean-Field Spin Models,"We propose a mean-field theory for nonequilibrium phase transitions to a
periodically oscillating state in spin models. A nonequilibrium generalization
of the Landau free energy is obtained from the join distribution of the
magnetization and its smoothed stochastic time derivative. The order parameter
of the transition is a Hamiltonian, whose nonzero value signals the onset of
oscillations. The Hamiltonian and the nonequilibrium Landau free energy are
determined explicitly from the stochastic spin dynamics. The oscillating phase
is also characterized by a non-trivial overlap distribution reminiscent of a
continuous replica symmetry breaking, in spite of the absence of disorder. An
illustration is given on an explicit kinetic mean-field spin model.",2211.08009v2
2022-12-07,Evaporation of Primordial Black Holes in the Early Universe: Mass and Spin Distributions,"Many cosmological phenomena lead to the production of primordial black holes
in the early Universe. These phenomena often create a population of black holes
with extended mass and spin distributions. As these black holes evaporate via
Hawking radiation, they can modify various cosmological observables, lead to
the production of dark matter, modify the number of effective relativistic
degrees of freedom, $N_{\rm eff}$, source a stochastic gravitational wave
background and alter the dynamics of baryogenesis. We consider the Hawking
evaporation of primordial black holes that feature non-trivial mass and spin
distributions in the early Universe. We demonstrate that the shape of such a
distribution can strongly affect most of the aforementioned cosmological
observables. We outline the numerical machinery we use to undertake this task.
We also release a new version of FRISBHEE that handles the evaporation of
primordial black holes with an arbitrary mass and spin distribution throughout
cosmic history.",2212.03878v2
2022-12-09,Using X-ray continuum-fitting to estimate the spin of MAXI J1305-704,"MAXI J1305-704 is a transient X-ray binary with a black hole primary. It was
discovered on April 9, 2012, during its only known outburst. MAXI J1305-704 is
also a high inclination low-mass X-ray binary with prominent dip features in
its light curves, so we check the full catalog of 92 \emph{Swift}/XRT
continuous observations of MAXI J1305-704, focusing only on the stable spectra.
We select 13 ``gold"" spectra for which the root mean square RMS <0.075 and the
coronal scattered fraction $f_{\mathrm{sc}} \lesssim 25 \%$. These ``gold"" data
are optimal thermal-state observations for continuum-fitting modeling, in which
the disk extends to the innermost-stable circular orbit and is geometrically
thin. The black hole spin was unknown for this object before. By utilizing the
X-ray continuum fitting method with the relativistic thin disk model
\texttt{kerrbb2} and supplying the known dynamical binary system parameters, we
find MAXI J1305-704 has a moderate spin ($a_{*}=0.87_{-0.13}^{+0.07}$) at a
68.3\% confidence level. This is the first determination of MAXI J1305-704's
spin.",2212.04653v1
2022-12-30,Single pair of type-III Weyl points half-metals: BaNiIO$_6$ as an example,"The realization of Weyl systems with the minimum nonzero number of Weyl
points (WPs) and full spin polarization remains challenging in topology physics
and spintronic. In this study, for the first time, we used first-principle
calculations and symmetry analysis to demonstrate that BaNiIO$_6$, a
dynamically and thermodynamically stable half-metallic material, hosts fully
spin-polarized single-pair WPs (SP-WPs) with a charge number ($\cal{C}$) of
$\pm$2 and a type-\uppercase\expandafter{\romannumeral3} band dispersion around
the Fermi level. Moreover, the fully spin-polarized SP-WPs induce
double-helicoid Fermi arcs on the (10$\overline{1}$0) surface. The
half-metallic state and the spin-polarized SP-WPs are robust to uniform strains
(from -10\% to +8\%) and on-site Hubbard-Coulomb interactions (from 0 eV to 6
eV). When +9 % or +10 % uniform strain is applied to the BaNiIO$_6$ system, it
hosts six additional type-\uppercase\expandafter{\romannumeral2} WPs with
$\lvert{\cal{C}}\rvert=1$ in the three-dimensional Brillouin zone in addition
to the two type-\uppercase\expandafter{\romannumeral3} WPs with
$\lvert{\cal{C}}\rvert=2$. We hope that this study will motivate future
research into SP-WPs half-metals.",2212.14751v1
2023-01-21,Replica theory for disorder-free spin-lattice glass transition on a tree-like simplex network,"A class of pyrochlore oxides, $A_2$Mo$_2$O$_7$ ($A =$ Ho, Y, Dy, Tb) with
magnetic ions on corner-sharing tetrahedra is known to exhibit spin-glass
transitions without appreciable amount of quenched disorder. Recently a
disorder-free theoretical model for such a system has been proposed which takes
into account not only spins but also lattice distortions as dynamical variables
[K. Mitsumoto, C. Hotta and H. Yoshino, Phys. Rev. Lett. 124, 087201 (2020)].
In the present paper we develop and analyze an exactly solvable disorder-free
mean-field model which is a higher-dimensional counterpart of the model. We
find the system exhibit complex free-energy landscape accompanying replica
symmetry breaking through the spin-lattice coupling.",2301.08884v1
2023-01-30,Magnetic properties of hematite revealed by an ab initio parameterized spin model,"Hematite is a canted antiferromagnetic insulator, promising for applications
in spintronics. Here, we present ab initio calculations of the tensorial
exchange interactions of hematite and use them to understand its magnetic
properties by parameterizing a semiclassical Heisenberg spin model. Using
atomistic spin dynamics simulations, we calculate the equilibrium properties
and phase transitions of hematite, most notably the Morin transition. The
computed isotropic and Dzyaloshinskii--Moriya interactions result in a N\'eel
temperature and weak ferromagnetic canting angle that are in good agreement
with experimental measurements. Our simulations show how dipole-dipole
interactions act in a delicate balance with first and higher-order on-site
anisotropies to determine the material's magnetic phase. Comparison with
spin-Hall magnetoresistance measurements on a hematite single-crystal reveals
deviations of the critical behavior at low temperatures. Based on a mean-field
model, we argue that these differences result from the quantum nature of the
fluctuations that drive the phase transitions.",2301.13094v1
2023-02-22,Inverse Magnus Effect Induced by Dilute Water Fog,"The inverse Magnus effect is a phenomenon in which a spinning sphere
experiences a lift force opposite to the conventional Magnus effect. This
effect is typically observed in the flow higher than a critical Reynolds number
or spin ratio. We experimentally studied the inverse Magnus effect on a
spinning sphere in a flow containing suspended micrometer size droplets. The
lift force was measured by injecting droplets into a closed return wind tunnel.
We investigated the threshold of the inverse Magnus effect for several types of
dispersed droplets. Our results indicate that the flow with suspended water
droplets significantly affects the onset of the inverse Magnus effect, causing
a decrease in the critical Reynolds number and spin ratio.",2302.11260v3
2023-02-28,Relaxation mechanisms in a disordered system with the Poisson level statistics,"We discuss the interplay between many-body localization and spin-symmetry. To
this end, we study the time evolution of several observables in the anisotropic
t-J model. Like the Hubbard chain, the studied model contains charge and spin
degrees of freedom, yet it has smaller Hilbert space and thus allows for
numerical studies of larger systems. We compare the field disorder that breaks
the Z_2 spin symmetry and a potential disorder that preserves the latter
symmetry. In the former case, sufficiently strong disorder leads to
localization of all studied observables, at least for the studied system sizes.
However, in the case of symmetry-preserving disorder, we observe that odd
operators under the Z_2 spin transformation relax towards the equilibrium value
at relatively short time scales that grow only polynomially with the disorder
strength. On the other hand, the dynamics of even operators and the level
statistics within each symmetry sector are consistent with localization. Our
results indicate that localization exists within each symmetry sector for
symmetry preserving disorder. Odd operators' apparent relaxation is due to
their time evolution between distinct symmetry sectors.",2302.14568v1
2023-03-05,Indirect Exchange Interaction Leads to Large Lattice Contribution to Magnetocaloric Entropy Change,"Materials with a large magnetocaloric response are highly desirable for
magnetic cooling applications. It is suggested that a strong spin-lattice
coupling tends to generate a large magnetocaloric effect, but no microscopic
mechanism has been proposed. In this work, we use spin lattice dynamics
simulation to examine the lattice contribution to the magnetocaloric entropy
change in bcc iron (Fe) and hcp gadolinium (Gd) with exchange interaction
parameters determined from ab initio calculations. We find that indirect
Ruderman Kittel Kasuya Yosida (RKKY) exchange interaction in hcp Gd leads to
longer range spin lattice coupling and more strongly influences the low
frequency long wavelength phonons. This results in a higher lattice
contribution towards the total magnetocaloric entropy change as compared to bcc
Fe with short range direct exchange interactions. Our analysis provides a
framework for understanding the magnetocaloric effect in magnetic materials
with strong spin lattice couplings. Our finding suggests that long range
indirect RKKY type exchange gives rise to a larger lattice contribution to the
magnetocaloric entropy change and is, thus, beneficial for magnetocaloric
materials.",2303.02565v1
2023-03-07,Models for quantum measurement of particles with higher spin,"The Curie-Weiss model for quantum measurement describes the dynamical
measurement of a spin-$\frac{1}{2}$ by an apparatus consisting of an Ising
magnet of many spins $\frac{1}{2}$ coupled to a thermal phonon bath. To measure
the $z$-component $s=-l,-l+1,\cdots,l$ of a spin $l$, a class of models is
designed along the same lines, which involve $2l$ order parameters. As required
for unbiased measurement, the Hamiltonian of the magnet, its entropy and the
interaction Hamiltonian possess an invariance under the permutation $s\to s+1$
mod $2l+1$. The theory is worked out for the spin-1 case, where the
thermodynamics is analyzed in detail, and for spins $\frac{3}{2},2,\frac{5}{2}$
the thermodynamics and the invariance is presented.",2303.03831v1
2023-03-16,State-independent robust heat-bath algorithmic cooling of nuclear spins,"In this work, we experimentally demonstrate the implementation of a recently
proposed robust and state-independent heat-bath algorithmic cooling (HBAC)
method [1] on an NMR quantum processor. While HBAC methods improve the purity
of a quantum system via iterative unitary entropy compression, they are
difficult to implement experimentally since they use sort operations that are
different for each iteration. The new robust HBAC method proved that optimal
HBAC is possible without prior state information and using a single fixed
operation. We modified the protocol to experimentally perform efficient cooling
of 13C and 15N spins and provide an optimal decomposition of this modified
protocol in terms of quantum gates. This is the first time that optimal HBAC
has been experimentally demonstrated on 15N spins. We examined the relaxation
dynamics of these algorithmically cooled spins, in order to ascertain the
effect of decoherence on the cooled states.",2303.09087v1
2023-03-22,Target normal single-spin asymmetry in inclusive electron-nucleon scattering in the 1/Nc expansion,"The target normal single-spin asymmetry in inclusive electron-nucleon
scattering is studied in the low-energy regime that includes the $\Delta$
resonance. The particular interest in the asymmetry resides in that it is
driven by two-photon exchange effects. It probes the spin-dependent absorptive
part of the two-photon exchange amplitude, which is free of infrared and
collinear singularities and represents the most pristine expression of
two-photon exchange dynamics. The study presented here uses the 1/Nc expansion
of QCD, which combines the $N$ and $\Delta$ through the emergent SU(4)
spin-flavor symmetry in the baryon sector and allows for a systematic
construction of the transition EM currents. The analysis includes the first
subleading corrections in the 1/Nc expansion and presents results for elastic
and inelastic final states. The asymmetry is found to be in the range
$10^{-3}-10^{-2}$. The $\Delta$ resonance plays an important role as an
intermediate state in the elastic asymmetry and as a final state in the
inclusive asymmetry.",2303.12681v1
2023-03-27,Refined Spin Wave Model and Multi-magnon Bound States in $Li_{2}CuO_{2}$,"Here we report a study of the spin dynamics in the ferromagnetic chain
compound $Li_{2}CuO_{2}$. Inelastic neutron scattering measurements allow for
the spin Hamiltonian to be determined using a $J_{1}-J_{2}$ $XXZ$-Heisenberg
spin chain model with weak interchain interactions. The primary exchange
parameters determined from our data are qualitatively consistent with those of
Lorenz $et$ $al.$ [Europhys. Lett. 88, 37002 (2009)], and our data allow for
the resolution of additional interchain exchange interactions. We also observe
the formation of two- and, potentially, three-magnon bound states. The
two-magnon bound state exists only in the magnetically ordered phase of this
material, consistent with stabilization by the weak, Ising-like exchange
anisotropy of the nearest-neighbor intrachain interaction. In contrast, the
potential three-magnon state persists in a finite temperature regime above
$T_{N}$, indicating an unconventional character. Our results establish
$Li_{2}CuO_{2}$ as an experimental platform for the study of exchange
anisotropy-stabilized bound states in a ferromagnetic chain.",2303.15639v2
2023-03-28,Engineering the formation of spin-defects from first principles,"The full realization of spin qubits for quantum technologies relies on the
ability to control and design the formation processes of spin defects in
semiconductors and insulators. We present a computational protocol to
investigate the synthesis of point-defects at the atomistic level, and we apply
it to the study of a promising spin-qubit in silicon carbide, the divacancy
(VV). Our strategy combines electronic structure calculations based on density
functional theory and enhanced sampling techniques coupled with first
principles molecular dynamics. We predict the optimal annealing temperatures
for the formation of VVs at high temperature and show how to engineer the Fermi
level of the material to optimize the defect's yield for several polytypes of
silicon carbide. Our results are in excellent agreement with available
experimental data and provide novel atomistic insights into point defect
formation and annihilation processes as a function of temperature.",2303.16319v1
2023-03-30,Exact steady states of the impurity-doped XXZ spin chain coupled to dissipators,"We give an exact matrix product steady state and matrix product forms of
local observables for the bulk impurity-doped XXZ spin model coupled to
dissipators at both ends, whose dynamics is described by the Lindblad quantum
master equation. We find that local magnetization is induced at the impurity
site when the spin current flows, which is contrary to the usual situation
where current suppresses magnetization due to heating. It is proved that this
current-induced magnetization survives in the thermodynamic limit, and the spin
current does not depend on the impurity strength. We discuss the role of bulk
integrability by comparing the results with those of non-integrable models
solved numerically by the quantum trajectory method.",2303.17084v3
2023-04-17,Geometric phase and a nonreciprocal spin wave circular polarizer,"We show that spin wave acquires a polarization-dependent geometric phase
along a cyclic trajectory of non-coplanar magnetizations in antiferromagnets.
Specifically, we demonstrate that a cyclic set of 90 degree antiferromagnetic
domain walls simultaneously introduce geometric and dynamic phases to spin
wave, and thus leads to asymmetric magnitude of overall phase for
left-/right-circular components. Based on the polarization-dependent phase, we
propose theoretically and confirm by micromagnetic simulations that, a
Mach-Zehner interferometer with cyclic 90 degree domain walls in one arm and
homogenous domain in the other arm, naturally acts as a spin wave circular
polarizer. Moreover, the circular polarizer has intrinsic nonreciprocity, which
filters opposite polarization in opposite propagation direction.",2304.08071v1
2023-04-27,Enhancing polarization transfer from nitrogen-vacancy centers in diamond to external nuclear spins via dangling bond mediators,"The use of nitrogen-vacancy centers in diamond as a non-invasive platform for
hyperpolarizing nuclear spins in molecular samples is a promising area of
research with the potential to enhance the sensitivity of nuclear magnetic
resonance experiments. Transferring NV polarization out of the diamond
structure has been achieved on nanoscale targets using dynamical nuclear
polarization methods, but extending this to relevant NMR volumes poses
significant challenges. One major technical hurdle is the presence of
paramagnetic defects in the diamond surface which can interfere with
polarization outflow. However, these defects can also be harnessed as
intermediaries for the interaction between NVs and nuclear spins. We present a
method that benefits from existing microwave sequences, namely the PulsePol, to
transfer polarization efficiently and robustly using dangling bonds or other
localized electronic spins, with the potential to increase polarization rates
under realistic conditions.",2304.14282v3
2023-05-26,Dynamical exchange-correlation potential formalism for spin-$\frac{1}{2}$ Heisenberg and Hubbard chains: the antiferromagnetic/half-filled case,"The exchange-correlation potential formalism previously introduced and
applied to the one-dimensional Hubbard model has been extended to spin systems
and applied to the case of the one-dimensional antiferromagnetic
spin$-\frac{1}{2}$ Heisenberg model. Within the spin exchange-correlation
potential formulation, a new sum rule for spin-systems is derived. The
exchange-correlation potential for the Heisenberg model is extrapolated from
exact diagonalization results of small antiferromagnetic Heisenberg clusters.
This procedure is also employed to revisit and computationally improve the
previous investigation of the exchange-correlation potential of the half-filled
Hubbard model, which was based on the exchange-correlation potential of the
dimer. Numerical comparisons with exact benchmark calculations for both the
Heisenberg and the Hubbard models indicate that, starting from the
exchange-correlation potential of a finite cluster, the extrapolation procedure
yields a one-particle spectral function with favorable accuracy at a relatively
low computational cost. In addition, a comparison between the ground state
energies for the one-dimensional Hubbard and Heisenberg models displays how the
well known similarity in behavior of the two models at large interactions
manifests within the exchange-correlation potential formalism.",2305.16879v1
2023-05-29,Light-induced weak ferromagnetism through nonlinear magnonic rectification,"Rectification describes the generation of a quasistatic component from an
oscillating field, such as an electric polarization in optical rectification,
or a structural distortion in nonlinear phononic rectification. Here, we
present a third fundamental process for magnetization, in which spin precession
is rectified along the coordinates of a nonlinearly driven magnon mode in an
antiferromagnet. We demonstrate theoretically that a quasistatic magnetization
can be induced by transient spin canting in response to the coherent excitation
of a chiral phonon mode that produces an effective magnetic field for the
spins. This mechanism, which we call nonlinear magnonic rectification, is
generally applicable to magnetic systems that exhibit infrared-active chiral
phonon modes. Our results serve as an example of light-induced weak
ferromagnetism and open a promising avenue towards creating dynamical spin
configurations that are not accessible in equilibrium.",2305.18656v2
2023-06-05,Dynamic Calculations of Magnetic Field and Implications on Spin Polarization and Spin Alignment in Heavy Ion Collisions,"Magnetic field plays a crucial role in various novel phenomena in heavy-ion
collisions. We solve the Maxwell equations numerically in a medium with
time-dependent electric conductivity by using the Finite-Difference Time-Domain
(FDTD) algorithm. We investigate the time evolution of magnetic fields in two
scenarios with different electric conductivities at collision energies ranging
from $\sqrt{s_\text{NN}}=$ 7.7 to 200 GeV. Our results suggest that the
magnetic field may not persist long enough to induce a significant splitting
between the global spin polarizations of $\Lambda$ and $\bar{\Lambda}$ at
freeze-out stage. However, our results do not rule out the possibility of the
magnetic field influencing the spin (anti-)alignment of vector mesons.",2306.02829v1
2023-06-22,Spin-echo and quantum versus classical critical fluctuations in TmVO$_4$,"Using spin-echo Nuclear Magnetic Resonance in the model Transverse-Field
Ising system TmVO$_4$, we show that low frequency quantum fluctuations at the
quantum critical point have a very different effect on $^{51}$V nuclear-spins
than classical low-frequency noise or fluctuations that arise at a finite
temperature critical point. Spin-echos filter out the low frequency classical
noise but not the quantum fluctuations. This allows us to directly visualize
the quantum critical fan and demonstrate the persistence of quantum
fluctuations at the critical coupling strength in TmVO$_4$ to high temperatures
in an experiment that remains transparent to finite temperature classical phase
transitions. These results show that while dynamical decoupling schemes can be
quite effective in eliminating classical noise in a qubit, a quantum critical
environment may lead to rapid entanglement and decoherence.",2306.13244v1
2023-06-26,Quantum phases and spectrum of collective modes in a spin-1 BEC with spin-orbital-angular-momentum coupling,"Motivated by the recent experiments [Chen et al., Phys. Rev. Lett 121, 113204
(2018), Chen et al., Phys. Rev. Lett. 121, 250401 (2018)], we investigate the
low-lying excitation spectrum of the ground-state phases of
spin-orbital-angular-momentum-coupled (SOAM-coupled) spin-1 condensates.At
vanishing detuning, a ferromagnetic SOAM-coupled spin-1 BEC can have two
ground-state phases, namely coreless and polar-core vortex states, whereas an
antiferromagnetic BEC supports only polar-core vortex solution. The angular
momentum per particle, longitudinal magnetization, and excitation frequencies
display discontinuities across the phase boundary between the coreless vortex
and polar-core vortex phases. The low-lying excitation spectrum evaluated by
solving the Bogoliubov-de-Gennes equations is marked by avoided crossings and
hence the hybridization of the spin and density channels. The spectrum is
further confirmed by the dynamical evolution of the ground state subjected to a
perturbation suitable to excite a density or a spin mode and a variational
analysis for the density-breathing mode.",2306.14669v2
2023-07-05,Spin as a probe of axion physics in general relativity,"The dynamics of spin in external electromagnetic, gravitational, and axion
fields is analysed in the framework of the gravitoelectromagnetism approach in
Einstein's general relativity theory. We consistently extend the recent studies
from the flat Minkowski geometry to the curved spacetime manifolds,
contributing to the discussion of the possible new role of a precessing spin as
an ``axion antenna'' that can be used to detect the hypothetical axion-like
dark matter. The formalism developed helps to clarify the subtle influence of
the gravitational/inertial and axion fields in the ultra-sensitive high-energy
spin experiments with charged particles and neutrons at accelerators and
storage rings devoted to testing fundamental physical symmetries, including
attempts to establish the nature of dark matter in the Universe.",2307.02567v1
2023-07-11,Critical steady states of all-to-all squeezed and driven superradiance: An analytic approach,"We analyse the properties across steady state phase transitions of two
all-to-all driven-dissipative spin models that describe possible dynamics of N
two-level systems inside an optical cavity. We show that the finite size
behaviour around the critical points can be captured correctly by carefully
identifying the relevant non-linearities in the Holstein-Primakoff
representation of spin operators in terms of bosonic variables. With these
tools, we calculate analytically various observables across the phase
transitions and obtain their finite size scalings, including numerical
prefactors. In particular, we look at the amount of spin squeezing carried by
the steady states, of relevance for quantum metrology applications, and
describe in analytical detail the mechanism by which the optimal spin squeezing
acquires logarithmic corrections that depend on the system size. We also
demonstrate that the logarithmic nature of these corrections is difficult to
characterize through numerical procedures for any experimentally realistic
and/or simulable values of particle number. We complement all of our analytical
arguments with numerical benchmarks.",2307.05115v2
2023-07-13,Strong-field scattering of two spinning black holes: Numerical Relativity versus post-Minkowskian gravity,"Highly accurate models of the gravitational-wave signal from coalescing
compact binaries are built by completing analytical computations of the binary
dynamics with non-perturbative information from numerical relativity (NR)
simulations. In this paper we present four sets of NR simulations of equal-mass
black hole binaries that undergo strong-field scattering: (i) we reproduce and
extend the nonspinning simulations first presented in [Damour \textit{et al.},
Phys.Rev.D 89 (2014) 8, 081503], (ii) we compute two suites of nonspinning
simulations at higher energies, probing stronger field interactions, (iii) we
present a series of \textit{spinning} simulations including, for the first
time, unequal-spin configurations. When comparing the NR scattering angles to
analytical predictions based on state-of-the-art post-Minkowskian (PM)
calculations, we find that PM-expanded scattering angles show poor convergence
towards NR data. By contrast, a resummed computation of scattering angles via a
spin-dependent, radiation-reacted, effective-one-body potential shows excellent
agreement for both nonspinning and spinning configurations.",2307.06999v2
2023-07-14,Gravitational partial-wave absorption from scattering amplitudes,"We study gravitational absorption effects using effective on-shell scattering
amplitudes. We develop an in-in probability-based framework involving plane-
and partial-wave coherent states for the incoming wave to describe the
interaction of the wave with a black hole or another compact object. We connect
this framework to a simplified single-quantum analysis. The basic ingredients
are mass-changing three-point amplitudes, which model the leading absorption
effects and a spectral-density function of the black hole. As an application,
we consider a non-spinning black hole that may start spinning as a consequence
of the dynamics. The corresponding amplitudes are found to correspond to
covariant spin-weighted spherical harmonics, the properties of which we
formulate and make use of. We perform a matching calculation to
general-relativity results at the cross-section level and derive the effective
absorptive three-point couplings. They are found to behave as ${\cal
O}(G_\text{Newton}^{s+1})$, where $s$ is the spin of the outgoing massive
state.",2307.07504v3
2023-08-03,Manifestation of topological phase in neutron spin rotation without adiabatic regime,"The Bitter-Dubbers (BD) experiment is an important experiment that originally
aimed to measure topological phase using polarized-neutron spin rotation in a
helical magnetic field under adiabatic conditions. Contrary to expectations,
upon reevaluation of the BD experiment, it has been found that adiabatic
conditions are not necessary for measuring topological phase. In scenarios
where the magnetic field is neither homogeneous nor strong enough, and the
neutron has a fast velocity, the topological phase can still be manifested. To
demonstrate this, we analytically solve the time-dependent Schrodinger equation
for the neutron spin rotation in general rotating systems. These exact
solutions are then utilized to investigate the nonadiabatic topological phase
under the conditions mentioned above. The numerical simulations of the
nonadiabatic topological phase have shown a strong concurrence with the BD
experimental data. This novel result extends our understanding of the
topological phase observed in neutron spin rotation, even in more complex and
dynamic scenarios beyond the originally required adiabatic conditions.",2308.01608v2
2023-08-10,Lagrangian formulation for free $6D$ infinite spin field,"We construct a Lagrangian that describes the dynamics of a six-dimensional
free infinite (continuous) spin field in $6D$ Minkowski space. The Lagrangian
is formulated in the framework of the BRST approach to higher spin field theory
and is based on a system of constraints defining an irreducible representation
of the corresponding Poincar\'e group. The field realization of generators in
the $6D$ Poincar\'e algebra and the second-, fourth-, and sixth-order Casimir
operators are obtained in explicit form using additional spinor coordinates.
Specific aspects of such a realization in six dimensions are discussed. We
derive the conditions that determine the irreducible representation $6D$
infinite spin field and reformulate them as operators in the Fock space forming
a first-class algebra in terms of commutators. These operators are used to
construct the BRST charge and the corresponding Lagrangian. We prove that the
conditions of the irreducible representation are reproduced as the consequence
of the Lagrangian equations of motion, which finally provides the correctness
of the results obtained.",2308.05622v2
2023-08-15,Quantum Spin Systems,"This work provides an overview of gapped quantum spin systems, including
concepts, techniques, properties, and results. The basic framework and objects
of interest for quantum spin systems are introduced, and the main ideas behind
methods for proving spectral gaps for frustration-free models are outlined.
After reviewing recent progress on several spectral gap conjectures, we discuss
quasi-locality of the Heisenberg dynamics and its utility in proving properties
of gapped quantum spin systems. Lieb-Robinson bounds have played a central role
in establishing exponential decay of ground state correlations, an area law for
one-dimensional systems, a many-body adiabatic theorem, and spectral gap
stability. They also aided in the development of the quasi-adiabatic
continuation, which is a useful for investigating gapped ground state phases,
both of which are also discussed.",2308.07848v1
2023-08-16,Pole skipping in holographic theories with gauge and fermionic fields,"Using covariant expansions, recent work showed that pole skipping happens in
general holographic theories with bosonic fields at frequencies
$\mathrm{i}(l_b-s) 2\pi T$, where $l_b$ is the highest integer spin in the
theory and $s$ takes all positive integer values. We revisit this formalism in
theories with gauge symmetry and upgrade the pole-skipping condition so that it
works without having to remove the gauge redundancy. We also extend the
formalism by incorporating fermions with general spins and interactions and
show that their presence generally leads to a separate tower of pole-skipping
points at frequencies $\mathrm{i}(l_f-s)2\pi T$, $l_f$ being the highest
half-integer spin in the theory and $s$ again taking all positive integer
values. We also demonstrate the practical value of this formalism using a
selection of examples with spins $0,\frac{1}{2},1,\frac{3}{2},2$.",2308.08191v2
2023-08-31,DFT+DMFT study of the magnetic susceptibility and the correlated electronic structure in transition-metal intercalated NbS$_2$,"The Co-intercalated NbS$_2$ (Co$_{1/3}$NbS$_2$) compound exhibits large
anomalous Hall conductance, likely due to the non-coplanar magnetic ordering of
Co spins. In this work, we study the relation between this novel magnetism and
the correlated electronic structure of Co$_{1/3}$NbS$_2$ by adopting dynamical
mean field theory (DMFT) to treat the correlation effect of Co $d$ orbitals. We
find that the hole doping of Co$_{1/3}$NbS$_2$ can tune the size of the Nb hole
pocket at the DMFT Fermi surface, producing features consistent with those
observed in angle resolved photoemission spectra [Phys. Rev. B 105, L121102
(2022)]. We also compute the momentum-resolved spin susceptibility, and
correlate it with the Fermi surface shape. We find that the magnetic ordering
wavevector of Co$_{1/3}$NbS$_2$ obtained from the peak in spin susceptibility
agrees with the one observed experimentally by neutron scattering; it is
compatible with commensurate non-coplanar $3q$ spin structure. We also discuss
how results change if some other than Co transition metal intercalations are
used.",2309.00112v1
2023-09-02,Predication of novel effects in rotational nuclei at high speed,"The study of high-speed rotating matter is a crucial research topic in
physics due to the emergence of novel phenomena. In this paper, we combined
cranking covariant density functional theory (CDFT) with a similar
renormalization group approach to decompose the Hamiltonian from the cranking
CDFT into different Hermit components, including the non-relativistic term, the
dynamical term, the spin-orbit coupling, and the Darwin term. Especially, we
obtained the rotational term, the term relating to Zeeman effect-like, and the
spin-rotation coupling due to consideration of rotation and spatial component
of vector potential. By exploring these operators, we aim to identify novel
phenomena that may occur in rotating nuclei. Signature splitting, Zeeman
effect-like, spin-rotation coupling, and spin current are among the potential
novelties that may arise in rotating nuclei. Additionally, we investigated the
observability of these phenomena and their dependence on various factors such
as nuclear deformation, rotational angular velocity, and strength of magnetic
field.",2309.00786v1
2023-09-12,Application of the path optimization method to a discrete spin system,"The path optimization method, which is proposed to control the sign problem
in quantum field theories with continuous degrees of freedom by machine
learning, is applied to a spin model with discrete degrees of freedom. The path
optimization method is applied by replacing the spins with dynamical variables
via the Hubbard-Stratonovich transformation, and the sum with the integral. The
one-dimensional (Lenz-)Ising model with a complex coupling constant is used as
a laboratory for the sign problem in the spin model. The average phase factor
is enhanced by the path optimization method, indicating that the method can
weaken the sign problem. Our result reproduces the analytic values with
controlled statistical errors.",2309.06018v2
2023-09-25,Spectral Crossovers and Universality in Quantum Spin-chains Coupled to Random Fields,"We study the spectral properties of and spectral-crossovers between different
random matrix ensembles (Poissonian, GOE, GUE) in correlated spin-chain
systems, in the presence of random magnetic fields, and the scalar
spin-chirality term, competing with the usual isotropic and time-reversal
invariant Heisenberg term. We have investigated these crossovers in the context
of the level-spacing distribution and the level-spacing ratio distribution. We
use random matrix theory (RMT) analytical results to fit the observed
Poissonian-to-GOE and GOE-to-GUE crossovers, and examine the relationship
between the RMT crossover parameter {\lambda} and scaled physical parameters of
the spin-chain systems in terms of a scaling exponent. We find that the
crossover behavior exhibits universality, in the sense that it becomes
independent of lattice size in the large Hamiltonian matrix dimension limit.",2309.14076v1
2023-09-28,Time Crystal Embodies Chimera in Periodically Driven Quantum Spin System,"Chimera states are a captivating occurrence in which a system composed of
multiple interconnected elements exhibits a distinctive combination of
synchronized and desynchronized behavior. The emergence of these states can be
attributed to the complex interdependence between quantum entanglement and the
delicate balance of interactions among system constituents. The emergence of
discrete-time crystal (DTC) in typical many-body periodically driven systems
occurs when there is a breaking of time translation symmetry. Coexisting
coupled DTC and a ferromagnetic dynamically many-body localized (DMBL) phase at
distinct regions have been investigated under the controlled spin rotational
error of a disorder-free spin-1/2 chain for different types of spin-spin
interactions. We contribute a novel approach for the emergence of the
DTC-DMBL-chimera phase, which is robust against external static fields in a
periodically driven quantum many-body system.",2309.16523v3
2023-10-24,O(1) benchmarking of precise rotation in a spin-squeezed Bose-Einstein condensate,"Benchmarking a high-precision quantum operation is a big challenge for many
quantum systems in the presence of various noises as well as control errors.
Here we propose an $O(1)$ benchmarking of a dynamically corrected rotation by
taking the quantum advantage of a squeezed spin state in a spin-1 Bose-Einstein
condensate. Our analytical and numerical results show that tiny rotation
infidelity, defined by $1-F$ with $F$ the rotation fidelity, can be calibrated
in the order of $1/N^2$ by only several measurements of the rotation error for
$N$ atoms in an optimally squeezed spin state. Such an $O(1)$ benchmarking is
possible not only in a spin-1 BEC but also in other many-spin or many-qubit
systems if a squeezed or entangled state is available.",2310.15473v1
2023-11-07,A pseudofermion functional renormalization group study of dipolar-octupolar pyrochlore magnets,"Motivated by recent experiments on Ce$_2$Zr$_2$O$_7$ that reveal a dynamic,
liquid-like ground state, we study the nearest neighbor XYZ Hamiltonian of
dipolar-octupolar pyrochlore magnets with the pseudofermion functional
renormalization group (PFFRG), which is numerically implemented by the
SpinParser software. Taking the interaction between the octupolar components to
be dominant and antiferromagnetic, we map out the phase diagram demarcating the
quantum disordered and magnetically ordered states. We identify four distinct
phases, namely the $0$-flux and $\pi$-flux quantum spin ices, and the
all-in-all-out magnetic orders along the local $z$ and $x$ axes. We further use
the static two-spin correlations output by the PFFRG algorithm to compute the
polarized neutron scattering cross-sections, which are able to capture several
qualitative features observed experimentally, in the materially relevant
parameter regime that stabilizes the $\pi$-flux quantum spin ice. Our results
provide support for a quantum spin liquid ground state in Ce$_2$Zr$_2$O$_7$.",2311.04269v1
2023-11-16,Hund electronic correlation in La$_3$Ni$_2$O$_7$ under high pressure,"By means of density functional theory plus dynamical mean-field theory
(DFT+DMFT), we investigate the correlated electronic structures of
La$_3$Ni$_2$O$_7$ under high pressure. Our calculations show that
La$_3$Ni$_2$O$_7$ is a multi-orbital Hund metal. Both the 3$d_{z^2}$ and
3$d_{x^2 - y^2}$ orbitals of Ni are close to be half filled and contribute the
bands across the Fermi level. Band renormalization and orbital selective
electronic correlation are observed. Through imaginary-time correlation
functions, the discovery of high-spin configuration, spin-frozen phase, and
spin-orbital separation shows that the system is in a frozen moment phase at
high temperatures above 290 K and is a Fermi liquid at low temperatures, which
is further comfirmed by the calculated spin, orbital, and charge
susceptibilities under high temperatures. Our study uncovers Hundness in
La$_3$Ni$_2$O$_7$ under high pressure.",2311.10066v1
2023-11-17,Robust universal quantum processors in spin systems via Walsh pulse sequences,"We propose a protocol to realize quantum simulation and computation in spin
systems with long-range interactions. Our approach relies on the local
addressing of single spins with external fields parametrized by Walsh
functions. This enables a mapping from a class of target Hamiltonians, defined
by the graph structure of their interactions, to pulse sequences. We then
obtain a recipe to implement arbitrary two-body Hamiltonians and universal
quantum circuits. Performance guarantees are provided in terms of bounds on
Trotter errors and total number of pulses. Additionally, Walsh pulse sequences
are shown to be robust against various types of pulse errors, in contrast to
previous hybrid digital-analog schemes of quantum computation. We demonstrate
and numerically benchmark our protocol with examples from the dynamics of spin
models, quantum error correction and quantum optimization algorithms.",2311.10600v2
2023-11-22,Quantum Sensing of Magnetic Fields with Molecular Spins,"Spins are prototypical systems with the potential to probe magnetic fields
down to the atomic scale limit. Exploiting their quantum nature through
appropriate sensing protocols allows to enlarge their applicability to fields
not always accessible by classical sensors. Here we first show that quantum
sensing protocols for AC magnetic fields can be implemented on molecular spin
ensembles embedded into hybrid quantum circuits. We then show that, using only
echo detection at microwave frequency and no optical readout, Dynamical
Decoupling protocols synchronized with the AC magnetic fields can enhance the
sensitivity up to $S = 10^{-10}-10^{-9}T/\sqrt{Hz}$ with a low (4-5) number of
applied pulses. These results paves the way for the development of strategies
to exploit molecular spins as quantum sensors.",2311.13504v1
2023-11-24,Criticality-Enhanced Precision in Phase Thermometry,"Temperature estimation of interacting quantum many-body systems is both a
challenging task and topic of interest in quantum metrology, given that
critical behavior at phase transitions can boost the metrological sensitivity.
Here we study non-invasive quantum thermometry of a finite, two-dimensional
Ising spin lattice based on measuring the non-Markovian dephasing dynamics of a
spin probe coupled to the lattice. We demonstrate a strong critical enhancement
of the achievable precision in terms of the quantum Fisher information, which
depends on the coupling range and the interrogation time. Our numerical
simulations are compared to instructive analytic results for the critical
scaling of the sensitivity in the Curie-Weiss model of a fully connected
lattice and to the mean-field description in the thermodynamic limit, both of
which fail to describe the critical spin fluctuations on the lattice the spin
probe is sensitive to. Phase metrology could thus help to investigate the
critical behaviour of finite many-body systems beyond the validity of
mean-field models.",2311.14578v2
2023-12-03,Thermodynamics of the Fredrickson-Andersen Model on the Bethe Lattice,"The statics of the Fredrickson-Andersen model (FAM) of the liquid-glass
transition is solved on the Bethe lattice (BL). The kinetic constraints of the
FAM imply on the BL an ergodicity-breaking transition to a (glassy) phase where
a fraction of spins of the system is permanently blocked, and the remaining
""free"" spins become non-trivially correlated. We compute several observables of
the ergodicity-broken phase, such as the self-overlap, the configurational
entropy and the spin-glass susceptibility, and we compare the analytical
predictions with numerical experiments. The cavity equations that we obtain
allow to define algorithms for fast equilibration and accelerated dynamics. We
find that at variance with spin-glass models, the correlations inside a state
do not exhibit a critical behavior.",2312.01430v1
2023-12-13,Spin fluctuations sufficient to mediate superconductivity in nickelates,"Infinite-layer nickelates show high-temperature superconductivity, and the
experimental phase diagram agrees well with the one simulated within the
dynamical vertex approximation (D$\Gamma$A). Here, we compare the
spin-fluctuation spectrum behind these calculations to resonant inelastic X-ray
scattering experiments. The overall agreement is good. This independent
cross-validation of the strength of spin fluctuations strongly supports the
scenario, advanced by D$\Gamma$A, that spin-fluctuations are the mediator of
the superconductivity observed in nickelates.",2312.08260v1
2023-12-25,Emergent Quadrupolar Order in the Spin-$1/2$ Kitaev-Heisenberg Model,"Motivated by the largely unexplored domain of multi-polar ordered spin states
in the Kitaev-Heisenberg (KH) systems we investigate the ground state dynamics
of the spin-$\frac{1}{2}$ KH model, focusing on quadrupolar (QP) order in 2-leg
ladder and two-dimensional honeycomb lattice geometries. Employing exact
diagonalization and density-matrix renormalization group methods, we analyze
the QP order parameter and correlation functions. Our findings reveal a robust
QP order across a wide range of the phase diagram, influenced by the interplay
between Heisenberg and Kitaev interactions. Notably, we observe an enhancement
of QP order near Kitaev quantum spin liquid (QSL) phases, despite the absence
of long-range spin-spin correlations. This highlights a complex relationship
between QP order and QSLs, offering new insights into quantum magnetism in
low-dimensional systems. Our findings provide a rational explanation for the
observed nonlinear magnetic susceptibility in $\alpha$-RuCl$_3$.",2312.15609v3
2024-01-24,Considerations and findings on beam vorticity dynamics,"This document is on considerations and findings on modelling of spinning
beams. Spinning has been proposed for stabilizing beams against perturbations
notably risen by non-linear space charge forces, see [Y.-L. Cheon et al.,
Effects of beam spinning on the fourth-order particle resonance of 3D bunched
beams in high-intensity linear accelerators, Phys. Rev. Accel. & Beams 25,
064002 (2022)]. Although not further treated therein, spinning can be
quantified by angular momentumor by vorticity. Considering vorticity revealed
that the latter has remarkable similarity w.r.t. its modelling along solenoid
channels to modelling the beam envelope. Matrices of vorticity transport,
corresponding phase advances, and Twiss parameters look very similar and are
partially even identical to their counterparts concerning envelopes.
Corresponding to emittance, the quantity of vortissance, being a constant of
motion, is defined. Unlike emittance, for vorticity-dominated beams it may take
imaginary values, causing Twiss parameters, and negative or zero phase advances
along a finite beam line section. This imposes considerable consequences on
respective periodic solutions.",2401.13644v2
2024-01-29,Quantum Fragmentation in the Extended Quantum Breakdown Model,"We introduce a one-dimensional (1D) extended quantum breakdown model
comprising a fermionic and a spin degree of freedom per site, and featuring a
spatially asymmetric breakdown-type interaction between the fermions and spins.
We analytically show that, in the absence of any magnetic field for the spins,
the model exhibits Hilbert space fragmentation within each symmetry sector into
exponentially many Krylov subspaces and hence displays non-thermal dynamics.
Here, we demonstrate that the fragmentation naturally occurs in an entangled
basis and thus provides an example of ""quantum fragmentation."" Besides
establishing the nature of fragmentation analytically, we also study the
long-time behavior of the entanglement entropy and its deviation from the
expected Page value as a probe of ergodicity in the system. Upon introducing a
non-trivial magnetic field for the spins, most of the Krylov subspaces merge
and the model becomes chaotic. Finally, we study the effects of strong
randomness on the system and observe behavior similar to that of many-body
localized systems.",2401.16480v1
2024-02-05,Realizing and detecting Stiefel-Whitney insulators in an optical Raman lattice,"We propose a feasible scheme to realize a four-band Stiefel-Whitney insultor
(SWI) with spin-orbit coupled ultracold atoms in an optical Raman lattice. Four
selected spin states are coupled by carefully designed Raman lasers, to
generate the desired spin-orbit interactions with spacetime inversion symmetry.
We map out a phase diagram with respect to the experimental parameters, where a
large topological phase region exists. We further present two distinct
detection methods to resolve the non-abelian band topology, in both equilibrium
and dynamical ways. The detection relies on the spin textures extracted from
the time-of-flight imaging, showing the tomographic signatures in the ground
states and long-time averaged patterns on certain submanifold via a
bulk-surface duality. Our work paves a realistic way to explore novel real
topology with quantum matters.",2402.02777v1
2024-02-26,Toward high-fidelity quantum information processing and quantum simulation with spin qubits and phonons,"We analyze the implementation of high-fidelity, phonon-mediated gate
operations and quantum simulation schemes for spin qubits associated with
silicon vacancy centers in diamond. Specifically, we show how the application
of continuous dynamical decoupling techniques can substantially boost the
coherence of the qubit states while increasing at the same time the variety of
effective spin models that can be implemented in this way. Based on realistic
models and detailed numerical simulations, we demonstrate that this decoupling
technique can suppress gate errors by more than two orders of magnitude and
enable gate infidelities below $\sim 10^{-4}$ for experimentally relevant noise
parameters. Therefore, when generalized to phononic lattices with arrays of
implanted defect centers, this approach offers a realistic path toward
moderate- and large-scale quantum devices with spins and phonons, at a level of
control that is competitive with other leading quantum-technology platforms.",2402.16960v1
2024-02-28,Hilbert Space Fragmentation and Subspace Scar Time-Crystallinity in Driven Homogeneous Central-Spin Models,"We study the stroboscopic non-equilibrium quantum dynamics of periodically
kicked Hamiltonians involving homogeneous central-spin interactions. The system
exhibits a strong fragmentation of Hilbert space into four-dimensional
Floquet-Krylov subspaces, which oscillate between two disjointed
two-dimensional subspaces and thus break the discrete time-translation symmetry
of the system. Our analytical and numerical analyses reveal that fully
polarized states of the satellite spins exhibit fragmentations that are stable
against perturbations and have high overlap with Floquet eigenstates of
atypically low bipartite entanglement entropy (scar states). We present
evidence of robust time-crystalline behavior in the form of a period doubling
of the total magnetization of fully polarized satellite spin states that
persists over long time scales. We compute non-equilibrium phase diagrams with
respect to a magnetic field, coupling terms, and pulse error for various
interaction types, including Heisenberg, Ising, XXZ, and XX. We also discuss
possible experimental realizations of scar time crystals in color center,
quantum dot, and rare-earth ion platforms.",2402.18001v1
2024-03-05,Magnon kinetic theory of the antiferromagnetic Hanle effect,"Motivated by the recently discovered magnonic Hanle effect in an insulating
antiferromagnet [Wimmer et al., Phys. Rev. Lett. 125, 247204 (2020)], we
develop a spin transport theory based on low-energy waves of antiferromagnetic
N\'eel order. These waves have two polarizations, which we describe in analogy
to optics using the Stokes vector on the Poincar\'e sphere. We find that the
polarization, which encodes the magnon spin angular momentum, changes
periodically with a frequency that is nonlinear in the magnetic field. This
explains the observed asymmetry in the Hanle signal as a function of the
magnetic field, along with other salient experimental features. By providing an
energy-resolved description of the spin injection, our theory combines the
kinetic transport of magnons with the coherent dynamics of their polarization
in an intuitive way. This opens a general perspective on a coherent control of
magnonic spin density in collinear antiferromagnets.",2403.03358v1
2024-03-13,Emergent Continuous Time Crystal in Dissipative Quantum Spin System without Driving,"Time crystal, a nonequilibrium phenomenon extending spontaneous symmetry
breaking into the temporal dimension, holds fundamental significance in
understanding quantum many-body physics. In this work, we explore the
nonequilibrium phase diagram of a two-dimensional dissipative Heisenberg spin
system in the absence of explicit driving. We numerically identify the
emergence of novel nonstationary oscillatory states by analyzing the spin
dynamics. These states are categorized as limit cycle and chaos based on the
Lyapunov exponent. Remarkably, the observed limit cycle behavior represents a
continuous time crystal (CTC), spontaneously breaking the continuous time
translation symmetry of the system. We further confirm those oscillatory
behaviors by studying the stability against local perturbations applied to the
system. Finally, we investigate the robustness of the emergent CTC by
introducing isotropic Gaussian-type white noise into the interactions. This
study provides many insights into the intricate interplay between
dissipation-induced decay processes and interaction-induced spin precession,
deepening our understanding of dissipative quantum many-body systems.",2403.08476v1
2024-03-18,Adiabatic Bottlenecks in Quantum Annealing and Nonequilibrium Dynamics of Paramagnons,"The correspondence between long-range interacting quantum spin glasses and
combinatorial optimization problems underpins the physical motivation for
adiabatic quantum computing. On one hand, in disordered (quantum) spin systems,
the focus is on exact methods such as the replica trick that allow the
calculation of system quantities in the limit of infinite system and ensemble
size. On the other hand, when solving a given instance of an optimization
problem, disorder-averaged quantities are of no relevance, as one is solely
interested in instance-specific, finite-size properties, in particular the true
solution. Here, we apply the nonequilibrium Green-function formalism to the
spin coherent-state path integral to obtain the statistical fluctuations and
the collective-excitation spectrum along the annealing path. For the example of
the quantum Sherrington-Kirkpatrick spin glass, by comparing to extensive
numerically exact results, we show that this method provides access to the
instance-specific bottlenecks of the annealing protocol.",2403.11548v1
1999-03-02,Dynamics of Vortices in Two-Dimensional Magnets,"Theories, simulations and experiments on vortex dynamics in
quasi-two-dimensional magnetic materials are reviewed. These materials can be
modelled by the classical two-dimensional anisotropic Heisenberg model with XY
(easy-plane) symmetry. There are two types of vortices, characterized by their
polarization (a second topological charge in addition to the vorticity): Planar
vortices have Newtonian dynamics (even-order equations of motion) and exhibit
strong discreteness effects, while non-planar vortices have non-Newtonian
dynamics (odd-order equations of motion) and smooth trajectories. The influence
of thermal fluctuations on single vortices is investigated. Different types of
noise and damping are discussed and implemented into the microscopic equations
which yields stochastic equations of motion for the vortices. The solutions of
the these equations are compared with Langevin dynamics simulations. Moreover,
noise-induced transitions between opposite polarizations of a vortex are
investigated. For temperatures above the Kosterlitz-Thouless vortex-antivortex
unbinding transition, a phenomenological theory, namely the vortex gas
approach, yields central peaks in the dynamic form factors for the spin
correlations. Such peaks are observed both in combined Monte Carlo- and Spin
Dynamics-Simulations and in inelastic neutron scattering experiments. However,
the assumption of ballistic vortex motion appears questionable.",9903037v1
2002-05-04,A dynamical mean-field theory approach to superconductivity and antiferromagnetism in a strongly correlated electron system,"We present the results of numerical studies of superconductivity and
antiferromagnetism in a strongly correlated electron system. To do this we
construct a Hubbard model on a lattice of self-consistently embedded multi-site
clusters by means of a dynamical mean-field theory in which intra-cluster
dynamics is treated essentially exactly. We show that a class of characteristic
features which have been seen in the excitation spectra of high-$T_{c}$
cuprates (e.g., pseudogap and the spin-flip resonance), as well as their
interplay with the onset of a pairing correlations, can be captured within a
dynamical mean-field theory in which short-wavelength dynamics are rigorously
treated. Thus we infer that the observation of the neutron scattering resonance
in the superconducting state of the cuprate superconductors does not appear to
be directly tied to their quasi-2D character. Although our approach is defined
strictly in terms of fermion degrees of freedom, we show that we can readily
identify the emergence of effective low energy bosonic degrees of freedom in
the presence of a well-defined broken symmetry phase as long as their dynamics
are dominated by short-range, short-wavelength fluctuations. Our results reveal
that the dynamics of staggered spin degrees of freedom builds up coherence and
a resonance-like sharp feature emerges as pairing correlations set in. Under
conditions of superconducting broken symmetry our approach thus extends static
BCS mean field theory to provide an exact treatment of quantum fluctuations of
the BCS order parameter.",0205086v1
2006-05-01,Glauber dynamics of phase transitions: SU(3) lattice gauge theory,"Motivated by questions about the QCD deconfining phase transition, we studied
in two previous papers Model A (Glauber) dynamics of 2D and 3D Potts models,
focusing on structure factor evolution under heating (heating in the gauge
theory notation, i.e., cooling of the spin systems). In the present paper we
set for 3D Potts models (Ising and 3-state) the scale of the dynamical effects
by comparing to equilibrium results at first and second order phase transition
temperatures, obtained by re-weighting from a multicanonical ensemble. Our
finding is that the dynamics entirely overwhelms the critical and non-critical
equilibrium effects.
  In the second half of the paper we extend our results by investigating the
Glauber dynamics of pure SU(3) lattice gauge on $N_{\tau} N_{\sigma}^3$
lattices directly under heating quenches from the confined into the deconfined
regime. The exponential growth factors of the initial response are calculated,
which give Debye screening mass estimates. The quench leads to competing vacuum
domains of distinct $Z_3$ triality, which delay equilibration of pure gauge
theory forever, while their role in full QCD remains a subtle question. As in
spin systems we find for pure SU(3) gauge theory a dynamical growth of
structure factors, reaching maxima which scale approximately with the volume of
the system, before settling down to equilibrium. Their influence on various
observables is studied and different lattice sizes are simulated to illustrate
an approach to a finite volume continuum limit. Strong correlations are found
during the dynamical process, but not in the deconfined phase at equilibrium.",0605001v1
2001-02-16,Atomic motion in magneto-optical double-well potentials: A new testing ground for quantum chaos,"We have identified ultra-cold atoms in magneto-optical double-well potentials
as a very clean setting in which to study the quantum and classical dynamics of
a nonlinear system with multiple degrees of freedom. In this system,
entanglement at the quantum level and chaos at the classical level arise from
nonseparable couplings between the atomic spin and its center of mass motion.
The main features of the chaotic dynamics are analyzed using action-angle
variables and Poincare surfaces of section. We show that for the initial state
prepared in current experiments [D. J. Haycock et al., Phys. Rev. Lett. 85,
3365 (2000)], the classical and quantum dynamics diverge, and the observed
experimental dynamics are best described by quantum mechanics. Furthermore, the
motion corresponds to tunneling through a dynamical potential barrier. The
coupling between the spin and the motional subsystems, which are very different
in nature from one another, leads to new questions regarding the transition
from regular quantum dynamics to chaotic classical motion.",0102085v2
2019-09-28,A study of dynamical effects in the observed second time-derivative of the spin or orbital frequencies of pulsars,"The observed values of the time-derivatives of the spin or orbital frequency
of pulsars are affected by their dynamical properties. We derive thorough
analytical expressions for such dynamical contributions in terms of the
Galactic coordinates, the proper motion, the pulsar distance, and the radial
velocity. We find that the effects of the dynamical terms in the
second-derivative of frequencies or parameters based on such second
derivatives, e.g., braking index, are usually negligible. However, unique
pulsars for which the effects of the dynamical terms are significant can exist.
In particular, dynamical effects can make the magnitude of the observed value
of the braking index to be in the order of thousand while the true value of it
is close to the theoretically expected value three, especially if the pulsars
lie close to the Galactic centre. Dynamics can also affect the value of the
second derivative of the orbital frequency of a binary pulsar at the first
decimal place. We also emphasize the fact that our expressions provide more
accurate results than pre-existing approximate ones that exclude some of the
terms. Comparison with a set of pulsars showed that the median value of the
difference between the results obtained by our method and a pre-existing method
is about 50 percent.",1909.13113v4
2021-03-19,Dynamical renormalization group for mode-coupling field theories with solenoidal constraint,"The recent inflow of empirical data about the collective behaviour of
strongly correlated biological systems has brought field theory and the
renormalization group into the biophysical arena. Experiments on bird flocks
and insect swarms show that social forces act on the particles' velocity
through the generator of its rotations, namely the spin, indicating that
mode-coupling field theories are necessary to reproduce the correct dynamical
behaviour. Unfortunately, a theory for three coupled fields - density, velocity
and spin - has a prohibitive degree of intricacy. A simplifying path consists
in getting rid of density fluctuations by studying incompressible systems. This
requires imposing a solenoidal constraint on the primary field, an unsolved
problem even for equilibrium mode-coupling theories. Here, we perform an
equilibrium dynamic renormalization group analysis of a mode-coupling field
theory subject to a solenoidal constraint; using the classification of Halperin
and Hohenberg, we can dub this case as a solenoidal Model G. We demonstrate
that the constraint produces a new vertex that mixes static and dynamical
coupling constants, and that this vertex is essential to grant the closure of
the renormalization group structure and the consistency of dynamics with
statics. Interestingly, although the solenoidal constraint leads to a
modification of the static universality class, we find that it does not change
the dynamical universality class, a result that seems to represent an exception
to the general rule that dynamical universality classes are narrower than
static ones. Our results constitute a solid stepping stone in the admittedly
large chasm towards developing an off-equilibrium mode-coupling theory of
biological groups.",2103.10914v1
2022-07-22,Spatial mixing and the random-cluster dynamics on lattices,"An important paradigm in the understanding of mixing times of Glauber
dynamics for spin systems is the correspondence between spatial mixing
properties of the models and bounds on the mixing time of the dynamics. This
includes, in particular, the classical notions of weak and strong spatial
mixing, which have been used to show the best known mixing time bounds in the
high-temperature regime for the Glauber dynamics for the Ising and Potts
models.
  Glauber dynamics for the random-cluster model does not naturally fit into
this spin systems framework because its transition rules are not local. In this
paper, we present various implications between weak spatial mixing, strong
spatial mixing, and the newer notion of spatial mixing within a phase, and
mixing time bounds for the random-cluster dynamics in finite subsets of
$\mathbb Z^d$ for general $d\ge 2$. These imply a host of new results,
including optimal $O(N\log N)$ mixing for the random cluster dynamics on torii
and boxes on $N$ vertices in $\mathbb Z^d$ at all high temperatures and at
sufficiently low temperatures, and for large values of $q$ quasi-polynomial (or
quasi-linear when $d=2$) mixing time bounds from random phase initializations
on torii at the critical point (where by contrast the mixing time from
worst-case initializations is exponentially large). In the same parameter
regimes, these results translate to fast sampling algorithms for the Potts
model on $\mathbb Z^d$ for general $d$.",2207.11195v3
2023-04-25,Dynamical process of a bit-width reduced Ising model with simulated annealing,"Ising machines have attracted attention as efficient solvers for
combinatorial optimization problems, which are formulated as ground-state
(lowest-energy) search problems of the Ising model. Due to the limited
bit-width of coefficients on Ising machines, the Ising model must be
transformed into a bit-width reduced (BWR) Ising model. According to previous
research, the bit-width reduction method, which adds auxiliary spins, ensures
that the ground state of the BWR Ising model is theoretically the same as the
Ising model before bit-width reduction (original Ising model). However, while
the dynamical process is closely related to solution accuracy, how the BWR
Ising model progresses towards the ground state remains to be elucidated.
Therefore, we compared the dynamical processes of these models using simulated
annealing (SA). Our findings reveal significant differences in the dynamical
process across models. Analysis from the viewpoint of statistical mechanics
found that the BWR Ising model has two characteristic properties: an effective
temperature and a slow relaxation. These properties alter the temperature
schedule and spin flip probability in the BWR Ising model, leading to
differences in the dynamical process. Therefore, to obtain the same dynamical
process as the original Ising model, we proposed SA parameters for the BWR
Ising model. We demonstrated the proposed SA parameters using a square lattice
Ising model, in which all coefficients were set uniformly to the same positive
values or randomly. Our experimental evaluations demonstrated that the
dynamical process of the BWR and original Ising model became closer.",2304.12796v2
1994-06-27,Order Parameter Flow in the SK Spin-Glass I: Replica Symmetry,"We present a theory to describe the dynamics of the Sherrington- Kirkpatrick
spin-glass with (sequential) Glauber dynamics in terms of deterministic flow
equations for macroscopic parameters. Two transparent assumptions allow us to
close the macroscopic laws. Replica theory enters as a tool in the calculation
of the time- dependent local field distribution. The theory produces in a
natural way dynamical generalisations of the AT- and zero-entropy lines and of
Parisi's order parameter function $P(q)$. In equilibrium we recover the
standard results from equilibrium statistical mechanics. In this paper we make
the replica-symmetric ansatz, as a first step towards calculating the order
parameter flow. Numerical simulations support our assumptions and suggest that
our equations describe the shape of the local field distribution and the
macroscopic dynamics reasonably well in the region where replica symmetry is
stable.",9406104v1
1996-04-24,Survival Probability of a Gaussian Non-Markovian Process: Application to the T=0 Dynamics of the Ising Model,"We study the decay of the probability for a non-Markovian stationary Gaussian
walker not to cross the origin up to time $t$. This result is then used to
evaluate the fraction of spins that do not flip up to time $t$ in the zero
temperature Monte-Carlo spin flip dynamics of the Ising model. Our results are
compared to extensive numerical simulations.",9604151v2
1997-02-07,Out of equilibrium dynamics in spin-glasses and other glassy systems,"We review recent theoretical progress on glassy dynamics, with special
emphasis on the importance and universality of the ``aging regime'', which is
relevant to many experimental situations. The three main subjects which we
address are: (i) Phenomenological models of aging (coarsening, trap models),
(ii) Analytical results for the low-temperature dynamics of mean-field models
(corresponding to the mode-coupling equations); and (iii) Simple non-disordered
models with glassy dynamics. We discuss the interrelation between these
approaches, and also with previous work in the field. Several open problems are
underlined -- in particular the precise relation between mean-field like (or
mode-coupling) descriptions and finite dimensional problems.",9702070v1
1999-07-27,Dynamic correlations in doped 1D Kondo insulator: Finite-T DMRG study,"The finite-T DMRG method is applied to the one-dimensional Kondo lattice
model to calculate dynamic correlation functions. Dynamic spin and charge
correlations, S_f(omega), S_c(omega), and N_c(omega), and quasiparticle density
of states rho(omega) are calculated in the paramagnetic metallic phase for
various temperatures and hole densities. Near half filling, it is shown that a
pseudogap grows in these dynamic correlation functions below the crossover
temperature characterized by the spin gap at half filling. A sharp peak at
omega=0 evolves at low temperatures in S_f(omega) and N_c(omega). This may be
an evidence of the formation of the collective excitations, and this confirms
that the metallic phase is a Tomonaga-Luttinger liquid in the low temperature
limit.",9907416v1
2000-04-13,Equilibrium and dynamical properties of the ANNNI chain at the multiphase point,"We study the equilibrium and dynamical properties of the ANNNI (axial
next-nearest-neighbor Ising) chain at the multiphase point. An interesting
property of the system is the macroscopic degeneracy of the ground state
leading to finite zero-temperature entropy. In our equilibrium study we
consider the effect of softening the spins. We show that the degeneracy of the
ground state is lifted and there is a qualitative change in the low temperature
behaviour of the system with a well defined low temperature peak of the
specific heat that carries the thermodynamic ``weight'' of the ground state
entropy. In our study of the dynamical properties, the stochastic Kawasaki
dynamics is considered. The Fokker-Planck operator for the process corresponds
to a quantum spin Hamiltonian similar to the Heisenberg ferromagnet but with
constraints on allowed states. This leads to a number of differences in its
properties which are obtained through exact numerical diagonalization,
simulations and by obtaining various analytic bounds.",0004207v1
2000-12-12,Nonequilibrium Critical Dynamics of the 2D XY model,"The nonequilibrium critical dynamics of the 2D XY model is investigated
numerically through Monte Carlo simulations and analytically in the spin-wave
approximation. We focus in particular on the behaviour of the two-time response
and correlation functions and show that the ageing dynamics depends on the
initial conditions. The presence of critical fluctuations leads to non-trivial
violations of the fluctuation-dissipation theorem apparently reminiscent of the
three dimensional Edwards-Anderson spin glass model. We compute for this reason
the finite-size overlap probability distribution function and find that it is
related to the finite-time fluctuation-dissipation ratio obtained in the out of
equilibrium dynamics, provided that the temperature is not very low.",0012194v2
2001-07-14,Slow dynamics and aging in a non-randomly frustrated spin system,"A simple, non-disordered spin model has been studied in an effort to
understand the origin of the precipitous slowing down of dynamics observed in
supercooled liquids approaching the glass transition. A combination of Monte
Carlo simulations and exact calculations indicates that this model exhibits an
entropy vanishing transition accompanied by a rapid divergence of time scales.
Measurements of various correlation functions show that the system displays a
hierarchy of time scales associated with different degrees of freedom. Extended
structures, arising from the frustration in the system, are identified as the
source of the slow dynamics. In the simulations, the system falls out of
equilibrium at a temperature $T_{g}$ higher than the entropy-vanishing
transition temperature and the dynamics below $T_{g}$ exhibits aging as
distinct from coarsening. The cooling rate dependence of the energy is also
consistent with the usual glass formation scenario.",0107322v2
2002-04-30,Langevin dynamics of the Coulomb frustrated ferromagnet: a mode-coupling analysis,"We study the Langevin dynamics of the soft-spin, continuum version of the
Coulomb frustrated Ising ferromagnet. By using the dynamical mode-coupling
approximation, supplemented by reasonable approximations for describing the
equilibrium static correlation function, and the somewhat improved dynamical
self-consistent screening approximation, we find that the system displays a
transition from an ergodic to a non-ergodic behavior. This transition is
similar to that obtained in the idealized mode-coupling theory of glassforming
liquids and in the mean-field generalized spin glasses with one-step replica
symmetry breaking. The significance of this result and the relation to the
appearance of a complex free-energy landscape are also discussed.",0204633v1
2003-02-22,The dynamics of quantum phases in a spinor condensate,"We discuss the quantum phases and their diffusion dynamics in a spinor-1
atomic Bose-Einstein condensate. For ferromagnetic interactions, we obtain the
exact ground state distribution of the phases associated with the total atom
number ($N$), the total magnetization (${\cal M}$), and the alignment (or
hypercharge) ($Y$) of the system. The mean field ground state is stable against
fluctuations of atom numbers in each of the spin components, and the phases
associated with the order parameter for each spin components diffuse while
dynamically recover the two broken continuous symmetries [U(1) and SO(2)] when
$N$ and ${\cal M}$ are conserved as in current experiments. We discuss the
implications to the quantum dynamics due to an external (homogeneous) magnetic
field. We also comment on the case of a spinor-1 condensate with
anti-ferromagnetic interactions.",0302464v1
2003-11-22,Influence of a Uniform Current on Collective Magnetization Dynamics in a Ferromagnetic Metal,"We discuss the influence of a uniform current, $\vec{j} $, on the
magnetization dynamics of a ferromagnetic metal. We find that the magnon energy
$\epsilon(\vec{q})$ has a current-induced contribution proportional to
$\vec{q}\cdot \vec{\cal J}$, where $\vec{\cal J}$ is the spin-current, and
predict that collective dynamics will be more strongly damped at finite ${\vec
j}$. We obtain similar results for models with and without local moment
participation in the magnetic order. For transition metal ferromagnets, we
estimate that the uniform magnetic state will be destabilized for $j \gtrsim
10^{9} {\rm A} {\rm cm}^{-2}$. We discuss the relationship of this effect to
the spin-torque effects that alter magnetization dynamics in inhomogeneous
magnetic systems.",0311522v1
2004-02-17,Approximation schemes for the dynamics of diluted spin models: the Ising ferromagnet on a Bethe lattice,"We discuss analytical approximation schemes for the dynamics of diluted spin
models. The original dynamics of the complete set of degrees of freedom is
replaced by a hierarchy of equations including an increasing number of global
observables, which can be closed approximately at different levels of the
hierarchy. We illustrate this method on the simple example of the Ising
ferromagnet on a Bethe lattice, investigating the first three possible
closures, which are all exact in the long time limit, and which yield more and
more accurate predictions for the finite-time behavior. We also investigate the
critical region around the phase transition, and the behavior of two-time
correlation functions. We finally underline the close relationship between this
approach and the dynamical replica theory under the assumption of replica
symmetry.",0402451v1
2005-02-18,Dynamics of coupled vortices in layered magnetic nanodots,"The spin dynamics are calculated for a model system consisting of
magnetically soft, layered nanomagnets, in which two ferromagnetic (F)
cylindrical dots, each with a magnetic vortex ground state, are separated by a
non-magnetic spacer (N). This permits a study of the effects of interlayer
magnetostatic interactions on the vortex dynamics. The system was explored by
applying the equations of motion for the vortex core positions. The restoring
force was calculated taking into account the magnetostatic interactions
assuming a realistic surface charge free spin distribution. For tri-layer F/N/F
dots with opposite chiralities and the same core polarizations (lowest energy
state), two eigenmodes are predicted analytically and confirmed via
micromagnetic simulations. One mode is in the sub-GHz range for submicron dot
diameters and corresponds to quasi-circular rotation of the cores about the dot
center. A second mode is in the MHz range corresponding to a small amplitude
rotation of the mean core position. The eigenfrequencies depend strongly on the
geometrical parameters of the system, suggesting that magnetostatic effects
play a dominant role in determining the vortex dynamics.",0502469v1
2005-04-27,Analytical study of tunneling times in flat histogram Monte Carlo,"We present a model for the dynamics in energy space of multicanonical
simulation methods that lends itself to a rather complete analytic
characterization. The dynamics is completely determined by the density of
states. In the \pm J 2D spin glass the transitions between the ground state
level and the first excited one control the long time dynamics. We are able to
calculate the distribution of tunneling times and relate it to the
equilibration time of a starting probability distribution. In this model, and
possibly in any model in which entering and exiting regions with low density of
states are the slowest processes in the simulations, tunneling time can be much
larger (by a factor of O(N)) than the equilibration time of the probability
distribution. We find that these features also hold for the energy projection
of single spin flip dynamics.",0504698v2
2005-07-08,Dimer and trimer fluctuations in the s=1/2 transverse XX chain,"Exact results for the dynamic dimer and trimer structure factors of the
one-dimensional s=1/2 XX model in a transverse magnetic field ($\parallel z$)
are presented and discussed in relation to known exact results for the dynamic
spin structure factors. In the framework of the Jordan-Wigner representation,
the accessible spectrum of the dimer fluctuation operator is limited to
two-fermion excitations whereas that of the trimer fluctuation operator
involves two-fermion and four-fermion excitations. The spectral boundaries,
soft modes, and singularity structure of the four-fermion excitation continuum
as probed by the dynamic trimer structure factor are examined and compared with
corresponding properties of the two-fermion excitation continuum, as probed by
the dynamic dimer and transverse spin structure factors.",0507203v1